The influence of carboxylesterase 1 polymorphism and cannabidiol on the hepatic metabolism of heroin.

Heroin (diamorphine) is a highly addictive opioid drug synthesized from morphine. The use of heroin and incidence of heroin associated overdose death has increased sharply in the US. Heroin is primarily metabolized via deacetylation (hydrolysis) forming the active metabolites 6-monoacetylmorphine (6-MAM) and morphine. A diminution in heroin hydrolysis is likely to cause higher drug effects and toxicities. In this study, we sought to determine the contribution of the major hepatic hydrolase carboxylesterase 1 (CES1) to heroin metabolism in the liver as well as the potential influence of one of its known genetic variants, G143E (rs71647871). Furthermore, given the potential therapeutic application of cannabidiol (CBD) for heroin addiction and the frequent co-abuse of cannabis and heroin, we also assessed the effects of CBD on heroin metabolism. In vitro systems containing human liver, wild-type CES1, and G143E CES1 S9 fractions were utilized in the assessment. The contribution of CES1 to the hydrolysis of heroin to 6-MAM was determined as 3.66%, and CES1 was unable to further catalyze 6-MAM under our assay conditions. The G143E variant showed a 3.2-fold lower intrinsic clearance of heroin as compared to the WT. CBD inhibited heroin and 6-MAM hydrolysis in a reversible manner, with IC50s of 14.7 and 12.1 μM, respectively. Our study results suggested only minor involvement of CES1 in heroin hydrolysis in the liver. Therefore, the G143E variant is unlikely to cause significant impact despite a much lower hydrolytic activity. CBD exhibited potent in vitro inhibition toward both heroin and 6-MAM hydrolysis, which may be of potential clinical relevance.