Cholestatic effect of large bilirubin loads and cholestasis protection conferred by cholic acid co-infusion: a molecular and ultrastructural study.
BACKGROUND
Large intravenous bilirubin loads block biliary phospholipid secretion, produce canalicular membrane lesions and cause canalicular cholestasis. Cholic acid co-infusion forestalls these untoward effects. The aim of this study was first to determine whether bilirubin overload causes cholestasis through reducing the activity or the hepatic expression of the bile salt export pump (bsep) or Na-taurocholate co-transporting polypeptide (ntcp) and, secondly, whether cholic acid co-infusion forestalls cholestasis by upregulating bsep, ntcp or phosphoglycoprotein 3 (pgp3) expressions or activities. A further aim was to determine whether large bilirubin infusions also produce ultrastructural changes inside hepatocytes.


METHODS
The effects of intravenous infusion of 2 g bilirubin over 150 min on hepatic expression of bsep, ntcp and pgp3 were studied in bile acid-depleted and cholic acid co-infused pigs, and related to canalicular bile acid transport and bile secretion. Effects on hepatocyte ultrastructural morphology were analysed by electron microscopy.


RESULTS
Bilirubin-induced cholestasis reflected marked diminution of bsep and pgp3 transport activities and not reduced hepatic expression of these transporters. Hepatocyte ultrastructural abnormalities were predominantly confined to the hepatocyte canalicular membrane in cholestatic livers. Cholic acid co-infusion with bilirubin conferred complete cholestasis protection through enhancing pgp3 and bsep transporter activities and not through upregulating their expression. Bilirubin infusion did not change ntcp expression.


CONCLUSIONS
Bilirubin-induced cholestasis is due to markedly impaired activity of the membrane-embedded bsep transporter consequent upon ultrastructural injury to the canalicular membrane. Cholic acid co-infusion with bilirubin enhances bsep and pgp3 activities and confers protection against canalicular membrane injury and bilirubin-induced cholestasis.
Labori
K J
KJ
Institute for Experimental Medical Research, Ullevaal University Hospital, Oslo, Norway.
Arnkvaern
K
K
Bjørnbeth
B A
BA
Press
C McL
CM
Raeder
M G
MG
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000187:drug effects / Q000378:metabolism; D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001653:Bile Ducts, Intrahepatic / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D001663:Bilirubin / Q000008:administration & dosage / Q000494:pharmacology*; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D002779:Cholestasis / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology*; D019826:Cholic Acid / Q000494:pharmacology*; D004347:Drug Interactions; D025461:Feedback, Physiological; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D007262:Infusions, Intravenous; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D008854:Microscopy, Electron; D029363:Organic Anion Transporters, Sodium-Dependent; D013552:Swine; D027981:Symporters
D018435:ATP Binding Cassette Transporter, Subfamily B; D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; C490548:Abcb11 protein, rat; D002352:Carrier Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; C484254:Pgp3 protein, Sus scrofa; D027981:Symporters; C071908:sodium-bile acid cotransporter; D019826:Cholic Acid; D001663:Bilirubin