Specific quinone reductase 2 inhibitors reduce metabolic burden and reverse Alzheimer's disease phenotype in mice

Biological aging can be described as accumulative, prolonged metabolic stress and is the major risk factor for cognitive decline and Alzheimer's disease (AD). Recently, we identified and described a quinone reductase 2 (QR2) pathway in the brain, in which QR2 acts as a removable memory constraint and metabolic buffer within neurons. QR2 becomes overexpressed with age, and it is possibly a novel contributing factor to age-related metabolic stress and cognitive deficit. We found that, in human cells, genetic removal of QR2 produced a shift in the proteome opposing that found in AD brains while simultaneously reducing oxidative stress. We therefore created highly specific QR2 inhibitors (QR2is) to enable evaluation of chronic QR2 inhibition as a means to reduce biological age-related metabolic stress and cognitive decline. QR2is replicated results obtained by genetic removal of QR2, while local QR2i microinjection improved hippocampal and cortical-dependent learning in rats and mice. Continuous consumption of QR2is in drinking water improved cognition and reduced pathology in the brains of AD-model mice (5xFAD), with a noticeable between-sex effect on treatment duration. These results demonstrate the importance of QR2 activity and pathway function in the healthy and neurodegenerative brain and what we believe to be the great therapeutic potential of QR2is as first-in-class drugs.

Tuning Butyrylcholinesterase Inactivation and Reactivation by Polymer-Based Protein Engineering

Organophosphate nerve agents rapidly inhibit cholinesterases thereby destroying the ability to sustain life. Strong nucleophiles, such as oximes, have been used as therapeutic reactivators of cholinesterase-organophosphate complexes, but suffer from short half-lives and limited efficacy across the broad spectrum of organophosphate nerve agents. Cholinesterases have been used as long-lived therapeutic bioscavengers for unreacted organophosphates with limited success because they react with organophosphate nerve agents with one-to-one stoichiometries. The chemical power of nucleophilic reactivators is coupled to long-lived bioscavengers by designing and synthesizing cholinesterase-polymer-oxime conjugates using atom transfer radical polymerization and azide-alkyne "click" chemistry. Detailed kinetic studies show that butyrylcholinesterase-polymer-oxime activity is dependent on the electrostatic properties of the polymers and the amount of oxime within the conjugate. The covalent coupling of oxime-containing polymers to the surface of butyrylcholinesterase slows the rate of inactivation of paraoxon, a model nerve agent. Furthermore, when the enzyme is covalently inhibited by paraoxon, the covalently attached oxime induced inter- and intramolecular reactivation. Intramolecular reactivation will open the door to the generation of a new class of nerve agent scavengers that couple the speed and selectivity of biology to the ruggedness and simplicity of synthetic chemicals.

Rapid Covalent-Probe Discovery by Electrophile-Fragment Screening

Covalent probes can display unmatched potency, selectivity, and duration of action; however, their discovery is challenging. In principle, fragments that can irreversibly bind their target can overcome the low affinity that limits reversible fragment screening, but such electrophilic fragments were considered nonselective and were rarely screened. We hypothesized that mild electrophiles might overcome the selectivity challenge and constructed a library of 993 mildly electrophilic fragments. We characterized this library by a new high-throughput thiol-reactivity assay and screened them against 10 cysteine-containing proteins. Highly reactive and promiscuous fragments were rare and could be easily eliminated. In contrast, we found hits for most targets. Combining our approach with high-throughput crystallography allowed rapid progression to potent and selective probes for two enzymes, the deubiquitinase OTUB2 and the pyrophosphatase NUDT7. No inhibitors were previously known for either. This study highlights the potential of electrophile-fragment screening as a practical and efficient tool for covalent-ligand discovery.

Fluorescent organophosphates: novel probes for studying aging-induced conformational changes in inhibited acetylcholinesterase and for localization of cholinesterase in nervous tissue

Aging of acetylcholinesterase (AChE) inhibited by certain organophosphates such as diisopropylfluorophosphate apparently involves dealkylation of the bound organophosphoryl moiety; this renders the inactive enzyme resistant to reactivation by quaternary oximes such as 2-pyridinealdoxime methiodide (2-PAM) which are used in therapy of organophosphate intoxication. The fluorescent pyrenyl organophosphates synthesized in this study were designed to detect putative conformational changes which might explain this resistance. The following inhibitors: 1-pyrenebutyl phosphorodichloride (PBPDC), 1-pyrenebutyl ethylphosphorochloridate (PBEPC), and 1-pyrenebutyl ethylphosphorofluoridate (PBEPF), react specifically with purified electric eel AChE (ki = 10(6)-10(7) M-1 min-1). AChE inhibited by PBEPC and PBEPF was readily reactivated by 2-PAM, while enzyme inhibited PBPDC could not be reactivated. Conjugates were prepared of both PBEPC and PBPDC with AChE, each containing one molecule of florophore per catalytic subunit. Thus two stoichiometric conjugates, PBEP-AChE (non-aged) and POBP-AChE (aged), were obtained. The two complexes exhibited identical absorption spectra, but differed in their steady-state fluorescence spectra. Although the wave-lenths of the excitation and emission spectra were similar, the pyrene fluorescence of the non-aged conjugate was ca. 50% quenched relative to the aged conjugate. Nanosecond fluorescence decay studies revealed two principal lifetime components of pyrene fluorescence. Both were longer for the aged (PBP-AChE) than for the non-aged (PBEP-AChE) conjugate and revealed a ca. 50% lower quantum yield for the non-aged as compared to the aged conjugate. A possible interpretation for these results is that in the aged conjugate the organophosphoryl moiety is less acessible to the external medium. Measurement of quenching of pyrene fluorescence in the aged and non-aged conjugates by the peripheral anionic site ligand propidium also indicated marked conformational differences between the two conjugates, and circular polarization of luminescence measurements revealed that propidium itself induced a substantial conformational change in both conjugates. Fluorescence lifetime measurements revealed that whereas propidium had little effect on the decay parameters for the non-aged conjugate it caused a decrease in lifetime and in relative quantum yield for the aged conjugate. PBEPF virtually eliminated cholinesterase activity in dissociated cord and brain cultures. Fluorescence microscopy reveals fine green fluorescent grains distinctly located throughout many neurons and glia. Labelling is much more pronounced in larger and older neurons. No specific fluorescence could be detected in cultures preincubated with nonfluorescent organophosphates.

Imidazole aldoximes effective in assisting butyrylcholinesterase catalysis of organophosphate detoxification

Intoxication by organophosphate (OP) nerve agents and pesticides should be addressed by efficient, quickly deployable countermeasures such as antidotes reactivating acetylcholinesterase or scavenging the parent OP. We present here synthesis and initial in vitro characterization of 14 imidazole aldoximes and their structural refinement into three efficient reactivators of human butyrylcholinesterase (hBChE) inhibited covalently by nerve agent OPs, sarin, cyclosarin, VX, and the OP pesticide metabolite, paraoxon. Rapid reactivation of OP–hBChE conjugates by uncharged and nonprotonated tertiary imidazole aldoximes allows the design of a new OP countermeasure by conversion of hBChE from a stoichiometric to catalytic OP bioscavenger with the prospect of oral bioavailability and central nervous system penetration. The enhanced in vitro reactivation efficacy determined for tertiary imidazole aldoximes compared to that of their quaternary N-methyl imidazolium analogues is attributed to ion pairing of the cationic imidazolium with Asp 70, altering a reactive alignment of the aldoxime with the phosphorus in the OP–hBChE conjugate.

Mechanism of interaction of novel uncharged, centrally active reactivators with OP-hAChE conjugates

A library of more than 200 novel uncharged oxime reactivators was used to select and refine lead reactivators of human acetylcholinesterase (hAChE) covalently conjugated with sarin, cyclosarin, VX, paraoxon and tabun. N-substituted 2-hydroxyiminoacetamido alkylamines were identified as best reactivators and reactivation kinetics of the lead oximes, RS41A and RS194B, were analyzed in detail. Compared to reference pyridinium reactivators, 2PAM and MMB4, molecular recognition of RS41A reflected in its Kox constant was compromised by an order of magnitude on average for different OP-hAChE conjugates, without significant differences in the first order maximal phosphorylation rate constant k(2). Systematic structural modifications of the RS41A lead resulted in several-fold improvement with reactivator, RS194B. Kinetic analysis indicated K(ox) reduction for RS194B as the main kinetic constant leading to efficient reactivation. Subtle structural modifications of RS194B were used to identify essential determinants for efficient reactivation. Computational molecular modeling of RS41A and RS194B interactions with VX inhibited hAChE, bound reversibly in Michaelis type complex and covalently in the pentacoordinate reaction intermediate suggests that the faster reactivation reaction is a consequence of a tighter RS194B interactions with hAChE peripheral site (PAS) residues, in particular with D74, resulting in lower interaction energies for formation of both the binding and reactivation states. Desirable in vitro reactivation properties of RS194B, when coupled with its in vivo pharmacokinetics and disposition in the body, reveal the potential of this oxime design as promising centrally and peripherally active antidotes for OP toxicity.

Refinement of structural leads for centrally acting oxime reactivators of phosphylated cholinesterases

We present a systematic structural optimization of uncharged but ionizable N-substituted 2-hydroxyiminoacetamido alkylamine reactivators of phosphylated human acetylcholinesterase (hAChE) intended to catalyze the hydrolysis of organophosphate (OP)-inhibited hAChE in the CNS. Starting with the initial lead oxime RS41A identified in our earlier study and extending to the azepine analog RS194B, reactivation rates for OP-hAChE conjugates formed by sarin, cyclosarin, VX, paraoxon, and tabun are enhanced severalfold in vitro. To analyze the mechanism of intrinsic reactivation of the OP-AChE conjugate and penetration of the blood-brain barrier, the pH dependence of the oxime and amine ionizing groups of the compounds and their nucleophilic potential were examined by UV-visible spectroscopy, (1)H NMR, and oximolysis rates for acetylthiocholine and phosphoester hydrolysis. Oximolysis rates were compared in solution and on AChE conjugates and analyzed in terms of the ionization states for reactivation of the OP-conjugated AChE. In addition, toxicity and pharmacokinetic studies in mice show significantly improved CNS penetration and retention for RS194B when compared with RS41A. The enhanced intrinsic reactivity against the OP-AChE target combined with favorable pharmacokinetic properties resulted in great improvement of antidotal properties of RS194B compared with RS41A and the standard peripherally active oxime, 2-pyridinealdoxime methiodide. Improvement was particularly noticeable when pretreatment of mice with RS194B before OP exposure was combined with RS194B reactivation therapy after the OP insult.

Oxime-assisted acetylcholinesterase catalytic scavengers of organophosphates that resist aging

The cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase, are primary targets of organophosphates (OPs). Exposure to OPs can lead to serious cardiovascular complications, respiratory compromise, and death. Current therapy to combat OP poisoning involves an oxime reactivator (2-PAM, obidoxime, TMB4, or HI-6) combined with atropine and on occasion an anticonvulsant. Butyrylcholinesterase, administered in the plasma compartment as a bio-scavenger, has also shown efficacy but is limited by its strict stoichiometric scavenging, slow reactivation, and a propensity for aging. Here, we characterize 10 human (h) AChE mutants that, when coupled with an oxime, give rise to catalytic reactivation and aging resistance of the soman conjugate. With the most efficient human AChE mutant Y337A/F338A, we show enhanced reactivation rates for several OP-hAChE conjugates compared with wild-type hAChE when reactivated with HI-6 (1-(2'-hydroxyiminomethyl-1'-pyridinium)-3-(4'-carbamoyl-1-pyridinium)). In addition, we interrogated an 840-member novel oxime library for reactivation of Y337A/F338A hAChE-OP conjugates to delineate the most efficient oxime-mutant enzyme pairs for catalytic bio-scavenging. Combining the increased accessibility of the Y337A mutation to oximes within the space-impacted active center gorge with the aging resistance of the F338A mutation provides increased substrate diversity in scavenging potential for aging-prone alkyl phosphate inhibitors.

New structural scaffolds for centrally acting oxime reactivators of phosphylated cholinesterases

We describe here the synthesis and activity of a new series of oxime reactivators of cholinesterases (ChEs) that contain tertiary amine or imidazole protonatable functional groups. Equilibration between the neutral and protonated species at physiological pH enables the reactivators to cross the blood-brain barrier and distribute in the CNS aqueous space as dictated by interstitial and cellular pH values. Our structure-activity analysis of 134 novel compounds considers primarily imidazole aldoximes and N-substituted 2-hydroxyiminoacetamides. Reactivation capacities of novel oximes are rank ordered by their relative reactivation rate constants at 0.67 mm compared with 2-pyridinealdoxime methiodide for reactivation of four organophosphate (sarin, cyclosarin, VX, and paraoxon) conjugates of human acetylcholinesterase (hAChE). Rank order of the rates differs for reactivation of human butyrylcholinesterase (hBChE) conjugates. The 10 best reactivating oximes, predominantly hydroxyimino acetamide derivatives (for hAChE) and imidazole-containing aldoximes (for hBChE) also exhibited reasonable activity in the reactivation of tabun conjugates. Reactivation kinetics of the lead hydroxyimino acetamide reactivator of hAChE, when analyzed in terms of apparent affinity (1/K(ox)) and maximum reactivation rate (k(2)), is superior to the reference uncharged reactivators monoisonitrosoacetone and 2,3-butanedione monoxime and shows potential for further refinement. The disparate pH dependences for reactivation of ChE and the general base-catalyzed oximolysis of acetylthiocholine reveal that distinct reactivator ionization states are involved in the reactivation of ChE conjugates and in conferring nucleophilic reactivity of the oxime group.

Psychosocial outcomes related to subjective threat from armed conflict events (STACE): Findings from the Israeli-Palestinian cross-cultural HBSC study

OBJECTIVE

This study investigates the relationship between exposure to armed conflict and terror events, and an array of mental and behavioral outcomes within a large cross-cultural scientifically representative sample of 24,935 Palestinian (7,430 West Bank and 7,217 Gaza) and Israeli (5,255 Jewish and 6,033 Arab) 11-, 13-, and 15-year-old school children. The children of the Middle East have been subjected to exposure from armed conflict and terrorism repeatedly with no adequate research or interventions aimed at shielding them from the hazards of such exposure to their mental and social well-being.

METHOD

This paper studies the relationship between a newly developed scale (STACE) measuring levels of subjective perceptions of threat/fear due to exposure to armed conflict events and its predicting association with six psychosocial and behavioral outcomes covering (1) poor mental health, (2) positive well-being, and (3) risk behaviors. It also examines the role of parental support in "buffering" the effects of exposure to armed conflict events within the four target populations.

RESULTS

Results showed that STACE has significant and strong effects on all six dependent variables representing (1) mental post trauma, (2) diminished well-being, and (3) elevated risk behaviors. STACE strongly affects all four populations with the greatest impact among the Jewish Israeli population and the least impact shown for the Arab Israeli youth. Parental support ("significant adult") has both a direct main effect on the outcomes of all six variables as well as a significant "buffering" effect on the impact of STACE on certain outcome variables (posttraumatic symptoms, life satisfaction, positive life perceptions, and tobacco use).

CONCLUSIONS AND PRACTICE IMPLICATIONS

Regardless of the type of armed conflict events, the perception of threat and fear that a child experiences has a universal significant negative impact on mental, social, and behavioral well-being. The importance of the existence of a supporting significant adult in exposed children's lives is also emphasized. The findings show major implications for the development of community-based interventions focusing on enhancing parental, and other adult support in the lives of children living in armed conflict regions of the world.

Characterization of asymmetric fluorogenic phosphonates as probes for developing organophosphorus hydrolases with broader stereoselectivity

Organophosphorus hydrolases (OPH) such as mammalian plama paraoxonase (PON1) detoxify asymmetric toxic organophosphorus (OP) nerve agents by preferentially hydrolyzing the less toxic P(+) optical isomer. In order to develop new OPHs with broader stereoselectivity we have prepared a series of asymmetric fluorogenic organophosphonates (Flu-OPs). Such Flu-OPs may serve as molecular probes for screening large libraries of OP hydrolases during directed evolution. Flu-OPs were prepared as methylphosphonates (MPs) diesters containing either ethyl (E), isopropyl (I), cyclohexyl (C) or pinacolyl (P) groups that are structural congeners of the nerve agents VX, sarin, cyclosarin and soman, respectively. The second ester bond was formed with fluorescent moieties that are either 3-cyano-4-methyl-7-hydroxy coumarin (MeCyC) or 1,3-dichloro-7-hydroxy 9,9-dimethyl-9H-acridin-2-one (DDAO). To further characterize the Flu-OPs as surrogates of their respective nerve agents, we have studied the reactivation of Flu-OP-inhibited AChE using 2-PAM and toxogonin (TOX). AChE was 90-95% inhibited by all Flu-OPs (0.36-0.9(M) and then was reactivated by either 2-PAM or TOX. TOX caused a more rapid reactivation than 2-PAM with the following rank order; EMP>IMP>CMP. TOX was also shown to be a better reactivator than 2-PAM for AChE inhibited by the nerve agents VX and cyclosarin. PMP-AChE could not be reactivated by either TOX or 2-PAM, similarly to aging of PMP-AChE formed by inhibition with soman. Racemic CMP-MeCyC was used for screening two new PON1 variants from a neutral library of PON1. These multiple mutation variants include replacement of active site amino acid residues. Neither mutation in these new variants appeared in PON1 variants previously discovered by directed evolution using symmetric Flu-OP. Detoxification rate of cylcosarin by these new PON1 variants was rather slow indicating the need to further screen PON1 clones using optically active Flu-OPs. Therefore, we have separated enzymatically the P(-) enantiomer of CMP-MeCyC and determined its 98% purity using chiral HPLC.

Enhanced stereoselective hydrolysis of toxic organophosphates by directly evolved variants of mammalian serum paraoxonase

We addressed the ability of various organophosphorus (OP) hydrolases to catalytically scavenge toxic OP nerve agents. Mammalian paraoxonase (PON1) was found to be more active than Pseudomonas diminuta OP hydrolase (OPH) and squid O,O-di-isopropyl fluorophosphatase (DFPase) in detoxifying cyclosarin (O-cyclohexyl methylphosphonofluoridate) and soman (O-pinacolyl methylphosphonofluoridate). Subsequently, nine directly evolved PON1 variants, selected for increased hydrolytic rates with a fluorogenic diethylphosphate ester, were tested for detoxification of cyclosarin, soman, O-isopropyl-O-(p-nitrophenyl) methyl phosphonate (IMP-pNP), DFP, and chlorpyrifos-oxon (ChPo). Detoxification rates were determined by temporal acetylcholinesterase inhibition by residual nonhydrolyzed OP. As stereoisomers of cyclosarin and soman differ significantly in their acetylcholinesterase-inhibiting potency, we actually measured the hydrolysis of the more toxic stereoisomers. Cyclosarin detoxification was approximately 10-fold faster with PON1 mutants V346A and L69V. V346A also exhibited fourfold and sevenfold faster hydrolysis of DFP and ChPo, respectively, compared with wild-type, and ninefold higher activity towards soman. L69V exhibited 100-fold faster hydrolysis of DFP than the wild-type. The active-site mutant H115W exhibited 270-380-fold enhancement toward hydrolysis of the P-S bond in parathiol, a phosphorothiolate analog of parathion. This study identifies three key positions in PON1 that affect OP hydrolysis, Leu69, Val346 and His115, and several amino-acid replacements that significantly enhance the hydrolysis of toxic OPs. GC/pulsed flame photometer detector analysis, compared with assay of residual acetylcholinesterase inhibition, displayed stereoselective hydrolysis of cyclosarin, soman, and IMP-pNP, indicating that PON1 is less active toward the more toxic optical isomers.

Development of the Bisquaternary Oxime HI-6 Toward Clinical Use in the Treatment of Organophosphate Nerve Agent Poisoning

The traditional therapeutic treatment of organophosphate cholinesterase inhibitor (nerve agents) poisoning consists of co-treatment with an antimuscarinic (atropine) and a reactivator of inhibited acetylcholinesterase (AChE), which contains a nucleophilic oxime function. Two oximes are presently widely available for clinical use, pralidoxime and obidoxime (toxogonin), but both offer little protection against important nerve agent threats. This has highlighted the real need for the development and availability of more effective oximes for human use, a search that has been going on for up to 30 years. However, despite the demonstration of more effective and safe oximes in animal experiments, no additional oximes have been licensed for human use. HI-6, (1-[[[4(aminocarbonyl)-pyridinio]methoxy]methyl]-2(hydroxyimino)pyridinium dichloride; CAS 34433-31-3) has been studied intensively and has been proved effective in a variety of species including non-human primates and appears from clinical experience to be safe in humans. These studies have led to the fielding of HI-6 for use against nerve agents by the militaries of the Czech republic, Sweden, Canada and under certain circumstances the Organisation for the Prohibition of Chemical Weapons. Nevertheless HI-6 has not been granted a license for clinical use, must be used only under restricted guidelines and is not available for civilian use as far as is known. This article will highlight those factors relating to HI-6 that pertain to the licensing of new compounds of this type, including the mechanism of action, the clinical and pre-clinical demonstration of safety and its efficacy against a variety of nerve agents particularly in non-human primates, since no relevant human population exists. This article also contains important data on the use of HI-6 in baboons, which has not been available previously. The article also discusses the possibility of successful therapy with HI-6 against poisoning in humans relative to doses used in non-human primates and relative to its ability to reactivate inhibited human AChE.

Muscarinic modulations of neuronal anticholinesterase responses

Anticholinesterases (antiChEs) are increasingly used for treating patients with neurodegenerative diseases, but the dependence of their effects on the integrity of cholinergic functions has not yet been analyzed at the molecular level. Here, we report that manipulation of muscarinic neurotransmission confers drastic changes on antiChE responses in the rat brain. In the brains of naïve, un-stressed rats, the irreversible organophosphate antiChE, diisopropylfluorophosphonate (DFP) induced post-treatment accumulation of catalytically active G1 monomers of acetylcholinesterase (AChE). Pre-treatment with the selective M1 muscarinic antagonist, pirenzepine, but not the general muscarinic antagonist, scopolamine, attenuated this G1 increase. DFP-enhanced AChE gene expression was accompanied by diverted splicing from the primary AChE-S mRNA variant, encoding G4 synaptic membrane AChE-S tetramers, to "readthrough" AChE-R mRNA, which encodes soluble G1 monomers. Both the mRNA increase and the shifted splicing were long lasting (>24 h) and common to the parietal cortex and hippocampal CA1 and CA3 neurons. Importantly, the splicing shift was maximal under DFP alone, as compared with sham-injected rats, and virtually preventable by pre-treatment with pirenzepine. In contrast, induction of AChE transcription was less dependent on muscarinic function, resulting in AChE-S but not AChE-R increases. Our findings demonstrate distinct regulation of the enhanced transcription and the alternative splicing reactions to antiChE treatment and shed new light on the differential responses to antiChEs of demented patients with increasingly impaired cholinergic neurotransmission.

Degradation of VX and sulfur mustard by enzymatic haloperoxidation

Chloroperoxidase (CPO) isolated from Caldariomyces fumago (20 U ml(-1)) together with urea hydrogenperoxide (UPER, 0.5 mM) and sodium chloride as co-substrate (NaCl, 0.5 M) caused rapid breakdown of VX (10 microM) (t((1/2)) = 8 s, 25 C, 50 mM tartarate, pH 2.75). Glucose oxidase (GOX, Aspergillus niger) and glucose were used as an alternative source for H(2)O(2). A mixture of GOX (20 U ml(-1)), glucose (GLU 0.45 M), CPO (20 U ml(-1)) and NaCl (0.5 M) caused a 3.8-fold slower degradation of VX (10 microM) (t((1/2)) = 30 s, 25 C, 50 mM tartarate, pH 2.75). The concentrations of H(2)O(2) and chlorine produced by this enzyme/substrate mixture depended mainly on the GLU concentration. Horseradish peroxidase (HRP) together with UPER (1 mM) and sodium iodide (NaI, 0.05 M) caused progressive degradation of VX that was more than 400-fold slower than with CPO (20 U ml(-1)), UPER (0.5 mM) and NaCl (0.5 M) (t((1/2)) = 55 min, 25 C, pH 8). Skin decontamination of VX by CPO was tested in pig-ear skin in vitro. The chemical agent VX (0.01 M, 100 microl) was degraded by 98% within 3 h of skin diffusion when a mixture of UPER/NaCl/CPO was applied 60 min prior to VX application. A mixture of UPER/NaCl without CPO also caused significant VX degradation (94%) during skin diffusion whereas it did not cause any VX degradation in solution. Degradation of VX in skin, obtained without exogenous CPO, may indicate involvement of endogenous intradermal haloperoxidase-like enzyme. Reagent UPER (1 mM) did not cause any degradation of VX in solution or during its skin diffusion. Furthermore, a mixture of CPO, UPER and NaCl caused rapid degradation of sulfur mustard (HD). Sulfur mustard (50 microM) incubated in the presence of CPO (4 U ml(-1)), UPER (0.05 M) and NaCl (0.5 M) at pH 2.75 and 30 C was oxidized by 97% and 99% within 5 and 10 min, respectively. The oxidation products HD sulfoxide, HD sulfone and HD sulfoxidevinyl were identified by GC/MS in the enzymatic chloroperoxidation mixture.

Nasal midazolam as a novel anticonvulsive treatment against organophosphate-induced seizure activity in the guinea pig

Seizures and status epilepticus, which may contribute to brain injury, are common consequences of exposure to organophosphorus (OP) cholinesterase inhibitors. Effective management of these seizures is critical. To investigate the efficacy of nasal midazolam as an anticonvulsive treatment for OP exposure, as compared to intramuscular midazolam, guinea pigs were connected to a recording swivel for electrocorticograph (ECoG) monitoring and clinical observation. The experimental paradigm consisted of pyridostigmine pretreatment (0.1 mg/kg i.m.) 20 min prior to sarin exposure (1.2x LD(50,) 56 micro g/kg i.m.). One minute post-exposure, atropine (3 mg/kg i.m.) and TMB-4 (1 mg/kg im) were administered. Within 3-8 min after sarin exposure all animals developed electrographic seizure activity (EGSA), with convulsive behavior. Treatment with midazolam (1 mg/kg i.m.) 10 min after the onset of EGSA abolished EGSA within 389+/-181 s. The same dose was not effective, in most cases, when given 30 min after onset. However, a higher dose (2 mg/kg) was found efficacious after 30 min (949+/-466 s). In contrast, nasal application of midazolam (1 mg/kg) was found most effective, with significant advantages, in amelioration of EGSA and convulsive behavior, when given 10 min (216+/-185 s) or 30 min (308+/-122 s) following the onset of EGSA ( P<0.001). Thus, nasal midazolam could be used as a novel, rapid and convenient route of application against seizure activity induced by nerve agent poisoning.

Determination of therapeutic doses of bisquaternary oximes in large animals

This report presents a non-lethal method for estimating a range of therapeutic doses of bisquaternary oximes that serve as antidotes against organophosphorus poisoning. We have estimated therapeutic oxime doses that are equivalent in their relative toxicity rather than selecting arbitrary fractions of their LD(50). Thus, toxic signs of the oximes HI-6, HLö-7, Toxogonin, AB-8 and AB-13 were monitored quantitatively in baboon monkeys and beagle dogs. Using Toxogonin as a reference oxime, a calculated unit of equivalent dose (CED) was defined as the oxime dose equal to the ratio between its minimal toxic dose (MTD) and the therapeutic ratio (TR) of Toxogonin i.e. CED = MTD/TR. Assuming that the tails of dose-response curves of toxicity for bisquaternary oximes are shallow and similar to one another, one could substitute the ED(10) for the MTD. The ED(10) values for bisquaternary oximes were estimated using the log-log model following experimental observations and quantitative scoring of toxic signs in dogs and monkeys. The MTD values then were calculated using the ED(10) values and the experimental therapeutic dose of the reference oxime Toxogonin. The following CED values were obtained for AB-8, AB-13, Toxogonin, HI-6 and HLö-7 in dogs (d) and monkeys (m): 98.7, 74.2, 30.0, 14.5 and 12.1 (d) and 281.9, 232.1, 41.7, 192.9 and 92.9 (m) micromol kg(-1), respectively. The antidotal efficacy of these oximes against poisoning by the nerve agent tabun was determined in dogs and monkeys. These dose-dependent efficacy data were obtained at 0.3 x CED, 1 x CED and 3 x CED of oximes in combination with atropine. These data provide comparative therapeutic values using oxime doses based on their relative toxicity. The highest antidotal efficacy against tabun in dogs was obtained for toxogonin, whereas HLö-7 and AB-13 were most efficacious in monkeys.

Oxidative biodegradation of phosphorothiolates by fungal laccase

Organophosphorus (OP) insecticides and nerve agents that contain P-S bond are relatively more resistant to enzymatic hydrolysis. Purified phenol oxidase (laccase) from the white rot fungus Pleurotus ostreatus (Po) together with the mediator 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS) displayed complete and rapid oxidative degradation of the nerve agents VX and Russian VX (RVX) and the insecticide analog diisopropyl-Amiton with specific activity: k(sp) = 2200, 667 and 1833 nmol min(-1) mg(-1), respectively (pH 7.4, 37 degrees C). A molar ratio of 1:20 for OP/ABTS and 0.05 M phosphate at pH 7.4 provided the highest degradation rate of VX and RVX. The thermostable laccase purified from the fungus Chaetomium thermophilium (Ct) in the presence of ABTS caused a 52-fold slower degradation of VX with k(sp) = 42 nmol min(-1) mg(-1). The enzymatic biodegradation products were identified by 31P-NMR and GC/MS analysis.

Inhibition of acetylcholinesterase and butyrylcholinesterase by chlorpyrifos-oxon

Phosphorothionate insecticides such as parathion (O,O-diethyl O-p-nitrophenyl phosphorothioate) and chlorpyrifos (CPS; O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate; Dursban) are metabolically converted by oxidative desulfuration into paraoxon and chlorpyrifos-oxon (CPO). The insecticidal action of chlorpyrifos stems from inhibition of acetylcholinesterase (AChE) by CPO, resulting in severe cholinergic toxicity. Sensory peripheral neuropathy was observed in people exposed environmentally to chlorpyrifos sprayed in confined areas. We have examined the kinetics of inhibition of AChE and butyrylcholinesterase (BChE) by paraoxon and CPO. The bimolecular rate constants (ki) for inhibition by paraoxon of recombinant human (rH) AChE, recombinant mouse (rM) AChE, and fetal bovine serum (FBS) AChE were 7.0, 4.0, and 3.2 x 10(5) M(-1) min(-1). The ki values for the inhibition by CPO of rH AChE, fetal bovine serum AChE, human RBC AChE, Torpedo AChE, and recombinant mouse (rM) AChE were 9.3, 2.2, 3.8, 8.0, and 5.1 x 10(6) M(-1) min(-1), respectively. Inhibition of human serum BChE, rH BChE, and rM BChE by CPO yielded ki values of 1.65, 1.67, and 0.78 x 10(9) M(-1) min(-1), respectively. The ki values obtained for BChE from various species were 160- to 750-fold larger than those of AChE from parallel sources. Inhibition of the single-site mutant A328Y of rH BChE by CPO displayed a 21-fold lower rate than that of wild-type rH BChE (ki, 7.9 x 10(7) vs 1.67 x 10(9) M(-1) min(-1)). The double mutant of acyl pocket residues of rH AChE, F295L/F297V, was inhibited by CPO with a 150-fold larger ki than wild type (1.5 x 10(9) vs 1.0 x 10(7) M(-1) min(-1)). The increased rate obtained with the double mutant displaying characteristics of the BChE active center provides a rationale for higher efficacy of CPO scavenging by BChE, compared with AChE.

Millimolar concentrations of ascorbic acid in purified human mononuclear leukocytes. Depletion and reaccumulation

Ascorbic acid (vitamin C) was found in isolated human mononuclear leukocytes and their purified components in millimolar concentration. Intracellular ascorbic acid was depleted greater than 96% during cell culture and was rapidly reaccumulated after addition of physiologic concentrations of ascorbic acid to the extracellular medium. Purified cells maintained concentration gradients of ascorbic acid as large as 100-fold across the plasma membrane. The ability to vary intracellular ascorbic acid concentrations over such a wide range makes it possible for the first time in these cells to study ascorbic acid function in direct relationship to intracellular concentration.

Interaction of an organophosphate with a peripheral site on acetylcholinesterase

O-Ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (MPT) is an active site directed inhibitor of acetylcholinesterase (AChE). Inhibition of the Electrophorus electricus (G4) enzyme follows classical second-order kinetics. However, inhibition of total mouse skeletal muscle AChE and inhibition of the individual molecular forms from muscle, including the monomeric species, do not proceed as simple irreversible bimolecular reactions. Similarly, complex inhibition kinetics are observed for the purified enzyme from Torpedo californica. AChE can be cross-linked with glutaraldehyde into a semisolid matrix. Under these conditions the abnormal concentration dependence for MPT inhibition is accentuated, and a range of MPT concentrations can be found where inhibition of polymerized AChE is far less than that observed at lower concentrations. Inhibition in certain concentration ranges is partially reversible after removal of all unbound ligand. Thus, there are two different modes of organophosphorus inhibition by MPT: the classical irreversible phosphorylation of the active site and a reversible interaction at a site peripheral to the active center. Propidium, a well-studied peripheral site ligand, can prevent the later interaction. Hence, the second site of MPT interaction with AChE may overlap or be linked to the peripheral anionic site of AChE characterized by the binding of propidium and other peripheral site inhibitors.

The muscarinic antagonists aprophen and benactyzine are noncompetitive inhibitors of the nicotinic acetylcholine receptor

Certain muscarinic antagonists (e.g., atropine, aprophen, and benactyzine) are used as antidotes for the treatment of organophosphate poisoning. We have studied the interaction of aprophen and benactyzine, both aromatic esters of diethylaminoethanol, with nicotinic acetylcholine receptor (AChR) in BC3H-1 intact muscle cells and with receptor-enriched membranes of Torpedo californica. Aprophen and benactyzine diminish the maximal carbamylcholine-elicited sodium influx into muscle cells without shifting Kact (carbamylcholine concentration eliciting 50% of the maximal 22Na+ influx). The concentration dependence for the inhibition of the initial rate of 22Na+ influx by aprophen and benactyzine occurs at lower concentrations (Kant = 3 and 50 microM, respectively) than those needed to inhibit the initial rate of [125I]-alpha-bungarotoxin binding to the agonist/antagonist sites of the AChR (Kp = 83 and 800 microM, respectively). The effective concentration for atropine inhibition of AChR response (Kant = 150 microM in BC3H-1 cells) is significantly higher than those obtained for aprophen and benactyzine. Both aprophen and benactyzine interact with the AChR in its desensitized state in BC3H-1 cells without further enhancing agonist affinity. Furthermore, these ligands do not alter the value of Kdes (equilibrium concentration of agonist which diminishes 50% of the maximal receptor response) in BC3H-1 muscle cells. The affinity of aprophen and benactyzine for the allosterically coupled noncompetitive inhibitor site of the AChR in Torpedo was determined using [3H]phencyclidine as a probe. Both compounds were found to preferentially associate with the high affinity (desensitized) state rather than the resting state of Torpedo AChR. There is a 14- to 23-fold increase in the affinity of aprophen and benactyzine for the AChR (KD = 0.7 and 28.0 microM in the desensitized state compared to 16.4 and 384 microM in the resting state, respectively). These data indicate that aprophen and benactyzine binding are allosterically regulated by the agonist sites of Torpedo AChR. Thus, aprophen and benactyzine are effective noncompetitive inhibitors of the AChR at concentrations of 1-50 microM, in either Torpedo or mammalian AChR. These concentrations correspond very well with the blood level of these drugs found in vivo to produce a therapeutic response against organophosphate poisoning.

Bay K 8644-induced changes in the ECG pattern of the rat and their inhibition by antianginal drugs

1. The effects of intracarotid administration of Bay K 8644 on the ECG pattern along with their reversal by antianginal drugs were investigated in anaesthetized rats. 2. Intracarotid injections of Bay K 8644 (0.5-50.0 micrograms kg-1) produced a dose-related transient increase in systemic blood pressure. 3. The pressor response was accompanied by ST segment elevation (0.5-10.0 micrograms kg-1), ST segment depression concomitant with the occurrence of arrhythmias (20.0 micrograms kg-1), or A-V block (50.0 micrograms kg-1). 4. ST segment elevation reached its maximal value within 15 s and could be observed for 30-240 s. 5. The increase in blood pressure was immediate (within 5 s) and short lasting (30-120 s). After the initial increase it returned to control levels (0.5-20.0 micrograms kg-1) or dropped below (50.0 micrograms kg-1). 6. The ST segment elevation caused by 5.0 micrograms kg-1 Bay K 8644 (submaximal dose) was blocked by antianginal drugs (e.g. nitroglycerin, nifedipine and diltiazem) and by the peripheral benzodiazepine receptor antagonist PK 11195. However, the pressor response was not blocked by any of the drugs used. 7. ST segment elevation (or depression) induced by intracarotid administration of Bay K 8644 provides a useful tool for the evaluation of potential antianginal drugs.

The relationship between alpha 1-adrenergic receptor occupation and the mobilization of intracellular calcium

We have simultaneously quantitated alpha 1-adrenergic receptor occupation and agonist-elicited Ca2+ mobilization monitored as unidirectional 45Ca2+ efflux from intact BC3H-1 muscle cells in order to examine the relationship between the number of surface receptors occupied and the functional response. [3H]Prazosin has been used to measure receptor number as well as the binding kinetics with surface receptors, and the observed equilibrium and kinetic constants are in close accord with values obtained previously in cellular homogenates. Since alpha 1-agonist-elicited 45Ca2+ efflux can be monitored over intervals of 3 min or less and prazosin dissociation from its receptor has a t 1/2 of 44 min, prazosin can be employed to produce a pseudoirreversible inactivation of receptors. A comparison of the remaining receptors and residual response reveals an inverse linear relationship between receptors inactivated by prazosin and 45Ca2+ efflux. A similar result is obtained following fractional receptor inactivation with the irreversible alkylating agent phenoxybenzamine. Parameters of receptor occupation and response also correlate well for the agonist phenylephrine and for the competitive antagonist phentolamine. The unitary relationship between sites available for occupation and response indicates that the alpha 1 receptor does not function as an oligomer where fewer bound antagonist molecules are required to block the receptor than sites of agonist occupation necessary for activation. Moreover, substantial evidence has accrued in intact smooth muscle for a receptor reserve or nonlinear coupling between alpha 1 receptor occupation and contraction in smooth muscle. Our findings demonstrate that such behavior does not exist for alpha 1 receptor-elicited mobilization of Ca2+ in the BC3H-1 muscle cell.

Oligomeric structure of muscarinic receptors is shown by photoaffinity labeling: subunit assembly may explain high- and low-affinity agonist states

The potent muscarinic photoaffinity reagent N-methyl-4-piperidyl p-azidobenzilate (azido-4NMPB) was used to covalently label specific muscarinic binding sites in various brain regions and in the heart. In the cortex and hippocampus, a single specifically labeled protein with an apparent molecular mass of 86,000 daltons was detected by gel electrophoresis. In the medulla pons, cerebellum, and cardiac atria, there was a 160,000-dalton band in addition to the 86,000-dalton polypeptide. Under certain conditions, alkali or hydroxylamine treatment dissociated both macromolecules into a single 40,000-dalton polypeptide. These results suggest that the muscarinic receptor exists in oligomeric forms and that a dimer and tetramer of a basic 40,000-dalton peptide may exist as interconvertible species. We propose a model to explain the biological architecture of the muscarinic receptors and suggest a possible correlation between the azido-4NMPB-labeled polypeptides and the two states of the receptor observed in agonist binding experiments.

Affinity labeling of muscarinic receptors in rat cerebral cortex with a photolabile antagonist

Highly potent photoaffinity probes for muscarinic binding sites were prepared by the incorporation of an azido group into the benzilic acid moiety in two compound, 3-quinuclidinyl benzilate (3QNB) and N-methyl-4-piperidyl benzilate (4NMPB). Inactivation of muscarinic sites in rat cortex depends on the formation of a reversible complex with the azides prior to their photolytic conversion to the highly reactive nitrenes. During photolysis, radiolabeled azido-4NMPB interacted specifically and with high affinity (Kd = 1.06 nM) with the muscarinic receptors, and the ligand could be covalently incorporated into a macromolecule of about 86,000 Mr, presumably the muscarinic receptor. The incorporation was almost stoichiometric when compared to determination of receptor density by reversible ligands. Atropine (10 microM) afforded specific protection (greater than 83%) of the receptor against inactivation by azido-[3H]4NMPB. This compound and the other ligands described here (i.e., amino-4NMPB, amino-3QNB, and azido-3QNB) represent powerful potential probes for the biochemical isolation and characterization of muscarinic receptors.

Synthesis and properties of 2-S-(N,N-dialkylamino)ethyl)thio-1,3,2-dioxaphosphorinane 2-oxide and of the corresponding quaternary derivatives as potential nontoxic antiglaucoma agents

A new series of cyclic organophosphorus esters, 2-S-[2'-N,N-dialkylamino)ethyl]thio-1,3,2-dioxaphosphorinane 2-oxide and their quaternary derivatives, was synthesized and studied as potential antiglaucoma agents. Thes compounds inhibit acetylcholinesterase (E.C.3.1.1.7)at a bimoecular rate constant (ki) in the range of 10(3)-10(4) M-1 min-1. Values of the affinity (K) and phosphorylation (k') rate constants for this enzyme indicate that k' is responsible for the relatively low values of ki as compared with similar data for the open-chain analogues, O,O-diethyl phosphorothiolates (10(6) M-1 min-1). The mammalian toxicity of the new compounds in terms of acute LD50 values in mice is 1-3 x 10(3) less than that of phospholine, an open-chain analogue. In an initial clinical trial, one member of the new series (alkyl = C2H5) caused a significant decrease of intraocular pressure in aphakic glaucoma, while phospholine proved to be ineffective.