Native low density lipoprotein increases the production of both nitric oxide and reactive oxygen species in the human umbilical vein endothelial cells

BackgroundNitric oxide synthases (NOSs) are a unique family of enzymes that catalyze the production of nitric oxide (NO) from l-arginine. Atherogenic action of oxidized low-density lipoproteins (oxLDL) may be mediated partly by the formation of NO in endothelial cells.ObjectiveThe objective of this study was to identify sources of reactive oxygen species (ROS) causing native LDL (nLDL)-induced senescence of cultured human umbilical vein endothelial cells (HUVECs).MethodsHUVECs were treated with nLDL and NO production was assessed using Griess reagent as substrate and spectrophotometry in the absence or presence of specific inhibitors of endothelial NOS (eNOS) and inducible NOS (iNOS). In addition, expression levels of eNOS and iNOS were measured with ELISA and western blotting, and ROS was evaluated using 2,7-dichlorofluorescin diacetate (DCF-DA) and a fluorescence microplate reader.ResultsNO formation in nLDL-treated HUVECs was significantly increased. Long-term treatment with nLDL up-regulated both eNOS and iNOS proteins. Such increase of NO production in HUVECs induced by nLDL was significantly suppressed by treatment with iNOS-selective inhibitor 1400W, but not by the eNOS-selective inhibitor L-NIO. Native LDL treatment uncoupled Hsp90, the regulatory binding protein of eNOS, from the enzyme in HUVECs. Native LDL also significantly increased ROS production in HUVECs.ConclusionThese findings suggest that oxidative stress originated from induction of iNOS and eNOS could be a causative factor for nLDL-induced senescence of HUVECs.