Identification of MDI Albumin Adducts with Liquid Chromatography Time of Flight and Tandem Mass Spectrometry and Mascot Software

摘要

While biomonitoring for diamine metabolites of diisocyanates [such as Methylene diphenyl diisocyanate (MDI) and Toluene diisocyanate (TDI)] in hydrolyzed biological fluids is routinely employed to measure occupational exposure to MDI or TDI, these markers are not specific for isocyanate exposure. An alternative and specific class of biomarker for isocyanate exposure is quantitation of protein adducts in blood or bronchoalveolar lavage fluid that retain the isocyanate moiety. The advantage of measuring protein adduct biomarkers is a slow turnover and therefore, a viable potential tool for monitoring long-term exposures. Successful identification of protein adducts of diisocyanates may also allow for correlation of patterns of adducts with various routes of exposure to the exposure chemicals. As albumin is the main component of proteins in plasma and lavage fluid, evaluation of an albumin adduct will allow for investigation of presystemic (bronchoalveloar) and systemic (plasma) sites of adduct formation. Therefore, identification of those albumin adducts is a critical step for conducting those studies. The current study is designed to develop an approach to identify the possible MDI adducted signature peptides from in vitro albumin incubations under physiological conditions. Both rat albumin and human albumin can form multiple MDI-amine [4-(4-isocyanatobrnzyl)aniline] or MDI-isocyanate [1, 1'-methanediylbis(4-isocyanatobenzene)] adducts, with up to 14 different adducts identified in the 5 mM MDI incubations. More adducts have been identified with human albumin than with the rat analog. The solvents used for dissolving MDI had an impact on adduct formation, with the DMSO-carrier reaction affording more identified adducts for rat albumin than acetone.