Inhibitory effects of selenium on cadmium-induced cytotoxicity in PC12 cells via regulating oxidative stress and apoptosis

Association of dietary selenium intake and all-cause mortality of Parkinson's disease and its interaction with blood cadmium level: a retrospective cohort study

BACKGROUND

Parkinson's disease (PD) is a slowly progressive neurodegenerating disease that may eventually lead to disabling condition and pose a threat to the health of aging populations. This study aimed to explore the association of two potential risk factors, selenium and cadmium, with the prognosis of Parkinson's disease as well as their interaction effect.

METHODS

Data were obtained from the National Health and Nutrition Examination Survey (NHANES) 2005-2006 to 2015-2016 and National Death Index (NDI). Participants were classified as Parkinson's patients by self-reported anti-Parkinson medications usage. Cox regression models and restricted cubic spline models were applied to evaluate the association between PD mortality and selenium intake level as well as blood cadmium level. Subgroup analysis was also conducted to explore the interaction between them.

RESULTS

A total of 184 individuals were included. In full adjusted cox regression model (adjusted for age, gender, race, hypertension, pesticide exposure, smoking status and caffeine intake), compared with participants with low selenium intake, those with normal selenium intake level were significantly associated with less risk of death (95%CI: 0.18-0.76, P = 0.005) while no significant association was found between low selenium intake group and high selenium group (95%CI: 0.16-1.20, P = 0.112). Restricted cubic spline model indicated a nonlinear relationship between selenium intake and PD mortality (P for nonlinearity = 0.050). The association between PD mortality and blood cadmium level was not significant (95%CI: 0.19-5.57, P = 0.112). However, the interaction term of selenium intake and blood cadmium showed significance in the cox model (P for interaction = 0.048). Subgroup analysis showed that the significant protective effect of selenium intake existed in populations with high blood cadmium but not in populations with low blood cadmium.

CONCLUSION

Moderate increase of selenium intake had a protective effect on PD mortality especially in high blood cadmium populations.

Selenium protects against Pb-induced renal oxidative injury in weaning rats and human renal tubular epithelial cells through activating NRF2

BACKGROUND

Lead (Pb) poisoning posing a crucial health risk, especially among children, causing devastating damage not only to brain development, but also to kidney function. Thus, an urgent need persists to identify highly effective, safe, and low-toxicity drugs for the treatment of Pb poisoning. The present study focused on exploring the protective effects of Se on Pb-induced nephrotoxicity in weaning rats and human renal tubular epithelial cells, and investigated the possible mechanisms.

METHODS

Forty weaning rats were randomly divided into four groups in vivo: control, Pb-exposed, Pb+Se and Se. Serum creatinine (Cr), urea nitrogen (BUN) and hematoxylin and eosin (H&E) staining were performed to evaluate renal function. The activities of antioxidant enzymes in the kidney tissue were determined. In vitro experiments were performed using human renal tubular epithelial cells (HK-2 cells). The cytotoxicity of Pb and Se was detected by 3-(4,5-dimethylthiazol-2yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. Inverted fluorescence microscope was used to investigate cell morphological changes and the fluorescence intensity of reactive oxygen species (ROS). The oxidative stress parameters were measured by a multi-detection reader. Nuclear factor-erythroid-2-related factor (NRF2) signaling pathways were measured by Western blot and reverse transcription polymerase chain reaction (RT-PCR) in HK-2 cells.

RESULTS

We found that Se alleviated Pb-induced kidney injury by relieving oxidative stress and reducing the inflammatory index. Se significantly increased the activity of the antioxidant enzymes glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT), whereas it decreased the excessive release of malondialdehyde (MDA) in the kidneys of weaning rats and HK-2 cells. Additionally, Se enhanced the antioxidant defense systems via activating the NRF2 transcription factor, thereby promoting the to downstream expression of heme oxygenase 1. Furthermore, genes encoding glutamate-cysteine ligase synthetase catalytic (GCLC), glutamate-cysteine ligase synthetase modifier (GCLM) and NADPH quinone oxidoreductase 1 (NQO1), downstream targets of NRF2, formed a positive feedback loop with NRF2 during oxidative stress responses. The MTT assay results revealed a significant decrease in cell viability with Se treatment, and the cytoprotective role of Se was blocked upon knockdown of NRF2 by small interfering RNA (siRNA). MDA activity results also showed that NRF2 knockdown inhibited the NRF2-dependent transcriptional activity of Se.

CONCLUSIONS

Our findings demonstrate that Se ameliorated Pb-induced nephrotoxicity by reducing oxidative stress both in vivo and in vitro. The molecular mechanism underlying Se's action in Pb-induced kidney injury is related to the activation of the NRF2 transcription factor and the activity of antioxidant enzymes, ultimately suppressing ROS accumulation.

Unveiling the functional diversity of ionotropic glutamate receptors in the Pacific oyster (Crassostrea gigas) by systematic studies

Ionotropic glutamate receptors (iGluRs), pivotal in mediating excitatory neurosignals within the central nervous system, are instrumental in environmental stress responses. In this investigation, 12 iGluRs identified in the Pacific oyster are herein designated as CgiGluRs, and further categorized into three distinct subfamilies based on their transmembrane domains. Cross-species evolutionary analysis unveiled a high degree of conservation in the sequence and structural attributes of these CgiGluRs. These receptors are ubiquitously distributed across various tissues, with pronounced expression in the oyster's mantle, labial palps, and gills, underlining their integral role in the oyster's environmental sensing mechanisms. Post the D-shaped larval stage, a marked upward trend in CgiGluRs expression was observed, denoting their critical involvement in oyster development beyond this phase. Exposure to five metals-cadmium (Cd), copper (Cu), zinc (Zn), mercury (Hg), and lead (Pb)-elicited a significant upregulation of CgGRIA4 expression, indicating a robust response to metal stress. A KEGG enrichment analysis on 142 genes, exhibiting parallel expression trends with CgGRIA4 under metal stress, suggests that CgGRIA4 could augment excitatory signal transmission by activating glutamatergic and dopaminergic synapses, thereby contributing to the metal stress response in the oyster. This inquiry not only bolsters our comprehension of the iGluRs gene family in metal stress response but also paves the way for future exploration of its cardinal role in cellular signaling and environmental adaptability.

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Association of urinary exposure to multiple metal(loid)s with kidney function from a national cross-sectional study

BACKGROUND

Arsenic (As), cadmium (Cd) and copper (Cu) are hazardous for kidney function, while the effects of selenium (Se) and zinc (Zn) were unexplored for the narrow safe range of intake. Interactions exists between these multiple metal/metalloid exposures, but few studies have investigated the effects.

METHODS

A cross-sectional survey was performed among 2210 adults across twelve provinces in China between 2020 and 2021. Urinary As, Cd, Cu, Se and Zn were measured using inductively coupled plasma-mass spectrometry (ICP-MS). Serum creatinine (Scr) and N-acetyl-beta-D glucosaminidases (urine NAG) were quantified in serum and urine, respectively. Kidney function was evaluated by the estimated glomerular filtration rate (eGFR). We employed logistic regression and Bayesian kernel machine regression (BKMR) models to explore the individual and joint effects of urinary metals/metalloids on the risk of impaired renal function (IRF) or chronic kidney disease (CKD), respectively.

RESULTS

Association was found between As (OR = 1.24, 95 % CI: 1.03, 1.48), Cd (OR = 1.65, 95 % CI: 1.35, 2.02), Cu (OR = 1.90, 95 % CI: 1.59, 2.29), Se (OR = 1.51, 95 % CI: 1.24, 1.85) and Zn (OR = 1.33, 95 % CI: 1.09, 1.64) and the risk of CKD. Moreover, we observed association between As (OR = 1.18, 95 % CI: 1.07, 1.29), Cu (OR = 1.14, 95 % CI: 1.04, 1.25), Se (OR = 1.15, 95 % CI: 1.06, 1.26) and Zn (OR = 1.12, 95 % CI: 1.02, 1.22) and the risk of IRF. Additionally, it was found that Se exposure may strength the association of urinary As, Cd and Cu with IRF. Furthermore, it is worth noting that Se and Cu contributed greatest to the inverse association in IRF and CKD, respectively.

CONCLUSION

Our findings suggested that metal/metalloid mixtures were associated with kidney dysfunction, Se and Cu were inverse factors. Additionally, interactions between them may affect the association. Further studies are needed to assess the potential risks for metal/metalloid exposures.

Minocycline Protects PC12 Cells Against Cadmium-Induced Neurotoxicity by Modulating Apoptosis

Cadmium (Cd) is a well-known heavy metal and a neurotoxic agent. Minocycline (Mino) is an anti-microbial agent with a lipophilic structure that crosses the blood-brain barrier and enters the cerebral tissue. In recent studies, Mino has been introduced as an antioxidant and anti-apoptotic chemical compound, and therefore, it was examined as a protective candidate against Cd-induced neurotoxicity. In this study, PC12 cells were exposed to Cd alone, or after being pre-treated with Mino. Initially, the cell viability and oxidative stress were analyzed using the MTT assay and fluorimetry, respectively. Then, Cd-induced apoptosis and Mino anti-apoptotic effect were evaluated in both intrinsic and extrinsic pathways using western blot analysis. Exposing PC12 cells to Cd for 24 h decreased cell viability and increased production of reactive oxygen species in comparison with the control group. Cd (35 μM) also elevated the level of caspase-8, Bax/Bcl-2, and caspase-3 proteins in the cells. Mino pre-treatment for 2 h (100 nM) increased the number of viable cells and decreased the production of reactive oxygen species, and the level of all apoptotic markers in comparison to Cd-treated cells. Considering all the evidence, it appears that Mino holds promising antioxidant and anti-apoptotic activity and can protect cells against Cd-induced oxidative stress and prevent apoptotic cell death.

Co-exposure to toxic metals and phthalates in pregnant women and their children's mental health problems aged four years - Taiwan Maternal and Infant Cohort Study (TMICS)

BACKGROUND

Childhood and adolescent mental health problems may increase the global burden of disease. Neurotoxic metals are associated with inflammation and cytotoxicity in the brain. In addition, prenatal phthalate ester (PAE) exposure is associated with cognitive function deficits. However, the effect of co-exposure to toxic metals, PAEs, and their association with child behavior is less well studied. Hence, we aimed to investigate prenatal co-exposure to the metals and PAEs and the consequent behavioral outcomes in early childhood.

METHODS

We followed pregnant women and their newborns from the Taiwan Maternal and Infant Cohort Study between 2015 and 2017, with a focus on women from the central, southern, and eastern areas of Taiwan. We quantified maternal urinary concentrations of metals and metabolites of PAEs as surrogates of prenatal exposure. We recorded the Child Behavior Checklist scores according to caregiver reports at 4 years of age, and identified Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5)-oriented problems.

RESULTS

Ultimately, 408 children were included in the statistical analysis. Maternal urinary copper levels were significantly associated with depressive problems (odds ratio [OR] = 2.13) in children. Maternal urinary concentrations of mono-n-butyl phthalate (MnBP) and mono-isobutyl phthalate (MiBP) were also significantly associated with depressive symptoms (odds ratio [OR] = 1.51 and 1.53, respectively). Further analysis considering prenatal co-exposure to metals and PAEs showed that co-exposure to these materials was significantly associated with autism spectrum problems (OR = 3.11).

CONCLUSIONS

We observed that prenatal single exposure or co-exposure to metals and PAEs may play a role in some DSM-5-oriented problems in children at 4 years of age. Reduction of exposure to toxic metals and PAEs in pregnancy is suggested to prevent increased mental health problems in children.

Selenite Ameliorates Cadmium-induced Cytotoxicity Through Downregulation of ROS Levels and Upregulation of Selenoprotein Thioredoxin Reductase 1 in SH-SY5Y Cells

Cadmium (Cd) as a ubiquitous toxic heavy metal in the environment, causes severe hazards to human health, such as cellular stress and organ injury. Selenium (Se) was reported to reduce Cd toxicity and the mechanisms have been intensively studied so far. However, it is not yet crystal clear whether the protective effect of Se against Cd-induced cytotoxicity is related to selenoproteins in nerve cells or not. In this study, we found that Cd inhibited selenoprotein thioredoxin reductase 1 (TrxR1; TXNRD1) and decreased the expression level of TrxR1, resulting in cellular oxidative stress, and Se supplements ameliorated Cd-induced cytotoxicity in SH-SY5Y cells. Mechanistically, the detoxification of Se against Cd is attributed to the increase of the cellular TrxR activity and upregulated TrxR1 protein level, culminating in strengthened antioxidant capacity. Results showed that Se supplements attenuated the ROS production and apoptosis in SH-SY5Y cells, and significantly mitigated Cd-induced SH-SY5Y cell death. This study may be a valuable reference for shedding light on the mechanism of Cd-induced cytotoxicity and the role of TrxR1 in Se-mitigated cytotoxicity of Cd in neuroblast cells, which may be helpful for understanding the therapeutic potential of Cd and Se in treating or preventing neurodegenerative diseases, like Alzheimer's disease (AD) and Parkinson's disease (PD).

Protective effect of selenium on vincristine-induced peripheral neuropathy in PC12 cell line

Vincristine-induced peripheral neuropathy (VIPN) is the main side effect and major reason for neuropathic pain in cancer survivors treated with vincristine. Vincristine, a chemotherapeutic antimitotic drug, is used frequently in combination chemotherapy. The primary purpose of the current study was to assess the protective effect of sodium selenite (SSe) on VIPN in vitro. Cytotoxicity effects of vincristine were evaluated using PC12 cells as a neuronal model. The cell culture studies were conducted in three groups based on the various treatments, including vincristine, SSe, and co-exposure to both compositions. Cell viability and cell cycle analyses were performed using MTT assay and flow cytometry, respectively. The level of mRNA expression of Bax and Bcl-2 was determined using qRT-PCR. According to the results, vincristine decreased the survival rate of PC12 cells. After 24 and 48 h exposure to different concentrations of vincristine (0.1-20 μΜ), the survival rate of PC12 cells decreased as compared to the control group. The results showed that treatment with 5 μΜ of vincristine resulted in apoptosis of PC12 cells. Interestingly,co-incubation of these cells with SSe significantly reduced the cell damage induced by vincristine. Furthermore, vincristine induced the inhibition of the G2 phase in PC 12 cells, and using SSe in combination with vincristine eliminated the inhibition of the cell cycle in the G2 phase. Briefly, our in vitro preliminary study showed that SSe might protect PC12 cells from vincristine-induced peripheral neuropathy during chemotherapy.

Nanoparticle Effects on Stress Response Pathways and Nanoparticle-Protein Interactions

Nanoparticles (NPs) are increasingly used in a wide variety of applications and products; however, NPs may affect stress response pathways and interact with proteins in biological systems. This review article will provide an overview of the beneficial and detrimental effects of NPs on stress response pathways with a focus on NP-protein interactions. Depending upon the particular NP, experimental model system, and dose and exposure conditions, the introduction of NPs may have either positive or negative effects. Cellular processes such as the development of oxidative stress, the initiation of the inflammatory response, mitochondrial function, detoxification, and alterations to signaling pathways are all affected by the introduction of NPs. In terms of tissue-specific effects, the local microenvironment can have a profound effect on whether an NP is beneficial or harmful to cells. Interactions of NPs with metal-binding proteins (zinc, copper, iron and calcium) affect both their structure and function. This review will provide insights into the current knowledge of protein-based nanotoxicology and closely examines the targets of specific NPs.

Protective Role of the Essential Trace Elements in the Obviation of Cadmium Toxicity: Glimpses of Mechanisms

Cadmium (Cd) is toxic non-essential heavy metal that precipitates adverse health effects in humans and animals. Chelation therapy, the typical treatment for cadmium toxicity, has certain safety and efficacy issues to treat long term cadmium toxicity, in particular. Recent studies have shown that essential trace elements can play important roles in obviating experimental Cd toxicity. This study organizes and reviews the prototypical evidences of the protective effects of essential trace elements against Cd toxicity in animals and attempts to point out the underlying mechanisms. Zinc, selenium, iron, and combinations thereof are reported to be active. The major mechanisms elucidated inter alia are-induction of metallothionein (MT) synthesis and Cd-MT binding (for zinc), modulation of oxidative stress and apoptosis, interference in cadmium absorption and accumulation from body-thereby maintenance of essential metal homeostasis and cytoprotection. Based on the findings, essential trace elements can be recommended for the susceptible population. The application of these trace elements appears beneficial for both the prevention and remediation of long-term Cd toxicity operative via multiple mechanisms with no or minimal adverse effects as compared to the conventional chelation therapy.

AMPK/PPAR-γ/NF-κB axis participates in ROS-mediated apoptosis and autophagy caused by cadmium in pig liver

The experiment was conducted to investigate the effects of Cadmium (Cd) on growth performance, blood biochemical parameters, oxidative stress, hepatocyte apoptosis and autophagy of weaned piglets. A total of 12 healthy weaned piglets were randomly assigned to the control and the Cd group, which were fed with a basal diet and the basal diet supplemented with 15 ± 0.242 mg/kg CdCl₂ for 30 d, respectively. Our results demonstrated that Cd significantly decreased final body weight, average daily feed intake (ADFI), average daily gain (ADG) and increased feed-to-gain (F/G) ratio (P < 0.05). For blood biochemical parameters, Cd treatment significantly decreased the red blood cell (RBC), hemoglobin (HGB), hematocrit (HCT), total protein, albumin, copper content and iron content (P < 0.05). In addition, liver injury was observed in the Cd-exposed group. Our results also demonstrated that Cd exposure contributed to the production of ROS, activated the AMPK/PPAR-γ/NF-κB pathway (increasing the expressions of P-AMPK/AMPK, NF-κB, I-κB-β, COX-2, and iNOS, decreasing the expressions of PPAR-γ and I-κB-α), finally induced autophagy (increasing the expressions of Beclin-1, the ratio of LC3-II/LC3-I and p62), and apoptosis (increasing the expressions of Bax, Bak, Caspase-9, and Caspase-3, decreasing the expression of Bcl-2). Overall, these findings revealed the vital role of AMPK/PPAR-γ/NF-κB pathway in Cd-induced liver apoptosis and autophagy, which provided deeper insights into a better understanding of Cd-induced hepatotoxicity.

Protective effects of selenium yeast against cadmium-induced necroptosis through miR-26a-5p/PTEN/PI3K/AKT signaling pathway in chicken kidney

Cadmium (Cd) is a ubiquitous environmental pollutant of increasing worldwide concern to both humans and animals. Selenium yeast (Se-Y) is an organic selenium source that has been shown an advantage in antagonizing Cd-induced liver necroptosis in chicken. Herein, we described the discovery path of Se-Y antagonism in Cd-induced renal necroptosis in chicken through targeting miR-26a-5p/PTEN/PI3K/AKT signaling pathway. We set up four groups of chickens at random: control group (0.5 mg/kg Na₂SeO₃), Se-Y group (0.5 mg/kg Se-Y), Se-Y+Cd group (0.5 mg/kg Se-Y and 150 mg/kg CdCl₂) and Cd group (150 mg/kg CdCl₂ and 0.5 mg/kg Na₂SeO₃). Interestingly, we found Se-Y, but not Na₂SeO₃, significantly blocked Cd accumulation in the kidney and alleviated Cd-induced necroptosis through inhibiting the expression of RIP1, RIP3 and MLKL. Se-Y, activated miR-26a-5p expression, thereby down-regulated the expression of PTEN, resulting in the up-regulation of PI3K/AKT signaling pathway and the inhibition of oxidative stress in both Se-Y and Cd treated chickens. Besides that, Se-Y could also specifically reduce the expression levels of heat shock protein 60 (HSP60), HSP70 and HSP90 in Se-Y and Cd co-treated chickens. Taken together, our results showed that Se-Y has an added value to antagonize Cd-induced necroptosis in chicken kidney by regulating the miR-26a-5p/PTEN/PI3K/AKT signaling pathway and HSPs, indicating that Se-Y could serve as an effective antagonist on Cd-induced renal necroptosis in chickens.

Trace elements in children with autism spectrum disorder: A meta-analysis based on case-control studies

Autism spectrum disorder (ASD) is a common childhood neurodevelopmental disorder that may be related to trace elements. However, reports on the relationship between them are still inconsistent. In this article, we conducted a meta-analysis on this issue. We searched the PubMed, EMBASE, and Cochrane databases as of November 15, 2019. A random-effects model was used, and subgroups of studies were analyzed using samples of different measurements. Twenty-two original articles were identified (18 trace elements, including a total of 1014 children with ASD and 999 healthy controls). In autistic children, the overall levels of barium (Ba), mercury (Hg), lithium (Li), and lead (Pb) were higher. There were significant differences in the levels of copper (Cu) in the hair and serum between autistic children and the control group. The levels of Hg, Li, Pb and selenium (Se) in the hair of autistic children were higher than those of healthy children, while the levels of zinc (Zn) in the blood were lower. Excessive exposure to toxic heavy metals and inadequate intake of essential metal elements may be associated with ASD. Preventing excessive exposure to toxic metals and correcting poor dietary behaviors may be beneficial for the prevention and treatment of the disease.

Mechanisms of Metal-Induced Mitochondrial Dysfunction in Neurological Disorders

Metals are actively involved in multiple catalytic physiological activities. However, metal overload may result in neurotoxicity as it increases formation of reactive oxygen species (ROS) and elevates oxidative stress in the nervous system. Mitochondria are a key target of metal-induced toxicity, given their role in energy production. As the brain consumes a large amount of energy, mitochondrial dysfunction and the subsequent decrease in levels of ATP may significantly disrupt brain function, resulting in neuronal cell death and ensuing neurological disorders. Here, we address contemporary studies on metal-induced mitochondrial dysfunction and its impact on the nervous system.

Amelioration of Metal-Induced Cellular Stress by α-Lipoic Acid and Dihydrolipoic Acid through Antioxidative Effects in PC12 Cells and Caco-2 Cells

α-Lipoic acid (ALA) and its reduced form dihydrolipoic acid (DHLA) are endogenous dithiol compounds with significant antioxidant properties, both of which have the potential to detoxify cells. In this study, ALA (250 μM) and DHLA (50 μM) were applied to reduce metal (As, Cd, and Pb)-induced toxicity in PC12 and Caco-2 cells as simultaneous exposure. Both significantly decreased Cd (5 μM)-, As (5 μM)-, and Pb (5 μM)-induced cell death. Subsequently, both ALA and DHLA restored cell membrane integrity and intracellular glutathione (GSH) levels, which were affected by metal-induced toxicity. In addition, DHLA protected PC12 cells from metal-induced DNA damage upon co-exposure to metals. Furthermore, ALA and DHLA upregulated the expression of survival-related proteins mTOR (mammalian target of rapamycin), Akt (protein kinase B), and Nrf2 (nuclear factor erythroid 2-related factor 2) in PC12 cells, which were previously downregulated by metal exposure. In contrast, in Caco-2 cells, upon co-exposure to metals and ALA, Nrf2 was upregulated and cleaved PARP-1 (poly (ADP-ribose) polymerase-1) was downregulated. These findings suggest that ALA and DHLA can counterbalance the toxic effects of metals. The protection of ALA or DHLA against metal toxicity may be largely due to an enhancement of antioxidant defense along with reduced glutathione level, which ultimately reduces the cellular oxidative stress.

Zinc-pretreatment triggers glutathione and Nrf2-mediated protection against inorganic mercury-induced cytotoxicity and intrinsic apoptosis in PC12 cells

Mercury (Hg) is a hazardous metal, poses environmental problems with severe human health effects; whereas zinc (Zn) is an essential micronutrient with antioxidant properties. The purpose of this research was to investigate the effect of Zn on inorganic Hg-induced cytotoxicity in the PC12 cells. The cells were treated with HgCl₂ (5 μM) for 48 h with/without 1 h prior ZnCl₂-treatment (100 μM) and deliberated for further analysis. After 48 h of incubation with only Hg²⁺, the cell showed reduced cell viability, compromised cell membrane, DNA degradation, depleted glutathione level, ROS generation and drastically increased apoptosis. Subsequently, Hg²⁺-treated cells demonstrated a significant downregulation of akt, mTOR, ERK1, Nrf2, HO1, Bcl-2, Bcl-xL, and upregulation of p53, Bax, cytochrome c and cleaved caspase 3, indicating intrinsic apoptosis induction. However, cells pretreated with Zn²⁺ before Hg²⁺-exposure showed a significant improvement in cell viability, cell membrane, DNA damage, glutathione level, ROS amount and apoptotic cells, with a significant upregulation in mTOR, akt, ERK1, Nrf2, HO1, Bcl-2 and Bcl-xL, and downregulation in p53, Bax, cytochrome c and cleaved caspase 3, indicating inhibition of apoptosis. The findings suggested that Zn²⁺-pretreatment not only improves glutathione content but also induces activation of Nrf2-HO1 pathway, which would tend to suppress Hg-cytotoxicity.

Effect of plasma selenium, red blood cell cadmium, total urinary arsenic levels, and eGFR on renal cell carcinoma

High total urinary arsenic concentrations and low estimated glomerular filtration rate (eGFR) increase the risk of renal cell carcinoma (RCC). This study aimed to determine whether other metals or metalloids can affect RCC. A total of 401 patients with RCC and 774 age- and sex-matched controls were recruited between November 2006 and December 2012 in Taiwan. Surgical resection or image-guided biopsy of renal tumors was performed to pathologically verify RCC. High-performance liquid chromatography linked to a hydride generator and atomic absorption spectrometer were used to measure the urinary arsenic species concentrations. Inductively coupled plasma mass spectrometry was used to determine plasma selenium and red blood cell cadmium and lead concentration. Plasma selenium levels were inversely related to RCC, whereas red blood cell cadmium levels were directly related to RCC. The odds ratio (OR) and 95% confidence interval (CI) were 0.14 (95% CI, 0.10-0.20) and 1.33 (95% CI, 1.03-1.72), respectively. A low plasma selenium level tended to interact with high total urinary arsenic levels or with high red blood cell cadmium concentration to increase the OR of RCC. In particular, low eGFR multiplicatively interacted with high red blood cell cadmium concentration to increase the OR of RCC (P_interaction=0.003). This study was the first to find a significant multiplicative interaction between eGFR and the red blood cell cadmium levels on the increased OR of RCC.

Selenium modulates inorganic mercury induced cytotoxicity and intrinsic apoptosis in PC12 cells

Mercury (Hg) in its all forms, including inorganic Hg (iHg) is an environmental contaminant due to toxicity and diseases in human. However, a little is known about the underlying mechanisms responsible for iHg toxicity. Selenium (Se) is an essential trace element, recognized as an antioxidant and protective agent against metal toxicities. The purpose of this research was to investigate ameliorations of Se counter to iHg-mediated toxicity in PC12 cells. Cytotoxic assays have been shown that iHg (5 μM) caused oxidative stress and intrinsic apoptosis via ROS generation, oxidizing glutathione, damaging DNA, degrading cell membrane integrity, down-regulating mTOR, p-mTOR, akt and ERK1, and up-regulating cleaved caspase 3 and cytochrome c release in PC12 cells 48 h after incubation. Co-treatment of Se (5 μM) inhibited intrinsic apoptosis and oxidative stress induced by iHg (5 μM) via inhibiting ROS formation, boosting GPx contents, increasing reduced glutathione, limiting DNA degradation, improving cell membrane integrity, up-regulating mTOR, p-mTOR, akt, ERK1 and caspase 3, and down-regulating cleaved caspase 3 and cytochrome c leakage in PC12 cells. In conclusion, these results recommended that excessive ROS generation acts a critical role in iHg-influenced oxidative stress and co-treatment of Se attenuates iHg-cytotoxicity through its antioxidant properties.

Maternal organic selenium supplementation during gestation improves the antioxidant capacity and reduces the inflammation level in the intestine of offspring through the NF-κB and ERK/Beclin-1 pathways

Selenium (Se) is postulated to protect against inflammation in the gut by attenuating oxidative stress. This study was conducted to investigate the effects of maternal 2-hydroxy-4-methylselenobutanoic acid (HMSeBA), an organic Se source, on the intestinal antioxidant capacity and inflammation level of the offspring and its possible mechanism. Forty-three sows were randomly assigned to receive one of the following three diets during gestation: control diet, sodium selenite (Na₂SeO₃) supplemented diet or HMSeBA supplemented diet, respectively. Samples were collected from the offspring at birth and weaning. The results showed that maternal HMSeBA supplementation significantly upregulated ileal GPX2 and SePP1 gene expression compared with the control and Na₂SeO₃ groups, while suppressed the expression of ileal IL-1β, IL-6 and NF-κB genes in newborn piglets compared with the control group. Moreover, maternal HMSeBA supplementation significantly increased the protein of ileal GPX2 and p-mTOR compared with the control and Na₂SeO₃ groups, but decreased the ileal p-NF-κB, Beclin-1 and p-ERK proteins in newborn piglets compared with the control group. The weaned piglets of the HMSeBA group had lower serum IL-1β and IL-6 than the piglets of the control group at 2 h of LPS challenge. In addition, after the LPS challenge, the HMSeBA group had a lower relative abundance of ileal p-NF-κB and Beclin-1 proteins than the control and Na₂SeO₃ groups. In conclusion, maternal HMSeBA supplementation during gestation can improve the offspring's intestinal antioxidant capacity and reduce the inflammation level by suppressing NF-κB and ERK/Beclin-1 signaling.

Analysis of Cadmium, Epigallocatechin Gallate, and Vitamin C Co-exposure on PC12 Cellular Mechanisms

Exposure to cadmium (Cd) is a risk factor to health impairments, wherein its cytotoxicity is attributed to induction of oxidative stress. Usage of anti-oxidants, however, can help lessen the damaging effects of Cd. The effect of Cd interaction with low concentration of dietary anti-oxidants, L-ascorbic acid and (-)-epigallocatechin gallate (EGCG), to PC12 cellular mechanisms was examined. The expected toxicity of Cd was observed on PC12 cells but addition of L-ascorbic acid ameliorated this effect. On the other hand, addition of EGCG was able to increase the cytotoxicity of Cd and to decrease the protective effect of L-ascorbic acid against Cd. Increase in LDH activity and decrease in free sulfhydryl levels indicated cell membrane damage and oxidative stress, respectively, in Cd- and EGCG-Cd-treated cells. Downregulation of pro-apoptotic proteins (pro-caspase-9, p53, and ERK1) was observed in cells treated with Cd alone and EGCG-Cd, while upregulation of autophagy-linked proteins (p62 and pBeclin1) was found on L-ascorbic acid-Cd combination treatments. These findings indicate that Cd causes cells to undergo an autophagy-enhanced cell death; low-concentration EGCG and L-ascorbic acid promotes cell survival individually; however, interaction of EGCG with Cd showed enhancement of Cd toxicity and antagonism of L-ascorbic acid efficiency.

Amelioration of butylated hydroxytoluene against inorganic mercury induced cytotoxicity and mitochondrial apoptosis in PC12 cells via antioxidant effects

Mercury (Hg) is a toxic metal, well-known for its dangerous health effects on human. Butylated hydroxytoluene (BHT) is a phenolic component generally consumed as a food additive as an antioxidant. However, BHT induced antioxidant properties against heavy metals-influenced toxicity are little studied. We hypothesized that BHT has a regulatory effect on Hg-induced cytotoxicity. The objective of this research was to assess the protecting effects of BHT against inorganic Hg (iHg)-toxicity in PC12 cells, where cells were treated with/without HgCl₂ (Hg²⁺) (5 μM) and BHT (100 μM) for 48 h and analyzed further. Cells treated by Hg caused a significant cell viability reduction, membrane damage, glutathione reduction, DNA fragmentation, ROS generation, with suppressed expressions of akt, mTOR, ERK1, Nrf2 and HO1; and elevated apoptotic expressions of p53, Bax, cytochrome c and active caspase 3. However, BHT and Hg²⁺ co-exposure showed prevention against Hg²⁺-toxicity by improving GSH content and inhibiting ROS generation and oxidative stress mediated damages. Additionally, BHT co-treatment inverted the pro-apoptotic proteins by augmenting pro-survival regulatory proteins akt, mTOR, ERK1, Nrf2 and HO1. These findings proved that BHT inhibits Hg²⁺-toxicity, hindering ROS generation and intrinsic apoptosis, via enhancing glutathione and antioxidants; and suggested BHT implications as therapeutic.

Selenium mitigates cadmium-induced crosstalk between autophagy and endoplasmic reticulum stress via regulating calcium homeostasis in avian leghorn male hepatoma (LMH) cells

Cadmium (Cd) is a toxic heavy metal and widespread in environment and food, which is adverse to human and animal health. Food intervention is a hot topic because it has no side effects. Selenium (Se) is an essential trace element, found in various fruits and vegetables. Many previous papers have described that Se showed ameliorative effects against Cd. However, the underlying mechanism of antagonistic effect of Se against Cd-induced cytotoxicity in avian leghorn male hepatoma (LMH) cells is unknown, the molecular mechanism of Se antagonistic effect on Cd-induced and calcium (Ca²⁺) homeostasis disorder and crosstalk of ER stress and autophagy remain to be explored. In order to confirm the antagonistic effect of Se on Cd-induced LMH cell toxicity, LMH cells were treated with CdCl₂ (2.5 μM) and Na₂SeO₃ (1.25 and 2.5 μM) for 24 h. In this study, Cd exposure induced cell death, disrupted intracellular Ca²⁺ homeostasis and Ca²⁺ homeostasis related regulatory factors, interfered with the cycle of cadherin (CNX)/calreticulin (CRT), and triggered ER stress and autophagy. Se intervention inhibited Cd-induced LDH release and crosstalk of ER stress and autophagy via regulating intracellular Ca²⁺ homeostasis. Moreover, Se mitigated Cd-induced Intracellular Ca²⁺ overload by Ca²⁺/calmodulin (CaM)/calmodulin kinase IV (CaMK-IV) signaling pathway. Herein, CNX/CRT cycle played a critical role for the protective effect of Se on Cd-induced hepatotoxicity. Based on these findings, we demonstrated that the application of Se is beneficial for prevention and alleviation of Cd toxicity.

Arsenic intoxication: general aspects and chelating agents

Arsenic (As) is widely used in the modern industry, especially in the production of pesticides, herbicides, wood preservatives, and semiconductors. The sources of As such as contaminated water, air, soil, but also food, can cause serious human diseases. The complex mechanism of As toxicity in the human body is associated with the generation of free radicals and the induction of oxidative damage in the cell. One effective strategy in reducing the toxic effects of As is the usage of chelating agents, which provide the formation of inert chelator–metal complexes with their further excretion from the body. This review discusses different aspects of the use of metal chelators, alone or in combination, in the treatment of As poisoning. Consideration is given to the therapeutic effect of thiol chelators such as meso-2,3-dimercaptosuccinic acid, sodium 2,3-dimercapto-1-propanesulfonate, 2,3-dimercaptopropanol, penicillamine, ethylenediaminetetraacetic acid, and other recent agents against As toxicity. The review also considers the possible role of flavonoids, trace elements, and herbal drugs as promising natural chelating and detoxifying agents.

Co-administration of Selenium with Inorganic Mercury Alters the Disposition of Mercuric Ions in Rats

Mercury (Hg) is a common environmental toxicant to which humans are exposed regularly through occupational and dietary means. Although selenium supplementation has been reported to prevent the toxic effects of Hg in animals, the mechanisms for this prevention are not well understood. The purpose of the current study was to determine the effects of selenium on the disposition and toxicity of Hg. Wistar rats were injected intravenously with a non-nephrotoxic dose (0.5 μmol kg^-1) or a nephrotoxic dose (2.5 μmol kg^-1) of HgCl₂ (containing radioactive Hg) with or without co-administration of sodium selenite (Na₂SeO₃). Twenty-four hours after exposure, rats were euthanized, and organs were harvested. Co-administration of SeO₃^2- with HgCl₂ reduced the renal burden of Hg and the urinary excretion of Hg while increasing the amount of Hg in blood and spleen. We propose that Hg reacts with reduced selenite in the blood to form large Hg-Se complexes that are unable to be filtered at the glomerulus. Consequently, these complexes remain in the blood and are able to accumulate in blood-rich organs. These complexes, which may have fewer toxic effects than other species of Hg, may be eliminated slowly over the course of weeks to months.

Regulatory effects of dihydrolipoic acid against inorganic mercury-mediated cytotoxicity and intrinsic apoptosis in PC12 cells

Mercury (Hg) is an extremely dangerous environmental contaminant, responsible for human diseases including neurological disorders. However, the mechanisms of inorganic Hg (iHg)-induced cell death and toxicity are little known. Dihydrolipoic acid (DHLA) is the reduced form of a naturally occurring compound lipoic acid, which act as a potent antioxidant through multiple mechanisms. So we hypothesized that DHLA has an inhibitory role on iHg-cytotoxicity. The purposes of this research were to investigate mechanism/s of cytotoxicity of iHg, as well as, the cyto-protection of DHLA against iHg induced toxicity using PC12 cells. Treatment of PC12 cells with HgCl₂ (Hg²⁺) (0-2.5 μM) for 48 h resulted in significant toxic effects, such as, cell viability loss, high level of lactate dehydrogenase (LDH) release, DNA damage, cellular glutathione (GSH) level decrease and increased Hg accumulation. In addition, protein level expressions of akt, p-akt, mTOR, GR, NFkB, ERK1, Nrf2 and HO-1 in cells were downregulated; and cleaved caspase 3 and cytochrome c release were upregulated after Hg²⁺ (2.5 μM) exposure and thus inducing apoptosis. Hg²⁺induced apoptosis was also confirmed by flow cytometry. However, pretreatment with DHLA (50 μM) for 3 h before Hg²⁺ (2.5 μM) exposure showed inhibition against iHg²⁺-induced cytotoxicity by reversing cell viability loss, LDH release, DNA damage, GSH decrease and inhibiting Hg accumulation. Moreover, DHLA pretreatment reversed the protein level expressions of akt, p-akt, mTOR, GR, NFkB, ERK1, Nrf2, HO-1, cleaved caspase 3 and cytochrome c. In conclusion, results showed that DHLA could attenuate Hg²⁺-induced cytotoxicity via limiting Hg accumulation, boosting up of antioxidant defense, and inhibition of apoptosis in cells.

Investigating the protective actions of D-pinitol against arsenic-induced toxicity in PC12 cells and the underlying mechanism

Arsenic is awfully toxic metalloid responsible for many human diseases all over the world. Contrastingly, D-pinitol is a naturally occurring bioactive dietary compound has antioxidant properties. The objective of this study is to elucidate the protective actions of D-pinitol on arsenic-induced cytotoxicity and explore its controlling role in biomolecular mechanisms in PC12 cells. Obtained results demonstrated that co-exposure of D-pinitol with arsenic increases cell viability, decreases DNA damage and protects PC12 cells from arsenic-induced cytotoxicity by increasing glutathione (GSH) level and glutathione reductase (GR). Protein expression of western blot analysis showed that co-exposure of D-pinitol and arsenic significantly inhibited arsenic-induced autophagy which further suppressed apoptosis through up-regulation of survival factors; mTOR, p-mTOR, Akt, p-Akt, NF-кB, Nrf2, ERK1, GR, Bcl-x and down-regulation of death factors; p53, Bax, cytochrome c, LC3, although arsenic regulated those factors negatively. These results of this study suggested that D-pinitol protects PC12 cells from arsenic-induced cytotoxicity.

Epidemiological study of kidney health in an area with high levels of soil cadmium and selenium: Does selenium protect against cadmium-induced kidney injury?

Chronic exposure to cadmium (Cd) can cause renal dysfunction. Studies of animals, cell cultures, and plants have found that selenium (Se) can effectively alleviate the hazard generated by Cd, but there has been little study of this in general human populations. This study recruited 313 subjects from China's Hubei Province, including 160 living in areas with high soil Cd and Se (exposure group) and 153 living in clean areas (control group). The levels of the following were detected: Cd and Se in blood (B-Cd and B-Se), urine (U-Cd and U-Se), and hair (H-Cd and H-Se); N-acetyl-β-D-glucosaminidase (U-NAG), β₂-microglobulin (U-β₂-MG), and albumin (U-ALB) in urine; and malondialdehyde (S-MDA), superoxide dismutase (S-SOD), and glutathione peroxidase (S-GSH-Px) in serum. In addition, the interactions between Cd and Se were assessed. The median levels of B-Cd, B-Se, U-Cd, U-Se, H-Cd, H-Se, S-MDA, and S-GSH-Px of exposure group (2.60 ng/mL, 238.90 ng/mL, 3.13 μg/g Cr, 45.43 μg/g Cr, 0.06 μg/g, 0.70 μg/g, 5.22 nmol/mL, and 308.89 U, respectively) were significantly higher than of controls (0.95 ng/mL, 130.50 ng/mL, 1.08 μg/g Cr, 30.51 μg/g Cr, 0.04 μg/g, 0.49 μg/g, 4.71 nmol/mL, and 267.54 U, respectively), but there were no significant differences in U-NAG, U-β₂-MG, U-ALB, or S-SOD between the two groups. U-NAG levels were significantly negatively associated with the interaction between Cd and Se (B: -0.511, 95% CI: -0.886, -0.136). Additionally, changes in the direction of the estimated regression coefficient in the low and high H-Se groups were observed for U-Cd and S-MDA (from 0.018 to -0.090), U-Cd and S-GSH-Px (from -0.039 to 0.101). This study found that populations living in areas with high levels of soil Cd and Se did not show greater Cd-induced renal tubular and glomerular injuries than the control population, which could attribute to the protective effects of Se. The protective effects may be related to the peculiar function of Se that Se can combine with free Cd to activate the antioxidant enzyme system.

GPx1-mediated DNMT1 expression is involved in the blocking effects of selenium on OTA-induced cytotoxicity and DNA damage

Ochratoxin A (OTA) is a potent nephrotoxin. Selenium (Se) is an essential micronutrient for humans and animals, and plays a key role in antioxidant defense. To date, little is known about the effect of Se on OTA-induced DNA damage. In this study, the protective effects of Se (from selenomethionine) against OTA-induced cytotoxicity and DNA damage were investigated by using PK15 cells as a model. The results showed that OTA at 4.0 μg/mL induced cytotoxicity and DNA damage. Se at 0.5, 1, 2 and 4 μM significantly blocked OTA-induced cytotoxicity and DNA damage. Furthermore, Se blocked the increases of DNMT1, DNMT3a and HDAC1 mRNA and protein expression, reversed the decreases of glutathione peroxidase 1 (GPx1) mRNA and protein expression, and promoted the increases of SOCS3 mRNA and protein expression induced by OTA. Overexpression of GPx1 by pcDNA3.1-GPx1 inhibited the OTA-induced DNMT1 expression, promoted OTA-induced SOCS3 expression, and prevented the OTA-induced cytotoxicity and DNA damage. In contrast, knock-down of GPx1 by using a GPx1-specific siRNA had the opposite effects. The results suggest that GPx1-mediated DNMT1 expression is involved in the blocking effects of selenium on OTA-induced cytotoxicity and DNA damage.

Selenium Treatment Enhanced Clearance of Salmonella in Chicken Macrophages (HD11)

As an important micronutrient, selenium (Se) plays many essential roles in immune response and protection against pathogens in humans and animals, but underlying mechanisms of Se-based control of salmonella growth within macrophages remain poorly elucidated. In this study, using RNA-seq analyses, we demonstrate that Se treatment (at an appropriate concentration) can modulate the global transcriptome of chicken macrophages HD11. The bioinformatic analyses (KEGG pathway analysis) revealed that the differentially expressed genes (DEGs) were mainly enriched in retinol and glutathione metabolism, revealing that Se may be associated with retinol and glutathione metabolism. Meanwhile, Se treatment increased the number of salmonella invading the HD11 cells, but reduced the number of salmonella within HD11 cells, suggesting that enhanced clearance of salmonella within HD11 cells was potentially modulated by Se treatment. Furthermore, RNA-seq analyses also revealed that nine genes including SIVA1, FAS, and HMOX1 were differentially expressed in HD11 cells infected with salmonella following Se treatment, and GO enrichment analysis showed that these DEGs were mainly enriched in an extrinsic apoptotic signaling pathway. In summary, these results indicate that Se treatment may not only affect retinol and glutathione metabolism in macrophages, but could also inhibit salmonella-induced macrophage apoptosis via an extrinsic apoptotic signaling pathway involving SIVA1.

Diethylnitrosamine aggravates cadmium-induced hepatorenal oxidative damage in prepubertal rats

The adverse health consequences of environmental, occupational, and dietary exposure to either diethylnitrosamine (DEN) or cadmium (Cd) have been widely investigated. However, because most environmental exposures to xenobiotics do not occur in isolation but in mixtures, the effects of simultaneous exposure to both DEN and Cd on hepatorenal function deserves investigation. The present study investigated the impact of 7 days oral co-exposure to 10 mg/kg body weight (b.w.) of DEN and 5 mg/kg b.w. of Cd on biomarkers of hepatic and renal functions, antioxidant defense systems, and oxidative stress indices in the liver and kidney of prepubertal rats. The results showed that the significant ( p < 0.05) increases in the levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, gamma glutamyl transferase, urea, and creatinine following separate administration of DEN and Cd to rats were further increased in the co-exposure group. Moreover, marked decreases in the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase as well as glutathione levels following individual administration of DEN and Cd to rats were exacerbated in the co-exposure group. Further, the marked increase in the lipid peroxidation level and the histopathological lesions in the liver and kidney of rats treated with DEN or Cd alone were intensified in the co-exposure group These findings indicate that co-exposure to DEN and Cd elicited more severe hepatic and renal oxidative damage in the rats, thus suggesting a greater risk to humans who are co-exposed to them.

Selenium cytotoxicity in Tetrahymena thermophila: New clues about its biological effects and cellular resistance mechanisms

Selenium is an essential micronutrient but at high concentrations can produce severe cytotoxicity and genomic damage. We have evaluated the cytotoxicity, ultrastructural and mitochondrial alterations of the two main selenium inorganic species; selenite and selenate, in the eukaryotic microorganism Tetrahymena thermophila. In this ciliate, selenite is more toxic than selenate. Their LC₅₀ values were calculated as 27.65 μM for Se(IV) and 56.88 mM for Se(VI). Significant levels of peroxides/hydroperoxides are induced under low-moderate selenite or selenate concentrations. Se(VI) exposures induce an immediate mitochondrial membrane depolarization. Selenium treated cells show an intense vacuolization and some of them present numerous discrete and small electrondense particles, probably selenium deposits. Mitochondrial fusion, an intense swelling in peripheral mitochondria and mitophagy are detected in selenium treated cells, especially in those exposed to Se (IV). qRT-PCR analysis of diverse genes, encoding relevant antioxidant enzymes or other proteins, like metallothioneins, involved in an environmental general stress response, have shown that they may be crucial against Se(IV) and/or Se (VI) cytotoxicity.

Selenium and zinc protections against metal-(loids)-induced toxicity and disease manifestations: A review

Metals are ubiquitous in the environment due to huge industrial applications in the form of different chemicals and from extensive mining activities. The frequent exposures to metals and metalloids are crucial for the human health. Trace metals are beneficial for health whereas non-essential metals are dangerous for the health and some are proven etiological factors for diseases including cancers and neurological disorders. The interactions of essential trace metals such as selenium (Se) and zinc (Zn) with non-essential metals viz. lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) in biological system are very critical and complex. A huge number of studies report the protective role of Se and Zn against metal toxicity, both in animal and cellular levels, and also explain the numerous mechanisms involved. However, it has been considered that a tiny dyshomeostasis in the metals/trace metals status in biological system could induce severe deleterious effects that can manifest to numerous diseases. Thus, in this particular review, we have demonstrated the critical protection mechanism/s of Se and Zn against Cd, Pb, As and Hg toxicity in a one by one manner to clarify the up-to-date findings and perspectives. Furthermore, biomolecular consequences are comprehensively presented in light of particular cellular/biomolecular events which are somehow linked to a subsequent disease. The analyzed reports support significant protection potential of Se and Zn, either alone or in combination with other agents, against each of the abovementioned non-essential metals. However, Se and Zn are still not being used as detoxifying agents due to some unexplained reasons. We hypothesized that Se could be a potential candidate for detoxifying As and Hg regardless of their chemical speciations, but requires intensive clinical trials. However, particularly Zn-Hg interaction warrants more investigations both in animal and cellular level.

Effects of soft electrophiles on selenium physiology

This review examines the effects of neurotoxic electrophiles on selenium (Se) metabolism. Selenium-dependent enzymes depend on the unique and elite functions of selenocysteine (Sec), the 21st proteinogenic amino acid, to perform their biochemical roles. Humans possess 25 selenoprotein genes, ~ half of which are enzymes (selenoenzymes) required for preventing, controlling, or reversing oxidative damage, while others participate in regulating calcium metabolism, thyroid hormone status, protein folding, cytoskeletal structure, Sec synthesis and Se transport. While selenoproteins are expressed in tissue dependent distributions and levels in all cells of all vertebrates, they are particularly important in brain development, health, and functions. As the most potent intracellular nucleophile, Sec is subject to binding by mercury (Hg) and other electron poor soft neurotoxic electrophiles. Epidemiological and environmental studies of the effects of exposures to methyl-Hg (CH₃Hg⁺), elemental Hg (Hg°), and/or other metallic/organic neurotoxic soft electrophiles need to consider the concomitant effects of all members of this class of toxicants in relation to the Se status of their study populations. The contributions of individual electrophiles' discrete and cooperative rates of Se sequestration need to be evaluated in relation to tissue Se reserves of the exposed populations to identify sensitive subgroups which may be at accentuated risk due to poor Se status. Additional study is required to examine possibilities of inherited, acquired, or degenerative neurological disorders of Se homeostasis that may influence vulnerability to soft electrophile exposures. Investigations of soft electrophile toxicity will be enhanced by considering the concomitant effects of combined exposures on tissue Se-availability in relation to pathological consequences during fetal development or in relation to etiologies of neurological disorders and neurodegenerative diseases. Since selenoenzymes are molecular "targets" of soft electrophiles, concomitant evaluation of aggregate exposures to these toxicants in relation to dietary Se intakes will assist regulatory agencies in their goals of improving and protecting public health.

Toxic metal(loid)-based pollutants and their possible role in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social interaction, verbal and non-verbal communication, and stereotypic behaviors. Many studies support a significant relationship between many different environmental factors in ASD etiology. These factors include increased daily exposure to various toxic metal-based environmental pollutants, which represent a cause for concern in public health. This article reviews the most relevant toxic metals, commonly found, environmental pollutants, i.e., lead (Pb), mercury (Hg), aluminum (Al), and the metalloid arsenic (As). Additionally, it discusses how pollutants can be a possible pathogenetic cause of ASD through various mechanisms including neuroinflammation in different regions of the brain, fundamentally occurring through elevation of the proinflammatory profile of cytokines and aberrant expression of nuclear factor kappa B (NF-κB). Due to the worldwide increase in toxic environmental pollution, studies on the role of pollutants in neurodevelopmental disorders, including direct effects on the developing brain and the subjects' genetic susceptibility and polymorphism, are of utmost importance to achieve the best therapeutic approach and preventive strategies.