Salivary uric acid at the acidic pH of the stomach is the principal defense against nitrite-derived reactive species: Sparing effects of chlorogenic acid and serum albumin

• Published in: Free radical biology & medicine Vol. 41; no. 12; pp. 1753 - 1763
• Main Authors: Pietraforte, Donatella, Castelli, Marco, Metere, Alessio, Scorza, Giuseppe, Samoggia, Paola, Menditto, Antonio, Minetti, Maurizio
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-12-2006
• Subjects: Animals; Ascorbic Acid - metabolism; Bovine serum albumin; Chlorogenic acid; Chlorogenic Acid - pharmacology; Free radicals; Gastric cancer; Human saliva; Humans; Hydrogen-Ion Concentration; Nitric Oxide - metabolism; Nitrogen Dioxide - metabolism; Oxygen - pharmacology; Reactive nitrogen species; Reactive Nitrogen Species - adverse effects; Saliva - chemistry; Serum Albumin, Bovine - pharmacology; Stomach - drug effects; Tyrosine - analogs & derivatives; Tyrosine - metabolism; Uric acid; Uric Acid - analysis; Uric Acid - metabolism; Uric Acid - pharmacology; Bovine serum albumin; Free radicals; AH 2; Reactive nitrogen species; Chlorogenic acid; HS; GGWA; Uric acid; BSA; Human saliva; NEM; GGYR; DBNBS; Gastric cancer; SCN
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2006.08.014

A complex antioxidant system is present in human saliva, with uric acid being the most concentrated component. Ascorbic acid, present at low concentrations in saliva, is actively secreted into the gastric lumen. We report that ascorbic acid added to human saliva at pH 2 was consumed within a few minutes, regenerating HNO
2, whereas uric acid was consumed relatively slowly in a nitrite-dependent manner. The consumption of uric acid was (i) rapid under normoxic conditions and slower at low oxygen tensions, (ii) coupled to
NO release, (iii) linked to the decrease in nitrite consumption and in nitrate formation, and (iv) unaffected by the nitrosation catalyst thiocyanate. Both chlorogenic acid and bovine serum albumin, representative of a phenol- and a protein-rich meal, respectively, were able to spare uric acid, although chlorogenic acid increased, whereas bovine serum albumin inhibited,
NO release. We hypothesize that the major role of uric acid in saliva at pH 2 could be to preserve the stomach from the formation of toxic nitrogen species and that low levels of uric acid, together with ascorbic acid consumption, may contribute to the high occurrence of tumors at the gastroesophageal junction and cardia. The sparing effects of dietary compounds may therefore be an important not fully appreciated effect.