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P Eyer

Publications and source records attributed to P Eyer.

At least 19 recordsLinked to original sources
PubMed2006

Lessons to be learnt from organophosphorus pesticide poisoning for the treatment of nerve agent poisoning.

The increasing threat of nerve agent use for terrorist purposes against civilian and military population calls for effective therapeutic preparedness. At present, administration of atropine and an oxime are recommended, although effectiveness of this treatment is not proved in clinical trials. Here, monitoring of intoxications with organophosphorus (OP) pesticides may be of help, as their actions are closely related to those of nerve agents and intoxication and therapy follow the same principles. To this end, the clinical course of poisoning and the effectiveness of antidotal therapy were investigated in patients requiring artificial ventilation being treated with atropine and obidoxime. However, poisoning with OP pesticides shows extremely heterogeneous pictures of cholinergic crisis frequently associated with clinical complications. To achieve valuable information for the therapy of nerve agent poisoning, cases resembling situations in nerve agent poisoning had to be extracted: (a) intoxication with OPs forming reactivatable OP-AChE-complexes with short persistence of the OP in the body resembling inhalational sarin intoxication; (b) intoxication with OPs resulting rapidly in an aged OP-AChE-complex resembling inhalational soman intoxication; (c) intoxications with OPs forming a reactivatable AChE-OP complex with prolonged persistence of the OP in the body resembling percutaneous VX intoxication. From these cases it was concluded that sufficient reactivation of nerve agent inhibited non-aged AChE should be possible, if the poison load was not too high and the effective oximes were administered early and with an appropriate duration. When RBC-AChE activity was higher than some 30%, neuromuscular transmission was relatively normal. Relatively low atropine doses (several milligrams) should be sufficient to cope with muscarinic symptoms during oxime therapy.

Animals↗
PubMed2006

Recent advances in evaluation of oxime efficacy in nerve agent poisoning by in vitro analysis.

The availability of highly toxic organophosphorus (OP) warfare agents (nerve agents) underlines the necessity for an effective medical treatment. Acute OP toxicity is primarily caused by inhibition of acetylcholinesterase (AChE). Reactivators (oximes) of inhibited AChE are a mainstay of treatment, however, the commercially available compounds, obidoxime and pralidoxime, are considered to be rather ineffective against various nerve agents, e.g. soman and cyclosarin. This led to the synthesis and investigation of numerous oximes in the past decades. Reactivation of OP-inhibited AChE is considered to be the most important reaction of oximes. Clinical data from studies with pesticide-poisoned patients support the assumption that the various reactions between AChE, OP and oxime, i.e. inhibition, reactivation and aging, can be investigated in vitro with human AChE. In contrast to animal experiments such in vitro studies with human tissue enable the evaluation of oxime efficacy without being affected by species differences. In the past few years numerous in vitro studies were performed by different groups with a large number of oximes and methods were developed for extrapolating in vitro data to different scenarios of human nerve agent poisoning. The present status in the evaluation of new oximes as antidotes against nerve agent poisoning will be discussed.

Animals↗
PubMed2006

Respiratory failure in acute organophosphorus pesticide self-poisoning.

BACKGROUND: Acute organophosphorus (OP) pesticide poisoning is a major clinical problem in the developing world. Textbooks ascribe most deaths to respiratory failure occurring in one of two distinct clinical syndromes: acute cholinergic respiratory failure or the intermediate syndrome. Delayed failure appears to be due to respiratory muscle weakness, but its pathophysiology is unclear. AIM: To describe the clinical patterns of OP-induced respiratory failure, and to determine whether the two syndromes are clinically distinct. DESIGN: Prospective study of 376 patients with confirmed OP poisoning. METHODS: Patients were observed throughout their admission to three Sri Lankan hospitals. Exposure was confirmed by butyrylcholinesterase and blood OP assays. RESULTS: Ninety of 376 patients (24%) required intubation: 52 (58%) within 2 h of admission while unconscious with cholinergic features. Twenty-nine (32%) were well on admission but then required intubation after 24 h while conscious and without cholinergic features. These two syndromes were not clinically distinct and had much overlap. In particular, some patients who required intubation on arrival subsequently recovered consciousness but could not be extubated, requiring ventilation for up to 6 days. DISCUSSION: Respiratory failure did not occur as two discrete clinical syndromes within distinct time frames. Instead, the pattern of failure was variable and overlapped in some patients. There seemed to be two underlying mechanisms (an early acute mixed central and peripheral respiratory failure, and a late peripheral respiratory failure) rather than two distinct clinical syndromes.

Acute Disease↗
PubMed2006

Analysis of inhibition, reactivation and aging kinetics of highly toxic organophosphorus compounds with human and pig acetylcholinesterase.

Organophosphorus compounds (OP) are in wide spread use as pesticides and highly toxic OP may be used as chemical warfare agents (nerve agents). OP inhibit acetylcholinesterase (AChE), therefore, standard treatment includes AChE reactivators (oximes) in combination with antimuscarinic agents. In the last decades, the efficacy of oximes has been investigated in various animal models, mostly in rodents. However, extrapolating animal data to humans is problematical because of marked differences between rodents and humans concerning the toxicokinetics of nerve agents, the pharmacokinetics of antidotes and the AChE enzyme kinetics. In order to improve the understanding of species differences and to enable a more reliable extrapolation of animal data to humans a study was initiated to investigate the effect of highly toxic nerve agents, i.e. VX, Russian VX (VR) and Chinese VX (CVX), with human and pig erythrocyte AChE. Hereby, the rate constants for the inhibition of AChE by these OP (ki) and for the spontaneous dealkylation (ka) and reactivation (ks) of OP-inhibited AChE as well as for the oxime-induced reactivation of OP-inhibited AChE by the oximes obidoxime, 2-PAM, HI 6, HLö 7 and MMB-4 were determined. Compared to human AChE pig AChE showed a lower sensitivity towards the investigated OP. Furthermore, a slower spontaneous dealkylation and reactivation of pig AChE was recorded. The potency of the investigated oximes was remarkably lower with OP-inhibited pig AChE. These data may contribute to a better understanding of species differences and may provide a kinetic basis for extrapolation of data from pig experiments to humans.

Acetylcholinesterase↗
PubMed2006

Application of kinetic-based computer modelling to evaluate the efficacy of HI 6 in percutaneous VX poisoning.

The rife use of organophosphorus compounds (OP) as pesticides and the exertion of highly toxic OP-type chemical warfare agents (nerve agents) during military conflicts and terrorist attacks in the past emphasize the necessity of the development of effective therapeutic countermeasures. Presently, standard treatment of poisoning by OP includes administration of atropine as an antimuscarinic agent and of oximes, e.g. obidoxime or pralidoxime, as reactivators of OP-inhibited acetylcholinesterase (AChE), but is considered to be rather ineffective with certain nerve agents. The evaluation of new oximes as antidotes is only possible by implementation of animal experiments for ethical reasons and therefore complicated by a limited extrapolation of animal data to humans due to marked species differences. A computer simulation based on combination of AChE kinetic data (inhibition, reactivation, aging) with OP toxicokinetics and oxime pharmacokinetics allows the calculation of AChE activities at different scenarios and may facilitate to define effective oxime concentrations and to optimize oxime dosage in OP poisoning. On the base of species-specific kinetic data this model was used to calculate AChE activities in humans and pigs after percutaneous exposure to 5 x LD50 VX and treatment with HI 6. Due to marked species differences between human and pig AChE the HI 6 dose that is necessary to cause a comparable reactivation of VX-inhibited pig AChE is conspicuously higher. Hence, designing animal experiments with the aid of computer modeling may reduce the number of animal experiments and allow a more reliable extrapolation of animal data to humans.

Administration, Cutaneous↗
PubMed2005

Formation and disposition of diethylphosphoryl-obidoxime, a potent anticholinesterase that is hydrolyzed by human paraoxonase (PON1).

The potential of pyridinium-4-aldoximes, such as obidoxime, to reactivate diethylphosphorylated acetylcholinesterases is not fully exploited due to the inevitable formation of phosphoryloximes (POX) with high anticholinesterase activity. Mono(diethylphosphoryl) obidoxime (DEP-obidoxime) was isolated for the first time showing remarkable stability under physiological conditions (half-life 13.5min; pH 7.1; 37 degrees C). The half-life was considerably extended to 20h at 0 degrees C, which facilitated the preparation and allowed isolation by HPLC. The structure was confirmed by mass spectrometry and the degradation pattern. DEP-obidoxime decomposed by an elimination reaction forming the intermediate nitrile that hydrolyzed mainly into the pyridone and cyanide. The intermediates were prepared and confirmed by mass spectroscopy. DEP-Obidoxime was an extremely potent inhibitor of human acetylcholinesterase approaching a second-order rate constant of 10(9)M(-1)min(-1) (pH 7.4; 37 degrees C). The nitrile and the pyridone were still good reactivators. In the presence of human plasma DEP-obidoxime was hydrolyzed into parent obidoxime. Calcium-dependence and sensitivity towards chelators, substitution pattern by other divalent cations and protein-modifying agents all pointed to human paraoxonase (hPON1) as the responsible protein with POX-hydrolase activity. Subjects, probably belonging to the homozygous (192)arginine subtype, were virtually devoid of POX-hydrolase activity while a highly purified hPON1 of the homozygous (192)glutamine subtype exhibited particularly high POX-hydrolase activity. Two parathion-poisoned patients with high and low POX-hydrolase activity responded well and poorly, respectively, to obidoxime treatment although the former patient had higher plasma paraoxon levels than the poor responder. Hence, the POX-hydrolase associated PON1 subtype may be another contributor that modulates pyridinium-4-aldoxime effectiveness.

Aryldialkylphosphatase↗
PubMed2002

Equipotent cholinesterase reactivation in vitro by the nerve agent antidotes HI 6 dichloride and HI 6 dimethanesulfonate.

The well-documented efficacy of HI 6 dichloride in reactivating acetylcholinesterase (AChE) inhibited by nerve agents is curtailed by its poor water-solubility at temperatures below 10 degrees C. This drawback can be circumvented by using HI 6 dimethanesulfonate, which has been developed in our laboratory. Since investigations on the efficacy of this new entity are lacking, it has been proposed that some bridging experiments be performed, aimed at demonstrating reactivator equivalence in vitro. The reactivating properties of the two salts were compared on human erythrocyte AChE inhibited with paraoxon, sarin, cyclosarin and agent VX. The comparison was extended to cynomolgus erythrocytes exposed in vitro for sarin and VX. Finally, mouse diaphragm preparations were circumfused with sarin, cyclosarin and VX and reactivation by each of the HI 6 salts was examined in muscle homogenates. AChE activity in erythrocyte suspensions was monitored by a modified Ellman procedure, muscle AChE by a radiometric assay. In all models tested no differences between the HI 6 salts could be detected ( P=0.05). From these data, equipotency in AChE reactivation by the two HI 6 salts can be anticipated.

Acetylcholinesterase↗
PubMed2002

Reactivation kinetics of acetylcholinesterase from different species inhibited by highly toxic organophosphates.

Standard treatment of poisoning by organophosphates (OP) includes the administration of an antimuscarinic agent, e.g. atropine, and of an acetylcholinesterase (AChE) reactivator (oxime). The presently available oximes, obidoxime and pralidoxime (2-PAM), are considered to be insufficient for highly toxic OPs, e.g. sarin. In the past decades numerous oximes were prepared and tested for their efficacy in OP poisoning, mostly in animal experiments. However, data indicate that the reactivating potency of oximes may be different in humans and animal species, which may hamper the extrapolation of animal data to humans and may pose a problem in the drug licensing of new compounds. In order to provide data for a better evaluation of the reactivating potency of oximes, experiments were undertaken to determine the reactivation rate constants of several oximes with human, rabbit, rat and guinea-pig AChE inhibited by the OPs sarin, cyclosarin and VX. The results show marked differences among the species, depending on the inhibitor and on the oxime, and indicate that the findings from animal experiments need careful evaluation before extrapolating these data to humans.

Acetylcholinesterase↗
PubMed2002

Oximes in acute organophosphorus pesticide poisoning: a systematic review of clinical trials.

BACKGROUND: Acute organophosphorus (OP) pesticide poisoning is widespread in the developing world. Standard treatment involves the administration of intravenous atropine and an oxime to counter acetylcholinesterase inhibition at the synapse, but the usefulness of oximes is uncertain. AIM: To assess the evidence on the use of oximes in OP poisoning. DESIGN: Systematic review. METHODS: We searched Medline, Embase, and Cochrane databases (last check 01/02/02) for 'organophosphate' or 'oxime' together with 'poisoning' or 'overdose'. We cross-referenced from other articles, and contacted experts to identify unpublished studies. A Web search engine [www.google.com] was also used, with the keywords 'organophosphate', 'oxime', and 'trial' (last check 01/02/02). RESULTS: We found two randomized controlled trials (RCTs) involving 182 patients treated with pralidoxime. The RCTs found no benefit with pralidoxime, and have been used to argue that pralidoxime should not be used in OP poisoning. DISCUSSION: The RCT authors must be congratulated for attempting important studies in a difficult environment. However, their studies did not take into account recently clarified issues regarding outcome, and their methodology is unclear. A generalized statement that pralidoxime should not be used in OP poisoning is not supported by the published results. Oximes may well be irrelevant in the overwhelming self-poisoning typical of the tropics, but a large RCT comparing the current WHO-recommended pralidoxime regimen (>30 mg/kg bolus followed by >8 mg/kg/h infusion) with placebo is needed for a definitive answer. Such a study should be designed to identify any patient subgroups that might benefit from oximes.

Acute Disease↗
PubMed2000

Effect of human plasma on the reactivation of sarin-inhibited human erythrocyte acetylcholinesterase.

The reactivation of organophosphate-inhibited acetylcholinesterase (AChE) by oximes inevitably results in the formation of highly reactive phosphoryloximes (POX), which are able to re-inhibit the enzyme. In this study, the dependence of POX formation on AChE concentration was investigated with sarin-inhibited human erythrocyte AChE (EryAChE). A marked dependence was found with obidoxime but not with the experimental oxime HI 6, suggesting great differences in the decomposition rates of the respective POXs. At a physiological erythrocyte content the reactivation of EryAChE was markedly affected by POX with obidoxime and pralidoxime (2-PAM) but not with the newer oximes HI 6 and HLö 7. Addition of extensively dialysed, sarin-treated human plasma reduced the reactivation by obidoxime and 2-PAM even more. Obidoxime and 2-PAM were superior to HI 6 and HLö 7 in reactivating butyrylcholinesterase (BChE). This effect was pronounced in diluted plasma, but was obscured in concentrated plasma, probably because of re-inhibition by the generated POX. Addition of native erythrocytes to sarin-treated plasma resulted in marked inhibition of EryAChE in the presence of obidoxime, suggesting a higher affinity of the POX for EryAChE. The results indicate that obidoxime and 2-PAM may reactivate sarin-inhibited AChE insufficiently due to re-inhibition by the POX formed. In addition, the re-inhibition of Ery-AChE may be aggravated by the POX that is produced during BChE reactivation. These reactions must be regarded as therapeutically detrimental and disqualify those oximes which are capable of forming stable POX by reactivation of BChE.

Acetylcholinesterase↗
PubMed2000

The phosphoryl oxime-destroying activity of human plasma.

The potential of obidoxime and other pyridinium-4-aldoximes to reactivate dimethyl- and diethylphosphorylated cholinesterases is markedly restricted by the inevitable formation of rather stable phosphoryl oximes (POXs) with high anticholinesterase activity. This effect is hardly seen with very dilute enzyme preparations, but becomes significant at physiological enzyme concentrations. Human plasma with the butyrylcholinesterase irreversibly blocked by soman was able to stimulate obidoxime-induced reactivation of concentrated erythrocyte acetylcholinesterase (Ery-AChE) to the same extent as was observed with a dilute preparation, suggesting phosphoryl oxime-destroying capacity. The inactivating factor, which was tentatively termed POX-hydrolase, had (1) a molecular weight of >100 kDa; (2) required Ca2+ , which could not be substituted by Zn2+ or Mg2+; and (3) lost its catalytic activity reversibly in the presence of ethylenediamine-tetraacetic acid (EDTA). The enzyme activity varied widely (20-fold) among different subjects and did not follow the activity pattern of human serum paraoxonase (PON1). Rabbit plasma with its particularly high paraoxonase content showed only weak POX-hydrolase activity. These data suggest POX-hydrolase to be a different entity. POX-hydrolase was most active with the putative phosphoryl-obidoxime from paraoxon-ethyl, less with the product from paraoxon-methyl and least with that from diisopropylfluorophosphate. The analogue TMB-4 reacted similarly to obidoxime. The putative phosphonyl oximes arising by the reaction of obidoxime with nerve agents were apparently not cleaved. The variation in POX-hydrolase activity may additionally contribute to the variable response to oxime therapy in patients with organophosphate insecticide poisoning.

Animals↗
PubMed2000

Intoxication with huperzine A, a potent anticholinesterase found in the fir club moss.

BACKGROUND: Herbs from Lycopodium are generally reputed to be nontoxic and are occasionally used for preparing a salubrious tea. In Europe, the common Lycopodium clavatum can be easily confused with Lycopodium selago, the fir club moss. CASE REPORT: We report 2 patients who drank a tea, erroneously prepared from dried herbs of Lycopodium selago, which resulted in sweating, vomiting, diarrhea, dizziness, cramps, and slurred speech. These symptoms were suggestive of a cholinergic mechanism. To elucidate the active principle, aqueous extracts of Lycopodium selago were checked for their suspected anticholinesterase activity using human erythrocytes as an enzyme source in a modified Ellman assay. The extracts did exhibit significant anticholinesterase activity. The anticholinesterase(s) were most effectively extracted with dichloromethane and isolated by high-performance liquid chromatography. The major compound with anticholinesterase activity co-chromatographed with authentic huperzine A, but had a 2-3-fold higher inhibitory potency than the racemic standard. The amount of huperzine A found in the Lycopodium selago sample used for the tea preparation was calculated to be sufficient for a relevant acetylcholinesterase inhibition. CONCLUSION: The signs and symptoms of Lycopodium selago poisoning are consistent with the anticholinesterase activity of huperzine A and should favorably respond to atropine therapy. This report demonstrates once more that laymen should not be encouraged to gather their remedies from "Mother Nature" without advanced botanical knowledge.

Alkaloids↗
PubMed1999

Modern strategies in therapy of organophosphate poisoning.

Considering the various microscopic reactions as well as toxicokinetic and pharmacokinetic principles in therapy of organophosphate poisoning, the administration of obidoxime by an initial bolus dose followed by continuous infusion appears rational. Using this protocol, six patients each with parathion or oxydemeton methyl poisoning were treated. In parathion poisoning, reactivation was possible up to 7 days. At paraoxon concentrations > 0.1 microM obidoxime only partially reactivated acetylcholinesterase (AChE) of erythrocytes in vivo although reactivation could be assessed in vitro, which roughly fitted theoretical calculations. AChE-inhibitory material was detected up to 5 days. Cholinergic signs soon subsided when AChE was above 20% of normal, and atropine plasma levels could be kept below 7 ng/ml. In one patient brain damage persisted. Oxydemeton methyl poisoning responded to obidoxime therapy only when the oxime was instituted shortly after poisoning. Out of six patients one died. No intermediate syndrome and no signs of permanent hepatic dysfunction were found in the 12 patients.

Acetylcholinesterase↗
PubMed1999

Dimethylphosphoryl-inhibited human cholinesterases: inhibition, reactivation, and aging kinetics.

Human poisoning by organophosphates bearing two methoxy groups, e.g. by malathion, paraoxon-methyl, dimethoate and oxydemeton-methyl, is generally considered to be rather resistant to oxime therapy. Since the oxime effectiveness is influenced not only by its reactivating potential but also by inhibition, aging and spontaneous reactivation kinetics, experiments were performed with human acetyl- (AChE) and butyrylcholinesterase (BChE) to determine the respective kinetic constants. The efficacy of obidoxime in reactivating dimethylphosphoryl-AChE was 40, 9 and 3 times higher than of HI 6, pralidoxime and HLö 7, respectively. Aging (t1/2 3.7 h) and spontaneous reactivation (t1/2 0.7 h) occurred concomitantly, with the portion of the aged enzyme being dependent on the presence of excess inhibitor. Calculation of steady-state AChE activity in the presence of inhibitor and oxime revealed that obidoxime was superior to pralidoxime. In addition, organophosphate concentrations up to 10(-6) M (paraoxon-methyl) and 10(-4) M (oxydemeton-methyl) could be counteracted at clinically relevant oxime concentrations (10 microM). These data indicate that oximes may effectively reactivate human dimethylphosphoryl-AChE. Failure of oximes may be attributed to megadose intoxications and to prolonged time intervals between poison uptake and oxime administration. The potency of the oximes to reactivate dimethylphosphoryl-BChE was much lower and the spontaneous reactivation slower (t1/2 9 h), while aging proceeded at a comparable rate. Thus, BChE activity determination for diagnosis and therapeutic monitoring may give no reliable information on AChE status.

Acetylcholinesterase↗
PubMed1999

Improved determination of acetylcholinesterase activity in human whole blood.

Determination of erythrocyte acetylcholinesterase (AChE) activity is the appropriate tool for the diagnosis of organophosphate exposure and intoxication. The original colorimetric Ellman procedure is disturbed by a high hemoglobin absorption at 412 nm. In our modified method the wavelength was changed to 436 nm. This reduced the indicator absorption to 80% and the hemoglobin absorption to 25%. The signal-to-noise ratio was further enhanced by reduction of pH and substrate concentration, thus making it possible to measure 3% residual activity. AChE activity was determined in whole blood samples in the presence of the selective butyrylcholinesterase inhibitor ethopropazine. Dilution of blood samples (1:100) stops secondary reactions in the presence of inhibitor (organophosphate) and reactivator (oxime). Normalization of the AChE activity to the hemoglobin content, determined as cyanmethemoglobin, prevented dilution errors. This modified approach provides a simple way for sensitive and precise determination of AChE activity in whole blood in the presence of organophosphates even with low-tech equipment.

Acetylcholinesterase↗
PubMed1998

Inhibition, reactivation and aging kinetics of cyclohexylmethylphosphonofluoridate-inhibited human cholinesterases.

Cyclohexylmethylphosphonofluoridate (cyclosarin) is a highly toxic organophosphate, which was shown to be rather resistant to conventional oxime therapy. To give more insight into the inhibition, reactivation and aging kinetics, human acetyl-(AChE) and butyrylcholinesterase (BChE) were inhibited by cyclosarin (k2 of 7.4 and 3.8 x 10(8) M(-1) min(-1), respectively; pH 7.4, 37 degrees C) and reactivated with obidoxime, pralidoxime and three experimental oximes. The new oxime HLö 7 (1-[[[4-aminocarbonyl)-pyridinio]-methoxy]-methyl]-2,4-bis-[ (hydroxyimino)methyl] pyridinium dimethanesulphonate) was shown to be superior to the other oximes. At oxime concentrations anticipated to be relevant in humans, obidoxime and pralidoxime were extremely weak reactivators of AChE. Aging velocity of BChE was almost fourfold higher compared to AChE (ka of 0.32 h(-1) and 0.08 h(-1), respectively). A substantial spontaneous reactivation was observed with AChE. These results support previous in vivo findings that obidoxime and pralidoxime are insufficient antidotes in cyclosarin poisoning. By contrast, HLö 7 was shown to be an extremely potent reactivator of human AChE and BChE, which supports its position as a broad-spectrum oxime.

Acetylcholinesterase↗