Quantitative analysis of oxidized vitamin B1 metabolites generated by hypochlorous acid

Thiamine, a water-soluble essential vitamin known as vitamin B1, acts as an important cofactor in various cellular processes, such as metabolism and energy production. Thiamine is also thought to have antioxidant effects as a singlet oxygen scavenger and a lipid peroxidation inhibitor. However, the oxidation mechanism and oxidized metabolites of thiamine are not completely established. In the present study, we investigated the oxidative reactivity of thiamine and found that three products were formed upon the reaction of thiamine with hypochlorous acid (HOCl). Based on the NMR and high resolution mass spectrometric analysis, the HOCl-oxidized metabolites of thiamine were identified as formylaminopyrimidine (FAP), thiamine sulfonic acid (TSA), and thiamine sulfinic ester (TSE). To evaluate the formation of these oxidized metabolites in vivo, we established a specific method for quantification of the oxidized thiamine metabolites using liquid chromatography-tandem mass spectrometry coupled with a stable isotope dilution method. Using this method, it was shown that the oxidized thiamine metabolites were generated in the culture media of phorbol-12-myristate-acetate-treated neutrophil-like cells in a myeloperoxidase-dependent manner. Moreover, significantly higher amounts of FAP and TSE were detected in the lung tissues of the lipopolysaccharide-treated mice compared to the controls. These findings provide not only insights into the oxidative metabolism of thiamine, but also the possibility that the oxidized thiamine metabolites may be potential biomarkers for HOCl-related oxidative stress.