Anti-inflammatory, antimicrobial and antioxidant properties of margaritaria nobilis, stylochiton lancifolius, drypetes principum, crescentia cujete and albizia glaberrima
This research work scientifically evaluated and validated the anti-inflammatory, antioxidant, antimicrobial activities and the acute oral toxicity profile of five (5) selected plants that find use in Ghanaian traditional medicine as agents for treating inflammatory condition s and infections. Ethanolic extracts of the rhizomes of Stylochiton lancifolius Pyer and Kotchy (Araceae), the stem barks of Margaritaria nobilis L.f (Müll Arg.) (Euphorbiaceae), Drypetes principum (Müll Arg.) Hutch (Putranjivaceae), Crescentia cujete Linn (Bignoniaceae), and Albizia glaberrima (Schum. & Thonn.) Benth (Leguminosae) were each assessed for their biological activities. The carrageenan-induced oedema in chicks model for in vivo anti-inflammatory activity indicated that the extracts and reference drugs significantly (p<0.0001) and dose-dependently inhibited oedema at all doses. The extract of C. cujete had the least ED50 value of 23.30±0.43 mg/kg body weight followed by D. principum, M. nobilis, A. glaberrima and S. lancifolius with ED50 of 37.25±1.22, 90.54±0.73, 164.90±1.63, and 181.50±1.06 mg/kg body weight respectively. The percentage inhibition of total oedema of each extract was comparable to Diclofenac, Dexamethasone and compound EMN1 (betulinic acid; isolated from M. nobilis stem bark). At doses of 300 mg/kg body weight, the percentage inhibition of total oedema of all the extracts ranged from 77.49 - 83.59% comparable with EMN1, Diclofenac and Dexamethasone which inhibited oedema at 67.83%, 81.62, and 82.47 (doses of 100, 30, and 10 mg/kg body weight) respectively. In vitro anti-inflammatory assays using human RBC membrane and egg albumin stabilisation models indicated that the extracts were comparable to the reference drugs; Diclofenac and Dexamethasone in terms of activity. Four Gram positive and four Gram negative bacteria and a fungus were employed in antimicrobial assays using the agar well diffusion and iv broth micro dilution models. The 70% ethanol extract of M. nobilis and C. cujete were the most active in the agar well diffusion assay showing activity against eight of the microorganisms. M. nobilis extract produced the highest zone of growth inhibition (22.93±0.27 mm) against Candida albicans at 10 mg/mL concentration. The activities of all the extracts at 10 mg/mL were comparable to Amoxicillin and ketoconazole at 5 mg/mL. Minimum inhibitory concentrations (MICs) of the extracts ranged from 100 to over 1000 µg/mL. The 70% ethanol extract of M. nobilis yielded the least MIC of 100 µg/mL against S. aureus and C. albicans, whereas that of C. cujete had the highest MIC of 1500 µg/mL against E. coli. Antioxidant activity was investigated using DPPH bioautography, DPPH radical scavenging assay, total antioxidant capacity and total phenol content. The IC 50 values in the radical scavenging assay indicated that the extracts of M. nobilis and S. lancifolius (9.96±0.03 and 31.58±0.17 µg/ml respectively) were more active than Ascorbic acid (38.30±0.00 µg/ml). The extracts of D. principum, A. glaberrima and C. cujete respectively inhibited 50% of DPPH at 49.09±0.39, 53.60±0.32, and 168.80±1.06 µg/ml. The Ascorbic acid and the Tannic acid equivalences had a repeated pattern as the radical scavenging assay. Stem bark extract of M. nobilis yielded the highest antioxidant capacity and phenol content. Acute oral toxicity studies according to the Organization for Economic Cooperation and Development (OECD) 2001 guidelines concluded that none of the extracts produced significant observational acute toxicity in the study animals. About 395 mg of compound (EMN1) characterized as betulinic acid was isolated from the 70% ethanol extract of M. nobilis. Based on these observed activities, the folkloric claims of effectiveness of these plants as safe anti -inflammatory, antioxidant and antimicrobial agents may be justified.
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Philosophy, 2015