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 occ upational asthma in exposed workers. TDI-induced asthma is associated with airway epithelium injury and repair, and subepithelial fibrosis. We investi gated the effect of TDI and its hydrolysis products, the 2,4- and 2,6-tolue nediamines (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 quie scent 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 2 0% 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 (10-1 5%, p < 0.05), whereas it tended to trigger cell growth at concentrations h igher than 10(-5) mol/L. 2,6-TDA exhibited both a cytotoxic and a prolifera tive effect on HLFs that depended on concentration, time of exposure and ce ll culture density. Significant cytotoxicity was only observed after 24 h o f 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 b oth a cytotoxic and a growth stimulatory effect on these cells. TDI and 2,4 -TDA are thus suggested to contribute to airway epithelium damage associate d with TDI-induced asthma, whereas 2,6-TDA might either trigger epithelial damage or induce cell proliferation that could contribute to epithelium rep air or subepithelial fibrosis.