Stereospecific hydrolysis of 8α9α and 89epoxyhexahydrocannabinols in the mouse in vivo and in vitro

1. After i.v. injections to the mouse, both 8α9 and 89epoxyhexahydro-cannabinols (EHHCs) were easily hydrolysed to 8$b,9αdihydroxyhexahydrocannabinol (dihydroxy-HHC) rather than 8α9dihydroxy-HHC in the liver. 2. 8,9-Dihydroxy-HHCs hydroxylated at the 2' or 3' position of a pentyl side-chain were identified in vivo as liver metabolites of the epoxides. 3. The same stereospecific hydrolysis of 8,9-EHHCs were observed in vitro using liver-microsomal fractions of mice, though both epoxides were resistant to enzymic hydrolysis. 4. Several monohydroxylated 8,9-EHHCs, together with small amounts of 8,9-dihydroxy-HHCs were identified as in vitro liver metabolites of the epoxides. These metabolites could be formed not only by epoxide hydrolase but also by a mono-oxygenase system involving cytochrome P-450. 5. The magnitude of the binding affinities of cannabinoids to cytochrome P-450 was ranked in the following order: δ⁸-tetrahydrocannabinol (spectral dissociation constant K^s = 9.4 μM) > 89EHHC (13.3 μM) > 8α9αEHHC (34.5 μM).