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.