Transformation of delta-1-tetrahydrocannabinol (THC) by rabbit liver microsomes

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.

Gas chromatographic and mass spectrometric studies on the metabolism and pharmacokinetics of delta 1-tetrahydrocannabinol in the rabbit

Gas chromatography-mass spectrometry has been used to investigate the in vivo hepatic metabolism of delta 1-tetrahydrocannabinol (delta 1-THC) in the New Zealand white rabbit. Sixteen metabolites were identified and shown to be present in different relative amounts compared with the hepatic metabolites of delta 1-THC produced by other species. The metabolic profile was also different from that reported from rabbit urine particularly with regard to the lower relative concentrations of acidic metabolites in the liver. The pharmacokinetics of delta 1-THC has been studied in the rabbit using the recently developed GC-MS method based on metastable ion monitoring. This revealed a terminal plasma delta 1-THC half life ranging from 34.16 to 59.30 h (mean 46.75 h) after a single dose and THC fat/plasma ratio of 10(3)-10(4):1.

Epoxide-diol pathway of delta 1-THC in the rat in vitro

1. 1 alpha, 2 alpha-Epoxyhexahydrocannabinol was identified as a metabolite of delta 1-tetrahydrocannabinol. 2. The two trans-1,2-dihydroxyhexahydrocannabinol isomers, 1 alpha, 2 beta-dihydroxyhexahydrocannabinol and 1 beta, 2 alpha-dihydroxyhexahydrocannabinol (as their acetates) were tentatively identified as metabolites from incubation of 1 alpha, 2 alpha-epoxyhexahydrocannabinol with rat hepatic microsomes in vitro. 3. The 1 alpha, 2 alpha-epoxyhexahydrocannabinol acetate was found to be a good substrate for epoxide hydratase as compared to styrene oxide. 4. The synthesis of metabolites of 1 alpha, 2 alpha-epoxyhexahydrocannabinol is described.

Stereospecific elimination of deuterium as a method for determining the stereochemistry of a number of metabolites of the tetrahydrocannabinols

The stereospecific elimination of the 3-deuterium atom from metabolites of [2H]-analogues of delta 1-tetrahydrocannabinol (delta 1-THC), delta 6-THC and delta 7-THC has been investigated as a possible method for determining the stereochemistry of metabolites substituted with hydroxy or acid groups in the terpene ring. Elimination of HCOOTMS was found to involve the 3-hydrogen of the axial but not the equatorial isomer of hexahydrocannabinol-7-oic acid, a metabolite of all three cannabinoids. Similar stereospecific eliminations were observed during the loss of TMSOH from the TMS derivatives of 5 alpha-hydroxy-delta 6-THC, 6 alpha-hydroxy-delta 1-THC and 1 alpha, 2 beta-dihydroxy-delta 1-THC. Loss of TMSOH from 1 alpha, 7- and 1 beta, 7-dihydroxy-HHC involved the 3-hydrogen in both cases but the isomers could be distinguished as their alkane-boronate derivatives; only the derivative of 1 alpha, 7-dihydroxy-HHC lost the boronate ring with stereospecific removal of the 3-hydrogen. The stereochemistry of the four isomers of 1,6-dihydroxy-HHC could not be determined in this way as the [M-TMSOH]+ ions from all four compounds had lost the 3-hydrogen, presumably as the result of 1,6-bond cleavage.

Acidic metabolites of delta1-tetrahydrocannabinol isolated from rabbit urine

The in vivo metabolism of delta1-tetrahydrocannabinol (delta1-THC) was investigated in the rabbit after i.v. administration. Thirteen acidic metabolites were isolated from rabbit urine and identified by gas chromatography-mass spectrometry and by proton magnetic resonance spectroscopy. One additional metabolite was tentatively identified. All but three were new metabolites and all but one were oxidized in the pentyl side chain. The metabolites included dicarboxylic acids, monocarboxylic acids and mono- or dihydroxylated derivatives thereof. However, the dicarboxylic acid metabolites were the most prominent.

More acidic metabolites of delta1-tetrahydrocannabinol isolated from rabbit urine

The in vivo metabolism of delta1-tetrahydrocannabinol (delta1-THC) was further investigated in the rabbit after i.v. administration. Nine acidic metabolites were isolated from a previously not investigated fraction of the urine and identified by gas chromatography-mass spectrometry and by proton magnetic resonance spectroscopy. The major metabolites were side-chain hydroxylated monocarboxylic acids. Three side-chains monocarboxylic acids hydroxylated in allylic positions in the isoprene moiety were also characterized. The metabolites 4''-hydroxy-delta1-THC-7-oic acid and 7-hydroxy-4'',5''-bisnor-delta1-THC-3''-oic acid were hitherto not identified. An earlier described dicarboxylic metabolite was present in high concentration. Further, the identity of an O-glucuronide as an in vivo urinary metabolite of delta1-THC was here for the first time unambiguously established by m.s. and p.m.r.

delta 1-Tetrahydrocannabinol and 1 alpha, 2 alpha-epoxyhexahydrocannabinol: mutagenicity investigation in the Ames test

1,2-Epoxyhexahydrocannabinol is a metabolite of delta 1-tetrahydrocannabinol. Because many epoxides are mutagens, we investigated 1,2-epoxyhexahydrocannabinol as well as delta 1-tetrahydrocannabinol for mutagenicity with Salmonella typhimurium TA1535, TA1537, TA98 and TA100 in the presence and in the absence of S9 mix from liver homogenate of rats treated with Aroclor 1254. Additionally, an epoxide hydratase inhibitor was used in some experiments. Whereas several other epoxides and further positive controls, not requiring activation or activated under the same conditions, respectively, showed strong mutagenicity, no indications of a mutagenic hazard by 1,2-epoxyhexahydrocannabinol or by delta 1-tetrahydrocannabinol were found.