Low-Dose Methylmercury-Induced Apoptosis and Mitochondrial DNA Mutation in Human Embryonic Neural Progenitor Cells

The role of DNA damage in neural stem cells ageing

Neural stem cells (NSCs) are pluripotent stem cells with the potential to differentiate into a variety of nerve cells. NSCs are susceptible to both intracellular and extracellular insults, thus causing DNA damage. Extracellular insults include ultraviolet, ionizing radiation, base analogs, modifiers, alkyl agents and others, while intracellular factors include Reactive oxygen species (ROS) radicals produced by mitochondria, mismatches that occur during DNA replication, deamination of bases, loss of bases, and more. When encountered with DNA damage, cells typically employ three coping strategies: DNA repair, damage tolerance, and apoptosis. NSCs, like many other stem cells, have the ability to divide, differentiate, and repair DNA damage to prevent mutations from being passed down to the next generation. However, when DNA damage accumulates over time, it will lead to a series of alterations in the metabolism of cells, which will cause cellular ageing. The ageing and exhaustion of neural stem cell will have serious effects on the body, such as neurodegenerative diseases. The purpose of this review is to examine the processes by which DNA damage leads to NSCs ageing and the mechanisms of DNA repair in NSCs.

The application of human-derived cell lines in neurotoxicity studies of environmental pollutants

As industrial and societal advancements progress, an increasing number of environmental pollutants linked to human existence have been substantiated to elicit neurotoxicity and developmental neural toxicity. For research in this field, human-derived neural cell lines have become excellent in vitro models. This study examines the utilization of immortalized cell lines, specifically the SH-SY5Y human neuroblastoma cell line, and neural cells derived from human pluripotent stem cells, in the investigation of neurotoxicity and developmental neural toxicity caused by environmental pollutants. The study also explores the culturing techniques employed for these cell lines and provides an overview of the standardized assays used to assess various biological endpoints. The environmental pollutants involved include a variety of organic compounds, heavy metals, and microplastics. The utilization of cell lines derived from human sources holds significant significance in elucidating the neurotoxic effects of environmental pollutants and the underlying mechanisms. Finally, we propose the possibility of improving the in vitro model of the human nervous system and the toxicity detection methods.

The Threat Posed by Environmental Contaminants on Neurodevelopment: What Can We Learn from Neural Stem Cells?

Exposure to chemicals may pose a greater risk to vulnerable groups, including pregnant women, fetuses, and children, that may lead to diseases linked to the toxicants' target organs. Among chemical contaminants, methylmercury (MeHg), present in aquatic food, is one of the most harmful to the developing nervous system depending on time and level of exposure. Moreover, certain man-made PFAS, such as PFOS and PFOA, used in commercial and industrial products including liquid repellants for paper, packaging, textile, leather, and carpets, are developmental neurotoxicants. There is vast knowledge about the detrimental neurotoxic effects induced by high levels of exposure to these chemicals. Less is known about the consequences that low-level exposures may have on neurodevelopment, although an increasing number of studies link neurotoxic chemical exposures to neurodevelopmental disorders. Still, the mechanisms of toxicity are not identified. Here we review in vitro mechanistic studies using neural stem cells (NSCs) from rodents and humans to dissect the cellular and molecular processes changed by exposure to environmentally relevant levels of MeHg or PFOS/PFOA. All studies show that even low concentrations dysregulate critical neurodevelopmental steps supporting the idea that neurotoxic chemicals may play a role in the onset of neurodevelopmental disorders.

Necrotic-like BV-2 microglial cell death due to methylmercury exposure

Methylmercury (MeHg) is a dangerous environmental contaminant with strong bioaccumulation in the food chain and neurotoxic properties. In the nervous system, MeHg may cause neurodevelopment impairment and potentially interfere with immune response, compromising proper control of neuroinflammation and aggravating neurodegeneration. Human populations are exposed to environmental contamination with MeHg, especially in areas with strong mining or industrial activity, raising public health concerns. Taking this into consideration, this work aims to clarify pathways leading to acute toxic effects caused by MeHg exposure in microglial cells. BV-2 mouse microglial cells were incubated with MeHg at different concentrations (0.01, 0.1, 1 and 10 µM) for 1 h prior to continuous Lipopolysaccharide (LPS, 0.5 μg/ml) exposure for 6 or 24 h. After cell exposure, reactive oxygen species (ROS), IL-6 and TNF-α cytokines production, inducible nitric oxide synthase (iNOS) expression, nitric oxide (NO) release, metabolic activity, propidium iodide (PI) uptake, caspase-3 and -9 activities and phagocytic activity were assessed. MeHg 10 µM decreased ROS formation, the production and secretion of pro-inflammatory cytokines IL-6, TNF-α, iNOS immunoreactivity, the release of NO in BV-2 cells. Furthermore, MeHg 10 µM decreased the metabolic activity of BV-2 and increased the number of PI-positive cells (necrotic-like cell death) when compared to the respective control group. Besides, MeHg did not interfere with caspase activity or the phagocytic profile of cells. The short-term effects of a high concentration of MeHg on BV-2 microglial cells lead to impaired production of several pro-inflammatory mediators, as well as a higher microglial cell death via necrosis, compromising their neuroinflammatory response. Clarifying the mechanisms underlying MeHg-induced neurotoxicity and neurodegeneration in brain cells is relevant to better understand acute and long-term chronic neuroinflammatory responses following MeHg exposure.

Oxygen as an important factor modulating in vitro MeHgCl toxicity associated with mitochondrial genes in hiPSCs

Mitochondria are energy factories of cells and important targets for methylmercury chloride (MgHgCl). Methylmercury (MeHg) is a well-known environmental toxicant that bioaccumulates in fish and shellfish. It readily crosses the placental barrier, making it a threat to correct fetal development. Despite being comprehensively investigated for years, this compound has not been assessed for its in vitro mitochondrial toxicity under different oxygen conditions. In this study, human induced pluripotent stem cells (hiPSCs) were used to evaluate the dependence of the expression of genes associated with pluripotency and mitochondria on atmospheric (21% O₂) and low (5% O₂) oxygen concentrations upon MeHgCl treatment. We showed that the toxicity of MeHgCl was strongly related to an increased mtDNA copy number and downregulation of the expression of an mtDNA replication and damage repair-associated gene POLG1 (Mitochondrial Polymerase Gamma Catalytic Subunit) in both tested oxygen conditions. In addition, the viability and mitochondrial membrane potential of hiPSCs were significantly lowered by MeHgCl regardless of the oxygen concentration. However, reactive oxygen species accumulation significantly increased only under atmospheric oxygen conditions; what was associated with increased expression of TFAM (Transcription Factor A, Mitochondrial) and NRF1 (Nuclear Respiratory Factor 1) and downregulation of PARK2 (Parkin RBR E3 Ubiquitin Protein Ligase). Taken together, our results demonstrated that MeHgCl could induce in vitro toxicity in hiPSCs through altering mitochondria-associated genes in an oxygen level-dependent manner. Thus, our work suggests that oxygen should be considered a factor was modulating the in vitro toxicity of environmental pollutants. Typical atmospheric conditions of in vitro culture significantly lower the predictive value of studies of such toxicity.

Advances on the Influence of Methylmercury Exposure during Neurodevelopment

Mercury (Hg) is a toxic heavy-metal element, which can be enriched in fauna and flora and transformed into methylmercury (MeHg). MeHg is a widely distributed environmental pollutant that may be harmful to fish-eating populations through enrichment of aquatic food chains. The central nervous system is a primary target of MeHg. Embryos and infants are more sensitive to MeHg, and exposure to MeHg during gestational feeding can significantly impair the homeostasis of offspring, leading to long-term neurodevelopmental defects. At present, MeHg-induced neurodevelopmental toxicity has become a hotspot in the field of neurotoxicology, but its mechanisms are not fully understood. Some evidence point to oxidative damage, excitotoxicity, calcium ion imbalance, mitochondrial dysfunction, epigenetic changes, and other molecular mechanisms that play important roles in MeHg-induced neurodevelopmental toxicity. In this review, advances in the study of neurodevelopmental toxicity of MeHg exposure during pregnancy and the molecular mechanisms of related pathways are summarized, in order to provide more scientific basis for the study of neurodevelopmental toxicity of MeHg.

Parkinson's Disease and the Metal-Microbiome-Gut-Brain Axis: A Systems Toxicology Approach

Parkinson's Disease (PD) is a neurodegenerative disease, leading to motor and non-motor complications. Autonomic alterations, including gastrointestinal symptoms, precede motor defects and act as early warning signs. Chronic exposure to dietary, environmental heavy metals impacts the gastrointestinal system and host-associated microbiome, eventually affecting the central nervous system. The correlation between dysbiosis and PD suggests a functional and bidirectional communication between the gut and the brain. The bioaccumulation of metals promotes stress mechanisms by increasing reactive oxygen species, likely altering the bidirectional gut-brain link. To better understand the differing molecular mechanisms underlying PD, integrative modeling approaches are necessary to connect multifactorial perturbations in this heterogeneous disorder. By exploring the effects of gut microbiota modulation on dietary heavy metal exposure in relation to PD onset, the modification of the host-associated microbiome to mitigate neurological stress may be a future treatment option against neurodegeneration through bioremediation. The progressive movement towards a systems toxicology framework for precision medicine can uncover molecular mechanisms underlying PD onset such as metal regulation and microbial community interactions by developing predictive models to better understand PD etiology to identify options for novel treatments and beyond. Several methodologies recently addressed the complexity of this interaction from different perspectives; however, to date, a comprehensive review of these approaches is still lacking. Therefore, our main aim through this manuscript is to fill this gap in the scientific literature by reviewing recently published papers to address the surrounding questions regarding the underlying molecular mechanisms between metals, microbiota, and the gut-brain-axis, as well as the regulation of this system to prevent neurodegeneration.

The Novel LncRNA AK035396 Drives Cardiomyocyte Apoptosis Through Mterf1 in Myocardial Ischemia/Reperfusion Injury

Background: Myocardial ischaemia/reperfusion (I/R) injury is still a major challenge in clinical treatment. The role of long non-coding RNA (lncRNA) in the regulation of myocardial I/R injury still needs to be elucidated.

Methods: The primary isolated neonatal mousse cardiomyocytes and adult mice were used to construct a myocardial ischemia-reperfusion model. qRT-PCR is used to verify gene expression in myocardial tissue and myocardial cells. The effect of AK035396 in primary cardiomyocytes and mouse myocardium was confirmed by TUNEL staining and in vitro flow cytometry experiments. RNA pulldown and Western blot were used to identify AK035396 interacting proteins. The expression of apoptosis-related proteins was identified by qRT-PCR and Western blot.

Results:In vivo and in vitro MIRI models, AK035396 was up-regulated after myocardial infarction. Functional studies have shown that knockdown of AK035396 reduces the apoptosis of primary cardiomyocytes and mouse myocardial tissue. AK035396 directly interacts with Mterf1 and inhibits the level of Mterf1. Further experiments have shown that inhibiting Mterf1 will promote the expression of mitochondrial genes COXII and CYTb and cause cell apoptosis.

Conclusion: AK035396 plays an important role in myocardial ischaemia-reperfusion injury by regulating the Mterf1-COXII/CYTb pathway.

Imaging Microstructural Damage and Alveolar Bone Loss in Rats Systemically Exposed to Methylmercury: First Experimental Evidence

The alveolar bone is an important mineralized structure of the periodontal support apparatus, and information about the methylmercury (MeHg) effects on the structural integrity is scarce. Therefore, this study aimed to investigate whether systemic, chronic, and low-dose exposure to MeHg can change the alveolar bone microstructure of rats. Adult Wistar rats (n = 30) were exposed to 0.04 mg/kg/day of MeHg or vehicle through intragastric gavage. The animals were euthanized after 60 days, and blood samples were collected for trolox equivalent antioxidant capacity (TEAC), glutathione (GSH), lipid peroxidation (LPO), and comet assays. The mandible of each animal was collected and separated into hemimandibles that were used to determine the total Hg level in the bone and to analyze microstructural damage and alveolar bone loss in terms of trabecular number (Tb.N), trabecular thickness (Tb.Th), bone volume fraction (BV/TV), and exposed root area of the second molars. MeHg exposure triggered oxidative stress in blood represented by lower levels of GSH and TEAC and the increase in LPO and DNA damage of the blood cells. High total Hg levels were found in the alveolar bone, and the microstructural analyses showed a reduction in Tb.N, Tb.Th, and BV/TV, which resulted in an increase in the exposed root area and a decrease in bone height. Long-term MeHg exposure promotes a systemic redox imbalance associated with microstructural changes and alveolar bone loss and may indicate a potential risk indicator for periodontal diseases.

Characterizing the Low-Dose Effects of Methylmercury on the Early Stages of Embryo Development Using Cultured Human Embryonic Stem Cells

BACKGROUND

Global concerns of methylmercury (MeHg) exposure have been raised, especially on its effects on pregnant women. Recent epidemiological studies have revealed associations between maternal blood/hair MeHg concentrations, adverse pregnancy outcomes, and developmental deficits. However, the underlying mechanisms remain unclear.

OBJECTIVES

In this study, we characterized the effects of MeHg exposure on undifferentiated human embryonic stem cells (hESCs) and extrapolated the effects to human embryonic development.

METHODS

hESCs were exposed to 0, 1, 5, 10, 50, 100 or 200nM MeHg for 24 h or 6 d. Cell adherence and colony formation and expansion were examined under the microscope. Cell attachment, viability/proliferation, apoptosis, stress response, cell cycle, autophagy, and expression of cell lineage marker genes and proteins were measured at the end of exposures.

RESULTS

Our results indicated that exposure to nanomolar concentrations of MeHg was associated with a) higher levels of reactive oxygen species (ROS) and hemeoxygenase-1 (HO-1), suggesting increased stress and adaptive responses; b) lower cellular adhesion, viability/proliferation, and colony formation and expansion; c) higher levels of apoptosis, reflected by higher cleaved caspase-3 expression and Annexin V binding; d) higher levels of cytoskeleton protein α-tubulin expression; e) higher rates of G1/S phase cell cycle arrest; and f) autophagy inhibition, as shown by a lower LC3BII/LC3BI ratio and accumulation of SQSTM1 (p62). These outcomes were accompanied by higher expressions of self-renewal genes or proteins or both, including OCT4, SOX2, NANOG, and cytokine receptor IL6ST, as well as pluripotency and the cell fate regulator cyclin D1.

DISCUSSION

These results revealed that under the selection pressure of exposure to low doses of MeHg, some hESCs underwent apoptosis, whereas others adapted and survived with enhanced self-renewal gene expression and specific morphological phenotypes. Findings from the present study provide in vitro evidence that low doses of MeHg adversely affect hESCs when exposed during a period of time that models embryonic pre-, during, and early postimplantation stages. https://doi.org/10.1289/EHP7349.

Methylmercury-induced cytotoxicity and oxidative biochemistry impairment in dental pulp stem cells: the first toxicological findings

BACKGROUND

Methylmercury (MeHg) is a potent toxicant able to harm human health, and its main route of contamination is associated with the consumption of contaminated fish and other seafood. Moreover, dental amalgams are also associated with mercury release on human saliva and may contribute to the accumulation of systemic mercury. In this way, the oral cavity seems to be the primary location of exposure during MeHg contaminated food ingestion and dental procedures but there is a lack of literature about its effects on dental tissues and the impact of this toxicity on human health. In this way, this study aimed to analyze the effects of different doses of MeHg on human dental pulp stem cells after short-term exposure.

METHODS

Dental pulp stem cells from human exfoliated deciduous teeth (SHED) were treated with 0.1, 2.5 and 5 µM of MeHg during 24 h. The MeHg effects were assessed by evaluating cell viability with Trypan blue exclusion assay. The metabolic viability was indirectly assessed by MTT reduction assay. In order to evaluate an indicative of antioxidant defense impairment, cells exposed to 0.1 and 5 µM MeHg were tested by measuring glutathione (GSH) level.

RESULTS

It was observed that cell viability decreased significantly after exposure to 2.5 and 5 µM of MeHg, but the metabolic viability only decreased significantly at 5 µM MeHg exposure, accompanied by a significant decrease in GSH levels. These results suggest that an acute exposure of MeHg in concentrations higher than 2.5 µM has cytotoxic effects and reduction of antioxidant capacity on dental pulp stem cells.

Heavy metals and adult neurogenesis

With extensive use in industrial and agriculture applications, overexposure to heavy metals has become a global public health concern. The nervous system is vulnerable to many heavy metals, including cadmium, lead, and mercury. However, the knowledge about the underlying mechanisms of these metals' neurotoxicity is still very limited. Adult neurogenesis is a process of generating functional neurons from adult neural progenitor/stem cells (aNPCs), which plays an important role in cognitive function and olfaction. The studies of adult neurogenesis provide new insights into mechanisms of heavy metal neurotoxicity. This review summarizes the current research about the effects of heavy metals on adult neurogenesis and discusses their importance in understanding the mechanisms of heavy metals neurotoxicity, as well as challenges and future directions.

Mechanisms of oxidative stress in methylmercury-induced neurodevelopmental toxicity

Methylmercury (MeHg) is a long-lasting organic environmental pollutant that poses a great threat to human health. Ingestion of seafood containing MeHg is the most important way by which it comes into contact with human body, where the central nervous system (CNS) is the primary target of MeHg toxicity. During periods of pre-plus postnatal, in particular, the brain of offspring is vulnerable to specific developmental insults that result in abnormal neurobehavioral development, even without symptoms in mothers. While many studies on neurotoxic effects of MeHg on the developing brain have been conducted, the mechanisms of oxidative stress in MeHg-induced neurodevelopmental toxicity is less clear. Hitherto, no single process can explain the many effects observed in MeHg-induced neurodevelopmental toxicity. This review summarizes the possible mechanisms of oxidative stress in MeHg-induced neurodevelopmental toxicity, highlighting modulation of Nrf2/Keap1/Notch1, PI3K/AKT, and PKC/MAPK molecular pathways as well as some preventive drugs, and thus contributes to the discovery of endogenous and exogenous molecules that can counteract MeHg-induced neurodevelopmental toxicity.

Cellular and Molecular Mechanisms Mediating Methylmercury Neurotoxicity and Neuroinflammation

Methylmercury (MeHg) toxicity is a major environmental concern. In the aquatic reservoir, MeHg bioaccumulates along the food chain until it is consumed by riverine populations. There has been much interest in the neurotoxicity of MeHg due to recent environmental disasters. Studies have also addressed the implications of long-term MeHg exposure for humans. The central nervous system is particularly susceptible to the deleterious effects of MeHg, as evidenced by clinical symptoms and histopathological changes in poisoned humans. In vitro and in vivo studies have been crucial in deciphering the molecular mechanisms underlying MeHg-induced neurotoxicity. A collection of cellular and molecular alterations including cytokine release, oxidative stress, mitochondrial dysfunction, Ca²⁺ and glutamate dyshomeostasis, and cell death mechanisms are important consequences of brain cells exposure to MeHg. The purpose of this review is to organize an overview of the mercury cycle and MeHg poisoning events and to summarize data from cellular, animal, and human studies focusing on MeHg effects in neurons and glial cells. This review proposes an up-to-date compendium that will serve as a starting point for further studies and a consultation reference of published studies.

Association between methylmercury environmental exposure and neurological disorders: A systematic review

The mercury-related central nervous system disorders have been extensively studied on animal models and human beings. However, clinical evidences of which neurological changes are in fact associated with mercury exposure remains controversial. This systematic review (Prospero registration under the number CRD42016041760) aimed to elucidate the association of methylmercury (MeHg) exposure with neurological alteration in populations living in MeHg-endemic risk area. A systematic search was performed according to the Preferred Reporting Items for Systematic Review and Meta-Analysis criteria using available databases PubMed, LILACS, Scopus, Web of Science, The Cochrane Library, OpenGrey and Google Scholar. A search of the following terms: "methylmercury compounds", "organomercury compounds", "neurologic manifestations", "memory disorders", "neurobehavioral manifestations" and "communication disorders" were performed in a systematic way. Studies focusing on MeHg exposure and subsequent neurological alteration on humans (>13 years) were included. Evaluation of methodological quality and risk of bias as well as the level of evidence was performed. Our results have identified 470 studies and six articles were eligible for systematic review inclusion criteria. The studies suggested alterations related to the psychosensory, motor and coordination system, as well as motor speech, hearing, visual impairment, mood alterations and loss of intelligent quotient. Of all the six studies, two presented a high risk of bias, with methodological problems related to the confounding factors and all studies presented evidence level ranged from very low to low. In this way our results revealed that a definitive demonstration of an association of MeHg and neurological alterations in human beings is still a pending subject. Future studies in this topic should take into consideration more confident and reliable methods to answer this question.

Associations of blood mercury and fatty acid concentrations with blood mitochondrial DNA copy number in the Seychelles Child Development Nutrition Study

BACKGROUND

Fish contains methylmercury (MeHg) which can cause oxidative stress and neurodevelopmental toxicity at sufficiently high doses. Fish also contains polyunsaturated fatty acids (PUFA) which have both antioxidant (n-3) and oxidant (n-6) properties. Mitochondrial DNA (mtDNA) is sensitive to oxidative stress but has not been previously studied in relation to MeHg exposure or PUFA status.

OBJECTIVE

To investigate the associations between MeHg exposure and PUFA status during pregnancy with relative mitochondrial DNA copy number (RmtDNAcn) in mothers and their newborns.

METHODS

In total, 1488 mother-child pairs from the Seychelles Child Development Study Nutrition Cohort 2 were included in this study. Total Hg was measured in maternal blood collected at 28 weeks' gestation, maternal hair at delivery, and in fetal cord blood. PUFA (n-3 and n-6) were measured only in maternal blood. RmtDNAcn was measured by qPCR in both maternal and cord blood.

RESULTS

Increasing maternal blood Hg (β = 0.001, 95%CI: 0.000, 0.002) and n-3 PUFA concentrations (β = 0.183, 95%CI: 0.048, 0.317) were associated with higher maternal RmtDNAcn. Increasing maternal n-6 PUFA (β = -0.103, 95%CI: -0.145, -0.062) and n-6/n-3 ratio (β = -0.011, 95%CI: -0.017, -0.004) were associated with lower maternal RmtDNAcn. Increasing fetal cord blood Hg was associated with lower fetal RmtDNAcn (β = -0.002, 95%CI: -0.004, -0.000). Neither maternal blood Hg nor PUFA status was associated with fetal RmtDNAcn.

CONCLUSIONS

Our findings suggest that MeHg and PUFA may influence mitochondrial homeostasis although the magnitude of these associations are small. Future studies should confirm the findings and explore the underlying mechanisms.

Mercury Involvement in Neuronal Damage and in Neurodegenerative Diseases

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis are characterized by a chronic and selective process of neuronal cell death. Although the causes of neurodegenerative diseases remain still unknown, it is now a well-established idea that more factors, such as genetic, endogenous, and environmental, are involved. Among environmental causes, the accumulation of mercury, a heavy metal considered a toxic agent, was largely studied as a probable factor involved in neurodegenerative disease course. Mercury exists in three main forms: elemental mercury, inorganic mercury, and organic mercury (methylmercury and ethylmercury). Sources of elemental mercury can be natural (volcanic emission) or anthropogenic (coal-fired electric utilities, waste combustion, hazardous-waste incinerators, and gold extraction). Moreover, mercury is still used as an antiseptic, as a medical preservative, and as a fungicide. Dental amalgam can emit mercury vapor. Mercury vapor, being highly volatile and lipid soluble, can cross the blood-brain barrier and the lipid cell membranes and can be accumulated into the cells in its inorganic forms. Also, methylmercury can pass through blood-brain and placental barriers, causing serious damage in the central nervous system. This review describes the toxic effects of mercury in cell cultures, in animal models, and in patients with neurodegenerative diseases. In vitro experiments showed that mercury exposure was principally involved in oxidative stress and apoptotic processes. Moreover, motor and cognitive impairment and neural loss have been confirmed in various studies performed in animal models. Finally, observational studies on patients with neurodegenerative diseases showed discordant data about a possible mercury involvement.

Post-translational modifications in MeHg-induced neurotoxicity

Mercury (Hg) exposure remains a major public health concern due to its widespread distribution in the environment. Organic mercurials, such as MeHg, have been extensively investigated especially because of their congenital effects. In this context, studies on the molecular mechanism of MeHg-induced neurotoxicity are pivotal to the understanding of its toxic effects and the development of preventive measures. Post-translational modifications (PTMs) of proteins, such as phosphorylation, ubiquitination, and acetylation are essential for the proper function of proteins and play important roles in the regulation of cellular homeostasis. The rapid and transient nature of many PTMs allows efficient signal transduction in response to stress. This review summarizes the current knowledge of PTMs in MeHg-induced neurotoxicity, including the most commonly PTMs, as well as PTMs induced by oxidative stress and PTMs of antioxidant proteins. Though PTMs represent an important molecular mechanism for maintaining cellular homeostasis and are involved in the neurotoxic effects of MeHg, we are far from understanding the complete picture on their role, and further research is warranted to increase our knowledge of PTMs in MeHg-induced neurotoxicity.

Oxidative Biochemistry Disbalance and Changes on Proteomic Profile in Salivary Glands of Rats Induced by Chronic Exposure to Methylmercury

Methylmercury (MeHg) is one of the most toxic mercury species, which can cause many systemic damages, but little is known about its effect in the salivary glands. This study aimed to analyze the mercury levels, oxidative stress, and proteomic profile in parotid, submandibular, and sublingual salivary glands of rats, after chronic MeHg intoxication. Two groups of twenty male Wistar rats (90 days of age) were used on the experiment. MeHg group was intoxicated by intragastric gavage with MeHg at a dose of 0.04 mg/kg/day for 60 days, while the control group received only oil. After the period of intoxication, the glands were collected for evaluation of total mercury levels, proteomic profile, and oxidative balance by analyzing the antioxidant capacity against peroxyl radicals (ACAP), lipid peroxidation (LPO), and nitrite levels. Our results have showed that mercury levels were significant in all three glands compared to the respective control. It also showed lower levels of ACAP, as well as higher LPO and nitrite levels. The proteomic profile presented impairments on structural components of cytoskeleton, metabolic pathways, and oxidative biochemistry. Thus, the exposure to MeHg was able to generate oxidative stress that could be associated with changes in the proteomic profile of salivary glands.

The Protective Roles of ROS-Mediated Mitophagy on 125I Seeds Radiation Induced Cell Death in HCT116 Cells

For many unresectable carcinomas and locally recurrent cancers (LRC), ¹²⁵I seeds brachytherapy is a feasible, effective, and safe treatment. Several studies have shown that ¹²⁵I seeds radiation exerts anticancer activity by triggering DNA damage. However, recent evidence shows mitochondrial quality to be another crucial determinant of cell fate, with mitophagy playing a central role in this control mechanism. Herein, we found that ¹²⁵I seeds irradiation injured mitochondria, leading to significantly elevated mitochondrial and intracellular ROS (reactive oxygen species) levels in HCT116 cells. The accumulation of mitochondrial ROS increased the expression of HIF-1α and its target genes BINP3 and NIX (BINP3L), which subsequently triggered mitophagy. Importantly, ¹²⁵I seeds radiation induced mitophagy promoted cells survival and protected HCT116 cells from apoptosis. These results collectively indicated that ¹²⁵I seeds radiation triggered mitophagy by upregulating the level of ROS to promote cellular homeostasis and survival. The present study uncovered the critical role of mitophagy in modulating the sensitivity of tumor cells to radiation therapy and suggested that chemotherapy targeting on mitophagy might improve the efficiency of ¹²⁵I seeds radiation treatment, which might be of clinical significance in tumor therapy.