Phenanthraquinone inhibits eNOS activity and suppresses vasorelaxation.

Diesel exhaust particles cause an impairment of endothelium-dependent vasorelaxation and are associated with cardiopulmonary-related diseases and mortality, but the mechanistic details are poorly understood. Since we reported previously that phenanthraquinone, an environmental chemical contained in diesel exhaust particles, suppresses neuronal nitric oxide synthase (nNOS) activity by shunting electrons away from the normal catalytic pathway, it was hypothesized that phenanthraquinone inhibits endothelial NOS (eNOS) activity and affects vascular tone. Therefore, the effects of phenanthraquinone on eNOS activity, endothelium-dependent relaxation, and blood pressure were examined in the present study. Phenanthraquinone inhibited NO formation evaluated by citrulline formed by total membrane fraction of bovine aortic endothelial cells with an IC(50) value of 0.6 microM. A kinetic study revealed that phenanthraquinone is a competitive inhibitor with respect to NADPH and a noncompetitive inhibitor with respect to L-arginine. Endothelium-dependent relaxation of rat aortic rings by ACh was significantly inhibited by phenanthraquinone (5 microM), whereas the endothelium-independent relaxation by nitroglycerin was not. Furthermore, an intraperitoneal injection of phenanthraquinone (0.36 mmol/kg) to rats resulted in an elevation of blood pressure (1.4-fold, P < 0.01); under this condition, plasma levels of stable NO metabolites, nitrite/nitrate, in phenanthraquinone-treated rats was reduced to 68% of control levels. The present findings suggest that phenanthraquinone has a potent inhibitory action on eNOS activity via a similar mechanism reported for nNOS, thereby causing the suppression of NO-mediated vasorelaxation and elevation of blood pressure.

Enzyme activity and protein content of superoxide dismutase isozymes in human renal cell carcinoma.

Alterations in renal superoxide dismutase (SOD) isozymes were examined in cancerous tissues of human renal cell carcinoma and the corresponding non-cancerous renal tissues. Cu,Zn-SOD activities in cancerous tissues were lower than those in normal tissues. Mn-SOD activities were varied in the cases examined, whereas no significant difference between cancerous and normal tissues was observed for Mn- or total-SOD activities. Immunoblot analysis showed that the loss in enzyme activity in cancerous tissue was greater than the decrease in protein content for either isozyme. The selective decrease in Cu,Zn-SOD activities in cancerous tissue observed in this study suggests that the cytoplasmic defense against free radical damage appears to be reduced in renal cell carcinoma.