Gemfibrozil ameliorates relapsing-remitting experimental autoimmune encephalomyelitis independent of peroxisome proliferator-activated receptor-alpha

Amelioration of experimental autoimmune encephalomyelitis by gemfibrozil in mice via PPARβ/δ: implications for multiple sclerosis

It is important to describe effective and non-toxic therapies for multiple sclerosis (MS), an autoimmune demyelinating disease. Experimental autoimmune encephalomyelitis (EAE) is an immune-mediated inflammatory disease that serves as a model for MS. Earlier we and others have shown that, gemfibrozil, a lipid-lowering drug, exhibits therapeutic efficacy in EAE. However, the underlying mechanism was poorly understood. Although gemfibrozil is a known ligand of peroxisome proliferator-activated receptor α (PPARα), here, we established that oral administration of gemfibrozil preserved the integrity of blood-brain barrier (BBB) and blood-spinal cord barrier (BSB), decreased the infiltration of mononuclear cells into the CNS and inhibited the disease process of EAE in both wild type and PPARα-/- mice. On the other hand, oral gemfibrozil was found ineffective in maintaining the integrity of BBB/BSB, suppressing inflammatory infiltration and reducing the disease process of EAE in mice lacking PPARβ (formerly PPARδ), indicating an important role of PPARβ/δ, but not PPARα, in gemfibrozil-mediated preservation of BBB/BSB and protection of EAE. Regulatory T cells (Tregs) play a critical role in the disease process of EAE/MS and we also demonstrated that oral gemfibrozil protected Tregs in WT and PPARα-/- EAE mice, but not PPARβ-/- EAE mice. Taken together, our findings suggest that gemfibrozil, a known ligand of PPARα, preserves the integrity of BBB/BSB, enriches Tregs, and inhibits the disease process of EAE via PPARβ, but not PPARα.

Neuroprotective effects of gemfibrozil in neurological disorders: Focus on inflammation and molecular mechanisms

BACKGROUND

Gemfibrozil (Gem) is a drug that has been shown to activate PPAR-α, a nuclear receptor that plays a key role in regulating lipid metabolism. Gem is used to lower the levels of triglycerides and reduce the risk of coronary heart disease in patients. Experimental studies in vitro and in vivo have shown that Gem can prevent or slow the progression of neurological disorders (NDs), including cerebral ischemia (CI), Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Neuroinflammation is known to play a significant role in these disorders.

METHOD

The literature review for this study was conducted by searching Scopus, Science Direct, PubMed, and Google Scholar databases.

RESULT

The results of this study show that Gem has neuroprotective effects through several cellular and molecular mechanisms such as: (1) Gem has the ability to upregulate pro-survival factors (PGC-1α and TFAM), promoting the survival and function of mitochondria in the brain, (2) Gem strongly inhibits the activation of NF-κB, AP-1, and C/EBPβ in cytokine-stimulated astroglial cells, which are known to increase the expression of iNOS and the production of NO in response to proinflammatory cytokines, (3) Gem protects dopamine neurons in the MPTP mouse model of PD by increasing the expression of PPARα, which in turn stimulates the production of GDNF in astrocytes, (4) Gem reduces amyloid plaque pathology, reduces the activity of glial cells, and improves memory, (5) Gem increases myelin genes expression (MBP and CNPase) via PPAR-β, and (6) Gem increases hippocampal BDNF to counteract depression.

CONCLUSION

According to the study, Gem was investigated for its potential therapeutic effect in NDs. Further research is needed to fully understand the therapeutic potential of Gem in NDs.

Role of fenofibrate in multiple sclerosis

Multiple sclerosis (MS) is the most frequent inflammatory and demyelinating disease of the central nervous system (CNS). The underlying pathophysiology of MS is the destruction of myelin sheath by immune cells. The formation of myelin plaques, inflammation, and injury of neuronal myelin sheath characterizes its neuropathology. MS plaques are multiple focal regions of demyelination disseminated in the brain's white matter, spinal cords, deep grey matter, and cerebral cortex. Fenofibrate is a peroxisome proliferative activated receptor alpha (PPAR-α) that attenuates the inflammatory reactions in MS. Fenofibrate inhibits differentiation of Th17 by inhibiting the expression of pro-inflammatory signaling. According to these findings, this review intended to illuminate the mechanistic immunoinflammatory role of fenofibrate in mitigating MS neuropathology. In conclusion, fenofibrate can attenuate MS neuropathology by modulating different pathways, including oxidative stress, autophagy, mitochondrial dysfunction, inflammatory-signaling pathways, and neuroinflammation.

Induction of IL-2 by interleukin-12 p40 homodimer and IL-12, but not IL-23, in microglia and macrophages: Implications for multiple sclerosis

The level of IL-2 increases markedly in serum and central nervous system (CNS) of patients with multiple sclerosis (MS) and animals with experimental allergic encephalomyelitis (EAE). However, mechanisms by which IL-2 is induced under autoimmune demyelinating conditions are poorly understood. The present study underlines the importance of IL-12p40 homodimer (p402), the so-called biologically inactive molecule, in inducing the expression of IL-2 in mouse BV-2 microglial cells, primary mouse and human microglia, mouse peritoneal macrophages, RAW264.7 macrophages, and T cells. Interestingly, we found that p402 and IL-12p70 (IL-12), but not IL-23, dose-dependently induced the production of IL-2 and the expression of IL-2 mRNA in microglial cells. Similarly, p402 also induced the activation of IL-2 promoter in microglial cells and RAW264.7 cells. Among various stimuli tested, p402 was the most potent stimulus followed by IFN-γ, bacterial lipopolysaccharide, HIV-1 gp120, and IL-12 in inducing the activation of IL-2 promoter in microglial cells. Moreover, p402, but not IL-23, increased NFATc2 mRNA expression and the transcriptional activity of NFAT. Furthermore, induction of IL-2 mRNA expression by over-expression of p40, but not by p19, cDNA indicated that p40, but not p19, is responsible for the induction of IL-2 mRNA in microglia. Finally, by using primary microglia from IL to 12 receptor β1 deficient (IL-12Rβ1-/-) and IL-12 receptor β2 deficient (IL-12Rβ2-/-) mice, we demonstrate that p402 induces the expression of IL-2 via IL-12Rβ1, but not IL-12Rβ2. In experimental autoimmune encephalomyelitis, an animal model of MS, neutralization of p402 by mAb a3-1d led to decrease in clinical symptoms and reduction in IL-2 in T cells and microglia. These results delineate a new biological function of p402, which is missing in the so-called autoimmune cytokine IL-23, and raise the possibility of controlling increased IL-2 and the disease process of MS via neutralization of p402.

Arachidonic acid-derived lipid mediators in multiple sclerosis pathogenesis: fueling or dampening disease progression?

BACKGROUND

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS), characterized by neuroinflammation, demyelination, and neurodegeneration. Considering the increasing prevalence among young adults worldwide and the disabling phenotype of the disease, a deeper understanding of the complexity of the disease pathogenesis is needed to ultimately improve diagnosis and personalize treatment opportunities. Recent findings suggest that bioactive lipid mediators (LM) derived from ω-3/-6 polyunsaturated fatty acids (PUFA), also termed eicosanoids, may contribute to MS pathogenesis. For example, disturbances in LM profiles and especially those derived from the ω-6 PUFA arachidonic acid (AA) have been reported in people with MS (PwMS), where they may contribute to the chronicity of neuroinflammatory processes. Moreover, we have previously shown that certain AA-derived LMs also associated with neurodegenerative processes in PwMS, suggesting that AA-derived LMs are involved in more pathological events than solely neuroinflammation. Yet, to date, a comprehensive overview of the contribution of these LMs to MS-associated pathological processes remains elusive.

MAIN BODY

This review summarizes and critically evaluates the current body of literature on the eicosanoid biosynthetic pathway and its contribution to key pathological hallmarks of MS during different disease stages. Various parts of the eicosanoid pathway are highlighted, namely, the prostanoid, leukotriene, and hydroxyeicosatetraenoic acids (HETEs) biochemical routes that include specific enzymes of the cyclooxygenases (COXs) and lipoxygenases (LOX) families. In addition, cellular sources of LMs and their potential target cells based on receptor expression profiles will be discussed in the context of MS. Finally, we propose novel therapeutic approaches based on eicosanoid pathway and/or receptor modulation to ultimately target chronic neuroinflammation, demyelination and neurodegeneration in MS.

SHORT CONCLUSION

The eicosanoid pathway is intrinsically linked to specific aspects of MS pathogenesis. Therefore, we propose that novel intervention strategies, with the aim of accurately modulating the eicosanoid pathway towards the biosynthesis of beneficial LMs, can potentially contribute to more patient- and MS subtype-specific treatment opportunities to combat MS.

Activation of PPARα Exhibits Therapeutic Efficacy in a Mouse Model of Juvenile Neuronal Ceroid Lipofuscinosis

Juvenile neuronal ceroid lipofuscinosis (JNCL) is a fatal inherited neurodegenerative disease of children that occurs because of defective function of the lysosomal membrane glycoprotein CLN3. JNCL features glial activation and accumulation of autofluorescent storage material containing subunit c of mitochondrial ATP synthase (SCMAS), ultimately resulting into neuronal loss. Until now, no effective therapy is available for JNCL. This study underlines the possible therapeutic importance of gemfibrozil, an activator of peroxisome proliferator-activated receptor α (PPARα) and a lipid-lowering drug approved by the Food and Drug Administration in an animal model of JNCL. Oral gemfibrozil treatment reduced microglial and astroglial activation, attenuated neuroinflammation, restored the level of transcription factor EB (TFEB; the master regulator of lysosomal biogenesis), and decreased the accumulation of storage material SCMAS in somatosensory barrel field (SBF) cortex of Cln3Δex7/8 (Cln3ΔJNCL) mice of both sexes. Accordingly, gemfibrozil treatment also improved locomotor activities of Cln3ΔJNCL mice. While investigating the mechanism, we found marked loss of PPARα in the SBF cortex of Cln3ΔJNCL mice, which increased after gemfibrozil treatment. Oral gemfibrozil also stimulated the recruitment of PPARα to the Tfeb gene promoter in vivo in the SBF cortex of Cln3ΔJNCL mice, indicating increased transcription of Tfeb in the CNS by gemfibrozil treatment via PPARα. Moreover, disease pathologies aggravated in Cln3ΔJNCL mice lacking PPARα (Cln3ΔJNCLΔPPARα) and gemfibrozil remained unable to decrease SCMAS accumulation, reduce glial activation, and improve locomotor performance of Cln3ΔJNCLΔPPARα mice. These results suggest that activation of PPARα may be beneficial for JNCL and that gemfibrozil may be repurposed for the treatment of this incurable disease.SIGNIFICANCE STATEMENT Despite intense investigations, no effective therapy is available for JNCL, an incurable inherited lysosomal storage disorder. Here, we delineate that oral administration of gemfibrozil, a lipid-lowering drug, decreases glial inflammation, normalizes and/or upregulates TFEB, and reduces accumulation of autofluorescent storage material in SBF cortex to improve locomotor activities in Cln3Δex7/8 (Cln3ΔJNCL) mice. Aggravation of disease pathology in Cln3ΔJNCL mice lacking PPARα (Cln3ΔJNCLΔPPARα) and inability of gemfibrozil to decrease SCMAS accumulation, reduce glial activation, and improve locomotor performance of Cln3ΔJNCLΔPPARα mice delineates an important role of PPARα in this process. These studies highlight a new property of gemfibrozil and indicate its possible therapeutic use in JNCL patients.

Glyceryl tribenzoate: A food additive with unique properties to be a substitute for cinnamon

Cinnamon is a regularly used natural seasoning and flavoring material throughout the world for eras. Recent laboratory studies have demonstrated that oral cinnamon may be beneficial for different neuroinflammatory and neurodegenerative disorders such as multiple sclerosis (MS), Parkinson's disease (PD), Alzheimer's disease (AD), and Lewy body diseases (LBD). However, cinnamon's certain limitations (e.g. unavailability of true Ceylon cinnamon throughout the world, impurities in ground cinnamon, etc.) have initiated an interest among researchers to find an alternate of cinnamon that can potentially deliver the same efficacy in the diseases mentioned above. Glyceryl tribenzoate (GTB) is a U.S. Food and Drug Administration (FDA)-approved flavoring ingredient that is used in food and food packaging industries. It has been found that similar to cinnamon, oral GTB is capable of upregulating regulatory T cells and suppressing the autoimmune disease process of experimental autoimmune encephalomyelitis, an animal model of MS. Moreover, both GTB and cinnamon metabolite sodium benzoate (NaB) have the potency to attenuate neurodegenerative pathology in a mouse model of Huntington disease (HD). Here, we have also demonstrated anti-inflammatory property of GTB in astrocytes and macrophages, a property that is also seen with cinnamon and its metabolite sodium benzoate (NaB). Therefore, here, we have made a sincere attempt to discuss the similarities and dissimilarities between cinnamon and GTB with a focus whether GTB has the potential to be considered as a substitute of cinnamon for neuroinflammatory and neurodegenerative disorders.

Oleamide, a Sleep-Inducing Supplement, Upregulates Doublecortin in Hippocampal Progenitor Cells via PPARα

BACKGROUND

Doublecortin (DCX), a microtubule associated protein, has emerged as a central biomarker of hippocampal neurogenesis. However, molecular mechanisms by which DCX is regulated are poorly understood.

OBJECTIVE

Since sleep is involved with the acquisition of memory and oleamide or 9-Octadecenamide (OCT) is a sleep-inducing supplement in human, we examined whether OCT could upregulate DCX in hippocampal progenitor cells (HPCs).

METHODS

We employed real-time PCR, western blot, immunostaining, chromatin immunoprecipitation, lentiviral transduction in HPCs, and the calcium influx assay.

RESULTS

OCT directly upregulated the transcription of Dcx in HPCs via activation of peroxisome proliferator-activated receptor α (PPARα), a lipid-lowering transcription factor. We observed that, HPCs of Ppara-null mice displayed significant impairment in DCX expression and neuronal differentiation as compared to that of wild-type mice. Interestingly, treatment with OCT stimulated the differentiation process of HPCs in wild-type, but not Ppara-null mice. Reconstruction of PPARα in mouse Ppara-null HPCs restored the expression of DCX, which was further stimulated with OCT treatment. In contrast, a dominant-negative mutant of PPARα significantly attenuated the stimulatory effect of OCT on DCX expression and suppressed neuronal differentiation of human neural progenitor cells. Furthermore, RNA microarray, STRING, chromatin immunoprecipitation, site-directed mutagenesis, and promoter reporter assay have identified DCX as a new target of PPARα.

CONCLUSION

These results indicate that OCT, a sleep supplement, directly controls the expression of DCX and suggest that OCT may be repurposed for stimulating the hippocampal neurogenesis.

Activation of PPARα enhances astroglial uptake and degradation of β-amyloid

[Figure: see text].

Gemfibrozil Protects Dopaminergic Neurons in a Mouse Model of Parkinson's Disease via PPARα-Dependent Astrocytic GDNF Pathway

Parkinson's disease (PD) is the most common neurodegenerative movement disorder in humans. Despite intense investigations, effective therapies are not yet available to halt the progression of PD. Gemfibrozil, a Food and Drug Administration-approved lipid-lowering drug, is known to decrease the risk of coronary heart disease by increasing the level of high-density lipoprotein cholesterol and decreasing the level of low-density lipoprotein cholesterol. This study underlines the importance of gemfibrozil in protecting dopaminergic neurons in an animal model of PD. Oral administration of the human equivalent dose of gemfibrozil protected tyrosine hydroxylase (TH)-positive dopaminergic neurons in the substantia nigra pars compacta and TH fibers in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-insulted mice of both sexes. Accordingly, gemfibrozil also normalized striatal neurotransmitters and improved locomotor activities in MPTP-intoxicated mice. Gemfibrozil-mediated protection of the nigrostriatal and locomotor activities in WT but not PPARα^-/- mice from MPTP intoxication suggests that gemfibrozil needs the involvement of peroxisome proliferator-activated receptor α (PPARα) in protecting dopaminergic neurons. While investigating further mechanisms, we found that gemfibrozil stimulated the transcription of glial-derived neurotrophic factor (GDNF) gene in astrocytes via PPARα and that gemfibrozil protected nigral neurons, normalized striatal fibers and neurotransmitters, and improved locomotor activities in MPTP-intoxicated Gfaf ^cre mice, but not Gdnf ^Δastro mice lacking GDNF in astrocytes. These findings highlight the importance of the PPARα-dependent astroglial GDNF pathway in gemfibrozil-mediated protection of dopaminergic neurons in an animal model of PD and suggest the possible therapeutic use of gemfibrozil in PD patients.SIGNIFICANCE STATEMENT Increasing the level of glial cell-derived neurotrophic factor (GDNF) in the brain is important for the protection of dopamine neurons in Parkinson's disease (PD). Although gene manipulation and GDNF protein infusion into the brain are available options, it seems from the therapeutic angle that the best option would be to stimulate/induce the production of GDNF in vivo in the brain of PD patients. Here, we delineate that gemfibrozil, a lipid-lowering drug, stimulates GDNF in astrocytes via peroxisome proliferator-activated receptor α (PPARα). Moreover, gemfibrozil protected nigral neurons, normalized striatal fibers and neurotransmitters, and improved locomotor activities from MPTP toxicity via the PPARα-dependent astroglial GDNF pathway. These studies highlight a new property of gemfibrozil and suggest its possible therapeutic use in PD patients.

Comparing the effects of two different strains of mycobacteria, Mycobacterium vaccae NCTC 11659 and M. vaccae ATCC 15483, on stress-resilient behaviors and lipid-immune signaling in rats

Stress-related disorders, such as posttraumatic stress disorder (PTSD), are highly prevalent and often difficult to treat. In rodents, stress-related, anxiety-like defensive behavioral responses may be characterized by social avoidance, exacerbated inflammation, and altered metabolic states. We have previously shown that, in rodents, subcutaneous injections of a heat-killed preparation of the soil-derived bacterium Mycobacterium vaccae NCTC 11659 promotes stress resilience effects that are associated with immunoregulatory signaling in the periphery and the brain. In the current study, we sought to determine whether treatment with a heat-killed preparation of the closely related M. vaccae type strain, M. vaccae ATCC 15483, would also promote stress-resilience in adult male rats, likely due to biologically similar characteristics of the two strains. Here we show that immunization with either M. vaccae NCTC 11659 or M. vaccae ATCC 15483 prevents stress-induced increases in hippocampal interleukin 6 mRNA expression, consistent with previous studies showing that M. vaccae NCTC 11659 prevents stress-induced increases in peripheral IL-6 secretion, and prevents exaggeration of anxiety-like defensive behavioral responses assessed 24 h after exposure to inescapable tail shock stress (IS) in adult male rats. Analysis of mRNA expression, protein abundance, and flow cytometry data demonstrate overlapping but also unique effects of treatment with the two M. vaccae strains on immunological and metabolic signaling in the host. These data support the hypothesis that treatment with different M. vaccae strains may immunize the host against stress-induced dysregulation of physiology and behavior.

Can cinnamon spice down autoimmune diseases?

Autoimmune diseases are one of the dreadful group of human diseases that have always been of keen interest to researchers. Due to complex and broad-spectrum nature, scientists are not yet able to pinpoint the pathogenesis of and delineate effective therapy against this group of diseases. However, it is becoming clear that a decrease in number and function of T regulatory cells (Treg), an increase in autoreactive Th1/Th17 cells and associated immunomodulation and inflammation participate in the pathogenesis of many autoimmune diseases. Cinnamon (Cinnamonum verum or Cinnamonum cassia) is a widely used natural spice and flavoring ingredient and its metabolite sodium benzoate (NaB) is a food-additive and FDA-approved drug against nonketotic hyperglycinemia (NKH) and urea cycle disorders (UCD). Recent studies indicate that cinnamon either in powder or extract form and NaB are capable of modulating different autoimmune pathways as well as protecting animals from different autoimmune disorders. Here, we have made an honest attempt to delineate such pieces of evidence with available anti-autoimmune mechanisms and analyze whether cinnamon supplements could be used to control the fury of autoimmune disorders.

Metformin as a Potential Agent in the Treatment of Multiple Sclerosis

Metformin, a synthetic derivative of guanidine, is commonly used as an oral antidiabetic agent and is considered a multi-vector application agent in the treatment of other inflammatory diseases. Recent studies have confirmed the beneficial effect of metformin on immune cells, with special emphasis on immunological mechanisms. Multiple Sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) characterized by various clinical courses. Although the pathophysiology of MS remains unknown, it is most likely a combination of disturbances of the immune system and biochemical pathways with a disruption of blood-brain barrier (BBB), and it is strictly related to injury of intracerebral blood vessels. Metformin has properties which are greatly desirable for MS therapy, including antioxidant, anti-inflammatory or antiplatelet functions. The latest reports relating to the cardiovascular disease confirm an increased risk of ischemic events in MS patients, which are directly associated with a coagulation cascade and an elevated pro-thrombotic platelet function. Hence, this review examines the potential favourable effects of metformin in the course of MS, its role in preventing inflammation and endothelial dysfunction, as well as its potential antiplatelet role.

Functional analysis of Epinephelus coioides peroxisome proliferative-activated receptor α (PPARα): Involvement in response to viral infection

Peroxisome proliferative-activated receptor α (PPARα) belongs to the superfamily of nuclear receptors (NR). Studies have demonstrated that PPARα functions in energy metabolism, hepatic function, immune response, cell cycle, and apoptosis. In teleost fish, few studies have investigated the role of PPARα in the immune response. In this study, the grouper PPARα gene (EcPPARα) was investigated for its role in viral infection. The open reading frame of EcPPARα encoded a protein of 469 amino acids and contained an N-terminal domain (NTD), a DNA-binding domain (DBD), a hinge region, and a C-terminal ligand-binding domain (LBD). Phylogenetic analysis revealed that EcPPARα was most closely related to homologous genes in Sander lucioperca and Perca flavescens. Upon challenge with SGIV (Singapore grouper iridovirus) and RGNNV (Red-spotted grouper nervous necrosis virus), EcPPARα expression levels were significantly upregulated in different tissues. Subcellular localization analysis showed that the EcPPARα protein localized throughout the cytoplasm and nucleus with diffuse intracellular expression patterns, which is consistent with the localization pattern of mammalian PPARs. Based on morphological observation of cytopathic effect (CPEs), viral gene expression mRNAs, and virus titer assays, the results presented here showed that an overexpression of EcPPARα promoted SGIV production in grouper spleen cells. Overexpression of EcPPARα significantly inhibited the expression of several cytokines, including interferon-related genes (IFN-γ, ISG15, MXI, MXII, MAVS and MDA5), inflammatory cytokines (IL-1β, IL-6, IL-8, TNF-α) and Toll like receptor adaptors (TRAF6 and MyD88). Luciferase activity of IFN-α, IFN-γ, ISRE and NF-κB promoters was also significantly decreased in EcPPARα overexpression cells. Due to these detected interferon-related genes and inflammatory cytokines play important antiviral effect against SGIV in grouper, we speculated that the promotion effect of EcPPARα on SGIV replication may be caused by down-regulation of interferon and inflammatory response. In addition, through apoptotic body observation, capspase-3 activity detection, and flow cytometry analysis, it was found that overexpression of EcPPARα promoted SGIV-induced apoptosis in fathead minnow (FHM) cells. These data may increase an understanding of the role of PPARα in fish antiviral immune responses and apoptosis.

Autophagy augmentation alleviates cigarette smoke-induced CFTR-dysfunction, ceramide-accumulation and COPD-emphysema pathogenesis

In this study, we aimed to investigate precise mechanism(s) of sphingolipid-imbalance and resulting ceramide-accumulation in COPD-emphysema. Where, human and murine emphysema lung tissues or human bronchial epithelial cells (Beas2b) were used for experimental analysis. We found that lungs of smokers and COPD-subjects with increasing emphysema severity demonstrate sphingolipid-imbalance, resulting in significant ceramide-accumulation and increased ceramide/sphingosine ratio, as compared to non-emphysema/non-smoker controls. Next, we found a substantial increase in emphysema chronicity-related ceramide-accumulation in murine (C57BL/6) lungs, while sphingosine levels only slightly increased. In accordance, the expression of the acid ceramidase decreased after CS-exposure. Moreover, CS-induced (sub-chronic) ceramide-accumulation was significantly (p < 0.05) reduced by treatment with TFEB/autophagy-inducing drug, gemfibrozil (GEM), suggesting that autophagy regulates CS-induced ceramide-accumulation. Next, we validated experimentally that autophagy/lipophagy-induction using an anti-oxidant, cysteamine, significantly (p < 0.05) reduces CS-extract (CSE)-mediated intracellular-ceramide-accumulation in p62 + aggresome-bodies. In addition to intracellular-accumulation, we found that CSE also induces membrane-ceramide-accumulation by ROS-dependent acid-sphingomyelinase (ASM) activation and plasma-membrane translocation, which was significantly controlled (p < 0.05) by cysteamine (an anti-oxidant) and amitriptyline (AMT, an inhibitor of ASM). Cysteamine-mediated and CSE-induced membrane-ceramide regulation was nullified by CFTR-inhibitor-172, demonstrating that CFTR controls redox impaired-autophagy dependent membrane-ceramide accumulation. In summary, our data shows that CS-mediated autophagy/lipophagy-dysfunction results in intracellular-ceramide-accumulation, while acquired CFTR-dysfunction-induced ASM causes membrane ceramide-accumulation. Thus, CS-exposure alters the sphingolipid-rheostat leading to the increased membrane- and intracellular- ceramide-accumulation inducing COPD-emphysema pathogenesis that is alleviated by treatment with cysteamine, a potent anti-oxidant with CFTR/autophagy-augmenting properties.

Exploiting the Therapeutic Potential of Endogenous Immunomodulatory Systems in Multiple Sclerosis-Special Focus on the Peroxisome Proliferator-Activated Receptors (PPARs) and the Kynurenines

Multiple sclerosis (MS) is a progressive neurodegenerative disease, characterized by autoimmune central nervous system (CNS) demyelination attributable to a disturbed balance between encephalitic T helper 1 (Th1) and T helper 17 (Th17) and immunomodulatory regulatory T cell (Treg) and T helper 2 (Th2) cells, and an alternatively activated macrophage (M2) excess. Endogenous molecular systems regulating these inflammatory processes have recently been investigated to identify molecules that can potentially influence the course of the disease. These include the peroxisome proliferator-activated receptors (PPARs), PPARγ coactivator-1alpha (PGC-1α), and kynurenine pathway metabolites. Although all PPARs ameliorate experimental autoimmune encephalomyelitis (EAE), recent evidence suggests that PPARα, PPARβ/δ agonists have less pronounced immunomodulatory effects and, along with PGC-1α, are not biomarkers of neuroinflammation in contrast to PPARγ. Small clinical trials with PPARγ agonists have been published with positive results. Proposed as immunomodulatory and neuroprotective, the therapeutic use of PGC-1α activation needs to be assessed in EAE/MS. The activation of indolamine 2,3-dioxygenase (IDO), the rate-limiting step of the kynurenine pathway of tryptophan (Trp) metabolism, plays crucial immunomodulatory roles. Indeed, Trp metabolites have therapeutic relevance in EAE and drugs with structural analogy to kynurenines, such as teriflunomide, are already approved for MS. Further studies are required to gain deeper knowledge of such endogenous immunomodulatory pathways with potential therapeutic implications in MS.

Oleoylethanolamide treatment reduces neurobehavioral deficits and brain pathology in a mouse model of Gulf War Illness

There are nearly 250,000 Gulf War (GW) veterans who suffer from Gulf War Illness (GWI), a multi-symptom condition that remains untreatable. The main objective was to determine if targeting peroxisomal function could be of therapeutic value in GWI. We performed a pilot study that showed accumulation of very long chain fatty acids (VLCFA), which are metabolized in peroxisomes, in plasma from veterans with GWI. We then examined if targeting peroxisomal β-oxidation with oleoylethanolamide (OEA) restores these lipids to the normal levels and mitigates neuroinflammation and neurobehavioral deficits in a well-established mouse model of GWI. In GWI mice, treatment with OEA corresponded with cognitive benefits and reduced fatigue and disinhibition-like behavior in GWI mice. Biochemical and molecular analysis of the brain tissue showed reduced astroglia and microglia staining, decreased levels of chemokines and cytokines, and decreased NFκB phosphorylation. Treatment with OEA reduced accumulation of peroxisome specific VLCFA in the brains of GWI mice. These studies further support the translational value of targeting peroxisomes. We expect that OEA may be a potential therapy for treating neurobehavioral symptoms and the underlying lipid dysfunction and neuroinflammation associated with GWI. Oleoylethanolamide is available as a dietary supplement, making it appealing for human translational studies.

Protective Effect of Gemfibrozil on Hepatotoxicity Induced by Acetaminophen in Mice: the Importance of Oxidative Stress Suppression

Purpose: Gemfibrozil (GEM) apart from agonist activity at peroxisome proliferator-activated receptor-alpha (PPAR-α) has antioxidant and anti-inflammatory properties. Accordingly, the present study was designed to investigate the protective effect of GEM on acute liver toxicity induced by acetaminophen (APAP) in mice.

Methods: In this study, mice divided in seven groups include, control group, APAP group, GEM group, three APAP groups pretreated with GEM at the doses of 25, 50 and 100 mg/kg respectively and APAP group pretreated with N-Acetyl cysteine. GEM, NAC or vehicle were administered for 10 days. In last day, GEM and NAC were gavaged 1 h before and 1 h after APAP injection. Twenty four hours after APAP, mice were sacrificed. Serum parameters include alanine aminotransferase (ALT), aspartate aminotransferase (AST) and liver tissue markers including catalase enzyme activity, reactive oxygen species (ROS), malondialdehyde and reduced glutathione (GSH) levels determined and histopathological parameters measured.

Results: GEM led to significant decrease in serum ALT and AST activities and increase in catalase activity and hepatic GSH level and reduces malondialdehyde and ROS levels in the liver tissue. In confirmation, histopathological findings revealed that GEM decrease degeneration, vacuolation and necrosis of hepatocytes and infiltration of inflammatory cells.

Conclusion: Present data demonstrated that GEM has antioxidant properties and can protect the liver from APAP toxicity, just in the same pathway that toxicity occurs by toxic ROS and that GEM may be an alternative therapeutic agent to NAC in APAP toxicity.

Master Autophagy Regulator Transcription Factor EB Regulates Cigarette Smoke-Induced Autophagy Impairment and Chronic Obstructive Pulmonary Disease-Emphysema Pathogenesis

AIMS

Recent studies have shown that cigarette smoke (CS)-induced oxidative stress impairs autophagy, resulting in aggresome-formation that correlates with severity of chronic obstructive pulmonary disease (COPD)-emphysema, although the specific step in autophagy pathway that is impaired is unknown. Hence, in this study, we aimed to evaluate the role of master autophagy transcription factor EB (TFEB) in CS-induced COPD-emphysema pathogenesis.

RESULTS

We first observed that TFEB accumulates in perinuclear spaces as aggresome-bodies in COPD lung tissues of tobacco smokers and severe emphysema subjects, compared with non-emphysema or nonsmoker controls. Next, Beas2b cells and C57BL/6 mice were exposed to either cigarette smoke extract (CSE) or subchronic-CS (sc-CS), followed by treatment with potent TFEB-inducing drug, gemfibrozil (GEM, or fisetin as an alternate), to experimentally verify the role of TFEB in COPD. Our in vitro results indicate that GEM/fisetin-mediated TFEB induction significantly (p < 0.05) decreases CSE-induced autophagy-impairment (Ub/LC3B reporter and autophagy flux assay) and resulting aggresome-formation (Ub/p62 coexpression/accumulation; immunoblotting and staining) by controlling reactive oxygen species (ROS) activity. Intriguingly, we observed that CS induces TFEB accumulation in the insoluble protein fractions of Beas2b cells, which shows a partial rescue with GEM treatment. Moreover, TFEB knockdown induces oxidative stress, autophagy-impairment, and senescence, which can all be mitigated by GEM-mediated TFEB induction. Finally, in vivo studies were used to verify that CS-induced autophagy-impairment (increased Ub, p62, and valosin-containing protein in the insoluble protein fractions of lung/cell lysates), inflammation (interleukin-6 [IL-6] levels in bronchoalveolar lavage fluid and iNOS expression in lung sections), apoptosis (caspase-3/7), and resulting emphysema (hematoxylin and eosin [H&E]) can be controlled by GEM-mediated TFEB induction (p < 0.05).

INNOVATION

CS exposure impairs autophagy in COPD-emphysema by inducing perinuclear localization of master autophagy regulator, TFEB, to aggresome-bodies.

CONCLUSION

TFEB-inducing drug(s) can control CS-induced TFEB/autophagy-impairment and COPD-emphysema pathogenesis. Antioxid. Redox Signal. 27, 150-167.

Unlike PPARgamma, neither other PPARs nor PGC-1alpha is elevated in the cerebrospinal fluid of patients with multiple sclerosis

Corroborating with prior experimental findings, we recently reported the pronounced elevation of peroxisome proliferator-activated receptor gamma (PPARγ) protein concentration in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS), in association with neuroinflammatory markers and clinical severity. Based on subsequent reports on the possible involvement of other PPARs and PPARγ coactivator-1alpha (PGC-1α) in neuroinflammation in MS, we analyzed the protein levels of PPARα, PPARβ/δ, and PGC-1α in a subset of CSF samples from the same cohort of relapsing-remitting MS patients. Unlike PPARγ, none of these proteins were found elevated in MS patients (n=25) compared to non-inflammatory controls (n=16), with the levels of PPARα and PPARβ/δ found generally below the limit of detection, and that of PGC-1α being detectable but comparable in both groups. The clinical and laboratory associations previously reported with PPARγ were however significant even in this smaller subset. The potential underlying causes of these differential alterations are discussed. The findings suggest that despite their proposed involvement in the regulation of inflammatory processes in MS, PPARα, PPARβ/δ, and PGC-1α proteins are not potential biomarkers of neuroinflammation in MS, and indicate a preferential role of PPARγ in the endogenous regulation of autoimmune response in the human CNS within its receptor family.

Gemfibrozil, food and drug administration-approved lipid-lowering drug, increases longevity in mouse model of late infantile neuronal ceroid lipofuscinosis

Late Infantile Neuronal Ceroid Lipofuscinosis (LINCL) is a rare neurodegenerative disease caused by mutations in the Cln2 gene that leads to deficiency or loss of function of the tripeptidyl peptidase 1 (TPP1) enzyme. TPP1 deficiency is known to cause the accumulation of autofluoroscent lipid-protein pigments in brain. Similar to other neurodegenerative disorders, LINCL is also associated with neuroinflammation and neuronal damage. Despite investigations, no effective therapy is currently available for LINCL. Therefore, we administered gemfibrozil (gem), an food and drug administration (FDA)-approved lipid-lowering drug, which has been shown to stimulate lysosomal biogenesis and induce anti-inflammation, orally, at a dose of 7.5 mg/kg body wt/day to Cln2^(-/-) mice. We observed that gem-fed Cln2^(-/-) mice lived longer by more than 10 weeks and had better motor activity compared to vehicle (0.1% Methyl cellulose) treatment. Gem treatment lowered the burden of storage materials, increased anti-inflammatory factors like SOCS3 and IL-1Ra, up-regulated anti-apoptotic molecule like phospho-Bad, and reduced neuronal apoptosis in the brain of Cln2^(-/-) mice. Collectively, this study reinforces a neuroprotective role of gem that may be of therapeutic interest in improving the quality of life in LINCL patients.

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.

Antigen presentation for priming T cells in central system

Generation of myelin antigen-specific T cells is a major event in neuroimmune responses that causes demyelination. The antigen-priming of T cells and its location is important in chronic and acute inflammation. In autoimmune multiple sclerosis, the effector T cells are considered to generate in periphery. However, the reasons for chronic relapsing-remitting events are obscure. Considering mechanisms, a feasible aim of research is to investigate the role of antigen-primed T cells in lupus cerebritis. Last thirty years of investigations emphasize the relevance of microglia and infiltrated dendritic cells/macrophages as antigen presenting cells in the central nervous system. The recent approach towards circulating B-lymphocytes is an important area in the context. Here, we analyze the existing findings on antigen presentation in the central nervous system. The aim is to visualize signaling events of myelin antigen presentation to T cells and lead to the strategy of future goals on immunotherapy research.

Neutralization of RANTES and Eotaxin Prevents the Loss of Dopaminergic Neurons in a Mouse Model of Parkinson Disease

Parkinson disease (PD) is second only to Alzheimer disease as the most common human neurodegenerative disorder. Despite intense investigation, no interdictive therapy is available for PD. Recent studies indicate that both innate and adaptive immune processes are active in PD. Accordingly, we found a rapid increase in RANTES (regulated on activation normal T cell expressed and secreted) and eotaxin, chemokines that are involved in T cell trafficking, in vivo in the substantia nigra pars compacta and the serum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. RANTES and eotaxin were also up-regulated in the substantia nigra pars compacta of post-mortem PD brains as compared with age-matched controls. Therefore, we investigated whether neutralization of RANTES and eotaxin could protect against nigrostriatal degeneration in MPTP-intoxicated mice. Interestingly, after peripheral administration, functional blocking antibodies against RANTES and eotaxin reduced the infiltration of CD4(+) and CD8(+) T cells into the nigra, attenuated nigral expression of proinflammatory molecules, and suppressed nigral activation of glial cells. These findings paralleled dopaminergic neuronal protection, normalized striatal neurotransmitters, and improved motor functions in MPTP-intoxicated mice. Therefore, we conclude that attenuation of the chemokine-dependent adaptive immune response may be of therapeutic benefit for PD patients.

PPARα in lysosomal biogenesis: A perspective

Lysosomes are membrane-bound vesicles containing hydrolytic enzymes, ubiquitously present in all eukaryotic cells. Classically considered to be central to the cellular waste management machinery, recent studies revealed the role of lysosomes in a wide array of cellular processes like, degradation, cellular development, programmed cell death, secretion, plasma membrane repair, nutritional responses, and lipid metabolism. We recently studied the regulation of TFEB, considered to be the master regulator of lysosomal biogenesis, by activation of peroxisomal proliferator activated receptor α (PPARα), one of the key regulators of lipid metabolism. In this article, we discuss how the recent finding could be put in to perspective with the previous findings that relate lysosomal biogenesis to lipid metabolism, and comment on the possibility of a bi-directional interplay between these two distinct cellular processes upon activation of PPARα.

R-flurbiprofen attenuates experimental autoimmune encephalomyelitis in mice

R-flurbiprofen is the non-cyclooxygenase inhibiting R-enantiomer of the non-steroidal anti-inflammatory drug flurbiprofen, which was assessed as a remedy for Alzheimer's disease. Because of its anti-inflammatory, endocannabinoid-modulating and antioxidative properties, combined with low toxicity, the present study assessed R-flurbiprofen in experimental autoimmune encephalomyelitis (EAE) models of multiple sclerosis in mice. Oral R-flurbiprofen prevented and attenuated primary progressive EAE in C57BL6/J mice and relapsing-remitting EAE in SJL mice, even if the treatment was initiated on or after the first flare of the disease. R-flurbiprofen reduced immune cell infiltration and microglia activation and inflammation in the spinal cord, brain and optic nerve and attenuated myelin destruction and EAE-evoked hyperalgesia. R-flurbiprofen treatment increased CD4(+)CD25(+)FoxP3(+) regulatory T cells, CTLA4(+) inhibitory T cells and interleukin-10, whereas the EAE-evoked upregulation of pro-inflammatory genes in the spinal cord was strongly reduced. The effects were associated with an increase of plasma and cortical endocannabinoids but decreased spinal prostaglandins, the latter likely due to R to S inversion. The promising results suggest potential efficacy of R-flurbiprofen in human MS, and its low toxicity may justify a clinical trial.

Activation of peroxisome proliferator-activated receptor α induces lysosomal biogenesis in brain cells: implications for lysosomal storage disorders

Lysosomes are ubiquitous membrane-enclosed organelles filled with an acidic interior and are central to the autophagic, endocytic, or phagocytic pathway. In contrast to its classical function as the waste management machinery, lysosomes are now considered to be an integral part of various cellular signaling processes. The diverse functionality of this single organelle requires a very complex and coordinated regulation of its activity with transcription factor EB (TFEB), a master regulator of lysosomal biogenesis, at its core. However, mechanisms by which TFEB is regulated are poorly understood. This study demonstrates that gemfibrozil, an agonist of peroxisome proliferator-activated receptor (PPAR) α, alone and in conjunction with all-trans-retinoic acid is capable of enhancing TFEB in brain cells. We also observed that PPARα, but not PPARβ and PPARγ, is involved in gemfibrozil-mediated up-regulation of TFEB. Reporter assay and chromatin immunoprecipitation studies confirmed the recruitment of retinoid X receptor α, PPARα, and PGC1α on the PPAR-binding site on the Tfeb promoter as well. Subsequently, the drug-mediated induction of TFEB caused an increase in lysosomal protein and the lysosomal abundance in cell. Collectively, this study reinforces the link between lysosomal biogenesis and lipid metabolism with TFEB at the crossroads. Furthermore, gemfibrozil may be of therapeutic value in the treatment of lysosomal storage disorders in which autophagy-lysosome pathway plays an important role.

Attenuation of microglial RANTES by NEMO-binding domain peptide inhibits the infiltration of CD8(+) T cells in the nigra of hemiparkinsonian monkey

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). Despite intense investigations, little is known about its pathological mediators. Here, we report the marked upregulation of RANTES (regulated on activation, normal T cell expressed and secreted) and eotaxin, chemokines that are involved in T cell trafficking, in the serum of hemiparkinsonian monkeys. Interestingly, 1-methyl-4-phenylpyridinium (MPP(+)), a Parkinsonian toxin, increased the expression of RANTES and eotaxin in mouse microglial cells. The presence of NF-κB binding sites in promoters of RANTES and eotaxin and down-regulation of these genes by NEMO-binding domain (NBD) peptide, selective inhibitor of induced NF-κB activation, in MPP(+)-stimulated microglial cells suggest that the activation of NF-κB plays an important role in the upregulation of these two chemokines. Consistently, serum enzyme-linked immuno assay (ELISA) and nigral immunohistochemistry further confirmed that these chemokines were strongly upregulated in MPTP-induced hemiparkinsonian monkeys and that treatment with NBD peptides effectively inhibited the level of these chemokines. Furthermore, the microglial upregulation of RANTES in the nigra of hemiparkinsonian monkeys could be involved in the altered adaptive immune response in the brain as we observed greater infiltration of CD8(+) T cells around the perivascular niche and deep brain parenchyma of hemiparkinsonian monkeys as compared to control. The treatment of hemiparkinsonian monkeys with NBD peptides decreased the microglial expression of RANTES and attenuated the infiltration of CD8(+) T cells in nigra. These results indicate the possible involvement of chemokine-dependent adaptive immune response in Parkinsonism.

Gemfibrozil attenuates the inflammatory response and protects rats from abdominal sepsis

Sepsis is a serious condition characterized by an infectious process that induces a severe systemic inflammatory response. In this study, the effects of gemfibrozil (GFZ) on the inflammatory response associated with abdominal sepsis were investigated using a rat model of cecal-ligation and puncture (CLP). Male Wistar rats were randomly divided into three groups: Sham-operated group (sham), where laparotomy was performed, the intestines were manipulated, and the cecum was ligated but not punctured; control group, subjected to CLP; and GFZ group, which received GFZ prior to undergoing CLP. The groups were then subdivided into three different time-points: 2, 4 and 24 h, indicating the time at which blood samples were obtained for analysis. Serum concentrations of tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), malondialdehyde (MDA), aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) were determined. The LDH, AST and ALT values were significantly elevated following CLP compared with those in the sham group, and GFZ treatment was able to reduce these elevations. GFZ also reduced the sepsis-induced elevations of TNF-α and IL-1. In conclusion, GFZ treatment was able to attenuate the inflammatory response associated with CLP-induced sepsis, by diminishing the release of inflammatory cytokines, thereby reducing tissue injury and oxidative stress.

Cinnamon ameliorates experimental allergic encephalomyelitis in mice via regulatory T cells: implications for multiple sclerosis therapy

Upregulation and/or maintenance of regulatory T cells (Tregs) during an autoimmune insult may have therapeutic efficacy in autoimmune diseases. Although several immunomodulatory drugs and molecules are available, most present significant side effects over long-term use. Cinnamon is a commonly used natural spice and flavoring material used for centuries throughout the world. Here, we have explored a novel use of cinnamon powder in protecting Tregs and treating the disease process of experimental allergic encephalomyelitis (EAE), an animal model of MS. Oral feeding of cinnamon (Cinnamonum verum) powder suppresses clinical symptoms of relapsing-remitting EAE in female PLP-TCR transgenic mice and adoptive transfer mouse model. Cinnamon also inhibited clinical symptoms of chronic EAE in male C57/BL6 mice. Dose-dependent study shows that cinnamon powder at a dose of 50 mg/kg body wt/d or higher significantly suppresses clinical symptoms of EAE in mice. Accordingly, oral administration of cinnamon also inhibited perivascular cuffing, maintained the integrity of blood-brain barrier and blood-spinal cord barrier, suppressed inflammation, normalized the expression of myelin genes, and blocked demyelination in the central nervous system of EAE mice. Interestingly, cinnamon treatment upregulated Tregs via reduction of nitric oxide production. Furthermore, we demonstrate that blocking of Tregs by neutralizing antibodies against CD25 abrogates cinnamon-mediated protection of EAE. Taken together, our results suggest that oral administration of cinnamon powder may be beneficial in MS patients and that no other existing anti-MS therapies could be so economical and trouble-free as this approach.

Peroxisome proliferator-activated receptors α and γ are linked with alcohol consumption in mice and withdrawal and dependence in humans

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR) agonists reduce voluntary ethanol (EtOH) consumption in rat models and are promising therapeutics in the treatment for drug addictions. We studied the effects of different classes of PPAR agonists on chronic EtOH intake and preference in mice with a genetic predisposition for high alcohol consumption and then examined human genomewide association data for polymorphisms in PPAR genes in alcohol-dependent subjects.

METHODS

Two different behavioral tests were used to measure intake of 15% EtOH in C57BL/6J male mice: 24-hour 2-bottle choice and limited access (3-hour) 2-bottle choice, drinking in the dark. We measured the effects of pioglitazone (10 and 30 mg/kg), fenofibrate (50 and 150 mg/kg), GW0742 (10 mg/kg), tesaglitazar (1.5 mg/kg), and bezafibrate (25 and 75 mg/kg) on EtOH intake and preference. Fenofibric acid, the active metabolite of fenofibrate, was quantified in mouse plasma, liver, and brain by liquid chromatography tandem mass spectrometry. Data from a human genome-wide association study (GWAS) completed in the Collaborative Study on the Genetics of Alcoholism (COGA) were then used to analyze the association of single nucleotide polymorphisms (SNPs) in different PPAR genes (PPARA, PPARD, PPARG, and PPARGC1A) with 2 phenotypes: DSM-IV alcohol dependence (AD) and the DSM-IV criterion of withdrawal.

RESULTS

Activation of 2 isoforms of PPARs, α and γ, reduced EtOH intake and preference in the 2 different consumption tests in mice. However, a selective PPARδ agonist or a pan agonist for all 3 PPAR isoforms did not decrease EtOH consumption. Fenofibric acid, the active metabolite of the PPARα agonist fenofibrate, was detected in liver, plasma, and brain after 1 or 8 days of oral treatment. The GWAS from COGA supported an association of SNPs in PPARA and PPARG with alcohol withdrawal and PPARGC1A with AD but found no association for PPARD with either phenotype.

CONCLUSIONS

We provide convergent evidence using both mouse and human data for specific PPARs in alcohol action. Reduced EtOH intake in mice and the genetic association between AD or withdrawal in humans highlight the potential for repurposing FDA-approved PPARα or PPARγ agonists for the treatment of AD.

"Disease modifying nutricals" for multiple sclerosis

The association between vitamin D and multiple sclerosis has (re)-opened new interest in nutrition and natural compounds in the prevention and treatment of this neuroinflammatory disease. The dietary amount and type of fat, probiotics and biologicals, salmon proteoglycans, phytoestrogens and protease inhibitor of soy, sodium chloride and trace elements, and fat soluble vitamins including D, A and E were all considered as disease-modifying nutraceuticals. Studies in experimental autoimmune encephalomyelitis mice suggest that poly-unsaturated fatty acids and their 'inflammation-resolving' metabolites and the gut microflora may reduce auto-aggressive immune cells and reduce progression or risk of relapse, and infection with whipworm eggs may positively change the gut-brain communication. Encouraged by the recent interest in multiple sclerosis-nutrition nature's pharmacy has been searched for novel compounds with anti-inflammatory, immune-modifying and antioxidative properties, the most interesting being the scorpion toxins that inhibit specific potassium channels of T cells and antioxidative compounds including the green tea flavonoid epigallocatechin-3-gallate, curcumin and the mustard oil glycoside from e.g. broccoli and sulforaphane. They mostly also inhibit pro-inflammatory signaling through NF-κB or toll-like receptors and stabilize the blood brain barrier. Disease modifying functions may also complement analgesic and anti-spastic effects of cannabis, its constituents, and of 'endocannabinoid enhancing' drugs or nutricals like inhibitors of fatty acid amide hydrolase. Nutricals will not solve multiple sclerosis therapeutic challenges but possibly support pharmacological interventions or unearth novel structures.

Interleukin-12 (IL-12), but not IL-23, induces the expression of IL-7 in microglia and macrophages: implications for multiple sclerosis

Interleukin-12 (IL-12) p70 and IL-23 are bioactive cytokines and their biological functions are becoming clear. Increased expression of IL-7 in the central nervous system as well as in peripheral immune cells is associated with multiple sclerosis and experimental allergic encephalomyelitis. Here, we describe the induction of IL-7 in primary mouse and human microglia, BV-2 microglial cells, mouse peritoneal macrophages and astrocytes by IL-12p70. Interestingly, IL-12 strongly induced the expression of IL-7 whereas IL-23 and other p40 family members remained weak inducers of IL-7 in these cell types. Consistently, IL-12, but not IL-23 and other p40 family members, induced IL-7 promoter-driven luciferase activity in microglial cells. Among various stimuli tested, IL-12 emerged as the most potent stimulus followed by bacterial lipopolysaccharide and HIV-1 gp120 in inducing the activation of IL-7 promoter in microglial cells. Furthermore, increase in IL-7 mRNA expression by over-expression of IL-12p35 subunit, but not p40 and IL-23 p19 subunit, confirm that p35, but not p40 and p19, is responsible for the induction of IL-7. Finally, by using primary microglia from IL-12 receptor β1-deficient (IL-12Rβ1(-/-)) and IL-12Rβ2(-/-) mice, we demonstrate that IL-12 induces the expression of IL-7 in microglia and macrophages via both IL-12Rβ2 and IL-12Rβ1. These studies delineate a novel biological function of IL-12 that is absent in IL-23 and other p40 family members.

Promoting return of function in multiple sclerosis: An integrated approach

Multiple sclerosis is a disease characterized by inflammatory demyelination, axonal degeneration and progressive brain atrophy. Most of the currently available disease modifying agents proved to be very effective in managing the relapse rate, however progressive neuronal damage continues to occur and leads to progressive accumulation of irreversible disability. For this reason, any therapeutic strategy aimed at restoration of function must take into account not only immunomodulation, but also axonal protection and new myelin formation. We further highlight the importance of an holistic approach, which considers the variability of therapeutic responsiveness as the result of the interplay between genetic differences and the epigenome, which is in turn affected by gender, age and differences in life style including diet, exercise, smoking and social interaction.

Effects of three different fibrates on intrahepatic cholestasis experimentally induced in rats

Background. Activation of PPAR α modulates cholesterol metabolism and suppresses bile acid synthesis. This study aims to evaluate the effect of PPAR α agonists, fenofibrate, bezafibrate, and gemfibrozil, on acute cholestasis induced by ethinylestradiol (EE) plus chlorpromazine (CPZ) in rats. Method. 100 male albino rats (150-200 gm) were divided randomly into 10 equal groups. Control group received 1% methylcellulose vehicle; disease group received CPZ plus EE for 5 consecutive days; four groups received either ursodeoxycholic acid, fenofibrate, bezafibrate, or gemfibrozil for 7 days; 2 days before EE + CPZ, three other groups received one of the three fibrates after GW6471, a selective PPAR α antagonist in addition to EE + CPZ. The final group received GW6471 alone. Results. The three fibrates showed marked reduction (P < 0.05) in serum levels of ALP, GGT, ALT, AST, total bile acids, bilirubin, TNF α , and IL-1 β and in hepatic malondialdehyde level as well as a significant increase in bile flow rate (P < 0.05) in addition to improvements in histopathological parameters compared to diseased group. In groups which received GW6471, these effects were completely abolished with fenofibrate and partially blocked with bezafibrate and gemfibrozil. Conclusion. Short-term administration of fibrates to EE/CPZ-induced intrahepatic cholestatic rats exerted beneficial effects on hepatocellular damage and apoptosis. Fenofibrate anticholestatic effect was solely PPAR α dependent while other mechanisms played part in bezafibrate and gemfibrozil actions.

Protection of Tregs, suppression of Th1 and Th17 cells, and amelioration of experimental allergic encephalomyelitis by a physically-modified saline

In multiple sclerosis (MS) and other autoimmune diseases, the autoreactive T cells overcome the resistance provided by the regulatory T cells (Tregs) due to a decrease in the number of Foxp3-expressing Tregs. Therefore, upregulation and/or maintenance of Tregs during an autoimmune insult may have therapeutic efficacy in autoimmune diseases. Although several immunomodulatory drugs and molecules are available, most present significant side effects over long-term use. Here we have undertaken an innovative approach to upregulate Tregs and achieve immunomodulation. RNS60 is a 0.9% saline solution generated by subjecting normal saline to Taylor-Couette-Poiseuille (TCP) flow under elevated oxygen pressure. RNS60, but not NS (normal saline), RNS10.3 (TCP-modified saline without excess oxygen) and PNS60 (saline containing excess oxygen without TCP modification), was found to upregulate Foxp3 and enrich Tregs in MBP-primed T cells. Moreover, RNS60, but not NS, RNS10.3 and PNS60, inhibited the production of nitric oxide (NO) and the expression of iNOS in MBP-primed splenocytes. Incubation of the cells with an NO donor abrogated the RNS60-mediated upregulation of Foxp3. These results suggest that RNS60 boosts Tregs via suppression of NO production. Consistent to the suppressive activity of Tregs towards autoreactive T cells, RNS60, but not NS, RNS10.3, or PNS60, suppressed the differentiation of Th17 and Th1 cells and shifted the balance towards a Th2 response. Finally, RNS60 treatment exhibited immunomodulation and ameliorated adoptive transfer of experimental allergic encephalomyelitis, an animal model of MS, via Tregs. These results describe a novel immunomodulatory property of RNS60 and suggest its exploration for therapeutic intervention in MS and other autoimmune disorders.

Gemfibrozil and fenofibrate, Food and Drug Administration-approved lipid-lowering drugs, up-regulate tripeptidyl-peptidase 1 in brain cells via peroxisome proliferator-activated receptor α: implications for late infantile Batten disease therapy

The classical late infantile neuronal ceroid lipofuscinosis (LINCLs) is an autosomal recessive disease, where the defective gene is Cln2, encoding tripeptidyl-peptidase I (TPP1). At the molecular level, LINCL is caused by accumulation of autofluorescent storage materials in neurons and other cell types. Currently, there is no established treatment for this fatal disease. This study reveals a novel use of gemfibrozil and fenofibrate, Food and Drug Administration-approved lipid-lowering drugs, in up-regulating TPP1 in brain cells. Both gemfibrozil and fenofibrate up-regulated mRNA, protein, and enzymatic activity of TPP1 in primary mouse neurons and astrocytes as well as human astrocytes and neuronal cells. Because gemfibrozil and fenofibrate are known to activate peroxisome proliferator-activated receptor-α (PPARα), the role of PPARα in gemfibrozil- and fenofibrate-mediated up-regulation of TPP1 was investigated revealing that both drugs up-regulated TPP1 mRNA, protein, and enzymatic activity both in vitro and in vivo in wild type (WT) and PPARβ(-/-), but not PPARα(-/-), mice. In an attempt to delineate the mechanism of TPP1 up-regulation, it was found that the effects of the fibrate drugs were abrogated in the absence of retinoid X receptor-α (RXRα), a molecule known to form a heterodimer with PPARα. Accordingly, all-trans-retinoic acid, alone or together with gemfibrozil, up-regulated TPP1. Co-immunoprecipitation and ChIP studies revealed the formation of a PPARα/RXRα heterodimer and binding of the heterodimer to an RXR-binding site on the Cln2 promoter. Together, this study demonstrates a unique mechanism for the up-regulation of TPP1 by fibrate drugs via PPARα/RXRα pathway.

PPARα as a therapeutic target in inflammation-associated diseases

INTRODUCTION

The nuclear receptor peroxisome proliferator-activated receptor alpha (PPARα) plays a major regulatory function of genes involved in energy metabolism and is a therapeutic target for dyslipidemia. The last decade provided a constellation of findings demonstrating that PPARα behaves as a modulator of both acute and chronic inflammation. PPARα became a rational potential therapeutic target for the treatment of inflammatory disorders.

AERAS COVERED

The ability of PPARα to control inflammatory signaling pathways via a diversity of molecular mechanisms is discussed. This review is especially focused on the global action of PPARα on inflammation in several tissues from data obtained in numerous cell types and in vivo models exposed to inflammatory stimuli.

EXPERT OPINION

Available PPARα agonists currently used in clinic belong to the class of hypolipidemic drugs but were not expected and not designed to act as anti-inflammatory drugs. To date, accumulating preclinical suggest evidence promising benefits when considering PPARα as a drug target to treat inflammatory disorders. However, clinical studies are needed to validate this concept. Drug design should also be directed toward the elaboration of PPARα agonists more specifically active in the control inflammatory signaling.

Gemfibrozil, a lipid-lowering drug, increases myelin genes in human oligodendrocytes via peroxisome proliferator-activated receptor-β

An increase in CNS remyelination and a decrease in CNS inflammation are important steps to halt the progression of multiple sclerosis. Earlier studies have shown that gemfibrozil, a lipid-lowering drug, has anti-inflammatory properties. The current study identified another novel property of gemfibrozil in stimulating the expression of myelin-specific genes (myelin basic protein, myelin oligodendrocyte glycoprotein, 2',3'-cyclic-nucleotide 3'-phosphodiesterase, and proteolipid protein (PLP)) in primary human oligodendrocytes, mixed glial cells, and spinal cord organotypic cultures. Although gemfibrozil is a known activator of peroxisome proliferator-activated receptor-α (PPAR-α), we were unable to detect PPAR-α in either gemfibrozil-treated or untreated human oligodendrocytes, and gemfibrozil increased the expression of myelin genes in oligodendrocytes isolated from both wild type and PPAR-α(-/-) mice. On the other hand, gemfibrozil markedly increased the expression of PPAR-β but not PPAR-γ. Consistently, antisense knockdown of PPAR-β, but not PPAR-γ, abrogated the stimulatory effect of gemfibrozil on myelin genes in human oligodendrocytes. Gemfibrozil also did not up-regulate myelin genes in oligodendroglia isolated from PPAR-β(-/-) mice. Chromatin immunoprecipitation analysis showed that gemfibrozil induced the recruitment of PPAR-β to the promoter of PLP and myelin oligodendrocyte glycoprotein genes in human oligodendrocytes. Furthermore, gemfibrozil treatment also led to the recruitment of PPAR-β to the PLP promoter in vivo in the spinal cord of experimental autoimmune encephalomyelitis mice and suppression of experimental autoimmune encephalomyelitis symptoms in PLP-T cell receptor transgenic mice. These results suggest that gemfibrozil stimulates the expression of myelin genes via PPAR-β and that gemfibrozil, a prescribed drug for humans, may find further therapeutic use in demyelinating diseases.

Gemfibrozil, a lipid-lowering drug, upregulates IL-1 receptor antagonist in mouse cortical neurons: implications for neuronal self-defense

Chronic inflammation is becoming a hallmark of several neurodegenerative disorders and accordingly, IL-1β, a proinflammatory cytokine, is implicated in the pathogenesis of neurodegenerative diseases. Although IL-1β binds to its high-affinity receptor, IL-1R, and upregulates proinflammatory signaling pathways, IL-1R antagonist (IL-1Ra) adheres to the same receptor and inhibits proinflammatory cell signaling. Therefore, upregulation of IL-1Ra is considered important in attenuating inflammation. The present study underlines a novel application of gemfibrozil (gem), a Food and Drug Administration-approved lipid-lowering drug, in increasing the expression of IL-1Ra in primary mouse and human neurons. Gem alone induced an early and pronounced increase in the expression of IL-1Ra in primary mouse cortical neurons. Activation of type IA p110α PI3K and Akt by gem and abrogation of gem-induced upregulation of IL-1Ra by inhibitors of PI3K and Akt indicate a role of the PI3K-Akt pathway in the upregulation of IL-1Ra. Gem also induced the activation of CREB via the PI3K-Akt pathway, and small interfering RNA attenuation of CREB abolished the gem-mediated increase in IL-1Ra. Furthermore, gem was able to protect neurons from IL-1β insult. However, small interfering RNA knockdown of neuronal IL-1Ra abrogated the protective effect of gem against IL-1β, suggesting that this drug increases the defense mechanism of cortical neurons via upregulation of IL-1Ra. Taken together, these results highlight the importance of the PI3K-Akt-CREB pathway in mediating gem-induced upregulation of IL-1Ra in neurons and suggest gem as a possible therapeutic treatment for propagating neuronal self-defense in neuroinflammatory and neurodegenerative disorders.

Gemfibrozil, a lipid-lowering drug, induces suppressor of cytokine signaling 3 in glial cells: implications for neurodegenerative disorders

Glial inflammation is an important feature of several neurodegenerative disorders. Suppressor of cytokine signaling (SOCS) proteins play a crucial role in inhibiting cytokine signaling and inflammatory gene expression in various cell types, including glial cells. However, mechanisms by which SOCS genes could be up-regulated are poorly understood. This study underlines the importance of gemfibrozil, a Food and Drug Administration-approved lipid-lowering drug, in up-regulating the expression of SOCS3 in glial cells. Gemfibrozil increased the expression of Socs3 mRNA and protein in mouse astroglia and microglia in both a time- and dose-dependent manner. Interestingly, gemfibrozil induced the activation of type IA phosphatidylinositol (PI) 3-kinase and AKT. Accordingly, inhibition of PI 3-kinase and AKT by chemical inhibitors abrogated gemfibrozil-mediated up-regulation of SOCS3. Furthermore, we demonstrated that gemfibrozil induced the activation of Krüppel-like factor 4 (KLF4) via the PI 3-kinase-AKT pathway and that siRNA knockdown of KLF4 abrogated gemfibrozil-mediated up-regulation of SOCS3. Gemfibrozil also induced the recruitment of KLF4 to the distal, but not proximal, KLF4-binding site of the Socs3 promoter. This study delineates a novel property of gemfibrozil in up-regulating SOCS3 in glial cells via PI 3-kinase-AKT-mediated activation of KLF4 and suggests that gemfibrozil may find therapeutic application in neuroinflammatory and neurodegenerative disorders.

Gemfibrozil, a lipid lowering drug, inhibits the activation of primary human microglia via peroxisome proliferator-activated receptor β

Microglial activation participates in the pathogenesis of various neuroinflammatory and neurodegenerative diseases. However, mechanisms by which microglial activation could be controlled are poorly understood. Peroxisome proliferator-activated receptors (PPAR) are transcription factors belonging to the nuclear receptor super family with diverse effect. This study underlines the importance of PPARβ/δ in mediating the anti-inflammatory effect of gemfibrozil, an FDA-approved lipid-lowering drug, in primary human microglia. Bacterial lipopolysachharides (LPS) induced the expression of various proinflammatory molecules and upregulated the expression of microglial surface marker CD11b in human microglia. However, gemfibrozil markedly suppressed proinflammatory molecules and CD11b in LPS-stimulated microglia. Human microglia expressed PPAR-β and -γ, but not PPAR-α. Interestingly, either antisense knockdown of PPAR-β or antagonism of PPAR-β by a specific chemical antagonist abrogated gemfibrozil-mediated inhibition of microglial activation. On the other hand, blocking of PPAR-α and -γ had no effect on gemfibrozil-mediated anti-inflammatory effect in microglia. These results highlight the fact that gemfibrozil regulates microglial activation by inhibiting inflammatory gene expression in a PPAR-β dependent pathway and further reinforce its therapeutic application in several neuroinflammatory and neurodegenerative diseases.

5, 8, 11, 14-eicosatetraynoic acid suppresses CCL2/MCP-1 expression in IFN-γ-stimulated astrocytes by increasing MAPK phosphatase-1 mRNA stability

Background

The peroxisome proliferator-activated receptor (PPAR)-α activator, 5,8,11,14-eicosatetraynoic acid (ETYA), is an arachidonic acid analog. It is reported to inhibit up-regulation of pro-inflammatory genes; however, its underlying mechanism of action is largely unknown. In the present study, we focused on the inhibitory action of ETYA on the expression of the chemokine, CCL2/MCP-1, which plays a key role in the initiation and progression of inflammation.

Methods

To determine the effect of ETYA, primary cultured rat astrocytes and microglia were stimulated with IFN-γ in the presence of ETYA and then, expression of CCL2/MCP-1 and MAPK phosphatase (MKP-1) were determined using RT-PCR and ELISA. MKP-1 mRNA stability was evaluated by treating actinomycin D. The effect of MKP-1 and human antigen R (HuR) was analyzed by using specific siRNA transfection system. The localization of HuR was analyzed by immunocytochemistry and subcellular fractionation experiment.

Results

We found that ETYA suppressed CCL2/MCP-1 transcription and secretion of CCL2/MCP-1 protein through up-regulation of MKP-1mRNA levels, resulting in suppression of c-Jun N-terminal kinase (JNK) phosphorylation and activator protein 1 (AP1) activity in IFN-γ-stimulated brain glial cells. Moreover, these effects of ETYA were independent of PPAR-α. Experiments using actinomycin D revealed that the ETYA-induced increase in MKP-1 mRNA levels reflected an increase in transcript stability. Knockdown experiments using small interfering RNA demonstrated that this increase in MKP-1 mRNA stability depended on HuR, an RNA-binding protein known to promote enhanced mRNA stability. Furthermore, ETYA-induced, HuR-mediated mRNA stabilization resulted from HuR-MKP-1 nucleocytoplasmic translocation, which served to protect MKP-1 mRNA from the mRNA degradation machinery.

Conclusion

ETYA induces MKP-1 through HuR at the post-transcriptional level in a receptor-independent manner. The mechanism revealed here suggests eicosanoids as potential therapeutic modulators of inflammation that act through a novel target.

Neuroprotection by dietary restriction and the PPAR transcription complex

Although the pathophysiology of neurodegenerative diseases is distinct for each disease, considerable evidence suggests that a single manipulation, dietary restriction, is strikingly protective against a wide range of such diseases. Thus pharmacological mimetics of dietary restrictions could prove widely protective across a range of neurodegenerative diseases. The PPAR transcription complex functions to re-program gene expression in response to nutritional deprivation as well as in response to a wide variety of lipophilic compounds. In mammals there are three PPAR homologs, which dimerize with RXR homologs and recruit coactivators Pgc1-alpha and Creb-binding protein (Cbp). PPARs are currently of clinical interest mainly because PPAR activators are approved for use in humans to reduce lipidemia and to improve glucose control in Type 2 diabetic patients. However, pharmacological enhancement of the activity of the PPAR complex is neuroprotective across a wide variety of models for neuropathological processes, including stroke, Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. Conversely activity of the PPAR transcriptional complex is reduced in a variety of neuropathological processes. The main mechanisms mediating the neuroprotective effects of the PPAR transcription complex appear to be re-routing metabolism away from glucose metabolism and toward alternative subtrates, and reduction in inflammatory processes. Recent evidence suggests that the PPAR transcriptional complex may also mediate protective effects of dietary restriction on neuropathological processes. Thus this complex represents one of the most promising for the development of pharmacological treatment of neurodegenerative diseases.

The PPAR alpha agonist gemfibrozil is an ineffective treatment for spinal cord injured mice

Peroxisome Proliferator Activated Receptor (PPAR)-α is a key regulator of lipid metabolism and recent studies reveal it also regulates inflammation in several different disease models. Gemfibrozil, an agonist of PPAR-α, is a FDA approved drug for hyperlipidemia and has been shown to inhibit clinical signs in a rodent model of multiple sclerosis. Since many studies have shown improved outcome from spinal cord injury (SCI) by anti-inflammatory and neuroprotective agents, we tested the efficacy of oral gemfibrozil given before or after SCI for promoting tissue preservation and behavioral recovery after spinal contusion injury in mice. Unfortunately, the results were contrary to our hypothesis; in our first attempt, gemfibrozil treatment exacerbated locomotor deficits and increased tissue pathology after SCI. In subsequent experiments, the behavioral effects were not replicated but histological outcomes again were worse. We also tested the efficacy of a different PPAR-α agonist, fenofibrate, which also modulates immune responses and is beneficial in several neurodegenerative disease models. Fenofibrate treatment did not improve recovery, although there was a slight trend for a modest increase in histological tissue sparing. Based on our results, we conclude that PPAR-α agonists yield either no effect or worsen recovery from spinal cord injury, at least at the doses and the time points of drug delivery tested here. Further, patients sustaining spinal cord injury while taking gemfibrozil might be prone to exacerbated tissue damage.

PPAR Alpha Regulation of the Immune Response and Autoimmune Encephalomyelitis

PPARs are members of the steroid hormone nuclear receptor superfamily and play an important role in the regulation of lipid metabolism, energy balance, artherosclerosis and glucose control. Recent studies suggest that they play an important role in regulating inflammation. This review will focus on PPAR-α regulation of the immune response. We describe how PPAR-α regulates differentiation of T cells by transactivation and/or interaction with other transcription factors. Moreover, PPAR-α agonists have been shown to ameliorate experimental autoimmune encephalomyelitis (EAE) in mice, suggesting that they could provide a therapy for human autoimmune diseases such as multiple sclerosis.

Regulation of Glial Cell Functions by PPAR-gamma Natural and Synthetic Agonists

In the recent years, the peroxisome proliferator-activated receptor-γ (PPAR-γ), a well known target for type II diabetes treatment, has received an increasing attention for its therapeutic potential in inflammatory and degenerative brain disorders. PPAR-γ agonists, which include naturally occurring compounds (such as long chain fatty acids and the cyclopentenone prostaglandin 15-deoxy Δ^12,14 prostaglandin J₂), and synthetic agonists (among which the thiazolidinediones and few nonsteroidal anti-inflammatory drugs) have shown anti-inflammatory and protective effects in several experimental models of Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, multiple sclerosis and stroke, as well as in few clinical studies. The pleiotropic effects of PPAR-γ agonists are likely to be mediated by several mechanisms involving anti-inflammatory activities on peripheral immune cells (macrophages and lymphocytes), as well as direct effects on neural cells including cerebral vascular endothelial cells, neurons, and glia. In the present article, we will review the recent findings supporting a major role for PPAR-γ agonists in controlling neuroinflammation and neurodegeneration through their activities on glial cells, with a particular emphasis on microglial cells as major macrophage population of the brain parenchyma and main actors in brain inflammation.

PPAR-gamma, Microglial Cells, and Ocular Inflammation: New Venues for Potential Therapeutic Approaches

The last decade has witnessed an increasing interest for the role played by the peroxisome proliferator-activated receptor-γ (PPAR-γ) in controlling inflammation in peripheral organs as well as in the brain. Activation of PPAR-γ has been shown to control the response of microglial cells, the main macrophage population found in brain parenchyma, and limit the inflammation. The anti-inflammatory capacity of PPAR-γ agonists has led to the hypothesis that PPAR-γ might be targeted to modulate degenerative brain diseases in which inflammation has been increasingly recognized as a significant component. Recent experimental evidence suggests that PPAR-γ agonists could be exploited to treat ocular diseases such as diabetic retinopathy, age-related macular degeneration, autoimmune uveitis, and optic neuritis where inflammation has relevant role. Additional PPAR-γ agonist beneficial effects could involve amelioration of retinal microcirculation and inhibition of neovascularization. However, PPAR-γ activation could, in some instances, aggravate the ocular pathology, for example, by increasing the synthesis of vascular endothelial growth factor, a proangiogenic factor that could trigger a vicious circle and further deteriorate retinal perfusion. The development of new in vivo and in vitro models to study ocular inflammation and how to modulate for the eye benefit will be instrumental for the search of effective therapies.

PPAR Regulation of Inflammatory Signaling in CNS Diseases

Central nervous system (CNS) is an immune privileged site, nevertheless inflammation associates with many CNS diseases. Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors that regulate immune and inflammatory responses. Specific ligands for PPARα, γ, and δ isoforms have proven effective in the animal models of multiple sclerosis (MS), Alzheimer's disease, Parkinson's disease, and trauma/stroke, suggesting their use in the treatment of neuroinflammatory diseases. The activation of NF-κB and Jak-Stat signaling pathways and secretion of inflammatory cytokines are critical in the pathogenesis of CNS diseases. Interestingly, PPAR agonists mitigate CNS disease by modulating inflammatory signaling network in immune cells. In this manuscript, we review the current knowledge on how PPARs regulate neuroinflammatory signaling networks in CNS diseases.