urate

Urate is the anionic form of uric acid, a heterocyclic compound that contains nitrogen and oxygen atoms arranged in a purine-like ring system. In aqueous solution at physiological pH, uric acid (pKa ≈ 5.4) loses a proton to become urate, which is the predominant species in the blood and extracellular fluids of most mammals. Urate is highly soluble in water but poorly soluble in lipid environments, a property that influences its distribution and excretion.

In humans, urate derives mainly from the catabolism of purine nucleotides, which are released during the turnover of nucleic acids, the degradation of dietary nucleic acids, and the metabolism of certain foods rich in purines such as meat, seafood, and legumes. The enzyme xanthine oxidase catalyzes the final steps of purine degradation, converting hypoxanthine to xanthine and subsequently to uric acid, which then equilibrates with urate.

Urate can form salts with various cations; the most common are sodium urate, potassium urate, calcium urate, and ammonium urate. These salts are the principal constituents of certain kidney stones and of the crystalline deposits that accumulate in joints during gout, a painful inflammatory arthritis. Elevated serum urate concentrations, termed hyperuricemia, increase the risk of gout, renal calculi, and may be associated with cardiovascular disease and metabolic syndrome, although causal relationships remain under investigation.

Beyond its role in pathology, urate functions as an antioxidant in plasma, contributing to the scavenging of singlet oxygen and peroxynitrite. It also participates in the regulation of blood pressure and endothelial function, likely through complex signaling pathways. Research continues to elucidate the balance between protective and harmful effects of urate in human health.