Abstract: 【ABSTRACT】 BACKGROUND＆AIM： To observe the antagonism of ginkgo biloba extract(GBE) to trichloroethylene(TCE)-induced elevation of nitric oxide，nitric oxide synthase activity and up-regulation of iNOS mRNA in keratinocyte;also to further explore effective protective agent for toxic dermatitis caused by TCE．MATERIALS AND METHODS：Primary cultured normal human keratinocytes in serum-free medium were treated with different concentrations of TCE for 4 h or pre-incubated with different concentrations of GBE for 2 h then with 2.0 mmol/L of TCE．Levels of NO generation and activity of iNOS and cNOS wrere measured according to the kit protocols，whilst RT-PCR was used to determine expression of iNOS mRNA．RESULTS：2.0 mmol/L of TCE could dramatically elevate NO generation and iNOS activity but not cNOS activity．While 10 mg/L,50 mg/L and 100 mg/L of GBE could partially decrease NO level and iNOS activity induced by 2.0 mmol/L of TCE，150 mg/L of GBE could fully attenuate the elevated NO level and iNOS activity．iNOS mRNA expression was up-regulated by 2.0 mmol/L of TCE and significantly inhibited by 150 mg/L of GBE． CONCLUSION： Trichloroethylene could up-regulate iNOS gene in keratinocyte, then generate large amount of NO. GBE could inhibit TCE-induced elevation of NO level and iNOS activity，as well as the induced iNOS mRNA up-regulation．Our in vitro study demonstrated that NO may be involved in dermato-toxicity of trichloroethylene and GBE can be a potential protective agent working through NO pathway．

Key words: ginkgo biloba extract, nitric oxide, nitric-oxide synthase, trichloroethylene, keratinocyte