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New study refutes speculation
that ginkgo inhibits MAO in human brain
Proposed mechanisms of action for the neuroprotective,
antidepressant, and anti-anxiety effects of ginkgo leaf extract
(Ginkgo biloba) include inhibition of the neurotransmitter
monoamine oxidase (MAO). Several earlier studies suggested that
ginkgo inhibited rat brain MAO in in vitro studies, but evidence
that ginkgo affected MAO concentrations in the human brain was
lacking. To shed light on the subject, researchers conducted a
small study in 10 healthy volunteers between the ages of 38 and
76. The study participants took 60 mg of the standardized ginkgo
leaf extract EGb 761 (Ginkgold, made by Nature's Way) twice daily
for four weeks, and changes were assessed using radiotracers at
baseline and at the end of treatment. Results showed that ginkgo
had no effect on levels of MAO A or B in the human brain, possibly
because ginkgo may not cross the blood-brain barrier. The researchers
commented, "Though we did not detect an effect of Ginkgo
biloba on brain MAO A and B, this does not rule out MAO A
and B inhibition in other organs." The researchers also observed
no effects on cerebral blood flow in this group of healthy subjects,
but speculated that the reactivity of cerebral vasculature may
be different in elderly subjects and in those with dementia.
Fowler JS, Wang G-J, Volkow ND, et al. Evidence that Ginkgo biloba
extract does not inhibit MAO A and B in living human brain.
Pharmacology Letters 2000; 66(9): 141-146.
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