Fermentation of sugars in our food by the numerous bacteria in our mouth produces acids that destroy our teeth to form caries cavities. These bacteria reside in plaque-like communities called "dental biofilms". Arginine, an amino acid naturally found in our saliva, has been shown to be helpful in preventing tooth decay. A few beneficial bacteria have an arginine deiminase system (ADS) that helps break down arginine to form alkali that can neutralize the acids. Increased availability of arginine helps in the multiplication of these beneficial bacteria, while at the same time inhibiting the growth of acid-producing bacteria. Recently, studies conducted outside the human body also showed that arginine availability changes the composition of dental biofilms.
To further prove these findings in the human mouth, a team of dentists and researchers led by Post.doc. Yumi C. Del Rey and Professor Sebastian Schlafer from Aarhus University in Denmark have conducted a clinical trial and published their findings in the International Journal of Oral Science .
They recruited 12 participants with active caries and prepared specialized dentures that allow for the collection of intact biofilms, spanning both sides of the jaw. The participants were instructed to dip the dentures in a sugar solution for 5 minutes, immediately followed by distilled water (as placebo) or arginine for 30 minutes, one on each side. This was to be repeated three times a day, with arginine treatment done on the same side each time. "The aim was to investigate the impact of arginine treatment on the acidity, type of bacteria, and the carbohydrate matrix of biofilms from patients with active caries," explains Sebastian Schlafer, professor at the Department of Dentistry and Oral Health. After 4 days, when the biofilm was developed, the dentures were removed for detailed analysis.
A special pH-sensitive dye called "C-SNARF-4" was used to analyze the acidity of the collected biofilms in different locations. Biofilms treated with arginine showed a significantly higher pH (lower acidity) at 10 and 35 minutes after a sugar challenge. "Our results revealed differences in acidity of the biofilms, with the ones treated with arginine being significantly more protected against acidification caused by sugar metabolism" says the first author, Yumi C. Del Rey.
Then, carbohydrate-binding proteins called lectins, tagged with a fluorescent dye, were used to stain two common carbohydrate components of the biofilms: fucose and galactose. These components make up a large portion of dental biofilms and may contribute to the creation of "acidic pockets" inside them. With arginine treatment, an overall reduction was seen in the amount of fucose-based carbohydrates, possibly making the biofilm less harmful. In addition, there was a change in the structure of the biofilm, with galactose-containing carbohydrates decreasing at the bottom and increasing at the top.
Further, to determine which bacteria were present in the biofilm, they sequenced all bacterial genomes using a technique called "16S rRNA gene sequencing". Though biofilms treated with arginine and placebo were predominantly dominated by Streptococcus and Veillonella species, arginine significantly reduced the mitis/oralis group of streptococci, which produce acid but are not strong producers of alkali, and slightly increased streptococci with considerable arginine metabolism, thereby improving the pH. Overall, arginine made the biofilms less harmful by reducing their acidity, altering their carbohydrate structure, and reshaping the microbiome within them.
Dental caries, being prevalent across all ages and regions, could be combated using strategies such as supplementation of arginine in toothpastes or oral rinses for people who are more susceptible to them. Arginine, being an amino acid naturally produced in our body and present in dietary proteins, is harmless and could find application even in children.
