Liver sinusoidal endothelial cells: Physiology and role in liver diseases

Liver sinusoidal endothelial cells (LSECs) are highly specialized endothelial cells representing the interface between blood cells on the one side and hepatocytes and hepatic stellate cells on the other side. LSECs represent a permeable barrier. Indeed, the association of 'fenestrae', absence of diaphragm and lack of basement membrane make them the most permeable endothelial cells of the mammalian body. They also have the highest endocytosis capacity of human cells. In physiological conditions, LSECs regulate hepatic vascular tone contributing to the maintenance of a low portal pressure despite the major changes in hepatic blood flow occurring during digestion. LSECs maintain hepatic stellate cell quiescence, thus inhibiting intrahepatic vasoconstriction and fibrosis development. In pathological conditions, LSECs play a key role in the initiation and progression of chronic liver diseases. Indeed, they become capillarized and lose their protective properties, and they promote angiogenesis and vasoconstriction. LSECs are implicated in liver regeneration following acute liver injury or partial hepatectomy since they renew from LSECs and/or LSEC progenitors, they sense changes in shear stress resulting from surgery, and they interact with platelets and inflammatory cells. LSECs also play a role in hepatocellular carcinoma development and progression, in ageing, and in liver lesions related to inflammation and infection. This review also presents a detailed analysis of the technical aspects relevant for LSEC analysis including the markers these cells express, the available cell lines and the transgenic mouse models. Finally, this review provides an overview of the strategies available for a specific targeting of LSECs.

IL-6 pathway in the liver: From physiopathology to therapy

Interleukin 6 (IL-6) is a pleiotropic four-helix-bundle cytokine that exerts multiple functions in the body. In the liver, IL-6 is an important inducer of the acute phase response and infection defense. IL-6 is furthermore crucial for hepatocyte homeostasis and is a potent hepatocyte mitogen. It is not only implicated in liver regeneration, but also in metabolic function of the liver. However, persistent activation of the IL-6 signaling pathway is detrimental to the liver and might ultimately result in the development of liver tumors. On target cells IL-6 can bind to the signal transducing subunit gp130 either in complex with the membrane-bound or with the soluble IL-6 receptor to induce intracellular signaling. In this review we describe how these different pathways are involved in the physiology and pathophyiology of the liver. We furthermore discuss how IL-6 pathways can be selectively inhibited and therapeutically exploited for the treatment of liver pathologies.

Mechanisms of acetaminophen-induced liver injury and its implications for therapeutic interventions

Acetaminophen (APAP) overdose is the leading cause of drug-induced acute liver failure in many developed countries. Mitochondrial oxidative stress is considered to be the predominant cellular event in APAP-induced liver injury. Accordingly, N-acetyl cysteine, a known scavenger of reactive oxygen species (ROS), is recommended as an effective clinical antidote against APAP-induced acute liver injury (AILI) when it is given at an early phase; however, the narrow therapeutic window limits its use. Hence, the development of novel therapeutic approaches that can offer broadly protective effects against AILI is clearly needed. To this end, it is necessary to better understand the mechanisms of APAP hepatotoxicity. Up to now, in addition to mitochondrial oxidative stress, many other cellular processes, including phase I/phase II metabolism, endoplasmic reticulum stress, autophagy, sterile inflammation, microcirculatory dysfunction, and liver regeneration, have been identified to be involved in the pathogenesis of AILI, providing new targets for developing more effective therapeutic interventions against APAP-induced liver injury. In this review, we summarize intracellular and extracellular events involved in APAP hepatotoxicity, along with emphatic discussions on the possible therapeutic approaches targeting these different cellular events.

Cell therapy for liver disease: From liver transplantation to cell factory

Work over several decades has laid solid foundations for the advancement of liver cell therapy. To date liver cell therapy in people has taken the form of hepatocyte transplantation for metabolic disorders with a hepatic basis, and for acute or chronic liver failure. Although clinical trials using various types of autologous cells have been implemented to promote liver regeneration or reduce liver fibrosis, clear evidence of therapeutic benefits have so far been lacking. Cell types that have shown efficacy in preclinical models include hepatocytes, liver sinusoidal endothelial cells, mesenchymal stem cells, endothelial progenitor cells, and macrophages. However, positive results in animal models have not always translated through to successful clinical therapies and more realistic preclinical models need to be developed. Studies defining the optimal repopulation by transplanted cells, including routes of cell transplantation, superior engraftment and proliferation of transplanted cells, as well as optimal immunosuppression regimens are required. Tissue engineering approaches to transplant cells in extrahepatic locations have also been proposed. The derivation of hepatocytes from pluripotent or reprogrammed cells raises hope that donor organ and cell shortages could be overcome in the future. Critical hurdles to be overcome include the production of hepatocytes from pluripotent cells with equal functional capacity to primary hepatocytes and long-term phenotypic stability in vivo.

Bile Acid Metabolism and Signaling in Cholestasis, Inflammation, and Cancer

Bile acids are synthesized from cholesterol in the liver. Some cytochrome P450 (CYP) enzymes play key roles in bile acid synthesis. Bile acids are physiological detergent molecules, so are highly cytotoxic. They undergo enterohepatic circulation and play important roles in generating bile flow and facilitating biliary secretion of endogenous metabolites and xenobiotics and intestinal absorption of dietary fats and lipid-soluble vitamins. Bile acid synthesis, transport, and pool size are therefore tightly regulated under physiological conditions. In cholestasis, impaired bile flow leads to accumulation of bile acids in the liver, causing hepatocyte and biliary injury and inflammation. Chronic cholestasis is associated with fibrosis, cirrhosis, and eventually liver failure. Chronic cholestasis also increases the risk of developing hepatocellular or cholangiocellular carcinomas. Extensive research in the last two decades has shown that bile acids act as signaling molecules that regulate various cellular processes. The bile acid-activated nuclear receptors are ligand-activated transcriptional factors that play critical roles in the regulation of bile acid, drug, and xenobiotic metabolism. In cholestasis, these bile acid-activated receptors regulate a network of genes involved in bile acid synthesis, conjugation, transport, and metabolism to alleviate bile acid-induced inflammation and injury. Additionally, bile acids are known to regulate cell growth and proliferation, and altered bile acid levels in diseased conditions have been implicated in liver injury/regeneration and tumorigenesis. We will cover the mechanisms that regulate bile acid homeostasis and detoxification during cholestasis, and the roles of bile acids in the initiation and regulation of hepatic inflammation, regeneration, and carcinogenesis.

Emerging evidence on the role of the Hippo/YAP pathway in liver physiology and cancer

The Hippo pathway and its regulatory target, YAP, has recently emerged as an important biochemical signaling pathway that tightly governs epithelial tissue growth. Initially defined in Drosophilia, this pathway has shown remarkable conservation in vertebrate systems with many components of the Hippo/YAP pathway showing biochemical and functional conservation. The liver is particularly sensitive to changes in Hippo/YAP signaling with rapid increases in liver size becoming manifest on the order of days to weeks after perturbation. The first identified direct targets of Hippo/YAP signaling were pro-proliferative and anti-apoptotic gene programs, but recent work has now implicated this pathway in cell fate choice, stem cell maintenance/renewal, epithelial to mesenchymal transition, and oncogenesis. The mechanisms by which Hippo/YAP signaling is changed endogenously are beginning to come to light as well as how this pathway interacts with other signaling pathways, and important details for designing new therapeutic interventions. This review focuses on the known roles for Hippo/YAP signaling in the liver and promising avenues for future study.

Alternatively activated macrophages promote resolution of necrosis following acute liver injury

BACKGROUND & AIM

Following acetaminophen (APAP) overdose, acute liver injury (ALI) can occur in patients that present too late for N-acetylcysteine treatment, potentially leading to acute liver failure, systemic inflammation, and death. Macrophages influence the progression and resolution of ALI due to their innate immunological function and paracrine activity. Syngeneic primary bone marrow-derived macrophages (BMDMs) were tested as a cell-based therapy in a mouse model of APAP-induced ALI (APAP-ALI).

METHODS

Several phenotypically distinct BMDM populations were delivered intravenously to APAP-ALI mice when hepatic necrosis was established, and then evaluated based on their effects on injury, inflammation, immunity, and regeneration. In vivo phagocytosis assays were used to interrogate the phenotype and function of alternatively activated BMDMs (AAMs) post-injection. Finally, primary human AAMs sourced from healthy volunteers were evaluated in immunocompetent APAP-ALI mice.

RESULTS

BMDMs rapidly localised to the liver and spleen within 4 h of administration. Injection of AAMs specifically reduced hepatocellular necrosis, HMGB1 translocation, and infiltrating neutrophils following APAP-ALI. AAM delivery also stimulated proliferation in hepatocytes and endothelium, and reduced levels of several circulating proinflammatory cytokines within 24 h. AAMs displayed a high phagocytic activity both in vitro and in injured liver tissue post-injection. Crosstalk with the host innate immune system was demonstrated by reduced infiltrating host Ly6C^hi macrophages in AAM-treated mice. Importantly, therapeutic efficacy was partially recapitulated using clinical-grade primary human AAMs in immunocompetent APAP-ALI mice, underscoring the translational potential of these findings.

CONCLUSION

We identify that AAMs have value as a cell-based therapy in an experimental model of APAP-ALI. Human AAMs warrant further evaluation as a potential cell-based therapy for APAP overdose patients with established liver injury.

LAY SUMMARY

After an overdose of acetaminophen (paracetamol), some patients present to hospital too late for the current antidote (N-acetylcysteine) to be effective. We tested whether macrophages, an injury-responsive leukocyte that can scavenge dead/dying cells, could serve as a cell-based therapy in an experimental model of acetaminophen overdose. Injection of alternatively activated macrophages rapidly reduced liver injury and reduced several mediators of inflammation. Macrophages show promise to serve as a potential cell-based therapy for acute liver injury.

Liver regeneration requires Yap1-TGFβ-dependent epithelial-mesenchymal transition in hepatocytes

BACKGROUND & AIMS

Chronic failure of mechanisms that promote effective regeneration of dead hepatocytes causes replacement of functional hepatic parenchyma with fibrous scar tissue, ultimately resulting in cirrhosis. Therefore, defining and optimizing mechanisms that orchestrate effective regeneration might prevent cirrhosis. We hypothesized that effective regeneration of injured livers requires hepatocytes to evade the growth-inhibitory actions of TGFβ, since TGFβ signaling inhibits mature hepatocyte growth but drives cirrhosis pathogenesis.

METHODS

Wild-type mice underwent 70% partial hepatectomy (PH); TGFβ expression and signaling were evaluated in intact tissue and primary hepatocytes before, during, and after the period of maximal hepatocyte proliferation that occurs from 24-72 h after PH. To determine the role of Yap1 in regulating TGFβ signaling in hepatocytes, studies were repeated after selectively deleting Yap1 from hepatocytes of Yap1^flox/flox mice.

RESULTS

TGFβ expression and hepatocyte nuclear accumulation of pSmad2 and Yap1 increased in parallel with hepatocyte proliferative activity after PH. Proliferative hepatocytes also upregulated Snai1, a pSmad2 target gene that promotes epithelial-to-mesenchymal transition (EMT), suppressed epithelial genes, induced myofibroblast markers, and produced collagen 1α1. Deleting Yap1 from hepatocytes blocked their nuclear accumulation of pSmad2 and EMT-like response, as well as their proliferation.

CONCLUSION

Interactions between the TGFβ and Hippo-Yap signaling pathways stimulate hepatocytes to undergo an EMT-like response that is necessary for them to grow in a TGFβ-enriched microenvironment and regenerate injured livers.

LAY SUMMARY

The adult liver has an extraordinary ability to regenerate after injury despite the accumulation of scar-forming factors that normally block the proliferation and reduce the survival of residual liver cells. We discovered that liver cells manage to escape these growth-inhibitory influences by transiently becoming more like fibroblasts themselves. They do this by reactivating programs that are known to drive tissue growth during fetal development and in many cancers. Understanding how the liver can control programs that are involved in scarring and cancer may help in the development of new treatments for cirrhosis and liver cancer.

Cannabinoid signaling and liver therapeutics

Over the last decade, the endocannabinoid system has emerged as a pivotal mediator of acute and chronic liver injury, with the description of the role of CB1 and CB2 receptors and their endogenous lipidic ligands in various aspects of liver pathophysiology. A large number of studies have demonstrated that CB1 receptor antagonists represent an important therapeutic target, owing to beneficial effects on lipid metabolism and in light of its antifibrogenic properties. Unfortunately, the brain-penetrant CB1 antagonist rimonabant, initially approved for the management of overweight and related cardiometabolic risks, was withdrawn because of an alarming rate of mood adverse effects. However, the efficacy of peripherally-restricted CB1 antagonists with limited brain penetrance has now been validated in preclinical models of NAFLD, and beneficial effects on fibrosis and its complications are anticipated. CB2 receptor is currently considered as a promising anti-inflammatory and antifibrogenic target, although clinical development of CB2 agonists is still awaited. In this review, we highlight the latest advances on the impact of the endocannabinoid system on the key steps of chronic liver disease progression and discuss the therapeutic potential of molecules targeting cannabinoid receptors.

Dietary fructose as a risk factor for non-alcoholic fatty liver disease (NAFLD)

Glucose is a major energy source for the entire body, while fructose metabolism occurs mainly in the liver. Fructose consumption has increased over the last decade globally and is suspected to contribute to the increased incidence of non-alcoholic fatty liver disease (NAFLD). NAFLD is a manifestation of metabolic syndrome affecting about one-third of the population worldwide and has progressive pathological potential for liver cirrhosis and cancer through non-alcoholic steatohepatitis (NASH). Here we have reviewed the possible contribution of fructose to the pathophysiology of NAFLD. We critically summarize the current findings about several regulators, and their potential mechanisms, that have been studied in humans and animal models in response to fructose exposure. A novel hypothesis on fructose-dependent perturbation of liver regeneration and metabolism is advanced. Fructose intake could affect inflammatory and metabolic processes, liver function, gut microbiota, and portal endotoxin influx. The role of the brain in controlling fructose ingestion and the subsequent development of NAFLD is highlighted. Although the importance for fructose (over)consumption for NAFLD in humans is still debated and comprehensive intervention studies are invited, understanding of how fructose intake can favor these pathological processes is crucial for the development of appropriate noninvasive diagnostic and therapeutic approaches to detect and treat these metabolic effects. Still, lifestyle modification, to lessen the consumption of fructose-containing products, and physical exercise are major measures against NAFLD. Finally, promising drugs against fructose-induced insulin resistance and hepatic dysfunction that are emerging from studies in rodents are reviewed, but need further validation in human patients.

Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS): impact of the inter-stages course on morbi-mortality and implications for management

BACKGROUND

Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) was recently developed to induce rapid hypertrophy and reduce post-hepatectomy liver failure in patients with insufficient remnant liver volume (RLV). However, mortality rates >12% have been reported. This study aimed to analyze the perioperative course of ALPPS and to identify factors associated with morbi-mortality.

METHODS

Between April 2011 and September 2013, 62 patients operated in 9 Franco-Belgian hepatobiliary centres underwent ALPPS for colorectal metastases (N = 50) or primary tumors, following chemotherapy (N = 50) and/or portal vein embolization (PVE; N = 9).

RESULTS

Most patients had right (N = 31) or right extended hepatectomy (N = 25) (median RLV/body weight ratio of 0.54% [0.21-0.77%]). RLV increased by 48.6% [-15.3 to 192%] 7.8 ± 4.5 days after stage1, but the hypertrophy decelerated beyond 7 days. Stage2 was cancelled in 3 patients (4.8%) for insufficient hypertrophy, portal vein thrombosis or death and delayed to ≥9 days in 32 (54.2%). Overall, 25 patients (40.3%) had major complication(s) and 8 (12.9%) died. Fourteen patients (22.6%) had post-stage1 complication of whom 5 (35.7%) died after stage2. Factors associated with major morbi-mortality were obesity, post-stage1 biliary fistula or ascites, and infected and/or bilious peritoneal fluid at stage2. The latter was the only predictor of Clavien ≥3 by multivariate analysis (OR: 4.9; 95% CI: 1.227-19.97; p = 0.025). PVE did not impact the morbi-mortality rates but prevented major cytolysis that was associated with poor outcome.

CONCLUSIONS

The inter-stages course was crucial in determining ALPPS outcome. The factors of high morbi-mortality rates associated with ALPPS are linked to the technique complexity.

The spleen in liver cirrhosis: revisiting an old enemy with novel targets

The spleen is a secondary lymphoid organ which can influence the progression of multiple diseases, notably liver cirrhosis. In chronic liver diseases, splenomegaly and hypersplenism can manifest following the development of portal hypertension. These splenic abnormalities correlate with and have been postulated to facilitate the progression of liver fibrosis to cirrhosis, although precise mechanisms remain poorly understood. In this review, we summarize the literature to highlight the mechanistic contributions of splenomegaly and hypersplenism to the development of liver cirrhosis, focusing on three key aspects: hepatic fibrogenesis, hepatic immune microenvironment dysregulation and liver regeneration. We conclude with a discussion of the possible therapeutic strategies for modulating splenic abnormalities, including the novel potential usage of nanomedicine in non-surgically targetting splenic disorders for the treatment of liver cirrhosis.

Hepato-protective effect of resveratrol against acetaminophen-induced liver injury is associated with inhibition of CYP-mediated bioactivation and regulation of SIRT1-p53 signaling pathways

Resveratrol (RES) has been shown to possess many pharmacological activities including protective effect against liver damage induced by hepatotoxins. In the present study, the hepato-protective effect of RES against acetaminophen (APAP)-induced liver injury in mice and the involved mechanisms was investigated. This study clearly demonstrated that administration of RES three days before APAP treatment significantly alleviated APAP-induced hepatotoxicity, as evidenced by morphological, histopathological, and biochemical assessments such as GSH content and serum ALT/AST activity. Treatment with RES resulted in significant inhibition of CYP2E1, CYP3A11, and CYP1A2 activities, and then caused significant inhibition of the bioactivation of APAP into toxic metabolite NAPQI. Pretreatment with RES significantly reduced APAP-induced JNK activation to protect against mitochondrial injury. Additionally, RES treatment significantly induced SIRT1 and then negatively regulated p53 signaling to induce cell proliferation-associated proteins including cyclin D1, CDK4, and PCNA to promote hepatocyte proliferation. This study demonstrated that RES prevents APAP-induced hepatotoxicity by inhibition of CYP-mediated APAP bioactivation and regulation of SIRT1, p53, cyclin D1 and PCNA to facilitate liver regeneration following APAP-induced liver injury.

Endothelial GATA4 controls liver fibrosis and regeneration by preventing a pathogenic switch in angiocrine signaling

BACKGROUND & AIMS

Angiocrine signaling by liver sinusoidal endothelial cells (LSECs) regulates hepatic functions such as growth, metabolic maturation, and regeneration. Recently, we identified GATA4 as the master regulator of LSEC specification during development. Herein, we studied the role of endothelial GATA4 in the adult liver and in hepatic pathogenesis.

METHODS

We generated adult Clec4g-icre^tg/0xGata4^fl/fl (Gata4^LSEC-KO) mice with LSEC-specific depletion of Gata4. Livers were analyzed by histology, electron microscopy, immunohistochemistry/immunofluorescence, in situ hybridization, and LSECs were isolated for gene expression profiling, ChIP- and ATAC-sequencing. Partial hepatectomy was performed to assess regeneration. We used choline-deficient, l-amino acid-defined (CDAA) diet and chronic carbon tetrachloride exposure to model liver fibrosis. Human single cell RNA-seq data sets were analyzed for endothelial alterations in healthy and cirrhotic livers.

RESULTS

Genetic Gata4 deficiency in LSECs of adult mice caused perisinusoidal liver fibrosis, hepatopathy and impaired liver regeneration. Sinusoidal capillarization and LSEC-to-continuous endothelial transdifferentiation were accompanied by a profibrotic angiocrine switch involving de novo endothelial expression of hepatic stellate cell-activating cytokine PDGFB. Increased chromatin accessibility and amplification by activated MYC mediated angiocrine Pdgfb expression. As observed in Gata4^LSEC-KO livers, CDAA diet-induced perisinusoidal liver fibrosis was associated with GATA4 repression, MYC activation and a profibrotic angiocrine switch in LSECs. Comparison of CDAA-fed Gata4^LSEC-KO and control mice demonstrated that endothelial GATA4 indeed protects against dietary-induced perisinusoidal liver fibrosis. In human cirrhotic livers, GATA4-positive LSECs and endothelial GATA4 target genes were reduced, while non-LSEC endothelial cells and MYC target genes including PDGFB were enriched.

CONCLUSIONS

Endothelial GATA4 protects against perisinusoidal liver fibrosis by repressing MYC activation and profibrotic angiocrine signaling at the chromatin level. Therapies targeting the GATA4/MYC/PDGFB/PDGFRβ axis offer a promising strategy for prevention and treatment of liver fibrosis.

LAY SUMMARY

The liver vasculature is supposed to play a major role in the development of liver fibrosis and cirrhosis, which can lead to liver failure and liver cancer. Herein, we discovered that structural and transcriptional changes induced by genetic deletion of the transcription factor GATA4 in the hepatic endothelium were sufficient to cause liver fibrosis. Activation of the transcription factor MYC and de novo expression of the "angiocrine" growth factor PDGFB were identified as downstream drivers of fibrosis and as potential therapeutic targets for this potentially fatal disease.

Concise Review: Liver Regenerative Medicine: From Hepatocyte Transplantation to Bioartificial Livers and Bioengineered Grafts

Donor organ shortage is the main limitation to liver transplantation as a treatment for end-stage liver disease and acute liver failure. Liver regenerative medicine may in the future offer an alternative form of therapy for these diseases, be it through cell transplantation, bioartificial liver (BAL) devices, or bioengineered whole organ liver transplantation. All three strategies have shown promising results in the past decade. However, before they are incorporated into widespread clinical practice, the ideal cell type for each treatment modality must be found, and an adequate amount of metabolically active, functional cells must be able to be produced. Research is ongoing in hepatocyte expansion techniques, use of xenogeneic cells, and differentiation of stem cell-derived hepatocyte-like cells (HLCs). HLCs are a few steps away from clinical application, but may be very useful in individualized drug development and toxicity testing, as well as disease modeling. Finally, safety concerns including tumorigenicity and xenozoonosis must also be addressed before cell transplantation, BAL devices, and bioengineered livers occupy their clinical niche. This review aims to highlight the most recent advances and provide an updated view of the current state of affairs in the field of liver regenerative medicine. Stem Cells 2017;35:42-50.

Liver resection for cancer: New developments in prediction, prevention and management of postresectional liver failure

Hepatic failure is a feared complication that accounts for up to 75% of mortality after extensive liver resection. Despite improved perioperative care, the increasing complexity and extensiveness of surgical interventions, in combination with an expanding number of resections in patients with compromised liver function, still results in an incidence of postresectional liver failure (PLF) of 1-9%. Preventive measures aim to enhance future remnant liver size and function. Numerous non-invasive techniques to assess liver function and predict remnant liver volume are being developed, along with introduction of novel surgical strategies that augment growth of the future remnant liver. Detection of PLF is often too late and treatment is primarily symptomatic. Current therapeutic research focuses on ([bio]artificial) liver function support and regenerative medicine. In this review we discuss the current state and new developments in prediction, prevention and management of PLF, in light of novel insights into the aetiology of this complex syndrome.

LAY SUMMARY

Liver failure is the main cause of death after partial liver resection for cancer, and is presumably caused by an insufficient quantity and function of the liver remnant. Detection of liver failure is often too late, and current treatment focuses on relieve of symptoms. New research initiatives explore artificial support of liver function and stimulation of regrowth of the remnant liver.

Model-guided identification of a therapeutic strategy to reduce hyperammonemia in liver diseases

BACKGROUND & AIMS

Recently, spatial-temporal/metabolic mathematical models have been established that allow the simulation of metabolic processes in tissues. We applied these models to decipher ammonia detoxification mechanisms in the liver.

METHODS

An integrated metabolic-spatial-temporal model was used to generate hypotheses of ammonia metabolism. Predicted mechanisms were validated using time-resolved analyses of nitrogen metabolism, activity analyses, immunostaining and gene expression after induction of liver damage in mice. Moreover, blood from the portal vein, liver vein and mixed venous blood was analyzed in a time dependent manner.

RESULTS

Modeling revealed an underestimation of ammonia consumption after liver damage when only the currently established mechanisms of ammonia detoxification were simulated. By iterative cycles of modeling and experiments, the reductive amidation of alpha-ketoglutarate (α-KG) via glutamate dehydrogenase (GDH) was identified as the lacking component. GDH is released from damaged hepatocytes into the blood where it consumes ammonia to generate glutamate, thereby providing systemic protection against hyperammonemia. This mechanism was exploited therapeutically in a mouse model of hyperammonemia by injecting GDH together with optimized doses of cofactors. Intravenous injection of GDH (720 U/kg), α-KG (280 mg/kg) and NADPH (180 mg/kg) reduced the elevated blood ammonia concentrations (>200 μM) to levels close to normal within only 15 min.

CONCLUSION

If successfully translated to patients the GDH-based therapy might provide a less aggressive therapeutic alternative for patients with severe hyperammonemia.

Salvage parenchymal liver transection for patients with insufficient volume increase after portal vein occlusion -- an extension of the ALPPS approach

BACKGROUND

Portal vein ligation (PVL) or embolization (PVE) are standard approaches to induce liver hypertrophy of the future liver remnant (FLR) prior to hepatectomy in primarily non-resectable liver tumors. However, this approach fails in about one third of patients. Recently, the new "ALPPS" approach has been described that combines PVL with parenchymal transection to induce rapid liver hypertrophy. This series explores whether isolated parenchymal transection boosts liver hypertrophy in scenarios of failed PVL/PVE.

METHODS

A multicenter database with 170 patients undergoing portal vein manipulation to increase the size of the FLR was screened for patients undergoing isolated parenchymal transection as a salvage procedure. Three patients who underwent PVL/PVE with subsequent insufficient volume gain and subsequently underwent parenchymal liver transection as a salvage procedure were identified. Patient characteristics, volume increase, postoperative complications and outcomes were analyzed.

RESULTS

The first patient underwent liver transection 16 weeks after failed PVL with a standardized FLR (sFLR) of 30%, which increased to 47% in 7 days. The second patient showed a sFLR of 25% 28 weeks after PVL and subsequent PVE of segment IV, which increased to 41% in 7 days after transection. The third patient underwent liver partition 8 weeks after PVE with a sFLR of 19%, which increased to 37% in six days. All patients underwent a R0 resection.

CONCLUSION

Failed PVE or PVL appears to represent a good indication for the isolated parenchymal liver transection according to the newly developed ALPPS approach.

Crosstalk between Nrf2 and Notch signaling

The transcription factor Nrf2 (nuclear factor, erythroid derived 2, like 2) belongs to the CNC-bZip protein family, forming a transcriptosome with its direct heterodimer partner, sMaf, and co-factors such as CBP/p300. Nrf2 binds to one or more AREs (antioxidant response elements) that are located in the gene regulatory regions of the hundreds of Nrf2 target genes. The AREs are key enhancers that are activated in response to endogenous or exogenous stresses to maintain cellular and tissue homeostasis. Data emanating from gene expression microarray analyses comparing Nrf2-disrupted and wild-type mouse embryonic fibroblasts (MEF) showed that expression of Notch1 and Notch-signaling-related genes were decreased in Nrf2-disrupted cells. This observation triggered our research on Nrf2-Notch crosstalk. A functional ARE has been identified upstream of the Notch1 major transcription start site. Furthermore, an Rbpjκ binding site is conserved on the promoters of Nrf2 among animal species. Notch1 is one of the transmembrane Notch family receptors that drive Notch signaling, together with the Rbpjκ transcription factor. After canonically accepting ligands such as Jags and Deltas, the receptor undergoes cleavage to yield the Notch intracellular domain, which translocates to the nucleus. Recent studies using conditional knockout mice indicate that Notch1 as well as Notch2 plays an important role postnatally in liver development and in maintenance of hepatic function. In this review, we summarize current understanding of the role of reciprocal transcriptional regulation between Nrf2 and Notch in adult liver from studies using Nrf2, Keap1, and Notch1 genetically engineered mice.

How important is donor age in liver transplantation?

The age of liver donors has been increasing in the past several years because of a donor shortage. In the United States, 33% of donors are age 50 years or older, as are more than 50% in some European countries. The impact of donor age on liver transplantation (LT) has been analyzed in several studies with contradictory conclusions. Nevertheless, recent analyses of the largest databases demonstrate that having an older donor is a risk factor for graft failure. Donor age is included as a risk factor in the more relevant graft survival scores, such as the Donor Risk Index, donor age and Model for End-stage Liver Disease, Survival Outcomes Following Liver Transplantation, and the Balance of Risk. The use of old donors is related to an increased rate of biliary complications and hepatitis C virus-related graft failure. Although liver function does not seem to be significantly affected by age, the incidence of several liver diseases increases with age, and the capacity of the liver to manage or overcome liver diseases or external injuries decreases. In this paper, the importance of age in LT outcomes, the role of donor age as a risk factor, and the influence of aging on liver regeneration are reviewed.

Liver cell transplantation for Crigler-Najjar syndrome type I: Update and perspectives

Liver cell transplantation is an attractive technique to treat liver-based inborn errors of metabolism. The feasibility and efficacy of the procedure has been demonstrated, leading to medium term partial metabolic control of various diseases. Crigler-Najjar is the paradigm of such diseases in that the host liver is lacking one function with an otherwise normal parenchyma. The patient is at permanent risk for irreversible brain damage. The goal of liver cell transplantation is to reduce serum bilirubin levels within safe limits and to alleviate phototherapy requirements to improve quality of life. Preliminary data on Gunn rats, the rodent model of the disease, were encouraging and have led to successful clinical trials. Herein we report on two additional patients and describe the current limits of the technique in terms of durability of the response as compared to alternative therapeutic procedures. We discuss the future developments of the technique and new emerging perspectives.

Platelets in liver disease, cancer and regeneration

Although viral hepatitis treatments have evolved over the years, the resultant liver cirrhosis still does not completely heal. Platelets contain proteins required for hemostasis, as well as many growth factors required for organ development, tissue regeneration and repair. Thrombocytopenia, which is frequently observed in patients with chronic liver disease (CLD) and cirrhosis, can manifest from decreased thrombopoietin production and accelerated platelet destruction caused by hypersplenism; however, the relationship between thrombocytopenia and hepatic pathogenesis, as well as the role of platelets in CLD, is poorly understood. In this paper, experimental evidence of platelets improving liver fibrosis and accelerating liver regeneration is summarized and addressed based on studies conducted in our laboratory and current progress reports from other investigators. In addition, we describe our current perspective based on the results of these studies. Platelets improve liver fibrosis by inactivating hepatic stellate cells, which decreases collagen production. The regenerative effect of platelets in the liver involves a direct effect on hepatocytes, a cooperative effect with liver sinusoidal endothelial cells, and a collaborative effect with Kupffer cells. Based on these observations, we ascertained the direct effect of platelet transfusion on improving several indicators of liver function in patients with CLD and liver cirrhosis. However, unlike the results of our previous clinical study, the smaller incremental changes in liver function in patients with CLD who received eltrombopag for 6 mo were due to patient selection from a heterogeneous population. We highlight the current knowledge concerning the role of platelets in CLD and cancer and anticipate a novel application of platelet-based clinical therapies to treat liver disease.

Highly efficient differentiation of functional hepatocytes from human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) hold great potential for use in regenerative medicine, novel drug development, and disease progression/developmental studies. Here, we report highly efficient differentiation of hiPSCs toward a relatively homogeneous population of functional hepatocytes. hiPSC-derived hepatocytes (hiHs) not only showed a high expression of hepatocyte-specific proteins and liver-specific functions, but they also developed a functional biotransformation system including phase I and II metabolizing enzymes and phase III transporters. Nuclear receptors, which are critical for regulating the expression of metabolizing enzymes, were also expressed in hiHs. hiHs also responded to different compounds/inducers of cytochrome P450 as mature hepatocytes do. To follow up on this observation, we analyzed the drug metabolizing capacity of hiHs in real time using a novel ultra performance liquid chromatography-tandem mass spectrometry. We found that, like freshly isolated primary human hepatocytes, the seven major metabolic pathways of the drug bufuralol were found in hiHs. In addition, transplanted hiHs engrafted, integrated, and proliferated in livers of an immune-deficient mouse model, and secreted human albumin, indicating that hiHs also function in vivo. In conclusion, we have generated a method for the efficient generation of hepatocytes from induced pluripotent stem cells in vitro and in vivo, and it appears that the cells function similarly to primary human hepatocytes, including developing a complete metabolic function. These results represent a significant step toward using patient/disease-specific hepatocytes for cell-based therapeutics as well as for pharmacology and toxicology studies.

The NADPH oxidase NOX4 inhibits hepatocyte proliferation and liver cancer progression

The NADPH oxidase NOX4 has emerged as an important source of reactive oxygen species in signal transduction, playing roles in physiological and pathological processes. NOX4 mediates transforming growth factor-β-induced intracellular signals that provoke liver fibrosis, and preclinical assays have suggested NOX4 inhibitors as useful tools to ameliorate this process. However, the potential consequences of sustained treatment of liver cells with NOX4 inhibitors are yet unknown. The aim of this work was to analyze whether NOX4 plays a role in regulating liver cell growth either under physiological conditions or during tumorigenesis. In vitro assays proved that stable knockdown of NOX4 expression in human liver tumor cells increased cell proliferation, which correlated with a higher percentage of cells in S/G2/M phases of the cell cycle, downregulation of p21(CIP1/WAF1), increase in cyclin D1 protein levels, and nuclear localization of β-catenin. Silencing of NOX4 in untransformed human and mouse hepatocytes also increased their in vitro proliferative capacity. In vivo analysis in mice revealed that NOX4 expression was downregulated under physiological proliferative situations of the liver, such as regeneration after partial hepatectomy, as well as during pathological proliferative conditions, such as diethylnitrosamine-induced hepatocarcinogenesis. Xenograft experiments in athymic mice indicated that NOX4 silencing conferred an advantage to human hepatocarcinoma cells, resulting in earlier onset of tumor formation and increase in tumor size. Interestingly, immunochemical analyses of NOX4 expression in human liver tumor cell lines and tissues revealed decreased NOX4 protein levels in liver tumorigenesis. Overall, results described here strongly suggest that NOX4 would play a growth-inhibitory role in liver cells.

Hepatoprotective effects of baicalein against CCl4-induced acute liver injury in mice

AIM: To investigate the hepatoprotective effect of baicalein against carbon tetrachloride (CCl₄)-induced liver damage in mice.

METHODS: Mice were orally administered with baicalein after CCl₄ injection, and therapeutic baicalein was given twice a day for 4 d. The anti-inflammation effects of baicalein were assessed directly by hepatic histology and serum alanine aminotranferease and aspartate aminotransferase measurement. Proliferating cell nuclear antigen was used to evaluate the effect of baicalein in promoting hepatocyte proliferation. Serum interleukin (IL)-6, IL-1β and tumor necrosis factor-α (TNF-α) levels were measured by enzyme-linked immunosorbent assay and liver IL-6, TNF-α, transforming growth factor-α (TGF-α), hepatocyte growth factor (HGF) and epidermal growth factor (EGF) genes expression were determined by quantitative real-time polymerase chain reaction.

RESULTS: CCl₄-induced acute liver failure model offers a survival benefit in baicalein-treated mice. The data indicated that the mRNA levels of IL-6 and TNF-α significantly increased within 12 h after CCl₄ treatment in baicalein administration groups, but at 24, 48 and 72 h, the expression of IL-6 and TNF-α was kept at lower levels compared with the control. The expression of TGF-α, HGF and EGF was enhanced dramatically in baicalein administration group at 12, 24, 48 and 72 h. Furthermore, we found that baicalein significantly elevated the serum level of TNF-α and IL-6 at the early phase, which indicated that baicalein could facilitate the initiating events in liver regeneration.

CONCLUSION: Baicalein may be a therapeutic candidate for acute liver injury. Baicalein accelerates liver regeneration by regulating TNF-α and IL-6 mediated pathways.