Interactive toxicity of the organophosphorus insecticides chlorpyrifos and methyl parathion in adult rats

Comparative valuation of the chlorpyrifos, acetamiprid, and lambda-cyhalothrin toxicity and their hematological and histopathological consequences in pigeons

Globally agrochemicals are widely used in the agricultural sectors, posing potential eco-toxicological risks and disrupting various lifeforms including birds. Thus, the current work was conducted to compare the acute toxic impacts of pesticides (e.g., chlorpyrifos, acetamiprid, and lambda-cyhalothrin) on the pigeon's health. In total 50 adult pigeons were purchased from a local market where these pigeons were fed on pollution-free food. Post adaptation period (15 days), the pigeons were arbitrarily separated into five distinct groups after having been identified in this manner by chance (each group containing 10 pigeons). Control group (group 1) was not treated with any pesticide while the remaining groups (groups 2, 3, and 4) were treated with 0.25-mg/kg body weight of chlorpyrifos, acetamiprid, lambda-cyhalothrin, and a mixture of all three pesticides (group 5), respectively. After 36 days of exposure, the groups that had been exposed to the pesticide showed a significant (p < 0.05) increase in both the total number of platelets and the number of white blood cells (WBCs), in comparison to the control group. On the other hand, the groups that were exposed to the insecticides had significantly lower levels of red blood cells (RBCs), hemoglobin (Hb), and packed cell volume (PCV) (p < 0.05). The value of mean corpuscular volume (MCV) was significantly (p < 0.05) reduced in acetamiprid-exposed group, while a significant increase was observed in other pesticide-exposed groups. Obvious histopathological changes were observed in the tissues of control group and no such changes were reported by control group. Necrosis, pyknosis, lymphocyte infiltration, congestion of blood, dissolution of plasma membrane, and vacuolation were observed in the livers of pesticide-treated pigeons. The intestinal study showed the formation of goblet cells, villi rupturing, degeneration of serosa, necrosis, and pyknosis in treated groups. Renal alterations, dilation of renal tubules, reduction of glomerulus tissue, and edema were observed. This study manifests that the uncontrolled use of pesticides impairs ecosystems and poses a substantial health risk to wildlife and ultimately to human.

Elucidating pesticide sensitivity of two endogeic earthworm species through the interplay between esterases and glutathione S-transferases

Earthworms are common organisms in soil toxicity-testing framework, and endogeic species are currently recommended due to their ecological role in agroecosystem. However, little is known on their pesticide metabolic capacities. We firstly compared the baseline activity of B-esterases and glutathione-S-transferase in Allolobophora chlorotica and Aporrectodea caliginosa. Secondly, vulnerability of these species to pesticide exposure was assessed by in vitro trials using the organophosphate (OP) chlorpyrifos-ethyl-oxon (CPOx) and ethyl-paraoxon (POx), and by short-term (7 days) in vivo metabolic responses in soil contaminated with pesticides. Among B-esterases, acetylcholinesterase (AChE) activity was abundant in the microsomal fraction (80% and 70% of total activity for A. caliginosa and A. chlorotica, respectively). Carboxylesterase (CbE) activities were measured using three substrates to examine species differences in isoenzyme and sensitivity to both in vitro and in vivo exposure. CbEs were mainly found in the cytosolic fraction (80% and 60% for A. caliginosa and A. chlorotica respectively). GST was exclusively found in the soluble fraction for both species. Both OPs inhibited B-esterases in a concentration-dependent manner. In vitro trials revealed a pesticide-specific response, being A. chlorotica AChE more sensitive to CPOx compared to POx. CbE activity was inhibited at the same extent in both species. The 7-d exposure showed A. chlorotica less sensitive to both OPs, which contrasted with outcomes from in vitro experiments. This non-related functional between both approaches for assessing pesticide toxicity suggests that other mechanisms linked with in vivo OP bioactivation and excretion could have a significant role in the OP toxicity in endogeic earthworms.

Monoclonal antibodies to fetal bovine serum acetylcholinesterase distinguish between acetylcholinesterases from ruminant and non-ruminant species

Two types of cholinesterases (ChEs) are present in mammalian blood and tissues: acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). While AChE regulates neurotransmission by hydrolyzing acetylcholine at the postsynaptic membranes and neuromuscular junctions, BChE in plasma has been suggested to be involved in detoxifying toxic compounds. This study was undertaken to establish the identity of circulating ChE activity in plasmas from domestic animals (bovine, ovine, caprine, porcine and equine) by assessing sensitivity to AChE-specific inhibitors (BW284c51 and edrophonium) and BChE-specific inhibitors (dibucaine, ethopropazine and Iso-OMPA) as well as binding to anti-FBS AChE monoclonal antibodies (MAbs). Based on the inhibition of ChE activity by ChE-specific inhibitors, it was determined that bovine, ovine and caprine plasma predominantly contain AChE, while porcine and equine plasma contain BChE. Three of the anti-FBS AChE MAbs, 4E5, 5E8 and 6H9, inhibited 85-98% of enzyme activity in bovine, ovine and caprine plasma, confirming that the esterase in these plasmas was AChE. These MAbs did not bind to purified recombinant human or mouse AChE, demonstrating that these MAbs were specific for AChEs from ruminant species. These MAbs did not inhibit the activity of purified human BChE, or ChE activity in porcine and equine plasma, confirming that the ChE in these plasmas was BChE. Taken together, these results demonstrate that anti-FBS AChE MAbs can serve as useful tools for distinguishing between AChEs from ruminant and non-ruminant species and BChEs.

Toxicokinetic and toxicodynamic studies of carbaryl alone or in binary mixtures with azinphos methyl in the freshwater gastropod Planorbarius corneus

Carbamate insecticides such as carbaryl and organophosphates such as azinphos-methyl share the ability to inhibit the activity of B-esterases. This study aimed to (1) assess the inhibitory effects of carbaryl on B-esterase activity in soft tissues and hemolymph of Planorbarius corneus; (2) establish whether binary mixtures of carbaryl and azinphos-methyl depart or not from a model of concentration addition on the inhibition of cholinesterase activity; (3) determine the bioconcentration and elimination of the pesticides. The results showed that exposure of gastropods to increasing concentrations of carbaryl (0.1-5 mg L^-1) for 48 h inhibited cholinesterase activity in a concentration-dependent manner, with an EC₅₀ of 1.4 ± 0.3 mg L^-1 and 1.2 ± 0.1 mg L^-1 for soft tissue and hemolymph, respectively. Carboxylesterase activity, measured with the substrates p-nitrophenyl butyrate and p-nitrophenyl acetate, was between 2.3 and 25 times more sensitive to carbaryl inhibition than cholinesterase activity. Binary mixtures corresponding to 0.5 EC₅₀ carbaryl + 0.5 EC₅₀ azinphos-methyl and 0.75 EC₅₀ carbaryl + 0.75 EC₅₀ azinphos-methyl produced inhibitions of cholinesterase activity similar to those of individual pesticides, following a model of concentration addition. Bioconcentration was analyzed using a one-compartment model. The absorption kinetics (k₁) for both pesticides alone (1.4 mg L^-1 of carbaryl or 1.8 mg L^-1 of azinphos-methyl) or mixed (1.4 mg L^-1 of carbaryl + 1.8 mg L^-1 of azinphos-methyl) were similar. The elimination kinetics ratio (k₂) estimated for the pesticides alone or in the mixtures showed that carbaryl was eliminated 3.5 times faster than azinphos-methyl. These results suggest that exposure of Planorbarius corneus to binary mixtures of carbaryl and azinphos-methyl for 48 h follow a concentration addition model on inhibition of cholinesterase activity and that the pesticide mixtures do not change the toxicokinetic parameters of the parent compounds.

Betanin reduces organophosphate induced cytotoxicity in primary hepatocyte via an anti-oxidative and mitochondrial dependent pathway

Organophosphates (OP) are potent pesticide commonly utilized in agricultural and domestic use. However, plentitude of data represent their side effects in different body tissues. We attempted to study whether betanin (a natural pigment) is able to mitigate some OPs-induced hepatotoxicity in primary rat hepatocytes. Cell viability, lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) formation, lipid peroxidation (LPO), glutathione (GSH) depletion and mitochondrial depolarization were tested as toxicity markers. The outcomes revealed that betanin (25μM) significantly increased cell viability, plummeted ROS formation and LPO, restored cellular GSH reservoirs and protected mitochondria after chlorpyrifos (CPF) (300μM), diazinon (DZN) (600μM) and dichlrovos (DDVP) (400μM) treatment. Taken together, all data suggests the potential protective role of betanin in OPs-induced hepatotoxicity in which the mechanism appears to be inhibition of ROS formation and mitochondrial protection.

Metabonomic analysis of quercetin against the toxicity of chronic exposure to a mixture of four organophosphate pesticides in rat plasma

1. A metabonomics approach was performed to investigate the effect of quercetin on the toxicity of chronic exposure to a mixture of four organophosphate pesticides (OPs) at their corresponding no-observed-adverse-effect level (NOAEL). The rats were divided into six groups (n = 10/group): control, two different doses of quercetin, OPs mixture and different doses of quercetin plus OPs mixture-treated groups. 2. Nine metabolites, including two quercetin metabolites and seven endogenous metabolites were identified in plasma. The intensities of metabolites significantly changed in the OP mixture-treated group compared with the control group (p < 0.01), such as lysoPE (16:0/0:0), lysoPC (17:0/0:0), lysoPC (15:0/0:0) and 4-pyridoxic acid, significantly increased; by contrast, the intensities of arachidonic acid and citric acid significantly decreased. Anomalous intensity changes in aforementioned metabolites were alleviated in the OP mixture plus 50 mg/kgċbw/d quercetin-treated group compared with the OP mixture-treated group (p < 0.05). 3. The results indicated that quercetin elicited partial protective effects against the toxicity induced by a mixture of OPs, which include regulation of lipid metabolism, improvement of tricarboxylic acid (TCA) cycle disorders, enhancement of antioxidant defence system to protect the liver.

Subchronic neurotoxicity of chlorpyrifos, carbaryl, and their combination in rats

Anticholinesterase pesticides have been widely used in agricultural and domestic settings and can be detected in the environment after long-term use. Although the acute toxic effects of chlorpyrifos and carbaryl have been well described, little is known about the chronic toxicity of the pesticides mixture. To investigate their chronic neurotoxicity, Wistar rats were exposed to chlorpyrifos, carbaryl, and their mixture (MIX) for 90 consecutive days. The activities of serum cholinesterase (ChE) as well as acetylcholinesterase (AChE) and neuropathy target esterase (NTE) in nerve tissues were determined. Furthermore, the histopathological examination was carried out. The results showed that ChE activity significantly decreased in all treated rats except the rats treated with low dose carbaryl. Treatment with middle- and high-dose chlorpyrifos and MIX in rats significantly inhibited AChE activity in the central nervous tissues, whereas treatment with carbaryl alone did not. In sciatic nerve, AChE activity was significantly inhibited by high-dose carbaryl and MIX, but not by chlorpyrifos alone. No significant NTE inhibition was observed in all treatment groups. Histopathological examination revealed that both chlorpyrifos and MIX treatment induced hippocampal damage. However, no obvious hippocampal damage was found in carbaryl-treated rats. Carbaryl and MIX, but not chlorpyrifos alone, induced pathological damage of sciatic nerve. Taken together, all of the results indicated that chlorpyrifos and carbaryl have different toxicological target tissues in nervous system and showed corresponding effects in the nervous tissues, which may reflect the different sensitivity of central and peripheral nervous tissues to different pesticides individually and in combination.

Chlorpyrifos induced testicular damage in rats: ameliorative effect of glutathione antioxidant

This study investigated the induction of oxidative stress in the testes of adult rats exposed to chlorpyrifos (CPF). CPF was administered orally, in a dose of 30 mg/kg body weight to male rats for 90 days, twice weekly. Coadministration of water-soluble nonenzymatic antioxidant glutathione (GSH) was performed in a dose of 100 mg/kg body weight, orally, for the same period. Another two groups of male rats were administered GSH and corn oil, respectively. The activities of superoxide dismutase and GSH reductase were decreased while the levels of lipid peroxidation were increased in the testicular tissues of the exposed animals. Testosterone level in the serum was significantly decreased. A decrease in the histochemical determination of testicular alkaline phosphatase was observed in CPF-treated rats. A significant decrease in all stages of spermatogenesis in the seminiferous tubules was recorded in the exposed animals. Coadministration of GSH restored these parameters.

Clinico-hematological and tissue changes induced by butachlor in male Japanese quail (Coturnix japonica)

The present experiment was executed to determine the pathological effects induced by concurrent feeding of butachlor (chloroacetanilide herbicide) in male Japanese quail. For this purpose mature male quail about 4-5weeks of age were procured from the local market and randomly divided into six equal groups (A-F). Butachlor was mixed in corn oil and administered orally for 30days using crop tube. Four birds from each group were killed at day 10, 20 and 30 of the experiment and blood was collected with and without anticoagulant. The birds in groups (A-D) did not reveal any clinical and behavioral alterations. Clinical signs like watery droppings, dullness, ruffled feather, depression, decrease frequency of crowing, mounting with pen mates and foam production were observed. Maximum intensity of these clinical signs and behavioral alterations were observed in group F throughout the experiment. Significant lower values of erythrocytes, hematocrit percent and hemoglobin were recorded. Significantly increased numbers of erythrocytes with micronuclei, lobed and notched nuclei were observed. Histopathologically, enlarged intertubular space, fewer numbers of round spermatids, necrotic spermatids and admixture of dead spermatids were observed in testes. The results revealed significant increase in serum lactate dehydrogenase (LDH), aspartate transaminase (AST), alanine transaminase (ALT) and urea concentrations. The results of present experimental study indicated that butachlor induces hematobiochemical and testicular changes in birds.

Emblica officinalis Garten fruits extract ameliorates reproductive injury and oxidative testicular toxicity induced by chlorpyrifos in male rats

Organophosphate pesticides have destroying properties on male reproduction and chlorpyrifos adversely affects the male reproductive system. Emblica offcinalis Garten plays a vital role to challenge many diseases in human body. We investigated the induction of oxidative stress in the male reproductive system of adult rats (Wistar Strain) exposed to widely used organophosphate pesticide, Chlorpyrifos, and tried to establish the ameliorative properties of Emblica officinalis Garten with respect to reproductive reconstruction in them. Rats were divided into 2 groups, control group and experimental group, and the experimental group was divided into 3 groups (G1-G3). All the groups had 5 rats each. Control group received water, experimental group, G1, received 20 mg/kg bw/day Emblica officinalis Garten, G2 received 12 mg/kg bw/day chlorpyrifos and G3 received 12 mg chlorpyrifos with 20 mg Emblica officinalis Garten /kg bw/day. Treatment was done orally from 30 days. Thereafter body weight, male reproductive organs weight, sperm count, sperm morphology, ACP, ALP, total protein, uric acid and testis and serum testosterone level were determined using standard methods. The changes recorded are indicative of infertility in male rats because of chlorpyrifos exposure. When the subjects were treated with Emblica officinalis Garten in conjunction with chlorpyrifos, these parameters exhibited recovery and when treated with Emblica officinalis Garten alone, these parameters were more or less near to the control group. This highlights the debilitating effect of chlorpyrifos and scavenging property of Emblica officinalis Garten.

Cholinesterase and carboxylesterase inhibition in Planorbarius corneus exposed to binary mixtures of azinphos-methyl and chlorpyrifos

Though pesticide mixtures are commonly encountered in fresh water systems, the knowledge of their effects on non-target aquatic species is scarce. The present investigation was undertaken to explore the in vivo inhibition of the freshwater gastropod snail Planorbarius corneus cholinesterase (ChE) and carboxylesterases (CES) activities by the organophosphorus pesticides azinphos-methyl (AZM) and chlorpyrifos (CPF). To this end, snails were exposed for 48 h to different concentrations of AZM and CPF in single-chemical and binary-mixture studies, and ChE and CES activities were measured in the whole soft body tissues and hemolymph. ChE activity was measured with acetylthiocholine as substrate and CES activity was measured with four substrates: p-nitrophenyl acetate, p-nitrophenyl butyrate, 1- and 2-naphthyl acetate. Single-chemical experiments showed that CPF was a more potent inhibitor of ChE activity than AZM (350 and 27 times for the whole soft tissue and hemolymph, respectively). CES were 15 times more sensitive than ChE when the activities were measured in the whole soft tissue of the animals exposed to AZM. Based on a default assumption of concentration addition, P. corneus snails were exposed to mixtures of AZM+CPF designed to yield predicted soft tissue ChE inhibitions of 31% (mixture 1), 50% (mixture 2) and 61% (mixture 3). Results showed that ChE inhibition produced by mixture 1 followed a model of concentration addition. In contrast, the other mixtures showed synergism, both in whole soft tissue and hemolymph. In addition, results obtained when the snails were exposed sequentially to the pesticides showed that the sequence AZM/CPF produced at 48 h a higher ChE inhibition than the sequence CPF/CPF. A range of metabolic pathways and responses associated with bioactivation or detoxification may play important roles in organophosphorus interactions. In particular, the data presented in the present study indicate that CES enzymes would be important factors in determining the effects of the mixtures of OPs on P. corneus ChE activity.

The effect of mixtures of organophosphate and carbamate pesticides on acetylcholinesterase and application of chemometrics to identify pesticides in mixtures

Organophosphate (OP) and carbamate (CP) pesticides act by the inhibition of acetylcholinesterase (AChE). This enables the use of this enzyme for the detection of these pesticides in the environment. While many studies have looked at the effect of single pesticides on AChE, the effect of mixtures of pesticides still requires extensive investigation. This is important to evaluate the cumulative risk in the case of simultaneous exposure to multiple pesticides. Therefore we examined the effect of five different pesticides (carbaryl, carbofuran, parathion, demeton-S-methyl, and aldicarb) on AChE activity to determine whether combinations had an additive, synergistic, or antagonistic inhibitory effect. Results indicated that the mixtures had an additive inhibitory effect on AChE activity. The data from the assays of the mixtures were used to develop and train an artificial neural network (ANN) which was then utilised successfully for the identification of pesticides and their concentrations in mixtures. This study is significant because it evaluated mixtures of OPs and CPs where previous studies focused on either OPs or CPs. Previous studies have only examined up to three pesticides while this study evaluated mixtures of five pesticides simultaneously. This is also the first study where an ANN was able to utilise data from the inhibition of a single enzyme to differentiate five different pesticides and their concentrations from mixtures.

Sub-chronic exposure to chlorpyrifos induces hematological, metabolic disorders and oxidative stress in rat: attenuation by glutathione

The current work aimed to investigate the different toxic effects of chlorpyrifos (CPF) in subchronic exposure. Two groups of Sprague-Dawley male rats were exposed to CPF alone in a dose of 30 mg/kg body weight, or CPF dose as previous plus glutathione (GSH) in a dose of 100 mg/kg body weight, for 90 days, twice weekly, orally. Another two groups of rat were given corn oil (control) or GSH. There is a significant decrease in hemoglobin concentration, haematocrit percentage, thrombocytic indices, total protein and albumin levels in CPF-exposed group. CPF induced hyperglycemia and significant increase in total cholesterol, but a significant decrease in triglyceride levels was obtained. A significant increase in the levels of lipid peroxidation was obtained while a significant decrease of the total antioxidant was recorded. The decrease in glycogen content and some histopathological changes were observed in liver after CPF exposure. Furthermore, co-administration of GSH can restore some of these alterations.

Alteration of leaf metabolism in Bt-transgenic rice (Oryza sativa L.) and its wild type under insecticide stress

Insecticide is always used to control the damage from pests, while the potential influence on plants is rarely known. Time-course metabolic changes of wild and Bacillus thuringiensis (Bt) transgenic rice (Oryza sativa L.) plants after insecticide treatment were investigated by using gas chromatography-mass spectrometry (GC-MS). A combined statistical strategy of 2-way ANOVA and multivariate analyses (principal component analysis and hierarchal cluster analysis) was performed to find the stress-associated effects. The results reveal that a wide range of metabolites were dynamically varied in both varieties as a response to insecticide, in multiple metabolic pathways, such as biosynthesis and metabolism of amino acids, carbohydrates, fatty acids, TCA cycle, and the shikimate/phenylpropanoid pathway, and most of the changes were correlated with the exposure time and dependent on the variety. A set of stress defenses were activated, including phytohormone signaling pathway, antioxidant defense system, shikimate-mediated secondary metabolism, and so on. In particular, insecticide led to much stronger regulations of signaling molecules (salicylate and the precursor of jasmonate) and antioxidants (α-tocopherol and dehydroascorbate/ascorbate) in Bt-transgenic variety at the early stage. Our results demonstrated that the Bt-transgenic rice had a more acute and drastic response to insecticide stress than its non-transgenic counterpart in antioxidant system and signaling regulation.

Binary mixtures of azinphos-methyl oxon and chlorpyrifos oxon produce in vitro synergistic cholinesterase inhibition in Planorbarius corneus

In this study, the cholinesterase (ChE) and carboxylesterase (CES) activities present in whole organism homogenates from Planorbarius corneus and their in vitro sensitivity to organophosphorous (OP) pesticides were studied. Firstly, a characterization of ChE and CES activities using different substrates and selective inhibitors was performed. Secondly, the effects of azinphos-methyl oxon (AZM-oxon) and chlorpyrifos oxon (CPF-oxon), the active oxygen analogs of the OP insecticides AZM and CPF, on ChE and CES activities were evaluated. Finally, it was analyzed whether binary mixtures of the pesticide oxons cause additive, antagonistic or synergistic ChE inhibition in P. corneus homogenates. The results showed that the extracts of P. corneus preferentially hydrolyzed acetylthiocholine (AcSCh) over propionylthiocholine (PrSCh) and butyrylthiocholine (BuSCh). Besides, AcSCh hydrolyzing activity was inhibited by low concentrations of BW284c51, a selective inhibitor of AChE activity, and also by high concentrations of substrate. These facts suggest the presence of a typical AChE activity in this species. However, the different dose-response curves observed with BW284c51 when using PrSCh or BuSCh instead of AcSCh suggest the presence of at least another ChE activity. This would probably correspond to an atypical BuChE. Regarding CES activity, the highest specific activity was obtained when using 2-naphthyl acetate (2-NA), followed by 1-naphthyl acetate (1-NA); p-nitrophenyl acetate (p-NPA), and p-nitrophenyl butyrate (p-NPB). The comparison of the IC(50) values revealed that, regardless of the substrate used, CES activity was approximately one order of magnitude more sensitive to AZM-oxon than ChE activity. Although ChE activity was very sensitive to CPF-oxon, CES activity measured with 1-NA, 2-NA, and p-NPA was poorly inhibited by this pesticide. In contrast, CES activity measured with p-NPB was equally sensitive to CPF-oxon than ChE activity. Several specific binary combinations of AZM-oxon and CPF-oxon caused a synergistic effect on the ChE inhibition in P. corneus homogenates. The degree of synergism tended to increase as the ratio of AZM-oxon to CPF-oxon decreased. These results suggest that synergism is likely to occur in P. corneus snails exposed in vivo to binary mixtures of the OPs AZM and CPF.

Protective effects of vitamins C and E against hepatotoxicity induced by methyl parathion in rats

Male rats were given vitamins C+E, methyl parathion, or both daily via gavage for seven weeks. Body weight was decreased while liver weight increased significantly at the end of fourth and seventh weeks in the methyl parathion- and methyl parathion plus vitamin-treated groups. Serum total protein, albumin, triglyceride, low density lipoprotein-cholesterol (VLDL-cholesterol) levels decreased, and serum alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyl-transferase (GGT), lactate dehydrogenase (LDH), and total cholesterol levels increased significantly in the methyl parathion- and the methyl parathion plus vitamin-treated rats. There was a statistically significant difference for all biochemical parameters when the methyl parathion plus vitamin-treated group was compared with methyl parathion-treated group. In electron microscopic investigation, cytopathological alterations were observed in hepatocytes of the methyl parathion- and the methyl parathion plus vitamin-treated rats. As a result, methyl parathion-induced hepatotoxicity is reduced by vitamins C+E, but vitamins C+E did not provide complete protection.

Review on the use of enzymes for the detection of organochlorine, organophosphate and carbamate pesticides in the environment

Pesticides are released intentionally into the environment and, through various processes, contaminate the environment. Three of the main classes of pesticides that pose a serious problem are organochlorines, organophosphates and carbamates. While pesticides are associated with many health effects, there is a lack of monitoring data on these contaminants. Traditional chromatographic methods are effective for the analysis of pesticides in the environment, but have limitations and prevent adequate monitoring. Enzymatic methods have been promoted for many years as an alternative method of detection of these pesticides. The main enzymes that have been utilised in this regard have been acetylcholinesterase, butyrylcholinesterase, alkaline phosphatase, organophosphorus hydrolase and tyrosinase. The enzymatic methods are based on the activation or inhibition of the enzyme by a pesticide which is proportional to the concentration of the pesticide. Research on enzymatic methods of detection, as well as some of the problems and challenges associated with these methods, is extensively discussed in this review. These methods can serve as a tool for screening large samples which can be followed up with the more traditional chromatographic methods of analysis.

Investigation of in vitro effects of ethephon and chlorpyrifos, either alone or in combination, on rat intestinal muscle contraction

A range of pesticides is widely used in pest management and the chances of exposure to multiple organophosphorus (OP) compounds simultaneously are high, especially from dietary and other sources. Although health hazards of individual OP insecticides have been relatively well characterized, there is lesser information on the interactive toxicity of multiple OP insecticides. The aim of this study is to elicit the possible interactions in case combined exposure of an OP pesticide chlorpyrifos (CPF) and a plant growth regulator ethephon (ETF) which are used worldwide. The ileum segments of 3 months old Wistar Albino male rats were used in isolated organ bath containing Tyrode solution. ETF and CPF were incubated (10(-7) M concentration) separately or in combination with each other to ileum and their effects on acetylcholine-induced contractions were studied. The data obtained from this study show that, single and combined exposure to the agents caused agonistic interactions with regard to potency of ACh whereas they caused a decrease on E(max) value of ACh. These findings suggest that exposure to these agents which have direct and indirect cholinergic effects, may cause developing clinical responses with small doses and earlier but the extent of toxicity will be lower.

Toxicodynamic analysis of the combined cholinesterase inhibition by paraoxon and methamidophos in human whole blood

Theoretical work has shown that the isobole method is not generally valid as a method for testing the absence or presence of interaction (in the biochemical sense) between chemicals. The present study illustrates how interaction can be tested by fitting a toxicodynamic model to the results of a mixture experiment. The inhibition of cholinesterases (ChE) in human whole blood by various dose combinations of paraoxon and methamidophos was measured in vitro. A toxicodynamic model describing the processes related to both OPs in inhibiting AChE activity was developed, and fit to the observed activities. This model, not containing any interaction between the two OPs, described the results from the mixture experiment well, and it was concluded that the OPs did not interact in the whole blood samples. While this approach of toxicodynamic modeling is the most appropriate method for predicting combined effects, it is not rapidly applicable. Therefore, we illustrate how toxicodynamic modeling can be used to explore under which conditions dose addition would give an acceptable approximation of the combined effects from various chemicals. In the specific case of paraoxon and methamidophos in whole blood samples, it was found that dose addition gave a reasonably accurate prediction of the combined effects, despite considerable difference in some of their rate constants, and mildly non-parallel dose-response curves. Other possibilities of validating dose-addition using toxicodynamic modeling are briefly discussed.

Methylmercury at low doses modulates the toxicity of PCB153 on PC12 neuronal cell line in asynchronous combination experiments

Me-Hg and PCB153 are known neurotoxic contaminants which tend to accumulate in food, particularly in fish. Aim of this study was to perform asynchronous and combined exposure to Me-Hg and PCB153 in a neuronal rat cell line (PC12) to better characterise the antagonism observed at some combination concentrations. PC12 cells were treated with three concentrations of Me-Hg (0.1-0.5-1.0 microM) and PCB153 at one concentration (175 microM) in single and combined asynchronous exposures, using viability (MTT assay) as end-point. At all concentrations used, a statistically significant antagonistic effect was observed when Me-Hg preceded PCB153 exposure, while effect was additive when PCB153 preceded Me-Hg exposure. The antagonism is particularly evident at low concentrations of Me-Hg (0.1 microM). In conclusion, combined asynchronous exposure showed that whereas Me-Hg can modulate PCB153 toxicity, the opposite seems not to be true. Therefore, the use of asynchronous exposure could be a promising approach to study the mechanisms of toxicity of binary mixtures.

Alteration of neurotrophins in the hippocampus and cerebral cortex of young rats exposed to chlorpyrifos and methyl parathion

Exposure to either chlorpyrifos (CPS) or methyl parathion (MPS) results in the inhibition of acetylcholinesterase and leads to altered neuronal activity which normally regulates critical genes such as the neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). The effects of postnatal exposure to CPS and MPS on the expression of messenger RNA (mRNA) and protein levels for NGF and BDNF were investigated in the frontal cerebral cortex (cortex) and hippocampus of rats. Oral administration of CPS (4.0 or 6.0 mg/kg), MPS (0.6 or 0.9 mg/kg), or the safflower oil vehicle was performed daily from postnatal day 10 (PND10) through PND20. Exposure induced significant effects on growth and cholinesterase activity. Increased NGF protein levels were observed in the hippocampus but not the cortex on PND20 with some reduction occurring on PND28 in both regions. These changes did not correlate with the changes in NGF mRNA. BDNF mRNA was increased in both regions on PND20 and PND28, whereas BDNF protein levels were increased on PND20. On PND12, c-fos mRNA, a marker of neuronal activation, was increased in both regions. Total BDNF protein was increased in the hippocampus but decreased in the cortex. No changes in NGF protein were observed. These results indicate that repeated developmental OP exposure during the postnatal period alters NGF and BDNF in the cortex and the hippocampus and the patterns of these alterations differ between regions.

Differential protein adduction by seven organophosphorus pesticides in both brain and thymus

There is a need for mechanistic understanding of the lasting ill health reported in several studies of workers exposed to organophosphorus (OP) pesticide. Although the acute toxicity is largely explicable by acetylcholinesterase inhibition and the lasting effects of frank poisoning by direct excitotoxicity or indirect consequences of the cholinergic syndrome, effects at lower levels of exposure would not be predicted from these mechanisms. Similarly, reversible interactions with nicotinic and muscarinic receptors in adults would not predict continuing ill health. Many OP pesticides produce protein adduction, and the lasting nature of this makes it a candidate mechanism for the production of continuing ill health. We found significant adduction of partially characterized protein targets in both rat brain and thymus by azamethiphos, chlorfenvinphos, chlorpyrifos-oxon, diazinon-oxon, dichlorvos and malaoxon, in vitro and pirimiphos-methyl in vivo. The diversity in the adduction pattern seen across these agents at low dose levels means that any longer term effects of adduction would be specific to specific organophosphates, rather than generic. This presents a challenge to epidemiology, as most exposures are to different agents over time. However, some adducted proteins are also expressed in blood, notably albumin, and so may provide exposure measures to increase the power of future epidemiological studies.

Cartap-induced cytotoxicity in mouse C2C12 myoblast cell line and the roles of calcium ion and oxidative stress on the toxic effects

Our previous study has demonstrated that instead of neuromuscular blockage cartap, an organonitrogen insecticide, could cause a marked irreversible Ca2+-dependent contracture in both isolated mouse and rabbit phrenic nerve-diaphragms. We further examined the potential of direct myocytotoxicity of cartap and the possible roles of calcium ion and oxidative stress on cartap-induced muscle cell injury using the mouse myoblast cell line, C2C12. Cartap exerted a dose- and time-dependent cytotoxic effect in C2C12 cells measured by MTT colorimetric assay and trypan blue dye exclusion. The extracellular activities of both creatine kinase (CK) and lactate dehydrogenase (LDH) were elevated in the cartap-treated groups at or greater than 100 microM. The isoenzymatic profiles showed that the elevations were mainly due to CK-3, LDH-3, and LDH-4. Following the addition of 0.5-2.5mM EGTA, a Ca2+ chelator, or 30-100 microM verapamil, an L-type Ca2+ channel blocker, the cartap-induced reduction in MTT metabolic rate of C2C12 cells was significantly restored in a dose-dependent manner in both EGTA and verapamil-treated cells. Furthermore, EGTA could significantly reduce the cartap-induced elevation in the levels of total extracellular CK and LDH activities. Additionally, cartap significantly increased the level of endogenous reactive oxygen species (ROS) in C2C12 cells in a dose- and time-dependent manner. The cartap-induced ROS generation could be significantly inhibited by antioxidants, including Vitamins C and E, catalase, and superoxide dismutase, with catalase the most effective. EGTA could significantly inhibit cartap-induced ROS generation in a dose-dependent manner. The results suggested that cartap could induce ROS generation in C2C12 cells via a Ca2+-dependent mechanism resulting in subsequent cytotoxicity, at least partially, to C2C12 cells. It is speculated that both Ca2+ and Ca2+-induced ROS may also play the central role on the myogenic contracture and myofiber injury of the diaphragm leading to respiratory failure and subsequent death in rabbits exposed ocularly to cartap.

Interactive toxicity of chlorpyrifos and parathion in neonatal rats: Role of esterases in exposure sequence-dependent toxicity

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.

Thermoregulatory response to an organophosphate and carbamate insecticide mixture: Testing the assumption of dose-additivity

Most toxicity data are based on studies using single compounds. This study assessed if there is an interaction between mixtures of the anticholinesterase insecticides chlorpyrifos (CHP) and carbaryl (CAR) using hypothermia and cholinesterase (ChE) inhibition as toxicological endpoints. Core temperature (T(c)) was continuously monitored by radiotelemetry in adult Long-Evans rats administered CHP at doses ranging from 0 to 50mg/kg and CAR doses of 0-150 mg/kg. The temperature index (TI), an integration of the change in T(c) over a 12h period, was quantified. Effects of mixtures of CHP and CAR in 2:1 and 1:1 ratios on the TI were examined and the data analyzed using a statistical model designed to assess significant departures from additivity for chemical mixtures. CHP and CAR elicited a marked hypothermia and dose-related decrease in the TI. The TI response to a 2:1 ratio of CHP:CAR was significantly less than that predicted by additivity. The TI response to a 1:1 ratio of CHP and CAR was not significantly different from the predicted additivity. Plasma and brain ChE activity were measured 4h after dosing with CHP, CAR, and mixtures in separate groups of rats. There was a dose-additive interaction for the inhibition of brain ChE for the 2:1 ratio, but an antagonistic effect for the 1:1 ratio. The 2:1 and 1:1 mixtures had an antagonistic interaction on plasma ChE. Overall, the departures from additivity for the physiological (i.e., temperature) and biochemical (i.e., ChE inhibition) endpoints for the 2:1 and 1:1 mixtures studies did not coincide as expected. An interaction between CHP and CAR appears to depend on the ratio of compounds in the mixture as well as the biological endpoint.

Malathion detoxification by human hepatic carboxylesterases and its inhibition by isomalathion and other pesticides

The organophosphorothioate (OPT) pesticide malathion (MAL) in mammals is readily hydrolyzed by mammalian carboxylesterases (CE). The reaction competes with the CYP-catalyzed formation of malaoxon (MOX), the toxic metabolite. Alterations or individual variations in CE activity may result in increased MOX formation, enhancing MAL toxicity. We have characterized the human hepatic CE activity in a panel of 18 human liver microsomes as well as the inhibitory effect of IsoMAL, a major impurity of MAL commercial formulations, parathion (PAR), chlorpyrifos (CPF), and chlorpyrifos-oxon (CPFO). CE activity showed a low level of variation among individuals (4-fold). The reaction consists of two different phases, differing in their affinity for mal (k(m1)=0.25-0.69 microm; K(m2)=10.3-26.8 microM). The relatively low K(m1) values confirmed that human CE efficiently detoxify MAL. IsoMAL was shown to be a potent noncompetitive inhibitor of MAL detoxification (K(i)=0.6 microM), with a higher inhibitory potency than CPF and PAR (K(i)=7.5 microM and 50 microM, respectively). These two latter compounds very likely act as mixed inhibitors. CPFO showed the highest inhibitory potency toward CE-mediated detoxification, being characterized by a K(i)=22 nM. The present results provide useful information for a better understanding of possible interactions between different OPTs and for assessing the potential cumulative risk for exposure to OPT mixtures.

Use of cholinesterase activity as an indicator for the effects of combinations of organophosphorus pesticides in water from environmental sources

Organophosphorus pesticides (OPs) are commonly detected in agricultural products, animal-derived foodstuffs, and environmental samples. Until now, the focus of research has been to evaluate the adverse effect of a single OP. While each OP may be present at concentrations under recognized as "no observed adverse effect level (NOAEL)", the combined effects of multiple OPs present at these low concentrations have not been sufficiently studied. Therefore, we developed an in vitro testing method to evaluate the toxicity of multiple OPs based on the degree of inhibition of cholinesterase (ChE) activity. This method requires only 10 min to complete and no specialized technology. We examined 15 OPs by this method and categorized them into three groups according to the degree of ChE inhibition. A relationship between the OPs' chemical structures and the degree of ChE inhibition emerged with the moiety -P-O-CN- showing the strongest action. The degree of ChE inhibition increased with multiple OPs, and the degree of inhibition seemed to be additive. These results demonstrate that the combined toxicity of multiple OPs present in food or environmental samples is an easily determined and toxicologically relevant measure of overall toxicity of complex OPs mixtures. It is possible to apply this testing method as a monitoring technique in water quality management in order to control OPs. As a result, this method can play the role for the potential risk reduction to the ecosystem and may contribute to the preservation of the environment.

Pharmacology and toxicology of cholinesterase inhibitors: uses and misuses of a common mechanism of action

Cholinesterase inhibitors have been used in the treatment of human diseases, the control of insect pests, and more notoriously as chemical warfare agents and weapons of terrorism. Most uses of cholinesterase inhibitors are based on a common mechanism of action initiated by inhibition of acetylcholinesterase (AChE). Extensive inhibition of this enzyme leads to accumulation of the neurotransmitter acetylcholine and enhanced stimulation of postsynaptic cholinergic receptors. This action is beneficial in cases where a reduction in cholinergic transmission contributes to clinical symptoms, e.g., low muscle tone in the autoimmune disorder myasthenia gravis due to loss of nicotinic receptors. Under normal conditions, however, extensive inhibition of AChE leads to excess synaptic acetylcholine levels, over-stimulation of cholinergic receptors, alteration of postsynaptic cell function and consequent signs of cholinergic toxicity. This biochemical cascade forms the basis for the use of anticholinesterase insecticides in pest control as well as for nerve agents in chemical warfare. Paradoxically, the short-acting cholinesterase inhibitor pyridostigmine, an important therapeutic agent in the treatment of myasthenia gravis, was used during the Persian Gulf War to prevent the long-term clinical consequences of possible organophosphate nerve agent exposure. As shown in the attacks in Matsumoto and Tokyo, these same nerve agents can be effectively used to inflict urban terror. Cholinesterase inhibitors thus share a common mechanism of pharmacological or toxicological action, ultimately modifying cholinergic signaling through disruption of acetylcholine degradation. While the use of cholinesterase inhibitors relies on their interaction with AChE, a variety of reports indicate that a number of cholinesterase inhibitors have additional sites of action that may have pharmacologic or toxicologic relevance. A variety of esterase and non-esterase enzymes, neurotransmitter receptors and elements of cell signaling pathways are targeted by some anticholinesterases. In some cases, these actions may occur at concentrations/dosages below those affecting cholinergic transmission. Studies of interactive toxicity of binary mixtures of common organophosphorus insecticides indicate that non-cholinesterase targets may be important in cumulative toxicity. Exposure to multiple anticholinesterases having selective effects on other macromolecules could confound the assumption of additivity in cumulative risk assessment. Knowledge of such selective additional targets may aid, however, in the optimization of strategies for poisoning therapy and in the further elucidation of mechanisms of toxicity for this class of compounds.

Pharmacokinetic and pharmacodynamic interaction for a binary mixture of chlorpyrifos and diazinon in the rat

Chlorpyrifos (CPF) and diazinon (DZN) are two commonly used organophosphorus (OP) insecticides and a potential exists for concurrent exposures. The primary neurotoxic effects from OP pesticide exposures result from the inhibition of acetylcholinesterase (AChE). The pharmacokinetic and pharmacodynamic impact of acute binary exposures of rats to CPF and DZN was evaluated in this study. Rats were orally administered CPF, DZN, or a CPF/DZN mixture (0, 15, 30, or 60 mg/kg) and blood (plasma and RBC), and brain were collected at 0, 3, 6, 12, and 24 h postdosing, urine was also collected at 24 h. Chlorpyrifos, DZN, and their respective metabolites, 3,5,6-trichloro-2-pyridinol (TCP) and 2-isopropyl-4-methyl-6-hydroxypyrimidine (IMHP), were quantified in blood and/or urine and cholinesterase (ChE) inhibition was measured in brain, RBC, and plasma. Coexposure to CPF/DZN at the low dose of 15/15 mg/kg did not alter the pharmacokinetics of CPF, DZN, or their metabolites in blood. A high binary dose of 60/60 mg/kg increased the C(max) and AUC and decreased the clearance for both parent compounds, likely due to competition between CPF and DZN for CYP450 metabolism. At lower doses, most likely to be encountered in occupational or environmental exposures, the pharmacokinetics were linear. A dose-dependent inhibition of ChE was noted in tissues for both the single and coexposures, and the extent of inhibition was plasma > RBC > or = brain. The overall relative potency for ChE inhibition was CPF/DZN > CPF > DZN. A comparison of the ChE response at the low binary dose (15/15 mg/kg), where there were no apparent pharmacokinetic interactions, suggested that the overall ChE response was additive. These experiments represent important data concerning the potential pharmacokinetic and pharmacodynamic interactions for pesticide mixtures and will provide needed insight for assessing the potential cumulative risk associated with occupational or environmental exposures to these insecticides.

Neurotoxicological and Statistical Analyses of a Mixture of Five Organophosphorus Pesticides Using a Ray Design

Environmental exposures generally involve chemical mixtures instead of single chemicals. Statistical models such as the fixed-ratio ray design, wherein the mixing ratio (proportions) of the chemicals is fixed across increasing mixture doses, allows for the detection and characterization of interactions among the chemicals. In this study, we tested for interaction(s) in a mixture of five organophosphorus (OP) pesticides (chlorpyrifos, diazinon, dimethoate, acephate, and malathion). The ratio of the five pesticides (full ray) reflected the relative dietary exposure estimates of the general population as projected by the US EPA Dietary Exposure Evaluation Model (DEEM). A second mixture was tested using the same dose levels of all pesticides, but excluding malathion (reduced ray). The experimental approach first required characterization of dose-response curves for the individual OPs to build a dose-additivity model. A series of behavioral measures were evaluated in adult male Long-Evans rats at the time of peak effect following a single oral dose, and then tissues were collected for measurement of cholinesterase (ChE) activity. Neurochemical (blood and brain cholinesterase [ChE] activity) and behavioral (motor activity, gait score, tail-pinch response score) endpoints were evaluated statistically for evidence of additivity. The additivity model constructed from the single chemical data was used to predict the effects of the pesticide mixture along the full ray (10-450 mg/kg) and the reduced ray (1.75-78.8 mg/kg). The experimental mixture data were also modeled and statistically compared to the additivity models. Analysis of the 5-OP mixture (the full ray) revealed significant deviation from additivity for all endpoints except tail-pinch response. Greater-than-additive responses (synergism) were observed at the lower doses of the 5-OP mixture, which contained non-effective dose levels of each of the components. The predicted effective doses (ED20, ED50) were about half that predicted by additivity, and for brain ChE and motor activity, there was a threshold shift in the dose-response curves. For the brain ChE and motor activity, there was no difference between the full (5-OP mixture) and reduced (4-OP mixture) rays, indicating that malathion did not influence the non-additivity. While the reduced ray for blood ChE showed greater deviation from additivity without malathion in the mixture, the non-additivity observed for the gait score was reversed when malathion was removed. Thus, greater-than-additive interactions were detected for both the full and reduced ray mixtures, and the role of malathion in the interactions varied depending on the endpoint. In all cases, the deviations from additivity occurred at the lower end of the dose-response curves.