Sodium fluoride generates ROS and alters transcription of genes for xenobiotic metabolizing enzymes in adult zebrafish (Danio rerio) liver: expression pattern of Nrf2/Keap1 (INrf2)

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.

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.

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.

Fluoride exposure causes behavioral, molecular and physiological changes in adult zebrafish (Danio rerio) and their offspring

Fluoride exposure through drinking water, foods, cosmetics, and drugs causes genotoxic effects, oxidative damage, and impaired cognitive abilities. In our study, the effects of fluoride on anxiety caused by the circadian clock and circadian clock changes in a zebrafish model were investigated at the molecular level on parents and the next generations. For this purpose, adult zebrafish were exposed to 1.5 ppm, 5 ppm, and 100 ppm fluoride for 6 weeks. At the end of exposure, anxiety-like behaviors and sleep/wake behaviors of the parent fish were evaluated with the circadian rhythm test and the novel tank test. In addition, antioxidant enzyme activities and melatonin levels in brain tissues were measured. In addition, morphological, physiological, molecular and behavioral analyzes of offspring taken from zebrafish exposed to fluoride were performed. In addition, histopathological analyzes were made in the brain tissues of both adult zebrafish and offspring, and the damage caused by fluoride was determined. The levels of BMAL1, CLOCK, PER2, GNAT2, BDNF and CRH proteins were measured by immunohistochemical analysis and significant changes in their levels were determined in the F^- treated groups. The data obtained as a result of behavioral and molecular analyzes showed that parental fluoride exposure disrupts the circadian rhythm, causes anxiety-like behaviors, and decreases the levels of brain antioxidant enzymes and melatonin in parents. In addition, delay in hatching, increase in death and body malformations, and decrease in blood flow velocity, and locomotor activity was observed in parallel with dose increase in offspring. On the other hand, an increase in offspring apoptosis rate, ROS level, and lipid accumulation was detected. As a result, negative effects of fluoride exposure on both parents and next generations have been identified.

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.

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.

Shinorine ameliorates chromium induced toxicity in zebrafish hepatocytes through the facultative activation of Nrf2-Keap1-ARE pathway

Hexavalent chromium, a heavy metal toxicant, abundantly found in the environment showed hepatotoxic potential in zebrafish liver and instigated the Nrf2-Keap1-ARE pathway as a cellular stress response as reported in our previous studies. In the present study we have evaluated the ameliorating effect of shinorine, a mycosporine like amino acid (MAAs) and a mammalian Keap1 antagonist against chromium induced stress in zebrafish hepatocytes. Shinorine was found to be effective in increasing the cell viability of chromium treated hepatocytes through curtailing the cellular ROS content. Trigonelline, an Nrf2 inhibitor was found to reduce the viability of hepatocyte cultures co-exposed to shinorine and chromium. In other words, trigonelline being an Nrf2 blocker neutralised the alleviating effect of shinorine. This indicated that shinorine mediated cyto-protection in Cr [VI]-intoxicated cells is Nrf2 dependent. Further, qRT-PCR analysis revealed comparatively higher expression of nfe2l2 and nqo1 in shinorine + chromium treated hepatocytes than cells exposed to chromium alone indicating a better functioning of Nrf2-Keap1-Nqo1 axis. To further confirm if shinorine can lead to disruption of Nrf2-Keap1 interaction in zebrafish hepatocytes and render cytoprotection to chromium exposure, our in silico analysis through molecular docking revealed that shinorine could bind to the active amino acid residues of the DGR domain, responsible for Nrf2-Keap1 interaction of all the three Keap1s evaluated. This is the first report about shinorine that ameliorates chromium induced toxicity through acting as an Nrf2-Keap1 interaction disruptor. We additionally carried out in-silico pharmacokinetic and ADMET studies to evaluate druglikeness of shinorine whose promising results indicated its potential to be developed as an ideal therapeutic candidate against toxicant induced pathological conditions.

Fluoride impairs ovary development by affecting oogenesis and inducing oxidative stress and apoptosis in female zebrafish (Danio rerio)

Previous studies have shown that waterborne fluoride exposure has adverse effects on the reproductive system of zebrafish. However, the underlying toxic mechanisms were still not clear. In the present study, female zebrafish were exposed to different concentrations of 0.787 (Control), 18.599, 36.832 mg/L of fluoride for 30 d and 60 d, and the effects of different doses of fluoride on ovary development, reproductive hormones, oogenesis, ROS content, antioxidant levels, and the expression of apoptosis-related genes and proteins in the ovaries of female zebrafish were analyzed. The results showed that ovarian weight and GSI were significantly decreased, FSH, LH and VTG levels were significantly reduced, the transcriptional profiles of oogenesis-related genes (tgfβ1, bmp15, gdf9, mprα, mprβ, ptg2β) were remarkably altered, ROS levels was notably increased, the SOD, CAT, GPx activities and GSH content as well as their mRNA expressions were significantly decreased, MDA content was remarkably increased, the expressions of apoptosis-related genes and proteins (caspase3, caspase8, caspase9, Fas-L, Cytochrome C, Bax and Bcl-2) were significantly changed, the ratio of Bax/Bcl-2 protein levels were notably increased. Taken together, this study demonstrated that fluoride exposure significantly affected ovarian development, decreased the reproductive hormones, affected oogenesis, induced oxidative stress, caused apoptosis through both extrinsic and intrinsic pathways in ovary of zebrafish. Indicating that oogenesis, oxidative stress, and apoptosis were responsible for the impairment of ovarian development.

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.

Effects and Molecular Mechanism of L-Type Calcium Channel on Fluoride-Induced Kidney Injury

This study aimed to investigate the role and molecular mechanism of L-type calcium channel (LTCC) on fluoride exposure-induced kidney injury. Subchronic and chronic fluoride exposures were included in the experiment. Each part contained 140 ICR male mice. They were randomly divided into 7 groups: control group, high-fluoride group (NaF 30 mg/L), low-fluoride group (NaF 5 mg/L), high/low-fluoride + agonist (FPL64176) group, high/low-fluoride + inhibitor (nifedipine) group. One week before the end of fluoride exposure, each mouse in the fluoride exposure group was injected intraperitoneally with LTCC agonist (FPL64176) or inhibitor (nifedipine) (5 mg/kg day). The apoptosis of kidney cell was observed by TUNEL, and the protein expression levels of Cav1.2 and CaM, CaMKII, Bcl-2, and Bax were detected by Western blot. Compared with the control group, the protein expression levels of Cav1.2, CaM, and Bax significantly increased, and those of CaMKII and Bcl-2 significantly decreased, the ratio of Bax/Bcl-2 also significantly increased, and the number of apoptotic kidney cells significantly increased in the high/low-fluoride group and in the high/low-fluoride + agonist group. The above indicators and fluoride exposure concentrations showed in time- and dose-dependent changes. Compared with the high/low-fluoride + agonist group, the protein expression level of the molecular in the kidney cells above mentioned was significantly opposite and the number of apoptotic kidney cells significantly decreased in the high/low-fluoride + inhibitor group. In conclusion, LTCC mediates the kidney injury induced by fluoride exposure in mice. Fluoride exposure induced abnormal expression of the Cav1.2 protein, Ca²⁺ signal transduction pathway, and apoptosis-regulated proteins, which is one of the molecular mechanisms. Nifedipine may be a new and effective anti-fluoride drug.

Dietary nanoencapsulated quercetin homeostated transcription of redox-status orchestrating genes in zebrafish (Danio rerio) exposed to silver nanoparticles

The present study assessed the protective effect of chitosan-nanoencapsulated quercetin (Qu-ChiNPs) against oxidative stress caused by silver nanoparticles (AgNPs). To this end, the transcription of prime genes regulating hepatic Keap1-Nrf2 pathway as well as downstream antioxidant enzymes were monitored prior to and after oxidative stress by AgNPs. Zebrafish (Danio rerio; n = 225) was assigned into five experimental groups based on feeding with diets supplemented with different additives as follows: negative and positive control groups, without additive; ChiNPs, 400 mg nanochitosan per kg diet; Quercetin, 400 mg free quercetin per kg diet; and Qu-ChiNPs, 400 mg Qu-ChiNPs per kg diet. At the end of the feeding trial (40 days), the experimental groups, except the negative control, were exposed to sublethal concentration of AgNPs (0.15 mg L^-1) for 96h. Before exposure to AgNPs, free quercetin-treated diet significantly upregulated Keap1, Nrf2, Cat, SOD, GPx, and GST genes in the liver tissue when compared with the control diet, whereas Qu-Chi.NPs downregulated their transcription to the lowest levels. After exposure to AgNPs, all genes exhibited different responses in the AgNPs-exposed groups. The highest transcription of Nrf2, Cat, SOD, GPx, and GST was observed in the positive group, with being upregulated about 8, 10, 8, 8, and 7 times, respectively, when compared to the respective ones in the negative control. However, Keap1 showed a reverse response with being transcripted 12 times lower. The quercetin treatments, especially Qu-Chi.NPs, significantly reduced the transcription of Nrf2, Cat, SOD, GPx, and GST genes, yet enhanced Keap1 expression. Qu-Chi.NPs reduced the expression of Nrf2, SOD, Cat, GPx, and GST about 11, 10, 15, 10, and 10 times, respectively, yet increased that of Keap1 about 12 times. Taken together, nanoencapsulation can improve the antioxidant efficacy of quercetin against AgNPs toxicity and might reduce involvement of the cellular antioxidant system through tuning redox status. More broadly, it would be interesting to assess the effects of Qu-Chi.NPs against other metallic and organic oxidative stressors or pollutants.

AMPK/p38/Nrf2 activation as a protective feedback to restrain oxidative stress and inflammation in microglia stimulated with sodium fluoride

Dysregulated activation of inflammation plays an important role in the development and progression of neuronal damage, and limiting the production of reactive oxygen species (ROS) can suppress the inflammatory signals. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a redox-sensing transcription factor that drives an adaptive cellular defense in response to oxidative stress. However, the implications of Nrf2 in sodium fluoride (NaF)-stimulated microglia and the underlying mechanisms remain obscure. In this study, we demonstrated that NaF activated the Nrf2 signaling and enhanced the downstream antioxidant protein levels, including heme oxygenase-1 and quinine oxidoreductase 1. NaF induced oxidative stress, as indicated by increased ROS level and malondialdehyde content, and reduced superoxide dismutase activity. Moreover, NaF promoted the nuclear translocation of NF-κB, thus increased the production of the pro-inflammatory cytokines tumor necrosis factor-α, interleukin (IL)-6, and IL-1β. However, these effects were relieved by overexpression of Nrf2. Meanwhile, knockdown of Nrf2 by shRNA exacerbated NaF-induced oxidative stress and inflammation in BV-2 cells and primary cultured microglia. Mechanistically, NaF-induced Nrf2 activation is AMPK/p38 dependent, as deletion of AMPK using siRNA blocked the activating effect of NaF on p38 and Nrf2. Notably, treatment of N-Acety-l-Cysteine attenuated AMPK/p38-dependent Nrf2 activation in microglia exposed to NaF. In conclusion, these data demonstrated for the first time that Nrf2 activation exerts a neuroprotective effect on NaF-stimulated redox imbalance and inflammation that is dependent on the AMPK/p38 pathway.

Excess dietary fluoride affects laying performance, egg quality, tissue retention, serum biochemical indices, and reproductive hormones of laying hens

The present study aimed to evaluate the effects of excess dietary fluoride (F) on laying performance, egg quality, tissue retention, serum biochemical indices, and serum reproductive hormones of laying hens. A total of 384 Hy-Line Gray hens, 37 wk old, were treated with sodium fluoride added to a corn-soybean meal basal diet at 0, 400, 800, and 1200 mg fluorine/kg feed. The results showed that dietary F levels at 800 and 1200 mg/kg markedly decreased ADFI, laying rate, average egg weight, and increased feed conversion ratio (FCR) (P < 0.05). Dietary F levels at 800 and 1200 mg/kg dramatically decreased the egg quality of albumen height, yolk color, eggshell strength, and eggshell thickness, and on the 49th D, 400 mg/kg F group significantly decreased the eggshell strength, compared to those of control group. Fluoride residues in tissues of hens were increased significantly with the increase of dietary F supplemental levels (P < 0.05). Fluoride concentrations were generally high in feces, eggshell, tibia, kidney, and ovary, and the highest in feces, following with eggshell and tibia, lower in kidney and ovary, and the lowest in serum. Serum uric acid levels and alanine aminotransferase activity increased significantly (P < 0.05), and glucose, triglycerides, and phosphorus decreased significantly (P < 0.05) in response to dietary F concentration, compared to those of the control group, respectively. Dietary F supplementation at 1200 mg/kg significantly decreased (P < 0.05) the estrogen concentrations in serum, compared to those of the control group. Concentrations of progesterone in the fluoride-treated groups were significantly (P < 0.05) decreased relative to those of the control group. In conclusion, these results indicated that the excessive ingestion of F has had a detrimental effect on egg laying rate and quality of eggs by damaging the function of the liver, kidney, and ovary of laying hens.

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.

Environmentally relevant concentration of chromium activates Nrf2 and alters transcription of related XME genes in liver of zebrafish

Fish is an excellent model to decipher the mechanism of toxicity of aquatic contaminants such as hexavalent chromium (Cr [VI]). The present study looked into the manifestation of stress in liver of zebrafish exposed to an environmentally relevant concentration (2 mgL^-1), and the functioning of the cytoprotective machinery that pacifies the formed stress. The results lead us to hypothesize that oxidative stress plays a key role in chromium-induced toxicity resulting in lipid peroxidation and extensive changes in tissue ultrastructure. In treated fish, production of reactive oxygen species, increase in reduced glutathione content and increase in malondialdehyde content along with enhanced catalase activity were evident. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) was found to increase both at transcriptional and translational level and its translocation into the nucleus was confirmed by fluorescence-based immunohistochemical studies. The mRNA levels of genes like Nqo1, Cyp1a and Cu/Zn Sod were found to increase whereas Ho1, Hsp70 and Ucp2 were down-regulated. The sensitivity of these genes towards Cr [VI] validates their candidature as important biomarkers of Cr [VI] exposure in zebrafish.

Interplay of ROS and behavioral pattern in fluoride exposed Drosophila melanogaster

Reactive oxygen species (ROS) is known to be associated with the process of aging and other health hazards. Organisms are compelled to compromise with body homeostasis when exposed to toxic substances. In the present study sodium fluoride (NaF) exposure (10-100 μgmL^-1) to Drosophila melanogaster in the parental (P) generation leads to increase in adult mortality and alteration in male-female ratio in the P and F1 (1st Filial) generation. Post-treatment alterations in selected behavioral traits (crawling, embedding and climbing) were observed in larvae and adults. Altered behavioral pattern was found to be associated with reduced mitochondrial activity and decreased number of viable brain cells in treated individuals. Interestingly, higher cholinesterase activities in treated males in comparison to females demonstrate a definite sex bias in NaF-induced response. Hyper-activation of antioxidant enzyme like catalase and reduced superoxide dismutase (SOD) and glutathione-s-transferase (GST) activity indicate a shift in the oxidative status after fluoride exposure. Additionally, increase in lipid peroxidation suggests enhancement in ROS which is further validated through increment in protein carbonyl content. Hence, the observations of the present study propose behavioral alterations resulting from increased ROS after chronic exposure to sub-lethal concentrations of NaF in D. melanogaster.

Acute Toxicity and Oxidative Stress Responses in Tadpole of Skittering Frog, Euphlyctis cyanophlyctis (Schneider, 1799) to Sodium Fluoride Exposure

This study evaluated the acute toxicity and oxidative stress responses to sodium fluoride (NaF) exposure in tadpoles of the skittering frog, Euphlyctis cyanophlyctis (Schneider 1799). The 96 h LC₅₀ value was found to be 647 mg/L. Biochemical tests were conducted at 10%, 20%, 30%, 40%, 50%, 60%, 70% and 80% of the 96 h LC₅₀ dose. Cholinesterase (ChE) activity was unaffected. Lipid peroxidation levels significantly increased (p < 0.05) at lower concentrations, but decreased significantly with increasing NaF concentrations. Glutathione S-transferase (GST) activity also increased significantly with increasing NaF concentrations. Alkaline phosphatase levels steadily decreased with increasing concentrations of NaF. The responses for the biochemical tests were summarized using an integrated biomarker response (IBR) index approach, which indicated that lower NaF exposures caused higher levels of oxidative stress responses overall. These findings suggest that the IBR index approach may be useful for the quantitative monitoring of NaF toxicity in amphibians.

Sodium fluoride induces apoptosis in mouse splenocytes by activating ROS-dependent NF-κB signaling

In this study, we investigated the roles of reactive oxygen species (ROS) and nuclear factor-κB (NF-κB) signaling in sodium fluoride-induced DNA damage and apoptosis in mouse splenocytes. Intragastric administration of 12, 24 or 48 mg/kg sodium fluoride resulted in a time- and dose-dependent increase in DNA fragmentation and apoptosis in mouse splenocytes on days 21 and 42. High ROS levels correlated with increased levels of phosphorylated IκB kinase and NF-κB p65 and decreased levels of inhibitory kappa B protein in splenocytes from mice treated with sodium fluoride. Moreover, splenocytes from sodium fluoride-treated mice showed high expression of pro-apoptotic proteins, including Bim, Bax, Bak, caspase-3 and poly ADP-ribose polymerase, and low expression of the anti-apoptotic proteins BcL-2 and BcL-xL. These results show that sodium fluoride induces apoptosis in mouse splenocytes by enhancing ROS-dependent NF-κB signaling.

Sodium fluoride exposure exerts toxic effects on porcine oocyte maturation

Excessive long-term fluoride intake is associated with several health problems, including infertility. However, limited information is available on the toxic effects of fluoride exposure on the female reproductive system, especially oocyte maturation. In this study, we investigated the toxic effect of sodium fluoride (NaF) exposure on porcine oocyte maturation and its possible underlying mechanisms. Our results showed that NaF exposure during porcine oocyte maturation inhibited cumulus cell expansion and impaired polar body extrusion. Cell cycle analysis showed that NaF exposure blocked meiotic resumption, disturbed spindle dynamics, disrupted chromosome separation, and increased aneuploidy in porcine oocytes. Moreover, NaF exposure disturbed mitochondrial function, triggered DNA damage response, and induced early apoptosis in porcine oocytes. NaF exposure also induced oxidative stress, decreased GSH level, and increased cathepsin B activity in and impaired the further development potential of porcine oocytes, as indicated by a decrease in blastocyst formation rate, increase in apoptosis, and inhibition of cell proliferation. Together, these results indicate that NaF exposure impairs the maturation capacity of porcine oocytes by inhibiting cumulus cell expansion, disturbing cytoskeletal dynamics, and blocking nuclear and cytoplasmic maturation, thus decreasing the quality and affecting the subsequent embryonic development potential of porcine oocytes.

Zebrafish: A Premier Vertebrate Model for Biomedical Research in Indian Scenario

The zebrafish (Danio rerio) is a versatile model organism that has been used in biomedical research for several decades to study a wide range of biological phenomena. There are many technical advantages of using zebrafish over other vertebrate models. They are readily available, hardy, easy, and inexpensive to maintain in the laboratory, have a short life cycle, and have excellent fecundity. Due to its optical clarity and reproducible capabilities, it has become one of the predominant models of human genetic diseases. Zebrafish research has made rapid strides in the United States and Europe, but in India the field is at an early stage and many researchers still remain unaware of the full research potential of this tiny fish. The zebrafish model system was introduced into India in the early 2000s. Up to now, more than 200 scientific referred articles have been published by Indian researchers. This review gives an overview of the current state of knowledge for zebrafish research in India, with the aim of promoting wider utilization of zebrafish for high level biological studies.

Putative mechanisms of genotoxicity induced by fluoride: a comprehensive review

Genotoxicity is the ability of an agent to produce damage on the DNA molecule. Considering the strong evidence for a relationship between genetic damage and carcinogenesis, to elucidate the putative mechanisms of genotoxicity induced by fluoride are important to measure the degree of risk involved to human populations. The purpose of this article is to provide a comprehensive review on genotoxicity induced by fluoride on the basis of its mechanisms of action. In the last 10 years, all published data showed some evidence related to genotoxicity, which is due to mitochondrial disruption, oxidative stress, and cell cycle disturbances. However, this is an area that still requires a lot of investigation since the published data are not sufficient for clarifying the genotoxicity induced by fluoride. Certainly, the new information will be added to those already established for regulatory purposes as a safe way to promote oral healthcare and prevent oral carcinogenesis.

Heme oxygenase-1 mitigates ferroptosis in renal proximal tubule cells

Ferroptosis is an iron-dependent form of regulated nonapoptotic cell death, which contributes to damage in models of acute kidney injury (AKI). Heme oxygenase-1 (HO-1) is a cytoprotective enzyme induced in response to cellular stress, and is protective against AKI because of its antiapoptotic and anti-inflammatory properties. However, the role of HO-1 in regulating ferroptosis is unclear. The purpose of this study was to elucidate the role of HO-1 in regulating ferroptotic cell death in renal proximal tubule cells (PTCs). Immortalized PTCs obtained from HO-1^+/+ and HO-1^-/- mice were treated with erastin or RSL3, ferroptosis inducers, in the presence or absence of antioxidants, an iron source, or an iron chelator. Cells were assessed for changes in morphology and metabolic activity as an indicator of cell viability. Treatment of HO-1^+/+ PTCs with erastin resulted in a time- and dose-dependent increase in HO-1 gene expression and protein levels compared with vehicle-treated controls. HO-1^-/- cells showed increased dose-dependent erastin- or RSL3-induced cell death in comparison to HO-1^+/+ PTCs. Iron supplementation with ferric ammonium citrate in erastin-treated cells decreased cell viability further in HO-1^-/- PTCs compared with HO-1^+/+ cells. Cotreatment with ferrostatin-1 (ferroptosis inhibitor), deferoxamine (iron chelator), or N-acetyl-l-cysteine (glutathione replenisher) significantly increased cell viability and attenuated erastin-induced ferroptosis in both HO-1^+/+ and HO-1^-/- PTCs. These results demonstrate an important antiferroptotic role of HO-1 in renal epithelial cells.

The toxic effects of chlorophenols and associated mechanisms in fish

Chlorophenols (CPs) are ubiquitous contaminants in the environment primarily released from agricultural and industrial wastewater. These compounds are not readily degraded naturally, and easily accumulate in organs, tissues and cells via food chains, further leading to acute and chronic toxic effects on aquatic organisms. Herein, we review the available literature regarding CP toxicity in fish, with special emphasis on the potential toxic mechanisms. CPs cause oxidative stress via generation of reactive oxygen species, induction of lipid peroxidation and/or oxidative DNA damage along with inhibition of antioxidant systems. CPs affect immune system by altering the number of mature B cells and macrophages, while suppressing phagocytosis and down-regulating the expression of immune factors. CPs also disrupt endocrine function by affecting hormone levels, or inducing abnormal gene expression and interference with hormone receptors. CPs at relatively higher concentrations induce apoptosis via mitochondria-mediated pathway, cell death receptor-mediated pathway, and/or DNA damage-mediated pathway. CPs at relatively lower concentrations promote cell proliferation, and foster cancers-prone environment by increasing the rate of point mutations and oxidative DNA lesions. These toxic effects in fish are induced directly by CPs per se or indirectly by their metabolic products. In addition, recent studies on the alteration of DNA methylation by CPs through high-throughput DNA sequencing analysis provide new insights into our understanding of the epigenetic mechanisms underlying CPs toxicity.

Calf Spleen Extractive Injection (CSEI), a small peptides enriched extraction, induces human hepatocellular carcinoma cell apoptosis via ROS/MAPKs dependent mitochondrial pathway

Calf Spleen Extractive Injection (CSEI), a small peptides enriched extraction, performs immunomodulatory activity on cancer patients suffering from radiotherapy or chemotherapy. The present study aims to investigate the anti-hepatocellular carcinoma effects of CSEI in cells and tumor-xenografted mouse models. In HepG2 and SMMC-7721 cells, CSEI reduced cell viability, enhanced apoptosis rate, caused reactive oxygen species (ROS) accumulation, inhibited migration ability, and induced caspases cascade and mitochondrial membrane potential dissipation. CSEI significantly inhibited HepG2-xenografted tumor growth in nude mice. In cell and animal experiments, CSEI increased the activations of pro-apoptotic proteins including caspase 8, caspase 9 and caspase 3; meanwhile, it suppressed the expressions of anti-apoptotic protein B-cell lymphoma 2 (Bcl-2) and anti-oxidation proteins, such as nuclear factor-erythroid 2 related factor 2 (Nrf2) and catalase (CAT). The enhanced phosphorylation of P38 and c-JunN-terminalkinase (JNK), and decreased phosphorylation of extra cellular signal-regulated protein kinase (ERKs) were observed in CSEI-treated cells and tumor tissues. CSEI-induced cell viability reduction was significantly attenuated by N-Acetyl-l-cysteine (a ROS inhibitor) pretreatment. All data demonstrated that the upregulated oxidative stress status and the altered mitogen-activated protein kinases (MAPKs) phosphorylation contributed to CSEI-driven mitochondrial dysfunction. Taken together, CSEI exactly induced apoptosis in human hepatocellular carcinoma cells via ROS/MAPKs dependent mitochondrial pathway.

Effect of 17α-methyltestosterone (MT) on oxidation stress in the liver of juvenile GIFT tilapia, Oreochromis niloticus

The normal dose of 17α-methyltestosterone (MT) used in fish farming was 60 mg/L, and now the analysis of residual androgens was carried out in waste water obtained from the Beijing area, which could be detected in levels ranging from 4.1 to 7.0 ng/L. For the purpose of aquatic early warning, the present study clearly demonstrated that chronic exposure by higher concentration of MT than environmental relevant concentrations could trigger oxidative stress response to juvenile tilapia by modulating hepatic antioxidant enzyme activities and gene transcription. Some antioxidative parameters (T-GSH, GSH/GSSG and MDA) were significant decreased under 0.5 mg/L MT exposure at 7 and 14 days. Some antioxidant enzymes (SOD, CAT and GST) and transcriptional changes (sod and cat) were revealed significant decreases for MT treated groups at 7 days. Total antioxidant capacity was significant increased only in 5 mg/L MT exposure groups, but GR activities were not affected all through the whole exposure period. Almost all of the antioxidant enzymatic genes detected in the present study were showed significant increments for MT exposure both at 14 and 21 days, and the genotoxicity profile of antioxidant enzymatic genes were revealed dose-dependent manner. This study presented evidence that MT could result in oxidative stress response in the early stages of GIFT tilapia.

Sodium fluoride affects zebrafish behaviour and alters mRNA expressions of biomarker genes in the brain: Role of Nrf2/Keap1

Sodium fluoride (NaF), used as pesticides and for industrial purposes are deposited in the water bodies and therefore affects its biota. Zebrafish exposed to NaF in laboratory condition showed hyperactivity and frequent surfacing activity, somersaulting and vertical swimming pattern as compared to the control group. Reactive oxygen species level was elevated and glutathione level was depleted along with increased malondialdehyde content in the brain. Levels of glutathione-s-transferase (GST), catalase (CAT) and superoxide dismutase were also elevated in the treatment groups. Expression of mRNA of nuclear factor erythroid 2 related factor 2 (Nrf2) and its inhibitor Kelch-like ECH-associated protein 1 (Keap1) during stress condition were observed along with Gst, Cat, NADPH: quinone oxidoreductase 1(Nqo1) and p38. Except Keap1, all other genes exhibited elevated expression. Nrf2/Keap1 proteins had similar expression pattern as their corresponding mRNA. The findings in this study might help to understand the molecular mechanism of fluoride induced neurotoxicity in fish.