Stereoselective Covalent Adduct Formation of Acyl Glucuronide Metabolite of Nonsteroidal Anti-Inflammatory Drugs with UDP-Glucuronosyltransferase

Synergistic and Additive Inhibition of UDP-Glucuronosyltransferase 1A9 by Endogenous and Foodborne Inhibitors

UDP-glucuronosyltransferases (UGTs) are responsible for inactivation of a variety of drugs, endogenous hormones and environmental toxicants. Chemical inhibitors are a common factor decreasing UGT activities and furtherly inducing health problems. Although simultaneously encountering different inhibitors is readily to occur, no information is available for combined inhibition of UGT. This in vitro study investigates the combined inhibition of human UGT1A9 by endogenous and foodborne inhibitors (magnolol, di-bromophenols, UDP). J values (the ratio of inhibitory rate to the remaining activity) are analysed to determine the combined inhibition type. The combined inhibition of di-bromophenols and UDP obeys additive inhibition, in which combined J values equal to the sum of individual J values in alone inhibition assays. Meanwhile, there is a synergistic effect between 2,4-di-bromophenol and magnolol with combination index values ranging from 0.10 to 0.85. Further assays indicate that 2,4-di-bromophenol decreases IC50 values for magnolol and vice versa. Kinetic analysis confirms that the two inhibitors and UGT1A9 can form a ternary complex with the inhibition constants of 0.0188 μM (magnolol) and 0.634 (2,4-di-bromophenol) μM. In summary, this study demonstrates that besides additive inhibition, synergistic inhibition is a probable occurrence in combined inhibition of UGT. It is suggested that the inhibitors can increase mutual inhibitory effects which deserves attentions in future UGT inhibition related studies.

Slc25a39 and Slc25a40 Expression in Mice with Bile Duct Ligation or Lipopolysaccharide Treatment

SLC25A39/40, involved in mitochondrial GSH (mGSH) import from the cytoplasm, is essential for protection against oxidative stress and mitochondrial dysfunction. We examined the effects of cholestasis, through bile duct ligation (BDL) and lipopolysaccharide (LPS)-induced inflammation in mice, on Slc25a39/40 expression. Additionally, we used human clear cell renal carcinoma (KMRC-1) cells to elucidate the mechanism of regulation of SLC25A39/40 expression in the kidneys after LPS treatment. BDL resulted in a decrease in Slc25a39 mRNA in the liver and a decrease in Slc25a39/40 mRNA and protein in the kidneys. Consequently, there was a significant decrease in mGSH levels in the kidneys of BDL mice compared with those in sham mice. LPS treatment resulted in increased Slc25a40 expression in the kidneys. In KMRC-1 cells, the combination treatment of LPS-RS or FPS-ZM1 with LPS suppressed the LPS-induced increase in SLC25A40, suggesting that SLC25A40 expression could be regulated by the signaling pathway via toll-like receptor 4 and the receptor for advanced glycation end products, respectively. Our findings contribute to understanding the role of mGSH in the maintenance of the mitochondrial redox state. To the best of our knowledge, this is the first study that demonstrates the changes in Slc25a39/40 expression in mice with cholestasis-associated renal injury and LPS-induced inflammation.