Chlorpyrifos Induced Region Specific Vulnerability in Rat CNS and Modulation by Age and Cold Stress: An Interactive Study

Chlorpyrifos induces the apoptosis and necroptosis of L8824 cells through the ROS/PTEN/PI3K/AKT axis

Excessive chlorpyrifos (CPF) in the environment causes toxicity to nontarget organisms by triggering oxidative stress. Phosphatase and tensin homolog deleted on chromosome ten (PTEN) plays an important role in controlling apoptosis and necrosis by negatively regulating the phosphatidylinositol 3-kinase/threonine kinase (PI3K/AKT) pathway. However, the effects of different concentrations of CPF on grass fish liver cell injury and the role of the ROS/PTEN/PI3K/AKT axis remain poorly understood. In this study, L8824 cells treated with different concentrations of CPF (0, 40, 60, or 80 μM) were used as the research object. The results showed that the median inhibitory concentration (IC50) was 112.226 μM. As the CPF concentrations increased, the ROS and MDA levels increased, and the T-AOC levels and SOD/GPx/GST activities decreased. As PTEN expression increased, PI3K/AKT, BCL-2, and Caspase-8 expression dramatically decreased. Conversely, RIPK1/RIPK3/MLKL and Bax/Cyt-c/Caspase-3 expression increased. Additionally, necroptosis increased in a dose-dependent manner, while apoptosis first increased and then decreased. In conclusion, our study showed that CPF could trigger oxidative stress and induce apoptosis and necroptosis in fish liver cells by regulating the ROS/PTEN/PI3K/AKT axis, and the type of damage induced was dose-dependent. These results are meaningful for toxicological studies of CPF and efforts to protect the ecosystem.

Monitoring of the Organophosphate Pesticide Chlorpyrifos in Vegetable Samples from Local Markets in Northern Thailand by Developed Immunoassay

Chlorpyrifos is an organophosphate pesticide that is wildly used among farmers for crop protection. However, there are concerns regarding its contamination in the environment and food chain. In the present study, an in-house indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) specific for detecting chlorpyrifos is developed and validated against gas chromatography–flame photometric detection (GC-FPD) as the conventional method. The developed ic-ELISA was used for detecting chlorpyrifos residue in vegetable samples. The developed ic-ELISA showed good sensitivity to chlorpyrifos at an IC₅₀ of 0.80 µg/kg, with low cross-reactivity to other organophosphate pesticides. The 160 samples were collected from local markets located in the Chiang Rai, Chiang Mai, and Nan provinces in northern Thailand. The positive rate of chlorpyrifos residues in the vegetable samples was 33.8%, with the highest levels found in cucumbers, coriander, and morning glory, at 275, 145, and 35.3 µg/kg, respectively. The highest median levels of chlorpyrifos found in the detected samples were Chinese cabbage (332 μg/kg), cucumber (146.3 μg/kg) and Chinese Kale (26.95 μg/kg). The developed ic-ELISA is suitable for the rapid quantitation of chlorpyrifos residues.

Potential role of N-acetylcysteine on chlorpyrifos-induced neurotoxicity in rats

Chlorpyrifos (CPF) is a widely used organophosphate insecticide with several harmful effects. N-acetylcysteine (NAC) represents an ideal antixenobiotic; it can directly enter endogenous biochemical processes and is used as adjunctive treatment for psychiatric disorders. We aimed to evaluate the neuroprotective effect of NAC as an antioxidant drug against CPF-induced neurotoxicity in adult male albino rat brains. Twenty-eight male Wister rats were allocated into four groups (n = 7) and were administered the following for 28 days: group I (control group), physiological saline (0.9% NaCl); group II (CPF group), 10 mg/kg body weight (BW) CPF; group III (NAC group), 100 mg/kg BW NAC; and group VI (CPF+NAC group), NAC 1 h before CPF. CPF intoxication resulted in acetylcholinesterase inhibition, reduced glutathione content, and elevated levels of malondialdehyde and nitric oxide, which are oxidative stress biomarkers. CPF also depleted the activity of antioxidant enzymes, superoxide dismutase and catalase, and levels of inflammatory mediators, tumor necrosis factor-α, interleukin (IL)-6, and IL-1β. Levels of vascular endothelial growth factor, Bax, and the proapoptotic caspases-3 also increased, while brain-derived neurotrophic factor level decreased. Additionally, CPF significantly diminished Bcl-2 (an antiapoptotic protein) in rat brain cortical tissue. NAC treatment was found to protect brain tissue by reversing the CPF-induced neurotoxicity. Our results show the antioxidant, antiinflammatory, and antiapoptotic effects of NAC on CPF-induced neurotoxicity in rat brain tissue.

Chlorpyrifos Induces the Expression of the Epstein-Barr Virus Lytic Cycle Activator BZLF-1 via Reactive Oxygen Species

Organophosphate pesticides (OPs) are among the most widely used synthetic chemicals for the control of a wide variety of pests, and reactive oxygen species (ROS) caused by OPs may be involved in the toxicity of various pesticides. Previous studies have demonstrated that a reactivation of latent Epstein-Barr virus (EBV) could be induced by oxidative stress. In this study, we investigated whether OPs could reactivate EBV through ROS accumulation. The Raji cells were treated with chlorpyrifos (CPF), one of the most commonly used OPs. Oxidative stress indicators and the expression of the EBV immediate-early gene BZLF-1 were determined after CPF treatment. Our results show that CPF induces oxidative stress as evidenced by decreased malondialdehyde (MDA) level, accompanied by an increase in ROS production, DNA damage, glutathione (GSH) level, and superoxide dismutase (SOD) and catalase (CAT) activity. Moreover, CPF treatment significantly enhances the expression of BZLF-1, and the increased BZLF-1 expression was ameliorated by N-acetylcysteine (NAC) incubation. These results suggest that OPs could contribute to the reactivation of the EBV lytic cycle through ROS induction, a process that may play an important role in the development of EBV-associated diseases.

Prenatal nicotine alters the developmental neurotoxicity of postnatal chlorpyrifos directed toward cholinergic systems: better, worse, or just "different?"

This study examines whether prenatal nicotine exposure sensitizes the developing brain to subsequent developmental neurotoxicity evoked by chlorpyrifos, a commonly-used insecticide. We gave nicotine to pregnant rats throughout gestation at a dose (3mg/kg/day) producing plasma levels typical of smokers; offspring were then given chlorpyrifos on postnatal days 1-4, at a dose (1mg/kg) that produces minimally-detectable inhibition of brain cholinesterase activity. We evaluated indices for acetylcholine (ACh) synaptic function throughout adolescence, young adulthood and later adulthood, in brain regions possessing the majority of ACh projections and cell bodies; we measured nicotinic ACh receptor binding, hemicholinium-3 binding to the presynaptic choline transporter and choline acetyltransferase activity, all known targets for the adverse developmental effects of nicotine and chlorpyrifos given individually. By itself nicotine elicited overall upregulation of the ACh markers, albeit with selective differences by sex, region and age. Likewise, chlorpyrifos alone had highly sex-selective effects. Importantly, all the effects showed temporal progression between adolescence and adulthood, pointing to ongoing synaptic changes rather than just persistence after an initial injury. Prenatal nicotine administration altered the responses to chlorpyrifos in a consistent pattern for all three markers, lowering values relative to those of the individual treatments or to those expected from simple additive effects of nicotine and chlorpyrifos. The combination produced global interference with emergence of the ACh phenotype, an effect not seen with nicotine or chlorpyrifos alone. Given that human exposures to nicotine and chlorpyrifos are widespread, our results point to the creation of a subpopulation with heightened vulnerability.

Mitochondrial dysfunction in aging rat brain regions upon chlorpyrifos toxicity and cold stress: an interactive study

Mitochondrial dysfunction and consequent energy depletion are the major causes of oxidative stress resulting to bring alterations in the ionic homeostasis causing loss of cellular integrity. Our previous studies have shown the age-associated interactive effects in rat central nervous system (CNS) upon co-exposure to chlorpyrifos (CPF) and cold stress leading to macromolecular oxidative damage. The present study elucidates a possible mechanism by which CPF and cold stress interaction cause(s) mitochondrial dysfunction in an age-related manner. In this study, the activity levels of Krebs cycle enzymes and electron transport chain (ETC) protein complexes were assessed in the isolated fraction of mitochondria. CPF and cold stress (15 and 20 °C) exposure either individually or in combination decreased the activity level of Krebs cycle enzymes and ETC protein complexes in discrete regions of rat CNS. The findings confirm that cold stress produces significant synergistic effect in CPF intoxicated aging rats. The synergism between CPF and cold stress at 15 °C caused a higher depletion of respiratory enzymes in comparison with CPF and cold stress alone and together at 20 °C indicating the extent of deleterious functional alterations in discrete regions of brain and spinal cord (SC) which may result in neurodegeneration and loss in neuronal metabolic control. Hence, co-exposure of CPF and cold stress is more dangerous than exposure of either alone. Among the discrete regions studied, the cerebellum and medulla oblongata appears to be the most susceptible regions when compared to cortex and SC. Furthermore, the study reveals a gradual decrease in sensitivity to CPF toxicity as the rat matures.

Prenatal dexamethasone augments the sex-selective developmental neurotoxicity of chlorpyrifos: implications for vulnerability after pharmacotherapy for preterm labor

Glucocorticoids are routinely given in preterm labor and are also elevated by maternal stress; organophosphate exposures are virtually ubiquitous, so coexposures to these two agents are pervasive. We administered dexamethasone to pregnant rats on gestational days 17-19 at a standard therapeutic dose (0.2mg/kg); offspring were then given chlorpyrifos on postnatal days 1-4, at a dose (1mg/kg) that produces barely-detectable (<10%) inhibition of brain cholinesterase activity. We evaluated indices for acetylcholine (ACh) synaptic function throughout adolescence, young adulthood and later adulthood, in brain regions possessing the majority of ACh projections and cell bodies; we measured nicotinic ACh receptor binding, hemicholinium-3 binding to the presynaptic choline transporter and choline acetyltransferase activity, all known targets for the adverse developmental effects of dexamethasone and chlorpyrifos given individually. Dexamethasone did not enhance the systemic toxicity of chlorpyrifos, as evidenced by weight gain and measurements of cholinesterase inhibition during chlorpyrifos treatment. Nevertheless, it enhanced the loss of presynaptic ACh function selectively in females, who ordinarily show sparing of organophosphate developmental neurotoxicity relative to males. Females receiving the combined treatment showed decrements in choline transporter binding and choline acetyltransferase activity that were unique (not found with either treatment alone), as well as additive decrements in nicotinic receptor binding. On the other hand, males given dexamethasone showed no augmentation of the effects of chlorpyrifos. Our findings indicate that prior dexamethasone exposure could create a subpopulation that is especially vulnerable to the adverse effects of organophosphates or other developmental neurotoxicants.

Cold stress offered modulation on chlorpyrifos toxicity in aging rat central nervous system

The adverse effects produced by chlorpyrifos (CPF) or cold stress alone in humans and animals are well documented, but there is no information available relating to the consequences of their co- exposure in an age-related manner. In this study, effects of sublethal doses of CPF were carried out in vivo, for 48 h to assess the biochemical perturbations in relation to interactions with cold stress (15°C and 20°C) in different age group rat CNS. A positive interaction of CPF with age of animal and cold exposure was observed resulting in marked decrease in the activity levels of AChE (P<0.05), ChAT (P<0.05), Na⁺, K⁺-ATPase (P<0.05), Ca²⁺-ATPase (P<0.05), and Mg²⁺-ATPase (P<0.05). The ANOVA and posthoc analysis showed that regulatory enzymes decreased significantly (P<0.05) on CPF exposure. Overall, the effect of co-exposure was appreciably different from either of the exposures. Synergistic interaction of CPF and cold stress at 15°C showed higher inhibition in comparison with CPF and cold stress alone and together at 20°C. Further, this study reveals that young animals are significantly vulnerable and sensitive than adults.

Reactive oxygen species regulated mitochondria-mediated apoptosis in PC12 cells exposed to chlorpyrifos

Reactive oxidative species (ROS) generated by environmental toxicants including pesticides could be one of the factors underlying the neuronal cell damage in neurodegenerative diseases. In this study we found that chlorpyrifos (CPF) induced apoptosis in dopaminergic neuronal components of PC12 cells as demonstrated by the activation of caspases and nuclear condensation. Furthermore, CPF also reduced the tyrosine hydroxylase-positive immunoreactivity in substantia nigra of the rat. In addition, CPF induced inhibition of mitochondrial complex I activity. Importantly, N-acetyl cysteine (NAC) treatment effectively blocked apoptosis via the caspase-9 and caspase-3 pathways while NAC attenuated the inhibition of mitochondrial complex I activity as well as the oxidative metabolism of dopamine (DA). These results demonstrated that CPF-induced apoptosis was involved in mitochondrial dysfunction through the production of ROS. In the response of cellular antioxidant systems to CPF, we found that CPF treatment increased HO-1 expression while the expression of CuZnSOD and MnSOD was reduced. In addition, we found that CPF treatment activated MAPK pathways, including ERK 1/2, the JNK, and the p38 MAP kinase in a time-dependent manner. NAC treatment abolished MAPK phosphorylation caused by CPF, indicating that ROS are upstream signals of MAPK. Interestingly, MAPK inhibitors abolished cytotoxicity and reduced ROS generation by CPF treatment. Our results demonstrate that CPF induced neuronal cell death in part through MAPK activation via ROS generation, suggesting its potential to generate oxidative stress via mitochondrial damage and its involvement in oxidative stress-related neurodegenerative disease.

Oxidative macromolecular alterations in the rat central nervous system in response to experimentally co-induced chlorpyrifos and cold stress: a comparative assessment in aging rats

Reactive oxygen species are generated as a result of a number of physiological and pathological processes which can promote multiple forms of oxidative damage including protein oxidation, and thereby influence the function of a diverse array of cellular processes. In our previous study we have reported that co-exposure to chlorpyrifos and cold stress in aging rats markedly influence the toxic outcome as a result of oxidative stress. In the present study, key neurochemical/enzymes were measured in order to evaluate the macromolecular alterations in response to experimentally co-induced chlorpyrifos and cold stress (15 and 20°C) either concurrently or individually in vivo for 48 h in discrete regions of brain and spinal cord of different age group rats. CPF and cold stress exposure either individually or in combination substantially increased the activity/levels of protein carbonyls, AST, ALT and decreased protein thiols, DNA, RNA and total proteins in discrete regions of CNS. Overall, the effects of co-exposure were appreciably different from either of the exposures. However, synergistic-action of CPF and cold stress at 15°C showed higher dyshomeostasis in comparison with CPF and cold stress alone and together at 20°C indicating the extent of oxidative macromolecular damage in discrete regions of brain and spinal cord. Furthermore, the present study demonstrates that macromolecular oxidative damage is highly pronounced in neonates and juveniles than the young adults.