In vivo rAAV-mediated human TGF-β overexpression reduces perifocal osteoarthritis and improves osteochondral repair in a large animal model at one year

OBJECTIVE

Osteoarthritis (OA) is a serious consequence of focal osteochondral defects. Gene transfer of human transforming growth factor beta (hTGF-β) with recombinant adeno-associated virus (rAAV) vectors offers a strategy to improve osteochondral repair. However, the long-term in vivo effects of such rAAV-mediated TGF-β overexpression including its potential benefits on OA development remain unknown.

METHOD

Focal osteochondral defects in minipig knees received rAAV-lacZ (control) or rAAV-hTGF-β in vivo. After one year, osteochondral repair and perifocal OA were visualized using validated macroscopic scoring, ultra-high-field MRI at 9.4 T, and micro-CT. A quantitative estimation of the cellular densities and a validated semi-quantitative scoring of histological and immunohistological parameters completed the analysis of microarchitectural parameters.

RESULTS

Direct rAAV-hTGF-β application induced and maintained significantly improved defect filling and safranin O staining intensity and overall cartilage repair at one year in vivo. In addition, rAAV-hTGF-β led to significantly higher chondrocyte densities within the cartilaginous repair tissue without affecting chondrocyte hypertrophy and minimized subarticular trabecular separation. Of note, rAAV-hTGF-β significantly improved the adjacent cartilage structure and chondrocyte density and reduced overall perifocal OA development after one year in vivo.

CONCLUSIONS

rAAV-hTGF-β treatment improves long-term osteochondral repair and delays the progression of perifocal OA in a translational model. These findings have considerable potential for targeted molecular approaches to treat focal osteochondral defects.

Local Application of Mineral-Coated Microparticles Loaded With VEGF and BMP-2 Induces the Healing of Murine Atrophic Non-Unions

Deficient angiogenesis and disturbed osteogenesis are key factors for the development of nonunions. Mineral-coated microparticles (MCM) represent a sophisticated carrier system for the delivery of vascular endothelial growth factor (VEGF) and bone morphogenetic protein (BMP)-2. In this study, we investigated whether a combination of VEGF- and BMP-2-loaded MCM (MCM + VB) with a ratio of 1:2 improves bone repair in non-unions. For this purpose, we applied MCM + VB or unloaded MCM in a murine non-union model and studied the process of bone healing by means of radiological, biomechanical, histomorphometric, immunohistochemical and Western blot techniques after 14 and 70 days. MCM-free non-unions served as controls. Bone defects treated with MCM + VB exhibited osseous bridging, an improved biomechanical stiffness, an increased bone volume within the callus including ongoing mineralization, increased vascularization, and a histologically larger total periosteal callus area consisting predominantly of osseous tissue when compared to defects of the other groups. Western blot analyses on day 14 revealed a higher expression of osteoprotegerin (OPG) and vice versa reduced expression of receptor activator of NF-κB ligand (RANKL) in bone defects treated with MCM + VB. On day 70, these defects exhibited an increased expression of erythropoietin (EPO), EPO-receptor and BMP-4. These findings indicate that the use of MCM for spatiotemporal controlled delivery of VEGF and BMP-2 shows great potential to improve bone healing in atrophic non-unions by promoting angiogenesis and osteogenesis as well as reducing early osteoclast activity.

Differences in growth and vascularization of ectopic menstrual and non-menstrual endometrial tissue in mouse models of endometriosis

STUDY QUESTION

Is there a difference in the growth and vascularization between murine endometriotic lesions originating from menstrual or non-menstrual endometrial fragments?

SUMMARY ANSWER

Endometriotic lesions developing from menstrual and non-menstrual tissue fragments share many similarities, but also exhibit distinct differences in growth and vascularization, particularly under exogenous estrogen stimulation.

WHAT IS KNOWN ALREADY

Mouse models are increasingly used in endometriosis research. For this purpose, menstrual or non-menstrual endometrial fragments serve for the induction of endometriotic lesions. So far, these two fragment types have never been directly compared under identical experimental conditions.

STUDY DESIGN, SIZE, DURATION

This was a prospective experimental study in a murine peritoneal and dorsal skinfold chamber model of endometriosis. Endometrial tissue fragments from menstruated (n = 15) and non-menstruated (n = 21) C57BL/6 mice were simultaneously transplanted into the peritoneal cavity or dorsal skinfold chamber of non-ovariectomized (non-ovx, n = 17), ovariectomized (ovx, n = 17) and ovariectomized, estrogen-substituted (ovx+E2, n = 17) recipient animals and analyzed throughout an observation period of 28 and 14 days, respectively.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The engraftment, growth and vascularization of the newly developing endometriotic lesions were analyzed by means of high-resolution ultrasound imaging, intravital fluorescence microscopy, histology and immunohistochemistry.

MAIN RESULTS AND THE ROLE OF CHANCE

Menstrual and non-menstrual tissue fragments developed into peritoneal endometriotic lesions without differences in growth, microvessel density and cell proliferation in non-ovx mice. Lesion formation out of both fragment types was markedly suppressed in ovx mice. In case of non-menstrual tissue fragments, this effect could be reversed by estrogen supplementation. In contrast, endometriotic lesions originating from menstrual tissue fragments exhibited a significantly smaller volume in ovx+E2 mice, which may be due to a reduced hormone sensitivity. Moreover, menstrual tissue fragments showed a delayed vascularization and a reduced blood perfusion after transplantation into dorsal skinfold chambers when compared to non-menstrual tissue fragments, indicating different vascularization modes of the two fragment types. To limit the role of chance, the experiments were conducted under standardized laboratory conditions. Statistical significance was accepted for a value of P < 0.05.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Endometriotic lesions were induced by syngeneic tissue transplantation into recipient mice without the use of pathological endometriotic tissue of human nature. Therefore, the results obtained in this study may not fully relate to human patients with endometriosis.

WIDER IMPLICATIONS OF THE FINDINGS

The present study significantly contributes to the characterization of common murine endometriosis models. These models represent important tools for studies focusing on the basic mechanisms of endometriosis and the development of novel therapeutic strategies for the treatment of this frequent gynecological disease. The presented findings indicate that the combination of different experimental models and approaches may be the most appropriate strategy to study the pathophysiology and drug sensitivity of a complex disease such as endometriosis under preclinical conditions.

STUDY FUNDING/COMPETING INTEREST(S)

There was no specific funding of this study. The authors have no conflicts of interest to declare.

Amlodipine accelerates bone healing in a stable closed femoral fracture model in mice

Calcium channel blockers (CCBs), which are widely used in the treatment of hypertension, have been shown to influence bone metabolism. However, there is little information on whether CCBs also influence the process of fracture healing. Therefore, the effect of the CCB amlodipine on bone healing was studied in a stable closed fracture model in mice using intramedullary screw fixation. Bone healing was investigated by radiology, biomechanics, histomorphometry and Western blot analysis 2 and 5 weeks after fracture healing. Animals were treated daily (post operatively) per os using a gavage with amlodipine low dose (1 mg/ kg body weight, n = 20), amlodipine high dose (3 mg/kg body weight, n = 20) or vehicle (NaCl) (control, n = 20) serving as a negative control. At 2 and 5 weeks, histomorphometric analysis revealed a significantly larger amount of bone tissue within the callus of amlodipine low-dose- and high-dose-treated animals when compared to controls. This was associated with a smaller amount of cartilaginous and fibrous tissue, indicating an acceleration of fracture healing. Biomechanics showed a slightly, but not significantly, higher bending stiffness in amlodipine low-dose- and high-dose-treated animals. Western blot analysis revealed a significantly increased expression of bone morphogenetic protein (BMP)-2 and vascular endothelial growth factor (VEGF). Moreover, the analysis showed a 5-fold higher expression of osteoprotegerin (OPG) and a 10-fold elevated expression of the receptor activator of NF-κB ligand (RANKL), indicating an increased bone turnover. These findings demonstrated that amlodipine accelerated fracture healing by stimulating bone formation, callus remodelling and osteoclast activity.

High glucose exposure promotes proliferation and in vivo network formation of adipose-tissue-derived microvascular fragments

High glucose concentrations have been shown to activate endothelial cells and promote angiogenesis. In the present study, it was investigated whether high glucose concentrations could improve the vascularisation capacity of adipose-tissue-derived microvascular fragments (ad-MVF). Ad-MVF were isolated from the epididymal fat pads of donor mice and cultivated for 24 h in University of Wisconsin (UW) solution supplemented with vehicle or 30 mM glucose. Protein expression, morphology, viability and proliferation of the cultivated ad-MVF were analysed by means of proteome profiler mouse angiogenesis array, scanning electron microscopy and immunohistochemistry. Additional cultivated ad-MVF were seeded on to collagen-glycosaminoglycan scaffolds to study their in vivo vascularisation capacity in the dorsal skinfold chamber model by intravital fluorescence microscopy, histology and immunohistochemistry. In vitro, high glucose exposure changed the protein expression pattern of ad-MVF with endoglin, interleukin (IL)-1β and monocyte chemoattractant protein (MCP)-1 as the most up-regulated pro-angiogenic factors. Moreover, high glucose exposure induced the formation of nanopores in the ad-MVF wall. In addition, ad-MVF contained significantly larger numbers of proliferating endothelial and perivascular cells while exhibiting a comparable number of apoptotic cells when compared to vehicle-treated controls. In vivo, scaffolds seeded with high-glucose-exposed ad-MVF exhibited an improved vascularisation and tissue incorporation. These findings demonstrated that the exposure of cultivated ad-MVF to high glucose concentrations is a promising approach to improve their in vivo performance as vascularisation units for tissue engineering and regenerative medicine.

Erythropoietin promotes network formation of transplanted adipose tissue-derived microvascular fragments

The seeding of tissue constructs with adipose tissue-derived microvascular fragments (ad-MVF) is an emerging pre-vascularisation strategy. Ad-MVF rapidly reassemble into new microvascular networks after in vivo implantation. Herein it was analysed whether this process was improved by erythropoietin (EPO). Ad-MVF were isolated from green fluorescent protein (GFP)+ as well as wild-type C57BL/6 mice and cultivated for 24 h in medium supplemented with EPO (20 IU/mL) or vehicle. Freshly isolated, non-cultivated ad-MVF served as controls. Protein expression, cell viability and proliferation of ad-MVF were assessed by proteome profiler array and fluorescence microscopy. GFP+ ad-MVF were seeded on collagen-glycosaminoglycan matrices, which were implanted into dorsal skinfold chambers of C57BL/6 mice, to analyse their vascularisation over 14 d by intravital fluorescence microscopy, histology and immunohistochemistry. Cultivation up-regulated the expression of pro- and anti-angiogenic factors within both vehicle- and EPO-treated ad-MVF when compared with non-cultivated controls. Moreover, EPO treatment suppressed cultivation-associated apoptosis and significantly increased the number of proliferating endothelial cells in ad-MVF when compared with vehicle-treated and non-cultivated ad-MVF. Accordingly, implanted matrices seeded with EPO-treated ad-MVF exhibited an improved vascularisation, as indicated by a significantly higher functional microvessel density. The matrices of the three groups contained a comparably large fraction of GFP+ microvessels originating from the ad-MVF, whereas the tissue surrounding the matrices seeded with EPO-treated ad-MVF exhibited a significantly increased microvessel density when compared with the other two groups. These findings indicated that EPO represents a promising cytokine to further boost the excellent vascularisation properties of ad-MVF in tissue-engineering applications.

Advances in in Vitro and in Vivo Models for Studying the Staphylococcal Factors Involved in Implant Infections

Implant infections due to staphylococci are one of the greatest threats facing patients receiving implant devices. For many years researchers have sought to understand the mechanisms involved in the adherence of the bacterium to the implanted device and the formation of the unique structure, the biofilm, which protects the indwelling bacteria from the host defence and renders them resistant to antibiotic treatment. A major goal has been to develop in vitro and in vivo models that adequately reflect the real-life situation. From the simple microtiter plate assay and scanning electron microscopy, tools for studying adherence and biofilm formation have since evolved to include specialised equipment for studying adherence, flow cell systems, real-time analysis of biofilm formation using reporter gene assays both in vitro and in vivo, and a wide variety of animal models. In this article, we discuss advances in the last few years in selected in vitro and in vivo models as well as future developments in the study of adherence and biofilm formation by the staphylococci.

Seeding density is a crucial determinant for the in vivo vascularisation capacity of adipose tissue-derived microvascular fragments

Adipose tissue-derived microvascular fragments (ad-MVF) represent effective vascularisation units for the seeding of dermal substitutes. However, particularly in case of extensive skin defects, the required amounts of donor fat tissue for the harvesting of ad-MVF may not always be available. Therefore, we herein determined the lowest ad-MVF density needed to induce a sufficient vascularisation and incorporation of seeded implants. Collagen-glycosaminoglycan matrices (Integra®; diameter: 4 mm) were seeded with 15,000 (HD), 10,000 (MD) and 5,000 (LD) ad-MVF and implanted into full-thickness skin defects within mouse dorsal skinfold chambers, to analyse their in vivo vascularisation and incorporation. Intravital fluorescence microscopy showed a comparable vascularisation of HD and MD ad-MVF-seeded Integra®, which was significantly higher when compared to LD ad-MVF-seeded Integra®. As assessed by photoacoustic imaging, this was associated with an increased oxygenation of the implants. Additional histological and immunohistochemical analyses revealed an enhanced cellular infiltration, collagen content, microvessel density and epithelialisation of HD and MD ad-MVF-seeded Integra®, indicating a better incorporation compared to LD ad-MVF-seeded implants. These findings demonstrate that 80,000 ad-MVF/cm² is the least required density to guarantee an effective vascularisation of the dermal substitute.

Potentials and limitations of Integra® flowable wound matrix seeded with adipose tissue-derived microvascular fragments

Adipose tissue-derived microvascular fragments (ad-MVF) represent promising vascularisation units for bioengineered Integra® matrix wound dressing (MWD). However, due to the sheet-like structure with small pore sizes, the seeding of this matrix with ad-MVF is mainly limited to its surface. Integra® flowable wound matrix (FWM) may be suitable to achieve a more homogeneous distribution and, thus, improved vascularisation, because this gel-like matrix allows for the direct admixture of ad-MVF during sample preparation. To test this hypothesis, we seeded MWD and FWM with an identical number of ad-MVF and assessed their distribution and inter-fragment distance within both matrices. Moreover, ad-MVF-seeded MWD and FWM were implanted into full-thickness skin defects within mouse dorsal skinfold chambers to analyse their vascularisation, epithelialisation and tissue incorporation using intravital fluorescence microscopy, histology and immunohistochemistry. Seeded FWM exhibited a more homogeneous ad-MVF distribution, when compared to MWD. This resulted in a significantly increased inter-fragment distance, preventing the reassembly of ad-MVF into new microvascular networks. Accordingly, the vascularisation of FWM was diminished after implantation, as indicated by a reduced functional microvessel density and blood perfusion. This was associated with a decreased tissue incorporation and epithelialisation of the matrix, when compared to ad-MVF-seeded MWD. Hence, the use of FWM as a carrier system may require a tremendous amount of ad-MVF to shorten their inter-fragment distance and, thus, to maintain their vascularisation capacity for tissue engineering applications.

IL-17C mediates the recruitment of tumor-associated neutrophils and lung tumor growth

Chronic obstructive pulmonary disease (COPD) is associated with an increased risk for lung cancer and an aberrant microbiota of the lung. Microbial colonization contributes to chronic neutrophilic inflammation in COPD. Nontypeable Haemophilus influenzae (NTHi) is frequently found in lungs of stable COPD patients and is the major pathogen triggering exacerbations. The epithelial cytokine interleukin-17C (IL-17C) promotes the recruitment of neutrophils into inflamed tissues. The purpose of this study was to investigate the function of IL-17C in the pulmonary tumor microenvironment. We subjected mice deficient for IL-17C (IL-17C^-/-) and mice double deficient for Toll-like receptor 2 and 4 (TLR-2/4^-/-) to a metastatic lung cancer model. Tumor proliferation and growth as well as the number of tumor-associated neutrophils was significantly decreased in IL-17C^-/- and TLR-2/4^-/- mice exposed to NTHi. The NTHi-induced pulmonary expression of IL-17C was dependent on TLR-2/4. In vitro, IL-17C increased the NTHi- and tumor necrosis factor-α-induced expression of the neutrophil chemokines keratinocyte-derived chemokine and macrophage inflammatory protein 2 in lung cancer cells but did not affect proliferation. Human lung cancer samples stained positive for IL-17C, and in non-small cell lung cancer patients with lymph node metastasis, IL-17C was identified as a negative prognostic factor. Our data indicate that epithelial IL-17C promotes neutrophilic inflammation in the tumor microenvironment and suggest that IL-17C links a pathologic microbiota, as present in COPD patients, with enhanced tumor growth.

BMP-2-coated mineral coated microparticles improve bone repair in atrophic non-unions

Atrophic non-unions are a major clinical problem. Mineral coated microparticles (MCM) are electrolyte-coated hydroxyapatite particles that have been shown in vitro to bind growth factors electrostatically and enable a tuneable sustained release. Herein, we studied whether MCM can be used in vivo to apply Bone Morphogenetic Protein-2 (BMP-2) to improve bone repair of atrophic non-unions. For this purpose, atrophic non-unions were induced in femurs of CD-1 mice (n = 48). Animals either received BMP-2-coated MCM (MCM + BMP; n = 16), uncoated MCM (MCM; n = 16) or no MCM (NONE; n = 16). Bone healing was evaluated 2 and 10 weeks postoperatively by micro-computed tomographic (µCT), biomechanical, histomorphometric and immunohistochemical analyses. µCT revealed more bone volume with more highly mineralised bone in MCM + BMP femurs. Femurs of MCM + BMP animals showed a significantly higher bending stiffness compared to other groups. Histomorphometry further demonstrated that the callus of MCM + BMP femurs was larger and contained more bone and less fibrous tissue. After 10 weeks, 7 of 8 MCM + BMP femurs presented with complete osseous bridging, whereas NONE femurs exhibited a non-union rate of 100 %. Of interest, immunohistochemistry could not detect macrophages within the callus, indicating a good biocompatibility of MCM. In conclusion, the local application of BMP-2-coated MCM improved bone healing in a challenging murine non-union model and, thus, should be of clinical interest in the treatment of non-unions.

The dorsal skinfold chamber: A versatile tool for preclinical research in tissue engineering and regenerative medicine

The dorsal skinfold chamber is a rodent model for non-invasive microcirculatory analyses of striated muscle and skin tissue throughout an observation period of 2-3 weeks. In combination with intravital fluorescence microscopy, this model allows the quantitative assessment of dynamic processes such as inflammation, angiogenesis, vascular remodelling and microcirculation. Accordingly, the dorsal skinfold chamber is increasingly used for preclinical research in tissue engineering and regenerative medicine. This includes studies on biocompatibility, vascularisation and incorporation of medical implants and artificial tissue constructs. Moreover, the chamber implantation procedure has been modified to analyse primary and secondary wound healing as well as revascularisation and blood perfusion of dermal substitutes, skin grafts and myocutaneous flaps. Hence, the dorsal skinfold chamber model does not only provide deep insights into fundamental regenerative mechanisms but also represents a versatile tool for the development of novel therapeutic strategies.

Tissue engineering and regenerative approaches to improving the healing of large bone defects

Despite the high innate regenerative capacity of bone, large osseous defects fail to heal and remain a clinical challenge. Healing such defects requires the formation of large amounts of bone in an environment often rendered hostile to osteogenesis by damage to the surrounding soft tissues and vasculature. In recent years, there have been intensive research efforts directed towards tissue engineering and regenerative approaches designed to overcome this multifaceted challenge. In this paper, we describe and critically evaluate the state-of-the-art approaches to address the various components of this intricate problem. The discussion includes (i) the properties of synthetic and natural scaffolds, their use in conjunction with cell and growth factor delivery, (ii) their vascularisation, (iii) the potential of gene therapies and (iv) the role of the mechanical environment. In particular, we present a critical analysis of where the field stands, and how it can move forward in a coordinated fashion.

Effects of macrophage-activating lipopeptide-2 (MALP-2) on the vascularisation of implanted polyurethane scaffolds seeded with microvascular fragments

The seeding of scaffolds with adipose tissue-derived microvascular fragments represents a promising strategy to establish a sufficient blood supply in tissue constructs. Herein, we analysed whether a single application of macrophage-activating lipopeptide-2 (MALP-2) at the implantation site further improves the early vascularisation of such microvessel-seeded constructs. Microvascular fragments were isolated from epididymal fat pads of C57BL/6 mice. The fragments were seeded on polyurethane scaffolds, which were implanted into mouse dorsal skinfold chambers exposed to MALP-2 or vehicle (control). The inflammatory host tissue response and the vascularisation of the scaffolds were analysed using intravital fluorescence microscopy, histology and immunohistochemistry. We found that the numbers of microvascular adherent leukocytes were significantly increased in MALP-2-treated chambers during the first 3 days after scaffold implantation when compared to controls. This temporary inflammation resulted in an improved vascularisation of the host tissue surrounding the implants, as indicated by a higher density of CD31-positive microvessels at day 14. However, the MALP-2-exposed scaffolds themselves presented with a lower functional microvessel density in their centre. In addition, in vitro analyses revealed that MALP-2 promotes apoptotic cell death of endothelial and perivascular cells in isolated microvascular fragments. Hence, despite the beneficial pro-angiogenic properties of MALP-2 at the implantation site, the herein evaluated approach may not be recommended to improve the vascularisation capacity of microvascular fragments in tissue engineering applications.

Obesity does not affect the healing of femur fractures in mice

Obesity is reported to be both protective and deleterious to bone. Lipotoxicity and inflammation might be responsible for bone loss through inhibition of osteoblasts and activation of osteoclasts. However, little is known whether obesity affects the process of fracture healing. Therefore, we studied the effect of high fat diet-induced (HFD) obesity on callus formation and bone remodelling in a closed femur fracture model in mice. Thirty-one mice were fed a diet containing 60kJ% fat (HFD) for a total of 20 weeks before fracture and during the entire postoperative observation period. Control mice (n=31) received a standard diet containing 10kJ% fat. Healing was analyzed using micro-CT, biomechanical, histomorphometrical, immunohistochemical, serum and protein biochemical analysis at 2 and 4 weeks after fracture. HFD-fed mice showed a higher body weight and increased serum concentrations of leptin and interleukin-6 compared to controls. Within the callus tissue Western blot analyses revealed a higher expression of transcription factor peroxisome proliferator-activated receptor y (PPARy) and a reduced expression of runt-related transcription factor 2 (RUNX2) and bone morphogenetic protein (BMP)-4. However, obesity did not affect the expression of BMP-2 and did not influence the receptor activator of nuclear factor κB (RANK)/RANK ligand/osteoprotegerin (OPG) pathway during fracture healing. Although the bones of HFD-fed animals showed an increased number of adipocytes within the bone marrow, HFD did not increase callus adiposity. In addition, radiological and histomorphometric analysis could also not detect significant differences in bone formation between HFD-fed animals and controls. Accordingly, HFD did not affect bending stiffness after 2 and 4 weeks of healing. These findings indicate that obesity does not affect femur fracture healing in mice.

Effect of Stabilization on the Healing Process of Femur Fractures in Aged Mice

BACKGROUND

The influence of mechanical stability on fracture healing has previously been studied in adult mice, but is poorly understood in aged animals. Therefore, we herein studied the effect of stabilization on the healing process of femur fractures in aged mice.

METHODS

Twenty-four 18-month-old CD-1 mice were stabilized after midshaft fracture of the femur with an intramedullary screw. In another 24 18-month-old mice, the femur fractures were left unstabilized. Bone healing was studied by radiological, biomechanical, histomorphometric, and protein expression analyses.

RESULTS

After 2 and 5 weeks of healing, the callus of nonstabilized fractures compared to stabilized fractures was significantly larger, containing a significantly smaller amount of osseous tissue and a higher amount of cartilaginous tissue. This was associated with a significantly lower biomechanical stiffness during the early phase of healing. However, during the late phase of fracture healing both nonstabilized and stabilized fractures showed a biomechanical stiffness of ∼40%. Of interest, Western blot analyses of callus tissue demonstrated that the expression of proteins related to angiogenesis, bone formation and remodeling, i.e. VEGF, CYR61, BMP-2, BMP-4, Col-2, Col-10, RANKL, OPG, did not differ between nonstabilized and stabilized fractures.

CONCLUSION

Nonstabilized fractures in aged mice show delayed healing and remodeling. This is not caused by an altered protein expression in the callus but rather by the excessive interfragmentary movements.

Characterization of the healing process in non-stabilized and stabilized femur fractures in mice

BACKGROUND

Although a variety of suitable fracture models for mice exist, in many studies bone healing was still analyzed without fracture stabilization. Because there is little information whether the healing of non-stabilized fractures differs from that of stabilized fractures, we herein studied the healing process of non-stabilized compared to stabilized femur fractures.

MATERIALS AND METHODS

Twenty-one CD-1 mice were stabilized after midshaft fracture of the femur with an intramedullary screw allowing micromovements and endochondral healing. In another 22 mice the femur fractures were left unstabilized. Bone healing was studied by radiological, biomechanical, histomorphometric and protein expression analyses.

RESULTS

Non-stabilized femur fractures revealed a significantly lower biomechanical stiffness compared to stabilized fractures. During the early phase of fracture healing non-stabilized fractures demonstrated a significantly lower amount of osseous tissue and a higher amount of cartilage tissue. During the late phase of fracture healing both non-stabilized and stabilized fractures showed almost 100 % osseous callus tissue. However, in stabilized fractures remodeling was almost completed with lamellar bone while non-stabilized fractures still showed large callus with great amounts of woven bone, indicating a delay in bone remodeling. Of interest, western blot analyses of callus tissue demonstrated in non-stabilized fractures a significantly reduced expression of vascular endothelial growth factor and a slightly lowered expression of bone morphogenetic protein-2 and collagen-10.

CONCLUSION

Non-stabilized femur fractures in mice show a marked delay in bone healing compared to stabilized fractures. Therefore, non-stabilized fracture models may not be used to analyze the mechanisms of normal bone healing.

Pre-cultivation of adipose tissue-derived microvascular fragments in porous scaffolds does not improve their in vivo vascularisation potential

Adipose tissue-derived microvascular fragments represent promising vascularisation units for implanted tissue constructs. However, their reassembly into functional microvascular networks takes several days, during which the cells inside the implants are exposed to hypoxia. In the present study, we analysed whether this critical phase may be overcome by pre-cultivation of fragment-seeded scaffolds prior to their implantation. Green fluorescent protein (GFP)-positive microvascular fragments were isolated from epididymal fat pads of male C57BL/6-TgN (ACTB-EGFP) 1Osb/J mice. Nano-size hydroxyapatite particles/poly (ester-urethane) scaffolds were seeded with these fragments and cultivated for 28 days. Subsequently, these scaffolds or control scaffolds, which were freshly seeded with GFP-positive microvascular fragments, were implanted into the dorsal skinfold chamber of C57BL/6 wild-type mice to study their vascularisation and incorporation by means of intravital fluorescence microscopy, histology and immunohistochemistry over 2 weeks. Pre-cultivation of microvascular fragments resulted in the loss of their native vessel morphology. Accordingly, pre-cultivated scaffolds contained a network of individual CD31/GFP-positive endothelial cells with filigrane cell protuberances. After implantation into the dorsal skinfold chamber, these scaffolds exhibited an impaired vascularisation, as indicated by a significantly reduced functional microvessel density and lower fraction of GFP-positive microvessels in their centre when compared to freshly seeded control implants. This was associated with a deteriorated incorporation into the surrounding host tissue. These findings indicate that freshly isolated, non-cultivated microvascular fragments should be preferred as vascularisation units. This would also facilitate their use in clinical practice during intra-operative one-step procedures.

Locally applied macrophage-activating lipopeptide-2 (MALP-2) promotes early vascularization of implanted porous polyethylene (Medpor®)

Porous polyethylene (Medpor®) is frequently used in craniofacial reconstructive surgery. Rapid vascularization of the biomaterial crucially contributes to its adequate incorporation without complications. Macrophage-activating lipopeptide-2 (MALP-2) is a toll-like receptor (TLR)-2/6 agonist with pro-angiogenic properties. Herein we analyzed whether local single-shot application of MALP-2 improves the angiogenic host tissue response to Medpor®. Medpor® (3 mm×3 mm×0.25 mm) was implanted into dorsal skinfold chambers of BALB/c mice topically exposed to different MALP-2 doses (0.1 and 0.5 μg) or vehicle (control). The vascularization of the implants and the inflammatory foreign body reaction was analyzed using intravital fluorescence microscopy, histology and immunohistochemistry over 14 days. MALP-2 treatment dose-dependently improved the vascularization of Medpor®, as indicated by a significantly higher functional microvessel density at the border and center of the implants when compared to controls. This was associated with a temporary increase of adherent leukocytes in host tissue venules during the first 3 days after implantation. At day 14, implants in MALP-2-treated chambers were surrounded by granulation tissue, which exhibited a significantly higher density of CD31-positive microvessels and number of F4/80-positive macrophages when compared to controls. Additional biomaterial-free chambers did not show any signs of angiogenesis when treated with MALP-2. This indicates that locally applied MALP-2 effectively stimulates the early vascularization of Medpor® without inducing any local or systemic side effects. Accordingly, this easy approach may further improve the rapid incorporation of this biomaterial at the implantation site.

Adipose tissue-derived microvascular fragments from aged donors exhibit an impaired vascularisation capacity

Adipose tissue-derived microvascular fragments are promising vascularisation units for applications in the field of tissue engineering. Elderly patients are the major future target population of such applications due to an increasing human life expectancy. Therefore, we herein investigated the effect of aging on the fragments' vascularisation capacity. Microvascular fragments were isolated from epididymal fat pads of adult (8 months) and aged (16 months) C57BL/6 donor mice. These fragments were seeded onto porous polyurethane scaffolds, which were implanted into dorsal skinfold chambers to study their vascularisation using intravital fluorescence microscopy, histology and immunohistochemistry. Scaffolds seeded with fragments from aged donors exhibited a significantly lower functional microvessel density and intravascular blood flow velocity. This was associated with an impaired vessel maturation, as indicated by vessel wall irregularities, constantly elevated diameters and a lower fraction of CD31/α-smooth muscle actin double positive microvessels in the implants' border and centre zones. Additional in vitro analyses revealed that microvascular fragments from adult and aged donors do not differ in their stem cell content as well as in their release of angiogenic growth factors, survival and proliferative activity under hypoxic conditions. However, fragments from aged donors exhibit a significantly lower number of matrix metalloproteinase -9-positive perivascular cells. Taken together, these findings demonstrate that aging is a crucial determinant for the vascularisation capacity of isolated microvascular fragments.

PTH [1-34]-induced alterations of the subchondral bone provoke early osteoarthritis

OBJECTIVE

To test the hypothesis that changes in the subchondral bone induced by parathyroid hormone (PTH [1-34]) reciprocally affect the integrity of the articular cartilage within a naïve osteochondral unit in vivo.

DESIGN

Daily subcutaneous injections of 10 μg PTH [1-34]/kg were given to adult rabbits for 6 weeks, controls received saline. Blood samples were continuously collected to monitor renal function. The subchondral bone plate and subarticular spongiosa of the femoral heads were separately assessed by micro-computed tomography. Articular cartilage was evaluated by macroscopic and histological osteoarthritis scoring, polarized light microscopy, and immunohistochemical determination of type-I, type-II, type-X collagen contents, PTH [1-34] receptor and caspase-3 expression. Absolute and relative extents of hyaline and calcified articular cartilage layers were measured histomorphometrically. The correlation between PTH-induced changes in subchondral bone and articular cartilage was determined.

RESULTS

PTH [1-34] enhanced volume, mineral density, and trabecular thickness within the subarticular spongiosa, and increased thickness of the calcified cartilage layer (all P < 0.05). Moreover, PTH [1-34] led to cartilage surface irregularities and reduced matrix staining (both P < 0.03). These early osteoarthritic changes correlated with and were ascribed to the increased thickness of the calcified cartilage layer (P = 0.026) and enhanced mineral density of the subarticular spongiosa (P = 0.001).

CONCLUSIONS

Modifications of the subarticular spongiosa by PTH [1-34] cause broadening of the calcified cartilage layer, resulting in osteoarthritic cartilage degeneration. These findings identify a mechanism by which PTH-induced alterations of the normal subchondral bone microarchitecture may provoke early osteoarthritis.

Combined blockade of angiotensin II type 1 receptor and activation of peroxisome proliferator-activated receptor-γ by telmisartan effectively inhibits vascularization and growth of murine endometriosis-like lesions

STUDY QUESTION

Is telmisartan effective in the treatment of endometriosis?

SUMMARY ANSWER

Combined blockade of angiotensin II type 1 receptor (AT1R) and activation of peroxisome proliferator-activated receptor (PPAR)-γ by telmisartan inhibits vascularization and growth of murine endometriosis-like lesions.

WHAT IS KNOWN ALREADY

AT1R and PPAR-γ are involved in the regulation of inflammation, proliferation and angiogenesis. These processes are also crucial for the pathogenesis of endometriosis and both receptors are expressed in endometrial tissue. Telmisartan is a partial agonist of PPAR-γ, which additionally blocks AT1R.

STUDY DESIGN, SIZE, DURATION

This was a randomized study in the mouse dorsal skinfold chamber and peritoneal model of endometriosis. Endometriosis-like lesions were induced in dorsal skinfold chambers of 21 female C57BL/6 mice, and in the peritoneal cavity of 15 additional animals, which were daily treated with an i.p. injection of pioglitazone (10 mg/kg, n = 12), telmisartan (10 mg/kg, n = 12) or vehicle (5% dimethyl sulfoxide (DMSO), n = 12) throughout an observation period of 14 and 28 days, respectively.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The anti-angiogenic actions of pioglitazone, a full PPAR-γ agonist, and telmisartan were firstly assessed in vitro by an aortic ring assay. Endometriosis-like lesions were induced in the dorsal skinfold chamber or peritoneal cavity and the effects of telmisartan and pioglitazone on their vascularization, immune cell content and growth were studied by intravital fluorescence microscopy, high-resolution ultrasound imaging as well as histological, immunohistochemical and immunofluorescent analyses. Additional quantitative real-time polymerase chain reaction (qRT-PCR) arrays served for gene expression profiling of the lesions. To limit the role of chance, the experiments were conducted under standardized laboratory conditions with appropriate vehicle-treated controls. Statistical significance was accepted for a value of P < 0.05.

MAIN RESULTS AND THE ROLE OF CHANCE

Telmisartan inhibited vascular sprout formation of aortic rings more effectively than pioglitazone. Accordingly, endometriosis-like lesions in dorsal skinfold chambers of telmisartan-treated animals exhibited a markedly lower functional microvessel density and blood perfusion. High-resolution ultrasound analyses of peritoneal endometriosis-like lesions revealed that the compound inhibited the stromal tissue growth, resulting in a significantly reduced final lesion volume. In contrast, the development of cysts did not differ between the groups. Moreover, telmisartan induced an up-regulation of PPAR-γ and a down-regulation of AT1R proteins in endometriosis-like lesions, which was associated with a decreased density of CD31-positive microvessels, a reduced immune cell content and a lower number of Ki67-positive proliferating cells. qRT-PCR arrays further demonstrated an inhibitory action of telmisartan on the expression of several angiogenic and inflammatory genes.

LIMITATIONS, REASONS FOR CAUTION

Endometriosis-like lesions were induced by syngeneic tissue transplantation into recipient mice without the use of pathological endometriotic tissue of human nature. Therefore, the results obtained in this study may not fully relate to human patients with endometriosis.

WIDER IMPLICATIONS OF THE FINDINGS

This study demonstrates that telmisartan inhibits vascularization, immune cell content and growth of endometriosis-like lesions. Accordingly, the combined blockade of AT1R and activation of PPAR-γ represents a promising new concept in the development of novel compounds for the treatment of endometriosis.

STUDY FUNDING/COMPETING INTEREST(S)

There was no specific funding of this study. The authors have no conflicts of interest to declare.

Generation of co-culture spheroids as vascularisation units for bone tissue engineering

Cell spheroids represent attractive building units for bone tissue engineering, because they provide a three-dimensional environment with intensive direct cell-cell contacts. Moreover, they allow for co-culture of both osteoblasts and vessel-forming cells, which may markedly increase their survival and vascularisation after transplantation. To test this hypothesis, we generated co-culture spheroids by aggregating different combinations of primary human osteoblasts (HOB), human dermal microvascular endothelial cells (HDMEC) and normal human dermal fibroblasts (NHDF) using the liquid overlay technique. Mono-culture spheroids consisting either of HOB or HDMEC served as controls. After in vitro characterisation, the different spheroids were transplanted into dorsal skinfold chambers of CD1 nu/nu mice to study in vivo their viability and vascularisation over a 2-week observation period by means of repetitive intravital fluorescence microscopy and immunohistochemistry. In vitro, co-culture spheroids containing HDMEC rapidly formed dense tubular vessel-like networks within 72 h and exhibited a significantly decreased rate of apoptotic cell death when compared to mono-culture HDMEC spheroids. After transplantation, these networks interconnected to the host microvasculature by external inosculation. Of interest, this process was most pronounced in HOB-HDMEC spheroids and could not further be improved by the addition of NHDF. Accordingly, HOB-HDMEC spheroids were larger when compared to the other spheroid types. These findings indicate that HOB-HDMEC spheroids exhibit excellent properties to preserve viability and to promote proliferation and vascularisation. Therefore, they may be used as functional vascularisation units in bone tissue engineering for the seeding of scaffolds or for the vitalisation of non-healing large bone defects.

[Practical courses for students can not only improve the teaching quality but can also increase the attractiveness of orthopaedic and trauma surgery]

BACKGROUND

Students often complain about a lack of teaching of practical skills. This may be a cause for the low attractiveness of surgical disciplines. We therefore established a practical course to improve teaching quality to inspire the students for orthopedic and trauma surgery.

METHODS

The platforms of the course included the teaching and acquisition of suture techniques, arthroscopy and osteosynthesis techniques. A total of 119 students participated in 9 courses and performed a detailed evaluation.

RESULTS

The main motivation to participate was (i) to acquire practical skills (93 %), (ii) to learn about orthopaedic and trauma surgery (66 %) and (iii) to facilitate decision-making for the occupational choice (21 %). 94 % judged the quality of the course as "excellent", and all 119 participants indicated that they would recommend the course to other students. 43 of 45 students, who had not yet decided on their occupational choice, indicated that the course stimulated them for a career in orthopaedic and trauma surgery.

CONCLUSION

This course not only can improve the teaching quality but also can increase the attractiveness of muskuloskeletal surgery.

Rodent animal models of delayed bone healing and non-union formation: a comprehensive review

Despite the growing knowledge on the mechanisms of fracture healing, delayed healing and non-union formation remain a major clinical challenge. Animal models are needed to study the complex process of normal and impaired fracture healing and to develop new therapeutic strategies. Whereas in the past mainly large animals have been used to study normal and impaired fracture healing, nowadays rodent models are of increasing interest. New osteosynthesis techniques for rat and mice have been developed during the last years, which allowed for the first time stable osteosynthesis in these animals comparable to the standards in large animals and humans. Based on these new implants, different models in rat and mice have been established to study delayed healing and non-union formation. Although in humans the terms delayed union and non-union are well defined, in rodents definitions are lacking. However, especially in scientific studies clear definitions are necessary to develop a uniform scientific language and allow comparison of the results between different studies. In this consensus report, we define the basic terms "union", "delayed healing" and "non-union" in rodent animal models. Based on a review of the literature and our own experience, we further provide an overview on available models of delayed healing and non-union formation in rats and mice. We further summarise the value of different approaches to study normal and delayed fracture healing as well as non-union formation, and discuss different methods of data evaluation.

RAGE blockade and hepatic microcirculation in experimental endotoxaemic liver failure

BACKGROUND

Activation of the receptor for advanced glycation endproducts (RAGE) causes sustained activation of multiple inflammatory pathways. Therefore, RAGE has potential as a new therapeutic target in sepsis. The aim of this study was to analyse whether RAGE blockade in vivo prevents microcirculatory dysfunction and subsequent tissue injury in endotoxaemic liver failure.

METHODS

The hepatic microcirculation was analysed using intravital fluorescence microscopy in murine livers exposed to galactosamine/lipopolysaccharide (G/L) and treated with an anti-RAGE antibody (abRAGE) either 12 h before or h after exposure to G/L. Blood and liver tissue samples were harvested for analysis of leucocyte tissue infiltration, apoptotic and necrotic damage as well as RAGE downstream pathway signalling.

RESULTS

Sinusoidal perfusion failure in livers exposed to G/L was reduced significantly by both pretreatment and post-treatment with abRAGE. Hepatic inflammation induced by exposure to G/L was also attenuated by abRAGE administration, as shown by a 55 per cent reduction in sinusoidal leucocyte stasis, a 65 per cent decrease in venular leucocyte rolling and adhesion, and an 85 per cent reduction in leucocyte tissue infiltration. Treatment with abRAGE markedly reduced hepatocellular apoptosis and necrosis in livers exposed to G/L, and blunted the rise in plasma high-mobility group protein B1 levels. Finally, G/L-induced activation of the mitogen-activated protein kinase cascade was also reduced significantly by blockade of RAGE.

CONCLUSION

RAGE plays an important role in mediating endotoxaemic liver damage. RAGE blockade may have potential therapeutic value. SURGICAL RELEVANCE: The innate immune response to endoxaemia is initiated by a group of pattern recognition receptors, including the receptor for advanced glycation endproducts (RAGE). As RAGE is well known for perpetuation of inflammatory processes, blockade of this receptor might be of particular value in reducing or even halting endoxaemia-related organ disorders. Using intravital fluorescence microscopy this study demonstrated in vivo that pretreatment, but also post-treatment, with a RAGE-blocking antibody attenuated hepatic microcirculatory deterioration and leucocyte recruitment, and thus diminished liver injury in a murine model of endotoxaemic organ failure. These data underline the important role of RAGE in the innate immune response and support the potential therapeutic value of blocking this pattern recognition receptor.

Three-dimensional spheroids of adipose-derived mesenchymal stem cells are potent initiators of blood vessel formation in porous polyurethane scaffolds

Adipose-derived mesenchymal stem cells (adMSCs) exhibit a high angiogenic activity. Accordingly, their incorporation into tissue constructs represents a promising vascularization strategy in tissue engineering. In the present study, we analyzed whether the efficacy of this approach can be improved by seeding adMSCs as three-dimensional spheroids onto porous scaffolds. Green fluorescent protein (GFP)-positive adMSCs expressing CD13, CD73, CD90 and CD117 were isolated from C57BL/6-TgN(ACTB-EGFP)1Osb/J mice for the generation of spheroids using the liquid overlay technique. Porous polyurethane scaffolds were seeded with these spheroids or a comparable number of individual adMSCs and implanted into the dorsal skinfold chamber of C57BL/6 wild-type mice. The vascularization of the implants was analyzed and compared to non-seeded scaffolds by means of intravital fluorescence microscopy and immunohistochemistry. The adMSC spheroids exhibited a homogeneous diameter of ~270μm and could easily be incorporated into the scaffolds by dynamic seeding. After implantation, they induced a strong angiogenic host tissue response, resulting in an improved scaffold vascularization with a significantly higher functional microvessel density when compared to non-seeded scaffolds and scaffolds seeded with individual adMSCs. Immunohistochemical analyses revealed that a high fraction of ~40% of all microvessels within the center of spheroid-seeded scaffolds developed from GFP-positive adMSCs. These vessels inosculated with ingrowing GFP-negative vessels of the host. This indicates that adMSC spheroids serve as individual vascularization units, promoting the simultaneous development of new microvascular networks at different locations inside implanted tissue constructs. Thus, adMSC spheroids may be used to increase the efficacy of MSC-based vascularization strategies in future tissue engineering applications.

Parathyroid hormone [1-34] improves articular cartilage surface architecture and integration and subchondral bone reconstitution in osteochondral defects in vivo

OBJECTIVE

The 1-34 amino acid segment of the parathyroid hormone (PTH [1-34]) mediates anabolic effects in chondrocytes and osteocytes. The aim of this study was to investigate whether systemic application of PTH [1-34] improves the repair of non-osteoarthritic, focal osteochondral defects in vivo.

DESIGN

Standardized cylindrical osteochondral defects were bilaterally created in the femoral trochlea of rabbits (n = 8). Daily subcutaneous injections of 10 μg PTH [1-34]/kg were given to the treatment group (n = 4) for 6 weeks, controls (n = 4) received saline. Articular cartilage repair was evaluated by macroscopic, biochemical, histological and immunohistochemical analyses. Reconstitution of the subchondral bone was assessed by micro-computed tomography. Effects of PTH [1-34] on synovial membrane, apoptosis, and expression of the PTH receptor (PTH1R) were determined.

RESULTS

Systemic PTH [1-34] increased PTH1R expression on both, chondrocytes and osteocytes within the repair tissue. PTH [1-34] ameliorated the macro- and microscopic aspect of the cartilaginous repair tissue. It also enhanced the thickness of the subchondral bone plate and the microarchitecture of the subarticular spongiosa within the defects. No significant correlations were established between these coexistent processes. Apoptotic levels, synovial membrane, biochemical composition of the repair tissue, and type-I/II collagen immunoreactivity remained unaffected.

CONCLUSIONS

PTH [1-34] emerges as a promising agent in the treatment of focal osteochondral defects as its systemic administration simultaneously stimulates articular cartilage and subchondral bone repair. Importantly, both time-dependent mechanisms of repair did not correlate significantly at this early time point and need to be followed over prolonged observation periods.

Resveratrol is a potent inhibitor of vascularization and cell proliferation in experimental endometriosis

STUDY QUESTION

Does the phytochemical compound resveratrol inhibit vascularization of endometriotic lesions?

SUMMARY ANSWER

Resveratrol suppresses the development of new microvessels in endometriotic lesions by inhibiting endothelial cell proliferation.

WHAT IS KNOWN ALREADY

Establishment and progression of endometriosis is crucially dependent on angiogenesis. Resveratrol is a pleiotropic agent, which dose-dependently suppresses the development of new blood vessels.

STUDY DESIGN, SIZE, DURATION

This was a randomized study in a mouse model of endometriosis. Twenty female BALB/c mice with surgically induced endometriosis were treated with resveratrol (40 mg/kg/day, n = 10) or vehicle (n = 10) for 4 weeks.

MATERIAL, SETTING, METHODS

Peritoneal and mesenteric endometriotic lesions were surgically induced by uterine tissue transplantation into the abdominal cavity of BALB/c mice. The animals were daily treated with resveratrol (40 mg/kg) or vehicle by oral gavage. Lesion growth, vascularization, apoptosis and cell proliferation were subsequently analyzed by means of high-resolution ultrasound imaging, caliper measurements, histology and immunohistochemistry throughout an observation period of 4 weeks.

MAIN RESULTS AND THE ROLE OF CHANCE

Resveratrol inhibited angiogenesis in peritoneal and mesenteric endometriotic lesions, as indicated by a significantly reduced microvessel density when compared with controls. Additional immunohistochemical analyses revealed that this was caused by a decreased proliferating activity of CD31-positive endothelial cells in the newly developing microvasculature of the lesions. In line with these findings, lesions in resveratrol-treated mice exhibited a reduced growth rate and a smaller final size than controls. This was associated with lower numbers of proliferating cell nuclear antigen- and Ki67-positive stromal and glandular cells. Apoptotic cells were not detectable in either group. To limit the role of chance, the experiments were conducted under standardized laboratory conditions with appropriate controls. Statistical significance was accepted for a value of P < 0.05.

LIMITATIONS, REASONS FOR CAUTION

Endometriotic lesions were surgically induced by uterine tissue transplantation without the use of pathological endometriotic tissue of human origin. Therefore, the results obtained in this mouse model may not fully correlate to human patients with endometriosis.

WIDER IMPLICATIONS OF THE FINDINGS

Resveratrol is a potent inhibitor of vascularization in endometriotic lesions. This, most probably, causes the suppression of lesion growth. Accordingly, resveratrol represents a promising candidate therapy for future phytochemical treatment of endometriosis.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by a grant of the 'Freunde des Universitätsklinikums des Saarlandes'. The authors have no conflicts of interest to declare.

External inosculation as a feature of revascularization occurs after free transplantation of murine liver grafts

The induction of angiogenesis is essential for successful engraftment of freely transplanted cells or cellular composites. How to augment angiogenesis to ensure an appropriate viability of the grafts is still under investigation. This study evaluated the proangiogenic capability of different syngeneic free liver transplants and elucidated the origin of the newly formed vascular network via use of an eGFP(+) /eGFP(-) (enhanced green fluorescent protein) cross-over design. Using intravital fluorescence microscopy, we found that neonatal and resected murine liver transplants implanted into dorsal skinfold chambers display a significantly enhanced vascularization compared to regular adult transplants. Immunohistochemically, less tissue hypoxia, apoptosis and macrophage infiltration was observed in the neonatal and resected transplants, which is in line with improved vascularization of those grafts. Additionally, electron microscopy revealed morphological hallmarks of liver cells. eGFP(+) liver transplants implanted on eGFP(-) recipients displayed vascular sprouting from the grafts themselves and connection to the recipients` microvasculature, which also undergoes transient proangiogenic response. This process is described as external inosculation, with microvessels exhibiting a chimeric nature of the endothelial lining. These data collectively show that proliferative stimulation is taking effect on angiogenic properties of free transplants and might provide a novel tool for modulating the revascularization of free grafts.

Vascularisation of porous scaffolds is improved by incorporation of adipose tissue-derived microvascular fragments

In tissue engineering, the generation of tissue constructs comprising preformed microvessels is a promising strategy to guarantee their adequate vascularisation after implantation. Herein, we analysed whether this may be achieved by seeding porous scaffolds with adipose tissue-derived microvascular fragments. Green fluorescent protein (GFP)-positive microvascular fragments were isolated by enzymatic digestion from epididymal fat pads of male C57BL/6-TgN(ACTB-EGFP)1Osb/J mice. Nano-size hydroxyapatite particles/poly(ester-urethane) scaffolds were seeded with these fragments and implanted into the dorsal skinfold chamber of C57BL/6 wild-type mice to study inosculation and vascularisation of the implants by means of intravital fluorescence microscopy, histology and immunohistochemistry over 2 weeks. Empty scaffolds served as controls. Vital microvascular fragments could be isolated from adipose tissue and seeded onto the scaffolds under dynamic pressure conditions. In the dorsal skinfold chamber, the fragments survived and exhibited a high angiogenic activity, resulting in the formation of GFP-positive microvascular networks within the implants. These networks developed interconnections to the host microvasculature, resulting in a significantly increased functional microvessel density at day 10 and 14 after implantation when compared to controls. Immunohistochemical analyses of vessel-seeded scaffolds revealed that >90 % of the microvessels in the implants' centre and ~60 % of microvessels in the surrounding host tissue were GFP-positive. This indicates that the scaffolds primarily vascularised by external inosculation. These novel findings demonstrate that the vascularisation of implanted porous scaffolds can be improved by incorporation of microvascular fragments. Accordingly, this approach may markedly contribute to the success of future tissue engineering applications in clinical practice.

A comparative evaluation of ablations produced by high-frequency coagulation-, argon plasma coagulation-, and cryotherapy devices in porcine liver

INTRODUCTION

Hepatic resection is the only curative treatment option for primary or metastatic malignancies of the liver. Although R1 resections can also lead to prolonged survival, the main surgical goal is complete tumor resection (R0). To achieve this, additional treatment of the resection margin with ablation devices is discussed. Using a porcine in vivo model, we therefore analyzed the effect of different ablation devices on depth and completeness of hepatic parenchymal cell destruction.

METHODS

Swabian-Hall strain pigs underwent ablation on the surface of the right, middle, or left liver lobe using seven different types of high-frequency (HF)-, cryotherapy (Cryo)-, or argon plasma coagulation (APC) devices. Penetration depth and volume were analyzed from histological sections. Severity of parenchymal cell destruction was assessed by a histomorphological score.

RESULTS

The greatest penetration depth was achieved with Cryo (10.4 ± 1.7 mm), whereas HF and APC exhibited a smaller penetration depth. However, HF and APC compared to Cryo achieved complete destruction of the intralobular architecture and hepatocellular morphology depending on the application time and the adjusted power.

CONCLUSION

HF, APC, and Cryo applied to the liver surface induce different parenchymal penetration depth and cell destruction. HF and APC are considered to be standard surgical instruments and therefore recommended as standard treatment, whereas Cryo may be used only if particularly deep penetration is required.

Hepatic arterial infusion with tumor necrosis factor-α induces early hepatic hyperperfusion

BACKGROUND

Hepatic arterial infusion (HAI) has been developed for high-dose regional chemotherapy of unresectable liver metastases or primary liver malignancies. While it is well known that high concentrations of tumor necrosis factor (TNF)-α damage tumor blood perfusion, there is no information on whether autochthonous liver perfusion is affected by HAI with TNF-α. Therefore, we investigated the effects of HAI with TNF-α on hepatic macro- and microvascular perfusion.

METHODS

Swabian Hall pigs were randomized into three groups. HAI was performed with either 20 or 40 µg/kg body weight TNF-α (n = 6 each group). Saline-treated animals served as controls (n = 6). Analyses during a 2-hour post-HAI observation period included systemic hemodynamics, portal venous and hepatic arterial blood flow, portal venous pressure, and the blood flow in the hepatic microcirculation.

RESULTS

HAI with TNF-α caused a slight decrease of mean arterial blood pressure (p < 0.001), which was compensated by a moderate increase of heart rate (p < 0.001). No further systemic side effects of TNF-α were observed. HAI with TNF-α further caused a slight but not significant decrease of portal venous blood flow (p = 0.737) in both experimental groups, paralleled by an increase of hepatic arterial blood flow (p = 0.023, 20 µg/kg; p = 0.034, 40 µg/kg) resulting in an overall hepatic hyperperfusion. The hepatic hyperperfusion after HAI with 20 µg/kg TNF-α was more pronounced and associated with a 40% decrease of the blood flow in the hepatic microcirculation (p = 0.009). HAI with 40 µg/kg TNF-α was only associated with a temporary and moderate total hepatic hyperperfusion and did not affect the blood flow in the hepatic microcirculation.

CONCLUSION

HAI with TNF-α causes a decrease of portal venous flow; however, this is overcompensated by an increased hepatic arterial blood flow, resulting in a total hepatic hyperperfusion. Moderate total hepatic hyperperfusion does not affect the blood flow in the hepatic microcirculation, while a persistent and more pronounced hyperperfusion may cause hepatic microcirculatory disturbances.

Pantoprazole, a proton pump inhibitor, delays fracture healing in mice

Proton pump inhibitors (PPIs), which are widely used in the treatment of dyspeptic problems, have been shown to reduce osteoclast activity. There is no information, however, on whether PPIs affect fracture healing. We therefore studied the effect of the PPI pantoprazole on callus formation and biomechanics during fracture repair. Bone healing was analyzed in a murine fracture model using radiological, biomechanical, histomorphometric, and protein biochemical analyses at 2 and 5 weeks after fracture. Twenty-one mice received 100 mg/kg body weight pantoprazole i.p. daily. Controls (n = 21) received equivalent amounts of vehicle. In pantoprazole-treated animals biomechanical analysis revealed a significantly reduced bending stiffness at 5 weeks after fracture compared to controls. This was associated with a significantly lower amount of bony tissue within the callus and higher amounts of cartilaginous and fibrous tissue. Western blot analysis showed reduced expression of the bone formation markers bone morphogenetic protein (BMP)-2, BMP-4, and cysteine-rich protein (CYR61). In addition, significantly lower expression of proliferating cell nuclear antigen indicated reduced cell proliferation after pantoprazole treatment. Of interest, the reduced expression of bone formation markers was associated with a significantly diminished expression of RANKL, indicating osteoclast inhibition. Pantoprazole delays fracture healing by affecting both bone formation and bone remodeling.

Increased exercise after stable closed fracture fixation does not affect fracture healing in mice

PURPOSE

The aim of the present study was to evaluate the systemic biological effect of increased exercise on bone repair after stable fracture fixation.

METHODS

Two groups of SKH-1h mice were studied. Animals of the first group (n=36) were housed in cages supplied with a running wheel, while mice of the second group (n=37) were housed in standard cages for control. Using a closed femur fracture model, bone repair was analysed by histomorphometry and biomechanical testing at 2 and 5 weeks. At 2 weeks, we additionally evaluated the expression of the proliferation marker PCNA (proliferating cell nuclear antigen) and the angiogenic and osteogenic growth factor VEGF (vascular endothelial growth factor). To standardise the mechanical conditions in the fracture gap, we used an intramedullary compression screw for stable fracture fixation.

RESULTS

Each mouse of the exercise group run a mean total distance of 23.5 km after 2 weeks and 104.3 km after 5 weeks. Histomorphometric analysis of the size and tissue composition of the callus could not reveal significant differences between mice undergoing exercise and controls. Accordingly, biomechanical testing showed a comparable torsional stiffness, peak rotation angle, and load at failure of the healing bones in the two groups. The expression of PCNA and VEGF did also not differ between mice of the exercise group and controls.

CONCLUSION

We conclude that increased exercise does not affect bone repair after stable fracture fixation.

Xanthohumol inhibits growth and vascularization of developing endometriotic lesions

BACKGROUND

Xanthohumol is a prenylated flavonoid isolated from hops, which is known to act as a pleiotropic cancer chemopreventive agent owing to its anti-proliferative, anti-inflammatory and anti-angiogenic properties. In the present study, we analyzed, for the first time, whether this dietary compound may also be used for the treatment of endometriosis.

METHODS

Peritoneal and mesenteric endometriotic lesions were surgically induced in BALB/c mice by uterine tissue transplantation into the abdominal cavity. The animals were treated daily with 100 µM xanthohumol (n= 8) or vehicle (control, n= 8) via the drinking water, starting 3 days before tissue transplantations. Lesion growth, cyst formation and vascularization were subsequently analyzed by means of high-resolution ultrasound imaging (at Day 0 and then once per week for 28 days), caliper measurements, western blotting, histology and immunohistochemistry over 4 weeks.

RESULTS

In the treatment and control groups, uterine grafts developed typical endometriotic lesions with cyst-like dilated glands surrounded by a vascularized endometrial stroma. However, xanthohumol efficiently decreased the size of these lesions at Day 28, independent of their localization within the peritoneal cavity, compared with control (peritoneal: P =0.041; mesenteric: P =0.038). This was associated with a reduced level of phosphoinositide 3-kinase protein. Moreover, vascularization of xanthohumol-treated lesions was suppressed, as indicated by a significantly lower microvessel density at Day 28 when compared with vehicle-treated controls (peritoneal: P =0.026; mesenteric: P =0.004). Additional analyses revealed that treatment with xanthohumol did not affect the histomorphology, proliferation and vascularization of the uterine horns and ovaries.

CONCLUSIONS

Taken together, these experimental findings suggest that xanthohumol inhibits the development of endometriotic lesions in mice without inducing serious side effects in the reproductive organs. Thus, xanthohumol represents a promising dietary phytochemical that, after further testing, may be considered for the use in the selective treatment of endometriotic lesions.

[Surgical research in Germany. Organization, quality and international competitiveness]

Surgical research in Germany is performed within surgical clinics by individual working groups or in surgical research divisions. Additionally, a few independent institutes and departments of surgical research have been established at medical faculties. The number of these institutions, however, is too small. To increase productivity in surgical research, structural changes are necessary, including additional establishment of further institutes and professorships. The quality of clinical research in surgery in Germany is critically discussed. International comparison shows that Germany has a low ranking with respect to the number of clinical studies published in leading surgical journals. However, there has been some improvement in the quality of clinical studies performed in surgical departments during the last 15 years. The establishment of the study center of the German Society of Surgery shows that excellent clinical studies with adequate numbers of patients can also be performed in Germany and can be published in leading journals. Accordingly, there is need to distribute the structures and the competence necessary to perform clinical studies in a standardized manner to all surgical departments involved in clinical research. The experimental surgical research in Germany is not adequately visible, although over the last 10 years the most relevant publications from institutions for surgical research have been placed in journals with a mean impact factor of 8. This may be due to the fact that 85% of these top publications are published in non-surgical journals. The aim for the future must therefore be to increase the impact factor and, thus, the attractiveness of surgical journals. This may be achieved by publishing the highest quality results from experimental surgical research not in non-surgical but in surgical journals.

Ghrelin protects musculocutaneous tissue from ischemic necrosis by improving microvascular perfusion

Persistent ischemia in musculocutaneous tissue may lead to wound breakdown and necrosis. The objective of this experimental study was to analyze, whether the gastric peptide ghrelin prevents musculocutaneous tissue from necrosis and to elucidate underlying mechanisms. Thirty-two C57BL/6 mice equipped with a dorsal skinfold chamber containing ischemic musculocutaneous tissue were allocated to four groups: 1) ghrelin; 2) Nω-nitro-l-arginine methyl ester (l-NAME); 3) ghrelin and l-NAME; and 4) control. Microcirculation, inflammation, angiogenesis, and tissue survival were assessed by fluorescence microscopy. Inducible and endothelial nitric oxide synthase (iNOS I and eNOS), vascular endothelial growth factor (VEGF), as well as nuclear factor κB (NF-κB) were assessed by Western blot analysis. Ghrelin-treated animals showed an increased expression of iNOS and eNOS in critically perfused tissue compared with controls. This was associated with arteriolar dilation, increased arteriolar perfusion, and a sustained functional capillary density. Ghrelin further upregulated NF-κB and VEGF and induced angiogenesis. Finally, ghrelin reduced microvascular leukocyte-endothelial cell interactions, apoptosis, and overall tissue necrosis ( P < 0.05 vs. control). Inhibition of nitric oxide by l-NAME did not affect the anti-inflammatory and angiogenic action of ghrelin but completely blunted the ghrelin-induced tissue protection by abrogating the arteriolar dilation, the improved capillary perfusion, and the increased tissue survival. Ghrelin prevents critically perfused tissue from ischemic necrosis. Tissue protection is the result of a nitric oxide synthase-mediated improvement of the microcirculation but not due to induction of angiogenesis or attenuation of inflammation. This might represent a promising, noninvasive, and clinically applicable approach to protect musculocutaneous tissue from ischemia.

Temporal and spatial vascularization patterns of unions and nonunions: role of vascular endothelial growth factor and bone morphogenetic proteins

BACKGROUND

Failure of fracture-healing with nonunion is a major clinical problem. Angiogenesis is closely linked to bone regeneration, but the role of angiogenesis in nonunion formation remains unclear. Because established nonunions are well vascularized, we hypothesized that lack of vascular endothelial growth factor (VEGF) expression and vascularization during the early time course of fracture-healing determine nonunion formation.

METHODS

In seventy-two CD-1 mice, a femoral osteotomy with a gap size of 1.80 mm (nonunion group) or a gap size of 0.25 mm (union group) was created and stabilized by a pin-clip technique. Healing was analyzed after three, seven, fourteen, twenty-one, twenty-eight, and seventy days by micro-computed tomography and histomorphometry. Vascularization was determined in different healing zones by immunohistochemical staining of PECAM-1 (platelet-endothelial cell adhesion molecule). Additional animals were analyzed after seven, fourteen, and twenty-one days with Western blot analysis of VEGF, bone morphogenetic protein (BMP)-2, and BMP-4 expression.

RESULTS

Micro-computed tomography and histomorphometry showed complete bone-bridging in the union group, whereas animals in the nonunion group showed atrophic nonunion formation. Vascularization increased from day 3 to day 7 in both groups, with a subsequent decrease after fourteen days. However, overall vascularization did not differ between unions and nonunions over time. It is of interest that vascularization within the endosteal healing zone was even higher in nonunions than in unions after fourteen days. Expression of VEGF was significantly higher in nonunions, while expression of BMP-2 and 4 and proliferating cell nuclear antigen were found significantly reduced compared with unions.

CONCLUSIONS

Because vascularization during the early time course of fracture-healing was not impaired despite the failure of bone-healing in nonunions, we rejected our hypothesis and accepted the null hypothesis that nonunion formation is not due to failure of VEGF-mediated angiogenesis. Failure of fracture-healing was associated with a decreased expression of BMP-2 and 4 and a disturbed ratio of angiogenic to osteogenic growth factors, which may be responsible for nonunion.

CLINICAL RELEVANCE

Because the intrinsic angiogenic response during nonunion formation was sufficient for adequate vascularization, treatment strategies for nonunions should focus on the stimulation of osteogenesis rather than on the stimulation of angiogenesis.

Erythropoietin stimulates bone formation, cell proliferation, and angiogenesis in a femoral segmental defect model in mice

The glycoprotein erythropoietin (EPO) has been demonstrated to stimulate fracture healing. The aim of the present study was to investigate the effect of EPO treatment on bone repair in a femoral segmental defect model. Bone repair was analyzed in mice which were treated by EPO (500IE/kg/d intraperitoneally; n=38) and in mice which received the vehicle for control (n=40). Two and 10 weeks after creating a 1.8mm femoral segmental defect, bone repair was studied by micro-CT, histology, and Western blot analysis. At 10 weeks, micro-CT and histomorphometric analyses showed a significantly higher bridging rate of the bone defects in EPO-treated animals than in controls. This was associated by a significantly higher bone volume within the segmental defects of the EPO-treated animals. At 2 weeks, Western blot analyses revealed a significantly higher expression of vascular endothelial growth factor (VEGF) in EPO-treated animals compared to controls. Accordingly, the number of blood vessels was significantly increased in the EPO group at 2 weeks. At 10 weeks, we found a significantly higher expression of proliferating cell nuclear antigen (PCNA) in EPO-treated animals when compared to controls. Western blot analyses showed no significant differences between the groups in the expression of the endothelial and inducible nitric oxide synthases (eNOS and iNOS) and the angiopoietin receptor Tie-2. Immunohistochemistry confirmed the results of the Western blot analyses, demonstrating a significantly higher number of VEGF- and PCNA-positive cells in EPO-treated animals than in controls at 2 and 10 weeks, respectively. We conclude that EPO is capable of stimulating bone formation, cell proliferation and VEGF-mediated angiogenesis in a femoral segmental defect model.

Small animal bone healing models: standards, tips, and pitfalls results of a consensus meeting

Small animal fracture models have gained increasing interest in fracture healing studies. To achieve standardized and defined study conditions, various variables must be carefully controlled when designing fracture healing experiments in mice or rats. The strain, age and sex of the animals may influence the process of fracture healing. Furthermore, the choice of the fracture fixation technique depends on the questions addressed, whereby intra- and extramedullary implants as well as open and closed surgical approaches may be considered. During the last few years, a variety of different, highly sophisticated implants for fracture fixation in small animals have been developed. Rigid fixation with locking plates or external fixators results in predominantly intramembranous healing in both mice and rats. Locking plates, external fixators, intramedullary screws, the locking nail and the pin-clip device allow different degrees of stability resulting in various amounts of endochondral and intramembranous healing. The use of common pins that do not provide rotational and axial stability during fracture stabilization should be discouraged in the future. Analyses should include at least biomechanical and histological evaluations, even if the focus of the study is directed towards the elucidation of molecular mechanisms of fracture healing using the largely available spectrum of antibodies and gene-targeted animals to study molecular mechanisms of fracture healing. This review discusses distinct requirements for the experimental setups as well as the advantages and pitfalls of the different fixation techniques in rats and mice.

The dorsal skinfold chamber: window into the dynamic interaction of biomaterials with their surrounding host tissue

The implantation of biomaterials into the human body has become an indispensable part of almost all fields of modern medicine. Accordingly, there is an increasing need for appropriate approaches, which can be used to evaluate the suitability of different biomaterials for distinct clinical indications. The dorsal skinfold chamber is a sophisticated experimental model, which has been proven to be extremely valuable for the systematic in vivo analysis of the dynamic interaction of small biomaterial implants with the surrounding host tissue in rats, hamsters and mice. By means of intravital fluorescence microscopy, this chronic model allows for repeated analyses of various cellular, molecular and microvascular mechanisms, which are involved in the early inflammatory and angiogenic host tissue response to biomaterials during the initial 2-3 weeks after implantation. Therefore, the dorsal skinfold chamber has been broadly used during the last two decades to assess the in vivo performance of prosthetic vascular grafts, metallic implants, surgical meshes, bone substitutes, scaffolds for tissue engineering, as well as for locally or systemically applied drug delivery systems. These studies have contributed to identify basic material properties determining the biocompatibility of the implants and vascular ingrowth into their surface or internal structures. Thus, the dorsal skinfold chamber model does not only provide deep insights into the complex interactions of biomaterials with the surrounding soft tissues of the host but also represents an important tool for the future development of novel biomaterials aiming at an optimisation of their biofunctionality in clinical practice.