Rubbing salt into wounded endothelium: Sodium potentiates proatherogenic effects of TNF-α under non-uniform shear stress

Increased consumption of sodium is a risk factor for hypertension and cardiovascular diseases. In vivo studies indicated that high dietary sodium may have a direct negative influence on endothelium. We investigated the effects of high sodium on the endothelial activation during early steps of atherogenesis. Endothelial cells (HUVECs) grown in a model of arterial bifurcations were exposed to shear stress in the presence of normal or high (+ 30 mmol/l) sodium. Adherent THP-1 cells, and the adhesion molecule expression were quantified. Sodium channel blockers, pathways' inhibitors, and siRNA against tonicity-responsive enhancer binding protein (TonEBP) were used to identify the mechanisms of sodium effects on endothelium. ApoE-deficient mice on low-fat diet received water containing normal or high salt (8% w/v) for four weeks, and the influence of dietary salt on inflammatory cell adhesion in the common carotid artery and carotid bifurcation was measured by intravital microscopy. In vitro, high sodium dramatically increased the endothelial responsiveness to tumour necrosis factor-a under non-uniform shear stress. Sodium-induced increase in monocytic cell adhesion was mediated by reactive oxygen species and the endothelial nitric oxygen synthase, and was sensitive to the knockdown of TonEBP. The results were subsequently confirmed in the ApoE-deficient mice. As compared with normal-salt group, high-salt intake significantly enhanced the adhesion of circulating CD11b+ cells to carotid bifurcations, but not to the straight segment of common carotid artery. In conclusion, elevated sodium has a direct effect on endothelial activation under atherogenic shear stress in vitro and in vivo, and promotes the endothelial-leukocyte interactions even in the absence of increased lipid concentrations.