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 fnding a proper cure. Orthotro-pic 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 li-mits the number of patients receiving the transplants. Since last two decades cell-based therapies have revolu-tionized the feld 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 preclinical 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 con-sidered as better site for transplanting humanized bio-engineered 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 inve-stigating 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 thr-ough intra-omental transplantation of ex vivo genera-ted bioengineered humanized livers and their further application in the management of ESLD as a supportive bridge for organ transplantation.

Hepatic stem cells: A viable approach for the treatment of liver cirrhosis

Liver cirrhosis is characterized by distortion of liver architecture, necrosis of hepatocytes and regenerative nodules formation leading to cirrhosis. Various types of cell sources have been used for the management and treatment of decompensated liver cirrhosis.Knowledge of stem cells has offered a new dimension for regenerative therapy and has been considered as one of the potential adjuvant treatment modality in patients with end stage liver diseases(ESLD). Human fetal hepatic progenitor cells are less immunogenic than adult ones. They are highly propagative and challenging to cryopreservation. In our earlier studies we have demonstrated that fetuses at 10-18 wk of gestation age contain a large number of actively dividing hepatic stem and progenitor cells which possess bipotent nature having potential to differentiate into bile duct cells and mature hepatocytes. Hepatic stem cell therapy for the treatment of ESLD is in their early stage of the translation. The emerging technology of decellularization and recellularization might offer a significant platform for developing bioengineered personalized livers to come over the scarcity of desired number of donor organs for the treatment of ESLD. Despite these significant advancements long-term tracking of stem cells in human is the most important subject nowadays in order to answer several unsettles issues regarding the route of delivery, the choice of stem cell type(s), the cell number and the timepoint of cell delivery for the treatment in a chronic setting. Answering to these questions will further contribute to the development of safer, noninvasive, and repeatable imaging modalities that could discover better cell therapeutic approaches from bench to bedside. Combinatorial approach of decellularization and nanotechnology could pave a way towards the better understanding in determination of cell fate posttransplantation.

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

AIM To develop appropriate humanized three-dimensional ex-vivo model system for drug testing. METHODS Bioengineered humanized livers were developed in this study using human hepatic stem cells repopulation within the acellularized liver scaffolds which mimics with the natural organ anatomy and physiology. Six cytochrome P-450 probes were used to enable efficient identification of drug metabolism in bioengineered humanized livers. The drug metabolism study in bioengineered livers was evaluated to identify the absorption, distribution, metabolism, excretion and toxicity responses.RESULTS The bioengineered humanized livers showed cellular and molecular characteristics of human livers. The bioengineered liver showed three-dimensional natural architecture with intact vasculature and extra-cellular matrix. Human hepatic cells were engrafted similar to the human liver. Drug metabolism studies provided a suitable platform alternative to available ex-vivo and in vivo models for identifying cellular and molecular dynamics of pharmacological drugs.CONCLUSION The present study paves a way towards the development of suitable humanized preclinical model systems for pharmacological testing. This approach may reduce the cost and time duration of preclinical drug testing and further overcomes on the anatomical and physiological variations in xenogeneic systems.

Current progress and emerging technologies for generating extrapancreatic functional insulin-producing cells

Diabetes has been one of the major concerns in recent years,due to the increasing rate of morbidity and mortality worldwide.The available treatment strategies for uncontrolled diabetes mellitus(DM)are pancreas or islet transplantation.However,these strategies are limited due to unavailability of quality pancreas/islet donors,life-long need of immunosuppression,and associated complications.Cell therapy has emerged as a promising alternative options to achieve the clinical benefits in the management of uncontrolled DM.Since the last few years,various sources of cells have been used to convert into insulin-producingβ-like cells.These extrapancreatic sources of cells may play a significant role inβ-cell turnover and insulin secretion in response to environmental stimuli.Stem/progenitor cells from liver have been proposed as an alternative choice that respond well to glucose stimuli under strong transcriptional control.The liver is one of the largest organs in the human body and has a common endodermal origin with pancreatic lineages.Hence,liver has been proposed as a source of a large number of insulinproducing cells.The merging of nanotechnology and 3D tissue bioengineering has opened a new direction for producing islet-like cells suitable for in vivo transplantation in a cordial microenvironment.This review summarizes extrapancreatic sources for insulin-secreting cells with reference to emerging technologies to fulfill the future clinical need.