Oxidation mechanism of 7-hydroxy-delta 8-tetrahydrocannabinol and 8-hydroxy-delta 9-tetrahydrocannabinol to the corresponding ketones by CYP3A11.
A cDNA isolated from a C57BL/6 mouse liver cDNA library had the identical nucleotide sequence in coding region with the mouse CYP3A11, and the NH(2)-terminal sequence was also identical to that of cytochrome P450 (P450) MDX-B, a microsomal alcohol oxygenase. The COS-7 cells transfected with the CYP3A11 expression vector formed 7-oxo-Delta(8)-tetrahydrocannabinol (7-oxo-Delta(8)-THC) from 7alpha- and 7beta-hydroxy-Delta(8)-THC. An immunologically related protein with P450 MDX-B was expressed in the COS-7 cell microsomes. The cell microsomes expressed CYP3A11; COS-3A11 catalyzed the oxidation of 7-hydroxy-Delta(8)-THC and 8-hydroxy-Delta(9)-THC to 7-oxo-Delta(8)-THC and 8-oxo-Delta(9)-THC, respectively, in a reconstituted system. (18)O derived from atmospheric oxygen was incorporated into about 30% of the corresponding ketones formed from 7alpha-hydroxy-Delta(8)-THC and 8beta-hydroxy-Delta(9)-THC by mouse hepatic microsomes, P450 MDX-B, and COS-3A11, although incorporation of the stable isotope into the oxidized metabolites from 7beta-hydroxy-Delta(8)-THC and 8alpha-hydroxy-Delta(9)-THC was negligible. (18)O, however, was not incorporated into 7-oxo-Delta(8)-THC formed from 7alpha-hydroxy-Delta(8)-THC by using cumene hydroperoxide instead of NADPH under (18)O(2). When (18)O-labeled 7alpha-hydroxy-Delta(8)-THC and 8beta-hydroxy-Delta(9)-THC were incubated with above enzymes under air, about 30% of the ketones formed released (18)O from a hydroxy group at the 7 and 8 positions in the course of the oxidation. These results suggest that 7alpha-hydroxy-Delta(8)-THC and 8beta-hydroxy-Delta(9)-THC may be oxidized to the corresponding ketones by CYP3A11 via a gem-diol pathway. 7beta-Hydroxy-Delta(8)-THC and 8alpha-hydroxy-Delta(9)-THC may be also converted to the ketones through a stereoselective dehydration of an enzyme-bound gem-diol rather than through a direct hydrogen extraction as a peroxy form of the enzyme.
Matsunaga
T
T
Department of Hygienic Chemistry, Faculty of Pharmaceutical Sciences, Hokuriku University, Kanazawa 920-1181, Japan.
Tanaka
H
H
Higuchi
S
S
Shibayama
K
K
Kishi
N
N
Watanabe
K
K
Yamamoto
I
I
D000818:Animals; D019556:COS Cells / Q000201:enzymology; D003001:Cloning, Molecular; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D013759:Dronabinol / Q000031:analogs & derivatives* / Q000378:metabolism*; D006168:Guinea Pigs; D007659:Ketones / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008862:Microsomes, Liver / Q000201:enzymology; D010084:Oxidation-Reduction
C109363:7-hydroxy-delta(8)-tetrahydrocannabinol; D007659:Ketones; C033935:8-hydroxy-delta(9)-tetrahydrocannabinol; D013759:Dronabinol; D003577:Cytochrome P-450 Enzyme System