PPARs in Liver Diseases and Cancer: Epigenetic Regulation by MicroRNAs

PPARs in Clinical Experimental Medicine after 35 Years of Worldwide Scientific Investigations and Medical Experiments

This year marks the 35th anniversary of Professor Walter Wahli's discovery of the PPARs (Peroxisome Proliferator-Activated Receptors) family of nuclear hormone receptors. To mark the occasion, the editors of the scientific periodical Biomolecules decided to publish a special issue in his honor. This paper summarizes what is known about PPARs and shows how trends have changed and how research on PPARs has evolved. The article also highlights the importance of PPARs and what role they play in various diseases and ailments. The paper is in a mixed form; essentially it is a review article, but it has been enriched with the results of our experiments. The selection of works was subjective, as there are more than 200,000 publications in the PubMed database alone. First, all papers done on an animal model were discarded at the outset. What remained was still far too large to describe directly. Therefore, only papers that were outstanding, groundbreaking, or simply interesting were described and briefly commented on.

Salidroside inhibits insulin resistance and hepatic steatosis by downregulating miR-21 and subsequent activation of AMPK and upregulation of PPARα in the liver and muscles of high fat diet-fed rats

This study evaluated if salidroside (SAL) alleviates high-fat diet (HFD)-induced non-alcoholic fatty liver disease (NAFLD) by downregulating miR-21. Rats (n = 8/group) were treated for 12 weeks as normal diet (control/ND), ND + agmoir negative control (NC) (150 µg/kg), ND + SAL (300 mg/kg), HFD, HFD + SAL, HFD + compound C (an AMPK inhibitor) (200 ng/kg), HFD + SAL + NXT629 (a PPAR-α antagonist) (30 mg/kg), and HFD + SAL + miR-21 agomir (150 µg/kg). SAL improved glucose and insulin tolerance and preserved livers in HFD-fed rats. In ND and HFD-fed rats, SAL reduced levels of serum and hepatic lipids and the hepatic expression of SREBP1, SREBP2, fatty acid (FA) synthase, and HMGCOAR. It also activated hepatic Nrf2 and increased hepatic/muscular activity of AMPK and levels of PPARα. All effects afforded by SAL were prevented by CC, NXT629, and miR-21 agmoir. In conclusion, activation of AMPK and upregulation of PPARα mediate the anti-steatotic effect of SAL.

The protective effects of sesamol and/or the probiotic, Lactobacillus rhamnosus, against aluminum chloride-induced neurotoxicity and hepatotoxicity in rats: Modulation of Wnt/β-catenin/GSK-3β, JAK-2/STAT-3, PPAR-γ, inflammatory, and apoptotic pathways

Introduction: Aluminium (Al) is accumulated in the brain causing neurotoxicity and neurodegenerative disease like Alzheimer's disease (AD), multiple sclerosis, autism and epilepsy. Hence, attenuation of Al-induced neurotoxicity has become a "hot topic" in looking for an intervention that slow down the progression of neurodegenerative diseases. Objective: Our study aims to introduce a new strategy for hampering aluminum chloride (AlCl3)-induced neurotoxicity using a combination of sesamol with the probiotic bacteria; Lactobacillus rhamnosus (L. rhamnosus) and also to test their possible ameliorative effects on AlCl3-induced hepatotoxicity. Methods: Sprague-Dawley male rats were randomly divided into five groups (n = 10/group) which are control, AlCl3, AlCl3 + Sesamol, AlCl3 + L. rhamnosus and AlCl3 + Sesamol + L. rhamnosus. We surveilled the behavioral, biochemical, and histopathological alterations centrally in the brain and peripherally in liver. Results: This work revealed that the combined therapy of sesamol and L. rhamnosus produced marked reduction in brain amyloid-β, p-tau, GSK-3β, inflammatory and apoptotic biomarkers, along with marked elevation in brain free β-catenin and Wnt3a, compared to AlCl3-intoxicated rats. Also, the combined therapy exerted pronounced reduction in hepatic expressions of JAK-2/STAT-3, inflammatory (TNF-α, IL-6, NF-κB), fibrotic (MMP-2, TIMP-1, α-SMA) and apoptotic markers, (caspase-3), together with marked elevation in hepatic PPAR-γ expression, compared to AlCl3 -intoxicated rats. Behavioral and histopathological assessments substantiated the efficiency of this combined regimen in halting the effect of neurotoxicity. Discussion: Probiotics can be used as an add-on therapy with sesamol ameliorate AlCl3 -mediated neurotoxicity and hepatotoxicity.

Multiview Robust Graph-Based Clustering for Cancer Subtype Identification

Cancer subtype identification is to classify cancer into groups according to their molecular characteristics and clinical manifestations and is the basis for more personalized diagnosis and therapy. Public datasets such as The Cancer Genome Atlas (TCGA) have collected a massive number of multi-omics data. The accumulation of these datasets provides unprecedented opportunities to study the mechanism of cancers and further identify cancer subtypes at a comprehensive level. In this paper, we propose a multi-view robust graph-based clustering (MRGC) method to effectively identify cancer subtypes. Our method first learns robust latent representations from the raw omics data to alleviate the influences of the noise, where a set of similarity matrices are then adaptively learned based on these new representations. Finally, a global similarity graph is obtained by exploiting the consensus structure from the graphs. As a result, the three parts in our method can reinforce each other in a mutual iterative manner. We conduct extensive experiments on both generic machine learning datasets and cancer datasets. The experimental results confirm that our model can achieve satisfactory clustering performance compared to several state-of-the-art approaches. Moreover, we convey the practicability of MRGC by carrying out a case study on hepatocellular carcinoma.

PPARγ signaling in hepatocarcinogenesis: Mechanistic insights for cellular reprogramming and therapeutic implications

Liver cancer or hepatocellular carcinoma (HCC) is leading cause of cancer-related mortalities globally. The therapeutic approaches for chronic liver diseases-associated liver cancers aimed at modulating immune check-points and peroxisome proliferator-activated receptor gamma (PPARγ) signaling pathway during multistep process of hepatocarcinogenesis that played a dispensable role in immunopathogenesis and outcomes of disease. Herein, the review highlights PPARγ-induced effects in balancing inflammatory (tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, IL-1) and anti-inflammatory cytokines (IL-10, transforming growth factor beta (TGF-β), and interplay of PPARγ, hepatic stellate cells and fibrogenic niche in cell-intrinsic and -extrinsic crosstalk of hepatocarcinogenesis. PPARγ-mediated effects in pre-malignant microenvironment promote growth arrest, cell senescence and cell clearance in liver cancer pathophysiology. Furthermore, PPARγ-immune cell axis of liver microenvironment exhibits an immunomodulation strategy of resident immune cells of the liver (macrophages, natural killer cells, and dendritic cells) in concomitance with current clinical guidelines of the European Association for Study of Liver Diseases (EASL) for several liver diseases. Thus, mechanistic insights of PPARγ-associated high value targets and canonical signaling suggest PPARγ as a possible therapeutic target in reprogramming of hepatocarcinogenesis to decrease burden of liver cancers, worldwide.

Hepatic circadian and differentiation factors control liver susceptibility for fatty liver disease and tumorigenesis

Hepatocellular carcinoma (HCC) is a leading cause of cancer deaths, and the most common primary liver malignancy to present in the clinic. With the exception of liver transplant, treatment options for advanced HCC are limited, but improved tumor stratification could open the door to new treatment options. Previously, we demonstrated that the circadian regulator Aryl Hydrocarbon-Like Receptor Like 1 (ARNTL, or Bmal1) and the liver-enriched nuclear factor 4 alpha (HNF4α) are robustly co-expressed in healthy liver but incompatible in the context of HCC. Faulty circadian expression of HNF4α- either by isoform switching, or loss of expression- results in an increased risk for HCC, while BMAL1 gain-of-function in HNF4α-positive HCC results in apoptosis and tumor regression. We hypothesize that the transcriptional programs of HNF4α and BMAL1 are antagonistic in liver disease and HCC. Here, we study this antagonism by generating a mouse model with inducible loss of hepatic HNF4α and BMAL1 expression. The results reveal that simultaneous loss of HNF4α and BMAL1 is protective against fatty liver and HCC in carcinogen-induced liver injury and in the "STAM" model of liver disease. Furthermore, our results suggest that targeting Bmal1 expression in the absence of HNF4α inhibits HCC growth and progression. Specifically, pharmacological suppression of Bmal1 in HNF4α-deficient, BMAL1-positive HCC with REV-ERB agonist SR9009 impairs tumor cell proliferation and migration in a REV-ERB-dependent manner, while having no effect on healthy hepatocytes. Collectively, our results suggest that stratification of HCC based on HNF4α and BMAL1 expression may provide a new perspective on HCC properties and potential targeted therapeutics.

New dawn for cancer cell death: Emerging role of lipid metabolism

BACKGROUND

Resistance to cell death, a protective mechanism for removing damaged cells, is a "Hallmark of Cancer" that is essential for cancer progression. Increasing attention to cancer lipid metabolism has revealed a number of pathways that induce cancer cell death.

SCOPE OF REVIEW

We summarize emerging concepts regarding lipid metabolic reprogramming in cancer that is mainly involved in lipid uptake and trafficking, de novo synthesis and esterification, fatty acid synthesis and oxidation, lipogenesis, and lipolysis. During carcinogenesis and progression, continuous metabolic adaptations are co-opted by cancer cells, to maximize their fitness to the ever-changing environmental. Lipid metabolism and the epigenetic modifying enzymes interact in a bidirectional manner which involves regulating cancer cell death. Moreover, lipids in the tumor microenvironment play unique roles beyond metabolic requirements that promote cancer progression. Finally, we posit potential therapeutic strategies targeting lipid metabolism to improve treatment efficacy and survival of cancer patient.

MAJOR CONCLUSIONS

The profound comprehension of past findings, current trends, and future research directions on resistance to cancer cell death will facilitate the development of novel therapeutic strategies targeting the lipid metabolism.

hsa-miR-518-5p/hsa-miR-3135b Regulates the REL/SOD2 Pathway in Ischemic Cerebral Infarction

Objectives

Ischemic cerebral infarction (ICI) is a fatal neurovascular disorder. A bioinformatics approach based on single-cell and bulk RNA-seq analyses was applied to investigate the pathways and genes involved in ICI and study the expression profile of these genes.

Methods

First, the aberrantly regulated “small-molecule ribonucleic acids” [microRNA (miRNAs)] and messenger RNAs (mRNAs) were analyzed using transcriptome data from the ischemic brain infarction dataset of the Gene Expression Omnibus (GEO) database. In mouse cerebrovascular monocytes, the single-cell regulatory network inference and clustering (SCENIC) workflow was used to identify key transcription factors (TFs). Then, the two miRNA-TF-mRNA interaction networks were constructed. Moreover, the molecular complex detection (MCODE) extracted the core sub-networks and identified the important TFs within these sub-networks. Finally, whole blood samples were collected for validation of the expression of critical molecules in ICI.

Results

We identified four cell types and 266 regulons in mouse cerebrovascular monocytes using SCENIC analysis. Moreover, 112 differently expressed miRNAs and 3,780 differentially expressed mRNAs were identified. We discovered potential biomarkers in ICI by building a miRNA-TF-mRNA interaction network. The hsa-miR-518-5p/hsa-miR-3135b/REL/SOD2 was found to play a potential role in ICI progression. The expression of REL and superoxide dismutase 2 (SOD2) was significantly elevated in the ICI group in the clinical cohort (P < 0.05). Furthermore, a REL expression was elevated in endothelial cells and fibroblasts at the single-cell level, indicating that REL is a cell-specific regulon. Functional enrichment analyses revealed that REL is primarily engaged in neurotransmitter activity and oxidative phosphorylation.

Conclusions

Our research uncovered novel biomarkers for ICI of neurovascular disease. The hsa-miR-518-5p/hsa-miR-3135b may regulate the REL/SOD2 pathway in ICI progression.

An insight into the role of telmisartan as PPAR-γ/α dual activator in the management of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common hepatic disease. It is rapidly emerging as the frequent cause for liver transplantation with the risk of disease recurrence, even after transplantation. Clinical evidence showed an abnormally altered expression of different peroxisome proliferator-activated receptor (PPAR) isotypes (PPAR-α/γ/δ) in NAFLD with an involvement in the induction of insulin resistance, hepatic steatosis, reactive oxygen species (ROS) formation, and hepatic inflammation. Recently, several dual PPAR-γ/α agonists were developed to simultaneously achieve the insulin-sensitizing effect of PPAR-γ as well as lipid catabolizing effect of PPAR-α. PPAR-α activation could counterbalance the steatogenic and adipogenic effects of PPAR-γ. But most of the drugs were ended in the initial level itself due to harmful adverse effects. In the present review, we discuss the possible mechanism of telmisartan, a typical angiotensin receptor blocker with excellent safety and pharmacokinetic profile, as a PPAR-γ/α dual agonist in the treatment of NAFLD.

Vinpocetine attenuates fluoxetine-induced liver damage in rats; Role of Nrf2 and PPAR-γ

BACKGROUND

Fluoxetine (FLX) has been widely used as first-line treatment in cases of depression and other neuropsychiatric disorders. Although its safety has been approved, the use of FLX was associated with liver injury and chronic liver disease. Vinpocetine (Vinpo), a nootropic drug, possesses antioxidant and anti-inflammatory effects.

OBJECTIVE

This study aimed to evaluate the protective effects of Vinpo on FLX-induced liver damage pointing to the role of peroxisome proliferator-activated receptor-gamma (PPAR-γ) and nuclear factor erythroid 2-related factor 2 (Nrf2).

METHODS

Rats were randomized to four groups: control group, Vinpo group (20 mg/kg/day; orally), FLX group (10 mg/kg/day; orally), and Vinpo + FLX group.

RESULTS

FLX-induced liver damage was evidenced through elevated liver function biomarkers and induced hepatic histopathological changes. Concurrent Vinpo treatment resulted in a significant decrease in hepatotoxicity biomarkers and histopathological alterations. FLX-induced oxidative stress and inflammation were attenuated by Vinpo. In addition, Vinpo attenuated the hepatic NRF2 and HO-1 levels and up-regulated PPAR-γ expression. Moreover, FLX elevated Bcl-2-associated X protein (Bax) mRNA expression and decreased B-cell lymphoma 2 (Bcl2) mRNA expression were markedly reversed by Vinpo.

CONCLUSION

Vinpo possesses ameliorative effects against FLX-induced liver injury in rats. This effect may be due to attenuation of oxidative stress and inflammation, in addition to upregulation of PPAR-γ expression.

PPARγ and TGFβ-Major Regulators of Metabolism, Inflammation, and Fibrosis in the Lungs and Kidneys

Peroxisome proliferator-activated receptor gamma (PPARγ) is a type II nuclear receptor, initially recognized in adipose tissue for its role in fatty acid storage and glucose metabolism. It promotes lipid uptake and adipogenesis by increasing insulin sensitivity and adiponectin release. Later, PPARγ was implicated in cardiac development and in critical conditions such as pulmonary arterial hypertension (PAH) and kidney failure. Recently, a cluster of different papers linked PPARγ signaling with another superfamily, the transforming growth factor beta (TGFβ), and its receptors, all of which play a major role in PAH and kidney failure. TGFβ is a multifunctional cytokine that drives inflammation, fibrosis, and cell differentiation while PPARγ activation reverses these adverse events in many models. Such opposite biological effects emphasize the delicate balance and complex crosstalk between PPARγ and TGFβ. Based on solid experimental and clinical evidence, the present review summarizes connections and their implications for PAH and kidney failure, highlighting the similarities and differences between lung and kidney mechanisms as well as discussing the therapeutic potential of PPARγ agonist pioglitazone.

PPARs as Metabolic Sensors and Therapeutic Targets in Liver Diseases

Carbohydrates and lipids are two components of the diet that provide the necessary energy to carry out various physiological processes to help maintain homeostasis in the body. However, when the metabolism of both biomolecules is altered, development of various liver diseases takes place; such as metabolic-associated fatty liver diseases (MAFLD), hepatitis B and C virus infections, alcoholic liver disease (ALD), and in more severe cases, hepatocelular carcinoma (HCC). On the other hand, PPARs are a family of ligand-dependent transcription factors with an important role in the regulation of metabolic processes to hepatic level as well as in other organs. After interaction with specific ligands, PPARs are translocated to the nucleus, undergoing structural changes to regulate gene transcription involved in lipid metabolism, adipogenesis, inflammation and metabolic homeostasis. This review aims to provide updated data about PPARs’ critical role in liver metabolic regulation, and their involvement triggering the genesis of several liver diseases. Information is provided about their molecular characteristics, cell signal pathways, and the main pharmacological therapies that modulate their function, currently engaged in the clinic scenario, or in pharmacological development.

Pan-PPAR agonist lanifibranor improves portal hypertension and hepatic fibrosis in experimental advanced chronic liver disease

BACKGROUND & AIMS

In advanced chronic liver disease (ACLD), deregulated hepatic necroinflammatory processes play a key role in the development of liver microvascular dysfunction, fibrogenesis, and increased hepatic vascular tone, resulting in progression of ACLD and portal hypertension. Given the current lack of an effective treatment, we aimed to characterise the effects of the pan-peroxisome proliferator-activated receptor (pan-PPAR) agonist lanifibranor in 2 preclinical models of ACLD, as well as in liver cells from patients with ACLD.

METHODS

Cirrhotic rats (thioacetamide or common bile duct ligation; TAA or cBDL) randomly received lanifibranor (100 mg/kg/day, po) or vehicle for 14 days (n = 12/group). PPAR expression, systemic and hepatic haemodynamics, presence of ascites, liver sinusoidal endothelial cell (LSEC) phenotype, hepatic stellate cell (HSC) activation, serum transaminases and albumin, hepatic macrophage infiltration, cytokine expression, and liver fibrosis were determined. Hepatic cells were isolated from the livers of patients with cirrhosis and their phenotype was evaluated after treatment with either lanifibranor or vehicle.

RESULTS

TAA-cirrhotic rats receiving lanifibranor showed significantly lower portal pressure compared with vehicle-treated animals (-15%; p = 0.003) without decreasing portal blood flow, indicating improved hepatic vascular resistance. Moreover, lanifibranor-treated TAA-rats showed decreased ascites, improved LSEC and HSC phenotypes, ameliorated hepatic microvascular function, reduced hepatic inflammation, and significant fibrosis regression (-32%; p = 0.020). These findings were confirmed in the cBDL rat model as well as in human liver cells from patients with cirrhosis, which exhibited phenotypic improvement upon treatment with lanifibranor.

CONCLUSIONS

Lanifibranor ameliorates fibrosis and portal hypertension in preclinical models of decompensated cirrhosis. Promising results in human hepatic cells further support its clinical evaluation for the treatment of ACLD.

LAY SUMMARY

Advanced chronic liver disease (ACLD) constitutes a serious public health issue for which safe and effective treatments are lacking. This study shows that lanifibranor improves portal hypertension and liver fibrosis, 2 key elements of the pathophysiology of ACLD, in preclinical models of the disease. Evaluation of lanifibranor in liver cells from patients with ACLD further supports its beneficial effects.

Effect of Chronic Western Diets on Non-Alcoholic Fatty Liver of Male Mice Modifying the PPAR-γ Pathway via miR-27b-5p Regulation

Western diets contribute to metabolic diseases. However, the effects of various diets and epigenetic mechanisms are mostly unknown. Here, six week-old C57BL/6J male and female mice were fed with a low-fat diet (LFD), high-fat diet (HFD), and high-fat high-fructose diet (HFD-HF) for 20 weeks. We determined that HFD-HF or HFD mice experienced significant metabolic dysregulation compared to the LFD. HFD-HF and HFD-fed male mice showed significantly increased body weight, liver size, and fasting glucose levels with downregulated PPARγ, SCD1, and FAS protein expression. In contrast, female mice were less affected by HFD and HFD-HF. As miR-27b contains a seed sequence in PPARγ, it was discovered that these changes are accompanied by male-specific upregulation of miR-27b-5p, which is even more pronounced in the HFD-HF group (p < 0.01 vs. LFD) compared to the HFD group (p < 0.05 vs. LFD). Other miR-27 subtypes were increased but not significantly. HFD-HF showed insignificant changes in fibrosis markers when compared to LFD. Interestingly, fat ballooning in hepatocytes was increased in HFD-fed mice compared to HFD-HF fed mice, however, the HFD-HF liver showed an increase in the number of small cells. Here, we concluded that chronic Western diet-composition administered for 20 weeks may surpass the non-alcoholic fatty liver (NAFL) stage but may be at an intermediate stage between fatty liver and fibrosis via miR-27b-5p-induced PPARγ downregulation.

Host genetics and gut microbiota cooperatively contribute to azoxymethane-induced acute toxicity in Collaborative Cross mice

Azoxymethane (AOM) is a widely used carcinogen to study chemical-induced colorectal carcinogenesis and is an agent for studying fulminant hepatic failure. The inter-strain susceptibility to acute toxicity by AOM has been reported, but its association with host genetics or gut microbiota remains largely unexplored. Here a cohort of genetically diverse Collaborative Cross (CC) mice was used to assess the contribution of host genetics and the gut microbiome to AOM-induced acute toxicity. We observed variation in AOM-induced acute liver failure across CC strains. Quantitative trait loci (QTL) analysis revealed three chromosome regions significantly associated with AOM toxicity. Genes located within these QTL, including peroxisome proliferator-activated receptor alpha (Ppara), were enriched for enzyme activator and nucleoside-triphosphatase regulator activity. We further demonstrated that the protein level of PPARα in liver tissues from sensitive strains was remarkably lower compared to levels in resistant strains, consistent with protective role of PPAR family in liver injury. We discovered that the abundance levels of gut microbial families Anaeroplasmataceae, Ruminococcaceae, Lactobacillaceae, Akkermansiaceae and Clostridiaceae were significantly higher in the sensitive strains compared to the resistant strains. Using a random forest classifier method, we determined that the relative abundance levels of these microbial families predicted AOM toxicity with the area under the receiver-operating curve (AUC) of 0.75. Combining the three genetic loci and five microbial families increased the predictive accuracy of AOM toxicity (AUC of 0.99). Moreover, we found that Ruminococcaceae and Lactobacillaceae acted as mediators between host genetics and AOM toxicity. In conclusion, this study shows that host genetics and specific microbiome members play a critical role in AOM-induced acute toxicity, which provides a framework for analysis of the health effects from environmental toxicants.

The potential ameliorative impacts of cerium oxide nanoparticles against fipronil-induced hepatic steatosis

Fipronil (FIP) is a phenylpyrazole insecticide that is commonly used in agricultural and veterinary fields for controlling a wide range of insects, but it is a strong environmentally toxic substance. Exposure to FIP has been reported to increase the hepatic fat accumulation through altered lipid metabolism, which ultimately can contribute to nonalcoholic fatty liver disease (NAFLD) development. The present study aimed to examine the function of cerium oxide nanoparticles (CeNPs) in protecting against hepatotoxicity and lipogenesis induced by FIP. Twenty-eight male albino rats were classified into four groups: FIP (5 mg/kg/day per os), CTR, CeNPs (35 mg/kg/day p.o.), and FIP + CeNPs (5 (FIP) + 35 (CeNPs) mg/kg/day p.o.) for 28 consecutive days. Serum lipid profiles, hepatic antioxidant parameters and pathology, and mRNA expression of adipocytokines were assessed. The results revealed that FIP increased cholesterol, height-density lipoprotein, triacylglyceride, low-density lipoprotein (LDL-c), and very-low-density lipoprotein (VLDL-c) concentrations. It also increased nitric oxide (NO) and malondialdehyde (MDA) hepatic levels and reduced glutathione peroxidase (GPx) and superoxide dismutase (SOD) enzyme activities. Additionally, FIP up-regulated the fatty acid-binding protein (FABP), acetyl Co-A carboxylase (ACC1), and peroxisome proliferator-activated receptor-alpha (PPAR-α). Immunohistochemically, a strong proliferation of cell nuclear antigen (PCNA), ionized calcium-binding adapter molecule 1 (Iba-1), cyclooxygenase-2 (COX-2) reactions in the endothelial cells of the hepatic sinusoids, and increased expression of caspase3 were observed following FIP intoxication. FIP also caused histological changes in hepatic tissue. The CeNPs counteracted the hepatotoxic effect of FIP exposure. So, this study recorded an ameliorative effect of CeNPs against FIP-induced hepatotoxicity.

Genetic polymorphisms of PPAR genes and human cancers: evidence for gene-environment interactions

Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription factors that play a role in lipid metabolism, cell proliferation, terminal differentiation, apoptosis, and inflammation. Although several cancer models have been suggested to explain PPARs' involvement in tumorigenesis, however, their role is still unclear. In this review, we examined associations of the different PPARs, polymorphisms and various types of cancer with a focus on gene-environment interactions. Reviewed evidence suggests that functional genetic variants of the different PPARs may modulate the relationship between environmental exposure and cancer risk. In addition, this report unveils the scarcity of reliable quantitative environmental exposure data when examining these interactions, and the current gaps in studying gene-environment interactions in many types of cancer, particularly colorectal, prostate, and bladder cancers.

Micro-RNAs 518d-3p and 618 Are Upregulated in Individuals With Type 1 Diabetes With Multiple Microvascular Complications

Objective: To compare the serum micro-RNAs (miRNAs) profile of individuals with type 1 diabetes without microvascular complications vs. those with multiple severe microvascular complications, in order to identify epigenetically modulated pathways in these two groups of individuals. Research Design and Methods: A total of 10 subjects were selected among individuals followed in the Diabetes Outpatient Clinic and sorted according to the absence or presence of all microvascular complications. Samples from these participants were used for evaluation of serum miRNA expression profile employing a qRT-PCR assay with hydrolysis probes based on the Taqman Low Density Arrays (TLDA) system. The top six most differentially expressed miRNAs between the aforementioned groups were validated by qRT-PCR in additional 47 type 1 diabetes individuals sorted according to the absence or presence of all microvascular complications and matched for age, sex, degree of metabolic control, diabetes duration, and age at diagnosis. Results: Twenty one out of three hundred and seventy seven miRNAs were upregulated in the group of individuals with all microvascular complications vs. the group without complications. The following miRs were validated: 518-3p, 34a-5p, 126-5p, 425-5p, 618, and 139-5p and logistic regression analyses showed that miRNA-518-3p and miRNA-618 were positively associated with multiple microvascular complications after adjustment for age, sex, diabetes duration, HbA₁c and use of statin, angiotensin-converting enzyme inhibitors and amlodipine. Conclusions: In this cohort of type 1 diabetes individuals, serum miR-518d-3p and miR-618 were upregulated in those with diabetes kidney disease, diabetes retinopathy, peripheral neuropathy, and cardiovascular autonomic neuropathy in comparison to individuals with no microvascular complications.

Effects of Dietary Polyunsaturated Fatty Acids on DNA Methylation and the Expression of DNMT3b and PPARα Genes in Rats

BACKGROUND

Previous studies have suggested a protective role for Polyunsaturated Fatty Acids (PUFA) against cancer, cardiovascular, and other diseases. To provide new insights into the in vivo effects of PUFA on gene expression, the effects of dietary PUFA on DNMT3b and PPARα gene expression and global DNA methylation were investigated in selected rat tissues.

METHODS

Thirty sprague-dawley rats were allotted into 3 dietary groups of ten animals each, received experimental diets containing PUFAs every day by gavages for 12 weeks as follows: control group fed a normal diet and water; n-3 PUFAs group received 300 mg/kg/day n-3 PUFAs supplementation; mixed-PUFAs group received 300 mg/kg/day of a mixture of n-3, -6, -9 PUFAs supplementations. The expressions of DNMT3b and PPARα genes were quantitated using real-time RT-PCR. The genome-wide 5-methylcytosine contents in rat tissues were determined by ELISA method.

RESULTS

The average expression of the DNMT3b mRNA was 50% lower in the colon and liver of rats fed the n-3- or mixed-PUFAs supplemented diet than control group (p=0.00). However, PPARα expression was significantly upregulated both in the colon and liver of PUFAs-supplemented rats (p<0.001). No significant difference was observed in the blood, colon, and liver DNA methylation levels between PUFAs-supplemented and control animals.

CONCLUSION

The results indicate that dietary PUFAs could modulate the expressions of PPARα and DNMT3b genes in various rat tissues. The findings of this study provide additional insights into the in vivo mechanism of PUFA-mediated regulation of gene expression and could provide an opportunity to develop personalized diets for related disease control.

Peroxisome proliferator activating receptor-γ and the podocyte

Over the past two decades it has become clear that the glomerular podocyte is a key cell in preventing albuminuria, kidney failure and cardiovascular morbidity. Understanding the key pathways that protect the podocyte in times of glomerular stress, which can also be therapeutically manipulated, are highly attractive. In the following review we assess the evidence that the peroxisome proliferator activating receptor (PPAR) agonists are beneficial for podocyte and kidney function with a focus on PPAR-γ. We explain our current understanding of the mechanisms of action of these agonists and the evidence they are beneficial in diabetic and non-diabetic kidney disease. We also outline why these drugs have not been widely used for kidney disease in the past but they may be in the future.

Tumor Suppressor PTPRJ Is a Target of miR-155 in Colorectal Cancer

PTPRJ is known for its antiproliferative role. Loss of heterozygosity (LOH) of PTPRJ has frequently been observed in various human cancers including colorectal cancer (CRC), lung cancer, and breast cancer. However, the function and mechanism of PTPRJ in CRC are not well understood. At the present study, we show that ectopic expression of PTPRJ inhibits cell growth, migration, and invasiveness in CRC cell line HCT116. Moreover, PTPRJ inhibits the tumorigenecity of HCT116 in a xenograft tumor model. MiR-155, the well-known oncomiR in CRC, is identified as an upstream factor of PTPRJ. MiR-155 directly binds to the 3' untranslated region of PTPRJ mRNA and suppresses the mRNA and protein levels of PTPRJ. Furthermore, the growth-promoting and AKT signaling activation effect of miR-155 was abrogated by PTPRJ overexpression, and vice versa. Our study reveals the crucial role of miR-155/PTPRJ/AKT axis in proliferation and migration of CRC cells and suggests a therapeutic potential of PTPRJ. J. Cell. Biochem. 118: 3391-3400, 2017. © 2017 Wiley Periodicals, Inc.

Apigenin, a modulator of PPARγ, attenuates HFD-induced NAFLD by regulating hepatocyte lipid metabolism and oxidative stress via Nrf2 activation

Lipid metabolic disorders and oxidative stress in the liver are key steps in the progression of nonalcoholic fatty liver disease (NAFLD), which is a major risk factor for the development of metabolic syndrome. To date, no pharmacological treatment for this condition has been approved. Our previous study has found that the food-derived compound apigenin (Api) significantly attenuates obesity-induced metabolic syndrome by acting as a peroxisome proliferator-activated receptor gamma modulator (PPARM). Herein, a high fat diet (HFD) induced NAFLD model was used to dig out whether Api had the effect on NAFLD. The results showed that Api had obvious effect in restraining NAFLD progression, including attenuating HFD induced lipid accumulation and oxidative stress in vivo. As a PPARM, although Api did significantly inhibit the expression of PPARγ target genes encoding the protein associated with lipid metabolism, it had no obvious activating effect on PPARγ. Interestingly, we found that Api promoted Nrf2 into the nucleus, thereby markedly activating Nrf2 to inhibit the lipid metabolism related genes and increase the oxidative stress related genes. Further Nrf2 knockdown/knockout and overexpression experiments showed that Api regulating PPARγ target genes was dependent on Nrf2 activation and the activation of Nrf2 counteracted the activation effect of PPARγ by Api. Importantly, we also found that Api might bind with Nrf2 via auto dock and ITC assay. Therefore, our results indicate that Api ameliorates NAFLD by a novel regulating mode of Nrf2 and PPARγ in inhibiting lipid metabolism and oxidative stress abnormity.

Methotrexate hepatotoxicity is associated with oxidative stress, and down-regulation of PPARγ and Nrf2: Protective effect of 18β-Glycyrrhetinic acid

18β-glycyrrhetinic acid (18β-GA) is a bioactive component of licorice with promising hepatoprotective activity. However, its protective mechanism on methotrexate (MTX) hepatotoxicity in not well defined. We investigated the hepatoprotective effect of 18β-GA, pointing to the role of peroxisome proliferator activated receptor gamma (PPARγ) and the redox-sensitive nuclear factor erythroid 2-related factor 2 (Nrf2). Wistar rats were orally administered 18β-GA (50 and 100 mg/kg) 7 days either before or after MTX injection. MTX induced significant increase in circulating liver function marker enzymes and bilirubin with concomitant declined albumin levels. Serum pro-inflammatory cytokines, and liver malondialdehyde and nitric oxide were significantly increased in MTX-induced rats. Treatment with 18β-GA significantly reduced serum enzymes of liver function, bilirubin and pro-inflammatory cytokines. 18β-GA attenuated MTX-induced oxidative stress and restored the antioxidant defenses. In addition, 18β-GA improved liver histological structure and decreased the expression of Bax whereas increased Bcl-2 expression. MTX-induced rats showed significant down-regulation of Nrf2, hemoxygenase-1 and PPARγ, an effect that was markedly reversed by 18β-GA supplemented either before or after MTX. In conclusion, 18β-GA protected against MTX-induced liver injury, possibly by activating Nrf2 and PPARγ, and subsequent attenuation of inflammation, oxidative stress and apoptosis. Therefore, 18β-GA can provide protection against MTX-induced hepatotoxicity.

Berberis vulgaris extract/β-cyclodextrin complex increases protection of hepatic cells via suppression of apoptosis and lipogenesis pathways

Berberis vulgaris (Bv) is well known worldwide for its healing properties. However, limited information is available concerning its mechanism of action and the increased hepatoprotective activity of formulated extracts. This study evaluated the protective effect of Bv bark extract against CCl₄-induced cytotoxicity in Huh7 cells, as well whether β-cyclodextrin complexation of the extract resulted in increased hepatoprotective effects. Huh7 cells were incubated for 48 h with 5, 7.5 and 10 µg/ml of unformulated or formulated Bv extract alone and in co-treatment with CCl₄. The effects on Huh7 cell growth and apoptosis were evaluated by MTT assay, caspase-3/7 activity and caspase-3 expression, whereas fatty acid changes were investigated by Oil red O staining and the detection of peroxisome proliferator-activated receptor-γ (PPARγ) expression using immunofluorescence. Ultrastructural alterations were observed by electron microscopy. The MTT assay showed that co-exposure to CCl₄ and 7.5 µg/ml formulated extract led to a 1.25-fold increase in cell viability compared with the non-formulated extract. Caspase-3/7 activity decreased by 50% and 70% following co-treatment with unformulated or formulated extract, compared with that in cells treated with CCl₄ alone. Furthermore, hepatocyte ultrastructure was protected from CCl₄-induced injury in the two co-treated groups, intracytoplasmic lipid accumulation decreased significantly and PPARγ expression was restored, in comparison with CCl₄-treated cells alone. Formulated and unformulated extracts were efficient against the anti-proliferative and pro-apoptotic actions of CCl₄ through suppression of CCl₄-induced caspase-3 activation and lipid accumulation. The protective effect of the formulated extract was more pronounced than that of the unformulated one, which may be due to its increased solubility.

MicroRNAs-Dependent Regulation of PPARs in Metabolic Diseases and Cancers

Peroxisome proliferator-activated receptors (PPARs) are a family of ligand-dependent nuclear receptors, which control the transcription of genes involved in energy homeostasis and inflammation and cell proliferation/differentiation. Alterations of PPARs' expression and/or activity are commonly associated with metabolic disorders occurring with obesity, type 2 diabetes, and fatty liver disease, as well as with inflammation and cancer. Emerging evidence now indicates that microRNAs (miRNAs), a family of small noncoding RNAs, which fine-tune gene expression, play a significant role in the pathophysiological mechanisms regulating the expression and activity of PPARs. Herein, the regulation of PPARs by miRNAs is reviewed in the context of metabolic disorders, inflammation, and cancer. The reciprocal control of miRNAs expression by PPARs, as well as the therapeutic potential of modulating PPAR expression/activity by pharmacological compounds targeting miRNA, is also discussed.

Gamma-Glutamylcysteine Ethyl Ester Protects against Cyclophosphamide-Induced Liver Injury and Hematologic Alterations via Upregulation of PPARγ and Attenuation of Oxidative Stress, Inflammation, and Apoptosis

Gamma-glutamylcysteine ethyl ester (GCEE) is a precursor of glutathione (GSH) with promising hepatoprotective effects. This investigation aimed to evaluate the hepatoprotective effects of GCEE against cyclophosphamide- (CP-) induced toxicity, pointing to the possible role of peroxisome proliferator activated receptor gamma (PPARγ). Wistar rats were given GCEE two weeks prior to CP. Five days after CP administration, animals were sacrificed and samples were collected. Pretreatment with GCEE significantly alleviated CP-induced liver injury by reducing serum aminotransferases, increasing albumin, and preventing histopathological and hematological alterations. GCEE suppressed lipid peroxidation and nitric oxide production and restored GSH and enzymatic antioxidants in the liver, which were associated with downregulation of COX-2, iNOS, and NF-κB. In addition, CP administration significantly increased serum proinflammatory cytokines and the expression of liver caspase-3 and BAX, an effect that was reversed by GCEE. CP-induced rats showed significant downregulation of PPARγ which was markedly upregulated by GCEE treatment. These data demonstrated that pretreatment with GCEE protected against CP-induced hepatotoxicity, possibly by activating PPARγ, preventing GSH depletion, and attenuating oxidative stress, inflammation, and apoptosis. Our findings point to the role of PPARγ and suggest that GCEE might be a promising agent for the prevention of CP-induced liver injury.

Brown seaweeds protect against azoxymethane-induced hepatic repercussions through up-regulation of peroxisome proliferator-activated receptor gamma and attenuation of oxidative stress

CONTEXT

Seaweeds of the genera Turbinaria and Padina have long been used as food and in traditional medicine for treating several diseases.

OBJECTIVE

The current study determines the protective efficacy of the brown seaweeds Turbinaria ornata (Turner) J. Agardh (Sargassaceae) and Padina pavonia (Linnaeus) J.V. Lamouroux (Dictyotaceae) against liver injury induced by azoxymethane (AOM).

MATERIALS AND METHODS

Male Swiss mice received 10 mg/kg AOM once a week for two consecutive weeks and then 100 mg/kg daily dose of either T. ornata or P. pavonia ethanolic extract. Thirteen weeks after the first AOM administration and 24 h after the last treatment, overnight fasted mice were sacrificed and samples collected.

RESULTS

Compared with the AOM group, both T. ornata and P. pavonia significantly decreased the activity of aminotransferases and the concentration of bilirubin while increased albumin levels in the serum. The antioxidative effect of both extracts was observed from the increased activity of superoxide dismutase and glutathione peroxidase activities in the liver, both of which were decreased by AOM. Moreover, the levels of malondialdehyde and nitric oxide were reduced, and histological findings also confirmed the antihepatotoxic activity. In addition, treatment with T. ornata and P. pavonia significantly increased PPARγ and decreased NF-κB expression in the liver of AOM-administered mice.

DISCUSSION AND CONCLUSION

Our findings indicate that the protective function of T. ornata and P. pavonia on AOM-induced liver injury may be possibly exerted by multiple pathways including abolishment of inflammation and oxidative damage, and activation of PPARγ.

The Role of Nuclear Receptors in the Pathophysiology, Natural Course, and Drug Treatment of NAFLD in Humans

Nonalcoholic fatty liver disease (NAFLD) describes steatosis, nonalcoholic steatohepatitis with or without fibrosis, and hepatocellular carcinoma, namely the entire alcohol-like spectrum of liver disease though observed in the nonalcoholic, dysmetabolic, individual free of competing causes of liver disease. NAFLD, which is a major public health issue, exhibits intrahepatic triglyceride storage giving rise to lipotoxicity. Nuclear receptors (NRs) are transcriptional factors which, activated by ligands, are master regulators of metabolism and also have intricate connections with circadian control accounting for cyclical patterns in the metabolic fate of nutrients. Several transcription factors, such as peroxisome proliferator-activated receptors, liver X receptors, farnesoid X receptors, and their molecular cascades, finely regulate energetic fluxes and metabolic pathways. Dysregulation of such pathways is heavily implicated in those metabolic derangements characterizing insulin resistance and metabolic syndrome and in the histogenesis of progressive NAFLD forms. We review the role of selected NRs in NAFLD pathogenesis. Secondly, we analyze the role of NRs in the natural history of human NAFLD. Next, we discuss the results observed in humans following administration of drug agonists or antagonists of the NRs pathogenically involved in NAFLD. Finally, general principles of treatment and lines of research in human NAFLD are briefly examined.

Ethanol and fatty acids impair lipid homeostasis in an in vitro model of hepatic steatosis

Excess ethanol consumption and fatty acid intake lead to a cumulative effect on liver steatosis through still unclear mechanisms. This study aimed to characterize the lipid homoeostasis alterations under the exposure of hepatocytes to ethanol alone or combined with fatty acids. FaO hepatoma cells were incubated in the absence (C) or in the presence of 100 mM ethanol (EtOH) or 0.35 mM oleate/palmitate (FFA) alone or in the combination (FFA/EtOH). Content of intra- and extra-cellular triglycerides (TAGs) and of lipid droplets (LDs), expression of lipogenic and lipolytic genes, and oxidative stress-related parameters were evaluated. Exposure to either FFAs or EtOH given separately led to steatosis which was augmented when they were combined. Our results show that FFA/EtOH: (i) increased the LD number, but reduced their size compared to separate treatments; (ii) up-regulated PPARγ and SREBP-1c and down-regulated sirtuin-1 (SIRT1); (iii) impaired FFA oxidation; (iv) did not change lipid secretion and oxidative stress. Our findings indicate that one of the major mechanisms of the metabolic interference between ethanol and fat excess is the impairment of FFA oxidation, in addition to lipogenic pathway stimulation. Interestingly, ethanol combined with FFAs led to a shift from macrovesicular to microvesicular steatosis that represents a more dangerous condition.

Protein-protein interaction network analysis of cirrhosis liver disease

AIM

Evaluation of biological characteristics of 13 identified proteins of patients with cirrhotic liver disease is the main aim of this research.

BACKGROUND

In clinical usage, liver biopsy remains the gold standard for diagnosis of hepatic fibrosis. Evaluation and confirmation of liver fibrosis stages and severity of chronic diseases require a precise and noninvasive biomarkers. Since the early detection of cirrhosis is a clinical problem, achieving a sensitive, specific and predictive novel method based on biomarkers is an important task.

METHODS

Essential analysis, such as gene ontology (GO) enrichment and protein-protein interactions (PPI) was undergone EXPASy, STRING Database and DAVID Bioinformatics Resources query.

RESULTS

Based on GO analysis, most of proteins are located in the endoplasmic reticulum lumen, intracellular organelle lumen, membrane-enclosed lumen, and extracellular region. The relevant molecular functions are actin binding, metal ion binding, cation binding and ion binding. Cell adhesion, biological adhesion, cellular amino acid derivative, metabolic process and homeostatic process are the related processes. Protein-protein interaction network analysis introduced five proteins (fibroblast growth factor receptor 4, tropomyosin 4, tropomyosin 2 (beta), lectin, Lectin galactoside-binding soluble 3 binding protein and apolipoprotein A-I) as hub and bottleneck proteins.

CONCLUSION

Our result indicates that regulation of lipid metabolism and cell survival are important biological processes involved in cirrhosis disease. More investigation of above mentioned proteins will provide a better understanding of cirrhosis disease.

Molecular regulation of miRNAs and potential biomarkers in the progression of hepatic steatosis to NASH

Increasing evidence suggests that microRNAs regulate diverse biological functions in the liver and play a very important function in metabolic-related disorders such as nonalcoholic fatty liver disease via regulating their target genes expression. In this review, we summarized the most recent progress in identification of miRNAs involving in the progression of liver steatosis and discussed the possible mechanisms by which miRNAs contribute to the diverse pathogenic liver injuries. We provide insights into the functional network of miRNAs by connecting miRNAs, their targets and biological pathways associated to hepatic steatosis and fibrosis, with important implications for our understanding of phenotypic-based disease pathogenesis. We also discuss the possible roles and challenges of miRNAs as biomarkers for drug-induced liver injury.

Promoter methylation status and expression of PPAR-γ gene are associated with prognosis of acute-on-chronic hepatitis B liver failure

Background

Peroxisome proliferator-activated receptor gamma (PPAR-γ) has been demonstrated to be involved in anti-inflammatory reactions, but its role in acute-on-chronic hepatitis B liver failure (ACHBLF) is unclear. Therefore, DNA methylation patterns and expression level of PPAR-γ gene were detected in peripheral blood mononuclear cells (PBMCs) from 81 patients with ACHBLF, 50 patients with chronic hepatitis B (CHB), and 30 healthy controls, and the possible role of PPAR-γ in ACHBLF was analyzed.

Results

We found that aberrant PPAR-γ promoter methylation was attenuated in ACHBLF patients compared with CHB patients and was responsible for the elevated PPAR-γ expression level, which was negatively correlated with total bilirubin and international normalized ratio. Plasma level of TNF-α and IL-6 in ACHBLF patients were higher than CHB patients and healthy controls and significantly reduced in unmethylated group. ACHBLF patients with PPAR-γ promoter methylation had poorer outcomes than those without. Correspondingly, PPAR-γ messenger RNA (mRNA) level was higher in survivors than non-survivors and gradually increased in survivors with time, while remained low level in non-survivors.

Conclusions

Aberrant promoter methylation decline and PPAR-γ expression rebound occurred in ACHBLF compared with CHB and could improve prognosis of ACHBLF by negatively regulating cytokines.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-015-0149-2) contains supplementary material, which is available to authorized users.

18β-Glycyrrhetinic acid exerts protective effects against cyclophosphamide-induced hepatotoxicity: potential role of PPARγ and Nrf2 upregulation

18β-Glycyrrhetinic acid (18β-GA) has been proposed as a promising hepatoprotective agent. The current study aimed to investigate the protective action and the possible mechanisms of 18β-GA against cyclophosphamide (CP)-induced liver injury in rats, focusing on the role of peroxisome proliferator-activated receptor gamma (PPARγ) and NF-E2-related factor-2 (Nrf2). Rats were administered 18β-GA at doses 25 and 50 mg/kg 2 weeks prior to CP injection. Five days after CP administration, animals were sacrificed and samples were collected. CP induced hepatic damage evidenced by the histopathological changes and significant increase in serum pro-inflammatory cytokines, liver marker enzymes, and liver lipid peroxidation and nitric oxide (NO) levels. 18β-GA counteracted CP-induced oxidative stress and inflammation as assessed by restoration of the antioxidant defenses and diminishing of pro-inflammatory cytokines, lipid peroxidation, and NO production. These hepatoprotective effects appear to depend on activation of Nrf2 and PPARγ, and subsequent suppression of nuclear factor-kappa B. In conclusion, the present study provides evidence that 18β-GA exerts hepatoprotective effects against CP through induction of antioxidant defenses and suppression of inflammatory response. This report also confers new information that 18β-GA protects liver against the toxic effect of chemotherapeutic alkylating agents via activation of Nrf2 and PPARγ.

Donor PPARα Gene Polymorphisms Influence the Susceptibility to Glucose and Lipid Disorders in Liver Transplant Recipients: A Strobe-Compliant Observational Study

Peroxisome proliferator-activated receptor α (PPARα) is an important regulator of glucose and lipid metabolism, and is predominantly expressed in the liver. We aimed to evaluate the effect of donor hepatic PPARα gene polymorphisms on the development of metabolic disorders following liver transplantation (LT).A total of 176 patients undergoing primary LT were included in this Review Board-approved study. Genomic DNA was extracted from fresh frozen donor liver tissues (biopsy specimens for pathological testing at surgery). Eight single nucleotide polymorphisms in the PPARα gene were chosen from either the HapMap CHB database or previous reports.The distribution of metabolic disorders differed significantly between the wild-type and variant genotypes of both the rs5767743 and rs5767700 loci (P < 0.05 for all). After an adjustment for other factors (body mass index and tacrolimus blood concentration), the rs5767743 genetic variant was found to be an independent protective factor (P = 0.005, odds ratio = 0.416 per C allele, 95% confidence interval  = 0.225-0.768). When compared with the wild-type genotype, the variant genotypes rs5767743 and rs5767700 correlated with significantly increased PPARα and CYP3A4 mRNA expression and lower tacrolimus trough concentration/dose ratios (P < 0.05 for all).Donor PPARα gene polymorphisms influence the susceptibility to metabolic disorders following LT and may also be associated with a fasten tacrolimus metabolism because of elevated CYP3A4 expression.

Epigenetic biomarkers in liver cancer

Liver cancer (hepatocellular carcinoma or HCC) is a major cancer worldwide. Research in this field is needed to identify biomarkers that can be used for early detection of the disease as well as new approaches to its treatment. Epigenetic biomarkers provide an opportunity to understand liver cancer etiology and evaluate novel epigenetic inhibitors for treatment. Traditionally, liver cirrhosis, proteomic biomarkers, and the presence of hepatitis viruses have been used for the detection and diagnosis of liver cancer. Promising results from microRNA (miRNA) profiling and hypermethylation of selected genes have raised hopes of identifying new biomarkers. Some of these epigenetic biomarkers may be useful in risk assessment and for screening populations to identify who is likely to develop cancer. Challenges and opportunities in the field are discussed in this chapter.

Platelet miRNAs and cardiovascular diseases

Activated platelets play a critical role in the acute complications of atherosclerosis that cause life-threatening ischemic events at late stages of the disease. The miRNAs are a novel class of small, non-coding RNAs that play a significant role in both inflammatory and cardiovascular diseases. The miRNAs are known to be present in platelets and exert important regulatory functions. Here we systematically examine the genes that are regulated by platelet miRNAs (miRNA-223,miRNA-126,miRNA-21, miRNA-24 and miRNA-197) and the association with cardiovascular disease risks. Platelet-secreted miRNAs could be novel biomarkers associated with cardiovascular diseases.

MicroRNA-130b regulates scleroderma fibrosis by targeting peroxisome proliferator-activated receptor γ

OBJECTIVES

To investigate the role of microRNA-130b (miR-130b) in systemic sclerosis (SSc) skin fibrosis and its regulatory effect on peroxisome proliferator-activated receptor γ (PPARγ).

METHODS

miR-130b was identified from microarray analyses in our previous studies. The expression of miR-130b, PPARγ, and fibrosis-related genes were determined by real-time PCR analysis. PPARγ protein levels were detected by immunohistochemistry and Western blot. Cells were transfected with microRNA mimics/inhibitor/scramble of miR-130b using Lipofectamine. Luciferase reporter gene assays were used to identify the direct target of miR-130b. Transforming growth factor β (TGF-β) was used for stimulation.

RESULTS

The expression of miR-130b was significantly upregulated and level of PPARγ was decreased in the dermis of the SSc skin biopsy samples and fibroblasts. Similar to human SSc, the same expression patterns of miR-130b, PPARγ, and fibrosis-related genes were observed in the bleomycin-induced skin fibrosis model; TGF-β induced the expression of miR-130b and fibrosis-related genes expression, but downregulated the expression of PPARγ. Overexpression of miR-130b in normal or SSc skin fibroblasts significantly decreased, and accordingly, knockdown of miR-130b increased the levels of PPARγ and fibrosis-related genes. In the reporter gene assay, cotransfection with miR-130b mimics significantly decreased the relative luciferase activity, which suggested a direct regulation of PPARγ by miR-130b.

CONCLUSIONS

These studies demonstrated that miR-130b played important profibrotic roles in SSc fibrosis, and enhanced TGF-β signaling through negative regulation of PPARγ expression. MiR-130b may be a potential therapeutic target in SSc fibrosis.

Hesperidin protects against cyclophosphamide-induced hepatotoxicity by upregulation of PPARγ and abrogation of oxidative stress and inflammation

The most important reason for the non-approval and withdrawal of drugs by the Food and Drug Administration is hepatotoxicity. Therefore, this study was undertaken to evaluate the protective effects of hesperidin against cyclophosphamide (CYP)-induced hepatotoxicity in Wistar rats. The rats received a single intraperitoneal dose of CYP of 200 mg/kg body mass, followed by treatment with hesperidin, orally, at doses of 25 and 50 mg/kg for 11 consecutive days. CYP induced hepatic damage, as evidenced by the significantly elevated levels of serum pro-inflammatory cytokines, serum transaminases, liver lipid peroxidation, and nitric oxide. As a consequence, there was reduced glutathione content, and the activities of the antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase, were markedly reduced. In addition, CYP administration induced a considerable downregulation of peroxisome proliferator activated receptor gamma (PPARγ) and upregulation of nuclear factor-kappa B (NF-κB) and inducible nitric oxide synthase (iNOS) mRNA expression. Hesperidin, in a dose-dependent manner, rejuvenated the altered markers to an almost normal state. In conclusion, hesperidin showed a potent protective effect against CYP-induced oxidative stress and inflammation leading to hepatotoxicity. The study suggests that hesperidin exerts its protective effect against CYP-induced hepatotoxicity through upregulation of hepatic PPARγ expression and abrogation of inflammation and oxidative stress.

Recent insights into the molecular pathophysiology of lipid droplet formation in hepatocytes

Triacyglycerols are a major energy reserve of the body and are normally stored in adipose tissue as lipid droplets (LDs). The liver, however, stores energy as glycogen and digested triglycerides in the form of fatty acids. In stressed condition such as obesity, imbalanced nutrition and drug induced liver injury hepatocytes accumulate excess lipids in the form of LDs whose prolonged storage leads to disease conditions most notably non-alcoholic fatty liver disease (NAFLD). Fatty liver disease has become a major health burden with more than 90% of obese, nearly 70% of overweight and about 25% of normal weight patients being affected. Notably, research in recent years has shown LD as highly dynamic organelles for maintaining lipid homeostasis through fat storage, protein sorting and other molecular events studied in adipocytes and other cells of living organisms. This review focuses on the molecular events of LD formation in hepatocytes and the importance of cross talk between different cell types and their signalling in NAFLD as to provide a perspective on molecular mechanisms as well as possibilities for different therapeutic intervention strategies.

Current role of fenofibrate in the prevention and management of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a common health problem with a high mortality burden due to its liver- and vascular-specific complications. It is associated with obesity, high-fat diet as well as with type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS). Impaired hepatic fatty acid (FA) turnover together with insulin resistance are key players in NAFLD pathogenesis. Peroxisome proliferator-activated receptors (PPARs) are involved in lipid and glucose metabolic pathways. The novel concept is that the activation of the PPARα subunit may protect from liver steatosis. Fenofibrate, by activating PPARα, effectively improves the atherogenic lipid profile associated with T2DM and MetS. Experimental evidence suggested various protective effects of the drug against liver steatosis. Namely, fenofibrate-related PPARα activation may enhance the expression of genes promoting hepatic FA β-oxidation. Furthermore, fenofibrate reduces hepatic insulin resistance. It also inhibits the expression of inflammatory mediators involved in non-alcoholic steatohepatitis pathogenesis. These include tumor necrosis factor-α, intercellular cell adhesion molecule-1, vascular cell adhesion molecule-1 and monocyte chemoattractant protein-1. Consequently, fenofibrate can limit hepatic macrophage infiltration. Other liver-protective effects include decreased oxidative stress and improved liver microvasculature function. Experimental studies showed that fenofibrate can limit liver steatosis associated with high-fat diet, T2DM and obesity-related insulin resistance. Few studies showed that these benefits are also relevant even in the clinical setting. However, these have certain limitations. Namely, these were uncontrolled, their sample size was small, fenofibrate was used as a part of multifactorial approach, while histological data were absent. In this context, there is a need for large prospective studies, including proper control groups and full assessment of liver histology.