RGD PEPTIDES REGULATE THE SPECIFIC ADHESION SCHEME OF OSTEOBLASTS TO HYDROXYAPATITE BUT NOT TO TITANIUM

Hydroxyapatite (HA) is a bioactive dental implant material which accel erates bone formation on its surface. The mechanism of this accelerati on is not clear. The elucidation of the cell adhesion might be the key to the understanding of the bioactive mechanism of HA. In this study, we analyzed the adhesion of HOS human osteoblasts onto HA and titaniu m to find the particular adhesion to HA. In short-term cultures in fet al bovine serum-pre-coated materials, a significantly higher number of cells adhered to HA than to titanium. In addition, serum-free conditi ons with phosphate-buffered saline pre-coating or bovine serum albumin pre-coating materials were tested. The results were nearly the same a mong all pre-coating conditions, suggesting that the quantity of cell adhesion was not affected by serum components. However, in the morphol ogical observations by SEM, the form of adhesion was found to differ a mong pre-coating conditions. The osteoblasts tightly adhered and sprea d onto both HA and titanium with serum pre-coating, whereas the cells loosely adhered and did not spread without serum. To evaluate the Arg- Gly-Asp (RGD) sequence-specific adhesion, we used synthetic RGD peptid es for a competitive inhibition test. The results showed that RGD pept ides remarkably inhibited the tight adhesion and spreading of osteobla sts onto HA, whereas they did not strongly inhibit adhesion and spread ing onto titanium. These results demonstrate that the regulation of ce ll adhesion to HA is different from that to titanium. Our study sugges ts that the RGD-containing serum proteins might have a major role in r egulating the specific adhesion of osteoblasts to HA, and in inducing enhanced cell growth and differentiation.