The pH-Responsive Property of Antimicrobial Peptide GH12 Enhances Its Anticaries Effects at Acidic pH

Abstract

Dental caries is closely related to the acidification of the biofilms on the tooth surface, in which cariogenic bacteria bring about a dramatic pH decrease and disrupt remineralisation equilibrium upon the fermentation of dietary sugars. Thus, approaches targeting the acidified niches with enhanced anticaries activities at acidic pH are highly desirable. In our previous study, a cationic amphipathic α-helical antimicrobial peptide GH12 (Gly-Leu-Leu-Trp-His-Leu-Leu-His-His-Leu-Leu-His-NH<sub>2</sub>) was designed with good stability, low cytotoxicity, and excellent antibacterial effects. Considering its potent antibacterial activity against the acidogenic bacteria and its histidine-rich sequence, it was speculated that GH12 might show enhanced antimicrobial effects at an acidic pH. In this study, the pH-responsive property of GH12 was determined to evaluate its potential as a smart acid-activated anticaries agent. GH12 possessed much lower minimal inhibitory concentrations and minimal bactericidal concentrations against various kinds of bacteria at pH 5.5 than at pH 7.2. Employing <i>Streptococcus mutans</i>, the principal caries pathogen, as the model system, it was found that GH12 showed much stronger bactericidal effects on both planktonic <i>S. mutans</i> and <i>S. mutans</i> embedded in the biofilm at pH 5.5. In addition, short-term treatment with GH12 showed much more effective inhibitory effects on water-insoluble exopolysaccharides synthesis and lactic acid production of the preformed <i>S. mutans</i> biofilm at pH 5.5. As for the mechanism exploration, it was found that the net positive charge of GH12 increased and the tryptophan fluorescence intensity heightened with the peak shifting towards the short wavelength at pH 5.5, which demonstrated that GH12 could be more easily attracted to the anionic microbial cell membranes and that GH12 showed stronger interactions with the lipid membranes. In conclusion, acidic pH enhanced the antibacterial and antibiofilm activities of GH12, and GH12 is a potential smart anticaries agent targeting the cariogenic acidic microenvironment.

Recent Advances in the Development of Antimicrobial and Antifouling Biocompatible Materials for Dental Applications

“…These properties were confirmed in vivo where GH12 reduced the incidence and severity of caries without causing any damage to the oral mucosa or other signs of ill health in rats [172]. Jiang and co-workers further showed that antimicrobial and antibiofilm activity of GH12 was improved at pH 5.5 than at pH 7.2, therefore, making this AMP a suitable candidate for the development of pH-responsive smart biomaterials in the acidic microenvironment of dental caries [173].…”

“…Despite its potent antimicrobial activity and inhibition of biofilms, AMPs perform poorly in the oral cavity due to rapid enzymatic degradation, poor target specificity in solution, anionic protein adsorption and the diluting effects of saliva which render the compound ineffective [167][168][169][170][171][172][173][174][175][176][177][178]. Therefore, strategies are required to improve its physiological in vitro and in vivo stability to harness the maximum antimicrobial and antifouling effects of this exciting class of biomaterials.…”

Annual review of selected scientific literature: A report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

“…In a second article by the same research group, the cationic amphipathic alpha-helical antimicrobial peptide GH12 also demonstrated good stability, low cytotoxicity, and excellent antibacterial effects. 480 Considering its strong antibacterial activity against the acidogenic microorganisms and its histidine-rich sequence, it was hypothesized that GH12 might show greater antimicrobial effects at an acidic pH. Therefore, this study evaluated if GH12 was activated directly by acid.…”

“…These are small peptides, typically 6 to 8 amino acids, that selectively bind to specific microorganisms resulting in cell death. While waiting for the completion of clinical phase III trials on the very promising antimicrobial peptide C16G2, 478 developed in the United States, interesting data were published in 2020 479,480 on GH12, another antimicrobial peptide developed in China. Because of the multifaceted microenvironment of dental plaque, new caries-prevention strategies must ecologically modulate bacterial communities to successfully reduce cariogenic potential.…”

Development and evaluation of a chewing gum containing antimicrobial peptide GH12 for caries prevention

“…In multispecies biofilms, GH12 could suppress the growth of S. mutans and enhance the ecological competitiveness of Streptococcus sanguinis and Streptococcus gordonii , resulting in changes in biofilm composition and inhibition of cariogenic properties [23]. In particular, acidic pH could enhance the antibacterial and antibiofilm activities of GH12 [24]. It has been confirmed that GH12 can arrest the onset and development of caries in rats [25].…”