Effects of legacy and emerging per- and polyfluoroalkyl substances on PPARα/β/γ regulation and osteogenic/adipogenic differentiation

Transcriptomics-based analysis reveals hexafluoropropylene oxide trimer acid (HFPO-TA) induced kidney damage and lipid metabolism disorders in SD rats

Hexafluoropropylene oxide trimer acid (HFPO-TA) is an emerging environmental pollutant that can accumulate in air and surface water. Currently, it has been widely used in fluoropolymer industry, which could cause serious environmental pollution. Due to the high bioaccumulation, the accumulation of pollutants may have an adverse effect on the normal physiological function of the kidneys. However, the toxic effects of HFPO-TA on the kidney are unknown. In this study, we investigated the toxic effects of HFPO-TA exposure on the rat kidney and its mechanism of action. Male SD rats were divided into 4 groups: control group (Ctrl group), L group (0.125 mg/kg/d), M group (0.5 mg/kg/d) and H group (2 mg/kg/d). After 14 consecutive days of gavage, periodic acid‑silver methenamine (PASM) and hematoxylin-eosin (HE) staining were used to examine the structure of the kidneys. We also used transcriptome sequencing (RNA-seq) to identify differentially expressed genes (DEGs) in the testes of rats in both the control and high dose groups. Besides, expression of key proteins was analyzed by immunohistochemistry. The results indicated that HFPO-TA can lead to injured renal capsule, change glomerular shape and have a significant impact on the protein expression levels of AQP2, p-AQP2 and PPARα. Additionally, the level of total cholesterol (TC) was obviously decreased after HFPO-TA exposure. RNA-seq analysis showed that HFPO-TA primarily affected peroxisome proliferator-activated receptor (PPAR) signaling pathway that is associated with lipid metabolism and cyclic adenosine monophosphate (cAMP) signaling pathway. In summary, exposure to HFPO-TA can lead to kidney damage and lipid metabolism disorders.

Prenatal exposure to perfluoroalkyl and polyfluoroalkyl substances and childhood bone mineral density: A prospective birth cohort study

BACKGROUND AND AIM

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) have demonstrated potential toxicity in skeletal development. However, the relationship between prenatal PFAS exposure and offspring bone health remains unclear in epidemiological studies. Therefore, we aim to investigate whether prenatal exposure to PFAS is associated with bone mineral density (BMD) in offspring.

METHOD

This study population included 182 mother-child pairs in the Shanghai Obesity and Allergy Cohort, enrolled during 2012-2013. 10 PFAS were measured by liquid chromatography-mass spectrometry (LC-MS) in cord plasma. The child's spinal BMD was measured using a dual-energy X-ray absorptiometry (DXA) scanner at the age of 8. Multivariable linear regression models were used to estimate the associations between individual PFAS concentrations (as a continuous variable or categorized into quartiles) and child BMD. Bayesian kernel machine regression (BKMR) was employed to explore the joint effects of PFAS mixtures on BMD.

RESULTS

Among the 10 PFAS, 8 of them had a detection rate >90% and were included in the subsequent analysis. We observed no significant associations between individual PFAS (as a continuous variable) and spinal BMD in 8-year-old children using the multivariable linear regression model. When treated as quartile categories, the second and fourth quartiles of perfluorobutane sulfonate (PFBS) was associated with higher BMD in the first lumbar vertebra, compared with the lowest quartile. BKMR analysis revealed no association between the PFAS mixture and child BMD.

CONCLUSION

We observed no associations of prenatal PFAS exposure with child BMD at 8 years of age. Given the inconsistent epidemiological evidence, further research is needed to confirm these findings from other studies or elucidate the potentially toxic effects of PFAS on bone.

Triclosan-loaded aged microplastics exacerbate oxidative stress and neurotoxicity in Xenopus tropicalis tadpoles via increased bioaccumulation

Microplastics and chlorine-containing triclosan (TCS) are widespread in aquatic environments and may pose health risks to organisms. However, studies on the combined toxicity of aged microplastics and TCS are limited. To investigate the toxic effects and potential mechanisms associated with co-exposure to TCS adsorbed on aged polyethylene microplastics (aPE-MPs) at environmentally relevant concentrations, a 7-day chronic exposure experiment was conducted using Xenopus tropicalis tadpoles. The results showed that the overall particle size of aPE-MPs decreased after 30 days of UV aging, whereas the increase in specific surface area improved the adsorption capacity of aPE-MPs for TCS, resulting in the bioaccumulation of TCS under dual-exposure conditions in the order of aPE-TCS > PE-TCS > TCS. Co-exposure to aPE-MPs and TCS exacerbated oxidative stress and neurotoxicity to a greater extent than a single exposure. Significant upregulation of pro-symptomatic factors (IL-β and IL-6) and antioxidant enzyme activities (SOD and CAT) indicated that the aPE-TCS combination caused more severe oxidative stress and inflammation. Molecular docking revealed the molecular mechanism of the direct interaction between TCS and SOD, CAT, and AChE proteins, which explains why aPE-MPs promote the bioaccumulation of TCS, causing increased toxicity upon combined exposure. These results emphasize the need to be aware of the combined toxicity caused by the increased ability of aged microplastics to carry contaminants.

Maternal F-53B exposure during pregnancy and lactation affects bone growth and development in male offspring

6:2 Chlorinated polyfluoroalkyl ether sulfonate (F-53B) is a new type of perfluorinated and polyfluoroalkyl substance (PFAS) that is used extensively in industry and manufacturing. F-53B causes damage to multiple mammalian organs. However, the impacts of F-53B on bone are unknown. Maternal exposure to F-53B is of particular concern because of the vulnerability of the developing fetus and newborn to contaminants from the mother. The goal of this study was to examine the impacts of maternal F-53B exposure on bone growth and development in offspring and to explore its underlying mechanisms. Herein, C57BL/6 J mice were given free access to deionized water containing 0, 0.57, or 5.7 mg/L F-53B during pregnancy and lactation. F-53B exposure resulted in impaired liver function, decreased IGF-1 secretion, dysregulation of bone metabolism and disruption of the dynamic balance between osteoblasts and osteoclasts in male offspring. F-53B inhibits longitudinal bone growth and development and causes osteoporosis in male offspring. F-53B may affect the growth and development of offspring bone via the IGF-1/OPG/RANKL/CTSK signaling pathway. This study provides new insights for the study of short stature and bone injury caused by F-53B.

Emerging perfluoroalkyl substances retard skeletal growth by accelerating osteoblasts senescence via ferroptosis

Due to the persistent nature and significant negative impacts of perfluorooctanoic acid (PFOA) on human health and other organisms, the emergence of new PFOA alternatives, such as perfluoro (2-methyl-3-oxhexanoic) acid (GenX) and perfluoro-3,6,9-trioxyundecanoic acid (PFO3TDA), have drawn significant attention. However, the toxic effects of PFOA and its substitutes on bones remain limited. In this study, we administered different concentrations of PFOA, GenX, and PFO3TDA via gavage to 3-week-old male BALB/C mice for four weeks. X-ray and micro-CT scans revealed shortening of the femur and tibia and significant reduction in bone density. Additionally, PFOA, GenX, and PFO3TDA promoted osteoblast senescence and impaired osteogenic capabilities. This was characterized by a decrease in the expression of osteogenesis-related genes (OCN, ALP, Runx2, etc.) and an increase in the expression of aging and inflammation-related factors (p16INK4a, P21, MMP3, etc). Furthermore, RNA sequencing revealed activation of the ferroptosis pathway in PFOA-treated osteoblasts, characterized by notable lipid peroxidation and excessive iron accumulation. Finally, by inhibiting the ferroptosis pathway with ferrostatin-1 (Fer-1), we effectively alleviated the senescence of MC3T3-E1 cells treated with PFOA, GenX, and PFO3TDA, and improved their osteogenic capabilities. Therefore, our study provides a new therapeutic insight into the impact of PFOA and its substitutes on bone growth and development.

Persistent metabolic toxicities following developmental exposure to hexafluoropropylene oxide trimer acid (HFPO-TA): Roles of peroxisome proliferator activated receptor gamma

BACKGROUND

Hexafluoropropylene oxide trimer acid (HFPO-TA), a perfluorooctanoic acid (PFOA) substitute, exhibited strong affinity and capability to activate peroxisome proliferator activated receptor gamma (PPARγ), a lipid metabolism regulator, suggesting potential to induce metabolic toxicities.

METHODS

Fertile chicken eggs were exposed to 0, 0.5, 1 or 2 mg/kg (egg weight) HFPO-TA and incubated until hatch. Serum from 0- and 3- month-old chickens were subjected to liquid chromatography ultra-high resolution mass spectrometry for HFPO-TA concentration, while liver, pancreas and adipose tissue samples were collected for histopathological assessments. In ovo PPARγ reporter and silencing system were established with lentivirus microinjection. qRT-PCR and immunohistochemistry were utilized to evaluate the expression levels of PPARγ downstream genes.

RESULTS

In 3-month-old animals developmentally exposed to HFPO-TA, adipose tissue hyperplasia, hepatic steatosis, pancreas islet hypertrophy and elevated serum free fatty acid / insulin levels were observed. Results of reporter assay and qRT-PCR indicated HFPO-TA-mediated PPARγ transactivation in chicken embryo. Silencing of PPARγ alleviated HFPO-TA-induced changes, while PPARγ agonist rosiglitazone mimicked HFPO-TA-induced effects. qRT-PCR and immunohistochemistry revealed that FASN and GPD1 were upregulated following developmental exposure to HFPO-TA in 3-month-old animals.

CONCLUSIONS

Developmental exposure to HFPO-TA induced persistent metabolic toxicities in chickens, in which PPARγ played a central role.

Comparative steroidogenic effects of hexafluoropropylene oxide trimer acid (HFPO-TA) and perfluorooctanoic acid (PFOA): Regulation of histone modifications

As a widely used alternative to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been detected in the environment and humans; however, little is known regarding its male reproductive toxicity. To compare the effects of HFPO-TA on steroid hormone synthesis with PFOA, we exposed Leydig cells (MLTC-1) to non-lethal doses (0.1, 1, and 10 μM) of PFOA and HFPO-TA for 48 h. It was found that the levels of steroid hormones, 17α-hydroxyprogesterone (OHP), androstenedione (ASD), and testosterone (T) were significantly increased in 1 and 10 μM of PFOA and HFPO-TA groups, with greater elevation being observed in the HFPO-TA groups than in the PFOA groups at 10 μM. We further showed that the two rate-limiting steroidogenic genes (Star and Cyp11a1) were up-regulated, while Hsd3b, Cyp17a1, and Hsd17b were down-regulated or unchanged after PFOA/HFPO-TA exposure. Moreover, PFOA exposure significantly up-regulated histone H3K4me1/3 and H3K9me1, while down-regulated H3K4me2 and H3K9me2/3 levels. By contrast, H3K4me2/3 and H3K9me2/3 were enhanced, while H3K4me1 and H3K9me1 were repressed after HFPO-TA treatment. It was further confirmed that H3K4me1/3 were increased and H3K9me2 was decreased in Star and Cyp11a1 promoters by PFOA, while HFPO-TA increased H3K4me2/3 and decreased H3K9me1 in the two gene promoters. Therefore, we propose that low levels of PFOA/HFPO-TA enhance the expression of Star and Cyp11a1 by regulating H3K4 and H3K9 methylation, thus stimulating the production of steroid hormones in MLTC-1 cells. Collectively, HFPO-TA exhibits stronger effects on steroidogenesis compared to PFOA, which may be ascribed to the distinct regulation of histone modifications. These data suggest that HFPO-TA does not appear to be a safer alternative to PFOA on the aspect of male reproductive toxicity.

Toxicity removal from contaminated water by constructed wetlands assessed using multiple biomarkers in human stem cell assays

Constructed wetlands (CWs) have been developed rapidly as a sustainable water treatment technique. However, the capability of CWs for remediating the contaminated water based on toxicity assessment remains largely unknown. Four surface flow CWs and two integrated surface-subsurface flow CWs, from five cities in central and eastern region of China were evaluated, concerning the adverse effects of effluents and the toxicity reduction efficiency. Human bone marrow mesenchymal stem cells (hBMSCs) were employed as a human relevant in vitro model. The influent extractions caused cytotoxicity in a dose-dependent manner. The non-cytotoxic dilutions of the influents enhanced the genotoxicity marker γ-H2AX and reactive oxygen species levels. In addition, the influent repressed the osteogenic and neurogenic differentiation, and stimulated the adipogenic differentiation. Cytotoxicity of the contaminated water was reduced by 54 %-86 % after treatment with CWs. CWs were effective to remove part of the sub-lethal effects, with lower reduction than cytotoxicity. The integrated biomarker response (IBR) value of the effluents from the six CWs is lower than that of four secondary and one tertiary wastewater treatment plants. The IBR of the six CWs influents were in the range of 8.6-10.6, with a reduction of 15-50 % after the pollution restoration in CWs. The two integrated surface-subsurface flow CWs achieved higher IBR removal than the four surface flow CWs, possibly due to improved treatment effects by the combined systems. Cytotoxic and genotoxic effects of polar fractions in the CW effluents were stronger than the medium-polar and the non-polar fractions. Besides, PPARγ agonists present in the effluents played crucial roles and ERα agonists may make modest contributions. The present study enhances understanding of the role of CWs in achieving safe wastewater reclamation and provides evidence for further improving toxicity reduction in CWs performance.

Hepatotoxicity and lipid metabolism disorders of 8:2 polyfluoroalkyl phosphate diester in zebrafish: In vivo and in silico evidence

8:2 polyfluoroalkyl phosphate diester (8:2 diPAP) has been shown to accumulate in the liver, but whether it induces hepatotoxicity and lipid metabolism disorders remains largely unknown. In this study, zebrafish embryos were exposed to 8:2 diPAP for 7 d. Hepatocellular hypertrophy and karyolysis were noted after exposure to 0.5 ng/L 8:2 diPAP, suggesting suppressed liver development. Compared to the water control, 8:2 diPAP led to significantly higher triglyceride and total cholesterol levels, but markedly lower levels of low-density lipoprotein, implying disturbed lipid homeostasis. The levels of two peroxisome proliferator activated receptor (PPAR) subtypes (pparα and pparγ) involved in hepatotoxicity and lipid metabolism were significantly upregulated by 8:2 diPAP, consistent with their overexpression as determined by immunohistochemistry. In silico results showed that 8:2 diPAP formed hydrogen bonds with PPARα and PPARγ. Among seven machine learning models, Adaptive Boosting performed the best in predicting the binding affinities of PPARα and PPARγ on the test set. The predicted binding affinity of 8:2 diPAP to PPARα (7.12) was higher than that to PPARγ (6.97) by Adaptive Boosting, which matched well with the experimental results. Our results revealed PPAR - mediated adverse effects of 8:2 diPAP on the liver and lipid metabolism of zebrafish larvae.

A structural basis for the activation of peroxisome proliferator-activated receptor gamma (PPARγ) by perfluorooctanoic acid (PFOA)

Perfluorooctanoic acid (PFOA) is a widespread environmental pollutant of the perfluoroalkyl substance (PFAS) class that is extremely resistant to environmental and metabolic degradation, leading to bioaccumulation. PFOA exposure has been linked to many health effects including endocrine disruption and metabolic dysregulation, but our understanding of the molecular mechanisms resulting in these outcomes remains incomplete. One target affected by PFOA is the ligand regulated nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) which plays a critical role in controlling metabolic homeostasis through regulating processes such as adipogenesis, glucose homeostasis, inflammation and osteogenesis. It has been previously established that PFOA activates PPARγ through binding to the PPARγ ligand binding domain (PPARγ LBD) leading to increased expression of PPARγ controlled target genes. However, the mechanism by which PFOA achieves this has remained elusive. Here, we employed a combination of X-ray crystallography and fluorescence polarization assays to provide a structural basis for PFOA mediated activation of PPARγ via binding to the PPARγ LBD. Using X-ray crystallography, the cocrystal structure of the PPARγ LBD:PFOA complex was solved. This revealed that PFOA occupies three distinct sites, two within the PPARγ LBD and one within the activation function 2 (AF2) on the protein surface. Structural comparison of PFOA binding with previously reported PPARγ:ligand complexes supports that PFOA activates PPARγ by a partial agonist mechanism at micromolar concentrations. Fluorescence polarization assays also revealed that PFOA binding to the AF2 is unlikely to occur in a cellular context and confirmed that PFOA behaves as a partial agonist in vitro, weakly recruiting a coactivator peptide to the AF2 of the PPARγ LBD. This discovery provides an advancement in understanding PFOA mediated regulation of PPARγ, giving new insight regarding regulation of PPARγ by PFAS and PFAS substitutes in general and can be applied to the design and assessment of safer PFAS.

Tissue-specific distribution and bioaccumulation of perfluoroalkyl acids, isomers, alternatives, and precursors in citrus trees of contaminated fields: Implication for risk assessment

The ingestion of fruits containing perfluoroalkyl acids (PFAAs) presents potential hazards to human health. This study aimed to fill knowledge gaps concerning the tissue-specific distribution patterns and bioaccumulation behavior of PFAAs and their isomers, alternatives, and precursors (collectively as per-/polyfluoroalkyl substances, PFASs) within citrus trees growing in contaminated fields. It also assessed the potential contribution of precursor degradation to human exposure risk of PFASs. High concentrations of total target PFASs (∑PFASstarget, 92.45-7496.16 ng/g dw) and precursors measured through the total oxidizable precursor (TOP) assay (130.80-13979.21 ng/g dw) were found in citrus tree tissues, and short-chain PFASs constituted the primary components. The total PFASs concentrations followed the order of leaves > fruits > branches, bark > wood, and peel > pulp > seeds. The average contamination burden of peel (∑PFASstarget: 57.75%; precursors: 71.15%) was highest among fruit tissues. Bioaccumulation factors (BAFs) and translocation potentials of short-chain, branched, or carboxylate-based PFASs exceeded those of their relatively hydrophobic counterparts, while ether-based PFASs showed lower BAFs than similar PFAAs in above-ground tissues of citrus trees. In the risk assessment of residents consuming contaminated citruses, precursor degradation contributed approximately 36.07% to total PFASs exposure, and therefore should not be ignored.

Triclocarban exhibits higher adipogenic activity than triclosan through peroxisome proliferator-activated receptors pathways

Previous epidemiological and animal studies have showed the lipid metabolic disruption of antimicrobial triclocarban (TCC) and triclosan (TCS). However, the present in vivo researches were mainly devoted to the hepatic lipid metabolism, while the evidence about the impacts of TCC/TCS on the adipose tissue is very limited and the potential mechanism is unclear, especially the molecular initiation events. Moreover, little is known about the toxic difference between TCC and TCS. This study aimed to demonstrate the differential adipogenic activity of TCC/TCS as well as the potential molecular mechanism via peroxisome proliferator-activated receptors (PPARα/β/γ). The in vitro experiment based on 3T3-L1 cells showed that TCC/TCS promoted the differentiation of preadipocytes into mature adipocytes at nanomolar to micromolar concentrations, which was approach to their human exposure levels. We revealed for the first time by reporter gene assay that TCC could activate three PPARs signaling pathways in a concentration-dependent manner, while TCS only activate PPARβ. The molecular docking strategy was applied to simulate the interactions of TCC/TCS with PPARs, which explained well the different PPARs activities between TCC and TCS. TCC up-regulated the mRNA expression of three PPARs, but TCS only up-regulated PPARβ and PPARγ significantly. Meanwhile, TCC/TCS also promoted the expression of adipogenic genes targeted by PPARs to different extent. The cellular and simulating studies demonstrated that TCC exerted higher adipogenic effects and PPARs activities than TCS. Our mice in vivo experiment showed that TCC could lead to adipocyte size increase, adipocyte lipid accumulation growing, fat weight and body weight gain at human-related exposure levels, and high fat diet exacerbated these effects. Moreover, male mice tended to be more susceptible to TCC induced obesogenic effect than female mice. This work highlights the potential obesogenic risks of TCC/TCS via PPARs signaling pathways, and TCC deserves more concerns for its higher activity.

Hexafluoropropylene oxide trimer acid exposure triggers necroptosis and inflammation through the Wnt/β-catenin/NF-κB axis in the liver

Hexafluoropropylene oxide trimer acid (HFPO-TA), an emerging alternative to perfluorooctanoic acid (PFOA), has recently been identified as a significant environmental pollutant. Nevertheless, there is a scarcity of studies regarding the hepatotoxic effects of HFPO-TA. Here, we investigated the types and potential mechanisms of liver damage caused by HFPO-TA. Initially, we validated that the introduction of HFPO-TA resulted in the Wnt/β-catenin signaling (W/β signaling) activation, as well as the induction of necroptosis and inflammation, both in the liver of mice and in HepG2 cells. Subsequently, we established that the W/β signaling mediated the necroptosis and inflammation observed in the liver and HepG2 cells exposed to HFPO-TA. Finally, we demonstrated that the phosphorylated form of NF-κB p65 (p-NF-κB p65) played a role in mediating the necroptosis and inflammation, and its activity could be regulated by the W/β signaling pathway in the liver of mice and HepG2 cells exposed to HFPO-TA. In conclusion, our investigation elucidates the role of HFPO-TA in inducing necroptosis and inflammation in the liver, which is facilitated through the activation of the W/β/NF-κB axis.

Reciprocal Effect of Environmental Stimuli to Regulate the Adipogenesis and Osteogenesis Fate Decision in Bone Marrow-Derived Mesenchymal Stem Cells (BM-MSCs)

Mesenchymal stem cells derived from bone marrow (BM-MSCs) can differentiate into adipocytes and osteoblasts. Various external stimuli, including environmental contaminants, heavy metals, dietary, and physical factors, are shown to influence the fate decision of BM-MSCs toward adipogenesis or osteogenesis. The balance of osteogenesis and adipogenesis is critical for the maintenance of bone homeostasis, and the interruption of BM-MSCs lineage commitment is associated with human health issues, such as fracture, osteoporosis, osteopenia, and osteonecrosis. This review focuses on how external stimuli shift the fate of BM-MSCs towards adipogenesis or osteogenesis. Future studies are needed to understand the impact of these external stimuli on bone health and elucidate the underlying mechanisms of BM-MSCs differentiation. This knowledge will inform efforts to prevent bone-related diseases and develop therapeutic approaches to treat bone disorders associated with various pathological conditions.