glutaminase and Multiple-Sclerosis

Glutaminase plays a critical role in the generation of glutamate, a key excitatory neurotransmitter in the CNS. Excess glutamate release from activated macrophages and microglia correlates with upregulated glutaminase suggesting a pathogenic role for glutaminase. Both glutaminase siRNA and small molecule inhibitors have been shown to decrease excess glutamate and provide neuroprotection in multiple models of disease, including HIV-associated dementia (HAD), multiple sclerosis and ischemia. Consequently, inhibition of glutaminase could be of interest for treatment of these diseases. Bis-2-(5-phenylacetimido-1,2,4-thiadiazol-2-yl)ethyl sulfide (BPTES) and 6-diazo-5-oxo-l-norleucine (DON), two most commonly used glutaminase inhibitors, are either poorly soluble or non-specific. Recently, several new BPTES analogs with improved physicochemical properties were reported. To evaluate these new inhibitors, we established a cell-based microglial activation assay measuring glutamate release. Microglia-mediated glutamate levels were significantly augmented by tumor necrosis factor (TNF)-α, phorbol 12-myristate 13-acetate (PMA) and Toll-like receptor (TLR) ligands coincident with increased glutaminase activity. While several potent glutaminase inhibitors abrogated the increase in glutamate, a structurally related analog devoid of glutaminase activity was unable to block the increase. In the absence of glutamine, glutamate levels were significantly attenuated. These data suggest that the in vitro microglia assay may be a useful tool in developing glutaminase inhibitors of therapeutic interest.

Topics: AIDS Dementia Complex; Animals; Biological Assay; Brain Ischemia; Cells, Cultured; Drug Evaluation, Preclinical; Glutamic Acid; Glutaminase; Mice; Microglia; Multiple Sclerosis; Neuroprotective Agents; Small Molecule Libraries; Tetradecanoylphorbol Acetate; Toll-Like Receptors; Tumor Necrosis Factor-alpha

The pathogenesis of multiple sclerosis (MS) remains to be elucidated and there is no curative therapy against MS, though we have several disease modifying drugs. In this symposium. I introduce several new strategies against development of autoimmune processes and axonal degeneration in MS. Several mechanisms regulate immune system not to attack self components. One of the most potent regulatory cells is CD4 + CD25 + FoxP + regulatory T cells (Treg), which suppress development of both T helper 1 and 2. Thus, to increase the number and function of Treg is an approach to suppress autoimmune diseases. We have found recently that midkine suppresses the development of Treg. and that suppression of midkine by RNA aptamer alleviates symptoms of experimental autoimmune encephalomyetitis, an animal model of MS. by expanding Treg. Another important strategy against MS is to suppress axonal degeneration which reportedly occurs from an early stage of MS. We have found that the most toxic agent from activated macrophages and microglia is glutamate that was produced by glutaminase and released through gap-junction. Thus, inhibitor for glutaminase and gap-junction may be other candidates to treat MS. Interferon-beta also effectively suppress glutamate production by these cells and subsequently suppress development of axonal degeneration.

Topics: Animals; Aptamers, Nucleotide; Autoimmunity; Axons; Cytokines; Enzyme Inhibitors; Gap Junctions; Glutamic Acid; Glutaminase; Humans; Interferon-beta; Macrophages; Microglia; Midkine; Multiple Sclerosis; Nerve Degeneration; T-Lymphocytes, Regulatory; Th1 Cells; Th2 Cells

Glutamate excitotoxicity mediated by the AMPA/kainate-type of glutamate receptors is known not only to damage neurons but also the myelin-producing cell of the central nervous system (CNS), the oligodendrocyte. In Multiple Sclerosis (MS), myelin, oligodendrocytes and axons are lost or damaged as a result of an inflammatory attack on the CNS. Activated immune cells produce glutamate in large quantities by deamidating glutamine via glutaminase. Thus, we hypothesized that during inflammation in MS, glutamate excitotoxicity may contribute to the lesion. This was addressed by treating mice sensitized to develop acute experimental autoimmune encephalomyelitis (EAE) with an AMPA/kainate antagonist, NBQX. Treatment resulted in substantial amelioration of disease, increased oligodendrocyte survival and reduced axonal damage, as indicated by the levels of dephosphorylated neurofilament-H. Despite the clinical differences, NBQX-treatment had no effect on lesion size and did not reduce the degree of CNS inflammation. In addition, NBQX did not alter the proliferative activity of antigen-primed T cells in vitro, further indicating a lack of effect at the level of the immune system. In separate studies, infiltrating immune cells present in perivascular cuffs, commonly the site of entry for invading immune cells, were found to express glutaminase in abundance, supporting the production of glutamate in inflammatory lesions. Thus, glutamate excitotoxicity appears to be an important mechanism in autoimmune demyelination and its prevention with AMPA/kainate antagonists may prove to be an effective therapy for MS.

Topics: Animals; Axons; Cell Death; Disease Models, Animal; Encephalomyelitis, Autoimmune, Experimental; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Glutaminase; Humans; Mice; Mice, Inbred Strains; Multiple Sclerosis; Myelitis; Neuroprotective Agents; Neurotoxins; Oligodendroglia; Quinoxalines; Receptors, AMPA