Effect of selected insecticides on growth rate and stress protein expression in cultured human A549 and SH-SY5Y cells

Two organochlorines (dienochlor, endosulfan) and one neonicotinoid (imidacloprid) insecticides were investigated as putative cellular aggressors, both as pure chemicals and as commercial formulations, in order to evaluate the additional toxicity due to additives present in the commercial formulations. Toxicity was evaluated on human cells in vitro, by culturing neuronal SH-SY5Y and pulmonary A549 cell lines for 3 days in the presence of increasing concentrations of the selected pesticides. LOEC (lowest observed effect concentration), IC50 (concentration leading to a 50% decrease of cell growth) and expression changes of molecular chaperones involved in cellular protein quality control were determined. The investigated molecular chaperones were the cytosolic resident heat shock proteins (HSP27, HSP72/73, and HSP90) and the glucose regulated proteins (GRP78, GRP94) located in the endoplasmic reticulum (ER). Organochlorines were found to be the most toxic in both A549 and SH-SY5Y cells, IC50 being respectively 0.95 and 0.36 μM for dienochlor, 34 and 20 μM for endosulfan, 1.8 and 1.5 mM for imidacloprid. This shows that neuronal cells were more sensitive than pulmonary cells. LOEC and IC50 appeared at lower concentrations of active molecule when using the commercial formulations Techn’ufan (endosulfan) and Confidor (imidacloprid), indicating an additional adverse effect of additives. Insecticide concentrations higher than IC50 were found to induce an underexpression of all cytosolic HSPs, probably resulting from a general inhibition of protein synthesis. HSP27 was found to be underexpressed at concentrations of imidacloprid or endosulfan (as Techn’ufan) lower than IC50. This underexpression of the anti-apoptotic HSP27 could contribute to the increase of cell mortality. GRP78 was up-regulated by endosulfan in A549, but not in SH-SY5Y cells, suggesting a damaging effect on proteins specific to pulmonary cells. Conversely, HSP72/73 was found to be down-regulated, resulting probably from the ER unfolded protein response (UPR) as previously reported [Skandrani, D., Gaubin, Y., Vincent, C., Beau, B., Murat, J.C., Soleilhavoup, J.P., Croute, F., 2006. Relationship between toxicity of selected insecticides and expression of stress protein (HSP, GRP) in cultured human cells: effects of commercial formulations versus pure active molecules. Biochim. Biophys. Acta 1760 (1), 95–103].