Combination treatment of Glatiramer Acetate and Minocycline affects phenotype expression of blood monocyte-derived dendritic cells in Multiple Sclerosis patients

Minocycline for the management of multiple sclerosis: repositioning potential, opportunities, and challenges

INTRODUCTION

Multiple sclerosis (MS) is a chronic demyelinating inflammatory disorder with variable clinical and pathologic characteristics reflecting multiple underlying pathophysiologic mechanisms. Repositioning of existing drugs for the new indications offers several advantages including significant reduction in the cost and time of drug development and exemption from early phase clinical trials. Minocycline has been reported to exhibit immunomodulation in several pre-clinical and clinical studies through suppression of migratory inflammatory cells, modulation of peripheral immune response, and inhibition of microglial activation within the CNS.

AREAS COVERED

Here, the authors review the repositioning potential of minocycline for the treatment of MS along with appraisal of the evidence obtained from preclinical and clinical research. The authors also discuss the advantages and potential safety concerns related to the use of minocycline for the management of MS.

EXPERT OPINION

Minocycline offers several distinct advantages in terms of well-known safety profile, lower cost of therapy, widespread availability, and being available as an oral formulation. The authors call upon the public and private funders to facilitate well designed and adequately powered randomized clinical trials that can provide conclusive evidence regarding the safety and efficacy of minocycline in patients with MS.

Multiple Sclerosis Treatments Affect Monocyte-Derived Microvesicle Production

Microvesicles (MVs) are released by immune cells especially of the myeloid lineage upon stimulation with ATP on its cognate receptor P2X7, both in physiological and pathological conditions. In multiple sclerosis (MS) the role of MVs remains little investigated. We aimed to compare the release of MVs in peripheral blood monocytes from MS patients with healthy donors (HDs) and to see how current MS treatment may affect such a production. We also assessed the treatment effect on M1 and M2 monocyte polarization and on the inflammasome components. Spectrophotometric quantification was performed to compare monocyte-derived MVs from 20 untreated relapsing-remitting MS patients and 20 HDs and to evaluate the effect of different treatments. Subgroups of nine interferon-beta and of five teriflunomide-treated MS patients were evaluated at baseline and after 2, 6, and 12 months of treatment. Six MS patients taking Fingolimod, after switching from a first-line therapy, were included in the study and analyzed only at 12 months of treatment. MVs analysis revealed that monocytes from MS patients produced vesicles in higher amounts than controls. All treatments reduced vesicle production but only teriflunomide was associated with a downregulation of purinergic P2X7 receptor and inflammasome components expression. The therapies modulated mRNA expression of both M1 and M2 monocyte markers. Our results, suggesting new molecular targets for drugs currently used in MS, may potentially provide useful novel evidence to approach the disease.

Role of the immunogenic and tolerogenic subsets of dendritic cells in multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated disorder in the central nervous system (CNS) characterized by inflammation and demyelination as well as axonal and neuronal degeneration. So far effective therapies to reverse the disease are still lacking; most therapeutic drugs can only ameliorate the symptoms or reduce the frequency of relapse. Dendritic cells (DCs) are professional antigen presenting cells (APCs) that are key players in both mediating immune responses and inducing immune tolerance. Increasing evidence indicates that DCs contribute to the pathogenesis of MS and might provide an avenue for therapeutic intervention. Here, we summarize the immunogenic and tolerogenic roles of DCs in MS and review medicinal drugs that may affect functions of DCs and have been applied in clinic for MS treatment. We also describe potential therapeutic molecules that can target DCs by inducing anti-inflammatory cytokines and inhibiting proinflammatory cytokines in MS.

Multiple sclerosis: molecular mechanisms and therapeutic opportunities

The pathophysiology of multiple sclerosis (MS) involves several components: redox, inflammatory/autoimmune, vascular, and neurodegenerative. All of them are supported by the intertwined lines of evidence, and none of them should be written off. However, the exact mechanisms of MS initiation, its development, and progression are still elusive, despite the impressive pace by which the data on MS are accumulating. In this review, we will try to integrate the current facts and concepts, focusing on the role of redox changes and various reactive species in MS. Knowing the schedule of initial changes in pathogenic factors and the key turning points, as well as understanding the redox processes involved in MS pathogenesis is the way to enable MS prevention, early treatment, and the development of therapies that target specific pathophysiological components of the heterogeneous mechanisms of MS, which could alleviate the symptoms and hopefully stop MS. Pertinent to this, we will outline (i) redox processes involved in MS initiation; (ii) the role of reactive species in inflammation; (iii) prooxidative changes responsible for neurodegeneration; and (iv) the potential of antioxidative therapy.

Glatiramer Acetate administration does not reduce damage after cerebral ischemia in mice

Inflammation plays a key role in ischemic stroke pathophysiology: microglial/macrophage cells and type-1 helper cells (Th1) seem deleterious, while type-2 helper cells (Th2) and regulatory T cells (Treg) seem protective. CD4 Th0 differentiation is modulated by microglial cytokine secretion. Glatiramer Acetate (GA) is an immunomodulatory drug that has been approved for the treatment of human multiple sclerosis by means of a number of mechanisms: reduced microglial activation and pro-inflammatory cytokine production, Th0 differentiation shifting from Th2 to Th2 and Treg with anti-inflammatory cytokine production and increased neurogenesis. We induced permanent (pMCAo) or transient middle cerebral artery occlusion (tMCAo) and GA (2 mg) or vehicle was injected subcutaneously immediately after cerebral ischemia. Mice were sacrificed at D3 to measure neurological deficit, infarct volume, microglial cell density and qPCR of TNFα and IL-1β (pro-inflammatory microglial cytokines), IFNγ (Th2 cytokine), IL-4 (Th2 cytokine), TGFβ and IL-10 (Treg cytokines), and at D7 to evaluate neurological deficit, infarct volume and neurogenesis assessment. We showed that in GA-treated pMCAo mice, infarct volume, microglial cell density and cytokine secretion were not significantly modified at D3, while neurogenesis was enhanced at D7 without significant infarct volume reduction. In GA-treated tMCAo mice, microglial pro-inflammatory cytokines IL-1β and TNFα were significantly decreased without modification of microglial/macrophage cell density, cytokine secretion, neurological deficit or infarct volume at D3, or modification of neurological deficit, neurogenesis or infarct volume at D7. In conclusion, Glatiramer Acetate administered after cerebral ischemia does not reduce infarct volume or improve neurological deficit in mice despite a significant increase in neurogenesis in pMCAo and a microglial pro-inflammatory cytokine reduction in tMCAo.

Use of engineered bone marrow stem cells to deliver brain derived neurotrophic factor under the control of a tetracycline sensitive response element in experimental allergic encephalomyelitis

Brain derived neurotrophic factor (BDNF) has neuroprotective properties but its use has been limited by poor penetration of the blood brain barrier. Treatment using bone marrow stem cells (BMSC) or retroviruses as vectors reduces the clinical and pathological severity of experimental allergic encephalomyelitis (EAE). We have refined the BMSC based delivery system by introducing a tetracycline sensitive response element to control BDNF expression. We have now tested that construct in EAE and have shown a reduction in both the clinical and pathological severity of the disease. Further, we looked for changes in sirtuin1 and nicotinamide phosphoribosyltransferase expression that would be consistent with a neuroprotective effect.

The prospects of minocycline in multiple sclerosis

Multiple sclerosis (MS) is the most common inflammatory demyelinating disease of the central nervous system (CNS). Although there are several approved drugs for MS, not all patients respond optimally to these drugs. More effective, well-tolerated therapeutic strategies for MS are necessary, either through the development of new medication or combination of existing ones. Minocycline is a traditional antibiotic with profound anti-inflammatory and neuroprotective effects and good tolerance for long-term use. The encouraging results from the animal model and clinical experiments on minocycline make it a promising candidate for MS treatment whether used alone or combined with other drugs. In this review, we summarized the pharmacological actions of minocycline and focused on its therapeutic effects and safety in experimental autoimmune encephalomyelitis (EAE) and MS. The data obtained here showed that minocycline would be an effective and safe therapy for MS.

Exogenous control of the expression of Group I CD1 molecules competent for presentation of microbial nonpeptide antigens to human T lymphocytes

Group I CD1 (CD1a, CD1b, and CD1c) glycoproteins expressed on immature and mature dendritic cells present nonpeptide antigens (i.e., lipid or glycolipid molecules mainly of microbial origin) to T cells. Cytotoxic CD1-restricted T lymphocytes recognizing mycobacterial lipid antigens were found in tuberculosis patients. However, thanks to a complex interplay between mycobacteria and CD1 system, M. tuberculosis possesses a successful tactic based, at least in part, on CD1 downregulation to evade CD1-dependent immunity. On the ground of these findings, it is reasonable to hypothesize that modulation of CD1 protein expression by chemical, biological, or infectious agents could influence host's immune reactivity against M. tuberculosis-associated lipids, possibly affecting antitubercular resistance. This scenario prompted us to perform a detailed analysis of the literature concerning the effect of external agents on Group I CD1 expression in order to obtain valuable information on the possible strategies to be adopted for driving properly CD1-dependent immune functions in human pathology and in particular, in human tuberculosis.

Role of gut commensal microflora in the development of experimental autoimmune encephalomyelitis

Mucosal tolerance has been considered a potentially important pathway for the treatment of autoimmune disease, including human multiple sclerosis and experimental conditions such as experimental autoimmune encephalomyelitis (EAE). There is limited information on the capacity of commensal gut bacteria to induce and maintain peripheral immune tolerance. Inbred SJL and C57BL/6 mice were treated orally with a broad spectrum of antibiotics to reduce gut microflora. Reduction of gut commensal bacteria impaired the development of EAE. Intraperitoneal antibiotic-treated mice showed no significant decline in the gut microflora and developed EAE similar to untreated mice, suggesting that reduction in disease activity was related to alterations in the gut bacterial population. Protection was associated with a reduction of proinflammatory cytokines and increases in IL-10 and IL-13. Adoptive transfer of low numbers of IL-10-producing CD25(+)CD4(+) T cells (>75% FoxP3(+)) purified from cervical lymph nodes of commensal bacteria reduced mice and in vivo neutralization of CD25(+) cells suggested the role of regulatory T cells maintaining peripheral immune homeostasis. Our data demonstrate that antibiotic modification of gut commensal bacteria can modulate peripheral immune tolerance that can protect against EAE. This approach may offer a new therapeutic paradigm in the treatment of multiple sclerosis and perhaps other autoimmune conditions.

Nicotinic acid-mediated activation of both membrane and nuclear receptors towards therapeutic glucocorticoid mimetics for treating multiple sclerosis

Acute attacks of multiple sclerosis (MS) are most commonly treated with glucocorticoids, which can provide life-saving albeit only temporary symptomatic relief. The mechanism of action (MOA) is now known to involve induction of indoleamine 2,3-dioxygenase (IDO) and interleukin-10 (IL-10), where IL-10 requires subsequent heme oxygenase-1 (HMOX-1) induction. Ectopic expression studies reveal that even small changes in expression of IDO, HMOX-1, or mitochondrial superoxide dismutase (SOD2) can prevent demyelination in experimental autoimmune encephalomyelitis (EAE) animal models of MS. An alternative to glucocorticoids is needed for a long-term treatment of MS. A distinctly short list of endogenous activators of both membrane G-protein-coupled receptors and nuclear peroxisome proliferating antigen receptors (PPARs) demonstrably ameliorate EAE pathogenesis by MOAs resembling that of glucocorticoids. These dual activators and potential MS therapeutics include endocannabinoids and the prostaglandin 15-deoxy-Δ^12,14-PGJ₂. Nicotinamide profoundly ameliorates and prevents autoimmune-mediated demyelination in EAE via maintaining levels of nicotinamide adenine dinucleotide (NAD), without activating PPAR nor any G-protein-coupled receptor. By comparison, nicotinic acid provides even greater levels of NAD than nicotinamide in many tissues, while additionally activating the PPARγ-dependent pathway already shown to provide relief in animal models of MS after activation of GPR109a/HM74a. Thus nicotinic acid is uniquely suited for providing therapeutic relief in MS. However nicotinic acid is unexamined in MS research. Nicotinic acid penetrates the blood brain barrier, cures pellagric dementia, has been used for over 50 years clinically without toxicity, and raises HDL concentrations to a greater degree than any pharmaceutical, thus providing unparalleled benefits against lipodystrophy. Summary analysis reveals that the expected therapeutic benefits of high-dose nicotinic acid administration far outweigh any known adverse risks in consideration for the treatment of multiple sclerosis.

The importance of NAD in multiple sclerosis

The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.

Minocycline and neurodegenerative diseases

Minocycline is a semi-synthetic, second-generation tetracycline analog which is effectively crossing the blood-brain barrier, effective against gram-positive and -negative infections. In addition to its own antimicrobacterial properties, minocycline has been reported to exert neuroprotective effects over various experimental models such as cerebral ischemia, traumatic brain injury, amyotrophic lateral sclerosis, Parkinson's disease, kainic acid treatment, Huntington' disease and multiple sclerosis. Minocycline has been focused as a neuroprotective agent over neurodegenerative disease since it has been first reported that minocycline has neuroprotective effects in animal models of ischemic injury [Yrjanheikki J, Keinanen R, Pellikka M, Hokfelt T, Koisinaho J. Tetracyclines inhibit microglial activation and are neuroprotective in global brain ischemia. Proc Natl Acad Sci USA 1998;95:15769-74; Yrjanheikki J, Tikka T, Keinanen R, Goldsteins G, Chan PH, Koistinaho J. A tetracycline derivative, minocycline, reduces inflammation and protects against focal cerebral ischemia with a wide therapeutic window. Proc Natl Acad Sci USA 1999;96:13496-500]. Recently, the effect of minocycline on Alzheimer's disease has been also reported. Although its precise primary target is not clear, the action mechanisms of minocycline for neuroprotection reported so far are; via; the inhibition of mitochondrial permeability-transition mediated cytochrome c release from mitochondria, the inhibition of caspase-1 and -3 expressions, and the suppression of microglial activation, involvement in some signaling pathways, metalloprotease activity inhibition. Because of the high tolerance and the excellent penetration into the brain, minocycline has been clinically tried for some neurodegenerative diseases such as stroke, multiple sclerosis, spinal cord injury, amyotropic lateral sclerosis, Hungtington's disease and Parkinson's disease. This review will briefly summarize the effects and action mechanisms of minocycline on neurodegenerative diseases.