Comparison of two preservation solutions in the protection of the pH regulation mechanism of perfused rat livers after 24 hours of cold storage

Exploration of Optimal pH in Hypothermic Machine Perfusion for Rat Liver Grafts Retrieved after Circulatory Death

Ex vivo hypothermic machine perfusion (HMP) is a strategy for controlling ischemia-reperfusion injury in donation after circulatory death (DCD) liver transplantation. The pH of blood increases with a decrease in temperature and water dissociation, leading to a decrease in [H⁺]. This study aimed to verify the optimal pH of HMP for DCD livers. Rat livers were retrieved 30 min post-cardiac arrest and subjected to 3-h cold storage (CS) in UW solution (CS group) or HMP with UW-gluconate solution (machine perfusion [MP] group) of pH 7.4 (original), 7.6, 7.8, and 8.0 (MP-pH 7.6, 7.8, 8.0 groups, respectively) at 7-10 °C. The livers were subjected to normothermic perfusion to simulate reperfusion after HMP. All HMP groups showed greater graft protection compared to the CS group due to the lower levels of liver enzymes in the former. The MP-pH 7.8 group showed significant protection, evidenced by bile production, diminished tissue injury, and reduced flavin mononucleotide leakage, and further analysis by scanning electron microscopy revealed a well-preserved structure of the mitochondrial cristae. Therefore, the optimum pH of 7.8 enhanced the protective effect of HMP by preserving the structure and function of the mitochondria, leading to reduced reperfusion injury in the DCD liver.

PBSH: a new improved cardiac preservation solution in comparison with three clinically proven solutions

INTRODUCTION

A solution under development at our institute, based on phosphate-buffered sucrose, has shown good preservation for kidneys and livers. This work used a refined version of this solution (PBSH-phosphate-buffered sucrose for the heart) in heart preservation, comparing it to solutions already widely used (University of Wisconsin, St. Thomas's, and Celsior solutions).

METHODS

Following an initial washout phase and control working mode on a Langendorff system, hearts were flushed with preservation solution and after 6 hours at 4 degrees C were then reperfused for 15 minutes followed by working heart mode for a further 30 minutes. Hemodynamic parameters were measured and compared with their preischemic values and expressed as percentage recovery. Enzyme measurement came from the collection of the initial 1.5 mL of the coronary effluent after the storage period. This was to test for creatine phosphokinase (CPK) and lactate dehydrogenase (LDH). Hearts were then placed immediately into liquid nitrogen for adenosine triphosphate (ATP), lactate, and creatine phosphate (CP) testing. Spectrophotometric analysis was used to assess both the release of CPK and LDH into the coronary effluent, and the level of ATP, lactate, and CP in the frozen heart tissue.

RESULTS

These results show that hearts that are preserved in PBSH are hemodynamically as well preserved as the hearts preserved in other solutions tested and their enzyme and lactate content is lower while having higher levels of energy compounds in these hearts.

CONCLUSION

Overall these results show that PBSH is at least as effective in cardiac preservation in the rat model of 6 hours of cold ischemia as these other widely used solutions tested.

Influence on energy kinetics and histology of different preservation solutions seen during cold ischemia in the liver

BACKGROUND AND PURPOSE

Cold flush preservation prolongs tissue viability during ischemia. However, there is little understanding of the effects of various preservation fluids on events during this period. A study of cold ischemia in rat livers was undertaken to compare biochemical and histological changes over time, using three preservation solutions: University of Wisconsin (UW), histidine-tryptophan-ketoglutarate (HTK), and Leeds solution (LS) under development at our institution. Leeds solution is a phosphate-based sucrose solution that like UW contains the impermeant lactobionate and the metabolite allopurinol (1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one) which acts as a competitive inhibitor of xanthine oxidase, stopping the breakdown of hypoxanthine to xanthine by oxidizing it to alloxanthine, inhibiting both the conversion of hypoxanthine to xanthine and the conversion of xanthine to uric acid.

MATERIALS AND METHODS

At various time points, samples were analyzed for adenosine triphospate (ATP) and metabolites by high-performance liquid chromatography as well as for histological changes.

RESULTS

In all livers, ATP, ADP, and AMP degraded over 4 hours. In UW and LS groups, degradation beyond hypoxanthine was halted, and it continued in the HTK group. This blockade led to a significant reduction in the accumulation of xanthine and uric acid. Histological analysis showed protected architecture and maintenance of reticulin scaffolds in the UW and LS groups, whereas tissue breakdown was seen from earlier time points in the HTK group. Additionally, throughout ischemia, signs of pathological injury were more pronounced with UW- than with LS-preserved tissue.

CONCLUSIONS

These results implied that cold ischemia in the liver is characterized by dynamic biochemical changes coincident with pathological injury which are initiated from the time of organ perfusion and influenced by the choice of the perfusion fluid. Allopurinol in UW and LS appears to be critical. We hypothesized that it may also affect the degree of subsequent reperfusion injury. The data supported the assertion that LS offerred improved preservation over UW, adding to the impetus to shorten ischemic times in clinical transplantation.

Addition of adenosine to University of Wisconsin solution: does it help?

Adenosine Triphosphate (ATP) precursors are sometimes added to preservation solutions in the belief that once the organ is reperfused, these precursors will build up ATP rapidly, returning it to its original metabolic state. This work studied ATP and metabolites during preservation of the rat liver using University of Wisconsin solution (UW), which contains adenosine, versus histidine tryptophan ketaglutarate solution a new phosphate-based preservation solution, or leeds solution (LS), which is under development at our institution (neither of the latter 2 contains adenosine). Tissue samples of perfused livers were analyzed for ATP and metabolites by high-performance liquid chromatography. UW did initially show the expected significant difference in overall adenosine levels, but the advantage had disappeared by 4 hours. At no time did UW show significantly higher levels of ATP; this was not seen following adenosine addition to LS. Only in living donor transplants where the cold ischemic time is short may there be some advantage to the addition of adenosine.

The role of preservation solution on acid-base regulation during machine perfusion of kidneys

To meet the current clinical organ demand, efficient preservation methods and solutions are needed to increase the number of viable kidneys for transplantation. In the present study, the influence of perfusion solution buffering strength on renal pH dynamics and regulation mechanisms during kidney ex vivo preservation was determined. Porcine kidneys were hypothermically machine perfused for 72 h with either Unisol-UHK or Belzer-Machine Perfusion solution, Belzer-MP solution. Renal perfusate samples were periodically collected and biochemically analyzed. The UHK solution, a Hepes-based solution (35 mM), provided a more efficient control of renal pH that, in turn, resulted in minor changes in the perfusate pH relative to baseline, in response to tissue CO2 and HCO3- production. In the perfusate of Belzer-MP kidney group a wider range of pH values were recorded and a pronounced pH reduction was seen in response to significant rises in pCO2 and HCO3- concentrations. The Belzer-MP solution, containing phosphate (25 mM) as its main buffer, and only 10 mM Hepes, had a greater buffering requirement to attenuate larger pH changes.

Acid-base buffering in organ preservation solutions as a function of temperature: new parameters for comparing buffer capacity and efficiency

Control of acidity and preventing intracellular acidosis are recognized as critical properties of an effective organ preservation solution. Buffer capacity and efficiency are therefore important for comparing the relative merits of preservation fluids for optimum hypothermic storage, but these parameters are not available for the variety of organ preservation solutions of interest in transplantation today. Moreover, buffer capacity is dependent upon both concentration and pH such that buffer capacity is not easily predicted for a complex solution containing multiple buffer species. Using standard electrometric methods to measure acid dissociation constants, this study was undertaken to determine the maximum and relative buffer capacities of a variety of new and commonly used hypothermic preservation solutions as a function of temperature. The reference data provided by these measurements show that comparative buffer capacity and efficiency vary widely between the commonly used solutions. Moreover, the fluids containing zwitterionic sulfonic acid buffers such as Hepes possess superior buffering for alpha-stat pH regulation in the region of physiological importance.