Amala Raman

Anti-diabetic properties and phytochemistry of Momordica charantia L. (Cucurbitaceae).

Unripe fruit, seeds and aerial parts of Momordica charantia Linn. (Cucurbitaceae) have been used in various parts of the world to treat diabetes. Oral administration of the fruit juice or seed powder causes a reduction in fasting blood glucose and improves glucose tolerance in normal and diabetic animals and in humans. Animal and in vitro data support both insulin secretagogue and insulinomimetic activity of the fruit. However, enhanced insulin levels in vivo in response to its administration have not been observed. Although a wide range of compounds have been isolated from Momordica charantia, notably steroidal compounds and proteins, the orally active antidiabetic principle has not been adequately identified. A polypeptide, p-insulin, produces hypoglycaemic effects in humans and animals on subcutaneous injection, but oral activity is questionable. Other reported hypoglycaemic principles from Momordica charantia include the sterol glucoside mixture charantin (fruit) and the pyrimidine nucleoside vicine (seeds). However these are only effective at doses too high to account for all the activity of the plant extract. Principal toxicity of Momordica charantia in animals is to the liver and reproductive system. These effects have not been reported in humans despite widespread use of the fruit medicinally and as a vegetable.

Antioxidant action and potential antidiabetic properties of an isoflavonoid-containing soyabean phytochemical extract (SPE)

The potential role of oestrogenic agents, antioxidants and intestinal glucose‐uptake inhibitors in the treatment of diabetes is briefly reviewed. Reports in the literature suggest that oestrogen replacement therapy may favourably modulate glucose homeostasis. A soya phytochemical extract (SPE) containing the isoflavone phytoestrogens genistein and daidzein (mostly in their glycone forms as genistin and daidzin) was investigated as an antioxidant and modulator of intestinal glucose‐transport. In the present study, SPE was found to protect against glucose‐induced oxidation of human low density lipoproteins (LDL) in vitro. Equol (a gut bacterial metabolite of daidzein) was a more effective antioxidant than daidzein or genistein in this system and was of similar antioxidant potency to the dietary flavonols quercetin and kaempferol and to the endogenous antioxidant 17β‐oestradiol. SPE was found to be an inhibitor of glucose uptake into rabbit intestinal brush border membrane vesicles in vitro, though of weaker potency than the classical sodium dependent glucose transporter (SGLT) inhibitor, phlorizin. Thus SPE displays a range of properties which may be of benefit in diabetes, namely as an oestrogenic agent, an inhibitor of intestinal glucose‐uptake and a preventive agent for glucose‐induced lipid peroxidation. Copyright

Antidiabetic and hypocholesterolaemic effects of fenugreek

The seeds of Trigonella foenum graecum (fenugreek) have been reported to have antidiabetic and hypocholesterolaemic properties in both animal models and humans. Activity has been attributed largely to fenugreeks saponin and high fibre content, and is probably not related to its major alkaloid trigonelline. Antihyperglycaemic effects have been linked to delayed gastric emptying caused by the fibre content, and to (unidentified) components that inhibit carbohydrate digestive enzymes. Fenugreek administration may increase plasma insulin levels in vivo. Its major free amino acid, 4‐hydroxyisoleucine, stimulates insulin secretion from perfused pancreas in vitro. The hypocholesterolaemic effect has been attributed to increased conversion of hepatic cholesterol to bile salts due to loss, in the faeces, of complexes of these substances with fenugreek fibre and saponins. Fenugreek treatment selectively reduces the LDL and VLDL fractions of total cholesterol, and HDL‐cholesterol has also been reported to increase in alloxan‐induced diabetic rats and type II diabetic individuals following treatment with fenugreek. Fenugreek administration has not been reported to cause any toxicological effects. Its regular consumption may therefore be beneficial in the management of diabetes and the prevention of atherosclerosis and coronary heart disease.

In vitro keratinocyte antiproliferant effect of Centella asiatica extract and triterpenoid saponins

Psoriasis is a hyperproliferative skin disorder estimated to be present in 1-3% of most populations. Conventional therapy using corticosteroids, Vitamin D analogs and cytotoxic agents eg psoralens is associated with low success rate and many side effects. Traditional plant remedies may provide leads for new treatments. A rapid-throughput, in vitro bioassay has been utilised to examine plants for inhibitory effects on the growth of SVK-14 keratinocytes. Centella asiatica, a reputed anti-psoriatic herb, has been compared against the psoralen-containing seeds of Psoralea corylifolia and the synthetic anti-psoriatic agent dithranol (anthralin). Aqueous extracts of Psoralea corylifolia and Centella asiatica inhibited keratinocyte replication with IC50 values of 18.4 +/- 0.6 microg/ml and 209.9 +/- 9.8 mg/ml respectively prior to treatment with polyvinylpolypyrrolidone (PVPP) and 36.3 +/- 3.3 mg/ml and 238.0 +/- 2.5 mg/ml respectively after PVPP treatment of the extracts. The effect produced by C. asiatica is thus unlikely to be due to phenolic compounds. It may, however, be due to its two constituent triterpenoid glycosides madecassoside and asiaticoside which had IC50 values of 8.6 +/- 0.6 microM respectively. These values were comparable to their concentrations in the crude extract and to the IC50 of dithranol (5.1 +/- 0.4 microM). These results suggest that the potential use of C. asiatica extracts as a topical anti-psoriatic agent is worthy of further investigation.

Sulphorhodamine B assay for measuring proliferation of a pigmented melanocyte cell line and its application to the evaluation of crude drugs used in the treatment of vitiligo.

A rapid 96-well plate assay using sulphorhodamine B (SRB) protein stain for cell number has been adopted to screen herbs used in traditional treatments of vitiligo for substances capable of stimulating melanocyte proliferation. Its applicability to melan-a cells, a mouse pigmented cell line, has been validated. SRB assay produced good linearity up to 11 x 10(4) cells/well and interference by melanin present in the cells accounted for less than 10% of the total optical density readings. The intra-assay variation was small but interassay variation was marked. For better assay precision, it is recommended that the results to be compared should be performed on the same day and controls should be plated in the same experiment, ideally in the same plate. Optimum conditions for exponential melan-a cell growth were established: viz. initial plating density (3-8 x 10(3) cells/well), incubation period (4 days) and foetal bovine serum concentration (5%). Under these conditions cells were responsive to the mitogen tetradecanoyl phorbol acetate (TPA). Out of 28 herbal extracts screened in this assay, significant stimulation (P < 0.05) of melanocyte proliferation was observed, in the absence of TPA, using aqueous extracts of Astragalus membranaceous root, Citrus reticulata peel, Dictamnus dasycarpus root bark. Ophiopogon japonicus root, Poria cocos sclerotium and Tribulus terrestris fruit.

Antimicrobial activities of the stembark of Kigelia pinnata

Chemical investigation showed that the aqueous extracts of the stembark of Kigelia pinnata contain iridoids as major components. In the light of the traditional uses of this plant, antimicrobial activities of the aqueous extracts and two major iridoids were tested against Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. The crude aqueous extracts showed significant antimicrobial activity which could be partially explained by the activity of the iridoids present.

Antimicrobial and antiinflammatory activities of extracts and constituents of Oroxylum indicum (L.) Vent

Dichloromethane extracts of the stembark and root of Oroxylum indicum were found to have antimicrobial activities against Gram positive bacteria (Bacillus subtilis and Staphylococcus aureus), Gramnegative bacteria (Escherichia coli and Pseudomonas aeruginosa) and a yeast (Candida albicans). Bioassay-guided chromatographic fractionation led to the isolation of flavonoids (bacailein and chrysin) and a naphthoquinone, lapachol. Lapachol was found active against the Gram-positive bacteria, 5 μg giving a zone of inhibition equivalent to that shown by 5 μg streptomycin, whereas 5 μg chrysin gave inhibition zones of equal size to 5 μg streptomycin against Candida albicans and Pseudomonas aeruginosa. The inhibitory activity of lapachol from O. indicum root against soya 5-lipoxygenase (IC(50) 0.79 μg/ml) was equivalent to that of the positive control fisetin (IC(50) 0.97 μg/ml) and 50 μg/ml of the dichloromethane extract of the rootbark gave 100% inhibition of leukocyte lipoxygenase. These activities might indicate an antiinflammatory effect for the dichloromethane extract, mainly due to the lapachol content.

Lipoxygenase inhibitors in the seeds of Aframomum danielli K. Schum (Zingiberaceae).

Alcohol and petrol extracts of the seeds of Aframomum danielli inhibit the soya 5-lipoxygenase enzyme and thus may show antiinflammatory activity. Compounds isolated from the active fractions were shown to be long chain polyprenyl benzoquinone derivatives. Phytylplastoquinone was isolated from the petrol extract and plastoquinone-7 (heptaplastoquinone) from the alcohol extract. The presence of these two known benzoquinones in A. danielli and their ability to inhibit 5-lipoxygenase are reported here for the first time.

Investigation of the effect of Angelica sinensis root extract on the proliferation of melanocytes in culture

Aqueous extracts of Angelica sinensis root, a herb commonly used in the treatment of vitiligo in Traditional Chinese Medicine, were tested for their activity on mouse melanocyte proliferation in culture. At concentrations of 0.5-2500 micrograms/ml, these extracts were not able to stimulate melanocyte cell division. On the contrary, they exerted a general cytotoxicity to the cells at higher concentrations. Cytotoxicity was reduced by prior treatment of the extract with polyvinylpolypyrrolidone, which was shown by thin layer chromatography to reduce the coumarin content.

Regulatory issues relating to herbal products-part 2: safety and toxicity.

ABSTRACT A significant proportion of the general public has the misconception that herbal products are safe because they are of natural origin. Toxicity may arise from inherent properties of the herbal ingredients that result in adverse reactions, which may be serious, or from interactions with conventional drug substances. Toxicity may also be caused by misuse, abuse, and overuse of products and by adulteration of products or misidentification of plants. Regulatory authorities are undertaking to provide a reasonable assurance of efficacy and improved safety of herbal products through monitoring programs and control of herbs that are known to be toxic. Action is taken by the authorities to protect public health when herbal preparations are shown or suspected to cause harm. Case reports of toxicity due to herbal products and actions taken by regulatory authorities are summarized in this article. In the European Union, applicants for marketing authorizations may be required to provide scientific proof of safety and efficacy by reference to bibliographic data, where available. The relevance and credibility of published data needs to be assessed against recommended criteria in order to avoid unnecessary repetition of tests on animals or humans.