Mitoxantrone repression of astrocyte activation: relevance to multiple sclerosis.

Mitoxantrone has been approved by the FDA for the treatment of multiple sclerosis (MS). However, the mechanisms by which mitoxantrone modulates MS are largely unknown. Activated astrocytes produce nitric oxide (NO), TNF-α, and IL-1ß, molecules which can be toxic to central nervous system (CNS) cells including oligodendrocytes, thus potentially contributing to the pathology associated with MS. MCP-1 is a chemokine believed to modulate the migration of monocytes to inflammatory lesions present in the CNS of MS patients. IL-12 and IL-23 have been demonstrated to play critical roles in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of MS, by contributing to the development of CD4(+) T cell lineages termed Th1 and Th17, respectively. The current study demonstrates that mitoxantrone inhibits lipopolysachharide (LPS) induction of NO, TNF-α, IL-1ß, and MCP-1 production by primary astrocytes. Mitoxantrone also inhibited IL-12 and IL-23 production by these cells. Furthermore, mitoxantrone suppressed the expression of C-reactive protein (CRP). Finally, we demonstrate that mitoxantrone suppressed LPS induction of NF-κB DNA-binding activity, suggesting a novel mechanism by which mitoxantrone suppresses the expression of proinflammatory molecules. Collectively, these studies demonstrate that mitoxantrone represses astrocyte production of potentially cytotoxic molecules, as well as molecules capable of altering T-cell phenotype. These in vitro studies suggest mechanisms by which mitoxantrone may modulate inflammatory diseases including MS.

Resveratrol effects on astrocyte function: relevance to neurodegenerative diseases.

Inflammatory molecules have been implicated in the pathogenesis of neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis. Resveratrol is an anti-fungal compound found in the skins of red grapes and other fruits and nuts. We examined the ability of resveratrol to inhibit lipopolysaccharide (LPS)-induced production of inflammatory molecules from primary mouse astrocytes. Resveratrol inhibited LPS-induced production of nitric oxide (NO); the cytokines tumor necrosis factor-alpha (TNF-α), interleukin 1-beta (IL-1ß), and IL-6; and the chemokine monocyte chemotactic protein-1 (MCP-1), which play critical roles in innate immunity, by astrocytes. Resveratrol also suppressed astrocyte production of IL-12p40 and IL-23, which are known to alter the phenotype of T cells involved in adaptive immunity. Finally resveratrol inhibited astrocyte production of C-reactive protein (CRP), which plays a role in a variety of chronic inflammatory disorders. Collectively, these studies suggest that resveratrol may be an effective therapeutic agent in neurodegenerative diseases initiated or maintained by inflammatory processes.

Peroxisome proliferator-activated receptor-alpha and retinoid X receptor agonists inhibit inflammatory responses of astrocytes.

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) plays a key role in lipid metabolism and inflammation. Recently, we demonstrated that administration of the PPAR-alpha agonists gemfibrozil and fenofibrate, inhibit the clinical signs of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). In the present study, we investigated the effects of PPAR-alpha agonists on primary mouse astrocytes, a cell type implicated in the pathology of MS and EAE. Our studies demonstrated that the PPAR-alpha agonists fenofibrate, and WY 14643 inhibited NO production by LPS-stimulated astrocytes in a dose-dependent manner. Additionally, PPAR-alpha agonists inhibited the secretion of the pro-inflammatory cytokines TNF-alpha, IL-1beta, and IL-6 by LPS-stimulated astrocytes. Fenofibrate inhibited NF-kappaB DNA binding activity, suggesting a mechanism by which PPAR-alpha agonists may regulate the expression of genes encoding these pro-inflammatory molecules. Retinoid X receptors (RXRs) physically interact with PPAR-alpha receptors, and the resulting heterodimers regulate the expression of PPAR-responsive genes. Interestingly, a combination of 9-cis RA and the PPAR-alpha agonists fenofibrate or gemfibrozil cooperatively inhibited NO, TNF-alpha, IL-1beta, IL-6, and MCP-1 production by these cells. Collectively, these results raise the possibility that PPAR-alpha and RXR agonists might be effective in the treatment of MS, where activated astrocytes are believed to contribute to disease pathology.

Peroxisome proliferator-activated receptor agonist regulation of glial activation: relevance to CNS inflammatory disorders.

Peroxisome proliferator-activated receptors (PPARs) play key roles in lipid metabolism and inflammation. Recent studies indicated that PPARs are also capable of modulating immune responses. Microglia and astrocytes are cells resident to the central nervous system (CNS) that function to protect against environmental insults including pathogens. However, following CNS inflammation, reactive gliosis occurs which is characterized by astrocyte hypertrophy and increased glial proliferation. Under such conditions, glia can become chronically activated and may contribute to the neuropathology associated with a variety of neuroinflammatory disorders including multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and stroke. A review of the role of PPAR agonists in modulating glial cell activation is presented. Included is a discussion of the molecular mechanisms of action of these PPAR agonists and the potential utility of these agents for the treatment of neuroinflammatory disorders.

Agonists for the peroxisome proliferator-activated receptor-alpha and the retinoid X receptor inhibit inflammatory responses of microglia.

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) plays a key role in lipid metabolism and inflammation. Recently, we demonstrated that administration of the PPAR-alpha agonists gemfibrozil and fenofibrate, inhibit the clinical signs of experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). In the present study we investigated the effects of PPAR-alpha agonists on primary mouse microglia, a cell type implicated in the pathology of MS and EAE. Our studies demonstrated that the PPAR-alpha agonists ciprofibrate, fenofibrate, gemfibrozil, and WY 14,643 each inhibited NO production by cytokine-stimulated microglia in a dose-dependent manner. However, fenofibrate and WY 14,643 were more potent inhibitors than gemfibrozil and ciprofibrate. In LPS-stimulated microglia, only fenofibrate and WY 14,643 significantly suppressed NO production. Additionally, PPAR-alpha agonists inhibited the secretion of the proinflammatory cytokines IL-1beta, TNF-alpha, IL-6, and IL-12 p40 and the chemokine MCP-1 by LPS-stimulated microglia. Retinoid X receptors (RXRs) physically interact with PPAR-alpha receptors, and the resulting heterodimers regulate the expression of PPAR-responsive genes. Interestingly, the RXR agonist 9-cis retinoic acid (9-cis RA) inhibited NO production by LPS-stimulated microglia. Furthermore, a combination of 9-cis RA and the PPAR-alpha agonist fenofibrate cooperatively inhibited NO production by these cells. A combination of these agonists also selectively inhibited the expression of proinflammatory cytokines including IL-1beta, TNF-alpha, and IL-6 by LPS-stimulated microglia. Collectively, these results raise the possibility that PPAR-alpha and RXR agonists might have benefit as a therapy in MS, where activated microglia are believed to contribute to disease pathology.

Hormone regulation of microglial cell activation: relevance to multiple sclerosis.

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of proteins. The role of PPARs in regulating the transcription of genes involved in glucose and lipid metabolism has been extensively characterized. Interestingly, PPARs have also been demonstrated to mediate inflammatory responses. Microglia participate in pathology associated with multiple sclerosis (MS). Upon activation, microglia produce molecules including NO and TNF-alpha that can be toxic to CNS cells including myelin-producing oligodendrocytes and neurons, which are compromised in the course of MS. Previously, we and others demonstrated that PPAR-gamma agonists including 15d-PGJ(2) are effective in the treatment of experimental autoimmune encephalomyelitis (EAE), an animal model of MS. PPAR-gamma modulation of EAE may occur, at least in part, by inhibition of microglial cell activation. Here, we indicate that 15d-PGJ(2) is a more potent inhibitor of microglial activation than thiazolidinediones, which are currently used to treat diabetes. Furthermore, 15d-PGJ(2) acts cooperatively with 9-cis retinoic acid, the ligand for the retinoid X receptor (RXR), in inhibiting microglial cell activation. This suggests that 15d-PGJ(2) and 9-cis RA inhibit cell activation through the formation of PPAR-gamma/RXR heterodimers. Interestingly, PGA(2), which like 15d-PGJ(2) is a cyclopentenone prostaglandin, but which unlike 15d-PGJ(2) does not bind PPAR-gamma, is a potent inhibitor of microglial cell activation. Collectively, these studies suggest that 15d-PGJ(2) inhibits microglial cell activation by PPAR-gamma-dependent as well as PPAR-gamma-independent mechanisms. The studies further suggest that the PPAR-gamma agonist 15d-PGJ(2) in combination with retinoids may be effective in the treatment of MS.

Cyclopentenone prostaglandins PGA2 and 15-deoxy-delta12,14 PGJ2 suppress activation of murine microglia and astrocytes: implications for multiple sclerosis.

The cyclopentenone prostaglandin (cPG) 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) has been identified as a potent antiinflammatory agent that is able to inhibit the activation of macrophages and microglia. Additionally, 15d-PGJ(2) is able to ameliorate the clinical manifestations of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Many biological effects of 15d-PGJ(2) have been attributed to the peroxisome proliferator activated receptor-gamma (PPAR-gamma). PGA(2), like 15d-PGJ(2), is a cPG. The aim of this study is to compare the relative effectiveness of these two cPGs in inhibiting the inflammatory response of mouse microglia and astrocytes, two cell types that upon activation may contribute to the pathology of EAE and MS. Purified primary mouse microglia and astrocytes were treated with either 15d-PGJ(2) or PGA(2) and then stimulated with either lipopolysaccharide (LPS) or a combination of interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha. The results show that 15d-PGJ(2) and PGA(2) both potently inhibited the production of nitrite, as well as proinflammatory cytokines and chemokines, from microglia and astrocytes. Generally, regulation of NO production was more sensitive to 15d-PGJ(2), however, cytokine and chemokine production was more sensitive to PGA(2) treatment. These results demonstrate for the first time that PGA(2) is a potent antiinflammatory mediator.

Peroxisome proliferator-activated receptor alpha agonists as therapy for autoimmune disease.

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. PPAR gamma ligands, which include the naturally occurring PG metabolite 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), as well as thiazolidinediones, have been shown to have anti-inflammatory activity. The PPAR alpha agonists, gemfibrozil, ciprofibrate, and fenofibrate, have an excellent track history as oral agents used to treat hypertriglyceridemia. In the present study, we demonstrate that these PPAR alpha agonists can increase the production of the Th2 cytokine, IL-4, and suppress proliferation by TCR transgenic T cells specific for the myelin basic protein Ac1-11, as well as reduce NO production by microglia. Oral administration of gemfibrozil and fenofibrate inhibited clinical signs of experimental autoimmune encephalomyelitis. More importantly, gemfibrozil was shown to shift the cytokine secretion of human T cell lines by inhibiting IFN-gamma and promoting IL-4 secretion. These results suggest that PPAR alpha agonists such as gemfibrozil and fenofibrate, may be attractive candidates for use in human inflammatory conditions such as multiple sclerosis.

Ligands for the peroxisome proliferator-activated receptor-gamma and the retinoid X receptor exert additive anti-inflammatory effects on experimental autoimmune encephalomyelitis.

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a member of the nuclear-receptor superfamily that binds to DNA with retinoid X receptors (RXRs) as PPAR-RXR heterodimers. In experimental autoimmune encephalomyelitis (EAE), the gene expression of PPAR-gamma was demonstrated in spinal cord during the course of EAE. Administration of 15-deoxy-(12,14)-prostaglandin J2 (15d-PGJ2) or 9-cis-retinoic acid (RA) alone at the onset of clinical signs of EAE reduced the severity of disease, however, their combination resulted in enhanced amelioration of disease. These results suggest that use of RXR specific ligands may be highly effective when combined with PPAR-gamma agonists in the treatment of autoimmune demyelinating diseases such as multiple sclerosis (MS).

Sex steroid regulation of microglial cell activation: relevance to multiple sclerosis.

Multiple sclerosis (MS) occurs more commonly in females than males. However, the mechanisms resulting in gender differences in MS are unknown. Several studies have suggested that sex steroids influence the development and severity of MS. For example, pregnancy influences MS symptoms, with remission in the third trimester of gestation, followed by exacerbation in the postpartum period. In addition, oral contraceptives containing female sex steroids have been associated with a lower risk of developing MS and decreased disability. Experimental autoimmune encephalomyelitis (EAE) is an autoimmune disorder initiated by T cells reactive against central nervous system (CNS) antigens. EAE is characterized by inflammation and demyelination of the CNS, and by remittent paralysis-features consistent with MS. Recent studies have suggested that female sex steroids may modulate EAE, at least in part, through effects on T cells. For example, sex steroids shift T cells toward a Th2 phenotype in vitro, and cytokines produced by Th2 cells generally suppress EAE. Activated microglia also are believed to contribute to MS pathology; perhaps due in part to production of nitric oxide (NO) and TNF-alpha, molecules which can be toxic to CNS cells, including oligodendrocytes. We are currently investigating the role of sex steroids in modulating microglial cell function in relation to MS. It is hoped that elucidation of the mechanisms by which sex steroids modulate CNS inflammation will lead to future therapies in the treatment of MS.