AICAR Protects Vascular Endothelial Cells from Oxidative Injury Induced by the Long-Term Palmitate Excess

Hyperlipidemia manifested by high blood levels of free fatty acids (FFA) and lipoprotein triglycerides is critical for the progression of type 2 diabetes (T2D) and its cardiovascular complications via vascular endothelial dysfunction. However, attempts to assess high FFA effects in endothelial culture often result in early cell apoptosis that poorly recapitulates a much slower pace of vascular deterioration in vivo and does not provide for the longer-term studies of endothelial lipotoxicity in vitro. Here, we report that palmitate (PA), a typical FFA, does not impair, by itself, endothelial barrier and insulin signaling in human umbilical vein endothelial cells (HUVEC), but increases NO release, reactive oxygen species (ROS) generation, and protein labeling by malondialdehyde (MDA) hallmarking oxidative stress and increased lipid peroxidation. This PA-induced stress eventually resulted in the loss of cell viability coincident with loss of insulin signaling. Supplementation with 5-aminoimidazole-4-carboxamide-riboside (AICAR) increased endothelial AMP-activated protein kinase (AMPK) activity, supported insulin signaling, and prevented the PA-induced increases in NO, ROS, and MDA, thus allowing to maintain HUVEC viability and barrier, and providing the means to study the long-term effects of high FFA levels in endothelial cultures. An upgraded cell-based model reproduces FFA-induced insulin resistance by demonstrating decreased NO production by vascular endothelium.

Automated summary

Hyperlipidemia, characterized by high levels of FFA and lipoprotein triglycerides, plays a critical role in the progression of T2D and cardiovascular complications. However, studying the effects of high FFA in endothelial culture often leads to cell apoptosis and fails to mimic the slow deterioration process in vivo. Our study shows that the typical FFA, palmitate (PA), does not impair endothelial barrier and insulin signaling on its own, but increases oxidative stress and lipid peroxidation. This eventually leads to cell death and loss of insulin signaling. Supplementation with AICAR protects against PA-induced oxidative stress and maintains cell viability and barrier function, providing a means to study the long-term effects of high FFA levels in endothelial cultures.