Engineering of implantable liver tissues

Biomimetic vascularized adipose-derived mesenchymal stem cells bone-periosteum graft enhances angiogenesis and osteogenesis in a male rabbit spine fusion model

Aims

Several artificial bone grafts have been developed but fail to achieve anticipated osteogenesis due to their insufficient neovascularization capacity and periosteum support. This study aimed to develop a vascularized bone-periosteum construct (VBPC) to provide better angiogenesis and osteogenesis for bone regeneration.

Methods

A total of 24 male New Zealand white rabbits were divided into four groups according to the experimental materials. Allogenic adipose-derived mesenchymal stem cells (AMSCs) were cultured and seeded evenly in the collagen/chitosan sheet to form cell sheet as periosteum. Simultaneously, allogenic AMSCs were seeded onto alginate beads and were cultured to differentiate to endothelial-like cells to form vascularized bone construct (VBC). The cell sheet was wrapped onto VBC to create a vascularized bone-periosteum construct (VBPC). Four different experimental materials - acellular construct, VBC, non-vascularized bone-periosteum construct, and VBPC - were then implanted in bilateral L4-L5 intertransverse space. At 12 weeks post-surgery, the bone-forming capacities were determined by CT, biomechanical testing, histology, and immunohistochemistry staining analyses.

Results

At 12 weeks, the VBPC group significantly increased new bone formation volume compared with the other groups. Biomechanical testing demonstrated higher torque strength in the VBPC group. Notably, the haematoxylin and eosin, Masson's trichrome, and immunohistochemistry-stained histological results revealed that VBPC promoted neovascularization and new bone formation in the spine fusion areas.

Conclusion

The tissue-engineered VBPC showed great capability in promoting angiogenesis and osteogenesis in vivo. It may provide a novel approach to create a superior blood supply and nutritional environment to overcome the deficits of current artificial bone graft substitutes.

Biocompatibility of the oxygen carrier polymerized human hemoglobin towards HepG2/C3A cells

Hemoglobin (Hb) based oxygen carriers (HBOCs) are designed to minimize the toxicity of extracellular Hb, while preserving its high oxygen-carrying capacity for oxygen delivery to cells. Polymerized human Hb (PolyHb) is a novel type of nanosized HBOC synthesized via glutaraldehyde-mediated crosslinking of free Hb, and which preserves the predominant quaternary state during the crosslinking reaction (low oxygen affinity tense (T) quaternary state PolyHb is synthesized at 0% Hb oxygen saturation, and high oxygen affinity relaxed (R) quaternary state PolyHb is synthesized at 100% Hb oxygen saturation). Major potential applications for PolyHbs, and HBOCs in general, include oxygenation of bioreactor systems containing large liver cell masses, and ex-vivo perfusion preservation of explanted liver grafts. The toxicity of these compounds toward liver cells must be evaluated before testing their use in these complex systems for oxygen delivery. Herein, we characterized the effect of PolyHbs on the hepatoma cell line HepG2/C3A, used as a model hepatocyte and as a cell line used in some investigational bioartificial liver support devices. HepG2/C3A cells were incubated in cell culture media containing PolyHbs or unmodified Hb at concentrations up to 50 mg/mL and for up to 6 days. PolyHbs were well tolerated at a dose of 10 mg/mL, with no significant decrease in cell viability; however, proliferation was inhibited as much as 10-fold after 6 days of exposure at 50 mg/mL. Secretion of albumin, and urea, as well as glucose and ammonia removal were measured in presence of 10 mg/mL of PolyHbs or unmodified Hb. In addition, methoxy- and ethoxy-resorufin deacetylase (MROD and EROD) activities, which reflect cytochrome P450 metabolism, were measured. R-state PolyHb displayed improved or intact activity in 3 out of 7 functions compared to unmodified Hb. T-state PolyHb displayed improved or intact activity in 4 out of 7 functions compared to unmodified Hb. Thus, PolyHbs, both in the R-state and T-state, are safer to use at a concentration of 10 mg/mL as compared to unmodified Hb in static culture liver-related applications.

A novel perfusion culture system for screening mitochondrial toxicity in primary mouse hepatocytes

The liver microphysiological system (MPS) model is an in-vitro culture method that mimics physiological blood flow, which enhances basal cellular functions. However, the liver MPS model has not been tested in the preclinical stage because of its obscure utility. It can overcome the major problem of conventional systems-rapid loss of mitochondrial activity in cultured hepatocytes due to limited oxygen supply-by supplying oxygen to cultured hepatocytes using a perfusion device. In this study, we developed a new perfusion culture system that can detect mitochondrial toxicity. Primary mouse hepatocytes were cultured under perfusion condition for 48 hr. The hepatocytes showed increased oxygen consumption and reduced lactate release. These results indicated that the ATP-production pathway was switched from glycolysis to mitochondrial oxidative phosphorylation in the perfusion culture system. Furthermore, ATP levels were considerably reduced in the perfusion culture system after exposure to phenformin, a mitochondrial complex I inhibitor. To summarize, the perfusion culture system could improve the mitochondrial activity in primary mouse hepatocytes, and thus, has potential implications in the detection of mitochondrial toxicity.

High density culture of pancreatic islet-like 3D tissue organized in oxygen-permeable porous scaffolds with external oxygen supply

Transplantation of macroencapsulated pancreatic islets within semipermeable membranes is a promising approach for the treatment of type 1 diabetes. Encapsulation beneficially isolates the implants from the host immune system. Deleteriously however, it also limits oxygen supply to the cells. This creates challenges in loading islets at the amount and density required to meet the practical demands of clinical usage. To overcome this challenge, we investigated the feasibility of using macroporous scaffolds made of an oxygen-permeable polymer, poly(dimethylsiloxane) (PDMS) by culturing pancreatic islet-like three-dimensional tissue made of a rat pancreatic beta cell line on the scaffolds. With external oxygenation, the density and function of cells on the PDMS scaffold were more than three times and almost two times higher than those without oxygenation, respectively. This suggests that the oxygenation afforded by the PDMS scaffolds allows for high-density loading of islet tissue into the devices.

Use of Primary Rat Hepatocytes for Prediction of Drug-Induced Mitochondrial Dysfunction

Mitochondrial dysfunction plays a central role in drug-induced liver injury. To evaluate drug-induced mitochondrial impairment, several isolated mitochondria- or cell line-based assays have been reported. Among them, culturing HepG2 cells in galactose provides a remarkable method to assess mitochondrial toxicity by activating mitochondrial aerobic respiration. We applied this assay to primary rat hepatocytes by culturing cells in galactose and hyperoxia to enhance the evaluation of metabolism-related drug-induced mitochondrial toxicity. Conventional culture of primary hepatocytes under high-glucose and hypoxic conditions could force cells to switch energy generation to glycolysis. By contrast, cells cultured in galactose and hyperoxia could maintain energy generation from mitochondrial aerobic respiration, which is consistent with physiological conditions, and consequently improve the susceptibility of cells to mitochondrial toxicants. Measuring the toxicities of test compounds in primary rat hepatocytes cultured in modified conditions provides a useful model to identify mitochondrial dysfunction-mediated drug-induced hepatotoxicity. © 2017 by John Wiley & Sons, Inc.

Long-term maintenance of human fetal hepatocytes and prolonged susceptibility to HBV infection by co-culture with non-parenchymal cells

Within a few days of being isolated, primary human hepatocytes undergo a rapid dedifferentiation process and lose susceptibility to hepatitis B virus (HBV) infection in vitro. This fact has limited their further application. In this study, a convenient and feasible method of preventing this dedifferentiation was established, by co-culturing human fetal hepatocytes with hepatic non-parenchymal cells to maintain the differentiation features of human fetal hepatocytes. Isolated hepatic cells were seeded at a low density, and cultured in dimethyl sulfoxide-free medium for a month to allow rapid proliferation of non-parenchymal cells. Subsequently, 2% dimethyl sulfoxide was added to induce formation of typical hepatic islands, in which hepatocytic features could be further maintained for up to an additional 3 months. These hepatic islands, formed of piled-up hepatocytes, were surrounded and invaded by non-parenchymal cells. Protein expression profiles showed that the human fetal hepatocytes underwent a rapid maturation process, and the hepatocytic features were well preserved. Most importantly, these human fetal hepatocytes still exhibited susceptibility to HBV infection after long-term maintenance, for as long as 10 weeks. This co-culture method has overcome the pre-existing disadvantages of primary human hepatocytes for virological studies, and provides a valuable approach to long-term maintenance of primary human hepatocytes for studies of HBV infection for prolonged periods.

The therapeutic potential of mesenchymal stem cell-derived extracellular vesicles

Extracellular vesicles (EVs), membrane vesicles that are secreted by a variety of mammalian cell types, have been shown to play an important role in intercellular communication. The contents of EVs, including proteins, microRNAs, and mRNAs, vary according to the cell type that secreted them. Accordingly, researchers have demonstrated that EVs derived from various cell types play different roles in biological phenomena. Considering the ubiquitous presence of mesenchymal stem cells (MSCs) in the body, MSC-derived EVs may take part in a wide range of events. In particular, MSCs have recently attracted much attention due to the therapeutic effects of their secretory factors. MSC-derived EVs may therefore provide novel therapeutic approaches. In this review, we first summarize the wide range of functions of EVs released from different cell types, emphasizing that EVs echo the phenotype of their parent cell. Then, we describe the various therapeutic effects of MSCs and pay particular attention to the significance of their paracrine effect. We then survey recent reports on MSC-derived EVs and consider the therapeutic potential of MSC-derived EVs. Finally, we discuss remaining issues that must be addressed before realizing the practical application of MSC-derived EVs, and we provide some suggestions for enhancing their therapeutic efficiency.