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

Am J Physiol Endocrinol Metab. 2011 Jan;300(1):E145-54. doi: 10.1152/ajpendo.00490.2010. Epub 2010 Oct 19.

Abstract

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-κB 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 μM) and glucose (5-20 mM) for evaluation of TLR2, TLR4, NF-κB, IL-1β, 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-κB activity, IL-1β, 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-κB activity and decreased IL-1β and MCP-1 expression. Silencing TLR2, TLR4, and p47phox with small inhibitory RNAs (siRNAs) significantly reduced superoxide release, NF-κB activity, IL-1β, 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-κB activity, and induced proinflammatory factor release.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line
  • Diabetes Mellitus, Type 2 / physiopathology
  • Enzyme Inhibitors / pharmacology
  • Fatty Acids, Nonesterified / metabolism*
  • Gene Expression Regulation
  • HEK293 Cells
  • Humans
  • Hyperglycemia / metabolism
  • Hyperglycemia / physiopathology*
  • Inflammation Mediators / metabolism*
  • Interleukin-1beta / metabolism
  • Lipopolysaccharide Receptors / metabolism
  • Monocytes / drug effects
  • Monocytes / metabolism*
  • NADPH Oxidases / antagonists & inhibitors
  • NF-kappa B / metabolism
  • RNA, Messenger / metabolism
  • RNA, Small Interfering
  • Reactive Oxygen Species / metabolism
  • Toll-Like Receptor 2 / genetics
  • Toll-Like Receptor 2 / metabolism
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism
  • Toll-Like Receptors / metabolism*

Substances

  • Enzyme Inhibitors
  • Fatty Acids, Nonesterified
  • IL1B protein, human
  • Inflammation Mediators
  • Interleukin-1beta
  • Lipopolysaccharide Receptors
  • NF-kappa B
  • RNA, Messenger
  • RNA, Small Interfering
  • Reactive Oxygen Species
  • TLR2 protein, human
  • TLR4 protein, human
  • Toll-Like Receptor 2
  • Toll-Like Receptor 4
  • Toll-Like Receptors
  • NADPH Oxidases