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 throug h the formation of peroxynitrite with superoxide. The extract of Ginkgo bil oba leaves (EGb) has been demonstrated to be a potent scavenger of free rad icals. Although EGb has been shown recently to inhibit NO production in mac rophages, its effect on NO production in endothelial cells is largely unkno wn. The objective of this study was to elucidate the mechanism by which EGb affects NO production in a human endothelial cell line (EGV304). After cel ls were incubated with EGb (10-100 mu g/mL) for 2 or 4 hr, the amounts of N O metabolites released by the cells were quantitated, and cellular NOS acti vities were determined following the conversion of [H-3]arginine to [H-3]ci trulline. NOS protein expression was determined by western immunoblotting a nalysis. mRNA levels were examined by reverse transcription-polymerase chai n reaction (RT-PCR) analysis. EGb (50 mu g/mL) caused a 30% reduction of NO metabolites released by endothelial cells. Following EGb treatment, cellul ar inducible NO synthase (iNOS) activity was reduced by 28% with a concomit ant reduction in the levels of iNOS protein mass and mRNA. There was no cha nge in the activity or protein mass of constitutive NO synthase in these ce lls. EGb inhibited NO production by attenuating the level of iNOS mRNA in E CV304 cells. Selective inhibition of iNOS by EGb may be therapeutically rel evant in modulating NO production in endothelial cells. (C) 1999 Elsevier S cience Inc.