Dual-function of thiocyanate on nitrite-induced formation of reactive nitrogen oxide species in human oral cavity: inhibition under neutral and enhancement under acidic conditions.

Salivary nitrate is reduced to nitric oxide (NO) via nitrite in the human oral cavity. The nitrite and NO formed can be transformed to reactive nitrogen oxide species (RNOS). In this investigation, RNOS formed in mixed whole saliva and its fractions were detected by the oxidation of aminophenyl fluorescein (APF) and the transformation of 3-amino-4-monomethylamino-2',7'-difluorofluorecein (DAF-FM) to its triazol form (DAF-FMT). Nitrite-induced oxidation of APF and formation of DAF-FMT increased as pH was decreased from 7 to 5 and SCN- inhibited the oxidation of APF and the formation of DAF-FMT around neutral pH and enhanced at pH about 5. The SCN- -dependent inhibition was due to the suppression of salivary peroxidase and the enhancement was due to the formation of NOSCN from HNO2 and SCN-. It is deduced that the increase in the concentrations of nitrite and H+ in the oral cavity may result in the enhanced formation of

Chlorogenic acid in coffee can prevent the formation of dinitrogen trioxide by scavenging nitrogen dioxide generated in the human oral cavity.

Coffee contains antioxidants like chlorogenic acid and its isomers. In this report, effects of coffee on the nitrite-induced N2O3 formation were studied using whole saliva and bacterial fraction prepared from the saliva. The formation of N2O3 was measured by fluorescence increase due to the transformation of 4,5-diaminofluorescein to triazolfluorescein. Coffee inhibited the nitrite-induced fluorescence increase, and 50% inhibition was observed at several microg of coffee/mL in bacterial fraction of saliva as well as whole saliva. During the inhibition of the fluorescence increase, concentration of chlorogenic acid and its isomers decreased. It is discussed that the reduction of NO2 by chlorogenic acid and its isomers contributed to the coffee-dependent inhibition of the fluorescence increase as N2O3 is formed from NO and NO2. When coffee was added to whole saliva, chlorogenic acid and its isomers bound to cells in the saliva. The rate of the fluorescence increase in bacterial fraction, which was prepared at defined periods after the ingestion of coffee, was increased to the rate before the ingestion of coffee with a half-time of about 1 h. This result suggests that chlorogenic acid and its isomers remained in the oral cavity for a few hours after ingestion of coffee. The significance of coffee drinking and rinsing of the mouth with coffee for the health of the oral cavity is proposed.