In vivo antimalarial activity, toxicity and phytochemical screening of selected antimalarial plants.

ETHNOPHARMACOLOGICAL RELEVANCE: Malaria continues to kill over a million people each year and in many populations affected by malaria, conventional drugs are often unaffordable or inaccessible. Historically, plants have been a prominent source of antimalarial drugs. Those plants currently used by indigenous people to treat malaria should be documented and investigated as potential sources of new antimalarial drugs. AIM OF THE STUDY: To investigate in vivo antimalarial activity, toxicity and carry out phytochemical screening of selected plants which have been used in traditional medicine for the treatment of malaria. MATERIALS AND METHODS: Organic and water extracts of four medicinal plants used for the treatment of malaria in traditional health systems of Msambweni people in Kenya were tested for antimalarial activity against Plasmodium berghei and brine shrimp lethality. They were also screened for their major phytochemical constituents. RESULTS: Aqueous extract of the stem bark of Adansonia digitata exhibited highest chemosuppression of parasitaemia, >60% in a murine model of Plasmodium berghei infected mice. Aqueous and organic extracts of Launaea cornuta and Zanthoxylum chalybeum were toxic to the brine shrimp (LD50<1000µg/ml) while aqueous and organic extracts of Adansonia digitata and aqueous extracts of Canthium glaucum were not toxic to brine shrimp (LD50>1000µg/ml). Phytochemical screening revealed the presence of alkaloids and flavonoids in all the crude extracts of the selected plant species studied. Sesquiterpene lactones and saponis were present in organic extracts but absent in the aqueous extracts of Adansonia digitata, Canthium glaucum, Launaea cornuta and Zanthoxylum chalybeum. CONCLUSION: The results showed that the crude extracts of Adansonia digitata and Canthium glaucum demonstrated promising antimalarial activity and there is potential for isolation of lead compounds from their extracts.

Evaluation of herbs as potential drugs/medicines.

Herbal drugs have been used since ancient times as medicines for the treatment of a wide range of diseases, for both human and livestock. A study conducted in the Lake Victoria Basin Kenya revealed vast knowledge and reliance on traditional medicine as a source of healthcare. The study documented 34 medicinal plant species distributed among 21 botanical families and 34 genera, used in the management of human ailments. The highest numbers of species were from the families Asteraceae and Leguminosae. The most commonly harvested plant parts were leaves (46.51%) and roots (34.88%). The most common growth forms utilised were herbs (40.54%) followed by shrubs (27.03%). The major methods of herbal drug preparation were concoction (31.03%) and decoction (24.14%) administered mainly through oral and dermal routes, (64.29%) and (32.14%) respectively. The use of herbal drugs as mixtures was reported to be a common practice by the herbal practitioners; 57.14% of the preparations were dispensed as mixtures while 42.86% of the preparations composed of single plants. A rich knowledge of medicinal plants was recognized and phytochemical and bioactivity analyses of these herbal plants are recommended to determine their safety and efficacy.

In vitro antifungal activity of Schizozygia coffaeoides bail. (Apocynaceae) extracts.

Leaf extracts of Schizozygia coffaeoides were investigated for antifungal activity using the disc diffusion assay technique. Petroleum ether 40-60 degrees C, dichloromethane-ethyl acetate (1:1) and methanol extracts were fungitoxic to Trichophyton mentagrophytes, Microsporum gypseum, Cladosporium cucumerinum and Candida albicans. The extracts were fungistatic in action.

Antiprotozoal properties of 16,17-dihydrobrachycalyxolide from Vernonia brachycalyx.

Extracts of the leaves from Vernonia brachycalyx showed in vitro activity against Plasmodium falciparum and promastigotes of Leishmania major. The germacrane dilactone 16,17-dihydrobrachycalyxolide (1) which was previously isolated from the aerial parts of the plant was shown to be the major antiplasmodial principle. An X-ray crystallographic analysis established the absolute configuration and some signals in the NMR spectra were reassigned. 16,17-Dihydrobrachycalyxolide (1) elicited a strong antiplasmodial and antileishmanial activity but also a high toxicity against human lymphocytes.

Antiprotozoal compounds from Asparagus africanus.

Two antiprotozoal compounds have been isolated from the roots of Asparagus africanus Lam. (Liliaceae), a new sapogenin, 2 beta, 12 alpha-dihydroxy-(25R)-spirosta-4,7-dien-3-one (1), which was named muzanzagenin, and the lignan (+)-nyasol (2), (Z)-(+)-4,4'-(3-ethenyl-1-propene-1,3-diyl)-bisphenol. The structure of the sapogenin was elucidated by MS and by 1D and 2D NMR methods and established by a single crystal X-ray analysis. (+)-Nyasol potently inhibits the growth of Leishmania major promastigotes, the IC50 being 12 microM, and moderately inhibits Plasmodium falciparum schizonts with the IC50 49 microM. These concentrations only moderately affect the proliferation of human lymphocytes. Muzanzagenin showed a moderate in vitro activity in all three tests, the IC50 against leishmania promastigotes was 70 microM, and against four different malaria schizont strains the IC50 values were 16, 163, 23, and 16 microM, respectively.

Two new antiprotozoal 5-methylcoumarins from Vernonia brachycalyx.

Two new isomeric 5-methylcoumarins, 2'-epicycloisobrachycoumarinone epoxide (1) and cycloisobrachycoumarinone epoxide (2), have been isolated from the roots of Vernonia brachycalyx by means of bioactivity-guided fractionation. The structures were elucidated by MS and NMR spectroscopic methods. Compounds 1 and 2 showed in vitro activity against Leishmania major promastigotes and against Plasmodium falciparum schizonts and demonstrated an inhibition on the proliferation of human lymphocytes, which was significantly weaker than the antiparasitic effects.

Potent antimalarial activity of the alkaloid nitidine, isolated from a Kenyan herbal remedy.

Bioassay-guided fractionation of extracts of Toddalia asiatica, a plant used by the Pokot tribe of Kenya to treat fevers, has yielded the alkaloid nitidine as the major antimalarial component. Fractions containing nitidine have in vitro 50% inhibitory concentrations against Plasmodium falciparum in the range of 9 to 108 ng/ml for a range of chloroquine-susceptible and -resistant strains. The results show a lack of cross-resistance between chloroquine and nitidine.

Ecdysteroids as regulators of host and parasite interactions: a study of interrelationships between Schistosoma mansoni and the host snail, Biomphalaria glabrata.

Ecdysteroids have been detected in trematode parasites and in several species of gastropod snails. The potential role of these and other hormones as regulators of host/parasite interactions is discussed. This study considers the role of ecdysteroids in the host parasite interactions between Schistosoma mansoni and Biomphalaria glabrata interactions. beta-Ecdysterone was found to be effective in stimulating host location activities in S. mansoni miracidia and in enhancing growth and egg production in B. glabrata. However, plant extracts rich in phytoecdysteroids were not attractive to miracidia and did not affect growth and egg production in snails. The potential role of ecysteroids in the process of parasitism and snail physiological processes is discussed. Plants rich in phytoecdysteroids do not appear to be of value in process which may interfere with the host parasite interactions in schistosomes.

Irritant principles of the mezereon family (Thymelaeaceae), V. New skin irritants and tumor promoters of the daphnane and 1 alpha-alkyldaphnane type from Synaptolepis kirkii and Synaptolepis retusa.

Seventeen mostly new, skin irritant diterpene esters (DTE) of the daphnane and 1 alpha-alkyldaphnane types were isolated from roots of Synaptolepis kirkii and Synaptolepis retusa. The parent alcohols of the daphnane types are shown to be 5 beta-hydroxyresiniferonol-6 alpha,7 alpha-oxide [1] and 5 beta, 12 beta-dihydroxyresiniferonol-6 alpha,7 alpha-oxide [2]. Ten of the daphnane types are 9,13,14-orthoesters and three are conventional esters involving tertiary or secondary hydroxyl groups at C-13 or C-14, respectively. The latter may be considered immediate precursors of corresponding orthoesters. The four 1 alpha-alkyldaphnane types are intramolecular 9,13,14-ortho-(2-hexadecenoic acid)-esters in which, formally, the second to last C atom of the orthoester moiety is linked covalently to C-1 alpha of the diterpene parent alcohols 1 or 2. Thus, in the new structure, a macrocyclic ring bridges the alpha side of the diterpene moiety in an "ansa" type manner. The irritancies on the mouse ear of the DTE obtained cover a wide range (I24 = 0.05-670 nmole-1). Some of them are considerably more irritant than the daphnane type standard simplexin. Structure/activity investigations reveal that an ester group instead of a free hydroxyl group at C-20 ("cryptic types"), or presence of a hydroxy or an acetoxy group in position 12 diminishes the irritancies of the daphnane types isolated, similar to what is known in corresponding tigliane types. In the standardized initiation/promotion protocol on the back skin of mice, some of the irritant DTE exhibit tumor-promoting activities higher than that of simplexin.

HPCL Separation and quantitative determination of valepotriates from Valeriana kilimandascharica.

Valepotriates, mainly isovaltrate and valtrate, have been separated and quantitatively estimated by reversed-phase HPLC in the leaves, flowers, stems and rhizomes of VALERIANA KILIMANDASCHARICA. The isovaltrate/valtrate concentration reaches a maximum of 5.89% in the leaves, 3.84% in the flowers, 3.17% in the stems and 5.15% in the rhizomes. A micro Bondapak C (18) column using MeOH-H (2)O mixtures as eluant is suitable for a baseline separation of isovaltrate, valtrate, acevaltrate and baldrinal at UV 254 nm in 15 min and didrovaltrate and IVHD-valtrat at UV 208 nm in 10 min. Relative standard deviation for quantitative determinations is approximately 1.5% for valepotriate contents of 1%. This method is adaptable for routine analysis of crude extracts.

Identification and estimation of an acetylcholine-like substance in the venom of Dendroaspis jamesoni.

An acetylcholine-like substance was isolated from desiccated Jameson's mamba venom by one-dimensional ascending paper chromatography. The migratory and staining properties of the substance were identical with those of standard acetylcholine. Pharmacological identification on various in vitro and in vivo biological test objects showed that the substance was acetylcholine. It was further confirmed by high-voltage paper electrophoresis. The acetylcholine content was 4.35--4.36 mg/g of desiccated venom as shown by two different biological assay methods, and the index of discrimination was found to be 1.1, further confirming that substance in snake venom was acetylcholine.