FIGURE 10.

Urate oxidation by peroxidases in human saliva. A, LPO and MPO activities were measured in diluted saliva supernatants from 14 healthy donors. B, the allantoin concentration in saliva supernatants was related to the concentration of LPO. Clear circles are for the individuals with low or no MPO activity. The association between parameters was determined using Pearson's correlation. C, allantoin formation was measured in saliva supernatants after incubation for 30 min at 37 °C with no additions (black bars), with added hydrogen peroxide (50 μm, white bars), and with added hydrogen peroxide and azide (1 mm, respectively, striped bars). Reactions were stopped by the addition of catalase (10 μg/ml). Significant differences (p < 0.05) from the control with no added hydrogen peroxide were determined using repeated measures ANOVA. Data are means and ranges of at least duplicate experiments. MPO-def, MPO-deficient. D, initial urate concentrations in saliva supernatants were compared with the increase in allantoin concentration formed by the addition of hydrogen peroxide (50 μm) as in C. The association between parameters was determined using Pearson's correlation.