Stimulated and Unstimulated Salivary Metabolites and Saliva Flow Rate in Children

Objectives: The objective of the present study was to determine the salivary flow and the metabolomic profile of stimulated and unstimulated saliva in children.
Methods: Children who attended FO-UERJ between 0 and 12 years of age were selected. Unstimulated and stimulated whole saliva after mechanical stimulus was collected. The samples were centrifuged at 12,000 g, 4^oC for 1h. The 1H CPMG and TOCSY spectra were acquired in a 500 MHz equipment. The data were extracted into 0.03 ppm buckets in AMIX, and multivariate analysis (PLS-DA and O-PLS-DA) was performed in Metaboanalyst 2.0. For other analyses, such as salivary flow, the data were tabulated in the SPSS 20.0 statistical package, analyzed descriptively, and through the Wilcoxon test. The confidence interval was set at 95%.
Results: The mean age was 7.5 (± 1.94) and 47.0% (n = 31) were female, 63.6% (n = 42). The median flow rate for unstimulated saliva was 0.74 (IC 0.10 – 2.40) and was statistically higher (p < 0.001; Wilcoxon test) than the mean rate of 0.39 (IC 0.00 – 1.80) for stimulated flow. Children older than 7 years old presented a higher stimulated flow rate than younger and children older than 8 years old also presented a higher difference between unstimulated and stimulated saliva flow rate (p = < 0.05; Mann-Whitney test). The PLS-DA and O-PLS-DA demonstrated a different profile in stimulated and unstimulated saliva. Acetate, glucose, propionate, and lysine presented in higher quantities in the unstimulated whole saliva when compared to stimulated saliva. Isoleucine, N-acetyl sugar, hydroxybutyrate, glutamate, leucine, propionate, butyrate, valine, isoleucine, succinate, saturated fatty acid, and histidine were found in greater amounts in stimulated saliva.
Conclusions: The stimulated saliva presented a higher flow rate and it seems that older children respond better to its stimulus. The mechanical stimulus increased the levels of the major metabolites.