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Aims: Organophosphates (OPCs), useful agents as pesticides, also represent a serious health hazard. Standard therapy with atropine and established oxime-type enzyme reactivators is unsatisfactory. Experimental data indicate that superior therapeutic results can be obtained when reversible cholinesterase inhibitors are administered before OPC exposure. Comparing the protective efficacy of five such cholinesterase inhibitors (physostigmine, pyridostigmine, ranitidine, tacrine, or K-27), we observed best protection for the experimental oxime K-27. The present study was undertaken in order to determine if additional administration of K-27 immediately after OPC (paraoxon) exposure can improve the outcome., Methods: Therapeutic efficacy was assessed in rats by determining the relative risk of death (RR) by Cox survival analysis over a period of 48 h. Animals that received only pretreatment and paraoxon were compared with those that had received pretreatment and paraoxon followed by K-27 immediately after paraoxon exposure., Results: Best protection from paraoxon-induced mortality was observed after pretreatment with physostigmine (RR = 0.30) and K-27 (RR = 0.34). Both substances were significantly more efficacious than tacrine (RR = 0.67), ranitidine (RR = 0.72), and pyridostigmine (RR = 0.76), which were less efficacious but still significantly reduced the RR compared to the no-treatment group (paraoxon only). Additional administration of K-27 immediately after paraoxon exposure (posttreatment) did not further reduce mortality. Statistical analysis between pretreatment before paraoxon exposure alone and pretreatment plus K-27 posttreatment did not show any significant difference for any of the pretreatment regimens., Conclusions: Best outcome is achieved if physostigmine or K-27 are administered prophylactically before exposure to sublethal paraoxon dosages. Therapeutic outcome is not further improved by additional oxime therapy immediately thereafter.

Organophosphorus compounds (OPCs), inhibitors of acetylcholinesterase (AChE), are useful agents as pesticides, but also represent a serious health hazard. Standard therapy with atropine and established oxime-type enzyme reactivators (pralidoxime, obidoxime) is unsatisfactory. Better therapeutic results are obtained, when reversible AChE inhibitors are administered before OPC exposure. This review summarizes the history of such a pretreatment approach and sums up a set of experiments undertaken in search of compounds that are efficacious when given before a broad range of OPCs. The prophylactic efficacy of 10 known AChE inhibitors, either already used clinically for different indications (physostigmine, pyridostigmine, ranitidine, tiapride, tacrine, amiloride, metoclopramide, methylene blue) or developed for possible therapeutic use in the future (7-methoxytacrine, K-27) was compared, when administered before exposure to six chemically diverse OPCs in the same experimental setting: ethyl-paraoxon, methyl-paraoxon, diisopropylfluorophosphate, terbufos sulfone, azinphos-methyl and dicrotophos. The experimental oxime K-27 was the most efficacious compound, affording best protection, when administered before terbufos sulfone, azinphos-methyl and dicrotophos, second best before ethyl- and methyl-paraoxon exposure and third best before diisopropylfluorophosphate administration. This ranking was similar to that of physostigmine, which was superior to the Food and Drug Administration-approved pretreatment for soman with pyridostigmine. Tiapride, amiloride, metoclopramide, methylene blue and 7-methoxytacrine did not achieve protection. No correlation was observed between the IC 50 of the reversible AChE inhibitors and their protective efficacy. These studies indicate that K-27 can be considered a very promising broad-spectrum prophylactic agent in case of imminent organophosphate exposure, which may be related to its AChE reactivating activity rather than its AChE inhibition., (© 2018 John Wiley & Sons, Ltd.)

Background: Reversible cholinesterase inhibitors, when given prophylactically before exposure to organophosphates, are able to decrease organophosphate-induced mortality. However, the efficacy of pyridostigmine, the only pre-treatment substance approved by the US Federal Drug Administration, is unsatisfactory., Methods: In search of a better prophylactic compound, we determined in vivo the protection conferred by five cholinesterase inhibitors (ranitidine, physostigmine, tacrine, K-27 and pyridostigmine), which were administered in equitoxic dosage (1/4 of LD01) 30 minutes before exposure to the organophosphate dicrotophos. Efficacy was measured in rats by Cox analysis calculating the relative risk of death (RR), RR being 1 for the reference group which received dicrotophos and no prophylaxis., Results: K-27 (RR=0.06), physostigmine (RR=0.15), pyridostigmine (RR=0.22) and tacrine (RR=0.28) significantly (p ≤ 0.05) reduced dicrotophos-induced mortality in comparison to the reference group (dicrotophos without pre-treatment), whereas ranitidine (RR=0.86) had no significant influence. The experimental oxime K-27, when given before dicrotophos exposure, conferred the best in vivo protection. This was significantly (p ≤ 0.05) more efficacious than pre-treatment with any other tested compound. The differences in efficacy between the second best compound, physostigmine, and the less efficacious substances (tacrine and pyridostigmine) were also statistically significant., Conclusion: These data indicate that K-27 can be considered a very efficacious prophylactic agent for organophosphate exposure., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

Pre-treatment with reversible acetylcholinesterase (AChE) inhibitors before organophosphorous compound (OPC) exposure can reduce OPC-induced mortality. However, pyridostigmine, the only substance employed for such prophylaxis, is merely efficacious against a limited number of OPCs. In search of more efficacious and broad-range alternatives, we have compared in vivo the ability of five reversible AChE inhibitors (pyridostigmine, physostigmine, ranitidine, tacrine and K-27) to reduce mortality induced by the OPC azinphos-methyl. Protection was quantified using Cox analysis by determining the relative risk (RR) of death in rats that were administered these AChE inhibitors in equitoxic dosage (25% of LD01) 30 min before azinphos-methyl exposure. Azinphos-methyl-induced mortality was significantly reduced by all five tested compounds as compared with the reference group that was only exposed to azinphos-methyl without prior pre-treatment (RR = 1). The most efficacious prophylactic agents were K-27 (RR = 0.15) and physostigmine (RR = 0.21), being significantly more efficacious than ranitidine (RR = 0.62) and pyridostigmine (RR = 0.37). Pre-treatment with tacrine (RR = 0.29) was significantly more efficacious than pre-treatment with ranitidine, but the difference between tacrine and pyridostigmine was not significant. Our results indicate that prophylactic administration of the oxime K-27 may be a promising alternative in cases of imminent OPC exposure., (Copyright © 2014 John Wiley & Sons, Ltd.)

Poisoning with organophosphorus compounds (OPCs) poses a serious threat worldwide. OPC-induced mortality can be significantly reduced by prophylactic administration of reversible acetylcholinesterase (AChE) inhibitors. The only American Food and Drug Administration (FDA)-approved substance for such pre-treatment (to soman exposure) is presently pyridostigmine, although its efficacy is controversial. In search for more efficacious and broad-spectrum alternatives, we have assessed in vivo the mortality-reducing efficacy of a group of five compounds with known AChE inhibitory activity (pyridostigmine, physostigmine, ranitidine, tacrine and K-27), when given in equitoxic dosage (25% of LD01 ) 30 min before exposure to the OPC terbufos sulfone. Protection was quantified in rats by determining the relative risk of death (RR) using Cox analysis, with RR = 1 for animals given only terbufos sulfone, but no pre-treatment. All tested AChE inhibitors reduced terbufos sulfone-induced mortality significantly (p ≤ 0.05) as compared with the non-treatment group (RR = 1: terbufos sulfone only). Best in vivo protection from terbufos sulfone-induced mortality was achieved, when K-27 was given before terbufos sulfone exposure (RR = 0.06), which was significantly (P ≤ 0.05) superior to the pre-treatment with all other tested compounds, for example tacrine (RR = 0.21), pyridostigmine (RR = 0.28), physostigmine (RR = 0.29) and ranitidine (RR = 0.33). The differences in efficacy between tacrine, pyridostigmine, physostigmine and ranitidine were not statistically significant. Prophylactic administration of an oxime (such as K-27) in case of imminent OPC exposure may be a viable option., (Copyright © 2013 John Wiley & Sons, Ltd.)

Reversible acetylcholinesterase (AChE) inhibitors can protect against the lethal effects of irreversible organophosphorus AChE inhibitors (OPCs), when administered before OPC exposure. We have assessed in vivo the mortality-reducing efficacy of a group of known AChE inhibitors, when given in equitoxic dosage before exposure to the OPC paraoxon. Protection was quantified in rats by determining the relative risk (RR) of death. Best in vivo protection from paraoxon-induced mortality was observed after prophylactic administration of physostigmine (RR = 0.30) or the oxime K-27 (RR = 0.34); both treatments were significantly superior to the pre-treatment with all other tested compounds, including the established substance pyridostigmine. Tacrine (RR = 0.67), ranitidine (RR = 0.72), pyridostigmine (RR = 0.76), tiapride (RR = 0.80) and 7-MEOTA (RR = 0.86) also significantly reduced the relative risk of paraoxon-induced death, but to a lesser degree. Methylene blue, amiloride and metoclopramide had an unfavorable effect (RR ≥ 1), significantly increasing mortality. When CNS penetration by prophylactic is undesirable K-27 is a promising alternative to pyridostigmine., (Copyright © 2012 John Wiley & Sons, Ltd.)

Prophylactic administration of reversible acetylcholinesterase (AChE) inhibitors can protect against the lethal effects of organophosphorus compounds (OPCs). The usefulness of pyridostigmine, the only compound approved by the Food and Drug Administration (FDA) for such pretreatment, has been questioned. In search for more efficacious alternatives, we have examined in vivo the efficacy of a group of ten compounds with known anti-AChE activity (pyridostigmine, metoclopramide, tiapride, ranitidine, physostigmine, tacrine, amiloride, methylene blue, 7- methoxytacrine and K-27) to reduce mortality induced by the OPC methyl-paraoxon. AChE inhibitors were given intraperitoneally in equitoxic dosage (25% of LD₀₁) 30 min before OPC exposure. Protection was quantified in rats by determining the relative risk of death (RR) by Cox analysis, with RR=1 for animals given only methyl-paraoxon, but no pretreatment. Only physostigmine (RR=0.39), K-27 (RR=0.40) and tacrine (RR=0.48) significantly (p≤ 0.05) reduced methylparaoxon- induced mortality, when given prophylactically. Pretreatment with pyridostigmine, ranitidine, tiapride, amiloride, metoclopramide and methylene blue did not significantly protect against the lethal effects of methyl-paraoxon. 7-methoxytacrine (7-MEOTA) significantly (p≤ 0.05) increased the relative risk of methyl-paraoxon-induced death (RR=1.31). These results indicate that pretreatment with pyridostigmine cannot be considered a broad-spectrum approach against OPC exposure. K-27 may be a suitable alternative if passage into the brain is contraindicated.

Prophylactic administration of reversible acetylcholinesterase (AChE) inhibitors before exposure to organophosphorus compounds (OPCs) can reduce OPC-induced mortality. Pyridostigmine is the only FDA-approved substance for such use. The AChE-inhibitory activity of known AChE inhibitors was quantified in vitro and their in vivo mortality-reducing efficacy was compared, when given prophylactically before the exposure to the OPC diisopropylfluorophosphate (DFP). The IC50 was measured in vitro for the known AChE inhibitors pyridostigmine, physostigmine, ranitidine, tiapride, tacrine, 7-methoxytacrine, amiloride, metoclopramide, methylene blue and the experimental oxime K-27. Their in vivo efficacy, when given as pretreatment, to protect rats from DFP-induced mortality was quantified by determining the relative risk of death (RR) by Cox analysis, with RR = 1 for animals given only DFP, but no pretreatment. Physostigmine was the strongest in vitro AChE-inhibitor (IC50 = 0.012 µ m), followed by 7-methoxytacrine, tacrine, pyridostigmine and methylene blue. Ranitidine (IC50 = 2.5 µ m), metoclopramide and amiloride were in the mid-range. Tiapride (IC50 = 256 µ m) and K-27 (IC50 = 414 µ m) only weakly inhibited RBC AChE activity. Best in vivo protection from DFP-induced mortality was achieved when physostigmine (RR = 0.02) or tacrine (RR = 0.05) was given before DFP exposure, which was significantly superior to the pretreatment with all other tested compounds, except K-27 (RR = 0.18). The mortality-reducing effect of pyridostigmine, ranitidine and 7-methoxytacrine was inferior, but still significant. Tiapride, methylene blue, metoclopramide and amiloride did not significantly improve DFP-induced mortality. K-27 may be a more efficacious alternative to pyridostigmine, when passage into the brain precludes administration of physostigmine or tacrine., (Copyright © 2010 John Wiley & Sons, Ltd.)

Summary: The cholinergic nervous system has been demonstrated to attenuate the inflammatory response during sepsis via the inhibitory action of acetylcholine (ACh) on macrophages. These findings were largely based on experimental sepsis models using endotoxin as the inducing agent. Herein, however, we report that the specific inhibition of acetylcholinesterase (AChE) renders animals more resistant to infection by a virulent strain of Salmonella enterica serovar Typhimurium, a Gram-negative enteric pathogen. Inhibition of AChE was induced by a subchronic exposure to paraoxon, a potent anti-cholinesterase metabolite of the organophosphorous compound parathion. Our findings indicate that inhibition of AChE enhanced survival of infected mice in a dose-dependent fashion and this correlated with efficient control of bacterial proliferation in target organs. Immunologically, inhibition of AChE enabled the animals to mount a more effective inflammatory anti-microbial response, and to secrete higher levels of interleukin-12, a key T helper type 1-promoting cytokine. The ACh-induced enhancement in resistance to infection was abrogated by co-administration of an oxime which can reactivate AChE. Hence, in a model of Gram-negative bacterial infection, cholinergic stimulation is shown to enhance the anti-microbial immune response leading to effective control of bacterial proliferation and enhanced animal survival.

Pyridostigmine (PSTG) is a carbamate inhibitor of cholinesterases. Carbamates are known to confer some protection from the lethal effects of (some) organophosphorus compounds. Recently, based on animal data, the FDA approved oral PSTG for pre-exposure treatment of soman. The purpose of the study was to quantify in vivo the effect of PSTG pre-treatment on survival in rats exposed to the organophosphate paraoxon (POX) with and without subsequent reactivator (pralidoxime) treatment. POX is a highly toxic non-neuropathic ethyl organophospate. Pralidoxime (PRX) is the enzyme reactivator used by some NATO armies. The prospective, controlled animal (rat) study included Group 1 that received 1 micromol POX ( approximately LD(75)); Group 2 that received 1 micromol PSTG followed 30 min later by 1 micromol POX; Group 3 that received 1 micromol PSTG followed 30 min later by 1 micromol POX and 50 micromol PRX; Group 4 that received 1 micromol POX and 50 micromol PRX; Group 5 that received 1 micromol PSTG; Group 6 that received 50 micromol PRX and Group 7 that received 1 micromol PSTG followed 30 min later by 50 micromol PRX. Each group contained six rats. The experiment was repeated twelve times (12 cycles). All substances were applied i.p. From surviving animals of eight cycles tail blood was taken for red blood cell acetylcholinesterase (RBC-AChE) measurements. The animals were monitored for 48 h and mortality (survival time) was recorded. RBC-AChE activities were determined. Mortality was analysed using Kaplan-Meier plots. Both PSTG and PRX statistically significantly decreased organophosphate induced mortality in the described model. While the same applies to their combination the decrease in mortality when using both PSTG and PRX is less than that achieved with their single use (but not significantly so). While certainly further work using different organophosphorus compounds and animal species are needed before a final conclusion is reached, the animal data presented does not support the combined use of PSTG and PRX.

Weak and reversible inhibitors of cholinesterase(s), when coadministered in excess with a more potent inhibitor such as organophosphates, can act in a protective manner. The benzamide compound, metoclopramide, confers some protection (putatively via this mechanism) for cholinesterases against inhibition by paraoxon both in vitro and in vivo, after chronic small-dose exposure. Tiapride is a related benzamide. In this study, we compared the protection by metoclopramide and tiapride in rats acutely exposed to large doses of paraoxon with the therapeutic "gold standard," pralidoxime. Group 1 received 1 micromol paraoxon (approximately 75% lethal dose), Group 2 received 50 micromol metoclopramide, Group 3 received 50 micromol tiapride, Group 4 received 50 micromol pralidoxime, Group 5 received 1 micromol paraoxon + 50 micromol metoclopramide, Group 6 1 micromol paraoxon + 50 micromol tiapride, and Group 7 1 micromol paraoxon + 50 micromol pralidoxime. All substances were administered intraperitoneally. The animals were monitored for 48 h and mortality was recorded at 30 min, 1, 2, 3, 4, 24, and 48 h. Blood was taken for red blood cell acetylcholinesterase measurements at baseline, 30 min, 24, and 48 h. With the exception of Group 7, in which some late mortality was observed, mortality occurred mainly in the first 30 min after paraoxon administration with minimal changes occurring thereafter. Mortality at 30 min was 0% in the metoclopramide, tiapride, and pralidoxime groups and 73 +/- 20 (paraoxon), 65 +/- 15 (paraoxon + metoclopramide), 38 +/- 14 (paraoxon + tiapride), and 13 +/- 19 (paraoxon + pralidoxime). Mortality at 48 h was 75 +/- 18 (paraoxon), 67 +/- 17 (paraoxon + metoclopramide), 42 +/- 16 (paraoxon + tiapride), and 27 +/- 24 (paraoxon + pralidoxime). Metoclopramide does not significantly influence mortality after acute large-dose paraoxon exposure. Both tiapride and pralidoxime significantly decreased mortality in our model. The protection conferred by tiapride was significantly less than that conferred by pralidoxime at 30 min, but was not significantly different at 24 and 48 h.

This study evaluated the protective effect of the benzamide compound metoclopramide (MCP) against inhibition by paraoxon (POX) as assessed by red blood cell acetylcholinesterase (RBC-AChE) activity. Three groups of 6 rats each were used. All substances were applied ip daily for 5 d, followed by a 2-d rest. The 7-d cycle was repeated 6 times. Group 1 received 100 nM POX, Group 2 received 50 microM MCP. Group 3 received 100 nM POX + 50 microM MCP. Red blood cell acetylcholinesterase measurements were performed at base line and then after each 7-d cycle. Enzyme activities were compared using the Mann-Whitney rank order test. Metoclopramide conferred significant in vivo protection from inhibition of RBC-AChE by POX.

Intoxications with organophosphorus compounds such as paraoxon (POX) are frequent. Oximes are the only enzyme reactivators clinically available. In vitro and in vivo studies have shown that l-lactate reduces the inhibition of plasma acetylcholine-esteratic activity (AChEA) (in vitro and in vivo) and plasma butyrylcholine-esteratic activity (BChEA) (at least in vitro and possibly in vivo) by POX. However, a short infusion of 10 g of lactate was unable to elevate the plasma lactate level for >3 h. In this study we tested a substance related to l-lactate, i.e. pyruvic acid. The purpose of this animal experimental study (female minipigs with historical control group) was to determine in vivo whether intravenous (i.v.) pyruvic acid application under normoxic/normocapnic/normohydrogenaemic conditions is able to elevate blood lactate levels and whether it is able to protect AChEA and BChEA from POX inhibition. Animals were anaesthetized, intubated and mechanically ventilated. Each received 1 mg kg(-1) body wt. of POX in 50 ml of saline over 50 min and 10 g (ca. 0.5 g kg(-1) body wt.) of i.v. pyruvic acid in 50 ml of saline over 50 min. They were compared with a historical control group of six animals that received only 1 mg kg(-1) body wt. of POX in 50 ml of saline over 50 min. In central venous blood measurements of plasma AChEA and BChEA, the measurements were performed before (baseline), immediately after POX (50 min after start) and 110, 170, 230, 290, 530 and 1010 min after the start of infusion. A 10 g aliquot of i.v. pyruvic acid had a statistically significant protective effect in vivo on AChEA but not on BChE activity. Further study of the in vivo effects of pyruvic acid and l-lactate after paraoxon intoxication and a formal comparison with standard oxime therapy seems warranted. Also, a combination therapy with l-lactate and pyruvic acid in vivo should be investigated., (Copyright 2003 John Wiley & Sons, Ltd.)

Objective: Intoxications with organophosphorous compounds such as paraoxon, an inhibitor of serine hydrolases, mainly butyrylcholinesterase and acetylcholinesterase, are frequent. Oximes are the only enzyme reactivators clinically available. In vitro studies have shown that L(+)-lactate reduces the inhibition of acetylcholinesteratic (AChEA) and butyrylcholinesteratic activity of plasma (BChEA) by paraoxon., Design: The purpose of this in vivo study was to determine whether intravenous L(+)-lactate application under normoxic/normocapnic/normohydrogenemic conditions is able to protect AChEA and BChEA from paraoxon inhibition., Setting: University research institute., Subjects: Eighteen female minipigs., Interventions: Animals were anesthetized, intubated, and mechanically ventilated. Every animal received 1 mg of paraoxon per kilogram of body weight in 50 mL of saline over 50 mins. In addition to receiving paraoxon, six pigs of 18 received 2.5 g (0.125 g kg-1 of body weight) of intravenous L(+)-lactate in 50 mL of saline over 50 mins, and six other pigs received 10 g of L(+)-lactate (0.5 g kg-1 of body weight), whereas the six remaining served as controls., Measurements and Main Results: In central venous blood, plasma acetylcholinesteratic and butyrylcholinesteratic activity were measured before paraoxon (baseline, 0 mins), immediately after paraoxon (50 mins after start), and 110, 170, 230, 290, 530, and 1010 mins after the start of infusion. Although 10 g of intravenous L(+)-lactate application had a statistically significant protective effect in vivo on AChEA, 2.5 g did not. No significant protective effect on BChEA was achieved with either 2.5 g or 10 g of L(+)-lactate., Conclusions: Ten grams of L(+)-lactate can increase AChEA when administered simultaneously with paraoxon. Further study of the in vivo effects of L(+)-lactate after paraoxon intoxication and a formal comparison with standard oxime therapy seem warranted. Also, methods for achieving a prolonged elevated lactate concentration in vivo should be investigated.