Identification of non-functional allelic variant of CYP1A2 in dogs

OBJECTIVES: Recently, we reported that AC-3933, a novel cognitive enhancer, is polymorphically hydroxylated in beagle dogs and that dogs could be phenotyped as extensive metabolizers (EM) or poor metabolizers (PM). AC-3933 polymorphic hydroxylation is caused by polymorphic expression of CYP1A2 protein in dog liver. METHODS: In order to clarify the mechanism of polymorphic expression of CYP1A2 protein in beagle dogs, we investigated, in this study, the sequence of CYP1A2 cDNA in EM and PM dogs. RESULTS: In PM dogs CYP1A2 gene, we discovered a nonsense mutation (C1117T) that induces a premature termination, and is associated with PM phenotype for AC-3933 hydroxylation. All PM dogs studied were homozygote of the mutant allele (m/m) and seemed to be CYP1A2-null phenotype as they lacked the heme-binding region in CYP1A2. These results indicate that the polymorphic expression of CYP1A2 protein observed in our previous study is caused by a single nucleotide polymorphism on CYP1A2 coding region. Furthermore, we developed a genotyping method for the mutant allele using a mismatch PCR-restriction fragment length polymorphism, and carried out frequency analysis in 149 beagle dogs. CONCLUSION: Our results indicate that more than 10% of the dogs studied were CYP1A2-null. Because CYP1A2-null phenotype in dogs affects the results of pharmacokinetic, toxicological and pharmacological studies of drug candidates, these findings are important in the pharmaceutical and the veterinary fields.