Gadolinium chloride-induced improvement of postischemic hepatic perfusion after warm ischemia is associated with reduced hepatic endothelin secretion

Molecular Mechanisms of Ischaemia-Reperfusion Injury and Regeneration in the Liver-Shock and Surgery-Associated Changes

Hepatic ischemia-reperfusion injury (IRI) represents a major challenge during liver surgery, liver preservation for transplantation, and can cause hemorrhagic shock with severe hypoxemia and trauma. The reduction of blood supply with a concomitant deficit in oxygen delivery initiates various molecular mechanisms involving the innate and adaptive immune response, alterations in gene transcription, induction of cell death programs, and changes in metabolic state and vascular function. Hepatic IRI is a major cause of morbidity and mortality, and is associated with an increased risk for tumor growth and recurrence after oncologic surgery for primary and secondary hepatobiliary malignancies. Therapeutic strategies to prevent or treat hepatic IRI have been investigated in animal models but, for the most part, have failed to provide a protective effect in a clinical setting. This review focuses on the molecular mechanisms underlying hepatic IRI and regeneration, as well as its clinical implications. A better understanding of this complex and highly dynamic process may allow for the development of innovative therapeutic approaches and optimize patient outcomes.

Complement Activation in Liver Transplantation: Role of Donor Macrosteatosis and Implications in Delayed Graft Function

The complement system anchors the innate inflammatory response by triggering both cell-mediated and antibody-mediated immune responses against pathogens. The complement system also plays a critical role in sterile tissue injury by responding to damage-associated molecular patterns. The degree and duration of complement activation may be a critical variable controlling the balance between regenerative and destructive inflammation following sterile injury. Recent studies in kidney transplantation suggest that aberrant complement activation may play a significant role in delayed graft function following transplantation, confirming results obtained from rodent models of renal ischemia/reperfusion (I/R) injury. Deactivating the complement cascade through targeting anaphylatoxins (C3a/C5a) might be an effective clinical strategy to dampen reperfusion injury and reduce delayed graft function in liver transplantation. Targeting the complement cascade may be critical in donor livers with mild to moderate steatosis, where elevated lipid burden amplifies stress responses and increases hepatocyte turnover. Steatosis-driven complement activation in the donor liver may also have implications in rejection and thrombolytic complications following transplantation. This review focuses on the roles of complement activation in liver I/R injury, strategies to target complement activation in liver I/R, and potential opportunities to translate these strategies to transplanting donor livers with mild to moderate steatosis.

Role of NK, NKT cells and macrophages in liver transplantation

Liver transplantation has become the treatment of choice for acute or chronic liver disease. Because the liver acts as an innate immunity-dominant organ, there are immunological differences between the liver and other organs. The specific features of hepatic natural killer (NK), NKT and Kupffer cells and their role in the mechanism of liver transplant rejection, tolerance and hepatic ischemia-reperfusion injury are discussed in this review.

A novel mouse model of depletion of stellate cells clarifies their role in ischemia/reperfusion- and endotoxin-induced acute liver injury

BACKGROUND & AIMS

Hepatic stellate cells (HSCs) that express glial fibrillary acidic protein (GFAP) are located between the sinusoidal endothelial cells and hepatocytes. HSCs are activated during liver injury and cause hepatic fibrosis by producing excessive extracellular matrix. HSCs also produce many growth factors, chemokines and cytokines, and thus may play an important role in acute liver injury. However, this function has not been clarified due to unavailability of a model, in which HSCs are depleted from the normal liver.

METHODS

We treated mice expressing HSV-thymidine kinase under the GFAP promoter (GFAP-Tg) with 3 consecutive (3 days apart) CCl4 (0.16 μl/g; ip) injections to stimulate HSCs to enter the cell cycle and proliferate. This was followed by 10-day ganciclovir (40 μg/g/day; ip) treatment, which is expected to eliminate actively proliferating HSCs. Mice were then subjected to hepatic ischemia/reperfusion (I/R) or endotoxin treatment.

RESULTS

CCl4/ganciclovir treatment caused depletion of the majority of HSCs (about 64-72%), while the liver recovered from the initial CCl4-induced injury (confirmed by histology, serum ALT and neutrophil infiltration). The magnitude of hepatic injury due to I/R or endotoxemia (determined by histopathology and serum ALT) was lower in HSC-depleted mice. Their hepatic expression of TNF-α, neutrophil chemoattractant CXCL1 and endothelin-A receptor also was significantly lower than the control mice.

CONCLUSIONS

HSCs play an important role both in I/R- and endotoxin-induced acute hepatocyte injury, with TNF-α and endothelin-1 as important mediators of these effects.

Hepatocytes produce TNF-α following hypoxia-reoxygenation and liver ischemia-reperfusion in a NADPH oxidase- and c-Src-dependent manner

Cell line studies have previously demonstrated that hypoxia-reoxygenation (H/R) leads to the production of NADPH oxidase 1 and 2 (NOX1 and NOX2)-dependent reactive oxygen species (ROS) required for the activation of c-Src and NF-κB. We now extend these studies into mouse models to evaluate the contribution of hepatocytes to the NOX- and c-Src-dependent TNF-α production that follows H/R in primary hepatocytes and liver ischemia-reperfusion (I/R). In vitro, c-Src-deficient primary hepatocytes produced less ROS and TNF-α following H/R compared with controls. In vivo, c-Src-KO mice also had impaired TNF-α and NF-κB responses following partial lobar liver I/R. Studies in NOX1 and p47phox knockout primary hepatocytes demonstrated that both NOX1 and p47phox are partially required for H/R-mediated TNF-α production. To further investigate the involvement of NADPH oxidases in the production of TNF-α following liver I/R, we performed additional in vivo experiments in knockout mice deficient for NOX1, NOX2, p47phox, Rac1, and/or Rac2. Cumulatively, these results demonstrate that NOX2 and its activator subunits (p47phox and Rac) control the secretion of TNF-α by the liver following I/R. Interestingly, in the absence of Kupffer cells and NOX2, NOX1 played a dominant role in TNF-α production following hepatic I/R. However, NOX1 deletion alone had little effect on I/R-induced TNF-α. Thus Kupffer cell-derived factors and NOX2 act to suppress hepatic NOX1-dependent TNF-α production. We conclude that c-Src and NADPH oxidase components are necessary for redox-mediated production of TNF-α following liver I/R and that hepatocytes play an important role in this process.

Molecular mechanisms of liver ischemia reperfusion injury: Insights from transgenic knockout models

Ischemia reperfusion injury is a major obstacle in liver resection and liver transplantation surgery. Understanding the mechanisms of liver ischemia reperfusion injury (IRI) and developing strategies to counteract this injury will therefore reduce acute complications in hepatic resection and transplantation, as well as expanding the potential pool of usable donor grafts. The initial liver injury is initiated by reactive oxygen species which cause direct cellular injury and also activate a cascade of molecular mediators leading to microvascular changes, increased apoptosis and acute inflammatory changes with increased hepatocyte necrosis. Some adaptive pathways are activated during reperfusion that reduce the reperfusion injury. IRI involves a complex interplay between neutrophils, natural killer T-cells cells, CD4+ T cell subtypes, cytokines, nitric oxide synthases, haem oxygenase-1, survival kinases such as the signal transducer and activator of transcription, Phosphatidylinositol 3-kinases/Akt and nuclear factor κβ pathways. Transgenic animals, particularly genetic knockout models, have become a powerful tool at elucidating mechanisms of liver ischaemia reperfusion injury and are complementary to pharmacological studies. Targeted disruption of the protein at the genetic level is more specific and maintained than pharmacological inhibitors or stimulants of the same protein. This article reviews the evidence from knockout models of liver IRI about the cellular and molecular mechanisms underlying liver IRI.

Hyperbaric oxygen therapy reduces the severity of ischaemia, preservation and reperfusion injury in a rat model of liver transplantation

BACKGROUND

  Approaches to increase organ availability for orthotopic liver transplantation (OLT) often result in the procurement of marginal livers that are more susceptible to ischaemia, preservation and reperfusion injury (IPRI).

METHODS

  The effects of post-OLT hyperbaric oxygen (HBO) therapy on IPRI in a syngeneic rat OLT model were examined at various time-points. The effects of IPRI and HBO on hepatocyte necrosis, apoptosis, proliferation, and sinusoidal morphology and ultrastructure were assessed.

RESULTS

  Post-OLT HBO therapy significantly reduced the severity of IPRI; both apoptosis [at 12 h: 6.4 ± 0.4% in controls vs. 1.6 ± 0.7% in the HBO treatment group (p < 0.001); at 48 h: 2.4 ± 0.2% in controls vs. 0.4 ± 0.1% in the HBO treatment group (p < 0.001)] and necrosis [at 12 h: 18.7 ± 1.8% in controls vs. 2.4 ± 0.4% in the HBO treatment group (p < 0.001); at 48 h: 8.5 ± 1.3% in controls vs. 3.4 ± 0.9% in the HBO treatment group (P= 0.019)] were decreased. Serum alanine transaminase was reduced [at 12 h: 1068 ± 920 IU/l in controls vs. 370 ± 63 IU/l in the HBO treatment group (P= 0.030); at 48 h: 573 ± 261 IU/l in controls vs. 160 ± 10 IU/l in the HBO treatment group (P= 0.029)]. Treatment with HBO also promoted liver regeneration [proliferation at 12 h: 4.5 ± 0.1% in controls vs. 1.0 ± 0.3% in the HBO treatment group (p < 0.001); at 48 h: 8.6 ± 0.7% in controls vs. 2.9 ± 0.2% in the HBO treatment group (p < 0.01)] and improved sinusoidal diameter and microvascular density index.

CONCLUSIONS

  Hyperbaric oxygen therapy has persistent positive effects post-OLT that may potentially transfer into clinical practice.

Alcohol pretreatment increases hepatic and pulmonary injury in experimental pancreatitis

BACKGROUND

Systemic complications including pancreatitis-associated lung injury (PALI) are critical factors that determine the outcome of severe necrotizing pancreatitis (SNP). The aim of the present study was to evaluate the role of chronic alcohol exposure on the development of PALI.

METHODS

48 rats were fed either a Lieber deCarli control or alcohol diet for 6 weeks. After completion, SNP was induced by intraductal infusion of bile salt followed by intravenous infusion of cerulein over 6 h. Control animals received i.v. Ringer's solution. Intravital microscopy of the liver was performed 6 h after induction of SNP to evaluate hepatic perfusion and leukocyte adhesion. Serum parameters, edema, inflammation, and histological changes were evaluated at 12 h. IL-6 levels were evaluated in portal venous and systemic blood as well as in pancreatic tissue homogenates.

RESULTS

Alcohol pretreatment did not affect pancreatic injury in SNP. PALI was aggravated after alcohol ingestion. These animals showed increased hepatic microcirculatory disturbances, compared to SNP alone. IL-6 showed peak levels in SNP with alcohol pretreatment, although they were also elevated in SNP alone. Systemic levels of IL-6 were higher than in the portal vein.

CONCLUSION

In SNP, alcoholic pretreatment increases pulmonary damage, while pancreatic injury is identical. The liver seems to participate in this effect by increased hepatic cytokine release.

Kupffer cell blockade improves the endotoxin-induced microcirculatory inflammatory response in obstructive jaundice

Cholestasis predisposes to hypersensitivity to LPS, leading to potential septic complications. We set out to characterize the involvement of Kupffer cell (KC) activation in the hepatic microcirculatory and structural consequences of obstructive jaundice in the presence and absence of acute endotoxemia. The hepatic microcirculatory consequences of 3-day extrahepatic bile duct ligation (BDL) were assessed in rats. The contributions of changes in hepatic perfusion, leukocyte influx, and proinflammatory cytokine release to the development of hepatic structural damage were also determined. Furthermore, the corresponding consequences of BDL in combination with acute (2-h) endotoxemia (1 mg kg(-1) LPS, i.v.) were compared with those observed after LPS alone. In a second series, the same protocols were applied in identical groups of rats where the KC function was inhibited with 24-h gadolinium chloride pretreatment (10 mg kg(-1), i.v.). Bile duct ligation induced minor inflammatory reactions but caused a marked reduction in hepatic sinusoidal perfusion and severe histological damage. LPS treatment, however, elicited an approximately 5-fold increase in leukocyte adherence in the central venules and pronounced IL-6 and TNF-alpha release, but without significant structural damage. The combination of BDL with LPS enhanced the perfusion failure, leukocyte sticking/deposition, and proinflammatory cytokine release; most of these changes can be effectively ameliorated by gadolinium chloride. In conclusion, when obstructive jaundice is followed by a second hit of LPS, perfusion failure, liver inflammation, and structural damage are enhanced, the KCs playing a decisive role in this scenario. Therapeutic strategies aimed at KC blockade can potentially reduce the risk of inflammatory complications in cholestasis.

Nrf2- and PPAR alpha-mediated regulation of hepatic Mrp transporters after exposure to perfluorooctanoic acid and perfluorodecanoic acid

Perfluorooctanoic acid and perfluorodecanoic acid (PFDA) are commonly used as emulsifiers and surfactants in fluoropolymer manufacturing and are known peroxisome proliferator-activated receptor alpha (PPAR alpha) agonists. PPAR alpha activation induces beta- and omega-oxidation enzymes such as Cyp4a14 and acyl-CoA oxidase, which are a likely cause of subsequent oxidative stress and peroxisome proliferation. Conversely, NF-E2-related factor-2 (Nrf2) is a transcription factor that protects against oxidative stress and inflammation by regulating several detoxification and xenobiotic transporter genes. Because PFDA markedly induces hepatic metabolism and oxidative stress, we hypothesized that PFDA exposure would increase expression of hepatic efflux multidrug resistance-associated protein (Mrp) transporters. A single PFDA dose (80 mg/kg) administered to mice increased hepatic Mrp3 (fourfold) and Mrp4 (31-fold) mRNA expression. Upregulation of Mrp3 and Mrp4 correlated with elevated serum-conjugated bilirubin and bile acids, respectively. To determine the mechanism of Mrp3 and Mrp4 induction, PFDA was administered to Nrf2-null mice, PPAR alpha-null mice, and mice pretreated with gadolinium chloride, a Kupffer cell-depleting chemical capable of inhibiting the inflammatory cytokine response. In both PPAR alpha- and Nrf2-null mice, maximal induction of Mrp3 and Mrp4 mRNA after PFDA administration was attenuated. Gadolinium chloride pretreatment reduced serum and hepatic tumor necrosis factor-alpha levels after PFDA treatment, as well as Mrp4 mRNA expression by 30%, suggesting that Kupffer cell-derived mediators may contribute to Mrp induction. Thus, after PFDA administration, the liver mounts a compensatory hepatoprotective response via PPAR alpha and Nrf2, markedly increasing Mrp3 and Mrp4 expression, with corresponding increases in serum of known Mrp3 and Mrp4 substrates.

Hyperbaric oxygen therapy and liver transplantation

Liver transplantation is the treatment of choice for end stage liver disease and is often used for primary liver malignancies. The main limitation of its wider application is the availability of suitable donor organs. The use of marginal donor organs, split-liver transplantation and living-related liver transplantation techniques contribute to increase the donor pool. However, the use of these techniques is associated with a higher risk of post transplantation organ dysfunction, predominantly due to ischaemia, preservation and reperfusion injury (IPRI). A number of studies have demonstrated that hyperbaric oxygen (HBO) therapy influences IPRI and consequential acute cellular rejection. This article reviews the rationale of HBO therapy in the field of transplantation with particular emphasis on liver transplantation.

Glycine blunts transplantative liver ischemia-reperfusion injury by downregulating interleukin 1 receptor associated kinase-4

AIM

To determine whether glycine could downregulate interleukin 1 receptor associated kinase-4 (IRAK-4) expression to interfere with lipopolysaccharides (LPS) signal transduction and blunt transplantative liver ischemia-reperfusion injury (I/RI).

METHODS

SD rats were randomly divided into two groups: donor animals of the glycine group (n=40) were given glycine (1.5 mL; 300 mmol/L, iv) 1 h before harvest, and the control group were treated with 1.5 mL physiological saline (n= 40). Orthotopic liver transplantation was then performed according to the Kamada technique. Ten animals in each group were followed up for 7 d after surgery to assess survival. The remaining animals in each group were divided into 3 subgroups (n=10) at 1h, 2 h and 6 h after portal vein reperfusion. Levels of LPS, serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and total bilirubin in portal circulation, as well as IRAK-4 and TNF-alpha expression, NF-kappaB transcriptional activity and morphological study of liver tissues were analyzed.

RESULTS

Reperfusion resulted in a significant elevation of LPS concentrations in each group persisting to the end of our study. However, glycine, which led to improved survival rate and liver function, significantly alleviated liver parenchyma cell damage by downregulating IRAK-4, TNF-alpha expression and NF-kappaB transcriptional activity compared with the control group.

CONCLUSION

Glycine can attenuate hepatic I/RI by downregulating IRAK-4 to interfere with LPS signal transduction.