Inhibitory effect of Ginkgo biloba extract on the expression of inducible nitric oxide synthase in endothelial cells.

Excessive production of nitric oxide (NO) may have cytotoxic effects through the formation of peroxynitrite with superoxide. The extract of Ginkgo biloba leaves (EGb) has been demonstrated to be a potent scavenger of free radicals. Although EGb has been shown recently to inhibit NO production in macrophages, its effect on NO production in endothelial cells is largely unknown. The objective of this study was to elucidate the mechanism by which EGb affects NO production in a human endothelial cell line (ECV304). After cells were incubated with EGb (10-100 microg/mL) for 2 or 4 hr, the amounts of NO metabolites released by the cells were quantitated, and cellular NOS activities were determined following the conversion of [3H]arginine to [3H]citrulline. NOS protein expression was determined by western immunoblotting analysis. mRNA levels were examined by reverse transcription-polymerase chain reaction (RT-PCR) analysis. EGb (50 microg/mL) caused a 30% reduction of NO metabolites released by endothelial cells. Following EGb treatment, cellular inducible NO synthase (iNOS) activity was reduced by 28% with a concomitant reduction in the levels of iNOS protein mass and mRNA. There was no change in the activity or protein mass of constitutive NO synthase in these cells. EGb inhibited NO production by attenuating the level of iNOS mRNA in ECV304 cells. Selective inhibition of iNOS by EGb may be therapeutically relevant in modulating NO production in endothelial cells.