Osteoporotic Rat Models for Evaluation of Osseointegration of Bone Implants

Influence of bisphosphonate treatment on bone substitute performance in osteoporotic conditions

OBJECTIVE

Considering the elevated number of osteoporotic patients in need of bone graft procedures, we here evaluated the effect of alendronate (ALN) treatment on the regeneration of bone defects in osteoporotic rats. Bone formation was histologically and histomorphometrically assessed in rat femoral condyle bone defects filled with bone graft (Bio-Oss®) or left empty.

METHODS

Male Wistar rats were induced osteoporotic through orchidectomy (ORX) and SHAM-operated. The animals were divided into three groups: osteoporotic (ORX), osteoporotic treated with ALN (ORX + ALN) and healthy (SHAM). Six weeks after ORX or SHAM surgeries, bone defects were created bilaterally in femoral condyles; one defect was filled with Bio-Oss® and the other one left empty. Bone regeneration within the defects was analyzed by histology and histomorphometry after 4 and 12 weeks.

RESULTS

Histological samples showed new bone surrounding Bio-Oss® particles from week 4 onward in all three groups. At week 12, the data further showed that ALN treatment of osteoporotic animals enhanced bone formation to a 10-fold increase compared to non-treated osteoporotic control. Bio-Oss® filling of the defects promoted bone formation at both implantation periods compared to empty controls.

CONCLUSION

Our histological and histomorphometric results demonstrate that the enteral administration of alendronate under osteoporotic bone conditions leverages bone defect regeneration to a level comparable to that in healthy bone. Additionally, Bio-Oss® is an effective bone substitute, increasing bone formation, and acting as an osteoconductive scaffold guiding bone growth in both healthy and osteoporotic bone conditions.

SIGNIFICANCE

Based on the results of this study, enteral use of ALN mitigates adverse effects of an osteoporotic condition on bone defect regeneration.

Regenerating Critical Size Rat Segmental Bone Defects with a Self-Healing Hybrid Nanocomposite Hydrogel: Effect of Bone Condition and BMP-2 Incorporation

The aim of the current study is to assess the biological performance of self-healing hydrogels based on calcium phosphate (CaP) nanoparticles and bisphosphonate (BP) conjugated hyaluronan (HA) in a critical size segmental femoral bone defect model in rats. Additionally, these hydrogels are loaded with bone morphogenetic protein 2 (BMP-2) and their performance is compared in healthy and osteoporotic bone conditions. Treatment groups comprise internal plate fixation and placement of a PTFE tube containing hydrogel (HA_BP -CaP) or hydrogel loaded with BMP-2 in two dosages (HA_BP -CaP-lowBMP2 or HA_BP -CaP-highBMP2). Twelve weeks after bone defect surgery, bone formation is analyzed by X-ray examination, micro-CT analysis, and histomorphometry. The data show that critical size, segmental femoral bone defects cannot be healed with HA_BP -CaP gel alone. Loading of the HA_BP -CaP gel with low dose BMP-2 significantly improve bone formation and resulted in defect bridging in 100% of the defects. Alternatively, high dose BMP-2 loading of the HA_BP -CaP gel does not improve bone formation within the defect area, but leads to excessive bone formation outside the defect area. Bone defect healing is not affected by osteoporotic bone conditions.

Pro-osteogenic Effects of WNT in a Mouse Model of Bone Formation Around Femoral Implants

Wnt signaling maintains homeostasis in the bone marrow cavity: if Wnt signaling is inhibited then bone volume and density would decline. In this study, we identified a population of Wnt-responsive cells as osteoprogenitor in the intact trabecular bone region, which were responsible for bone development and turnover. If an implant was placed into the long bone, this Wnt-responsive population and their progeny contributed to osseointegration. We employed Axin2Cre^CreERT2/+;R26^mTmG/+ transgenic mouse strain in which Axin2-positive, Wnt-responsive cells, and their progeny are permanently labeled by GFP upon exposure to tamoxifen. Each mouse received femoral implants placed into a site prepared solely by drilling, and a single-dose liposomal WNT3A protein was used in the treatment group. A lineage tracing strategy design allowed us to identify cells actively expressing Axin2 in response to Wnt signaling pathway. These tools demonstrated that Wnt-responsive cells and their progeny comprise a quiescent population residing in the trabecular region. In response to an implant placed, this population becomes mitotically active: cells migrated into the peri-implant region, up-regulated the expression of osteogenic proteins. Ultimately, those cells gave rise to osteoblasts that produced significantly more new bone in the peri-implant region. Wnt-responsive cells directly contributed to implant osseointegration. Using a liposomal WNT3A protein therapeutic, we showed that a single application at the time of implant placed was sufficient to accelerate osseointegration. The Wnt-responsive cell population in trabecular bone, activated by injury, ultimately contributes to implant osseointegration. Liposomal WNT3A protein therapeutic accelerates implant osseointegration in the long bone.

Histological and Histomorphometric Analyses of Bone Regeneration in Osteoporotic Rats Using a Xenograft Material

We evaluated the effect of osteoporotic induction after eight weeks of initial healing of bone defects grafted with a xenograft material in a rat model. Bone defects were created in the femoral condyles of 16 female Wistar rats (one defect per rat). The defects were filled with bovine bone (Inter-Oss) granules. After eight weeks of bone healing, rats were randomly ovariectomized (OVX) or sham-operated (SHAM). At 14 weeks of bone healing, all animals were euthanized. Bone specimens were harvested and processed for histological and histomorphometric analyses to assess new bone formation (N-BF%), remaining bone graft (RBG%) and trabecular bone space (Tb.Sp%) within the defect area. After 14 weeks of bone healing, histological evaluation revealed a significant alteration in trabecular bone in OVX rats compared to SHAM rats. There was lower N-BF% in OVX rats (22.5% ± 3.0%) compared to SHAM rats (37.7% ± 7.9%; p < 0.05). Additionally, the RBG% was significantly lower in OVX (23.7% ± 5.8%) compared to SHAM (34.8% ± 9.6%; p < 0.05) rats. Finally, the Tb.Sp% was higher in OVX (53.8% ± 7.7%) compared to SHAM (27.5% ± 14.3%; p < 0.05) rats. In conclusion, within the limitations of this study, inducing an osteoporotic condition in a rat model negatively influenced bone regeneration in the created bone defect and grafted with a xenograft material.

Histomorphometric Evaluation of Peri-Implant Bone Response to Intravenous Administration of Zoledronate (Zometa®) in an Osteoporotic Rat Model

We evaluated the response to peri-implant bone placed in the femoral condyle of osteoporotic rats, following intravenous zoledronate (ZOL) treatment in three settings: pre-implantation (ZOL-Pre), post-implantation (ZOL-Post), and pre- + post-implantation (ZOL-Pre+Post). Twenty-four female Wistar rats were ovariectomized (OVX). After 12 weeks, the rats received titanium implants in the right femoral condyle. ZOL (0.04 mg/kg, weekly) was administered to six rats 4 weeks pre-implantation and was stopped at implant placement. To another six rats, ZOL was given post-implantation and continued for 6 weeks. Additional six rats received ZOL treatment pre- and post-implantation. Control animals received weekly saline intravenous injections. At 6 weeks post-implantation, samples were retrieved for histological evaluation of the percentage of bone area (%BA) and of the percentage of bone-to-implant contact (%BIC). BA% for ZOL-Pre (29.6% ± 9.0%) and ZOL-Post (27.9% ± 5.6%) rats were significantly increased compared to that of the controls (17.3% ± 3.9%, p < 0.05). In contrast, ZOL-Pre+Post rats (20.4% ± 5.0%) showed similar BA% compared to Saline controls (p = 0.731). BIC% revealed a significant increase for ZOL-Post (65.8% ± 16.9%) and ZOL-Pre+Post (68.3% ± 10.0%) rats compared with that of Saline controls (43.3% ± 9.6%, p < 0.05), while ZOL-Pre rats (55.6% ± 19%) showed a BIC% comparable to that of Saline controls (p = 0.408). Our results suggest that receiving intravenous ZOL treatment before or after implant placement enhances peri-implant bone responses in terms of bone area. However, the effect of different ZOL treatment regimens on BIC% was found to be inconclusive.

Impact of Single or Combined Drug Therapy on Bone Regeneration in Healthy and Osteoporotic Rats

Complications in bone regeneration in patients with systemic impaired bone metabolism (e.g., osteoporosis) represent a rapidly increasing clinical challenge. Alendronate and simvastatin are drugs commonly used to promote bone metabolism in osteoporotic conditions. The aim of this study was to evaluate initial bone regeneration within osseous defects grafted with beta-tricalcium phosphate (β-TCP) in adjunction with systemic coadministrations of alendronate and simvastatin (i.e., daily subcutaneous injection for 3 weeks) in healthy and osteoporotic rats. Eighty Wistar female rats were ovariectomized (OVX; n = 40) or sham operated (n = 40). Six weeks later, osseous defects (a 3-mm critical-sized defect) were created in the left femoral condyles and then grafted with β-TCP. From the day following graft installation, OVX and sham animals received for 3 weeks a daily subcutaneous injection of alendronate (50 μg/kg of body weight) and simvastatin (5 mg/kg of body weight), alone or in combination. A control group was included, which received subcutaneous saline administration. At the end of the 3 weeks, rats were euthanized and specimens (femoral condyles) were retrieved for histological evaluation and histomorphometric measurements, that is, bone area (BA%) and remaining bone graft (RBG%). In osteoporotic rats, 3 weeks of daily subcutaneous injection of combined therapy (alendronate plus simvastatin) led to a significant (p < 0.05) increase in BA% and a significant decrease in RBG% compared to healthy controls in osseous defects grafted with β-TCP (BA%: 28.6 ± 12.0 vs. 18.2 ± 7.6, RBG% 61.3 ± 11.1 vs. 70.7 ± 7.3). No significant differences in BA% and RBG% were found in the OVX rats for single treatments. Furthermore, healthy controls showed similar BA% and RBG% upon single or combined therapy compared to nontreated control rats. Daily coinjections (for 3 weeks) of alendronate plus simvastatin result in a significant enhancement of bone regeneration within osseous defects grafted with β-TCP in osteoporotic rats. Despite the expected effects on osteoporotic bone, our study did not confirm the hypothesized benefit of alendronate and simvastatin on bone regeneration in osseous defects in healthy conditions. The efficacy of the combination drug therapy on bone regeneration demands further investigation to elucidate molecular and cellular aspects underlying this therapy.

Tibolone, alendronate, and simvastatin enhance implant osseointegration in a preclinical in vivo model

OBJECTIVES

The objective of the study was to evaluate and compare the effect of different drugs such as simvastatin, alendronate, and tibolone for titanium implant osseointegration enhancement.

MATERIALS AND METHODS

Eighty female albino Wistar rats were equally divided into five groups: Group I (ovariectomy), Group II (sham ovariectomy), Group III (alendronate + ovariectomy), Group IV (simvastatin + ovariectomy), and Group V (tibolone + ovariectomy). Three months after ovariectomy, we performed bilateral titanium intramedullary nailing in all groups, followed by oral administration of alendronate, simvastatin, or tibolone for 12 weeks. Examinations included micro-CT, mechanical pull-out test, histology, and bone serum markers.

RESULTS

Peri-implant micro-CT analysis showed a significantly higher overall bone tissue in tibolone compared to the ovariectomy group, while no significant difference was found between the treatment groups. Sham ovariectomy, alendronate, and tibolone groups had a higher body mass density compared to ovariectomy and simvastatin groups. All treatment groups had a greater thickness of the peri-implant compact bone layer compared to ovariectomy group, but the results were not statistically significant. Tibolone presented the highest values in pull-out test, but alendronate showed more consistently positive results compared to other groups. Osteocalcin had in the tibolone group almost three times the value in the ovariectomy group, but the results were not statistically significant.

CONCLUSION

The hypothesis that alendronate, simvastatin, and tibolone enhance the osseointegration process of intramedullary titanium implants in ovariectomized rats has been accepted, while tibolone could offer the best results.

Hybrid particles derived from alendronate and bioactive glass for treatment of osteoporotic bone defects

Novel hybrid particles are synthesized using alendronate and bioactive glass, which can stimulate regeneration of osteoporotic bone defects.

Alendronate release from calcium phosphate cement for bone regeneration in osteoporotic conditions

Osteoporosis represents a major health problem in terms of compromising bone strength and increasing the risk of bone fractures. It can be medically treated with bisphosphonates, which act systemically upon oral or venous administration. Further, bone regenerative treatments in osteoporotic conditions present a challenge. Here, we focused on the development of a synthetic bone substitute material with local diminishing effects on osteoporosis. Composites were created using calcium phosphate cement (CPC; 60 wt%) and polylactic-co-glycolic acid (PLGA; 40 wt%), which were loaded with alendronate (ALN). In vitro results showed that ALN-loaded CPC/PLGA composites presented clinically suitable properties, including setting times, appropriate compressive strength, and controlled release of ALN, the latter being dependent on composite degradation. Using a rat femoral condyle bone defect model in osteoporotic animals, ALN-loaded CPC/PLGA composites demonstrated stimulatory effects on bone formation both within and outside the defect region.

Effect of lycopene on titanium implant osseointegration in ovariectomized rats

Background

Lycopene prevents bone loss in osteopenic models. However, the role of lycopene in the success rate of dental implants under osteopenic conditions remains unknown. The aim of this study was to evaluate whether lycopene prevents delayed implant osseointegration in an ovariectomized (OVX) rat model.

Methods

Thirty female Sprague-Dawley rats were randomly divided into the following groups: OVX with vehicle (OVX group), OVX with lycopene (OVX + lycopene group) and sham-operated with vehicle (sham group). Twelve weeks after ovariectomy or sham operation, titanium implants were placed into the distal metaphysis of the bilateral femurs of each rat. These rats were subsequently gavaged with lycopene (50 mg/kg/day) or vehicle. After 12 weeks of gavage, all rats were sacrificed, and specimens were harvested. Sample osseointegration was evaluated by biomechanical testing, 3D micro-computed tomography (micro-CT) analysis and histomorphometric analysis.

Results

Compared with the OVX group, the OVX + lycopene group showed a 69.3% increase in the maximum push-out force (p < 0.01). Micro-CT data for the femurs in the OVX + lycopene group showed significantly higher bone volume, trabecular thickness and less trabecular space than did those in the OVX group. The bone area (BA) around the implant and bone contact (BC) with the implant were increased by 72.3% (p < 0.01) and 51.4% (p < 0.01) in the OVX + lycopene group, respectively, compared with those in the OVX group. There was no significant difference in the mechanical test, micro-CT scanning and histomorphometric data between the OVX + lycopene and sham groups (p > 0.05).

Conclusions

Lycopene improved implant osseointegration, fixation and bone formation under osteopenic conditions, suggesting that lycopene is a promising therapeutic agent to prevent delayed implant osseointegration and bone loss under osteopenic conditions.

Preclinical models for orthopedic research and bone tissue engineering

In this review, we broadly define and discuss the preclinical rodent models that are used for orthopedics and bone tissue engineering. These range from implantation models typically used for biocompatibility testing and high-throughput drug screening, through to fracture and critical defect models used to model bone healing and severe orthopedic injuries. As well as highlighting the key methods papers describing these techniques, we provide additional commentary based on our substantive practical experience with animal surgery and in vivo experimental design. This review also briefly touches upon the descriptive and functional outcome measures and power calculations that are necessary for an informative study. Obtaining informative and relevant research outcomes can be very dependent on the model used, and we hope this evaluation of common models will serve as a primer for new researchers looking to undertake preclinical bone studies. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:832-840, 2018.

Bone remodeling and mechanobiology around implants: Insights from small animal imaging

Anchorage of orthopedic implants depends on the interfacial bonding between the implant and the host bone as well as on the mass and microstructure of peri-implant bone, with all these factors being continuously regulated by the biological process of bone (re)modeling. In osteoporotic bone, implant integration may be jeopardized not only by lower peri-implant bone quality but also by reduced intrinsic regeneration ability. The first aim of this review is to provide a critical overview of the influence of osteoporosis on bone regeneration post-implantation. Mechanical stimulation can trigger bone formation and inhibit bone resorption; thus, judicious administration of mechanical loading can be used as an effective non-pharmacological treatment to enhance implant anchorage. Our second aim is to report recent achievements on the application of external mechanical stimulation to improve the quantity of peri-implant bone. The review focuses on peri-implant bone changes in osteoporotic conditions and following mechanical loading, prevalently using small animals and in vivo monitoring approaches. We intend to demonstrate the necessity to reveal new biological information on peri-implant bone mechanobiology to better target implant anchorage and fracture fixation in osteoporotic conditions. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:584-593, 2018.

Methods to Improve Osseointegration of Dental Implants in Low Quality (Type-IV) Bone: An Overview

Nowadays, dental implants have become more common treatment for replacing missing teeth and aim to improve chewing efficiency, physical health, and esthetics. The favorable clinical performance of dental implants has been attributed to their firm osseointegration, as introduced by Brånemark in 1965. Although the survival rate of dental implants over a 10-year observation has been reported to be higher than 90% in totally edentulous jaws, the clinical outcome of implant treatment is challenged in compromised (bone) conditions, as are frequently present in elderly people. The biomechanical characteristics of bone in aged patients do not offer proper stability to implants, being similar to type-IV bone (Lekholm &amp; Zarb classification), in which a decreased clinical fixation of implants has been clearly demonstrated. However, the search for improved osseointegration has continued forward for the new evolution of modern dental implants. This represents a continuum of developments spanning more than 20 years of research on implant related-factors including surgical techniques, implant design, and surface properties. The methods to enhance osseointegration of dental implants in low quality (type-IV) bone are described in a general manner in this review.

Inhibition of cathepsin K promotes osseointegration of titanium implants in ovariectomised rats

The bone mineral deficiency in osteoporosis poses a threat to the long-term outcomes of endosseous implants. The inhibitors of cathepsin K (CatK) significantly affect bone turnover, bone mineral density (BMD) and bone strength in the patients with osteoporosis. Therefore, we hypothesised that the application of a CatK inhibitor (CatKI) could increase the osseointegration of endosseous implants under osteoporotic conditions. Odanacatib (ODN), a highly selective CatKI, was chosen as the experimental drug. Sixteen rats were randomised into 4 groups: sham, ovariectomy (OVX) with vehicle, OVX with low-dose ODN (5 mg/kg) and OVX with high-dose ODN (30 mg/kg). Titanium implants were placed into the distal metaphysis of bilateral femurs of each OVX rat. After 8 weeks of gavaging, CatKI treatment increased the removal torque, BMD and bone-to-implant contact (BIC). Moreover, high-dose CatKI exerted a better influence than low-dose CatKI. Furthermore, CatKI treatment not only robustly suppressed CatK gene (CTSK) expression, but also moderately reduced expression of the osteoblast-related genes Runx2, Collagen-1, BSP, Osterix, OPN, SPP1 and ALP. Thus, CatKI could affect the osteoblast-related genes, although the balance of bone turnover was achieved mainly by CatK inhibition. In conclusion, CatKI prevented bone loss and aided endosseous implantation in osteoporotic conditions.

The effects of SOST on implant osseointegration in ovariectomy osteoporotic mice

OBJECTIVE

Osteoporosis is a risk factor for implant fixation failure. The inhibition of sclerostin effectively improves bone formation and bone remodeling. Therefore, this study investigated whether SOST deficiency enhances the osseointegration of implants in a mouse model of osteoporosis induced by ovariectomy (OVX).

DESIGN

Osteoporosis was induced in female C57BL/6 and SOST deficient mice by OVX. Titanium implants were placed in the bilateral distal aspects of the femurs. Implants underwent sandblasting and acid-etching after which the structure, surface roughness and chemical components were investigated using scanning electron microscopy (SEM) and energy spectrum analyses. Undecalcified slices, μ-CT, histology analyses and mechanical tests were used to evaluate the osseointegration of implants. The results were compared using one-way ANOVA between four groups.

RESULTS

Sandblasting and acid-etching increased the roughness of the implants. OVX surgery reduced bone formation around the implants in both WT and SOST^-/- mice. However, implant osseointegration was significantly improved in the SOST^-/- OVX mice compared to the WT OVX mice.

CONCLUSIONS

Inhibition of the SOST gene improved implant fixation in the OVX osteoporotic mice, which suggests a strategy for enhancing implant osseointegration in clinical patients with osteoporosis.

The performance of CPC/PLGA and Bio-Oss® for bone regeneration in healthy and osteoporotic rats

The current study aimed to evaluate the biological performance of calcium phosphate cement (CPC) with polylactic-co-glycolic acid (PLGA) micro-particles and Bio-Oss^® in ovariectomized and healthy rats. Thirty-two Wistar rats received alternating experimental CPC/PLGA and Bio-Oss^® in femoral condyle defects in both femurs 6 weeks after ovariectomy (OVX, n = 16) or sham operation (SHAM, n = 16). Six weeks after OVX or SHAM surgery, bone morphology was analyzed by in vivo computed tomography (CT) to confirm osteoporotic bone condition. Analysis of bone formation and material remnants at 4 and 12 weeks after material implantation was performed by micro-CT, descriptive histology, histomorphometry and bone dynamics by fluorochrome labeling. The in vivo CT scans showed effective induction of osteoporotic bone condition by ovariectomy. Our data showed CPC/PLGA degraded relatively faster and more steadily. However, Bio-Oss^® had significantly less material remnants and showed significantly more bone formation compared to CPC/PLGA. Overall, our data showed relatively high amounts of CPC/PLGA for each time point, hampering new bone formation within the defect area. Osteoporotic conditions proved to significantly affect degradation rates, but did not significantly influence bone formation. An osteoporotic bone condition affects degradation of CPC/PLGA, which is vital information for its potential use in osteoporotic conditions. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 131-142, 2018.

Hydroxyapatite-doped alginate beads as scaffolds for the osteoblastic differentiation of mesenchymal stem cells

This work investigates the role of an osteoblastic matrix component, hydroxyapatite (HA), in modular alginate scaffolds to support osteoblastic differentiation of human mesenchymal stem cells for the purpose of tissue engineered bone constructs. This system is first evaluated in a tubular perfusion bioreactor, which has been shown to improve osteoblastic differentiation over static culture conditions. HMSCs in alginate scaffolds that contain HA show increased osteoblastic gene expression compared to cells in pure alginate scaffolds, as well as significantly more matrix production and mineralization. The differentiated hMSCs and cell-laid matrix are ultimately evaluated in an in vivo site specific model. Implantation of these scaffolds with preformed matrix into the rat femoral condyle defects results in abundant bone growth and significant incorporation of the scaffold into the surrounding tissue. The developed mineralized matrix, induced in part by the HA component in the scaffold, could lead to increased tissue development in critically sized defects, and should be included in future implant strategies. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2325-2333, 2016.

Bone regeneration and gene expression in bone defects under healthy and osteoporotic bone conditions using two commercially available bone graft substitutes

Biosilicate(®) and Bio-Oss(®) are two commercially available bone substitutes, however, little is known regarding their efficacy in osteoporotic conditions. The purpose of this study was to evaluate the osteogenic properties of both materials, at tissue and molecular level. Thirty-six Wistar rats were submitted to ovariectomy (OVX) for inducing osteoporotic conditions and sham surgery (SHAM) as a control. Bone defects were created in both femurs, which were filled with Biosilicate(®) or Bio-Oss(®), and empty defects were used as control. For the healthy condition both Biosilicate(®) and Bio-Oss(®) did not improve bone formation after 4 weeks. Histomorphometric evaluation of osteoporotic bone defects with bone substitutes showed more bone formation, significant for Bio-Oss(®). Molecular biological evaluation was performed by gene-expression analysis (Runx-2, ALP, OC, OPG, RANKL). The relative gene expression was increased with Biosilicate(®) for all genes in OVX rats and for Runx-2, ALP, OC and RANKL in SHAM rats. In contrast, with Bio-Oss(®), the relative gene expression of OVX rats was similar for all three groups. For SHAM rats it was increased for Runx-2, ALP, OC and RANKL. Since both materials improved bone regeneration in osteoporotic conditions, our results suggest that bone defects in osteoporotic conditions can be efficiently treated with these two bone substitutes.