Antiinfective activity of higher plants

Ideally, the plants used for anti-infective therapy should be toxic to infectious organisms and devoid of toxicity for human beings. The aim is to obtain the highest possible favourable ratio between the dose toxic to man and that active against the agent of infection. Biochemical differences between the infective agent and the host should allow the finding of plant constituents that are selectively toxic to the infecting organism.

The plants used for anti-infective therapy can be divided into two groups: I Anti-infective higher plants

These include:

(a) antibacterial plants;

(b) antifungal plants;

(c) antiviral plants;

(d) antiprotozoal plants;

(e) antimetazoal plants (anthelmintics).

II Plants with insecticidal and molluscicidal activity (parasitic hosts)

(a) insecticidal plants;

(b) molluscicidal plants.

The term antibiotics, which was first given to substances produced by fungi and bacteria that inhibit the vital processes of certain microorganisms other than the species producing them, has been extended by many authors to those constituents of higher plants which have similar effects in very low concentrations (e.g. Paris and Moyse, 1965). Those constituents which act on pathogenic fungi, viruses and protozoa are also included (Patel etal., 1967) and the term has been used in this sense throughout the book.

The antibacterials inhibit the multiplication of bacteria and can be either bactericidal or bacteriostatic. The lowest concentration that completely inhibits the microorganisms after exposure in vitro for a specified period is referred to as the minimum inhibiting concentration (MIC). Conventional antibacterial drugs are known to inhibit cell division in the microorganisms by interfering with p-aminobenzoic acid, which is a co-factor in the synthesis of folic acid, others interfere with protein synthesis in the bacteria, others again attack the cytoplasmic membrane by dissociating its lipoproteic structure and another group of antibacterial drugs inhibit the building up of new cell walls during cell division by blocking the enzyme transpeptidase, which controls their synthesis.

The main endemic bacterial diseases in West Africa include leprosy, tuberculosis, occasionally cholera, bacillary dysentery, enteric fevers and undulant fever.

The demand for antifungal drugs is considerable in a warm, damp climate in which fungal diseases are rife. The diseases are mainly ringworm (Tinea imbricata, T. cruris, T. pedis, T. unguium), caused by e.g. Epidermophyton floccosum, E. concen-tricum, Trichophyton mentagrophytes, T. rubrum and Nocardia minutissima; pityriasis versicolor (Tinea versicolor), caused by e.g. Cladiosporum mansoni and Malessesia furfur; and aspergillosis (in lungs), caused by Aspergillus fumigatus. Many of the antimycotic drugs are used in topical application.

Virus diseases in West Africa include yellow fever, rabies, poliomyelitis and trachoma, but of course dengue, influenza and measles also occur. As opposed to the bacteria, which have their own reproductive system, viruses use certain syntheses of the cell itself for their reproduction. This explains why they can change the function of normal cells. No relevant information about the action of antiviral drugs has emerged from the pharmacological tests described in this section.

The main protozoal diseases in West Africa are malaria (parasite genus Plasmodium); African trypanosomiasis; leishmaniasis, including kala-azar (visceral form) and that caused by Leishmania tropica (oriental sore); and, rarely, amoebiasis (amoebic dysentery, parasite Entamoeba histolytica) and giardiasis (parasite Giardia intestinalis (Lamblia)).

Metazoal diseases in West Africa are caused by nematodes, trematodes and cestodes. The main infectious agents include (Manson-Bahr, 1952):

Nematodes acting on the intestine; hookworm (Ancylostoma duodenale), whipworm (Trichuris trichiura), pinworm (Oxyuris vermicularis), roundworm (Ascaris lumbricoides), trichinöse (Trichinella spiralis) Nematodes acting on tissues: guinea worm (Wucheria bancrofti) (filariasis), guinea worm (Dracunculus medinensis) (dracontiasis) Nematodes acting on eyes: blinding worm (Onchocerca volvulus) (onchocerciasis), eye worm (Loa Loa filaria) (loa loa filariasis). Trematodes: flukes (Schistosoma mansoni) (bilharzia) Cestodes: adult and larval tapeworms (Taenia solium, T. saginata, Echinococcus granulosis, Hymenolepis nana)

Plants with anti-infective activity which have already been described in Chapter 2 for their action on the cardiovascular system are indicated hereunder by CV. Similarly, the plants already described in Chapter 3 for their effects on the nervous system are indicated by N.

The plants marked by an asterisk (*) in the enumeration of the constituents at the beginning of each action group are described in this text, the others can be found in the corresponding tables. Often several uses are indicated after each plant name, in which case a dagger (f) is placed after the use under which the description of the plant can be found.

So far, anti-infective experimentation with plants has been very superficial. Often, the testing amounts to little more than in vitro exposure of material to organisms which may or may not be pathogenic to man. Nevertheless, the tests carried out by many authors on non-pathogenic organisms are indicated here: some organisms formerly believed to be non-pathogenic have lately been found to be possibly pathogenic or may be pathogenic to cattle or domestic pets.

The organisms discussed below that are considered non-pathogenic arz Aspergillus flavus, Bacillus cereus, B. subtilis, B. mycoides, B. megaterium, Giardia muris (rodents), Micrococcus leirodeicticus, Mycobacterium smegmatis, Mycob. phlei. Penicillin chrysogenum, Saccharomyces cerevisiae, Sarcina lutea and probably Penicillin echyogenum. Paramecia, a formerly much-used genus for testing, has been abandoned.

I Plants with antibiotic activity

A great variety of components belonging to different chemical groups were found to have antibiotic activities. Similar observations had been made by Lechat et al. (1978) and Brannon and Fuller (1973) concerning the antibiotics isolated from Streptomycetaceae and Thallophytae and were explained by them by the fact that the different antibiotics attack different sites in the pathogenic organisms

Comparison of the MIC of essential oils from plants in vitro tests with their tissue concentrations active in vivo showed that the mechanism of their anti-infectious action is different from that of the antibiotic type of action. Antibiotics require an in vivo concentration in the tissues that is equal to, or greater than, their minimum active concentration in vitro. In the case of essential oils, however, concentrations in the blood of about one-hundredth of their active concentration in vitro have been shown to heal patients with acute or chronic infections. Thus patients have been cured with essential oil arriving in the organism in doses quite insufficient to deal with the infectious agent in the laboratory, the in vitro activity of the essential oils being 100 times higher than that of antibiotics, whilst in vivo the actions are comparable. The results of tests on 268 clinical cases (Valnet et al., 1978) suggest that essential oils have a general action on the organism of the patients. Valnet and co-workers call the microbiocidal use of the oils 'aromatotherapy' and their test-records 'aromatograms'. They believe that the action of the essential oils is based on a global action which modifies the general condition of the patient (action on neuro-endocrine functions?)

(a) Antibacterial plants

Active constituents

The plant constituents with antibacterial action are tentatively grouped according to their main chemical groups.

Phenols. In Anacardium occidentale* the aromatic phenols cardol and anacardol (decarboxylated derivatives of anacardic acid) are not only bactericidal! and antifungal but also vermicidal and protozoicidal. The phenol chloropherin in Chlorophora excelsa is antibacterial and antifungal and in Ocimum viride, thymol (also vermicidal) and eugenol are antimicrobial.

Quinones. The napthoquinone plumbagin, found in Plumbago zeylanica * and also in Diospyros mespiliformis and Drosera indica *, is antibacterial,! antifungal, antiprotozoal and anthelmintic, and the benzoquinone from Embelia schimperi* is slightly antibacterial but mainly anthelmintic.!

Acids. Citric acid in Btyophyllum pinnatum*, is antibacterial and the fatty acids with a cyclopentene nucleus (chaulmoogric and gorlic acids) in Caloncoba echinata * act on the lepra bacillus. The acidic phenols gallic acid (and ethylgallate) are reported to be antibacterial in Bombax spp. and antibacterial and anthelmintic in Acacia farnesiana and Mangifera indica.

Alkaloids. Berberine in Argemone mexicana (also found in Chasmanthera dependens) is said to be antimicrobial and antiprotozoal; sanguinarine acts as a lipolytic pro-drug and is antifungal. Cryptolepine in Cryptolepis sanguinolenta * and Sida spp., canthine-6-one, chelerythrine and berberine in Zanthoxylum zanthoxyloides* and solanine in Solanum nodiflorum are all antibacterial;! and this also applies to the indole alkaloids of Strychnos afzeli and funiferine from Tiliacorafunifera.

Flavonoids. Ageratum conyzoides* contains an antibacterial! fiavone (the plant extract is also anthelmintic in vitro). Combretum micranthum* and C. racemosum* are antibacterial;! they contain flavonoids, alkaloids (combretines) and catechuic tannins. Canscora decussta* (xanthones) inhibits Mycobacterium tuberculosis* and is also antiviral, whilst Psidium guaijava* has three flavonoids with a strong antibacterial! effect on Mycob. tuberculosis. The flavonoids of Uvaria chamae* act on Mycob. smegmatis*; they are also reported to be larvicidal.

Sulphur heterosides. Allicin in Allium * spp. is antibacterial! and antifungal and this is also the case for the isothiocyanate glucosides in Capparis decidua * (glucocappa-rin), Lepidium sativum (glucotropeolin), Moringa oleifera* (rhamnosyl-oxyben-zylisothiocyanate); and Carica papaya* seeds (tropaeolin). Cleomin from Ritchiea longipedicillata* is antibacterial and anthelmintic! (mainly). Hydrogen cyanide (HCN) found in Acalypha wilkesiana * may account for the antibacterial action of this plant.

Terpenoids. Antibacterial activity is reported for Borreria verticillata* (sesquiterpene lactone), Xylopia aethiopica* (diterpene, xylopic acid), Azadirachta indica* (seeds, triterpenoids, also antiviral) and Ekebergia senegalensis* (stembark, meliacins). The leaves of Azadirachta are insecticidal and those of Ekebergia are ichthyotoxic.

Proteolytic enzymes. Papain from Carica papaya, calotropine from Calotropa procera and bromelain from Ananas comosus are able to digest bacterial and parasitic cells and bromelain even digests worms.

Poly acetylenes and phenylheptatriene from Eclipta prostrata and Bidens pilosa

(leaves) respectively, have a strong UV-mediated toxicity to bacteria and Candida and are also toxic to insects and larvae (Wat et al., 1978,1979, 1980).

Anacardium occidentale L. (Fig. 4.1) ANACARDIACEAE

Cashew nut tree This tree has been described earlier (CV).

P Anacardic acid, which constitutes 39% of the 'cashew balsam' from the fleshy parts of the fruit (Gellerman and Schlenk, 1968) and is found also in crude extracts of cashew nut shells (Rahman et al., 1978), is a mixture of 6-(»-C15-alkyl) salicylic acids with side chains varying in degrees of unsaturation. Anacardic acid has been found to have moderate bactericidal activity against Staphylococcus aureus (Ogunlana and Ramstad, 1975). Investigation of certain decarboxylated derivatives of anacardic acid, cardol and anacardol, showed that these were not only bactericidal but also fungicidal, vermicidal, protozoicidal, parasiticidal and even anti-enzymatic (Eichbaum et al., 1950; Jacquemain, 1959; Gulati et al., 1964; Laurens and Paris, 1977). More recently anacardic acid, its acetate and the fully saturated analogues have been found to be very active against Mycobacterium smegmatis and moderately active against Bacillus subtilis. Good antifungal action against Trichophyton menta-grophytes and moderate action against Saccharomyces cerevisiae have also been reported (Adawadkar and El-Sohly, 1981). The antimicrobial activity of anacardic

Fig. 4.1. Anacardium occidentale L.

Fig. 4.1. Anacardium occidentale L.

Images Ancylostomasis

acids (which are also the main constituents of Ginko biloba) had been reported earlier by Gellerman et al. (1969). The anthelmintic action of the Anacardium nut-shell liquid had been tested before in ancylostomiasis, ascaridiasis and trichuriasis and had given satisfactory results (Eichbaum etal., 1950). It has further been shown that the molluscicidal activity of crude extracts of nut shells requires both the unsaturated side chain and the carboxyl group of anacardic acid (Sullivan et al., 1982).

The antibacterial activity of metallic complexes of anarcardic acid with mercury, zinc, copper, manganese and cobalt was the subject of tests by Chattopadhyaya and Khare (1970) against 17 test organisms. The strongest antimicrobial activity of anacardic acid proved to be against Staphylococcus aureus. The mercury complex was particularly active against Staph, aureus, Streptococcus pyogenes, Escherichia coli and Bacillus pumilis.

Another Anarcadiaceae, Heeria insignis (Del.) O. Ktze. has also been found to have antimicrobial activity; it gives positive reactions for tannins and saponins. In West Africa it is much employed as an anthelmintic and antidysenteric (Delaveau et al., 1979).

Plumbago zeylanica L. PLUMBAGINACEAE

Ceylon leadwort

L The root is a vesicant and counter-irritant. Dried and pulverized it is added to a maize pap as a remedy for parasitic skin diseases and in Southern Nigeria the leaves are put in soup as a remedy for worms and for fever. In Ghana the root is administered as an enema to treat piles (Dalziel, 1937). In the Ivory Coast and Upper Volta it is used in the treatment of leprosy (Kerharo and Bouquet, 1950).

C The roots contain plumbagin or plumbagol, a 2-methyl-5-hydroxy-l,4-naphthoquinone, in amounts of 1.26% in the Ivory Coast (Paris and Moyse-Mignon, 1949; van der Vijver and Lotter, 1971). (Plumbagin is also found in Diospyros and Drosera spp.) The leaves and stems of P. zeylanica contain only very small amounts in addition to a fixed and a volatile oil (Watt and Breyer-Brandwijk, 1962).

P Plumbagin has vitamin K action and antibacterial properties. In India it is also said to stimulate the secretion of sweat, urine and bile and to have a stimulating action on the nervous system and on the muscular tissue (Bhatia and Lai, 1933). In a concentration of 1:50000, plumbagin has a marked antibiotic action on staphylococci and certain pathogenic fungi (Coccidoides imminentis, Histoplasma capsulatum, Trichophyton ferrugineum) and on parasitic protozoa (Carrara and Lorenzi, 1946; Van der Vijver and Lotter, 1971). Intravenous injections in patients with boils, anthrax or cystitis have been well tolerated and brought about a rapid recovery (Saint Rat etal., 1946,1948; Saint Rat and Luteraan, 1947; Blanchon etal., 1948; Vichkanova et al., 1973a). Experimental Microsporum infections in mice have been healed by local applications of 0.25-0.5% solutions in 40% alcohol or 1% emulsions of plumbagin (Vichkanova et al., 1973a). In vitro, the growth of Staphylococcus aureus, Streptococcus pyogenes and Pneumococcus has been completely inhibited by solutions of plumbagin at concentrations of 1:100000; that of Mycobacterium tuberculosis at concentrations of 1:50000 and the growth of Escherichia coli and Salmonella at concentrations of 1:10000 (Skinner, 1955; Oliver, 1960; Vic-hkanova et al., 1973b). Antispasmodic activity of plumbagin was also reported, by Bezanger-Beauquesne and Vanlerenberghe (1955), but it proved inactive in the treatment of infection by Haemophilus pertussis, Plumbagin (isolated from P. capensis) showed a potent antifeedant activity against larvae of the army worms (Spondoptera exempta) at 10 p.p.m. and of S. littoralis at 20 p.p.m., and caused their complete inhibition at a concentration of 12.5 /xg/ml; it has proved to be antimicrobial in Candida utilis and Saccharomyces cerevisiae (Kubo et al., 1980).

Drosera indica L. DROSERACEAE

L The plant is used in India as a powerful rubefacient and a maceration is applied topically to corns in Vietnam (Chopra et al., 1956).

C The plant contains naphthoquinones, mainly plumbagin (see Plumbago zeylanica) (Bezanger-Beauquesne and Vanlerenberghe, 1955).

P Drosera rotundifolia, D. coryifolia and D. intermedia have been reported to prevent bronchospasms produced by acetylcholine or histamine and to decontract in vitro spasms of the intestine caused by acetylcholine or barium chloride. They are said to be antitussive and to prevent coughing induced by excitation of the larynx nerve in the rabbit (Paris and Moyse, 1967, pp. 227-9). The napthoquinones also have an antimicrobial action; a plumbagin solution inhibits the growth of Staphylococci, Streptococci and Pneumococci in concentrations of 1:50 000 and has been used against whooping cough although practically no action against Haemophilus pertussis was noted (Bezanger and Vanlerenberghe, 1955) and is used in the treatment of other severe, persistent coughs. France was said to use about ten tons yearly in 1969 as an antitussive (Paris and Moyse, 1967, Vol. II, p. 229). Denoel (1958) reported that plumbagin is an isomer of phthiocol, a constituent of the tubercle bacillus, and some authors suppose that substitution of phthiocol explains the activity of Drosera on the respiratory tract. In fact certain plumbagol-sulphamide compounds showed an antituberculostatic activity in vitro. According to Vichkanova et al. (1973a) the antimicrobial spectrum of plumbagin includes Gram-positive and Gram-negative bacteria, influenza virus, pathogenic fungi and parasitic protozoa. However, they report it to be ineffective against Giardia muris (a protozoan parasite to rodents) and tuberculosis in mice when administered orally for 5 days. They successfully treated experimental Microsporum infections in guinea pigs by local application of 0.25-0.5% solutions in 40% alcohol or 1% emulsions of plumbagin.

Bryophyllum pinnatum (Lam.) Oken syn. (B. calycinum Salisb., Cotelydonpinnata Lam., Kalanchoepinnata (Lam.) Pers.) CRASSULACEAE

Never die or Resurrection plant (from viviparous properties)

L The crushed leaves (or the juice squeezed out after heating) are mixed with sheabutter and oil and the mixture is applied to abscesses, swellings, ulcers and burns or used to rub the bodies of young children suffering from fever. The juice is also applied for earache and ophthalmia (Dalziel, 1937). In India, where the leaves are also used as an application on bruises, wounds, boils and insect bites, the leaves of an Indian species (Kalanchoe laciniata) are similarly used and are said to allay irritation and promote healing; the juice is considered styptic and is also administered in the treatment of bilious diarrhoea and lithiasis (Chopra et al., 1956).

C The leaves contain bryophyllin, potassium malate and ascorbic, malic, isocitric and citric acids (Mehta and Bhat, 1952; Chopra et al., 1956; Gaind and Gupta, 1969).

P Studies of the antimicrobial activity of the juice obtained from the heated leaves, using the agar diffusion method, showed an inhibition zone of more than 20 mm when used on test organisms of Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa. It has also been noted that the heated leaf, when applied to inflamed areas, produces a soothing effect, keeping wounds clean and preventing them from going septic (Boakaiji Yiadom, 1977).

Caloncoba echinata (Oliv.) Gilg syn. (Oncoba echinata Oliv.) FLACOURTIACEAE Caloncoba glauca (P. Beauv). Gilg syn. (Ventenatia glaucaP. Beau v., Oncoba glauca (P. Beauv.) Hook, f., C. dusennii) Caloncoba Welwitschii (Oliv.) Gilg Gorli

L A lotion made from the plant is used by several native tribes in Guinea, Sierra Leone and Ghana for pustular eruptions of the skin. The seeds contained in the fruit capsule have long been known to contain chaulmoogric acid but the toxic ingredients of the acid cause nausea and vomiting and irritation of the mucous membrane of the stomach, and hydnocarpic acid is therefore preferred (Dalziel, 1937). The Caloncoba spp. are not used much in modern leprosy treatment.

C The three Caloncoba spp. have nearly the same constituents as chaulmoogra oil, which is obtained by squeezing out the fresh ripe seeds of Taraktogenus kurzii from Burma. However, the oil of the Caloncoba spp. is less appreciated than chaulmoogra or mainly hydnocarpus oil (from Hydnocarpus spp.) as the seeds are very small, extraction is laborious and the fat is less suitable for injection. The Caloncoba spp. contain in general 30-50% lipids of which 1-3% is non-saponifiable. The fat consists in West Africa of 60-80% chaulmoogric acid (against 50-70% hydnocarpic acid in Hydnocarpus spp. which have been acclimatized in Nigeria, the Cameroons, Guinea and the Ivory Coast); the remaining lipids consist in both cases of 8-15% gorlic acid and 10-12% of ordinary fats (oleic and palmitic acids) (Chevalier, 1928; Pelt, 1959; Paris and Moyse, 1963). Both chaulmoogric and hydnocarpic acids have saturated side chains.

P In 1967 there were some 10-12 million lepers in the world (Paris and Moyse, 1967). Chaulmoogra remains a classic medicine although often associated with sulphones, which are more effective in the malignant forms of the disease, and might be used as a suspension of diaminodiphenylsulphone in acetylchaulmoograte. The treatment is lengthy (250 ml/year is required) and should be combined with an adequate diet. Chaulmoogra oil is also used for certain skin complaints (lupus) and as a parasiticide in veterinary medicine (Pelt, 1959; Zenan and Podkorny, 1963).

Cryptolepis sanguinolenta (Lindl.) Schltr. ASCLEPIADACEAE

The hypotensive and antipyretic properties of this plant have already been briefly described (CV). In local medicine it is also reputed to be active in the treatment of urogenital infections and malaria. Hence Dwuma Badu et al. (1978) and Boakaiji Yiadom (1979) have carried out antibacterial tests. In those against urogenital pathogens the aqueous extracts of the roots showed antimicrobial activity against Neisseria gonorrhoeae, Escherichia coli and Candida albicans but not against Pseudomonas aeruginosa. With 20.0 and 10.0 g/1 solutions the inhibition zones were approximately equivalent to those produced by a solution of 25 /xg/ml of trihydrate of ampicillin used as a control, only the effect on Candida albicans was slightly weaker, especially with the smaller dose. The effect of 5.0 g/1 was inferior to that of the control for all the test organisms. Cryptolepine has no plasmocidal effect (Boakaiji Yiadom, 1979).

Similar effects were reported with the hydrochloride of cryptolepine (an indoloquinoline alkaloid isolated from the roots) (Gellert et al., 1951; Dwuma Badu et al., 1978; Boakaiji Yiadom and Heman Ackah, 1979). Recently, Bamgbose and Noamesi (1981) have reported an inhibition by cryptolepine of carrageenan-induced oedema.

Zanthoxylum zanthoxyloides (Lam.) Watson syn. (Fagara zanthoxyloides Lam., F. senegalensis (DC.) Chev., Z. senegalense (DC.) Chev., Z. polygonum Schum.)

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