RESUMO
Phenacetin is widely used as an in vitro probe to measure CYP1A2 activity across species. To investigate whether phenacetin can be used as an in vivo probe substrate to phenotype CYP1A2 activity in dogs, beagle dogs previously genotyped for a single nucleotide polymorphism that yields an inactive CYP1A2 protein were selected and placed into one of three groups: CC (wild-type), CT (heterozygous), or TT (homozygous mutants). The dogs were dosed with phenacetin orally at 5 and 15 mg/kg and intravenously at 15 mg/kg. Plasma samples were analyzed by liquid chromatography-tandem mass spectrometry, and phenacetin and its primary metabolite, acetaminophen, were monitored. After intravenous dosing, all groups showed similar exposure of phenacetin irrespective of genotype. After oral dosing at 15 mg/kg, the exposure of phenacetin in CC and CT dogs was similar, but phenacetin exposure was 2-fold greater in TT dogs. Exposure of the metabolite, acetaminophen, was similar in all groups; however, the mean acetaminophen/phenacetin ratio in TT dogs was 1.7 times less than that observed in CC dogs. Similar trends between the groups of dogs with respect to phenacetin exposure were also observed after a lower 5 mg/kg p.o. dose of phenacetin; however, a proportionally greater amount of acetaminophen was generated. Although oral exposure of phenacetin was 2-fold higher and acetaminophen exposure was 2-fold lower in CYP1A2-deficient (TT) dogs, these results were considered modest and suggest that phenacetin is not a selective or robust in vivo probe to measure CYP1A2 enzyme activity in the dog.
Assuntos
Analgésicos não Narcóticos/farmacocinética , Citocromo P-450 CYP1A2/metabolismo , Fenacetina/farmacocinética , Acetaminofen/sangue , Administração Oral , Algoritmos , Analgésicos não Narcóticos/administração & dosagem , Analgésicos não Narcóticos/sangue , Animais , Biotransformação , Códon de Terminação , Citocromo P-450 CYP1A2/deficiência , Citocromo P-450 CYP1A2/genética , Cães , Relação Dose-Resposta a Droga , Meia-Vida , Heterozigoto , Homozigoto , Infusões Intravenosas , Masculino , Taxa de Depuração Metabólica , Mutação , Fenacetina/administração & dosagem , Fenacetina/sangue , Polimorfismo de Nucleotídeo Único , Especificidade por SubstratoRESUMO
A single nucleotide polymorphism in the dog CYP1A2 gene causes these animals to be CYP1A2 deficient (i.e., lack functional CYP1A2 enzyme activity). Genotyping a colony of 79 dogs revealed 77% wild-type, 19% heterozygous, and 4% homozygous mutant animals. These genetic frequencies are significantly different from those previously reported and illustrate that different sources and populations of dogs can have dramatically different frequencies of this polymorphism.