Bq. Xu et al., ETHYLMORPHINE O-DEETHYLATION IN ISOLATED RAT HEPATOCYTES - INVOLVEMENT OF CODEINE O-DEMETHYLATION ENZYME-SYSTEMS, Biochemical pharmacology, 49(4), 1995, pp. 453-460
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) i
n rats. In the present study, the O-deethylation of EM was examined an
d compared with that of CD in suspensions of freshly-isolated hepatocy
tes 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 detecti
on. EM had a similar pattern of metabolism to that of CD in suspension
s of hepatocytes from Wistar rats. Both EM and CD were O-dealkylated t
o form M plus morphine-3-glucuronide (M3G) and N-demethylated to form
norethylmorphine (NEM) or norcodeine (NCD), respectively, which were f
urther metabolized to normorphine (NM) and finally glucuronidated to n
ormorphine 3-glucuronide (NM3G). As compared to hepatocytes from Wista
r rats, DA rats were characterized by a markedly decreased formation (
70-75% reduction) of M plus M3G from both EM and CD. Quinine, quinidin
e, propafenone and sparteine all inhibited EM O-deethylation as well a
s CD O-demethylation. Quinine was the most potent inhibitor of both th
ese O-dealkylations (K-i = 0.2 mu M for both EM and CD, respectively).
Quinine as well as the other inhibitors inhibited both EM and CD O-de
alkylation competitively and with small differences in K-i versus EM a
nd 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 sep
arate cell suspensions were plotted. In conclusion all findings indica
ted that the enzyme responsible for O-demethylation of CD, CYP2D1 was
also responsible for the O-deethylation of EM to M.