No abstract

We previously demonstrated that cannabidiol (CBD) was a potent mechanism-based inhibitor of human cytochrome P450 1A1 (CYP1A1). However, the moiety of CBD that contributes to the potent mechanism-based inhibition of human CYP1A1 remains unknown. Thus, the effects of compounds structurally related to CBD on CYP1A1 activity were examined with recombinant human CYP1A1 in order to characterize the structural requirements for potent inactivation by CBD. When preincubated in the presence of NADPH for 20min, olivetol, which corresponds to the pentylresorcinol moiety of CBD, enhanced the inhibition of the 7-ethoxyresorufin O-deethylase activity of CYP1A1. In contrast, d-limonene, which corresponds to the terpene moiety of CBD, failed to inhibit CYP1A1 activity in a metabolism-dependent manner. Pentylbenzene, which lacks two free phenolic hydroxyl groups, also did not enhance CYP1A1 inhibition. On the other hand, preincubation of the CBD-2'-monomethyl ether (CBDM) and CBD-2',6'-dimethyl ether (CBDD) enhanced the inhibition of CYP1A1 activity. Inhibition by cannabidivarin (CBDV), which possessed a propyl side chain, was strongly potentiated by its preincubation. Orcinol, which has a methyl group, augmented CYP1A1 inhibition, whereas its derivative without an alkyl side chain, resorcinol, did not exhibit any metabolism-dependent inhibition. The preincubation of CBD-hydroxyquinone did not markedly enhance CYP1A1 inhibition. We further confirmed that olivetol, CBDM, CBDD, CBDV, and orcinol, as well as CBD (kinact=0.215min(-1)), inactivated CYP1A1 activity; their kinact values were 0.154, 0.0638, 0.0643, 0.226, and 0.0353min(-1), respectively. These results suggest that the methylresorcinol structure in CBD may have structurally important roles in the inactivation of CYP1A1.

Our recent work has shown that cannabidiol (CBD) exhibits the most potent direct inhibition of human cytochrome P450 1A1 (CYP1A1) among the CYP enzymes examined. However, the mechanism underlying this CBD inhibition remains to be clarified. Thus, to elucidate the structural requirements for the potent inhibition by CBD, the effects of CBD and its structurally related compounds on CYP1A1 activity were investigated with recombinant human CYP1A1. Olivetol, which corresponds to the pentylresorcinol moiety of CBD, inhibited the 7-ethoxyresorufin O-deethylase activity of CYP1A1; its inhibitory effect (IC 50 =13.8 µm)was less potent than that of CBD (IC 50 =0.355 µm). In contrast, d-limonene, which corresponds to the terpene moiety of CBD, only slightly inhibited CYP1A1 activity. CBD-2′-monomethyl ether (CBDM) and CBD-2′,6′-dimethyl ether inhibited CYP1A1 activity with IC 50 values of 4.07 and 23.0 µm, respectively, indicating that their inhibitory effects attenuated depending on the level of methylation on the free phenolic hydroxyl groups in the pentylresorcinol moiety of CBD. Cannabidivarin inhibited CYP1A1 activity, although its inhibitory potency (IC 50 =1.85 µm) was lower than that of CBD. The inhibitory effects of Δ 9 -tetrahydrocannabinol and cannabielsoin (IC 50 s ≈10 µm), which contain a free phenolic hydroxyl group and are structurally constrained, were less potent than that of CBDM, which contains a free phenolic hydroxyl group and is rotatable between pentylresorcinol and terpene moieties. These results suggest that the pentylresorcinol structure in CBD may have structurally important roles in direct CYP1A1 inhibition, although the whole structure of CBD is required for overall inhibition.Key words cannabidiol; cytochrome P450 1A1; direct inhibition; structural requirement; pentylresorcinol Cannabidiol (CBD), one of the major constituents in marijuana, 1) is not psychoactive but has several pharmacological effects such as prolonging drug-induced sleep, antiepileptic, anxiolytic, and antiemetic actions.2) CBD is also known to inhibit hepatic microsomal drug metabolism in mammals. [3][4][5] A previous clinical study has shown that the administration of CBD reduces the systemic clearance of hexobarbital, which is metabolized by cytochrome P450 2C9 (CYP2C9), in human subjects.6) In vitro studies by Jaeger et al. 7) and us 8-13) demonstrated that CBD inhibits catalytic activities of CYP1A1, CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A5 in human liver microsomes and/or recombinant CYP enzymes. Interestingly, we have recently reported that the CBD-mediated direct inhibition of human CYP1A1 activity is the strongest among those of CYP activities reported so far.8) In addition, CYP1A1 was more potently inhibited by CBD than by the other major phytocannabinoids examined. 8) CYP1A1 is expressed in various tissues including the liver and lung, [14][15][16] although the constitutive expression level is very low. In general, hepatic and pulmonary CYP1A1 is induced by exposure to tobacco smoke. 17,18) C...