Hypercholesterolemia impairs endothelium-dependent relaxations in common carotid arteries of apolipoprotein e-deficient mice.

BACKGROUND AND PURPOSE The effects of Western-type fat diet on endothelium-dependent relaxations and vascular structure in carotid arteries from a mouse model of human atherosclerosis are not known. Our objective was to characterize the mechanisms underlying endothelial dysfunction in apoE-deficient mice. METHODS C57BL/6J and apoE-deficient mice were fed for 26 weeks with a lipid-rich Western-type diet. Changes in the intraluminal diameter of pressurized common carotid arteries (ID 450 micrometer) were measured in vitro with a video dimension analyzer. Endothelial NO synthase protein content was evaluated by Western blotting. Intracellular cGMP and cAMP levels were determined by radioimmunoassay. RESULTS No morphological changes were observed in the carotid arteries of apoE-deficient mice. However, endothelium-dependent relaxations to acetylcholine (10(-9) to 10(-5) mol/L) were impaired (maximal relaxation 52+/-7% versus 83+/-5% for control mice, P<0.05). Treatment of arteries with NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester inhibited relaxations to acetylcholine to the same extent in apoE-deficient mice as in control mice. Preincubation of carotid arteries with cell-permeable superoxide dismutase mimetic Mn(III) tetra(4-benzoic acid)porphyrin chloride almost normalized NO-mediated relaxations to acetylcholine (75+/-5%, P<0.05). Endothelium-dependent relaxations to calcium ionophore and endothelium-independent relaxations to NO donor diethylammonium(Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate were unchanged in apoE-deficient mice. In addition, no changes in endothelial NO synthase protein expression and cGMP/cAMP levels were found in carotid arteries of apoE-deficient mice. CONCLUSIONS In carotid arteries of apoE-deficient mice, hypercholesterolemia causes impairment of receptor-mediated activation of eNOS. Increased superoxide anion production in endothelial cells appears to be coupled to activation of cholinergic receptors and is responsible for hypercholesterolemia-induced endothelial dysfunction. The apoE-deficient mouse carotid artery is a valuable new experimental model of endothelial dysfunction.