A pathological feature in atherosclerosis is the dysfunction and death of vascular endothelial cells (EC). Oxidized low-density lipoprotein (LDL), known to accumulate in the atherosclerotic arterial walls, impairs endothelium-dependent relaxation and causes EC apoptosis. A major bioactive ingredient of the oxidized LDL is lysophosphatidylcholine (LPC), which at higher concentrations causes apoptosis and necrosis in various EC. There is hitherto no report on LPC-induced cytotoxicity in brain EC. In this work, we found that LPC caused cytosolic Ca overload, mitochondrial membrane potential decrease, p38 activation, caspase 3 activation and eventually apoptotic death in mouse cerebral bEND.3 EC. In contrast to reported reactive oxygen species (ROS) generation by LPC in other EC, LPC did not trigger ROS formation in bEND.3 cells. Pharmacological inhibition of p38 alleviated LPC-inflicted cell death. We examined whether heparin could be cytoprotective: although it could not suppress LPC-triggered Ca signal, p38 activation and mitochondrial membrane potential drop, it did suppress LPC-induced caspase 3 activation and alleviate LPC-inflicted cytotoxicity. Our data suggest LPC apoptotic death mechanisms in bEND.3 might involve mitochondrial membrane potential decrease and p38 activation. Heparin is protective against LPC cytotoxicity and might intervene steps between mitochondrial membrane potential drop/p38 activation and caspase 3 activation.

Eicosapentaenoic acid (EPA), an omega-3 fatty acid abundant in fish oil, protects endothelial cells (EC) from lipotoxicity and triggers EC NO release. The latter is related to an elevation of cytosolic Ca. Although EPA has been shown to cause human EC cytosolic Ca elevation, the mechanism is unclear. Microfluorimetric imaging was used here to measure free cytosolic Ca concentration. EPA was shown to cause intracellular Ca release in mouse cerebral cortex endothelial bEND.3 cells; interestingly, the EPA-sensitive intracellular Ca pool(s) appeared to encompass and was larger than the Ca pool mobilized by sarcoplasmic-endoplasmic reticulum Ca-ATPase inhibition by cyclopiazonic acid. EPA also opened a Ca influx pathway pharmacologically distinct from store-operated Ca influx. Surprisingly, EPA-triggered Ca influx was Ni-insensitive; and EPA did not trigger Mn influx. Further, EPA-triggered Ca influx did not involve Na-Ca exchangers. Thus, our results suggest EPA triggered unusual mechanisms of Ca release and Ca influx in EC.

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Quercetin is a flavonol polyphenol widely found in many vegetables, grains, and fruits. Quercetin has been shown to inhibit proliferation and invasion of various glioma cells and is regarded as a potential anticancer agent against glioma. However, whether and how this drug could affect brain blood vessels and endothelial cells (EC) are less understood. Further, there is hitherto no report on how quercetin affects brain EC Ca2+ homeostasis. In this report, we investigated the effects of quercetin on Ca2+ homeostasis in mouse brain bEnd.3 EC. We demonstrated that quercetin raised cytosolic Ca2+ level in a concentration‐dependent manner. Quercetin‐triggered Ca2+ signal composed of both internal Ca2+ release and extracellular Ca2+ influx. Quercetin caused Ca2+ release from the endoplasmic reticulum, and consistently, inhibition of inositol 1,4,5‐trisphosphate receptor (IP3R) by xestospongin C (XeC) suppressed quercetin‐triggered Ca2+ release. Quercetin also caused Ca2+ release from lysosomes, an observation in concordance with the inhibition of quercetin‐triggered Ca2+ release by trans‐Ned‐19, a blocker of two‐pore channels. As quercetin depleted intracellular Ca2+ storage, it suppressed ATP‐induced Ca2+ release and thereby blunted ATP‐triggered Ca2+ signaling. In addition, quercetin co‐treatment significantly suppressed ATP‐stimulated nitric oxide release. Our work therefore showed, for the first time, quercetin perturbed intracellular Ca2+ stores and strongly suppressed ATP‐triggered response in bEnd.3 cells.

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