Environmental toxicants, brown adipose tissue, and potential links to obesity and metabolic disease

Low-dose tire wear chemical 6PPD-Q exposure elicit fatty liver via promoting fatty acid biosynthesis in ICR mice

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) as a major metabolite of tire wear chemical 6PPD has been demonstrated to be an emerging burden of exposure in human populations, via contamination from drinking water, air particulate matter and food sources. Whilst increasing attention has been moved toward its adverse effect, the potential hepatotoxicity of 6PPD-Q in mammals at realistic dose remains unknown. Here, the toxic effects of 6PPD-Q at environmentally relevant dose on the liver of adult mice and its underlying mechanism were investigated through an integrative approach combining transcriptomic and lipidomic analyses. We found that 6PPD-Q exposure induced excessive lipid deposition following three weeks of exposure, ultimately contributing to the pathogenesis of fatty liver disease. Mechanistically, 6PPD-Q exposure caused a remarkable increase in the contents of fatty acids within the hepatic tissue of mice by enhancing their biosynthesis, thereby facilitating lipid deposition. In summary, this study provides a new understanding on the endocrine disrupting effects of 6PPD-Q on hepatic lipid metabolism and how it may contribute to elevated risk of fatty liver disease. Our findings call for a potential public health attention on the risk assessment of 6PPD-Q, particularly towards the risk of chronic metabolic diseases.

Pollution, stress response, and obesity: A systematic review

Limited literature addresses the association between pollution, stress, and obesity, and knowledge synthesis on the associations between these three topics has yet to be made. Two reviewers independently conducted a systematic review of MEDLINE, Embase, and Web of Science Core Collection databases to identify studies dealing with the effects of semi-volatile organic compounds, pesticides, conservatives, and heavy metals on the psychosocial stress response and adiposity in humans, animals, and cells. The quality of papers and risk assessment were evaluated with ToxRTool, BEES-C instrument score, SYRCLE's risk of bias tool, and CAMARADES checklist. A protocol for the systematic review was registered on PROSPERO. Of 1869 identified references, 63 were eligible after title and abstract screening, 42 after full-text reading, and risk of bias and quality assessment. An important body of evidence shows a positive association between pollution, stress response, and obesity. Pollution stimulates the hypothalamic-pituitary-adrenal axis by activating the glucocorticoid receptor signaling and transcriptional factors responsible for adipocyte differentiation, hyperphagia, and obesity. Endocrine-disrupting chemicals also alter the Peroxisome Proliferator-activated Receptor gamma pathway to promote adipocyte hyperplasia and hypertrophy. However, these associations depend on sex, age, and pollutant type. Our findings evidence that pollution promotes stress, leading to obesity.

Monitoring Mouse Surface Temperature During Stress with a Thermal Camera: A Low-Cost Infrared Videography System for Evaluating Murine Metabolism

Energy is required for life, and organisms obtain their energy from fuel sources to enable both anabolic and catabolic processes. Some of this energy is radiated as heat, which can be quantified as a measure of metabolic rate. In some cases, environmental toxicants can alter metabolic energy in undesirable ways, and characterization of new pharmaceuticals can determine the efficacy of desirable metabolic rate manipulation or identify off-target adverse effects. Current methods to directly measure heat production in laboratory mice are expensive, can be laborious, and make it challenging to monitor animals in ways that are multiplexed, robust, and non-invasive. We present a set of protocols for assembling and deploying a simple, low-cost thermal camera to monitor and record thermogenic activity, modified from prior work. Parts used to build this system currently cost approximately $150 USD and, when assembled, can record mouse temperatures as well as ambient cage temperatures up to twice per second for extended periods. By using multiplexed cameras in a diurnal mouse incubator system, the thermogenic capacity of several mice can be simultaneously recorded and graphed. Exogenous agents and genotypes that alter metabolism can be readily identified with this technology. In this set of protocols, we describe the assembly of the thermal video camera device, its use, and related data capture and analysis methods. © 2025 The Author(s). Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Assembling thermal camera for thermogenic stress test Basic Protocol 2: In vivo measurement of mouse temperature under different ambient conditions.

Maternal neonicotinoid pesticide exposure impairs glucose metabolism by deteriorating brown fat thermogenesis

BACKGROUND

Neonicotinoids (NEOs) are well-designed highly selective pesticides that target nicotinic acetylcholine receptors. However, their extensive use, accumulation, and biomagnification pose significant risks to humans. Increasing evidence has suggested that NEOs may affect glucose homeostasis, but little research has linked NEOs exposure to gestational diabetes mellitus (GDM), which is the most common disease in pregnancy. We here aimed to investigate the association between NEOs exposure and GDM occurrence.

METHODS

100 pregnant women who completed a 75 g oral glucose tolerance test (OGTT) at 24-28 weeks of gestation were enrolled. Urinary concentrations of seven widely used NEOs were quantified using ultra-high performance liquid chromatography multiple reaction monitoring mass spectrometry (UHPLC-MRM-MS/MS). Correlation analysis revealed the associations between NEOs concentrations and glucose homeostasis parameters. The toxic effects of thiamethoxam (TMX) and clothianidin (CLO) were assessed using pregnant mice, and the potential mechanism in impairing glucose disposition regarding brown adipose tissue (BAT) thermogenesis has been elucidated.

RESULTS

Among the 100 urine samples, 88 % were contaminated by NEOs with concentrations ranging from 2.50 to 491.34 nmol/L. TMX and CLO were the most frequently detected NEOs, highly detected in women with GDM. Moreover, we found statistically significant associations between TMX concentrations and 1hBG, and 2hBG. Exposure to mixed NEOs during gestation resulted in elevated glucose levels and impaired insulin sensitivity in normal pregnant and GDM mice models. In addition, we found the metabolic disorders induced by NEOs were linked to the deterioration of BAT thermogenesis in vivo.

CONCLUSION

In general, we demonstrated that prenatal exposures to NEOs were associated with an increased risk of GDM by deteriorating the thermogenic capacity of BAT.

Carvacrol acetate activated Nrf2 modulates mitophagy for the treatment of neurocyte oxidative stress induced by chlorpyrifos

This study explored the protective effect and potential mechanism of carvacrol acetate (CAA) on the oxidation of chlorpyrifos (CPF). A model of oxidative stimulus damage was established in Sprague-Dawley rats by subcutaneous injection of the CPF poison. PC12 cells were used to construct an oxidative injury model using CPF, and the protective effects and mechanism of action of CAA against CPF-induced oxidative damage were explored in vitro. The key role of Nuclear factor erythroid-2-related factor 2 (Nrf2) in alleviating CPF-induced damage via CAA was further confirmed by administering Nrf2 inhibitors to PC12 cells. Administration of CAA significantly enhanced the locomotor ability of the rats, alleviated neuronal pathological alterations, and increased the number of Nissl bodies, while increasing autophagic bodies. In vitro, CAA promoted cell survival and augmented the mitochondrial membrane potential. It decreased both intra- and extracellular levels of reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), while markedly elevating mitochondrial DNA (mtDNA) copy number. Moreover, PC12 cells treated with Nrf2 inhibitors failed to exhibit any improvement in survival rate when treated with CAA after a toxic insult. Furthermore, ROS and MDA levels were not significantly reduced, SOD enzyme activity did not increase, and mitochondrial membrane potential and mtDNA copy number did not improve. Western blot analysis showed that the expression of Tfam, Beclin1, and LC3II/LC3I proteins in the CAA group decreased significantly after Nrf2 inhibition. These findings suggest that CAA modulates mitochondrial function and autophagy by regulating the Nrf2 signalling pathway to mitigate the toxic damage. Finally, the effect of the autophagy inhibitor, 3-MA, on PC12 cells suggests that CAA promotes mitophagy by participating in the Nrf2 pathway, thereby preventing CPF-induced oxidative stress damage.

Adaptation of Brown Adipose Tissue in Response to Chronic Exposure to the Environmental Pollutant 1,1-Dichloro-2,2-bis(p-chlorophenyl) Ethylene (DDE) and/or a High-Fat Diet in Male Wistar Rats

Brown adipose tissue (BAT) participates in thermogenesis and energy homeostasis. Studies on factors capable of influencing BAT function, such as a high-fat diet (HFD) or exposure to environmental pollutants, could be useful for finding metabolic targets for maintaining energy homeostasis. We evaluated the effect of chronic exposure to dichlorodiphenyldichloroethylene (DDE), the major metabolite of dichlorodiphenyltrichloroethane (DDT), and/or a HFD on BAT morphology, mitochondrial mass, dynamics, and oxidative stress in rats. To this end, male Wistar rats were treated for 4 weeks with a standard diet, or a HFD alone, or together with DDE. An increase in paucilocular adipocytes and the lipid droplet size were observed in HFD-treated rats, which was associated with a reduction in mitochondrial mass and in mitochondrial fragmentation, as well as with increased oxidative stress and upregulation of the superoxide dismutase-2. DDE administration mimics most of the effects induced by a HFD on BAT, and it aggravates the increase in the lipid droplet size when administered together with a HFD. Considering the known role of oxidative stress in altering BAT functionality, it could underlie the ability of both DDE and a HFD to induce similar metabolic adaptations in BAT, leading to reduced tissue thermogenesis, which can result in a predisposition to the onset of energy homeostasis disorders.

Weighing in on the role of brown adipose tissue for treatment of obesity

Brown adipose tissue (BAT) activation is an emerging target for obesity treatments due to its thermogenic properties stemming from its ability to shuttle energy through uncoupling protein 1 (Ucp1). Recent rodent studies show how BAT and white adipose tissue (WAT) activity can be modulated to increase the expression of thermogenic proteins. Consequently, these alterations enable organisms to endure cold-temperatures and elevate energy expenditure, thereby promoting weight loss. In humans, BAT is less abundant in obese subjects and impacts of thermogenesis are less pronounced, bringing into question whether energy expending properties of BAT seen in rodents can be translated to human models. Our review will discuss pharmacological, hormonal, bioactive, sex-specific and environmental activators and inhibitors of BAT to determine the potential for BAT to act as a therapeutic strategy. We aim to address the feasibility of utilizing BAT modulators for weight reduction in obese individuals, as recent studies suggest that BAT's contributions to energy expenditure along with Ucp1-dependent and -independent pathways may or may not rectify energy imbalance characteristic of obesity.