Osteogenic growth peptide normally stimulated by blood loss and marrow ablation has local and systemic effects on fracture healing in rats

Osteogenic growth peptide, a histone H4-related, 14-amino-acid peptide, is an active mediator of local, as well as systemic, osteogenic activity in re sponse to marrow ablation, trauma, and blood loss. In this study, the effec t of exogenous osteogenic growth peptide on the healing of femoral fracture s in rats was investigated. A fracture at the midshaft of the femur was cre ated in 50 rats. Half of the rats were injected subcutaneously with 25 ng o f osteogenic growth peptide per rat per day for the first 7 days after frac ture. Radiographs were taken each week, and the diameter of the callus was measured. The femurs of four animals from each group were harvested 1, 2, 3 , and 4 weeks after fracture. Two femurs from each group were sectioned for histologic examination, and two were sectioned for measurement of density and mineral content. Marrow was aspirated from the contralateral femurs to establish adhering cell cultures, which were examined for osteogenicity. At 2 weeks, a large increase in mitogenicity and osteogenicity was seen in th e marrow-derived cultures from the rats treated with osteogenic growth pept ide; this increase was sustained through 4 weeks. Extraction of RNA from th e contralateral marrow (systemic expression) and callus (local expression) for amplification with reverse transcription-polymerase chain reaction reve aled greater systemic expression of transforming growth factors beta(1), be ta(2), and beta(3), fibroblast growth factor-2, insulin-like growth factor- 1, and aggrecan throughout the 4 weeks after fracture, whereas types IIA an d IIB collagen, link protein, and fibroblast growth factor receptor-3 had a greater local expression. The specimens treated with osteogenic growth pep tide had a stronger expression of transforming growth factor-pi, both local ly and systemically. The average diameter of the callus was greater for the treated rats at all time intervals, and peak diameters were 7.58 mm at 3 w eeks for the treated rats and 6.64 mm at 2 weeks and 6.63 mm at 3 weeks for the controls. Histological study revealed an earlier organization and fast er healing of the treated fractures, as evidenced by the larger, earlier ap pearance of cartilaginous soft callus and the more rapid organization of br idging trabecular bone. No statistical significance was obtained when these comparisons were made between the groups. These results suggest that osteo genic growth peptide can be used to promote earlier proliferation and diffe rentiation of osteogenic cells in marrow and bone-repair callus, possibly t hrough its effect on the transforming growth factor-beta family.