Suppression of TNF-alpha secretion by azelastine in a rat mast (RBL-2H3) cell line: evidence for differential regulation of TNF-alpha release, transcription, and degranulation.
The mast cell plays a pivotal role in initiating allergic inflammation by secreting several cytokines including TNF-alpha, in addition to granule mediators such as histamine. Anti-allergic drugs including azelastine prevent immediate-type hypersensitivity by inhibiting mast cell degranulation, as well as blocking histamine H1 receptors. However, their effects on cytokine release from mast cells remain unknown. In a rat mast RBL-2H3 cell line, azelastine inhibited Ag- and ionomycin-induced TNF-alpha release with IC50 values of 25.7 +/- 3.4 microM and 1.66 +/- 0.45 microM, respectively. These effects were observed at lower concentrations than needed for the inhibition of degranulation. In Ag-stimulated cells, azelastine also inhibited TNF-alpha mRNA expression, TNF-alpha protein synthesis and release, and, possibly related to these effects, Ca2+ influx. In ionomycin-stimulated cells, however, azelastine inhibited TNF-alpha release to a greater extent than mRNA expression/protein synthesis and Ca2+ influx, suggesting that azelastine inhibits the release process more potently than transcription or production of TNF-alpha by interfering with a signal other than Ca2+. Azelastine added 1 h after ionomycin stimulation also immediately blocked subsequent release of TNF-alpha, which had been produced in the cells, without affecting Ca2+ influx. Pretreatment with 1 microM azelastine inhibited ionomycin-induced, but not Ag-induced, protein kinase C translocation to the membranes. These results suggest that the release process of TNF-alpha in mast cells is regulated by a mechanism distinct from that of degranulation, and that in Ca2+-ionophore-stimulated cells, it is also different from that of transcription/production, and possibly involves protein kinase C activation.
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Department of Pharmacology, Institute of Pharmaceutical Sciences, Hiroshima University School of Medicine, Japan. ihide@ipc.hiroshima-u.ac.jp
Toriu
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Nuibe
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Inoue
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Hide
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Yamamoto
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Nakata
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D000818:Animals; D018926:Anti-Allergic Agents / Q000494:pharmacology*; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D015550:Cell Degranulation / Q000187:drug effects / Q000276:immunology*; D002460:Cell Line; D008407:Mast Cells / Q000276:immunology* / Q000378:metabolism; D010793:Phthalazines / Q000494:pharmacology*; D051381:Rats; D014158:Transcription, Genetic / Q000187:drug effects*; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000378:metabolism*
D018926:Anti-Allergic Agents; D000894:Anti-Inflammatory Agents, Non-Steroidal; D010793:Phthalazines; D014409:Tumor Necrosis Factor-alpha; C020976:azelastine