Ginkgo biloba extract inhibits oxygen species production generated by phorbol myristate acetate stimulated human leukocytes

A Ginkgo biloba extract (Gbe) containing flavonoids, among other compounds, was tested for the release of activated oxygen species ( $O_2^{ - \cdot } $ , H₂O₂, OH^.) during the stimulation of human neutrophils (PMNs) by a soluble agonist. The extract slows down O₂-consumption (respiratory burst) of stimulated cells by its inhibitory action on NADPH-oxidase, the enzyme responsible for the reduction of O₂ to $O_2^{ - \cdot } $ . Consequently, superoxide anion ( $O_2^{ - \cdot } $ ) and hydrogen peroxide (H₂O₂) production is significantly decreased when the PMNs stimulation is done in the presence of the extract at concentrations of 500, 250 and 125 μg/ml. Moreover, the hydroxyl radical generation (OH^.) is very much decreased at concentrations as low as 15.6 μg Gbe/ml, which indicates that the extract also has free radical scavenging activity. Gbe is able at least to reduce very severel the activity of myeloperoxidase contained in neutrophils. This enzyme, secreted into the intra and extracellular medium, catalyzes the oxidation of chloride (Cl⁻) by H₂O₂ to yield strong oxidants (HOCl, chloramines) which are implicated in inflammatory processes