Antioxidant and angiotensin-converting enzyme inhibitory potential of South African traditional medicinal plants and plant-derived compounds

Plants used in African traditional medicine to manage hypertension are potential angiotensin-converting enzyme (ACE) inhibitors. We, therefore, aimed to determine the antioxidant and anti-hypertensive properties of the methanol extracts of six plants, namely, Artemisia afra Jacq. ex Willd., Clausena anisata, Dombeya rotundifolia, Sclerocarya birrea, Rhus chirindensis, and Warbugia salutaris and selected compounds, viz., 3fi-taraxerol, fi-amyrin, oleanolic acid, hesperidin, nicotinamide, and quercetin. The antioxidant and anti-hypertensive activities were determined using the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay, the nitric oxide (NO) scavenging assay and the ACE inhibition assay respectively. D. rotundifolia (IC50: 63.02 +/- 0.5 mu g/mL), 3fi-taraxerol (IC50: <1 mu g/mL), fi-amyrin (IC50: 105.04 +/- 1.36 mu g/mL), oleanolic acid (IC50: 32.20 +/- 0.20 mu g/mL) and quercetin (IC50: <1 mu g/mL) displayed strong DPPH free radical scavenging activity ranging from 80 to 90%. Additionally, D. rotundifolia demonstrated 72% inhibition against NO displaying the lowest IC50 of 63.45 +/- 2.9 mu g.mL. A 75-87% inhibition was noted for 3fi-taraxerol (IC50: <1 mu g/mL), fi-amyrin (IC50: <1 mu g/mL), oleanolic acid (IC50: <1 mu g/mL) and quercetin (IC50: 125.02 +/- 1.77 mu g/mL), similar to ascorbic acid (standard). A significant ACE inhibitory activity of 92% with the lowest IC50 (110.16 +/- 0.12 mu g.mL) was demonstrated for D. rotundifolia followed by R. chirendensis (79%), S. birrea (67%), A. afra (54%) and C. anisata (54%). Our findings suggest that these medicinal plants and bioactive compounds have great antihypertensive potential via inhibitory effects on ACE in the renin-angiotensin-aldosterone system pathway.