Phytochemical investigations of lonchocarpus eriocalyx (harms), alysicarpus ovalifolius (schumach) and erythrina abyssinica (dc) for antiplasmodial, larvicidal, mosquitocidal and antimicrobial activities

Abstract

Management of parasitic disease continues to be a burden and a major public health problem the world over today. Malaria is most lethal of the parasitic vector-borne diseases due to drug and vector resistance to the available chemotherapeutics and vector management strategies, respectively. Bacterial and fungal infections are opportunistic to persons with compromised immunity yet the available drugs are associated with occasional treatment failures while antibiotic resistance is growing relentlessly. Drug research and development (R&D) is out-paced by the rate of resistance by these disease causing organisms. This has necessitated a fall back to natural botanical sources such as Lonchocarpus eriocalyx (Harms), Alysicarpus ovalifolius (Schumach) and Erythrina abyssinica (DC). Root decoction from L. eriocalyx is used to manage fever, malaria and as a mosquito repellant, A. ovalifolius is used for bleeding piles and cough relief while concoctions from E. abyssinica are used to manage fever, malaria and fungal infections. However, the phytochemicals responsible for these activities have not been fully identified. This study evaluated crude extracts and pure isolates for antiplasmodial, larvicidal, mosquitocidal and antimicrobial activities, isolated and characterized compounds from active extracts. Air-dried and pulverized plant parts were sequentially soaked in solvents of varying polarities and subsequently subjected to chromatographic fractionation. Structures of isolated compounds were elucidated using physical and spectroscopic methods and compared with literature data. Concentrations inhibiting 50% of parasite and micro-organisms (IC50) of active extracts and isolates were also determined. The stem bark of L. eriocalyx yielded lupeol (27), quercetin (65), apigenin (68), friedelin (133), -sitosterol (134), lupenone (135), -sitosterol -3-O-glucoside (136), chrysin (137), morinhydrate (138), quercetin-3-O-glucoside (139), 4’,5-dihydroxystilbene-3-O-glucoside (140) and rutin (141). Quercetin, apigenin, -sitosterol, -sitosterol-3-O-glucoside, quercetin-3-O-glucoside, plumbagin (142), orientin (143), mohanimbine (144), koenimbine (145) and koenidine (146) were obtained from root bark of A. ovalifolius while the leaves of E. abyssinica yielded 7-hydroxy-4’-methoxy-3-prenylisoflavone (147) and erythrinasinate A (148). Koenidine was the most active against W2 and D6 strains of P. falciparum with IC50 values of 63.07±0.01 and 54.19±0.04 g/mL, respectively. However the activity of mefloquine used as a positive control was superior. Mohanimbine was highly active against A. gambie larvae with 82.3±0.01% mortality although this activity was lower than temephos used as a positive control. The DCM extracts of E. abyssinica showed intermediate activity against S. aureus with zones of inhibition of 15.3±0.1 mm compared to amoxyllin (19.5±0.1 mm). This extract also inhibited the growth of C. albicans with 13.2±0.1 mm zone of inhibition compared to fluconazole (17.3±0.2 mm). Terpenoids, flavonoids and carbazole alkaloids were the major constituents of the three plants. This research has confirmed the presence of bioactive secondary metabolites in these plants and scientifically validates their use in folk medicine. The isolates can be used as templates and developed into drugs to support the existing strategies in the management of parasitic diseases.