Ischemia/reperfusion injury in vascularized tissue allotransplantation: tissue damage and clinical relevance

Intraluminal oxygen can keep small bowel mucosa intact in a segmental ischemia model

Intestinal preservation for transplantation is accompanied by hypoperfusion with long periods of ischemia with total blood cessation and absolute withdrawal of oxygen leading to structural damage. The application of intraluminal oxygen has been successfully tested in small-animal series during storage and transport of the organ but have been so far clinically unrelatable. In this study, we tested whether a simple and clinically approachable method of intraluminal oxygen application could prevent ischemic damage in a large animal model, during warm ischemia time. We utilised a local no-flow ischemia model of the small intestine in pigs. A low-flow and high-pressure intraluminal oxygen deliverance system was applied in 6 pigs and 6 pigs served as a control group. Mucosal histopathology, hypoxia and barrier markers were evaluated after two hours of no-flow conditions, in both treatment and sham groups, and in healthy tissue. Macro- and microscopically, the luminal oxygen delivered treatment group showed preserved small bowel's appearance, viability, and mucosal integrity. A gradual deterioration of histopathology and barrier markers and increase in hypoxia-inducible factor 1-α expression towards the sites most distant from the oxygen application was observed. Intraluminal low-flow, high oxygen delivery can preserve the intestinal mucosa during total ischemia of the small intestine. This finding can be incorporated in methods to overcome small bowel ischemia and improve intestinal preservation for transplantation.

Successful Extension of Vascularized Composite Allograft Perfusion Cold Storage to 24 h in a Rat Hindlimb Transplant Model

Background

Vascularized composite allograft transplantation is a treatment option for complex tissue injuries; however, ischemia reperfusion injury and high acute rejection rates remain a challenge. Hypothermic machine perfusion using acellular storage perfusate is a potential solution. This study evaluated the University of Wisconsin Kidney Preservation Solution-1 (KPS-1) compared with normal saline (NS) for preservation of donor rat hindlimbs subjected to 24 h of ex vivo perfusion cold storage.

Methods

Hindlimbs were subjected to 24-h perfusion cold storage with heparinized KPS-1 (n = 6) or heparinized NS (n = 6). Flow, resistance, and pH were measured continuously. At the end of the 24-h period, tissue was collected for histological analysis of edema and apoptosis.

Results

KPS-1 perfused limbs showed significantly less edema than the NS group, as evidenced by lower limb weight gain (P < 0.001) and less interfascicular space (P < 0.001). KPS-perfused muscle had significantly less cell death than NS-perfused muscle based on terminal deoxynucleotidyl transferase dUTP nick-end labeling (P < 0.001) and cleaved caspase-3 staining (P = 0.045). During hypothermic machine perfusion, a significant decrease in pH over time was detected in both groups, with a significantly greater decline in pH in the KPS-1 group than in the NS group. There were no significant differences overall and over time in flow rate or vascular resistance between the KPS and NS groups.

Conclusions

Perfusion with KPS-1 can successfully extend vascularized composite allograft perfusion cold storage for 24 h in a rat hindlimb model without significant edema or cell death.

Machine Perfusion Enables 24-h Preservation of Vascularized Composite Allografts in a Swine Model of Allotransplantation

The current gold standard for preserving vascularized composite allografts (VCA) is 4°C static cold storage (SCS), albeit muscle vulnerability to ischemia can be described as early as after 2 h of SCS. Alternatively, machine perfusion (MP) is growing in the world of organ preservation. Herein, we investigated the outcomes of oxygenated acellular subnormothermic machine perfusion (SNMP) for 24-h VCA preservation before allotransplantation in a swine model. Six partial hindlimbs were procured on adult pigs and preserved ex vivo for 24 h with either SNMP (n = 3) or SCS (n = 3) before heterotopic allotransplantation. Recipient animals received immunosuppression and were followed up for 14 days. Clinical monitoring was carried out twice daily, and graft biopsies and blood samples were regularly collected. Two blinded pathologists assessed skin and muscle samples. Overall survival was higher in the SNMP group. Early euthanasia of 2 animals in the SCS group was linked to significant graft degeneration. Analyses of the grafts showed massive muscle degeneration in the SCS group and a normal aspect in the SNMP group 2 weeks after allotransplantation. Therefore, this 24-h SNMP protocol using a modified Steen solution generated better clinical and histological outcomes in allotransplantation when compared to time-matched SCS.

Normothermic Ex Situ Machine Perfusion of Vascularized Composite Allografts with Oxygen Microcarriers for 12 Hours Using Real-Time Mitochondrial Redox Quantification

BACKGROUND

Normothermic ex situ perfusion of vascularized composite allografts (VCAs) necessitates high oxygen demand and, thus, increased metabolic activity, which, in turn, requires the use of blood-based perfusion solutions. However, blood-derived perfusates, in turn, constitute an antigenic load. To circumvent this immunogenic problem, we used a perfusate enriched with acellular dextrane oxygen microcarriers to perfuse rat hindlimbs.

METHODS

Rat hindlimbs (n = 11) were perfused with either (non-), oxygenated dextrane-enriched Phoxilium, or Phoxilium enriched with dextrane oxygen microcarriers (MO2) for 12 h at 37 °C or stored on ice. Oxygenation of the skeletal muscle was assessed with Raman spectroscopy, tissue pO2-probes, and analysis of the perfusate. Transmission electronic microscopy was utilized to assess the ultrastructure of mitochondria of the skeletal muscle.

RESULTS

For all evaluated conditions, ischemia time until perfusion was comparable (22.91 ± 1.64 min; p = 0.1559). After 12 h, limb weight increased significantly by at least 81%, up to 124% in the perfusion groups, and by 27% in the static cold storage (SCS) group. Raman spectroscopy signals of skeletal muscle did not differ substantially among the groups during either perfusion or static cold storage across the duration of the experiment. While the total number of skeletal muscle mitochondria decreased significantly compared to baseline, mitochondrial diameter increased in the perfusion groups and the static cold storage group.

CONCLUSION

The use of oxygen microcarriers in ex situ perfusion of VCA with acellular perfusates under normothermic conditions for 12 h facilitates the maintenance of mitochondrial structure, as well as a subsequent recovery of mitochondrial redox status over time, while markers of muscle injury were lower compared to conventional oxygenated acellular perfusates.

Methods of ex vivo analysis of tissue status in vascularized composite allografts

Vascularized composite allotransplantation can improve quality of life and restore functionality. However, the complex tissue composition of vascularized composite allografts (VCAs) presents unique clinical challenges that increase the likelihood of transplant rejection. Under prolonged static cold storage, highly damage-susceptible tissues such as muscle and nerve undergo irreversible degradation that may render allografts non-functional. Skin-containing VCA elicits an immunogenic response that increases the risk of recipient allograft rejection. The development of quantitative metrics to evaluate VCAs prior to and following transplantation are key to mitigating allograft rejection. Correspondingly, a broad range of bioanalytical methods have emerged to assess the progression of VCA rejection and characterize transplantation outcomes. To consolidate the current range of relevant technologies and expand on potential for development, methods to evaluate ex vivo VCA status are herein reviewed and comparatively assessed. The use of implantable physiological status monitoring biochips, non-invasive bioimpedance monitoring to assess edema, and deep learning algorithms to fuse disparate inputs to stratify VCAs are identified.

Biomaterials-based immunomodulation enhances survival of murine vascularized composite allografts

Vascularized composite allotransplantation (VCA) is a restorative option for patients suffering from severe tissue defects not amenable to conventional reconstruction. However, the toxicities associated with life-long multidrug immunosuppression to enable allograft survival and induce immune tolerance largely limit the broader application of VCA. Here, we investigate the potential of targeted immunomodulation using CTLA4-Ig combined with a biological porcine-derived extracellular matrix (ECM) scaffold that elicits a pro-regenerative Th2 response to promote allograft survival and regulate the inflammatory microenvironment in a stringent mouse orthotopic hind limb transplantation model (BALB/c to C57BL/6). The median allograft survival time (MST) increased significantly from 15.0 to 24.5 days (P = 0.0037; Mantel-Cox test) after adding ECM to the CTLA4-Ig regimen. Characterization of the immune infiltration shows a pro-regenerative phenotype prevails over those associated with inflammation and rejection including macrophages (F4/80^hi+CD206^hi+MHCII^low), eosinophils (F4/80^lowSiglec-F⁺), and T helper 2 (Th2) T cells (CD4⁺IL-4⁺). This was accompanied by an increased expression of genes associated with a Type 2 polarized immune state such as Il4, Ccl24, Arg1 and Ym1 within the graft. Furthermore, when ECM was applied along with a clinically relevant combination of CTLA4-Ig and Rapamycin, allograft survival was prolonged from 33.0 to 72.5 days (P = 0.0067; Mantel-Cox test). These studies implicate the clinical exploration of combined regimens involving local application of pro-regenerative, immunomodulatory biomaterials in surgical wound sites with targeted co-stimulatory blockade to reduce adverse effects of immunosuppression and enhance graft survival in VCA.

Superior preservation of capillaries, myofibrils and mitochondria after long-term extracorporeal perfusion of free muscle flaps - A descriptive electron microscopy study

BACKGROUND

Extracorporeal perfusion (ECP) is a promising technique for prolonged tissue preservation, but might have side effects. For instance, increased radical oxygen species or capillary endothelial damage.

OBJECTIVE

To assess ultra-morphological muscle damage during 36-hour ECP of porcine musculocutaneous flaps, hypothesizing that it would delay the onset of damage compared to static cold storage (SCS).

METHODS

Bilateral flaps were retrieved from three Dutch Landrace pigs. Three flaps were preserved for 36 hours by hypothermic storage 4-6°C (control group) and three flaps by ECP with cooled University of Wisconsin solution. Muscle biopsies were taken at 0 h, 12 h and 36 h and assessed with transmission electron microscopy.

RESULTS

Muscle architecture was best preserved by ECP, with a delayed onset and decreased severity of muscle damage. After 36 hours, damage was two-fold lower in ECP-flaps compared to SCS-flaps. Myofibril architecture was best preserved. Mitochondria were greatly preserved with swelling being the most prominent feature. Capillaries were moderately but differently damaged during ECP, with focal endothelial thinning as opposed to luminal obstruction in SCS-preserved flaps.

CONCLUSIONS

This experiment described favourable cellular preservation of skeletal muscle flaps during ECP compared to SCS. Results showed less severe ultra-morphological damage and a later onset of damage.

Is there life on the airway tree? A pilot study of bronchial cell vitality and tissue morphology in the ex vivo lung perfusion (EVLP) era of lung transplantation

BACKGROUND

Ex vivo lung perfusion (EVLP) is a relevant procedure to increase the lung donor pool but could potentially increase the airway tree ischemic injury risk.

METHODS

This study aimed to evaluate the direct effect of EVLP on the airway tree by evaluating bronchial cell vitality and tissue signs of injury on a series of 117 bronchial rings collected from 40 conventional and 19 EVLP-treated lung grafts. Bronchial rings and related scraped bronchial epithelial cells were collected before the EVLP procedure and surgical anastomosis.

RESULTS

The preimplantation interval was significantly increased in the EVLP graft group (p < 0.01). Conventional grafts presented cell viability percentages of 47.07 ± 23.41 and 49.65 ± 21.25 in the first and second grafts which did not differ significantly from the EVLP group (first graft 50.54 ± 25.83 and second graft 50.22 ± 20.90 cell viability percentage). No significant differences in terms of histopathological features (edema, inflammatory infiltrate, and mucosa ulceration) were observed comparing conventional and EVLP samples. A comparison of bronchial cell viability and histopathology of EVLP samples retrieved at different time intervals revealed no significant differences. Accordingly, major bronchial complications after lung transplant were not observed in both groups.

CONCLUSIONS

Based on these data, we observed that EVLP did not significantly impact bronchial cell vitality and airway tissue preservation nor interfere with bronchial anastomosis healing, further supporting it as a safe and useful procedure.

Gluconate-Lactobionate-Dextran Perfusion Solutions Attenuate Ischemic Injury and Improve Function in a Murine Cardiac Transplant Model

Static cold storage is the cheapest and easiest method and current gold standard to store and preserve donor organs. This study aimed to compare the preservative capacity of gluconate-lactobionate-dextran (Unisol) solutions to histidine-tryptophan-ketoglutarate (HTK) solution. Murine syngeneic heterotopic heart transplantations (Balb/c-Balb/c) were carried out after 18 h of static cold storage. Cardiac grafts were either flushed and stored with Unisol-based solutions with high-(UHK) and low-potassium (ULK) ± glutathione, or HTK. Cardiac grafts were assessed for rebeating and functionality, histomorphologic alterations, and cytokine expression. Unisol-based solutions demonstrated a faster rebeating time (UHK 56 s, UHK + Glut 44 s, ULK 45 s, ULK + Glut 47 s) compared to HTK (119.5 s) along with a better contractility early after reperfusion and at the endpoint on POD 3. Ischemic injury led to a significantly increased leukocyte recruitment, with similar degrees of tissue damage and inflammatory infiltrate in all groups, yet the number of apoptotic cells tended to be lower in ULK compared to HTK. In UHK- and ULK-treated animals, a trend toward decreased expression of proinflammatory markers was seen when compared to HTK. Unisol-based solutions showed an improved preservative capacity compared with the gold standard HTK early after cardiac transplantation. Supplemented glutathione did not further improve tissue-protective properties.

Genetic modification of limbs using ex vivo machine perfusion

Genetic engineering is a promising tool to repair genetic disorders, improve graft function or to reduce immune responses towards the allografts. Ex vivo organ perfusion systems have the potential to mitigate ischemic-reperfusion injury, prolong preservation time or even rescue organ function. We aim to combine both technologies to develop a modular platform allowing the genetic modification of vascularized composite (VC) allografts. Rat hind limbs were perfused ex vivo under subnormothermic conditions with lentiviral vectors. Specific perfusion conditions such as controlled pressure, temperature and flow rates were optimized to support the genetic modification of the limbs. Genetic modification was detected in vascular, muscular and dermal limb tissues. Remarkably, skin follicular and interfollicular keratinocytes as well as endothelial cells (ECs) showed stable transgene expression. Furthermore, levels of injury markers such as lactate, myoglobin and lactate dehydrogenase (LDH) as well as histological analyses showed that ex vivo limb perfusion with lentiviral vectors did not cause tissue damage and limb cytokine secretion signatures were not significantly affected. The use of ex vivo VC perfusion in combination with lentiviral vectors allows an efficient and stable genetic modification of limbs representing a robust platform to genetically engineer limbs towards increasing graft survival after transplantation.

Preservation solutions for attenuation of ischemia-reperfusion injury in vascularized composite allotransplantation

Vascularized composite allotransplantation represents the final level of the reconstructive ladder, offering treatment options for severe tissue loss and functional deficiencies. Vascularized composite allotransplantation is particularly susceptible to ischemia–reperfusion injury and requires preservation techniques when subjected to extended storage times prior to transplantation. While static cold storage functions to reduce ischemic damage and is widely employed in clinical settings, there exists no consensus on the ideal preservation solution for vascularized composite allotransplantation. This review aims to highlight current clinical and experimental advances in preservation solution development and their critical role in attenuating ischemia–reperfusion injury in the context of vascularized composite allotransplantation.

Comparison of Acellular Solutions for Ex-situ Perfusion of Amputated Limbs

INTRODUCTION

Hypothermic ex-situ machine perfusion (MP) has been shown to be a promising alternative to static cold storage (SCS) for preservation of solid organs for transplantation and vascularized composite allotransplantation. Perfusion with blood-based perfusion solutions in austere environments is problematic due to their need for appropriate storage and short shelf life, making it impractical for military and emergency use. Acellular perfusion has been shown to be effective, but the ideal perfusate solution for MP of amputated limbs is yet to be determined. The purpose of this study is to evaluate the efficacy of alternative perfusate solutions, such as dextran-enriched Phoxilium, Steen, and Phoxilium in ex-vivo hypothermic MP of amputated limbs in a porcine model.

MATERIALS AND METHODS

Amputated forelimbs from Yorkshire pigs (n = 8) were preserved either in SCS (n = 2) at 4°C for 12 hours or machine-perfused at 10°C for 12 hours with oxygenated perfusion solutions (n = 6) at a constant flow rate. The perfusates used include modified Steen-solution, Phoxilium (PHOX), or Phoxilium enriched with dextran-40 (PHODEX). The perfusate was exchanged after 1 and 6 hours of perfusion. Machine data were recorded continuously. Perfusate samples for clinical chemistry, blood gas analysis, and muscle biopsies were procured at specific timepoints and subsequently analyzed. In this semi in-vivo study, limb replantation has not been performed.

RESULTS

After amputation, every limb was successfully transferred and connected to our perfusion device. The mean total ischemia time was 77.5 ± 5.24 minutes. The temperature of the perfusion solution was maintained at 10.18 ± 2.01°C, and perfusion pressure at 24.48 ± 10.72 mmHg. Limb weight increased by 3% in the SCS group, 36% in the PHODEX group, 25% in the Steen group, and 58% in the PHOX group after 12 hours. This increase was significant in the PHOX group compared with the SCS group. All perfusion groups showed a pressure increase of 10.99 mmHg over time due to edema. The levels of HIF-1a decreased over time in all groups except the Steen and the PHODEX group. The biomarkers of muscle injury in the perfusate samples, such as creatine kinase and lactate-dehydrogenase, showed a significant difference between groups, with highest values in the PHODEX group. No significant differences were found in the results of the blood gas analysis.

CONCLUSION

With the exception of significantly higher levels of creatine kinase and lactate dehydrogenase, MP with dextran-enriched Phoxilium provides similar results as that of the commercially available perfusates such as Steen, without the need for cold storage, and at circa 5% of the cost of the Steen solution. Further large-scale replantation studies are necessary to evaluate the efficacy of dextran-enriched Phoxilium as an alternate perfusate solution.

Myogenic progenitor cell transplantation for muscle regeneration following hindlimb ischemia and reperfusion

Background

Muscle is severely affected by ischemia/reperfusion injury (IRI). Quiescent satellite cells differentiating into myogenic progenitor cells (MPC) possess a remarkable regenerative potential. We herein established a model of local application of MPC in murine hindlimb ischemia/reperfusion to study cell engraftment and differentiation required for muscle regeneration.

Methods

A clamping model of murine (C57b/6 J) hindlimb ischemia was established to induce IRI in skeletal muscle. After 2 h (h) warm ischemic time (WIT) and reperfusion, reporter protein expressing MPC (TdTomato or Luci-GFP, 1 × 10⁶ cells) obtained from isolated satellite cells were injected intramuscularly. Surface marker expression and differentiation potential of MPC were analyzed in vitro by flow cytometry and differentiation assay. In vivo bioluminescence imaging and histopathologic evaluation of biopsies were performed to quantify cell fate, engraftment and regeneration.

Results

2h WIT induced severe IRI on muscle, and muscle fiber regeneration as per histopathology within 14 days after injury. Bioluminescence in vivo imaging demonstrated reporter protein signals of MPC in 2h WIT animals and controls over the study period (75 days). Bioluminescence signals were detected at the injection site and increased over time. TdTomato expressing MPC and myofibers were visible in host tissue on postoperative days 2 and 14, respectively, suggesting that injected MPC differentiated into muscle fibers. Higher reporter protein signals were found after 2h WIT compared to controls without ischemia, indicative for enhanced growth and/or engraftment of MPC injected into IRI-affected muscle antagonizing muscle damage caused by IRI.

Conclusion

WIT-induced IRI in muscle requests increased numbers of injected MPC to engraft and persist, suggesting a possible rational for cell therapy to antagonize IRI. Further investigations are needed to evaluate the regenerative capacity and therapeutic advantage of MPC in the setting of ischemic limb injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02208-w.

Hypothermic Ex Situ Perfusion of Human Limbs With Acellular Solution for 24 Hours

BACKGROUND

Machine perfusion (MP) has evolved as a promising approach for the ex situ preservation in organ transplantation. However, the literature on the use of MP in human vascularized composite allografts is scarce. The aim of this study was to evaluate the effects of hypothermic MP with an acellular perfusate in human upper extremities and compare with the current gold standard of static cold storage (SCS).

METHODS

Six upper extremities were assigned to either MP (n = 3) or SCS (n = 3) conditions for 24 h. MP-extremities were perfused with oxygenated Steen solution at a constant pressure of 30 mm Hg and 10°C.

RESULTS

Median total ischemia time was 213 min (range, 127-222 min). Myoglobin, creatine-kinase (CK) showed increased levels at the start of MP (medians: myoglobin: 4377 ng/mL, CK: 1442 U/L), peaking 6 h after perfusate exchange (medians: myoglobin: 9206 ng/mL, CK: 3995 U/L) at timepoint 24. Lactate levels decreased from a median of 6.9-2.8 mmol/L over time. Expression of hypoxia-inducible factor 1-alpha peaked in the SCS-group after 8 h, followed by a decrease. Increased hypoxia-inducible factor 1-alpha expression in the MP group was delayed until 20 h. Perfusion pressure, temperature, and circuit flow were maintained at median of 30.88 mm Hg, 9.77°C, and 31.13 mL/min, respectively. Weight increased 1.4% in the SCS group and 4.3% in the MP group over 24 h.

CONCLUSIONS

Hypothermic ex situ perfusion with an oxygenated acellular Steen solution may extend the allowable extracorporeal preservation time by a factor of 4-6 compared to SCS and holds promise to be beneficial for vascularized composite allograft recipients and victims of traumatic major limb amputation.

Vascularized composite allotransplantation versus solid organ transplantation: innate-adaptive immune interphase

PURPOSE OF REVIEW

Vascularized composite allotransplantation (VCA), a life-enhancing treatment for patients with complex tissue defects, trauma or illness, expounds upon the foundation of solid organ transplantation (SOT), the gold standard in end-stage organ failure. As innate and adaptive immunity remain the fundamental concern, this review highlights divergent immunobiology responses in VCA and SOT recipients.

RECENT FINDINGS

Host innate immune activation drives peritransplant tissue ischemia-reperfusion injury (IRI). Despite the direct relationship between ischemia-reperfusion (IR)-stress and cell-mediated acute rejection, the mechanism of how IRI may affect VCA loss needs investigation. With skin grafts being highly immunogenic, the incidence of cell-mediated rejection is higher in VCA than SOT; whereas ex-vivo perfusion may exert cytoprotection against IRI in VCA and SOT. New treatment concepts, such as topical immunosuppression or cell-based tolerogenic therapies, may avoid systemic immunosuppression in VCA. Although antibody-mediated rejection is relatively rare in VCA and its disease seems to be distinct from that in SOT, little is known as to whether and how IRI may influence humoral immune rejection cascade in VCA or SOT.

SUMMARY

Further understanding of the innate-adaptive immune crosstalk should contribute to much needed development of novel therapies to improve VCA outcomes, based on strategies established in SOT.

Indian Subcontinent's First Bilateral Supracondylar Level Upper Limb Transplantation

Introduction This is the first case of supracondylar level transplant from the Indian subcontinent, performed for a bilateral below elbow amputee. It has a completely different set of challenges for the transplant team, with a relatively shorter ischemia time window.

The technical considerations for the same have been discussed in detail in this article.

Materials and Methods The patient was a 19-year-old female who lost her both upper limbs at proximal forearm level due to severe crush injury following a road traffic accident. Insufficient bone length on either side necessitated a supracondylar level transplant. The preoperative workup included detailed clinical evaluation, biochemical, and psychological evaluation.

The donor was a young brain-dead, male patient from a hospital, 30 minutes away. The donor and recipient preparations in this case were unique. The recipient’s own elbow flexors and extensors were used while the elbow joint was from the donor. The specific challenges we faced during this procedure have been described in detail.

Results The transplantation has been a complete technical success, with the patient rehabilitated back to her independent life style. This article describes only the technical considerations. The functional recovery aspect is part of an another soon to be published manuscript.

Conclusion Supracondylar level arm-transplant requires a highly coordinated team effort with precise preoperative planning, along with meticulous attention to detail to achieve a successful outcome. In properly selected patients, it could be a life-changing procedure, worth all the effort.

Vitrification and storage of oral mucosa epithelial cell sheets

Shipping time and shipping delays might affect the quality of the stem cells based engineered "organs." In our laboratory, we have developed a limbal stem cell deficient (LSCD) rabbit model. To reverse the LSCD, we cultured oral mucosal epithelial cells for 2-3 weeks and engineered cultured autologous oral mucosa epithelial cell sheets (CAOMECS), which were grafted on the LSCD cornea. The purpose of this study was to vitrify CAOMECS and to store it until the CAOMECS can be grafted onto patients. CAOMECS were vitrified in LN₂ for up to 204 days. We tested two different methods of vitrification with different solutions; however, CAOMECS were only viable when they were not stored in a vitrification solution; results were only reported from this CAOMECS. On the basis of hematoxylin and eosin staining, we showed that the CAOMECS morphology was well preserved after long-term storage in LN₂ . Most of the preservation solutions maintained the CAOMECS phenotype (Ki67, proliferating cell nuclear antigen (PCNA), Beta-Catenin, ZO-1, E-Cadherin, CK3, CK4, CK13). The exception was the solution composed with ethylene glycol and Dimethyl sulfoxide (DMSO): this resulted in loss of DeltaN-p63 expression. DeltaN-p63 is an important marker for cell proliferation. The expression of proteins involved in cell-cell connection and the differentiation markers were maintained. Apoptosis was not detected in the thawed CAOMECS. We demonstrated that CAOMECS can be stored long-term in LN₂ without affecting their morphology and phenotype.

Extracorporeal Perfusion in Vascularized Composite Allotransplantation: Current Concepts and Future Prospects

Severe injuries of the face and limbs remain a major challenge in today's reconstructive surgery. Vascularized composite allotransplantation (VCA) has emerged as a promising approach to restore these defects. Yet, there are major obstacles preventing VCA from broad clinical application. Two key restrictions are (1) the graft's limited possible ischemia time, keeping the potential donor radius extremely small, and (2) the graft's immunogenicity, making extensive lifelong monitoring and immunosuppressive treatment mandatory. Machine perfusion systems have demonstrated clinical success addressing these issues in solid organ transplantation by extending possible ischemia times and decreasing immunogenicity. Despite many recent promising preclinical trials, machine perfusion has not yet been utilized in clinical VCA. This review presents latest perfusion strategies in clinical solid organ transplantation and experimental VCA in light of the specific requirements by the vascularized composite allograft's unique tissue composition. It discusses optimal settings for temperature, oxygenation, and flow types, as well as perfusion solutions and the most promising additives. Moreover, it highlights the implications for the utility of VCA as therapeutic measure in plastic surgery, if machine perfusion can be successfully introduced in a clinical setting.

Emerging technologies in organ preservation, tissue engineering and regenerative medicine: a blessing or curse for transplantation?

Since the beginning of transplant medicine in the 1950s, advances in surgical technique and immunosuppressive therapy have created the success story of modern organ transplantation. However, today more than ever, we are facing a huge discrepancy between organ supply and demand, limiting the potential for transplantation to save and improve the lives of millions. To address the current limitations and shortcomings, a variety of emerging new technologies focusing on either maximizing the availability of organs or on generating new organs and organ sources hold great potential to eventully overcoming these hurdles. These advances are mainly in the field of regenerative medicine and tissue engineering. This review gives an overview of this emerging field and its multiple sub-disciplines and highlights recent advances and existing limitations for widespread clinical application and potential impact on the future of transplantation.

Graft-implanted, enzyme responsive, tacrolimus-eluting hydrogel enables long-term survival of orthotopic porcine limb vascularized composite allografts: A proof of concept study

Background

Currently, patients receiving vascularized composite allotransplantation (VCA) grafts must take long-term systemic immunosuppressive therapy to prevent immunologic rejection. The morbidity and mortality associated with these medications is the single greatest barrier to more patients being able to receive these life-enhancing transplants. In contrast to solid organs, VCA, exemplified by hand or face transplants, allow visual diagnosis of clinical acute rejection (AR), directed biopsy and targeted graft therapies. Local immunosuppression in VCA could reduce systemic drug exposure and limit adverse effects. This proof of concept study evaluated, in a large animal forelimb VCA model, the efficacy and tolerability of a novel graft-implanted enzyme-responsive, tacrolimus (TAC)—eluting hydrogel platform, in achieving long-term graft survival.

Methods

Orthotopic forelimb VCA were performed in single haplotype mismatched mini-swine. Controls (n = 2) received no treatment. Two groups received TAC hydrogel: high dose (n = 4, 91 mg TAC) and low dose (n = 4, 49 mg TAC). The goal was to find a dose that was tolerable and resulted in long-term graft survival. Limbs were evaluated for clinical and histopathological signs of AR. TAC levels were measured in serial blood and skin tissue samples. Tolerability of the dose was evaluated by monitoring animal feeding behavior and weight.

Results

Control limbs underwent Banff Grade IV AR by post-operative day six. Low dose TAC hydrogel treatment resulted in long-term graft survival time to onset of Grade IV AR ranging from 56 days to 93 days. High dose TAC hydrogel also resulted in long-term graft survival (24 to 42 days), but was not well tolerated.

Conclusion

Graft-implanted TAC-loaded hydrogel delays the onset of Grade IV AR of mismatched porcine forelimb VCA grafts, resulting in long term graft survival and demonstrates dose-dependent tolerability.

Critical Ischemia Time, Perfusion, and Drainage Function of Vascularized Lymph Nodes

BACKGROUND

Vascularized lymph node transfer is a promising surgical treatment for lymphedema. This study investigated the effect of ischemia on the lymphatic drainage efficiency of vascularized lymph node flaps and the critical ischemia time of lymph nodes.

METHODS

Twenty-four lymph nodes containing groin flaps in 12 Sprague-Dawley rats were dissected. Clamping of the vascular pedicle was performed for 0, 1, 3, 5, 6, or 7 hours; then, each was allowed to reperfuse by means of the vascular pedicle for 1 hour. Perfusion and ischemic changes were assessed using indocyanine green lymphography; laser Doppler flowmetry; and histologic studies with associated lymphatic vessel endothelial hyaluronan receptor-1, CD68, 4',6-diamidino-2-phenylindole, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling, and glutathione assay stains.

RESULTS

The mean latency period of the groin lymph node flaps was 247 ± 67, 83 ± 15, 72 ± 42, 30 ± 18, and 245 ± 85 seconds in the 0-, 1-, 3-, 5-, and 6-hour groups, respectively. Perfusion detected by laser Doppler was 85.2 ± 14.5, 87.2 ± 36.7, 129.8 ± 33.7, 140.4 ± 148.5, 156.1 ± 91.4, and 41.2 ± 34.8 perfusion units at ischemia times of 0, 1, 3, 5, 6, and 7 hours, respectively. Cell damage measured by glutathione was 46.8 ± 10.2, 67.7 ± 14.2, 62.8 ± 15.4, 126.6 ± 5.9, 259.0 ± 70.3, and 109.1 ± 27.5 at ischemia times of 0, 1, 3, 5, 6, and 7 hours, respectively. Histologically, as ischemia time increased, hemorrhage and congestion became more severe.

CONCLUSIONS

The critical ischemia time of vascularized lymph nodes is 5 hours in the rodent animal model, verified by indocyanine green lymphatic fluid uptake, laser Doppler perfusion, and histologic assessments. Interestingly, lymphatic drainage and perfusion of vascularized lymph nodes were improved with an increased ischemia time before the critical 5 hours was reached.

Successful Long-term Extracorporeal Perfusion of Free Musculocutaneous Flaps in a Porcine Model

BACKGROUND

Extracorporeal perfusion is a technique that aims to safely prolong tissue preservation by reducing ischemia-reperfusion injury. Free muscle flaps provide a sensitive research model due to their low ischemic tolerance. However, long-term perfusion of free muscle flaps is scarcely researched. The aim of this study was to compare tissue damage in musculocutaneous flaps during 36 h of extracorporeal perfusion versus static cold storage.

MATERIALS AND METHODS

Bilateral free rectus abdominis flaps were harvested from five Dutch Landrace pigs (weight: 53-59 kg). Flaps were treated for 36 h according to the following study groups: (1) cold storage at 4°C-6°C (n = 4), (2) perfusion with histidine-tryptophan-ketoglutarate (HTK) at 8°C-10°C (n = 3), (3) perfusion with University of Wisconsin solution (UW) at 8°C-10°C (n = 3). Perfusion fluid samples (creatinine kinase, blood gas) and biopsies for quantitative polymerase chain reaction were collected at multiple time points. Microcirculation was assessed at 24 h of preservation using indocyanine-green fluorescence angiography. Flap weight was measured at the start and end of the preservation period.

RESULTS

Successful and stable perfusion for 36 h was achieved in all perfused flaps. The mean creatinine kinase increase in the perfusion fluid was comparable in both the groups (UW: +43,144 U/L, HTK: +44,404 U/L). Mean lactate was higher in the UW group than in the HTK group (6.57 versus 1.07 mmol/L). There were homogenous and complete perfusion patterns on indocyanine-green angiography in both the perfusion groups, in contrast to incomplete and inhomogeneous patterns during cold storage. Expression of genes related to apoptosis and inflammation was lower in perfused flaps than in the cold storage group. Weight increase was highest in the HTK group (78%; standard deviation [SD], 29%) compared with UW (22%; SD, 22%) and cold storage (0.7%; SD, 4%).

CONCLUSIONS

Long-term extracorporeal perfusion of free rectus abdominis flaps is feasible. Outcomes in the perfusion groups seemed superior compared to cold storage. Hypotheses gained from this research need to be further explored in a replantation setting.

Advances in machine perfusion, organ preservation, and cryobiology: potential impact on vascularized composite allotransplantation

PURPOSE OF REVIEW

In this review, we discuss novel strategies that allow for extended preservation of vascularized composite allografts and their potential future clinical implications for the field of vascularized composite allotransplantation (VCA).

RECENT FINDINGS

The current gold standard in tissue preservation - static cold preservation on ice - is insufficient to preserve VCA grafts for more than a few hours. Advancements in the field of VCA regarding matching and allocation, desensitization, and potential tolerance induction are all within reasonable reach to achieve; these are, however, constrained by limited preservation time of VCA grafts. Although machine perfusion holds many advantages over static cold preservation, it currently does not elongate the preservation time. More extreme preservation techniques, such as cryopreservation approaches, are, however, specifically difficult to apply to composite tissues as the susceptibility to ischemia and cryoprotectant agents varies greatly by tissue type.

SUMMARY

In the current scope of extended preservation protocols, high subzero approaches of VCA grafts will be particularly critical enabling technologies for the implementation of tolerance protocols clinically. Ultimately, advances in both preservation techniques and tolerance induction have the potential to transform the field of VCA and eventually lead to broad applications in reconstructive transplantation.

Pioglitazone Protects Against Renal Ischemia-Reperfusion Injury via the AMP-Activated Protein Kinase-Regulated Autophagy Pathway

Renal ischemia-reperfusion injury (IRI) is a major cause of acute renal failure. Our previous studies have shown that pioglitazone, a peroxisome proliferators-activated receptor (PPAR)-γ agonist used in type 2 diabetes, protects against renal IRI; however, the molecular mechanism underlying the renoprotective effects of pioglitazone is still unclear. In this study, we investigated the role of AMP-activated protein kinase (AMPK)-regulated autophagy in renoprotection by pioglitazone in IRI. To investigate whether pioglitazone protects renal cells from IRI, an in vivo renal IRI model was used. Cell apoptosis in the kidneys was determined by TUNEL staining. Western blotting was used to determine the expression of AMPK, autophagy-related proteins, and caspase-3/8 proteins in the kidneys. In a rat model of IRI, pioglitazone decreased the increased serum creatinine and urea nitrogen, improved renal histological score, and decreased the cell injury. Pioglitazone also increased AMPK phosphorylation, inhibited p62 and cleaved caspase-3/8 proteins, and activated autophagy-related proteins LC3 II and Beclin-1 in the kidneys of IRI rats. Moreover, GW9662, as a selective inhibitor of PPAR-γ, inhibited the protective effects of pioglitazone. These results suggest that pioglitazone exerts its protective effects in renal IRI via activation of an AMPK-regulated autophagy signaling pathway.

c-Jun N-Terminal Kinases (JNKs) in Myocardial and Cerebral Ischemia/Reperfusion Injury

In this article, we review the literature regarding the role of c-Jun N-terminal kinases (JNKs) in cerebral and myocardial ischemia/reperfusion injury. Numerous studies demonstrate that JNK-mediated signaling pathways play an essential role in cerebral and myocardial ischemia/reperfusion injury. JNK-associated mechanisms are involved in preconditioning and post-conditioning of the heart and the brain. The literature and our own studies suggest that JNK inhibitors may exert cardioprotective and neuroprotective properties. The effects of modulating the JNK-depending pathways in the brain and the heart are reviewed. Cardioprotective and neuroprotective mechanisms of JNK inhibitors are discussed in detail including synthetic small molecule inhibitors (AS601245, SP600125, IQ-1S, and SR-3306), ion channel inhibitor GsMTx4, JNK-interacting proteins, inhibitors of mixed-lineage kinase (MLK) and MLK-interacting proteins, inhibitors of glutamate receptors, nitric oxide (NO) donors, and anesthetics. The role of JNKs in ischemia/reperfusion injury of the heart in diabetes mellitus is discussed in the context of comorbidities. According to reviewed literature, JNKs represent promising therapeutic targets for protection of the brain and the heart against ischemic stroke and myocardial infarction, respectively. However, different members of the JNK family exert diverse physiological properties which may not allow for systemic administration of non-specific JNK inhibitors for therapeutic purposes. Currently available candidate JNK inhibitors with high therapeutic potential are identified. The further search for selective JNK3 inhibitors remains an important task.