Acute poisoning by chlorpyrifos differentially impacts survival and cardiorespiratory function in normotensive and hypertensive rats.

Hypertension is the most important and well-known risk factor for cardiovascular disease (CVD). Recently, acute organophosphate (OP) poisoning has also been pointed as a CVD risk factor. Despite this evidence, no studies have contrasted the acute toxicosis and cardiovascular (CV) effects of OP poisoning under conditions of normotension and hypertension. In this work, adult male normotensive Wistar and Spontaneously Hypertensive rats (SHR) were intraperitoneally injected with saline or chlorpyrifos (CPF), an OP compound, monitored for acute toxicosis signs and 24-h survival. After poisoning, blood pressure, heart rate and ventilation were recorded, the Bezold-Jarisch Reflex (BJR), the Chemoreflex (CR) were chemically activated, as well as the cardiac autonomic tone (AUT) was assessed. Erythrocyte and brainstem acetylcholinesterase and plasmatic butyrylcholinesterase (BuChE) activities were measured as well as lipid peroxidation, advanced oxidation protein products (AOPP), nitrite/nitrate levels, expression of catalase, TNFα and angiotensin-I converting enzyme (ACE-1) within the brainstem. CPF induced a much more pronounced acute toxicosis and 33 % lethality in SHR. CPF poisoning impaired ventilation in SHR, the BJR reflex responses in Wistar rats, and the chemoreflex tachypneic response in both strains. CPF inhibited activity of cholinesterases in both strains, increased AOPP and nitrite/nitrate levels and expression of TNFα and ACE-1 in the brainstem of Wistar rats. Interestingly, SHR presented a reduced intrinsic BuChE activity, an important bioscavenger. Our findings show that, CPF at sublethal doses in normotensive rats lead to lethality and much more pronounced acute toxicity signs in the SHR. We also showed that cardiorespiratory reflexes were differentially impacted after CPF poisoning in both strains and that the cardiorespiratory disfunction seems to be associated with interference in cholinergic transmission, oxidative stress and inflammation. These results points to an increased susceptibility to acute toxicosis in hypertension, which may impose a significant risk to vulnerable populations.

Intermittent exposure to chlorpyrifos results in cardiac hypertrophy and oxidative stress in rats.

Forbidden in some countries due to its proven toxicity to humans, chlorpyrifos (CPF) still stands as an organophosphate pesticide (OP) highly used worldwide. Cardiotoxicity assessment is an unmet need in pesticide regulation and should be deeply studied through different approaches to better inform and generate an appropriate regulatory response to OP use. In the present study, we used our 4-week intermittent OP exposure model in rats to address the CPF effects on cardiac morphology allied with cardiovascular functional and biomolecular evaluation. Rats were intermittently treated with CPF at doses of 7 mg/kg and 10 mg/kg or saline (i.p.) and assessed for cardiac morphology (cardiomyocyte diameter and collagen content), cardiopulmonary Bezold-Jarisch reflex (BJR) function, cardiac autonomic tone, left ventricle (LV) contractility, cardiac expression of NADPH oxidase (Nox2), catalase (CAT), superoxide dismutase 1 (SOD1), superoxide dismutase 2 (SOD2) and cardiac levels of advanced oxidation protein products (AOPP) and thiobarbituric acid reactive substances (TBARS). Plasma butyrylcholinesterase (BuChE) and brainstem acetylcholinesterase (AChE) were also measured. Intermittent exposure to CPF induced cardiac hypertrophy, increasing cardiomyocyte diameter and collagen content. An impairment of cardioinhibitory BJR responses and an increase in cardiac vagal tone were also observed in CPF-treated animals without changes in LV contractility. CPF exposure increased cardiac Nox-2, CAT, SOD1, and TBARS levels and inhibited plasma BuChE and brainstem AChE activities. Our data showed that intermittent exposure to CPF induces cardiac hypertrophy together with cardiovascular reflex impairment, imbalance of autonomic tone and oxidative stress, which may bring significant cardiovascular risk to individuals exposed to OP compounds seasonally.

A single dose of the organophosphate triazophos induces fear extinction deficits accompanied by hippocampal acetylcholinesterase inhibition.

Acute organophosphate (OP) poisoning, particularly by suicide attempts, generates high mortality and morbidity. Few studies have systematically addressed the consequences of acute OP intoxication on cognition and memory of survivors. Preclinical evidence suggests that acute OP-induced effects are associated with inhibiting the brain acetylcholinesterase (AChE) enzyme. The OP triazophos has been used worldwide, although its effects on mnemonic processing are yet to be investigated. Based on the above, the present study investigated whether acute triazophos intoxication interferes with the expression and extinction of contextual fear memory in rats. Hippocampal and amygdalar AChE activity and plasma butyrylcholinesterase (BChE) were measured at the end of the experiment to confirm the cholinergic overstimulation. Independent cohorts of animals intoxicated with triazophos were evaluated in the novel object recognition (NOR) test, a less aversive associative memory task. At the dose of 15 mg/kg, triazophos administered immediately after contextual fear conditioning impaired the extinction but not the expression of freezing behavior. Triazophos poisoning induced no changes in the discrimination index in the NOR test. Triazophos inhibited the AChE activity in a time- and brain region-dependent manner. Our findings suggest that fear memory extinction deficits induced by acute triazophos intoxication are accompanied by hippocampal AChE inhibition. The deficient fear extinction associated with acute OP poisoning may represent a behavioral and biochemical phenotype helpful to study mechanisms of neurotoxicity and treatment approach of OP suicide survivors.

Intermittent Exposure to Chlorpyrifos Differentially Impacts Neuroreflex Control of Cardiorespiratory Function in Rats.

Previous studies showed that chlorpyrifos (CPF) acute exposure impaired cardiorespiratory reflexes. Evidence also indicates that continuous exposure to organophosphorus compounds impairs cardiovascular function. However, the effect of intermittent exposure to CPF, as may be experienced in the real world, on tonic and reflex cardiorespiratory function remains unexplored. Wistar rats were injected with saline or CPF for 4 weeks (3 times/week) or 12 weeks (once/week) at the doses of 7 mg/kg and 10 mg/kg. After exposure, blood pressure (BP), heart rate (HR), respiratory rate (fR), tidal volume (VT), and minute volume (VE) were recorded. Systolic BP and pulse interval (PI) variability, HR spectrum, spontaneous baroreflex and chemoreflex function were also evaluated. Plasma butyrylcholinesterase and brainstem acetylcholinesterase activities were quantified. Enzymatic activity of the CPF animals was reduced after both treatment periods. Baseline BP, HR, and fR, as well as systolic BP and PI variability indices, did not change, after CPF treatment. VT and VE were elevated in CPF animals. CPF exposure increased the very low-frequency component of the HR spectrum. Baroreflex gain was reduced after CPF 4-week exposure. Chemoreflex bradycardia was reduced in the CPF-treated rats. These data show that intermittent exposure to CPF impairs cardiorespiratory function in rats. These results may have important clinical implications for workers seasonally exposed to these compounds.

Atropine counteracts the depressive-like behaviour elicited by acute exposure to commercial chlorpyrifos in rats.

Acute organophosphate (OP) poisoning induces well-known signs of toxicosis related to acetylcholinesterase (AChE) inhibition. However, the relationship between acute OP poisoning and the onset of psychiatric disorders remains unclear. Thus, we investigated behavioural and biochemical consequences of acute exposure to the OP chlorpyrifos in male rats and also the effectiveness of the antidotes atropine and pralidoxime on reversing these changes. A sub-lethal dose of commercial chlorpyrifos (20 mg/kg, i.p.) elicited signs of acute toxicosis during the first hours after its injection in rats. Twenty-four hours after treatment, this single dose of chlorpyrifos induced a depressive-like behaviour in the rat forced swimming test without impairing locomotor activity. At this time (24 h), chlorpyrifos decreased plasma butyrylcholinesterase (BChE) activity and hippocampal, striatal and prefrontal cortical AChE activity in rats. The behavioural and biochemical consequences of acute chlorpyrifos poisoning do not seem to be long lasting, since 30 days later they were absent. We evaluated whether these behavioural and biochemical consequences of acute chlorpyrifos treatment would be reversed by the antidotes atropine (10 mg/kg i.p.) and/or pralidoxime (40 mg/kg; i.p.) given 1 h after poisoning. Pralidoxime partially reactivated the AChE activity in the prefrontal cortex, but not in the hippocampus and striatum. Atropine attenuated the depressive-like behaviour induced by chlorpyrifos in rats. Our results suggest that acute chlorpyrifos poisoning induces a transient depressive-like behaviour possible related to hippocampal AChE inhibition. They suggest that treatment with atropine and pralidoxime seems to be insufficient to counteract all the effects of OP acute poisoning, at least in rats.