Advances in organ preservation for transplantation

Numerical modeling of oxygen diffusion in tissue spheroids undergoing fusion using function representation and finite volumes

A three-dimensional cell culture called a spheroid serves as a foundational entity in a wide variety of modern tissue engineering applications, including 3D-bioprinting and preclinical drug testing. Lack of oxygen within tissue spheroids hinders metabolism of cells and eventually leads to cell death. Prevention of necrosis is crucial to success of tissue engineering methods and such prevention requires estimation of cell viability in the spheroid. We propose a novel approach for numerical modeling of diffusion in tissue spheroids during their fusion. The approach is based on numerical solutions of partial differential equations and the application of Function Representation (FRep) framework for geometric modeling. We present modeling of oxygen diffusion based on meshes derived from the geometry of fusing spheroids, a method for selecting optimal spheroid size, and several statistics for estimating cellular viability. Our findings provide insights into oxygen diffusion in three-dimensional cell cultures thus improving the robustness of biotechnological methods that employ tissue spheroids.

Ex vivo lung perfusion and the Organ Care System: a review

With the increasing prevalence of heart failure and end-stage lung disease, there is a sustained interest in expanding the donor pool to alleviate the thoracic organ shortage crisis. Efforts to extend the standard donor criteria and to include donation after circulatory death have been made to increase the availability of suitable organs. Studies have demonstrated that outcomes with extended-criteria donors are comparable to those with standard-criteria donors. Another promising approach to augment the donor pool is the improvement of organ preservation techniques. Both ex vivo lung perfusion (EVLP) for the lungs and the Organ Care System (OCS, TransMedics) for the heart have shown encouraging results in preserving organs and extending ischemia time through the application of normothermic regional perfusion. EVLP has been effective in improving marginal or borderline lungs by preserving and reconditioning them. The use of OCS is associated with excellent short-term outcomes for cardiac allografts and has improved utilization rates of hearts from extended-criteria donors. While both EVLP and OCS have successfully transitioned from research to clinical practice, the costs associated with commercially available systems and consumables must be considered. The ex vivo perfusion platform, which includes both EVLP and OCS, holds the potential for diverse and innovative therapies, thereby transforming the landscape of thoracic organ transplantation.

Organ storage in renal transplantation

PURPOSE OF REVIEW

Kidney transplantation is vital for those with end-stage renal disease, enhancing quality of life and longevity. It is the preferred treatment but is hindered by a global disparity between donor kidney availability and demand. Therefore, optimizing organ storage techniques is crucial to mitigate the effects of ischemia reperfusion injury in available organs. Recent interest has centered on innovative methods like oxygenated normothermic perfusion and abdominal regional perfusion.

RECENT FINDINGS

Multiple recent metanalyses, including a Cochrane review, confirm the benefits of hypothermic machine perfusion (HMP) for deceased donor kidneys, demonstrating its utility and cost effectiveness. The benefits of oxygenated normothermic perfusion have been seen in retrospective data sets but not in prospective trials. Abdominal regional perfusion (aNRP) is gaining interest, especially for liver transplantation, but kidney specific data are scant.

SUMMARY

High-quality evidence backs the use of HMP for deceased donor kidneys. Despite interest in other techniques, clinical evidence for their benefits in kidney transplantation is lacking. The gap between innovation and verified success emphasizes the need for continued research and collaboration between medical professionals, researchers, and ethical committees. This review aims to further illuminate the complexities and advancements in the field, bridging the knowledge gap and aiding in the continual pursuit of excellence in transplantation.

Is the Organ Care System (OCS) Still the First Choice With Emerging New Strategies for Donation After Circulatory Death (DCD) in Heart Transplant?

The scarcity of donor hearts continues to be a challenge in transplants for advanced heart failure patients. With an increasing number of patients on the waiting list for a heart transplant, the discrepancy in the number between donors and recipients is gradually increasing and poses a new challenge that plagues the healthcare systems when it comes to the heart. Several technologies have been developed to expand the donor pool in recent years. One such method is the organ care system (OCS). The standard method of organ preservation is the static cold storage (SCS) method which allows up to four hours of safe preservation of the heart. However, beyond four hours of cold ischemia, the incidence of primary graft dysfunction increases significantly. OCS keeps the heart perfused close to the physiological state beyond the four hours with superior results, which allows us to travel further and longer distances, leading to expansion in the donor pool. In this review, we discuss the OCS system, its advantages, and shortcomings.

Mitochondrial respiratory chain and Krebs cycle enzyme function in human donor livers subjected to end-ischaemic hypothermic machine perfusion

INTRODUCTION

Marginal human donor livers are highly susceptible to ischaemia reperfusion injury and mitochondrial dysfunction. Oxygenation during hypothermic machine perfusion (HMP) was proposed to protect the mitochondria but the mechanism is unclear. Additionally, the distribution and uptake of perfusate oxygen during HMP are unknown. This study aimed to examine the feasibility of mitochondrial function analysis during end-ischaemic HMP, assess potential mitochondrial viability biomarkers, and record oxygenation kinetics.

METHODS

This was a randomised pilot study using human livers retrieved for transplant but not utilised. Livers (n = 38) were randomised at stage 1 into static cold storage (n = 6), hepatic artery HMP (n = 7), and non-oxygen supplemented portal vein HMP (n = 7) and at stage 2 into oxygen supplemented and non-oxygen supplemented portal vein HMP (n = 11 and 7, respectively). Mitochondrial parameters were compared between the groups and between low- and high-risk marginal livers based on donor history, organ steatosis and preservation period. The oxygen delivery efficiency was assessed in additional 6 livers using real-time measurements of perfusate and parenchymal oxygen.

RESULTS

The change in mitochondrial respiratory chain (complex I, II, III, IV) and Krebs cycle enzyme activity (aconitase, citrate synthase) before and after 4-hour preservation was not different between groups in both study stages (p > 0.05). Low-risk livers that could have been used clinically (n = 8) had lower complex II-III activities after 4-hour perfusion, compared with high-risk livers (73 nmol/mg/min vs. 113 nmol/mg/min, p = 0.01). Parenchymal pO2 was consistently lower than perfusate pO2 (p ≤ 0.001), stabilised in 28 minutes compared to 3 minutes in perfusate (p = 0.003), and decreased faster upon oxygen cessation (75 vs. 36 minutes, p = 0.003).

CONCLUSIONS

Actively oxygenated and air-equilibrated end-ischaemic HMP did not induce oxidative damage of aconitase, and respiratory chain complexes remained intact. Mitochondria likely respond to variable perfusate oxygen levels by adapting their respiratory function during end-ischaemic HMP. Complex II-III activities should be further investigated as viability biomarkers.

Early Graft Dysfunction Following Kidney Transplantation: Can Thermographic Imaging Play a Predictive Role?

The shortage of organs and the growing need for them over recent years have led to the adoption of less stringent donor acceptance criteria, resulting in the approval of marginal organs for transplant, especially from elderly donors. This implies a higher risk of graft dysfunction, a higher frequency of immunological and vascular complications, and shorter graft survival. Several strategies have been implemented in clinical practice to assess graft quality and suitability for transplantation. We have started to test the prospective intraoperative use of thermo-vision cameras during graft reperfusion. Images were acquired using the FLIR One Pro thermo-vision camera for android devices. We hypothesized that thermal images would give a better perspective about the quality of arterial perfusion and graft revascularization of the renal cortex. Thermo-vision cameras provide an easy-to-use, noninvasive, cost-effective tool for the global assessment of kidney graft cortical microcirculation in the immediate post-reperfusion period, providing additional data on the immediate viability and function of a graft.

Pharmaceutical design and development of perfluorocarbon nanocolloids for oxygen delivery in regenerative medicine

Perfluorocarbons (PFCs) have been investigated as oxygen carriers for several decades in varied biomedical applications. PFCs are chemically and biologically inert, temperature and storage stable, pose low to no infectious risk, can be commercially manufactured, and have well established gas transport properties. In this review, we highlight design and development strategies for their successful application in regenerative medicine, transplantation and organ preservation. Effective tissue preservation strategies are key to improving outcomes of extremity salvage and organ transplantation. Maintaining tissue integrity requires adequate oxygenation to support aerobic metabolism. The use of whole blood for oxygen delivery is fraught with limitations of poor shelf stability, infectious risk, religious exclusions and product shortages. Other agents also face clinical challenges in their implementation. As a solution, we discuss new ways of designing and developing PFC-based artificial oxygen carriers by implementing modern pharmaceutical quality by design and scale up manufacturing methodologies.

Functional survival of rat pituitary gland in hypothermic storage for pituitary transplantation

PURPOSE

Deteriorated pituitary function can lead to serious complications that might need lifelong hormone replacement therapy. However, long-term hormone administration can have significant adverse effects. Thus, it would be more desirable to restore pituitary function by pituitary transplantation. In this study, we investigated functional preservation of extracted pituitary gland in special preservation solution under hypothermic condition for pituitary transplantation.

METHODS

We obtained nineteen pituitary glands from 250-300 g male Sprague-Dawley rats via parapharyngeal approach. These extracted glands were divided into three pieces and stored in histidine-tryptophan-ketoglutarate (HTK) solution at 4 °C and compared to their corresponding glands stored in phosphate buffer saline (PBS). Light and electron microscopic examinations were performed to identify morphological changes of pituitary gland at 0,3, and 7 days after storage. TUNEL assay to confirm cell viability, and adenosine-triphosphate (ATP) concentration were also serially examined.

RESULTS

Tissue architecture and cellular viability of specimens preserved in HTK solution for 3 days were considerably maintained and similar to those in normal pituitary gland (0 day specimen). In contrast, specimens stored in PBS were markedly destroyed after 3 days of storage. After 7 days of storage, significant degeneration occurred in tissues stored in both HTK and PBS. However, tissue architecture was preserved more in specimens stored in HTK solution than those stored in PBS. ATP concentration decreased more rapidly in specimens stored in PBS solution, but there was no statistical significance (p= 0.055).

CONCLUSIONS

Extracted rat pituitary gland supplemented with special preservation solution could be preserved for 3 days under hypothermic condition.

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.

Hypothermic Machine Perfusion Versus Static Cold Storage in Deceased Donor Kidney Transplantation: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Static cold storage (SCS) and hypothermic machine perfusion (HMP) are two primary options for renal allograft preservation. Compared with SCS, HMP decreased the incidence of delayed graft function (DGF) and protected graft function. However, more evidence is still needed to prove the advantages of the HMP. In this study, the outcomes of kidney grafts from the two preservation methods were compared by conducting a systematic review and meta-analysis. Randomized controlled trials (RCTs) comparing the effect of hypothermic machine perfusion and static cold storage in deceased donor kidney transplantation were identified through searches of the MEDLINE, EMBASE, and Cochrane databases between January 1, 1980 and December 30, 2017. The primary endpoints were delayed graft function and graft survival. Secondary endpoints included primary non-function (PNF), graft renal function, duration of DGF, acute rejection, postoperative hospital stay and patient survival. Summary effects were calculated as risk ratio (RR) with 95% confidence interval (CI) or mean difference (MD) with 95% confidence intervals (CI). A total of 13 RCTs were included, including 2048 kidney transplant recipients. The results indicated that compared with SCS, HMP decreased the incidence of DGF (RR 0.78, 95% CI 0.69-0.87, P < 0.0001), and improved the graft survival at 3 years (RR 1.06, 95% CI 1.02-1.11, P = 0.009). There was no significant difference in other endpoints. HMP might be a more desirable method of preservation for kidney grafts. The long-term outcomes of kidney allografts stored by hypothermic machine perfusion still need to be further investigated.

Organ donation: the reality of an intensive care unit in Portugal

OBJECTIVE

To clinically and demographically characterize potential organ donors admitted to a general intensive care unit and analyze data on donated organs.

METHODS

This retrospective study was conducted from 2010 to 2015 and analyzed demographic and clinical variables and the number of harvested organs and tissues.

RESULTS

A total of 92 potential organ donors were identified, of whom eight were non-effective donors and 84 were effective donors (59.5% were expanded criteria donors). The mean age of the potential donors was 60.7 years, and the majority were men. Hemorrhagic stroke accounted for 55.4% of brain deaths. The most common blood type among the donors was A Rh+ (43.5%), and the most common comorbidity was arterial hypertension (43.3%). The most frequently collected organs were the kidneys (84.5%) and liver (66.7%). The average number of organs harvested per donor was 2.8, and this ratio was smaller for donors with expanded criteria compared to other donors.

CONCLUSION

In most cases, potential organ donors died of brain death, were older than middle age, were male and were victims of a hemorrhagic stroke. The majority of the donors were expanded criteria donors and donated an average of two to three organs. The organs donated most frequently were the kidneys and liver.

Current insights into extracorporeal perfusion of free tissue flaps and extremities: a systematic review and data synthesis

BACKGROUND

Extracorporeal perfusion is a promising new technique for prolonged preservation of free flaps and extremities; however, uncertainties on perfusion settings and efficacy still exist. No overview of literature is currently available. This review systematically appraised available evidence comparing extracorporeal perfusion to static storage.

MATERIALS AND METHODS

An electronic systematic search was performed on June 12, 2016, in MEDLINE and EMBASE. Articles were included when evaluating the effect of extracorporeal perfusion of free flaps or extremities compared to that of a control group. Two independent researchers conducted the selection process, critical appraisal, and data extraction.

RESULTS

Of 3485 articles screened, 18 articles were included for further analyzation. One article studied discarded human tissue; others were studies conducted on rats, pigs, or dogs. Perfusion periods varied from 1 h to 10 d; eight articles also described replantation. Risk of bias was generally scored high; none of the articles was excluded based on these scores. Tissue vitality showed overall better results in the perfused groups, more pronounced when perfusing over 6 h. The development of edema was a broadly described side effect of perfusion.

CONCLUSIONS

Although tissue vitality outcomes seem to favor extracorporeal perfusion, this is difficult to objectify because of large heterogeneity and poor quality of the available evidence. Future research should focus on validating outcome measures, edema prevention, perfusion settings, and maximum perfusion time for safe replantation and be preferably performed on large animals to increase translation to clinical settings.

Extra-corporeal normothermic machine perfusion of the porcine kidney: working towards future utilization in Australasia

BACKGROUND

The ongoing supply-demand gap with respect to donor kidneys for transplantation necessitates the increased use of higher kidney donor profile index and/or donation after circulatory death (DCD) kidneys. Machine perfusion (MP) preservation has become increasingly popular as a means to preserve such organs. Human data regarding normothermic kidney MP (NMP) is in its infancy, and such a system has not been established in the Australasian clinical setting.

METHODS

Modified cardio-pulmonary bypass technology was utilized to develop a viable NMP kidney perfusion system using a porcine DCD model. System development and optimization occurred in two stages, with system components added in each experiment to identify optimal perfusion conditions.

RESULTS

Device functionality was demonstrated by the successful perfusion of and urine production by, eight porcine kidneys. Urine production diminished in the presence of colloid in the perfusate. Pressure-controlled (compared with flow-controlled) perfusion is preferable as a safe perfusion pressure range can be maintained. More physiologic perfusion conditions are achieved if oxygenation is provided by an oxygen/carbon dioxide mixture compared to 100% oxygen.

CONCLUSION

A viable and reproducible NMP system was established and tested in porcine kidneys, which was able to simulate graft function extra-corporeally. Further work is required to identify the most optimal perfusion conditions. Prior to its utilization in clinical transplantation, the system should be tested in non-transplanted human kidneys.

A systematic review and meta-analysis of cold in situ perfusion and preservation of the hepatic allograft: Working toward a unified approach

The efficacy of cold in situ perfusion and static storage of the liver is a possible determinant of transplantation outcomes. The aim of this study was to determine whether there is evidence to substantiate a preference for a particular perfusion route (aortic or dual) or perfusion/preservation solution in donation after brain death (DBD) liver transplantation. The Embase, MEDLINE, and Cochrane databases were used (1980-2017). Random effects modeling was used to estimate effects on transplantation outcomes based on (1) aortic or dual in situ perfusion and (2) the use of University of Wisconsin (UW), histidine tryptophan ketoglutarate (HTK), Celsior, and/or Institut Georges Lopez-1 (IGL-1) solutions for perfusion/preservation. A total of 22 articles were included (2294 liver transplants). The quality of evidence ranged from very low to moderate Grading of Recommendations, Assessment, Development and Evaluations score. Meta-analyses were conducted for 14 eligible studies. Although there was no difference in the primary nonfunction (PNF) rate, a higher peak alanine aminotransferase (ALT) was recorded in dual compared with aortic-only UW-perfused livers (standardized mean difference, 0.24; 95% confidence interval, 0.01-0.47); a back-table portal venous flush was undertaken in the majority of aortic-only perfused livers. There were no relevant differences in peak enzymes, PNF, thrombotic graft loss, biliary complications, or 1-year graft survival in comparisons between dual-perfused livers using UW, HTK, Celsior, or IGL-1. In conclusion, there is no significant evidence that aortic-only perfusion of the DBD liver compromises transplantation outcomes, and it may be favored because of its simplicity. However, there is currently insufficient evidence to advocate for the use of any particular perfusion/preservation fluid over the others. Liver Transplantation 23 1615-1627 2017 AASLD.

Successful Dual Kidney Transplantation After Hypothermic Oxygenated Perfusion of Discarded Human Kidneys

BACKGROUND The recovery of discarded human kidneys has increased in recent years and impels to use of unconventional organ preservation strategies that improve graft function. We report the first case of human kidneys histologically discarded and transplanted after hypothermic oxygenated perfusion (HOPE). CASE REPORT Marginal kidneys from a 78-year-old woman with brain death were declined by Italian transplant centers due to biopsy score (right kidney: 6; left kidney: 7). We recovered and preserved both kidneys through HOPE and we revaluated their use for transplantation by means of perfusion parameters. The right kidney was perfused for 1 h 20 min and the left kidney for 2 h 30 min. During organ perfusion, the renal flow increased progressively. We observed an increase of 34% for the left kidney (median flow 52 ml/min) and 50% for the right kidney (median flow 24 ml/min). Both kidneys had low perfusate's lactate levels. We used perfusion parameters as important determinants of the organ discard. Based on our previous organ perfusion experience, the increase of renal flow and the low level of lactate following 1 h of HOPE lead us to declare both kidneys as appropriate for dual kidney transplantation (DKT). No complications were reported during the transplant and in the post-transplant hospital stay. The recipient had immediate graft function and serum creatinine value of 0.95 mg/dL at 3 months post-transplant. CONCLUSIONS HOPE provides added information in the organ selection process and may improve graft quality of marginal kidneys.