Peroxisome proliferator-activated receptor-α and liver cancer: where do we stand?

Graft repair during machine perfusion: a current overview of strategies

PURPOSE OF REVIEW

With changing donor characteristics (advanced age, obesity), an increase in the use of extended criteria donor (ECD) livers in liver transplantation is seen. Machine perfusion allows graft viability assessment, but still many donor livers are considered nontransplantable. Besides being used as graft viability assessment tool, ex situ machine perfusion offers a platform for therapeutic strategies to ameliorate grafts prior to transplantation. This review describes the current landscape of graft repair during machine perfusion.

RECENT FINDINGS

Explored anti-inflammatory therapies, including inflammasome inhibitors, hemoabsorption, and cellular therapies mitigate the inflammatory response and improve hepatic function. Cholangiocyte organoids show promise in repairing the damaged biliary tree. Defatting during normothermic machine perfusion shows a reduction of steatosis and improved hepatobiliary function compared to nontreated livers. Uptake of RNA interference therapies during machine perfusion paves the way for an additional treatment modality.

SUMMARY

The possibility to repair injured donor livers during ex situ machine perfusion might increase the utilization of ECD-livers. Application of defatting agents is currently explored in clinical trials, whereas other therapeutics require further research or optimization before entering clinical research.

A novel peroxisome-related gene signature predicts clinical prognosis and is associated with immune microenvironment in low-grade glioma

Low-grade glioma (LGG), a common primary tumor, mainly originates from astrocytes and oligodendrocytes. Increasing evidence has shown that peroxisomes function in the regulation of tumorigenesis and development of cancer. However, the prognostic value of peroxisome-related genes (PRGs) in LGG has not been reported. Therefore, it is necessary to construct a prognostic risk model for LGG patients based on the expression profiles of peroxisome-related genes. Our study mainly concentrated on developing a peroxisome-related gene signature for overall survival (OS) prediction in LGG patients. First, according to these peroxisome-related genes, all LGG patients from The Cancer Genome Atlas (TCGA) database could be divided into two subtypes. Univariate Cox regression analysis was used to find prognostic peroxisome-related genes in TCGA_LGG dataset, and least absolute shrinkage and selection operator Cox regression analysis was employed to establish a 14-gene signature. The risk score based on the signature was positively associated with unfavorable prognosis. Then, multivariate Cox regression incorporating additional clinical characteristics showed that the 14-gene signature was an independent predictor of LGG. Time-dependent ROC curves revealed good performance of this prognostic signature in LGG patients. The performance about predicting OS of LGG was validated using the GSE107850 dataset derived from the Gene Expression Omnibus (GEO) database. Furethermore, we constructed a nomogram model based on the gene signature and age, which showed a better prognostic power. Gene ontology (GO) and Kyoto Encylopedia of Genes and Genomes (KEGG) analyses showed that neuroactive ligand-receptor interaction and phagosome were enriched and that the immune status was decreased in the high-risk group. Finally, cell counting kit-8 (CCK8) were used to detect cell proliferation of U251 and A172 cells. Inhibition of ATAD1 (ATPase family AAA domain-containing 1) and ACBD5 (Acyl-CoA binding-domain-containing-5) expression led to significant inhibition of U251 and A172 cell proliferation. Flow cytometry detection showed that ATAD1 and ACBD5 could induce apoptosis of U251 and A172 cells. Therefore, through bioinformatics methods and cell experiments, our study developed a new peroxisome-related gene signature that migh t help improve personalized OS prediction in LGG patients.

Exploring the effects of epigallocatechin gallate on lipid metabolism in the rat steatotic liver during normothermic machine perfusion: Insights from lipidomics and RNA sequencing

BACKGROUND

Hepatic steatosis is the leading cause of discarded liver grafts. Defatting steatotic liver grafts using drug combinations during ex vivo normothermic machine perfusion (NMP) has been reported. However, the effectiveness of NMP in reducing fat content using epigallocatechin gallate (EGCG) as a single defatting agent and its effect on lipid metabolism are poorly investigated.

METHODS

In this study, an NMP system was set up to perfuse a steatotic liver from a rat model with 10 mM EGCG. Livers without EGCG served as NMP controls, whereas static cold-preserved livers in the University of Wisconsin medium were used as static cold storage controls. Liver enzyme, reactive oxygen species (ROS), histology, and lipid content assessments were conducted post-perfusion, complemented by lipidomics, RNA sequencing, and western blotting to determine the lipid metabolism changes.

RESULTS

EGCG during NMP reduced hepatocellular injury markers and defatted steatotic liver grafts. Additionally, we observed a significant increase in triglyceride (TG) content in the perfusate post-NMP in the NMP + EGCG group, suggesting TG output from the liver. Furthermore, lipidomics analysis revealed that EGCG primarily affected metabolites involved in glycerophospholipid (GP) and glycerolipid (GL) metabolism. Further, the RNA sequencing indicated the modulation of these metabolic pathways via ECGC, which was associated with the downregulated Lpin1 and Gpat3 expression.

CONCLUSIONS

EGCG defats steatotic livers as a single defatting agent during NMP by promoting GL and GP metabolism via decreasing Lpin1 and Agpat9 levels.

Lipid-lowering drugs and cancer: an updated perspective

Statins and non-statin medications used for the management of dyslipidemia have been shown to possess antitumor properties. Since the use of these drugs has steadily increased over the past decades, more knowledge is required about their relationship with cancer. Lipid-lowering agents are heterogeneous compounds; therefore, it remains to be revealed whether anticancer potential is a class effect or related to them all. Here, we reviewed the literature on the influence of lipid-lowering medications on various types of cancer during development or metastasis. We also elaborated on the underlying mechanisms associated with the anticancer effects of antihyperlipidemic agents by linking the reported in vivo and in vitro studies.

Understanding the Role of Polyunsaturated Fatty Acids in the Development and Prevention of Cancer

Polyunsaturated fatty acids (PUFAs), notably omega-3 (n-3) and omega-6 (n-6), have received much attention owing to their multifaceted effects not only in the management of diverse pathological conditions but also in the maintenance of overall health of an individual. A disproportionately high n-6 to n-3 ratio contributes to the development of various disorders including cancer, which ranks as a leading cause of death worldwide with profound social and economic burden. Epidemiological studies and clinical trials combined with the animal and cell culture models have demonstrated the beneficial effects of n-3 PUFAs in reducing the risk of various cancer types including breast, prostate and colon cancer. The anti-cancer actions of n-3 PUFAs are mainly attributed to their role in the modulation of a wide array of cellular processes including membrane dynamics, apoptosis, inflammation, angiogenesis, oxidative stress, gene expression and signal transduction pathways. On the contrary, n-6 PUFAs have been shown to exert pro-tumor actions; however, the inconsistent findings and controversial data emphasize upon the need to further investigation. Nevertheless, one of the biggest challenges in future is to optimize the n-6 to n-3 ratio despite the genetic predisposition, age, gender and disease severity. Moreover, a better understanding of the potential risks and benefits as well as the cellular and molecular mechanisms of the basic actions of these PUFAs is required to explore their role as adjuvants in cancer therapy. All these aspects will be reviewed in this chapter.

RAE1 promotes nitrosamine-induced malignant transformation of human esophageal epithelial cells through PPARα-mediated lipid metabolism

Esophageal cancer (EC) is the sixth cause of cancer-related deaths and still is a significant public health problem globally. Nitrosamines exposure represents a major health concern increasing EC risks. Exploring the mechanisms induced by nitrosamines may contribute to the prevention and early detection of EC. However, the mechanism of nitrosamine carcinogenesis remains unclear. Ribonucleic acid export 1 (RAE1), has an important role in mediating diverse cancer types, but, to date, there has been no study for any functional role of RAE1 in esophageal carcinogenesis. Here, we successfully verified the nitrosamine-induced malignant transformation cell (MNNG-M) by xenograft tumor model, based on which it was found that RAE1 was upregulation in the early stage of nitrosamine-induced esophageal carcinogenesis and EC tissues. RAE1 knockdown led to severe blockade in G2/M phase and significant inhibition of proliferation of MNNG-M cells, whereas RAE1 overexpression had the opposite effect. In addition, peroxisome proliferator-activated receptor-alpha (PPARα), was demonstrated as a downstream target gene of RAE1, and its down-regulation reduced lipid accumulation, resulting in causing cells accumulation in the G2/M phase. Mechanistically, we found that RAE1 regulates the lipid metabolism by maintaining the stability of PPARα mRNA. Taken together, our study reveals that RAE1 promotes malignant transformation of human esophageal epithelial cells (Het-1A) by regulating PPARα-mediated lipid metabolism to affect cell cycle progression, and offers a new explanation of the mechanisms underlying esophageal carcinogenesis.

Accumulation of Linoleic Acid by Altered Peroxisome Proliferator-Activated Receptor-α Signaling Is Associated with Age-Dependent Hepatocarcinogenesis in Ppara Transgenic Mice

Long-term ligand activation of PPARα in mice causes hepatocarcinogenesis through a mechanism that requires functional PPARα. However, hepatocarcinogenesis is diminished in both Ppara-null and PPARA-humanized mice, yet both lines develop age-related liver cancer independently of treatment with a PPARα agonist. Since PPARα is a master regulator of liver lipid metabolism in the liver, lipidomic analyses were carried out in wild-type, Ppara-null, and PPARA-humanized mice treated with and without the potent agonist GW7647. The levels of hepatic linoleic acid in Ppara-null and PPARA-humanized mice were markedly higher compared to wild-type controls, along with overall fatty liver. The number of liver CD4+ T cells was also lower in Ppara-null and PPARA-humanized mice and was negatively correlated with the elevated linoleic acid. Moreover, more senescent hepatocytes and lower serum TNFα and IFNγ levels were observed in Ppara-null and PPARA-humanized mice with age. These studies suggest a new role for PPARα in age-associated hepatocarcinogenesis due to altered lipid metabolism in Ppara-null and PPARA-humanized mice and the accumulation of linoleic acid as part of an overall fatty liver that is associated with loss of CD4+ T cells in the liver in both transgenic models. Since fatty liver is a known causal risk factor for liver cancer, Ppara-null and PPARA-humanized mice are valuable models for examining the mechanisms of PPARα and age-dependent hepatocarcinogenesis.

Therapeutic effect of fenofibrate for non-alcoholic steatohepatitis in mouse models is dependent on regime design

Background: Non-alcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver diseases. In most cases, NAFLD progresses from benign steatosis to steatohepatitis (NASH), and then to cirrhosis. No treatment is currently approved for NAFLD/NASH in the clinic. Fenofibrate (FENO) has been clinically used to treat dyslipidemia for more than a half century, but its effects on NASH are not established. FENO's half-life is quite different between rodent and human. The aim of this study was to investigate the potential of pharmacokinetic-based FENO regime for NASH treatment and the underlying mechanisms. Methods: Two typical mouse NASH models, methionine-choline deficient (MCD) diet-fed mice and choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD)-fed mice, were used. MCD model was designed as therapeutic evaluation in experiment 1 and CDAHFD model was designed as preventive in experiment 2. Three doses of FENO (5, 25, 125 mg/kg), two times a day (BID), were administered to the above models. Serum markers of liver injury, cholestasis, and the histology of liver tissues were investigated. Normal mice were used as a model in experiment 3 for toxicity evaluation, Quantitative-PCR and Western Blot assays were used to investigate the inflammatory responses, bile acid synthesis as well as lipid catabolism. Results: Mice on the MCD and CDAHFD diets developed steatohepatitis as expected. Treatment with FENO (25 mg/kg·BID) significantly decreased hepatic steatosis, inflammation and fibrosis in both therapeutic and preventive models. In the MCD model, the therapeutic action of FENO (25 mg/kg·BID) and 125 mg/kg·BID on histopathology and the expression of inflammatory cytokines were comparable. In reducing macrophage infiltration and bile acid load, FENO (25 mg/kg·BID) was superior to 125 mg/kg·BID. In all the aspects mentioned above, FENO (25 mg/kg·BID) was the best among the 3 doses in the CDAHFD model. In a third experiment, the effects of FENO (25 mg/kg·BID) and 125 mg/kg·BID on lipid catabolism were comparable, but 125 mg/kg·BID increased the expression of inflammatory factors and bile acid load. In both models, FENO (5 mg/kg·BID) showed little effect in hepatic steatosis and inflammation, neither the adverse effects. FENO (125 mg/kg·BID) aggravated liver inflammation, increased bile acid synthesis, and promoted the potential of liver proliferation. In toxicity risk assay, FENO (25 mg/kg·BID) treatment showed low potential to trigger bile acid synthesis, inflammation and hepatocyte proliferation. Conclusion: A new regime, FENO (25 mg/kg·BID) is potentially a therapeutic strategy for the NASH treatment. Translational medicine is warranted to prove its effectiveness in the clinic.

A systematic and comprehensive analysis of T cell exhaustion related to therapy in lung adenocarcinoma tumor microenvironment

Background: T cell exhaustion (TEX) is an important immune escape mechanism, and an in-depth understanding of it can help improve cancer immunotherapy. However, the prognostic role of TEX in malignant lung adenocarcinoma (LUAD) remains unclear. Methods: Through TCGA and GEO datasets, we enrolled a total of 498 LUAD patients. The patients in TCGA-LUAD were unsupervised clustered into four clusters according to TEX signaling pathway. WGCNA analysis, survival random forest analysis and lasso regression analysis were used to select five differentially expressed genes among different clusters to construct a TEX risk model. The risk model was subsequently validated with GEO31210. By analyzing signaling pathways, immune cells and immune checkpoints using GSEA, GSVA and Cibersortx, the relationship between TEX risk score and these variables was evaluated. In addition, we further analyzed the expression of CCL20 at the level of single-cell RNA-seq and verified it in cell experiments. Results: According to TEX signaling pathway, people with better prognosis can be distinguished. The risk model constructed by CD109, CCL20, DKK1, TNS4, and TRIM29 genes could further accurately identify the population with poor prognosis. Subsequently, it was found that dendritic cells, CD44 and risk score were closely related. The final single-cell sequencing suggested that CCL2O is a potential therapeutic target of TEX, and the interaction between TEX and CD8 + T is closely related. Conclusion: The classification of T cell depletion plays a crucial role in the clinical decision-making of lung adenocarcinoma and needs to be further deepened.

The Role of PPARs in Breast Cancer

Breast cancer is a malignant tumor with high morbidity and lethality. Its pathogenesis is related to the abnormal expression of many genes. The peroxisome proliferator-activated receptors (PPARs) are a class of ligand-dependent transcription factors in the nuclear receptor superfamily. They can regulate the transcription of a large number of target genes, which are involved in life activities such as cell proliferation, differentiation, metabolism, and apoptosis, and regulate physiological processes such as glucose metabolism, lipid metabolism, inflammation, and wound healing. Further, the changes in its expression are associated with various diseases, including breast cancer. The experimental reports related to "PPAR" and "breast cancer" were retrieved from PubMed since the discovery of PPARs and summarized in this paper. This review (1) analyzed the roles and potential molecular mechanisms of non-coordinated and ligand-activated subtypes of PPARs in breast cancer progression; (2) discussed the correlations between PPARs and estrogen receptors (ERs) as the nuclear receptor superfamily; and (3) investigated the interaction between PPARs and key regulators in several signaling pathways. As a result, this paper identifies PPARs as targets for breast cancer prevention and treatment in order to provide more evidence for the synthesis of new drugs targeting PPARs or the search for new drug combination treatments.

A time differentiated dietary intervention effect on the biomarkers of exposure to pyrethroids and neonicotinoids pesticides

Tailoring medical models to the right person or risk subgroups delivered at the right time is important in personalized medicine/prevention initiatives. The CIRCA-CHEM randomized 2x2 crossover pilot trial investigated whether the consumption of fruits/vegetables within a time-restricted daily window would affect urinary biomarkers of exposure to neonicotinoids (6-chloronicotinic acid, 6-CN) and pyrethroids (3-phenoxybenzoic acid, 3-PBA) pesticides, a biomarker of oxidative damage (4-hydroxynonenal, 4-HNE) and the associated urinary NMR metabolome. A statistically significant difference (p < 0.001) in both creatinine-adjusted 6-CN and 3-PBA levels was observed between the two-time dietary intervention windows (morning vs. evening). In the evening intervention period, pesticides biomarker levels were higher compared to the baseline, whereas in the morning period, pesticide levels remained unchanged. Positive associations were observed between pesticides and 4-HNE suggesting a diurnal chrono-window of pesticide toxicity. The discovery of a chronotoxicity window associated with chrono-disrupted metabolism of food contaminants may find use in personalized medicine initiatives.

Adverse Effects of Perfluorooctane Sulfonate on the Liver and Relevant Mechanisms

Perfluorooctane sulfonate (PFOS) is a persistent, widely present organic pollutant. PFOS can enter the human body through drinking water, ingestion of food, contact with utensils containing PFOS, and occupational exposure to PFOS, and can have adverse effects on human health. Increasing research shows that the liver is the major target of PFOS, and that PFOS can damage liver tissue and disrupt its function; however, the exact mechanisms remain unclear. In this study, we reviewed the adverse effects of PFOS on liver tissue and cells, as well as on liver function, to provide a reference for subsequent studies related to the toxicity of PFOS and liver injury caused by PFOS.

Myeloid peroxisome proliferator-activated receptor α deficiency accelerates liver regeneration via IL-6/STAT3 pathway after 2/3 partial hepatectomy in mice

Background

Liver regeneration is a fundamental process for sustained body homeostasis and liver function recovery after injury. Emerging evidence demonstrates that myeloid cells play a critical role in liver regeneration by secreting cytokines and growth factors. Peroxisome proliferator-activated receptor α (PPARα), the target of clinical lipid-lowering fibrate drugs, regulates cell metabolism, proliferation, and survival. However, the role of myeloid PPARα in partial hepatectomy (PHx)-induced liver regeneration remains unknown.

Methods

Myeloid-specific PPARa-deficient (Ppara ^Mye-/-) mice and the littermate controls (Ppara ^fl/fl) were subjected to sham or 2/3 PHx to induce liver regeneration. Hepatocyte proliferation and mitosis were assessed by immunohistochemical (IHC) staining for 5-bromo-2'-deoxyuridine (BrdU) and Ki67 as well as hematoxylin and eosin (H&E) staining. Macrophage and neutrophil infiltration into livers were reflected by IHC staining for galectin-3 and myeloperoxidase (MPO) as well as flow cytometry analysis. Macrophage migration ability was evaluated by transwell assay. The mRNA levels for cell cycle or inflammation-related genes were measured by quantitative real-time RT-PCR (qPCR). The protein levels of cell proliferation related protein and phosphorylated signal transducer and activator of transcription 3 (STAT3) were detected by Western blotting.

Results

Ppara ^Mye-/- mice showed enhanced hepatocyte proliferation and mitosis at 32 h after PHx compared with Ppara ^fl/fl mice, which was consistent with increased proliferating cell nuclear antigen (Pcna) mRNA and cyclinD1 (CYCD1) protein levels in Ppara ^Mye-/- mice at 32 h after PHx, indicating an accelerated liver regeneration in Ppara ^Mye-/- mice. IHC staining showed that macrophages and neutrophils were increased in Ppara ^Mye-/- liver at 32 h after PHx. Livers of Ppara ^Mye-/- mice also showed an enhanced infiltration of M1 macrophages at 32 h after PHx. In vitro, Ppara-deficient bone marrow-derived macrophages (BMDMs) exhibited markedly enhanced migratory capacity and upregulated M1 genes Il6 and Tnfa but downregulated M2 gene Arg1 expressions. Furthermore, the phosphorylation of STAT3, a key transcript factor mediating IL6-promoted hepatocyte survival and proliferation, was reinforced in the liver of Ppara ^Mye-/- mice after PHx.

Conclusions

This study provides evidence that myeloid PPARα deficiency accelerates PHx-induced liver regeneration via macrophage polarization and consequent IL-6/STAT3 activation, thus providing a potential target for manipulating liver regeneration.

Bempedoic acid as a PPARα activator: new perspectives for hepatic steatosis treatment in a female rat experimental model

INTRODUCTION

In its initial stages, nonalcoholic fatty liver disease presents hypertriglyceridemia and accumulation of lipids in the liver (hepatic steatosis). Bempedoic acid is an ATP:citrate lyase inhibitor that promotes a dual inhibition of the synthesis of cholesterol and fatty acids. However, its effect in the prevention / treatment of hepatic steatosis and hypertriglyceridemia has not been investigated. The aim of our work has been to elucidate whether bempedoic acid, through a mechanism other than ATP:citrate lyase inhibition, reverses these metabolic alterations.

EXPERIMENTAL DESIGN

The study was carried out in female Sprague-Dawley rats fed, for three months, with a high fat diet supplemented with fructose (10% w/v) in drinking water. During the last month, bempedoic acid (30mg/kg/day) was administered to a group of animals. Zoometric and plasmatic parameters were analyzed, gene and protein expression analysis were performed in liver samples and PPAR-PPRE binding activity was determined.

RESULTS

Our interventional model developed hepatic steatosis and hypertriglyceridemia. Despite an increase in total caloric intake, there was no increase in body weight of the animals. The administration of bempedoic acid significantly reduced hepatic steatosis and promoted a marked hepatocyte hypertrophy. There was a 66% increase in the liver weight of the animals treated with the drug that was not accompanied by modifications in the markers of inflammation, oxidative stress, or endoplasmic reticulum stress. Bempedoic acid activated the peroxisome proliferator activated nuclear receptor (PPARα) and its target genes.

CONCLUSIONS

Bempedoic acid could be an effective therapy for the treatment of fatty liver and associated cardiovascular risk. Bempedoic acid has other mechanisms of action besides the inhibition of ATP: citrate lyase, such as the activation of PPARα, which could explain the reduction in hepatic steatosis and the increase in liver weight observed in animals treated with the drug.

The role of mouse and human peroxisome proliferator-activated receptor-α in modulating the hepatic effects of perfluorooctane sulfonate in mice

Perfluorooctane sulfonate (PFOS) is a stable environmental contaminant that can activate peroxisome proliferator-activated receptor alpha (PPARα). In the present work, the specific role of mouse and human PPARα in mediating the hepatic effects of PFOS was examined in short-term studies using wild type, Ppara-null and PPARA-humanized mice. Mice fed 0.006 % PFOS for seven days (∼10 mg/kg/day), or 0.003 % PFOS for twenty-eight days (∼5 mg/kg/day), exhibited higher liver and serum PFOS concentrations compared to controls. Relative liver weights were also higher following exposure to dietary PFOS in all three genotypes as compared vehicle fed control groups. Histopathological examination of liver sections from mice treated for twenty-eight days with 0.003 % PFOS revealed a phenotype consistent with peroxisome proliferation, in wild-type and PPARA-humanized mice that was not observed in Ppara-null mice. With both exposures, expression of the PPARα target genes, Acox1, Cyp4a10, was significantly increased in wild type mice but not in Ppara-null or PPARA-humanized mice. By contrast, expression of the constitutive androstane receptor (CAR) target gene, Cyp2b10, and the pregnane X receptor (PXR) target gene, Cyp3a11, were higher in response to PFOS administration in all three genotypes compared to controls for both exposure periods. These results indicate that mouse PPARα can be activated in the liver by PFOS causing increased expression of Acox1, Cyp4a10 and histopathological changes in the liver. While histopathological analyses indicated the presence of mouse PPARα-dependent hepatic peroxisome proliferation in wild-type (a response associated with activation of PPARα) and a similar phenotype in PPARA-humanized mice, the lack of increased Acox1 and Cyp4a10 mRNA by PFOS in PPARA-humanized mice indicates that the human PPARα was not as responsive to PFOS as mouse PPARα with this dose regimen. Moreover, results indicate that hepatomegaly caused by PFOS does not require mouse or human PPARα and could be due to effects induced by activation of CAR and/or PXR.

Targeting Peroxisome Proliferator-Activated Receptor-β/δ (PPARβ/δ) for the Treatment or Prevention of Alcoholic Liver Disease

Excessive, chronic alcohol consumption can lead to alcoholic liver disease. The etiology of alcoholic liver disease is multifactorial and is influenced by alterations in gene expression and changes in fatty acid metabolism, oxidative stress, and insulin resistance. These events can lead to steatosis, fibrosis, and eventually to cirrhosis and liver cancer. Many of these functions are regulated by peroxisome proliferator-activated receptors (PPARs). Thus, it is not surprising that PPARs can modulate the mechanisms that cause alcoholic liver disease. While the roles of PPARα and PPARγ are clearer, the role of PPARβ/δ in alcoholic liver disease requires further clarification. This review summarizes the current understanding based on recent studies that indicate that PPARβ/δ can likely be targeted for the treatment and/or the prevention of alcoholic liver disease.

A Novel Multidrug Combination Mitigates Rat Liver Steatosis Through Activating AMPK Pathway During Normothermic Machine Perfusion

BACKGROUND

Hepatic steatosis is now the leading cause of liver discards in deceased donors. Previous studies [Yarmush formula (Y) defatting] have successfully reduced the fat content by treating rat steatotic livers on extracorporeal normothermic machine perfusion (NMP) with a multidrug combination including the GW compounds that were linked to an increased risk of carcinogenesis.

METHODS

We developed a novel multidrug combination by replacing the GW compounds with 2 polyphenols, epigallocatechin-3-gallate (E) and resveratrol (R). Sixteen rat livers were placed on NMP and assigned to control, Y defatting, Y + E + R defatting, or Y'-GW + E + R defatting groups (Y'-GW = 90% dose-reduced Y defatting, n = 4/group).

RESULTS

All livers in defatting groups had significant decreases in hepatic triglyceride content at the end of the experiment. However, livers treated with our novel Y'-GW + E + R combination had evidence of increased metabolism and less hepatocyte damage and carcinogenic potential. Our Y'-GW + E + R combination had increased phosphorylation of AMP-activated protein kinase (P = 0.019) and acetyl-CoA carboxylase (P = 0.023) compared with control; these were not increased in Y + E + R group and actually decreased in the Y group. Furthermore, the Y'-GW + E + R group had less evidence of carcinogenic potential with no increase in AKT phosphorylation compared with control (P = 0.089); the Y (P = 0.031) and Y + E + R (P = 0.035) groups had striking increases in AKT phosphorylation. Finally, our Y'-GW + E + R showed less evidence of hepatocyte damage with significantly lower perfusate alanine aminotransferase (P = 0.007) and aspartate aminotransferase (P = 0.014) levels.

CONCLUSIONS

We have developed a novel multidrug combination demonstrating promising defatting efficacy via activation of the AMP-activated protein kinase pathway with an optimized safety profile and reduced hepatotoxicity during ex vivo NMP.

The transcription factors CREBH, PPARa, and FOXO1 as critical hepatic mediators of diet-induced metabolic dysregulation

The liver is a critical mediator of lipid and/or glucose homeostasis and is a primary organ involved in dynamic changes during feeding and fasting. Additionally, hepatic-centric pathways are prone to dysregulation during pathophysiological states including metabolic syndrome (MetS) and non-alcoholic fatty liver disease. Omics platforms and GWAS have elucidated genes related to increased risk of developing MetS and related disorders, but mutations in these metabolism-related genes are rare and cannot fully explain the increasing prevalence of MetS-related pathologies worldwide. Complex interactions between diet, lifestyle, environmental factors, and genetic predisposition jointly determine inter-individual variability of disease risk. Given the complexity of these interactions, researchers have focused on master regulators of metabolic responses incorporating and mediating the impact of multiple environmental cues. Transcription factors are DNA binding, terminal executors of signaling pathways that modulate the cellular responses to complex metabolic stimuli and are related to the control of hepatic lipid and glucose homeostasis. Among numerous hepatic transcription factors involved in regulating metabolism, three emerge as key players in transducing nutrient sensing, which are dysregulated in MetS-related perturbations in both clinical and preclinical studies: cAMP Responsive Element Binding Protein 3 Like 3 (CREB3L3), Peroxisome Proliferator Activated Receptor Alpha (PPAR), and Forkhead Box O1 (FOXO1). Additionally, these three transcription factors appear to be amenable to dietary and/or nutrient-based therapies, being potential targets of nutritional therapy. In this review we aim to describe the activation, regulation, and impact of these transcription factors in the context of metabolic homeostasis. We also summarize their perspectives in MetS and nutritional therapies.

Species differences between mouse and human PPARα in modulating the hepatocarcinogenic effects of perinatal exposure to a high-affinity human PPARα agonist in mice

Evidence suggests that species differences exist between rodents and humans in their biological responses to ligand activation of PPARα. Moreover, neonatal/postnatal rodents may be more sensitive to the effects of activating PPARα. Thus, the present studies examined the effects of chronic ligand activation of PPARα initiated during early neonatal development and continued into adulthood on hepatocarcinogenesis in mice. Wild-type, Ppara-null, or PPARA-humanized mice were administered a potent, high affinity human PPARα agonist GW7647, and cohorts of mice were examined over time. Activation of PPARα with GW7647 increased expression of known PPARα target genes in liver and was associated with hepatomegaly, increased hepatic cytotoxicity and necrosis, increased expression of hepatic MYC, and a high incidence of hepatocarcinogenesis in wild-type mice. These effects did not occur or were largely diminished in Ppara-null and PPARA-humanized mice, although background levels of hepatocarcinogenesis were also noted in both Ppara-null and PPARA-humanized mice. More fatty change (steatosis) was also observed in both Ppara-null and PPARA-humanized mice independent of GW7647 administration. Results from these studies indicate that the mouse PPARα is required to mediate hepatocarcinogenesis induced by GW7647 in mice and that activation of the human PPARα with GW7647 in PPARA-humanized mice are diminished compared to wild-type mice. Ppara-null and PPARA-humanized mice are valuable tools for examining species differences in the mechanisms of PPARα-induced hepatocarcinogenesis, but background levels of liver cancer observed in aged Ppara-null and PPARA-humanized mice must be considered when interpreting results from studies that use these models. These results also demonstrate that early life exposure to a potent human PPARα agonist does not enhance sensitivity to hepatocarcinogenesis.

Diminished hepatocarcinogenesis by a potent, high affinity human PPARα agonist in PPARA-humanized mice

Ppara-null and PPARA-humanized mice are refractory to hepatocarcinogenesis caused by the peroxisome proliferator-activated receptor-α (PPARα) agonist Wy-14,643. However, the duration of these earlier studies was limited to approximately one year of treatment, and the ligand used has higher affinity for the mouse PPARα compared to the human PPARα. Thus, the present study examined the effect of long-term administration of a potent, high affinity human PPARα agonist (GW7647) on hepatocarcinogenesis in wild-type, Ppara-null, or PPARA-humanized mice. In wild-type mice, GW7647 caused hepatic expression of known PPARα target genes, hepatomegaly, hepatic MYC expression, hepatic cytotoxicity, and a high incidence of hepatocarcinogenesis. By contrast, these effects were essentially absent in Ppara-null mice or diminished in PPARA-humanized mice, although hepatocarcinogenesis was observed in both genotypes. Enhanced fatty change (steatosis) was also observed in both Ppara-null and PPARA-humanized mice independent of GW7647. PPARA-humanized mice administered GW7647 also exhibited increased necrosis after five weeks of treatment. Results from these studies demonstrate that the mouse PPARα is required for hepatocarcinogenesis induced by GW7647 administered throughout adulthood. Results also indicate that a species difference exists between rodent and human PPARα in the response to ligand activation of PPARα. The hepatocarcinogenesis observed in control and treated Ppara-null mice is likely mediated in part by increased hepatic fatty change, whereas the hepatocarcinogenesis observed in PPARA-humanized mice may also be due to enhanced fatty change and cytotoxicity that could be influenced by minimal activity of the human PPARα in this mouse line on downstream mouse PPARα target genes. The Ppara-null and PPARA-humanized mouse models are valuable tools for examining the mechanisms of PPARα-induced hepatocarcinogenesis but the background level of liver cancer must be controlled for in the design and interpretation of studies that use these mice.

Serum levels of circulating microRNA-107 are elevated in patients with early-stage HCC

Background

Early detection of hepatocellular carcinoma (HCC), the most common primary liver malignancy, is crucial to offer patients a potentially curative treatment strategy such as surgical resection or liver transplantation (LT). However, easily accessible biomarkers facilitating an early diagnosis of HCC as well as a reliable risk prediction are currently missing. The microRNA(miR)-107 has recently been described as a driver of HCC in both murine and human HCC but data on circulating miR-107 in HCC patients are scarce. In the present study, we evaluated a potential diagnostic and/or prognostic role of circulating miR-107 in patients undergoing tumor resection or LT for early-stage HCC.

Methods

The Kmplot bioinformatic tool was used to query publicly available databases (including TCGA, GEO and EGA) in order to analyse the prognostic value of tumoral miR-107 expression in HCC patients (n = 372). Serum levels of miR-107 were measured by qPCR in n = 45 HCC patients undergoing surgical tumor resection (n = 37) or LT (n = 8) as well as n = 18 healthy control samples. Results were correlated with clinical data.

Results

A high tumoral expression of miR-107 was associated with a significantly better overall survival compared to patients with low miR-107 expression levels (HR 0.69, 95% CI 0.48–0.99, p = 0.041). In addition, serum levels of miR-107 were significantly higher in HCC patients when compared to healthy controls. However, miR-107 serum levels in HCC patients were independent of different disease etiology, tumor stage or tumor grading. HCC patients with baseline miR-107 expression levels above a calculated ideal prognostic cut-off value (9.82) showed a clear trend towards an impaired overall survival (p = 0.119).

Conclusion

Tumoral miR-107 expression levels are a potential prognostic marker in early stage HCC. Furthermore, we describe a potential role of circulating miR-107 levels as a diagnostic biomarker in patients with early-stage HCC.

Branched-Chain Fatty Acids as Mediators of the Activation of Hepatic Peroxisome Proliferator-Activated Receptor Alpha by a Fungal Lipid Extract

The study aimed to test the hypothesis that monomethyl branched-chain fatty acids (BCFAs) and a lipid extract of Conidiobolus heterosporus (CHLE), rich in monomethyl BCFAs, are able to activate the nuclear transcription factor peroxisome proliferator-activated receptor alpha (PPARalpha). Rat Fao cells were incubated with the monomethyl BCFAs 12-methyltridecanoic acid (MTriA), 12-methyltetradecanoic acid (MTA), isopalmitic acid (IPA) and 14-methylhexadecanoic acid (MHD), and the direct activation of PPARalpha was evaluated by reporter gene assay using a PPARalpha responsive reporter gene. Furthermore, Fao cells were incubated with different concentrations of the CHLE and PPARalpha activation was also evaluated by using the reporter gene assay, and by determining the mRNA concentrations of selected PPARalpha target genes by real-time RT-PCR. The reporter gene assay revealed that IPA and the CHLE, but not MTriA, MHD and MTA, activate the PPARalpha responsive reporter gene. CHLE dose-dependently increased mRNA concentrations of the PPARalpha target genes acyl-CoA oxidase (ACOX1), cytochrome P450 4A1 (CYP4A1), carnitine palmitoyltransferase 1A (CPT1A) and solute carrier family 22 (organic cation/carnitine transporter), member 5 (SLC22A5). In conclusion, the monomethyl BCFA IPA is a potent PPARalpha activator. CHLE activates PPARalpha-dependent gene expression in Fao cells, an effect that is possibly mediated by IPA.

Role of peroxisome proliferator-activated receptors in stroke prevention and therapy-The best is yet to come?

Role of peroxisome proliferator-activated receptors (PPARs) in the pathophysiology of stroke and protective effects of PPAR ligands have been widely investigated in the last 20 years. Activation of all three PPAR isoforms, but especially PPAR-γ, was documented to limit postischemic injury in the numerous in vivo, as well as in in vitro studies. PPARs have been demonstrated to act on multiple mechanisms and were shown to activate multiple protective pathways related to inflammation, apoptosis, BBB protection, neurogenesis, and oxidative stress. The aim of this review was to summarize two decades of PPAR research in stroke with emphasis on in vivo animal studies. We focus on each PPAR receptor separately and detail their implication in stroke. This review also discusses recent clinical efforts in the field and the epidemiological data with regard to role of PPAR polymorphisms in susceptibility to stroke, and tries to draw conclusions and describe future perspectives.

Perfluorooctane sulfonate alters gut microbiota-host metabolic homeostasis in mice

Perfluorooctane sulfonate (PFOS) is a persistent environmental chemical whose biological effects are mediated by multiple mechanisms. Recent evidence suggests that the gut microbiome may be directly impacted by and/or alter the fate and effects of environmental chemicals in the host. Thus, the aim of this study was to determine whether PFOS influences the gut microbiome and its metabolism, and the host metabolome. Four groups of male C57BL/6 J mice were fed a diet with or without 0.003 %, 0.006 %, or 0.012 % PFOS, respectively. 16S rRNA gene sequencing, metabolomic, and molecular analyses were used to examine the gut microbiota of mice after dietary PFOS exposure. Dietary PFOS exposure caused a marked change in the gut microbiome compared to controls. Dietary PFOS also caused dose-dependent changes in hepatic metabolic pathways including those involved in lipid metabolism, oxidative stress, inflammation, TCA cycle, glucose, and amino acid metabolism. Changes in the metabolome correlated with changes in genes that regulate these pathways. Integrative analyses also demonstrated a strong correlation between the alterations in microbiota composition and host metabolic profiles induced by PFOS. Further, using isolated mouse cecal contents, PFOS exposure directly affected the gut microbiota metabolism. Results from these studies demonstrate that the molecular and biochemical changes induced by PFOS are mediated in part by the gut microbiome, which alters gene expression and the host metabolome in mice.

Advancing Aptamers as Molecular Probes for Cancer Theranostic Applications-The Role of Molecular Dynamics Simulation

Theranostics cover emerging technologies for cell biomarking for disease diagnosis and targeted introduction of drug ingredients to specific malignant sites. Theranostics development has become a significant biomedical research endeavor for effective diagnosis and treatment of diseases, especially cancer. An efficient biomarking and targeted delivery strategy for theranostic applications requires effective molecular coupling of binding ligands with high affinities to specific receptors on the cancer cell surface. Bioaffinity offers a unique mechanism to bind specific target and receptor molecules from a range of non-targets. The binding efficacy depends on the specificity of the affinity ligand toward the target molecule even at low concentrations. Aptamers are fragments of genetic materials, peptides, or oligonucleotides which possess enhanced specificity in targeting desired cell surface receptor molecules. Aptamer-target binding results from several inter-molecular interactions including hydrogen bond formation, aromatic stacking of flat moieties, hydrophobic interaction, electrostatic, and van der Waals interactions. Advancements in Systematic Evolution of Ligands by Exponential Enrichment (SELEX) assay has created the opportunity to artificially generate aptamers that specifically bind to desired cancer and tumor surface receptors with high affinities. This article discusses the potential application of molecular dynamics (MD) simulation to advance aptamer-mediated receptor targeting in targeted cancer therapy. MD simulation offers real-time analysis of the molecular drivers of the aptamer-receptor binding and generate optimal receptor binding conditions for theranostic applications. The article also provides an overview of different cancer types with focus on receptor biomarking and targeted treatment approaches, conventional molecular probes, and aptamers that have been explored for cancer cells targeting.

Anti-NASH Drug Development Hitches a Lift on PPAR Agonism

Non-alcoholic fatty liver disease (NAFLD) affects one-third of the population worldwide, of which a substantial number of patients suffer from non-alcoholic steatohepatitis (NASH). NASH is a severe condition characterized by steatosis and concomitant liver inflammation and fibrosis, for which no drug is yet available. NAFLD is also generally conceived as the hepatic manifestation of the metabolic syndrome. Consequently, well-established drugs that are indicated for the treatment of type 2 diabetes and hyperlipidemia are thought to exert effects that alleviate the pathological features of NASH. One class of these drugs targets peroxisome proliferator-activated receptors (PPARs), which are nuclear receptors that play a regulatory role in lipid metabolism and inflammation. Therefore, PPARs are now also being investigated as potential anti-NASH druggable targets. In this paper, we review the mechanisms of action and physiological functions of PPARs and discuss the position of the different PPAR agonists in the therapeutic landscape of NASH. We particularly focus on the PPAR agonists currently under evaluation in clinical phase II and III trials. Preclinical strategies and how refinement and optimization may improve PPAR-targeted anti-NASH drug testing are also discussed. Finally, potential caveats related to PPAR agonism in anti-NASH therapy are stipulated.

WY-14643 Regulates CYP1B1 Expression through Peroxisome Proliferator-Activated Receptor α-Mediated Signaling in Human Breast Cancer Cells

Human cytochrome P450 1B1 (CYP1B1)-mediated biotransformation of endobiotics and xenobiotics plays an important role in the progression of human breast cancer. In this study, we investigated the effects of WY-14643, a peroxisome proliferator-activated receptor α (PPARα) agonist, on CYP1B1 expression and the related mechanism in MCF7 breast cancer cells. We performed quantitative reverse transcription-polymerase chain reaction, transient transfection, and chromatin immunoprecipitation to evaluate the effects of PPARα on peroxisome proliferator response element (PPRE)-mediated transcription. WY-14643 increased the protein and mRNA levels of CYP1B1, as well as promoter activity, in MCF-7 cells. Moreover, WY-14643 plus GW6471, a PPARα antagonist, significantly inhibited the WY-14643-mediated increase in CYP1B1 expression. PPARα knockdown by a small interfering RNA markedly suppressed the induction of CYP1B1 expression by WY-14643, suggesting that WY-14643 induces CYP1B1 expression via a PPARα-dependent mechanism. Bioinformatics analysis identified putative PPREs (−833/−813) within the promoter region of the CYP1B1 gene. Inactivation of these putative PPREs by deletion mutagenesis suppressed the WY-14643-mediated induction of CYP1B1 promoter activation. Furthermore, WY-14643 induced PPARα to assume a form capable of binding specifically to the PPRE-binding site in the CYP1B1 promoter. Our findings suggest that WY-14643 induces the expression of CYP1B1 through activation of PPARα.

PPAR Receptors Expressed from Vectors Containing CMV Promoter Can Enhance Self-Transcription in the Presence of Fatty Acids from CLA-Enriched Egg Yolks-A Novel Method for Studies of PPAR Ligands

PPAR receptors are ligand-dependent transcription factors activated in response to various small lipophilic ligands controlling the expression of different genes involved in cellular differentiation, development, metabolism, and tumorigenesis. Unexpectedly, our previous studies have shown that single plasmid-based expression of PPARs under the control of CMV promoter/enhancer was significantly elevated in the presence of PPAR agonists. Here we show that the PPAR reporters controlled by the CMV promoter/enhancer, that was shown to contain three internal non-canonical PPRE elements, can be used as a fast screening system for more effective PPAR ligands. This model allowed us to confirm our previous results indicating that fatty acids of CLA-enriched egg yolks (EFA-CLAs) are efficient PPAR ligands that can specifically upregulate the expression of PPARα and PPARγ leading to downregulation of MCF-7 cancer cell proliferation. We also show that synthetic cis9,trans11CLA is more effective in transactivation of PPARγ, while trans10,cis12CLA of PPARα receptor indicating the selectivity of the CLA isomers. This report presents a novel, fast, and reliable strategy for simple testing of PPAR ligands using PPAR expressing plasmids containing the CMV promoter/enhancer that can trigger the positive feedback loop of PPAR self-transcription in the presence of PPAR ligands.

Regulatory mechanisms mediated by peroxisome proliferator-activated receptor-β/δ in skin cancer

Considerable progress has been made during the past 20 years towards elucidating the role of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) in skin cancer. In 1999, the original notion that PPARβ/δ was involved with epithelial cell function was postulated based on a correlation between PPARβ/δ expression and the induction of messenger RNAs encoding proteins that mediate terminal differentiation in keratinocytes. Subsequent studies definitively revealed that PPARβ/δ could induce terminal differentiation and inhibit proliferation of keratinocytes. Molecular mechanisms have since been discovered to explain how this nuclear receptor can be targeted for preventing and treating skin cancer. This includes the regulation of terminal differentiation, mitotic signaling, endoplasmic reticulum stress, and cellular senescence. Interestingly, the effects of activating PPARβ/δ can preferentially target keratinocytes with genetic mutations associated with skin cancer. This review provides the history and current understanding of how PPARβ/δ can be targeted for both nonmelanoma skin cancer and melanoma and postulates how future approaches that modulate PPARβ/δ signaling may be developed for the prevention and treatment of these diseases.

Metabolomic insights into pathophysiological mechanisms and biomarker discovery in clear cell renal cell carcinoma

INTRODUCTION

Clear cell renal cell carcinoma (ccRCC) is a metabolic disease, of which the incidence rate is increasing worldwide. Renal carcinoma is characterized by mutations in target genes involved in metabolic pathways. Metabolic reprogramming covers different processes such as aerobic glycolysis, fatty acid metabolism, and the utilization of tryptophan, glutamine, and arginine. In the era of the multi-omics approach (with integrated transcriptomics, proteomics, and metabolomics), discovering biomarkers for early diagnosis is gaining renewed importance. Areas covered: In this review, we discuss the pathophysiological mechanisms underlying ccRCC metabolic reprogramming. In addition, we describe the emerging metabolomics-based biomarkers differentially expressed in ccRCC and the rationale for the recently developed drugs specifically targeting the ccRCC metabolome. Expert opinion: A number of metabolic pathways will be explored in future years, and many of these pathways are potential therapeutic targets and may serve as diagnostic and prognostic biomarkers of ccRCC.

Inverse Association of Fibrates and Liver Cancer: A Population-Based Case-Control Study in Taiwan

This large-scale case-control study in Taiwan elucidated the potential connection between fibrate use and liver cancer by using the Longitudinal Health Insurance Database 2005 with a propensity-score-matching design. In total, 4173 patients diagnosed as having liver cancer were included as cases, and 4173 propensity-score-matched patients without liver cancer were identified as controls. The association between previous fibrate use and liver cancer occurrence was demonstrated using conditional logistic regression. Fibrate use was noted in 371 (8.89%) cases and 481 (11.53%) controls. After adjustments, the cases had significantly lower odds of previous fibrate use than did the controls (adjusted odds ratio 0.70, 95%CI 0.60-0.82); moreover, regardless of the patients' sex, age group, and comorbidities, the cases were less likely to have used fibrates than were the controls. Dose-dependent analysis revealed that 1-695 cumulative defined daily doses of fibrates may significantly induce a protective effect for liver cancer. Although other fibrate dose intervals did not reach statistical significance, the dose-response curve presented the trend of a protective effect for liver cancer among the fibrate users. In summary, fibrate use had a significant protective effect against liver cancer in this Asian population.

Molecular Actions of PPARα in Lipid Metabolism and Inflammation

Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor of clinical interest as a drug target in various metabolic disorders. PPARα also exhibits marked anti-inflammatory capacities. The first-generation PPARα agonists, the fibrates, have however been hampered by drug-drug interaction issues, statin drop-in, and ill-designed cardiovascular intervention trials. Notwithstanding, understanding the molecular mechanisms by which PPARα works will enable control of its activities as a drug target for metabolic diseases with an underlying inflammatory component. Given its role in reshaping the immune system, the full potential of this nuclear receptor subtype as a versatile drug target with high plasticity becomes increasingly clear, and a novel generation of agonists may pave the way for novel fields of applications.

Identification of activation of tryptophan-NAD+ pathway as a prominent metabolic response to thermally oxidized oil through metabolomics-guided biochemical analysis

Consumption of thermally oxidized oil is associated with metabolic disorders, but oxidized oil-elicited changes in the metabolome are not well defined. In this study, C57BL/6 mice were fed the diets containing either control soybean oil or heated soybean oil (HSO) for 4 weeks. HSO-responsive metabolic events were examined through untargeted metabolomics-guided biochemical analysis. HSO directly contributed to the presence of new HSO-derived metabolites in urine and the decrease of polyunsaturated fatty acid-containing phospholipids in serum and the liver. HSO disrupted redox balance by decreasing hepatic glutathione and ascorbic acid. HSO also activated peroxisome proliferator-activated receptors, leading to the decrease of serum triacylglycerols and the changes of cofactors and products in fatty acid oxidation pathways. Most importantly, multiple metabolic changes, including the decrease of tryptophan in serum; the increase of NAD⁺ in the liver; the increases of kynurenic acid, nicotinamide and nicotinamide N-oxide in urine; and the decreases of the metabolites from pyridine nucleotide degradation in the liver indicated that HSO activated tryptophan-NAD⁺ metabolic pathway, which was further confirmed by the upregulation of gene expression in this pathway. Because NAD⁺ and its metabolites are essential cofactors in many HSO-induced metabolic events, the activation of tryptophan-NAD⁺ pathway should be considered as a central metabolic response to the exposure of HSO.

Evaluation of subchronic exposure to triclosan on hepatorenal and reproductive toxicities in prepubertal male rats

Triclosan (TCS), a common antimicrobial ingredient, is present in many consumer products, including soaps, shampoos, and toothpaste. Owing to its widespread use, potential adverse effects on animals and humans may arise from lifetime exposure, but data on chronic prepubertal exposure of TCS are still lacking. The aim of the present study was to investigate the influence of subchronic TCS exposure (0.25, 25, 250, or 750 mg/kg) on target organ toxicity in prepubertal male rats. After daily administration of TCS to rats by oral gavage for 60 d, a significant reduction in body weight and relative weights of liver, kidneys, testes, and adrenal glands was observed in the 750-mg/kg (high dose) group. Serum alanine aminotransferase and aspartate aminotransferase activities as well as levels of blood urea nitrogen, and creatinine were significantly increased at 750 mg/kg TCS. Further, TCS (750 mg/kg) elevated the protein expressions of hepatic CYP2B1, RXR/PPAR, and levels of malondialdehyde. High-dose TCS exposure induced histological changes as evidenced by reduction of Bowman's space, occlusion of the tubular lumen, and degeneration of tubular epithelial cells in the kidney. Tubular necrosis was confirmed as evidenced by a rise in expression of high mobility group box 1 renal protein. Daily sperm production was significantly diminished by high doses of TCS with marked inhibition of androgen receptor protein expression. Our results indicated that subchronic exposure to excessively high concentrations of 750 mg/kg TCS induced hepatorenal and reproductive toxicities in prepubertal male rats; however, the biological relevance of these findings is questionable as these drug levels are not encountered in the environment.

PPARα, a predictor of patient survival in glioma, inhibits cell growth through the E2F1/miR-19a feedback loop

Nuclear receptors such as peroxisome proliferator-activated receptor α (PPARα) are potential therapeutic targets. In this study, we found that PPARα expression was lower in high grade gliomas and PPARα was an independent prognostic factor in GBM patients. PPARα agonism or overexpression inhibited glioma cell proliferation, invasion, and aerobic glycolysis as well as suppressed glioma growth in an orthotopic model. Bioinformatic analysis and luciferase reporter assays showed that miR-19a decreased PPARα expression. E2F1 knockdown up-regulated PPARα and inhibited cell proliferation, invasion, and aerobic glycolysis, but this activity was blocked by miR-19a. Knockdown of E2F1 decreased miR-19a by inhibiting the miR-19a promoter. Moreover, PPARα repressed E2F1 via the p21 pathwayby modulating the transcriptional complexes containing E2F1 and pRB proteins. These results suggest that the E2F1/miR19a/PPARα feedback loop is critical for glioma progression.

The Anticancer Potential of Peroxisome Proliferator-Activated Receptor Antagonists

The effects on cancer-cell proliferation and differentiation mediated by peroxisome proliferator-activated receptors (PPARs) have been widely studied, and pleiotropic outcomes in different cancer models and under different experimental conditions have been obtained. Interestingly, few studies report and little preclinical evidence supports the potential antitumor activity of PPAR antagonists. This review focuses on recent findings on the antitumor in vitro and in vivo effects observed for compounds able to inhibit the three PPAR subtypes in different tumor models, providing a rationale for the use of PPAR antagonists in the treatment of tumors expressing the corresponding receptors.

Redox Regulation of Homeostasis and Proteostasis in Peroxisomes

Peroxisomes are highly dynamic intracellular organelles involved in a variety of metabolic functions essential for the metabolism of long-chain fatty acids, d-amino acids, and many polyamines. A byproduct of peroxisomal metabolism is the generation, and subsequent detoxification, of reactive oxygen and nitrogen species, particularly hydrogen peroxide (H2O2). Because of its relatively low reactivity (as a mild oxidant), H2O2 has a comparatively long intracellular half-life and a high diffusion rate, all of which makes H2O2 an efficient signaling molecule. Peroxisomes also have intricate connections to mitochondria, and both organelles appear to play important roles in regulating redox signaling pathways. Peroxisomal proteins are also subject to oxidative modification and inactivation by the reactive oxygen and nitrogen species they generate, but the peroxisomal LonP2 protease can selectively remove such oxidatively damaged proteins, thus prolonging the useful lifespan of the organelle. Peroxisomal homeostasis must adapt to the metabolic state of the cell, by a combination of peroxisome proliferation, the removal of excess or badly damaged organelles by autophagy (pexophagy), as well as by processes of peroxisome inheritance and motility. More recently the tumor suppressors ataxia telangiectasia mutate (ATM) and tuberous sclerosis complex (TSC), which regulate mTORC1 signaling, have been found to regulate pexophagy in response to variable levels of certain reactive oxygen and nitrogen species. It is now clear that any significant loss of peroxisome homeostasis can have devastating physiological consequences. Peroxisome dysregulation has been implicated in several metabolic diseases, and increasing evidence highlights the important role of diminished peroxisomal functions in aging processes.

The PPARα-dependent rodent liver tumor response is not relevant to humans: addressing misconceptions

A number of industrial chemicals and therapeutic agents cause liver tumors in rats and mice by activating the nuclear receptor peroxisome proliferator-activated receptor α (PPARα). The molecular and cellular events by which PPARα activators induce rodent hepatocarcinogenesis have been extensively studied elucidating a number of consistent mechanistic changes linked to the increased incidence of liver neoplasms. The weight of evidence relevant to the hypothesized mode of action (MOA) for PPARα activator-induced rodent hepatocarcinogenesis is summarized here. Chemical-specific and mechanistic data support concordance of temporal and dose-response relationships for the key events associated with many PPARα activators. The key events (KE) identified in the MOA are PPARα activation (KE1), alteration in cell growth pathways (KE2), perturbation of hepatocyte growth and survival (KE3), and selective clonal expansion of preneoplastic foci cells (KE4), which leads to the apical event-increases in hepatocellular adenomas and carcinomas (KE5). In addition, a number of concurrent molecular and cellular events have been classified as modulating factors, because they potentially alter the ability of PPARα activators to increase rodent liver cancer while not being key events themselves. These modulating factors include increases in oxidative stress and activation of NF-kB. PPARα activators are unlikely to induce liver tumors in humans due to biological differences in the response of KEs downstream of PPARα activation. This conclusion is based on minimal or no effects observed on cell growth pathways and hepatocellular proliferation in human primary hepatocytes and absence of alteration in growth pathways, hepatocyte proliferation, and tumors in the livers of species (hamsters, guinea pigs and cynomolgus monkeys) that are more appropriate human surrogates than mice and rats at overlapping dose levels. Despite this overwhelming body of evidence and almost universal acceptance of the PPARα MOA and lack of human relevance, several reviews have selectively focused on specific studies that, as discussed, contradict the consensus opinion and suggest uncertainty. In the present review, we systematically address these most germane suggested weaknesses of the PPARα MOA.

Imaging Monitoring of Kupffer Cell Function and Hepatic Oxygen Saturation in Preneoplastic Changes During Cholangiocarcinogenesis

We investigated serial changes of the Kupffer cell (KC) function and hepatic oxygen saturation (sO₂) using contrast-enhanced ultrasound imaging (CEUS) and photoacoustic imaging (PAI) in preneoplastic changes during cholangiocarcinogenesis induced by obstructive cholangitis and N-nitrosodimethylamine in a mouse model. The CEUS and PAI were performed to assess Sonazoid contrast agent uptake by KC and changes in the sO₂ of liver parenchyma. An extensive bile ductular reaction, cystic dilatation, and epithelial hyperplasia with dysplastic changes were noted in the experimental group. During the preneoplastic changes, the parenchymal echogenicity on the Kupffer-phase of CEUS was continuously decreased in the experimental group, and which means that the Sonazoid phagocytosis by KC was decreased. The number of KCs was increased in the CD68 analysis, indicating functionally impaired KCs. There was a simultaneous serial decrease in sO₂ on PAI measurement of the experimental group during the preneoplastic changes. The experimental group also showed significantly higher expression of hypoxia-inducible factor-1α and vascular endothelial growth factor protein. Our study demonstrated that KC dysfunction and hypoxic environmental changes were the factors influencing preneoplastic change during cholangiocarcinogenesis, and we could non-invasively monitor these changes using CEUS and PAI.

Inhibition of JNK signalling mediates PPARα-dependent protection against intrahepatic cholestasis by fenofibrate

BACKGROUND AND PURPOSE

Fenofibrate, a PPARα agonist, is the most widely prescribed drug for treating hyperlipidaemia. Although fibrate drugs are reported to be beneficial for cholestasis, their underlying mechanism has not been determined.

EXPERIMENTAL APPROACH

Wild-type mice and Pparα-null mice were pretreated orally with fenofibrate for 3 days, following which α-naphthylisothiocyanate (ANIT) was administered to induce cholestasis. The PPARα agonist WY14643 and JNK inhibitor SP600125 were used to determine the role of PPARα and the JNK pathway, respectively, in cholestatic liver injury. The same fenofibrate regimen was applied to investigate its beneficial effects on sclerosing cholangitis in a DDC-induced cholestatic model.

KEY RESULTS

Fenofibrate, 25 mg·kg^-1 twice a day, totally attenuated ANIT-induced cholestasis and liver injury as indicated by biochemical and histological analyses. This protection occurred in wild-type, but not in Pparα-null, mice. Alterations in bile acid synthesis and transport were found to be an adaptive response rather than a direct effect of fenofibrate. WY14643 attenuated ANIT-induced cholestasis and liver injury coincident with inhibition of JNK signalling. Although SP600125 did not affect cholestasis, it inhibited liver injury in the ANIT model when the dose of fenofibrate used was ineffective. Fenofibrate was also revealed to have a beneficial effect in the sclerosing cholangitis model.

CONCLUSIONS AND IMPLICATIONS

These data suggest that the protective effects of fenofibrate against cholestasis-induced hepatic injury are dependent on PPARα and fenofibrate dose, and are mediated through inhibition of JNK signalling. This mechanism of fenofibrate protection against intrahepatic cholestasis may offer additional therapeutic opportunities for cholestatic liver diseases.

Effects of PPARα inhibition in head and neck paraganglioma cells

Head and neck paragangliomas (HNPGLs) are rare tumors that may cause important morbidity, because of their tendency to infiltrate the skull base. At present, surgery is the only therapeutic option, but radical removal may be difficult or impossible. Thus, effective targets and molecules for HNPGL treatment need to be identified. However, the lack of cellular models for this rare tumor hampers this task. PPARα receptor activation was reported in several tumors and this receptor appears to be a promising therapeutic target in different malignancies. Considering that the role of PPARα in HNPGLs was never studied before, we analyzed the potential of modulating PPARα in a unique model of HNPGL cells. We observed an intense immunoreactivity for PPARα in HNPGL tumors, suggesting that this receptor has an important role in HNPGL. A pronounced nuclear expression of PPARα was also confirmed in HNPGL-derived cells. The specific PPARα agonist WY14643 had no effect on HNPGL cell viability, whereas the specific PPARα antagonist GW6471 reduced HNPGL cell viability and growth by inducing cell cycle arrest and caspase-dependent apoptosis. GW6471 treatment was associated with a marked decrease of CDK4, cyclin D3 and cyclin B1 protein expression, along with an increased expression of p21 in HNPGL cells. Moreover, GW6471 drastically impaired clonogenic activity of HNPGL cells, with a less marked effect on cell migration. Notably, the effects of GW6471 on HNPGL cells were associated with the inhibition of the PI3K/GSK3β/β-catenin signaling pathway. In conclusion, the PPARα antagonist GW6471 reduces HNPGL cell viability, interfering with cell cycle and inducing apoptosis. The mechanisms affecting HNPGL cell viability involve repression of the PI3K/GSK3β/β-catenin pathway. Therefore, PPARα could represent a novel therapeutic target for HNPGL.

Peroxisome Proliferator-Activated Receptor α Activation Suppresses Cytochrome P450 Induction Potential in Mice Treated with Gemfibrozil

Gemfibrozil, a peroxisome proliferator-activated receptor α (PPARα) agonist, is widely used for hypertriglyceridaemia and mixed hyperlipidaemia. Drug-drug interaction of gemfibrozil and other PPARα agonists has been reported. However, the role of PPARα in cytochrome P450 (CYP) induction by fibrates is not well known. In this study, wild-type mice were first fed gemfibrozil-containing diets (0.375%, 0.75% and 1.5%) for 14 days to establish a dose-response relationship for CYP induction. Then, wild-type mice and Pparα-null mice were treated with a 0.75% gemfibrozil-containing diet for 7 days. CYP3a, CYP2b and CYP2c were induced in a dose-dependent manner by gemfibrozil. In Pparα-null mice, their mRNA level, protein level and activity were induced more than those in wild-type mice. So, gemfibrozil induced CYP, and this action was inhibited by activated PPARα. These data suggested that the induction potential of CYPs was suppressed by activated PPARα, showing a potential role of this receptor in drug-drug interactions and metabolic diseases treated with fibrates.

Non-clinical safety evaluation and risk assessment to human of aleglitazar, a dual PPAR α/γ agonist, and its major human metabolite

The non-clinical safety profile of aleglitazar, a peroxisome proliferator activated receptor alpha/gamma agonist, and its major human metabolite M6 was studied in a complete package consisting of drug metabolism and pharmacokinetics characterization, safety pharmacology, genotoxicity, repeat dose toxicity, reproductive toxicity and carcinogenicity studies. These studies identified the following main targets similar to other PPAR agonists: red blood cell parameters, liver, heart, kidney, ovaries, testes, bone marrow, adipose tissue, and fluid accumulation. Additionally, and in the 12-month monkey study only, an increased incidence of generalized hair loss/thinning was observed in all groups including controls. In the rat carcinogenicity study there was no statistically significant increase in tumors. In the mouse carcinogenicity study, there was an increased incidence of angiomatous tumors and there were three males with gallbladder adenoma. No relevant compound-related effects were observed in safety pharmacology, genotoxicity, and a 28-day immunotoxicity rat study. Effects observed in reproductive toxicity studies were similar to those known for other PPARγ agonists. Separate studies with the human metabolite M6 did not reveal findings that would prevent human dosing. Overall, the results from the non-clinical safety studies conducted with aleglitazar and the human metabolite M6 were considered to support the clinical Phase 3 program.

PPARs in the central nervous system: roles in neurodegeneration and neuroinflammation

Over 25 years have passed since peroxisome proliferators-activated receptors (PPARs), were first described. Like other members of the nuclear receptors superfamily, PPARs have been defined as critical sensors and master regulators of cellular metabolism. Recognized as ligand-activated transcription factors, they are involved in lipid, glucose and amino acid metabolism, taking part in different cellular processes, including cellular differentiation and apoptosis, inflammatory modulation and attenuation of acute and chronic neurological damage in vivo and in vitro. Interestingly, PPAR activation can simultaneously reprogram the immune response, stimulate metabolic and mitochondrial functions, promote axonal growth, induce progenitor cells to differentiate into myelinating oligodendrocytes, and improve brain clearance of toxic molecules such as β-amyloid peptide. Although the molecular mechanisms and cross-talk with different molecular pathways are still the focus of intense research, PPARs are considered potential therapeutic targets for several neuropathological conditions, including degenerative disorders such as Alzheimer's, Parkinson's and Huntington's disease. This review considers recent advances regarding PPARs, as well as new PPAR agonists. We focus on the mechanisms behind the neuroprotective effects exerted by PPARs and summarise the roles of PPARs in different pathologies of the central nervous system, especially those associated with degenerative and inflammatory mechanisms.

A Molecular Dynamics-Shared Pharmacophore Approach to Boost Early-Enrichment Virtual Screening: A Case Study on Peroxisome Proliferator-Activated Receptor α

Molecular dynamics (MD) simulations can be used, prior to virtual screening, to add flexibility to proteins and study them in a dynamic way. Furthermore, the use of multiple crystal structures of the same protein containing different co-crystallized ligands can help elucidate the role of the ligand on a protein's active conformation, and then explore the most common interactions between small molecules and the receptor. In this work, we evaluated the contribution of the combined use of MD on crystal structures containing the same protein but different ligands to examine the crucial ligand-protein interactions within the complexes. The study was carried out on peroxisome proliferator-activated receptor α (PPARα). Findings derived from the dynamic analysis of interactions were then used as features for pharmacophore generation and constraints for generating the docking grid for use in virtual screening. We found that information derived from short multiple MD simulations using different molecules within the binding pocket of the target can improve the early enrichment of active ligands in the virtual screening process for this receptor. In the end we adopted a consensus scoring based on docking score and pharmacophore alignment to rank our dataset. Our results showed an improvement in virtual screening performance in early recognition when screening was performed with the Molecular dYnamics SHAred PharmacophorE (MYSHAPE) approach.

Hepatotoxic Effects of Fenofibrate in Spontaneously Hypertensive Rats Expressing Human C-Reactive Protein

Dyslipidemia and inflammation play an important role in the pathogenesis of cardiovascular and liver disease. Fenofibrate has a well-known efficacy to reduce cholesterol and triglycerides. Combination with statins can ameliorate hypolipidemic and anti-inflammatory effects of fibrates. In the current study, we tested the anti-inflammatory and metabolic effects of fenofibrate alone and in combination with rosuvastatin in a model of inflammation and metabolic syndrome, using spontaneously hypertensive rats expressing the human C-reactive protein transgene (SHR-CRP transgenic rats). SHR-CRP rats treated with fenofibrate alone (100 mg/kg body weight) or in combination with rosuvastatin (20 mg/kg body weight) vs. SHR-CRP untreated controls showed increased levels of proinflammatory marker IL6, increased concentrations of ALT, AST and ALP, increased oxidative stress in the liver and necrotic changes of the liver. In addition, SHR-CRP rats treated with fenofibrate, or with fenofibrate combined with rosuvastatin vs. untreated controls, exhibited increased serum triglycerides and reduced HDL cholesterol, as well as reduced hepatic triglyceride, cholesterol and glycogen concentrations. These findings suggest that in the presence of high levels of human CRP, fenofibrate can induce liver damage even in combination with rosuvastatin. Accordingly, these results caution against the possible hepatotoxic effects of fenofibrate in patients with high levels of CRP.

Detection of non-genotoxic hepatocarcinogens and prediction of their mechanism of action in rats using gene marker sets

Several studies have successfully detected hepatocarcinogenicity in rats based on gene expression data. However, prediction of hepatocarcinogens with certain mechanisms of action (MOAs), such as enzyme inducers and peroxisome proliferator-activated receptor α (PPARα) agonists, can prove difficult using a single model and requires a highly toxic dose. Here, we constructed a model for detecting non-genotoxic (NGTX) hepatocarcinogens and predicted their MOAs in rats. Gene expression data deposited in the Open Toxicogenomics Project-Genomics Assisted Toxicity Evaluation System (TG-GATEs) was used to investigate gene marker sets. Principal component analysis (PCA) was applied to discriminate different MOAs, and a support vector machine algorithm was applied to construct the prediction model. This approach identified 106 probe sets as gene marker sets for PCA and enabled the prediction model to be constructed. In PCA, NGTX hepatocarcinogens were classified as follows based on their MOAs: cytotoxicants, PPARα agonists, or enzyme inducers. The prediction model detected hepatocarcinogenicity with an accuracy of more than 90% in 14- and 28-day repeated-dose studies. In addition, the doses capable of predicting NGTX hepatocarcinogenicity were close to those required in rat carcinogenicity assays. In conclusion, our PCA and prediction model using gene marker sets will help assess the risk of hepatocarcinogenicity in humans based on MOAs and reduce the number of two-year rodent bioassays.