Adherence of uremic erythrocytes to vascular endothelium decreases endothelial nitric oxide synthase expression

High prevalence of atherosclerotic cardiovascular events accounts for much of the mortality among patients suffering from end-stage renal disease (ESRD). Endothelial dysfunction as a pathogenic mechanism might contribute to increasing the cardiovascular risk of ESRD. Reduced endothelium-dependent vasodilation has consistently been observed in chronic renal failure patients. Since nitric oxide (NO) is the principal endothelium-derived vasodilator, a reduction in the NO bioavailability may be envisaged in ESRD patients.

To clarify whether exposure to erythrocytes from ESRD patients might modulate NO release by the endothelium, we evaluated endothelial NO synthase (eNOS) protein levels (Western blot), eNOS mRNA quantity (real-time PCR), and NOS activity (conversion of L-[3H] arginine in L-[3H] citruline) in endothelial cultures stimulated by erythrocytes from healthy subjects and ESRD patients.

A time-dependent decrease in eNOS protein levels was evident in cultures treated with erythrocytes from ESRD patients. This observation was consistent with the decreased eNOS mRNA quantities induced by erythrocytes from such patients. Moreover, compared to controls, NOS activity exhibited a significant reduction after incubation with erythrocytes from ESRD patients. The observed eNOS reduction induced by erytrocytes from ESRD patients was totally abolished by annexin V, able to mask red blood cell (RBC) surface-exposed phosphatidylserine.

These findings suggest that adhesion of erythrocytes from ESRD patients to vascular endothelium may cause a decrease in the levels of eNOS mRNA and protein, and inhibition of NOS activity. This might contribute to endothelial dysfunction, and may play a role in the pathogenesis of cardiovascular disease in ESRD patients.