Partial Purification and Characterization of Angiotensin Converting Enzyme Inhibitory Alkaloids and Flavonoids from the Leaves and Seeds of Moringa oleifera

Abstract

Aim: In the present study, the alkaloid, flavonoid and saponin-rich extracts of the leaves and seeds of Moringa oleifera were partially-purified and the ACE inhibitory activities and patterns of inhibition determined. Methodology: Alkaloids, flavonoids and saponins were extracted from the leaves and seeds of Moringa oleifera. They were then partially-purified via thin layer chromatography and column chromatography. The Angiotensin Converting Enzyme (ACE) inhibitory activities of each fraction was determined using Cushman and Cheung method with some modifications on the assay conditions, while the mechanisms of inhibition investigated using Lineweaver-Burk plots. Results: The alkaloid-rich extracts of the leaves (6.27±0.12 mg/ml) and seeds (2.04±0.95 mg/ml) as well as flavonoid-rich extracts of the leaves (1.20±0.31 mg/ml) and seeds (2.16±0.56 mg/ml) of M. oleifera inhibited ACE at concentrations significantly (P <.05) lower than the saponin-rich extracts (26.01±1.02 and 24.32±2.31 mg/ml for the leaves and seeds, respectively). Thus, both alkaloid and flavonoid-rich extracts were further purified via thin layer chromatography and column chromatography. Of the four fractions obtained from the alkaloid-rich leaf extract, the ACE inhibitory activity of fraction 2 (0.46±0.01 mg/ml) was significantly higher (P <.05), while fraction 1 (0.07±0.01 mg/ml) of the alkaloid-rich seed extract significantly (P <.05) inhibited ACE compared to other fractions. For the flavonoid-rich extracts, fractions 3 (0.03±0.01 mg/ml) and 4 (0.42±0.03 mg/ml) obtained from the leaves and seeds, respectively, significantly (P <.05) inhibited ACE than other fractions. From the kinetic studies, fractions 1 and 2 exhibited uncompetitive types of inhibition with a decrease in Vmax and corresponding decrease in Km at 0.5 mg and 1.0 mg of inhibitor, respectively. Fractions 3 and 4 were competitive inhibitors of ACE, as the Km increased with increasing concentration of inhibitor, while Vmax remain unchanged. In conclusion, this study has demonstrated the ACE inhibitory activity of alkaloids and flavonoids from the seeds and leaves of Moringa oleifera and their potential as source of ACE inhibitors that may be beneficial for the management of hypertension.