Modulation of immune response by organophosphorus pesticides: fishes as a potential model in immunotoxicology

The multi-level effect of chlorpyrifos during clownfish metamorphosis

Chemical pollution in coastal waters, particularly from agricultural runoff organophosphates, poses a significant threat to marine ecosystems, including coral reefs. Pollutants such as chlorpyrifos (CPF) are widely used in agriculture and have adverse effects on marine life and humans. In this paper, we investigate the impact of CPF on the metamorphosis of a coral reef fish model, the clownfish Amphiprion ocellaris, focusing on the disruption of thyroid hormone (TH) signalling pathways. Our findings reveal that by reducing TH levels, CPF exposure impairs the formation of characteristic white bands in clownfish larvae, indicative of metamorphosis progression. Interestingly, TH treatment can rescue these effects, establishing a direct causal link between CPF effect and TH disruption. The body shape changes occurring during metamorphosis are also impacted by CPF exposure, shape changes are less advanced in CPF-treated larvae than in control conditions. Moreover, transcriptomic analysis elucidates CPF's effects on all components of the TH signalling pathway. Additionally, CPF induces systemic effects on cholesterol and vitamin D metabolism, DNA repair, and immunity, highlighting its broader TH-independent impacts. Pollutants are often overlooked in marine ecosystems, particularly in coral reefs. Developing and enhancing coral reef fish models, such as Amphiprion ocellaris (Cuvier, 1830), offers a more comprehensive understanding of how chemical pollution affects these ecosystems. This approach provides new insights into the complex mechanisms underlying CPF toxicity during fish metamorphosis, shedding light on the broader impact of environmental pollutants on marine organisms.

Prenatal Exposure to Herbicide 2,4-Dichlorophenoxyacetic Acid (2,4D) Exacerbates Zika Virus Neurotoxicity In Vitro and In Vivo

Zika virus (ZIKV) infection during pregnancy can lead to a set of congenital malformations known as Congenital ZIKV syndrome (CZS), whose main feature is microcephaly. The geographic distribution of CZS in Brazil during the 2015-2017 outbreak was asymmetrical, with a higher prevalence in the Northeast and Central-West regions of the country, despite the ubiquitous distribution of the vector Aedes aegypti, indicating that environmental factors could influence ZIKV vertical transmission and/or severity. Here we investigate the involvement of the most used agrochemicals in Brazil with CZS. First, we exposed human neuroblastoma SK-N-AS cells to the 15 frequently used agrochemical molecules or derivative metabolites able to cross the blood-brain barrier. We found that a derived metabolite from a widely used herbicide in the Central-West region, 2,4-dichlorophenoxyacetic acid (2,4D), exacerbates ZIKV neurotoxic effects in vitro. We validate this observation by demonstrating vertical transmission leading to microcephaly in the offspring of immunocompetent C57BL/6J mice exposed to water contaminated with 0.025 mg/L of 2,4D. Newborn mice whose dams were exposed to 2,4D and infected with ZIKV presented a smaller brain area and cortical plate size compared to the control. Also, embryos from animals facing the co-insult of ZIKV and 2,4D exposition presented higher Caspase 3 positive cells in the cortex, fewer CTIP2+ neurons and proliferative cells at the ventricular zone, and a higher viral load. This phenotype is followed by placental alterations, such as vessel congestion, and apoptosis in the labyrinth and decidua. We also observed a mild spatial correlation between CZS prevalence and 2,4D use in Brazil's North and Central-West regions, with R2 = 0.4 and 0.46, respectively. Our results suggest that 2,4D exposition facilitates maternal vertical transmission of ZIKV, exacerbating CZS, possibly contributing to the high prevalence of this syndrome in Brazil's Central-West region compared to other regions.

Distribution of organophosphorus pesticides and its potential connection with probiotics in sediments of a shallow freshwater lake

Despite the serious health threats due to wide use of organophosphorus pesticides (OPPs) have been experimentally claimed to be remediated by probiotic microorganisms in various food and organism models, the interactions between OPPs and probiotics in the natural wetland ecosystem was rarely investigated. This study delves into the spatial and temporal distribution, contamination levels of OPPs in the Baiyangdian region, the diversity of probiotic communities in varying environmental contexts, and the potential connection with OPPs on these probiotics. In typical shallow lake wetland ecosystem-Baiyangdian lake in north China, eight OPPs were identified in the lake sediments, even though their detection rates were generally low. Malathion exhibited the highest average content among these pesticides (9.51 ng/g), followed by fenitrothion (6.70 ng/g). Conversely, chlorpyrifos had the lowest detection rate at only 2.14%. The region near Nanliu Zhuang (F10), significantly influenced by human activities, displayed the highest concentration of total OPPs (136.82 ng/g). A total of 145 probiotic species spanning 78 genera were identified in Baiyangdian sediments. Our analysis underscores the relations of environmental factors such as phosphatase activity, pH, and electrical conductivity (EC) with probiotic community. Notably, several high-abundance probiotics including Pseudomonas chlororaphis, Clostridium sp., Lactobacillus fermentum, and Pseudomonas putida, etc., which were reported to exhibit significant potential for the degradation of OPPs, showed strongly correlations with OPPs in the Baiyangdian lake sediments. The outcomes of this research offer valuable insights into the spatiotemporal dynamics of OPPs in natural large lake wetland and the probability of their in-situ residue bioremediation through the phosphatase pathway mediated by probiotic such as Lactic acid bacteria in soils/sediments contaminated with OPPs.

Effects of methomyl on the intestinal microbiome and hepatic transcriptome of tilapia, and the modifying effects of mint co-culture

Methomyl (MET) is an oxime carbamate insecticide that can contaminate aquatic systems resulting in toxicological effects. It can harm some fish species possibly through the anti-oxidative, phagosome pathway. Mint is one of the most widely herbal plants exhibiting antioxidant activities. In this study, we investigated the impact of MET on the antioxidant system of Oreochromis niloticus in presence of mint as a floating bed. Results revealed that the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase, and glutathione S-transferase significantly decreased and the GSH content significantly increased in the intestine. The hepatic peroxisome proliferator-activated receptor (PPAR) signalling pathway, carbon metabolism, renal phosphoinositide 3-kinase (PI3K)-Akt, mitogen-activated protein kinase (MAPK) signalling pathway, and phagosomes were significantly affected. Upon long-term exposure, circadian rhythm and phagosomes were enriched in the liver and kidney. However, mint increased the enriched pathways of Toll-like receptor, PPAR, p53, NF-kappa B, MAPK, oestrogen, and B cell receptor signalling pathways. MET with different concentrations destroyed the balance of gut microbiota, mint decreased Verrucomicrobia and Akkermansia for the maintenance resulted from MET. Cetobacterium had a positive impact on total nitrogen (TN), chemical oxygen demand (CODMn), and glutathione reductase (GR), while Akkermansia had a positive impact on feed conversion ratio (FCR), SOD and CAT, and the abundance of both decreased due to MET exposure. High mint density removed more concentrations of nitrogen and phosphorus in the tilapia cultivation wastewater. Therefore, planting with mint can alleviate the toxicological effects produced by MET, shape the intestinal microbiota, and strengthen the connection between water quality and the metabolic parameters.

Dietary Sargassum angustifolium (Macro-Algae, Sargassaceae) extract improved antioxidant defense system in diazionon-exposed common carp, Cyprinus carpio

The effects of different dietary levels of algae (Sargassum angustifolium) extract were investigated on the antioxidant system of common carp, Cyprinus carpio. Fish (30.2 ± 2.1 g) were fed 0 (control), 5, 10 and 15 g/kg basal diet of Sargassum angustifolium extract (SAE) for 60 days and then exposed to an environmentally relevant concentration of diazinon (2 mg/l) for 24 h. The biochemical assays were conducted in two times including at the end of feeding period and after 24 h exposure to diazinon. According to the results, malondialdehyde (MDA) levels in the liver remained unchanged (P>0.01) during feeding period, while significantly increased in response to diazinon in control and fish fed 5 and 10 g/kg diet SAE (P<0.01). The hepatic metabolic enzymes (AST: Aspartate aminotransferase, ALT: alanine aminotransferase, LDH: lactate dehydrogenase, CK: creatine kinase) showed no significant changes in all groups during feeding period, while these enzymes increased in Non-SAE supplemented fish and those fed 5 and 10 g/kg SAE after exposure to diazinon (P<0.01). Although little elevations were observed in the activity of hepatic antioxidant enzymes (CAT: catalase, SOD: superoxide dismutase, GPx: Glutathione peroxidase) in fish fed SAE, these elevations were not significant (P>0.01). After exposure to diazinon, antioxidant enzymes significantly decreased in control and fish fed 5 g/kg diet SAE, while the fish of 10 and 15 g/kg diet SAE treatments showed significant elevations (P<0.01). The antioxidant-related genes (sod, cat, gpx) significantly expressed more in response to dietary SAE compared to control (P<0.01). After exposure to diazinon, all groups showed significant elevations in antioxidant-related genes (P<0.01). In conclusion, the results of the present study revealed the antioxidant enhancing effects of SAE at dietary levels of 10 and 15 g/kg diet, which this effect may be attributed to some antioxidant components in the chemical composition of the macro-algae or to the direct effect of SAE on antioxidant defence system of the fish.

Potential protective effects of chrysin against immunotoxicity induced by diazinon

Acute intoxication with diazinon (DZN) as a pesticide causes mortality and morbidity annually. This study shows the impact of sub-acute toxicity of DZN 20 mg/kg and the protective activities of chrysin (CH) as a flavone under the flavonoids family (12.5, 25 and 50 mg/kg) were assessed on BALB/c mouse immune system. The changes in morphological and functional properties of the immune system on thymus, spleen and liver histopathology, sub-populations of T lymphocytes, cytokines levels, transcription factors, complement function, phagocytosis, specific and total antibody productions were considered. The histopathological effects of DZN on the spleen and thymus were not significant, but the liver was damaged remarkably. In the presence of CH, the toxic effect of DZN is suppressed. DZN significantly decreased the number of whole blood TCD4⁺, TCD8⁺ and NK cells and suppressed the phagocytosis, delayed-type hypersensitivity (DTH) responses to sheep red blood cell (SRBC). Furthermore, it suppressed specific anti-SRBC-Ab, total IgG and IgM production, T-bet expression, and IFN-γ production. In contrast, DZN did not significantly affect complement function and the number of NK cells, TCD4⁺ and TCD8⁺ splenocytes. However, it potentiated the expression of GATA-3, ROR-γt and FOXP3 gene expression and consequently produced IL-4, IL-10, IL-17 and TGF-β in whole blood. CH not only significantly increased the variables mentioned above at 12.5, 25 and 50 mg/kg but also could overcome the toxic effects of DZN on whole blood lymphocyte sub-populations and specific and total Ab production in 25 and 50 mg/kg concentrations, phagocytosis and DTH responses in 50 mg/kg, and modulation of the transcription factors and cytokine production, mainly in 25 and 50 mg/kg. In conclusion, DZN in sub-acute doses could remarkably deteriorate immune responses. However, CH can overcome the toxic effects of DZN on the immune components and functions of the immune system.

Cognitive Impairment and Neurodegenerative Diseases Development Associated with Organophosphate Pesticides Exposure: a Review Study

A significant body of literature emphasizes the role of insecticide, particularly organophosphates (OPs), as the major environmental factor in the etiology of neurodegenerative diseases. This review aims to study the relationship between OP insecticide exposure, cognitive impairment, and neurodegenerative disease development. Human populations, especially in developing countries, are frequently exposed to OPs due to their extensive applications. The involvement of various signaling pathways in OP neurotoxicity are reported, but the OP-induced cognitive impairment and link between OP exposure and the pathophysiology of neurodegenerative diseases are not clearly understood. In the present review, we have therefore aimed to come to new conclusions which may help to find protective and preventive strategies against OP neurotoxicity and may establish a possible link between organophosphate exposure, cognitive impairment, and OP-induced neurotoxicity. Moreover, we discuss the findings obtained from animal and human research providing some support for OP-induced cognitive impairment and neurodegenerative disorders.

Pesticide Pollution: Detrimental Outcomes and Possible Mechanisms of Fish Exposure to Common Organophosphates and Triazines

Pesticides are well known for their high levels of persistence and ubiquity in the environment, and because of their capacity to bioaccumulate and disrupt the food chain, they pose a risk to animals and humans. With a focus on organophosphate and triazine pesticides, the present review aims to describe the current state of knowledge regarding spatial distribution, bioaccumulation, and mode of action of frequently used pesticides. We discuss the processes by which pesticides and their active residues are accumulated and bioconcentrated in fish, as well as the toxic mechanisms involved, including biological redox activity, immunotoxicity, neuroendocrine disorders, and cytotoxicity, which is manifested in oxidative stress, lysosomal and mitochondrial damage, inflammation, and apoptosis/autophagy. We also explore potential research strategies to close the gaps in our understanding of the toxicity and environmental risk assessment of organophosphate and triazine pesticides.

How advanced are we on the consequences of oral exposure to food contaminants on the occurrence of chronic non communicable diseases?

The development of an individual during fetal life and childhood is characterized by rapid growth as well as gradual maturation of organs and systems. Beyond the nutritional intake in essential nutrients, food contaminants can permanently influence the way organs mature and function. These processes are called "programming" and play an essential role in the occurrence of non-communicable chronic diseases throughout the lifespan. Populations as pregnant women, fetuses and young children are vulnerable and particularly sensitive to food contaminants which can induce epigenetic modifications transmissible to future generations. Among these contaminants, pesticides are found in most food matrices exposing humans to cocktails of molecules through variable concentrations and duration of exposure. The Maillard reaction products (MRPs) represent other food contaminants resulting from heat treatment of food. Modern diet, rich in fats and sugars, is also rich in neoformed pathogenic compounds, Advanced Glycation End products (AGEs), the levels of which depend on the heat treatment of foods and eating habits and whose effects on health are controversial. In this review, we have chosen to present the current knowledge on the impacts of selected pesticides and MRPs, on the risk of developing during life non-communicable chronic diseases such as IBD, metabolic disorders or allergies. A large review of literature was performed via Pubmed, and the most appropriate studies were summarised.

Raising the Alarm: Environmental Factors in the Onset and Maintenance of Chronic (Low-Grade) Inflammation in the Gastrointestinal Tract

Chronic inflammatory disease of the gastrointestinal (GI) tract is defined by several pathophysiological characteristics, such as dysbiosis of the microbiota, epithelial barrier hyperpermeability, systemic dissemination of endotoxins and chronic inflammation. In addition to well-reported environmental factors in non-communicable disease, such as smoking, diet, and exercise, humans are frequently exposed to myriads more environmental factors, from pesticides to food additives. Such factors are ubiquitous across both our diet and indoor/outdoor environments. A major route of human exposure to these factors is ingestion, which frequently occurs due to their intentional addition (intentional food additives) and/or unintentional contamination (unintentional food contaminants) of food products-often linked to environmental pollution. Understanding how this persistent, diverse exposure impacts GI health is of paramount importance, as deterioration of the GI barrier is proposed to be the first step towards systemic inflammation and chronic disease. Therefore, we aim to evaluate the impact of ingestion of environmental factors on inflammatory processes in the GI tract. In this review, we highlight human exposure to intentional food additives (e.g. emulsifiers, bulking agents) and unintentional food contaminants (e.g. persistent organic pollutants, pesticides, microplastics), then present evidence for their association with chronic disease, modification of the GI microbiota, increased permeability of the GI barrier, systemic dissemination of endotoxins, local (and distal) pro-inflammatory signalling, and induction of oxidative stress and/or endoplasmic reticulum stress. We also propose a link to NLRP3-inflammasome activation. These findings highlight the contribution of common environmental factors towards deterioration of GI health and the induction of pathophysiology associated with onset and maintenance of chronic inflammation in the GI tract.

Organophosphorus Pesticides as Modulating Substances of Inflammation through the Cholinergic Pathway

Organophosphorus pesticides (OPs) are widespread insecticides used for pest control in agricultural activities and the control of the vectors of human and animal diseases. However, OPs’ neurotoxic mechanism involves cholinergic components, which, beyond being involved in the transmission of neuronal signals, also influence the activity of cytokines and other pro-inflammatory molecules; thus, acute and chronic exposure to OPs may be related to the development of chronic degenerative pathologies and other inflammatory diseases. The present article reviews and discusses the experimental evidence linking inflammatory process with OP-induced cholinergic dysregulation, emphasizing the molecular mechanisms related to the role of cytokines and cellular alterations in humans and other animal models, and possible therapeutic targets to inhibit inflammation.

Immunotoxicological effects of insecticides in exposed fishes

Biologically active compounds used in agriculture that develop near aquatic environments easily spill into rivers or lakes. As a result, insecticides, herbicides and fungicides are observed worldwide in aquatic environments and accumulated in aquatic organism. Many insecticides, including organochlorine and organophosphate, have long been banned long ago because of their high persistence and non-target toxicity. However, previous studies have shown that persistent pesticides remain in aquatic organisms. The immune system is the first defense mechanism against exposure to persistent organic pollutants or pesticides that have been released into the aquatic environment. Many insecticides have been reported to cause immunotoxicity, which is represented by alteration of phagocytic and lysozyme activity. Recent studies show that immunotoxicity by insecticides exerts a more complex mechanism in fish. Insecticides induce immunotoxic effects, such as the release of inflammatory cytokines from head kidney macrophages and inhibition of immune cell proliferation in fish, which can lead to death in severe cases. Even currently used pesticides, such as pyrethroid, with low bioaccumulation have been shown to induce immunotoxicological effects in fish when exposed continuously. Therefore, this review describes the types and bioaccumulation of insecticides that cause immunotoxicity and detailed immunotoxicological mechanisms in fish tissues.

The cytoskeleton as a non-cholinergic target of organophosphate compounds

Current organophosphate (OP) toxicity research now considers potential non-cholinergic mechanisms for these compounds, since the inhibition of acetylcholinesterase (AChE) cannot completely explain all the adverse biological effects of OP. Thanks to the development of new strategies for OP detection, some potential molecular targets have been identified. Among these molecules are several cytoskeletal proteins, including actin, tubulin, intermediate filament proteins, and associated proteins, such as motor proteins, microtubule-associated proteins (MAPs), and cofilin. in vitro, ex vivo, and some in vivo reports have identified alterations in the cytoskeleton following OP exposure, including cell morphology defects, cells detachments, intracellular transport disruption, aberrant mitotic spindle formation, modification of cell motility, and reduced phagocytic capability, which implicate the cytoskeleton in OP toxicity. Here, we reviewed the evidence indicating the cytoskeletal targets of OP compounds, including their strategies, the potential effects of their alterations, and their possible participation in neurotoxicity, embryonic development, cell division, and immunotoxicity related to OP compounds exposure.

Evaluation of triazophos induced immunotoxicity of spleen and head kidney in fresh water teleost, Channa punctata

The utilization of pesticides has increased for destroying pests and protecting crops in the agriculture field. Triazophos is a commonly used organophosphorous insecticide that causes alterations in haematological and histological parameters in fish. The present study was designed to evaluate the effect of triazophos induced innate and cell mediated immunotoxicity in freshwater teleost, Channa punctata. Fishes were exposed to triazophos at concentrations 5 and 10% of LC₅₀ value for 10 and 20 days. Splenic and head kidney macrophage phagocytosis, nitric oxide production and superoxide production were assayed to evaluate the innate immunity. Cell-mediated immunity was measured through splenic and head kidney lymphocyte proliferation in presence of T and B cell mitogens. Results of the present study revealed that macrophage phagocytosis was significantly reduced after in vivo triazophos treatment. Differential suppressive effect of triazophos was also observed where mitogen induced splenic and head kidney lymphocyte proliferations were reduced after 10 and 20 days treatment. Concentration dependent effect of triazophos was observed in in vivo studies where the production of reactive oxygen and nitrogen intermediates were suppressed. This study describes the first investigation of the effect of triazophos on immune functions and will help to determine appropriate ecotoxicity and immunotoxicity in freshwater teleosts.

Analysis of suppressive effects of pesticide triazophos on leucocyte immune responses in a teleost, Channa Punctatus

Triazophos is a commonly used organophosphate insecticide, which inhibits the acetylcholinesterase enzyme and causes paralysis and death of insects. Impact of the pesticides on immunity has scarcely been investigated, especially in fishes. The present study was designed to analyze the immunotoxic role of in vitro triazophos exposure to the leucocytes in freshwater teleost, Channa punctatus. Triazophos, at in vitro concentrations of 0.1, 0.5, and 1 µg ml^-1, was used to study leucocyte phagocytosis, superoxide production, nitrite release, and lymphocyte proliferation. Dose-dependent suppression of various immune responses was observed. Nitrite release and superoxide production by leucocytes were reduced in cultures incubated with triazophos. Mitogen-induced lymphocyte proliferation was significantly reduced at 0.5 and 1 µg ml^-1 but not at 0.1 µg ml^-1 concentration of pesticide. The biphasic suppressive effect was also discovered while evaluating phagocytic response. These investigations describe the effects of pesticide on immune responses in C. punctatus, which are helpful in understanding the immunotoxicity in fish. Substantially more researches are required to help design the measures to combat ecotoxicity in freshwater bodies.

Alterations in the non-neuronal cholinergic system induced by in-vitro exposure to diazoxon in spleen mononuclear cells of Nile tilapia (O. niloticus)

Organophosphate pesticides as diazinon disrupt the neuroimmune communication, affecting the innate and adaptive immune response of the exposed organisms. Since the target molecule of diazinon is typically the acetylcholinesterase enzyme (AChE), the existence of a non-neuronal cholinergic system in leukocytes makes them susceptible to alterations by diazinon. Therefore, the aim of this work was to evaluate the activity of AChE, acetylcholine (ACh) concentration, and the expression of nicotinic ACh receptors (nAChR) and muscarinic ACh receptors (mAChR) in spleen mononuclear cells (SMNC) of Nile tilapia (O. niloticus) exposed in vitro to diazoxon, a diazinon metabolite. SMNC were exposed in-vitro to 1 nM, 1 μM, and 10 μM diazoxon for 24 h. The enzyme activity of AChE was then evaluated by spectrophotometry, followed by ACh quantification by ultra-performance liquid chromatography. Finally, mAChR and nAChR expression was evaluated by RT-qPCR. The results indicate that AChE levels are significantly inhibited at 1 and 10 μM diazoxon, while the relative expression of (M3, M4, and M5) mAChR and (β2) nAChR is reduced significantly as compared against SMNC not exposed to diazoxon. However, ACh levels show no significant difference with respect to the control group. The data indicate that diazoxon directly alters elements in the cholinergic system of SMNC by AChE inhibition or indirectly through the interaction with AChR, which is likely related to the immunotoxic properties of diazinon and its metabolites.

In-vitro effect of diazoxon, a metabolite of diazinon, on proliferation, signal transduction, and death induction in mononuclear cells of Nile tilapia fish (Oreochromis niloticus)

The immune response of teleosts (bonefish) is altered by diazinon (DZN), an organophosphate pesticide. It has been suggested that such alteration is due to the extraneuronal cholinergic system in fish leukocytes that renders these cells a target of pesticides. Diazoxon (DZO), the oxon metabolite of DZN, has been attributed immunotoxic effects. Still, to date there are no reports on the effects of DZO upon parameters involved in the signaling cascade of immune response cells. Therefore, this work evaluated the effect of DZO on key parameters of cell signaling (intracellular Ca²⁺ flux, ERK 1/2 phosphorylation), cell proliferation, and antiproliferative processes (apoptosis, senescence, mitochondrial membrane potential) in spleen mononuclear cells of Nile tilapia fish. The results obtained show that DZO does not affect cell proliferation but causes a lack of response to stimulation with PMA and ionomycin to release intracellular calcium. In addition, it inhibits ERK 1/2 phosphorylation and causes loss of mitochondrial membrane potential, apoptosis, and senescence. These results suggest that the lack of cell response to release intracytoplasmic Ca²⁺ inhibits ERK which disrupts the mitochondrial membrane potential, leading to cell apoptosis and senescence. These findings prove that DZO significantly affects key parameters involved in the survival of immune response cells.

Characterization and molecular evolution of claudin genes in the Pungitius sinensis

Claudins are a family of integrated membrane-bound proteins involving in paracellular tightness, barrier forming, ion permeability, and substrate selection at tight junctions of chordate epithelial and endothelial cells. Here, 39 putative claudin genes were identified in the Pungitius sinensis based on the high throughput RNA-seq. Conservative motif distribution in each group suggested functional relevance. Divergence of duplicated genes implied the species' adaptation to the environment. In addition, selective pressure analyses identified one site, which may accelerate functional divergence in this protein family. Pesticides cause environmental pollution and have a serious impact on aquatic organisms when entering the water. The expression pattern of most claudin genes was affected by organophosphorus pesticide, indicating that they may be involved in the immune regulation of organisms and the detoxification of xenobiotics. Protein-protein network analyses also exhibited 439 interactions, which implied the functional diversity. It will provide some references for the functional study on claudin genes.

Antioxidative and immunoprotective potential of Chlorella vulgaris dietary supplementation against chlorpyrifos-induced toxicity in Nile tilapia

This study highlighted the effects of chronic chlorpyrifos (CPF) exposure on Nile tilapia (Oreochromis niloticus) and the benefits of using dietary Chlorella vulgaris (Ch) to ameliorate CPF-induced toxicity. Genes encoding antioxidant enzymes and stress-responsive proteins in the liver as well as cytokine expression in the spleen and head kidney were evaluated in O. niloticus fed with a basal diet or diets containing 1, 2, and 3% of supplementary Ch against 15 mg/L CPF at 4 and 8 weeks. CPF-exposed groups displayed a notable induction in the hepatic expression of heat shock protein 70/hsp70, glutathione peroxidase/GPx, and glutathione synthase/GSS, while glutathione reductase/GSR was markedly decreased. The mRNA levels of interleukin 1β/IL-1β, TNF-α, transforming growth factor β1/TGFβ1, and interleukin 8/ IL-8 in the spleen and head kidney increased significantly after CPF exposure. Interestingly, Ch supplementation, particularly at levels 2 and 3%, was able to modulate the stress and immune-related genes of Nile tilapia sub-chronically exposed to CPF. These outcomes provide valuable insights regarding the toxic impact of chronic exposure to CPF in fish at the molecular level and a better understanding of the Ch dietary vital roles. Besides, our findings encourage adequate monitoring of pesticide levels owing to its impacts on fish health and human as a final consumer.

Transcriptome-Based Identification and Molecular Evolution of the Cytochrome P450 Genes and Expression Profiling under Dimethoate Treatment in Amur Stickleback (Pungitius sinensis)

Cytochrome P450s (CYPs) are a family of membrane-bound mono-oxygenase proteins, which are involved in cell metabolism and detoxification of various xenobiotic substances. In this study, we identified 58 putative CYP genes in Amur stickleback (Pungitius sinensis) based on the transcriptome sequencing. Conserved motif distribution suggested their functional relevance within each group. Some present recombination events have accelerated the evolution of this gene family. Moreover, a few positive selection sites were identified, which may have accelerated the functional divergence of this family of proteins. Expression patterns of these CYP genes were investigated and indicated that most were affected by dimethoate treatment, suggesting that CYPs were involved in the detoxication of dimethoate. This study will provide a foundation for the further functional investigation of CYP genes in fishes.

Comparative Analysis of the aquaporin Gene Family in 12 Fish Species

Simple Summary

Aquaporins (Aqps) are a group of membrane proteins. In this study, 166 Aqp genes were identified in 12 fish species. Gene organization, motif distribution, recombination, and selection pressure were performed to investigate their evolutionary characteristics. In addition, expression profiles of Aqps were also examined under pathogens infection and organophosphorus pesticide stress. This study will provide a useful reference for further functional study.

Abstract

Aquaporins (Aqps) are a class of water channel proteins that play key roles in many physiological functions and cellular processes. Here, we analyzed 166 putative Aqp genes in 12 fish species and divided them into four groups. Gene organization and motif distribution analyses suggested potentially conserved functions in each group. Several recombination events were identified in some members, which accelerate their divergence in evolution. Furthermore, a few positive selection sites were identified, and mutations at these sites could alter the stability of Aqp proteins. In addition, expression profiles of some Aqp genes under pathogen infection and organophosphorus pesticide stress were also investigated. The result implied that several Aqp genes may affect different immune responses and osmoregulation. This study provides a comparative analysis of the fish Aqp gene family to facilitate further functional analyses.

Muscarinic acetylcholine receptor expression in brain and immune cells of Oreochromis niloticus

Nervous and immune systems maintain a bidirectional communication, expressing receptors for neurotransmitters and cytokines. Despite being well established in mammals, this has been poorly described in lower vertebrates as fishes. Experimental evidence shows that the neurotransmitter acetylcholine (ACh) regulates the immune response. In this research, we evaluated mRNA levels of muscarinic acetylcholine receptor (mAChR) in spleen mononuclear cells of Nile tilapia (Oreochromis niloticus) and compared the expression levels of immune cells with the brain. The mAChR subtypes (M2-M5A) were detected in both tissues, but mAChRs mRNA levels were higher in immune cells. This data have a potential use in biomedical and comparative immunology fields.

Expression of immune, antioxidant and stress related genes in different organs of common carp exposed to indoxacarb

The aim of the present study was to investigate the effects of chronic exposure of common carp (Cyprinus carpio) to indoxacarb on immune, antioxidant and stress gene expression. After 21 days exposure to 0, 0.75, 1.5 and 3 ppm indoxacarb, expression of IL-1β, IL-8, IL-10, TNF-α, IFN-γ, SOD, CAT, HSP70, IGF-I and IGF-II were assessed in liver, kidney and gills. In general, exposure to low concentration of indoxacarb increased inflammatory cytokine gene expression (IL-1β, IL-8, IL-10, TNF-α and IFN-γ) and inhibits inflammatory cytokines' expression at higher concentrations. The assessment of antioxidant gene expression (SOD and CAT) in different organs indicate that they were increased by low concentrations of indoxacarb to deal with primary oxidative situation. However, higher concentrations of indoxacarb caused reduction in oxidative gene expression. IGF genes expression in liver significantly increased at a concentration of 0.75 ppm treatment, then it decreased at 1.5 ppm indoxacarb and increased again by increasing in the indoxacarb concentration to 3 ppm. The expression of HSP70 in kidney showed a significant elevation in 0.75 and 1.5 ppm treatments compared with 3 ppm treatment and the control group. The expression of this gene in liver was significantly increased in 1.5 and 3 ppm treatments. The same pattern of expression was also observed in gill. Overall, indoxacarb exposure affects common carp health at transcription levels. Changes in the genes expression generally suggest that indoxacarb exposure led to interference in inflammation, oxidative stress and tissue damage.

Phagocytosis and ROS production as biomarkers in Nile tilapia (Oreochromis niloticus) leukocytes by exposure to organophosphorus pesticides

Organophosphorus pesticides (OPs) are broad-spectrum insecticides. One of the commonly used OPs is diazinon (DZN). The aim of this study was to evaluate the immunotoxic effect of DZN on phagocytic parameters of blood leukocytes using the teleost fish Oreochromis niloticus as a study model. For this purpose, fish were exposed in vivo to 0.97, 1.95 and 3.97 mg/L of DZN for 6 and 24 h. Our results indicated that phagocytic active cells decreased in fish exposed in vivo to 0.97 and 1.95 mg/L of DZN for 6 and 24 h. Regarding ROS production, H₂O₂ and O₂^- levels were higher on fish exposed to 1.95 mg/L for 6 and 24 h, while H₂O₂ production increased at 0.97 mg/L for 24 h. From this we can conclude that phagocytic parameters are sensitive to assess the effect of acute intoxication with organophosphorus pesticides on Nile tilapia.

Comparative analysis of the tetraspanin gene family in six teleost fishes

Tetraspanins are a family of membrane proteins, which play important roles in many aspects of cell biology and physiology via binding other tetraspanins or proteins. In this study, we identified 251 putative tetraspanin genes in 6 teleost fishes. Conserved gene organization and motif distribution suggested their functional relevance existing in each group. Synteny analyses implied conserved and dynamic evolution characteristics of this gene family in several vertebrates. We also found that some recombination events have accelerated the evolution of this gene family. Moreover, a few positive selection sites were identified. Expression patterns of some tetraspanins were further studied under organophosphorus stress using transcriptome sequencing. Functional network analyses identified some interacting genes that exhibited 174 interactions, which reflected the diversity of tetraspanin binding proteins. The results will provide a foundation for the further functional investigation of the tetraspanin genes in fishes.

Mechanisms of organophosphorus pesticide toxicity in the context of airway hyperreactivity and asthma

Numerous epidemiologic studies have identified an association between occupational exposures to organophosphorus pesticides (OPs) and asthma or asthmatic symptoms in adults. Emerging epidemiologic data suggest that environmentally relevant levels of OPs may also be linked to respiratory dysfunction in the general population and that in utero and/or early life exposures to environmental OPs may increase risk for childhood asthma. In support of a causal link between OPs and asthma, experimental evidence demonstrates that occupationally and environmentally relevant OP exposures induce bronchospasm and airway hyperreactivity in preclinical models. Mechanistic studies have identified blockade of autoinhibitory M2 muscarinic receptors on parasympathetic nerves that innervate airway smooth muscle as one mechanism by which OPs induce airway hyperreactivity, but significant questions remain regarding the mechanism(s) by which OPs cause neuronal M2 receptor dysfunction and, more generally, how OPs cause persistent asthma, especially after developmental exposures. The goals of this review are to 1) summarize current understanding of OPs in asthma; 2) discuss mechanisms of OP neurotoxicity and immunotoxicity that warrant consideration in the context of OP-induced airway hyperreactivity and asthma, specifically, inflammatory responses, oxidative stress, neural plasticity, and neurogenic inflammation; and 3) identify critical data gaps that need to be addressed in order to better protect adults and children against the harmful respiratory effects of low-level OP exposures.

Screening for Lactobacillus plantarum Strains That Possess Organophosphorus Pesticide-Degrading Activity and Metabolomic Analysis of Phorate Degradation

This work performed a large scale assessment for organophosphorus pesticides (OPPs) degradation activity of 121 Lactobacillus (L.) plantarum strains. Six L. plantarum strains (P9, IMAU80110, IMAU40100, IMAU10585, IMAU10209, and IMAU80070) were found to possess high capacity of degrading three commonly used OPPs, namely dimethoate, phorate, and omethoate; and they were selected for more detailed characterization. Moreover, the three OPPs were mainly detected in the culture supernatants but not in the cell extracts, further confirming that the OPPs were degraded rather than absorbed by the cells. Among the six selected strains, P9 was most tolerant to gastrointestinal juices and bile. We thus used ultra-high performance liquid chromatography electron spray ionization coupled with time-of-flight mass spectrometry (UPLC/ESI-Q-TOF/MS) to generate the metabolomic profiles of the strain P9 growing in MRS medium with and without containing phorate. By using orthogonal partial least squares discriminant analysis, we identified some potential phorate-derived degradative products. This work has identified novel lactic acid bacteria resources for application in pesticide degradation. Our results also shed light on the phorate degradation mechanism by L. plantarum P9.

Alterations of cytochrome P450 and the occurrence of persistent organic pollutants in tilapia caged in the reservoirs of the Iguaçu River

Environmental chemicals originating from human activities, such as persistent organic pollutants (POPs), may interfere with the endocrine system of aquatic organisms. The effect of these chemicals on biota and human populations is of high public concern but remains poorly understood, especially in aquatic environments of South America. The aim of this study was to investigate the bioavailability of POPs and the related effects in caged male tilapia (Oreochromis niloticus) in four cascading reservoirs of the Iguaçu River, Southern Brazil. POPs including organochlorine pesticides (OCPs), polychlorinated biphenyl (PCBs), and polybrominated diphenyl ethers (PBDEs) were determined in the reservoir water and tissue samples of tilapia after two months of exposure. The PCB levels in water (14.7 ng L^-1) were 14 times higher than the limits permitted by the Brazilian legislation in the Salto Santiago (SS) reservoir. Similarly, concentrations of aldrin and its metabolites (6.05 ng L^-1) detected in the water sample of the Salto Osório (SO) reservoir were also above the permitted limits. RT-qPCR analysis revealed different transcript levels of cytochrome P450 enzymes (CYP1A and CYP3A) in the liver among the four groups, with induced activity in tilapia from the SS reservoir. Quantification of the CYP3A mRNA expression and catalytic activity showed higher values for fish caged at the SS reservoir. The fish from this site also had a higher number of eosinophils observed in the testes. Although overt measurements of endocrine disruption were not observed in caged fish, alteration of CYP enzymes with co-occurrence of organochlorine contaminants in water may suggest bioavailability of contaminants from agricultural sources to biota. Additional studies with feral or caged animals for a longer duration may be necessary to evaluate the risks of the waterways to humans and wildlife.

Immune response induced by major environmental pollutants through altering neutrophils in zebrafish larvae

Environmental pollutants may cause adverse effects on the immune system of aquatic organisms. However, the cellular effects of pollutants on fish immune system are largely unknown. Here, we exploited the transgenic zebrafish Tg(lysC:DsRed2) larva as a preliminary screening system to evaluate the potential inflammatory effects of environmental pollutants. Tg(lysC:DsRED2) larvae aged 7-day-postfertilization (7 dpf) were treated with selected environmental chemicals for 24 h (24 h) and the number of neutrophils were quantified using both image analysis and fluorescence activated cell sorting (FACS). We found that the numbers of neutrophils in the Tg(lysC:DsRED2) larvae were significantly increased by most of the organic chemicals tested, including E2 (17β-estradiol), BPA (Bisphenol-A), NDEA (N-nitrosodiethylamine), 4-NP (4-Nitrophenol) and Lindane (γ-hexachlorocyclohexane). Neutrophil numbers were also increased by all the metals tested (Na2HAsO4· 7H2O, Pb(NO3)2, HgCl₂, CdCl2, CuSO₄·5H₂O, ZnSO4, and K2Cr2O7). The only exception was TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), which significantly reduced the number of neutrophils after exposure. Additionally, the transcription of genes (lyz, mpo, tnfα and il8) related to fish immune system were significantly modulated upon exposure to some of the selected chemicals such as E2, TCDD, Cu and Cd. This study revealed that representatives of major categories of environmental pollutants could cause an acute inflammatory response in zebrafish larvae as shown by alterations in the neutrophils, which may imply a common immunotoxicity mechanism for most environmental pollutants. This study has also demonstrated that Tg(lyz:DsRed2) transgenic zebrafish is an excellent tool for screening environmental chemicals with potential inflammatory effects through FACS-facilitated neutrophil counting.

Immune competence assessment in marine medaka (Orzyias melastigma)-a holistic approach for immunotoxicology

Many anthropogenic pollutants in coastal marine environments can induce immune impairments in wild fish and reduce their survival fitness. There is a pressing need to establish sensitive and high throughput in vivo tools to systematically evaluate the immunosuppressive effects of contaminants in marine teleosts. This study reviewed a battery of in vivo immune function detection technologies established for different biological hierarchies at molecular (immune function pathways and genes by next generation sequencing (NGS)), cellular (leukocytes profiles by flow cytometry), tissues/organ system (whole adult histo-array), and organism (host resistance assays (HRAs)) levels, to assess the immune competence of marine medaka Oryzias melastigma. This approach enables a holistic assessment of fish immune competence under different chemical exposure or environmental scenarios. The data obtained will also be useful to unravel the underlying immunotoxic mechanisms. Intriguingly, NGS analysis of hepatic immune gene expression profiles (male > female) are in support of the bacterial HRA findings, in which infection-induced mortality was consistently higher in females than in males. As such, reproductive stages and gender-specific responses must be taken into consideration when assessing the risk of immunotoxicants in the aquatic environment. The distinct phenotypic sexual dimorphism and short generation time (3 months) of marine medaka offer additional advantages for sex-related immunotoxicological investigation.

Assessment of complex water pollution with heavy metals and Pyrethroid pesticides on transcript levels of metallothionein and immune related genes

Alteration of immunological function of an aquatic organism can be used as an indicator for evaluating the direct effect of exposure to pollutants. The aim of this work is to assess the impact of complex water pollution with special reference to Pyrethroid pesticides and heavy metals on mRNA transcript levels of Metallothionine and some immune related genes of Nile tilapia (Oreochromas Niloticus). Residues of six heavy metals and six Pyrethroid were assessed in water as well as fish tissues at three different sites of Lake Burullus, located at Northern Egypt. Variations of water physicochemical properties associated with different levels of heavy metals at the three different sections were recorded. Tissue residues of Fe, Mn and Zn, Cu, Ni exceed water levels in contrast to elevated water level of Pb. All assessed Pyrethroids are detected in fish tissue samples with higher concentration (3-42 folds) than that found in water samples especially Cypermethrin. Significant down-regulation of expression levels of metallothionein (MT) at the three sections of the lake was observed. The expression of immune related genes (IgM) and inflammatory cytokines (TNF, IL.8 and IL.1) were affected. IgM and TNF were significantly down-regulated at eastern and western section of the lake; meanwhile the expression of IL8 is down regulated at the three sections of the lack. IL1 was significantly up-regulated at eastern and middle sections. We conclude that, variable gene expression of MT and immune-related genes at the three sections of the lack impose different response to complex water pollution in relation to variable aquatic environment.

Characteristics of selected bioaccumulative substances and their impact on fish health

The aim of this article was to evaluate the influence and effects of chosen bioaccumulative substances i.e. heavy metals, pesticides, and polychlorinated biphenyls (PCBs) on fish, as well as provide information on time trends and potential threat to human health. Chemical substances which pollute water may affect living organisms in two ways. First of all, large amounts of chemical substances may cause sudden death of a significant part of the population of farmed fish, without symptoms (i.e. during breakdown of factories or industrial sewage leaks). However, more frequently, chemical substances accumulate in tissues of living organisms affecting them chronically. Heavy metals, pesticides, and polychlorinated biphenyls are persistent substances with a long-lasting biodegradation process. In a water environment they usually accumulate in sediments, which makes them resistant to biodegradation processes induced by, e.g., the UV light. These substances enter the fish through direct consumption of contaminated water or by contact with skin and gills. Symptoms of intoxication with heavy metals, pesticides, and PCBs may vary and depend on the concentration and bioavailability of these substances, physicochemical parameters of water, and the fish itself.

Occupational and environmental exposure to pesticides and cytokine pathways in chronic diseases (Review)

Pesticides can exert numerous effects on human health as a consequence of both environmental and occupational exposures. The available knowledge base suggests that exposure to pesticides may result in detrimental reproductive changes, neurological dysfunction and several chronic disorders, which are defined by slow evolution and long-term duration. Moreover, an ever increasing amount of data have identified an association between exposure to pesticides and the harmful effects on the immune system. The real impact of alterations in humoral cytokine levels on human health, in particular in the case of chronic diseases, is still unclear. To date, studies have suggested that although exposure to pesticides can affect the immune system functionally, the development of immune disorders depends on the dose and duration of exposure to pesticides. However, many of the respective studies exhibit limitations, such as a lack of information on exposure levels, differences in the pesticide administration procedures, difficulty in characterizing a prognostic significance to the weak modifications often observed and the interpretation of obtained results. The main challenge is not just to understand the role of individual pesticides and their combinations, but also to determine the manner and the duration of exposure, as the toxic effects on the immune system cannot be separated from these considerations. There is a clear need for more well-designed and standardized epidemiological and experimental studies to recognize the exact association between exposure levels and toxic effects and to identify useful biomarkers of exposure. This review focuses on and critically discusses the immunotoxicity of pesticides and the impact of cytokine levels on health, focusing on the development of several chronic diseases.