Human age-declined saliva metabolic markers determined by LC-MS

Metabolites in human biofluids reflect individual physiological body states influenced by various factors. Using liquid chromatography-mass spectrometry (LC-MS), we conducted non-targeted, non-invasive, comprehensive metabolomics using saliva of 27 healthy volunteers in Okinawa, consisting of 13 young (30 ± 3 yr) and 14 elderly (76 ± 4 yr) people. Quantitative analysis of whole 99 saliva metabolites has been scarce. Twenty-one of 99 salivary metabolites quantified appear to be statistically age-linked. Their abundances decline with advancing age, except for ATP, which increased 1.96-fold in the elderly, possibly due to reduced ATP consumption. Fourteen age-linked and highly correlated compounds function in a metabolic network of amino acids, purines/pyrimidines, the pentose-phosphate pathway and glycolysis/gluconeogenesis. The remaining seven metabolites, while age-linked, but less strongly correlated, include ATP, muscle-related acetyl-carnosine, carnitine, N-methyl-histidine and creatinine, RNA-related dimethyl-xanthine, N-methyl-adenosine, anti-oxidation related glutathione disulfide, and N-methyl-adenosine. These metabolites together may provide detailed information on the metabolic network of oral aging, which is required to understand the functional decline of oral activity during human aging.