The human saliva metabolome

Saliva is a clear, watery biofluid produced by the salivary glands to protect and lubricate the oral cavity. While mostly composed of water (99 %), the chemical composition of saliva is known to change quite dramatically in response to a variety of different physiological states, stimuli, insults and stressors. Unfortunately, among the human biofluids typically used in medical testing (such as blood and urine), saliva is rarely used. Given that saliva is the most easily accessible and readily obtained biofluid, this is rather unfortunate. Part of the reluctance to use saliva in medical testing likely has to do with the fact that its chemical composition is not well known. Here, a comprehensive characterization of the human saliva metabolome is presented. Multiple analytical platforms including nuclear magnetic resonance spectroscopy, gas chromatography mass spectrometry, direct flow injection/liquid chromatography mass spectrometry, inductively coupled plasma mass spectrometry, and high performance liquid chromatography were employed to quantify the metabolites that can be commonly detected in human saliva. Using this multiplatform approach, we were able to quantify and/or identify 308 salivary metabolites or metabolite species in human saliva. This experimental work was complemented with computer-aided literature mining that led to the identification and annotation of another 708 salivary metabolites. The combined collection of 853 non-redundant salivary metabolites or metabolite species together with their concentrations, related literature references, and links to their known disease associations are freely available at http://www.hmdb.ca/.