Perfusion preservation maintains myocardial ATP levels and reduces apoptosis in an ex vivo rat heart transplantation model

Metabolic and transcriptomic insights into temperature controlled hypothermic preservation of human donor hearts

BACKGROUND

Heart transplantation (HT) is the gold standard for end-stage heart disease. Donor heart preservation is an important factor that influences post-transplant success. Recently, temperature-controlled storage has demonstrated reduced primary graft dysfunction compared to standard cold storage though mechanisms are poorly understood. We hypothesized that alterations in gene expression and metabolomics offer insight into improved outcomes observed with temperature-controlled storage.

METHODS

We conducted a comprehensive study to investigate the metabolic and transcriptomic responses of donor hearts preserved for 6 hours using a temperature-controlled hypothermic preservation (TCHP) system compared to conventional static cold storage (SCS). Metabolic assessments were carried out using high-resolution 1H and 31P nuclear magnetic resonance (NMR), and liquid chromatography/mass spectrometry (LC-MS) analysis on tissues obtained from various cardiac regions. Lactate, alanine, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), nicotinamide adenine dinucleotide (NAD), reduced nicotinamide adenine dinucleotide (NADH), phosphocreatine, and inorganic phosphate were measured, and metabolite ratios were calculated. Transcriptomic profiling was conducted using high throughput RNA sequencing followed by bioinformatic analysis to explore gene expression changes associated with different preservation methods.

RESULTS

Metabolic analyses revealed largely similar profiles between hearts preserved with TCHP and SCS. Energy metabolite ratios were comparable between preservation methods. Transcriptomic analysis unveiled a high correlation between preservation methods but also showed differential gene expression in energy metabolism and inflammation/immune-related pathways.

CONCLUSIONS

Our study demonstrates that TCHP maintains similar high-energy phosphate reserves to SCS but leads to alterations in gene expression of several metabolic and immunomodulatory pathways. These findings may offer important insight into reduced primary graft dysfunction observed in TCHP- hearts.

CPA toxicity screening of cryoprotective solutions in rat hearts

In clinical practice, donor hearts are transported on ice prior to transplant and discarded if cold ischemia time exceeds ∼5 h. Methods to extend these preservation times are critically needed, and ideally, this storage time would extend indefinitely, enabling improved donor-to-patient matching, organ utilization, and immune tolerance induction protocols. Previously, we demonstrated successful vitrification and rewarming of whole rat hearts without ice formation by perfusion-loading a cryoprotective agent (CPA) solution prior to vitrification. However, these hearts did not recover any beating even in controls with CPA loading/unloading alone, which points to the chemical toxicity of the cryoprotective solution (VS55 in Euro-Collins carrier solution) as the likely culprit. To address this, we compared the toxicity of another established CPA cocktail (VEG) to VS55 using ex situ rat heart perfusion. The CPA exposure time was 150 min, and the normothermic assessment time was 60 min. Using Celsior as the carrier, we observed partial recovery of function (atria-only beating) for both VS55 and VEG. Upon further analysis, we found that the VEG CPA cocktail resulted in 50 % lower LDH release than VS55 (N = 4, p = 0.017), suggesting VEG has lower toxicity than VS55. Celsior was a better carrier solution than alternatives such as UW, as CPA + Celsior-treated hearts spent less time in cardiac arrest (N = 4, p = 0.029). While we showed substantial improvement in cardiac function after exposure to vitrifiable concentrations of CPA by improving both the CPA and carrier solution formulation, further improvements will be required before we achieve healthy cryopreserved organs for transplant.

Intracellular ATP Concentration and Implication for Cellular Evolution

Crystalline lens and striated muscle exist at opposite ends of the metabolic spectrum. Lens is a metabolically quiescent tissue, whereas striated muscle is a mechanically dynamic tissue with high-energy requirements, yet both tissues contain millimolar levels of ATP (>2.3 mM), far exceeding their underlying metabolic needs. We explored intracellular concentrations of ATP across multiple cells, tissues, species, and domains to provide context for interpreting lens/striated muscle data. Our database revealed that high intracellular ATP concentrations are ubiquitous across diverse life forms including species existing from the Precambrian Era, suggesting an ancient highly conserved role for ATP, independent of its widely accepted view as primarily "metabolic currency". Our findings reinforce suggestions that the primordial function of ATP was non-metabolic in nature, serving instead to prevent protein aggregation.

Cardiac Graft Assessment in the Era of Machine Perfusion: Current and Future Biomarkers

Heart transplantation remains the treatment of reference for patients experiencing end‐stage heart failure; unfortunately, graft availability through conventional donation after brain death is insufficient to meet the demand. Use of extended‐criteria donors or donation after circulatory death has emerged to increase organ availability; however, clinical protocols require optimization to limit or prevent damage in hearts possessing greater susceptibility to injury than conventional grafts. The emergence of cardiac ex situ machine perfusion not only facilitates the use of extended‐criteria donor and donation after circulatory death hearts through the avoidance of potentially damaging ischemia during graft storage and transport, it also opens the door to multiple opportunities for more sensitive monitoring of graft quality. With this review, we aim to bring together the current knowledge of biomarkers that hold particular promise for cardiac graft evaluation to improve precision and reliability in the identification of hearts for transplantation, thereby facilitating the safe increase in graft availability. Information about the utility of potential biomarkers was categorized into 5 themes: (1) functional, (2) metabolic, (3) hormone/prohormone, (4) cellular damage/death, and (5) inflammatory markers. Several promising biomarkers are identified, and recommendations for potential improvements to current clinical protocols are provided.

The Role of Metabolomics in Current Concepts of Organ Preservation

In solid organ transplantation (Tx), both survival rates and quality of life have improved dramatically over the last few decades. Each year, the number of people on the wait list continues to increase, widening the gap between organ supply and demand. Therefore, the use of extended criteria donor grafts is growing, despite higher susceptibility to ischemia-reperfusion injury (IRI) and consecutive inferior Tx outcomes. Thus, tools to characterize organ quality prior to Tx are crucial components for Tx success. Innovative techniques of metabolic profiling revealed key pathways and mechanisms involved in IRI occurring during organ preservation. Although large-scale trials are needed, metabolomics appears to be a promising tool to characterize potential biomarkers, for the assessment of graft quality before Tx and evaluate graft-related outcomes. In this comprehensive review, we summarize the currently available literature on the use of metabolomics in solid organ Tx, with a special focus on metabolic profiling during graft preservation to assess organ quality prior to Tx.

Effect of Shenfu Injection on Isolated Empty Beating Hearts from Miniature Pigs

OBJECTIVE

To investigate the effect of Shenfu (SF) injection on donor heart preservation.

METHODS

Twelve pigs were randomly divided into SF group (n=6) and control group (n=6). After eight hours of perfusion, the differences in hemoglobin, the expression of Bcl-2 and BAX, and changes in the myocardial ultrastructure were compared to illustrate the effects of SF injection in heart preservation.

RESULTS

The differences in free hemoglobin between the SF group and the control group were statistically significant (P=0.001), and there was significant interaction of groups with times (P=0.019), but the perfusion time may not be associated with the hemoglobin concentration (P=0.616). According to Western blotting analysis, the expression of Bcl-2 was higher in the SF group than in the control group, while the expression of BAX was not different between the two groups. As to ultrastructural changes, both groups exhibited mitochondrial swelling and myofilament lysis, but the degree of damage in the SF group was smaller.

CONCLUSION

Our study suggests that the application of SF injection for heart preservation may protect against cardiomyocytes and erythrocytes apoptosis, and Bcl-2 protein may play a role in these physiological processes.

Cardiac donation after circulatory death

PURPOSE OF REVIEW

Increasing number of patients with end-stage heart failure and those with improved survivorship from selective utilization of implantable mechanical circulatory support devices have added further burden and complexity to the transplant waitlist and on the rate-limiting availability of donor hearts from the standard pathway of donation after brain death. Unlike this conventional route, the increasing clinical use of donation after circulatory death (DCD) donor hearts necessitates a closer understanding of the logistics involved in the DCD process as well as of the risks associated with the unique pathophysiological consequences in this setting.

RECENT FINDINGS

Notwithstanding a higher incidence of delayed graft function, the clinical utilization of DCD hearts for cardiac transplantation over the past five years has demonstrated this to be a well-tolerated and strategic alternative with excellent medium-term clinical outcomes.

SUMMARY

The uptake of DCD heart transplantation remains selective and currently confined to Australia, the United Kingdom, Belgium, and more recently the USA. A more significant adoption will only come about through: a concerted effort to resolve the ethical and clinical controversies; a better understanding of postconditioning strategies; continued resolve to reduce the obligatory period of warm ischemia; and from better extracorporeal platforms that permit functional viability assessment of the DCD donor heart.

Myocardial Functional Decline During Prolonged Ex Situ Heart Perfusion

BACKGROUND

Myocardial function declines in a time-dependent fashion during ex situ heart perfusion. Cell death and metabolic alterations may contribute to this phenomenon, limiting the safe perfusion period and the potential of ex situ heart perfusion to expand the donor pool. Our aim was to investigate the etiology of myocardial functional decline in ex situ perfused hearts.

METHODS

Cardiac function, apoptosis, effectors and markers of cell death, and metabolic function were assessed in healthy pig hearts perfused for 12 hours. These hearts were perfused in nonworking mode or working mode.

RESULTS

Cardiac function declined during ex situ heart perfusion regardless of perfusion mode but was significantly better preserved in the hearts perfused in working mode (11-hour cardiac index/1-hour cardiac index: working mode, 33%; nonworking mode, 10%; p = 0.025). The rate of apoptosis was higher in the ex situ perfused hearts compared with in vivo samples (apoptotic cells: in vivo, 0.13%; working mode, 0.54%; nonworking mode, 0.88%; p < 0.001), but the absolute values were low and out of proportion to the decline in function in either group. Myocardial dysfunction at the end of the perfusion interval was partially rescued by delivery of a pyruvate bolus.

CONCLUSIONS

A significant decline in myocardial function occurs over time in hearts preserved ex situ that is out of proportion to the magnitude of myocyte cell death present in dysfunctional hearts. Alterations in myocardial substrate utilization during prolonged ex situ heart perfusion may contribute to this phenomenon and represent an avenue to improve donor heart preservation.

(13)C glucose labelling studies using 2D NMR are a useful tool for determining ex vivo whole organ metabolism during hypothermic machine perfusion of kidneys

Background

The aim of this study is to determine the feasibility of using nuclear magnetic resonance (NMR) tracer studies (¹³C-enriched glucose) to detect ex vivo de novo metabolism in the perfusion fluid and cortical tissue of porcine kidneys during hypothermic machine perfusion (HMP).

Methods

Porcine kidneys (n = 6) were subjected to 24 h of HMP using the Organ Recovery Systems LifePort Kidney perfusion device. Glucose, uniformly enriched with the stable isotope ¹³C ([U-¹³C] glucose), was incorporated into KPS-1-like perfusion fluid at a concentration of 10 mM. Analysis of perfusate was performed using both 1D ¹H and 2D ¹H,¹³C heteronuclear single quantum coherence (HSQC) NMR spectroscopy. The metabolic activity was then studied by quantifying the proportion of key metabolites containing ¹³C in both perfusate and tissue samples.

Results

There was significant enrichment of ¹³C in a number of central metabolites present in both the perfusate and tissue extracts and was most pronounced for lactate and alanine. The total amount of enriched lactate (per sample) in perfusion fluid increased during HMP (31.1 ± 12.2 nmol at 6 h vs 93.4 ± 25.6 nmol at 24 h p < 0.01). The total amount of enriched alanine increased in a similar fashion (1.73 ± 0.89 nmol at 6 h vs 6.80 ± 2.56 nmol at 24 h p < 0.05). In addition, small amounts of enriched acetate and glutamic acid were evident in some samples.

Conclusions

This study conclusively demonstrates that de novo metabolism occurs during HMP and highlights active metabolic pathways in this hypothermic, hypoxic environment. Whilst the majority of the ¹³C-enriched glucose is metabolised into glycolytic endpoint metabolites such as lactate, the presence of non-glycolytic pathway derivatives suggests that metabolism during HMP is more complex than previously thought. Isotopic labelled ex vivo organ perfusion studies using 2D NMR are feasible and informative.

Hypothermic machine perfusion increases A20 expression which protects renal cells against ischemia/reperfusion injury by suppressing inflammation, apoptosis and necroptosis

There is an urgent need to improve the quality of donor organs obtained after cardiac death. In the present study, we examined the potential mechanisms through which A20 protects renal cells against ischemia/reperfusion injury (IRI) following either hypothermic machine perfusion (HMP) or static cold storage (CS) of the kidneys in a rabbit model. The expression of markers of apoptosis, necroptosis and inflammation in frozen kidney tissues were detected by western blot analysis, RT-qPCR and ELISA. Compared with the CS group, A20 expression was significantly higher in the tissue from the HMP group (P<0.01). By contrast, the expression of nuclear factor-κB (NF-κB) and tumor necrosis factor-α (TNF-α) was significantly lower in HMP group (P<0.01), whereas IκBα expression was significantly higher (P<0.01). The expression of apoptosis signal-regulating kinase 1 (ASK1), phosphorylated (p-)c-Jun N-terminal kinase (JNK) and activated caspase-3 in the HMP group was significantly downregulated compared with that in the CS group (all P<0.01). In addition, A20 inhibited receptor-interacting protein kinase 3 (RIPK3)-mediated necroptosis in the kidney. RIPK3 expression in the HMP group was significantly lower than that in the CS group (P<0.01), although the levels in both groups were higher than those in the sham group (P<0.01). Based on these findings, we propose a novel mechanism underlying the anti-apoptotic effect of A20 in renal cells in which A20 binds to ASK1 and promotes the degradation of ASK1 leading to the suppression of JNK activation and eventually, to the blockade of apoptosis. Thus, HMP reduces inflammation, apoptosis and necroptosis by upregulating the expression of A20; this mechanism may be responsible for protecting the kidney against IRI.

Successful transplantation in canines after long-term coronary sinus machine perfusion preservation of donor hearts

BACKGROUND

Machine perfusion is a promising strategy for donor heart preservation, but delivery of perfusate through the aorta may be limited by aortic valve incompetence. We hypothesized that retrograde machine perfusion preservation through the coronary sinus avoided this issue and allowed for recovery of donor hearts after long-term storage.

METHODS

Canine hearts were procured after arrest with 1 liter University of Wisconsin Machine Perfusion Solution (UWMPS) and preserved for 14 hours by static hypothermic storage (Static group, n = 5) or retrograde machine perfusion through the coronary sinus (RP group, n = 5). Myocardial oxygen consumption (MVo2) and lactate were monitored in perfused hearts. Hearts were implanted and reperfused for 6 hours. The pre-load recruitable stroke work was determined as a measure of myocardial function. Cardiac enzyme release was quantified. Cell death was evaluated by TUNEL (terminal deoxynucleotidyltransferase-mediated deoxy uridine triphosphate nick-end label).

RESULTS

MVo2 decreased initially then stabilized. Lactate accumulation was low in RP hearts. All RP hearts separated from cardiopulmonary bypass. All Static hearts required a return to bypass (p < .05). Pre-load recruitable stroke work in RP hearts was increased (55 ± 7 mm Hg) compared with Static (20 ± 11 mm Hg, p < .05) and did not differ from baseline values. Creatine kinase release was greater in Static group hearts (102 ± 16 IU/liter/g) than in RP hearts (51 ± 8 IU/liter/g, p < .05). The fraction of TUNEL-positive cells was higher in the Static group, but this difference was not significant.

CONCLUSIONS

Retrograde machine perfusion can preserve donor hearts for long intervals. Cardiac function after implantation suggested excellent myocardial protection. Retrograde machine perfusion appears promising for extending the donor ischemic interval and improving results of heart transplantation.

Hypothermic continuous machine perfusion enables preservation of energy charge and functional recovery of heart grafts in an ex vivo model of donation following circulatory death

OBJECTIVES

Cardiac transplantation using hearts from donors after circulatory death (DCD) is critically limited by the unavoidable warm ischaemia and its related unpredictable graft function. Inasmuch as hypothermic machine perfusion (MP) has been shown to improve heart preservation, we hypothesized that MP could enable the use of DCD hearts for transplantation.

METHODS

We recovered 16 pig hearts following anoxia-induced cardiac arrest and cardioplegia. Grafts were randomly assigned to two different groups of 4-h preservation using either static cold storage (CS) or MP (Modified LifePort© System, Organ Recovery Systems©, Itasca, Il). After preservation, the grafts were reperfused ex vivo using the Langendorff method for 60 min. Energetic charge was quantified at baseline, post-preservation and post-reperfusion by measuring lactate and high-energy phosphate levels. Left ventricular contractility parameters were assessed both in vivo prior to ischaemia and ex vivo during reperfusion.

RESULTS

Following preservation, the hearts that were preserved using CS exhibited higher lactate levels (57.1 ± 23.7 vs 21.4 ± 12.2 µmol/g; P < 0.001), increased adenosine monophosphate/adenosine triphosphate ratio (0.53 ± 0.25 vs 0.11 ± 0.11; P < 0.001) and lower phosphocreatine/creatine ratio (9.7 ± 5.3 vs 25.2 ± 11; P < 0.001) in comparison with the MP hearts. Coronary flow was similar in both groups during reperfusion (107 ± 9 vs 125 ± 9 ml/100 g/min heart; P = ns). Contractility decreased in the CS group, yet remained well preserved in the MP group.

CONCLUSION

MP preservation of DCD hearts results in improved preservation of the energy and improved functional recovery of heart grafts compared with CS.

Hypothermic Machine Perfusion Decreases Renal Cell Apoptosis During Ischemia/Reperfusion Injury via the Ezrin/AKT Pathway

This study aimed to explore the potential mechanisms of hypothermic machine perfusion (HMP)-a more efficient way to preserve kidneys from donors after cardiac death than static cold storage (CS), then to provide the basis for further improving donor quality. Twelve healthy male New Zealand rabbits (12 weeks old, weighing 3.0 ± 0.3 kg) were randomly divided into two groups: the HMP group and CS group (n = 6). Rabbits' left kidney was subjected to 35 min of warm ischemic time by clamping the left renal pedicle and 1 h of reperfusion. The kidneys were then hypothermically (4-8°C) preserved in vivo for 4 h with HCA-II solution using HMP or CS methods. Then rabbits underwent a right nephrectomy and the kidney tissues were collected after 24 h of reperfusion. TUNEL staining was performed on paraffin sections to detect apoptosis, and the expressions of cleaved caspase-3, ezrin, AKT, and p-AKT in frozen kidney tissues were detected by Western blotting. The ezrin expression was further confirmed by immunohistochemistry analysis. The apoptosis rate and expression of cleaved caspase-3 in the HMP group were significantly lower than the CS group (P < 0.001 and P = 0.002), meanwhile the expression of cleaved caspase-3 in the HMP and CS groups was significantly increased compared with the normal group (P = 0.035 and P < 0.001), and the expression of ezrin and p-AKT in the HMP group was significantly higher than the CS group (P = 0.005, 0.014). HMP decreased the renal cell apoptosis rate during ischemia/reperfusion injury via the ezrin/AKT pathway.

Hypothermic continuous machine perfusion improves metabolic preservation and functional recovery in heart grafts

The number of heart transplants is decreasing due to organ shortage, yet the donor pool could be enlarged by improving graft preservation. Hypothermic machine perfusion (MP) has been shown to improve kidney, liver, or lung graft preservation. Sixteen pig hearts were recovered following cardioplegia and randomized to two different groups of 4-hour preservation using either static cold storage (CS) or MP (Modified LifePort© System, Organ Recovery Systems, Itasca, Il). The grafts then underwent reperfusion on a Langendorff for 60 min. Energetic metabolism was quantified at baseline, postpreservation, and postreperfusion by measuring lactate and high-energy phosphates. The contractility index (CI) was assessed both in vivo prior to cardioplegia and during reperfusion. Following reperfusion, the hearts preserved using CS exhibited higher lactate levels (56.63 ± 23.57 vs. 11.25 ± 3.92 μmol/g; P < 0.001), increased adenosine monophosphate/adenosine triphosphate (AMP/ATP) ratio (0.4 ± 0.23 vs. 0.04 ± 0.04; P < 0.001), and lower phosphocreatine/creatine (PCr/Cr) ratio (33.5 ± 12.6 vs. 55.3 ± 5.8; P <0.001). Coronary flow was similar in both groups during reperfusion (107 ± 9 vs. 125 + /-9 ml/100 g/min heart; P = ns). CI decreased in the CS group, yet being well-preserved in the MP group. Compared with CS, MP resulted in improved preservation of the energy state and more successful functional recovery of heart graft.

Pyruvate kinase isoenzyme M2 expression correlates with survival of cardiomyocytes after allogeneic rat heterotopic heart transplantation

The aim of our study was to assess correlations between PKM2 and the survival of cardiomyocytes after heart transplantation in rat. The PKM2, Bcl-xl, active caspase-3 proteins were detected by western blot, and PKM2 was testified by immunohistochemistry and immunofluorescence. At the same time, active caspase-3, α-actinin, VCAM-1, and CD4 were detected by immunofluorescence. Compared with rare expression in syngeneic Lewis rat hearts, the PKM2 protein level in allogeneic hearts was detected at various survival times after transplantation, which prominently expressed on day five postoperatively. In addition, we examined the expression of Bcl-xl and active caspase-3 in allogeneic hearts, which has a similar expression pattern with PKM2. Immunohistochemical and immunofluorescent methods displayed that PKM2 was widely expressed in cardiac tissue, and active caspase-3 was also expressed in cardiomyocytes. However, the PKM2 was not expressed in T cells and other immune response cells. These results suggested that PKM2 may regulate the survival of cardiomyocytes in acute rejection after heart transplantation in rat.

Preservation of donor hearts using hypothermic oxygenated perfusion

BACKGROUND

Hypothermic machine perfusion of donor hearts enables continuous aerobic metabolism and washout of toxic metabolic byproducts. We evaluated the effect of machine perfusion on cardiac myocyte integrity in hearts preserved for 4 h in a novel device that provides pulsatile oxygenated hypothermic perfusion (Paragonix Sherpa Perfusion™ Cardiac Transport System).

MATERIAL AND METHODS

Pig hearts were harvested and stored in Celsior® solution for 4 h using either conventional cold storage on ice (4-h CS, n=6) or the Sherpa device (4-h pulsatile perfusion (PP), n=6). After cold preservation, hearts were evaluated using a non-working heart Langendorff system. Controls (n=3) were reperfused immediately after organ harvest. Biopsies were taken from the apex of the left ventricle before storage, after storage, and after reperfusion to measure ATP content and endothelin-1 in the tissue. Ultrastructural analysis using electron microscopy was performed.

RESULTS

Four-hour CS, 4-h PP, and control group did not show any significant differences in systolic or diastolic function (+dP/dt, -dP/dt, EDP). Four-hour PP hearts showed significantly more weight gain than 4-h CS after preservation, which shows that machine perfusion led to myocardial edema. Four-hour CS led to higher endothelin-1 levels after preservation, suggesting more endothelial dysfunction compared to 4-h PP. Electron microscopy revealed endothelial cell rupture and damaged muscle fibers in the 4-h CS group after reperfusion, but the cell structures were preserved in the 4-h PP group.

CONCLUSIONS

Hypothermic pulsatile perfusion of donor hearts leads to a better-preserved cell structure compared to the conventional cold storage method. This may lead to less risk of primary graft failure after orthotopic heart transplantation.

Recovery of donor hearts after circulatory death with normothermic extracorporeal machine perfusion

OBJECTIVES

A severe donor organ shortage leads to the death of a substantial number of patients who are listed for transplantation. The use of hearts from donors after circulatory death could significantly expand the donor organ pool, but due to concerns about their viability, these are currently not used for transplantation. We propose short-term ex vivo normothermic machine perfusion (MP) to improve the viability of these ischaemic donor hearts.

METHODS

Hearts from male Lewis rats were subjected to 25 min of global in situ warm ischaemia (WI) (37°C), explanted, reconditioned for 60 min with normothermic (37°C) MP with diluted autologous blood and then stored for 4 h at 0-4°C in Custodiol cold preservation solution. Fresh and ischaemic hearts stored for 4 h in Custodiol were used as controls. Graft function was assessed in a blood-perfused Langendorff circuit.

RESULTS

During reconditioning, both the electrical activity and contractility of the ischaemic hearts recovered rapidly. Throughout the Langendorff reperfusion, the reconditioned ischaemic hearts had a higher average heart rate and better contractility compared with untreated ischaemic controls. Moreover, the reconditioned ischaemic hearts had higher tissue adenosine triphosphate levels and a trend towards improved tissue redox state. Perfusate levels of troponin T, creatine kinase and lactate dehydrogenase were not significantly lower than those of untreated ischaemic controls. The micro- and macroscopic appearance of the reconditioned ischaemic hearts were improved compared with ischaemic controls, but in both groups myocardial damage and oedema were evident.

CONCLUSIONS

Our results indicate that functional recovery from global WI is possible during short-term ex vivo reperfusion, allowing subsequent cold storage without compromising organ viability. We expect that once refined and validated, this approach may enable safe transplantation of hearts obtained from donation after circulatory death.

Metabolic characteristics of human hearts preserved for 12 hours by static storage, antegrade perfusion, or retrograde coronary sinus perfusion

OBJECTIVE

Machine perfusion of donor hearts is a promising strategy to increase the donor pool. Antegrade perfusion is effective but can lead to aortic valve incompetence and nonnutrient flow. Experience with retrograde coronary sinus perfusion of donor hearts has been limited. We tested the hypothesis that retrograde perfusion could support myocardial metabolism over an extended donor ischemic interval.

METHODS

Human hearts from donors that were rejected or not offered for transplantation were preserved for 12 hours in University of Wisconsin Machine Perfusion Solution by: (1) static hypothermic storage; (2) hypothermic antegrade machine perfusion; or (3) hypothermic retrograde machine perfusion. Myocardial oxygen consumption (MVO2), and lactate accumulation were measured. Ventricular tissue was collected for proton and phosphorus 31 magnetic resonance spectroscopy (MRS) to evaluate the metabolic state of the myocardium. Myocardial water content was determined at the end of the experiment.

RESULTS

Stable perfusion parameters were maintained throughout the perfusion period with both perfusion techniques. Lactate/alanine ratios were lower in perfused hearts compared with static hearts (P<.001). Lactate accumulation (antegrade 2.0±0.7 mM, retrograde 1.7±0.1 mM) and MVO2 (antegrade 0.25±0.2 mL, retrograde 0.26±0.3 mL O2/min/100 g) were similar in machine-perfused groups. High-energy phosphates were better preserved in both perfused groups (P<.05). Left ventricular myocardial water content was increased in retrograde perfused hearts (80.2±0.8%) compared with both antegrade perfused hearts (76.6±0.8%, P=.02) and static storage hearts (76.7±1%, P=.02).

CONCLUSIONS

Machine perfusion by either the antegrade or the retrograde technique can support myocardial metabolism over long intervals. Machine perfusion seems promising for long-term preservation of human donor hearts.

Low-flow perfusion preservation versus static preservation for isolated rat heart: effects on recovery of myocardial function

BACKGROUND

Clinically, donor hearts cannot be preserved for >6 hours between explantation and recipient implantation. A better approach is needed to preserve donor hearts for a longer time. We tested whether low-flow perfusion (LFP) could satisfactorily preserve isolated rat hearts with histidine-tryptophan-ketoglutarate (HTK) solution or Fuwai modified (FWM) solution.

METHODS

We divided 32 male Sprague-Dawley rats randomly into 4 groups (n = 8): H1, H2, F1, and F2. The Langendorff heart model immersed isolated hearts in the H1 and F1 groups in HTK or FWM solution for 8 hours at 4 °C. Isolated hearts in the H2 and F2 groups were low-flow perfused with HTK solution and FWM solution for 8 hours at a pressure of 10 cmH(2)O at 4 °C. After 60 minutes reperfusion, we measured recovery of cardiac function, myocardial water content, and leakage of myocardial enzymes.

RESULTS

After reperfusion, no cardiac rebeating was observed among F1 group hearts; in addition, they showed significantly higher myocardial water content and lactate dehydrogenase leakage compared with the other 3 groups (P < .05). The recovery rates of cardiac function among H2 hearts were better than the other 3 groups (P < .05); their myocardial water content and enzyme leakage were less than the other 3 groups (P < .05).

CONCLUSIONS

Hypothermic LFP was better than static storage to preserve isolated rat hearts. HTK solution afforded better myocardial protection than FWM.

Continuous perfusion of donor hearts with oxygenated blood cardioplegia improves graft function

Donor hearts cannot be preserved beyond 6h using cold storage (CS). Improving preservation methods may permit prolonged storage of donor heart. We compared graft function in large animal model after prolonged preservation (8h) using continuous perfusion (CP) and CS method. Twenty-four miniature pigs were used as donors and recipients. Donor hearts were either stored in University of Wisconsin solution (UW solution) for 8h at 0-4°C (CS group, n=6) or were continuously perfused with oxygenated blood cardioplegia at 26°C for 8h (CP group, n=6). After preservation, hearts were transplanted into recipients and reperfused for 3h. Left ventricular (LV) function, cardiac output (CO), malondialdehyde (MDA) and adenosine triphosphate (ATP) levels, and water content were measured. Although water content of CP hearts was higher than that of CS, LV contractility and diastolic function of CP hearts were superior to those of CS. In addition, CP hearts performed better than CS hearts on CO in working heart state. ATP was better preserved and MDA levels were lower in CP hearts compared with those of CS (P<0.0001). Donor hearts can be preserved longer using continuous perfusion with oxygenated blood cardioplegia and this method prevents time-dependent ischemic injury.

Machine perfusion or cold storage in organ transplantation: indication, mechanisms, and future perspectives

Most organs are currently preserved by cold storage (CS) prior to transplantation. However, as more so called marginal donor organs are utilized, machine perfusion has regained clinical interest. Recent studies have demonstrated advantages of pulsatile perfusion over CS preservation for kidney transplantation. However, it remains unclear whether there is a significant benefit of one preservation method over the other in general, or, whether the utilization of particular preservation approaches needs to be linked to organ characteristics. Proposed protective mechanisms of pulsatile perfusion remain largely obscure. It can be speculated that pulsatile perfusion may not only provide nutrition and facilitate the elimination of toxins but also trigger protective mechanisms leading to the amelioration of innate immune responses. Those aspects may be of particular relevance when utilizing grafts with suboptimal quality which may have an increased vulnerability to ischemia/reperfusion injury and compromised repair mechanisms. This review aims to enunciate the principles of organ perfusion and preservation as they relate to indication, aspects of organ protection and to highlight future developments.

An in vivo autotransplant model of renal preservation: cold storage versus machine perfusion in the prevention of ischemia/reperfusion injury

There is increasing proof that organ preservation by machine perfusion is able to limit ischemia/reperfusion injury in kidney transplantation. This study was designed to compare the efficiency in hypothermic organ preservation by machine perfusion or cold storage in an animal model of kidney autotransplantation. Twelve pigs underwent left nephrectomy after warm ischemic time; the organs were preserved in machine perfusion (n = 6) or cold storage (n = 6) and then autotransplanted with immediate contralateral nephrectomy. The following parameters were compared between the two groups of animals: hematological and urine indexes of renal function, blood/gas analysis values, histological features, tissue adenosine-5'-triphosphate (ATP) content, perforin gene expression in kidney biopsies, and organ weight changes were compared before and after preservation. The amount of cellular ATP was significantly higher in organs preserved by machine perfusion; moreover, the study of apoptosis induction revealed an enhanced perforin expression in the kidneys, which underwent simple hypothermic preservation compared to the machine-preserved ones. Organ weight was significantly decreased after cold storage, but it remained quite stable for machine-perfused kidneys. The present model seems to suggest that organ preservation by hypothermic machine perfusion is able to better control cellular impairment in comparison with cold storage.

Myocardial perfusion characteristics during machine perfusion for heart transplantation

BACKGROUND

Optimal parameters for machine perfusion preservation of hearts prior to transplantation have not been determined. We sought to define regional myocardial perfusion characteristics of a machine perfusion device over a range of conditions in a large animal model.

METHODS

Dog hearts were connected to a perfusion device (LifeCradle, Organ Transport Systems, Inc, Frisco, TX) and cold perfused at differing flow rates (1) at initial device startup and (2) over the storage interval. Myocardial perfusion was determined by entrapment of colored microspheres. Myocardial oxygen consumption (MVO(2)) was estimated from inflow and outflow oxygen differences. Intra-myocardial lactate was determined by (1)H magnetic resonance spectroscopy.

RESULTS

MVO(2) and tissue perfusion increased up to flows of 15 mL/100 g/min, and the ratio of epicardial:endocardial perfusion remained near 1:1. Perfusion at lower flow rates and when low rates were applied during startup resulted in decreased capillary flow and greater non-nutrient flow. Increased tissue perfusion correlated with lower myocardial lactate accumulation but greater edema.

CONCLUSIONS

Myocardial perfusion is influenced by flow rates during device startup and during the preservation interval. Relative declines in nutrient flow at low flow rates may reflect greater aortic insufficiency. These factors may need to be considered in clinical transplant protocols using machine perfusion.

Preserving and evaluating hearts with ex vivo machine perfusion: an avenue to improve early graft performance and expand the donor pool

Cardiac transplantation remains the first choice for the surgical treatment of end stage heart failure. An inadequate supply of donor grafts that meet existing criteria has limited the application of this therapy to suitable candidates and increased interest in extended criteria donors. Although cold storage (CS) is a time-tested method for the preservation of hearts during the ex vivo transport interval, its disadvantages are highlighted in hearts from the extended criteria donor. In contrast, transport of high-risk hearts using hypothermic machine perfusion (MP) provides continuous support of aerobic metabolism and ongoing washout of metabolic byproducts. Perhaps more importantly, monitoring the organ's response to this intervention provides insight into the viability of a heart initially deemed as extended criteria. Obviously, ex vivo MP introduces challenges, such as ensuring homogeneous tissue perfusion and avoiding myocardial edema. Though numerous groups have experimented with this technology, the best perfusate and perfusion parameters needed to achieve optimal results remain unclear. In the present review, we outline the benefits of ex vivo MP with particular attention to how the challenges can be addressed in order to achieve the most consistent results in a large animal model of the ideal heart donor. We provide evidence that MP can be used to resuscitate and evaluate hearts from animal and human extended criteria donors, including the non-heart beating donor, which we feel is the most compelling argument for why this technology is likely to impact the donor pool.

Benefits of Perfusion Preservation in Canine Hearts Stored for Short Intervals

BACKGROUND

Continuous perfusion of donor hearts for transplantation has been proposed to improve graft function or extend preservation intervals, but the effects on cellular metabolism, myocyte loss, and myocardial edema are not well-defined.

METHODS

Hearts from mongrel dogs were instrumented with sonomicrometry crystals and left ventricular (LV) catheters. LV function was quantified by the preload-recruitable stroke work (PRSW) relationship. Hearts were arrested with a modified Celsior solution, and stored in cold solution (n=6) or placed in a device providing continuous perfusion of this solution at 10 mL/100 g/min (n=6). After 4 h of storage, left atrial samples were frozen, extracted, and analyzed by magnetic resonance spectroscopy (MRS). Hearts were then transplanted into recipient dogs and reperfused for 6 h with function measured hourly. At end-experiment, LV specimens were assayed for water content and apoptosis. Serum CK-MB levels were measured.

RESULTS

LV functional recovery was excellent in both groups over 6 h of reperfusion. MRS revealed a dramatic decrease in tissue lactate in hearts protected with continuous perfusion (P<0.01). Apoptotic cell counts were significantly lower in post-reperfusion heart tissue in animals undergoing a continuous perfusion strategy (P<0.01). CK-MB levels and LV water content were similar in both groups.

CONCLUSIONS

Although both methods of preservation lead to good early graft function after 4 h of protected ischemia, continuous preservation dramatically reduces tissue lactate accumulation without increasing myocardial edema and may reduce tissue damage during storage and reperfusion. It appears promising as a method to improve results of cardiac transplantation.

Use of diffusion tensor imaging to predict myocardial viability after warm global ischemia: possible avenue for use of non-beating donor hearts

BACKGROUND

The assessment of myocardial viability after global warm ischemia (WI) but before reperfusion is challenging. We hypothesized that fractional anisotropy (FA), a magnetic resonance imaging (MRI) parameter of water diffusion that characterizes cellular integrity within tissues, provides a rapid and useful method for evaluating the viability of hearts after WI.

METHODS

Dog hearts were exposed to 60 minutes of WI after exanguination, explanted and preserved in a cold, non-beating state for 6 hours, using continuous perfusion (CP) or static cold storage (CS). Toward the end of preservation, a global FA assessment, acquired using MRI, was compared with analyses obtained from myocardial biopsies that included adenosine triphosphate (ATP), endothelin-1 (ET-1) and caspase-3 levels, light microscopy and tetrazolium staining. Functional recovery was analyzed after restoration of blood flow on a non-working Langendorff preparation.

RESULTS

FA measured at the end of CP showed strong correlations with all parameters of functional recovery (developed pressure, R = 0.60; dP/dt, R = 0.96; -dP/dt, R = 0.96). Although FA also correlated with tissue levels of ATP, ET-1 and caspase-3 (R = 0.77, -0.84, -0.64), recovery of myocardial function did not correlate with these markers or any other conventional analyses of myocardial injury (troponin I, changes on light microscopy or tetrazolium staining).

CONCLUSIONS

FA, an MRI-based parameter that indicates cellular integrity, was found to reflect better myocardial ATP stores, less induction of ET-1 and caspase-3 and improved functional recovery of hearts after global WI. As a clinically applicable tool capable of rapidly differentiating reversible from lethal injury, diffusion tensor imaging may prove useful in the eventual adoption of non-beating donor hearts for transplantation.

Hypothermic perfusion preservation: the future of organ preservation revisited?

Hypothermic perfusion preservation (HPP) was an integral step in the development of early clinical transplantation programmes, and considerable progress was made in understanding the basic principles underlying the technique. In subsequent years, the development of better preservation solutions for cold hypoxic storage, along with pragmatic choices made on grounds of costs and logistics, saw a fall in the application of HPP. More recently, the acute shortage of suitable organ donors and the inevitable pressure to use organs from sub-optimal (or expanded criteria) donors, has forced a re-evaluation of HPP, and the development of a new generation of HPP machines and associated perfusion solutions. This review sets out the historical development of HPP across the range of organs in which the method was originally investigated, describes the biological benefits and drawbacks associated with HPP, and sets out the most recent literature on the topic (including comments on the interest in use of higher temperatures in organ perfusion).