XDH and chronic kidney disease: The production of reactive oxygen species (ROS) by a variety of enzymes (e.g., nicotinamide adenine dinucleotide phosphate oxidase (NADPH), xanthine oxidase, lipoxygenase) as well as a decreased activity of enzymatic (e.g., superoxide dismutase, catalase) and low molecular weight antioxidants (e.g., glutathione) result in an increased systemic activity of ROS in chronic kidney disease (CKD) [1,2].