(d) Antiprotozoal plants
General tests for antiprotozoals were formerly carried out on paramecia, which are non-pathogenic to man, but these proved to be of no value. The malaria parasites, of which the most malignant is Plasmodium falciparum, have two main phases: intracorporal, in Man, and extracorporal or exogenous in the mosquito (Anopheles). The intracorporal phase has three distinct cycles: asexual (schizogony), sexual (sporogony) and an extra-erythrocytic cycle in the liver. Thus Man is an intermediary; the mosquito is the final host in which the sexual cycle is completed. Trypanosomiasis is also conveyed by an animal vector, the tsetse fly (Glossina morsitans). Similarly, in leishmania tropica the intermediate host is Phlebotomus papatassi and visceral leishmaniasis is transmitted through the sandfly Phlebotomus argentipes. In bilharzia the vector is the freshwater snail. In all these cases, prophylactic action against insects and molluscs is an essential part of any campaign against the disease.
The activity of chemical constituents (e.g. alkaloids) against protozoa such as Trypanosoma lewisi is determined by the method of Hopp el al. (1976) in terms of the immobility produced on the organism and is expressed as the average percentage of non-motile organisms from four microscopic fields. Phenol and pentamidine are comparatively tested as controls. In looking at the effects registered in this chapter, it appears that in their activity against protozoa, the constituents seem to be chemically less varied than in the preceding groups. Many are alkaloids.
Plasmodium spp. Apart from the antimalarial action of the alkaloid quinine from Cinchona spp., which has been known for many years, brucine (or bruceolides?) from Brucea antidysenterica, funiferine from Tiliacora funifera, rhynchophylline from Crossopteryx febrifuga and meliacins from Trichilia roka are said to act against Plasmodium berghi.
Activity against Leishmania tropica has been observed with the alkaloids echitamine from Alstonia boonei and berberine (also anti-amoebic) from Argemone mexicana. The latter species also contains sanguinarine, which is trypanocidal. Berberine is also found in Chasmanthera dependens, which has both anti-leishmania and trypanocidal action. At one time berberine was also believed to be antimalarial but Chopra et al. (1938) could show that berberine acts on the spleen, increasing its volume and rhythmic contractions, and that the parasites thus liberated in the peripheral circulation are then able to respond to quinine action. The diagnosis of latent malaria as carried out by certain specialists is based on this property. Harmane derivatives in certain plants like Acacia nilotica, Newbouldia laevis and Pauridiantha lyalli are also antiprotozoal.
The motility of Trypanosoma lewisi can be inhibited by harmine, harmol, harmane chloride, palmatine iodide and, most of all, sanguinarine derivatives (nitrate and sulphate). These compounds caused 70-100% immobility of the test organisms after 1-24 h. The most active is sanguinarine from Argemone mexicana; it causes 100% non-motility even at dilutions of 1:40000 and in vitro had eighty times the activity of pentamidine on Trypanosoma lewisi. Palmatine from Zanthoxylum santhoxyloides,
Chasmanthera dependens and Cocculus and Tinospora spp., at dilutions of 1:8000 led to 95% non-motility after 1 h, but at dilutions of 1:16 000 only 70% non-motility was achieved after 24 h (Hopp et al., 1976; Al-Shamma and Mitscher, 1979; Al-Shamma et al., 1981). (The antiprotozoal action of Zanthoxylum zanthoxyloides and of Anacardium, Plumbago, Drosera etc. have been mentioned under Antibacterial plants.)
Conessine from Holarrhena floribunda * bark has proved to be very active against Entamoeba histolytica in intestinal and hepatic amoebiasis, preventing multiplication of the amoeba. It was found to produce neurological side-effects and therefore its clinical use was suspended. (Conessine is also active against Trichomonas vaginalis and is now mostly used in the topical treatment of trichomoniasis.) Other antiprotozoal alkaloids have been found in Alchomea cordifolia (alchornine) and Mitragyna inermis (rhynchophylline). Anti-amoebic effects have been observed with carpaine from Carica papaya leaves, an ethanolic extract of Phyllanthus niruri* and borrerine (closely related to emetine) from Borreria vertkillata. Antiprotozoal activity is also associated with some terpenoid and meliacin constituents. Thus Curcuma domestica * rhizomes and the aerial parts of Euphorbia tirucalli* have also been reported as active anti-amoebics, owing to the presence of sesquiterpenic ketones (turmerones) and terpenoids, respectively, and the anti-amoebic effect of Euphorbia hirta* has been attributed to euphosterol.
Paramecia are mentioned as responding to the meliacins from Khaya senegalensis, Crossopteryx febrifuga* and Trichilia roka* and to pseudocedrelin fromPseudocedrela kotschyi*, whilst Melia azedarach does not seem to be active against paramecia (Spencer et al., 1947a). On the other hand, the triterpenic saponins in Paullinia pinnata* are said to be active paramecidals. It is interesting to observe from this list that the majority of the plants with antiprotozoal action are plants which show a depressive action on the central nervous system.
L The leaves and juice are used locally as a dressing for fractures and mixed with shea butter as an embrocation for pain, sprains, etc. An extract of the bark is given in the treatment of venereal disease and as a tonic for physical and nervous debility (Dalziel, 1937).
C The alkaloid berberine has been found in the roots. The related species C. palmata from Mozambique contains bitter principles without nitrogen such as colombin, chasmanthin, palmarin and 2-3% of alkaloids of the berberine group, namely, colombamine, jateorhizine and palmatine (Oliver-Bever, 1968).
P C. dependens is used as a bitter tonic. Berberine sulphate is used in India in the treatment of oriental sores; it inhibits Leishmania tropica in concentrations of 1:80000. The alkaloid is also a uterine stimulant (Oliver-Bever, 1968).
Curcuma domestica Valeton syn. (C. longa L.) ZINGIBERACEAE
L The plant is cultivated in West Africa in the forest areas and often grown in native compounds as a dye plant for leather, palm fibre, etc. It is used amongst Moslems as an anthelmintic, an eye wash and an ointment for skin diseases (Dalziel, 1937). In India turmeric is the main constituent of curry powder and is used in local medicine (fresh juice) as an anthelmintic and antiparasitic in the treatment of many skin diseases. It is also said to be an ant repellent (Chopra et al., 1956). In Vietnam turmeric is taken as an anthelmintic and diaphoretic.
C A colouring matter has been isolated from the rhizomes. It contains the curcumines belonging to the dicmnamoyl-methane group and an aromatic oil, turmeric oil (0.24% in the fresh rhizomes), composed of 25% terpene-carbon derivatives and 65% of sesquiterpenic ketones (turmerones) (Paris and Moyse, 1967, p. 78).
P Sodium curcuminate administered intravenously to dogs in a dose of 24 mg/kg doubles the rate of bile flow without any appreciable disturbance of the blood pressure and respiration. It has in addition a powerful antibacterial action against Micrococcus pyogenes var. aureus (Ramprasad and Sirsi, 1956). Basu (1971) compared the antibacterial action of C. domestica to that of penicillin on Gram-positive organisms and that of streptomycin on Gram-negative organisms, and showed that C. domestica was less active than these antibiotics. Antiprotozoal activity against Entamoeba histolytica has been reported for the alcoholic extracts of the rhizomes (Dhar et al., 1968).
L In India E. tirucalli latex is used as a fish poison. It is applied medicinally to warts and used in the treatment of rheumatism and neuralgia (Chopra et al., 1956). In contact with the eye it is a dangerous poison, producing inflammation of the cornea and iris (Crowder and Sexton, 1964). Ingestion of'remedies' containing the latex can produce ulceration of the gastrointestinal mucous membrane (Crowder, 1964 in Kerharo, 1968).
C The latex contains 75-82% of a resin and 14-15% of a rubber. From the latex three terpenic alcohols have been isolated: taraxasterol, tirucallol and euphol (Haines and Warren, 1949, 1950; McDonald et al., 1949). From the fresh latex, isoeuphorol has been obtained, which, when the latex is dried out, is replaced in a few months by euphorone, a ketone. The stem of E. tirucalli has been found to contain hentriacon-tane, hentriacontanol, ^-sitosterol, taraxerol, 3,3'-di-o-methylellagic acid, ellagic acid and also a glucoside which on hydrolysis produces kaempferol and glucose (Gupta and Mahadevan, 1967).
P Alcoholic extracts of the aerial parts of E. tirucalli were shown to possess antiprotozoal activity against Entamoeba histolytica (Dhar et al., 1968; Rao and Gupta, 1970). The protozoal effect of Euphorbia hirta might be due to euphosterol, also reported to be present in this plant (Watt and Breyer-Brandwijk, 1962). A fraction of lyophilized extract, at a dilution of 1:200, had after 48 h the same anti-amoebic effect as emetine hydrochloride at a dilution of 1:80 000 after 24 h (Ndir and Pousset, 1981).
The alcoholic and aqueous extracts of the stems were observed to reduce adenocarcinoma and sarcoma to a considerable extent (Abbot et al., 1966).
Holarrhena floribunda (Don.) Dur. & Schinz var. floribunda syn. (H. africana DC., H. wulfsbergii Stapf, Rondeletia floribunda Don.) APOCYNACEAE
Conessi or kurchi bark
P Holarrhena alkaloids and berberine hydrochloride were studied on intestinal amoebiasis in rats and on hepatic amoebiasis in hamsters and their activity was compared to that of emetine hydrochloride. All the alkaloidal fractions oí Holarrhena effectively reduced the infection in rats and hamsters. Kurchamine appeared to be one of the most promising active compounds. Berberine showed marked effectiveness in both types of infection (Bertho, 1944). Berberine is also remarkably toxic against Leishmania tropica, inhibiting the growth of Leishmania in vitro at a 1:80000 dilution. A 2% solution injected at the base of the lesion caused healing after 2-3 administrations (Chopra et al., 1932).
Clinical tests with conessine on patients with intestinal and hepatic amoebiasis have been found to give results comparable to those obtained with emetine. Use of conessine must, however, be closely supervised, as in some cases it can produce neurological troubles (vertigo, sleeplessness, agitation, anxiety and delirium) (Cros-nier et al., 1948; Tanguy et al. ,1948; Alain et al., 1949; Siguier et al., 1949). For this reason the administration of conessine in cases of dysentery has been discontinued and the substance is now limited to the external treatment of Trichomonas vaginalis and urethritis (Godet, 1950).
L Used locally for dysentery and intestinal spasms in Ghana. Sometimes used as a bitter stomachic and for constipation, the leaves of the plant are also chewed to cure hiccups. An infusion is sometimes used for genito-urinary disorders (Dalziel, 1937).
C In the aerial parts, three crystalline lignans including phyllanthine, hypophyllan-thine and quercitin have been found (Krishnamurti and Seshadri, 1946). Five flavonoids have been identified: quercitin, astralgin, quercitrin, isoquercitrin and rutin (Nara et al., 1977). Four leucodelphinidine alkaloids were separated from the leaves and stems, one of them being an enanthiomorph of securinine (Stanislas et al., 1967; Rouffiac and Parello, 1969).
P Extracts of P. niruri (by 50% ethanol) have extensive antibacterial, antifungal and antiviral action. They also act on Entamoeba histolytica (protozoa) but not on the malaria parasite Plasmodium berghei, and they are anthelmintic to Hymenolepsis nana. The extracts have depressive action on the isolated guinea pig ileum and have an anticancer action on Friend leukaemia virus (Dhar et al., 1968). Aqueous extracts of the leaves have been found to hsve an oral hypoglycaemic effect comparable to that of tolbutamide (Ramakrishnan, 1969).
The maximum dose of an extract of the whole plant tolerated by the mouse is 1 g/kg, given orally (Dhar et al., 1968).
Pseudocedrela kotschyi (Schweinf.) Harms syn. (Cedrela kotschyi Schweinf., P. chevalieri DC.) MELIACEAE
Dry zone cedar
L The rootbark is used in Nigeria and Togo as a febrifuge and also in the treatment of dysentery and rheumatism (Dalziel, 1937).
C The bark contains 1% of a bitter non-nitrogenous principle, pseudocedrelin, which is related to calicedrin. Pseudocedrelin is an unsaturated phenolic lactone with OH and OCH3 groups. In the wood oil, Ekong and Olagbeni (1967), Ekong et al. (1968, 1969b) and Taylor (1979) found meliacins (limonoids), including 7-desacetoxy-7-oxogedunin and the pseudrelones A, B and C. Each of these consists of a single limonoid alcohol which is esterified with various acids. In the bark 8.5% of mineral substances, 14.6% of tannins, a saponin and 1% of lipids w.ere also reported.
P Pseudocedrelin in a dilution of 1/10 000 kills paramecia in 20 min and the bark (3 g/1) is toxic to goldfish inducing death after 1 h, whilst greater dilutions have a stupefying action. In guinea pigs with experimentally induced hyperthermia, 0.05 g/kg pseudocedrelin given subcutaneously or intraperitoneally produces a lowering of the temperature of 2-3°C compared with control animals.
Carapa procera DC. syn. (C. guineensis Sweet ex Juss., C. touloucouna Guill. et Perr., C. gummiflua DC., C. velutina DC., C. microcarpa Chev.) MELIACEAE Crabwood, Monkey cola
L The bark exudes a gum resin, is bitter, and is said to have antipyretic and tonic properties. It is used in Nigeria in the treatment of fevers and as a general tonic. It is also given to women during pregnancy. In addition, it is a component of native cough mixtures and anthelmintic remedies, and is applied externally as a dressing for sores. In the Congo area, the bark, cut up and mixed with palm wine, is used as a quinine substitute.
C From the plant collected in the Casamance, a bitter principle named tulukinin, which is closely related to calicedrin, was isolated together with 19.5% mineral compounds and 12% tannins. This bitter principle was also found in the seed oil (Moyse-Mignon, 1942). Later, Bevan etal. (1963) obtained from the Nigerian plants a crystalline substance analogous to the triterpenoid of the limonin group obtained from Cedrela odorata. It was called carapin and its structure was identified as a bicyclononalid (Bevan et al., 1963, 1965).
P The toxicity of the rootbark extract in mice was found to be 1.28 g/kg. It appeared to be inactive as an antimalarial agent (Popp et al., 1968).
Trichilia roka (Forsk.) Chiov. syn. (T. emetica Vahl, Eleaja roka Forsk.)
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