Design by Nature: Emerging Applications of Native Liver Extracellular Matrix for Cholangiocyte Organoid-Based Regenerative Medicine

Liver tissue engineering using decellularized scaffolds: Current progress, challenges, and opportunities

Liver transplantation represents the only definitive treatment for patients with end-stage liver disease. However, the shortage of liver donors provokes a dramatic gap between available grafts and patients on the waiting list. Whole liver bioengineering, an emerging field of tissue engineering, holds great potential to overcome this gap. This approach involves two main steps; the first is liver decellularization and the second is recellularization. Liver decellularization aims to remove cellular and nuclear materials from the organ, leaving behind extracellular matrices containing different structural proteins and growth factors while retaining both the vascular and biliary networks. Recellularization involves repopulating the decellularized liver with appropriate cells, theoretically from the recipient patient, to reconstruct the parenchyma, vascular tree, and biliary network. The aim of this review is to identify the major advances in decellularization and recellularization strategies and investigate obstacles for the clinical application of bioengineered liver, including immunogenicity of the designed liver extracellular matrices, the need for standardization of scaffold fabrication techniques, selection of suitable cell sources for parenchymal repopulation, vascular, and biliary tree reconstruction. In vivo transplantation models are also summarized for evaluating the functionality of bioengineered livers. Finally, the regulatory measures and future directions for confirming the safety and efficacy of bioengineered liver are also discussed. Addressing these challenges in whole liver bioengineering may offer new solutions to meet the demand for liver transplantation and improve patient outcomes.

Graft repair during machine perfusion: a current overview of strategies

PURPOSE OF REVIEW

With changing donor characteristics (advanced age, obesity), an increase in the use of extended criteria donor (ECD) livers in liver transplantation is seen. Machine perfusion allows graft viability assessment, but still many donor livers are considered nontransplantable. Besides being used as graft viability assessment tool, ex situ machine perfusion offers a platform for therapeutic strategies to ameliorate grafts prior to transplantation. This review describes the current landscape of graft repair during machine perfusion.

RECENT FINDINGS

Explored anti-inflammatory therapies, including inflammasome inhibitors, hemoabsorption, and cellular therapies mitigate the inflammatory response and improve hepatic function. Cholangiocyte organoids show promise in repairing the damaged biliary tree. Defatting during normothermic machine perfusion shows a reduction of steatosis and improved hepatobiliary function compared to nontreated livers. Uptake of RNA interference therapies during machine perfusion paves the way for an additional treatment modality.

SUMMARY

The possibility to repair injured donor livers during ex situ machine perfusion might increase the utilization of ECD-livers. Application of defatting agents is currently explored in clinical trials, whereas other therapeutics require further research or optimization before entering clinical research.

Global Literature Analysis of Organoid and Organ-on-Chip Research

Organoids and cells in organ-on-chip platforms replicate higher-level anatomical, physiological, or pathological states of tissues and organs. These technologies are widely regarded by academia, the pharmacological industry and regulators as key biomedical developments. To map advances in this emerging field, a literature analysis of 16,000 article metadata based on a quality-controlled text-mining algorithm is performed. The analysis covers titles, keywords, and abstracts of categorized academic publications in the literature and preprint databases published after 2010. The algorithm identifies and tracks 149 and 107 organs or organ substructures modeled as organoids and organ-on-chip, respectively, stem cell sources, as well as 130 diseases, and 16 groups of organisms other than human and mouse in which organoid/organ-on-chip technology is applied. The analysis illustrates changing diversity and focus in organoid/organ-on-chip research and captures its geographical distribution. The downloadable dataset provided is a robust framework for researchers to interrogate with their own questions.

Bioinspired Bioinks for the Fabrication of Chemomechanically Relevant Standalone Disease Models of Hepatic Steatosis

Hepatotoxicity-related issues are poorly predicted during preclinical experimentation, as its relevance is limited by the inadequacy to screen all the non-physiological subclasses of the population. These pitfalls can be solved by implementing complex in vitro models of hepatic physiology and pathologies in the preclinical phase. To produce these platforms, extrusion-based bioprinting is focused on, since it allows to manufacture tridimensional cell-laden constructs with controlled geometries, in a high-throughput manner. Different bioinks, whose formulation is tailored to mimic the chemomechanical environment of hepatic steatosis, the most prevalent hepatic disorder worldwide, are proposed. Internally crosslinked alginate hydrogels are chosen as structural components of the inks. Their viscoelastic properties (G' = 512-730 Pa and G″ = 94-276 Pa, depending on frequency) are tuned to mimic those of steatotic liver tissue. Porcine hepatic ECM is introduced as a relevant biochemical cue. Sodium oleate is added to recall the accumulation of lipids in the tissue. Downstream analyses on 14-layered bioprinted structures cultured for 10 days reveal the establishment of steatotic-like features (intracellular lipid vesicles, viability decrease up to ≈50%) without needing external conditionings. The presented bioinks are thus suitable to fabricate complex models of hepatic steatosis to be implemented in a high-throughput experimental frame.

Novel approach for reconstruction of the three-dimensional biliary system in decellularized liver scaffold using hepatocyte progenitors

Reconstruction of the biliary system is indispensable for the regeneration of transplantable liver grafts. Here, we report the establishment of the first continuous three-dimensional biliary system scaffold for bile acid excretion using a novel method. We confirmed the preservation of the liver-derived extracellular matrix distribution in the scaffold. In addition, hepatocyte progenitors decellularized via the bile duct by slow-speed perfusion differentiated into hepatocyte- and cholangiocyte-like cells, mimicking hepatic cords and bile ducts, respectively. Furthermore, qRT-PCR demonstrated increased ALB, BSEP, and AQP8 expression, revealing bile canaliculi- and bile duct-specific genetic patterns. Therefore, we concluded that locally preserved extracellular matrices in the scaffold stimulated hepatic progenitors and provided efficient differentiation, as well as regeneration of a three-dimensional continuous biliary system from hepatic cords through bile ducts. These findings suggest that organ-derived scaffolds can be utilized for the efficient reconstruction of functional biliary systems.

Evaluation of Vascular Endothelial Growth Factor Gene Expression in Recellularized Liver Tissue by Mouse Embryo Fibroblast

Background

The aim of the present study was to evaluate alterations in the vegf gene expression as an angiogenic factor in mouse embryo fibroblasts seeded on the decellularized liver fragments.

Methods

Liver tissue samples (n = 10) collected from adult male mice were randomly divided into decellularized and native control groups. Tissues were decellularized by treating with 1% Triton X-100 and 0.1% SDS for 24 hours and assessed by H&E staining and SEM. Then DNA content analysis and toxicity tests were performed. By centrifugation, DiI-labeled mouse embryo fibroblasts were seeded on each scaffold and cultured for one week. The recellularized scaffolds were studied by H&E staining, SEM, and LSCM. After RNA extraction and cDNA synthesis, the expression of the vegf gene in these samples was investigated using real-time RT-PCR.

Results

Our observations showed that the decellularized tissues had morphology and porous structure similar to the control group, and their DNA content significantly reduced (p < 0.05) and reached to 4.12% of the control group. The MTT test indicated no significant cellular toxicity for the decellularized scaffolds. Light microscopy, SEM, and LSCM observations confirmed the attachment and penetration of embryonic fibroblast cells on the surface and into different depths of the scaffolds. There was no statistically significant difference in terms of vegf gene expression in the cultured cells in the presence and absence of a scaffold.

Conclusion

The reconstructed scaffold had no effect on vegf gene expression. Decellularized mouse liver tissue recellularized by embryonic fibroblasts could have an application in regenerative medicine.

Toward Transplantation of Liver Organoids: From Biology and Ethics to Cost-effective Therapy

Liver disease is a common cause of morbidity and mortality, and many patients would benefit from liver transplantation. However, because of a shortage of suitable donor livers, even of those patients who are placed on the donor liver waiting list, many do not survive the waiting time for transplantation. Therefore, alternative treatments for end-stage liver disease need to be explored. Recent advances in organoid technology might serve as a solution to overcome the donor liver shortage in the future. In this overview, we highlight the potential of organoid technology for cell therapy and tissue engineering approaches. Both organoid-based approaches could be used as treatment for end-stage liver disease patients. Additionally, organoid-based cell therapy can also be used to repair liver grafts ex vivo to increase the supply of transplantable liver tissue. The potential of both approaches to become clinically available is carefully assessed, including their clinical, ethical, and economic implications. We provide insight into what aspects should be considered further to allow alternatives to donor liver transplantation to be successfully clinically implemented.

Hep3Gel: A Shape-Shifting Extracellular Matrix-Based, Three-Dimensional Liver Model Adaptable to Different Culture Systems

Drug-induced hepatotoxicity is a leading cause of clinical trial withdrawal. Therefore, in vitro modeling the hepatic behavior and functionalities is not only crucial to better understand physiological and pathological processes but also to support drug development with reliable high-throughput platforms. Different physiological and pathological models are currently under development and are commonly implemented both within platforms for standard 2D cultures and within tailor-made chambers. This paper introduces Hep3Gel: a hybrid alginate-extracellular matrix (ECM) hydrogel to produce 3D in vitro models of the liver, aiming to reproduce the hepatic chemomechanical niche, with the possibility of adapting its shape to different manufacturing techniques. The ECM, extracted and powdered from porcine livers by a specifically set-up procedure, preserved its crucial biological macromolecules and was embedded within alginate hydrogels prior to crosslinking. The viscoelastic behavior of Hep3Gel was tuned, reproducing the properties of a physiological organ, according to the available knowledge about hepatic biomechanics. By finely tuning the crosslinking kinetics of Hep3Gel, its dualistic nature can be exploited either by self-spreading or adapting its shape to different culture supports or retaining the imposed fiber shape during an extrusion-based 3D-bioprinting process, thus being a shape-shifter hydrogel. The self-spreading ability of Hep3Gel was characterized by combining empirical and numerical procedures, while its use as a bioink was experimentally characterized through rheological a priori printability evaluations and 3D printing tests. The effect of the addition of the ECM was evident after 4 days, doubling the survival rate of cells embedded within control hydrogels. This study represents a proof of concept of the applicability of Hep3Gel as a tool to develop 3D in vitro models of the liver.

Advances in Tumor Organoids for the Evaluation of Drugs: A Bibliographic Review

Tumor organoids are defined as self-organized three-dimensional assemblies of heterogeneous cell types derived from patient samples that mimic the key histopathological, genetic, and phenotypic characteristics of the original tumor. This technology is proposed as an ideal candidate for the evaluation of possible therapies against cancer, presenting advantages over other models which are currently used. However, there are no reports in the literature that relate the techniques and material development of tumor organoids or that emphasize in the physicochemical and biological properties of materials that intent to biomimicry the tumor extracellular matrix. There is also little information regarding the tools to identify the correspondence of native tumors and tumoral organoids (tumoroids). Moreover, this paper relates the advantages of organoids compared to other models for drug evaluation. A growing interest in tumoral organoids has arisen from 2009 to the present, aimed at standardizing the process of obtaining organoids, which more accurately resemble patient-derived tumor tissue. Likewise, it was found that the characteristics to consider for the development of organoids, and therapeutic responses of them, are cell morphology, physiology, the interaction between cells, the composition of the cellular matrix, and the genetic, phenotypic, and epigenetic characteristics. Currently, organoids have been used for the evaluation of drugs for brain, lung, and colon tumors, among others. In the future, tumor organoids will become closer to being considered a better model for studying cancer in clinical practice, as they can accurately mimic the characteristics of tumors, in turn ensuring that the therapeutic response aligns with the clinical response of patients.

Scalable Production of Size-Controlled Cholangiocyte and Cholangiocarcinoma Organoids within Liver Extracellular Matrix-Containing Microcapsules

Advances in biomaterials, particularly in combination with encapsulation strategies, have provided excellent opportunities to increase reproducibility and standardization for cell culture applications. Herein, hybrid microcapsules are produced in a flow-focusing microfluidic droplet generator combined with enzymatic outside-in crosslinking of dextran-tyramine, enriched with human liver extracellular matrix (ECM). The microcapsules provide a physiologically relevant microenvironment for the culture of intrahepatic cholangiocyte organoids (ICO) and patient-derived cholangiocarcinoma organoids (CCAO). Micro-encapsulation allowed for the scalable and size-standardized production of organoids with sustained proliferation for at least 21 days in vitro. Healthy ICO (n = 5) expressed cholangiocyte markers, including KRT7 and KRT19, similar to standard basement membrane extract cultures. The CCAO microcapsules (n = 3) showed retention of stem cell phenotype and expressed LGR5 and PROM1. Furthermore, ITGB1 was upregulated, indicative of increased cell adhesion to ECM in microcapsules. Encapsulated CCAO were amendable to drug screening assays, showing a dose-response response to the clinically relevant anti-cancer drugs gemcitabine and cisplatin. High-throughput drug testing identified both pan-effective drugs as well as patient-specific resistance patterns. The results described herein show the feasibility of this one-step encapsulation approach to create size-standardized organoids for scalable production. The liver extracellular matrix-containing microcapsules can provide a powerful platform to build mini healthy and tumor tissues for potential future transplantation or personalized medicine applications.

Advances of Engineered Hydrogel Organoids within the Stem Cell Field: A Systematic Review

Organoids are novel in vitro cell culture models that enable stem cells (including pluripotent stem cells and adult stem cells) to grow and undergo self-organization within a three-dimensional microenvironment during the process of differentiation into target tissues. Such miniature structures not only recapitulate the histological and genetic characteristics of organs in vivo, but also form tissues with the capacity for self-renewal and further differentiation. Recent advances in biomaterial technology, particularly hydrogels, have provided opportunities to improve organoid cultures; by closely integrating the mechanical and chemical properties of the extracellular matrix microenvironment, with novel synthetic materials and stem cell biology. This systematic review critically examines recent advances in various strategies and techniques utilized for stem-cell-derived organoid culture, with particular emphasis on the application potential of hydrogel technology in organoid culture. We hope this will give a better understanding of organoid cultures for modelling diseases and tissue engineering applications.

Liver scaffolds obtained by decellularization: A transplant perspective in liver bioengineering

Liver transplantation is the only definitive treatment for many diseases that affect this organ, however, its quantity and viability are reduced. The study of liver scaffolds based on an extracellular matrix is a tissue bioengineering strategy with great application in regenerative medicine. Collectively, recent studies suggest that liver scaffold transplantation may assist in reestablishing hepatic function in preclinical diseased animals, which represents a great potential for application as a treatment for patients with liver disease in the future. This review focuses on useful strategies to promote liver scaffold transplantation and the main open questions about this context. We outline the current knowledge about ex vivo bioengineered liver transplantation, including the surgical techniques, recipient survival time, scaffold preparation before transplantation, and liver disease models. We also highlight the current limitations and future directions regarding in vivo bioengineering techniques.