Three-Dimensional Cell Co-Culture Liver Models and Their Applications in Pharmaceutical Research

Microgel-based modular 3D in vitro microfluidic cell culture platforms

The combination of 3D in vitro cell culture and microfluidic technology has emerged as a powerful approach in biomedical engineering. It offers a more physiologically relevant model compared to traditional 2D cell cultures by allowing the assembly of micro-sized cellular structures, known as microgels. These microgels can be prepared and fabricated to mimic the in vivo characteristics of an ECM. We report here an economical and feasible microfluidic 3D in vitro culture platform that offers real-time monitoring of cellular proliferation by encapsulating pH-sensing carbon dots (CDs) with cells in the microgels. These CDs were shown to effectively evaluate proliferation within cell-encapsulated microgels in comparison with the traditional Alamar blue assay. The biggest advantage of this platform is its ability to co-culture different cell types, achieved by encapsulating the cells within individual microgels, spatially separating them while maintaining close proximity. In this modular system, each microgel acts as a unit of a specific cell type, allowing easy retrieval of cells and control over cell densities. We established the efficacy of this concept by co-culturing Huh-7 and NIH-3T3 cells within different microgel combinations, under both static and dynamic flow conditions. The heterotypic interactions were explored by assessing the functionality using albumin assay and CYP3A4 gene expression studies, along with performing drug toxicity assays. The functionality studies confirmed results from existing literature studies by showing an improved hepatic function in the presence of NIH-3T3, even in the dynamic state. This platform can be expanded to include multiple cell types, creating a complex tissue-like effect without requiring spatial patterning techniques.

In vitro liver models for toxicological research

Drug-induced liver injury (DILI) presents a major challenge not only in new drug development but also in post-marketing withdrawals and the safety of food, cosmetics, and chemicals. Experimental model organisms such as the rodents have been widely used for preclinical toxicological testing. However, the tension exists associated with the ethical and sustainable use of animals in part because animals do not necessarily inform the human-specific ADME (adsorption, dynamics, metabolism and elimination) profiling. To establish alternative models in humans, in vitro hepatic tissue models have been proposed, ranging from primary hepatocytes, immortal hepatocytes, to the development of new cell resources such as stem cell-derived hepatocytes. Given the evolving number of novel alternative methods, understanding possible combinations of cell sources and culture methods will be crucial to develop the context-of-use assays. This review primarily focuses on 3D liver organoid models for conducting. We will review the relevant cell sources, bioengineering methods, selection of training compounds, and biomarkers towards the rationale design of in vitro toxicology testing.

State-of the-art and future perspective in co-culture systems for tendon engineering

Tendon is a connective tissue that links bone to muscle, allowing for maintenance of skeleton posture, joint movement, energy storage and transmission of muscle force to bone. Tendon is a hypocellular and hypovascular tissue of poor self-regeneration capacity. Current surgical treatments are of limited success, frequently resulting in reinjury. Upcoming cell therapies are primarily based on tenocytes, a cell population of limited self-renewal capacity in vitro or mesenchymal stromal cells, a cell population prone to ectopic bone formation in vivo. Over the years mono- or multi- factorial cell culture technologies have failed to effectively maintain tenocyte phenotype in culture during expansion or to prime mesenchymal stromal cells towards tenogenic lineage prior to implantation. Upon these limitations the concept of co-culture was conceived. Here, we comprehensively review and discuss tenogenic differentiation of mesenchymal stromal cells through direct or indirect culture with tenocytes in an attempt to generate a tenocyte or a tendon-like cell population for regenerative medicine purposes.

Organoids, tissue slices and organotypic cultures: Advancing our understanding of pancreatic ductal adenocarcinoma through in vitro and ex vivo models

Pancreatic ductal adenocarcinoma (PDAC) has one of the worst prognoses of all common solid cancers. For the large majority of PDAC patients, only systemic therapies with very limited efficacy are indicated. In addition, immunotherapies have not brought the advances seen in other cancer types. Several key characteristics of PDAC contribute to poor treatment outcomes, and in this review, we will discuss how these characteristics are best captured in currently available ex vivo or in vitro model systems. For instance, PDAC is hallmarked by a highly desmoplastic and immune-suppressed tumor microenvironment that impacts disease progression and therapy resistance. Also, large differences in tumor biology exist between and within tumors, complicating treatment decisions. Furthermore, PDAC has a very high propensity for locally invasive and metastatic growth. The use of animal models is often not desirable or feasible and several in vitro and ex vivo model systems have been developed, such as organotypic cocultures and tissue slices, among others. However, the absence of a full host organism impacts the ability of these models to accurately capture the characteristics that contribute to poor outcomes in PDAC. We will discuss the caveats and advantages of these model systems in the context of PDAC's key characteristics and provide recommendations on model choice and the possibilities for optimization. These considerations should be of use to researchers aiming to study PDAC in the in vitro setting.

Fibrotic liver extracellular matrix induces cancerous phenotype in biomimetic micro-tissues of hepatocellular carcinoma model

BACKGROUND

Despite considerable advancements in identifying factors contributing to the development of hepatocellular carcinoma (HCC), the pathogenesis of HCC remains unclear. In many cases, HCC is a consequence of prolonged liver fibrosis, resulting in the formation of an intricate premalignant microenvironment. The accumulation of extracellular matrix (ECM) is a hallmark of premalignant microenvironment. Given the critical role of different matrix components in regulating cell phenotype and function, this study aimed to elucidate the interplay between the fibrotic matrix and malignant features in HCC.

METHODS

Liver tissues from both control (normal) and carbon tetrachloride (CCl4)-induced fibrotic rats were decellularized using sodium dodecyl sulfate (SDS) and Triton X-100. The resulting hydrogel from decellularized ECM was processed into micro-particles via the water-in-oil emulsion method. Micro-particles were subsequently incorporated into three-dimensional liver biomimetic micro-tissues (MTs) comprising Huh-7 cells, human umbilical vein endothelial cells (HUVECs), and LX-2 cells. The MTs were evaluated using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay at day 11, immunofluorescence staining, immunoblotting, and spheroid migration assay at day 14 after co-culture.

RESULTS

Fibrotic matrix from CCl4-treated rat livers significantly enhanced the growth rate of the MTs and their expression of CCND1 as compared to the normal one. Fibrotic matrix, also induced the expression of epithelial-to-mesenchymal transition (EMT)-associated genes such as TWIST1, ACTA2, MMP9, CDH2, and VIMENTIN in the MTs as compared to the normal matrix. Conversely, the expression of CDH1 and hepatic maturation genes HNF4A, ALB, CYP3A4 was decreased in the MTs when the fibrotic matrix was used. Furthermore, the fibrotic matrix increased the migration of the MTs and their secretion of alpha-fetoprotein.

CONCLUSIONS

Our findings suggest a regulatory role for the fibrotic matrix in promoting cancerous phenotype, which could potentially accelerate the progression of malignancy in the liver.

Ex Vivo Tools and Models in MASLD Research

Metabolic dysfunction-associated fatty liver disease (MASLD) presents a growing global health challenge with limited therapeutic choices. This review delves into the array of ex vivo tools and models utilized in MASLD research, encompassing liver-on-a-chip (LoC) systems, organoid-derived tissue-like structures, and human precision-cut liver slice (PCLS) systems. Given the urgent need to comprehend MASLD pathophysiology and identify novel therapeutic targets, this paper aims to shed light on the pivotal role of advanced ex vivo models in enhancing disease understanding and facilitating the development of potential therapies. Despite challenges posed by the elusive disease mechanism, these innovative methodologies offer promise in reducing the utilization of in vivo models for MASLD research while accelerating drug discovery and biomarker identification, thereby addressing critical unmet clinical needs.

An Ultrathin Coating of Microcapsules Enhances the Function of Encapsulated Hepatocyte Spheroids

Maintaining the differentiated phenotype and function of primary hepatocytes in vitro and in vivo represents a distinct challenge. Our paper describes microcapsules comprised of a bioactive polymer and overcoated with an ultrathin film as a means of maintaining the function of entrapped hepatocytes for at least two weeks. We previously demonstrated that heparin (Hep)-based microcapsules improved the function of entrapped primary hepatocytes by capturing and releasing cell-secreted inductive signals, including hepatocyte growth factor (HGF). Further enhancement of hepatic function could be gained by loading exogenous HGF into microcapsules. In this study, we demonstrate that an ultrathin coating of tannic acid (TA) further enhances endogenous HGF signaling for entrapped hepatocytes and increases by 2-fold the rate of uptake of exogenous HGF by Hep microcapsules. Hepatocytes in overcoated microcapsules exhibited better function and hepatic gene expression than in capsules without a TA coating. Our study showcases the potential application of ultrathin coatings to modulate the bioactivity of microcapsules and may enable the use of encapsulated hepatocytes for modeling drug toxicity or treating liver diseases.

Fast formation and maturation enhancement of human liver organoids using a liver-organoid-on-a-chip

Background: Spatial and functional hepatic zonation, established by the heterogeneous tissue along the portal-central axis of the liver, is important for ensuring optimal liver function. Researchers have attempted to develop reliable hepatic models to mimic the liver microenvironment and analyze liver function using hepatocytes cultured in the developed systems. However, mimicking the liver microenvironment in vitro remains a great challenge owing to the lack of perfusable vascular networks in the model systems and the limitation in maintaining hepatocyte function over time. Methods: In this study, we established a microphysiological system that operated under continuous flush medium flow, thereby allowing the supply of nutrients and oxygen to liver organoids and the removal of waste and release of cytokines therefrom, similar to the function of blood vessels. Results: The application of microphysiological system to organoid culture was advantageous for reducing the differentiation time and enhancing the functional maturity of human liver organoid. Conclusion: Hence, our microphysiological culture system might open the possibility of the miniaturized liver model system into a single device to enable more rational in vitro assays of liver response.

Liver-on-chips for drug discovery and development

Recent FDA modernization act 2.0 has led to increasing industrial R&D investment in advanced in vitro 3D models such as organoids, spheroids, organ-on-chips, 3D bioprinting, and in silico approaches. Liver-related advanced in vitro models remain the prime area of interest, as liver plays a central role in drug clearance of compounds. Growing evidence indicates the importance of recapitulating the overall liver microenvironment to enhance hepatocyte maturity and culture longevity using liver-on-chips (LoC) in vitro. Hence, pharmaceutical industries have started exploring LoC assays in the two of the most challenging areas: accurate in vitro-in vivo extrapolation (IVIVE) of hepatic drug clearance and drug-induced liver injury. We examine the joint efforts of commercial chip manufacturers and pharmaceutical companies to present an up-to-date overview of the adoption of LoC technology in the drug discovery. Further, several roadblocks are identified to the rapid adoption of LoC assays in the current drug development framework. Finally, we discuss some of the underexplored application areas of LoC models, where conventional 2D hepatic models are deemed unsuitable. These include clearance prediction of metabolically stable compounds, immune-mediated drug-induced liver injury (DILI) predictions, bioavailability prediction with gut-liver systems, hepatic clearance prediction of drugs given during pregnancy, and dose adjustment studies in disease conditions. We conclude the review by discussing the importance of PBPK modeling with LoC, digital twins, and AI/ML integration with LoC.

Analysis of culture and RNA isolation methods for precision-cut liver slices from cirrhotic rats

Precision-cut liver slices (PCLS) are increasingly used as a model to investigate anti-fibrotic therapies. However, many studies use PCLS from healthy animals treated with pro-fibrotic stimuli in culture, which reflects only the early stages of fibrosis. The effects of different culture conditions on PCLS from cirrhotic animals has not been well characterized and there is no consensus on optimal methods. In this study, we report a method for the collection and culture of cirrhotic PCLS and compare the effect of common culture conditions on viability, function, and gene expression. Additionally, we compared three methods of RNA isolation and identified a protocol with high yield and purity. We observed significantly increased albumin production when cultured with insulin-transferrin-selenium and dexamethasone, and when incubated on a rocking platform. Culturing with insulin-transferrin-selenium and dexamethasone maintained gene expression closer to the levels in fresh slices. However, despite stable viability and function up to 4 days, we found significant changes in expression of key genes by day 2. Interestingly, we also observed that cirrhotic PCLS maintain viability in culture longer than slices from healthy animals. Due to the influence of matrix stiffness on fibrosis and hepatocellular function, it is important to evaluate prospective anti-fibrotic therapies in a platform that preserves tissue biomechanics. PCLS from cirrhotic animals represent a promising tool for the development of treatments for chronic liver disease.

3D bioprinting of liver models: A systematic scoping review of methods, bioinks, and reporting quality

Background

Effective communication is crucial for broad acceptance and applicability of alternative methods in 3R biomedical research and preclinical testing. 3D bioprinting is used to construct intricate biological structures towards functional liver models, specifically engineered for deployment as alternative models in drug screening, toxicological investigations, and tissue engineering. Despite a growing number of reviews in this emerging field, a comprehensive study, systematically assessing practices and reporting quality for bioprinted liver models is missing.

Methods

In this systematic scoping review we systematically searched MEDLINE (Ovid), EMBASE (Ovid) and BioRxiv for studies published prior to June 2nd, 2022. We extracted data on methodological conduct, applied bioinks, the composition of the printed model, performed experiments and model applications. Records were screened for eligibility and data were extracted from included articles by two independent reviewers from a panel of seven domain experts specializing in bioprinting and liver biology. We used RAYYAN for the screening process and SyRF for data extraction. We used R for data analysis, and R and Graphpad PRISM for visualization.

Results

Through our systematic database search we identified 1042 records, from which 63 met the eligibility criteria for inclusion in this systematic scoping review. Our findings revealed that extrusion-based printing, in conjunction with bioinks composed of natural components, emerged as the predominant printing technique in the bioprinting of liver models. Notably, the HepG2 hepatoma cell line was the most frequently employed liver cell type, despite acknowledged limitations. Furthermore, 51% of the printed models featured co-cultures with non-parenchymal cells to enhance their complexity. The included studies offered a variety of techniques for characterizing these liver models, with their primary application predominantly focused on toxicity testing. Among the frequently analyzed liver markers, albumin and urea stood out. Additionally, Cytochrome P450 (CYP) isoforms, primarily CYP3A and CYP1A, were assessed, and select studies employed nuclear receptor agonists to induce CYP activity.

Conclusion

Our systematic scoping review offers an evidence-based overview and evaluation of the current state of research on bioprinted liver models, representing a promising and innovative technology for creating alternative organ models. We conducted a thorough examination of both the methodological and technical facets of model development and scrutinized the reporting quality within the realm of bioprinted liver models. This systematic scoping review can serve as a valuable template for systematically evaluating the progress of organ model development in various other domains. The transparently derived evidence presented here can provide essential support to the research community, facilitating the adaptation of technological advancements, the establishment of standards, and the enhancement of model robustness. This is particularly crucial as we work toward the long-term objective of establishing new approach methods as reliable alternatives to animal testing, with extensive and versatile applications.

High-Voltage Electrostatic Field Hydrogel Microsphere 3D Culture System Improves Viability and Liver-like Properties of HepG2 Cells

Three-dimensional (3D) hepatocyte models have become a research hotspot for evaluating drug metabolism and hepatotoxicity. Compared to two-dimensional (2D) cultures, 3D cultures are better at mimicking the morphology and microenvironment of hepatocytes in vivo. However, commonly used 3D culture techniques are not suitable for high-throughput drug screening (HTS) due to their high cost, complex handling, and inability to simulate cell-extracellular matrix (ECM) interactions. This article describes a method for rapid and reproducible 3D cell cultures with ECM-cell interactions based on 3D culture instrumentation to provide more efficient HTS. We developed a microsphere preparation based on a high-voltage electrostatic (HVE) field and used sodium alginate- and collagen-based hydrogels as scaffolds for 3D cultures of HepG2 cells. The microsphere-generating device enables the rapid and reproducible preparation of bioactive hydrogel microspheres. This 3D culture system exhibited better cell viability, heterogeneity, and drug-metabolizing activity than 2D and other 3D culture models, and the long-term culture characteristics of this system make it suitable for predicting long-term liver toxicity. This system improves the overall applicability of HepG2 spheroids in safety assessment studies, and this simple and controllable high-throughput-compatible method shows potential for use in drug toxicity screening assays and mechanistic studies.

Development of an Induced Pluripotent Stem Cell-Based Liver-on-a-Chip Assessed with an Alzheimer's Disease Drug

Liver-related drug metabolism is a key aspect of pharmacokinetics and possible toxicity. From this perspective, the availability of advanced in vitro models for drug testing is still an open need, also to the end of reducing the burden of in vivo experiments. In this scenario, organ-on-a-chip is gaining attention as it couples a state-of-the art in vitro approach to the recapitulation of key in vivo physiological features such as fluidodynamics and a tri-dimensional cytoarchitecture. We implemented a novel liver-on-a-chip (LoC) device based on an innovative dynamic device (MINERVA 2.0) where functional hepatocytes (iHep) have been encapsulated into a 3D hydrogel matrix interfaced through a porous membrane with endothelial cells (iEndo)]. Both lines were derived from human-induced pluripotent stem cells (iPSCs), and the LoC was functionally assessed with donepezil, a drug approved for Alzheimer's disease therapy. The presence of iEndo and a 3D microenvironment enhanced the expression of liver-specific physiologic functions as in iHep, after 7 day perfusion, we noticed an increase of albumin, urea production, and cytochrome CYP3A4 expression compared to the iHep static culture. In particular, for donepezil kinetics, a computational fluid dynamic study conducted to assess the amount of donepezil diffused into the LoC indicated that the molecule should be able to pass through the iEndo and reach the target iHep construct. Then, we performed experiments of donepezil kinetics that confirmed the numerical simulations. Overall, our iPSC-based LoC reproduced the in vivo physiological microenvironment of the liver and was suitable for potential hepatotoxic screening studies.