title: Inhibition of human liver microsomal CYP by nateglinide.
abstract: OBJECTIVE
  Nateglinide is metabolized by CYP2C9 and CYP3A4, therefore drug-drug interactions through cytochrome P450 (CYP) inhibition may occur. In this study, we examined the inhibitory effects of nateglinide and its major metabolite N-[trans-4-(1-hydroxy-1-methylethyl)-cyclohexanecarbonyl]-D-phenylalanine (M1) on various CYP isoforms in human liver microsomes.
  
  
  METHODS
  We used typical substrates (7-ethoxyresorufin for CYP1A1/2, tolbutamide for CYP2C9, S-mephenytoin for CYP2C19, bufuralol for CYP2D6, chlorzoxazone for CYP2E1 and midazolam for CYP3A4) in the evaluation of the inhibitory effects, and examined the possibility of mechanism-based inhibition (MBI) by evaluating the influence of pre-incubation in the inhibition.
  
  
  RESULTS
  The results showed that nateglinide inhibited CYP2C9 and CYP2C19 with an IC50(app) (apparent value of the 50% inhibitory concentration) of 125 micromol/l and 946 micromol/l, respectively, while M1 did not inhibit any of the CYP isoforms. The inhibition constant (K(i)) value of the inhibitory effect of nateglinide on CYP2C9 and the 1 + I(in,max,u)/K(i) value were estimated (where I(in,max,u)= the maximum unbound concentration of nateglinide). The 1 + I(in,max,u)/K(i) value was 1.02 (close to 1), suggesting a low risk of drug-drug interactions. The influence of pre-incubation on the inhibition by nateglinide of CYP3A4, CYP2C9 and CYP2C19 was examined. The results revealed that the inhibition of CYP by nateglinide was not influenced by pre-incubation, and that the possibility of MBI is very low.
  
  
  CONCLUSIONS
  The possibility of drug-drug interactions involving nateglinide that might be attributable to CYP inhibition is low.
authors.affiliation: Pharmaceutical Company, Ajinomoto Co., Inc., Kawasaki, Japan. toshiyuki_takanohash@ajinomoto.com
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takanohashi
authors.forename: Satoru
authors.initials: S
authors.lastname: Kubo
authors.forename: Akira
authors.initials: A
authors.lastname: Nakayama
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Mihara
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hayashi
mesh_terms: D003510:Cyclohexanes / Q000494:pharmacology*; D065692:Cytochrome P-450 CYP3A Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D004347:Drug Interactions; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D008099:Liver / Q000378:metabolism*; D008861:Microsomes; D000077715:Nateglinide; D004364:Pharmaceutical Preparations / Q000378:metabolism; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D012306:Risk
chemical_list: D003510:Cyclohexanes; D065692:Cytochrome P-450 CYP3A Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D007004:Hypoglycemic Agents; D004364:Pharmaceutical Preparations; C400322:cytochrome P-450 CYP2C subfamily; D000077715:Nateglinide; D010649:Phenylalanine; D003577:Cytochrome P-450 Enzyme System