Bioengineered humanized livers as better three-dimensional drug testing model system

Advanced Multi-Dimensional Cellular Models as Emerging Reality to Reproduce In Vitro the Human Body Complexity

A hot topic in biomedical science is the implementation of more predictive in vitro models of human tissues to significantly improve the knowledge of physiological or pathological process, drugs discovery and screening. Bidimensional (2D) culture systems still represent good high-throughput options for basic research. Unfortunately, these systems are not able to recapitulate the in vivo three-dimensional (3D) environment of native tissues, resulting in a poor in vitro–in vivo translation. In addition, intra-species differences limited the use of animal data for predicting human responses, increasing in vivo preclinical failures and ethical concerns. Dealing with these challenges, in vitro 3D technological approaches were recently bioengineered as promising platforms able to closely capture the complexity of in vivo normal/pathological tissues. Potentially, such systems could resemble tissue-specific extracellular matrix (ECM), cell–cell and cell–ECM interactions and specific cell biological responses to mechanical and physical/chemical properties of the matrix. In this context, this review presents the state of the art of the most advanced progresses of the last years. A special attention to the emerging technologies for the development of human 3D disease-relevant and physiological models, varying from cell self-assembly (i.e., multicellular spheroids and organoids) to the use of biomaterials and microfluidic devices has been given.

Advancements in stem cell-derived hepatocyte-like cell models for hepatotoxicity testing

Drug-induced liver injury (DILI) is one of the leading causes of clinical trial failures and high drug attrition rates. Currently, the commonly used hepatocyte models include primary human hepatocytes (PHHs), animal models, and hepatic cell lines. However, these models have disadvantages that include species-specific differences or inconvenient cell extraction methods. Therefore, a novel, inexpensive, efficient, and accurate model that can be applied to drug screening is urgently needed. Owing to their self-renewable ability, source abundance, and multipotent competence, stem cells are stable sources of drug hepatotoxicity screening models. Because 3D culture can mimic the in vivo microenvironment more accurately than can 2D culture, the former is commonly used for hepatocyte culture and drug screening. In this review, we introduce the different sources of stem cells used to generate hepatocyte-like cells and the models for hepatotoxicity testing that use stem cell-derived hepatocyte-like cells.

Biofabrication of cell-laden allografts of goat urinary bladder scaffold for organ reconstruction/regeneration

INTRODUCTION

Bladder dysfunction has been considered as one of the most critical health conditions with no proper treatment. Current therapeutic approaches including enterocystoplasty have several limitations. Hence, biofabrication of cell-laden biological allografts using decellularized Goat urinary bladder scaffolds for organ reconstruction/regeneration was major objective of this study.

MATERIALS AND METHODS

An efficient method for decellularization of Goat urinary bladder (N = 3) was developed by perfusion of gradient change of detergents through ureter. The retention of organ architecture, extracellular matrix composition, mechanical properties and removal of cellular components was characterized using histological, cellular and molecular analysis. Further, mesenchymal stem cells (MSCs) from human umbilical cord blood (UCB) were used for preparing biological construct of decellularized urinary bladder (DUB) scaffolds to augment the urinary bladder reconstruction/regeneration.

RESULTS

The decellularization method adopted in this study generated completely DUB scaffolds within 10 h at 100 mm Hg pressure and constant flow rate of 1 mL/min. The DUB scaffold retains organ architecture, ECM composition, and mechanical strength. No significant amount of residual nucleic acid was observed post-decellularization. Furthermore, MSCs derived from human UCB engrafted and proliferated well on DUB scaffolds in highly aligned manner under xeno-free condition.

CONCLUSION

Biofabricated humanized urinary bladder constructs provides xeno-free allografts for future application in augmenting urinary bladder reconstruction/regeneration with further development.

Liver Bioreactor Design Issues of Fluid Flow and Zonation, Fibrosis, and Mechanics: A Computational Perspective

Tissue engineering, with the goal of repairing or replacing damaged tissue and organs, has continued to make dramatic science-based advances since its origins in the late 1980’s and early 1990’s. Such advances are always multi-disciplinary in nature, from basic biology and chemistry through physics and mathematics to various engineering and computer fields. This review will focus its attention on two topics critical for tissue engineering liver development: (a) fluid flow, zonation, and drug screening, and (b) biomechanics, tissue stiffness, and fibrosis, all within the context of 3D structures. First, a general overview of various bioreactor designs developed to investigate fluid transport and tissue biomechanics is given. This includes a mention of computational fluid dynamic methods used to optimize and validate these designs. Thereafter, the perspective provided by computer simulations of flow, reactive transport, and biomechanics responses at the scale of the liver lobule and liver tissue is outlined, in addition to how bioreactor-measured properties can be utilized in these models. Here, the fundamental issues of tortuosity and upscaling are highlighted, as well as the role of disease and fibrosis in these issues. Some idealized simulations of the effects of fibrosis on lobule drug transport and mechanics responses are provided to further illustrate these concepts. This review concludes with an outline of some practical applications of tissue engineering advances and how efficient computational upscaling techniques, such as dual continuum modeling, might be used to quantify the transition of bioreactor results to the full liver scale.

A Hepatic Scaffold from Decellularized Liver Tissue: Food for Thought

Allogeneic liver transplantation is still deemed the gold standard solution for end-stage organ failure; however, donor organ shortages have led to extended waiting lists for organ transplants. In order to overcome the lack of donors, the development of new therapeutic options is mandatory. In the last several years, organ bioengineering has been extensively explored to provide transplantable tissues or whole organs with the final goal of creating a three-dimensional growth microenvironment mimicking the native structure. It has been frequently reported that an extracellular matrix-based scaffold offers a structural support and important biological molecules that could help cellular proliferation during the recellularization process. The aim of the present review is to underline the recent developments in cell-on-scaffold technology for liver bioengineering, taking into account: (1) biological and synthetic scaffolds; (2) animal and human tissue decellularization; (3) scaffold recellularization; (4) 3D bioprinting; and (5) organoid technology. Future possible clinical applications in regenerative medicine for liver tissue engineering and for drug testing were underlined and dissected.

Recent development and biomedical applications of decellularized extracellular matrix biomaterials

Decellularized matrix (dECM) is isolated extracellular matrix of tissues from its original inhabiting cells, which has emerged as a promising natural biomaterial for tissue engineering, aiming at support, replacement or regeneration of damaged tissues. The dECM can be easily obtained from tissues/organs of various species by adequate decellularization methods, and mimics the structure and composition of the native extracellular matrix, providing a favorable cellular environment. In this review, we summarize the recent developments in the preparation of dECM materials, including decellularization, crosslinking and sterilization. Also, we cover the advances in the utilization of dECM biomaterials in regeneration medicine in pre-clinic and clinical trials. Moreover, we highlight those emerging medical benefits of dECM beyond tissue engineering, such as cell transplantation, in vitro/in vivo model and therapeutic cues delivery. With the advances in the preparation and broader application, the dECM biomaterials could become the gold scaffold and pharmaceutical excipients in medical sciences.

Technological advancements for the development of stem cell-based models for hepatotoxicity testing

Stem cells are characterized by their self-renewal capacity and their ability to differentiate into multiple cell types of the human body. Using directed differentiation strategies, stem cells can now be converted into hepatocyte-like cells (HLCs) and therefore, represent a unique cell source for toxicological applications in vitro. However, the acquired hepatic functionality of stem cell-derived HLCs is still significantly inferior to primary human hepatocytes. One of the main reasons for this is that most in vitro models use traditional two-dimensional (2D) setups where the flat substrata cannot properly mimic the physiology of the human liver. Therefore, 2D-setups are progressively being replaced by more advanced culture systems, which attempt to replicate the natural liver microenvironment, in which stem cells can better differentiate towards HLCs. This review highlights the most recent cell culture systems, including scaffold-free and scaffold-based three-dimensional (3D) technologies and microfluidics that can be employed for culture and hepatic differentiation of stem cells intended for hepatotoxicity testing. These methodologies have shown to improve in vitro liver cell functionality according to the in vivo liver physiology and allow to establish stem cell-based hepatic in vitro platforms for the accurate evaluation of xenobiotics.

Engineering bio-mimetic humanized neurological constructs using acellularized scaffolds of cryopreserved meningeal tissues

Spinal cord injury (SCI) is one of the most precarious conditions which have been one of the major reasons for continuous increasing mortality rate of SCI patients. Currently, there is no effective treatment modality for SCI patients posing major threat to the scientific and medical community. The available strategies don't mimic with the natural processes of nervous tissues repair/regeneration and majority of the approaches may induce the additional fibrotic or immunological response at the injury site and are not readily available on demand. To overcome these hurdles, we have developed a ready to use bioengineered human functional neurological construct (BHNC) for regenerative applications in SCI defects. We used cryopreserved meningeal tissues (CMT) for bioengineering these neurological constructs using acellularization and repopulation technology. The technology adopted herein generates intact neurological scaffolds from CMT and retains several crucial structural, biochemical and mechanical cues to enhance the regenerative mechanisms. The neurogenic differentiation on CMT scaffolds was almost similar to the freshly prepared meningeal scaffolds and mimics with the natural nervous tissue developmental mechanisms which offer intact 3D-microarchitecture and hospitable microenvironment enriched with several crucial neurotrophins for long-term cell survival and function. Functional assessment of developed BHNC showed highly increased positive staining for pre-synaptic granules of Synapsis-1 along with MAP-2 antibody with punctuate distribution in axonal regions of the neuronal cells which was well supported by the gene expression analysis of functional transcripts. Given the significant improvement in the field may enable to generate more such ready to use functional BHNC for wider applicability in SCI repair/regeneration.

Bioengineered functional humanized livers: An emerging supportive modality to bridge the gap of organ transplantation for management of end-stage liver diseases

End stage liver diseases (ESLD) represent a major, neglected global public health crisis which requires an urgent action towards finding a proper cure. Orthotropic liver transplantation has been the only definitive treatment modality for ESLD. However, shortage of donor organs, timely unavailability, post-surgery related complications and financial burden on the patients limits the number of patients receiving the transplants. Since last two decades cell-based therapies have revolutionized the field of organ/tissue regeneration. However providing an alternative organ source to address the donor liver shortage still poses potential challenges. The developments made in this direction provide useful futuristic approaches, which could be translated into pre-clinical and clinical settings targeting appropriate applications in specific disease conditions. Earlier studies have demonstrated the applicability of this particular approach to generate functional organ in rodent system by connecting them with portal and hepatic circulatory networks. However, such strategy requires very high level of surgical expertise and also poses the technical and financial questions towards its future applicability. Hence, alternative sites for generating secondary organs are being tested in several types of disease conditions. Among different sites, omentum has been proved to be more appropriate site for implanting several kinds of functional tissue constructs without eliciting much immunological response. Hence, omentum may be considered as better site for transplanting humanized bioengineered ex vivo generated livers, thereby creating a secondary organ at intra-omental site. However, the expertise for generating such bioengineered organs are limited and only very few centres are involved for investigating the potential use of such implants in clinical practice due to gap between the clinical transplant surgeons and basic scientists working on the concept evolution. Herein we discuss the recent advances and challenges to create functional secondary organs through intra-omental transplantation of ex vivo generated bioengineered humanized livers and their further application in the management of ESLD as a supportive bridge for organ transplantation.

Molecular dynamics of pancreatic transcription factors in bioengineered humanized insulin producing neoorgan

BACKGROUND

The present study has been aimed to identify molecular dynamics of pancreatic transcription factors (pTFs) during events of directed trans-differentiation of human hepatic progenitor cells (hHPCs) into insulin producing cells (InPCs) within bioengineered humanized neoorgan. The study demonstrates applicability of acellularized whole splenic scaffold (ASOS) to generate insulin producing humanized transplantable neoorgan through activation of pancreatic transcription factors.

METHODS

An efficient acellularization process was developed for xenogeneic rat spleen using change in different gradients of reagents perfusion through splenic artery for varying time points. The acellularized xenogeneic spleen scaffold was characterized thoroughly for preservation of extra-cellular matrix and retention of organ specific vasculature and mechanical properties. Further scaffolds were sterilized and repopulated with hHPCs which were triggered using a stage wise induction with growth factors and hyperglycemic challenge for trans-differentiation into InPCs. Dynamics of pTFs alone or simultaneously during induction process was identified using gene expression analysis and immunological staining.

RESULTS

The cells within the engineered neoorgan respond to growth factors and extrinsic hyperglycemic challenge and generate large number of InPCs under controlled dynamic regulation of pTFs. Highly controlled regulation of pTFs generates higher percentage of Nkx-6.1+/C-peptide+ cells within the engineered splenic scaffolds. Generation of high percentage of insulin and C-peptide positive cells in three-dimensional organ architecture responded better to hyperglycemic stimuli and produced higher quantity of insulin than 2D-culture system.

CONCLUSION

The present study provides a novel platform for designing effective regenerative strategies using whole organ scaffolds to control hyperglycemia under tight regulation of pTFs using humanized neoorgan system.