Free fatty acids in the presence of high glucose amplify monocyte inflammation via Toll-like receptors

Dasu MR, Jialal I. Free fatty acids in the presence of high glucose amplify monocyte inflammation via Toll-like receptors. Am J Physiol Endocrinol Metab 300: E145-E154, 2011. First published October 19, 2010; doi:10.1152/ajpendo.00490.2010.-Type 2 diabetes (T2DM) is characterized by hyperglycemia, dyslipidemia, and increased inflammation. Previously, we showed that high glucose (HG) induces Toll-like receptor (TLR) expression, activity, and inflammation via NF-kappa B followed by cytokine release in vitro and in vivo. Here, we determined how HG-induced inflammation is affected by free fatty acids (FFA) in human monocytes. THP-1 monocytic cells, CD14(+) human monocytes, and transiently transfected HEK293 cells were exposed to various FFA (0-500 mu M) and glucose (5-20 mM) for evaluation of TLR2, TLR4, NF-kappa B, IL-1 beta, monocyte chemoattractant protein-1 (MCP-1), and superoxide release. In THP-1 cells, palmitate increased cellular TLR2 and TLR4 expression, generated reactive oxygen species (ROS), and increased NF-kappa B activity, IL-1 beta, and MCP-1 release in a dose-and time-dependent manner. Similar data were observed with stearate and FFA mixture but not with oleate. Conversely, NADPH oxidase inhibitor treatment repressed glucose and palmitate-stimulated ROS generation and NF-kappa B activity and decreased IL-1 beta and MCP-1 expression. Silencing TLR2, TLR4, and p47phox with small inhibitory RNAs (siRNAs) significantly reduced superoxide release, NF-kappa B activity, IL-1 beta, and MCP-1 secretion in HG and palmitate-treated THP-1 cells. Moreover, data from transient transfection experiments suggest that TLR6 is required for TLR2 and MD2 for TLR4 to augment inflammation in FFA- and glucose-exposed cells. These findings were confirmed with human monocytes. We conclude that FFA exacerbates HG-induced TLR expression and activity in monocytic cells with excess superoxide release, enhanced NF-kappa B activity, and induced proinflammatory factor release.