IN-VITRO CELLULAR-RESPONSES TO BIOERODIBLE PARTICLES LOADED WITH RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN-2

Porous 50:50 poly(d,l lactide-co-glycolide) microspheres containing va rying amounts of ''free'' recombinant human bone morphogenetic protein -2 (rhBMP-2) were evaluated for their ability to induce/enhance expres sion of osteoblastic characteristics by pluripotent mesenchymal cells in vitro. ''Free'' protein (F-p) is defined as protein present on the surface and within the porous matrix of the microspheres. Four prepara tions of bioerodible particles (BEP) were used: blank-without rhBMP-2; low F-p-24 mu g of free rhBMP-2 per g of particles; medium F-p-403 mu g/g; and high F-p-884 mu g/g. C3H10T1/2 cells (C3H) and bone marrow s tromal cells (BMC) were cultured with 1 mg of BEP for up to 4 weeks, a nd cell growth and expression of osteogenic responses were determined weekly. For both cell types, control cultures (neither BEP nor rhBMP-2 ) and cultures with blank BEP exhibited no or minimal osteoblastic cha racteristics. Compared to control and blank BEP cultures, C3H cells re sponded to particles having medium and high amounts of free rhBMP-2 wi th increased cell growth and alkaline phosphatase activity, but osteoc alcin secretion and mineralization were not markedly influenced. Low F -p BEP enhanced only the alkaline phosphatase activity of C3H cells. I n contrast, although growth was not affected, rhBMP-2-loaded BEP incre ased alkaline phosphatase activity, osteocalcin secretion, and mineral ization in BMC cultures in a dose-dependent manner (i.e., blank < low < medium < high F-p). (C) 1998 John Wiley & Sons, Inc.