Effect of toluene diisocyanate and its corresponding amines on viability and growth of human lung fibroblasts in culture

Toluene diisocyanate (TDI) is a highly volatile chemical known to cause occupational asthma in exposed workers. TDI-induced asthma is associated with airway epithelium injury and repair, and subepithelial fibrosis. We investigated the effect of TDI and its hydrolysis products, the 2,4- and 2,6-toluenediamines (TDA), on viability and growth of human lung fibroblasts (HLFs) in culture, using a tetrazolium-based cell viability assay. The effects of increasing concentrations of each of these chemicals were evaluated on quiescent cells seeded at two densities (2500 and 5000 cells/well) and treated for 24 or 48 h. TDI (10^–4–10^–5 mol/L, as a mixture of 80% 2,4-TDI and 20% 2,6-TDI) exhibited a partial but significant cytotoxic effect (10–24%, p<0.05) on HLFs. This effect was observed at both cell densities, and was time- and concentration-dependent. 2,4-TDA, at lower concentrations (10^–8–10^–6 mol/L) applied for 48 h, also partially reduced HLF viability (10–15%, p<0.05), whereas it tended to trigger cell growth at concentrations higher than 10^–5 mol/L. 2,6-TDA exhibited both a cytotoxic and a proliferative effect on HLFs that depended on concentration, time of exposure and cell culture density. Significant cytotoxicity was only observed after 24 h of treatment with 10^–7–10^–6 mol/L 2,6-TDA, and reached greater intensity in cells cultured at the highest density. In contrast, 2,6-TDA stimulated HLF growth only after 48 h of incubation at 10^–4 mol/L on cells cultured at the lowest density. Taken together, our results showed that TDI and 2,4-TDA somewhat decreased HLF viability, whereas 2,6-TDA appeared to exhibit both a cytotoxic and a growth stimulatory effect on these cells. TDI and 2,4-TDA are thus suggested to contribute to airway epithelium damage associated with TDI-induced asthma, whereas 2,6-TDA might either trigger epithelial damage or induce cell proliferation that could contribute to epithelium repair or subepithelial fibrosis.