Locally applied Simvastatin improves fracture healing in mice

Molecular enhancement of fracture healing - Is there a role for Bone Morphogenetic Protein-2, parathyroid hormone, statins, or sclerostin-antibodies?

Enhancement of fracture healing has been a hot topic over the last two decades. This narrative review article is aimed to provide an update on current clinical use and evidence on four clinically available agents in the treatment of fracture healing: bone morphogenetic proteins-2 (BMP-2), parathyroid hormone, statins and sclerostin-antibodies. After first promising results from animal and clinical studies in the early 2000s, BMP-2 was studied mainly in open tibia shaft fractures treated with intramedullary nailing. There are conflicting results from different randomized clinical trials (RCTs) regarding fracture healing time and complications compared to BMP-2 free control treatment in open tibia fractures, as BMP-2 could not show significant differences in patients treated with reamed nails compared to BMP-2 free control treatment with reamed nailing only. Given that fact, its official use was limited in Europe to open tibia shaft fractures treated with unreamed tibial nailing by the European Medical Agency (EMA). Another more recent RCT failed to show equivalence of BMP- 2 together with allograft versus autograft for the treatment of tibia fractures with critical size defects. Recombinant human parathyroid hormone has proven anabolic effects on bone metabolism and is commonly used in treatment of severe osteoporosis. Different animal trials suggested an enhancement effect in fracture healing by PTH. In several clinical trials, PTH seems to have a stimulative effect for lower limb fractures. Statins, commonly used in treatment of dyslipidemia, could also enhance fracture healing in animal trials, especially when they were applied locally at the fracture site. For statins, there is only one RCT that failed to show significant effects for the oral administration of statins in undisplaced distal radius fractures. The role of sclerostin in fracture healing has more and more been understood. Application of sclerostin antibodies has been shown to be beneficial for fracture healing in animal trials. However, no RCTs on the effect of sclerostin antibodies on fracture healing have been performed yet. In conclusion, the "magic bullet" for molecular enhancement of fracture healing has not been identified yet, at least not with its optimal dosage and delivery method.

Dual drug-delivering polycaprolactone-collagen scaffold to induce early osteogenic differentiation and coupled angiogenesis

Bone regeneration is a multi-step, overlapping process, in which angiogenesis and osteogenesis are the key players. Several attempts have been made to promote angiogenesis-coupled osteogenesis using scaffolding technology. However, the recreation of functional vasculature during bone regeneration is an unparalleled challenge. In this study, a dual drug-delivering polycaprolactone-collagen fibrous scaffold is reported to promote early osteogenesis and angiogenesis. Simvastatin as a pro-angiogenic and dexamethasone as an osteoinductive drug were encapsulated to functionalize the electrospun fibers. The optically transparent fibrous mat represented the sustained and sequential release of drugs for 28 days. The fibrous mesh increased cell proliferation and enhanced the osteogenic differentiation up to 21 days. The alkaline phosphatase activity and mineral deposition were comparatively higher on dual drug-releasing fibers when compared to control fibers. The dual drug-releasing osteoconductive fibers demonstrated osteogenesis as early as 7 days with a 3.7 and 1.5 fold increase in the expression of osteogenic differentiation markers (RUNX2 and osteocalcin), respectively. In vitro angiogenesis using primary human umbilical vein endothelial cells (pHUVECs) showed no significant difference in cell proliferation among control fibers and dual drug-releasing fibers. However, the angioinductive nature of simvastatin released from the fibers demonstrated tube formation and 2 fold higher angiogenic score. The mRNA and protein expression study of angiogenic markers (VEGFR2 and eNOS) by polymerase chain reaction and western blotting depicted the angioinducing potential of dual drug-releasing fibers. VEGFR2 and eNOS mRNA expressions increased by 1.1 and 1.6 fold, respectively, whereas their protein expression increased by 3.2 and 1.7 fold, respectively. The overall results demonstrate the synergistic effect of osteoconductive substrate and osteoinductive dual drugs to promote early osteogenesis, and release of the pro-angiogenic drug promotes angiogenesis.

Adjuvant drug-assisted bone healing: Part III - Further strategies for local and systemic modulation

In this third in a series of reviews on adjuvant drug-assisted bone healing, further approaches aiming at influencing the healing process are discussed. Local and systemic modulation of bone metabolism is pursued with use of a number of drugs with completely different indications, which are characterized by a pleiotropic spectrum of action. These include drugs used to treat lipid disorders (HMG-CoA reductase inhibitors), hypertension (ACE inhibitors), osteoporosis (bisphosphonates), cancer (proteasome inhibitors) and others. Potential applications to enhance bone healing are discussed.

Locally Applied Simvastatin as an Adjunct to Promote Spinal Fusion in Rats

STUDY DESIGN

Basic Science.

OBJECTIVE

To determine if locally delivered simvastatin can enhance bone formation in a rat spinal fusion model.

SUMMARY OF BACKGROUND DATA

The bone-anabolic properties of statins in fracture healing are well established, however, few studies have evaluated the impact of locally delivered statins in spinal fusion.

METHODS

We formulated poly(lactic-co-glycolic acid) (PLGA) nanoparticles by adapting previously published techniques. Two types of nanoparticles were created: simvastatin nanoparticles (SimNP) and nanoparticles without simvastatin (BlankNP). Drug elution from SimNP was characterized. Osteoblastic differentiation was analyzed using MC3T3-E1 cells cultured in differentiation medium containing SimNP or BlankNP. Forty male 12 week old outbred Wistar rats underwent uninstrumented posterolateral fusion using iliac crest bone graft and BlankNP, SimNP or simvastatin drug. X-rays to assess bone formation were obtained at 4 weeks and 9 weeks post-operatively. Spines were explanted at 9 weeks for micro-CT analysis, and a blinded manual assessment of fusion (MAF).

RESULTS

SimNP achieved a release efficiency of 74.1% with ∼50% release occurring in the first day. Simvastatin and SimNP treated cells showed significantly greater expression of osteopontin (OPN) and osteocalcin (OCN). On micro-CT analysis, SimNP animals had higher bone volume and percent bone volume (bone volume/total volume) than control animals. SimNP rats had higher X-ray scores at 4 weeks (p=0.010) and 9 weeks (p<0.001) relative to BlankNP. MAF showed that SimNP had a higher fusion rate than BlankNP (42.9% vs. 0%, p=0.006).

CONCLUSION

We were able to validate that sustained release of simvastatin via a PLGA nanoparticle. SimNP was able to induce an increase in mineralization as well as an increase in markers of bone formation. X-ray analysis, micro-CT quantification, and MAF assessment of SimNP treated rats showed significantly greater bone formation and fusion mass strength relative to vehicle treated animals. Simvastatin may be a safe, cost-effective bone anabolic agent for use in spinal fusion.

LEVEL OF EVIDENCE

N/A.

Dual functional approaches for osteogenesis coupled angiogenesis in bone tissue engineering

Bone fracture healing is a multistep and overlapping process of inflammation, angiogenesis and osteogenesis. It is initiated by inflammation, causing the release of various cytokines and growth factors. It leads to the recruitment of stem cells and formation of vasculature resulting in the functional bone formation. This combined phenomenon is used by bone tissue engineers from past few years to address the problem of vasculature and osteogenic differentiation during bone regeneration. In this review, we have discussed all major studies reporting the dual functioning approach to promote osteogenesis coupled angiogenesis using various scaffolds. These scaffolds are broadly classified into four types based on the nature of their structural and functional components. The functionality of the scaffold is either due to the structural components or the loaded cargo which conducts or induces the coupled functionality. Dual delivery system for osteoinductive and angioinductive factors ensures the co-delivery of two different types of molecules to induce osteogenesis and angiogenesis. Single delivery scaffold for angioinductive and osteoinductive molecule releases single type of molecules which could induce both angiogenesis and osteogenesis. Osteoconductive scaffold consisted of bone constituents releases angioinductive factors. Osteoconductive and angioconductive scaffold composed of components which provide the native substrate features for osteogenesis and angiogenesis. This review article also discusses the studies highlighting the synergism of physico-chemical stimuli as dual functioning feature to enhance angiogenesis and osteogenesis simultaneously. In addition, this article covers one of the least discussed area of the bone regeneration i.e. 'cartilage formation as a median between angiogenesis and osteogenesis'.

STATINS AND BONE HEALTH: A MINI REVIEW

Statins are a widely prescribed class of medications that inhibit similar pathways as the anti-resorptive bisphosphonate drugs. Statins target the mevalonate pathway by blocking HMG-CoA reductase. Several recent meta-analyses concluded statins are osteoprotective in the general population. Here we present current literature exploring the mechanisms underlying the putative osteoprotective effects of statins. We also review recent clinical studies, ranging from observational cohort studies to randomized clinical trials, testing the effect of statins on bone health in various populations.

Role of Simvastatin on fracture healing and osteoporosis: a systematic review on in vivo investigations

Simvastatin is a lipid lowering drug whose beneficial role on bone metabolism was discovered in 1999. Several in vivo studies evaluated its role on osteoporosis and fracture healing, however, controversial results are seen in the literature. For this reason, Simvastatin has not been the focus of any clinical trials as yet. This systematic review clears the mechanisms of action of Simvastatin on bone metabolism and focuses on in vivo investigations that have evaluated its role on osteoporosis and fracture repair to find out (i) whether Simvastatin is effective on treatment of osteoporosis and fracture repair, and (ii) which of the many available protocols may have the ability to be translated in the clinical setting. Simvastatin induces osteoinduction by increasing osteoblast activity and differentiation and inhibiting their apoptosis. It also reduces osteoclastogenesis by decreasing both the number and activity of osteoclasts and their differentiation. Controversial results between the in vivo studies are mostly due to the differences in the route of administration, dose, dosage and carrier type. Local delivery of Simvastatin through controlled drug delivery systems with much lower doses and dosages than the systemic route seems to be the most valuable option in fracture healing. However, systemic delivery of Simvastatin with much higher doses and dosages than the clinical ones seems to be effective in managing osteoporosis. Simvastatin, in a particular range of doses and dosages, may be beneficial in managing osteoporosis and fracture injuries. This review showed that Simvastatin is effective in the treatment of osteoporosis and fracture healing.

Locally Applied Simvastatin Promotes Bone Formation in a Rat Model of Spinal Fusion

Simvastatin, an inexpensive lipid-lowering drug widely used to prevent cardiovascular disorders, is known to increase osteoblastic activity, inhibit osteoclastic activity, and stimulate osteoblastic production of bone morphogenetic protein 2. Furthermore, local simvastatin application increased bone formation in animal models of fracture or bone defects. We investigated the effect of locally applied simvastatin in a rat model of spinal fusion. We performed posterolateral lumbar fusion surgery with iliac crest autograft in 36 rats divided into group I (n = 17; implanted with a gelatin scaffold) and group II (n = 19; implanted with a gelatin scaffold infused with 0.5 mg simvastatin). The rats were euthanized at 6 or 12 weeks postoperatively, and the spines were explanted and assessed. The fusion rates in group II (16.7%: 6 weeks, 30%: 12 weeks) were considerably higher than those in groups I (0%: 6 weeks, 0%: 12 weeks). The 6- and 12-week radiographic scores were significantly higher in group II than in group I. High-resolution micro-computerized tomography revealed that the tissue and bone volumes of the callus tended to be higher in group II than in group I. Histologic analysis of the spines explanted after 12 weeks demonstrated new bone formation between the transverse processes in group II, but thicker and wider individual trabeculae with fibrotic tissue and muscle fiber between the transverse processes in group I. Locally applied simvastatin was efficacious in accelerating bone formation in our rat model of spinal fusion, supporting its potential clinical application as a promoter of bone morphogenesis in spinal fusion. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1942-1948, 2017.

Microparticle-embedded fibroin/alginate beads for prolonged local release of simvastatin hydroxyacid to mesenchymal stem cells

In the present work, we propose silk fibroin/alginate (SF/Alg) beads embedding simvastatin-loaded biodegradable microparticles as a versatile platform capable of tuning SVA release and in so doing osteogenic effects. In a first part of the study, microparticles of poly(lactic-co-glycolic) acid incorporating simvastatin either as lactone (SVL) or as hydroxyacid form (SVA) were prepared by spray-drying. While SVA-loaded microparticles released the drug in three days, long-term release of SVA could be obtained from SVL-loaded microparticles. In this latter case, SVL was promptly transformed to the osteogenic active SVA during release. When tested on mesenchymal stem cells, a time- and dose-dependent effect of SVL-loaded microparticles on cell proliferation and alkaline phosphatase (ALP) activity was found. Thereafter, SVL-loaded microparticles were embedded in SF/Alg beads to limit the initial simvastatin burst and to achieve easier implantation as well. Microparticle-embedded beads showed no cytotoxicity while ALP activity increased. If correctly exploited, the developed system may be suitable as osteogenic polymer scaffolds releasing correct amount of the drug locally for long time-frames.

Local pamidronate influences fracture healing in a rodent femur fracture model: an experimental study

Background

Bisphosphonates are a main component in the therapy of osteoporosis and other bone resorptive diseases. Previous studies have shown a positive effect of systemically applied bisphosphonates on fracture healing. Nevertheless high doses are related to side effects like osteonecrosis of the jaw, nephrotoxis and gastrointestinal symptoms. In this study we investigated the effect of locally applied pamidronate on fracture healing.

Methods

In a rodent model a simple femur fracture was set in female Wistar rats. We performed intramedullary fixation of the fracture and placed a collagen matrix around the fracture area. One group was treated with pamidronate, the other group with placebo via the matrix.

To investigate the volume and quality of the callus we used micro-CT (μCT) and histology after 14 and 28 days.

Results

Our results show a positive influence of local applied pamidronate on callus volume. After 14 days an insignificant increase of callus volume in the treated animals was seen. 28 days after trauma the increase of callus volume in the treatment group was significantly higher in comparison to the control group. Osteonecrosis was not seen.

Conclusions

Locally applied bisphosphonates increase the callus volume in fracture healing.

Simvastatin-doped pre-mixed calcium phosphate cement inhibits osteoclast differentiation and resorption

Simvastatin, a cholesterol lowering drug, has been shown to have positive effects on fracture healing and bone regeneration based on its dual effect; bone anabolic and anti-resorptive. In this study the focus has been on the anti-resorptive effect of the drug and its impact on the degradation of acidic calcium phosphate cement. The drug was added to the pre-mixed acidic cement in three different doses (0.1, 0.25 and 0.5 mg/g cement) and the release was measured. Furthermore the effect of the loaded cements on osteoclast differentiation and resorption was evaluated by TRAP activity, number of multinucleated cells, gene expression and calcium ion concentration in vitro using murine bone marrow macrophages. The simvastatin did not affect the cell proliferation while it clearly inhibited osteoclastic differentiation at all three doses as shown by TRAP staining, TRAP activity and gene expression. Consistent with these results, simvastatin also impaired resorption of cements by osteoclasts as indicated by reduced calcium ion concentrations. In conclusion, our findings suggest that simvastatin-doped pre-mixed acidic calcium phosphate cement inhibits the osteoclastic mediated resorption of the cement thus slowing down the degradation rate. In addition with simvastatin's bone anabolic effect it makes the cement-drug combination a promising bone graft material, especially useful for sites with compromised bone formation.

Local delivery of controlled-release simvastatin to improve the biocompatibility of polyethylene terephthalate artificial ligaments for reconstruction of the anterior cruciate ligament

The Ligament Advanced Reinforcement System has recently been widely used as the primary graft of choice in anterior cruciate ligament (ACL) reconstruction. But the biological graft-bone healing still remains a problem. Previous studies have shown that simvastatin (SIM) stimulates bone formation. The objective of this study was to investigate whether surface coating with collagen containing low-dose SIM microsphere could enhance the surface biocompatibility of polyethylene terephthalate (PET) artificial ligaments to accelerate graft-to-bone healing. The in vitro studies demonstrated that bone marrow stromal cells on the collagen-coated PET scaffolds (COL/PET) and simvastatin/collagen-coated PET scaffolds (SIM/COL/PET) proliferated vigorously. Compared with the PET group and the COL/PET group, SIM could induce bone marrow stromal cells' osteoblastic differentiation, high alkaline phosphatase activity, more mineralization deposition, and more expression of osteoblast-related genes, such as osteocalcin, runt-related transcription factor 2, bone morphogenetic protein-2, and vascular endothelial growth factor, in the SIM/COL/PET group. In vivo, rabbits received ACL reconstruction with different scaffolds. Histological analysis demonstrated that graft-bone healing was significantly greater with angiogenesis and osteogenesis in the SIM/COL/PET group than the other groups. In addition, biomechanical testing at the eighth week demonstrated a significant increase in the ultimate failure load and stiffness in the SIM/COL/PET group. The low dose of SIM-sustained release from SIM/COL/PET promoted the graft-bone healing via its effect on both angiogenesis and osteogenesis. This study suggested that collagen containing low-dose SIM microsphere coating on the surface of PET artificial ligaments could be potentially applied for ACL reconstruction.

Novel effects of simvastatin on uterine fibroid tumors: in vitro and patient-derived xenograft mouse model study

OBJECTIVE

Uterine leiomyomas represent a common gynecologic problem with no satisfactory long-term medical treatment. The purpose of this study is to examine the effects of simvastatin on uterine leiomyoma, both in vitro and in vivo.

STUDY DESIGN

This is a laboratory-based experimental study. For in vitro studies, we used human and rat leiomyoma cells. For in vivo studies, we used immunodeficient mice supplemented with estrogen/progesterone pellets xenografted with human leiomyoma tissue explant.

RESULTS

For in vitro studies, cells were treated with different concentrations of simvastatin for 48 hours. Simvastatin induced dose-dependent apoptosis in leiomyoma cells as measured by a fluorometric caspase-3 activity assay, and inhibited proliferation as demonstrated by an (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay (both were significant at 5 and 10 μM). In addition, simvastatin decreased Akt signaling pathway phosphorylation as examined using Western blot analysis. For in vivo studies, animals were treated for 28 days with simvastatin (20 μg/gm body weight/day) vs vehicle control. The treatment inhibited tumor growth as measured weekly using calipers and/ or ultrasound (P < .01). Finally, simvastatin decreased expression of the proliferation marker Ki67 in xenograft tumor tissue as examined by immunohistochemistry (P = .02).

CONCLUSION

Simvastatin can be a promising treatment for uterine leiomyoma. Further studies, including pharmacokinetic and drug delivery studies, are required.

Simvastatin prodrug micelles target fracture and improve healing

Simvastatin (SIM), a widely used anti-lipidemic drug, has been identified as a bone anabolic agent. Its poor water solubility and the lack of distribution to the skeleton, however, have limited its application in the treatment of bone metabolic diseases. In this study, an amphiphilic macromolecular prodrug of SIM was designed and synthesized to overcome these limitations. The polyethylene glycol (PEG)-based prodrug can spontaneously self-assemble to form micelles. The use of SIM trimer as the prodrug's hydrophobic segment allows easy encapsulation of additional free SIM. The in vitro studies showed that SIM/SIM-mPEG micelles were internalized by MC3T3 cells via lysosomal trafficking and consistently induced expression of both BMP2 and DKK1 mRNA, suggesting that the prodrug micelle retains the biological functions of SIM. After systemic administration, optical imaging suggests that the micelles would passively target to bone fracture sites associated with hematoma and inflammation. Furthermore, flow cytometry study revealed that SIM/SIM-mPEG micelles had preferred cellular uptake by inflammatory and resident cells within the fracture callus tissue. The treatment study using a mouse osteotomy model validated the micelles' therapeutic efficacy in promoting bone fracture healing as demonstrated by micro-CT and histological analyses. Collectively, these data suggest that the macromolecular prodrug-based micelle formulation of SIM may have great potential for clinical management of impaired fracture healing.

Evaluation of bone repair of critical size defects treated with simvastatin-loaded poly(lactic-co-glycolic acid) microspheres in rat calvaria

PURPOSE

Statins are hypolipemiant drugs with osteoinductive effect. We evaluated the potential of simvastatin loaded into poly(lactic-co-glycolic acid) (PLGA) microspheres to heal critical size defects in rat calvaria.

METHODS

PLGA scaffolds (50:50 ratio) were synthesized as pure membranes or as microspheres loaded with 2.5% simvastatin. Critical size defects (5-mm diameter) were created in the parietal bone of 3-month-old male Wistar rats; they were either left filled with blood clot (C group), covered with a PLGA membrane (M group) or with PLGA microspheres loaded with simvastatin (MSI group) or not (MM group), and then covered with the PLGA membrane. The defects were evaluated after 30 or 60 days by light and electron microscopy, immunohistochemistry for osteopontin (OPN), bone sialoprotein (BSP) and osteoadherin (OSAD), and immunocytochemistry for OPN.

RESULTS

Scanning electron microscopy showed that the calvarial defects treated with MSI were almost completely healed after 60 days, while groups M and C presented less bone formation, whereas the bone matrix formed into the defects of MSI group was more organized and mature. The immunolabeling for OPN and BSP on the matrix in groups C and M showed typical areas of primary bone unlike the MSI that presented weak labeling at the formed area. In the MSI group, there was an intense immunostaining for OSAD in osteoid, as well as in osteocyte cytoplasm. The immunocytochemistry showed intense labeling for OPN with homogeneous distribution in the interfibrillar spaces in all groups after 30 days and after 60 days; however, while C and M groups exhibited similar aspect, the MSI specimens showed weak labeling. The ultrastructural evaluation showed the interaction between the biomaterial and the surrounding tissue where some cells established intimate contact with microspheres.

CONCLUSIONS

The repair of critical size bone defects was accelerated and enhanced by the implantation of simvastatin-loaded PLGA microspheres.

Percutaneous lovastatin accelerates bone healing but is associated with periosseous soft tissue inflammation in a canine tibial osteotomy model

Experimental studies have shown the ability of statins to stimulate bone formation when delivered locally or in large oral doses, however most have been studied in rodents. This anabolic effect is through the selective activation of BMP-2. Our purpose was to determine the effects of local treatment with lovastatin on bone healing in mammals as a preclinical animal model. We administered lovastatin (6 mg/kg) by percutaneous injection to a canine tibial osteotomy stabilized with external fixation. We found that lovastatin improved bone healing after a single injection into the fracture site assessed by serial radiography and histology at bone union. However, lovastatin treatment resulted in adverse local soft tissue inflammation. These results suggest that percutaneous lovastatin injection may be a useful adjuvant treatment over the course of bone healing to augment fracture repair, although further investigation into the mechanism of soft tissue adverse effects is warranted.

Statins, bone metabolism and treatment of bone catabolic diseases

The discovery that statins had bone anabolic properties initiated many investigations into their use for treatment of bone catabolic diseases, such as osteoporosis. This paper reviews the molecular basis of statin's role in bone metabolism, and animal and human studies on the impact of systemic statins on osteoporosis-induced bone fracture incidence and healing, and on bone density. Limitations of systemic statins are described along with alternative dosing strategies, including local applications and bone-targeting systemic preparations. The principal findings of this review are: (1) traditional oral dosing with statins results in minimal efficacy in the treatment of osteoporosis; (2) local applications of statins show promise in the treatment of accessible bony defects, such as periodontitis; and (3) systemically administered statins which can target bone or inflammation near bone may be the safest and most effective strategy in the treatment of osseous deficiencies.

Local delivery of controlled-release simvastatin/PLGA/HAp microspheres enhances bone repair

Statins are used clinically for reduction of cholesterol synthesis to prevent cardiovascular disease. Previous in vitro and in vivo studies have shown that statins stimulate bone formation. However, orally administered statins may be degraded during first-pass metabolism in the liver. This study aimed to prevent this degradation by developing a locally administered formulation of simvastatin that is encapsulated in poly(lactic-co-glycolic acid)/hydroxyapatite (SIM/PLGA/HAp) microspheres with controlled-release properties. The effect of this formulation of simvastatin on bone repair was tested using a mouse model of gap fracture bridging with a graft of necrotic bone. The simvastatin released over 12 days from 3 mg and 5 mg of SIM/PLGA/HAp was 0.03-1.6 μg/day and 0.05-2.6 μg/day, respectively. SIM/PLGA/HAp significantly stimulated callus formation around the repaired area and increased neovascularization and cell ingrowth in the grafted necrotic bone at week 2 after surgery. At week 4, both 3 mg and 5 mg of SIM/PLGA/HAp increased neovascularization, but only 5 mg SIM/PLGA/HAp enhanced cell ingrowth into the necrotic bone. The low dose of simvastatin released from SIM/PLGA/HAp enhanced initial callus formation, neovascularization, and cell ingrowth in the grafted bone, indicating that SIM/PLGA/HAp facilitates bone regeneration. We suggest that SIM/PLGA/HAp should be developed as an osteoinductive agent to treat osteonecrosis or in combination with an osteoconductive scaffold to treat severe bone defects.

Statins induce biochemical changes in the Achilles tendon after chronic treatment

Statins have been widely prescribed as lipid-lowering drugs and are associated with tendon rupture. Therefore, this study aimed to evaluate the possible biochemical changes in the Achilles tendon of rats after chronic treatment with statins. Dosages of statins were calculated using allometric scaling with reference to the 80mg/day and 20mg/day, doses recommended for humans. The rats were divided into the following groups: treated with simvastatin (S-20 and S-80), treated with atorvastatin (A-20 and A-80), and the control group that received no treatment (C). Measurements of low-density lipoprotein (LDL) in the plasma were performed. The levels of non-collagenous proteins, glycosaminoglycans (GAGs) and hydroxyproline were quantified. Western blotting for collagen I was performed, and the presence of metalloproteinases (MMPs)-2 and -9 was investigated through zymography. The concentration of non-collagenous proteins in S-20 was less than the C group. There was a significant increase in pro-MMP-2 activity in A-80 group and in active MMP-2 in S-20 group compared to the C group. A significant increase in latent MMP-9 activity was observed in both the A-80 and S-20 groups when compared to C group. In the A-20 group, there was a lower amount of collagen I in relation to C group. In addition, a higher concentration of hydroxyproline was found in the S-20 group than the C group. The analysis of GAGs showed a significant increase in the A-20 group when compared to C group. The treatment induced remarkable alterations in the Achilles tendon and the response of the tissue seems to depend of the used statin dosage. The presence of MMP-2 and MMP-9 is evidence of the degradation and remodeling processes in the extracellular matrix of the tendons. Our results show that statins induce imbalance of extracellular matrix components and possibly induce microdamage in tendons.

Influence of statins locally applied from orthopedic implants on osseous integration

Background

Simvastatin increases the expression of bone morphogenetic protein 2 (BMP-2) in osteoblasts, therefore it is important to investigate the influence of statins on bone formation, fracture healing and implant integration. The aim of the present study was to investigate the effect of Simvastatin, locally applied from intramedullary coated and bioactive implants, on bone integration using biomechanical and histomorphometrical analyses.

Methods

Eighty rats received retrograde nailing of the femur with titanium implants: uncoated vs. polymer-only (poly(D,L-lactide)) vs. polymer plus drug coated (either Simvastatin low- or high dosed; “SIM low/ high”). Femurs were harvested after 56 days for radiographic and histomorphometric or biomechanical analysis (push-out).

Results

Radiographic analysis revealed no pathological findings for animals of the control and SIM low dose group. However, n=2/10 animals of the SIM high group showed osteolysis next to the implant without evidence of bacterial infection determined by microbiological analysis. Biomechanical results showed a significant decrease in fixation strength for SIM high coated implants vs. the control groups (uncoated and PDLLA). Histomorphometry revealed a significantly reduced total as well as direct bone/implant contact for SIM high- implants vs. controls (uncoated and PDLLA-groups). Total contact was reduced for SIM low vs. uncoated controls. Significantly reduced new bone formation was measured around SIM high coated implants vs. both control groups.

Conclusions

This animal study suggests impaired implant integration with local application of Simvastatin from intramedullary titanium implants after 8 weeks when compared to uncoated or carrier-only coated controls.

Dissolution medium responsive simvastatin release from biodegradable apatite cements and the therapeutic effect in osteoporosis rats

Bio-convertible artificial bone with slow release of anti-osteoporosis drug is useful to treat osteoporosis. Apatite cement containing 6% simvastatin (APD) had lower crystallinity than natural bone. In-vitro drug release tests in simulated body fluid (pH 7.8) and acetate buffer (pH 4.5) were performed at 37.0 C as physical models of osteoblast and osteoclast conditions (SOB and SOC). The device had lower drug release rate under SOB, but significantly higher rates under SOC. The simvastatin release rate changed depending on dissolution media, it repeated twice, and the rate under SOC was 15 times higher than under SOB. The device showed dissolution medium responsive drug release. After implantation of the APD in osteoporosis rats, the bone mineral density was evaluated by the x-ray computed tomography. The result indicated that the bone mineral density of APD implanted rat was significantly higher than that of control diseased. The result indicated that the device was therapeutically useful to bone regeneration.

Therapeutic effect of local administration of low-dose simvastatin-conjugated gelatin hydrogel for fracture healing

Several reports have shown the therapeutic effect of statins on bone formation and neovascularization. However, the effect of the systemic administration of statins is limited due to its metabolism in the liver and clearance in the digestive system. In addition, high-dose administration may cause adverse side effects. To avoid low-efficacy/frequent side effects of high-dose statin treatment, we utilized biodegradable gelatin hydrogel as a drug delivery system of statin for fracture healing. A femoral fracture was created in rats with periosteum cauterization leading to nonunion at 8 weeks postfracture. Rats received local administration of either simvastatin-conjugated gelatin hydrogel (ST-Gel group) or gelatin hydrogel alone (Gel group). Approximately 70% of animals in the ST-Gel group achieved fracture union radiographically and histologically, while only 7% of animals achieved fracture healing in the Gel group. Functional bone healing was also significantly greater with increased angiogenesis- and osteogenesis-related growth factor expressions in periosteal granulation tissue in the ST-Gel group than in the Gel group. Simvastatin locally applied with gelatin hydrogel to fracture sites at a dose similar to that used in clinical settings successfully induced fracture union in a rat unhealing bone fracture model via its effect on both angiogenesis and osteogenesis.

Serum bone formation marker correlation with improved osseointegration in osteoporotic rats treated with simvastatin

OBJECTIVE

Simvastatin has been shown to enhance osseointegration of pure titanium implants in osteoporotic rats. This study aimed to evaluate the relationship between the serum level of bone formation markers and the osseointegration of pure titanium implants in osteoporotic rats treated with simvastatin.

MATERIALS AND METHODS

Fifty-four female Sprague-Dawley rats, aged 3 months, were randomly divided into three groups: Sham-operated group (SHAM; n = 18), ovariectomized group (OVX; n = 18), and ovariectomized with simvastatin treatment group (OVX + SIM; n = 18). Fifty-six days after ovariectomy, screw-shaped titanium implants were inserted into the tibiae. Simvastatin was administered orally at 5 mg/kg each day after the placement of the implant in the OVX + SIM group. The animals were killed at either 28 or 84 days after implantation and the undecalcified tissue sections were processed for histological analysis. Total alkaline phosphatase (ALP), bone-specific alkaline phosphatase (BALP) and bone Gla protein (BGP) were measured in all animal sera collected at the time of euthanasia and correlated with the histological assessment of osseointegration.

RESULTS

The level of ALP in the OVX group was higher than the SHAM group at day 28, with no differences between the three groups at day 84. The level of BALP in the OVX + SIM group was significantly higher than both OVX and SHAM groups at days 28. Compared with day 28, the BALP level of all three groups showed a significant decrease at day 84. There were no significant differences in BGP levels between the three groups at day 28, but at day 84, the OVX + SIM group showed significantly higher levels than both the OVX and SHAM groups. There was a significant increase in BGP levels between days 28 and 84 in the OVX + SIM group. The serum bone marker levels correlated with the histological assessment showing reduced osseointegration in the OVX compared to the SHAM group which is subsequently reversed in the OVX + SIM group.

CONCLUSION

The results from this study indicate that the serum level of bone formation markers, especially BALP and BGP, could be correlated with the degree of osseointegration around titanium implants in osteoporotic rats treated with simvastatin.

Evaluation of the osteoconductivity of α-tricalcium phosphate, β-tricalcium phosphate, and hydroxyapatite combined with or without simvastatin in rat calvarial defect

The purpose of this study is to evaluate the osteoconductivity of three different bone substitute materials: α-tricalcium phosphate (α-TCP), (β-TCP), and hydroxyapatite (HA), combined with or without simvastatin, which is a cholesterol synthesis inhibitor stimulating BMP-2 expression in osteoblasts. We used 72 Wistar rats and prepared two calvarial bone defects of 5 mm diameter in each rat. Defects were filled with the particles of 500-750 μm diameter combined with or without simvastatin at 0.1 mg dose for each defect. In the control group, defects were left empty. Animals were divided into seven groups: α-TCP, β-TCP, HA, α-TCP with simvastatin, β-TCP with simvastatin, HA with simvastatin, and control. The animals were sacrificed at 6 and 8 weeks. The calvariae were dissected out and analyzed with micro CT. The specimens were evaluated histologically and histomorphometrically. In α-TCP group, the amount of newly formed bone was significantly more than both HA and control groups but not significantly yet more than β-TCP group. Degradation of α-TCP was prominent and β-TCP showed slower rate while HA showed the least degradation. Combining the materials with Simvastatin led to increasing in the amount of newly formed bone. These results confirmed that α-TCP, β-TCP, and HA are osteoconductive materials acting as space maintainer for bone formation and that combining these materials with simvastatin stimulates bone regeneration and it also affects degradability of α-TCP and β-TCP. Conclusively, α-TCP has the advantage of higher rate of degradation allowing the more bone formation and combining α-TCP with simvastatin enhances this property.

Characterization and biodistribution of human mesenchymal stem cells transduced with lentiviral-mediated BMP2

Recently, the genetic modification of mesenchymal stem cells (MSCs) has led to increased differentiation potential. For the therapeutic application of genetically modified MSCs, it is crucial to evaluate their characteristics and safety. In this study, we investigated the effects of bone morphogenetic protein 2 (BMP2) gene transfer on the characteristics and biodistribution of human MSCs. Lentiviral-mediated BMP2 transduction to MSCs enhanced osteocyte differentiation and decreased adipocyte differentiation. Although there is no significant difference in cell proliferation capacity, MSCs transduced BMP2 proliferate somewhat higher than nontransduced or GFP transduced MSCs. No significant changes were observed in surface antigen expression in genetically modified MSCs. In vivo transplantation of lentiviral-mediated BMP2 gene transferred MSCs to nude mice did not result in tumor formation. To evaluate the biodistribution of genetically modified cells, MSCs carrying BMP2 were injected into the tail vein of femur fractured mice. The introduced MSCs were detected in the spleen, testis and fractured femur 28 days post-implantation. These findings suggest that diverse safety tests for genetically modified MSCs should be considered, particularly when a lentivirus mediated gene transfer method is used.

Simvastatin induces osteogenic differentiation of murine embryonic stem cells

Statins are potent inhibitors of cholesterol synthesis. Several statins are available with different molecular and pharmacokinetic properties. Simvastatin is more lipophilic than pravastatin and has a higher affinity to phospholipid membranes than atorvastatin, allowing its passive diffusion through the cell membrane. In vitro studies on bone marrow stromal cells, osteoblast-like cells, and embryonic stem cells have shown statins to have cholesterol-independent anabolic effects on bone metabolism; alas, statins were supplemented in osteogenic medium, which does not facilitate elucidation of their potential osteoinductive properties. Embryonic stem cells (ESCs), derived from the inner cell mass of the blastocyst, are unique in that they enjoy perpetual self-proliferation, are pluripotent, and are able to differentiate toward all the cellular lineages composing the body, including the osteogenic lineage. Consequently, ESCs represent a potentially potent cell source for future clinical cellular therapies of various bone diseases, even though there are several hurdles that still need to be overcome. Herein we demonstrate, for the first time to our knowledge, that simvastatin induces murine ESC (mESC) differentiation toward the osteogenic lineage in the absence of osteoinductive supplements. Specifically, we found that a simvastatin concentration in the micromolar range and higher was toxic to the cells and that an effective concentration for osteoinduction is 0.1 nM, as shown by increased alizarin red staining as well as increased osteocalcin and osetrix gene expression. These results suggest that in the future, lipophilic simvastatin may provide a novel pharmacologic agent for bone tissue engineering applications.

Farnesyl pyrophosphate inhibits epithelialization and wound healing through the glucocorticoid receptor

Farnesyl pyrophosphate (FPP), a key intermediate in the mevalonate pathway and protein farnesylation, can act as an agonist for several nuclear hormone receptors. Here we show a novel mechanism by which FPP inhibits wound healing acting as an agonist for glucocorticoid receptor (GR). Elevation of endogenous FPP by the squalene synthetase inhibitor zaragozic acid A (ZGA) or addition of FPP to the cell culture medium results in activation and nuclear translocation of the GR, a known wound healing inhibitor. We used functional studies to evaluate the effects of FPP on wound healing. Both FPP and ZGA inhibited keratinocyte migration and epithelialization in vitro and ex vivo. These effects were independent of farnesylation and indicate that modulation of FPP levels in skin may be beneficial for wound healing. FPP inhibition of keratinocyte migration and wound healing proceeds, in part, by repression of the keratin 6 gene. Furthermore, we show that the 3-hydroxy-3-methylglutaryl-CoA-reductase inhibitor mevastatin, which blocks FPP formation, not only promotes epithelialization in acute wounds but also reverses the effect of ZGA on activation of the GR and inhibition of epithelialization. We conclude that FPP inhibits wound healing by acting as a GR agonist. Of special interest is that FPP is naturally present in cells prior to glucocorticoid synthesis and that FPP levels can be further altered by the statins. Therefore, our findings may provide a better understanding of the pleiotropic effects of statins as well as molecular mechanisms by which they may accelerate wound healing.

Simvastatin locally applied from a biodegradable coating of osteosynthetic implants improves fracture healing comparable to BMP-2 application

Many clinical and experimental investigations address the influence of statins on bone formation and fracture healing. Simvastatin was shown to increase the expression of Bone morphogenetic protein (BMP-2), which is one of the most potent growth factors targeting bone formation. In this study, the effect of simvastatin locally applied from a bioactive polymer coating of implants on fracture healing was investigated. A closed fracture of the right tibia of 5-month-old Sprague-Dawley rats was performed. Intramedullary stabilization was achieved with uncoated vs. polymer-only coated vs. polymer plus drug coated titanium Kirschner wires. Test substances (either simvastatin low- or high dosed or BMP-2) were incorporated into a biodegradable layer of poly(d,l-lactide). Tibiae were harvested after 28 or 42 days, respectively and underwent biomechanical testing (torsional stiffness and maximum load) and histomorphometric analysis. Radiographic results demonstrated progressed callus consolidation in the BMP-2- and simvastatin-treated groups compared to the uncoated group at both timepoints. The simvastatin-high-dosed group revealed an increased torsional stiffness and significantly elevated maximum load (d 28) compared to control group as well as a significant increase in both parameters at d 42. BMP-2-treated animals showed significantly elevated maximum load and stiffness at the early timepoint and elevated torsional stiffness after d 42. The histomorphometric analysis revealed a significantly decreased cartilage area for BMP-2 treated animals at d 28. Even though an increase of mineralized areas among periosteal callus was found at d 42 for simvastatin-high as well as BMP-2 treated animals, no significant difference could be detected at both timepoints compared to the uncoated group. However, simvastatin-high treated animals revealed significantly reduced cartilage areas within the periosteal callus at d 42. The present study revealed a dose-dependent effect and improved fracture healing under local application of simvastatin. Biomechanical, radiographic and histomorphometric properties showed comparable results to BMP-2- treated animals in this study.

Quantitative measures of femoral fracture repair in rats derived by micro-computed tomography

Although fracture healing is frequently studied in pre-clinical models of long bone fractures using rodents, there is a dearth of objective quantitative techniques to assess successful healing. Biomechanical testing is possibly the most quantitative and relevant to a successful clinical outcome, but it is a destructive technique providing little insight into the cellular mechanisms associated with healing. The advent of X-ray computed tomography (CT) has provided the opportunity to quantitatively and non-destructively assess bone structure and density, but it is unknown how measurements derived using this technology relate to successful healing. To examine possible relationships, we used a pre-clinical model to test for statistically significant correlations between quantitative characteristics of the callus by micro-CT (microCT) and the bending strength, stiffness, and energy-to-failure of the callus as assessed by three-point bending of excised bones. A closed, transverse fracture was generated in the mid-shaft of rat femurs by impact loading. Shortly thereafter, the rats received a one-time, local injection of either the vehicle or one of four doses of lovastatin. Following sacrifice after 4 weeks of healing, fractured femurs were extracted for microCT analysis and then three-point bending. Setting the region of interest to be 3.2 mm above and below the fracture line, we acquired standard and new microCT-derived measurements. The mineralized callus volume and the mineral density of the callus correlated positively with callus strength (rxy = -0.315, p = 0.016 and rxy = 0.444, p<0.0005, respectively) and stiffness (rxy = -0.271, p = 0.040 and rxy = 0.325, p = 0.013, respectively), but the fraction of the callus that mineralized and the moment of inertia of the callus did not. This fraction did correlate with energy-to-failure (rxy = -0.343, p = 0.0085). Of the microCT-derived measurements, quantifying defects within the outer bridging cortices of the callus produced the strongest correlation with both callus strength (rxy = 0.557, p<0.0001) and stiffness (rxy = 0.468, p = 0.0002). By both reducing structural defects and increasing mineralization, lovastatin appears to increase the callus strength.

Transdermal lovastatin enhances fracture repair in rats

Statins have been shown to stimulate BMP2 transcription and bone formation. This raises the possibility that they could be useful for enhancing rates of fracture repair. Observational studies in patients treated with oral statins for lipid-lowering have been controversial. The likely reason for their inconsistent effects is that the statin concentration reaching the periphery was too low after oral administration to produce a reproducible biologic effect. Thus, we examined the effects of lovastatin (LV) given transdermally in a well-described preclinical model of fracture repair. Effects on the healing fracture callus were assessed by biomechanical strength, radiographs, and quantitative morphology. LV was administered transdermally (TD) for 5 days after fracture in several doses (0.1-5 mg/kg/d) and compared with vehicle-treated control rats and rats treated with LV by oral gavage (PO) at 5-25 mg/kg/d for 5 days from the day of fracture. Radiological evaluation of bones treated with TD LV showed enhanced fracture repair at 2 and 6 wk. BMD in the callus area at 6 wk was also increased in the TD group compared with vehicle-treated controls (p < 0.05). The force required to break TD-treated bones (0.1 mg/kg/d for 5 days) was 42% greater than vehicle-treated controls (p < 0.02), and there was a 90% increase in stiffness (p < 0.01). PO LV at much higher doses (10 and 25 mg/kg/d) showed increased stiffness but no change in other biomechanical properties. By histological examination, a significant increase was also observed in the size of the callus, surrounding proliferating cell nuclear antigen-positive cells, and osteoblast and osteoclast number in TD-treated rats compared with controls at day 8 after fracture (n = 6). In summary, we found that TD LV in low doses accelerates fracture healing, whereas 10-fold the lipid-lowering dose was required to produce any effect when it was administered orally. These studies provide valuable information on the potential of statins and TD delivery as a new and effective therapeutic modality in fracture repair.

Fracture healing in HIV-positive populations

Highly active anti-retroviral therapy has transformed HIV into a chronic disease with a long-term asymptomatic phase. As a result, emphasis is shifting to other effects of the virus, aside from immunosuppression and mortality. We have reviewed the current evidence for an association between HIV infection and poor fracture healing.

The increased prevalence of osteoporosis and fragility fractures in HIV patients is well recognised. The suggestion that this may be purely as a result of highly active anti-retroviral therapy has been largely rejected. Apart from directly impeding cellular function in bone remodelling, HIV infection is known to cause derangement in the levels of those cytokines involved in fracture healing (particularly tumour necrosis factor-α) and appears to impair the blood supply of bone.

Many other factors complicate this issue, including a reduced body mass index, suboptimal nutrition, the effects of anti-retroviral drugs and the avoidance of operative intervention because of high rates of wound infection. However, there are sound molecular and biochemical hypotheses for a direct relationship between HIV infection and impaired fracture healing, and the rewards for further knowledge in this area are extensive in terms of optimised fracture management, reduced patient morbidity and educated resource allocation. Further investigation in this area is overdue.

Modelling neurofibromatosis type 1 tibial dysplasia and its treatment with lovastatin

BACKGROUND

Bowing and/or pseudarthrosis of the tibia is a known severe complication of neurofibromatosis type 1 (NF1). Mice with conditionally inactivated neurofibromin (Nf1) in the developing limbs and cranium (Nf1Prx1) show bowing of the tibia caused by decreased bone mineralisation and increased bone vascularisation. However, in contrast to NF1 patients, spontaneous fractures do not occur in Nf1Prx1 mice probably due to the relatively low mechanical load. We studied bone healing in a cortical bone injury model in Nf1Prx1 mice as a model for NF1-associated bone disease. Taking advantage of this experimental model we explore effects of systemically applied lovastatin, a cholesterol-lowering drug, on the Nf1 deficient bone repair.

METHODS

Cortical injury was induced bilaterally in the tuberositas tibiae in Nf1Prx1 mutant mice and littermate controls according to a method described previously. Paraffin as well as methacrylate sections were analysed from each animal. We divided 24 sex-matched mutant mice into a lovastatin-treated and an untreated group. The lovastatin-treated mice received 0.15 mg activated lovastatin by daily gavage. The bone repair process was analysed at three consecutive time points post injury, using histological methods, micro computed tomography measurements and in situ hybridisation. At each experimental time point, three lovastatin-treated mutant mice, three untreated mutant mice and three untreated control mice were analysed. The animal group humanely killed on day 14 post injury was expanded to six treated and six untreated mutant mice as well as six control mice.

RESULTS

Bone injury repair is a complex process, which requires the concerted effort of numerous cell types. It is initiated by an inflammatory response, which stimulates fibroblasts from the surrounding connective tissue to proliferate and fill in the injury site with a provisional extracellular matrix. In parallel, mesenchymal progenitor cells from the periost are recruited into the injury site to become osteoblasts. In Nf1Prx1 mice bone repair is delayed and characterised by the excessive formation and the persistence of fibro-cartilaginous tissue and impaired extracellular matrix mineralisation. Correspondingly, expression of Runx2 is downregulated. High-dose systemic lovastatin treatment restores Runx2 expression and accelerates new bone formation, thus improving cortical bone repair in Nf1Prx1 tibia. The bone anabolic effects correlate with a reduction of the mitogen activated protein kinase pathway hyper-activation in Nf1-deficient cells.

CONCLUSION

Our data suggest the potential usefulness of lovastatin, a drug approved by the US Food and Drug Administration in 1987 for the treatment of hypercholesteraemia, in the treatment of Nf1-related fracture healing abnormalities. The experimental model presented here constitutes a valuable tool for the pre-clinical stage testing of candidate drugs, targeting Nf1-associated bone dysplasia.