4-Hexylphenol influences adipogenic differentiation and hepatic lipid accumulation in vitro

Disinfection Byproducts of Haloacetaldehydes Disrupt Hepatic Lipid Metabolism and Induce Lipotoxicity in High-Fat Culture Conditions

Unhealthy lifestyles, obesity, and environmental pollutants are strongly correlated with the development of nonalcoholic fatty liver disease (NAFLD). Haloacetaldehyde-associated disinfection byproducts (HAL-DBPs) at various multiples of concentrations found in finished drinking water together with high-fat (HF) were examined to gauge their mixed effects on hepatic lipid metabolism. Using new alternative methods (NAMs), studying effects in human cells in vitro for risk assessment, we investigated the combined effects of HF and HAL-DBPs on hepatic lipid metabolism and lipotoxicity in immortalized LO-2 human hepatocytes. Coexposure of HAL-DBPs at various multiples of environmental exposure levels with HF increased the levels of triglycerides, interfered with de novo lipogenesis, enhanced fatty acid oxidation, and inhibited the secretion of very low-density lipoproteins. Lipid accumulation caused by the coexposure of HAL-DBPs and HF also resulted in more severe lipotoxicity in these cells. Our results using an in vitro NAM-based method provide novel insights into metabolic reprogramming in hepatocytes due to coexposure of HF and HAL-DBPs and strongly suggest that the risk of NAFLD in sensitive populations due to HAL-DBPs and poor lifestyle deserves further investigation both with laboratory and epidemiological tools. We also discuss how results from our studies could be used in health risk assessments for HAL-DBPs.

3-tert-Butyl-4-hydroxyanisole perturbs renal lipid metabolism in vitro by targeting androgen receptor-regulated de novo lipogenesis

The widespread usage of 3-tert-butyl-4-hydroxyanisole (3-BHA) as an anthropogenic antioxidant has caused considerable environmental contamination and frequent detection in diverse human-derived samples. 3-BHA can promote adipogenesis and impair hepatic lipid metabolism, while its effects on renal lipid homeostasis remain to be uncertain. Herein, using the human kidney 2 (HK-2) cell experiments, 3-BHA was found to cause a significant reduction in lipid accumulation of the HK-2 cells in both exposure concentration- and duration-dependent manners. Exposure to 3-BHA lowered the transcriptional expressions of sterol regulatory element-binding protein 1 (SREBP1) and acetyl-CoA carboxylase (ACC), as well as ACC activity, indicating the inhibition in the process of de novo lipogenesis in HK-2 cells. On this basis, the mechanism study suggested that the reduced glucose absorption and accelerated glycolysis were concomitantly involved. The antagonism of 3-BHA on the transactivation of androgen receptor (AR) contributed to the lowered de novo lipogenesis and the consequent intracellular lipid reduction. The metabolomics data further confirmed the imbalance of lipid homeostasis and dysregulation of de novo lipogenesis. The new findings on the impaired renal lipid metabolism induced by 3-BHA warranted proper care about the usage of this chemical as a food additive.

Studying paraben-induced estrogen receptor- and steroid hormone-related endocrine disruption effects via multi-level approaches

Increasing concerns have been raised on the health risks of parabens in the regard of their widespread applications and potential endocrine disrupting activities. In this study, four typical parabens, including methyl paraben (MeP), ethyl paraben (EtP), propyl paraben (PrP), and butyl paraben (BuP) were systematically investigated for their estrogen receptor- and steroid hormone-related endocrine disruptions using multi-level approaches. Paraben exposure promoted the proliferation of MCF-7 cells, increased the luciferase activity in MVLN cells, and induced the vitellogenin (vtg) expression in zebrafish larvae, showing the typical estrogenic effects. The in vitro protein assays further revealed that PrP and BuP could bind with two isoforms of estrogen receptors (ERs). The estrogenic activities of parabens were predicted to be positively correlated with their chemical structure complexity by using molecular docking analysis. Furthermore, the synthesis and secretion of estradiol (E2) and testosterone (T) were significantly disturbed in H295R cells and zebrafish larvae, which could be regulated by paraben-induced transcriptional disturbance in both in vitro steroidogenesis and in vivo hypothalamic-pituitary-gonadal (HPG) axis. Parabens could disturb the endocrine system by activating the ERs and disrupting the steroid hormone synthesis and secretion, suggesting their potential deleterious risks to the environment and human health.

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.

Perfluorodecanoic acid promotes adipogenesis via NLRP3 inflammasome-mediated pathway in HepG2 and 3T3-L1 cells

Perfluorodecanoic acid (PFDA) is a toxic persistent pollutant that is extensively used in food applications, such as food packaging and cookware. Emerging evidence indicates that PFDA exposure were associated with higher plasma triglyceride concentration in human. In contrast, it is unknown how PFDA might affect adipogenesis. To explore the effects and underlying mechanisms of PFDA on lipid metabolism in this study, both HepG2 cells and 3T3-L1 differentiation model were used. The results showed that PFDA promoted the cellular triglyceride accumulation and triglyceride content in concentration-dependent manners. Furthermore, PFDA activated the NLRP3 inflammasome, which is crucial for the induction of lipogenic genes expression including fatty acid synthase (FAS), hydroxymethylglutaryl coenzyme A synthase (HMGCS), and stearoyl-CoA desaturase 1 (SCD1). Additionally, PFDA-induced adipogenesis was abolished by caspase-1 inhibitor and siNLRP3 in HepG2 cells. Moreover, after PFDA treatment, the expression of SREBP1, an important regulator of lipid metabolism, was increased, as well as its target genes, and PFDA-induced SREBP1 enhanced expression can be abolished by caspase-1 inhibitor and siNLRP3 as well. Together, these results provide to understanding of the potential health implications of exposure to PFDA on lipid accumulation, and suggest that PFDA can promote adipogenesis via an NLRP3 inflammasome-mediated SREBP1 pathway.

Constructing an MCF-7 breast cancer cell-based transient transfection assay for screening RARα (Ant)agonistic activities of emerging phenolic compounds

The screening of compounds with endocrine disrupting effects has been attracting increasing attention due to the continuous release of emerging chemicals into the environment. Testing the (ant)agonistic activities of these chemicals on the retinoic acid receptor α (RARα), a vital nuclear receptor, is necessary to explain their perturbation in the endocrine system in vivo. In the present study, MCF-7 breast carcinoma cells were transiently transfected with a RARα expression vector (pEF1α-RARα-RFP) and a reporter vector containing a retinoic acid reaction element (pRARE-TA-Luc). Under optimized conditions, the performance of the newly constructed system was evaluated for its feasibility in screening the (ant)agonistic effects of emerging phenolic compounds on RARα. The results showed that this transient transfection cell model responded well to stimulation with (ant)agonists of RARα, and the EC₅₀ and IC₅₀ values were 0.87 nM and 2.67 μM for AM580 and Ro41-5253, respectively. Its application in testing several emerging phenolic compounds revealed that triclosan (TCS) and tetrabromobisphenol A (TBBPA) exerted notable RARα antagonistic activities. This newly developed bioassay based on MCF-7 is promising in identifying the agonistic or antagonistic activities of xenobiotics on RARα and has good potential for studying RARα signaling-involved toxicological effects of emerging chemicals of concern.

Obesity II: Establishing causal links between chemical exposures and obesity

Obesity is a multifactorial disease with both genetic and environmental components. The prevailing view is that obesity results from an imbalance between energy intake and expenditure caused by overeating and insufficient exercise. We describe another environmental element that can alter the balance between energy intake and energy expenditure: obesogens. Obesogens are a subset of environmental chemicals that act as endocrine disruptors affecting metabolic endpoints. The obesogen hypothesis posits that exposure to endocrine disruptors and other chemicals can alter the development and function of the adipose tissue, liver, pancreas, gastrointestinal tract, and brain, thus changing the set point for control of metabolism. Obesogens can determine how much food is needed to maintain homeostasis and thereby increase the susceptibility to obesity. The most sensitive time for obesogen action is in utero and early childhood, in part via epigenetic programming that can be transmitted to future generations. This review explores the evidence supporting the obesogen hypothesis and highlights knowledge gaps that have prevented widespread acceptance as a contributor to the obesity pandemic. Critically, the obesogen hypothesis changes the narrative from curing obesity to preventing obesity.

Impact of brominated flame retardants on lipid metabolism: An in vitro approach

Brominated flame retardants (BFRs) are chemicals employed to lower the flammability of several objects. These endocrine disruptor chemicals are lipophilic and persistent in the environment. Due to these characteristics some have been restricted or banned by the European Union, and replaced by several new chemicals, the novel BFRs (NBFRs). BFRs are widely detected in human samples, such as adipose tissue and some were linked with altered thyroid hormone levels, liver toxicity, diabetes and metabolic syndrome in humans. However, the disturbance in lipid metabolism caused by BFRs with emphases to NBFRs remains poorly understood. In this study, we used a pre-adipocyte (3T3-L1) cell line and a hepatocyte (HepG2) cell line to investigate the possible lipid metabolism disruption caused by four BFRs: hexabromobenzene (HBB), pentabromotoluene (PBT), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB) and hexabromocyclododecane (HBCD). For that purpose, proliferation and Oil Red O assays, as well as, medium fatty acids profile evaluation using Gas chromatography and RNA extraction for quantitative RT-PCR assays were performed. We detected a significant reduction in the proliferation of preadipocytes and an increased lipid accumulation during differentiation caused by HBB. This BFR also lead to a significant increased expression of IL-1β and decreased expression of PGC-1α and adiponectin. Nevertheless, PBT, TBB and HBCD show to increase lipid accumulation in hepatocytes. PBT also display a significant increase of PPARγ gene expression. Lipid accumulation in the cells can occur by diverse mechanisms depending on the BFR. These results highlight the importance of endocrine disruptor compounds in obesity etiopathogeny.