Singular effects of PPAR agonists on nonalcoholic fatty liver disease of diet-induced obese mice

Effects of In Utero PFOS Exposure on Epigenetics and Metabolism in Mouse Fetal Livers

Prenatal exposure to perfluorooctanesulfonate (PFOS) increases fetus' metabolic risk; however, the investigation of the underlying mechanism is limited. In this study, pregnant mice in the gestational days (GD, 4.5-17.5) were exposed to PFOS (0.3 and 3 μg/g of body weight). At GD 17.5, PFOS perturbed maternal lipid metabolism and upregulated metabolism-regulating hepatokines (Angptl4, Angptl8, and Selenop). Mass-spectrometry imaging and whole-genome bisulfite sequencing revealed, respectively, selective PFOS localization and deregulation of gene methylation in fetal livers, involved in inflammation, glucose, and fatty acid metabolism. PCR and Western blot analysis of lipid-laden fetal livers showed activation of AMPK signaling, accompanied by significant increases in the expression of glucose transporters (Glut2/4), hexose-phosphate sensors (Retsat and ChREBP), and the key glycolytic enzyme, pyruvate kinase (Pk) for glucose catabolism. Additionally, PFOS modulated the expression levels of PPARα and PPARγ downstream target genes, which simultaneously stimulated fatty acid oxidation (Cyp4a14, Acot, and Acox) and lipogenesis (Srebp1c, Acaca, and Fasn). Using human normal hepatocyte (MIHA) cells, the underlying mechanism of PFOS-elicited nuclear translocation of ChREBP, associated with a fatty acid synthesizing pathway, was revealed. Our finding implies that in utero PFOS exposure altered the epigenetic landscape associated with dysregulation of fetal liver metabolism, predisposing postnatal susceptibility to metabolic challenges.

Emerging therapeutic options for non-alcoholic fatty liver disease: A systematic review

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) has become a prevalent cause of chronic liver disease and ranks third among the causes of transplantation. In the United States alone, annual medical costs are approximately 100 billion dollars. Unfortunately, there is no Federal Drug Administration (FDA)-approved medication for its treatment. However, various clinical trials are investigating several therapeutic classes that could potentially treat NAFLD. It is valuable to have a compilation of the data available on their efficacy.

AIM

To assess the efficacy of cyclophilin inhibitors, fibroblast growth factor 21 analogs (FGF21), and dual and pan peroxisome proliferator-activated receptor (PPAR) agonists for treating NAFLD.

METHODS

A comprehensive literature search using keywords including cyclophilin inhibitor, FGF agonist, pan-PPAR agonists, dual-PPAR agonist, NAFLD, non-alcoholic steatohepatitis, and fatty liver was conducted on October 29, 2022, in PubMed, EMBASE, Cochrane Library, Scopus and Web of Science. Animal and human research, case reports, and published articles in English from all countries with patients aged 18 and above were included. Only articles with a National Institutes of Health (NIH) Quality Assessment score of five or higher out of eight points were included. Articles that were narrative or systematic reviews, abstracts, not in English, focused on patients under 18 years old, did not measure outcomes of interest, were inaccessible, or had a low NIH Quality Assessment score were excluded. Each article was screened by two independent researchers evaluating relevance and quality. Resources were scored based on the NIH Quality Assessment Score; then, pertinent data was extracted in a spreadsheet and descriptively analyzed.

RESULTS

Of the 681 records screened, 29 met the necessary criteria and were included in this review. These records included 12 human studies and 17 animal studies. Specifically, there were four studies on cyclophilin inhibitors, four on FGF agonists/analogs, eleven on pan-PPAR agonists, and ten on dual-PPAR agonists. Different investigational products were assessed: The most common cyclophilin inhibitor was NV556; FGF agonists and analogs was Efruxifermin; pan-PPAR agonists was Lanifibranor; and dual-PPAR agonists was Saroglitazar. All classes were found to be statistically efficacious for the treatment of NAFLD, with animal studies demonstrating improvement in steatosis and/or fibrosis on biopsy and human studies evidencing improvement in different metabolic parameters and/or steatosis and fibrosis on FibroScan (P < 0.05).

CONCLUSION

The data analyzed in this review showed clinically significant improvement in individual histological features of NAFLD in both animal and human trials for all four classes, as well as good safety profiles (P < 0.05). We believe this compilation of information will have positive clinical implications in obtaining an FDA-approved therapy for NAFLD.

Peroxisome proliferator-activated receptors as targets to treat metabolic diseases: Focus on the adipose tissue, liver, and pancreas

The world is experiencing reflections of the intersection of two pandemics: Obesity and coronavirus disease 2019. The prevalence of obesity has tripled since 1975 worldwide, representing substantial public health costs due to its comorbidities. The adipose tissue is the initial site of obesity impairments. During excessive energy intake, it undergoes hyperplasia and hypertrophy until overt inflammation and insulin resistance turn adipocytes into dysfunctional cells that send lipotoxic signals to other organs. The pancreas is one of the organs most affected by obesity. Once lipotoxicity becomes chronic, there is an increase in insulin secretion by pancreatic beta cells, a surrogate for type 2 diabetes mellitus (T2DM). These alterations threaten the survival of the pancreatic islets, which tend to become dysfunctional, reaching exhaustion in the long term. As for the liver, lipotoxicity favors lipogenesis and impairs beta-oxidation, resulting in hepatic steatosis. This silent disease affects around 30% of the worldwide population and can evolve into end-stage liver disease. Although therapy for hepatic steatosis remains to be defined, peroxisome proliferator-activated receptors (PPARs) activation copes with T2DM management. Peroxisome PPARs are transcription factors found at the intersection of several metabolic pathways, leading to insulin resistance relief, improved thermogenesis, and expressive hepatic steatosis mitigation by increasing mitochondrial beta-oxidation. This review aimed to update the potential of PPAR agonists as targets to treat metabolic diseases, focusing on adipose tissue plasticity and hepatic and pancreatic remodeling.

Peroxisome proliferator-activated receptors-alpha and gamma synergism modulate the gut-adipose tissue axis and mitigate obesity

AIM

To evaluate the effects of single PPARα or PPARγ activation, and their synergism (combined PPARα/γ activation) upon the gut-adipose tissue axis, focusing on the endotoxemia and upstream interscapular brown adipose tissue (iBAT) function in high-saturated fat-fed mice.

METHODS

Male C57BL/6 mice received a control diet (C, 10% lipids) or a high-fat diet (HF, 50% lipids) for 12 weeks. Then, the HF group was divided to receive the treatments for four weeks: HFγ (pioglitazone, 10 mg/kg), HFα (WY-14643, 3.5 mg/kg), and HFα/γ (tesaglitazar, 4 mg/kg).

RESULTS

The HF group exhibited overweight, oral glucose intolerance, gut dysbiosis, altered gut permeability, and endotoxemia, culminating in iBAT whitening. The downregulation of LPS-Tlr4 signaling underpinned reduced inflammation and improved lipid metabolism in iBAT in the HFα/γ group, the unique to show normalized body mass and increased energy expenditure.

CONCLUSION

PPARα/γ synergism treated obesity by ameliorating the gut-adipose tissue axis, where restored gut microbiota and permeability controlled endotoxemia and rescued iBAT whitening through favored thermogenesis.

Cyclosorus terminans Extract Ameliorates Insulin Resistance and Non-Alcoholic Fatty Liver Disease (NAFLD) in High-Fat Diet (HFD)-Induced Obese Rats

Interruptins A and B exhibited anti-diabetic, anti-inflammatory, and anti-oxidative effects. This study aimed to investigate the therapeutic ability of extract enriched by interruptins A and B (EEI) from an edible fern Cyclosorus terminans on insulin resistance and non-alcoholic fatty liver disease (NAFLD) in a high-fat diet (HFD)-induced obese rats and elucidate their possible mechanisms. HFD-induced obese rats were treated with EEI for 2 weeks. Real-time polymerase chain reaction (PCR) was used to examine the molecular basis. We found that EEI supplementation significantly attenuated body and liver weight gain, glucose intolerance, and insulin resistance. Concurrently, EEI increased liver and soleus muscle glycogen storage and serum high-density lipoprotein (HDL) levels. EEI also attenuated NAFLD, as indicated by improving liver function. These effects were associated with enhanced expression of insulin signaling genes (Slc2a2, Slc2a4, Irs1 and Irs2) along with diminished expression of inflammatory genes (Il6 and Tnf). Furthermore, EEI led to the suppression of lipogenesis genes, Srebf1 and Fasn, together with an increase in fatty acid oxidation genes, Ppara and Cpt2, in the liver. These findings suggest that EEI could ameliorate HFD-induced insulin resistance and NAFLD via improving insulin signaling pathways, inflammatory response, lipogenesis, and fatty acid oxidation.

Gene repression through epigenetic modulation by PPARA enhances hepatocellular proliferation

Peroxisome proliferator-activated receptor α (PPARA) is a key mediator of lipid metabolism and inflammation. Activation of PPARA in rodents causes hepatocyte proliferation, but the underlying mechanism is poorly understood. This study focused on genes repressed by PPARA and analyzed the mechanism by which PPARA promotes hepatocyte proliferation in mice. Activation of PPARA by agonist treatment was autoregulated, and induced expression of the epigenetic regulator UHRF1 via activation of the newly described PPARA target gene E2f8, which, in turn, regulates Uhrf1. UHRF1 strongly repressed the expression of CDH1 via methylation of the Cdh1 promoter marked with H3K9me3. Repression of CDH1 by PPARA activation was reversed by PPARA deficiency or knockdown of E2F8 or UHRF1. Furthermore, a forced expression of CDH1 inhibited expression of the Wnt signaling target genes such as Myc after PPARA activation, and suppressed hepatocyte hyperproliferation. These results demonstrate that the PPARA-E2F8-UHRF1-CDH1 axis causes epigenetic regulation of hepatocyte proliferation.

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PPARA activation induces the UHRF1 expression via novel PPARA target gene E2f8

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Induction of UHRF1 by PPARA activation represses Cdh1 gene marked with H3K9me3

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CDH1 suppresses hepatocyte proliferation after PPARA activation

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Autoinduction of PPARA by agonist enhances cell proliferation via E2F8-UHRF1-CDH1

Cytochrome P450-derived fatty acid epoxides and diols in angiogenesis and stem cell biology

Cytochrome P450 (CYP) enzymes are frequently referred to as the third pathway for the metabolism of arachidonic acid. While it is true that these enzymes generate arachidonic acid epoxides i.e. the epoxyeicosatrienoic acids (EETs), they are able to accept a wealth of ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) to generate a large range of regio- and stereo-isomers with distinct biochemical properties and physiological actions. Probably the best studied are the EETs which have well documented effects on vascular reactivity and angiogenesis. CYP enzymes can also participate in crosstalk with other PUFA pathways and metabolize prostaglandin G₂ and H₂, which are the precursors of effector prostaglandins, to affect macrophage function and lymphangiogenesis. The activity of the PUFA epoxides is thought to be kept in check by the activity of epoxide hydrolases. However, rather than being inactive, the diols generated have been shown to regulate neutrophil activation, stem and progenitor cell proliferation and Notch signaling in addition to acting as exercise-induced lipokines. Excessive production of PUFA diols has also been implicated in pathologies such as severe respiratory distress syndromes, including COVID-19, and diabetic retinopathy. This review highlights some of the recent findings related to this pathway that affect angiogenesis and stem cell biology.

Legumes as Functional Food for Cardiovascular Disease

Legumes are an essential food source worldwide. Their high-quality proteins, complex carbohydrates, dietary fiber, and relatively low-fat content make these an important functional food. Known to possess a multitude of health benefits, legume consumption is associated with the prevention and treatment of cardiovascular diseases (CVD). Legume crude protein isolates and purified peptides possess many cardiopreventive properties. Here, we review selected economically valued legumes, their taxonomy and distribution, biochemical composition, and their protein components and the mechanism(s) of action associated with cardiovascular health. Most of the legume protein studies had shown upregulation of low-density lipoprotein (LDL) receptor leading to increased binding and uptake, in effect significantly reducing total lipid levels in the blood serum and liver. This is followed by decreased biosynthesis of cholesterol and fatty acids. To understand the relationship of identified genes from legume studies, we performed gene network analysis, pathway, and gene ontology (GO) enrichment. Results showed that the genes were functionally interrelated while enrichment and pathway analysis revealed involvement in lipid transport, fatty acid and triglyceride metabolic processes, and regulatory processes. This review is the first attempt to collate all known mechanisms of action of legume proteins associated with cardiovascular health. This also provides a snapshot of possible targets leading to systems-level approaches to further investigate the cardiometabolic potentials of legumes.

Carya cathayensis leaf extract attenuates ectopic fat deposition in liver, abdomen and aortic arch in ovariectomized rats fed a high-fat diet

BACKGROUND

Carya cathayensis¹is a commercially cultivated plant in the Zhejiang Province, China. Its nuts exhibit properties of tonifying kidneys and relieving asthma. There have been a few pharmacological studies addressing the function of the leaves of this plant. Our previous studies on C. cathayensis leaf extract (CCE) showed a significant inhibitory effect on weight gain in mice fed a high-fat diet, particularly in female mice.

HYPOTHESIS/PURPOSE

To investigate the biological and molecular mechanisms underlying the regulation of ectopic adipose tissue deposition by CCE in ovariectomized rats fed a high-fat diet.

STUDY DESIGN

Female Sprague-Dawley rats were ovariectomized and treated with CCE (50, 100, and 200 mg/kg body weight, oral) or estradiol (1 mg/kg body weight, oral) for 8 weeks.

METHODS

CCE was subjected to high-performance liquid chromatography to quantify major components. Body weight gain, abdominal fat coefficient, and aortic arch fat coefficient were determined; serum was collected for biochemical analysis; tissues were collected for histopathological examination, quantitative polymerase chain reaction (Q-PCR), and western blotting.

RESULTS

The total flavonoid content was determined to be 57.30% in the CCE and comprised chrysin, cardamomin, pinostrobin chalcone, and pinocembrin. Compared with the model group (OVX), CCE treatment reduced body weight gain, abdominal and aortic arch fat coefficients, serum and hepatic lipid profiles, including total cholesterol (TC), total triglycerides (TG), and free fatty acids (FFA) levels; decreased lipid droplets in liver cells; decreased fat accumulation in the aortic arch blood vessel wall and increased its smoothness; decreased the diameter of abdominal fat cells; and reduced serum leptin and adiponectin levels significantly. Serum adiponectin levels significantly correlated with serum TG and hepatic TC levels. Leptin levels positively correlated with serum TG levels and negatively correlated with hepatic TG. Leptin mRNA, peroxisome proliferator-activated receptor (PPARγ) mRNA, and protein expression levels in abdominal adipose tissue were significantly down-regulated. Adiponectin mRNA levels were slightly reduced but not significantly.

CONCLUSION

CCE attenuated ectopic fat deposition induced by deficient estrogen and a high-fat diet in rats; this may be associated with activated leptin sensitivity, improved leptin resistance, and regulated adiponectin levels. CCE may improve adipose function to regulate adipocyte differentiation by down-regulating PPARγ. Overall, these results suggest that CCE is a potential phytoestrogen.

Effect of Adrenergic Agonists on High-Fat Diet-Induced Hepatic Steatosis in Mice

The autonomic nervous system, consisting of sympathetic and parasympathetic branches, plays an important role in regulating metabolic homeostasis. The sympathetic nervous system (SNS) regulates hepatic lipid metabolism by regulating adrenergic receptor activation, resulting in the stimulation of hepatic very-low-density lipoprotein-triglyceride (TG) production in vivo. However, only a few studies on the relationship between SNS and hepatic steatosis have been reported. Here, we investigate the effect of adrenergic receptor agonists on hepatic steatosis in mice fed a high-fat diet (HFD). The α-adrenergic receptor agonist phenylephrine (10 mg/kg/d) or the β-adrenergic receptor agonist isoproterenol (30 mg/kg/d) was coadministered with HFD to male mice. After five weeks, hepatic steatosis, TG levels, and hepatic fat metabolism-related biomarkers were examined. HFD treatment induced hepatic steatosis, and cotreatment with phenylephrine, but not isoproterenol, attenuated this effect. Phenylephrine administration upregulated the mRNA levels of hepatic peroxisome proliferator-activated receptor alpha and its target genes (such as carnitine palmitoyltransferase 1) and increased hepatic β-hydroxybutyrate levels. Additionally, phenylephrine treatment increased the expression of the autophagosomal marker LC3-II but decreased that of p62, which is selectively degraded during autophagy. These results indicate that phenylephrine inhibits hepatic steatosis through stimulation of β-oxidation and autophagy in the liver.

Evaluation of Waste Mushroom Compost as a Feed Supplement and Its Effects on the Fat Metabolism and Antioxidant Capacity of Broilers

Simple Summary

Mushroom waste compost is the main byproduct when cultivating mushrooms. Due to its high mycelium content, mushroom waste compost may improve animal health by increasing antioxidant capacity. Furthermore, increasing evidence suggests that supplementing animal diets with fiber could improve body composition and health. The results showed that supplementation with mushroom waste compost accelerates adipolysis and enhances the antioxidant capacity of broilers. Among all treatment groups, broilers given dietary supplementation with 0.5% mushroom waste compost showed improved feed conversion rate and the highest adipose metabolism.

Abstract

Pennisetum purpureum Schum No. 2 waste mushroom compost (PWMC) is the main byproduct when cultivating Pleurotus eryngii. Due to the high mycelium levels in PWMC, it may have potential as a feed supplement for broilers. This study investigated the effects of PWMC supplementation on antioxidant capacity and adipose metabolism in broilers. In the study, 240 broilers were randomly allocated to one of four treatment groups: basal diet (control), 0.5%, 1%, or 2% PWMC supplementation. Each treatment group had 60 broilers, divided into three replicates. The results showed that supplementation with 0.5% PWMC decreased the feed conversion rate (FCR) from 1.36 to 1.28, compared to the control. Supplementation with 0.5% or 2% PWMC decreased glucose and triglyceride levels, compared to the control (p < 0.0001), the concentrations of adiponectin and oxytocin increased from 5948 to 5709, 11820, and 7938 ng/ mL; and 259 to 447, 873, and 963 pg/ mL, respectively. Toll-like receptor 4 was slightly increased in the 0.5% and 1% PWMC groups. Both interferon-γ (IFN-γ) and interleukin-1ß (IL-1ß) were significantly decreased, by about three to five times for IFN-γ (p < 0.0001) and 1.1 to 1.6 times for IL-1ß (p = 0.0002). All antioxidant-related mRNA, including nuclear factor erythroid 2–related factor 2 (Nrf-2) and superoxidase dismutase-1 (SOD-1), increased significantly following PWMC supplementation. Both claudin-1 and zonula occludens 1 increased, especially in the 2% PWMC group. Excitatory amino acid transporter 3 (EAAT3) significantly increased by about 5, 12, and 11 times in the 0.5%, 1%, and 2% PWMC groups. All adipolysis-related mRNA were induced in the PWMC treatment groups, further enhancing adipolysis. Overall, 0.5% PWMC supplementation was recommended due to its improving FCR, similar antioxidant capacity, and upregulated adipolysis.

Maternal diets enriched in olive oil regulate lipid metabolism and levels of PPARs and their coactivators in the fetal liver in a rat model of gestational diabetes mellitus

In a rat model of gestational diabetes mellitus (GDM) programmed in the offspring of neonatal streptozotocin-induced (nSTZ) diabetic rats, lipids are accumulated in the fetal liver in a sex-dependent way. Here, we evaluated whether maternal diets enriched in olive oil in rats that will develop GDM ameliorate lipid metabolic impairments in the fetal livers. Pregnant offspring of control and nSTZ diabetic rats (F0) were fed a 6% olive oil-supplemented diet throughout the F1 gestation. We evaluated maternal metabolic parameters as well as lipid content, expression of lipid metabolizing enzymes and protein expression of PLIN2, PPARs and PPAR coactivators in the fetal livers. The offspring of nSTZ diabetic rats developed GDM regardless of the maternal treatment. Hypertriglyceridemia in GDM rats was prevented by the olive oil-enriched maternal treatment. In the livers of male fetuses of GDM rats, the maternal olive oil-supplemented diet prevented lipid overaccumulation and prevented the increase in PPARγ and PPARδ levels. In the livers of female fetuses of GDM rats, the maternal olive oil supplementation prevented the increase in PPARδ levels and the reduction in PGC1α levels, but did not prevent the reduced lipid content. Control and GDM rats showed a reduction of lipid metabolic enzymes in the fetal livers, which was associated with reduced levels of the PPAR coactivators PGC-1α and SRC-1 in males and of SRC-1 in females. These results suggest powerful effects of a maternal olive oil-supplemented diet in the fetal liver, possibly providing benefits in the fetuses and offspring from GDM rats.

Role of cytochrome P450-derived, polyunsaturated fatty acid mediators in diabetes and the metabolic syndrome

Over the last decade, cases of metabolic syndrome and type II diabetes have increased exponentially. Exercise and ω-3 polyunsaturated fatty acid (PUFA)-enriched diets are usually prescribed but no therapy is effectively able to restore the impaired glucose metabolism, hypertension, and atherogenic dyslipidemia encountered by diabetic patients. PUFAs are metabolized by different enzymes into bioactive metabolites with anti- or pro-inflammatory activity. One important class of PUFA metabolizing enzymes are the cytochrome P450 (CYP) enzymes that can generate a series of bioactive products, many of which have been attributed protective/anti-inflammatory and insulin-sensitizing effects in animal models. PUFA epoxides are, however, further metabolized by the soluble epoxide hydrolase (sEH) to fatty acid diols. The biological actions of the latter are less well understood but while low concentrations may be biologically important, higher concentrations of diols derived from linoleic acid and docosahexaenoic acid have been linked with inflammation. One potential application for sEH inhibitors is in the treatment of diabetic retinopathy where sEH expression and activity is elevated as are levels of a diol of docosahexaenoic acid that can induce the destabilization of the retina vasculature.

Adelmidrol protects against non-alcoholic steatohepatitis in mice

Non-alcoholic steatohepatitis (NASH) is a more serious condition of non-alcoholic fatty liver disease (NAFLD), a widely spread type of chronic liver disease. Oxidative stress and inflammation induced by lipotoxicity are involved in hepatic injury of NASH. This work aimed to investigate the possible protective effect of adelmidrol (PPAR α and γ agonist) against NASH in mice.Thirty-six mice were divided into six equal groups: sham-operated, NASH, vehicle, adelmidrol 5 mg/kg, adelmidrol 10 mg/kg, and adelmidrol 20 mg /kg. Adelmidrol was injected intraperitoneally once daily for 7 weeks along with high-fat diet (HFD). Mice were euthanized, and livers were removed for light microscopic examination and detection of reduced glutathione (GSH) content while blood samples were collected for assessment of transaminases (ALT& AST), tumor necrosis factor (TNF-α), matrix metalloproteinase-1 (MMP-1), adiponectin, cholesterol, high-density lipoprotein (HDL), and triglyceride. NASH mice had increments in MMP-1, TNF-α, AST, ALT, triglyceride, and cholesterol levels while HDL, adiponectin levels, and GSH content were decreased with vesicular steatosis, lobular inflammation, hepatocyte ballooning, and degeneration. Administration of adelmidrol decreased MMP-1, TNF-α, AST, ALT, triglyceride, and cholesterol levels while increased HDL, adiponectin levels, and GSH content as well as ameliorated the histopathological changes. Adelmidrol protected mice from NASH; an effect could be attributed to its anti-inflammatory and antioxidant actions.

New Lipid Mediators in Retinal Angiogenesis and Retinopathy

Retinal diseases associated with vascular destabilization and the inappropriate proliferation of retinal endothelial cells have major consequences on the retinal vascular network. In extreme cases, the development of hypoxia, the upregulation of growth factors, and the hyper-proliferation of unstable capillaries can result in bleeding and vision loss. While anti-vascular endothelial growth factor therapy and laser retinal photocoagulation can be used to treat the symptoms of late stage disease, there is currently no treatment available that can prevent disease progression. Cytochrome P450 enzymes metabolize endogenous substrates (polyunsaturated fatty acids) to bioactive fatty acid epoxides that demonstrate biological activity with generally protective/anti-inflammatory and insulin-sensitizing effects. These epoxides are further metabolized by the soluble epoxide hydrolase (sEH) to fatty acid diols, high concentrations of which have vascular destabilizing effects. Recent studies have identified increased sEH expression and activity and the subsequent generation of the docosahexaenoic acid-derived diol; 19,20-dihydroxydocosapentaenoic acid, as playing a major role in the development of diabetic retinopathy. This review summarizes current understanding of the roles of cytochrome P450 enzyme and sEH–derived PUFA mediators in retinal disease.

Conophylline inhibits high fat diet-induced non-alcoholic fatty liver disease in mice

Conophylline (CnP), a vinca alkaloid extracted from the leaves of the tropical plant Tabernaemontana divaricate, attenuates hepatic fibrosis in mice. We have previously shown that CnP inhibits non-alcoholic steatohepatitis (NASH) using a methionine-choline-deficient (MCD) diet-fed mouse model. However, little is known about the CnP mediated inhibition of hepatic steatosis in high-fat diet-induced non-alcoholic fatty liver disease (NAFLD) mouse models. CnP (0.5 and 1 μg/g/body weight) was co-administered along with a high-fat diet to male BALB/c mice. After nine weeks of administering the high-fat diet, hepatic steatosis, triglyceride, and hepatic fat metabolism-related markers were examined. Administration of a high-fat diet for 9 weeks was found to induce hepatic steatosis. CnP dose-dependently attenuated the high-fat diet-induced hepatic steatosis. The diet also attenuated hepatic peroxisome proliferator-activated receptor alpha (PPARA) mRNA levels. PPARA is known to be involved in β-oxidation. CnP upregulated the mRNA levels of hepatic PPARA and its target genes, such as carnitine palmitoyl transferase 1 (CPT1) and CPT2, in a dose-dependent manner in the liver. Furthermore, levels of hepatic β-hydroxybutyrate, which is a type of ketone body, were increased by CnP in a dose-dependent manner. Finally, CnP increased the expression of the autophagosomal marker LC3-II and decreased the expression of p62, which are known to be selectively degraded during autophagy. These results indicate that CnP inhibits hepatic steatosis through the stimulation of β-oxidation and autophagy in the liver. Therefore, CnP might prove to be a suitable therapeutic target for NAFLD.

Silybum marianum oil attenuates hepatic steatosis and oxidative stress in high fat diet-fed mice

In the present study, the effects of Silybum marianum oil (SMO) on hepatic steatosis and oxidative stress were investigated during the development of nonalcoholic fatty liver disease (NAFLD) in high fat diet (HFD)-fed mice. The results showed that body weight, fat mass, and serum biochemical parameters such as triglyceride, free fatty acid, glucose and insulin were reduced by SMO treatment. Meanwhile, SMO decreased the histological injury of liver and the levels of hepatic triglyceride, cholesterol and free fatty acid in HFD-fed mice. SMO administration elevated the activities of superoxide dismutase (SOD) and catalase (CAT) and reduced the level of malondialdehyde (MDA) in the liver. Enzyme linked immunosorbent assay showed that SMO significantly decreased the levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in HFD mice. Furthermore, the mRNA levels of sterol regulatory element binding protein 1c (SREBP-1c), fatty acid synthase (FAS) and liver X receptor α (LXRα) were lower, but peroxisome proliferator-activated receptor α (PPARα) was higher in mice treated with SMO compared with the HFD group. The results indicated that SMO could play a certain protective role against HFD-induced NAFLD, and the protective effects might be associated with attenuating lipid accumulation, oxidative stress and inflammation, improving lipid metabolism.

Differential actions of PPAR-α and PPAR-β/δ on beige adipocyte formation: A study in the subcutaneous white adipose tissue of obese male mice

Background and aims

Obesity compromises adipocyte physiology. PPARs are essential to adipocyte plasticity, but its isolated role in the browning phenomenon is not clear. This study aimed to examine whether activation of PPAR-α or PPAR-β/δ could induce beige cell depots in the subcutaneous white adipose tissue of diet-induced obese mice.

Material and methods

Sixty animals were randomly assigned to receive a control diet (C, 10% lipids) or a high-fat diet (HF, 50% lipids) for ten weeks. Then each group was re-divided to begin the treatments that lasted 4 weeks, totalizing six groups: C, C-α (C plus PPAR-α agonist, 2.5 mg/kg BM), C-β (C plus PPAR-β/δ agonist, 1 mg/kg BM), HF, HF-α (HF plus PPAR-α agonist), HF-β (HF plus PPAR-β/δ agonist).

Results

HF animals presented with overweight, glucose intolerance and subcutaneous white adipocyte hypertrophy. Both treatments significantly attenuated these parameters. Browning, verified by UCP1 positive beige cells and enhanced body temperature, was just observed in PPAR-α treated groups. PPAR-α agonism also elicited an enhanced gene expression of the thermogenesis effector UCP1, the beige-selective gene TMEM26 and the PRDM16, an essential gene for brown-like phenotype maintenance in the beige adipocytes when compared to their counterparts. The enhanced CIDEA and the reduced UCP1 gene levels might justify the white phenotype predominance after the treatment with the PPAR-β/δ agonist.

Conclusions

This work provides evidence that the PPAR-β/δ agonist ameliorated metabolic disorders through enhanced beta-oxidation and better tolerance to glucose, whereas the PPAR-α agonism was confirmed as a promising therapeutic target for treating metabolic diseases via beige cell induction and enhanced thermogenesis.

Melatonin suppresses platelet activation and function against cardiac ischemia/reperfusion injury via PPARγ/FUNDC1/mitophagy pathways

Platelet activation is a major (patho-) physiological mechanism that underlies ischemia/reperfusion (I/R) injury. In this study, we explored the molecular signals for platelet hyperactivity and investigated the beneficial effects of melatonin on platelet reactivity in response to I/R injury. After reperfusion, peroxisome proliferator-activated receptor γ (PPARγ) was progressively downregulated in patients with acute myocardial infarction undergoing coronary artery bypass grafting (CABG) surgery and in mice with I/R injury model. Loss of PPARγ was closely associated with FUN14 domain containing 1 (FUNDC1) dephosphorylation and mitophagy activation, leading to increased mitochondrial electron transport chain complex (ETC.) activity, enhanced mitochondrial respiratory function, and elevated ATP production. The improved mitochondrial function strongly contributed to platelet aggregation, spreading, expression of P-selectin, and final formation of micro-thromboses, eventually resulting in myocardial dysfunction and microvascular structural destruction. However, melatonin powerfully suppressed platelet activation via restoration of the PPARγ content in platelets, which subsequently blocked FUNDC1-required mitophagy, mitochondrial energy production, platelet hyperactivity, and cardiac I/R injury. In contrast, genetic ablation of PPARγ in platelet abolished the beneficial effects of melatonin on mitophagy, mitochondrial ATP supply, and platelet activation. Our results lay the foundation for the molecular mechanism of platelet activation in response to I/R injury and highlight that the manipulation of the PPARγ/FUNDC1/mitophagy pathway by melatonin could be a novel strategy for cardioprotection in the setting of cardiac I/R injury.

Acacetin from Traditionally Used Saussurea involucrata Kar. et Kir. Suppressed Adipogenesis in 3T3-L1 Adipocytes and Attenuated Lipid Accumulation in Obese Mice

Acacetin, a flavone that can be isolated from the Saussurea involucrata plant, has anti-tumor and anti-inflammatory properties that ameliorate airway hyperresponsiveness in asthmatic mice. This study investigated whether acacetin has anti-adipogenic effects in 3T3-L1 adipocytes and whether it regulates the inflammatory response in adipocytes and macrophages. It also investigated whether acacetin ameliorates lipid accumulation in high-fat diet- (HFD) induced obese mice. Differentiated 3T3-L1 cells were treated with acacetin. The glycerol levels in the culture medium were measured, and the expression of proteins and genes involved in adipogenesis and lipolysis were assayed by Western blot and real-time PCR, respectively. Inflammatory cytokine signaling pathway activity was assessed in macrophages that were treated with acacetin and cultured with differentiated medium from 3T3-L1 cells. Intraperitoneal injections of acacetin were administered to HFD-induced obese mice twice a week for 10 weeks. Acacetin significantly increased the levels of glycerol in the culture medium and significantly inhibited lipid accumulation in adipocytes. Acacetin reduced the expression of adipogenesis-related transcription factors, including the expression of the CCAAT/enhancer-binding protein; it also increased sirtuin 1 expression and AMPK phosphorylation in adipocytes. In macrophages cultured with differentiated media from 3T3-L1 adipocytes, acacetin reduced the levels of inflammatory mediators and the activity of the mitogen-activated protein kinase and NF-κB pathways. In obese mice, acacetin reduced both body weight and visceral adipose tissue weight. These results demonstrate that acacetin inhibited adipogenesis in adipocytes and in obese mice. Acacetin also reduced the inflammatory response of macrophages that were stimulated with differentiated media from 3T3-L1 cells.

Rosuvastatin limits the activation of hepatic stellate cells in diet-induced obese mice

AIM

The aim of this study was to investigate the effects of rosuvastatin in a model of diet-induced obesity and non-alcoholic fatty liver disease, with attention to the activation of hepatic stellate cells (HSCs).

METHOD

Male C57BL/6 mice received a control diet (C; 10% energy as lipids) or a high-fat diet (HF; 50% energy as lipids) for 12 weeks, followed by 7 weeks of treatment. Group CR received control diet + rosuvastatin; group HFR received high-fat diet + rosuvastatin.

RESULTS

The HF group showed higher insulin, total cholesterol, triacylglycerol, and leptin levels than the C group, all of which were significantly diminished by rosuvastatin in the HFR group. The HF group had greater steatosis and activated HSCs than the C group, whereas rosuvastatin diminished the steatosis (less 21%, P < 0.001) and significantly inhibited the activation of the HSCs in the HFR group compared to the HF group. The sterol regulatory element-binding protein-1 and the peroxisome proliferator-activated receptor (PPAR)-γ protein expressions were increased in HF animals and reduced after treatment in the HFR group. By contrast, low PPAR-α and carnitine palmitoyltransferase-1 expressions were found in the HF group, and were restored by rosuvastatin treatment in the HFR group.

CONCLUSION

Rosuvastatin mitigated hepatic steatosis by modulating PPAR balance, favoring PPAR-α over PPAR-γ downstream effects. The effects were accompanied by a diminishing of insulin resistance, the anti-inflammatory adipokine profile, and HSC activation, avoiding non-alcoholic fatty liver disease progression and non-alcoholic steatohepatitis onset in this model.

Hepatic lipid accumulation: cause and consequence of dysregulated glucoregulatory hormones

Fatty liver can be diet, endocrine, drug, virus or genetically induced. Independent of cause, hepatic lipid accumulation promotes systemic metabolic dysfunction. By acting as peroxisome proliferator-activated receptor (PPAR) ligands, hepatic non-esterified fatty acids upregulate expression of gluconeogenic, beta-oxidative, lipogenic and ketogenic genes, promoting hyperglycemia, hyperlipidemia and ketosis. The typical hormonal environment in fatty liver disease consists of hyperinsulinemia, hyperglucagonemia, hypercortisolemia, growth hormone deficiency and elevated sympathetic tone. These endocrine and metabolic changes further encourage hepatic steatosis by regulating adipose tissue lipolysis, liver lipid uptake, de novo lipogenesis (DNL), beta-oxidation, ketogenesis and lipid export. Hepatic lipid accumulation may be induced by 4 separate mechanisms: (1) increased hepatic uptake of circulating fatty acids, (2) increased hepatic de novo fatty acid synthesis, (3) decreased hepatic beta-oxidation and (4) decreased hepatic lipid export. This review will discuss the hormonal regulation of each mechanism comparing multiple physiological models of hepatic lipid accumulation. Nonalcoholic fatty liver disease (NAFLD) is typified by increased hepatic lipid uptake, synthesis, oxidation and export. Chronic hepatic lipid signaling through PPARgamma results in gene expression changes that allow concurrent activity of DNL and beta-oxidation. The importance of hepatic steatosis in driving systemic metabolic dysfunction is highlighted by the common endocrine and metabolic disturbances across many conditions that result in fatty liver. Understanding the mechanisms underlying the metabolic dysfunction that develops as a consequence of hepatic lipid accumulation is critical to identifying points of intervention in this increasingly prevalent disease state.

Liver and Metformin: Lessons of a fructose diet in mice

Studies show that the continuous consumption of fructose can lead to nonalcoholic fatty liver disease (NAFLD) and steatohepatitis. We aimed to investigate the role of Metformin in an animal model of liver injury caused by fructose intake, focusing on the molecular markers of lipogenesis, beta-oxidation, and antioxidant defenses. Male three months old C57BL/6 mice were divided into control group (C) and fructose group (F, 47% fructose), maintained for ten weeks. After, the groups received Metformin or vehicle for a further eight weeks: control (C), control + Metformin (CM), fructose (F), and fructose + Metformin (FM). Fructose resulted in hepatic steatosis, insulin resistance and lower insulin sensitivity in association with higher mRNA levels of proteins linked with de novo lipogenesis and increased lipid peroxidation. Fructose diminished mRNA expression of antioxidant enzymes, and of proteins responsible for mitochondrial biogenesis. Metformin reduced de novo lipogenesis and increased the expression of proteins related to mitochondrial biogenesis, thereby increasing beta-oxidation and decreasing lipid peroxidation. Also, Metformin upregulated the expression and activity of antioxidant enzymes, providing a defense against increased reactive oxygen species generation. Therefore, a significant reduction in triglyceride accumulation in the liver, steatosis and lipid peroxidation was observed in the FM group. In conclusion, fructose increases de novo lipogenesis, reduces the antioxidant defenses, and diminishes mitochondrial biogenesis. After an extended period of fructose intake, Metformin treatment, even in continuing the fructose intake, can reverse, at least partially, the liver injury and prevents NAFLD progression to more severe states.

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Fructose increases lipogenesis and lipid peroxidation, reduces the antioxidant defenses, and mitochondrial biogenesis.

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Metformin mechanism of action remains partially understood and controversial.

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Metformin can reverse the liver injury preventing the progression to more severe states.

Browning of white adipose tissue: lessons from experimental models

Beige or brite (brown-in-white) adipocytes are present in white adipose tissue (WAT) and have a white fat-like phenotype that when stimulated acquires a brown fat-like phenotype, leading to increased thermogenesis. This phenomenon is known as browning and is more likely to occur in subcutaneous fat depots. Browning involves the expression of many transcription factors, such as PR domain containing 16 (PRDM16) and peroxisome proliferator-activated receptor (PPAR)-γ, and of uncoupling protein (UCP)-1, which is the hallmark of thermogenesis. Recent papers pointed that browning can occur in the WAT of humans, with beneficial metabolic effects. This fact indicates that these cells can be targeted to treat a range of diseases, with both pharmacological and nutritional activators. Pharmacological approaches to induce browning include the use of PPAR-α agonist, adrenergic receptor stimulation, thyroid hormone administration, irisin and FGF21 induction. Most of them act through the induction of PPAR-γ coactivator (PGC) 1-α and the consequent mitochondrial biogenesis and UCP1 induction. About the nutritional inducers, several compounds have been described with multiple mechanisms of action. Some of these activators include specific amino acids restriction, capsaicin, bile acids, Resveratrol, and retinoic acid. Besides that, some classes of lipids, as well as many plant extracts, have also been implicated in the browning of WAT. In conclusion, the discovery of browning in human WAT opens the possibility to target the adipose tissue to fight a range of diseases. Studies have arisen showing promising results and bringing new opportunities in thermogenesis and obesity control.

Bezafibrate Attenuates Pressure Overload-Induced Cardiac Hypertrophy and Fibrosis

Background. Peroxisome proliferator-activated receptor-α (PPAR-α) is closely associated with the development of cardiac hypertrophy. Previous studies have indicated that bezafibrate (BZA), a PPAR-α agonist, could attenuate insulin resistance and obesity. This study was designed to determine whether BZA could protect against pressure overload-induced cardiac hypertrophy. Methods. Mice were orally given BZA (100 mg/kg) for 7 weeks beginning 1 week after aortic banding (AB) surgery. Cardiac hypertrophy was assessed based on echocardiographic, histological, and molecular aspects. Moreover, neonatal rat ventricular cardiomyocytes (NRVMs) were used to investigate the effects of BZA on the cardiomyocyte hypertrophic response in vitro. Results. Our study demonstrated that BZA could alleviate cardiac hypertrophy and fibrosis in mice subjected to AB surgery. BZA treatment also reduced the phosphorylation of protein kinase B (AKT)/glycogen synthase kinase-3β (GSK3β) and mitogen-activated protein kinases (MAPKs). BZA suppressed phenylephrine- (PE-) induced hypertrophy of cardiomyocyte in vitro. The protective effects of BZA were abolished by the treatment of the PPAR-α antagonist in vitro. Conclusions. BZA could attenuate pressure overload-induced cardiac hypertrophy and fibrosis.

Does bilirubin prevent hepatic steatosis through activation of the PPARα nuclear receptor?

Several large population studies have demonstrated a negative correlation between serum bilirubin levels and the development of obesity, hepatic steatosis, and cardiovascular disease. Despite the strong correlative data demonstrating the protective role of bilirubin, the mechanism by which bilirubin can protect against these pathologies remains unknown. Bilirubin has long been known as a powerful antioxidant and also has anti-inflammatory actions, each of which may contribute to the protection afforded by increased levels. We have recently described a novel function of bilirubin as a ligand for the peroxisome proliferator-activated receptor-alpha (PPARα), which we show specifically binds to the nuclear receptor. Bilirubin may function as a selective PPAR modulator (SPPARM) to control lipid accumulation and blood glucose. However, it is not known to what degree bilirubin activation of PPARα is responsible for the protection afforded to reduce hepatic steatosis. We hypothesize that bilirubin, acting as a novel SPPARM, increases hepatic fatty acid metabolism through a PPARα-dependent mechanism which reduces hepatic lipid accumulation and protects against hepatic steatosis and non-alcoholic fatty liver disease (NAFLD).

Pyrazinamide induced hepatic injury in rats through inhibiting the PPARα pathway

Pyrazinamide (PZA) causes serious hepatotoxicity, but little is known about the exact mechanism by which PZA induced liver injury. The peroxisome proliferator-activated receptors alpha (PPARα) is highly expressed in the liver and modulates the intracellular lipidmetabolism. So far, the role of PPARα in the hepatotoxicity of PZA is unknown. In the present study, we described the hepatotoxic effects of PZA and the role of PPARα and its target genes in the downstream pathway including L-Fabp, Lpl, Cpt-1b, Acaa1, Apo-A1 and Me1 in this process. We found PZA induced the liver lipid metabolism disorder and PPARα expressionwas down-regulated which had a significant inverse correlation with liver injury degree. These changeswere ameliorated by fenofibrate, the co-treatment that acts as a PPARα agonist. In contrast, short-termstarvation significantly aggravated the severity of PZA-induced liver injury. In conclusion, this study demonstrated the critical role played by PPARα in PZA-induced hepatotoxicity and provided a better understanding of the molecular mechanisms underlying PZA-induced liver injury. Copyright © 2016 John Wiley & Sons, Ltd.

A Combination of Leucine, Metformin, and Sildenafil Treats Nonalcoholic Fatty Liver Disease and Steatohepatitis in Mice

Sirt1, AMPK, and eNOS modulate hepatic energy metabolism and inflammation and are key players in the development of NASH. L-leucine, an allosteric Sirt1 activator, synergizes with low doses of metformin or sildenafil on the AMPK-eNOS-Sirt1 pathway to reverse mild NAFLD in preclinical mouse models. Here we tested a possible multicomponent synergy to yield greater therapeutic efficacy in NAFLD/NASH. Liver cells and macrophages or an atherogenic diet induced NASH mouse model was treated with two-way and three-way combinations. The three-way combination Sild-Met-Leu increased hepatic fatty acid oxidation and reduced lipogenic gene expression and inflammatory marker in vitro. In mice, Sild-Met-Leu reduced the diet induced increases of ALT, TGFβ, PAI-1, IL1β, and TNFα, hepatic collagen expression, and nearly completely reversed hepatocyte ballooning and triglyceride accumulation, while all two-way combinations had only modest effects. Therefore, these data provide preclinical evidence for therapeutic efficacy of Sild-Met-Leu in the treatment of NAFLD and NASH.