Role of NF-kappaB as effector of IPC in donor livers before liver transplantation in rats

Ischemic preconditioning modulates ROS to confer protection in liver ischemia and reperfusion

Ischemia reperfusion (IR) injury is a significant cause of morbidity and mortality in liver transplantation. When oxygen is reintroduced to the liver graft it initiates a cascade of molecular reactions leading to the release of reactive oxygen species (ROS) and pro-inflammatory cytokines. These soluble mediators propagate a sterile immune response to cause significant tissue damage. Ischemic preconditioning (IPC) is one method that reduces hepatocellular injury by altering the immune response and inhibiting the production of ROS. Studies quantifying the effects of IPC in humans have demonstrated an improved liver enzyme panel in patients receiving grafts pretreated with IPC as compared to patients receiving the standard of care. In our review, we explore current literature in the field in order to describe the mechanism through which IPC regulates the production of ROS and improves IR injury.

Wnt agonist stimulates liver regeneration after small-for-size liver transplantation in rats

AIM

Liver regeneration is inhibited in small-for-size grafts, which plays a role in the failure of partial liver grafts after transplantation. The Wnt/β-catenin signaling pathway plays a critical role in liver development, regeneration and homeostasis. In this study, we investigated whether pharmacological activation of Wnt signaling improves liver regeneration after small-for-size liver transplantation.

METHODS

The livers of male Sprague-Dawley rats were reduced to approximately 50% and 30% of their original sizes and transplanted. A Wnt agonist (2-amino-4-[3,4-[methylenedioxy]benzylamino]-6-[3-methoxyphenyl] pyrimidine], 5 mg/kg bodyweight) or an equal volume of vehicle was administrated i.p. into the donor 1 h before the transplantation. Tissue and blood samples were collected at various times after transplantation, and a survival study was performed.

RESULTS

Hepatic expression of active β-catenin and its downstream target gene Axin2 were decreased in 30% of liver grafts after transplantation while the Wnt agonist increased their expression similar to the 50% liver grafts. The Wnt agonist reversed inhibition of cyclin D1 expression and adenosine triphosphate production in the 30% liver grafts compared with the 50% grafts. The Wnt agonist also attenuated hepatocellular injury and increased the hepatocyte proliferation response, liver regeneration rate and survival after transplantation of the 30% liver graft.

CONCLUSION

Activation of Wnt/β-catenin signaling in liver grafts by pharmacological pretreatment can accelerate regeneration in a partial liver transplant model.

Searching for NF-kappaB-based treatments of ischemia reperfusion injury

When a tissue becomes ischemic, a host of changes occur at the cellular level that lead to a shift in transcriptional activity of many inflammatory and cytoprotective compounds, a process which is extensively controlled through a family of transcription factors known as nuclear factor kappa-B (NF-kappaB). This shift in activity paradoxically results in both a cytoprotective effect at the cellular level and upon reperfusion, a generally destructive inflammatory response, a phenomenon referred to as ischemia reperfusion (IR) injury. To date, a number of methods of modifying the activity of NF-kappaB through either physiologic or pharmacologic manipulation have been developed and studied in animal models of IR injury and in some cases in human clinical trials. Nearly every method of NF-kappaB antagonism has demonstrated a discrete protective effect allowing investigators to reduce myocardial infarct sizes by 60% and cerebral infarct sizes by 57% relative to untreated control animals. The problem of IR injury is all too common and represents a discrete threat not only to the tissues directly involved in the ischemic event, but also to distal sites as well as is seen in the evolution of acute respiratory distress and severe inflammatory response syndromes. In the course of this review, the nature of NF-kappaB and its involvement in IR injury is examined along with the efficacy of the various NF-kappaB-based investigational treatment developed to date.

Ischemic preconditioning improves rat kidney allograft function after ischemia/reperfusion injury: the role of tumor necrosis factor-alpha

OBJECTIVE

The aim of this study was to investigate the early protection of ischemic preconditioning (IPC) and its mechanisms in transplanted rat kidneys.

MATERIALS AND METHODS

Thirty-six male Sprague-Dawley (SD) rat donors and recipients were randomly divided into the following groups: sham-operated group (A; n = 6); untreated transplantation group (B; n = 6); and treatment group (C; n = 6). Group A was subjected to exploratory laparotomy. Group B received orthotopic transplantation. Group C underwent a 15-minute period of ischemia followed by a 10-minute reperfusion before orthotopic transplantation. We assessed the serum creatinine (SCr), blood urea nitrogen (BUN), and to evaluate the degree of kidney graft ischemia/reperfusion injury: tumor necrosis factor-alpha (TNF-alpha), IkappaB kinase-beta (IKK-beta), and nuclear factor-kappa B (NF-kappaB) P65 subunit mRNA expressions.

RESULTS

The levels of SCr and BUN in groups C and B were greater than in the sham-operated group (P < .01), but there was no significant difference between the C and B groups at 24 hours after transplantation (P > .05). The degree of renal graft tubular injury in group C was significantly less compared with group B (P < .01). TNF-alpha transcription levels at 24 hours after transplantation were significantly less compared with the non-IPC group (P < .01). However, no significant difference was observed in IKK-beta mRNA and P65 mRNA expressions between groups C and B (P > .05).

CONCLUSIONS

A 1-cycle schedule of preconditioning (15 min/10 min) attenuated renal graft ischemia/reperfusion injury in the early phase. IPC can improve rat kidney allograft function after ischemia/reperfusion injury. The inhibitory effects on TNF-alpha and on positive feedback signaling of TNF-alpha/NF-kappaB pathways may play important roles in renal graft protection in the early stage.

Role of Kupffer cells in the induction of tolerance of orthotopic liver transplantation in rats

Because the role of Kupffer cells (KCs) in liver transplantation (LT) tolerance is not well understood, we investigated their role in liver allograft acceptance in rats. Male Sprague-Dawley rats were randomly assigned to either an LT group or a transplantation group pretreated with GdCl(3) (Gd group). The rats were postoperatively sacrificed at indicated times for histology and assessment of KC function, nuclear factor kappa B (NF-kappaB) activity, and cytokine production. KCs and T cells (TCs) were isolated from allografts to assess Fas/Fas ligand (FasL) expression. Cytotoxicity of KCs against TCs was monitored by coculturing of (3)H-thymidine TCs with KCs at various effector-to-target ratios. The results were as follows. First, grafts were spontaneously accepted in the LT group with evident apoptosis of TCs; however, inhibition of KCs by pretreatment with GdCl(3) decreased TC apoptosis and shortened the survival of allografts. Second, KCs in the LT group had increased levels of FasL messenger RNA and protein with respect to that in the Gd group. Third, by in vitro cocultivation assays, KCs induced TC apoptosis though elevated expression of FasL, and this process could be blocked by anti-FasL antibody. Fourth, there was a positive correlation between activation of NF-kappaB and FasL expression in KCs and interleukin-4 production in the LT group, and the activation of NF-kappaB was inhibited by pretreatment with GdCl(3). In conclusion, KC-induced depletion of TCs via the Fas/FasL pathway might play a critical role in LT tolerance. However, the tolerance is abrogated by suppression of FasL and IL-4 expression via inhibition of NF-kappaB activity by GdCl(3).

Improvement of recipient survival after small size graft liver transplantation in rats with preischemic manipulation or administering antisense against nuclear factor-kappaB

The survival rate of small size graft liver transplantation (SSGLT) in rats is inversely related to graft volume. The present study aims to evaluate the protective effects of preischemic manipulation (PIM) and oligodeoxynucleotide (ODN) antisense against NF-kappaB on graft failure and animal survival. The protective effects of PIM and NF-kappaB ODN antisense were investigated in a rat SSGLT model. The graft function and survival of recipient animals over 3 weeks were monitored, and in situ staining for apoptotic cells in the graft tissue was examined. Both PIM and NF-kappaB antisense treatment significantly improved the survival of small graft-transplanted rats compared with the SSGLT group, lowered serum levels of alanine and aspartate aminotransferases, as well as tumor necrosis factor-alpha (TNF-alpha) levels, and minimized apoptotic cell counts in the liver sections. Moreover, the enhanced activation of NF-kappaB in the SSGLT group was diminished in both PIM and NF-kappaB antisense-treated groups. The findings suggest that enhanced NF-kappaB activation and TNF-alpha production may be involved in the ischemia/reperfusion-associated small size graft injury, and that PIM and antisense against NK-kappaB are effective in the attenuation of the small size graft injury, and improve the recipient animal survival.

Ischemic preconditioning in solid organ transplantation: from experimental to clinics

This study reviews the current understanding of ischemic preconditioning (IP) in experimental and clinical setting, and the mechanisms that mediate the complex processes involved as a tool to protect against ischemia and reperfusion (I/R) injury, but is not intended as a complete literature review of preconditioning. IP has been mainly elucidated in cardiac ischemia. Recent reports confirm the efficacy of pre- and postconditioning in cardiac surgery and percutaneous coronary interventions in humans. IP utilizes endogenous as well as distant mechanisms in skeletal muscle, liver, lung, kidney, intestine and brain in animal models to convey varying degrees of protection from I/R injury. Specifically, preconditioned tissues exhibit altered energy metabolism, better electrolyte homeostasis and genetic reorganization, as well as less oxygen-free radicals and activated neutrophils release, reduced apoptosis and better microcirculatory perfusion. To date, there are few human studies, but recent trials suggest that human liver, lung and skeletal muscle acquire protection after IP. Present data address the potential therapeutic application of IP in the prevention of I/R damage specially aimed at clinical transplantation. IP is ubiquitous but more research is required to fully translate these findings to the clinical arena.

Impaired hepatic regeneration by ischemic preconditioning in a rat model of small-for-size liver transplantation

OBJECTIVE

Graft size is one of the major risk factors in adult-to-adult living donor liver transplantation and rapid regeneration is an essential post-operative requirement. Ischemic preconditioning (IPC) has been shown to be an effective strategy in the reduction of hepatic ischemia-reperfusion injury and stimulation of liver regeneration. This study was designed to evaluate the effects of IPC on liver regeneration in small-for-size liver grafts.

METHODS

We employed a rat orthotopic liver transplantation model using small-for-size (30%) grafts, in the presence or absence (control) of IPC (10 min of ischemia followed by 15 min of reperfusion). Survival rate, graft injury, hepatocellular proliferation, cell cycle progression, Stat3 activation, as well as TNF-alpha and IL-6 expression were assessed.

RESULTS

IPC significantly enhanced the extent of graft injury and hindered hepatic regeneration in small-for-size liver grafts. The 7-day survival rate was also reduced by IPC, but failed to reach statistical significance. IPC did not affect TNF-alpha levels, but significantly decreased the elevation of IL-6 after reperfusion. These findings were correlated with down-regulation of cyclin E and cyclin D1, and decreased numbers of PCNA-positive nuclei in IPC grafts. These results were inconsistent with Stat3 activation, as P-Stat3 exhibited a stronger and prolonged pattern of expression in the IPC group, compared to controls.

CONCLUSIONS

Ischemic preconditioning may impair liver regeneration in small-for-size liver grafts by decreasing IL-6 and blunting cell cycle progression, through a mechanism at least partially independent of Stat3.

Role of ischaemic preconditioning in liver regeneration following major liver resection and transplantation

Liver ischaemic preconditioning (IPC) is known to protect the liver from the detrimental effects of ischaemic-reperfusion injury (IRI), which contributes significantly to the morbidity and mortality following major liver surgery. Recent studies have focused on the role of IPC in liver regeneration, the precise mechanism of which are not completely understood. This review discusses the current understanding of the mechanism of liver regeneration and the role of IPC in this setting. Relevant articles were reviewed from the published literature using the Medline database. The search was performed using the keywords “liver”, “ischaemic reperfusion”, “ischaemic preconditioning”, “regeneration”, “hepatectomy” and “transplantation”. The underlying mechanism of liver regeneration is a complex process involving the interaction of cytokines, growth factors and the metabolic demand of the liver. IPC, through various mediators, promotes liver regeneration by up-regulating growth-promoting factors and suppresses growth-inhibiting factors as well as damaging stresses. The increased understanding of the cellular mechanisms involved in IPC will enable the development of alternative treatment modalities aimed at promoting liver regeneration following major liver resection and transplantation.