Nitric oxide in liver transplantation: pathobiology and clinical implications

Nitric oxide-mediated effects of L-ornithine-L-aspartate in acute toxic liver injury

This study was aimed to investigate nitric oxide-dependent mechanisms of L-ornithine-L-aspartate (LOLA) action in acute toxic liver injury in rats. Acute hepatitis was induced in Wistar rats using 50% oil solution of tetrachloromethane (CCl4) intragastrically (2 g/kg) twice in a 24 hour interval. Intraperitoneal treatment with LOLA (200 mg/kg) was started 6 hours after the second CCl4 administration and maintained for 3 consecutive days. L-Nω-Nitroarginine Methyl Ester (L-NAME) was used intraperitoneally (10 mg/kg). In CCl4-induced hepatitis, LOLA restores the structure of hepatocytes and prevents aminotransferases, alkaline phosphatase and gamma-glutamyl transferase elevation. It decreases total bilirubin concentration but does not affect increased cholesterol level. LOLA augments urea concentration, total protein level in blood and liver as well as serum and liver content of nitrite anions. LOLA enhances activity of catalase, glutathione S-transferase, manganese superoxide dismutase, increases reduced glutathione level and total antioxidant capacity and decreases thiobarbituric acid reactive substances level. The concomitant use of L-NAME inhibits the action of LOLA to enhance nitrite anions synthesis both in serum and liver, to delay the recovery of hepatocytes, to counteract LOLA effect against blood total protein reduction, to prevent the decline in aminotransferases, alkaline phosphatase,, gamma-glutamyl transferase and glutathione S-transferase activity and to reduce catalase activity and reduced glutathione level. Therefore, in CCl4-induced hepatitis, LOLA effectively prevents cytolysis and cholestasis, improves liver metabolism and protects against oxidative stress. Partially, these changes occur in nitric oxide-mediated mechanism since the use of L-NAME declines most of LOLA effects.

Melatonin and its protective role in attenuating warm or cold hepatic ischaemia/reperfusion injury

Although the liver is the only organ with regenerative capacity, various injury factors induce irreversible liver dysfunction and end‐stage liver disease. Liver resection and liver transplantation (LT) are effective treatments for individuals with liver failure, liver cirrhosis and liver cancers. The remnant or transplanted liver tissues will undergo hepatic ischaemia/reperfusion (IR), which leads to oxidative stress, inflammation, immune injury and liver damage. Moreover, systemic ischaemia induced by trauma, stroke, myocardial ischaemia, haemorrhagic shock and other injury factors also induces liver ischaemia/reperfusion injury (IRI) in individuals. Hepatic IRI can be divided into warm IRI, which is induced by liver surgery and systemic ischaemia, and cold IRI, which is induced by LT. Multiple studies have shown that melatonin (MT) acts as an endogenous free radical scavenger with antioxidant capacity and is also able to attenuate hepatic IRI via its anti‐inflammatory and antiapoptotic capacities. In this review, we discuss the potential mechanisms and current strategies of MT administration in liver surgery for protecting against warm or cold hepatic IRI. We highlight strategies to improve the efficacy and safety of MT for attenuating hepatic IRI in different conditions. After the potential mechanisms underlying the interactions between MT and other important cellular processes during hepatic IR are clarified, more opportunities will be available to use MT to treat liver diseases in the future.

Distinct gut microbial compositional and functional changes associated with impaired inhibitory control in patients with cirrhosis

Most cirrhosis etiologies, such as alcohol, hepatitis C, and obesity, involve behavior that require the loss of inhibitory control. Once cirrhosis develops, patients can also develop cognitive impairment due to minimal hepatic encephalopathy (MHE). Both processes could have distinct imprints on the gut-liver-brain axis. Determine the impact of inhibitory control versus traditional cirrhosis-related cognitive performance on gut microbial composition and function. Outpatients with cirrhosis underwent two tests for MHE: inhibitory control test (MHEICT, computerized associated with response inhibition) and psychometric hepatic encephalopathy score (MHEPHES, paper-pencil HE-specific associated with subcortical impairment) along with stool collection for metagenomics. MHEICT/not, MHEPHES/not, and discordant (positive on one test but negative on the other) were analyzed for demographics, bacterial species, and gut-brain modules (GBM) using multi-variable analyses. Ninety-seven patients [47 (49%) MHEPHES, 76 (78%) MHEICT, 41 discordant] were enrolled. MHEPHES/not: Cirrhosis severity was worse in MHEPHES without differences in alpha/beta diversity on bacterial species or GBMs. Pathobionts (Enterobacteriaceae) and γ-amino-butryic acid (GABA) synthesis GBM were higher in MHEPHES. MHEICT/not: We found similar cirrhosis severity and metagenomic alpha/beta diversity in MHEICT versus not. However, alpha/beta diversity of GBMs were different in MHEICT versus No-MHE patients. Alistipes ihumii, Prevotella copri, and Eubacterium spp. were higher, while Enterococcus spp. were uniquely lower in MHEICT versus no-MHE and discordant comparisons. GBMs belonging to tryptophan, menaquinone, GABA, glutamate, and short-chain fatty acid synthesis were also unique to MHEICT. Gut microbial signature of impaired inhibitory control, which is associated with addictive disorders that can lead to cirrhosis, is distinct from cirrhosis-related cognitive impairment.

Ischemia/Reperfusion Injury in the Aged Liver: The Importance of the Sinusoidal Endothelium in Developing Therapeutic Strategies for the Elderly

The liver endothelium plays a key role in the progression and resolution of liver diseases in young and adult individuals. However, its role in older people remains unknown. We have herein evaluated the importance of the sinusoidal endothelium in the pathophysiology of acute liver injury, and investigated the applicability of simvastatin, in aged animals. Eighteen-months-old male Wistar rats underwent 60 minutes of partial warm ischemia followed by 2 hours of reperfusion (WIR). A group of aged rats received simvastatin for 3 days before WIR. Endothelial phenotype, parenchymal injury, oxidative and nitrosative stress, and fenestrae dynamics were analyzed. The effects of WIR and simvastatin were investigated in primary LSEC from aged animals. The results of this study demonstrated that WIR significantly damages the liver endothelium and its effects are markedly worse in old animals. WIR-aged livers exhibited reduced vasodilation and sinusoidal capillarization, associated with liver damage and cellular stress. Simvastatin prevented the detrimental effects of WIR in aged livers. In conclusion, the liver sinusoidal endothelium of old animals is highly vulnerable to acute insult, thus targeted protection is especially relevant in preventing liver damage. Simvastatin represents a useful therapeutic strategy in aging.

Tender coconut water suppresses hepatic inflammation by activating AKT and JNK signaling pathways in an in vitro model of sepsis

Tender coconut water (TCW) is a natural plant product rich in phytochemicals and protects against toxic liver injury. However, the mechanism by which TCW inhibits inflammation and tissue damage is unknown. We examined the effect of TCW on primary rat hepatocyte viability, cytokine-induced gene expression and proinflammatory signaling in an in vitro model of sepsis. We observed that TCW improved hepatocyte viability and protected hepatocytes against cytokine-mediated cell death. TCW suppressed IL-1β-mediated increases in Nos2, Tnf, and Il6 mRNA and increased heme oxygenase 1 (HMOX1) protein. TCW inhibited iNOS expression through activation of AKT and JNK pathways since inhibition of PI3K and JNK signaling reduced TCW's effect on iNOS protein expression and activity. These results demonstrate that TCW reduces proinflammatory gene expression and hepatocyte injury produced by elevated inflammatory cytokines and nitric oxide production.

Thymoquinone mitigate ischemia-reperfusion-induced liver injury in rats: a pivotal role of nitric oxide signaling pathway

Oxidative and nitrosative stress-induced endothelial cell damage play an essential role in the pathogenesis of hepatic ischemia-reperfusion (IR) injury. IR is associated with reduced eNOS expression and exacerbated by superimposed stress. NOSTRIN induces intracellular endothelial nitric oxide synthase (eNOS) translocation and inducible nitric oxide synthase (iNOS) increases nitric oxide (NO) production. Our aim was to assess hepatic expression of iNOS, eNOS, and NOSTRIN in IR with or without N-acetylcysteine (NAC) or thymoquinone (TQ) pretreatment and to compare their hepatoprotective effects. Surgical induction of IR was performed by occlusion of hepatic pedicle for 30 min with mini-clamp and reperfused for 30 min. The effects of TQ (20 mg/kg/day) or NAC (300 mg/kg/day) administered orally for 10 days were evaluated by serum ALT and AST, oxidative stress parameters, NO production, and histopathological analysis. Also, localization and expression of iNOS, eNOS, and NOSTRIN were assessed by immunofluorescence. TQ or NAC pretreatment significantly decreased elevated serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and myeloperoxidase (MPO) activities, malondialdehyde (MDA) level, and NO production. In addition, they restored the depleted GSH content and alleviated histopathological changes. Furthermore, they up-regulated eNOS and down-regulated iNOS and NOSTRIN expressions. TQ exerts its hepatoprotective effect, at least in part, by nitric oxide signaling pathway through modulation of iNOS, eNOS, and NOSTRIN expressions as well as suppression of oxidative stress.

Melatonin role preventing steatohepatitis and improving liver transplantation results

Liver steatosis is a prevalent process that is induced due to alcoholic or non-alcoholic intake. During the course of these diseases, the generation of reactive oxygen species, followed by molecular damage to lipids, protein and DMA occurs generating organ cell death. Transplantation is the last-resort treatment for the end stage of both acute and chronic hepatic diseases, but its success depends on ability to control ischemia-reperfusion injury, preservation fluids used, and graft quality. Melatonin is a powerful endogenous antioxidant produced by the pineal gland and a variety of other because of its efficacy in organs; melatonin has been investigated to improve the outcome of organ transplantation by reducing ischemia-reperfusion injury and due to its synergic effect with organ preservation fluids. Moreover, this indolamine also prevent liver steatosis. That is important because this disease may evolve leading to an organ transplantation. This review summarizes the observations related to melatonin beneficial actions in organ transplantation and ischemic-reperfusion models.

Akt: A Therapeutic Target in Hepatic Ischemia-Reperfusion Injury

BACKGROUND

Liver transplantation is the second most common transplant procedure in the United States. A leading cause of post-transplantation organ dysfunction is I/R injury. During I/R injury, the serine/threonine kinase Akt is activated, stimulating downstream mediators to promote cellular survival. Due to the cellular effects of Akt, therapeutic manipulation of the Akt pathway can help reduce cellular damage during hepatic I/R that occurs during liver transplantation.

OBJECTIVE

A full description of therapeutic options available that target Akt to reduce hepatic I/R injury has not been addressed within the literature. The purpose of this review is to illuminate advances in the manipulation of Akt that can be used to therapeutically target I/R injury in the liver.

METHODS

An in depth literature review was performed using the Scopus and PubMed databases. A total of 75 published articles were utilized for this manuscript. Terminology searched includes a combination of "hepatic ischemia/reperfusion injury", "Akt/PKB", "preconditioning" and "postconditioning."

RESULTS

Four principal methods that reduce I/R injury include hepatic pre- and postconditioning, pharmacological intervention and future miRNA/gene therapy. Discussed therapies used serum alanine aminotransferase levels, liver histology and phosphorylation of downstream mediators to confirm the Akt protective effect.

CONCLUSION

The activation of Akt from the reviewed therapies has resulted in predictable reduction in hepatocyte damage using the previously mentioned measurements. In a clinical setting, these therapies could potentially be used in combination to achieve better outcomes in hepatic transplant patients. Evidence supporting reduced I/R injury through Akt activation warrants further studies in human clinical trials.

Potential benefits of melatonin in organ transplantation: a review

Organ transplantation is a useful therapeutic tool for patients with end-stage organ failure; however, graft rejection is a major obstacle in terms of a successful treatment. Rejection is usually a consequence of a complex immunological and nonimmunological antigen-independent cascade of events, including free radical-mediated ischemia-reperfusion injury (IRI). To reduce the frequency of this outcome, continuing improvements in the efficacy of antirejection drugs are a top priority to enhance the long-term survival of transplant recipients. Melatonin (N-acetyl-5-methoxytryptamine) is a powerful antioxidant and ant-inflammatory agent synthesized from the essential amino acid l-tryptophan; it is produced by the pineal gland as well as by many other organs including ovary, testes, bone marrow, gut, placenta, and liver. Melatonin has proven to be a potentially useful therapeutic tool in the reduction of graft rejection. Its benefits are based on its direct actions as a free radical scavenger as well as its indirect antioxidative actions in the stimulation of the cellular antioxidant defense system. Moreover, it has significant anti-inflammatory activity. Melatonin has been found to improve the beneficial effects of preservation fluids when they are enriched with the indoleamine. This article reviews the experimental evidence that melatonin is useful in reducing graft failure, especially in cardiac, bone, otolaryngology, ovarian, testicular, lung, pancreas, kidney, and liver transplantation.

Cromoglycate, not ketotifen, ameliorated the injured effect of warm ischemia/reperfusion in rat liver: role of mast cell degranulation, oxidative stress, proinflammatory cytokine, and inducible nitric oxide synthase

Hepatic ischemia/reperfusion (ISCH/REP) is a major clinical problem that is considered to be the most common cause of postoperative liver failure. Recently, mast cells have been proposed to play an important role in the pathophysiology of ISCH/REP in many organs. In contrast, the role played by mast cells during ISCH/REP-induced liver damage has remained an issue of debate. This study aimed to investigate the protective role of mast cells in order to search for an effective therapeutic agent that could protect against fatal ISCH/REP-induced liver damage. A model of warm ISCH/REP was induced in the liver of rats. Four groups of rats were used in this study: Group I: SHAM (normal saline, intravenously [iv]); Group II: ISCH/REP; Group III: sodium cromoglycate + ISCH/REP (CROM + ISCH/REP), and Group IV: ketotifen (KET) + ISCH/REP (KET + ISCH/REP). Liver damage was assessed both histopathologically and biochemically. Mast cell degranulation was assessed histochemically. Lipid peroxidation (malondialdehyde [MDA]) as well as the levels of glutathione (GSH), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α), the formation of nitric oxide (NO), and the expression of inducible NO synthase (iNOS) were determined. The results of this study revealed increased mast cell degranulation in the liver during the acute phase of ISCH/REP. Moreover, CROM, but not KET, decreased the activity of alanine aminotransferase, aspartate aminotransferase, and lactic dehydrogenase and maintained normal liver tissue histology. Both CROM and KET protected against mast cell degranulation in the liver. In addition, both CROM and KET decreased IL-6 and TNF-α. However, CROM, but not KET, decreased MDA formation and increased GSH. Furthermore, KET, but not CROM, increased both NO formation and iNOS expression. In conclusion, this study clearly demonstrated mast cell degranulation in warm ISCH/REP in the liver of rats. More importantly, CROM, but not KET, ameliorated the effect of ISCH/REP-induced injury in rat liver. CROM may protect the liver through mast cell stabilization, inhibition of TNF-α, IL-6, MDA, and iNOS and increased GSH. KET may maintain ISCH/REP-induced liver injury through the NO/iNOS pathway.

Improvement of liver injury and survival by JNK2 and iNOS deficiency in liver transplants from cardiac death mice

BACKGROUND & AIMS

Inclusion of liver grafts from cardiac death donors (CDD) would increase the availability of donor livers but is hampered by a higher risk of primary non-function. Here, we seek to determine mechanisms that contribute to primary non-function of liver grafts from CDD with the goal to develop strategies for improved function and outcome, focusing on c-Jun-N-terminal kinase (JNK) activation and mitochondrial depolarization, two known mediators of graft failure.

METHODS

Livers explanted from wild-type, inducible nitric oxide synthase knockout (iNOS(-/-)), JNK1(-/-) or JNK2(-/-) mice after 45-min aorta clamping were implanted into wild-type recipients. Mitochondrial depolarization was detected by intravital confocal microscopy in living recipients.

RESULTS

After transplantation of wild-type CDD livers, graft iNOS expression and 3-nitrotyrosine adducts increased, but hepatic endothelial NOS expression was unchanged. Graft injury and dysfunction were substantially higher in CDD grafts than in non-CDD grafts. iNOS deficiency and inhibition attenuated injury and improved function and survival of CDD grafts. JNK1/2 and apoptosis signal-regulating kinase-1 activation increased markedly in wild-type CDD grafts, which was blunted by iNOS deficiency. JNK inhibition and JNK2 deficiency, but not JNK1 deficiency, decreased injury and improved function and survival of CDD grafts. Mitochondrial depolarization and binding of phospho-JNK2 to Sab, a mitochondrial protein linked to the mitochondrial permeability transition, were higher in CDD than in non-CDD grafts. iNOS deficiency, JNK inhibition and JNK2 deficiency all decreased mitochondrial depolarization and blunted ATP depletion in CDD grafts. JNK inhibition and deficiency did not decrease 3-nitrotyrosine adducts in CDD grafts.

CONCLUSION

The iNOS-JNK2-Sab pathway promotes CDD graft failure via increased mitochondrial depolarization, and is an attractive target to improve liver function and survival in CDD liver transplantation recipients.

Effects of ischemic preconditioning in a pig model of large-for-size liver transplantation

OBJECTIVE

In most cases of pediatric liver transplantation, the clinical scenario of large-for-size transplants can lead to hepatic dysfunction and a decreased blood supply to the liver graft. The objective of the present experimental investigation was to evaluate the effects of ischemic preconditioning on this clinical entity.

METHODS

Eighteen pigs were divided into three groups and underwent liver transplantation: a control group, in which the weights of the donors were similar to those of the recipients, a large-for-size group, and a large-for-size + ischemic preconditioning group. Blood samples were collected from the recipients to evaluate the pH and the sodium, potassium, aspartate aminotransferase and alanine aminotransferase levels. In addition, hepatic tissue was sampled from the recipients for histological evaluation, immunohistochemical analyses to detect hepatocyte apoptosis and proliferation and molecular analyses to evaluate the gene expression of Bax (pro-apoptotic), Bcl-XL (anti-apoptotic), c-Fos and c-Jun (immediate-early genes), ischemia-reperfusion-related inflammatory cytokines (IL-1, TNF-alpha and IL-6, which is also a stimulator of hepatocyte regeneration), intracellular adhesion molecule, endothelial nitric oxide synthase (a mediator of the protective effect of ischemic preconditioning) and TGF-beta (a pro-fibrogenic cytokine).

RESULTS

All animals developed acidosis. At 1 hour and 3 hours after reperfusion, the animals in the large-for-size and large-for-size + ischemic preconditioning groups had decreased serum levels of Na and increased serum levels of K and aspartate aminotransferase compared with the control group. The molecular analysis revealed higher expression of the Bax, TNF-alpha, I-CAM and TGF-beta genes in the large-for-size group compared with the control and large-for-size + ischemic preconditioning groups. Ischemic preconditioning was responsible for an increase in c-Fos, IL-1, IL-6 and e-NOS gene expression.

CONCLUSION

Ischemia-reperfusion injury in this model of large-for-size liver transplantation could be partially attenuated by ischemic preconditioning.

A review of melatonin in hepatic ischemia/reperfusion injury and clinical liver disease

Ischemia/reperfusion injury (IRI) can lead to cellular and, eventually, organ dysfunction, with the liver being one of the most frequently affected organs. Melatonin, a molecule that has notable antioxidant and anti-inflammatory properties, has been shown to protect against hepatic IRI. The purpose of this review is to summarize the protective effects of melatonin on hepatic IRI. The review initially summarizes the antioxidant properties of melatonin. We then discuss the protective effects of melatonin against endothelial and mitochondrial dysfunction. Thereafter, we introduce some information covering melatonin-related signaling pathways, including heme oxygenase-1 (HO-1), toll-like receptor (TLR), c-Jun N-terminal kinase (JNK), and so on. Furthermore, the clinical application of melatonin to hepatic diseases is considered. Finally, the safety of melatonin is evaluated. Taken together, the information compiled in this review will serve as a comprehensive reference regarding the pharmacological benefits of melatonin on hepatic IRI, aid in the design of future experimental research, and promote melatonin as a new therapeutic target.

Impact of venous-systemic oxygen persufflation with nitric oxide gas on steatotic grafts after partial orthotopic liver transplantation in rats

BACKGROUND

Steatotic livers are associated with poor graft function after transplantation. We investigated the effects of venous-systemic oxygen persufflation with nitric oxide gas (VSOP-NO) on steatotic partial livers after transplantation.

METHODS

Steatotic livers induced by fasting for 2 days and subsequent refeeding for 3 days with a fat-free, carbohydrate-rich diet were reduced in size by 50% and transplanted into Lewis rats after 3 hr of cold storage in histidine-tryptophan-ketoglutarate solution. Gaseous oxygen with nitric oxide (40 ppm) was insufflated into the grafts through the suprahepatic vena cava during cold storage (VSOP-NO group; n=20). Transplantation of cold-static stored steatotic and normal grafts served as controls (Steatotic-Control and Normal-Control, respectively; n=20 for each group).

RESULTS

The graft microcirculation and portal venous flow were increased by VSOP-NO compared with Steatotic-Control (P<0.001 for both). Serum alanine aminotransferase and interleukin-6 levels were lower in VSOP-NO versus Steatotic-Control group (P=0.03 for both). Messenger RNA expression for inducible nitric oxide synthase, which was increased in Steatotic-Control livers 3 hr after transplantation (P=0.02 vs. that at 1 hr), was suppressed by VSOP-NO. Although serum nitrite levels were decreased 1 hr after transplantation in Steatotic-Control (P=0.06 vs. Normal-Control), the VSOP-NO group showed increased levels comparable to Normal-Control. In livers 24 hr after transplantation, moderate vacuolization of hepatocytes by histology with the immunohistochemical expression of nitrotyrosine, indicative of nitrative stress, was found in Steatotic-Control, whereas these findings were less apparent in VSOP-NO-treated livers.

CONCLUSIONS

Application of VSOP-NO for steatotic partial livers reduces hepatocellular damage and improves graft viability and microcirculation after transplantation.

Role of inducible nitric oxide synthase in mitochondrial depolarization and graft injury after transplantation of fatty livers

This study investigated the role of inducible nitric oxide synthase (iNOS) in failure of ethanol-induced fatty liver grafts. Rat livers were explanted 20 h after gavaging with ethanol (5 g/kg) and storing in UW solution for 24h before implantation. Hepatic oil red O staining-positive areas increased from ∼2 to ∼33% after ethanol treatment, indicating steatosis. iNOS expression increased ∼8-fold after transplantation of lean grafts (LG) and 25-fold in fatty grafts (FG). Alanine aminotransferase release, total bilirubin, hepatic necrosis, TUNEL-positive cells, and cleaved caspase-3 were higher in FG than LG. A specific iNOS inhibitor 1400W (5 μM in the cold-storage solution) blunted these alterations by >42% and increased survival of fatty grafts from 25 to 88%. Serum nitrite/nitrate and hepatic nitrotyrosine adducts increased to a greater extent after transplantation of FG than LG, indicating reactive nitrogen species (RNS) overproduction. Phospho-c-Jun and phospho-c-Jun N-terminal kinase-1/2 (JNK1/2) were higher in FG than in LG, indicating more JNK activation in fatty grafts. RNS formation and JNK activation were blunted by 1400W. Mitochondrial polarization and cell death were visualized by intravital multiphoton microscopy of rhodamine 123 and propidium iodide, respectively. After implantation, viable cells with depolarized mitochondria were 3-fold higher in FG than in LG and 1400W decreased mitochondrial depolarization in FG to the levels of LG. Taken together, iNOS is upregulated after transplantation of FG, leading to excessive RNS formation, JNK activation, mitochondrial dysfunction, and severe graft injury. The iNOS inhibitor 1400W could be an effective therapy for primary nonfunction of fatty liver grafts.

Age-related differences in hepatic ischemia/reperfusion: gene activation, liver injury, and protective effect of melatonin

BACKGROUND

Ischemia/reperfusion (I/R) causes functional and structural damage to liver cells, this being more pronounced with increasing age of the tissue. Melatonin is a pineal indole that has been shown to play an important role as a free radical scavenger and anti-inflammatory molecule.

MATERIAL AND METHODS

The age-dependent responses to I/R were compared in 2-mo-old and 14-mo-old male Wistar rats. After 35 min of hepatic ischemia followed by 36 h of reperfusion, rats were sacrificed. Sham-operated control rats underwent the same protocol without real vascular occlusion. Animals were intraperitoneally injected with 10 mg/kg melatonin 24 h before the operation, at the time of surgery, and 12 and 24 h after it. The tissues were submitted to histopathologic evaluation. The levels of ALT and AST were analyzed in plasma. The expression of TNF-α, IL-1β, IL-10, MCP-1, IFN-γ, iNOS, eNOS, Bad, Bax, Bcl2, AIF, PCNA, and NFKB1 genes were detected by RT-PCR in hepatic tissue.

RESULTS

I/R was associated with significant increases in the expression of pro-inflammatory and pro-apoptotic genes in liver. Older rats submitted to I/R were found to respond with increased liver damage as compared with young rats, with serum ALT and AST levels significantly higher than in young animals. Mature rats also showed more evident increases in expression of pro-inflammatory cytokines (IL-1β, MCP-1, and IFN-γ) as well as a decrease in the mRNA expression of IL-10 as compared with young animals. Pro-apoptotic genes (Bax, Bad, and AIF) were significantly enhanced in liver after I/R, without differences between young and mature animals. However, the expression of Bcl2 gene did not show any change. Melatonin treatment was able to lower the expression of pro-inflammatory cytokines and pro-apoptotic genes and to improve liver function, as indicated by normalization of plasma AST and ALT levels and by reduction of necrosis and microsteatosis areas.

CONCLUSIONS

Melatonin treatment was able to reduce the I/R-stimulated pro-inflammatory and pro-apoptotic genes in the rat liver. Since older animals showed a more marked increase in inflammation and in liver injury, the treatment was more effective in those subjects.

Effect of polyethylene glycol in pig intestinal allotransplantation without immunosuppression

OBJECTIVES

We evaluated whether IGL-1, a graft preservation solution containing polyethylene glycol, improves the outcome of small bowel grafts in comparison to the University of Wisconsin (UW) solution in a pig allotransplantation model.

MATERIALS AND METHODS

Seventeen pigs were randomly allocated to group 1 (n = 10; intestinal allotransplantation with IGL-1) and group 2 (n = 7; allotransplantation with UW). Pigs received no immunosuppression and were sacrificed on postoperative d (POD) 8. Intestinal specimens were obtained from the animal immediately before cold flushing (T0), 2 h after graft reperfusion (T1), and at sacrifice (T2).

RESULTS

Survival rate to POD 8 was 50% in group 1 compared with 16% in group 2 (P < 0.05); 62% of pigs in group 1 did not present any acute cellular rejection (ACR) compared to 16% in group 2 (P < 0.05). Severe ACR rate was 25% in group 1 and 66% in group 2 (P < 0.05). iNOS activity and intestinal caspase 3 levels increased significantly between T0 and T1 in group 1 compared to group 2 (P < 0.05). Cell necrosis increased significantly between TO and T1 in group 2 compared with group 1 (P < 0.05) whereas cell apoptosis was significantly higher at T1 compared with T0 in group 1 in comparison to group 2.

CONCLUSIONS

Our results show that IGL-1 improves intestinal graft viability as compared to UW solution, possibly by reducing graft immunogenicity and by favoring intestinal epithelial repair.

How to protect liver graft with nitric oxide

Organ preservation and ischemia reperfusion injury associated with liver transplantation play an important role in the induction of graft injury. One of the earliest events associated with the reperfusion injury is endothelial cell dysfunction. It is generally accepted that endothelial nitric oxide synthase (e-NOS) is cell-protective by mediating vasodilatation, whereas inducible nitric oxide synthase mediates liver graft injury after transplantation. We conducted a critical review of the literature evaluating the potential applications of regulating and promoting e-NOS activity in liver preservation and transplantation, showing the most current evidence to support the concept that enhanced bioavailability of NO derived from e-NOS is detrimental to ameliorate graft liver preservation, as well as preventing subsequent graft reperfusion injury. This review deals mainly with the beneficial effects of promoting “endogenous” pathways for NO generation, via e-NOS inducer drugs in cold preservation solution, surgical strategies such as ischemic preconditioning, and alternative “exogenous” pathways that focus on the enrichment of cold storage liquid with NO donors. Finally, we also provide a basic bench-to-bed side summary of the liver physiology and cell signalling mechanisms that account for explaining the e-NOS protective effects in liver preservation and transplantation.

Inhibition of inducible nitric oxide synthase prevents graft injury after transplantation of livers from rats after cardiac death

This study investigated the roles of inducible nitric oxide synthase (iNOS) in the failure of rat liver grafts from cardiac death donors (GCDD). Livers were explanted after 30-minute aorta clamping and implanted after 4-hour storage in University of Wisconsin solution. The iNOS expression increased slightly in grafts from non-cardiac death donors (GNCDD) but markedly in GCDD. Serum nitrite and nitrate and hepatic 3-nitrotyrosine adducts, indicators of NO and peroxynitrite production, respectively, were substantially higher after transplantation of GCDD than GNCDD. Production of reactive nitrogen species (RNS) was largely blocked by 1400W (N-[1-naphthyl]ethylenediamine dihydrochloride; 5 μM), a specific iNOS inhibitor. Alanine aminotransferase release, bilirubin, necrosis, and apoptosis were 6.4-fold, 6.5-fold, 2.3-fold, and 2.7-fold higher, respectively, after transplantation of GCDD than GNCDD. The inhibitor 1400W effectively blocked these alterations and also increased survival of GCDD to 80% from 33%. Increased RNS production and failure of GCDD were associated with activation of c-Jun-N-terminal kinase (JNK), an effect that was blocked by inhibition of iNOS. Inhibition of JNK also improved the outcome after transplantation of GCDD. Together, the data indicate that iNOS increases substantially in GCDD, leading to RNS overproduction, JNK activation, and more severe graft injury. Inhibitors of iNOS are suggested as effective therapies to improve the outcome after transplantation of GCDD.

Inhibition of inducible nitric oxide synthase prevents mitochondrial damage and improves survival of steatotic partial liver grafts

BACKGROUND

Steatotic liver grafts are excluded for partial liver transplantation because of increased risk of primary nonfunction. Mechanisms underlying the failure of fatty partial liver grafts (FPG) remain unknown. This study investigated whether inducible nitric oxide synthase (iNOS) plays a role in failure of FPG.

METHODS

Fatty livers were induced by feeding rats a high-fat high-fructose diet for 2 weeks. Hepatic triglyceride was approximately 9-fold higher in rats fed the high-fat high-fructose diet than those fed a low-fat low-fructose diet. Lean and fatty liver explants were reduced in size ex vivo to approximately one third, stored in the University of Wisconsin cold storage solution for 2 hr, and implanted.

RESULTS

Posttransplantational hepatic iNOS expression and reactive nitrogen species (RNS) formation (nitrite and nitrate levels and 3-nitrotyrosine adducts) increased more profoundly in FPG than in lean partial grafts (LPG). Serum alanine aminotransferase and bilirubin were 2- and 5.5-fold higher after transplantation of FPG than LPG. 5-Bromo-2'-deoxyuridine incorporation was 25% in LPG but only 5% in FPG, and graft weight increased by 64% in LPG while remaining unchanged in FPG. All rats that received FPG died, whereas all those receiving LPG survived. N-(1-naphtyl)ethylendiamine dihydrochloride (5 microM), a specific iNOS inhibitor, largely blunted the production of RNS, prevented the increase of alanine aminotransferase and bilirubin, restored liver regeneration, and improved survival of FPG. Mitochondrial cytochrome c oxidase-IV, ATP synthase-beta, and NADH dehydrogenase-3 decreased markedly in FPG, and these effects were blocked by N-(1-naphtyl)ethylendiamine dihydrochloride.

CONCLUSION

Thus, hepatic steatosis causes failure of partial liver grafts, most likely by increasing RNS that leads to mitochondrial damage and dysfunction.

Inhibition of inducible nitric oxide synthase worsens liver damage regardless of lipopolysaccharide treatment in small-for-size liver transplantation

OBJECTIVE

In small-for-size liver transplantation, portal hypertension aggravates endotoxin from the gut which accelerates the activation of inducible nitric oxide synthase (iNOS). However, there is little knowledge as to the effects of iNOS inhibitors on small-for-size graft damage. Our study was designed to investigate the role of an iNOS inhibitor both with and without lipopolysaccharide (LPS) treatment in ischemia-reperfusion injury of small-for-size liver transplantation.

METHODS

Subjecting Sprague-Dawley rats to small-for-size grafts liver transplantation, we investigated the time course of changes in hepatic expression of iNOS and endothelial nitric oxide synthase (eNOS). Meantime, we also investigated the effects of iNOS inhibitor, both with and without LPS treatment, at 6h after reperfusion.

RESULTS

While iNOS mRNA expression reached a peak at 3h, the highest protein level occurred at 6h after reperfusion. Aminoguanidine (AG) significantly inhibited mRNA and protein expressions of iNOS, but not that of eNOS. However, LPS accelerated activation of iNOS, but suppressed the expression of eNOS. Meanwhile, compared with the untreated group, those treated with AG or LPS experienced worsened liver function and tissue damage, promoting neutrophil infiltration in the liver tissue. The difference between the LPS group and the LPS+AG group was found to be significant. In addition, AG and LPS treatments up-regulated the protein expression of ICAM-1 and NF-kappaB p65.

CONCLUSION

In a small-for-size model of rat liver transplantation, regardless of LPS treatment, the inhibitor of iNOS, AG, attenuated iNOS expression, but worsened liver function and tissue damage. The subsequent increased neutrophil infiltration in liver tissue may be associated with up-regulation of ICAM-1 and NF-kappaB expressions.

The cytoprotective effects of addition of activated protein C into preservation solution on small-for-size grafts in rats

Small-for-size liver grafts are a serious obstacle for partial orthotopic liver transplantation. Activated protein C (APC), a potent anticoagulant serine protease, is known to have cell-protective properties due to its anti-inflammatory and antiapoptotic activities. This study was designed to examine the cytoprotective effects of a preservation solution containing APC on small-for-size liver grafts, with special attention paid to ischemia-reperfusion injury and shear stress in rats. APC exerted cytoprotective effects, as evidenced by (1) increased 7-day graft survival; (2) decreased initial portal pressure and improved hepatic microcirculation; (3) decreased levels of aminotransferase and improved histological features of hepatic ischemia-reperfusion injury; (4) suppressed infiltration of neutrophils and monocytes/macrophages; (5) reduced hepatic expression of tumor necrosis factor alpha and interleukin 6; (6) decreased serum levels of hyaluronic acid, which indicated attenuation of sinusoidal endothelial cell injury; (7) increased hepatic levels of nitric oxide via up-regulated hepatic endothelial nitric oxide synthesis expression together with down-regulated hepatic inducible nitric oxide synthase expression; (8) decreased hepatic levels of endothelin 1; and (9) reduced hepatocellular apoptosis by down-regulated caspase-8 and caspase-3 activities. These results suggest that a preservation solution containing APC is a potential novel and safe product for small-for-size liver transplantation, alleviating graft injury via anti-inflammatory and antiapoptotic effects and vasorelaxing conditions.

Role of ischemic preconditioning in liver surgery and hepatic transplantation

INTRODUCTION

The purpose of this review is to summarize intraoperative surgical strategies available to decrease ischemia-reperfusion injury associated with liver resection and liver transplantation.

MATERIAL AND METHOD

We conducted a critical review of the literature evaluating the potential applications of hepatic ischemic preconditioning (IPC) for hepatic resection surgery and liver transplantation. In addition, we provide a basic bench-to-bedside summary of the liver physiology and cell signaling mechanisms that account for the protective effects seen with hepatic IPC.

The role of nitric oxide and ferritin in the pathogenesis of alcoholic liver disease: a controlled clinical study

The role of ferritin in fibrogenesis of liver parenchyma in patients with alcoholic liver disease has been investigated in previous studies. Ferritin was shown to be an indirect marker of ferum deposition in liver parenchyma in alcohol liver disease. The aim of the present study was to examine the role of nitric oxide (NO) in the pathogenesis of alcoholic liver disease as well as the influence of NO on iron (ferritin) metabolism in patients with alcoholic liver disease. Serum concentrations of NO and iron markers (iron, total iron binding capacity, ferritin) were measured in 30 male patients (aged 20-60 years) with alcoholic liver disease, as well as from a control group (30 male patients (aged 20-60 years) without liver disease). NO concentration was detected by measuring production of nitrates and nitrites using classical colorimetric Griess reactions. There was a statistically significant increase in serum NO concentration in patients with alcoholic liver disease compared to the control group (mean +/- SEM; 41,2 +/- 25,3 vs. 28,9 +/- 12,3 mmol/dm3, respectively; p<0,03). Similarly, serum iron levels (18,7 +/- 8,2 vs. 13,2 +/- 10,2 g/100 cm3, respectively; p<0,03) and serum total iron binding capacity (51,3 +/- 13,9 vs. 41,4 +/- 11,4 micromol/dm3, respectively; p<0,005) were also significantly higher in patients with alcoholic liver disease compared to control patients. The serum concentration of ferritin was 27% higher in patients with alcoholic liver disease than in the control group; however this was not statistically significant (283,2 +/- 291,0 vs. 222,9 +/- 252,0 g, respectively; p<0,4). There was no correlation between NO and ferritin in the investigated groups. These results suggest a possible role of NO and iron in the pathogenesis of alcoholic liver disease. NO and iron may be used as non-invasive predictors of liver damage. Also the role of iron in sera, and its deposition in liver parenchyma, could be used in clinical practice, especially in regards to assessing the fibrogenesis of liver parenchyma induced by ferritin.

Beneficial effects of rutin and L-arginine coadministration in a rat model of liver ischemia-reperfusion injury

Reperfusion following liver ischemia results in oxidative stress leading to liver injury. The aim of this study was to investigate the combined effects of two antioxidant agents, rutin and L-arginine, in rat liver ischemia-reperfusion (I/R). Male Wistar rats were divided into five groups: 1) sham operated, 2) I/R, 3) I/R+rutin, 4) I/R+L-arginine, and 5) I/R+rutin+L-arginine. Plasmatic and hepatic levels of alanine transaminase (ALT), aspartate transaminase (AST), lipid peroxides (LOOH), and thiol groups (RSH) were examined, as well as DNA fragmentation and liver histopathology. Furthermore, to elucidate the pathophysiological processes involved in the antioxidant mechanism(s) of rutin and L-arginine, we assessed the expression of inducible (iNOS) and endothelial nitric oxide synthase (eNOS) isoforms and heme oxygenase-1 (HO-1), both playing key roles in the biochemical cascade of liver injury. Significant increase in plasmatic ALT and AST activities were observed in untreated I/R rats compared with sham-operated animals, whereas treatment with rutin or L-arginine in I/R rats reduced hepatic damage. Interestingly, combined therapy with rutin and L-arginine resulted in a further reduction of plasmatic ALT and AST activities compared with rutin or L-arginine alone. These results were further confirmed by the analysis of DNA fragmentation, LOOH, RSH groups, and liver histopathology, which showed the highest protective effects following the coadministration of rutin and L-arginine. Finally, the combined therapy protocol resulted in a significant induction of liver HO-1 and a concomitant reduction of iNOS expression that may both be responsible for the beneficial effects of the proposed pharmacological protocol.

Nitric oxide: A useful indicator in acute allograft rejection after liver transplantation

The aim of this study was to monitor serum nitric oxide levels at various times, intraoperatively and following liver transplantation in humans. Nitric oxide production was assessed by cadmium reduction method in 15 patients undergoing liver transplantation. We observed strong correlation between nitric oxide production and allograft rejection. Sustained rise in nitric oxide level after transplantation might provide an indication of acute allograft rejection. Therefore measurement of nitric oxide, a stable end product appears to be an excellent marker that can help in the development of strategies intended to improve graft viability and patient's survival.

Effect of ischemia-reperfusion on the incidence of acute cellular rejection and timing of histologic hepatitis C virus recurrence after liver transplantation

BACKGROUND

Because of a critical shortage of deceased donor (DD) livers, more extended criteria allografts are being utilized; these allografts are at increased risk for ischemia-reperfusion injury (IRI). We assessed whether, in a large cohort of patients transplanted for hepatitis C virus (HCV) either via a DD or live donor (LD), there was a relationship between the degree of IRI and the frequency and timing of acute cellular rejection (ACR) and histologic HCV recurrence.

METHODS

During an 8-year study, patients were separated into four groups based on peak alanine aminotransferase (ALT) levels and three groups based on severity of IRI on postreperfusion liver biopsy.

RESULTS

The mean follow-up time of 433 DD and 44 LD recipients was 1212 days. We noted a strong correlation in DD between peak ALT and the histologic degree of IRI (P = .01). There was no difference in the incidence or grade of ACR among the four groups. There was no correlation between the severity of IRI and the incidence or time to histologic recurrence of HCV.

CONCLUSIONS

The magnitude of peak ALT correlated with the severity of IRI on postreperfusion liver biopsy. Among this large HCV cohort, there was no correlation between the severity of IRI and the incidence or timing of histologic HCV recurrence or incidence of ACR.

Hepatic microcirculatory failure

Liver ischemia has been considered a frequent problem in medical practice, and can be associated to a number of surgical and clinical situations, such as massive hepatic resections, sepsis, liver trauma, circulatory shock and liver transplantation. After restoring blood flow, the liver is further subjected to an additional injury more severe than that induced by ischemia. On account of the complexity of mechanisms related to pathophysiology of ischemia and reperfusion (I/R) injury, this review deals with I/R effects on sinusoidal microcirculation, especially when steatosis is present. Alterations in hepatic microcirculation are pointed as a main factor to explain lower tolerance of fatty liver to ischemia-reperfusion insult. The employment of therapeutic strategies that interfere directly with vasoactive mediators (nitric oxide and endothelins) acting on the sinusoidal perfusion seem to be determinant for the protection of the liver parenchyma against I/R. These approaches could be very suitable to take advantage of marginal specimens as fatty livers, in which the microcirculatory disarrangements hamper its employment in liver transplantation.

[Treatment of recurrent hepatitis C virus infection after liver transplantation]

The main indication of liver transplantation is the final stage of liver cirrhosis developed in hepatitis C virus (HCV) infection. The recurrence of HCV infection after transplantation is a common situation. The recurrent hepatitis C is a progressive disease, in 20 percent of patients it produces liver cirrhosis without treatment beside immunosuppression within 5 years. The treatment of recurrent HCV infection is the most important factor of the survival in patients with transplantation. The authors review the factors influencing the progression of recurrent HCV infection on the basis of literary data and also on their observation. They discuss in details the effect of immunosuppressive treatment, the importance in the selection of corresponding immunosuppressive drugs. They review the main keypoints in the diagnosis of recurrent hepatitis C, underline the important role of liver biopsy carried out according to the protocol in the diagnosis, furthermore the hard consultation among pathologist, hepatologist and surgeon. They demonstrate the observations with the treatment of patients on the waiting list, the results in the early, preemptive treatment of recurrent chronic hepatitis, furthermore the treatment modalities and the results in patients with chronic hepatitis C histologically proved. The drug of choice of chronic hepatitis C after transplantation is the combined therapy with pegylated interferon and ribavirin. This therapy is able to assure virus-free stage in 20-50 percent of patients. In the virus-free patients the inflammatory activity in the liver significantly decreases, the histologic activity index improves. There are data showing the effect of treatment for inhibiting the fibrosis, but multicenter studies are necessary for the confirmation of these data. The advantage of early antiviral therapy without histologic alteration has not been confirmed by most of the trials. The anaemia and the neutropenia are frequent side effects in this patient group, that is why the applications of erythropoietin and granulocyte stimulating factor are recommended. Further trials and clinical studies are necessary for the optimal treatment of patients with recurrent hepatitis C, and to determine the dosage of pegylated interferon and ribavirin, to decrease the duration of therapy and the side effects, finally to achieve a healing phase of higher degree.

Gene transduction of an active mutant of akt exerts cytoprotection and reduces graft injury after liver transplantation

Akt is expected to be an effective target for the treatment of ischemia-reperfusion injury (I/R) due to its anti-apoptotic properties and its ability to activate the endothelial nitric oxide synthase (eNOS) enzyme. Therefore, this study was aimed to determine the efficacy of an active mutant of Akt (myr-Akt) to decrease I/R injury in a model of orthotopic liver transplantation in pigs. In addition, we analyzed the contribution of nitric oxide in the Akt-mediated effects by using an eNOS mutant (S1179DeNOS) that mimics the phosphorylation promoted by Akt in the eNOS sequence. Donors were treated with adenoviruses codifying for myr-Akt, S1179DeNOS or beta-galactosidase 24 h before liver harvesting. Then, liver grafts were orthotopically transplanted into their corresponding recipients. Levels of transaminases and lactate dehydrogenase (LDH) increased in all recipients after 24 h of transplant. However, transaminases and LDH levels were significantly lower in the myr-Akt group compared with vehicle. The percentage of apoptotic cells and the amount of activated-caspase 3 protein were also markedly reduced in myr-Akt-treated grafts after 4 days of liver transplant compared with vehicle and S1179DeNOS groups. In conclusion, myr-Akt gene therapy effectively exerts cytoprotection against hepatic I/R injury regardless of the Akt-dependent eNOS activation.

Effects of Huoxue Huayu injection I pretreatment and ischemic preconditioning on liver ischemia and reperfusion injury in rats

AIM: To investigate the effects of Huoxue Huayu injection I (HHI-I) pretreatment and ischemic preconditioning (IP) on hepatic ischemia and reperfusion (I/R) injury in rats and compare their efficacity.

METHODS: Eighty healthy adult male Sprague-Dawley rats were randomly and averagely divided into 4 groups: sham operation (SO) group, I/R group, ischemia preconditioning (IP) group, and HHI-I pretreatment group. After partial hepatic I/R model was made, the rats of each group were sacrificed to determine serum alanine aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), tissue malondialdehyde (MDA) and superoxide dismutase (SOD) level 1、3、6、24 h after reperfusion, respectively. Tissue tumor necrosis factor alpha (TNF-α) and intercellular adhesion molecule-1 (ICAM-1) mRNA levels were determined by reverse transcription-polymerase chain reaction after 1 h of reperfusion. Liver histology was observed after 3 h of reperfusion.

RESULTS: The activities of ALT, AST, LDH, the level of MDA, and the expression of TNF-α, ICAM-1 mRNA in I/R, IP, and HHI-I group were significantly higher than those in SO group, but they were markedly lower in IP and HHI-I group than those in I/R group. The activities of ALT, AST, LDH in HHI-I group were significantly lower than those in IP group (ALT: 2378.8 ± 303.4 nkat/L vs 2840.6 ± 248.4 nkat/L; AST: 2887.2 ± 270.1 nkat/L vs 4567.6 ± 275.1 nkat/L; LDH: 10550.4 ± 710.1 nkat/L vs 12164.1 ± 735.1 nkat/L; all P < 0.05). As compared with that in the IP group, the level of MDA in HHI-I group was decreased at the 3^rd and 6^th hour (17.35 ± 1.39 nmol/g vs 21.66 ± 1.84 nmol/g, P < 0.05), and the mRNA expression of TNF-α and ICAM-1 were decreased (TNF-α: 0.54 ± 0.06 vs 0.78 ± 0.08; ICAM-1: 0.43 ± 0.03 vs 0.69 ± 0.11, both P < 0.01). The level of SOD in I/R, IP and HHI-I group was markedly lower than that in SO group (P < 0.05), but it was significantly higher in IP and HHI-I group than that in I/R group (P < 0.05). The SOD level in the animals received HHI-I was significantly increased in comparison with that in IP group (136.00 ± 12.50 nmol/g vs 124.70 ± 9.32 nmol/g, P < 0.05). Microscopy showed that liver injury in the HHI-I-treated animals and IP-treated animals were attenuated as compared with that in I/R group.

CONCLUSION: HHI-I and IP pretreatment can alleviate I/R-induced liver injury, and the former is superior to the latter. The protective mechanism of HHI-I may be associated with the improvement of liver microcirculation, elimination of tissue anoxia, transcription inhibition of cytokine and cell adhesion molecule such as TNF-α and ICAM-1, and decrease of neutrophil infiltration.

The response of the hepatocyte to ischemia

BACKGROUND

Ischemia-reperfusion (I/R) injury associated with hepatic resections and liver transplantation remains a serious complication in clinical practice, in spite of several attempts to solve the problem.

AIMS

To evaluate the response of the hepatocyte to ischemia

METHODS

Published data are thus revised.

RESULTS

The response of the hepatocyte to ischemia is based on the sensitivity of hepatocytes to different types of ischemia, the kind of cell death of the hepatocyte when it is subjected to ischemia, and on the response of the hepatocyte to the different times and extents of ischemia. Clinical factors including starvation, graft, age, and hepatic steatosis, all of which contribute to enhancing liver susceptibility to ischemia/reperfusion injury.

CONCLUSION

Ischemic preconditioning, based on the induction of a brief ischemia to the liver prior to a prolonged ischemia, has been applied in tumor hepatic resections for reducing hepatic I/R injury and recent clinical studies suggest that this surgical strategy could be appropriate for liver transplantation.

El preacondicionamiento isquémico del hígado: de las bases moleculares a la aplicación clínica

Ischemia-reperfusion injury is produced when an organ is deprived of blood flow (ischemia), which is then restored (reperfusion). In certain circumstances, this injury leads to irreversible organ damage. Several therapeutic strategies have been used to reduce the severity of this injury. One of these strategies is the application of brief and repetitive episodes of ischemia-reperfusion before prolonged ischemia-reperfusion (ischemic preconditioning). In the present article we review the molecular mechanisms through which ischemic preconditioning confers protection against ischemia-reperfusion injury. The application of ischemic preconditioning during liver surgery is discussed, both in normothermic situations such as liver resection and in situations of low temperature such as liver transplantation.

FK330, a novel inducible nitric oxide synthase inhibitor, prevents ischemia and reperfusion injury in rat liver transplantation

Nitric oxide (NO), produced via inducible NO synthase (iNOS), is implicated in the pathophysiology of liver ischemia/reperfusion injury (IRI). We examined the effects of a novel iNOS inhibitor, FK330 (FR260330), in well-defined rat liver IRI models. In a model of liver cold ischemia followed by ex vivo reperfusion, treatment with FK330 improved portal venous flow, increased bile production and decreased hepatocellular damage. FK330 prevented IRI in rat model of 40-h cold ischemia followed by syngeneic orthotopic liver transplantation (OLT), as evidenced by: (1) increased OLT survival (from 20% to 80%); (2) decreased hepatocellular damage (serum glutamic oxaloacetic transaminase/glutamic pyruvic transaminase levels); (3) improved histological features of IRI; (4) reduced intrahepatic leukocyte infiltration, as evidenced by decreased expression of P-selectin/intracellular adhesion molecule 1, ED-1/CD3 cells and neutrophils; (5) depressed lymphocyte activation, as evidenced by expression of pro-inflammatory cytokine (TNF-alpha, IL-1beta, IL-6) and chemokine (IP-10, MCP-1, MIP-2) programs; (6) prevented hepatic apoptosis and down-regulated Bax/Bcl-2 ratio. Thus, by modulating leukocyte trafficking and cell activation patterns, treatment of rats with FK330, a specific iNOS inhibitor, prevented liver IRI. These results provide the rationale for novel therapeutic approaches to maximize organ donor pool through the safer use of liver grafts despite prolonged periods of cold ischemia.

[Ischemia-reperfusion syndrome associated with liver transplantation: an update]

Ischemia-reperfusion (I/R) injury is the main cause of both initial graft dysfunction and primary failure in liver transplantation. The search for therapeutic strategies to prevent I/R injury has led to research into promising drugs, although most have not been used clinically. Gene therapy requires better transfection techniques, avoiding vector toxicity, and ethical debate before being used clinically. Ischemic preconditioning is the first therapeutic strategy used in clinical practice to reduce I/R injury in hepatectomies for tumors. Future research will provide data on the effectiveness of ischemic preconditioning in reducing I/R injury associated with liver transplantation, and in reducing the vulnerability of steatotic grafts to I/R syndrome so that they can be used in transplantation, thus relieving the organ shortage.

Changes of nitric oxide and endothelin, thromboxane A2 and prostaglandin in cirrhotic patients undergoing liver transplantation

AIM: To investigate the perioperative changes of nitric oxide (NO) and endothelin (ET), thromboxane A₂ (TXA₂) and prostaglandin (PGI₂) during liver transplantation in end-stage liver disease patients.

METHODS: Twenty-seven patients with end-stage cirrhosis undergoing liver transplantation were enrolled in this prospective study. Blood samples were obtained from superior vena at five different surgical stages. Plasma concentrations of nitrate and nitrite were determined to reflect plasma NO levels. Plasma levels of ET-1, 6-keto-PGF1 alpha and thromboxane B₂ (TXB₂), the latter two being stable metabolites of PGI₂ and TXA₂ respectively, were measured.

RESULTS: The NO level decreased significantly after vascular cross-clamping and increased significantly at 30 min after reperfusion. While the ET levels at 30 min after clamping and after reperfusion were significantly elevated. The ratio of NO/ET decreased significantly at 30 min after vascular cross-clamping and at the end of surgery. The PGI₂ level and the TXA₂ during liver transplantation were significantly higher than the baseline level, but the ratio of TXA₂/PGI₂ decreased significantly at 30 min after clamping.

CONCLUSION: NO/ET and TXA₂/PGI₂ change during liver transplantation. Although the precise mechanism remains unknown, they may play a role in the pathobiology of a variety of liver transplant-relevant processes.

Past and future approaches to ischemia-reperfusion lesion associated with liver transplantation

Ischemia-reperfusion (I/R) injury associated with liver transplantation remains a serious complication in clinical practice, in spite of several attempts to solve the problem. The present review focuses on the complexity of I/R injury, summarizing conflicting results obtained from the literature about the mechanisms responsible for it. We also review the therapeutic strategies designed in past years to reduce I/R injury, attempting to explain why most of them have not been applied clinically. These strategies include improvements in pharmacological treatments, modifications of University of Wisconsin (UW) preservation solution based on a variety of additives, and gene therapy. Finally, we will consider new potential protective strategies using trimetazidine, 5-amino-4-imidazole carboxamide riboside (AICAR), melatonin, modulators of the renin-angiotensin system (RAS) and the phosphatidylinositol-3-OH kinase (PI3K)-Akt and the p42/p44 extracellular signal-regulated kinases (Erk 1/2) pathway. These strategies have shown promising results for I/R injury but have not been tested in experimental liver transplantation to date. Moreover, we will review ischemic preconditioning, taking into account the recent clinical studies that suggest that this surgical strategy could be appropriate for liver transplantation.

Donor graft adenoviral iNOS gene transfer ameliorates rat liver transplant preservation injury and improves survival

The exact role of inducible NOS (iNOS) in liver ischemia/reperfusion (I/R) injury is controversial. This study was designed to investigate whether donor liver pretreatment with adenovirus encoding iNOS (AdiNOS) ameliorates I/R injury associated with liver transplantation. Orthotopic syngeneic LEW rat liver transplantation (OLT) was performed after 18 or 24 hours' preservation in cold UW. AdiNOS or control gene vector (AdLacZ) was delivered to the liver by donor intravenous pretreatment 4 days before graft harvesting. Uninfected grafts also served as control. Recipients were sacrificed 1 to 48 hours posttransplantation. An abundant hepatic iNOS protein expression and marked serum NO elevation was observed in the AdiNOS-treated group, without affecting endothelial nitric oxide synthase (eNOS) expression, before harvesting and after OLT. AdiNOS pretreatment markedly improved liver function assessed by serum aspartate aminotransferase/alanine aminotransferase levels and reduced liver necrosis formation. AdiNOS treatment also was associated with reduced ICAM-1 mRNA expression and neutrophil accumulation in the liver graft after OLT compared with untransfected or AdLacZ-treated group. Furthermore, AdiNOS delivery significantly improved transplant survival, compared with AdLacZ or saline controls. AdiNOS pretreatment did not attenuate I/R-induced apoptotic cell death in the liver graft. Administration of a selective inhibitor for iNOS abrogated the protection afforded by AdiNOS pretreatment. In conclusion, donor pretreatment with AdiNOS led to improved liver graft injury and posttransplantation survival. Downregulation of ICAM-1 mRNA and neutrophil infiltration may be associated with the mechanisms by which AdiNOS pretreatment confer the protection against transplant-associated hepatic I/R injury.

Dual role of vascular endothelial growth factor in hepatic ischemia-reperfusion injury

BACKGROUND

Vascular endothelial growth factor (VEGF), a major angiogenic factor, mediates a variety of disease conditions through promotion of angiogenesis. It also plays a critical role as a potent proinflammatory cytokine in a variety of physiologic and pathologic immune responses. In the present study, we evaluated the expression of VEGF in hepatic warm ischemia-reperfusion (I/R) injury and examined the effect of recombinant human (rh)VEGF administration in an established murine model.

METHOD

The expression of VEGF in the liver was assessed by quantitative real-time polymerase chain reaction and immunohistochemistry during I/R injury using 70% partial hepatic ischemia model. The effect of rhVEGF administration on I/R injury was evaluated by measuring liver function and histology. In addition, local inducible nitric oxide synthase (iNOS) and endothelial NO synthase expressions were examined to address the underlying mechanisms.

RESULTS

The local expression of VEGF was significantly up-regulated at 2 hours after reperfusion after 60 minutes of ischemia compared with that in the naive liver. VEGF was expressed predominantly in CD11b+ cells infiltrating into the ischemic liver. The administration of rhVEGF had a significant protective effect on ischemic injury in the liver. This effect was associated with the up-regulation of iNOS expression in the rhVEGF-treated liver.

CONCLUSION

We demonstrate a dual role of VEGF in hepatic warm I/R injury. Although endogenous VEGF is expressed and functional to initiate hepatic I/R injury, exogenous rhVEGF has a beneficial effect on the ischemic liver. These data may provide new insights into the role of VEGF as well as pathophysiology of hepatic I/R injury.

Deoxycholyltaurine-induced vasodilation of rodent aorta is nitric oxide- and muscarinic M3 receptor-dependent

Emerging evidence indicates that some secondary bile acids interact functionally with muscarinic cholinergic receptors. Using thoracic aortic rings prepared from rats and mice, we examined the mechanism of deoxycholyltaurine-induced vasorelaxation. Increasing concentrations of both acetylcholine (1 nM to 0.1 mM) and deoxycholyltaurine (0.1 microM to 1 mM) stimulated relaxation of phenylephrine-constricted rings prepared from rat thoracic aortae. These effects were reduced by endothelial denudation and by treatment with an inhibitor of nitric oxide formation and with a synthetic acetylcholine:bile acid hybrid that acts as a muscarinic receptor antagonist. Likewise, both acetylcholine (1 nM to 0.1 mM) and deoxycholyltaurine (0.1 microM to 0.1 mM) stimulated relaxation of phenylephrine-constricted rings prepared from mouse thoracic aortae. These effects were reduced by endothelial denudation, addition of an inhibitor of nitric oxide formation, and by muscarinic M(3) receptor knockout. We conclude that the systemic vasodilatory actions of deoxycholyltaurine are mediated in part by a nitric oxide-, muscarinic M(3) receptor-dependent mechanism. In advanced liver disease, interaction of serum bile acids with endothelial muscarinic receptors may explain nitric oxide overproduction in the systemic circulation and resulting peripheral arterial vasodilation.

Ischaemic preconditioning in transplantation and major resection of the liver

BACKGROUND

Ischaemia-reperfusion injury (IRI) contributes significantly to the morbidity and mortality of transplantation and major resection of the liver. Its severity is reduced by ischaemic preconditioning (IP), the precise mechanisms of which are not completely understood. This review discusses the pathophysiology and role of IP in this clinical setting.

METHODS

A Medline search was performed using the keywords 'ischaemic preconditioning', 'ischaemia-reperfusion injury', 'transplantation' and 'hepatic resection'. Additional articles were obtained from references within the papers identified by the Medline search.

RESULTS AND CONCLUSION

The mechanisms underlying hepatic IRI are complex, but IP reduces the severity of such injury in several animal models and in recent human trials. Increased understanding of the cellular processes involved in IP is of importance in the development of treatment strategies aimed at improving outcome after liver transplantation and major hepatic resection.

The effect of Viagra (sildenafil citrate) on liver injury caused by chronic ethanol intragastric feeding in rats

Rats fed with ethanol and a nutritious diet intragastrically develop liver pathologic changes associated with cyclic elevation of blood and urinary ethanol levels (BAL and UAL cycle). At the peaks of the UAL cycle, the livers are hypoxic. When the liver portal hepatic blood flow is temporarily clamped for 2 min and then released, the livers at the peak UAL fail to recover completely compared to the control livers and the livers at the UAL cycle troughs. Viagra was fed to the ethanol-fed rats to enhance the effects of nitric oxide. Since nitric oxide is known to increase hepatic blood flow, it was anticipated that Viagra would prevent the liver hypoxia at the UAL cycle peaks and also improve the post-clamp recovery from the post-clamp ischemia challenge. Viagra tended to improve the post-clamp recovery of the liver surface pO2 levels of the ethanol-fed rats probably by slowing O2 consumption as result of NO inhibition of mitochondrial cytochrome c oxidase activity. However, Viagra increased the pathology score when fed with ethanol. For this reason, Viagra is a two-edged sword. On the one hand, it tended to be protective in the post-ischemic injury in the ethanol-fed rats and on the other hand, it enhanced the liver injury caused by ethanol. Viagra did not affect the UAL cycle.

A Study of the Metabolites of Ischemia-Reperfusion Injury and Selected Amino Acids in the Liver Using Microdialysis during Transplantation

BACKGROUND

Preservation and ischemia-reperfusion injury still impact the outcome of orthotopic liver transplantation. The authors used microdialysis with a view to monitoring its effect on graft function.

METHODS

A microdialysis catheter was inserted into the graft immediately after reperfusion and perfused with an isotonic solution for 48 hr. Metabolites of the ischemia-reperfusion injury and selected amino acids were studied. There were 18 patients, with a median age of 52 years (range, 38-62 years), 8 of whom were men. Lactate, pyruvate, glycerol, and glucose levels were measured. In addition, alanine, arginine, citrulline, gamma-aminobutyric acid (GABA), glutamate, glutamine, glycine, and taurine were determined.

RESULTS

All grafts functioned well. High lactate, pyruvate, and glycerol levels were observed in the immediate postoperative period. These showed a significant rapid decrease and stabilized to baseline levels. Alanine, glutamate, GABA, and taurine levels declined significantly to baseline values. Arginine levels were low immediately postreperfusion and then increased, reaching significantly higher values beyond 19 hr.

CONCLUSIONS

These data may represent "normal" changes seen in the immediate posttransplant period because all grafts functioned well. Two important metabolic fates of arginine in the liver are in the detoxification of ammonia by means of the urea cycle, and in the synthesis of nitric oxide (NO). Low extracellular arginine may reflect influx of the amino acid into hepatocytes, resulting in formation of NO in the presence of inducible NO synthase or conversion to ornithine in the presence of arginase in the urea cycle. As the organ stabilizes, restriction of arginine uptake may give rise to the observed increase in extracellular arginine.

Cornea Graft Endothelial Cells Undergo Apoptosis by Way of an Alternate (Caspase-Independent) Pathway

PURPOSE

To look for apoptosis pathways involved in corneal endothelial cell death during acute graft rejection and to evaluate the potential role of nitric oxide in this process.

MATERIALS AND METHODS

Corneal buttons from Brown-Norway rats were transplanted into Lewis rat corneas. At different time intervals after transplantation, apoptosis was assessed by diamino-2-phenylindol staining and annexin-V binding on flat-mount corneas, and by terminal transferase dUTP nick end labeling (TUNEL), caspase-3 dependent and leukocyte elastase inhibitor (LEI)/LDNase II caspase-independent pathways on sections. Inducible nitric oxide synthase (NOS-II) expression and the presence of nitrotyrosine were assayed by immunohistochemistry.

RESULTS

Graft endothelial cells demonstrated nuclear fragmentation and LEI nuclear translocation, annexin-V binding, and membranes bleb formation. Apoptosis associated with caspase-3 activity or TUNEL-positive reaction was not observed at any time either in the graft or in the recipient corneal endothelial cells. During 14 days posttransplantation, the recipient corneal endothelial cells remained unaltered and their number unchanged in all studied corneas. NOS-II was expressed in infiltrating cells present within the graft. This expression was closely associated with the presence of nitrotyrosine in endothelial and infiltrating cells.

CONCLUSION

During the time course of corneal graft rejection, graft endothelial cells undergo apoptosis. Apoptosis is caspase 3 independent and TUNEL negative and is, probably, carried out by an alternative pathway driven by an LEI/L-Dnase II. Peroxynitrite formation may be an additional mechanism for cell toxicity and programmed cell death of the graft endothelial cells during the rejection process in this model.