Therapeutic Target In Multiple Sclerosis Research Articles

CD138 as a Specific CSF Biomarker of Multiple Sclerosis.

The aim of this study was to identify novel biomarkers for multiple sclerosis (MS) diagnosis and prognosis, addressing the critical need for specific and prognostically valuable markers in the field. We conducted an extensive proteomic investigation, combining analysis of (1) CSF proteome from symptomatic controls, fast and slow converters after clinically isolated syndromes, and patients with relapsing-remitting MS (n = 10 per group) using label-free quantitative proteomics and (2) oligodendrocyte secretome changes under proinflammatory or proapoptotic conditions using stable isotope labeling by amino acids in cell culture. Proteins exhibiting differential abundance in both proteomic analyses were combined with other putative MS biomarkers, yielding a comprehensive list of 87 proteins that underwent quantification through parallel reaction monitoring (PRM) in a novel cohort, comprising symptomatic controls, inflammatory neurologic disease controls, and patients with MS at various disease stages (n = 10 per group). The 11 proteins that passed this qualification step were subjected to a new PRM assay within an expanded cohort comprising 158 patients with either MS at different disease stages or other inflammatory or noninflammatory neurologic disease controls. This study unveiled a promising biomarker signature for MS, including previously established candidates, such as chitinase 3-like protein 1, chitinase 3-like protein 2, chitotriosidase, immunoglobulin kappa chain region C, neutrophil gelatinase-associated lipocalin, and CD27. In addition, we identified novel markers, namely cat eye syndrome critical region protein 1 (adenosine deaminase 2, a therapeutic target in multiple sclerosis) and syndecan-1, a proteoglycan, also known as plasma cell surface marker CD138 and acting as chitinase 3-like protein 1 receptor implicated in inflammation and cancer signaling. CD138 exhibited good diagnostic accuracy in distinguishing MS from inflammatory neurologic disorders (area under the curve [AUC] = 0.85, CI 0.75-0.95). CD138 immunostaining was also observed in the brains of patients with MS and cultured oligodendrocyte precursor cells but was absent in astrocytes. These findings identify CD138 as a specific CSF biomarker for MS and suggest the selective activation of the chitinase 3-like protein 1/CD138 pathway within the oligodendrocyte lineage in MS. They offer promising prospects for improving MS diagnosis and prognosis by providing much-needed specificity and clinical utility. This study provides Class II evidence that CD138 distinguishes multiple sclerosis from other inflammatory neurologic disorders with an AUC of 0.85 (95% CI 0.75-0.95).

Altered Expression of B Cell Receptor Signaling Pathway Genes in Peripheral Blood of Patients with Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune neurodegenerative disease and has adverse implications. The exact mechanism of its pathogenesis is not fully understood and remains to be elucidated. In the current study we aimed to identify key genes that can serve as potential biomarkers and therapeutic targets for MS and shed light on pathogenesis mechanisms involved in MS.
 We analyzed a gene expression dataset (GES21942) and found 266 differentially expressed genes (DEGs) including 183 upregulated and 83 downregulated genes in MS patients compared to controls. Then we conducted pathway enrichment on DEGs and selected the top enriched pathway i.e., B cell receptor signaling pathway, and 5 genes of this pathway (CR2, BLK, BLNK, RASGRP3, and KRAS) for further investigation in our clinical samples. We recruited 50 MS patients and 50 controls and assessed the expression of selected genes in the circulation of patients versus controls.
 Expression of CR2, BLK, BLNK, and RASGRP3 were significantly higher in MS cases compared with controls. There was no significant difference in expression of KRAS between patients and controls. All of the selected genes with differential expression had noticeable diagnostic power and CR2 was the most robust gene in differentiating MS cases from controls. Additionally, a combination of genes resulted in enhanced diagnostic power.
 Collectively our results suggest that the B cell receptor signaling pathway and the selected genes from this pathway may be implicated in the pathogenesis of MS and each of these genes can be considered as potential diagnostic biomarkers and therapeutic targets.

Alpha Calcitonin Gene-related Peptide, Neuropeptide Y, and Substance P as Biomarkers for Diagnosis and Disease Activity and Severity in Multiple Sclerosis.

Alpha calcitonin gene-related peptide (aCGRP), neuropeptide Y (NPY), and substance P (SP) are neuropeptides that have emerged recently as potent immunomodulatory factors with potential as novel biomarkers and therapeutic targets in multiple sclerosis (MS). The study aimed to detect serum levels of aCGRP, NPY, and SP in MS patients versus healthy controls and their association with disease activity and severity. Serum levels were measured in MS patients and age and sex-matched healthy controls using ELISA. We included 67 MS patients: 61 relapsing-remitting MS (RR-MS) and 6 progressive MS (PR-MS), and 67 healthy controls. Serum NPY level was found to be lower in MS patients than in healthy controls (p < 0.001). Serum aCGRP level was higher in PR-MS compared to RR-MS (p = 0.007) and healthy controls (p = 0.001), and it positively correlated with EDSS (r = 0.270, p = 0.028). Serum NPY level was significantly higher in RR-MS and PR-MS than in healthy controls (p < 0.001 and p = 0.001, respectively), and it was lower in patients with mild or moderate/severe disease than in healthy controls (p < 0.001). Significant inverse correlations were found between SP level and MS disease duration (r = -0.279, p = 0.022) and duration of current DMT (r = -0.315, p = 0.042). Lower serum levels of NPY were revealed in MS patients compared to healthy controls. Since serum levels of aCGRP are significantly associated with disease activity and severity, it is a potential disease progression marker.

Autotaxin in encephalitogenic CD4 T cells as a therapeutic target for multiple sclerosis.

Multiple sclerosis (MS) is an immune-mediated inflammatory disease of the CNS. A defining characteristic of MS is the ability of autoreactive T lymphocytes to cross the blood-brain barrier and mediate inflammation within the CNS. Previous work from our lab found the gene Enpp2 to be highly upregulated in murine encephalitogenic T cells. Enpp2 encodes for the protein autotaxin, a secreted glycoprotein that catalyzes the production of lysophosphatidic acid and promotes transendothelial migration of T cells from the bloodstream into the lymphatic system. The present study sought to characterize autotaxin expression in T cells during CNS autoimmune disease and determine its potential therapeutic value. Myelin-activated CD4 T cells upregulated expression of autotaxin in vitro, and ex vivo analysis of CNS-infiltrating CD4 T cells showed significantly higher autotaxin expression compared with cells from healthy mice. In addition, inhibiting autotaxin in myelin-specific T cells reduced their encephalitogenicity in adoptive transfer studies and decreased in vitro cell motility. Importantly, using two mouse models of MS, treatment with an autotaxin inhibitor ameliorated EAE severity, decreased the number of CNS infiltrating T and B cells, and suppressed relapses, suggesting autotaxin may be a promising therapeutic target in the treatment of MS.

Inflammasomes as a Prognostic Marker and Possible Therapeutic Target in Multiple Sclerosis: A Rapid Review of the Literature

Introduction: Inflammasomes are multiprotein complexes innate to the immune system that, upon activation, initiate a chain reaction culminating in the production of cytokines IL-1 and IL-18. Recent studies have suggested a connection between inflammasome activation and neurological diseases such as multiple sclerosis (MS). In this review, we aimed to evaluate the role of inflammasomes as potential therapeutic agents and prognostic markers of MS. Methods: Through a database search, 156 articles were identified. Of these, we selected articles focusing on observational and interventional studies that either directly measured the expression of inflammasomes or the levels of cytokines or interleukin as outcomes. After applying a snowball sampling strategy, this review ultimately included nine studies. Results: Our search yielded nine studies published between 2010 and 2022—9 observational studies included case-control and cohort designs. All studies comprised adult populations, 20–72 years of age. All studies incorporated a control group. We selected studies that utilized surrogate measures to evaluate outcomes such as inflammasome expression of NLRP3 or similar genes and assess cytokine levels such as IL-1β, IL-18, IL-23, and TNF. Discussion: Overall, the revised studies suggest a possible role for inflammasomes components, including ASC and caspase-1, which have been evaluated as potential prognostic markers in MS. Therapeutic strategies have focused on the inhibition of NLRP3, which is one of the most prominent and studied inflammasomes, by IFN-β.

The Gut-Brain Axis as a Therapeutic Target in Multiple Sclerosis.

The CNS is very susceptible to oxidative stress; the gut microbiota plays an important role as a trigger of oxidative damage that promotes mitochondrial dysfunction, neuroinflammation, and neurodegeneration. In the current review, we discuss recent findings on oxidative-stress-related inflammation mediated by the gut-brain axis in multiple sclerosis (MS). Growing evidence suggests targeting gut microbiota can be a promising strategy for MS management. Intricate interaction between multiple factors leads to increased intra- and inter-individual heterogeneity, frequently painting a different picture in vivo from that obtained under controlled conditions. Following an evidence-based approach, all proposed interventions should be validated in clinical trials with cohorts large enough to reach significance. Our review summarizes existing clinical trials focused on identifying suitable interventions, the suitable combinations, and appropriate timings to target microbiota-related oxidative stress. Most studies assessed relapsing-remitting MS (RRMS); only a few studies with very limited cohorts were carried out in other MS stages (e.g., secondary progressive MS-SPMS). Future trials must consider an extended time frame, perhaps starting with the perinatal period and lasting until the young adult period, aiming to capture as many complex intersystem interactions as possible.

Perspectives for the Use of a Multiomics Approach for Finding New Diagnostic Associations and Therapeutic Targets in Multiple Sclerosis

Perspectives for the Use of a Multiomics Approach for Finding New Diagnostic Associations and Therapeutic Targets in Multiple Sclerosis

Modulation of the Microglial Nogo-A/NgR Signaling Pathway as a Therapeutic Target for Multiple Sclerosis

Current therapeutics targeting chronic phases of multiple sclerosis (MS) are considerably limited in reversing the neural damage resulting from repeated inflammation and demyelination insults in the multi-focal lesions. This inflammation is propagated by the activation of microglia, the endogenous immune cell aiding in the central nervous system homeostasis. Activated microglia may transition into polarized phenotypes; namely, the classically activated proinflammatory phenotype (previously categorized as M1) and the alternatively activated anti-inflammatory phenotype (previously, M2). These transitional microglial phenotypes are dynamic states, existing as a continuum. Shifting microglial polarization to an anti-inflammatory status may be a potential therapeutic strategy that can be harnessed to limit neuroinflammation and further neurodegeneration in MS. Our research has observed that the obstruction of signaling by inhibitory myelin proteins such as myelin-associated inhibitory factor, Nogo-A, with its receptor (NgR), can regulate microglial cell function and activity in pre-clinical animal studies. Our review explores the microglial role and polarization in MS pathology. Additionally, the potential therapeutics of targeting Nogo-A/NgR cellular mechanisms on microglia migration, polarization and phagocytosis for neurorepair in MS and other demyelination diseases will be discussed.

Endocannabinoid levels in peripheral blood mononuclear cells of multiple sclerosis patients treated with dimethyl fumarate

The endocannabinoid system (ECS), a signalling network with immunomodulatory properties, is a potential therapeutic target in multiple sclerosis (MS). Dimethyl fumarate (DMF) is an approved drug for MS whose mechanism of action has not been fully elucidated; the possibility exists that its therapeutic effects could imply the ECS. With the aim of studying if DMF can modulate the ECS, the endocannabinoids 2-arachidonoylglycerol (2-AG), anandamide (AEA), oleoylethanolamide (OEA) and palmitoylethanolamide (PEA) were determined by liquid chromatography-mass spectrometry in peripheral blood mononuclear cells from 21 healthy donors (HD) and 32 MS patients at baseline and after 12 and 24 months of DMF treatment. MS patients presented lower levels of 2-AG and PEA compared to HD. 2-AG increased at 24 months, reaching HD levels. AEA and PEA remained stable at 12 and 24 months. OEA increased at 12 months and returned to initial levels at 24 months. Patients who achieved no evidence of disease activity (NEDA3) presented the same modulation over time as EDA3 patients. PEA was modulated differentially between females and males. Our results show that the ECS is dysregulated in MS patients. The increase in 2-AG and OEA during DMF treatment suggests a possible role of DMF in ECS modulation.

Visualizing Sphingosine-1-Phosphate Receptor 1(S1P1) Signaling During Central Nervous System De- and Remyelination.

Multiple sclerosis (MS) is an inflammatory-demyelinating disease of the central nervous system (CNS) mediated by aberrant auto-reactive immune responses. The current immune-modulatory therapies are unable to protect and repair immune-mediated neural tissue damage. One of the therapeutic targets in MS is the sphingosine-1-phosphate (S1P) pathway which signals via sphingosine-1-phosphate receptors 1-5 (S1P1-5). S1P receptors are expressed predominantly on immune and CNS cells. Considering the potential neuroprotective properties of S1P signaling, we utilized S1P1-GFP (Green fluorescent protein) reporter mice in the cuprizone-induced demyelination model to investigate in vivo S1P - S1P1 signaling in the CNS. We observed S1P1 signaling in a subset of neural stem cells in the subventricular zone (SVZ) during demyelination. During remyelination, S1P1 signaling is expressed in oligodendrocyte progenitor cells in the SVZ and mature oligodendrocytes in the medial corpus callosum (MCC). In the cuprizone model, we did not observe S1P1 signaling in neurons and astrocytes. We also observed β-arrestin-dependent S1P1 signaling in lymphocytes during demyelination and CNS inflammation. Our findings reveal β-arrestin-dependent S1P1 signaling in oligodendrocyte lineage cells implying a role of S1P1 signaling in remyelination.

Natural Killer Cells in Multiple Sclerosis: Entering the Stage.

Studies investigating the immunopathology of multiple sclerosis (MS) have largely focused on adaptive T and B lymphocytes. However, in recent years there has been an increased interest in the contribution of innate immune cells, amongst which the natural killer (NK) cells. Apart from their canonical role of controlling viral infections, cell stress and malignancies, NK cells are increasingly being recognized for their modulating effect on the adaptive immune system, both in health and autoimmune disease. From different lines of research there is now evidence that NK cells contribute to MS immunopathology. In this review, we provide an overview of studies that have investigated the role of NK cells in the pathogenesis of MS by use of the experimental autoimmune encephalomyelitis (EAE) animal model, MS genetics or through ex vivo and in vitro work into the immunology of MS patients. With the advent of modern hypothesis-free technologies such as single-cell transcriptomics, we are exposing an unexpected NK cell heterogeneity, increasingly blurring the boundaries between adaptive and innate immunity. We conclude that unravelling this heterogeneity, as well as the mechanistic link between innate and adaptive immune cell functions will lay the foundation for the use of NK cells as prognostic tools and therapeutic targets in MS and a myriad of other currently uncurable autoimmune disorders.

TH17 cells in multiple sclerosis dislodge another brick in the wall.

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[Opportunities of multi-omics approach for the search for new diagnostic and therapeutic targets in multiple sclerosis].

Multiple sclerosis is an extremely heterogeneous disease and, despite intensive research, no selective biomarkers have been identified for this pathology, and therefore its diagnosis in the early stages is still challenging. One of the most powerful tools for studying the pathogenesis of multiple sclerosis is the multi-omics approach, which makes it possible to characterize cells involved in the disease progression in the most detailed and versatile way. This review will describe the current directions of research in multiple sclerosis using high-throughput technologies. Also, an assessment of the demand for the use of a multi-omics approach was carried out.

Ofatumumab for relapsing forms of multiple sclerosis.

In recent years, B cells have been extensively studied as a therapeutic target in multiple sclerosis (MS). Particularly, anti-CD20 monoclonal antibodies (MAbs) such as rituximab or ocrelizumab have proven to be effective in treating various forms of MS. Ofatumumab, a second-generation anti-CD20 IgG1κ fully human MAb, binds to a different, membrane-proximal epitope of CD20 compared with other anti-CD20 MAbs, thus ensuring a slower dissociation rate. This results in dose-dependent B-cell depletion mainly exerted through a mechanism of complement-dependent cytotoxicity. The repletion kinetic is faster than that of rituximab or ocrelizumab. Ofatumumab is the first approved drug for relapsing forms of MS that is administered via subcutaneous injection every 4 weeks. Two phase II and two phase III clinical trials have shown that it is effective in reducing the annualized relapse rate and clinical disability worsening, as well as in suppressing magnetic resonance imaging (MRI) disease activity. The safety profile of the drug has proven to be favorable, with good tolerability and low immunogenic risk. Moreover, the subcutaneous injection grants an easier way of administration. The current evidence on ofatumumab efficacy and safety is reviewed in the present article.

S100B Protein as a Therapeutic Target in Multiple Sclerosis: The S100B Inhibitor Arundic Acid Protects from Chronic Experimental Autoimmune Encephalomyelitis.

S100B is an astrocytic protein behaving at high concentration as a damage-associated molecular pattern molecule. A direct correlation between the increased amount of S100B and inflammatory processes has been demonstrated, and in particular, the inhibitor of S100B activity pentamidine has been shown to ameliorate clinical scores and neuropathologic-biomolecular parameters in the relapsing-remitting experimental autoimmune encephalomyelitis mouse model of multiple sclerosis. This study investigates the effect of arundic acid (AA), a known inhibitor of astrocytic S100B synthesis, in the chronic experimental autoimmune encephalomyelitis, which is another mouse model of multiple sclerosis usually studied. By the daily evaluation of clinical scores and neuropathologic-molecular analysis performed in the spinal cord, we observed that the AA-treated group showed lower severity compared to the vehicle-treated mice, particularly in the early phase of disease onset. We also observed a significant reduction of astrocytosis, demyelination, immune infiltrates, proinflammatory cytokines expression and enzymatic oxidative reactivity in the AA-treated group. Overall, our results reinforce the involvement of S100B in the development of animal models of multiple sclerosis and propose AA targeting the S100B protein as a focused potential drug to be considered for multiple sclerosis treatment.

TAMI-35. DETECTING SINGLE-CELL INTERACTIONS IN ORGANOTYPIC CULTURES OF GLIOBLASTOMA USING BARCODED RABIES VIRUS

Abstract Cell-cell interactions are thought to drive tumor-promoting signals in the microenvironment of glioblastoma, but standard approaches for single cell analysis do not directly identify cell interactions and the mechanisms that mediate them. We recently developed a novel method to analyze cell-cell interactions—rabies barcode interaction detection followed by sequencing (RABID-seq), which combines barcoded viral tracing and single-cell RNA sequencing (scRNAseq). RABID-seq was first implemented in transgenic mice to investigate the interactions of astrocytes with other cells in the CNS enabling the study of astrocyte connectome perturbations and candidate therapeutic targets in multiple sclerosis and its pre-clinical model, experimental autoimmune encephalomyelitis (EAE). Here, we report the first use of RABID-seq in human tissues in organotypic cultures established from three IDH-wildtype glioblastoma (GBM) patients. In organotypic GBM cultures, initial infection by pseudotyped barcoded rabies virus deficient for viral glycoprotein was achieved after previous culture transduction with a lentivirus containing the avian TVA receptor and rabies glycoprotein under the human EF1a promoter. We employed this system to initially infect approximately 1,000 malignant or non malignant cells in the tumor microenvironment. After five days, infected cells were isolated from cultures and processed for single cell analysis using SMART seq. We were able to capture at least 6,000 interacting cells per tumor specimen, from which barcodes were recovered and cDNA was sent for sequencing. Here we present connectomic data from our initial cohort of three glioblastoma patients as an introduction to RABID-seq, with a focus on astrocyte-tumor interactions. Candidate mechanisms of cellular interactions will undergo functional validation in murine models of glioblastoma.

InVitro and In Vivo Investigation of S1PR1 Expression in the Central Nervous System Using [3H]CS1P1 and [11C]CS1P1.

Sphingosine-1-phosphate receptor 1 (S1PR1) is ubiquitously expressed among all tissues and plays key roles in many physiological and cellular processes. In the central nervous system (CNS), S1PR1 is expressed in different types of cells including neurons, astrocytes, and oligodendrocyte precursor cells. S1PR1 has been recognized as a novel therapeutic target in multiple sclerosis and other diseases. We previously reported a promising S1PR1-specific radioligand, [11C]CS1P1 (previously named [11C]TZ3321), which is under clinical investigation for human use. In the current study, we performed a detailed characterization of [3H]CS1P1 for its binding specificity to S1PR1 in CNS using autoradiography and immunohistochemistry in human and rat CNS tissues. Our data indicate that [3H]CS1P1 binds to S1PR1 in human frontal cortex tissue with a Kd of 3.98 nM and a Bmax of 172.5 nM. The distribution of [3H]CS1P1 in human and rat CNS tissues is consistent with the distribution of S1PR1 detected by immunohistochemistry studies. Our microPET studies of [11C]CS1P1 in a nonhuman primate (NHP) show a standardized uptake value of 2.4 in the NHP brain, with test-retest variability of 0.23% among six different NHPs. Radiometabolite analysis in the plasma samples of NHP and rat, as well as in rat brain samples, showed that [11C]CS1P1 was stable in vivo. Kinetic modeling studies using a two-compartment tissue model showed that the positron emission tomography (PET) data fit the model well. Overall, our study provides a detailed characterization of [3H]CS1P1 binding to S1PR1 in the CNS. Combined with our microPET studies in the NHP brain, our data suggest that [11C]CS1P1 is a promising radioligand for PET imaging of S1PR1 in the CNS.

Reviewing the Significance of Blood-Brain Barrier Disruption in Multiple Sclerosis Pathology and Treatment.

The disruption of blood–brain barrier (BBB) for multiple sclerosis (MS) pathogenesis has a double effect: early on during the onset of the immune attack and later for the CNS self-sustained ‘inside-out’ demyelination and neurodegeneration processes. This review presents the characteristics of BBB malfunction in MS but mostly highlights current developments regarding the impairment of the neurovascular unit (NVU) and the metabolic and mitochondrial dysfunctions of the BBB’s endothelial cells. The hypoxic hypothesis is largely studied and agreed upon recently in the pathologic processes in MS. Hypoxia in MS might be produced per se by the NVU malfunction or secondary to mitochondria dysfunction. We present three different but related terms that denominate the ongoing neurodegenerative process in progressive forms of MS that are indirectly related to BBB disruption: progression independent of relapses, no evidence of disease activity and smoldering demyelination or silent progression. Dimethyl fumarate (DMF), modulators of S1P receptor, cladribine and laquinimode are DMTs that are able to cross the BBB and exhibit beneficial direct effects in the CNS with very different mechanisms of action, providing hope that a combined therapy might be effective in treating MS. Detailed mechanisms of action of these DMTs are described and also illustrated in dedicated images. With increasing knowledge about the involvement of BBB in MS pathology, BBB might become a therapeutic target in MS not only to make it impenetrable against activated immune cells but also to allow molecules that have a neuroprotective effect in reaching the cell target inside the CNS.

PD-1/PD-L1 Axis as a Potential Therapeutic Target for Multiple Sclerosis: A T Cell Perspective.

The programmed cell death protein-1/programmed death ligand-1 (PD-1/PD-L1) axis is a widely studied immune checkpoint that modulates signaling pathways related to T cell activation. The use of PD-1/PD-L1 inhibitors is a promising immune therapy strategy for cancer patients. However, individuals treated with PD-1/PD-L1 inhibitors may develop immune-related adverse events due to excessive immune reactions. Multiple sclerosis (MS) is a chronic demyelinating and neurodegenerative disease of the central nervous system. T cells and the PD-1/PD-L1 axis play vital roles in the pathogenesis of MS. A better understanding of the complex relationship between the PD-1/PD-L1 axis and T cells may extend our knowledge of the molecular mechanisms and therapeutic approaches for MS. In this review, we summarize the most recent findings regarding the role of the PD-1/PD-L1 axis in MS and discuss the potential therapeutic strategies to modulate the expression of PD-1/PD-L1 in MS.

Immunosuppressive Amino-Acid Catabolizing Enzymes in Multiple Sclerosis.

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease that affects the central nervous system. Although the pathogenesis of MS is not yet fully elucidated, several evidences suggest that autoimmune processes mediated by Th1, Th17, and B cells play an important role in the development of the disease. Similar to other cells, immune cells need continuous access to amino acids (AA) in order to maintain basal metabolism and maintain vitality. When immune cells are activated by inflammation or antigenic signals, their demand for AA increases rapidly. Although AA deprivation itself may weaken the immune response under certain conditions, cells also have AA sensitive pathways that can activate intense alterations in cell metabolism based on changes in AA levels. Several data indicate that cells expressing enzymes that can degrade AA can regulate the functions of antigen-presenting cells and lymphocytes, revealing that the AA pathways are essential for controlling the function, and survival of immune cells, as well as immune cell gene expression. Basal AA catabolism may contribute to immune homeostasis and prevent autoimmunity, while increased AA catalytic activity may enhance immune suppression. In addition, there is increasing evidence that some downstream AA metabolites are important biological mediators of autoimmune response regulation. Two of the most important AA that modulate the immune response are L-Tryptophan (Trp) and L-Arginine (Arg). Tryptophan is catabolized through 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) 1 and IDO2 enzymes, while three other enzymes catabolize Arg: inducible nitric oxide synthetase (iNOS), and two arginase isoforms (ARG1, ARG2). Genes encoding IDO, iNOS and ARG are induced by inflammatory cues such as cytokines, a key feature that distinguishes them from enzymes that catabolize other AA. Evidence suggests that AA catabolism is decreased in MS patients and that this decrease has functional consequences, increasing pro-inflammatory cytokines and decreasing Treg cell numbers. These effects are mediated by at least two distinct pathways involving serine/threonine kinases: the general control nonderepressible 2 kinase (GCN2K) pathway; and the mammalian target of rapamycin (mTOR) pathway. Similarly, IDO1-deficient mice showed exacerbation of experimental autoimmune encephalomyelitis (EAE), increased Th1 and Th17 cells, and decreased Treg cells. On the contrary, the administration of downstream Trp metabolite 3-HAA, inhibits Th1/Th17 effector cells and promotes Treg response by up-regulating TGF-β production by dendritic cells, thereby improving EAE. Collectively, these observations stand out the significance of AA catabolism in the regulation of the immune responses in MS patients. The molecules related to these pathways deserve further exploration as potential new therapeutic targets in MS