The toxicity of organophosphate compounds towards cultured PC12 cells.

The effects of three representative organophosphates (OPs), tricresyl phosphate (TCP), triphenyl phosphite (TPP) and paraoxon (POX) on the proliferation and viability of rat PC12 pheochromocytoma cells were studied. With respect to its IC50, TCP was at least an order of magnitude more potent in its antiproliferative activity than both TPP and POX. All test OPs were cytotoxic at concentrations inhibiting cell proliferation. No compound inhibited cell growth below 10 micrograms/ml. For TCP and TPP the estimated IC50 values from proliferation assays were lower than published LD50 values in vivo, whereas paraoxon was much less toxic in vitro than in vivo. Subcytotoxic levels of TCP (1 micrograms/ml) were found to inhibit the maintenance of neurites on cells grown in the presence of nerve growth factor.