CyA and OxLDL cause endothelial dysfunction in isolated arteries through endothelin-mediated stimulation of O-2(-) formation

Background. Cyclosporin A (CyA) and oxidized low-density lipoprotein (OxLDL ) cause endothelial dysfunction, partly through stimulation of O-2(-) forma tion (which can inactivate nitric oxide). We investigated whether CyA and O xLDL potentiate their influence on oxidative stress, whether endothelin (ET ) is a mediator of CyA- and OxLDL-induced O-2(-) formation, and whether enh anced oxidative stress results in further attenuation of endothelium-depend ent vasodilation. Methods and results. Human LDL was oxidized by Cu++. O-2(-) formation of is olated rat aortic rings was measured using a chemiluminescence assay. Incub ation (60 min) of aortic rings with CyA (10 ng-10 mu g/ml) or with OxLDL (3 00 mu g/ml) caused a significant, dose-dependent increase of the basal O-2( -) formation. Pretreatment of the aortic rings with CyA (10 ng/ml) further enhanced the OxLDL-induced O-2(-) formation by factor 1.9. The enhancement of the OxLDL-induced stimulation of O-2(-) formation by CyA could be comple tely blocked by BQ123, a selective endothelin-1 (ET-1) receptor antagonist. Likewise, exogenously applied ET-1 (1 nM) potentiated the OxLDL-induced O- 2(-) formation by factor 1.8. Endothelium-dependent dilation was measured i n isolated rings of rabbit aorta superfused with physiological salt solutio n in an organ bath. Incubation of the aortic rings with CyA (10 mu g/ml, 60 min) or with OxLDL (300 mu g/ml, 60 min) alone did not attenuate endotheli um-dependent dilations. However, coincubation of the aortic rings with CyAOxLDL in the presence of diethyl-dithiocarbamate, an inhibitor of the endog enous superoxide dismutase, caused a 60% inhibition of acetylcholine-induce d dilator responses. Conclusions. Coincubation of isolated aortic rings with CyA and OxLDL cause s a potent enhancement of vascular O-2(-) formation. ET-1 seems to be media tor of the CyA-induced O-2(-) formation. Enhanced oxidative stress results in further attenuation of endothelium dependent vasodilation.