Evaluation of anti-leishmanial activities of Olea europaea, Kigelia africana, Terminalia mollis, Croton macrostachyus, and Bridella micrantha extracts

Abstract

Leishmaniasis pose a significant medical concern worldwide which if left untreated, can be fatal. Although expensive and toxic, pentavalent antimonial drugs are the first-line treatment for leishmaniasis raising the need to find an alternative. Plants extracts contain several bioactive compounds that may offer alternative therapeutic signifcance to already developed antileismanial drugs. Based on folkloric information, a number of plants such as Olea europaea, Kigelia africana, Terminalia mollis, Croton macrostachyus, and Bridella micrantha are used to cure Leishmaniasis in the endemic regions in Baringo County. However, no studies have been done to find out the phytochemical compounds, as well as the anti-leishmanial properties. The aim of this study was to investigate the anti-leishmanial activity of Olea europaea, Kigelia africana, Terminalia mollis, Croton macrostachyus, and Bridella micrantha extracts. The plants were collected from Marigat in Baringo County (Kenya), air-dried, ground into fine particles, and extracted at the KEMRI Center for Traditional Medicine and Drug Research. Completely randomized design (CRD) was used in the in vivo studies. In vitro investigations were carried on L. major promastigotes to determine inhibitory concentrations (IC50) and Minimum Inhibition Concentrations (MIC) and toxicity on Vero cells. A total of 35 mice, 6 in each experimental group were used. For in vivo bioassays, the mice were injected intradermally on the left posterior footpad with 1×106 stationary phase flagellate forms of cultured L. major, and then housed for 4 weeks to allow disease manifestation. Differences between treatment groups exposed to different drugs were examined using logistic regression for each parameter studied. Phytochemical components of bark of the plants contain glycoside, terpenoids, tannins, flavonoids, steroids, and saponins. T. mollis contaned higher concentration of tannins, phenols, alkaloids, and anthraquinone. The crude extracts from the plants significantly inhibited promastogote and amastigote growth (P ˂ 0.05) after 24 hours of exposure, with the standard drug (Amphotericin B) being the most effective, while T. mollis was highly potent on amastigote among the plant extracts, then, C. macrostachyus, while O. europeae was least effective. Among the plant extracts, T. mollis had the highest efficacy (IC50 = 85.5 mg/l) in promastigote, while the least effective was O. europaea. In amastigotes, T. mollis exhibited the highest anti-amastigote activity (IC50 = 96.5 mg/l). The Leishman Donovan Units (LDU) of the L. major infection was lowest (0.12 × 106) in L. major-infected mice treated with T. mollis, while that of O. europeae was highest (4.12 × 106). After four weeks, mice administered with T. mollis demonstrated the greatest decrease in lesion diameter (0.68 ± 0.07 mm). Therapy with T. mollis, resulted in a considerably greater lesion reduction in mice. After 4 weeks of treatment, mice administered with O. europeae had the smallest reduction in lesion diameters of all the drugs examined. After 24 hours of treatment, the different drugs significantly influenced mammalian cell survival (P ˂ 0.05), with percentage cell viability of herbal medications, B. microstachyus, and O. africana causing the most toxic effects. It is concluded that among the extracts from the back of the five test plants, T. mollis at concentraton 85.5 to 96 mg/l was the most effective against Leishmania infection. Over all, the results obtained from the crude extracts screening, suggest that these may be promising sources for the development of new drugs for controlling leishmaniasis. The study recommends the use of T. mollis as the most effective plant extract in management of leishmaniases.