Cholesterol 7α-hydroxylase knockout mouse:: A model for monohydroxy bile acid-related neonatal cholestasis

Background & Aims: Cyp 7-/- mice lack a functional cholesterol 7 alpha-hydroxylase enzyme and develop cholestasis before up-regulation of 27-hydroxycholesterol 7 alpha-hydroxylase activity. Because 7 alpha-hydroxylation is not the initial step in this metabolic pathway, we tested the hypothesis that cholesterol 7 alpha-hydroxylase is expressed at an earlier step and leads to the production of monohydroxy bile acids. Methods: Polymerase chain reaction with specific oligonucleotides was used to detect messenger RNA (mRNA) coding for cholesterol 27-hydroxylase in 5-day-old normal and Cyp 7-/- mice. Gas-liquid chromatography-mass spectrometry and reverse isotope dilution were used to identify intermediates in the cholesterol 27-hydroxylase metabolic pathway. Light and electron microscopy were used to evaluate the morphological appearance of the liver. Results: mRNA for cholesterol 27-hydroxylase was identified in the liver and spleen. The monohydroxy bile acids 3 beta-hydroxy-5-cholenoate and 27-hydpoxy-5 beta-cholanoate together with their precursor, 27-hydroxycholesterol, were identified in liver homogenates. Cholestasis, present focally, was manifested as dilated bile canaliculi, partial loss of microvilli, and retention of electron-dense biliary material. Conclusions: The cholesterol 27-hydroxylase metabolic pathway of bile acid synthesis is expressed in neonatal life. The absence of 7 alpha-hydroxylase activities unmasks the cholestatic potential of monohydroxy bile acids. The Cyp 7-/- knockout mouse mimics cholestatic events known to occur in humans and provides a unique opportunity for studying regulatory determinants.