Quantitation of 4,4'-methylene diphenyl diisocyanate human serum albumin adducts

Bioactive peptides in the pancreatin-hydrolysates of whey protein support cell proliferation and scavenge reactive oxygen species

Whey protein (WP) in milk shows physiologically active functions such as cholesterol control and immune system strengthening. In this study, we performed hydrolysis and peptide polarity fractionation to enhance the efficacy and diversity of its physiological activities, using the digesting enzyme, pancreatin. Our results indicate that hydrolysis significantly increased the cell proliferation of the WP fractions, with the lower-polarity fractions showing greater efficacy in this regard. Our results indicate that hydrolysis significantly increases cell proliferation of the WP fractions. Additionally, we confirmed differences in the antioxidant activity of the WP fractions as a function of polarity was confirmed via scavenging 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay in vitro. WP itself did not show anti-inflammatory efficacy. However, all the hydrolyzed fractions downregulated the mRNA expression levels of inflammatory cytokines in all treated cell lines and, based on a senescence-associated (SA)-β-galactosidase assay, the fraction with the lowest polarity (F6) inhibited cellular senescence to the greatest extent. Furthermore, we identified the peptide sequences with various physiological activities from whey protein hydrolysates through mass spectrometry. Taken together, our results indicate that the fractionation of WP via hydrolysis generates novel functions including promoting cellular cell proliferation, anti-inflammatory effects, and enhancing antioxidant and anti-cellular senescence.

Methylenediphenyl diisocyanate lysine conjugates in the urine of workers exposed to methylenediphenyl diisocyanate

Diisocyanates have long been a leading cause of occupational asthma. As control often relies on personal protective equipment and there is the potential for skin uptake, biological monitoring is often used to assess worker exposure. Current routine biological monitoring methods do not distinguish between a diisocyanate and the corresponding diamine exposure in urine samples; therefore, a specific urinary biomarker is desirable. Urine samples were obtained from a group of workers exposed to methylenediphenyl diisocyanate (MDI) where aerosol generation was unlikely. Lysine conjugates of MDI were extracted from urine by solid phase extraction; analysis was performed by liquid chromatography tandem mass spectrometry. Acetylated MDI-lysine (acMDI-Lys) conjugates were detected in 73% of samples tested from persons with exposure to MDI compared to 93% of samples that were positive for methylene dianiline (MDA) in hydrolysed urine. There was a weak but significant positive correlation between the two biomarkers (r² = 0.377). This is the first report detecting and quantifying acMDI-Lys in the urine of workers exposed to MDI, and acMDI-Lys may be a useful non-invasive biomarker in discriminating between MDI and MDA exposures.

Absorption, distribution, metabolism, and excretion of methylene diphenyl diisocyanate and toluene diisocyanate: Many similarities and few differences

Methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) are high production volume chemicals used for the manufacture of polyurethanes. For both substances, the most relevant adverse health effects after overexposure in the workplace are isocyanate-induced asthma, lung function decrement and, to a much lesser extent, skin effects. Over the last two decades many articles have addressed the reactivity of MDI and TDI in biological media and the associated biochemistry, which increased the understanding of their biochemical and physiological behavior. In this review, these new insights with respect to similarities and differences concerning the adsorption, distribution, metabolism, and excretion (ADME) of these two diisocyanates and the implications on their toxicities are summarized. Both TDI and MDI show very similar behavior in reactivity to biological macromolecules, distribution, metabolism, and excretion. Evidence suggests that the isocyanate (NCO) group is scavenged at the portal-of-entry and is not systemically available in unbound reactive form. This explains the lack of other than portal-of-entry toxicity observed in repeated-dose inhalation tests.

Quo vadis blood protein adductomics?

Chemicals are measured regularly in air, food, the environment, and the workplace. Biomonitoring of chemicals in biological fluids is a tool to determine the individual exposure. Blood protein adducts of xenobiotics are a marker of both exposure and the biologically effective dose. Urinary metabolites and blood metabolites are short term exposure markers. Stable hemoglobin adducts are exposure markers of up to 120 days. Blood protein adducts are formed with many xenobiotics at different sites of the blood proteins. Newer methods apply the techniques developed in the field of proteomics. Larger adducted peptides with 20 amino acids are used for quantitation. Unfortunately, at present the methods do not reach the limits of detection obtained with the methods looking at single amino acid adducts or at chemically cleaved adducts. Therefore, to progress in the field new approaches are needed.

Dilysine-Methylene Diphenyl Diisocyanate (MDI), a Urine Biomarker of MDI Exposure?

Biomonitoring of methylene diphenyl diisocyanate (MDI) in urine may be useful in industrial hygiene and exposure surveillance approaches toward disease (occupational asthma) prevention and in understanding pathways by which the internalized chemical is excreted. We explored possible urine biomarkers of MDI exposure in mice after respiratory tract exposure to MDI, as glutathione (GSH) reaction products (MDI-GSH), and after skin exposure to MDI dissolved in acetone. LC-MS analyses of urine identified a unique m/ z 543.29 [M + H]+ ion from MDI-exposed mice but not from controls. The m/ z 543.29 [M + H]+ ion was detectable within 24 h of a single MDI skin exposure and following multiple respiratory tract exposures to MDI-GSH reaction products. The m/ z 543.29 [M + H]+ ion possessed properties of dilysine-MDI, including (a) an isotope distribution pattern for a molecule with the chemical formula C27H38N6O6, (b) the expected collision-induced dissociation (CID) fragmentation pattern upon MS/MS, and (c) a retention time in reversed-phase LC-MS identical to that of synthetic dilysine-MDI. Further MDI-specific Western blot studies suggested albumin (which contains multiple dilysine sites susceptible to MDI carbamylation) as a possible source for dilysine-MDI and the presence of MDI-conjugated albumin in urine up to 6 days after respiratory tract exposure. Two additional [M + H]+ ions ( m/ z 558.17 and 863.23) were found exclusively in urine of mice exposed to MDI-GSH via the respiratory tract and possessed characteristics of previously described cyclized MDI-GSH and oxidized glutathione (GSSG)-MDI conjugates, respectively. Together the data identify urinary biomarkers of MDI exposure in mice and possible guidance for future translational investigation.

LC-UV-MS and MS/MS Characterize Glutathione Reactivity with Different Isomers (2,2' and 2,4' vs. 4,4') of Methylene Diphenyl-Diisocyanate

Methylene diphenyl diisocyanate (MDI), the most abundantly produced diisocyanate worldwide, is among the best recognized chemical causes of occupational asthma. The bulk of synthesized MDI, the 4,4' isomer, has been the focus of most biochemical research to date. The biological reactivity of other MDI isomers (2,2' and 2,4'), present at concentrations approaching 50% in some commercial products, remains less clear. We hypothesized 2,2' and 2,4' MDI react with glutathione (GSH), a major anti-oxidant of the lower airways, similarly to 4,4' MDI, and that the products could be characterized using a combination of LC-UV-MS and MS/MS. Purified 2,2' and 2,4' MDI isomers were mixed with GSH in pH-buffered aqueous phase at 37°C and reaction products were analyzed at varying time points. Within minutes, S-linked bis(GSH)-MDI conjugates were detectable as the dominant [M+H]⁺ ion, with an 865.25 m/z and more intense [M+2H]²⁺ ions of the same nominal mass. Upon longer reaction, [M+H]+ ions with greater retention times and the 558.17 m/z expected for mono(GSH)-MDI reaction products were observed, and exhibited MS/MS collision-induced dissociation (CID)-fragmentation patterns consistent with cyclized structures. Compared with 4,4' MDI, 2,2' and 2,4' isomers exhibit similar rapid reactivity with GSH and formation of bis(GSH)-MDI conjugates, but greater formation of cyclized mono(GSH) conjugates following extended reaction times (10 minutes to 2 hours). Further translational studies will be required to determine if the present in vitro findings extend to the complex lower airway microenvironment in vivo.

Mass spectrometry-based analysis of murine bronchoalveolar lavage fluid following respiratory exposure to 4,4'-methylene diphenyl diisocyanate aerosol

1. Diisocyanates are highly reactive electrophiles utilized in the manufacture of a wide range of polyurethane products and have been identified as causative agents of occupational allergic respiratory disease. However, in spite of the significant occupational health burden associated with diisocyanate-induced asthma, the mechanism of disease pathogenesis remains largely unknown. 2. To better understand the fate of inhaled diisocyanates, a nose-only aerosol exposure system was constructed and utilized to expose a BALB/c mouse model to an aerosol generated from 4,4'-methylene diphenyl diisocyanate (MDI). Tissue and bronchoalveolar lavage samples were evaluated 4 and 24 h post-exposure for evidence of diisocyanate-protein haptenation, and a label-free quantitative proteomics strategy was employed to evaluate relative changes to the protein content of the cellular fraction of the lavage fluid. 3. Following MDI aerosol exposure, expression of the number of proteins with immunological or xenobiotic metabolism relevance is increased, including endoplasmin, cytochrome P450 and argininosuccinate synthase. Western blot analysis indicated MDI-conjugated protein in the lavage fluid, which was identified as serum albumin. 4. Tandem mass spectrometry analysis of MDI-albumin revealed MDI conjugation occurs at a dilysine motif at Lys525, as well as at a glutamine-lysine motif at Lys414, in good agreement with previously published in vitro data on diisocyanate-conjugated serum albumin.

Biomonitoring Human Albumin Adducts: The Past, the Present, and the Future

Serum albumin (Alb) is the most abundant protein in blood plasma. Alb reacts with many carcinogens and/or their electrophilic metabolites. Studies conducted over 20 years ago showed that Alb forms adducts with the human carcinogens aflatoxin B1 and benzene, which were successfully used as biomarkers in molecular epidemiology studies designed to address the role of these chemicals in cancer risk. Alb forms adducts with many therapeutic drugs or their reactive metabolites such as β-lactam antibiotics, acetylsalicylic acid, acetaminophen, nonsteroidal anti-inflammatory drugs, chemotherapeutic agents, and antiretroviral therapy drugs. The identification and characterization of the adduct structures formed with Alb have served to understand the generation of reactive metabolites and to predict idiosyncratic drug reactions and toxicities. The reaction of candidate drugs with Alb is now exploited as part of the battery of screening tools to assess the potential toxicities of drugs. The use of gas chromatography-mass spectrometry, liquid chromatography, or liquid chromatography-mass spectrometry (LC-MS) enabled the identification and quantification of multiple types of Alb xenobiotic adducts in animals and humans during the past three decades. In this perspective, we highlight the history of Alb as a target protein for adduction to environmental and dietary genotoxicants, pesticides, and herbicides, common classes of medicinal drugs, and endogenous electrophiles, and the emerging analytical mass spectrometry technologies to identify Alb-toxicant adducts in humans.

Isotope Dilution UPLC-APCI-MS/MS Method for the Quantitative Measurement of Aromatic Diamines in Human Urine: Biomarkers of Diisocyanate Exposure

Urinary diamines are biomarkers of diisocyanate exposure. Diisocyanates are considered as skin and respiratory sensitizers and are the most frequently reported cause of occupational asthma. Herein we report on the development and validation of an ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the measurement of five aromatic diamines, 4,4'-methylenedianiline (MDA), 2,4-toluenediamine (4TDA), 2,6-toluenediamine (6TDA), 1,5-naphthalenediamine (NDA), and p-phenylenediamine (PPDA) in human urine. The method incorporates sample preparation steps, which include a 4 h acid hydrolysis followed by high-throughput solid-phase extraction prior to chromatographic separation. Chromatographic separation was achieved using a C18 reversed phase column with gradient elution of basic mobile phases (pH 9.2). The duty cycle of the method was less than 5 min, including both the column equilibration and autosampler movement. Analytical detection was performed using positive ion atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS/MS) in scheduled multiple reaction monitoring (sMRM) mode. Excellent linearity was observed over standard calibration curve concentration ranges of 3 orders of magnitude with method detection limit ranging from 10 to 100 pg/mL. The interday and intraday reproducibility and accuracy were within ±15%. This method is fast, accurate, and reproducible and is suitable for assessment of exposure to the most common aromatic diisocyanates within targeted groups as well as larger population studies such as the National Health and Nutrition Examination Survey (NHANES).

Comparison of biological effects with albumin adducts of 4,4'-methylenediphenyl diisocyanate in workers

Lung sensitization and asthma are the main health effects of 4,4'-methylenediphenyl diisocyanate (MDI). Albumin adducts (isocyanate-specific adducts) of MDI might be involved in the etiology of sensitization reactions. Albumin adducts of MDI were analyzed in sera of diisocyanate-exposed worker with and without diisocyanate occupational asthma (DA), as well as in exposed workers with and without diisocyanate-specific IgG antibodies. In DA-positive workers and IgG-positive workers, albumin adducts were significantly higher versus workers without DA and those who were specific IgG negative. The odds ratio to be DA-positive was 57 times larger for workers with adduct levels above 230 fmol/mg. The odds ratio to be IgG-positive was 10 times larger for workers with adduct levels above 113 fmol/mg. Therefore, albumin adducts appear to be a good predictor of the biological effects. The albumin-adduct levels in workers without biological effects were in the range of the adduct levels found in previous studies of healthy MDI-factory and construction site workers.