Relationships between the metabolome and the fatty acid composition of human saliva; effects of stimulation

Saliva is a biological fluid that is easy to collect and is of considerable interest as a source of biomarkers. To date, its protein composition has been the most extensively studied but its metabolic composition is also of real interest. However, the composition of saliva is complex and dependent on numerous factors, among which stimulation is source of many variations. The aim of this work was to study the effects of a stimulating condition (chewing) versus a resting condition on the human salivary metabolome. Saliva from 16 subjects was collected on three occasions and studied using nuclear magnetic resonance. The two conditions could be separated by PLS-DA analysis. Fatty acids, some organic acids and amino acids, probably arising from the degradation of prolin-rich proteins, were over-represented in stimulated saliva, whereas taurine, and propionate were over-represented in resting saliva. To clarify further the identification of fatty acids, the free and total fatty acid contents were studied by gas chromatography. The principal fatty acids identified were oleic, stearic and palmitic acids. It was also possible to separate the two conditions of stimulation by PLS-DA. These results show that the regulation of saliva and sampling conditions must be taken into account when studying markers in saliva.