Effect of a hepatocyte growth factor/heparin-immobilized collagen system on albumin synthesis and spheroid formation by hepatocytes

Fabrication of a decellularized liver matrix-based hepatic patch for the repair of CCl4-induced liver injury

This article primarily introduces a new treatment for liver fibrosis/cirrhosis. We developed a hepatic patch by combining decellularized liver matrix (DLM) with the hepatocyte growth factor (HGF)/heparin-complex and evaluated its restorative efficacy. In vitro prophylactic results, the HGF/heparin-DLM patches effectively mitigated CCl4-induced hepatocyte toxicity and restored the cytotoxicity levels to the baseline levels by day 5. Furthermore, these patches restored albumin synthesis of injured hepatocytes to more than 70% of the normal levels within 5 days. In vitro therapeutic results, the urea synthesis of the injured hepatocytes reached 91% of the normal levels after 10 days of culture, indicating successful restoration of hepatic function by the HGF/heparin-DLM patches in both prophylactic and therapeutic models. In vivo results, HGF/heparin-DLM patches attached to the liver and gut exhibited a significant decrease in collagen content (4.44 times and 2.77 times, respectively) and an increase in glycogen content (1.19 times and 1.12 times, respectively) compared to the fibrosis group after 1 week, separately. In summary, liver function was restored and inflammation was inhibited through the combined effects of DLM and the HGF/heparin-complex in fibrotic liver. The newly designed hepatic patch holds promise for both in vitro and in vivo regeneration therapy and preventive health care for liver tissue engineering.

Prospective Application of Tannic Acid in Acetaminophen (APAP)-Induced Acute Liver Failure

This study investigated the effect of tannic acid (TA), a natural plant-derived polyphenol, on hepatocyte viability and function, focusing on both hepatoprotective and hepatocurative aspects within liver failure models. In an in vitro prevention model, the TA-containing group exhibited 1.5-fold and 59-fold higher relative cell viability and albumin synthesis, respectively, in injured mature hepatocytes (MHs) and 1.14-fold and 1.10-fold higher values in injured small hepatocytes (SHs), compared with the TA-free group. In the in vitro curative model, the TA-containing group exhibited 3.25-fold and 113-fold higher relative cell viability and albumin synthesis, respectively, in injured MHs and 0.36-fold and 3.55-fold higher values in injured SHs, compared with the TA-free group. In the in vivo disease model, the administration of 300 μL of 1 μg/mL TA significantly mitigated acute liver failure damage and post-APAP toxicity in mice. This was evident in serum analysis, where the levels of alanine transaminase, aspartate aminotransferase, and total bilirubin notably decreased, in agreement with histological observations. The study findings reveal that TA can enhance hepatic function at specific additive concentrations. Furthermore, even when injured by APAP, hepatocytes could revert to their preinjury state after additional TA supplementation. Additionally, pretreating hepatocytes with TA can alleviate subsequent damage. Thus, TA holds clinical potential in the treatment of APAP-induced liver failure.

Monitoring Cultured Rat Hepatocytes Using RNA-Seq In Vitro

Compared to other techniques, RNA sequencing (RNA-Seq) has the advantage of having details of the expression abundance of all transcripts in a single run. In this study, we used RNA-Seq to monitor the maturity and dynamic characteristics of in vitro hepatocyte cultures. Hepatocytes, including mature hepatocytes and small hepatocytes, were analyzed in vitro using RNA-Seq and quantitative polymerase chain reaction (qPCR). The results demonstrated that the gene expression profiles measured by RNA-Seq showed a similar trend to the expression profiles measured by qPCR, and can be used to infer the success of in vitro hepatocyte cultures. The results of the differential analysis, which compared mature hepatocytes against small hepatocytes, revealed 836 downregulated and 137 upregulated genes. In addition, the success of the hepatocyte cultures could be explained by the gene list screened from the adopted gene enrichment test. In summary, we demonstrated that RNA-Seq could become an effective method for monitoring the whole transcriptome of hepatocyte cultures and provide a more comprehensive list of factors related to the differentiation of small hepatocytes into mature hepatocytes. This monitoring system not only shows high potential in medical applications but may also be a novel method for the clinical diagnosis of liver-related diseases.

Scaffolds Based on Silk Fibroin with Decellularized Rat Liver Microparticles: Investigation of the Structure, Biological Properties and Regenerative Potential for Skin Wound Healing

The development of advanced biomaterials and constructs for accelerated recovery of damaged tissues is a key direction in regenerative medicine. Biocompatible scaffolds based on natural biopolymers are widely used for these tasks. Organ decellularization enables obtaining a cell-free extracellular matrix (ECM) with preserved composition and biological activity. The objectives of the present work were combining these two approaches for the development of a composite scaffold based on silk fibroin and ECM microparticles and assessing its structure, biological properties, and regenerative potential. ECM microparticles were obtained by grinding the decellularized matrix of Wistar rat liver in liquid nitrogen. Scaffolds in the form of films were prepared by the casting method. The sinuous and rough topography of the scaffold surface was assessed by the scanning probe nanotomography (SPNT) technique. The inclusion of ECM microparticles in the composition did not affect the elasticity and tensile strength of the scaffolds. The obtained scaffold was non-toxic to cells, maintained high levels of adhesion and proliferation of mouse 3T3 fibroblast and Hep-G2 cells, and showed high regenerative potential, which was studied in the experimental model of full-thickness rat skin wound healing. The wound healing was accelerated by 1.74 times in comparison with the control.

Development of a 3D porous chitosan/gelatin liver scaffold for a bioartificial liver device

Functional artificial livers (FALs), with embedded hepatocytes that perform the functions of a normal liver, have been developed during the past decades. It is important to note that the liver scaffold, which is a biologically functional core of bioartificial livers, plays a vital role in the bio-cartridge within a bioartificial liver. In this study, a three-dimensional (3D) liver scaffold for in vitro cultures was fabricated by freeze-drying a chitosan/gelatin (CG) solution. A CG scaffold has advantages such as (i) inexpensive and easy-to-make; (ii) easy to fabricate with varying compressive modulus by changing the concentration of glutaraldehyde; (iii) non-cytotoxicity; and (iv) porous structure is similar to extracellular matrix (ECM), thus facilitating hepatocyte adhesion and proliferation. The results revealed that the compressive modulus and maintainability of a CG scaffold was correlated to the increase in glutaraldehyde. Furthermore, hepatocyte viability and hepatic functions showed the best performances with a 0.61% glutaraldehyde-CG scaffold. This CG scaffold not only had higher hepatocyte biocompatibility and mechanical strength, but also maintained hepatic functions and viability in vitro cultures; especially, the mechanical properties of 0.61% glutaraldehyde-CG scaffold were very similar to those in normal liver. The CG scaffold as a liver scaffold may have high potential for further bioartificial liver design in the near future.

HGF Gene Delivering Alginate/Galactosylated Chitosan Sponge Scaffold for Three-Dimensional Coculture of Hepatocytes/3T3 Cells

Gene delivery from tissue engineering scaffold is a novel strategy in regulating long-term growth and function of cells in vitro culture. In this study, a hepatocyte growth factor plasmid/polyetherimide (pHGF/PEI) polyplex delivering alginate (AL)/galactosylated chitosan (GC) (pHGF/PEI-AL/GC) sponge scaffold was prepared for the in vitro coculture of hepatocytes/3T3 cells. The pHGF/PEI polyplex released for 6 days in the sponge scaffold with weight ratio of AL/GC being 3:1 and fixed amount of pHGF being 40 μg (24-well scaffold). In addition, the 3T3 cells culturing in the pHGF/PEI-AL/GC sponge scaffold could be continually transfected and expressed the exogenous HGF for 6 days. Furthermore, the albumin secretion and urea synthesis of hepatocytes were significantly enhanced when cocultured with 3T3 cells in the pHGF/PEI-AL/GC sponge scaffold compared with that in the AL/GC sponge without pHGF. In summary, the preparation of AL/GC sponge scaffold delivering pHGF/PEI polyplex is a critical significance for maintaining the long-term survival and function of primary hepatocytes in vitro.

Numerical Investigations of Hepatic Spheroids Metabolic Reactions in a Perfusion Bioreactor

Miniaturized culture systems of hepatic cells are emerging as a strong tool facilitating studies related to liver diseases and drug discovery. However, the experimental optimization of various parameters involved in the operation of these systems is time-consuming and expensive. Hence, developing numerical tools predicting the function of such systems can significantly reduce the associated cost. In this paper, a perfusion-based three dimensional (3D) bioreactor comprising encapsulated human liver hepatocellular carcinoma (HepG2) spheroids are analyzed. The flow and mass transfer equations for oxygen as well as different metabolites such as albumin, glucose, glutamine, ammonia, and urea were solved in three different domains, i.e., free flow, hydrogel, and spheroid porous media sections. Since the spheroids were encapsulated inside the hydrogel, shear stress imposed on them were found to be less than tolerable thresholds. The predicted cumulative albumin concentration over the 7 days of culture period showed a good agreement with the experimental data. Based on the critical role of oxygen supply to the hepatocytes, a parametric study was performed and the effect of various parameters was investigated. Results illustrated that convection mechanism was the dominant transport mechanism in the main-stream section contrary to the intra spheroids parts where the diffusion was the prevailing transport mechanism. In the hydrogel parts, the rate of diffusion and convection mechanisms were almost identical. As expected, higher perfusion rate would provide high oxygen level for the cells and, smaller spheroids with a diameter of 100 μm were at the low risk of hypoxic conditions due to short diffusive oxygen penetration depth. Numerical results evidenced that spheroids with diameter size >200 μm at low porosities (ε = 0.2-0.3) were at risk of oxygen depletion, especially at locations near the core center. Therefore, these results could be beneficial in preventing hypoxic conditions during in vitro experiments. The presented numerical model provides a numerical platform which can help researchers to design and optimize complex bioreactors and obtain numerical indexes of the main metabolites in a very short time prior to any fabrications. Such numerical indexes can be helpful in certifying the outcomes of forensic investigations.

Novel sericin-based hepatocyte serum-free medium and sericin’s effect on hepatocyte transcriptome

AIM

To develop a novel hepatocyte serum-free medium based on sericin, and to explore the effect of sericin on the hepatocyte transcriptome.

METHODS

A controlled trial comparing novel serum-free medium and other media: C3A cells were cultured in our novel serum-free medium, HepatoZYME, complete medium (DMEM/F12 with 100 mL/L FBS), and DMEM/F12, and then cell attachment, proliferation, and function as well as the biocompatibility of the media were assessed. A comparative study of serum-free media with or without 2 mg/mL sericin: the effect of sericin on C3A growth was assessed by cell viability and proliferation, the effect of sericin on C3A cell cycle distribution was determined by flow cytometry, and the effect of sericin on the C3A transcriptome was assessed by gene-chip array and RT-qPCR.

RESULTS

More C3A cells attached to the plate containing our serum-free medium than to those containing HepatoZYME and DMEM/F12 at 24 h post-seeding. Both the viability and proliferation rate of C3A cells in sericin-based serum-free medium were superior to those of cells in HepatoZYME and DMEM/F12 (P < 0.001). The content of albumin and urea in our serum-free medium was significantly higher than that in HepatoZYME and DMEM/F12 throughout the whole culture period (P < 0.001) and was similar to that in complete medium at day 3, 4, and 5. In part 2, cell viability and proliferation were greater in the presence of 2 mg/mL sericin (P < 0.001), as was the proportion of cells in S phase (16.21% ± 0.98% vs 12.61% ± 0.90%, P < 0.01). Gene-chip array analysis indicated that the expression of CCR6, EGFR, and FOS were up-regulated by 2 mg/mL sericin, and RT-qPCR revealed that the expression of CCR6, EGFR, FOS, AKT1, JNK1, NFkB1, MMP-9, MEK2, ERK1/2 and MYC was up-regulated by 2 mg/mL sericin (P < 0.05).

CONCLUSION

We developed a novel hepatocyte serum-free medium. Sericin probably enhances cell attachment through the CCR6-Akt-JNK-NF-κB pathway and promotes cell proliferation through CCR6-mediated activation of the ERK1/2-MAPK pathway.

Monitoring cytochrome P450 activity in living hepatocytes by chromogenic substrates in response to drug treatment or during cell maturation

The metabolic activity of hepatocytes is a central prerequisite for drug activity and a key element in drug-drug interaction. This central role in metabolism largely depends on the activity of the cytochrome P450 (CYP450) enzyme family, which is not only dependent on liver cell maturation but is also controlled in response to drug and chemical exposure. Here, we report the use of VividDye fluorogenic CYP450 substrates to directly measure and continuously monitor metabolic activity in living hepatocytes. We observed time- and dose-dependent correlation in response to established and putative CYP450 inducers acting through the aryl hydrocarbon receptor and drug combinations. Using repetitive addition of VividDye fluorogenic substrate on a daily basis, we demonstrated the new application of VividDye for monitoring the maturation and dedifferentiation of hepatic cells. Despite a lack of high specificity for individual CYP450 isoenzymes, our approach enables continuous monitoring of metabolic activity in living cells with no need to disrupt cultivation. Our assay can be integrated in in vitro liver-mimetic models for on-line monitoring and thus should enhance the reliability of these tissue model systems.

Heparin/Collagen 3D Scaffold Accelerates Hepatocyte Differentiation of Wharton's Jelly-Derived Mesenchymal Stem Cells

Both mature and stem cell-derived hepatocytes lost their phenotype and functionality under conventional culture conditions. However, the 3D scaffolds containing the main extracellular matrix constitutions, such as heparin, may provide appropriate microenvironment for hepatocytes to be functional. The current study aimed to investigate the efficacy of the differentiation capability of hepatocytes derived from human Wharton's jelly mesenchymal stem cells (WJ-MSCs) in 3D heparinized scaffold. In this case, the human WJ-MSCs were cultured on the heparinized and non-heparinized 2D collagen gels or within 3D scaffolds in the presence of hepatogenic medium. Immunostaining was performed for anti-alpha fetoprotein, cytokeratin-18 and -19 antibodies. RT-PCR was performed for detection of hepatic nuclear factor-4 (HNF-4), albumin, cytokeratin-18 and -19, glucose-6-phosphatase (G6P), c-met and Cyp2B. The results indicated that hepatogenic media induced the cells to express early liver-specific markers including HNF4, albumin, cytokeratin-18 and 19 in all conditions. The cells cultured on both heparinized culture conditions expressed late liver-specific markers such as G6P and Cyp2B as well. Besides, the hepatocytes differentiated in 3D heparinized scaffolds stored more glycogen that indicated they were more functional. Non-heparinized 2D gel was the superior condition for cholangiocyte differentiation as indicated by higher levels of cytokeratin 19 expression. In conclusion, the heparinized 3D scaffolds provided a microenvironment to mimic Disse space. Therefore, 3D heparinized collagen scaffold can be suggested as a good vehicle for hepatocyte differentiation.

Biomaterials and Culture Technologies for Regenerative Therapy of Liver Tissue

Regenerative approach has emerged to substitute the current extracorporeal technologies for the treatment of diseased and damaged liver tissue. This is based on the use of biomaterials that modulate the responses of hepatic cells through the unique matrix properties tuned to recapitulate regenerative functions. Cells in liver preserve their phenotype or differentiate through the interactions with extracellular matrix molecules. Therefore, the intrinsic properties of the engineered biomaterials, such as stiffness and surface topography, need to be tailored to induce appropriate cellular functions. The matrix physical stimuli can be combined with biochemical cues, such as immobilized functional groups or the delivered actions of signaling molecules. Furthermore, the external modulation of cells, through cocultures with nonparenchymal cells (e.g., endothelial cells) that can signal bioactive molecules, is another promising avenue to regenerate liver tissue. This review disseminates the recent approaches of regenerating liver tissue, with a focus on the development of biomaterials and the related culture technologies.

Effects of Differentiation and Antisenescence from BMSCs to Hepatocy-Like Cells of the PAAm-IGF-1/TNF-α Biomaterial

Aiming at the cells' differentiation phenomenon and senescence problem in liver tissue engineering, this work is designed to synthesize three different chargeable polymers (polypropylene acid (PAAc), polyethylene glycol (PEG), and polypropylene amine (PAAm)) coimmobilized by the insulin-like growth factor 1 (IGF-1) and tumor necrosis factor-α (TNF-α). We explore the hepatocyte differentiation effect and the antisenecence effect of PSt-PAAm-IGF-1/TNF-α biomaterial which was selected from the three different chargeable polymers in bone marrow mesenchymal stem cells (BMSCs). Our work will establish a model for studying the biochemical molecular regulation mechanism and signal transduction pathway of cell senescence in liver tissue engineering, which provide a molecular basis for developing biomaterials for liver tissue engineering.

Collagen and Elastin Biomaterials for the Fabrication of Engineered Living Tissues

Collagen and elastin represent the two most predominant proteins in the body and are responsible for modulating important biological and mechanical properties. Thus, the focus of this review is the use of collagen and elastin as biomaterials for the fabrication of living tissues. Considering the importance of both biomaterials, we first propose the notion that many tissues in the human body represent a reinforced composite of collagen and elastin. In the rest of the review, collagen and elastin biosynthesis and biophysics, as well as molecular sources and biomaterial fabrication methodologies, including casting, fiber spinning, and bioprinting, are discussed. Finally, we summarize the current attempts to fabricate a subset of living tissues and, based on biochemical and biomechanical considerations, suggest that future tissue-engineering efforts consider direct incorporation of collagen and elastin biomaterials.

Modulation of Huh7.5 spheroid formation and functionality using modified PEG-based hydrogels of different stiffness

Physical cues, such as cell microenvironment stiffness, are known to be important factors in modulating cellular behaviors such as differentiation, viability, and proliferation. Apart from being able to trigger these effects, mechanical stiffness tuning is a very convenient approach that could be implemented readily into smart scaffold designs. In this study, fibrinogen-modified poly(ethylene glycol)-diacrylate (PEG-DA) based hydrogels with tunable mechanical properties were synthesized and applied to control the spheroid formation and liver-like function of encapsulated Huh7.5 cells in an engineered, three-dimensional liver tissue model. By controlling hydrogel stiffness (0.1–6 kPa) as a cue for mechanotransduction representing different stiffness of a normal liver and a diseased cirrhotic liver, spheroids ranging from 50 to 200 μm were formed over a three week time-span. Hydrogels with better compliance (i.e. lower stiffness) promoted formation of larger spheroids. The highest rates of cell proliferation, albumin secretion, and CYP450 expression were all observed for spheroids in less stiff hydrogels like a normal liver in a healthy state. We also identified that the hydrogel modification by incorporation of PEGylated-fibrinogen within the hydrogel matrix enhanced cell survival and functionality possibly owing to more binding of autocrine fibronectin. Taken together, our findings establish guidelines to control the formation of Huh7.5 cell spheroids in modified PEGDA based hydrogels. These spheroids may serve as models for applications such as screening of pharmacological drug candidates.

Hybrid organoids consisting of extracellular matrix gel particles and hepatocytes for transplantation

Hepatocyte transplantation is a potential therapy for treating various liver diseases. However, oxygen shortage leading to loss of hepatocyte function becomes a limitation following hepatocyte transplantation. To overcome this problem, we developed a hybrid organoid, consisting of growth factor (GF)-immobilizable gel particles combined with hepatocytes. Benefits of the hybrid organoid were evaluated in three groups: (i) hybrid organoid consisting of cells and GF-immobilizable gel particles (HG-C); (ii) hybrid organoid consisting of cells and gel particles (G-C); and (iii) cells suspended in collagen (C-C). We found liver-specific functions of HG-C were maintained longer than in the other conditions during in vitro culture. Furthermore, after transplantation, HG-C was effective in maintaining viability of transplanted hepatocytes and promoting angiogenesis around the hepatocytes. In summary, transplantation of HG-C is a potential method for future liver tissue engineering.

Simple surface coating of electrospun poly-L-lactic acid scaffolds to induce angiogenesis

Tissue-engineered constructs often fail due to poor integration with the patient’s tissues. Specifically, they fail to be neovascularised, leading to the death and loss of the implanted tissues. Thus, there is a need to produce angiogenic materials to improve tissue integration. We describe the development of a layer-by-layer approach to coat electrospun scaffolds to help promote angiogenesis into these biomaterials once implanted. Electrospun poly-L-lactic acid was coated comparing two different techniques – one using alternative layers of polyethyleneImine (PEI) and polyacrylic Acid (PAC) and one with alternative layers of PEI and heparin for a total of seven layers in both cases. Both scaffolds were then coated with heparin as the final layer. The scaffold coated with alternate PEI and PAC showed a clear ability to bind the most heparin. This scaffold was then studied further for its ability to bind vascular endothelial growth factor, which was confirmed using an ELISA. The scaffold coated with seven alternate layers of PEI and PAC and heparin was then implanted in a chick chorionic allantoic membrane (CAM) assay. After a period of 7 days in the CAM, the coated scaffold showed strong angiogenic activity. In contrast, the uncoated scaffolds did not promote angiogenesis. We conclude that this approach to functionalising scaffolds is effective within a clinically relevant time period (7 days in an in-vivo angiogenic model) and suggest this will be useful for improving integration of scaffolds once implanted.

Differentiation-Promoting Medium Additives for Hepatocyte Cultivation and Cryopreservation

Isolated primary hepatocytes are considered as the reference system for in vitro hepatic methods. Following the isolation of primary hepatocytes from liver tissue, an unfavorable process named dedifferentiation is initiated leading to the attenuation of the hepatocellular phenotype both at the morphological and functional level. Freshly isolated hepatocytes can be used immediately or can be cryopreserved for future purposes. Currently, a number of antidedifferentiation strategies exist to extend the life span of isolated hepatocytes. The addition of differentiation-promoting compounds to the hepatocyte culture medium is the oldest and simplest antidedifferentiation approach applied. In the present chapter, the most commonly used medium additives for cultivation and cryopreservation of primary hepatocytes are reviewed.

Liver extracellular matrix providing dual functions of two-dimensional substrate coating and three-dimensional injectable hydrogel platform for liver tissue engineering

Decellularization of tissues or organs can provide an efficient strategy for preparing functional scaffolds for tissue engineering. Microstructures of native extracellular matrices and their biochemical compositions can be retained in the decellularized matrices, providing tissue-specific microenvironments for efficient tissue regeneration. Here, we report the versatility of liver extracellular matrix (LEM) that can be used for two-dimensional (2D) coating and three-dimensional (3D) hydrogel platforms for culture and transplantation of primary hepatocytes. Collagen type I (Col I) has typically been used for hepatocyte culture and transplantation. In this study, LEM was compared with Col I in terms of biophysical and mechanical characteristics and biological performance for enhancing cell viability, differentiation, and hepatic functions. Surface properties of LEM coating and mechanical properties and gelation kinetics of LEM hydrogel could be manipulated by adjusting the LEM concentration. In addition, LEM hydrogel exhibited improved elastic properties, rapid gelation, and volume maintenance compared to Col I hydrogel. LEM coating significantly improved hepatocyte functions such as albumin secretion and urea synthesis. More interestingly, LEM coating upregulated hepatic gene expression of human adipose-derived stem cells, indicating enhanced hepatic differentiation of these stem cells. The viability and hepatic functions of primary hepatocytes were also significantly improved in LEM hydrogel compared to Col I hydrogel both in vitro and in vivo. Albumin and hepatocyte transcription factor expression was upregulated in hepatocytes transplanted in LEM hydrogels. In conclusion, LEM can provide functional biomaterial platforms for diverse applications in liver tissue engineering by promoting survival and maturation of hepatocytes and hepatic commitment of stem cells. This study demonstrates the feasibility of decellularized matrix for both 2D coating and 3D hydrogel in liver tissue engineering.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Bioresponsive hydrogel scaffolding systems for 3D constructions in tissue engineering and regenerative medicine

Among the diversity of scaffolding systems available, hydrogel remains a popular choice for tissue engineering applications. The current state-of-the-art bioresponsive hydrogels demand intricate designs in pursuit of acquiring desired timely responses, such as controlled release of biological factors, changes in mechanical properties and scaffold degradation, at the same rate as the natural extracellular matrix. In this review, a variety of bioresponsive hydrogels are discussed; in particular, bioactive and biodegradable hydrogels that facilitate cellular development and tissue morphogenesis are highlighted. Bioactive hydrogels are designed to deliver biomolecules such as cell-adhesive moieties and instructive ligands at close proximity to the cell for better uptake or exposure. Biodegradable hydrogels provide transient scaffolding support for therapeutic cell settlement while gradually degrading in response to physical or enzymatic stimuli. In addition, biomechanical stimuli from hydrogels can induce mutual constructive responses on cells and, hence, will also be covered in this review.

Rapid formation of size-controlled three dimensional hetero-cell aggregates using micro-rotation flow for spheroid study

Spheroids that are formed from aggregated cells have enhanced biological function compared to individual cells. In particular, hetero-spheroids composed of different types of cells, such as hepatocytes and endothelial cells, express tissue specific functions at a high level, which is advantageous for more precise drug screening and biological research. In this study, we propose rapid formation of size-controlled three-dimensional hetero-cell aggregates consisting of hepatocytes and endothelial cells using micro-rotation flow. Based on previous data, these aggregates are expected to ultimately become hetero-spheroids. The hepatocytes are coated with collagen gel films less than 200 nm thick, which were experimentally verified to increase adhesion strength between hepatocytes and endothelial cells. Gel-coated hepatocytes and endothelial cells are collected in an array by micro-rotational flow, thereby forming hetero-cell aggregates within 2 min. This array allowed the size of the three-dimensional cell aggregates to be hydrodynamically controlled, with standard deviations of less than 19%, by varying the cell density of the medium without altering the device geometry. Endothelial cells were successfully and uniformly dispersed in the aggregates. The proposed microfluidic device, with its capability of rapidly forming size-controlled hetero-cell aggregates, will offer an efficient experimental platform for future hetero-spheroid study that will contribute to drug screening and regenerative medicine.

Rat primary hepatocytes show enhanced performance and sensitivity to acetaminophen during three-dimensional culture on a polystyrene scaffold designed for routine use

The in vitro evaluation of hepatotoxicity is an essential stage in the research and development of new pharmaceuticals as the liver is one of the most commonly impacted organs during preclinical toxicity studies. Fresh primary hepatocytes in monolayer culture are the most commonly used in vitro model of the liver but often exhibit limited viability and/or reduction or loss of important liver-specific functions. These limitations could potentially be overcome using three-dimensional (3D) culture systems, but their experimental nature and limited use in liver toxicity screening and drug metabolism has impaired their uptake into commercial screening programs. In this study we use a commercially available polystyrene scaffold developed for routine 3D cell culture to maintain primary rat hepatocytes for use in metabolism and toxicity studies over 72 h. We show that primary hepatocytes retain their natural cuboidal morphology with significantly higher viability (>74%) than cells grown in monolayer culture (maximum of 57%). Hepatocytes in the 3D scaffolds exhibit differential expression of genes associated with phase I, II, and III drug metabolism under basal conditions compared with monolayer culture and can be induced to stably express significantly higher levels of the cytochrome-P450 enzymes 1A2, 2B1, and 3A2 over 48 h. In toxicity studies the hepatocytes in the 3D scaffolds also show increased sensitivity to the model toxicant acetaminophen. These improvements over monolayer culture and the availability of this new easy to use 3D scaffold system could facilitate the uptake of 3D technologies into routine drug screening programs.