Perioperative glucocorticosteroid treatment delays early healing of a mandible wound by inhibiting osteogenic differentiation

Fracture Healing in the Setting of Endocrine Diseases, Aging, and Cellular Senescence

More than 2.1 million age-related fractures occur in the United States annually, resulting in an immense socioeconomic burden. Importantly, the age-related deterioration of bone structure is associated with impaired bone healing. Fracture healing is a dynamic process which can be divided into four stages. While the initial hematoma generates an inflammatory environment in which mesenchymal stem cells and macrophages orchestrate the framework for repair, angiogenesis and cartilage formation mark the second healing period. In the central region, endochondral ossification favors soft callus development while next to the fractured bony ends, intramembranous ossification directly forms woven bone. The third stage is characterized by removal and calcification of the endochondral cartilage. Finally, the chronic remodeling phase concludes the healing process. Impaired fracture healing due to aging is related to detrimental changes at the cellular level. Macrophages, osteocytes, and chondrocytes express markers of senescence, leading to reduced self-renewal and proliferative capacity. A prolonged phase of "inflammaging" results in an extended remodeling phase, characterized by a senescent microenvironment and deteriorating healing capacity. Although there is evidence that in the setting of injury, at least in some tissues, senescent cells may play a beneficial role in facilitating tissue repair, recent data demonstrate that clearing senescent cells enhances fracture repair. In this review, we summarize the physiological as well as pathological processes during fracture healing in endocrine disease and aging in order to establish a broad understanding of the biomechanical as well as molecular mechanisms involved in bone repair.

Dexamethasone-loaded β-cyclodextrin for osteogenic induction of mesenchymal stem/progenitor cells and bone regeneration

Dexamethasone (DEX) is a glucocorticoid commonly used as an in vitro osteogenic inducer of mesenchymal stem/progenitor cells (abbreviated MSCs). However, several studies investigating the effects of glucocorticoids on bone regeneration through systemic injections have demonstrated negative impacts of the drugs at high concentration on the healing of hard tissues. These contrasting evidences suggest that application of glucocorticoids should be limited to low dosages but at the same time a long enough treatment period is preferred, which prompted us to evaluate the effects of different local release systems of DEX on MSC differentiation and bone repair. Two types of DEX-loaded β-cyclodextrin (CD) complexes, including CD/DEX and CD/AD-DEX, were fabricated via host-guest interactions and characterized by FTIR, 1H-NMR, MS-ESI, and UV-vis. The results demonstrated that these CD-based assemblies released DEX in differentiated profiles, with CD/DEX releasing significantly faster than CD/AD-DEX. Although CD/DEX were slightly more powerful than CD/AD-DEX in inducing rat bone marrow MSCs (rBMSCs) into osteogenic lineage in vitro, CD/AD-DEX was advantageous over CD/DEX in accelerating bone regeneration over a time period of 4 weeks in a rat tibia defect model. The results suggest that DEX-loaded assemblies via host-guest interactions are flexible in modulating DEX release patterns and have great potential in bone tissue engineering.

PAI-1 is involved in delayed bone repair induced by glucocorticoids in mice

Glucocorticoid (GC) treatments induce osteoporosis and chronic GC treatments have been suggested to induce delayed bone repair; however, the mechanisms by which GC induces delayed bone repair remain unclear. We herein investigated the roles of plasminogen activator inhibitor-1 (PAI-1) in GC-induced effects on bone repair after femoral bone injury using female mice with a PAI-1 deficiency and their wild-type counterparts. Dexamethasone (Dex) increased plasma PAI-1 levels as well as PAI-1 mRNA levels in the adipose tissues and muscles of wild-type mice. PAI-1 deficiency significantly blunted Dex-induced delayed bone repair in mice. Moreover, PAI-1 deficiency significantly blunted Runx2 mRNA levels suppressed by Dex as well as Dex-induced osteoblast apoptosis at the damaged site 7 days after bone injury in mice. On the other hand, PAI-1 deficiency did not affect adipogenic gene expression enhanced by Dex at the damaged site 7 days after bone injury in mice. In conclusion, we herein showed for the first time that PAI-1 is involved in delayed bone repair after bone injury induced by GC in mice. PAI-1 may influence early stage osteoblast differentiation and apoptosis during the osteoblastic restoration phase of the bone repair process.

Cyclosporine A impairs bone repair in critical defects filled with different osteoconductive bone substitutes

The aim of this study was to assess the influence of cyclosporine administration on the repair of critical-sized calvaria defects (CSDs) in rat calvaria filled with diverse biomaterials. Sixty animals were divided into two groups: the control (CTR) group (saline solution) and the cyclosporine (CCP) group (cyclosporine, 10 mg/kg/day). These medications were administered daily by gavage, beginning 15 days before the surgical procedure and lasting until the day the animals were euthanized. A CSD (5 mm Ø) was made in the calvaria of each animal, which was allocated to one of 3 subgroups, according to the biomaterial used to fill the defect: coagulum (COA), deproteinized bovine bone (DBB), or biphasic calcium phosphate ceramics of hydroxyapatite and β-phosphate tricalcium (HA/TCP). Euthanasia of the animals was performed 15 and 60 days after the surgical procedure (n = 5 animals/period/subgroup). Bone repair (formation) assessment was performed through microtomography and histometry, while the analyses of the expression of the BMP2, Osteocalcin, and TGFβ1 proteins were performed using immunohistochemistry. The CSDs not filled with biomaterials demonstrated lower bone formation in the CCP group. At 15 days, less bone formation was observed in the CSDs filled with DBB, a smaller volume of mineralized tissue was observed in the CSDs filled with HA/TCP, and the expression levels of BMP2 and osteocalcin were lower in the CCP group compared to the CTR group. The use of cyclosporine impaired bone repair in CSD, and this effect can be partially explained by the suppression of BMP2 and osteocalcin expression.

Effects of different pre-operative doses of dexamethasone on alveolar repair in rats

Dexamethasone has been widly used in oral and maxillofacial surgery for controlling of postoperative surgical inflammation. Despite its clinical effectiveness, several studies have demonstrated the negative impact of this drug on the healing of soft and hard tissues. This study aimed to assess the effects of different pre-operative doses of dexamethasone on alveolar repair. Sixty rats were divided into four groups of 15 animals each. Single pre-operative doses of dexamethasone equivalent to human doses of 4 mg (Group 4 mg), 8 mg (Group 8 mg), and 12 mg (Group 12 mg), calculated by allometric dose extrapolation, were administered; and rats in the Control Group were injected with saline solution. The animals were anesthetized, and their left mandibular first molars (M1) were removed. After three, seven, and 40 days, 5 animals from each group were euthanized, and bone samples of M1 alveolus were collected for radipgraphic, histomorphological and histometric evaluation of the early and late phases of alveolar healing. At three days, Group 12 mg presented reduced radiographic density, percentage of collagen, and connective matrix compared with the Control Group. At 7 days, the percentage of bone was increased in the Control Group compared to Groups 8 mg and 12 mg (P < 0.05). It can be concluded that a single pre-operative dose of 12 mg of dexamethasone affected the early stages of alveolar repair in rats.

Effect of postoperative steroids on clinical outcomes and radiographic findings of horizontal alveolar ridge augmentation: A retrospective study

BACKGROUND

The purpose of the study was to investigate if the prescription of oral postoperative steroids has an effect on clinical outcomes of horizontal ridge augmentation including implant placement and characteristics of the grafted bone.

METHODS

A retrospective chart review of 73 horizontal ridge augmentation cases was completed to assess the clinical outcomes, 53 of those cases were further assessed radiographically. Information was gathered regarding surgical technique, grafting materials, postoperative healing, medications used postoperatively, bone growth, and density changes as quantified on a cone-beam computed tomography (CBCT) scan. Statistical analysis was completed to identify whether the use of postoperative oral steroids altered outcomes.

RESULTS

Steroids were used postoperatively following various horizontal ridge augmentation procedures. The use of tenting screws and resorbable membranes with a combination of osseous allograft and xenograft was used in 73 cases, 53 of which had preoperative and postoperative CBCT scans. Graft exposure occurred in five of the cases (9%), with the majority (n = 4) among those with postoperative steroids, but this was not statistically significant (P-value = 0.6510). Use of steroids was also not significantly associated with the number of courses of antibiotics (P-value > 0.05), but it was significantly associated with increased number of postoperative visits (P-value < 0.05). Among the subset for radiographic analysis (n = 53), there were significant clinical and radiographic dimensional changes in alveolar ridge width with an average horizontal bone gain of 3.6 mm. There were no statistically significant differences found in radiographic linear bone gain or clinical outcomes with the addition of steroids. A marginally statistically significant in the density of grafted bone was found with the addition of steroids (P-value > 0.05).

CONCLUSION

The prescription of postoperative steroids did not make a significant difference in clinical outcomes, success of implant placement or on radiographic assessment of grafted sites following horizontal alveolar ridge augmentation.

Molecular mechanisms of glucocorticoids on skeleton and bone regeneration after fracture

Glucocorticoid hormones (GCs) have profound effects on bone metabolism. Via their nuclear hormone receptor - the GR - they act locally within bone cells and modulate their proliferation, differentiation, and cell death. Consequently, high glucocorticoid levels - as present during steroid therapy or stress - impair bone growth and integrity, leading to retarded growth and glucocorticoid-induced osteoporosis, respectively. Because of their profound impact on the immune system and bone cell differentiation, GCs also affect bone regeneration and fracture healing. The use of conditional-mutant mouse strains in recent research provided insights into the cell-type-specific actions of the GR. However, despite recent advances in system biology approaches addressing GR genomics in general, little is still known about the molecular mechanisms of GCs and GR in bone cells. Here, we review the most recent findings on the molecular mechanisms of the GR in general and the known cell-type-specific actions of the GR in mesenchymal cells and their derivatives as well as in osteoclasts during bone homeostasis, GC excess, bone regeneration and fracture healing.

Induced global deletion of glucocorticoid receptor impairs fracture healing

Although endogenous glucocorticoids (GCs) are important regulators of bone integrity and the immune system, their role in bone repair after fracture-a process highly dependent on inflammation and bone formation-is unclear. Because most effects of GCs are mediated by the glucocorticoid receptor (GR), we used an inducible global GR knockout (GR^{gtROSACreERT2}) mouse model to eliminate endogenous GC action in all cells contributing to bone repair. The healing process was analyzed by cytokine/chemokine multiplex analysis, flow cytometry, histology, gene-expression analysis, microcomputed tomography, and biomechanical analysis. We observed increased early systemic and local inflammatory responses, as well as a significantly higher number of T cells infiltrating the fracture callus. Later in the healing process, we found impaired endochondral ossification in the absence of the GR, leading to persistent cartilage in the calli of the GR^{gtROSACreERT2} mice, decreased bending stiffness, and a significantly lower proportion of healed bones. Collectively, our data show that the absence of the GR significantly impairs fracture healing associated with a defective cartilage-to-bone transition, underscoring an important role of GCs during fracture healing.-Rapp, A. E., Hachemi, Y., Kemmler, J., Koenen, M., Tuckermann, J., Ignatius, A. Induced global deletion of glucocorticoid receptor impairs fracture healing.

Osteogenic differentiation of human mesenchymal stem cells in the absence of osteogenic supplements: A surface-roughness gradient study

The use of biomaterials to direct osteogenic differentiation of human mesenchymal stem cells (hMSCs) in the absence of osteogenic supplements is thought to be part of the next generation of orthopedic implants. We previously engineered surface-roughness gradients of average roughness (Ra) varying from the sub-micron to the micrometer range (∼0.5-4.7 μm), and mean distance between peaks (RSm) gradually varying from ∼214 μm to 33 μm. Here we have screened the ability of such surface-gradients of polycaprolactone to influence the expression of alkaline phosphatase (ALP), collagen type 1 (COL1) and mineralization by hMSCs cultured in dexamethasone (Dex)-deprived osteogenic induction medium (OIM) and in basal growth medium (BGM). Ra∼1.53 μm/RSm∼79 μm in Dex-deprived OI medium, and Ra∼0.93 μm/RSm∼135 μm in BGM consistently showed higher effectiveness at supporting the expression of the osteogenic markers ALP, COL1 and mineralization, compared to the tissue culture polystyrene (TCP) control in complete OIM. The superior effectiveness of specific surface-roughness revealed that this strategy may be used as a compelling alternative to soluble osteogenic inducers in orthopedic applications featuring the clinically relevant biodegradable polymer polycaprolactone.

STATEMENT OF SIGNIFICANCE

Biodegradable polymers, such as polycaprolactone (PCL), are promising materials in the field of tissue engineering and regenerative medicine, which aims at creating viable options to replace permanent orthopedic implants. The material, cells, and growth-stimulating factors are often referred to as the key components of engineered tissues. In this article, we studied the hypothesis of specific surface modification of PCL being capable of inducing mesenchymal stem cell differentiation in bone cells in the absence of cell-differentiating factors. The systematic investigation of the linearly varying surface-roughness gradient showed that an average PCL roughness of 0.93 μm alone can serve as a compelling alternative to soluble osteogenic inducers in orthopedic applications featuring the clinically relevant biodegradable polymer polycaprolactone.

Influence of perioperative dexamethasone on delayed union in mandibular fractures: A clinical and radiological study

Background

The aim was to clarify the occurrence of delayed union after surgical treatment of mandibular fracture and investigate whether an association exists between perioperative use of dexamethasone and delayed union.

Material and Methods

Thirty-seven patients were included in a prospective randomized study. Of these patients, 19 (51.4%) were randomized to receive a total dose of 30 mg of dexamethasone and 18 (48.6%) served as controls. Patients underwent clinical and radiological investigation immediately, one month, three months and six months postoperatively. Radiographs were evaluated by an experienced, blinded senior oral radiologist.

Results

Delayed fracture union was found in 9 patients (24.3%). It was associated significantly with angle fractures (p=0.012). Delayed union occurred more frequently in patients who received dexamethasone (36.8%) than in those who did not (11.1%) (p=0.068). The association of infection with delayed union was significant (p=0.027). Moreover, dexamethasone was significantly (p=0.019) associated with delayed fracture union with concomitant infection. Gender, age group, smoking habit, treatment delay and duration of surgery were not associated with delayed union.

Conclusions

Infection was associated with delayed union. Short-term high-dose dexamethasone predisposed to complicated fracture union, especially in patients with angle fractures. The relationship between dexamethasone and delayed bone healing without infection remains unresolved.

Key words:Mandibular, radiology, fracture union, dexamethasone.

Textural entropy as a potential feature for quantitative assessment of jaw bone healing process

INTRODUCTION

The aim of the study was to propose and evaluate textural entropy as a parameter for bone healing assessment.

MATERIAL AND METHODS

One hundred and twenty radiographs with loss of bone architecture were investigated (a bone defect was circumscribed - ROI DEF). A reference region (ROI REF) of the same surface area as the ROI DEF was placed in a field distant from the defect, where a normal, trabecular pattern of bone structure was well visualized. Data of three time points were investigated: T0 - immediately after the surgical procedure, T1 - 3 months post-op, and T2 - 12 months post-op.

RESULTS

Textural entropy as a parameter describing bone structure regeneration was selected based on Fisher coefficient (F) evaluation. F was highest in T0 (3.4) and was decreasing later in T1 (1.7) and T2 (1.0 - means final lack of difference in the structure to reference bone). Textural entropy is a measure of structure disarrangement which in a bone defect region attains minimal value due to structural homogeneity, i.e. low complexity of the texture. The calculated parameter in the investigated material revealed a gradual increase inside the bone defect (p < 0.05), i.e. increase of complexity in a time-dependent manner starting from immediate post-op (T0 = 2.51; T1 = 2.68) up to most complex 1 year post-operational (T2 = 2.73), reaching the reference level of a normal bone.

CONCLUSIONS

Textural entropy may be useful for computer assisted evaluation of bone regeneration process. The complexity of the texture corresponds to mature trabecular bone formation.

Copaiba oil effect on experimental jaw defect in Wistar rats

PURPOSE

To evaluate the effects of copaiba oil on jaw defects repair in Wistar rats treated with bioglass or adipose tissue.

METHODS

A jaw defect was randomly created in forty-two rats and filled with bioglass or adipose tissue. The two groups (Gbio and Gcell) were subdivided in three subgroups with seven animals each according to gavage administration: control (distillated water), oil (copaiba oil) and melox (meloxicam). Euthanasia was performed after forty post-operative days. The bone formation was analyzed regarding the histological aspects.

RESULTS

The osteoclasts activity was observed only in four subgroups (p=0.78). Regarding the osteoblasts presence, it was very similar between the subgroups, the difference was due to Gcell-melox (p=0.009) that presented less osteoblastic activity. The inflammatory cells were more evident in Gcell-melox subgroup, however, there was no difference in comparison with the other subgroups (p=0.52). Bone formation was observed in all subgroups, just two animals showed no bone formation even after 40 days. More than 50% of bone matrix mineralization was observed in 56% (23 animals) of the analyzed areas. The bone matrix mineralization was not different between subgroups (p=0.60).

CONCLUSIONS

The subgroups that received copaiba oil showed bone repair, although not statistically significant in comparison to subgroups treated with meloxicam or controls. Copaiba oil administered by gavage had no effect on bone repair in this experimental model.