Background: Patients with advanced chronic renal disease (CRD) suffer from excessive morbidity and mortality due to complications of accelerated atherosclerosis. Recombinant human erythropoietin (EPO), which is routinely used to treat the anaemia present in approximately 90% of dialysis-dependent patients with end-stage renal disease, may induce vascular dysfunction by reducing nitric oxide (NO) availability. Pathophysiologic concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), are found in patients with CRD and correlate with vascular disease and cardiovascular mortality. The aim of the current study was to investigate the effect of EPO on ADMA concentrations and NO generation in vitro and in vivo. Furthermore, we wanted to study the effect of EPO on the expression of the enzymes that regulate ADMA metabolism and NO generation.
Methods: Human umbilical vein endothelial cells (HUVECs) were exposed to therapeutic concentrations of EPO. The expression and metabolic activity of dimethylarginine dimethylaminohydrolase II (DDAH II), the enzyme that degrades ADMA, was evaluated. Following subcutaneous administration of EPO to Balb/c mice for 10 weeks, serum ADMA concentrations were determined. Systolic blood pressure was measured noninvasively. Urinary nitrite and nitrate (NOx) concentrations were assessed by Griess assay. Protein expression of DDAH and NOS in livers and kidneys was measured by western blotting.
Results: EPO suppressed ADMA elaboration by HUVECs. Systolic blood pressure and serum concentrations of ADMA were significantly elevated in EPO-treated mice. The protein expression of DDAH I in the kidney and liver was upregulated while hepatic expression of DDAH II was decreased and renal DDAH II expression remained unchanged by EPO administration. However, EPO augmented urinary NOx concentrations as well as the expression of NOS 1 and NOS 2 in the kidney.
Conclusion: In spite of elevating serum ADMA concentrations, EPO does not appear to compromise overall NO generation in Balb/c mice.