Mechanism of endothelial dysfunction in apolipoprotein E-deficient mice

Endothelium-dependent relaxations mediated by NO are impaired in a mouse mo del of human atherosclerosis, Our objective was to characterize the mechani sms 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-dep endent relaxations to acetylcholine (10(-9) to 10(-5) mol/L) and Ca2+ ionop hore (10(-9) to 10(-6) mol/L) and endothelium-independent relaxations to di ethylammonium (Z)-1 -(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA-NONOat e, 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 demons trated throughout the aortic wall but mainly in smooth muscle cells of apoE -deficient mice. CuZn-superoxide dismutase (SOD) and Mn-SOD protein express ions were unaltered in the aorta exposed to hypercholesterolemia. A cell-pe rmeable 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-Cit rulline assay showed a decrease of Ca2+-dependent NOS activity in aortas fr om apoE-deficient mice compared with C57BL/6J mice (P <0.05), whereas NO sy nthase protein expression was unchanged. In addition, cGMP levels were sign ificantly reduced in the aortas of apoE-deficient mice (P <0.05). Our resul ts demonstrate that in apoE-deficient mice on a Western-type fat diet, impa irment of endothelial function is caused by increased production of O-2(-) and reduced endothelial NO synthase enzyme activity. Thus, chemical inactiv ation of NO with O-2(-) and reduced biosynthesis of NO are key mechanisms r esponsible for endothelial dysfunction in aortas of atherosclerotic apoE-de ficient mice.