OBJECTIVETo design a kind of biomimetic polypeptide of dentin matrix protein-1 (DMP-1), which can bind to dentine collagen fibers and initiate mineralization.

METHODSA novel polypeptide was developed by connecting the collagen binding domain of DMP-1 "DSESSEEDR" to the hydrophilic C-terminal of amelogenin "TKREEVD". The polypeptide was synthetically prepared by standard solid-phase peptide synthesis. Human dentine slices were completely demineralized by hydrochloric acid to expose the dentine collagen. Fluorescein isothiocyanate coupled polypeptide was applied to the exposed dentine collagen. Fluorescent microscopy was used to examine the polypeptide specially bond to the dentine collagen. Nucleation and growth of hydroxyapatite was initiated by immersing the polypeptide into calcium chloride and sodium hypophosphate solutions respectively. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area diffraction (SAD) were used to examine the hydroxyapatites formed. RESULTS Fluorescent dentine collagen was identified in the demineralized dentine specimens. Nucleation and growth of crystals were detected after immersing the polypeptide into calcium chloride and sodium hypophosphate solutions by SEM and TEM. SAD confirmed the crystals were hydroxyapatites.

CONCLUSIONThe polypeptide of "DSESSEEDRTKREEVD" can simulate DMP-1 binding collagen and initiate hydroxyapatite nucleation and growth. It may be a potential molecular tool for dentine remineralization.

Biomimetics ; Calcium Phosphates ; Collagen ; Dentin ; Durapatite ; Humans ; Microscopy, Electron, Scanning ; Microscopy, Electron, Transmission ; Peptides

Objective To investigate the inhibition effect of dopamine on the activity of matrix metalloproteinases(MMP) and the effect of dopamine on degradation of dentin collagen for its potential use in caries treatment and dentin adhesive.Methods In the experiment of MMP activity test,2.0 g/L dopamine+ 1.0 g/L highly purified collagenase type Ⅶ from Clostridium histolyticum served as the experimental group,and deionized water+ 1.0 g/L highly purified collagenase type Ⅶ from Clostridium histolyticum served as the negative control group,and 2％ chlorhexidine + 1.0 g/L highly purified collagenase type Ⅶ from Clostridium histolyticum served as the positive control group,and the mixture volume ratio of the two ingredients in every group was 1∶9.After 15 minutes,the enzyme activity of each sample was tested by MMP activity colerimetric quantitative detection kits,and the test was repeated 5 times in each group.In the experiment of collagen degradation,the dentin slices were demineralized with 37％ phosphoric acid for 1 min.In sequence,2 dentin slices were used to observe the morphology,and the remaining 30 dentine slices were randomly divided into three groups(n=10) according to random number table:the negative control ones were stored in 100 μl deionized water and 900 μl collagenase(7 days,37 ℃),the positive control ones were stored in 100 μl chlorhexidine and 900 μl collagenase(7 days,37 ℃) and the experimental specimens were stored in 100 μl dopamine and 900 μl collagenase(7 days,37 ℃).The degraded collagen was investigated by assaying hydroxyproline.The framework of collagen was evaluated with field emission scanning electron microscope(FE-SEM).Results The statistical results of completely random design ANOVA showed that the MMP activity and the amount of degraded collagen of the negative control group [(0.089±0.011) μmol · min-1· mg-1 and (2 837±201) μg/cm2] were significantly higher than those of the positive control group[(0.038± 0.006) μmol · min-1 · mg-1 and (1 288± 172) μg/cm2] and the experimental group[(0.030±0.009) μmol· min-1· mg-1 and (1 389±255) μg/cm2](P＜0.05).SEM observation indicated that the structural integrity of the collagen network on dentin still existed in experiment samples and positive control groups,however,collagen fibrils were destructed and the structural integrity disappeared in the negative control groups.Conclusions Dopamine may inhibit MMP activity and reduce the amount of degraded collagen.