The Behaviors of Long-Term Cryopreserved Human Hepatocytes on Different Biomaterials

Bioactive Nanogels Mimicking the Antithrombogenic Nitric Oxide-Release Function of the Endothelium

Nitric oxide (NO) plays a significant role in controlling the physiology and pathophysiology of the body, including the endothelial antiplatelet function and therefore, antithrombogenic property of the blood vessels. This property of NO can be exploited to prevent thrombus formation on artificial surfaces like extracorporeal membrane oxygenators, which when come into contact with blood lead to protein adsorption and thereby platelet activation causing thrombus formation. However, NO is extremely reactive and has a very short biological half-life in blood, so only endogenous generation of NO from the blood contacting material can result into a stable and kinetically controllable local delivery of NO. In this regards, highly hydrophilic bioactive nanogels are presented which can endogenously generate NO in blood plasma from endogenous NO-donors thereby maintaining a physiological NO flux. It is shown that NO releasing nanogels could initiate cGMP-dependent protein kinase signaling followed by phosphorylation of vasodilator-stimulated phosphoprotein in platelets. This prevents platelet activation and aggregation even in presence of highly potent platelet activators like thrombin, adenosine 5'-diphosphate, and U46619 (thromboxane A2 mimetic).

Prediction of tumor metastasis via extracellular vesicles-treated platelet adhesion on a blood vessel chip

In preclinical and clinical studies, it has been demonstrated that tumor-educated platelets play a critical role in tumorigenesis, cancer development, and metastasis. Unlike the role of cancer-derived chemokines in platelet activation, the role of cancer-derived extracellular vesicles (EVs) has remained elusive. Here, we found that interleukin-8 (IL-8) in cancer-derived EVs contributed to platelet activation by increasing P-selectin expression and ligand affinity, resulting in increased platelet adhesion on the human vessel-mimicking microfluidic system. Furthermore, platelet adhesion levels on vessels treated with human plasma-derived EVs demonstrated good discrimination between breast cancer patients with metastasis and those without, with the area under the curve (AUC) value of 0.88. While EpCAM expression on EVs could detect the existence of a tumor (AUC = 0.89), it performed poorly in predicting metastasis (AUC = 0.42). We believe that these findings shed light on the role of the interaction between cancer-derived EVs and platelets in pre-metastatic niche formation and tumor metastasis, potentially leading to the development of platelet-tumor interaction-based novel diagnostic and therapeutic strategies.

Effect of Recombinant Human Perlecan Domain V Tethering Method on Protein Orientation and Blood Contacting Activity on Polyvinyl Chloride

Surface modification of biomaterials is a promising approach to control biofunctionality while retaining the bulk biomaterial properties. Perlecan is the major proteoglycan in the vascular basement membrane that supports low levels of platelet adhesion but not activation. Thus, perlecan is a promising bioactive for blood-contacting applications. This study furthers the mechanistic understanding of platelet interactions with perlecan by establishing that platelets utilize domains III and V of the core protein for adhesion. Polyvinyl chloride (PVC) is functionalized with recombinant human perlecan domain V (rDV) to explore the effect of the tethering method on proteoglycan orientation and bioactivity. Tethering of rDV to PVC is achieved via either physisorption or covalent attachment via plasma immersion ion implantation (PIII) treatment. Both methods of rDV tethering reduce platelet adhesion and activation compared to the pristine PVC, however, the mechanisms are unique for each tethering method. Physisorption of rDV on PVC orientates the molecule to hinder access to the integrin-binding region, which inhibits platelet adhesion. In contrast, PIII treatment orientates rDV to allow access to the integrin-binding region, which is rendered antiadhesive to platelets via the glycosaminoglycan (GAG) chain. These effects demonstrate the potential of rDV biofunctionalization to modulate platelet interactions for blood contacting applications.

Primary hepatocytes and their cultures for the testing of drug-induced liver injury

Drug-induced liver injury is a major reason for discontinuation of drug development and withdrawal of drugs from the market. Intensive efforts in the last decades have focused on the establishment and finetuning of liver-based in vitro models for reliable prediction of hepatotoxicity triggered by drug candidates. Of those, primary hepatocytes and their cultures still are considered the gold standard, as they provide an acceptable reflection of the hepatic in vivo situation. Nevertheless, these in vitro systems cope with gradual deterioration of the differentiated morphological and functional phenotype. The present paper gives an overview of traditional and more recently introduced strategies to counteract this dedifferentiation process in an attempt to set up culture models that can be used for long-term testing purposes. The relevance and applicability of such optimized cultures of primary hepatocytes for the testing of drug-induced cholestatic liver injury is demonstrated.

Development of an oxygenation culture method for activating the liver-specific functions of HepG2 cells utilizing a collagen vitrigel membrane chamber

We recently developed a collagen vitrigel membrane (CVM) chamber possessing a scaffold composed of high-density collagen fibrils. In this study, we first confirmed that the advantage of CVM chamber in comparison to the traditional culture chamber with porous polyethylene terephthalate membrane is to preserve a culture medium poured in its inside even though the under side is not a liquid phase but solid and gas phases. Subsequently, we designed three different culture systems to grow HepG2 cells in a culture medium (liquid phase) on the CVM which the under side is a culture medium, a plastic surface (solid phase) or 5 % CO₂ in air (gas phase) and aimed to develop a brief culture method useful for activating the liver-specific functions and analyzing the pharmacokinetics of fluorescein diacetate. HepG2 cells cultured for 2 days on the liquid–solid interface and subsequently for 1 day on the liquid–gas interface represented excellent cell viability and morphology in comparison to the others, and remarkably improved albumin secretion and urea synthesis to almost the same level of freshly isolated human hepatocytes and CYP3A4 activity to about half the level of differentiated HepaRG cells. Also, the cells rapidly absorbed fluorescein diacetate, distributed it in cytosol, metabolized it into fluorescein, and speedily excreted fluorescein into both bile canaliculus-like networks and extracellular solution. These data suggest that hepatic structure and functions of monolayered HepG2 cells can be induced within a day after the oxygenation from beneath the CVM.

Primary Hepatocytes in Sandwich Culture

Hepatocytes in sandwich configuration constitute of primary hepatocytes cultured between two layers of extracellular matrix. Sandwich-cultured hepatocytes maintain expression of liver-specific proteins and gradually form intact bile canaliculi with functional biliary excretion of endogenous compounds and xenobiotics. Both freshly isolated and cryopreserved hepatocytes can be used to establish sandwich cultures. Therefore, this preclinical model has become an invaluable in vitro tool to evaluate hepatobiliary drug transport, metabolism, hepatotoxicity, and drug interactions. In this chapter, commonly used procedures to cultivate primary hepatocytes from human and rat in sandwich configuration are described.

Biomaterials for liver tissue engineering

Liver extracellular matrix (ECM) composition, topography and biomechanical properties influence cell-matrix interactions. The ECM presents guiding cues for hepatocyte phenotype maintenance, differentiation and proliferation both in vitro and in vivo. Current understanding of such cell-guiding cues along with advancement of techniques for scaffold fabrication has led to evolution of matrices for liver tissue culture from simple porous scaffolds to more complex 3D matrices with microarchitecture similar to in vivo. Natural and synthetic polymeric biomaterials fabricated in different topographies and porous matrices have been used for hepatocyte culture. Heterotypic and homotypic cell interactions are necessary for developing an adult liver as well as an artificial liver. A high oxygen demand of hepatocytes as well as graded oxygen distribution in liver is another challenging attribute of the normal liver architecture that further adds to the complexity of engineered substrate design. A balanced interplay of cell-matrix interactions along with cell-cell interactions and adequate supply of oxygen and nutrient determines the success of an engineered substrate for liver cells. Techniques devised to incorporate these features of hepatic function and mimic liver architecture range from maintaining liver cells in mm-sized tailor-made scaffolds to a more bottoms up approach that starts from building the microscopic subunit of the whole tissue. In this review, we discuss briefly various biomaterials used for liver tissue engineering with respect to design parameters such as scaffold composition and chemistry, biomechanical properties, topography, cell-cell interactions and oxygenation.

Sandwich-cultured hepatocytes: utility for in vitro exploration of hepatobiliary drug disposition and drug-induced hepatotoxicity

INTRODUCTION

The sandwich-cultured hepatocyte (SCH) model has become an invaluable in vitro tool for studying hepatic drug transport, metabolism, biliary excretion and toxicity. The relevant expression of many hepatocyte-specific functions together with the in vivo-like morphology favor SCHs over other preclinical models for evaluating hepatobiliary drug disposition and drug-induced hepatotoxicity.

AREAS COVERED

In this review, the authors highlight recommended procedures required for reproducibly culturing hepatocytes in sandwich configuration. It also provides an overview of the SCH model characteristics as a function of culture time. Lastly, the article presents a summary of the most prominent applications of the SCH model, including hepatic drug clearance prediction, drug-drug interaction potential and drug-induced hepatotoxicity.

EXPERT OPINION

When human (cryopreserved) hepatocytes are used to establish sandwich cultures, the model appears particularly valuable to quantitatively investigate clinically relevant mechanisms related to in vivo hepatobiliary drug disposition and hepatotoxicity. Nonetheless, the SCH model would largely benefit from better insight into the fundamental cell signaling mechanisms that are critical for long-term in vitro maintenance of the hepatocytic phenotype. Studies systematically exploring improved cell culture conditions (e.g., co-cultures or extracellular matrix modifications), as well as in vitro work identifying key transcription factors involved in hepatocyte differentiation are currently emerging.

Primary hepatocyte cultures for pharmaco-toxicological studies: at the busy crossroad of various anti-dedifferentiation strategies

Continuously increasing understanding of the molecular triggers responsible for the onset of diseases, paralleled by an equally dynamic evolution of chemical synthesis and screening methods, offers an abundance of pharmacological agents with a potential to become new successful drugs. However, before patients can benefit of newly developed pharmaceuticals, stringent safety filters need to be applied to weed out unfavourable drug candidates. Cost effectiveness and the need to identify compound liabilities, without exposing humans to unnecessary risks, has stimulated the shift of the safety studies to the earliest stages of drug discovery and development. In this regard, in vivo relevant organotypic in vitro models have high potential to revolutionize the preclinical safety testing. They can enable automation of the process, to match the requirements of high-throughput screening approaches, while satisfying ethical considerations. Cultures of primary hepatocytes became already an inherent part of the preclinical pharmaco-toxicological testing battery, yet their routine use, particularly for long-term assays, is limited by the progressive deterioration of liver-specific features. The availability of suitable hepatic and other organ-specific in vitro models is, however, of paramount importance in the light of changing European legal regulations in the field of chemical compounds of different origin, which gradually restrict the use of animal studies for safety assessment, as currently witnessed in cosmetic industry. Fortunately, research groups worldwide spare no effort to establish hepatic in vitro systems. In the present review, both classical and innovative methodologies to stabilize the in vivo-like hepatocyte phenotype in culture of primary hepatocytes are presented and discussed.

Cells and materials for liver tissue engineering

Liver transplantation is currently the most efficacious treatment for end-stage liver diseases. However, one main problem with liver transplantation is the limited number of donor organs that are available. Therefore, liver tissue engineering based on cell transplantation that combines materials to mimic the liver is under investigation with the goal of restoring normal liver functions. Tissue engineering aims to mimic the interactions among cells with a scaffold. Particular materials or a matrix serve as a scaffold and provide a three-dimensional environment for cell proliferation and interaction. Moreover, the scaffold plays a role in regulating cell maturation and function via these interactions. In cultures of hepatic lineage cells, regulation of cell proliferation and specific function using biocompatible synthetic, biodegradable bioderived matrices, protein-coated materials, surface-modified nanofibers, and decellularized biomatrix has been demonstrated. Furthermore, beneficial effects of addition of growth factor cocktails to a flow bioreactor or coculture system on cell viability and function have been observed. In addition, a system for growing stem cells, liver progenitor cells, and primary hepatocytes for transplantation into animal models was developed, which produces hepatic lineage cells that are functional and that show long-term proliferation following transplantation. The major limitation of cells proliferated with matrix-based transplantation systems is the high initial cell loss and dysfunction, which may be due to the absence of blood flow and the changes in nutrients. Thus, the development of vascular-like scaffold structures, the formation of functional bile ducts, and the maintenance of complex metabolic functions remain as major problems in hepatic tissue engineering and will need to be addressed to enable further advances toward clinical applications.

Effects of time culture and prototypical cytochrome P450 3A (CYP3A) inducers on CYP2B22, CYP2C, CYP3A and nuclear receptor (NR) mRNAs in long-term cryopreserved pig hepatocytes (CPHs)

In the present study, transcriptional and post-translational effects of culturing time and prototypical cytochrome P450 3A (CYP3A) inducers on principal nuclear receptors (NRs), CYP2B22, 2C and 3A were investigated in long-term stored (~10 years) cryopreserved pig hepatocytes (CPHs). In the time-course study, a crush and rise effect was observed for pregnane X receptor (NR1I2) and constitutive androstane receptor (NR1I3) mRNAs, while a time-dependent increase of retinoid X receptor alpha (NR2B1) was noticed. Cytochrome P450 gene expression profiles were down-regulated as a function of time. In the induction study, an increase of NR1I2, NR1I3 and NR2B1 mRNAs was observed in dexamethasone-exposed CPHs. About CYPs, an overall up-regulation was seen in CPHs exposed to phenobarbital, while dexamethasone and rifampicin up-regulated only CYP3A. In both studies, transcriptional CYP results were confirmed at the post-translational level (immunoblotting and enzyme activities), except for CYP2B immunoblotting in the induction study. The present data demonstrate that long-term stored CPHs may be used to investigate mechanisms involved in CYPs regulation, expression and function; provide further info about NR regulation of CYPs, and confirm species-differences in these mechanisms of regulation; finally, they suggest the usefulness and relevance of gene expression profiling to early detect any modulation of CYP expression and bioactivity.

Artificial organs 2011: a year in review

In this Editor's Review, articles published in 2011 are organized by category and briefly summarized. As the official journal of The International Federation for Artificial Organs, The International Faculty for Artificial Organs, and the International Society for Rotary Blood Pumps, Artificial Organs continues in the original mission of its founders "to foster communications in the field of artificial organs on an international level."Artificial Organs continues to publish developments and clinical applications of artificial organ technologies in this broad and expanding field of organ replacement, recovery, and regeneration from all over the world. We take this time also to express our gratitude to our authors for offering their work to this journal. We offer our very special thanks to our reviewers who give so generously of time and expertise to review, critique, and especially provide meaningful suggestions to the author's work whether eventually accepted or rejected. Without these excellent and dedicated reviewers, the quality expected from such a journal would not be possible. We also express our special thanks to our Publisher, Wiley-Blackwell, for their expert attention and support in the production and marketing of Artificial Organs. In this Editor's Review, that historically has been widely well-received by our readership, we aim to provide a brief reflection of the currently available worldwide knowledge that is intended to advance and better human life while providing insight for continued application of technologies and methods of organ replacement, recovery, and regeneration. We look forward to recording further advances in the coming years.