Identification and characterization of the FMO2 gene in Rattus norvegicus: a good model to study metabolic and toxicological consequences of the FMO2 polymorphism.

Background: In lung of many animal species flavin-containing monooxygenase 2 (FMO2) is a 535-amino acid residues drug-metabolizing enzyme. In humans FMO2 exhibits a genetic polymorphism. The major allele encodes a truncated FMO2, the minor allele a full-length FMO2. In laboratory rats we previously reported a FMO2 gene encoding a truncated FMO2 (432-AA residues). In these strains, a double deletion leads to the appearance of a premature stop codon. All laboratory rat strains were derived from the same wild ancestor, Rattus norvegicus.

Methods: A PCR-based method able to specifically recognize either the wild-type or the mutant allele was developed to investigate a putative FMO2 polymorphism in a population of wild rats. The FMO2 gene was analyzed in 42 wild rats.

Results: A genetic FMO2 polymorphism similar to that described in humans was found in R. norvegicus. We observed three different genotypes: homozygotes for the wild-type FMO2 (33.3%), homozygotes for the mutant FMO2 (38.1%) and heterozygotes (28.6%). Comparative FMO2 mRNA and protein expressions in lungs were studied by reverse transcription-PCR and western blotting. FMO2 mRNA expression was identical between the three groups. In contrast, major differences in the expression of FMO2 protein were detected. FMO2 was strongly expressed in lungs of homozygotes for the wild-type FMO2, faintly expressed in lungs of heterozygotes and non-expressed in lungs of homozygotes for the mutant FMO2. Comparative catalytic properties of lung microsomes were studied by the determination of the oxygenation of methimazole. FMO2 genetic polymorphism was associated with major differences in the S-oxidative metabolism.