Carbon-carbon Bond Cleavage Catalyzed by Human Cytochrome P450 Enzymes: α-ketol as the Key Intermediate Metabolite in Sequential Metabolism of Olanexidine

• Published in: Drug metabolism letters Vol. 14; no. 1; p. 41
• Main Authors: Hu, Yiding, Xiao, Yi, Rao, Zhesui, Kumar, Vasant, Liu, Hanlan, Lu, Chuang
• Format: Journal Article
• Language: English
• Published: United Arab Emirates 2021
• Subjects: Biguanides; Carbon; Catalysis; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Humans; Microsomes, Liver; metabolic pathway; metabolism; ketol; cytochrome P450 enzyme; Olanexidine; Carbon-carbon bond cleavage
• ISSN: 1874-0758
• DOI: 10.2174/1872312813666191125095818

Carbon-carbon bond cleavage of a saturated aliphatic moiety is rarely seen in xenobiotic metabolism. Olanexidine (Olanedine®), containing an n-octyl (C ) side chain, was mainly metabolized to various shortened side chain (C to C ) acid-containing metabolites in vivo in preclinical species. In liver microsomes and S9, the major metabolites of olanexidine were from multi-oxidation on its n-octyl (C ) side chain. However, the carbon-carbon bond cleavage mechanism of n-octyl (C ) side chain, and enzyme(s) responsible for its metabolism in human remained unknown. A pair of regioisomers of α-ketol-containing C side chain olanexidine analogs (3,2-ketol olanexidine and 2,3-ketol olanexidine) were synthesized, followed by incubation in human liver microsomes, recombinant human cytochrome P450 enzymes or human hepatocytes, and subsequent metabolite identification using LC/UV/MS. Multiple shortened side chain (C to C ) metabolites were identified, including C , C and C - acid and C -hydroxyl metabolites. Among 19 cytochrome P450 enzymes tested, CYP2D6, CYP3A4 and CYP3A5 were identified to catalyze carbon-carbon bond cleavage. 3,2-ketol olanexidine and 2,3-ketol olanexidine were confirmed as the key intermediates in carbon-carbon bond cleavage. Its mechanism is proposed that a nucleophilic addition of iron-peroxo species, generated by CYP2D6 and CYP3A4/5, to the carbonyl group caused the carbon-carbon bond cleavage between the adjacent hydroxyl and ketone groups. As results, 2,3-ketol olanexidine formed a C side chain acid metabolite. While, 3,2-ketol olanexidine formed a C side chain aldehyde intermediate, which was either oxidized to a C side chain acid metabolite or reduced to a C side chain hydroxyl metabolite.