Microglia Remodelling and Neuroinflammation Parallel Neuronal Hyperactivation Following Acute Organophosphate Poisoning.

Organophosphate (OP) compounds include highly toxic chemicals widely used both as pesticides and as warfare nerve agents. Existing countermeasures are lifesaving, but do not alleviate all long-term neurological sequelae, making OP poisoning a public health concern worldwide and the search for fully efficient antidotes an urgent need. OPs cause irreversible acetylcholinesterase (AChE) inhibition, inducing the so-called cholinergic syndrome characterized by peripheral manifestations and seizures associated with permanent psychomotor deficits. Besides immediate neurotoxicity, recent data have also identified neuroinflammation and microglia activation as two processes that likely play an important, albeit poorly understood, role in the physiopathology of OP intoxication and its long-term consequences. To gain insight into the response of microglia to OP poisoning, we used a previously described model of diisopropylfluorophosphate (DFP) intoxication of zebrafish larvae. This model reproduces almost all the defects seen in poisoned humans and preclinical models, including AChE inhibition, neuronal epileptiform hyperexcitation, and increased neuronal death. Here, we investigated in vivo the consequences of acute DFP exposure on microglia morphology and behaviour, and on the expression of a set of pro- and anti-inflammatory cytokines. We also used a genetic method of microglial ablation to evaluate the role in the OP-induced neuropathology. We first showed that DFP intoxication rapidly induced deep microglial phenotypic remodelling resembling that seen in M1-type activated macrophages and characterized by an amoeboid morphology, reduced branching, and increased mobility. DFP intoxication also caused massive expression of genes encoding pro-inflammatory cytokines Il1ß, Tnfα, Il8, and to a lesser extent, immuno-modulatory cytokine Il4, suggesting complex microglial reprogramming that included neuroinflammatory activities. Finally, microglia-depleted larvae were instrumental in showing that microglia were major actors in DFP-induced neuroinflammation and, more importantly, that OP-induced neuronal hyperactivation was markedly reduced in larvae fully devoid of microglia. DFP poisoning rapidly triggered massive microglia-mediated neuroinflammation, probably as a result of DFP-induced neuronal hyperexcitation, which in turn further exacerbated neuronal activation. Microglia are thus a relevant therapeutic target, and identifying substances reducing microglial activation could add efficacy to existing OP antidote cocktails.

Engineering Dynamic Surface Peptide Networks on ButyrylcholinesteraseG117H for Enhanced Organophosphosphorus Anticholinesterase Catalysis.

The single residue mutation of butyrylcholinesterase (BChEG117H) hydrolyzes a number of organophosphosphorus (OP) anticholinesterases. Whereas other BChE active site/proximal mutations have been investigated, none are sufficiently active to be prophylactically useful. In a fundamentally different computer simulations driven strategy, we identified a surface peptide loop (residues 278-285) exhibiting dynamic motions during catalysis and modified it via residue insertions. We evaluated these loop mutants using computer simulations, substrate kinetics, resistance to inhibition, and enzyme reactivation assays using both the choline ester and OP substrates. A slight but significant increase in reactivation was noted with paraoxon with one of the mutants, and changes in KM and catalytic efficiency were noted in others. Simulations suggested weaker interactions between OP versus choline substrates and the active site of all engineered versions of the enzyme. The results indicate that an improvement of OP anticholinesterase hydrolysis through surface loop engineering may be a more effective strategy in an enzyme with higher intrinsic OP compound hydrolase activity.

Hydrolyzing activities of phenyl valerate sensitive to organophosphorus compounds paraoxon and mipafox in human neuroblastoma SH-SY5Y cells.

The molecular targets of best known neurotoxic effects associated to acute exposure to organophosphorus compounds (OPs) are serine esterases located in the nervous system, although there are other less known neurotoxic adverse effects associated with chronic exposure to OPs whose toxicity targets are still not identified. In this work we studied sensitivity to the non-neuropathic OP paraoxon and to the neuropathic OP mipafox of phenyl valerate esterases (PVases) in intact and lysed human neuroblastoma SH-SY5Y cells. The main objective was to discriminate different unknown pools of esterases that might be potential targets of chronic effects from those esterases already known and recognized as targets to these acute neurotoxicity effects. Two components of PVases of different sensitivities were discriminated for paraoxon in both intact and lysed cells; while the two components inhibitable by mipafox were found only for intact cells. A completely resistant component to paraoxon of around 30% was found in both intact and lysed cells; while a component of slightly lower amplitude (around 20%) completely resistant to mipafox was also found for both preparations (intact and lysed cells). The comparison of the results between the intact cells and the lysed cells suggests that the plasma membrane could act as a barrier that reduced the bioavailability of mipafox to PVases. This would imply that the discrimination of the different esterases should be made in lysed cells. However, those studies which aim to determine the physiological role of these esterases should be necessarily conducted in intact cultured cells.

Formyl Met-Leu-Phe-Stimulated FPR1 Phosphorylation in Plate-Adherent Human Neutrophils: Enhanced Proteolysis but Lack of Inhibition by Platelet-Activating Factor.

N-formyl-Met-Leu-Phe (fMLF) is a model PAMP/DAMP driving human PMN to sites of injury/infection utilizing the GPCR, FPR1. We examined a microtiter plate format for measurement of FPR1 phosphorylation in adherent PMN at high densities and found that a new phosphosensitive FPR1 fragment, 25K-FPR1, accumulates in SDS-PAGE extracts. 25K-FPR1 is fully inhibited by diisopropylfluorophosphate PMN pretreatment but is not physiologic, as its formation failed to be significantly perturbed by ATP depletion, time and temperature of adherence, or adherence mechanism. 25K-FPR1 was minimized by extracting fMLF-exposed PMN in lithium dodecylsulfate at 4°C prior to reduction/alkylation. After exposure of adherent PMN to a 5 log range of PAF before or after fMLF, unlike in suspension PMN, no inhibition of fMLF-induced FPR1 phosphorylation was observed. However, PAF induced the release of 40% of PMN lactate dehydrogenase, implying significant cell lysis. We infer that PAF-induced inhibition of fMLF-dependent FPR1 phosphorylation observed in suspension PMN does not occur in the unlysed adherent PMN. We speculate that although the conditions of the assay may induce PAF-stimulated necrosis, the cell densities on the plates may approach levels observed in inflamed tissues and provide for an explanation of PAF's divergent effects on FPR1 phosphorylation as well as PMN function.

Aminoalcohol-Induced Activation of Organophosphorus Hydrolase (OPH) towards Diisopropylfluorophosphate (DFP).

Aminoalcohols have been addressed as activating buffers for alkaline phosphatase. However, there is no record on the buffer activation regarding organophosphorus hydrolase (OPH). Here we reported the activating effects of aminoalcohols on OPH-catalyzed hydrolysis of diisopropylfluorophosphate (DFP), an analog molecule of G-type warfare agents. The kinetic parametors kcat, Vmax and kcat/Km in the OPH reaction were remarkably increased in the buffers (pH 8.0, 25°C) containing aminoalcohols with C2 between nitrogen (N) and oxygen (O) in their structures, including triethanolamine (TEA), diethanolamine, monoethanolamine, 1-amino-2-propanol, 2-amino-2-methyl-1-propanol, and triisopropanolamine. In contrast, much lower or no rate-enhancing effects were observed in the adding of amines, alcohols, amine/alcohol mixtures, or 3-amino-1-propanol (C3 between N and O). The 300 mM TEA further increased DFP-degrading activities of OPH mutants F132Y and L140Y, the previously reported OPH mutants with desirable activities towards DFP. However, the treatment of ethylenediaminetetraacetate (EDTA) markedly abolished the TEA-induced activation of OPH. The product fluoride effectively inhibited OPH-catalyzed hydrolysis of DFP by a linear mixed inhibition (inhibition constant Ki ~ 3.21 mM), which was partially released by TEA adding at initial or later reaction stage. The obtained results indicate the activation of OPH by aminoalcohol buffers could be attributed to the reduction of fluoride inhibition, which would be beneficial to the hydrolase-based detoxification of organophosphofluoridate.

Efficient Surface Display of Diisopropylfluorophosphatase (DFPase) in E. coli for Biodegradation of Toxic Organophosphorus Compounds (DFP and Cp).

Compounds including organophosphorus pesticides (OPs) and chemical nerve agents are toxic compounds synthesized recently which disrupt the mechanisms of neural transmission. Therefore, a critical requirement is the development of a bio-refining technology to facilitate the biodegradation of organophosphorus pollutants. The diisopropylfluorophosphatase (DFPase, EC 3.1.8.2) from the ganglion and brain of Loligo vulgaris acts on P-F bonds present in some OPs. Intracellular production of OPs-degrading enzymes or the use of native bacteria and fungi leads to a low degradation rate of OPs due to a mass transfer issue which reduces the overall catalytic efficiency. To overcome this challenge, we expressed DFPase on the surface of E. coli for the first time by employing the N-terminal domain of the ice nucleation protein (InaV-N) as an anchoring motif. Tracking the recombinant protein confirmed that DFPase is successfully located on the outer membrane. Further studies on its activity to degrade diisopropylfluorophosphate (DFP) showed its significant ability for the biodegradation of diisopropylfluorophosphate (DFP) with a specific activity of 500 U/mg of wet cell weight. Recombinant cells could also degrade chlorpyrifos (Cp) with an activity equivalent to a maximum value of 381.44 U/ml with a specific activity of 476.75 U/mg of cell, analyzed using HPLC technique. The optimum activity of purified DFPase was found at 30 °C. A more increased activity was also obtained in the presence of glucose-mineral-salt (GMS) supplemented with tryptone and 100 mg/L Co(2+) ion. These results highlight the high potential of the InaV-N anchoring domain to produce an engineered bacterium that can be used in the bioremediation of pesticide-contaminated environments.

Hydrolysis of DFP and the nerve agent (S)-sarin by DFPase proceeds along two different reaction pathways: implications for engineering bioscavengers.

Organophosphorus (OP) nerve agents such as (S)-sarin are among the most highly toxic compounds that have been synthesized. Engineering enzymes that catalyze the hydrolysis of nerve agents ("bioscavengers") is an emerging prophylactic approach to diminish their toxic effects. Although its native function is not known, diisopropyl fluorophosphatase (DFPase) from Loligo vulgaris catalyzes the hydrolysis of OP compounds. Here, we investigate the mechanisms of diisopropylfluorophosphate (DFP) and (S)-sarin hydrolysis by DFPase with quantum mechanical/molecular mechanical umbrella sampling simulations. We find that the mechanism for hydrolysis of DFP involves nucleophilic attack by Asp229 on phosphorus to form a pentavalent intermediate. P-F bond dissociation then yields a phosphoacyl enzyme intermediate in the rate-limiting step. The simulations suggest that a water molecule, coordinated to the catalytic Ca(2+), donates a proton to Asp121 and then attacks the tetrahedral phosphoacyl intermediate to liberate the diisopropylphosphate product. In contrast, the calculated free energy barrier for hydrolysis of (S)-sarin by the same mechanism is highly unfavorable, primarily because of the instability of the pentavalent phosphoenzyme species. Instead, simulations suggest that hydrolysis of (S)-sarin proceeds by a mechanism in which Asp229 could activate an intervening water molecule for nucleophilic attack on the substrate. These findings may lead to improved strategies for engineering DFPase and related six-bladed ß-propeller folds for more efficient degradation of OP compounds.

Persistent and high-level expression of human liver prolidase in vivo in mice using adenovirus.

Human liver prolidase, a metal-dependent dipeptidase, is being tested as a potential catalytic bioscavenger against organophosphorus (OP) chemical warfare nerve agents. The purpose of this study was to determine whether persistent and high-levels of biologically active and intact recombinant human (rHu) prolidase could be introduced in vivo in mice using adenovirus (Ad). Here, we report that a single intravenous injection of Ad containing the prolidase gene with a 6× histidine-tag (Ad-prolidase) introduced high-levels of rHu prolidase in the circulation of mice which peaked on days 5-7 at 159 ± 129 U/mL. This level of prolidase is ~120 times greater than that of the enzyme level in mice injected with Ad-null virus. To determine if all of Ad-prolidase-produced rHu prolidase was exported into the circulation, enzyme activity was measured in a variety of tissues. Liver contained the highest levels of rHu prolidase on day 7 (5647 ± 454 U/g) compared to blood or any other tissue. Recombinant Hu prolidase hydrolyzed DFP, a simulant of OP nerve agents, in vitro. In vivo, prolidase overexpression extended the survival of 4 out of 6 mice by 4-8h against exposure to two 1× LD(50) doses of DFP. In contrast, overexpression of mouse butyrylcholinesterase (BChE), a proven stoichiometric bioscavenger of OP compounds, protected 5 out of 6 mice from DFP lethality and surviving mice showed no symptoms of DFP toxicity. In conclusion, the results suggest that gene delivery using Ad is capable of introducing persistent and high levels of human liver prolidase in vivo. The gene-delivered prolidase hydrolyzed DFP in vitro but provided only modest protection in vivo in mice, delaying the death of the animals by only 4-8h.

Esterase inhibitors as ester-containing drug stabilizers and their hydrolytic products: potential contributors to the matrix effects on bioanalysis by liquid chromatography/tandem mass spectrometry.

RATIONALE: Esterase inhibitors are widely used to stabilize ester-containing drugs in biological matrices for quantitative liquid chromatography/tandem mass spectrometry (LC/MS/MS) assays. These co-existing inhibitors could cause matrix effects on bioanalysis and jeopardize the assay performance. We therefore developed an LC/MS/MS methodology to monitor the fate of inhibitors and evaluate their matrix effects, which is described in this study. METHODS: Human plasma containing 20 mM of diisopropylfluorophosphate (DFP), paraoxon, eserine, phenylmethylsulfonyl fluoride (PMSF) or 2-thenoyltrifluoroacetone (TTFA) was extracted by liquid-liquid extraction (LLE) and analyzed by an LC/MS/MS assay for BMS-068645 (a model drug) with additional pre-optimized selected reaction monitoring (SRM) transitions using positive/negative electrospray ionization (ESI) mode for each inhibitor. Hydrolytic products were characterized by product ion or neutral loss scan LC/MS/MS analysis. The matrix effect contribution from each inhibitor was evaluated by post-column infusion of BMS-068645. RESULTS: In the extracted samples by LLE, SRM chromatograms revealed the presence of paraoxon, eserine and TTFA with peak intensity of >2.50E08. Three DFP hydrolytic products, diisopropyl phosphate (DP), triisopropyl phosphate (TP) and DP dimer, and one PMSF hydrolytic product, phenymethanesulfonic acid (PMSA), were identified in the extracted samples. In post-column infusion profiles, ion suppression or enhancement was observed in the retention time regions of eserine (~10% suppression), paraoxon (~70% enhancement) and DP dimer (~20% suppression). CONCLUSIONS: The SRM transitions described here make it possible to directly monitor the inhibitors and their hydrolytic products. In combination with post-column infusion, this methodology provides a powerful tool to routinely monitor the matrix effects-causing inhibitors, so that their matrix effects on the bioanalysis can be evaluated and minimized.

Differences in amino acid residues in the binding pockets dictate substrate specificities of mouse senescence marker protein-30, human paraoxonase1, and squid diisopropylfluorophosphatase.

Senescence marker protein-30 (SMP-30) is a candidate enzyme that can function as a catalytic bioscavenger of organophosphorus (OP) nerve agents. We purified SMP-30 from mouse (Mo) liver and compared its hydrolytic activity towards various esters, lactones, and G-type nerve agents with that of human paraoxonase1 (Hu PON1) and squid diisopropylfluorophosphatase (DFPase). All three enzymes contain one or two metal ions in their active sites and fold into six-bladed ß-propeller structures. While Hu PON1 hydrolyzed a variety of lactones, the only lactone that was a substrate for Mo SMP-30 was d-(+)-gluconic acid δ-lactone. Squid DFPase was much more efficient at hydrolyzing DFP and G-type nerve agents as compared to Mo SMP-30 or Hu PON1. The K(m) values for DFP were in the following order: Mo SMP-30>Hu PON1>squid DFPase, suggesting that the efficiency of DFP hydrolysis may be related to its binding in the active sites of these enzymes. Thus, homology modeling and docking were used to simulate the binding of DFP and selected δ-lactones in the active sites of Hu SMP-30, Hu PON1, and squid DFPase. Results from molecular modeling studies suggest that differences in metal-ligand coordinations, the hydrophobicity of the binding pockets, and limited space in the binding pocket due to the presence of a loop, are responsible for substrate specificities of these enzymes.

Detection, quantification, and microlocalisation of targets of pesticides using microchannel plate autoradiographic imagers.

Organophosphorus (OP) compounds are a diverse chemical group that includes nerve agents and pesticides. They share a common chemical signature that facilitates their binding and adduction of acetylcholinesterase (AChE) within nerve synapses to induce cholinergic toxicity. However, this group diversity results in non-uniform binding and inactivation of other secondary protein targets, some of which may be adducted and protein activity influenced, even when only a relatively minor portion of tissue AChE is inhibited. The determination of individual OP protein binding targets has been hampered by the sensitivity of methods of detection and quantification of protein-pesticide adducts. We have overcome this limitation by the employment of a microchannel plate (MCP) autoradiographic detector to monitor a radiolabelled OP tracer compound. We preincubated rat thymus tissue in vitro with the OP pesticides, azamethiphos-oxon, chlorfenvinphos-oxon, chlorpyrifos-oxon, diazinon-oxon, and malaoxon, and then subsequently radiolabelled the free OP binding sites remaining with 3H-diisopropylfluorophosphate (3H-DFP). Proteins adducted by OP pesticides were detected as a reduction in 3H-DFP radiolabelling after protein separation by one dimensional polyacrylamide gel electrophoresis and quantitative digital autoradiography using the MCP imager. Thymus tissue proteins of molecular weights -28 kDa, 59 kDa, 66 kDa, and 82 kDa displayed responsiveness to adduction by this panel of pesticides. The 59 kDa protein target (previously putatively identified as carboxylesterase I) was only significantly adducted by chlorfenvinphos-oxon (p < 0.001), chlorpyrifos-oxon (p < 0.0001), and diazinon-oxon (p < 0.01), the 66 kDa protein target (previously identified as serum albumin) similarly only adducted by the same three pesticides (p < 0.0001), (p < 0.001), and (p < 0.01), and the 82 kDa protein target (previously identified as acyl peptide hydrolase) only adducted by chlorpyrifos-oxon (p < 0.0001) and diazinon-oxon (p < 0.001), when the average values of tissue AChE inhibition were 30%, 35%, and 32% respectively. The -28 kDa protein target was shown to be heterogeneous in nature and was resolved to reveal nineteen 3H-DFP radiolabelled protein spots by two dimensional polyacrylamide gel electrophoresis and MCP autoradiography. Some of these 3H-DFP proteins spots were responsive to adduction by preincubation with chlorfenvinphos-oxon. In addition, we exploited the useful spatial resolution of the MCP imager (-70 mm) to determine pesticide micolocalisation in vivo, after animal dosing and autoradiography of brain tissue sections. Collectively, MCP autoradiographic imaging provided a means to detect targets of OP pesticides, quantify their sensitivity of adduction relative to tissue AChE inhibition, and highlighted that these common pesticides exhibit specific binding character to protein targets, and therefore their toxicity will need to be evaluated on an individual compound basis. In addition, MCP autoradiography afforded a useful method of visualisation of the localisation of a small radiolabelled tracer within brain tissue.

Identification of the catalytic residues of carboxylesterase from Arthrobacter globiformis by diisopropyl fluorophosphate-labeling and site-directed mutagenesis.

The role of amino acid residues in the enzymatic activity of carboxylesterase from Arthrobacter globiformis was analyzed by diisopropyl fluorophosphate (DFP) labeling and site-directed mutagenesis. The electrospray ionization mass spectrometric (ESI-MS) analysis of the esterase, covalently labeled by DFP, showed stoichiometric incorporation of the inhibitor into the enzyme. The further comparison of endopeptidase-digested fragments between native and DFP-labeled esterase by fast atom bombardment mass spectrometric (FAB-MS) analysis as well as site-directed mutagenesis indicated that Ser59 in the consensus sequence Ser-X-X-Lys, which is conserved exclusively in penicillin-binding proteins and some esterases, served as a catalytic nucleophile. In addition, the results obtained from analysis of the mutants at position 62 suggested the importance of the basic amino acid side chain at this position, and suggested the significance of this residue acting directly as a general base rather than its involvement in the maintenance of the optimum hydrogen-bonding network at the active site.

Decontamination of chemical and biological warfare agents with a single multi-functional material.

We report the synthesis of new polymers based on a dimethylacrylamide-methacrylate (DMAA-MA) co-polymer backbone that support both chemical and biological agent decontamination. Polyurethanes containing the redox enzymes glucose oxidase and horseradish peroxidase can convert halide ions into active halogens and exert striking bactericidal activity against gram positive and gram negative bacteria. New materials combining those biopolymers with a family of N-alkyl 4-pyridinium aldoxime (4-PAM) halide-acrylate co-polymers offer both nucleophilic activity for the detoxification of organophosphorus nerve agents and internal sources of halide ions for generation of biocidal activity. Generation of free bromine and iodine was observed in the combined material resulting in bactericidal activity of the enzymatically formed free halogens that caused complete kill of E. coli (>6 log units reduction) within 1 h at 37 degrees C. Detoxification of diisopropylfluorophosphate (DFP) by the polyDMAA MA-4-PAM iodide component was dose-dependent reaching 85% within 30 min. A subset of 4-PAM-halide co-polymers was designed to serve as a controlled release reservoir for N-hydroxyethyl 4-PAM (HE 4-PAM) molecules that reactivate nerve agent-inhibited acetylcholinesterase (AChE). Release rates for HE 4-PAM were consistent with hydrolysis of the HE 4-PAM from the polymer backbone. The HE 4-PAM that was released from the polymer reactivated DFP-inhibited AChE at a similar rate to the oxime antidote 4-PAM.

Mass spectral characterization of organophosphate-labeled lysine in peptides.

Organophosphate (OP) esters bind covalently to the active site serine of enzymes in the serine hydrolase family. Recently, mass spectrometry identified covalent binding of OPs to tyrosine in a wide variety of proteins when purified proteins were incubated with OPs. In the current work, manual inspection of tandem mass spectrometry (MS/MS) data led to the realization that lysines also make a covalent bond with OPs. OP-labeled lysine residues were found in seven proteins that had been treated with either chlorpyrifos oxon (CPO) or diisopropylfluorophosphate (DFP): human serum albumin (K212, K414, K199, and K351), human keratin 1 (K211 and K355), human keratin 10 (K163), bovine tubulin alpha (K60, K336, K163, K394, and K401), bovine tubulin beta (K58), bovine actin (K113, K291, K326, K315, and K328), and mouse transferrin (K296 and K626). These results suggest that OP binding to lysine is a general phenomenon. Characteristic fragments specific for CPO-labeled lysine appeared at 237.1, 220.0, 192.0, 163.9, 128.9, and 83.9amu. Characteristic fragments specific for DFP-labeled lysine appeared at 164.0, 181.2, and 83.8amu. This new OP-binding motif to lysine suggests new directions to search for mechanisms of long-term effects of OP exposure and in the search for biomarkers of OP exposure.

Mass spectrometry identifies covalent binding of soman, sarin, chlorpyrifos oxon, diisopropyl fluorophosphate, and FP-biotin to tyrosines on tubulin: a potential mechanism of long term toxicity by organophosphorus agents.

Chronic low dose exposure to organophosphorus poisons (OP) results in cognitive impairment. Studies in rats have shown that OP interfere with microtubule polymerization. Since microtubules are required for transport of nutrients from the nerve cell body to the nerve synapse, it has been suggested that disruption of microtubule function could explain the learning and memory deficits associated with OP exposure. Tubulin is a major constituent of microtubules. We tested the hypothesis that OP bind to tubulin by treating purified bovine tubulin with sarin, soman, chlorpyrifos oxon, diisopropylfluorophosphate, and 10-fluoroethoxyphosphinyl-N-biotinamidopentyldecanamide (FP-biotin). Tryptic peptides were isolated and analyzed by mass spectrometry. It was found that OP bound to tyrosine 83 of alpha tubulin in peptide TGTYR, tyrosine 59 in beta tubulin peptide YVPR, tyrosine 281 in beta tubulin peptide GSQQYR, and tyrosine 159 in beta tubulin peptide EEYPDR. The OP reactive tyrosines are located either near the GTP binding site or within loops that interact laterally with protofilaments. It is concluded that OP bind covalently to tubulin, and that this binding could explain cognitive impairment associated with OP exposure.

In vitro percutaneous penetration of organophosphorus compounds using full-thickness and split-thickness pig and human skin.

Organophosphorus compounds (OPs), such as pesticides and chemical warfare agents like sarin (GB), soman (GD) and VX, are highly toxic compounds. The OP vapours and their liquid forms are readily absorbed through the skin, therefore, protecting the skin of people who are potentially exposed to these agents is crucial. The development of effective countermeasures relies on a better knowledge of the percutaneous penetration of such molecules. The purpose of this present study is to determine the in vitro percutaneous penetration parameters of two pesticides DSM and DFP, as potential simulants of V and G agents, respectively, using four in vitro systems: full-thickness and split-thickness human abdominal and pig-ear skin membranes mounted on static diffusion cells. Based on the toxicokinetic parameters of the percutaneous penetration of DSM and DFP, we demonstrated that (a) pig-ear skin is a relevant model to predict the in vitro human skin permeability taking into account a 2-fold difference between these two species (b) both full and split-thickness skin membranes could be used indiscriminately, (c) DSM and DFP would be appropriate surrogates for V and G agents to perform skin permeation studies.

Mutant of Bungarus fasciatus acetylcholinesterase with low affinity and low hydrolase activity toward organophosphorus esters.

Enzymes hydrolysing highly toxic organophosphate esters (OPs) are promising alternatives to pharmacological countermeasures against OPs poisoning. Bungarus fasciatus acetylcholinesterase (BfAChE) was engineered to acquire organophosphate hydrolase (OPase) activity by reproducing the features of the human butyrylcholinesterase G117H mutant, the first mutant designed to hydrolyse OPs. The modification consisted of a triple mutation on the (122)GFYS(125) peptide segment, resulting in (122)HFQT(125). This substitution introduced a nucleophilic histidine above the oxyanion hole, and made space in that region. The mutant did not show inhibition by excess acetylthiocholine up to 80 mM. The k(cat)/K(m) ratio with acetylthiocholine was 4 orders of magnitude lower than that of wild-type AChE. Interestingly, due to low affinity, the G122H/Y124Q/S125T mutant was resistant to sub-millimolar concentrations of OPs. Moreover, it had hydrolysing activity with paraoxon, echothiophate, and diisopropyl phosphofluoridate (DFP). DFP was characterised as a slow-binding substrate. This mutant is the first mutant of AChE capable of hydrolysing organophosphates. However, the overall OPase efficiency was greatly decreased compared to G117H butyrylcholinesterase.

Reduction of neuropathy target esterase does not affect neuronal differentiation, but moderate expression induces neuronal differentiation in human neuroblastoma (SK-N-SH) cell line.

Neuropathy target esterase (NTE) is inhibited and aged by organophosphorus compounds that induce delayed neuropathy in human and some sensitive animals. NTE has been proposed to play a role in neurite outgrowth and process elongation during neurodifferentiation. However, to date, there is no direct evidence of the relevance of NTE in neurodifferentiation under physiological conditions. In this study, we have investigated a possible role for NTE in the all-trans retinoic acid-induced differentiation of neuroblastoma cells. The functional inactivation of NTE by RNA interference indicated that reduction of NTE does not affect process outgrowth or differentiation of the cells, although moderate expression of NTE by expression of the NTE esterase domain accelerates the elongation of neurite processes. Mipafox, a neurotoxic organophosphate, was shown to block process outgrowth and differentiation in cells that have lowered NTE activity due to RNA interference, suggesting that mipafox may interact with other molecules to exert its effect in this context.

Molecular interaction between organophosphorus acid anhydrolase and diisopropylfluorophosphate.

Organophosphorus acid anhydrolases (OPAA; E.C.3.1.8.2) are a class of enzymes that hydrolyze a variety of toxic acetylcholinesterase-inhibiting organophosphorus (OP) compounds, including pesticides and fluorine-containing chemical nerve agents. In this paper, subphase conditions have been optimized to obtain stable OPAA Langmuir films, and the diisopropylfluorophosphate (DFP) hydrolysis reaction catalyzed by OPAA in aqueous solution and at the air-water interface was studied. OPAA-DFP interactions were investigated utilizing different spectroscopic techniques, that is, circular dichroism and fluorescence in aqueous solution and infrared reflection absorption spectroscopies at the air-water interface. The characterization of OPAA and its secondary structure in aqueous solution and as a monolayer at the air-water interface in the absence and in the presence of DFP dissolved in aqueous solution or in the aqueous subphase demonstrated significantly distinctive features. The research described herein demonstrated that OPAA can be used in an enzyme-based biosensor for DFP detection.

Analysis of active-site amino-acid residues of human serum paraoxonase using competitive substrates.

Serum paraoxonase (PON1) is a calcium-dependent six-fold beta-propeller protein structurally similar to the di-isopropylfluorophosphatase (DFPase) found in the squid Loligo vulgaris. Human serum paraoxonase (HuPON1) has been shown to hydrolyze an array of substrates even though relatively little is known about its physiological role(s) or its catalytic mechanism. Through site-directed mutagenesis studies, designed from a DFPase-like homology model, and from a crystal structure of a hybrid PON1 molecule, amino-acid residues essential for enzyme function, including H115 and F222, have been identified. It was shown previously that, when H115 is replaced with tryptophan, the resulting enzyme hydrolyzes paraoxon but not phenyl acetate. This study shows that, when present simultaneously, phenyl acetate competitively inhibits paraoxon hydrolysis by H115W. Conversely, when F222 is replaced with tyrosine, mutant F222Y can hydrolyze phenyl acetate but not paraoxon. The presence of DFP, an inhibitor of both arylesterase and paraoxonase activities of wild-type HuPON1 (mean Ki=0.48+/-0.15 mM), has no effect on the ability of F222Y to catalyze the hydrolysis of phenyl acetate, suggesting that the F222Y mutant is unable to bind DFP. Together, the results suggest that, in wild-type HuPON1, H115 and F222 are important in determining substrate binding and specificity, but are not likely to be directly involved in substrate hydrolysis.