Follow up studies on the respiratory pattern and total cholinesterase activities in dichlorvos-poisoned rats

How does organophosphorus chemical warfare agent exposure affect respiratory physiology in mice?

In the absence of appropriate medical care, exposure to organophosphorus nerve agents, such as VX, can lead to respiratory failure, and potentially death by asphyxiation. Despite the critical role of respiratory disturbances in organophosphorus-induced toxicity, the nature and underlying mechanisms of respiratory failure remain poorly understood. This study aimed to characterize respiratory alterations by determining their type and duration in mice exposed to a subcutaneous sublethal dose of VX. Respiratory ventilation in Swiss mice was monitored using dual-chamber plethysmography for up to 7 days post-exposure. Cholinesterase activity was assessed via spectrophotometry, and levels of inflammatory biomarkers were quantified using Luminex technology in blood and tissues involved in respiration (diaphragm, lung, and medulla oblongata). Additionally, a histological study was conducted on these tissues to ensure their structural integrity. Ventilatory alterations appeared 20-25 minutes after the injection of 0.9 LD50 VX and increased until the end of the recording, i.e., 40 minutes after intoxication. Concurrent with the occurrence of apnea, increased inspiratory and expiratory times resulted in a significant decrease in respiratory rate in exposed mice compared to controls. Ventilatory amplitude and, consequently, minute volume were reduced, while specific airway resistance significantly increased, indicating bronchoconstriction. These ventilatory effects persisted up to 24 or even 72 hours post-intoxication, resolving on the 7th day. They were correlated with a decrease in acetylcholinesterase activity in the diaphragm, which persisted for up to 72 hours, and with the triggering of an inflammatory reaction in the same tissue. No significant histologic lesions were observed in the examined tissues. The ventilatory alterations observed up to 72 hours post-VX exposure appear to result from a functional failure of the respiratory system rather than tissue damage. This comprehensive characterization contributes to a better understanding of the respiratory effects induced by VX exposure, which is crucial for developing specific medical countermeasures.

Colorimetric assay based on peroxidase-like activity of dodecyl trimethylammonium bromide-tetramethyl zinc (4-pyridinyl) porphyrin for detection of organophosphorus pesticides

A simple and sensitive colorimetric assay for detecting organophosphorus pesticides (OPs) was developed based on 3,3',5,5'-tetramethylbenzidine (TMB)/hydrogen peroxide (H₂O₂)/dodecyl trimethylammonium bromide (DTAB)-tetramethyl zinc (4-pyridinyl) porphyrin (ZnTPyP). In this system, based on the peroxidase-like activity of DTAB-ZnTPyP, H₂O₂ decomposes to produce hydroxyl radicals, which oxidize TMB, resulting in blue oxidation products. The OPs (trichlorfon, dichlorvos, and thimet) were first combined with DTAB-ZnTPyP through electrostatic interactions. The OPs caused a decrease in the peroxidase-like activity of DTAB-ZnTPyP due to spatial site blocking. At the same time, π-interactions occurred between them, and these interactions also inhibited the oxidation of TMB (652 nm), thus making the detection of OPs possible. The limits of detection for trichlorfon, dichlorvos, and thimet were 0.25, 1.02, and 0.66 μg/L, respectively, and the corresponding linear ranges were 1-35, 5-45, and 1-40 μg/L, respectively. Moreover, the assay was successfully used to determine OPs in cabbage, apple, soil, and traditional Chinese medicine samples (the recovery ratios were 91.8-109.8%), showing a great promising potential for detecting OPs also in other complex samples.

Safety and Efficacy of New Oximes to Reverse Low Dose Diethyl-Paraoxon-Induced Ventilatory Effects in Rats

Background: Oximes are used in addition to atropine to treat organophosphate poisoning. However, the efficiency of oximes is still a matter of debate. In vitro experiments suggested than new oximes are more potent than the commercial oximes. However, the antidotal activity of new oximes has not been assessed in vivo. Methods: The aim of this work was to assess the safety and efficiency of new oximes compared to pralidoxime in a rat model of diethyl paraoxon-induced non-lethal respiratory toxicity. Results: Safety study of oximes showed no adverse effects on ventilation in rats. KO-33, KO-48, KO-74 oximes did not exhibit significant antidotal effect in vivo. In contrast, KO-27 and BI-6 showed evidence of antidotal activity by normalization of respiratory frequency and respiratory times. KO-27 became inefficient only during the last 30 min of the study. In contrast, pralidoxime demonstrated to be inefficient at 30 min post injection. Inversely, the antidotal activity of BI-6 occurred lately, within the last 90 min post injection. Conclusion: This study showed respiratory safety of new oximes. Regarding, the efficiency, KO-27 revealed to be a rapid acting antidote toward diethylparaoxon-induced respiratory toxicity, meanwhile BI-6 was a late-acting antidote. Simultaneous administration of these two oximes might result in a complete and prolonged antidotal efficiency.

Comparison of the Respiratory Toxicity and Total Cholinesterase Activities in Dimethyl Versus Diethyl Paraoxon-Poisoned Rats

The chemical structure of organophosphate compounds (OPs) is a well-known factor which modifies the acute toxicity of these compounds. We compared ventilation at rest and cholinesterase activities in male Sprague-Dawley rats poisoned with dimethyl paraoxon (DMPO) and diethyl paraoxon (DEPO) at a subcutaneous dose corresponding to 50% of the median lethal dose (MLD). Ventilation at rest was recorded by whole body plethysmography. Total cholinesterase activities were determined by radiometric assay. Both organophosphates decreased significantly the respiratory rate, resulting from an increase in expiratory time. Dimethyl-induced respiratory toxicity spontaneously reversed within 120 min post-injection. Diethyl-induced respiratory toxicity was long-lasting, more than 180 min post-injection. Both organophosphates decreased cholinesterase activities from 10 to 180 min post-injection with the same degree of inhibition of total cholinesterase within an onset at the same times after injection. There were no significant differences in residual cholinesterase activities between dimethyl and diethyl paraoxon groups at any time. The structure of the alkoxy-group is a determinant factor of the late phase of poisoning, conditioning duration of toxicity without significant effects on the magnitude of alteration of respiratory parameters. For same duration and magnitude of cholinesterase inhibition, there was a strong discrepancy in the time-course of effects between the two compounds.

Dose-response modeling of reactivating potency of oximes K027 and K203 against a direct acetylcholinesterase inhibitor in rat erythrocytes

Inhibition of acethylcholinesterase (AChE) as a key molecular event induced by organophosphate (OP) pesticides and nerve agents presents a human health concern. In efficacy testing of experimental oximes, potential antidotes in OP poisoning, reactivation of OP-inhibited AChE is used as specific endpoint. However, according to our best knowledge, so far oximes have not been quantitatively evaluated by comprehensive benchmark dose (BMD) approach, that would improve both identification and quantification of the effect and allow more rigorous comparison of efficacies. Thus, we have examined in vivo dose-response relationship for two promising experimental oximes, K203 and K027, concerning reactivation of erythrocyte AChE inhibited by dichlorvos (DDVP). Groups of Wistar rats were treated with six different doses of oximes (i.m) immediately after DDVP challenge (s.c) and AChE was measured 60 min later. Dose-response modeling was done by PROAST software 65.5 (RIVM, The Nederlands). BMD-covariate method resulted in four-parameter model from both exponential and Hill model families as the best estimate of relationship between AChE activity and oxime dose, with potency parameter being oxime-dependent. Oxime K027 was shown to be 1.929-fold more potent considering that 58% increase in AChE activity was achived with the dose BMD₅₈-K027 = 52 μmol/kg in contrast to BMD₅₈-K203 = 100 μmol/kg.

Paper-based analytical devices for environmental analysis

The field of paper-based microfluidics has experienced rapid growth over the past decade. Microfluidic paper-based analytical devices (μPADs), originally developed for point-of-care medical diagnostics in resource-limited settings, are now being applied in new areas, such as environmental analyses. Low-cost paper sensors show great promise for on-site environmental analysis; the theme of ongoing research complements existing instrumental techniques by providing high spatial and temporal resolution for environmental monitoring. This review highlights recent applications of μPADs for environmental analysis along with technical advances that may enable μPADs to be more widely implemented in field testing.