title: Connecting glutathione with immune responses to occupational methylene diphenyl diisocyanate exposure.
abstract: Methylene diphenyl diisocyanate (MDI) is among the leading chemical causes of occupational asthma world-wide, however, the mechanisms of disease pathogenesis remain unclear. This study tests the hypothesis that glutathione (GSH) reacts with MDI to form quasi-stable conjugates, capable of mediating the formation of MDI-conjugated "self" protein antigens, which may participate in pathogenic inflammatory responses. To test this hypothesis, an occupationally relevant dose of MDI (0.1%w/v) was reacted with varying concentrations of GSH (10μM-10mM), and the reaction products were characterized with regard to mass/structure, and ability to carbamoylate human albumin, a major carrier protein for MDI in vivo. LC-MS/MS analysis of GSH-MDI reaction products identified products possessing the exact mass of previously described S-linked bis(GSH)-MDI and its partial hydrolysis product, as well as novel cyclized GSH-MDI structures. Upon co-incubation of GSH-MDI reaction products with human albumin, MDI was rapidly transferred to specific lysines of albumin, and the protein's native conformation/charge was altered, based on electrophoretic mobility. Three types of modification were observed, intra-molecular MDI cross-linking, addition of partially hydrolyzed MDI, and addition of "MDI-GSH", where MDI's 2nd NCO had reacted with GSH's "N-terminus". Importantly, human albumin carbamoylated by GSH-MDI was specifically recognized by serum IgG from MDI exposed workers, with binding dependent upon the starting GSH concentration, pH, and NaCl levels. Together, the data define a non-enzymatic, thiol-mediated transcarbamoylating mechanism by which GSH may promote immune responses to MDI exposure, and identify specific factors that might further modulate this process.
authors.affiliation: Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA. adam.wisnewski@yale.edu
authors.forename: Adam V
authors.initials: AV
authors.lastname: Wisnewski
authors.forename: Jian
authors.initials: J
authors.lastname: Liu
authors.forename: Carrie A
authors.initials: CA
authors.lastname: Redlich
mesh_terms: D000328:Adult; D000418:Albumins / Q000276:immunology / Q000378:metabolism; D000485:Allergens / Q000009:adverse effects / Q000276:immunology / Q000378:metabolism; D059366:Asthma, Occupational / Q000209:etiology* / Q000276:immunology / Q000378:metabolism; D001559:Benzhydryl Compounds / Q000009:adverse effects / Q000276:immunology* / Q000378:metabolism*; D016022:Case-Control Studies; D005260:Female; D005978:Glutathione / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000276:immunology* / Q000378:metabolism*; D006801:Humans; D017953:Isocyanates / Q000009:adverse effects / Q000276:immunology* / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure; D053719:Tandem Mass Spectrometry
chemical_list: D000418:Albumins; D000485:Allergens; D001559:Benzhydryl Compounds; D017953:Isocyanates; C510947:methylenediphenyl diisocyanate-glutathione adduct; C005969:4,4'-diphenylmethane diisocyanate; D005978:Glutathione
keywords: Albumin; Carbamoylation; Exposure; GSH; GSSG; Glutathione (GSH); HDI; MDI; MDI(∗); Methylene diphenyl diisocyanate (MDI); TDI; hexamethylene diisocyanate; methylene diphenyl diisocyanate; oxidized glutathione; partially hydrolyzed methylene diphenyl diisocyanate; reduced glutathione; toluene diisocyanate