Uric acid is a ubiquitous end product of purine metabolism in humans that is mainly excreted in urine, whereas in other mammals it is further metabolized to allantoin by uricase. The final two steps in its production are catalyzed by xanthine oxidase, which generates superoxide. Uric acid acts as a potent peroxynitrite scavenger and antioxidant. However, high levels of serum uric acid (>120 μg/ml), termed hyperuricemia, are associated with gout, kidney stones, metabolic syndrome, hypertension, renal disease, and cardiovascular disease. Uric acid in the form of monosodium urate crystals has been proposed to trigger interleukin-1β-mediated inflammation by activating the NOD-like receptor protein 3 inflammasome.
Sodium urate is the sodium salt of uric acid. In gout, it is observed in synovial fluid. Sodium urate has been shown to precipitate calcium oxalate from urine. It is also known to reverse the inhibitory effects of reactive oxygen and nitrogen metabolites on gelatinase A activity. Excess sodium urate in soft tissues results in a condition referred to as tophi.
