Reduced inflammatory response and increased microcirculatory disturbances during hepatic ischemia-reperfusion injury in steatotic livers of ob/ob mice

Multimodal modulation of hepatic ischemia/reperfusion-induced injury by phytochemical agents: A mechanistic evaluation of hepatoprotective potential and safety profiles

BACKGROUND

Hepatic ischemia-reperfusion (I/R) injury is a clinically fundamental phenomenon that occurs through liver resection surgery, trauma, shock, and transplantation.

AIMS OF THE REVIEW

This review article affords an expanded and comprehensive overview of various natural herbal ingredients that have demonstrated hepatoprotective effects against I/R injury through preclinical studies in animal models.

MATERIALS AND METHODS

For the objective of this investigation, an extensive examination was carried out utilizing diverse scientific databases involving PubMed, Google Scholar, Science Direct, Egyptian Knowledge Bank (EKB), and Research Gate. The investigation was conducted based on specific identifiable terms, such as hepatic ischemia/reperfusion injury, liver resection and transplantation, cytokines, inflammation, NF-kB, interleukins, herbs, plants, natural ingredients, phenolic extract, and aqueous extract.

RESULTS

Bioactive ingredients derived from ginseng, curcumin, resveratrol, epigallocatechin gallate, quercetin, lycopene, punicalagin, crocin, celastrol, andrographolide, silymarin, and others and their effects on hepatic IRI were discussed. The specific mechanisms of action, signaling pathways, and clinical relevance for attenuation of liver enzymes, cytokine production, immune cell infiltration, oxidative damage, and cell death signaling in rodent studies are analyzed in depth. Their complex molecular actions involve modulation of pathways like TLR4, NF-κB, Nrf2, Bcl-2 family proteins, and others.

CONCLUSION

The natural ingredients have promising values in the protection and treatment of various chronic aggressive clinical conditions, and that need to be evaluated on humans by clinical studies.

Effect of Pringle maneuver on prognosis of patients with colorectal cancer liver metastases after liver resection: a meta-analysis

PURPOSE

Pringle maneuver (PM) is a double-edged sword in liver resection, which is beneficial in reducing blood loss but also causes ischemia-reperfusion injury which may stimulate the outgrowth of micrometastases. The impact of PM on tumor recurrence remains controversial. This study aimed to assess whether PM has effect on the prognosis of colorectal cancer liver metastases (CRLM) after hepatectomy.

METHODS

PubMed and the Cochrane Library databases were searched. The PM is defined as the portal triad clamping for several minutes, followed by several minutes of reperfusion, repeated as needed. Prolonged PM was defined as continuous clamping ≥ 20 min or ≥ 3 cycles for maximally 15-min intermittent ischemia.

RESULTS

Eleven studies encompassing 4054 patients were included in this meta-analysis. The pooled hazard ratio (HR) did not show significant differences between PM and non-PM groups for disease-free survival (DFS) (HR = 0.91, 95% confidence interval (CI) 0.76-1.11, P = 0.36) and overall survival (HR = 1.03, 95% CI 0.76-1.39, P = 0.87). Subgroup analysis revealed that prolonged PM has adverse impact on DFS (HR 1.75, 95% CI = 1.28-2.40, P = 0.0005). However, non-prolonged PM is a protective factor for DFS (HR 0.82, 95% CI = 0.73-0.92, P = 0.001).

CONCLUSION

These findings suggested that prolonged PM may have an adverse impact on the DFS of patients with CRLM and non-prolonged PM is a protective factor for DFS. Further prospective multicenter studies are warranted.

The Protective Effect of Nutraceuticals on Hepatic Ischemia-Reperfusion Injury in Wistar Rats

Nutraceuticals are bioactive compounds present in foods, utilized to ameliorate health, prevent diseases, and support the proper functioning of the human body. They have gained attention due to their ability to hit multiple targets and act as antioxidants, anti-inflammatory agents, and modulators of immune response and cell death. Therefore, nutraceuticals are being studied to prevent and treat liver ischemia-reperfusion injury (IRI). This study evaluated the effect of a nutraceutical solution formed by resveratrol, quercetin, omega-3 fatty acid, selenium, ginger, avocado, leucine, and niacin on liver IRI. IRI was performed with 60 min of ischemia and 4 h of reperfusion in male Wistar rats. Afterward, the animals were euthanized to study hepatocellular injury, cytokines, oxidative stress, gene expression of apoptosis-related genes, TNF-α and caspase-3 proteins, and histology. Our results show that the nutraceutical solution was able to decrease apoptosis and histologic injury. The suggested mechanisms of action are a reduction in gene expression and the caspase-3 protein and a reduction in the TNF-α protein in liver tissue. The nutraceutical solution was unable to decrease transaminases and cytokines. These findings suggest that the nutraceuticals used favored the protection of hepatocytes, and their combination represents a promising therapeutic proposal against liver IRI.

Endothelial Cell Dysfunction and Nonalcoholic Fatty Liver Disease (NAFLD): A Concise Review

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. It is strongly associated with obesity, type 2 diabetes (T2DM), and other metabolic syndrome features. Reflecting the underlying pathogenesis and the cardiometabolic disorders associated with NAFLD, the term metabolic (dysfunction)-associated fatty liver disease (MAFLD) has recently been proposed. Indeed, over the past few years, growing evidence supports a strong correlation between NAFLD and increased cardiovascular disease (CVD) risk, independent of the presence of diabetes, hypertension, and obesity. This implies that NAFLD may also be directly involved in the pathogenesis of CVD. Notably, liver sinusoidal endothelial cell (LSEC) dysfunction appears to be implicated in the progression of NAFLD via numerous mechanisms, including the regulation of the inflammatory process, hepatic stellate activation, augmented vascular resistance, and the distortion of microcirculation, resulting in the progression of NAFLD. Vice versa, the liver secretes inflammatory molecules that are considered pro-atherogenic and may contribute to vascular endothelial dysfunction, resulting in atherosclerosis and CVD. In this review, we provide current evidence supporting the role of endothelial cell dysfunction in the pathogenesis of NAFLD and NAFLD-associated atherosclerosis. Endothelial cells could thus represent a "golden target" for the development of new treatment strategies for NAFLD and its comorbid CVD.

Targeting the Hepatic Microenvironment to Improve Ischemia/Reperfusion Injury: New Insights into the Immune and Metabolic Compartments

Hepatic ischemia/reperfusion injury (IRI) is mainly characterized by high activation of immune inflammatory responses and metabolic responses. Understanding the molecular and metabolic mechanisms underlying development of hepatic IRI is critical for developing effective therapies for hepatic IRI. Recent advances in research have improved our understanding of the pathogenesis of IRI. During IRI, hepatocyte injury and inflammatory responses are mediated by crosstalk between the immune cells and metabolic components. This crosstalk can be targeted to treat or reverse hepatic IRI. Thus, a deep understanding of hepatic microenvironment, especially the immune and metabolic responses, can reveal new therapeutic opportunities for hepatic IRI. In this review, we describe important cells in the liver microenvironment (especially non-parenchymal cells) that regulate immune inflammatory responses. The role of metabolic components in the diagnosis and prevention of hepatic IRI are discussed. Furthermore, recent updated therapeutic strategies based on the hepatic microenvironment, including immune cells and metabolic components, are highlighted.

Halogenation Activity of Mammalian Heme Peroxidases

Mammalian heme peroxidases are fascinating due to their unique peculiarity of oxidizing (pseudo)halides under physiologically relevant conditions. These proteins are able either to incorporate oxidized halides into substrates adjacent to the active site or to generate different oxidized (pseudo)halogenated species, which can take part in multiple (pseudo)halogenation and oxidation reactions with cell and tissue constituents. The present article reviews basic biochemical and redox mechanisms of (pseudo)halogenation activity as well as the physiological role of heme peroxidases. Thyroid peroxidase and peroxidasin are key enzymes for thyroid hormone synthesis and the formation of functional cross-links in collagen IV during basement membrane formation. Special attention is directed to the properties, enzymatic mechanisms, and resulting (pseudo)halogenated products of the immunologically relevant proteins such as myeloperoxidase, eosinophil peroxidase, and lactoperoxidase. The potential role of the (pseudo)halogenated products (hypochlorous acid, hypobromous acid, hypothiocyanite, and cyanate) of these three heme peroxidases is further discussed.

Effects of systemic inflammation due to hepatic ischemia-reperfusion injury upon lean or obese visceral adipose tissue

Purpose:

To evaluate how the induction of liver damage by ischemia and reperfusion affects the adipose tissue of lean and obese mice.

Methods:

Lean and diet-induced obese mice were subjected to liver ischemia (30 min) followed by 6 h of reperfusion. The vascular stromal fraction of visceral adipose tissue was analyzed by cytometry, and gene expression was evaluated by an Array assay and by RT-qPCR. Intestinal permeability was assessed by oral administration of fluorescein isothiocyanate (FITC)-dextran and endotoxemia by serum endotoxin measurements using a limulus amebocyte lysate assay.

Results:

It was found that, after liver ischemia and reperfusion, there is an infiltration of neutrophils, monocytes, and lymphocytes, as well as an increase in the gene expression that encode cytokines, chemokines and their receptors in the visceral adipose tissue of lean mice. This inflammatory response was associated with the presence of endotoxemia in lean mice. However, these changes were not observed in the visceral adipose tissue of obese mice.

Conclusions:

Liver ischemia and reperfusion induce an acute inflammatory response in adipose tissue of lean mice characterized by an intense chemokine induction and leukocyte infiltration; however, inflammatory alterations are already present at baseline in the obese adipose tissue and liver ischemia and reperfusion do not injure further.

The role of MLKL in Hepatic Ischemia-Reperfusion Injury of Alcoholic Steatotic Livers

Alcohol-related liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD) are the primary causes of chronic liver disease in western countries. Liver transplantation is currently one of the most efficient approaches to save patients with liver failure, which is often associated with hepatic ischemia-reperfusion (IR) injury. IR injury is exacerbated by hepatic steatosis, yet the mechanism remains elusive. Necroptosis is a form of regulated cell death mediated by receptor-interacting protein kinase 1 (RIP1), RIP3 and mixed lineage kinase domain-like (MLKL) protein, which has been implicated in the pathogenesis of ALD and NAFLD. Though necroptosis plays an important role in IR injury of high fat diet - induced steatotic livers, the role of necroptosis in IR injury of ethanol - induced steototic livers has not been investigated. In the present study, we used chronic plus binge alcohol (Gao-binge) feeding followed by IR surgery to investigate IR liver injury with ethanol-associated steatosis. We found that the levels of key necroptotic proteins MLKL and RIP3 increased in alcohol-fed mouse livers. Moreover, we observed increased liver injury after IR in control diet-fed mice, which was further exacerbated by alcohol feeding based on serum alanine aminotransferase (ALT) levels and TUNEL staining of necrotic cells. Hepatic neutrophil infiltration also increased in alcohol-fed mice after IR surgery. However, deletion of Mlkl did not protect against IR liver injury in alcohol-fed mice compared with matched wild-type mice. In conclusion, alcoholic steatosis promotes IR injury, which seems to be independent of MLKL-mediated necroptosis.

Inflammatory processes in the liver: divergent roles in homeostasis and pathology

The hepatic immune system is designed to tolerate diverse harmless foreign moieties to maintain homeostasis in the healthy liver. Constant priming and regulation ensure that appropriate immune activation occurs when challenged by pathogens and tissue damage. Failure to accurately discriminate, regulate, or effectively resolve inflammation offsets this balance, jeopardizing overall tissue health resulting from an either  overly tolerant or an overactive inflammatory response. Compelling scientific and clinical evidence links dysregulated hepatic immune and inflammatory responses upon sterile injury to several pathological conditions in the liver, particularly nonalcoholic steatohepatitis and ischemia-reperfusion injury. Murine and human studies have described interactions between diverse immune repertoires and nonhematopoietic cell populations in both physiological and pathological activities in the liver, although the molecular mechanisms driving these associations are not clearly understood. Here, we review the dynamic roles of inflammatory mediators in responses to sterile injury in the context of homeostasis and disease, the clinical implications of dysregulated hepatic immune activity and therapeutic developments to regulate liver-specific immunity.

The Role of the Key Effector of Necroptotic Cell Death, MLKL, in Mouse Models of Disease

Necroptosis is an inflammatory form of lytic programmed cell death that is thought to have evolved to defend against pathogens. Genetic deletion of the terminal effector protein—MLKL—shows no overt phenotype in the C57BL/6 mouse strain under conventional laboratory housing conditions. Small molecules that inhibit necroptosis by targeting the kinase activity of RIPK1, one of the main upstream conduits to MLKL activation, have shown promise in several murine models of non-infectious disease and in phase II human clinical trials. This has triggered in excess of one billion dollars (USD) in investment into the emerging class of necroptosis blocking drugs, and the potential utility of targeting the terminal effector is being closely scrutinised. Here we review murine models of disease, both genetic deletion and mutation, that investigate the role of MLKL. We summarize a series of examples from several broad disease categories including ischemia reperfusion injury, sterile inflammation, pathogen infection and hematological stress. Elucidating MLKL’s contribution to mouse models of disease is an important first step to identify human indications that stand to benefit most from MLKL-targeted drug therapies.

Genistein Modulated Lipid Metabolism, Hepatic PPARγ, and Adiponectin Expression in Bilateral Ovariectomized Rats with Nonalcoholic Steatohepatitis (NASH)

The aim of this study was to evaluate the protective effects of genistein on lipid accumulation and apoptosis in estrogen deficient rats with NASH. Female Sprague-Dawley rats (n = 48) were divided into ovariectomized (OVX) and non-OVX groups. Each group was then sub-divided into 3 subgroups; control, NASH (rats fed with a high-fat, high-fructose (HFHF) diet), and NASH+Gen (rats fed with HFHF diet plus daily genistein at 16 mg/kg BW). Results showed that HFHF diet induced liver fat accumulation in both non-OVX and OVX rats, which was evidenced by hepatic steatosis on liver pathology and increased hepatic free fatty acid (FFA) and triglyceride levels. Hepatic fat accumulation was significantly more severe in NASH rats with OVX than non-OVX. Hepatocyte apoptosis was more severe in NASH groups compared with that in control groups. Genistein administration significantly improved histopathology of NASH in both non-OVX and OVX rats and attenuated hepatic lipid accumulation, oxidative stress, and hepatocyte apoptosis. Genistein also down-regulated PPARγ and up-regulated adiponectin expression. In summary, NASH could be worsened by estrogen deficiency, indicating the protective action of estrogen on NASH. Genistein administration alleviated hepatic steatosis and apoptosis through the down-regulation of PPARγ and up-regulation of adiponectin expression.

Mitochondrial oxidative injury: a key player in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become the most prevalent liver disease worldwide. NAFLD is tightly linked to the metabolic syndrome, insulin resistance, and oxidative stress. Globally, its inflammatory form, nonalcoholic steatohepatitis (NASH), has become the main cause of liver-related morbidity and mortality, mainly due to liver cirrhosis and primary liver cancer. One hallmark of NASH is the presence of changes in mitochondrial morphology and function that are accompanied by a blocked flow of electrons in the respiratory chain, which increases formation of mitochondrial reactive oxygen species in a self-perpetuating vicious cycle. Consequences are oxidation of DNA bases and mitochondrial DNA depletion that are coupled with genetic and acquired mitochondrial DNA mutations, all impairing the resynthesis of respiratory chain polypeptides. In general, several maladaptations of pathways that usually maintain energy homeostasis occur with the early and late excess metabolic stress in NAFLD and NASH. We discuss the interplay between hepatocyte mitochondrial stress and inflammatory responses, focusing primarily on events initiated and maintained by mitochondrial free radical-induced damage in NAFLD. Importantly, mitochondrial oxidative stress and dysfunction are modulated by key pharmacological targets that are related to excess production of reactive oxygen species, mitochondrial turnover and the mitochondrial unfolded protein response, mitophagy, and mitochondrial biogenesis. However, the efficacy of such interventions depends on NAFLD/NASH disease stage.

Improvement of steatotic rat liver function with a defatting cocktail during ex situ normothermic machine perfusion is not directly related to liver fat content

There is a significant organ shortage in the field of liver transplantation, partly due to a high discard rate of steatotic livers from donors. These organs are known to function poorly if transplanted but make up a significant portion of the available pool of donated livers. This study demonstrates the ability to improve the function of steatotic rat livers using a combination of ex situ machine perfusion and a "defatting" drug cocktail. After 6 hours of perfusion, defatted livers demonstrated lower perfusate lactate levels and improved bile quality as demonstrated by higher bile bicarbonate and lower bile lactate. Furthermore, defatting was associated with decreased gene expression of pro-inflammatory cytokines and increased expression of enzymes involved in mitochondrial fatty acid oxidation. Rehabilitation of marginal or discarded steatotic livers using machine perfusion and tailored drug therapy can significantly increase the supply of donor livers for transplantation.

Metabolic and lipidomic profiling of steatotic human livers during ex situ normothermic machine perfusion guides resuscitation strategies

There continues to be a significant shortage of donor livers for transplantation. One impediment is the discard rate of fatty, or steatotic, livers because of their poor post-transplant function. Steatotic livers are prone to significant ischemia-reperfusion injury (IRI) and data regarding how best to improve the quality of steatotic livers is lacking. Herein, we use normothermic (37°C) machine perfusion in combination with metabolic and lipidomic profiling to elucidate deficiencies in metabolic pathways in steatotic livers, and to inform strategies for improving their function. During perfusion, energy cofactors increased in steatotic livers to a similar extent as non-steatotic livers, but there were significant deficits in anti-oxidant capacity, efficient energy utilization, and lipid metabolism. Steatotic livers appeared to oxidize fatty acids at a higher rate but favored ketone body production rather than energy regeneration via the tricyclic acid cycle. As a result, lactate clearance was slower and transaminase levels were higher in steatotic livers. Lipidomic profiling revealed ω-3 polyunsaturated fatty acids increased in non-steatotic livers to a greater extent than in steatotic livers. The novel use of metabolic and lipidomic profiling during ex situ normothermic machine perfusion has the potential to guide the resuscitation and rehabilitation of steatotic livers for transplantation.

Receptor-Interacting Serine/Threonine-Protein Kinase 3 (RIPK3)-Mixed Lineage Kinase Domain-Like Protein (MLKL)-Mediated Necroptosis Contributes to Ischemia-Reperfusion Injury of Steatotic Livers

Increased hepatic ischemia-reperfusion (IR) injury in steatotic livers is a major reason for rejecting the use of fatty livers for liver transplantation. Necroptosis is implicated in the pathogenesis of fatty liver diseases. Necroptosis is regulated by three key proteins: receptor-interacting serine/threonine-protein kinase (RIPK)-1, RIPK3, and mixed-lineage kinase domain-like protein (MLKL). Here, we found that marked steatosis of the liver was induced when a Western diet was given in mice; steatosis was associated with the inhibition of hepatic proteasome activities and with increased levels of key necroptosis-related proteins. Mice fed a Western diet had more severe liver injury, as demonstrated by increases in serum alanine aminotransferase and necrotic areas of liver, after IR than did mice fed a control diet. Although hepatic steatosis was not different between Mlkl knockout mice and wild-type mice, Mlkl knockout mice had decreased hepatic neutrophil infiltration and inflammation and were protected from hepatic IR injury, irrespective of diet. Intriguingly, Ripk3 knockout or Ripk3 kinase-dead knock-in mice were protected against IR injury at the late phase but not the early phase, irrespective of diet. Overall, our findings indicate that liver steatosis exacerbates hepatic IR injury via increased MLKL-mediated necroptosis. Targeting MLKL-mediated necroptosis may help to improve outcomes in steatotic liver transplantation.

CXCR6 deficiency ameliorates ischemia-reperfusion injury by reducing the recruitment and cytokine production of hepatic NKT cells in a mouse model of non-alcoholic fatty liver disease

Fatty liver is used for transplantation due to organ shortage, but prone to cause complications like ischemia-reperfusion injury (IRI). NKT cells as a bridge between innate and adaptive immunity were reported to infiltrate the liver at the early phase of IRI induced in normal liver. However, the localization mechanism of NKT cells is not precise, and the role of NKT cells in fatty liver IRI is poorly understood. In present murine IRI model of non-alcoholic fatty liver disease, we demonstrated that although the number reduced in fatty liver, NKT cells still activated and accumulated to fatty liver following IRI, and contributed to IRI by producing inflammatory cytokine IFN-γ. We revealed that NKT cells in fatty liver expressed more CXCR6, a vital chemokine receptor; meanwhile, the ligand CXCL16 mRNA expression level in fatty liver was up-regulated. The up-regulation of the CXCR6/CXCL16 axis in fatty liver happened in IRI, which maybe endow NKT cells more chemotaxis. We further found CXCR6 deficiency reduced the recruitment of NKT cells in a tissue-dependent manner, and impaired the IFN-γ producing capacity of hepatic NKT cells. Serum ALT level and hepatic histology were both improved in CXCR6 deficient mice. The results provide evidence of the pathogenic role of NKT cells in fatty liver IRI, and important localization mechanism involving up-regulated CXCR6/CXCL16. Deficiency of CXCR6 protects the fatty liver from IRI by reducing the recruitment and cytokine production of hepatic NKT cells.

Oxidant Stress and Lipid Peroxidation in Acetaminophen Hepatotoxicity

Acetaminophen (APAP) overdose is the most frequent cause of liver injury and acute liver failure in many western countries. The mechanism of APAP-induced hepatocyte necrosis has been investigated extensively. The formation of a reactive metabolite and its binding to cellular proteins was initially thought to be responsible for cell death. A competing hypothesis was introduced that questioned the relevance of protein binding and instead suggested that P450-derived oxidant stress and lipid peroxidation causes APAP-induced liver injury. However, work over the last 15 years has reconciled some of these apparent contradictory hypotheses. This review summarizes the present state of knowledge on the role of reactive oxygen species (ROS) in APAP hepatotoxicity. Detailed investigations into the sources and relevance of the oxidant stress have clearly shown the critical role of the electron transport chain of mitochondria as main source of the oxidant stress. Other potential sources of ROS such as cytochrome P450 enzymes or NADPH oxidase on phagocytes are of limited relevance. The mitochondria-derived superoxide and peroxynitrite formation is initiated by the binding of the reactive metabolite to mitochondrial proteins and the amplification by mitogen activated protein kinases. The consequences of this oxidant stress are the opening of the mitochondrial membrane permeability transition pore with cessation of ATP synthesis, nuclear DNA fragmentation and ultimately cell necrosis. Lipid peroxidation is not a relevant mechanism of cell death but can be a marker of ROS formation. These mechanistic insights suggest that targeting mitochondrial oxidant stress is a promising therapeutic option for APAP hepatotoxicity.

Oxidative Stress and Acute Hepatic Injury

Reactive oxygen species have long been implicated in the pathophysiology of acute liver injury. However, the translation of these findings to the clinic and the development of therapeutic agents have been slow mainly due to the poor mechanistic understanding of the pathophysiology and the many indirect approaches used to characterize the role of oxidant stress in liver injury. The current review discusses in depth the sources of reactive oxygen, the oxidants involved and the impact of this oxidant stress in the mechanism of cell death in 3 different clinically relevant acute liver injury models.

C-C Chemokine Ligand-5 is critical for facilitating macrophage infiltration in the early phase of liver ischemia/reperfusion injury

CCL5/RANTES, a chemoattractant for myeloid cells, is induced by hepatic ischemia/reperfusion injury (IRI). The roles of CCL5 in hepatic IRI were carried out by means of CCL5 immunodepletion, antagonistic competition by Met-CCL5, and treatment with recombinant murine CCL5 (rmCCL5). Depletion or inhibition of CCL5 reduced severity of hepatic IRI, whereas rmCCL5 treatment aggravated liver IRI as manifested in elevated serum alanine aminotransferase (ALT) and tissue myeloperoxidase (MPO) levels. Moreover, IRI severity was reduced in CCL5-knockout (CCL5-KO) mice versus wildtype (WT) mice, with drops in serum ALT level, intrahepatic MPO activity, and histological pathology. Bone marrow transplantion (BMT) studies show that myeloid cells and tissue cells are both required for CCL5-aggravated hepatic IRI. The profile of liver-infiltrating leukocyte subsets after hepatic reperfusion identified CD11b+ cells as the only compartment significantly reduced in CCL5-KO mice versus WT controls at early reperfusion phase. The role of CCL5 recruiting CD11b+ cells in early reperfusion was validated by in vitro transwell migration assay of murine primary macrophages (broadly characterized by their CD11b expression) in response to liver lysates after early reperfusion. Taken together, our results demonstrate a sequence of early events elicited by CCL5 chemoattracting macrophage that result in inflammatory aggravation of hepatic IRI.

Loss of pericyte smoothened activity in mice with genetic deficiency of leptin

BACKGROUND

Obesity is associated with multiple diseases, but it is unclear how obesity promotes progressive tissue damage. Recovery from injury requires repair, an energy-expensive process that is coupled to energy availability at the cellular level. The satiety factor, leptin, is a key component of the sensor that matches cellular energy utilization to available energy supplies. Leptin deficiency signals energy depletion, whereas activating the Hedgehog pathway drives energy-consuming activities. Tissue repair is impaired in mice that are obese due to genetic leptin deficiency. Tissue repair is also blocked and obesity enhanced by inhibiting Hedgehog activity. We evaluated the hypothesis that loss of leptin silences Hedgehog signaling in pericytes, multipotent leptin-target cells that regulate a variety of responses that are often defective in obesity, including tissue repair and adipocyte differentiation.

RESULTS

We found that pericytes from liver and white adipose tissue require leptin to maintain expression of the Hedgehog co-receptor, Smoothened, which controls the activities of Hedgehog-regulated Gli transcription factors that orchestrate gene expression programs that dictate pericyte fate. Smoothened suppression prevents liver pericytes from being reprogrammed into myofibroblasts, but stimulates adipose-derived pericytes to become white adipocytes. Progressive Hedgehog pathway decay promotes senescence in leptin-deficient liver pericytes, which, in turn, generate paracrine signals that cause neighboring hepatocytes to become fatty and less proliferative, enhancing vulnerability to liver damage.

CONCLUSIONS

Leptin-responsive pericytes evaluate energy availability to inform tissue construction by modulating Hedgehog pathway activity and thus, are at the root of progressive obesity-related tissue pathology. Leptin deficiency inhibits Hedgehog signaling in pericytes to trigger a pericytopathy that promotes both adiposity and obesity-related tissue damage.

Results of the TOP Study: Prospectively Randomized Multicenter Trial of an Ex Vivo Tacrolimus Rinse Before Transplantation in EDC Livers

Background

Organ shortage results in the transplantation of extended donor criteria (EDC) livers which is associated with increased ischemia-reperfusion injury (IRI). Experimental studies indicate that an organ rinse with the calcineurin inhibitor tacrolimus before implantation protects against IRI. The tacrolimus organ perfusion study was initiated to examine the effects of ex vivo tacrolimus perfusion on IRI in transplantation of EDC livers.

Methods

A prospective randomized multicenter trial comparing ex vivo perfusion of marginal liver grafts (≥2 EDC according to Eurotransplant manual) with tacrolimus (20 ng/mL) or histidine-tryptophane-ketoglutarate solution (control) was carried out at 5 German liver transplant centers (Munich Ludwig-Maximilians University, Berlin, Heidelberg, Mainz, Regensburg) between October 2011 and July 2013. Primary endpoint was the maximum alanine transaminase (ALT) level within 48 hours after transplantation. Secondary endpoints were aspartate transaminase (AST), prothrombine ratio, and graft-patient survival within an observation period of 1 week. After an interim analysis, the study was terminated by the scientific committee after the treatment of 24 patients (tacrolimus n = 11, Control n = 13).

Results

Tacrolimus rinse did not reduce postoperative ALT peaks compared with control (P = 0.207; tacrolimus: median, 812; range, 362-3403 vs control: median, 652; range, 147-2034). Moreover, ALT (P = 0.100), prothrombine ratio (P = 0.553), and bilirubin (P = 0.815) did not differ between the groups. AST was higher in patients treated with tacrolimus (P = 0.011). Survival was comparable in both groups (P > 0.05).

Conclusions

Contrary to experimental findings, tacrolimus rinse failed to improve the primary endpoint of the study (ALT). Because 1 secondary endpoint (AST) was even higher in the intervention group, the study was terminated prematurely. Thus, tacrolimus rinse cannot be recommended in transplantation of EDC livers.

The novel TLR9 antagonist COV08-0064 protects from ischemia/reperfusion injury in non-steatotic and steatotic mice livers

Ischemia/reperfusion (I/R) injury constitutes a major reason for failure of liver surgeries and transplantation. I/R injury is more severe in steatotic livers and limits their use in transplantation. Here, we present a novel and selective Toll-like receptor 9 (TLR9) antagonist COV08-0064 and test its potential to protect from I/R-induced injury in normal and steatotic livers. The in vivo effects of COV08-0064 pretreatment were investigated on normal chow diet (NCD) and high fat diet (HFD)-fed mice subjected to segmental (70%) warm hepatic I/R. Also, the in vitro effects of COV08-0064 were elucidated in murine macrophages and dendritic cells. Mice on a HFD had pronouncedly greater hepatic I/R injury than mice on a NCD. COV08-0064-pretreatment to both NCD and HFD-fed mice reduced hepatic I/R injury. COV08-0064-pretreatment was associated with less production of the liver inflammatory cytokines and mediators TNF-α, IL-1β, IL-6, NLRP3, iNOS and MCP-1. These manifestations were preceded with inhibition of JNK and ERK phosphorylation and TLR9 cleavage in the liver. COV08-0064 enhanced the hepatic expression of the endogenous anti-inflammatory cytokines IL-10 and IL-1Ra at the early phase I/R injury. In vitro, COV08-0064 selectively blocked mRNA upregulation of TNF-α, IL-1β, NLRP3 and MCP-1 in macrophages and IFN-β mRNA in dendritic cells induced by the TLR9 agonist CpG-ODN. These effects were concordant with inhibition of JNK, ERK, IκBα and IKKα/β phosphorylation. In conclusion, TLR9 signaling inhibition by COV08-0064 may be an effective approach in liver surgeries including transplantation to limit I/R-injury and overcome the shortages in the donor pool by incorporating steatotic livers.

The neuroimmune guidance cue netrin-1 controls resolution programs and promotes liver regeneration

Hepatic ischemia/reperfusion (I/R) is a major adverse reaction to liver transplantation, hemorrhagic shock, or resection. Recently, the anti-inflammatory properties of the axonal guidance cue netrin-1 were reported. Here, we demonstrate that netrin-1 also impacts the resolution of inflammation and promotes hepatic repair and regeneration during liver I/R injury. In initial studies, we investigated the induction of netrin-1 and its receptors in murine liver tissues after I/R injury. Hepatic I/R injury was performed in mice with a partial genetic netrin-1 deficiency (Ntn1(+/-) ) or wild-type C57BL/6 treated with exogenous netrin-1 to examine the endogenous and therapeutically administered impact of netrin-1. These investigations were corroborated by studies determining the characteristics of intravascular leukocyte flow, clearance of apoptotic neutrophils (polymorphonuclear cells [PMNs]), production of specialized proresolving lipid mediators (SPMs), generation of specific growth factors contributing to the resolution of inflammation, and liver repair. Hepatic I/R was associated with a significant reduction of netrin-1 transcript and protein in murine liver tissue. Subsequent studies in netrin-1-deficient mice revealed lower efficacies in reducing PMN infiltration, proinflammatory cytokine levels, and hepatic-specific injury enzymes. Conversely, mice treated with exogenous netrin-1 exhibited increased liver protection and repair, reducing neutrophil influx into the injury site, decreasing proinflammatory mediators, increasing efferocytosis of apoptotic PMNs, and stimulating local endogenous biosynthesis of SPMs and the generation of specific growth factors. Finally, genetic studies implicated the A2B adenosine receptor in netrin-1-mediated protection during hepatic I/R injury.

CONCLUSION

The present study indicates a previously unrecognized role for netrin-1 in liver protection and its contribution to tissue homeostasis and regeneration.

Intereukin-10 and Kupffer cells protect steatotic mice livers from ischemia-reperfusion injury

Steatotic livers are more sensitive to ischemia/reperfusion (I/R) and are thus routinely rejected for transplantation because of their increased rate of primary nonfunction (PNF). Lean livers have less I/R-induced damage and inflammation due to Kupffer cells (KC), which are protective after total, warm, hepatic I/R with associated bowel congestion. This protection has been linked to KC-dependent expression of the potent anti-inflammatory cytokine interleukin-10 (IL-10). We hypothesized that pretreatment with exogenous IL-10 would protect the steatotic livers of genetically obese (ob/ob) mice from inflammation and injury induced by I/R. Lean and ob/ob mice were pretreated with either IL-10 or liposomally-encapsulated bisphosphonate clodronate (shown to deplete KC) prior to total, warm, hepatic I/R. IL-10 pretreatment increased survival of ob/ob animals at 24 hrs post-I/R from 30% to 100%, and significantly decreased serum ALT levels. At six hrs post-I/R, IL-10 pretreatment increased IL-10 mRNA expression, but suppressed up-regulation of the pro-inflammatory cytokine IL-1β mRNA. However, ALT levels were elevated at six hrs post-I/R in KC-depleted animals. These data reveal that pretreatment with IL-10 protects steatotic livers undergoing I/R, and that phagocytically active KC retain a hepatoprotective role in the steatotic environment.

Ischemia–reperfusion injury in patients with fatty liver and the clinical impact of steatotic liver on hepatic surgery

Hepatic steatosis is one of the most common hepatic disorders in developed countries. The epidemic of obesity in developed countries has increased with its attendant complications, including metabolic syndrome and non-alcoholic fatty liver disease. Steatotic livers are particularly vulnerable to ischemia/reperfusion injury, resulting in an increased risk of postoperative morbidity and mortality after liver surgery, including liver transplantation. There is growing understanding of the molecular and cellular mechanisms and therapeutic approaches for treating ischemia/reperfusion injury in patients with steatotic livers. This review discusses the mechanisms underlying the susceptibility of steatotic livers to ischemia/reperfusion injuries, such as mitochondrial dysfunction and signal transduction alterations, and summarizes the clinical impact of steatotic livers in the setting of hepatic resection and liver transplantation. This review also describes potential therapeutic approaches, such as ischemic and pharmacological preconditioning, to prevent ischemia/reperfusion injury in patients with steatotic livers. Other approaches, including machine perfusion, are also under clinical investigation; however, many pharmacological approaches developed through basic research are not yet suitable for clinical application.

Prolonged diet-induced obesity in mice modifies the inflammatory response and leads to worse outcome after stroke

Background

Obesity increases the risk for ischaemic stroke and is associated with worse outcome clinically and experimentally. Most experimental studies have used genetic models of obesity. Here, a more clinically relevant model, diet-induced obesity, was used to study the impact of obesity over time on the outcome and inflammatory response after stroke.

Methods

Male C57BL/6 mice were maintained on a high-fat (60 % fat) or control (12 % fat) diet for 2, 3, 4 and 6 months when experimental stroke was induced by transient occlusion of the middle cerebral artery (MCAo) for either 20 (6-month diet) or 30 min (2-, 3-, 4- and 6-month diet). Ischaemic damage, blood–brain barrier (BBB) integrity, neutrophil number and chemokine expression in the brain were assessed at 24 h. Plasma chemokine levels (at 4 and 24 h) and neutrophil number in the liver (at 24 h) were measured. Physiological parameters (body weight and blood glucose) were measured in naïve control- and high-fat-fed mice at all time points and blood pressure at 3 and 6 months. Blood cell counts were also assessed in naïve 6-month control- and high-fat-fed mice.

Results

Mice fed a high-fat diet for 6 months had greater body weight, blood glucose and white and red blood cell count but no change in systolic blood pressure. After 4 and 6 months of high-fat feeding, and in the latter group with a 30-min (but not 20-min) occlusion of the MCA, obese mice had greater ischaemic brain damage. An increase in blood–brain barrier permeability, chemokine expression (CXCL-1 and CCL3), neutrophil number and microglia/macrophage cells was observed in the brains of 6-month high-fat-fed mice after 30-min MCAo. In response to stroke, chemokine (CXCL-1) expression in the plasma and liver was significantly different in obese mice (6-month high-fat fed), and a greater number of neutrophils were detected in the liver of control but not obese mice.

Conclusions

The detrimental effects of diet-induced obesity on stroke were therefore dependent on the severity of obesity and length of ischaemic challenge. The altered inflammatory response in obese mice may play a key role in its negative impact on stroke.

Intestinal ischemic preconditioning ameliorates hepatic ischemia/reperfusion injury in rats: role of heme oxygenase 1 in the second window of protection

Preconditioning by brief ischemia protects not only the concerned organ but also other distant organs against subsequent lethal damage; this is called remote ischemic preconditioning (RIPC). This study was designed to investigate the impact of intestinal RIPC on hepatic ischemia/reperfusion injury (IRI) with a special interest in heme oxygenase 1 (HO-1) induction in the second window of protection (SWOP). Male Wistar rats were randomly assigned to 1 of 2 groups: an RIPC group or a sham group. Before hepatic IRI, either intestinal RIPC, consisting of 2 cycles of 4-minute superior mesenteric artery clamping separated by 11 minutes of declamping (RIPC group), or a sham procedure (sham group) was performed. After 48 hours of recovery, the rats were exposed to 30 minutes of total hepatic IRI. Transaminase releases and proinflammatory cytokines were determined at several time points after reperfusion. Histopathological analysis and animal survival were also investigated. Intestinal RIPC significantly lowered transaminase release (alanine aminotransferase at 2 hours: 873.3 ± 176.4 IU/L for the RIPC group versus 3378.7 ± 871.1 IU/L for the sham group, P < .001) as well as proinflammatory cytokine production (tumor necrosis factor α at 2 hours: 930 ± 42 versus 387 ± 17 pg/μL, P < .001). The morphological integrity of the liver and the ileum was maintained significantly better with intestinal RIPC; this reached statistical significance not only in Suzuki's liver injury score (3.5 ± 0.2 versus 0.7 ± 0.5, P = .007) but also in Park's score for intestinal damage (4.0 ± 0.4 versus 2.0 ± 0.2, P = .007). Animal survival was also markedly improved (83.1% versus 15.4%, P < .001). As a mechanism underlying this protection, HO-1 was substantially induced in liver tissue, especially in hepatocytes, with remarkable up-regulation of bradykinin in the portal blood, whereas HO-1 protein induction in enterocytes was not significant. In conclusion, intestinal RIPC remarkably attenuates hepatic IRI in the SWOP, presumably by HO-1 induction in hepatocytes.

Expression of HIF-1α and NF-κB in non-alcoholic fat liver disease in rats

AIM: To investigate the role of hypoxia-inducible factor -1α (HIF-1α) and nuclear transcription factor κB (NF-κB) in the development of non-alcoholic fat liver disease (NAFLD) using a rat model.

METHODS: Fifty SD rats were randomly divided into five groups (a normal group, a 4 wk model group, an 8 wk group, a 12 wk and a 16 wk group). NAFLD was induced in rats by administration of a high fat diet. Serum biochemical parameters were tested, and fiver histological changes were observed. HIF-1α and NF-κB mRNA expression was detected by real-time PCR.

RESULTS: Compared with the normal group, significant elevations of serum alanine amiotransferase (ALT), triglyceride (TG), and cholesterol (CHOL) and reduction of high-density lipoprotein cholesterol (HDL-C) were observed in rats given a high fat diet for 12 wk or 16 wk (P < 0.05). In the model groups, liver steatosis, inflammation grade and degree of fibrosis were significantly aggravated. HIF-1α and NF- κB expression increased gradually with the severity of NAFLD (P < 0.05).

CONCLUSION: HIF-1α/NF-κB signaling may be related to the development of NAFLD.

Biomarkers distinguish apoptotic and necrotic cell death during hepatic ischemia/reperfusion injury in mice

Hepatic ischemia/reperfusion (IRP) injury is a significant clinical problem during tumor-resection surgery (Pringle maneuver) and liver transplantation. However, the relative contribution of necrotic and apoptotic cell death to the overall liver injury is still controversial. To address this important issue with a standard murine model of hepatic IRP injury, plasma biomarkers of necrotic cell death such as micro-RNA 122, full-length cytokeratin 18 (FK18), and high-mobility group box 1 (HMGB1) protein and plasma biomarkers of apoptosis such as plasma caspase-3 activity and caspase-cleaved fragment of cytokeratin 18 (CK18) coupled with markers of inflammation (hyperacetylated HMGB1) were compared by histological features in hematoxylin and eosin-stained and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL)-stained liver sections. After 45 minutes of hepatic ischemia and 1 to 24 hours of reperfusion, all necrosis markers increased dramatically in plasma by 40- to >10,000-fold over the baseline with a time course similar to that of alanine aminotransferase. These data correlated well with histological characteristics of necrosis. Within the area of necrosis, most cells were TUNEL positive; initially (≤3 hours of reperfusion), the staining was restricted to nuclei, but it later spread to the cytosol, and this is characteristic of karyorrhexis during necrotic cell death. In contrast, the lack of morphological evidence of apoptotic cell death and relevant caspase-3 activity in the postischemic liver correlated well with the absence of caspase-3 activity and CK18 (except for a minor increase at 3 hours of reperfusion) in plasma. A quantitative comparison of FK18 (necrosis) and CK18 (apoptosis) release indicated dominant cell death by necrosis during IRP and only a temporary and very minor degree of apoptosis. These data suggest that the focus of future research should be the elucidation of necrotic signaling mechanisms to identify relevant targets, which may be used to attenuate hepatic IRP injury.

Involvement of the nuclear factor-κB pathway in the adhesion of neutrophils to renal tubular cells after injury induced by neonatal postasphyxial serum

Nuclear factor κB (NF-κB) plays an important role in the regulation of inflammatory proteins. However, it is unclear whether the NF-κB/intercellular adhesion molecule-1 (ICAM-1) pathway is involved in the adhesion of neutrophils and renal injury after hypoxia-ischemia (HI) in neonates. In this report we investigated whether NF-κB and its downstream molecule ICAM-1 were involved in renal injury induced by postasphyxial serum (PS) from neonates. Human renal proximal tubular (HK-2) cells were preincubated with 10 % fetal calf serum (control), 20 % neonatal PS, or 20 % PS plus pyrolidine dithiocarbamate (PDTC). The expression of IκBα, NF-κB p65, and ICAM-1 in HK-2 cells was determined by Western blot and/or immunohistochemistry. Nuclear translocation of NF-κB p65 in HK-2 cells was detected by immunofluorescence and Western blot. The ICAM-1 mRNA was determined by RT-PCR. Then HK-2 cells were cultured with neutrophils from neonates with asphyxia. After HK-2 cells had been cultured with neutrophils, we detected myeloperoxidase (MPO) activity, the leakage rate of lactate dehydrogenase (LDH), and cell viability. We found that PS preincubation resulted in significantly decreased IκBα expression and increased expression of NF-κB and ICAM-1, and facilitated the nuclear translocation of NF-κB in HK-2 cells. PS preincubation increased MPO activity, leading to elevated leakage rates of LDH and decreased cell viability after neutrophil exposure. Furthermore, the inhibition of NF-κB activity by PDTC significantly upregulated IκBα expression, decreased NF-κB and ICAM-1 expression, downregulated the nuclear translocation of NF-κB, and decreased MPO activity. This leads to decreased leakage rates of LDH and increased cell viability after neutrophil exposure. Our findings suggest that NF-κB/ICAM-1 pathway may be involved in neutrophil-endothelial interactions and neonatal renal injury after HI.

Strategies to rescue steatotic livers before transplantation in clinical and experimental studies

The shortage of donor livers has led to an increased use of organs from expanded criteria donors. Included are livers with steatosis, a metabolic abnormality that increases the likelihood of graft complications post-transplantation. After a brief introduction on the etiology, pathophysiology, categories and experimental models of hepatic steatosis, we herein review the methods to rescue steatotic donor livers before transplantation applied in clinical and experimental studies. The methods span the spectrum of encouraging donor weight loss, employing drug therapy, heat shock preconditioning, ischemia preconditioning and selective anesthesia on donors, and the treatment on isolated grafts during preservation. These methods work at different stages of transplantation process, although share similar molecular mechanisms including lipid metabolism stimulation through enzymes or nuclear receptor e.g., peroxisomal proliferator-activated receptor, or anti-inflammation through suppressing cytokines e.g., tumor necrosis factor-α, or antioxidant therapies to alleviate oxidative stress. This similarity of molecular mechanisms implies possible future attempts to reinforce each approach by repeating the same treatment approach at several stages of procurement and preservation, as well as utilizing these alternative approaches in tandem.

Leukotriene B4 type-1 receptor signaling promotes liver repair after hepatic ischemia/reperfusion injury through the enhancement of macrophage recruitment

Recruited macrophages play a critical role in liver repair after acute liver injury. Leukotriene B4 (LTB4) is a potent chemoattractant for macrophages. In this study, we investigated the role of LTB4 receptor type 1 (BLT1) in liver repair during hepatic ischemia/reperfusion (I/R) injury. BLT1-knockout mice (BLT1(-/-)) or their wild-type counterparts (WT) were subjected to partial hepatic I/R. Compared with WT, BLT1(-/-) exhibited delayed liver repair and hepatocyte proliferation accompanied by a 70% reduction in the recruitment of macrophages and a 70-80% attenuation in hepatic expression of epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), and VEGF receptor 1 (VEGFR1). Disruption of BLT1 signaling also reduced the expression of EGF by 67% on recruited macrophages expressing VEGFR1 in the injured liver. Treatment of WT mice with an EGF-neutralizing antibody delayed liver repair and reduced macrophage recruitment, compared with control immunoglobulin G (IgG). BLT1 signaling enhanced the expression of VEGF, VEGFR1, and EGF in isolated peritoneal macrophages in vitro. These results indicate that BLT1 signaling plays a role in liver repair after hepatic I/R through enhanced expression of EGF in recruited macrophages and that the development of a specific agonist for BLT1 could be useful for liver recovery from acute liver injury.

Plasma and liver acetaminophen-protein adduct levels in mice after acetaminophen treatment: dose-response, mechanisms, and clinical implications

At therapeutic doses, acetaminophen (APAP) is a safe and effective analgesic. However, overdose of APAP is the principal cause of acute liver failure in the West. Binding of the reactive metabolite of APAP (NAPQI) to proteins is thought to be the initiating event in the mechanism of hepatotoxicity. Early work suggested that APAP-protein binding could not occur without glutathione (GSH) depletion, and likely only at toxic doses. Moreover, it was found that protein-derived APAP-cysteine could only be detected in serum after the onset of liver injury. On this basis, it was recently proposed that serum APAP-cysteine could be used as diagnostic marker of APAP overdose. However, comprehensive dose-response and time course studies have not yet been done. Furthermore, the effects of co-morbidities on this parameter have not been investigated. We treated groups of mice with APAP at multiple doses and measured liver GSH and both liver and plasma APAP-protein adducts at various timepoints. Our results show that protein binding can occur without much loss of GSH. Importantly, the data confirm earlier work that showed that protein-derived APAP-cysteine can appear in plasma without liver injury. Experiments performed in vitro suggest that this may involve multiple mechanisms, including secretion of adducted proteins and diffusion of NAPQI directly into plasma. Induction of liver necrosis through ischemia-reperfusion significantly increased the plasma concentration of protein-derived APAP-cysteine after a subtoxic dose of APAP. While our data generally support the measurement of serum APAP-protein adducts in the clinic, caution is suggested in the interpretation of this parameter.

Protocol TOP-Study (tacrolimus organ perfusion): a prospective randomized multicenter trial to reduce ischemia reperfusion injury in transplantation of marginal liver grafts with an ex vivo tacrolimus perfusion

BACKGROUND

Critical organ shortage results in the utilization of extended donor criteria (EDC) liver grafts. These marginal liver grafts are prone to increased ischemia reperfusion injury (IRI) which may contribute to deteriorated graft function and survival. Experimental data have shown that the calcineurin inhibitor tacrolimus exerts protective effects on hepatic IRI when applied intravenously or directly as a hepatic rinse. Therefore, the aim of the present study is to examine the effects of an ex vivo tacrolimus perfusion on IRI in transplantation of EDC liver grafts.

METHODS/DESIGN

The TOP-Study (tacrolimus organ perfusion) is a randomized multicenter trial comparing the ex vivo tacrolimus perfusion of marginal liver grafts with placebo. We hypothesize that a tacrolimus rinse reduces IRI, potentially improving organ survival following transplantation of EDC livers. The study includes livers with two or more EDC, according to Eurotransplant International Foundation's definition of EDC livers. Prior to implantation, livers randomized to the treatment group are rinsed with tacrolimus at a concentration of 20 ng/ml in 1000 ml Custodiol solution and in the placebo group with Custodiol alone. The primary endpoint is the maximum serum alanine transamninase (ALT) level within the first 48 hours after surgery; however, the study design also includes a 1-year observation period following transplantation. The TOP-Study is an investigator-initiated trial sponsored by the University of Munich Hospital. Seven other German transplant centers are participating (Berlin, Frankfurt, Heidelberg, Mainz, Münster, Regensburg, Tübingen) and aim to include a total of 86 patients.

DISCUSSION

Tacrolimus organ perfusion represents a promising strategy to reduce hepatic IRI following the transplantation of marginal liver grafts. This treatment may help to improve the function of EDC grafts and therefore safely expand the donor pool in light of critical organ shortage.

TRIAL REGISTER

EudraCT number: 2010-021333-31, ClinicalTrials.gov identifier: NCT01564095.

Type of steatosis influences microcirculation and fibrogenesis in different rat strains

This study investigates the impact of rat strain on the development of nonalcoholic fatty liver disease (NAFLD) focusing on morphological features and microcirculation. Male rats of Lewis, Wistar, and Sprague Dawley (n = 6 per strain and group) were randomized into a high-fat group which was fed with a special high-fat nutrition for a 3-week period and a control group which received standard nutrition. Intravital microscopy was used for the evaluation of microcirculation and correlated to morphological changes using a fatty liver scoring system. All three strains receiving a high-fat diet developed a grade 3 steatosis (>66% liver cell steatosis). Whereas Lewis showed a solely microvesicular steatosis, Wistar developed a mixed form and Sprague Dawley showed a pure macrovesicular steatosis and the highest degree of fibrosis and hepatocyte damage. Microcirculatory results revealed that sinusoidal density was already affected by a microvesicular steatosis and decreased with increasing macrovesicular proportion (Lewis: 18%, Wistar: 31%, Sprague Dawley: 23%). The degree of steatosis correlates with reduced blood flow velocity in central veins as well as in sinusoids (Lewis: 28%, Wistar: 39%, Sprague Dawley 44%). The densities of hepatocytes and hepatic stellate cells were only impaired once macrovesicular cell steatosis (Wistar and Sprague Dawley) was present. The development of NAFLD in the rat revealed strain-specific morphological features correlating with microcirculatory changes that should be considered in further studies using these models.

Chemical composition of hepatic lipids mediates reperfusion injury of the macrosteatotic mouse liver through thromboxane A(2)

BACKGROUND & AIMS

Chemical composition of hepatic lipids is an evolving player in steatotic liver ischemia/reperfusion (I/R) injury. Thromboxane A(2) (TXA(2)) is a vasoactive pro-inflammatory lipid mediator derived from arachidonic acid (AA), an omega-6 fatty acid (Ω-6 FA). Reduced tolerance of the macrosteatotic liver to I/R may be related to increased TXA(2) synthesis due to the predominance of Ω-6 FAs.

METHODS

TXA(2) levels elicited by I/R in ob/ob and wild type mice were assessed by ELISA. Ob/ob mice were fed Ω-3 FAs enriched diet to reduce hepatic synthesis of AA and TXA(2) or treated with selective TXA(2) receptor blocker before I/R.

RESULTS

I/R triggered significantly higher hepatic TXA(2) production in ob/ob than wild type animals. Compared with ob/ob mice on regular diet, Ω-3 FAs supplementation markedly reduced hepatic AA levels before ischemia and consistently blunted hepatic TXA(2) synthesis after reperfusion. Sinusoidal perfusion and hepatocellular damage were significantly ameliorated despite downregulation of heme oxygenase-1. Hepatic transcript and protein levels of IL-1β and neutrophil recruitment were significantly diminished after reperfusion. Moreover, TXA(2) receptor blockage conferred similar protection without modification of the histological pattern of steatosis. A stronger protection was achieved in the steatotic compared with lean animals.

CONCLUSIONS

Enhanced I/R injury in the macrosteatotic liver is explained, at least partially, by TXA(2) mediated microcirculatory failure rather than size-related mechanical compression of the sinusoids by lipid droplets. TXA(2) blockage may be a simple strategy to include steatotic organs and overcome the shortage of donor organs for liver transplantation.

Multidrug donor preconditioning protects steatotic liver grafts against ischemia-reperfusion injury

BACKGROUND

Graft dysfunction of steatotic livers (SL) still remains a major challenge in liver transplantation. Different mechanisms are thought to be involved in the impaired tolerance of SL to ischemia-reperfusion injury. Thus, different pharmacologic strategies may need to be combined to effectively protect SL and to reduce graft dysfunction after transplantation. Therefore, we analyzed the effectiveness of a multidrug donor preconditioning (MDDP) procedure to protect SL from cold ischemia-reperfusion injury.

METHODS

Liver steatosis was induced by a high-carbohydrate, fat-free diet. A total of 24 Sprague-Dawley rats were divided into 3 groups (n = 8 each), including a control group with nonsteatotic livers (Con), a vehicle-treated SL group (SL-Con), and a SL group undergoing MDDP (SL-MDDP), including pentoxyphylline, glycine, deferoxamine, N-acetylcysteine, erythropoietin, melatonin, and simvastatin. MDDP was applied before liver perfusion with 4°C histidine-tryptophan-ketoglutarate (HTK) solution and organ harvest. After 24 hours of cold storage in HTK, postischemic reperfusion was performed in an isolated liver reperfusion model using 37°C Krebs-Henseleit bicarbonate buffer.

RESULTS

After 60 minutes of reperfusion, SL showed a significant reduction of bile flow as well as a marked increase of liver enzyme levels and apoptotic cell death compared with Con. This was associated with an increased malondialdehyde formation, interleukin-1 production, and leukocytic tissue infiltration. MDDP completely abolished the inflammatory response and was capable of significantly reducing parenchymal dysfunction and injury.

CONCLUSIONS

MDDP decreases SL injury after cold storage and reperfusion. The concept of MDDP as a simple and safe preoperative regime, thus may be of interest in clinical use, expanding the donor pool from marginal donors.

The effect of hepatic ischemia reperfusion injury in a murine model of nonalcoholic steatohepatitis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) refers to an increasingly diagnosed condition involving triglyceride accumulation into hepatocytes resulting in a broad spectrum of liver injury. The progression of NAFLD, a relatively benign condition, to nonalcoholic steatohepatitis (NASH) involves the hepatic infiltration of inflammatory cells and subsequent hepatocellular injury. Ischemia/reperfusion (I/R) injury of the liver is a major complication of liver resection, hepatic trauma, and liver transplantation. To date, there have been no studies that have evaluated the effects of hepatic I/R on models of NASH.

OBJECTIVE

Evaluate the effects of hepatic I/R on a mouse model of NASH.

METHODS

A mouse model of progressive NASH was developed and evaluated using C57BL/6 mice fed a methionine choline deficient diet for 3, 6, 9, and 12 wk. Mice subsequently underwent 90 min of partial hepatic ischemia with reperfusion of 1, 4, and 8 h. Mice were sacrificed after the indicated periods, and blood and liver samples were taken for analysis.

RESULTS

Mice fed the MCD diet showed a rapid induction of hepatic steatosis, inflammation, and fibrosis by 3 wk that persisted over the 12-wk period of diet, as demonstrated by histologic examination, alanine aminotransferase (ALT), and liver content of myeloperoxidase (MPO). The response to I/R in livers with progressive NASH fed MCD diet for 3, 6, 9, and 12 wk showed marked neutrophil recruitment and hepatocyte necrosis.

CONCLUSION

These data suggest the inflammatory response from I/R is augmented in livers with NASH histopathology compared with normal liver.

Effect of remote ischemic preconditioning on liver ischemia/reperfusion injury using a new mouse model

Ischemic preconditioning of remote organs (RIPC) reduces liver ischemia/reperfusion (IR) injury in the rabbit and rat. Mice are the only species available with a large number of transgenic strains. This study describes development and validation of a mouse model of hindlimb RIPC that attenuates liver IR injury. Mice were allocated to 4 groups: (1) Sham surgery; (2) RIPC: 6 cycles of 4 × 4 minutes ischemia/reperfusion of hindlimb; (3) IR: 40 minutes lobar (70%) hepatic ischemia and 2 hours reperfusion; (4) RIPC+IR: RIPC followed by IR group procedures. Plasma liver aminotransferases and hepatic histopathological and transmission electron microscopy studies were performed at the end of the experiment. Hepatic microcirculatory blood flow was measured throughout the experiment. Postoperative complications and animal survival were evaluated. Hindlimb RIPC using a tourniquet resulted in limb paralysis. Hindlimb RIPC using direct clamping of the femoral vessels showed no side effects. Compared to liver IR alone, RIPC+IR reduced plasma aminotransferases (P < 0.05) and histopathological and ultrastructural features of injury. Hepatic microcirculatory blood flow was preserved in the RIPC+IR compared to IR group (P < 0.05). There was no mortality in any of the groups. By demonstrating a consistent improvement in these features of liver IR injury with antecedent hindlimb RIPC and by minimizing experimental confounding variables, we validated this mouse model. In conclusion, we describe a validated mouse model of hindlimb RIPC that reduces liver IR injury. With the availability of transgenic mice strains, this model should prove useful in unraveling the mechanisms of protection of hindlimb RIPC.

Liver ischemia/reperfusion injury: processes in inflammatory networks--a review

Liver ischemia/reperfusion (IR) injury is typified by an inflammatory response. Understanding the cellular and molecular events underpinning this inflammation is fundamental to developing therapeutic strategies. Great strides have been made in this respect recently. Liver IR involves a complex web of interactions between the various cellular and humoral contributors to the inflammatory response. Kupffer cells, CD4+ lymphocytes, neutrophils, and hepatocytes are central cellular players. Various cytokines, chemokines, and complement proteins form the communication system between the cellular components. The contribution of the danger-associated molecular patterns and pattern recognition receptors to the pathophysiology of liver IR injury are slowly being elucidated. Our knowledge on the role of mitochondria in generating reactive oxygen and nitrogen species, in contributing to ionic disturbances, and in initiating the mitochondrial permeability transition with subsequent cellular death in liver IR injury is continuously being expanded. Here, we discuss recent findings pertaining to the aforementioned factors of liver IR, and we highlight areas with gaps in our knowledge, necessitating further research.

Hepatic lipotoxicity and the pathogenesis of nonalcoholic steatohepatitis: the central role of nontriglyceride fatty acid metabolites

A significant body of evidence now forces us to rethink the causes of NASH. Once thought to be a disease caused by triglyceride accumulation in hepatocytes with subsequent oxidant stress and lipid peroxidation causing inflammation and fibrosis, new data from animal studies and a limited number of human studies now provide convincing evidence that triglyceride accumulation does not cause insulin resistance or cellular injury in the liver. The lipotoxic liver injury hypothesis for the pathogenesis of NASH suggests that we need to focus our therapeutic efforts on reducing the burden of fatty acids going to the liver or being synthesized in the liver. This can be accomplished by improving insulin sensitivity at the level of adipose tissue to prevent inappropriate peripheral lipolysis and by preventing unnecessary de novo lipogenesis in the liver. Excess carbohydrates are the major substrates for de novo lipogenesis, and thus, reducing carbohydrate consumption through dietary changes and increasing muscle glucose uptake through exercise remain important cornerstones of treatment and prevention of lipotoxic liver injury, a disease hitherto called NASH.

High fat diet-induced liver steatosis promotes an increase in liver mitochondrial biogenesis in response to hypoxia

Mitochondrial DNA (mtDNA) copy number plays a key role in the pathophysiology of metabolic syndrome-related phenotypes, but its role in non-alcoholic fatty liver disease (NAFLD) is not well understood. We evaluated the molecular mechanisms that may be involved in the regulation of liver mtDNA content in a high-fat-induced rat model of NAFLD. In particular, we tested the hypothesis that liver mtDNA copy number is associated with liver expression of HIF-1α. Rats were given either standard chow diet (SCD, n= 10) or high-fat diet (HFD, n= 15) for 20 weeks. Subsequently, mtDNA quantification using nuclear DNA (nDNA) as a reference was carried out using real time quantitative PCR. HFD induced a significant increase in liver mtDNA/nDNA ratio, which significantly correlated with the liver triglyceride content (R: 0.29, P < 0.05). The liver mtDNA/nDNA ratio significantly correlated with the hepatic expression of HIF-1α mRNA (R: 0.37, P < 0.001); liver HIF-1α mRNA was significantly higher in the HFD group. In addition, liver cytochrome c oxidase subunit IV isoform 1 (COX4I1) mRNA expression was also positively correlated with liver mtDNA content. The hepatic expression of mRNA of transcriptional factors that regulate mitochondrial biogenesis, including peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) and PGC-1β, nuclear respiratory factor-1 (NRF-1), peroxisome proliferator-activated receptor δ and Tfam, was not associated with the liver mtDNA content. Neither hepatocyte apoptosis nor oxidative stress was involved in the HIF-1α-mediated increase in mtDNA copy number. In conclusion, we found that HFD promotes an increase in liver mitochondrial biogenesis in response to hypoxia via HIF-1α, probably to enhance the mitochondrial function as well as to accommodate the metabolic load.

Preconditioning, organ preservation, and postconditioning to prevent ischemia-reperfusion injury to the liver

Ischemia and reperfusion lead to injury of the liver. Ischemia-reperfusion injury is inevitable in liver transplantation and trauma and, to a great extent, in liver resection. This article gives an overview of the mechanisms involved in this type of injury and summarizes protective and treatment strategies in clinical use today. Intervention is possible at different time points: during harvesting, during the period of preservation, and during implantation. Liver preconditioning and postconditioning can be applied in the transplant setting and for liver resection. Graft optimization is merely possible in the period between the harvest and the implantation. Given that there are 3 stages in which a surgeon can intervene against ischemia-reperfusion injury, we have structured the review as follows. The first section reviews the approaches using surgical interventions, such as ischemic preconditioning, as well as pharmacological applications. In the second section, static organ preservation and machine perfusion are addressed. Finally, the possibility of treating the recipient or postconditioning is discussed.

Leukocyte transmigration in inflamed liver: A role for endothelial cell-selective adhesion molecule

BACKGROUND/AIMS

This study was designed to investigate the role of endothelial cell-selective adhesion molecule (ESAM), a recently discovered receptor expressed in endothelial tight junctions and platelets, for leukocyte migration in inflamed liver.

METHODS

The role of ESAM for leukocyte migration in the liver was analyzed using ESAM-deficient mice in a model of warm hepatic ischemia-reperfusion (90min/30-360min).

RESULTS

As shown by immunostaining, ESAM is expressed in sinusoids as well as in venules and is not upregulated upon I/R. Emigrated leukocytes were quantified in tissue sections. Postischemic neutrophil transmigration was significantly attenuated in ESAM-/- mice after 2h of reperfusion, whereas it was completely restored after 6h. In contrast, T-cell migration did not differ between ESAM+/+ and ESAM-/- mice. Using intravital microscopy, we demonstrate that ESAM deficiency attenuates I/R-induced vascular leakage after 30min of reperfusion. The I/R-induced elevation in AST/ALT activity, the sinusoidal perfusion failure, and the number of TUNEL-positive hepatocytes were comparable between ESAM+/+ and ESAM-/- mice.

CONCLUSIONS

ESAM is expressed in the postischemic liver and mediates neutrophil but not T-cell transmigration during early reperfusion. ESAM deficiency attenuates I/R-induced vascular leakage and does not affect leukocyte adherence. Despite the effect on neutrophil migration, ESAM-deficiency does not protect from I/R-induced injury.

Portal triad clamping versus vascular exclusion for vascular control during hepatic resection: a systematic review and meta-analysis

OBJECTIVE

To compare the clinical outcome of patients undergoing liver resection under portal triad clamping (PTC) versus hepatic vascular exclusion (HVE).

METHODS

A systematic literature search was performed following the guidelines of the Cochrane collaboration. Randomized controlled trials (RCT) comparing PTC to any technique of HVE were eligible for inclusion. Two authors independently assessed methodological quality of included trials and extracted data on overall morbidity, mortality, cardiopulmonary and hepatic morbidity, intraoperative blood loss, transfusion rates, postoperative transaminase and bilirubin levels, prothrombin time, and hospital stay. Meta-analyses were performed using a random-effects model.

RESULTS

Of the 1,383 identified references, four RCTs were finally included. These trials compared PTC to selective hepatic vascular exclusion (SHVE), total hepatic vascular exclusion (THVE), and a modified technique of HVE (MTHVE), respectively. Meta-analyses revealed no significant difference in morbidity and mortality between PTC and techniques of HVE. Further analyses showed significantly reduced overall morbidity for the PTC compared to the THVE group. There was a significantly lower transfusion rate for HVE compared to PTC.

CONCLUSION

Hepatic vascular exclusion does not offer any benefit regarding outcome of patients undergoing hepatic resection compared to PTC alone. Further, well-designed RCTs evaluating adequate vascular control in major hepatectomy and in patients with underlying liver disease appear justified.