IDENTIFICATION OF ANTIMALARIAL AND LARVICIDAL COMPOUNDS FROM Trichilia megalantha HARMS AND Trichilia welwitschii C.D.C. (MELIACEAE)

Abstract

Malaria is the second leading cause of death from infectious diseases in Africa. The global burden of malaria is increasing due to drug-resistant parasites and insecticideresistant mosquitoes. Meliaceae has been known to possess antimalarial, larvicidal and other properties but many Nigerian Trichilia species have not been investigated. Thus there is dearth of information on the antimalarial and larvicidal activities of Trichilia megalantha (TM) and Trichilia welwitschii (TW). Therefore, this study investigated the antimalarial and larvicidal activities of both plants. Leaf, stem bark and root of TM (FHI 109556) and TW (FHI 109557) were extracted by maceration in methanol. The extracts (100-800 mg/kg) were subjected to in vivo mousemodel 4-day suppressive antimalarial evaluation using Plasmodium berghei ANKA strain. Toxicity was determined in vivo in mice and in vitro using 3-(4, 5-dimethylthiazol- 2-yl)-2, 5-diphenyltetrazolium bromide (MTT) and brine shrimp lethality (BSL) assays. The larvicidal activities of extracts and compounds were evaluated on Anopheles gambiae larvae. Antioxidant activity was also investigated with 1, 1- diphenyl-2- picrylhydrazyl radical. Chloroquine, N, N-diethyl-3-methylbenzamide (DEET), gallic acid, doxorubicin and etopoxide were used as positive controls in the antimalarial, larvicidal, antioxidant, cytoxicity and BSL assays, respectively. Isolation of compounds was done using repeated column chromatography and high performance liquid chromatography. Structures of compounds were elucidated by spectroscopy (IR, UV, NMR and MS). Linear regression was used to determine 50% lethality concentration iii (LC50), 50% inhibitory concentration (IC50) and 50% cytotoxic concentration (CC50). Data were analysed using ANOVA and Student’s t-test at p = 0.05. The stem bark extract of TM had the highest chemo-suppression (100%) at 200 mg/kg in the antimalarial assay of the extracts tested against P. berghei berghei. The leaf of TW had 93.4% compared to chloroquine, which had 98.0%. In the larvicidal assay, the stem bark extract of TM was the most toxic, with an LC50 of 74.0 μg/mL, while DEET had 120.2 μg/mL. In the BSL assay, all the extracts were found to be non-toxic with LC50 > 1000 μg/mL as compared to etopoxide (7.46 μg/mL). The ethyl acetate fraction of TM stem bark showed antioxidant activity with IC50 of 25.37±1.46 μg/mL, while gallic acid had 23.44 ± 0.43 μg/mL. Both plant extracts did not produce any significant changes in haematological, biochemical, and histological parameters of animals used. Seven compounds were isolated from active extracts namely; Ursolic acid (1), lupeol (2), scopoletin (3), β- sitosterol (4), stigmasterol (5) and stigmastenone (6) from TM and 3,3′,4-tri-O- methyl ellagic acid (7) from TW. Ursolic acid, lupeol and scopoletin had chemo-suppression of 93.4%, 88.3% and 58.5%, respectively against P. berghei, while 3,3′,4-tri-O- methyl ellagic acid from TW had 75.8% chemosuppression. Lupeol from TM had the highest larvicidal activity on An. gambiae larvae with LC50 of 6.20 μg/mL. Ursolic acid from Trichilia megalantha and 3,3′,4-tri-O-methyl ellagic acid from Trichilia welwitschii exhibited antimalarial activity. Lupeol with larvicidal activity was obtained from Trichilia megalantha. These plants could provide lead for antimalarial drug discovery and development. iv Keywords: Malaria, Larvicidal compounds, Trichilia megalantha, Trichilia welwitschii