Kupffer cells suppress perfluorononanoic acid-induced hepatic peroxisome proliferator-activated receptor α expression by releasing cytokines

Per- and polyfluoroalkyl substances alter innate immune function: evidence and data gaps

Per- and polyfluoroalkyl substances (PFASs) are a large class of compounds used in a variety of processes and consumer products. Their unique chemical properties make them ubiquitous and persistent environmental contaminants while also making them economically viable and socially convenient. To date, several reviews have been published to synthesize information regarding the immunotoxic effects of PFASs on the adaptive immune system. However, these reviews often do not include data on the impact of these compounds on innate immunity. Here, current literature is reviewed to identify and incorporate data regarding the effects of PFASs on innate immunity in humans, experimental models, and wildlife. Known mechanisms by which PFASs modulate innate immune function are also reviewed, including disruption of cell signaling, metabolism, and tissue-level effects. For PFASs where innate immune data are available, results are equivocal, raising additional questions about common mechanisms or pathways of toxicity, but highlighting that the innate immune system within several species can be perturbed by exposure to PFASs. Recommendations are provided for future research to inform hazard identification, risk assessment, and risk management practices for PFASs to protect the immune systems of exposed organisms as well as environmental health.

Effects of per- and polyfluoroalkyl substances on the liver: Human-relevant mechanisms of toxicity

Per- and polyfluoroalkyl substances (PFAS) are abundantly used in a plethora of products with applications in daily life. As a result, PFAS are widely distributed in the environment, thus providing a source of exposure to humans. The majority of human exposure to PFAS is attributed to the human diet, which encompasses drinking water. Their chemical nature grants persistent, accumulative and toxic properties, which are currently raising concerns. Over the past few years, adverse effects of PFAS on different organs have been repeatedly documented. Numerous epidemiological studies established a clear link between PFAS exposure and liver toxicity. Likewise, effects of PFAS on liver homeostasis, lipid metabolism, bile acid metabolism and hepatocarcinogenesis have been reported in various in vitro and in vivo studies. This review discusses the role of PFAS in liver toxicity with special attention paid to human relevance as well as to the mechanisms underlying the hepatotoxic effects of PFAS. Future perspectives and remaining knowledge gaps were identified to enhance future PFAS risk assessment.

Comparing the obesogenic effect and regulatory mechanisms of long-term exposure to per/polyfluoroalkyl substances with different terminal groups in Caenorhabditis elegans

Per/polyfluoroalkyl substances (PFASs) are ubiquitous, bioaccumulative, and recalcitrant contaminants, posing global exposure and health risks. The effects of chemical structures on toxicities and the mechanisms of their obesogenic effects were largely unclear. This study used the model organism Caenorhabditis elegans to assess the impact of long-term exposure to different PFASs (PFNA, PFOSA, PFBS, PFHxS, 6:2 FTS, 4:2 FTS, PFOA, and PFOS) on growth and lipid metabolism and discussed the obesogenic mechanisms of selected PFASs. The growth assays indicated longer carbon-fluorine (-CF) chains and total fluorine atoms increased developmental toxicity of PFASs, while at 8 -CF chain-length, PFNA (-COOH terminal), PFOS (-SO3 terminal), and PFOSA (-SO2NH2 terminal) exhibited differential growth inhibition. With the toxicity ranking of PFNA > PFOS > PFOSA, all PFASs significantly induced total lipid accumulation and perturbed the lipid composition in C. elegans. All three PFASs significantly induced lipogenesis gene expression and partially suppressed lipolysis genes. The results suggested that the disruption of lipid metabolism of PFOSA depends on sbp-1, while PFNA and PFOS depend on nhr-49. In conclusion, long-term exposure to PFNA, PFOSA, and PFOS triggers obesogenic effects in organisms by distinct molecular mechanisms.

Association between serum perfluoroalkyl substances concentrations and non-alcoholic fatty liver disease among Korean adults: a cross-sectional study using the National Environmental Health Survey cycle 4

Background

Perfluoroalkyl substances (PFAS) are widely used in industry and daily life due to their useful properties. They have a long half-life, accumulate in the body, and there is evidence that they are associated with biomarkers of lipid metabolism and liver damage. This may suggest non-alcoholic fatty liver disease (NAFLD) caused by PFAS. However, since there has been no study analyzing the relationship between PFAS and NAFLD in the entire population in Korea. We sought to confirm the relationship between serum PFAS concentration and NAFLD prevalence in Korean adults using the Korean National Environmental Health Survey (KoNEHS) cycle 4.

Methods

The study was conducted on 2,529 subjects in 2018-2019 among KoNEHS participants. For the diagnosis of NAFLD, the hepatic steatosis index (HSI) was used, and the geometric mean and concentration distribution of serum PFAS were presented. Logistic regression was performed to confirm the increase in the risk of NAFLD due to changes in PFAS concentration, and the odds ratio and 95% confidence interval (CI) were calculated.

Results

In both adjusted and unadjusted models, an increased odds ratio was observed with increasing serum concentrations of total PFAS and perfluorooctane sulfonate (PFOS) in the non-obese group. In the adjusted model, the odds ratios for serum total PFAS and PFOS were 6.401 (95% CI: 1.883-21.758) and 7.018 (95% CI: 2.688-18.319).

Conclusions

In this study, a higher risk of NAFLD based on HSI was associated with serum total PFAS, PFOS in non-obese group. Further research based on radiological or histological evidence for NAFLD diagnosis and long-term prospective studies are necessary. Accordingly, it is necessary to find ways to reduce exposure to PFAS in industry and daily life.

Inflammaging and fatty acid oxidation in monocytes and macrophages

Fatty acid oxidation (FAO), primarily known as β-oxidation, plays a crucial role in breaking down fatty acids within mitochondria and peroxisomes to produce cellular energy and preventing metabolic dysfunction. Myeloid cells, including macrophages, microglia, and monocytes, rely on FAO to perform essential cellular functions and uphold tissue homeostasis. As individuals age, these cells show signs of inflammaging, a condition that includes a chronic onset of low-grade inflammation and a decline in metabolic function. These lead to changes in fatty acid metabolism and a decline in FAO pathways. Recent studies have shed light on metabolic shifts occurring in macrophages and monocytes during aging, correlating with an altered tissue environment and the onset of inflammaging. This review aims to provide insights into the connection of inflammatory pathways and altered FAO in macrophages and monocytes from older organisms. We describe a model in which there is an extended activation of receptor for advanced glycation end products, nuclear factor-κB (NF-κB) and the nod-like receptor family pyrin domain containing 3 inflammasome within macrophages and monocytes. This leads to an increased level of glycolysis, and also promotes pro-inflammatory cytokine production and signaling. As a result, FAO-related enzymes such as 5' AMP-activated protein kinase and peroxisome proliferator-activated receptor-α are reduced, adding to the escalation of inflammation, accumulation of lipids, and heightened cellular stress. We examine the existing body of literature focused on changes in FAO signaling within macrophages and monocytes and their contribution to the process of inflammaging.

Effects of swimming exercise combined with silymarin and vitamin C supplementation on hepatic inflammation, oxidative stress, and histopathology in elderly rats with high-fat diet-induced liver damage

OBJECTIVES

The aim of this study was to demonstrate that swimming exercise combined with silymarin and vitamin C supplementation improves hepatic inflammation, oxidative stress, and liver histopathology in elderly rats with high-fat diet-induced liver damage.

METHODS

Forty elderly male Wistar rats were randomly assigned to five groups (n = 8 in each): a normal diet (control), a high-fat diet (HFD), HFD + silymarin and vitamin C supplementation (HFD+Sup), HFD + swimming exercise (HFD+Exe), and HFD+Sup+Exe group (HFD+Sup+Exe). The non-alcoholic fatty liver model was induced for 6 wk in the HFD groups. After 6 wk of consuming an HFD, a daily supplemental gavage was administered to rats as an intervention along with HFD in the supplement groups for 8 wk. Moreover, rats in the exercise groups were subjected to swimming exercise training 5 d/wk for the same period.

RESULTS

The combination of swimming training and supplementation caused significant decreases in liver inflammatory biomarkers tumor necrosis factor-α and interleukin-1β while increasing total antioxidant capacity and peroxisome proliferator-activated receptor α (P < 0.05).

CONCLUSION

In elderly rats with liver injury caused by an HFD, the combination of exercise and silymarin with vitamin C supplementation effectively reduced oxidative stress, liver inflammation, fat accumulation, and regulated liver enzymes.

Extracellular Vesicles altered by a Per- and Polyfluoroalkyl Substance Mixture: In Vitro Dose-Dependent Release, Chemical Content, and MicroRNA Signatures involved in Liver Health

Per- and polyfluoroalkyl substances (PFAS) have emerged as high priority contaminants due to their ubiquity and pervasiveness in the environment. Numerous PFAS co-occur across sources of drinking water, including areas of North Carolina (NC) with some detected concentrations above the Environmental Protection Agency's health advisory levels. While evidence demonstrates PFAS exposure induces harmful effects in the liver, the involvement of extracellular vesicles (EVs) as potential mediators of these effects has yet to be evaluated. This study set out to evaluate the hypothesis that PFAS mixtures induce dose-dependent release of EVs from liver cells, with exposures causing differential loading of microRNAs (miRNAs) and PFAS chemical signatures. To test this hypothesis, a defined PFAS mixture was prioritized utilizing data collected by the NC PFAS Testing Network. This mixture contained three substances, PFOS, PFOA, and PFHxA, selected based upon co-occurrence patterns and the inclusion of both short-chain (PFHxA) and long-chain (PFOA and PFOS) substances. HepG2 liver cells were exposed to equimolar PFAS, and secreted EVs were isolated from conditioned media and characterized for count and molecular content. Exposures induced a dose-dependent release of EVs carrying miRNAs that were differentially loaded upon exposure. These altered miRNA signatures were predicted to target mRNA pathways involved in hepatic fibrosis and cancer. Chemical concentrations of PFOS, PFOA, and PFHxA were also detected in both parent HepG2 cells and their released EVs, specifically within a 15-fold range after normalizing for protein content. This study therefore established EVs as novel biological responders and measurable endpoints for evaluating PFAS-induced toxicity.

A systematic evidence map of chronic inflammation and immunosuppression related to per- and polyfluoroalkyl substance (PFAS) exposure

BACKGROUND

The ability to induce chronic inflammation and immunosuppression are two key characteristics of carcinogens and important forms of immunotoxicity. The National Toxicology Program (NTP) evaluated the immunotoxicity of two per- and polyfluoroalkyl substances (PFASs), PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate), in 2016. However, the potential pro-inflammatory and immunosuppressive effects of other PFASs remain largely uncharacterized.

METHODS

We developed an expanded set of search terms pertaining to the chronic inflammatory and immunosuppressive effects of PFASs based on those of the International Agency for Research on Cancer (IARC) and NTP. To confirm searching effectiveness and scope, we compared our search term results with those of IARC and NTP for both PFASs and two other known carcinogens, chromium (VI) and benzene. Systematic evidence maps (SEMs) were also produced using Tableau to visualize the distribution of study numbers and types reporting immunotoxic effects and specific biomarkers elicited by PFAS exposures.

RESULTS

In total, 1155 PFAS studies were retrieved, of which 321 qualified for inclusion in our dataset. Using our search terms, we identified a greater number of relevant studies than those obtained using IARC and NTP's search terms. From the SEM findings, increased cytokine production strengthened an association between PFAS exposure and chronic inflammation, and decreased B-cell activation and altered levels of T-cell subtypes and immunoglobulins confirmed PFAS-induced immunosuppression.

CONCLUSION

Our SEM findings confirm that several PFASs commonly found in both in the environment, including those that are lesser-known, may induce immunosuppression and chronic inflammation, two key characteristics of carcinogens. This approach, including development of search terms, study screening process, data coding, and evidence mapping visualizations, can be applied to other key characteristics of chemical carcinogens.

Consideration of pathways for immunotoxicity of per- and polyfluoroalkyl substances (PFAS)

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are of public health concern, because of their ubiquitous and extremely persistent occurrence, and depending on their structure, their bio-accumulative, mobile and toxic properties. Human health effects associated with exposure to PFAS include adverse effects on the immune system. In 2020, EFSA (the European Food Safety Authority) defined adverse effects on the immune system as the most critical effect for human health risk assessment, based on reduced antibody responses to childhood vaccines and similar effects observed in experimental animal studies. Likewise, the U.S. EPA (Environmental Protection Agency) considers PFAS-induced immunotoxicity, especially in children, as the critical effect for risk assessment. However, the mechanisms by which antibody concentrations are impacted are not completely understood. Furthermore, other targets of the immune system functions have been reported in the literature.

OBJECTIVE

The aim of this review is to explore PFAS-associated immune-related effects. This includes, relevant mechanisms that may underlie the observed effects on the immune system, immunosuppression as well as immunoenhancement, such as i) modulation of cell signalling and nuclear receptors, such as NF-κB and PPARs; ii) alteration of calcium signalling and homoeostasis in immune cells; iii) modulation of immune cell populations; iv) oxidative stress and v) impact on fatty acid metabolism & secondary effects on the immune system.

METHODS

A literature research was conducted using three databases (Web of Science, PubMed, and Scopus), which were searched in July 2021 for relevant studies published in the time frame from 2018 to 2021. In total, 487 publications were identified as potentially eligible and following expert-based judgement, articles relevant for mechanisms of PFAS induced immunotoxicity are discussed.

CONCLUSIONS

Taken together, we show that there is substantial evidence from both in vitro and in vivo experimental as well as epidemiological studies, supporting that various PFAS, not only PFOA and PFOS, affect multiple aspects of the immune system. Timing of exposure is critical, because the developing immune system is especially vulnerable to toxic insults, resulting in a higher risk of particularly adverse immune effects but also other organs later in life.

Endocrine disrupting chemicals: A promoter of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent liver disorder. With the improvement in human living standards, the prevalence of NAFLD has been increasing in recent years. Endocrine-disrupting chemicals (EDCs) are a class of exogenous chemicals that simulate the effects of hormones in the body. There has been growing evidence regarding the potential effects of EDCs on liver health, especially in NAFLD. This paper aims to summarize the major EDCs that contribute to the growing burden of NAFLD and to raise public awareness regarding the hazards posed by EDCs with the objective of reducing the incidence of NAFLD.

Mangiferin Ameliorates Obesity-Associated Inflammation and Autophagy in High-Fat-Diet-Fed Mice: In Silico and In Vivo Approaches

Obesity-induced insulin resistance is the fundamental cause of metabolic syndrome. Accordingly, we evaluated the effect of mangiferin (MGF) on obesity and glucose metabolism focusing on inflammatory response and autophagy. First, an in silico study was conducted to analyze the mechanism of MGF in insulin resistance. Second, an in vivo experiment was conducted by administering MGF to C57BL/6 mice with high-fat-diet (HFD)-induced metabolic disorders. The in silico analysis revealed that MGF showed a high binding affinity with macrophage-related inflammatory cytokines and autophagy proteins. In the in vivo study, mice were divided into three groups: normal chow, HFD, and HFD + MGF 150 mg/kg. MGF administration to obese mice significantly improved the body weight, insulin-sensitive organs weights, glucose and lipid metabolism, fat accumulation in the liver, and adipocyte size compared to HFD alone. MGF significantly reduced the macrophages in adipose tissue and Kupffer cells, inhibited the gene expression ratio of tumor necrosis factor-α and F4/80 in adipose tissue, reduced the necrosis factor kappa B gene, and elevated autophagy-related gene 7 and fibroblast growth factor 21 gene expressions in the liver. Thus, MGF exerted a therapeutic effect on metabolic diseases by improving glucose and lipid metabolism through inhibition of the macrophage-mediated inflammatory responses and activation of autophagy.

Exposure to per- and Polyfluoroalkyl Substances and Markers of Liver Injury: A Systematic Review and Meta-Analysis

BACKGROUND

Experimental evidence indicates that exposure to certain pollutants is associated with liver damage. Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic chemicals widely used in industry and consumer products and bioaccumulate in food webs and human tissues, such as the liver.

OBJECTIVE

The objective of this study was to conduct a systematic review of the literature and meta-analysis evaluating PFAS exposure and evidence of liver injury from rodent and epidemiological studies.

METHODS

PubMed and Embase were searched for all studies from earliest available indexing year through 1 December 2021 using keywords corresponding to PFAS exposure and liver injury. For data synthesis, results were limited to studies in humans and rodents assessing the following indicators of liver injury: serum alanine aminotransferase (ALT), nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, or steatosis. For human studies, at least three observational studies per PFAS were used to conduct a weighted z-score meta-analysis to determine the direction and significance of associations. For rodent studies, data were synthesized to qualitatively summarize the direction and significance of effect.

RESULTS

Our search yielded 85 rodent studies and 24 epidemiological studies, primarily of people from the United States. Studies focused primarily on legacy PFAS: perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), and perfluorohexanesulfonic acid. Meta-analyses of human studies revealed that higher ALT levels were associated with exposure to PFOA (z-score= 6.20, p<0.001), PFOS (z-score= 3.55, p<0.001), and PFNA (z-score= 2.27, p=0.023). PFOA exposure was also associated with higher aspartate aminotransferase and gamma-glutamyl transferase levels in humans. In rodents, PFAS exposures consistently resulted in higher ALT levels and steatosis.

CONCLUSION

There is consistent evidence for PFAS hepatotoxicity from rodent studies, supported by associations of PFAS and markers of liver function in observational human studies. This review identifies a need for additional research evaluating next-generation PFAS, mixtures, and early life exposures. https://doi.org/10.1289/EHP10092.

Perfluorooctane sulfonate induces heart toxicity involving cardiac apoptosis and inflammation in rats

Perfluorooctane sulfonate (PFOS) is a persistent pollutant that exerts toxicity and induces cardiogenesis in humans and animals. Yet, the effect of PFOS exposure on cardiac toxicity in adult rats has, to our knowledge, not been reported and the mechanism still remains unknown. The present study aimed to investigate the toxicity of PFOS on rat hearts and any associated mechanisms. Rats were exposed to 0 (control), 1 and 10 mg/kg PFOS every other day for 14 days. Body weight and heart weight were recorded. The serum levels of lactic dehydrogenase (LDH), creatine kinase (CK), creatine kinase-isoenzyme-MB (CK-MB) and cardiac troponin-T (cTn-T) in heart tissues were measured using biochemical assays. TUNEL staining and western blotting were applied to analyze levels of apoptosis in rat hearts. Pathological assessment and immunohistochemistry analysis of heart tissues were used to evaluate the levels of PFOS-induced cardiotoxicity and inflammatory infiltration. PFOS exposure at the dosage of 10 mg/kg significantly increased the percentage of heart to body weight; however, it did not alter the body weight. At 10 mg/kg, PFOS significantly increased expression levels of myocardial injury markers, such as cTn-T, LDH, CK and CK-MB, while 1 mg/kg PFOS upregulated the expression level of cTn-T in rats. Notably, cardiac fibrosis and myocardiac hypertrophy appeared in the 10 mg/kg PFOS group. In addition, TUNEL-positive cells were significantly increased by exposure to 10 mg/kg PFOS in rat heart tissues. The protein expressions profiles of p53 and Bax were also significantly upregulated in the 10 mg/kg PFOS group. Inflammatory infiltration, detected by anaylzing expression levels of IL-1β and TNF-α, was significantly raised by 10 mg/kg PFOS exposure. In conclusion, these results demonstrated that 10 mg/kg PFOS-induced cardiac toxicity in rats, which was associated with an increase in apoptosis and the expression of proinflammatory cytokines.

Autophagy mediates perfluorooctanoic acid-induced lipid metabolism disorder and NLRP3 inflammasome activation in hepatocytes

Perfluorooctanoic acid (PFOA) has applications in numerous industrial products and is an industrial waste that is persistently present in the environment. Exposure to PFOA results in nonalcoholic fatty liver disease (NAFLD). However, the underlying mechanisms remain unclear. In this study, male C57BL/6 mice were exposed to PFOA (1 mg/kg/day) for 4 weeks to evaluate the effect of PFOA, and the human liver cell line (L-02) was used to observe the direct effect of PFOA in vitro. After PFOA exposure, the expression of genes related to hepatic lipogenesis, the NLRP3 inflammasome, and autophagy were measured. We found that exposure to PFOA induced lipid accumulation and stimulated lipogenesis in both mouse livers and L-02 cells. In addition, increased NLRP3 aggregation and enhanced production of IL-1β occurred after PFOA treatment. We also found that PFOA exposure induced autophagosome formation and p62 accumulation, indicating blockage of autophagic flux. Rapamycin alleviated PFOA-induced lipid accumulation and NLRP3 inflammasome activation by activating autophagic flux. Conversely, chloroquine, an autophagic flux inhibitor, exacerbated PFOA-induced lipid accumulation and NLRP3 inflammasome activation. Collectively, these results provide evidence to show that PFOA-induced blockade of autophagic flux causes an increase in lipid synthesis and inflammation in vivo and in vitro.

Effect of perfluorooctane sulphonate-induced Kupffer cell activation on hepatocyte proliferation through the NF-κB/TNF-α/IL-6-dependent pathway

Perfluorooctane sulfonate (PFOS), one member of polyfluoroalkyl chemicals (PFASs), persist in the environment and are found in relatively high concentrations in animal livers. PFOS has been shown to induce tumour of the liver in rats following chronic dietary administration. However, the molecular mechanisms involved in PFOS-induced hepatocellular hypertrophy are still not well characterized. In this study, male Sprague-Dawley rats were daily gavaged with PFOS (1 or 10 mg/kg body weight) for 28 days. Rat primary cultured Kupffer cells or hepatocytes were exposed to 100 μM PFOS for 0-48 h. Our results showed that PFOS exposure caused serious hepatocellular damage and obvious inflammatory cell infiltration and increased serum tumour necrosis factor-ɑ (TNF-α) and interleukin-6 (IL-6) levels. Particularly, PFOS exposure triggered Kupffer cell activation and significantly upregulated the expression of proliferating cell nuclear antigen (PCNA), c-Jun, c-MYC and Cyclin D1 (CyD1) in liver. In vitro, PFOS significantly induced production of TNF-α and IL-6 in Kupffer cells and increased PCNA, c-Jun, c-MYC and CyD1 expression in the primary hepatocytes co-cultured with Kupffer cells. However, Kupffer cell activation was mostly abolished by anti-TNF-α or anti-IL6 treatment. Furthermore, blockage of TNF-α and IL-6 significantly inhibited hepatocyte proliferation by gadolinium chloride (GdCl₃) pre-treatment in PFOS-treated mice and primary cultured Kupffer cells. On the other hand, NF-κB inhibitor (PDTC) and c-Jun amino-terminal kinase (JNK) inhibitor (SP600125) significantly inhibited production of PFOS-induced TNF-α and IL-6. Taken together, these data suggest that PFOS induces Kupffer cell activation, leading to hepatocyte proliferation by through the NF-κB/TNF-ɑ/IL-6-dependent pathway.

Perfluorooctane sulphonate induces oxidative hepatic damage via mitochondria-dependent and NF-κB/TNF-α-mediated pathway

Perfluorooctane sulphonate (PFOS) has been reported to accumulate in liver and cause damage. The molecular mechanism of the PFOS-induced hepatotoxicity has not been completely elucidated. The aim of the present study was to investigate whether PFOS-induced oxidative stress plays an important role in liver damage, and if so, what pathway it undergoes for the mechanism of its toxicological action. Male Sprague-Dawley (SD) rats were orally administrated with PFOS at single dose of 1 or 10 mg/kg body weight for 28 consecutive days. Increased serum levels of liver enzymes and abnormal ultra structural changes were observed in the PFOS-exposed rats. Particularly, PFOS exposure significantly increased intracellular reactive oxygen species (ROS) and nitric oxide (NO) production, but weakened intracellular antioxidant defence by inhibiting catalase and superoxide dismutase activities. Signal transduction studies showed that PFOS exposure significantly elevated inducible nitric oxide synthase (iNOS), Bax, cytochrome c, cleaved caspase-9 and cleaved caspase-3, indicating the mitochondria-dependent apoptotic pathway was activated. On the other hand, significant alterations of the PFOS-induced protein expression of NF-κB and IκBα in association with an enhanced level of TNF-α were observed. Taken together, these results indicate that mitochondria play an important role in PFOS-induced hepatotoxicity.

Perfluoroalkyl acids-induced liver steatosis: Effects on genes controlling lipid homeostasis

Persistent presence of perfluoroalkyl acids (PFAAs) in the environment is due to their extensive use in industrial and consumer products, and their slow decay. Biochemical tests in rodent demonstrated that these chemicals are potent modifiers of lipid metabolism and cause hepatocellular steatosis. However, the molecular mechanism of PFAAs interference with lipid metabolism remains to be elucidated. Currently, two major hypotheses are that PFAAs interfere with mitochondrial beta-oxidation of fatty acids and/or they affect the transcriptional activity of peroxisome proliferator-activated receptor α (PPARα) in liver. To determine the ability of structurally-diverse PFAAs to cause steatosis, as well as to understand the underlying molecular mechanisms, wild-type (WT) and PPARα-null mice were treated with perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), or perfluorohexane sulfonate (PFHxS), by oral gavage for 7days, and their effects were compared to that of PPARα agonist WY-14643 (WY), which does not cause steatosis. Increases in liver weight and cell size, and decreases in DNA content per mg of liver, were observed for all compounds in WT mice, and were also seen in PPARα-null mice for PFOA, PFNA, and PFHxS, but not for WY. In Oil Red O stained sections, WT liver showed increased lipid accumulation in all treatment groups, whereas in PPARα-null livers, accumulation was observed after PFNA and PFHxS treatment, adding to the burden of steatosis observed in control (untreated) PPARα-null mice. Liver triglyceride (TG) levels were elevated in WT mice by all PFAAs and in PPARα-null mice only by PFNA. In vitro β-oxidation of palmitoyl carnitine by isolated rat liver mitochondria was not inhibited by any of the 7 PFAAs tested. Likewise, neither PFOA nor PFOS inhibited palmitate oxidation by HepG2/C3A human liver cell cultures. Microarray analysis of livers from PFAAs-treated mice indicated that the PFAAs induce the expression of the lipid catabolism genes, as well as those involved in fatty acid and triglyceride synthesis, in WT mice and, to a lesser extent, in PPARα-null mice. These results indicate that most of the PFAAs increase liver TG load and promote steatosis in mice We hypothesize that PFAAs increase steatosis because the balance of fatty acid accumulation/synthesis and oxidation is disrupted to favor accumulation.

The impact of PPARα activation on whole genome gene expression in human precision cut liver slices

Background

Studies in mice have shown that PPARα is an important regulator of lipid metabolism in liver and key transcription factor involved in the adaptive response to fasting. However, much less is known about the role of PPARα in human liver.

Methods

Here we set out to study the function of PPARα in human liver via analysis of whole genome gene regulation in human liver slices treated with the PPARα agonist Wy14643.

Results

Quantitative PCR indicated that PPARα is well expressed in human liver and human liver slices and that the classical PPARα targets PLIN2, VLDLR, ANGPTL4, CPT1A and PDK4 are robustly induced by PPARα activation. Transcriptomics analysis indicated that 617 genes were upregulated and 665 genes were downregulated by PPARα activation (q value < 0.05). Many genes induced by PPARα activation were involved in lipid metabolism (ACSL5, AGPAT9, FADS1, SLC27A4), xenobiotic metabolism (POR, ABCC2, CYP3A5) or the unfolded protein response, whereas most of the downregulated genes were involved in immune-related pathways. Among the most highly repressed genes upon PPARα activation were several chemokines (e.g. CXCL9-11, CCL8, CX3CL1, CXCL6), interferon γ-induced genes (e.g. IFITM1, IFIT1, IFIT2, IFIT3) and numerous other immune-related genes (e.g. TLR3, NOS2, and LCN2). Comparative analysis of gene regulation by Wy14643 between human liver slices and primary human hepatocytes showed that down-regulation of gene expression by PPARα is much better captured by liver slices as compared to primary hepatocytes. In particular, PPARα activation markedly suppressed immunity/inflammation-related genes in human liver slices but not in primary hepatocytes. Finally, several putative new target genes of PPARα were identified that were commonly induced by PPARα activation in the two human liver model systems, including TSKU, RHOF, CA12 and VSIG10L.

Conclusion

Our paper demonstrates the suitability and superiority of human liver slices over primary hepatocytes for studying the functional role of PPARα in human liver. Our data underscore the major role of PPARα in regulation of hepatic lipid and xenobiotic metabolism in human liver and reveal a marked immuno-suppressive/anti-inflammatory effect of PPARα in human liver slices that may be therapeutically relevant for non-alcoholic fatty liver disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1969-3) contains supplementary material, which is available to authorized users.

Transcriptomic signatures of peroxisome proliferator-activated receptor α (PPARα) in different mouse liver models identify novel aspects of its biology

Background

The peroxisome proliferator-activated receptor alpha (PPARα) is a ligand-activated transcription factor that regulates lipid catabolism and inflammation and is hepatocarcinogenic in rodents. It is presumed that the functions of PPARα in liver depend on cross-talk between parenchymal (hepatocytes) and non-parenchymal (Kupffer and endothelial cells) fractions as well as inter-organ interactions. In order to determine how cellular composition and inter-organ interactions influence gene expression upon pharmacological activation of PPARα, we performed a meta-analysis of transcriptomics data obtained from mouse hepatocytes (containing only the parenchymal fraction), mouse liver slices (containing both fractions), and mouse livers exposed to a PPARα agonist. The aim was to obtain a comprehensive view of common and model-specific PPARα-dependent genes and biological processes to understand the impact of cross-talk between parenchymal and non-parenchymal fractions as well as the effect of inter-organ interactions on the hepatic PPARα transcriptome.

To this end we analyzed microarray data of experiments performed in mouse primary hepatocytes treated with the PPARα agonist Wy14643 for 6 or 24 h (in vitro), mouse precision cut liver slices treated with Wy14643 for 24 h (ex vivo), and livers of wild type and Ppara knockout mice treated with Wy14643 for 6 h or 5 days (in vivo).

Results

In all models, activation of PPARα significantly altered processes related to various aspects of lipid metabolism. In ex vivo and in vivo models, PPARα activation significantly regulated processes involved in inflammation; these processes were unaffected in hepatocytes. Only in vivo models showed significant regulation of genes involved in coagulation, carcinogenesis, as well as vesicular trafficking and extracellular matrix.

Conclusions

PPARα-dependent regulation of genes/processes involved in lipid metabolism is mostly independent of the presence of non-parenchymal cells or systemic factors, as it was observed in all liver models. PPARα-dependent regulation of inflammatory genes requires the presence of non-parenchymal cells, as it was observed only ex vivo and in vivo. However, the full spectrum of PPARα biology at the level of lipid metabolism, immunity, carcinogenesis, as well as novel aspects of PPARα signaling such as coagulation, vesicular trafficking and the extracellular matrix, seems to require systemic factors, as it was observed exclusively in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1106) contains supplementary material, which is available to authorized users.

Associations between serum concentrations of perfluoroalkyl acids and serum lipid levels in a Chinese population

Perfluoroalkyl acids (PFAAs) have been used in a variety of products for many years and have been detected worldwide in human serum. Previous studies have suggested the potential effects of PFAAs on serum lipids. To investigate the associations between serum concentrations of PFAAs and serum lipid levels, 133 participants were randomly selected from the people coming for health check-up in Yuanyang Red Cross Hospital of Henan, China. Linear regression analysis revealed that perfluoro-octanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA), with a median concentration of 1.43, 0.37, and 0.19 ng/mL, respectively, were positively associated with total cholesterol (TC). Those in the highest quartile of PFOA exposure had ln-TC levels 0.24 mmol/L higher than those in the lowest quartile. For PFNA and PFDA, effect estimates were 0.25 and 0.16 mmol/L, respectively. A positive association between high-density lipoprotein cholesterol (HDLC) and PFDA was found, and there was a 0.18 mmol/L increase of HDLC for the top PFDA quartile compared with the lowest quartile. PFOA and PFNA were positively associated with low-density lipoprotein cholesterol (LDLC). Ln-LDLC levels of people in both top PFOA and PFNA quartiles were 0.33 mmol/L higher than those in the lowest quartiles. Logistic regression analysis indicated that increased PFOA and PFOS quartiles were positively associated with an increased risk of abnormal TC and LDLC when controlling for no confounding factors.

Hydrocellular foam dressing promotes wound healing along with increases in hyaluronan synthase 3 and PPARα gene expression in epidermis

BACKGROUND

Hydrocellular foam dressing, modern wound dressing, induces moist wound environment and promotes wound healing: however, the regulatory mechanisms responsible for these effects are poorly understood. This study was aimed to reveal the effect of hydrocellular foam dressing on hyaluronan, which has been shown to have positive effects on wound healing, and examined its regulatory mechanisms in rat skin.

METHODOLOGY/PRINCIPAL FINDINGS

We created two full-thickness wounds on the dorsolateral skin of rats. Each wound was covered with either a hydrocellular foam dressing or a film dressing and hyaluronan levels in the periwound skin was measured. We also investigated the mechanism by which the hydrocellular foam dressing regulates hyaluronan production by measuring the gene expression of hyaluronan synthase 3 (Has3), peroxisome proliferator-activated receptor α (PPARα), and CD44. Hydrocellular foam dressing promoted wound healing and upregulated hyaluronan synthesis, along with an increase in the mRNA levels of Has3, which plays a primary role in hyaluronan synthesis in epidermis. In addition, hydrocellular foam dressing enhanced the mRNA levels of PPARα, which upregulates Has3 gene expression, and the major hyaluronan receptor CD44.

CONCLUSIONS/SIGNIFICANCE

These findings suggests that hydrocellular foam dressing may be beneficial for wound healing along with increases in hyaluronan synthase 3 and PPARα gene expression in epidermis. We believe that the present study would contribute to the elucidation of the mechanisms underlying the effects of hydrocellular foam dressing-induced moist environment on wound healing and practice evidence-based wound care.