Hydroxysafflor Yellow A Blocks HIF-1 alpha Induction of NOX2 and Protects ZO-1 Protein in Cerebral Microvascular Endothelium

Zonula occludens-1 (ZO-1) is a tight junction protein in the cerebrovascular endothelium, responsible for blood-brain barrier function. Hydroxysafflor yellow A (HSYA) is a major ingredient of safflower (Carthamus tinctorius L.) with antioxidative activity. This study investigated whether HSYA protected ZO-1 by targeting ROS-generating NADPH oxidases (NOXs). HSYA administration reduced cerebral vascular leakage with ZO-1 protection in mice after photothrombotic stroke, largely due to suppression of ROS-associated inflammation. In LPS-stimulated brain microvascular endothelial cells, HSYA increased the ratio of NAD+/NADH to restore Sirt1 induction, which bound to Von Hippel-Lindau to promote HIF-1 alpha degradation. NOX2 was the predominant isoform of NOXs in endothelial cells and HIF-1 alpha transcriptionally upregulated p47phox and Nox2 subunits for the assembly of the NOX2 complex, but the signaling cascades were blocked by HSYA via HIF-1 alpha inactivation. When oxidate stress impaired ZO-1 protein, HSYA attenuated carbonyl modification and prevented ZO-1 protein from 20S proteasomal degradation, eventually protecting endothelial integrity. In microvascular ZO-1 deficient mice, we further confirmed that HSYA protected cerebrovascular integrity and attenuated ischemic injury in a manner that was dependent on ZO-1 protection. HSYA blocked HIF-1 alpha/NOX2 signaling cascades to protect ZO-1 stability, suggestive of a potential therapeutic strategy against ischemic brain injury.