ANTIOXIDANT ACTIVITY OF RAT PAROTID-SALIVA

Background: The healing-promotion property of saliva has been observed in the past, but its underlying mechanism has never been elucidated. We hypothesized a mechanism based on salivary proteins binding to redo x active metal ions, rendering them nonactive in their capacity for fr ee radical production. Methods: Examination of this mechanism was cond ucted by comparing the redox activity of protein-rich saliva with prot ein-poor saliva. We also examined the redox activity mediated by these 2 kinds of saliva following the in vitro addition of iron,, copper, a nd manganese. Saliva samples were analyzed for their redox activity by measuring the ascorbate-driven and saliva (diluted 1:2)-mediated conv ersion of salicylate to its 2,3- and 2,5-dihydroxybenzoates and catech ol metabolites. Results: The concentrations of;salicylate metabolites formed by protein-rich saliva were significantly lower by 45% (P<.05), 66% (P<.01), and 54% (P<.O5), respectively, when compared with those formed by protein-poor saliva. The capacity of saliva in suppressing r edox activity was found to be inversely related to the concentrations of iron and copper added (but not manganese), but correlated well with the protein content. When the highest concentrations of iron (15 mu m ol/L) and copper (10 mu mol/L were added to protein-rich saliva, the c oncentrations of salicylate metabolites produced were only 0.3% to 1% of those of non-saliva-containing controls (P<.01). However, when thes e concentrations of iron and copper were added to protein-poor saliva, significantly higher values of redox activity were detected, and the concentrations of the salicylate derivatives produced were 2.1% to 8.1 % of those of non-saliva-containing controls (P<.01). In contrast, whe n the lowest concentrations of iron (2 mu mol/L) and copper (0.1 mu mo l/L) were added, derivatives were produced (P<.01). Conclusion: These results substantiate our hypothesis that saliva has a profound capacit y for reducing redox activity rendered by transition metal ions, corre lating well with its protein content.