Connecting glutathione with immune responses to occupational methylene diphenyl diisocyanate exposure

Chem Biol Interact. 2013 Sep 5;205(1):38-45. doi: 10.1016/j.cbi.2013.06.005. Epub 2013 Jun 20.


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.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Albumins / immunology
  • Albumins / metabolism
  • Allergens / adverse effects
  • Allergens / immunology
  • Allergens / metabolism
  • Asthma, Occupational / etiology*
  • Asthma, Occupational / immunology
  • Asthma, Occupational / metabolism
  • Benzhydryl Compounds / adverse effects
  • Benzhydryl Compounds / immunology*
  • Benzhydryl Compounds / metabolism*
  • Case-Control Studies
  • Female
  • Glutathione / adverse effects
  • Glutathione / analogs & derivatives*
  • Glutathione / immunology*
  • Glutathione / metabolism*
  • Humans
  • Isocyanates / adverse effects
  • Isocyanates / immunology*
  • Isocyanates / metabolism*
  • Male
  • Middle Aged
  • Occupational Exposure
  • Tandem Mass Spectrometry


  • Albumins
  • Allergens
  • Benzhydryl Compounds
  • Isocyanates
  • methylenediphenyl diisocyanate-glutathione adduct
  • 4,4'-diphenylmethane diisocyanate
  • Glutathione