Background: Quercetin and trans-resveratrol (trans-RSV) are plant polyphenols reported to reduce inflammation or insulin resistance associated with obesity. Recently, we showed that grape powder extract, which contains quercetin and trans-RSV, attenuates markers of inflammation in human adipocytes and macrophages and insulin resistance in human adipocytes. However, we do not know how quercetin and trans-RSV individually affected these outcomes.
Objective: The aim of this study was to examine the extent to which quercetin and trans-RSV prevented inflammation or insulin resistance in primary cultures of human adipocytes treated with tumor necrosis factor-α (TNF-α)-an inflammatory cytokine elevated in the plasma and adipose tissue of obese, diabetic individuals.
Design: Cultures of human adipocytes were pretreated with quercetin and trans-RSV followed by treatment with TNF-α. Subsequently, gene and protein markers of inflammation and insulin resistance were measured.
Results: Quercetin, and to a lesser extent trans-RSV, attenuated the TNF-α-induced expression of inflammatory genes such as interleukin (IL)-6, IL-1β, IL-8, and monocyte chemoattractant protein-1 (MCP-1) and the secretion of IL-6, IL-8, and MCP-1. Quercetin attenuated TNF-α-mediated phosphorylation of extracellular signal-related kinase and c-Jun-NH₂ terminal kinase, whereas trans-RSV attenuated only c-Jun-NH₂ terminal kinase phosphorylation. Quercetin and trans-RSV attenuated TNF-α-mediated phosphorylation of c-Jun and degradation of inhibitory κB protein. Quercetin, but not trans-RSV, decreased TNF-α-induced nuclear factor-κB transcriptional activity. Quercetin and trans-RSV attenuated the TNF-α-mediated suppression of peroxisome proliferator-activated receptor γ (PPARγ) and PPARγ target genes and of PPARγ protein concentrations and transcriptional activity. Quercetin prevented the TNF-α-mediated serine phosphorylation of insulin receptor substrate-1 and protein tyrosine phosphatase-1B gene expression and the suppression of insulin-stimulated glucose uptake, whereas trans-RSV prevented only the TNF-α-mediated serine phosphorylation of insulin receptor substrate-1.
Conclusion: These data suggest that quercetin is equally or more effective than trans-RSV in attenuating TNF-α-mediated inflammation and insulin resistance in primary human adipocytes.