Mechanism of Endothelial Dysfunction in Apolipoprotein E–Deficient Mice

Abstract

Abstract-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 Ϫ9 to 10 Ϫ5 mol/L) and Ca 2ϩ ionophore (10 Ϫ9 to 10 Ϫ6 mol/L) and endothelium-independent relaxations to diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA-NONOate, 10 Ϫ10 to 10 Ϫ5 mol/L) compared with aortic rings from C57BL/6J mice (PϽ0.05). By use of confocal microscopy of an oxidative fluorescent probe (dihydroethidium), increased superoxide anion (O 2 Ϫ ) 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 Ϫ5 mol/L), reduced O 2 Ϫ production and partially normalized relaxations to acetylcholine and DEA-NONOate in apoE-deficient mice (PϽ0.05). [ 14 C]L-Citrulline assay showed a decrease of Ca 2ϩ -dependent NOS activity in aortas from apoE-deficient mice compared with C57BL/6J mice (PϽ0.05), whereas NO synthase protein expression was unchanged. In addition, cGMP levels were significantly reduced in the aortas of apoE-deficient mice (PϽ0.05). 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 Ϫ and reduced endothelial NO synthase enzyme activity. Key Words: endothelium Ⅲ nitric oxide Ⅲ superoxide anion Ⅲ apolipoprotein E Ⅲ atherosclerosis A therosclerosis is a chronic process, which can be triggered by cardiovascular risk factors such as hypercholesterolemia, aging, hypertension, and diabetes mellitus. 1 Endothelium-derived vasoactive factors play an important regulatory role in vascular homeostasis and pathogenesis of atherosclerosis because of the strategic position of the endothelium between the vascular smooth muscle cells (VSMCs) and the circulating blood. 2,3 NO is a potent vasodilator that is formed in endothelial cells from L-arginine by endothelial NO synthase (eNOS), which is constitutively expressed. 4 -6 NO production is activated by the stimulation of cell surface receptors or by mechanical forces such as shear stress. 7,8 Accumulating evidence suggests that alterations in the NO pathway play a central role in endothelial dysfunction induced by hypercholesterolemia. This may be of major importance inasmuch as NO can substantially inhibit several components of the atherogenic process, such as VSMC contraction and proliferation, platelet aggregation, and monocyte adhesion. 9,10 Previous studies identified 3 mechanisms responsible for reduced bioavailability of NO in arteries exposed to hypercholester...

Antiinflammatory actions of inorganic nitrate stabilize the atherosclerotic plaque

“…Our assessment of the distribution of both anions demonstrated a generalized reduction in the levels of nitrate but not nitrite in ApoE KO compared with WT mice across all of the compartments assessed, an observation also reported to occur in patients with coronary artery disease (23). The underlying mechanism of this effect is thought to be because of the endothelial dysfunction exhibited by these mice as a result of reduced eNOS activity (25). In contrast to our work, some studies suggest that reduced levels of plasma nitrite and not nitrate more accurately reflect disease severity and vascular flow responses (24,26).…”

Reduction of Blood Pressure, Plasma Cholesterol, and Atherosclerosis by Elevated Endothelial Nitric Oxide

“…A 1.5-fold increase is also rather low in terms of possible drug or gene therapy applications. Second, the observed increase in atherosclerosis is explained by measurements indicating that the overexpressed eNOS enzyme is dysfunctional in the mouse model used by Ozaki et al This finding is not unexpected, given the moderate level of overexpression in their mice, because it has been previously reported that endogenous eNOS is indeed dysfunctional in terms of NO production in apoE0 mice fed a Western type diet (45). The results from the Ozaki et al study are probably (at least in part) explained by the construct used, which consists of cDNA (often leading to low expression levels) and a heterologous promoter.…”

Angiotensin-(1–7) Modulates Renal Vascular Resistance Through Inhibition of p38 Mitogen-Activated Protein Kinase in Apolipoprotein E–Deficient Mice

“…9,24,29 In these mice, mechanisms of proper vasorelaxation and vasoconstriction are compromised because of hypercholesterolemia. 7,27,30 Previously, we showed that apoE(−/−) fed on a highfat diet exhibit impaired endo thelialdependent vasorelaxation. 24 Chronic Ang(1-7) treat ment improved NO bioavailability and, therefore, ameliorated endothelial dysfunction in these mice.…”

“…27 To test whether Ang(1-7) affects ROS production, renal oxygen radical levels and Figure 2A and 2B, chronic Ang(1-7) treatment significantly reduced urinary 8isoprostane levels and lucigeninenhanced chemiluminescence in renal cortex samples.…”