XDH and metabolic syndrome: Chronic hyperglycemia and dyslipidemia lead to increased production of ROS through the activation of various enzymes such as mitochondrial respiratory chain enzymes, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX), uncoupled endothelial nitric oxide synthase (eNOS), cyclooxygenase, and xanthine oxidase (XO).