Neurotoxicity and esterase inhibition studies in hen brain and lymphocytes

Inhibition of neuropathy target esterase (NTE) and its dealkylation ("aging") is important in the genesis of organophosphate (OP) induced delayed neuropathy (OPIDN). An in vitro assay was devised which incorporates metabolic activation, NTE inhibition and measurement of aging into one assay. This approach and in vivo NTE aging assays were used to evaluate the delayed neuropathic potential of various forms of the pesticide methamidophos (analytical grade, technical grade, L({dollar}-{dollar}) and D(+) isomer). Technical methamidophos produced more "aged" NTE than analytical methamidophos (22% versus 6% aged NTE in vivo at 35 mg/kg dose). GC-MS and TLC analysis revealed contaminants in technical methamidophos (phosphoroamidothioic acid, methyl-O,O-dimethyl ester and phosphorothioic acid, O,O,S-trimethyl ester) that may have contributed to the higher level of aged NTE. L({dollar}-{dollar}) and D(+) isomers of methamidophos (5 mM) in vitro produced 6 and 4% aged NTE, respectively, making a stereochemical-related delayed neurotoxic effect unlikely.; The delayed neuropathic potential of acephate was determined by comparing its ability to inhibit brain AChE to its capacity to inhibit NTE. Inhibition studies in vivo indicate that acephate is a stronger inhibitor of AChE than of NTE. The ID{dollar}sb{lcub}50{rcub}{dollar} for acephate inhibition of AChE (10.2 mg/kg) and NTE (1260 mg/kg) suggests that acute exposure to acephate will not induce OPIDN in hens. Treatment of chick embryo brain in vitro with acephate (1.5 to 12 mM, 1 hour incubation; with metabolic activation) produced low levels of aged NTE (5%) and low total NTE inhibition ({dollar}<{dollar}25%).; NTE from cultured lymphocytes was studied. Avian lymphoid cell line (RP9) NTE specific activity was less than that of primary hen lymphocytes. Most of this activity (92%) was associated with the microsomal fraction in both RP9 and primary lymphocytes fractionated by centrifugation. A (3H) -DFP labeling profile of primary hen lymphocyte membrane proteins using SDS-PAGE gels revealed peaks corresponding to 62,000-M{dollar}sb{lcub}rm r{rcub}{dollar}, 111,000-M{dollar}sb{lcub}rm r{rcub}{dollar} and 155,000-M{dollar}sb{lcub}rm r{rcub}{dollar} proteins.; Primary hen lymphocytes exposed to 0.1 mM technical methamidophos for 2 hours resulted in 50% NTE inhibition. NTE activity recovered in cultured lymphocytes after exposure to 0.5 mM methamidophos for 1 hour. Cultures had 39% of control activity immediately after exposure and 59% 24 hours later.