title: Inhibition of hydroxyapatite growth by casein, a potential salivary phosphoprotein homologue.
abstract: Salivary phosphoproteins are essential in tooth mineral regulation but are often overlooked in vitro. This study aimed to evaluate the effect of casein, as a salivary phosphoprotein homologue, on the deposition and growth of hydroxyapatite (HA) on tooth surfaces. Hydroxyapatite growth was quantified using seeded crystal systems. Artificial saliva (AS) containing HA powder and 0, 10, 20, 50, or 100 μg ml(-1) of casein, or 100 μg ml(-1) of dephosphorylated casein (Dcasein), was incubated for 0-8 h at 37°C, pH 7.2. Calcium concentrations were measured using atomic absorption spectroscopy (AAS). Surface precipitation of HA on bovine enamel and dentine blocks, incubated in similar conditions for 7 d, was examined using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) with selected area electron diffraction (SAED). Casein adsorption was assessed using modified Lowry assays and zeta-potential measurements. The AAS results revealed a concentration-dependent inhibition of calcium consumption. Hydroxyapatite precipitation occurred when no casein was present, whereas precipitation of HA was apparently completely inhibited in casein-containing groups. Adsorption data demonstrated increasingly negative zeta-potential with increased casein concentration and an affinity constant similar to proline-rich proteins with Langmuir modelling. Casein inhibited the deposition and growth of HA primarily through the binding of esterized phosphate to HA active sites, indicating its potential as a mineral-regulating salivary phosphoprotein homologue in vitro.
authors.affiliation: Department of Cariology and Operative Dentistry, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Maria J R H
authors.initials: MJ
authors.lastname: Romero
authors.affiliation: Department of Cariology and Operative Dentistry, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Syozi
authors.initials: S
authors.lastname: Nakashima
authors.affiliation: Department of Cariology and Operative Dentistry, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Nikaido
authors.affiliation: Instrumental Analysis Research Center, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Shizuko
authors.initials: S
authors.lastname: Ichinose
authors.affiliation: International Exchange Center, Tokyo Medical and Dental University, Tokyo, Japan.|Department of Restorative Dentistry, University of Washington School of Dentistry, Seattle, WA, USA.
authors.forename: Alireza
authors.initials: A
authors.lastname: Sadr
authors.affiliation: Department of Cariology and Operative Dentistry, Division of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Junji
authors.initials: J
authors.lastname: Tagami
mesh_terms: D000327:Adsorption; D000818:Animals; D002118:Calcium / Q000737:chemistry; D002364:Caseins / Q000737:chemistry*; D002417:Cattle; D011232:Chemical Precipitation; D003460:Crystallization; D003461:Crystallography; D003804:Dentin / Q000737:chemistry / Q000648:ultrastructure; D017886:Durapatite / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010710:Phosphates / Q000737:chemistry; D010750:Phosphoproteins / Q000737:chemistry; D011392:Proline / Q000737:chemistry; D012464:Saliva, Artificial / Q000737:chemistry; D012471:Salivary Proteins and Peptides / Q000737:chemistry; D013054:Spectrophotometry, Atomic; D013696:Temperature; D013997:Time Factors; D014089:Tooth Remineralization
chemical_list: D002364:Caseins; D010710:Phosphates; D010750:Phosphoproteins; D012464:Saliva, Artificial; D012471:Salivary Proteins and Peptides; D017886:Durapatite; D011392:Proline; D002118:Calcium
keywords: apatite; casein; mineral regulation; pellicle; salivary phosphoproteins