Investigation of the inhibitory effects of homocysteine and copper on nitric oxide-mediated relaxation of rat isolated aorta

1 Elevated plasma levels of homocysteine (HC) and copper have both been associated with the development of inflammatory vascular diseases, such as atherosclerosis. In this study, the effects of a combination of HC and copper on nitric oxide (NO)-mediated relaxation of isolated rat aortic rings were investigated. 2 Exposure to HC (10-100 mu M; 30 min) had no effect on relaxation to acetylcholine (ACh; 0.01-10 mu M, n = 4). Pre-incubation of aortic rings with a higher concentration of HC for an extended period (1 mM: 180 min) significantly inhibited endothelium-dependent relaxation (n=4), but this inhibition was prevented by the presence of the copper chelator bathocuprione (10 mu M, 180 min, n = 6). 3 Exposure to HC (100 mu M) and copper (10-100 mu M; 30 min) caused a copper concentration-dependent inhibition of endothelium-dependent relaxation (n=4). This inhibitory effect was reduced in the presence of either superoxide dismutase (SOD; 100 u ml(-1); n=4) or catalase (100 u ml(-1); n=4), and further reduced by the presence of both enzymes (n=5). 4 HC and copper (100 mu M; 30 min) significantly inhibited endothelium-independent relaxation to glyceryl trinitrate (0.01-10 mu M; n=8). In contrast, HC (1 mM), alone or in combination with copper (100 mu M), did not inhibit relaxation to the endothelium-independent relaxant sodium nitroprusside (0.01-10 mu M; n=4). 5 These data indicate that the presence of copper greatly enhances the inhibitory actions of HC on NO-mediated relaxation of isolated aortic rings. The reduction of inhibition by catalase and SOD indicates a possible role for copper-catalyzed generation of superoxide and hydrogen peroxide leading to an increased inactivation or decreased production of endothelium-derived NO.