Identification of non-functional allelic variant of CYP1A2 in dogs

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.

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.

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.

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.