Effect of warm ischemia time and organ perfusion technique on liver microvascular preservation in a non-heart-beating rat model

The Benefits of Fibrinolysis Combined with Venous Systemic Oxygen Persufflation (VSOP) in a Rat Model of Donation after Circulatory Death and Orthotopic Liver Transplantation

Organ shortage has led to the increasing utilization of livers retrieved from donors after circulatory death (DCD). These pre-damaged organs are susceptible to further warm ischemia and exhibit minimal tolerance for cold storage. The aim was thus to examine the effects of fibrinolysis combined with Venous Systemic Oxygen Persufflation (VSOP) on the preservation of DCD livers in vivo. Livers of male Lewis rats were explanted after 45 min of warm ischemia, cold-stored for 18 h, and transplanted into a recipient animal. Livers were left untreated or underwent either VSOP or fibrinolysis via Streptokinase (SK) or received combined SK and VSOP. Combined treatment exhibited improved microvascular flow at 168 h (p = 0.0009) and elevated microperfusion velocity at 24 h post-transplantation (p = 0.0007). Combination treatment demonstrated increased portal venous flow (PVF) at 3 and 24 h post-transplantation (p = 0.0004, p < 0.0001), although SK and VSOP analogously achieved increases at 24 h (p = 0.0036, p = 0.0051). Enzyme release was decreased for combination treatment (p = 0.0002, p = 0.0223) and lactate dehydrogenase (LDH) measurements were lower at 24 h post-transplantation (p = 0.0287). Further supporting findings have been obtained in terms of serum cytokine levels and in the alterations of endothelial injury markers. The combination treatment of SK + VSOP might provide improved organ integrity and viability and may therefore warrant further investigation as a potential therapeutic approach in the clinical setting of DCD.

Evolution of dynamic, biochemical, and morphological parameters in hypothermic machine perfusion of human livers: A proof-of-concept study

INTRODUCTION

Hypothermic machine perfusion (HMP) is increasingly investigated as a means to assess liver quality, but data on viability markers is inconsistent and the effects of different perfusion routes and oxygenation on perfusion biomarkers are unclear.

METHODS

This is a single-centre, randomised, multi-arm, parallel study using discarded human livers for evaluation of HMP using arterial, oxygen-supplemented venous and non-oxygen-supplemented venous perfusion. The study included 2 stages: in the first stage, 25 livers were randomised into static cold storage (n = 7), hepatic artery HMP (n = 10), and non-oxygen-supplemented portal vein HMP (n = 8). In the second stage, 20 livers were randomised into oxygen-supplemented and non-oxygen-supplemented portal vein HMP (n = 11 and 9, respectively). Changes in dynamic, biochemical, and morphologic parameters during 4-hour preservation were compared between perfusion groups, and between potentially transplantable and non-transplantable livers.

RESULTS

During arterial perfusion, resistance was higher and flow was lower than venous perfusion (p = 0.001 and 0.01, respectively); this was associated with higher perfusate markers during arterial perfusion (p>0.05). Supplementary oxygen did not cause a significant alteration in the studied parameters. Morphology was similar between static and dynamic preservation groups. Perfusate markers were 2 fold higher in non-transplantable livers (p>0.05).

CONCLUSIONS

Arterial only perfusion might not be adequate for graft perfusion. Hepatocellular injury markers are accessible and easy to perform and could offer insight into graft quality, but large randomised trials are needed to identify reliable quality assessment biomarkers.

Determination of an adequate perfusion pressure for continuous dual vessel hypothermic machine perfusion of the rat liver

Hypothermic machine perfusion (HMP) provides better protection against ischemic damage of the kidney compared to cold-storage. The required perfusion pressures needed for optimal HMP of the liver are, however, unknown. Rat livers were preserved in University of Wisconsin organ preservation solution enriched with acridine orange (AO) to stain viable cells and propidium iodide (PI) to detect dead cells. Perfusion pressures of 12.5%, 25% or 50% of physiologic perfusion pressures were compared. Intravital fluorescence microscopy was used to assess liver perfusion by measuring the percentage of AO staining. After 1-h, the perfusion pressure of 12.5% revealed 72% +/- 3% perfusion of mainly the acinary zones one and two. The perfusion pressure of 25% and 50% showed complete perfusion. Furthermore, 12.5% showed 14.7 +/- 3.6, 25% showed 3.7 +/- 0.9, and 50% showed 11.2 +/- 1.4 PI positive cells. One hour was followed by another series of experiments comprising 24-h preservation. In comparison with 24-h cold-storage, HMP at 25% showed less PI positive cells and HMP at 50% showed more PI positive cells. In summary, perfusion at 25% showed complete perfusion, demonstrated by AO staining, with minimal cellular injury, shown with PI. This study indicates that fine-tuning of the perfusion pressure is crucial to balance (in)complete perfusion and endothelial injury.

Endoplasmic and vascular surface activation during organ preservation: refining upon the benefits of machine perfusion

The endoplasmic reticulum (ER) represents a subcellular target reactive to various cytosolic impairments. The involvement of ER-stress in organ preservation was investigated, comparing machine preservation, cold storage (CS) and a novel concept of only temporary perfusion after procurement. Rat livers were retrieved 30 min after cardiac arrest and preserved for 18 h by CS, oxygenated machine perfusion for 18 h (18 h MP) or for 2 h with subsequent CS for 16 h (2 h MP + 16 h CS). Upon reperfusion, 18 h MP significantly improved enzyme leakage (ALT, LDH) and promoted a 2-fold increase of metabolic recovery compared to CS. However, vascular stress, evaluated by endothelin-release, was significantly elevated after 18 h MP. Interestingly, better viability was obtained using the short-term perfusion protocol (2 h MP + 16 h CS), which further reduced enzyme leakage, maintained energetic recovery and mitigated endothelin-release compared to 18 h MP. Caspase 12-mRNA was upregulated in the 18 h MP-group but unchanged after CS or 2 h MP + 16 h CS. Activation/cleavage of caspase 12 protein was significantly enhanced after 18 h MP and very low in the 2 h MP + 16 h CS-group. Correspondingly, electron microscopy showed ultrastructural alterations of ER after CS and especially after 18 h MP but not after 2 h MP + 16 h CS. At this time mitochondrial appearance was unaffected in all groups, suggesting the ER to be an early subcellular target of preservation injury. In our model, ER and vascular endothelium were best protected by only temporary machine perfusion, which also maintained overall graft viability.

Synergistic value of fibrinolysis and hypothermic aerobic preservation with oxygen in the protection of livers from non-heart-beating donors: an experimental model

The chronic organ shortage has led to the reconsideration of marginal donor pools such as non-heart-beating donors (NHBD). The use of these livers is limited due to their minimal tolerance for cold preservation. The aim of this study was to examine the combination of two different therapeutic strategies for the preservation of livers from NHBD. The livers of male Wistar rats were harvested after the induction of cardiac arrest via phrenotomy (30, 90 minutes). Livers were perfused with 10 mL of UW solution (UW), followed by hypothermic preservation with or without insufflation of gaseous oxygen (O2). In one group a fibrinolytic preflush (10 mL of Ringer's containing 7500 IU of streptokinase) was performed with subsequent preservation with O2 (O2+SK). After storage (24 h/4 degrees C/UW) livers were reperfused in vitro. Livers retrieved from heart beating donors served as controls. The results showed that even after only 30 minutes of warm ischemia livers displayed a serious disturbance in vascular perfusion (portal venous pressure, PVP = 7.4 +/- 0.2* versus control: 4.1 +/- 0.5 mmHg), associated with a more than 10-fold increase in enzyme release (ALT: 26819 +/- 513* versus control 683 +/- 152 mU/g/L), which was consistent with a significant depression in bile synthesis (1.21 +/- 0.35* versus 19.36 +/- 2.16 microL/g/45 min). However, these impairments could be prevented with O2. Even after 90 minutes of WI, the function was significant better using aerobic preservation (ALT: 3204 +/- 549 mU/g/L). With a supplementary fibrinolytic preflush, we effectively preserved livers up to 90 minutes of WI with results comparable to livers from heart beating donors with no WI (ALT: 1623 +/- 432 mU/g/L). The combination of these two techniques represents a new therapeutic approach for livers with extended or unclear WI periods in non-heart-beating donors (*P <.05 versus control).

Quantification of hepatic microcirculation heterogeneity of perfusion: Effects of endothelin-1

Stress alters hepatic perfusion heterogeneously leading to mismatch of oxygen supply and demand. Endothelin-1 (ET-1) has been linked to stress-mediated microcirculation disruption; however, perfusion heterogeneity is difficult to quantify. Therefore, we developed an image analysis based automated methodology for quantification of heterogeneity (Ht) of perfusion from hepatic intravital microscopy images (HIVM). In vivo assessment of the liver microcirculation flow distribution, before and after ET-1 infusion, was performed in male Sprague-Dawley rats using HIVM combined with FITC-labeled RBC infusion. Our method aimed to analyze parallel/spatial and series/temporal intralobular Ht of perfusion as well as interlobular Ht of perfusion and was based on automated RBC detection, tracking, and motion analysis. Compared with manual analysis, this method detected 40 times more RBC without increasing false positives (<0.5%). At baseline, parallel/spatial Ht was higher than series/temporal Ht of perfusion which suggested higher hepatic stellate cells asynchrony between sinusoids than within the same sinusoid. Following ET-1 infusion, parallel/spatial Ht transiently increased contrasting with a decrease in series/temporal Ht. In conclusion, we proposed a HIVM analysis methodology that allows assessment of Ht of perfusion within and between hepatic lobules and improved our understanding of ET-1 mediated effects on the hepatic microcirculation.

Hypothermic machine perfusion of the liver and the critical balance between perfusion pressures and endothelial injury

Hypothermic machine perfusion (HMP) provides better protection against cold ischemic injury than cold storage in marginal donor kidneys. Also, in liver transplantation a switch from static cold storage to HMP could be beneficial as it would allow longer preservation times and the use of marginal donors. A critical question concerning application of HMP in liver preservation is the crucial balance between perfusion pressure and occurrence of endothelial injury. Rat livers were cold-perfused for 24 hours to study perfusion pressures for both hepatic artery and portal vein. Cold storage served as control and was compared to HMP-preserved livers using a mean arterial perfusion pressure of 25 mm Hg and a portal perfusion pressure of 4 mm Hg (25% of normothermic liver circulation) and to HMP at 50 mm Hg and 8 mm Hg perfusion, respectively (50% of normothermic liver circulation). UW solution was enriched with 14.9 micromol/L propidium iodide (PI) to stain for dead cells and with an additional 13.5 micromol/L acridine orange to stain for viable hepatocytes. A low PI-positive cell count was found using HMP at 25% of normal circulation compared to cold storage. The PI count was high for the HMP group perfused at just 50% of normal circulation compared to HMP at 25% and compared to cold storage. In summary, for liver HMP, perfusion at 25% showed complete perfusion with minimal cellular injury. HMP using perfusion pressures of 25 mm Hg for the hepatic artery and 4 mm Hg for the portal vein is feasible without induction of endothelial injury.

Survival transplantation of preserved non-heart-beating donor rat livers: preservation by hypothermic machine perfusion

BACKGROUND

Non-heart-beating donor (NHBD) livers are an untapped source with the potential to provide relief to the current donor shortage problem. Hypothermic machine perfusion (MP) has the potential to reclaim and preserve these marginal donor organs.

METHODS

This study compared 5-day survival in a rat NHBD liver transplantation model with simple cold storage (SCS) and MP-preserved tissues that had experienced 30 min of warm ischemia followed by a 5-hr preservation period with the University of Wisconsin solution. Total release of lactate dehydrogenase (LDH) and alanine aminotransferase (ALT) were determined at major time points. Bilirubin levels and histology were examined after 5-day survival.

RESULTS

Six of seven control livers and five of six MP livers survived, whereas SCS tissues had survival in zero of seven. The results showed that MP livers had reduced release of LDH and ALT after 5 hr of storage, 5.07+/-1.42 and 2.02+/-0.69 U (mean+/-SE), respectively, compared with SCS, 15.54+/-0.81 and 3.41.3+/-0.73 U, respectively. Bilirubin values after 5-day survival of MP livers (1.17+/-0.49 mg/dL) were comparable to controls (0.91+/-0.36 mg/dL). Histology confirms that SCS displayed increased necrosis and MP tissue showed regions of near normal hepatic structure.

CONCLUSIONS

These results suggest that MP for 5 hr improves survival and reduces cellular damage of liver tissue that has experienced 30 min of warm ischemia when compared with SCS tissues. Further studies need to be conducted, but this study suggests that MP preservation has the potential to reclaim and preserve NHBD liver tissues.

Functional recovery of preserved livers following warm ischemia: improvement by machine perfusion preservation

BACKGROUND

Hypothermic machine perfusion preservation has the potential to relieve the current donor shortage problem by reclaiming and preserving marginal donor organs including those from viable non-heart-beating donors. A number of problems exist with the current machine perfusion technology for preserving livers, and much research is needed to determine the clinical impact of this technology in preserving non-heart-beating donor livers.

METHODS

This study was conducted to compare the poststorage function and microcirculation of simple cold stored and machine perfusion preserved livers that had experienced 30 min of warm ischemia followed by a 10 hr preservation period. In an isolated rat liver perfusion model, lactate dehydrogenase activity, indocyanine green secretion, and portal pressure values were determined at major time points. An intravital microscopy was conducted to assess microcirculation.

RESULTS

The results showed an increase in flow homogeneity of machine perfused livers, which correlated with the reduction in portal pressure when compared with simple cold storage (5.4+/-0.4 vs. 8.7+/-0.6 mm Hg). A reduction in lactate dehydrogenase levels in the perfusate (333+/-22 vs.103+/-8 U/L) and an increase in bile production of the machine perfused livers (4.9+/-0.5 vs. 33.2+/-1.7 microg/min/g liver) and indocyanine green secretion (11.7+/-1.7 vs. 21.2+/-2.1 Abs/g bile) were observed at all time points (mean+/-SE of final point given). Intravital microscopic examination indicated that large regions of non flow, as indicated by the absence of fluorescein isothiocyanate-labeled albumin, were observed in the simple cold stored tissue, whereas machine perfused liver showed increase flow homogeneity. Values of bile production, indocyanine secretion, and cellular damages were comparable with controls. Histologic examination confirmed that simple cold stored tissue displayed increased vacuolization, and machine perfused tissue showed regions of normal hepatic structure.

CONCLUSION

These results suggest that machine perfusion for 10 hr improves both poststorage function and microcirculation while reducing cellular damage of liver tissue that has experienced 30 min of warm ischemia, when compared with simple cold storage. Further studies need to be conducted, but this study suggests that machine perfusion preservation has the potential to reclaim and preserve liver tissues after warm ischemic insult.

Liver and kidney preservation by perfusion

The clinical boundaries of transplantation have been set in an era of simple cold storage. Research in organ preservation has led to the development of flush solutions that buffer the harsh molecular conditions which develop during ischaemia, and provide stored organs that are fit to sustain life after transplantation. Although simple and efficient, this method might be reaching its limit with respect to the duration, preservation, and the quality of organs that can be preserved. In addition, flush preservation does not allow for adequate viability assessment. There is good evidence that preservation times will be extended by the provision of continuous cellular substrate. Stimulation of in-vivo conditions by ex-vivo perfusion could also mean that marginal organs will be salvaged for transplantation. Perfusion will also allow for assessing the viability of organs before transplantation in a continuous fashion. The cumulative effect of these benefits would include expansion of the donor pool, less risk of primary non-function, and extension of the safe preservation period. Use of non-heart-beating donors, international organ sharing, and precise calculation of the risk of primary organ failure could become standard.

Advantages of Celsior solution in graft preservation from non-heart-beating donors in a canine liver transplantation model

BACKGROUND

The optimal method for preserving livers from non-heart-beating donors (NHBD) is still unknown. We compared the Celsior solution, a new extracellular-type, low-potassium, low-viscosity preservation solution, with the University of Wisconsin (UW) solution in a canine orthotopic liver transplantation from NHBD.

MATERIALS AND METHODS

Fourteen adult mongrel dogs, weighing 9 to 17 kg, were divided into two groups: the Celsior or the UW group (n = 7 each). The thoracic descending aorta and supradiaphragmatic inferior vena cava were cross-clamped for 20 min to induce warm ischemia as a NHBD model. The liver was flushed with the respective cold preservation solution and then stored at 4 degrees C for 4 h. The grafts were transplanted using the piggy-back technique under portal decompression by leaving the native right lobe as a temporary shunt.

RESULTS

The duration of liver flushing out (min) was shorter (P < 0.05), and the serum glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, lactate dehydrogenase, lactate, and alpha-glutathione S-transferase concentrations 2 and 6 h after reperfusion of the graft (RPF) were lower (P < 0.05) in the Celsior group than in the UW group. Hepatic tissue blood flow (HTBF) did not deteriorate as much (P < 0.05) in the Celsior group. The serum endothelin-1 level was lower (P < 0.05) in the Celsior group 2 h after RPF. Histopathology of liver specimens revealed portal congestion and hepatocyte necrosis with neutrophil infiltration in the UW group, while these findings were mild in the Celsior group.

CONCLUSIONS

The Celsior solution improves vascular endothelial injury in livers from NHBDs and may have advantages in graft flush and preservation of grafts from NHBDs.