TRAIL enhances paracetamol-induced liver sinusoidal endothelial cell death in a Bim- and Bid-dependent manner

Innate immune regulation in inflammation resolution and liver regeneration in drug-induced liver injury

Drug-induced liver injury (DILI) is an acute liver injury that poses a significant threat to human health. In severe cases, it can progress into chronic DILI or even lead to liver failure. DILI is typically caused by either intrinsic hepatotoxicity or idiosyncratic metabolic or immune responses. In addition to the direct damage drugs inflict on hepatocytes, the immune responses and liver inflammation triggered by hepatocyte death can further exacerbate DILI. Initially, we briefly discussed the differences in immune cell activation based on the type of liver cell death (hepatocytes, cholangiocytes, and LSECs). We then focused on the role of various immune cells (including macrophages, monocytes, neutrophils, dendritic cells, liver sinusoidal endothelial cells, eosinophils, natural killer cells, and natural killer T cells) in both the liver injury and liver regeneration stages of DILI. This article primarily reviews the role of innate immune regulation mediated by these immune cells in resolving inflammation and promoting liver regeneration during DILI, as well as therapeutic approaches targeting these immune cells for the treatment of DILI. Finally, we discussed the activation and function of liver progenitor cells (LPCs) during APAP-induced massive hepatic necrosis and the involvement of chronic inflammation in DILI.

Drug-induced oxidative stress actively prevents caspase activation and hepatocyte apoptosis

Cell death is a fundamental process in health and disease. Emerging research shows the existence of numerous distinct cell death modalities with similar and intertwined signaling pathways, but resulting in different cellular outcomes, raising the need to understand the decision-making steps during cell death signaling. Paracetamol (Acetaminophen, APAP)-induced hepatocyte death includes several apoptotic processes but eventually is executed by oncotic necrosis without any caspase activation. Here, we studied this paradoxical form of cell death and revealed that APAP not only fails to activate caspases but also strongly impedes their activation upon classical apoptosis induction, thereby shifting apoptosis to necrosis. While APAP intoxication results in massive drop in mitochondrial respiration, low cellular ATP levels could be excluded as an underlying cause of missing apoptosome formation and caspase activation. In contrast, we identified oxidative stress as a key factor in APAP-induced caspase inhibition. Importantly, caspase inhibition and the associated switch from apoptotic to necrotic cell death was reversible through the administration of antioxidants. Thus, exemplified by APAP-induced cell death, our study stresses that cellular redox status is a critical component in the decision-making between apoptotic and necrotic cell death, as it directly affects caspase activity.

Insights gained into the injury mechanism of drug and herb induced liver injury in the hepatic microenvironment

Drug-Induced Liver Injury (DILI) and herb Induced Liver Injury (HILI) continues to pose a substantial challenge in both clinical practice and drug development, representing a grave threat to patient well-being. This comprehensive review introduces a novel perspective on DILI and HILI by thoroughly exploring the intricate microenvironment of the liver. The dynamic interplay among hepatocytes, sinusoidal endothelial cells, Kupffer cells, hepatic stellate cells, cholangiocytes, and the intricate vascular network assumes a central role in drug metabolism and detoxification. Significantly, this microenvironment is emerging as a critical determinant of susceptibility to DILI and HILI. The review delves into the multifaceted interactions within the liver microenvironment, providing valuable insights into the complex mechanisms that underlie DILI and HILI. Furthermore, we discuss potential strategies for mitigating drug-induced liver injury by targeting these influential factors, emphasizing their clinical relevance. By highlighting recent advances and future prospects, our aim is to shed light on the promising avenue of leveraging the liver microenvironment for the prevention and mitigation of DILI and HILI. This deeper understanding is crucial for advancing clinical practices and ensuring patient safety in the realm of DILI and HILI.

Inhibition of 15-prostaglandin dehydrogenase attenuates acetaminophen-induced liver injury via suppression of apoptosis in liver endothelial cells

Hepatic microvascular disruption caused by injury to liver sinusoidal endothelial cells (LSECs) is an aggravating factor for drug-induced liver injury (DILI). It is suggested that prostaglandin E2 (PGE2) may be able to attenuate LSEC injury. However, it is also known that 15-keto PGE2, a metabolite of PGE2 produced by 15-prostaglandin dehydrogenase (15-PGDH) that is not a ligand of PGE2 receptors, suppresses inflammatory acute liver injury as a ligand of peroxisome proliferator-activated receptor γ. In this study, we aimed to understand whether 15-PGDH activity is essential for preventing DILI by suppressing hepatic microvascular disruption in a mouse model of acetaminophen (APAP)-induced liver injury. To inhibit 15-PGDH activity prior to APAP-induced LSEC injury, we administered the 15-PGDH inhibitor, SW033291, 1 h before and 3 h after APAP treatment. We observed that LSEC injury preceded hepatocellular injury in APAP administered mice. Hepatic endogenous PGE2 levels did not increase up till the initiation of LSEC injury but rather increased after hepatocellular injury. Moreover, hepatic 15-PGDH activity was downregulated in APAP-induced liver injury. The inhibition of 15-PGDH attenuated LSEC injury and subsequently hepatic injury by inhibiting apoptosis in APAP administered mice. Our in vitro studies also suggested that PGE2 inhibited APAP-induced apoptosis via the EP4/PI3K pathway in endothelial cells. Therefore, a decrease in 15-PGDH activity would be beneficial for preventing APAP-induced liver injury by attenuating LSEC injury.

Non-canonical BIM-regulated energy metabolism determines drug-induced liver necrosis

Paracetamol (acetaminophen, APAP) overdose severely damages mitochondria and triggers several apoptotic processes in hepatocytes, but the final outcome is fulminant necrotic cell death, resulting in acute liver failure and mortality. Here, we studied this switch of cell death modes and demonstrate a non-canonical role of the apoptosis-regulating BCL-2 homolog BIM/Bcl2l11 in promoting necrosis by regulating cellular bioenergetics. BIM deficiency enhanced total ATP production and shifted the bioenergetic profile towards glycolysis, resulting in persistent protection from APAP-induced liver injury. Modulation of glucose levels and deletion of Mitofusins confirmed that severe APAP toxicity occurs only in cells dependent on oxidative phosphorylation. Glycolytic hepatocytes maintained elevated ATP levels and reduced ROS, which enabled lysosomal recycling of damaged mitochondria by mitophagy. The present study highlights how metabolism and bioenergetics affect drug-induced liver toxicity, and identifies BIM as important regulator of glycolysis, mitochondrial respiration, and oxidative stress signaling.

Coculture model of a liver sinusoidal endothelial cell barrier and HepG2/C3a spheroids-on-chip in an advanced fluidic platform

The liver is one of the main organs involved in the metabolism of xenobiotics and a key organ in toxicity studies. Prior to accessing the hepatocytes, xenobiotics pass through the hepatic sinusoid formed by liver sinusoidal endothelial cells (LSECs). The LSECs barrier regulates the kinetics and concentrations of the xenobiotics before their metabolic processing by the hepatocytes. To mimic this physiological situation, we developed an in vitro model reproducing an LSECs barrier in coculture with a hepatocyte biochip, using a fluidic platform. This technology made dynamic coculture and tissue crosstalk possible. SK-HEP-1 and HepG2/C3a cells were used as LSECs and as hepatocyte models, respectively. We confirmed the LSECs phenotype by measuring PECAM-1 and stabilin-2 expression levels and the barrier's permeability/transport properties with various molecules. The tightness of the SK-HEP-1 barrier was enhanced in the dynamic coculture. The morphology, albumin secretion, and gene expression levels of markers of HepG2/C3a were not modified by coculture with the LSECs barrier. Using acetaminophen, a well-known hepatotoxic drug, to study tissue crosstalk, there was a reduction in the expression levels of the LSECs markers stabilin-2 and PECAM-1, and a modification of those of CLEC4M and KDR. No HepG2/C3a toxicity was observed. The metabolisation of acetaminophen by HepG2/C3a monocultures and cocultures was confirmed. Although primary cells are required to propose a fully relevant model, the present approach highlights the potential of our system for investigating xenobiotic metabolism and toxicity.

Efferocytosis in liver disease

The process of dead cell clearance by phagocytic cells, called efferocytosis, prevents inflammatory cell necrosis and promotes resolution and repair. Defective efferocytosis contributes to the progression of numerous diseases in which cell death is prominent, including liver disease. Many gaps remain in our understanding of how hepatic macrophages carry out efferocytosis and how this process goes awry in various types of liver diseases. Thus far, studies have suggested that, upon liver injury, liver-resident Kupffer cells and infiltrating monocyte-derived macrophages clear dead cells, limit inflammation, and, through macrophage reprogramming, repair liver damage. However, in unusual settings, efferocytosis can promote liver disease. In this review, we will focus on efferocytosis in various types of acute and chronic liver diseases, including metabolic dysfunction-associated steatohepatitis. Understanding the mechanisms and consequences of efferocytosis by hepatic macrophages has the potential to shed new light on liver disease pathophysiology and to guide new treatment strategies to prevent disease progression.

The evolving role of liver sinusoidal endothelial cells in liver health and disease

LSECs are a unique population of endothelial cells within the liver and are recognized as key regulators of liver homeostasis. LSECs also play a key role in liver disease, as dysregulation of their quiescent phenotype promotes pathological processes within the liver including inflammation, microvascular thrombosis, fibrosis, and portal hypertension. Recent technical advances in single-cell analysis have characterized distinct subpopulations of the LSECs themselves with a high resolution and defined their gene expression profile and phenotype, broadening our understanding of their mechanistic role in liver biology. This article will review 4 broad advances in our understanding of LSEC biology in general: (1) LSEC heterogeneity, (2) LSEC aging and senescence, (3) LSEC role in liver regeneration, and (4) LSEC role in liver inflammation and will then review the role of LSECs in various liver pathologies including fibrosis, DILI, alcohol-associated liver disease, NASH, viral hepatitis, liver transplant rejection, and ischemia reperfusion injury. The review will conclude with a discussion of gaps in knowledge and areas for future research.

Angiocrine Signaling in Sinusoidal Health and Disease

Liver sinusoidal endothelial cells (LSECs) are key players in maintaining hepatic homeostasis. They also play crucial roles during liver injury by communicating with liver cell types as well as immune cells and promoting portal hypertension, fibrosis, and inflammation. Cutting-edge technology, such as single cell and spatial transcriptomics, have revealed the existence of distinct LSEC subpopulations with a clear zonation in the liver. The signals released by LSECs are commonly called "angiocrine signaling." In this review, we summarize the role of angiocrine signaling in health and disease, including zonation in healthy liver, regeneration, fibrosis, portal hypertension, nonalcoholic fatty liver disease, alcohol-associated liver disease, aging, drug-induced liver injury, and ischemia/reperfusion, as well as potential therapeutic advances. In conclusion, sinusoidal endotheliopathy is recognized in liver disease and promising preclinical studies are paving the path toward LSEC-specific pharmacotherapies.

Investigation of the metabolomic crosstalk between liver sinusoidal endothelial cells and hepatocytes exposed to paracetamol using organ-on-chip technology

Organ-on-chip technology is a promising in vitro approach recapitulating human physiology for the study of responses to drug exposure. Organ-on-chip cell cultures have paved new grounds for testing and understanding metabolic dose-responses when evaluating pharmaceutical and environmental toxicity. Here, we present a metabolomic investigation of a coculture of liver sinusoidal endothelial cells (LSECs, SK-HEP-1) with hepatocytes (HepG2/C3a) using advanced organ-on-chip technology. To reproduce the physiology of the sinusoidal barrier, LSECs were separated from hepatocytes by a membrane (culture insert integrated organ-on-chip platform). The tissues were exposed to acetaminophen (APAP), an analgesic drug widely used as a xenobiotic model in liver and HepG2/C3a studies. The differences between the SK-HEP-1, HepG2/C3a monocultures and SK-HEP-1/HepG2/C3a cocultures, treated or not with APAP, were identified from metabolomic profiles using supervised multivariate analysis. The pathway enrichment coupled with metabolite analysis of the corresponding metabolic fingerprints contributed to extracting the specificity of each type of culture and condition. In addition, we analysed the responses to APAP treatment by mapping the signatures with significant modulation of the biological processes of the SK-HEP-1 APAP, HepG2/C3a APAP and SK-HEP-1/HepG2/C3a APAP conditions. Furthermore, our model shows how the presence of the LSECs barrier and APAP first pass can modify the metabolism of HepG2/C3a. Altogether, this study demonstrates the potential of a "metabolomic-on-chip" strategy for pharmaco-metabolomic applications predicting individual response to drugs.

Neutralizing serum amyloid a protects against sinusoidal endothelial cell damage and platelet aggregation during acetaminophen-induced liver injury

Serum amyloid A (SAA) is an acute response protein that mainly produced by hepatocytes, and it can promote endothelial dysfunction via a pro-inflammatory and pro-thrombotic effect in atherosclerosis and renal disease. Overdose of Acetaminophen (APAP) will cause hepatotoxicity accompany with hepatocyte necrosis, liver sinusoidal endothelial cells (LSECs) damage and thrombosis in liver. However, whether SAA plays a role in APAP-induced liver toxicity remains unclear. Here, we evaluated the Saa1/2 expression in APAP-induced liver injury, and found that Saa1/2 production was significantly increased in an autocrine manner in APAP injury model. Moreover, we used neutralizing antibody (anti-SAA) to block the function of serum Saa1/2. We found that neutralizing serum Saa1/2 protected against APAP-induced liver injuries and increased the survival rate of mice that were treated with lethal dose APAP. Further investigations showed that blocking Saa1/2 reduced APAP-induced sinusoidal endothelium damage, hemorrhage and thrombosis. In addition, in vitro experiments showed that Saa1/2 augmented the toxic effect of APAP on LSECs, and Saa1/2 promoted platelets aggregation on LSECs cell membrane. Taken together, this study suggests that Saa1/2 may play a critical role in APAP-induced liver damages through platelets aggregation and sinusoidal damage. Therefore, we conceptually demonstrate that inhibition of SAA may be a potential intervention for APAP-directed acute liver injuries.

Hepatoprotective effect of Pandanus odoratissimus seed extracts on paracetamol-induced rats

CONTEXT

Pandanus odoratissimus Linn. (Pandanaceae) seed extract is known to have antioxidant activities. However, the potential hepatoprotective effect is still unclear.

OBJECTIVE

To investigate the hepatoprotection aspect of P. odoratissimus methanol extract towards paracetamol-induced rats.

MATERIALS AND METHODS

Thirty male Sprague-Dawley rats were randomly divided into six equal groups: one group served as the healthy control and five groups with hepatotoxicity (hepatotoxic control and 4 treatment groups). The oral treatment of paracetamol-induced hepatotoxicity of 3 g/kg using three different concentrations of P. odoratissimus (300, 600 and 900 mg/kg), and silymarin (200 mg/kg) groups were administered once a day for 14 days. Enzyme activities and protein levels in serum were determined in rats at the end of the treatments. The histopathology of rat livers was observed under an electron microscope with 10× magnification.

RESULTS

Pandanus odoratissimus significantly decreased the serum glutamic-oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), alkaline phosphatase (ALP) and γ-glutamyl transferase (GGT) activities in induced-paracetamol rat serum (p < 0.05). Moreover, P. odoratissimus significantly decreased total bilirubin and direct bilirubin levels (p < 0.05). It significantly blocked the decline of serum albumin and protein levels (p < 0.05). Histopathological changes amplified paracetamol-induced liver damage and the hepatoprotective effect of P. odoratissimus in the liver.

DISCUSSION AND CONCLUSIONS

Pandanus odoratissimus improved the hepatoprotective effect in a concentration-dependent manner by reducing related hepatic enzyme and protein markers, suggesting as a useful agent in hepatotoxicity treatment, and it can be generalized to a broader study population in different hepatotoxic animal models.

Home pharmacological therapy in early COVID-19 to prevent hospitalization and reduce mortality: Time for a suitable proposal

The COVID‐19 pandemic is a highly dramatic concern for mankind. In Italy, the pandemic exerted its major impact throughout the period of February to June 2020. To date, the awkward amount of more than 134,000 deaths has been reported. Yet, post‐mortem autopsy was performed on a very modest number of patients who died from COVID‐19 infection, leading to a first confirmation of an immune‐thrombosis of the lungs as the major COVID‐19 pathogenesis, likewise for SARS. Since then (June–August 2020), no targeted early therapy considering this pathogenetic issue was approached. The patients treated with early anti‐inflammatory, anti‐platelet, anticoagulant and antibiotic therapy confirmed that COVID‐19 was an endothelial inflammation with immuno‐thrombosis. Patients not treated or scarcely treated with the most proper and appropriate therapy and in the earliest, increased the hospitalization rate in the intensive care units and also mortality, due to immune‐thrombosis from the pulmonary capillary district and alveoli. The disease causes widespread endothelial inflammation, which can induce damage to various organs and systems. Therapy must be targeted in this consideration, and in this review, we demonstrate how early anti‐inflammatory therapy may treat endothelia inflammation and immune‐thrombosis caused by COVID‐19, by using drugs we are going to recommend in this paper.

Advanced preclinical models for evaluation of drug-induced liver injury - consensus statement by the European Drug-Induced Liver Injury Network [PRO-EURO-DILI-NET]

Drug-induced liver injury (DILI) is a major cause of acute liver failure (ALF) and one of the leading indications for liver transplantation in Western societies. Given the wide use of both prescribed and over the counter drugs, DILI has become a major health issue for which there is a pressing need to find novel and effective therapies. Although significant progress has been made in understanding the molecular mechanisms underlying DILI, our incomplete knowledge of its pathogenesis and inability to predict DILI is largely due to both discordance between human and animal DILI in preclinical drug development and a lack of models that faithfully recapitulate complex pathophysiological features of human DILI. This is exemplified by the hepatotoxicity of acetaminophen (APAP) overdose, a major cause of ALF because of its extensive worldwide use as an analgesic. Despite intensive efforts utilising current animal and in vitro models, the mechanisms involved in the hepatotoxicity of APAP are still not fully understood. In this expert Consensus Statement, which is endorsed by the European Drug-Induced Liver Injury Network, we aim to facilitate and outline clinically impactful discoveries by detailing the requirements for more realistic human-based systems to assess hepatotoxicity and guide future drug safety testing. We present novel insights and discuss major players in APAP pathophysiology, and describe emerging in vitro and in vivo pre-clinical models, as well as advanced imaging and in silico technologies, which may improve prediction of clinical outcomes of DILI.

Liver-specific Bid silencing inhibits APAP-induced cell death in mice

Acetaminophen (APAP)-induced acute liver failure (ALF) is a life-threatening disease with only a few treatment options available. Though extensive research has been conducted for more than 40 years, the underlying pathomechanisms are not completely understood. Here, we studied as to whether APAP-induced ALF can be prevented in mice by silencing the BH3-interacting domain death agonist (Bid) as a potential key player in APAP pathology. For silencing Bid expression in mice, siRNA^Bid was formulated with the liver-specific siRNA delivery system DBTC and administered 48 h prior to APAP exposure. Mice which were pre-treated with HEPES (vehicle^HEPES) and siRNA^Luci served as siRNA controls. Hepatic pathology was assessed by in vivo fluorescence microscopy, molecular biology, histology and laboratory analysis 6 h after APAP or PBS exposure. Application of siRNA^Bid caused a significant decrease of mRNA and protein expression of Bid in APAP-exposed mice. Off-targets, such as cytochrome P450 2E1 and glutathione, which are known to be consumed under APAP intoxication, were comparably reduced in all APAP-exposed mice, underlining the specificity of Bid silencing. In APAP-exposed mice non-sterile inflammation with leukocyte infiltration and perfusion failure remained almost unaffected by Bid silencing. However, the Bid silencing reduced hepatocellular damage, evident by a remarkable decrease of DNA fragmented cells in APAP-exposed mice. In these mice, the expression of the pro-apoptotic protein Bax, which recently gained importance in the cell death pathway of regulated necrosis, was also significantly reduced, in line with a decrease in both, necrotic liver tissue and plasma transaminase activities. In addition, plasma levels of HMGB1, a marker of sterile inflammation, were significantly diminished. In conclusion, the liver-specific silencing of Bid expression did not protect APAP-exposed mice from microcirculatory dysfunction, but markedly protected the liver from necrotic cell death and in consequence from sterile inflammation. The study contributes to the understanding of the molecular mechanism of the APAP-induced pathogenic pathway by strengthening the importance of Bid and Bid silencing associated effects.

Death Receptor Interactions With the Mitochondrial Cell Death Pathway During Immune Cell-, Drug- and Toxin-Induced Liver Damage

Due to its extensive vascularization and physiological function as a filter and storage organ, the liver is constantly exposed to infectious and tumorigenic threat, as well as damaging actions of xenobiotics. Detoxification reactions are essential for the excretion of harmful substances, but harbor also the risk of “side effects” leading to dangerous metabolites of otherwise harmless substances, a well known effect during paracetamol overdose. These drugs can have detrimental effects, which often involves the induction of sterile inflammation and activation of the immune system. Therefore, the role of certain immune cells and their effector molecules in the regulation of drug-induced liver damage are of special interest. Hepatocytes are type II cells, and death receptor (DR)-induced cell death (CD) requires amplification via the mitochondrial pathway. However, this important role of the mitochondria and associated CD-regulating signaling complexes appears to be not restricted to DR signaling, but to extend to drug-induced activation of mitochondrial CD pathways. We here discuss the role of members of the TNF family, with a focus on TRAIL, and their interactions with the Bcl-2 family in the crosstalk between the extrinsic and intrinsic CD pathway during xenobiotic-induced liver damage.

Development of a New Conditionally Immortalized Human Liver Sinusoidal Endothelial Cells

Liver sinusoidal endothelial cells (LSECs), which are specialized endothelial cells that line liver sinusoids, have been reported to participate in a variety of liver functions, such as blood macromolecule clearance and factor VIII production. In addition, LSECs play crucial roles in liver regeneration following acute liver injury, as well as the development and progression of liver diseases or drug-induced hepatotoxicity. However, the molecular mechanisms underlying their roles remain mostly unknown. Therefore, in order to contribute to the clarification of those mechanisms, herein we report on the development of a new immortalized human LSEC (HLSEC) line. To produce this cell line, two immortalized genes were introduced into the primary HLSECs, which eventually resulted in the establishment of the HLSEC/conditionally immortalized, clone-J (HLSEC/ciJ). Consistent with the two-immortalized gene expression, HLSEC/ciJ showed excellent proliferation activity. Additionally, the results of gene expression analyses showed that several LSEC (as well as pan-endothelial) marker mRNAs and proteins were clearly expressed in HLSEC/ciJ. Furthermore, we found that adherence junction proteins were localized at the cell border in the HLSEC/ciJ monolayer, and that the cells exhibited a tube-like structure formation property. Taken together, the results obtained thus far indicate that we have successfully immortalized HLSECs, resulting in creation of HLSEC/ciJ, a cell line that possesses infinite proliferation ability while retaining possession of at least some HLSEC features. We believe that the HLSEC/ciJ have the potential to provide a valuable and unlimited alternative source of HLSECs for use in liver/LSEC physiology/pathophysiology, pharmacology, and toxicology studies.

Liver cell injury caused by bad habits

Apoptosis and necrosis of liver cells induced by environmental or genetic factors are the main features of liver injury. Liver injury is usually caused by apoptosis of liver cells, which is controlled by a complex regulatory system involved in liver damage and secondary inflammation. This article aims to review liver injury caused by bad habits and the underlying molecular mechanisms.

Acetaminophen cytotoxicity is ameliorated in a human liver organotypic co-culture model

Organotypic liver culture models for hepatotoxicity studies that mimic in vivo hepatic functionality could help facilitate improved strategies for early safety risk assessment during drug development. Interspecies differences in drug sensitivity and mechanistic profiles, low predictive capacity, and limitations of conventional monocultures of human hepatocytes, with high attrition rates remain major challenges. Herein, we show stable, cell-type specific phenotype/cellular polarity with differentiated functionality in human hepatocyte-like C3A cells (enhanced CYP3A4 activity/albumin synthesis) when in co-culture with human vascular endothelial cells (HUVECs), thus demonstrating biocompatibility and relevance for evaluating drug metabolism and toxicity. In agreement with in vivo studies, acetaminophen (APAP) toxicity was most profound in HUVEC mono-cultures; whilst in C3A:HUVEC co-culture, cells were less susceptible to the toxic effects of APAP, including parameters of oxidative stress and ATP depletion, altered redox homeostasis, and impaired respiration. This resistance to APAP is also observed in a primary human hepatocyte (PHH) based co-culture model, suggesting bidirectional communication/stabilization between different cell types. This simple and easy-to-implement human co-culture model may represent a sustainable and physiologically-relevant alternative cell system to PHHs, complementary to animal testing, for initial hepatotoxicity screening or mechanistic studies of candidate compounds differentially targeting hepatocytes and endothelial cells.

Acetaminophen induces JNK/p38 signaling and activates the caspase-9-3-dependent cell death pathway in human mesenchymal stem cells

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug. Generally, the therapeutic dose of APAP is clinically safe, however, high doses of APAP can cause acute liver and kidney injury. Therefore, the majority of previous studies have focussed on elucidating the mechanisms of APAP-induced hepatotoxicity and nephrotoxicity, in addition to examining ways to treat these conditions in clinical cases. However, few studies have reported APAP-induced intoxication in human stem cells. Stem cells are important in cell proliferation, differentiation and repair during human development, particularly during fetal and child development. At present, whether APAP causes cytotoxic effects in human stem cells remains to be elucidated, therefore, the present study aimed to investigate the cellular effects of APAP treatment in human stem cells. The results of the present study revealed that high-dose APAP induced more marked cytotoxic effects in human mesenchymal stem cells (hMSCs) than in renal tubular cells. In addition, increased levels of hydrogen peroxide (H2O2), phosphorylation of c-Jun N-terminal kinase and p38, and activation of caspase-9/-3 cascade were observed in the APAP-treated hMSCs. By contrast, antioxidants, including vitamin C reduced APAP-induced augmentations in H2O2 levels, but did not inhibit the APAP-induced cytotoxic effects in the hMSCs. These results suggested that high doses of APAP may cause serious damage towards hMSCs.

Long-term coculture strategies for primary hepatocytes and liver sinusoidal endothelial cells

Hepatocytes and their in vitro models are essential tools for preclinical screening studies for drugs that affect the liver. Most of the current models primarily focus on hepatocytes alone and lack the contribution of non-parenchymal cells (NPCs), which are significant through both molecular and the response of the NPCs themselves. Models that incorporate NPCs alongside hepatocytes hold the power to enable more realistic recapitulation and elucidation of cell interactions and cumulative drug response. Hepatocytes and liver sinusoidal endothelial cells (LSECs) account for ∼ 80% of the liver mass where the LSECs line the walls of blood vessels, and act as a barrier between hepatocytes and blood. Culturing LSECs with hepatocytes to generate multicellular physiologically relevant in vitro liver models has been a major hurdle since LSECs lose their phenotype rapidly after isolation. To this end, we describe the application of collagen gel (1) in a sandwich and (2) as an intervening extracellular matrix layer to coculture hepatocytes with LSECs for extended periods. These coculture configurations provide environments wherein hepatocyte and LSECs, through cell-cell contacts and/or secretion factors, lead to enhanced function and stability of the cocultures. Our results show that in these configurations, hepatocytes and LSECs maintained their phenotypes when cultured together as a mixture, and showed stable secretion and metabolic activity for up to 4 weeks. Immunostaining for sinusoidal endothelial 1 (SE-1) antibody demonstrated retention of LSEC phenotype during the culture period. In addition, LSECs cultured alone maintained high viability and SE-1 expression when cultured within a collagen sandwich configuration up to 4 weeks. Albumin production of the cocultures was 10-15 times higher when LSECs were cultured as a bottom layer (with an intervening collagen layer) and as a mixture in a sandwich configuration, and native CYP 1A1/2 activity was at least 20 times higher than monoculture controls. Together, these data suggest that collagen gel-based hepatocyte-LSEC cocultures are highly suitable models for stabilization and long-term culture of both cell types. In summary, these results indicate that collagen gel-based hepatocyte-LSEC coculture models are promising for in vitro toxicity testing, and liver model development studies.

Depolarization Controls TRAIL-Sensitization and Tumor-Selective Killing of Cancer Cells: Crosstalk with ROS

Conventional genotoxic anti-cancer drugs target the proliferative advantage of tumor cells over normal cells. This kind of approach lacks the selectivity of treatment to cancer cells, because most of the targeted pathways are essential for the survival of normal cells. As a result, traditional cancer treatments are often limited by undesirable damage to normal cells (side-effects). Ideal anti-cancer drugs are expected to be highly effective against malignant tumor cells with minimal cytotoxicity toward normal cells. Such selective killing can be achieved by targeting pathways essential for the survival of cancer cells, but not normal cells. As cancer cells are characterized by their resistance to apoptosis, selective apoptosis induction is a promising approach for selective killing of cancer cells. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising tumor-selective anti-cancer drug. However, the congenital and acquired resistance of some cancer cell types, including malignant melanoma cells, currently impedes effective TRAIL therapy, and an innovative approach that can override TRAIL resistance is urgently required. Apoptosis is characterized by cell shrinkage caused by disruption of the maintenance of the normal physiological concentrations of K(+) and Na(+) and intracellular ion homeostasis. The disrupted ion homeostasis leads to depolarization and apoptosis. Recent evidence suggests that depolarization is an early and prerequisite event during TRAIL-induced apoptosis. Moreover, diverse natural products and synthetic chemicals capable of depolarizing the cell membrane exhibit tumor-selective killing and TRAIL-sensitizing effects. Here, we discuss the role of depolarization in selective killing of cancer cells in connection with the emerging concept that oxidative stress is a critical mediator of mitochondrial and endoplasmic reticulum dysfunctions and serves as a tumor-selective target in cancer treatment.

Dual role of acetaminophen in promoting hepatoma cell apoptosis and kidney fibroblast proliferation

Acetaminophen (APAP), is a safe analgesic and antipyretic drug at therapeutic dose, and is widely used in the clinic. However, high doses of APAP can induce hepatotoxicity and nephrotoxicity. Most studies have focused on high‑dose APAP‑induced acute liver and kidney injury. So far, few studies have investigated the effects of the therapeutic dose (1/10 of the high dose) or of the low dose (1/100 of the high dose) of APAP on the cells. The aim of this study was to investigate the cellular effects of therapeutic- or low‑dose APAP treatment on hepatoma cells and kidney fibroblasts. As expected, high‑dose APAP treatment inhibited while therapeutic and low‑dose treatment did not inhibit cell survival of kidney tubular epithelial cells. In addition, therapeutic-dose treatment induced an increase in the H2O2 level, activated the caspase‑9/‑3 cascade, and induced cell apoptosis of hepatoma cells. Notably, APAP promoted fibroblast proliferation, even at low doses. This study demonstrates that different cellular effects are exerted upon treatment with different APAP concentrations. Our results indicate that treatment with the therapeutic dose of APAP may exert an antitumor activity on hepatoma, while low‑dose treatment may be harmful for patients with fibrosis, since it may cause proliferation of fibroblasts.

Blocks to thyroid cancer cell apoptosis can be overcome by inhibition of the MAPK and PI3K/AKT pathways

Current treatment for recurrent and aggressive/anaplastic thyroid cancers is ineffective. Novel targeted therapies aimed at the inhibition of the mutated oncoprotein BRAF^V600E have shown promise in vivo and in vitro but do not result in cellular apoptosis. TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis in a tumor-selective manner by activating the extrinsic apoptotic pathway. Here, we show that a TRAIL-R2 agonist antibody, lexatumumab, induces apoptosis effectively in some thyroid cancer cell lines (HTh-7, TPC-1 and BCPAP), while more aggressive anaplastic cell lines (8505c and SW1736) show resistance. Treatment of the most resistant cell line, 8505c, using lexatumumab in combination with the BRAF^V600E inhibitor, PLX4720, and the PI3K inhibitor, LY294002, (triple-drug combination) sensitizes the cells by triggering both the extrinsic and intrinsic apoptotic pathways in vitro as well as 8505c orthotopic thyroid tumors in vivo. A decrease in anti-apoptotic proteins, pAkt, Bcl-xL, Mcl-1 and c-FLIP, coupled with an increase in the activator proteins, Bax and Bim, results in an increase in the Bax to Bcl-xL ratio that appears to be critical for sensitization and subsequent apoptosis of these resistant cells. Our results suggest that targeting the death receptor pathway in thyroid cancer can be a promising strategy for inducing apoptosis in thyroid cancer cells, although combination with other kinase inhibitors may be needed in some of the more aggressive tumors initially resistant to apoptosis.

Molecular mechanisms of hepatic apoptosis

Apoptosis is a prominent feature of liver diseases. Causative factors such as alcohol, viruses, toxic bile acids, fatty acids, drugs, and immune response, can induce apoptotic cell death via membrane receptors and intracellular stress. Apoptotic signaling network, including membrane death receptor-mediated cascade, reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, lysosomal permeabilization, and mitochondrial dysfunction, is intermixed each other, but one mechanism may dominate at a particular stage. Mechanisms of hepatic apoptosis are complicated by multiple signaling pathways. The progression of liver disease is affected by the balance between apoptotic and antiapoptotic capabilities. Therapeutic options of liver injury are impacted by the clear understanding toward mechanisms of hepatic apoptosis.

Molecular mechanisms of hepatic apoptosis

Apoptosis is a prominent feature of liver diseases. Causative factors such as alcohol, viruses, toxic bile acids, fatty acids, drugs, and immune response, can induce apoptotic cell death via membrane receptors and intracellular stress. Apoptotic signaling network, including membrane death receptor-mediated cascade, reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, lysosomal permeabilization, and mitochondrial dysfunction, is intermixed each other, but one mechanism may dominate at a particular stage. Mechanisms of hepatic apoptosis are complicated by multiple signaling pathways. The progression of liver disease is affected by the balance between apoptotic and antiapoptotic capabilities. Therapeutic options of liver injury are impacted by the clear understanding toward mechanisms of hepatic apoptosis.