Modeling inflammation-drug interactions in vitro: a rat Kupffer cell-hepatocyte coculture system

NOX4 promotes Kupffer cell inflammatory response via ROS-NLRP3 to aggravate liver inflammatory injury in acute liver injury

AIM

This work aimed to investigate the mechanism of NOX4 in promoting Kupffer cells (KCs) activation and tissue inflammatory response in acute liver injury.

METHODS

Initially, the mouse KCs were cultured in vitro. Thereafter, the NOX4 overexpression plasmid was transfected into KCs to construct the overexpression cell line. Then, KCs inflammatory response was induced by LPS + Nigericin treatment. CCK-8 assay was performed to detect cell viability, flow cytometry (FCM) was conducted to measure cell apoptosis, enzyme-linked immunosorbent assay (ELISA) was performed to detect inflammatory factor levels in the culture medium, NLRP3 and ASC expression in cells was detected by immunofluorescence (IF) staining, and ROS expression was detected by the DCFH-DA probe. Furthermore, the expression levels of NLRP3, ASC and Caspase-1 proteins were detected by Western-Blot (WB) assay. Furthermore, cells were pre-treated with NOX inhibitor or NAC to suppress NOX4 expression or ROS production, aiming to further investigate the effect on KCs inflammatory response. In mouse experiments, the NOX4 knockdown mice and wild-type (WT) mice were adopted for carrying out experiments. The mouse model of ALI was constructed with LPS and D-GalN treatment. Thereafter, the changes in tissue samples were detected by H&E staining, NLRP3 expression was measured by histochemical staining, inflammatory factors in tissues were analyzed by ELISA, and the levels of NLRP3, ASC and Caspase-1 proteins in tissues were detected by WB assay.

RESULTS

LPS induced KCs inflammatory response. NOX4 overexpression decreased the mouse viability and increased the apoptosis rate. The levels of inflammatory factors were up-regulated in the culture medium. In addition, ROS were activated, and the positive cell number increased. Moreover, NOX4 promoted NLRP3 activation and significantly increased the expression of NLRP3 and ASC. Pretreatment with NOX4 inhibitor or NAC antagonized the effects of NOX4 and suppressed the KCs inflammatory response. In the mouse model, NOX4 knockdown significantly suppressed the activation and inflammatory response of microglial cells in tissues, reducing the NLRP3 expression in tissues.

CONCLUSION

NOX4 activates the NLRP3 inflammasome via ROS to promote inflammatory response in KCs and the release of inflammatory factors, suppressing NOX4 can improve ALI in mice, and NOX4 is promising as a new target for ALI treatment.

Recent Advances in Models of Immune-Mediated Drug-Induced Liver Injury

Hepatic inflammation is a key feature of a variety of liver diseases including drug-induced liver injury (DILI), orchestrated by the innate immune response (Kupffer cells, monocytes, neutrophils, dendritic cells) and the adaptive immune system (T cells and natural killer T cells). In contrast to acute DILI, prediction of immune-mediated DILI (im-DILI) has been more challenging due to complex disease pathogenesis, lack of reliable models and limited knowledge of underlying mechanisms. This review summarizes in vivo and in vitro systems that have been used to model im-DILI. In particular, the review focuses on state-of-the-art in vitro human-based multicellular models which have been developed to supplement the use of in vivo models due to interspecies variation and increasing ethical concerns regarding animal use. Advantages of the co-cultures in maintaining hepatocyte functions and importantly, introducing heterotypic cell-cell interactions to mimic inflammatory hepatic microenvironment are discussed. Challenges regarding cell source and incorporation of different cells with physical cell-cell contact are outlined and potential solutions are proposed. It is likely that better understanding of the interplay of immune cells in liver models will allow for the development of more accurate systems to better predict hepatotoxicity and stratification of drugs that can cause immune-mediated effects.

Cardiomyocyte microvesicles: proinflammatory mediators after myocardial ischemia?

Myocardial infarction is a frequent complication of cardiovascular disease leading to high morbidity and mortality worldwide. Elevated C-reactive protein (CRP) levels after myocardial infarction are associated with heart failure and poor prognosis. Cardiomyocyte microvesicles (CMV) are released during hypoxic conditions and can act as mediators of intercellular communication. MicroRNA (miRNA) are short non-coding RNA which can alter cellular mRNA-translation. Microvesicles (MV) have been shown to contain distinct patterns of miRNA from their parent cells which can affect protein expression in target cells. We hypothesized that miRNA containing CMV mediate hepatic CRP expression after cardiomyocyte hypoxia. H9c2-cells were cultured and murine cardiomyocytes were isolated from whole murine hearts. H9c2- and murine cardiomyocytes were exposed to hypoxic conditions using a hypoxia chamber. Microvesicles were isolated by differential centrifugation and analysed by flow cytometry. Next-generation-sequencing was performed to determine the miRNA-expression profile in H9c2 CMV compared to their parent cells. Microvesicles were incubated with a co-culture model of the liver consisting of THP-1 macrophages and HepG2 cells. IL-6 and CRP expression in the co-culture was assessed by qPCR and ELISA. CMV contain a distinct pattern of miRNA compared to their parent cells including many inflammation-related miRNA. CMV induced IL-6 expression in THP-1 macrophages alone and CRP expression in the hepatic co-culture model. MV from hypoxic cardiomyocytes can mediate CRP expression in a hepatic co-culture model. Further studies will have to show whether these effects are reproducible in-vivo.

Drug-induced organ injury in coronavirus disease 2019 pharmacotherapy: Mechanisms and challenges in differential diagnosis and potential protective strategies

The world is currently facing an unprecedented pandemic caused by a newly recognized and highly pathogenic coronavirus disease 2019 (COVID‐19; induced by SARS‐CoV‐2 virus), which is a severe and ongoing threat to global public health. Since COVID‐19 was officially declared a pandemic by the World Health Organization in March 2020, several drug regimens have rapidly undergone clinical trials for the management of COVID‐19. However, one of the major issues is drug‐induced organ injury, which is a prominent clinical challenge. Unfortunately, most drugs used against COVID‐19 are associated with adverse effects in different organs, such as the kidney, heart, and liver. These side effects are dangerous and, in some cases, they can be lethal. More importantly, organ injury is also a clinical manifestation of COVID‐19 infection. These adverse reactions are increasingly recognized as outcomes of COVID‐19 infection. Therefore, the differential diagnosis of drug‐induced adverse effects from COVID‐19‐induced organ injury is a clinical complication. This review highlights the importance of drug‐induced organ injury, its known mechanisms, and the potential therapeutic strategies in COVID‐19 pharmacotherapy. We review the potential strategies for the differential diagnosis of drug‐induced organ injury. This information can facilitate the development of therapeutic strategies, not only against COVID‐19 but also for future outbreaks of other emerging infectious diseases.

Adverse drug events are well‐known and common clinical problems in COVID‐19 patients.

The differential diagnosis of adverse drug effects and disease‐induced organ injury is a clinical challenge.

Obtaining a detailed history and biochemical analysis of blood‐based biomarkers from the patients as soon as they are admitted is critical for differential diagnosis of drug or disease‐induced organ injury.

Advances in generating liver cells from pluripotent stem cells as a tool for modeling liver diseases

Developing robust in vitro models of the liver is essential for studying the pathogenesis of liver diseases, hepatotoxicity testing, and regenerative medicine. Earlier studies were conducted using cell lines derived from hepatomas. Due to the inherent limitations of cell lines, researchers used primary human hepatocytes (PHHs), which are considered a gold standard for in vitro modeling of the liver. However, due to the high cost of PHHs and lack of donors, researchers have sought an alternative source for functional liver cells. Pluripotent stem cells (PSCs) emerged as a viable alternative due to their plasticity and high proliferative capacity. This review gives an overview of the major advances that have been achieved to develop protocols to generate liver cells such as hepatocytes, cholangiocytes, and Küpffer cells from PSCs. We also discuss their application in modeling the pathogenesis of liver diseases such as drug‐induced liver injury, acute liver failure, and hepatic steatosis.

Naturally-Derived Biomaterials for Tissue Engineering Applications

Naturally-derived biomaterials have been used for decades in multiple regenerative medicine applications. From the simplest cell microcarriers made of collagen or alginate, to highly complex decellularized whole-organ scaffolds, these biomaterials represent a class of substances that is usually first in choice at the time of electing a functional and useful biomaterial. Hence, in this chapter we describe the several naturally-derived biomaterials used in tissue engineering applications and their classification, based on composition. We will also describe some of the present uses of the generated tissues like drug discovery, developmental biology, bioprinting and transplantation.

Quantitative Analysis of Hepatic Toxicity in Rats Induced by Inhalable Silica Nanoparticles Using Acoustic Radiation Force Imaging

OBJECTIVES

The purposes of this study were to verify whether inhalable silicon dioxide (SiO₂ ) nanoparticles could induce hepatic injury and to investigate the relationship between the exposure time and SiO₂ nanoparticle dosage by using acoustic radiation force impulse imaging (ARFI).

METHODS

A total of 72 rats were randomly separated into 9 groups with 8 in each: blank control group, 0.9% normal saline group, polyacrylate (PPE) group, 25%, 50%, and 100% SiO₂ groups, and 25%, 50%, and 100% SiO₂ /PPE groups with inhaled SiO₂ nanoparticle concentrations similar to the SiO₂ groups. After successful modeling and design, the hepatic shear wave velocity (SWV) values of the 9 groups were obtained on days 3, 7, 14, 21, and 28 by using ARFI, and the intragroup and intergroups differences in the SWVs were compared. The serum alanine aminotransferase (ALT) and aspartate aminotransferase were tested and compared on day 28. Hepatic tissues were collected for histologic observation on day 28.

RESULTS

The pathologic results verified that inhalable SiO₂ nanoparticles could induce hepatic injury. Compared with the control group, the hepatic SWV and serum ALT values in the SiO₂ groups and SiO₂ /PPE groups were elevated (P < .05). The dosage and exposure time of SiO₂ played a key role in the elevation of the SWV in the SiO₂ and SiO₂ /PPE groups. The correlation between the ALT level and SWV was significant on day 28 (P < .05).

CONCLUSIONS

Inhalable SiO₂ nanoparticles and SiO₂ /PPE were able to induce hepatic injury in rats. Using ARFI to evaluate hepatic toxicity induced by SiO₂ nanoparticles was effective in this study.

Challenges on the road to a multicellular bioartificial liver

Over recent years, the progress in the development of a bioartificial liver (BAL) as an extracorporeal device or as a tissue engineered transplantable organ has been immense. However, many important BAL characteristics that are necessary to meet clinical demands have not been sufficiently addressed. This review describes the existing challenges in the development of a BAL for clinical applications, highlighting multicellularity and sinusoidal microarchitecture as crucial BAL characteristics to fulfil various liver functions. Currently available sources of nonparenchymal liver cells, such as endothelial cells, cholangiocytes and macrophages, used in BAL development are defined. Also, we discuss the recent studies on the reconstruction of the complex liver sinusoid microarchitecture using various liver cell types. Moreover, we highlight some other aspects of a BAL, such as liver zonation and formation of a vascular as well as biliary network for an adequate delivery, biotransformation and removal of substrates and waste products. Finally, the benefits of a multicellular BAL for the pharmaceutical industry are briefly described. Copyright © 2016 John Wiley & Sons, Ltd.

Hydroxyapatite nanoparticle-induced mitochondrial energy metabolism impairment in liver cells: in vitro and in vivo studies

Hydroxyapatite nanoparticles (HAP-NPs) have been extensively developed as drug carriers, bone implants, coating materials, etc. in the human body. However, research focusing on the potential side effects of HAP-NPs on the mitochondria-associated energy metabolism in liver cells is lacking. In this study, HAP-NPs with a long diameter of 80 nm and a short diameter of 20 nm were evaluated for their ability to induce mitochondrial energy metabolism dysfunction in vitro and in vivo. In the in vitro system, the buffalo rat hepatocyte (BRL) cell line was directly exposed to the HAP-NPs. The results of these experiments showed that the HAP-NPs induced inhibition of mitochondrial dehydrogenase activity, which was accompanied by a decrease in the mitochondrial membrane potential (MMP). In addition, HAP-NPs elevated the hepatic levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and decreased the levels of GSH and SOD. These data indicated that HAP-NPs induced a lowered rate of electron transfer in the mitochondrial respiratory chain, accompanied by a decrease in the activity of the mitochondrial respiratory chain complexes I, II and III. Furthermore, HAP-NPs induced a decline in the enzymatic expression in the Krebs cycle. We also investigated the role of Kupffer cells (KCs, rat-derived) in the effects induced by the HAP-NPs. The supernatant from the HAP-NP-treated KCs was used to stimulate the BRL cells. We observed that the HAP-NPs had the ability to induce KC activation. The activation of KCs then led to the release of tumor necrosis factor-α (TNF-α), nitric oxide (NO) and reactive oxygen species (ROS), and induced the inhibition of mitochondrial respiratory chain complexes I, II and III in the BRL cells. In the in vivo study, the TEM examination revealed mitochondrial swelling and vacuolar degeneration in the HAP-NP-treated hepatocytes. In addition, the amount of succinate (Suc), an intermediate in the mitochondrial Krebs cycle, also declined in the ¹ H NMR spectroscopic measurements. Copyright © 2017 John Wiley & Sons, Ltd.

Evaluation of a human in vitro hepatocyte-NPC co-culture model for the prediction of idiosyncratic drug-induced liver injury: A pilot study

•

Co-cultures of liver and immune cells can be used to detect iDILI compounds.

•

Pro-inflammatory factors are involved in the development of iDILI.

•

The co-exposure of a drug candidate with TNF might be sufficient to predict iDILI.

Interactions between hepatocytes and immune cells as well as inflammatory episodes are frequently discussed to play a critical role in the alteration of the individual susceptibility to idiosyncratic drug-induced liver injury (iDILI). To evaluate this hypothesis and to face the urgent need for predictive in vitro models, we established two co-culture systems based on two human cell lines in presence or absence of pro-inflammatory factors (LPS, TNF), i.e. hepatoma HepG2 cells co-cultured with monocytic or macrophage-like THP-1 cells. HepG2 monocultures served as control scenario. Mono- or co-cultures were treated with iDILI reference substances (Troglitazone [TGZ], Trovafloxacin [TVX], Diclofenac [DcL], Ketoconazole [KC]) or their non-iDILI partner compounds (Rosiglitazone, Levofloxacin, Acetylsalicylic Acid, Fluconazole). The liver cell viability was subsequently determined via WST-Assay. An enhanced cytotoxicity (synergy) or a hormetic response compared to the drug effect in the HepG2 monoculture was considered as iDILI positive. TGZ synergized in co-cultures with monocytes without an additional pro-inflammatory stimulus, while DcL and KC showed a hormetic response. All iDILI drugs synergized with TNF in the simple HepG2 monoculture, indicating its relevance as an initiator of iDILI. KC showed a synergy when co-exposed to both, monocytes and LPS, while TVX and DcL showed a synergy under the same conditions with macrophages. All described iDILI responses were not observed with the corresponding non-iDILI partner compounds. Our first results confirm that an inflammatory environment increases the sensitivity of liver cells towards iDILI compounds and point to an involvement of pro-inflammatory factors, especially TNF, in the development of iDILI.

In Vitro Intestinal and Liver Models for Toxicity Testing

The human body is exposed to hundreds of chemicals every day. Many of these toxicants have unknown effects on the body that can be deleterious. Furthermore, chemicals can have a synergistic effect, resulting in toxic responses of cocktails at relatively low individual exposure levels. The gastrointestinal (GI) tract and the liver are the first organs to be exposed to ingested pharmaceuticals and environmental chemicals. As a result, these organs often experience extensive damage from xenobiotics and their metabolites. In vitro models offer a promising method for testing toxic effects. Many advanced in vitro models have been developed for GI and liver toxicity. These models strive to recapitulate the in vivo organ architecture to more accurately model chemical toxicity. In this review, we discuss many of these advances, in addition to recent efforts to integrate the GI and the liver in vitro for a more holistic toxicity model.

Adverse outcome pathway development from protein alkylation to liver fibrosis

In modern toxicology, substantial efforts are undertaken to develop alternative solutions for in vivo toxicity testing. The adverse outcome pathway (AOP) concept could facilitate knowledge-based safety assessment of chemicals that does not rely exclusively on in vivo toxicity testing. The construction of an AOP is based on understanding toxicological processes at different levels of biological organisation. Here, we present the developed AOP for liver fibrosis and demonstrate a linkage between hepatic injury caused by chemical protein alkylation and the formation of liver fibrosis, supported by coherent and consistent scientific data. This long-term process, in which inflammation, tissue destruction, and repair occur simultaneously, results from the complex interplay between various hepatic cell types, receptors, and signalling pathways. Due to the complexity of the process, an adequate liver fibrosis cell model for in vitro evaluation of a chemical's fibrogenic potential is not yet available. Liver fibrosis poses an important human health issue that is also relevant for regulatory purposes. An AOP described with enough mechanistic detail might support chemical risk assessment by indicating early markers for downstream events and thus facilitating the development of an in vitro testing strategy. With this work, we demonstrate how the AOP framework can support the assembly and coherent display of distributed mechanistic information from the literature to support the use of alternative approaches for prediction of toxicity. This AOP was developed according to the guidance document on developing and assessing AOPs and its supplement, the users' handbook, issued by the Organisation for Economic Co-operation and Development.

Isolation and co-culture of rat parenchymal and non-parenchymal liver cells to evaluate cellular interactions and response

The liver is a central organ in the human body, and first line of defense between host and external environment. Liver response to any external perturbation is a collective reaction of resident liver cells. Most of the current in vitro liver models focus on hepatocytes, the primary metabolic component, omitting interactions and cues from surrounding environment and non-parenchymal cells (NPCs). Recent studies suggest that contributions of NPCs are vital, particularly in disease conditions, and outcomes of drugs and their metabolites. Along with hepatocytes, NPCs–Kupffer (KC), sinusoidal endothelial (LSEC) and stellate cells (SC) are major cellular components of the liver. Incorporation of primary cells in in vitro liver platforms is essential to emulate the functions of the liver, and its overall response. Herein, we isolate individual NPC cell fractions from rat livers and co-culture them in a transwell format incorporating primary rat hepatocytes with LSECs, SCs, and KCs. Our results indicate that the presence and contributions of multiple cells within the co-culture capture the interactions between hepatocytes and NPC, and modulates the responses to inflammatory stimulus such as LPS. The isolation and co-culture methods could provide a stable platform for creating in vitro liver models that provide defined functionality beyond hepatocytes alone.

Characterization of chemical-induced sterile inflammation in vitro: application of the model compound ketoconazole in a human hepatic co-culture system

Liver injury as a result of a sterile inflammation is closely linked to the activation of immune cells, including macrophages, by damaged hepatocytes. This interaction between immune cells and hepatocytes is as yet not considered in any of the in vitro test systems applied during the generation of new drugs. Here, we established and characterized a novel in vitro co-culture model with two human cell lines, HepG2 and differentiated THP-1. Ketoconazole, an antifungal drug known for its hepatotoxicity, was used as a model compound in the testing of the co-culture. Single cultures of HepG2 and THP-1 cells were studied as controls. Different metabolism patterns of ketoconazole were observed for the single and co-culture incubations as well as for the different cell types. The main metabolite N-deacetyl ketoconazole was found in cell pellets, but not in supernatants of cell cultures. Global proteome analysis showed that the NRF2-mediated stress response and the CXCL8 (IL-8) pathway were induced by ketoconazole treatment under co-culture conditions. The upregulation and ketoconazole-induced secretion of several pro-inflammatory cytokines, including CXCL8, TNF-α and CCL3, was observed in the co-culture system only, but not in single cell cultures. Taking together, we provide evidence that the co-culture model applied might be suitable to serve as tool for the prediction of chemical-induced sterile inflammation in liver tissue in vivo.

Protective Effects of Agmatine against Chlorpromazine- Induced Toxicity in the Liver of Wistar Rats

The metabolic pathways of chlorpromazine (CPZ) toxicity were tracked by assessing oxidative/nitrosative stress markers. The main objective of the study was to test the hypothesis that agmatine (AGM) prevents oxidative/nitrosative stress in the liver of Wistar rats 15 days after administration of CPZ. All tested substances were administered intraperitoneally (i.p.) for 15 consecutive days. The rats were divided into four groups: the control group (C, 0.9 % saline solution), the CPZ group (CPZ, 38.7 mg/kg b.w.), the CPZ+AGM group (AGM, 75 mg/kg b.w. immediately after CPZ, 38.7 mg/kg b.w. i.p.) and the AGM group (AGM, 75 mg/kg b.w.).

Rats were decapitated 15 days after the appropriate treatment. In the CPZ group, CPZ concentration was significantly increased compared to C values (p<0.01), while AGM treatment induced the significant decrease in CPZ concentration in the CPZ+AGM group (p<0.05) and the AGM group (p<0.01). CPZ application to healthy rats did not lead to any changes of lipid peroxidation in the liver compared to the C group, but AGM treatment decreased that parameter compared to the CPZ group (p<0.05). In CPZ liver homogenates, nitrite and nitrate concentrations were increased compared to controls (p<0.001), and AGM treatment diminished that parameter in the CPZ group (p<0.05), as well as in the AGM group (p<0.001). In CPZ animals, glutathione level and catalase activity were decreased in comparison with C values (p<0.01 respectively), but AGM treatment increased the activity of catalase in comparison with CPZ animals (p<0.05 respectively). Western blot analysis supported biochemical findings in all groups. Our results showed that treatment with AGM significantly supressed the oxidative/nitrosative stress parameters and restored antioxidant defense in rat liver.

Experimental models of hepatotoxicity related to acute liver failure

Acute liver failure can be the consequence of various etiologies, with most cases arising from drug-induced hepatotoxicity in Western countries. Despite advances in this field, the management of acute liver failure continues to be one of the most challenging problems in clinical medicine. The availability of adequate experimental models is of crucial importance to provide a better understanding of this condition and to allow identification of novel drug targets, testing the efficacy of new therapeutic interventions and acting as models for assessing mechanisms of toxicity. Experimental models of hepatotoxicity related to acute liver failure rely on surgical procedures, chemical exposure or viral infection. Each of these models has a number of strengths and weaknesses. This paper specifically reviews commonly used chemical in vivo and in vitro models of hepatotoxicity associated with acute liver failure.

Application of biomaterials to advance induced pluripotent stem cell research and therapy

Derived from any somatic cell type and possessing unlimited self-renewal and differentiation potential, induced pluripotent stem cells (iPSCs) are poised to revolutionize stem cell biology and regenerative medicine research, bringing unprecedented opportunities for treating debilitating human diseases. To overcome the limitations associated with safety, efficiency, and scalability of traditional iPSC derivation, expansion, and differentiation protocols, biomaterials have recently been considered. Beyond addressing these limitations, the integration of biomaterials with existing iPSC culture platforms could offer additional opportunities to better probe the biology and control the behavior of iPSCs or their progeny in vitro and in vivo. Herein, we discuss the impact of biomaterials on the iPSC field, from derivation to tissue regeneration and modeling. Although still exploratory, we envision the emerging combination of biomaterials and iPSCs will be critical in the successful application of iPSCs and their progeny for research and clinical translation.

A new animal model for Polygonum multiflorum Thunb-induced liver injury in rats and its potential mechanisms

The model is established successfully with the activation of LPS. Its pathogenesis is associated with the expression of mTLR4 in rats' liver. MicroRNA-122 is certificated to be an ideal potential serum biomarker for this model.

miR-146a ameliorates liver ischemia/reperfusion injury by suppressing IRAK1 and TRAF6

A critical role of the Toll-like receptor(TLR) and its downstream molecules, including IL-1 receptor-associated kinase 1(IRAK1) and tumor necrosis factor receptor- associated factor 6(TRAF6), in the pathogenesis of liver ischemia/reperfusion (I/R) injury has been documented. Recently a microRNA, miR-146a, was identified as a potent negative regulator of the TLR signaling pathway. In this study, we investigated the role of miR-146a to attenuate TLR signaling and liver I/R injury in vivo and in vitro. miR-146a was decreased in mice Kupffer cells following hepatic I/R, whereas IRAK1 and TRAF6 increased. Overexpression of miR-146a directly decreased IRAK1 and TRAF6 expression and attenuated the release of proinflammatory cytokines through the inactivation of NF-κB P65 in hypoxia/reoxygenation (H/R)-induced macrophages, RAW264.7 cells. Knockdown experiments demonstrated that IRAK1 and TRAF6 are two potential targets for reducing the release of proinflammatory cytokines. Moreover, co-culture assays indicated that miR-146a decreases the apoptosis of hepatocytes after H/R. In vivo administration of Ago-miR-146a, a stable version of miR-146a in vivo, protected against liver injury in mice after I/R via inactivation of the TLR signaling pathway. We conclude that miR-146a ameliorates liver ischemia/reperfusion injury in vivo and hypoxia/reoxygenation injury in vitro by directly suppressing IRAK1 and TRAF6.

SiO₂ nanoparticle-induced impairment of mitochondrial energy metabolism in hepatocytes directly and through a Kupffer cell-mediated pathway in vitro

The liver has been shown to be a primary target organ for SiO₂ nanoparticles in vivo, and may be highly susceptible to damage by these nanoparticles. However, until now, research focusing on the potential toxic effects of SiO₂ nanoparticles on mitochondria-associated energy metabolism in hepatocytes has been lacking. In this work, SiO₂ nanoparticles 20 nm in diameter were evaluated for their ability to induce dysfunction of mitochondrial energy metabolism. First, a buffalo rat liver (BRL) cell line was directly exposed to SiO₂ nanoparticles, which induced cytotoxicity and mitochondrial damage accompanied by decreases in mitochondrial dehydrogenase activity, mitochondrial membrane potential, enzymatic expression in the Krebs cycle, and activity of the mitochondrial respiratory chain complexes I, III and IV. Second, the role of rat-derived Kupffer cells was evaluated. The supernatants from Kupffer cells treated with SiO₂ nanoparticles were transferred to stimulate BRL cells. We observed that SiO₂ nanoparticles had the ability to activate Kupffer cells, leading to release of tumor necrosis factor-α, nitric oxide, and reactive oxygen species from these cells and subsequently to inhibition of mitochondrial respiratory chain complex I activity in BRL cells.

Assembly of human organs from stem cells to study liver disease

Recently, significant developments in the field of liver tissue engineering have raised new possibilities for the study of complex physiological and pathophysiological processes in vitro, as well as the potential to assemble entire organs for transplantation. Human-induced pluripotent stem cells have been differentiated into relatively functional populations of hepatic cells, and novel techniques to generate whole organ acellular three-dimensional scaffolds have been developed. In this review, we highlight the most recent advances in organ assembly regarding the development of liver tissue in vitro. We emphasize applications that involve multiple types of cells with a biomimetic spatial organization for which three-dimensional configurations could be used for drug development or to explain mechanisms of disease. We also discuss applications of liver organotypic surrogates and the challenges of translating the highly promising new field of tissue engineering into a proven platform for predicting drug metabolism and toxicity.

Synergistic effects of pyrrolizidine alkaloids and lipopolysaccharide on preterm delivery and intrauterine fetal death in mice

Preterm birth is the leading cause of death for newborn infants, and lipopolysaccharide (LPS) is commonly used to induce preterm delivery in experimental animals. Pyrrolizidine alkaloids (PAs) are widespread and occur in foods, herbs, and other plants. This study was to investigate the synergistic effects of LPS and two representative PAs, retrorsine (RTS) and monocrotaline (MCT), on preterm delivery and fetal death. Pregnant Kunming mice were divided into seven groups: control, RTS, MCT, LPS, RTS+LPS and two MCT+LPS groups. Animals in PAs and PAs+LPS groups were dosed intragastrically with RTS (10mg/kg) or MCT (20 mg/kg or 60 mg/kg) from gestational day (GD) 9 to GD16; mice given LPS were injected intraperitoneally with 150 μg/kg on GD15.5. Latencies to delivery, numbers of pups live and dead at birth were recorded, and livers of live neonates were collected. The incidence of LPS-induced preterm birth was enhanced in dams pretreated with MCT, and combination of PAs and LPS increased fetal mortality from PAs. The enhancement of LPS-induced preterm delivery and fetal demise in animals exposed chronically to PAs and other substances found in foods and beverages consumed widely by humans merits further focused investigation.

Current challenges and controversies in drug-induced liver injury

Current key challenges and controversies encountered in the identification of potentially hepatotoxic drugs and the assessment of drug-induced liver injury (DILI) are covered in this article. There is substantial debate over the classification of DILI itself, including the definition and validity of terms such as 'intrinsic' and 'idiosyncratic'. So-called idiosyncratic DILI is typically rare and requires one or more susceptibility factors in individuals. Consequently, it has been difficult to reproduce in animal models, which has limited the understanding of its underlying mechanisms despite numerous hypotheses. Advances in predictive models would also help to enable preclinical elimination of drug candidates and development of novel biomarkers. A small number of liver laboratory tests have been routinely used to help identify DILI, but their interpretation can be limited and confounded by multiple factors. Improved preclinical and clinical biomarkers are therefore needed to accurately detect early signals of liver injury, distinguish drug hepatotoxicity from other forms of liver injury, and differentiate mild from clinically important liver injury. A range of potentially useful biomarkers are emerging, although so far most have only been used preclinically, with only a few validated and used in the clinic for specific circumstances. Advances in the development of genomic biomarkers will improve the prediction and detection of hepatic injury in future. Establishing a definitive clinical diagnosis of DILI can be difficult, since it is based on circumstantial evidence by excluding other aetiologies and, when possible, identifying a drug-specific signature. DILI signals based on standard liver test abnormalities may be affected by underlying diseases such as hepatitis B and C, HIV and cancer, as well as the concomitant use of hepatotoxic drugs to treat some of these conditions. Therefore, a modified approach to DILI assessment is justified in these special populations and a suggested framework is presented that takes into account underlying disease when evaluating DILI signals in individuals. Detection of idiosyncratic DILI should, in some respects, be easier in the postmarketing setting compared with the clinical development programme, since there is a much larger and more varied patient population exposure over longer timeframes. However, postmarketing safety surveillance is currently limited by the quantity and quality of information available to make an accurate diagnosis, the lack of a control group and the rarity of cases. The pooling of multiple healthcare databases, which could potentially contain different types of patient data, is advised to address some of these deficiencies.

Kupffer cell-mediated hepatic injury induced by silica nanoparticles in vitro and in vivo

Silica nanoparticles (SiO₂ NPs) have been shown to exert cytotoxic effects in hepato-cytes and to cause liver injury. In the liver, Kupffer cells (KCs), as the resident macrophages, play an important role in the normal physiology and homeostasis of the liver. Nevertheless, few studies have attempted to clarify the role of KCs in hepatic injury induced by SiO₂ NPs. In this study, we treated Buffalo rat liver (BRL) cells with the supernatants of SiO₂ NP-stimulated KCs to determine KC-mediated hepatotoxicity and its underlying preliminary mechanism. We also examined the response of KCs and liver injury in vivo after the administration of SiO₂ NPs. The results showed that KCs stimulated by SiO₂ NPs release large amounts of reactive oxygen species, tumor necrosis factor-α and nitric oxide. After BRL cells were cultured with the supernatants of SiO₂ NP-stimulated KCs, the viability of BRL cells was reduced, and increases in aspartate aminotransferase and lactate dehydrogenase leakage were observed. Exposure to SiO₂ NPs in vivo caused KC hyperplasia, hepatic inflammation, and oxidative stress, which led to changes in the biochemical composition of the liver. These data suggest that SiO₂ NPs activate KCs to mediate hepatic injury and that the preliminary mechanism involves the release of bioactive substances from KCs.

A long-term three dimensional liver co-culture system for improved prediction of clinically relevant drug-induced hepatotoxicity

Drug-induced liver injury (DILI) is the major cause for liver failure and post-marketing drug withdrawals. Due to species-specific differences in hepatocellular function, animal experiments to assess potential liabilities of drug candidates can predict hepatotoxicity in humans only to a certain extent. In addition to animal experimentation, primary hepatocytes from rat or human are widely used for pre-clinical safety assessment. However, as many toxic responses in vivo are mediated by a complex interplay among different cell types and often require chronic drug exposures, the predictive performance of hepatocytes is very limited. Here, we established and characterized human and rat in vitro three-dimensional (3D) liver co-culture systems containing primary parenchymal and non-parenchymal hepatic cells. Our data demonstrate that cells cultured on a 3D scaffold have a preserved composition of hepatocytes, stellate, Kupffer and endothelial cells and maintain liver function for up to 3months, as measured by the production of albumin, fibrinogen, transferrin and urea. Additionally, 3D liver co-cultures maintain cytochrome P450 inducibility, form bile canaliculi-like structures and respond to inflammatory stimuli. Upon incubation with selected hepatotoxicants including drugs which have been shown to induce idiosyncratic toxicity, we demonstrated that this model better detected in vivo drug-induced toxicity, including species-specific drug effects, when compared to monolayer hepatocyte cultures. In conclusion, our results underline the importance of more complex and long lasting in vitro cell culture models that contain all liver cell types and allow repeated drug-treatments for detection of in vivo-relevant adverse drug effects.

In vitro models for liver toxicity testing

Over the years, various liver-derived in vitro model systems have been developed to enable investigation of the potential adverse effects of chemicals and drugs. Liver tissue slices, isolated microsomes, perfused liver, immortalized cell lines, and primary hepatocytes have been used extensively. Immortalized cell lines and primary isolated liver cells are currently most widely used in vitro models for liver toxicity testing. Limited throughput, loss of viability, and decreases in liver-specific functionality and gene expression are common shortcomings of these models. Recent developments in the field of in vitro hepatotoxicity include three-dimensional tissue constructs and bioartificial livers, co-cultures of various cell types with hepatocytes, and differentiation of stem cells into hepatic lineage-like cells. In an attempt to provide a more physiological environment for cultured liver cells, some of the novel cell culture systems incorporate fluid flow, micro-circulation, and other forms of organotypic microenvironments. Co-cultures aim to preserve liver-specific morphology and functionality beyond those provided by cultures of pure parenchymal cells. Stem cells, both embryonic- and adult tissue-derived, may provide a limitless supply of hepatocytes from multiple individuals to improve reproducibility and enable testing of the individual-specific toxicity. This review describes various traditional and novel in vitro liver models and provides a perspective on the challenges and opportunities afforded by each individual test system.

Organotypic liver culture models: meeting current challenges in toxicity testing

Prediction of chemical-induced hepatotoxicity in humans from in vitro data continues to be a significant challenge for the pharmaceutical and chemical industries. Generally, conventional in vitro hepatic model systems (i.e. 2-D static monocultures of primary or immortalized hepatocytes) are limited by their inability to maintain histotypic and phenotypic characteristics over time in culture, including stable expression of clearance and bioactivation pathways, as well as complex adaptive responses to chemical exposure. These systems are less than ideal for longer-term toxicity evaluations and elucidation of key cellular and molecular events involved in primary and secondary adaptation to chemical exposure, or for identification of important mediators of inflammation, proliferation and apoptosis. Progress in implementing a more effective strategy for in vitro-in vivo extrapolation and human risk assessment depends on significant advances in tissue culture technology and increasing their level of biological complexity. This article describes the current and ongoing need for more relevant, organotypic in vitro surrogate systems of human liver and recent efforts to recreate the multicellular architecture and hemodynamic properties of the liver using novel culture platforms. As these systems become more widely used for chemical and drug toxicity testing, there will be a corresponding need to establish standardized testing conditions, endpoint analyses and acceptance criteria. In the future, a balanced approach between sample throughput and biological relevance should provide better in vitro tools that are complementary with animal testing and assist in conducting more predictive human risk assessment.

LIVER TISSUE MODEL FOR DRUG TOXICITY SCREENING

Understanding the mechanisms involved in the biotransformation of new drugs and their toxicological implications is important for drug development. In this regard, a lot of effort has been put into research to recreate the liver tissue in the laboratory for the purpose of drug screening. This has also helped to minimize the use of laboratory animal and reduce incidence of post-market withdrawal of drugs. Despite the progress made so far, cell source remains a major limitation since primary human hepatocytes are scarce and the various cell alternatives do not express all the genes found in the normal liver. In terms of tissue construct, there is a current shift to 3D models since the cell–cell interactions found in the 3D configuration enhance the morphology and function of hepatocytes. Furthermore, the engineered tissue's performance can be optimized by cocultures, perfusion-based systems, and the use of scaffolds. Nanotechnology seems promising in the field of tissue engineering, as it has been proven that cell–matrix interactions at the nano level can influence greatly on the outcome of the tissue. The review explores the various cell sources, the 3D model, flow-based systems, cocultures, and nanoscaffolds use in hepatocytes in vitro drug testing

Effects of CYP inhibitors on precocene I metabolism and toxicity in rat liver slices

We present a comprehensive in vitro approach to assessing metabolism-mediated hepatotoxicity using male Sprague-Dawley rat liver slices incubated with the well characterized hepatotoxicant, precocene I, and inhibitors of cytochrome P450 (CYP) enzymes. This approach combines liquid chromatography mass spectrometry (LC MS) detection methods with multiple toxicity endpoints to enable identification of critical metabolic pathways for hepatotoxicity. The incubations were performed in the absence and presence of the non-specific CYP inhibitor, 1-aminobenzotriazole (ABT) and isoform-specific inhibitors. The metabolite profile of precocene I in rat liver slices shares some features of the in vivo profile, but also had a major difference in that epoxide dihydrodiol hydrolysis products were not observed to a measurable extent. As examples of our liver slice metabolite identification procedure, a minor glutathione adduct and previously unreported 7-O-desmethyl and glucuronidated metabolites of precocene I are reported. Precocene I induced hepatocellular necrosis in a dose- and time-dependent manner. ABT decreased the toxicity of precocene I, increased exposure to parent compound, and decreased metabolite levels in a dose-dependent manner. Of the isoform-specific CYP inhibitors tested for an effect on the precocene I metabolite profile, only tranylcypromine was noticeably effective, indicating a role of CYPs 2A6, 2C9, 2Cl9, and 2E1. With respect to toxicity, the order of CYP inhibitor effectiveness was ABT>diethyldithiocarbamate∼tranylcypromine>ketoconazole. Furafylline and sulfaphenazole had no effect, while quinidine appeared to augment precocene I toxicity. These results suggest that rat liver slices do not reproduce the reported in vivo biotransformation of precocene I and therefore may not be an appropriate model for precocene I metabolism. However, these results provide an example of how small molecule manipulation of CYP activity in an in vitro model can be used to confirm metabolism-mediated toxicity.

Liver tissue engineering in the evaluation of drug safety

Assessment of drug-liver interactions is an integral part of predicting the safety profile of new drugs. Existing model systems range from in vitro cell culture models to FDA-mandated animal tests. Data from these models often fail, however, to predict human liver toxicity, resulting in costly failures of clinical trials. In vitro screens based on cultured hepatocytes are now commonly used in early stages of development, but many toxic responses in vivo seem to be mediated by a complex interplay among several different cell types. We discuss some of the evolving trends in liver cell culture systems applied to drug safety assessment and describe an experimental model that captures complex liver physiology through incorporation of heterotypic cell-cell interactions, 3D architecture and perfused flow. We demonstrate how heterotypic interactions in this system can be manipulated to recreate an inflammatory environment and apply the model to test compounds that potentially exhibit idiosyncratic drug toxicity. Finally, we provide a perspective on how the range of existing and emerging in vitro liver culture approaches, from simple to complex, might serve needs across the range of stages in drug discovery and development, including applications in molecular therapeutics.

Sulindac metabolism and synergy with tumor necrosis factor-alpha in a drug-inflammation interaction model of idiosyncratic liver injury

Sulindac (SLD) is a nonsteroidal anti-inflammatory drug (NSAID) that has been associated with a greater incidence of idiosyncratic hepatotoxicity in human patients than other NSAIDs. In previous studies, cotreatment of rats with SLD and a modestly inflammatory dose of lipopolysaccharide (LPS) led to liver injury, whereas neither SLD nor LPS alone caused liver damage. In studies presented here, further investigation of this animal model revealed that the concentration of tumor necrosis factor-alpha (TNF-alpha) in plasma was significantly increased by LPS at 1 h, and SLD enhanced this response. Etanercept, a soluble TNF-alpha receptor, reduced SLD/LPS-induced liver injury, suggesting a role for TNF-alpha. SLD metabolites in plasma and liver were determined by LC/MS/MS. Cotreatment with LPS did not increase the concentrations of SLD or its metabolites, excluding the possibility that LPS contributed to liver injury through enhanced exposure to SLD or its metabolites. The cytotoxicities of SLD and its sulfide and sulfone metabolites were compared in primary rat hepatocytes and HepG2 cells; SLD sulfide was more toxic in both types of cells than SLD or SLD sulfone. TNF-alpha augmented the cytotoxicity of SLD sulfide in primary hepatocytes and HepG2 cells. These results suggest that TNF-alpha can enhance SLD sulfide-induced hepatotoxicity, thereby contributing to liver injury in SLD/LPS-cotreated rats.

Increased sensitivity for troglitazone-induced cytotoxicity using a human in vitro co-culture model

Drug-induced hepatotoxicity is a major reason for withdrawal of drugs from development as well as from the market. A major problem predicting hepatotoxicity is the lack of suitable predictive in vitro system. Drug-induced hepatotoxicity is usually associated with the recruitment of immune cells to the liver accelerating an inflammatory response often initiated by activation of the Kupffer cells. In order to evaluate whether the introduction of inflammatory cells could increase the sensitivity for drug-induced cytotoxicity we developed an in vitro co-culture system based on two human cell lines; a hepatoma (Huh-7) and monocytic (THP-1) cell line. As model drugs we chose two peroxisome proliferator activated receptor gamma (PPAR gamma) agonists, the hepatotoxic troglitazone and the non-hepatotoxic rosiglitazone. In the co-cultures, troglitazone caused an enhanced cytotoxicity as compared to single cultures of either cell line, whereas little cytotoxicity was seen after treatment with rosiglitazone. Troglitazone treatment increased gene expression of pro-inflammatory mediators and stress-related genes in both cell types, which in general was more pronounced in co-cultures than in single cell cultures. Based on these results we suggest that co-cultures of human hepatoma cells and monocytes might provide an important in vitro system for better prediction of cytotoxicity mediated by potential hepatotoxins.

Synergistic drug-cytokine induction of hepatocellular death as an in vitro approach for the study of inflammation-associated idiosyncratic drug hepatotoxicity

Idiosyncratic drug hepatotoxicity represents a major problem in drug development due to inadequacy of current preclinical screening assays, but recently established rodent models utilizing bacterial LPS co-administration to induce an inflammatory background have successfully reproduced idiosyncratic hepatotoxicity signatures for certain drugs. However, the low-throughput nature of these models renders them problematic for employment as preclinical screening assays. Here, we present an analogous, but high-throughput, in vitro approach in which drugs are administered to a variety of cell types (primary human and rat hepatocytes and the human HepG2 cell line) across a landscape of inflammatory contexts containing LPS and cytokines TNF, IFN gamma, IL-1 alpha, and IL-6. Using this assay, we observed drug-cytokine hepatotoxicity synergies for multiple idiosyncratic hepatotoxicants (ranitidine, trovafloxacin, nefazodone, nimesulide, clarithromycin, and telithromycin) but not for their corresponding non-toxic control compounds (famotidine, levofloxacin, buspirone, and aspirin). A larger compendium of drug-cytokine mix hepatotoxicity data demonstrated that hepatotoxicity synergies were largely potentiated by TNF, IL-1 alpha, and LPS within the context of multi-cytokine mixes. Then, we screened 90 drugs for cytokine synergy in human hepatocytes and found that a significantly larger fraction of the idiosyncratic hepatotoxicants (19%) synergized with a single cytokine mix than did the non-hepatotoxic drugs (3%). Finally, we used an information theoretic approach to ascertain especially informative subsets of cytokine treatments for most highly effective construction of regression models for drug- and cytokine mix-induced hepatotoxicities across these cell systems. Our results suggest that this drug-cytokine co-treatment approach could provide a useful preclinical tool for investigating inflammation-associated idiosyncratic drug hepatotoxicity.

Hepatotoxic interaction of sulindac with lipopolysaccharide: role of the hemostatic system

Sulindac (SLD) is a nonsteroidal anti-inflammatory drug (NSAID) that has been associated with a greater incidence of idiosyncratic hepatotoxicity in human patients than other NSAIDs. One hypothesis regarding idiosyncratic adverse drug reactions is that interaction of a drug with a modest inflammatory episode precipitates liver injury. In this study, we tested the hypothesis that lipopolysaccharide (LPS) interacts with SLD to cause liver injury in rats. SLD (50 mg/kg) or its vehicle was administered to rats by gavage 15.5 h before LPS (8.3 x 10(5) endotoxin unit/kg) or its saline vehicle (i.v.). Thirty minutes after LPS treatment, SLD or vehicle administration was repeated. Rats were killed at various times after treatment, and serum, plasma, and liver samples were taken. Neither SLD nor LPS alone caused liver injury. Cotreatment with SLD/LPS led to increases in serum biomarkers of both hepatocellular injury and cholestasis. Histological evidence of liver damage was found only after SLD/LPS cotreatment. As a result of activation of hemostasis induced by SLD/LPS cotreatment, fibrin and hypoxia were present in liver tissue before the onset of hepatotoxicity. Heparin treatment reduced hepatic fibrin deposition and hypoxia and protected against liver injury induced by SLD/LPS cotreatment. These results indicate that cotreatment with nontoxic doses of LPS and SLD causes liver injury in rats, and this could serve as a model of human idiosyncratic liver injury. The hemostatic system is activated by SLD/LPS cotreatment and plays an important role in the development of SLD/LPS-induced liver injury.