Antimicrobial activity

There is some debate as to whether the antimicrobial effect of bearberry is due to hydroquinone esters such as arbutin or to free hydroquinone.¹³ The antimicrobial activities of arbutin and an aqueous extract of bearberry were tested in vitro against bacterial strains implicated in urinary tract infections. The antibacterial activity of arbutin was directly correlated with the beta-glucosidase activity of the bacteria. (This enzyme converts arbutin into free hydroquinone.) The highest enzyme activity was found in Streptococcus, Klebsiella and Enterobacter, the lowest in Escherichia coli.¹⁵ Arbutin (128 μg/L) inhibited three of eight clinical isolates of Pseudomonas aeruginosa tested in vitro.¹⁶ Arbutin and hydroquinone inhibited the growth of Ureaplasma urealyticum and Mycoplasma hominis in vitro.¹⁷ These bacteria are associated with non-gonococcal urethritis.

Piceoside, a glucoside isolated from bearberry, did not demonstrate antibacterial activity in vitro, but its aglycone p-hydroxyacetophenone showed activity against Proteus vulgaris, Enterobacter aerogenes and Bacillus subtilis.¹⁸ Another study found antimicrobial activity for bearberry extracts in vitro against E. coli, Proteus vulgaris, Enterobacter aerogenes, Streptococcus faecalis, Staphylococcus aureus, Salmonella typhi and Candida albicans.¹⁹ The summer and autumn leaves were more potent than the winter leaves.²⁰

The antibacterial activity of various agents was tested in vitro using 74 different strains of bacteria isolated from the urinary tract including E. coli, Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus and species of Enterobacter, Citrobacter and Klebsiella. Urine was collected from healthy volunteers 3 h after oral administration of 0.1 g or 1.0 g of arbutin; several synthetic antibiotics were also tested. Of all test substances, only gentamicin, nalidixic acid and urine collected after intake of 1.0 g of arbutin and adjusted to pH 8 were active against every strain used.²¹

A hydroethanolic extract of bearberry was amongst the most active of 14 traditional Canadian medicinal plants tested against a wide variety of strains of Neisseria gonorrhoeae, including isolates resistant to antibiotics.²² A minimum inhibiting concentration of 32 μg/mL was demonstrated in vitro.

A study of the dry leaf extract of bearberry on the course of acute bacterial pyelonephritis (caused by E. coli) in white rats showed that bearberry extract (25 mg/kg) had a marked antibacterial and nephroprotective effect.²³

Samples of both normal urine and urine collected from healthy subjects after consuming bearberry tea were compared for resistance to bacterial contamination. Urine from the bearberry tea drinkers was more bacteriostatic than normal urine samples. However, the addition of arbutin to normal urine did not result in the same bacteriostatic activity. A series of solutions were then tested for their inhibition of the growth of strains of Staph. aureus and E. coli in vitro. The solutions included hydroquinone, methylhydroquinone and arbutin, normal urine and urine from bearberry tea drinkers. They were tested at normal pH and at pH elevated to 8.0 by the addition of potassium hydroxide. Only the hydroquinone and methylhydroquinone solutions inhibited bacterial growth at normal pH. However, incubation of bacteria with bearberry tea drinkers’ urine adjusted to pH 8 also resulted in inhibition of bacterial growth. This inhibitory effect was also seen for urine adjusted to pH 8 from subjects given pure arbutin.²⁴ The authors suggested that antibacterial activity would only occur when the excretion products of arbutin (hydroquinone paired with glucuronate and sulphate) appear in sufficiently high concentrations in an alkaline urine. It was hypothesised that at an alkaline pH these excretion products of arbutin released small amounts of free hydroquinone in the presence of bacteria, thereby conferring antibacterial activity to the urine. The maximum antibacterial effect from the hydroquinone glucuronides and sulphates formed from arbutin was obtained about 3 to 4 h after taking the herb.²⁵ Free hydroquinone is only excreted in trace amounts, which is desirable given the toxic potential of this agent.

A recent paper has expressed a contradictory view. In this study, urine was collected from four healthy individuals after ingestion of 420 mg of arbutin.²⁶ The samples were added to an E. coli suspension and it was noted that the concentration of hydroquinone in bacteria was 20-fold higher than a control. The authors commented that the pH of urine is unlikely to be important, as the intracellular pH of E. coli is not affected by urine alkalinisation. They concluded that deconjugating enzymes such as beta-glucuronidases found in the bacteria enrich and deconjugate hydroquinone glucuronides and/or sulphates regardless of pH. The pH of the test urine was not stated, but in the study design attempts to increase it to more than 6.5 via a vegetarian diet were instituted.

Urine produced by a healthy person consuming a meat and fish diet is typically in the pH range 4.5 to 6.0; a vegetarian diet will make urine more alkaline. A urine of pH >7 during a urinary tract infection indicates infection by a micro-organism capable of splitting urea, with the release of ammonia.²⁷ Urea-splitting organisms include Proteus spp., Klebsiella spp., some Citrobacter spp., some Haemophilus spp., Bilophila wadsworthia, the yeast Cryptococcus neoformans and several other bacteria and fungi.²⁸ Infection with these organisms should be particularly susceptible to treatment with bearberry if alkaline urine does enhance its activity. Alkalinisation of the urine with buffering agents (for example containing sodium bicarbonate, sodium citrate, citric acid and tartaric acid) in conjunction with bearberry intake may prove to be clinically effective for the treatment of cystitis caused by non-urea-splitting bacteria, but given the conflicting findings noted above, this requires further research.

The antibacterial effect of bearberry may also be useful in the gastrointestinal tract. An aqueous extract of bearberry was found to modulate cell surface hydrophobicity and demonstrated antibacterial effects on ten strains of Helicobacter pylori in vitro.²⁹ The research team concluded that the hydrolysable tannins were largely responsible, as pure tannic acid produced comparable results.

Anti-inflammatory and antiallergic activities

Co-administration of arbutin (50 mg/kg, oral) and indomethacin (subcutaneous) showed an inhibitory effect on swelling in a delayed-type hypersensitivity model, which was stronger than that of indomethacin alone.³⁰ In the same model, arbutin (10 and 50 mg/kg, oral) plus prednisolone or dexamethasone showed stronger effects than each of the anti-inflammatory drugs alone.³¹ Arbutin may therefore have a synergistic anti-inflammatory activity on type IV allergic reaction-induced inflammation. In the same model, oral administration of a bearberry methanolic extract (100 mg/kg) demonstrated an inhibitory effect on swelling. When administered simultaneously with subcutaneous prednisolone, the inhibitory effect was more potent than that of prednisolone alone.³²

Although ointments containing 1% and 2% aqueous extract of bearberry did not inhibit the ear swelling caused by experimentally induced contact dermatitis or carrageenan-induced paw oedema in rats and mice, they did increase the anti-inflammatory effect of a steroid ointment (dexamethasone). Co-administration of bearberry did not increase the side effects of dexamethasone.³³ Topical doses of bearberry might also increase the anti-inflammatory effects of other steroid-like compounds, such as plant-derived saponins.

Effect on melanin synthesis

Arbutin at a concentration of 5×10⁻⁵ M decreased melanin content to approximately 39% when compared to untreated melanoma cells in vitro, without affecting cell growth. Tyrosinase activity also dropped significantly in the arbutin-treated cells. (This enzyme is involved in melanin synthesis.) Arbutin was not hydrolysed to hydroquinone, suggesting that the observed inhibitory effect was for arbutin itself, not hydroquinone.³⁴ Further studies have revealed that the depigmenting mechanism of arbutin in humans involves inhibition of melanosomal tyrosinase activity, rather than the suppression of expression and synthesis of tyrosinase.³⁵

A 50% methanolic extract of bearberry inhibited melanin synthesis in vitro. Both the bearberry extract and arbutin had an inhibitory effect on tyrosinase activity and inhibited the production of melanin by both tyrosinase and autoxidation.⁷ Bearberry extract could have a bleaching effect on freckles and may assist in the control of hyperpigmentary disorders.

Other activity

Oral doses of arbutin (50 mg/kg) suppressed experimentally induced cough reflex. The effect of arbutin was stronger than that of the non-narcotic antitussive dropropizine and comparable to that of codeine.³⁶

Oral administration of a bearberry infusion (3 g/L in drinking water) to healthy rats fed a standard diet containing calcium (8 g/kg) and magnesium (2 g/kg) did not induce significant diuresis, nor affect calcium or citrate concentration levels.³⁷

Aqueous and methanolic extracts of bearberry have demonstrated in vitro molluscicidal activity against the freshwater snail Biomphalaria glabrata (the intermediate host of schistosomiasis). The methanol extract was active at a concentration of 50 ppm.³⁸

A methanol extract of bearberry showed algicidal activity when tested in ponds. It is believed the tannins precipitated the algal proteins.³⁹

Urinary disorders

In a double blind, placebo-controlled, randomised clinical trial, 57 women who had experienced at least three episodes of cystitis during the preceding year received either herbal medicine or placebo. The herbal medicine consisted of bearberry extract (standardised for arbutin and methylarbutin content) and extract of dandelion root and leaf (dose of individual herbs not specified). Treatment for 1 month significantly reduced the recurrence of cystitis during the 1-year follow-up period, with no incidence of cystitis in the herbal group and a 23% occurrence in the placebo group (p<0.05). No side effects were reported.⁴⁵

Antimicrobial and antiparasitic activity

Berberine possesses extensive antimicrobial activity and does appear, in general, to be more active against Gram-positive bacteria (see Table 1). However, most of the research has been published before 2000, with relatively few studies conducted since.

Table 1 In vitro sensitivity of micro-organisms to berberine^33,44–46

Berberine sulphate blocked the adhesion of a uropathogenic strain of E. scherichia coli, in vitro. The reduction in adherence is related to the loss of the synthesis and expression of fimbriae (hairlike appendages) on the surface of the berberine-treated bacteria. Inhibition of microbial adherence results in termination of infection and may explain the anti-infectious activity of berberine in E. coli urinary tract infections, since the direct antimicrobial activity of berberine against E. coli is relatively low (see Table 1).²³ Berberine reduces FtsZ (a protein involved in bacterial cell division) in E. coli, thereby inhibiting the replication of this organism.²⁴

Berberine has also demonstrated antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) in vitro.²⁵ It was effective against all strains of MRSA, with 90% growth inhibition obtained at concentrations of 64 μg/mL or less. Berberine also restored the efficacy of antibiotics commonly used for MRSA. It was found to have an additive effect when combined with ampicillin, and a synergistic activity with oxacillin. Another study found that berberine chloride exhibited antimicrobial activity against all 43 tested strains of Staph. aureus.²⁶ Biofilm formed by Staphylococcus epidermidis is a common cause of infection in orthopaedic joint prostheses. Berberine was found to inhibit Staph. epidermidis adhesion to titanium alloy at a concentration of 45 μg/mL and prevented biofilm formation.^27,28

Berberine sulphate has demonstrated antimycotic activity against several fungal species (see Table 1). Relatively high concentrations of 10 to 25 mg/mL inhibited the growth of Alternaria, Aspergillus flavus, Asp. fumigatus, Candida albicans, Curvularia, Drechslera, Fusarium, Mucor, Penicillium, Rhizopus oryzae and Scopulariopsis. The growth of Syncephalastrum was inhibited by a concentration of 50 mg/mL.²⁹ The minimum inhibitory concentration (MIC) of the antifungal drug fluconazole against Candida albicans was 1.9 μg/mL. However, this decreased to 0.48 μg/mL in the presence of just 1.9 μg/mL berberine.³⁰

Berberine and protoberberine derivatives exhibited a potency comparable to that of quinine in vitro against two clones of human malaria: Plasmodium berghei and P. falciparum. None of the compounds, however, were active in P. berghei-parasitised mice.³¹ Berberine sulphate inhibited the growth of Entamoeba histolytica, Giardia lamblia and Trichomonas vaginalis in vitro and induced morphological changes in the parasites.³² Berberine chloride (1 μg/mL) significantly inhibited the growth of Leishmania donovani promastigotes by approximately 50%, in vitro. A concentration of 5 μg/mL resulted in complete inhibition of growth. L. donovani causes visceral leishmaniasis.³³ A recent study confirmed a half maximal inhibitory concentration (IC⁵⁰) for berberine chloride of 2.6 μg/mL against L. donovani promastigotes.³⁴ The mechanism involved was apoptosis following enhanced oxidative damage.

In vivo berberine demonstrated significant activity (greater than 50% suppression of lesion size) against Leishmania braziliensis panamensis in golden hamsters.³⁵ In both the 8-day and long-term models of L. donovani infection in hamsters, berberine markedly diminished the parasitic load, rapidly improved the haematological picture and was less toxic than pentamidine. Berberine sulphate administered into the lesion (1% four times per week) was found to be highly effective against cutaneous leishmaniasis in dogs. Cutaneous leishmaniasis (oriental sore) is caused by the protozoan Leishmania tropica.³⁶

Berberine hydrochloride demonstrated a high degree of activity against E. histolytica in vitro with a minimum amoebicidal concentration of 10 μg/mL. Oral administration of berberine (100 mg/kg) to rats with experimental amoebiasis (protozoal infection) reduced the infection by 83%. Berberine also reduced the level of infection to 20% in infected hamsters.³⁷

Studies have shown that certain antimicrobial agents can block the adherence of micro-organisms to host cells at doses much lower than those needed to kill cells or inhibit cell growth. At concentrations below the MIC, berberine caused an increase in release of lipoteichoic acid (LTA) from streptococci. LTA is the major ligand responsible for the adherence of the bacteria to host cells, including host cell receptors (fibronectin). Release of LTA from the streptococcal cells means a reduction in the capacity of the bacteria to adhere to the host. Berberine also interfered with bacterial adherence by directly preventing the complexing of LTA with fibronectin or by dissolving the complexes once they were formed.³⁸ (See also the berberine research above regarding biofilms.)

Antimicrobial research on hydrastine is more limited. It exhibited relatively weaker killing activity than berberine against Staph. aureus and Streptococcus sanguis.³⁹ An MIC⁵⁰ of 100 μg/mL was demonstrated against Helicobacter pylori (see also later under Pharmacodynamics of the herbs).⁴⁰ The effect of hydrastine on the protoscolices (larvae) of the tapeworm Echinococcus granulosus was measured in vitro and in vivo. Hydrastine at 0.3% concentration produced 70% mortality of the larvae in both experiments.⁴¹

Berberine demonstrated in vitro antiviral activity against herpes simplex virus types 1 and 2 with an IC⁵⁰ of 82 and 90 μg/mL, respectively.⁴² The in vitro antiviral activity (IC⁵⁰) of berberine chloride against human cytomegalovirus using the plaque assay was 0.68 μM (0.25 μg/mL), which was similar to the drug ganciclovir.⁴³

Antidiarrhoeal activity

Oral doses of berberine (>25 mg/kg) and Geranium extract (a source of tannins) showed significant inhibition of diarrhoea in mice, and both substances inhibited spontaneous peristalsis in rat intestine. Comparison with atropine and papaverine indicated that the antidiarrhoeal activity of berberine differs from that of Geranium extract.⁴⁷ Intragastric administration of berberine sulphate reduced the purging effect of castor oil or Cassia angustifolia (senna) leaf in mice. It did not affect the gastrointestinal transport of Chinese ink in normal mice.⁴⁸

A goal of therapy for diarrhoeal diseases is to decrease stool water. This can be done in two ways: by increasing the absorption of water and electrolytes or decreasing the stimulated secretion of fluid. Berberine probably does the latter.⁴⁹ It did not significantly alter normal ileal water and electrolyte transport as measured in vivo⁵⁰ and in vitro.⁵¹ However, it inhibited secretion caused by Vibrio. cholerae and E. coli heat-labile enterotoxins, even when administered after the enterotoxin had bound to intestinal mucosa. The antisecretory effect was therefore not dependent on the type of enterotoxin.⁵² In contrast, while simultaneous oral administration of berberine (0.1 mg/rat) and E. coli enterotoxin resulted in a significant reduction in fluid accumulation (p<0.01), treatment with berberine prior to or after the enterotoxin was ineffective.⁵³ Two studies are contradictory as to whether berberine alters cholera toxin-induced stimulation of the adenylate cyclase–cAMP system.^44,54 Hence, the exact mechanism of action of berberine is not certain, but its site of action appears to be distal to second messenger production and may be at a level common to all stimuli of colonic chloride secretion.⁵⁵

A more recent investigation of the antidiarrhoeal activity of berberine used a model of thyroid hormone-induced diarrhoea in rats and measured gastrointestinal peptides.⁵⁶ While both plasma motilin and gastrin were elevated by thyroxine, they were normalised by the berberine (60 mg/kg/day for 7 days, oral). As a result, berberine also normalised increases in the number and volume of intestinal goblet cells.

Cardiovascular activity

A review concluded that berberine possesses a range of cardiovascular properties, including positive inotropic, negative chronotropic, antiarrhythmic and vasodilatory activities.⁵⁷ An in vitro study indicated that berberine inhibits voltage-dependent and ATP-sensitive potassium channels, hence the hypoglycaemic and antiarrhythmic activity of berberine might be due to its potassium channel-blocking effect.⁵⁸ Intravenous administration of berberine (1 mg/kg) decreased the amplitude of delayed after-depolarisations and blocked arrhythmias in rabbit ventricular muscles. The mechanism of antiarrhythmic activity of berberine might therefore instead be due to suppression of delayed after-depolarisations caused by a decrease in sodium influx.⁵⁹

Berberine prevented the development of pressure-overload-induced left ventricular hypertrophy in vivo after aortic banding.⁶⁰ Oral administration of 10 mg/kg decreased left ventricular and diastolic pressures, and whole heart and left ventricular weights were lower after 8 weeks of treatment. A follow-up study was conducted to investigate the effects of berberine on catecholamine levels in a similar experimental model.⁶¹ Plasma and left ventricular levels of adrenaline and noradrenaline were decreased after treatment with berberine. Berberine (5 to 10 mg/kg) improved cardiac contractility and inhibited left ventricular remodelling (especially myocardial fibrosis) in a rat model of hypertension.⁶² Such effects might be partially associated with increased nitric oxide (NO) and cAMP in left ventricular tissue.

Administration of berberine sulphate increased the number of thrombocytes, decreased the activity of factor XIII and promoted blood coagulation in intact and gamma-irradiated rats and mice.⁶³ Berberine inhibited platelet aggregation and platelet adhesiveness in rats with reversible middle cerebral artery occlusion. Thromboxane B₂ levels after treatment with berberine were lower than levels in untreated ischaemic controls. The decline of platelet aggregation and decrease of thromboxane B₂ may be one of the important factors behind the anti-ischaemic activity of berberine.⁶⁴ Berberine also markedly inhibited clot retraction in vitro, which may be due to direct inhibition of calcium ion influx.⁶⁵

Recent research has also focused on the cholesterol-lowering activity of berberine and its mechanism of action. The compound upregulates hepatic LDL (low density lipoprotein) receptor expression in vitro via post-transcriptional mRNA stabilisation.⁶⁶ This appears to be mediated by the extracellular signal-regulated kinase signalling pathway. Canadine, along with two other constituents of Hydrastis, have also demonstrated the same ability.⁶⁷ While berberine and the whole root preparation of Hydrastis both upregulated the expression of LDL receptors in a human liver cell line (HepG2 cells), the latter preparation was more effective (see also later in this monograph). Berberine was also found to inhibit cholesterol and triglyceride synthesis in HepG2 cells by increasing AMP-activated protein kinase (AMPK).⁶⁸

Oral administration of berberine (50 and 100 mg/kg/day) to hyperlipidaemic hamsters for 10 days resulted in 26% and 42% decreases in total cholesterol and LDL-cholesterol, respectively. A 3.5-fold increase in hepatic LDL receptor mRNA and a 2.6-fold increase in LDL protein was seen in hamsters taking the higher dose.⁶⁹ LDL receptors in the liver increase the uptake and clearance of cholesterol from the bloodstream. The same researchers found that a combination of berberine (90 mg/kg/day, oral) and simvastatin (6 mg/kg/day, oral) in food-induced hyperlipidaemic rats was more effective than either agent alone at reducing serum LDL-cholesterol (p<0.01). A more effective reduction of serum triglyceride levels was also demonstrated.⁷⁰ The combination also upregulated LDL receptor mRNA in the rat livers to a level 1.6 times higher than either monotherapy, with a corresponding reduction of liver fat storage and improvement in hepatic histology.

A different research group investigated the effect of berberine and plant stanols (inhibitors of cholesterol absorption from the diet) on plasma cholesterol levels in rats with diet-induced hyperlipidaemia. Berberine (100 mg/kg/day, oral) slightly, but not significantly, lowered plasma total cholesterol, while the plant stanols (1% in diet) showed a borderline significant reduction (18%, p=0.067).⁷¹ However, the combination markedly and significantly lowered plasma total cholesterol (41%, p=0.0002). Follow-up research by the same investigators sought to understand the mechanisms involved. Diet-induced hyperlipidaemic hamsters were chosen as the experimental model, since these animals are regarded as a good correlate for human cholesterol metabolism.⁷² Using the same doses as above, it was again demonstrated that total plasma cholesterol was most reduced by the combination (43%, p=0.0001).⁷³ Neither berberine nor the plant stanols affected plasma triglyceride levels, whereas their combination resulted in a significant 37% reduction (p<0.001). As to the possible sites of action of berberine, a series of tests suggested that it interfered with intestinal cholesterol absorption in a different manner to the stanols, possibly by interfering with micelle formation. In addition bile acid synthesis was increased, which can increase cholesterol clearance via the digestive tract. In contrast, cholesterol synthesis by the liver was also increased (this is a known property of other cholesterol absorption inhibitors), but not by enough to counter the cholesterol-lowering mechanisms. Contrary to research cited above, the authors found that berberine did not affect hepatic LDL receptor mRNA expression.

Tissue factor (TF) plays an essential role in coagulation by binding factor VII, which activates factor X. TF is expressed in cells within the atherosclerotic vessel wall, is induced by inflammatory mediators and enhances plaque thrombogenicity. Human aortic endothelial cells treated with berberine (1 to 30 μM) exhibited enhanced TF expression following inflammatory stimulants.⁷⁴ This was via stabilisation of TF mRNA. Also berberine countered the inhibitory effects of statins on endothelial TF in vitro. Berberine also enhanced TF and inhibited TFPI (tissue factor pathway inhibitor), a TF antagonist, in ApoE⁻/⁻ mice after oral doses of 100 mg/kg/day. The authors suggested that this prothrombotic effect of berberine indicates it should be considered with caution as a cholesterol-lowering agent and that large-scale clinical trials are needed to prove its safety in this regard. In addition, berberine might promote atherosclerosis and foam cell formation by inducing scavenger receptor-A expression in macrophages (which mediates LDL uptake), as determined by in vitro and in vivo (mice, 5 mg/kg/day, ip) experiments.⁷⁵

On the other hand, berberine might reduce the incidence or pathogenesis of arterial disease by other mechanisms: in vitro berberine inhibited lysophosphatidylcholine-induced vascular smooth muscle cell (VSMC) proliferation and migration via inhibition of intracellular reactive oxygen species, suggesting potential in the prevention of atherosclerosis.⁷⁶ Berberine also inhibited the in vitro growth and migration of VSMC induced by platelet-derived growth factor.⁷⁷ LDL oxidation and LDL-induced cytotoxic effects on human endothelial cells were also reduced by berberine in vitro.⁷⁸ Atherosclerotic plaque rupture is usually the initiating event in a heart attack. Overproduction of MMPs (matrix metalloproteinases) by macrophages can lead to plaque rupture by degrading the extracellular matrix. Berberine reduced MMP-9 expression in activated macrophages in vitro.⁷⁹

Berberine might benefit vascular endothelial cell integrity and function by improving protective mechanisms, such as increasing the production of NO and enhancing resistance to hyperglycaemic-induced injury. This was observed in blood vessels and vascular endothelial cells taken from mice and rats.⁸⁰ In human studies, 1.2 g/day (oral) of berberine for 30 days mobilised circulating endothelial progenitor cells (improving small artery elasticity),⁸¹ augmented their function (a result of enhanced plasma NO levels)⁸² and reduced circulating endothelial microparticles in parallel with improved flow-mediated vasodilation.⁸³ This suggests berberine has beneficial effects on human vascular endothelial health.

Anticancer activity

There have been numerous investigations into the anticancer properties of berberine, mainly via in vitro studies using human and animal cancer cell lines. A 2009 systematic review cited more than 100 studies, with most published since the year 2000.⁸⁴ Antiproliferative activity at concentrations typically up to 100 μM (about 34 μg/mL) has been demonstrated in vitro for a range of tumour cell lines including liver, lung, breast, uterus, melanoma, prostate and leukaemia. According to the review, the antiproliferative effect of berberine is relatively slow and gentle, requiring exposure times of at least 24 h for significant effects. Various mechanisms underlying this antiproliferative/cytotoxic activity of berberine have been proposed, but the most widely investigated mechanism is its role in cell cycle arrest (with sometimes conflicting results). Induction of apoptosis is another possible key mechanism, via regulation of reactive oxygen species production, mitochondrial transmembrane potential and NF-kappaB activation. Other possible anticancer mechanisms according to the review include transcriptional regulation of some oncogene and carcinogenesis-related gene expression, interaction with DNA and RNA, and inhibition of key enzymes such as DNA topoisomerase.

The review also notes studies, relatively few in number, where berberine has inhibited metastasis, invasion and angiogenesis in vitro, especially via MMP inhibition. Despite earlier studies suggesting that berberine might be relatively inactive against cancer in vivo, later studies have demonstrated significant effects. The review cites studies for Dalton’s lymphoma ascites tumour cells in mice (ip treatment was more effective than oral) and human tongue squamous carcinoma, also in mice (berberine 10 mg/kg, ip). Berberine has also prevented cancer development in models of chemical carcinogenesis.

Another 2009 review of the antineoplastic activity of berberine noted many of the same studies and came to similar conclusions regarding mechanisms of action.⁸⁵ The review also included additional positive in vivo studies for berberine including inhibition of leukaemia cells and lung tumours inoculated into mice (berberine dose 100 mg/kg, oral). Berberine also strongly suppressed the growth of human prostate cancer xenografts in mice. This review did caution that antagonistic activity of berberine on chemotherapeutic drugs has been observed in vitro, due to the upregulation of multidrug resistance pumps in cancer cells. Hence there is a risk that co-administered berberine might compromise cancer chemotherapy. However, in vivo research is needed to clarify this issue.

Anti-inflammatory activity

Berberine was shown to inhibit COX-2 transcription in human colon cancer cells (at >0.3 μM)⁸⁶ and reduce COX-2 protein (but not enzyme activity) in an oral cancer cell line in vitro (1, 10 and 100 μM).⁸⁷ Activator protein 1 (AP-1) activity was also decreased in human hepatoma cells⁸⁸ and oral cancer cells treated with berberine.⁸⁷ AP-1 is a pro-inflammatory transcription factor also involved in carcinogenesis.

Berberine inhibited cellular proliferation of human peripheral lymphocytes in vitro. Some effects of berberine, especially its anti-inflammatory activity, may arise in part from the inhibition of DNA synthesis in activated lymphocytes.⁸⁹ The phytochemical also suppressed pro-inflammatory responses via AMPK activation in macrophages in vitro.⁹⁰ Berberine suppressed the induction of the interleukin IL-1beta and tumour necrosis factor (TNF)-alpha by inflammatory agents in human lung cells in vitro.⁹¹

The alkaloid berbamine demonstrated suppressive effects via ip administration on delayed hypersensitivity and mixed lymphocyte reactions and significantly prolonged allograft survival, compared with untreated transplanted mice.⁹² In an early study berberine significantly inhibited the proliferative response of spleen cells to mitogens in vitro and reduced the amount of haemolytic plaque-forming cells. The ratio of CD4+ to CD8+ cells was decreased, which may be one of the mechanisms of action.⁹³

An ethanol extract of Berberis, three alkaloidal fractions and isolated alkaloids (berberine and oxyacanthine) were applied by the ip route in acute inflammation models. The ethanol extract demonstrated the highest anti-inflammatory activity. It also demonstrated activity in chronic inflammation (adjuvant arthritis). The two fractions containing only protoberberines and berberine suppressed the delayed-type hypersensitivity reaction. The other fraction (containing protoberberines and bisbenzylisoquinoline alkaloids) and berberine reduced the antibody response against sheep red blood cells in vivo.⁹⁴

Researchers assessed the effect of berberine in a colitis model in rats.⁹⁵ Oral berberine (15 mg/kg/day for 7 days) reduced histological lesions, tissue damage and myeloperoxidase activity. IL-8 was also reduced in vitro when berberine was added to inflamed rectal mucosa tissue.⁹⁵

The isoquinoline alkaloids berberine, berbamine, palmatine, oxyacanthine, magnoflorine and columbamine were isolated from the root bark of a Turkish Berberis plant (B. crataegina) and investigated for their anti-inflammatory and antinociceptive effects in various in vivo models.⁹⁶ Berberine, berbamine and palmatine were found to be effective in a dose-dependent manner in mice at oral doses of 100 and/or 200 mg/kg. The antipyretic activity of the three alkaloids in mice was particularly marked, with doses of 25 to 50 mg/kg proving active.

Berberine pretreatment (5 and 10 mg/kg, ip) inhibited the production of exudate and the prostaglandin PGE₂ in carrageenan-induced inflammation in rats.⁹⁰ The acute inflammatory response induced by lipopolysaccharide (LPS) in broiler chickens was largely mitigated by berberine (15 mg/kg, oral).⁹⁷ Berberine also attenuated LPS-induced acute lung injury by inhibiting TNF-alpha production and expression and activation of phospholipase A₂ in mice (50 mg/kg, oral).⁹⁸

Neurological activity

A recent review examined the neurological potential of berberine.⁹⁹ The authors noted that, like many alkaloids, it readily crosses the blood-brain barrier and has exhibited neuroprotective, antidepressant and anxiolytic activities in various test models. The alkaloid is reported to modulate neurotransmitters and their receptor systems in the brain in vitro and in vivo, exhibiting D2 dopamine antagonist activity and noradrenaline, serotonin and dopamine transporter inhibition. In one study berberine (50 mg/kg, oral) significantly reversed amyloid-beta memory damage in rats¹⁰⁰ and in another it exhibited antidepressant activity in mice (5 to 20 mg/kg, ip).¹⁰¹ Oral doses of berberine (mice, 20 mg/kg) potentiated the effect of antidepressant drugs in a depression model and increased noradrenaline and serotonin levels in the hippocampus and frontal cortex.¹⁰² Berberine (100 and 500 mg/kg, oral) displayed anxiolytic activity in mice, with effects comparable to diazepam (1 mg/kg) and buspirone (2 mg/kg).¹⁰³

Anticonvulsant activity has also been demonstrated in various models in mice (10 and 20 mg/kg, ip).¹⁰⁴ This was attributed to a modulation of neurotransmitter systems. Berberine also significantly improved scopolamine-induced amnesia in rats. This anti-amnesic effect of berberine may be related to an increase in activity in the peripheral and central cholinergic neuronal systems.¹⁰⁵

Antidiabetic activity

Much recent research has focused on the antidiabetic properties of berberine. One in vitro mechanistic study compared the glucose-lowering effects of berberine with metformin and troglitazone.¹⁰⁶ Similar to metformin, berberine reduced the uptake of glucose by hepatocytes in an insulin-independent manner. Another in vitro study found that it increased glucose uptake by adipocytes via an insulin-independent mechanism that may involve AMPK.¹⁰⁷ Further to this berberine and dihydroberberine were found to inhibit mitochondrial respiratory complex I in vitro, thereby activating AMPK and improving insulin action.¹⁰⁸ Results from another in vitro study suggested that inhibition of DPP IV (human dipeptidyl peptidase IV) is another possible hypoglycaemic mechanism of berberine.¹⁰⁹

In vitro models of insulin resistance have provided further information. Berberine reversed free-fatty-acid (FFA) induced insulin resistance in adipocytes.¹¹⁰ It also reduced insulin resistance through protein kinase C-dependent upregulation of the insulin receptor in cultured human liver cells¹¹¹ and improved FFA-induced insulin resistance in muscle cells by inhibiting fatty acid uptake.¹¹² Berberine also modulated insulin signalling transduction in insulin-resistant muscle cells.¹¹³

In cultured rat glomerular mesangial cells exposed to high glucose, incubation with berberine significantly decreased cell proliferation and aldose reductase activity.¹¹⁴ Aldose reductase facilitates the conversion of excess cellular glucose into toxic metabolites, which probably facilitates the development of diabetic nephropathy. In the same model, berberine also inhibited fibronectin and collagen accumulation, suggesting a renoprotective effect.¹¹⁵

The hypoglycaemic activity of berberine has been demonstrated in a number of in vivo studies. One in vivo study investigated the activity of berberine in streptozotocin-induced diabetic rats and found that oral doses (187.5 and 562.5 mg/kg) significantly reduced fasting blood glucose, triglycerides, total cholesterol, FFAs and apolipoprotein B, and increased HDL-cholesterol and apolipoprotein AI in a dose-dependent manner.¹¹⁶ A follow-up in vivo experiment in normal mice found that berberine increased serum insulin and decreased blood glucose after oral doses of 93.75, 187.5 and 562.5 mg/kg.¹¹⁶

One study examined the metabolic effects of berberine in models of diabetes and insulin resistance in vivo, and in insulin-responsive cell lines in vitro.¹¹⁷ In a diabetic mouse model, berberine (5 mg/kg/day, ip) reduced body weight and significantly improved glucose tolerance. Similarly, berberine (380 mg/kg/day, oral) reduced body weight and plasma triglycerides and improved the activity of insulin in Wistar rats fed a high fat diet. Berberine also reduced lipogenesis by downregulating the genes involved, and was found to upregulate those involved in energy expenditure in both muscle and adipose tissue. The in vitro arm of the study showed once again that berberine increased AMPK activity. It also increased GLUT4 (glucose transporter type 4) translocation and reduced lipid accumulation in adipocytes. Another study explored the impact of berberine on diabetes induced by alloxan and a high fat and cholesterol diet in rats.¹¹⁸ Oral administration of berberine (100 and 200 mg/kg) significantly decreased fasting blood glucose levels, total cholesterol, LDL-cholesterol and triglycerides, whilst increasing HDL-cholesterol, NO, superoxide dismutase and glutathione peroxidase. Histopathological results demonstrated that berberine was able to restore damaged pancreatic tissue,¹¹⁸ which was also found in another study.¹¹⁹ Similar favourable effects on lowering insulin and plasma glucose and on metabolism (including lipid levels) have been demonstrated in other in vivo studies.^{111,119,120–123}

As touched on above, berberine has also demonstrated favourable effects in animal models of insulin resistance, suggesting a possible role in the management of metabolic syndrome. In dietary obese rats, berberine (250 mg/kg/day, oral for 5 weeks) markedly increased insulin sensitivity.¹²⁴ Associated in vitro experiments suggested that it stimulates glycolysis, and the observed increase in AMPK activation is a consequence of the associated mitochondrial inhibition.¹²⁴ In high-fat-diet rats, berberine (150 mg/kg/day, oral for 6 weeks) significantly decreased plasma glucose and insulin levels, along with a reduction in body weight and improvement of blood lipid profiles.¹²⁵ In rats with fructose-induced insulin resistance, berberine (187.5 mg/kg/day, oral for 4 weeks) reduced plasma insulin, insulin resistance and triglyceride levels, but did not change plasma glucose.¹²⁶

One possible antidiabetic mechanism of berberine could be via the inhibition of intestinal disaccharidases, thereby retarding postprandial sugar absorption. Berberine (100 mg/kg/day, oral) attenuated intestinal disaccharidase activities in streptozotocin-induced diabetic rats,¹²⁷ a finding that was also observed in vitro.¹²⁸ These results were supported in another investigation that found berberine significantly lowered postprandial blood glucose (PBG) following sucrose or maltose loading in normal rats.¹²⁹

Berberine also inhibits aldose reductase activity in vivo. It ameliorated renal injury in streptozotocin-induced diabetic rats at 200 mg/kg/day (oral) by suppressing both oxidative stress and aldose reductase activity, as well as lowering blood glucose.^114,130 The alkaloid also demonstrated some protective activity against retinal pathology in a diabetic rat model.¹³¹

Other activity

Berberine reduced the tonic contraction induced by carbachol in isolated longitudinal muscle of gastric fundus. It mainly acted by inhibiting extracellular calcium entry induced by both carbachol and potassium chloride.¹³² Comparative examinations were made of the relative activity of various isoquinoline alkaloids on isolated mouse intestine and uterus. Berberine, palmatine, jatrorrhizine, dihydroberberine and dihydropalmatine caused marked contraction of uterus. Only tetrahydroberberine, tetrahydropalmatine and tetrahydrojatrorrhizine showed strong papaverine-like spasmolytic activity on intestine.¹³³ Berberine was also found to inhibit the influx of extracellular calcium and calcium-release from intracellular stores in smooth muscle cells of guinea pig colon in a dose-dependent manner.¹³⁴

Acute doses of berberine (2.5 mg/rat, oral) significantly increased the secretion of bilirubin in experimental hyperbilirubinaemia (p<0.05), without affecting the functional capacity of the liver. Chronic administration of 5 mg/day for 8 days abolished the effect, resulting in normal biliary bilirubin excretion.¹³⁵

An in vitro study conducted on the sebaceous glands of the hamster ear found that lipogenesis was suppressed 63% by 100 μM berberine (p<0.01). Lipogenesis was also suppressed by wogonin, a flavonoid in Scutellaria baicalensis. Herbal medicines containing berberine and/or wogonin may therefore be useful in the treatment of acne vulgaris, especially topically. It is likely that berberine inhibits lipogenesis at the level of synthesis of triglyceride from FFA.¹³⁶

Intragastric administration of berberine sulphate significantly inhibited the increased vascular permeability induced by intraperitoneal acetic acid in mice. Subcutaneous administration markedly inhibited the increased vascular permeability in rats and inhibited mouse ear swelling.³⁷

Berberine inhibited osteoclast formation and survival in vitro¹³⁷ and promoted osteoblast differentiation.¹³⁸ In another in vitro study it inhibited osteoclast formation, differentiation and bone resorption.¹³⁹

Berberine (3 mg/kg/day, ip for 36 days) reduced weight gain and food intake, inhibited adipogenesis and lowered serum glucose, triglycerides and total cholesterol in high-fat-diet-induced obese mice.¹⁴⁰ It improved lipid dysregulation in obese mice at 5 mg/kg/day ip by controlling central and peripheral AMPK activity.¹⁴¹

Berberine has an antiurolithic effect that is mediated through multiple pathways. In Wistar rats, berberine (5 to 20 mg/kg, ip) increased urine output accompanied by increased pH and sodium and potassium excretion and decreased calcium excretion, similar to the diuretic drug hydrochlorothiazide.¹⁴² At 10 mg/kg (ip) it also prevented and eliminated chemically induced calcium oxalate crystal deposition in renal tubules and protected against the deleterious effects of lithogenic treatment, including weight loss and oxidative stress.

Antimicrobial activity

A more efficient inhibition of growth was observed for a 1:4 tincture of Berberis compared with 0.2% berberine chloride solution against a variety of microorganisms in vitro. This effect of the Berberis tincture was the result of a higher concentration of berberine (0.31%) and the presence of other active components, including alkaloids.¹⁴³

A 70% alcohol–water extract of Hydrastis and the major isolated alkaloids berberine, hydrastine, canadine and canadaline all demonstrated antibacterial activity against Staph. aureus, E. coli, Streptococcus sanguis and Pseudomonas aeruginosa in vitro.³⁹ The whole extract was as active or more than pure berberine in terms of MIC values, despite the lower content of alkaloids. However, its killing activity was weaker than berberine. The crude methanolic extract of Hydrastis was found to inhibit Helicobacter pylori in vitro, with an MIC⁵⁰ of 12.5 μg/mL.⁴⁰ Berberine and beta-hydrastine were considered to be the most active constituents with MIC⁵⁰ values of 12.5 and 100 μg/mL, respectively.

Hydrastis was among the most potent of 21 herbal extracts screened for in vitro activity against Helicobacter pylori, but sage (Salvia officinalis) was more active.¹⁴⁴ The Hydrastis extract exhibited only relatively modest activity against Campylobacter jejuni.

Effect on smooth muscle

Berberine caused a slow diminution of tone, amplitude, rate and response to acetylcholine in rat uterus. Hydrastine increased the rate of uterine contraction, with slowly decreasing tone and amplitude. Berberine and hydrastine together produced a rapid decrease in tone and amplitude, similar to that produced by Hydrastis extract.¹⁴⁵ The author commented that, although commonly regarded as a uterine stimulant, Hydrastis was in fact a uterine sedative in this model. Hydrastis extract and the total crude alkaloids of Hydrastis demonstrated spasmolytic activity on isolated mouse intestine and uterus.¹⁴⁶

In contrast, an alcohol extract of Hydrastis exerted a vasoconstrictive activity in rabbit aorta. It also inhibited the contraction of rabbit aorta induced by adrenaline, serotonin and histamine in vitro. However, berberine and hydrastine did not show this vasoconstrictive effect. Berberine demonstrated some inhibitory activity on aortic contraction induced by adrenaline, but hydrastine was inactive.¹⁴⁷ The observed vasoconstrictive activity of Hydrastis extract may be due to the presence of hydrastinine, a decomposition product of hydrastine.

The four major alkaloids of Hydrastis (berberine, hydrastine, canadine and canadaline) were tested on rabbit aorta strips for adrenolytic activity (inhibition of adrenaline-induced contraction). The total extract had a lower adrenolytic potency than the alkaloid mixture. The authors suggested that berberine, canadine and canadaline acted synergistically and the presence of other compounds (in particular hydrastine) probably counteracted their activity.¹⁴⁸

Another study by the same research group found that the major alkaloids of Hydrastis evoked contractile activity in isolated guinea pig ileum through an indirect cholinergic mechanism, acting on acetylcholine release from nerve endings. They demonstrated differing contractile potencies for the alkaloids, depending on chemical structure.¹⁴⁹

In confirmation of earlier research, an ethanolic extract of Hydrastis exhibited reversible relaxant activity on spontaneous contractions in non-pregnant rat uterus and also on contractions induced by serotonin, oxytocin and acetylcholine.¹⁵⁰ The extract also relaxed carbachol precontracted guinea pig trachea. An ethanolic extract of Hydrastis induced strong relaxation in rabbit bladder detrusor muscle, but the four major individual alkaloids were inactive.¹⁵¹

Other activity

Berberis tincture increased contractions in isolated rabbit intestine and demonstrated cholagogue activity in guinea pigs and cholekinetic activity in rats.¹⁵²

An extract of Berberis aristata root inhibited the PAF-induced aggregation of rabbit platelets in a dose-dependent manner in vitro. It also inhibited the binding of radiolabelled PAF to rabbit platelets in a competitive manner.¹⁵³

Conflicting results have been recorded for Berberis in pyresis. An early study demonstrated an antipyretic effect for Berberis decoction in rabbits with fever.¹⁵⁴ However, in a later study water, chloroform and hexane extracts showed no activity.¹⁵⁵

A study of the action of bitters was conducted in 1956 on the stomach of a man named Tom, who had an occluded oesophagus and a gastric fistula.² Bitters were administered by mouth and swallowed into the blind oesophagus; the resulting salivary volume and gastric secretion were compared with direct administration into the stomach. In the 96 experiments conducted it was found that there was considerable variation in effects of the bitters. Hydrastis was the most active herb and gentian was virtually inactive at the levels tested (see also Chapter 2).¹⁵⁶

Hydrastis tincture (0.06 mL/mouse) showed some anti-carcinogenic and hepatoprotective activity in p-dimethylaminoazobenzene-induced hepatocarcinogenesis in mice.¹⁵⁷

Hypercholesterolaemic hamsters received either berberine (15 mg/kg/day, ip) or Hydrastis extract (containing berberine 7.5 mg/kg/day, ip).⁶⁷ The Hydrastis significantly lowered plasma total cholesterol, LDL-cholesterol, triglycerides and FFAs, and to the same extent as the berberine. It also significantly reduced liver fat storage, and hepatic LDL receptor mRNA was increased. The observation that berberine from Hydrastis has a longer intracellular retention time in hepatocytes than berberine alone suggests the existence of an unknown multidrug resistance pump inhibitor in the herb.⁶⁷

The innate effects of Hydrastis and Astragalus on pro-inflammatory cytokines produced by cultured macrophages were examined using two different commercial preparations.¹⁵⁸ Both Hydrastis and Astragalus were found to exhibit little to no direct effect on stimulation of mouse macrophages, with only Astragalus able to affect production of TNF-alpha when used in high concentrations. However, both herbs were able to modify responses from LPS-stimulated macrophages, reducing production of TNF-alpha, IL-6, IL-10 and IL-12 in a dose-dependent manner.

The antigen-specific immunomodulatory potential of Hydrastis (6.6 g/L of drinking water) was assessed in rats over 6 weeks.¹⁵⁹ The rats were periodically injected with an antigen (keyhole limpet haemocyanin) over this time period. Hydrastis caused an increase in the primary IgM response in the first 2 weeks only, but had no major impact on IgG production.

Berberis vulgaris is widely used in Pakistan for the treatment of kidney stones. To evaluate its antiurolithic potential, the aqueous-methanol extract of Berberis root bark was tested in an animal model of urolithiasis in male Wistar rats.¹⁶⁰ The extract (50 mg/kg/day, ip) inhibited calcium crystal deposition in renal tubules and protected against associated changes including polyuria, weight loss, impaired renal function and the development of oxidative stress in the kidneys (see also a study by the same group in the berberine section of this monograph).

Diarrhoea and cholera

As noted previously, berberine possesses broad antimicrobial activity in vitro. Of interest to intestinal health, Chinese researchers found that berberine may have a selective antimicrobial effect. Using the more comprehensive microcalorimetric method (which measures the energy changes of bacterial growth), they measured IC₅₀ values of berberine towards Bacillus shigae (a harmful bacterium), Bifidobacterium adolescentis (a commensal or probiotic) and E. coli (a bacterium of the intermediate flora). IC₅₀ values were 75 μg/mL for Bacillus shigae, 101 μg/mL for E. coli and 806 μg/mL for Bifidobacterium adolescentis. This suggests that, at an intestinal concentration sufficient to inhibit the growth of harmful and intermediate flora, berberine would have little effect on probiotic flora.¹⁷⁰ Due to the low oral bioavailability of berberine, the intestine is exposed to most of the dose and hence relevant enteric antimicrobial concentrations could well be achieved.

Results from an early uncontrolled clinical study suggested that berberine hydrochloride therapy (50 mg orally every 8 h for the first 2 days, and then tapering off) might be useful for cholera and severe diarrhoea.¹⁷¹ Data collected for 620 patients suggested berberine was superior to chloramphenicol in some respects. A parallel, open clinical trial comparing berberine and a variety of antidiarrhoeal drug combinations was conducted in 100 children suffering from gastroenteritis of less than 5 days’ duration. Fifty children up to 6 months old received 25 mg of berberine four times a day; older children received 50 mg initially and 25 mg every 6 h; another 50 children received one of several antidiarrhoeal drugs. The state of hydration and number of stools passed were used to assess the treatment. Berberine demonstrated effective antidiarrhoeal action and compared well with the standard antidiarrhoeal drugs. Patients on berberine improved faster, although the lack of a placebo group weakens the value of this finding.¹⁷²

In a randomised, placebo-controlled, double blind clinical trial, the effects of berberine, tetracycline and tetracycline plus berberine were studied in 400 patients presenting with acute watery diarrhoea. Of this number, 185 patients had cholera and 215 non-cholera diarrhoea. At the dosage used (100 mg four times daily) berberine did not show significant anti-secretory activity in either group. A reduction in stool volume and cAMP concentrations in stools was observed, although not significant.¹⁷³ In a later trial, a larger dose of berberine of 200 mg four times daily plus tetracycline (2 g/day) was compared with tetracycline alone using a randomised, double blind clinical design involving 74 patients infected with V. cholerae. No statistically significant differences were observed between the two groups.¹⁷⁴

One hundred and sixty-five adult men with diarrhoea caused by enterotoxigenic E. coli or Vibrio cholerae were treated in a randomised, controlled clinical trial. In patients with E. coli diarrhoea, mean stool volume decreased significantly (p<0.05) in the first 8 h after treatment with 400 mg berberine sulphate, compared with controls. Over the first 24 h period significantly more patients taking berberine stopped having diarrhoea compared with controls (42% versus 20%, p<0.05). Only limited effects against diarrhoea caused by V. cholerae were observed, with no significant difference found between patients treated with 1200 mg berberine sulphate plus tetracycline and those treated with tetracycline alone.¹⁷⁵

The conclusion to draw from these clinical studies is that berberine is probably valuable for some forms of acute infectious diarrhoea, particularly E. coli infection, but has no value in the treatment of V. cholerae infection (cholera).

Other gastrointestinal effects

Small intestinal transit time in 20 healthy human volunteers was significantly delayed after oral administration of 1.2 g of berberine (p<0.01). Hence the antidiarrhoeal property of berberine might be further mediated by its ability to delay small intestinal transit.¹⁷⁶

A clinical trial compared the effects of the antiulcer drug ranitidine and four antibacterial drugs, one of which was berberine (300 mg twice daily), in patients with H. pylori-associated duodenal ulcer disease. Although the antibacterial drugs were more effective at H. pylori clearance and improving gastritis, ranitidine was more effective for ulcer healing.¹⁷⁷

Trachoma

Fifty-one patients with clinically active trachoma lesions (stages I and II) were treated for 8 weeks with eyedrops containing either 0.2% berberine chloride or 20% of the antitrachoma drug sulfacetamide in an open label trial. Sulfacetamide eyedrops gave the better clinical results, but the infective agent (Chlamydia trachomatis) remained present in the conjunctiva and relapses of symptoms occurred. Berberine-treated patients showed only very mild ocular symptoms after treatment and were negative for the infective agent. No relapses occurred among these patients.¹⁷⁸

A single blind, placebo-controlled clinical trial was conducted in 96 children with trachoma stage IIa or IIb over a period of 3 months. Berberine eyedrops (0.2%) were compared with berberine plus neomycin ointment, sulfacetamide or a placebo. In patients treated with berberine alone, 83% were clinically cured (p<0.001), but only 50% were microbiologically cured. The response rate was higher in those treated with berberine plus neomycin (88%) and lower in the sulfacetamide (73%) and placebo (0%) groups (no p values provided). The berberine treatment was better tolerated than sulfacetamide.¹⁷⁹

Giardiasis

After berberine was administered at a dose of 5 mg/kg/day for 6 days to 25 giardiasis patients between the ages of 1 and 10 years, 68% became negative for the presence of Giardia cysts. In a similar group receiving placebo, only 25% experienced a parasitological cure. Metronidazole at a dose of 10 mg/kg/day for 6 days was 100% effective in another nine patients.¹⁸⁰

A clinical trial involving children (ages from 5 months to 14 years) with giardiasis compared the effect of berberine with established antigiardial drugs. Of the group of 42 patients who received 10 mg/kg/day of berberine orally for 10 days, 90% had negative stool specimens upon completion of treatment, although a small number of cases relapsed 1 month later. This result compared favourably with the three other antigiardial drugs investigated, including metronidazole.¹⁸¹

Liver cirrhosis

Patients with cirrhosis of the liver have high plasma concentrations of tyramine, resulting in cardiovascular and neurologic complications. An uncontrolled clinical trial investigated the effect of oral berberine on hypertyraminaemia in cirrhotic patients over several months. Oral administration of berberine (600 to 800 mg/day) corrected hypertyraminaemia and prevented the elevation of plasma tyramine levels following chemical tyramine stimulation. This effect was probably due to inhibition by berberine of bacterial tyrosine decarboxylase in the intestine.¹⁸²

Diabetes mellitus

In an early uncontrolled clinical trial, the effect of berberine was investigated in 60 patients with varying levels of type 2 diabetes mellitus. Oral doses (300 to 500 mg three times a day) were prescribed for 1 to 3 months, together with a therapeutic diet for 1 month. Major symptoms of diabetes disappeared, strength improved, blood pressure normalised and blood lipids decreased. Fasting glycaemic levels in 60% of patients were better controlled.¹⁸³

More recent trials have delivered impressive results, although they did involve the use of relatively high doses of berberine. In a randomised, double blind, placebo-controlled trial in 116 type 2 diabetes patients with dyslipidaemia, berberine (1000 mg/day) for 3 months significantly improved a range of metabolic parameters.¹⁸⁴ Relative to placebo, berberine significantly lowered body weight, systolic blood pressure, fasting blood glucose (FBG), postload blood glucose, HbA_1c, triglycerides, total and LDL-cholesterol, liver transaminases and IL-6 (p<0.0001 to p=0.038). Compared with baseline, berberine lowered fasting plasma glucose by 20%, HbA_1c by 12%, triglycerides by 36% and LDL-cholesterol by 21%. No serious adverse events occurred, but five patients in the berberine group complained of constipation, compared to just one in the placebo group (p=0.207 for frequency of constipation between the two groups).

Two different trials were described in the one publication.¹⁸⁵ In the first controlled (and presumably open label) trial, 36 adults with newly diagnosed type 2 diabetes were randomly assigned to berberine or metformin (1500 mg/day of each) over 3 months, with 31 patients completing the study. Berberine demonstrated similar activity to metformin in terms of reductions in HbA_1c, FBG and PBG and had reduced these significantly by the end of the trial, compared with baseline (p<0.01). In the second open label trial, 48 adults with poorly controlled type 2 diabetes received berberine (1500 mg/day) in addition to their current treatments for 3 months. If gastrointestinal side effects occurred, the dose of berberine was reduced to 900 mg/day. Compared with baseline, by the end of the trial there were significant reductions (p<0.01 to p<0.001) in HbA_1c (10%), FBG (21%), PBG (34%), fasting insulin (28%), HOMA-IR (a measure of insulin resistance, 45%) and LDL-cholesterol (14%). The incidence of functional gastrointestinal adverse events in both trials for berberine was 34.5% (mainly in the first 4 weeks), with flatulence the most common complaint (19%). Berberine was decreased in 14 (24%) patients in the second trial as a consequence of gastrointestinal side effects, with a successful resolution.

In a randomised, double blind, three-arm controlled trial involving 97 patients with type 2 diabetes, berberine treatment (1000 mg/day) was compared with metformin (1500 mg/day) and rosiglitazone (4 mg/day) over a 2-month period.¹⁸⁶ All three treatments significantly lowered FBG and HbA_1c by a similar amount, but only berberine significantly lowered plasma triglycerides compared with baseline. Following berberine therapy, liver transaminases were significantly lowered (p<0.01), serum insulin had declined by 28.2% (p<0.01) and insulin receptor expression on peripheral blood lymphocytes was significantly elevated by 3.6-fold (p<0.01). A second trial in patients with liver disease was also included in this publication, motivated by the observation that current drugs for type 2 diabetes can cause adverse hepatic effects. This open label trial included 35 patients with either type 2 diabetes or insulin resistance (impaired fasting glucose) in conjunction with chronic hepatitis B or C. They were administered berberine (1000 mg/day) for 2 months. Berberine significantly lowered FBG, triglycerides and transaminases in all patient subgroups (p<0.01 or p 0.001).

A comprehensive metabonomic analysis was performed to understand the potential mechanisms of action of berberine in patients with both type 2 diabetes and dyslipidaemia.¹⁸⁷ Sixty patients were randomly selected for analysis from the trial described above.¹⁸⁴ Compared with placebo, patients before and after berberine treatment could be separated into distinct clusters in terms of changes in global serum metabolites. There was a highly significant decrease in the serum concentration of 13 FFAs following berberine, 10 of these also differed statistically from placebo. These results suggest that berberine downregulates the high level of FFAs seen in type 2 diabetes.

Cardiovascular disease

Twelve patients with refractory congestive heart failure (CHF) were studied before and during berberine intravenous infusion (at rates of 0.02 and 0.2 mg/kg/min for 30 min) in an acute single-dose study. The lower infusion dose produced no significant circulatory changes, apart from a reduction in heart rate. The higher dose produced marked and significant changes indicative of cardiotonic activity.¹⁸⁸ Some time later, a randomised, placebo-controlled clinical trial was instigated to evaluate the safety and efficacy of oral berberine in congestive heart failure.¹⁸⁹ One hundred and 56 patients were randomised into two groups and all received appropriate conventional medications such as ACE (angiotensin- converting enzyme) inhibitors, diuretics, digoxin and nitrates. The active group was also given 1.2 to 2.0 g/day of berberine. After 8 weeks, the berberine group displayed a significant improvement in left ventricular ejection fraction and exercise capacity, less dyspnoea and a decrease in the frequency and complexity of ventricular premature complexes (a marker of CHF). Additionally, the mortality rate of patients in the berberine group was almost half that of the control group during the 24-month follow-up period. A prior 2-week study in 56 patients with CHF found more significant decreases in the frequency and complexity of ventricular premature complexes and increases in left ventricular ejection fraction when plasma concentrations of berberine reached levels higher than 0.11 μg/mL (after oral doses of berberine of 1200 mg/day).¹⁹⁰

Berberine also lowers elevated blood lipids, including those in patients with type 2 diabetes (see above). A single blind clinical trial compared the effects of daily oral administration of berberine (500 mg/day) with a combination including berberine, policosanol, red yeast extract, folic acid and astaxanthin for 4 weeks in 40 patients with moderate hypercholesterolaemia. Compared with baseline readings, the berberine and the berberine combination significantly reduced total cholesterol (16% and 20%), LDL-cholesterol (20% and 25%), apolipoprotein B (15% and 29%) and triglycerides (22% and 26%). Both treatments also increased HDL-cholesterol (by 6.6% and 5.1%, respectively, p<0.05 for both).¹⁹¹

Even more striking results were obtained in an earlier randomised, placebo-controlled trial that investigated the effects of oral berberine (1000 mg/day) in 43 hypercholesterolaemic patients. After 3 months of treatment, berberine reduced total cholesterol by 29%, LDL-cholesterol by 25% and triglycerides by 35% (p<0.0001 compared with baseline).⁶⁹

One clinical trial assessed the value of combining berberine with simvastatin. In this randomised, controlled (presumably open) three-arm trial, 63 patients with hyperlipidaemia received either berberine (1000 mg/day), simvastatin (20 mg/day) or their combination for 2 months.⁷⁰ All patient groups exhibited significant reductions in total cholesterol, LDL-cholesterol and triglycerides compared with baseline readings (p<0.05 to p<0.001). The effect of the combination on these parameters was significantly better than either berberine (p<0.05) or simvastatin (p<0.01) alone. In terms of LDL-cholesterol, the reductions after berberine, simvastatin and their combination were 23.8%, 14.3% and 31.8%, respectively.

In an open label comparative trial, 86 hyperlipidaemic patients also suffering from chronic hepatitis B (n=51), chronic hepatitis C (n=18) or alcoholic liver cirrhosis (n=17) were given either berberine (1000 mg/day, n=70) or silymarin (210 mg/day, n=16 and only in hepatitis B patients) for 3 months.¹⁹² Compared with baseline, berberine significantly reduced total cholesterol, LDL-cholesterol and triglycerides in all patient groups (p<0.001 or p<0.0001), whereas silymarin in the hepatitis B patients only lowered triglycerides (p<0.05). Both silymarin and berberine significantly lowered hepatic transaminases (p<0.001 or p<0.0001). The authors concluded that, unlike some current conventional treatments, berberine appeared well-suited as a treatment for lipid dysfunction in liver patients. It should be noted that the dose of silymarin used in the trial was relatively low.

The lipid-lowering effects of berberine (500 mg/day) and ezetimibe (10 mg/day) were compared in 195 patients with hypercholesterolaemia in a 3-month (presumably open label) clinical trial.¹⁹³ Berberine was more effective than ezetimibe in terms of lowering total cholesterol (24.1% versus 21.7%, p=0.002) and LDL-cholesterol (31.7% versus 29.3%, p=0.03) from baseline. Both treatments lowered triglycerides by about 17%. Only two patients reported gastrointestinal intolerance to berberine. No significant adverse effects, including AST, ALT and CPK levels, were observed during the two treatments.

Radioprotective activity

Given the traditional role of berberine-containing herbs in China for the treatment of diarrhoea, the impact of berberine on radiation-induced acute intestinal syndrome (RIAIS) was explored.¹⁹⁴ RIAIS includes side effects such as nausea, vomiting, abdominal pain, loss of appetite, diarrhoea, colitis and proctitis. Thirty-six patients with seminoma (a type of testicular cancer) or lymphoma, and another 42 with cervical cancer, were randomly administered either berberine (900 mg/day) or a placebo for 4 and 5 weeks, respectively. The berberine was given just prior to and during abdominal or pelvic radiotherapy. Berberine had significantly improved the incidence and severity of RIAIS in both patient groups by the end of the trial (p<0.05). Berberine (900 mg/day) also reduced existing RIAIS in a separate group of eight patients. The treatment was well tolerated.

In a prior randomised, double blind, placebo-controlled study, the effect of 6 weeks of berberine (20 mg/kg/day) on radiation-induced lung injury (RILI) was assessed in 90 patients undergoing treatment for non-small cell lung cancer.¹⁹⁵ The incidence of RILI was significantly lower in the berberine group compared with the placebo group at 6 weeks and at a 6-month follow-up (45.2% versus 72.1% and 35.7% versus 65.1%, respectively, both p<0.05). Two measures of radiation-induced lung tissue damage (soluble intercellular adhesion molecule-1 and transforming growth factor beta 1) were also significantly reduced at 6 weeks compared with the placebo (p<0.01 for both), and two measures of lung function were significantly improved at 6 months.

Other effects

Ten patients with cutaneous leishmaniasis received a 1% berberine salt solution intralesionally at weekly intervals for a period of 2 months. A blood sample was taken from the patients before and after treatment. The lesions showed evidence of healing after the second injection. Two patients dropped out of this uncontrolled trial, and of the remaining eight, healing was complete by 4 to 8 weeks.¹⁹⁶

Berberine sulphate, given on its own and in a combined treatment at a dose of 15 mg/day for 15 days, increased platelet count in patients with primary and secondary thrombocytopenia.¹⁹⁷

Two hundred and fifteen patients with chloroquine-resistant malaria were randomised into three groups: 82 patients received pyrimethamine and berberine chloride (1500 mg/day), 64 patients received pyrimethamine and tetracycline, and 69 patients received pyrimethamine and co-trimoxazole, all for 3 days. The clearance rate of asexual parasitaemia after treatment was 74% in the berberine group, 67% in the tetracycline group and 48% in the co-trimoxazole group. Berberine was more effective in clearing the parasite than the other antimicrobial agents when used in conjunction with pyrimethamine.¹⁹⁸

Vascular protective and anti-oedema activity

Anthocyanins improved functional disturbances of the fine blood vessels, especially capillaries,¹⁶ were more effective in protecting damaged capillaries than flavonoids¹⁷ and stimulated capillary repair.¹⁸ Anthocyanin-rich bilberry extracts demonstrated endothelium-dependent relaxation in coronary arteries in vitro. Extract concentrations too low to directly alter coronary vascular tone still protected the arteries from reactive oxygen species.¹⁹

Oral administration of bilberry extract in vivo reduced microvascular impairments due to ischaemia-reperfusion injury, resulting in preservation of endothelium, attenuation of leucocyte adhesion and improvement of capillary perfusion.²⁰ A separate study indicated that increased arteriolar vasomotion might also contribute to these effects.²¹

Oral administration to rats of bilberry extract (equivalent to 180 mg/kg anthocyanins per day) for 12 days maintained normal permeability of the blood-brain barrier and limited the increase in vascular permeability in the skin and aorta wall after induced hypertension. Interaction with collagen within blood vessel walls is believed to be partly responsible for this vasoprotective activity.²²

Oral administration of bilberry extract (equivalent to 72 to 144 mg/kg anthocyanins) demonstrated significant vasoprotective and anti-oedema effects in vivo. Activity was stronger and longer lasting than that of rutin, and was not due to a specific antagonism of inflammatory mediators such as histamine or bradykinin. The anti-oedema activity was also observed after topical application (but resulted in persistent colouration due to the anthocyanins).²³

Effects on vision

Anthocyanins have demonstrated an affinity for the pigmented epithelium of the retina in vitro.²⁴ Bilberry hastened the regeneration of rhodopsin (visual purple) in vitro and in vivo after injection.²⁵

Senescence-accelerated OXYS rats were given either control diets or those supplemented with 25% bilberry extract (equivalent to 20 mg/kg body weight). After 3 months, more than 70% of control rats had cataract and macular degeneration, while the bilberry completely prevented such damage in the lens and retina.²⁶

Bilberry extract improved the viability of cultured human corneal epithelial cells.²⁷ Neuroprotective activity against retinal neuronal damage was demonstrated in vitro and in mice for bilberry and its main anthocyanin constituents. The bilberry extract was administered to the mice by intravitreous injection (10 or 100 μg per eye).

Antioxidant activity

Anthocyanins have demonstrated in vitro antioxidant activity in a number of models, including scavenging of superoxide anions, inhibition of lipid peroxidation,²⁸ and upregulation of haeme-oxygenase and glutathione-S-transferase-pi.²⁹ Fifteen bilberry anthocyanins, particularly as aglycones,³⁰ and bilberry catechins and procyanidins³¹ have all shown appreciable activity.

Bilberry extract also demonstrated antioxidant activity in vitro by inhibiting the potassium ion loss induced by free radicals in human erythrocytes, and by inhibiting cellular reactions induced by oxidant compounds.^32,33 A concentration-dependent inhibition of oxysterol formation (cholesterol oxides) was observed in vitro for bilberry extract after photo-induced oxidation of human low-density lipoproteins (LDL).³⁴ Aqueous extract of bilberry also demonstrated potent protective activity on human LDL particles during in vitro copper-mediated oxidation.³⁵ Dietary bilberry powder supplementation (1.6 g/mouse) protected against intestinal oxidative damage following ischaemia-reperfusion injury.³⁶

A US team investigating the effects of antioxidant foods on mental ageing found that, while some fruits such as strawberries gave promising results, blueberry supplementation was particularly effective at reversing the negative effects of ageing on balance and coordination.³⁷ The team found that anthocyanins in blueberries showed the most activity in penetrating cells and providing antioxidant protection,³⁸ and were even present in the brains of elderly rats after they were fed blueberries for 8 weeks. The more anthocyanins found in the brains of the rats, the better they were at negotiating a complex maze.³⁹ In fact, blueberries in the diet appeared to exert a rejuvenating effect on the brain cells of elderly rats, making them behave more like young rats.⁴⁰ Such effects are also likely for the anthocyanins in bilberry.

Wound healing activity

Anthocyanins have demonstrated collagen-stabilising activity in vitro.⁴¹ Two anthocyanins from bilberry protected collagen against non-enzymatic proteolytic activity in vitro and therefore may protect collagen from degradation during inflammatory processes.⁴² Anthocyanins stimulated mucopolysaccharide biosynthesis in experimentally induced granuloma in vivo.⁴³ Bilberry extract induced active phagocytosis and intense cell regeneration from human umbilical cord and demonstrated growth-promoting activity for fibroblasts and smooth muscle cells in vitro.^44,45

Bilberry extract was reported to accelerate the process of spontaneous healing of experimental wounds after topical application.⁴⁶ Topical bilberry extract significantly improved the healing of experimental skin wounds after it had been delayed by a steroidal anti-inflammatory agent. The wound healing activity was more potent than that of the selected triterpenoids of Centella asiatica (gotu kola).⁴⁷

Cardiovascular activity

Bilberry extract exhibited a significant, dose-dependent inhibition of angiotensin-converting enzyme in cultured endothelial cells from human umbilical veins.⁴⁸ The anthocyanin myrtillin chloride was also active, but not anthocyanin aglycones (anthocyanidins).

Addition of either bilberries or yeast-fermented bilberries at 0.02% to the diet of apoE-deficient mice led to a significant inhibition of atherosclerotic plaque development, whereas no effect on oxidative stress or lipid profiles was observed.⁴⁹ Later work by the same group using just a fermented bilberry extract at 0.02% of diet demonstrated a reduction in serum cholesterol together with altered expression of aortic genes related to atherosclerosis development.⁵⁰

Bilberry anthocyanins (0.01 to 1.0 mg/L) significantly attenuated ischaemia-reperfusion injury in isolated rat hearts.⁵¹

Bilberry extract demonstrated strong antiplatelet activity in vitro and, at dosages equivalent to up to 144 mg/kg anthocyanins, prolonged bleeding time without affecting blood coagulation in vivo.⁵² Inhibition of platelet aggregation was demonstrated from the blood of healthy volunteers after oral administration of an extract equivalent to 173 mg anthocyanins/day for 30 to 60 days. The mechanism of action may depend on an increase in the concentration of cAMP and/or a decrease in the concentration of platelet thromboxane.⁵³

Gastrointestinal effects

Several biomarkers of colon cancer including colonic cell proliferation were reduced in Fischer 344 male rats by a diet supplemented with a bilberry extract.⁵⁴ These findings were supported by another study in mice that supplemented bilberry at the high level of 10% of diet. Similarly, dietary bilberry extract reduced colon tumour number in a mouse model, an effect that was not related to ellagic acid.⁵⁵

Cyanidin chloride (an anthocyanin from bilberry) demonstrated promising antiulcer activity in vivo. Gastric mucus production was increased without affecting gastric secretion.^56,57 Bilberry extract (equivalent to 9 to 72 mg/kg anthocyanins) demonstrated significant dose-dependent antiulcer activity, in some cases exhibiting stronger activity than carbenoxolone or cimetidine.⁴⁷ More recently, oral administration of bilberry anthocyanins (30 and 100 mg/kg) significantly protected against ethanol-induced gastric ulceration in mice.

Bilberry extract (1, 5 and 10 mg/kg, ip) helped to induce the resolution of liver fibrosis in mice with chemical liver injury, partially by downregulating fibrogenic cytokines.⁵⁸ The extract (50 to 200 mg/kg, oral) also reduced restraint-induced liver injury in mice.⁵⁹ Attenuation of mitochondrial dysfunction was identified as a key mechanism. In addition, the bilberry extract increased glutathione and ascorbate levels and decreased oxidative parameters in the same model at the same doses.⁶⁰

Other activity

Phenolic compounds present in bilberries and other berries (cranberry, cloudberry, raspberry and strawberry) selectively inhibit the growth of human gastrointestinal pathogens such as salmonella and staphylococcus.⁶¹ An effect in reducing bacterial adherence to gut epithelium may be a factor.

Oral administration of 500 mg/kg bilberry extract for 10 days to mice treated with doxorubicin (10 mg/kg) partially restored the toxicity-induced changes by increasing red blood cell and bone marrow counts. Dietary supplementation with the extract at 1% also significantly suppressed doxorubicin-induced myocardial damage.⁶²

Five-day oral administration of bilberry extract (50 to 200 mg/kg) attenuated potassium bromate-induced kidney damage in mice.⁶³ Oxidative parameters were also improved, indicating reduced oxidative stress. Bilberry extract (2.7% of diet) reduced blood glucose and enhanced insulin sensitivity in type 2 diabetic mice via activation of AMP-activated protein kinase.⁶⁴

Peripheral vascular disorders and venous disorders

In open trials, bilberry extract (equivalent to 86 to 173 mg anthocyanins per day) improved oedema and subjective symptoms of lower limb varicose syndrome,⁷³ reduced protein exudate of varicose ulcers⁴³ and decreased the total drainage time after reactive hyperaemia in chronic venous insufficiency.⁷⁴ Bilberry extract (57 to 115 mg anthocyanins per day for 2 to 3 months) provided relief for venous disorders including haemorrhoids during pregnancy.^75,76 A review of open trials from 1979 to 1985 involving a total of 568 patients with venous insufficiency of the lower limbs concluded that bilberry extract caused rapid disappearance of symptoms and improvements in venous microcirculation and lymph drainage.⁷⁷ Mobilisation of finger joints was improved in patients with Raynaud’s syndrome.⁷⁸

Bilberry extract (equivalent to 173 mg anthocyanins per day) or placebo was administered for 30 days in a single blind, placebo-controlled clinical trial in 60 patients with venous insufficiency. Significant reduction in the severity of symptoms (oedema, sensation of pain, paraesthesia, cramping pain) was observed for the treated group after 4 weeks’ treatment (p<0.01).⁷⁹

In a double blind, placebo-controlled trial, 47 patients with peripheral vascular disorders of various origins were treated with bilberry extract (equivalent to 173 mg anthocyanins per day) or placebo for 30 days. The treated group experienced a reduction in subjective symptoms including paraesthesia, pain, heaviness and oedema.⁷⁸

Microcirculation disorders including retinopathy

In open trials, bilberry extract (equivalent to 57 to 288 mg anthocyanins per day) improved symptoms caused by decreased capillary resistance (petechiae, bruising and faecal occult blood),⁴⁴ reduced the microcirculatory changes induced by cortisone therapy in patients with asthma and chronic bronchitis,⁸⁰ and improved diabetic retinopathy with a marked reduction or even disappearance of retinic haemorrhages.⁸¹ Post-operative complications from surgery of the nose were reduced in patients who received bilberry extract (equivalent to 115 mg anthocyanins per day) administered for 7 days before and 10 days after surgery.⁸²

In a placebo-controlled trial, bilberry extract (equivalent to 115 mg anthocyanins per day for 12 months) improved early phase diabetic retinopathy, as indicated by a reduction of hard exudate at the posterior pole.⁸³

In a double blind, placebo-controlled clinical trial, 14 patients with diabetic and/or hypertensive retinopathy received bilberry extract (equivalent to 115 mg anthocyanins per day) or placebo for 1 month. Significant improvements in the ophthalmoscopic and angiographic patterns were observed in 77% to 90% of treated patients.⁸⁴

Visual disorders

In open trials conducted as early as 1964, bilberry extract (including isolated anthocyanins), alone or in combination with beta-carotene and retinol, improved vision in healthy subjects and in patients with visual disorders such as myopia.^85,86 Enlargement of visual range was observed for patients with pigmentary retinitis⁸⁷ and retinal sensitivity was improved in patients with hemeralopia (defective vision in bright light).⁸⁸

Visual perception improved in 76% of myopic patients receiving 150 mg/day bilberry extract and retinol for 15 days.⁸⁹ Similar results were obtained for patients with simple glaucoma.⁹⁰

Three placebo-controlled trials^91–93 and two open studies^85,94 have demonstrated improvement in night vision in a number of settings. However more recent research⁹⁵ and a systematic review⁹⁶ have cast doubt on the validity of such findings.

Other conditions

In open trials, bilberry extract was administered post-operatively in conjunction with anti-inflammatory and analgesic drugs to patients who had undergone haemorrhoidectomy. Bilberry reduced post-operative symptoms (itching and oedema).^97,98

In a placebo-controlled trial, bilberry extract (equivalent to 115 mg anthocyanins per day for 180 days) was effective in reducing nosebleed caused by abnormal capillary fragility of the mucous membranes.⁹⁹

In a double blind, placebo-controlled trial, 30 women with chronic primary dysmenorrhoea were treated with bilberry extract (equivalent to 115 mg anthocyanins per day) for 3 days before and during menstruation. Bilberry significantly reduced symptoms of dysmenorrhoea such as pelvic and lumbosacral pain, mammary tension, headache, nausea and heaviness of lower limbs (p<0.01).¹⁰⁰

In a controlled trial, 62 volunteers at increased risk of cardiovascular disease were randomised to receive either 330 mL/day of bilberry juice or water for 4 weeks.¹⁰¹ Supplementation with bilberry juice resulted in significant decreases in plasma levels of several inflammatory factors or measures regulated by NF-kappaB. Unexpectedly, an increase of TNF-alpha was observed. Plasma quercetin and p-coumaric acid increased in the bilberry group.

Naturally occurring anthocyanins possess colorectal cancer chemopreventive properties in rodent models. Hence, a human investigation was undertaken to determine if an anthocyanin-rich standardised bilberry extract caused pharmacodynamic changes consistent with chemopreventive efficacy, and generated measurable levels of anthocyanins in blood, urine and target tissue.¹⁰² Twenty-five colorectal cancer patients scheduled to undergo resection of the primary tumour or liver metastases received extract containing 0.5 to 2.0 g anthocyanins daily for 7 days before surgery. Anthocyanins and their methyl and glucuronide metabolites were identified in plasma, colorectal tissue and urine, but not in liver. Anthocyanin concentrations in plasma and urine were roughly dose-dependent, reaching approximately 179 ng/g in tumour tissue at the highest dose. Proliferation in tumour tissue was decreased by an average of 7% for all patients on bilberry compared with pre-intervention values. The authors concluded that repeated administration of bilberry anthocyanins exerts pharmacodynamics effects and generates concentrations of anthocyanins in humans resembling those active in a murine adenoma model sensitive to the chemopreventive properties of anthocyanins. Studies of doses containing less than 0.5 g bilberry anthocyanins are necessary to determine if they may be appropriate as colorectal cancer chemopreventive agents.