Dehydroascorbate protection against dioxin-induced toxicity in the beta-cell line INS-1E

Dioxin-Induced PAI-1 Expression: A Novel Pathway to Pancreatic β-Cell Failure in Type 2 Diabetes

Exposure to environment-polluting chemicals (EPCs), which are ligands of the aryl hydrocarbon receptor (AhR), is associated with the development of type 2 diabetes (T2D). This study explores the mechanisms by which AhR ligands contribute to β-cell failure in T2D. Incubation of RINm5F rat pancreatic β-cells with low-dose 2,3,7,8-tetrachlorodibenzodioxin (TCDD), the most potent AhR ligand, inhibited glucose-stimulated insulin secretion (GSIS). A single injection of TCDD in wild type mice reduced the size of Langerhans islets, but not in AhR liver knock-out mice (AhR-LKO). RNA-seq database analysis identified Serpine1, encoding for plasminogen activator inhibitor type-1 (PAI-1) as a TCDD-mediated secretory protein that is synthesized in an AhR-dependent manner in the liver. Elevated PAI-1 levels were shown to induce Caspase-3/7-dependent apoptosis in RINm5F cells, suggesting a novel pathway through which EPCs exacerbate T2D. These findings support the hypothesis that chronic exposure to AhR ligands may directly inhibit GSIS in pancreatic β-cells and indirectly induce β-cell apoptosis through increased PAI-1. This study provides new insights into the EPC-PAI-1 axis as a missing link between pancreatic β-cell failure and the progression of T2D and offers a potential target for therapeutic intervention.

Combinatorial pathway disruption is a powerful approach to delineate metabolic impacts of endocrine disruptors

The prevalence of metabolic diseases, such as obesity, diabetes, metabolic syndrome and chronic liver diseases among others, has been rising for several years. Epidemiology and mechanistic (in vivo, in vitro and in silico) toxicology have recently provided compelling evidence implicating the chemical environment in the pathogenesis of these diseases. In this review, we will describe the biological processes that contribute to the development of metabolic diseases targeted by metabolic disruptors, and will propose an integrated pathophysiological vision of their effects on several organs. With regard to these pathomechanisms, we will discuss the needs, and the stakes of evolving the testing and assessment of endocrine disruptors to improve the prevention and management of metabolic diseases that have become a global epidemic since the end of last century.

Vitamin C protects against hypoxia, inflammation, and ER stress in primary human preadipocytes and adipocytes

Dysregulation of adipose tissue involves increased cellular hypoxia, ER stress, and inflammation and altered adipokine production, contributing to the aetiology of obesity-related diseases including type 2 diabetes and cardiovascular disease. This study aimed to investigate the effects of Vitamin C supplementation on these processes in primary human preadipocytes and adipocytes. Treatment of preadipocytes and adipocytes with the proinflammatory cytokine TNFα and palmitic acid (PA), to mimic the obesogenic milieu, significantly increased markers of hypoxia, ER stress and inflammation and reduced secretion of high molecular weight (HMW) adiponectin. Importantly, Vitamin C abolished TNFα+PA induced hypoxia and significantly reduced the increases in ER stress and inflammation in both cell types. Vitamin C also significantly increased the secretion of HMW adiponectin from adipocytes. These findings indicate that Vitamin C can reduce obesity-associated cellular stress and thus provide a rationale for future investigations.

Persistent organic pollutants and β-cell toxicity: a comprehensive review

Persistent organic pollutants (POPs) are a diverse family of contaminants that show widespread global dispersion and bioaccumulation. Humans are continuously exposed to POPs through diet, air particles, and household and commercial products; POPs are consistently detected in human tissues, including the pancreas. Epidemiological studies show a modest but consistent correlation between exposure to POPs and increased diabetes risk. The goal of this review is to provide an overview of epidemiological evidence and an in-depth evaluation of the in vivo and in vitro evidence that POPs cause β-cell toxicity. We review evidence for six classes of POPs: dioxins, polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), flame retardants, and per- and polyfluoroalkyl substances (PFAS). The available data provide convincing evidence implicating POPs as a contributing factor driving impaired glucose homeostasis, β-cell dysfunction, and altered metabolic and oxidative stress pathways in islets. These findings support epidemiological data showing that POPs increase diabetes risk and emphasize the need to consider the endocrine pancreas in toxicity assessments. Our review also highlights significant gaps in the literature assessing islet-specific endpoints after both in vivo and in vitro POP exposure. In addition, most rodent studies do not consider the impact of biological sex or secondary metabolic stressors in mediating the effects of POPs on glucose homeostasis and β-cell function. We discuss key gaps and limitations that should be assessed in future studies.

Selective beta-cell toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin on isolated pancreatic islets

An association between exposure to environmental pollutants and diabetes risk has been repeatedly shown by epidemiological studies. However, the biological basis of this association still need to be clarified. In this research we explored the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure on isolated pancreatic islets. After 1, 6 and 24 h exposure of isolated islets to different concentrations (1-50 nM) of TCDD we assayed: i) cell survival; ii) ultrastructure; iii) glucose-stimulated insulin secretion (GSIS); iv) expression of selected genes. A significant, dose-related increase of both necrosis and apoptosis was observed isolated rat islets after 24 h exposure to TCDD. The electron microscopic analysis revealed, at the same time point, the presence of several ultrastructural alterations (mitochondrial swelling, increased mitophagy, dilation of the endoplasmic reticulum) that, very interestingly, were exclusively observed in beta cells and not in other endocrine cells. Similar results were obtained in isolated human islets. GSIS was rapidly (1 h) and persistently (6 and 24 h) decreased by TCDD exposure even at the smallest concentration (1 nM). TCDD exposure significantly affected gene expression in isolated islets: Glut2, Gck, Bcl-xL, MafA, Pdx1 FoxO1 and IRE1 gene expression was significantly decreased, whereas Puma, DP5, iNOS and Chop gene expression was significantly increased after 6 h exposure to TCDD. In conclusion, our results clearly indicated that pancreatic beta cells represent not only a sensitive but also a specific target of the toxic action of dioxin.

Endocrine-disrupting chemicals and risk of diabetes: an evidence-based review

The purpose of this study was to review the epidemiological and experimental evidence linking background exposure to a selection of environmental endocrine-disrupting chemicals (EDCs) with diabetes and impaired glucose metabolism. The review summarises the literature on both cross-sectional and prospective studies in humans, as well as experimental in vivo and in vitro studies. The findings were subjected to evidence grading according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) classification. We found >40 cross-sectional and seven prospective studies regarding EDCs and risk of diabetes. Taken together, there is moderate evidence for a relationship between exposure to dichlorodiphenyldichloroethylene (p,p'-DDE), a metabolite of the pesticide dichlorodiphenyltrichloroethane, and diabetes development. Regarding polychlorinated biphenyls (PCBs), it is likely that the rodent models used are not appropriate, and therefore the evidence is poorer than for p,p'-DDE. For other EDCs, such as bisphenol A, phthalates and perfluorinated chemicals, the evidence is scarce, since very few prospective studies exist. Brominated flame retardants do not seem to be associated with a disturbed glucose tolerance. Thus, evidence is accumulating that EDCs might be involved in diabetes development. Best evidence exists for p,p'-DDE. For other chemicals, both prospective studies and supporting animal data are still lacking.

Hyperpolarized 13 C magnetic resonance evaluation of renal ischemia reperfusion injury in a murine model

Acute kidney injury (AKI) is a major risk factor for the development of chronic kidney disease (CKD). Persistent oxidative stress and mitochondrial dysfunction are implicated across diverse forms of AKI and in the transition to CKD. In this study, we applied hyperpolarized (HP) ¹³ C dehydroascorbate (DHA) and ¹³ C pyruvate magnetic resonance spectroscopy (MRS) to investigate the renal redox capacity and mitochondrial pyruvate dehydrogenase (PDH) activity, respectively, in a murine model of AKI at baseline and 7 days after unilateral ischemia reperfusion injury (IRI). Compared with the contralateral sham-operated kidneys, the kidneys subjected to IRI showed a significant decrease in the HP ¹³ C vitamin C/(vitamin C + DHA) ratio, consistent with a decrease in redox capacity. The kidneys subjected to IRI also showed a significant decrease in the HP ¹³ C bicarbonate/pyruvate ratio, consistent with impaired PDH activity. The IRI kidneys showed a significantly higher HP ¹³ C lactate/pyruvate ratio at day 7 compared with baseline, although the ¹³ C lactate/pyruvate ratio was not significantly different between the IRI and contralateral sham-operated kidneys at day 7. Arterial spin labeling magnetic resonance imaging (MRI) demonstrated significantly reduced perfusion in the IRI kidneys. Renal tissue analysis showed corresponding increased reactive oxygen species (ROS) and reduced PDH activity in the IRI kidneys. Our results show the feasibility of HP ¹³ C MRS for the non-invasive assessment of oxidative stress and mitochondrial PDH activity following renal IRI.

Environmental Contaminants and Pancreatic Beta-Cells

Despite health policies as well as clinical and research efforts, diabetes prevalence is still rising around the world. A multitude of causes have been suggested for this increase, mostly related to familial background, the occidental diet which is rich in fat/carbohydrates, and sedentary life style. Type 2 diabetes involves malfunctions of the primary pancreatic beta-cells, usually attributed to local damage; however, it can be associated with other stressful environmental agents, such as chemical contaminants from food, plastic and air, among others. Indeed, exposure to these chemical agents during perinatal and adolescent life can increase the risk of developing cardiometabolic diseases later in life. This review explores data showing which environmental chemical agents may produce injury in beta-cells and further impair the insulinotropic process of type 2 diabetes. Additionally, it points the need to also consider unusual causes of metabolic diseases, such as environmental contaminants.

Association of dioxin and other persistent organic pollutants (POPs) with diabetes: epidemiological evidence and new mechanisms of beta cell dysfunction

The worldwide explosion of the rates of diabetes and other metabolic diseases in the last few decades cannot be fully explained only by changes in the prevalence of classical lifestyle-related risk factors, such as physical inactivity and poor diet. For this reason, it has been recently proposed that other "nontraditional" risk factors could contribute to the diabetes epidemics. In particular, an increasing number of reports indicate that chronic exposure to and accumulation of a low concentration of environmental pollutants (especially the so-called persistent organic pollutants (POPs)) within the body might be associated with diabetogenesis. In this review, the epidemiological evidence suggesting a relationship between dioxin and other POPs exposure and diabetes incidence will be summarized, and some recent developments on the possible underlying mechanisms, with particular reference to dioxin, will be presented and discussed.

The aryl receptor inhibitor epigallocatechin-3-gallate protects INS-1E beta-cell line against acute dioxin toxicity

The aim of this research was to investigate the mechanism(s) underlying the acute toxicity of dioxin in pancreatic beta cells and to evaluate the protective effects of epigallocatechin-3-gallate (EGCG), the most abundant of the green tea's catechins and a powerful inhibitor of the aryl hydrocarbon receptor (AhR). Using the insulin-secreting INS-1E cell line we have explored the effect of 1h exposure to different concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), alone or in the presence of EGCG, on: (a) cell survival; (b) cellular ultrastructure; (c) intracellular calcium levels; (d) mitochondrial membrane potential; (e) glucose-stimulated insulin secretion and (f) activation of MAP kinases. Our results demonstrate that TCDD is highly toxic for INS-1E cells, suggesting that pancreatic beta cells should be considered a relevant and sensitive target for dioxin acute toxicity. EGCG significantly protects INS-1E cells against TCDD-induced toxicity in terms of both cell survival and preservation of cellular ultrastructure. The mechanism of this protective effect seems to be related to: (a) the ability of EGCG to preserve the mitochondrial function and thus to prevent the TCDD-induced inhibition of glucose-stimulated insulin secretion and (b) the ability of EGCG to inhibit the TCDD-induced activation of selected kinases, such as e.g. ERK 1/2 and JNK. Our results clearly show that EGCG is able to protect pancreatic beta cells against dioxin acute toxicity and indicate the mitochondrion as the most likely target for this beneficial effect.

Ascorbic acid improves embryonic cardiomyoblast cell survival and promotes vascularization in potential myocardial grafts in vivo

Organ restoration via cell therapy and tissue transplantation is limited by impaired graft survival. We tested the hypothesis that ascorbic acid (AA) reduces cell death in myocardial grafts both in vitro and in vivo and introduced a new model of autologous graft vascularization for later transplantation. Luciferase (Fluc)- and green fluorescent protein (GFP)-expressing H9C2 cardiomyoblasts were seeded in gelatin scaffolds to form myocardial artificial grafts (MAGs). MAGs were supplemented with AA (5 or 50 mumol/L) or plain growth medium. Bioluminescence imaging showed increased cell photon emission from day 1 to 5 in grafts supplemented with 5 mumol/L (p < 0.001) and 50 mumol/L (p < 0.01) AA. The amount of apoptotic cells in plain MAGs was significantly higher than in AA-enriched grafts. In our in vitro model, AA also enhanced H9C2 cell myogenic differentiation. For in vivo studies, MAGs containing H9C2-GFP-Fluc cells and enriched with AA (n = 10) or phosphate-buffered saline (n = 10) were implanted in the renal pouch of Wistar rats. At day 6, postimplantation bioluminescence signals decreased by 74% of baseline in plain MAGs versus 36% in AA-enriched MAGs (p < 0.0001). AA grafts contained significantly higher amounts of blood vessels, GFP(+) donor cells, and endothelial cells. In this study, we identified AA as a potent supplement that improves cardiomyoblast survival and promotes neovascularization in bioartificial grafts.