Pope C

References (31)

Title : Concentration-dependent effects of chlorpyrifos oxon on peroxisome proliferator-activated receptor signaling in MCF-7 cells - Herriage_2021_Toxicol.In.Vitro_78_105268
Author(s) : Herriage S , Chen G , Pope C
Ref : Toxicol In Vitro , 78 :105268 , 2021
Abstract : Chlorpyrifos oxon (CPO) is the active metabolite of the organophosphorus pesticide, chlorpyrifos. CPO is a potent inhibitor of acetylcholinesterase (AChE) and other serine hydrolases including fatty acid amide hydrolase (FAAH). AChE is critical in regulating cholinergic signaling while FAAH catalyzes the inactivation of fatty acid signaling lipids including the endocannabinoid (eCB) N-arachidonylethanolamine (anandamide, AEA) and eCB-like metabolites (e.g., oleoylethanolamide, OEA). AEA and OEA are both peroxisome proliferator-activated receptor (PPAR) agonists that regulate numerous genes involved in lipid metabolism and energy homeostasis. We used the MCF-7 human breast cancer cell line, which expresses AChE, FAAH and PPAR alpha and gamma subtypes, to evaluate the potential effects of CPO on PPAR-related gene expression in an in vitro human cell system. CPO elicited relatively similar concentration-dependent inhibition of both AChE and FAAH. Marked concentration- and time-dependent changes in the expression of four selected PPAR-related genes, LXRalpha, ACOX1, ABCG2 and AGPAT2, were noted. These findings suggest chlorpyrifos may influence lipid metabolism through blocking the degradation of eCBs or eCB-like metabolites and in turn affecting PPAR receptor activation. The results highlight the potential for non-cholinesterase actions of this common insecticide metabolite through disruption of PPAR signaling including effects on lipid metabolism, immune function and inflammation.
ESTHER : Herriage_2021_Toxicol.In.Vitro_78_105268
PubMedSearch : Herriage_2021_Toxicol.In.Vitro_78_105268
PubMedID: 34756920

Title : Dose- and time-related effects of acute diisopropylfluorophosphate intoxication on forced swim behavior and sucrose preference in rats - Liu_2021_Neurotoxicol_82_82
Author(s) : Liu J , Hester K , Pope C
Ref : Neurotoxicology , 82 :82 , 2021
Abstract : Acute intoxication by organophosphorus anticholinesterases (OPs) has been associated with depression and other neuropsychiatric disorders. We previously reported that adult male rats treated with diisopropylfluorophosphate (2.5 mg/kg, sc) showed acute cholinergic signs followed by changes (increased immobility/decreased swimming) in the forced swim test (a measure of behavioral despair) for at least one month. This study was conducted to evaluate the further persistence of changes in the forced swim test out to 4 months and to compare responses in a sucrose preference test, a measure of anhedonia. Adult male rats were treated with vehicle (peanut oil, 1 mL/kg, sc) or DFP (2.0, 2.25 or 2.5 mg/kg) followed by sacrifice 4 h later for measurement of OP-sensitive serine hydrolases (cholinesterase [ChE], fatty acid amide hydrolase [FAAH], and monoacylglycerol lipase [MAGL]) in hippocampus. Additional rats were treated similarly and evaluated for functional signs of acute toxicity from 30 min to 6 days, and then motor activity, forced swim behavior and sucrose preference at approximately 1 week, 1 month and 4 months after dosing. All dosages of DFP elicited serine hydrolase inhibition (ChE, 92-96 %; FAAH, 46-63 %; MAGL, 26-33 %). Body weight was reduced in all DFP-treated groups during the first two weeks, and lethality was noted with the higher dosages. Involuntary movements were elicited in all DFP treatment groups during the first week, but both time of onset and rate of recovery were dose-related. There was a significant reduction in ambulation at one week after the highest dosage (2.5 mg/kg), but no other significant locomotor changes were noted. Immobility was increased and swimming was decreased in the forced swim test at all three time-points by 2.25 mg/kg DFP, and at 2 of 3 time-points by the other dosages. While length of water deprivation and time after DFP dosing affected sucrose preference, DFP treatment had no main effect. We conclude that the forced swim test (a measure of behavioral despair/coping mechanism for inescapable stress) is a robust and persistent neurobehavioral consequence of acute DFP intoxication while sucrose preference, a measure of anhedonia and a common symptom of major clinical depression, is not affected.
ESTHER : Liu_2021_Neurotoxicol_82_82
PubMedSearch : Liu_2021_Neurotoxicol_82_82
PubMedID: 33232745

Title : Effects of Chlorpyrifos on Cholinesterase and Serine Lipase Activities and Lipid Metabolism in Brains of Rainbow Trout (Oncorhynchus mykiss) - Greer_2019_Toxicol.Sci_172_146
Author(s) : Greer JB , Magnuson JT , Hester K , Giroux M , Pope C , Anderson T , Liu J , Dang V , Denslow ND , Schlenk D
Ref : Toxicol Sci , 172 :146 , 2019
Abstract : Chlorpyrifos is an organophosphorus insecticide that elicits acute toxicity through inhibition of acetylcholinesterase (AChE), leading to acetylcholine accumulation and prolonged stimulation of cholinergic receptors throughout the central and peripheral nervous systems. Previous studies have indicated that neurodevelopment may also be impaired through alternative pathways, including reduction of cAMP catalyzed downstream events. The upstream initiating events that underlie non-cholinergic neurological actions of chlorpyrifos and other organophosphorus compounds remain unclear. To investigate the potential role of disruption of fatty acid signaling as a mechanism of toxicity, lipid metabolism and fatty acid profiles were examined to identify alterations that may play a critical role in upstream signaling in the CNS. Juvenile rainbow trout were treated for 7 days with nominal chlorpyrifos concentrations previously reported to diminish olfactory responses (10, 20, and 40 microg/L). While lethality was noted higher doses, measured chlorpyrifos concentrations of 1.38 microg/L (nominal concentration 10 microg/L) significantly reduced the activity of AChE and two serine lipases, monoacylglycerol lipase and fatty acid amide hydrolase in the brain. Reductions in lysophosphatidylethanolamines (16:0; 18:0, 18:1, and 22:6) derived from the phosphatidylethanolamines and free fatty acids (Palmitic acid16:0; Linolenic acid18:3; Eicosadienoic acid 20:2; Arachidonic acid 20:4; and Docosahexaenoic acid 22:6) were also noted, suggesting that chlorpyrifos inhibited the metabolism of selected phospholipid signaling precursors at sublethal concentrations. These results indicate that in addition to AChE inhibition, environmentally relevant chlorpyrifos exposure alters serine lipase activity and lipid metabolites in the trout brain, which may compromise neuronal signaling and impact neurobehavioral responses in aquatic animals.
ESTHER : Greer_2019_Toxicol.Sci_172_146
PubMedSearch : Greer_2019_Toxicol.Sci_172_146
PubMedID: 31359069

Title : Engineering Dynamic Surface Peptide Networks on ButyrylcholinesteraseG117H for Enhanced Organophosphosphorus Anticholinesterase Catalysis - Hester_2019_Chem.Res.Toxicol_32_1801
Author(s) : Hester KP , Bhattarai K , Jiang H , Agarwal PK , Pope C
Ref : Chemical Research in Toxicology , 32 :1801 , 2019
Abstract : The single residue mutation of butyrylcholinesterase (BChEG117H) hydrolyzes a number of organophosphosphorus (OP) anticholinesterases. Whereas other BChE active site/proximal mutations have been investigated, none are sufficiently active to be prophylactically useful. In a fundamentally different computer simulations driven strategy, we identified a surface peptide loop (residues 278-285) exhibiting dynamic motions during catalysis and modified it via residue insertions. We evaluated these loop mutants using computer simulations, substrate kinetics, resistance to inhibition, and enzyme reactivation assays using both the choline ester and OP substrates. A slight but significant increase in reactivation was noted with paraoxon with one of the mutants, and changes in KM and catalytic efficiency were noted in others. Simulations suggested weaker interactions between OP versus choline substrates and the active site of all engineered versions of the enzyme. The results indicate that an improvement of OP anticholinesterase hydrolysis through surface loop engineering may be a more effective strategy in an enzyme with higher intrinsic OP compound hydrolase activity.
ESTHER : Hester_2019_Chem.Res.Toxicol_32_1801
PubMedSearch : Hester_2019_Chem.Res.Toxicol_32_1801
PubMedID: 31411024

Title : Comparative in vitro and in vivo effects of chlorpyrifos oxon in the outbred CD-1 mouse (Mus musculus) and great plains toad (Anaxyrus cognatus) - Anderson_2018_Environ.Toxicol.Chem_37_1898
Author(s) : Anderson T , Liu J , McMurry S , Pope C
Ref : Environ Toxicol Chem , 37 :1898 , 2018
Abstract : We compared biochemical, functional, and behavioral responses to the organophosphorus anticholinesterase chlorpyrifos oxon (CPO) in mice (Mus musculus, CD-1) and toads (Anaxyrus cognatus, Great Plains toad). Toads were substantially less sensitive to acute lethality of CPO based on the maximum tolerated (nonlethal) dose (toads, 77 mg/kg; mice, 5.9 mg/kg). Sublethal exposures led to classical signs of toxicity (increased involuntary movements, autonomic secretions) in mice but hypoactivity in toads. Motor performance in an inclined plane test was not affected by CPO in mice but was altered at the highest dosage in toads. Acetylcholinesterase (AChE), butyrylcholinesterase, monoacylglycerol lipase, and fatty acid amide hydrolase activities in brain were inhibited in mice but not in toads, and fatty acid amide hydrolase activity in the liver was inhibited in both species. Toad brain AChE was less sensitive to in vitro inhibition by CPO (50% inhibitory concentration [IC50; 20 min, 37 degrees C], 101 vs 7.8 nM; IC50 [20 min, 26 degrees C], 149 vs 6.2 nM), and studies of inhibitor kinetics indicated substantially lower anticholinesterase potency of CPO against the toad brain enzyme. Using an in vitro indirect inhibition assay, preincubation of CPO with toad brain homogenate was more effective than an equivalent mouse brain homogenate at reducing CPO potency. These data suggest that the relatively low sensitivity of toads to cholinergic toxicity is based on the low sensitivity of brain AChE, which in turn may be attributable to more effective target-site detoxification. Environ Toxicol Chem 2018;37:1898-1906. (c) 2018 SETAC.
ESTHER : Anderson_2018_Environ.Toxicol.Chem_37_1898
PubMedSearch : Anderson_2018_Environ.Toxicol.Chem_37_1898
PubMedID: 29573455

Title : Polyionic complexes of butyrylcholinesterase and poly-l-lysine-g-poly(ethylene glycol): Comparative kinetics of catalysis and inhibition and in vitro inactivation by proteases and heat - Hester_2017_Chem.Biol.Interact_275_86
Author(s) : Hester K , Liu J , Flynn N , Sultatos LG , Geng L , Brimijoin S , Ramsey JD , Hartson S , Ranjan A , Pope C
Ref : Chemico-Biological Interactions , 275 :86 , 2017
Abstract : We previously reported that recombinant human butyrylcholinesterase (rhBChE) complexed with a series of copolymers of poly-l-lysine (PLL) with grafted (polyethylene) glycol (PEG) (i.e., PLL-g-PEG) showed reduced catalytic activity but relatively similar concentration-dependent inactivation of the organophosphorus inhibitor paraoxon. Herein, we compared the kinetics of catalysis (using butyrylthiocholine as the substrate) and inhibition (using four different inhibitors) of free and copolymer-complexed rhBChE. Using scanning electron microscopy, polyionic complexes of rhBChE with three different PLL-g-PEG copolymers (based on PLL size) appeared as spheroid-shaped particles with relatively similar particle sizes (median diameter = 35 nm). Relatively similar particle sizes were also noted using dynamic light scattering (mean = 26-35 nm). The three copolymer-complexed enzymes exhibited reduced kcat (30-33% reduction), but no significant changes in Km. Inhibitory potency (as reflected by the bimolecular rate constant, ki) was similar among the free and copolymer-complexed enzymes when paraoxon was the inhibitor, whereas statistically significant reductions in ki (16-60%) were noted with the other inhibitors. Sensitivity to inactivation by proteases and heat was also compared. Copolymer-complexed enzymes showed lesser time-dependent inactivation by the proteases trypsin and pronase and by heat compared to the free enzyme. Understanding the unique properties of PLL-g-PEG-BChE complexes may lead to enhanced approaches for use of BChE and other protein bioscavengers.
ESTHER : Hester_2017_Chem.Biol.Interact_275_86
PubMedSearch : Hester_2017_Chem.Biol.Interact_275_86
PubMedID: 28756151

Title : Subacute pyridostigmine exposure increases heart rate recovery and cardiac parasympathetic tone in rats - Bharadwaj_2017_Clin.Exp.Pharmacol.Physiol_44_872
Author(s) : Bharadwaj M , Pope C , Davis M , Katz S , Cook C , Maxwell L
Ref : Clinical & Experimental Pharmacology & Physiology , 44 :872 , 2017
Abstract : Heart rate recovery (HRR) describes the rapid deceleration of heart rate after strenuous exercise and is an indicator of parasympathetic tone. A reduction in parasympathetic tone occurs in patients with congestive heart failure, resulting in prolonged HRR. Acetylcholinesterase inhibitors, such as pyridostigmine, can enhance parasympathetic tone by increasing cholinergic input to the heart. The objective of this study was to develop a rodent model of HRR to test the hypothesis that subacute pyridostigmine administration decreases cholinesterase activity and accelerates HRR in rats. Ten days after implantation of radiotelemetry transmitters, male Sprague Dawley rats were randomized to control (CTL) or treated (PYR; 0.14 mg/mL pyridostigmine in the drinking water, 29 days) groups. Rats were exercised on a treadmill to record HRR, and blood samples were collected on days 0, 7, 14, and 28 of pyridostigmine administration. Total cholinesterase and acetylcholinesterase (AChE) activity in plasma was decreased by 32%-43% and 57%-80%, respectively, in PYR rats on days 7-28, while plasma butyrylcholinesterase activity did not significantly change. AChE activity in red blood cells was markedly reduced by 64%-66%. HRR recorded 1 minute after exercise was higher in the PYR group on days 7, 14 and 28, and on day 7 when HRR was estimated at 3 and 5 minutes. Autonomic tone was evaluated pharmacologically using sequential administration of muscarinic (atropine) and adrenergic (propranolol) blockers. Parasympathetic tone was increased in PYR rats as compared with the CTL group. These data support the study hypothesis that subacute pyridostigmine administration enhances HRR by increasing cardiac parasympathetic tone.
ESTHER : Bharadwaj_2017_Clin.Exp.Pharmacol.Physiol_44_872
PubMedSearch : Bharadwaj_2017_Clin.Exp.Pharmacol.Physiol_44_872
PubMedID: 28440910

Title : Comparative effects of parathion and chlorpyrifos on endocannabinoid and endocannabinoid-like lipid metabolites in rat striatum - Liu_2015_Neurotoxicol_50_20
Author(s) : Liu J , Parsons L , Pope C
Ref : Neurotoxicology , 50 :20 , 2015
Abstract : 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, 2ml/kg, sc), parathion (27mg/kg) or chlorpyrifos (280mg/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.
ESTHER : Liu_2015_Neurotoxicol_50_20
PubMedSearch : Liu_2015_Neurotoxicol_50_20
PubMedID: 26215119

Title : In vitro characterization of cationic copolymer-complexed recombinant human butyrylcholinesterase - Pope_2015_Biochem.Pharmacol_98_531
Author(s) : Pope C , Uchea C , Flynn N , Poindexter K , Geng L , Brimijoin S , Hartson S , Ranjan A , Ramsey JD , Liu J
Ref : Biochemical Pharmacology , 98 :531 , 2015
Abstract : Effective use of exogenous human BChE as a bioscavenger for organophosphorus toxicants (OPs) is hindered by its limited availability and rapid clearance. Complexes made from recombinant human BChE (rhBChE) and copolymers may be useful in addressing these problems. We used in vitro approaches to compare enzyme activity, sensitivity to inhibition, stability and bioscavenging capacity of free enzyme and copolymer-rhBChE complexes (C-BCs) based on one of nine different copolymers, from combinations of three molecular weights (MW) of poly-l-lysine (PLL; high MW, 30-70kDa; medium MW, 15-30kDa; low MW, 4-15kDa) and three grafting ratios of poly(ethylene glycol) (PEG; 2:1, 10:1, 20:1). Retarded protein migration into acrylamide gels stained for BChE activity was noted with all copolymers as the copolymer-to-protein ratio was increased. BChE activity of C-BCs was lower relative to free enzyme, with the 2:1 grafting ratio showing generally greater reduction. Free enzyme and C-BCs showed relatively similar in vitro sensitivity to inhibition by paraoxon, but use of the 20:1 grafting ratio led to lower potencies. Through these screening assays we selected three C-BCs (high, medium and low MW; 10:1 grafting) for further characterizations. BChE activity was higher in C-BCs made with the medium and low compared to high MW-based copolymer. C-BCs generally showed higher stability than free enzyme when maintained for long periods at 37 degrees C or following incubation with chymotrypsin. Free enzyme and C-BCs were similarly effective at inactivating paraoxon in vitro. While these results are promising for further development, additional studies are needed to evaluate in vivo performance.
ESTHER : Pope_2015_Biochem.Pharmacol_98_531
PubMedSearch : Pope_2015_Biochem.Pharmacol_98_531
PubMedID: 26456723

Title : The cannabinoid receptor antagonist AM251 increases paraoxon and chlorpyrifos oxon toxicity in rats - Liu_2014_Neurotoxicol_46C_12
Author(s) : Liu J , Pope C
Ref : Neurotoxicology , 46C :12 , 2014
Abstract : 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 ( approximately 2 fold), FAAH ( approximately 8 fold), and MAGL ( approximately 19 fold). Rats were treated with vehicle, PO (0.3 and 0.6mg/kg, sc) or CPO (6 and 12mg/kg, sc) and subsets treated with AM251 (3mg/kg, ip; 30min 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.
ESTHER : Liu_2014_Neurotoxicol_46C_12
PubMedSearch : Liu_2014_Neurotoxicol_46C_12
PubMedID: 25447325

Title : Comparative effects of chlorpyrifos in wild type and cannabinoid Cb1 receptor knockout mice - Baireddy_2011_Toxicol.Appl.Pharmacol_256_324
Author(s) : Baireddy P , Liu J , Hinsdale M , Pope C
Ref : Toxicol Appl Pharmacol , 256 :324 , 2011
Abstract : Endocannabinoids (eCBs) modulate neurotransmission by inhibiting the release of a variety of neurotransmitters. The cannabinoid receptor agonist WIN 55.212-2 (WIN) can modulate organophosphorus (OP) anticholinesterase toxicity in rats, presumably by inhibiting acetylcholine (ACh) release. Some OP anticholinesterases also inhibit eCB-degrading enzymes. We studied the effects of the OP insecticide chlorpyrifos (CPF) on cholinergic signs of toxicity, cholinesterase activity and ACh release in tissues from wild type (+/+) and cannabinoid CB1 receptor knockout (-/-) mice. Mice of both genotypes (n=5-6/treatment group) were challenged with CPF (300 mg/kg, 2 ml/kg in peanut oil, sc) and evaluated for functional and neurochemical changes. Both genotypes exhibited similar cholinergic signs and cholinesterase inhibition (82-95% at 48h after dosing) in cortex, cerebellum and heart. WIN reduced depolarization-induced ACh release in vitro in hippocampal slices from wild type mice, but had no effect in hippocampal slices from knockouts or in striatal slices from either genotype. Chlorpyrifos oxon (CPO, 100 muM) reduced release in hippocampal slices from both genotypes in vitro, but with a greater reduction in tissues from wild types (21% vs 12%). CPO had no significant in vitro effect on ACh release in striatum. CPF reduced ACh release in hippocampus from both genotypes ex vivo, but reduction was again significantly greater in tissues from wild types (52% vs 36%). In striatum, CPF led to a similar reduction (20-23%) in tissues from both genotypes. Thus, while CB1 deletion in mice had little influence on the expression of acute toxicity following CPF, CPF- or CPO-induced changes in ACh release appeared sensitive to modulation by CB1-mediated eCB signaling in a brain-regional manner.
ESTHER : Baireddy_2011_Toxicol.Appl.Pharmacol_256_324
PubMedSearch : Baireddy_2011_Toxicol.Appl.Pharmacol_256_324
PubMedID: 21672545

Title : Dose-related gene expression changes in forebrain following acute, low-level chlorpyrifos exposure in neonatal rats - Ray_2010_Toxicol.Appl.Pharmacol_248_144
Author(s) : Ray A , Liu J , Ayoubi P , Pope C
Ref : Toxicol Appl Pharmacol , 248 :144 , 2010
Abstract : Chlorpyrifos (CPF) is a widely used organophosphorus insecticide (OP) and putative developmental neurotoxicant in humans. The acute toxicity of CPF is elicited by acetylcholinesterase (AChE) inhibition. We characterized dose-related (0.1, 0.5, 1 and 2mg/kg) gene expression profiles and changes in cell signaling pathways 24h following acute CPF exposure in 7-day-old rats. Microarray experiments indicated that approximately 9% of the 44,000 genes were differentially expressed following either one of the four CPF dosages studied (546, 505, 522, and 3,066 genes with 0.1, 0.5, 1.0 and 2.0mg/kg CPF). Genes were grouped according to dose-related expression patterns using K-means clustering while gene networks and canonical pathways were evaluated using Ingenuity Pathway Analysis(R). Twenty clusters were identified and differential expression of selected genes was verified by RT-PCR. The four largest clusters (each containing from 276 to 905 genes) constituted over 50% of all differentially expressed genes and exhibited up-regulation following exposure to the highest dosage (2mg/kg CPF). The total number of gene networks affected by CPF also rose sharply with the highest dosage of CPF (18, 16, 18 and 50 with 0.1, 0.5, 1 and 2mg/kg CPF). Forebrain cholinesterase (ChE) activity was significantly reduced (26%) only in the highest dosage group. Based on magnitude of dose-related changes in differentially expressed genes, relative numbers of gene clusters and signaling networks affected, and forebrain ChE inhibition only at 2mg/kg CPF, we focused subsequent analyses on this treatment group. Six canonical pathways were identified that were significantly affected by 2mg/kg CPF (MAPK, oxidative stress, NFKappaB, mitochondrial dysfunction, arylhydrocarbon receptor and adrenergic receptor signaling). Evaluation of different cellular functions of the differentially expressed genes suggested changes related to olfactory receptors, cell adhesion/migration, synapse/synaptic transmission and transcription/translation. Nine genes were differentially affected in all four CPF dosing groups. We conclude that the most robust, consistent changes in differential gene expression in neonatal forebrain across a range of acute CPF dosages occurred at an exposure level associated with the classical marker of OP toxicity, AChE inhibition. Disruption of multiple cellular pathways, in particular cell adhesion, may contribute to the developmental neurotoxicity potential of this pesticide.
ESTHER : Ray_2010_Toxicol.Appl.Pharmacol_248_144
PubMedSearch : Ray_2010_Toxicol.Appl.Pharmacol_248_144
PubMedID: 20691718

Title : Cholinesterase inhibition and acetylcholine accumulation following intracerebral administration of paraoxon in rats - Ray_2009_Toxicol.Appl.Pharmacol_236_341
Author(s) : Ray A , Liu J , Karanth S , Gao Y , Brimijoin S , Pope C
Ref : Toxicol Appl Pharmacol , 236 :341 , 2009
Abstract : 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.
ESTHER : Ray_2009_Toxicol.Appl.Pharmacol_236_341
PubMedSearch : Ray_2009_Toxicol.Appl.Pharmacol_236_341
PubMedID: 19272400

Title : Recombinant expression and biochemical characterization of the catalytic domain of acetylcholinesterase-1 from the African malaria mosquito, Anopheles gambiae - Jiang_2009_Insect.Biochem.Mol.Biol_39_646
Author(s) : Jiang H , Liu S , Zhao P , Pope C
Ref : Insect Biochemistry & Molecular Biology , 39 :646 , 2009
Abstract : Acetylcholinesterases (AChEs) and their genes from susceptible and resistant insects have been extensively studied to understand the molecular basis of target site insensitivity. Due to the existence of other resistance mechanisms, however, it can be problematic to correlate directly a mutation with the resistant phenotype. An alternative approach involves recombinant expression and characterization of highly purified wild-type and mutant AChEs, which serves as a reliable platform for studying structure-function relationships. We expressed the catalytic domain of Anopheles gambiae AChE1 (r-AgAChE1) using the baculovirus system and purified it 2,500-fold from the conditioned medium to near homogeneity. While K(M)'s of r-AgAChE1 were comparable for ATC, AbetaMTC, PTC, and BTC, V(max)'s were substantially different. The IC(50)'s for eserine, carbaryl, paraoxon, BW284C51, malaoxon, and ethopropazine were 8.3, 72.5, 83.6, 199, 328, and 6.59 x 10(4) nM, respectively. We determined kinetic constants for inhibition of r-AgAChE1 by four of these compounds. The enzyme bound eserine or paraoxon stronger than carbaryl or malaoxon. Because the covalent modification of r-AgAChE1 by eserine occurred faster than that by the other compounds, eserine is more potent than paraoxon, carbaryl, and malaoxon. Furthermore, we found that choline inhibited r-AgAChE1, a phenomenon related to the enzyme activity decrease at high concentrations of acetylcholine.
ESTHER : Jiang_2009_Insect.Biochem.Mol.Biol_39_646
PubMedSearch : Jiang_2009_Insect.Biochem.Mol.Biol_39_646
PubMedID: 19607916
Gene_locus related to this paper: anoga-ACHE1

Title : Pharmacological enhancement of endocannabinoid signaling reduces the cholinergic toxicity of diisopropylfluorophosphate - Nallapaneni_2008_Neurotoxicol_29_1037
Author(s) : Nallapaneni A , Liu J , Karanth S , Pope C
Ref : Neurotoxicology , 29 :1037 , 2008
Abstract : Diisopropylfluorophosphate (DFP) elicits cholinergic toxicity by inhibiting acetylcholinesterase, leading to accumulation of the neurotransmitter acetylcholine and excessive stimulation of cholinergic receptors throughout the body. Endocannabinoids inhibit the release of neurotransmitters including acetylcholine via a widely distributed retrograde signaling pathway. Endocannabinoid signaling is therefore a potential therapeutic target for the management of OP poisoning. We first evaluated the relative in vitro and in vivo (2.5mg/kg, sc) effects of DFP on cholinesterase, fatty acid amide hydrolase (FAAH, an endocannabinoid degrading enzyme), monoacylglycerol lipase (MAGL, another endocannabinoid degrading enzyme) and cannabinoid receptor (CB1) binding in rat hippocampus. The effects of WIN 55212-2 (cannabinoid receptor agonist, 1.5mg/kg), URB597 (FAAH inhibitor, 3mg/kg), URB602 (MAGL inhibitor, 10mg/kg) or AM404 (endocannabinoid uptake inhibitor, 10mg/kg) on DFP toxicity were then examined. Adult male rats were given either peanut oil or DFP followed immediately by vehicle or one of the four cannabinomimetic drugs. Functional signs of toxicity were evaluated for 24h and then rats were sacrificed for neurochemical measurements. DFP inhibited cholinesterase, FAAH, MAGL and CB1 receptor binding in vitro in a concentration-dependent manner, with highest and lowest potency against cholinesterase and FAAH, respectively. In vivo, DFP inhibited hippocampal cholinesterase (89%) and FAAH (42%), but had no significant effect on MAGL or CB1 binding. Rats treated with DFP alone showed typical signs of cholinergic toxicity including involuntary movements and excessive secretions (SLUD signs). WIN 55212-2, URB597, URB602 and AM404 all significantly reduced involuntary movements following DFP exposure in a time-dependent manner, and most (URB597, URB602 and AM404) also significantly reduced DFP-induced SLUD signs. These results suggest that enhancing endocannabinoid signaling can attenuate the acute toxicity of DFP and provide rationale for further investigations on the role of endocannabinoids in cholinergic toxicity.
ESTHER : Nallapaneni_2008_Neurotoxicol_29_1037
PubMedSearch : Nallapaneni_2008_Neurotoxicol_29_1037
PubMedID: 18765251

Title : Modulation of parathion toxicity by glucose feeding: Is nitric oxide involved? - Liu_2007_Toxicol.Appl.Pharmacol_219_106
Author(s) : Liu J , Gupta RC , Goad JT , Karanth S , Pope C
Ref : Toxicol Appl Pharmacol , 219 :106 , 2007
Abstract : Glucose feeding can markedly exacerbate the toxicity of the anticholinesterase insecticide, parathion. We determined the effects of parathion on brain nitric oxide and its possible role in potentiation of toxicity by glucose feeding. Adult rats were given water or 15% glucose in water for 3 days and challenged with vehicle or parathion (18 mg/kg, s.c.) on day 4. Functional signs, plasma glucose and brain cholinesterase, citrulline (an indicator of nitric oxide production) and high-energy phosphates (HEPs) were measured 1-3 days after parathion. Glucose feeding exacerbated cholinergic toxicity. Parathion increased plasma glucose (15-33%) and decreased cortical cholinesterase activity (81-90%), with no significant differences between water and glucose treatment groups. In contrast, parathion increased brain regional citrulline (40-47%) and decreased HEPs (18-40%) in rats drinking water, with significantly greater changes in glucose-fed rats (248-363% increase and 31-61% decrease, respectively). We then studied the effects of inhibiting neuronal nitric oxide synthase (nNOS) by 7-nitroindazole (7NI, 30 mg/kg, i.p. x4) on parathion toxicity and its modulation by glucose feeding. Co-exposure to parathion and 7NI led to a marked increase in cholinergic signs of toxicity and lethality, regardless of glucose intake. Thus, glucose feeding enhanced the accumulation of brain nitric oxide following parathion exposure, but inhibition of nitric oxide synthesis was ineffective at counteracting increased parathion toxicity associated with glucose feeding. Evidence is therefore presented to suggest that nitric oxide may play both toxic and protective roles in cholinergic toxicity, and its precise contribution to modulation by glucose feeding requires further investigation.
ESTHER : Liu_2007_Toxicol.Appl.Pharmacol_219_106
PubMedSearch : Liu_2007_Toxicol.Appl.Pharmacol_219_106
PubMedID: 17178140

Title : Comparative in vivo effects of parathion on striatal acetylcholine accumulation in adult and aged rats - Karanth_2007_Toxicology_239_167
Author(s) : Karanth S , Liu J , Ray A , Pope C
Ref : Toxicology , 239 :167 , 2007
Abstract : Aged rats are more sensitive to the acute toxicity of the prototype organophosphate insecticide, parathion. We compared the acute effects of parathion on diaphragm and brain regional cholinesterase activity, muscarinic receptor binding and striatal acetylcholine levels in 3- and 18-month-old male Sprague-Dawley rats. Adult and aged rats were surgically implanted with a microdialysis cannula into the right striatum 5-7 days prior to parathion treatment. Rats were given either vehicle (peanut oil, 2 ml/kg) or one of a range of dosages of parathion (adult: 1.8, 3.4, 6.0, 9.0, 18 and 27 mg/kg, s.c.; aged: 1.8, 3.4, 6 and 9 mg/kg, s.c.) and body weight, functional signs of toxicity, and nocturnal motor activity were recorded for seven days. Three and seven days after parathion treatment, microdialysis samples were collected and rats were subsequently sacrificed for biochemical measurements. Higher dosages of parathion led to significant time-dependent reductions in body weight in both age groups. Rats in both age groups treated with lower dosages showed few overt signs of cholinergic toxicity while equitoxic high dosages (adult, 27 mg/kg; aged, 9 mg/kg) elicited marked signs of cholinergic toxicity (involuntary movements and SLUD [i.e., acronym for Salivation, Lacrimation, Urination and Defecation] signs) with peak effects being noted 3-4 days after treatment. Nocturnal activity (ambulation and rearing) was reduced in both age groups following parathion dosing, with more prominent effects in adults and rearing being more consistently affected. Dose- and time-dependent inhibition of cholinesterase activity was noted in both diaphragm and striatum. Total muscarinic receptor ([(3)H]quinuclidinyl benzilate, QNB) binding was significantly lower in aged rats, and both total binding and muscarinic agonist ([(3)H]oxotremorine methiodide] binding was significantly reduced in both age-groups treated with the highest dosages of parathion (adult, 27 mg/kg; aged, 9 mg/kg). In contrast to relatively similar levels of cholinesterase inhibition, striatal extracellular acetylcholine levels were significantly lower (2.2- to 2.9-fold) in aged rats at both 3 and 7 day time-points compared to adult rats treated with equitoxic dosages (i.e., 9 and 27 mg/kg, respectively). No age-related differences in in vitro striatal acetylcholine synthesis or in vivo acetylcholine accumulation following direct infusion of the cholinesterase inhibitor neostigmine (1 microM) were noted. While aged rats are more sensitive than adults to the acute toxicity of parathion, lesser acetylcholine accumulation was noted in the striatum of aged rats exhibiting similar levels of cholinesterase inhibition. These findings suggest that lesser acetylcholine accumulation may be required to elicit cholinergic signs in the aged rat, possibly based on aging-associated changes in muscarinic receptor density.
ESTHER : Karanth_2007_Toxicology_239_167
PubMedSearch : Karanth_2007_Toxicology_239_167
PubMedID: 17707571

Title : Effects of acute chlorpyrifos exposure on in vivo acetylcholine accumulation in rat striatum - Karanth_2006_Toxicol.Appl.Pharmacol_216_150
Author(s) : Karanth S , Liu J , Mirajkar N , Pope C
Ref : Toxicol Appl Pharmacol , 216 :150 , 2006
Abstract : This study examined the acute effects of chlorpyrifos (CPF) on cholinesterase inhibition and acetylcholine levels in the striatum of freely moving rats using in vivo microdialysis. Adult, male Sprague-Dawley rats were treated with vehicle (peanut oil, 2 ml/kg) or CPF (84, 156 or 279 mg/kg, sc) and functional signs of toxicity, body weight and motor activity recorded. Microdialysis was conducted at 1, 4 and 7 days after CPF exposure for measurement of acetylcholine levels in striatum. Rats were then sacrificed and the contralateral striatum and diaphragm were collected for biochemical measurements. Few overt signs of cholinergic toxicity were noted in any rats. Body weight gain was significantly affected in the high-dose (279 mg/kg) group only, while motor activity (nocturnal rearing) was significantly reduced in all CPF-treated groups at one day (84 mg/kg) or from 1-4 days (156 and 279 mg/kg) after dosing. Cholinesterase activities in both diaphragm and striatum were markedly inhibited (50-92%) in a time-dependent manner, but there were relatively minimal dose-related changes. In contrast, time- and dose-dependent changes in striatal acetylcholine levels were noted, with significantly higher levels noted in the high-dose group compared to other groups. Maximal increases in striatal acetylcholine levels were observed at 4-7 days after dosing (84 mg/kg, 7-9-fold; 156 mg/kg, 10-13-fold; 279 mg/kg, 35-57-fold). Substantially higher acetylcholine levels were noted when an exogenous cholinesterase inhibitor was included in the perfusion buffer, but CPF treatment-related differences were substantially lower in magnitude under those conditions. The results suggest that marked differences in acetylcholine accumulation can occur with dosages of CPF eliciting relatively similar degrees of cholinesterase inhibition. Furthermore, the minimal expression of classic signs of cholinergic toxicity in the presence of extensive brain acetylcholine accumulation suggests that some compensatory process(es) downstream from synaptic neurotransmitter accumulation limits the expression of toxicity following acute CPF exposure.
ESTHER : Karanth_2006_Toxicol.Appl.Pharmacol_216_150
PubMedSearch : Karanth_2006_Toxicol.Appl.Pharmacol_216_150
PubMedID: 16777161

Title : Modulation of paraoxon toxicity by the cannabinoid receptor agonist WIN 55,212-2 - Nallapaneni_2006_Toxicology_227_173
Author(s) : Nallapaneni A , Liu J , Karanth S , Pope C
Ref : Toxicology , 227 :173 , 2006
Abstract : Cannabinoids can reduce the pre-synaptic release of acetylcholine and other neurotransmitters in the mammalian brain through a retrograde signaling pathway. Organophosphorus insecticides elicit toxicity by inhibiting acetylcholinesterase and thereby increasing synaptic acetylcholine levels. Several studies suggest that some organophosphorus toxicants can potentially modify cannabinergic signaling by direct binding to cannabinoid receptors and inhibition of enzymes responsible for cannabinoid degradation (i.e., fatty acid amide hydrolase and monoacylglycerol lipase). We hypothesized that exposure to the cannabinoid receptor agonist WIN 55,212-2 (WIN) could alter the acute toxicity of the prototype anticholinesterase, paraoxon. In vitro, paraoxon inhibited hippocampal cholinesterase and fatty acid amide hydrolase activities, and displaced specific binding to the cannabinoid receptor ligand ([(3)H]CP 55,940) in a concentration-dependent manner. WIN (0.5, 1.5 or 5mg/kg/day) had a complex dose-related effect on locomotor activity when evaluated for 2h after either the first or last of seven daily exposures, and significantly decreased hippocampal CB1 binding following repeated dosing. Four hours after dosing, paraoxon (0.4 mg/kg, sc) elicited classical signs of cholinergic toxicity and significantly reduced hippocampal cholinesterase and fatty acid amide hydrolase activities as well as [(3)H]CP 55,940 binding. A single exposure to WIN (1.5 mg/kg) significantly reduced involuntary movements and SLUD signs following acute paraoxon exposure (0.4 and 0.6 mg/kg, sc). In contrast, when rats were challenged with paraoxon (0.4 mg/kg) after the seventh daily exposure to WIN (1.5mg/kg/day), involuntary movements were significantly increased at later timepoints, while SLUD signs were unaffected. These results suggest that acute and repeated exposure to cannabinoid agonists may differentially modify acute cholinergic toxicity, possibly through modulation of acetylcholine release and adaptation in cannabinergic signaling associated with repeated cannabinoid exposures.
ESTHER : Nallapaneni_2006_Toxicology_227_173
PubMedSearch : Nallapaneni_2006_Toxicology_227_173
PubMedID: 16956707

Title : Interactive toxicity of chlorpyrifos and parathion in neonatal rats: role of esterases in exposure sequence-dependent toxicity - Kacham_2006_Toxicol.Appl.Pharmacol_210_142
Author(s) : Kacham R , Karanth S , Baireddy P , Liu J , Pope C
Ref : Toxicol Appl Pharmacol , 210 :142 , 2006
Abstract : We previously reported that sequence of exposure to chlorpyrifos and parathion in adult rats can markedly influence toxic outcome. In the present study, we evaluated the interactive toxicity of chlorpyrifos (8 mg/kg, po) and parathion (0.5 mg/kg, po) in neonatal (7 days old) rats. Rats were exposed to the insecticides either concurrently or sequentially (separated by 4 h) and sacrificed at 4, 8, and 24 h after the first exposure for biochemical measurements (cholinesterase activity in brain, plasma, and diaphragm and carboxylesterase activity in plasma and liver). The concurrently-exposed group showed more cumulative lethality (15/24) than either of the sequential dosing groups. With sequential dosing, rats treated initially with chlorpyrifos prior to parathion (C/P) exhibited higher lethality (7/23) compared to those treated with parathion before chlorpyrifos (P/C; 1/24). At 8 h after initial dosing, brain cholinesterase inhibition was significantly greater in the C/P group (59%) compared to the P/C group (28%). Diaphragm and plasma cholinesterase activity also followed a relatively similar pattern of inhibition. Carboxylesterase inhibition in plasma and liver was relatively similar among the treatment groups across time-points. Similar sequence-dependent differences in brain cholinesterase inhibition were also noted with lower binary exposures to chlorpyrifos (2 mg/kg) and parathion (0.35 mg/kg). In vitro and ex vivo studies compared relative oxon detoxification of carboxylesterases (calcium-insensitive) and A-esterases (calcium-sensitive) in liver homogenates from untreated and insecticide pretreated rats. Using tissues from untreated rats, carboxylesterases detoxified both chlorpyrifos oxon and paraoxon, while A-esterases only detoxified chlorpyrifos oxon. With parathion pretreatment, A-esterases still detoxified chlorpyrifos oxon while liver from chlorpyrifos pretreated rats had little apparent effect on paraoxon. We conclude that while neonatal rats are less capable than adults at detoxifying many organophosphorus insecticides including chlorpyrifos and parathion, toxicant-selective differences in detoxification play a role in sequence-dependent toxicity in both neonatal and adult rats with these two insecticides.
ESTHER : Kacham_2006_Toxicol.Appl.Pharmacol_210_142
PubMedSearch : Kacham_2006_Toxicol.Appl.Pharmacol_210_142
PubMedID: 16260018

Title : Dietary modulation of parathion-induced neurotoxicity in adult and juvenile rats - Liu_2005_Toxicology_210_135
Author(s) : Liu J , Karanth S , Pope C
Ref : Toxicology , 210 :135 , 2005
Abstract : Previous studies indicated that dietary glucose (15% in drinking water) could markedly exacerbate the toxicity of parathion in adult rats. The present study evaluated the effect of consumption of the commonly used sweetener, high fructose corn syrup (HFCS), on parathion toxicity in adult and juvenile rats. Animals were given free access to either water or 15% HFCS in drinking water for a total of 10 days and challenged with parathion (6 or 18 mg/kg, s.c., for juveniles or adults, respectively) on the 4th day. Signs of cholinergic toxicity, body weight and chow/fluid intake were recorded daily. Acetylcholinesterase (AChE) activity and immunoreactivity (AChE-IR) in frontal cortex and diaphragm were measured at 2, 4, and 7 days after parathion. As HFCS was associated with significant reduction in chow intake, adult rats were also pair-fed to evaluate the effect of similar reduced chow intake alone on parathion toxicity. The results indicated that the cholinergic toxicity of parathion was significantly increased by HFCS feeding in both age groups. The excess sugar consumption, however, did not significantly affect parathion-induced AChE inhibition in either tissue or either age group. Enzyme immunoreactivity in frontal cortex was generally not affected in either age group while diaphragm AChE-IR was significantly reduced by parathion and HFCS alone in adult animals at 2 and 4 days timepoints, and more so by the combination of sugar feeding and parathion exposure in both age groups. Food restriction alone did not exacerbate parathion toxicity. While the mechanism(s) remains unclear, we conclude that voluntary consumption of the common sweetener HFCS can markedly amplify parathion acute toxicity in both juvenile and adult rats.
ESTHER : Liu_2005_Toxicology_210_135
PubMedSearch : Liu_2005_Toxicology_210_135
PubMedID: 15840427

Title : Interactive effects of paraoxon and pyridostigmine on blood-brain barrier integrity and cholinergic toxicity - Song_2004_Toxicol.Sci_78_241
Author(s) : Song X , Pope C , Murthy R , Shaikh J , Lal B , Bressler JP
Ref : Toxicol Sci , 78 :241 , 2004
Abstract : The effect of the organophosphorous insecticide paraoxon on the integrity of the blood-brain barrier (BBB) and permeability of pyridostigmine (PYR), a peripheral inhibitor of cholinesterase activity, was examined in Long Evans rats. The integrity of the BBB was examined by measuring the number of capillaries leaking horseradish peroxidase, which was injected into the heart. Treatment with paraoxon at 100 microg/kg, intramuscularly, resulted in a 3- to 4-fold increase in the number of leaky capillaries in young rats (25 to 30 days old) but not in older rats (90 days old). Interestingly, young rats treated with PYR (30 mg/kg, po) 50 min before treatment with paraoxon showed an inhibited effect of paraoxon on the BBB. Furthermore, no increase in the degree of inhibition of acetylcholinesterase activity was observed in young rats treated with PYR before paraoxon compared with young rats treated with paraoxon alone. Cholinergic toxicity, as assessed by changes in behavior, was not observed in young rats treated with paraoxon alone; but, slight signs of cholinergic toxicity were observed in rats treated with PYR. Young rats treated with both PYR and paraoxon did not exhibit more extensive signs of toxicity than rats treated with paraoxon alone or PYR alone. The results indicate that treatment with paraoxon can compromise BBB permeability at dosages that do not induce cholinergic toxicity, but only in young rats. Also, PYR pre-exposure appears to protect the BBB from the paraoxon-induced alterations.
ESTHER : Song_2004_Toxicol.Sci_78_241
PubMedSearch : Song_2004_Toxicol.Sci_78_241
PubMedID: 14976354

Title : Interactive toxicity of the organophosphorus insecticides chlorpyrifos and methyl parathion in adult rats - Karanth_2004_Toxicol.Appl.Pharmacol_196_183
Author(s) : Karanth S , Liu J , Olivier K, Jr. , Pope C
Ref : Toxicol Appl Pharmacol , 196 :183 , 2004
Abstract : The acute interactive toxicity following exposure to two common organophosphorus (OP) insecticides, chlorpyrifos (CPF) and methyl parathion (MPS), was investigated in adult male rats. Oral LD1 values were estimated by dose-response studies (CPF = 80 mg/kg; MPS = 4 mg/kg, in peanut oil, 1 ml/kg). Rats were treated with both toxicants (0.5 or 1 x LD1) either concurrently or sequentially, with 4-h intervals between dosing. Functional signs of toxicity (1-96 h) and cumulative lethality (96 h) were recorded. Rats treated with CPF (1 x LD1) did not show any signs of toxicity although MPS (1 x LD1) elicited slight to moderate signs (involuntary movements) within 1-2 h. Concurrent exposure (LD1 dosages of both CPF and MPS) caused slight signs of toxicity only apparent between 24 and 48 h after dosing. When rats were treated sequentially with MPS first followed by CPF 4 h later, slight signs of toxicity were noted between 6 and 24 h, whereas reversing the sequence resulted in 100% lethality within 1 h of the second dosage. Following exposure to lower dosages (0.5 x LD1), the CPF first group showed higher signs of cholinergic toxicity compared with MPS first or concurrent groups. Cholinesterase inhibition in plasma, diaphragm, and frontal cortex was generally higher in rats treated sequentially with CPF first than in those treated initially with MPS from 4 to 24 h after dosing. Plasma and liver carboxylesterase inhibition at 4 h was also significantly higher in the CPF first (62-90%) compared with MPS first (22-43%) group, while at 8 and 24 h, there was no significant difference between any of the treatment groups. ChE inhibition assays to evaluate in vitro hepatic detoxification of oxons indicated that carboxylesterase (CE)- and A-esterase-mediated pathways are markedly less important for methyl paraoxon (MPO) than chlorpyrifos oxon (CPO) detoxification. CPF pretreatment blocked hepatic detoxification of methyl paraoxon while MPS pretreatment had minimal effect on hepatic CPO detoxification ex vivo. These findings suggest that the sequence of exposure to two insecticides that elicit toxicity through a common mechanism can markedly influence the cumulative action at the target site (acetylcholinesterase, AChE) and consequent functional toxicity.
ESTHER : Karanth_2004_Toxicol.Appl.Pharmacol_196_183
PubMedSearch : Karanth_2004_Toxicol.Appl.Pharmacol_196_183
PubMedID: 15081265

Title : In vitro inhibition of blood cholinesterase activities from horse, cow, and rat by tetrachlorvinphos - Karanth_2003_Int.J.Toxicol_22_429
Author(s) : Karanth S , Pope C
Ref : Int J Toxicol , 22 :429 , 2003
Abstract : The organophosphorus insecticide tetrachlorvinphos (TCVP) is commonly used as a feed-through larvicide in many livestock species, including cattle and horses. Cholinesterase (ChE) activity in blood (generally plasma or whole blood) is often employed to assess organophosphorus insecticide intoxication in animals as well as humans. In many species, including horse and man, plasma contains predominantly butyrylcholinesterase whereas red blood cells in all species express exclusively acetylcholinesterase. To evalulate the comparative interaction of TCVP with blood ChEs in different species, we compared the in vitro sensitivity of ChE activity in plasma and erythrocytes from horse, cow, and rat. Horse plasma ChE was most sensitive (IC(50), 30 minutes, 30 degrees C = 97 nM), whereas horse erythrocyte ChE activity was least sensitive (IC(50) > 1 mM). In contrast, cow plasma ChE showed lower sensitivity (IC(50) = 784 microM) to inhibition by TCVP than erythrocyte ChE (IC(50) = 216 microM). Rat plasma and erythrocyte ChE activities had relatively similar sensitivity to TCVP (IC(50) = 54 microM and 78 microM, respectively). The results suggest that plasma and erythrocyte ChE from horse, cow, and rat show marked species- and blood fraction-dependent differences in sensitivity to TCVP. Knowledge of such differences in sensitivity of blood ChE activities to TCVP may be important in the clinical interpretation of intoxication with this pesticide across species.
ESTHER : Karanth_2003_Int.J.Toxicol_22_429
PubMedSearch : Karanth_2003_Int.J.Toxicol_22_429
PubMedID: 14680990

Title : Age-related effects of chlorpyrifos and parathion on acetylcholine synthesis in rat striatum - Karanth_2003_Neurotoxicol.Teratol_25_599
Author(s) : Karanth S , Pope C
Ref : Neurotoxicology & Teratology , 25 :599 , 2003
Abstract : We compared the in vivo effects of two organophosphorus (OP) insecticides, chlorpyrifos (CPF) and parathion (PS) on acetylcholine (ACh) synthesis in neonatal, juvenile and adult rats. Basal levels of ACh synthesis were highest in adult rats, intermediate in juveniles and lowest in neonates. Following high (maximum tolerated dosage) subcutaneous exposure to either insecticide, relatively similar degrees of cholinesterase inhibition were noted, but the time to peak reduction varied among the age groups. CPF had no effect on ACh synthesis in neonates, increased synthesis in juveniles and decreased synthesis in adults, but only in the low dose group. PS had more consistent effects on ACh synthesis, decreasing transmitter synthesis in neonates (24 h after dosing) but increasing synthesis in juveniles and adults at both 4 and 24 h after exposure. Selective changes in neurotransmitter synthesis may contribute to differential age-related toxicity of these agents.
ESTHER : Karanth_2003_Neurotoxicol.Teratol_25_599
PubMedSearch : Karanth_2003_Neurotoxicol.Teratol_25_599
PubMedID: 12972073

Title : In vitro effects of organophosphorus anticholinesterases on muscarinic receptor-mediated inhibition of acetylcholine release in rat striatum - Liu_2002_Toxicol.Appl.Pharmacol_178_102
Author(s) : Liu J , Chakraborti T , Pope C
Ref : Toxicol Appl Pharmacol , 178 :102 , 2002
Abstract : The aim of the present study was to evaluate the in vitro modulation of muscarinic autoreceptor function by the organophosphorus (OP) anticholinesterases chlorpyrifos oxon, paraoxon, and methyl paraoxon. Acetylcholine (ACh) release was studied by preloading slices from rat striatum with [3H]choline and depolarizing with potassium (20 mM) in perfusion buffer containing hemicholinium-3 (to prevent reuptake of radiolabeled choline). Under these conditions, chlorpyrifos oxon, paraoxon, and methyl paraoxon (0.1-10 microM) all reduced ACh release in a concentration-dependent manner. Addition of the carbamate acetylcholinesterase (AChE) inhibitor physostigmine (20 microM) to the perfusion buffer also decreased ACh release. When physostigmine was present, the three oxons had no additional effect on ACh release. Concentration-dependent inhibition of AChE activity in striatal slices perfused with chlorpyrifos oxon (0.1, 1, and 10 microM) suggested AChE inhibition was responsible for oxon-mediated alterations in ACh release. To differentiate between direct and indirect actions of the OP toxicants on muscarinic autoreceptors, we compared the effects of the oxons on ACh release under two conditions, i.e., tissues were perfused with buffer containing only hemicholinium-3 or with buffer containing hemicholinium-3, physostigmine, and the nonselective muscarinic receptor blocker atropine (100 nM). In the presence of only hemicholinium-3, concentration-dependent inhibition of ACh release was again noted for all oxons, similar to the effects of the muscarinic agonists carbachol and cis-dioxolane. In the presence of physostigmine and atropine, the relative potencies of all agents were markedly reduced. Interestingly, carbachol, cis-dioxolane, paraoxon, and methyl paraoxon all decreased ACh release as before, but chlorpyrifos oxon (100-300 microM) actually increased ACh release. Together, the results suggest that chlorpyrifos oxon, paraoxon, and methyl paraoxon can activate muscarinic autoreceptors indirectly through inhibition of AChE. Both paraoxon and methyl paraoxon also directly activate whereas chlorpyrifos oxon blocks muscarinic autoreceptor function. Qualitative differences in the direct actions of these oxons at this presynaptic regulatory site could contribute to differential toxicity with high-dose exposures.
ESTHER : Liu_2002_Toxicol.Appl.Pharmacol_178_102
PubMedSearch : Liu_2002_Toxicol.Appl.Pharmacol_178_102
PubMedID: 11814330

Title : Acute and Repeated Restraint Stress Have Little Effect on Pyridostigmine Toxicity or Brain Regional Cholinesterase Inhibition in Rats - Song_2002_Toxicol.Sci_69_157
Author(s) : Song X , Tian H , Bressler J , Pruett S , Pope C
Ref : Toxicol Sci , 69 :157 , 2002
Abstract : Pyridostigmine, a carbamate cholinesterase (ChE) inhibitor, has been used for decades in the treatment of the autoimmune disorder myasthenia gravis and was used prophylactically to protect soldiers from possible organophosphorus nerve agent exposures during the Persian Gulf War. Pyridostigmine is a charged, quaternary compound and thus would not be expected to easily pass the blood-brain barrier. Some studies have suggested, however, that stress may alter blood-brain barrier integrity and allow pyridostigmine to enter the brain. We evaluated the effects of acute and repeated restraint stress on functional signs of cholinergic toxicity (i.e., autonomic dysfunction and involuntary movements) and brain regional cholinesterase inhibition following either acute or repeated pyridostigmine exposures. The acute, oral maximum-tolerated dosage (MTD) of pyridostigmine was estimated at 30 mg/kg. Peak ChE inhibition in whole blood occurred from 0.5 to 4 h after MTD exposure, whereas minimal (<20%) brain ChE inhibition was noted. For acute restraint studies, rats were either (1) restrained for 90 min and then given pyridostigmine (30 mg/kg, po), (2) given pyridostigmine and immediately restrained for 60 min, or (3) restrained for 3 h, given pyridostigmine, and restrained for an additional 60 min. In all cases, rats were evaluated for cholinergic toxicity (SLUD signs and involuntary movements) and sacrificed 1 h after pyridostigmine treatment. Plasma corticosterone was significantly elevated immediately after a single 60-min session of acute restraint stress, but returned to control levels by 1 and 3 h later. Pyridostigmine-induced toxicity was not enhanced nor was brain ChE inhibition altered by acute restraint stress. Blood-brain barrier permeability, assessed by accumulation of horseradish peroxidase in brain regions following intracardiac injection, was not increased by restraint stress. For repeated restraint studies, rats were given pyridostigmine (0, 3, or 10 mg/kg/day) immediately prior to daily restraint (60 min) for 14 consecutive days. Plasma corticosterone was elevated at 1 and 7 days but not at 14 days. Pyridostigmine-treated rats in both dosage groups exhibited slight signs of toxicity for the first 3-5 days, after which cholinergic signs dissipated. Repeated restraint had little effect on functional signs of pyridostigmine toxicity, however. Whole blood and diaphragm ChE were markedly reduced 1 h after the last treatment, but stress had no influence on ChE inhibition in either peripheral or central tissues. The results suggest that acute and repeated restraint stress have little effect on pyridostigmine neurotoxicity or apparent entry of pyridostigmine into the brain.
ESTHER : Song_2002_Toxicol.Sci_69_157
PubMedSearch : Song_2002_Toxicol.Sci_69_157
PubMedID: 12215670

Title : Inhibition of forskolin-stimulated cAMP formation in vitro by paraoxon and chlorpyrifos oxon in cortical slices from neonatal, juvenile, and adult rats - Olivier_2001_J.Biochem.Mol.Toxicol_15_263
Author(s) : Olivier K, Jr. , Liu J , Pope C
Ref : J Biochem Mol Toxicol , 15 :263 , 2001
Abstract : Parathion (PS) and chlorpyrifos (CPF) are organophosphorus insecticides, which elicit toxicity following biotransformation to the potent acetylcholinesterase inhibitors, paraoxon (PO) and chlorpyrifos oxon (CPO). Both oxons have also been shown to interact directly with muscarinic receptors coupled to inhibition of adenylyl cyclase. Immature animals are more sensitive than adults to the acute toxicity of PS and CPF but little is known regarding possible age-related differences in interactions between these toxicants and muscarinic receptors. We compared the inhibition of forskolin-stimulated cAMP formation by PO and CPO (1 nM-1 mM) in vitro in brain slices from 7-, 21-, and 90-day-old rats to the effects of well-known muscarinic agonists, carbachol and oxotremorine (100 microM). Both agonists inhibited cAMP formation in tissues from all age groups and both were more effective in adult and juvenile (20-26% inhibition) than in neonatal (12-13% inhibition) tissues. Atropine (10 microM) completely blocked agonist-induced inhibition in all cases. PO maximally inhibited (37-46%) cAMP formation similarly in tissues from all age groups, but atropine blocked those effects only partially and only in tissues from 7-day-old rats. CPO similarly inhibited cAMP formation across age groups (27-38%), but ATR was partially effective in tissues from all three age groups. Both oxons were markedly more potent in tissues from younger animals. We conclude that PO and CPO can directly inhibit cAMP formation through muscarinic receptor-dependent and independent mechanisms and that the developing nervous system may be more sensitive to these noncholinesterase actions.
ESTHER : Olivier_2001_J.Biochem.Mol.Toxicol_15_263
PubMedSearch : Olivier_2001_J.Biochem.Mol.Toxicol_15_263
PubMedID: 11835623

Title : In Vivo Interaction between Chlorpyrifos and Parathion in Adult Rats: Sequence of Administration Can Markedly Influence Toxic Outcome - Karanth_2001_Toxicol.Appl.Pharmacol_177_247
Author(s) : Karanth S , Olivier K, Jr. , Liu J , Pope C
Ref : Toxicol Appl Pharmacol , 177 :247 , 2001
Abstract : Organophosphorus insecticides (OPs) generally act through a common mechanism of toxicity initiated by inhibition of acetylcholinesterase (AChE). We studied the in vivo interactive toxicity of two common OPs, chlorpyrifos (CPF) and parathion (PS), in adult male rats. Dose-response studies estimated the acute oral LD1 values for the two OPs (CPF = 80 mg/kg po; PS = 4 mg/kg po) and these dosages or relative proportions were used to evaluate interactive toxicity. Three treatment strategies were evaluated: CPF followed by PS 4 h later (CPF-1st), PS followed by CPF 4 h later (PS-1st), and simultaneous (concurrent) exposures. Using LD1 dosages, rats in the CPF-1st and concurrent groups exhibited more cholinergic toxicity (i.e., salivation, lacrimation, urination, and diarrhea signs and involuntary movements) and higher lethality (7/8 and 6/8, respectively, beginning 1 h after PS) than those in the PS-1st group (2/8 lethality, beginning 3 days after CPF). Sequential exposures to lower dosages (CPF vs PS: 60 vs 3 mg/kg; 40 vs 2 mg/kg) led to more extensive neurotoxicity in the CPF-1st group compared to the other groups. Following lower dosages (40 vs 2 mg/kg), brain ChE inhibition was more extensive in the CPF-1st group at all time points (64-85%) and the concurrent group at 4 and 24 h after exposure (46-83%) compared to rats receiving PS first (7-48%). No differences were noted however, in plasma (71-93% inhibition) or liver (72-81%) cholinesterase activities nor were there group-related differences in plasma (50-60% inhibition) or liver (>85% inhibition) carboxylesterase activities. Incubation of liver samples with oxons in the presence or absence of calcium (i.e., 2 mM CaCl(2) or EGTA) prior to addition of ChE (striatal sample) substantially blocked ChE inhibition by CPO (IC50: without liver = 4 nM; liver + calcium = 279 nM; liver + EGTA = 48 nM) but had lesser effects on PO-mediated inhibition (IC50: without liver = 17 nM; liver + EGTA = 56 nM; liver + calcium = 57 nM). Liver homogenate from animals preexposed to PS substantially decreased ChE inhibition by CPO when calcium was included (IC50: +EGTA = 8 nM; +calcium = 225 nM), but liver homogenate from animals preexposed to CPF was ineffective at blocking PO-induced inhibition (IC50: +EGTA = 16 nM; +calcium = 16 nM). We conclude that prior inhibition of carboxylesterase activity impacts toxicity of subsequent exposure to PS more than CPF because of more active detoxification of CPO by A-esterase. Together, these findings indicate that interactive toxicity from combined exposures to two OP insecticides can be markedly influenced by the sequence of administration.
ESTHER : Karanth_2001_Toxicol.Appl.Pharmacol_177_247
PubMedSearch : Karanth_2001_Toxicol.Appl.Pharmacol_177_247
PubMedID: 11749124

Title : Developmental changes in carbachol-stimulated inositolphosphate release in pigmented rat retina - Tandon_1993_Curr.Eye.Res_12_439
Author(s) : Tandon P , Pope C , Padilla S , Tilson HA , Harry GJ
Ref : Current Eye Research , 12 :439 , 1993
Abstract : Carbachol-stimulated release of inositolphosphates (IP) was studied in the whole retina from Long-Evans rats of different ages (day 5, 10, 15, 20, adult) following in vitro incorporation of [3H]myo-inositol. Unlike the albino rat retina, the pigmented retina was highly light-sensitive, making it necessary to dark adapt the animals and perform retinal dissections under low illumination to prevent light-induced IP release. Retinae from postnatal day 10 rats showed the highest amount of carbachol-stimulated IP released. This response to carbachol decreased with age until postnatal day 20 when it reached adult levels. The pigmented rat retina showed a sharp fall in the degree of carbachol (1 mM)-stimulated IP released at the time of eye-opening (450% above basal in retinae from 10 day old animals, as compared to 230% above basal in 15 day old retinae). Basal release of IP was not altered in the retina during development. Muscarinic cholinergic receptor density was, however, found to increase 5 fold with age, reaching adult levels by PND 20. Retinal weight and protein per retina also increased (four fold) from day 5 to adult; however, the in vitro incorporation of [3H]myo-inositol into phosphoinositides (calculated as per mg protein) did not change during development. Thus, in animals prior to eye opening, a much higher proportion of phosphoinositides appears to be hydrolyzed upon muscarinic receptor stimulation. During retinal development a change in sensitivity to the agonist-sensitive pool(s) of phosphoinositides may occur and/or there may be alterations in the efficacy of receptor coupling to the second messenger system resulting in the disassociation observed between the drastic increase in receptor number and the apparent decrease in receptor-stimulated release of IP.
ESTHER : Tandon_1993_Curr.Eye.Res_12_439
PubMedSearch : Tandon_1993_Curr.Eye.Res_12_439
PubMedID: 8344068

Title : Murine susceptibility to organophosphorus-induced delayed neuropathy (OPIDN) - Veronesi_1991_Toxicol.Appl.Pharmacol_107_311
Author(s) : Veronesi B , Padilla S , Blackmon K , Pope C
Ref : Toxicol Appl Pharmacol , 107 :311 , 1991
Abstract : This study reports that CD-1 strain mice are neuropathologically and biochemically responsive to acute doses of tri-ortho-cresyl phosphate (TOCP). Young (25-30 g) male and female animals were exposed (po) to a single dose of TOCP (580-3480 mg/kg) and sampled for neurotoxic esterase (NTE) activity at 24 and 44 hr postexposure and for neuropathic damage 14 days later. Biochemically, high intragroup variability existed at the lower doses, and at higher levels of TOCP exposure (i.e., greater than or equal to 1160 mg/kg), mean brain NTE inhibition never exceeded 68%. Hen and mouse brain NTE activity, assayed in vitro for sensitivity to inhibition by tolyl saligenin phosphate (TSP), the active neurotoxic metabolite of TOCP, showed similar IC50 values. Histologically, highly variable spinal cord damage was recorded throughout treatment groups and mean damage scores followed a dose-response pattern with no apparent correlation to threshold (i.e., greater than or equal to 65%) inhibition of brain NTE activity. Topographically, axonal degeneration in the mouse spinal cord predominated in the lateral and ventral columns of the upper cervical cord. Unlike the rat, which displays degeneration in the upper cervical cord's dorsal columns (i.e., gracilis fasciculus) in response to TOCP intoxication, treated mice showed minimal damage to this tract. To examine this discrepancy further, ultrastructural morphometric analysis of axon diameters in the cervical cord was performed in control mice and rats. These results indicated that in both species, the largest diameter (greater than or equal to 4 microns) axons are housed in the ventral columns of the cervical spinal cord, suggesting that axon length and diameter may not be the only criteria underlying fiber tract vulnerability in OPIDN.
ESTHER : Veronesi_1991_Toxicol.Appl.Pharmacol_107_311
PubMedSearch : Veronesi_1991_Toxicol.Appl.Pharmacol_107_311
PubMedID: 1994513