Dysfunctional endothelial nitric oxide biosynthesis in healthy smokers with impaired endothelium-dependent vasodilatation

Background-The mechanisms involved in the dysfunction of both endothelium-d ependent vasodilatation (EDV) and NO biosynthesis related to smoking are un clear. In this study, EDV was assessed in healthy smokers and nonsmokers in vivo and, using serum from the same individuals, was related to the NO bio synthetic pathway in vitro. Methods and Results-Flow-mediated EDV of the brachial artery was measured i n 23 male patients (8 nonsmokers and 15 smokers). Serum was collected, adde d to confluent (approximate to 85%) monolayers of human umbilical vein endo thelial cells (HUVECs), and incubated for 12 hours. Basal and substance P-s timulated NO production was measured. The HUVECs used for measuring basal N O production were lysed, and both endothelial NO synthase (eNOS) protein ex pression and eNOS activity were determined. EDV was lower in smokers compar ed with nonsmokers (P <0.001). HUVECs treated with serum from smokers compa red with nonsmokers showed significantly lower basal (P <0.0001) and stimul ated (P <0.02) NO production, higher eNOS expression (P<0.0001), but lower eNOS activity (P<less than>0.004). There was a significant positive correla tion between in vivo EDV and in vitro substance P-stimulated NO production (rho=0.57, P <0.01) and between basal NO production and eNOS activity (r=0. 54, P <0.008) and a negative correlation between basal NO production and eN OS protein expression (r= -0.60, P <0.003). Conclusions-This is the first study to combine an in vivo model with a near -physiological in vitro model to demonstrate an association between decreas ed NO production and reduced EDV. Cigarette smoking was associated with red uced EDV, NO generation, and eNOS activity in the presence of increased eNO S protein expression.