Potent inhibition of human cytochrome P450 3A isoforms by cannabidiol: Role of phenolic hydroxyl groups in the resorcinol moiety

Abstract

Aims

In this study, we examined the inhibitory effects of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), cannabidiol (CBD), and cannabinol (CBN), the three major cannabinoids, on the activity of human cytochrome P450 (CYP) 3A enzymes. Furthermore, we investigated the kinetics and structural requirement for the inhibitory effect of CBD on the CYP3A activity.

Main methods

Diltiazem N-demethylase activity of recombinant CYP3A4, CYP3A5, CYP3A7, and human liver microsomes (HLMs) in the presence of cannabinoids was determined.

Key findings

Among the three major cannabinoids, CBD most potently inhibited CYP3A4 and CYP3A5 (IC₅₀ = 11.7 and 1.65 μM, respectively). The IC₅₀ values of Δ⁹-THC and CBN for CYP3A4 and CYP3A5 were higher than 35 μM. For CYP3A7, Δ⁹-THC, CBD, and CBN inhibited the activity to a similar extent (IC₅₀ = 23–31 μM). CBD competitively inhibited the activity of CYP3A4, CYP3A5, and HLMs (K_i = 1.00, 0.195, and 6.14 μM, respectively). On the other hand, CBD inhibited the CYP3A7 activity in a mixed manner (K_i = 12.3 μM). Olivetol partially inhibited all the CYP3A isoforms tested, whereas d-limonene showed lack of inhibition. The lesser inhibitory effects of monomethyl and dimethyl ethers of CBD indicated that the ability of CYP3A inhibition by the cannabinoid attenuated with the number of methylation on the phenolic hydroxyl groups in the resorcinol moiety.

Significance

This study indicated that CBD most potently inhibited catalytic activity of human CYP3A enzymes, especially CYP3A4 and CYP3A5. These results suggest that two phenolic hydroxyl groups in the resorcinol moiety of CBD may play an important role in the CYP3A inhibition.

Introduction

Marijuana is one of the most widely abused drugs in the world. Marijuana leaves contain at least 70 cannabinoids (ElSohly and Slade, 2005). Among them, Δ⁹-tetrahydrocannabinol (Δ⁹-THC), cannabidiol (CBD), and cannabinol (CBN) are the three major constituents (Fig. 1). Δ⁹-THC is a primary psychoactive component of marijuana (Pertwee, 2008). CBD is not psychoactive but has several pharmacological effects such as drug-induced sleep prolongation, antiepileptic, anxiolytic, and antiemetic actions (Mechoulam et al., 2002). CBN is thought to exert minimal pharmacological effects in the central nervous system.

These major cannabinoids are known to be extensively metabolized by hepatic microsomal cytochrome P450 (CYP) (Huestis, 2005, Watanabe et al., 2007). Bornheim et al. and we previously demonstrated that the hepatic metabolism of Δ⁹-THC, CBD, and CBN is predominantly catalyzed by CYP2C and CYP3A (Bornheim and Correia, 1991, Bornheim et al., 1992, Watanabe et al., 1995, Watanabe et al., 2007). On the other hand, these major cannabinoids have been reported to inhibit CYP-mediated drug metabolism in livers from experimental animals (Fernandes et al., 1973, Chan and Tse, 1978, Watanabe et al., 1981, Hamajima et al., 1983). Furthermore, a previous clinical study has shown that the administration of CBD decreases the systemic clearance of hexobarbital, which is metabolized by CYP2C9, in human subjects (Benowitz et al., 1980). Jaeger et al. (1996) have reported that CBD inhibits cyclosporine and Δ⁹-THC oxidations catalyzed by CYP3A in human liver microsomes (HLMs). More recently, we have shown that Δ⁹-THC, CBD, and CBN inhibit catalytic activities of human CYP1 enzymes (Yamaori et al., 2010). These findings suggest that the administration of cannabinoids or marijuana may lead to drug interactions with drugs or toxicants metabolized by these CYP enzymes.

Human CYP3A subfamily is involved in the metabolism of more than 50% of drugs clinically used. The human CYP3A subfamily expressed in the liver consists of at least three members: CYP3A4 (Guengerich et al., 1986, Molowa et al., 1986), CYP3A5 (Aoyama et al., 1989, Wrighton et al., 1989), and CYP3A7 (Kitada et al., 1985). CYP3A4, which is the most abundant isoform expressed in adult human livers (Shimada et al., 1994), is capable of metabolizing structurally diverse compounds, such as diltiazem, midazolam, erythromycin, and cyclosporine (Rendic, 2002). CYP3A5, which is polymorphically expressed in the liver (Kuehl et al., 2001), also can catalyze oxidations of a variety of drugs (Aoyama et al., 1989, Williams et al., 2002, Yamaori et al., 2003, Yamaori et al., 2004). The catalytic activity of CYP3A5 is equal or lower as compared with that of CYP3A4, although some drugs, such as diltiazem and midazolam, are more efficiently metabolized by CYP3A5 than by CYP3A4 (Gorski et al., 1994, Yamaori et al., 2004). CYP3A7, which is a major isoform expressed in fetal human livers (Kitada et al., 1985, Komori et al., 1990), is suggested to play a key role in the metabolism of endogenous compounds and xenobiotics during the fetal period (Kitada et al., 1985, Kitada et al., 1987, Chen et al., 2000). These findings reveal that human CYP3A subfamily is one of the most important enzyme groups in the hepatic drug metabolism. Furthermore, these findings indicate the possibility of frequent occurrence of drug interactions caused by CYP3A enzymes. Thus, it is very important to elucidate possible interactions of marijuana or its components including cannabinoids with various compounds metabolized by CYP3A enzymes. However, the potency and mechanism of cannabinoid inhibition against individual isoforms of human CYP3A subfamily remain to be clarified.

In the present study, we investigated the inhibitory effects of the three major cannabinoids (Δ⁹-THC, CBD, and CBN) on human CYP3A-mediated oxidation. We report herein that CBD is a potent inhibitor against human CYP3A enzymes. In addition, our study suggests that two phenolic hydroxyl groups in the resorcinol moiety of CBD may have structurally important role in the CYP3A inhibition.