STUDIES ON THE ROLE OF NEUROTOXIC ESTERASE IN ORGANOPHOSPHOROUS COMPOUND-INDUCED DELAYED NEUROTOXICITY.

摘要

Neurotoxic esterase (NTE) is a protein with esterase activity that is proposed to be the site at which organophosphorous compound (OP) induced delayed neurotoxicity (OPIDN) is initiated. The role of NTE in OPIDN in unknown. The studies described in this dissertation were designed to further elucidate potential mechanisms underlying the involvement of NTE in OPIDN.; The prophylactic effect of phenylmethylsulfonyl fluoride (PMSF) was found to be correlated with the time course of inhibition of NTE by PMSF and two neurotoxic OPs, and is therefore most likely to be due to the prevention of the binding of the OP to the initiation site.; A membrane bound protein labelled with ('3)H-diisopropyl phosphorofluoridate (DiFP) with an apparent molecular weight of 160K was the major binding site with a specificity similar to that of NTE. DiFP was found to phosphorylate this protein at a rate similar to the rate at which NTE is inhibited. Two other bands (99K and 115K) were also found to have a paraoxon-sensitive, mipafox-insensitive component.; Recovery of NTE activity following in vivo inhibition by DiFP was found to be slower in hen brain when compared to chicks or rats. Although recovery in hen sciatic nerve was found to be more rapid than in brain, there was a delay in the onset of recovery in nerve which increased with the distance from the spinal cord, which may contribute to the greater sensitivity of longer axons to OPIDN. Differences in recovery in peripheral nerve were not found to be correlated with differences in susceptibility between species or between young and adult animals.; The anterograde transport rate for NTE was estimated to be about 300 mm/day. Since exchange between mobile and stationary transport pools appeared to be rapid, it is concluded that the proximo-distal delay in NTE recovery is due to a dilution of newly synthesized NTE by inhibited NTE as it is transported down the nerve.; Paraoxon was found to reversibly reduce the reaction rate of mipafox with two NTE isozymes (NTE(,A) and NTE(,B)). A greater reduction in the reaction rate of mipafox with NTE(,A) makes distinction of the two isozymes in the presence of paraoxon impossible. The ratios of these isozymes were found to be similar in brain and sciatic nerve. Since there was clearly no NTE(,A) in three cultured cell lines derived from human lymphocytes, NTE(,A) may be unique to the nervous system.