The Impact of Uric Acid on Human Health: Beyond Gout and Kidney Stones

In most primates, including humans, uric acid (UA) is the end product of purine metabolism due to the loss of hepatic uricase activity during evolution. This loss resulted in higher serum urate concentrations (3.5-7.5 mg/dL) than normally observed in other mammals (0.05-2 mg/dL). About 70% of the daily urate burden is eliminated via the kidneys and the remainder via the intestines, where gut bacteria break it down. Urate is freely filtered through the glomerular capillaries, and most of the filtered urate is reabsorbed so that only an amount equivalent to about 10% of the filtered load is excreted in the urine. Virtually all of the renal urate reabsorption takes place in proximal convoluted tubules. Many transport proteins connected with urate have been identified. However, the best studied are URAT1 and GLUT9, which function in concert to translocate urate from the proximal tubule lumen to the peritubular fluid, the first in the apical membrane and the second in the basolateral membrane. Genetic mutations, as well as drugs that alter the function of these transporters, can affect urate homeostasis resulting in abnormal serum levels, which may, in turn, be involved in the pathogenesis of chronic metabolic and inflammatory diseases, including most features of the metabolic syndrome, hypertension, cardiovascular disease, and chronic kidney disease. Several mechanisms are thought to provide the link between urate and these disorders, including reactive oxygen species (oxidative stress) and both acute and chronic inflammation. This mini-review summarizes the basic human biology of UA and its association with and potential involvement in developing chronic diseases beyond gout and nephrolithiasis.