Studies on esterases in the chicken central nervous system (original) (raw)

Neurotoxic esterase in peripheral nerve: Assay, inhibition, and rate of resynthesis

Toxicology and Applied Pharmacology, 1982

The potential neurotoxicity of organophosphate esters is usually evaluated by measuring neurotoxic esterase (NTE) inhibition in brains taken from dosed birds. An improved method to measure NTE in peripheral nerve has been developed and used to compare brain, spinal cord, and peripheral nerve NTE inhibition both in vitro and in vivo after a single dose of several organophosphates. Brain and spinal cord NTE activities are a good mirror of NTE activity of the sciatic nerve. The rate of resynthesis of NTE in peripheral nerves after inhibition with an effective dose of a neurotoxic organophosphate was similar to that in other nervous tissues.

Histochemical demonstration of neurotoxic esterase

Journal of Histochemistry & Cytochemistry, 1989

We developed a histochemical method for localizing neurotoxic esterase (NTE), defined as the phenylvalerate (PV)-hydrolyzing esterase that is resistant to 40 microM paraoxon (A) but inactivated by paraoxon plus 50 microM mipafox (B). NTE is considered to be the target enzyme in the production of organophosphorus ester-induced delayed neurotoxicity (OPIDN). Cryostat sections were incubated in a medium containing alpha-naphthyl valerate and 6-benzamido-4-methoxy-m-toluidine diazonium chloride (fast violet B) after treatment with the above-mentioned inhibitors, leading to formation of an aqueous insoluble precipitate at sites of enzymatic activity. NTE activity was estimated as staining detectable in A but not in B. In the central nervous system (CNS) of chicken, NTE appeared to be present primarily in the somata of most neurons, but at sites indistinguishable from those of the other inhibitor-resistant and -sensitive alpha-naphthyl valerate-hydrolyzing esterases. It could not be disti...

Lymphocyte and brain neurotoxic esterase: Dose and time dependence of inhibition in the hen examined with three organophosphorus esters

Toxicology and Applied Pharmacology, 1986

1986). Toxicol. Appl. Pharmacol. 83,1-9. Certain organic phosphorus esters produce sensorimotor axonopathy in man and other species. There is an excellent correlation between the capacity of an organophosphorus compound to produce axonopathy and its ability to inhibit brain neurotoxic esterase (NTE) in hens. Because NTE is present in peripheral lymphocytes of both hen and man, it has been suggested that the lymphocyte enzyme might be useful both in experimental and clinical situations as an indicator of exposure to organophosphorus compounds producing axonopathy. Diethyl 4-nitrophenyl phosphate (paraoxon), tri-Zcresyl phosphate (TOCP), methyl 2,5dichloro+bromophenyl phenylphosphonothionate (leptophos), and di-n-butyl-2,2-dichlorovinyl phosphate (di-n-butyl dichlorvos, DBDCV) were used to examine the relationship between lymphocyte and brain NTE inhibition in hens. As expected, paraoxon (0.75 mgjkg) did not inhibit NTE in brain or lymphocytes. TOCP (10 to 100 mgjkg), leptophos (25 to 150 mg/kg), and DBDCV (1 .O to 4.0 mg/kg) inhibited both brain and lymphocyte NTE activity in a doserelated manner with good correlation of inhibition between tissues taken 24 hr after exposure (r2 = 0.53 to 0.67; p < 0.020 to 0.001). However, correlation of inhibition between tissues taken from animals killed 48 hr after exposures was poor (r' = 0.15 to 0.30; p < 0.10 to 0.05), with consistently less inhibition of lymphocyte NTE relative to brain NTE. This study indicates that assay of lymphocyte NTE can provide a good monitor of exposure to axonotoxic organophosphorus compounds within 24 hr between exposure and measurement. o 1986 Academic mess, IW.

Properties of partly preinhibited hen brain neuropathy target esterase

Chemico-Biological Interactions, 1993

NTE inhibitors cause different toxicological consequences (protection, induction or potentiation/promotion of neuropathy) depending on the order of dosing. These effects might be explained in terms of several phosphorylable sites with 'allosteric irreversible' behaviour. Brain neuropathy target esterase (NTE) has been preinhibited with phenylmethylsulphonyl fluoride (PMSF) (0, 5, 10, 15, 30 and 60 ~M) or with diisopropylphoshoro fluoridate (DFP) (0, 0.2, 0.5, and 1 #M) at 37°C for 30 min. After washing by centrifugation, tissues were then reinhibited with a range of PMSF (0 to 80 #M) or DFP (0 to 1 ~M) concentrations. The slopes of the inhibition curves (log % activity vs. concentration) of pretreated tissues were identical to those of the non-pretreated tissues, with non-distinguishable I50 values. It is concluded that allosteric effects are not likely to be involved in membrane-bound NTE of hen brain.

A stable preparation of hen brain neuropathy target esterase for rapid biochemical assessment of neurotoxic potential of organophosphates

Chemico-biological interactions, 1999

Neuropathy target esterase (NTE) is a molecular target for organophosphate-induced delayed neurotoxicity (OPIDN). This enzyme has proved to be an excellent tool for the assessment of neuropathic potential of organophosphates (OP), in particular by comparison of an OP inhibitory activity in vitro against NTE and acetylcholinesterase. A large-scale OP screening for delayed neurotoxicity was largely prevented by the lack of an available stable preparation of NTE. To obtain a stable NTE preparation the influence of intensive freezing and subsequent lyophilization of paraoxon-preinhibited (P2+P3) hen brain membrane fraction on NTE properties has been studied using two neuropathic OP: mipafox and O,O-dipropyldichlorovinyl phosphate (PrDChVP). It was shown that lyophilization preserved a high NTE specific activity and did not alter the inhibitor characteristics of the enzyme. A long-term storage study showed that lyophilized NTE preparation exhibited inhibitory features actually identical ...

Evidence for the existence of neurotoxic esterase in neural and lymphatic tissue of the adult hen

Biochemical Pharmacology, 1982

Hen brain and spinal cord contain a number of esterases that hydrolyze phenyl valerate (PV). Most of this activity is sensitive to inhibition by micromolar concentrations of paraoxon. Included among the paraoxon-resistant esterases is neurotoxic esterase (NTE), which is inhibited in vivo and in vitro by certain organophosphorus compounds, such as mipafox, which cause delayed neurotoxicity. Since published information on the NTE content of non-neural tissues was heretofore lacking, a comprehensive study was undertaken of the occurrence of this enzyme in tissues of the adult hen (Callus gallus domesticus), the species of choice in the study of organophosphorus-induced delayed neurotoxicity. Complete differential titration curves of PV esterase activity were obtained by preincubation of each tissue homogenate with a wide range of concentrations of paraoxon, a non-neurotoxic compound, plus or minus mipafox, a neurotoxic compound, followed by PV esterase assay. Brain NTE activity was determined to be 2426 + 104 nmoles.min-'+ (g wet weight)-' (mean f S.E.M.). Titration of other tissues resulted in the following NTE activities, expressed as percentages of brain NTE activity: spinal cord (21%), peripheral nerve (1.7%), gastrocnemius muscle (O%), pectoralis muscle (O%), heart (14%), liver (O%), kidney (O%), spleen (70%), spleen lymphocytes (26%), and blood lymphocytes (24%). Using an abbreviated procedure, erythrocytes and plasma showed no NTE activity. These results indicate that NTE has limited distribution among the tissues of the adult hen and is present in lymphatic as well as neural tissue.

Inhibition of Hen Brain Acetylcholinesterase and Neurotoxic Esterase by Chlorpyrifos in Vivo and Kinetics of Inhibition by Chlorpyrifos Oxon in Vitro: Application to Assessment of Neuropathic Risk 1

O,O-diethyl 3,5,6-trichloro-2-pyridyl phosphorothionate; Dursban) is a widely used broad-spectrum organophosphorus (OP) insecticide. Because some OP compounds can cause a sensory-motor distal axonopathy called OP compound-induced delayed neurotoxicity (OPIDN), CPS has been evaluated for this paralytic effect. Early studies of the neurotoxicity of CPS in young and adult hens reported reversible leg weakness but failed to detect OPIDN. More recently, a human case of mild OPIDN was reported to result from ingestion of a massive dose (about 300 mg/kg) in a suicide attempt. Subsequent experiments in adult hens (the currently accepted animal model of choice for studies of OPIDN) showed that doses of CPS in excess of the LDso in atropine-treated animals inhibited brain neurotoxic esterase (NTE) and produced mild to moderate ataxia. Considering the extensive use of CPS and its demonstrated potential for causing OPIDN at supralethal doses, additional data are needed to enable quantitative estimates to be made of the neuropathic risk of this compound. Previous work has shown that the ability of OP insecticides to cause acute cholinergic toxicity versus OPIDN can be predicted from their relative tendency to inhibit the intended target, acetylcholinesterase i Portions of this research were presented at the 28th annual meeting of the Society of Toxicology, (ACHE), versus the putative neuropathic target, NTE, in brain tissue. The present study was designed to clarify the magnitude of neuropathic risk associated with CPS exposures by measuring hen brain AChE and NTE inhibition following dosing in vivo and determining the bimolecular rate constant of inhibition (ki) for each enzyme by the active metabolite, CPS oxon (CPO), in vitro. CPS administered to atropine-treated adult hens at 0, 75, 150, and 300 mg/kg po in corn oil produced mean values for brain AChE inhibition 4 days after dosing of 0, 58, 75, and 86%, respectively, and mean values for brain NTE inhibition of 0, 21, 40, and 77%, respectively. Only the high dose (six times the unprotected LDso in hens) produced NTE inhibition above the presumed threshold of 70%, and these animals were in extremis from cholinergic toxicity at the time of euthanization despite continual treatment with atropine. When 150 mg/kg CPS po in corn oil was given to atropine-treated hens on Day 0, inhibition on Days 1, 2, 4, 8, and 16 for brain AChE was 86, 82, 72, 44, and 29%, respectively, and for brain NTE was 30, 28, 38, 29, and 6%, respectively. No signs of OPIDN were observed in any of the animals during the 16-day study period. Kinetic studies of the inhibition of hen brain AChE and NTE by CPO in vitro demonstrated that CPO exhibits high potency and extraordinary selectivity for its intended target, ACHE. The ki values were 15.5/~M -1 min -1 for AChE and 0.145/.tM -1 min -I for NTE. The calculated fixed-time (20-min) 15o values were 2.24 nM for AChE and 239 nM for NTE, yielding an /so ratio for NTE/ AChE of 107. These results may be compared with data compiled for other OP compounds with respect to NTE/AChE 15o ratios and the corresponding doses required to produce OPIDN relative to the LDs0. In general, NTE/AChE/5o ratios greater than 1 indicate that the dose required to produce OPIDN is greater than the LDs0. Taken together, the results of this study indicate that acute exposures to CPS would not be expected to cause OPIDN except under extreme conditions such as attempted suicides involving medically assisted survival of doses considerably in excess of the LDso. 9 1993 Society of Toxicology.

Inhibition of Neurotoxic Esterasein Vitroby Novel Carbamates

Toxicology and Applied Pharmacology, 1997

synthesized from different amino acid methyl ester precur-Inhibition of Neurotoxic Esterase in Vitro by Novel Carbamates. sors with the R-group of each compound being derived from RANDALL, J. C., AMBROSO, J. L., GROUTAS, W. C., BRUBAKER, the side chain of the starting amino acid. Accordingly, each M. J., AND RICHARDSON, R. J. (1997). Toxicol. Appl. Pharmacol. analog is designated by the amino acid precursor used for 143, 173-178.