title: Alterations of CYP3A4 and P-glycoprotein activity in vivo with time in renal graft recipients.
abstract: BACKGROUND
  Catabolism by intestinal and hepatic cytochrome P450 3A4 (CYP3A4), and excretion by P-glycoprotein (PGP), has a major influence on oral bioavailability of calcineurin inhibitors. In this study, the activity of intestinal and hepatic CYP3A4 and PGP in vivo was assessed in renal transplant recipients during the first year after transplantation (Tx).
  
  
  METHODS
  Stable Caucasian renal transplant patients were tested at 1 week, 3 months, and 1 year after Tx, and compared with the results obtained in drug-free healthy volunteers. Intestinal and hepatic CYP3A4 and PGP activity were determined by measurement of (14)C-excretion dynamics in breath and urine after oral and intravenous administration of [N-methyl-(14)C]-erythromycin.
  
  
  RESULTS
  Compared with 1 week after Tx, intestinal and hepatic CYP3A4 activity significantly decreased at 3 months and 1 year after Tx (-33% and -45%; -7% and -33%, respectively). Compared with the healthy volunteers, intestinal and hepatic CYP3A4 activity of the patients was significantly increased at 1 week after Tx, but normalized at 1 year after Tx. A similar pattern, though not significant, was seen for intestinal PGP activity.
  
  
  CONCLUSIONS
  Phenotypic expression of hepatic and intestinal CYP3A4 was increased immediately after Tx, but gradually decreased to basal levels toward the end of the first year after Tx. The most plausible explanation for this evolution was the tapering of corticosteroid (CS) doses. These findings may also explain the increasing bioavailability of tacrolimus with time after Tx.
authors.affiliation: Department of Medicine, Division of Nephrology, University Hospital Gasthuisberg, Leuven, Belgium.
authors.forename: Wim P D
authors.initials: WP
authors.lastname: Lemahieu
authors.forename: Bart D
authors.initials: BD
authors.lastname: Maes
authors.forename: Kirstin
authors.initials: K
authors.lastname: Verbeke
authors.forename: Yves F Ch
authors.initials: YF
authors.lastname: Vanrenterghem
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D016022:Case-Control Studies; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005260:Female; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D016030:Kidney Transplantation; D008099:Liver / Q000378:metabolism; D008297:Male; D011184:Postoperative Period; D013997:Time Factors
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human