Effect of Saccharolactone on CYP-mediated Metabolism of Xenobiotics

Background: Saccharolactone is used as a β-glucuronidase inhibitor in in vitro micro-somal and recombinant uridine diphosphoglucuronosyl transferases (rUGTs) incubations to en-hance glucuronide pathway and, thereby, formation of glucuronide metabolites. We investigated its effect on CYP mediated metabolism of drugs (compound-174, phenacetin and quinidine) using human liver microsomes (HLM) supplemented with Phase-1 and Phase-2 co-factors. Methods: Compounds were incubated in HLM supplemented with co-factors to assess Phase-1 (NADPH) and Phase-2 (NADPH, alamethicin, saccharolactone and UDPGA) metabolism. CYP phenotype assay for compound-174 was conducted in HLM (± 1-ABT) and human recombinant CYP isoforms. CYP inhibition profile of saccharolactone was also generated in HLM. Results: The metabolism of compound-174, phenacetin and quinidine in HLM significantly de-creased in reactions containing additional components like alamethicin, saccharolactone and UD-PGA and indicated that the addition of saccharolactone inhibited the metabolism. Phenacetin and quinidine are known substrates of CYP1A2 and CYP3A4 isoforms. The metabolism of com-pound-174 was significantly inhibited in the presence of 1-ABT in HLM, and CYP3A4 and CYP2C8 isoforms were found to be the predominant isoforms responsible for its metabolism. Fur-ther evaluation of CYP inhibition in HLM indicated saccharolactone to be a strong inhibitor of CYP1A2, 2D6, 3A4 and 2C8 isoforms with IC50 values of less than 4 mM. Conclusion: The findings indicated that saccharolactone being a strong inhibitor of CYP1A2, 2D6, 3A4 and 2C8 isoforms (IC50 < 4 mM), resulted in significant inhibition of the metabolism of compound-174, phenacetin and quinidine in HLM and caution should be exercised in using it with proper titration of the concentrations.