CHOLESTEROL 7-ALPHA-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-hydr oxylation is not the initial step in this metabolic pathway, we tested the hypothesis that cholesterol 7 alpha-hydroxylase is expressed at a n 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-hydroxyl ase in 5-day-old normal and Cyp 7-/- mice. Gas-liquid chromatography-m ass spectrometry and reverse isotope dilution were used to identify in termediates in the cholesterol 27-hydroxylase metabolic pathway. Light and electron microscopy were used to evaluate the morphological appea rance of the liver. Results: mRNA for cholesterol 27-hydroxylase was i dentified in the liver and spleen. The monohydroxy bile acids 3 beta-h ydroxy-5-cholenoate and 27-hydpoxy-5 beta-cholanoate together with the ir precursor, 27-hydroxycholesterol, were identified in liver homogena tes. Cholestasis, present focally, was manifested as dilated bile cana liculi, partial loss of microvilli, and retention of electron-dense bi liary material. Conclusions: The cholesterol 27-hydroxylase metabolic pathway of bile acid synthesis is expressed in neonatal life. The abse nce of 7 alpha-hydroxylase activities unmasks the cholestatic potentia l of monohydroxy bile acids. The Cyp 7-/- knockout mouse mimics choles tatic events known to occur in humans and provides a unique opportunit y for studying regulatory determinants.