Generation of uniform liver spheroids from human pluripotent stem cells for imaging-based drug toxicity analysis

Microfluidic human physiomimetic liver model as a screening platform for drug induced liver injury

The pre-clinical animal models often fail to predict intrinsic and idiosyncratic drug induced liver injury (DILI), thus contributing to drug failures in clinical trials, black box warnings and withdrawal of marketed drugs. This suggests a critical need for human-relevant in vitro models to predict diverse DILI phenotypes. In this study, a porcine liver extracellular matrix (ECM) based biomaterial ink with high printing fidelity, biocompatibility and tunable rheological and mechanical properties is formulated for supporting both parenchymal and non-parenchymal cells. Further, we applied 3D printing and microfluidic technology to bioengineer a human physiomimetic liver acinus model (HPLAM), recapitulating the radial hepatic cord-like structure with functional sinusoidal microvasculature network, biochemical and biophysical properties of native liver acinus. Intriguingly, the human derived hepatic cells incorporated HPLAM cultured under physiologically relevant microenvironment, acts as metabolic biofactories manifesting enhanced hepatic functionality, secretome levels and biomarkers expression over several weeks. We also report that the matured HPLAM reproduces dose- and time-dependent hepatotoxic response of human clinical relevance to drugs typically recognized for inducing diverse DILI phenotypes as compared to conventional static culture. Overall, the developed HPLAM emulates in vivo like functions and may provide a useful platform for DILI risk assessment to better determine safety and human risk.

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.

Stem Cell-Based Strategies: The Future Direction of Bioartificial Liver Development

Acute liver failure (ALF) results from severe liver damage or end-stage liver disease. It is extremely fatal and causes serious health and economic burdens worldwide. Once ALF occurs, liver transplantation (LT) is the only definitive and recommended treatment; however, LT is limited by the scarcity of liver grafts. Consequently, the clinical use of bioartificial liver (BAL) has been proposed as a treatment strategy for ALF. Human primary hepatocytes are an ideal cell source for these methods. However, their high demand and superior viability prevent their widespread use. Hence, finding alternatives that meet the seed cell quality and quantity requirements is imperative. Stem cells with self-renewing, immunogenic, and differentiative capacities are potential cell sources. MSCs and its secretomes encompass a spectrum of beneficial properties, such as anti-inflammatory, immunomodulatory, anti-ROS (reactive oxygen species), anti-apoptotic, pro-metabolomic, anti-fibrogenesis, and pro-regenerative attributes. This review focused on the recent status and future directions of stem cell-based strategies in BAL for ALF. Additionally, we discussed the opportunities and challenges associated with promoting such strategies for clinical applications.

3D hepatic organoid production from human pluripotent stem cells

Hepatic organoids might provide a golden opportunity for realizing precision medicine in various hepatic diseases. Previously described hepatic organoid protocols from pluripotent stem cells rely on complicated multiple differentiation steps consisting of both 2D and 3D differentiation procedures. Therefore, the spontaneous formation of hepatic organoids from 2D monolayer culture is associated with a low-throughput production, which might hinder the standardization of hepatic organoid production and hamper the translation of this technology to the clinical or industrial setting. Here we describe the stepwise and fully 3D production of hepatic organoids from human pluripotent stem cells. We optimized every differentiation step by screening for optimal concentrations and timing of differentiation signals in each differentiation step. Hepatic organoids are stably expandable without losing their hepatic functionality. Moreover, upon treatment of drugs with known hepatotoxicity, we found hepatic organoids are more sensitive to drug-induced hepatotoxicity compared with 2D hepatocytes differentiated from PSCs, making them highly suitable for in vitro toxicity screening of drug candidates. The standardized fully 3D protocol described in the current study for producing functional hepatic organoids might serve as a novel platform for the industrial and clinical translation of hepatic organoid technology.

Human chemically-derived hepatic progenitors (hCdHs) as a source of liver organoid generation: Application in regenerative medicine, disease modeling, and toxicology testing

BACKGROUND & AIMS

Several types of human stem cells from embryonic (ESCs) and induced pluripotent (iPSCs) to adult tissue-specific stem cells are commonly used to generate 3D liver organoids for modeling tissue physiology and disease. We have recently established a protocol for direct conversion of primary human hepatocytes (hPHs) from healthy donor livers into bipotent progenitor cells (hCdHs). Here we extended this culture system to generate hCdH-derived liver organoids for diverse biomedical applications.

METHODS

To obtain hCdHs, hPHs were cultured in reprogramming medium containing A83-01 and CHIR99021 for 7 days. Liver organoids were established from hCdHs (hCdHOs) and human liver cells (hLOs) using the same donor livers for direct comparison, as well as from hiPSCs. Organoid properties were analyzed by standard in vitro assays. Molecular changes were determined by RT-qPCR and RNA-seq. Clinical relevance was evaluated by transplantation into FRG mice, modeling of alcohol-related liver disease (ARLD), and in vitro drug-toxicity tests.

RESULTS

hCdHs were clonally expanded as organoid cultures with low variability between starting hCdH lines. Similar to the hLOs, hCdHOs stably maintained stem cell phenotype based on accepted criteria. However, hCdHOs had an advantage over hLOs in terms of EpCAM expression, efficiency of organoid generation and capacity for directed hepatic differentiation as judged by molecular profiling, albumin secretion, glycogen accumulation, and CYP450 activities. Accordingly, FRG mice transplanted with hCdHOs survived longer than mice injected with hLOs. When exposed to ethanol, hCdHOs developed stronger ARLD phenotype than hLOs as evidenced by transcriptional profiling, lipid accumulation and mitochondrial dysfunction. In drug-induced injury assays in vitro, hCdHOs showed a similar or higher sensitivity response than hPHs.

CONCLUSION

hCdHOs provide a novel patient-specific stem cell-based platform for regenerative medicine, toxicology testing and modeling liver diseases.

3D bioprinting of dECM-incorporated hepatocyte spheroid for simultaneous promotion of cell-cell and -ECM interactions

The cell spheroid technology, which greatly enhances cell-cell interactions, has gained significant attention in the development of in vitro liver models. However, existing cell spheroid technologies still have limitations in improving hepatocyte-extracellular matrix (ECM) interaction, which have a significant impact on hepatic function. In this study, we have developed a novel bioprinting technology for decellularized ECM (dECM)-incorporated hepatocyte spheroids that could enhance both cell-cell and -ECM interactions simultaneously. To provide a biomimetic environment, a porcine liver dECM-based cell bio-ink was developed, and a spheroid printing process using this bio-ink was established. As a result, we precisely printed the dECM-incorporated hepatocyte spheroids with a diameter of approximately 160-220 μm using primary mouse hepatocyte (PMHs). The dECM materials were uniformly distributed within the bio-printed spheroids, and even after more than 2 weeks of culture, the spheroids maintained their spherical shape and high viability. The incorporation of dECM also significantly improved the hepatic function of hepatocyte spheroids. Compared to hepatocyte-only spheroids, dECM-incorporated hepatocyte spheroids showed approximately 4.3- and 2.5-fold increased levels of albumin and urea secretion, respectively, and a 2.0-fold increase in CYP enzyme activity. These characteristics were also reflected in the hepatic gene expression levels of ALB, HNF4A, CPS1, and others. Furthermore, the dECM-incorporated hepatocyte spheroids exhibited up to a 1.8-fold enhanced drug responsiveness to representative hepatotoxic drugs such as acetaminophen, celecoxib, and amiodarone. Based on these results, it can be concluded that the dECM-incorporated spheroid printing technology has great potential for the development of highly functional in vitro liver tissue models for drug toxicity assessment.

Improvements in Maturity and Stability of 3D iPSC-Derived Hepatocyte-like Cell Cultures

Induced pluripotent stem cell (iPSC) technology enables differentiation of human hepatocytes or hepatocyte-like cells (iPSC-HLCs). Advances in 3D culturing platforms enable the development of more in vivo-like liver models that recapitulate the complex liver architecture and functionality better than traditional 2D monocultures. Moreover, within the liver, non-parenchymal cells (NPCs) are critically involved in the regulation and maintenance of hepatocyte metabolic function. Thus, models combining 3D culture and co-culturing of various cell types potentially create more functional in vitro liver models than 2D monocultures. Here, we report the establishment of 3D cultures of iPSC-HLCs alone and in co-culture with human umbilical vein endothelial cells (HUVECs) and adipose tissue-derived mesenchymal stem/stromal cells (hASCs). The 3D cultures were performed as spheroids or on microfluidic chips utilizing various biomaterials. Our results show that both 3D spheroid and on-chip culture enhance the expression of mature liver marker genes and proteins compared to 2D. Among the spheroid models, we saw the best functionality in iPSC-HLC monoculture spheroids. On the contrary, in the chip system, the multilineage model outperformed the monoculture chip model. Additionally, the optical projection tomography (OPT) and electrical impedance tomography (EIT) system revealed changes in spheroid size and electrical conductivity during spheroid culture, suggesting changes in cell-cell connections. Altogether, the present study demonstrates that iPSC-HLCs can successfully be cultured in 3D as spheroids and on microfluidic chips, and co-culturing iPSC-HLCs with NPCs enhances their functionality. These 3D in vitro liver systems are promising human-derived platforms usable in various liver-related studies, specifically when using patient-specific iPSCs.

Role of three-dimensional cell culture in therapeutics and diagnostics: an updated review

Drug development and testing are a tedious and expensive process with a high degree of uncertainty in the clinical success and preclinical validation of manufactured therapeutic agents. Currently, to understand the drug action, disease mechanism, and drug testing, most therapeutic drug manufacturers use 2D cell culture models to validate the drug action. However, there are many uncertainties and limitations with the conventional use of 2D (monolayer) cell culture models for drug testing that are primarily attributed due to poor mimicking of cellular mechanisms, disturbance in environmental interaction, and changes in structural morphology. To overcome such odds and difficulties in the preclinical validation of therapeutic medications, newer in vivo drug testing cell culture models with higher screening efficiencies are required. One such promising and advanced cell culture model reported recently is the "three-dimensional cell culture model." The 3D cell culture models are reported to show evident benefits over conventional 2D cell models. This review article outlines and describes the current advancement in cell culture models, their types, significance in high-throughput screening, limitations, applications in drug toxicity screening, and preclinical testing methodologies to predict in vivo efficacy.

Progress and promise of alternative animal and non-animal methods in biomedical research

Cell culture and invertebrate animal models reflect a significant evolution in scientific research by providing reliable evidence on the physiopathology of diseases, screening for new drugs, and toxicological tests while reducing the need for mammals. In this review, we discuss the progress and promise of alternative animal and non-animal methods in biomedical research, with a special focus on drug toxicity.

Pluripotent Stem Cell-Derived Hepatocyte-like Cells: Induction Methods and Applications

The development of regenerative medicine provides new options for the treatment of end-stage liver diseases. Stem cells, such as bone marrow mesenchymal stem cells, embryonic stem cells, and induced pluripotent stem cells (iPSCs), are effective tools for tissue repair in regenerative medicine. iPSCs are an appropriate source of hepatocytes for the treatment of liver disease due to their unlimited multiplication capacity, their coverage of the entire range of genetics required to simulate human disease, and their evasion of ethical implications. iPSCs have the ability to gradually produce hepatocyte-like cells (HLCs) with homologous phenotypes and physiological functions. However, how to induce iPSCs to differentiate into HLCs efficiently and accurately is still a hot topic. This review describes the existing approaches for inducing the differentiation of iPSCs into HLCs, as well as some challenges faced, and summarizes various parameters for determining the quality and functionality of HLCs. Furthermore, the application of iPSCs for in vitro hepatoprotective drug screening and modeling of liver disease is discussed. In conclusion, iPSCs will be a dependable source of cells for stem-cell therapy to treat end-stage liver disease and are anticipated to facilitate individualized treatment for liver disease in the future.

Development of fish liver PLHC-1 spheroids and its applicability to investigate the toxicity of plastic additives

Fish liver cell lines are valuable tools to understand the toxicity of chemicals in aquatic vertebrates. While conventional 2D cell cultures grown in monolayers are well established, they fail to emulate toxic gradients and cellular functions as in in-vivo conditions. To overcome these limitations, this work focuses on the development of Poeciliopsis lucida (PLHC-1) spheroids as a testing platform to evaluate the toxicity of a mixture of plastic additives. The growth of spheroids was monitored over a period of 30 days, and spheroids 2-8 days old and sized between 150 and 250 µm were considered optimal for conducting toxicity tests due to their excellent viability and metabolic activity. Eight-day-old spheroids were selected for lipidomic characterization. Compared to 2D-cells, the lipidome of spheroids was relatively enriched in highly unsaturated phosphatidylcholines (PCs), sphingosines (SPBs), sphingomyelins (SMs) and cholesterol esters (CEs). When exposed to a mixture of plastic additives, spheroids were less responsive in terms of decreased cell viability and generation of reactive oxygen species (ROS), but were more sensitive than cells growing in monolayers for lipidomic responses. The lipid profile of 3D-spheroids was similar to a liver-like phenotype and it was strongly modulated by exposure to plastic additives. The development of PLHC-1 spheroids represents an important step towards the application of more realistic in-vitro methods in aquatic toxicity studies.

Three-dimensional (3D) cell culture studies: a review of the field of toxicology

Traditional two-dimensional (2D) cell culture employed for centuries is extensively used in toxicological studies. There is no doubt that 2D cell culture has made significant contributions to toxicology. However, in today's world, it is necessary to develop more physiologically relevant models. Three-dimensional (3D) cell culture, which can recapitulate the cell's microenvironment, is, therefore, a more realistic model compared to traditional cell culture. In toxicology, 3D cell culture models are a powerful tool for studying different tissues and organs in similar environments and behave as if they are in in vivo conditions. In this review, we aimed to present 3D cell culture models that have been used in different organ toxicity studies. We reported the results and interpretations obtained from these studies. We aimed to highlight 3D models as the future of cell culture by reviewing 3D models used in different organ toxicity studies.

Quantitative chemometric phenotyping of three-dimensional liver organoids by Raman spectral imaging

Confocal Raman spectral imaging (RSI) enables high-content, label-free visualization of a wide range of molecules in biological specimens without sample preparation. However, reliable quantification of the deconvoluted spectra is needed. Here we develop an integrated bioanalytical methodology, qRamanomics, to qualify RSI as a tissue phantom calibrated tool for quantitative spatial chemotyping of major classes of biomolecules. Next, we apply qRamanomics to fixed 3D liver organoids generated from stem-cell-derived or primary hepatocytes to assess specimen variation and maturity. We then demonstrate the utility of qRamanomics for identifying biomolecular response signatures from a panel of liver-altering drugs, probing drug-induced compositional changes in 3D organoids followed by in situ monitoring of drug metabolism and accumulation. Quantitative chemometric phenotyping constitutes an important step in developing quantitative label-free interrogation of 3D biological specimens.

Unsung versatility of elastin-like polypeptide inspired spheroid fabrication: A review

Lately, 3D cell culture technique has gained a lot of appreciation as a research model. Augmented with technological advancements, the area of 3D cell culture is growing rapidly with a diverse array of scaffolds being tested. This is especially the case for spheroid cultures. The culture of cells as spheroids provides opportunities for unanticipated vision into biological phenomena with its application to drug discovery, metabolic profiling, stem cell research as well as tumor, and disease biology. Spheroid fabrication techniques are broadly categorised into matrix-dependent and matrix-independent techniques. While there is a profusion of spheroid fabrication substrates with substantial biological relevance, an economical, modular, and bio-compatible substrate for high throughput production of spheroids is lacking. In this review, we posit the prospects of elastin-like polypeptides (ELPs) as a broad-spectrum spheroid fabrication platform. Elastin-like polypeptides are nature inspired, size-tunable genetically engineered polymers with wide applicability in various arena of biological considerations, has been employed for spheroid culture with profound utility. The technology offers a cheap, high-throughput, reproducible alternative for spheroid culture with exquisite adaptability. Here, we will brief the applicability of 3D cultures as compared to 2D cultures with spheroids being the focal point of the review. Common approaches to spheroid fabrication are discussed with existential limitations. Finally, the versatility of elastin-like polypeptide inspired substrates for spheroid culture has been discussed.

Covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) as electrochemical sensors for the efficient detection of pharmaceutical residues

Pharmaceutical residues are the undecomposed remains from drugs used in the medical and food industries. Due to their potential adverse effects on human health and natural ecosystems, they are of increasing worldwide concern. The acute detection of pharmaceutical residues can give a rapid examination of their quantity and then prevent them from further contamination. Herein, this study summarizes and discusses the most recent porous covalent-organic frameworks (COFs) and metal-organic frameworks (MOFs) for the electrochemical detection of various pharmaceutical residues. The review first introduces a brief overview of drug toxicity and its effects on living organisms. Subsequently, different porous materials and drug detection techniques are discussed with materials' properties and applications. Then the development of COFs and MOFs has been addressed with their structural properties and sensing applications. Further, the stability, reusability, and sustainability of MOFs/COFs are reviewed and discussed. Besides, COFs and MOFs' detection limits, linear ranges, the role of functionalities, and immobilized nanoparticles are analyzed and discussed. Lastly, this review summarized and discussed the MOF@COF composite as sensors, the fabrication strategies to enhance detection potential, and the current challenges in this area.

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.

Pump-less, recirculating organ-on-a-chip (rOoC) platform

We developed a novel, pump-less directional flow recirculating organ-on-a-chip (rOoC) platform that creates controlled unidirectional gravity-driven flow by a combination of a 3D-tilting system and an optimized microfluidic layout. The rOoC platform was assembled utilizing a layer-to-layer fabrication technology based on thermoplastic materials. It features two organoid compartments supported by two independent perfusion channels and separated by a hydrogel barrier. We developed a computational model to predict wall shear stress values and then measured the flow rate in the microfluidic channels with micro-Particle-Image-Velocimetry (μPIV). The suitability of the rOoC for functional culture of endothelial cells was tested using HUVECs seeded in the perfusion channels. HUVECs aligned in response to the directional flow, formed a barrier and were able to sprout into the organoid compartments. Next, we demonstrated the viability of human stem-cell derived liver organoids in the organoid compartments. Finally, we show the possibility to circulate immune cells in the microfluidic channels that retain viability without being trapped or activated. The rOoC platform allows growing and connecting of two or more tissue or organ representations on-chip with the possibility of applying gradients, endothelial barriers, microvasculature and circulating cells independent of external tubing and support systems.

Spheroid Engineering in Microfluidic Devices

Two-dimensional (2D) cell culture techniques are commonly employed to investigate biophysical and biochemical cellular responses. However, these culture methods, having monolayer cells, lack cell-cell and cell-extracellular matrix interactions, mimicking the cell microenvironment and multicellular organization. Three-dimensional (3D) cell culture methods enable equal transportation of nutrients, gas, and growth factors among cells and their microenvironment. Therefore, 3D cultures show similar cell proliferation, apoptosis, and differentiation properties to in vivo. A spheroid is defined as self-assembled 3D cell aggregates, and it closely mimics a cell microenvironment in vitro thanks to cell-cell/matrix interactions, which enables its use in several important applications in medical and clinical research. To fabricate a spheroid, conventional methods such as liquid overlay, hanging drop, and so forth are available. However, these labor-intensive methods result in low-throughput fabrication and uncontrollable spheroid sizes. On the other hand, microfluidic methods enable inexpensive and rapid fabrication of spheroids with high precision. Furthermore, fabricated spheroids can also be cultured in microfluidic devices for controllable cell perfusion, simulation of fluid shear effects, and mimicking of the microenvironment-like in vivo conditions. This review focuses on recent microfluidic spheroid fabrication techniques and also organ-on-a-chip applications of spheroids, which are used in different disease modeling and drug development studies.

Multicellular Tumor Spheroids in Nanomedicine Research: A Perspective

Multicellular tumor spheroids are largely exploited in cancer research since they are more predictive than bi-dimensional cell cultures. Nanomedicine would benefit from the integration of this three-dimensional in vitro model in screening protocols. In this brief work, we discuss some of the issues that cancer nanomedicine will need to consider in the switch from bi-dimensional to three-dimensional multicellular tumor spheroid models.

Dextran sulfate prevents excess aggregation of human pluripotent stem cells in 3D culture by inhibiting ICAM1 expression coupled with down-regulating E-cadherin through activating the Wnt signaling pathway

Background

Human pluripotent stem cells (hPSCs) have great potential in applications for regenerative medicine and drug development. However, 3D suspension culture systems for clinical-grade hPSC large-scale production have been a major challenge. Accumulating evidence has demonstrated that the addition of dextran sulfate (DS) could prevent excessive adhesion of hPSCs from forming larger aggregates in 3D suspension culture. However, the signaling and molecular mechanisms underlying this phenomenon remain elusive.

Methods

By using a cell aggregate culture assay and separating big and small aggregates in suspension culture systems, the potential mechanism and downstream target genes of DS were investigated by mRNA sequence analysis, qRT-PCR validation, colony formation assay, and interference assay.

Results

Since cellular adhesion molecules (CAMs) play important roles in hPSC adhesion and aggregation, we assumed that DS might prevent excess adhesion through affecting the expression of CAMs in hPSCs. As expected, after DS treatment, we found that the expression of CAMs was significantly down-regulated, especially E-cadherin (E-cad) and intercellular adhesion molecule 1 (ICAM1), two highly expressed CAMs in hPSCs. The role of E-cad in the adhesion of hPSCs has been widely investigated, but the function of ICAM1 in hPSCs is hardly understood. In the present study, we demonstrated that ICAM1 exhibited the capacity to promote the adhesion in hPSCs, and this adhesion was suppressed by the treatment with DS. Furthermore, transcriptomic analysis of RNA-seq revealed that DS treatment up-regulated genes related to Wnt signaling resulting in the activation of Wnt signaling in which SLUG, TWIST, and MMP3/7 were highly expressed, and further inhibited the expression of E-cad.

Conclusion

Our results demonstrated that DS played an important role in controlling the size of hPSC aggregates in 3D suspension culture by inhibiting the expression of ICAM1 coupled with the down-regulation of E-cad through the activation of the Wnt signaling pathway. These results represent a significant step toward developing the expansion of hPSCs under 3D suspension condition in large-scale cultures.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02890-4.

An Algorithm Framework for Drug-Induced Liver Injury Prediction Based on Genetic Algorithm and Ensemble Learning

In the process of drug discovery, drug-induced liver injury (DILI) is still an active research field and is one of the most common and important issues in toxicity evaluation research. It directly leads to the high wear attrition of the drug. At present, there are a variety of computer algorithms based on molecular representations to predict DILI. It is found that a single molecular representation method is insufficient to complete the task of toxicity prediction, and multiple molecular fingerprint fusion methods have been used as model input. In order to solve the problem of high dimensional and unbalanced DILI prediction data, this paper integrates existing datasets and designs a new algorithm framework, Rotation-Ensemble-GA (R-E-GA). The main idea is to find a feature subset with better predictive performance after rotating the fusion vector of high-dimensional molecular representation in the feature space. Then, an Adaboost-type ensemble learning method is integrated into R-E-GA to improve the prediction accuracy. The experimental results show that the performance of R-E-GA is better than other state-of-art algorithms including ensemble learning-based and graph neural network-based methods. Through five-fold cross-validation, the R-E-GA obtains an ACC of 0.77, an F1 score of 0.769, and an AUC of 0.842.

Efficiently generate functional hepatic cells from human pluripotent stem cells by complete small-molecule strategy

BACKGROUND

Various methods have been developed to generate hepatic cells from human pluripotent stem cells (hPSCs) that rely on the combined use of multiple expensive growth factors, limiting industrial-scale production and widespread applications. Small molecules offer an attractive alternative to growth factors for producing hepatic cells since they are more economical and relatively stable.

METHODS

We dissect small-molecule combinations and identify the ideal cocktails to achieve an optimally efficient and cost-effective strategy for hepatic cells differentiation, expansion, and maturation.

RESULTS

We demonstrated that small-molecule cocktail CIP (including CHIR99021, IDE1, and PD0332991) efficiently induced definitive endoderm (DE) formation via increased endogenous TGF-β/Nodal signaling. Furthermore, we identified that combining Vitamin C, Dihexa, and Forskolin (VDF) could substitute growth factors to induce hepatic specification. The obtained hepatoblasts (HBs) could subsequently expand and mature into functional hepatocyte-like cells (HLCs) by the established chemical formulas. Thus, we established a stepwise strategy with complete small molecules for efficiently producing scalable HBs and functionally matured HLCs. The small-molecule-derived HLCs displayed typical functional characteristics as mature hepatocytes in vitro and repopulating injured liver in vivo.

CONCLUSION

Our current small-molecule-based hepatic generation protocol presents an efficient and cost-effective platform for the large-scale production of functional human hepatic cells for cell-based therapy and drug discovery using.

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.

Application of triple co-cultured cell spheroid model for exploring hepatotoxicity and metabolic pathway of AFB1

The toxicity evaluation suffers from the absence of suitable models capable of replicating in the co-cultured cell microenvironment and the function of specific tissues in vitro. Motivated by this urgent need, this study aimed to describe a novel three-dimensional (3D) liver spheroid model. The model consisted of a triple co-culture of HepG2, EA.hy 926, and LX-2. Subsequently, it was used for the toxicity evaluation of aflatoxin B1 (AFB1), and its advantages over the two-dimensional (2D) model and the mono-type cell spheroid model were assessed. This study examined the effects of AFB1 on cell viability, proliferation, mitochondria, oxidative stress, and cell membranes. The results revealed that AFB1 greatly affected 2D cell membranes and oxidative stress levels (0.01 μg/mL; 24 h), and could also significantly affect 2D cell viability, proliferation, and mitochondria levels (1 μg/mL; 24 h). On the contrary, 3D cells were less susceptible to AFB1. Combined with the analysis of gene expression, both metabolic activation (cytochrome P450; CYP450) and detoxification efficiency (drug-metabolizing enzymes) were found to be higher in 3D cells than in 2D cells. Moreover, 3D cells in triple co-culture outperformed mono-type cell spheroids. Therefore, the advanced 3D co-cultured spheroid model constructed in this study allowed us to more realistically simulate the microenvironment in vitro, and was a valuable and precise model to study mycotoxins.

HiPSC-Derived Hepatocyte-like Cells Can Be Used as a Model for Transcriptomics-Based Study of Chemical Toxicity

Traditional toxicity risk assessment approaches have until recently focussed mainly on histochemical readouts for cell death. Modern toxicology methods attempt to deduce a mechanistic understanding of pathways involved in the development of toxicity, by using transcriptomics and other big data-driven methods such as high-content screening. Here, we used a recently described optimised method to differentiate human induced pluripotent stem cells (hiPSCs) to hepatocyte-like cells (HLCs), to assess their potential to classify hepatotoxic and non-hepatotoxic chemicals and their use in mechanistic toxicity studies. The iPSC-HLCs could accurately classify chemicals causing acute hepatocellular injury, and the transcriptomics data on treated HLCs obtained by TempO-Seq technology linked the cytotoxicity to cellular stress pathways, including oxidative stress and unfolded protein response (UPR). Induction of these stress pathways in response to amiodarone, diclofenac, and ibuprofen, was demonstrated to be concentration and time dependent. The transcriptomics data on diclofenac-treated HLCs were found to be more sensitive in detecting differentially expressed genes in response to treatment, as compared to existing datasets of other diclofenac-treated in vitro hepatocyte models. Hence iPSC-HLCs generated by transcription factor overexpression and in metabolically optimised medium appear suitable for chemical toxicity detection as well as mechanistic toxicity studies.

Induction and Maturation of Hepatocyte-Like Cells In Vitro: Focus on Technological Advances and Challenges

Limited by the poor proliferation and restricted sources of adult hepatocytes, there is an urgent need to find substitutes for proliferation and cultivation of mature hepatocytes in vitro for use in disease treatment, drug approval, and toxicity testing. Hepatocyte-like cells (HLCs), which originate from undifferentiated stem cells or modified adult cells, are considered good candidates because of their advantages in terms of cell source and in vitro expansion ability. However, the majority of induced HLCs are in an immature state, and their degree of differentiation is heterogeneous, diminishing their usability in basic research and limiting their clinical application. Therefore, various methods have been developed to promote the maturation of HLCs, including chemical approaches, alteration of cell culture systems, and genetic manipulation, to meet the needs of in vivo transplantation and in vitro model establishment. This review proposes different cell types for the induction of HLCs, and provide a comprehensive overview of various techniques to promote the generation and maturation of HLCs in vitro.

Challenges for the Applications of Human Pluripotent Stem Cell-Derived Liver Organoids

The current organoid culture systems allow pluripotent and adult stem cells to self-organize to form three-dimensional (3D) structures that provide a faithful recapitulation of the architecture and function of in vivo organs. In particular, human pluripotent stem cell-derived liver organoids (PSC-LOs) can be used in regenerative medicine and preclinical applications, such as disease modeling and drug discovery. New bioengineering tools, such as microfluidics, biomaterial scaffolds, and 3D bioprinting, are combined with organoid technologies to increase the efficiency of hepatic differentiation and enhance the functional maturity of human PSC-LOs by precise control of cellular microenvironment. Long-term stabilization of hepatocellular functions of in vitro liver organoids requires the combination of hepatic endodermal, endothelial, and mesenchymal cells. To improve the biological function and scalability of human PSC-LOs, bioengineering methods have been used to identify diverse and zonal hepatocyte populations in liver organoids for capturing heterogeneous pathologies. Therefore, constructing engineered liver organoids generated from human PSCs will be an extremely versatile tool in in vitro disease models and regenerative medicine in future. In this review, we aim to discuss the recent advances in bioengineering technologies in liver organoid culture systems that provide a timely and necessary study to model disease pathology and support drug discovery in vitro and to generate cell therapy products for transplantation.

Poly(vinyl alcohol-co-itaconic acid) hydrogels grafted with several designed peptides for human pluripotent stem cell culture and differentiation into cardiomyocytes

We developed poly(vinyl alcohol-co-itaconic acid) (PV) hydrogels grafted with laminin-derived peptides that had different joint segments and several specific designs, including dual chain motifs. PV hydrogels grafted with a peptide derived from laminin-β4 (PMQKMRGDVFSP) containing a joint segment, dual chain motif and cationic amino acid insertion could attach human pluripotent stem (hPS) cells and promoted high expansion folds in long-term culture (over 10 passages) with low differentiation rates, whereas hPS cells attached poorly on PV hydrogels grafted with laminin-α5 peptides that had joint segments with and without a cationic amino acid or on PV hydrogels grafted with laminin-β4 peptides containing the joint segment only. The inclusion of a cationic amino acid in the laminin-β4 peptide was critical for hPS cell attachment on PV hydrogels, which contributed to the zeta potential shifting to higher values (3-4 mV enhancement). The novel peptide segment-grafted PV hydrogels developed in this study supported hPS cell proliferation, which induced better hPS cell expansion than recombinant vitronectin-coated dishes (gold standard of hPS cell culture dishes) in xeno-free culture conditions. After long-term culture on peptide-grafted hydrogels, hPS cells could be induced to differentiate into specific lineages of cells, such as cardiomyocytes, with high efficiency.

Human Pluripotent Stem Cell-Derived Hepatocyte-Like Cells and Organoids for Liver Disease and Therapy

Liver disease is a global health issue that has caused an economic burden worldwide. Organ transplantation is the only effective therapy for end-stage liver disease; however, it has been hampered by a shortage of donors. Human pluripotent stem cells (hPSCs) have been widely used for studying liver biology and pathology as well as facilitating the development of alternative therapies. hPSCs can differentiate into multiple types of cells, which enables the generation of various models that can be applied to investigate and recapitulate a range of biological activities in vitro. Here, we summarize the recent development of hPSC-derived hepatocytes and their applications in disease modeling, cell therapy, and drug discovery. We also discuss the advantages and limitations of these applications and critical challenges for further development.

Three-Dimensional Liver Culture Systems to Maintain Primary Hepatic Properties for Toxicological Analysis In Vitro

Drug-induced liver injury (DILI) is the major reason for failures in drug development and withdrawal of approved drugs from the market. Two-dimensional cultures of hepatocytes often fail to reliably predict DILI: hepatoma cell lines such as HepG2 do not reflect important primary-like hepatic properties and primary human hepatocytes (pHHs) dedifferentiate quickly in vitro and are, therefore, not suitable for long-term toxicity studies. More predictive liver in vitro models are urgently required in drug development and compound safety evaluation. This review discusses available human hepatic cell types for in vitro toxicology analysis and their usage in established and emerging three-dimensional (3D) culture systems. Generally, 3D cultures maintain or improve primary hepatic functions (including expression of drug-metabolizing enzymes) of different liver cells for several weeks of culture, thus allowing long-term and repeated-dose toxicity studies. Spheroid cultures of pHHs have been comprehensively tested, but also other cell types such as HepaRG benefit from 3D culture systems. Emerging 3D culture techniques include usage of induced pluripotent stem-cell-derived hepatocytes and primary-like upcyte cells, as well as advanced culture techniques such as microfluidic liver-on-a-chip models. In-depth characterization of existing and emerging 3D hepatocyte technologies is indispensable for successful implementation of such systems in toxicological analysis.