Evidence that Ginkgo biloba extract does not inhibit MAO A and B in livinghuman brain

Extracts of Ginkgo biloba have been reported to reversibly inhibit both mon oamine oxidase (MAO) A and B in rat brain in vitro leading to speculation t hat MAO inhibition may contribute to some of its central nervous system eff ects. Here we have used positron emission tomography (PET) to measure the e ffects of Ginkgo biloba on human brain MAO A and B in 10 subjects treated f or 1 month with 120 mg/day of the Ginkgo biloba extract EGb 761, using [C-1 1]clorgyline and [C-11]L-deprenyl-D2 to measure MAO A and B respectively. A three-compartment model was used to calculate the plasma to brain transfer constant K-1 which is related to blood flow, and lambda k3, a model term w hich is a function of the concentration of catalytically active MAO molecul es. Ginkgo biloba administration did not produce significant changes in bra in MAO A or MAO B suggesting that mechanisms other than MAO inhibition need to be considered as mediating some of its CNS effects. (C) 2000 Elsevier S cience Inc.