Gaining New Biological and Therapeutic Applications into the Liver with 3D In Vitro Liver Models

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.

A comprehensive overview of advanced dynamic in vitro intestinal and hepatic cell culture models

Orally administered drugs pass through the gastrointestinal tract before being absorbed in the small intestine and metabolised in the liver. To test the efficacy and toxicity of drugs, animal models are often employed; however, they are not suitable for investigating drug-tissue interactions and making reliable predictions, since the human organism differs drastically from animals in terms of absorption, distribution, metabolism and excretion of substances. Likewise, simple static in vitro cell culture systems currently used in preclinical drug screening often do not resemble the native characteristics of biological barriers. Dynamic models, on the other hand, provide in vivo-like cell phenotypes and functionalities that offer great potential for safety and efficacy prediction. Herein, current microfluidic in vitro intestinal and hepatic models are reviewed, namely single- and multi-tissue micro-bioreactors, which are associated with different methods of cell cultivation, i.e., scaffold-based versus scaffold-free.

The Material World of 3D-Bioprinted and Microfluidic-Chip Models of Human Liver Fibrosis

Biomaterials are extensively used to mimic cell-matrix interactions, which are essential for cell growth, function, and differentiation. This is particularly relevant when developing in vitro disease models of organs rich in extracellular matrix, like the liver. Liver disease involves a chronic wound-healing response with formation of scar tissue known as fibrosis. At early stages, liver disease can be reverted, but as disease progresses, reversion is no longer possible, and there is no cure. Research for new therapies is hampered by the lack of adequate models that replicate the mechanical properties and biochemical stimuli present in the fibrotic liver. Fibrosis is associated with changes in the composition of the extracellular matrix that directly influence cell behavior. Biomaterials could play an essential role in better emulating the disease microenvironment. In this paper, the recent and cutting-edge biomaterials used for creating in vitro models of human liver fibrosis are revised, in combination with cells, bioprinting, and/or microfluidics. These technologies have been instrumental to replicate the intricate structure of the unhealthy tissue and promote medium perfusion that improves cell growth and function, respectively. A comprehensive analysis of the impact of material hints and cell-material interactions in a tridimensional context is provided.

Scaffold-mediated liver regeneration: A comprehensive exploration of current advances

The liver coordinates over 500 biochemical processes crucial for maintaining homeostasis, detoxification, and metabolism. Its specialized cells, arranged in hexagonal lobules, enable it to function as a highly efficient metabolic engine. However, diseases such as cirrhosis, fatty liver disease, and hepatitis present significant global health challenges. Traditional drug development is expensive and often ineffective at predicting human responses, driving interest in advanced in vitro liver models utilizing 3D bioprinting and microfluidics. These models strive to mimic the liver's complex microenvironment, improving drug screening and disease research. Despite its resilience, the liver is vulnerable to chronic illnesses, injuries, and cancers, leading to millions of deaths annually. Organ shortages hinder liver transplantation, highlighting the need for alternative treatments. Tissue engineering, employing polymer-based scaffolds and 3D bioprinting, shows promise. This review examines these innovative strategies, including liver organoids and liver tissue-on-chip technologies, to address the challenges of liver diseases.

Keeping It Organized: Multicompartment Constructs to Mimic Tissue Heterogeneity

Tissue engineering aims at replicating tissues and organs to develop applications in vivo and in vitro. In vivo, by engineering artificial constructs using functional materials and cells to provide both physiological form and function. In vitro, by engineering three-dimensional (3D) models to support drug discovery and enable understanding of fundamental biology. 3D culture constructs mimic cell-cell and cell-matrix interactions and use biomaterials seeking to increase the resemblance of engineered tissues with its in vivo homologues. Native tissues, however, include complex architectures, with compartmentalized regions of different properties containing different types of cells that can be captured by multicompartment constructs. Recent advances in fabrication technologies, such as micropatterning, microfluidics or 3D bioprinting, have enabled compartmentalized structures with defined compositions and properties that are essential in creating 3D cell-laden multiphasic complex architectures. This review focuses on advances in engineered multicompartment constructs that mimic tissue heterogeneity. It includes multiphasic 3D implantable scaffolds and in vitro models, including systems that incorporate different regions emulating in vivo tissues, highlighting the emergence and relevance of 3D bioprinting in the future of biological research and medicine.

Advancements in Research on Constructing Physiological and Pathological Liver Models and Their Applications Utilizing Bioprinting Technology

In recent decades, significant progress has been made in liver tissue engineering through the use of 3D bioprinting technology. This technology offers the ability to create personalized biological structures with precise geometric design capabilities. The complex and multifaceted nature of liver diseases underscores the need for advanced technologies to accurately mimic the physiological and mechanical characteristics, as well as organ-level functions, of liver tissue in vitro. Bioprinting stands out as a superior option over traditional two-dimensional cell culture models and animal models due to its stronger biomimetic advantages. Through the use of bioprinting, it is possible to create liver tissue with a level of structural and functional complexity that more closely resembles the real organ, allowing for more accurate disease modeling and drug testing. As a result, it is a promising tool for restoring and replacing damaged tissue and organs in the field of liver tissue engineering and drug research. This article aims to present a comprehensive overview of the progress made in liver tissue engineering using bioprinting technology to provide valuable insights for researchers. The paper provides a detailed account of the history of liver tissue engineering, highlights the current 3D bioprinting methods and bioinks that are widely used, and accentuates the importance of existing in vitro liver tissue models based on 3D bioprinting and their biomedical applications. Additionally, the article explores the challenges faced by 3D bioprinting and predicts future trends in the field. The progress of 3D bioprinting technology is poised to bring new approaches to printing liver tissue in vitro, while offering powerful tools for drug development, testing, liver disease modeling, transplantation, and regeneration, which hold great academic and practical significance.

The native liver as inspiration to create superior in vitro hepatic models

Drug induced liver injury (DILI) is one of the major reasons of drug withdrawal during the different phases of drug development. The later in the drug development a drug is discovered to be toxic, the higher the economical as well as the ethical impact will be. In vitro models for early detection of drug liver toxicity are under constant development, however to date a superior model of the liver is still lacking. Ideally, a highly reliable model should be established to maintain the different hepatic cell functionalities to the greatest extent possible, during a period of time long enough to allow for tracking of the toxicity of compounds. In the case of DILI, toxicity can appear even after months of exposure. To reach this goal, an in vitro model should be developed that mimics the in vivo liver environment, function and response to external stimuli. The different approaches for the development of liver models currently used in the field of tissue engineering will be described in this review. Combining different technologies, leading to optimal materials, cells and 3D-constructs will ultimately lead to an ideal superior model that fully recapitulates the liver.

The individual and combined effects of ochratoxin A with citrinin and their metabolites (ochratoxin B, ochratoxin C, and dihydrocitrinone) on 2D/3D cell cultures, and zebrafish embryo models

Ochratoxin A and citrinin are nephrotoxic mycotoxins produced by Aspergillus, Penicillium, and/or Monascus species. The combined effects of ochratoxin A and citrinin have been examined in more studies; however, only limited data are available regarding the co-exposure to their metabolites. In this investigation, the individual toxic effects of ochratoxin A, ochratoxin B, ochratoxin C, citrinin, and dihydrocitrinone were tested as well as the combinations of ochratoxin A with the latter mycotoxins were examined on 2D and 3D cell cultures, and on zebrafish embryos. Our results demonstrate that even subtoxic concentrations of certain mycotoxins can increase the toxic impact of ochratoxin A. In addition, typically additive effects or synergism were observed as the combined effects of mycotoxins tested. These observations highlight that different cell lines (e.g. MDBK vs. MDCK), cell cultures (e.g. 2D vs. 3D), and models (e.g. in vitro vs. in vivo) can show different (sometimes opposite) impacts. Mycotoxin combinations considerably increased miR-731 levels in zebrafish embryos, which is an early marker of the toxicity on kidney development. These results underline that the co-exposure to mycotoxins (and/or mycotoxin metabolites) should be seriously considered, since even the barely toxic mycotoxins (or metabolites) in combinations can cause significant toxicity.

Organoid engineering with microfluidics and biomaterials for liver, lung disease, and cancer modeling

As life expectancy improves and the number of people suffering from various diseases increases, the need for developing effective personalized disease models is rapidly rising. The development of organoid technology has led to better recapitulation of the in vivo environment of organs, and can overcome the constraints of existing disease models. However, for more precise disease modeling, engineering approaches such as microfluidics and biomaterials, that aid in mimicking human physiology, need to be integrated with the organoid models. In this review, we introduce key elements for disease modeling and recent engineering advances using both liver and lung organoids. Due to the importance of personalized medicine, we also emphasize patient-derived cancer organoid models and their engineering approaches. These organoid-based disease models combined with microfluidics, biomaterials, and co-culture systems will provide a powerful research platform for understanding disease mechanisms and developing precision medicine; enabling preclinical drug screening and drug development. STATEMENT OF SIGNIFICANCE: The development of organoid technology has led to better recapitulation of the in vivo environment of organs, and can overcome the constraints of existing disease models. However, for more precise disease modeling, engineering approaches such as microfluidics and biomaterials, that aid in mimicking human physiology, need to be integrated with the organoid models. In this review, we introduce liver, lung, and cancer organoids integrated with various engineering approaches as a novel platform for personalized disease modeling. These engineered organoid-based disease models will provide a powerful research platform for understanding disease mechanisms and developing precision medicine.

Use of human tissue stem cell-derived organoid cultures to model enterohepatic circulation

The use of human tissue stem cell-derived organoids has advanced our knowledge of human physiological and pathophysiological processes that are unable to be studied using other model systems. Increased understanding of human epithelial tissues including intestine, stomach, liver, pancreas, lung, and brain have been achieved using organoids. However, it is not yet clear whether these cultures recapitulate in vivo organ-to-organ signaling or communication. In this work, we demonstrate that mature stem cell-derived intestinal and liver organoid cultures each express functional molecules that modulate bile acid uptake and recycling. These organoid cultures can be physically coupled in a Transwell system and display increased secretion of fibroblast growth factor 19 (FGF19) (intestine) and downregulation of P450 enzyme cholesterol 7 α-hydroxylase (CYP7A) (liver) in response to apical exposure of the intestine to bile acids. This work establishes that organoid cultures can be used to study and therapeutically modulate interorgan interactions and advance the development of personalized approaches to medical care.NEW & NOTEWORTHY Interorgan signaling is a critical feature of human biology and physiology, yet has remained difficult to study due to the lack of in vitro models. Here, we demonstrate that physical coupling of ex vivo human intestine and liver epithelial organoid cultures recapitulates in vivo interorgan bile acid signaling. These results suggest that coupling of multiple organoid systems provides new models to investigate interorgan communication and advances our knowledge of human physiological and pathophysiological processes.

Establishing a 3D In Vitro Hepatic Model Mimicking Physiologically Relevant to In Vivo State

Three-dimensional (3D) bioprinting is a promising technology to establish a 3D in vitro hepatic model that holds great potential in toxicological evaluation. However, in current hepatic models, the central area suffers from hypoxic conditions, resulting in slow and weak metabolism of drugs and toxins. It remains challenging to predict accurate drug effects in current bioprinted hepatic models. Here, we constructed a hexagonal bioprinted hepatic construct and incorporated a spinning condition with continuous media stimuli. Under spinning conditions, HepG2 cells in the bioprinted hepatic construct exhibited enhanced proliferation capacity and functionality compared to those under static conditions. Additionally, the number of spheroids that play a role in boosting drug-induced signals and responses increased in the bioprinted hepatic constructs cultured under spinning conditions. Moreover, HepG2 cells under spinning conditions exhibited intensive TGFβ-induced epithelial-to-mesenchymal transition (EMT) and increased susceptibility to acetaminophen (APAP)-induced hepatotoxicity as well as hepatotoxicity prevention by administration of N-acetylcysteine (NAC). Taken together, the results of our study demonstrate that the spinning condition employed during the generation of bioprinted hepatic constructs enables the recapitulation of liver injury and repair phenomena in particular. This simple but effective culture strategy facilitates bioprinted hepatic constructs to improve in vitro modeling for drug effect evaluation.

SARS-CoV-2 and tissue damage: current insights and biomaterial-based therapeutic strategies

The effect of SARS-CoV-2 infection on humanity has gained worldwide attention and importance due to the rapid transmission, lack of treatment options and high mortality rate of the virus. While scientists across the world are searching for vaccines/drugs that can control the spread of the virus and/or reduce the risks associated with infection, patients infected with SARS-CoV-2 have been reported to have tissue/organ damage. With most tissues/organs having limited regenerative potential, interventions that prevent further damage or facilitate healing would be helpful. In the past few decades, biomaterials have gained prominence in the field of tissue engineering, in view of their major role in the regenerative process. Here we describe the effect of SARS-CoV-2 on multiple tissues/organs, and provide evidence for the positive role of biomaterials in aiding tissue repair. These findings are further extrapolated to explore their prospects as a therapeutic platform to address the tissue/organ damage that is frequently observed during this viral outbreak. This study suggests that the biomaterial-based approach could be an effective strategy for regenerating tissues/organs damaged by SARS-CoV-2.

iPSC-derived hepatocytes generated from NASH donors provide a valuable platform for disease modeling and drug discovery

Non-alcoholic fatty liver disease (NAFLD) affects 30-40% of adults and 10% of children in the US. About 20% of people with NAFLD develop non-alcoholic steatohepatitis (NASH), which may lead to cirrhosis and liver cancer, and is projected to be a leading cause of liver transplantation in the near future. Human induced pluripotent stem cells (iPSC) from NASH patients are useful for generating a large number of hepatocytes for NASH modeling applications and identification of potential drug targets. We developed a novel defined in vitro differentiation process to generate cryopreservable hepatocytes using an iPSC panel of NASH donors and apparently healthy normal (AHN) controls. iPSC-derived hepatocytes displayed stage specific phenotypic markers, hepatocyte morphology, with bile canaliculi. Importantly, both fresh and cryopreserved definitive endoderm and hepatoblasts successfully differentiated to pure and functional hepatocytes with increased CYP3A4 activity in response to rifampicin and lipid accumulation upon fatty acid (FA) treatment. End-stage hepatocytes integrated into three-dimensional (3D) liver organoids and demonstrated increased levels of albumin secretion compared to aggregates consisting of hepatocytes alone. End-stage hepatocytes derived from NASH donors demonstrated spontaneous lipidosis without FA supplementation, recapitulating a feature of NASH hepatocytes in vivo Cryopreserved hepatocytes generated by this protocol across multiple donors will provide a critical cell source to facilitate the fundamental understanding of NAFLD/NASH biology and potential high throughput screening applications for preclinical evaluation of therapeutic targets.