The Abdominal Aortic Aneurysm and Intraluminal Thrombus: Current Concepts of Development and Treatment

Myeloperoxidase (MPO) is an abundant mammalian phagocyte hemoprotein thought to primarily mediate host defense reactions. Although its microbicidal functions are well established in vitro, humans deficient in MPO are not at unusual risk of infection. MPO was observed herein to modulate the vascular signaling and vasodilatory functions of nitric oxide (NO) during acute inflammation. After leukocyte degranulation, MPO localized in and around vascular endothelial cells in a rodent model of acute endotoxemia and impaired endothelium-dependent relaxant responses, to which MPO-deficient mice were resistant. Altered vascular responsiveness was due to catalytic consumption of NO by substrate radicals generated by MPO. Thus MPO can directly modulate vascular inflammatory responses by regulating NO bioavailability.

To test whether deficiency in endothelial nitric oxide synthase (eNOS) affects atherosclerosis development, we compared lesion formation in apolipoprotein E (apoE)/eNOS-double knockout (DKO) and apoE-knockout (KO) control animals. After 16 weeks of "Western-type" diet, apoE/eNOS-DKO males and females showed significant increases in lesion area of 93.6% and 59.2% compared with apoE-KO mice. All apoE/eNOS-DKO animals studied developed peripheral coronary arteriosclerosis, associated with perivascular and myocardial fibrosis, whereas none of the apoE-KO mice did. Transthoracic echocardiography showed a significantly increased left ventricular wall thickness and decreased fractional shortening in DKO animals. Mean arterial pressure was increased in DKO mice and was comparable in degree to eNOS-KO animals. Male DKO animals developed atherosclerotic abdominal aneurysms and aortic dissection. eNOS deficiency increases atherosclerosis in Western-type diet-fed apoE-KO animals and introduces coronary disease and an array of cardiovascular complications, including spontaneous aortic aneurysm and dissection. This phenotype constitutes the first murine model to demonstrate distal coronary arteriosclerosis associated with evidence of myocardial ischemia, infarction, and heart failure. Hypertrophy and reduced left ventricular function cannot be explained by increased blood pressure alone, because eNOS-KO animals do not develop these complications.