Curcumin and resveratrol inhibit nuclear factor-kappaB-mediated cytokine expression in adipocytes

Background: Adipocytes express inflammatory mediators that contribute to the low-level, chronic inflammation found in obese subjects and have been linked to the onset of cardiovascular disorders and insulin resistance associated with type 2 diabetes mellitus. A reduction in inflammatory gene expression in adipocytes would be expected to reverse this low-level, inflammatory state and improve cardiovascular function and insulin sensitivity. The natural products, curcumin and resveratrol, are established anti-inflammatory compounds that mediate their effects by inhibiting activation of NF-kappa B signaling. In the present study, we examined if these natural products can inhibit NF-kappa B activation in adipocytes and in doing so reduce cytokine expression. Methods: Cytokine (TNF-alpha, IL-1 beta, IL-6) and COX-2 gene expression in 3T3-L1-derived adipocytes was measured by quantitative real-time PCR (qRT-PCR) with or without TNF alpha-stimulation. Cytokine protein and prostaglandin E-2 (PGE(2)) expression were measured by ELISA. Effects of curcumin and resveratrol were evaluated by treating TNF alpha-stimulated adipocytes with each compound and 1) assessing the activation state of the NF-kappa B signaling pathway and 2) measuring inflammatory gene expression by qRT-PCR and ELISA. Results: Both preadipocytes and differentiated adipocytes express the genes for TNF-alpha, IL-6, and COX-2, key mediators of the inflammatory response. Preadipocytes were also found to express IL-1 beta; however, IL-1 beta expression was absent in differentiated adipocytes. TNF-alpha treatment activated NF-kappa B signaling in differentiated adipocytes by inducing I kappa B degradation and NF-kappa B translocation to the nucleus, and as a result increased IL-6 (6-fold) and COX-2 (2.5-fold) mRNA levels. TNF-alpha also activated IL-1 beta gene expression in differentiated adipocytes, but had no effect on endogenous TNF-alpha mRNA levels. No detectable TNF-alpha or IL-1 beta was secreted by adipocytes. Curcumin and resveratrol treatment inhibited NF-kappa B activation and resulted in a reduction of TNF-alpha, IL-1 alpha, IL-6, and COX-2 gene expression (IC50 = 2 mu M) and a reduction of secreted IL-6 and PGE(2) (IC50 similar to 20 mu M). Conclusion: Curcumin and resveratrol are able to inhibit TNF alpha-activated NF-kappa B signaling in adipocytes and as a result significantly reduce cytokine expression. These data suggest that curcumin and resveratrol may provide a novel and safe approach to reduce or inhibit the chronic inflammatory properties of adipose tissue.