Analysis of the reactivity of [14C]toluene diisocyanate (TDI) in an isolated, perfused lung model

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.

Determination of isocyanate specific albumin-adducts in workers exposed to toluene diisocyanates

Toluene diisocyanates (2,4-TDI and 2,6-TDI) are important intermediates in the chemical industry. Among the main damages after low levels of TDI exposure are lung sensitization and asthma. It is therefore necessary to have sensitive and specific methods to monitor isocyanate exposure of workers. Urinary metabolites or protein adducts have been used as biomarkers in workers exposed to TDI. However, with these methods it was not possible to determine if the biomarkers result from exposure to TDI or to the corresponding toluene diamines (TDA). This work presents a new procedure for the determination of isocyanate-specific albumin adducts. Isotope dilution mass spectrometry was used to measure the adducts in albumin present in workers exposed to TDI. 2,4-TDI and 2,6-TDI formed adducts with lysine: N(ϵ)-[({3-amino-4-methylphenyl}amino)carbonyl]-lysine, N(ϵ)-[({5-amino-2-methylphenyl}amino)carbonyl]-lysine, and N(ϵ)- [({3-amino-2-methylphenyl}amino)carbonyl]-lysine. In future studies, this new method can be applied to measure TDI-exposures in workers.

Comparison of the binding potential of various diisocyanates on DNA in vitro

Inhalation of diisocyanate vapors is associated with immediate-type hypersensitivity reactions and direct toxic responses. The genotoxic effects of diisocyanates have not been clarified. The aim of this study was to examine the changes in DNA following in vitro exposure to three most commonly used diisocyanates (toluene diisocyanate, TDI; methylenediphenyl-4,4'-diisocyanate, MDI; and hexamethylene diisocyanate, HDI) and to compare their binding potential using melting behavior of DNA and electrophoresis studies in DNA. Following incubation of DNA with MDI (pure and mix) and HDI we found no differences in the melting behavior compared to the control calf thymus DNA. However, DNA treated with TDI showed differences in the shape of the native DNA curves due to changes in hyperchromicity and exhibited 14% more DNA reconstitution after renaturation. The small changes in the melting behavior of native DNA do not suggest the formation of DNA intrastrand cross-links but rather conformational changes of single- and double-stranded DNA. These conformational changes were further explored by agarose electrophoresis of native and denatured calf thymus DNA. Control and all diisocyanate-exposed DNA showed no differences in the size of native DNA fragments. Conversely, electrophoresis of TDI mix-incubated DNA, following denaturation, showed a distinct reduction in the double-stranded DNA fragment size compared to the control, MDI-denatured (pure and mix), and HDI-denatured DNA. These findings may help to better understand the mechanisms of the genotoxic effect of TDI.

An isolated perfused lung model with real time data collection and analysis of lung function

Our primary purpose in making this report has been to describe an isolated perfused lung system which permits the real time collection and analysis of lung mechanical functioning. The distinct advantage of our system lies in its capacity for breath by breath data acquisition and analysis. In addition, because of the modular nature of the components, the system can be readily expanded or contracted depending on the type of experiment being conducted. As configured, the lung mechanic parameters of air flow, lung volume, transpulmonary pressure, pulmonary artery pressure, weight, resistance, elastance (inverse of compliance), and positive end expiratory pressure were monitored, recorded, and evaluated simultaneously throughout the experimental period. We present the results of a 3-h study with control lungs illustrating the stability of these measurements throughout the entire period. Also included is a brief discussion of 3-h studies which show a progressive loss of viability in lungs treated with the redox cycler nitrofurantoin.