Rat Mandibular Distraction Osteogenesis: Part III. Gradual Distraction versus Acute Lengthening

Abstract

Distraction osteogenesis is a well-established method of endogenous tissue engineering. This technique has significantly augmented our armamentarium of reconstructive craniofacial procedures. Although the histologic and ultrastructural changes associated with distraction osteogenesis have been extensively described, the molecular mechanisms governing successful membranous distraction remain unknown. Using an established rat model, the molecular differences between successful (i.e., osseous union with gradual distraction) and ineffective (i.e., fibrous union with acute lengthening) membranous bone lengthening was analyzed. Herein, the first insight into the molecular mechanisms of successful membranous bone distraction is provided. In addition, these data provide the foundation for future targeted therapeutic manipulations designed to improve osseous regeneration. Vertical mandibular osteotomies were created in 52 adult male Sprague-Dawley rats, and the animals were fitted with customized distraction devices. Twenty-six animals underwent immediate acute lengthening (3 mm; a length previously shown to result in fibrous union) and 26 animals were gradually distracted (after a 3-day latency period, animals were distracted 0.25 mm twice daily for 6 days; total = 3 mm). Four mandibular regenerates were harvested from each group for RNA analysis on 5, 7, 9, 23, and 37 days postoperatively (n = 40). Two mandibular regenerates were also harvested from each group and prepared for immunohistochemistry on postoperative days 5, 7, and 37 (n = 12). In addition to the 52 experimental animals, 4 control rats underwent sham operations (skin incision only) and mandibular RNA was immediately collected. Control and experimental specimens were analyzed for collagen I, osteocalcin, tissue inhibitor of metalloproteinase-1, and vascular endothelial growth factor mRNA and protein expression. In this study, marked elevation of critical extracellular matrix molecules (osteocalcin and collagen I) during the consolidation phase of gradual distraction compared with acute lengthening is demonstrated. In addition, the expression of an inhibitor of extracellular matrix turnover, tissue inhibitor of metalloproteinase-1, remained strikingly elevated in gradually distracted animals. Finally, this study demonstrated that neither gradual distraction nor acute lengthening appreciably alters vascular endothelial growth factor expression. These results suggest that gradual distraction osteogenesis promotes successful osseous bone repair by regulating the expression of bone-specific extracellular matrix molecules. In contrast, decreased production or increased turnover of bone scaffolding proteins (i.e., collagen) or regulators of mineralization (i.e., osteocalcin) may lead to fibrous union during acute lengthening.

Expression of vascular endothelial growth factor and its receptors after mandibular distraction osteogenesis

“…This result is in agreement with those of other studies 12,31 , which reported that VEGF expression is highest during the early consolidation period of DO. RICHARD et al 22 also reported that bone formation activity increased the most 6 days after distraction, when the VEGF expression level was at its highest.…”

“…After distraction, increased neovascularization during osteogenesis has been observed by scanning electron microscopy 4 and angiography 23 . The expression of many osteogenic and angiogenic factors has been detected during DO 20,27,31 . Of these factors, VEGF is probably the most important for angiogenesis and osteogenesis.…”

Study of the Tissue Reaction of the Region of the Midpalatine Suture of Rats after Disjunction with Spring Anchored in Mini-Implants

“…The author reports that OCC in its primary structure is a protein produced by osteoblasts during the bone mineralization phase, with a high affinity for mineral ions such as Ca2 + and hydroxyapatite crystals. VIEIRA [41] also stated that osteocalcin is produced almost exclusively by osteoblasts and its measure is highly specific for bone tissue, thus, correlates well with histological analyzes of formation and mineralization, as confirmed by WARREN et al [42].…”

Bone regeneration during distraction osteogenesis

“…12 Mechanical stimulation during active distraction is believed to facilitate bone regeneration in the distraction gap. 26,43,44 As distraction starts, the soft callus between the two separated bone segments is elongated and deforms. Active distraction creates pressure, fl uid fl ow, tensile strain, and tissue dilatation (local deformation occurring equally in all directions) within and around the distraction area.…”

“…In other experimental studies, high distraction rates (about 2.0 mm/day) resulted in excessive tissue damage and favored fi brous tissue formation. 1,44,59,67 The data suggest that not only the type of loading but also the rate of distraction infl uences cell differentiation and thus the outcome of bone regeneration.…”