Antibacterial efficacy of casein-derived peptides against Enterococcus faecalis

Top-Down Glycopeptidomics Reveals Intact Glycomacropeptide Is Digested to a Wide Array of Peptides in Human Jejunum

BACKGROUND

Bovine milk κ-casein-derived caseinomacropeptide (CMP) is produced in large quantities during cheese-making and has various biological activities demonstrated via in vitro and in vivo experiments. Previous studies examined protein degradation and peptide release after casein or whey protein consumption. However, whether purified intact CMP that is partially glycosylated survives intact to its presumed site of bioactivity within the gut remains unknown.

OBJECTIVES

The aim of this study was to determine the extent to which purified intact CMP (including glycosylated forms) is digested into peptide fragments within the jejunum of healthy human adults after consumption.

METHODS

Jejunal fluids were collected from 3 adult participants (2 men and 1 woman, age: 27 ± 7 y; BMI: 23 ± 1 kg/m2) for 3 h after consuming 37.5 g of purified intact CMP. CMP and CMP-derived peptides were isolated from the collected jejunal fluids by ethanol precipitation and solid-phase extraction and identified by MS-based top-down glycopeptidomics. Relative abundances of CMP and CMP-derived peptides were compared qualitatively between the feed and the jejunal fluids.

RESULTS

Intact CMP was dominant in feeding material, accounting for 90% of the total ion abundance of detected peptides, and in very low abundance (<2%) in the jejunal fluids. CMP-derived fragment peptides ranging from 11 to 20 amino acids in length were predominant (accounting for 68-88% of the total peptide ion abundance) in jejunal fluids during 1-3 h post consumption.

CONCLUSIONS

This study demonstrates that intact CMP (including glycosylated forms) is mostly digested in the human jejunum, releasing a wide array of CMP-derived peptide fragments. Some of the CMP-derived peptides with high homology to known bioactive peptides consistently survived across 3 h of digestion. Therefore, future research should examine the biological effects of the partially digested form-the CMP-derived fragments-rather than those of intact CMP.

Potential applications of antimicrobial peptides and their mimics in combating caries and pulpal infections

Antimicrobial peptides (AMPs) are short cationic host-defense molecules that provide the early stage of protection against invading microbes. They also have important modulatory roles and act as a bridge between innate and acquired immunity. The types and functions of oral AMPs were reviewed and experimental reports on the use of natural AMPs and their synthetic mimics in caries and pulpal infections were discussed. Natural AMPs in the oral cavity, predominantly defensins, cathelicidins and histatins, possess antimicrobial activities against oral pathogens and biofilms. Incomplete debridement of microorganisms in root canal space may precipitate an exacerbated immune response that results in periradicular bone resorption. Because of their immunomodulatory and wound healing potentials, AMPs stimulate pro-inflammatory cytokine production, recruit host defense cells and regulate immuno-inflammatory responses in the vicinity of the pulp and periapex. Recent rapid advances in the development of synthetic AMP mimics offer exciting opportunities for new therapeutic initiatives in root canal treatment and regenerative endodontics.

STATEMENT OF SIGNIFICANCE

Identification of new therapeutic strategies to combat antibiotic-resistant pathogens and biofilm-associated infections continues to be one of the major challenges in modern medicine. Despite the presence of commercialization hurdles and scientific challenges, interests in using antimicrobial peptides as therapeutic alternatives and adjuvants to combat pathogenic biofilms have never been foreshortened. Not only do these cationic peptides possess rapid killing ability, their multi-modal mechanisms of action render them advantageous in targeting different biofilm sub-populations. These factors, together with adjunctive bioactive functions such as immunomodulation and wound healing enhancement, render AMPs or their synthetic mimics exciting candidates to be considered as adjuncts in the treatment of caries, infected pulps and root canals.