Cholesterol 7-hydroxylase knockout mouse: a model for monohydroxy bile acid-related neonatal cholestasis.
OBJECTIVE
Cyp 7-/- mice lack a functional cholesterol 7alpha-hydroxylase enzyme and develop cholestasis before up-regulation of 27-hydroxycholesterol 7alpha-hydroxylase activity. Because 7alpha-hydroxylation is not the initial step in this metabolic pathway, we tested the hypothesis that cholesterol 27-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 3beta-hydroxy-5-cholenoate and 3alpha-hydroxy-5beta-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 7alpha-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.
Arnon
R
R
Division of Pediatric Gastroenterology and Nutrition, Columbia College of Physicians and Surgeons, Columbia University, New York, NY, USA.
Yoshimura
T
T
Reiss
A
A
Budai
K
K
Lefkowitch
J H
JH
Javitt
N B
NB
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001647:Bile Acids and Salts / Q000502:physiology*; D001648:Bile Canaliculi / Q000473:pathology / Q000648:ultrastructure; D002779:Cholestasis / Q000235:genetics* / Q000378:metabolism; D002793:Cholic Acids / Q000378:metabolism; D002855:Chromatography, Thin Layer; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004195:Disease Models, Animal; D008401:Gas Chromatography-Mass Spectrometry; D006888:Hydroxycholesterols / Q000378:metabolism; D008095:Lithocholic Acid / Q000378:metabolism; D008099:Liver / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008817:Mice, Mutant Strains / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D012016:Reference Values; D013154:Spleen / Q000378:metabolism; D013253:Steroid 12-alpha-Hydroxylase / Q000235:genetics*
D001647:Bile Acids and Salts; D002793:Cholic Acids; D006888:Hydroxycholesterols; D012333:RNA, Messenger; C014596:3 beta-hydroxy-delta 5-cholenic acid; D008095:Lithocholic Acid; C076996:27-hydroxycholesterol; D003577:Cytochrome P-450 Enzyme System; C035248:7 alpha-hydroxy-4-cholesten-3-one-12 alpha monooxygenase; D013253:Steroid 12-alpha-Hydroxylase