Identification of human drug-metabolizing enzymes involved in the metabolism of SNI-2011.
In vitro studies were conducted to identify human drug-metabolizing enzymes involved in the metabolism of SNI-2011 ((+/-)-cis-2-methylspiro [1,3-oxathiolane-5,3'-quinuclidine] monohydrochloride hemihydrate, cevimeline hydrochloride hydrate). When 14C-SNI-2011 was incubated with human liver microsomes, SNI-2011 trans-sulfoxide and cis-sulfoxide were detected as major metabolites. These oxidations required NADPH, and were markedly inhibited by SKF-525A, indicating that cytochrome P450 (CYP) was involved. In a chemical inhibition study, metabolism of SNI-2011 in liver microsomes was inhibited (35-65%) by CYP3A4 inhibitors (ketoconazole and troleandomycin) and CYP2D6 inhibitors (quinidine and chlorpromazine). Furthermore, using microsomes containing cDNA-expressed CYPs, it was found that high rates of sulfoxidation activities were observed with CYP2D6 and CYP3A4. On the other hand, when 14C-SNI-2011 was incubated with human kidney microsomes, SNI-2011 N-oxide was identified as a major metabolite. This N-oxidation required NADPH, and was completely inhibited by thiourea, indicating that flavin-containing monooxygenase (FMO) was involved. In addition, microsomes containing cDNA-expressed FMO1, a major isoform in human kidney, mainly catalyzed N-oxidation of SNI-2011, but microsomes containing FMO3, a major isoform in adult human liver, did not. These results suggest that SNI-2011 is mainly catalyzed to sulfoxides and N-oxide by CYP2D6/3A4 in liver and FMOI in kidney, respectively.
Washio
T
T
Research Institute of Life Science, Snow Brand Milk Products Co, Ltd, Shimotsuga-gun, Tochigi, Japan. washio-t-e@pop16.odn.ne.jp
Arisawa
H
H
Kohsaka
K
K
Yasuda
H
H
D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D018076:DNA, Complementary / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007313:Insecta; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D018721:Muscarinic Agonists / Q000737:chemistry / Q000378:metabolism; D010105:Oxygenases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D011812:Quinuclidines / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D013876:Thiophenes
D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D018721:Muscarinic Agonists; D011812:Quinuclidines; D013876:Thiophenes; D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; C020066:dimethylaniline monooxygenase (N-oxide forming); C059240:cevimeline