Effects of cecropin-XJ on growth and adherence of oral cariogenic bacteria in vitro

Background CecropinXJ belongs to cecropinB, which is the most potent antibacterial peptide found naturally The aim of this study was to investigate the effects of cecropinXJ on growth and adherence of oral cariogenic bacteriaMethods Four oral cariogenic bacteria (Streptococcus mutans, Lactobacillus acidophilus, Actinomyces viscosus and Actinomyces naeslundii) were chosen for this experiment The minimal inhibitory concentrations (MICs) and reductive percent of bacterial growth were used to assay the antibacterial activity of cecropinXJ Mammalian cytotoxicity of cecropinXJ was tested with human periodontal membrane fibroblasts by tetrazolium (MTT) colorimetric assay The bacterial morphological changes induced by cecropinXJ were examined on scanning electron microscope (SEM) The influence of cecropinXJ on bacterial adhesion to salivacoated hydroxyapatite (SHA) was measured by scintillation countingResults The MICs of cecropinXJ for inhibition of the growth of four bacteria ranged from 40 to 428 μmol/L with the highest susceptible to A naeslundii and the lowest susceptible to L acidophilus At pH 68, 55 and 82, 1/2 MIC of cecropinXJ reduced the number of viable bacteria by 409%, 678% and 328% for S mutans and by 281%, 572% and 379% for L acidophilus The activities against Smutans and L acidophilus increased at pH 55 compared with pH 68 (P<001, respectively) In present of 50% saliva, 1/2 MIC of the peptide decreased the direct count of viable cells by 292% and 144% for S mutans and L acidophilus, respectively (P<001 and P>005, respectively), whereas almost no reduction counts were detected in the presence of 20% serum for both bacteria (P>005, respectively) Mammalian cytotoxicity of cecropinXJ from 10 to 100 μmol/L exhibited no cytotoxicity against human periodontal membrane fibroblasts (P>005) Bacterial morphological changes induced by MIC of cecropinXJ examined on SEM showed cell surface disruption Furthermore, the ability of A naeslundii adhesion to SHA decreased significantly with MIC of cecropinXJ for 10 and 20 minutes (P=0001 and 0000, respectively), and S mutans, A viscosus to SHA decreased significantly with MIC of cecropinXJ for 20 minutes( P=0000, respectively) Conclusions CecropinXJ exhibited bactericidal action against cariogenic pathogens, and the antibacterial activity enhanced in the acid environment The results also demonstrate that cecropinXJ prevents S mutans and actinomyces adsorption to SHA These findings suggest that CecropinXJ may have potential to prevent caries

Difference of adherence, proliferation and osteogenesis of mesenchymal stem cells cultured on different HA/ZrO2 composites

Objective： To study the adherence, proliferation and osteogenesis of mesenchymal stem cells （MSCs） cultured on different HA/ZrO2 composites. Methods： The simplex and graded HA/ZrO2 compo- sites were prepared using dry-laid method. The surface topography of the composites was observed by scanning electron microscope （SEM）. The MSCs were isolated from rabbits and cultured on experimental groups （simplex HA/ ZrO2 composite, graded HA/ZrO2 composite, pure HA or pure ZrO2 coatings respectively） and control group （ordinary culture plate）. Then, we observed the adherence, proliferation and osteogenesis of the MSCs, detected the cellular alkaline phosphatase （ALP） activities, extracted total RNA and detected the mRNA expression of collagen I, osteocalcin and osteopontin using the reverse transcription and poly- merase chain reaction （RT-PCR） method. Results： The SEM images confirmed that the surface of the simplex HA/ZrO2 composite was coverd by discontiguous HA layer with clear visualization of the partial ZrO2 matrix, while the surface of the graded HA/ZrO2 composite was fairly rough with porosity. X-ray diffraction showed that after high temperature sintering, the ZrO2 phase still remained, while the HA phase was transformed to β-Ca3 （po4）2＇α-Ca3（PO4）2 and CaZrO3 phases on the surface of both composites. Cell culture indicated that the HA/ ZrO2 composites supported cell attachment. Neither ALP expression nor mRNA expression of collagen I, osteocalcin or osteopontin from RT-PCR results showed significant deviation among four groups. Conclusion： Among these four composites, the graded HA]ZrO2 composite promotes the MSCs proliferation and the osteogenic differentiation to a certain extent.