Cyclo-DfKRG peptide modulates in vitro and in vivo behavior of human osteoprogenitor cells on titanium alloys.

The first aim of the present study was to investigate the capacity of a cyclo-DfKRG-coated hydroxyapatite-titanium alloy (Ti-HA-RGD) to activate in vitro human osteoprogenitor cells adhesion and differentiation. The second purpose was to examine in vivo the role of a autologous cell seeding on cyclo-DfKRG-functionalized materials to provide bone repair after implantation in femoral condyle of rabbits. Our in vitro results have demonstrated that both titanium alloy functionalized with hydroxyapatite (Ti-HA-RGD and Ti-HA) contributed to higher cell adhesion than titanium alloy alone respectively 85 and 55% vs 15% compared to tissue culture polystyrene after one hour of cell seeding. As for differentiation, after 3 days of culture, Ti-HA presented the highest increase of ALP mRNA of all surfaces studied. Ti-HA-RGD showed an intermediate value about half as high as Ti-HA. Moreover after 3 days, both Ti-HA and Ti-HA-RGD surfaces showed the highest increase of cbfa1 mRNA expression. Two weeks following implantation, in vivo findings revealed that percentage of lacunae contact observed with pre-cellularized Ti-HA-RGD samples remains significantly lower than with Ti-HA group (10.5+/-9.6 % vs 33.7+/-11.5 %, P<0.03). Meanwhile, RGD peptide coating had no significant additional effect on the bone implant contact and area. Moreover, histomorphometry analysis revealed that implantation of pre-cellularized RGD coated materials with ROP cells increased significantly peri-implant fibrous area (24+/-11.6% vs 3+/-1.7% for Ti-HA-RGD, P<0.02). RGD coatings demonstrated osteoblastic adhesion, differentiation and in vivo bone regeneration at most equivalent to HA coatings.