Luteoloside protects the vascular endothelium against iron overload injury via the ROS/ADMA/DDAHⅡ/eNOS/NO pathway

Iron overload injury is considered to be a part of blood stasis syndrome of arthralgia in traditional Chinese medicine. Its primary therapies include clearing heat and detoxification, activating blood circulation, and removing blood stasis. Lonicera japonica flos (LJF) has long been known as an excellent antipyretic and antidote. Luteoloside (Lut) is one of the main components of LJF and exhibits antioxidant, anti-inflammatory, and cytoprotective properties. However, the protection of Lut against iron overload injury and its underlying mechanisms remain unclear. Therefore, HUVECs were exposed to 50 μmol·L⁻¹ iron dextran for 48 h to establish an iron overload damage model and the effects of Lut were assessed. Our results showed that 20 μmol·L⁻¹ Lut not only increased cell viability and weakened LDH activity, but also significantly up-regulated DDAHⅡ expression and activity, increased p-eNOS/eNOS ratio and NO content, and reduced ADMA content in HUVECs exposed to iron overload. Furthermore, Lut significantly attenuated intracellular/mitochondrial ROS generation, improved SOD, CAT, and GSH-Px activities, reduced MDA content, maintained MMP, inhibited mPTP opening, prevented cyt c from mitochondria released into cytoplasm, reduced cleaved-caspase3 expression, and ultimately decreased cell apoptosis induced by iron overload. The effects of Lut were similar to those of L-arginine (an ADMA competitive substrate), cyclosporin A (a mPTP blocker agent), and edaravone (a free radical scavenger) as positive controls. However, addition of pAD/DDAHⅡ-shRNA adenovirus reversed the above beneficial effects of Lut. In conclusion, Lut can protect HUVECs against iron overload injury via the ROS/ADMA/DDAHⅡ/eNOS/NO pathway. The mitochondria are the target organelles of Lut’s protective effects.