Abstract
Erythropoietin (EPO), used clinically for renal anemia, reportedly exerts beneficial pleiotropic effects in various tissues. Recent studies suggest that nitric oxide (NO) plays an important role in EPO-induced tissue protection. The present study investigated whether recombinant human EPO (rHuEPO) exhibits vasoprotective effects even in the NO synthase-inhibited state. Rats that received a NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), in drinking water (0.7 mg/ml) were treated with rHuEPO (75 U/kg, s.c.) three times a week for 2 weeks. The administration of rHuEPO to L-NAME-treated rats had no effect on hematocrit values or increased blood pressure. Vasodilation in response to acetylcholine in the aortic ring was impaired in the L-NAME-treated rats, and improved by rHuEPO. Immunohistochemical staining revealed that infiltration by macrophages and expression of osteopontin were enhanced in the L-NAME-treated rat aorta, and the overexpression was suppressed by rHuEPO. rHuEPO also attenuated medial hyperplasia. Activation of Akt signaling was evident in rHuEPO-treated rats as the increased expression of phosphorylated Akt. rHuEPO enhanced the expression of antioxidant enzymes such as Cu/Zn-superoxide dismutase and heme oxygenase-1 in the aorta. In addition, rHuEPO reduced NADPH oxidase-dependent superoxide production and enhanced the expression of suppressor of cytokine signaling-1(SOCS-1) in the L-NAME-treated rat aorta. These results suggest that a low dose of rHuEPO results in the normalization of endothelial function and vascular inflammation beyond hematopoiesis even in a pharmacologically NO synthase-inhibited state. These effects might be due to the antioxidant properties of rHuEPO. SOCS-1 overexpression would play an important role in suppressing NADPH oxidase activation.