Abstract

Two active polysaccharide fractions (SF1 and SF2) purified from dried safflower petals ( Carthamus tinctorius L.) stimulated the synthesis of various cytokines by peritoneal macrophages. In a number of cell types, SF1 and SF2 induced a rapid degradation of IκBα essential for the activation of the transcription factor NF-κB. Toll-like receptor 4 (TLR4), but not TLR2, was expressed in all cell lines that responded to SF1 and SF2. Enforced expression of TLR4 and MD-2 rendered responsiveness to SF1 and SF2. Moreover, these safflower polysaccharides failed to induce the production of TNF-α and NO by peritoneal macrophages prepared from C3H/HeJ mice that have a point mutation in the Tlr4 gene. Thus, these observations clearly indicate that safflower polysaccharides activate the NF-κB signaling pathway via TLR4.

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