Graft dysfunction following liver transplantation: role of free radicals

Prediction of late allograft dysfunction following liver transplantation by immunological blood biomarkers

BACKGROUND

An accelerated course of hepatic fibrosis may occur in liver transplantation (LT) patients despite normal or slightly abnormal liver blood tests.

AIM

To identify screening tools based on blood biomarkers to predict late allograft dysfunction in LT recipients.

METHODS

174 LT recipients were enrolled. Liver biopsy, liver functional tests, cytokine quantitation in serum, as well as soluble MHC class I polypeptide-related sequence A and B (sMICA/sMICB) and soluble UL16 binding protein 2 (sULBP2) were performed.

RESULTS

Patients with late graft dysfunction had a significantly higher donor age, lower albumin level, higher alanine (ALT) and aspartate aminotransferase (AST), gamma-glutamyl transpeptidase (GGT), total bilirubin and alkaline phosphatase (ALP), higher sMICA, sULBP2, higher interleukin (IL) 6, interferon γ and lower IL10 in serum as compared to recipients without allograft dysfunction. In order to provide a better statistical accuracy for discriminating 5-year allograft dysfunction from other less progressive subtype of allograft injury, we established a predictive model, based on 7 parameters (serum ALP, ALT, AST, GGT, sMICA, IL6 and albumin) which provided an Area Under the Receiver Operating Characteristics (AUROC) curve of 0.905.

CONCLUSIONS

Blood-based biomarkers can significantly improve prediction of late liver allograft outcome in LT patients. The new developed score comprising serum parameters, with an excellent AUROC, can be reliably used for diagnosing late allograft dysfunction in transplanted patients.

Ascorbic acid improves thrombotic function of platelets during living donor liver transplantation by modulating the function of the E3 ubiquitin ligases c-Cbl and Cbl-b

OBJECTIVE

To investigate the effect of ascorbic acid (AA) on hemostatic function during living donor liver transplantation (LDLT).

METHODS

Blood samples from 21 LDLT recipients were taken within 30 minutes after induction and at 120 minutes after reperfusion. Rotational thromboelastography (TEG) and western blot analysis were used to analyze for fibrinolysis and functional changes in c-Cbl and Cbl-b, respectively. TEG test samples were prepared as one of three groups: C group (0.36 mL of blood), N group (0.324 mL of blood + 0.036 mL of 0.9% normal saline), and A group (0.324 mL of blood + 0.036 mL of 200 µmol/L-AA dissolved in 0.9% normal saline).

RESULTS

AA decreased fibrinolysis and increased clot rigidity at baseline and 120 minutes after reperfusion. Cbl-b expression was significantly increased at baseline and 120 minutes after reperfusion in the A group compared with the C and N groups. However, c-Cbl phosphorylation was most significantly decreased in the A group at baseline and 120 minutes after reperfusion.

CONCLUSION

AA can significantly decrease fibrinolysis and improve clot rigidity in LT recipients during LDLT, and functional changes in Cbl-b and c-Cbl might represent the underlying mechanism. AA may be considered for use during LDLT to decrease hyperfibrinolysis.

Hydrogen peroxide mobilizes Ca2+ through two distinct mechanisms in rat hepatocytes

AIM

Hydrogen peroxide (H2O2) is produced during liver transplantation. Ischemia/reperfusion induces oxidation and causes intracellular Ca2+ overload, which harms liver cells. Our goal was to determine the precise mechanisms of these processes.

METHODS

Hepatocytes were extracted from rats. Intracellular Ca2+ concentrations ([Ca2+](i)), inner mitochondrial membrane potentials and NAD(P)H levels were measured using fluorescence imaging. Phospholipase C (PLC) activity was detected using exogenous PIP2. ATP concentrations were measured using the luciferin-luciferase method. Patch-clamp recordings were performed to evaluate membrane currents.

RESULTS

H2O2 increased intracellular Ca2+ concentrations ([Ca2+](i)) across two kinetic phases. A low concentration (400 micromol/L) of H2O2 induced a sustained elevation of [Ca2+](i) that was reversed by removing extracellular Ca2+. H2O2 increased membrane currents consistent with intracellular ATP concentrations. The non-selective ATP-sensitive cation channel blocker amiloride inhibited H2O2-induced membrane current increases and [Ca2+](i) elevation. A high concentration (1 mmol/L)of H2O2 induced an additional transient elevation of [Ca2+](i), which was abolished by the specific PLC blocker U73122 but was not eliminated by removal of extracellular Ca2+. PLC activity was increased by 1 mmol/L H2O2 but not by 400 micromol/L H2O2.

CONCLUSIONS

H2O2 mobilizes Ca2+ through two distinct mechanisms. In one, 400 micromol/L H2O2-induced sustained [Ca2+](i) elevation is mediated via a Ca2+ influx mechanism, under which H2O2 impairs mitochondrial function via oxidative stress,reduces intracellular ATP production, and in turn opens ATP-sensitive, non-specific cation channels, leading to Ca2+ influx.In contrast, 1 mmol/L H2O2-induced transient elevation of [Ca2+](i) is mediated via activation of the PLC signaling pathway and subsequently, by mobilization of Ca2+ from intracellular Ca2+ stores.

Experimental results and clinical impact of using autologous rectus fascia sheath for vascular replacement

Vascular complications are major causes of graft failure in liver transplantation. The use of different vascular grafts is common but the results are controversial. The aim of this study was to create an 'ideal' arterial interponate for vascular replacements in the clinical field. An autologous, tubular graft prepared from the posterior rectus fascia sheath was used for iliac artery replacement in dogs for 1, 3, 6 and 12 months. Forty-one grafts were implanted and immunosuppression was used in separate groups. The patency rate was followed by Doppler ultrasound. Thirty-seven grafts remained patent, 2 cases with thrombosis and 2 cases with stenosis occurred. There was no evidence of necrosis or aneurysmatic formation. The histological analysis included conventional light microscopic and immunohistochemical examinations for CD34 and factor VIII. The explanted grafts showed signs of arterialisation, appearance of elastin fibres, and smooth muscle cells after 6 months. Electron microscopy showed intact mitochondrial structures without signs of hypoxia. In conclusion, the autologous graft presents acceptable long-term patency rate. It is easy to handle and the concept of beneficial presence of the anti-clot mesothelium until endothelialisation seems to work. The first clinical use was already reported by our group with more than 2 years survival.

Reperfusion injury in liver transplantation

Reperfusion injury occurring in the transplanted liver is a complex lesion and has been the focus of considerable research over the past decade. This section will review recent major developments in understanding the mechanisms involved and their application to clinical transplantation.

Morphometric analysis of primary graft non-function in liver transplantation

AIMS

Primary graft non-function (PNF) is a life-threatening condition that is thought to be the consequence of microcirculation injury. The aim of the present study was to assess, with a computerized morphometric model, the morphological changes at reperfusion in liver biopsy specimens from patients who developed PNF after liver transplantation.

METHODS AND RESULTS

Biopsy specimens were obtained at maximum ischaemia and at the end of reperfusion. Morphology included many stereological parameters, such as volumes of all parenchymal components, surface density, size distribution and mean diameter of hepatocytes. Other variables examined were intensive care unit stay, degree of steatosis, serum liver function tests and ischaemic time. In the postoperative period, the PNF group showed elevated serum levels of alanine transferase, decreased daily rate of bile production and prothrombin activity. Blood lactates were significantly higher in the PNF group than in a control group. When comparing groups, the volumetric parameters related to hepatocytes and sinusoids and the surface densities of the hepatic cells showed an inverse relationship. At the end of reperfusion, in PNF group the volume fraction of hepatocyte cytoplasm was decreased; in contrast, the volume fraction of sinusoidal lumen was markedly increased. The cell profiles showed the same inverse trend: the surface density of the parenchymal border of hepatocytes was decreased in PNF when compared with the control group, while the surface density of the vascular border was increased. In the PNF group, the surface density of the sinusoidal bed was directly correlated with alanine transferase, daily rate of bile production, prothrombin activity and cold ischaemic time.

CONCLUSIONS

The alterations in hepatic architecture, as demonstrated by morphometric analysis in liver transplant recipients that developed PNF, provide additional information that may represent useful viability markers of the graft to complement conventional histological analysis.

Experimental vascular graft for liver transplantation

Hepatic artery thrombosis is a major cause of graft failure in liver transplantation. Use of donor interponates are common, but results are controversial because of necrosis or thrombosis after rejection. Reperfusion injury, hypoxia and free radical production determinate the survival. The aim of the study was to create an 'ideal' arterial interponate. Autologous, tubular graft lined with mesothelial cells, prepared from the posterior rectus fascia sheath, was used for iliac artery replacement in eight mongrel dogs for six months under immunosuppression. Patency rate was followed by Doppler ultrasound. Eight grafts remained patent and another two are patent after one year. The patency rate was good (median Doppler flow: 370 cm/sec) and there was no necrosis, thrombosis or aneurysmatic formation. The grafts showed viable morphology with neoangiogenesis, appearance of elastin, smooth muscle and endothelial cells. Electron microscopy showed intact mitochondrial structures without signs of hypoxia. Tissue oxygenation was good in all cases with normal (< 30 ng/ml) myeloperoxidase production. In conclusion, this autologous graft presents good long-term patency rate. Viability, arterialisation and low thrombogenicity are prognostic factors indicating usability of the graft in the clinical practice without the risk of rejection. Further investigations such as cell cultures and standardisation are necessary.

Protein kinase activation by warm and cold hypoxia- reoxygenation in primary-cultured rat hepatocytes-JNK(1)/SAPK(1) involvement in apoptosis

Ischemia-reperfusion procedures induced severe hepatic damages owing to different processes related to hypoxia and reoxygenation (H/R) phases, including the consecutive oxygen free radical (OFR) release. Stress-activated protein kinases (SAPKs) could be activated by extracellular stimuli. The aim of this study was to show whether H/R stress conditions could stimulate these kinases, and especially c-jun-N-terminal kinase (JNK(1)/SAPK(1)), to reveal a potential role of JNK(1)/SAPK(1) in the control of hepatocyte apoptosis. Primary cultured rat hepatocytes, isolated from other liver cells and blood flow, were subjected to warm and cold hypoxia-reoxygenation phases mimicking surgical and transplant conditions. The activation status of SAPKs was evaluated by immunoprecipitation or Western-blotting experiments, whereas apoptosis was assessed by measuring caspase activation and internucleosomal DNA fragmentation in vitro and by TUNEL reaction, in vivo. Hypoxia, and especially hypoxia-reoxygenation, significantly increased JNK(1)/SAPK(1) activation in cultured hepatocytes. Either in warm or cold conditions, OFR scavengers (N-Acetylcystein, Di-Phenyleneiodonium, Deferoxamine) decreased this stimulation. Warm ischemia-reperfusion also led to JNK activation. Hypoxia and especially hypoxia-reoxygenation induced programmed cell death in vivo and in vitro. This last phenomenon was inhibited when hepatocytes were treated with SB 202190, which was described as a potent inhibitor of p38 and JNK activities. Altogether, these results confirmed that JNK(1)/SAPK(1) was activated during the hypoxia-reoxygenation process, and that this activity participated in the onset of the apoptosis program.

Induction of peroxiredoxins in transplanted livers and demonstration of their in vitro cytoprotection activity

Peroxiredoxin (Prx)-I and -II belong to a new class of antioxidants. Here, we report that they are induced by ischemia/reperfusion (I/R) in transplanted livers. Hypothesizing that Prxs are induced to protect liver from oxidative damage, we transduced these human genes into murine NIH-3T3 cells. The overexpressed Prxs made the cells more resistant to t-butylhydroperoxide-induced apoptosis. These results indicate that Prx-I and Prx-II are induced by the transplantation process and can protect cells against oxidant damage in tissue culture. Thus, proper genetic manipulations of Prxs may be useful in increasing the success rate of organ transplantation.

Heat shock preconditioning on mitochondria during warm ischemia in rat livers

BACKGROUND

The aim of this study was to investigate the effects of stress tolerance from heat shock preconditioning on changes in mitochondrial functions during ischemia-reperfusion injury of the liver.

MATERIALS AND METHODS

Rats were divided into a heat shock group (group HS) and a control group (group C). In group HS, rats received heat shock pretreatment 48 h prior to ischemia-reperfusion. Heat shock pretreatment was performed in a water bath at 42 degrees C for 15 min under general anesthesia. In group C, the same treatment was done with the water bath at 37 degrees C instead of at 42 degrees C. A 30-min warm ischemia by cramping the hepatoduodinal ligament (Pringle's maneuver) followed by a 60-min reperfusion was administered to all rats. Changes in membrane potential of hepatic mitochondria (MPM); mitochondrial respiratory function before ischemia (n = 5), after ischemia (n = 10), and after reperfusion (n = 10); and ATP recovery after reperfusion were compared between the groups.

RESULTS

After a 30-min ischemia, MPM in group C decreased significantly and did not recover even after reperfusion. On the other hand, MPM in group HS was maintained even after a 30-min ischemia and 60 min into reperfusion as well. The respiratory control ratio (RCR) of the mitochondria in group C decreased to as low as 5.06 +/- 0.72 after a 30-min ischemia, but in group HS, RCR was maintained near a normal level. The ATP level recovered significantly earlier in group HS than in group C after reperfusion.

CONCLUSIONS

Heat shock preconditioning of the liver protected mitochondria from loss of membrane integrity during ischemia and contributed to their ability to produce energy-rich phosphates during reperfusion.

Indocyanine green clearance reflects reperfusion injury following liver transplantation and is an early predictor of graft function

BACKGROUND/AIMS

Primary graft dysfunction is difficult to predict. We have previously shown that indocyanine green clearance measured at 24 h following orthotopic liver transplantation predicts graft survival and outcome. We prospectively evaluated the use of indocyanine green clearance (with a cut-off value of 200 ml/min) as a marker of graft function following orthotopic liver transplantation and investigated its relationship with the markers of reperfusion injury during orthotopic liver transplantation.

METHODS

In all patients indocyanine green clearance was measured at 24 h. Repeated blood samples were taken before, during the anhepatic and reperfusion phase and up to 12 h following orthotopic liver transplantation to measure the levels of neutrophil elastase and reactive oxygen intermediates. All patients studied had normal hepatic arterial pulse on Doppler-ultrasound post orthotopic liver transplantation.

RESULTS

All patients with indocyanine green clearance >200 ml/min recovered following orthotopic liver transplantation and remained well up to 3 months of follow up. Four patients had an indocyanine green clearance <200 ml/min; three were re-transplanted for graft failure within 3 days of the transplant, while one survived after prolonged intensive support and hospitalization. Indocyanine green clearance significantly correlated with reactive oxygen intermediates production and neutrophil elastase during orthotopic liver transplantation (r=-0.61, p<0.002 and r=-0.66, p<0.0009, respectively). Indocyanine green clearance was also significantly correlated with alanine aminotransferase and prothrombin time at 24 h post-transplantation (r=-0.35, p<0.02 and r=-0.4, p<0.0077, respectively).

CONCLUSION

Indocyanine green reflects the degree of reperfusion injury and is a good early marker of primary graft function. Indocyanine green clearance over 200 ml/min is associated with favorable outcome.

From cytoprotection to tumor suppression: the multifactorial role of peroxiredoxins

In the past decade, a new family of highly conserved antioxidant enzymes, Peroxiredoxins (Prxs), have been discovered and defined. There are two major Prx subfamilies: one subfamily uses two conserved cysteines (2-Cys) and the other uses 1-Cys to scavenge reactive oxygen species (ROS). This review focuses on the four mammalian 2-Cys members (Prx I-IV) that utilize thioredoxin as the electron donor for antioxidation. The array of biological activities of these proteins suggests that they may be evolutionarily important for cell function. For example, Prxs are capable of protecting cells from ROS insult and regulating the signal transduction pathways that utilize c-Abl, caspases, nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) to influence cell growth and apoptosis. Prxs are also essential for red blood cell (RBC) differentiation and are capable of inhibiting human immunodeficiency virus (HIV) infection and organ transplant rejection. Distribution patterns indicate that Prxs are highly expressed in the tissues and cells at risk for diseases related to ROS toxicity, such as Alzheimer's and Parkinson's diseases and atherosclerosis. This interesting correlation suggests that Prxs are protective against ROS toxicity, yet overwhelmed by oxidative stress in some cells. Prxs tend to form large aggregates at high concentrations, a feature that may interfere with their normal protective function or may even render them cytotoxic. Imbalance in the expression of subtypes can also potentially increase their susceptibility to oxidative stress. Understanding the function and biological role of Prxs may lead to important discoveries about the cellular dysfunction of ROS-related diseases ranging from atherosclerosis to cancer to neurodegenerative diseases.

Propofol preserves the viability of isolated rat hepatocyte suspensions under an oxidant stress

The purpose of this study was to investigate whether propofol protects rat hepatocyte suspensions against an oxidant attack by a free radical generator 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH). Rat hepatocyte suspensions (2 x 10(6) cells/mL) were prepared using Seglen's collagenase perfusion technique. Suspensions were treated with AAPH (50 mM) alone, propofol (28 microM) plus AAPH, or, in a separate experiment, with either AAPH alone or 10% intralipid (0.5 microL/mL) plus AAPH. Each experiment had untreated control suspensions. Cell viability was measured at 1, 2, and 3 h using the trypan blue exclusion test and expressed as a percentage of the initial number of viable cells. Cells taken from control at time 0 h and each experimental group at 1 h from five separate hepatocyte preparations were examined by electron microscopy. Control cell viability decreased with time. The addition of AAPH significantly reduced viability compared with control (P < 0.0001); pretreatment with propofol significantly attenuated this effect at 1 h (P = 0.0008), but 10% intralipid had no effect. Electron microscopy revealed structural changes in cell membranes that could have accounted for the inability to exclude trypan blue. In conclusion, a 28-microM concentration of propofol protects rat hepatocytes from an oxidant stress sufficient to cause cell death at 1 h.

IMPLICATIONS

Oxidants contribute to tissue injury in a variety of situations. We have shown that the anesthetic propofol improves survival of liver cells exposed to oxidant injury at blood concentrations achieved in anesthetized patients. These effects may be relevant during transplantation and critical illness.