XDH and endothelial dysfunction: Following the initial stage, the progression of endothelial dysfunction is characterized by the retention of LDL in endothelial cells, leading to its modification to oxidized LDL (ox-LDL) through the activity of enzymes like NADPH oxidases (NOX), lipoxygenases, xanthine oxidase (XO), myeloperoxidase (MPO), mitochondria reactive oxygen species (ROS) and uncoupled endothelial nitric oxide synthase (eNOS) (48, 49).