In vitro metabolism of cannabidiol in the rabbit: identification of seventeen new metabolites including thirteen dihydroxylated in the isopropenyl chain

Human Metabolites of Cannabidiol: A Review on Their Formation, Biological Activity, and Relevance in Therapy

Cannabidiol (CBD), the main nonpsychoactive constituent of Cannabis sativa, has shown a wide range of therapeutically promising pharmacological effects either as a sole drug or in combination with other drugs in adjunctive therapy. However, the targets involved in the therapeutic effects of CBD appear to be elusive. Furthermore, scarce information is available on the biological activity of its human metabolites which, when formed in pharmacologically relevant concentration, might contribute to or even account for the observed therapeutic effects. The present overview summarizes our current knowledge on the pharmacokinetics and metabolic fate of CBD in humans, reviews studies on the biological activity of CBD metabolites either in vitro or in vivo, and discusses relevant drug–drug interactions. To facilitate further research in the area, the reported syntheses of CBD metabolites are also catalogued.

A novel metabolite, an oxepin formed from cannabidiol with guinea-pig hepatic microsomes

The metabolic formation of an oxepin derivative, 3-pentyl-6,7,7a,8,9,11a-hexahydro-1,7-dihydroxy-7,10- dimethyldibenzo-[b,d]-oxepin, from cannabidiol was studied in-vitro using guinea-pig hepatic microsomes. The hepatic microsomes catalysed the formation of the metabolite from cannabidiol and 8S, 9-epoxycannabidiol in the presence of an NADPH-generating system and 3, 3, 3-trichloropropene-1, 2-oxide. 8S, 9-Epoxycannabidiol was thought to be an intermediate in the formation of the metabolite, which was identified by gas chromatography-mass spectrometry. The metabolite synthesized from 8S, 9-epoxycannabidiol diacetate exhibited catalepsy, hypothermia and pentobarbitone-induced sleep prolongation in mice, although the pharmacological effect was less potent than that of delta 9-tetrahydrocannabinol.

Recent advances in the metabolism of cannabinoids

This review describes recent advances in the metabolism of cannabinoids. Cannabidiol was metabolized to cannabielsoin, 6 beta-hydroxymethyl-delta 9-tetrahydrocannabinol and an oxepine derivative through epoxide intermediates by hepatic microsomal enzymes containing cytochrome P450 of animals. Cannabidiol inactivated cytochrome P450 UT-2 (CYP2C11) not equal to in male rats and a member of 3A subfamily in mouse liver. These inactivations may be very important because serious drug-drug interactions will occur in the case that cannabidiol is co-administered with drugs which are metabolized mainly by the enzyme system containing these P450 isozymes. A member of cytochrome P450 belonging to 2C subfamily was the major isozymes responsible for the cannabinoid metabolism in many experimental animals and that of 3A subfamily made some contribution to the metabolism of cannabinoids by human hepatic microsomes. Microsomal aldehyde oxygenase, a particular isozyme of cytochrome P450 catalyzing the oxidation of 11-oxo-tetrahydrocannabinol to tetrahydrocannabinol-11-oic acid, was found for the first time by the authors. Cytochrome P450 MUT-2 (CYP2C29) is the major isozyme responsible for the microsomal aldehyde oxygenase activity in mouse hepatic microsomes.

Comparative metabolism of cannabidiol in dog, rat and man

Urinary metabolites of cannabidiol (CBD) were extracted from human, dog and rat urine, concentrated by chromatography on Sephadex LH-20, and identified by GC/MS. Over 50 metabolites were identified with considerable species variation. CBD was excreted in substantial concentration from human urine, both in the free state and as its glucuronide. In dog, unusual glucoside conjugates of three metabolites (4''- and 5''-hydroxy and 6-oxo-CBD), not excreted in the unconjugated state, were found as the major metabolites at early times after drug administration. Other metabolites in all three species were mainly acids. Side-chain hydroxylated derivatives of CBD-7-oic acid were particularly abundant in human urine but much less so in dog. In the latter species the major oxidized metabolites were the products of beta-oxidation with further hydroxylation at C-6. A related, but undefined pathway, resulted in loss of three carbon atoms from the side-chain of CBD in man with the production of 2''-hydroxy-tris,nor-CBD-7-oic acid. Previous experiments indicate that 3'-hydroxy-metabolites are the precursors of compounds having this side-chain. Metabolism by the epoxide-diol pathway, resulting in dihydro-diol formation from the delta-8-double bond, gave metabolites in both dog and human urine. It was concluded that CBD could be used as a probe of the mechanism of several types of biotransformation, particularly those related to carboxylic acid metabolism, as intermediates of the type not usually seen with endogenous compounds were excreted in substantial concentration.

Comparative in vitro metabolism of the cannabinoids

The metabolism of delta-9-tetrahydrocannabinol (delta-9-THC), delta-8-THC, delta-11-THC, cannabidiol (CBD), cannabinol (CBN), cannabichromene (CBC), cannabigerol (CBG) and the equatorial-isomer of hexahydrocannabinol (HHC) was studied in microsomal preparations obtained from rats, mice, guinea pigs, rabbits, hamsters, gerbils and a cat. Identification of metabolites was by GC/MS and quantification by gas chromatography. Major metabolites were monohydroxylated compounds but the pattern of hydroxylation varied considerably between the species, no doubt reflecting the variable nature of the cytochrome P-450 mixed-function oxidases. Although the primary carbon allylic to the endocyclic double bond of tricyclic cannabinoids was usually the major site of attack, the 4' (side-chain, omega-1 position) and the terpene ring were usually favoured by the cat and hamster respectively. The guinea pig generally produced more metabolites hydroxylated in the side-chain (all positions) than did the other species. The results from HHC were very similar to those from THC, namely hydroxylation at C-11 in most species, and the production of high concentrations of 8 alpha-hydroxy-HHC in the mouse and 8 beta-hydroxy-HHC in the hamster. As this molecule lacks the double bond of the THCs and, hence, the allylic nature of C-11 and C-8, the results suggest that it is the orientation of the molecule to the active site of the cytochrome P-450 mixed-function oxidase rather than the reactivity of the C-H bond that governs the position of hydroxylation.

Urinary metabolites of cannabidiol in dog, rat and man and their identification by gas chromatography-mass spectrometry

Urinary metabolites of cannabidiol (CBD), a non-psychoactive cannabinoid of potential therapeutic interest, were extracted from dog, rat and human urine, concentrated by chromatography on Sephadex LH-20 and examined by gas chromatography-mass spectrometry as trimethylsilyl (TMS), [2H9]TMS, methyl ester-TMS and methyloxime-TMS derivatives. Fragmentation of the metabolites under electron-impact gave structurally informative fragment ions; computer-generated single-ion plots of these diagnostic ions were used extensively to aid metabolite identification. Over fifty metabolites were identified with considerable species variation. CBD was excreted in substantial concentration in human urine, both in the free state and as its glucuronide. In dog, unusual glucoside conjugates of three metabolites (4"- and 5"-hydroxy- and 6-oxo-CBD), not excreted in the unconjugated state, were found as the major metabolites at early times after drug administration. Other metabolites in all three species were mainly acids. Side-chain hydroxylated derivatives of CBD-7-oic acid were particularly abundant in human urine but much less so in dog. In the latter species the major oxidized metabolites were the products of beta-oxidation with further hydroxylation at C-6. A related, but undefined pathway resulted in loss of three carbon atoms from the side-chain of CBD in man with production of 2"-hydroxy-tris,nor-CBD-7-oic acid. Metabolism by the epoxide-diol pathway, resulting in dihydro-diol formation from the delta-8 double bond, gave metabolites in both dog and human urine. It was concluded that CBD could be used as a probe of the mechanism of several types of biotransformation; particularly those related to carboxylic acid metabolism as intermediates of the type not usually seen with endogenous compounds were excreted in substantial concentration.