Internal standard high-performance liquid chromatography method for the determination of obidoxime in urine of organophosphate-poisoned patients

Effects of Charged Oxime Reactivators on the HK-2 Cell Line in Renal Toxicity Screening

Oxime cholinesterase reactivators (oximes) are used to counteract organophosphate intoxication. Charged oximes are administered via intramuscular or intravenous injection when the majority of dose is unmetabolized and is excreted as urine. In this study, the effects of selected double charged oximes were determined in the HK-2 cell line as a model for renal toxicity screening. Some effects on dehydrogenase activity were found for obidoxime, asoxime (syn. HI-6), K027, and K203. The effects of K868 and K869 were found to be unreliable due to rapid degradation of both chlorinated oximes in the assay medium, resulting for K868 in an isoxazole-pyridinium product.

A dual-mode nanoprobe for the determination of parathion methyl based on graphene quantum dots modified silver nanoparticles

We developed a highly sensitive and selective method for double-signal analysis (fluorescence and ultraviolet-visible spectrophotometry) of organophosphorus pesticides (OPs), based on reversible quenching of graphene quantum dots (GQDs; fluorophores) with silver nanoparticles (AgNPs; absorbers). We used acetylcholinesterase to catalytically convert acetylthiocholine into thiocholine. In turn, by competitive binding to the AgNPs, the produced thiocholine displaces AgNPs from the GQDs and thus induces fluorescence recovery. However, OP analytes inhibit the activity of acetylcholinesterase and, in so doing, retain the silver-graphene nanoparticle complex and fluorescence quenching. The degree of quenching is proportional to the concentration of OPs; the detection limit is as low as 0.017 μg/L. The ultraviolet-visible absorption of GQDs/AgNPs at 390 nm decreases-because of AgNP aggregation that occurs after desorption from the GQDs-and the absorbance is linearly proportional to the OP concentration. Our system has good selectivity to substances that are commonly present in water and vegetables. We successfully applied our method to OP analysis in water, apple, and carrot samples.

Reversed-phase ion-pair chromatography-diode array detection of the bispyridinium compound MB327: plasma analysis of a potential novel antidote for the treatment of organophosphorus poisoning

In the case of poisoning by organophosphorus nerve agents or pesticides, there is still a lack of pharmacological treatment of the cholinergic crisis selectively targeting the nicotinic acetylcholine receptor. Recently, the compound MB327 was identified as a potential novel lead structure to close this gap, thus demanding a quantitative assay for initial pharmacokinetic (PK) studies. MB327 is a salt consisting of the dicationic bispyridinium compound (BPC) 1,1´-(propane-1,3-diyl)bis(4-tert-butylpyridinium) and two iodide counter ions. Due to the permanent positive charge of the BPC, an isocratic reversed-phase ion-pair chromatographic separation (RPIPC) was developed using heptanesulfonic acid as ion-pairing reagent and 45% v/v methanol as organic modifier (1 mL/min). Selective UV-detection (230 nm) was done by a diode array detector (DAD) for reliable, rugged, precise (RSD < 7%) and accurate (96-104%) quantitative analysis of 50 μL swine plasma (linear range 1-1000 µg BPC/mL plasma, lower limit of quantification 2 µg/mL). During method validation, diverse parameters essential for the chromatographic process were investigated to generate van´t Hoff, van Deemter and width plots allowing calculation of thermodynamic data like the distribution constant K (5.7 ± 0.3), change in enthalpy, ΔH(0) : -23.66 kJ/mol, and entropy, ΔS(0) : -65 J/(mol*K). In addition, RPIPC-DAD analysis enabled calculation of molar absorptivities of the BPC, ε230 : 17 400 ± 1100 L/(mol*cm), and iodide, ε230 : 9900 ± 400 L/(mol*cm), which determination was hampered by interference with each other in conventional cuvette UV-spectrophotometric measurements. Finally, the RPIPC-DAD procedure was applied to samples from an in vivo study of swine.

Chromatographic analysis of toxic phosphylated oximes (POX): a brief overview

Poisoning with organophosphorus compounds (OP), e.g. pesticides and nerve agents, causes inhibition of acetylcholinesterase (AChE) by phosphylation of the active site serine residue. Consequently, accumulation of stimulating acetylcholine in the synaptic cleft induces cholinergic crisis which ultimately may lead to death. For standard causal therapy, enzyme reactivators are administered representing oxime derivatives of quarternary pyridinium compounds, e.g. pralidoxime (2-PAM), obidoxime and HI 6. The mechanism of action includes removal of the phosphyl moiety by a nucleophilic attack of the oximate molecule substituting the enzyme and forming a phosphylated oxime (POX). POX is produced in stoichiometric amounts of reactivated enzyme and exhibits a significantly enhanced toxicity (inhibition rate constant) when compared to the parent OP. However, stability of POX under physiological conditions appears to be highly limited. Nevertheless, the presence of POX reveals a potential critical issue for both therapeutic efficacy in vivo and pharmacokinetic and pharmacodynamic (PK-PD) modelling based on cholinesterase activity data. Detailed characterization represents an important need for elaboration of the entire oxime pharmacology.Nevertheless, reports on POX toxicity and analysis are quite rare and may therefore be indicative of the challenge of POX analysis. This review provides a concise overview of chromatographic approaches applied to POX separation. Chromatography represents the key technology for POX purification and quantification in kinetic in vitro studies using buffers and biological fluids. Applications based on reversed-phase chromatography (RPC), ion pair chromatography (IPC) and an affinity approach as well as thin layer chromatography (TLC) are discussed and novel applications and data are presented.

Evaluation of medical countermeasures against organophosphorus compounds: the value of experimental data and computer simulations

Despite extensive research for more than six decades on medical countermeasures against poisoning by organophosphorus compounds (OP) the treatment options are meagre. The presently established acetylcholinesterase (AChE) reactivators (oximes), e.g. obidoxime and pralidoxime, are insufficient against a number of nerve agents and there is ongoing debate on the benefit of oxime treatment in human OP pesticide poisoning. Up to now, the therapeutic efficacy of oximes was mostly evaluated in animal models but substantial species differences prevent direct extrapolation of animal data to humans. Hence, it was considered essential to establish relevant experimental in vitro models for the investigation of oximes as antidotes and to develop computer models for the simulation of oxime efficacy in different scenarios of OP poisoning. Kinetic studies on the various interactions between erythrocyte AChE from various species, structurally different OP and different oximes provided a basis for the initial assessment of the ability of oximes to reactivate inhibited AChE. In the present study, in vitro enzyme-kinetic and pharmacokinetic data from a minipig model of dimethoate poisoning and oxime treatment were used to calculate dynamic changes of AChE activities. It could be shown that there is a close agreement between calculated and in vivo AChE activities. Moreover, computer simulations provided insight into the potential and limitations of oxime treatment. In the end, such data may be a versatile tool for the ongoing discussion of the pros and cons of oxime treatment in human OP pesticide poisoning.

Measurement of K-27, an oxime-type cholinesterase reactivator by high-performance liquid chromatography with electrochemical detection from different biological samples

K-27 is a bisquaternary asymmetric pyridinium aldoxime-type cholinesterase reactivator of use in the treatment of poisoning with organophosphorous esterase inhibitors. A sensitive, simple and reliable reverse-phase high-performance liquid chromatographic method with electrochemical detection was developed for the measurement of K-27 concentrations in rat brain, cerebrospinal fluid, serum and urine samples. Male Wistar rats were treated intramuscularly with K-27 and the samples were collected 60 min later. Separation was carried out on an octadecyl silica stationary phase and a disodium phosphate solution (pH 3.7) containing citric acid, octane sulphonic acid and acetonitrile served as mobile phase. Measurements were carried out at 30 degrees C at E(ox) 0.65 V. The calibration curve was linear through the range of 10-250 ng/mL. Accuracy, precision and the limit of detection calculated were satisfactory according to internationally accepted criteria. Limit of quantitation was 10 ng/mL. The method developed is reliable and sensitive enough for monitoring K-27 levels from different biological samples including as little as 10 microL of cerebrospinal fluid. The method--with slight modification in the composition of the mobile phase--can be used to measure a wide range of other related pyridinium aldoxime-type cholinesterase reactivators.

High-performance liquid chromatographic determination of the plasma concentration of K-27, a novel oxime-type cholinesterase reactivator

A simple and reliable HPLC method for the determination of the plasma level of K-27, an oxime type antidote of use in organophosphorus poisoning is presented. Separation was carried out by HPLC using an octyl silica stationary phase and a mobile phase consisting of 93% phosphate buffer (pH 2.6) containing octane sulfate sodium salt, and 7% methanol. Quantitative absorbance was monitored at 286 nm. The calibration curve was linear through the range of 1.25-200 microg/mL, that is well beyond the detected plasma level range of K-27. Limit of quantitation was 5 microg/mL. Intra-day and inter-day precisions of the HPLC determinations gave standard deviations as 0.77 and 2.67%, respectively. Following intramuscular administration of 50 micromol (22.31 mg) K-27 in rats, the maximum of K-27 concentration in plasma was reached at about 15 min giving 186 microg/mL and the t(1/2) was 85 min. K-27 displays initial (from 15 trough 120 min) zero order elimination kinetics. Similar results have been found after intraperitoneal administration.

HPLC analysis of K-48 concentration in plasma

K-48 is a new oxime-type compound to be used as an enzyme reactivator in the treatment of exposure to organophosphorous compounds. Plasma concentration of K-48 can be determined using reversed-phase HPLC. Analysis using octyl silica stationary phase and ultraviolet-absorbance detection is fast and simple. K-48 displays a relatively high dose-normalized area under the curve as compared to pralidoxime, which might be beneficial for an antidote. After i.m. administration of 50 mumol K-48, the time course of the concentration can be approximated by a straight line between 15 and 120 min meaning the elimination follows zero-order kinetics.

Development and validation of a reversed-phase HPLC method for the determination of ezetimibe in pharmaceutical dosage forms

Ezetimibe belongs to a group of selective and very effective 2-azetidione cholesterol absorption inhibitors that act on the level of cholesterol entry into enterocytes. A rapid, specific reversed-phase HPLC method has been developed for assaying ezetimibe in pharmaceutical dosage forms. The assay involved an isocratic elution of ezetimibe in a Kromasil 100 C18 column using a mobile phase composition of water (pH 6.8, 0.05%, w/v 1-heptane sulfonic acid) and acetonitrile (30:70, v/v). The flow rate was 0.5 ml/min and the analyte monitored at 232 nm. The assay method was found to be linear from 0.5 to 50 microg/ml. All the validation parameters were within the acceptance range. The developed method was successfully applied to estimate the amount of ezetimibe in tablets.

Measurement of serum pralidoxime methylsulfate (Contrathion®) by high-performance liquid chromatography with electrochemical detection

Pralidoxime methylsulfate (Contrathion) is widely used to treat organophosphate poisoning. Despite animal and human studies, the usefulness of Contrathion therapy remains a matter of debate. Therapeutic dosage regimens need to be clarified and availability of a reliable method for plasma pralidoxime quantification would be helpful in this process. We here describe a high-performance liquid chromatography technique with electrochemical detection to measure pralidoxime concentrations in human serum using guanosine as an internal standard. The assay was linear between 0.25 and 50 microg mL(-1) with a quantification limit of 0.2 microg mL(-1). The analytical precision was satisfactory, with variation coefficients lower 10%. This assay was applied to the analysis of a serum from an organophosphorate poisoned patient and treated by Contrathion infusions (100 and 200 mg h(-1)) after a loading dose (400 mg).

Simple high-performance liquid chromatographic method for determination of atropine and obidoxime in a parenteral injection device

Atropine and obidoxime in a parenteral injection device are determined by simple HPLC method simultaneously without any pretreatment at 228 nm. The relative standard deviations (R.S.D.) were below 1.6% for the compounds. The correlation coefficient was greater than 0.999 for both compounds in the calibration range. The recoveries at 5 mg/L concentration averaged as 95% for atropine and 102% for obidoxime. The uncertainty of the measurements for atropine and obidoxime was 2.8% and 2.4%, respectively.