Oxidative one-carbon cleavage of the octyl side chain of olanexidine, a novel antimicrobial agent, in dog liver microsomes

Oral Exposure to Benzalkonium Chlorides in Male and Female Mice Reveals Sex-Dependent Alteration of the Gut Microbiome and Bile Acid Profile

Benzalkonium chlorides (BACs) are commonly used disinfectants in a variety of consumer and food-processing settings, and the COVID-19 pandemic has led to increased usage of BACs. The prevalence of BACs raises the concern that BAC exposure could disrupt the gastrointestinal microbiota, thus interfering with the beneficial functions of the microbes. We hypothesize that BAC exposure can alter the gut microbiome diversity and composition, which will disrupt bile acid homeostasis along the gut-liver axis. In this study, male and female mice were exposed orally to d 7 -C12- and d 7 -C16-BACs at 120 µg/g/day for one week. UPLC-MS/MS analysis of liver, blood, and fecal samples of BAC-treated mice demonstrated the absorption and metabolism of BACs. Both parent BACs and their metabolites were detected in all exposed samples. Additionally, 16S rRNA sequencing was carried out on the bacterial DNA isolated from the cecum intestinal content. For female mice, and to a lesser extent in males, we found that treatment with either d 7 -C12- or d 7 -C16-BAC led to decreased alpha diversity and differential composition of gut bacteria with notably decreased actinobacteria phylum. Lastly, through a targeted bile acid quantitation analysis, we observed decreases in secondary bile acids in BAC-treated mice, which was more pronounced in the female mice. This finding is supported by decreases in bacteria known to metabolize primary bile acids into secondary bile acids, such as the families of Ruminococcaceae and Lachnospiraceae. Together, these data signify the potential impact of BACs on human health through disturbance of the gut microbiome and gut-liver interactions.

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

BACKGROUND

Carbon-carbon bond cleavage of a saturated aliphatic moiety is rarely seen in xenobiotic metabolism. Olanexidine (Olanedine®), containing an n-octyl (C₈) side chain, was mainly metabolized to various shortened side chain (C₄ to C₆) 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 (C₈) side chain. However, the carbon-carbon bond cleavage mechanism of n-octyl (C₈) side chain, and enzyme(s) responsible for its metabolism in human remained unknown.

METHODS

A pair of regioisomers of α-ketol-containing C₈ 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.

RESULTS

Multiple shortened side chain (C₄ to C₆) metabolites were identified, including C₄, C₅ and C₆- acid and C₆-hydroxyl metabolites. Among 19 cytochrome P450 enzymes tested, CYP2D6, CYP3A4 and CYP3A5 were identified to catalyze carbon-carbon bond cleavage.

CONCLUSION

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 C₆ side chain acid metabolite. While, 3,2-ketol olanexidine formed a C₆ side chain aldehyde intermediate, which was either oxidized to a C₆ side chain acid metabolite or reduced to a C₆ side chain hydroxyl metabolite.

Oxidative carbon-carbon bond cleavage is a key step in spiroacetal biosynthesis in the fruit fly Bactrocera cacuminata

The early steps of spiroacetal biosynthesis in the fruit fly Bactrocera cacuminata (Solanum fly) have been investigated using a series of deuterium-labeled, oxygenated fatty acid like compounds. These potential spiroacetal precursors were administered to male flies, and their volatile emissions were analyzed for specific deuterium incorporation by GC/MS. This has allowed the order of early oxidative events in the biosynthetic pathway to be determined. Together with the already well-established later steps, the results of these in vivo investigations have allowed essentially the complete delineation of the spiroacetal biosynthetic pathway, beginning from products of primary metabolism. A fatty acid equivalent undergoes a series of enzyme-mediated oxidations leading to a trioxygenated fatty acid like species that includes a vicinal diol. This moiety then undergoes enzyme-mediated oxidative carbon-carbon bond cleavage as the key step to generate the C9 unit of the final spiroacetal. This is the first time such an oxidative transformation has been reported in insects. A final hydroxylation step is followed by spontaneous spiro-cyclization. This distinct pathway adds further to the complexity and diversity of biosynthetic pathways to spiroacetals.