COMPARISON OF HUMAN OSTEOBLASTS AND OSTEOGENIC CELLS FROM HETEROTOPICBONE

Heterotopic ossification is a common complication in which hone develo ps in soft tissues, Although frequently benign, in some patients the c ondition becomes painful, restricts motion, and requires surgical inte rvention, This condition and the cells responsible for it are poorly c haracterized, Using cell culture techniques, this study compares the p erformance of osteogenic cells obtained from heterotopic ossification with trabecular osteoblasts isolated from the same patient, Cells isol ated from trabecular bone samples and heterotopic ossification sites f rom six patients were evaluated for osteocalcin production after expos ure to 1,25-dihydroxycholecaleiferol, alkaline phosphatase activity, t yping and synthesis of collagen, cell proliferation, and total protein content, Samples of heterotopic ossification and trabecular bone from three of the patients were examined histologically, Heterotopic ossif ication derived cells were shown to produce osteocalcin, Type 1 collag en, and alkaline phosphatase activity, They also had increased rates o f collagen synthesis, alkaline phosphatase activity, and cell prolifer ation compared with the normal osteoblasts, Initial tissue from the he terotopic ossification sites showed increased numbers of osteocytes/mm (2) compared with normal trabecular bone, Although heterotopic ossific ation derived cells functioned qualitatively like osteoblasts, they ex hibited elevated levels of activities traditionally ascribed to osteob lasts, such as collagen synthesis and alkaline phosphatase activity.