Comparative in vivo effects of parathion on striatal acetylcholine accumulation in adult and aged rats

Multi-disciplinary investigation identifies increased potency of ethyl-parathion inhaled within a soil-dust matrix to cause acetylcholinesterase-dependent molecular impacts

Neurotoxicity investigations of inhaled organophosphorus pesticide (OP), ethyl-parathion (EP), were conducted in Sprague Dawley rats comparing exposures to EP volatilized at 0, 1, 10, and 20 mg/m3 versus EP incorporated into soil dust (5 mg/m3) at 0, 0.0095, 0.09, and 0.185 mg/mg3. All exposures were sublethal, caused no respiratory effects, and no effects on balance and coordination behavior. Both volatilized and dust-incorporated EP exposures significantly decreased acetylcholinesterase (AChE) activity in plasma and hippocampus tissue. Correspondingly, plasma and hippocampal dopamine levels spiked in these exposures suggesting compensatory cholinergic / dopaminergic signal balancing. The EP exposures significantly increased expression of pro-inflammatory genes, including MAPK-14, IL6, IL1β, and TNF-α, while global RNA-seq results identified significant enrichment of inflammation, oxidative stress, and apoptosis pathways. Remarkably, dust-incorporated EP impacted similar molecular endpoints as volatilized EP but at concentrations two orders of magnitude lower highlighting potentially increased potency of EP incorporated into soil dust.

Outcomes of elderly patients with organophosphate intoxication

This study analysed the clinical patterns and outcomes of elderly patients with organophosphate intoxication. A total of 71 elderly patients with organophosphate poisoning were seen between 2008 and 2017. Patients were stratified into two subgroups: survivors (n = 57) or nonsurvivors (n = 14). Chlorpyrifos accounted for 33.8% of the cases, followed by methamidophos (12.7%) and mevinphos (11.3%). Mood, adjustment and psychotic disorder were noted in 39.4%, 33.8% and 2.8% of patients, respectively. All patients were treated with atropine and pralidoxime therapies. Acute cholinergic crisis developed in all cases (100.0%). The complications included respiratory failure (52.1%), aspiration pneumonia (50.7%), acute kidney injury (43.7%), severe consciousness disturbance (25.4%), shock (14.1%) and seizures (4.2%). Some patients also developed intermediate syndrome (15.5%) and delayed neuropathy (4.2%). The nonsurvivors suffered higher rates of hypotension (P < 0.001), shock (P < 0.001) and kidney injury (P = 0.001) than survivors did. Kaplan-Meier analysis indicated that patients with shock suffered lower cumulative survival than did patients without shock (log-rank test, P < 0.001). In a multivariate-Cox-regression model, shock was a significant predictor of mortality after intoxication (odds ratio 18.182, 95% confidence interval 2.045-166.667, P = 0.009). The mortality rate was 19.7%. Acute cholinergic crisis, intermediate syndrome, and delayed neuropathy developed in 100.0%, 15.5%, and 4.2% of patients, respectively.

Toxicity Evaluation of the Subacute Diazinon in Aged Male Rats: Hematological Aspects

Background & Objective

Age-dependent Organophosphates (OPs) toxicity is a controversial topic. The present study was designed to investigate the effect of the sub-acute exposure to diazinon (DZN), one of the main OPs insecticides, on the hematological alterations in adult and aged male rats.

Methods

For the aim of this approach, the adult and aged rats were administered with DZN (15 mg/kg, orally) for 4 weeks. Then, the blood samples were collected from the retro-orbital sinus for measuring red blood cell (RBC), hemoglobin (Hb), hematocrit (Hct), platelets (PLT), MCV (mean corpuscular volume), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin (MCHC).

Results

The obtained results indicated that DZN significantly decreased RBCs (4.93 ± 0.41), Htc (28.12 ± 1.21), Hb (10.31 ± 0.36), MCHC (30.51 ± 2.04), MCV (62.86 ± 2.58), and PLT (265.6 ± 34.81) values in the adult and aged rats versus the age-matched control rats. Moreover, RBC, Hb, and Htc levels de-creased significantly in the aged rats versus adult rats. However, no significant differences were observed between MCHC, MCV, and PLT levels in adult and aged rats. Moreover, the MCH concentration did not change in any group. Additionally, DZN did not deteriorate the hematological alterations in the aged rats versus adult rats.

Conclusion

the present study showed that the toxicity of DZN is not associated with age. However, more studies should be conducted to confirm this finding.

Aging-related changes in the sensitivity of behavioral effects of the neonicotinoid pesticide clothianidin in male mice

Neonicotinoids, which act as agonists of the nicotinic acetylcholine receptors of insects, are widely used pesticides worldwide. Although epidemiological studies revealed that the detection amounts of neonicotinoids in urine are higher in the elderly population than other age-groups, there is no available information regarding the risks of neonicotinoids to older mammals. This study was aimed to investigate aging-related differences in the behavioral effects of the neonicotinoid pesticide clothianidin (CLO). We acutely administered a sub-NOAEL level (5 mg/kg) of CLO to adult (12-week-old) and aging (90-week-old) mice and conducted four behavioral tests focusing on the emotional behavior. In addition, we measured the concentrations of CLO and its metabolites in blood, brain and urine. There were age-related changes in most parameters in all behavioral tests, and CLO significantly decreased the locomotor activity in the open field test and elevated plus-maze test in the aging group, but not in the adult group. The concentrations of most CLO and its metabolites were significantly higher in the blood and brain and were slightly lower in the urine in the aging group compared to the adult group. These findings should contribute to our understanding of age-related differences in the adverse effects of neonicotinoids in mammals.

Allopregnanolone and perampanel as adjuncts to midazolam for treating diisopropylfluorophosphate-induced status epilepticus in rats

Combinations of midazolam, allopregnanolone, and perampanel were assessed for antiseizure activity in a rat diisopropylfluorophosphate (DFP) status epilepticus model. Animals receiving DFP followed by atropine and pralidoxime exhibited continuous high-amplitude rhythmical electroencephalography (EEG) spike activity and behavioral seizures for more than 5 hours. Treatments were administered intramuscularly 40 min after DFP. Seizures persisted following midazolam (1.8 mg/kg). The combination of midazolam with either allopregnanolone (6 mg/kg) or perampanel (2 mg/kg) terminated EEG and behavioral status epilepticus, but the onset of the perampanel effect was slow. The combination of midazolam, allopregnanolone, and perampanel caused rapid and complete suppression of EEG and behavioral seizures. In the absence of DFP, animals treated with the three-drug combination were sedated but not anesthetized. Animals that received midazolam alone exhibited spontaneous recurrent EEG seizures, whereas those that received the three-drug combination did not, demonstrating antiepileptogenic activity. All combination treatments reduced neurodegeneration as assessed with Fluoro-Jade C staining to a greater extent than midazolam alone, and most reduced astrogliosis as assessed by GFAP immunoreactivity but had mixed effects on markers of microglial activation. We conclude that allopregnanolone, a positive modulator of the GABAA receptor, and perampanel, an AMPA receptor antagonist, are potential adjuncts to midazolam in the treatment of benzodiazepine-refractory organophosphate nerve agent-induced status epilepticus.

Age-Related Diazinon Toxicity Impact on Blood Glucose, Lipid Profile and Selected Biochemical Indices in Male Rats

Background:

Diabetes and its complications are age-related diseases. Low-grade inflammation plays the main role in the aging processes. Diazinon (DZN), an organophosphate pesticide, has been found to induce metabolic disturbances.

Objective:

The present study was designed to investigate the impact of DZN on age-related changes on inflammatory cells, blood glucose concentration, lipid profile, and liver and kidney function indices in adult and aged rats.

Methods:

Male rats (2 and 16 month old) were orally administrated with DZN (15  mg/kg) for 4 weeks. Then the blood was obtained for measuring inflammatory cells, lipid profile, glucose and serum biochemical indices such as liver enzymes, albumin, total protein, creatinine (Cr), urea, and uric acid in the serum of adult and aged male rats.

Results:

DZN increased the blood levels of glucose and the percentage of lymphocytes and also serum levels of TChol, TG, LDL-c, AST, ALT, ALP, LDH, Cr, urea, and uric acid in the adult and aged rats versus the aged matched control rats (p< 0.001). A marked reduction in HDL-c levels, total protein, albumin, and in the percentage of neutrophils were seen in the adult and aged animals exposed to DZN versus the aged matched control rats. DZN also increased the levels of LDL-c and ALT in the aged rats versus adult animals.

Conclusion:

The present study indicated that DZN can cause metabolic disturbance. However, the age-dependent effects of DZN on metabolic indices were not be confirmed by the present data.

Age-Related Susceptibility to Epileptogenesis and Neuronal Loss in Male Fischer Rats Exposed to Soman and Treated With Medical Countermeasures

Elderly individuals compose a large percentage of the world population; however, few studies have addressed the efficacy of current medical countermeasures (MCMs) against the effects of chemical warfare nerve agent exposure in aged populations. We evaluated the efficacy of the anticonvulsant diazepam in an old adult rat model of soman (GD) poisoning and compared the toxic effects to those observed in young adult rats when anticonvulsant treatment is delayed. After determining their respective median lethal dose (LD50) of GD, we exposed young adult and old adult rats to an equitoxic 1.2 LD50 dose of GD followed by treatment with atropine sulfate and the oxime HI-6 at 1 min after exposure, and diazepam at 30 min after seizure onset. Old adult rats that presented with status epilepticus were more susceptible to developing spontaneous recurrent seizures (SRSs). Neuropathological analysis revealed that in rats of both age groups that developed SRS, there was a significant reduction in the density of mature neurons in the piriform cortex, thalamus, and amygdala, with more pronounced neuronal loss in the thalamus of old adult rats compared with young adult rats. Furthermore, old adult rats displayed a reduced density of cells expressing glutamic acid decarboxylase 67, a marker of GABAergic interneurons, in the basolateral amygdala and piriform cortex, and a reduction of astrocyte activation in the piriform cortex. Our observations demonstrate the reduced effectiveness of current MCM in an old adult animal model of GD exposure and strongly suggest the need for countermeasures that are more tailored to the vulnerabilities of an aging population.

Comparative effects of parathion and chlorpyrifos on endocannabinoid and endocannabinoid-like lipid metabolites in rat striatum

Parathion and chlorpyrifos are organophosphorus insecticides (OPs) that elicit acute toxicity by inhibiting acetylcholinesterase (AChE). The endocannabinoids (eCBs, N-arachidonoylethanolamine, AEA; 2-arachidonoylglycerol, 2AG) are endogenous neuromodulators that regulate presynaptic neurotransmitter release in neurons throughout the central and peripheral nervous systems. While substantial information is known about the eCBs, less is known about a number of endocannabinoid-like metabolites (eCBLs, e.g., N-palmitoylethanolamine, PEA; N-oleoylethanolamine, OEA). We report the comparative effects of parathion and chlorpyrifos on AChE and enzymes responsible for inactivation of the eCBs, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), and changes in the eCBs AEA and 2AG and eCBLs PEA and OEA, in rat striatum. Adult, male rats were treated with vehicle (peanut oil, 2 ml/kg, sc), parathion (27 mg/kg) or chlorpyrifos (280 mg/kg) 6-7 days after surgical implantation of microdialysis cannulae into the right striatum, followed by microdialysis two or four days later. Additional rats were similarly treated and sacrificed for evaluation of tissue levels of eCBs and eCBLs. Dialysates and tissue extracts were analyzed by LC-MS/MS. AChE and FAAH were extensively inhibited at both time-points (85-96%), while MAGL activity was significantly but lesser affected (37-62% inhibition) by parathion and chlorpyrifos. Signs of toxicity were noted only in parathion-treated rats. In general, chlorpyrifos increased eCB levels while parathion had no or lesser effects. Early changes in extracellular AEA, 2AG and PEA levels were significantly different between parathion and chlorpyrifos exposures. Differential changes in extracellular and/or tissue levels of eCBs and eCBLs could potentially influence a number of signaling pathways and contribute to selective neurological changes following acute OP intoxications.

Assessment of biochemical and behavioral effects of carbaryl and methomyl in Brown-Norway rats from preweaning to senescence

Factors impacting life stage-specific sensitivity to chemicals include toxicokinetic and toxicodynamic changes. To evaluate age-related differences in the biochemical and behavioral impacts of two typical N-methyl carbamate pesticides, we systematically compared their dose-response and time-course in preweanling (postnatal day, PND, 18) and adult male Brown Norway rats (n=9-10/dose or time) ranging from adolescence to senescence (1, 4, 12, 24 mo). Carbaryl was administered orally at 3, 7.5, 15, or 22.5mg/kg and data were collected at 40 min after dosing, or else given at 3 or 15 mg/kg and data collected at 30, 60, 120, and 240 min. Methomyl was studied only in adult and senescent rat (4, 12, 24 mo) in terms of dose-response (0.25. 0.6, 1.25, 2.5mg/kg) and time-course (1.25mg/kg at 30, 60, 120, 240 min). Motor activity as well as brain and erythrocyte (RBC) cholinesterase (ChE) activity were measured in the same animals. In the carbaryl dose-response, PND18 rats were the most sensitive to the brain ChE-inhibiting effects of carbaryl, but 12- and 24-mo rats showed more motor activity depression even at similar levels of brain ChE inhibition. We have previously reported that brain ChE inhibition, but not motor activity effects, closely tracked carbaryl tissue levels. There were no age-related differences in methomyl-induced ChE inhibition across doses, but greater motor activity depression was again observed in the 12- and 24-mo rats. Carbaryl time-course data showed that motor activity depression reached a maximum later, and recovered slower, in the 12- and 24-mo rats compared to the younger ages; slowest recovery and maximal effects were seen in the 24-mo rats. Acetylcholinesterase sensitivity (concentration-inhibition curves) was measured in vitro using control tissues from each age. Inhibitory concentrations of carbaryl were somewhat lower in PND18, 12-, and 24-mo tissues compared to 1- and 4-mo, but there were no differences with methomyl-treated tissues. Thus, in the dose-response and time-course, there were dissociations between brain ChE inhibition and the magnitude as well as recovery of motor activity changes. The explanation for this dissociation is unclear, and is likely due to early development followed by aging-related decline in both kinetic parameters and neurological responsiveness.

The cannabinoid receptor antagonist AM251 increases paraoxon and chlorpyrifos oxon toxicity in rats

Organophosphorus anticholinesterases (OPs) elicit acute toxicity by inhibiting acetylcholinesterase (AChE), leading to acetylcholine accumulation and overstimulation of cholinergic receptors. Endocannabinoids (eCBs, e.g., arachidonoyl ethanolamide [AEA] and 2-arachidonoyl glycerol [2-AG]) are neuromodulators that regulate neurotransmission by reducing neurotransmitter release. The eCBs are degraded by the enzymes fatty acid amide hydrolase (FAAH, primarily involved in hydrolysis of AEA) and monoacylglycerol lipase (MAGL, primarily responsible for metabolism of 2-AG). We previously reported that the cannabinoid receptor agonist WIN 55,212-2 reduced cholinergic toxicity after paraoxon exposure. This study compared the effects of the cannabinoid receptor antagonist AM251 on acute toxicity following either paraoxon (PO) or chlorpyrifos oxon (CPO). CPO was more potent in vitro than PO at inhibiting AChE (≈ 2 fold), FAAH (≈ 8 fold), and MAGL (≈ 19 fold). Rats were treated with vehicle, PO (0.3 and 0.6 mg/kg, sc) or CPO (6 and 12 mg/kg, sc) and subsets treated with AM251 (3mg/kg, ip; 30 min after OP). Signs of toxicity were recorded for 4h and rats were then sacrificed. OP-treated rats showed dose-related involuntary movements, with AM251 increasing signs of toxicity with the lower dosages. PO and CPO elicited excessive secretions, but AM251 had no apparent effect with either OP. Lethality was increased by AM251 with the higher dosage of PO, but no lethality was noted with either dosage of CPO, with or without AM251. Both OPs caused extensive inhibition of hippocampal AChE and FAAH (>80-90%), but only CPO inhibited MAGL (37-50%). These results provide further evidence that eCB signaling can influence acute OP toxicity. The selective in vivo inhibition of MAGL by CPO may be important in the differential lethality noted between PO and CPO with AM251 co-administration.

Paraoxon, 4-nitrophenyl phosphate and acetate are substrates of α- but not of β-, γ- and ζ-carbonic anhydrases

Carbonic anhydrases (CAs, EC 4.2.1.1) belonging to α-, β-, γ- and ζ-classes and from various organisms, ranging from the bacteria, archaea to eukarya domains, were investigated for their esterase/phosphatase activity with 4-nitrophenyl acetate, 4-nitrophenyl phosphate and paraoxon as substrates. Only α-CAs showed esterase/phosphatase activity, whereas enzymes belonging to the β-, γ- and ζ-classes were completely devoid of such activity. Paraoxon, the metabolite of the organophosphorus insecticide parathione, was a much better substrate for several human/murine α-CA isoforms (CA I, II and XIII), with k(cat)/K(M) in the range of 2681.6-4474.9M(-1)s(-1), compared to 4-nitrophenyl phosphate (k(cat)/K(M) of 14.9-1374.4M(-1)s(-1)).

Cholinesterase inhibition and acetylcholine accumulation following intracerebral administration of paraoxon in rats

We evaluated the inhibition of striatal cholinesterase activity following intracerebral administration of paraoxon assaying activity either in tissue homogenates ex vivo or by substrate hydrolysis in situ. Artificial cerebrospinal fluid (aCSF) or paraoxon in aCSF was infused unilaterally (0.5 microl/min for 2 h) and ipsilateral and contralateral striata were harvested for ChE assay ex vivo. High paraoxon concentrations were needed to inhibit ipsilateral striatal cholinesterase activity (no inhibition at <0.1 mM; 27% at 0.1 mM; 79% at 1 mM paraoxon). With 3 mM paraoxon infusion, substantial ChE inhibition was also noted in contralateral striatum. ChE histochemistry generally confirmed these concentration- and side-dependent effects. Microdialysates collected for up to 4 h after paraoxon infusion inhibited ChE activity when added to striatal homogenate, suggesting prolonged efflux of paraoxon. Since paraoxon efflux could complicate acetylcholine analysis, we evaluated the effects of paraoxon (0, 0.03, 0.1, 1, 10 or 100 microM, 1.5 microl/min for 45 min) administered by reverse dialysis through a microdialysis probe. ChE activity was then monitored in situ by perfusing the colorimetric substrate acetylthiocholine through the same probe and measuring product (thiocholine) in dialysates. Concentration-dependent inhibition was noted but reached a plateau of about 70% at 1 microM and higher concentrations. Striatal acetylcholine was below the detection limit at all times with 0.1 microM paraoxon but was transiently elevated (0.5-1.5 h) with 10 microM paraoxon. In vivo paraoxon (0.4 mg/kg, sc) in adult rats elicited about 90% striatal ChE inhibition measured ex vivo, but only about 10% inhibition measured in situ. Histochemical analyses revealed intense AChE and glial fibrillary acidic protein staining near the cannula track, suggesting proliferation of inflammatory cells/glia. The findings suggest that ex vivo and in situ cholinesterase assays can provide very different views into enzyme-inhibitor interactions. Furthermore, the proliferation/migration of cells containing high amounts of cholinesterase just adjacent to a dialysis probe could affect the recovery and thus detection of extracellular acetylcholine in microdialysis studies.