XDH and Hyperglycemia: The NADPH-derived ROS production is associated with the downregulation of 8-oxoguanine glycosylase and subsequent activation of PKC in high glucose-treated HUVECs (Xie et al., 2020); (2) xanthine oxidase (XO) inhibitor allopurinol can prevent hyperglycemia-induced generation of ROS, which indicates that XO may be the major contributor of ROS (Eleftheriadis et al., 2018); (3) uncoupled eNOS can induce the increase of oxidative stress in diabetic mice (Sasaki et al., 2008).