title: Oxidation of quercetin by salivary components. Quercetin-dependent reduction of salivary nitrite under acidic conditions producing nitric oxide.
abstract: Under acidic conditions, nitrite is protonated to nitrous acid (pK(a) = 3.2-3.4) that can be transformed into nitric oxide by self-decomposition and reduction. When sodium nitrite was mixed with quercetin at pH 1-2, quercetin was oxidized producing nitric oxide. In addition to quercetin, kaempferol and quercetin 4'-glucoside were also oxidized by nitrous acid, but oxidation of apigenin, luteolin, and rutin was slow compared to oxidation of the above flavonols. These results suggested that flavonols, which have a free hydroxyl group at carbon position 3, can readily reduce nitrous acid to nitric oxide. When the pH of saliva was decreased to 1-2, formation of nitric oxide was observed. The nitric oxide formation was enhanced by quercetin, and during this process quercetin was oxidized. These results indicate that there is a possibility of reactions between phenolics and nitrous acid derived from salivary nitrite in the stomach.
authors.affiliation: tKyushu Dental University, Kitakyushu, 803-8580 Japan. takahama@kyu-dent.ac.jp
authors.forename: Umeo
authors.initials: U
authors.lastname: Takahama
authors.forename: Takayuki
authors.initials: T
authors.lastname: Oniki
authors.forename: Sachiko
authors.initials: S
authors.lastname: Hirota
mesh_terms: D005419:Flavonoids; D006801:Humans; D006863:Hydrogen-Ion Concentration; D044949:Kaempferols; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism*; D009608:Nitrous Acid / Q000737:chemistry; D010084:Oxidation-Reduction; D011794:Quercetin / Q000031:analogs & derivatives* / Q000737:chemistry*; D012463:Saliva / Q000737:chemistry*; D012977:Sodium Nitrite / Q000737:chemistry*
chemical_list: D005419:Flavonoids; D044949:Kaempferols; D009569:Nitric Oxide; C006552:kaempferol; D011794:Quercetin; C080613:spiraeoside; D012977:Sodium Nitrite; D009608:Nitrous Acid