Obesogens, stem cells and the maternal programming of obesity

ENDOCRINE DISRUPTING CHEMICALS AND OBESITY: THE EVOLVING STORY OF OBESOGENS

Increase in obesity pandemic all over the world consequently leads to the investigation of possible causes. In addition to the traditional explanation using the so-called caloric model, the field of endocrine disruptors (EDs), especially subgroup called obesogens, offered more light on the pathogenetic mechanisms involved. After the Second World War a correlation between an increased production of exogenous pollutants and actual obesity epidemic was suggested. "Obesogen hypothesis" implies that molecules called obesogens inadequately stimulate the development of adipose cells and lipid accumulation in existing adipose cells, as well as change metabolic balance or hormonal control of appetite and satiety, leading to an increase in body fat mass. The list of obesogens includes some industrial chemicals, biocides, pharmaceuticals, pollutants, and smoke. EDs from the group of obesogens may exert their effects by the impairment in the programming development of adipocytes, by an increase in energetic depot in the adipose tissue, and by influencing neuroendocrine control of appetite and satiety. Increased scientific evidence on obesogens and their mechanisms of action may help to prevent obesity and mitigate deleterious effects of the environment on human life and development. New translational studies are needed to explain the possible mechanism proposed.

Phthalate Exposure and Long-Term Epigenomic Consequences: A Review

Phthalates are esters of phthalic acid which are used in cosmetics and other daily personal care products. They are also used in polyvinyl chloride (PVC) plastics to increase durability and plasticity. Phthalates are not present in plastics by covalent bonds and thus can easily leach into the environment and enter the human body by dermal absorption, ingestion, or inhalation. Several in vitro and in vivo studies suggest that phthalates can act as endocrine disruptors and cause moderate reproductive and developmental toxicities. Furthermore, phthalates can pass through the placental barrier and affect the developing fetus. Thus, phthalates have ubiquitous presence in food and environment with potential adverse health effects in humans. This review focusses on studies conducted in the field of toxicogenomics of phthalates and discusses possible transgenerational and multigenerational effects caused by phthalate exposure during any point of the life-cycle.

Differential Toxicity of Alkylphenols in JEG-3 Human Placental Cells: Alteration of P450 Aromatase and Cell Lipid Composition

Alkylphenols (APs) are a diverse class of chemicals that can cross the placental barrier and interfere with embryonic and fetal development. This work investigates the comparative toxicity, ability to inhibit aromatase activity, and to alter the lipid composition of 10 alkylphenols in the human placenta choriocarcinoma cell line JEG-3. Among the selected APs, 4-dodecylphenol (DP), 4-heptylphenol (HP), and 4-cumylphenol (CP) showed the highest cytotoxicity (EC50: 18-65 µM). Aromatase inhibition was closely related to the hydrophobicity of APs. HP significantly induced the generation of reactive oxygen species (ROS) (43-fold), inhibited placental aromatase activity (IC50: 41 µM), and induced a general dose-dependent depletion of polyunsaturated lipids (10-20 µM), which were attributed to high levels of oxidative stress. In contrast, 2,4,6-tri-tert-butylphenol (TTBP) significantly induced the intracellular accumulation of triacylglycerides (TGs), whereas DP increased the synthesis of phosphatidylcholines (PCs) and TGs at the expense of diacylglycerides (DGs). Overall, this study evidences the different modes of action of alkylphenols in human placental JEG-3 cells, describes differential lipidomic fingerprints, and highlights DP, HP, CP, and TTBP as the ones that caused the most harmful effects.

Endocrine Disrupting Chemicals: An Occult Mediator of Metabolic Disease

Endocrine disrupting chemicals (EDCs), a heterogeneous group of exogenous chemicals that can interfere with any aspect of endogenous hormones, represent an emerging global threat for human metabolism. There is now considerable evidence that the observed upsurge of metabolic disease cannot be fully attributed to increased caloric intake, physical inactivity, sleep deficit, and ageing. Among environmental factors implicated in the global deterioration of metabolic health, EDCs have drawn the biggest attention of scientific community, and not unjustifiably. EDCs unleash a coordinated attack toward multiple components of human metabolism, including crucial, metabolically-active organs such as hypothalamus, adipose tissue, pancreatic beta cells, skeletal muscle, and liver. Specifically, EDCs' impact during critical developmental windows can promote the disruption of individual or multiple systems involved in metabolism, via inducing epigenetic changes that can permanently alter the epigenome in the germline, enabling changes to be transmitted to the subsequent generations. The clear effect of this multifaceted attack is the manifestation of metabolic disease, clinically expressed as obesity, metabolic syndrome, diabetes mellitus, and non-alcoholic fatty liver disease. Although limitations of EDCs research do exist, there is no doubt that EDCs constitute a crucial parameter of the global deterioration of metabolic health we currently encounter.

Diet and Contaminants: Driving the Rise to Obesity Epidemics?

The obesity epidemic is spreading worldwide without reversal trend and despite specific policies oriented to dietary habits and lifestyle, which seem to have modest effects. Genetic factors only partly explain the rise, whereas environmental factors seem to play a key role, mainly by gene-environment interactions through epigenetic mechanisms. A number of animal and human studies point to maternal diet, intestinal microbiota and chemicals introduced as contaminants with food, all factors able to increase the risk of obesity. Widely diffused toxics (mainly BPA, phthalates, pesticides) are able to promote obesity in children and adults, mainly by acting on the differentiation pathway linking multipotent stromal stem cell to mature adipocyte, modulating epigenetic factors and influencing a series of mechanisms finally leading to altered dietary habits, increased adipocyte formation and fat storage. Furthermore, the adipose tissue is an important target for several chemicals (mainly POPs) which represent a threat to metabolic health. In conclusion, besides excessive individual energy intake and inadequate lifestyle, other broadly diffused and modifiable factors (mainly ingestion of toxic chemicals with food) seem to have a critical role in the rapid epidemiological growing of obesity, also considering trans-generational transmission of risk and later development of obesity due to exposure during early life. Further studies are needed, to better assess interactions between cumulative effects of toxic food contaminants and modification of diet and lifestyle, and to verify the efficacy of primary prevention strategies acting on all these factors and potentially able to reverse the continuous rising of the obesity epidemic.

Organotins in obesity and associated metabolic disturbances

The objective of the present study was to review the mechanisms of organotin-induced adipogenesis, obesity, and associated metabolic disturbances. Peroxisome proliferator-activated receptor γ (PPARγ) and retinoid X receptor α (RXRα) activation is considered as the key mechanism of organotin-induced adipogenesis. Particularly, organotin exposure results in increased adipogenesis both in cell and animal models. Moreover, transgenerational inheritance of organotin-induced obese phenotype was demonstrated in vivo. At the same time, the existing data demonstrate that organotin compounds (OTCs) induces aberrant expression of PPARγ-targeted genes, resulting in altered of adipokine, glucose transporter, proinflammatory cytokines levels, and lipid and carbohydrate metabolism. The latter is generally characterized by hyperglycemia and insulin resistance. Other mechanisms involved in organotin-induced obesity may include estrogen receptor and corticosteroid signaling, altered DNA methylation, and gut dysfunction. In addition to cellular effects, organotin exposure may also affect neural circuits of appetite regulation, being characterized by neuropeptide Y (NPY) up-regulation in parallel with of pro-opiomelanocortin (POMC), Agouti-related protein (AgRP), and cocaine and amphetamine regulated transcript (CART) down-regulation in the arcuate nucleus. These changes result in increased orexigenic and reduced anorexigenic signaling, leading to increased food intake. The existing data demonstrate that organotins are potent adipogenic agents, however, no epidemiologic studies have been performed to reveal the association between organotin exposure and obesity and the existing indirect human data are contradictory.

miR‑330‑5p inhibits H2O2‑induced adipogenic differentiation of MSCs by regulating RXRγ

The elucidation of the underlying molecular mechanism of H2O2‑induced adipocyte differentiation in mesenchymal stem cells (MSCs) is important for the development of treatments for metabolic diseases. The aim of the present study was to identify microRNA (miR)‑330‑5p, which targets retinoid X receptor γ (RXRγ) and to determine the function of H2O2‑induced adipogenic differentiation of MSCs. During differentiation of MSCs into adipocytes induced by H2O2, miR‑330‑5p expression was decreased with a concomitant increase in RXRγ expression. A luciferase assay with RXRγ 3'‑untranslated region (UTR) reporter plasmid, including the miR‑330‑5p‑binding sequences, identified that the introduction of miR‑330‑5p decreases luciferase activity. However, it did not affect the activity of mutated RXRγ 3'‑UTR reporter. Enforced expression of miR‑330‑5p significantly inhibited adipocyte differentiation by decreasing RXRγ mRNA and protein levels. In contrast, inhibition of the endogenous miR‑330‑5p promoted the formation of lipid droplets by rescuing RXRγ expression. Furthermore, the effects of inhibition of RXRγ were similar to those of overexpression of miR‑330‑5p on H2O2‑induced adipogenic differentiation from MSCs. miR‑330‑5p inhibits H2O2‑induced adipogenic differentiation of MSCs, and this is dependent on RXRγ. Taken together, the results of the present study revealed that miR‑330‑5p acts as a critical regulator of RXRγ, and is able to determinate the fate of MSCs to differentiate into adipocytes. This suggests that miR‑330‑5p and RXRγ may be target molecules for controlling metabolic diseases.

Prenatal Exposure to Endocrine Disruptors and Reprogramming of Adipogenesis: An Early-Life Risk Factor for Childhood Obesity

Obesity is a global health problem. It is characterized by excess adipose tissue that results from either increase in the number of adipocytes or increase in adipocytes size. Adipocyte differentiation is a highly regulated process that involves the activation of several transcription factors culminating in the removal of adipocytes from the cell cycle and induction of highly specific proteins. Several other factors, including hormones, genes, and epigenetics, are among the most important triggers of the differentiation process. Although the main contributing factors to obesity are high caloric intake, a sedentary lifestyle, and genetic predisposition, strong evidence supports a role for life exposure to environmental pollutants. Endocrine-disrupting chemicals are exogenous, both natural and man-made, chemicals that disrupt the body signaling processes, thus interfering with the endocrine system. Several studies have shown that prenatal exposure to endocrine disruptors modulates the mechanisms, by which multipotent mesenchymal stem cells differentiate into adipocytes. This review discusses adipocytes differentiation and highlights the possible mechanisms of prenatal exposure to endocrine disruptors in reprogramming of adipogenesis and induction of obesity later in life. Therefore, this review provides knowledge that reduction of early life exposure to these chemicals could open the door for new strategies in the prevention of obesity, especially during childhood.

Chemical and non-chemical stressors affecting childhood obesity: a systematic scoping review

Childhood obesity in the United States has doubled over the last three decades and currently affects 17% of children and adolescents. While much research has focused on individual behaviors impacting obesity, little research has emphasized the complex interactions of numerous chemical and non-chemical stressors found in a child's environment and how these interactions affect a child's health and well-being. The objectives of this systematic scoping review were to (1) identify potential chemical stressors in the context of non-chemical stressors that impact childhood obesity; and, (2) summarize our observations for chemical and non-chemical stressors in regards to child-specific environments within a community setting. A review was conducted to identify chemical and non-chemical stressors related to childhood obesity for the childhood life stages ranging from prenatal to adolescence. Stressors were identified and grouped into domains: individual behaviors, family/household behaviors, community stressors, and chemical exposures. Stressors were related to the child and the child's everyday environments and used to characterize child health and well-being. This review suggests that the interactions of chemical and non-chemical stressors are important for understanding a child's overall health and well-being. By considering these relationships, the exposure science research community can better design and implement strategies to reduce childhood obesity.

Endocrine Disruptors Leading to Obesity and Related Diseases

The review aims to comprehensively present the impact of exposure to endocrine disruptors (EDs) in relation to the clinical manifestation of obesity and related diseases, including diabetes mellitus, metabolic syndrome, cardiovascular diseases, carcinogenesis and infertility. EDs are strong participants in the obesity epidemic scenery by interfering with cellular morphological and biochemical processes; by inducing inflammatory responses; and by presenting transcriptional and oncogenic activity. Obesity and lipotoxicity enhancement occur through reprogramming and/or remodeling of germline epigenome by exposure to EDs. Specific population groups are vulnerable to ED exposure due to current dietary and environmental conditions. Obesity, morbidity and carcinogenicity induced by ED exposure are an evolving reality. Therefore, a new collective strategic approach is deemed essential, for the reappraisal of current global conditions pertaining to energy management.

Endocrine disruptors induce perturbations in endoplasmic reticulum and mitochondria of human pluripotent stem cell derivatives

Persistent exposure to man-made endocrine disrupting chemicals during fetal endocrine development may lead to disruption of metabolic homeostasis contributing to childhood obesity. Limited cellular platforms exist to test endocrine disrupting chemical-induced developmental abnormalities in human endocrine tissues. Here we use an human-induced pluripotent stem cell-based platform to demonstrate adverse impacts of obesogenic endocrine disrupting chemicals in the developing endocrine system. We delineate the effects upon physiological low-dose exposure to ubiquitous endocrine disrupting chemicals including, perfluoro-octanoic acid, tributyltin, and butylhydroxytoluene, in endocrine-active human-induced pluripotent stem cell-derived foregut epithelial cells and hypothalamic neurons. Endocrine disrupting chemicals induce endoplasmic reticulum stress, perturb NF-κB, and p53 signaling, and diminish mitochondrial respiratory gene expression, spare respiratory capacity, and ATP levels. As a result, normal production and secretion of appetite control hormones, PYY, α-MSH, and CART, are hampered. Blocking NF-κB rescues endocrine disrupting chemical-induced aberrant mitochondrial phenotypes and endocrine dysregulation, but not ER-stress and p53-phosphorylation changes.Harmful chemicals that disrupt the endocrine system and hormone regulation have been associated with obesity. Here the authors apply a human pluripotent stem cell-based platform to study the effects of such compounds on developing gut endocrine and neuroendocrine systems.

Metabolism disrupting chemicals and metabolic disorders

The recent epidemics of metabolic diseases, obesity, type 2 diabetes(T2D), liver lipid disorders and metabolic syndrome have largely been attributed to genetic background and changes in diet, exercise and aging. However, there is now considerable evidence that other environmental factors may contribute to the rapid increase in the incidence of these metabolic diseases. This review will examine changes to the incidence of obesity, T2D and non-alcoholic fatty liver disease (NAFLD), the contribution of genetics to these disorders and describe the role of the endocrine system in these metabolic disorders. It will then specifically focus on the role of endocrine disrupting chemicals (EDCs) in the etiology of obesity, T2D and NAFLD while finally integrating the information on EDCs on multiple metabolic disorders that could lead to metabolic syndrome. We will specifically examine evidence linking EDC exposures during critical periods of development with metabolic diseases that manifest later in life and across generations.

Endocrine disruptors and obesity

The increasing incidence of obesity is a serious global public health challenge. Although the obesity epidemic is largely fueled by poor nutrition and lack of exercise, certain chemicals have been shown to potentially have a role in its aetiology. A substantial body of evidence suggests that a subclass of endocrine-disrupting chemicals (EDCs), which interfere with endocrine signalling, can disrupt hormonally regulated metabolic processes, especially if exposure occurs during early development. These chemicals, so-called 'obesogens' might predispose some individuals to gain weight despite their efforts to limit caloric intake and increase levels of physical activity. This Review discusses the role of EDCs in the obesity epidemic, the latest research on the obesogen concept, epidemiological and experimental findings on obesogens, and their modes of action. The research reviewed here provides knowledge that health scientists can use to inform their research and decision-making processes.

Childhood obesity: a (re) programming disease?

The aim of our article was to review the current literature on the effects of metabolic (re) programming on childhood obesity. PubMed/MEDLINE was the data source used to track the studies. Descriptors applied: children obesity, epigenetic, metabolic programming, exercise and nutrition. The focus was to analyze and discuss the international findings on the theme. The gathering of the papers was performed between June and August 2014. The search of articles with the descriptors used found 33.054 studies. In all, 5.709 studies were selected by crossing chosen keywords. Among these, after careful reading of the titles, 712 papers were considered potential as references. After applying inclusion/exclusion criteria, 50 studies were selected from 132 eligible abstracts. Most studies linked the development and treatment of obesity from epigenetically stimulated metabolic programming during the early stages of pregnancy and life. This review provides theoretical basis to the understanding that the programmed development of childhood obesity may be linked to early exposure to environmental factors, such as (nutrition and regular practice of exercise) and stimulus can epigenetically alter the modulation of the obesogenic metabolic behavior during pregnancy and the developmental stages of children and/or postpone the pathophysiologic disease stage to adulthood.

Transgenerational inheritance of prenatal obesogen exposure

Obesity and metabolic syndrome diseases have exploded into an epidemic of global proportions. The generally accepted cause of obesity is overconsumption of calorie-dense food and diminished physical activity (the calories in-calories out model). However, emerging evidence demonstrates that environmental factors can predispose exposed individuals to gain weight, irrespective of diet and exercise. The environmental obesogen model proposes that chemical exposure during critical stages in development can influence subsequent adipogenesis, lipid balance and obesity. Obesogens are chemicals that inappropriately stimulate adipogenesis and fat storage. Numerous obesogens have been identified in recent years and some of these have been shown to act through the peroxisome proliferator activated receptor gamma, the master regulator of adipogenesis. Others act through as yet unidentified pathways. Notably, some of these obesogens elicit transgenerational effects on a variety of health endpoints, including obesity in offspring after exposure of pregnant F0 females. Thus, prenatal exposure to xenobiotic compounds can have lasting, potentially permanent effects on the offspring of exposed animals. Transgenerational effects of chemical exposure raise the stakes in the debate about whether and how endocrine disrupting chemicals should be regulated.

The obesogenic effect of high fructose exposure during early development

Obesogens are compounds that disrupt the function and development of adipose tissue or the normal metabolism of lipids, leading to an increased risk of obesity and associated diseases. Evidence for the adverse effects of industrial and agricultural obesogens, such as tributyltin, bisphenol A and other organic pollutants is well-established. Current evidence suggests that high maternal consumption of fat promotes obesity and increased metabolic risk in offspring, but less is known about the effects of other potential nutrient obesogens. Widespread increase in dietary fructose consumption over the past 30 years is associated with chronic metabolic and endocrine disorders and alterations in feeding behaviour that promote obesity. In this Perspectives, we examine the evidence linking high intakes of fructose with altered metabolism and early obesity. We review the evidence suggesting that high fructose exposure during critical periods of development of the fetus, neonate and infant can act as an obesogen by affecting lifelong neuroendocrine function, appetite control, feeding behaviour, adipogenesis, fat distribution and metabolic systems. These changes ultimately favour the long-term development of obesity and associated metabolic risk.

Metabolic disruption in male mice due to fetal exposure to low but not high doses of bisphenol A (BPA): evidence for effects on body weight, food intake, adipocytes, leptin, adiponectin, insulin and glucose regulation

Exposure to bisphenol A (BPA) is implicated in many aspects of metabolic disease in humans and experimental animals. We fed pregnant CD-1 mice BPA at doses ranging from 5 to 50,000μg/kg/day, spanning 10-fold below the reference dose to 10-fold above the currently predicted no adverse effect level (NOAEL). At BPA doses below the NOAEL that resulted in average unconjugated BPA between 2 and 200pg/ml in fetal serum (AUC0-24h), we observed significant effects in adult male offspring: an age-related change in food intake, an increase in body weight and liver weight, abdominal adipocyte mass, number and volume, and in serum leptin and insulin, but a decrease in serum adiponectin and in glucose tolerance. For most of these outcomes non-monotonic dose-response relationships were observed; the highest BPA dose did not produce a significant effect for any outcome. A 0.1-μg/kg/day dose of DES resulted in some but not all low-dose BPA outcomes.

Obesogens, stem cells and the developmental programming of obesity

Obesogens are chemicals that directly or indirectly lead to increased fat accumulation and obesity. Obesogens have the potential to disrupt multiple metabolic signalling pathways in the developing organism that can result in permanent changes in adult physiology. Prenatal or perinatal exposure to obesogenic endocrine disrupting chemicals has been shown to predispose an organism to store more fat from the beginning of its life. For example, excess oestrogen or cortisol exposure in the womb or during early life resulted in an increased susceptibility to obesity and metabolic syndrome later in life. This review focuses on the effects of environmental chemicals, such as the model obesogen, tributyltin (TBT), on the development of obesity. We discuss evidence linking the obesogenic effects of TBT with its ability to activate the peroxisome proliferator-activated receptor gamma and stimulate adipogenesis. We also discuss how TBT and other environmental obesogens may lead to epigenetic changes that predispose exposed individuals to subsequent weight gain and obesity. This suggests that humans, who have been exposed to obesogenic chemicals during sensitive windows of development, might be pre-programmed to store increased amounts of fat, resulting in a lifelong struggle to maintain a healthy weight and exacerbating the deleterious effects of poor diet and inadequate exercise.

The estrogenic endocrine disrupting chemical bisphenol A (BPA) and obesity

There is increasing experimental and epidemiological evidence that fetal programming of genetic systems is a contributing factor in the recent increase in adult obesity and other components of metabolic syndrome. In particular, there is evidence that epigenetic changes associated with the use of manmade chemicals may interact with other factors that influence fetal and postnatal growth in contributing to the current obesity epidemic. The focus of this review is on the developmental effects of estrogenic endocrine disrupting chemicals (EDCs), and more specifically on effects of exposure to the estrogenic EDC bisphenol A (BPA), on adipocytes and their function, and the ultimate impact on adult obesity; BPA exposure also results in impaired reproductive capacity. We discuss the interaction of EDCs with other factors that impact growth during fetal and neonatal life, such as placental blood flow and nutrient transport to fetuses, and how these influence fetal growth and abnormalities in homeostatic control systems required to maintain normal body weight throughout life.

Endocrine disrupting chemicals and the developmental programming of adipogenesis and obesity

Obesity and related disorders are a burgeoning public health epidemic, particularly in the U.S. Currently 34% of the U.S. population is clinically obese (BMI > 30) and 68% are overweight (BMI > 25), more than double the worldwide average and 10-fold higher than Japan and South Korea. Obesity occurs when energy intake exceeds energy expenditure; however, individuals vary widely in their propensity to gain weight and accrue fat mass, even at identical levels of excess caloric input. Clinical, epidemiological, and biological studies show that obesity is largely programmed during early life, including the intrauterine period. The environmental obesogen hypothesis holds that prenatal or early life exposure to certain endocrine disrupting chemicals can predispose exposed individuals to increased fat mass and obesity. Obesogen exposure can alter the epigenome of multipotent stromal stem cells, biasing them toward the adipocyte lineage at the expense of bone. Hence, humans exposed to obesogens during early life might have an altered stem cell compartment, which is preprogrammed toward an adipogenic fate. This results in a higher steady state number of adipocytes and potentially a lifelong struggle to maintain a healthy weight, which can be exacerbated by societal influences that promote poor diet and inadequate exercise. This review focuses on the developmental origins of the adipocyte, the relationship between adipocyte number and obesity, and how obesogenic chemicals may interfere with the highly efficient homeostatic mechanisms regulating adipocyte number and energy balance.