PPARs: regulators of metabolism and as therapeutic targets in cardiovascular disease. Part I: PPAR-α

Linc01230, transcriptionally regulated by PPARγ, is identified as a novel modifier in endothelial function

Evidence is growing that PPARγ could improve the bioavailability of NO in pathological conditions to maintain endothelial function by activating Akt/eNOS pathway. LincRNAs participate in regulating development of cardiovascular diseases. Although investigations have been made to delineate the function of PPARγ and lincRNAs, little is known about the regulation relationship between them, especially in endothelial cells. In this study, we not only verified that PPARγ could antagonize the adverse effects brought from ox-LDL, but also found a novel factor related to PPARγ, named linc01230. According to our study, PPARγ transcriptionally regulated linc01230 by specifically combining with two binding regions, which have superposition effect, in the upstream of linc01230 promoter. In addition, linc01230 reduced ox-LDL induced endothelial dysfunction and affected the phosphorylation of Akt. These results conclude linc01230 as a novel modifier in PPARγ-mediated activation of Akt in endothelial function.

Oleoylethanolamide differentially regulates glycerolipid synthesis and lipoprotein secretion in intestine and liver

Dietary fat absorption takes place in the intestine, and the liver mobilizes endogenous fat to other tissues by synthesizing lipoproteins that require apoB and microsomal triglyceride transfer protein (MTP). Dietary fat triggers the synthesis of oleoylethanolamide (OEA), a regulatory fatty acid that signals satiety to reduce food intake mainly by enhancing neural PPARα activity, in enterocytes. We explored OEA's roles in the assembly of lipoproteins in WT and Ppara ^-/- mouse enterocytes and hepatocytes, Caco-2 cells, and human liver-derived cells. In differentiated Caco-2 cells, OEA increased synthesis and secretion of triacylglycerols, apoB secretion in chylomicrons, and MTP expression in a dose-dependent manner. OEA also increased MTP activity and triacylglycerol secretion in WT and knockout primary enterocytes. In contrast to its intestinal cell effects, OEA reduced synthesis and secretion of triacylglycerols, apoB secretion, and MTP expression and activity in human hepatoma Huh-7 and HepG2 cells. Also, OEA reduced MTP expression and triacylglycerol secretion in WT, but not knockout, primary hepatocytes. These studies indicate differential effects of OEA on lipid synthesis and lipoprotein assembly: in enterocytes, OEA augments glycerolipid synthesis and lipoprotein assembly independent of PPARα. Conversely, in hepatocytes, OEA reduces MTP expression, glycerolipid synthesis, and lipoprotein secretion through PPARα-dependent mechanisms.

Identification of a Novel PPAR-γ Agonist through a Scaffold Tuning Approach

Peroxisome proliferator-activated receptors (PPARs) are important targets in metabolic diseases including obesity, metabolic syndrome, diabetes, and non-alcoholic fatty liver disease. Recently, they have been highlighted as attractive targets for the treatment of cardiovascular diseases and chronic myeloid leukemia. The PPAR agonist structure is consists of a polar head, a hydrophobic tail, and a linker. Each part interacts with PPARs through hydrogen bonds or hydrophobic interactions to stabilize target protein conformation, thus increasing its activity. Acidic head is essential for PPAR agonist activity. The aromatic linker plays an important role in making hydrophobic interactions with PPAR as well as adjusting the head-to-tail distance and conformation of the whole molecule. By tuning the scaffold of compound, the whole molecule could fit into the ligand-binding domain to achieve proper binding mode. We modified indol-3-ylacetic acid scaffold to (indol-1-ylmethyl)benzoic acid, whereas 2,4-dichloroanilide was fixed as the hydrophobic tail. We designed, synthesized, and assayed the in vitro activity of novel indole compounds with (indol-1-ylmethyl)benzoic acid scaffold. Compound 12 was a more potent PPAR-γ agonist than pioglitazone and our previous hit compound. Molecular docking studies may suggest the binding between compound 12 and PPAR-γ, rationalizing its high activity.

Polyurethane Nanoparticle-Loaded Fenofibrate Exerts Inhibitory Effects on Nonalcoholic Fatty Liver Disease in Mice

Polyurethane (PU) nanoparticles are potential drug carriers. We aimed to study the in vitro and in vivo efficacy of biodegradable PU nanoparticles loaded with fenofibrate (FNB-PU) on nonalcoholic fatty liver disease (NAFLD). FNB-PU was prepared by a green process, and its preventive effects on NAFLD were investigated on HepG2 cells and mice. FNB-PU showed sustained in vitro FNB release profile. Compared to FNB crude drug, FNB-PU significantly decreased triglyceride content in HepG2 cells incubated with oleic acid and in livers of mice with NAFLD induced by a methionine choline deficient diet, and increased plasma FNB concentration of the mice. FNB-PU increased absorption of FNB and therefore enhanced the inhibitory effects of FNB on NAFLD.

Dynamic Macrophages: Understanding Mechanisms of Activation as Guide to Therapy for Atherosclerotic Vascular Disease

An emerging theory is that macrophages are heterogenous; an attribute that allows them to change behavior and execute specific functions in disease processes. This review aims to describe the current understanding on factors that govern their phenotypic changes, and provide insights for intervention beyond managing classical risk factors. Evidence suggests that metabolic reprogramming of macrophages triggers either a pro-inflammatory, anti-inflammatory or pro-resolving behavior. Dynamic changes in bioenergetics, metabolome or influence from bioactive lipids may promote resolution or aggravation of inflammation. Direct cell-to-cell interactions with other immune cells can also influence macrophage activation. Both paracrine signaling and intercellular molecular interactions either co-stimulate or co-inhibit activation of macrophages as well as their paired immune cell collaborator. More pathways of activation can even be uncovered by inspecting macrophages in the single cell level, since differential expression in key gene regulators can be screened in higher resolution compared to conventional averaged gene expression readouts. All these emerging macrophage activation mechanisms may be further explored and consolidated by using approaches in network biology. Integrating these insights can unravel novel and safer drug targets through better understanding of the pro-inflammatory activation circuitry.

Decreased expression of peroxisome proliferator-activated receptor alpha indicates unfavorable outcomes in hepatocellular carcinoma

Introduction

Hepatocellular carcinoma (HCC) has a close relationship with lipid metabolism. Peroxisome proliferator-activated receptor α (PPARα) plays a crucial role in the regulation of fatty acid oxidation in the liver. However, the role of PPARα in HCC remains unclear.

Methods

A total of 804 HCC specimens were collected to construct a tissue microarray and for immunohistochemical analysis. The relationship between PPARα expression and clinical features of HCC patients was analyzed. Kaplan–Meier analysis was conducted to assess the prognostic value of PPARα expression levels.

Results

The expression of PPARα in HCC was noticeably decreased in HCC tissues. HCC patients with high levels of PPARα expression in cytoplasm had smaller tumors (P=0.027), less vascular invasion (P=0.049), and a higher proportion of complete involucrum (P=0.038). Kaplan–Meier analysis showed that HCC patients with low PPARα expression in the cytoplasm had significantly worse outcomes in terms of overall survival (P<0.001), disease-free survival (P=0.024), and the probability of recurrence (P=0.037). Similarly, overall survival was significantly shorter in HCC patients with negative PPARα expression in the nucleus (P=0.034). Multivariate Cox analyses indicated that tumor size (P=0.001), TNM stage (P<0.001), vascular invasion (P<0.001), and PPARα expression in the cytoplasm (P<0.001) were found to be independent prognostic variables for overall survival.

Conclusion

Our data revealed that PPARα expression was decreased in HCC samples. High PPARα expression was correlated with longer survival times in HCC patients, and served as an independent factor for better outcomes. Our study therefore provides a promising biomarker for prognostic prediction and a potential therapeutic target for HCC.

Structures of PPARγ complexed with lobeglitazone and pioglitazone reveal key determinants for the recognition of antidiabetic drugs

Peroxisome proliferator-activator receptor (PPAR) γ is a nuclear hormone receptor that regulates glucose homeostasis, lipid metabolism, and adipocyte function. PPARγ is a target for thiazolidinedione (TZD) class of drugs which are widely used for the treatment of type 2 diabetes. Recently, lobeglitazone was developed as a highly effective TZD with reduced side effects by Chong Kun Dang Pharmaceuticals. To identify the structural determinants for the high potency of lobeglitazone as a PPARγ agonist, we determined the crystal structures of the PPARγ ligand binding domain (LBD) in complex with lobeglitazone and pioglitazone at 1.7 and 1.8 Å resolutions, respectively. Comparison of ligand-bound PPARγ structures revealed that the binding modes of TZDs are well conserved. The TZD head group forms hydrogen bonds with the polar residues in the AF-2 pocket and helix 12, stabilizing the active conformation of the LBD. The unique p-methoxyphenoxy group of lobeglitazone makes additional hydrophobic contacts with the Ω-pocket. Docking analysis using the structures of TZD-bound PPARγ suggested that lobeglitazone displays 12 times higher affinity to PPARγ compared to rosiglitazone and pioglitazone. This structural difference correlates with the enhanced affinity and the low effective dose of lobeglitazone compared to the other TZDs.

Bile Acids in Nonalcoholic Fatty Liver Disease: New Concepts and therapeutic advances

Nonalcoholic liver disease (NAFLD) is a major emerging health burden that is a common cause of illness and death worldwide. NAFLD can progress into nonalcoholic steatohepatitis (NASH) which is a severe form of liver disease characterized by inflammation and fibrosis. Further progression leads to cirrhosis, which predisposes patients to hepatocellular carcinoma or liver failure. The mechanism of the progression from simple steatosis to NASH is unclear. However, there are theories and hypothesis which support the link between disruption of the bile acids homeostasis and the progression of this disorder. Previous studies have been demonstrated that alterations to these pathways can lead to dysregulation of energy balance and increased liver inflammation and fibrosis. In this review, we summarized the current knowledge of the interaction between BA and the process related to the development of NAFLD, besides, the potential targets for novel therapies.

Oryzanol Modifies High Fat Diet-Induced Obesity, Liver Gene Expression Profile, and Inflammation Response in Mice

In Western countries and China, the dietary habit of high calories usually results in hyperlipidemia, which is closely associated with cardiovascular diseases. In the study, we investigated the antihyperlipidemic effect of oryzanol and its molecular mechanism in the high fat diet (HFD) mouse model. In total, 60 ICR mice were randomly divided into control group, HFD group, and HFD+Ory group. The mice from the HFD+Ory group were additionally fed with 100 mg/kg of oryzanol by intragastric administration. Our data indicated that oryzanol treatment for 10 weeks significantly reduced bodyweight, liver weight, and adipose tissues weight of the mice; lowered the contents of total cholesterol (TC), triglycerides (TG), and low density lipoprotein-cholesterol (LDL-C); and elevated high density lipoprotein-cholesterol (HDL-C) in the plasma of HFD mice. Compared with the HFD group, H&E staining showed that oryzanol treatment decreased the size of fat droplets of liver tissues and the size of adipocytes. Gene chip data found that oryzanol administration caused 32 genes to increase expressions while 60 genes had reduced expressions in the liver tissues of HFD mice. IPA software was used to analyze the protein interaction network and found that transcript factor NF-κB located in the central role of network, meaning NF-κB may have important function in the lipid-lowering effect of oryzanol. Western blotting and RT-qPCR confirmed that lipid metabolism-related gene expressions were obviously regulated by oryzanol administration. Oryzanol also inhibited expressions of inflammatory factor in the liver tissues of HDF mice. Taken together, our data indicate that oryzanol treatment can regulate lipid metabolism-related gene expressions and inhibit HDF-caused obesity in mice.

PPARs: regulators of metabolism and as therapeutic targets in cardiovascular disease. Part II: PPAR-β/δ and PPAR-γ

The PPARs are a subfamily of three ligand-inducible transcription factors, which belong to the superfamily of nuclear hormone receptors. In mammals, the PPAR subfamily consists of three members: PPAR-α, PPAR-β/δ and PPAR-γ. PPARs control the expression of a large number of genes involved in metabolic homeostasis, lipid, glucose and energy metabolism, adipogenesis and inflammation. PPARs regulate a large number of metabolic pathways that are implicated in the pathogenesis of metabolic diseases such as metabolic syndrome, Type 2 diabetes mellitus, nonalcoholic fatty liver disease and cardiovascular disease. The aim of this review is to provide up-to-date information about the biochemical and metabolic actions of PPAR-β/δ and PPAR-γ, the therapeutic potential of their agonists currently under clinical development and the cardiovascular disease outcome of clinical trials of PPAR-γ agonists, pioglitazone and rosiglitazone.