Angiotensin type 1 receptor blocker reduces intimal neovascularization and plaque growth in apolipoprotein E-deficient mice.

The interactions between the renin-angiotensin system and neovascularization in atherosclerotic plaque development are unclear. We investigated the effects of angiotensin II type 1 receptor antagonism in the pathogenesis of atherosclerosis in apolipoprotein E-deficient (ApoE(-/-)) mice with a special focus on plaque neovascularization. ApoE(-/-) mice fed a high-fat diet were randomly assigned to 1 of 2 groups and administered vehicle or olmesartan for 12 weeks. Quantification of plaque areas at the aortic root and in the thoracic and abdominal aorta revealed that, in all 3 of the regions, olmesartan reduced intimal neovessel density and the mRNA levels of toll-like receptor (TLR) 2 and TLR4. Olmesartan increased the levels of collagen and elastin, reduced the level of macrophages in the aortic root, and reduced the mRNA and the activity of matrix metalloproteinase (MMP) 2 in aortic roots and thoracic aortas. Aortic ring assay revealed that olmesartan-treated ApoE(-/-) mice had a markedly lower angiogenic response than that of untreated ApoE(-/-) mice. Bone marrow-derived endothelial progenitor cell-like c-Kit(+) cells from olmesartan-treated ApoE(-/-) mice showed marked impairment of cellular functions and lower expression of TLR2/TLR4 and MMP-2 compared with those of untreated controls. MMP-2 deficiency reduced intimal neovessel density and atherosclerotic lesion formation. Olmesartan and small-interfering RNA targeting TLR2 reduced the levels of TLR2, and MMP-2 mRNA induced angiotensin II in cultured endothelial cells. Angiotensin II type 1 receptor antagonism appears to inhibit intimal neovascularization in ApoE(-/-) mice, partly by reducing TLR2/TLR4-mediated inflammatory action and MMP activation, thus decreasing atherosclerotic plaque growth and increasing plaque instability.