Retention mechanism of imidazoles in connective tissue. IV. Identificationof a nucleophilic imadazolone metabolite in rats

Formation of a nucleophilic 4(5H)(or 5(4H))-imidazolone structure has been postulated from in vitro studies to be one of the causative elements involv ed in the retention of drugs with imidazole moiety in connective tissue. To confirm this, we searched for the imidazolone-related metabolite in rats a fter intravenous dosing of 2-methylimidazole (2MI; C-14-labeled and unlabel ed form, 3 and 300 mu mol/kg body weight) as a model compound. The excreted urine, the major route of elimination of the compound, was collected and a nalyzed using the HPLC/MS system with a counterion effect for metabolite se paration. 2-Methyl-4(5H)(or 5(4H))-imidazolone (2MIone) was identified as a urinary metabolite by chromatographic and mass-spectral inspection with th e corresponding authentic standard. Pretreatment of rats with either SKF-52 5A (50 mg/kg, i.p,) or cimetidine (200 mg/kg, i.p.) significantly increased the excreted amount of 2MIone in urine and the irreversible binding of 2MI equivalents in the aortic tissue, whereas both factors were reduced by pre treatment with triethylenetetramine dihydrochloride (150 mg/kg/d for 5 d, s .c,), These results support the aforementioned deduction, and also raise th e possibility that a cytochrome P450-independent, copper-related metabolic reaction might be involved in the imidazolone formation in vivo.