Unravelling the role of arbuscular mycorrhizal fungi in mitigating the oxidative burst of plants under drought stress.

With continued climate changes, soil drought stress has become the main limiting factor for crop growth in arid and semi-arid regions. A typical characteristic of drought stress is the burst of reactive oxygen species (ROS), causing oxidative damage. Plant-associated microbes, such as arbuscular mycorrhizal fungi (AMF), can regulate physiological and molecular responses to tolerate drought stress, and they have a strong ability to cope with drought-induced oxidative damage via enhanced antioxidant defence systems. AMF produce a limited oxidative burst in the arbuscule-containing root cortical cells. Similar to plants, AMF modulate a fungal network in enzymatic (e.g. GmarCuZnSOD and GintSOD1) and non-enzymatic (e.g. GintMT1, GinPDX1 and GintGRX1) antioxidant defence systems to scavenge ROS. Plants also respond to mycorrhization to enhance stress tolerance via metabolites and the induction of genes. The present review provides an overview of the network of plant - arbuscular mycorrhizal fungus dialogue in mitigating oxidative stress. Future studies should involve identifying genes and transcription factors from both AMF and host plants in response to drought stress, and utilize transcriptomics, proteomics and metabolomics to clarify a clear dialogue mechanism between plants and AMF in mitigating oxidative burst.

Pharmacokinetics of K117 and K127, two novel antidote candidates to treat Tabun poisoning.

AIMS: K117 and K127 are bis-pyridinium aldoximes but K117 is a bis-pyridinium bis-aldoxime while K127 has only one single aldoxime in addition to its amide substituent. Is there any difference in pharmacokinetics in these compounds that otherwise have the same chemical structure? Both K117 and K127 are developed as antidotes in acetylcholinesterase and butyrylcholinesterase poisoning in terrorist attacks or intoxication with other organophosphorous compounds. Their distributions have been scouted in the bodies of rats. MAIN METHODS: White male Wistar rats were intramuscularly injected. The animals were sacrificed, tissue samples were homogenized, and either K117 or K127 concentrations were determined using reversed-phase high-performance liquid chromatography. KEY FINDINGS: Both K117 and K127 were present in all tissues that were analyzed including blood (serum), the brains, cerebrospinal fluid, the eyes, livers, kidneys, lungs and testes. Their pharmacokinetics and body distributions are similar. SIGNIFICANCE: Either K117 or K127 meets the essential requirements for antidotes. Dose dependence and kinetics of their distribution were compared to that of other pyridinium aldoximes.

Some Possibilities to Study New Prophylactics against Nerve Agents.

Nerve agents belong to the most dangerous chemical warfare agents and can be/were misused by terrorists. Effective prophylaxis and treatment is necessary to diminish their effect. General principles of prophylaxis are summarized (protection against acetylcholinesterase inhibition, detoxification, treatment "in advance" and use of different drugs). They are based on the knowledge of mechanism of action of nerve agents. Among different examinations, it is necessary to test prophylactic effectivity in vivo and compare the results with protection in vitro. Chemical and biological approaches to the development of new prophylactics would be applied simultaneously during this research. Though the number of possible prophylactics is relatively high, the only four drugs were introduced into military medical practice. At present, pyridostigmine seems to be common prophylactic antidote; prophylactics panpal (tablets with pyridostigmine, trihexyphenidyl and benactyzine), transant (transdermal patch containing HI-6) are other means introduced into different armies as prophylactics. Scavenger commercionally available is Protexia®. Future development will be focused on scavengers, and on other drugs either reversible cholinesterase inhibitors (e.g., huperzine A, gallantamine, physostigmine, acridine derivatives) or other compounds.

The concept of hybrid molecules of tacrine and benzyl quinolone carboxylic acid (BQCA) as multifunctional agents for Alzheimer's disease.

Novel tacrine-benzyl quinolone carboxylic acid (tacrine-BQCA) hybrids were designed based on multi-target directed ligands (MTLDs) paradigm, synthesized and evaluated in vitro as inhibitors of human acetylcholinesterase (hAChE) and human butyrylcholinesterase (hBChE). Tacrine moiety is represented herein as 7-methoxytacrine, 6-chlorotacrine or unsubstituted tacrine forming three different families of seven members, i.e. 21 compounds in overall. Introducing BQCA, a positive modulator of M1 muscarinic acetylcholine receptors (mAChRs), the action of novel compounds on M1 mAChRs was evaluated via Fluo-4 NW assay on the Chinese hamster ovarian (CHO-M1WT2) cell line. All the novel tacrine-BQCA hybrids were able to block the action of hAChE and hBChE in micromolar to nanomolar range. The hAChE kinetic profile of 5p was found to be mixed-type which is consistent with our docking experiments. Moreover, selected ligands were assessed for their potential hepatotoxicity on HepG2 cell line and presumable permeation through the blood-brain barrier by PAMPA assay. Expected agonistic profile towards M1 mAChRs delivered by BQCA moiety was not confirmed. From all the hybrids, 5o can be highlighted as non-selective cholinesterase inhibitor (hAChE IC50 = 74.5 nM; hBChE IC50 = 83.3 nM) with micromolar antagonistic activity towards M1 mAChR (IC50 = 4.23 µM). A non-selective pattern of cholinesterase inhibition is likely to be valuable during the onset as well as later stages of AD.

Assessment of DNA-binding affinity of cholinesterase reactivators and electrophoretic determination of their effect on topoisomerase I and II activity.

In this paper, we describe the biochemical properties and biological activity of a series of cholinesterase reactivators (symmetrical bisquaternary xylene-linked compounds, K106-K114) with ctDNA. The interaction of the studied derivatives with ctDNA was investigated using UV-Vis, fluorescence, CD and LD spectrometry, and electrophoretic and viscometric methods. The binding constants K were estimated to be in the range 1.05 × 10(5)-5.14 × 10(6) M(-1) and the percentage of hypochromism was found to be 10.64-19.28% (from UV-Vis titration). The used methods indicate that the studied samples are groove binders. Electrophoretic methods proved that the studied compounds clearly influence calf thymus Topo I (at 5 µM concentration, except for compounds K107, K111 and K114 which were effective at higher concentrations) and human Topo II (K110 partially inhibited Topo II effects even at 5 µM concentration) activity.

The interaction of quaternary reversible acetylcholinesterase inhibitors with the nicotinic receptor.

Acetylcholinesterase inhibitors (AChEIs) are used in the treatment of myasthenia gravis (MG). We investigated the effects of AChEIs on peripheral nicotinic receptors (nAChR), which play a crucial role in the treatment of MG symptoms. The positive modulation of those receptors by AChE inhibitors could have an added value to the anti-AChE activity and might be useful in the therapy of MG. Furthermore, to estimate the potential drawbacks of the compounds, cytotoxicity has been assessed on various cell lines. The whole-cell mode of the patch-clamp method was employed. The experiments were performed on medulloblastoma/rhabdomyosarcoma cell line TE671 expressing human embryonic muscle-like receptor with subunits alpha2betagammadelta. The effect of the compounds on cell viability was measured by standard MTT assay (Sigma Aldrich) on ACHN (renal cell adenocarcinoma), HeLa (immortal cell line derived from a cervical carcinoma), HEPG2 (hepatocellular carcinoma) and BJ (skin fibroblasts) cell lines. No positive modulation by the tested AChE inhibitors was observed. Moreover, the compounds exhibited antagonistic activity on the peripheral nAChR. Standard drugs used in MG treatment were shown to be less potent inhibitors of muscle-type nAChR than the newly synthesized compounds. The new compounds showed very little effect on cell viability, and toxicities were comparable to standards. Newly synthesized AChEIs inhibited peripheral nAChR. Furthermore, the inhibition was higher than that of standards used for the treatment of MG. They could be used for the study of nAChR function, thanks to their high antagonizing potency and fast recovery of receptor activity after their removal. However, since no positive modulation was observed, the new compounds do not seem to be promising candidates for MG treatment, even though their cytotoxic effect was relatively low.

The summary on non-reactivation cholinergic properties of oxime reactivators: the interaction with muscarinic and nicotinic receptors.

Organophosphorus inhibitors (OP) of acetylcholinesterase (AChE) represent a group of highly toxic compounds. The treatment of OP intoxication is, however, insufficiently ensured. Currently, two main categories of drugs-anticholinergics and oxime reactivators- are employed as antidotes. Oximes have been reported to act at several levels of the cholinergic transmission, and among the non-reactivation effects, the interaction with cholinergic receptors stands out. This review addresses issues correlated with non-reactivating effects of oxime reactivators with a special focus on the muscarinic and nicotinic receptors, but involvement of other cholinergic structures such as AChE and choline uptake carriers are discussed too. It can be concluded that the oxime reactivators show a variation in their antagonistic effect on the muscarinic and nicotinic receptors, which is likely to be of significance in the treatment of OP poisoning. In vitro data reported oximes to exert higher efficacy on the muscarinic M2 subtype than on the AChE. However, this effect seemed to be subtype specific since the antagonistic M3 effect was lower. Also, and importantly, the antimuscarinic effect was larger than that on nicotinic receptors. Even though atropine showed a much higher muscarinic antagonism, it is supposed that non-reactivation properties of oxime reactivators play a significant role in the treatment of OP poisoning.

The interaction of standard oxime reactivators with hemicholinium-3 sensitive choline carriers.

Organophosphorus poisoning manifests as a cholinergic syndrome due to an inhibition of acetylcholinesterase. It is treated symptomatically by anticholinergics and oxime reactivators are used as causal antidotes. Reactivators possess a complex mechanism of action and interact at various levels of the cholinergic transmission. The aim of this study was to investigate the effect of standard oxime reactivators (HI-6, obidoxime, trimedoxime, methoxime and pralidoxime) on the hemicholinium-3 sensitive carriers, which are involved in the high-affinity choline uptake (HACU) transport, a key regulatory step in the synthesis of acetylcholine. The activity of the carriers was estimated in vitro on hippocampal synaptosomes using the substrate (3H)-choline and the competitive inhibitor (3H)-hemicholinium-3. Furthermore, the effect of the reactivators on the fluidity of hippocampal membranes was assessed. All tested compounds, except methoxime, showed an acute inhibitory effect on the carriers, however, only at µM concentrations. Trimedoxime showed the highest potency to inhibit HACU among all tested compounds (I(max) 62%, IC(50)=3 µM). All compounds, except HI-6, influenced also a membrane fluidity in the region of the hydrophilic heads of phospholipid bilayer, nevertheless, only methoxime was able to penetrate more deeply into the hydrocarbon core. We suggest that the direct interaction of oxime reactivators with the carrier protein (HI-6 and trimedoxime) and/or the changes in carrier conformation mediated by alterations in membrane fluidity (trimedoxime, obidoxime and pralidoxime) could occur here. The influence of reactivators on the carriers could be unfavorable in the case of their prolonged administration in vivo. From this point of view, the application of methoxime appears to be the best.

Two possibilities how to increase the efficacy of antidotal treatment of nerve agent poisonings.

Highly toxic organophosphorus inhibitors of acetylcholinesterase referred as nerve agents are considered to be among the most dangerous chemical warfare agents. The oximes represent very important part of medical countermeasures of nerve agent poisonings. They are used to reactivate the nerve agent-inhibited acetylcholinesterase. Despite long-term research activities, there is no single, broad-spectrum oxime suitable for the antidotal treatment of poisoning with all organophosphorus agents. There are two approaches how to increase and broaden the effectiveness of antidotal treatment of poisoning with nerve agents - to develop new structural analogues of currently available oximes and/or to combine currently available or newly developed oximes. The review describes the evaluation of the potency of newly developed oximes (especially the oxime K203) or combinations of oximes to reactivate nerve agent-inhibited acetylcholinesterase and to counteract the acute toxicity of nerve agents in comparison with single commonly used oxime (obidoxime, trimedoxime or HI-6).

Biochemical insight into soman intoxication and treatment with atropine, HI-6, trimedoxime, and K203 in a rat model.

OBJECTIVE: The present experiment is based on biochemical assessment of nerve agent soman intoxication and atropine, respectively atropine and HI-6, trimedoxime or K203 treatment in rats. BACKGROUND: Nerve agents are toxic substances irreversibly inhibiting enzyme acetylcholinesterase (AChE). Treatment is typically based on application of atropine and oxime reactivator. Atropine is able to protect overstimulation of muscarinic acetylcholine receptors. Application of oxime reactivator enable return of AChE activity and full suppression of intoxication. METHODS: In a total, fifteen biochemical markers were assayed in plasma or blood of intoxicated animals. 42 rats were divided into 7 groups each 6 individuals. The first group was exposed to atropine; the second group was exposed to one LD50 of soman and atropine. The groups 3-5 were exposed in a same way as the second group and were treated with oxime reactivators: HI-6 (group 3), trimedoxime (4) and K203 (5). The sixth group was control treated with saline solution only. The last (seventh) group was intoxicated with soman only. RESULTS: The most striking shifts were found for blood acetylcholinesterase and plasma creatinine, glucose, inorganic phosphate as well as uric acid. Lactate dehydrogenase and aspartate aminotransferase assays were useless due to soman interference. CONCLUSION: It was demonstrated that treatment was able to protect poisoned animals from metabolic disorder represented by hyperglycemia and nephropathy represented by hyperuricemia and elevated creatinine. Soman exposure and treatment with the oxime reactivators and/or atropine contains quite complex and still not well understood side mechanisms (Tab. 2, Fig. 1, Ref. 25).

The effect of oxime reactivators on muscarinic receptors: functional and binding examinations.

The antidotal treatment of organophosphorus poisoning is still a problematic issue since no versatile antidote has been developed yet. In our study, we focused on an interesting property, which does not relate to the reactivation of inhibited acetylcholinesterase (AChE) of some oximes, but refers to their anti-muscarinic effects which may contribute considerably to their treatment efficacy. One standard reactivator (HI-6) and two new compounds (K027 and K203) have been investigated for their antimuscarinic properties. Anti-muscarinic effects were studies by means of an in vitro stimulated atrium preparation (functional test), the [(3)H]-QNB binding assay and G-protein coupled receptor assay (GPCR, beta-Arrestin Assay). Based on the functional data HI-6 demonstrates the highest anti-muscarinic effect. However, only when comparing [(3)H]-QNB binding results and GPCR data, K203 shows a very promising compound with regard to anti-muscarinic potency. The therapeutic impact of these findings has been discussed.

Oxime reactivators and their in vivo and in vitro effects on nicotinic receptors.

Current treatment of organophosphorus poisoning, resulting in overstimulation and desensitization of muscarinic and nicotinic receptors by acetylcholine (ACh), consists of the administration of atropine and oxime reactivators. However, no versatile oxime reactivator has been developed yet and some mortality still remains after application of standard atropine treatment, probably due to its lack of antinicotinic action. In our study, we focused on the interesting non-acetylcholinesterase property of oximes, i.e. antinicotinic effect of reactivators. Two standard reactivators (HI-6, obidoxime) and two new compounds (K027 and K203) were chosen for in vitro (patch clamp) and in vivo (nerve-evoked muscle contraction) testings. Both examinations showed antinicotinic effects of the reactivators. In vitro inhibition of acetylcholine-evoked currents by obidoxime, HI-6 and K203 was equivalent while K027 was less potent. Similar order of potency was observed by the in vivo examinations. We thus confirm previous in vitro results, which describe antinicotinic effects of oxime reactivators, and furthermore, we show in vivo antagonism of oxime reactivators exerted by the inhibition of ACh effect on the nicotinic receptor in the neuromuscular junction. Taking together, the effects of tested oxime reactivators indicate an antagonism on both embryonic and adult form of the muscle nicotinic receptors.

Macrophage-assisted inflammation and pharmacological regulation of the cholinergic anti-inflammatory pathway.

Macrophages play an important role in the immune system. They also participate in multiple processes including angiogenesis and triggering of inflammation. The present study summarizes pieces of knowledge on the importance of macrophages in disease, especially the inflammation. Special attention is paid to the cholinergic anti-inflammatory pathway (CAP) associated with the nicotinic acetylcholine receptor (nAChR) and the parasympathetic nervous system. The current pharmacological effectiveness in suppressing the inflammation in general and the septic shock in particular, is limited. CAP was discovered recently and it seems to be a suitable target for the development of new drugs. Moreover, available drugs binding to either nAChR or acetylcholinesterase (AChE) are candidates for either an inhibition or enhancement of CAP. Though the current scientific databases do not include all necessary data on the association of CAP with body functions and the research is quite intensive, the objective of the present review is to introduce the current trends and to critically evaluate CAP and macrophage-associated pathways.

Pralidoxime--the gold standard of acetylcholinesterase reactivators--reactivation in vitro efficacy.

OBJECTIVE: In this work, we aim to summarize the universality of this compound, its reactivation potential when different cholinesterase inhibitors are used. BACKGROUND: Pralidoxime is considered as a gold standard of acetylcholinesterase reactivators--antidotes used in case of nerve agent poisonings. It has been commercially available for many years. However, several studies deem this oxime an old-fashion antidote. METHODS: Pralidoxime was synthesized at our department. The reactivating efficacy was tested on 10% (w/v) rat brain homogenate that had been incubated with appropriate inhibitor for 30 minutes to reach 96% inhibition of AChE. Then, pralidoxime was added for 10 minutes. Measurements were performed at 25 degrees C, pH 8, and 10(-3) and 10(-5) M concentrations of AChE reactivators. The activities of brain AChE were measured by a potentiostatic method. RESULTS: No sufficient reactivation was achieved at the concentration of 10(-5) M, which is a concentration that can be reached after administration of therapeutic doses. At a higher dose (10(-3) M), pralidoxime reactivated AChE inhibited by paraoxon, chlorpyrifos, Russian VX, VX and sarin. CONCLUSION: From the obtained results, it is clear that pralidoxime seems to be a poor reactivator of AChE inhibited by organophosphorous AChE inhibitors and thus cannot be labeled as a universal reactivator (Tab. 1, Fig. 3, Ref. 31).

Novel acetylcholinesterase reactivator K112 and its cholinergic properties.

The oxime reactivator K112 is a member of the new group of xylene linker-containing AChE reactivators. Its cholinergic properties could be of importance at OP poisoning and are not related to the AChE reactivation that has been studied. It has been found that, despite of reactivating potency, this compound has additional effects. These cholinergic effects include a weak inhibition of AChE (IC(50)=43.8 ± 4.88 µM), inhibition of binding to the porcine muscarinic M2 receptor (IC(50)=4.36 µM) and finally, the inhibition of HACU (68.4 ± 9.9%), a key regulatory step in the synthesis of ACh. The inhibition of the binding of (3H)-HC-3 (64.7 ± 4.7%) and the influence on the membrane fluidity have also been observed. Blocking properties of K112 on the muscarinic receptors have been revealed in the in vitro experiment (rat urinary bladder) and in the in vivo experiment (rat heart BPM) as well. All these cholinergic properties could significantly contribute to the antidotal effect of K112 at the poisoning by the organophosphates.

Structure-activity relationship of quaternary acetylcholinesterase inhibitors - outlook for early myasthenia gravis treatment.

Myasthenia gravis is a rare autoimmune neuromuscular junction disorder mainly caused by antibodies being targeted against the muscle acetylcholine receptors (AChRs). The loss of AChRs leads to a defect in neuromuscular transmission resulting in muscle weakness and fatigue. Although once an often fatal illness, Myasthenia gravis can now be well managed with relatively safe and effective treatments. However, the severe myasthenic cases associated with thymus tumors remain often fatal exception in the management of the disease. The early treatment includes the use of acetylcholinesterase inhibitors (AChEI) which enhance neuromuscular transmission. To ensure a peripheral effect, charged molecules are used, particularly quaternary ammonium salts. The structure of AChEIs has been continuously modified to obtain the optimal ratio between AChE inhibition and potential side-effects. This review summarizes progress in the use of quaternary compounds as AChE inhibitors in vitro with respect to their structure and inhibitory ability. Namely, carbamic acid esters, piperidinium and pyridinium salts, bisquaternary pyridinium salts and heterogeneous quaternary inhibitors are all discussed. Among data found in the literature, many compounds have shown promising inhibition of AChE when compared to commercial standards (pyridostigmine, neostigmine). Besides a promising inhibitory ability, selectivity for AChE versus butyrylcholinesterase (BChE) for the most potent compounds (sub-nanomolar IC(50)) was also identified.

Interaction of nerve agent antidotes with cholinergic systems.

The poisoning with organophosphorus compounds represents a life threatening danger especially in the time of terroristic menace. No universal antidote has been developed yet and other therapeutic approaches not related to reactivation of acetylcholinesterase are being investigated. This review describes the main features of the cholinergic system, cholinergic receptors, cholinesterases and their inhibitors. It also focuses on the organophosphorus nerve agents, their properties, effects and a large part describes various possibilities in treatments, mainly traditional oxime therapies based on reactivation of AChE. Furthermore, non-cholinesterase coupled antidotal effects of the oximes are thoroughly discussed. These antidotal effects principally include oxime interactions with muscarinic and nicotinic receptors.

Pyridinium aldoxime analysis by HPLC: the method for studies on pharmacokinetics and stability.

Reversed-phase separation of various pyridinium aldoximes requires a certain concentration of ion-pairing agent, as their chemical structures contain two quaternary amines in the pyridinium ring. Adequate mobile phase is scouted on the basis of retention of pyridinium aldoxime (using the graph of k' versus concentration of an ion-pairing agent) compared to the chromatogram of the background peaks originated from the homogenate. Change in the ion-pairing agent concentration was more expressed for the elution of K-203 than that of the background peaks from the serum, brain and cerebrospinal fluid. Stability of K-203 was investigated using HPLC. Determination of K-203 in tissue samples requires homogenization using either trichloroacetic acid or perchloric acid. Fast degradation takes place at acidic pH. Adjusting pH to neutral in the possible shortest time frame helps to avoid degradation. Degradation of K-203 was easily followed by HPLC separation and monitoring the elution with an ultraviolet absorbance detector at 276 nm. Amperometric detection indicates only the decrease of K-203 content.

Efficacy of two new asymmetric bispyridinium oximes (K-27 and K-48) in rats exposed to diisopropylfluorophosphate: comparison with pralidoxime, obidoxime, trimedoxime, methoxime, and HI-6.

Introduction. The new K-oximes, K-27 [1-(4-hydroxyimino-methylpyridinium)-4-(4-carbamoylpyridinium) propane dibromide] and K-48 [1-(4-hydroxyimino-methylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide], show good in vitro efficacy in protecting acetylcholinesterase from inhibition by different organophosphorus compounds (OPCs), including nerve agents. To assess their efficacy in vivo, the extent of oxime-conferred protection from mortality induced by diisopropylfluorophosphate (DFP) was quantified and compared with that of five established oximes. Materials and Methods. Rats received DFP intraperitoneally in a dosage of 6, 8, or 10 micromol/rat and immediately thereafter intraperitoneal injections of K-27, K-48, pralidoxime, obidoxime, trimedoxime, methoxime, or HI-6. The relative risk (RR) of death over time (48 h) was estimated by Cox survival analysis, comparing results with the no-treatment group. Results. Best protection was observed when K-27 was used, reducing the RR of death to 19% of control RR (p < or = 0.005), whereas obidoxime (RR = 26%, p < or = 0.01), K-48 (RR = 29%, p < or = 0.005) and methoxime (RR = 26%, p < or = 0.005) were comparable. The RR of death was reduced only to about 35% of control by HI-6, to 45% by trimedoxime, and to 59% by 2-PAM (p < or = 0.005). Whereas the differences between the best oximes (K-27, obidoxime, methoxime, and K-48) were not statistically significant; these four oximes were significantly more effective than 2-PAM (p < or = 0.05). The efficacy of K-27 was also significantly higher than that of HI-6, trimedoxime, and 2-PAM (p < or = 0.05). Conclusion. Our data provide further evidence that K-27 is a very promising candidate for the treatment of intoxication with a broad spectrum of OPCs.

Efficacy of eight experimental bispyridinium oximes against paraoxon-induced mortality: comparison with the conventional oximes pralidoxime and obidoxime.

Recently, several experimental K-oximes with two functional aldoxime groups have been synthesized that show excellent in vitro efficacy in protecting acetylcholinesterase (AChE) from inhibition by a broad variety of organophosphorus compounds (OPCs). However, oximes themselves are also AChE inhibitors, albeit at higher concentrations, which is a major cause of their toxicity and may be a dose-limiting factor in oxime therapy. To assess the efficacy of the experimental K-oximes in vivo, the extent of oxime-conferred protection from mortality induced by paraoxon was quantified. Rats received paraoxon in a dosage of 1, 5, or 10 mumol, and immediately thereafter intraperitoneal injections of the respective oxime at a dosage of half the LD(01). The relative risk of death (RR) over time was estimated by Cox survival analysis for treatment with experimental K-oximes (K-53, K-74, K-75, K-107, K-108, and K-113), with the clinically available oximes pralidoxime (2-PAM) and obidoxime, and with the well-characterized K-oximes K-27 and K-48, comparing results with the no-treatment group. Best protection was conferred by K-27, reducing the RR to 20% of controls (P