Junro Yamashita

Effect of zoledronate on oral wound healing in rats

Purpose: Osteonecrosis of the jaw (ONJ) is a growing concern in patients who receive bisphosphonates that target osteoclasts. As osteoclasts play multifunctional roles in the bone marrow, their suppression likely affects bone homeostasis and alters wound healing of the jaw. The objective was to delineate the impact of osteoclast suppression in the bone marrow and wound healing of the jaw. Experimental Design: Zoledronate was administered to senile rats for 14 weeks. A portion of the gingiva was removed to denude the palatal bone. Gene expression in the bone marrow was assessed and histologic sections were analyzed to determine the wound healing status. Results: Angiogenesis-related genes, CD31 and VEGF-A, were not altered by zoledronate. VEGF-C, which plays a role in lymphangiogenesis, was suppressed. There was a decrease in gene expression of Tcirg1 and MMP-13. Bone denudation caused extensive osteocyte death indicative of bone necrosis. In zoledronate-treated rats, the necrotic bone was retained in the wound while, in controls, osteoclastic resorption of the necrotic bone was prominent. Even though large necrotic bone areas existed in zoledronate-treated rats, overlaying soft tissue healed clinically. Immunohistochemical staining showed rich vascularity in the overlaying soft tissue. Conclusions: Zoledronate therapy impacts bone marrow by suppressing genes associated with lymphangiogenesis and tissue remodeling, such as VEGF-C and MMP-13. Zoledronate was associated with impaired osseous wound healing but had no effect on angiogenic markers in the bone marrow or soft tissue wound healing. Zoledronate selectively blunts healing in bone but does not affect soft tissue healing in the oral cavity. Clin Cancer Res; 17(6); 1405–14. ©2010 AACR.

Antiresorptives and Osteonecrosis of the Jaw

Osteonecrosis of the jaw (ONJ) is an uncommon condition noted to occur in patients who are receiving osteoclast-targeted antiresorptive therapy. The incidence of ONJ in patients taking oral antiresorptives for the management of osteoporosis is low (approximately 1:100,000), whereas it is higher (∼10%) in patients taking intravenous bisphosphonates for the treatment of metastatic bone diseases. The etiology and pathophysiology of ONJ is unclear. No established preventive or treatment modalities are currently available. Although ONJ is a rare condition, it is imperative for oral care providers to have updated knowledge, as a large number of patients on antiresorptives are seeking oral care. In this comprehensive review, we focus on ONJ and bisphosphonate therapy and dissect the currently available evidence to establish a clinical approach to assess risk, preventive measures, and management of ONJ.

Role of Bcl2 in osteoclastogenesis and PTH anabolic actions in bone.

Introduction: B‐cell leukemia/lymphoma 2 (Bcl2) is a proto‐oncogene best known for its ability to suppress cell death. However, the role of Bcl2 in the skeletal system is unknown. Bcl2 has been hypothesized to play an important anti‐apoptotic role in osteoblasts during anabolic actions of PTH. Although rational, this has not been validated in vivo; hence, the impact of Bcl2 in bone remains unknown.

Intra-oral PTH Administration Promotes Tooth Extraction Socket Healing

Intermittent parathyroid hormone (PTH) administration increases systemic and craniofacial bone mass. However, the effect of PTH therapy on healing of tooth extraction sites is unknown. The aims of this study were to determine the effect of PTH therapy on tooth extraction socket healing and to examine whether PTH intra-oral injection promotes healing. The mandibular first molars were extracted in rats, and subcutaneous PTH was administered intermittently for 7, 14, and 28 days. In a second study, maxillary second molars were extracted, and PTH was administered by either subcutaneous or intra-oral injection to determine the efficacy of intra-oral PTH administration. Healing was assessed by micro-computed tomography and histomorphometric analyses. PTH therapy accelerated the entire healing process and promoted both hard- and soft-tissue healing by increasing bone fill and connective tissue maturation. PTH therapy by intra-oral injection was as effective as subcutaneous injection in promoting tooth extraction socket healing. The findings suggest that PTH therapy promotes tooth extraction socket healing and that intra-oral injections can be used to administer PTH.

The Zinc Finger Mutation C417R of I-κB Kinase γ Impairs Lipopolysaccharide- and TNF-Mediated NF-κB Activation through Inhibiting Phosphorylation of the I-κB Kinase β Activation Loop

The activation of the I-κB kinase (IKK) complex by TNF or LPS stimulates phosphorylation and degradation of I-κBα, leading to the nuclear translocation of NF-κB. The IKK complex is mainly composed of two catalytic subunits, IKKα and IKKβ, and a chaperon subunit IKKγ. Although IKKγ does not have catalytic activity, it is essential for IKK activation induced by multiple stimuli. Importantly, the key residue cysteine 417 at the zinc finger domain of IKKγ has been found to be mutated to arginine (IKKγC417R) in a human genetic disorder called the anhydrotic ectodermal dysplasia with immunodeficiency. To understand the underlying mechanisms of immunodeficiency, we examined whether the IKKγC417R mutant modified IKK activation and NF-κB transcription stimulated by LPS or TNF in human monocytes. We found that overexpression of IKKγC417R severely impaired LPS- and TNF-induced I-κBα phosphorylation and degradation in a dominant-negative fashion. Also, LPS- and TNF-induced NF-κB transcription was inhibited by IKKγC417R. The reconstitution of IKKγ, but not IKKγC417R, in IKKγ-deficient cells restored NF-κB signaling, indicating the zinc finger structure of IKKγ plays a key role in IKK activation. Moreover, C417R mutation in IKKγ abolished both LPS- and TNF-induced phosphorylation of the activation loop of IKKβ. Collectively, our results indicated that the zinc finger structure of IKKγ plays a key role in LPS- and TNF-induced NF-κB activation. The anhydrotic ectodermal dysplasia with immunodeficiency patients’ immunodeficiency may be associated with NF-κB defect in response to bacterial stimulation.

Increased Numbers of Nonattached Osteoclasts After Long-Term Zoledronic Acid Therapy in Mice

Osteoclasts are key players in the maintenance of bone, which is an endocrine target and organ. Bisphosphonates, used for the management of metastatic bone diseases and osteoporosis, suppress osteoclasts. However, the impact of continuously suppressed osteoclasts is unknown. In this study, mice received zoledronic acid (ZA) for 13 months, nearly half the lifespan of mice, and the effects of continual osteoclast suppression on the bone environment and oral wound healing were determined. ZA therapy suppressed osteoclasts, resulting in significantly more bone mass compared with control. Despite continuous and intense suppression of bone loss in mice receiving ZA, serum calcium levels were maintained in the normal range. No differences were noted in serum tartrate-resistant acid phosphatase (TRAP) 5b levels between ZA-treated and control mice. Histomorphometric analyses of bones revealed that ZA therapy significantly decreased osteoclasts on the bone surface but, instead, substantially increased TRAP(+) mononuclear cells and osteoclasts that were not on the bone surface. When oral trauma was induced, such TRAP(+) mononuclear and nonattached osteoclasts increased considerably with increased inflammatory cell infiltration in the wounds. As a result, oral wound healing was hindered at the connective tissue level. Healing of the epithelium was unaffected. These findings indicate that the continual suppression of osteoclasts does not affect serum calcium levels and that long-term ZA therapy stimulates nonattached osteoclast and TRAP(+) mononuclear cell formation that are expanded rapidly in response to oral trauma. Caution should be exercised when using the serum TRAcP5b to estimate the efficacy of antiresorptive therapy.

Force level and strain patterns during bilateral mandibular osteodistraction

PURPOSE Recent reports have demonstrated that device orientation is important during mandibular distraction osteogenesis. The purpose of this study was to evaluate the force level and strain patterns on the mandible during bilateral osteodistraction with devices oriented either parallel to the body of the mandible or parallel to the sagittal axis of distraction. MATERIALS AND METHODS Five unembalmed human cadaver mandibles were placed in a specially designed apparatus for stabilization of the proximal segments during distraction. A force transducer was attached to the lateral aspect of the inferior ramus, and strain gauges were attached to the mandibular bone segments proximal and distal to the distraction device. Lateral force and bone strains were then measured at 5 and 10 mm of distraction. Osteodistraction proceeded first with the devices placed parallel to the mandibular body, then parallel to the axis of distraction. RESULTS Significantly greater lateral forces were seen when the devices were oriented parallel to the mandibular body. With this device orientation, increased tensile strains were seen at the labial symphysis and medial ramus, and increased compressive strains were found at the lingual symphysis and lateral ramus. However, when the devices were oriented parallel to the axis of distraction, the forces and strains were not detected. CONCLUSIONS The results suggest that device orientation has important biomechanical effects on lateral forces and strain patterns during mandibular osteodistraction.

Updates on osteonecrosis of the jaw

Purpose of reviewOsteonecrosis of the jaw (ONJ) is an uncommon condition noted to occur in patients with cancer who are receiving intravenous bisphosphonates. The cause of ONJ remains unknown. The leading hypotheses addressing the mechanism of ONJ are reviewed here. Recent findingsThe present clinical data suggest that ONJ may occur in approximately 5% of patients with metastatic bone disease. The ability to predict an individuals risk of developing ONJ remains elusive. It is likely that an altered bone microenvironment and/or host defense mechanisms effected by medications used to treat patients with metastatic bone disease contributes to the development of ONJ. Medications that significantly reduce osteoclastic activity are associated with ONJ. Preclinical models of ONJ are being developed but to establish such an intricate systemic condition in animals is challenging. SummaryThe ONJ field has progressed via knowledge gained by case reports, population-based studies, and emerging animal models. Still, there are myths that need to be resolved and important clues that need to be investigated. Understanding the pathophysiology of this condition will be critical to improve patient care. Communications between oncologists, dentists, basic scientists, and patients are central to effective treatment and research for this condition.

Chemotherapeutic and antiresorptive combination therapy suppressed lymphangiogenesis and induced osteonecrosis of the jaw-like lesions in mice

Osteonecrosis of the jaw (ONJ) is a serious adverse event that occurs predominantly in patients on both antiresorptive and antineoplastic therapies. However, how these combination therapies are connected to the high frequency of ONJ in this particular patient population is unclear. This studys aim was to determine a mechanism of ONJ associated with the combination therapy of antiresorptives and chemotherapeutics. Mice received zoledronic acid (ZA) in conjunction with melphalan or dexamethasone. The maxillary first molars were extracted 3 weeks after the initiation of treatment and wound healing assessed at 4 weeks post-extractions using microcomputed tomography and immunohistochemistry. Mice receiving the combination treatment of ZA and melphalan developed ONJ-like lesions, while ONJ-like lesions were not found in mice on ZA or melphalan monotherapy, or the combination treatment of ZA and dexamethasone. ONJ lesions were characterized by a lack of epithelium, exposed necrotic bone, severe inflammatory cell infiltration, and minimal bone formation. Fluorescent immunohistochemistry showed that lymphatic vessel formation was significantly suppressed in ONJ-like lesions with a concomitant decrease in F4/80(+) macrophages expressing vascular endothelial growth factor C (VEGFC). Interestingly, significantly suppressed lymphatics were also found in the draining lymph nodes of mice on the combination treatment of ZA and melphalan. Thus, suppressed lymphangiogenesis was strongly associated with the development of ONJ-like lesions in the current study. Since lymphangiogenesis is critical in the resolution of inflammation during wound healing, inflammation control may serve as a potential strategy to prevent ONJ.

Significance of the epithelial collar on the subepithelial connective tissue graft.

BACKGROUND Most clinicians adopt two versions of the subepithelial connective tissue graft (SCTG) procedure, SCTG with or without the epithelial collar on the graft combined with a coronally advanced flap (CAF). However, limited evidence is available to determine whether a retained epithelial collar on an SCTG is needed for a better outcome. The goal of this study was to compare the clinical outcomes of the two SCTG techniques (i.e., SCTG with or without an epithelial collar). METHODS Twenty patients with Miller Class I or II gingival defects >/=2.0 mm were recruited for the study. The patients were randomly assigned to receive an SCTG with a retained epithelial collar + CAF (SCTGE; n = 10) or an SCTG without an epithelial collar + CAF (SCTGN; n = 10). Clinical parameters, including recession depth, recession width (RW), width of keratinized gingiva (KW), clinical attachment level (CAL), probing depth (PD), gingival index (GI), and plaque index (PI), were assessed at baseline and 3 and 6 months after surgery. RESULTS SCTGE and SCTGN groups exhibited significant root coverage at 3 and 6 months compared to baseline (P <0.05). The SCTGE group had mean root coverage of 97.50% +/- 7.90% at 6 months compared to 89.10% +/- 25.93% in the SCTGN group, with no significant difference between the groups. At 6 months, complete root coverage was seen in nine of 10 and seven of 10 subjects from SCTGE and SCTGN groups, respectively. Mean KW at 3 months for the SCTGE group was 4.10 +/- 1.10 mm, whereas in the SCTGN group it was 2.75 +/- 0.68 mm. Mean RW was 0 mm and 1.20 +/- 1.60 mm for SCTGE and SCTGN groups, respectively. KW and RW were statistically significantly different between the two groups at 3 months; however, this significance was not seen at 6 months. Other clinical parameters (CAL, PD, thickness of the recipient gingival tissue, PI, GI, and the wound healing index) showed no significant differences between the groups at any time point. CONCLUSIONS Both SCTG techniques (with or without the epithelial collar) provided predictable and successful root coverage (>/=89%). This study suggests that a retained epithelial collar on the SCTG may not provide a significant benefit with regard to clinical parameters.