We evaluated the osteoprogenitor response to rhBMP-2 and DBM in a transgenic mouse critical sized defect. The mice expressed Col3.6GFPtopaz (a pre-osteoblastic marker), Col2.3GFPemerald (an osteoblastic marker) and a-smooth muscle actin (a-SMACherry, a pericyte/myofibroblast marker). We assessed defect healing at various time points using radiographs, frozen, and conventional histologic analyses. GFP signal in regions of interest corresponding to the areas of new bone formation was quantified using a novel computer assisted algorithm. All defects treated with rhBMP-2 healed. In contrast, the majority of the defects in the DBM (27/30) and control (28/30) groups did not heal. Quantitation of pre-osteoblasts demonstrated a maximal response (% GFPþ cells/ TV) in the Col3.6GFPtopaz mice at day 7 (7.2% AE 6.0, p < 0.05 compared to days 14, 21, 28, and 56). The maximal response of the Col2.3GFP cells was seen at days 14 (8.04% AE 5.0) and 21 (8.31% AE 4.32), p < 0.05. In contrast, DBM and control groups showed a limited osteogenic response at all time points. In conclusion, we demonstrated that the BMP and DBM induce vastly different osteogenic responses which should influence their clinical application as bone graft substitutes. ß

Threshold changes in serum calcium and PTH, checked hours after surgery, can be used together to accurately predict whether a patient will become hypocalcemic after thyroidectomy.

The role that transduced mouse bone marrow stromal cells (mBMSCs) engineered to overexpress human bone morphogenetic protein 2 (BMP-2) play in healing critical-sized skeletal defects is largely unknown. We evaluated the interaction between host osteoprogenitor cells and donor mBMSCs transduced with either a lentiviral (LV) vector-expressing red fluorescent protein (RFP) with or without BMP-2 that were implanted into a critical-sized femoral defect. Radiographs taken at the time of killing were evaluated using a five-point scaled scoring system. Frozen histologic sections were analyzed to assess both the transduced cells' role in bone repair and the local osteoprogenitor response. There was complete radiographic bridging in 94% of group I (LV-RFPch-BMP-2-cmyc) and 100% of group III (recombinant human BMP-2) specimens. Radiographs demonstrated a lack of healing in group II (LV-RFPch). Mouse BMSCs transduced with an LV-RFPch-BMP-2 vector were able to induce host cells to differentiate down an osteoblastic lineage and heal a critical-sized defect. However, the donor cells appeared to be functioning as a delivery vehicle of BMP-2 rather than actually differentiating into osteoblasts capable of participating in bone repair as evidenced by a lack of colocalization of the transduced cells to the sites of skeletal repair where the host progenitor cells were found.