EFFECT OF BASIC FIBROBLAST GROWTH-FACTOR ON ANGIOGENESIS AND GROWTH OF ISOGRAFTED BONE - QUANTITATIVE IN-VITRO IN-VIVO ANALYSIS IN MICE

Basic fibroblast growth factor (bFGF), a constituent of bone and carti lage matrix, has been shown to be a potent mitogen for osteoblasts and chondrocytes and yet an inhibitor of chondrocyte terminal differentia tion in cell culture. To characterize the effect of bFGF on bone forma tion, whole neonatal murine femora were cultured in the presence or ab sence of bFGF and a neutralizing antibody against bFGF. In vitro, femo ral elongation was provided by cartilage growth only; the calcified di aphyseal zone stained by oxytetracycline did not increase. When bFGF w as added to the culture medium, longitudinal growth of the proximal an d distal cartilage was inhibited in a dose-dependent manner (p < 0.05) , and the number of hypertrophic chondrocytes in the growth plate was reduced. This phenomenon was absent in the presence of a neutralizing antibody, which when given alone significantly promoted femoral elonga tion. In contrast, in vivo after transplantation into adult mice beari ng dorsal skin fold chambers, femora rapidly calcified after revascula rization. This observation supports the notion that bone formation lar gely depends on angiogenesis-mediated events. To verify this hypothesi s, angiogenesis and bone formation were quantified using bFGF known to be a stimulator of angiogenesis. Calcification of grafted femora was accelerated by bFGF given intraperitoneally. The neutralizing antibody slightly suppressed angiogenesis and femoral elongation (not statisti cally significant), whereas intravenous injections of both substances did not reveal a significant modulatory effect. In vivo the effect of systemically administered bFGF was inhomogeneous, but there was a stro ng correlation between angiogenesis and endochondral calcification (p < 0.001). These results suggest that exogenous bFGF modulates bone for mation in vitro by inhibition of terminal differentiation of chondrocy tes in the growth plate, and angiogenesis and concomitant in vivo even ts are pivotal in the promotion of rapid bone formation.