Organophosphate cytotoxicity: the effects on protein metabolism in cultured neuroblastoma cells

Diisopropylfluorophosphate has been reported to cause an early inhibition of proteosynthesis in the spinal ganglia of cats. If organophosphorus compounds can cause a partial blockage of protein synthesis, normal turnover of neuronal proteins could establish conditions similar to those which ocur in Wallerian degeneration. In this study neuroblastoma 2-A cells, a homogenous cell system which exhibits many of the functional properties of normal neurons, was used to establish dose-response relationships of three organophosphorus compounds: Tri-o-tolyl-phosphate (TOTP), Diisopropylfluorophosphate (DFP) and dicrotophos. The incorporation of 14C from glucose was used as an indicator of metabolic activity and the incorporation of L-leu-cine-14C as an indicator of proteosynthetic activity. The rates of incorporation of labeled precursors as effected by three dose levels of each organophosphorus compound were measured in logarithmically growing cells and in cells in a stationary growth phase in media without serum. The cells were also observed under phase-contrast microscopy. The organophosphorus compounds caused the neurites to have a shrunken, rough and irregular appearance. Swelling along the length of the neurites were also observed, especially with the DFP-treated cells. All three compounds caused a dose-related reduction in the accumulation of 14C activity from glucose which was probably a measure of cytotoxicity. DFP and TOTP caused an inhibition of the uptake of leucine-14C while dicrotophos did not. The results suggest that neurotoxic organophosphate compounds depress the rate of protein synthesis which may be responsible for the degenerative syndrome.