The effects of gestational arsenic exposure and dietary selenium deficiency on selenium and selenoenzymes in maternal and fetal tissues in mice

Bisphenol A and selenium deficiency exposure induces pyroptosis and myogenic differentiation disorder in chicken muscle stomach

Bisphenol A (BPA), which is commonly found in the environment due to its release from the use of plastics and food overpacks, has become a major stressor for environmental sustainability and livestock and poultry farming health. Selenium (Se) deficiency causes structural damage and inflammatory responses to the digestive system and muscle tissue, and there is a potential for concurrent space-time exposure to nutritional deficiency diseases and environmental toxicants in livestock and poultry. The mechanisms of damage to chicken muscular stomach from BPA or/and Se deficiency treatment are still not known. Here, we established a chicken model of BPA (20 mg/kg) or/and Se deficiency (0.039 mg/kg) exposure, and detected histopathological changes in the muscular stomach tissue, the levels of iNOS/NO pathway, IL-6/JAK/STAT3 pathway, pyroptosis, and myogenic differentiation by H&E staining, immunofluorescence staining, real-time quantitative PCR, and western blot methods. The data revealed that BPA or Se deficiency exposure caused gaps between muscle fibers with inflammatory cell infiltration; up-regulation of the iNOS/NO pathway and IL-6/JAK/STAT3 pathway; up-regulation of NLRP3/Caspase-1-dependent pyroptosis related genes; down-regulation of muscle-forming differentiation (MyoD, MyoG, and MyHC) genes. The combination of BPA and Se deficiency was associated with higher toxic impairment than alone exposure. In conclusion, we discovered that BPA and Se deficiency caused myogastric pyroptosis and myogenic differentiation disorder. These findings provide a theoretical basis for the co-occurrence of animal nutritional deficiency diseases and environmental toxicant exposures in livestock and poultry farming, and may provide important insights into limiting the production of harmful substances.

Bisphenol A Regulates the TNFR1 Pathway and Excessive ROS Mediated by miR-26a-5p/ADAM17 Axis to Aggravate Selenium Deficiency-Induced Necroptosis in Broiler Veins

Selenium (Se) deficiency can affect the expression of microRNA (miRNA) and induce necroptosis, apoptosis, etc., resulting in damage to various tissues and organs. Bisphenol A (BPA) exposure can cause adverse consequences such as oxidative stress, endothelial dysfunction, and atherosclerosis. The toxic effects of combined treatment with Se-deficiency and BPA exposure may have a synergistic effect. We replicated the BPA exposure and Se-deficiency model in broiler to investigate whether the combined treatment of Se-deficiency and BPA exposure induced necroptosis and inflammation of chicken vascular tissue via the miR-26A-5p/ADAM17 axis. We found that Se deficiency and BPA exposure significantly inhibited the expression of miR-26a-5p and increased the expression of ADAM17, thereby increasing reactive oxygen species (ROS) production. Subsequently, we discovered that the tumor necrosis factor receptor (TNFR1), which was highly expressed, activated the necroptosis pathway through receptor-interacting protein kinase 1 (RIPK1), receptor-interacting protein kinase 3 (RIPK3), and mixed-lineage kinase domain-like (MLKL), and regulated the heat shock proteins-related genes expressions and inflammation-related genes expressions after exposure to BPA and selenium deficiency. In vitro, we found that miR-26a-5p knockdown and increased ADAM17 can induce necroptosis by activating the TNFR1 pathway. Similarly, both N-Acetyl-L-cysteine (NAC), Necrostatin-1 (Nec-1), and miR-26a-5p mimic prevented necroptosis and inflammation caused by BPA exposure and Se deficiency. These results suggest that BPA exposure activates the miR-26a-5p/ADAM17 axis and exacerbates Se deficient-induced necroptosis and inflammation through the TNFR1 pathway and excess ROS. This study lays a data foundation for future ecological and health risk assessments of nutrient deficiencies and environmental toxic pollution.

New insights into brain injury in chickens induced by bisphenol A and selenium deficiency-Mitochondrial reactive oxygen species and mitophagy-apoptosis crosstalk homeostasis

Bisphenol A (BPA), a component of plastic products, can penetrate the blood-brain barrier and pose a threat to the nervous system. Selenium (Se) deficiency can also cause nervous system damage. Resulting from the rapid industrial development, BPA pollution and Se deficiency often coexist. However, it is unclear whether brain damage in chickens caused by BPA exposure and Se deficiency is related to the crosstalk disorder between mitophagy and apoptosis. In this study, 60 chickens (1 day old) were fed with a diet that contained 20 mg/kg BPA but was insufficient in Se (only 0.039 mg/kg) for 42 days to establish a chicken brain injury model. In vitro, the primary chicken embryo brain neurons were treated for 24 h with Se-deficient medium containing 75 μM BPA. The results showed that BPA exposure and Se deficiency inhibited the expression of the mitochondrial respiratory chain complex in brain neurons, and a large number of mitochondrial reactive oxygen species were released. Furthermore, the expression levels of mitochondrial fusion proteins (OPA1, Mfn1, and Mfn2) decreased, while the expression levels of mitochondrial fission proteins (Drp1, Mff, and Fis1) increased, thus exacerbating mitochondrial division. In addition, the results of immunofluorescence and flow cytometry analysis, as well as the elevated expressions of mitophagy related genes (PINK1, Parkin, ATG5, and LC3II/I) and pro-apoptotic markers (Bax, Cytc, Caspase3, and Caspase9) indicated that BPA exposure and Se deficiency disrupted the crosstalk homeostasis between mitophagy and apoptosis. However, this crosstalk homeostasis was restored after Mito-Tempo and Rapamycin treatment. In contrast, 3-methyladenine treatment exacerbated this crosstalk disorder. In conclusion, BPA exposure and Se deficiency can induce mitochondrial reactive oxygen species bursts and disorders of mitochondrial dynamics by destroying the mitochondrial respiratory chain complex. The result is indicative of an imbalance in mitochondrial autophagy and apoptosis crosstalk homeostasis, which damages the chicken brain.

Bisphenol A aggravate selenium deficiency-induced apoptosis via miR-215-3p/Dio1 to activate ROS/PI3K/AKT pathway in chicken arterial

Both bisphenol A (BPA) and selenium (Se) deficiency can affect the expression of microRNAs (miRNAs), which can specifically regulate its target mRNA and induce apoptosis, and play a significant role in cardiovascular injury diseases. To explore the mechanism of apoptosis induced by BPA and Se deficiency in chicken arterial endothelial tissue and the role of miRNAs in this process, the model of BPA exposure/Se deficiency in chicken and PAEC cells have been employed. The targeting relationship between miR-215-3p and iodothyronine deiodinase 1 (Dio1) in PAEC was verified by double luciferase gene report. The level of miR-215-3p was detected by qRT-PCR. The oxidative stress level of arterial endothelial cells was detected by oxidative stress kit and DCFH-DA probe method. The PI3K/AKT pathway, mitochondrial dynamics, and apoptosis-related genes were detected by qRT-PCR and western blot. The mitochondrial ATP level and nitric oxide synthases (NOSs) level were detected with the kit. TUNEL, acridine orange/ethidium bromide, and flow cytometry were used to detect the level of apoptosis. The results showed that BPA exposure and Se deficiency led to overexpression of miR-215-3p, aggravated oxidative stress, inhibited activation of PI3K/AKT pathway, promoted mitochondrial division, increased expression of apoptosis related genes, and finally led to apoptosis of chicken arterial endothelial cells. We also established knockdown/overexpression models of miR-215-3p and Dio1 in vitro, and found that overexpression of miR-215-3p and knockout of Dio1 can induce apoptosis. Interestingly, miR-215-3p-Inhibitor and N-acetyl- l-cysteine (NAC) partially prevented apoptosis caused by BPA exposure and Se deficiency, and LY294002 aggravated apoptosis. These results suggest that BPA exposure aggravates the apoptosis of Se deficient arterial endothelial cells in chickens by regulating the ROS/PI3K/AKT pathway activated by miR-215-3p/Dio1. The miR-215-3p/Dio1 axis provides a new way to understand the toxic mechanism of BPA exposure and Se deficiency, and reveals a new regulatory model of apoptosis damage in vascular diseases.

Low levels of arsenic exposure during pregnancy and maternal and neonatal thyroid hormone parameters: The determinants for these associations

BACKGROUND

The potential maternal and neonatal thyrotoxicity associated with exposure to arsenic during pregnancy is very limited and unclear.

OBJECTIVES

This study aimed to examine the associations between arsenic exposure levels in maternal and cord serum and maternal and neonatal thyroid hormone parameters in a prospective birth cohort study.

METHODS

The study including 2089 mother-neonate pairs was based upon Ma'an Shan birth cohort study in China. The exposure variables including maternal serum arsenic levels in the first, second and third trimester and average arsenic exposure level during pregnancy and cord serum arsenic level. Maternal serum TSH and FT4 levels in the first, second and third trimester and cord serum TSH and FT4 levels were determined using the electrochemiluminescence immunoassay with Cobas Elecsys 411. Linear mixed models were used to examine associations between arsenic exposure variables during pregnancy and maternal thyroid hormone parameters, and multiple linear regression analyses were used to examine associations between arsenic exposure during pregnancy and neonatal thyroid hormone parameters. Bayesian kernal machine regression (BKMR) analyses based on a kernel function were also used to examine the effects of exposure to metal mixtures (arsenic, mercury, cadmium and selenium).

RESULTS

The geometric means of arsenic exposure levels across 3 trimesters were 1.74 μg/L, 1.81 μg/L and 1.99 μg/L, respectively, and 1.90 μg/L in cord serum; the geometric means of maternal FT4 levels across 3 trimesters were 16.91 pmol/L, 11.91 pmol/L and 13.16 pmol/L, respectively, and 16.10 pmol/L in cord serum; the geometric means of maternal TSH levels across 3 trimesters were 1.27 μIU/mL, 2.32 μIU/mL and 2.08 μIU/mL, respectively, and 8.47 μIU/mL in cord serum. Maternal serum arsenic levels in the first, seond, third trimester and average arsenic exposure level during pregnancy were all not associated with maternal thyroid hormone parameters after adjustment for all the covariates, the adjusted β (95% CI) were -0.002 (-0.10 to 0.09), 0.05 (-0.05 to 0.16), -0.09 (-0.17 to 0.003) and -0.05 (-0.22 to 0.11) for maternal FT4, respectively; and -0.005 (-0.04 to 0.03), -0.003 (-0.04 to 0.03), -0.004 (-0.03 to 0.02) and -0.01 (-0.06 to 0.04) for maternal lnTSH, respectively. Maternal serum arsenic levels in the first, second trimester and average arsenic exposure level during pregnancy were all inversely associated with neonatal FT4 level after adjustment for all the confounders, the adjusted β (95% CI) were -0.19 (-0.31 to -0.07), -0.14 (-0.26 to -0.01), -0.22 (-0.42 to -0.02), respectively; and cord serum arsenic level was positively related with neonatal TSH level, the adjusted β (95% CI) were 0.04 (0.001 to 0.08). The adverse joint toxic effect of the four metals in maternal serum in the first trimester and in cord serum on neonatal thyroid hormone parameters were also found.

CONCLUSIONS

In this study, exposure to low levels of arsenic during pregnancy could directly affect neonatal thyroid hormone parameters without being mediated by maternal effect of exposure, and maternal serum arsenic levels in the first, second trimester and average arsenic exposure level during pregnancy and cord serum arsenic level may be risk factors affecting neonatal thyroid hormones. These findings indicate that neonates are more sensitive to the thyrotoxicity of arsenic exposure even at low levels. In addition, the adverse joint toxic effect of metal mixtures is also worthy of attention.

Relationship between arsenic and selenium in workers occupationally exposed to inorganic arsenic

The interaction between arsenic (As) and selenium (Se) has been one of the most extensively studied. The antagonism between As and Se suggests that low Se status plays an important role in aggravating arsenic toxicity in diseases development. The objective of this study was to assess the Se contents in biological samples of inorganic As exposed workers (n=61) and in non-exposed subjects (n=52). Median (Me) total arsenic concentration in urine of exposed workers was 21.83μg/g creat. (interquartile range (IQR) 15.49-39.77) and was significantly higher than in the control group - (Me 3.75μg/g creat. (IQR 2.52-9.26), p<0.0001). The median serum Se concentrations in the study group and the control were: 54.20μg/l (IQR 44.2-73.10μg/l) and 55.45μg/l (IQR 38.5-69.60μg/l) respectively and did not differ significantly between the groups. In the exposed group we observed significantly higher urine concentrations of selenosugar 1 (SeSug 1) and selenosugar 3 (SeSug3) than in the control group Me: 1.68μg/g creat. (IQR 1.25-2.97 vs Me: 1.07μg/g creat. (IQR 0.86-1.29μg/g), p<0.0001 for SeSug1; Me: 0.45μg/g creat. (IQR 0.26-0.69) vs Me: 0.28μg/g creat. (IQR 0.17-0.45μg/g), p=0.0021). In the multivariate model, after adjusting to cofounders (age, BMI, job seniority time, consumption of fish and seafood and smoking habits) the high rate of arsenic urine wash out (measured as a sum of iAs+MMA+DMA) was significantly associated with the high total selenium urine excretion (B=0.14 (95%CI (confidence interval) 0.05-0.23)). Combination of both arsenic and selenium status to assess the risk of arsenic-induced diseases requires more studies with regard to both the analysis of speciation, genetics and the influence of factors such as nutritional status.

Reproductive and Developmental Toxicity of Arsenic in Rodents: A Review

Arsenic is a recognized reproductive toxicant in humans and induces malformations, especially neural tube defects, in laboratory animals. Early studies showed that murine malformations occurred only when a high dose of inorganic arsenic was given by intravenous or intraperitoneal injection in early gestation. Oral gavage of inorganic arsenic at maternally toxic doses caused reduced fetal body weight and increased resorptions. Recently, arsenic reproductive and developmental toxicity has been studied in situations more similar to human exposures and using broader endpoints, such as behavioral changes and gene expression. For the general population, exposure to arsenic is mostly oral, particularly via drinking water, repeated and prolonged over time. In mice and rats, methylated or inorganic arsenic via drinking water or by repeated oral gavage induced male and female reproductive and developmental toxicities. Furthermore, at nonmaternally toxic levels, inorganic arsenic given to pregnant dams via drinking water affected fetal brain development and postnatal behaviors. However, arsenic given by repeated oral gavage to pregnant mice and rats was not morphologically teratogenic. In this review of arsenic reproductive and developmental toxicity in rats and mice, the authors summarize recent in vivo studies and discuss possible underlying mechanisms. The influences of folate, selenium, zinc, and arsenic methylation on arsenic reproductive and developmental toxicity are also discussed.

Arsenic Toxicity in Male Reproduction and Development

Arsenic is a toxic metalloid that exists ubiquitously in the environment, and affects global health problems due to its carcinogenicity. In most populations, the main source of arsenic exposure is the drinking water. In drinking water, chronic exposure to arsenic is associated with increased risks of various cancers including those of skin, lung, bladder, and liver, as well as numerous other non-cancer diseases including gastrointestinal and cardiovascular diseases, diabetes, and neurologic and cognitive problems. Recent emerging evidences suggest that arsenic exposure affects the reproductive and developmental toxicity. Prenatal exposure to inorganic arsenic causes adverse pregnancy outcomes and children's health problems. Some epidemiological studies have reported that arsenic exposure induces premature delivery, spontaneous abortion, and stillbirth. In animal studies, inorganic arsenic also causes fetal malformation, growth retardation, and fetal death. These toxic effects depend on dose, route and gestation periods of arsenic exposure. In males, inorganic arsenic causes reproductive dysfunctions including reductions of the testis weights, accessory sex organs weights, and epididymal sperm counts. In addition, inorganic arsenic exposure also induces alterations of spermatogenesis, reductions of testosterone and gonadotrophins, and disruptions of steroidogenesis. However, the reproductive and developmental problems following arsenic exposure are poorly understood, and the molecular mechanism of arsenic-induced reproductive toxicity remains unclear. Thus, we further investigated several possible mechanisms underlying arsenic-induced reproductive toxicity.

Effect of subchronic exposure to arsenic on levels of essential trace elements in mice brain and its gender difference

The interactions of toxic metals with essential metals may result in disturbances in the homeostasis of essential elements. However, there are few reports about toxic effect of arsenic (As) on the levels of essential trace elements in the central nervous system. To investigate whether subchronic exposure to As disturbs levels of main essential trace elements in the brain of mice and whether the gender difference in the response to As are altered, the concentrations of As, Iron (Fe), copper (Cu), selenium (Se), zinc (Zn) and Chromium (Cr) in the cerebrum and cerebellum of mice exposed to As subchronically were examined by inductively coupled plasma-mass spectrometry (ICP-MS). The gender difference in the changed levels of these essential trace elements was also statistically analyzed. The concentration of As was significantly higher in the cerebrum or cerebellum of mice exposed to As than that in control group (P < 0.05). It indicates that As can accumulate in brain of mice after subchronic exposure. The concentrations of Fe, Se and Cr in the cerebrum or cerebellum were significantly lower in mice exposed to As than those in control group (P < 0.05). On the contrary, the concentration of Cu in the cerebrum or cerebellum was significantly higher in mice exposed to As (P < 0.05). Our results indicate that subchronic exposure to As may decrease the levels of Fe, Se and Cr or increase the level of Cu in the brain of mice. Moreover, the significant gender difference was found relative to the effect of As on concentration of Se in cerebrum and concentrations of Cu and Se in cerebellum of mice. Therefore, more experiments are required to further understand mechanisms whereby As interacts with essential elements in brain and induces the gender difference.

Studies on scavenger receptors under experimental hypercholesterolemia: modulation on selenium supplementation

Scavenger receptors (SR) are the cell surface proteins that can bind and internalize modified lipoproteins. Because ox-LDL seems to play a key role in foam cell formation during atherogenesis, SR may be critical for pathogenesis of atherosclerosis. The present study was aimed to study the effect of selenium (Se) supplementation on SR, i.e., SRB1 and CD36 under experimental hypercholesterolemia. Male Sprague Dawley rats were divided into three groups and fed on the control diet, high cholesterol diet (HCD), and HCD + Se, respectively, for a period of 4 months. Selenium and reactive oxygen species (ROS) levels were estimated in serum and liver respectively. mRNA expression using RT-PCR and protein expression using ELISA were analyzed for SRB1 and CD36 receptors. Selenium levels decreased whereas ROS levels increased under experimental hypercholesterolemic state. Selenium supplementation (1 ppm), however, diminished the HCD-induced ROS levels. Furthermore, the protein expression of SRB1 was significantly reduced in HCD group in comparison to the control group. On the other hand, HCD-induced increase in CD36 mRNA and protein expression decreased significantly on Se supplementation. In conclusion, CD36 receptors seem to play a pro-atherogenic role under hypercholesterolemic state. Selenium supplementation, in addition, might prove to be a therapeutically valuable approach in near future to limit the adverse effect of hypercholesterolemia.

Evaluation of selenium in biological sample of arsenic exposed female skin lesions and skin cancer patients with related to non-exposed skin cancer patients

The antagonistic effects between selenium (Se) and arsenic (As) suggest that low Se status plays an important role in arsenism development. The objective of present study was to assess Se contents in biological samples of As exposed females have skin lesions and cancer with related to non-exposed skin cancer patients. The biological samples (blood and scalp hair) of As exposed group comprises, female skin cancer (ESC) patients admitted in cancer hospitals have skin lesions (ESL) and exposed referents have not both diseases (ER), belongs to As exposed area of Pakistan. For comparative purposes, age matched female skin cancerous patient (RP) and non-cancerous females (NER) belong to non-exposed areas were also selected. The As and Se in acid digests of biological samples were pre-concentrated by complexing with chelating agent (ammonium pyrrolidinedithiocarbamate), and resulted complexes were extracted into non-ionic extractant (Triton X-114), prior to analysis by electrothermal atomic absorption spectrometry. The enhancement factor of about 25 was obtained by pre-concentrating 10 mL of sample solutions. The accuracy of the optimized procedure was evaluated by using certified reference material (BCR 397) with certified values for Se and As and standard addition method at three concentration levels in real samples. No significant differences was observed (p>0.05) when comparing the values obtained by the proposed method, added and certified values of both elements. The biological samples of ESC patients had 2-3 folds higher As and lower Se levels as compared to RP (p<0.001). Understudied exposed referents have high level of As and lower Se contents as compared to referents subjects of non-exposed area (p<0.01). The higher concentration of As and lower levels of Se in biological samples of cancerous patients are consisted with reported studies.

Arsenite-induced apoptosis is prevented by selenite in A375 cell line

Arsenic trioxide induces apoptosis and clinical remission in patients diagnosed with acute promyelocytic leukemia. The human malignant melanoma A375 cells were treated with NaAsO2 (0.1–130 μM) and also treated with combined 10 μM NaAsO2 and 10 μM Na2SeO3. NaAsO2 arrested cell growth in the G1 phase and induced apoptosis in a concentration- and time-dependent manner. In contrast, administration of Na2SeO3 antagonized the cell growth inhibition and apoptosis induced by NaAsO2. The NaAsO2 treatment resulted in a marked increase in p53 protein as early as 4 h and in Bcl-2 protein level by 12 h. In addition, p53 downregulation accompanied the combined treatment of NaAsO2 and Na2SeO3. Thus, our results indicate upregulation of p53 and Bcl-2 play acrucial role in the NaAsO2-induced G1 arrest and apoptosis of A375 cells and that downregulation p53 appears to contribute to the inhibition by Na2SeO3 of the effects induced by NaAsO2.

Effect of selenium on hypothyroidism induced by methimazole (MMI) in lactating rats and their pups

The present study was undertaken to assess the effect of selenium (Se) on hypothyroidism induced by methimazole (MMI) in lactating rats and their pups. Rats were randomly divided into four groups of six each: group I served as a negative control which received standard diet; group II received orally MMI (250 mg L -1 ); group II received both MMI (250 mg L -1 , orally) and Se (0.5 mg/kg of diet); group IV served as a positive control and received Se (0.5 mg Na 2 SeO 3 /kg of diet). Treatments were started from the 14th day of pregnancy until postnatal day 14. In the MMI-exposed group, the body weight of 14-day-old pups diminished compared to controls; besides, a hypertrophy of the thyroid glands was observed. Co-administration of Se through the diet restored these parameters to near normal values. In the MMI-treated group, thyroid iodine contents and plasma thyroid hormone levels significantly decreased, while plasma TSH levels increased in pups and their mothers. These biochemical modifications corresponded histologically to closed follicles, increased vascularity and a reduction in colloid volume. Co-treatment with Se ameliorated these parameters. We concluded that the supplementation of Se in diet had beneficial effects on hypothyroidism during a critical period of life.

Effects of arsenic on maternal and fetal health

Arsenic, which is commonly found in drinking water, is a potent toxicant, but little is known about its effects on maternal health. Arsenic's modes of action include enzyme inhibition and oxidative stress as well as immune, endocrine, and epigenetic effects. A couple of studies reported increased blood pressure and anemia during pregnancy. Susceptibility to arsenic is dependent on the biomethylation, which occurs via one-carbon metabolism. Methylarsonic acid and dimethylarsinic acid are main metabolites in urine, and elevated methylarsonic acid is considered a general risk factor. Arsenic easily passes the placenta, and a few human studies indicate a moderately increased risk of impaired fetal growth and increased fetal and infant mortality. The fetus and infant are probably partly protected by the increased methylation of arsenic during pregnancy and lactation; the infant is also protected by low arsenic excretion in breast milk. Early-life exposure may induce changes that will become apparent much later in life.

Levels of As, Cd, Pb, Cu, Se and Zn in bovine kidneys and livers in Jamaica

Paired liver and kidney samples from 100 free-range cattle in different parts of Jamaica were analyzed for essential and non-essential trace elements. We found significant enrichment of elements in the kidney (K) compared to the liver (L) with the K/L concentration ratios being 5.2 for Cd, 4.1 for Pb, 3.5 for Se and 2.1 for As, but the Cu contents of the kidney were significantly higher with the K/L ratio of 0.45. A large number of kidney and liver samples showed Cu concentrations in the ranges that were associated with deficiency effects in mammals. About 15% of the hepatic samples had Zn concentrations below 20 microg/g, suggesting that there might be zinc insufficiency in some of the animals. Positive associations were found between the metals in both the kidney and liver. On average, the intake of Cd from consumption of both bovine kidney and liver from the island was estimated to be 5.2 microg/day, equivalent to about 7% of the provisional tolerable daily intake (PTDI), although anyone who habitually consumed the few kidneys or livers with >40 microg/g cadmium may be at some risk of exceeding the PTDI. The consumption of offal from local animals did not appear to be an important dietary source of any of the essential microelements.

Effects of selenium on the structure and function of recombinant human S-adenosyl-L-methionine dependent arsenic (+3 oxidation state) methyltransferase in E. coli

The effects of Se(IV) on the structure and function of recombinant human arsenic (+3 oxidation state) methyltransferase (AS3MT) purified from the cytoplasm of Escherichia coli were studied. The coding region of human AS3MT complementary DNA was amplified from total RNA extracted from HepG2 cell by reverse transcription PCR. Soluble and active human AS3MT was expressed in the E. coli with a Trx fusion tag under a lower induction temperature of 25 degrees C. Spectra (UV-vis, circular dichroism, and fluorescence) were first used to probe the interaction of Se(IV) and recombinant human AS3MT and the structure-function relationship of the enzyme. The recombinant human AS3MT had a secondary structure of 29.0% alpha-helix, 23.9% beta-pleated sheet, 17.9% beta-turn, and 29.2% random coil. When Se(IV) was added, the content of the alpha-helix did not change, but that of the beta-pleated sheet increased remarkably in the conformation of recombinant human AS3MT. Se(IV) inhibited the enzymatic methylation of inorganic As(III) in a concentration-dependent manner. The IC(50) value for Se(IV) was 2.38 muM. Double-reciprocal (1/V vs. 1/[inorganic As(III)]) plots showed Se(IV) to be a noncompetitive inhibitor of the methylation of inorganic As(III) by recombinant human AS3MT with a K (i) value of 2.61 muM. We hypothesized that Se(IV) interacts with the sulfhydryl group of cysteine(s) in the structural residues rather than the cysteines of the active site (Cys156 and Cys206). When Se(IV) was combined with cysteine(s) in the structural residues, the conformation of recombinant human AS3MT changed and the enzymatic activity decreased. Considering the quenching of tryptophan fluorescence, Cys72 and/or Cys226 are deduced to be primary targets for Se(IV).

Chronic low-level arsenic exposure causes gender-specific alterations in locomotor activity, dopaminergic systems, and thioredoxin expression in mice

Arsenic (As) is a toxic metalloid widely present in the environment. Human exposure to As has been associated with the development of skin and internal organ cancers and cardiovascular disorders, among other diseases. A few studies report decreases in intelligence quotient (IQ), and sensory and motor alterations after chronic As exposure in humans. On the other hand, studies of rodents exposed to high doses of As have found alterations in locomotor activity, brain neurochemistry, behavioral tasks, and oxidative stress. In the present study both male and female C57Bl/6J mice were exposed to environmentally relevant doses of As such as 0.05, 0.5, 5.0, or 50 mg As/L of drinking water for 4 months, and locomotor activity was assessed every month. Male mice presented hyperactivity in the group exposed to 0.5 mg As/L and hypoactivity in the group exposed to 50 mg As/L after 4 months of As exposure, whereas female mice exposed to 0.05, 0.5, and 5.0 mg As/L exhibited hyperactivity in every monthly test during As exposure. Furthermore, striatal and hypothalamic dopamine content was decreased only in female mice. Also decreases in tyrosine hydroxylase (TH) and cytosolic thioredoxin (Trx-1) mRNA expression in striatum and nucleus accumbens were observed in male and female mice, respectively. These results indicate that chronic As exposure leads to gender-dependent alterations in dopaminergic markers and spontaneous locomotor activity, and down-regulation of the antioxidant capacity of the brain.

Mechanism of selenium-induced inhibition of arsenic-enhanced UVR carcinogenesis in mice

BACKGROUND

Hairless mice that ingested arsenite in drinking water exhibited more than a 5-fold enhancement of ultraviolet radiation (UVR) carcinogenesis, whereas arsenite alone was carcinogenically inactive. Dietary organoselenium blocked the cancer enhancement effect of arsenic but not cancer induction by UVR.

OBJECTIVE

In this study we sought to explain selenium blockage of As enhancement by establishing the extent that As and Se tissue distributions are coincident or divergent.

METHODS

We used the X-ray fluorescence microprobe at the Advanced Photon Source (Argonne National Laboratory) to probe sections of skin and liver from hairless mice exposed to a) UVR, b) UVR + As, c) UVR + organoselenium, or d) UVR + As + organoselenium.

RESULTS

We found elevated levels of As in the skin epithelium (hair follicles and epidermis) and diffusely in the liver of mice exposed to UVR + As. Arsenic was entirely absent in skin in mice exposed to UVR + As + organoselenium, but a diffuse low level was seen in the liver. As and Se locations were consistently divergent in skin; As was more diffusely distributed, whereas Se was strongly associated with membranes. X-ray absorption near-edge spectra are consistent with the presence of the seleno-bis(S-glutathionyl) arsinium ion in the liver.

CONCLUSIONS

Supplemental Se was uncommonly effective at preventing even a trace of As in skin at 14 or 196 days of continuous exposure to As in drinking water. Traces of the seleno-bis(S-glutathionyl) arsinium ion in the liver suggested that formation of this compound was more likely to be responsible for the As-blocking effect of Se than was a mechanism based on antioxidation.

Methodological evaluation of method for dietary heavy metal intake

Exposure to environmental pollutants is an important problem of environmental toxicology. Heavy metals are regarded as toxic to living organisms because of their tendency to accumulate in selected tissues. Moreover, their presence is a causative agent of various sorts of disorders, including neuro-, nephro-, carcino-, terato-, and immunological. Exposures of human to environmental chemicals can occur simultaneously from various sources. One exposure route is ingestion of hazardous chemicals through contaminated food and beverages. Considering the above-mentioned menace, efforts should be focused on the estimation of dietary intakes of potential toxic agents by consumers. Dietary exposure assessment to nonnutrients is usually performed by combining 2 sets of data-the concentration of elemental contaminants in various food products and the consumption data of these food items. A variety of approaches exist for evaluating exposure to food chemicals, and the method chosen is influenced, among others, by the intended goal, the availability of data, cost, and time frame. Moreover, it is also important to note how accurate and detailed the information concerning toxic elements intake needs to be. There are a number of sources of food consumption data currently used in exposure assessments, which range from 1 d to habitual intake. Frequently, the heavy metals for which dietary exposure is of interest are present in trace and ultra-trace quantities. Hence, an analytical technique with sufficient sensitivity is required for the accurate determination of these chemicals in food samples. It is important to remember that the accuracy of quantitative analysis is strongly dependent on the sampling and preparation steps.

Health effects of early life exposure to arsenic

Inorganic arsenic is a potent human carcinogen and general toxicant. More than one hundred million people are exposed to elevated concentrations, mainly via drinking water, but also via industrial emissions. Arsenic is metabolized via methylation and reduction reactions, methylarsonic acid and dimethylarsinic acid being the main metabolites excreted in urine. Both inorganic arsenic and its methylated metabolites easily pass the placenta and both experimental and human studies have shown increased risk of impaired foetal growth and increased foetal loss. Recent studies indicate that prenatal arsenic exposure also increases the risk of adverse effects during early childhood. There is a growing body of evidence that the intrauterine or early childhood exposure to arsenic also induces changes that will become apparent much later in life. One epidemiological study indicated that exposure to arsenic in drinking water during early childhood or in utero was associated with an increased mortality in young adults from both malignant and non-malignant lung disease. Furthermore, a series of experimental animal studies provide strong support for late effects of arsenic, including various forms of cancer, following intrauterine arsenic exposure. The involved modes of action include epigenetic effects, mainly via DNA hypomethylation, endocrine effects (most classes of steroid hormones), immune suppression, neurotoxicity, and interaction with enzymes critical for foetal development and programming.

Arsenic as an endocrine disruptor: arsenic disrupts retinoic acid receptor-and thyroid hormone receptor-mediated gene regulation and thyroid hormone-mediated amphibian tail metamorphosis

BACKGROUND

Chronic exposure to excess arsenic in drinking water has been strongly associated with increased risks of multiple cancers, diabetes, heart disease, and reproductive and developmental problems in humans. We previously demonstrated that As, a potent endocrine disruptor at low, environmentally relevant levels, alters steroid signaling at the level of receptor-mediated gene regulation for all five steroid receptors.

OBJECTIVES

The goal of this study was to determine whether As can also disrupt gene regulation via the retinoic acid (RA) receptor (RAR) and/or the thyroid hormone (TH) receptor (TR) and whether these effects are similar to previously observed effects on steroid regulation.

METHODS AND RESULTS

Human embryonic NT2 or rat pituitary GH3 cells were treated with 0.01-5 microM sodium arsenite for 24 hr, with or without RA or TH, respectively, to examine effects of As on receptor-mediated gene transcription. At low, noncytotoxic doses, As significantly altered RAR-dependent gene transcription of a transfected RAR response element-luciferase construct and the native RA-inducible cytochrome P450 CYP26A gene in NT2 cells. Likewise, low-dose As significantly altered expression of a transfected TR response element-luciferase construct and the endogenous TR-regulated type I deiodinase (DIO1) gene in a similar manner in GH3 cells. An amphibian ex vivo tail metamorphosis assay was used to examine whether endocrine disruption by low-dose As could have specific pathophysiologic consequences, because tail metamorphosis is tightly controlled by TH through TR. TH-dependent tail shrinkage was inhibited in a dose-dependent manner by 0.1- 4.0 microM As.

CONCLUSIONS

As had similar effects on RAR- and TR-mediated gene regulation as those previously observed for the steroid receptors, suggesting a common mechanism or action. Arsenic also profoundly affected a TR-dependent developmental process in a model animal system at very low concentrations. Because RAR and TH are critical for both normal human development and adult function and their dysregulation is associated with many disease processes, disruption of these hormone receptor-dependent processes by As is also potentially relevant to human developmental problems and disease risk.

Interactions between arsenic-induced toxicity and nutrition in early life

Exposure to arsenic through drinking water is a major public health problem affecting most countries, although the situation is particularly severe in low-income nations. The health consequences of chronic arsenic exposure include increased risk for various forms of cancer and numerous noncancer effects, including diabetes, skin diseases, chronic cough, and toxic effects on liver, kidney, cardiovascular system, and peripheral and central nervous systems. In recent years increasing reports of effects on fetal and child development have appeared. There seems to be a wide variation in susceptibility to arsenic toxicity, which is likely to be related to factors such as variation in arsenic metabolism, nutrition, host-related defense mechanisms, and genetic predisposition. The main mechanisms of arsenic-nutrition interactions include arsenic-induced oxidative stress, which requires nutrient-dependent defense systems, and arsenic metabolism (methylation) via 1-carbon metabolism, which requires methyl groups, folic acid, vitamin B-12, and betaine for the remethylation of homocysteine to methionine. An efficient first methylation step in combination with a slow second methylation step seems to be most critical from a toxicological point of view. A third mode of arsenic-nutrition interaction involves epigenetic effects and fetal programming via DNA methylation.

Protective effects of selenium on mercury-induced DNA damage in mussel haemocytes

Little is known of the antioxidant role of selenium (Se) in aquatic invertebrates. We investigated the effects of Se on mercury-induced DNA damage in haemocytes from Mytilus edulis using alkaline single cell gel electrophoresis, that is, the Comet assay. The basal percentage tail DNA value for mussel haemocytes was 9.8+/-0.2% (mean+/-S.E.M., n=70). Exposing mussels to Hg(2+) (nominal concentration 20 microgL(-1)) for three days led to an increase in tail DNA to 61.1+/-1.8% (n=10). With added Se (as selenite, nominal concentration 4 microgL(-1)), Hg-induced DNA damage was reduced to 39.5+/-3.1% (n=10). Se pre-exposure also provided some protection against Hg-induced DNA damage (% tail DNA=51.0+/-2.9%, n=10). Basal glutathione peroxidase (GPx) activity in cell-free haemolymph was 93.7+/-3.5 nmol min(-1)mg(-1) (mean+/-S.E.M., n=70). Increases in GPx activity were seen when Se was added during and/or after exposure to Hg. For example, a 3-4-fold increase was seen after three days exposure to Hg in the presence of added Se. Interestingly GPx activity doubled after three days in the presence of added Se alone, but was unchanged after exposure to HgCl(2) alone. These results suggest that the availability of Se in the natural environment could affect the antioxidant status of mussels, and consequently could affect levels of DNA damage.

Gender differences in the disposition and toxicity of metals

There is increasing evidence that health effects of toxic metals differ in prevalence or are manifested differently in men and women. However, the database is small. The present work aims at evaluating gender differences in the health effects of cadmium, nickel, lead, mercury and arsenic. There is a markedly higher prevalence of nickel-induced allergy and hand eczema in women compared to men, mainly due to differences in exposure. Cadmium retention is generally higher in women than in men, and the severe cadmium-induced Itai-itai disease was mainly a woman's disease. Gender differences in susceptibility at lower exposure are uncertain, but recent data indicate that cadmium has estrogenic effects and affect female offspring. Men generally have higher blood lead levels than women. Lead accumulates in bone and increased endogenous lead exposure has been demonstrated during periods of increased bone turnover, particularly in women in pregnancy and menopause. Lead and mercury, in the form of mercury vapor and methylmercury, are easily transferred from the pregnant women to the fetus. Recent data indicate that boys are more susceptible to neurotoxic effects of lead and methylmercury following exposure early in life, while experimental data suggest that females are more susceptible to immunotoxic effects of lead. Certain gender differences in the biotransformation of arsenic by methylation have been reported, and men seem to be more affected by arsenic-related skin effect than women. Experimental studies indicate major gender differences in arsenic-induced cancer. Obviously, research on gender-related differences in health effects caused by metals needs considerable more focus in the future.

Effects of low-level arsenic exposure on the developmental toxicity of anilofos in rats

In view of the increased use of anilofos for crop protection and ever increasing arsenic levels in drinking water in many countries, the coexistence of arsenic and anilofos in the environment is a reality and simultaneous exposure of humans and animals to these contaminants could be potentially hazardous. The aim of the present study was to examine whether coexposure to arsenic at the groundwater contamination level could alter the embryofetal toxicity of anilofos in rat model. Anilofos (100 mg kg(-1) day(-1)) and sodium arsenite (1 mg arsenic kg(-1) day(-1)) were administered by gavage either individually or in combination to the pregnant rats from day 6 to day 15 of gestation. Arsenic did not produce any significant effects either on maternal or fetal parameters at the given dose. Anilofos alone significantly decreased maternal weight gain, feed and water intakes, gravid uterine weights, number of live fetuses and fetal body weights and increased resorptions. There were increased incidences of gross, skeletal and visceral anomalies in the fetuses of anilofos-treated group. The main skeletal abnormality was increased intercostal space, while the visceral anomaly was an interventricular septal defect. Treatment with the combination of arsenic and anilofos significantly enhanced the fetal changes with much greater magnitude compared with the effects produced by anilofos alone. Anomalies such as midfacial cleft, exencephaly and anophthalmia were seen only in the fetuses of the combination group. The results show that anilofos interferes with embryofetal development and coexposure with arsenic at environmentally realistic concentrations produces additive or synergistic effects on the developmental toxicity of anilofos in rats.

Effects of perinatal exposure to low doses of cadmium or methylmercury on thyroid hormone metabolism in metallothionein-deficient mouse neonates

Perinatal exposure to cadmium (Cd) or methylmercury (MeHg) results in impaired neurodevelopment. Thyroid hormone is essential for normal brain development. However, the issue whether Cd or MeHg, especially at low doses, interrupts thyroid hormone action remains to be investigated. In the present study, effects of perinatal exposure to low levels of Cd or MeHg on thyroid hormone metabolism were examined using metallothionein I and II (MT-I/II) null or wild-type neonatal mice. Dams were exposed to 10 mg/L water of Cd or 5 mg/kg chow of MeHg from gestational day 0 to post-natal day 10 (PND 10). Sera, livers and brains were collected from neonates on PND 10. Iodothyronine deiodinase activities and serum thyroxine (T4) concentrations were measured. MeHg exposure failed to induce changes in serum T4 levels and liver type 1 deiodinase (D1) and brain type 2 deiodinase (D2) activities regardless of the MT genotype. However, exposure to MeHg resulted in a decrease in brain type 3 deiodinase (D3) activity in MT-I/II null and wild-type neonates. In contrast, exposure to Cd resulted in a decrease in serum T4 levels in MT-I/II null neonates. Consistently, brain D2 activity was increased in Cd-exposed MT-I/II null neonates. No significant changes in liver D1 and brain D3 activities were induced by Cd administration. Our study demonstrates that perinatal exposure to low doses of Cd or MeHg can induce changes in brain deiodinase activities in the neonates, suggesting that thyroid hormone metabolism in fetuses and neonates might be a potential target of Cd and MeHg.