PPARalpha activation abolishes LDL-stimulated IL-8 production via AP-1 deactivation in human aortic smooth muscle cells

Non-alcoholic fatty liver disease: a metabolic burden promoting atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) has become the fastest growing chronic liver disease, with a prevalence of up to 25% worldwide. Individuals with NAFLD have a high risk of disease progression to cirrhosis, hepatocellular carcinoma (HCC), and liver failure. With the exception of intrahepatic burden, cardiovascular disease (CVD) and especially atherosclerosis (AS) are common complications of NAFLD. Furthermore, CVD is a major cause of death in NAFLD patients. Additionally, AS is a metabolic disorder highly associated with NAFLD, and individual NAFLD pathologies can greatly increase the risk of AS. It is increasingly clear that AS-associated endothelial cell damage, inflammatory cell activation, and smooth muscle cell proliferation are extensively impacted by NAFLD-induced systematic dyslipidemia, inflammation, oxidative stress, the production of hepatokines, and coagulations. In clinical trials, drug candidates for NAFLD management have displayed promising effects for the treatment of AS. In this review, we summarize the key molecular events and cellular factors contributing to the metabolic burden induced by NAFLD on AS, and discuss therapeutic strategies for the improvement of AS in individuals with NAFLD.

PPARs: Key Regulators of Airway Inflammation and Potential Therapeutic Targets in Asthma

Asthma affects approximately 300 million people worldwide, significantly impacting quality of life and healthcare costs. While current therapies are effective in controlling many patients' symptoms, a large number continue to experience exacerbations or treatment-related adverse effects. Alternative therapies are thus urgently needed. Accumulating evidence has shown that the peroxisome proliferator-activated receptor (PPAR) family of nuclear hormone receptors, comprising PPARα, PPARβ/δ, and PPARγ, is involved in asthma pathogenesis and that ligand-induced activation of these receptors suppresses asthma pathology. PPAR agonists exert their anti-inflammatory effects primarily by suppressing pro-inflammatory mediators and antagonizing the pro-inflammatory functions of various cell types relevant to asthma pathophysiology. Experimental findings strongly support the potential clinical benefits of PPAR agonists in the treatment of asthma. We review current literature, highlighting PPARs' key role in asthma pathogenesis and their agonists' therapeutic potential. With additional research and rigorous clinical studies, PPARs may become attractive therapeutic targets in this disease.

Reverse Translational Study of Fenofibrate's Observed Effects in Diabetes-Associated Retinopathy

Clinical trials suggest that fenofibrate reduces the progression of retinopathies in patients with type 2 diabetes. Furthermore, patients with retinopathies have elevated levels of inflammatory chemokines and dysfunctional retinal angiogenesis. Therefore, we investigated the effects of fenofibrate on the production of inflammatory chemokines and genes associated with angiogenesis. Retinal pigment epithelial cells (RPECs) were cultured with IL-1β and fenofibrate ranging from 1-50 μM. ENA-78, IL-8, and RANTES were measured in cell culture by ELISA. ENA-78, ABCA1, and ABCG1 gene expression were tested by RT-PCR. IL-1β significantly induced the production of ENA-78, IL-8, and RANTES. Fenofibrate at concentrations of 25-50 uM blunted the IL-1β induced production of ENA-78 (p < 0.05) with no significant effects on RANTES and IL-8. Fenofibrate also reduced the expression of the ENA-78 gene as well as ABCA1 and ABCG1, which are genes involved in angiogenesis. Fenofibrate decreases ENA-78 production and ABCA1/ABCG1 gene expression in RPECs.

Fenofibrate Attenuates Neutrophilic Inflammation in Airway Epithelia: Potential Drug Repurposing for Cystic Fibrosis

A hallmark of cystic fibrosis (CF) lung disease is neutrophilic airway inflammation. Elevated neutrophil counts have been associated with decreased forced expiratory volume in 1 second and poor clinical measures in patients with CF. Interleukin 8 (IL-8), epithelial neutrophil activating protein 78 (ENA-78), tumor necrosis factor alpha (TNF-α), granulocyte macrophage colony-stimulating factor (GM-CSF), and granulocyte colony-stimulating factor (G-CSF) contribute to neutrophil activation and disease pathogenesis in the airways of patients with CF. Drugs that modify the production of these chemokines in the airways could potentially benefit CF patients. Thus, we determined the effects of fenofibrate on their production in cell populations obtained from the airways. Human small airway epithelial cells and CF bronchial epithelial cells were treated with IL-1β to induce inflammation. We cotreated the cells with fenofibrate at concentrations ranging from 10 to 50 μM to determine if this drug could attenuate the inflammation. IL-8, ENA-78, TNF-α, GM-CSF, and G-CSF production were measured from the cell culture supernates by ELISA. ANOVA statistical testing was conducted using SPSS 17.0. IL-1β increased the production of each of the chemokines by several fold. Fenofibrate reduced IL-1β induced production of each of these neutrophilic chemokines at the concentrations used. IL-1β increases the production of neutrophilic chemokines in airway epithelial cells. Cotreatment with fenofibrate blunts these processes. Fenofibrate should be explored as a therapeutic option to modulate the abundant neutrophilic inflammation observed in CF.

Modulatory effect of fenofibrate on endothelial production of neutrophil chemokines IL-8 and ENA-78

PURPOSE

The PPAR-alpha agonists (fibrates) are commonly used in the treatment of dyslipidemia. It has been hypothesized that the cardio-protective effects of fibrates are partially due to immunomodulatory effects. However, there is a paucity of data regarding the effect of fibrates on neutrophilic chemokines such as epithelial neutrophil activating protein (ENA-78) and interleukin (IL)-8. We investigated the influence of fenofibrate on IL-1β-stimulated production of ENA-78 and IL-8 from human endothelial cells (HUVECs).

METHODS

HUVECs were cultured in the presence or absence of IL-1β and fenofibrate ranging from 1-50 uM. ENA-78 and IL-8 were measured and normalized to total protein content in cell culture supernates by multiplex immunofluorescence detection. Experimental samples were measured in triplicate. Significance was set at P < 0.05 by ANOVA with correction for multiple comparisons.

RESULTS

Endothelial production of both ENA-78 and IL-8 was induced by the proinflammatory cytokine IL-1β. ENA-78 concentrations increased by more than 160-fold over constitutively produced ENA-78 upon IL-1β stimulation (mean ± SEM: 10,129 ± 1591 pg/mg vs. 61 ± 9.5 mg/mg; P < 0.0001). IL-8 concentrations increased by slightly over 5-fold (6145 ± 860 pg/mg vs. 1160 ± 201 pg/mg; P = 0.0003). ENA-78 protein and mRNA were significantly reduced by fenofibrate while no drug effects were observed on IL-8 production.

CONCLUSIONS

Fenofibrate blunts IL-1β-mediated ENA-78 production with no effect on IL-8. This represents a novel mechanism by which fenofibrate exerts anti-inflammatory effects and should be further explored.

The synthetic cannabinoid R(+)WIN55,212-2 augments interferon-β expression via peroxisome proliferator-activated receptor-α

We have demonstrated that R(+)WIN55,212-2, a synthetic cannabinoid that possesses cannabimimetic properties, acts as a novel regulator of Toll-like receptor 3 (TLR3) signaling to interferon (IFN) regulatory factor 3 (IRF3) activation and IFN-β expression, and this is critical for manifesting its protective effects in a murine multiple sclerosis model. Here we investigated the role of peroxisome proliferator-activated receptor-α (PPARα) in mediating the effects of R(+)WIN55,212-2 on this pathway. Data herein demonstrate that the TLR3 agonist poly(I:C) promotes IFN-β expression and R(+)WIN55,212-2 enhances TLR3-induced IFN-β expression in a stereoselective manner via PPARα. R(+)WIN55,212-2 promotes increased transactivation and expression of PPARα. Using the PPARα antagonist GW6471, we demonstrate that R(+)WIN55,212-2 acts via PPARα to activate JNK, activator protein-1, and positive regulatory domain IV to transcriptionally regulate the IFN-β promoter. Furthermore, GW6471 ameliorated the protective effects of R(+)WIN55,212-2 during the initial phase of experimental autoimmune encephalomyelitis. Overall, these findings define PPARα as an important mediator in manifesting the effects of R(+)WIN55,212-2 on the signaling cascade regulating IFN-β expression. The study adds to our molecular appreciation of potential therapeutic effects of R(+)WIN55,212-2 in multiple sclerosis.

Gemfibrozil, stretching arms beyond lipid lowering

Gemfibrozil is long known for its ability to reduce the level of triglycerides in the blood circulation and to decrease the risk of hyperlipidemia. However, a number of recent studies reveal that apart from its lipid-lowering effects, gemfibrozil can also regulate many other signaling pathways responsible for inflammation, switching of T-helper cells, cell-to-cell contact, migration, and oxidative stress. In this review, we have made an honest attempt to analyze various biological activities of gemfibrozil and associated mechanisms that may help to consider this drug for different human disorders as primary or adjunct therapy.

PPAR activators and COX inhibitors selectively block cytokine-induced COX-2 expression and activity in human aortic smooth muscle cells

Atherosclerotic complications are related to the unstable character of the plaque rather than its volume. Vulnerable plaques often contain a large lipid core, a reduced content of smooth muscle cells (SMCs), and an accumulation of inflammatory cells. Regulation of this inflammatory response is an essential element in chronic inflammatory diseases such as atherosclerosis. Nuclear receptors and particularly peroxisome proliferator-activated receptors (PPARs) have emerged as therapeutic targets with a widespread impact on the treatment of metabolic disorders because they can modulate gene expression involved in lipid and glucose homeostasis and can exert anti-inflammatory properties. However, little is known about nuclear receptor effects on SMC inflammation, which produces large amounts of IL-6 and prostanoids. The aim of this study was to evaluate anti-inflammatory properties of nuclear receptor activators in a human physiological SMC model. We show that PPAR activators, as well as liver X receptor alpha, farnesoid X receptor and retinoid X receptor alpha activators, inhibit IL-1beta-induced SMC 6-keto PGF1alpha synthesis, an index of cyclooxygenase (COX)-2 activity, with IC(50) between 1 and 69 microM. In contrast, PPARgamma activators, as exemplified by rosiglitazone and pioglitazone, were unable to inhibit cytokine-induced 6-keto PGF1alpha synthesis. We also demonstrate for the first time that the COX-2 inhibitor rofecoxib can reduce 6-keto PGF1alpha production by both enzymatic inhibition and transcriptional repression. These results show that some nuclear receptor activators have SMC anti-inflammatory properties due to COX-2 inhibition which could participate in their anti-atherosclerotic properties beyond lipid impacts.

Nuclear receptors and inflammatory diseases

It is well known that the steroid hormone glucocorticoid and its nuclear receptor regulate the inflammatory process, a crucial component in the pathophysiological process related to human diseases that include atherosclerosis, obesity and type II diabetes, inflammatory bowel disease, Alzheimer's disease, multiple sclerosis, and liver tumors. Growing evidence demonstrates that orphan and adopted orphan nuclear receptors, such as peroxisome proliferator-activated receptors, liver x receptors, the farnesoid x receptor, NR4As, retinoid x receptors, and the pregnane x receptor, regulate the inflammatory and metabolic profiles in a ligand-dependent or -independent manner in human and animal models. This review summarizes the regulatory roles of these nuclear receptors in the inflammatory process and the underlying mechanisms.

Epoxygenases and peroxisome proliferator-activated receptors in mammalian vascular biology

Epoxygenases, particularly of the CYP2C and CYP2J families, are important lipid-metabolizing enzymes. Epoxygenases are found throughout the cardiovascular system where their lipid products, particularly the epoxyeicosatrienoic acids (EETs), which are arachidonic acid metabolites, have the potential to regulate vascular tone, cellular proliferation, migration, inflammation and cardiac function. The receptors for EETs are, however, poorly understood. The peroxisome proliferator-activated receptors (PPARs) are a family of three (alpha, beta/delta and gamma) nuclear receptors that are activated by lipid metabolites. Activation of PPAR alpha and PPAR gamma, similar to the longer term effects of EETs, causes the inhibition of vascular cell proliferation, migration and inflammation. Interestingly, EETs and their metabolites have recently been found to active both PPAR alpha and PPAR gamma. The epoxygenase-EET-PPAR pathway may therefore represent a novel endogenous protective pathway by which short-lived lipid mediators control vascular cell activation.

PPARγ activation abolishes LDL-induced proliferation of human aortic smooth muscle cells via SOD-mediated down-regulation of superoxide

Native LDL would be a mitogenic and chemotactic stimulus of VSMC proliferation and differentiation in the atherosclerotic lesion where endothelial disruption occurred. In previous studies, our group investigated the molecular mechanisms by which LDL induces IL-8 production and by which PPARalpha activation abolishes LDL effects in human aortic SMCs (hAoSMCs). Herein is the first report of PPARgamma activation by troglitazone (TG) exerting its inhibitory effects on LDL-induced cell proliferation via generation not of H(2)O(2), but of O2(.-), and the subsequent activation of Erk1/2 in hAoSMCs. Moreover, in this study TG abolished the LDL-accelerated G(1)-S progression to control levels via down-regulation of active cyclinD1/CDK4 and cyclinE/CDK2 complexes and up-regulation of p21(Cip1) expression. TG exerted its anti-proliferative effects through the up-regulation of basal superoxide dismutase (SOD) expression. This data suggests that the regulation of O2(.-) is located at the crossroads between LDL signaling and cell proliferation.

Regulation of inflammation by PPARs: a future approach to treat lung inflammatory diseases?

Lung inflammatory diseases, such as acute lung injury (ALI), asthma, chronic obstructive pulmonary disease (COPD) and lung fibrosis, represent a major health problem worldwide. Although glucocorticoids are the most potent anti-inflammatory drug in asthma, they exhibit major side effects and have poor activity in lung inflammatory disorders such as ALI or COPD. Therefore, there is growing need for the development of alternative or new therapies to treat inflammation in the lung. Peroxisome proliferator-activated receptors (PPARs), including the three isotypes PPARalpha, PPARbeta (or PPARdelta) and PPARgamma, are transcription factors belonging to the nuclear hormone receptor superfamily. PPARs, and in particular PPARalpha and PPARgamma, are well known for their critical role in the regulation of energy homeostasis by controlling expression of a variety of genes involved in lipid and carbohydrate metabolism. Synthetic ligands of the two receptor isotypes, the fibrates and the thiazolidinediones, are clinically used to treat dyslipidaemia and type 2 diabetes, respectively. Recently however, PPARalpha and PPARgamma have been shown to exert a potent anti-inflammatory activity, mainly through their ability to downregulate pro-inflammatory gene expression and inflammatory cell functions. The present article reviews the current knowledge of the role of PPARalpha and PPARgamma in controlling inflammation, and presents different findings suggesting that PPARalpha and PPARgamma activators may be helpful in the treatment of lung inflammatory diseases.

Anti-atherogenic properties of fibrates may be largely due to their anti-inflammatory effects

Current understanding of the pathophysiology of atherosclerosis has undergone a remarkable evolution. Compelling evidence has evolved at both the basic science and clinical level for the importance of inflammation in the pathogenesis of atherosclerosis and its complications. Recent research has shown that both systemic and local inflammation plays a central role in all phases of the atherosclerotic process. Inflammatory cells dominate early atherosclerotic lesions, inflammatory cytokines accelerate progression of the lesions, and activation of inflammation can elicit acute coronary syndromes. Robust clinical studies have affirmed that fibrates are anti-atherogenic and can improve the cardiovascular risk profile. Fibrates not only modulate the serum concentrations of triglyceride and cholesterol, but also inhibit systemic inflammatory statue and inflammatory response in vascular cells. Fibrates act anti-inflammatory effects in monocyte/macrophage, T lymphocyte, endothelial cells, vascular smooth muscle cells and adipocytes. Since atherosclerosis is now regarded as an inflammatory disease and those inflammatory cells play critical important roles in the initiation and development of atherosclerosis, we hypothesize that anti-atherogenic properties of fibrates may be largely due to their anti-inflammatory effects.

Peroxisome proliferator-activated receptors and inflammation

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptors family. PPARs are a family of 3 ligand-activated transcription factors: PPARalpha (NR1C1), PPARbeta/delta (NUC1; NR1C2), and PPARgamma (NR1C3). PPARalpha, -beta/delta, and -gamma are encoded by different genes but show substantial amino acid similarity, especially within the DNA and ligand binding domains. All PPARs act as heterodimers with the 9-cis-retinoic acid receptors (retinoid X receptor; RXRs) and play important roles in the regulation of metabolic pathways, including those of lipid of biosynthesis and glucose metabolism, as well as in a variety of cell differentiation, proliferation, and apoptosis pathways. Recently, there has been a great deal of interest in the involvement of PPARs in inflammatory processes. PPAR ligands, in particular those of PPARalpha and PPARgamma, inhibit the activation of inflammatory gene expression and can negatively interfere with pro-inflammatory transcription factor signaling pathways in vascular and inflammatory cells. Furthermore, PPAR levels are differentially regulated in a variety of inflammatory disorders in man, where ligands appear to be promising new therapies.