Rosiglitazone prevents nutritional fibrosis and steatohepatitis in mice

Curative role of natural PPARγ agonist in non-alcoholic fatty liver disease (NAFLD)

NAFLD is a condition that develops when the liver accumulates excess fat without alcohol consumption. This chronic liver ailment progresses along with insulin resistant and is typically not diagnosed until the patients have cirrhosis. Nuclear hormone receptor superfamily PPARs are essential for metabolism of fatty acids and glucose. In liver, lipid metabolism is regulated by nuclear receptors and PPARα, and PPARβ/δ encourages fatty acid β-oxidation. PPAR-γ, an energy-balanced receptor is a crucial regulator in NAFLD. The partial activation of PPAR-γ could lead to increased level of adiponectin and insulin sensitivity, thus improved NAFLD. Because of less side effects, natural compounds are emerged as potential therapeutic agents for NAFLD by PPARγ agonists. Although the results from preclinical studies are promising, further research is needed to determine the potential dosing and efficacy of mentioned compounds in human subjects. In this review, we summarize the effect of natural PPARγ agonist in the NAFLD.

Fibrotic pathways and fibroblast-like synoviocyte phenotypes in osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis, characterized by osteophyte formation, cartilage degradation, and structural and cellular alterations of the synovial membrane. Activated fibroblast-like synoviocytes (FLS) of the synovial membrane have been identified as key drivers, secreting humoral mediators that maintain inflammatory processes, proteases that cause cartilage and bone destruction, and factors that drive fibrotic processes. In normal tissue repair, fibrotic processes are terminated after the damage has been repaired. In fibrosis, tissue remodeling and wound healing are exaggerated and prolonged. Various stressors, including aging, joint instability, and inflammation, lead to structural damage of the joint and micro lesions within the synovial tissue. One result is the reduced production of synovial fluid (lubricants), which reduces the lubricity of the cartilage areas, leading to cartilage damage. In the synovial tissue, a wound-healing cascade is initiated by activating macrophages, Th2 cells, and FLS. The latter can be divided into two major populations. The destructive thymocyte differentiation antigen (THY)1─ phenotype is restricted to the synovial lining layer. In contrast, the THY1+ phenotype of the sublining layer is classified as an invasive one with immune effector function driving synovitis. The exact mechanisms involved in the transition of fibroblasts into a myofibroblast-like phenotype that drives fibrosis remain unclear. The review provides an overview of the phenotypes and spatial distribution of FLS in the synovial membrane of OA, describes the mechanisms of fibroblast into myofibroblast activation, and the metabolic alterations of myofibroblast-like cells.

Futile cycles: Emerging utility from apparent futility

Futile cycles are biological phenomena where two opposing biochemical reactions run simultaneously, resulting in a net energy loss without appreciable productivity. Such a state was presumed to be a biological aberration and thus deemed an energy-wasting "futile" cycle. However, multiple pieces of evidence suggest that biological utilities emerge from futile cycles. A few established functions of futile cycles are to control metabolic sensitivity, modulate energy homeostasis, and drive adaptive thermogenesis. Yet, the physiological regulation, implication, and pathological relevance of most futile cycles remain poorly studied. In this review, we highlight the abundance and versatility of futile cycles and propose a classification scheme. We further discuss the energetic implications of various futile cycles and their impact on basal metabolic rate, their bona fide and tentative pathophysiological implications, and putative drug interactions.

Targeting nuclear receptors for NASH/MASH: From bench to bedside

The onset of metabolic dysfunction-associated steatohepatitis (MASH) or non-alcoholic steatohepatitis (NASH) represents a tipping point leading to liver injury and subsequent hepatic complications in the natural progression of what is now termed metabolic dysfunction-associated steatotic liver diseases (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD). With no pharmacological treatment currently available for MASH/NASH, the race is on to develop drugs targeting multiple facets of hepatic metabolism, inflammation, and pro-fibrotic events, which are major drivers of MASH. Nuclear receptors (NRs) regulate genomic transcription upon binding to lipophilic ligands and govern multiple aspects of liver metabolism and inflammation. Ligands of NRs may include hormones, lipids, bile acids, and synthetic ligands, which upon binding to NRs regulate the transcriptional activities of target genes. NR ligands are presently the most promising drug candidates expected to receive approval from the United States Food and Drug Administration as a pharmacological treatment for MASH. This review aims to cover the current understanding of NRs, including nuclear hormone receptors, non-steroid hormone receptors, circadian NRs, and orphan NRs, which are currently undergoing clinical trials for MASH treatment, along with NRs that have shown promising results in preclinical studies.

PPARγ agonist treatment reduces fibroadipose tissue in secondary lymphedema by exhausting fibroadipogenic PDGFRα+ mesenchymal cells

Secondary lymphedema occurs in up to 20% of patients after lymphadenectomy performed for the surgical management of tumors involving the breast, prostate, uterus, and skin. Patients develop progressive edema of the affected extremity due to retention of protein-rich lymphatic fluid. Despite compression therapy, patients progress to chronic lymphedema in which noncompressible fibrosis and adipose tissue are deposited within the extremity. The presence of fibrosis led to our hypothesis that rosiglitazone, a PPARγ agonist that inhibits fibrosis, would reduce fibrosis in a mouse model of secondary lymphedema after hind limb lymphadenectomy. In vivo, rosiglitazone reduced fibrosis in the hind limb after lymphadenectomy. Our findings verified that rosiglitazone reestablished the adipogenic features of TGF-β1-treated mesenchymal cells in vitro. Despite this, rosiglitazone led to a reduction in adipose tissue deposition. Single-cell RNA-Seq data obtained from human tissues and flow cytometric and histological evaluation of mouse tissues demonstrated increased presence of PDGFRα+ cells in lymphedema; human tissue analysis verified these cells have the capacity for adipogenic and fibrogenic differentiation. Upon treatment with rosiglitazone, we noted a reduction in the overall quantity of PDGFRα+ cells and LipidTOX+ cells. Our findings provide a framework for treating secondary lymphedema as a condition of fibrosis and adipose tissue deposition, both of which, paradoxically, can be prevented with a pro-adipogenic agent.

Production, Exacerbating Effect, and EV-Mediated Transcription of Hepatic CCN2 in NASH: Implications for Diagnosis and Therapy of NASH Fibrosis

Non-alcoholic steatohepatitis (NASH) is characterized by steatosis, hepatocyte ballooning, and inflammation and may progress to include increasingly severe fibrosis, which portends more serious disease and is predictive of patient mortality. Diagnostic and therapeutic options for NASH fibrosis are limited, and the underlying fibrogenic pathways are under-explored. Cell communication network factor 2 (CCN2) is a well-characterized pro-fibrotic molecule, but its production in and contribution to NASH fibrosis requires further study. Hepatic CCN2 expression was significantly induced in NASH patients with F3-F4 fibrosis and was positively correlated with hepatic Col1A1, Col1A2, Col3A1, or αSMA expression. When wild-type (WT) or transgenic (TG) Swiss mice expressing enhanced green fluorescent protein (EGFP) under the control of the CCN2 promoter were fed up to 7 weeks with control or choline-deficient, amino-acid-defined diet with high (60%) fat (CDAA-HF), the resulting NASH-like hepatic pathology included a profound increase in CCN2 or EGFP immunoreactivity in activated hepatic stellate cells (HSC) and in fibroblasts and smooth muscle cells of the vasculature, with little or no induction of CCN2 in other liver cell types. In the context of CDAA-HF diet-induced NASH, Balb/c TG mice expressing human CCN2 under the control of the albumin promoter exhibited exacerbated deposition of interstitial hepatic collagen and activated HSC compared to WT mice. In vitro, palmitic acid-treated hepatocytes produced extracellular vesicles (EVs) that induced CCN2, Col1A1, and αSMA in HSC. Hepatic CCN2 may aid the assessment of NASH fibrosis severity and, together with pro-fibrogenic EVs, is a therapeutic target for reducing NASH fibrosis.

PPAR-γ signaling in nonalcoholic fatty liver disease: Pathogenesis and therapeutic targets

Non-alcoholic fatty liver disease (NAFLD), currently the leading cause of global chronic liver disease, has emerged as a major public health problem, more efficient therapeutics of which are thus urgently needed. Peroxisome proliferator-activated receptor γ (PPAR-γ), ligand-activated transcription factors of the nuclear hormone receptor superfamily, is considered a crucial metabolic regulator of hepatic lipid metabolism and inflammation. The role of PPAR-γ in the pathogenesis of NAFLD is gradually being recognized. Here, we outline the involvement of PPAR-γ in the pathogenesis of NAFLD through adipogenesis, insulin resistance, inflammation, oxidative stress, endoplasmic reticulum stress, and fibrosis. In addition, the evidence for PPAR-γ- targeted therapy for NAFLD are summarized. Altogether, PPAR-γ is a promising therapeutic target for NAFLD, and the development of drugs that can balance the beneficial and undesirable effects of PPAR-γ will bring new light to NAFLD patients.

PharmOmics: A species- and tissue-specific drug signature database and gene-network-based drug repositioning tool

Drug development has been hampered by a high failure rate in clinical trials due to our incomplete understanding of drug functions across organs and species. Therefore, elucidating species- and tissue-specific drug functions can provide insights into therapeutic efficacy, potential adverse effects, and interspecies differences necessary for effective translational medicine. Here, we present PharmOmics, a drug knowledgebase and analytical tool that is hosted on an interactive web server. Using tissue- and species-specific transcriptome data from human, mouse, and rat curated from different databases, we implemented a gene-network-based approach for drug repositioning. We demonstrate the potential of PharmOmics to retrieve known therapeutic drugs and identify drugs with tissue toxicity using in silico performance assessment. We further validated predicted drugs for nonalcoholic fatty liver disease in mice. By combining tissue- and species-specific in vivo drug signatures with gene networks, PharmOmics serves as a complementary tool to support drug characterization and network-based medicine.

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Development of PharmOmics, a platform for drug repositioning and toxicity prediction

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Contains >18000 species/tissue-specific gene signatures for 941 drugs and chemicals

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Benchmarked and validated network-based drug repositioning and toxicity prediction

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PharmOmics is freely accessible via an online web server to facilitate user access

PPARγ attenuates hepatic inflammation and oxidative stress of non‑alcoholic steatohepatitis via modulating the miR‑21‑5p/SFRP5 pathway

Inflammation and oxidative stress are key steps in the progression of non‑alcoholic steatohepatitis (NASH). Intervention in these two processes will therefore benefit NASH treatment. Peroxisome proliferator‑activated receptor γ (PPARγ), as a multiple functional transcription factor, has been reported to be involved in the prevention of NASH progression. However, the mechanism by which PPARγ prevents NASH remains to be elucidated. The present study demonstrated that the level of PPARγ was inversely correlated with that of microRNA (miRNA/miRs)‑21‑5p in both mice and humans with NASH. Activation of PPARγ inhibited lipid droplet accumulation, hepatic inflammation and oxidative stress by downregulating miR‑21‑5p in an in vitro model. Luciferase reporter and chromatin immunoprecipitation assays demonstrated that PPARγ suppressed transcriptional activity of miR‑21‑5p and bound to miR‑21‑5p promoter region. Furthermore, PPARγ downregulated miR‑21‑5p while miR‑21‑5p upregulated secreted frizzled‑related protein 5 (SFRP5) by targeting the 3'‑UTR of its mRNA. In vivo experiments revealed that PPARγ repressed inflammation and oxidative stress and miR‑21‑5p expression while increased SFRP5 level in a NASH mouse model. In summary, PPARγ attenuates inflammation and oxidative stress in NASH by modulating the miR‑21‑5p/SFRP5 pathway, thus holding promise of a new target for NASH treatment.

Co-administration of obeticholic acid and simvastatin protects against high-fat diet-induced non-alcoholic steatohepatitis in mice

Non-alcoholic steatohepatitis (NASH) has no approved therapy. The farnesoid X nuclear receptor (FXR) agonist obeticholic acid (OCA) has shown promise as a drug for NASH, but can adversely affect plasma lipid profiles. Therefore, the present study aimed to investigate the effects and underlying mechanisms of OCA in combination with simvastatin (SIM) in a high-fat diet (HFD)-induced model of NASH. C57BL/6J mice were fed with a HFD for 16 weeks to establish the NASH model. The mice were randomly divided into the following five groups: HFD, HFD + OCA, HFD + SIM, HFD + OCA + SIM and control. After 16 weeks, the mice were sacrificed under anesthesia. The ratios of liver weight to body weight (Lw/Bw) and of abdominal adipose tissue weight to body weight were calculated. Serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total cholesterol, triglycerides and low-density lipoprotein were measured. Liver sections were stained with hematoxylin and eosin. The protein levels of FXR, small heterodimeric partner (SHP) and cytochrome P450 family 7 subfamily A member 1 (CYP7A1) in the liver were detected by western blotting, while the mRNA levels of FXR, SHP, CYP7A1, bile salt export pump, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), sterol regulatory element binding protein-1 (SREBP1) and fatty acid synthase (FASN) were examined by reverse transcription-quantitative polymerase chain reaction. The administration of OCA with or without SIM reduced the liver inflammation score compared with those of the HFD and HFD + SIM groups, with no significant difference between the HFD + OCA and HFD + OCA + SIM groups. The steatosis score followed similar trends to the inflammation score. In HFD-fed mice, OCA combined with SIM prevented body weight gain compared with that in HFD and HFD + OCA groups, and reduced the Lw/Bw ratio compared with that in the HFD and HFD + SIM groups. In addition to preventing HFD-induced increases of ALT and AST, the combination of OCA and SIM reduced the mRNA levels of IL-6, TNF-α, SREBP1 and FASN. On the basis of these results, it may be concluded that the strategy of combining OCA with SIM represents an effective pharmacotherapy for NASH.

Molecular updates on berberine in liver diseases: Bench to bedside

Liver diseases are life-threatening illnesses and are the major cause of mortality and morbidity worldwide. These may include liver fibrosis, liver cirrhosis, and drug-induced liver toxicity. Liver diseases have a wide prevalence globally and the fifth most common cause of death among all gastrointestinal disorders. Several novel therapeutic approaches have emerged for the therapy of liver diseases that may provide better clinical outcomes with improved safety. The use of phytochemicals for the amelioration of liver diseases has gained considerable popularity. Berberine (BBR), an isoquinoline alkaloid of the protoberberine type, has emerged as a promising molecule for the treatment of gastrointestinal disorders. Accumulating studies have proved the hepatoprotective effects of BBR. BBR has been shown to modulate multiple signaling pathways implicated in the pathogenesis of liver diseases including Akt/FoxO2, PPAR-γ, Nrf2, insulin, AMPK, mTOR, and epigenetic pathways. In the present review, we have emphasized the important pharmacological activities and mechanisms of BBR in liver diseases. Further, we have reviewed various pharmacokinetic and toxicological barriers of this promising phytoconstituent. Finally, formulation-based novel approaches are also summarized to overcome the clinical hurdles for BBR.

Drugs for Non-alcoholic Steatohepatitis (NASH): Quest for the Holy Grail

Nonalcoholic fatty liver disease (NAFLD) is a global epidemic that is likely to become the most common cause of chronic liver disease in the next decade, worldwide. Though numerous drugs have been evaluated in clinical trials, most of them have returned inconclusive results and shown poorly-tolerated adverse effects. None of the drugs have been approved by the Food and Drug Administration for treating biopsy-proven non-alcoholic steatohepatitis (NASH). Vitamin E and pioglitazone have been extensively used in treatment of biopsy-proven nondiabetic NASH patients. Although some amelioration of inflammation has been seen, these drugs did not improve the fibrosis component of NASH. Therefore, dietary modification and weight reduction have remained the cornerstone of treatment of NASH; moreover, they have shown to improve histological activity as well as fibrosis. The search for an ideal drug or 'Holy Grail' within this landscape of possible agents continues, as weight reduction is achieved only in less than 10% of patients. In this current review, we summarize the drugs for NASH which are under investigation, and we provide a critical analysis of their up-to-date results and outcomes.

Transcriptional Regulation of Metabolic Pathways via Lipid-Sensing Nuclear Receptors PPARs, FXR, and LXR in NASH

Nonalcoholic fatty liver disease comprises a wide spectrum of liver injuries from simple steatosis to steatohepatitis and cirrhosis. Nonalcoholic steatohepatitis (NASH) is defined when liver steatosis is associated with inflammation, hepatocyte damage, and fibrosis. A genetic predisposition and environmental insults (ie, dietary habits, obesity) are putatively responsible for NASH progression. Here, we present the impact of the lipid-sensing nuclear receptors in the pathogenesis and treatment of NASH. In detail, we discuss the pros and cons of the putative transcriptional action of the fatty acid sensors (peroxisome proliferator-activated receptors), the bile acid sensor (farnesoid X receptor), and the oxysterol sensor (liver X receptors) in the pathogenesis and bona fide treatment of NASH.

Crosstalk between PPARs and gut microbiota in NAFLD

Nonalcoholic fatty liver disease (NAFLD) has become the most common liver disorder in both China and worldwide. It ranges from simple steatosis and progresses over time to nonalcoholic steatohepatitis (NASH), advanced liver fibrosis, cirrhosis, or hepatocellular carcinoma(HCC). Furthermore, NAFLD and its complications impose a huge health burden to society. The microbiota is widely connected and plays an active role in human physiology and pathology, and it is a hidden 'organ' in determining the state of the host, in terms of homeostasis, or disease. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptorsuperfamily and can regulate multiple pathways involved in metabolism, and serve as effective targets forthe treatment of many types of metabolic syndromes, including NAFLD. The purpose of this review is to integrate related articles on gut microbiota, PPARs and NAFLD, and present a balanced overview on how the microbiota can possibly influence the development of NAFLD through PPARs.

SGLT2 inhibitor ipragliflozin alone and combined with pioglitazone prevents progression of nonalcoholic steatohepatitis in a type 2 diabetes rodent model

Nonalcoholic steatohepatitis (NASH) has become the most common cause of chronic liver disease worldwide in recent years. The pathogenesis of NASH is closely linked to metabolic diseases such as insulin resistance, obesity, dyslipidemia, and type 2 diabetes. However, there is currently no pharmacological agent for preventing the progression of NASH. Sodium-glucose cotransporter (SGLT) 2 inhibitors increase urinary glucose excretion by inhibiting renal glucose reabsorption, and improve various pathological conditions of type 2 diabetes, including insulin resistance. In the present study, we examined the effects of ipragliflozin, a SGLT2-selective inhibitor, alone and in combination with pioglitazone on NASH in high-fat diet-fed KK/A^y type 2 diabetic mice. Type 2 diabetic mice with NASH exhibited steatosis, inflammation, and fibrosis in the liver as well as hyperglycemia, insulin resistance, and obesity, features that are observed in human NASH. Four-week repeated administration of ipragliflozin (0.1-3 mg/kg) led to significant improvements in hyperglycemia, insulin resistance, and obesity in addition to hyperlipidemia and liver injury including hepatic steatosis and fibrosis. Moreover, ipragliflozin reduced inflammation and oxidative stress in the liver. Repeated administration of pioglitazone (3-30 mg/kg) also significantly improved various parameters of diabetes and NASH, excluding obesity. Furthermore, combined treatment comprising ipragliflozin (1 mg/kg) and pioglitazone (10 mg/kg) additively improved these parameters. These findings indicate that the SGLT2-selective inhibitor ipragliflozin improves hyperglycemia as well as NASH in type 2 diabetic mice. Therefore, treatment with ipragliflozin monotherapy or coadministered with pioglitazone is expected to be a potential therapeutic option for the treatment of type 2 diabetes with NASH.

Peroxisome Proliferator-Activated Receptors and Their Novel Ligands as Candidates for the Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a major health issue worldwide, frequently associated with obesity and type 2 diabetes. Steatosis is the initial stage of the disease, which is characterized by lipid accumulation in hepatocytes, which can progress to non-alcoholic steatohepatitis (NASH) with inflammation and various levels of fibrosis that further increase the risk of developing cirrhosis and hepatocellular carcinoma. The pathogenesis of NAFLD is influenced by interactions between genetic and environmental factors and involves several biological processes in multiple organs. No effective therapy is currently available for the treatment of NAFLD. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that regulate many functions that are disturbed in NAFLD, including glucose and lipid metabolism, as well as inflammation. Thus, they represent relevant clinical targets for NAFLD. In this review, we describe the determinants and mechanisms underlying the pathogenesis of NAFLD, its progression and complications, as well as the current therapeutic strategies that are employed. We also focus on the complementary and distinct roles of PPAR isotypes in many biological processes and on the effects of first-generation PPAR agonists. Finally, we review novel and safe PPAR agonists with improved efficacy and their potential use in the treatment of NAFLD.

Therapeutic potential of PPARγ natural agonists in liver diseases

Peroxisome proliferator‐activated receptor gamma (PPARγ) is a vital subtype of the PPAR family. The biological functions are complex and diverse. PPARγ plays a significant role in protecting the liver from inflammation, oxidation, fibrosis, fatty liver and tumours. Natural products are a promising pool for drug discovery, and enormous research effort has been invested in exploring the PPARγ‐activating potential of natural products. In this manuscript, we will review the research progress of PPARγ agonists from natural products in recent years and probe into the application potential and prospects of PPARγ natural agonists in the therapy of various liver diseases, including inflammation, hepatic fibrosis, non‐alcoholic fatty liver and liver cancer.

Protective role of arnebin-1 in rats with nonalcoholic fatty liver disease

Objective

To examine the effects of arnebin-1 on nonalcoholic fatty liver disease (NAFLD) induced by a high-fat diet (HFD).

Methods

Male Sprague–Dawley rats were fed an HFD for 10 weeks and then treated with arnebin-1 at a dose of 5, 10 or 20 mg/kg/day by gavage for a further 12 weeks of a 22-week HFD. Peripheral blood and liver tissues were collected for biochemical and histopathological examination. The mechanisms of arnebin-1 on liver fibrosis and insulin resistance (IR) were determined by Western blotting and real-time quantitative polymerase chain reaction.

Results

Arnebin-1 treatment attenuated the increase of total cholesterol, triglycerides, low-density lipoprotein cholesterol, aspartate aminotransferase and alanine aminotransferase in serum and lipid accumulation in the livers of HFD-fed rats. Furthermore, arnebin-1 abrogated HFD-induced liver fibrosis and the increase of fibrotic biomarkers. The HFD-induced decrease of hepatic proliferator-activated receptor γ and pro-matrix-metalloproteinase (MMP)-9 levels and the increase of tissue inhibitor of metalloproteinase-1 (TIMP-1) levels were reversed after arnebin-1. Arnebin-1 attenuated IR through activating the insulin receptor substrate-1/Akt/mTOR signalling pathway.

Conclusion

This study demonstrated that arnebin-1 ameliorates NAFLD, in part, by attenuating hepatic fibrosis and IR, suggesting that arnebin-1 may be a therapeutic agent for NAFLD treatment.

Peroxisome Proliferator-Activated Receptors and Their Agonists in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. In addition to the liver-related morbidity and mortality, NAFLD is now also associated with various extrahepatic diseases. Pathogenesis of NAFLD is multifactorial with limited pharmacotherapy options for the treatment of patients with NAFLD. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that are involved in the transcriptional regulation of lipid metabolism, glucose homeostasis, energy balance, inflammation, and atherosclerosis. PPAR agonists are attractive options for treatment of NAFLD as they can act at multiple targets involved in the pathogenesis of NAFLD. We reviewed the available literature on the pathophysiological role of PPARs and use of PPAR agonists in the treatment of NAFLD. Original studies and review articles available on PubMed regarding the role of PPARs in the pathogenesis and utility of PPAR agonists in the treatment of NAFLD were included in this review article. ClinicalTrials.gov and Clinical Trials Registry-India sites were searched for ongoing studies on saroglitazar. The available literature suggests that PPARs play an important role in the pathogenesis of NAFLD. Use of PPAR gamma agonists is associated with histological improvement in NAFLD. Dual PPAR agonists with no or minimal PPAR gamma activity are being explored in the treatment of NAFLD. Because of the pathophysiological role of PPARs in NAFLD, PPAR agonists are attractive options for the treatment of patients with NAFLD. Dual PPAR agonists without significant gamma activity appear promising for the treatment of NAFLD.

Role of peroxisome proliferator-activated receptors in non-alcoholic fatty liver disease inflammation

Overweight and obesity have been identified as the most important risk factors for many diseases, including cardiovascular disease, type 2 diabetes and lipid disorders, such as non-alcoholic fatty liver disease (NAFLD). The metabolic changes associated with obesity are grouped to define metabolic syndrome, which is one of the main causes of morbidity and mortality in industrialized countries. NAFLD is considered to be the hepatic manifestation of metabolic syndrome and is one of the most prevalent liver diseases worldwide. Inflammation plays an important role in the development of numerous liver diseases, contributing to the progression to more severe stages, such as non-alcoholic steatohepatitis and hepatocellular carcinoma. Peroxisome proliferator-activated receptors (PPARs) are binder-activated nuclear receptors that are involved in the transcriptional regulation of lipid metabolism, energy balance, inflammation and atherosclerosis. Three isotypes are known: PPAR-α, PPARδ/β and PPAR-γ. These isotypes play different roles in diverse tissues and cells, including the inflammatory process. In this review, we discuss current knowledge on the role PPARs in the hepatic inflammatory process involved in NAFLD as well as new pharmacological strategies that target PPARs.

Pioglitazone suppresses inflammation and fibrosis in nonalcoholic fatty liver disease by down-regulating PDGF and TIMP-2: Evidence from in vitro study

BACKGROUND

The prevalence of nonalcoholic fatty liver disease (NAFLD) has been increasing worldwide. Pioglitazone is a pharmacologic agonist of peroxisome proliferators-activated receptor-γ (PPAR-γ) that was reported to ameliorate hepatic steatosis and inflammatory changes.

OBJECTIVE

We aimed to evaluate the effects of pioglitazone in NAFLD and investigate the underlying mechanism by testing platelet derived growth factor (PDGF) and tissue inhibitory of metalloproteinase-2 (TIMP-2).

METHODS

A total of C57BL/6 wild-type mice were randomized to three groups, control group (NC, n= 60), high-fat control group (HF, n= 60), and pioglitazone treatment group (L,n= 60). Mice were administrated with high-fat diet to construct NAFLD model. Enzyme-linked immunosorbent assay (ELISA) was used to measure protein expression of PDGF and TIMP-2. Liver histology samples were stained with hematoxylin and eosin (H&E).

RESULTS

Upon pioglitazone treatment, the PDGF and TIMP-2 expression levels were decreased compared with high-fat diet-fed mice devoid of drug stimulation. Analysis of liver histology showed pioglitazone treatment could reduce steatosis and inflammatory changes, which was helpful to inhibit hepatic fibrosis in NAFLD mice.

CONCLUSIONS

The study showed pioglitazone might exert an inhibitory effect on hepatic inflammation and fibrosis in NAFLD. Moreover, this study provided novel evidence for the promising clinical application of pioglitazone in intervening NAFLD.

Honokiol attenuates diet-induced non-alcoholic steatohepatitis by regulating macrophage polarization through activating peroxisome proliferator-activated receptor γ

BACKGROUND AND AIM

Non-alcoholic steatohepatitis (NASH) may develop into hepatic cirrhosis. This study aimed to investigate whether honokiol could prevent NASH induced by high-cholesterol and high-fat (CL) diet in mice and the possible mechanism involved.

METHODS

Mice were fed with CL diet for 12 weeks to establish a NASH model; honokiol (0.02% w/w in diet) was added to evaluate its effect on NASH. Murine peritoneal macrophages, RAW264.7 and ANA-1 cells, were used to explore the possible mechanisms of honokiol on macrophage polarization.

RESULTS

Mice developed NASH after fed with CL diet for 12 weeks. Honokiol supplementation alleviated insulin resistance, hepatic steatosis, inflammation, and fibrosis induced by CL diet. Immunohistochemistry showed that honokiol induced more M2 macrophages in livers compared with CL diet alone. Honokiol decreased M1 marker genes (TNFα and MCP-1) and increased M2 marker gene (YM-1, IL-10, IL-4R and IL-13) expression in mice liver compared with CL diet. Moreover, treatment with honokiol lowered alanine aminotransferase and aspartate aminotransferase in serum and preserved liver from lipid peroxidation, evidenced by lowered hepatic malondialdehyde level. Honokiol has antioxidant function, as honokiol upregulated hepatic glutathione and superoxide dismutase level and downregulated hepatic CYP2E1 protein level. Hepatic peroxisome proliferator-activated receptor γ (PPARγ) and its target genes were upregulated by honokiol. Furthermore, honokiol (10 μM) treatment in mouse peritoneal cells, RAW264.7 cells and ANA-1 cells, led to M2 macrophage polarization, whereas a PPARγ antagonist, GW9662, abolished this effect of honokiol.

CONCLUSIONS

Honokiol can attenuate CL diet-induced NASH and the mechanism in which possibly is polarizing macrophages to M2 phenotype via PPARγ activation.

Interactions between TGF-β1, canonical WNT/β-catenin pathway and PPAR γ in radiation-induced fibrosis

Radiation therapy induces DNA damage and inflammation leading to fibrosis. Fibrosis can occur 4 to 12 months after radiation therapy. This process worsens with time and years. Radiation-induced fibrosis is characterized by fibroblasts proliferation, myofibroblast differentiation, and synthesis of collagen, proteoglycans and extracellular matrix. Myofibroblasts are non-muscle cells that can contract and relax. Myofibroblasts evolve towards irreversible retraction during fibrosis process. In this review, we discussed the interplays between transforming growth factor-β1 (TGF-β1), canonical WNT/β-catenin pathway and peroxisome proliferator-activated receptor gamma (PPAR γ) in regulating the molecular mechanisms underlying the radiation-induced fibrosis, and the potential role of PPAR γ agonists. Overexpression of TGF-β and canonical WNT/β-catenin pathway stimulate fibroblasts accumulation and myofibroblast differentiation whereas PPAR γ expression decreases due to the opposite interplay of canonical WNT/β-catenin pathway. Both TGF-β1 and canonical WNT/β-catenin pathway stimulate each other through the Smad pathway and non-Smad pathways such as phosphatidylinositol 3-kinase/serine/threonine kinase (PI3K/Akt) signaling. WNT/β-catenin pathway and PPAR γ interact in an opposite manner. PPAR γ agonists decrease β-catenin levels through activation of inhibitors of the WNT pathway such as Smad7, glycogen synthase kinase-3 (GSK-3 β) and dickkopf-related protein 1 (DKK1). PPAR γ agonists also stimulate phosphatase and tensin homolog (PTEN) expression, which decreases both TGF-β1 and PI3K/Akt pathways. PPAR γ agonists by activating Smad7 decrease Smads pathway and then TGF-β signaling leading to decrease radiation-induced fibrosis. TGF-β1 and canonical WNT/β-catenin pathway promote radiation-induced fibrosis whereas PPAR γ agonists can prevent radiation-induced fibrosis.

PPARs and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) encompasses a range of liver pathology ranging from simple steatosis to varying degrees of inflammation, hepatocyte injury and fibrosis. Without intervention it can progress to end-stage liver disease and hepatocellular carcinoma. Given its close association with obesity, the prevalence of NAFLD has increased dramatically worldwide. Currently, there are no FDA-approved medications for the treatment of NAFLD and although lifestyle modifications with appropriate diet and exercise have been shown to be beneficial, this has been difficult to achieve and sustain for the majority of patients. As such, the search for effective therapeutic agents is an active area of research. Peroxisome proliferator-activated receptors (PPARs) belong to a class of nuclear receptors. Because of their key role in the transcriptional regulation of mediators of glucose and lipid metabolism, PPAR ligands have been investigated as possible therapeutic agents. Here we review the current evidence from preclinical and clinical studies investigating the therapeutic potential of PPAR ligands for the treatment of NAFLD.

Targeting the mitochondrial pyruvate carrier attenuates fibrosis in a mouse model of nonalcoholic steatohepatitis

Diseases of the liver related to metabolic syndrome have emerged as the most common and undertreated hepatic ailments. The cause of nonalcoholic fatty liver disease is the aberrant accumulation of lipid in hepatocytes, though the mechanisms whereby this leads to hepatocyte dysfunction, death, and hepatic fibrosis are still unclear. Insulin-sensitizing thiazolidinediones have shown efficacy in treating nonalcoholic steatohepatitis (NASH), but their widespread use is constrained by dose-limiting side effects thought to be due to activation of the peroxisome proliferator-activated receptor γ. We sought to determine whether a next-generation thiazolidinedione with markedly diminished ability to activate peroxisome proliferator-activated receptor γ (MSDC-0602) would retain its efficacy for treating NASH in a rodent model. We also determined whether some or all of these beneficial effects would be mediated through an inhibitory interaction with the mitochondrial pyruvate carrier 2 (MPC2), which was recently identified as a mitochondrial binding site for thiazolidinediones, including MSDC-0602. We found that MSDC-0602 prevented and reversed liver fibrosis and suppressed expression of markers of stellate cell activation in livers of mice fed a diet rich in trans-fatty acids, fructose, and cholesterol. Moreover, mice with liver-specific deletion of MPC2 were protected from development of NASH on this diet. Finally, MSDC-0602 directly reduced hepatic stellate cell activation in vitro, and MSDC-0602 treatment or hepatocyte MPC2 deletion also limited stellate cell activation indirectly by affecting secretion of exosomes from hepatocytes.

CONCLUSION

Collectively, these data demonstrate the effectiveness of MSDC-0602 for attenuating NASH in a rodent model and suggest that targeting hepatic MPC2 may be an effective strategy for pharmacologic development. (Hepatology 2017;65:1543-1556).

Hepatocyte-specific, PPARγ-regulated mechanisms to promote steatosis in adult mice

Peroxisome proliferator-activated receptor γ (PPARγ) is the target for thiazolidinones (TZDs), drugs that improve insulin sensitivity and fatty liver in humans and rodent models, related to a reduction in hepatic de novo lipogenesis (DNL). The systemic effects of TZDs are in contrast to reports suggesting hepatocyte-specific activation of PPARγ promotes DNL, triacylglycerol (TAG) uptake and fatty acid (FA) esterification. As these hepatocyte-specific effects of PPARγ could counterbalance the positive therapeutic actions of systemic delivery of TZDs, the current study used a mouse model of adult-onset, liver (hepatocyte)-specific PPARγ knockdown (aLivPPARγkd). This model has advantages over existing congenital knockout models, by avoiding compensatory changes related to embryonic knockdown, thus better modeling the impact of altering PPARγ on adult physiology, where metabolic diseases most frequently develop. The impact of aLivPPARγkd on hepatic gene expression and endpoints in lipid metabolism was examined after 1 or 18 weeks (Chow-fed) or after 14 weeks of low- or high-fat (HF) diet. aLivPPARγkd reduced hepatic TAG content but did not impact endpoints in DNL or TAG uptake. However, aLivPPARγkd reduced the expression of the FA translocase (Cd36), in 18-week Chow- and HF-fed mice, associated with increased NEFA after HF feeding. Also, aLivPPARγkd dramatically reduced Mogat1 expression, that was reflected by an increase in hepatic monoacylglycerol (MAG) levels, indicative of reduced MOGAT activity. These results, coupled with previous reports, suggest that Cd36-mediated FA uptake and MAG pathway-mediated FA esterification are major targets of hepatocyte PPARγ, where loss of this control explains in part the protection against steatosis observed after aLivPPARγkd.

The anti-hepatic fibrosis activity of ergosterol depended on upregulation of PPARgamma in HSC-T6 cells

Advanced glycation endproducts (AGEs) were shown to play an important role in metabolic syndrome and were suggested to contribute to the development of hepatic fibrosis. Evidence indicates that AGEs resulted in hepatic fibrosis coupled to the activation of the receptor for AGEs (RAGE) in hepatic stellate cells (HSCs). NADPH oxidase is downstream of the RAGE signaling pathway, resulting in an increase in reactive oxygen species (ROS), alpha-smooth muscle actin (alpha-SMA), RAGE, and matrix metalloproteinase-9 (MMP-9). This study was designed to evaluate the effects of ergosterol on RAGE signaling in HSC-T6 cells. Ergosterol suppressed the activation of HSC-T6 cells induced by AGEs, and attenuated overexpressions of alpha-SMA, MMP-9, and epithelial-mesenchymal transition (EMT) markers, including N-cadherin and vimentin. We also found that these inhibitory effects of ergosterol on the activation of HSCs were dependent on peroxisome proliferator-activated receptor-gamma (PPARgamma) confirmed by PPARgamma reporter assay and PPARgamma knockdown. In addition, ergosterol also showed an inhibitory effect on the generation of AGEs, fructosamine, and α-dicarbonyl compounds in this study. Our results show that ergosterol can be used as a protective agent against hepatic fibrosis caused by induction of AGEs.

Diosmin attenuates radiation-induced hepatic fibrosis by boosting PPAR-γ expression and hampering miR-17-5p-activated canonical Wnt-β-catenin signaling

BACKGROUND

Liver fibrosis is one of the major complications from upper right quadrant radiotherapy. MicroRNA-17-5p (miR-17-5p) is hypothesized to act as a regulator of hepatic stellate cell (HSCs) activation by activation of the canonical Wnt-β-catenin pathway. Diosmin (Dios), a citrus bioflavonoid, is known to possess potent antioxidant, anti-inflammatory, and anti-apoptotic properties.

PURPOSE

To explore the molecular mechanisms that underlie radiation-induced liver fibrosis, and to evaluate the possible influence of Dios on the miR-17-5p-Wnt-β-catenin signaling axis during fibrogenesis provoked by irradiation (IRR) in rats. Also, the effect of Dios on hepatic peroxisome proliferator activated receptor-γ (PPAR-γ) expression as a regulator for HSC activation was considered.

METHODS

We administered 100 mg·(kg body mass)^-1·day^-1 (per oral) of Dios were administered to IRR-exposed rats (overall dose of 12 Gy on 6 fractions of 2 Gy each) for 6 successive weeks.

RESULTS

Data analysis revealed that Dios treatment mitigated oxidative stress, enhanced antioxidant defenses, alleviated hepatic inflammatory responses, abrogated pro-fibrogenic cytokines, and stimulated PPAR-γ expression. Dios treatment repressed the miR-17-5p activated Wnt-β-catenin signaling induced by IRR. Moreover, Dios treatment restored the normal hepatic architecture and reversed pathological alterations induced by IRR.

CONCLUSION

We hypothesize that the stimulation of PPAR-γ expression and interference with miR-17-5p activated Wnt-β-catenin signaling mediates the antifibrotic properties of Dios.

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.

Potential effects of curcumin on peroxisome proliferator-activated receptor-γ in vitro and in vivo

Natural peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists are found in food and may be important for health through their anti-inflammatory properties. Curcumin (Cur) is a bright yellow spice, derived from the rhizome of Curcuma longa Linn. It has been shown to have many biological properties that appear to operate through diverse mechanisms. Some of these potentially beneficial effects of Cur are due to activation of the nuclear transcription factor PPAR-γ. It is reported (using in vitro and in vivo models) that Cur plays a potential role against several diseases. In this review article, we present the current literature on the effects of Cur on the modulation of inflammatory processes that are mediated through PPAR-γ.

Pharmacological Intervention in Hepatic Stellate Cell Activation and Hepatic Fibrosis

The activation and transdifferentiation of hepatic stellate cells (HSCs) into contractile, matrix-producing myofibroblasts (MFBs) are central events in hepatic fibrogenesis. These processes are driven by autocrine- and paracrine-acting soluble factors (i.e., cytokines and chemokines). Proof-of-concept studies of the last decades have shown that both the deactivation and removal of hepatic MFBs as well as antagonizing profibrogenic factors are in principle suitable to attenuate ongoing hepatic fibrosis. Although several drugs show potent antifibrotic activities in experimental models of hepatic fibrosis, there is presently no effective pharmaceutical intervention specifically approved for the treatment of liver fibrosis. Pharmaceutical interventions are generally hampered by insufficient supply of drugs to the diseased liver tissue and/or by adverse effects as a result of affecting non-target cells. Therefore, targeted delivery systems that bind specifically to receptors solely expressed on activated HSCs or transdifferentiated MFBs and delivery systems that can improve drug distribution to the liver in general are urgently needed. In this review, we summarize current strategies for targeted delivery of drugs to the liver and in particular to pro-fibrogenic liver cells. The applicability and efficacy of sequestering molecules, selective protein carriers, lipid-based drug vehicles, viral vectors, transcriptional targeting approaches, therapeutic liver- and HSC-specific nanoparticles, and miRNA-based strategies are discussed. Some of these delivery systems that had already been successfully tested in experimental animal models of ongoing hepatic fibrogenesis are expected to translate into clinically useful therapeutics specifically targeting HSCs.

TLR4‑dependent signaling pathway modulation: A novel mechanism by which pioglitazone protects against nutritional fibrotic steatohepatitis in mice

Activation of the innate immune system is involved in the development of chronic liver diseases, including nonalcoholic steatohepatitis. Toll‑like receptor 4 (TLR4) is one of the sensors of the innate immune system. The aim of the present study was to elucidate the role of the TLR4‑dependent signaling pathway, and examine the effect of pioglitazone on hepatic fibrosis, through modulation of the TLR4 pathway in a mouse model of nutritional fibrotic steatohepatitis. Male C57BL/6J mice were fed a methionine‑choline deficient (MCD) diet for 8 weeks to induce nonalcoholic fibrotic steatohepatitis. The PPARγ agonist, pioglitazone, and PPARγ inhibitor, GW9662, were administered to the mice, respectively. The effects of the induction of PPARγ on liver biochemistry and histology, the modulation of TLR4 and its downstream pathway, and the expression levels of inflammatory and fibrogenic genes were assessed using reverse transcription‑quantitative polymerase chain reaction and Western blot analyses. The MCD‑fed mice exhibited progressive hepatic steatosis, necrotic inflammation and fibrosis, along with increase levels of serum alanine aminotransferase and aspartate aminotransferase, accompanied by the upregulation of TLR4, the TLR4‑myeloid differentiation primary response gene 88‑dependent pathway and downstream genes, and proinflammatory and profibrotic genes; and downregulation of basic membrane protein and activin membrane‑bound inhibitor. The administration of pioglitazone was found to reverse hepatic nutritional fibrosis via restoration of the expression levels of proinflammatory and profibrotic genes in the MCD‑fed mice. The results of the present study provide novel evidence supporting the protective role of pioglitazone in ameliorating nutritional fibrotic steatohepatitis, through modulation of the TLR4‑mediated signaling pathway.

Hepatoprotective and Anti-fibrotic Agents: It's Time to Take the Next Step

Hepatic fibrosis and cirrhosis cause strong human suffering and necessitate a monetary burden worldwide. Therefore, there is an urgent need for the development of therapies. Pre-clinical animal models are indispensable in the drug discovery and development of new anti-fibrotic compounds and are immensely valuable for understanding and proofing the mode of their proposed action. In fibrosis research, inbreed mice and rats are by far the most used species for testing drug efficacy. During the last decades, several hundred or even a thousand different drugs that reproducibly evolve beneficial effects on liver health in respective disease models were identified. However, there are only a few compounds (e.g., GR-MD-02, GM-CT-01) that were translated from bench to bedside. In contrast, the large number of drugs successfully tested in animal studies is repeatedly tested over and over engender findings with similar or identical outcome. This circumstance undermines the 3R (Replacement, Refinement, Reduction) principle of Russell and Burch that was introduced to minimize the suffering of laboratory animals. This ethical framework, however, represents the basis of the new animal welfare regulations in the member states of the European Union. Consequently, the legal authorities in the different countries are halted to foreclose testing of drugs in animals that were successfully tested before. This review provides a synopsis on anti-fibrotic compounds that were tested in classical rodent models. Their mode of action, potential sources and the observed beneficial effects on liver health are discussed. This review attempts to provide a reference compilation for all those involved in the testing of drugs or in the design of new clinical trials targeting hepatic fibrosis.

Effects of a combination of puerarin, baicalin and berberine on the expression of proliferator-activated receptor-γ and insulin receptor in a rat model of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a prevalent disease, with a clinical spectrum ranging from simple fatty liver disease to nonalcoholic steatohepatitis and cirrhosis. Puerarin, baicalin and berberine are herbal products widely used in Asia, which are believed to possess therapeutic benefits for alleviating the symptoms of NAFLD. In the present study, a rat model of NAFLD, induced by a high-fat diet, was established and orthographical experimentation was used to investigate the effects of various combinations of puerarin, baicalin and berberine on the hepatic expression of proliferator-activated receptor (PPAR)-γ and insulin receptor (IR). The present study demonstrated that serum levels of total cholesterol, alanine transaminase and low-density lipoproteins were significantly decreased in the puerarin-dominated groups (P<0.05 vs. the model group), whereas the concentrations of tumor necrosis factor-α and interleukin-6 were significantly improved in the baicalin- and berberine-dominated groups (P<0.05 vs. the model group). Furthermore, as compared with the control group, the levels of PPAR-γ/IR mRNA and protein expression were significantly decreased in the model group (P<0.01), and significantly increased in the rosiglitazone group and some of the orthogonal experiment groups (P<0.01). In conclusion, a combination of puerarin, baicalin and berberine induced favorable effects on NAFLD by upregulating hepatic PPAR-γ and IR expression levels, and different proportions of monomer compositions exerted variable positive effects on various stages of NAFLD.

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.

Revisiting PPARγ as a target for the treatment of metabolic disorders

As the prevalence of obesity has increased explosively over the last several decades, associated metabolic disorders, including type 2 diabetes, dyslipidemia, hypertension, and cardiovascular diseases, have been also increased. Thus, new strategies for preventing and treating them are needed. The nuclear peroxisome proliferator-activated receptors (PPARs) are involved fundamentally in regulating energy homeostasis; thus, they have been considered attractive drug targets for addressing metabolic disorders. Among the PPARs, PPARγ is a master regulator of gene expression for metabolism, inflammation, and other pathways in many cell types, especially adipocytes. It is a physiological receptor of the potent anti-diabetic drugs of the thiazolidinediones (TZDs) class, including rosiglitazone (Avandia). However, TZDs have undesirable and severe side effects, such as weight gain, fluid retention, and cardiovascular dysfunction. Recently, many reports have suggested that PPARγ could be modulated by post-translational modifications (PTMs), and modulation of PTM has been considered as novel approaches for treating metabolic disorders with fewer side effects than the TZDs. In this review, we discuss how PTM of PPARγ may be regulated and issues to be considered in making novel anti-diabetic drugs that can modulate the PTM of PPARγ. [BMB Reports 2014; 47(11): 599-608]

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.

NHE1 deficiency in liver: implications for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease NAFLD is closely associated with the dysregulation of lipid homeostasis. Diet-induced hepatic steatosis, which can initiate NAFLD progression, has been shown to be dramatically reduced in mice lacking the electroneutral Na(+)/H(+) exchanger NHE1 (Slc9a1). In this study, we investigated if NHE1 deficiency had effects in liver that could contribute to the apparent protection against aberrant lipid accumulation. RT-PCR and immunoblot analyses of wild-type and NHE1-null livers revealed an expression profile that strongly suggested attenuation of both de novo lipogenesis and hepatic stellate cell activation, which is implicated in liver fibrosis. This included upregulation of the farnesoid X receptor FXR, peroxisome proliferator-activated receptor PPARγ, its co-activator PGC1α, and sestrin 2, an antioxidant protein involved in hepatic metabolic homeostasis. Furthermore, expression levels of the pro-lipogenic liver X receptor LXRα, and acetyl CoA carboxylases 1 and 2 were downregulated. These changes were associated with evidence of reduced cellular stress, which persisted even upon exposure to a high-fat diet, and the better preservation of insulin signaling, as evidenced by protein kinase B/Akt phosphorylation (Ser473). These results indicate that NHE1 deficiency may protect against NAFLD pathogenesis, which is significant given the availability of highly specific NHE1 inhibitors.

Review article: The prevention and reversal of hepatic fibrosis in autoimmune hepatitis

BACKGROUND

Immunosuppressive treatment of autoimmune hepatitis can prevent or reverse hepatic fibrosis, but these anti-fibrotic effects are inconsistent secondary gains.

AIM

To describe the anti-fibrotic effects of current therapies for autoimmune hepatitis, discuss the pathogenic mechanisms of hepatic fibrosis that might be targeted by anti-fibrotic interventions, indicate the non-invasive diagnostic tests of hepatic fibrosis that must be validated in autoimmune hepatitis and to suggest promising treatment opportunities.

METHODS

Studies cited in PubMed from 1972 to 2013 for autoimmune hepatitis, hepatic fibrosis, cirrhosis, anti-fibrotic therapy and non-invasive tests of hepatic fibrosis were selected.

RESULTS

Hepatic fibrosis improves in 53-57% of corticosteroid-treated patients with autoimmune hepatitis; progressive fibrosis slows or is prevented in 79%; and cirrhosis may be reversed. Progressive hepatic fibrosis is associated with liver inflammation, and the inability to fully suppress inflammatory activity within 12 months is associated with progression to cirrhosis (54%) and death or need for liver transplantation (15%). Liver tissue examination remains the gold standard for assessing hepatic fibrosis, but laboratory and radiological tests may be useful non-invasive methods to measure the fibrotic response. Severe liver inflammation can confound radiological assessments, and the preferred non-invasive test in autoimmune hepatitis is uncertain. Individualised treatment adjustments and adjunctive anti-fibrotic therapies are poised for study in this disease.

CONCLUSIONS

The prevention and reversal of hepatic fibrosis are achievable objectives in autoimmune hepatitis. Strategies that evaluate individualised therapies adjusted to the rapidity and completeness of the inflammatory response, and the use of adjunctive anti-fibrotic interventions, must be evaluated.

Peroxisome proliferator-activated receptor-γ activators monascin and rosiglitazone attenuate carboxymethyllysine-induced fibrosis in hepatic stellate cells through regulating the oxidative stress pathway but independent of the receptor for advanced glycation end products signaling

Advanced glycation end products (AGEs) signaling through its receptors (RAGE) results in an increase in reactive oxygen species (ROS) and is thought to contribute to hepatic fibrosis via hyperglycemia. Carboxymethyllysine (CML) is a key AGE, with highly reactive dicarbonyl metabolites. We investigated the inhibitory effect of Monascus -fermented metabolite monascin and rosiglitazone on CML-induced RAGE signaling in hepatic stellate cells (HSCs) and its resulting antihepatic fibrosis activity. We found that monascin and rosiglitazone upregulated peroxisome proliferator-activated receptor-γ (PPAR-γ) to attenuate α-smooth muscle actin (SMA) and ROS generation in CML-treated HSCs in a RAGE activation-independent pathway. Therefore, monascin may delay or inhibit the progression of liver fibrosis through the activation of PPAR-γ and might prove to be a major antifibrotic mechanism to prevent liver disease.

PPARγ signaling and metabolism: the good, the bad and the future

Thiazolidinediones (TZDs) are potent insulin sensitizers that act through the nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ) and are highly effective oral medications for type 2 diabetes. However, their unique benefits are shadowed by the risk for fluid retention, weight gain, bone loss and congestive heart failure. This raises the question as to whether it is possible to build a safer generation of PPARγ-specific drugs that evoke fewer side effects while preserving insulin-sensitizing potential. Recent studies that have supported the continuing physiologic and therapeutic relevance of the PPARγ pathway also provide opportunities to develop newer classes of molecules that reduce or eliminate adverse effects. This review highlights key advances in understanding PPARγ signaling in energy homeostasis and metabolic disease and also provides new explanations for adverse events linked to TZD-based therapy.

Peroxisome proliferator-activated receptor-γ as a therapeutic target for hepatic fibrosis: from bench to bedside

Hepatic fibrosis is a dynamic chronic liver disease occurring as a consequence of wound-healing responses to various hepatic injuries. This disorder is one of primary predictors for liver-associated morbidity and mortality worldwide. To date, no pharmacological agent has been approved for hepatic fibrosis or could be recommended for routine use in clinical context. Cellular and molecular understanding of hepatic fibrosis has revealed that peroxisome proliferator-activated receptor-γ (PPARγ), the functioning receptor for antidiabetic thiazolidinediones, plays a pivotal role in the pathobiology of hepatic stellate cells (HSCs), whose activation is the central event in the pathogenesis of hepatic fibrosis. Activation of PPARγ inhibits HSC collagen production and modulates HSC adipogenic phenotype at transcriptional and epigenetic levels. These molecular insights indicate PPARγ as a promising drug target for antifibrotic chemotherapy. Intensive animal studies have demonstrated that stimulation of PPARγ regulatory system through gene therapy approaches and PPARγ ligands has therapeutic promise for hepatic fibrosis induced by a variety of etiologies. At the same time, thiazolidinedione agents have been investigated for their clinical benefits primarily in patients with nonalcoholic steatohepatitis, a common metabolic liver disorder with high potential to progress to fibrosis and liver-related death. Although some studies have shown initial promise, none has established long-term efficacy in well-controlled randomized clinical trials. This comprehensive review covers the 10-year discoveries of the molecular basis for PPARγ regulation of HSC pathophysiology and then focuses on the animal investigations and clinical trials of various therapeutic modalities targeting PPARγ for hepatic fibrosis.

Methionine-restricted C57BL/6J mice are resistant to diet-induced obesity and insulin resistance but have low bone density

Dietary methionine restriction (MR) extends lifespan, an effect associated with reduction of body weight gain, and improvement of insulin sensitivity in mice and rats as a result of metabolic adaptations in liver, adipose tissue and skeletal muscle. To test whether MR confers resistance to adiposity and insulin resistance, C57BL/6J mice were fed a high fat diet (HFD) containing either 0.86% methionine (control fed; CF) or 0.12% methionine (methionine-restricted; MR). MR mice on HFD had lower body weight gain despite increased food intake and absorption efficiency compared to their CF counterparts. MR mice on HFD were more glucose tolerant and insulin sensitive with reduced accumulation of hepatic triglycerides. In plasma, MR mice on HFD had higher levels of adiponectin and FGF21 while leptin and IGF-1 levels were reduced. Hepatic gene expression showed the downregulation of Scd1 while Pparg, Atgl, Cd36, Jak2 and Fgf21 were upregulated in MR mice on HFD. Restriction of growth rate in MR mice on HFD was also associated with lower bone mass and increased plasma levels of the collagen degradation marker C-terminal telopeptide of type 1 collagen (CTX-1). It is concluded that MR mice on HFD are metabolically healthy compared to CF mice on HFD but have decreased bone mass. These effects could be associated with the observed increase in FGF21 levels.

PPARs in Liver Diseases and Cancer: Epigenetic Regulation by MicroRNAs

Peroxisome-proliferator-activated receptors (PPARs) are ligand-activated nuclear receptors that exert in the liver a transcriptional activity regulating a whole spectrum of physiological functions, including cholesterol and bile acid homeostasis, lipid/glucose metabolism, inflammatory responses, regenerative mechanisms, and cell differentiation/proliferation. Dysregulations of the expression, or activity, of specific PPAR isoforms in the liver are therefore believed to represent critical mechanisms contributing to the development of hepatic metabolic diseases, disorders induced by hepatic viral infections, and hepatocellular adenoma and carcinoma. In this regard, specific PPAR agonists have proven to be useful to treat these metabolic diseases, but for cancer therapies, the use of PPAR agonists is still debated. Interestingly, in addition to previously described mechanisms regulating PPARs expression and activity, microRNAs are emerging as new important regulators of PPAR expression and activity in pathophysiological conditions and therefore may represent future therapeutic targets to treat hepatic metabolic disorders and cancers. Here, we reviewed the current knowledge about the general roles of the different PPAR isoforms in common chronic metabolic and infectious liver diseases, as well as in the development of hepatic cancers. Recent works highlighting the regulation of PPARs by microRNAs in both physiological and pathological situations with a focus on the liver are also discussed.

Update on pparγ and nonalcoholic Fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common initial presentation of obesity and insulin resistance. Uninterrupted progression of hepatic lipid accumulation often leads to fatty liver disease and eventually cirrhosis. Insulin resistance is one of the characteristics of type 2 diabetes. Several types of treatment have been employed against type 2 diabetes some of which ameliorate NAFLD. The frequent line of treatment to improve insulin sensitivity is the use of thiazolidinediones (TZD) which activate the nuclear receptor, peroxisome proliferator activated receptor gamma (Pparγ). Although TZDs are proven to be very effective in promoting insulin sensitivity, its actions on Pparγ have been complicated, specifically on NAFLD. According to studies in different models, Pparγ manifests both beneficial and undesirable effects on NAFLD. This paper will focus on the current knowledge of Pparγ and its effect on NAFLD.

Inhibitory effects of Ecklonia cava extract on high glucose-induced hepatic stellate cell activation

Nonalcoholic steatohepatitis (NASH) is a disease closely associated with obesity and diabetes. A prevalence of type 2 diabetes and a high body mass index in cryptogenic cirrhosis may imply that obesity leads to cirrhosis. Here, we examined the effects of an extract of Ecklonia cava, a brown algae, on the activation of high glucose-induced hepatic stellate cells (HSCs), key players in hepatic fibrosis. Isolated HSCs were incubated with or without a high glucose concentration. Ecklonia cava extract (ECE) was added to the culture simultaneously with the high glucose. Treatment with high glucose stimulated expression of type I collagen and α-smooth muscle actin, which are markers of activation in HSCs, in a dose-dependent manner. The activation of high glucose-treated HSCs was suppressed by the ECE. An increase in the formation of intracellular reactive oxygen species (ROS) and a decrease in intracellular glutathione levels were observed soon after treatment with high glucose, and these changes were suppressed by the simultaneous addition of ECE. High glucose levels stimulated the secretion of bioactive transforming growth factor-β (TGF-β) from the cells, and the stimulation was also suppressed by treating the HSCs with ECE. These results suggest that the suppression of high glucose-induced HSC activation by ECE is mediated through the inhibition of ROS and/or GSH and the downregulation of TGF-β secretion. ECE is useful for preventing the development of diabetic liver fibrosis.