Free fatty acids in the presence of high glucose amplify monocyte inflammation via Toll-like receptors.
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.
Laboratory for Atherosclerosis and Metabolic Research, University of California Davis Medical Center, Sacramento, CA 95817, USA. ravi.dasu@ucdmc.ucdavis.edu
Mohan R
MR
Dasu
Ishwarlal
I
Jialal
D002460:Cell Line; D003924:Diabetes Mellitus, Type 2 / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism / Q000503:physiopathology*; D018836:Inflammation Mediators / Q000378:metabolism*; D053583:Interleukin-1beta / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors; D016328:NF-kappa B / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species / Q000378:metabolism; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism; D051193:Toll-Like Receptors / Q000378:metabolism*
D004791:Enzyme Inhibitors; D005230:Fatty Acids, Nonesterified; C508585:IL1B protein, human; D018836:Inflammation Mediators; D053583:Interleukin-1beta; D018950:Lipopolysaccharide Receptors; D016328:NF-kappa B; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D019255:NADPH Oxidases