Whole liver engineering: A promising approach to develop functional liver surrogates

Abstract

Liver donor shortage remains the biggest challenge for patients with end-stage liver failures. While bioartificial liver devices have been developed as temporary supports for patients waiting for transplantation, their applications have been limited clinically.Whole liver engineering is a biological scaffold based regenerative medicine approach that holds promise for developing functional liver surrogates. Significant advancements have been made since the first report in 2010. This review focuses on the recent achievements of whole liver engineering studies. K E Y W O R D Sdecellularization, endothelialization, recellularization, transplantation, whole liver engineering | INTRODUCTIONLiver is the largest internal organ responsible for important physiological functions, including vitamin storage, protein synthesis and detoxification. For patients with end-stage liver failures, that are often associated with hepatitis, bile duct-related diseases or liver cancers, liver transplantation has become the golden treatment. It provides better quality of life and cost effectiveness. The 5-year survival rate following liver transplantation is above 70%. However, the number of patients who needs a transplant still exceeds available donors. In the USA alone, it was reported that more than 16 000 patients need transplantation yearly but only 6000 liver transplantations are performed due to shortage of suitable donors.1 According to US Department of Health and Human Services, the shortage of eligible donors results in 18 deaths every day. There is a need for innovative approaches to develop functional liver surrogates for end-stage liver failure patients.Bioartificial liver devices (BAL) have been developed to temporarily function as surrogates for patients waiting for liver transplants. The BAL systems are extracorporeal, which consist of an artificial component (ie, the bioreactor) and a biological component (ie, hepatocytes).BAL systems have significantly prolonged the animal survival rate in preclinical studies and also have been applied in clinical trials. 2,3However, currently there are no strong evidence supporting the survival benefits of patients utilizing these devices and the incapability to prolong hepatocyte functions has limited their applications clinically. Figure 1 shows the concept of biological scaffold based whole liver engineering. | BioreactorBioreactors are designed to mimic the in vivo physiological environment such that an optimal growth condition is created for cells to repopulate the whole organ scaffolds. Several key components are required to build an appropriate bioreactor, including nutrient/waste exchange, temperature control, gas supply, real time monitoring of biomolecules of interest and organ-type specific stimuli. For example, the presence of air-liquid interface has been shown to induce ciliogenesis in tracheal regeneration 39 and physical stimuli such as ventilation were found beneficial to recellularized lung scaffold culture. 37Identifying specific stimuli that facilitate liver...

Identification of tissue sections from decellularized liver scaffolds for repopulation experiments

“…Based on the assumption that only marginal human donor organs with morphological changes will be available for allogeneic tissue engineering [ 22 ], we induced similar structural alterations [ 23 , 24 , 25 ] in mice. We used an established perfusion protocol for the subsequent decellularization procedure [ 3 , 18 ] and investigated the effect of the induced structural alterations on the decellularization process and quality. This experimental approach allowed us to demonstrate the feasibility of decellularization in both, native livers and structurally altered organs.…”

“…This decellularization process is performed by perfusing the liver with ionic or non-ionic detergents, resulting in a cell-free scaffold. During the repopulation process, the cell-free scaffold must be reseeded with either organ-specific parenchymal and non-parenchymal cells, progenitor cells or stem cells to generate a potentially functional organ [ 2 , 3 ].…”

Portal venous repopulation of decellularised rat liver scaffolds with syngeneic bone marrow stem cells

“…To date, the majority of studies evaluating repopulation of liver scaffolds have focused on hepatocyte replacement using a variety of cell sources including primary hepatocytes, human foetal liver cells, hepatocyte cell lines and induced pluripotent stem cell (iPSC)‐derived hepatocytic cells (reviewed by Meng, Assiri, Dhar, & Broering, 2017), demonstrating engraftment of the cells in liver lobules and evidence of a degree of hepatocyte function, such as expression of albumin, drug metabolism enzymes and production of bile acids.…”

“…Where investigated, recellularisation of the hepatic vasculature has been examined using cell lines like MS1 or primary endothelial cells such as human umbilical vein endothelial cells (HUVEC; Meng et al, 2017), cardiac microvascular endothelial cells (Uygun et al, 2010), mature LSECs (Kojima et al, 2018) or nonsyngeneic mesenchymal stem cells (Kadota et al, 2014). However, seen from the perspective of potential clinical applicability, the use of such cells is restricted by concerns regarding oncogenic potential, lack of immunological syngeneicity and limited capacity in generating adequate cell numbers.…”

Liver regeneration biology: Implications for liver tumour therapies

“…In the latter case, microcarriers and biodegradable polymer scaffolds have been described, resulting in albumin production and clearance of bilirubin and urea metabolites[ 120 ]. These efforts have laid the ground for three-dimensional scaffolds[ 121 ] which are either biological membranes[ 122 ], collagen sponges[ 123 ], or synthetic hydrogels[ 124 ], and which enable the production of hepatic organoids. In another approach to liver regeneration, chimeric murine models have been developed, whereby mouse liver is extensively repopulated with human hepatocytes, thus permitting the study of liver disease ( e.g.…”