Cholesterol in foods of animal origin is readily oxidized during processing and storage when it is exposed to air, high temperature, free radicals, and singlet oxygen. A number of evidence suggest that some endogenously oxidized cholesterol act as an inhibitor of sterol biosynthesis, or cytotoxic and atherogenic agents in various in vitro assays. However, physiological effects of exogenous oxidized cholesterol remain poorly understood. This review is a summary on the level of various oxidized cholesterols in processed foods and deleterious effects of dietary oxidized cholesterol on metabolism and cytofunctions.

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Many reports on toxicological and physiological significance of oxidized cholesterols, which were detected in animals and humans, have been issued. In this manuscript, focus was put on cholesterol 5α-hydroperoxide (Ch 5α-OOH), cholesterol 7α-and 7β-hydroperoxides (Ch 7-OOH), and cholesterol 5, 6α- and 5, 6β-epoxides. Following topics on the oxidized cholesterols were introduced : 1) A highly sensitive bioanalysis method for the hydroperoxides was established with an HPLC system equipped with a chemiluminescence detector, 2) Ch 7-OOH in rat skin is a good marker for aging, 3) Ch 7-OOH is a good marker for free radical dependent-lipid peroxidation in vivo, 4) Evidence for occurrence of the labile activated oxygen species, singlet oxygen, in a living animal was presented by detection of Ch 5α-OOH in rats pretreated with oral doses of pheophorbide a and subsequent visible light irradiation, 5) A phospholipid peroxide dependent stereochemical mechanism for the formation of cholesterol 5, 6α-epoxide and 5, 6β-epoxide, which were suggested as systemic carcinogens, was introduced.

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Oxysterols are present in human atherosclerotic plaque and atherogenic plasma low-density lipoprotein (LDL) subfractions, and it has been suggested that they play a role in the initiation and development of atherosclerosis. 27-Hydroxycholesterol, one of the most abundant oxysterols found in atherosclerotic lesions and circulating plasma, is one of the enzymic products of cholesterol catabolic pathways to bile acids, and is involved in the elimination of excess cholesterol from peripheral tissues such as the artery wall. Conversely, oxysterols generated by free radical-mediated oxidation (e.g., C-7 and C-5, 6 oxidation products) are considered to have atherogenic effects on cellular cholesterol metabolism (i.e., biosynthesis, uptake, esterification, and efflux) and blood vessels (vascular reactivity and angiotoxicity). But there is no direct evidence yet in humans that oxysterols contribute to the development of atherosclerosis.

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