Chronic arsenic exposure impairs adaptive thermogenesis in male C57BL/6J mice

Glycemic Changes Related to Arsenic Exposure: An Overview of Animal and Human Studies

BACKGROUND

Arsenic (As) is a risk factor associated with glycemic alterations. However, the mechanisms of action and metabolic aspects associated with changes in glycemic profiles have not yet been completely elucidated. Therefore, in this review, we aimed to investigate the metabolic aspects of As and its mechanism of action associated with glycemic changes.

METHODS

We searched the PubMed (MEDLINE) and Google Scholar databases for relevant articles published in English. A combination of free text and medical subject heading keywords and search terms was used to construct search equations. The search yielded 466 articles; however, only 50 were included in the review.

RESULTS

We observed that the relationship between As exposure and glycemic alterations in humans may be associated with sex, smoking status, body mass index, age, occupation, and genetic factors. The main mechanisms of action associated with changes induced by exposure to As in the glycemic profile identified in animals are increased oxidative stress, reduced expression of glucose transporter type 4, induction of inflammatory factor expression and dysfunction of pancreatic β cells.

CONCLUSIONS

Therefore, As exposure may be associated with glycemic alterations according to inter-individual differences.

Combined threats of climate change and contaminant exposure through the lens of bioenergetics

Organisms face energetic challenges of climate change in combination with suites of natural and anthropogenic stressors. In particular, chemical contaminant exposure has neurotoxic, endocrine-disrupting, and behavioral effects which may additively or interactively combine with challenges associated with climate change. We used a literature review across animal taxa and contaminant classes, but focused on Arctic endotherms and contaminants important in Arctic ecosystems, to demonstrate potential for interactive effects across five bioenergetic domains: (1) energy supply, (2) energy demand, (3) energy storage, (4) energy allocation tradeoffs, and (5) energy management strategies; and involving four climate change-sensitive environmental stressors: changes in resource availability, temperature, predation risk, and parasitism. Identified examples included relatively equal numbers of synergistic and antagonistic interactions. Synergies are often suggested to be particularly problematic, since they magnify biological effects. However, we emphasize that antagonistic effects on bioenergetic traits can be equally problematic, since they can reflect dampening of beneficial responses and result in negative synergistic effects on fitness. Our review also highlights that empirical demonstrations remain limited, especially in endotherms. Elucidating the nature of climate change-by-contaminant interactive effects on bioenergetic traits will build toward determining overall outcomes for energy balance and fitness. Progressing to determine critical species, life stages, and target areas in which transformative effects arise will aid in forecasting broad-scale bioenergetic outcomes under global change scenarios.

Association between Heavy Metals, Metalloids and Metabolic Syndrome: New Insights and Approaches

Metabolic syndrome (MetS) is an important public health issue that affects millions of people around the world and is growing to pandemic-like proportions. This syndrome is defined by the World Health Organization (WHO) as a pathologic condition characterized by abdominal obesity, insulin resistance, hypertension, and hyperlipidemia. Moreover, the etiology of MetS is multifactorial, involving many environmental factors, including toxicant exposures. Several studies have associated MetS with heavy metals exposure, which is the focus of this review. Environmental and/or occupational exposure to heavy metals are a major risk, contributing to the development of chronic diseases. Of particular note, toxic metals such as mercury, lead, and cadmium may contribute to the development of MetS by altering oxidative stress, IL-6 signaling, apoptosis, altered lipoprotein metabolism, fluid shear stress and atherosclerosis, and other mechanisms. In this review, we discuss the known and potential roles of heavy metals in MetS etiology as well as potential targeted pathways that are associated with MetS. Furthermore, we describe how new approaches involving proteomic and transcriptome analysis, as well as bioinformatic tools, may help bring about an understanding of the involvement of heavy metals and metalloids in MetS.

Impaired white adipose tissue fatty acid metabolism in mice fed a high-fat diet worsened by arsenic exposure, primarily affecting retroperitoneal adipose tissue

Fatty acid (FA) metabolism dysfunction of white adipose tissue (WAT) underlies obesity and insulin resistance in response to high calorie intake and/or endocrine-disrupting chemicals (EDCs), among other factors. Arsenic is an EDC that has been associated with metabolic syndrome and diabetes. However, the combined effect of a high-fat diet (HFD) and arsenic exposure on WAT FA metabolism has been little studied. FA metabolism was evaluated in visceral (epididymal and retroperitoneal) and subcutaneous WAT of C57BL/6 male mice fed control or HFD (12 and 40% kcal fat, respectively) for 16 weeks together with an environmentally relevant chronic arsenic exposure through drinking water (100 μg/l) during the second half of the study. In mice fed HFD, arsenic potentiated the increase of serum markers of selective insulin resistance in WAT and fatty acid re-esterification and the decrease in the lipolysis index. Retroperitoneal was the WAT most affected, where the combination of arsenic and HFD in contrast to HFD, generated higher weight, larger adipocytes, increased triglyceride content, and decreased fasting stimulated lipolysis evidenced by lower phosphorylation of HSL and perilipin. At the transcriptional level, arsenic in mice fed either diet downregulated genes involved in fatty acid uptake (LPL, CD36), oxidation (PPARα, CPT1), lipolysis (ADRß3) and glycerol transport (AQP7 and AQP9). Additionally, arsenic potentiated hyperinsulinemia induced by HFD, despite a slight increase in weight gain and food efficiency. Thus, the second hit of arsenic in sensitized mice by HFD worsens fatty acid metabolism impairment in WAT, mainly retroperitoneal, along with an exacerbated insulin resistance phenotype.

Decoupling the adsorption mechanisms of arsenate at molecular level on modified cube-shaped sponge loaded superparamagnetic iron oxide nanoparticles

In this study, a commercial cube-shaped open-celled cellulose sponge adsorbent was modified by in-situ co-precipitation of superparamagnetic iron oxide nanoparticles (SPION) and used to remove As(V) from aqueous solutions. Fe K-edge X-ray absorption spectroscopy (XAS) and TEM identified maghemite as the main iron phase of the SPION nanoparticles with an average size 13 nm. Batch adsorption experiments at 800 mg/L showed a 63% increase of adsorption capacity when loading 2.6 wt.% mass fraction of SPION in the cube-sponge. Experimental determination of the adsorption thermodynamic parameters indicated that the As(V) adsorption on the composite material is a spontaneous and exothermic process. As K-edge XAS results confirmed that the adsorption enhancement on the composite can be attributed to the nanoparticles loaded. In addition, adsorbed As(V) did not get reduced to more toxic As(III) and formed a binuclear corner-sharing complex with SPION. The advantageous cube-shape of the sponge-loaded SPION composite together with its high affinity and good adsorption capacity for As(V), good regeneration capability and the enhanced-diffusion attributed to its open-celled structure make this adsorbent a good candidate for industrial applications.

SOX2 modulated astrocytic process plasticity is involved in arsenic-induced metabolic disorders

Metabolic disorders induced by arsenic exposure have attracted great public concern. However, it remains unclear whether hypothalamus-based central regulation mechanisms are involved in this process. Here, we exposed mice to 100 μg/L arsenic in drinking water and established a chronic arsenic exposure model. Our study revealed that chronic arsenic exposure caused metabolic disorders in mice including impaired glucose metabolism and decreased energy expenditure. Arsenic exposure also impaired glucose sensing and the activation of proopiomelanocortin (POMC) neurons in the hypothalamus. In particular, arsenic exposure damaged the plasticity of hypothalamic astrocytic process. Further research revealed that arsenic exposure inhibited the expression of sex-determining region Y-Box 2 (SOX2), which decreased the expression level of insulin receptors (INSRs) and the phosphorylation of AKT. The conditional deletion of astrocytic SOX2 exacerbated arsenic-induced effects on metabolic disorders, the impairment of hypothalamic astrocytic processes, and the inhibition of INSR/AKT signaling. Furthermore, the arsenic-induced impairment of astrocytic processes and inhibitory effects on INSR/AKT signaling were reversed by SOX2 overexpression in primary hypothalamic astrocytes. Together, we demonstrated here that chronic arsenic exposure caused metabolic disorders by impairing SOX2-modulated hypothalamic astrocytic process plasticity in mice. Our study provides evidence of novel central regulatory mechanisms underlying arsenic-induced metabolic disorders and emphasizes the crucial role of SOX2 in regulating the process plasticity of adult astrocytes.

The pesticide chlorpyrifos promotes obesity by inhibiting diet-induced thermogenesis in brown adipose tissue

Obesity results from a caloric imbalance between energy intake, absorption and expenditure. In both rodents and humans, diet-induced thermogenesis contributes to energy expenditure and involves the activation of brown adipose tissue (BAT). We hypothesize that environmental toxicants commonly used as food additives or pesticides might reduce BAT thermogenesis through suppression of uncoupling protein 1 (UCP1) and this may contribute to the development of obesity. Using a step-wise screening approach, we discover that the organophosphate insecticide chlorpyrifos suppresses UCP1 and mitochondrial respiration in BAT at concentrations as low as 1 pM. In mice housed at thermoneutrality and fed a high-fat diet, chlorpyrifos impairs BAT mitochondrial function and diet-induced thermogenesis, promoting greater obesity, non-alcoholic fatty liver disease (NAFLD) and insulin resistance. This is associated with reductions in cAMP; activation of p38MAPK and AMPK; protein kinases critical for maintaining UCP1 and mitophagy, respectively in BAT. These data indicate that the commonly used pesticide chlorpyrifos, suppresses diet-induced thermogenesis and the activation of BAT, suggesting its use may contribute to the obesity epidemic.

Adipotropic effects of heavy metals and their potential role in obesity

Epidemiological studies demonstrated an association between heavy metal exposure and the incidence of obesity and metabolic syndrome. However, the particular effects of metal toxicity on adipose tissue functioning are unclear. Therefore, recent findings of direct influence of heavy metals (mercury, cadmium, and lead) and metalloid (arsenic) on adipose tissue physiology are discussed while considering existing gaps and contradictions. Here, we provide a literature review addressing adipose tissue as a potential target of heavy metal toxicity. Experimental in vivo studies demonstrated a significant influence of mercury, cadmium, lead, and arsenic exposure on body adiposity. In turn, in vitro experiments revealed both up- and downregulation of adipogenesis associated with aberrant expression of key adipogenic pathways, namely CCAAT/enhancer-binding protein (C/EBP) and peroxisome proliferator-activated receptor gamma (PPARγ). Comparison of the existing studies on the basis of dose and route of exposure demonstrated that the effects of heavy metal exposure on adipose tissue may be dose-dependent, varying from increased adipogenesis at low-dose exposure to inhibition of adipose tissue differentiation at higher doses. However, direct dose-response data are available in a single study only for arsenic. Nonetheless, both types of these effects, irrespective of their directionality, contribute significantly to metabolic disturbances due to dysregulated adipogenesis. Particularly, inhibition of adipocyte differentiation is known to reduce lipid-storage capacity of adipose tissue, leading to ectopic lipid accumulation. In contrast, metal-associated stimulation of adipogenesis may result in increased adipose tissue accumulation and obesity. However, further studies are required to reveal the particular dose- and species-dependent effects of heavy metal exposure on adipogenesis and adipose tissue functioning.

Obesogens: How They Are Identified and Molecular Mechanisms Underlying Their Action

Adult and childhood obesity have reached pandemic level proportions. The idea that caloric excess and insufficient levels of physical activity leads to obesity is a commonly accepted answer for unwanted weight gain. This paradigm offers an inconclusive explanation as the world continually moves towards an unhealthier and heavier existence irrespective of energy balance. Endocrine disrupting chemicals (EDCs) are chemicals that resemble natural hormones and disrupt endocrine function by interfering with the body's endogenous hormones. A subset of EDCs called obesogens have been found to cause metabolic disruptions such as increased fat storage, in vivo. Obesogens act on the metabolic system through multiple avenues and have been found to affect the homeostasis of a variety of systems such as the gut microbiome and adipose tissue functioning. Obesogenic compounds have been shown to cause metabolic disturbances later in life that can even pass into multiple future generations, post exposure. The rising rates of obesity and related metabolic disease are demanding increasing attention on chemical screening efforts and worldwide preventative strategies to keep the public and future generations safe. This review addresses the most current findings on known obesogens and their effects on the metabolic system, the mechanisms of action through which they act upon, and the screening efforts through which they were identified with. The interplay between obesogens, brown adipose tissue, and the gut microbiome are major topics that will be covered.

Choice of Laboratory Rodent Diet May Confound Data Interpretation and Reproducibility

The reproducibility of experimental data is challenged by many factors in both clinical and preclinical research. In preclinical studies, several factors may be responsible, and diet is one variable that is commonly overlooked, especially by those not trained in nutrition. In particular, grain-based diets contain complex ingredients, each of which can provide multiple nutrients, non-nutrients, and contaminants, which may vary from batch to batch. Thus, even when choosing the same grain-based diet used in the past by others, its composition will likely differ. In contrast, purified diets contain refined ingredients that offer the ability to control the composition much more closely and maintain consistency from one batch to the next, while minimizing the presence of non-nutrients and contaminants. In this article, we provide several different examples or scenarios showing how the diet choice can alter data interpretation, potentially affecting reproducibility and knowledge gained within any given field of study.