Abstract 325: Palmitic Acid Enhances the Stimulatory Effect of Lipopolysaccharide on Interleukin 6 Expression in Cardiac Microvascular Endothelial Cells by Increasing Ceramide Production via both De Novo Synthesis and Sphingomyelin Hydrolysis
Host inflammatory response mediated by toll-like receptor (TLR)4, a pattern recognition receptor for lipopolysaccharide (LPS), plays an important role in cardiovascular complication of diabetes. Although it is known that patients with type 2 diabetes or/and obesity have increased plasma free fatty acids (FAs), and saturated FAs such as palmitic acid (PA) increase host inflammatory response, the interaction between saturated FAs and LPS-elicited TLR4 signaling has not been well elucidated. Since it is known that neovascularization in advanced atherosclerotic plaques contributes to plaque destabilization, we investigated the mechanism whereby PA interacts with LPS for pro-inflammatory gene expression in cardiac microvascular (MIC) endothelial cells (ECs). We found that while LPS at 5 ng/ml stimulated a robust interleukin (IL)-6 secretion in cardiac MIC ECs, 100 μM of PA further augmented the stimulation by more than 2-fold (Control, 4.4; LPS, 41.3, PA, 6.0, LPS+PA, 89.0 ng/ml). Besides IL-6, PA also enhanced the stimulatory effect of LPS on tumor necrosis factor (TNF)α (Control, 2.6; LPS, 38.5, PA, 13.8, LPS+PA, 58.0 pg/ml). Time course study showed that IL-6 expression induced by LPS peaked at 4 h and dropped sharply after the peak. In contrast, addition of PA to LPS delayed the peak to 8 h and stimulated a second peak at 24 h after a transient drop at 12 h. Consistently, quantification of IL-6 in medium showed that IL-6 level in culture medium of cells treated by LPS alone plateaued at 8 h, but addition of PA to LPS led to a continuous liner increase in IL-6 in culture medium up to 48 h. Our further investigation showed that PA and LPS had a synergistic effect on the production of total ceramides and, in particular, C16 ceramide. The involvement of the synergistic effect of LPS and PA on ceramide production in IL-6 upregulation was indicated by the findings that myriocin and fumonisin B1, the inhibitors of ceramide de novo synthesis, and GW4869, an inhibitor of sphingomyelin hydrolysis, reduced IL-6 secretion by cells treated with LPS and PA significantly. Taken together, this study has demonstrated that PA enhances the stimulatory effect of LPS on IL-6 expression in cardiac MIC ECs by increasing ceramide production via both de novo synthesis and sphingomyelin hydrolysis.
- © 2013 by American Heart Association, Inc.