Ribavirin ameliorates experimental autoimmune encephalomyelitis in rats and modulates cytokine production

Intrinsic ecto-5'-Nucleotidase/A1R Coupling may Confer Neuroprotection to the Cerebellum in Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is widely used animal model of multiple sclerosis (MS). The disease is characterized by demyelination and neurodegeneration triggered by infiltrated autoimmune cells and their interaction with astrocytes and microglia. While neuroinflammation is most common in the spinal cord and brainstem, it is less prevalent in the cerebellum, where it predisposes to rapid disease progression. Because the induction and progression of EAE are tightly regulated by adenosinergic signaling, in the present study we compared the adenosine-producing and -degrading enzymes, ecto-5'-nucleotidase (eN/CD73) and adenosine deaminase (ADA), as well as the expression levels of adenosine receptors A1R and A2AR subtypes in nearby areas around the fourth cerebral ventricle-the pontine tegmentum, the choroid plexus (CP), and the cerebellum. Significant differences in histopathological findings were observed between pontine tegmentum and cerebellum on the same horizontal section level. Reactive astrogliosis and massive infiltration of CD4 + cells and macrophages in CP and pontine tegmentum resulted in local demyelination. In cerebellum, there was no evidence of infiltrates, microgliosis and neuroinflammation at the same sectional level. In addition, Bergman glia showed no signs of reactive gliosis. As for adenosinergic signaling, significant upregulation of eN/CD73 was observed in all areas studied, but in association with different adenosine receptor subtypes. In CP and pons, overexpression of eN/CD73 was coupled with induction of A2AR, whereas in cerebellum, a modest increase in eN/CD73 in resident Bergman glia was accompanied by a strong induction of A1R in the same type of astrocytes. Thus, the presence of specialized astroglia and intrinsic differences in adenosinergic signaling may play a critical role in the differential regional susceptibility to EAE inflammation.

Expression of functionally distinct ecto-5'-nucleotidase/CD73 glycovariants in reactive astrocytes in experimental autoimmune encephalomyelitis and neuroinflammatory conditions in vitro

Ecto-5'-nucleotidase/CD73 (eN/CD73) is a membrane-bound enzyme involved in extracellular production of adenosine and a cell adhesion molecule involved in cell-cell interactions. In neuroinflammatory conditions such as experimental autoimmune encephalomyelitis (EAE), reactive astrocytes occupying active demyelination areas significantly upregulate eN/CD73 and express additional eN/CD73 variants. The present study investigated whether the different eN/CD73 variants represent distinct glycoforms and the functional consequences of their expression in neuroinflammatory states. The study was performed in animals at different stages of EAE and in primary astrocyte cultures treated with a range of inflammatory cytokines. Upregulation at the mRNA, protein, and functional levels, as well as the appearance of multiple eN/CD73 glycovariants were detected in the inflamed spinal cord tissue. At the peak of the disease, eN/CD73 exhibited higher AMP turnover and lower enzyme-substrate affinity than the control group, which was attributed to altered glycosylation under neuroinflammatory conditions. A subsequent in vitro study showed that primary astrocytes upregulated eN/CD73 and expressed the multiple glycovariants upon stimulation with TNFα, IL-1β, IL-6, and ATP, with the effect occurring at least in part via induction of JAK/STAT3 signaling. Experimental removal of glycan moieties from membrane glycoproteins by PNGaseF decreased eN/CD73 activity but had no effect on the enzyme's involvement in astrocyte migration. Our results suggest that neuroinflammatory states are associated with the appearance of functionally distinct eN/CD73 glycovariants, which may play a role in the development of the reactive astrocyte phenotype.

The Function of the Hypothalamic-Pituitary-Adrenal Axis During Experimental Autoimmune Encephalomyelitis: Involvement of Oxidative Stress Mediators

Multiple sclerosis (MS) is an inflammatory, demyelinating disease with an unknown origin. Previous studies showed the involvement of the hypothalamic–pituitary–adrenal (HPA) axis to susceptibility to autoimmune diseases, including MS, and its best-characterized animal model, experimental autoimmune encephalomyelitis (EAE). During MS/EAE, innate immune cells are activated and release cytokines and other inflammatory mediators, leading to a vicious cycle of inflammation. In response to inflammation, the activated HPA axis modulates immune responses via glucocorticoid activity. Because the mechanisms involving oxidative stress to the HPA axis are relatively unrevealed, in this study, we investigate the inflammatory and oxidative stress status of HPA axis during EAE. Our results reveal an upregulation of Pomc gene expression, followed by POMC and ACTH protein increase at the peak of the EAE in the pituitary. Also, prostaglandins are well-known contributors of HPA axis activation, which increases during EAE at the periphery. The upregulated Tnf expression in the pituitary during the peak of EAE occurred. This leads to the activation of oxidative pathways, followed by upregulation of inducible NO synthase expression. The reactive oxidant/nitrosative species (ROS/RNS), such as superoxide anion and NO, increase their levels at the onset and peak of the disease in the pituitary and adrenal glands, returning to control levels at the end of EAE. The corticotrophs in the pituitary increased in number and volume at the peak of EAE that coincides with high lipid peroxidation levels. The expression of MC2R in the adrenal glands increases at the peak of EAE, where strong induction of superoxide anion and malondialdehyde (MDA), reduced total glutathione (GSH) content, and catalase activity occurred at the peak and end of EAE compared with controls. The results obtained from this study may help in understanding the mechanisms and possible pharmacological modulation in MS and demonstrate an effect of oxidative stress exposure in the HPA activation during the course of EAE.

The Potassium Channel Kv1.5 Expression Alters During Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a chronic, inflammatory, neurodegenerative disease with an autoimmune component. It was suggested that potassium channels, which are involved in crucial biological functions may have a role in different diseases, including MS and its animal model, experimental autoimmune encephalomyelitis (EAE). It was shown that voltage-gated potassium channels Kv1.5 are responsible for fine-tuning in the immune physiology and influence proliferation and differentiation in microglia and astrocytes. Here, we explored the cellular distribution of the Kv1.5 channel, together with its transcript and protein expression in the male rat spinal cord during different stages of EAE. Our results reveal a decrease of Kv1.5 transcript and protein level at the peak of disease, where massive infiltration of myeloid cells occurs, together with reactive astrogliosis and demyelination. Also, we revealed that the presence of this channel is not found in infiltrating macrophages/microglia during EAE. It is interesting to note that Kv1.5 channel is expressed only in resting microglia in the naïve animals. Predominant expression of Kv1.5 channel was found in the astrocytes in all experimental groups, while some vimentin⁺ cells, resembling macrophages, are devoid of Kv1.5 expression. Our results point to the possible link between Kv1.5 channel and the pathophysiological processes in EAE.

Induction of NTPDase1/CD39 by Reactive Microglia and Macrophages Is Associated With the Functional State During EAE

Purinergic signaling is critically involved in neuroinflammation associated with multiple sclerosis (MS) and its major inflammatory animal model, experimental autoimmune encephalomyelitis (EAE). Herein, we explored the expression of ectonucleoside triphosphate diphosphohydrolase1 (NTPDase1/CD39) in the spinal cord, at the onset (Eo), peak (Ep), and end (Ee) of EAE. Several-fold increase in mRNA and in NTPDase1 protein levels were observed at Eo and Ep. In situ hybridization combined with fluorescent immunohistochemistry showed that reactive microglia and infiltrated mononuclear cells mostly accounted for the observed increase. Colocalization analysis revealed that up to 80% of Iba1 immunoreactivity and ∼50% of CD68 immunoreactivity was colocalized with NTPDase1, while flow cytometric analysis revealed that ∼70% of mononuclear infiltrates were NTPDase1+ at Ep. Given the main role of NTPDase1 to degrade proinflammatory ATP, we hypothesized that the observed up-regulation of NTPDase1 may be associated with the transition between proinflammatory M1-like to neuroprotective M2-like phenotype of microglia/macrophages during EAE. Functional phenotype of reactive microglia/macrophages that overexpress NTPDase1 was assessed by multi-image colocalization analysis using iNOS and Arg1 as selective markers for M1 and M2 reactive states, respectively. At the peak of EAE NTPDase1 immunoreactivity showed much higher co-occurrence with Arg1 immunoreactivity in microglia and macrophages, compared to iNOS, implying its stronger association with M2-like reactive phenotype. Additionally, in ∼80% of CD68 positive cells NTPDase1 was coexpressed with Arg1 compared to negligible fraction coexpresing iNOS and ∼15% coexpresing both markers, additionally indicating prevalent association of NTPDase1 with M2-like microglial/macrophages phenotype at Ep. Together, our data suggest an association between NTPDase1 up-regulation by reactive microglia and infiltrated macrophages and their transition toward antiinflammatory phenotype in EAE.

Animal models of multiple sclerosis: Focus on experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic, progressive disorder of the central nervous system (CNS) that affects more than two million people worldwide. Several animal models resemble MS pathology; the most employed are experimental autoimmune encephalomyelitis (EAE) and toxin- and/or virus-induced demyelination. In this review we will summarize our knowledge on the utility of different animal models in MS research. Although animal models cannot replicate the complexity and heterogeneity of the MS pathology, they have proved to be useful for the development of several drugs approved for treatment of MS patients. This review focuses on EAE because it represents both clinical and pathological features of MS. During the past decades, EAE has been effective in illuminating various pathological processes that occur during MS, including inflammation, CNS penetration, demyelination, axonopathy, and neuron loss mediated by immune cells.

Further understanding of the immunopathology of multiple sclerosis: impact on future treatments

INTRODUCTION

The understanding of the immunopathogenesis of multiple sclerosis (MS) has expanded with more research into T-cell subtypes, cytokine contributors, B-cell participation, mitochondrial dysfunction, and more. Treatment options have rapidly expanded with three relatively recent oral therapy alternatives entering the arena.

AREAS COVERED

In the following review, we discuss current mechanisms of immune dysregulation in MS, how they relate to current treatments, and the impact these findings will have on the future of therapy. Expert commentary: The efficacy of these medications and understanding their mechanisms of actions validates the immunopathogenic mechanisms thought to underlie MS. Further research has exposed new targets, while new promising therapies have shed light on new aspects into the pathophysiology of MS.

Low-dose ribavirin treatments attenuate neuroinflammatory activation of BV-2 Cells by interfering with inducible nitric oxide synthase

Microglia play a key role in defending central nervous system from various internal and external threats. However, their excessive and/or chronic activation is associated with deleterious effects in a variety of neurodegenerative diseases. Previously, we have shown that ribavirin when applied in clinically relevant dosage (10 μM) modulates activated microglia in complex fashion inducing both anti- and proinflammatory effects, simultaneously causing cytotoxicity. Here, we examined potential of low-dose ribavirin (0.1 and 1 μM) to modulate activated BV-2 microglia. Morphological and functional activation of BV-2 cells was achieved with lipopolysaccharide (LPS) stimulation. Our results demonstrated that low-dose ribavirin did not induce cell death, while 10 μM ribavirin promoted LPS induced apoptosis. We determined that 1 μM ribavirin was equally efficient in deactivation of LPS induced morphological changes as 10 μM ribavirin treatment. Ribavirin showed halfway success in reducing markers of functional activation of microglia. Namely, none of the doses had effect on LPS triggered production of proinflammatory cytokine tumor necrosis factor alpha. On the other hand, low-dose ribavirin proved its effectiveness in reduction of another inflammatory mediator, nitric oxide, by inhibiting inducible form of nitric oxide synthase. Our results imply that low-dose ribavirin may alleviate nitrosative stress during neuroinflammation.

The effect of ribavirin on reactive astrogliosis in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of CNS inflammatory and demyelinating disease multiple sclerosis. Microglia and astrocytes represent two related cell types involved in the brain pathology in EAE. Accumulations of hypertrophic reactive astrocytes, intensely stained with glial fibrillary acidic protein (GFAP), which also expressed vimentin, are prominent features of EAE lesions. Recent studies from our laboratory reported that ribavirin attenuated the disease process in EAE by reducing clinical and histological manifestations. EAE was induced in genetically susceptible Dark Agouti rats with syngeneic spinal cord homogenate in complete Freund's adjuvant. Real time PCR and immunohistochemistry were used for determination of GFAP and vimentin gene and tissue expression. We have observed the increased gene and tissue expression of GFAP and vimentin in EAE rats. Ribavirin treatment significantly decreased the number of reactive astrocytes at the peak of disease. At the end of the disease, we have observed reactive GFAP(+) and vimentin(+) astrocytes in both immunized and ribavirin-treated groups, accompanied by increased level of GFAP mRNA. The present study indicates that ribavirin may have the ability to attenuate astrocyte proliferation and glial scaring at the peak of the disease and modulate the astroglial response to EAE during the time-course of the disease.

Immunomodulatory effects of antimicrobial agents. Part I: antibacterial and antiviral agents

Despite impressive therapeutic progresses in the battle against infections, microorganisms are still a threat to mankind. With hundreds of antibacterial molecules, major concerns remain about the emergence of resistant and multidrug-resistant pathogens. On the other hand, the antiviral drug armamentarium is comprised of only a few dozens of compounds which are highly pathogen specific, and resistance is also a concern. According to Arturo Casadevall (Albert Einstein College of Medicine, NY, USA), we have now entered the third era of anti-infective strategy, which intends to favor the interplay between active molecules and the immune system. The first part of this review focuses on the potential immunomodulating properties of anti-infective agents, beginning with antibacterial and antiviral agents.

Chemical inducers and transcriptional markers of oligodendrocyte differentiation

Oligodendrocytes generate and maintain myelin, which is essential for axonal function and protection of the mammalian central nervous system. To advance our molecular understanding of differentiation by these cells, we screened libraries of pharmacologically active compounds and identified inducers of differentiation of Oli-neu, a stable cell line of mouse oligodendrocyte precursors (OPCs). We identified four broad classes of inducers, namely, forskolin/cAMP (protein kinase A activators), steroids (glucocorticoids and retinoic acid), ErbB2 inhibitors, and nucleoside analogs, and confirmed the activity of these compounds on rat primary oligodendrocyte precursors and mixed cortical cultures. We also analyzed transcriptional responses in the chemically induced mouse and rat OPC differentiation processes and compared these with earlier studies. We confirm the view that ErbB2 is a natural signaling component that is required for OPC proliferation, whereas ErbB2 inhibition or genetic knockdown results in OPC differentiation.

New drug therapies for multiple sclerosis

PURPOSE OF REVIEW

Multiple sclerosis (MS) is an autoimmune and inflammatory disease of the central nervous system (CNS) that causes neurological disability in young adults and that to date has no cure. Until now, expensive and only partially efficacious therapies have become available. For this reason, researchers, clinicians and pharmaceutical companies are currently investigating new drugs for the treatment of MS. Here, we review the most recent data on drug candidates for MS.

RECENT FINDINGS

In the preclinical phase, such drug candidates have shown a beneficial effect on the onset of experimental autoimmune encephalomyelitis (microtubule-stabilizing drugs, MS14, Lithium, GEMSP...), a decrease in CNS cell infiltrates (recombinant T cell receptor ligand, lovastatin-rolipram, ribavirin, GEMSP...), prevention of demyelination (lovastatin-rolipram, calpain inhibitor, lithium...); and a reduction of axonal loss (phenytoin, lovastatin-rolipram, calpain inhibitor). In clinical trials, drug candidates against MS have shown safety (rituximab, ustekinumab, intravenous immunoglobulin, laquinimod, BHT-3009, fumarate, chaperonin 10, GEMSP...), an improvement of gadolinium-enhanced lesions (protiramer, fingolimod, laquinimod, BHT-3009, fumarate, daclizumab...), and an improvement of the relapse rate (fingolimod, fumarate...).

SUMMARY

Future research into MS should focus on a combination of therapies and on the development of drugs directed against the remitting and progressive phases of the disease. In this sense, MS is a very complex multifactorial disease that requires treatment able to cover all the aspects of MS and not only the anti-inflammatory aspect.

Time-course changes in ectonucleotidase activities during experimental autoimmune encephalomyelitis

The aim of the present study was to analyze the activities of extracellular purine metabolizing enzymes, CD39 (apyrase, EC 3.6.1.5) and CD73 (ecto-5' nucleotidase, EC 3.1.3.5) in experimental autoimmune encephalomyelitis (EAE). The levels of ATP, ADP and AMP hydrolysis were analyzed in the blood serum and in the rat spinal cord plasma membrane preparation 8, 15 and 25 days after induction of EAE. The animals were divided in three groups: control (saline), CFA (adjuvant-only) and EAE (CFA and homogenate of spinal cords). Eight days after immunization, ATP, ADP and AMP hydrolysis in the blood serum and spinal cord membrane preparations were unaffected in EAE compared to both, control and CFA group. In the peak of disease, ATP, ADP and AMP hydrolysis in EAE group showed significant decrease in the blood serum and prominent increase in the spinal cord membrane preparation compared to CFA and control group. At the end of illness, as judged by disappearance of clinical manifestation of EAE, ATP, ADP and AMP hydrolysis, although closer to CFA levels, were still significantly different in respect to the CFA group. Modulation of ATP, ADP and AMP hydrolysis suggests that they operate during EAE and might represent the basis of novel therapeutic strategies in immune-mediated diseases, such as MS.