[Importance of graft arterialization in rat liver transplantation]

Donor gluconate rescues livers from uncontrolled donation after cardiac death

BACKGROUND

Ischemia from organ preservation or donation causes cells and tissues to swell owing to loss of energy-dependent mechanisms of control of cell volume. These volume changes cause substantial preservation injury, because preventing these changes by adding cell impermeants to preservation solutions decreases preservation injury. The objective of this study was to assess if this effect could be realized early in uncontrolled donation after cardiac death (DCD) livers by systemically loading donors with gluconate immediately after death to prevent accelerated swelling injury during the warm ischemia period before liver retrieval.

METHODS

Uncontrolled DCD rat livers were cold-stored in University of Wisconsin solution for 24 hours and reperfused on an isolated perfused liver (IPL) device for 2 hours or transplanted into a rat as an allograft for 7 days. Donors were pretreated with a solution of the impermeant gluconate or a saline control immediately after cardiac death. Livers were retrieved after 30 minutes.

RESULTS

In vivo, gluconate infusion in donors immediately before or after cardiac death prevented DCD-induced increases in total tissue water, decreased vascular resistance, increased oxygen consumption and synthesis of adenosine triphosphate, increased bile production, decreased lactate dehydrogenase release, and decreased histology injury scores after reperfusion on the IPL relative to saline-treated DCD controls. In the transplant model, donor gluconate pretreatment significantly decreased both alanine aminotransferase the first day after transplantation and total bilirubin the seventh day after transplantation.

CONCLUSION

Cell and tissue swelling plays a key role in preservation injury of uncontrolled DCD livers, which can be mitigated by early administration of gluconate solutions to the donor immediately after death.

Arterialisation of the portal vein as a model for the induction of hepatic fibrosis: description of microsurgical models in the rat

Within the framework of liver transplantation, arterialisation of the portal vein in the case of non-recanalisable thrombosis has been reactivated. However, one of the consequences of this vascular reconstruction is the development of hepatic fibrosis. Clinical experience has shown that the development of fibrosis can be avoided by reducing portal inflow. We present, as a model for the induction of hepatic fibrosis, techniques of PVA, including transplantation. For PVA, several different techniques were used: the first with reduction of the portal inflow over a stent inserted in the right renal artery (PVA-B), the second with unrestricted flow using an aortic-portal segment (PVA-APS). The third technique was orthotopic liver transplantation with unrestricted portal arterialisation (OLTx-APS). Portal blood flow was measured with an ultrasonic flow probe. To determine the degree of hepatic fibrosis the amount of hydroxyproline was measured. Quantification of relative transcript levels of procollagen I was effected with real-time PCR using the TaqMan technology on a lightcycler instrument. The extracellular matrix was visualised with picro-sirius staining. Measurements with the ultrasonic probe showed a significant increase in flow rates, both with reduced (PVA-B) and unrestricted inflow (PVA-APS; OLTx-APS). The lowest survival rate (58%) was found in the group with unrestricted portal inflow. The reason for this was a high rate of thrombosis in the in the portal vascular tree (4 out of 12). In the OLTx-APS group four animals died within the first 3 postoperative days (69%), as a result of protracted postoperative shock. The overall survival rate was the highest (85%) in the group undergoing PVA with reduction of the portal inflow. PVA with unrestricted inflow was followed by a significant increase in extracellular collagen, which showed a clear correlation with the increase in the amount of hydroxyproline, the level of the mRNA for procollagen I and picro-sirius staining. With the operative PVA techniques presented herein, different arterial flow rates in the portal vein can be investigated. In our opinion these techniques represent an excellent animal model for studying the genesis of fibrosis and antifibrotic substances. By regulating the blood flow in the arterialised portal vein hepatic fibrosis can be reduced or even avoided. After a brief period of learning the microsurgical techniques, the surgeon can limit clamping times and achieve good results with these techniques.

Impact of hepatic rearterialization on reperfusion injury and outcome after mouse liver transplantation

BACKGROUND

Nonarterialized mouse liver transplantation is a well-established model for immunologic studies on rejection and tolerance mechanisms. However, the importance of graft arterialization has-in contrast to rat liver transplantation-not been thoroughly examined in the mouse model. The aim of the current study was to investigate the impact of arterial reconstruction on long-term graft survival, histologic alterations, ischemic liver damage, and early immunologic activation pathways.

METHODS AND RESULTS

All recipients of arterialized (n=6) and nonarterialized (n=8) syngeneic liver grafts survived indefinitely. There were no differences in their histologic architecture, including no evidence of bile duct proliferation, periductal fibrosis, or alterations in serum transaminases, in long-term survivors from either group. Twenty-four hours after syngeneic liver transplantation, aspartate aminotransferase and alanine aminotransferase levels were increased to an equivalent extent in both groups, in agreement with early reperfusion injury and solitary traumatic injuries as assessed histologically (n=3 per group). Visualized by immunohistochemistry, intercellular adhesion molecule-1 expression was increased on sinusoidal and hepatic vein endothelium at both 1 and 100 days after transplantation, in both arterialized and nonarterialized grafts. Messenger RNA for interleukin-1, interferon-gamma, and tumor necrosis factor-alpha were measured by real-time polymerase chain reaction 24 hr after transplantation. No significant changes in the expression of cytokine mRNA levels were observed.

CONCLUSIONS

Arterialization of mouse liver grafts does not appear to have a major impact on survival rate or the degree of immunologic activation. Therefore, the value of arterial reconstruction in mouse liver transplantation for experimental investigations is negligible.

Surgical techniques of orthotopic rat liver transplantation

Liver transplantation in rats is frequently used as a transplantation model. Although liver transplantation in larger laboratory animals such as dogs and pigs is technically easier, the rat has become the most important subject for experimental liver transplantation because of the availability of genetically defined animals. Numerous surgical techniques have been developed that permit the investigator to carry out studies with high clinical relevance. In this article the principal models of orthotopic rat liver transplantation and their technical modifications of vessel anastomoses, rearterialization, and bile duct reconstruction techniques are reviewed. More than 20 transplantation models are described in detail and demonstrated with clear illustrations. Finally, the advantages and uses of all the surgical procedures (e.g., suture and cuff anastomoses, bile duct anastomoses, and rearterialization techniques), specific problems, and survival criteria are discussed and the experiences of investigators who applied these techniques are analyzed. In conclusion, an overview and critical evaluation of all surgical techniques of orthotopic rat liver transplantation are given, together with instructions for learning these techniques.

Long-term consequence of rat orthotopic liver transplantation with and without hepatic arterial reconstruction: a clinical, pathological, and hemodynamic study

Our aim was to investigate the time-related changes in various parameters following orthotopic rat liver transplantation with (AOLT) and without (NOLT) arterial reconstruction in male Lewis rats. Body weight and biochemical parameters were measured weekly, and a liver biopsy was obtained at 4, 8, and 12 weeks. Hemodynamics were evaluated at 12 weeks using the microsphere technique and compared with matched controls. Following AOLT, rats gained weight normally without any noticeable complication. In NOLT, two subgroups (NOLT-1 and NOLT-2) could clearly be identified retrospectively. In the NOLT-1 group, the body weight increased normally, although animals presented transient cholestasis. In these rats, the ductular proliferation found at 4 weeks had regressed by the 12th week with near-normal biopsies. By contrast, in the NOLT-2 group, rats did not gain body weight and had persistent cholestasis. Marked ductular proliferation with increasing fibrosis was observed, resulting in a secondary biliary cirrhosis by the 12th week. Surprisingly, rearterialization of the grafted liver occurred in both NOLT-1 and NOLT-2 irrespective of their clinical course. All transplanted rats showed portal hypertension with marked portosystemic shunts, probably caused by the portal cuff. However, a hyperdynamic circulatory state was only observed in the NOLT-2 group with cirrhotic changes. These findings further show the combined role of an intact hepatic innervation and of hepatocellular insufficiency in the genesis of the hyperdynamic circulatory state associated with portal hypertension.

Bile secretory function of the arterialized versus nonarterialized rat liver allograft

Arterialized and nonarterialized rat models of orthotopic liver transplantation are widely used for studying various aspects of graft function. Although bile duct damage has been implicated in graft nonarterialization, any impact on graft secretory function is unknown. This study sought to investigate whether nonarterialized orthotopic liver transplantation (NOLT) is a valid model for studying bile formation after the animal has fully recovered from the perioperative period. Twenty-four-hour bile collections were performed on eight arterialized and eight nonarterialized rats 4 weeks after transplantation to avoid the confounding effects of preservation-reperfusion injury and perioperative stress. Eight unoperated rats were used as control. There was no difference in mortality or biliary complications between the two transplant groups. The nonarterialized rats exhibited a higher serum aminotransferase level, but serum bilirubin was normal. NOLT resulted in more portal lymphocytic infiltration and bile ductular proliferation. Despite these histologic changes, bile duct epithelial cells remained intact, and spontaneous graft rearterialization was evident in the NOLT group. Bile salt secretion, pool size, and synthesis in both transplant groups did not differ from unoperated rats. NOLT did not adversely affect either bile acid-dependent or bile acid-independent flow. Biliary cholesterol secretion was markedly reduced in both transplant groups, resulting in a more favorable cholesterol saturation index. In conclusion, hepatic allograft secretory function is well maintained at 4 weeks even in the absence of hepatic arterial reanastomosis. Compensatory mechanisms possibly prevent irreversible hepatobiliary damage in NOLT. The NOLT model is quite reasonable to study bile formation after transplantation.

Impact of arterialization on hepatic oxygen supply, tissue energy phosphates, and outcome after liver transplantation in the rat

The importance of arterial reconstruction in experimental orthotopic rat liver transplantation is widely acknowledged in the literature. Non-rearterialization of the graft leads to impaired microcirculation and, in chronic models, to severe hepatobiliary damage, together with bile duct proliferation and fibrosis in such livers. The aim of the current study was to investigate the impact of rearterialization on hepatic oxygen tension (pO2), hepatic tissue content of adenine nucleotides, early graft function, and postoperative outcome. Orthotopic liver transplantation was performed in 27 male inbred rats. Ten rats underwent rearterialization and while 17 did not. A group of sham-operated animals (n = 6) served as controls. After reperfusion, liver grafts without arterial reconstruction showed significantly reduced levels of oxygen tension (mean +/- SD, 3.79 +/- 2.20 vs. 10.03 +/- 2.84 mmHg; P < 0.05) and a clear shift toward lower pO2 values in the pO2 histograms, as compared with arterialized grafts. Without arterialization, the level of liver ATP was 65% of that in sham animals, compared with 84% in arterialized livers. Without arterialization, bile secretion was reduced (0.42 +/- 0.04 vs. 0.71 +/- 0.06 mg/min x g liver; (P < 0.001), and the postoperative course of serum alanine transaminase, bilirubin, and alkaline phosphatase revealed severe hepatobiliary damage. These findings allow us to conclude that graft rearterialization is essential to ensure both an adequate oxygen supply and maintenance of tissue ATP. Arterialization may thus be a necessary part of liver transplantation models in this animal species, and should be considered when designing studies on the biochemical, microcirculatory, and histopathological status of the graft.

[Orthotopic liver transplantation with arterial re-anastomosis in the rat--a detailed description of technique and analysis of possible errors]

Liver transplantation (LTX) in the rat is a frequently used transplantation model. In the present study we give a detailed description of the suture technique for all anastomoses, except the bile duct, with arterialization of the transplanted liver over an aortoceliac segment to the recipient's aorta. Using this technique, we finally achieved survival rates of 80%. During the development stages, the main cause of death was an exceedingly long anhepatic time (> 20 min); later on, complications occurred only from insufficient anastomoses. The advantage of the suture technique over the cuff technique is that a more physiological anastomosis is obtained with less trauma to the recipient when using rearterialization. Despite the complicated suture technique, the anhepatic time can be well reduced to below 20 min.