Effects of the nerve agent VX on hiPSC-derived motor neurons

Poisoning with the organophosphorus nerve agent VX can be life-threatening due to limitations of the standard therapy with atropine and oximes. To date, the underlying pathomechanism of VX affecting the neuromuscular junction has not been fully elucidated structurally. Results of recent studies investigating the effects of VX were obtained from cells of animal origin or immortalized cell lines limiting their translation to humans. To overcome this limitation, motor neurons (MN) of this study were differentiated from in-house feeder- and integration-free-derived human-induced pluripotent stem cells (hiPSC) by application of standardized and antibiotic-free differentiation media with the aim to mimic human embryogenesis as closely as possible. For testing VX sensitivity, MN were initially exposed once to 400 µM, 600 µM, 800 µM, or 1000 µM VX and cultured for 5 days followed by analysis of changes in viability and neurite outgrowth as well as at the gene and protein level using µLC-ESI MS/HR MS, XTT, IncuCyte, qRT-PCR, and Western Blot. For the first time, VX was shown to trigger neuronal cell death and decline in neurite outgrowth in hiPSC-derived MN in a time- and concentration-dependent manner involving the activation of the intrinsic as well as the extrinsic pathway of apoptosis. Consistent with this, MN morphology and neurite network were altered time and concentration-dependently. Thus, MN represent a valuable tool for further investigation of the pathomechanism after VX exposure. These findings might set the course for the development of a promising human neuromuscular test model and patient-specific therapies in the future.

Effects of organophosphates on precision-cut kidney slices

Organophosphate (OP) poisoning, both accidental and with suicidal intent, is a global medical challenge. While the primary toxicity of these pesticides is based on the inhibition of acetylcholinesterase (AChE), case reports describe patients developing OP-mediated renal insufficiency. We set out to investigate possible pathomechanisms utilizing rat precision-cut kidney slices (PCKS). Depending on the method of investigation, PCKS were observed for a maximum of 10 days. PCKS exposed to OP compounds (malaoxon, malathion, paraoxon, parathion) showed a dose-dependent loss of viability and a reduction of total protein content over the course of 10 days. A concentration of 500 µM OP showed the most differences between OP compounds. After two days of incubation parathion showed a significantly lower level of viability than malathion. The respective effects of paraoxon and malaoxon were not significantly different from the control. However, effects of OP were only observed in concentrations exceeding those that were needed to achieve significant AChE inhibition in rat kidney tissue. In addition, we observed histological changes, without inducing LDH leakage. Overall, results suggest that OP exert effects in kidney tissue, that exceed those expected from the sole inhibition of AChE and vary between compounds. Without signs of necrosis, findings call for studies that address other possible pathomechanisms, including inflammatory response, oxidative stress or activation of apoptosis to further understand the nephrotoxicity of OP compounds. Monitoring oxon concentration over time, we demonstrated reduced enzyme-inhibiting properties in the presence of PCKS, suggesting interactions between OP compound and kidney tissue.

Protein networking: nicotinic acetylcholine receptors and their protein-protein-associations

Nicotinic acetylcholine receptors (nAChR) are complex transmembrane proteins involved in neurotransmission in the nervous system and at the neuromuscular junction. nAChR disorders may lead to severe, potentially fatal pathophysiological states. To date, the receptor has been the focus of basic and applied research to provide novel therapeutic interventions. Since most studies have investigated only the nAChR itself, it is necessary to consider the receptor as part of its protein network to understand or elucidate-specific pathways. On its way through the secretory pathway, the receptor interacts with several chaperones and proteins. This review takes a closer look at these molecular interactions and focuses especially on endoplasmic reticulum biogenesis, secretory pathway sorting, Golgi maturation, plasma membrane presentation, retrograde internalization, and recycling. Additional knowledge regarding the nAChR protein network may lead to a more detailed comprehension of the fundamental pathomechanisms of diseases or may lead to the discovery of novel therapeutic drug targets.

Identification of ligands binding to MB327-PAM-1, a binding pocket relevant for resensitization of nAChRs

Desensitization of nicotinic acetylcholine receptors (nAChRs) can be induced by overstimulation with acetylcholine (ACh) caused by an insufficient degradation of ACh after poisoning with organophosphorus compounds (OPCs). Currently, there is no generally applicable treatment for OPC poisoning that directly targets the desensitized nAChR. The bispyridinium compound MB327, an allosteric modulator of nAChR, has been shown to act as a resensitizer of nAChRs, indicating that drugs binding directly to nAChRs can have beneficial effects after OPC poisoning. However, MB327 also acts as an inhibitor of nAChRs at higher concentrations and can thus not be used for OPC poisoning treatment. Consequently, novel, more potent resensitizers are required. To successfully design novel ligands, the knowledge of the binding site is of utmost importance. Recently, we performed in silico studies to identify a new potential binding site of MB327, MB327-PAM-1, for which a more affine ligand, UNC0646, has been described. In this work, we performed ligand-based screening approaches to identify novel analogs of UNC0646 to help further understand the structure-affinity relationship of this compound class. Furthermore, we used structure-based screenings and identified compounds representing four new chemotypes binding to MB327-PAM-1. One of these compounds, cycloguanil, is the active metabolite of the antimalaria drug proguanil and shows a higher affinity towards MB327-PAM-1 than MB327. Furthermore, cycloguanil can reestablish the muscle force in soman-inhibited rat muscles. These results can act as a starting point to develop more potent resensitizers of nAChR and to close the gap in the treatment after OPC poisoning.

Disulfide-adducts with cysteine residues in human serum albumin prove exposure to malodorous mercaptans in vitro

Malodorants are mixtures containing mercaptans, which trigger the flight instinct upon exposure and might thus be deployed in military and civilian defense scenarios. Exposure to mercaptans might lead to unconsciousness, thus representing a possible threat for health. Therefore, we developed and validated a bioanalytical procedure for the simultaneous detection and identification of corresponding biomarkers for the verification of exposure to mercaptans. Disulfide-adducts of ethyl mercaptan (SEt), n-butyl mercaptan (SnBu), tert-butyl mercaptan (StBu) and iso-amyl mercaptan (SiAm) with cysteine (Cys) residues in human serum albumin (HSA) were formed by in vitro incubation of human plasma. After pronase-catalyzed proteolysis, reaction products were identified as adducts of the single amino acid Cys and the dipeptide cysteine-proline (Cys34Pro) detected by a sensitive μLC-ESI MS/MS method working in the scheduled multiple reaction monitoring (sMRM) mode. Dose-response studies showed linearity for the yield of Cys34Pro-adducts in the range from 6 nM to 300 μM of mercaptans in plasma and limits of identification (LOI) were in the range from 60 nM to 6 μM. Cys34-adducts showed stability for at least 6 days in plasma (37 °C). The presented disulfide-biomarkers expand the spectrum for bioanalytical verification procedures and might be helpful to prove exposure to malodorants.

Inhibition kinetics of acetylcholinesterase and butyrylcholinesterase from various species by 2-(2-cresyl)-4H-1,3,2-benzodioxaphosphorin-2-oxide (CBDP)

The aerotoxic syndrome has been associated with exposure to tricresyl phosphate (TCP), which is used as additive in hydraulic fluids and engine lubricants. The toxic metabolite 2-(2-cresyl)-4H-1,3,2-benzodioxaphosphorin-2-oxide (CBDP) is formed from the TCP isomer tri-ortho-cresyl phosphate (TOCP) in vivo and is known to react with the active site serine in acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) resulting in the inhibition of the enzymes. Previous in vitro studies showed pronounced species differences in the inhibition kinetics of cholinesterases by organophosphorus compounds (OP), which must be considered in the development of relevant animal models for the investigation of OP poisoning and the aerotoxic syndrome. The present study was designed to investigate the inhibition kinetics of human, Cynomolgus monkey, pig, mini pig, guinea pig, mouse, and rat AChE as well as BChE by CBDP under standardized conditions. There were similar rate constants for the inhibition (ki) of human, Cynomolgus monkey and mouse AChE by CBDP. In contrast, the ki values obtained for guinea pig, mini pig, pig, and rat AChE were 2.8- to 5.9-fold lower than that of human AChE. The results of the present study confirmed CBDP as one of the most potent inhibitors of human BChE, indicating a ki value of 3.24 ± 0.33 ×108M-1min-1, which was about 1,140-fold higher than that of human AChE. Accordingly, a markedly more pronounced inhibition rate of BChE from the species guinea pig, mini pig, pig, rat, Cynomolgus monkey, and mouse by CBDP was found as compared to those of AChE from the respective sources, indicating 2.0- to 89.6-fold higher ki values.

Synthesis and Biological Evaluation of Novel MB327 Analogs as Resensitizers for Desensitized Nicotinic Acetylcholine Receptors after Intoxication with Nerve Agents

Poisoning with organophosphorus compounds, which can lead to a cholinergic crisis due to the inhibition of acetylcholinesterase and the subsequent accumulation of acetylcholine (ACh) in the synaptic cleft, is a serious problem for which treatment options are currently insufficient. Our approach to broadening the therapeutic spectrum is to use agents that interact directly with desensitized nicotinic acetylcholine receptors (nAChRs) in order to induce functional recovery after ACh overstimulation. Although MB327, one of the most prominent compounds investigated in this context, has already shown positive properties in terms of muscle force recovery, this compound is not suitable for use as a therapeutic agent due to its insufficient potency. By means of in silico studies based on our recently presented allosteric binding pocket at the nAChR, i.e. the MB327-PAM-1 binding site, three promising MB327 analogs with a 4-aminopyridinium ion partial structure (PTM0056, PTM0062 and PTM0063) were identified. In this study, we present the synthesis and biological evaluation of a series of new analogs of the aforementioned compounds with a 4-aminopyridinium ion partial structure (PTM0064-PTM0072), as well as hydroxy-substituted analogs of MB327 (PTMD90-0012 and PTMD90-0015) designed to substitute entropically unfavorable water clusters identified during molecular dynamics simulations. The compounds were characterized in terms of their binding affinity towards the aforementioned binding site by applying the UNC0642 MS Binding Assays and in terms of their muscle force reactivation in rat diaphragm myography. More potent compounds were identified compared to MB327, as some of them showed a higher affinity towards MB327-PAM-1 and also a higher recovery of neuromuscular transmission at lower compound concentrations. To improve the treatment of organophosphate poisoning, direct targeting of nAChRs with appropriate compounds is a key step, and this study is an important contribution to this research.

Trauma-toxicology: concepts, causes, complications

Trauma and toxic substances are connected in several aspects. On the one hand, toxic substances can be the reason for traumatic injuries in the context of accidental or violent and criminal circumstances. Examples for the first scenario is the release of toxic gases, chemicals, and particles during house fires, and for the second scenario, the use of chemical or biological weapons in the context of terroristic activities. Toxic substances can cause or enhance severe, life-threatening trauma, as described in this review for various chemical warfare, by inducing a tissue trauma accompanied by break down of important barriers in the body, such as the blood-air or the blood-gut barriers. This in turn initiates a "vicious circle" as the contribution of inflammatory responses to the traumatic damage enhances the macro- and micro-barrier breakdown and often results in fatal outcome. The development of sophisticated methods for detection and identification of toxic substances as well as the special treatment of the intoxicated trauma patient is summarized in this review. Moreover, some highly toxic substances, such as the protein toxins from the pathogenic bacterium Clostridioides (C.) difficile, cause severe post-traumatic complications which significantly worsens the outcome of hospitalized patients, in particular in multiply injured trauma patients. Therefore, novel pharmacological options for the treatment of such patients are necessarily needed and one promising strategy might be the neutralization of the toxins that cause the disease. This review summarizes recent findings on the molecular and cellular mechanisms of toxic chemicals and bacterial toxins that contribute to barrier breakdown in the human body as wells pharmacological options for treatment, in particular in the context of intoxicated trauma patients. "trauma-toxicology" comprises concepts regrading basic research, development of novel pharmacological/therapeutic options and clinical aspects in the complex interplay and "vicious circle" of severe tissue trauma, barrier breakdown, pathogen and toxin exposure, tissue damage, and subsequent clinical complications.

Suitability of human HepaRG cells and liver spheroids as in vitro model to investigate the bioactivation of the organothiophosphate pesticide parathion

Organophosphorus compounds (OP) constitute a large group of chemicals including pesticides and nerve agents. Organothiophosphate pesticides require cytochrome P450-mediated oxidative desulphuration in the liver to form corresponding oxons, which are potent inhibitors of the enzyme acetylcholinesterase (AChE). Human HepaRG cells are a promising tool to study liver-specific functions and have been shown to maintain drug metabolizing enzymes. This research describes for the first time the in vitro metabolic activation of an organothiophosphate to its active oxon by two different HepaRG cell-based models. Monolayer cultures and liver spheroids were exposed to the model OP parathion and the quantification of the corresponding oxon was performed with an AChE inhibition assay. Our results showed a time- and dose-dependent cytochrome P450 catalyzed bioactivation and a superior metabolism capacity of the monolayer HepaRG model in comparison with the liver spheroids. Finally, HepaRG cells can be assessed as a metabolically competent cell model intermediate between cell-free preparations and intact animals and as suitable to study OP metabolism in the human liver.

Uncharged mono- and bisoximes: In search of a zwitterion to countermeasure organophosphorus intoxication

The current study imposes a new class of organophosphorus (OP)-inhibited cholinesterase reactivators by conceptualizing a family of asymmetric bisoximes with various reactivating scaffolds. Several novel nucleophilic warheads were investigated, putting forward 29 novel reactivating options, by evaluating their nucleophilicity and ability to directly decompose OP compounds. Adopting the so-called zwitterionic strategy, 17 mono-oxime and nine bisoxime reactivators were discovered with major emphasis on the bifunctional-moiety approach. Compounds were compared with clinically used standards and other known experimentally highlighted reactivators. Our results clearly favor the concept of asymmetric bisoximes as leading reactivators in terms of efficacy and versatility. These top-ranked compounds were characterized in detail by reactivation kinetics parameters and evaluated for potential CNS availability. The highlighted molecules 55, 57, and 58 with various reactivating warheads, surpassed the reactivating potency of pralidoxime and several notable uncharged reactivators. The versatility of lead drug candidate 55 was also inspected on OP-inhibited butyrylcholinesterase, revealing a much higher rate compared to existing clinical antidotes.

Screening for new ligands of the MB327-PAM-1 binding site of the nicotinic acetylcholine receptor

Intoxications with organophosphorus compounds (OPCs) effect a severe impairment of cholinergic neurotransmission that, as a result of overstimulation may lead to desensitization of nicotinic acetylcholine receptors (nAChRs) and finally to death due to respiratory paralysis. So far, therapeutics, that are capable to address and revert desensitized neuromuscular nAChRs into their resting, i.e. functional state are still missing. Still, among a class of compounds termed bispyridinium salts, which are characterized by the presence of two pyridinium subunits, constituents have been identified, that can counteract organophosphate poisoning by resensitizing desensitized nAChRs. According to comprehensive modeling studies this effect is mediated by an allosteric binding site at the nAChR termed MB327-PAM-1 site. For MB327, the most prominent representative of the bispyridinium salts and all other analogues studied so far, the affinity for the aforementioned binding site and the intrinsic activity measured in ex vivo and in in vivo experiments are distinctly too low, to meet the criteria to be fulfilled for therapeutic use. Hence, in order to identify new compounds with higher affinities for the MB327-PAM-1 binding site, as a basic requirement for an enhanced potency, two compound libraries, the ChemDiv library with 60 constituents and the Tocriscreen Plus library with 1280 members have been screened for hit compounds addressing the MB327-PAM-1 binding site, utilizing the [2H6]MB327 MS Binding Assay recently developed by us. This led to the identification of a set of 10 chemically diverse compounds, all of which exhibit an IC50 value of ≤ 10 µM (in the [2H6]MB327 MS Binding Assay), which had been defined as selection criteria. The three most affine ligands, which besides a quinazoline scaffold share similarities with regard to the substitution pattern and the nature of the substituents, are UNC0638, UNC0642 and UNC0646. With binding affinities expressed as pKi values of 6.01 ± 0.10, 5.97 ± 0.05 and 6.23 ± 0.02, respectively, these compounds exceed the binding affinity of MB327 by more than one log unit. This renders them promising starting points for the development of drugs for the treatment of organophosphorus poisoning by addressing the MB327-PAM-1 binding site of the nAChR.

Restoration of nerve agent impaired neuromuscular transmission in rat diaphragm by bispyridinium non-oximes - Structure-activity relationships

Organophosphate (OP) poisoning is currently treated with atropine, oximes and benzodiazepines. The nicotinic signs, i.e., respiratory impairment, can only be targeted indirectly via the use of oximes as reactivators of OP-inhibited acetylcholinesterase. Hence, compounds selectively targeting nicotinic acetylcholine receptors (nAChRs) might fundamentally improve current treatment options. The bispyridinium compound MB327 has previously shown some therapeutic effect against nerve agents in vitro and in vivo. Nevertheless, compound optimization was deemed necessary, due to limitations (e.g., toxicity and efficacy). The current study investigated a series of 4-tert-butyl bispyridinium compounds and of corresponding bispyridinium compounds without substituents in a rat diaphragm model using an indirect field stimulation technique. The length of the respective linker influenced the ability of the bispyridinium compounds to restore muscle function in rat hemidiaphragms. The current data show structure-activity relationships for a series of bispyridinium compounds and provide insight for future structure-based molecular modeling.

Toxicokinetic analysis of the highly toxic nerve agent VX in commercially available multi-organ-chips - Ways to overcome compound absorption

Organ-on-a-chip technology is considered a next-generation platform in pharmacology and toxicology. Nevertheless, this novel technology still faces several challenges concerning the respective materials which are used for these microfluidic devices. Currently available organ-chips are most often based on polydimethylsiloxane (PDMS). However, this material has strong limitations regarding compound binding. The current study investigated options to reduce compound absorption of the highly toxic nerve agent VX (1000 µmol/L) in a commercially available organ-chip. In addition, surface effects on degradation products of VX were investigated. The alternative polymer cyclic olefin copolymers (CoC) showed significantly less compound absorption compared to PDMS. Furthermore, a coating of PDMS- and CoC-based chips was investigated. The biocompatible polymer polyethyleneimine (PEI) successfully modified PDMS and CoC surfaces and further reduced compound absorption. A previously examined VX concentration after 72 h of 141 ± 10 µmol/L VX could be increased to 442 ± 54 µmol/L. Finally, the respective concentrations of VX and degradation products accounted for > 90% of the initial concentration of 1000 µmol/L VX. The currently described surface modification might be a first step towards the optimization of organ-on-a-chip surfaces, facilitating a better comparability of different studies and results.

AChE reactivation in precision-cut lung slices following organophosphorus compound poisoning

Precision-cut lung slices (PCLS) are a suitable model for analyzing the acetylcholinesterase (AChE) activity and subsequent effects after exposure to organophosphorus (OP) compounds. In this study, the AChE activity was determined in intact PCLS for the first time. Since the current standard therapy for OP poisoning (atropine + oxime + benzodiazepine) lacks efficiency, reliable models to study novel therapeutic substances are needed. Models should depict pathophysiological mechanisms and help to evaluate the beneficial effects of new therapeutics. Here PCLS were exposed to three organophosphorus nerve agents (OPNAs): sarin (GB), cyclosarin (GF), and VX. They were then treated with three reactivators: HI-6, obidoxime (OBI), and a non-oxime (NOX-6). The endpoints investigated in this study were the AChE activity and the airway area (AA) change. OPNA exposure led to very low residual AChE activities. Depending on the reactivator properties different AChE reactivation results were measured. GB-inhibited PCLS-AChE was reactivated best, followed by VX and GF. To substantiate these findings and to understand the connection between the molecular and the functional levels in a more profound way the results were correlated to the AA changes. These investigations underline the importance of reactivator use and point to the possibilities for future improvements in the treatment of OPNA-exposed victims.

MS Binding Assays with UNC0642 as reporter ligand for the MB327 binding site of the nicotinic acetylcholine receptor

Intoxications with organophosphorus compounds (OPCs) based chemical warfare agents and insecticides may result in a detrimental overstimulation of muscarinic and nicotinic acetylcholine receptors evolving into a cholinergic crisis leading to death due to respiratory failure. In the case of the nicotinic acetylcholine receptor (nAChR), overstimulation leads to a desensitization of the receptor, which cannot be pharmacologically treated so far. Still, compounds interacting with the MB327 binding site of the nAChR like the bispyridinium salt MB327 have been found to re-establish the functional activity of the desensitized receptor. Only recently, a series of quinazoline derivatives with UNC0642 as one of the most prominent representatives has been identified to address the MB327 binding site of the nAChR, as well. In this study, UNC0642 has been utilized as a reporter ligand to establish new Binding Assays for this target. These assays follow the concept of MS Binding Assays for which by assessing the amount of bound reporter ligand by mass spectrometry no radiolabeled material is required. According to the results of the performed MS Binding Assays comprising saturation and competition experiments it can be concluded, that UNC0642 used as a reporter ligand addresses the MB327 binding site of the Torpedo-nAChR. This is further supported by the outcome of ex vivo studies carried out with poisoned rat diaphragm muscles as well as by in silico studies predicting the binding mode of UNC0646, an analog of UNC0642 with the highest binding affinity, in the recently proposed binding site of MB327 (MB327-PAM-1). With UNC0642 addressing the MB327 binding site of the Torpedo-nAChR, this and related quinazoline derivatives represent a promising starting point for the development of novel ligands of the nAChR as antidotes for the treatment of intoxications with organophosphorus compounds. Further, the new MS Binding Assays are a potent alternative to established assays and of particular value, as they do not require the use of radiolabeled material and are based on a commercially available compound as reporter ligand, UNC0642, exhibiting one of the highest binding affinities for the MB327 binding site known so far.

Recombinant cellular model system for human muscle-type nicotinic acetylcholine receptor α12β1δε

The human muscle-type nicotinic acetylcholine receptor α12β1δε (nAChR) is a complex transmembrane receptor needed for drug screening for disorders like congenital myasthenic syndromes and multiple pterygium syndrome. Until today, most models are still using the nAChR from Torpedo californica electric ray. A simple reproducible cellular system expressing functional human muscle-type nAChR is still missing. This study addressed this issue and further tested the hypothesis that different chaperones, both biological and chemical, and posttranslational modification supporting substances as well as hypothermic incubation are able to increase the nAChR yield. Therefore, Gibson cloning was used to generate transfer plasmids carrying the sequence of nAChR or chosen biological chaperones to support the nAChR folding in the cellular host. Viral transduction was used for stable integration of these transgenes in Chinese hamster ovary cells (CHO). Proteins were detected with Western blot, in-cell and on-cell Western, and the function of the receptor with voltage clamp analysis. We show that the internalization of nAChR into plasma membranes was sufficient for detection and function. Additional transgenic overexpression of biological chaperones did result in a reduced nAChR expression. Chemical chaperones, posttranslational modification supporting substances, and hypothermic conditions are well-suited supporting applications to increase the protein levels of different subunits. This study presents a stable and functional cell line that expresses human muscle-type nAChR and yields can be further increased using the chemical chaperone nicotine without affecting cell viability. The simplified access to this model system should enable numerous applications beyond drug development. Graphical abstract created with http://biorender.com.

The suitability of a polydimethylsiloxane-based (PDMS) microfluidic two compartment system for the toxicokinetic analysis of organophosphorus compounds

Organ-on-a-chip platforms are an emerging technology in experimental and regulatory toxicology (species-specific differences, ethical considerations). They address gaps between in vivo and in vitro models. However, there are still certain limitations considering material, setup and applicability. The current study examined the suitability of a commercially available polydimethylsiloxane-based (PDMS) organ-chip for the toxicokinetic characterization of the highly toxic nerve agent VX and the organophosphate pesticide parathion. The respective concentrations of 1000 µmol/L and 100 µmol/L VX and parathion were chosen deliberately high in order to study concentrations even if high compound absorption by PDMS might occur. Neuronal and liver spheroids, totaling 2 × 106 cells were used to study concentration changes of VX and parathion. In addition, VX enantiomers were quantified. The current study suggests a significant absorption of VX, respectively parathion by PDMS. This might require future investigation of alternative materials or coatings to limit absorption for organophosphorus compounds in toxicokinetic studies.

Evidence of nerve agent VX exposure in rat plasma by detection of albumin-adducts in vitro and in vivo

VX is a highly toxic organophosphorus nerve agent that reacts with a variety of endogenous proteins such as serum albumin under formation of adducts that can be targeted by analytical methods for biomedical verification of exposure. Albumin is phosphonylated by the ethyl methylphosphonic acid moiety (EMP) of VX at various tyrosine residues. Additionally, the released leaving group of VX, 2-(diisopropylamino)ethanethiol (DPAET), may react with cysteine residues in diverse proteins. We developed and validated a microbore liquid chromatography-electrospray ionization high-resolution tandem mass spectrometry (µLC-ESI MS/HR MS) method enabling simultaneous detection of three albumin-derived biomarkers for the analysis of rat plasma. After pronase-catalyzed cleavage of rat plasma proteins single phosphonylated tyrosine residues (Tyr-EMP), the Cys34(-DPAET)Pro dipeptide as well as the rat-specific LeuProCys448(-DPAET) tripeptide were obtained. The time-dependent adduct formation in rat plasma was investigated in vitro and biomarker formation during proteolysis was optimized. Biomarkers were shown to be stable for a minimum of four freeze-and-thaw cycles and for at least 24 h in the autosampler at 15 °C thus making the adducts highly suited for bioanalysis. Cys34(-DPAET)Pro was superior compared to the other serum biomarkers considering the limit of identification and stability in plasma at 37 °C. For the first time, Cys34(-DPAET)Pro was detected in in vivo specimens showing a time-dependent concentration increase after subcutaneous exposure of rats underlining the benefit of the dipeptide disulfide biomarker for sensitive analysis.

A pharmacologically pre-contracted smooth muscle bowel model for the study of highly-potent opioid receptor agonists and antagonists

Isolated organ models are a versatile tool for pharmacological and toxicological research. Small bowel has been used to assess the inhibition of smooth muscle contraction by opioids. In the present study, we set out to establish a pharmacologically stimulated rat bowel model. The effects of carfentanil, remifentanil and the new synthetic opioid U-48800 and their respective antagonists naloxone, nalmefene and naltrexone were studied in a small bowel model in rats. The IC₅₀ values of the tested opioids were as follows: carfentanil (IC₅₀ = 0.02 µmol/L, CI 0.02-0.03 µmol/L) ≫ remifentanil (IC₅₀ = 0.51 µmol/L, CI 0.40-0.66 µmol/L) ≫ U-48800 (IC₅₀ = 1.36 µmol/L, CI 1.20-1.54 µmol/L). The administration of the opioid receptor antagonists naloxone, naltrexone and nalmefene led to progressive, parallel rightward shifts of the dose-response curves. Naltrexone was most potent in antagonizing the effects of U-48800, whereas naltrexone and nalmefene were most effective in antagonizing the effects of carfentanil. In summary, the current model seems to be a robust tool to study opioid effects in a small bowel model without the necessity of using electrical stimulation.

Structural and Functional Analysis of a Highly Active Designed Phosphotriesterase for the Detoxification of Organophosphate Nerve Agents Reveals an Unpredicted Conformation of the Active Site Loop

Neurotoxic organophosphorus compounds (OPs) pose a severe threat if misused in military conflicts or by terrorists. Administration of a hydrolytic enzyme that can decompose the circulating nerve agent into non-toxic metabolites in vivo offers a potential treatment. A promising candidate is the homo-dimeric phosphotriesterase originating from the bacterium Brevundimonas diminuta (BdPTE), which has been subject to several rational and combinatorial protein design studies. A series of engineered versions with much improved catalytic efficiencies toward medically relevant nerve agents was described, carrying up to 22 mutations per enzyme subunit. To provide a basis for further rational design, we have determined the crystal structure of the highly active variant 10-2-C3(C59V/C227V)─stabilized against oxidation by substitution of two unpaired Cys residues─in complex with a substrate analogue at 1.5 Å resolution. Unexpectedly, the long loop segment (residues 253-276) that covers the active site shows a totally new conformation, with drastic structural deviations up to 19 Å, which was neither predicted in any of the preceding protein design studies nor seen in previous crystallographic analyses of less far evolved enzyme versions. Inspired by this structural insight, additional amino acid exchanges were introduced and their effects on protein stability as well as on the catalytic efficiency toward several neurotoxic OPs were investigated. Somewhat surprisingly, our results suggest that the presently available engineered version of BdPTE, in spite of its design on the basis of partly false structural assumptions, constitutes a fairly optimized enzyme for the detoxification of relevant OP nerve agents.

Engineering of a phosphotriesterase with improved stability and enhanced activity for detoxification of the pesticide metabolite malaoxon

Organophosphorus (OP) pesticides are still widely applied but pose a severe toxicological threat if misused. For in vivo detoxification, the application of hydrolytic enzymes potentially offers a promising treatment. A well-studied example is the phosphotriesterase of Brevundimonas diminuta (BdPTE). Whereas wild-type BdPTE can hydrolyse pesticides like paraoxon, chlorpyrifos-oxon and mevinphos with high catalytic efficiencies, kcat/KM >2 × 107 M-1 min-1, degradation of malaoxon is unsatisfactory (kcat/KM ≈ 1 × 104 M-1 min-1). Here, we report the rational engineering of BdPTE mutants with improved properties and their efficient production in Escherichia coli. As result, the mutant BdPTE(VRNVVLARY) exhibits 37-fold faster malaoxon hydrolysis (kcat/KM = 4.6 × 105 M-1 min-1), together with enhanced expression yield, improved thermal stability and reduced susceptibility to oxidation. Therefore, this BdPTE mutant constitutes a powerful candidate to develop a biocatalytic antidote for the detoxification of this common pesticide metabolite as well as related OP compounds.

Human HepaRG liver spheroids: cold storage protocol and study on pyridinium oxime-induced hepatotoxicity in vitro

Oximes play an essential role in the therapy of organophosphorus compound (OP) poisoning by reactivating inhibited acetylcholinesterase. Impairment of liver function was observed in OP poisoning and associated with obidoxime treatment by some reports. In this study human three-dimensional HepaRG spheroids were used as complex in vitro model to investigate oxime-induced liver toxicity. In this context, cold storage of liver spheroids at 4 °C in standard culture medium and in optimized tissue preservation solutions of up to 72 h was assessed. Cold storage in standard culture medium resulted in a complete loss of viability whereas an optimized tissue preservation solution preserved viability. Separately from that liver spheroids were exposed to the four oximes pralidoxime, obidoxime, HI-6, MMB-4 and cytotoxicity (effective concentration, EC₅₀) was determined with an ATP-based assay at several time points. The release of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and albumin secretion was measured in supernatants. The same parameters were assessed with diclofenac as positive hepatotoxic control and with the OP pesticides malathion and malaoxon alone or in the presence of obidoxime. All individual tested oximes and OP showed a low cytotoxicity with effective concentrations mostly >2,000 μM. In contrast, the exposure to malaoxon in the presence of 1,000 μM obidoxime resulted in a marked decrease of viability and an increased release of AST indicating risk of liver injury only if oxime antidotes are strongly overdosed.

A case report of severe pirimiphos-methyl intoxication: Clinical findings and cholinesterase status

A 63-year-old male was admitted to a district hospital after ingesting ethanol and pirimiphos-methyl (PM) with suicidal intentions. History included alcoholic cirrhosis with alcoholism, adiposity, diabetes with cerebral microangiopathy, chronic renal insufficiency, heparin-induced thrombocytopenia, and status post necrotizing fasciitis. Emergency medical service reported an alert patient without signs of cholinergic crisis; activated charcoal and atropine were administered. Upon hospital arrival, he received fluid resuscitation, activated charcoal, and atropine. He was transferred to a toxicology unit the next day. On admission, he had no cholinergic signs (dry mucous membranes, warm skin, and mydriatic pupils) requiring small atropine doses (0.5 mg per hour). Four hours after admission, he developed bradycardia and respiratory distress, necessitating intubation. He received atropine by continuous infusion for 7 days (248 mg total) and obidoxime (bolus and continuous infusion). PM, pirimiphos-methyl-oxon (PMO), and phosphorylated tyrosine (Tyr) adducts derived from human serum albumin were analyzed in vivo. Cholinesterase status (acetylcholinesterase (AChE), butyrylcholinesterase (BChE), inhibitory activity of patient plasma and reactivatability, and phosphorylated BChE-derived nonapeptides) was measured in vivo. Obidoxime and atropine were monitored. PM and PMO were detectable, PM with maximum concentration ∼24 h post admission (p.a.) and PMO at ∼18 h p.a. Tyr adducts were detectable. AChE in vivo was suppressed on admission, increased continuously after starting obidoxime, and reached maximum activity after ∼30 h. AChE in vivo and reactivatability remained at the same level until the end of monitoring. BChE was already suppressed on admission; termination of the antidote treatment was possible after BChE had recovered to 1/5th of its normal value and extubation was possible after BChE had recovered to 2/5th. While a substantial part of BChE was already aged on admission, aging continued peaking at ∼24 h p.a. After initiating obidoxime treatment, plasma levels increased until obidoxime plasma levels reached a steady state. On admission, plasma atropine level was low; it increased with the start of the continuous infusion. Afterward, the level dropped to a steady state. The clinical course was characterized by bouts of pneumonia, necessitating re-intubation and prolonged ventilation, sepsis, delirium, and a peripheral neuropathy. After psychiatric evaluation, the patient was discharged to a neurological rehabilitation facility after 77 days of hospital care.

Broad‐Spectrum Antidote Discovery by Untangling the Reactivation Mechanism of Nerve‐Agent‐Inhibited Acetylcholinesterase

Reactivators are vital for the treatment of organophosphorus nerve agent (OPNA) intoxication but new alternatives are needed due to their limited clinical applicability. The toxicity of OPNAs stems from covalent inhibition of the essential enzyme acetylcholinesterase (AChE), which reactivators relieve via a chemical reaction with the inactivated enzyme. Here, we present new strategies and tools for developing reactivators. We discover suitable inhibitor scaffolds by using an activity‐independent competition assay to study non‐covalent interactions with OPNA‐AChEs and transform these inhibitors into broad‐spectrum reactivators. Moreover, we identify determinants of reactivation efficiency by analysing reactivation and pre‐reactivation kinetics together with structural data. Our results show that new OPNA reactivators can be discovered rationally by exploiting detailed knowledge of the reactivation mechanism of OPNA‐inhibited AChE.

Oximes should be used routinely in organophosphate poisoning

In poisoning with organophosphorus compounds, patients can only profit from the regeneration of acetylcholinesterase, when the poison load has dropped below a toxic level. Every measure that allows an increase of synaptic AChE activity at the earliest is essential for timely termination of the cholinergic crisis. Only a drug induced reactivation allows to achieve fast restoration of the inhibited AChE. Obidoxime and pralidoxime have proved to be able to reactivate inhibited cholinesterase thereby saving life of poisoned animals. A plasma level of obidoxime or pralidoxime allowing reactivation in humans poisoned by OP can be adjusted. There is no doubt that obidoxime and pralidoxime are able to reactivate OP inhibited AChE activity in poisoned patients thereby increasing AChE activity and contributing substantially to terminate cholinergic crisis. Hence, a benefit may be expected when substantial reactivation is achieved. A test system allowing determination of red blood cell AChE activity, reactivatability, inhibitory equivalents and BChE activity is available for relatively low cost. If any reactivation is possible while inhibiting equivalents are present, oxime therapy should be maintained. In particular, when balancing the benefit risk assessment, obidoxime or palidoxime should be given as soon as possible and as long as a substantial reactivation may be expected.

Post-VX exposure treatment of rats with engineered phosphotriesterases

The biologically stable and highly toxic organophosphorus nerve agent (OP) VX poses a major health threat. Standard medical therapy, consisting of reactivators and competitive muscarinic receptor antagonists, is insufficient. Recently, two engineered mutants of the Brevundimonas diminuta phosphotriesterase (PTE) with enhanced catalytic efficiency (k_cat/K_M = 21 to 38 × 10⁶ M⁻¹ min⁻¹) towards VX and a preferential hydrolysis of the more toxic P(−) enantiomer were described: PTE-C23(R152E)-PAS(100)-10-2-C3(I106A/C59V/C227V/E71K)-PAS(200) (PTE-2), a single-chain bispecific enzyme with a PAS linker and tag having enlarged substrate spectrum, and 10-2-C3(C59V/C227V)-PAS(200) (PTE-3), a stabilized homodimeric enzyme with a double PASylation tag (PAS-tag) to reduce plasma clearance. To assess in vivo efficacy, these engineered enzymes were tested in an anesthetized rat model post-VX exposure (~ 2LD₅₀) in comparison with the recombinant wild-type PTE (PTE-1), dosed at 1.0 mg kg⁻¹ i.v.: PTE-2 dosed at 1.3 mg kg⁻¹ i.v. (PTE-2.1) and 2.6 mg kg⁻¹ i.v. (PTE-2.2) and PTE-3 at 1.4 mg kg⁻¹ i.v. Injection of the mutants PTE-2.2 and PTE-3, 5 min after s.c. VX exposure, ensured survival and prevented severe signs of a cholinergic crisis. Inhibition of erythrocyte acetylcholinesterase (AChE) could not be prevented. However, medulla oblongata and diaphragm AChE activity was partially preserved. All animals treated with the wild-type enzyme, PTE-1, showed severe cholinergic signs and died during the observation period of 180 min. PTE-2.1 resulted in the survival of all animals, yet accompanied by severe signs of OP poisoning. This study demonstrates for the first time efficient detoxification in vivo achieved with low doses of heterodimeric PTE-2 as well as PTE-3 and indicates the suitability of these engineered enzymes for the development of highly effective catalytic scavengers directed against VX.

Optimization of long-term cold storage of rat precision-cut lung slices with a tissue preservation solution

Precision-cut lung slices (PCLS) are used as ex vivo model of the lung to fill the gap between in vitro and in vivo experiments. To allow optimal utilization of PCLS, possibilities to prolong slice viability via cold storage using optimized storage solutions were evaluated. Rat PCLS were cold stored in DMEM/F-12 or two different preservation solutions for up to 28 days at 4°C. After rewarming in DMEM/F-12, metabolic activity, live/dead staining, and mitochondrial membrane potential was assessed to analyze overall tissue viability. Single-cell suspensions were prepared and proportions of CD45⁺, EpCAM⁺, CD31⁺, and CD90⁺ cells were analyzed. As functional parameters, TNF-α expression was analyzed to detect inflammatory activity and bronchoconstriction was evaluated after acetylcholine stimulus. After 14 days of cold storage, viability and mitochondrial membrane potential were significantly better preserved after storage in solution 1 (potassium chloride rich) and solution 2 (potassium- and lactobionate-rich analog) compared with DMEM/F-12. Analysis of cell populations revealed efficient preservation of EpCAM⁺, CD31⁺, and CD90⁺ cells. Proportion of CD45⁺ cells decreased during cold storage but was better preserved by both modified solutions than by DMEM/F-12. PCLS stored in solution 1 responded substantially longer to inflammatory stimulation than those stored in DMEM/F-12 or solution 2. Analysis of bronchoconstriction revealed total loss of function after 14 days of storage in DMEM/F-12 but, in contrast, a good response in PCLS stored in the optimized solutions. An improved base solution with a high potassium chloride concentration optimizes cold storage of PCLS and allows shipment between laboratories and stockpiling of tissue samples.

Investigation of cardiac glycosides from oleander in a human induced pluripotent stem cells derived cardiomyocyte model

The ingestion of Nerium oleander and Thevetia peruviana are common causes for poisoning in Southeast Asia. All parts of the oleander shrub contain cardiac glycosides of the cardenolide type. These glycosides act via inhibition of a Na⁺/K⁺-ATPase which might cause severe arrhythmia and subsequent death in oleander-poisoned patients. The current study uses human induced pluripotent stem cells derived cardiomyocytes (hiPSC-CM) in a microelectrode array (MEA) system to assess the cardiac effects of neriifolin, oleandrin, digitoxigenin, peruvoside and thevetin A from the oleander plant. Digoxin was used as established reference compound. All tested compounds showed a corrected field potential duration (FPDc) shortening and was the lowest for 600 nM digitoxigenin with -36.9 ± 1.2 %. Next to the dose-dependent pro-arrhythmic potential, a complete beat arrest of the spontaneously beating hiPSC-CM was observed at a concentration of 300 nM for neriifolin, 600 nM for oleandrin and 1000 nM for digitoxigenin and peruvoside. Thevetin A did not cause arrhythmia up to a final concentration of 1000 nM. Thus, it was possible to establish a cardiac effect rank order of the tested substances: neriifolin > oleandrin > digitoxigenin = peruvoside > digoxin > thevetin A.

Catalytic activity and stereoselectivity of engineered phosphotriesterases towards structurally different nerve agents in vitro

Highly toxic organophosphorus nerve agents, especially the extremely stable and persistent V-type agents such as VX, still pose a threat to the human population and require effective medical countermeasures. Engineered mutants of the Brevundimonas diminuta phosphotriesterase (BdPTE) exhibit enhanced catalytic activities and have demonstrated detoxification in animal models, however, substrate specificity and fast plasma clearance limit their medical applicability. To allow better assessment of their substrate profiles, we have thoroughly investigated the catalytic efficacies of five BdPTE mutants with 17 different nerve agents using an AChE inhibition assay. In addition, we studied one BdPTE version that was fused with structurally disordered PAS polypeptides to enable delayed plasma clearance and one bispecific BdPTE with broadened substrate spectrum composed of two functionally distinct subunits connected by a PAS linker. Measured kcat/KM values were as high as 6.5 and 1.5 × 108 M-1 min-1 with G- and V-agents, respectively. Furthermore, the stereoselective degradation of VX enantiomers by the PASylated BdPTE-4 and the bispecific BdPTE-7 were investigated by chiral LC-MS/MS, resulting in a several fold faster hydrolysis of the more toxic P(-) VX stereoisomer compared to P(+) VX. In conclusion, the newly developed enzymes BdPTE-4 and BdPTE-7 have shown high catalytic efficacy towards structurally different nerve agents and stereoselectivity towards the toxic P(-) VX enantiomer in vitro and offer promise for use as bioscavengers in vivo.

Release of protein-bound nerve agents by excess fluoride from whole blood: GC-MS/MS method development, validation, and application to a real-life denatured blood sample

In analogy to the fluoride-induced regeneration of butyrylcholinesterase (BChE) inhibited by nerve agents a method was developed and optimized for whole blood samples. Compared to the plasma method, regeneration grade was found to be higher for cyclosarin (GF), i-butylsarin from VR, and n-butylsarin from CVX, but lower for sarin (GB), fluorotabun from tabun (GA), and ethylsarin from VX. Regeneration grade of soman (GD) is the same for both matrices because it is released from serum albumin and not from cholinesterases. The method was fully validated for GB and GF to prove selectivity, linearity (n = 6), limit of determination (LOD1), reproducibility (within day (n = 8) and from day to day (n = 8)), effectiveness of extraction, matrix effect, and sample stability (after sample preparation and during three freeze/thaw cycles). The other agents were tested for selectivity, linearity (n = 2), limit of determination, and stability after sample preparation. The method showed high selectivity, good linearity up to the protein's saturation concentration (GB: R² = 0.9995, GF: 0.9968), and high reproducibility (GB: C.V. 5.9-13.7%, GF: 4.9-10.3%). The limits of determination (calculated from the spiked amount of the original agent) were found with 0.3 ng/mL VX, 0.5 ng/mL GB, 1 ng/mL VR, 0.5 ng/mL GA, 1 ng/mL CVX, and 8 ng/mL GD. In the case of GF, it was found with 4 ng/mL using Isolute ENV + SPE cartridges as for the other analytes and with 2.5 ng/mL using Isolute C8 EC SPE cartridges instead. This method was then applied to a denatured whole blood sample obtained from an individual exposed to GB. While previously only the GB metabolite isopropyl methylphosphonic acid (IMPA) could be detected in this blood sample it was now possible to successfully release GB from the blood proteins by excess fluoride.

Inhibition of an organophosphate-detoxifying bacterial phosphotriesterase by albumin and plasma thiol components

The phosphotriesterase of the bacterium Brevundimonas diminuta (BdPTE) is a naturally occurring enzyme that catalyzes the hydrolysis of organophosphate (OP) nerve agents as well as pesticides and offers a potential treatment of corresponding intoxications. While BdPTE mutants with improved catalytic efficiencies against several OPs have been described, unexpectedly, less efficient breakdown of an OP was observed upon application in an animal model compared with in vitro measurements. Here, we describe detailed inhibition studies with the high-activity BdPTE mutant 10-2C3(C59M/C227A) by human plasma components, indicating that this enzyme is inhibited by serum albumin. The inhibitory activity is mediated by depletion of crucial zinc ions from the BdPTE active site, either via the known high-affinity zinc binding site of albumin or via chemical complex formation with its free thiol side chain at position Cys34. Albumin pre-charged with zinc ions or carrying a chemically blocked Cys34 side chain showed significantly reduced inhibitory activity; in fact, the combination of both measures completely abolished BdPTE inhibition. Consequently, the available zinc ion concentration in blood plays an important role for BdPTE activity in vivo and should be taken into account for therapeutic development and application of a catalytic OP scavenger.

Translating the Concept of Bispecific Antibodies to Engineering Heterodimeric Phosphotriesterases with Broad Organophosphate Substrate Recognition

We have adopted the concept of bispecific antibodies, which can simultaneously block or cross-link two different biomolecular targets, to create bispecific enzymes by exploiting the homodimeric quaternary structure of bacterial phosphotriesterases (PTEs). The PTEs from Brevundimonas diminuta and Agrobacterium radiobacter, whose engineered variants can efficiently hydrolyze organophosphorus (OP) nerve agents and pesticides, respectively, have attracted considerable interest for the treatment of the corresponding intoxications. OP nerve agents and pesticides still pose a severe toxicological threat in military conflicts, including acts of terrorism, as well as in agriculture, leading to >100000 deaths per year. In principle, engineered conventional homodimeric PTEs may provoke hydrolytic inactivation of individual OPs in vivo, and their application as catalytic bioscavengers via administration into the bloodstream has been proposed. However, their narrow substrate specificity would necessitate therapeutic application of a set or mixture of different enzymes, which complicates biopharmaceutical development. We succeeded in combining subunits from both enzymes and to stabilize their heterodimerization by rationally designing electrostatic steering mutations, thus breaking the natural C2 symmetry. The resulting bispecific enzyme from two PTEs with different bacterial origin exhibits an ultrabroad OP substrate profile and allows the efficient detoxification of both nerve agents and pesticides. Our approach of combining two active sites with distinct substrate specificities within one artificial dimeric biocatalyst-retaining the size and general properties of the original enzyme without utilizing protein mixtures or much larger fusion proteins-not only should facilitate biological drug development but also may be applicable to oligomeric enzymes with other catalytic activities.

Influence of cyclic and acyclic cucurbiturils on the degradation pathways of the chemical warfare agent VX

The highly toxic nerve agent VX is a methylphosphonothioate that degrades via three pathways in aqueous solution, namely through the hydrolysis of the P-O or P-S bonds, or the cleavage of the C-S bond at the 2-aminoethyl residue. In the latter case, an aziridinium ion and a phosphonothioate is formed. Here it is shown that acyclic or cyclic cucurbiturils inhibit these reactions in phosphate buffer at physiological pH and thus stabilise the nerve agent. When using unbuffered basic solutions as the reaction medium, however, in which the P-S or P-O bonds are normally hydrolysed preferentially, cucurbiturils turned out to strongly shift VX degradation towards the cleavage of the C-S bond. Cucurbit[7]uril, in particular, has a so pronounced effect under suitable conditions that it almost completely suppresses the formation of products resulting from the other degradation pathways. Investigations involving VX analogues in combination with computational methods suggest that one reason for the reaction control exerted by the cucurbiturils is the preorganisation of VX for aziridinium ion formation. In addition, cucurbit[7]uril also lowers the transition state of the reaction by stabilising the positive charge developing on the way to the product. Cucurbiturils thus have a marked effect on the reactivity of a highly toxic nerve agent, which potentially allows using them for decontamination purposes.

In Vitro Interaction of Organophosphono- and Organophosphorothioates with Human Acetylcholinesterase

The implementation of the Chemical Weapons Convention (CWC) in 1997 was a milestone in the prohibition of chemical warfare agents (CWA). Yet, the repeated use of CWA underlines the ongoing threat to the population. Organophosphorus (OP) nerve agents still represent the most toxic CWA subgroup. Defensive research on nerve agents is mainly focused on the "classical five", namely tabun, sarin, soman, cyclosarin and VX, although Schedule 1 of the CWC covers an unforeseeable number of homologues. Likewise, an uncounted number of OP pesticides have been produced in previous decades. Our aim was to determine the in vitro inhibition kinetics of selected organophosphono- and organophosphorothioates with human AChE, as well as hydrolysis of the agents in human plasma and reactivation of inhibited AChE, in order to derive potential structure-activity relationships. The investigation of the interactions of selected OP compounds belonging to schedule 1 (V-agents) and schedule 2 (amiton) of the CWC with human AChE revealed distinct structural effects of the P-alkyl, P-O-alkyl and N,N-dialkyl residues on the inhibitory potency of the agents. Irrespective of structural modifications, all tested V-agents presented as highly potent AChE inhibitors. The high stability of the tested agents in human plasma will most likely result in long-lasting poisoning in vivo, having relevant consequences for the treatment regimen. In conclusion, the results of this study emphasize the need to investigate the biological effects of nerve agent analogues in order to assess the efficacy of available medical countermeasures.

Organophosphorus compounds and oximes: a critical review

Organophosphorus (OP) pesticides and nerve agents still pose a threat to the population. Treatment of OP poisoning is an ongoing challenge and burden for medical services. Standard drug treatment consists of atropine and an oxime as reactivator of OP-inhibited acetylcholinesterase and is virtually unchanged since more than six decades. Established oximes, i.e. pralidoxime, obidoxime, TMB-4, HI-6 and MMB-4, are of insufficient effectiveness in some poisonings and often cover only a limited spectrum of the different nerve agents and pesticides. Moreover, the value of oximes in human OP pesticide poisoning is still disputed. Long-lasting research efforts resulted in the preparation of countless experimental oximes, and more recently non-oxime reactivators, intended to replace or supplement the established and licensed oximes. The progress of this development is slow and none of the novel compounds appears to be suitable for transfer into advanced development or into clinical use. This situation calls for a critical analysis of the value of oximes as mainstay of treatment as well as the potential and limitations of established and novel reactivators. Requirements for a straightforward identification of superior reactivators and their development to licensed drugs need to be addressed as well as options for interim solutions as a chance to improve the therapy of OP poisoning in a foreseeable time frame.

Synthesis and in vitro evaluation of novel non-oximes for the reactivation of nerve agent inhibited human acetylcholinesterase

Since several decades oximes have been used as part of treatment of nerve agent intoxication with the aim to restore the biological function of the enzyme acetylcholinesterase after its covalent inhibition by organophosphorus compounds such as pesticides and nerve agents. Recent findings have illustrated that, besides oximes, certain Mannich phenols can reactivate the inhibited enzyme very effectively, and may therefore represent an attractive complementary class of reactivators. In this paper we further probe the effect of structural variation on the in vitro efficacy of Mannich phenol based reactivators. Thus, we present the synthesis of 14 compounds that are close variants of the previously reported 4-amino-2-(1-pyrrolidinylmethyl)-phenol, a very effective non-oxime reactivator, and 3 dimeric Mannich phenols. All compounds were assessed for their ability to reactivate human acetylcholinesterase inhibited by the nerve agents VX, tabun, sarin, cyclosarin and paraoxon in vitro. It was confirmed that the potency of the compounds is highly sensitive to small structural changes, leading to diminished reactivation potency in many cases. However, the presence of 4-substituted alkylamine substituents (as exemplified with the 4-benzylamine-variant) was tolerated. More surprisingly, the dimeric compounds demonstrated non-typical behavior and displayed some reactivation potency as well. Both findings may open up new avenues for designing more effective non-oxime reactivators.

A case report of cholinesterase inhibitor poisoning: cholinesterase activities and analytical methods for diagnosis and clinical decision making

Suicidal ingestion of organophosphorus (OP) or carbamate (CM) compounds challenges health care systems worldwide, particularly in Southeast Asia. The diagnosis and treatment of OP or CM poisoning is traditionally based on the clinical appearance of the typical cholinergic toxidrome, e.g. miosis, salivation and bradycardia. Yet, clinical signs might be inconclusive or even misleading. A current case report highlights the importance of enzymatic assays to provide rapid information and support clinicians in diagnosis and rational clinical decision making. Furthermore, the differentiation between OP and CM poisoning seems important, as an oxime therapy will most probably not provide benefit in CM poisoning, but—as every pharmaceutical product—it might result in adverse effects. The early identification of the causing agent and the amount taken up in the body are helpful in planning of the therapeutic regimen including experimental strategies, e.g. the use of human blood products to facilitate scavenging of the toxic agent. Furthermore, the analysis of biotransformation products and antidote levels provides additional insights into the pathophysiology of OP or CM poisoning. In conclusion, cholinesterase activities and modern analytical methods help to provide a more effective treatment and a thorough understanding of individual cases of OP or CM poisoning.

Impact of soman and acetylcholine on the effects of propofol in cultured cortical networks

Patients intoxicated with organophosphorous compounds may need general anaesthesia to enable mechanical ventilation or for control of epileptiform seizures. It is well known that cholinergic overstimulation attenuates the efficacy of general anaesthetics to reduce spontaneous network activity in the cortex. However, it is not clear how propofol, the most frequently used intravenous anaesthetic today, is affected. Here, we investigated the effects of cholinergic overstimulation induced by soman and acetylcholine on the ability of propofol to depress spontaneous action potential activity in organotypic cortical slices measured by extracellular voltage recordings. Cholinergic overstimulation by co-application of soman and acetylcholine (10 μM each) did not reduce the relative inhibition of propofol (1.0 μM; mean normalized action potential firing rate 0.49 ± 0.06 of control condition, p < 0.001, Wilcoxon signed rank test) but clearly reduced its efficacy. Co-application of atropine (10 nM) did not improve the efficacy. Propofol preserved its relative inhibitory potential but did not produce a degree of neuronal depression which can be expected to assure hypnosis in humans. Since a combination with atropine did not improve its efficacy, an increase in dosage will probably be necessary when propofol is used in victims suffering from organophosphorous intoxication.

Screening of chiral shift reagents suitable to generically separate the enantiomers of V-agents by 31P-NMR spectroscopy

Fourteen amino acids protected at the N-terminal and at their side chains were screened for resolving the enantiomers of V-agents by NMR. While none of the shift reagents tested showed really effective separation in proton NMR, two of them (BOC-Gln(Xan)-OH, 16, and Z-Arg(Z)₂-OH), 21, with 16 superior to 21) were found suitable to separate the enantiomers of all V-agent homologues involved in the test by ³¹P-NMR. Molar ratios investigated were 1:0.5, 1:1, 1:1.5, 1:2, and 1:3 with the V-agent set to 1 throughout the experiments. All these ratios were more or less effective, but 1:3 was found to separate the V-agents the most reliable way. It is postulated that three chiral solvating molecules are then coordinated around the organophosphate: ion pair formation with the amino nitrogen of the V agent side chain, hydrogen bonding provided by the PO unit, and extension of coordination at the phosphorus atom itself. After chiral separation of VX by semi-preparative LC-MS the enantiomers were examined with both configurations of 16 releasing four different ³¹P NMR peaks which correspond to four different complexes: R-S₃, R-R₃, S-R₃, and S-S₃. Comparing these results with literature data it is assumed that (+)-VX corresponds to the R_P configuration and (-)-VX to the S_P-configuration.

Early diagnosis of nerve agent exposure with a mobile test kit and implications for medical countermeasures: a trigger to react

Recent uses of nerve agents underline the need of early diagnosis as trigger to react (initiating medical countermeasures, avoiding cross-contamination). As organophosphorus (OP) pesticide poisoning exerts the same pathomechanism, that is, inhibition of the pivotal enzyme acetylcholinesterase (AChE), a portable cholinesterase (ChE) test kit was applied in an emergency room for rapid diagnosis of OP poisoning. OP nerve agents or pesticides result in the inhibition of AChE. As AChE is also expressed on erythrocytes, patient samples are easily available. However, in most clinics only determination of plasma butyrylcholinesterase (BChE) is established which lacks a pathophysiological correlate, shows higher variability in the population and behaves different regarding inhibition by OP and reactivation by oximes. The ChE test kit helped to diagnose atypical cases of OP poisoning, for example, missing of typical muscarinic symptoms, and resulted in administration of pralidoxime, the oxime used in Serbia. The ChE test kit also allows an initial assessment whether an oxime therapy is successful. In one case report, AChE activity increased after oxime administration indicating therapeutic success whereas BChE activity did not. With only BChE at hand, this therapeutic effect would have been missed. As inhibition of AChE or BChE activity is determined, the CE-certified device is a global diagnostic tool for all ChE inhibitors including carbamates which might also be misused as chemical weapon. The ChE test kit is a helpful point-of-care device for the diagnosis of ChE inhibitor poisoning. Its small size and easy menu-driven use advocate procurement where nerve agent and OP pesticide exposure are possible.

A catalytic bioscavenger with improved stability and reduced susceptibility to oxidation for treatment of acute poisoning with neurotoxic organophosphorus compounds

Organophosphorus (OP)¹ nerve agents pose a severe toxicological threat, both after dissemination in military conflicts and by terrorists. Hydrolytic enzymes, which may be administered into the blood stream of victims by injection and can decompose the circulating nerve agent into non-toxic metabolites in vivo, could offer a treatment. Indeed, for the phosphotriesterase found in the bacterium Brevundimonas diminuta (BdPTE),² engineered versions with improved catalytic efficiencies have been described; yet, their biochemical stabilities are insufficient for therapeutic use. Here, we describe the application of rational protein design to develop novel mutants of BdPTE that are less susceptible to oxidative damage. In particular, the replacement of two unpaired cysteine residues by more inert amino acids led to higher stability while maintaining high catalytic activity towards a broad spectrum of substrates, including OP pesticides and V-type nerve agents. The mutant BdPTE enzymes were produced in Escherichia coli, purified to homogeneity, and their biochemical and enzymological properties were assessed. Several candidates both revealed enhanced thermal stability and were less susceptible to oxidative stress, as demonstrated by mass spectrometry. These mutants of BdPTE may show promise for the treatment of acute intoxications by nerve agents as well as OP pesticides.

Efficacy of an organophosphorus hydrolase enzyme (OpdA) in human serum and minipig models of organophosphorus insecticide poisoning

Objectives: Current therapeutic options for organophosphorus (OP) insecticide self-poisoning including atropine and oximes are inadequate and case fatality may exceed 20%. An OP hydrolase enzyme, OpdA, has been used for environmental cleansing of OP insecticides and prevented death in rat and non-human primate models of OP insecticide poisoning if given very quickly after exposure. We here tested OpdA's ability to break down OP insecticides in human serum and in clinically relevant minipig models of OP insecticide poisoning.Methods: Human serum was spiked with seven diverse WHO Class II OP insecticides (chlorpyrifos, quinalphos, diazinon, dimethoate, fenthion, phenthoate, and profenofos) and the effect of OpdA on degradation measured. The pharmacodynamic and clinical effects of OpdA treatment were studied in Gottingen minipigs orally poisoned with agricultural formulations of dimethoate EC40 or methyl parathion EC60; pharmacodynamic effects were also assessed in profenofos EC50-poisoned pigs.Results: OpdA effectively hydrolysed OP insecticides in human serum, with rates varying from 856 (SD 44) down to 0.107 (SD 0.01) moles of substrate hydrolysed/mole of enzyme/sec (k_cat) for quinalphos and phenthoate, respectively, although at rates 2-3 log orders less than found in vitro in buffered solution. It showed clinical benefit in minipig models, reducing the dose of noradrenaline required to sustain an adequate mean arterial pressure after dimethoate (mean 0.149 [SD 0.10] μg/kg/h vs. 1.07 [SD 0.77] μg/kg/h, p < .0001) and methyl parathion (mean 0.077 [SD 0.08] μg/kg/h vs. 0.707 [SD 0.49] μg/kg/h, p < .0001) poisoning. OpdA reduced blood OP insecticide concentration and acetylcholinesterase inhibition after poisoning by dimethoate, methyl parathion, and profenofos insecticides.Conclusions: In vitro incubation of OpdA in human serum showed hydrolysis of diverse OP insecticides, although at lower rates than found in buffer solutions. This activity results in clinical and pharmacodynamic efficacy in vivo against several OP insecticides. These results support the testing of OpdA in further animal models before considering human trials to determine whether it may become an urgently required novel therapeutic agent for OP insecticide self-poisoning.

The in vitro protective effects of the three novel nanomolar reversible inhibitors of human cholinesterases against irreversible inhibition by organophosphorous chemical warfare agents

Acetylcholinesterase (AChE) is an enzyme which terminates the cholinergic neurotransmission, by hydrolyzing acetylcholine at the nerve and nerve-muscle junctions. The reversible inhibition of AChE was suggested as the pre-treatment option of the intoxications caused by nerve agents. Based on our derived 3D-QSAR model for the reversible AChE inhibitors, we designed and synthesized three novel compounds 8-10, joining the tacrine and aroylacrylic acid phenylamide moieties, with a longer methylene chain to target two distinct, toplogically separated anionic areas on the AChE. The targeted compounds exerted low nanomolar to subnanomolar potency toward the E. eel and human AChE's as well as the human BChE and showed mixed inhibition type in kinetic studies. All compounds were able to slow down the irreversible inhibition of the human AChE by several nerve agents including tabun, soman and VX, with the estimated protective indices around 5, indicating a valuable level of protection. Putative noncovalent interactions of the selected ligand 10 with AChE active site gorge were finally explored by molecular dynamics simulation suggesting a formation of the salt bridge between the protonated linker amino group and the negatively charged Asp74 carboxylate side chain as a significant player for the successful molecular recognition in line with the design strategy. The designed compounds may represent a new class of promising leads for the development of more effective pre-treatment options.

New Resensitizers for the Nicotinic Acetylcholine Receptor by Ligand-Based Pharmacophore Modeling

INTRODUCTION

Irreversible inhibition of the acetylcholinesterase upon intoxication with organophosphorus compounds leads to an accumulation of acetylcholine in the synaptic cleft and a subsequent desensitization of nicotinic acetylcholine receptors which may ultimately result in respiratory failure. A direct intervention at the nicotinic acetylcholine receptor (nAChR) was proposed as an alternative therapeutic approach to the treatment with atropine and oximes.

METHODS

The bispyridinium compound MB327 has been found to recover functional activity of nAChR thus representing a promising starting point for the development of new drugs for the treatment of organophosphate poisoning. Recent solid-supported membrane-based electrophysiological experiments have identified symmetrically substituted bispyridinium compounds e.g. MB327, MB583, and PTM0001 that are able to resensitize nAChR of Torpedo californica. In addition, six compounds have been found not to show any resensitizing potential and were thus classified as inactive. This set of active and inactive bispyridinium compounds was taken to develop a pharmacophore model and in silico screening of a virtual database of bispyridinium compounds to identify new compounds that are able to restore the functional activity of desensitized nAChR.

RESULTS

Screening of a virtual compound database of symmetrically substituted bispyridinium compounds with the derived pharmacophore yielded several promising compounds which satisfy the pharmacophore and ought to have the same or even better resensitizing effect on nAChR as the parent compound MB327.

COPD and asthma therapeutics for supportive treatment in organophosphate poisoning

Context: Nerve agents like sarin or VX have repeatedly been used in military conflicts or homicidal attacks, as seen in Syria or Malaysia 2017. Together with pesticides, nerve agents assort as organophosphorus compounds (OP), which inhibit the enzyme acetylcholinesterase. To counteract subsequent fatal symptoms due to acetylcholine (ACh) accumulation, oximes plus atropine are administered, a regimen that lacks efficacy in several cases of OP poisoning. New therapeutics are in development, but still need evaluation before clinical employment. Supportive treatment with already approved drugs presents an alternative, whereby compounds from COPD and asthma therapy are likely options. A recent pilot study by Chowdhury et al. included β2-agonist salbutamol in the treatment of OP-pesticide poisoned patients, yielding ambiguous results concerning the addition. Here, we provide experimental data for further investigations regarding the value of these drugs in OP poisoning. Methods: By video-microscopy, changes in airway area were analyzed in VX-poisoned rat precision cut lung slices (PCLS) after ACh-induced airway contraction and subsequent application of selected anticholinergics/β2-agonists. Results: Glycopyrrolate and ipratropium efficiently antagonized an ACh-induced airway contraction in VX-poisoned PCLS (EC₅₀ glycopyrrolate 15.8 nmol/L, EC₅₀ ipratropium 2.3 nmol/L). β2-agonists formoterol and salbutamol had only negligible effects when solely applied in the same setting. However, combination of formoterol or salbutamol with low dosed glycopyrrolate or atropine led to an additive effect compared to the sole application [50.6 ± 8.8% airway area increase after 10 nmol/L formoterol +1 nmol/L atropine versus 11.7 ± 9.2% (10 nmol/L formoterol) or 8.6 ± 5.9% (1 nmol/L atropine)]. Discussion: We showed antagonizing effects of anticholinergics and β2-agonists on ACh-induced airway contractions in VX-poisoned PCLS, thus providing experimental data to support a prospective comprehensive clinical study. Conclusions: Our results indicate that COPD and asthma therapeutics could be a valuable addition to the treatment of OP poisoning.