Stevioside, a natural noncaloric sweetener isolated from Stevia rebaudiana Bertoni, possesses anti-inflammatory and antitumor promoting properties; however, no information is available to explain its activity. The aim of this study was to elucidate the anti-inflammatory and immunomodulatory activities of stevioside and its metabolite, steviol. Stevioside at 1 mM significantly suppressed lipopolysaccharide (LPS)-induced release of TNF-alpha and IL-1beta and slightly suppressed nitric oxide release in THP-1 cells without exerting any direct toxic effect, whereas steviol at 100 microM did not. Activation of IKKbeta and transcription factor NF-kappaB were suppressed by stevioside, as demonstrated by Western blotting. Furthermore, only stevioside induced TNF-alpha, IL-1beta, and nitric oxide release in unstimulated THP-1 cells. Release of TNF-alpha could be partially neutralized by anti-TLR4 antibody. This study suggested that stevioside attenuates synthesis of inflammatory mediators in LPS-stimulated THP-1 cells by interfering with the IKKbeta and NF-kappaB signaling pathway, and stevioside-induced TNF-alpha secretion is partially mediated through TLR4.
Stevioside, isolated from Stevia rebaudiana, is a commercial sweetener. It was previously demonstrated that stevioside attenuates NF-kappaB-dependent TNF-alpha and IL-1beta synthesis in LPS-stimulated monocytes. The present study examined the effects of stevioside and its metabolite, steviol, on human colon carcinoma cell lines. High concentrations of stevioside (2-5 mM) and steviol (0.2-0.8 mM) decreased cell viability in T84, Caco-2, and HT29 cells. Stevioside (2 mM) potentiated TNF-alpha-mediated IL-8 release in T84 cells. However, steviol (0.01-0.2 mM) significantly suppressed TNF-alpha-induced IL-8 release in all three cell lines. In T84 cells, steviol attenuated TNF-alpha-stimulated IkappaB --> NF-kappaB signaling. Chloride transport was stimulated by steviol (0.1 mM) > stevioside (1 mM) at 30 min. Two biological effects of steviol in the colon are demonstrated for the first time: stimulation of Cl(-) secretion and attenuation of TNF-alpha-stimulated IL-8 production. The immunomodulatory effects of steviol appear to involve NF-kappaB signaling. In contrast, at nontoxic concentrations stevioside affects only Cl(-) secretion.
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