title: Involvement of human CYP1A isoenzymes in the metabolism and drug interactions of riluzole in vitro.
abstract: Cytochrome P450 (CYP) and uridine diphosphate glucuronosyltransferase (UGT) isoenzymes involved in riluzole oxidation and glucuronidation were characterized in (1) kinetic studies with human hepatic microsomes and isoenzyme-selective probes and (2) metabolic studies with genetically expressed human CYP isoenzymes from transfected B-lymphoblastoid and yeast cells. In vitro incubation of [14C]riluzole (15 microM) with human hepatic microsomes and NADPH or UDPGA cofactors resulted in formation of N-hydroxyriluzole (K(m) = 30 microM) or an unidentified glucuroconjugate (K(m) = 118 microM). Human microsomal riluzole N-hydroxylation was most strongly inhibited by the CYP1A2 inhibitor alpha-naphthoflavone (IC50 = 0.42 microM). Human CYP1A2-expressing yeast microsomes generated N-hydroxyriluzole, whereas human CYP1A1-expressing yeast microsomes generated N-hydroxyriluzole, two additional hydroxylated derivatives and an O-dealkylated derivative. CYP1A2 was the only genetically expressed human P450 isoenzyme in B-lymphoblastoid microsomes to metabolize riluzole. Riluzole glucuronidation was inhibited most potently by propofol, a substrate for the human hepatic UGT HP4 (UGT1.8/9) isoenzyme. In vitro, human hepatic microsomal hydroxylation of riluzole (15 microM) was weakly inhibited by amitriptyline, diclofenac, diazepam, nicergoline, clomipramine, imipramine, quinine and enoxacin (IC50 approximately 200-500 microM) and cimetidine (IC50 = 940 microM). Riluzole (1 and 10 microM) produced a weak, concentration-dependent inhibition of CYP1A2 activity and showed competitive inhibition of methoxyresorufin O-demethylase. Thus, riluzole is predominantly metabolized by CYP1A2 in human hepatic microsomes to N-hydroxyriluzole; extrahepatic CYP1A1 can also be responsible for the formation of several other metabolites. Direct glucuronidation is a relatively minor metabolic route. In vivo, riluzole is unlikely to exhibit significant pharmacokinetic drug interaction with coadministered drugs that undergo phase I metabolism.
authors.affiliation: Drug Metabolism and Pharmacokinetics Department, Rhône-Poulenc Rorer Research and Development, Antony, France. gerard.sanderink@rhone-poulenc.com
authors.forename: G J
authors.initials: GJ
authors.lastname: Sanderink
authors.forename: B
authors.initials: B
authors.lastname: Bournique
authors.forename: J
authors.initials: J
authors.lastname: Stevens
authors.forename: M
authors.initials: M
authors.lastname: Petry
authors.forename: M
authors.initials: M
authors.lastname: Martinet
mesh_terms: D001711:Biotransformation; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000502:physiology*; D004347:Drug Interactions; D005260:Female; D005965:Glucuronates / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000502:physiology*; D008297:Male; D018696:Neuroprotective Agents / Q000378:metabolism*; D010084:Oxidation-Reduction; D019782:Riluzole; D013844:Thiazoles / Q000378:metabolism*
chemical_list: D005965:Glucuronates; D007527:Isoenzymes; D018696:Neuroprotective Agents; D013844:Thiazoles; D019782:Riluzole; D003577:Cytochrome P-450 Enzyme System