In Vitro Antioxidant Activity of Extracts and Coumarins from the Stem Bark of Mammea africana Sabine

The present study aimed at evaluating the in vitro antioxidant activity (AOA) of the aqueous and methylene chloride/methanol (CH2Cl2-MeOH) extracts of Mammea africana and isolating the active principle(s). The AOA of the aqueous and CH2Cl2-MeOH extracts (3-1000 µg/ml) as well as compounds isolated (1-300 µg/ml) through bio-guided fractionation of the CH2Cl2-MeOH extract was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH), nitric oxide (NO) production and beta carotene bleaching tests. The aqueous and CH2Cl2-MeOH extracts exhibited a concentration dependent antiradical activity on DPPH with respective EC50 of 2.00 and 5.24 µg/ml. The purification of the CH2Cl2-MeOH extract yielded two coumarins: 4-phenylcoumarins (1) and 4-n-propylcoumarins (2) that exhibited potent radical scavenging activity with EC50 of 7.61 and 22.92 µg/ml, respectively. Plant extracts, fractions and compounds tested substantially increase NO production at high concentrations and exerted a protective effect against the oxidation of beta carotene at all the concentrations used; with a 400% inhibition obtained with the CH2Cl2 fraction at the concentration of 300µg/ml. The above results demonstrate that aqueous and CH2Cl2-MeOH M. africana possess potent AOA and could improve cardiovascular diseases where an increase in NO bioavailability is required. Compounds 1 and 2 are at least partially responsible for these activities.