Experimental liver models: From cell culture techniques to microfluidic organs-on-chip

Advances in liver organoids: replicating hepatic complexity for toxicity assessment and disease modeling

The lack of in vivo accurate human liver models hinders the investigation of liver-related diseases, injuries, and drug-related toxicity, posing challenges for both basic research and clinical applications. Traditional cellular and animal models, while widely used, have significant limitations in replicating the liver's complex responses to various stressors. Liver organoids derived from human pluripotent stem cells, adult stem cells primary cells, or tissues can mimic diverse liver cell types, major physiological functions, and architectural features. Recent advancements in the field have shown that some liver organoids have sufficient accuracy to replicate specific aspects of the human liver's complexity. This review highlights recent progress in liver organoid research, with a particular emphasis on their potential for toxicity assessment and disease modeling. The intrinsic advantages of liver organoids include higher sensitivity and suitability for long-term studies, which enhance the predictive value in drug and nanomaterial toxicity testing. The integration of liver organoids with microfluidic devices enables the simulation of the liver microenvironment and facilitates high-throughput drug screening. The liver organoids also serve as ideal platforms for studying liver diseases such as hepatitis, liver fibrosis, viral liver diseases, and monogenic diseases. Additionally, this review discusses the advantages and limitations of liver organoids along with potential avenues for future research.

Management of intrahepatic cholangiocarcinoma: a review for clinicians

Intrahepatic cholangiocarcinoma (iCCA) is an aggressive liver malignancy that arises from second-order biliary epithelial cells. Its incidence is gradually increasing worldwide. Well-known risk factors have been described, although in many cases, they are not identifiable. Treatment options are continuously expanding, but the prognosis of iCCA remains dismal. R0 liver resection remains the only curative treatment, but only a limited number of patients can benefit from it. Frequently, major hepatectomies are needed to completely remove the tumour. This could contraindicate surgery or increase postoperative morbidity in patients with chronic liver disease and small remnant liver volume. In cases of anticipated inadequate future liver remnant, regenerative techniques may be used to expand resectability. The role and extent of lymphadenectomy in iCCA are still matters of debate. Improvements in iCCA diagnosis and better understanding of genetic profiles might lead to optimized surgical approaches and drug therapies. The role of neoadjuvant and adjuvant therapies is broadening, gaining more and more acceptance in clinical practice. Combining surgery with locoregional therapies and novel drugs, such as checkpoint-inhibitors and molecular-targeted molecules, might improve treatment options and survival rates. Liver transplantation, after very poor initial results, is now receiving attention for the treatment of patients with unresectable very early iCCA (i.e. <2 cm) in cirrhotic livers, showing survival outcomes comparable to those of hepatocellular carcinoma. Ongoing prospective protocols are testing the efficacy of liver transplantation for patients with unresectable, advanced tumours confined to the liver, with sustained response to neoadjuvant treatment. In such a continuously changing landscape, the aim of our work is to review the state-of-the-art in the surgical and medical treatment of iCCA.

Evaluation of the Leaves and Seeds of Cucurbitaceae Plants as a New Source of Bioactive Compounds for Colorectal Cancer Prevention and Treatment

BACKGROUND/OBJECTIVES

The Cucurbitaceae family represents an important source of bioactive compounds with antioxidant, antimicrobial, anti-inflammatory and antitumor activities. This study aims to investigate the potential application of Cucurbitaceae leaves and seed extracts to prevent and treat colorectal cancer (CRC).

METHODS

Four extracts (ethanol extracts and protein extracts and hydrolysates) from the leaves and seeds of cucurbits were tested in T-84, HCT-15 and HT-29 CRC cells. The antitumor, antiangiogenic, antioxidant and chemopreventive potentials and bioactive composition of the active extracts were characterized.

RESULTS

Cold ethanolic extracts from the leaves and seeds of two interspecific Cucurbita genera (CLU01002 and COK01001) exhibited potent antiproliferative, specific and non-hepatotoxic activity against CRC cell lines, with a slight synergistic effect in combination with oxaliplatin. This antitumor activity was related to G2/M cell cycle arrest, the extrinsic apoptosis pathway, cytokinesis inhibition and autophagy. The extracts also inhibited tumor clonogenicity and angiogenesis, and modulated cancer stem cell (CSC) gene expression, as well as expressing antioxidant and chemopreventive cellular capabilities. Finally, phenolic and cucurbitane-type triterpenoid compounds (pengxianencins and cucurbitacins) were tentatively identified in the active extracts by UPLC-MS analysis and bioguided fractionation.

CONCLUSIONS

Extracts from leaves the and seeds of two interspecific Cucurbita genera (CLU01002 and COK01001) may contribute to the improvement of prevention and treatment strategies for CRC patients.

Liver-on-a-Chip Integrated with Label-Free Optical Biosensors for Rapid and Continuous Monitoring of Drug-Induced Toxicity

Drug toxicity assays using conventional 2D static cultures and animal studies have limitations preventing the translation of potential drugs to the clinic. The recent development of organs-on-a-chip platforms provides promising alternatives for drug toxicity/screening assays. However, most studies conducted with these platforms only utilize single endpoint results, which do not provide real-time/ near real-time information. Here, a versatile technology is presented that integrates a 3D liver-on-a-chip with a label-free photonic crystal-total internal reflection (PC-TIR) biosensor for rapid and continuous monitoring of the status of cells. This technology can detect drug-induced liver toxicity by continuously monitoring the secretion rates and levels of albumin and glutathione S-transferase α (GST-α) of a 3D liver on-a-chip model treated with Doxorubicin. The PC-TIR biosensor is based on a one-step antibody functionalization with high specificity and a detection range of 21.7 ng mL-1 to 7.83 x 103 ng mL-1 for albumin and 2.20 ng mL-1 to 7.94 x 102 ng mL-1 for GST-α. This approach provides critical advantages for the early detection of drug toxicity and improved temporal resolution to capture transient drug effects. The proposed proof-of-concept study introduces a scalable and efficient plug-in solution for organ-on-a-chip technologies, advancing drug development and in vitro testing methods by enabling timely and accurate toxicity assessments.

Combining human liver ECM with topographically featured electrospun scaffolds for engineering hepatic microenvironment

Liver disease cases are rapidly expanding worldwide, and transplantation remains the only effective cure for end-stage disease. There is an increasing demand for developing potential drug treatments, and regenerative therapies using in-vitro culture platforms. Human decellularized extracellular matrix (dECM) is an appealing alternative to conventional animal tissues as it contains human-specific proteins and can serve as scaffolding materials. Herein we exploit this with human donor tissue from discarded liver which was not suitable for transplant using a synergistic approach to combining biological and topographical cues in electrospun materials as an in-vitro culture platform. To realise this, we developed a methodology for incorporating human liver dECM into electrospun polycaprolactone (PCL) fibres with surface nanotopographies (230-580 nm). The hybrid scaffolds were fabricated using varying concentrations of dECM; their morphology, mechanical properties, hydrophilicity and stability were analysed. The scaffolds were validated using HepG2 and primary mouse hepatocytes, with subsequent results indicating that the modified scaffolds-maintained cell growth and influenced cell attachment, proliferation and hepatic-related gene expression. This work demonstrates a novel approach to harvesting the potential from decellularized human tissues in the form of innovative in-vitro culture platforms for liver.

Convenient rapid prototyping microphysiological niche for mimicking liver native basement membrane: Liver sinusoid on a chip

Liver is responsible for the metabolization processes of up to 90 % of compounds and toxins in the body. Therefore liver-on-a-chip systems, as an in vitro promising cell culture platform, have great importance for fundamental science and drug development. In most of the liver-on-a-chip studies, seeding cells on both sides of a porous membrane, which represents the basement membrane, fail to resemble the native characteristics of biochemical, biophysical, and mechanical properties. In this study, polycarbonate (PC) and polyethylene terephthalate (PET) membranes were coated with gelatin to address this issue by accurately mimicking the native basement membrane present in the space of Disse. Various coating methods were used, including doctor blade, gel micro-injection, electrospinning, and spin coating. Spin coating was demonstrated to be the most effective technique owing to the ability to produce thin gel thickness with desirable surface roughness for cell interactions on both sides of the membrane. HepG2 and EA.HY926 cells were seeded on the upper and bottom sides of the gelatin-coated PET membrane and cultured on-chip for 7 days. Cell viability increased from 90 % to 95 %, while apoptotic index decreased. Albumin secretion notably rose between days 1-7 and 4-7, while GST-α secretion decreased from day 1 to day 7. In conclusion, the optimized spin coating process reported here can effectively modify the membranes to better mimic the native basement membrane niche characteristics.

Guidelines for mitochondrial RNA analysis

Mitochondria are the energy-producing organelles of mammalian cells with critical involvement in metabolism and signaling. Studying their regulation in pathological conditions may lead to the discovery of novel drugs to treat, for instance, cardiovascular or neurological diseases, which affect high-energy-consuming cells such as cardiomyocytes, hepatocytes, or neurons. Mitochondria possess both protein-coding and noncoding RNAs, such as microRNAs, long noncoding RNAs, circular RNAs, and piwi-interacting RNAs, encoded by the mitochondria or the nuclear genome. Mitochondrial RNAs are involved in anterograde-retrograde communication between the nucleus and mitochondria and play an important role in physiological and pathological conditions. Despite accumulating evidence on the presence and biogenesis of mitochondrial RNAs, their study continues to pose significant challenges. Currently, there are no standardized protocols and guidelines to conduct deep functional characterization and expression profiling of mitochondrial RNAs. To overcome major obstacles in this emerging field, the EU-CardioRNA and AtheroNET COST Action networks summarize currently available techniques and emphasize critical points that may constitute sources of variability and explain discrepancies between published results. Standardized methods and adherence to guidelines to quantify and study mitochondrial RNAs in normal and disease states will improve research outputs, their reproducibility, and translation potential to clinical application.

From Chips-in-Lab to Point-of-Care Live Cell Device: Development of a Microfluidic Device for On-Site Cell Culture and High-Throughput Drug Screening

Live cell assays provide real-time data of cellular responses. In combination with microfluidics, applications such as automated and high-throughput drug screening on live cells can be accomplished in small devices. However, their application in point-of-care testing (POCT) is limited by the requirement for bulky equipment to maintain optimal cell culture conditions. In this study, we propose a POCT device that allows on-site cell culture and high-throughput drug screening on live cells. We first observe that cell viabilities are substantially affected by liquid evaporation within the microfluidic device, which is intrinsic to the polydimethylsiloxane (PDMS) material due to its hydrophobic nature and nanopatterned surface. The unwanted PDMS-liquid-air interface in the cell culture environment can be eliminated by maintaining a persistent humidity of 95-100% or submerging the whole microfluidic device under water. Our results demonstrate that in the POCT device equipped with a water tank, both primary cells and cell lines can be maintained for up to 1 week without the need for external cell culture equipment. Moreover, this device is powered by a standard alkali battery and can automatically screen over 5000 combinatorial drug conditions for regulating neural stem cell differentiation. By monitoring dynamic variations in fluorescent markers, we determine the optimal doses of platelet-derived growth factor and epidermal growth factor to suppress proinflammatory S100A9-induced neuronal toxicities. Overall, this study presents an opportunity to transform lab-on-a-chip technology from a laboratory-based approach to actual point-of-care devices capable of performing complex experimental procedures on-site and offers significant advancements in the fields of personalized medicine and rapid clinical diagnostics.

Preclinical Models of Hepatocellular Carcinoma: Current Utility, Limitations, and Challenges

Hepatocellular carcinoma (HCC), the predominant primary liver tumor, remains one of the most lethal cancers worldwide, despite the advances in therapy in recent years. In addition to the traditional chemically and dietary-induced HCC models, a broad spectrum of novel preclinical tools have been generated following the advent of transgenic, transposon, organoid, and in silico technologies to overcome this gloomy scenario. These models have become rapidly robust preclinical instruments to unravel the molecular pathogenesis of liver cancer and establish new therapeutic approaches against this deadly disease. The present review article aims to summarize and discuss the commonly used preclinical models for HCC, evaluating their strengths and weaknesses.

Advances and challenges in organ-on-chip technology: toward mimicking human physiology and disease in vitro

Organs-on-chips have been tissues or three-dimensional (3D) mini-organs that comprise numerous cell types and have been produced on microfluidic chips to imitate the complicated structures and interactions of diverse cell types and organs under controlled circumstances. Several morphological and physiological distinctions exist between traditional 2D cultures, animal models, and the growing popular 3D cultures. On the other hand, animal models might not accurately simulate human toxicity because of physiological variations and interspecies metabolic capability. The on-chip technique allows for observing and understanding the process and alterations occurring in metastases. The present study aimed to briefly overview single and multi-organ-on-chip techniques. The current study addresses each platform's essential benefits and characteristics and highlights recent developments in developing and utilizing technologies for single and multi-organs-on-chips. The study also discusses the drawbacks and constraints associated with these models, which include the requirement for standardized procedures and the difficulties of adding immune cells and other intricate biological elements. Finally, a comprehensive review demonstrated that the organs-on-chips approach has a potential way of investigating organ function and disease. The advancements in single and multi-organ-on-chip structures can potentially increase drug discovery and minimize dependency on animal models, resulting in improved therapies for human diseases.

High-Scale 3D-Bioprinting Platform for the Automated Production of Vascularized Organs-on-a-Chip

3D bioprinting possesses the potential to revolutionize contemporary methodologies for fabricating tissue models employed in pharmaceutical research and experimental investigations. This is enhanced by combining bioprinting with advanced organs-on-a-chip (OOCs), which includes a complex arrangement of multiple cell types representing organ-specific cells, connective tissue, and vasculature. However, both OOCs and bioprinting so far demand a high degree of manual intervention, thereby impeding efficiency and inhibiting scalability to meet technological requirements. Through the combination of drop-on-demand bioprinting with robotic handling of microfluidic chips, a print procedure is achieved that is proficient in managing three distinct tissue models on a chip within only a minute, as well as capable of consecutively processing numerous OOCs without manual intervention. This process rests upon the development of a post-printing sealable microfluidic chip, that is compatible with different types of 3D-bioprinters and easily connected to a perfusion system. The capabilities of the automized bioprint process are showcased through the creation of a multicellular and vascularized liver carcinoma model on the chip. The process achieves full vascularization and stable microvascular network formation over 14 days of culture time, with pronounced spheroidal cell growth and albumin secretion of HepG2 serving as a representative cell model.

In Vitro Human Liver Model for Toxicity Assessment with Clinical and Preclinical Instrumentation

The existing in vitro toxicological models lack translational potential, which makes difficult the application of gathered information to clinical usage. To tackle this issue, we built a model with four different types of primary liver cells: hepatic sinusoidal endothelial cells, hepatic stellate cells, Kupffer cells and hepatocytes. We cultured them in different combinations of composition and volumes of cell medium, hepatocyte proportions of total cells and additions of extracellular matrixes. We added rifampicin (RIF), ibuprofen (IBU) and 5-fluorouracil (5-FU) to this model and observed the microanatomy and physiology changes for a week with preclinical and clinical instruments. Among the different model configurations, we selected the feature combination of the in vitro model that had similar biomarker values to those measured in clinical diagnostics. When we exposed the selected model configuration to RIF, IBU and 5-FU, we observed similar glucose, triglyceride and albumin dynamics as in vivo (from clinical data). Therefore, we have built an in vitro liver model that resembles the liver microenvironment, and we have analysed it with clinical instrumentation to facilitate data translation. Furthermore, during these observations, we found that Kupffer and LSEC cells are suitable candidates for the search for clinical diagnostic markers of liver function.

Reducing Inert Materials for Optimal Cell-Cell and Cell-Matrix Interactions within Microphysiological Systems

In the pursuit of achieving a more realistic in vitro simulation of human biological tissues, microfluidics has emerged as a promising technology. Organ-on-a-chip (OoC) devices, a product of this technology, contain miniature tissues within microfluidic chips, aiming to closely mimic the in vivo environment. However, a notable drawback is the presence of inert material between compartments, hindering complete contact between biological tissues. Current membranes, often made of PDMS or plastic materials, prevent full interaction between cell types and nutrients. Furthermore, their non-physiological mechanical properties and composition may induce unexpected cell responses. Therefore, it is essential to minimize the contact area between cells and the inert materials while simultaneously maximizing the direct contact between cells and matrices in different compartments. The main objective of this work is to minimize inert materials within the microfluidic chip while preserving proper cellular distribution. Two microfluidic devices were designed, each with a specific focus on maximizing direct cell-matrix or cell-cell interactions. The first chip, designed to increase direct cell-cell interactions, incorporates a nylon mesh with regular pores of 150 microns. The second chip minimizes interference from inert materials, thereby aiming to increase direct cell-matrix contact. It features an inert membrane with optimized macropores of 1 mm of diameter for collagen hydrogel deposition. Biological validation of both devices has been conducted through the implementation of cell migration and cell-to-cell interaction assays, as well as the development of epithelia, from isolated cells or spheroids. This endeavor contributes to the advancement of microfluidic technology, aimed at enhancing the precision and biological relevance of in vitro simulations in pursuit of more biomimetic models.

Cholangiocarcinoma-on-a-chip: A human 3D platform for personalised medicine

BACKGROUND & AIMS

Cholangiocarcinoma (CCA) is a primary liver tumour characterised by a poor prognosis and limited therapeutic options. Available 3D human CCA models fail to faithfully recapitulate the tumour niche. We aimed to develop an innovative patient-specific CCA-on-chip platform.

METHODS

A CCA tumour microenvironment was recapitulated on a microfluidic three-channel chip using primary CCA cells, cancer-associated fibroblasts (CAFs), endothelial cells, and T cells isolated from CCA specimens (n = 6). CAF and CCA cells were co-cultured in the central channel, flanked by endothelial cells in one lateral channel, recreating a tubular structure. An extensive characterisation of this platform was carried out to investigate its diffusion ability, hydrogel properties, and changes in matrix composition. Cell phenotype and functional properties were assessed.

RESULTS

Primary cells seeded on the microfluidic device were shown to reproduce the architectural structure and maintain the original phenotype and functional properties. The tumour niche underwent a deep remodelling in the 3D device, with an increase in hydrogel stiffness and extracellular matrix deposition, mimicking in vivo CCA characteristics. T cells were incorporated into the device to assess its reliability for immune cell interaction studies. Higher T cell migration was observed using cells from patients with highly infiltrated tumours. Finally, the drug trial showed the ability of the device to recapitulate different drug responses based on patient characteristics.

CONCLUSIONS

We presented a 3D CCA platform that integrates the major non-immune components of the tumour microenvironment and the T cell infiltrate, reflecting the CCA niche. This CCA-on-chip represents a reliable patient-specific 3D platform that will be of help to further elucidate the biological mechanisms involved in CCA and provide an efficient tool for personalised drug testing.

IMPACT AND IMPLICATIONS

An innovative patient-specific cholangiocarcinoma (CCA)-on-chip platform was successfully developed, integrating the major components of the tumour microenvironment (tumour cells, cancer-associated fibroblasts, endothelial cells, and immune infiltrate) and faithfully mimicking the CCA niche. This CCA-on-chip represents a powerful tool for unravelling disease-associated cellular mechanisms in CCA and provides an efficient tool for personalised drug testing.

Coculture model of a liver sinusoidal endothelial cell barrier and HepG2/C3a spheroids-on-chip in an advanced fluidic platform

The liver is one of the main organs involved in the metabolism of xenobiotics and a key organ in toxicity studies. Prior to accessing the hepatocytes, xenobiotics pass through the hepatic sinusoid formed by liver sinusoidal endothelial cells (LSECs). The LSECs barrier regulates the kinetics and concentrations of the xenobiotics before their metabolic processing by the hepatocytes. To mimic this physiological situation, we developed an in vitro model reproducing an LSECs barrier in coculture with a hepatocyte biochip, using a fluidic platform. This technology made dynamic coculture and tissue crosstalk possible. SK-HEP-1 and HepG2/C3a cells were used as LSECs and as hepatocyte models, respectively. We confirmed the LSECs phenotype by measuring PECAM-1 and stabilin-2 expression levels and the barrier's permeability/transport properties with various molecules. The tightness of the SK-HEP-1 barrier was enhanced in the dynamic coculture. The morphology, albumin secretion, and gene expression levels of markers of HepG2/C3a were not modified by coculture with the LSECs barrier. Using acetaminophen, a well-known hepatotoxic drug, to study tissue crosstalk, there was a reduction in the expression levels of the LSECs markers stabilin-2 and PECAM-1, and a modification of those of CLEC4M and KDR. No HepG2/C3a toxicity was observed. The metabolisation of acetaminophen by HepG2/C3a monocultures and cocultures was confirmed. Although primary cells are required to propose a fully relevant model, the present approach highlights the potential of our system for investigating xenobiotic metabolism and toxicity.

Insight to Biofabrication of Liver Microtissues for Disease Modeling: Challenges and Opportunities

In the last decade, liver diseases with high mortality rates have become one of the most important health problems in the world. Organ transplantation is currently considered the most effective treatment for compensatory liver failure. An increasing number of patients and shortage of donors has led to the attention of reconstructive medicine methods researchers. The biggest challenge in the development of drugs effective in chronic liver disease is the lack of a suitable preclinical model that can mimic the microenvironment of liver problems. Organoid technology is a rapidly evolving field that enables researchers to reconstruct, evaluate, and manipulate intricate biological processes in vitro. These systems provide a biomimetic model for studying the intercellular interactions necessary for proper organ function and architecture in vivo. Liver organoids, formed by the self-assembly of hepatocytes, are microtissues and can exhibit specific liver characteristics for a long time in vitro. Hepatic organoids are identified as an impressive tool for evaluating potential cures and modeling liver diseases. Modeling various liver diseases, including tumors, fibrosis, non-alcoholic fatty liver, etc., allows the study of the effects of various drugs on these diseases in personalized medicine. Here, we summarize the literature relating to the hepatic stem cell microenvironment and the formation of liver Organoids.

Microphysiological Constructs and Systems: Biofabrication Tactics, Biomimetic Evaluation Approaches, and Biomedical Applications

In recent decades, microphysiological constructs and systems (MPCs and MPSs) have undergone significant development, ranging from self-organized organoids to high-throughput organ-on-a-chip platforms. Advances in biomaterials, bioinks, 3D bioprinting, micro/nanofabrication, and sensor technologies have contributed to diverse and innovative biofabrication tactics. MPCs and MPSs, particularly tissue chips relevant to absorption, distribution, metabolism, excretion, and toxicity, have demonstrated potential as precise, efficient, and economical alternatives to animal models for drug discovery and personalized medicine. However, current approaches mainly focus on the in vitro recapitulation of the human anatomical structure and physiological-biochemical indices at a single or a few simple levels. This review highlights the recent remarkable progress in MPC and MPS models and their applications. The challenges that must be addressed to assess the reliability, quantify the techniques, and utilize the fidelity of the models are also discussed.

A method to generate perfusable physiologic-like vascular channels within a liver-on-chip model

The human vasculature is essential in organs and tissues for the transport of nutrients, metabolic waste products, and the maintenance of homeostasis. The integration of vessels in in vitro organs-on-chip may, therefore, improve the similarity to the native organ microenvironment, ensuring proper physiological functions and reducing the gap between experimental research and clinical outcomes. This gap is particularly evident in drug testing and the use of vascularized models may provide more realistic insights into human responses to drugs in the pre-clinical phases of the drug development pipeline. In this context, different vascularized liver models have been developed to recapitulate the architecture of the hepatic sinusoid, exploiting either porous membranes or bioprinting techniques. In this work, we developed a method to generate perfusable vascular channels with a circular cross section within organs-on-chip without any interposing material between the parenchyma and the surrounding environment. Through this technique, vascularized liver sinusoid-on-chip systems with and without the inclusion of the space of Disse were designed and developed. The recapitulation of the Disse layer, therefore, a gap between hepatocytes and endothelial cells physiologically present in the native liver milieu, seems to enhance hepatic functionality (e.g., albumin production) compared to when hepatocytes are in close contact with endothelial cells. These findings pave the way to numerous further uses of microfluidic technologies coupled with vascularized tissue models (e.g., immune system perfusion) as well as the integration within multiorgan-on-chip settings.

Reproducibility and Robustness of a Liver Microphysiological System PhysioMimix LC12 under Varying Culture Conditions and Cell Type Combinations

The liver is one of the key organs for exogenous and endogenous metabolism and is often a target for drug- and chemical-driven toxicity. A wide range of experimental approaches has been established to model and characterize the mechanisms of drug- and chemical-induced hepatotoxicity. A number of microfluidics-enabled in vitro models of the liver have been developed, but the unclear translatability of these platforms has hindered their adoption by the pharmaceutical industry; to achieve wide use for drug and chemical safety evaluation, demonstration of reproducibility and robustness under various contexts of use is required. One of these commercially available platforms is the PhysioMimix LC12, a microfluidic device where cells are seeded into a 3D scaffold that is continuously perfused with recirculating cell culture media to mimic liver sinusoids. Previous studies demonstrated this model's functionality and potential applicability to preclinical drug development. However, to gain confidence in PhysioMimix LC12's robustness and reproducibility, supplementary characterization steps are needed, including the assessment of various human hepatocyte sources, contribution of non-parenchymal cells (NPCs), and comparison to other models. In this study, we performed replicate studies averaging 14 days with either primary human hepatocytes (PHHs) or induced pluripotent stem cell (iPSC)-derived hepatocytes, with and without NPCs. Albumin and urea secretion, lactate dehydrogenase, CYP3A4 activity, and metabolism were evaluated to assess basal function and metabolic capacity. Model performance was characterized by different cell combinations under intra- and inter-experimental replication and compared to multi-well plates and other liver platforms. PhysioMimix LC12 demonstrated the highest metabolic function with PHHs, with or without THP-1 or Kupffer cells, for up to 10-14 days. iPSC-derived hepatocytes and PHHs co-cultured with additional NPCs demonstrated sub-optimal performance. Power analyses based on replicate experiments and different contexts of use will inform future study designs due to the limited throughput and high cell demand. Overall, this study describes a workflow for independent testing of a complex microphysiological system for specific contexts of use, which may increase end-user adoption in drug development.

Pumped and pumpless microphysiological systems to study (nano)therapeutics

Fluidic microphysiological systems (MPS) are microfluidic cell culture devices that are designed to mimic the biochemical and biophysical in vivo microenvironments of human tissues better than conventional petri dishes or well-plates. MPS-grown tissue cultures can be used for probing new drugs for their potential primary and secondary toxicities as well as their efficacy. The systems can also be used for assessing the effects of environmental nanoparticles and nanotheranostics, including their rate of uptake, biodistribution, elimination, and toxicity. Pumpless MPS are a group of MPS that often utilize gravity to recirculate cell culture medium through their microfluidic networks, providing some advantages, but also presenting some challenges. They can be operated with near-physiological amounts of blood surrogate (i.e., cell culture medium) that can recirculate in bidirectional or unidirectional flow patterns depending on the device configuration. Here we discuss recent advances in the design and use of both pumped and pumpless MPS with a focus on where pumpless devices can contribute to realizing the potential future role of MPS in evaluating nanomaterials. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

NAFLD-Related HCC: Focus on the Latest Relevant Preclinical Models

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and one of the deadliest cancers worldwide. Despite extensive research, the biological mechanisms underlying HCC's development and progression remain only partially understood. Chronic overeating and/or sedentary-lifestyle-associated obesity, which promote Non-Alcoholic Fatty Liver Disease (NAFLD), have recently emerged as worrying risk factors for HCC. NAFLD is characterized by excessive hepatocellular lipid accumulation (steatosis) and affects one quarter of the world's population. Steatosis progresses in the more severe inflammatory form, Non-Alcoholic Steatohepatitis (NASH), potentially leading to HCC. The incidence of NASH is expected to increase by up to 56% over the next 10 years. Better diagnoses and the establishment of effective treatments for NAFLD and HCC will require improvements in our understanding of the fundamental mechanisms of the disease's development. This review describes the pathogenesis of NAFLD and the mechanisms underlying the transition from NAFL/NASH to HCC. We also discuss a selection of appropriate preclinical models of NAFLD for research, from cellular models such as liver-on-a-chip models to in vivo models, focusing particularly on mouse models of dietary NAFLD-HCC.

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.

Experimental models of fatty liver diseases: Status and appraisal

Fatty liver diseases, including alcohol-associated liver disease (ALD) and nonalcoholic fatty liver disease nonalcoholic fatty liver disease (NAFLD), affect a large number of people worldwide and become one of the major causes of end-stage liver disease, such as liver cirrhosis and hepatocellular carcinoma (HCC). Unfortunately, there are currently no approved pharmacological treatments for ALD or NAFLD. This situation highlights the urgent need to explore new intervention targets and discover effective therapeutics for ALD and NAFLD. The lack of properly validated preclinical disease models is a major obstacle to the development of clinical therapies. ALD and NAFLD models have been in the development for decades, but there are still no models that recapitulate the full spectrum of ALD and NAFLD. Throughout this review, we summarize the current in vitro and in vivo models used for research on fatty liver diseases and discuss the advantages and limitations of these models.

Microneedle array facilitates hepatic sinusoid construction in a large-scale liver-acinus-chip microsystem

Hepatic sinusoids play a key role in maintaining high activities of liver cells in the hepatic acinus. However, the construction of hepatic sinusoids has always been a challenge for liver chips, especially for large-scale liver microsystems. Herein, we report an approach for the construction of hepatic sinusoids. In this approach, hepatic sinusoids are formed by demolding a self-developed microneedle array from a photocurable cell-loaded matrix in a large-scale liver-acinus-chip microsystem with a designed dual blood supply. Primary sinusoids formed by demolded microneedles and spontaneously self-organized secondary sinusoids can be clearly observed. Benefiting from significantly enhanced interstitial flows by formed hepatic sinusoids, cell viability is witnessed to be considerably high, liver microstructure formation occurs, and hepatocyte metabolism is enhanced. In addition, this study preliminarily demonstrates the effects of the resulting oxygen and glucose gradients on hepatocyte functions and the application of the chip in drug testing. This work paves the way for the biofabrication of fully functionalized large-scale liver bioreactors.

In Vitro Hepatic Models to Assess Herb-Drug Interactions: Approaches and Challenges

A newfound appreciation for the benefits of herbal treatments has emerged in recent decades. However, herbal medication production still needs to establish standardized protocols that adhere to strict guidelines for quality assurance and risk minimization. Although the therapeutic effects of herbal medicines are extensive, the risk of herb-drug interactions remains a serious concern, limiting their use. Therefore, a robust, well-established liver model that can fully represent the liver tissue is required to study potential herb-drug interactions to ensure herbal medicines' safe and effective use. In light of this, this mini review investigates the existing in vitro liver models applicable to detecting herbal medicines' toxicity and other pharmacological targets. This article analyzes the benefits and drawbacks of existing in vitro liver cell models. To maintain relevance and effectively express the offered research, a systematic strategy was employed to search for and include all discussed studies. In brief, from 1985 to December 2022, the phrases "liver models", "herb-drug interaction", "herbal medicine", "cytochrome P450", "drug transporters pharmacokinetics", and "pharmacodynamics" were combined to search the electronic databases PubMed, ScienceDirect, and the Cochrane Library.

Liver Regeneration and Immunity: A Tale to Tell

The physiological importance of the liver is demonstrated by its unique and essential ability to regenerate following extensive injuries affecting its function. By regenerating, the liver reacts to hepatic damage and thus enables homeostasis to be restored. The aim of this review is to add new findings that integrate the regenerative pathway to the current knowledge. An optimal regeneration is achieved through the integration of two main pathways: IL-6/JAK/STAT3, which promotes hepatocyte proliferation, and PI3K/PDK1/Akt, which in turn enhances cell growth. Proliferation and cell growth are events that must be balanced during the three phases of the regenerative process: initiation, proliferation and termination. Achieving the correct liver/body weight ratio is ensured by several pathways as extracellular matrix signalling, apoptosis through caspase-3 activation, and molecules including transforming growth factor-beta, and cyclic adenosine monophosphate. The actors involved in the regenerative process are numerous and many of them are also pivotal players in both the immune and non-immune inflammatory process, that is observed in the early stages of hepatic regeneration. Balance of Th17/Treg is important in liver inflammatory process outcomes. Knowledge of liver regeneration will allow a more detailed characterisation of the molecular mechanisms that are crucial in the interplay between proliferation and inflammation.

In Vitro Models for the Study of Liver Biology and Diseases: Advances and Limitations

In vitro models of liver (patho)physiology, new technologies, and experimental approaches are progressing rapidly. Based on cell lines, induced pluripotent stem cells or primary cells derived from mouse or human liver as well as whole tissue (slices), such in vitro single- and multicellular models, including complex microfluidic organ-on-a-chip systems, provide tools to functionally understand mechanisms of liver health and disease. The International Society of Hepatic Sinusoidal Research (ISHSR) commissioned this working group to review the currently available in vitro liver models and describe the advantages and disadvantages of each in the context of evaluating their use for the study of liver functionality, disease modeling, therapeutic discovery, and clinical applicability.

Advances in the application of 3D tumor models in precision oncology and drug screening

Traditional tumor models cannot perfectly simulate the real state of tumors in vivo, resulting in the termination of many clinical trials. 3D tumor models’ technology provides new in vitro models that bridge the gap between in vitro and in vivo findings, and organoids maintain the properties of the original tissue over a long period of culture, which enables extensive research in this area. In addition, they can be used as a substitute for animal and in vitro models, and organoids can be established from patients’ normal and malignant tissues, with unique advantages in clinical drug development and in guiding individualized therapies. 3D tumor models also provide a promising platform for high-throughput research, drug and toxicity testing, disease modeling, and regenerative medicine. This report summarizes the 3D tumor model, including evidence regarding the 3D tumor cell culture model, 3D tumor slice model, and organoid culture model. In addition, it provides evidence regarding the application of 3D tumor organoid models in precision oncology and drug screening. The aim of this report is to elucidate the value of 3D tumor models in cancer research and provide a preclinical reference for the precise treatment of cancer patients.

Development of Liver-on-Chip Integrating a Hydroscaffold Mimicking the Liver’s Extracellular Matrix

The 3Rs guidelines recommend replacing animal testing with alternative models. One of the solutions proposed is organ-on-chip technology in which liver-on-chip is one of the most promising alternatives for drug screening and toxicological assays. The main challenge is to achieve the relevant in vivo-like functionalities of the liver tissue in an optimized cellular microenvironment. Here, we investigated the development of hepatic cells under dynamic conditions inside a 3D hydroscaffold embedded in a microfluidic device. The hydroscaffold is made of hyaluronic acid and composed of liver extracellular matrix components (galactosamine, collagen I/IV) with RGDS (Arg-Gly-Asp-Ser) sites for cell adhesion. The HepG2/C3A cell line was cultured under a flow rate of 10 µL/min for 21 days. After seeding, the cells formed aggregates and proliferated, forming 3D spheroids. The cell viability, functionality, and spheroid integrity were investigated and compared to static cultures. The results showed a 3D aggregate organization of the cells up to large spheroid formations, high viability and albumin production, and an enhancement of HepG2 cell functionalities. Overall, these results highlighted the role of the liver-on-chip model coupled with a hydroscaffold in the enhancement of cell functions and its potential for engineering a relevant liver model for drug screening and disease study.

Advancements in the Alcohol-Associated Liver Disease Model

Alcohol-associated liver disease (ALD) is an intricate disease that results in a broad spectrum of liver damage. The presentation of ALD can include simple steatosis, steatohepatitis, liver fibrosis, cirrhosis, and even hepatocellular carcinoma (HCC). Effective prevention and treatment strategies are urgently required for ALD patients. In previous decades, numerous rodent models were established to investigate the mechanisms of alcohol-associated liver disease and explore therapeutic targets. This review provides a summary of the latest developments in rodent models, including those that involve EtOH administration, which will help us to understand the characteristics and causes of ALD at different stages. In addition, we discuss the pathogenesis of ALD and summarize the existing in vitro models. We analyse the pros and cons of these models and their translational relevance and summarize the insights that have been gained regarding the mechanisms of alcoholic liver injury.

Advances in Organ-on-a-Chip Materials and Devices

The organ-on-a-chip (OoC) paves a way for biomedical applications ranging from preclinical to clinical translational precision. The current trends in the in vitro modeling is to reduce the complexity of human organ anatomy to the fundamental cellular microanatomy as an alternative of recreating the entire cell milieu that allows systematic analysis of medicinal absorption of compounds, metabolism, and mechanistic investigation. The OoC devices accurately represent human physiology in vitro; however, it is vital to choose the correct chip materials. The potential chip materials include inorganic, elastomeric, thermoplastic, natural, and hybrid materials. Despite the fact that polydimethylsiloxane is the most commonly utilized polymer for OoC and microphysiological systems, substitute materials have been continuously developed for its advanced applications. The evaluation of human physiological status can help to demonstrate using noninvasive OoC materials in real-time procedures. Therefore, this Review examines the materials used for fabricating OoC devices, the application-oriented pros and cons, possessions for device fabrication and biocompatibility, as well as their potential for downstream biochemical surface alteration and commercialization. The convergence of emerging approaches, such as advanced materials, artificial intelligence, machine learning, three-dimensional (3D) bioprinting, and genomics, have the potential to perform OoC technology at next generation. Thus, OoC technologies provide easy and precise methodologies in cost-effective clinical monitoring and treatment using standardized protocols, at even personalized levels. Because of the inherent utilization of the integrated materials, employing the OoC with biomedical approaches will be a promising methodology in the healthcare industry.

Distinct Roles of the Sister Nuclear Receptors PXR and CAR in Liver Cancer Development

Pregnane X receptor (PXR) and constitutively active receptor/constitutive androstane receptor (CAR) are xenobiotic-responsible transcription factors belonging to the same nuclear receptor gene subfamily and highly expressed in the liver. These receptors are activated by a variety of chemicals and play pivotal roles in many liver functions, including xenobiotic metabolism and disposition. Phenobarbital, an enzyme inducer and liver tumor promoter, activates both rodent and human CAR but causes liver tumors only in rodents. Although the precise mechanism for phenobarbital/CAR-mediated liver tumor formation remains to be established, intracellular pathways, including the Hippo pathway/Yes-associated protein-TEA-domain family members system and β-catenin signaling, seem to be involved. In contrast to CAR, previous findings by our group suggest that PXR activation does not promote hepatocyte proliferation but it enhances the proliferation induced by various stimuli. Moreover, and surprisingly, PXR may have antitumor effects in both rodents and humans by targeting inflammatory cytokine signals, angiogenesis and epithelial-mesenchymal transition. In this review, we summarize the current knowledge on the associations of PXR and CAR with hepatocyte proliferation and liver tumorigenesis and their molecular mechanisms and species differences. SIGNIFICANCE STATEMENT: Pregnane X receptor and constitutively active receptor/constitutive androstane receptor have very similar functions in the gene regulation associated with xenobiotic disposition, as suggested by their identification as xenosensors for enzyme induction. In contrast, recent reports clearly suggest that these receptors play distinct roles in the control of hepatocyte proliferation and liver cancer development. Understanding these differences at the molecular level may help us evaluate the human safety of chemical compounds and develop novel drugs targeting liver cancers.

Co-Culture of Human Primary Hepatocytes and Nonparenchymal Liver Cells in the Emulate® Liver-Chip for the Study of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a significant public health issue, but standard animal tests and clinical trials sometimes fail to predict DILI due to species differences and the relatively low number of human subjects involved in preapproval studies of a new drug, respectively. In vitro models have long been used to aid DILI prediction, with primary human hepatocytes (PHHs) being generally considered the gold standard. However, despite many efforts and decades of work, traditional culture methods have been unsuccessful in either fully preserving essential liver functions after isolation of PHHs or in emulating interactions between PHHs and hepatic nonparenchymal cells (NPCs), both of which are essential for the development of DILI under in vivo conditions. Recently, various liver-on-a-chip (Liver-Chip) systems have been developed to co-culture hepatocytes and NPCs in a three-dimensional environment on microfluidic channels, enabling better maintenance of primary liver cells and thus improved DILI prediction. The Emulate® Liver-Chip is a commercially available system that can recapitulate some in vivo DILI responses associated with certain compounds whose liver safety profile cannot be accurately evaluated using conventional approaches involving PHHs or animal models due to a lack of innate immune responses or species-dependent toxicity, respectively. Here, we describe detailed procedures for the use of Emulate® Liver-Chips for co-culturing PHHs and NPCs for the purpose of DILI evaluation. First, we describe the procedures for preparing the Liver-Chip. We then outline the steps needed for sequential seeding of PHHs and NPCs in the prepared Liver-Chips. Lastly, we provide a protocol for utilizing cells maintained in perfusion culture in the Liver-Chips to evaluate DILI, using acetaminophen as an example. In all, use of this system and the procedures described here allow better preservation of the functions of human primary liver cells, resulting in an improved in vitro model for DILI assessment. © 2022 Wiley Periodicals LLC. This article has been contributed to by US Government employees and their work is in the public domain in the USA. Basic Protocol 1: Liver-Chip preparation Basic Protocol 2: Seeding primary human hepatocytes and nonparenchymal cells on Liver-Chips Basic Protocol 3: Perfusion culture for the study of acetaminophen-induced liver injury.

Liver organ-on-chip models for toxicity studies and risk assessment

The liver is a key organ that plays a pivotal role in metabolism and ensures a variety of functions in the body, including homeostasis, synthesis of essential components, nutrient storage, and detoxification. As the centre of metabolism for exogenous molecules, the liver is continuously exposed to a wide range of compounds, such as drugs, pesticides, and environmental pollutants. Most of these compounds can cause hepatotoxicity and lead to severe and irreversible liver damage. To study the effects of chemicals and drugs on the liver, most commonly, animal models or in vitro 2D cell cultures are used. However, data obtained from animal models lose their relevance when extrapolated to the human metabolic situation and pose ethical concerns, while 2D static cultures are poorly predictive of human in vivo metabolism and toxicity. As a result, there is a widespread need to develop relevant in vitro liver models for toxicology studies. In recent years, progress in tissue engineering, biomaterials, microfabrication, and cell biology has created opportunities for more relevant in vitro models for toxicology studies. Of these models, the liver organ-on-chip (OoC) has shown promising results by reproducing the in vivo behaviour of the cell/organ or a group of organs, the controlled physiological micro-environment, and in vivo cellular metabolic responses. In this review, we discuss the development of liver organ-on-chip technology and its use in toxicity studies. First, we introduce the physiology of the liver and summarize the traditional experimental models for toxicity studies. We then present liver OoC technology, including the general concept, materials used, cell sources, and different approaches. We review the prominent liver OoC and multi-OoC integrating the liver for drug and chemical toxicity studies. Finally, we conclude with the future challenges and directions for developing or improving liver OoC models.

Comparison of Hydrogen Peroxide Secretion From Living Cells Cultured in Different Formats Using Hydrogel-Based LSPR Substrates

Reactive oxygen species (ROS), a number of reactive molecules and free radicals derived from molecular oxygen, are generated as by-products during mitochondrial electron transport within cells. Physiologically, cells are capable of metabolizing the ROS exploiting specific mechanisms. However, if excessive ROS accumulate inside the cells, it will cause the cells apoptosis or necrosis. Hydrogen peroxide (H₂O₂) is one of the essential ROS often participating in chemical reactions in organisms and regulating homeostasis in the body. Therefore, rapid and sensitive detection of H₂O₂ is a significant task in cell biology research. Furthermore, it has been found that cells cultured in different formats can result in different cellular responses and biological activities. In order to investigate the H₂O₂ secretion from the cells cultured in different formats, a hydrogel-based substrate is exploited to separate relatively large molecular (e.g., proteins) for direct measurement of H₂O₂ secreted from living cells in complete cell culture medium containing serum. The substrate takes advantage of the localized surface plasmon resonance (LSPR) method based on enzyme immunoprecipitation. In addition, the H₂O₂ secreted from the cells cultured in different dimensions (suspension of single cells and three-dimensional cell spheroids) treated with identical drugs is measured and compared. The spheroid samples can be prepared with ample amount using a designed microfluidic device with precise control of size. The results show that the H₂O₂ secretion from the cells are great affected by their culture formats.

A Comprehensive Evaluation of Sdox, a Promising H2S-Releasing Doxorubicin for the Treatment of Chemoresistant Tumors

Sdox is a hydrogen sulfide (H₂S)-releasing doxorubicin effective in P-glycoprotein-overexpressing/doxorubicin-resistant tumor models and not cytotoxic, as the parental drug, in H9c2 cardiomyocytes. The aim of this study was the assessment of Sdox drug-like features and its absorption, distribution, metabolism, and excretion (ADME)/toxicity properties, by a multi- and transdisciplinary in silico, in vitro, and in vivo approach. Doxorubicin was used as the reference compound. The in silico profiling suggested that Sdox possesses higher lipophilicity and lower solubility compared to doxorubicin, and the off-targets prediction revealed relevant differences between Dox and Sdox towards several cancer targets, suggesting different toxicological profiles. In vitro data showed that Sdox is a substrate with lower affinity for P-glycoprotein, less hepatotoxic, and causes less oxidative damage than doxorubicin. Both anthracyclines inhibited CYP3A4, but not hERG currents. Unlike doxorubicin, the percentage of zebrafish live embryos at 72 hpf was not affected by Sdox treatment. In conclusion, these findings demonstrate that Sdox displays a more favorable drug-like ADME/toxicity profile than doxorubicin, different selectivity towards cancer targets, along with a greater preclinical efficacy in resistant tumors. Therefore, Sdox represents a prototype of innovative anthracyclines, worthy of further investigations in clinical settings.

From NAFLD to MAFLD: Aligning Translational In Vitro Research to Clinical Insights

Although most same-stage non-alcoholic fatty liver disease (NAFLD) patients exhibit similar histologic sequelae, the underlying mechanisms appear to be highly heterogeneous. Therefore, it was recently proposed to redefine NAFLD to metabolic dysfunction-associated fatty liver disease (MAFLD) in which other known causes of liver disease such as alcohol consumption or viral hepatitis do not need to be excluded. Revised nomenclature envisions speeding up and facilitating anti-MAFLD drug development by means of patient stratification whereby each subgroup would benefit from distinct pharmacological interventions. As human-based in vitro research fulfils an irrefutable step in drug development, action should be taken as well in this stadium of the translational path. Indeed, most established in vitro NAFLD models rely on short-term exposure to fatty acids and use lipid accumulation as a phenotypic benchmark. This general approach to a seemingly ambiguous disease such as NAFLD therefore no longer seems applicable. Human-based in vitro models that accurately reflect distinct disease subgroups of MAFLD should thus be adopted in early preclinical disease modeling and drug testing. In this review article, we outline considerations for setting up translational in vitro experiments in the MAFLD era and allude to potential strategies to implement MAFLD heterogeneity into an in vitro setting so as to better align early drug development with future clinical trial designs.

Multi-Organs-on-Chips for Testing Small-Molecule Drugs: Challenges and Perspectives

Organ-on-a-chip technology has been used in testing small-molecule drugs for screening potential therapeutics and regulatory protocols. The technology is expected to boost the development of novel therapies and accelerate the discovery of drug combinations in the coming years. This has led to the development of multi-organ-on-a-chip (MOC) for recapitulating various organs involved in the drug-body interactions. In this review, we discuss the current MOCs used in screening small-molecule drugs and then focus on the dynamic process of drug absorption, distribution, metabolism, and excretion. We also address appropriate materials used for MOCs at low cost and scale-up capacity suitable for high-performance analysis of drugs and commercial high-throughput screening platforms.