Current Perspective: 3D Spheroid Models Utilizing Human-Based Cells for Investigating Metabolism-Dependent Drug-Induced Liver Injury

Processing-induced reduction in dianthrones content and toxicity of Polygonum multiflorum: Insights from ultra-high performance liquid chromatography triple quadrupole mass spectrometry analysis and toxicological assessment

BACKGROUND

Polygonum multiflorum-induced liver injury (PM-DILI) has significantly hindered its clinical application and development.

METHODS

This study investigates the variation in content and toxicity of dianthrones, the toxic components of P. multiflorum, during different processing cycles. We employed the ultra-high-performance liquid chromatography triple quadrupole mass spectrometry method to quantify six dianthrones in raw P. multiflorum and formulations processed with a method called nine cycles of steaming and sunning. Additionally, toxicity assessments were conducted using human normal liver cell line L02 and zebrafish embryos.

RESULTS

Results indicate a gradual reduction in dianthrones content with increasing processing cycles. Processed formulations exhibited significantly reduced cytotoxicity in L02 cells and hepatotoxicity in zebrafish embryos.

CONCLUSIONS

Our findings elucidate the relationship between processing cycles and P. multiflorum toxicity, providing theoretical support for its safe use.

Long-term 3D cell culture models for hepatitis B virus studies

Primary human hepatocyte (PHH) models have limited longevity and require high inoculum for HBV infection with minimal spread. We aimed to develop 3D cell culture models to overcome the limitations of existing models and to expand their utility for drug-related studies. Here, we report the establishment of two spheroid models utilizing de novo HBV-infected mouse-passaged (mp)PHH and mpPHH isolated from HBV-infected liver chimeric mice (HBV-mpPHH). Our data demonstrates that our models maintain detectable infection and human albumin levels up to 75 days, and therefore have enhanced longevity compared to existing models. As a proof-of-concept we used our de novo HBV-infected model as a drug-testing platform to validate an HBV capsid assembly modulator (CpAM). We report that we have established two HBV-infected 3D cell culture models and have characterized these models as practical and novel approaches with the potential to enhance the relevance and scope of in vitro HBV studies.

Pathway-Based Similarity Measurement to Quantify Transcriptomics Similarity Between Human Tissues and Preclinical Models

Accurate clinical translation of preclinical research remains challenging, primarily due to species-specific differences and disease and patient heterogeneity. An important recent advancement has been development of microphysiological systems that consist of multiple human cell types that recapitulate key characteristics of their respective human systems, allowing essential physiologic processes to be accurately assessed during drug development. However, an unmet need remains regarding a quantitative method to evaluate the similarity between diverse sample types for various contexts of use (CoU)-specific pathways. To address this gap, this study describes the development of pathway-based similarity measurement (PBSM), which leverages RNA-seq data and pathway-based information to assess the human relevance of preclinical models for specific CoU. PBSM offers a quantitative method to compare the transcriptomic similarity of preclinical models to human tissues, shown here as proof of concept for liver and cardiac tissues, enabling improved model selection and validation. Thus, PBSM can successfully support CoU selection for preclinical models, assess the impact of different gene sets on similarity calculations, and differentiate among various in vitro and in vivo models. PBSM has the potential to reduce the translational gap in drug development by allowing quantitative evaluation of the similarity of preclinical models to human tissues, facilitating model selection, and improving understanding of context-specific applications. PBSM can serve as a foundation for enhancing the physiological relevance of in vitro models and supporting the development of more effective therapeutic interventions.

A pumpless liver-on-a-chip for drug hepatotoxicity analysis

This study presents the development and validation of an innovative microfluidic liver-on-a-chip device utilizing gravity-driven perfusion for the evaluation of drug hepatotoxicity. This research involved the construction of a hydrogel-based coculture chip that integrates liver parenchymal and stellate cells within a tri-channel configuration. The assembly and operation of the liver-on-a-chip and its accompanying custom rocker were straightforward. The cells in the chip maintained high viability and continuously synthesized liver albumin over extended culture durations. Acetaminophen (APAP), a hepatic injury-inducing drug, was utilized as a positive control in hepatic toxicity assays on the chip. The liver chip exhibited hepatotoxic responses comparable to those observed in 2D models. Furthermore, in this study we evaluated the effects of two plant-derived natural compounds, aristolochic acid I (AA) and its analog aristolactam AII (AL), in both 2D cell models and the liver-on-a-chip system. AA, known for its hepatorenal toxicity, was observed to cause hepatotoxicity in both the 2D models and on the chip. The flow cytometry and mRNA sequencing results confirmed the propensity of these compounds to induce liver cell apoptosis. Notably, AL, previously considered nontoxic, provoked a significant decrease in the hepatic functionality marker albumin exclusively in the liver chip but not in 2D models, indicating the liver chip's enhanced sensitivity to toxic substances. In summary, this pumpless liver-on-a-chip is a simple yet powerful tool for drug hepatotoxicity studies.

Human Hepatobiliary Organoids: Recent Advances in Drug Toxicity Verification and Drug Screening

Many drug and therapeutic modalities have emerged over the past few years. However, successful commercialization is dependent on their safety and efficacy evaluations. Several preclinical models are available for drug-screening and safety evaluations, including cellular- and molecular-level models, tissue and organoid models, and animal models. Organoids are three-dimensional cell cultures derived from primary tissues or stem cells that are structurally and functionally similar to the original organs and can self-renew, and they are used to establish various disease models. Human hepatobiliary organoids have been used to study the pathogenesis of diseases, such as hepatitis, liver fibrosis, hepatocellular carcinoma, primary sclerosing cholangitis and biliary tract cancer, as they retain the physiological and histological characteristics of the liver and bile ducts. Here, we review recent research progress in validating drug toxicity, drug screening and personalized therapy for hepatobiliary-related diseases using human hepatobiliary organoid models, discuss the challenges encountered in current research and evaluate the possible solutions.

In Situ Self-Assembling Liver Spheroids with Synthetic Nanoscaffolds for Preclinical Drug Screening Applications

Drug-induced liver injury (DILI) is one of the most common reasons for acute liver failure and a major reason for the withdrawal of medications from the market. There is a growing need for advanced in vitro liver models that can effectively recapitulate hepatic function, offering a robust platform for preclinical drug screening applications. Here, we explore the potential of self-assembling liver spheroids in the presence of electrospun and cryomilled poly(caprolactone) (PCL) nanoscaffolds for use as a new preclinical drug screening tool. This study investigated the extent to which nanoscaffold concentration may have on spheroid size and viability and liver-specific biofunctionality. The efficacy of our model was further validated using a comprehensive dose-dependent acetaminophen toxicity protocol. Our findings show the strong potential of PCL-based nanoscaffolds to facilitate in situ self-assembly of liver spheroids with sizes under 350 μm. The presence of the PCL-based nanoscaffolds (0.005 and 0.01% w/v) improved spheroid viability and the secretion of critical liver-specific biomarkers, namely, albumin and urea. Liver spheroids with nanoscaffolds showed improved drug-metabolizing enzyme activity and greater sensitivity to acetaminophen compared to two-dimensional monolayer cultures and scaffold-free liver spheroids. These promising findings highlight the potential of our nanoscaffold-based liver spheroids as an in vitro liver model for drug-induced hepatotoxicity and drug screening.

Prediction of Acute Hepatotoxicity With Human Pluripotent Stem Cell-Derived Hepatic Organoids

Recent development of hepatic organoids (HOs) derived from human pluripotent stem cells (hPSCs) provides an alternative in vitro model that can mimic the human liver detoxification pathway for drug safety assessment. By recapitulating the high level of maturity and drug-metabolizing capacity of the liver in a three-dimensional organoid culture, HOs may allow researchers to assess drug toxicity and metabolism more accurately than animal models or hepatocellular carcinoma cells. Although this promising potential has contributed to the development of various protocols, only a few protocols are available to generate functional HOs with guaranteed CYP450 enzymatic activity, the key feature driving toxic responses during drug metabolism. Based on previously published protocols, we describe an optimized culture method that can substantially increase the expression and activity of CYP450s, in particular CYP3A4, CYP2C9, and CYP2C19, in HOs. To generate mass-produced and highly reproducible HOs required as models for toxicity evaluation, we first generated hepatic endodermal organoids (HEOs) from hPSCs capable of in vitro proliferation and cryopreservation. The stepwise protocol includes generating HEOs as well as efficient methods to enhance CYP450 expression and activity in terminally differentiated HOs. Furthermore, we present a simple protocol for the assessment of HO cytotoxicity, one of the hallmarks of drug-induced acute hepatotoxicity. The protocols are relatively straightforward and can be successfully used by laboratories with basic experience in culturing hPSCs. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Generation of hepatic endodermal organoids from human pluripotent stem cells Basic Protocol 2: Expansion and cryopreservation of hepatic endodermal organoids Basic Protocol 3: Differentiation of hepatic organoids from hepatic endodermal organoids Basic Protocol 4: Evaluation of hepatotoxicity using hepatic organoids Support Protocol: Human pluripotent stem cell culture.

Advantages of Using 3D Spheroid Culture Systems in Toxicological and Pharmacological Assessment for Osteogenesis Research

Bone differentiation is crucial for skeletal development and maintenance. Its dysfunction can cause various pathological conditions such as rickets, osteoporosis, osteogenesis imperfecta, or Paget's disease. Although traditional two-dimensional cell culture systems have contributed significantly to our understanding of bone biology, they fail to replicate the intricate biotic environment of bone tissue. Three-dimensional (3D) spheroid cell cultures have gained widespread popularity for addressing bone defects. This review highlights the advantages of employing 3D culture systems to investigate bone differentiation. It highlights their capacity to mimic the complex in vivo environment and crucial cellular interactions pivotal to bone homeostasis. The exploration of 3D culture models in bone research offers enhanced physiological relevance, improved predictive capabilities, and reduced reliance on animal models, which have contributed to the advancement of safer and more effective strategies for drug development. Studies have highlighted the transformative potential of 3D culture systems for expanding our understanding of bone biology and developing targeted therapeutic interventions for bone-related disorders. This review explores how 3D culture systems have demonstrated promise in unraveling the intricate mechanisms governing bone homeostasis and responses to pharmacological agents.

Investigation of TGF-α-overexpressing mouse hepatocytes (TAMH) cultured as spheroids for use in hepatotoxicity screening of drug candidates

The immortalized mouse liver cell line TAMH has been described as a valuable tool for studying hepatotoxic mechanisms, but until now, it has only been reported to grow as a monolayer in culture. However, culturing hepatocytes as three-dimensional (3D) spheroids has been shown to result in improved liver-specific functions (e.g., metabolic capacity) by better mimicking the in vivo environment. This approach may lead to more reliable detection of drug-induced liver injury (DILI) in the early phase of drug discovery, preventing post-marketing drug withdrawals. Here, we investigated the cultivation of TAMH as 3D spheroids, characterizing them with optical and transmission electron microscopy as well as analyzing their gene expression at mRNA level (especially drug-metabolizing enzymes) compared to TAMH monolayer. In addition, comparisons were made with spheroids grown from the human hepatoblastoma cell line HepG2, another current spheroid model. The results indicate that TAMH spheroids express hepatic structures and show elevated levels of some of the key phase I and II drug-metabolizing enzymes, in contrast to TAMH monolayer. The in vitro hepatotoxic potencies of the drugs acetaminophen and flupirtine maleate were found to be very similar between TAMH spheroidal and the monolayer cultures. Both the advantages and disadvantages of TAMH spheroids as an in vitro hepatotoxicity model compared to monolayer model are discussed.

Combination of melt-electrospun poly-ε-caprolactone scaffolds and hepatocyte-like cells from footprint-free hiPSCs to create 3D biohybrid constructs for liver tissue engineering

The liver is a vital organ with numerous functions, including metabolic functions, detoxification, and the synthesis of secretory proteins. The increasing prevalence of liver diseases requires the development of effective treatments, models, and regenerative approaches. The field of liver tissue engineering represents a significant advance in overcoming these challenges. In this study, 3D biohybrid constructs were created by combining hepatocyte-like cells (HLCs) derived from patient-specific footprint-free human induced pluripotent stem cells (hiPSCs) and 3D melt-electrospun poly-ε-caprolactone (PCL) scaffolds. First, a differentiation procedure was established to obtain autologous HCLs from hiPSCs reprogrammed from renal epithelial cells using self-replicating mRNA. The obtained cells expressed hepatocyte-specific markers and exhibited important hepatocyte functions, such as albumin synthesis, cytochrome P450 activity, glycogen storage, and indocyanine green metabolism. Biocompatible PCL scaffolds were fabricated by melt-electrospinning and seeded with pre-differentiated hepatoblasts, which uniformly attached to the fibers of the scaffolds and successfully matured into HLCs. The use of patient-specific, footprint-free hiPSC-derived HLCs represents a promising cell source for personalized liver regeneration strategies. In combination with biocompatible 3D scaffolds, this innovative approach has a broader range of applications spanning liver tissue engineering, drug testing and discovery, and disease modeling.

The 3Rs in Experimental Liver Disease

Patients with cirrhosis present multiple physiological and immunological alterations that play a very important role in the development of clinically relevant secondary complications to the disease. Experimentation in animal models is essential to understand the pathogenesis of human diseases and, considering the high prevalence of liver disease worldwide, to understand the pathophysiology of disease progression and the molecular pathways involved, due to the complexity of the liver as an organ and its relationship with the rest of the organism. However, today there is a growing awareness about the sensitivity and suffering of animals, causing opposition to animal research among a minority in society and some scientists, but also about the attention to the welfare of laboratory animals since this has been built into regulations in most nations that conduct animal research. In 1959, Russell and Burch published the book "The Principles of Humane Experimental Technique", proposing that in those experiments where animals were necessary, everything possible should be done to try to replace them with non-sentient alternatives, to reduce to a minimum their number, and to refine experiments that are essential so that they caused the least amount of pain and distress. In this review, a comprehensive summary of the most widely used techniques to replace, reduce, and refine in experimental liver research is offered, to assess the advantages and weaknesses of available experimental liver disease models for researchers who are planning to perform animal studies in the near future.

Liver three-dimensional cellular models for high-throughput chemical testing

Drug-induced hepatotoxicity is a leading cause of drug withdrawal from the market. High-throughput screening utilizing in vitro liver models is critical for early-stage liver toxicity testing. Traditionally, monolayer human hepatocytes or immortalized liver cell lines (e.g., HepG2, HepaRG) have been used to test compound liver toxicity. However, monolayer-cultured liver cells sometimes lack the metabolic competence to mimic the in vivo condition and are therefore largely appropriate for short-term toxicological testing. They may not, however, be adequate for identifying chronic and recurring liver damage caused by drugs. Recently, several three-dimensional (3D) liver models have been developed. These 3D liver models better recapitulate normal liver function and metabolic capacity. This review describes the current development of 3D liver models that can be used to test drugs/chemicals for their pharmacologic and toxicologic effects, as well as the advantages and limitations of using these 3D liver models for high-throughput screening.

Comparison of two supporting matrices for patient-derived cancer cells in 3D drug sensitivity and resistance testing assay (3D-DSRT)

Central to the success of functional precision medicine of solid tumors is to perform drug testing of patient-derived cancer cells (PDCs) in tumor-mimicking ex vivo conditions. While high throughput (HT) drug screening methods have been well-established for cells cultured in two-dimensional (2D) format, this approach may have limited value in predicting clinical responses. Here, we describe the results of the optimization of drug sensitivity and resistance testing (DSRT) in three-dimensional (3D) growth supporting matrices in a HT mode (3D-DSRT) using the hepatocyte cell line (HepG2) as an example. Supporting matrices included widely used animal-derived Matrigel and cellulose-based hydrogel, GrowDex, which has earlier been shown to support 3D growth of cell lines and stem cells. Further, the sensitivity of ovarian cancer PDCs, from two patients included in the functional precision medicine study, was tested for 52 drugs in 5 different concentrations using 3D-DSRT. Shortly, in the optimized protocol, the PDCs are embedded with matrices and seeded to 384-well plates to allow the formation of the spheroids prior to the addition of drugs in nanoliter volumes with acoustic dispenser. The sensitivity of spheroids to drug treatments is measured with cell viability readout (here, 72 h after addition of drugs). The quality control and data analysis are performed with openly available Breeze software. We show the usability of both matrices in established 3D-DSRT, and report 2D vs 3D growth condition dependent differences in sensitivities of ovarian cancer PDCs to MEK-inhibitors and cytotoxic drugs. This study provides a proof-of-concept for robust and fast screening of drug sensitivities of PDCs in 3D-DSRT, which is important not only for drug discovery but also for personalized ex vivo drug testing in functional precision medicine studies. These findings suggest that comparing results of 2D- and 3D-DSRT is essential for understanding drug mechanisms and for selecting the most effective treatment for the patient.

HepaRG cells undergo increased levels of post-differentiation patterning in physiologic conditions when maintained as 3D cultures in paper-based scaffolds

Monolayer cultures of hepatocytes lack many aspects of the liver sinusoid, including a tissue-level organization that results from extracellular matrix interactions and gradients of soluble molecules that span from the portal triad to the central vein. We measured the activity and transcript levels of drug-metabolizing enzymes in HepaRG cells maintained in three different culture configurations: as monolayers, seeded onto paper scaffolds that were pre-loaded with a collagen matrix, and when seeded directly into the paper scaffolds as a cell-laden gel. Drug metabolism was significantly decreased in the presence of the paper scaffolds compared to monolayer configurations when cells were exposed to standard culture conditions. Despite this decreased function, transcript levels suggest the cells undergo increased polarization and adopt a biliary-like character in the paper scaffolds, including the increased expression of transporter proteins (e.g., ABCB11 and SLOC1B1) and the KRT19 cholangiocyte marker. When exposed to representative periportal or perivenous culture conditions, we observed in vivo zonal-like patterns, including increased cytochrome P450 (CYP) activity and transcript levels in the perivenous condition. This increased CYP activity is more pronounced in the laden configuration, supporting the need to include multiple aspects of the liver microenvironment to observe the post-differentiation processing of hepatocytes.

Current Research Trends in the Application of In Vitro Three-Dimensional Models of Liver Cells

The liver produces and stores various nutrients that are necessary for the body and serves as a chemical plant, metabolizing carbohydrates, fats, hormones, vitamins, and minerals. It is also a vital organ for detoxifying drugs and exogenous harmful substances. Culturing liver cells in vitro under three-dimensional (3D) conditions is considered a primary mechanism for liver tissue engineering. The 3D cell culture system is designed to allow cells to interact in an artificially created environment and has the advantage of mimicking the physiological characteristics of cells in vivo. This system facilitates contact between the cells and the extracellular matrix. Several technically different approaches have been proposed, including bioreactors, chips, and plate-based systems in fluid or static media composed of chemically diverse materials. Compared to conventional two-dimensional monolayer culture in vitro models, the ability to predict the function of the tissues, including the drug metabolism and chemical toxicity, has been enhanced by developing three-dimensional liver culture models. This review discussed the methodology of 3D cell cultures and summarized the advantages of an in vitro liver platform using 3D culture technology.

Metabolic clearance of select opioids and opioid antagonists using hepatic spheroids and recombinant cytochrome P450 enzymes

The opioid crisis is a pressing public health issue, exacerbated by the emergence of more potent synthetic opioids, particularly fentanyl and its analogs. While competitive antagonists exist, their efficacy against synthetic opioids is largely unknown. Furthermore, due to the short durations of action of current antagonists, renarcotization remains a concern. In this study, metabolic activity was characterized for fentanyl-class opioids and common opioid antagonists using multiple in vitro systems, namely, cytochrome P450 (CYP) enzymes and hepatic spheroids, after which an in vitro-in vivo correlation was applied to convert in vitro metabolic activity to predictive in vivo intrinsic clearance. For all substrates, intrinsic hepatic metabolism was higher than the composite of CYP activities, due to fundamental differences between whole cells and single enzymatic reactions. Of the CYP isozymes investigated, 3A4 yielded the highest absolute and relative metabolism across all substrates, with largely negligible contributions from 2D6 and 2C19. Comparative analysis highlighted elevated lipophilicity and diminished CYP3A4 activity as potential considerations for the development of more efficacious opioid antagonists. Finally, antagonists with a high degree of molecular similarity exhibited comparable clearance, providing a basis for structure-metabolism relationships. Together, these results provide multiple screening criteria for early stage drug discovery involving opioid countermeasures.

In Vitro Models for Studying Chronic Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a major clinical problem in terms of patient morbidity and mortality, cost to healthcare systems and failure of the development of new drugs. The need for consistent safety strategies capable of identifying a potential toxicity risk early in the drug discovery pipeline is key. Human DILI is poorly predicted in animals, probably due to the well-known interspecies differences in drug metabolism, pharmacokinetics, and toxicity targets. For this reason, distinct cellular models from primary human hepatocytes or hepatoma cell lines cultured as 2D monolayers to emerging 3D culture systems or the use of multi-cellular systems have been proposed for hepatotoxicity studies. In order to mimic long-term hepatotoxicity in vitro, cell models, which maintain hepatic phenotype for a suitably long period, should be used. On the other hand, repeated-dose administration is a more relevant scenario for therapeutics, providing information not only about toxicity, but also about cumulative effects and/or delayed responses. In this review, we evaluate the existing cell models for DILI prediction focusing on chronic hepatotoxicity, highlighting how better characterization and mechanistic studies could lead to advance DILI prediction.

Evaluation of Pharmaceuticals for DNA Damage in the Chicken Egg Genotoxicity Assay (CEGA)

DNA damage is an established initiating event in the mutagenicity and carcinogenicity of genotoxic chemicals. Accordingly, assessment of this endpoint is critical for chemicals which are being developed for use in humans. To assess the ability of the Chicken Egg Genotoxicity Assay (CEGA) to detect genotoxic pharmaceuticals, a set of 23 compounds with different pharmacological and reported genotoxic effects was tested for the potential to produce nuclear DNA adducts and strand breaks in the embryo-fetal livers using the ³²P-nucleotide postlabeling (NPL) and comet assays, respectively. Due to high toxicity, two aneugens, colchicine and vinblastine, and an autophagy inhibitor, hydroxychloroquine, could not be evaluated. Out of the 20 remaining pharmaceuticals, 10 including estrogen modulators, diethylstilbestrol and tamoxifen, antineoplastics cyclophosphamide, etoposide, and mitomycin C, antifungal griseofulvin, local anesthetics lidocaine and prilocaine, and antihistamines diphenhydramine and doxylamine, yielded clear positive outcomes in at least one of the assays. The antihypertensive vasodilator hydralazine and antineoplastics streptozotocin and teniposide, produced only DNA strand breaks, which were not dose-dependent, and thus, the results with these 3 pharmaceuticals were considered equivocal. No DNA damage was detected for 7 compounds, including the purine antagonist 6-thioguanine, antipyretic analgesics acetaminophen and phenacetin, antibiotic ciprofloxacin, antilipidemic clofibrate, anti-inflammatory ibuprofen, and sedative phenobarbital. However, low solubility of these compounds limited dosages tested in CEGA. Overall, results in CEGA were largely in concordance with the outcomes in other systems in vitro and in vivo, indicating that CEGA provides reliable detection of DNA damaging activity of genotoxic compounds. Further evaluations with a broader set of compounds would support this conclusion.

In vitro cell-based models of drug-induced hepatotoxicity screening: progress and limitation

Drug-induced liver injury (DILI) is one of the major causes of post-approval withdrawal of therapeutics. As a result, there is an increasing need for accurate predictive in vitro assays that reliably detect hepatotoxic drug candidates while reducing drug discovery time, costs, and the number of animal experiments. In vitro hepatocyte-based research has led to an improved comprehension of the underlying mechanisms of chemical toxicity and can assist the prioritization of therapeutic choices with low hepatotoxicity risk. Therefore, several in vitro systems have been generated over the last few decades. This review aims to comprehensively present the development and validation of 2D (two-dimensional) and 3D (three-dimensional) culture approaches on hepatotoxicity screening of compounds and highlight the main factors affecting predictive power of experiments. To this end, we first summarize some of the recognized hepatotoxicity mechanisms and related assays used to appraise DILI mechanisms and then discuss the challenges and limitations of in vitro models.

Mimicking Native Liver Lobule Microarchitecture In Vitro with Parenchymal and Non-parenchymal Cells Using 3D Bioprinting for Drug Toxicity and Drug Screening Applications

Bioengineering an in vitro liver model recapitulating the native liver microarchitecture consisting of parenchymal and non-parenchymal cells is crucial in achieving cellular crosstalk and hepatic metabolic functions for accurate hepatotoxicity prediction. Bioprinting holds the promise of engineering constructs with precise control over the spatial distribution of multiple cells. Two distinct tissue-specific liver extracellular matrix (ECM)-based bioinks with excellent printability and rheological attributes are formulated for supporting parenchymal and non-parenchymal cells. A physiologically relevant human vascularized liver model is bioprinted with a novel liver ECM-based bioink laden with human adipose mesenchymal stem cell-derived hepatocyte-like cells (HLCs), human umbilical vein endothelial cells (HUVECs), and human hepatic stellate cells (HHSCs) using an extrusion-based bioprinting approach and validated for hepatotoxicity assessment. The HLC/HUVEC/HHSC-laden liver model resembles native alternate cords of hepatocytes with a functional sinusoidal lumen-like network in both horizontal and vertical directions, demonstrating enhanced albumin production, urea synthesis, and cytochrome P450 (CPR) activity. Furthermore, the liver model is evaluated for drug toxicity assessment following 24 h exposure to different concentrations of (i) non-hepatotoxicants aspirin and dexamethasone, (ii) idiosyncratic hepatotoxicant trovafloxacin mesylate, and (iii) clinical hepatotoxicant acetaminophen and troglitazone. A follow-up cell viability and metabolic competence evaluation by estimating DNA concentration, lactate dehydrogenase activity, and CPR activity revealed a dose-dependent clinically relevant hepatotoxic response. These results corroborated that the developed clinically relevant vascularized liver model is affordable and would aid pharmaceutical companies in speeding up the drug development and provide a robust platform for hepatotoxicity screening.

Applied Hepatic Bioengineering: Modeling the Human Liver Using Organoid and Liver-on-a-Chip Technologies

The liver is the most important metabolic hub of endo and xenobiotic compounds. Pre-clinical studies using rodents to evaluate the toxicity of new drugs and cosmetics may produce inconclusive results for predicting clinical outcomes in humans, moreover being banned in the European Union. Human liver modeling using primary hepatocytes presents low reproducibility due to batch-to-batch variability, while iPSC-derived hepatocytes in monolayer cultures (2D) show reduced cellular functionality. Here we review the current status of the two most robust in vitro approaches in improving hepatocyte phenotype and metabolism while mimicking the hepatic physiological microenvironment: organoids and liver-on-chip. Both technologies are reviewed in design and manufacturing techniques, following cellular composition and functionality. Furthermore, drug screening and liver diseases modeling efficiencies are summarized. Finally, organoid and liver-on-chip technologies are compared regarding advantages and limitations, aiming to guide the selection of appropriate models for translational research and the development of such technologies.

Human Three-Dimensional Hepatic Models: Cell Type Variety and Corresponding Applications

Owing to retained hepatic phenotypes and functions, human three-dimensional (3D) hepatic models established with diverse hepatic cell types are thought to recoup the gaps in drug development and disease modeling limited by a conventional two-dimensional (2D) cell culture system and species-specific variability in drug metabolizing enzymes and transporters. Primary human hepatocytes, human hepatic cancer cell lines, and human stem cell-derived hepatocyte-like cells are three main hepatic cell types used in current models and exhibit divergent hepatic phenotypes. Primary human hepatocytes derived from healthy hepatic parenchyma resemble in vivo-like genetic and metabolic profiling. Human hepatic cancer cell lines are unlimitedly reproducible and tumorigenic. Stem cell-derived hepatocyte-like cells derived from patients are promising to retain the donor's genetic background. It has been suggested in some studies that unique properties of cell types endue them with benefits in different research fields of in vitro 3D modeling paradigm. For instance, the primary human hepatocyte was thought to be the gold standard for hepatotoxicity study, and stem cell-derived hepatocyte-like cells have taken a main role in personalized medicine and regenerative medicine. However, the comprehensive review focuses on the hepatic cell type variety, and corresponding applications in 3D models are sparse. Therefore, this review summarizes the characteristics of different cell types and discusses opportunities of different cell types in drug development, liver disease modeling, and liver transplantation.

Organoid Technology: A Reliable Developmental Biology Tool for Organ-Specific Nanotoxicity Evaluation

Engineered nanomaterials are bestowed with certain inherent physicochemical properties unlike their parent materials, rendering them suitable for the multifaceted needs of state-of-the-art biomedical, and pharmaceutical applications. The log-phase development of nano-science along with improved "bench to beside" conversion carries an enhanced probability of human exposure with numerous nanoparticles. Thus, toxicity assessment of these novel nanoscale materials holds a key to ensuring the safety aspects or else the global biome will certainly face a debacle. The toxicity may span from health hazards due to direct exposure to indirect means through food chain contamination or environmental pollution, even causing genotoxicity. Multiple ways of nanotoxicity evaluation include several in vitro and in vivo methods, with in vitro methods occupying the bulk of the "experimental space." The underlying reason may be multiple, but ethical constraints in in vivo animal experiments are a significant one. Two-dimensional (2D) monoculture is undoubtedly the most exploited in vitro method providing advantages in terms of cost-effectiveness, high throughput, and reproducibility. However, it often fails to mimic a tissue or organ which possesses a defined three-dimensional structure (3D) along with intercellular communication machinery. Instead, microtissues such as spheroids or organoids having a precise 3D architecture and proximate in vivo tissue-like behavior can provide a more realistic evaluation than 2D monocultures. Recent developments in microfluidics and bioreactor-based organoid synthesis have eased the difficulties to prosper nano-toxicological analysis in organoid models surpassing the obstacle of ethical issues. The present review will enlighten applications of organoids in nanotoxicological evaluation, their advantages, and prospects toward securing commonplace nano-interventions.

Bioengineered Liver Cell Models of Hepatotropic Infections

Hepatitis viruses and liver-stage malaria are within the liver infections causing higher morbidity and mortality rates worldwide. The highly restricted tropism of the major human hepatotropic pathogens-namely, the human hepatitis B and C viruses and the Plasmodium falciparum and Plasmodium vivax parasites-has hampered the development of disease models. These models are crucial for uncovering the molecular mechanisms underlying the biology of infection and governing host-pathogen interaction, as well as for fostering drug development. Bioengineered cell models better recapitulate the human liver microenvironment and extend hepatocyte viability and phenotype in vitro, when compared with conventional two-dimensional cell models. In this article, we review the bioengineering tools employed in the development of hepatic cell models for studying infection, with an emphasis on 3D cell culture strategies, and discuss how those tools contributed to the level of recapitulation attained in the different model layouts. Examples of host-pathogen interactions uncovered by engineered liver models and their usefulness in drug development are also presented. Finally, we address the current bottlenecks, trends, and prospect toward cell models' reliability, robustness, and reproducibility.

3D human liver spheroids for translational pharmacology and toxicology

Drug development is a failure-prone endeavour, and more than 85% of drugs fail during clinical development, showcasing that current preclinical systems for compound selection are clearly inadequate. Liver toxicity remains a major reason for safety failures. Furthermore, all efforts to develop pharmacological therapies for a variety of chronic liver diseases, such as non-alcoholic steatohepatitis (NASH) and fibrosis, remain unsuccessful. Considering the time and expense of clinical trials, as well as the substantial burden on patients, new strategies are thus of paramount importance to increase clinical success rates. To this end, human liver spheroids are becoming increasingly utilized as they allow to preserve patient-specific phenotypes and functions for multiple weeks in culture. We here review the recent application of such systems for i) predictive and mechanistic analyses of drug hepatotoxicity, ii) the evaluation of hepatic disposition and metabolite formation of low clearance drugs and iii) the development of drugs for metabolic and infectious liver diseases, including NASH, fibrosis, malaria and viral hepatitis. We envision that with increasing dissemination, liver spheroids might become the new gold standard for such applications in translational pharmacology and toxicology.