title: Leflunomide inhibits activation of inducible nitric oxide synthase in rat astrocytes.
abstract: Highly reactive gaseous free radical nitric oxide (NO), generated by astrocytes and infiltrating macrophages is implicated in inflammatory destruction of brain tissue, including that occurring in multiple sclerosis. Therefore, the influence of immunosuppressive drug leflunomide on inducible nitric oxide synthase (iNOS)-dependent NO production in rat astrocytes and macrophages was investigated. Under the same cultivating conditions, leflunomide's active metabolite A77 1726 caused a dose-dependent decrease of NO production in IFN-gamma+LPS-stimulated primary astrocytes, but not in macrophages. While A77 1726 did not alter iNOS enzymatic activity, it markedly suppressed IFN-gamma+LPS-triggered expression of iNOS mRNA in astrocytes. In the presence of transcription inhibitor actinomycin D, A77 1726 failed to inhibit astrocyte NO production, suggesting transcriptional regulation of iNOS by leflunomide. This assumption was further supported by the ability of A77 1726 to inhibit IFN-gamma+LPS-induced expression of mRNA for an important iNOS transcription factor IRF-1. PD98059, a specific inhibitor of mitogen-activated protein kinase kinase (MAPKK/MEK), but not genistein, an unselective protein tyrosine kinase inhibitor, completely mimicked cell type-specific inhibition of NO synthesis by A77 1726. Therefore, previously described inhibition of MEK/MAP pathway by leflunomide could present a possible mechanism for A77 1726-mediated suppression of iNOS activation in astrocytes. Accordingly to results obtained with primary astrocytes, both A77 1726 and PD98059 significantly reduced IFN-gamma+LPS-induced NO synthesis in the cultures of rat astrocytoma cell line C6. The ability to suppress iNOS induction in astrocytes supports potential use of leflunomide in the treatment of multiple sclerosis and other NO-dependent inflammatory brain disorders.
authors.affiliation: Institute for Biological Research, 29 Novembra 142, 11000, Belgrade, Yugoslavia. georgije_zw@yahoo.com
authors.forename: D
authors.initials: D
authors.lastname: Miljkovic
authors.forename: T
authors.initials: T
authors.lastname: Samardzic
authors.forename: M
authors.initials: M
authors.lastname: Mostarica Stojkovic
authors.forename: S
authors.initials: S
authors.lastname: Stosic-Grujicic
authors.forename: D
authors.initials: D
authors.lastname: Popadic
authors.forename: V
authors.initials: V
authors.lastname: Trajkovic
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000201:enzymology*; D001254:Astrocytoma / Q000378:metabolism; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects*; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007202:Indicators and Reagents; D007371:Interferon-gamma / Q000494:pharmacology; D007555:Isoxazoles / Q000494:pharmacology*; D000077339:Leflunomide; D008070:Lipopolysaccharides / Q000494:pharmacology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013778:Tetrazolium Salts; D013844:Thiazoles
chemical_list: D007166:Immunosuppressive Agents; D007202:Indicators and Reagents; D007555:Isoxazoles; D008070:Lipopolysaccharides; D018696:Neuroprotective Agents; D012333:RNA, Messenger; D013778:Tetrazolium Salts; D013844:Thiazoles; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D011505:Protein-Tyrosine Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C022616:thiazolyl blue; D000077339:Leflunomide