ANALYSIS OF IMIPRAMINE AND 3 METABOLITES PRODUCED BY ISOZYME CYP2D6 EXPRESSED IN A HUMAN CELL-LINE

1. A commercially-available human cytochrome P450 isozyme (CYP2D6) pre paration was used in imipramine metabolism studies. This isozyme catal ysed both aromatic C-oxidation and N-demethylation. 2-Hydroxyimipramin e was the major metabolite; desipramine was isolated in a significant amount and 2-hydroxydesipramine was a trace metabolite. 2. To prevent decomposition of metabolites during the analytical procedure, the meta bolism mixture was derivatized with acetic anhydride prior to extracti on, and the derivatized metabolites were separated and quantified by g .l.c. with N/P detection. The analytical procedure had excellent sensi tivity and was capable of routinely quantifying imipramine and its met abolites down to the 0.36 nmol level. 3. In excess of 90% of drug and metabolites was consistently recovered when metabolism was conducted o ver a 5-60-min duration. 4. The formation of the secondary metabolite, 2-hydroxydesimipramine, from imipramine proceeds by two pathways, via desipramine and via 2-hydroxyimipramine; the former is the preferred pathway. 5. CYP2D6 catalyses C-hydroxylation of imipramine to 2-hydrox imipramine more efficiently than its N-demethylation to desipramine. A lso, the C-hydroxylation of imipramine to 2-hydroxyimipramine proceeds more efficiently than the conversion of desipramine to 2-hydroxydesip ramine.