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Analysis and physiologic significance of cholesterol epoxide in animal tissues
Author(s) -
Black Homer S.
Publication year - 1980
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02534024
Subject(s) - epoxide , sterol , chemistry , triol , substrate (aquarium) , in vivo , chromatography , biochemistry , cholesterol , organic chemistry , biology , diol , ecology , microbiology and biotechnology , catalysis
Abstract The presence of 5α,6α‐epoxy‐cholestan‐3β‐ol, an oxidation product of cholesterol, has been demonstrated in a variety of animal tissues. No definitive biologic role for this sterol has been forthcoming, although the physiologic implications of its occurrence are many. The presence of the epoxide in ultraviolet (UV)‐irradiated skin was detected by a combination of thin layer chromatography (TLC) and gas liquid radiochromatographic (radio‐GLC) techniques in 1971 and led to the suggestion that it might be responsible for the carcinogenic properties of UV. Subsequently, in vivo levels of this sterol in the skin of UV‐irradiated animals were quantitated by radio‐GLC after TLC separation and preparation of the radiolabeled acetate ester. Presence of the compound in mouse liver was detected by GLC of the trimethylsilyl (TMS) ether and confirmed by mass spectrometry (MS). In all cases, however, in vivo quantitations were complicated by substrate induction of sterol epoxide hydrase, an enzyme that hydrates the epoxide to form cholestan‐3β,5α,6β‐triol (triol). Consequently, the relationship of the sterol epoxide to UV‐carcinogenesis is as yet unclear and recent studies suggest that if this sterol is involved, then further metabolism of the compound must be required. A practical means of examining the metabolites of the epoxide was developed, employing radio‐TLC scanning. Using this procedure, the relationships of substrate concentration, time of reaction and pH optimum to reaction rate were determined. Although in short term in vitro incubations of liver homogenates the bulk of epoxide is hydrated to triol, several other metabolites are detectable by TLC autoradiography. Even though the case for direct involvement of cholesterol epoxide in the etiology of carcinogenesis or other diseases is equivocal, the epoxide or its metabolites may yet prove valuable as a diagnostic aid in revealing abnormal function associated with certain diseases.