The inhibitory effect of neuropathic organophosphate esters on neurite outgrowth in cell cultures: A basis for screening for delayed neurotoxicity.

Organophosphates have previously been tested for the induction of delayed neuropathy in adult hens. An alternative in vitro test, which avoids the severe suffering caused by the test in hens, has been developed using permanent cell lines from a rat-brain glioma (C-6) or from a mouse-brain neuroblastoma (N-18). Addition of dibutyryl cAMP to these cell cultures triggers the development of neurite-like processes; the development of these processes is inhibited by the addition of various organophosphate compounds and this inhibition serves as an indicator of neurotoxicity. 26 compounds with positive results in the in vivo test in hens, and eight analogues with negative results were tested in vitro. An almost perfect correlation between the in vivo and in vitro results was found; two compounds with weak positive results in vitro (O,O,S-trimethyl phosphorothioate and O,S,S-trimethyl phosphorothioate) yielded negative results in hens but this discrepancy may be related to their bioavailability in hens. The in vitro test is recommended to avoid the pain and stress caused by testing in vivo in hens.