Coexistence of Oxidized Lipids and α-Tocopherol in All Lipoprotein Density Fractions Isolated From Advanced Human Atherosclerotic Plaques

Abstract

Abstract-After investigation of the contents and redox status of antioxidants and lipids in homogenates of both normal artery and atherosclerotic plaque, we now investigated them in the density fractions (very low, low, high, and protein fractions) of atherosclerotic plaque freshly obtained from carotid endarterectomy. By using the optimum extraction method (homogenization in carbonate buffer) and after density gradient ultracentrifugation, we isolated and characterized density fractions of plaque for apolipoproteins, size and contents of ␣-tocopherol (␣-TOH), unesterified cholesterol, cholesteryl linoleate (Ch18:2), and hydroxides and hydroperoxides of Ch18:2, ie, Ch18:2-O(O)H. The distribution of apolipoproteins was more heterogeneous than that in the corresponding lipoproteins isolated from blood, and the majority of material in all plaque density fractions was present in large particles eluting in the void volume of gel-filtration columns. The content of unesterified cholesterol per unit of protein in low-and high-density fractions was 10-fold that in corresponding plasma lipoproteins. Low-and very-low-density fractions contained most of the lesion lipids and ␣-TOH. Two to five percent of lesion Ch18:2 was present as Ch18:2-O(O)H and distributed more or less equally among all density fractions, yet the content of ␣-TOH per unit of Ch18:2 was higher than that in corresponding plasma lipoproteins. These results demonstrate that ␣-TOH and oxidized lipids coexist in all lesion density fractions, further supporting the notion that large proportions of lipids in lipoproteins of advanced stages of atherosclerosis are oxidized. However, although not ruling it out, our results do not support the suggestion that advanced stages of atherosclerosis are associated with gross deficiencies in the lipoproteins' vitamin E content. (Arterioscler Thromb Vasc

Disease Stage-Dependent Accumulation of Lipid and Protein Oxidation Products in Human Atherosclerosis

“…29 In addition, the levels of CE-O(O)H per parent detected in the most severe aortic lesions (2.4%) were less than that observed for carotid lesions (3.5%) processed freshly within 2 hours of resection. 13 Further, we compared analytes from various grades of lesion derived from the same aortic tissue sample and verified that artifactual oxidation of CE did not occur during sample processing. As CEs are more susceptible to oxidation than cholesterol, Tyr and Phe, the results obtained therefore likely represent the situation in vivo.…”

“…12,13 Herein we report on the characterization of antioxidants, lipid, oxidized lipid, and proteins from the intimal lipoprotein fraction of human aorta representing the earlier spectrum of the disease process.…”

“…CE-containing polyunsaturated lipids are the primary targets for one-electron mediated oxidation, and oxidized CEs are found in lesions 12,13,26,27 but are essentially absent in plasma LDL. 13 CE hydroperoxides (CE-OOH) were not detected in early lesions, ie, stages I-III (Table 2).…”

“…CE-containing polyunsaturated lipids are the primary targets for one-electron mediated oxidation, and oxidized CEs are found in lesions 12,13,26,27 but are essentially absent in plasma LDL. 13 CE hydroperoxides (CE-OOH) were not detected in early lesions, ie, stages I-III (Table 2). However, they were detected in fibro-fatty and advanced lesions, albeit at much lower amounts (Ͻ2.5%) than the sum of CE hydroperoxides and hydroxides (CE-O(O)H) (Table 2) indicating that CE hydroxides (ie, CE-OH) were the major product.…”

“…10 Low ␣-TOH to cholesterol content has been reported in advanced lesions, 11 although our earlier studies with advanced human lesions showed normal levels of ␣-TOH per cholesteryl ester (CE). 12,13 Expressing ␣-TOH per CE is more appropriate as the vitamin scavenges peroxyl radicals produced during the peroxidation of fatty acids containing bisallylic hydrogen; 14 CE represent the major source of such fatty acids in lipoproteins and lesions, whereas cholesterol does not contain bisallylic hydrogen.…”