A possible mechanism for combined arsenic and fluoride induced cellular and DNA damage in mice

Arsenic and fluoride are major contaminants of drinking water. Mechanisms of toxicity following individual exposure to arsenic or fluoride are well known. However, it is not explicit how combined exposure to arsenic and fluoride leads to cellular and/or DNA damage. The present study was planned to assess (i) oxidative stress during combined chronic exposure to arsenic and fluoride in drinking water, (ii) correlation of oxidative stress with cellular and DNA damage and (iii) mechanism of cellular damage using IR spectroscopy. Mice were exposed to arsenic and fluoride (50 ppm) either individually or in combination for 28 weeks. Arsenic or fluoride exposure individually led to a significant increase in reactive oxygen species (ROS) generation and associated oxidative stress in blood, liver and brain. Individual exposure to the two toxicants showed significant depletion of blood glutathione (GSH) and glucose 6-phosphate dehydrogenase (G6PD) activity, and single-stranded DNA damage using a comet assay in lymphocytes. We also observed an increase in the activity of ATPase, thiobarbituric acid reactive substance (TBARS) and a decreased, reduced and oxidized glutathione (GSH?:?GSSG) ratio in the liver and brain. Antioxidant enzymes like superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) were decreased and increased in liver and brain respectively. The changes were more pronounced in liver compared to brain suggesting liver to be more susceptible to the toxic effects of arsenic and fluoride. Interestingly, combined exposure to arsenic and fluoride resulted in less pronounced toxic effects compared to their individual effects based on biochemical variables, IR spectra, DNA damage (TUNEL and comet assays) and histopathological observations. IR spectra suggested that arsenic or fluoride perturbs the strength of protein and amide groups; however, the shifts in peaks were not pronounced during combined exposure. These results thus highlight the role of arsenic- or fluoride-induced oxidative stress, DNA damage and protein interaction as the major determinants of toxicity, along with the differential toxic effects during arsenic-fluoride interaction during co-exposure. The study further corroborates our earlier observations that at the higher concentration co-exposures to these toxicants do not elicit synergistic toxicity.     

Interactive effect of arsenic and fluoride on cardio-respiratory disorders in male rats: possible role of reactive oxygen species

Epidemiological evidence demonstrates positive correlation between environmental and occupational arsenic or fluoride exposure and risk to various cardio-respiratory disorders. Arsenic-exposure has been associated with atherosclerosis, hypertension, cerebrovascular diseases, ischemic heart disease, and peripheral vascular disorders, whereas Fluoride-exposure manifests cardiac irregularities and low blood pressure (BP). Present study aims to study the combined effects of these toxicants on various cardio-respiratory variables in male rats. Single intravenous (i.v.) dose of arsenic (1, 5, 10 mg/kg) or fluoride (5, 10, 20, 36.5 mg/kg) either alone or in combination were administered. Individual exposure to arsenic or fluoride led to a significant depletion of mean arterial pressure, heart rate (HR), respiration rate and neuromuscular (NM) transmission in a dose-dependent manner. These changes were accompanied by increased levels of blood reactive oxygen species (ROS) and decreased glutathione (GSH) concentrations. An increase in the blood acetyl cholinesterase (AChE) activity was observed in both arsenic or fluoride exposed rats. These changes were significantly more pronounced in arsenic-exposed animals than in fluoride. During combined exposure to arsenic (5 mg/kg) + fluoride (20 mg/kg) or arsenic (10 mg/kg) + fluoride (36.5 mg/kg) the toxic effects were more pronounced compared to individual toxicities of arsenic or fluoride alone. However, combined exposure to arsenic (5 mg/kg) + fluoride (36.5 mg/kg) resulted in antagonistic effects on variables suggestive of altered cardio-respiratory function and oxidative stress. The results from the present study suggest that arsenic or fluoride individually demonstrate cardio-respiratory failure at all doses whereas during combination exposure these toxins show variable toxicities; both synergistic and antagonistic effects depending upon the dose. Moreover, it may be concluded that arsenic and/or fluoride cardio-respiratory toxicity may be mediated via oxidative stress. However, these results are new in the discipline thus requires further exploration.     

Arsenic and fluoride: two major ground water pollutants

Increasing human activities have modified the global cycle of heavy metals, non metals and metalloids. Both arsenic and fluoride are ubiquitous in the environment. Thousands of people are suffering from the toxic effects of arsenicals and fluorides in many countries all over the world. These two elements are recognized worldwide as the most serious inorganic contaminants in drinking water. Many studies have reported as regards to simple fluorosis and arsenicosis, but the knowledge of the joint action of these two elements is lacking and the results derived from previous studies were inconclusive. Contradictory results were reported in experimental studies in which different joint actions such as independent, synergistic and antagonistic effects were observed. This indicates that interaction mechanism of these two elements is considerable complicated and requires extensive studies. When two different types of toxicants are simultaneously going inside a human body they may function independently or can act as synergistic or antagonistic to one another. Thus there is an urge to resolve the question that how arsenic and fluoride act in condition of concomitant exposure. Although there have been reports in literature of individual toxicity of arsenic and fluoride however, there is very little known about the effects following the combined exposure to these toxicants. This review focused on recent developments in the research on the condition of individual exposure to arsenic and fluoride along with the recent updates of their combined exposure to better understand the joint action of these two toxicants.     

Combined administration of iron and monoisoamyl-DMSA in the treatment of chronic arsenic intoxication in mice

Co-administration of iron in combination with monoisoamyl dimercaptosuccinic acid (MiADMSA) against chronic arsenic poisoning in mice was studied. Mice preexposed to arsenic (25 ppm in drinking water for 6 months) mice were treated with MiADMSA (50 mg/kg, intraperitoneally) either alone or in combination with iron (75 or 150 mg/kg, orally) once daily for 5 days. Arsenic exposure led to a significant depletion of blood δ-aminolevulinic acid dehydratase (ALAD) activity, hematocrit, and white blood cell (WBC) counts accompanied by small decline in blood hemoglobin level. Hepatic reduced glutathione (GSH) level, catalase and superoxide dismutase (SOD) activities showed a significant decrease while, oxidized glutathione (GSSG) and thiobarbituric acid-reactive substances (TBARS) levels increased on arsenic exposure, indicating arsenic-induced hepatic oxidative stress. Liver aspartate and alanine transaminases (AST and ALT) activities also decreased significantly on arsenic exposure. Kidney GSH, GSSG, catalase level and SOD activities remained unchanged, while, TBARS level increased significantly following arsenic exposure. Brain GSH, glutathione peroxidase (GPx), and SOD activities decreased, accompanied by a significant elevation of TBARS level after chronic arsenic exposure. Treatment with MiADMSA was marginally effective in reducing ALAD activity, while administration of iron was ineffective when given alone. Iron when co-administered with MiADMSA restored blood ALAD activity. Administration of iron alone had no beneficial effects on hepatic oxidative stress, while in combination with MiADMSA it produced significant decline in hepatic TBARS level compared to the individual effect of MiADMSA. Renal biochemical variables were insensitive to any of the treatments. Combined administration of iron with MiADMSA also had no additional beneficial effect over the individual protective effect of MiADMSA on brain oxidative stress. Interestingly, combined administration of iron with MiADMSA provided more pronounced depletion of blood arsenic, while no additional beneficial effects on tissue arsenic level over the individual effect of MiADMSA were noted. The results lead us to conclude that iron supplementation during chelation has some beneficial effects particularly on heme synthesis pathway and blood arsenic concentration.     

Lithium Treatment Aggregates the Adverse Effects on Erythrocytes Subjected to Arsenic Exposure

The present study was designed to investigate the effects of lithium treatment on red blood cells which were given arsenic exposure. Long-term lithium therapy is being extensively used for the treatment of bipolar disorders. Arsenic is a group I carcinogen and a major toxic pollutant in drinking water that affects millions of people worldwide. Male SD rats were segregated into four groups, viz. normal control, lithium treated, arsenic treated, and lithium + arsenic treated. Lithium was supplemented as lithium carbonate at a dose level of 1.1 g/kg diet for a period of 8 weeks. Arsenic was given in the form of sodium arsenite at a dose level of 100 ppm in drinking water, ad libitum, for the same period. Lysates of red blood cells were used to investigate the effects of lithium and arsenic treatments on anti-oxidant enzymes, reduced glutathione (GSH), and lipid peroxidation (LPO) levels. Various hematological parameters, activities of Na⁺ K⁺ ATPase and delta-aminolevulinic acid dehydratase (δ-ALAD) were also assessed. A significant reduction was observed in the activities of antioxidant enzymes, GSH levels, total erythrocyte counts, Na⁺ K⁺ ATPase, and ALAD enzyme activities in lysates of red blood cells when exposed either to lithium or arsenic. In addition, a significant increase in the levels of malondialdehyde (MDA), lymphocytes, neutrophils, and total leukocytes was also observed following lithium as well as arsenic treatments. However, when arsenic-treated rats were subjected to lithium treatment, a pronounced alteration was noticed in all the above parameters. Therefore, we conclude that lithium supplementation to the arsenic-treated rats enhances the adverse effects on red blood cells and therefore use of lithium may not be medicated to patients who are vulnerable to arsenic exposure through drinking water. It can also be inferred that adverse effects of lithium therapy may get aggravated in patients thriving in the arsenic-contaminated area.

     

Curcumin encapsulated in chitosan nanoparticles: a novel strategy for the treatment of arsenic toxicity

Water-soluble nanoparticles of curcumin were synthesized, characterized and applied as a stable detoxifying agent for arsenic poisoning. Chitosan nanoparticles of less than 50 nm in diameter containing curcumin were prepared. The particles were characterized by TEM, DLS and FT-IR. The therapeutic efficacy of the encapsulated curcumin nanoparticles (ECNPs) against arsenic-induced toxicity in rats was investigated. Sodium arsenite (2mg/kg) and ECNPs (1.5 or 15 mg/kg) were orally administered to male Wistar rats for 4 weeks to evaluate the therapeutic potential of ECNPs in blood and soft tissues. Arsenic significantly decreased blood δ-aminolevulinic acid dehydratase (δ-ALAD) activity, reduced glutathione (GSH) and increased blood reactive oxygen species (ROS). These changes were accompanied by increases in hepatic total ROS, oxidized glutathione, and thiobarbituric acid-reactive substance levels. By contrast, hepatic GSH, superoxide dismutase and catalase activities significantly decreased on arsenic exposure, indicative of oxidative stress. Brain biogenic amines (dopamine, norepinephrine and 5-hydroxytryptamine) levels also showed significant changes on arsenic exposure. Co-administration of ECNPs provided pronounced beneficial effects on the adverse changes in oxidative stress parameters induced by arsenic. The results indicate that ECNPs have better antioxidant and chelating potential (even at the lower dose of 1.5 mg/kg) compared to free curcumin at 15 mg/kg. The significant neurochemical and immunohistochemical protection afforded by ECNPs indicates their neuroprotective efficacy. The formulation provides a novel therapeutic regime for preventing arsenic toxicity.     

Effects of Combined Exposure to Chronic High-Fat Diet and Arsenic on Thyroid Function and Lipid Profile in Male Mouse

The thyroid is one of the major endocrine glands that contribute to body and fat metabolism. The present study evaluated the effects of combined exposure to chronic high-fat diet (HFD) and arsenic on thyroid function and lipid profile. In this experimental study, 72 male Naval Medical Research Institute mice were divided into six groups and fed HFD or low-fat diet (LFD) while being exposed to 25 or 50 ppm of arsenic in drinking water for 20 weeks. After 24 h of the last experimental day, blood samples were collected for hormonal and biochemical measurements. The data indicated that exposure to HFD alone increased the levels of triiodothyronine (T3), thyroid-stimulating hormone (TSH), leptin, lipid profile, reactive oxygen species (ROS), and malondialdehyde (MDA) and decreased the levels of high-density lipoprotein, albumin, adiponectin, and glutathione sulfhydryl reductase (GSH), whereas exposure to arsenic alone decreased the levels of T3 and GSH and increased the levels of TSH, leptin, ROS, MDA, and T4/T3 ratio compared to those in the control LFD group. Furthermore, concomitant administration of HFD and arsenic decreased the lipid profile and levels of T4, albumin, total protein, T3, and GSH and increased the levels of TSH, adiponectin, leptin, ROS, MDA, and T4/T3 ratio compared to those in the control LFD or HFD group. In conclusion, combined exposure to HFD and arsenic induced hypothyroidism via reduction of thyroid hormones and enhancement of plasma TSH and T3 uptake levels concomitant with hypolipidemia, hyperleptinemia, hyperadiponectinemia, induction of oxidative stress, and reduction of GSH levels.     

基于Wnt信号通路探讨氟砷混合暴露的生物暴露限值

慢性氟砷联合中毒是全世界的一个重大公共卫生问题,影响着数千万人.目前该病病因清楚,但发病机制未明,且无特效治疗方法,因此,早期预防尤为重要.生物暴露限值旨在探讨外源化学物引起机体有害效应的最高容许浓度.为了探讨氟砷混合暴露的生物暴露限值(BEL),本研究通过比较对照及氟砷联合暴露地区环境介质中的氟、砷含量,分析氟、砷与Wnt信号通路关键蛋白的剂量-效应及剂量-反应关系,利用基准剂量法估算氟砷混合暴露的生物暴露限值.结果表明: 氟砷联合暴露地区煤、黏土、室内空气、室外空气、辣椒、大米中的氟含量以及煤、黏土、室外空气、辣椒、大米中的砷含量均高于对照;随着氟、砷暴露水平的增加,糖原合酶激酶3β(GSK3β)、β-连环蛋白(β-catenin)含量以及Wnt/β连环蛋白信号通路拮抗蛋白(DKK1)、GSK3β、β-catenin的异常检出率逐渐增加,但DKK1含量显著降低;基于Wnt信号通路,氟砷混合暴露的生物暴露限值UF为0.52 mg·g^-1Cr,UAs为6.59 μg·g^-1Cr.本研究对于早期预防氟砷联合中毒引起的机体损伤具有重要的指导意义.     

Combined administration of N-acetylcysteine and monoisoamyl DMSA on tissue oxidative stress during arsenic chelation therapy

The present study deals with the therapeutic potential of combined administration of N-acetylcysteine (NAC) along with monoisoamyl DMSA (MiADMSA) against chronic arsenic poisoning in guinea pigs. Animal were exposed to 50 ppm arsenic in drinking water for 8 mo and subsequently treated for 5 consecutive days with 100 mg/kg NAC (orally) and MiADMSA (intraperitoneally), individually or in combination (50 mg/kg each). Arsenic exposure produced a significant depletion of blood δ-aminolevulinic acid dehydrate (ALAD) activity, increased the blood zinc protoporphyrin (ZPP) level, and reduced blood and liver glutathione (GSH) levels in guinea pigs. Hepatic oxidized glutathione (GSSG) and thiobarbituric acid reactive substance (TBARS) levels showed a marked increase, whereas hepatic alkaline phosphatase (ALP) activity decreased and acid phosphatase (ACP) activity increased on arsenic exposure. Significant depletion of liver transaminase activities on arsenic exposure suggests organ injury. Administration of MiADMSA, alone and in combination with NAC after arsenic exposure, was able to significantly enhance hepatic GSH and to reduce GSSG and TBARS levels compared to the arsenic control. Biochemical variables indicative of liver injury generally remained insensitive to any of these treatments. The recoveries in parameters indicative of oxidative stress were more marked in guinea pigs treated with combined administration of NAC and MiADMSA than monotherapy. Interestingly, there was a more pronounced depletion of arsenic from blood and tissues after combined treatment with NAC plus MiADMSA than MiADMSA. Blood and tissues copper, zinc, iron, and calcium concentrations showed a significant increase after arsenic exposure, which showed improvement, particularly after combined administration of MiADMSA and NAC. Based on these data, a proposal can be made that greater effectiveness in chelation treatment against chronic arsenic poisoning (i.e., turnover in the oxidative stress and removed of arsenic from the system) could be achieved by combined administration of an antioxidant (preferably having a thiol moiety) with MiADMSA.     

Response of arsenic-induced oxidative stress,DNA damage,and metal imbalance to combined administration of DMSA and monoisoamyl-DMSA during chronic arsenic poisoning in rats

Arsenic and its compounds cause adverse health effects in humans. Current treatment employs administration of thiol chelators, such as meso-2,3-dimercaptosuccinic acid (DMSA) and sodium 2,3-dimercaptopropane 1-sulfonate (DMPS), which facilitate its excretion from the body. However, these chelating agents are compromised by number of limitations due to their lipophobic nature, particularly in case of chronic poisoning. Combination therapy is a new approach to ensure enhanced removal of metal from the body, reduced doses of potentially toxic chelators, and no redistribution of metal from one organ to another, following chronic metal exposure. The present study attempts to investigate dose-related effects of two thiol chelators, DMSA and one of its new analogues, monoisoamyl dimercaptosuccinic acid (MiADMSA), when administered in combination with the aim of achieving normalization of altered biochemical parameters suggestive of oxidative stress and depletion of inorganic arsenic following chronic arsenic exposure. Twenty-five adult male Wistar rats were given 25 ppm arsenic for 10 weeks followed by chelation therapy with the above chelating agents at a dose of 0.3 mmol/kg (orally) when administered individually or 0.15 mmol/kg and 0.3 mmol/kg (once daily for 5 consecutive days), respectively, when administered in combination. Arsenic exposure led to the inhibition of blood δ-aminolevulinic acid dehydratase (ALAD) activity and depletion of glutathione (GSH) level. These changes were accompanied by significant depletion of hemoglobin, RBC and Hct as well as blood superoxide dismutase (SOD) acitivity. There was an increase in hepatic and renal levels of thiobarbituric acid-reactive substances, while GSH:GSSG ratio decreased significantly, accompanied by a significant increase in metallothionein (MT) in hepatocytes. DNA damage based on denaturing polyacrylamide gel electrophoresis revealed significant loss in the integrity of DNA extracted from the liver of arsenic-exposed rats compared to that of normal animals. These changes were accompanied by a significant elevation in blood and soft-tissue arsenic concentration. Co-administration of DMSA and MiADMSA at lower dose (0.15 mmol/kg) was most effective not only in reducing arsenic-induced oxidative stress but also in depleting arsenic from blood and soft tissues compared to other treatments. This combination was also able to repair DNA damage caused following arsenic exposure. We thus recommend combined administration of DMSA and MiADMSA for achieving optimum effects of chelation therapy.     

Effects of combined administration of captopril and DMSA on arsenite induced oxidative stress and blood and tissue arsenic concentration in rats

We compared the therapeutic efficacy of captopril and a thiol chelating agent, meso 2,3-dimercaptosuccinic acid (DMSA) either individually or in combination against arsenite induced oxidative stress and mobilization of metal in rats. Animals were exposed to 100 ppm arsenite as sodium arsenite in drinking water for six weeks followed by treatment with DMSA (50 mg/kg, orally), captopril (50 mg/kg, intraperitoneally) either alone or in combination, once daily for 5 consecutive days. Arsenite exposure led to a significant depletion of blood delta-aminolevulinic acid dehydratase (ALAD) activity, glutathione and platelet levels while significantly increased the level of reactive oxygen species (in RBCs). Hepatic reduced glutathione (GSH) level showed a significant decrease while, thiobarbituric acid reactive substances (TBARS) levels increased on arsenite exposure indicating arsenite induced hepatic oxidative stress. Kidney GSH, GSSG, catalase and TBARS remained unchanged on arsenite exposure. Treatment with DMSA was effective in increasing ALAD activity while, captopril was ineffective when given alone. Captopril when co-administered with DMSA also provided no additional beneficial effect on blood ALAD activity but significant brought altered platelet counts back to the normal value. In contrast, administration of captopril alone provided significant beneficial effects on hepatic oxidative stress, and in combination with DMSA provided a more pronounced recovery in the TBARS level compared to the individual effect of DMSA and captopril. Renal biochemical variables remained insensitive to arsenite and any of the treatments. Interestingly, combined administration of captopril with DMSA had a remarkable effect in depleting total arsenic concentration from blood and soft tissues. These results lead us to conclude that captopril administration during chelation treatment had some beneficial effects particularly on the protection of inhibited blood ALAD activity, and depletion of arsenic level. The study supports our earlier conclusion that a co-administration of an antioxidant is more beneficial than monotherapy with the chelating agents, in order to achieve optimal effects of chelation in arsenite toxicity.     

Suppression of N-nitrosodiethylamine induced hepatocarcinogenesis by silymarin in rats

Antioxidants are one of the key players in tumorigenesis, several natural and synthetic antioxidants were shown to have anticancer effects. In the present investigation the efficacy of silymarin on the antioxidant status of N-nitrosodiethylamine (NDEA) induced hepatocarcinogenesis in Wistar albino male rats were assessed. The animals were divided into five groups. The animals in the groups 1 and 3 were normal control and silymarin control, respectively. Groups 2, 4 and 5 were administered with 0.01% NDEA in drinking water for 15 weeks to induce hepatocellular carcinoma (HCC). Starting 1 week prior to NDEA administration group 4 animals were treated with silymarin in diet for 16 weeks, 10 weeks after NDEA administration group 5 animals were treated with silymarin and continued till the end of the experiment period (16 weeks). After the experimental period the body weight, relative liver weight, number of nodules, size of nodules, the levels of lipid peroxidation, glutathione (GSH), and the activities of antioxidant enzymes were assessed in both haemolysate and liver tissue. In group 2 hepatocellular carcinoma induced animals there was an increase in the number of nodules, relative liver weight. The levels of lipid peroxides were elevated with subsequent decrease in the body weight, (glutathione) GSH, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD). In contrast, silymarin + NDEA treated groups 4 and 5 animals showed a significant decrease in the number of nodules with concomitant decrease in the lipid peroxidation status. The levels of GSH and the activities of antioxidant enzymes in both haemolysate and liver were improved when compared with hepatocellular carcinoma induced group 2 animals. The electron microscopy studies were also carried out which supports the chemopreventive action of the silymarin against NDEA administration during liver cancer progression. These findings suggest that silymarin suppresses NDEA induced hepatocarcinogenesis by modulating the antioxidant defense status of the animals.     

Lipid peroxidation and antioxidant systems in the blood of young rats subjected to chronic fluoride toxicity

Wistar albino rats were exposed to 30 or 100 ppm fluoride in drinking water during their fetal, weanling and post-weaning stages of life up to puberty. Extent of lipid peroxidation and response of the antioxidant systems in red blood cells and plasma to prolonged fluoride exposure were assessed in these rats in comparison to the control rats fed with permissible level (0.5 ppm) of fluoride. Rats treated with 100 ppm fluoride showed enhanced lipid peroxidation as evidenced by elevated malondialdehyde (MDA) levels in red blood cells but, 30 ppm fluoride did not cause any appreciable change in RBC MDA level. 30 ppm fluoride-intake resulted in increased levels of total and reduced glutathione in red blood cells and ascorbic acid in plasma while 100 ppm fluoride resulted in decreases in these levels. The activity of RBC glutathione peroxidase was elevated in both the fluoride-treated groups, more pronounced increase was seen with 100 ppm. Reduced to total glutathione ratio in RBC and uric acid levels in plasma decreased in both the groups. RBC superoxide dismutase activity decreased significantly on high-fluoride treatment. These results suggest that long-term high-fluoride intake at the early developing stages of life enhances oxidative stress in the blood, thereby disturbing the antioxidant defense of rats. Increased oxidative stress could be one of the mediating factors in the pathogenesis of toxic manifestations of fluoride.     

Fluoride and Arsenic Exposure Impairs Learning and Memory and Decreases mGluR5 Expression in the Hippocampus and Cortex in Rats

Fluoride and arsenic are two common inorganic contaminants in drinking water that are associated with impairment in child development and retarded intelligence. The present study was conducted to explore the effects on spatial learning, memory, glutamate levels, and group I metabotropic glutamate receptors (mGluRs) expression in the hippocampus and cortex after subchronic exposure to fluoride, arsenic, and a fluoride and arsenic combination in rats. Weaned male Sprague-Dawley rats were assigned to four groups. The control rats drank tap water. Rats in the three exposure groups drank water with sodium fluoride (120 mg/L), sodium arsenite (70 mg/L), and a sodium fluoride (120 mg/L) and sodium arsenite (70 mg/L) combination for 3 months. Spatial learning and memory was measured in Morris water maze. mGluR1 and mGluR5 mRNA and protein expression in the hippocampus and cortex was detected using RT-PCR and Western blot, respectively. Compared with controls, learning and memory ability declined in rats that were exposed to fluoride and arsenic both alone and combined. Combined fluoride and arsenic exposure did not have a more pronounced effect on spatial learning and memory compared with arsenic and fluoride exposure alone. Compared with controls, glutamate levels decreased in the hippocampus and cortex of rats exposed to fluoride and combined fluoride and arsenic, and in cortex of arsenic-exposed rats. mGluR5 mRNA and protein expressions in the hippocampus and mGluR5 protein expression in the cortex decreased in rats exposed to arsenic alone. Interestingly, compared with fluoride and arsenic exposure alone, fluoride and arsenic combination decreased mGluR5 mRNA expression in the cortex and protein expression in the hippocampus, suggesting a synergistic effect of fluoride and arsenic. These data indicate that fluoride and arsenic, either alone or combined, can decrease learning and memory ability in rats. The mechanism may be associated with changes of glutamate level and mGluR5 expression in cortex and hippocampus.     

Effects of fluoride on hepatic antioxidant system and transcription of Cu/Zn SOD gene in young pigs

Thirty-two barrows (Duroc x Landrace x Yorkshire) were randomly divided into four groups, each of which included eight pigs. The groups received the same basal diet supplemented with 0, 100, 250 and 400mg/kg fluoride, respectively. The malondialdehyde (MDA) and glutathione (GSH) levels, antioxidant enzymes activities and zinc/copper superoxide dismutase (Cu/Zn SOD) mRNA content in the liver were determined to evaluate the fluoride hepatic intoxication. Results showed the increased lipid peroxides (LPO) level and the reduced GSH content, along with a concomitant decrease in the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px). Moreover, the level of hepatic Cu/Zn SOD mRNA was also significantly reduced. We suggest the mechanism of fluoride injuring the liver as follows: fluoride causes a decrease in Cu/Zn SOD mRNA and the reduced activities of antioxidant enzymes, leads to the declined ability of scavenging free radicals with excessive production of LPO, which seriously damages the hepatic structure and function.     

Genotoxic evaluation of chronic fluoride exposure: sister-chromatid exchange study

As part of a continuing investigation, this study was conducted to examine the genotoxic effects of chronic exposure to sodium fluoride (NaF) in drinking water on the frequency of sister-chromatid exchange (SCE) in the bone-marrow cells of male Chinese hamsters. Animals at about 3 weeks of age were randomly assigned to 6 groups, each with at least 3 hamsters, and were maintained on a low fluoride diet (less than 0.2 ppm F) throughout the experiment. At 4 weeks of age, the animals in groups I-V began to receive drinking water containing fluoride at concentrations of 0, 1, 10, 50 and 75 ppm, respectively. Group VI was treated with cyclophosphamide and served as the positive control. The animals were sacrificed at 24 weeks of age by cervical dislocation. The humeri and plasma were analyzed for fluoride content, which was found to increase with the increase in fluoride concentration in drinking water. Slides of chromosomes from bone-marrow cells were prepared and blindly examined for the frequency of SCE. The mean scores of SCE for the hamsters receiving drinking water containing F concentrations up to 75 ppm for 21 weeks ranged from 4.28 to 6.28 per cell, and were not significantly different from those of the negative controls (4.60-5.44/cell). The results indicated that chronic fluoride exposure had no effect on the frequency of SCE in Chinese hamster bone-marrow cells under the conditions of the present investigation.     

Erythrocyte glutathione metabolism in human chronic fluoride toxicity.

Chronic exposure of humans to toxic levels of fluoride in drinking water resulted in significant increase in blood GSH content with significant increase in the activities of erythrocyte glutathione metabolising enzymes viz., gamma-glutamylcysteine synthetase (E.C. 6.3.2.2), gamma-glutamyltranspeptidase (E.C. 2.3.2.2), GST (E.C. 2.5.1.18), GSH-Px (E.C. 1.11.1.9) and GR (E.C. 1.6.4.2). The data suggested a form of adaptation on the part of the erythrocytes to counteract the oxidative stress in red blood cells of fluorotic patients.     

Oxidative Damage Induced by Arsenic in Mice or Rats: A Systematic Review and Meta-Analysis

In this meta-analysis, studies reporting arsenic-induced oxidative damage in mouse models were systematically evaluated to provide a scientific understanding of oxidative stress mechanisms associated with arsenic poisoning. Fifty-eight relevant peer-reviewed publications were identified through exhaustive database searching. Oxidative stress indexes assessed included superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), glutathione peroxidase (GPx), glutathione-s-transferase (GST), glutathione reductase (GR), oxidized glutathione (GSSG), malondialdehyde (MDA), and reactive oxygen species (ROS). Our meta-analysis showed that arsenic exposure generally suppressed measured levels of the antioxidants, SOD, CAT, GSH, GPx, GST, and GR, but increased levels of the oxidants, GSSG, MDA, and ROS. Arsenic valence was important and GR and MDA levels increased to a significantly (P < 0.05) greater extent upon exposure to As³⁺ than to As⁵⁺. Other factors that contributed to a greater overall oxidative effect from arsenic exposure included intervention time, intervention method, dosage, age of animals, and the sample source from which the indexes were estimated. Our meta-analysis effectively summarized a wide range of studies and detected a positive relationship between arsenic exposure and oxidative damage. These data provide a scientific basis for the prevention and treatment of arsenic poisoning.     

Metabolic adaptations to arsenic-induced oxidative stress in male wistar rats

The present study was planned to investigate the effect of arsenic in rats on several biochemical indices of oxidative stress. Rats were exposed to arsenite in drinking water for upto 12 weeks. Chronic exposure to arsenic for a period of 12 weeks significantly (p < 0.05) increased arsenic burden in blood, liver, and kidney. Several intrinsic antioxidant defenses were activated after a 4-week exposure to arsenic. Some remained elevated, but others became depressed over a longer exposure period. Alterations in most of the biochemical variables reached statistical significant (p < 0.05). Arsenic significantly (p < 0.01) reduced mRNA expression of the superoxide dismutase 2 (SOD2) gene with respect to the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene. These observations indicated that prolong exposure to arsenic causes induction of oxidative stress and biochemical alterations.