We cultured human osteoblasts from trabecular bone explants and confirmed their phenotype by alkaline phosphatase assay, increased cyclic adenosine monophosphate production in response to prostaglandin E2 and radiographic micro-analysis of nodules of calcification. The osteoblasts were seeded on to demineralised human bone fragments and examined at ten-day intervals over a 50-day period by scanning electron microscopy. During this time the bank bone became progressively repopulated by the cultured osteoblasts. This system may offer a means of graft enhancement in elective orthopaedic and maxifiofacial surgery by delivery of cultured autologous human osteoblasts to bone defects.

Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) has been used to map the extracellular secretory activity of normal osteoblasts. The proteins osteonectin, bone sialoprotein, and both the C-telopeptide of collagen I together with collagen I have now been positionally identified. In addition the secretory differences which exist between normal and Pagetic osteoblasts have been mapped with the Pagetic osteoblasts shown to consistently secrete an altered 30 kDa C-telopeptide of collagen type I. The use of the diphosphonate Pamidronate in the treatment of Paget's disease of bone has beneficial effects with suppression of the bone isoenzyme marker alkaline phosphatase. It has been reported that diphosphonates directly inhibit human osteoblast secretory function as well as osteoclast metabolism. The effects of Pamidronate on the secretory activity of normal and Pagetic osteoblast cultures was also investigated. The extracellular protein secretion of normal and Pagetic osteoblasts was not affected by Pamidronate treatment as assessed by 2-D PAGE. This technique allows a comprehensive multiparameter assessment of extracellular secretory activity in normal and diseased states. The findings show that the Pagetic osteoblasts cultured in vitro are functionally abnormal and they support the hypothesis that the underlying problem in Paget's disease is characterised by disorder of osteoblast and osteoclast interactions.

Normal human skin fibroblast primary cell lines secrete over 50 proteins into culture medium. These have been mapped previously using two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and this technique has now been used to investigate extracellular protein secretion by human osteoblasts in vitro. We report the mapping of a number of consistent markers specific to the osteoblast. In particular, one protein chain with posttranslational modifications was found to be unique to the osteoblast extracellular protein map. The absence of the N- and O-glycoforms of collagenase from the osteoblast profile in this study concurs with findings reported using the immunoprecipitation functional assay and Northern blot analysis. The use of 2-D PAGE in phenotypic assessment provides a more complete analysis than the standard range of single-parameter tests for osteoblasts. Mapping of extracellular and cellular proteins in addition to bone matrix protein analysis will allow a comprehensive analysis of normal osteoblast function. This technique may also be applied to the study of osteoblasts in relation to bone disease and in assessing the phenotypic shift within a normal osteoblast culture.