γ-Tocotrienol inhibits lipopolysaccharide-induced interlukin-6 and granulocyte colony-stimulating factor by suppressing C/EBPβ and NF-κB in macrophages

Cytokines generated from macrophages contribute to pathogenesis of inflammation-associated diseases. Here we show that gamma-tocotrienol (gamma-TE), a natural vitamin E form, inhibits lipopolysaccharide (LPS)-induced interleukin (IL)-6 production without affecting tumor necrosis factor alpha (TNF-alpha), IL-10 or cyclooxygenase-2 (COX-2) up-regulation in murine RAW264.7 macrophages. Mechanistic studies indicate that nuclear factor kappa B (NF-kappa B), but not c-Jun NH(2)-terminal protein kinase, p38 or extracellular signal-regulated kinase mitogen-activated protein kinases (MAPKs), is important to IL-6 production and that gamma-TE treatment blocks NF-kappa B activation. In contrast, COX-2 appears to be regulated by p38 MAPK in RAW cells, but gamma-TE has no effect on LPS-stimulated p38 phosphorylation. Despite necessary for IL-6, NF-kappa B activation by TNF-alpha or other cytokines is not sufficient for IL-6 induction with exception of LPS. CCAAT/enhancer-binding protein (C/EBP)beta appears to be involved in IL-6 formation because LPS induces C/EBP beta up-regulation, which parallels IL-6 production, and knockdown of C/EBP beta with small interfering RNA results in diminished IL-6. LPS but not individual cytokines is capable of stimulating C/EBP beta and IL-6 in macrophages. Consistent with its dampening effect on IL-6, gamma-TE blunts LPS-induced up-regulation of C/EBP beta without affecting C/EBP delta. gamma-TE also decreases LPS-stimulated granulocyte colony-stimulating factor (G-CSF), a C/EBP beta target gene. Compared with RAW264.7 cells, gamma-TE shows similar or stronger inhibitory effects on LPS-triggered activation of NF-kappa B, C/EPB beta and C/EBP delta and more potently suppresses IL-6 and G-CSF in bone marrow-derived macrophages. Our study demonstrates that gamma-TE has antiinflammatory activities by inhibition of NF-kappa B and C/EBPs activation in macrophages. (C) 2013 Elsevier Inc. All rights reserved.