Resveratrol and pterostilbene inhibit TNF‐α stimulated activation of NF‐kB and its upstream TAK1 in macrophages via modulation of sphingolipids

Abstract

Nuclear factor‐kB (NF‐kB) plays a key role in inflammatory responses and cancer development. Inhibition of NF‐kB has been shown to attenuate inflammation and cancer progression. Resveratrol (Res), a polyphenol rich in grapes and red wine, has been reported to inhibit NF‐kB signaling in macrophages. However, the underlying mechanism is not completely understood. Pterostilbene (Pte), a natural dimethylated analog of Res found in blueberries, is believed to have higher bioavailability than Res. While there are few studies on the effect of Pte on NF‐kB signaling, here we compared the effect of Res and Pte on modulating NF‐kB signaling and investigated potential underlying mechanisms in Raw 264.7 macrophages. Both Res and Pte inhibited TNF‐α induced phosphorylation of IkBα in a time‐ and dose‐ dependent manner. Res showed stronger inhibitory effect than Pte in this activity. Consistently, Res was stronger than Pte in blocking TNF‐α induced degradation of IkBα and inhibiting p65 phosphorylation in the nucleus. Furthermore, we found that both Res and Pte potently inhibited TNF‐α‐induced phosphorylation of TAK1, a key upstream signaling for NF‐kB activation. In search for the underlying mechanisms, we observed that Res treatment induced intracellular elevation of ceramides, sphingosine and dihydrosphingosine. Intriguingly, co‐treatment of C17 sphingosine and C8 ceramide attenuated TNF‐α‐induced phosphorylation of IkBα, mimicking the effect of Res. Our study demonstrates that Res inhibits NF‐kB and its upstream signaling TAK1 possibly via modulation of sphingolipid metabolism. Studies are undertaken to further investigate modulation effect of Pte on sphingolipid metabolism.