Molecular and cellular assessment of ginkgo biloba extract as a possible ophthalmic drug.

We have investigated the biochemical and cell biological basis of the reported beneficiary effects of the leaf extracts of the plant Ginkgo biloba, which has been used as a possible ophthalmic drug. The antioxidant, antimicrobial, anti-apoptotic and cytoprotective properties of the standardized extract called EGb761 were assayed. Chemical stresses were induced in cells using alloxan or dexamethasone, and the effect of EGb761 on them was studied using the MTT and TUNEL assays. Its ability to modulate the activities of some antioxidant enzymes was tested in vitro. In addition, cataract was induced in rats through selenite injection, and the effect of EGb761 administration on the progression of cataract was studied using slit lamp examination. Ginkgo biloba was found to be an excellent antioxidant. It readily scavenges reactive oxygen and nitrogen radicals and inhibits oxidative modifications that occur to proteins in vitro. It enters intact cells and protects them from alloxan-mediated and light-mediated stress, and the nuclear DNA from single strand breaks. It also effectively inhibits chemically induced apoptosis. It does not modulate the activities of endogenous antioxidant enzymes, nor does it have any significant antimicrobial activity. Unlike some other plant extracts, it is not phototoxic. In experiments wherein selenite cataract was induced in laboratory rats, treatment with the extract significantly retards the progression of lens opacification in vivo. Ginkgo biloba's inherent antioxidant, antiapoptotic and cytoprotective action and potential anticataract ability appear to be some of the factors responsible for its beneficial effects.