Co-culture of Hepatocytes and Kupffer Cells as an In Vitro Model of Inflammation and Drug-Induced Hepatotoxicity

Vagus nerve modulates acute-on-chronic liver failure progression via CXCL9

BACKGROUND

Hepatic inflammatory cell accumulation and the subsequent systematic inflammation drive acute-on-chronic liver failure (ACLF) development. Previous studies showed that the vagus nerve exerts anti-inflammatory activity in many inflammatory diseases. Here, we aimed to identify the key molecule mediating the inflammatory process in ACLF and reveal the neuroimmune communication arising from the vagus nerve and immunological disorders of ACLF.

METHODS

Proteomic analysis was performed and validated in ACLF model mice or patients, and intervention animal experiments were conducted using neutralizing antibodies. PNU-282987 (acetylcholine receptor agonist) and vagotomy were applied for perturbing vagus nerve activity. Single-cell RNA sequencing (scRNA-seq), flow cytometry, immunohistochemical and immunofluorescence staining, and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) technology were used for in vivo or in vitro mechanistic studies.

RESULTS

The unbiased proteomics identified C-X-C motif chemokine ligand 9 (CXCL9) as the greatest differential protein in the livers of mice with ACLF and its relation to the systematic inflammation and mortality were confirmed in patients with ACLF. Interventions on CXCL9 and its receptor C-X-C chemokine receptor 3 (CXCR3) improved liver injury and decreased mortality of ACLF mice, which were related to the suppressing of hepatic immune cells' accumulation and activation. Vagus nerve stimulation attenuated while vagotomy aggravated the expression of CXCL9 and the severity of ACLF. Blocking CXCL9 and CXCR3 ameliorated liver inflammation and increased ACLF-associated mortality in ACLF mice with vagotomy. scRNA-seq revealed that hepatic macrophages served as the major source of CXCL9 in ACLF and were validated by immunofluorescence staining and flow cytometry analysis. Notably, the expression of CXCL9 in macrophages was modulated by vagus nerve-mediated cholinergic signaling.

CONCLUSIONS

Our novel findings highlighted that the neuroimmune communication of the vagus nerve-macrophage-CXCL9 axis contributed to ACLF development. These results provided evidence for neuromodulation as a promising approach for preventing and treating ACLF.

Investigation on ABCC6-Deficient Human Hepatocytes Generated by CRISPR-Cas9 Genome Editing

Patients affected by the rare disease pseudoxanthoma elasticum (PXE) exhibit the calcification of elastic fibers in ocular, dermal, and vascular tissues. These symptoms are triggered by mutations in the ATP-binding cassette transporter subfamily C member 6 (ABCC6), whose substrate remains unknown. Interestingly, ABCC6 is predominantly expressed in the liver tissue, leading to the hypothesis that PXE is a metabolic disorder. We developed a genome-editing system targeting ABCC6 in human immortalized hepatocytes (HepIms) for further investigations. The HepIms were transfected with an ABCC6-specific clustered regulatory interspaced short palindromic repeat (CRISPR-Cas9) genome-editing plasmid, resulting in the identification of a heterozygous (htABCC6HepIm) and a compound heterozygous (chtABCC6HepIm) clone. These clones were analyzed for key markers associated with the PXE pathobiochemistry. Hints of impaired lipid trafficking, defects in the extracellular matrix remodeling, the induction of calcification inhibitor expression, and the down regulation of senescence and inflammatory markers in ABCC6-deficienct HepIms were found. Our ABCC6 knock-out model of HepIms provides a valuable tool for studying the metabolic characteristics of PXE in vitro. The initial analysis of the clones mirrors various features of the PXE pathobiochemistry and provides an outlook on future research approaches.

A new human autologous hepatocyte/macrophage co-culture system that mimics drug-induced liver injury-like inflammation

The development of in vitro hepatocyte cell culture systems is crucial for investigating drug-induced liver injury (DILI). One prerequisite for monitoring DILI related immunologic reactions is the extension of primary human hepatocyte (PHH) cultures towards the inclusion of macrophages. Therefore, we developed and characterized an autologous co-culture system of PHH and primary human hepatic macrophages (hepM) (CoC1). We compared CoC1 with a co-culture of the same PHH batch + M0 macrophages derived from THP1 cells (CoC2) in order to represent a donor independent macrophage reaction. Then, we treated the mono- and co-cultures with drugs that cause DILI-menadione (MEN, 1 or 10 µM, 3 h), diclofenac (DIC, 0.5 or 5 mM, 6 h), or acetaminophen (APAP, 0.5 or 5 mM, 6 h)-and assessed culture stability, cell activity, macrophage differentiation, cytokine production and cell viability. Without drug treatment, CoC1 was the most stable over a culture time of up to 60 h. Cytokine array analysis revealed a proinflammatory profile of PHH mono-cultures due to isolation stress but showed different influences of hepM and M0 on the cytokine profile in the co-cultures. MEN, DIC and APAP treatment led to donor-dependent signs of cell stress and toxicity. HepM can either promote or reduce the DILI effects donor dependently in CoC1. CoC2 are slightly less sensitive than CoC1 in representing DILI. In summary, we present a new autologous co-culture system that can mimic DILI in a donor-dependent manner. This cellular system could be useful for new drug testing strategies and reducing animal testing.

Exacerbated hepatotoxicity in in vivo and in vitro non-alcoholic fatty liver models by biomineralized copper sulfide nanoparticles

Copper sulfide nanoparticles (NPs) synthesized through biomineralization have significant commercial potential as photothermal agents, while the safety evaluation of these NPs, especially for patients with non-alcoholic fatty liver (NAFL), remains insufficient. To explore the differential hepatotoxicity of copper sulfide NPs in NAFL conditions, we synthesized large-sized (LNPs, 15.1 nm) and small-sized (SNPs, 3.5 nm) BSA@Cu2-xS NPs. A NAFL rat model fed with high fat diet (HFD) was successfully established for a 14-day subacute toxicity study by daily repeated administration of BSA@Cu2-xS NPs. Our findings from serum biochemistry and histopathological examinations revealed that copper sulfide at both sizes NPs induced more pronounced liver damage in NAFL rats than rats fed with normal diet. Transcriptome sequencing analysis showed that LNPs activated inflammation and DNA damage repair pathways in the livers of NAFL rats, while SNPs displayed minimal inflammation. A three-dimensional spheroid model of NAFL developed in our in-house cell spheroid culture honeycomb chips demonstrated that LNPs, but not SNPs, triggered a distinct release of inflammatory factors and increased reactive oxygen species through Kupffer cells. These results highlight that NAFL condition exacerbated the hepatotoxicity of BSA@Cu2-xS NPs, with SNPs emerging as safer photothermal agents compared to LNPs, suggesting superior potential for clinical applications.

Sodium-glucose cotransporter 2 inhibitors ameliorate ER stress-induced pro-inflammatory cytokine expression by inhibiting CD36 in NAFLD progression in vitro

Sodium-dependent glucose cotransporter-2 (SGLT2) inhibitors, antidiabetic drugs that reduce blood sugar levels by inhibiting glucose reabsorption in the renal proximal tubules, also ameliorate nonalcoholic fatty liver disease (NAFLD). This study aimed to examine the effects of SGLT2 inhibition on hepatic steatosis and nonalcoholic steatohepatitis (NASH) using an in vitro model of NAFLD progression. HepG2 cells and a coculture of Hepa1c1c7 and Raw 264.7 cells were treated with 400 μM palmitic acid (PA), followed by treatment with or without 10 μM empagliflozin and dapagliflozin. In HepG2 cells, PA increased hepatic lipid accumulation, the expression of pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β), exocytosis mediators (VAMP3 and SNAP23), and ER stress markers (GRP78, PERK, IRE1α, ATF6, ATF4, and CHOP), and the gene and protein expression of CD36. SGLT2 inhibitors reversed the effects of PA. SGLT2 inhibition via siRNA reduced proinflammatory-cytokine gene expression in thapsigargin-treated HepG2 cells. Transfection with CD36 siRNA reversed the elevated ATF4 and CHOP expression in PA-treated HepG2 cells. SGLT2 inhibition via an SGTL2 inhibitor and SGLT2 siRNA reduced CD36, Tnf-α, Il-6, Il-1β, Vamp2, Snap23, Atf4, and Chop expression in the PA-treated Hepa1c1c7-Raw 264.7 cell coculture and suppressed Tnf-α release in the Hepa1c1c7-Raw 264.7 cell coculture treated with lipopolysaccharide and PA. These findings indicate that SGLT2 inhibitors inhibited NAFLD progression by reducing hepatic lipid accumulation and inflammation.

The Long-Term Impact of Polysaccharide-Coated Iron Oxide Nanoparticles on Inflammatory-Stressed Mice

Since iron oxide nanoparticles (IONPs) are expected to be important tools in medical care, patients with inflammatory diseases will be increasingly exposed to IONPs in the future. Here, we assessed the short- and long-term impact of polysaccharide (PS)-coated IONPs on mice with persistent systemic inflammation. To this end, PS-IONPs were synthetized by a core-shell method. Mice were regularly injected with sterile zymosan. PS-IONPs were administered intravenously. At specific nanoparticle injection post-observation times, the organ iron concentration was determined via atomic absorption spectrometry, the expression of NF-κB-related proteins using SDS-PAGE and immunoblotting, as well as body weight and haemograms. Finally, the mediator secretion in blood plasma was analysed using multiplexed ELISA. Our data show that PS-IONPs induce short-term changes of iron levels in distinct organs and of NF-κB p65 and p50, p100, COX-2s, and Bcl-2 protein expression in the liver of inflammatory stressed mice. In the long term, there was an attenuated expression of several NF-κB-related proteins and attenuated features of inflammatory-based anaemia in blood. PS-IONPs weakly influenced the blood cytokine levels. PS-IONPs are biocompatible, but given their short-term pro-inflammatory impact, they should prospectively be applied with caution in patients with inflammatory diseases of the liver.

hiPSC-derived macrophages improve drug sensitivity and selectivity in a macrophage-incorporating organoid culture model

Accurate simulation of different cell type interactions is crucial for physiological and precisein vitrodrug testing. Human tissue-resident macrophages are critical for modulating disease conditions and drug-induced injuries in various tissues; however, their limited availability has hindered their use inin vitromodeling. Therefore, this study aimed to create macrophage-containing organoid co-culture models by directly incorporating human-induced pluripotent stem cell (hiPSC)-derived pre-macrophages into organoid and scaffold cell models. The fully differentiated cells in these organoids exhibited functional characteristics of tissue-resident macrophages with enriched pan-macrophage markers and the potential for M1/M2 subtype specialization upon cytokine stimulation. In a hepatic organoid model, the integrated macrophages replicated typical intrinsic properties, including cytokine release, polarization, and phagocytosis, and the co-culture model was more responsive to drug-induced liver injury than a macrophage-free model. Furthermore, alveolar organoid models containing these hiPSC-derived macrophages also showed increased drug and chemical sensitivity to pulmonary toxicants. Moreover, 3D adipocyte scaffold models incorporating macrophages effectively simulated in vivo insulin resistance observed in adipose tissue and showed improved insulin sensitivity on exposure to anti-diabetic drugs. Overall, the findings demonstrated that incorporating hiPSC-derived macrophages into organoid culture models resulted in more physiological and sensitivein vitrodrug evaluation and screening systems.

Exosomes regulate SIRT3-related autophagy by delivering miR-421 to regulate macrophage polarization and participate in OSA-related NAFLD

PURPOSE

To analyze the role of and mechanism underlying obstructive sleep apnea (OSA)-derived exosomes in inducing non-alcoholic fatty liver (NAFLD).

METHODS

The role of OSA-derived exosomes was analyzed in inducing hepatocyte fat accumulation in mice models both in vivo and in vitro.

RESULTS

OSA-derived exosomes caused fat accumulation and macrophage activation in the liver tissue. These exosomes promoted fat accumulation; steatosis was more noticeable in the presence of macrophages. Macrophages could internalize OSA-derived exosomes, which promoted macrophage polarization to the M1 type. Moreover, it inhibited sirtuin-3 (SIRT3)/AMP-activated protein kinase (AMPK) and autophagy and promoted the activation of nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasomes. The use of 3-methyladenine (3-MA) to inhibit autophagy blocked NLRP3 inflammasome activation and inhibited the M1 polarization of macrophages. miR-421 targeting inhibited SIRT3 protein expression in the macrophages. miR-421 was significantly increased in OSA-derived exosomes. Additionally, miR-421 levels were increased in OSA + NAFLD mice- and patient-derived exosomes. In the liver tissues of OSA and OSA + NAFLD mice, miR-421 displayed similar co-localization with the macrophages. Intermittent hypoxia-induced hepatocytes deliver miR-421 to the macrophages via exosomes to inhibit SIRT3, thereby participating in macrophage M1 polarization. After OSA and NAFLD modeling in miR-421-/- mice, liver steatosis and M1 polarization were significantly reduced. Additionally, in the case of miR-421 knockout, the inhibitory effects of OSA-derived exosomes on SIRT3 and autophagy were significantly alleviated. Furthermore, their effects on liver steatosis and macrophage M1 polarization were significantly reduced.

CONCLUSIONS

OSA promotes the delivery of miR-421 from the hepatocytes to macrophages. Additionally, it promotes M1 polarization by regulating the SIRT3/AMPK-autophagy pathway, thereby causing NAFLD.

In Vitro Hepatotoxicity of Routinely Used Opioids and Sedative Drugs

A hepatocyte cell line was used to determine the hepatotoxicity of sedatives and opioids, as the hepatotoxicity of these drugs has not yet been well characterized. This might pose a threat, especially to critically ill patients, as they often receive high cumulative doses for daily analgosedation and often already have impaired liver function due to an underlying disease or complications during treatment. A well-established biosensor based on HepG2/C3A cells was used for the determination of the hepatotoxicity of commonly used sedatives and opioids in the intensive care setting (midazolam, propofol, s-ketamin, thiopental, fentanyl, remifentanil, and sufentanil). The incubation time was 2 × 3 days with clinically relevant (Cmax) and higher concentrations (C5× and C10×) of each drug in cell culture medium or human plasma. Afterward, we measured the cell count, vitality, lactate dehydrogenase (LDH), mitochondrial dehydrogenase activity, cytochrome P 450 1A2 (CYP1A2), and albumin synthesis. All tested substances reduced the viability of hepatocyte cells, but sufentanil and remifentanil showed more pronounced effects. The cell count was diminished by sufentanil in both the medium and plasma and by remifentanil only in plasma. Sufentanil and remifentanil also led to higher values of LDH in the cell culture supernatant. A reduction of mitochondrial dehydrogenase activity was seen with the use of midazolam and s-ketamine. Microalbumin synthesis was reduced in plasma after its incubation with higher concentrations of sufentanil and remifentanil. Remifentanil and s-ketamine reduced CYP1A2 activity, while propofol and thiopental increased it. Our findings suggest that none of the tested sedatives and opioids have pronounced hepatotoxicity. Sufentanil, remifentanil, and s-ketamine showed moderate hepatotoxic effects in vitro. These drugs should be given with caution to patients vulnerable to hepatotoxic drugs, e.g., patients with pre-existing liver disease or liver impairment as part of their underlying disease (e.g., hypoxic hepatitis or cholestatic liver dysfunction in sepsis). Further studies are indicated for this topic, which may use more complex cell culture models and global pharmacovigilance reports, addressing the limitation of the used cell model: HepG2/C3A cells have a lower metabolic capacity due to their low levels of CYP enzymes compared to primary hepatocytes. However, while the test model is suitable for parental substances, it is not for toxicity testing of metabolites.

Vascularized Hepatocellular Carcinoma on a Chip to Control Chemoresistance through Cirrhosis, Inflammation and Metabolic Activity

Understanding the effects of inflammation and cirrhosis on the regulation of drug metabolism during the progression of hepatocellular carcinoma (HCC) is critical for developing patient-specific treatment strategies. In this work, we created novel three-dimensional vascularized HCC-on-a-chips (HCCoC), composed of HCC, endothelial, stellate, and Kupffer cells tuned to mimic normal or cirrhotic liver stiffness. HCC inflammation was controlled by tuning Kupffer macrophage numbers, and the impact of cytochrome P450-3A4 (CYP3A4) was investigated by culturing HepG2 HCC cells transfected with CYP3A4 to upregulate expression from baseline. This model allowed for the simulation of chemotherapeutic delivery methods such as intravenous injection and transcatheter arterial chemoembolization (TACE). We showed that upregulation of metabolic activity, incorporation of cirrhosis and inflammation, increase vascular permeability due to upregulated inflammatory cytokines leading to significant variability in chemotherapeutic treatment efficacy. Specifically, we show that further modulation of CYP3A4 activity of HCC cells by TACE delivery of doxorubicin provides an additional improvement to treatment response and reduces chemotherapy-associated endothelial porosity increase. The HCCoCs were shown to have utility in uncovering the impact of the tumor microenvironment (TME) during cancer progression on vascular properties, tumor response to therapeutics, and drug delivery strategies.

Microphysiological Models for Mechanistic-Based Prediction of Idiosyncratic DILI

Drug-induced liver injury (DILI) is a major contributor to high attrition rates among candidate and market drugs and a key regulatory, industry, and global health concern. While acute and dose-dependent DILI, namely, intrinsic DILI, is predictable and often reproducible in preclinical models, the nature of idiosyncratic DILI (iDILI) limits its mechanistic understanding due to the complex disease pathogenesis, and recapitulation using in vitro and in vivo models is extremely challenging. However, hepatic inflammation is a key feature of iDILI primarily orchestrated by the innate and adaptive immune system. This review summarizes the in vitro co-culture models that exploit the role of the immune system to investigate iDILI. Particularly, this review focuses on advancements in human-based 3D multicellular models attempting to supplement in vivo models that often lack predictability and display interspecies variations. Exploiting the immune-mediated mechanisms of iDILI, the inclusion of non-parenchymal cells in these hepatoxicity models, namely, Kupffer cells, stellate cells, dendritic cells, and liver sinusoidal endothelial cells, introduces heterotypic cell-cell interactions and mimics the hepatic microenvironment. Additionally, drugs recalled from the market in the US between 1996-2010 that were studies in these various models highlight the necessity for further harmonization and comparison of model characteristics. Challenges regarding disease-related endpoints, mimicking 3D architecture with different cell-cell contact, cell source, and the underlying multi-cellular and multi-stage mechanisms are described. It is our belief that progressing our understanding of the underlying pathogenesis of iDILI will provide mechanistic clues and a method for drug safety screening to better predict liver injury in clinical trials and post-marketing.

An Immunological Perspective on the Mechanism of Drug Induced Liver Injury: Focused on Drugs for Treatment of Hepatocellular Carcinoma and Liver Transplantation

The liver is frequently exposed to potentially toxic materials, and it is the primary site of clearance of foreign agents, along with many innate and adaptive immune cells. Subsequently, drug induced liver injury (DILI), which is caused by medications, herbs, and dietary supplements, often occurs and has become an important issue in liver diseases. Reactive metabolites or drug-protein complexes induce DILI via the activation of various innate and adaptive immune cells. There has been a revolutionary development of treatment drugs for hepatocellular carcinoma (HCC) and liver transplantation (LT), including immune checkpoint inhibitors (ICIs), that show high efficacy in patients with advanced HCC. Along with the high efficacy of novel drugs, DILI has become a pivotal issue in the use of new drugs, including ICIs. This review demonstrates the immunological mechanism of DILI, including the innate and adaptive immune systems. Moreover, it aims to provide drug treatment targets, describe the mechanisms of DILI, and detail the management of DILI caused by drugs for HCC and LT.

Human Liver Organoid Models for Assessment of Drug Toxicity at the Preclinical Stage

The hepatotoxicity of drugs is one of the leading causes of drug withdrawal from the pharmaceutical market and high drug attrition rates. Currently, the commonly used hepatocyte models include conventional hepatic cell lines and animal models, which cannot mimic human drug-induced liver injury (DILI) due to poorly defined dose-response relationships and/or lack of human-specific mechanisms of toxicity. In comparison to 2D culture systems from different cell sources such as primary human hepatocytes and hepatomas, 3D organoids derived from an inducible pluripotent stem cell (iPSC) or adult stem cells are promising accurate models to mimic organ behavior with a higher level of complexity and functionality owing to their ability to self-renewal. Meanwhile, the heterogeneous cell composition of the organoids enables metabolic and functional zonation of hepatic lobule important in drug detoxification and has the ability to mimic idiosyncratic DILI as well. Organoids having higher drug-metabolizing enzyme capacities can culture long-term and be combined with microfluidic-based technologies such as organ-on-chips for a more precise representation of human susceptibility to drug response in a high-throughput manner. However, there are numerous limitations to be considered about this technology, such as enough maturation, differences between protocols and high cost. Herein, we first reviewed the current preclinical DILI assessment tools and looked at the organoid technology with respect to in vitro detoxification capacities. Then we discussed the clinically applicable DILI assessment markers and the importance of liver zonation in the next generation organoid- based DILI models.

Performance assessment and economic analysis of a human Liver-Chip for predictive toxicology

BACKGROUND

Conventional preclinical models often miss drug toxicities, meaning the harm these drugs pose to humans is only realized in clinical trials or when they make it to market. This has caused the pharmaceutical industry to waste considerable time and resources developing drugs destined to fail. Organ-on-a-Chip technology has the potential improve success in drug development pipelines, as it can recapitulate organ-level pathophysiology and clinical responses; however, systematic and quantitative evaluations of Organ-Chips' predictive value have not yet been reported.

METHODS

870 Liver-Chips were analyzed to determine their ability to predict drug-induced liver injury caused by small molecules identified as benchmarks by the Innovation and Quality consortium, who has published guidelines defining criteria for qualifying preclinical models. An economic analysis was also performed to measure the value Liver-Chips could offer if they were broadly adopted in supporting toxicity-related decisions as part of preclinical development workflows.

RESULTS

Here, we show that the Liver-Chip met the qualification guidelines across a blinded set of 27 known hepatotoxic and non-toxic drugs with a sensitivity of 87% and a specificity of 100%. We also show that this level of performance could generate over $3 billion annually for the pharmaceutical industry through increased small-molecule R&D productivity.

CONCLUSIONS

The results of this study show how incorporating predictive Organ-Chips into drug development workflows could substantially improve drug discovery and development, allowing manufacturers to bring safer, more effective medicines to market in less time and at lower costs.

Inflammatory signaling on cytochrome P450-mediated drug metabolism in hepatocytes

Cytochrome P450 (CYP450) enzymes are membrane-bound blood proteins that are vital to drug detoxification, cell metabolism, and homeostasis. CYP450s belonging to CYP families 1-3 are responsible for nearly 80% of oxidative metabolism and complete elimination of approximately 50% of all common clinical drugs in humans liver hepatocytes. CYP450s can affect the body's response to drugs by altering the reaction, safety, bioavailability, and toxicity. They can also regulate metabolic organs and the body's local action sites to produce drug resistance through altered drug metabolism. Genetic polymorphisms in the CYP gene alone do not explain ethnic and individual differences in drug efficacy in the context of complex diseases. The purpose of this review is to summarize the impact of new inflammatory-response signaling pathways on the activity and expression of CYP drug-metabolizing enzymes. Included is a summary of recent studies that have identified drugs with the potential to regulate drug-metabolizing enzyme activity. Our goal is to inspire the development of clinical drug treatment processes that consider the impact of the inflammatory environment on drug treatment, as well as provide research targets for those studying drug metabolism.

Resident Macrophages and Their Potential in Cardiac Tissue Engineering

Many facets of tissue engineered models aim at understanding cellular mechanisms to recapitulate in vivo behavior, to study and mimic diseases for drug interventions, and to provide a better understanding toward improving regenerative medicine. Recent and rapid advances in stem cell biology, material science and engineering, have made the generation of complex engineered tissues much more attainable. One such tissue, human myocardium, is extremely intricate, with a number of different cell types. Recent studies have unraveled cardiac resident macrophages as a critical mediator for normal cardiac function. Macrophages within the heart exert phagocytosis and efferocytosis, facilitate electrical conduction, promote regeneration, and remove cardiac exophers to maintain homeostasis. These findings underpin the rationale of introducing macrophages to engineered heart tissue (EHT), to more aptly capitulate in vivo physiology. Despite the lack of studies using cardiac macrophages in vitro, there is enough evidence to accept that they will be key to making EHTs more physiologically relevant. In this review, we explore the rationale and feasibility of using macrophages as an additional cell source in engineered cardiac tissues. Impact statement Macrophages play a critical role in cardiac homeostasis and in disease. Over the past decade, we have come to understand the many vital roles played by cardiac resident macrophages in the heart, including immunosurveillance, regeneration, electrical conduction, and elimination of exophers. There is a need to improve our understanding of the resident macrophage population in the heart in vitro, to better recapitulate the myocardium through tissue engineered models. However, obtaining them in vitro remains a challenge. Here, we discuss the importance of cardiac resident macrophages and potential ways to obtain cardiac resident macrophages in vitro. Finally, we critically discuss their potential in realizing impactful in vitro models of cardiac tissue and their impact in the field.

Yeast β-glucan with different degrees of oxidation: Capability of adsorbing lead ions and protective effect against lead-induced PC12 cytotoxicity

This study investigated the adsorption behavior of Pb²⁺ by three different oxidized yeast β-glucans (OYG) and their effect on lead-induced PC12 cytotoxicity. The analysis revealed that the adsorption kinetics conformed to pseudo-first-order model and the adsorption capacities for Pb²⁺ (36.50, 41.61 and 50.31 μg/mg for OYG1-3) showed a positive correlation with oxidation degree (15.2%, 47.3% and 71.2% for OYG1-3). Additionally, the lead adsorption by OYGs showed an endothermic process and the adsorption capacity increased with the increasing Pb²⁺ concentration in the aqueous phase. Then, it was found that OYGs were biocompatible and could increase cell viability from 60% to 80% during lead stress. Nuclear staining revealed an inhibitory effect of OYGs on cell apoptosis, with the best performance for OYG3. Furthermore, OYGs could significantly suppress lead-induced production of reactive oxygen species (ROS) and nitric oxide (NO) in PC12 cells. Specifically, when being supplemented with 20 μg/mL OYG3, the increase of fluorescence intensity caused by the production of ROS and NO in PC12 cells were significantly alleviated from 2.65 and 2.6 to 1.23 and 1.35-fold, respectively. Our findings indicate that OYGs could adsorb lead effectively and protect PC12 cells from lead-induced cytotoxicity.

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.

The Role of Cytochrome P450 Enzymes in COVID-19 Pathogenesis and Therapy

Coronavirus disease 2019 (COVID-19) has become a new public health crisis threatening the world. Dysregulated immune responses are the most striking pathophysiological features of patients with severe COVID-19, which can result in multiple-organ failure and death. The cytochrome P450 (CYP) system is the most important drug metabolizing enzyme family, which plays a significant role in the metabolism of endogenous or exogenous substances. Endogenous CYPs participate in the biosynthesis or catabolism of endogenous substances, including steroids, vitamins, eicosanoids, and fatty acids, whilst xenobiotic CYPs are associated with the metabolism of environmental toxins, drugs, and carcinogens. CYP expression and activity are greatly affected by immune response. However, changes in CYP expression and/or function in COVID-19 and their impact on COVID-19 pathophysiology and the metabolism of therapeutic agents in COVID-19, remain unclear. In this analysis, we review current evidence predominantly in the following areas: firstly, the possible changes in CYP expression and/or function in COVID-19; secondly, the effects of CYPs on the metabolism of arachidonic acid, vitamins, and steroid hormones in COVID-19; and thirdly, the effects of CYPs on the metabolism of therapeutic COVID-19 drugs.

Exploiting maleimide-functionalized hyaluronan hydrogels to test cellular responses to physical and biochemical stimuli

Currentin vitrothree-dimensional (3D) models of liver tissue have been limited by the inability to study the effects of specific extracellular matrix (ECM) components on cell phenotypes. This is in part due to limitations in the availability of chemical modifications appropriate for this purpose. For example, hyaluronic acid (HA), which is a natural ECM component within the liver, lacks key ECM motifs (e.g. arginine-glycine-aspartic acid (RGD) peptides) that support cell adhesion. However, the addition of maleimide (Mal) groups to HA could facilitate the conjugation of ECM biomimetic peptides with thiol-containing end groups. In this study, we characterized a new crosslinkable hydrogel (i.e. HA-Mal) that yielded a simplified ECM-mimicking microenvironment supportive of 3D liver cell culture. We then performed a series of experiments to assess the impact of physical and biochemical signaling in the form of RGD peptide incorporation and transforming growth factorß(TGF-ß) supplementation, respectively, on hepatic functionality. Hepatic stellate cells (i.e. LX-2) exhibited increased cell-matrix interactions in the form of cell spreading and elongation within HA-Mal matrices containing RGD peptides, enabling physical adhesions, whereas hepatocyte-like cells (HepG2) had reduced albumin and urea production. We further exposed the encapsulated cells to soluble TGF-ßto elicit a fibrosis-like state. In the presence of TGF-ßbiochemical signals, LX-2 cells became activated and HepG2 functionality significantly decreased in both RGD-containing and RGD-free hydrogels. Altogether, in this study we have developed a hydrogel biomaterial platform that allows for discrete manipulation of specific ECM motifs within the hydrogel to better understand the roles of cell-matrix interactions on cell phenotype and overall liver functionality.

Arabic gum plus colistin coated moxifloxacin-loaded nanoparticles for the treatment of bone infection caused by Escherichia coli

Osteomyelitis is an inflammatory process of bone and bone marrow that may even lead to patient death. Even though this disease is mainly caused by Gram-positive organisms, the proportion of bone infections caused by Gram-negative bacteria, such as Escherichia coli, has significantly increased in recent years. In this work, mesoporous silica nanoparticles have been employed as platform to engineer a nanomedicine able to eradicate E. coli- related bone infections. For that purpose, the nanoparticles have been loaded with moxifloxacin and further functionalized with Arabic gum and colistin (AG+CO-coated MX-loaded MSNs). The nanosystem demonstrated high affinity toward E. coli biofilm matrix, thanks to AG coating, and marked antibacterial effect because of the bactericidal effect of moxifloxacin and the disaggregating effect of colistin. AG+CO-coated MX-loaded MSNs were able to eradicate the infection developed on a trabecular bone in vitro and showed pronounced antibacterial efficacy in vivo against an osteomyelitis provoked by E. coli. Furthermore, AG+CO-coated MX-loaded MSNs were shown to be essentially non-cytotoxic with only slight effect on cell proliferation and mild hepatotoxicity, which might be attributed to the nature of both antibiotics. In view of these results, these nanoparticles may be considered as a promising treatment for bone infections caused by enterobacteria, such as E. coli, and introduce a general strategy against bone infections based on the implementation of antibiotics with different but complementary activity into a single nanocarrier. STATEMENT OF SIGNIFICANCE: In this work, we propose a methodology to address E.coli bone infections by using moxifloxacin-loaded mesoporous silica nanoparticles coated with Arabic gum containing colistin (AG+CO-coated MX-loaded MSNs). The in vitro evaluation of this nanosystem demonstrated high affinity toward E. coli biofilm matrix thanks to the Arabic gum coating, a disaggregating and antibacterial effect of colistin, and a remarkable antibiofilm action because of the bactericidal ability of moxifloxacin and colistin. This anti-E. coli capacity of AG+CO-coated MX-loaded MSNs was brought out in an in vivo rabbit model of osteomyelitis where the nanosystem was able to eradicate more than 90% of the bacterial load within the infected bone.

A preliminary study of the innate immune memory of Kupffer cells induced by PEGylated nanoemulsions

The accelerated blood clearance (ABC) phenomenon describes a dilemma of polyethylene glycol (PEG) applied in drug delivery system (DDS) caused by its immunogenicity, that results in the enhanced blood clearance rate and increased hepatic and splenic accumulation after secondary injection of PEGylated nanocarriers. However, the ABC index, as the judgement of ABC phenomenon, only describes the accelerated blood clearance rate, but ignores the enhanced hepatic and splenic accumulation. Therefore, we proposed the hepatic accumulation (HA) index and the splenic accumulation (SA) index as supplements for assessing the ABC phenomenon, to emphasize the contribution of liver and spleen, especially the liver, possessing the most population of tissue resident macrophages. By altering the first injection site from the tail vein to the liver portal vein, there was no impact on anti-PEG IgM production, and the secondary hepatic accumulation of PEGylated nanoemulsions (PE) was observed to be proportionate to the first PE stimulation strength on the liver. We also determined that Kupffer cells (KCs) were the main contributor to this enhancement. On this basis, we revealed a definite phenomenon that PE could induce innate immune memory in KCs, by enhancing the phagocytosis of KCs toward PE during the secondary stimulation. The PE-stimulated KCs could carry this memory to the naïve rats through adoptive transfer, resulting in increased hepatic accumulation in the recipient rats without antibody production. Studies examining the phagocytosis of KCs in vivo, ex vivo and in vitro revealed that the memory of KCs against PE triggered by first-stimulated PE could be maintained independently of other cells or components until 21 days after the first stimulation, and possessing specificity to PEG, which was invalid to long-circulating GE (GM1 modified nanoemulsions). The discovery of immune memory in KCs induced by PE highlights the importance of focusing on the relationship between the innate immune system and PEGylated nanocarriers during the development of DDS to improve medication safety in the clinic.

The Immunological Mechanisms and Immune-Based Biomarkers of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) has become one of the major challenges of drug safety all over the word. So far, about 1,100 commonly used drugs including the medications used regularly, herbal and/or dietary supplements, have been reported to induce liver injury. Moreover, DILI is the main cause of the interruption of new drugs development and drugs withdrawn from the pharmaceutical market. Acute DILI may evolve into chronic DILI or even worse, commonly lead to life-threatening acute liver failure in Western countries. It is generally considered to have a close relationship to genetic factors, environmental risk factors, and host immunity, through the drug itself or its metabolites, leading to a series of cellular events, such as haptenization and immune response activation. Despite many researches on DILI, the specific biomarkers about it are not applicable to clinical diagnosis, which still relies on the exclusion of other causes of liver disease in clinical practice as before. Additionally, circumstantial evidence has suggested that DILI is mediated by the immune system. Here, we review the underlying mechanisms of the immune response to DILI and provide guidance for the future development of biomarkers for the early detection, prediction, and diagnosis of DILI.

Advances in HBV infection and replication systems in vitro

Background

Hepatitis B virus (HBV) is a DNA virus belonging to the Hepadnaviridae family that has limited tissue and species specificity. Due to the persistence of HBV covalently closed circular DNA (cccDNA) in host cells after HBV infection, current antiviral drugs cannot eradicate HBV. Therefore, the development of an active cell culture system supporting HBV infection has become the key to studying HBV and developing effective therapeutic drugs.

Main body

This review summarizes the significant research achievements in HBV cell culture systems in vitro, including embryonic hepatocytes and primary hepatocytes, which support the virus infection process most similar to that in the body and various liver tumor cells. The discovery of the bile-acid pump sodium-taurocholate co-transporting polypeptide (NTCP) as the receptor of HBV has advanced our understanding of HBV biology. Subsequently, various liver cancer cells overexpressing NTCP that support HBV infection have been established, opening a new door for studying HBV infection. The fact that induced pluripotent stem cells that differentiate into hepatocyte-like cells support HBV infection provides a novel idea for the establishment of an HBV cell culture system.

Conclusion

Because of the host and tissue specificity of HBV, a suitable in vitro HBV infection system is critical for the study of HBV pathogenesis. Nevertheless, recent advances regarding HBV infection in vitro offer hope for better studying the biological characteristics of HBV, the pathogenesis of hepatitis B, the screening of anti-HBV drugs and the mechanism of carcinogenesis.

Glucocorticoids as Regulators of Macrophage-Mediated Tissue Homeostasis

Our immune system has evolved as a complex network of cells and tissues tasked with maintaining host homeostasis. This is evident during the inflammatory responses elicited during a microbial infection or traumatic tissue damage. These responses seek to eliminate foreign material or restore tissue integrity. Even during periods without explicit disturbances, the immune system plays prominent roles in tissue homeostasis. Perhaps one of the most studied cells in this regard is the macrophage. Tissue-resident macrophages are a heterogenous group of sensory cells that respond to a variety of environmental cues and are essential for organ function. Endogenously produced glucocorticoid hormones connect external environmental stress signals with the function of many cell types, producing profound changes in immune cells, including macrophages. Here, we review the current literature which demonstrates specific effects of glucocorticoids in several organ systems. We propose that tissue-resident macrophages, through glucocorticoid signaling, may play an underappreciated role as regulators of organ homeostasis.

Novel indirect co-culture of immortalised hepatocytes with monocyte derived macrophages is characterised by pro-inflammatory cytokine networks

The liver is composed of different cell populations. Interactions of different cell populations can be investigated by a newly established indirect co-culture system consisting of immortalised primary human hepatocytes and human monocyte derived macrophages (MDMs). Using the time-dependent cytokine secretion of the co-cultures and single cultures, correlation networks (including the cytokines G-CSF, CCL3, MCP-1, CCL20, FGF, TGF-β1, GM-CSF, IL-8 IL-6, IL-1β, and IL-18) were generated and the correlations were validated by application of IL-8 and TNF-α-neutralising antibodies. The data reveal that IL-8 is crucial for the interaction between hepatocytes and macrophages in vitro. In addition, transcriptome analyses showed that a change in the ratio between macrophages and hepatocytes may trigger pro-inflammatory signalling pathways of the acute phase response and the complement system (release of, e.g., certain cyto- and chemokines). Using diclofenac and LPS showed that the release of cytokines is increasing with higher ratios of MDMs. Altogether, we could demonstrate that the current co-culture system is better suited to mirror the in vivo situation when compared to previously established co-culture systems composed of HepG2 and differentiated THP-1 cells. Further, our data reveal that the cytokine IL-8 is crucial for the interaction between hepatocytes and macrophages in vitro.

TNFα enhances trovafloxacin-induced in vitro hepatotoxicity by inhibiting protective autophagy

Trovafloxacin (TVX) is associated with idiosyncratic drug-induced liver injury (iDILI) and inflammation-mediated hepatotoxicity. However, the inflammatory stress-regulated mechanisms in iDILI remain unclear. Herein, we elucidated the novel role of tumor-necrosis factor alpha (TNFα), an inflammatory stress factor, in TVX-induced in vitro hepatotoxicity and synergistic toxicity. TVX specifically induced synergistic toxicity in HepG2 cells with TNFα, which inhibits autophagy. TVX-treated HepG2 cells induced protective autophagy by inhibiting the expression of mTOR signaling proteins, while ATG5 knockdown in HepG2 cells, responsible for the impairment of autophagy, enhanced TVX-induced toxicity due to the increase in cytochrome C release and JNK pathway activation. Interestingly, the expression of mTOR signal proteins, which were suppressed by TVX, disrupted the negative feedback of the PI3K/AKT pathway and TNFα rebounded p70S6K phosphorylation. Co-treatment with TVX and TNFα inhibited protective autophagy by maintaining p70S6K activity, which enhanced TVX-induced cytotoxicity. Phosphorylation of p70S6K was inhibited by siRNA knockdown and rapamycin to restore TNFα-inhibited autophagy, which prevented the synergistic effect on TVX-induced cytotoxicity. These results indicate that TVX activates protective autophagy in HepG2 cells exposed to toxicity and an imbalance in negative feedback regulation of autophagy by TNFα synergistically enhanced the toxicity. The finding from this study may contribute to a better understanding of the mechanisms underlying iDILI associated with inflammatory stress.

Recent Progress in Prediction Systems for Drug-induced Liver Injury Using in vitro Cell Culture

BACKGROUND

In order to avoid drug-induced liver injury (DILI), in vitro assays, which enable the assessment of both metabolic activation and immune reaction processes that ultimately result in DILI, are needed.

OBJECTIVE

In this study, the recent progress in the application of in vitro assays using cell culture systems is reviewed for potential DILI-causing drugs/xenobiotics and a mechanistic study on DILI, as well as for the limitations of in vitro cell culture systems for DILI research.

METHODS

Information related to DILI was collected through a literature search of the PubMed database.

RESULTS

The initial biological event for the onset of DILI is the formation of cellular protein adducts after drugs have been metabolically activated by drug metabolizing enzymes. The damaged peptides derived from protein adducts lead to the activation of CD4+ helper T lymphocytes and recognition by CD8+ cytotoxic T lymphocytes, which destroy hepatocytes through immunological reactions. Because DILI is a major cause of drug attrition and drug withdrawal, numerous in vitro systems consisting of hepatocytes and immune/inflammatory cells, or spheroids of human primary hepatocytes containing non-parenchymal cells have been developed. These cellular-based systems have identified DILIinducing drugs with approximately 50% sensitivity and 90% specificity.

CONCLUSION

Different co-culture systems consisting of human hepatocyte-derived cells and other immune/inflammatory cells have enabled the identification of DILI-causing drugs and of the actual mechanisms of action.

iPSC-Derived Liver Organoids: A Journey from Drug Screening, to Disease Modeling, Arriving to Regenerative Medicine

Liver transplantation is the most common treatment for patients suffering from liver failure that is caused by congenital diseases, infectious agents, and environmental factors. Despite a high rate of patient survival following transplantation, organ availability remains the key limiting factor. As such, research has focused on the transplantation of different cell types that are capable of repopulating and restoring liver function. The best cellular mix capable of engrafting and proliferating over the long-term, as well as the optimal immunosuppression regimens, remain to be clearly well-defined. Hence, alternative strategies in the field of regenerative medicine have been explored. Since the discovery of induced pluripotent stem cells (iPSC) that have the potential of differentiating into a broad spectrum of cell types, many studies have reported the achievement of iPSCs differentiation into liver cells, such as hepatocytes, cholangiocytes, endothelial cells, and Kupffer cells. In parallel, an increasing interest in the study of self-assemble or matrix-guided three-dimensional (3D) organoids have paved the way for functional bioartificial livers. In this review, we will focus on the recent breakthroughs in the development of iPSCs-based liver organoids and the major drawbacks and challenges that need to be overcome for the development of future applications.

Characterization of a long-term mouse primary liver 3D tissue model recapitulating innate-immune responses and drug-induced liver toxicity

Three-dimensional liver in vitro systems have recently attracted a lot of attention in drug development. These systems help to gain unprecedented insights into drug-induced liver injury (DILI), as they more closely reproduce liver biology, and as drug effects can be studied in isolated and controllable microenvironments. Many groups established human-based in vitro models but so far neglected the animal equivalent, although the availability of both models would be desirable. Animal in vitro models enable back- and forward translation of in vitro and in vivo findings, bridge the gap between rodent in vivo and human in vitro scenarios, and ultimately support the interpretation of data generated with preclinical species and humans. Since mice are often used in drug development and physiologically relevant in vitro systems are lacking, we established, for the first time, a mouse liver model that encompasses primary parenchymal and non-parenchymal cells with preserved viability and functionality over three weeks. Using our three-dimensional liver spheroids, we were able to predict the toxicity of known DILI compounds, demonstrated the interaction cascades between the different cell types and showed evidence of drug-induced steatosis and cholestasis. In summary, our mouse liver spheroids represent a valuable in vitro model that can be applied to study DILI findings, reported from mouse studies, and offers the potential to detect immune-mediated drug-induced liver toxicity.

In vitro and in vivo synergistic efficacy of ceritinib combined with programmed cell death ligand-1 inhibitor in anaplastic lymphoma kinase-rearranged non-small-cell lung cancer

Both ceritinib (CER) and programmed cell death (PD)-1/PD ligand-1 (PD-L1) have brought significant breakthroughs for anaplastic lymphoma kinase (ALK)-rearranged non-small-cell lung cancer (NSCLC). However, the overall clinical efficacy of either CER or PD-1/PD-L1 inhibitor monotherapy has been limited to a large extent. In addition, the antitumor effect of combined CER and PD-L1 inhibitor in ALK-rearranged NSCLC is not fully understood. In H2228 cells, we examined the tumor killing effect of CER plus PD-L1 inhibitor in vitro by quantitative RT-PCR, flow cytometry, ELISA, western blot analysis, PBMC coculture system, and plasmid and transfection experiments. A Ba/F3 (EML4-ALK-WT) xenograft mouse model was also utilized to further evaluate the synergistic anticancer effects of CER and PD-L1 inhibitor in vivo. The coculture system of PBMCs with H2228 cells promotes the expression of PD-L1 and phospho-ERK, and combined treatments facilitate lymphocyte proliferation and activation, inhibit PD-L1 expression, and enhance lymphocyte cytotoxicity and cell death. In the in vivo NSCLC xenograft model, the volumes of tumors treated with CER and PD-L1 inhibitor in combination were significantly smaller than those treated with CER or PD-L1 alone. The relative tumor growth inhibitions were 84.9%, 20.0%, and 91.9% for CER, PD-L1 inhibitor, and CER plus PD-L1 groups, respectively. Ceritinib could synergize with PD-1/PD-L1 blockade to yield enhanced antitumor responses along with favorable tolerability of adverse effects. Ceritinib and PD-L1 inhibitor combined produced a synergistic antineoplastic efficacy in vitro and in vivo, which provides a key insight and proof of principle for evaluating CER plus PD-L1 blockade as combination therapy in clinical therapeutic practice.

The Influence of Chronic Liver Diseases on Hepatic Vasculature: A Liver-on-a-chip Review

In chronic liver diseases and hepatocellular carcinoma, the cells and extracellular matrix of the liver undergo significant alteration in response to chronic injury. Recent literature has highlighted the critical, but less studied, role of the liver vasculature in the progression of chronic liver diseases. Recent advancements in liver-on-a-chip systems has allowed in depth investigation of the role that the hepatic vasculature plays both in response to, and progression of, chronic liver disease. In this review, we first introduce the structure, gradients, mechanical properties, and cellular composition of the liver and describe how these factors influence the vasculature. We summarize state-of-the-art vascularized liver-on-a-chip platforms for investigating biological models of chronic liver disease and their influence on the liver sinusoidal endothelial cells of the hepatic vasculature. We conclude with a discussion of how future developments in the field may affect the study of chronic liver diseases, and drug development and testing.

Functionality of primary hepatic non-parenchymal cells in a 3D spheroid model and contribution to acetaminophen hepatotoxicity

In addition to hepatocytes, the liver comprises a host of specialised non-parenchymal cells which are important to consider in the development of in vitro models which are both physiologically and toxicologically relevant. We have characterized a 3D co-culture system comprising primary human hepatocytes (PHH) and non-parenchymal cells (NPC) and applied it to the investigation of acetaminophen-induced toxicity. Firstly, we titrated ratios of PHH:NPC and confirmed the presence of functional NPCs via both immunohistochemistry and activation with both LPS and TGF-β. Based on these data we selected a ratio of 2:1 PHH:NPC for further studies. We observed that spheroids supplemented with NPCs were protected against acetaminophen (APAP) toxicity as determined by ATP (up to threefold difference in EC50 at day 14 compared to hepatocytes alone) and glutathione depletion, as well as miR-122 release. APAP metabolism was also altered in the presence of NPCs, with significantly lower levels of APAP-GSH detected. Expression of several CYP450 enzymes involved in the bioactivation of APAP was also lower in NPC-containing spheroids. Spheroids containing NPCs also expressed higher levels of miRNAs which have been implicated in APAP-induced hepatotoxicity, including miR-382 and miR-155 which have potential roles in liver regeneration and inflammation, respectively. These data indicate that the interaction between hepatocytes and NPCs can have significant metabolic and toxicological consequences important for the correct elucidation of hepatic safety mechanisms.

Towards improved hepatocyte cultures: Progress and limitations

Hepatotoxicity is among the most frequent reasons for drug withdrawal from the market. Therefore, there is an urgent need for reliable predictive in vitro tests, which unfailingly identify hepatotoxic drug candidates, reduce drug development time, expenses and the number of test animals. Currently, human hepatocytes represent the gold standard. However, the use of hepatocytes is challenging since the cells are not constantly available and lose their metabolic activity in culture. To solve these problems many different approaches have been developed in the past decades. The aim of this review is to present these approaches and to discuss the possibilities and limitations as well as future opportunities and directions.

Three-Dimensional Spheroids With Primary Human Liver Cells and Differential Roles of Kupffer Cells in Drug-Induced Liver Injury

Drug-induced liver injury (DILI) remains a challenge and a leading risk for drug discovery. Three-dimensional liver spheroids made from primary human hepatocytes (PHHs) with, or without, other liver cell types can provide more physiological relevance. In comparison to conventional 2-dimensional monolayer culture, our tests with 100 drugs of known DILI status indicate that PHH spheroids are significantly more sensitive in detecting drug-induced hepatotoxicity. To evaluate the role of Kupffer cells (KCs) in drug-induced liver toxicity, we have established conditions for generating co-culture spheroids with PHH and KCs. Inflammatory responses as shown by interleukin 6 secretion can be recapitulated in co-culture spheroids when treated with endotoxin lipopolysaccharides. KCs potentiated the cytotoxicity induced by trovafloxacin in co-culture spheroids at 48 h, but the differences between PHH spheroids and co-culture spheroids became less obvious after a 5-day treatment. Interestingly, a protective role of KCs was shown in co-culture spheroids treated with both acetaminophen and lipopolysaccharides. Additional tests with 14 DILI compounds comparing PHH spheroids and co-culture spheroids showed differential roles of KCs that were compound dependent. In summary, these 3-dimensional liver spheroid models are useful tools to understand the complex mechanisms underlying DILI.

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.

Microphysiological systems for ADME-related applications: current status and recommendations for system development and characterization

Over the last decade, progress has been made on the development of microphysiological systems (MPS) for absorption, distribution, metabolism, and excretion (ADME) applications. Central to this progress has been proof of concept data generated by academic and industrial institutions followed by broader characterization studies, which provide evidence for scalability and applicability to drug discovery and development. In this review, we describe some of the advances made for specific tissue MPS and outline the desired functionality for such systems, which are likely to make them applicable for practical use in the pharmaceutical industry. Single organ MPS platforms will be valuable for modelling tissue-specific functions. However, dynamic organ crosstalk, especially in the context of disease or toxicity, can only be obtained with the use of inter-linked MPS models which will enable scientists to address questions at the intersection of pharmacokinetics (PK) and efficacy, or PK and toxicity. In the future, successful application of MPS platforms that closely mimic human physiology may ultimately reduce the need for animal models to predict ADME outcomes and decrease the overall risk and cost associated with drug development.

The importance of transporters and cell polarization for the evaluation of human stem cell-derived hepatic cells

One of the most promising applications of human pluripotent stem cells is their utilization for human-based pharmacological models. Despite the fact that membrane transporters expressed in the liver play pivotal role in various hepatic functions, thus far only little attention was devoted to the membrane transporter composition of the stem cell-derived liver models. In the present work, we have differentiated HUES9, a human embryonic stem cell line, toward the hepatic lineage, and monitored the expression levels of numerous differentiation marker and liver transporter genes with special focus on ABC transporters. In addition, the effect of bile acid treatment and polarizing culturing conditions on hepatic maturation has been assessed. We found that most transporter genes crucial for hepatic functions are markedly induced during hepatic differentiation; however, as regards the transporter composition the end-stage cells still exhibited dual, hepatocyte and cholangiocyte character. Although the bile acid treatment and sandwich culturing only slightly influenced the gene expressions, the stimulated cell polarization resulted in formation of bile canaliculi and proper localization of transporters. Our results point to the importance of membrane transporters in human stem cell-derived hepatic models and demonstrate the relevance of cell polarization in generation of applicable cellular models with correctly localized transporters. On the basis of our observations we suggest that conventional criteria for the evaluation of the quality of stem cell-derived hepatocyte-like cells ought to be augmented with additional elements, such as polarized and functional expression of hepatic transporters.

Hepatocellular HO-1 mediated iNOS-induced hepatoprotection against liver ischemia reperfusion injury

Hepatocyte-derived inducible nitric oxide synthase (iNOS) was proved to impart protection against liver ischemia reperfusion (I/R) injury in our prior analysis. However, the mechanism for this hepatoprotection remains incompletely understood. Bone marrow chimeric mice were generated using expression of iNOS in a hepatocyte-selective manner against an iNOS-knockout background. The function of heme oxygenase 1 (HO-1) in iNOS-stimulated hepatoprotection and the molecular mechanisms were explored in vitro and in vivo, respectively. Hepatocyte-derived iNOS conferred protection from I/R injury and anoxia/reoxygenation stimulation. Mechanistically, iNOS activated nuclear factor erythroid 2-related factor 2 (Nrf-2) and subsequently, stimulated the transcription of HO-1. Results from our study led to the conclusion that HO-1 is another potent mediator of iNOS-mediated protection after liver I/R.

The application of omics-based human liver platforms for investigating the mechanism of drug-induced hepatotoxicity in vitro

Drug-induced liver injury (DILI) complicates safety assessment for new drugs and poses major threats to both patient health and drug development in the pharmaceutical industry. A number of human liver cell-based in vitro models combined with toxicogenomics methods have been developed as an alternative to animal testing for studying human DILI mechanisms. In this review, we discuss the in vitro human liver systems and their applications in omics-based drug-induced hepatotoxicity studies. We furthermore present bioinformatic approaches that are useful for analyzing toxicogenomic data generated from these models and discuss their current and potential contributions to the understanding of mechanisms of DILI. Human pluripotent stem cells, carrying donor-specific genetic information, hold great potential for advancing the study of individual-specific toxicological responses. When co-cultured with other liver-derived non-parenchymal cells in a microfluidic device, the resulting dynamic platform enables us to study immune-mediated drug hypersensitivity and accelerates personalized drug toxicology studies. A flexible microfluidic platform would also support the assembly of a more advanced organs-on-a-chip device, further bridging gap between in vitro and in vivo conditions. The standard transcriptomic analysis of these cell systems can be complemented with causality-inferring approaches to improve the understanding of DILI mechanisms. These approaches involve statistical techniques capable of elucidating regulatory interactions in parts of these mechanisms. The use of more elaborated human liver models, in harmony with causality-inferring bioinformatic approaches will pave the way for establishing a powerful methodology to systematically assess DILI mechanisms across a wide range of conditions.

Three-Dimensional Spheroid Primary Human Hepatocytes in Monoculture and Coculture with Nonparenchymal Cells

Recent advances in the development of various culture platforms are promising for achieving more physiologically relevant in vitro hepatic models using primary human hepatocytes (PHHs). Previous studies have shown the value of PHHs three-dimensional (3D) spheroid models, cultured in low cell number (1330-2000 cells/3D spheroid), to study long-term liver function as well as pharmacological drug effects and toxicity. In this study, we report that only plateable PHHs aggregate and form compact 3D spheroids with a success rate of 79%, and 96% reproducibility. Out of 3D spheroid forming PHH lots, 65% were considered stable (<50% ATP decrease) over the subsequent 14 days of culture, with reproducibility of a given PHH lot being 82%. We also report successful coculturing of PHHs with human liver nonparenchymal cells (NPCs). Crude P1_c-NPC fractions were obtained by low centrifugation of the PHH supernatant fraction followed by a few days of culture before harvesting and cryopreservation. At aggregation of PHHs/P1_c-NPCs (2:1 ratio 3D spheroids), liver sinusoidal endothelial cells, Kupffer cells, and hepatic stellate cells were successfully integrated and remained present throughout the subsequent 14-day culture period as revealed by mRNA expression markers and immunostaining. Increased mRNA expression of albumin (ALB), apolipoprotein B (APOB), cytochrome P450 3A4 (CYP3A4), and increased albumin secretion compared to PHH 3D spheroid monocultures highlighted that in a 3D spheroid coculture, configuration with NPCs, PHH functionality is increased. We thus achieved the development of a more integrated coculture model system requiring low cell numbers, of particular interest due to the scarcity of human liver NPCs.

Multi-cellular transitional organotypic models to investigate liver fibrosis

Hepatic fibrosis is the result of wound healing and inflammation resulting in organ dysfunction. Hepatocytes, liver sinusoidal endothelial cells (LSECs), Kupffer cells (KCs), and hepatic stellate cells (HSCs) play critical roles in fibrogenesis. As the liver undergoes fibrosis, there are populations of cells that are healthy, fibrotic as well as those undergoing fibrosis. We investigated how a varying mechanical environment could induce changes in hepatic cells. In this study, a gradient in the mechanical properties of the microenvironment resulted in transitioning phenotypes in hepatic cells. We have designed detachable polyelectrolyte multilayers (PEMs) whose elastic moduli ranged from 21 to 43 kPa to serve as Space of Disse mimics. We assembled novel 3D organotypic liver models comprised of hepatocytes, LSECs, HSCs, KCs, and the Space of Disse mimic. We demonstrate how cells in contact with a mechanical gradient exhibit different properties compared to cells cultured using non-gradient PEMs. Significant differences were observed in HSC and KC proliferation between 3D cultures assembled with gradient and non-gradient PEMs. While HSCs on the stiffer regions of the gradient PEMs expressed both GFAP and α-SMA, cells in cultures assembled with homogeneous 43 kPa multilayers primarily expressed α-SMA. Over an 8-day culture, the elastic modulus in the 21 and 43 kPa regions of the gradient PEMs increased by 1.6 and 3.7-fold, respectively. This was accompanied by a 4-fold increase in hydroxyproline. Such in vitro tissues can be used to investigate the effects of liver fibrosis. STATEMENT OF SIGNIFICANCE: We have assembled a liver model assembled with four major primary hepatic cell types to investigate how a varying mechanical environment induces changes in hepatic cells. In this study, a gradient in the mechanical properties of the microenvironment results in transitioning phenotypes in hepatic cells. Our goal was to investigate the interplay between mechanical properties and a multi-cellular engineered liver tissue. In these models, Kupffer cell proliferation and hepatic stellate cell activation occurred due to mechanical cues and inter-cellular signaling across a distance of 2000 μm. These models are unique, in that, fibrosis was initiated purely through changes to the microenvironment. These models were not exposed to fibrogenic factors nor were the models assembled with cells from fibrotic rats. To the best of our knowledge, these are the first liver models that capture how a gradient microenvironment can result in transitioning cellular phenotypes.

Preparation and Culture of Human Liver Resident Immune Cells

Co-cultivation of tumor cells and liver resident immune cells or other non-parenchymal cells (NPCs) from the same donor is important for the study of cancer metastasis. So far, little is known about the mechanism of tumor cell or pathogen clearance, leukocyte infiltration, and immune cell recruitment in the human liver. To investigate these processes in vitro, the use of primary human hepatocytes and non-parenchymal cell, especially immune cell, co-culture systems play essential roles in the establishment of cell-cell and cell-extracellular matrix communications similar to native liver tissues. Hepatic non-parenchymal cells mainly comprise liver sinusoid endothelial cells (LSECs), microvascular endothelial cells, hepatic stellate cells, Kupffer cells (KCs), natural killer T (iNKT) cells, and dendritic cells (DCs). Here we describe procedures for preparation, isolation, and culture of human liver resident immune cells and other non-parenchymal cells. © 2018 by John Wiley & Sons, Inc.