Exogenous or endogenous elevation of glucocorticoids (GC) has been associated with adverse effects on the vascular system including enhanced levels of reactive oxygen species (ROS), although mechanisms and consequences are not completely resolved, yet.

We therefore stimulated human microvascular endothelial and smooth muscle cells as well as mouse aortae and pulmonary arteries with increasing concentrations of the synthetic GC dexamethasone (DEX). We observed a rapid but sustained elevation in ROS production at a concentration of 10 nM which was dependent on the GC receptor. Depletion of the NADPH oxidase subunits NOX2 or NOX4 by RNAi decreased vascular ROS production by DEX. Similarly, DEX-stimulated ROS production was limited in vessels derived from NOX2-/- mice. On the contrary, DEX induced NOX4 mRNA and protein levels further confirming the importance of NADPH oxidases for vascular ROS formation stimulated by low dose DEX treatment.

Subsequently, DEX enhanced activity of the hypoxia-inducible transcription factor HIF and increased the levels of HIF-1alpha and HIF-2alpha as well as of their target gene plasminogen activator inhibitor-1 while these responses were diminished upon depletion of NOX2 or NOX4. Interestingly, DEX treatment also enhanced vascular cell proliferation and tube formation dependent on NADPH oxidases, ROS and the HIF system.

Since enhanced ROS production and HIF activation have been associated with vascular dysfunction and remodelling induction of this pathway may contribute to adverse vascular effects observed upon DEX treatment.