title: Effect of CYP3A5 polymorphism on tacrolimus metabolic clearance in vitro.
abstract: Previous investigations of solid organ transplant patients treated with tacrolimus showed that individuals carrying a CYP3A5*1 allele have lower dose-adjusted trough blood concentrations compared with homozygous CYP3A5*3 individuals. The objective of this investigation was to quantify the contribution of CYP3A5 to the hepatic and renal metabolic clearance of tacrolimus. Four primary tacrolimus metabolites, 13-O-desmethyl tacrolimus (13-DMT) (major), 15-O-desmethyl tacrolimus, 31-O-desmethyl tacrolimus (31-DMT), and 12-hydroxy tacrolimus (12-HT), were generated by human liver microsomes and heterologously expressed CYP3A4 and CYP3A5. The unbound tacrolimus concentration was low (4-15%) under all incubation conditions. For CYP3A4 and CYP3A5, V(max) was 8.0 and 17.0 nmol/min/nmol enzyme and K(m,u) was 0.21 and 0.21 muM, respectively. The intrinsic clearance of CYP3A5 was twice that of CYP3A4. The formation rates of 13-DMT, 31-DMT, and 12-HT were >or=1.7-fold higher, on average, in human liver microsomes with a CYP3A5*1/*3 genotype compared with those with a homozygous CYP3A5*3/*3 genotype. Tacrolimus disappearance clearances were 15.9 +/- 9.8 ml/min/mg protein and 6.1 +/- 3.6 ml/min/mg protein, respectively, for the two genotypes. In vitro to in vivo scaling using both liver microsomes and recombinant enzymes yielded higher predicted in vivo tacrolimus clearances for patients with a CYP3A5*1/*3 genotype compared with those with a CYP3A5*3/*3 genotype. In addition, formation of 13-DMT was 13.5-fold higher in human kidney microsomes with a CYP3A5*1/*3 genotype compared with those with a CYP3A5*3/*3 genotype. These data suggest that CYP3A5 contributes significantly to the metabolic clearance of tacrolimus in the liver and kidney.
authors.affiliation: Department of Pharmaceutics, University of Washington, Seattle, 98195-7610, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Dai
authors.forename: Mary F
authors.initials: MF
authors.lastname: Hebert
authors.forename: Nina
authors.initials: N
authors.lastname: Isoherranen
authors.forename: Connie L
authors.initials: CL
authors.lastname: Davis
authors.forename: Christopher
authors.initials: C
authors.lastname: Marsh
authors.forename: Danny D
authors.initials: DD
authors.lastname: Shen
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Thummel
mesh_terms: D000465:Algorithms; D000483:Alleles; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007166:Immunosuppressive Agents / Q000378:metabolism* / Q000493:pharmacokinetics; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism; D011110:Polymorphism, Genetic; D013056:Spectrophotometry, Ultraviolet; D016559:Tacrolimus / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: D007166:Immunosuppressive Agents; D003577:Cytochrome P-450 Enzyme System; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; D016559:Tacrolimus