Relationship of Wound Healing and Angiogenesis to the Cell Kinetics of the Initial Osteogenic Response in Orthopedically Expanded Anterior Maxillary Suture in the Rat

Abstract

Following sutural expansion, wound healing and angiogenesis precede bone formation. The purpose of this study was to examine angiogenic and subsequent osteogenic responses during a 96 hour time-course following sutural expansion. Fifty rats were divided into: (1) control group that received only angiogenic induction via injection of 5 ng/gm recombinant human endothelial cell growth factor (rhECGF); (2) experimental group that received orthopedic expansion and rhECGF; (3) sham group that received expansion and NaCl injection; and (4) baseline group that received no expansion or injection. Both experimental and sham groups were subdivided further to conduct experiments of 1, 2, 3, and 4 days. All rats were injected with 3H-thymidine (1.0 μCi/gm) 1 hour before euthanasia to label DNA of S-phase cells. The premaxilla was dissected free and demineralized. Sections (4 μm thick) were stained with hematoxylin and eosin. Angiogenesis and cell migration were analyzed using a previously established cell kinetics model. The cells were divided into four categories according to nuclear volume: A cells (40-79 μm3), B cells (80-119 μm3), C cells (120-169 μm 3), and D cells (~169 μm3). ANOVA was used to test the hypothesis that enhancement of angiogenesis stimulates reestablishment of osteogenic capability. Blood vessel number, area and endothelial cell labeled index significantly increased in experimental groups, but no difference was found between control and baseline groups (i.e., rhECGF treatment alone). Labeled-pericyte index and activated pericyte's numbers in the experimental group were also higher than in the sham groups. Compared to sham groups, A+A' cell numbers were significantly higher during the first two days in the experimental groups, followed by a rapid decrease at days three and four; C+D cell number peaked at day three. These results demonstrate that supplemental rhECGF enhances angiogenesis in expanded suture but not in nonexpanded suture. Data also suggest that pericytes may serve as a bridge between angiogenesis and osteogenesis.