Katalinic MajaInstitute for Medical Research and Occupational Health; Ksaverska cesta 2; HR-10000 Zagreb. +38514682551 CroatiaPhone : +38514673188 Fax : Send E-Mail to Katalinic Maja
Title: Insulin, dibutyryl-cAMP, and glucose modulate expression of patatin-like domain containing protein 7 in cultured human myotubes Mis K, Lulic AM, Mars T, Pirkmajer S, Katalinic M Ref: Front Endocrinol (Lausanne), 14:1139303, 2023 : PubMed
Expression of patatin-like phospholipase domain containing protein 7 (PNPLA7), also known as neuropathy target esterase-related esterase (NRE), a lysophospholipase, increases with fasting and decreases with feeding in mouse skeletal muscle, indicating it is regulated by insulin, counterregulatory hormones, such as glucocorticoids and catecholamines, and/or nutrients. In cultured mouse adipocytes insulin reduces Pnpla7 expression, underscoring the possibility that insulin regulates PNPLA7 in skeletal muscle. The first aim of this study was to establish whether PNPLA7 is functionally expressed in cultured human skeletal muscle cells. The second aim was to determine whether PNPLA7 is regulated by insulin, glucocorticoids, cAMP/protein kinase A pathway, and/or glucose. Cultured human skeletal muscle cells expressed PNPLA7 mRNA and protein. Gene silencing of PNPLA7 in myoblasts reduced the phosphorylation of 70 kDa ribosomal protein S6 kinase and ribosomal protein S6 as well as the abundance of alpha1-subunit of Na(+),K(+)-ATPase and acetyl-CoA carboxylase, indirectly suggesting that PNPLA7 is functionally important. In myotubes, insulin suppressed PNPLA7 mRNA at 1 g/L glucose, but not at low (0.5 g/L) or high (4.5 g/L) concentrations. Treatment with synthetic glucocorticoid dexamethasone and activator of adenylyl cyclase forskolin had no effect on PNPLA7 regardless of glucose concentration, while dibutyryl-cAMP, a cell-permeable cAMP analogue, suppressed PNPLA7 mRNA at 4.5 g/L glucose. The abundance of PNPLA7 protein correlated inversely with the glucose concentrations. Collectively, our results highlight that PNPLA7 in human myotubes is regulated by metabolic signals, implicating a role for PNPLA7 in skeletal muscle energy metabolism.
Sets of 346 herbicides in use and 163 no longer in use were collected from open access online sources and compared in silico with cholinesterases inhibitors (ChI) and drugs in terms of physicochemical profile and estimated toxic effects on human health. The screening revealed at least one potential adverse consequence for each herbicide class assigned according to their mode of action on weeds. The classes with most toxic warnings were K1, K3/N, F1 and E. The selection of 11 commercial herbicides for in vitro biological tests on human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), the enzymes involved in neurotoxicity and detoxification of various xenobiotics, respectively, was based mainly on the structural similarity with inhibitors of cholinesterases. Organophosphate anilofos and oxyacetanilide flufenacet were the most potent inhibitors of AChE (25 microM) and BChE (6.4 microM), respectively. Glyphosate, oxadiazon, tembotrione and terbuthylazine were poor inhibitors with an estimated IC(50) above 100 microM, while for glyphosate the IC(50) was above 1 mM. Generally, all of the selected herbicides inhibited with a slight preference towards BChE. Cytotoxicity assays showed that anilofos, bensulide, butamifos, piperophos and oxadiazon were cytotoxic for hepatocytes (HepG2) and neuroblastoma cell line (SH-SY5Y). Time-independent cytotoxicity accompanied with induction of reactive oxygen species indicated rapid cell death in few hours. Our results based on in silico and in vitro analyses give insight into the potential toxic outcome of herbicides in use and can be applied in the design of new molecules with a less impact on humans and the environment.
Seven pyridoxal dioxime quaternary salts (1-7) were synthesized with the aim of studying their interactions with human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The synthesis was achieved by the quaternization of pyridoxal monooxime with substituted 2-bromoacetophenone oximes (phenacyl bromide oximes). All compounds, prepared in good yields (43-76%) and characterized by 1D and 2D NMR spectroscopy, were evaluated as reversible inhibitors of cholinesterase and/or reactivators of enzymes inhibited by toxic organophosphorus compounds. Their potency was compared with that of their monooxime analogues and medically approved oxime HI-6. The obtained pyridoxal dioximes were relatively weak inhibitors for both enzymes (K(i) = 100-400 M). The second oxime group in the structure did not improve the binding compared to the monooxime analogues. The same was observed for reactivation of VX-, tabun-, and paraoxon-inhibited AChE and BChE, where no significant efficiency burst was noted. In silico analysis and molecular docking studies connected the kinetic data to the structural features of the tested compound, showing that the low binding affinity and reactivation efficacy may be a consequence of a bulk structure hindering important reactive groups. The tested dioximes were non-toxic to human neuroblastoma cells (SH-SY5Y) and human embryonal kidney cells (HEK293).
Title: Cytotoxicity-related effects of imidazolium and chlorinated bispyridinium oximes in SH-SY5Y cells Zandona A, Zorbaz T, Mis K, Pirkmajer S, Katalinic M Ref: Arh Hig Rada Toksikol, 73:277, 2022 : PubMed
Current research has shown that several imidazolium and chlorinated bispyridinium oximes are cytotoxic and activate different mechanisms or types of cell death. To investigate this further, we analysed interactions between these oximes and acetylcholine receptors (AChRs) and how they affect several signalling pathways to find a relation between the observed toxicities and their effects on these specific targets. Chlorinated bispyridinium oximes caused time-dependent cytotoxicity by inhibiting the phosphorylation of STAT3 and AMPK without decreasing ATP and activated ERK1/2 and p38 MAPK signal cascades. Imidazolium oximes induced a time-independent and significant decrease in ATP and inhibition of the ERK1/2 signalling pathway along with phosphorylation of p38 MAPK, AMPK, and ACC. These pathways are usually triggered by a change in cellular energy status or by external signals, which suggests that oximes interact with some membrane receptors. Interestingly, in silico analysis also indicated that the highest probability of interaction for all of our oximes is with the family of G-coupled membrane receptors (GPCR). Furthermore, our experimental results showed that the tested oximes acted as acetylcholine antagonists for membrane AChRs. Even though oxime interactions with membrane receptors need further research and clarification, our findings suggest that these oximes make promising candidates for the development of specific therapies not only in the field of cholinesterase research but in other fields too, such as anticancer therapy via altering the Ca(2+) flux involved in cancer progression.
The fluorinated bis-pyridinium oximes were designed and synthesized with the aim of increasing their nucleophilicity and potential to reactivate phosphorylated human recombinant acetylcholinesterase (AChE) and human purified plasmatic butyrylcholinesterase (BChE) in relation to chlorinated and non-halogenated oxime analogues. Compared to non-halogenated oximes, halogenated oximes showed lower pK(a) of the oxime group (fluorinated < chlorinated < non-halogenated) along with higher level of oximate anion formation at the physiological pH, and had a higher binding affinity of both AChE and BChE. The stability tests showed that the fluorinated oximes were stable in water, while in buffered environment di-fluorinated oximes were prone to rapid degradation, which was reflected in their lower reactivation ability. Mono-fluorinated oximes showed comparable reactivation to non-halogenated (except asoxime) and mono-chlorinated oximes in case of AChE inhibited by sarin, cyclosarin, VX, and tabun, but were less efficient than di-chlorinated ones. The same trend was observed in the reactivation of inhibited BChE. The advantage of halogen substituents in the stabilization of oxime in a position optimal for in-line nucleophilic attack were confirmed by extensive molecular modelling of pre-reactivation complexes between the analogue oximes and phosphorylated AChE and BChE. Halogen substitution was shown to provide oximes with additional beneficial properties, e.g., fluorinated oximes gained antioxidative capacity, and moreover, halogens themselves did not increase cytotoxicity of oximes. Finally, the in vivo administration of highly efficient reactivator and the most promising analogue, 3,5-di-chloro-bispyridinium oxime with trimethylene linker, provided significant protection of mice exposed to sarin and cyclosarin.
The treatment of central nervous system (CNS) diseases related to the decrease of neurotransmitter acetylcholine in neurons is based on compounds that prevent or disrupt the action of acetylcholinesterase and butyrylcholinesterase. A series of thirteen quinuclidine carbamates were designed using quinuclidine as the structural base and a carbamate group to ensure the covalent binding to the cholinesterase, which were synthesized and tested as potential human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitors. The synthesized compounds differed in the substituents on the amino and carbamoyl parts of the molecule. All of the prepared carbamates displayed a time-dependent inhibition with overall inhibition rate constants in the 10(3) M(-1) min(-1) range. None of the compounds showed pronounced selectivity for any of the cholinesterases. The in silico determined ability of compounds to cross the blood-brain barrier (BBB) revealed that six compounds should be able to pass the BBB by passive transport. In addition, the compounds did not show toxicity toward cells that represented the main models of individual organs. By machine learning, the most optimal regression models for the prediction of bioactivity were established and validated. Models for AChE and BChE described 89 and 90% of the total variations among the data, respectively. These models facilitated the prediction and design of new and more potent inhibitors. Altogether, our study confirmed that quinuclidinium carbamates are promising candidates for further development as CNS-active drugs, particularly for Alzheimer's disease treatment.
Oximes, investigated as antidotes against organophosphates (OP) poisoning, are known to display toxic effects on a cellular level, which could be explained beyond action on acetylcholinesterase as their main target. To investigate this further, we performed an in vitro cell-based evaluation of effects of two structurally diverse oxime groups at concentrations of up to 800 microM, on several cell models: skeletal muscle, kidney, liver, and neural cells. As indicated by our results, compounds with an imidazolium core induced necrosis, unregulated cell death characterized by a cell burst, increased formation of reactive oxygen species, and activation of antioxidant scavenging. On the other hand, oximes with a pyridinium core activated apoptosis through specific caspases 3, 8, and/or 9. Interestingly, some of the compounds exhibited a synergistic effect. Moreover, we generated a pharmacophore model for each oxime series and identified ligands from public databases that map to generated pharmacophores. Several interesting hits were obtained including chemotherapeutics and specific inhibitors. We were able to define the possible structural features of tested oximes triggering toxic effects: chlorine atoms in combination with but-2(E)-en-1,4-diyl linker and adding a second benzene ring with substituents such as chlorine and/or methyl on the imidazolium core. Such oximes could not be used in further OP antidote development research, but could be introduced in other research studies on new specific targets. This could undoubtedly result in an overall improved wider use of unexplored oxime database created so far in OP antidotes field of research in a completely new perspective.
This study investigated the levels and distribution of polychlorinated biphenyls (PCBs) and organochlorine pesticides in three tissue types of farmed Bluefin tuna (Thunnus thynnus): muscle, liver and branchiae. Seven adult species were caught in 2015 at a tuna farm in the Croatian Adriatic. The organochlorine compound levels decreased in the following order: liver > muscle > branchiae while contaminant distribution in all three tissues followed the same order: PCB DDT > HCH ~ HCB. The found POP levels indicated moderate pollution of farmed tuna and were below all limits set by current laws. Furthermore, no cytotoxic effect of the POP mixture extracted from tuna liver samples on human neuroblastoma cells was observed.
We evaluated the potential of nine vitamin B3 scaffold-based derivatives as acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitors, as a starting point for the development of novel drugs for treating disorders with cholinergic neurotransmission-linked pathology. As the results indicate, all compounds reversibly inhibited both enzymes in the micromolar range pointing to the preference of AChE over BChE for binding the tested derivatives. Molecular docking studies revealed the importance of interactions with AChE active site residues Tyr337 and Tyr124, which dictated most of the observed differences. The most potent inhibitor of both enzymes with K(i) of 4 M for AChE and 8 M for BChE was the nicotinamide derivative 1-(4'-phenylphenacyl)-3-carbamoylpyridinium bromide. Such a result places it within the range of several currently studied novel cholinesterase inhibitors. Cytotoxicity profiling did not classify this compound as highly toxic, but the induced effects on cells should not be neglected in any future detailed studies and when considering this scaffold for drug development.
A library of 14 mono-oxime quinuclidinium-based compounds with alkyl or benzyl substituent were synthesized and characterized in vitro as potential antidotes for organophosphorus compounds (OP) poisoning treatment. We evaluated their potency for reversible inhibition and reactivation of OP inhibited human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and evaluated interactions by molecular docking studies. The reactivation was notable for both AChE and BChE inhibited by VX, cyclosarin, sarin and paraoxon, if quinuclidinium compounds contained the benzyl group attached to the quinuclidinium moiety. Out of all 14, oxime Q8 [4-bromobenzyl-3-(hydroxyimino)quinuclidinium bromide] was singled out as having the highest determined overall reactivation rate of approximately 20,000 M(-1) min(-1) for cyclosarin-inhibited BChE. Furthermore, this oxime in combination with BChE exhibited a capability to act as a bioscavenger of cyclosarin, degrading within 2 h up to 100-fold excess of cyclosarin concentration over the enzyme. Molecular modeling revealed that the position of the cyclohexyl moiety conjugated with the active site serine of BChE directs the favorable positioning of the quinuclidinium ring and the bromophenyl moiety of Q8, which makes phosphonylated-serine easily accessible for the nucleophilic displacement by the oxime group of Q8. This result presents a novel scaffold for the development of new BChE-based bioscavengers. Furthermore, a cytotoxic effect was not observed for Q8, which also makes it promising for further in vivo reactivation studies.
Nerve agents, the deadliest chemical warfare agents, are potent inhibitors of acetylcholinesterase (AChE) and cause rapid cholinergic crisis with serious symptoms of poisoning. Oxime reactivators of AChE are used in medical practice in treatment of nerve agent poisoning, but the search for novel improved reactivators with central activity is an ongoing pursuit. Among the numerous oximes synthesized, in vitro reactivation is a standard approach in biological evaluation with little attention given to the pharmacokinetic properties of the compounds. This study reports a comprehensive physicochemical, pharmacokinetic, and safety profiling of five 3-hydroxy-2-pyridine aldoximes, which were recently shown to be potent AChE reactivators. The oxime JR595 was singled out as highly metabolically stable in human liver microsomes and non-cytotoxic oxime for SH-SY5Y neuroblastoma and 1321N1 astrocytoma cell lines and its pharmacokinetic profile was determined after intramuscular administration in mice. JR595 was rapidly absorbed into blood after 15 min with simultaneous distribution to the brain at up to about 40% of its blood concentration; however, it was eliminated both from the brain and blood within an hour. In addition, the MDCKII-MDR1 cell line assay showed that oxime JR595 was not a P-glycoprotein efflux pump substrate. Furthermore, preliminary antidotal study against multiple LD50 doses of VX and sarin in mice showed the potential of JR595 to provide desirable therapeutic outcomes with future improvements in its circulation time.
Acetylcholinesterase (AChE), an enzyme that degrades the neurotransmitter acetylcholine, when covalently inhibited by organophosphorus compounds (OPs), such as nerve agents and pesticides, can be reactivated by oximes. However, tabun remains among the most dangerous nerve agents due to the low reactivation efficacy of standard pyridinium aldoxime antidotes. Therefore, finding an optimal reactivator for prophylaxis against tabun toxicity and for post-exposure treatment is a continued challenge. In this study, we analyzed the reactivation potency of 111 novel nucleophilic oximes mostly synthesized using the CuAAC triazole ligation between alkyne and azide building blocks. We identified several oximes with significantly improved in vitro reactivating potential for tabun-inhibited human AChE, and in vivo antidotal efficacies in tabun-exposed mice. Our findings offer a significantly improved platform for further development of antidotes and scavengers directed against tabun and related phosphoramidate exposures, such as the Novichok compounds.
Tabun represents the phosphoramidate class of organophosphates that are covalent inhibitors of acetylcholinesterase (AChE), an essential enzyme in neurotransmission. Currently used therapy in counteracting excessive cholinergic stimulation consists of a muscarinic antagonist (atropine) and an oxime reactivator of inhibited AChE, but the classical oximes are particularly ineffective in counteracting tabun exposure. In a recent publication (Kovarik et al., 2019), we showed that several oximes prepared by the Huisgen 1,3 dipolar cycloaddition and related precursors efficiently reactivate the tabun-AChE conjugate. Herein, we pursue the antidotal question further and examine a series of lead precursor molecules, along with triazole compounds, as reactivators of two AChE mutant enzymes. Such studies should reveal structural subtleties that reside within the architecture of the active center gorge of AChE and uncover intimate mechanisms of reactivation of alkylphosphate conjugates of AChE. The designated mutations appear to minimize steric constraints of the reactivating oximes within the impacted active center gorge. Indeed, after initial screening of the triazole oxime library and its precursors for the reactivation efficacy on Y337A and Y337A/F338A human AChE mutants, we found potentially active oxime-mutant enzyme pairs capable of degrading tabun in cycles of inhibition and reactivation. Surprisingly, the most sensitive ex vivo reactivation of mutant AChEs occurred with the alkylpyridinium aldoximes. Hence, although the use of mutant enzyme bio-scavengers in humans may be limited in practicality, bioscavenging and efficient neutralization of tabun itself or phosphoramidate mixtures of organophosphates might be achieved efficiently in vitro or ex vivo with these mutant AChE combinations.
The antidotal property of oximes is attributed to their ability to reactivate acetylcholinesterase (AChE) inhibited by organophosphorus compounds (OP) such as pesticides and nerve warfare agents. Understanding their interactions within the active site of phosphylated AChE is of great significance for the search for more efficient reactivators, especially in the case of the most resistant OP to reactivation, tabun. Therefore, herein we studied the interactions and reactivation of tabun-inhibited AChE by site-directed mutagenesis and a series of bispyridinium oximes. Our results indicated that the replacement of aromatic residues with aliphatic ones at the acyl pocket and choline binding site mostly interfered with the stabilisation of the oxime's pyridinium ring(s) within the active site gorge needed to obtain the proper orientation of the oxime group toward the phosphorylated active site serine. However, in the case of W286A, the mutation in the peripheral binding site by preventing a pi-pi interaction with one of the oxime's pyridinium rings allowed a more favourable position of the oxime for a nucleophilic attack on the phosphorylated catalytic serine. The mutation resulted in a 2-5 fold increase in the reactivation rates when compared to the AChE wild type. Therefore, it seems that aromatic amino acids at the peripheral binding site presented a limitation in bispyridinium oxime reactivation efficiency of tabun-phosphorylated AChE. Moreover, this is further corroborated by the reactivation by mono-pyridinium oxime 2-PAM, in which mutations at the peripheral site did not influence either the affinity or reactivation of tabun-inhibited AChE.
A new series of 3-hydroxy-2-pyridine aldoxime compounds have been designed, synthesised and tested in vitro, in silico, and ex vivo as reactivators of human acetylcholinesterase (hAChE) and butyrylcholinesterase (hBChE) inhibited by organophosphates (OPs), for example, VX, sarin, cyclosarin, tabun, and paraoxon. The reactivation rates of three oximes (16-18) were determined to be greater than that of 2-PAM and comparable to that of HI-6, two pyridinium aldoximes currently used by the armies of several countries. The interactions important for a productive orientation of the oxime group within the OP-inhibited enzyme have been clarified by molecular-modelling studies, and by the resolution of the crystal structure of the complex of oxime 17 with Torpedo californica AChE. Blood-brain barrier penetration was predicted for oximes 15-18 based on their physicochemical properties and an in vitro brain membrane permeation assay. Among the evaluated compounds, two morpholine-3-hydroxypyridine aldoxime conjugates proved to be promising reactivators of OP-inhibited cholinesterases. Moreover, efficient ex vivo reactivation of phosphylated native cholinesterases by selected oximes enabled significant hydrolysis of VX, sarin, paraoxon, and cyclosarin in whole human blood, which indicates that the oximes have scavenging potential.
Six chlorinated bispyridinium mono-oximes, analogous to potent charged reactivators K027, K048, and K203, were synthesized with the aim of improving lipophilicity and reducing the p Ka value of the oxime group, thus resulting in a higher oximate concentration at pH 7.4 compared to nonchlorinated analogues. The nucleophilicity was examined and the p Ka was found to be lower than that of analogous nonchlorinated oximes. All the new compounds efficiently reactivated human AChE inhibited by nerve agents cyclosarin, sarin, and VX. The most potent was the dichlorinated analogue of oxime K027 with significantly improved ability to reactivate the conjugated enzyme due to improved binding affinity and molecular recognition. Its overall reactivation of sarin-, VX-, and cyclosarin-inhibited AChE was, respectively, 3-, 7-, and 8-fold higher than by K027. Its universality, PAMPA permeability, favorable acid dissociation constant coupled with its negligible cytotoxic effect, and successful ex vivo scavenging of nerve agents in whole human blood warrant further analysis of this compound as an antidote for organophosphorus poisoning.
Title: New Cinchona Oximes Evaluated as Reactivators of Acetylcholinesterase and Butyrylcholinesterase Inhibited by Organophosphorus Compounds Katalinic M, Zandona A, Ramic A, Zorbaz T, Primozic I, Kovarik Z Ref: Molecules, 22:, 2017 : PubMed
For the last six decades, researchers have been focused on finding efficient reactivators of organophosphorus compound (OP)-inhibited acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). In this study, we have focused our research on a new oxime scaffold based on the Cinchona structure since it was proven to fit the cholinesterases active site and reversibly inhibit their activity. Three Cinchona oximes (C1, C2, and C3), derivatives of the 9-oxocinchonidine, were synthesized and investigated in reactivation of various OP-inhibited AChE and BChE. As the results showed, the tested oximes were more efficient in the reactivation of BChE and they reactivated enzyme activity to up to 70% with reactivation rates similar to known pyridinium oximes used as antidotes in medical practice today. Furthermore, the oximes showed selectivity towards binding to the BChE active site and the determined enzyme-oxime dissociation constants supported work on the future development of inhibitors in other targeted studies (e.g., in treatment of neurodegenerative disease). Also, we monitored the cytotoxic effect of Cinchona oximes on two cell lines Hep G2 and SH-SY5Y to determine the possible limits for in vivo application. The cytotoxicity results support future studies of these compounds as long as their biological activity is targeted in the lower micromolar range.
Title: Pyridoxal oxime derivative potency to reactivate cholinesterases inhibited by organophosphorus compounds Busic V, Katalinic M, Sinko G, Kovarik Z, Gaso-Sokac D Ref: Toxicol Lett, 262:114, 2016 : PubMed
Organophosphorus (OP) nerve agents (sarin, tabun VX and soman) inhibit the enzyme acetylcholinesterase (AChE, EC 3.1.1.7) by binding to its active site while preventing neurotransmission in the cholinergic synapses. The protection and treatment of this kind of poisoning are still a challenge as we are yet to discover an antidote that would be effective in all cases of poisoning. To aid the search for more efficient antidotes, we evaluated the ability of nine pyridoxal oxime derivatives, prepared by a novel synthetic pathway, to reactivate recombinant human AChE and the related purified human plasma butyrylcholinesterase (BChE, EC 3.1.1.8) inhibited by VX, tabun and paraoxon. Oximes are derivatives of vitamin B6 bearing a phenacyl moiety attached to the quaternary nitrogen atom and having various substituents on the phenyl ring. As the results have shown, the tested oximes were in general more efficient in the reactivation of OP-inhibited BChE than AChE. The highest observed rate was in the case of VX-inhibited BChE reactivation, where kobs was 0.0087min-1 and the reactivation maximum of 90% was achieved within 5h. The cholinesterases displayed a binding affinity for these derivatives in a mumolar range no matter the substituent on their rings which was in accordance with the molecular modelling results showing a similar binding pattern for all oximes within the active site of both AChE and BChE. Such a positioning reveals also that hydroxy and a metoxy substituents at the vicinity of the oxime moiety present a possible steric hindrance explaining the reactivation results.
A well-considered treatment of acute nerve agents poisoning involves the exogenous administration of butyrylcholinesterase (BChE, EC 3.1.1.8) as a stoichiometric bioscavenger efficient in preventing cholinergic crises caused by acetylcholinesterase (AChE, EC 3.1.1.7) inhibition. An additional improvement in medical countermeasures would be to use oximes that could reactivate BChE as well to upgrade bioscavenging from stoichiometric to oxime-assisted catalytic. Therefore, in this paper we investigated the potency of 39 imidazolium and benzimidazolium oximes (36 compounds synthesized for the first time) to be considered as the reactivators specifically designed for reactivation of phosphylated human BChE. Their efficiency in the reactivation of paraoxon-, VX-, and tabun-inhibited human BChE, as well as human AChE was tested and compared with the efficiencies of HI-6 and obidoxime, used in medical practice today. A comprehensive analysis was performed for the most promising oximes defining kinetic parameters of reactivation as well as interactions with uninhibited BChE. Furthermore, experimental data were compared with computational studies (docking, QSAR analysis) as a starting point in future oxime structure refinement. Considering the strict criteria set for in vivo applications, we determined the cytotoxicity of lead oximes on two cell lines. Among the tested oxime library, one imidazolium compound was selected for preliminary in vivo antidotal study in mice. The obtained protection in VX poisoning outlines its potential in development oxime-assisted OP-bioscavenging with BChE.
Even if organophosphorus (OP) nerve agents were banned entirely, their presence would remain a problem as weapons of terror (like in Syria). Oxime antidotes currently used in medical practice still fall short of their therapeutic purpose, as they fail to fully restore the activity of cholinesterases, the main target for OPs. As orphan drugs, these antidotes are tested too seldom for anybody's benefit. Over the last few decades, search for improved reactivators has reached new levels, but the translation of data obtained in vitro to in vivo application is still a problem that hinders efficient therapy. In this study, we tested the strengths and weaknesses of extrapolating pyridinium oxime antidotes reactivation efficiency from in vitro to in vivo application. Our results show that this extrapolation is possible with well-determined kinetic constants, but that it also largely depends on oxime circulation time and its tissue-specific distribution. This suggests that pharmacokinetic studies should be planned at the early stages of antidote development. Special attention should also be given to improving oxime distribution throughout the organism to overcome this major constraint in improving overall OP therapy.
Exposure to the nerve agent soman is difficult to treat due to the rapid dealkylation of the soman-acetylcholinesterase (AChE) conjugate known as aging. Oxime antidotes commonly used to reactivate organophosphate inhibited AChE are ineffective against soman, while the efficacy of the recommended nerve agent bioscavenger butyrylcholinesterase is limited by strictly stoichiometric scavenging. To overcome this limitation, we tested ex vivo, in human blood, and in vivo, in soman exposed mice, the capacity of aging-resistant human AChE mutant Y337A/F338A in combination with oxime HI-6 to act as a catalytic bioscavenger of soman. HI-6 was previously shown in vitro to efficiently reactivate this mutant upon soman, as well as VX, cyclosarin, sarin, and paraoxon, inhibition. We here demonstrate that ex vivo, in whole human blood, 1 muM soman was detoxified within 30 min when supplemented with 0.5 muM Y337A/F338A AChE and 100 muM HI-6. This combination was further tested in vivo. Catalytic scavenging of soman in mice improved the therapeutic outcome and resulted in the delayed onset of toxicity symptoms. Furthermore, in a preliminary in vitro screen we identified an even more efficacious oxime than HI-6, in a series of 42 pyridinium aldoximes, and 5 imidazole 2-aldoxime N-propylpyridinium derivatives. One of the later imidazole aldoximes, RS-170B, was a 2-3-fold more effective reactivator of Y337A/F338A AChE than HI-6 due to the smaller imidazole ring, as indicated by computational molecular models, that affords a more productive angle of nucleophilic attack.
Title: The cholinergic and non-cholinergic effects of organophosphates and oximes in cultured human myoblasts Katalinic M, Mis K, Pirkmajer S, Grubic Z, Kovarik Z, Mars T Ref: Chemico-Biological Interactions, 203:144, 2013 : PubMed
Organophosphorus compounds (OPs) and oximes may interfere with other molecules than AChE in the living systems, affecting in this way various cellular processes and underlying mechanisms. These non-cholinergic effects may contribute to the clinical status in OP poisoning and therefore deserve equal scientific attention. Here, we investigated the effects of tabun and oxime K048 on the processes known to be involved in muscle response to the environmental factors, like IL-6 release and the regulation of the heat shock proteins (HSPs). While IL-6 stimulates muscle regeneration, which follows well known OP-induced myopathy, HSPs have cytoprotective effect against various stress factors including xenobiotics. All our experiments were carried out on cultured human myoblasts, as the precursors of muscle regeneration. We found unchanged AChE mRNA level after tabun/K048 treatment meaning that tabun and K048 did not interfere with the transcription or stability of this mRNA in the time period tested, even if AChE catalytic activity was significantly affected. On the other hand, after myoblast exposure to tabun, we observed significant changes in the protein levels of HSP 27 and in the secretion of IL-6. Namely, secretion of IL-6 decreased to 53% and the level of HSP 27 increased by 34% compared to the control level. Both effects were attenuated if myoblasts were pretreated with oxime K048, but not if they were treated with K048 after exposure to tabun. The molecular mechanism underlying these effects remains to be elucidated. However, it seems that these effects could be associated with OPs and oximes as a specific group of compounds rather than as a specific compound itself. Overall, the effects of OPs and oximes demonstrated here might play an important role in muscle regeneration which importantly determines the final outcome of OP myotoxicity.
Title: Reactivation of Tabun-inhibited Acetylcholinesterase Investigated by Two Oximes and Mutagenesis Katalinic M, Kovarik Z Ref: Croatica Chemica Acta, 85:209", 2012 : PubMed
The reactivation of tabun-inhibited AChE site-directed mutants assisted by two bispyridinium oximes, K048 (N-[4-(4-hydroxyiminomethylpyridinio)butyl]-4-carbamoylpyridinium dibromide) and K033 ((N,N' -butano)bis(2-hydroxyiminomethylpyridinium bromide) was studied to analyse the constraints on oxime-assisted reactivation. AChE was modified within the acyl (F295L, F297I) and choline (Y337A) binding site of the active site gorge. Results show that introduced mutations affected both the affinity of phosphorylated enzyme for oximes and the rate of nucleophilic displacement of phosphoryl moiety from the catalytic serine. Mutations significantly lowered the overall reactivation efficacy of K048, but slightly enhanced the potency of K033 to reactivate tabun-inhibited AChE. It seems that the replacement of aromatic residues with the aliphatic ones at the acyl and choline binding site greatly interfered with the stabilization of the oxime's pyridinium ring(s) within the active site gorge needed to obtain the proper orientation of the oxime group toward the phosphorylated active site serine.
Title: [Cholinesterases: structure, role, and inhibition] Bosak A, Katalinic M, Kovarik Z Ref: Arh Hig Rada Toksikol, 62:175, 2011 : PubMed
Enzymes acetylcholinesterase (AChE; E.C. 3.1.1.7) and butyrylcholinesterase (BChE; E.C. 3.1.1.8) have intensively been investigated in biomedicine and toxicology due to important role in organisms. Even if structurally homologous, they differ in catalytic activity, specificity, for substrates, and selectivity in binding to many ligands. This paper compiles the results of research on cholinesterases and their interactions with ligands and inhibitors, and identifies amino acids of active sites involved in these interactions.
A conjugate of pyridine-4-aldoxime and atropine (ATR-4-OX) was synthesized and its antidotal efficiency was tested in vitro on tabun- or paraoxon-inhibited acetylcholinesterase (AChE) of human erythrocytes as well as in vivo using soman-, tabun- or paraoxon-poisoned mice. Its genotoxic profile was assessed on human lymphocytes in vitro and was found acceptable for further research. ATR-4-OX showed very weak antidotal activity, inadequate for soman or tabun poisoning. Conversely, it was effective against paraoxon poisoning both in vitro and in vivo. All animals treated with 5 % or 25 % LD(50) doses of the new oxime survived after administration of 10.0 or 16.0 LD(50) doses of paraoxon, respectively. Based on the persistence of toxicity symptoms in mice, the atropine moiety had questionable effects in attenuating such symptoms. It appears that ATR-4-OX has a therapeutic effect related to the reactivation of phosphylated AChE, but not to receptor antagonization.
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.
Organophosphorus compounds pose a potential threat to both military and civilian populations. Since post-exposure therapy has its limitations, our research was focused on the possibility of improving pretreatment in order to limit the toxic effects of tabun. We determined the protective index of various combinations of atropine, oximes (K074, K048, and TMB-4(Trimedoxime)), and pyridostigmine given to mice before tabun intoxication. Although the tested oximes showed very good therapeutic efficacy in tabun-poisoned mice, the given pretreatments improved therapy against tabun poisoning. These regimens ensured survival of all animals up to 25.2 LD(50) of tabun. Our results indicate that even pretreatment with atropine alone is sufficiently effective in enhancing the survival of mice poisoned by multiple doses of tabun, if oxime therapy follows. K048 is our oxime of choice for future research, as it shows better protective and reactivating potency.
Title: Synthesis and evaluation of novel analogues of vitamin B6 as reactivators of tabun and paraoxon inhibited acetylcholinesterase Gaso-Sokac D, Katalinic M, Kovarik Z, Busic V, Kovac S Ref: Chemico-Biological Interactions, 187:234, 2010 : PubMed
A series of novel pyridinium oximes was prepared by reactions of quaternization of pyridoxal oxime with substituted phenacyl bromides in acetone at room temperature. The structures of compounds were determined according to the data obtained by IR spectroscopy, mass spectrometry, (1)H and (13)C nuclear magnetic resonance spectroscopy as well as by elemental analysis. We tested pyridoxal oxime (1) and five prepared oximes in 1mM concentration as reactivators of human erythrocytes acetylcholinesterase (AChE) inhibited by organophosphorus compounds tabun and paraoxon: 1-phenacyl-3-hydroxy-4-hydroxyiminomethyl-5-hydroxymethyl-2-methylpyridinium bromide (2), 1-(4'-chlorophenacyl)-3-hydroxy-4-hydroxyiminomethyl-5-hydroxymethyl-2-methylpyri dinium bromide (3), 1-(4'-fluorophenacyl)-3-hydroxy-4-hydroxyiminomethyl-5-hydroxymethyl-2-methylpyri dinium bromide (4), 3-hydroxy-4-hydroxyiminomethyl-5-hydroxymethyl-2-methyl-1-(4'-methylphenacyl)pyri dinium bromide (5), 3-hydroxy-4-hydroxyiminomethyl-5-hydroxymethyl-2-methyl-1-(4'-methoxyphenacyl)pyr idinium bromide (6). However, tested oximes were not efficient in reactivation of either tabun or paraoxon inhibited AChE. The maximum restored enzyme activity in 24h was below 25%. Therefore, this class of compounds cannot be considered as potential improvement in a search for new and more efficient antidotes against OP poisoning.
Selected flavonoids: galangin, kaempferol, quercetin, myricetin, fisetin, apigenin, luteolin and rutin, reversibly inhibited human butyrylcholinesterase (BChE, EC 3.1.1.8). Inhibition potency of the flavonoids we attributed to their chemical structure, i.e., the number of OH groups and their side on the phenyl ring. The most potent BChE inhibitor among the tested flavonoids was galangin, which showed 12 times higher preference for binding to BChE (7 micromol/L) than to the related enzyme human acetylcholinesterase (AChE, EC 3.1.1.7). Docking study showed that flavonoids bind to the BChE active site by forming multiple hydrogen bonds and pi-pi interactions. The UV-VIS (200-500 nm) absorption spectra of the flavonoid phosphate buffer solution (pH 7.4), with the exception of rutin, revealed time dependant changes indicating precipitation of flavonoids or in the case of myricetin, a change in the chemical structure resulting in a BChE non-inhibiting specie. Selected flavonoids showed no cytotoxic effect on HepG2 and A549 cell lines at concentrations up to 200 micromol/L. Cytotoxicity was observed only for fisetin, apigenin and luteolin in the THP-1 cell line with IC50 of 30, 60 and 70 micromol/L, respectively.
Butyrylcholinesterase is considered to be an endogenous stoichiometric bioscavenger of organophosphorus compounds (OPs), but due to limited concentration of BChE in the organism, stoichiometric reduction of OP is not always sufficient. This can be improved by creating a pseudo-catalytic scavenger adding oximes as reactivators of inhibited exogenous BChE. In order to improve the BChE bioscavenging function in tabun or paraoxon poisoning, we tested in vitro reactivation of phosphorylated human plasma BChE by bispyridinium oximes varying in the length and type of the linker between rings, and in the position of the oxime group on the ring. Among the tested oximes, the most potent reactivators of tabun-inhibited BChE were K117 [1,1'-(2,2'-oxybis(ethane-2,1-diyl))bis(4-hydroxyiminomethyl pyridinium) bromide] and K127 [4-carbamoyl-1-(2-(2-(4-(hydroxyiminomethyl) pyridinium-1-yl)ethoxy)ethyl)pyridinium bromide]. Reactivation by these oximes (1mM) reached about 50% of control activity after only 20 min; however, reactivation stopped at 70%. Reactivation of paraoxon-inhibited BChE by all of the selected oximes was slow. Using molecular mechanics, we performed docking of the oximes to tabun-inhibited BChE in order to discuss possible structural modifications of bispyridinium oximes to improve reactivation of phosphorylated BChE.
We studied bispyridinium oxime K203 [(E)-1-(4-carbamoylpyridinium)-4-(4-hydroxyiminomethylpyridinium)-but-2-ene dibromide] with tabun-inhibited human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in vitro, and its antidotal effect on tabun-poisoned mice and rats in vivo. We compared it with oximes K048 and TMB-4, which have proven the most efficient oxime antidotes in tabun poisoning by now. Tabun-inhibited AChE was completely reactivated by K203, with the overall reactivation rate constant of 1806 L mol(-1) min(-1). This means that K203 is a very potent reactivator of tabun-inhibited AChE. In addition, K203 reversibly inhibited AChE (Ki = 0.090 mmol L(-1)) and BChE (K(i) = 0.91 mmol L(-1)), and exhibited its protective effect against phosphorylation of AChE by tabun in vitro. In vivo, a quarter of the LD50 K203 dose insured survival of all mice after the application of as many as 8 LD50 doses of tabun, which is the highest dosage obtained compared to K048 and TMB-4. Moreover, K203 showed high therapeutic potency in tabun-poisoned rats, preserving cholinesterase activity in rat plasma up to 60 min after poisoning. This therapeutic improvement obtained by K203 in tabun-poisoning places this oxime in the spotlight for further development.
