Endothelium-derived hyperpolarizing factor synthase (cytochrome P4502C9) is a functionally significant source of reactive oxygen species in coronary arteries

In the porcine coronary artery, a cytochrome P450 (CYP) isozyme homologous to CYP 2C8/9 has been identified as an endothelium-derived hyperpolarizing factor (EDHF) synthase. As some CYP enzymes are reported to generate reacti ve oxygen species (ROS), we hypothesized that the coronary EDHF synthase ma y modulate vascular homeostasis by the simultaneous production of ROS and e poxyeicosatrienoic acids. In bradykinin-stimulated coronary arteries, antis ense oligonucleotides against CYP 2C almost abolished EDHF-mediated respons es but potentiated nitric oxide (NO)-mediated relaxation, The selective CYP 2C9 inhibitor sulfaphenazole and the superoxide anion (O-2(-)) scavengers Tiron and nordihydroguaretic acid also induced a leftward shift in the NO-m ediated concentration-relaxation curve to bradykinin. CYP activity and O-2( -) production, determined in microsomes prepared from cells overexpressing CYP 2C9, were almost completely inhibited by sulfaphenazole. Sulfaphenazole did not alter the activity of either CYP 2C8, the leukocyte NADPH oxidase, or xanthine oxidase. ROS generation in coronary artery rings, visualized u sing either ethidium or dichlorofluorescein fluorescence, was detected unde r basal conditions, The endothelial signal was attenuated by CYP 2C antisen se treatment as well as by sulfaphenazole. In isolated coronary endothelial cells, bradykinin elicited a sulfaphenazole-sensitive increase in ROS prod uction. Although 11,12 epoxyeicosatrienoic acid attenuated the activity of nuclear factor-KB in cultured human endothelial cells, nuclear factor-kappa B activity was enhanced after the induction or overexpression of CYP 2C9, a s was the expression of vascular cell adhesion molecule-1. These results su ggest that a CYP isozyme homologous to CYP 2C9 is a physiologically relevan t generator of ROS in coronary endothelial cells and modulates both vascula r tone and homeostasis.