ethylmorphine and morphine-3-glucuronide

The O-dealkylation of ethylmorphine (EM) and codeine (CD) to morphine (M) co-segregates with debrisoquine/sparteine genetic polymorphism in man. CD O-demethylation is catalysed by cytochrome P450 2D1 (CYP2D1) in rats. In the present study, the O-deethylation of EM was examined and compared with that of CD in suspensions of freshly-isolated hepatocytes prepared by a collagenase method from Wistar rats with and without CYP2D1 inhibitors. Isolated hepatocytes were also prepared from Dark Agouti (DA) rats deficient in CYP2D1, and were incubated with EM or CD. EM, CD and their metabolites were quantified by HPLC with UV detection. EM had a similar pattern of metabolism to that of CD in suspensions of hepatocytes from Wistar rats. Both EM and CD were O-dealkylated to form M plus morphine-3-glucuronide (M3G) and N-demethylated to form norethylmorphine (NEM) or norcodeine (NCD), respectively, which were further metabolized to normorphine (NM) and finally glucuronidated to normorphine-3-glucuronide (NM3G). As compared to hepatocytes from Wistar rats, DA rats were characterized by a markedly decreased formation (70 approximately 75% reduction) of M plus M3G from both EM and CD. Quinine, quinidine, propafenone and sparteine all inhibited EM O-deethylation as well as CD O-demethylation. Quinine was the most potent inhibitor of both these O-dealkylations (Ki = 0.2 microM for both EM and CD, respectively). Quinine as well as the other inhibitors inhibited both EM and CD O-dealkylation competitively and with small differences in Ki versus EM and CD, respectively. The metabolism of EM to M plus M3G and that of CD to M plus M3G was highly correlated when results from the various separate cell suspensions were plotted. In conclusion all findings indicated that the enzyme responsible for O-demethylation of CD, CYP2D1 was also responsible for the O-deethylation of EM to M.

Topics: Animals; Cytochrome P-450 CYP2D6; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Ethylmorphine; Female; Liver; Male; Mixed Function Oxygenases; Morphine Derivatives; Rats; Rats, Wistar

The metabolism of ethylmorphine has been studied in suspensions of isolated rat hepatocytes. Early during incubation, the two major metabolic intermediates detected were morphine and norethylmorphine following N- and O-dealkylation of ethylmorphine, respectively. During subsequent incubation the concentration of the second metabolic intermediate, normorphine increased, before the concentration peaked at approximately 20 microM (100 microM ethylmorphine). Both morphine and normorphine were glucuronidated to form morphine-3-glucuronide and normorphine-3-glucuronide, respectively, which appeared to be the major metabolic end products. The percentage of ethylmorphine metabolized to morphine-3-glucuronide was found to be dependent on the initial concentration of ethylmorphine. With increasing initial ethylmorphine concentration the relative formation of morphine-3-glucuronide was reduced (29 +/- 10% at 5 microM, 18 +/- 5% at 20 microM, and 15 +/- 4% at 100 microM mean +/- S.D., n = 10). The concentrations of ethylmorphine and its metabolites were found to be higher in liver cells than in medium. Thus the ratios between the intra-/extra-cellular concentrations of ethylmorphine increased somewhat from an initial value of 4 during the period for which ethylmorphine could be detected intracellularly. The drug metabolites all exhibited ratios above 10 for the initial 100 min. of incubation. With time these ratios showed a decline, but even for prolonged incubation the ratios were 5 or higher for the end products. Thus considerable drug concentration gradients existed across the cell membrane of isolated rat hepatocytes.

Topics: Animals; Cells, Cultured; Chromatography, High Pressure Liquid; Ethylmorphine; Liver; Male; Morphine Derivatives; Rats; Rats, Wistar