A novel dual-action antimicrobial peptide for caries management

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 to KR12. The secondary structure of GA-KR12 was evaluated by circular dichroism spectroscopy. The stability was evaluated by high -performance liquid chromatography. The cytotoxicity was evaluated by a mitochondrial dehydrogenase activ-ity assay. The antimicrobial properties against common cariogenic species were evaluated by minimum inhib-itory concentration (MIC) and minimum bactericidal/fungicidal concentration (MBC/MFC). The morphology of cariogenic species was analysed by transmission electron microscope (TEM). To assess the mineralising effect of GA-KR12 on enamel, 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: GA-KR12 did not exhibit cytotoxicity against HGF. Around 82% of the GA-KR12 remained in human saliva at 37 degrees C for 1 h. The MIC and MBC/MFC against the tested species were 10-320 mu M and 20-1,280 mu M, respectively. GA-KR12 induced remarkable morphological defects in the tested species. The enamel treated with GA-KR12 had smaller lesion depths (p < 0.001), less mineral loss (p < 0.001) and higher calcium-to-phosphorus molar ratios (p < 0.001) than those in the enamel treated with 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. Conclusions: This study developed a biocompatible and stable peptide which inhibited the growth of cariogenic species and mineralised the enamel caries. Clinical significance: The novel dual-action peptide, GA-KR12, is potential applicable in the management of caries.