Professor Peter Houghton, head of the pharmacognosy research group, King's College London, chaired the Conference's sessions of research contributions in pharmacognosy. Other research involving natural products was presented during the poster sessions as part of the science programme. The following represents a selection of some of the contributions in the field of pharmacognosy.
Anti-inflammatory compounds from myrrh G. R. Battu, I. J. Zeitlin and A. I. Gray (University of Strathclyde) described a study in which they had used a colorimetric assay to measure the inhibitory activity of molecules isolated from a Kenyan myrrh, Commiphora kua, against myeloperoxidase, an enzyme which initiates oxidative tissue damage in chronic inflammation. Inflamed paw extracts were incubated with or without test substances (compounds from C kua and indomethacin) in phosphate buffer containing dianisidine and hydrogen peroxide before absorbance was measured at 440nm. The authors also assessed the compounds' anti-inflammatory activity after oral administration using the carrageenan-induced rat paw oedema model.
Six compounds with inhibitory activity against myeloperoxidase were identified. Dose-response curves were obtained for these molecules and indomethacin, and equipotent molar ratios at 40 per cent inhibition were determined. The results indicated that one of the molecules tested, mansumbinoic acid, was almost five times as potent as indomethacin in inhibiting the production of toxic oxidants by myeloperoxidase, and almost as active as indomethacin in suppressing carrageenan-induced acute inflammation. Another compound, 4-methoxy-1,2,3,4-tetradehydropolygamain, was found to be 2.6 times more potent than indomethacin in inhibiting myeloperoxidase.
Anti-inflammatory components of feverfew The activity of feverfew (Tanacetum parthenium), a medicinal plant used for the treatment of migraine, has been attributed to the presence of sesquiterpene lactones, of which parthenolide is the major constituent. Little is known, however, about the lipophilic flavonoids of T parthenium.
M. C. Pasquali, C. Rostron, M. I. Berry and M. W. Powell (Liverpool John Moores university) purified the flavonol 6-hydroxy-kaempferol-3,6,4'-trimethylether (santin) from a methanol-chloroform extract of dried powdered T parthenium by silica gel TLC and characterised the compound by its chromatographic Rf value, UV spectroscopy and GC-MS. Values obtained (Rf = 0.19 in toluene-acetone; UV spectra lmax in methanol 248) were similar to those reported previously for santin, showing that the extraction procedure was efficient for santin.
Antimycobacterial testing Around a third of the world's population is infected with the tubercle bacillus Mycobacterium tuberculosis, and tuberculosis (TB) is responsible for two to three million deaths per year worldwide. The development of multi-drug-resistant strains of mycobacteria is in part responsible for the high incidence of TB, and there remains an urgent need to develop novel antimycobacterial agents.
S. M. Newton, C. Lau and C. W. Wright (University of Bradford) used M aurum and M smegmatis, species that have been shown to have similar drug sensitivity profiles to that of M tuberculosis, to investigate the antimycobacterial activity of several plant species used in traditional medicine for the treatment of TB or leprosy. Crude methanolic extracts of 42 plant species from 33 families were prepared to give final concentrations ranging from around 15 to 500µg/ml. In vitro screening for antimycobacterial activity involved both positive (streptomycin; minimum inhibitory concentration [MIC] 0.49µg/ml) and negative (ampicillin) control drugs; inhibition of the growth of organisms in the presence of each test sample was determined by measuring the optical density of the mycobacteria at 550nm.
The most promising MIC values were obtained for Sanguinaria canadensis (31.25µg/ml), Commiphora mukul (31.25µg/ml) and Psoralea corylifolia (62.5µg/ml) in studies using M aurum. While these findings are encouraging, the authors emphasise that further work will be needed to determine whether extracts of these species are also active against M tuberculosis.
Medicinal plants for memory improvement? Inflammatory mechanisms have been implicated in the pathogenesis of Alzheimer's disease, and therefore anti-inflammatory agents may offer some protection against the development of this disease.
M.-J. Howes, P. J. Houghton and J. R. Hoult (King's College London) investigated the anti-inflammatory activity of several plants, including Salvia miltiorrhiza (root), Withania somnifera (root), Apocynum lancifolium (leaves), Rosmarinus officinalis (leaves) and Ziziphus jujuba (seeds), used traditionally for central nervous system disorders. The group used a radioimmunoassay to assess the activity of aqueous and ethanolic extracts of the plant parts at concentrations of 50µg/ml against enzymes involved in the arachidonic acid cascade in rat peritoneal leucocytes that express pathways for both cyclo-oxygenase (COX) and 5-lipoxygenase (5-LOX) activity. The ability of the extracts to inhibit the formation of the proinflammatory eicosanoids leukotriene B4 and thromboxane B2 was compared with that of indomethacin (a COX inhibitor) and ZM-211965 (a 5-LOX inhibitor) as positive controls.
Of all the extracts screened, both aqueous and ethanolic extracts of S miltiorrhiza root demonstrated significant reductions in eicosanoid generation. Subsequent work using aqueous and ethanolic extracts of S miltiorrhiza root at concentrations of 25, 50, 100 and 200µg/ml demonstrated that the ethanolic extract was highly active with regard to inhibition of both leukotriene B4 and thromboxane B2.
Research has also established that increasing brain concentrations of acetylcholine by inhibition of acetylcholinesterase is a useful therapeutic strategy for the treatment of memory loss associated with early stages of Alzheimer's disease. Against this background, P. J. Houghton, K. Shipman and M.-J. Howes (King's College London) tested water, ethanol and chloroform extracts and fractions of W somnifera roots for acetylcholinesterase inhibition. The authors reported that all extracts showed acetylcholinesterase inhibitory activity, and that one of the fractions, which was shown by thin-layer chromatography to comprise a single constituent, had an IC50 of 2.2±0.3mg/ml.
Sublingual cannabis preparation in a phase one study Over the past year there have been several significant developments in clinical research with cannabis preparations. One area has focused on the development of non-oral formulations. G. W. Guy, M. E. Flint. P. J. Robson and B. A. Whittle (GW Pharmaceuticals, Salisbury) presented the findings from a phase one study of three sublingual cannabis-based medicine extracts in six healthy volunteers. The three extracts consisted of a preparation containing predominantly delta-9-tetrahydrocannabinol (THC), one containing predominantly cannabidiol (CBD) and one containing a 1:1 ratio of THC to CBD. The effects of these extracts after a single-dose sublingual administration (total dose 20mg THC and/or 20mg CBD in eight increments at 10-minute intervals) on subjective effects (such as mood and relaxation) and objective parameters (such as conjunctival reddening and tachycardia), were compared with those of placebo.
According to the authors, subjective effects were greater with the preparations containing THC than with the preparation containing CBD; effects usually persisted for around three to four hours. Perceived effects with placebo were slight and transient. Cognitive function assessments showed a slight THC-associated decrease in performance in a test of spatial working memory, and there were similar trends in impairment of reaction time and vigilance tasks.
The authors concluded that the study had shown that cannabis-based extracts administered sublingually were well tolerated at doses likely to be higher than those needed by many patients. Sublingual administration appears to offer an alternative route of dosing which should result in a more rapid onset of activity, and which avoids the substantial first-pass effect on cannabinoid absorption associated with oral administration.
Medicinal plants for gastric ulcers The fresh and dried leaves of Portulaca oleracea have been used traditionally to treat several conditions, including gastric ulcers. M. W. Islam, M. N. M. Zakaria, R. Radhakrishnan, X. M. Liu, H. B. Chen, K. Chan and A. Al-Attas (Ministry of Health, Abu Dhabi) investigated the effects of a 10 per cent ethanolic extract of P oleracea on gastric mucosal injury caused by non-steroidal anti-inflammatory drugs (NSAIDs) (indomethacin, phenylbutazone) and cytodestructive agents (80 per cent ethanol and 0.2M NaOH) in rats.
P oleracea ethanolic extract administered intraperitoneally at doses of 100, 200, and 400mg/kg produced significant dose-related inhibition of gastric damage caused by NSAIDs, compared with control. Oral doses of 200 and 400mg/kg produced a significant inhibitory effect on gastric mucosal lesions caused by the cytodestructive agents used.
The authors suggested that the antiulcer and cytoprotective effects of P oleracea demonstrated in this study may be due to the presence in the leaves of the antioxidants omega-3 fatty acids, ascorbic acid and a-tocopherol, which have previously been shown to protect against gastric mucosal injury.
Further work has been carried out on the antigastric ulcer effects of a combination of P oleracea and Salvadora persica (Aarak tree), which has also been used traditionally for the treatment of ulcers. An orally administered combination of a 10 per cent ethanolic extract of the two species at doses of 100 and 200mg/kg of each species demonstrated significant dose-related inhibition of gastric damage caused by indomethacin, phenylbutazone, 80 per cent ethanol and 0.2M NaOH.
Teaching pharmacognosy Over the past decade there has been a decline in the teaching of pharmacognosy in UK schools of pharmacy. At the same time, the void has begun to be filled by other institutions at which pharmacognosy is researched and taught on non-pharmacy courses. By contrast, many other European countries, the US and Japan have strong pharmacognosy research groups within their schools and colleges of pharmacy.
M. Al-Shahib, F. Smith and J. Barnes (School of Pharmacy, London) carried out a postal questionnaire survey of all 16 UK schools of pharmacy in April, 2000, to explore the teaching of natural products and related areas, such as herbal medicine, in the MPharm programme.
Fifteen (94 per cent) of the 16 schools responded; the one that did not respond is known to have a strong pharmacognosy group. Of the 15 responding schools, 13 (87 per cent) stated that their MPharm syllabus includes teaching of pharmacognosy and related areas as part of the core curriculum. The median number of hours teaching (as formal lectures, laboratory-based practicals and interactive tutorials/small group sessions) each student receives in this area over the MPharm course is 52 (range 5 to 69 hours; upper quartile 55 hours, lower quartile 36 hours).
Nine respondents (60 per cent) stated that the MPharm course allows selection of an option on pharmacognosy and related areas, with a median of 52 hours teaching as defined earlier (range 10 to 128 hours; upper quartile 63 hours, lower quartile 39 hours). Eleven schools (73 per cent) stated that pharmacy students are able to undertake a research project in pharmacognosy or related areas. Thirteen schools (87 per cent) stated that their MPharm course includes teaching on herbal medicines or areas of complementary and alternative medicine as part of the core or option programme. Of these, 11 provided estimates of the number of hours teaching in these areas, giving a median of eight hours (range 3 to 38 hours). - Ms Jo Barnes (research fellow, School of Pharmacy, University of London).