A Novel Dual-Action Antimicrobial Peptide for Caries Management

Abstract

Objectives: To develop a novel dual-action peptide with antimicrobial and mineralising properties. Methods: A novel peptide, namely GA-KR12, was synthesised through grafting gallic acid (GA) to KR12, a fragment of the human antimicrobial peptide cathelicidin. The antimicrobial properties against six common cariogenic species (Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus, Lactobacillus rhamnosus, Actinomyces naeslundii and Candida albicans) were evaluated by the minimum inhibitory concentration (MIC) and the minimum bactericidal/fungicidal concentration (MBC/MFC). The morphology of cariogenic species was analysed by transmission electron microscope (TEM). The mineralising effect of GA-KR12 on enamel was evaluated using a pH-cycling model. The lesion depths, mineral loss, surface morphology, calcium-to-phosphorus ratio and crystal characteristics were determined using micro-computed tomography, scanning electron microscopy (SEM) and energy dispersive spectroscopy X-ray diffraction, respectively. Results: The MIC and MBC/MFC of GA-KR12 against the tested species were 10-320 μM and 20-1,280 μM, respectively. TEM showed that GA-KR12 induced remarkable morphological defects in the six species. GA-KR12 did not exhibit cytotoxicity against human gingival fibroblasts at concentrations up to 2,560 μM. The table below summarizes the lesion depths, mineral loss and calcium-to-phosphorus molar ratios of enamel treated with GA-KR12, KR12, GA and water. SEM showed a well-organised prism pattern in enamel treated with GA-KR12. X-ray diffraction revealed that the hydroxyapatite on the enamel treated with GA-KR12 was better crystalised than that on the enamel without treatment. Conclusions: This study developed a peptide which inhibited the growth of common cariogenic species and mineralised enamel caries.