Aging Of Neuropathy Target Esterase Research Articles

SARM1-mediated wallerian degeneration: A possible mechanism underlying organophosphorus-induced delayed neuropathy

Some organophosphorus compounds (OPs) can cause a type of delayed neurotoxicity in human being, which is known as organophosphorus-induced delayed neuropathy (OPIDN). Signs and symptoms of the patients include tingling and sensory loss of the hands and feet, followed by progressive muscle weakness in the lower and upper limbs, and ataxia. Pathologically, OPIDN are characterized by distal sensorimotor axonopathy due to the distal axonal degeneration of nerve tracts located in central and peripheral nervous systems. The morphological pattern of the distal axonopathy is similar to Wallerian degeneration that occurs after nerve injury in vitro. It is generally acknowledged that inhibition and subsequent aging of neuropathy target esterase (NTE) is required for the occurrence of OPIDN. However, the underlying mechanisms through which NTE triggers axonal degeneration in OPIDN is still largely unclear. Recently, sterile alpha and toll/interleukin receptor motif-containing protein 1（SARM1) has been identified as a key player in Wallerian degeneration. In physical and chemical transection of axons, SARM1 was found to promotes axon degeneration by hydrolyzing NAD+. By contrast, SARM1 deficiency could prevent neuron degeneration in response to a wide range of insults. Furthermore, SARM1 can also translocate to mitochondria and cause mitochondrial damage, thus triggering axon degeneration and neuron death. These findings suggested the existence of a pathway in axonal degeneration that might be targeted therapeutically. Here, we hypothesize that SARM1 activation after NTE inhibition and aging might be an etiological factor in OPIDN that regulates Wallerian-like degeneration. Analysing SARM1 mediated NAD degeneration pathway and its upstream activators in OPIDN could contribute to the development of novel therapies to treat OPIDN.

Analysis of the neurotoxic effects of neuropathic organophosphorus compounds in adult zebrafish

Inhibition and aging of neuropathy target esterase (NTE) by exposure to neuropathic organophosphorus compounds (OPs) can result in OP-induced delayed neuropathy (OPIDN). In the present study we aimed to build a model of OPIDN in adult zebrafish. First, inhibition and aging of zebrafish NTE activity were characterized in the brain by using the prototypic neuropathic compounds cresyl saligenin phosphate (CBDP) and diisopropylphosphorofluoridate (DFP). Our results show that, as in other animal models, zebrafish NTE is inhibited and aged by both neuropathic OPs. Then, a neuropathic concentration inhibiting NTE activity by at least 70% for at least 24 h was selected for each compound to analyze changes in phosphatidylcholines (PCs), lysophosphatidylcholines (LPCs) and glycerolphosphocholine (GPC) profiles. In spite to the strong inhibition of the NTE activity found for both compounds, only a mild increase in the LPCs level was found after 48 h of the exposure to DFP, and no effect were observed by CBDP. Moreover, histopathological evaluation and motor function outcome analyses failed to find any neurological abnormalities in the exposed fish. Thus, our results strongly suggest that zebrafish is not a suitable species for the development of an experimental model of human OPIDN.

In vitro study of the neuropathic potential of the organophosphorus compounds fenamiphos and profenofos: Comparison with mipafox and paraoxon

Organophosphorus-induced delayed neuropathy (OPIDN) is a central-peripheral distal axonopathy that develops 8–14days after poisoning by a neuropathic organophosphorus compound (OP). Several OPs that caused OPIDN were withdrawn from the agricultural market due to induction of serious delayed effects. Therefore, the development of in vitro screenings able to differentiate neuropathic from non-neuropathic OPs is of crucial importance. Thus, the aim of this study was to evaluate the differences in the neurotoxic effects of mipafox (neuropathic OP) and paraoxon (non-neuropathic OP) in SH-SY5Y human neuroblastoma cells, using the inhibition and aging of neuropathy target esterase (NTE), inhibition of acetylcholinesterase (AChE), activation of calpain, neurite outgrowth, cytotoxicity and intracellular calcium as indicators. Additionally, the potential of fenamiphos and profenofos to cause acute and/or delayed effects was also evaluated. Mipafox had the lowest IC50 and induced the highest percentage of aging of NTE among the OPs evaluated. Only mipafox was able to cause calpain activation after 24h of incubation. Concentrations of mipafox and fenamiphos which inhibited at least 70% of NTE were also able to reduce neurite outgrowth. Cytotoxicity was higher in non-neuropathic than in neuropathic OPs while the intracellular calcium levels were higher in neuropathic than in non-neuropathic OPs. In conclusion, the SH-SY5Y cellular model was selective to differentiate neuropathic from non-neuropathic OPs; fenamiphos, but not profenofos presented results compatible with the induction of OPIDN.

In vitro study of the neuropathic potential of the organophosphorus compounds trichlorfon and acephate

Organophosphorus-induced delayed neuropathy (OPIDN) is a central and peripheral distal axonopathy characterized by ataxia and paralysis. Trichlorfon and acephate are two organophosphorus compounds (OPs) used worldwide as insecticide and which cause serious effects to non-target species. Despite that, the neuropathic potential of these OPs remains unclear. The present study addressed the neurotoxic effects and the neuropathic potential of trichlorfon and acephate in SH-SY5Y human neuroblastoma cells, by evaluating inhibition and aging of neuropathy target esterase (NTE), inhibition of acetylcholinesterase (AChE), neurite outgrowth, cytotoxicity and intracellular calcium. Additionally, the effects observed were compared to those of two well-studied OPs: mipafox (known as neuropathic) and paraoxon (known as non-neuropathic). Trichlorfon and mipafox presented the lowest percentage of reactivation of inhibited NTE and the lowest ratio IC50 NTE/IC50 AChE. Moreover, they caused inhibition and aging of at least 70% of the activity of NTE at sub-lethal concentrations. All these effects have been associated with induction of OPIDN. When assayed at these concentrations, trichlorfon and mipafox reduced neurite outgrowth and increased intracellular calcium, events implicated in the development of OPIDN. Acephate caused effects similar to those caused by paraoxon (non-neuropathic OP) and was only able to inhibit 70% of NTE activity at lethal concentrations. These findings suggest that trichlorfon is potentially neuropathic, whereas acephate is not.

Further studies toward a mouse model for biochemical assessment of neuropathic potential of organophosphorus compounds.

Inhibition and aging of neuropathy target esterase (NTE) by neuropathic organophosphorus (OP) compounds triggers OP compound-induced delayed neuropathy (OPIDN), whereas inhibition of acetylcholinesterase (AChE) produces cholinergic toxicity. The neuropathic potential of an OP compound is defined by its relative inhibitory potency toward NTE vs. AChE assessed by enzyme assays following dosing in vivo or after incubations of direct-acting compounds or active metabolites with enzymes in vitro. The standard animal model of OPIDN is the adult hen, but its large size and high husbandry costs make this species a burdensome model for assessing neuropathic potential. Although the mouse does not readily exhibit clinical signs of OPIDN, it displays axonal lesions and expresses brain AChE and NTE. Therefore, the present research was performed as a further test of the hypothesis that inhibition of mouse brain AChE and NTE could be used to assess neuropathic potential using mouse brain preparations in vitro or employing mouse brain assays following dosing of OP compounds in vivo. Excellent correlations were obtained for inhibition kinetics in vitro of mouse brain enzymes vs. hen brain and human recombinant enzymes. Furthermore, inhibition of mouse brain AChE and NTE after dosing with OP compounds afforded ED(50) ratios that agreed with relative inhibitory potencies assessed in vitro. Taken together, results with mouse brain enzymes demonstrated consistent correspondence between in vitro and in vivo predictors of neuropathic potential, thus adding to previous studies supporting the validity of a mouse model for biochemical assessment of the ability of OP compounds to produce OPIDN.

Neuropathy target esterase (NTE): overview and future

Neuropathy target esterase (NTE) was discovered by M.K. Johnson in his quest for the entity responsible for the striking and mysterious paralysis brought about by certain organophosphorus (OP) esters. His pioneering work on OP neuropathy led to the view that the biochemical lesion consisted of NTE that had undergone OP inhibition and aging. Indeed, nonaging NTE inhibitors failed to produce disease but protected against neuropathy from subsequently administered aging inhibitors. Thus, inhibition of NTE activity was not the culprit; rather, formation of an abnormal protein was the agent of the disorder. More recently, however, Paul Glynn and colleagues showed that whereas conventional knockout of the NTE gene was embryonic lethal, conditional knockout of central nervous system NTE produced neurodegeneration, suggesting to these authors that the absence of NTE rather than its presence in some altered form caused disease. We now know that NTE is the 6th member of a 9-protein family called patatin-like phospholipase domain-containing proteins, PNPLA1–9. Mutations in the catalytic domain of NTE (PNPLA6) are associated with a slowly developing disease akin to OP neuropathy and hereditary spastic paraplegia called NTE-related motor neuron disorder (NTE-MND). Furthermore, the NTE protein from affected individuals has altered enzymological characteristics. Moreover, closely related PNPLA7 is regulated by insulin and glucose. These seemingly disparate findings are not necessarily mutually exclusive, but we need to reconcile recent genetic findings with the historical body of toxicological data indicating that inhibition and aging of NTE are both necessary in order to produce neuropathy from exposure to certain OP compounds. Solving this mystery will be satisfying in itself, but it is also an enterprise likely to pay dividends by enhancing our understanding of the physiological and pathogenic roles of the PNPLA family of proteins in neurological health and disease, including a potential role for NTE in diabetic neuropathy.

An alternative in vitro method for detecting neuropathic compounds based on acetylcholinesterase inhibition and on inhibition and aging of neuropathy target esterase (NTE)

Organophosphorus-induced delayed polyneuropathy (OPIDP) is a syndrome induced by certain organophosphorus compounds (OPs) through a mechanism based on the inhibition and further modification (aging) of neuropathy target esterase (NTE). OECD guidelines for testing the capability of OPs to trigger OPIDP include two in vivo tests with hens. Activities of acetylcholinesterase and NTE found in SH-SY5Y human neuroblastoma cells were inhibited by 10 different OPs with kinetics similar to those found with chicken brain enzymes (model system for in vivo and in vitro–ex vivo assays). NTE in SH-SY5Y cells inhibited by these OPs aged and reactivated similarly to that described for hen brain NTE ex vivo. In short, we have developed an alternative methodology for predicting the capability of OPs to induce OPIDP based on the inhibition kinetics of acetylcholinesterase and NTE and on the capability of OPs to age the inhibited NTE from SH-SY5Y cell line. The results obtained always agreed with the previously reported ex vivo results with hen brain. The developed methodology correctly predicted the neuropathic potential of the tested OPs in eight cases. The in vivo–in vitro discrepancies with two of the tested compounds can be explained on the basis of differences between in vivo and in vitro biotransformation.

The Homeostasis of Phosphatidylcholine and Lysophosphatidylcholine in Nervous Tissues of Mice was not Disrupted after Administration of Tri-o-cresyl Phosphate

Neuropathy target esterase (NTE) is proven to act as a lysophospholipase (LysoPLA) in mice and phospholipase B (PLB) in cultured mammalian cells. In sensitive species, organophosphate (OP)-induced delayed neurotoxicity is initiated when NTE is inhibited by > 70% and then aged. It is hypothesized that homeostasis of phosphatidylcholine (PC) and/or lysophosphatidylcholine (LPC) in mice might be disrupted by the OPs since NTE and other phospholipases could be inhibited. To test this hypothesis, we treated mice using tri-o-cresyl phosphate (TOCP), which can inhibit and age NTE. Phenylmethylsulfonyl fluoride (PMSF), which inhibits NTE but cannot age, was used as a negative control. Effects on activity of NTE, LysoPLA, and PLB, the levels of PC, LPC, and glycerophosphocholine (GPC), and the aging of NTE in the brain, spinal cord, and sciatic nerve were examined. The results showed that the activities of NTE, NTE-LysoPLA, LysoPLA, NTE-PLB, and PLB were significantly inhibited in both TOCP- and PMSF-treated mice, and the inhibition of NTE and NTE-LysoPLA or NTE-PLB showed a high correlation coefficient. The NTE inhibited by TOCP was of the aged type, while nearly all NTE inhibited by PMSF was of the unaged type. Although the GPC level was remarkedly decreased, no significant change of PC and LPC levels was observed. However, the inhibition of these enzymes in mice by TOCP exhibited different characteristics from the TOCP-treated hens that we previously reported, which indicates that these enzymes were inhibited and then recovered more rapidly in mice than in hens. All results suggest that PC and LPC homeostasis was not disrupted in mice after exposure to TOCP. Differences in inhibition of NTE, LysoPLA, and PLB activities by TOCP between mice and hens may elucidate why these two species display different signs after exposure to the same neuropathic OPs.

QUANTITATIVE STRUCTURE-ACTIVITY RELATIONSHIPS PREDICT THE DELAYED NEUROTOXICITY POTENTIAL OF A SERIES OF O-ALKYL-O-METHYLCHLOROFORMIMINO PHENYLPHOSPHONATES

Inhibition of acetylcholinesterase (AChE) versus inhibition and aging of neuropathy target esterase (NTE) by organophosphorus (OP) compounds in vivo can give rise to distinct neurological consequences: acute cholinergic toxicity versus OP compound-induced delayed neurotoxicity (OPIDN). Previous work has shown that the relative potency of an OP compound to react with NTE versus AChE in vitro may predict its capability to produce OPIDN. The present study was conducted to evaluate further the validity of such predictions and to enhance them with quantitative structure-activity relationships (QSAR) using a homologous series of alkyl phenylphos-phonates, (RO)C6H5P(O)ON=CClCH3 (PhP; R=alkyl). Neuropathic potential of PhP was assessed by measuring ki(NTE)/ki(AChE) ratios in vitro and comparing these with ED50 ratios in vivo. Selectivity for NTE increased with rising R-group hydrophobicity. The ki(NTE)/ki(AChE) ratios were 0.42 (methyl), 3.6 (ethyl), 15 (isopropyl), 36 (propyl), 69 (isobutyl), 105 (butyl), and 124 (pentyl). Ratios >1 suggest the potential to produce OPIDN at doses lower than the LD50. Inhibition of NTE and AChE in hen brain in vivo was studied 24 h after im injection of hens with increasing doses of methyl and butyl derivatives. Analysis of dose-response curves yielded ED50(AChE)/ED50(NTE) ratios of 0.86 for methyl PhP and 22.1 for butyl PhP. These results predict that the butyl derivative should be more neuropathic than the methyl analogue. Excellent correspondence between in vivo and in vitro predictions of neuropathic potential indicate that valid predictive QSAR models may be based on the in vitro approach. Adoption of this system would result in reducing experimental animal use, lowering costs, accelerating data production, and enabling standardization of a biochemically based risk assessment of the neuropathic potential of OP compounds.

Inhibition and aging of neuropathy target esterase by the stereoisomers of a phosphoramidate related to methamidophos

Discrepancies in the aging reaction between neuropathy target esterase (NTE) inhibited in vitro and in vivo by racemic mixtures of O-alkyl O-2,5-dichlorophenyl phosphoramidates have been observed. It suggested the existence of differences in the interactions (inhibition and aging) between NTE and each stereoisomers of the above mentioned compounds. In order to verify this hypothesis, stereoisomers of O-hexyl O-2,5-dichlorophenyl phosphoramidate (HDCP) were isolated by chiral column chromatography, followed by the evaluation of NTE inhibition and aging for each stereoisomers. The loss of reactivation capacity by KF was used as criterion of aging. The stereoisomer S-(−)-HDCP inhibited hen brain NTE with an I 50 of 7.6 nM for 30 min of incubation, this being similar to the value obtained for the racemic mixture ( I 50=6.2 nM), and much lower than that recorded for R-(+)-HDCP ( I 50=191 nM). NTE inhibited by HDCP racemic mixture and the stereoisomer S-(−)-HDCP was reactivated by KF after 20 h of incubation at 37°C. The NTE inhibited by R-(+)-HDCP could not be fully reactivated after inhibition.

Inhibition and aging of neuropathy target esterase by organophosphorus compound in bovine chromaffin cells

Inhibition and aging of neuropathy target esterase by organophosphorus compound in bovine chromaffin cells

Inhibition and aging of neuropathy target esterase by organophosphorus compound in bovine chromaffin cells

Inhibition and aging of neuropathy target esterase by organophosphorus compound in bovine chromaffin cells