osteogenic-growth-peptide and Hemorrhage

Osteogenic growth peptide, a histone H4-related, 14-amino-acid peptide, is an active mediator of local, as well as systemic, osteogenic activity in response to marrow ablation, trauma, and blood loss. In this study, the effect of exogenous osteogenic growth peptide on the healing of femoral fractures in rats was investigated. A fracture at the midshaft of the femur was created in 50 rats. Half of the rats were injected subcutaneously with 25 ng of osteogenic growth peptide per rat per day for the first 7 days after fracture. 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 the marrow-derived cultures from the rats treated with osteogenic growth peptide; this increase was sustained through 4 weeks. Extraction of RNA from the contralateral marrow (systemic expression) and callus (local expression) for amplification with reverse transcription-polymerase chain reaction revealed greater systemic expression of transforming growth factors beta1, beta2, and beta3, fibroblast growth factor-2, insulin-like growth factor-1, and aggrecan throughout the 4 weeks after fracture, whereas types IIA and IIB collagen, link protein, and fibroblast growth factor receptor-3 had a greater local expression. The specimens treated with osteogenic growth peptide had a stronger expression of transforming growth factor-beta1, both locally 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 weeks 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 faster healing of the treated fractures, as evidenced by the larger, earlier appearance of cartilaginous soft callus and the more rapid organization of bridging trabecular bone. No statistical significance was obtained when these comparisons were made between the groups. These results suggest that osteogenic growth peptide can be used to promote earlier proliferation and differentiation of osteogenic ce

Topics: Animals; Bone Density; Bone Marrow; Cell Differentiation; Cell Division; Fracture Healing; Growth Substances; Hemorrhage; Histones; Intercellular Signaling Peptides and Proteins; Peptides; Rats; Rats, Sprague-Dawley; RNA, Messenger

Direct physical injury to bone marrow is associated with a systemic osteogenic response. However, blood loss, a condition that stimulates hemopoietic stem cells, also may activate osteoprogenitor cells in the bone marrow. To determine if bleeding induces a systemic osteogenic response, the mineral appositional rates and osteoblast numbers were determined in the bones of rats that were subjected to controlled cardiac bleeding and compared with those of rats subjected to ablation of their tibial bone marrow. In addition, a study of the kinetics of the osteogenic responses during the first 10 days after operative treatment was performed by quantitating the serum levels of biochemical indices known to be associated with systemic bone formation. The results showed that animals that sustained acute blood loss (1% or 3% body weight) or injury to their tibial bone marrow had statistically significant increases in mineral appositional rate, osteoblast number, and serum levels of osteogenic growth peptide. The kinetics studies showed that osteogenic growth peptide levels peaked on the tenth postoperative day and declined sharply thereafter. An enhancement of serum osteocalcin activity occurred only on the second postoperative day, was increased in all experimental groups when compared with untreated control animals, but immediately declined to baseline levels. Alkaline phosphatase activities increased in the experimental groups, peaking on Day 10 after tibial bone marrow ablation and on Day 12 in the group that underwent bleeding. These findings suggest that bleeding alone, independent of any skeletal trauma, may evoke a systemic osteogenic response. This response is similar in its timing and magnitude to that which has been shown to follow direct physical injury to bone marrow. The observation that systemic bone formation follows bone marrow activation induced by two different stimuli suggests that these responses may be mediated by common regulatory mechanisms. The ability to trigger or control these responses may form the basis for future therapeutic strategies to enhance bone formation.

Topics: Alkaline Phosphatase; Animals; Bone Remodeling; Enzyme-Linked Immunosorbent Assay; Growth Substances; Hematopoiesis; Hemorrhage; Histones; Intercellular Signaling Peptides and Proteins; Male; Osteocalcin; Osteogenesis; Peptides; Phlebotomy; Rats; Rats, Sprague-Dawley