Cryopreservation of rat precision-cut liver and kidney slices by rapid freezing and vitrification

Multiscale transport and 4D time-lapse imaging in precision-cut liver slices (PCLS)

Background

Monitoring cellular processes across different levels of complexity, from the cellular to the tissue scale, is important for understanding tissue structure and function. However, it is challenging to monitor and estimate these structural and dynamic interactions within three-dimensional (3D) tissue models.

Objective

The aim of this study was to design a method for imaging, tracking, and quantifying 3D changes in cell morphology (shape and size) within liver tissue, specifically a precision-cut liver slice (PCLS). A PCLS is a 3D model of the liver that allows the study of the structure and function of liver cells in their native microenvironment.

Methods

Here, we present a method for imaging liver tissue during anisosmotic exposure in a multispectral four-dimensional manner. Three metrics of tissue morphology were measured to quantify the effects of osmotic stress on liver tissue. We estimated the changes in the volume of whole precision cut liver slices, quantified the changes in nuclei position, and calculated the changes in volumetric responses of tissue-embedded cells.

Results

During equilibration with cell-membrane-permeating and non-permeating solutes, the whole tissue experiences shrinkage and expansion. As nuclei showed a change in position and directional displacement under osmotic stress, we demonstrate that nuclei could be used as a probe to measure local osmotic and mechanical stress. Moreover, we demonstrate that cells change their volume within tissue slices as a result of osmotic perturbation and that this change in volume is dependent on the position of the cell within the tissue and the duration of the exposure.

Conclusion

The results of this study have implications for a better understanding of multiscale transport, mechanobiology, and triggered biological responses within complex biological structures.

Technologies for Vitrification Based Cryopreservation

Cryopreservation is a unique and practical method to facilitate extended access to biological materials. Because of this, cryopreservation of cells, tissues, and organs is essential to modern medical science, including cancer cell therapy, tissue engineering, transplantation, reproductive technologies, and bio-banking. Among diverse cryopreservation methods, significant focus has been placed on vitrification due to low cost and reduced protocol time. However, several factors, including the intracellular ice formation that is suppressed in the conventional cryopreservation method, restrict the achievement of this method. To enhance the viability and functionality of biological samples after storage, a large number of cryoprotocols and cryodevices have been developed and studied. Recently, new technologies have been investigated by considering the physical and thermodynamic aspects of cryopreservation in heat and mass transfer. In this review, we first present an overview of the physiochemical aspects of freezing in cryopreservation. Secondly, we present and catalog classical and novel approaches that seek to capitalize on these physicochemical effects. We conclude with the perspective that interdisciplinary studies provide pieces of the cryopreservation puzzle to achieve sustainability in the biospecimen supply chain.

Cryopreservation of Whole Rat Livers by Vitrification and Nanowarming

Liver cryopreservation has the potential to enable indefinite organ banking. This study investigated vitrification-the ice-free cryopreservation of livers in a glass-like state-as a promising alternative to conventional cryopreservation, which uniformly fails due to damage from ice formation or cracking. Our unique "nanowarming" technology, which involves perfusing biospecimens with cryoprotective agents (CPAs) and silica-coated iron oxide nanoparticles (sIONPs) and then, after vitrification, exciting the nanoparticles via radiofrequency waves, enables rewarming of vitrified specimens fast enough to avoid ice formation and uniformly enough to prevent cracking from thermal stresses, thereby addressing the two main failures of conventional cryopreservation. This study demonstrates the ability to load rat livers with both CPA and sIONPs by vascular perfusion, cool them rapidly to an ice-free vitrified state, and rapidly and homogenously rewarm them. While there was some elevation of liver enzymes (Alanine Aminotransferase) and impaired indocyanine green (ICG) excretion, the nanowarmed livers were viable, maintained normal tissue architecture, had preserved vascular endothelium, and demonstrated hepatocyte and organ-level function, including production of bile and hepatocyte uptake of ICG during normothermic reperfusion. These findings suggest that cryopreservation of whole livers via vitrification and nanowarming has the potential to achieve organ banking for transplant and other biomedical applications.

Rapid joule heating improves vitrification based cryopreservation

Cryopreservation by vitrification has far-reaching implications. However, rewarming techniques that are rapid and scalable (both in throughput and biosystem size) for low concentrations of cryoprotective agent (CPA) for reduced toxicity are lacking, limiting the potential for translation. Here, we introduce a joule heating-based platform technology, whereby biosystems are rapidly rewarmed by contact with an electrical conductor that is fed a voltage pulse. We demonstrate successful cryopreservation of three model biosystems with thicknesses across three orders of magnitude, including adherent cells (~4 µm), Drosophila melanogaster embryos (~50 µm) and rat kidney slices (~1.2 mm) using low CPA concentrations (2-4 M). Using tunable voltage pulse widths from 10 µs to 100 ms, numerical simulation predicts that warming rates from 5 × 104 to 6 × 108 °C/min can be achieved. Altogether, our results present a general solution to the cryopreservation of a broad spectrum of cellular, organismal and tissue-based biosystems.

Effect of cryoprotectants on rat kidney decellularization by freeze-thaw process

To overcome the shortage of organ donors and morbidity and mortality caused by lifetime immunosuppression, development of a transplantable graft to permanently replace the organ function is required. This study is focused on the effects of a freeze-thaw process and cryoprotectants on the ultrastructure and composition of decellularization scaffolds. Results showed that cryoprotectants and freezing temperatures had significant effects on the decellularization scaffold. The vascular network integrity at -20 °C was better than that at -80 °C. For low-concentration cryoprotectants, 10% dimethyl sulfoxide and 5% trehalose could achieve a better balance between preserving the vascular tree and decellularization. For high-concentration cryoprotectants (vitrification solutions VS55 and VS83), the vascular network integrity was best because of the absence of freezing damage and ice-induced disruption of cells, but the decellularization effect was poor because the cells remained in the scaffold. Collagen, elastic fiber, protein, and mechanical properties of the scaffold could be retained after decellularization using the freeze-thaw method. Further studies and further optimization of the freeze-thaw decellularization protocol are necessary for clinical applications.

Organotypic platform for studying cancer cell metastasis

Metastasis is the leading cause of mortality in cancer patients. To migrate to distant sites, cancer cells would need to adapt their behaviour in response to different tissue environments. Thus, it is essential to study this process in models that can closely replicate the tumour microenvironment. Here, we evaluate the use of organotypic liver and brain slices to study cancer metastasis. Morphological and viability parameters of the slices were monitored daily over 3 days in culture to assess their stability as a realistic 3D tissue platform for in vitro metastatic assays. Using these slices, we evaluated the invasion of MDA-MB-231 breast cancer cells and of a subpopulation that was selected for increased motility. We show that the more aggressive invasion of the selected cells likely resulted not only from their lower stiffness, but also from their lower adhesion to the surrounding tissue. Different invasion patterns in the brain and liver slices were observed for both subpopulations. Cells migrated faster in the brain slices (with an amoeboid-like mode) compared to in the liver slices (where they migrated with mesenchymal or collective migration-like modes). Inhibition of the Ras/MAPK/ERK pathway increased cell stiffness and adhesion forces, which resulted in reduced invasiveness. These results illustrate the potential for organotypic tissue slices to more closely mimic in vivo conditions during cancer cell metastasis than most in vitro models.

Winter is coming: the future of cryopreservation

The preservative effects of low temperature on biological materials have been long recognised, and cryopreservation is now widely used in biomedicine, including in organ transplantation, regenerative medicine and drug discovery. The lack of organs for transplantation constitutes a major medical challenge, stemming largely from the inability to preserve donated organs until a suitable recipient is found. Here, we review the latest cryopreservation methods and applications. We describe the main challenges-scaling up to large volumes and complex tissues, preventing ice formation and mitigating cryoprotectant toxicity-discuss advantages and disadvantages of current methods and outline prospects for the future of the field.

Principles of Ice-Free Cryopreservation by Vitrification

Vitrification is an alternative to cryopreservation by freezing that enables hydrated living cells to be cooled to cryogenic temperatures in the absence of ice. Vitrification simplifies and frequently improves cryopreservation because it eliminates mechanical injury from ice, eliminates the need to find optimal cooling and warming rates, eliminates the importance of differing optimal cooling and warming rates for cells in mixed cell type populations, eliminates the need to find a frequently imperfect compromise between solution effects injury and intracellular ice formation, and can enable chilling injury to be "outrun" by using rapid cooling without a risk of intracellular ice formation. On the other hand, vitrification requires much higher concentrations of cryoprotectants than cryopreservation by freezing, which introduces greater risks of both osmotic damage and cryoprotectant toxicity. Fortunately, a large number of remedies for the latter problem have been discovered over the past 35 years, and osmotic damage can in most cases be eliminated or adequately controlled by paying careful attention to cryoprotectant introduction and washout techniques. Vitrification therefore has the potential to enable the superior and convenient cryopreservation of a wide range of biological systems (including molecules, cells, tissues, organs, and even some whole organisms), and it is also increasingly recognized as a successful strategy for surviving harsh environmental conditions in nature. But the potential of vitrification is sometimes limited by an insufficient understanding of the complex physical and biological principles involved, and therefore a better understanding may not only help to improve present outcomes but may also point the way to new strategies that may be yet more successful in the future. This chapter accordingly describes the basic principles of vitrification and indicates the broad potential biological relevance of this alternative method of cryopreservation.

Diffusion Limited Cryopreservation of Tissue with Radiofrequency Heated Metal Forms

Cryopreserved tissues are increasingly needed in biomedical applications. However, successful cryopreservation is generally only reported for thin tissues (≤1 mm). This work presents several innovations to reduce cryoprotectant (CPA) toxicity and improve tissue cryopreservation, including 1) improved tissue warming rates through radiofrequency metal form and field optimization and 2) an experimentally verified predictive model to optimize CPA loading and rewarming to reduce toxicity. CPA loading is studied by microcomputed tomography (µCT) imaging, rewarming by thermal measurements, and modeling, and viability is measured after loading and/or cryopreservation by alamarBlue and histology. Loading conditions for three common CPA cocktails (6, 8.4, and 9.3 m) are designed, and then fast cooling and metal forms rewarming (up to 2000 °C min-1 ) achieve ≥90% viability in cryopreserved 1-2 mm arteries with various CPAs. Despite high viability by alamarBlue, histology shows subtle changes after cryopreservation suggesting some degree of cell damage especially in the central portions of thicker arteries up to 2 mm. While further studies are needed, these results show careful CPA loading and higher metal forms warming rates can help reduce CPA loading toxicity and improve outcomes from cryopreservation in tissues while also offering new protocols to preserve larger tissues ≥1 mm in thickness.

Control of ice recrystallization in liver tissues using small molecule carbohydrate derivatives

Minimizing ice recrystallization injury in tissues and organs has historically been sought using biological antifreeze proteins. However, the size of these compounds can limit permeation and their potential immunogenicity disqualifies them from use in several cryopreservation applications. Novel small molecule carbohydrate-derived ice recrystallization inhibitors (IRIs) are not subject to these constraints, and thus we sought to evaluate the ability of a highly active IRI to permeate liver tissue and control recrystallization. Rat liver tissue blocks (0.5 mm²) were incubated with the IRI for 6 h at 22 °C and subsequently plunged in liquid nitrogen. Ice crystals within the tissue were fixed using a formal acetic alcohol fixative as it was rewarmed from -80 °C to 22 °C over the course of 48 h. The untreated control demonstrated a gradient of increasing crystal size from the exterior to the interior region of the tissue; however, the IRI-treated condition had no such gradient and exhibited small crystals throughout. Threshold segmentation confirmed a significant reduction in the ice crystal size within the interior region of the IRI-treated condition, suggesting the IRI permeated throughout and effectively controlled recrystallization within the tissue.

Review of non-permeating cryoprotectants as supplements for vitrification of mammalian tissues

Vitrification of mammalian tissues is important in the areas of human assisted reproduction, animal reproduction, and regenerative medicine. Non-permeating cryoprotectants (CPAs), particularly sucrose, are increasingly used in conjunction with permeating CPAs for vitrification of mammalian tissues. Combining non-permeating and permeating CPAs was found to further improve post-thaw viability and functionalities of vitrified mammalian tissues, showing the potential applications of such tissues in various clinical and veterinary settings. With the rising demand for the use of non-permeating CPAs in vitrification of mammalian tissues, there is a strong need for a timely and comprehensive review on the supplemental effects of non-permeating CPAs toward vitrification outcomes of mammalian tissues. In this review, we first discuss the roles of non-permeating CPAs including sugars and high molecular weight polymers in vitrification. We then summarize the supplemental effects of non-permeating CPAs on viability and functionalities of mammalian embryos, and ovarian, testicular, articular cartilage, tracheal, and kidney tissues following vitrification. Lastly, challenges associated with the use of non-permeating CPAs in vitrification of mammalian tissues are briefly discussed.

Impacts of different synthetic polymers on vitrification of ovarian tissue

Type and concentration of cryoprotective agents (CPAs) are important factors which influence the likelihood of a successful ovarian tissue vitrification outcome. In an attempt to address this factor, the present study was conducted to evaluate the impacts of different synthetic polymers (Supercool X-1000, Supercool Z-1000 and PVP K-12) on vitrification of bovine ovarian tissue. From each ovarian pair, fragments were recovered and immediately fixed for analysis (fresh control) or submitted to vitrification, either or not followed by in vitro culture for one or five days. Vitrification was performed using the ovarian tissue cryosystem (OTC) system. The ovarian tissues were intended for histological and viability analysis [Reactive oxygen species (ROS) production and degenerate cells assay (Ethidium homodimer-1)], as well as immunolocalization of AQP3 and AQP9 were measured. The results showed that during almost all the periods after warming, in treatment groups which contain polymer (X-1000, Z-1000 and PVP), the percentage of morphologically normal follicles was the highest in the X-1000 samples. Furthermore, post-thawed X-1000 group revealed stronger labeling for AQP9 in primordial and transitional follicles, when compared with others. However, morphology after cryopreservation did not correlate with follicle viability and function where the levels of degeneration and tissue damage of PVP K-12 group were lower in comparison with X-1000 group and only in PVP K-12 group, ROS level was similar to that of the fresh control group. We believe that in addition to permeating CPAs, the addition of one (Supercool X-1000) or maybe a combination (Supercool X-1000 and PVP K-12) of non-permeating polymers could be useful to improve the outcome for vitrified bovine ovarian tissue.

Protective effects of phenolic acids on mercury-induced DNA damage in precision-cut kidney slices

Objective(s):

Precision-cut tissue slices are considered an organotypic 3D model widely used in biomedical research. The comet assay is an important screening test for early genotoxicity risk assessment that is mainly applied on in vitro models. The aim of the present study was to provide a 3D organ system for determination of genotoxicity using a modified method of the comet assay since the stromal components from the original tissue make this technique complicated.

Materials and Methods:

A modified comet assay technique was validated using precision-cut hamster kidney slices to analyze the antigenotoxic effect of the phenolic compounds caffeic acid, chlorogenic acid, and rosmarinic acid in tissue slices incubated with 15 µM HgCl₂. Cytotoxicity of the phenolic compounds was studied in Vero cells, and by morphologic analysis in tissue slices co-incubated with HgCl₂ and phenolic compounds.

Results:

A modification of the comet assay allows obtaining better and clear comet profiles for analysis. Non-cytotoxic concentrations of phenolic acids protected kidney tissue slices against mercury-induced DNA damage, and at the same time, were not nephrotoxic. The highest protection was provided by 3 µg/ml caffeic acid, although 6 µg/ml rosmarinic and 9 µg/ml chlorogenic acids also exhibited protective effects.

Conclusion:

This is the first time that a modification of the comet assay technique is reported as a tool to visualize the comets from kidney tissue slices in a clear and simple way. The phenolic compounds tested in this study provided protection against mercury-induced genotoxic damage in precision-cut kidney slices.

Effects of new synthetic cryoprotectant agents on histological characteristics of various classes of vitrified bovine pre-antral follicles

Previous studies have reported many discrepancies about the best type and concentration of cryoprotective agents (CPAs) and biological variability among various pre-antral follicle classes after cryopreservation of ovarian tissue. The aim of this study was to investigate the impacts of some synthetic polymers on histological characteristics of different types of pre-antral follicles after bovine ovarian tissue vitrification. From each bovine ovarian pair, fragments were recovered and immediately fixed for analysis (fresh control group) or submitted to vitrification (sucrose, X-1000, Z-1000 and polyvinylpyrrolidone groups), either followed by in vitro culture for 1 or 5 days. In this case, although, the addition of X-1000 resulted in greater percentages of normal follicles for almost all pre-antral follicle classes compared to those of other groups, there are some exceptions. These results indicate that the inclusion of polyvinylpyrrolidone in the freezing media can improve the morphology of the post-warmed transitional follicles and cultured primordial follicles on day five more than other CPAs. According to the results of this study, it can be concluded that although ovarian tissue cryopreservation is often performed to preserve the primordial follicles, by choosing the best combination of permeating and non-permeating CPAs (synthetic polymers), more advanced stages of bovine pre-antral follicles, transitional, primary and secondary follicles, may also survive the cryopreservation process.

Studying non-alcoholic fatty liver disease: the ins and outs of in vivo, ex vivo and in vitro human models

The prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing. Determining the pathogenesis and pathophysiology of human NAFLD will allow for evidence-based prevention strategies, and more targeted mechanistic investigations. Various in vivo, ex situ and in vitro models may be utilised to study NAFLD; but all come with their own specific caveats. Here, we review the human-based models and discuss their advantages and limitations in regards to studying the development and progression of NAFLD. Overall, in vivo whole-body human studies are advantageous in that they allow for investigation within the physiological setting, however, limited accessibility to the liver makes direct investigations challenging. Non-invasive imaging techniques are able to somewhat overcome this challenge, whilst the use of stable-isotope tracers enables mechanistic insight to be obtained. Recent technological advances (i.e. normothermic machine perfusion) have opened new opportunities to investigate whole-organ metabolism, thus ex situ livers can be investigated directly. Therefore, investigations that cannot be performed in vivo in humans have the potential to be undertaken. In vitro models offer the ability to perform investigations at a cellular level, aiding in elucidating the molecular mechanisms of NAFLD. However, a number of current models do not closely resemble the human condition and work is ongoing to optimise culturing parameters in order to recapitulate this. In summary, no single model currently provides insight into the development, pathophysiology and progression across the NAFLD spectrum, each experimental model has limitations, which need to be taken into consideration to ensure appropriate conclusions and extrapolation of findings are made.

Subzero organ preservation: the dawn of a new ice age?

PURPOSE OF REVIEW

Herein, we review the field of subzero organ preservation with a focus on recent developments in hepatic supercooling.

RECENT FINDINGS

Organ preservation is making a rapid shift from the decade old standard of storage on ice toward techniques that improve organ availability as well as preservation time. Long-term organ preservation would have tremendous benefits to the organ transplantation field, including better organ allocation, donor-recipient matching, as well as reduced preservation injury, and subsequent improvement of donor organ use. The formation of ice has proven an important limiting factor and novel techniques attempt to control or prevent freezing using cryoprotective agents, and highly controlled cooling regimens. Various techniques have been employed over the previous decades, including true organ freezing, vitrification, and subzero nonfreezing or supercooling. For most techniques, successful transplantation following long-term subzero preservation has remained elusive. Supercooling, however, recently delivered the first promising results, yielding survival after up to 4 days of supercooled preservation at -6°C.

SUMMARY

As the field of organ preservation undergoes significant development, the field of subzero preservation also receives renewed interest. Although many obstacles remain to be overcome to make subzero preservation feasible, novel techniques are beginning to show their potential in achieving long-term preservation.

Freezing/Thawing without Cryoprotectant Damages Native but not Decellularized Porcine Renal Tissue

Whole organ decellularization of porcine renal tissue and recellularization with a patient's own cells would potentially overcome immunorejection, which is one of the most significant problems with allogeneic kidney transplantation. However, there are obstacles to achieving this goal, including preservation of the decellularized extracellular matrix (ECM), identifying the proper cell types, and repopulating the ECM before transplantation. Freezing biological tissue is the best option to avoid spoilage; however, it may damage the structure of the tissue or disrupt cellular membranes through ice crystal formation. Cryoprotectants have been used to repress ice formation during freezing, although cell toxicity can still occur. The effect of freezing/thawing on native (n = 10) and decellularized (n = 10) whole porcine kidneys was studied without using cryoprotectants. Results showed that the elastic modulus of native kidneys was reduced by a factor of 22 (P < 0.0001) by freezing/thawing or decellularization, while the elastic modulus for decellularized ECM was essentially unchanged by the freezing/thawing process (p = 0.0636). Arterial pressure, representative of structural integrity, was also reduced by a factor of 52 (P < 0.0001) after freezing/thawing for native kidneys, compared to a factor of 43 (P < 0.0001) for decellularization and a factor of 4 (P < 0.0001) for freezing/thawing decellularized structures. Both freezing/thawing and decellularization reduced stiffness, but the reductions were not additive. Investigation of the microstructure of frozen/thawed native and decellularized renal tissues showed increased porosity due to cell removal and ice crystal formation. Orcein and Sirius staining showed partial damage to elastic and collagen fibers after freezing/thawing. It was concluded that cellular damage and removal was more responsible for reducing stiffness than fibril destruction. Cell viability and growth were demonstrated on decellularized frozen/thawed and non-frozen samples using human renal cortical tubular epithelial (RCTE) cells over 12 d. No adverse effect on the ability to recellularize after freezing/thawing was observed. It is recommended that porcine kidneys be frozen prior to decellularization to prevent contamination, and after decellularization to prevent protein denaturation. Cryoprotectants may still be necessary, however, during storage and transportation after recellularization.

A three-dimensional collagen-sponge-based culture system coated with simplified recombinant fibronectin improves the function of a hepatocyte cell line

Hepatocytes are widely used in pharmaceutical drug discovery tests, but their hepatic functions decrease rapidly during in vitro culture. Many culture systems have been devised to address this problem. We here report that a three-dimensional (3D) collagen-based scaffold coated with simplified recombinant fibronectin (FN) enhanced the function of a hepatocyte cell line. The developed culture system uses a honeycomb collagen sponge coated with collagen-binding domain (CBD)-cell attachment site (CAS), a chimeric protein comprising the CBD and CAS of FN. The function of HepG2 cells grown on honeycomb collagen sponge coated with CBD-CAS was investigated by determining the messenger RNA (mRNA) expression levels of several genes. The mRNA expression level of albumin increased 3.25 times in cells grown on CBD-CAS-coated honeycomb collagen sponge for 3 days; the expression level of CCAAT/enhancer binding protein (C/EBPα) increased 40-fold after 1 d and up to 150-fold after 3 d. These results suggested that CBD-CAS-coated honeycomb collagen sponge could improve the functions of hepatocytes by inducing C/EBPα expression. The activation of cytochrome P450 (CYP) enzymes in HepG2 cells grown on CBD-CAS-coated honeycomb collagen sponge was measured at the mRNA level and was found to increase between two and six times compared to cells grown without the CBD-CAS coating, showing that this culture system induced CYP gene expression and thus may be useful in drug metabolism assays.

Vitrification of kidney precursors as a new source for organ transplantation

Kidney transplantation from deceased or living human donors has been limited by donor availability as opposed to the increasing demand, and by the risk of allograft loss rejection and immunosuppressive therapy toxicity. In recent years, xenotransplantation of developed kidney precursor cells has offered a novel solution for the unlimited supply of human donor organs. Specifically, transplantation of kidney precursors in adult hosts showed that intact embryonic kidneys underwent maturation, exhibiting functional properties, and averted humoural rejection post-transplantation from non-immunosuppressed hosts. Even if supply and demand could be balanced using xenotransplants or lab-grown organs from regenerative medicine, the future of these treatments would still be compromised by the ability to physically distribute the organs to patients in need and to produce these products in a way that allows adequate inventory control and quality assurance. Kidney precursors originating from fifteen-day old rabbit embryos were vitrified using Cryotop® as a device and VM3 as vitrification solution. After 3 months of storage in liquid nitrogen, 18 kidney precursors were transplanted into non-immunosuppressed adult hosts by laparoscopy surgery. Twenty-one days after allotransplantation, 9 new kidneys were recovered. All the new kidneys recovered exhibited significant growth and mature glomeruli. Having achieved these encouraging results, we report, for the first time, that it is possible to create a long-term biobank of kidney precursors as an unlimited source of organs for transplantation, facilitating the inventory control and distribution of organs.

Airway contractility in the precision-cut lung slice after cryopreservation

An emerging tool in airway biology is the precision-cut lung slice (PCLS). Adoption of the PCLS as a model for assessing airway reactivity has been hampered by the limited time window within which tissues remain viable. Here we demonstrate that the PCLS can be frozen, stored long-term, and then thawed for later experimental use. Compared with the never-frozen murine PCLS, the frozen-thawed PCLS shows metabolic activity that is decreased to an extent comparable to that observed in other cryopreserved tissues but shows no differences in cell viability or in airway caliber responses to the contractile agonist methacholine or the relaxing agonist chloroquine. These results indicate that freezing and long-term storage is a feasible solution to the problem of limited viability of the PCLS in culture.

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.

Induction of albumin expression in HepG2 cells using immobilized simplified recombinant fibronectin protein

Optimization of the extracellular environment is very important for hepatocyte function in vitro. We expressed new chimeric proteins of the collagen-binding domain (CBD) with cell attachment site (CAS) of fibronectin to enhance hepatocyte function, and the CBD-CAS proteins were immobilized on collagen-coated plates. We hypothesized that the high density of CAS would increase activity of the integrin-dependent intracellular signaling pathway, thus inducing hepatocyte function. Expression of albumin in the human hepatocyte cell line HepG2 was assessed on CBD-CAS-immobilized dishes. The results indicated that the CBD-CAS-immobilized plates induced albumin expression. Immobilized CBD-CAS induced activation of focal adhesion kinase and integrin-ligand clustering on the cell membrane. These results suggest that immobilized CBD-CAS improves the function of HepG2 cells. This system could therefore be applied to drug metabolism assay in the development of new drugs.

Complement mediated renal inflammation induced by donor brain death: role of renal C5a-C5aR interaction

Kidneys retrieved from brain-dead donors have impaired allograft function after transplantation compared to kidneys from living donors. Donor brain death (BD) triggers inflammatory responses, including both systemic and local complement activation. The mechanism by which systemic activated complement contributes to allograft injury remains to be elucidated. The aim of this study was to investigate systemic C5a release after BD in human donors and direct effects of C5a on human renal tissue. C5a levels were measured in plasma from living and brain-dead donors. Renal C5aR gene and protein expression in living and brain-dead donors was investigated in renal pretransplantation biopsies. The direct effect of C5a on human renal tissue was investigated by stimulating human kidney slices with C5a using a newly developed precision-cut method. Elevated C5a levels were found in plasma from brain-dead donors in concert with induced C5aR expression in donor kidney biopsies. Exposure of precision-cut human kidney slices to C5a induced gene expression of pro-inflammatory cytokines IL-1 beta, IL-6 and IL-8. In conclusion, these findings suggest that systemic generation of C5a mediates renal inflammation in brain-dead donor grafts via tubular C5a-C5aR interaction. This study also introduces a novel in vitro technique to analyze renal cells in their biological environment.

Morphological and functional preservation of pre-antral follicles after vitrification of macaque ovarian tissue in a closed system

STUDY QUESTION

What are the appropriate conditions to vitrify the macaque ovarian cortex in a large-volume, closed system that will preserve functional pre-antral follicles?

SUMMARY ANSWER

The combination of glycerol, ethylene glycol (EG) and polymers with cooling in liquid nitrogen (LN2) vapor and a two-step warming procedure was able to preserve tissue and follicle morphology as well as function of a small population of secondary follicles in the macaque ovarian cortex following vitrification in a closed system.

WHAT IS KNOWN ALREADY

For prepubertal cancer patients or those who require immediate cancer therapy, ovarian tissue cryopreservation offers the only hope for future fertility. However, the efficacy of live birth from the transplantation of cryopreserved ovarian tissue is still unclear. In addition, live birth from cryopreserved ovarian tissue has only been demonstrated after tissue autotransplantation, which poses the risk of transmitting metastatic cancer cells back to the cancer survivor in certain cancers.

STUDY DESIGN, SIZE, DURATION

Non-human primate model, n = 4, randomized, control versus treatment. End-points were collected from tissue histology, tissue culture (48 h) and isolated secondary follicle culture (6 weeks).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Two vitrification solutions (VSs) containing EG + glycerol (VEG) and EG + dimethylsulfoxide (VED) were examined for vitrification, devitrification and thermodynamic properties. Once the optimal VS was determined, macaque ovarian cortical pieces (3 × 3 × 0.5 mm(3)) were divided into fresh and two vitrified groups (VEG and VED). For the vitrification groups, tissues were exposed to 1/4, 1/2 and 1× VS for 5 min/step as well as 1× VS + polymers for 1 min at 37°C, loaded into high-security straws with 1 ml of VS + polymers, heat sealed and cooled in LN2 vapor. Samples were warmed in a 40°C water bath and cryoprotective agents were diluted with 1, 0.5, 0.25 and 0 M sucrose. Tissues were fixed for histological analysis and cultured with bromodeoxyuridine (BrdU). Secondary follicles from VEG tissues were encapsulated and cultured (n = 24/treatment/animal). Follicle health, diameter and steroid [progesterone, androstenedione (A4), estradiol (E2)] production were analyzed weekly.

MAIN RESULTS AND THE ROLE OF CHANCE

Dense stroma and intact pre-antral follicles were observed using VS containing 27% glycerol, 27% EG and 0.8% polymers with cooling in LN2 vapor and a two-step warming. Higher cooling and warming rates led to fracturing. BrdU uptake was evident in granulosa cells of growing follicles in fresh and vitrified tissues. Secondary follicles from fresh tissues (70 ± 12%) and tissues vitrified with VEG (52 ± 2%) showed similar survival rates (all data: mean ± SEM; P > 0.05). For both groups, the initial follicle diameter was similar and increased (P < 0.05) by Week 3, but diameters in vitrified follicles were smaller (P < 0.05) by Week 6 (566 ± 27 µm) than those of the fresh follicles (757 ± 26 µm). Antrum formation rates were lower (P < 0.05) for vitrified (37 ± 6%) relative to fresh (64 ± 8%) follicles. There was no significant change in levels in culture media of E2, P4 and A4 between fresh and VEG groups at any time point during culture.

LIMITATIONS, REASONS FOR CAUTION

Only in vitro studies are reported. Future in vivo tissue transplantation studies will be needed to confirm long-term function and fertility potential of vitrified ovarian tissues.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first demonstration of antral follicle development during 3D culture following ovarian tissue vitrification in a closed system using primate ovarian tissue. While diminished antrum formation and slower growth in vitro reflect residual cryodamage, continued development of ovarian tissue vitrification based on cryobiology principles using a non-human primate model will identify safe, practical and efficient protocols for eventual clinical use. Tissue function following heterotopic transplantation is currently being examined.

STUDY FUNDING/COMPETING INTEREST(S)

National Institutes of Health (NIH) Oncofertility Consortium UL1 RR024926 (1RL1-HD058293, HD058295, PL1 EB008542), the Eunice Kennedy Shriver NICHD/NIH (U54 HD018185) and ONPRC 8P51OD011092-53. G.M.F. works for the company that makes the polymers used in the current study.

Porcine oocyte vitrification in optimized low toxicity solution with open pulled straws

One of the greatest challenges for reproductive cryobiologists today is to develop an efficient cryopreservation method for human and domestic animal oocytes. The objective of the present study was to optimize a low toxicity solution called VM3 to vitrify porcine oocytes using an open pulled straw (OPS) device and to evaluate the effects on viability, chromosomal organization and cortical granules distribution. Two experiments were conducted in this study. Firstly, we determined the minimum concentration of cryoprotectant present in the VM3 solution required (7.6 M) for vitrification using an OPS device. The appearance of opacity was observed when using a cooling solution at –196°C; no observable opacity was noted as vitrification. In addition, the ultrastructure of oocytes in VM3 or VM3 optimized solution was examined using cryo-scanning electron microscopy. The minimum total cryoprotectant concentration present in VM3 solution necessary for apparent vitrification was 5.6 M when combined with use of an OPS device. Use of both vitrification solutions showed a characteristic plasticized surface. In the second experiment, the relative cytotoxicity of vitrification solutions (VM3 and VM3 optimized) was studied. Oocyte viability, chromosomal organization and the cortical granules distribution were assessed by fluorescent stain. After warming, oocyte survival rate was similar to that of fresh oocytes. The vitrification process significantly reduced correct chromosomal organization and cortical granules distribution rates compared with the fresh oocytes group. However, correct chromosomal organization and cortical granules distribution rates did not differ among oocytes placed in different vitrification solutions. In conclusion, our data demonstrated that the VM3 solution can be optimized and that reduction in concentration to 5.6 M enabled vitrification of oocytes with an OPS device, however use of the VM3 optimised solution had no beneficial effect on vitrification of porcine oocytes.

Analysis of gene expression changes to elucidate the mechanism of chilling injury in precision-cut liver slices

The exact mechanism of chilling injury (by a decrease of temperature to sub-physiological values), especially in the intact organ, is yet unknown. Precision-cut liver slices (PCLS), which closely resemble the organ from which they are derived, are an ideal in vitro model to study the mechanism of chilling injury in the intact organ. In the present study we were able to separate chilling injury from other damaging events such as cryoprotectant toxicity and ice-crystal injury and performed micro-array analysis of regulated genes. Pathway analysis revealed that different stress responses, lipid/fatty acid and cholesterol biosynthesis and metabolism were affected by chilling. This indicates that the cell-membrane might be the primary site and sensor for chilling, which may initiate and amplify downstream intracellular signaling events. Most importantly, we were able to identify gene expression responses from stellate cells and Kupffer cells suggesting the involvement of all liver cell types in the injury. In conclusion, a broad spectrum of previously unknown gene expression changes induced by chilling was identified in the tissue. This is the first report of a systematic investigation on the mechanism of chilling injury in integrated tissue by micro-array analysis under conditions in which other sources of injury are minimal.

Effects of cryoprotectant addition and washout methods on the viability of precision-cut liver slices

Successful vitrification of organ slices is hampered by both osmotic stress and chemical toxicity of cryoprotective agents (CPAs). In the present study, we focused on the effect of osmotic stress on the viability of precision-cut liver slices (PCLS) by comparing different CPA solutions and different methods of loading and unloading the slices with the CPAs. For this purpose, we developed a gradient method to load and unload CPAs with the intention of minimizing sudden changes in osmolarity and thereby avoiding osmotic stress in the slices in comparison with the commonly used step-wise loading/unloading approach. With this gradient method, the CPA solution was introduced at a constant rate into a specially designed mixing chamber containing the slices. We showed that immediate mixing of the infused CPA and the chamber constituents occurred, which enabled us to control the CPA concentration to which PCLS were exposed as a function of time. With this method, CPA concentration versus time profiles were varied using various commercially available CPA mixtures [VMP, VM3, M22, and modified M22 (mM22)]. The viability of PCLS was determined after CPA loading and unloading and subsequent incubation during 3h at 37°C. Despite the reduction of osmotic stress, the viability of slices did not improve with gradual loading and unloading and remained considerably lower than that of untreated slices. The toxicity of the three CPA solutions did not correlate with either their potential osmotic effects or their total concentrations, and did not change strongly with exposure time in 100% CPA. The most likely explanation for these observations is that PCLS are not very sensitive to osmotic changes of the magnitude imposed in our study, and chemical toxicity of the CPA solutions is the main barrier to be overcome. The chemical toxicity of the CPAs used in this study probably originates from a source other than the total concentration of the solutions. The presented gradient method using the specially designed chamber is more time and cost effective than the step-wise method and can be universally applied to efficiently evaluate different CPA solutions.

Synthetic polymers improve vitrification outcomes of macaque ovarian tissue as assessed by histological integrity and the in vitro development of secondary follicles

Ovarian tissue cryopreservation is the only proven option for fertility preservation in female cancer patients who are prepubertal or require immediate treatment. However it remains unclear which cryopreservation protocol is best in cases where the tissue may contain cancerous cells, as these should be matured in vitro rather than autografted. This study evaluated different cryoprotectant exposure times and whether the addition of synthetic polymers (Supercool X-1000, Z-1000 and polyvinylpyrrolidone [PVP K-12]) to the vitrification solution is beneficial to tissue morphology, cellular proliferation and subsequent in vitro function of secondary follicles. Pieces of macaque (n=4) ovarian cortex were exposed to vitrification solution containing glycerol (25%, v/v) and ethylene glycol (25%, v/v) for 3 or 8 min, without (V3, V8) or with (VP3, VP8) polymers (0.2% [v/v] X-1000, 0.4% Z-1000 and 0.2% PVP). Fresh and vitrified tissues were fixed for histology and phosphohistone H3 (PPH3) analysis, or used for secondary follicle isolation followed by encapsulated 3D culture. Five-week follicle survival and growth, as well as steroid hormones (estradiol [E(2)], progesterone, androstenedione) were measured weekly. Morphology of the stroma and preantral follicles as well as PPH3 expression, was preserved in all vitrified tissues. Vitrification with polymers and shorter incubation time (VP3) increased in vitro follicle survival and E(2) production compared to other vitrified groups. Thus, a short exposure of macaque ovarian tissue to a vitrification solution containing synthetic polymers preserves morphology and improves in vitro function of secondary follicles.

Preparation and incubation of precision-cut liver and intestinal slices for application in drug metabolism and toxicity studies

Precision-cut tissue slices (PCTS) are viable ex vivo explants of tissue with a reproducible, well defined thickness. They represent a mini-model of the organ under study and contain all cells of the tissue in their natural environment, leaving intercellular and cell-matrix interactions intact, and are therefore highly appropriate for studying multicellular processes. PCTS are mainly used to study the metabolism and toxicity of xenobiotics, but they are suitable for many other purposes. Here we describe the protocols to prepare and incubate rat and human liver and intestinal slices. Slices are prepared from fresh liver by making a cylindrical core using a drill with a hollow bit, from which slices are cut with a specially designed tissue slicer. Intestinal tissue is embedded in cylinders of agarose before slicing. Slices remain viable for 24 h (intestine) and up to 96 h (liver) when incubated in 6- or 12-well plates under 95% O(2)/5% CO(2) atmosphere.

Building a tiered approach to in vitro predictive toxicity screening: a focus on assays with in vivo relevance

One of the greatest challenges facing the pharmaceutical industry today is the failure of promising new drug candidates due to unanticipated adverse effects discovered during preclinical animal safety studies and clinical trials. Late stage attrition increases the time required to bring a new drug to market, inflates development costs, and represents a major source of inefficiency in the drug discovery/development process. It is generally recognized that early evaluation of new drug candidates is necessary to improve the process. Building in vitro data sets that can accurately predict adverse effects in vivo would allow compounds with high risk profiles to be deprioritized, while those that possess the requisite drug attributes and a lower risk profile are brought forward. In vitro cytotoxicity assays have been used for decades as a tool to understand hypotheses driven questions regarding mechanisms of toxicity. However, when used in a prospective manner, they have not been highly predictive of in vivo toxicity. Therefore, the issue may not be how to collect in vitro toxicity data, but rather how to translate in vitro toxicity data into meaningful in vivo effects. This review will focus on the development of an in vitro toxicity screening strategy that is based on a tiered approach to data collection combined with data interpretation.

Hepatocyte cryopreservation: Is it time to change the strategy?

Liver cell transplantation presents clinical benefit in patients with inborn errors of metabolism as an alternative, or at least as a bridge, to orthotopic liver transplantation. The success of such a therapeutic approach remains limited by the quality of the transplanted cells. Cryopreservation remains the best option for long-term storage of hepatocytes, providing a permanent and sufficient cell supply. However, isolated adult hepatocytes are poorly resistant to such a process, with a significant alteration both at the morphological and functional levels. Hence, the aim of the current review is to discuss the state of the art regarding widely-used hepatocyte cryopreservation protocols, as well as the assays performed to analyse the post-thawing cell quality both in vitro and in vivo. The majority of studies agree upon the poor quality and efficiency of cryopreserved/thawed hepatocytes as compared to freshly isolated hepatocytes. Intracellular ice formation or exposure to hyperosmotic solutions remains the main phenomenon of cryopreservation process, and its effects on cell quality and cell death induction will be discussed. The increased knowledge and understanding of the cryopreservation process will lead to research strategies to improve the viability and the quality of the cell suspensions after thawing. Such strategies, such as vitrification, will be discussed with respect to their potential to significantly improve the quality of cell suspensions dedicated to liver cell-based therapies.

Drug interactions

Drugs for allergy are often taken in combination with other drugs, either to treat allergy or other conditions. In common with many pharmaceuticals, most such drugs are subject to metabolism by P450 enzymes and to transmembrane transport. This gives rise to considerable potential for drug-drug interactions, to which must be added consideration of drug-diet interactions. The potential for metabolism-based drug interactions is increasingly being taken into account during drug development, using a variety of in silico and in vitro approaches. Prediction of transporter-based interactions is not as advanced. The clinical importance of a drug interaction will depend upon a number of factors, and it is important to address concerns quantitatively, taking into account the therapeutic index of the compound.

Evolving concepts in liver tissue modeling and implications for in vitro toxicology

The development of human cell models stably expressing functional properties of the in vivo cells they are derived from for predicting toxicity of chemicals is a major challenge. For mimicking the liver, a major target of toxic chemicals, primary hepatocytes represent the most pertinent model. Their use is limited by interdonor functional variability and early phenotypic changes although their lifespan can be extended not only by culturing in a 2D dimension under sophisticated conditions but also by the use of synthetic and natural scaffolds as 3D supporting templates that allow cells to have a more stable microenvironment. Hepatocytes derived from stem cells could be the most appropriate alternative but up to now only liver progenitors/hepatoblasts are obtained in vitro. A few hepatocyte cell lines have retained a variable set of liver-specific functions. Among them are the human hepatoma HepaRG cells that express drug metabolism capacity at levels close to those found in primary hepatocytes making them a suitable model for both acute and chronic toxicity studies. New screening strategies are now proposed based on miniaturized and automated systems; they include the use of microfluidic chips and cell chips coupled with high content imaging analysis. Toxicogenomics technologies (particularly toxicotranscriptomics) have emerged as promising in vitro approaches for better identification and discrimination of cellular responses to chemicals. They should allow to discriminate compounds on the basis of the identification of a set of markers and/specific signaling pathways.