Peroxisome proliferator-activated receptor-alpha contributes to the anti-inflammatory activity of glucocorticoids

Promising biomarkers and therapeutic targets for the management of Parkinson's disease: recent advancements and contemporary research

Parkinson's disease (PD) is one of the progressive neurological diseases which affect around 10 million population worldwide. The clinical manifestation of motor symptoms in PD patients appears later when most dopaminergic neurons have degenerated. Thus, for better management of PD, the development of accurate biomarkers for the early prognosis of PD is imperative. The present work will discuss the potential biomarkers from various attributes covering biochemical, microRNA, and neuroimaging aspects (α-synuclein, DJ-1, UCH-L1, β-glucocerebrosidase, BDNF, etc.) for diagnosis, recent development in PD management, and major limitations with current and conventional anti-Parkinson therapy. This manuscript summarizes potential biomarkers and therapeutic targets, based on available preclinical and clinical evidence, for better management of PD.

Interactions between nuclear receptors glucocorticoid receptor α and peroxisome proliferator-activated receptor α form a negative feedback loop

Both nuclear receptors glucocorticoid receptor α (GRα) and peroxisome proliferator-activated receptor α (PPARα) are involved in energy and lipid metabolism, and possess anti-inflammation effects. Previous studies indicate that a regulatory loop may exist between them. In vivo and in vitro studies showed that glucocorticoids stimulate hepatic PPARα expression via GRα at the transcriptional level. This stimulation of PPARα by GRα has physiological relevance and PPARα is involved in many glucocorticoid-induced pathophysiological processes, including gluconeogenesis and ketogenesis during fasting, insulin resistance, hypertension and anti-inflammatory effects. PPARα also synergizes with GRα to promote erythroid progenitor self-renewal. As the feedback, PPARα inhibits glucocorticoid actions at pre-receptor and receptor levels. PPARα decreases glucocorticoid production through inhibiting the expression and activity of type-1 11β-hydroxysteroid dehydrogenase, which converts inactive glucocorticoids to active glucocorticoids at local tissues, and also down-regulates hepatic GRα expression, thus forming a complete and negative feedback loop. This negative feedback loop sheds light on prospective multi-drug therapeutic treatments in inflammatory diseases through a combination of glucocorticoids and PPARα agonists. This combination may potentially enhance the anti-inflammatory effects while alleviating side effects on glucose and lipid metabolism due to GRα activation. More investigations are needed to clarify the underlying mechanism and the relevant physiological or pathological significance of this regulatory loop.

Emerging Therapeutic Strategies for Parkinson’s Disease and Future Prospects: A 2021 Update

Parkinson’s disease (PD) is a neurodegenerative disorder pathologically distinguished by degeneration of dopaminergic neurons in the substantia nigra pars compacta. Muscle rigidity, tremor, and bradykinesia are all clinical motor hallmarks of PD. Several pathways have been implicated in PD etiology, including mitochondrial dysfunction, impaired protein clearance, and neuroinflammation, but how these factors interact remains incompletely understood. Although many breakthroughs in PD therapy have been accomplished, there is currently no cure for PD, only trials to alleviate the related motor symptoms. To reduce or stop the clinical progression and mobility impairment, a disease-modifying approach that can directly target the etiology rather than offering symptomatic alleviation remains a major unmet clinical need in the management of PD. In this review, we briefly introduce current treatments and pathophysiology of PD. In addition, we address the novel innovative therapeutic targets for PD therapy, including α-synuclein, autophagy, neurodegeneration, neuroinflammation, and others. Several immunomodulatory approaches and stem cell research currently in clinical trials with PD patients are also discussed. Moreover, preclinical studies and clinical trials evaluating the efficacy of novel and repurposed therapeutic agents and their pragmatic applications with encouraging outcomes are summarized. Finally, molecular biomarkers under active investigation are presented as potentially valuable tools for early PD diagnosis.

Reprogramming of glucocorticoid receptor function by hypoxia

Here, we investigate the impact of hypoxia on the hepatic response of glucocorticoid receptor (GR) to dexamethasone (DEX) in mice via RNA-sequencing. Hypoxia causes three types of reprogramming of GR: (i) much weaker induction of classical GR-responsive genes by DEX in hypoxia, (ii) a number of genes is induced by DEX specifically in hypoxia, and (iii) hypoxia induces a group of genes via activation of the hypothalamic-pituitary-adrenal (HPA) axis. Transcriptional profiles are reflected by changed GR DNA-binding as measured by ChIP sequencing. The HPA axis is induced by hypothalamic HIF1α and HIF2α activation and leads to GR-dependent lipolysis and ketogenesis. Acute inflammation, induced by lipopolysaccharide, is prevented by DEX in normoxia but not during hypoxia, and this is attributed to HPA axis activation by hypoxia. We unfold new physiological pathways that have consequences for patients suffering from GC resistance.

Glucocorticoid-Induced Leucine Zipper (GILZ) in Cardiovascular Health and Disease

Glucocorticoids (GCs) are essential in regulating functions and homeostasis in many biological systems and are extensively used to treat a variety of conditions associated with immune/inflammatory processes. GCs are among the most powerful drugs for the treatment of autoimmune and inflammatory diseases, but their long-term usage is limited by severe adverse effects. For this reason, to envision new therapies devoid of typical GC side effects, research has focused on expanding the knowledge of cellular and molecular effects of GCs. GC-induced leucine zipper (GILZ) is a GC-target protein shown to mediate several actions of GCs, including inhibition of the NF-κB and MAPK pathways. GILZ expression is not restricted to immune cells, and it has been shown to play a regulatory role in many organs and tissues, including the cardiovascular system. Research on the role of GILZ on endothelial cells has demonstrated its ability to modulate the inflammatory cascade, resulting in a downregulation of cytokines, chemokines, and cellular adhesion molecules. GILZ also has the capacity to protect myocardial cells, as its deletion makes the heart, after a deleterious stimulus, more susceptible to apoptosis, immune cell infiltration, hypertrophy, and impaired function. Despite these advances, we have only just begun to appreciate the relevance of GILZ in cardiovascular homeostasis and dysfunction. This review summarizes the current understanding of the role of GILZ in modulating biological processes relevant to cardiovascular biology.

Peroxisome Proliferator-Activated Receptors: Experimental Targeting for the Treatment of Inflammatory Bowel Diseases

The peroxisome proliferator-activated receptors (PPARs) are a group of nuclear receptor proteins that promote ligand-dependent transcription of target genes that regulate energy production, lipid metabolism, and inflammation. The PPAR superfamily comprises three subtypes, PPARα, PPARγ, and PPARβ/δ, with differential tissue distributions. In addition to their different roles in the regulation of energy balance and carbohydrate and lipid metabolism, an emerging function of PPARs includes normal homeostasis of intestinal tissue. PPARα activation represses NF-κB signaling, which decreases the inflammatory cytokine production by different cell types, while PPARγ ligands can inhibit activation of macrophages and the production of inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and Il-1β. In this regard, the anti-inflammatory responses induced by PPAR activation might restore physiopathological imbalances associated with inflammatory bowel diseases (IBD). Thus, PPARs and their ligands have important therapeutic potential. This review briefly discusses the roles of PPARs in the physiopathology and therapies of the most important IBDs, ulcerative colitis (UC), and Crohn's disease (CD), as well some new experimental compounds with PPAR activity as promising drugs for IBD treatment.

Comparative Evaluation of Gemcabene and Peroxisome Proliferator-Activated Receptor Ligands in Transcriptional Assays of Peroxisome Proliferator-Activated Receptors: Implication for the Treatment of Hyperlipidemia and Cardiovascular Disease

Gemcabene, a late-stage clinical candidate, has shown efficacy for LDL-C, non-HDL cholesterol, apoB, triglycerides, and hsCRP reduction, all risk factors for cardiovascular disease. In rodents, gemcabene showed changes in targets, including apoC-III, apoA-I, peroxisomal enzymes, considered regulated through peroxisome proliferator-activated receptor (PPAR) gene activation, suggesting a PPAR-mediated mechanism of action for the observed hypolipidemic effects observed in rodents and humans. In the current study, the gemcabene agonist activity against PPAR subtypes of human, rat, and mouse were compared with known lipid lowering PPAR activators. Surprisingly, gemcabene showed no or little PPAR-α transactivation compared with reference agonists, which showed concentration-dependent transactivation against human PPAR-α of 2.4- to 30-fold (fenofibric acid), 17-fold (GW590735), and 2.3- to 25-fold (WY-14643). These agents also showed robust transactivation of mouse and rat PPAR-α in a concentration-dependent manner. The known PPAR-δ agonists, GW1516, L165041, and GW0742, showed potent agonist activity against human, mouse, and rat receptors (ranging from 165- to 396-fold). By contrast, gemcabene at the highest concentration tested (300 μM) showed no response in mouse and rat and a marginal response against human PPAR-δ receptors (3.2-fold). For PPAR-γ, gemcabene showed no agonist activity against all 3 species at 100 μM and marginal activity (3.6- to 5-fold) at 300 μM. By contrast, the known agonists, rosiglitazone, indomethacin, and muraglitazar showed strong activation against the mouse, rat, and human PPAR-γ receptors. No clear antagonist activity was observed with gemcabene against any PPAR subtypes for all 3 species over a wide range of concentrations. In summary, the transactivation studies rule out gemcabene as a direct agonist or antagonist of PPAR-α, PPAR-γ, and PPAR-δ receptors of these 3 species. These data suggest that the peroxisomal effects observed in rodents and the lipid regulating effects observed in rodents and humans are not related to a direct activation of PPAR receptors by gemcabene.

Pathway-Based Analysis of the Liver Response to Intravenous Methylprednisolone Administration in Rats: Acute Versus Chronic Dosing

Pharmacological time-series data, from comparative dosing studies, are critical to characterizing drug effects. Reconciling the data from multiple studies is inevitably difficult; multiple in vivo high-throughput -omics studies are necessary to capture the global and temporal effects of the drug, but these experiments, though analogous, differ in (microarray or other) platforms, time-scales, and dosing regimens and thus cannot be directly combined or compared. This investigation addresses this reconciliation issue with a meta-analysis technique aimed at assessing the intrinsic activity at the pathway level. The purpose of this is to characterize the dosing effects of methylprednisolone (MPL), a widely used anti-inflammatory and immunosuppressive corticosteroid (CS), within the liver. A multivariate decomposition approach is applied to analyze acute and chronic MPL dosing in male adrenalectomized rats and characterize the dosing-dependent differences in the dynamic response of MPL-responsive signaling and metabolic pathways. We demonstrate how to deconstruct signaling and metabolic pathways into their constituent pathway activities, activities which are scored for intrinsic pathway activity. Dosing-induced changes in the dynamics of pathway activities are compared using a model-based assessment of pathway dynamics, extending the principles of pharmacokinetics/pharmacodynamics (PKPD) to describe pathway activities. The model-based approach enabled us to hypothesize on the likely emergence (or disappearance) of indirect dosing-dependent regulatory interactions, pointing to likely mechanistic implications of dosing of MPL transcriptional regulation. Both acute and chronic MPL administration induced a strong core of activity within pathway families including the following: lipid metabolism, amino acid metabolism, carbohydrate metabolism, metabolism of cofactors and vitamins, regulation of essential organelles, and xenobiotic metabolism pathway families. Pathway activities alter between acute and chronic dosing, indicating that MPL response is dosing dependent. Furthermore, because multiple pathway activities are dominant within a single pathway, we observe that pathways cannot be defined by a single response. Instead, pathways are defined by multiple, complex, and temporally related activities corresponding to different subgroups of genes within each pathway.

Glucocorticoid-Induced Leucine Zipper: A Novel Anti-inflammatory Molecule

Glucocorticoids (GCs) are the most commonly used drugs for treatment of autoimmune and inflammatory diseases. Their efficacy is due to their ability to bind cytoplasmic receptors (glucocorticoid receptors, GR) and other cytoplasmic proteins, thus regulating gene expression. Although GCs are potent life-saving drugs, their therapeutic effects are transitory and chronic use of GCs is accompanied by serious side effects. Therefore, new drugs are needed to replace GCs. We have identified a gene, glucocorticoid-induced leucine zipper (GILZ or tsc22d3), that is rapidly and invariably induced by GCs. Human GILZ is a 135-amino acid protein that mediates many GC effects, including inhibition of the NF-κB and MAPK pathways. Similar to GCs, GILZ exerts anti-inflammatory activity in experimental disease models, including inflammatory bowel diseases and arthritis. While transgenic mice that overexpress GILZ are more resistant, GILZ knockout mice develop worse inflammatory diseases. Moreover, the anti-inflammatory effect of GCs is attenuated in GILZ-deficient mice. Importantly, in vivo delivery of recombinant GILZ protein cured colitis and facilitated resolution of lipopolysaccharide-induced inflammation without apparent toxic effects. A synthetic GILZ-derived peptide, corresponding to the GILZ region that interacts with NF-κB, was able to suppress experimental autoimmune encephalomyelitis. Collectively, these findings indicate that GILZ is an anti-inflammatory molecule that may serve as the basis for designing new therapeutic approaches to inflammatory diseases.

Molecular Actions of PPARα in Lipid Metabolism and Inflammation

Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor of clinical interest as a drug target in various metabolic disorders. PPARα also exhibits marked anti-inflammatory capacities. The first-generation PPARα agonists, the fibrates, have however been hampered by drug-drug interaction issues, statin drop-in, and ill-designed cardiovascular intervention trials. Notwithstanding, understanding the molecular mechanisms by which PPARα works will enable control of its activities as a drug target for metabolic diseases with an underlying inflammatory component. Given its role in reshaping the immune system, the full potential of this nuclear receptor subtype as a versatile drug target with high plasticity becomes increasingly clear, and a novel generation of agonists may pave the way for novel fields of applications.

PPARs and pain

Chronic pain is a common cause of disability worldwide and remains a global health and socio-economic challenge. Current analgesics are either ineffective in a significant proportion of patients with chronic pain or associated with significant adverse side effects. The PPARs, a family of nuclear hormone transcription factors, have emerged as important modulators of pain in preclinical studies and therefore a potential therapeutic target for the treatment of pain. Modulation of nociceptive processing by PPARs is likely to involve both transcription-dependent and transcription-independent mechanisms. This review presents a comprehensive overview of preclinical studies investigating the contribution of PPAR signalling to nociceptive processing in animal models of inflammatory and neuropathic pain. We examine current evidence from anatomical, molecular and pharmacological studies demonstrating a role for PPARs in pain control. We also discuss the limited evidence available from relevant clinical studies and identify areas that warrant further research. LINKED ARTICLES: This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Co-Activation of Glucocorticoid Receptor and Peroxisome Proliferator-Activated Receptor-γ in Murine Skin Prevents Worsening of Atopic March

Children with atopic dermatitis show an increased risk to develop asthma later in life, a phenomenon referred to as "atopic march," which emphasizes the need for secondary prevention therapies. This study aimed to investigate whether relief of skin inflammation by glucocorticoids and peroxisome proliferator-activated receptor agonists might influence the subsequent development of asthma in a murine model for the atopic march in which mice were repeatedly exposed to house dust mite via the skin, followed by exposure to house dust mite in lungs. To abrogate atopic dermatitis, mice received topical treatment with glucocorticoid receptor/peroxisome proliferator-activated receptor-γ agonists. Nuclear receptor ligand effects were assessed on primary keratinocytes and dendritic cells, as central players in skin inflammation. Prior house dust mite-induced skin inflammation aggravates allergic airway inflammation and induces a mixed T helper type 2/T helper type 17 response in the lungs. Cutaneous combined activation of glucocorticoid receptor/peroxisome proliferator-activated receptor-γ reduced skin inflammation to a higher extent compared to single activation. Additive anti-inflammatory effects were more prominent in dendritic cells, as compared to keratinocytes. Alleviation of allergic skin inflammation by activation of glucocorticoid receptor/peroxisome proliferator-activated receptor-γ appeared insufficient to avoid the allergic immune response in the lungs, but efficiently reduced asthma severity by counteracting the Th17 response. Glucocorticoid receptor/peroxisome proliferator-activated receptor-γ co-activation represents a potent remedy against allergic skin inflammation and worsening of atopic march.

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.

Inhibition of pulmonary β-carotene 15, 15'-oxygenase expression by glucocorticoid involves PPARα

β-carotene 15,15'-oxygenase (BCO1) catalyzes the first step in the conversion of dietary provitamin A carotenoids to vitamin A. This enzyme is expressed in a variety of developing and adult tissues, suggesting that its activity may regulate local retinoid synthesis. Vitamin A and related compounds (retinoids) are critical regulators of lung epithelial development, integrity, and injury repair. A balance between the actions of retinoids and glucocorticoids (GCs) promotes normal lung development and, in particular, alveolarization. Alterations in this balance, including vitamin A deficiency and GC excess, contribute to the development of chronic lung disorders. Consequently, we investigated if GCs counteract retinoid effects in alveolar epithelial cells by mechanisms involving BCO1-dependent local vitamin A metabolism. We demonstrate that BCO1 is expressed in human fetal lung tissue and human alveolar epithelial-like A549 cells. Our results indicate A549 cells metabolize β-carotene to retinal and retinoic acid (RA). GCs exposure using dexamethasone (DEX) decreases BCO1 mRNA and protein levels in A549 cells and reduces BCO1 promoter activity via inhibiting peroxisome proliferator-activated receptor γ (PPARγ) DNA binding. DEX also induces expression of PPARα, which in turn most likely causes a decrease in PPARγ/RXRα heterodimer binding to the bco1 gene promoter and consequent inhibition of bco1 gene expression. PPARα knockdown with siRNA abolishes DEX-induced suppression of BCO1 expression, confirming the requirement for PPARα in this DEX-mediated BCO1 mechanism. Taken together, these findings provide the first evidence that GCs regulate vitamin A (retinoid) signaling via inhibition of bco1 gene expression in a PPARα-dependent manner. These results explicate novel aspects of local GC:retinoid interactions that may contribute to alveolar tissue remodeling in chronic lung diseases that affect children and, possibly, adults.

PPARs in the central nervous system: roles in neurodegeneration and neuroinflammation

Over 25 years have passed since peroxisome proliferators-activated receptors (PPARs), were first described. Like other members of the nuclear receptors superfamily, PPARs have been defined as critical sensors and master regulators of cellular metabolism. Recognized as ligand-activated transcription factors, they are involved in lipid, glucose and amino acid metabolism, taking part in different cellular processes, including cellular differentiation and apoptosis, inflammatory modulation and attenuation of acute and chronic neurological damage in vivo and in vitro. Interestingly, PPAR activation can simultaneously reprogram the immune response, stimulate metabolic and mitochondrial functions, promote axonal growth, induce progenitor cells to differentiate into myelinating oligodendrocytes, and improve brain clearance of toxic molecules such as β-amyloid peptide. Although the molecular mechanisms and cross-talk with different molecular pathways are still the focus of intense research, PPARs are considered potential therapeutic targets for several neuropathological conditions, including degenerative disorders such as Alzheimer's, Parkinson's and Huntington's disease. This review considers recent advances regarding PPARs, as well as new PPAR agonists. We focus on the mechanisms behind the neuroprotective effects exerted by PPARs and summarise the roles of PPARs in different pathologies of the central nervous system, especially those associated with degenerative and inflammatory mechanisms.

Regulation of Ketone Body Metabolism and the Role of PPARα

Ketogenesis and ketolysis are central metabolic processes activated during the response to fasting. Ketogenesis is regulated in multiple stages, and a nuclear receptor peroxisome proliferator activated receptor α (PPARα) is one of the key transcription factors taking part in this regulation. PPARα is an important element in the metabolic network, where it participates in signaling driven by the main nutrient sensors, such as AMP-activated protein kinase (AMPK), PPARγ coactivator 1α (PGC-1α), and mammalian (mechanistic) target of rapamycin (mTOR) and induces hormonal mediators, such as fibroblast growth factor 21 (FGF21). This work describes the regulation of ketogenesis and ketolysis in normal and malignant cells and briefly summarizes the positive effects of ketone bodies in various neuropathologic conditions.

Amelioration of experimental colitis after short-term therapy with glucocorticoid and its relationship to the induction of different regulatory markers

The clinical benefits of short-term therapy with glucocorticoids (GC) in patients with inflammatory bowel disease (IBD) are widely known. However, the effects of this treatment towards the re-establishment of the regulatory network in IBD are not fully explored. We have evaluated the immunological effects of the abbreviated GC therapy in experimental colitis induced by 3% dextran sulphate sodium in C57BL/6 mice. Treatment with GC improved disease outcome, constrained circulating leucocytes and ameliorated intestinal inflammation. The control of the local inflammatory responses involved a reduction in the expression of interferon-γ and interleukin-1β, associated with augmented mRNA levels of peroxisome proliferator-activated receptors (α and γ) in intestine. Furthermore, there was a reduction of CD4⁺ T cells producing interferon-γ, together with an increased frequency of the putative regulatory population of T cells producing interleukin-10, in spleen. These systemic alterations were accompanied by a decrease in the proliferative potential of splenocytes of mice treated in vivo with GC. Notably, treatment with GC also led to an increase in the frequency of the regulatory markers GITR, CTLA-4, PD-1, CD73 and FoxP3, more prominently in spleen. Taken together, our results pointed to a role of GC in the control of leucocyte responsiveness and re-establishment of a regulatory system, which probably contributed to disease control and the restoration of immune balance. Finally, this is the first time that GC treatment was associated with the modulation of a broad number of regulatory markers in an experimental model of colitis.

Peroxisome proliferator-activated receptors (PPARs) as therapeutic target in neurodegenerative disorders

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and they serve to be a promising therapeutic target for several neurodegenerative disorders, which includes Parkinson disease, Alzheimer's disease, Huntington disease and Amyotrophic Lateral Sclerosis. PPARs play an important role in the downregulation of mitochondrial dysfunction, proteasomal dysfunction, oxidative stress, and neuroinflammation, which are the major causes of the pathogenesis of neurodegenerative disorders. In this review, we discuss about the role of PPARs as therapeutic targets in neurodegenerative disorders. Several experimental approaches suggest potential application of PPAR agonist as well as antagonist in the treatment of neurodegenerative disorders. Several epidemiological studies found that the regular usage of PPAR activating non-steroidal anti-inflammatory drugs is effective in decreasing the progression of neurodegenerative diseases including PD and AD. We also reviewed the neuroprotective effects of PPAR agonists and associated mechanism of action in several neurodegenerative disorders both in vitro as well as in vivo animal models.

Systemic administration of WY-14643, a selective synthetic agonist of peroxisome proliferator activator receptor-alpha, alters spinal neuronal firing in a rodent model of neuropathic pain

Background and aims

The clinical management of chronic neuropathic pain remains a global health challenge. Current treatments are either ineffective, or associated with unwanted side-effects. The development of effective, safe therapies requires the identification of novel therapeutic targets using clinically relevant animal models of neuropathic pain.

Peroxisome proliferator activated receptor alpha (PPARα), is a member of the nuclear hormone family of transcription factors, which is widely distributed in the peripheral and central nervous systems. Pharmacological studies report antinociceptive effects of PPARα agonists following systemic administration in rodent models of neuropathic pain, however the neuronal mechanisms and sites of action mediating these effects are unclear.

The aim of this study was to investigate the effects of systemic administration of the synthetic PPARα agonist, WY-14643 on mechanically-evoked responses of spinal cord dorsal horn wide dynamic range (WDR) neurones in the spinal nerve ligated (SNL) model of neuropathic pain in rats. In addition, comparative molecular analysis of mRNA coding for PPARα and PPARα protein expression in the spinal cord of sham-operated and neuropathic rats was performed.

Methods

Lumbar L5–L6 spinal nerve ligation was performed in male Sprague–Dawley rats (110–130 g) under isoflurane anaesthesia. Sham controls underwent similar surgical conditions, but without ligation of the L5–L6 spinal nerves. Hindpaw withdrawal thresholds were measured on the day of surgery -day 0, and on days- 2, 4, 7, 10 and 14 post-surgery. At day 14 extracellular single-unit recordings of spinal (WDR) dorsal horn neurons were performed in both sham and SNL neuropathic rats under anaesthesia. The effects of intraperitoneal (i.p.) administration of WY-14643 (15 and 30 mg/kg) or vehicle on evoked responses of WDR neurons to punctate mechanical stimulation of the peripheral receptive field of varying bending force (8–60 g) were recorded. In a separate cohort of SNL and sham neuropathic rats, the expression of mRNA coding for PPARα and protein expression in the ipsilateral and contralateral spinal cord was determined using quantitative real time polymerase chain reaction (qRT-PCR) and western blotting techniques respectively.

Results

WY-14643 (15 and 30mg/kg i.p.) rapidly attenuated mechanically evoked (8, 10 and 15g) responses of spinal WDR neurones in SNL, but not sham-operated rats. Molecular analysis revealed significantly increased PPARα protein, but not mRNA, expression in the ipsilateral spinal cord of SNL, compared to the contralateral side in SNL rats. There were no changes in PPARα mRNA or protein expression in the sham controls.

Conclusion

The observation that levels of PPARα protein were increased in ipsilateral spinal cord of neuropathic rats supports a contribution of spinal sites of action mediating the effects of systemic WY-14643. Our data suggests that the inhibitory effects of a PPARα agonist on spinal neuronal responses may account, at least in part, for their analgesic effects of in neuropathic pain.

Implication

Selective activation of PPARα in the spinal cord may be therapeutically relevant for the treatment of neuropathic pain.

N-Acylethanolamine-hydrolyzing acid amidase inhibition increases colon N-palmitoylethanolamine levels and counteracts murine colitis

N-Palmitoylethanolamine or palmitoylethanolamide (PEA) is an anti-inflammatory compound that was recently shown to exert peroxisome proliferator-activated receptor-α-dependent beneficial effects on colon inflammation. The actions of PEA are terminated following hydrolysis by 2 enzymes: fatty acid amide hydrolase (FAAH), and the less-studied N-acylethanolamine-hydrolyzing acid amidase (NAAA). This study aims to investigate the effects of inhibiting the enzymes responsible for PEA hydrolysis in colon inflammation in order to propose a potential therapeutic target for inflammatory bowel diseases (IBDs). Two murine models of IBD were used to assess the effects of NAAA inhibition, FAAH inhibition, and PEA on macroscopic signs of colon inflammation, macrophage/neutrophil infiltration, and the expression of proinflammatory mediators in the colon, as well as on the colitis-related systemic inflammation. NAAA inhibition increases PEA levels in the colon and reduces colon inflammation and systemic inflammation, similarly to PEA. FAAH inhibition, however, does not increase PEA levels in the colon and does not affect the macroscopic signs of colon inflammation or immune cell infiltration. This is the first report of an anti-inflammatory effect of a systemically administered NAAA inhibitor. Because NAAA is the enzyme responsible for the control of PEA levels in the colon, we put forth this enzyme as a potential therapeutic target in chronic inflammation in general and IBD in particular.

A role for PPARα in the medial prefrontal cortex in formalin-evoked nociceptive responding in rats

BACKGROUND AND PURPOSE

The nuclear hormone receptor, PPARα, and its endogenous ligands, are involved in pain modulation. PPARα is expressed in the medial prefrontal cortex (mPFC), a key brain region involved in both the cognitive-affective component of pain and in descending modulation of pain. However, the role of PPARα in the mPFC in pain responding has not been investigated. Here, we investigated the effects of pharmacological modulation of PPARα in the rat mPFC on formalin-evoked nociceptive behaviour and the impact of formalin-induced nociception on components of PPARα signalling in the mPFC.

EXPERIMENTAL APPROACH

The effects of intra-mPFC microinjection of a PPARα agonist (GW7647) or a PPARα antagonist (GW6471) on formalin-evoked nociceptive behaviour in rats were studied. Quantitative real-time PCR and LC-MS/MS were used to study the effects of intraplantar injection of formalin on PPARα mRNA expression and levels of endogenous ligands, respectively, in the mPFC.

KEY RESULTS

Intra-mPFC administration of GW6471, but not GW7647, resulted in delayed onset of the early second phase of formalin-evoked nociceptive behaviour. Furthermore, formalin-evoked nociceptive behaviour was associated with significant reductions in mPFC levels of endogenous PPARα ligands (N-palmitoylethanolamide and N-oleoylethanolamide) and a 70% reduction in PPARα mRNA but not protein expression.

CONCLUSIONS AND IMPLICATIONS

These data suggest that endogenous ligands may act at PPARα in the mPFC to play a facilitatory/permissive role in second phase formalin-evoked nociceptive behaviour in rats.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Dexamethasone inhibits the maturation of newly formed neurons and glia supplemented with polyunsaturated fatty acids

Stress bears a negative impact on adult neurogenesis. High levels of corticoids have been shown to inhibit neural stem cell proliferation, and are considered responsible for the loss of neural precursors. Their effects on the differentiation of the glial and neuronal lineages have been less studied. We examined the effect of dexamethasone (Dex), a synthetic glucocorticoid, on the differentiation of rat neural stem cells in vitro. Dex had no effect on the differentiation of cells cultured under standard conditions. Since we previously determined that NSC, when cultured under classical conditions, were deprived of polyunsaturated fatty acids (PUFA), and displayed phospholipid compositions very different from the in vivo figures [1], we examined the effect of Dex under PUFA supplementation. Dex impaired neuron and oligodendrocyte maturation in PUFA-supplemented cells, demonstrated by the reduction of neurite lengths and oligodendrocyte sizes. This effect was mediated by the glucocorticoid receptor (GR), since it was eliminated by mifepristone, a GR antagonist, and could be relayed by a reduction of ERK phosphorylation. We determined that GR was associated with PPAR β and α under basal conditions, and that this association was disrupted when PUFA were added in combination with Dex. We assumed that this effect on the receptor status enabled the effect of Dex on PUFA supplemented cells, since we determined that the binding to the glucocorticoid response element was higher in cells incubated with PUFA and Dex. In conclusion, corticoids can impair NSC differentiation, and consequently impact the entire process of neurogenesis.

Lipids derived from virulent Francisella tularensis broadly inhibit pulmonary inflammation via toll-like receptor 2 and peroxisome proliferator-activated receptor α

Francisella tularensis is a Gram-negative facultative intracellular pathogen that causes an acute lethal respiratory disease in humans. The heightened virulence of the pathogen is linked to its unique ability to inhibit Toll-like receptor (TLR)-mediated inflammatory responses. The bacterial component and mechanism of this inhibition are unknown. Here we show that lipids isolated from virulent but not attenuated strains of F. tularensis are not detected by host cells, inhibit production of proinflammatory cytokines by primary macrophages in response to known TLR ligands, and suppress neutrophil recruitment in vivo. We further show that lipid-mediated inhibition of inflammation is dependent on TLR2, MyD88, and the nuclear hormone and fatty acid receptor peroxisome proliferator-activated receptor α (PPARα). Pathogen lipid-mediated interference with inflammatory responses through the engagement of TLR2 and PPARα represents a novel manipulation of host signaling pathways consistent with the ability of highly virulent F. tularensis to efficiently evade host immune responses.

Combination therapy with melatonin and dexamethasone in a mouse model of traumatic brain injury

Traumatic brain injury (TBI) is a major cause of preventable death and morbidity in young adults. This complex condition is characterized by a significant blood-brain barrier leakage that stems from cerebral ischemia, inflammation, and redox imbalances in the traumatic penumbra of the injured brain. Recovery of function after TBI is partly through neuronal plasticity. In order to test whether combination therapy with melatonin and dexamethasone (DEX) might improve functional recovery, a controlled cortical impact (CCI) was performed in adult mice, acting as a model of TBI. Once trauma has occurred, combating these exacerbations is the keystone of an effective TBI therapy. The therapy with melatonin (10  mg/kg) and DEX (0.025  mg/kg) is able to reduce edema and brain infractions as evidenced by decreased 2,3,5-triphenyltetrazolium chloride staining across the brain sections. Melatonin- and DEX-mediated improvements in tissue histology shown by the reduction in lesion size and an improvement in apoptosis level further support the efficacy of combination therapy. The combination therapy also blocked the infiltration of astrocytes and reduced CCI-mediated oxidative stress. In addition, we have also clearly demonstrated that the combination therapy significantly ameliorated neurological scores. Taken together, our results clearly indicate that combination therapy with melatonin and DEX presents beneficial synergistic effects, and we consider it an avenue for further development of novel combination therapeutic agents in the treatment of TBI that are more effective than a single effector molecule.

Cigarette smoke increases BLT2 receptor functions in bronchial epithelial cells: in vitro and ex vivo evidence

Leukotriene B(4) (LTB(4)) is a neutrophil chemotactic molecule with important involvement in the inflammatory responses of chronic obstructive pulmonary disease (COPD). Airway epithelium is emerging as a regulator of innate immune responses to a variety of insults including cigarette smoke, the major risk factor for COPD. In this study we have explored whether cigarette smoke extracts (CSE) or soluble mediators present in distal lung fluid samples (mini-bronchoalveolar lavages) from smokers alter the expression of the LTB(4) receptor 2 (BLT2) and peroxisome proliferator-activated receptor-α (PPAR-α) in bronchial epithelial cells. We also evaluated the effects of CSE on the expression of intercellular adhesion molecule 1 (ICAM-1) and on the binding of signal transducer and activator of transcription 1 (STAT-1) to ICAM-1 promoter as well as the adhesiveness of neutrophils to bronchial epithelial cells. CSE and mini-bronchoalveolar lavages from smokers increased BLT2 and ICAM-1 expression as well as the adhesiveness of neutrophils to bronchial epithelial cells and decreased PPAR-α expression. CSE induced the activation of STAT-1 and its binding to ICAM-1 promoter. These findings suggest that, in bronchial epithelial cells, CSE promote a prevalent induction of pro-inflammatory BLT2 receptors and activate mechanisms leading to increased neutrophil adhesion, a mechanism that contributes to airway neutrophilia and to tissue damage.

Acute Psychological Stress Accelerates Reverse Cholesterol Transport via Corticosterone-Dependent Inhibition of Intestinal Cholesterol Absorption

Rationale:

Psychological stress is associated with an increased risk of cardiovascular diseases. However, the connecting mechanisms of the stress-inducing activation of the hypothalamic-pituitary-adrenal axis with atherosclerosis are not well-understood.

Objective:

To study the effect of acute psychological stress on reverse cholesterol transport (RCT), which transfers peripheral cholesterol to the liver for its ultimate fecal excretion.

Methods and Results:

C57Bl/6J mice were exposed to restraint stress for 3 hours to induce acute psychological stress. RCT in vivo was quantified by measuring the transfer of [ 3 H]cholesterol from intraperitoneally injected mouse macrophages to the lumen of the small intestine within the stress period. Surprisingly, stress markedly increased the contents of macrophage-derived [ 3 H]cholesterol in the intestinal lumen. In the stressed mice, intestinal absorption of [ 14 C]cholesterol was significantly impaired, the intestinal mRNA expression level of peroxisome proliferator–activated receptor-α increased, and that of the sterol influx transporter Niemann-Pick C1–like 1 decreased. The stress-dependent effects on RCT rate and peroxisome proliferator–activated receptor-α gene expression were fully mimicked by administration of the stress hormone corticosterone (CORT) to nonstressed mice, and they were blocked by the inhibition of CORT synthesis in stressed mice. Moreover, the intestinal expression of Niemann-Pick C1–like 1 protein decreased when circulating levels of CORT increased. Of note, when either peroxisome proliferator-activated receptor α or liver X receptor α knockout mice were exposed to stress, the RCT rate remained unchanged, although plasma CORT increased. This indicates that activities of both transcription factors were required for the RCT-accelerating effect of stress.

Conclusions:

Acute psychological stress accelerated RCT by compromising intestinal cholesterol absorption. The present results uncover a novel functional connection between the hypothalamic-pituitary-adrenal axis and RCT that can be triggered by a stress-induced increase in circulating CORT.

Lack of effect of chronic pre-treatment with the FAAH inhibitor URB597 on inflammatory pain behaviour: evidence for plastic changes in the endocannabinoid system

BACKGROUND AND PURPOSE

Elevating levels of endocannabinoids with inhibitors of fatty acid amide hydrolase (FAAH) is a major focus of pain research, purported to be a safer approach devoid of cannabinoid receptor-mediated side effects. Here, we have determined the effects of sustained pharmacological inhibition of FAAH on inflammatory pain behaviour and if pharmacological inhibition of FAAH was as effective as genetic deletion of FAAH on pain behaviour.

EXPERIMENTAL APPROACH

Effects of pre-treatment with a single dose, versus 4 day repeated dosing with the selective FAAH inhibitor, URB597 (i.p. 0.3 mg·kg⁻¹), on carrageenan-induced inflammatory pain behaviour and spinal pro-inflammatory gene induction were determined in rats. Effects of pain induction and of the drug treatments on levels of arachidonoyl ethanolamide (AEA), palmitoyl ethanolamide (PEA) and oleolyl ethanolamide (OEA) in the spinal cord were determined.

KEY RESULTS

Single, but not repeated, URB597 treatment significantly attenuated the development of inflammatory hyperalgesia (P < 0.001, vs. vehicle-treated animals). Neither mode of URB597 treatment altered levels of AEA, PEA and OEA in the hind paw, or carrageenan-induced paw oedema. Single URB597 treatment produced larger increases in AEA, PEA and OEA in the spinal cord, compared with those after repeated administration. Single and repeated URB597 treatment decreased levels of immunoreactive N-acylphosphatidylethanolamine phospholipase D (NAPE-PLD) in the spinal cord and attenuated carrageenan-induced spinal pro-inflammatory gene induction.

CONCLUSION AND IMPLICATIONS

Changes in the endocannabinoid system may contribute to the loss of analgesic effects following repeated administration of low dose URB597 in this model of inflammatory pain.

Evaluation of the antifibrotic effect of fenofibrate and rosiglitazone on bleomycin-induced pulmonary fibrosis in rats

Idiopathic pulmonary fibrosis is the most prevalent chronic fibrosing lung disease. Peroxisome proliferator-activated receptors-gamma agonists provide potential therapy for fibrotic diseases of the lung. Peroxisome proliferator-activated receptors-alpha agonists may be helpful in the treatment of lung inflammatory diseases, however their therapeutic potential on the "fibro-proliferative" process and extracellular matrix accumulation in idiopathic pulmonary fibrosis has been less well studied. So, the present study was conducted to evaluate the anti-fibrotic effects of fenofibrate (peroxisome proliferator-activated receptors-alpha agonist) alone and in combination with rosiglitazone (peroxisome proliferator-activated receptors-gamma agonist) on lung injury induced by bleomycin administration. Oral administration of either rosiglitazone (5 mg/kg/d) or fenofibrate (100 mg/kg/d) for 14 days, attenuated the severity of bleomycin-induced lung injury and fibrosis through decreasing lung water contents, lung fibrotic grading, lung hydroxyproline contents and lung transforming growth factor-beta1 levels; with no significant difference between them. Combined low doses of rosiglitazone (1 mg/kg/d) and fenofibrate (30 mg/kg/d) provided more benefits than full separate doses of each on the deleterious effects accompanied bleomycin administration. These findings suggested the potential use of peroxisome proliferator-activated receptors-alpha ligands as anti-fibrotic agents in lung fibrosis. Additionally, the concurrent administration of fenofibrate and rosiglitazone in low doses has synergistic effect and enhanced the beneficial effects afforded by either fenofibrate or rosiglitazone.

Ulcerative colitis impairs the acylethanolamide-based anti-inflammatory system reversal by 5-aminosalicylic acid and glucocorticoids

Studies in animal models and humans suggest anti-inflammatory roles on the N-acylethanolamide (NAE)-peroxisome proliferators activated receptor alpha (PPARα) system in inflammatory bowel diseases. However, the presence and function of NAE-PPARα signaling system in the ulcerative colitis (UC) of humans remain unknown as well as its response to active anti-inflammatory therapies such as 5-aminosalicylic acid (5-ASA) and glucocorticoids. Expression of PPARα receptor and PPARα ligands-biosynthetic (NAPE-PLD) and -degrading (FAAH and NAAA) enzymes were analyzed in untreated active and 5-ASA/glucocorticoids/immunomodulators-treated quiescent UC patients compared to healthy human colonic tissue by RT-PCR and immunohistochemical analyses. PPARα, NAAA, NAPE-PLD and FAAH showed differential distributions in the colonic epithelium, lamina propria, smooth muscle and enteric plexus. Gene expression analysis indicated a decrease of PPARα, PPARγ and NAAA, and an increase of FAAH and iNOS in the active colitis mucosa. Immunohistochemical expression in active colitis epithelium confirmed a PPARα decrease, but showed a sharp NAAA increase and a NAPE-PLD decrease, which were partially restored to control levels after treatment. We also characterized the immune cells of the UC mucosa infiltrate. We detected a decreased number of NAAA-positive and an increased number of FAAH-positive immune cells in active UC, which were partially restored to control levels after treatment. NAE-PPARα signaling system is impaired during active UC and 5-ASA/glucocorticoids treatment restored its normal expression. Since 5-ASA actions may work through PPARα and glucocorticoids through NAE-producing/degrading enzymes, the use of PPARα agonists or FAAH/NAAA blockers that increases endogenous PPARα ligands may yield similar therapeutics advantages.

Anticancer Properties of PPARalpha-Effects on Cellular Metabolism and Inflammation

Peroxisome proliferator-activated receptors (PPARs) have lately attracted much attention as therapeutic targets. Previously, PPAR ligands were associated with the treatment of diabetes, hyperlipidemia and cardiovascular diseases, as they modulate the expression of genes regulating glucose and lipid metabolism. Recently, PPAR ligands have been also considered as potential anticancer agents, with relatively low systemic toxicity. The emerging evidence for antiproliferative, proapoptotic, antiinflammatory and potential antimetastatic properties of PPARα ligands prompted us to discuss possible roles of PPARα in tumor suppression. PPARα activation can target cancer cells energy balance by blocking fatty acid synthesis and by promoting fatty acid β-oxidation. In the state of limited nutrient availability, frequently presents in the tumor microenvironment, PPARα cooperates with AMP-dependent protein kinase in: (i) repressing oncogenic Akt activity, (ii) inhibiting cell proliferation, and (iii) forcing glycolysis-dependent cancer cells into “metabolic catastrophe.” Other potential anticancer effects of PPARα include suppression of inflammation, and upregulation of uncoupling proteins (UCPs), which attenuates mitochondrial reactive oxygen species production and cell proliferation. In conclusion, there are strong premises that the low-toxic and well-tolerated PPAR ligands should be considered as new therapeutic agents to fight disseminating cancer, which represents the major challenge for modern medicine and basic research.

Macrophages, PPARs, and Cancer

Mononuclear phagocytes often function as control switches of the immune system, securing the balance between pro- and anti-inflammatory reactions. For this purpose and depending on the activating stimuli, these cells can develop into different subsets: proinflammatory classically activated (M1) or anti-inflammatory alternatively activated (M2) macrophages. The expression of the nuclear peroxisome proliferator-activated receptors (PPARs) is regulated by M1- or M2-inducing stimuli, and these receptors are generally considered to counteract inflammatory M1 macrophages, while actively promoting M2 activation. This is of importance in a tumor context, where M1 are important initiators of inflammation-driven cancers. As a consequence, PPAR agonists are potentially usefull for inhibiting the early phases of tumorigenesis through their antagonistic effect on M1. In more established tumors, the macrophage phenotype is more diverse, making it more difficult to predict the outcome of PPAR agonism. Overall, in our view current knowledge provides a sound basis for the clinical evaluation of PPAR ligands as chemopreventive agents in chronic inflammation-associated cancer development, while cautioning against the unthoughtful application of these agents as cancer therapeutics.

Constitutive expression of drug metabolizing enzymes and related transcription factors in cattle testis and their modulation by illicit steroids

In veterinary species, little information about extrahepatic drug metabolism is actually available. Therefore, the presence of foremost drug metabolizing enzymes (DMEs) and related transcription factors mRNAs was initially investigated in cattle testis; then, their possible modulation following the in vivo exposure to illicit growth promoters (GPs), which represent a major issue in cattle farming, was explored. All target genes were expressed in cattle testis, albeit to a lower extent compared to liver ones; furthermore, illicit protocols containing dexamethasone and 17β-oestradiol significantly up-regulated cytochrome P450 1A1, 2E1, oestrogen receptor-α and peroxisome proliferator-activated receptor-α mRNA levels. Overall, the constitutive expression of foremost DMEs and related transcription factors was demonstrated for the first time in cattle testis and illicit GPs were shown to affect pre-transcriptionally some of them, with possible consequences upon testicular xenobiotic drug metabolism.

Effects of perfluorooctane sulfonate (PFOS) exposure on markers of inflammation in female B6C3F1 mice

Perfluorooctane sulfonate (PFOS; 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluoro-1-octanesulfonic acid) has been reported to alter humoral immune functions, but inflammatory processes following PFOS exposure have not been fully characterized. Therefore, the current study, assessed TNF-α and IL-6 concentrations in serum and peritoneal lavage fluid, numbers of splenoctyes expressing intracellular TNF-α, IL-6, IL-10 or IL-1, and ex vivo TNF-α and IL-6 production by peritoneal macrophages following either in vivo or in vitro LPS exposure. Adult female B6C3F1 mice were exposed orally for 28 days to 0, 1, 3, or 300 mg PFOS/kg total administered dose [TAD] (e.g., 0, 0.0331, 0.0993 or 9.93 mg/kg/day). Body and spleen masses were significantly reduced in the highest PFOS treatment group compared to the control group, whereas liver mass was significantly increased. Serum TNF-α levels were significantly decreased following exposure to 1 mg PFOS/kg TAD as compared to controls, while serum IL-6 levels were increased. IL-6 concentrations in peritoneal lavage fluid decreased with increasing dose. PFOS treatment did not alter numbers of splenocytes expressing intracellular levels of TNF-α, IL-10 or IL-1. Numbers of splenocytes expressing intracellular levels of IL-6 were significantly decreased in the 3 mg/kg treatment as compared to controls. Overall, these data suggest that PFOS exposure can alter some inflammatory processes, which could potentially lead to misdirected inflammatory responses.

PPAR-alpha in cutaneous inflammation

Peroxisome proliferator-activated receptor (PPAR)-alpha is a fatty acid activated transcription factors that belongs to the nuclear hormone receptor family. Primarily PPAR-alpha serves as a lipid sensor. While PPAR-alpha controls enzymes from the lipid and glucose metabolism in the liver, heart and muscles, PPAR-alpha is also involved in skin homeostasis. PPAR-alpha controls keratinocyte proliferation/differentiation, contributes to wound healing and regulates skin inflammation. PPAR-alpha activation exerts anti-inflammatory effects in various skin conditions such as irritant and allergic contact dermatitis, atopic dermatitis and UV-induced erythema, rendering investigations into the functions of PPAR-alpha necessary to provide better understandings to treat many inflammatory skin disorders.

Natural peroxisome proliferator-activated receptor-alpha agonist cream demonstrates similar therapeutic response to topical steroids in atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) requires permanent skin care.

OBJECTIVE

A cream containing 2% SO (sunflower oleodistillate), with peroxisome proliferator-activated receptor-alpha (PPAR-α) agonist properties, has been compared to a topical steroid (hydrocortisone butyro-propionate 1 mg/g).

METHODS

An open, randomized study included two groups of 40 children (aged 3 months to 4 years). Group A applied the steroid and group B applied the 2% SO cream, twice a day. SCORAD (SCORing Atopic Dermatitis) was determined at D0, D7 and D21 and quality of life (QoL) at D0 and D21.

RESULTS

SCORAD was similar at D0 (37.2 versus 36.9), D7 (18.9 versus 19.2) (-49% and -48%) and D21 (11 versus 9.4) (-70% and -75%) (p < 0.01 versus D0). The Infant Dermatitis Quality of Life and Dermatitis Family Impact Questionnaire improved similarly by 65%/67% in group A and 72%/75% in group B at D21 (p < 0.01 versus D0).

CONCLUSION

A 2% SO cream has demonstrated therapeutic properties, using clinical scores and QoL, comparable to those of a topical steroid.

GW0742, a high-affinity PPAR -beta/delta agonist, inhibits acute lung injury in mice

Several lines of evidence suggest a biological role for peroxisome proliferator-activated receptor (PPAR) beta/delta in the pathogenesis of a number of diseases. The aim of this study was to investigate the effects of a high-affinity PPAR-beta/delta agonist, GW0742, in a mouse model of carrageenan (CAR)-induced pleurisy. Injection of CAR into the pleural cavity of mice elicited an acute inflammatory response characterized by accumulation of fluid containing a large number of neutrophils (polymorphonuclear leukocytes) in the pleural cavity, infiltration of polymorphonuclear leukocytes in lung tissues and subsequent lipid peroxidation, and increased production of nitrite/nitrate, TNF-alpha, and IL-1beta. Furthermore, CAR induced lung apoptosis (Bax and Bcl-2 expression), and nitrotyrosine formation was determined by immunohistochemical analysis of lung tissues. Administration of GW0742 (0.3 mg/kg, i.p. bolus) 30 min before and 30 min after a challenge with CAR caused a reduction in all the parameters of inflammation measured. Thus, based on these findings, we propose that a PPAR-beta/delta agonist such as GW0742 may be useful in the treatment of various inflammatory diseases.

Role of PPAR-delta in the development of zymosan-induced multiple organ failure: an experiment mice study

Background

Peroxisome proliferator-activated receptor (PPAR)-beta/delta is a nuclear receptor transcription factor that regulates gene expression in many important biological processes. It is expressed ubiquitously, especially white adipose tissue, heart, muscle, intestine, placenta and macrophages but many of its functions are unknown. Saturated and polyunsaturated fatty acids activate PPAR-beta/delta, but physiological ligands have not yet been identified. In the present study, we investigated the anti-inflammatory effects of PPAR-beta/delta activation, through the use of GW0742 (0,3 mg/kg 10% Dimethyl sulfoxide (DMSO) i.p), a synthetic high affinity ligand, on the development of zymosan-induced multiple organ failure (MOF).

Methods

Multiple organ failure (MOF) was induced in mice by administration of zymosan (given at 500 mg/kg, i.p. as a suspension in saline). The control groups were treated with vehicle (0.25 ml/mouse saline), while the pharmacological treatment was the administration of GW0742 (0,3 mg/kg 10% DMSO i.p. 1 h and 6 h after zymosan administration). MOF and systemic inflammation in mice was assessed 18 hours after administration of zymosan.

Results

Treatment with GW0742 caused a significant reduction of the peritoneal exudate formation and of the neutrophil infiltration caused by zymosan resulting in a reduction in myeloperoxidase activity. The PPAR-beta/delta agonist, GW0742, at the dose of 0,3 mg/kg in 10% DMSO, also attenuated the multiple organ dysfunction syndrome caused by zymosan. In pancreas, lung and gut, immunohistochemical analysis of some end points of the inflammatory response, such as inducible nitric oxide synthase (iNOS), nitrotyrosine, poly (ADP-ribose) (PAR), TNF- and IL-1as well as FasL, Bax, Bcl-2 and apoptosis, revealed positive staining in sections of tissue obtained from zymosan-injected mice. On the contrary, these parameters were markedly reduced in samples obtained from mice treated with GW0742

Conclusions

In this study, we have shown that GW0742 attenuates the degree of zymosan-induced non-septic shock in mice.

PPAR-alpha contributes to the anti-inflammatory activity of 17beta-estradiol

Because studies have shown that 17beta-estradiol (E2) produces anti-inflammatory effects after various adverse circulatory conditions, we have recently demonstrated that E2 significantly reduced the acute lung injury. Moreover, previous results suggest that peroxisome proliferator-activated receptor-alpha (PPAR-alpha), an intracellular transcription factor activated by fatty acids, plays a role in the control of inflammation. With the aim to characterize the role of PPAR-alpha in estrogen-mediated anti-inflammatory activity, we tested the efficacy of E2 in an experimental model of lung inflammation, carrageenan-induced pleurisy, comparing ovariectomized wild-type (WT) and PPAR-alpha lacking (PPAR-alphaKO) mice. Results indicate that E2-mediated anti-inflammatory activity is weakened in PPAR-alphaKO mice, compared with WT control groups. In particular, E2 was less effective in PPAR-alphaKO, compared with WT mice, in inhibition of cell migration as well as lung injury, NF-kB activation, TNF-alpha production, and inducible nitric-oxide synthase (iNOS) activation. Moreover, macrophages from PPAR-alphaKO were less susceptible to E2-induced iNOS inhibition in vitro compared with macrophages from WT mice. Moreover, the results indicate that PPAR-alpha was required for estrogen receptor up-regulation, following E2 treatment. These results show for the first time that PPAR-alpha contributes to the anti-inflammatory activity of E2.

The role of endogenous and exogenous ligands for the peroxisome proliferator-activated receptor alpha (PPAR-alpha) in the regulation of inflammation in macrophages

The aim of the present study was to evaluate the role of endogenous and exogenous peroxisome proliferator-activated receptor alpha (PPAR-alpha), a nuclear receptor, on the regulation of inflammation in macrophages. To address this question, we have stimulated peritoneal macrophages from PPAR-alpha wild-type mice and PPAR-alpha knockout mice (PPAR-alpha) with 10 microg/mL LPS and 100 U/mL IFN-gamma. We report here that the absence of a functional PPAR-alpha gene in PPAR-alpha knockout mice resulted in a significant augmentation of various inflammatory parameters in peritoneal macrophages. In particular, we have clearly demonstrated that PPAR-alpha gene deletion increases (1) the mitogen-activated protein kinase phosphorylation (extracellular signal-regulated kinase, c-Jun NH2-terminal kinase, and p38), (2) nuclear factor-kappaB activation, (3) IkappaB-alpha degradation, (4) iNOS expression and NO formation, and (5) cyclooxygenase 2 expression and prostaglandin E2 formation caused by LPS/IFN-gamma stimulation. On the contrary, the incubation of peritoneal macrophages from PPAR-alpha wild type with clofibrate (2 mM) at 2 h before the LPS and IFN-gamma stimulation significantly reduced the expression and the release of the proinflammatory mediators. To elucidate whether the protective effects of clofibrate is related to activation of the PPAR-alpha receptor, we also investigated the effect of clofibrate treatment on PPAR-alpha-deficient mice. The absence of the PPAR-alpha receptor significantly abolished the protective effect of the PPAR-alpha agonist against LPS/IFN-gamma-induced macrophage inflammation. In conclusion, our study demonstrates that the endogenous and exogenous PPAR-alpha ligands reduce the degree of macrophage inflammation caused by LPS/IFN-gamma stimulation.

Targeting PPAR receptors in the airway for the treatment of inflammatory lung disease

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. PPARgamma regulates several metabolic pathways by binding to sequence-specific PPAR response elements in the promoter region of genes involved in lipid biosynthesis and glucose metabolism. However, more recently PPARgamma, PPARalpha and PPARbeta/delta agonists have been demonstrated to exhibit anti-inflammatory and immunomodulatory properties thus opening up new avenues for research. The actions of PPARgamma and PPARalpha activation are thought to be due to their ability to down regulate pro-inflammatory gene expression and inflammatory cell functions, and as such makes them an attractive target for novel drug intervention. Interestingly, PPARbeta/delta has been shown to be involved in wound healing, angiogenesis, lipid metabolism and thrombosis. In this review we will focus on the data describing the beneficial effects of these ligands in the airway and in the pulmonary vasculature and in vivo in animal models of allergic and occupational asthma, chronic obstructive pulmonary disease and pulmonary fibrosis. A clinical trial is underway to examine the effect of rosiglitazone in asthma patients and the outcome of this trial is awaited with much anticipation. In conclusion, PPARs are novel targets for lung disease and continued work with these ligands may result in a potential new treatment for chronic inflammatory lung diseases.

PPARalpha blocks glucocorticoid receptor alpha-mediated transactivation but cooperates with the activated glucocorticoid receptor alpha for transrepression on NF-kappaB

Glucocorticoid receptor alpha (GRalpha) and peroxisome proliferator-activated receptor alpha (PPARalpha) are transcription factors with clinically important immune-modulating properties. Either receptor can inhibit cytokine gene expression, mainly through interference with nuclear factor kappaB (NF-kappaB)-driven gene expression. The present work aimed to investigate a functional cross-talk between PPARalpha- and GRalpha-mediated signaling pathways. Simultaneous activation of PPARalpha and GRalpha dose-dependently enhances transrepression of NF-kappaB-driven gene expression and additively represses cytokine production. In sharp contrast and quite unexpectedly, PPARalpha agonists inhibit the expression of classical glucocorticoid response element (GRE)-driven genes in a PPARalpha-dependent manner, as demonstrated by experiments using PPARalpha wild-type and knockout mice. The underlying mechanism for this transcriptional antagonism relies on a PPARalpha-mediated interference with the recruitment of GRalpha, and concomitantly of RNA polymerase II, to GRE-driven gene promoters. Finally, the biological relevance of this phenomenon is underscored by the observation that treatment with the PPARalpha agonist fenofibrate prevents glucocorticoid-induced hyperinsulinemia of mice fed a high-fat diet. Taken together, PPARalpha negatively interferes with GRE-mediated GRalpha activity while potentiating its antiinflammatory effects, thus providing a rationale for combination therapy in chronic inflammatory disorders.

Peroxisome proliferator-activated receptor-alpha modulates the anti-inflammatory effect of glucocorticoids in a model of inflammatory bowel disease in mice

Glucocorticoids (GCs) are effective anti-inflammatory agents widely used in therapeutic approach to treatment of inflammatory bowel disease (IBD). Previous results suggest that peroxisome proliferator-activated receptor [alpha] (PPAR-[alpha]), an intracellular transcription factor activated by fatty acids, plays a role in control of inflammation. With the aim to characterize the role of PPAR-[alpha] in GC-mediated anti-inflammatory activity, we tested the efficacy of dexamethasone (DEX), a synthetic GC specific for GR, in an experimental model of IBD induced by dinitrobenzene sulfonic acid, comparing mice lacking PPAR-[alpha] (PPAR-[alpha]KO) with wild-type (WT) mice. Results indicate that DEX-mediated anti-inflammatory activity is weakened in PPAR-[alpha]KO mice as compared with WT controls. In particular, DEX was less effective in PPAR-[alpha]KO compared with WT mice, as evaluated by inhibition of proinflammatory cytokines production, cell migration, oxidative stress, apoptosis, and colon injury. These results indicate that PPAR-[alpha] can contribute to the anti-inflammatory activity of GCs in IBD.

Pleural mesothelial cells express both BLT2 and PPARalpha and mount an integrated response to pleural leukotriene B4

Leukotriene B(4) (LTB(4)) plays a crucial role in the recruitment of neutrophils into the pleural space. We identified for the first time the mechanisms by which LTB(4) interacts with mesothelial cells and recruits neutrophils in the pleural compartment. Primary pleural mesothelial cells express both the proinflammatory receptor for LTB(4) BLT2, and the anti-inflammatory receptor for LTB(4), PPARalpha. Parapneumonic pleural effusions highly increase BLT2 expression and, via BLT2 activation, increase the adhesion between mesothelial cells and neutrophils and the expression of ICAM-1 on mesothelial cells. The block of PPARalpha further increases both cell adhesion and ICAM-1 expression. BLT2 activation promotes the activation, on mesothelial cells, of STAT-1 but not the activation of NF-kappaB transcription factor. The increase of ICAM-1 expression is achieved via increased tyrosine phosphorylation activity since herbimycin, a tyrosine kinase inhibitor, reduces and since Na orthovanadate, a tyrosine phosphatase inhibitor, further increases ICAM-1 expression. This study demonstrates that pleural mesothelial cells, expressing both proinflammatory and anti-inflammatory LTB(4) receptors, are able to mount an integrated response to LTB(4) with a prevalence of BLT2 activities in the presence of an inflammatory milieu within the pleura.

Tissue-specific glucocorticoid action: a family affair

Glucocorticoids exert a wide variety of physiological and pathological responses, most of which are mediated by the ubiquitously expressed glucocorticoid receptor (GR). The glucocorticoid response varies among individuals, as well as within tissues from the same individual, and this phenomenon can be partially explained through understanding the process of generating bioavailable ligand and the molecular heterogeneity of GR. This review focuses on the recent advances in our understanding of prereceptor ligand metabolism, GR subtypes and GR polymorphisms. Furthermore, we evaluate the impact of tissue- and individual-specific diversity in the glucocorticoid pathway on human health and disease.