Alteration of cellular lipids and lipid metabolism markers in RTL-W1 cells exposed to model endocrine disrupters

The Role of Endocrine Disruptors Bisphenols and Phthalates in Obesity: Current Evidence, Perspectives and Controversies

Excess body weight constitutes one of the major health challenges for societies and healthcare systems worldwide. Besides the type of diet, calorie intake and the lack of physical exercise, recent data have highlighted a possible association between endocrine-disrupting chemicals (EDCs), such as bisphenol A, phthalates and their analogs, and obesity. EDCs represent a heterogeneous group of chemicals that may influence the hormonal regulation of body mass and adipose tissue morphology. Based on the available data from mechanistic, animal and epidemiological studies including meta-analyses, the weight of evidence points towards the contribution of EDCs to the development of obesity, associated disorders and obesity-related adipose tissue dysfunction by (1) impacting adipogenesis; (2) modulating epigenetic pathways during development, enhancing susceptibility to obesity; (3) influencing neuroendocrine signals responsible for appetite and satiety; (4) promoting a proinflammatory milieu in adipose tissue and inducing a state of chronic subclinical inflammation; (5) dysregulating gut microbiome and immune homeostasis; and (6) inducing dysfunction in thermogenic adipose tissue. Critical periods of exposure to obesogenic EDCs are the prenatal, neonatal, pubertal and reproductive periods. Interestingly, EDCs even at low doses may promote epigenetic transgenerational inheritance of adult obesity in subsequent generations. The aim of this review is to summarize the available evidence on the role of obesogenic EDCs, specifically BPA and phthalate plasticizers, in the development of obesity, taking into account in vitro, animal and epidemiologic studies; discuss mechanisms linking EDCs to obesity; analyze the effects of EDCs on obesity in critical chronic periods of exposure; and present interesting perspectives, challenges and preventive measures in this research area.

Application of In Vitro Models for Studying the Mechanisms Underlying the Obesogenic Action of Endocrine-Disrupting Chemicals (EDCs) as Food Contaminants-A Review

Obesogenic endocrine-disrupting chemicals (EDCs) belong to the group of environmental contaminants, which can adversely affect human health. A growing body of evidence supports that chronic exposure to EDCs can contribute to a rapid increase in obesity among adults and children, especially in wealthy industrialized countries with a high production of widely used industrial chemicals such as plasticizers (bisphenols and phthalates), parabens, flame retardants, and pesticides. The main source of human exposure to obesogenic EDCs is through diet, particularly with the consumption of contaminated food such as meat, fish, fruit, vegetables, milk, and dairy products. EDCs can promote obesity by stimulating adipo- and lipogenesis of target cells such as adipocytes and hepatocytes, disrupting glucose metabolism and insulin secretion, and impacting hormonal appetite/satiety regulation. In vitro models still play an essential role in investigating potential environmental obesogens. The review aimed to provide information on currently available two-dimensional (2D) in vitro animal and human cell models applied for studying the mechanisms of obesogenic action of various industrial chemicals such as food contaminants. The advantages and limitations of in vitro models representing the crucial endocrine tissue (adipose tissue) and organs (liver and pancreas) involved in the etiology of obesity and metabolic diseases, which are applied to evaluate the effects of obesogenic EDCs and their disruption activity, were thoroughly and critically discussed.

Dysregulation of lipid metabolism in PLHC-1 and ZFL cells exposed to tributyltin an all-trans retinoic acid

There is increasing awareness that exposure to endocrine disrupters interferes with lipid homeostasis in vertebrates, including fish. Many of these compounds exert their action by binding to nuclear receptors, such as peroxisome proliferator-activated receptors and retinoid X receptor. This work investigates the use of fish liver cells (PLHC-1 and ZFL cells) for the screening of metabolic and lipid disrupters in the aquatic environment by assessing changes in the cell's lipidome after exposure to the model compounds, tributyltin chloride and all-trans retinoic acid. Lipid extracts, analyzed by FIA-ESI (+/-) Orbitrap, evidenced the intracellular accumulation of triglycerides and diglycerides in both cell models after exposure to 100 and 200 nM tributyltin chloride for 24 h. Exposure to 1 μM all-trans retinoic acid led to a significant accumulation of triglycerides in PLHC-1 cells, while few triglycerides were accumulated in ZFL cells. Retinoic acid (cyp26b1, cyp3a65, lrata) and lipid metabolism (fasn, scd, elovl6) related genes were up-regulated by tributyltin chloride and all-trans retinoic acid, while only all-trans retinoic acid down-regulated the expression of dgat1a. The two cell models show sensitivity and responses to tributyltin chloride and all-trans retinoic acid comparable to those previously reported in mammalian cells. These results support the use of fish liver cells as alternative models for the detection of contaminants that act as lipid disrupters in the aquatic environment.

PLHC-1 topminnow liver cells: An alternative model to investigate the toxicity of plastic additives in the aquatic environment

Plasticizers are widespread environmental contaminants that have been described as obesogens in terrestrial vertebrates. However, its effects on fish lipids homeostasis are almost unknown. This work explores the use of PLHC-1 cells as an alternative model to assess the disruption of hepatic lipids by plastic additives and to gather information on the mode of action of these chemicals in fish. PLHC-1 lipid extracts were analyzed by flow injection coupled to high resolution mass spectrometry (FIA-ESI(+/-)-Orbitrap-Exactive) after 24 h exposure of the cells to the selected plasticizers: dibutyl phthalate (DBP), di-(2-ethylhexyl) phthalate (DEHP), bisphenol A (BPA), bisphenol F (BPF), and chlorinated bisphenol A diglycidyl ether (BADGE·2HCl). The analysis of the culture medium and the intracellular concentration of the chemicals revealed the highest bioconcentration of BADGE·2HCl, DBP and DEHP, which was in agreement with the strongest alteration of the cells lipidome. BADGE·2HCl induced a significant depletion of triacylglycerides (TGs), while DEHP and DBP stimulated the accumulation of TGs. Exposure to BPF induced the generation of reactive oxygen species in PLHC-1 cells and a significant depletion of phosphatidylcholine (PC)- and phosphatidylethanolamine (PE)-plasmalogens, and TGs (cell depots of polyunsaturated fatty acids). Overall, this study evidences different modes of action of plastic additives in topminnow liver cells, describes differential lipidomic signatures, and highlights the higher lipotoxicity of BADGE·2HCl and BPF compared to BPA.

Environmental exposure of northern pike to a primary wastewater effluent: Impact on the lipidomic profile and lipid metabolism

Lipids play important roles in growth, reproduction, locomotion, and migration of fish. Municipal effluents, which are complex mixtures of biological and chemical compounds including flame retardants, have been shown to alter lipid metabletabolism in environmentally and experimentally exposed fish. Down-regulation of several genes coding for fatty acid metabolism enzymes has previously been reported in male northern pike (Esox lucius) collected in the St. Lawrence River (QC, Canada) downstream of a major primary wastewater treatment plant (WWTP) point of discharge. The main objective of this study was to investigate the effects of exposure to the Montreal's WWTP effluent on the lipidomic profile (i.e., fatty acids, acylcarnitines, and phospholipids) as well as the transcription of genes related to lipid metabolism in the liver of northern pike collected upstream and downstream of this WWTP effluent. Halogenated flame retardant concentrations were also determined in pike liver and used as markers of exposure to this effluent. Greater concentrations of saturated and monounsaturated lysophosphatidylcholines (LPCs) and lower concentrations of polyunsaturated LPCs were determined in the liver of pike collected downstream of the WWTP compared to those collected upstream. Lower mRNA levels of peroxisome proliferator-activated receptor alpha (pparα), a major regulator of lipid metabolism, were also measured in pike exposed to Montreal's WWTP effluent. In addition, the relative contributions (%) of LPC 18:2 and LPC14:0, compounds used as markers of obesity and inflammation, were significantly correlated with halogenated flame retardant concentrations and fish girth. Results of the present study suggest that chronic environmental exposure to a primary WWTP effluent can modulate the transcription of genes related to lipid metabolism, and hence affect the hepatic phospholipid composition of pike from the St. Lawrence River.

Linking chemical exposure to lipid homeostasis: A municipal waste water treatment plant influent is obesogenic for zebrafish larvae

Obesity, a risk factor for the development of type-2 diabetes, hypertension, cardiovascular disease, hepatic steatosis and some cancers, has been ranked in the top 10 health risk in the world by the World Health Organization. Despite the growing body of literature evidencing an association between the obesity epidemic and specific chemical exposure across a wide range of animal taxa, very few studies assessed the effects of chemical mixtures and environmental samples on lipid homeostasis. Additionally, the mode of action of several chemicals reported to alter lipid homeostasis is still poorly understood. Aiming to fill some of these gaps, we combined an in vivo assay with the model species zebrafish (Danio rerio) to screen lipid accumulation and evaluate expression changes of key genes involved in lipid homeostasis, alongside with an in vitro transactivation assay using human and zebrafish nuclear receptors, retinoid X receptor α and peroxisome proliferator-activated receptor γ. Zebrafish larvae were exposed from 4 th day post-fertilization until the end of the experiment (day 18), to six different treatments: experimental control, solvent control, tributyltin at 100 ng/L Sn and 200 ng/L Sn (positive control), and wastewater treatment plant influent at 1.25% and 2.5%. Exposure to tributyltin and to 2.5% influent led to a significant accumulation of lipids, with white adipose tissue deposits concentrating in the perivisceral area. The highest in vitro tested influent concentration (10%) was able to significantly transactivate the human heterodimer PPARγ/RXRα, thus suggesting the presence in the influent of HsPPARγ/RXRα agonists. Our results demonstrate, for the first time, the ability of complex environmental samples from a municipal waste water treatment plant influent to induce lipid accumulation in zebrafish larvae.

Changes in expression of microRNA potentially targeting key regulators of lipid metabolism in primary gilthead sea bream hepatocytes exposed to phthalates or flame retardants

Metabolism disrupting chemicals (MDCs) belong to the group of endocrine-disrupting chemicals (EDCs) and are known to affect endocrine and metabolic functions of liver. There is growing evidence that MDCs may also act modulating the expression levels of micro ribonucleic acids (miRNAs) and thus affecting post-transcriptional expression of hundreds of target genes. Herein, we used a gilthead sea bream in vitro hepatocyte model for analyzing the effects of an exposure to phthalates (i.e. DiDP) or flame retardants (i.e.TMCP) on the expression levels of three miRNAs (i.e. MiR133, MiR29 and MiR199a) selected on the basis of their regulatory roles in signaling pathways related to lipid metabolism. Following computational identification of genes that are regulated by the selected miRNAs, we identified six miRNA targets to be tested in differential gene expression analysis. To determine whether lipid metabolism was altered we have also measured the intracellular total cholesterol and triglyceride levels. The results of our study show that DiDP/TMCP exposure leads to a general decrease in the expression profiles of each miRNA leading to a corresponding upregulation of almost all their putative targets. In addition, these findings were also associated to a corresponding increased hepatocellular lipid content. The present study thus contributes to support the importance of these small molecules in regulating MDC-induced expression of genes associated with hepatic lipid metabolism and highlights the need for more toxicological studies examining miRNAs transcriptional regulatory networks controlling metabolic alterations in fish.

Transcriptional effects of phospholipid fatty acid profile on rainbow trout liver cells exposed to methylmercury

Lipids, and their constitutive fatty acids, are key nutrients for fish health as they provide energy, maintain cell structure, are precursors of signalling molecules and act as nuclear receptor ligands. These specific roles may be of crucial importance in a context of exposure to pollutants. We recently showed that the fatty acid profile of rainbow trout liver cell phospholipids modulates sensitivity to an acute methylmercury challenge. In order to investigate mechanisms of effects, we herein tested whether specific polyunsaturated fatty acids (PUFAs) may protect cells from methylmercury through decreasing intracellular mercury accumulation and/or enhancing cellular defences (e.g. via modulation of gene expression patterns). We also investigated the inverse relationship and assessed the impact of methylmercury on cellular fatty acid metabolism. To do so, the fatty acid composition of rainbow trout liver cell phospholipids was first modified by incubating them in a medium enriched in a specific PUFA from either the n-3 family (alpha-linolenic acid, ALA; eicosapentaenoic acid, EPA) or the n-6 family (linoleic acid, LA; arachidonic acid, AA). Cells were then exposed to methylmercury (0.15 or 0.50 μM) for 24 h and sampled thereafter for assessing phospholipid fatty acid profile, intracellular total mercury burden, and expression pattern of genes involved in fatty acid metabolism, synthesis of PUFA-derived signalling molecules and stress response. We observed that cells incorporated the given PUFA and some biotransformation products in their phospholipids. Methylmercury had few impacts on this cellular phospholipid composition. None of the PUFA enrichments affected the cellular mercury burden, suggesting that the previously observed cytoprotection conferred by ALA and EPA was not linked to a global decrease in cellular accumulation of mercury. Fatty acid enrichments and methylmercury exposure both modulated gene expression patterns. Genes involved in the synthesis of PUFA-derived signalling molecules, in stress response and the orphan cytochrome P450 20A1 were identified as possible sites of interaction between fatty acids and methylmercury in rainbow trout liver cells.

Di-2-ethylhexyl phthalate (DEHP) exposure disturbs lipid metabolism in juvenile yellow catfish Tachysurus fulvidraco

This study was conducted to determine the mechanism by which di-2-ethylhexyl phthalate (DEHP) exposure influences lipid metabolism of juvenile yellow catfish Tachysurus fulvidraco. Fish were exposed to three DEHP concentrations (0, 0·1 and 0·5 mg l^-1 DEHP) for 8 weeks. Fatty acid synthase (FAS) activity significantly decreased with increasing DEHP concentrations, the highest value was in the Tween control group, whereas the lowest activities of carnitine palmitoyltransferase (CPT) and lipoprotein lipase (LPL) were in this group. The messenger (m)RNA levels of 6-phospho-gluconate dehydrogenase (6PGD), FAS and acetyl-CoA carboxylase a (ACCa) significantly increased with increasing DEHP concentration, the highest values were in the 0·5 mg l^-1 DEHP group. The mRNA level of peroxisome proliferator-activated receptor γ (PPARγ) was lower in Tween control than in fish exposed to 0·1 and 0·5 mg l^-1 DEHP. The highest mRNA level of ACCb was in the 0·1 mg l^-1 DEHP group. These results indicate that DEHP exposure can disturb lipid metabolism at the enzymatic and mRNA levels in Pelteobagrus fulvidraco.

Obesogens in the aquatic environment: an evolutionary and toxicological perspective

The rise of obesity in humans is a major health concern of our times, affecting an increasing proportion of the population worldwide. It is now evident that this phenomenon is not only associated with the lack of exercise and a balanced diet, but also due to environmental factors, such as exposure to environmental chemicals that interfere with lipid homeostasis. These chemicals, also known as obesogens, are present in a wide range of products of our daily life, such as cosmetics, paints, plastics, food cans and pesticide-treated food, among others. A growing body of evidences indicates that their action is not limited to mammals. Obesogens also end up in the aquatic environment, potentially affecting its ecosystems. In fact, reports show that some environmental chemicals are able to alter lipid homeostasis, impacting weight, lipid profile, signaling pathways and/or protein activity, of several taxa of aquatic animals. Such perturbations may give rise to physiological disorders and disease. Although largely unexplored from a comparative perspective, the key molecular components implicated in lipid homeostasis have likely appeared early in animal evolution. Therefore, it is not surprising that the obesogen effects are found in other animal groups beyond mammals. Collectively, data indicates that suspected obesogens impact lipid metabolism across phyla that have diverged over 600 million years ago. Thus, a consistent link between environmental chemical exposure and the obesity epidemic has emerged. This review aims to summarize the available information on the effects of putative obesogens in aquatic organisms, considering the similarities and differences of lipid homeostasis pathways among metazoans, thus contributing to a better understanding of the etiology of obesity in human populations. Finally, we identify the knowledge gaps in this field and we set future research priorities.

Tributyltin and triphenyltin exposure promotes in vitro adipogenic differentiation but alters the adipocyte phenotype in rainbow trout

Numerous environmental pollutants have been identified as potential obesogenic compounds affecting endocrine signaling and lipid homeostasis. Among them, well-known organotins such as tributyltin (TBT) and triphenyltin (TPT), can be found in significant concentrations in aquatic environments. The aim of the present study was to investigate in vitro the effects of TBT and TPT on the development and lipid metabolism of rainbow trout (Onchorynchus mykiss) primary cultured adipocytes. Results showed that TBT and TPT induced lipid accumulation and slightly enhanced peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT enhancer binding protein alpha (C/EBPα) protein expression when compared to a control, both in the presence or absence of lipid mixture. However, the effects were higher when combined with lipid, and in the absence of it, the organotins did not cause complete mature adipocyte morphology. Regarding gene expression analyses, exposure to TBT and TPT caused an increase in fatty acid synthase (fasn) mRNA levels confirming the pro-adipogenic properties of these compounds. In addition, when added together with lipid, TBT and TPT significantly increased cebpa, tumor necrosis factor alpha (tnfa) and ATP-binding cassette transporter 1 (abca1) mRNA levels suggesting a synergistic effect. Overall, our data highlighted that TBT and TPT activate adipocyte differentiation in rainbow trout supporting an obesogenic role for these compounds, although by themselves they are not able to induce complete adipocyte development and maturation suggesting that these adipocytes might not be properly functional.

Utilization of Mytilus digestive gland cells for the in vitro screening of potential metabolic disruptors in aquatic invertebrates

In vertebrate systems, many endocrine disruptors (EDs) can also interfere with energy and lipid metabolism, thus acting as metabolic disruptors. At the cellular level, these effects are mainly mediated by interactions with nuclear receptors/transcription factors, leading to the modulation of genes involved in lipid homeostasis, as well as by rapid, receptor-independent pathways. Several potential metabolic disruptors are found in aquatic environments. In fish, different EDs have been shown to affect hepatic lipid homeostasis both in vivo and in vitro. However, little information is available in aquatic invertebrates due to our poor knowledge of the regulatory pathways of lipid metabolism. In this work, primary cell cultures from the digestive gland of the bivalve Mytilus galloprovincialis were utilized to investigate the effects of model EDs (bisphenol A (BPA) and perfluorooctane sulphonate (PFOS)) on lipid homeostasis. Both compounds (at 24 and 3h of exposure) increased intracellular lipid and tryglyceride-TAG content, with strongest effects of PFOS at 10^-7M. Acyl-CoA oxidase activity was unaffected, whereas some changes in the activity of glycolytic, antioxidant/biotransformation enzymes were observed; however, no clear relationship was found with lipid accumulation. Evaluation of mitochondrial membrane potential Δψm and determination of extracellular TAG content indicate that PFOS interferes with mitochondrial function and lipid secretion, whereas BPA mainly affects lipid secretion. Experiments with specific inhibitors showed that activation of PI-3 kinase and extracellularly regulated mitogen-activated protein kinase (ERK MAPK) plays a key role in mediating lipid accumulation. Mussel digestive gland cells represent a simple in vitro model for screening the metabolic effects of EDs in marine invertebrates.

Digestive enzymatic patterns as possible biomarkers of endocrine disruption in the red mullet (Mullus barbatus): A preliminary investigation

During two seasonal trawl surveys (April and October, 2012), red mullet specimens were caught from two sites of the northern Sicilian coast (Western Mediterranean), characterized by different degrees of pollution, to assess whether their digestive enzymes could be cost-effective diagnostic tools for endocrine disruption. Pepsin, chymotrypsin, carboxypeptidases A and B, amylase and lipase were measured in the digestive tract of each fish. During both samplings, significant differences in the digestive enzymatic patterns of fish collected from the two sites were found. In April, pepsin and lipase contents were significantly lower in fish from the most impacted site than in those from the reference site. In October, the enzymatic patterns showed trends different from spring, with controversial results for carboxypeptidases A and B and amylase. Pepsin and lipase patterns suggest a detrimental effect played by organic pollutants and the use of these enzymes as possible biomarkers of exposure to endocrine disruptors.

Micromanaging metabolism-a role for miRNAs in teleost energy metabolism

MicroRNAs (miRNAs) are small, non-protein coding RNA sequences, which are found in most eukaryotes. Since their initial discovery, miRNAs have emerged as important regulators of many biological processes. One of the most important processes profoundly regulated by miRNAs is energy metabolism. Traditionally, metabolic functions of miRNAs have been studied in genome-sequenced mammalian organisms, especially the mouse model. However, partially driven by commercial interest in aquaculture, increasingly feasible large-scale molecular techniques have resulted in the characterization of miRNA repertoires, and importantly, several genome sequences of several (commercially important) teleost species, which also hold important roles as research models in the comparative physiology of energy metabolism. This review aims to introduce the recent advances in miRNA research in teleost fish and to describe the current knowledge of miRNA function in teleost energy metabolism. The most pressing research needs and questions to determine metabolic roles of miRNAs in teleost models are presented, as well as applicable technical approaches and current bottlenecks. Rainbow trout, which possess the advantages of newly available molecular tools and a long history as comparative research model in teleost energy metabolism, are discussed as a promising research model to address these questions.