Cell protective antioxidants from the root bark of Lannea velutina A. Rich., a Malian medicinal plant

Abstract

Antioxidants (radical scavengers and 15-lipoxygenase inhibitors) in semipolar extracts of root bark from the Malian medicinal plant Lannea velutina have been investigated. A series of proanthocyanidins with degree of polymerization from 2 to more than 12 have been isolated, in addition to the monomeric substance, catechin. The major constituents have a degree of polymerization of ten or more. Most structures are proposed to be derived from a common biosynthetic route in which catechin is introduced as the terminal unit and epicatechin units are extenders. Catechin, dimeric, trimeric, decameric and dodecameric proanthocyanidins have been assayed as scavengers of the stable free radical diphenylpicrylhydrazyl and as inhibitors of the peroxidizing enzyme 15-lipoxygenase. All of them were shown to be effective radical scavengers (50% radical scavenging at concentrations of 5-7 microgram/mL) and 15- lipoxygenase inhibitors (50% inhibition at 10 - 18 microgram/mL). When epicatechin and trimeric proanthocyanidin were tested as antioxidants in cells, they gave a significant reduction in endogenously produced reactive oxygen species (ROS).