Objectives: The salivary protein statherin is an inhibitor of spontaneous and secondary precipitation of hydroxyapatite (HAp), binds calcium, and is detected in enamel pellicle. The N-terminus of statherin is responsible for HAp and enamel binding. Our aim was to measure the effect of a 21 amino-acid peptide (StN21) identical to the N-terminus of statherin on the rate of demineralisation of HAp.
Methods: StN21 (with phosphoserine residues) was chemically synthesised. HAp pellets (5×5×2 mm, coated with acid resistant varnish, leaving an exposed surface) were equilibrated with a solution saturated wrt HAp for 24 h. The HAp pellets were submerged in different solutions containing various concentrations of StN21 in a modified phosphate buffer for 24 h to coat the exposed surface with StN21. Controls were HAp mixed with buffer only, and HAp coated with lysozyme. The demineralising solution (0.1 mol l-1 acetic acid, buffered to pH 4, containing 1.0 mmol l-1 calcium and 0.6 mmol l-1 phosphate) was circulated past the HAp pellets at 0.4 ml min-1. Scanning microradiography (SMR) was used to measure the rate of demineralisation (RDHAp). SMR details: two lines, 12 points per line; scanning time 30s per point; total time 2 weeks. Presence of coated StN21 after experiment was confirmed by SDS-PAGE.
Results: RDHAp control was 5.6 ×10-5 g cm-2 h-1. RDHAp of StN21 coated HAp pellets was much lower and decreased with increasing StN21 concentration (2.2, 1.9, 1.7 and 1.8 ×10-5 g cm-2 h-1 at StN21 concentrations 0.75, 1.13, 1.88 and 3.76 ×10-4 mol l-1, respectively). RDHAp of the lysozyme-coated negative control was 4.9 ×10-5 g cm-2 h-1.
Conclusion: Coating exposed surface of HAp pellets with a statherin-like polypeptide significantly reduces the rate of demineralisation.