Uric acid is a major antioxidant in human nasal airway secretions

Airway mucosal surfaces are potentially subjected to a variety of oxidant stresses. Airway submucosal glands secrete a variety of compounds that may protect the airways from injury. Cholinergically induced nasal submucosal gland secretion has recently been found to contain a low molecular weight nasal antioxidant. In this report, the isolation and identification of this nasal secretory antioxidant are described. Concentrated, cholinergically induced human nasal secretions were fractionated through a 10-kDa sieve and subjected to DEAE anion-exchange chromatography. Fractions containing antioxidant activity were subjected to gel filtration with Bio-Gel P-2 gel (resolution range, 200-2000 Da). The resultant antioxidant fractions were then desalted by gel filtration over the same column equilibrated in HPLC-grade water, yielding only a single peak with antioxidant activity. The absorption spectrum of the purified antioxidant revealed peaks at 238 and 292 nm at pH 7. These peaks shifted to 230 and 280 nm in 0.1 M HCl and 226 and 296 nm in 0.1 M NaOH. Sodium borohydride reduction of the antioxidant had no effect on the UV absorption, whereas platinum-catalyzed hydrogenation ablated all absorption peaks. Uric acid had identical absorption peaks and showed the same chromatographic behavior as the nasal antioxidant activity on both gel filtration and DEAE columns. Uricase (which degrades uric acid) metabolized both uric acid and the purified antioxidant. Uric acid was shown to have antioxidant activity at concentrations greater than 1.5 microM. These data indicate that nasal secretions contain uric acid that serves as an antioxidant.