Impact of in vitro heavy metal exposure on pancreatic β-cell function

Heavy metal exposure and metabolomics analysis: an emerging frontier in environmental health

Exposure to heavy metals in various populations can lead to extensive damage to different organs, as these metals infiltrate and bioaccumulate in the human body, causing metabolic disruptions in various organs. To comprehensively understand the metal homeostasis, inter-organ "traffic," and extensive metabolic alterations resulting from heavy metal exposure, employing complementary analytical methods is crucial. Metabolomics is pivotal in unraveling the intricacies of disease vulnerability by furnishing thorough understandings of metabolic changes linked to different metabolic diseases. This field offers exciting prospects for enhancing the disease prevention, early detection, and tailoring treatment approaches to individual needs. This article consolidates the existing knowledge on disease-linked metabolic pathways affected by the exposure of diverse heavy metals providing concise overview of the underlying impact mechanisms. The main aim is to investigate the connection between the altered metabolic pathways and long-term complex health conditions induced by heavy metals such as diabetes mellitus, cardiovascular diseases, renal disorders, inflammation, neurodegenerative diseases, reproductive risks, and organ damage. Further exploration of common pathways may unveil the shared targets for treating associated pathological conditions. In this article, the role of metabolomics in disease susceptibility is emphasized that metabolomics is expected to be routinely utilized for the diagnosis and monitoring of diseases and practical value of biomarkers derived from metabolomics, as well as determining their appropriate integration into extensive clinical settings.

Metalloestrogens exposure and risk of gestational diabetes mellitus: Evidence emerging from the systematic review and meta-analysis

BACKGROUND

Metalloestrogens are metals and metalloid elements with estrogenic activity found everywhere. Their impact on human health is becoming more apparent as human activities increase.

OBJECTIVE

Our aim is to conduct a comprehensive systematic review and meta-analysis of observational studies exploring the correlation between metalloestrogens (specifically As, Sb, Cr, Cd, Cu, Se, Hg) and Gestational Diabetes Mellitus (GDM).

METHODS

PubMed, Web of Science, and Embase were searched to examine the link between metalloestrogens (As, Sb, Cr, Cd, Cu, Se, and Hg) and GDM until December 2023. Risk estimates were derived using random effects models. Subgroup analyses were conducted based on study countries, exposure sample, exposure assessment method, and detection methods. Sensitivity analyses and adjustments for publication bias were carried out to assess the strength of the findings.

RESULTS

Out of the 389 articles identified initially, 350 met our criteria and 33 were included in the meta-analysis, involving 141,175 subjects (9450 cases, 131,725 controls). Arsenic, antimony, and copper exposure exhibited a potential increase in GDM risk to some extent (As: OR = 1.28, 95 % CI [1.08, 1.52]; Sb: OR = 1.73, 95 % CI [1.13, 2.65]; Cu: OR = 1.29, 95 % CI [1.02, 1.63]), although there is a high degree of heterogeneity (As: Q = 52.93, p < 0.05, I2 = 64.1 %; Sb: Q = 31.40, p < 0.05, I2 = 80.9 %; Cu: Q = 21.14, p < 0.05, I2 = 71.6 %). Conversely, selenium, cadmium, chromium, and mercury exposure did not exhibit any association with the risk of GDM in our study.

DISCUSSION

Our research indicates that the existence of harmful metalloestrogens in the surroundings has a notable effect on the likelihood of GDM. Hence, we stress the significance of environmental elements in the development of GDM and the pressing need for relevant policies and measures.

Sex-specific transgenerational effects of preconception exposure to arsenite: metabolic phenotypes of C57BL/6 offspring

Chronic exposure to inorganic arsenic (iAs) has been linked to diabetes in both humans and mice, but the role of iAs exposure prior to conception and its transgenerational effects are understudied. The present study investigated transgenerational effects of preconception iAs exposure in C57BL/6J mice, focusing on metabolic phenotypes of G1 and G2 offspring. Body composition and diabetes indicators, including fasting blood glucose, fasting plasma insulin, glucose tolerance, and indicators of insulin resistance and beta cell function, were examined in both generations. The results suggest that the preconception iAs exposure in the parental (G0) generation induced diabetic phenotypes in G1 and G2 offspring in a sex-dependent manner. G1 females from iAs-exposed parents developed insulin resistance while no significant effects were found in G1 males. In the G2 generation, insulin resistance was observed only in males from iAs-exposed grandparents and was associated with higher bodyweights and adiposity. Similar trends were observed in G2 females from iAs-exposed grandparents, but these did not reach statistical significance. Thus, preconception iAs exposure altered metabolic phenotype across two generations of mouse offspring. Future research will investigate the molecular mechanisms underlying these transgenerational effects, including epigenomic and transcriptomic profiles of germ cells and tissues from G0, G1 and G2 generations.

Arsenic metabolism, diabetes prevalence, and insulin resistance among Mexican Americans: A mendelian randomization approach

Background

Differences in arsenic metabolism capacity may influence risk for type 2 diabetes, but the mechanistic drivers are unclear. We evaluated the associations between arsenic metabolism with overall diabetes prevalence and with static and dynamic measures of insulin resistance among Mexican Americans living in Starr County, Texas.

Methods

We utilized data from cross-sectional studies conducted in Starr County, Texas, from 2010-2014. A Mendelian randomization approach was utilized to evaluate the associations between arsenic metabolism and type 2 diabetes prevalence using the intronic variant in the arsenic methylating gene, rs9527, as the instrumental variable for arsenic metabolism. To further assess mechanisms for diabetes pathogenesis, proportions of the urinary arsenic metabolites were employed to assess the association between arsenic metabolism and insulin resistance among participants without diabetes. Urinary biomarkers of arsenic metabolites were modeled as individual proportions of the total. Arsenic metabolism was evaluated both with a static outcome of insulin resistance, homeostatic measure of assessment (HOMA-IR), and a dynamic measure of insulin sensitivity, Matsuda Index.

Results

Among 475 Mexican American participants from Starr County, higher metabolism capacity for arsenic is associated with higher diabetes prevalence driven by worse insulin resistance. Presence of the minor T allele of rs9527 is independently associated with an increase in the proportion of monomethylated arsenic (MMA%) and is associated with an odds ratio of 0.50 (95% CI: 0.24, 0.90) for type 2 diabetes. This association was conserved after potential covariate adjustment. Furthermore, among participants without type 2 diabetes, the highest quartile of MMA% was associated with 22% (95% CI: -33.5%, -9.07%) lower HOMA-IR and 56% (95% CI: 28.3%, 91.3%) higher Matsuda Index for insulin sensitivity.

Conclusions

Arsenic metabolism capacity, indicated by a lower proportion of monomethylated arsenic, is associated with increased diabetes prevalence driven by an insulin resistant phenotype among Mexican Americans living in Starr County, Texas.

Does maternal low-dose cadmium exposure increase the risk of offspring to develop metabolic syndrome and/or type 2 diabetes?

Cadmium is a hazardous metal with multiple organ toxicity that causes great harm to human health. Cadmium enters the human body through occupational exposure, diet, drinking water, breathing, and smoking. Cadmium accumulation in the human body is associated with increased risk of developing obesity, cardiovascular disease, diabetes, and metabolic syndrome (MetS). Cadmium uptake is enhanced during pregnancy and can cross the placenta affecting placental development and function. Subsequently, cadmium can pass to fetus, gathering in multiple organs such as the liver and pancreas. Early-life cadmium exposure can induce hepatic oxidative stress and pancreatic β-cell dysfunction, resulting in insulin resistance and glucose metabolic dyshomeostasis in the offspring. Prenatal exposure to cadmium is also associated with increasing epigenetic effects on the offspring's multi-organ functions. However, whether and how maternal exposure to low-dose cadmium impacts the risks of developing type 2 diabetes (T2D) in the young and/or adult offspring remains unclear. This review collected available data to address the current evidence for the potential role of cadmium exposure, leading to insulin resistance and the development of T2D in offspring. However, this review reveals that underlying mechanisms linking prenatal cadmium exposure during pregnancy with T2D in offspring remain to be adequately investigated.

Relationships Between Urinary Metals and Diabetes Traits Among Mexican Americans in Starr County, Texas, USA

Hispanics/Latinos have higher rates of type 2 diabetes (T2D), and the origins of these disparities are poorly understood. Environmental endocrine-disrupting chemicals (EDCs), including some metals and metalloids, are implicated as diabetes risk factors. Data indicate that Hispanics/Latinos may be disproportionately exposed to EDCs, yet they remain understudied with respect to environmental exposures and diabetes. The objective of this study is to determine how metal exposures contribute to T2D progression by evaluating the associations between 8 urinary metals and measures of glycemic status in 414 normoglycemic or prediabetic adults living in Starr County, Texas, a Hispanic/Latino community with high rates of diabetes and diabetes-associated mortality. We used multivariable linear regression to quantify the differences in homeostatic model assessments for pancreatic β-cell function, insulin resistance, and insulin sensitivity (HOMA-β, HOMA-IR, HOMA-S, respectively), plasma insulin, plasma glucose, and hemoglobin A1c (HbA1c) associated with increasing urinary metal concentrations. Quantile-based g-computation was utilized to assess mixture effects. After multivariable adjustment, urinary arsenic and molybdenum were associated with lower HOMA-β, HOMA-IR, and plasma insulin levels and higher HOMA-S. Additionally, higher urinary copper levels were associated with a reduced HOMA-β. Lastly, a higher concentration of the 8 metal mixtures was associated with lower HOMA-β, HOMA-IR, and plasma insulin levels as well as higher HOMA-S. Our data indicate that arsenic, molybdenum, copper, and this metal mixture are associated with alterations in measures of glucose homeostasis among non-diabetics in Starr County. This study is one of the first to comprehensively evaluate associations of urinary metals with glycemic measures in a high-risk Mexican American population.

Association between Plasma Trace Element Concentrations in Early Pregnancy and Gestational Diabetes Mellitus in Shanghai, China

(1) Background: Trace elements play important roles in gestational diabetes mellitus (GDM), but the results from reported studies are inconsistent. This study aimed to examine the association between maternal exposure to V, Cr, Mn, Co, Ni, and Se in early pregnancy and GDM. (2) Methods: A nested case-control study with 403 GDM patients and 763 controls was conducted. Trace elements were measured using inductively coupled plasma-mass spectrometry in plasma collected from pregnant women in the first trimester of gestation. We used several statistical methods to explore the association between element exposure and GDM risk. (3) Results: Plasma V and Ni were associated with increased and decreased risk of GDM, respectively, in the single-element model. V and Mn were found to be positively, and Ni was found to be negatively associated with GDM risk in the multi-element model. Mn may be the main contributor to GDM risk and Ni the main protective factor against GDM risk in the quantile g computation (QGC). 6.89 μg/L~30.88 μg/L plasma Ni was identified as a safe window for decreased risk of GDM. (4) Conclusions: V was positively associated with GDM risk, while Ni was negatively associated. Ni has dual effects on GDM risk.

In vitro toxic interaction of arsenic and hyperglycemia in mitochondria: an important implication of increased vulnerability in pre-diabetics

Environmental pollutants and lifestyle both contribute to the rapidly increasing prevalence of type 2 diabetes mellitus (T2DM) worldwide. Evidence suggests that exposure to environmental contaminants such as arsenic is associated with impaired glucose metabolism and insulin signaling. In the present study, isolated rat liver mitochondria (1 mg/ml) were co-exposed to low concentration of arsenic trioxide (ATO) ( IC₂₅ = 40 µM) and hyperglycemic condition (20, 40, 80, 160 mM glucose or 20, 40, 80, 160 mM pyruvate (PYR)). Mitochondrial dehydrogenase activity (complex II), glutathione content (GSH), reactive oxygen species (ROS), lipid peroxidation, mitochondrial membrane potential (ΔΨ), and mitochondrial swelling were then evaluated in the presence of ATO 40 µM and PYR 40 mM. Unexpectedly, glucose alone (20, 40, 80, 160 mM) had no toxic effect on mitochondria, even at very high concentrations and even when combined with ATO. Interestingly, PYR at low concentrations (≤ 10 mM) has a protective effect on mitochondria, but at higher concentrations (≥ 40 mM) with ATO, it decreased the complex II activity and increased mitochondrial ROS production, lipid peroxidation, GSH depletion, mitochondrial membrane damage, and swelling (p < 0.05). In conclusion, PYR but not glucose increased ATO mitochondrial toxicity even at low concentrations. These results suggest that pre-diabetics with non-clinical hyperglycemia, who are inevitably exposed to low concentrations of arsenic through food and water, may develop mitochondrial dysfunction that accelerates their progression to diabetes over time.

The Association Between Cadmium Exposure and Gestational Diabetes Mellitus: A Systematic Review and Meta-Analysis

Objective

Several studies have evaluated the association of cadmium exposure with the risk of gestational diabetes mellitus (GDM). However, the findings among these studies have been inconsistent. To further investigate the relationship, we carried out a meta-analysis to clarify the relationship between cadmium exposure and GDM risk.

Methods

Five databases (Scopus, PubMed, Web of Science, Cochrane, and CNKI) were searched for eligible studies until September 09, 2021. The quality of eligible studies was evaluated using the Newcastle–Ottawa quality assessment scale (NOS). The summary odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by random-effects models due to high heterogeneity. Sensitivity analysis was performed to explore the robustness of the results. Publication bias was evaluated by Egger's test and Begg's test. We also conducted meta-regression analysis and subgroup analysis to assess the potential sources of heterogeneity.

Results

A total of 10 studies with 32,000 participants related to our issue were included. Comparing the highest vs. lowest categories of cadmium exposure, no significant association was observed between cadmium exposure and the risk of GDM (OR = 1.16, 95% CI = 0.92–1.46, and P = 0.206). No publication bias was found in Begg's and Egger's tests (all P > 0.05). Meta-regression suggested that publication year was the potentially heterogeneous source (P = 0.034). Subgroup analysis of publication year showed that the OR of studies before the year of 2016 was 4.05 (95% CI = 1.87–8.76, P < 0.001), and prospective cohort studies showed a borderline increased GDM risk (OR = 1.15, 95% CI = 0.99–1.33, and P = 0.061).

Conclusion

Our results indicated no significant association between cadmium exposure and GDM risk. Further high-quality prospective studies, especially those using standard analytic methods for cadmium exposure, are warranted to confirm the results.

Targeting pancreatic beta cell death in type 2 diabetes by polyphenols

Diabetes is a very complex disease which is characterized by the appearance of insulin resistance that is primarily compensated by an increase in pancreatic beta cell mass, generating hyperinsulinemia. After time, pancreatic beta cells die by apoptosis appearing in the second phase of the disease, and characterized by hypoinsulinemia. There are multiple conditions that can alter pancreatic beta cell homeostasis and viability, being the most relevant ones; ER stress, cytotoxicity by amylin, mTORC1 hyperactivity, oxidative stress, mitochondrial dysfunction, inflammation and alterations in autophagy/mitophagy flux. In addition, the possible effects that different polyphenols could exert in the modulation of these mechanisms and regulating pancreatic beta cell viability are analyzed. It is necessary a profound analysis and understanding of all the possible mechanisms involved in the control and maintenance of pancreatic beta cell viability to develop more accurate and target treatments for controlling beta cell homeostasis and preventing or even reversing type 2 diabetes mellitus.

Low-level cadmium doses do not jeopardize the insulin secretion pathway of β-cell models until the onset of cell death

BACKGROUND

Cadmium is an inescapable environmental pollutant that permeates the food chain and has been debatably associated with diabetes in humans.

PURPOSE AND PROCEDURES

To probe the specific impact of low-level cadmium exposure on insulin production, largely sub-cytotoxic (50-500 nM) concentrations of cadmium chloride challenged the INS-1 and MIN6 rodent models of pancreatic β-cells for the longest possible time, up to 4 days, before sub-culturing.

MAIN FINDINGS

The concentration of detectable oxidants, the pattern of the actin cytoskeleton, the translocation of β-catenin, the activity of protein phosphatases, calcium traffic, and the phosphorylation status of several key signaling nodes, such as AMP kinase and mitogen activated kinases including nuclear translocation of Extracellular signal-Regulated Kinase, were all insensitive to the applied very low cadmium doses. Accordingly, low-level cadmium exposure did not alter the insulin secretion ability, the functional hallmark of β-cells, before the onset of cell death.

CONCLUSIONS

These data define an operational toxicological threshold for these cellular models of β-cells that should be useful to address insulin secretion and the diabetogenic effects of chronic low-level cadmium exposure in animal models and in humans.

Dietary Selenium Deficiency Partially Mimics the Metabolic Effects of Arsenic

Chronic arsenic exposure via drinking water is associated with diabetes in human pop-ulations throughout the world. Arsenic is believed to exert its diabetogenic effects via multiple mechanisms, including alterations to insulin secretion and insulin sensitivity. In the past, acute arsenicosis has been thought to be partially treatable with selenium supplementation, though a potential interaction between selenium and arsenic had not been evaluated under longer-term exposure models. The purpose of the present study was to explore whether selenium status may augment arsenic's effects during chronic arsenic exposure. To test this possibility, mice were exposed to arsenic in their drinking water and provided ad libitum access to either a diet replete with selenium (Control) or deficient in selenium (SelD). Arsenic significantly improved glucose tolerance and decreased insulin secretion and β-cell function in vivo. Dietary selenium deficiency resulted in similar effects on glucose tolerance and insulin secretion, with significant interactions between arsenic and dietary conditions in select insulin-related parameters. The findings of this study highlight the complexity of arsenic's metabolic effects and suggest that selenium deficiency may interact with arsenic exposure on β-cell-related physiological parameters.

Inappropriately sweet: Environmental endocrine-disrupting chemicals and the diabetes pandemic

Afflicting hundreds of millions of individuals globally, diabetes mellitus is a chronic disorder of energy metabolism characterized by hyperglycemia and other metabolic derangements that result in significant individual morbidity and mortality as well as substantial healthcare costs. Importantly, the impact of diabetes in the United States is not uniform across the population; rather, communities of color and those with low income are disproportionately affected. While excessive caloric intake, physical inactivity, and genetic susceptibility are undoubted contributors to diabetes risk, these factors alone fail to fully explain the rapid global rise in diabetes rates. Recently, environmental contaminants acting as endocrine-disrupting chemicals (EDCs) have been implicated in the pathogenesis of diabetes. Indeed, burgeoning data from cell-based, animal, population, and even clinical studies now indicate that a variety of structurally distinct EDCs of both natural and synthetic origin have the capacity to alter insulin secretion and action as well as global glucose homeostasis. This chapter reviews the evidence linking EDCs to diabetes risk across this spectrum of evidence. It is hoped that improving our understanding of the environmental drivers of diabetes development will illuminate novel individual-level and policy interventions to mitigate the impact of this devastating condition on vulnerable communities and the population at large.

Prospective association of metal levels with gestational diabetes mellitus and glucose: A retrospective cohort study from South China

OBJECTIVE

To explore the prospective correlation between serum metals before 24 weeks' gestation and gestational diabetes mellitus (GDM) or glucose in the late second trimester among southern Chinese pregnant women.

METHODS

A total of 8169 pregnant women were included in our retrospective cohort study. Logistic regression was used to investigate the relationships between metals (Manganese [Mn], copper [Cu], lead [Pb], calcium [Ca], zinc [Zn], magnesium [Mg]) and GDM. Quantile regression was performed to detect the shifts and associations with metals and three time-points glucose distribution of oral glucose tolerance test (OGTT) focused on the 10th, 50th, and 90th percentiles. Weighted quantile sum (WQS) regression was used to explore the relationship of metal mixtures and GDM as well as glucose.

RESULTS

Maternal serum concentrations of metals were assessed at mean 16.55 ± 2.92 weeks' gestation. Women with under weight might have 25% decreased risk of GDM for every 50% increase in Cu concentration within the safe limits. A 50% increase in Mn and Zn levels was related to a 0.051 μmol/L (95% CI: 0.033-0.070) and 0.059 μmol/L (95% CI: 0.040-0.079) increase in mean fasting plasma glucose of OGTT (OGTT0), respectively. The magnitude of association with Mn was smaller at the upper tail of OGTT0 distribution, while the magnitude of correlation with Zn was greater at the upper tail. However, there was a 0.012 mmol/L (95% CI: -0.017 to -0.008), 0.028 mmol/L (95% CI: -0.049 to -0.007), and 0.036 mmol/L (95% CI: -0.057 to -0.016) decrease in mean OGTT0 levels for every 50% increase in Pb, Ca, and Mg, respectively. The negative association of Pb, Ca, and Mg was greater at the lower tail of OGTT0 distribution. No significant relationship was observed in Cu and mean OGTT0 level (-0.010 mmol/L, 95% CI: -0.021 to 0.001), however, it showed a protective effect at the upper tail (-0.034 mmol/L, 95% CI: -0.049 to -0.017). No obvious correlation was found between metals and postprandial glucose levels (OGTT1 and OGTT2 from OGTT). The WQS index was significantly related to OGTT0 (P < 0.001). The contribution of Mn (80.19%) to metal mixture index was the highest related to OGTT0, followed by Cu (19.81%).

CONCLUSIONS

Higher Mn and Zn but lower Pb, Ca, and Mg concentrations within a certain range before 24 weeks' gestation might prospectively impair fasting plasma glucose during pregnancy; a greater focus is required on Mn. It could provide early markers of metal for predicting later glucose and suggest implement intervention for pregnant women.

Fasting Plasma Glucose Mediates the Prospective Effect of Maternal Metal Level on Birth Outcomes: A Retrospective and Longitudinal Population-Based Cohort Study

OBJECTIVE

Previously, we found that the presence of maternal serum metals before the 24th week of gestation prospectively increased fasting plasma glucose (FPG) at 24-28 weeks. We further explored the prospective association between levels of metals and neonatal outcomes and assessed the mediating effects of FPG on these relationships.

METHODS

A total of 7,644 pregnant women were included in a retrospective cohort study, and the relationships between metals [manganese (Mn), copper (Cu), lead (Pb), zinc (Zn), and magnesium (Mg)] and birth outcomes were explored. Quantile and linear regressions were performed to detect the shifts and associations between metals and neonatal size distribution focused on the 10th, 50th, and 90th percentiles. Mediation analysis was performed to assess the mediating effect of FPG on metals and birth outcomes.

RESULTS

After adjustment, a 50% increase in Mn and Zn levels was related to a 0.136-cm (95% CI: 0.067-0.205) and 0.120-cm (95% CI: 0.046-0.193) increase in head circumference, respectively. Based on head circumference distribution, the magnitude of the association with Mn was smaller at the upper tail, while the magnitude of correlation with Zn was greater at the upper tail. A 50% increase in Mn and Zn levels was related to a 0.135-cm (95% CI: 0.058-0.212) and 0.095-cm (95% CI: 0.013-0.178) increase in chest circumference, respectively. The magnitude of the association with Mn increased with increasing chest circumference, while the magnitude of correlation with Zn decreased with increasing chest circumference. FPG explained 10.00% and 17.65% of the associations of Mn with head and chest circumference. A positive indirect effect of Zn associated with head circumference (0.004, 95% CI: 0.002-0.006) and chest circumference (0.005, 95% CI: 0.003-0.008) through FPG was also observed, and the estimated proportion of the mediating effect was 13.79% and 26.32%, respectively.

CONCLUSION

Maternal serum Mn and Zn levels before the 24th week of gestation may prospectively increase the circumference of the neonatal head and chest. FPG at 24-28 weeks had positive mediating effects on these relationships. Further research is needed to identify a balance between maternal blood glucose and birth size.

Roles of oxidative stress, apoptosis, and inflammation in metal-induced dysfunction of beta pancreatic cells isolated from CD1 mice

The diabetogenic effects of metals including lead (Pb), mercury (Hg), cadmium (Cd), and molybdenum (Mo) have been reported with poorly identified underlying mechanisms. The current study assessed the effect of metals on the roles of oxidative stress, apoptosis, and inflammation in beta pancreatic cells isolated from CD-1 mice, via different biochemical assays. Data showed that the tested metals were cytotoxic to the isolated cells with impaired glucose stimulated insulin secretion (GSIS). This was associated with increased reactive oxygen species (ROS) production, lipid peroxidation, antioxidant enzymes activities, active proapoptotic caspase-3 (cas-3), inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) levels in the intoxicated cells. Furthermore, antioxidant-reduced glutathione (GSH-R), cas-3 inhibitor z-VAD-FMK, IL-6 inhibitor bazedoxifene (BZ), and TNF-α inhibitor etanercept (ET) were found to significantly decrease metal-induced cytotoxicity with improved GSIS in metals' intoxicated cells. In conclusion, oxidative stress, apoptosis, and inflammation can play roles in metals-induced diabetogenic effect.

Arsenal of Phytochemicals to Combat Against Arsenic-Induced Mitochondrial Stress and Cancer

Significance: Phytochemicals are important dietary constituents with antioxidant properties. They affect various signaling pathways involved in the overall maintenance of interior milieu of the cell. Arsenic, an environmental toxicant, is well known for its deleterious consequences, such as various diseases, including cancers in humans. Mitochondria are the cell's powerhouse that fuel all metabolic energy requirements. Dysfunctional mitochondria due to stressors may lead to abnormal functioning of the organelle, hampering the crucial cellular cross talks and ultimately leading to cancer. Application of phytochemicals against arsenic-induced mitochondrial disorders may be a preventive measure to counteract the ruinous impacts of the metalloid. Recent Advances: In recent years, extensive research on the role of mitochondria in cancer gives a better understanding of the areas the organelle covers in maintaining a healthy cell or in inducing carcinogenicity. Detailed knowledge of the mitochondrial governances would enable researchers to administer numerous phytochemicals to ameliorate altered oxidative phosphorylation, mitochondrial membrane potential (MMP), mitochondrial oxidative stress, unfolded protein response, glycolysis, or even apoptosis. Critical Issues: In this review, we have addressed how various phytochemicals belonging to diverse classes combat against arsenic-induced mitochondrial oxidative stress, depletion of MMP, cell cycle abrogation, apoptosis, glycolytic damages, oncogenic regulations, chaperones, mitochondrial complexes, and mitochondrial membrane pore formation in both in vitro and in vivo models. Future Directions: Insightful application of mitoprotective phytochemicals against arsenic-induced mitochondrial oxidative stress and carcinogenesis may guide researchers to develop preclinical chemopreventive agents to fight arsenic toxicity in humans.

Sex-dependent effects of preconception exposure to arsenite on gene transcription in parental germ cells and on transcriptomic profiles and diabetic phenotype of offspring

Chronic exposure to inorganic arsenic (iAs) has been linked to diabetic phenotypes in both humans and mice. However, diabetogenic effects of iAs exposure during specific developmental windows have never been systematically studied. We have previously shown that in mice, combined preconception and in utero exposures to iAs resulted in impaired glucose homeostasis in male offspring. The goal of the present study was to determine if preconception exposure alone can contribute to this outcome. We have examined metabolic phenotypes in male and female offspring from dams and sires that were exposed to iAs in drinking water (0 or 200 μg As/L) for 10 weeks prior to mating. The effects of iAs exposure on gene expression profiles in parental germ cells, and pancreatic islets and livers from offspring were assessed using RNA sequencing. We found that iAs exposure significantly altered transcript levels of genes, including diabetes-related genes, in the sperm of sires. Notably, some of the same gene transcripts and the associated pathways were also altered in the liver of the offspring. The exposure had a more subtle effect on gene expression in maternal oocytes and in pancreatic islets of the offspring. In female offspring, the preconception exposure was associated with increased adiposity, but lower blood glucose after fasting and after glucose challenge. HOMA-IR, the indicator of insulin resistance, was also lower. In contrast, the preconception exposure had no effects on blood glucose measures in male offspring. However, males from parents exposed to iAs had higher plasma insulin after glucose challenge and higher insulinogenic index than control offspring, indicating a greater requirement for insulin to maintain glucose homeostasis. Our results suggest that preconception exposure may contribute to the development of diabetic phenotype in male offspring, possibly mediated through germ cell-associated inheritance. Future research can investigate role of epigenetics in this phenomenon. The paradoxical outcomes in female offspring, suggesting a protective effect of the preconception exposure, warrant further investigation.

Emerging Links between Cadmium Exposure and Insulin Resistance: Human, Animal, and Cell Study Data

Recent research has helped clarify the role of cadmium (Cd) in various pathological states. We have demonstrated Cd involvement in pancreatic cancer, as well as the bioaccumulation of Cd in the pancreas. Bioaccumulation and increased toxicity suggest that Cd may also be involved in other pancreas-mediated diseases, like diabetes. Cd falls into the category of "hyperglycemic" metals, i.e., metals that increase blood glucose levels, which could be due to increased gluconeogenesis, damage to β-cells leading to reduced insulin production, or insulin resistance at target tissue resulting in a lack of glucose uptake. This review addresses the current evidence for the role of Cd, leading to insulin resistance from human, animal, and in vitro studies. Available data have shown that Cd may affect normal insulin function through multiple pathways. There is evidence that Cd exposure results in the perturbation of the enzymes and modulatory proteins involved in insulin signal transduction at the target tissue and mutations of the insulin receptor. Cd, through well-described mechanisms of oxidative stress, inflammation, and mitochondrial damage, may also alter insulin production in β-cells. More work is necessary to elucidate the mechanisms associated with Cd-mediated insulin resistance.

Geraniol attenuates oxidative stress, bioaccumulation, serological and histopathological changes during aluminum chloride-hepatopancreatic toxicity in male Wistar rats

Aluminum chloride (AlCl₃) has different industrial applications including manufacturing paint and water treatment. The present study was designed to evaluate the alleviating effect of geraniol against AlCl₃-induced hepatopancreatic toxicity. To this end, forty male Wistar rats were divided into control (0.9% NaCl, IP), geraniol (100 mg/kg orally), AlCl₃ (70 mg/kg, IP), and AlCl₃ (70 mg/kg, IP) plus geraniol (100 mg/kg orally) groups and then were treated daily for 28 days. Based on the results, serum cholesterol, triglyceride, as well as liver and pancreas enzymes increased significantly (P < 0.05) while the level of insulin significantly decreased in AlCl₃-treated rats compared to the control group (P < 0.05). The presence of geraniol relieved the toxic effects of AlCl₃ as well. On the other hand, the level of malondialdehyde (MDA) increased in the AlCl₃-treated group while the activities of glutathione peroxidase and the total antioxidant activity demonstrated a reduction. However, the MDA level decreased while the antioxidant enzymes increased in co-treated with geraniol group. Histopathological examination revealed that simultaneous treatment with geraniol in AlCl₃ intoxicated rats ameliorate the liver lesions such as necrosis, inflammatory cell infiltration, vacuolar degeneration, along with hyperemia and the cell density of the Langerhans islands. Finally, the results indicated that geraniol attenuated the side effect of AlCl₃-induced hepatopancreatic toxicity.

Exposure to inorganic arsenic and its methylated metabolites alters metabolomics profiles in INS-1 832/13 insulinoma cells and isolated pancreatic islets

Inorganic arsenic (iAs) is an environmental diabetogen, but mechanisms underlying its diabetogenic effects are poorly understood. Exposures to arsenite (iAsIII) and its methylated metabolites, methylarsonite (MAsIII) and dimethylarsinite (DMAsIII), have been shown to inhibit glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells and isolated pancreatic islets. GSIS is regulated by complex mechanisms. Increase in ATP production through metabolism of glucose and other substrates is the ultimate trigger for GSIS in β-cells. In the present study, we used metabolomics to identify metabolites and pathways perturbed in cultured INS-1 832/13 rat insulinoma cells and isolated murine pancreatic islets by exposures to iAsIII, MAsIII and DMAsIII. We found that the exposures perturbed multiple metabolites, which were enriched primarily in the pathways of amino acid, carbohydrate, phospholipid and carnitine metabolism. However, the effects of arsenicals in INS-1 832/13 cells differed from those in the islets and were exposure specific with very few overlaps between the three arsenicals. In INS-1 832/13 cells, all three arsenicals decreased succinate, a metabolite of Krebs cycle, which provides substrates for ATP synthesis in mitochondria. Acetylcarnitine was decreased consistently by exposures to arsenicals in both the cells and the islets. Acetylcarnitine is usually found in equilibrium with acetyl-CoA, which is the central metabolite in the catabolism of macronutrients and the key substrate for Krebs cycle. It is also thought to play an antioxidant function in mitochondria. Thus, while each of the three trivalent arsenicals perturbed specific metabolic pathways, which may or may not be associated with GSIS, all three arsenicals appeared to impair mechanisms that support ATP production or antioxidant defense in mitochondria. These results suggest that impaired ATP production and/or mitochondrial dysfunction caused by oxidative stress may be the mechanisms underlying the inhibition of GSIS in β-cells exposed to trivalent arsenicals.

Multiple metal concentrations and gestational diabetes mellitus in Taiyuan, China

BACKGROUND

The association between multiple metal concentrations and gestational diabetes mellitus (GDM) is poorly understood.

METHODS

A total of 776 women with GDM and an equal number of controls were included in the study. Concentrations of metals in participants' blood (nickel (Ni), arsenic (As), cadmium (Cd), antimony (Sb), thallium (Tl), mercury (Hg), lead (Pb)) were measured using inductively coupled plasma-mass. We used unconditional logistical regression models to estimate the associations between metals and GDM. We also employed weighted quantile sum (WQS) regression and principal components analysis (PCA) to examine metal mixtures in relation to GDM.

RESULTS

An increased risk of GDM was associated with As (OR = 1.49, 95% CI: 1.11, 2.01 for the 2nd tertile vs. the 1st tertile) and Hg (OR = 1.43, 95% CI: 1.09, 1.88 for the 3rd tertile vs. the 1st tertile). In WQS analysis, the WQS index was significantly associated with GDM (OR = 1.20, 95% CI: 1.02, 1.41). The major contributor to the metal mixture index was Hg (69.2%), followed by Pb (12.8%), and As (11.3%). Based on PCA, the second principal component, which was characterized by Hg, Ni, and Pb, was associated with an increased risk of GDM (OR = 1.46, 95% CI: 1.02, 2.08 for the highest quartile vs. the lowest quartile).

CONCLUSIONS

Our study results suggest that high metal levels are associated with an increased risk of GDM, and this increased risk is mainly driven by Hg and, to a lesser extent, by Ni, Pb, and As.

Arsenic is more potent than cadmium or manganese in disrupting the INS-1 beta cell microRNA landscape

Diabetes is a metabolic disorder characterized by fasting hyperglycemia and impaired glucose tolerance. Laboratory and population studies have shown that inorganic arsenic (iAs) can impair these pathways. Other metals including cadmium (Cd) and manganese (Mn) have also been linked to diabetes phenotypes. MicroRNAs, short non-coding RNAs that regulate gene expression, have emerged as potential drivers of metabolic dysfunction. MicroRNAs responsive to metal exposures in vitro have also been reported in independent studies to regulate insulin secretion in vivo. We hypothesize that microRNA dysregulation may associate with and possibly contribute to insulin secretion impairment upon exposure to iAs, Cd, or Mn. We exposed insulin secreting rat insulinoma cells to non-cytotoxic concentrations of iAs (1 µM), Cd (5 µM), and Mn (25 µM) for 24 h followed by small RNA sequencing to identify dysregulated microRNAs. RNA sequencing was then performed to further investigate changes in gene expression caused by iAs exposure. While all three metals significantly inhibited glucose-stimulated insulin secretion, high-throughput sequencing revealed distinct microRNA profiles specific to each exposure. One of the most significantly upregulated microRNAs post-iAs treatment is miR-146a (~ + 2-fold), which is known to be activated by nuclear factor κB (NF-κB) signaling. Accordingly, we found by RNA-seq analysis that genes upregulated by iAs exposure are enriched in the NF-κB signaling pathway and genes down-regulated by iAs exposure are enriched in miR-146a binding sites and are involved in regulating beta cell function. Notably, iAs exposure caused a significant decrease in the expression of Camk2a, a calcium-dependent protein kinase that regulates insulin secretion, has been implicated in type 2 diabetes, and is a likely target of miR-146a. Further studies are needed to elucidate potential interactions among NF-kB, miR-146a, and Camk2a in the context of iAs exposure.

Non-monotonic dose-response effects of arsenic on glucose metabolism

BACKGROUND

Inorganic arsenic (iAs) is a widespread environmental toxin. In addition to being a human carcinogen, its effect on diabetes has started to gain recognition recently. Insulin is the key hormone regulating systemic glucose metabolism. The in vivo effect of iAs on insulin sensitivity has not been directly addressed.

OBJECTIVES

Here we use mouse models to dissect the dose-dependent effects of iAs on glucose metabolism in vivo.

METHODS

We performed hyperinsulinemic-euglycemic clamp, the gold standard analysis of systemic insulin sensitivity. We also performed dynamic metabolic testings and RNA-seq analysis.

RESULTS

We found that a low-dose exposure (0.25 ppm iAs in drinking water) caused glucose intolerance in adult male C57BL/6 mice, likely by disrupting glucose-induced insulin secretion without affecting peripheral insulin sensitivity. However, a higher-dose exposure (2.5 ppm iAs) had diminished effects on glucose tolerance despite disrupted pancreatic insulin secretion. Insulin Clamp analysis showed that 2.5 ppm iAs actually enhanced systemic insulin sensitivity by simultaneously enhancing insulin-stimulated glucose uptake in skeletal muscles and improved insulin-mediated suppression of endogenous glucose production. RNA-seq analysis of skeletal muscles revealed that 2.5 ppm iAs regulated expression of many genes involved in the metabolism of fatty acids, pyruvate, and amino acids.

CONCLUSION

These findings suggest that iAs has opposite glycemic effects on distinct metabolic tissues at different dose thresholds. Such non-monotonic dose-response effects of iAs on glucose tolerance shed light on the complex interactions between iAs and the systemic glucose metabolism, which could potentially help reconcile some of the conflicting results in human epidemiological studies.

Braving the Element: Pancreatic β-Cell Dysfunction and Adaptation in Response to Arsenic Exposure

Type 2 diabetes mellitus (T2DM) is a serious global health problem, currently affecting an estimated 451 million people worldwide. T2DM is characterized by hyperglycemia and low insulin relative to the metabolic demand. The precise contributing factors for a given individual vary, but generally include a combination of insulin resistance and insufficient insulin secretion. Ultimately, the progression to diabetes occurs only after β-cells fail to meet the needs of the individual. The stresses placed upon β-cells in this context manifest as increased oxidative damage, local inflammation, and ER stress, often inciting a destructive spiral of β-cell death, increased metabolic stress due to further insufficiency, and additional β-cell death. Several pathways controlling insulin resistance and β-cell adaptation/survival are affected by a class of exogenous bioactive compounds deemed endocrine disrupting chemicals (EDCs). Epidemiological studies have shown that, in several regions throughout the world, exposure to the EDC inorganic arsenic (iAs) correlates significantly with T2DM. It has been proposed that a lifetime of exposure to iAs may exacerbate problems with both insulin sensitivity as well as β-cell function/survival, promoting the development of T2DM. This review focuses on the mechanisms of iAs action as they relate to known adaptive and maladaptive pathways in pancreatic β-cells.