Oxidative stress resulting from exposure of a human salivary gland cells to paraoxon: An in vitro model for organophosphate oral exposure

Paraoxon exposure induces superoxide formation in human salivary gland cells at 4h as determined by fluorescence assay (dihydroethidium). •Human salivary gland (HSG) cells show a cytotoxic response to paraoxon exposure when analyzed by MTT assays but not LDH assays.•Paraoxon induces the formation of superoxide in HSG cells as demonstrated by dihydroethidium analysis.•Genes associated with reactive oxygen species were upregulated in paraoxon-treated HSG cells. Organophosphate (OP) compounds are used as insecticides, acaricides, and chemical agents and share a common neurotoxic mechanism of action. The biochemical alterations leading to many of the deleterious effects have been studied in neuronal cell lines, however, non-neuronal toxic effects of OPs are far less well characterized in vitro, and specifically in cell lines representing oral routes of exposure. To address this void, the human salivary gland (HSG) cell line, representing likely interactions in the oral cavity, was exposed to the representative OP paraoxon (PX; O,O-diethyl-p-nitrophenoxy phosphate) over a range of concentrations (0.01–100μM) and analyzed for cytotoxicity. PX induced cytotoxicity in HSG cells at most of the exposure concentrations as revealed by MTT assay, however, the release of LDH only occurred at the highest concentration of PX tested (100μM) at 48h. Slight increases in cellular ATP levels were measured in PX-exposed (10μM) HSG cells at 24h. Exposing HSG cells to 10μM PX also led to an increase in DNA fragmentation prior to loss of cellular membrane integrity implicating reactive oxygen species (ROS) as a trigger of toxicity. The ROS genes gss, gstm2, gstt2 and sod2 were upregulated, and the presence of superoxide following 10μM PX exposure was determined via dihydroethidium fluorescence studies further implicating PX-induced oxidative stress in HSG cells.