Effects of combined action of proline-rich peptides of human saliva with antimicrobial proteins

BACKGROUND: The substances that make up mixed saliva exhibit activity against bacteria, viruses and fungi. Among them are various cationic antimicrobial peptides: alpha- and beta-defensins, cathelicidins, histatins, but their concentration is relatively low. On the other hand, saliva widely contains a fraction of proline-rich proteins and products of their proteolysis — peptides, the functions of which currently remain poorly studied and unclear. The study of the antimicrobial activity of proline-rich proteins, in particular, when they act together with antimicrobial peptides, and the deciphering of the molecular and cellular basis for the implementation of the protective functions of proline-rich peptides is an urgent task in medicine and biology. The data obtained will help to understand the mechanisms of anti-infective protection of the oral cavity with the participation of the innate immune system, and in the future will allow the creation of drugs based on proline-rich proteins in humans and animals.

AIM: Study of the individual antibacterial action of proline-rich salivary proteins, their combined action with the antimicrobial proteins lactoferrin and lysozyme, as well as with one of the most significant endogenous protective peptides — cathelicidin LL-37 on the formation of bacterial biofilms.

MATERIALS AND METHODS: Human lactoferrin and egg lysozyme were used in the work. The minimum inhibitory concentrations of peptides against gram-negative and gram-positive bacteria were estimated using serial dilutions in a liquid nutrient medium. Using serial dilutions using the “chessboard” method, it was shown that proline-rich proteins can increase the antibacterial activity of innate immunity peptides present in the oral cavity. The ability of combinations of cationic proline-rich peptides with cathelicidin LL-37 to prevent the formation of bacterial biofilms was studied.

RESULTS: In the presence of proline-rich peptides, the antimicrobial activity of some antimicrobial peptides and proteins present in saliva against planktonic bacteria increases. The combined action of proline-rich proteins with LL-37 increases the inhibition of bacterial biofilm formation.

CONCLUSIONS: As a result of the study, it was shown that the analyzed cationic proline-rich peptides of human saliva exhibit anti-inflammatory effects, which suggests their significant role in the regulation of inflammatory processes in the oral cavity, as well as their participation in recovery processes.