Identifying sources and estimating glandular output of salivary TIMP-1

Tissue inhibitor of metalloproteinases 1 (TIMP-1) has been identified as a potential biomarker in diseases such as cancer, cardiovascular diseases and diabetes. Since TIMP-1 resides in most tissues and bodily fluids, we evaluated the potential of using saliva to obtain reproducible TIMP-1 measurements in a non-invasive manner.

Samples of unstimulated and stimulated whole saliva and saliva collected from individual glands were analysed for TIMP-1 content. A TIMP-1 ELISA was validated for use in saliva testing and the most optimal sampling and handling procedures for reproducible measurements identified. Western blotting and MALDI-TOF mass spectrometry were used for confirmatory analyses.

The TIMP-1 ELISA was found suitable for saliva measurements. All saliva secretions contained TIMP-1, but in different concentrations ranging from 2.81 ng/mL in submandibular/sublingual saliva to 173.88 ng/mL in parotid saliva. TIMP-1 concentrations were influenced to a varying degree by fluctuations in flow. We found the lowest output in submandibular/sublingual saliva stimulated with 0.5% citric acid (3.56 ng/min) and highest output in chewing-stimulated whole saliva (267.01 ng/min).

This study shows that saliva contains authentic TIMP-1, the concentration of which was found to depend on gland type and salivary flow. Stimulated whole saliva is suggested as a reliable and easily accessible source for TIMP-1 determinations in bodily fluids.