Mixture effect of arsenic and fluoride at environmentally relevant concentrations in zebrafish (Danio rerio) liver: Expression pattern of Nrf2 and related xenobiotic metabolizing enzymes

Mixture of arsenic and chromium alters antioxidant, DNA repair and tumor suppressor gene expressions in zebrafish brain at environmental concentrations

Arsenic (As) and chromium (Cr) are two harmful toxicants as well as carcinogens which can coexist in polluted surface water and groundwater. This coexistence leads to mixture effects in animals including fish. Both of these heavy metals are reported to manifest reactive oxygen species (ROS) mediated toxicity. Though individual neurotoxic effects have been reported, their mixture effects, its mechanism and cellular responses against oxidative stress and DNA damages remain unknown. The present study evaluated the individual and mixture effects of As and Cr at their environmentally relevant concentrations in zebrafish (Danio rerio) brain after 15, 30 and 60 days of exposure. Nrf2, a transcription factor is involved in the expressional regulation of enzymes needed to maintain cellular redox homeostasis. This study reported the expressional pattern of Nrf2 and its associated xenobiotic metabolizing enzyme Nqo1 and other markers of oxidative stress such as ROS generation, reduced glutathione level, lipid peroxidation and catalase activity. Increased malondialdehyde (MDA) content, glutathione level, and catalase activity indicated oxidative stress in exposed groups. In addition, this study revealed expressional alterations of neurotoxicity marker (ache), DNA repair (ogg1, apex1, creb1, polb, mlh1, msh2 and msh6) and tumor suppressor (p53, brca2) genes. Results of ROS generation, MDA level, histopathological analysis, gene expression and immunofluorescence study confirmed that As and Cr did not show antagonistic effects in combination rather indicated additive effects which was dose-dependent but not always linear.

Combined heavy metals (As and Pb) affects antioxidant status and lipid metabolism in zebrafish (Danio rerio)

The potential risk of coexistence of mixed heavy metals in the aquatic environment has increased with the development of technology. Lead (Pb) and arsenic (As) are among the most widely applied heavy metals, whose single toxicity has been extensively investigated, but their combined toxicity has been reported relatively rarely. In this study, different concentrations of Pb (40 μg/L, 4 mg/L), As (32 μg/L, 3.2 mg/L) and their combinations (40 μg/L + 32 μg/L, 4 mg/L + 3.2 mg/L) were set up for 30 days to establish a heavy metal exposure model in zebrafish. Pathological sections, biochemical parameters and gene expression analysis were used to assess the toxicity effects of oxidative damage and lipid metabolism in the liver. Our results showed that combined exposure of As and Pb resulted in elevated ROS and MDA levels and upregulated expression of genes related to the Nrf2-Keap1/Are signaling pathway in female zebrafish, causing enhanced oxidative stress. Moreover, mixture of As and Pb was able to cause abnormal upregulation of lipid metabolism-related genes and reduced activity of fatty acid synthase (FAS) in the liver of female zebrafish. The abnormal decrease of carnitine palmitoyl transferase (CPT-1) and gene cpt1a in males were also observed. These results contributed to hepatic Triglyceride (TG) excessive accumulation, ultimately triggering a disturbance of lipid metabolism. These findings indicated that chronic exposure to As and Pb was capable of producing adverse effects on oxidative stress and lipid metabolism in fish in a sex-specific manner. This study provides new perspective for evaluating the combined effects of heavy metals in the aquatic environment.

Oxidative stress and mitochondrial dysfunctions induced by cyanobacterial microcystin-LR in primary grass carp hepatocytes

Microcystin-LR (MC-LR), a cyclic heptapeptide produced by freshwater cyanobacteria, induces a range of liver injuries. However, the mechanisms underlying MC-LR toxicity in primary hepatocytes of aquatic organisms remains poorly understood. In this study, we investigated the effects of MC-LR on oxidative stress and mitochondrial function using primarily cultured grass carp hepatocytes. The results revealed that IC50 of MC-LR on grass carp primary liver cells for 24 hours was 2.40 μmol/L. Based on 24h-IC50, concentrations of 0, 0.30, 0.60, and 1.20 μmol/L were used in subsequent experiments. MC-LR exposure led to a significant reduction in cell viability, induced abnormal cell morphology, and caused plasma membrane rupture, as indicated by elevated LDH activity in a concentration-dependent manner. Additionally, MC-LR exposure induced oxidative stress, resulting in increased ROS levels and downregulation of genes associated with oxidative stress, including keap1, nrf2, cat, sod1, gpx, gst, and gr (P<0.05). Furthermore, the electron microscopy results showed that MC-LR caused damage to the ultrastructure of primary hepatocytes, including mitochondrial membrane rupture, vacuolation, and induction of mitochondrial autophagy. Moreover, MC-LR exposure elevated intracellular Ca2+ concentration, reduced MMP and ATP levels, and inhibited mitochondrial respiratory chain complex I activity (P<0.05). qRT-PCR analysis demonstrated that MC-LR treatment significantly decreased the transcriptional levels of genes related to mitochondrial quality control including pgc-1α, tfam, nrf1, drp1, opa1, mfn1, and mfn2 (P<0.05). Collectively, our findings highlight that MC-LR causes oxidative stress and impairs mitochondrial function, leading to further hepatocyte damage, which provides insights into the mechanisms of MC-LR-induced hepatotoxicity and offers valuable references for further investigations.

Esculin, a Coumarin Glucoside Prevents Fluoride-Induced Oxidative Stress and Cardiotoxicity in Zebrafish Larvae

Fluoride (F-) is a major groundwater contaminant spread across the world. In excess concentrations, F- can be detrimental to living beings. F- exposure is linked to cellular redox dyshomeostasis, leading to oxidative stress-mediated pathologies including heart dysfunction. Due to its potent antioxidant properties, various phytochemicals are found to alleviate the symptoms of F- toxicity. Hence, we explore the protective effect of esculin (Esc), a coumarin glucoside on F--induced oxidative stress and cardiotoxicity in zebrafish larvae. The experimental groups consisted of NaF (50 ppm) and Esc (100 μM) groups treated alone and in combination with a control group for 6 h. The groups were maintained till 78 hpf after which the level of oxidants (ROS, LPO, and PCC) and antioxidants (GST, GSH, GPx, SOD, and CAT) were assessed. The results revealed that Esc pretreatment restored the depleted antioxidant markers and reduced the levels of oxidant in the Esc+NaF group, exhibiting its antioxidant potential. In addition, analyses of the heartbeat rate and hemoglobin integrity using o-Dianisidine staining were conducted in the control and experimental groups. Esc treatment prevents F- induced cardiac changes including tachycardia and altered blood flow. Further, the mRNA expression level of antioxidant genes (nrf2, gstp1, hmox1a, prdx1, and nqo1) and cardiac developmental genes (bmp2b, nkx2.5, myh6, and myl7) confirmed that Esc acts as a potent free radical scavenger and antioxidant defense enhancer, protecting zebrafish larvae from NaF-induced oxidative stress and heart dysfunction.

Acute arsenic exposure induces cyto-genotoxicity and histological alterations in Labeo rohita

BACKGROUND

Arsenic emerges as most potent hazardous element ranked as number one in ATSDR (Agency for Toxic Substances and Disease Registry) list, can easily accumulate in fish, transported to humans via consumption and affect humans and aquatic organisms. Considering above, current experiment designed to evaluate cyto-genotoxicity and histological alterations induced by arsenic in Labeo rohita used as an animal model.

METHODS

By applying complete randomized design sampling acclimatized individuals of Labeo rohita (10 batches of 10 each with triplicates) were exposed to nine definitive doses (12, 14, 16, 18, 20, 22, 24, 26 and 28 mgL-1) of arsenic in glass aquaria to determine 96-h lethal concentration (LC50) of arsenic. Control group without arsenic was also run simultaneously. After 96-h exposure various histo-biochemical parameters were evaluated in all experimental groups.

RESULTS

The 96-h lethal concentration of arsenic was found to be 20.2 mgL-1. Upon arsenic exposure, oxidative stress biomakers: catalase (CAT), superoxide dismutase (SOD) and lipid per oxidation (LPO) and accumulation of arsenic in all targeted organs were considerably (p ≤ 0.05) increased in dose dependent manner and in comparison, to unexposed (control) group. Serum liver function enzymes, immunological status (albumin, globulin and total protein), cortisol level and cytochrome P450 gene expression remarkably (p ≤ 0.05) altered on arsenic exposure. The histological analysis also showed destructive alterations on exposure to arsenic in gill and liver tissues.

CONCLUSION

These results confirmed that exposure of arsenic led to pronounced deleterious alterations in Labeo rohita and evidencing the need for monitoring alarmingly increasing concentration of arsenic.

Oxidative Stress in Kidney of Zebrafish due to Individual and Combined Exposure to Amoxicillin, Arsenic, and Fluoride: Involving Nrf2-Keap1-ARE Pathway

Toxic manifestations of different antibiotics and metal compounds have been studied comprehensively in the last decades; however, their co-toxicity on aquatic organisms is poorly investigated. This study aimed to evaluate the oxidative stress imposed on zebrafish kidney tissue when exposed to amoxicillin (AMX, 10 μg/L) alone or in combination with 50 μg/L of As2O3 (equivalent to 37.87 μg/L of As) and/or 15 mg/L of NaF (equivalent to 6.8 mg/L of F) for 15 days. We observed increased levels of cellular ROS, MDA, and GSH along with increased activity of CAT enzyme in all the treated groups. Disrupted histoarchitecture, including degeneration of tubular cells, vacuolation, and necrotic spots, was indicative of oxidative damage. mRNA expression of stress responsive genes like nrf2, gpx1, hsp70, keap1, nqo1, cat, and ho1 corroborated the data. Translocation of Nrf2 from cytoplasm to nucleus and its subsequent expression was higher for all the treated groups. Moreover, the mixture effects of AMX + As + F were more severe than the other combinations, while unique exposure with AMX had minimum effects. Highlighting the involvement of the Nrf2-Keap1-ARE pathway, these findings make us aware of the synergistic response of AMX, As, and F in the ecosystem, putting forward a great threat to humankind.

Focus on cognitive impairment induced by excessive fluoride: An update review

Fluorosis is a global public health concern. Prolonged exposure to excessive fluoride causes fluoride accumulation in the hippocampus, resulting in cognitive dysfunction. Cell death is necessary for maintaining tissue function and morphology, and changes in the external morphology of nerve cells and the function of many internal organelles are typical features of cell death; however, it is also a typical feature of cognitive impairment caused by fluorosis. However, the pathogenesis of cognitive impairment caused by different degrees of fluoride exposure varies. Herein, we provide an overview of cognitive impairment caused by excessive fluoride exposure in different age groups, and the underlying mechanisms for cognitive impairment in various model organisms. The mechanisms underlying these impairments include oxidative stress, synaptic and neurotransmission dysfunction, disruption of mitochondrial and energy metabolism, and calcium channel dysregulation. This study aims to provide potential insights that serve as a reference for subsequent research on the cognitive function caused by excessive fluoride.

Poison in the water: Arsenic's silent assault on fish health

Arsenic occurs across the world in freshwater and marine environments, menacing the survival of aquatic organisms. Organic and inorganic forms of this substance can be found, in which the inorganic form is more hazardous than the organic form. Most aquatic bodies contain inorganic arsenic species, but organic species are believed to be the dominant form of arsenic in the majority of fish. Natural and anthropogenic both are the sources of water contamination with arsenic. Its bioaccumulation and transfer from one trophic level to another in the aquatic food chain make arsenic a vital environmental issue. Continuous exposure to low concentrations of arsenic in aquatic organisms including fish leads to its bioaccumulation, which may affect organisms of higher trophic levels including large fishes or humans. Humans can be exposed to arsenic through the consumption of fish contaminated with arsenic. Hence, the present review facilitates our understanding about sources of arsenic, its bioaccumulation, food chain transfer, and its effect on the fish health. Also, "Poison in the Water: Arsenic's Silent Assault on Fish Health" serves as a wake-up call to recognize the pressing need to address arsenic contamination in water bodies. By understanding its devastating impact on fish health, we can strive to implement sustainable practices and policies that safeguard our precious aquatic environments and ensure the well-being of both wildlife and human communities that depend on them.

Arsenic and chromium induced hepatotoxicity in zebrafish (Danio rerio) at environmentally relevant concentrations: Mixture effects and involvement of Nrf2-Keap1-ARE pathway

Arsenic (As) and chromium (Cr), two well-known cytotoxic and carcinogenic metals are reported to coexist in industrial effluents and groundwater. Their individual toxicities have been thoroughly studied but the combined effects, especially the mechanism of toxicity and cellular stress response remain unclear. Considering co-exposure as a more realistic scenario, current study compared the individual and mixture effects of As and Cr in the liver of zebrafish (Danio rerio). Fish were exposed to environmentally relevant concentrations of As and Cr for 15, 30 and 60 days. ROS generation, biochemical stress parameters like lipid peroxidation, reduced glutathione content, catalase activity and histological alterations were studied. Results showed increase in ROS production, MDA content and GSH level; and vicissitude in catalase activity as well as altered histoarchitecture, indicating oxidative stress conditions after individual and combined exposure of As and Cr which were additive in nature. This study also included the expression of Nrf2, the key regulator of antioxidant stress responses and its nuclear translocation. Related antioxidant and xenobiotic metabolizing enzyme genes like keap1, nqo1, ho1, mnsod and cyp1a were also studied. Overall results indicated increased nrf2, nqo1, ho1, mnsod expression at all time points and increased cyp1a expression after 60 days exposure. Emphasizing on the Nrf2-Keap1 pathway, this study exhibited additive or sometimes synergistic effects of As and Cr in zebrafish liver.

Decreased Arsenic Disposition and Alteration of its Metabolic Profile in mice Coexposed to Fluoride

Inorganic arsenic (iAs) and fluoride (iF) are ubiquitous elements whose coexistence is frequent in several regions of the world due to the natural contamination of water sources destined for human consumption. It has been reported that coexposure to these two elements in water can cause toxic effects on health, which are controversial since antagonistic and synergistic effects have been reported. However, there is little information on the possible toxicological interaction between concurrent exposure to iAs and iF on the iAs metabolism profile.The goal of this study was to determine the effect of iF exposure on iAs methylation patterns in the urine and the tissues of female mice of the C57BL/6 strain, which were divided into four groups and exposed daily for 10 days through drinking water as follows: purified water (control); arsenite 1 mg/L, fluoride 50 mg/L and arsenite & fluoride 1:50 mg/L.To characterize the iAs methylation pattern in concomitant iF exposure, iAs and its methylated metabolites (MAs and DMAs) were quantified in the tissues and the urine of mice was exposed to iAs alone or in combination. Our results showed a statistically significant decrease in the arsenic species concentrations and altered relative proportions of arsenic species in tissues and urine in the As-iF coexposure group compared to the iAs-exposed group. These findings show that iF exposure decreases arsenic disposition and alters methylation capacity.Nevertheless, additional studies are required to elucidate the mechanisms involved in the iAs-iF interaction through iF exposure affecting iAs disposition and metabolism.

Lead induced genotoxicity and hepatotoxicity in zebrafish (Danio rerio) at environmentally relevant concentration: Nrf2-Keap1 regulated stress response and expression of biomarker genes

Genotoxic and hepatotoxic potentials of Pb at an environmentally relevant concentration (5 ppm) in zebrafish were investigated in the present study. Erythrocytic nuclear abnormality tests revealed the increased frequencies of abnormal erythrocytes after Pb exposure, indicating a strong genotoxic potential of Pb. Multiple stress-related parameters were further evaluated in liver, the major detoxifying organ. Pb caused increased production of ROS, which in turn caused severe oxidative stress. As a result, lipid peroxidation was increased, whereas reduced glutathione level and catalase activity was decreased. Alterations in liver histoarchitecture also served as evidence of Pb-induced hepatotoxicity. Pb-induced ROS stress triggered upregulation of Nrf2, Nqo1, Ho1; downregulation of Keap1, and altered mRNA expressions of Mn-sod, Cu/Zn-sod, gpx1, cyp1a, ucp2 suggesting involvement of Nrf2-Keap1-ARE signaling in cellular defence. Nrf2-keap1 is a sensitive biomarker of Pb-induced ROS stress. Overexpression of Hsp70 and other genes in hepatocytes might help cell survival under oxidative stress generation.

Environmentally relevant lead alters nuclear integrity in erythrocytes and generates oxidative stress in liver of Anabas testudineus: Involvement of Nrf2-Keap1 regulation and expression of biomarker genes

Genotoxic and hepatotoxic effects of lead (Pb) on a freshwater fish, climbing perch (Anabas testudineus) were studied at an environmentally relevant concentration (43.3 ppm). The genotoxic potential of Pb was confirmed by micronucleus study, with increased frequencies of erythrocytic nuclear alterations like lobed, blebbed, notched, fragmented, and micronuclei were observed in erythrocytes in treated groups as compared to control. Inorganic Pb induces oxidative stress which is a consequence of elevated level of Reactive Oxygen Species. Hepatotoxicity was assessed both by the oxidative stress and cellular responses that emerged due to the toxic assault of Pb in the liver, the most important detoxifying organ. Upregulation of xenobiotic metabolizing enzyme like catalase was evident after 15, 30, and 90 days of exposure, and a profound effect was observed on 30th days. The level of lipid peroxidation and reduced glutathione was increased after Pb exposure. Histoarchitectural damages of liver were distinctly evident in treated fish. Western blot analysis confirmed the expressional alterations of stress-responsive marker proteins like Nrf2, Keap1, Hsp70, and Nqo1. Pb exposure resulted in increased expression of Hsp70, Nrf2, and Nqo1, whereas Keap1 was downregulated, suggesting the involvement of Nrf2-Keap1 regulation as a cytoprotective mechanism against Pb toxicity.

Effects of water fluoridation on early embryonic development of zebrafish

Fluoride has strong electronegativity and exposes diversely in nature. Water fluoridation is the most pervasive form of occurrence, representing a significant threat to human health. In this study, we investigate the morphometric and physiological alterations triggered by fluoride stimulation during the embryogenesis of zebrafish and reveal its putative effects of stage- and/or dose-dependent. Fluoride exhibits potent biological activity and can be extensively absorbed by the yolk sac, exerting significant effects on the development of multiple organs. This is primarily manifested as restricted nutrient utilization and elevated levels of lipid peroxidation, further leading to the accumulation of superoxide in the yolk sac, liver, and intestines. Moreover, pericardial edema exerts pressure on the brain and eye development, resulting in spinal curvature and reduced body length. Besides, acute fluoride exposure with varying concentrations has led to diverse teratogenic outcomes. A low dose of water fluoridation tends to induce abnormal development of the embryonic yolk sac, while vascular malformation is widely observed in all fluoride-treated groups. The effect of fluoride exposure on blood circulation is universally present, even in zebrafish larvae that do not exhibit obvious deformities. Their swimming behavior is also affected by water fluoridation, resulting in reduced activity and delayed reactions. In conclusion, this study provides valuable insights into the monitoring of environmental quality related to water fluoridation and disease prevention.

Fluoride exposure confers NRF2 activation in hepatocyte through both canonical and non-canonical signaling pathways

Due to the high abundance in the Earth's crust and industrial application, fluoride is widely present in our living environment. However, excessive fluoride exposure causes toxicity in different organs. As the most important detoxification and excretion organ, liver is more easily involved in fluoride toxicity than other organs, and oxidative stress is considered as the key mechanism related with fluoride hepatotoxicity. In this study, we mainly investigated the role of nuclear factor erythroid-derived 2-like 2 (NRF2, a core transcription factor in oxidative stress) in fluoride exposure-induced hepatotoxicity as well as the related mechanism. Herein, liver cells (BNL CL.2) were treated with fluoride in different concentrations. The hepatotoxicity and NRF2 signaling pathway were analyzed respectively. Our results indicated that excessive fluoride (over 1 mM) resulted in obvious toxicity in hepatocyte and activated NRF2 and NRF2 target genes. The increased ROS generation after fluoride exposure suppressed KEAP1-induced NRF2 ubiquitylation and degradation. Meanwhile, fluoride exposure also led to blockage of autophagic flux and upregulation of p62, which contributed to activation of NRF2 via competitive binding with KEAP1. Both pharmaceutical activation and genetic activation of NRF2 accelerated fluoride exposure-induced hepatotoxicity. Thus, the upregulation of NRF2 in hepatocyte after fluoride exposure can be regarded as a cellular self-defense, and NRF2-KEAP1 system could be a novel molecular target against fluoride exposure-induced hepatotoxicity.

Curcumin alleviates bisphenol AF-induced oxidative stress and apoptosis in caprine endometrial epithelial cells via the Nrf2 signaling pathway

Bisphenol AF (BPAF), a BPA-substitute, has been widely used in industrial compounds throughout the world. Several studies have shown that BPAF has endocrine interference and reproductive toxicity. However, the toxic effects of BPAF on pregnancy and placenta of goats are still unclear. Therefore, the objective of this study was to reveal the toxic effect of BPAF by using an in vitro culture model of caprine endometrial epithelial cells (EECs) and further attempted to alleviate the toxicity by curcumin pretreatment. The results showed that BPAF induces significant effects on EECs, including decreased cell viability and mitochondrial membrane potential (△ψm), elevating intracellular reactive oxygen species (ROS), promoting cell apoptosis through upregulating the expression of Bax, Cytochrome c, and downregulating the expression of Bcl-2. Meanwhile, BPAF induced dysregulation of oxidative stress by increasing the levels of malondialdehyde (MDA) and glutathione peroxidase (GSH-Px) but decreasing the activities of superoxide dismutase (SOD). However, curcumin pretreatment could significantly attenuate BPAF-induced toxic effects in EECs. Further study revealed that BPAF treatment could activate mitogen-activated protein kinase (MAPK) pathway and nuclear factor-erythroid 2-related factor 2 (Nrf2) expression, but curcumin pretreatment significantly inhibited the activation of MAPK signal pathway and Nrf2 expression induced by BPAF. Overall, this study indicated that curcumin could prevent BPAF-induced EECs cytotoxicity, which provides a potential therapeutic strategy for female infertility associated with BPAF exposure.

Chronic exposure to environmentally relevant concentration of fluoride impairs osteoblast's collagen synthesis and matrix mineralization: Involvement of epigenetic regulation in skeletal fluorosis

Globally, 200 million people are suffering from toxic manifestations of Fluoride(F), dental and skeletal fluorosis; unfortunately, there is no treatment. To unravel the pathogenesis of skeletal fluorosis, we established fluorosis mice by treating environmentally relevant concentration of F (15 ppm NaF) through drinking water for 4 months. As in skeletal fluorosis, locomotor disability, crippling deformities occur and thus, our hypothesis was F might adversely affects collagen which gives the bone tensile strength. This work inevitably had to be carried out on osteoblast cells, responsible for synthesis, deposition, and mineralization of bone matrix. Isolated osteoblast cells were confirmed by ALP activity and mineralized nodules formation. Expression of collagen Col1a1, Col1a2, COL1A1 was significantly reduced in treated mice. Further, a study revealed the involvement of epigenetic regulation by promoter hypermethylation of Col1a1; expressional alterations of transcription factors, calcium channels and other genes e.g., Cbfa-1, Tgf-β1, Bmp1, Sp1, Sp7, Nf-Kb p65, Bmp-2, Bglap, Gprc6a and Cav1.2 are associated with impairment of collagen synthesis, deposition and decreased mineralization thus, enfeebling bone health. This study indicates the possible association of epigenetic regulation in skeletal fluorosis. However, no association was found between polymorphisms in the Col1a1 (RsaI, HindIII) and Col1a2 (RsaI, HindIII) genes with fluorosis in mice.

A Short Review of the Toxicity of Dentifrices-Zebrafish Model as a Useful Tool in Ecotoxicological Studies

This review aims to summarize the literature data regarding the effects of different toothpaste compounds in the zebrafish model. Danio rerio provides an insight into the mechanisms of the ecotoxicity of chemicals as well as an assessment of their fate in the environment to determine long-term environmental impact. The regular use of adequate toothpaste with safe active ingredients possessing anti-bacterial, anti-inflammatory, anti-oxidant, and regenerative properties is one of the most effective strategies for oral healthcare. In addition to water, a typical toothpaste consists of a variety of components, among which three are of predominant importance, i.e., abrasive substances, fluoride, and detergents. These ingredients provide healthy teeth, but their environmental impact on living organisms are often not well-known. Each of them can influence a higher level of organization: subcellular, cellular, tissue, organ, individual, and population. Therefore, it is very important that the properties of a chemical are detected before it is released into the environment to minimize damage. An important part of a chemical risk assessment is the estimation of the ecotoxicity of a compound. The zebrafish model has unique advantages in environmental ecotoxicity research and has been used to study vertebrate developmental biology. Among others, the advantages of this model include its external, visually accessible development, which allows for providing many experimental manipulations. The zebrafish has a significant genetic similarity with other vertebrates. Nevertheless, translating findings from zebrafish studies to human risk assessment requires careful consideration of these differences.

Ameliorative effects of different doses of selenium against fluoride-triggered apoptosis and oxidative stress-mediated renal injury in rats through the activation of Nrf2/HO-1/NQO1 signaling pathway

Excess fluoride (F) exposure can cause oxidative stress in the kidney. As an antioxidant, selenium (Se) can potentially protect the kidney from F-induced injury in rats. Hence, the histopathological, renal biochemical, oxidative stress, and apoptotic-related indices upon exposure to 100 mg/L sodium fluoride (NaF) and various doses of sodium selenite (Na₂SeO₃; 0.5, 1, and 2 mg/L) were assessed. Our results demonstrated that F-mediated renal structural damage and apoptosis elevated the content of serum creatinine (SCr), inhibited the activity of catalase (CAT) in serum, and increased the production of reactive oxygen species (ROS) in kidney and malondialdehyde (MDA) in serum. Interestingly, 1 mg/L dietary supplementation of Se tangibly mitigated these injuries. Furthermore, F could also change the gene and protein expression of the nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and NAD(P)H quinone oxidoreductase1 (NQO1). Concomitantly, the different concentrations of Se notably alleviated their expression. Taken together, 1-2 mg/L Se ameliorated F-induced renal injury through oxidative stress and apoptosis-related routes. The recorded ameliorative effects might be related to the activation of the Nrf2/HO-1/NQO1 signaling pathway.

Co-exposure to arsenic and fluoride to explore the interactive effect on oxidative stress and autophagy in myocardial tissue and cell

Co-contamination of arsenic and fluoride is widely distributed in groundwater. However, little is known about the interactively influence of arsenic and fluoride, especially the combined mechanism in cardiotoxicity. Cellular and animal models exposure to arsenic and fluoride were established to assess the oxidative stress and autophagy mechanism of cardiotoxic damage using the factorial design, a widely used statistical method for assessing two factor interventions. In vivo, combined exposure to high arsenic (50 mg/L) and high fluoride (100 mg/L) induced myocardial injury. The damage is accompanied by accumulation of myocardial enzyme, mitochondrial disorder, and excessive oxidative stress. Further experiment identified that arsenic and fluoride induced the accumulation of autophagosome and increased expression level of autophagy related genes during the cardiotoxicity process. These findings were further demonstrated through the in vitro model of arsenic and fluoride-treated the H9c2 cells. Additionally, combined of arsenic-fluoride exposure possesses the interactively influence on oxidative stress and autophagy, contributing to the myocardial cell toxicity. In conclusion, our data suggest that oxidative stress and autophagy are involved in the process of cardiotoxic injury, and that these indicators showed interaction effect in response to the combined exposure of arsenic and fluoride.

Differential susceptibility to arsenic in glutathione S-transferase omega 2 (GST-O2)-targeted freshwater water flea Daphnia magna mutants

To examine the role of glutathione S-transferase omega class (GST-O2) genes in the biotransformation and detoxification in Daphnia magna, various responses such as in vivo endpoints, arsenic speciation, enzymatic activities, and gene expression pathways related to arsenic metabolism were investigated in wild-type (WT) and GST-O2-mutant-type (MT) fleas produced by CRISPR/Cas9. Sensitivity to arsenic in MT fleas was higher than in WT fleas. Also, the reduction rate of arsenate (As^V) to arsenite (As^III) in the MT group was significantly lower and led to accumulation of higher arsenic concentrations, resulting in decreased protection against arsenic toxicity. Relative mRNA expression of other GST genes in the GST-O2-targeted MT group generally increased but the enzymatic activity of GST decreased compared with the WT group. Oxidative stress on arsenic exposure was more strongly induced in the MT group compared with the WT group, resulting in a decrease in the ability to defend against toxicity in GST-O2-targeted mutant D. magna. Our results suggest that GST-O2 plays an important role in arsenic biotransformation and detoxification functions in D. magna.

Role of oxidative stress-mediated cell death and signaling pathways in experimental fluorosis

Free radicals and other oxidants have enticed the interest of researchers in the fields of biology and medicine, owing to their role in several pathophysiological conditions, including fluorosis (Fluoride toxicity). Radical species affect cellular biomolecules such as nucleic acids, proteins, and lipids, resulting in oxidative stress. Reactive oxygen species-mediated oxidative stress is a common denominator in fluoride toxicity. Fluorosis is a global health concern caused by excessive fluoride consumption over time. Fluoride alters the cellular redox homeostasis, and its toxicity leads to the activation of cell death mechanisms like apoptosis, autophagy, and necroptosis. Even though a surfeit of signaling pathways is involved in fluorosis, their toxicity mechanisms are not fully understood. Thus, this review aims to understand the role of reactive species in fluoride toxicity with an outlook on the effects of fluoride in vitro and in vivo models. Also, we emphasized the signal transduction pathways and the mechanism of cell death implicated in fluoride-induced oxidative stress.

Phosphorus Nutrition in Songpu Mirror Carp (Cyprinus carpio Songpu) During Chronic Carbonate Alkalinity Stress: Effects on Growth, Intestinal Immunity, Physical Barrier Function, and Intestinal Microflora

Carbonate alkalinity is a major environmental stress factor affecting aquatic feed configuration, which easily causes oxidative stress and hypoimmunity for fish. Hence, the purpose of the study is to assess the potential effect of phosphorus on growth, intestinal oxidation resistance, physical barrier function, and microflora for Songpu mirror carp (Cyprinus carpio Songpu) (initial average weight of 2.95 ± 0.21 g) reared at the high-concentration carbonate alkalinity environment. A two-factor, three-level (2 × 3) design was applied, in which diets with three different phosphorus levels (3.6, 7.0, and 10.5 g/kg dry matter) were randomly assigned to 0 and 15 mmol/L carbonate alkalinity groups with three replicate aquariums. After the 8-week trial, we found that weight gain rate (WGR), specific growth rate (SGR), protein efficiency ratio (PER), and lipase and amylase activities in the intestine significantly (p < 0.05) declined with increasing carbonate alkalinity. Carbonate alkalinity of 15 mmol/L significantly reduced glutathione peroxidase (GSHPx) activities in the intestine (p < 0.05). The relative expressions of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), glutathione peroxidase 1a (GPX1a), Clautin3, Clautin11, and tumor necrosis factor β (TNF-β) in the intestine were markedly downregulated by increasing carbonate alkalinity levels (p < 0.05), whilst the relative expressions of interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) in the intestine were markedly upregulated (p < 0.05). At the 15 mmol/L carbonate alkalinity treatment, Songpu mirror carp suffer from hypoimmunity status with failed digestion, antioxidant, inflammation, and immune response, thereby inducing impaired growth. Additionally, significant increments in the abundance of Proteobacteria and a significant decrease in the abundance of Fusobacteria and the Firmicutes/Bacteroidetes ratio were caused due to excessively high carbonate alkalinity (15 mmol/L) and excessively low dietary phosphorus supply (3.6 g/kg). Collectively, 7.0 g/kg dietary phosphorus supplementation was effective in promoting intestinal antioxidant enzyme activities and the corresponding gene expression via the Keap1-Nrf2 signaling pathway and in enhancing intestinal immunity by upregulating anti-inflammatory and downregulating pro-inflammatory genes. Appropriate dietary phosphorus supply could promote the formation of beneficial microflora in freshwater, and it has the potential ability to transfer the adverse effect of carbonate alkalinity stress to the structural composition of intestinal microflora. Hence, consideration should be given to suitable phosphorus supply for fish under the chronic carbonate alkalinity stress.

Gene expression profiling in liver of zebrafish exposed to ethylhexyl methoxycinnamate and its photoproducts

In recent decades, the ecotoxicological potential of organic ultraviolet filters (OU-VFs) has received growing attention. However, the toxicity of its photoproducts or transformation products on freshwater vertebrates has been little explored. Therefore, the aim of the present study is to evaluate the possible adverse effects of ethylhexyl methoxycinnamate (EHMC) and its photoproducts [2-ethylhexanol (2-EH) and 4-methoxybenzaldehyde (4-MBA)] on the expression of stress-responsive and antioxidant genes. For this, zebrafish (Danio rerio) adults were exposed to pollutants at an environmentally relevant concentration (3 μg/L) and evaluated after 7, 14, and 21 days of exposure. The results of the principal component analysis (PCA) and two-way repeated measures (RM) ANOVA revealed that EHMC, 2-EH, and 4-MBA exposure caused significant downregulation of the genes hsp70, nrf2, cyp1a, ahr, sod1, sod2, cat, gstp1, gpx1a, gss, and gsr (on all trial days) in the liver of the animals. On the other hand, taken together, our data did not show significant differences between the effects induced by EHMC and its photoproducts. The genes evaluated in the present study play a major role in regulating the defensive antioxidant response against EHMC and its photoproducts. Additionally, our study provides an insight into the mechanisms of those OU-VFs in freshwater fish.

Synergistic effects of arsenic and fluoride on oxidative stress and apoptotic pathway in Leydig and Sertoli cells

Excessive intake of arsenic (As) and fluoride (F), which are present in underground drinking water, have adverse effects on human health, and especially on the male reproductive system. In this regard, it's critical to figure out how As and F affect Leydig and Sertoli cells, which are key cells in the male reproductive system. The goal of this study was to determine the synergistic effects of co-exposure of As and F, via drinking water, on Leydig and Sertoli cells, which are models for the male reproductive system, as well as the mechanisms underlying these effects in terms of oxidative damage and apoptosis. Leydig and Sertoli cells were exposed to concentrations of 7.7 µM (0.57 ppm) As and 0.4 mM (7.24 ppm) F based on the highest daily intake of drinking water for 24 h. The present results revealed that As and/or F treatment reduced cell viability and proliferation in Leydig and Sertoli cells, elevated lactate dehydrogenase, a cytotoxicity marker, and triggered oxidative stress and apoptosis. Furthermore, it has been proven that when As and F are exposed in combination, they have a synergistic effect. In conclusion, by revealing the harmful effects of As and F on Leydig and Sertoli cells, and thus on male infertility, it is possible to reduce As and F exposure to prevent infertility after exposure to these molecules not only separately but also together. It will be considered to determine new action and action plans to reduce As and F exposure.

Reliable fluorescence technique to detect the antibiotic colistin, a possible environmental threat due to its overuse

Colistin, considered a drug of last resort as it is effective towards multidrug-resistant Gram-negative bacterial infections. Oral administration of colistin in the poultry industry is a common practice, not only to prevent and reduce bacterial infections, but also as a rapid-growth promoter. Long-term exposure to any antibiotic will eventually lead to the development of bacterial resistance towards all antibiotics through various mechanisms in the physiological system and environment. Chicken is the most consumed source of animal protein for humans throughout the world. In addition, the manure of poultry, containing traces of the used antibiotics, is being used in farming. Exposure to excess amounts of colistin causes a great concern not only to the humans but to the environment as a whole. In the present contribution, colistin has been detected in chicken hepatocyte cells through in vivo confocal microscopy. In addition, the amount of colistin in the chicken excrements has been estimated. A simple chemosensor NAF, a dye-based on napthaldehyde furfural, was developed for the detection of colistin, supplemented with experimental evidence and theoretical calculations.

Long-term exposure of the binary mixture of cadmium and mercury damages the developed ovary of adult zebrafish

The toxicity of the binary mixture of cadmium (Cd) and mercury (Hg) on the ovary of adult zebrafish was evaluated in the present study. Adult female zebrafish were exposed to cadmium chloride (1 mg/L), mercury chloride (30 µg/L), and a binary mixture of both metals for 21 days. The toxic effects of both metals on the ovary were investigated by evaluating the oxidative stress markers and related gene expression in ovarian tissue along with the histopathological examination. The significantly decreased level of GSH and increased level of MDA in ovarian tissue of adult female zebrafish exposed to Cd + Hg indicated that the exposure of binary mixture of Cd and Hg caused more lipid peroxidation in the ovary. The significant changes in expression of mRNA of catalase (CAT) and nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) were not observed in the ovary of zebrafish exposed to the binary mixture. Upon histological evaluation, a decreased number of full-growth (mature) oocytes along with degenerative changes due to Cd exposure were noticed, while ovary of zebrafish of the Hg-exposed group had shown a decreased number of pre-and early vitellogenic oocytes along with atretic previtellogenic oocytes compared to the control group. The ovary of zebrafish of the Cd + Hg-exposed group had shown a decreased number of previtellogenic oocytes with marked pathological changes in mature oocytes. Present findings elucidate that simultaneous long-term exposure of Cd and Hg compared to individual exposure significantly damaged the various stages of oocytes of an ovary of adult zebrafish.

The presence of polystyrene nanoplastics enhances the MCLR uptake in zebrafish leading to the exacerbation of oxidative liver damage

The accumulation of diminutive plastic waste in the environment, including microplastics and nanoplastics, has threatened the health of multiple species. Nanoplastics can adsorb the pollutants from the immediate environment, and may be used as carriers for pollutants to enter organisms and bring serious ecological risk. To evaluate the toxic effects of microcystin-LR (MCLR) on the liver of adult zebrafish (Danio rerio) in the presence of 70 nm polystyrene nanoplastics (PSNPs), zebrafish were exposed to MCLR alone (0, 0.9, 4.5 and 22.5 μg/L) and a mixture of MCLR + PSNPs (100 μg/L) for three months. The results indicated that groups with combined exposure to MCLR and PSNPs further enhanced the accumulation of MCLR in the liver when compared to groups only exposed to MCLR. Cellular swelling, fat vacuolation, and cytoarchitectonic damage were observed in zebrafish livers after exposure to MCLR, and the presence of PSNPs exacerbated these adverse effects. The results of biochemical tests showed the combined effect of MCLR + PSNPs enhanced MCLR-induced hepatotoxicity, which could be attributed to the altered levels of reactive oxygen species, malondialdehyde and glutathione, and activities of catalase. The expression of genes related to antioxidant responses (p38a, p38b, ERK2, ERK3, Nrf2, HO-1, cat1, sod1, gax, JINK1, and gstr1) was further performed to study the mechanisms of MCLR combined with PSNPs aggravated oxidative stress of zebrafish. The results showed that PSNPs could improve the bioavailability of MCLR in the zebrafish liver by acting as a carrier and accelerate MCLR-induced oxidative stress by regulating the levels of corresponding enzymes and genes.

Grub polypeptide extracts protect against oxidative stress through the NRF2-ARE signaling pathway

Grub polypeptide extracts (GPEs) have antioxidant effects; however, their underlying molecular mechanisms are unknown. This study explored the antioxidant molecular mechanism of GPE via the nuclear factor-erythroid 2-related factor 2 (NRF2)-antioxidant response element (ARE) signaling pathway in C2C12 muscle satellite cells exposed to oxidative stress. The effects of GPE/or H2O2 on C2C12 were investigated by the MTT (3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) viability assay and immunofluorescence and small interfering RNA (siRNA) analyses. The cell viability, cell damage, intracellular reactive oxygen species (ROS) levels, and NRF2 signaling pathways related to proteins were measured. GPE significantly increased the antioxidant capacity of cells, evident by increased cell viability and decreased lactate dehydrogenase leakage, DNA damage, malondialdehyde content, and ROS level. GPE also markedly increased mRNA expression levels and activities of antioxidant enzymes including superoxidase 1 and 2, catalase, and glutathione peroxidase. In addition, GPE increased the gene and protein expression of NRF2 and heme oxygenase 1 by promoting NRF2 translocation from the cytoplasm to the nucleus and activating NRF2-ARE signaling pathways. The antioxidant effects of GPE through these signaling pathways were further confirmed by NRF2-specific siRNA silencing. Thus, GPE enhances antioxidant capacity and alleviates oxidative damage of C2C12 cells via the NRF2-ARE signaling pathway.

Toxicity mechanisms of arsenic compounds in aquatic organisms

Arsenic is a toxic metalloid that is widely distributed in the environment due to its persistence and accumulative properties. The occurrence, distribution, and biological effects of arsenic in aquatic environments have been extensively studied. Acute and chronic toxicities to arsenic are associated with fatal effects at the individual and molecular levels. The toxicity of arsenic in aquatic organisms depends on its speciation and concentration. In aquatic environments, inorganic arsenic is the dominant form. While trivalent arsenicals have greater toxicity compared with pentavalent arsenicals, inorganic arsenic can assume a variety of forms through biotransformation in aquatic organisms. Biotransformation mechanisms and speciation of arsenic have been studied, but few reports have addressed the relationships among speciation, toxicity, and bioavailability in biological systems. This paper reviews the modes of action of arsenic along with its toxic effects and distribution in an attempt to improve our understanding of the mechanisms of arsenic toxicity in aquatic organisms.

Calcium and Vitamin D Supplementation Effectively Alleviates Dental and Skeletal Fluorosis and Retain Elemental Homeostasis in Mice

Fluoride (F) is an essential trace element, but chronic exposure beyond the permissible limit (1.5 ppm) effectuates dental and skeletal fluorosis. Although 200 million people across the world are suffering from toxic manifestations of F, till now proper treatment is not available. In this study, we assessed the effectiveness of calcium and vitamin D supplementation for alleviation of fluorosis. Swiss albino mice were divided into 6 groups; group I-control group (received drinking water ˂ 0.5 ppm F; within the permissible limit), group II-treated with 15 ppm of sodium fluoride (NaF) for 4 months, group III-treated with 15 ppm of NaF for 8 months through drinking water. Group IV-orally treated with 15 ppm NaF for 4 months, thereafter received only drinking water for next 4 months, group V-orally treated with 15 ppm NaF for 4 months, thereafter received drinking water supplemented with calcium and vitamin D (2.5-g calcium kg^-1 diet and 1000 IU vitamin D kg^-1 diet) for next 4 months, and group VI was treated with 15 ppm of NaF through drinking water as well as supplemented with calcium and vitamin D for 4 months. NaF treatment caused dental fluorosis, skeletal fluorosis, and alteration of bone's metal profile. Substitution of NaF-containing water with normal drinking water reduced the severity of fluorosis but supplementation of calcium and vitamin D effectively alleviated dental and skeletal fluorosis, reduced F deposition, and retained elemental homeostasis of the bone. Our findings strongly support that calcium and vitamin D act as redeemer of fluorosis. Graphical Abstract.

NRF2 signalling pathway: New insights and progress in the field of wound healing

As one of the most common pathological processes in the clinic, wound healing has always been an important topic in medical research. Improving the wound healing environment, shortening the healing time and promoting fast and effective wound healing are hot and challenging issues in clinical practice. The nuclear factor-erythroid-related factor 2 (NFE2L2 or NRF2) signalling pathway reduces oxidative damage and participates in the regulation of anti-oxidative gene expression in the process of oxidative stress and thus improves the cell protection. Activation of the NRF2 signalling pathway increases the resistance of the cell to chemical carcinogens and inflammation. The signal transduction pathway regulates anti-inflammatory and antioxidant effects by regulating calcium ions, mitochondrial oxidative stress, autophagy, ferroptosis, pyroptosis and apoptosis. In this article, the role of the NRF2 signalling pathway in wound healing and its research progress in recent years are reviewed. In short, the NRF2 signalling pathway has crucial clinical significance in wound healing and is worthy of further study.

Hepatic oxidative damage and Nrf2 pathway protein changes in rats following long-term manganese exposure

This study investigated hepatic oxidative damage in rats following long-term manganese (Mn) exposure and clarified the underlying mechanisms. Forty-eight rats (SPF, male) were randomly assigned to receive low (10 mg/kg, n = 16) or high doses of Mn (50 mg/kg, n = 16) or sterilized distilled water (control group, n = 16). Rats were euthanized after 12 months, and liver Mn levels and histopathological changes were determined. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels and liver malondialdehyde (MDA), glutathione peroxidase (GSH-PX), nuclear factor E2-related factor-2 (Nrf2), heme oxygenase-1 (HO-1), and NAD(P)H quinine oxidoreductase-1 (NQO1) levels were also determined. The Mn concentration and relative liver weights were significantly higher in the high-dose Mn group than in the control and low-dose Mn exposure groups. Low-dose Mn exposure resulted in mild expansion of hepatic sinuses and intact nuclei, whereas high-dose exposure led to pathological alterations in hepatocytes. High-dose Mn treatment significantly increased AST, ALT, and MDA activities and decreased GSH-PX activity. Additionally, liver Nrf2, HO-1, and NQO1 protein expression were markedly reduced by Mn exposure. Under the study conditions, long-term low-dose Mn exposure resulted in slight pathological changes in liver structure, but high-dose Mn exposure affected both liver structure and function, which might be related to the inhibition of Nrf2 expression, suppression of the transcription of its underlying antioxidant genes, and down regulation of the corresponding proteins. Consequently, the antioxidant capacity in the rat liver was weakened.

Combined effect of arsenic and fluoride at environmentally relevant concentrations in zebrafish (Danio rerio) brain: Alterations in stress marker and apoptotic gene expression

Arsenic and fluoride are two naturally occurring toxicants to which various organisms including a major part of the human populations are co-exposed to. However, interactions between them inside body are quite complicated and needs proper evaluation. Inconclusive reports regarding their combined effects on brain prompted us to conduct this study where we investigated their individual as well as combined effects on female zebrafish brain at environmentally relevant concentrations (50 μgL^-1 arsenic trioxide and 15 mgL^-1 sodium fluoride) after different time intervals (15, 30 and 60 days). Persistent near-basal level of GSH, least increased MDA content and catalase activity portrayed arsenic and fluoride co-exposure as less toxic which was corroborated with far less damage caused in the histoarchitecture of optic tectum region in midbrain. Stress-responsive genes viz., Nrf2 and Hsp70 were overexpressed after individual as well as combined exposures, indicating a common cellular response to combat the formed oxidative stresses. Biphasic response of AChE upon individual exposure confirmed their neurotoxic effects too. Expression profile of p53 (unaltered), Bax (lower or near-basal) and Bcl2 (comparatively higher), along with absence of DNA fragmentation indicated no induction of apoptosis in the co-exposed group. Tissue accumulation of arsenic and fluoride was significantly less in the brain of co-exposed zebrafish when compared to their individual exposures. This preliminary study indicates an antagonistic effect of these two toxicants in zebrafish brain and needs further studies involving oxidative stress independent markers to understand the detailed molecular mechanism.

Chronic exposure to environmentally relevant concentration of fluoride alters Ogg1 and Rad51 expressions in mice: Involvement of epigenetic regulation

Chronic exposure to fluoride (F) beyond the permissible limit (1.5 ppm) is known to cause detrimental health effects by induction of oxidative stress-mediated DNA damage overpowering the DNA repair machinery. In the present study, we assessed F induced oxidative stress through monitoring biochemical parameters and looked into the effect of chronic F exposure on two crucial DNA repair genes Ogg1 and Rad51 having important role against ROS induced DNA damages. To address this issue, we exposed Swiss albino mice to an environmentally relevant concentration of fluoride (15 ppm NaF) for 8 months. Results revealed histoarchitectural damages in liver, brain, kidney and spleen. Depletion of GSH, increase in lipid peroxidation and catalase activity in liver and brain confirmed the generation of oxidative stress. qRT-PCR result showed that expressions of Ogg1 and Rad51 were altered after F exposure in the affected organs. Promoter hypermethylation was associated with the downregulation of Rad51. F-induced DNA damage and the compromised DNA repair machinery triggered intrinsic pathway of apoptosis in liver and brain. The present study indicates the possible association of epigenetic regulation with F induced neurotoxicity.

Bio-inspired materials for defluoridation of water: A review

The polluted water sources pose a serious issue concerning the various health hazards they bring along. Due to various uncontrolled anthropogenic and industrial activities, a great number of pollutants have gained entry into the water systems. Among all the emerging contaminants, anionic species such as fluoride cause a major role in polluting the water bodies because of its high reactivity with other elements. The need for water remediation has led the research community to come up with several physicochemical and electrochemical methods to remove fluoride contamination. Among the existing methods, biosorption using bio and modified biomaterials has been extensively studied for defluoridation, as they are cheap, easily available and effectively recyclable when compared to other methods for defluoridation. Adding on, these materials are non-toxic and are safe to use compared to many other synthetic materials that are toxic and require high-cost design requirements. This review focuses on the recent developments made in the defluoridation techniques by biosorption using bio and modified biomaterials and defines the current perspectives of fluoride removal specifically using biomaterials.

Environmentally relevant concentration of chromium induces nuclear deformities in erythrocytes and alters the expression of stress-responsive and apoptotic genes in brain of adult zebrafish

Heavy metal contamination of water body has become a serious threat to aquatic life forms specially to fish. Hexavalent chromium (Cr [VI]) is one of the most potent heavy metal toxicant. It is present in aquatic environment at concentrations beyond permissible limit. Considering the fact that toxic effects are function of the exposure concentration, studies involving toxicological risk assessment should be done at environmentally relevant concentration. Therefore we studied the toxic effects of Cr [VI] to zebrafish at an environmentally relevant concentration (2 mg L^-1). We monitored the genotoxic potential of Cr [VI] in erythrocytes through a simple reliable microscopic assay and found an increase in frequency of micronucleated erythrocytes along with erythrocytes with blebbed, lobed and notched nuclei. In addition, Cr [VI] induced neurotoxicity, being a least reported event was also investigated. Histological alterations in brain, elevated GSH and MDA content and increased catalase activity indicated oxidative stress-mediated damage. This was further confirmed through expressional alteration of Ucp2. Upregulation of Nrf2, Nqo1 and Ho1 clearly indicated the involvement of Nrf2-ARE system in stress response against Cr [VI] induced neurotoxicity. The transcriptional induction of apoptotic genes such as Bax, Caspase 9 and Caspase 3 along with downregulation of Bcl2 indicated that the cytoprotective system failed to counter the induced stress. Interestingly, there was upregulation of AChE gene, which could be correlated with the upregulated apoptotic genes. This study provides an insight on the neurotoxic stress of Cr [VI] on the zebrafish yet at an environmentally relevant concentration. Moreover the induction of nuclear anomalies in the erythrocytes can serve as extremely sensitive endpoints of toxicological stress indicators of aquatic contaminants like Cr [VI].

Environmental exposure of arsenic and fluoride and their combined toxicity: A recent update

Environmental exposure to arsenic (As) and fluoride (F) in the recent year has been increased because of excessive use of naturally contaminated ground water. Surface water is also regularly contaminated with these elements in various industrial areas. Arsenicosis and fluorosis upon individual exposure of As and F are reported in many studies. A syndrome of endemic As poisoning and fluorosis occurs during concurrent exposure of As and F. Previous reports showed synergistic, antagonistic and independent effects of these two compounds, although few recent reports also revealed antagonistic effects after co-exposure. Interaction during intestinal absorption and influence of F on As metabolism might be the cause of antagonism. The synergism/antagonism is thought to depend on the dose and duration of the co-exposure. However, the detailed mechanism is still not fully understood and needs further studies. Removal technologies of As and F from contaminated water is available but removal of such contaminants from food is yet to be developed. Antioxidants are useful to mitigate the toxic effects of As and F. This review focused on the effect of co-exposure, amelioration as well as removal techniques of As and F.