Salivary thiocyanate/nitrite inhibits hydroxylation of 2-hydroxybenzoic acid induced by hydrogen peroxide/Fe(II) systems under acidic conditions: possibility of thiocyanate/nitrite-dependent scavenging of hydroxyl radical in the stomach.
Formation of OH radicals in the stomach is possible by Fenton-type reactions, as gastric juice contains ascorbic acid (AA), iron ions and H2O2. An objective of the present study is to elucidate the effects of salivary SCN- and NO2- on the hydroxylation of salicylic acid which was induced by H2O2/Fe(II) and AA/H2O2/Fe(II) systems. Thiocyanate ion inhibited the hydroxylation of salicylic acid by the above systems in acidic buffer solutions and in acidified saliva. The inhibition by SCN- was deduced to be due to SCN- -dependent scavenging of OH radicals. Nitrite ion could enhance the SCN- -dependent inhibition of the hydroxylation induced by AA/H2O2/Fe(II) systems. The enhancement was suggested to be due to scavenging of OH radicals by NO which was formed by the reactions among AA, HNO2 and SCN- contained in the reaction mixture. The concentrations of SCN- and NO2-, which were effective for the inhibition, were in ranges of their normal salivary concentrations. These results suggest that salivary SCN- can cooperate with NO2- to protect stomach from OH radicals formed by AA/H2O2/Fe(II) systems under acidic conditions.
Takahama
Umeo
U
Department of Bioscience, Kyushu Dental University, Kitakyushu 803-8580, Japan. takahama@kyu-dent.ac.jp
Oniki
Takayuki
T
D000143:Acids / Q000378:metabolism; D001205:Ascorbic Acid / Q000378:metabolism; D005296:Ferrous Compounds / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000494:pharmacology*; D005753:Gastric Mucosa / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D017665:Hydroxyl Radical / Q000378:metabolism; D006900:Hydroxylation / Q000187:drug effects; D009573:Nitrites / Q000494:pharmacology*; D010084:Oxidation-Reduction; D020156:Salicylic Acid / Q000378:metabolism*; D012463:Saliva / Q000737:chemistry*; D013861:Thiocyanates / Q000494:pharmacology*
D000143:Acids; D005296:Ferrous Compounds; D016166:Free Radical Scavengers; D009573:Nitrites; D013861:Thiocyanates; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide; D020156:Salicylic Acid; C031760:thiocyanate; D001205:Ascorbic Acid