Mechanism of endothelial dysfunction in apolipoprotein E-deficient mice

Endothelium-dependent relaxations mediated by NO are impaired in a mouse model of human atherosclerosis, Our objective was to characterize the mechanisms underlying endothelial dysfunction in aortas of apolipoprotein E (apoE)-deficient mice, treated for 26 to 29 weeks with a lipid-rich Western-type diet. Aortic rings from apoE-deficient mice showed impaired endothelium-dependent relaxations to acetylcholine (10(-9) to 10(-5) mol/L) and Ca2+ ionophore (10(-9) to 10(-6) mol/L) and endothelium-independent relaxations to diethylammonium (Z)-1 -(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA-NONOate, 10(-10) to 10(-5) mol/L) compared with aortic rings from C57BL/6J mice (P <0.05), By use of confocal microscopy of an oxidative fluorescent probe (dihydroethidium), increased superoxide anion (O-2(-)) production was demonstrated throughout the aortic wall but mainly in smooth muscle cells of apoE-deficient mice. CuZn-superoxide dismutase (SOD) and Mn-SOD protein expressions were unaltered in the aorta exposed to hypercholesterolemia. A cell-permeable SOD mimetic, Mn(III) tetra(4-benzoic acid) porphyrin chloride (10-5 mol/L), reduced O-2(-) production and partially normalized relaxations to acetylcholine and DEA-NONOate in apoE-deficient mice (P <0.05). [C-14]L-Citrulline assay showed a decrease of Ca2+-dependent NOS activity in aortas from apoE-deficient mice compared with C57BL/6J mice (P <0.05), whereas NO synthase protein expression was unchanged. In addition, cGMP levels were significantly reduced in the aortas of apoE-deficient mice (P <0.05). Our results demonstrate that in apoE-deficient mice on a Western-type fat diet, impairment of endothelial function is caused by increased production of O-2(-) and reduced endothelial NO synthase enzyme activity. Thus, chemical inactivation of NO with O-2(-) and reduced biosynthesis of NO are key mechanisms responsible for endothelial dysfunction in aortas of atherosclerotic apoE-deficient mice.