A series of experimental studies proposed several possible underlying mechanisms [29–32]: (1) UA crystals may cause direct kidney toxicity by depositing within the kidney; (2) elevated uric acid might induce intrarenal oxidative stress and mitochondrial dysfunction, leading to damage to endothelial cells, smooth muscle cells, kidney tubular cells, and activation of the renin-angiotensin system; and (3) SUA might be a risk factor for metabolic syndrome, diabetes, and hypertension, which could accelerate the development of CKD [32]. Here, REN is linked to chronic kidney disease.