Abstract-The lipid-lowering antioxidant probucol can inhibit atherosclerosis in animals and restenosis in humans.However, probucol has been shown to promote atherosclerosis in the aortic root of apolipoprotein E-deficient (apoEϪ/Ϫ) mice. In the current study, we examined the effects of probucol on both lesion formation at 4 sites along the aorta and lipoprotein oxidation in the plasma and aortas of apoEϪ/Ϫ mice receiving a diet containing 21.2% (wt/wt) fat and 0.15% (wt/wt) cholesterol without or with 1% (wt/wt) probucol. After 6 months, controls had developed lesions at all sites investigated. Lesion development was strongly (Pϭ0.0001) affected by probucol, but this effect was not uniform: lesion size was increased in the aortic root but significantly decreased in the arch, the descending thoracic aorta, and proximal abdominal aorta. Plasma and aortas of probucol-treated mice contained high concentrations of probucol and its metabolites (bisphenol and diphenoquinone); increased vitamin C; markedly decreased very low density lipoprotein (but not low density lipoprotein and high density lipoprotein); and decreased cholesterol, cholesteryl esters, triglycerides, vitamin E, and oxidized lipids compared with controls. Interestingly, probucol treatment did not decrease the proportion of aortic lipids that were oxidized. Plasma vitamin C and bisphenol, but not probucol, protected plasma lipids from ex vivo oxidation by peroxyl radicals. These results show that as in other species, probucol can inhibit lesion formation in most parts of the aorta of apoEϪ/Ϫ mice. This effect may involve lipid oxidation-independent mechanisms localized within the vessel wall as well as lipid lowering.
Oxidation of lipoproteins is thought to be an early event in atherogenesis. To evaluate whether aortic lipoprotein lipid (per)oxidation contributes to atherosclerosis, we investigated the time-dependent changes to lipids and antioxidants in plasma and aortas of apolipoprotein E gene knockout (apoE Ϫ / Ϫ ) mice receiving a high fat diet, and compared these changes with lesion development. Circulating buoyant lipoproteins and associated cholesterol (C), cholesteryl esters (CE), and ␣ -tocopherol ( ␣ -TOH) increased within 1 month then remained largely constant up to 6 months. Coenzyme Q (CoQ) remained unchanged for the first 3 months and increased marginally after 6 months. With increasing duration of the diet, plasma lipids showed an increased propensity to undergo peroxyl radical-induced (per)oxidation. Absolute concentrations of aortic C, hydroperoxides and hydroxides of CE (CE-O(O)H) and ␣ -TOH increased gradually while aortic CE increased more markedly with changes to cholesteryl linoleate being most pronounced. Aortic CoQ remained largely unchanged. Overall, the extent of aortic CE (per)oxidation remained low ( р 1%) and the ratio of incremental changes of ␣ -TOH to oxidizable lipid remained unchanged. Aortic biochemistry paralleled lesion formation, particularly that in the descending thoracic aorta. Together, our results show that progressing atherosclerosis in apoE Ϫ / Ϫ mice is associated with increased aortic lipid (per)oxidation as assessed by the concentrations of CE-O(O)H, measured directly by HPLC. This supports the oxidation theory. Measurement of aortic CE-O(O)H may be useful for mechanistic studies studying the relationship between inhibition of in vivo lipid (per)oxidation and atherosclerosis. -Letters, J.
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