DISCRIMINATION OF CARBOXYLESTERASES OF CHICKEN NEURAL TISSUE BY INHIBITION WITH A NEUROPATHIC, NONNEUROPATHIC ORGANOPHOSPHORUS COMPOUNDS AND NEUROPATHY PROMOTER

Carboxylesterases are enzymes present in neural and other tissues that are sensitive to organophosphorus compounds. The esterase activity in particulate forms, resistant to paraoxon and sensitive to mipafox hav e been implicated in the initiation of organophosphorus-induced delaye d polyneuropathy (OPIDP) and is called neuropathy target esterase (P-N TE). Certain esterases inhibitors such as phenylmethylsulfonyl fluorid e (PMSF), can also irreversibly inhibit P-NTE and by this mechanism PM SF 'protects' from further effect of neuropathic OPs. However, if PMSF is dosed after a low non-neuropathic dose of a neuropathic OF, its ne urotoxicity is 'promoted', causing severe neuropathy. The molecular ta rget of promotion has not yet been identified and it has been shown th at it is unlikely to be the P-NTE. In order to discriminate the differ ent esterases, we used non-neuropathic (paraoxon), and neurophatic org anophosphorus compounds (mipafox, DFP) and a neuropathy promoter (PMSF ). They were used alone or in concurrent inhibition to study particula te and soluble fractions of brain, spinal cord and sciatic nerve of ch icken. From the experimental data, a matrix was constructed and equati ons deduced to estimate the proportions of the different potential act ivity fractions that can be discriminated by their sensitivity to the tested inhibitors. It was deduced that only combinations of up to thre e inhibitors can be used for the analysis with consistent results. In all tissues, inside the paraoxon sensitive activity, most of the activ ity was sensitive either to mipafox, to PMSF or both. In all fractions , except brain soluble fractions, within the paraoxon resistant activi ty, a mipafox sensitive component was detected that is operationally c onsidered NTE (P-NTE and S-NTE in particulate and soluble fractions, r espectively). Most of this activity Nas also sensitive to PMSF, and th is should be considered the target of organophosphorus inducing neurop athy and of PMSF protective effect. Either in brain and spinal cord. a significant amount of the activity resistant to 40 mu M paraoxon and 250 mu M mipafox (usually called 'C' activity) is sensitive to PMSF. I t could be a good candidate to contain the target of the promotion eff ect of PMSF as well as the S-NTE activity that is also PMSF sensitive. (C) 1997 Elsevier Science Ireland Ltd.