Identification of Novel Metabolites of Vildagliptin in Rats: Thiazoline-Containing Thiol Adducts Formed via Cysteine or Glutathione Conjugation

Abstract

Vildagliptin (VG), a dipeptidyl peptidase-4 inhibitor, is used for treating type 2 diabetes. On rare occasions, VG causes liver injury as an adverse reaction. One case report suggested the involvement of immune responses in the hepatotoxicity, but the underlying mechanisms are unknown. We recently reported that VG binds covalently in vitro to L-cysteine to produce a thiazoline acid metabolite, M407, implying that the covalent binding may trigger the immune-mediated hepatotoxicity. There was no evidence, however, that such a thiazoline acid metabolite was formed in vivo. In the present study, we administered a single oral dose of VG to male Sprague-Dawley rats, and detected M407 in plasma. The sum of urinary and fecal excretions of M407 reached approximately 2% of the dose 48 hours postdosing. Using bile duct-cannulated rats, we demonstrated that M407 was secreted into bile as a glucuronide, designated as M583. Another newly identified thiazoline metabolite of VG, the cysteinylglycine conjugate M464, was detected in urine, feces, and bile. The formation of M464 was confirmed by in vitro incubation of VG with glutathione even in the absence of metabolic enzymes. A glutathione adduct against the nitrile moiety M611 was also detected in vitro but not in vivo. In summary, we found three new thiazoline-containing thiol adduct metabolites in VG-administered rats. Nonenzymatic covalent binding of VG would likely occur in humans, and it may be relevant to predicting adverse reactions.No potential conflicts of interest relevant to this article are reported.

Profiling and Identification of Omeprazole Metabolites in Mouse Brain and Plasma by Isotope Ratio-Monitoring Liquid Chromatography-Mass Spectrometric Method

“…administration study), and it might be related to active transporters, which can preferably influx compounds with the cysteine moiety. This is in line with the results of increased brain uptake of cysteine conjugated substances in the literatures [49,50].…”

2-cyanopyridine derivatives enable N-terminal cysteine bioconjugation and peptide bond cleavage of glutathione under aqueous and mild conditions

“…These results strongly support the reaction mechanism described in Scheme 1 , including the formation of 2-amidethiazolidine intermediate B and subsequent irreversible thiazoline formation with the release of ammonia. 8,11 c …”

“…Two reaction mechanisms for thiazoline ring formation have been proposed to date, 5,8 one of which is described in Scheme 1. 8 This proposed reaction mechanism suggests that cysteine-containing peptide chains could be cleaved by a reaction between 2-cyanopyridine derivatives and thiols.…”

“…Two reaction mechanisms for thiazoline ring formation have been proposed to date, 5,8 one of which is described in Scheme 1. 8 This proposed reaction mechanism suggests that cysteine-containing peptide chains could be cleaved by a reaction between 2-cyanopyridine derivatives and thiols. The nucleophilic addition of the thiol group of cysteine to 2-cyanopyridine leads to the reversible formation of thioimidate A , which is then cyclized by intramolecular nucleophilic addition of the amide nitrogen in cysteine to give 2-amidethiazolidine intermediate B .…”

Unusual Biotransformation Reactions of Drugs and Drug Candidates

“…7). (Mizuno et al, 2019) Another related metabolite M407, corresponding cysteine analogue of M464, has also been observed. These two metabolites are detected in rat urine, feces and bile and authors speculate that vildagliptin can react covalently with cysteine In our previous reviews, we had included several dimerization reactions initiated by P450 mediated radical formation.…”