Vascular peroxidase 1 (VPO1) has been proved to be associated with vascular endothelial cell apoptosis by producing reactive oxygen species. However, the contribution of VPO1 to the development of vascular remodeling (VR) remains to be fully characterized. We explored the role of VPO1 in VR in spontaneously hypertensive rats (SHRs) and the underlying mechanism of losartan in inhibiting VR. Compared to Wistar-Kyoto (WKY) rats, the SHR showed remodeling of their vascular walls. The level of VPO1 and the hydrogen peroxide (H2O2) concentration were increased in the SHRs. However, the SHRs pretreated with losartan showed significant inhibition of blood pressure and VR and decreased levels of VPO1 and H2O2 compared to the non-treated SHRs. Angiotensin II significantly increased the expressions of MMP-2, MMP-9 and the concentrations of H2O2 and hypochlorous acid (HOCl) in vascular smooth muscle cells (VSMCs). However, only the H2O2 level increased in VSMCs when transfected with VPO1 shRNA. These results support a critical but previously unrecognized role of VPO1 in VR and suggest that therapies to reduce VPO1 may be novel approaches for VR. (C) 2017 Elsevier Inc. All rights reserved.