RESPONSE OF HUMAN OSTEOBLASTS TO IMPLANT MATERIALS - INTEGRIN-MEDIATED ADHESION

The initial interaction of the human osteoblast-like cell line Saos-2 with orthopaedic implant materials was analyzed to determine the mecha nism by which these cells adhere to implant surfaces. Saos-2 cells wer e allowed to attach to disks composed of the orthopaedic implant mater ials Tivanium (Ti6Al4V) and Zimaloy (CoCrMo) and to control disks of g lass and plastic. Serum had no effect on the number of cells that atta ched to Tivanium and Zimaloy at 4 or 24 hours but did increase the num ber of cells that attached to glass at 24 hours. Collagen synthesis wa s determined by [H-3]proline incorporation into collagenase-digestible protein and noncollagen protein. A significant increase of 19% was fo und for collagen synthesized in cells cultured on Zimaloy for 24 hours compared with glass, with no differences on Tivanium and plastic. How ever, collagenase-digestible protein and noncollagen protein were incr eased the most (204 and 198%, respectively) on Tivanium compared with glass. To determine if integrins were involved in cell attachment to i mplant materials, the peptide GRGDSP (Gly-Arg-Gly-Asp-Ser-Pro), which blocks integrin receptors through the Arg-Gly-Asp sequence, was added to the cells in serum-free medium. This peptide inhibited cell adhesio n by 28% on Tivanium and 40% on Zimaloy but had no effect on glass and plastic. The control peptide GRADSP (Gly-Arg-Ala-Asp-Ser-Pro) had no effect on adhesion. Inhibition of protein synthesis and enzymatic remo val of surface proteins did not affect the ability of Arg-Gly-Asp pept ides to inhibit cell attachment to the implant materials. These result s suggest that integrins are able to bind directly to Tivanium and Zim aloy. Western blot analysis of integrin protein demonstrated changes i n many integrin subunits, depending on the substrate to which cells at tached. In particular, the beta(1) integrin subunit was increased 3.8 to 9.5-fold at 24 hours. To determine specifically which integrins may be involved in adhesion, antibodies to integrins were added. An antib ody to the fibronectin receptor, alpha(5) beta(1), significantly inhib ited binding of cells to Tivanium by 63% and to Zimaloy by 49% and had no effect on glass. The vitronectin receptor antibody, alpha(v) beta( 3)/beta(5), did not alter cell adhesion. In conclusion, osteoblast-lik e cells appear to be capable of attaching directly to implant material s through integrins. The type of substrate determines which integrins and extracellular matrix proteins are expressed by osteoblasts. These data provide information on how implant materials may affect osteoblas t differentiation and bone growth.