Proliferation rates of HepG2 cells encapsulated in alginate are increased in a microgravity environment compared with static cultures

Effect of supramolecular peptide hydrogel scaffold charge on HepG2 viability and spheroid formation

Supramolecular bioinspired self-assembling peptide hydrogel (SAPH) scaffolds represent a class of fully defined synthetic materials whose chemical and mechanical properties can be finely engineered. In this study, the relationship between SAPHs physicochemical properties and HepG2 cells viability, spheroid formation and function are discussed. We first report that negatively charged SAPHs promote hepatocyte proliferation and spheroids formation in vitro 3D culture while positively charged SAPHs lead to hepatocyte death irrespective of the hydrogel mechanical properties. More specifically HepG2 cultured in 3D in E(FKFE)2 negatively charged SAPH maintained a differentiated phenotype and assembled into well-defined spheroids with strong cell-cell interactions. Furthermore, HepG2 spheroids responded to acetaminophen exposure with upregulation of key CYP450 enzymes expression clearly showing their potential for drug toxicity testing. These findings demonstrate how fine-tuned functional SAPH scaffolds can be used to identify key scaffolds parameters affecting cells. In this case we demonstrated the potential of negatively charged SAPHs for the 3D culture of HepG2 with potential applications in drug screening.

Rotating culture regulates the formation of HepaRG-derived liver organoids via YAP translocation

BACKGROUND

Liver organoid serves as an alternative model for liver pathophysiology in carbohydrate or lipid metabolism and xenobiotic metabolism transformation. Biomechanical cues including spaceflight mission can affect liver organoid construction and their related functions, but their underlying mechanisms are not fully understood yet. Here, a rotating cell culture device, namely Rotating Flat Chamber (RFC), was specifically designed for adhering cells or cell aggregated to elucidate the effects of altered gravity vector on HepaRG-derived liver organoids construction.

RESULTS

The organoids so formed under RFC presented the fast growth rate and large projection area. Meanwhile, the expressions of two pluripotency markers of SOX9 and CD44 were enhanced. This finding was positively correlated with the increased YAP expression and nuclear translocation as well as the elevated α4β6-integrin expression. Inhibition of YAP expression and nuclear translocation decreased the expression of SOX9 and CD44 under RFC, thereby attenuating the pluripotency of HepaRG-derived liver organoids.

CONCLUSIONS

In conclusion, we proposed a novel liver organoid construction method using rotating culture, by which the pluripotency of liver organoids so constructed is mediated by α4β6-integrin and YAP translocation. This work furthered the understanding in how the gravity vector orientation affects the construction of liver organoids and the related mechanotransductive pathways.

mRNA transcriptome profiling of human hepatocellular carcinoma cells HepG2 treated with Catharanthus roseus-silver nanoparticles

BACKGROUND

The demand for the development of cancer nanomedicine has increased due to its great therapeutic value that can overcome the limitations of conventional cancer therapy. However, the presence of various bioactive compounds in crude plant extracts used for the synthesis of silver nanoparticles (AgNPs) makes its precise mechanisms of action unclear.

AIM

To assessed the mRNA transcriptome profiling of human HepG2 cells exposed to Catharanthus roseus G. Don (C. roseus)-AgNPs.

METHODS

The proliferative activity of hepatocellular carcinoma (HepG2) and normal human liver (THLE3) cells treated with C. roseusAgNPs were measured using MTT assay. The RNA samples were extracted and sequenced using BGIseq500 platform. This is followed by data filtering, mapping, gene expression analysis, differentially expression genes analysis, Gene Ontology analysis, and pathway analysis.

RESULTS

The mean IC₅₀ values of C. roseusAgNPs on HepG2 was 4.38 ± 1.59 μg/mL while on THLE3 cells was 800 ± 1.55 μg/mL. Transcriptome profiling revealed an alteration of 296 genes. C. roseusAgNPs induced the expression of stress-associated genes such as MT, HSP and HMOX-1. Cellular signalling pathways were potentially activated through MAPK, TNF and TGF pathways that are responsible for apoptosis and cell cycle arrest. The alteration of ARF6, EHD2, FGFR3, RhoA, EEA1, VPS28, VPS25, and TSG101 indicated the uptake of C. roseus-AgNPs via both clathrin-dependent and clathrin-independent endocytosis.

CONCLUSION

This study provides new insights into gene expression study of biosynthesised AgNPs on cancer cells. The cytotoxicity effect is mediated by the aberrant gene alteration, and more interestingly the unique selective antiproliferative properties indicate the C. roseusAgNPs as an ideal anticancer candidate.

Potential Roles of YAP/TAZ Mechanotransduction in Spaceflight-Induced Liver Dysfunction

Microgravity exposure during spaceflight causes the disordered regulation of liver function, presenting a specialized mechano-biological coupling process. While YAP/TAZ serves as a typical mechanosensitive pathway involved in hepatocyte metabolism, it remains unclear whether and how it is correlated with microgravity-induced liver dysfunction. Here, we discussed liver function alterations induced by spaceflight or simulated effects of microgravity on Earth. The roles of YAP/TAZ serving as a potential bridge in connecting liver metabolism with microgravity were specifically summarized. Existing evidence indicated that YAP/TAZ target gene expressions were affected by mechanotransductive pathways and phase separation, reasonably speculating that microgravity might regulate YAP/TAZ activation by disrupting these pathways via cytoskeletal remodeling or nuclear deformation, or disturbing condensates formation via diffusion limit, and then breaking liver homeostasis.

Medical 3D Printing: Tools and Techniques, Today and Tomorrow

Three-dimensional printing is a still-emerging technology with high impact for the medical community, particularly in the development of tissues for the clinic. Many types of printers are under development, including extrusion, droplet, melt, and light-curing technologies. Herein we discuss the various types of 3D printers and their strengths and weaknesses concerning tissue engineering. Despite the advantages of 3D printing, challenges remain in the development of large, clinically relevant tissues. Advancements in bioink development, printer technology, tissue vascularization, and cellular sourcing/expansion are discussed, alongside future opportunities for the field. Trends regarding in situ printing, personalized medicine, and whole organ development are highlighted. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Small-Scale Fluidized Bed Bioreactor for Long-Term Dynamic Culture of 3D Cell Constructs and in vitro Testing

With the increasing interest in three-dimensional (3D) cell constructs that better represent native tissues, comes the need to also invest in devices, i.e., bioreactors, that provide a controlled dynamic environment similar to the perfusion mechanism observed in vivo. Here a laboratory-scale fluidized bed bioreactor (sFBB) was designed for hydrogel (i.e., alginate) encapsulated cells to generate a dynamic culture system that produced a homogenous milieu and host substantial biomass for long-term evolution of tissue-like structures and “per cell” performance analysis. The bioreactor design, conceptualized through scale-down empirical similarity rules, was initially validated through computational fluid dynamics analysis for the distributor capacity of homogenously dispersing the flow with an average fluid velocity of 4.596 × 10^–4 m/s. Experimental tests then demonstrated a consistent fluidization of hydrogel spheres, while maintaining shape and integrity (606.9 ± 99.3 μm diameter and 0.96 shape factor). It also induced mass transfer in and out of the hydrogel at a faster rate than static conditions. Finally, the sFBB sustained culture of alginate encapsulated hepatoblastoma cells for 12 days promoting proliferation into highly viable (>97%) cell spheroids at a high final density of 27.3 ± 0.78 million cells/mL beads. This was reproducible across multiple units set up in parallel and operating simultaneously. The sFBB prototype constitutes a simple and robust tool to generate 3D cell constructs, expandable into a multi-unit setup for simultaneous observations and for future development and biological evaluation of in vitro tissue models and their responses to different agents, increasing the complexity and speed of R&D processes.

HepaRG Self-Assembled Spheroids in Alginate Beads Meet the Clinical Needs for Bioartificial Liver

In liver tissue engineering, cell culture in spheroids is now well recognized to promote the maintenance of hepatic functions. However, the process leading to spheroids formation is time consuming, costly, and not easy to scale-up for further use in human bioartificial liver (BAL) applications. In this study, we encapsulated HepaRG cells (precursors of hepatocyte-like cells) in 1.5% alginate beads without preforming spheroids. Starting from a given hepatic biomass, we analyzed cell differentiation and metabolic performance for further use in a fluidized-bed BAL. We observed that cells self-rearranged as aggregates within the beads and adequately differentiated over time, in the absence of any differentiating factors classically used. On day 14 postencapsulation, cells displayed a wide range of hepatic features necessary for the treatment of a patient in acute liver failure. These activities include albumin synthesis, ammonia and lactate detoxification, and the efficacy of the enzymes involved in the xenobiotic metabolism (such as CYP1A1/2). Impact statement It has been recognized that culturing cells in spheroids (SPHs) is advantageous as they better reproduce the three-dimensional physiological microenvironment. This approach can be exploited in bioartificial liver applications, where obtaining a functional hepatic biomass is the major challenge. Our study describes an original method for culturing hepatic cells in alginate beads that makes possible the autonomous formation of SPHs after 3 days of culture. In turn, the cells differentiate adequately and display a wide range of hepatic features. They are also capable of treating a pathological plasma model. Finally, this setup can easily be scaled-up to treat acute liver failure.

Cryopreservation and re-culture of a 2.3 litre biomass for use in a bioartificial liver device

For large and complex tissue engineered constructs to be available on demand, long term storage using methods, such as cryopreservation, are essential. This study optimised parameters such as excess media concentration and warming rates and used the findings to enable the successful cryopreservation of 2.3 litres of alginate encapsulated liver cell spheroids. This volume of biomass is typical of those required for successful treatment of Acute Liver Failure using our Bioartificial Liver Device. Adding a buffer of medium above the biomass, as well as slow (0.6°C/min) warming rates was found to give the best results, so long as the warming through the equilibrium melting temperature was rapid. After 72 h post thaw-culture, viable cell number, glucose consumption, lactate production, and alpha-fetoprotein production had recovered to pre-freeze values in the 2.3 litre biomass (1.00 ± 0.05, 1.19 ± 0.10, 1.23 ± 0.18, 2.03 ± 0.04 per ml biomass of the pre-cryopreservation values respectively). It was also shown that further improvements in warming rates of the biomass could reduce recovery time to < 48 h. This is the first example of a biomass of this volume being successfully cryopreserved in a single cassette and re-cultured. It demonstrates that a bioartificial liver device can be cryopreserved, and has wider applications to scale-up large volume cryopreservation.

Impact of Storage at -80°C on Encapsulated Liver Spheroids After Liquid Nitrogen Storage

For many bioengineered tissues to have practical clinical application, cryopreservation for use on demand is essential. This study examined different thermal histories on warming and short holding periods at different subzero temperatures on subsequent functional recoveries of alginate encapsulated liver spheroids (ELS) for use in a bioartificial liver device. This mimicked transport at liquid nitrogen (−196°C) or dry ice (∼−80°C) temperatures. Holding at −80°C on warming after −196°C storage resulted in ELS expressing significant (p < 0.001) damage compared with direct thaw from liquid nitrogen, with viable cell number falling from 74.0 ± 8.4 million viable cells/mL without −80°C storage to 1.9 ± 0.6 million viable cells/mL 72 h post-thaw after 8 days storage at −80°C. Even 1 day at −80°C after −196°C storage resulted in lower viability (down 21% 24 h post-thaw), viable cell count (down 29% 24 h post-thaw), glucose, and alpha-1-fetoprotein production (reduced by 59% and 95% 24 h from 1 day post-thaw, respectively). Storage at −80°C was determined to be harmful only during the warming cycle. Chemical measurements of the alginate component of ELS were unchanged by cryogenic exposure in either condition.

Microgravity as a means to incorporate HepG2 aggregates in polysaccharide-protein hybrid scaffold

Tissue culture under microgravity provides a venue which promotes cell-cell association while avoiding the detrimental effects of high shear stress. Hepatocytes cultured on carriers or entrapped within matrices under simulated microgravity conditions showed improved cell function and proliferation. In the present study, a new approach was adopted where a non-cell adherent scaffold was incorporated with hepatospheroids (HepG2) under microgravity. Gum arabic (GA) was cross-linked with gelatin (GA-Gel) and collagen (GA-Col) to prepare non-cell adherent scaffolds. Microgravity experiments with GA-Gel and GA-Col indicated that GA-Col is a better substrate compared to GA-Gel. Microgravity experiments of GA-Col scaffolds with HepG2 cells confirmed that the non-adherent surface with porous architecture can incorporate hepatocyte spheroids and maintain liver specific functions. Albumin and urea synthesis of hepatocytes was sustained up to 6 days under microgravity conditions in the presence of GA-Col scaffold. This new approach of using non-cell adherent matrix and microgravity environment for developing biological substitutes will be beneficial in tissue engineering, bioartificial liver devices and in vitro safety assessment of drugs.

Biomek Cell Workstation: A Flexible System for Automated 3D Cell Cultivation

The shift from 2D cultures to 3D cultures enables improvement in cell culture research due to better mimicking of in vivo cell behavior and environmental conditions. Different cell lines and applications require altered 3D constructs. The automation of the manufacturing and screening processes can advance the charge stability, quality, repeatability, and precision. In this study we integrated the automated production of three 3D cell constructs (alginate beads, spheroid cultures, pellet cultures) using the Biomek Cell Workstation and compared them with the traditional manual methods and their consequent bioscreening processes (proliferation, toxicity; days 14 and 35) using a high-throughput screening system. Moreover, the possible influence of antibiotics (penicillin/streptomycin) on the production and screening processes was investigated. The cytotoxicity of automatically produced 3D cell cultures (with and without antibiotics) was mainly decreased. The proliferation showed mainly similar or increased results for the automatically produced 3D constructs. We concluded that the traditional manual methods can be replaced by the automated processes. Furthermore, the formation, cultivation, and screenings can be performed without antibiotics to prevent possible effects.

Rapid large-scale culturing of microencapsulated hepatocytes: a promising approach for cell-based hepatic support

INTRODUCTION

The efficacy of any bioartificial liver device requires both rapid production and proper bioactivity of the cells for the bioreactor. The goal of this study was to observe the effect of spinner speed and cell density on the proliferation of microencapsulated immortalized human hepatocytes (HepLL) and human hepatoma (HepG2) cells.

MATERIALS AND METHODS

Alginate-chitosan microcapsulated HepG2 and HepLL cells were randomly divided into 2 groups, and each group was further divided into 8 subgroups according to embedded cell density and spinner speed. The growth, metabolism, and functions of the encapsulated cells in each group were evaluated.

RESULTS

In each group, the cell number, ammonium removal, albumin synthesis, and diazepam clearance increased significantly with the spinner speed, whereas embedded cell density had no impact. Albumin synthesis, removal of ammonium, and diazepam clearance were significantly higher in the microencapsulated HepLL groups than in HepG2 cells at any time point, without any significant difference in cell numbers.

CONCLUSIONS

Spinner culture significantly promoted microencapsulated HepLL and HepG2 cell bioactivity. Wrapped cells had optimal function on day 10 in rolling culture groups. These data show that HepLL cells would be a promising candidate for cell-based liver support therapy.

Three-dimensional culture in a microgravity bioreactor improves the engraftment efficiency of hepatic tissue constructs in mice

Tissue-engineered liver using primary hepatocytes has been considered a valuable new therapeutic modality as an alternative to whole organ liver transplantation for different liver diseases. The development of clinically feasible liver tissue engineering approaches, however, has been hampered by the poor engraftment efficiency of hepatocytes. We developed a three-dimensional (3D) culture system using a microgravity bioreactor (MB), biodegradable scaffolds and growth-factor-reduced Matrigel to construct a tissue-engineered liver for transplantation into the peritoneal cavity of non-obese diabetic severe combined immunodeficient mice. The number of viable cells in the hepatic tissue constructs was stably maintained in the 3D MB culture system. Hematoxylin-eosin staining and zonula occludens-1 expression revealed that neonatal mouse liver cells were reorganized to form tissue-like structures during MB culture. Significantly upregulated hepatic functions (albumin secretion, urea production and cytochrome P450 activity) were observed in the MB culture group. Post-transplantation analysis indicated that the engraftment efficiency of the hepatic tissue constructs prepared in MB cultures was higher than that of those prepared in the static cultures. Higher level of hepatic function in the implants was confirmed by the expression of albumin. These findings suggest that 3D MB culture systems may offer an improved method for creating tissue-engineered liver because of the higher engraftment efficiency and the reduction of the initial cell function loss.

Evaluation of encapsulated liver cell spheroids in a fluidised-bed bioartificial liver for treatment of ischaemic acute liver failure in pigs in a translational setting

Liver failure is an increasing problem. Donor-organ shortage results in patients dying before receiving a transplant. Since the liver can regenerate, alternative therapies providing temporary liver-support are sought. A bioartificial-liver would temporarily substitute function in liver failure buying time for liver regeneration/organ-procurement. Our aim: to develop a prototype bioartificial-liver-machine (BAL) comprising a human liver-derived cell-line, cultured to phenotypic competence and deliverable in a clinical setting to sites distant from its preparation. The objective of this study was to determine whether its use would improve functional parameters of liver failure in pigs with acute liver failure, to provide proof-of-principle. HepG2 cells encapsulated in alginate-beads, proliferated in a fluidised-bed-bioreactor providing a biomass of 4-6 × 10(10)cells, were transported from preparation-laboratory to point-of-use operating theatre (6000 miles) under perfluorodecalin at ambient temperature. Irreversible ischaemic liver failure was induced in anaesthetised pigs, after portal-systemic-shunt, by hepatic-artery-ligation. Biochemical parameters, intracranial pressure, and functional-clotting were measured in animals connected in an extracorporeal bioartificial-liver circuit. Efficacy was demonstrated comparing outcomes between animals connected to a circuit containing alginate-encapsulated cells (Cell-bead BAL), and those connected to circuit containing alginate capsules without cells (Empty-bead BAL). Cells of the biomass met regulatory standards for sterility and provenance. All animals developed progressive liver-failure after ischaemia induction. Efficacy of BAL was demonstrated since animals connected to a functional biomass (+ cells) had significantly smaller rises in intracranial pressure, lower ammonia levels, more bilirubin conjugation, improved acidosis and clotting restoration compared to animals connected to the circuit without cells. In the +cell group, human proteins accumulated in pigs' plasma. Delivery of biomass using a short-term cold-chain enabled transport and use without loss of function over 3 days. Thus, a fluidised-bed bioreactor containing alginate-encapsulated HepG2 cell-spheroids improved important parameters of acute liver failure in pigs. The system can readily be up-scaled and transported to point-of-use justifying development at clinical scale.

Bioengineering the liver: scale-up and cool chain delivery of the liver cell biomass for clinical targeting in a bioartificial liver support system

Acute liver failure has a high mortality unless patients receive a liver transplant; however, there are insufficient donor organs to meet the clinical need. The liver may rapidly recover from acute injury by hepatic cell regeneration given time. A bioartificial liver machine can provide temporary liver support to enable such regeneration to occur. We developed a bioartificial liver machine using human-derived liver cells encapsulated in alginate, cultured in a fluidized bed bioreactor to a level of function suitable for clinical use (performance competence). HepG2 cells were encapsulated in alginate using a JetCutter to produce ∼500 μm spherical beads containing cells at ∼1.75 million cells/mL beads. Within the beads, encapsulated cells proliferated to form compact cell spheroids (AELS) with good cell-to-cell contact and cell function, that were analyzed functionally and by gene expression at mRNA and protein levels. We established a methodology to enable a ∼34-fold increase in cell density within the AELS over 11-13 days, maintaining cell viability. Optimized nutrient and oxygen provision were numerically modeled and tested experimentally, achieving a cell density at harvest of >45 million cells/mL beads; >5×10(10) cells were produced in 1100 mL of beads. This process is scalable to human size ([0.7-1]×10(11)). A short-term storage protocol at ambient temperature was established, enabling transport from laboratory to bedside over 48 h, appropriate for clinical translation of a manufactured bioartificial liver machine.

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.

An appropriate selection of a 3D alginate culture model for hepatic Huh-7 cell line encapsulation intended for viral studies

Three-dimensional (3D) culture systems have been introduced to provide cells with a biomimetic environment that is similar to in vivo conditions. Among the polymeric molecules available, sodium-alginate (Na-alg) salt is a material that is currently employed in different areas of drug delivery and tissue engineering, because it offers biocompatibility and optimal chemical properties, and its gelation with calcium chloride provides calcium-alginate (Ca-alg) scaffolds with mechanical stability and relative permeability. In this work, four different preparations of Ca-alg beads with varying Na-alg viscosity and concentration were used for a human hepatoma cell line (Huh-7) encapsulation. The effects of Ca-alg bead preparation on structural cell organization, liver-specific functions, and the expression of specific receptors implicated in hepatotropic virus permissivity were evaluated. Hepatic cells were cultured in 500 μm diameter Ca-alg beads for 7 days under dynamic conditions. For all culture systems, cell viability reached almost 100% at day 7. Cell proliferation was concomitantly followed by hepatocyte organization in aggregates, which adopted two different morphologies (spheroid aggregates or multicellular channel-like structures), depending on Ca-alg bead preparation. These cellular organizations established a real 3D hepatocyte architecture with cell polarity, cell junctions, and abundant bile canaliculi possessing microvillus-lined channels. The functionality of these 3D cultures was confirmed by the production of albumin and the exhibition of CYP1A activity over culture time, which were variable, according to Ca-alg bead condition. The expression of specific receptors of hepatitis C virus by Huh-7 cells suggests encouraging data for the further development of a new viral culture system in Ca-alg beads. In summary, this 3D hepatic cell culture represents a promising physiologically relevant system for further in vitro studies and demonstrates that an adequate encapsulation condition can be selected for each target application in liver tissue engineering, specifically in viral studies.

Storage temperatures for cold-chain delivery in cell therapy: a study of alginate-encapsulated liver cell spheroids stored at -80°c or -170°c for up to 1 year

INTRODUCTION

A bioartificial liver comprising alginate-encapsulated liver cell spheroids (ELS) could bridge the gap to transplant or spontaneous recovery in acute liver failure, but will be required for emergency use, necessitating cryopreservation. A cryopreservation protocol has been developed, but beyond this, the feasibility of cold-chain storage is considered here. Cryopreservation will be increasingly required for timely delivery of tissue and bioengineered products, and significant, but often, over-looked factors that impact on cost and ease of clinical application are the storage temperature and useful preservation time. Storage in the vapor phase of liquid nitrogen (∼-170°C) is the gold standard, but for safety and economic purposes, storing ELS in electric freezers at -80°C may be preferable.

METHODS

ELS were cryopreserved using an optimized protocol and stored at either -80°C or at -170°C for up to 1 year. ELS were removed from storage after 1, 2, 3, 6, 9, or 12 months, and recovery was assessed 24 h postwarming. Cell recovery was assessed using viability (fluorescent staining with image analysis), cell number (nuclei count), and functional (hepatospecific protein enzyme-linked immunosorbent assay) assays.

RESULTS

Viability, the viable cell number, and function of ELS stored at -170°C were maintained at similar values throughout the year. In contrast, ELS stored at -80°C exhibited decreased viability, viable cell numbers, and function by as early as 1 month. Progressive deterioration was subsequently observed. After 12 months of storage at -80°C, viable cell recovery of ELS was ∼15% that of ELS stored at -170°C.

CONCLUSIONS

While convenience and cost might support the use of -80°C for storage of multicellular bioengineered products such as ELS, results indicate rapid deterioration in functional recoveries after only a few weeks. This study demonstrates that storage temperature is an important consideration in regenerative medicine and caution should be applied by limiting storage at -80°C to only a few weeks.

Encapsulation of Huh-7 cells within alginate-poly(ethylene glycol) hybrid microspheres

Novel calcium alginate poly(ethylene glycol) hybrid microspheres (Ca-alg-PEG) were developed and evaluated as potentially suitable materials for cell microencapsulation. Grafting 5-13% of the backbone units of sodium alginate (Na-alg) with α-amine-ω-thiol PEG maintained the gelling capacity in presence of calcium ions, while thiol end groups allowed for preparing chemically crosslinked hydrogel via spontaneous disulfide bond formation. The combination of these two gelling mechanisms yielded Ca-alg-PEG. Human hepatocellular carcinoma cells (Huh-7) were encapsulated in Ca-alg-PEG and calcium alginate beads (Ca-alg), and cultured for 2 weeks under agitation conditions. Immediately after completion of the microencapsulation, the cell viability was 60% and similar in Ca-alg-PEG and Ca-alg. The proliferation of Huh-7 encapsulated in Ca-alg-PEG was slightly higher than in Ca-alg. Accelerated proliferation after 2 weeks was observed for the encapsulation in Ca-alg-PEG. The production of albumin confirmed the functionality of the encapsulated Huh-7 cells. The study confirms the suitability of Ca-alg-PEG and the one-step technology for cell microencapsulation.

Alginate-encapsulated HepG2 cells in a fluidized bed bioreactor maintain function in human liver failure plasma

Alginate-encapsulated HepG2 cells cultured in microgravity have the potential to serve as the cellular component of a bioartificial liver. This study investigates their performance in normal and liver failure (LF) human plasma over 6-8 h in a fluidized bed bioreactor. After 8 days of microgravity culture, beads containing 1.5 x 10(9) cells were perfused for up to 8 h at 48 mL/min with 300 mL of plasma. After exposure to 90% LF plasma, vital dye staining showed maintained cell viability, while a 7% increase in lactate dehydrogenase activity indicated minimal cell damage. Glucose consumption, lactate production, and a 4.3-fold linear increase in alpha-fetoprotein levels were observed. Detoxificatory function was demonstrated by quantification of bilirubin conjugation, urea synthesis, and Cyp450 1A activity. These data show that in LF plasma, alginate-encapsulated HepG2 cells can maintain viability, and metabolic, synthetic, and detoxificatory activities, indicating that the system can be scaled-up to form the biological component of a bioartificial liver.

Fluorescence optical detection in situ for real-time monitoring of cytochrome P450 enzymatic activity of liver cells in multiple microfluidic devices

We describe an in situ fluorescence optical detection system to demonstrate real-time and non-invasive detection of reaction products in a microfluidic device while under perfusion within a standard incubator. The detection system is designed to be compact and robust for operation inside a mammalian cell culture incubator for quantitative detection of fluorescent signal from microfluidic devices. When compared to a standard plate reader, both systems showed similar biphasic response curves with two linear regions. Such a detection system allows real-time measurements in microfluidic devices with cells without perturbing the culture environment. In a proof-of-concept experiment, the cytochrome P450 1A1/1A2 activity of a hepatoma cell line (HepG2/C3A) was monitored by measuring the enzymatic conversion of ethoxyresorufin to resorufin. The hepatoma cell line was embedded in Matrigel(TM) construct and cultured in a microfluidic device with medium perfusion. The response of the cells, in terms of P450 1A1/1A2 activity, was significantly different in a plate well system and the microfluidic device. Uninduced cells showed almost no activity in the plate assay, while uninduced cells in Matrigel(TM) with perfusion in a microfluidic device showed high activity. Cells in the plate assay showed a significant response to induction with 3-Methylcholanthrene while cells in the microfluidic device did not respond to the inducer. These results demonstrate that the system is a potentially useful method to measure cell response in a microfluidic system.

Monolayer and spheroid culture of human liver hepatocellular carcinoma cell line cells demonstrate distinct global gene expression patterns and functional phenotypes

Understanding cell biology of three-dimensional (3D) biological structures is important for more complete appreciation of in vivo tissue function and advancing ex vivo organ engineering efforts. To elucidate how 3D structure may affect hepatocyte cellular responses, we compared global gene expression of human liver hepatocellular carcinoma cell line (HepG2) cells cultured as monolayers on tissue culture dishes (TCDs) or as spheroids within rotating wall vessel (RWV) bioreactors. HepG2 cells grown in RWVs form spheroids up to 100 mum in diameter within 72 h and up to 1 mm with long-term culture. The actin cytoskeleton in monolayer cells show stress fiber formation while spheroids have cortical actin organization. Global gene expression analysis demonstrates upregulation of structural genes such as extracellular matrix, cytoskeletal, and adhesion molecules in monolayers, whereas RWV spheroids show upregulation of metabolic and synthetic genes, suggesting functional differences. Indeed, liver-specific functions of cytochrome P450 activity and albumin production are higher in the spheroids. Enhanced liver functions require maintenance of 3D structure and environment, because transfer of spheroids to a TCD results in spheroid disintegration and subsequent loss of function. These findings illustrate the importance of physical environment on cellular organization and its effects on hepatocyte processes.

Effects of dispensing pressure and nozzle diameter on cell survival from solid freeform fabrication-based direct cell writing

Novel technologies are emerging that incorporate cells as part of the building blocks for various biomanufacturing processes, such as solid freeform fabricated tissue constructs for tissue regeneration, three-dimensional pharmacokinetic models, cell-based microelectromechanical systems, sensors, and microfluidic devices. However, the effects of these biomanufacturing processes on cells have not been fully studied. This paper examines the effect of solid freeform fabrication-based direct cell writing process, focusing on dispensing pressure and nozzle size, on the viability and functional behavior of HepG2 cells encapsulated within alginate. Our experimental results revealed a process-induced mechanical damage to cell membrane integrity, causing a quantifiable loss in cell viability due to incremental increases and decreases in the studied process parameters of dispensing pressure and nozzle size, respectively. The experimental results also suggested that cells may require a recovery period following direct cell writing biofabrication. The general finding of this study may be applicable to freeform fabrication of cell-based tissue constructs and three-dimensional biological models.

Cells for bioartificial liver devices: the human hepatoma-derived cell line C3A produces urea but does not detoxify ammonia

Extrahepatic bioartificial liver devices should provide an intact urea cycle to detoxify ammonia. The C3A cell line, a subclone of the hepatoma-derived HepG2 cell line, is currently used in this context as it produces urea, and this has been assumed to be reflective of ammonia detoxification via a functional urea cycle. However, based on our previous findings of perturbed urea-cycle function in the non-urea producing HepG2 cell line, we hypothesized that the urea produced by C3A cells was via a urea cycle-independent mechanism, namely, due to arginase II activity, and therefore would not detoxify ammonia. Urea was quantified using (15)N-ammonium chloride metabolic labelling with gas chromatography-mass spectrometry. Gene expression was determined by real-time reverse transcriptase-PCR, protein expression by western blotting, and functional activities with radiolabelling enzyme assays. Arginase inhibition studies used N(omega)-hydroxy-nor-L-arginine. Urea was detected in C3A conditioned medium; however, (15)N-ammonium chloride-labelling indicated that (15)N-ammonia was not incorporated into (15)N-labelled urea. Further, gene expression of two urea cycle genes, ornithine transcarbamylase and arginase I, were completely absent. In contrast, arginase II mRNA and protein was expressed at high levels in C3A cells and was inhibited by N(omega)-hydroxy-nor-L-arginine, which prevented urea production, thereby indicating a urea cycle-independent pathway. The urea cycle is non-functional in C3A cells, and their urea production is solely due to the presence of arginase II, which therefore cannot provide ammonia detoxification in a bioartificial liver system. This emphasizes the continued requirement for developing a component capable of a full repertoire of liver function.

Microfluidic scaffolds for tissue engineering

Most methods to culture cells in three dimensions depend on a cell-seedable biomaterial to define the global structure of the culture and the microenvironment of the cells. Efforts to tailor these scaffolds have focused on the chemical and mechanical properties of the biomaterial itself. Here, we present a strategy to control the distributions of soluble chemicals within the scaffold with convective mass transfer via microfluidic networks embedded directly within the cell-seeded biomaterial. Our presentation of this strategy includes: a lithographic technique to build functional microfluidic structures within a calcium alginate hydrogel seeded with cells; characterization of this process with respect to microstructural fidelity and cell viability; characterization of convective and diffusive mass transfer of small and large solutes within this microfluidic scaffold; and demonstration of temporal and spatial control of the distribution of non-reactive solutes and reactive solutes (that is, metabolites) within the bulk of the scaffold. This approach to control the chemical environment on a micrometre scale within a macroscopic scaffold could aid in engineering complex tissues.

Significant survival prolongation in pigs with fulminant hepatic failure treated with a novel microgravity-based bioartificial liver

The aim of this study was to evaluate the efficacy and safety of our novel Innsbruck Bioartificial Liver (IBAL; US patent no. 10/641275), which contains aggregates of porcine hepatocytes grown under simulated microgravity, in a porcine model of fulminant hepatic failure (FHF). FHF was induced by a combination of 75-80% liver resection and ischemia of the remnant segments for 60 min in 12 pigs. Two experimental groups were studied: the control group (n = 5) received standard intensive care and the study group (n = 5) received IBAL treatment. The survival of pigs with FHF was significantly prolonged by about 150% with IBAL treatment as compared to controls (controls: 20.4 +/- 2.8 h, IBAL: 51.0 +/- 2.2 h; P = 0.00184). In addition, intracranial pressure, blood ammonia, lactate, aspartate aminotransferase, and alkaline phosphatase levels were lower in the IBAL group than in controls, indicating metabolic activity of porcine hepatocytes in the bioreactor. No adverse effects were observed.

Ornithine transcarbamylase and arginase I deficiency are responsible for diminished urea cycle function in the human hepatoblastoma cell line HepG2

A possible cell source for a bio-artificial liver is the human hepatblastoma-derived cell line HepG2 as it confers many hepatocyte functions, however, the urea cycle is not maintained resulting in the lack of ammonia detoxification via this cycle. We investigated urea cycle activity in HepG2 cells at both a molecular and biochemical level to determine the causes for the lack of urea cycle expression, and subsequently addressed reinstatement of the cycle by gene transfer. Metabolic labelling studies showed that urea production from 15N-ammonium chloride was not detectable in HepG2 conditioned medium, nor could 14C-labelled urea cycle intermediates be detected. Gene expression data from HepG2 cells revealed that although expression of three urea cycle genes Carbamoyl Phosphate Synthase I, Arginosuccinate Synthetase and Arginosuccinate Lyase was evident, Ornithine Transcarbamylase and Arginase I expression were completely absent. These results were confirmed by Western blot for arginase I, where no protein was detected. Radiolabelled enzyme assays showed that Ornithine Transcarbamylase functional activity was missing but that Carbamoyl Phosphate Synthase I, Arginosuccinate Synthetase and Arginosuccinate Lyase were functionally expressed at levels comparable to cultured primary human hepatocytes. To restore the urea cycle, HepG2 cells were transfected with full length Ornithine Transcarbamylase and Arginase I cDNA constructs under a CMV promoter. Co-transfected HepG2 cells displayed complete urea cycle activity, producing both labelled urea and urea cycle intermediates. This strategy could provide a cell source capable of urea synthesis, and hence ammonia detoxificatory function, which would be useful in a bio-artificial liver.

Functional analysis of encapsulated hepatic progenitor cells

A major challenge in developing therapies based on progenitor or stem cell populations (from sources other than bone marrow) involves developing a mode to deliver these cells in a manner that optimizes their viability, engraftment, proliferation, and differentiation. We have previously isolated a hepatic progenitor cell (HPC) population from adult liver tissue that differentiates into hepatic and biliary cell subtypes. We postulated that, using electrostatic encapsulation, we could reproducibly generate an ex vivo environment for the HPCs. We also theorized that this approach would foster cellular viability and function of the progenitor cell population. Using this encapsulation process, we consistently produced beads with uniform diameters between 200 and 700 microm. In vitro analysis of the encapsulated beads demonstrated extended periods of viability and function based on albumin production, urea metabolism, and glycogen storage. In conclusion, HPC encapsulation fosters the subsequent differentiation of HPCs into functional cells while maintaining their viability in long-term culture. These results demonstrate the efficacy of this method using somatic-derived progenitor cell populations and pave the way for clinical therapies.