Ginkgo Extract May Protect Brain During Stroke 10-09-08

Regular use of ginkgo extract -- widely touted for preserving memory -- may help prevent brain damage during a stroke, according to findings from an animal study.

Mice given daily doses of Ginkgo biloba before induction of a stroke had roughly half the infarct volume and neurological defects as untreated mice, said Sylvain Doré, Ph.D., of Johns Hopkins University, and colleagues.

Starting doses of the plant extract given at five minutes and 4.5 hours after a stroke also appeared to reduce infarct size (P<0.01), they reported online in Stroke.

If the benefits are confirmed in human trials, ginkgo could be useful as prophylaxis for patients at high risk of stroke or to minimize symptoms after a stroke, Dr. Doré said.

But this type of use in humans is still far off, he noted, and cautioned that patients should consult with their physicians before trying over-the-counter ginkgo products, which are often not standardized and can interact with medications.

Prior studies have found ginkgo to have neuroprotective and antioxidant effects in ischemia, Alzheimer's disease, and other cardiovascular and neurological disorders, the researchers said.

Direct antioxidant action had been suggested as the mechanism for these effects, but it's unlikely that ginkgo reaches high enough serum levels, Dr. Doré said.

However, his group's experiments showed that a highly standardized ginkgo extract (EGb761) called the body's own antioxidant system into action by elevating expression of heme oxygenase-1, Dr. Doré said.

Ginkgo "allows organs -- here the brain -- to build resistance against potential stress such as a stroke," he said.

In the study, mice given the ginkgo extract at a dose of 100 mg/kg daily for a week before induction of cerebral ischemia had significantly less neurological dysfunction 24 hours after the reperfusion compared with those treated with placebo (P<0.01). The difference was about one point on a four-point scale.

Infarct volume averaged just under 30% for pretreated mice compared with about 60% for those in the placebo group (P<0.01).

Mice given a lower daily ginkgo dose of 50 mg/kg also had a significant reduction in infarct volume (P<0.05).

However, none of these effects were seen with pretreatment in mice genetically engineered to lack heme oxygenase-1, suggesting this antioxidant system was necessary for the neuroprotective effects of ginkgo, the researchers said.

The infarct volumes and subsequent neurological dysfunction scores for these heme oxygenase-1 knockout mice were similar to those of both placebo-treated knockout mice and untreated wild-type mice.

Post-ischemic treatment with ginkgo also appeared effective in reducing brain injury, the researchers found.

Mice given the extract orally at a dose of 100 mg/kg either five minutes or 4.5 hours after reperfusion had significantly better neurological scores and lower infarct volumes than placebo-treated mice at 24 hours (all P<0.01 or P<0.05).

But these effects faded to statistical insignificance by 72 hours with the exception of lower infarct volume for the mice treated five minutes after reperfusion (P<0.05).

Cell line experiments suggested that the whole extract was more effective than individual components, produced a dose-dependent increase in transcription of heme oxygenase-1, and protected mouse neurons from peroxide and glutamate-induced cell death.