Ornithine decarboxylase activity in tooth surface plaque from monkeys (Macaca fascicularis) fed pyridoxine, phytate and invert sugar

Amino acid composition and amino acid-metabolic network in supragingival plaque

Dental plaque metabolizes both carbohydrates and amino acids. The former can be degraded to acids mainly, while the latter can be degraded to various metabolites, including ammonia, acids and amines, and associated with acid-neutralization, oral malodor and tissue inflammation. However, amino acid metabolism in dental plaque is still unclear. This study aimed to elucidate what kinds of amino acids are available as metabolic substrates and how the amino acids are metabolized in supragingival plaque, by a metabolome analysis. Amino acids and the related metabolites in supragingival plaque were extracted and quantified comprehensively by CE-TOFMS. Plaque samples were also incubated with amino acids, and the amounts of ammonia and amino acid-related metabolites were measured. The concentration of glutamate was the highest in supragingival plaque, while the ammonia-production was the highest from glutamine. The obtained metabolome profile revealed that amino acids are degraded through various metabolic pathways, including deamination, decarboxylation and transamination and that these metabolic systems may link each other, as well as with carbohydrate metabolic pathways in dental plaque ecosystem. Moreover, glutamine and glutamate might be the main source of ammonia production, as well as arginine, and contribute to pH-homeostasis and counteraction to acid-induced demineralization in supragingival plaque.

Food components and caries

For many decades, sugars have been the dietary constituents receiving the most attention in relation to their effects on dental caries. Frequently, however, there is little relationship between the amount of sugar in a food and its ability to induce caries. Therefore, it is clear that constituents in the diet can influence the ability of plaque to lower the pH of sugar solutions. For instance, replacing sugar in foods with xylitol, sorbitol, saccharin, or aspartame may lead to a reduction in the incidence of dental caries. All these sugar substitutes are non-cariogenic, and some may possess cariostatic properties. The presence of arginine-rich proteins in the diet may provide a ready source of this amino acid, which is the substrate for the arginine deiminase pathway which can result in a rapid elevation of plaque pH values. Proline can act as an acceptor for protons from lactate in the Stickland reaction. This is a major but much-neglected metabolic pathway in dental plaque. The presence of fat in experimental diets has been shown to affect their cariogenicity. The effects have been ascribed to enhanced clearance of sugars from the mouth. It is also conceivable that several fatty acids express a potent antibacterial effect. The presence of calcium and phosphorus has been shown to influence the cariogenicity of foods; the effect, however, is restricted to the food containing the minerals. Evidence suggests that pyridoxine (vitamin B6) may exert a cariostatic effect by enhancing decarboxylation activity in dental plaque. It is clear that sugar alone is not the sole determinant of whether food is cariogenic. Furthermore, myriad substances may hinder or enhance the caries-promoting properties of sugars in the diet.