We have previously reported that salivary
glycine and
proline levels are increased to nearly butanoate level in elderly people. In order to identify the source of
glycine and
proline, we performed high-performance liquid chromatography analysis of
amino acid production to a total of seven oral cells before and after stimulation with
inflammation inducers. We found that production of
amino acids (per a given number of cells) by normal oral mesenchymal cells (gingival fibroblast, pulp cell, periodontal ligament fibroblast) was approximately three-fold that of
oral squamous cell carcinoma cell lines (HSC-2, HSC-3, HSC-4, Ca9-22), and that production of
glycine and especially
proline by all these seven cells was much lower than that of
glutamine and
glutamic acid. Treatment of three oral mesenchymal cells with
interleukin (IL)-1β or lipopoly-saccharide (LPS) reproducibly increased the production of
glutamic acid and
glutamine, but not that of
glycine and
proline.
Glycine and
proline only marginally stimulated the
IL-8 production by IL-1β-stimulated gingival fibroblast, whereas
glycine dose-dependently inhibited the
nitric oxide production by
lipopolysaccharide-stimulated mouse macrophage-like RAW264.7 cells. These data demonstrated that normal oral mesenchymal cells are not the major source of
glycine and
proline that accumulates in the saliva of aged people, suggesting the involvement of the deregulation of
collagen metabolism during aging.