Identification of novel reaction products of methylene-bis-phenylisocyanate (“MDI”) with oxidized glutathione in aqueous solution and also during incubation of MDI with a murine hepatic S9 fraction

•Methylene diphenyl-diisocyanate (MDI) reacts with oxidized and reduced glutathione.•Oxidized glutathione (GSSG) forms stable N-linked conjugates with MDI.•Reduced glutathione (GSH) forms stable N- and reversible S- linkages with MDI.•Data suggest MDI conjugates to GSSG and GSH upon incubation with an S9 fraction.•MDI-GSSG conjugates may be stable metabolites, amenable to exposure surveillance.

Methylene diphenyl diisocyanate (MDI) is an important industrial chemical and asthmagenic respiratory sensitizer, however its metabolism remains unclear. In this study we used LC-MS and LC-MS/MS to identify novel reaction products of MDI with oxidized glutathione (GSSG), including an 837 m/z [M + H]+ ion corresponding to GSSG bound (via one of its N-termini) to partially hydrolyzed MDI, and an 863 m/z [M + H]+ ion corresponding to GSSG cross-linked by MDI (via its two γ-glutamine N-termini). Further studies with heavy isotope labeled and native reduced glutathione (GSH) identified an [M + H]+ ion corresponding to previously described mono(GSH)-MDI, and evidence for “oligomeric” GSH-MDI conjugates. This study also investigated transformational changes in MDI after incubation with an S9 fraction prepared from murine liver. LC-MS analyses of the S9 reaction products revealed the formation of [M + H]+ ions with m/z's and retention times identical to the newly described GSSG-MDI (837 and 863) conjugates and the previously described mono(GSH)-MDI conjugate. Together the data identify novel biological transformations of MDI, which could have implications for exposure-related health effects, and may help target future in vivo studies of metabolism.

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