Short-term molecular and cellular effects of ischemia/reperfusion on vascularized lymph node flaps in rats

Cilostazol promotes blood vessel formation and bone regeneration in a murine non-union model

Non-unions represent a major complication in trauma and orthopedic surgery. Many factors contribute to bone regeneration, out of which an adequate vascularization has been recognized as crucial. The phosphodiesterase-3 (PDE-3) inhibitor cilostazol has been shown to exert pro-angiogenic and pro-osteogenic effects in a variety of preclinical studies. Hence, we herein investigated the effects of cilostazol on bone regeneration in an atrophic non-union model in mice. For this purpose, a 1.8 mm femoral segmental defect was stabilized by pin-clip fixation and the animals were treated daily with 30 mg/kg body weight cilostazol or saline (control) per os. At 2, 5 and 10 weeks after surgery the healing of femora was analyzed by X-ray, biomechanics, photoacoustic imaging, and micro-computed tomography (µCT). To investigate the cellular composition and the growth factor expression of the callus tissue additional histological, immunohistochemical and Western blot analyses were performed. Cilostazol-treated animals showed increased bone formation within the callus, resulting in an enhanced bending stiffness when compared to controls. This was associated with a more pronounced expression of vascular endothelial growth factor (VEGF), a higher number of CD31-positive microvessels and an increased oxygen saturation within the callus tissue. Furthermore, cilostazol induced higher numbers of tartrate-resistant acidic phosphate (TRAP)-positive osteoclasts and CD68-positive macrophages. Taken together, these findings demonstrate that cilostazol is a promising drug candidate for the adjuvant treatment of atrophic non-unions in clinical practice.

Sildenafil, a phosphodiesterase-5 inhibitor, stimulates angiogenesis and bone regeneration in an atrophic non-union model in mice

Non-union formation represents a major complication in trauma and orthopedic surgery. The phosphodiesterase-5 (PDE-5) inhibitor sildenafil has been shown to exert pro-angiogenic and pro-osteogenic effects in vitro and in vivo. Therefore, the aim of the present study was to analyze the impact of sildenafil in an atrophic non-union model in mice. After creation of a 1.8 mm segmental defect, mice femora were stabilized by pin-clip fixation. Bone regeneration was analyzed by means of X-ray, biomechanics, photoacoustic and micro-computed tomography (µCT) imaging as well as histological, immunohistochemical and Western blot analyses at 2, 5 and 10 weeks after surgery. The animals were treated daily with either 5 mg/kg body weight sildenafil (n = 35) or saline (control; n = 35) per os. Bone formation was markedly improved in defects of sildenafil-treated mice when compared to controls. This was associated with a higher bending stiffness as well as an increased number of CD31-positive microvessels and a higher oxygen saturation within the callus tissue. Moreover, the bone defects of sildenafil-treated animals contained more tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts and CD68-positive macrophages and exhibited a higher expression of the pro-angiogenic and pro-osteogenic markers cysteine rich protein (CYR)61 and vascular endothelial growth factor (VEGF) when compared to controls. These findings demonstrate that sildenafil acts as a potent stimulator of angiogenesis and bone regeneration in atrophic non-unions.

Photoacoustic imaging for the study of oxygen saturation and total hemoglobin in bone healing and non-union formation

Non-union formation represents a major complication in trauma surgery. Adequate vascularization has been recognized as vital for bone healing. However, the role of vascularization in the pathophysiology of non-union formation remains elusive. This is due to difficulties in studying bone microcirculation in vivo. Therefore, we herein studied in a murine osteotomy model whether photoacoustic imaging may be used to analyze vascularization in bone healing and non-union formation. We found that oxygen saturation within the callus tissue is significantly lower in non-unions compared to unions and further declines over time. Moreover, the amount of total hemoglobin (HbT) within the callus tissue was markedly reduced in non-unions. Correlation analyses showed a strong positive correlation between microvessel density and HbT, indicating that photoacoustically determined HbT is a valid parameter to assess vascularization during bone healing. In summary, photoacoustic imaging is a promising approach to study vascular function and tissue oxygenation in bone regeneration.

Animal models in lymph node transfer surgery: A systematic review

BACKGROUND AND AIM

Lymph node transfer surgery (LNTS) is indicated in secondary lymphedema (LE) patients who do not respond to conservative therapy. Animal models are the spearhead of LE research and were used to pioneer most of the surgical interventions currently in practice. We conducted a systematic review of the literature to explore animal models dedicated to LNTS to compare different species, techniques, and outcomes.

METHODS

Four databases were searched: PubMed, Cumulative Index of Nursing and Allied Health Literature, Scopus, and Web of Science. We used the Preferred Reporting Items for Systematic Reviews and Meta-Analysis as our basis of organization.

RESULTS

Avascular lymph node graft (ALNG) and vascularized lymph node transfer (VLNT) effectively treated LE and lead to better outcomes than controls. Whole ALNGs are superior to fragmented ALNGs. Larger fragments are more likely to be reintegrated into the lymphatic system than small fragments. VLNT was superior to whole and fragmented ALNG. Increasing the number of VLNT resulted in better outcomes. Adipose-derived stem cells improved outcomes of VLNT; vascular endothelial growth factor C and D and platelet-rich plasma improved outcomes for ALNG. Cryopreservation of lymph nodes (LNs) did not affect outcomes for ALNG. The critical ischemia and venous occlusion time for LN flaps were 4-5 and 4 h, respectively. The critical time for reperfusion injury was 2 h. Some of the novel models included venous LNT, and cervical adipocutaneous flap to groin.

CONCLUSION

Current evidence from animals favors VLNT over other surgical interventions. Several pharmacological therapies significantly improved outcomes of ALNG and VLNT.

RELEVANCE TO PATIENTS

LE is a chronic condition affecting millions of patients worldwide. LNTS is becoming more popular as a LE treatment. Animal models have led the LE research for decades and developing new models for LE are essential for LE research. This systematic review aims to summarize the existing animal models dedicated to LNTS. We believe that this review is critical to guide researchers in the selection of the model that is best fit for their hypothesis-driven experiments.

Animal Models Used in the Research of Vascularized Lymph Node Transfer: A Systematic Review

BACKGROUND

Lymphedema is a common adverse consequence of breast cancer therapy, while still relatively little is known about its pathophysiology. Several treatment options emerged over the past decades, and among them, vascularized lymph node transfer (VLNT) seems to be particularly promising. Animal models are indispensable to improve our understanding of the underlying processes surrounding the transplantation of a vascularized lymph node. This review aimed to systematically evaluate animal models of VLNT and compare their advantages and disadvantages.

MATERIALS AND METHODS

A systematic review of literature in the Scopus, Web of Science, and Ovid MEDLINE databases was conducted according to the PRISMA guidelines to identify all studies on animal models used for the research of VLNT. The algorithm used in search of articles was "Vascularized Lymph Node Transfer" AND "Model". Articles were manually verified for relevance to the topic. The resulting models were assessed for their suitability for VLNT research.

RESULTS

The literature search yielded a total of 233 studies after duplicates removal. Of those, 217 were excluded based on title and abstract review. Another study was excluded after reviewing the full-text article leaving 15 eligible studies to be included in this review article.

CONCLUSIONS

Rats were found to be the most dominantly used animal model in the VLNT research, although other models had their benefits. The main areas of study were the functionality of VLNT within or without a preinduced lymphedema, its response to ischemia, and clarification of lymphatic pathways reestablishment following VLNT.