Objective-Macrophage-mediated oxidation of low-density lipoprotein (LDL) by enzymes, such as the lipoxygenases, is considered of major importance for the formation of oxidized LDL during atherogenesis. Macrophages have been identified in hypoxic areas in atherosclerotic plaques. Methods and Results-To investigate the role of hypoxia in macrophage-mediated LDL oxidation, we incubated human monocyte-derived macrophages with LDL under normoxic (21% O 2 ) or hypoxic (0% O 2 ) conditions. The results showed that hypoxic macrophages oxidized LDL to a significantly higher extent than normoxic cells. Interestingly, the mRNA and protein expression of 15-lipoxygenase-2 (15-LOX-2) as well as the activity of this enzyme are elevated in macrophages incubated at hypoxia. Both the unspliced 15-LOX-2 and the spliced variant 15-LOX-2sv-a are found in macrophages. In addition, 15-LOX-2 was identified in carotid plaques in some macrophage-rich areas but was only expressed at low levels in nondiseased arteries. Conclusions-In summary, these observations show for the first time that 15-LOX-2 is expressed in hypoxic macrophages and in atherosclerotic plaques and suggest that 15-LOX-2 may be one of the factors involved in macrophage-mediated LDL oxidation at hypoxia. A n early phenomenon in atherosclerosis is the retention, oxidation, and accumulation of low-density lipoprotein (LDL) in the vessel wall. 1,2 Oxidized LDL (oxLDL), one of the key players in atherogenesis, attracts monocytes to the vessel wall where they differentiate into macrophages. 3,4 Oxidation of LDL mediated by macrophages is considered to be of major importance for the formation of oxLDL within the atherosclerotic plaque. Enzymes involved in this process are 15-lipoxygenase (15-LOX), 5,6 myeloperoxidase (MPO), 7 and NADPH oxidase. 8 Macrophages in the arterial wall take up oxLDL through scavenger receptors and accumulate oxLDL as cholesterol esters, which results in foam cell formation.The thickness of the arterial wall increases as the atherosclerotic plaque develops. This leads to an impaired diffusion, which results in oxygen and nutrient deficiency in the deeper portion of the arterial intima and in atherosclerotic plaques. Simultaneously, oxygen consumption by cells within the plaque rises, 9,10 which could be because of the increased number of energy-consuming foam cells. 10 In healthy tissues, oxygen tension is 20 to 70 mm Hg (2.5% to 9% O 2 ). However, in diseased tissue, eg, in atherosclerotic plaques, inadequate perfusion may reduce O 2 tension to below 10 mm Hg (Ͻ1% O 2 ) in some regions. 11 Results from our laboratory have previously shown that areas of hypoxia occur within atherosclerotic plaques in cholesterol-fed rabbits. 12 Hypoxia may lead to retention of macrophages in these areas, because it has been shown that macrophage migration is reduced by hypoxia. 13 The role of hypoxia in the development of atherosclerotic plaques is not known. In this study, we have explored the effect of hypoxia on macrophage-mediated LDL oxidation and the expression o...

No abstract

No abstract

CD14 is a predictor of inflammation and associated with atherosclerosis. We analyzed 118 carotid plaques from patients with symptomatic carotid artery stenosis for expression of the macrophage markers CD14, CD68 and the angiotensin II type 1 receptor (AT1-R). CD14 staining was significantly increased in thrombotic carotid plaques. AT1-R staining was found in macrophage-rich areas, and AT1-R mRNA was detected in plaque macrophages isolated with anti-CD14 immunobeads. In patients treated with an angiotensin receptor blocker, expression of CD14 and CD68 in carotid plaque and serum levels of inflammatory markers were lower than in untreated patients. In vitro, expression of CD14 in human monocyte-derived macrophages was increased by exposure to lipopolysaccharide and decreased by exposure to an angiotensin receptor blocker. Thus, inhibition of the innate immune responsive lipopolysaccharide receptor CD14 in macrophages, rather than AT1-R inhibition, may help explain the anti-inflammatory effects of angiotensin receptor blockade.