Identification and characterisation of adducts between serum albumin and 4,4?-methylenediphenyl diisocyanate (MDI) in human plasma

Abstract

Diisocyanates are potent inducers of airways disease. Methylenediphenyl diisocyanate (MDI) is a widely used diisocyanate in the chemical industry. The aim of this study was to identify major and also immunologically relevant protein conjugates of MDI in plasma. Plasma was obtained from an MDI-exposed worker. The plasma was dialysed and then fractionated using ion exchange chromatography (IEC) and gel filtration. These fractions and also aliquots of unfractioned plasma were hydrolysed, derivatised and analysed for isocyanate adduct content using gas chromatography-mass spectrometry. In addition, immunologically relevant proteins were identified through specific IgG immunoblotting using pooled sera from two exposed workers. It was shown by dialysis that 96% of the hydrolysed MDI derivatives were protein bound and that 95% of the MDI adducts co-eluted with serum albumin in plasma using IEC. All MDI-protein adducts co-eluted with serum albumin using gel filtration. IgG immunoblotting showed a major 66 kDa protein and also some intermolecular reactions in serum albumin. This study shows serum albumin to be the major protein in plasma that forms adducts in vivo with MDI. Thus, a quick and simple quantitative method for biological monitoring may be developed for MDI exposure. The results also showed that MDI-specific IgG antibodies preferentially bind to the serum albumin in in-vitro-synthesised MDI-plasma protein conjugates.

Addendum to 4,4'‐Methylene diphenyl diisocyanate (inhalable fraction)[BAT Value Documentation, 2007]

“…It was also shown in vitro that MDI-specific IgG antibodies are selectively bound to the MDI protein conjugates (Johannesson et al 2004). The HSA adducts are considered to be the primary inductors of T cell-dependent B-lymphocyte stimulation (see Documentation 2000).…”

4,4′‐Methylene diphenyl diisocyanate (MDI) [101‐68‐8] and “polymeric” MDI (PMDI) [9016‐87‐9] [MAK Value Documentation, 2008]

“…Around 95% of the total MDI adducts in human plasma are albumin adducts (Johannesson et al 2004;Sennbro et al 2003). A 70-kDa protein adduct was found as the main product in the blood of rats after 4-hour inhalation of 14 C-MDI (0.06 and 0.4 mg/m 3 ) (Brown et al 1994).…”

Biomarkers of exposure in Monday morning urine samples as a long-term measure of exposure to aromatic diisocyanates

“…In the blood it has been shown that the diisocyanates are mainly bound to serum albumin (Lind et al 1997a;Johannesson et al 2004) and the half-life of the adducts in plasma has been reported to be 21 days which is similar to that of albumin (Lind et al 1997b). The adducts will be excreted in urine as low-molecular weight conjugates (Lind et al 1996) when the proteins are degraded.…”