Novel dual-action antimicrobial peptide may effectively manage caries: Study

John YunNiu and colleagues from the Faculty of Dentistry, The University of Hong Kong, Hong Kong, China carried out the present study with the objective to develop a novel dual-action peptide with antimicrobial and mineralising properties.

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 activity assay. The antimicrobial properties against common cariogenic species were evaluated by minimum inhibitory 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.

The results showed that -

a. GA-KR12 did not exhibit cytotoxicity against HGF. Around 82% of the GA-KR12 remained in human saliva at 37°C for 1 h.

b. The MIC and MBC/MFC against the tested species were 10-320 μM and 20-1,280 μM, respectively. c. GA-KR12 induced remarkable morphological defects in the tested species.

d. 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.

e. 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.

Hence, the authors concluded that "this study developed a biocompatible and stable peptide which inhibited the growth of cariogenic species and mineralised the enamel caries."