Sulfotransferase-catalyzed biotransformation of liguzinediol and comparison of its metabolism in different species using UFLC-QTOF-MS

Liguzinediol (2,5-dihydroxymethyl-3,6-dimethylpyrazine, LZDO) is a potential agent for the low-risk treatment of heart failure. 2-N-acetylcysteine-LZDO (2-NAC-LZDO) and 2-cysteine-LZDO (2-Cys-LZDO) are major LZDO metabolites found in the pharmacokinetic studies of rats and beagle dogs. To elucidate the biotransformation pathway and related enzymes, an incubation system with 3′-phosphoadenosine-5′-phosphosulfate (PAPS) as a cofactor and N-acetylcysteine (NAC) as a trapping agent was established using liver cytosol. An ultra-flow liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry (UFLC-QTOF-MS) method was used to identify the major metabolites. 2-NAC-LZDO could be detected among four species (humans, monkeys, dogs, and rats) and is the dominant metabolite in human liver cytosol (HLC). The sulfotransferase (SULT) inhibitors 2,6-dichloro-4-nitrophenol (DCNP) and quercetin at a concentration of 1 μM, suppressed 2-NAC-LZDO formation in HLC by 87 and 46%, respectively. This result suggested that sulfotransferase was involved in 2-NAC-LZDO formation. The metabolism of LZDO in different species indicated that SULT activity in dogs, rats, and monkeys was higher than that in humans. Further SULT phenotyping revealed that SULT1A1 is the predominant enzyme involved in the sulfation of LZDO. The underlying mechanism for the biotransformation of LZDO was demonstrated. The potential pathway is via the sulfation of LZDO to form sulfate, and the spontaneous cleavage of the sulfate group to generate highly reactive electrophilic cations, which can bind to NAC to form the major metabolites.