Interaction of neuroprotective substances with human brain superoxide dismutase. An in vitro study.

Human brain total superoxide dismutase activity (SOD) was assayed in the presence of increasing concentrations of neuroprotectives. Superoxide-dependent nitrobluetetrazolium (NBT) reduction served as control for direct radical interaction of these substances. High concentrations of the dopamimetic substances L-DOPA slightly and the monoamine oxidase B inhibitor selegiline more effectively inhibit SOD activity. The MAO-B inhibitor RO 16-6491 (N-(2-aminoethyl)-4-chlorobenzamide hydrochloride) has no effect on SOD enzyme activity. Reduced glutathione stimulates SOD activity. Moreover it exhibits slight activity in scavenging radicals in vitro. Oxidized glutathione and vitamin E are unable to do so. Ascorbic acid mimics the activity of reduced glutathione, but directly interacts with NBT reduction. Thioctic acid shows no effect on SOD activity but stimulates superoxide-dependent NBT reduction. The Ginkgo biloba extract EGb 761 is highly active in inhibiting superoxide-dependent NBT reduction as well as SOD activity.