| Definition | 5b-Cholestane-3a,7a,12a,25-tetrol is an intermediates in the bile acid synthetic pathway, and is secreted into the bile and urine following glucuronidation and does not undergo enterohepatic circulation. In cerebrotendinous xanthomatosis (CTX), a bile acid synthesis disorder caused by sterol 27-hydroxylase (CYP27) deficiency, early intermediates and cholestanol accumulate in a variety of tissues, and glucuronides of 25-hydroxylated bile alcohols are released in bile, blood, and urine. Bile acid synthesis from cholesterol is tightly regulated via a feedback mechanism mediated by the farnesoid X receptor (FXR), a nuclear receptor activated by bile acids. Synthesis via the classic pathway is initiated by a series of cholesterol ring modifications and followed by the side chain cleavage. The enhanced cholesterol 7a-hydroxylase (CYP7A1) expression in CYP27 deficiency may be the result of decreased flux of bile acids and bile alcohols into the liver, while production of FXR-activating 5b-Cholestane-3a,7a,12a,25-tetrol is increased. (PMID 15145977 ) [HMDB] |
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