[Proliferative responses of osteoblasts in expanding pre-maxillary suture determined using sustained-release bromodeoxyuridine].

Purpose: The purpose of this study was to examine the proliferative responses of osteoblasts in expanding pre-maxillary suture using sustained-release bromodeoxyuridine (BrdU).

Methods: Poloxamer thermosensitive BrdU gel was prepared and injected to the rats subcutaneously. Blood samples were collected and subjected to high performance liquid chromatography (HPLC) for quantitative determination of BrdU levels in serum. Blood samples collected from rats received a single intraperitoneal injection of BrdU solution were served as control. Forty male Sprague-Dawley rats, 35 days of age, were randomly allotted into the experimental and control groups. Experimental animals were subjected to pre-maxillary suture expansion by helix spring. Both groups were given either a single intraperitoneal injection of BrdU solution (10mg/100g) or a single subcutateous injection of thermosensitive gel (10mg/100g) after 24 hours. Animals in each group were sacrificed at 48h and 96h (n=5). Proliferative cells were identified by BrdU immunostaining.

Results: 6h after subcutaneous injection of BrdU thermosensitive gel, 1.21μg BrdU per mL serum was still identified. BrdU immunostaining also showed labeled proliferating cells in pre-maxillary suture. On the other hand, 3h after intraperitoneal injection of BrdU solution, little trace of BrdU (0.17μg/mL) could be detected. BrdU immunostaining did not show labeled cells in pre-maxillary suture. 48h after inter-premaxillary suture expansion, a plenty of BrdU labeled osteoblasts were present along the suture-bone interface. 96h after expansion, some of these labeled cells were embedded in the newly formed bone matrix.

Conclusions: Sustained-release BrdU thermosensitive gel could be used practically and effectively to label proliferative osteoblasts in vivo. Mechanical stretch stimulates proliferation of osteoprogenitor cells, which then differentiate into osteoblasts and secret bone matrix, leading to new bone formation in the suture.