Cryopreservation of human hematopoietic cells with membrane stabilizers and bioantioxidants as additives in the conventional freezing medium

Trehalose in cryopreservation. Applications, mechanisms and intracellular delivery opportunities

Cryopreservation is crucial to fields including immune and stem cell therapies, reproductive technology, blood banking, regenerative medicine and across all biotechnology. During cryopreservation, cryoprotectants are essential to protect cells from the damage caused by exposure to freezing temperatures. The most common penetrating cryoprotectants, such as DMSO and glycerol do not give full recovery and have a cytotoxicity limit on the concentration which can be applied. The non-reducing disaccharide trehalose has been widely explored and used to supplement these, inspired by its use in nature to aid survival at extreme temperatures and/or desiccation. However, trehalose has challenges to its use, particular its low membrane permeability, and how its protective role compares to other sugars. Here we review the application of trehalose and its reported benefit and seek to show where chemical tools can improve its function. In particular, we highlight emerging chemical methods to deliver (as cargo, or via selective permeation) into the intracellular space. This includes encapsulation, cell penetrating peptides or (selective) modification of hydroxyls on trehalose.

Cryopreservation of organoids: Strategies, innovation, and future prospects

Organoid technology has demonstrated unique advantages in multidisciplinary fields such as disease research, tumor drug sensitivity, clinical immunity, drug toxicology, and regenerative medicine. It will become the most promising research tool in translational research. However, the long preparation time of organoids and the lack of high-quality cryopreservation methods limit the further application of organoids. Although the high-quality cryopreservation of small-volume biological samples such as cells and embryos has been successfully achieved, the existing cryopreservation methods for organoids still face many bottlenecks. In recent years, with the development of materials science, cryobiology, and interdisciplinary research, many new materials and methods have been applied to cryopreservation. Several new cryopreservation methods have emerged, such as cryoprotectants (CPAs) of natural origin, ice-controlled biomaterials, and rapid rewarming methods. The introduction of these technologies has expanded the research scope of cryopreservation of organoids, provided new approaches and methods for cryopreservation of organoids, and is expected to break through the current technical bottleneck of cryopreservation of organoids. This paper reviews the progress of cryopreservation of organoids in recent years from three aspects: damage factors of cryopreservation of organoids, new protective agents and loading methods, and new technologies of cryopreservation and rewarming.

Oxidative Stress and Oocyte Cryopreservation: Recent Advances in Mitigation Strategies Involving Antioxidants

Oocyte cryopreservation is widely used in assisted-reproductive technology and animal production. However, cryopreservation not only induces a massive accumulation of reactive oxygen species (ROS) in oocytes, but also leads to oxidative-stress-inflicted damage to mitochondria and the endoplasmic reticulum. These stresses lead to damage to the spindle, DNA, proteins, and lipids, ultimately reducing the developmental potential of oocytes both in vitro and in vivo. Although oocytes can mitigate oxidative stress via intrinsic antioxidant systems, the formation of ribonucleoprotein granules, mitophagy, and the cryopreservation-inflicted oxidative damage cannot be completely eliminated. Therefore, exogenous antioxidants such as melatonin and resveratrol are widely used in oocyte cryopreservation to reduce oxidative damage through direct or indirect scavenging of ROS. In this review, we discuss analysis of various oxidative stresses induced by oocyte cryopreservation, the impact of antioxidants against oxidative damage, and their underlying mechanisms. We hope that this literature review can provide a reference for improving the efficiency of oocyte cryopreservation.

Trehalose can effectively protect sheep epididymis epithelial cells from oxidative stress

Trehalose, a naturally nontoxic disaccharide that does not exist in mammals, stabilizes cell membrane integrity under oxidative stress conditions, the mechanism of which is still unclear. Here, we analyzed the effects of trehalose on sheep epididymis epithelial cell (EEC) proliferation and its possible mechanisms. To study the effect of trehalose on EECs, EECs were isolated from testes of 12-month-old sheep; cell counting kit-8 (CCK-8) was used to measure the growth of the cells. Cell proliferation was evaluated by assaying cell cycle and apoptosis, and RT-PCR was utilized to identify the epididymal molecular markers glutathione peroxidase 5 (GPX5) and androgen receptor (AR). Next, reactive oxygen species (ROS) content was evaluated by a dichloro-dihydro-fluorescein diacetate (DCFH-DA) probe. Superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities were evaluated by enzyme chemistry methods, and GPX5 expression was evaluated by qRT-PCR and enzyme-linked immunosorbent assay (ELISA). The results showed that 100 mM trehalose significantly improved the proliferation potential of EECs, in which the cells could be serially passaged 14 times with continued normal GPX5 and AR marker gene expression in vitro. The trehalose can increase significantly a proportion of EECs in S phase (P<0.01) and decrease significantly the apoptotic rate of EECs (P<0.01) compared to the control. Moreover, the trehalose decreased ROS significantly (P<0.01) and increased CAT (P<0.01) and GSH-Px (P<0.05) activities significantly in EECs. GPX5 mRNA and protein expression were also significantly upregulated in trehalose-treated EECs (P<0.05 and P<0.01 respectively). Our study suggested that exogenous trehalose exhibited antioxidant activity through increasing the activities of CAT, GSH-Px, and the expression level of GPX5 and could be employed to maintain vitality of sheep EECs during long-term in vitro culture.

Differentiated Cells Derived from Hematopoietic Stem Cells and Their Applications in Translational Medicine

Hematopoietic stem cells (HSCs) and their development are one of the most widely studied model systems in mammals. In adults, HSCs are predominantly found in the bone marrow, from where they maintain homeostasis. Besides bone marrow and mobilized peripheral blood, cord blood is also being used as an alternate allogenic source of transplantable HSCs. HSCs from both autologous and allogenic sources are being applied for the treatment of various conditions like blood cancers, anemia, etc. HSCs can further differentiate to mature blood cells. Differentiation process of HSCs is being extensively studied so as to obtain a large number of pure populations of various differentiated cells in vitro so that they can be taken up for clinical trials. The ability to generate sufficient quantity of clinical-grade specialized blood cells in vitro would take the field of hematology a step ahead in translational medicine.

Accelerating cryoprotectant diffusion kinetics improves cryopreservation of pancreatic islets

Cryopreservation offers the potential to increase the availability of pancreatic islets for treatment of diabetic patients. However, current protocols, which use dimethyl sulfoxide (DMSO), lead to poor cryosurvival of islets. We demonstrate that equilibration of mouse islets with small molecules in aqueous solutions can be accelerated from > 24 to 6 h by increasing incubation temperature to 37 °C. We utilize this finding to demonstrate that current viability staining protocols are inaccurate and to develop a novel cryopreservation method combining DMSO with trehalose pre-incubation to achieve improved cryosurvival. This protocol resulted in improved ATP/ADP ratios and peptide secretion from β-cells, preserved cAMP response, and a gene expression profile consistent with improved cryoprotection. Our findings have potential to increase the availability of islets for transplantation and to inform the design of cryopreservation protocols for other multicellular aggregates, including organoids and bioengineered tissues.

The roles of reactive oxygen species and antioxidants in cryopreservation

Cryopreservation has facilitated advancement of biological research by allowing the storage of cells over prolonged periods of time. While cryopreservation at extremely low temperatures would render cells metabolically inactive, cells suffer insults during the freezing and thawing process. Among such insults, the generation of supra-physiological levels of reactive oxygen species (ROS) could impair cellular functions and survival. Antioxidants are potential additives that were reported to partially or completely reverse freeze-thaw stress-associated impairments. This review aims to discuss the potential sources of cryopreservation-induced ROS and the effectiveness of antioxidant administration when used individually or in combination.

A modified perlite protocol with a mixed dimethyl sulfoxide and trehalose cryoprotectant improves the viability of frozen cultures of ectomycorrhizal basidiomycetes

Homolka's perlite protocol (HPP) was evaluated for cryopreservation of a wide range of ectomycorrhizal basidiomycete cultures, then a modified perlite protocol (MPP), in which cryoprotectant was added just before freezing rather than during the culturing process, was applied to cryosensitive strains that failed to survive when HPP was used. Further modifications of MPP with various cryoprotectants were explored to improve the cryopreservation of hard-to-preserve strains. The efficacy of HPP was assessed in 111 strains of 38 species of basidiomycetes of various cryosensitivities. After freezing strains using HPP, the viability and colony diameter of the strains were examined after 2 wk, 6 mo, and 1 y of storage at -80 C. Of the 111 strains tested, 91 survived after 1 y of storage with high viability of 80% or more, whereas the remaining 20 strains exhibited low and unstable viability. For those selected cryosensitive strains that did not survive well when HPP was used, MPP was applied with a mixture of cryoprotectants, dimethyl sulfoxide (DMSO), glycerol, and trehalose, at different concentrations and combinations. Toxicity testing of the cryoprotectants in the nonfrozen state revealed that 12% (v/v) glycerol was highly toxic for six strains (four species), whereas DMSO (5% and 10% [v/v]) was less toxic than glycerol. The viability of the cryosensitive strains after freezing demonstrated that DMSO was more efficient than glycerol, and trehalose enhanced the cryoprotective effects of both glycerol and DMSO when MPP was used for cryopreservation. Our comparative analysis of MPP with various combinations and concentrations of cryoprotectants revealed that a mixture of 5% DMSO and 10% trehalose was the most effective cryoprotectant, and that using MPP with this cryoprotectant was applicable to many cryosensitive strains.

Optimization of the harvesting and freezing conditions of human cell lines for DNA damage analysis by the alkaline comet assay

The comet assay is a commonly used method for in vitro and in vivo genotoxicity assessment. This versatile assay can be performed in a wide range of tissues and cell types. Although most of the studies use samples immediately processed after collection, frozen biological samples can also be used. The present study aimed to optimize a collection and freezing protocol to minimize the DNA damage associated with these procedures in human cell line samples for comet assay analysis. This study was conducted in glial A172 and lung alveolar epithelial A549 cells. Two cell detachment methods (mechanical vs enzymatic) and two cryoprotective media [FBS + 10% DMSO vs Cell Culture Media (CCM) + 10% DMSO] were tested, and DNA damage assessed at four time points following storage at -80 °C (one, two, four and eight weeks). In both cell lines, no differences in % tail intensity were detected between fresh and frozen cells up to eight weeks, irrespective of the harvesting method and freezing medium used. However, freshly isolated A172 cells exhibited a significant lower DNA damage when resuspended in CCM + 10% DMSO, while for A549 fresh cells the preferable harvesting method was the enzymatic one since it induced less DNA damage. Although both harvesting methods and cryoprotective media tested were found suitable, our data indicate that enzymatic harvesting and cryopreservation in CCM + 10% DMSO is a preferable method for DNA integrity preservation of human cell line samples for comet assay analysis. Our data also suggest that CCM is a preferable and cost-effective alternative to FBS in cryopreservation media. This optimized protocol allows the analysis of in vitro cell samples collected and frozen at different locations, with minimal interference on the basal DNA strand break levels in samples kept frozen up to eight weeks.

Low molecular-weight hyaluronan as a cryoprotectant for the storage of microencapsulated cells

The low-temperature storage of therapeutic cell-based products plays a crucial role in their clinical translation for the treatment of diverse diseases. Although dimethylsulfoxide (DMSO) is the most successful cryoprotectant in slow freezing of microencapsulated cells, it has shown adverse effects after cryopreserved cell-based products implantation. Therefore, the search of alternative non-toxic cryoprotectants for encapsulated cells is continuously investigated to move from bench to the clinic. In this work, we investigated the low molecular-weight hyaluronan (low MW-HA), a natural non-toxic and non-sulfated glycosaminoglycan, as an alternative non-permeant cryoprotectant for the slow freezing cryopreservation of encapsulated cells. Cryopreservation with low MW-HA provided similar metabolic activity, cell dead and early apoptotic cell percentage and membrane integrity after thawing, than encapsulated cells stored with either DMSO 10% or Cryostor 10. However, the beneficial outcomes with low MW-HA were not comparable to DMSO with some encapsulated cell types, such as the human insulin secreting cell line, 1.1B4, maybe explained by the different expression of the CD44 surface receptor. Altogether, we can conclude that low MW-HA represents a non-toxic natural alternative cryoprotectant to DMSO for the cryopreservation of encapsulated cells.

Advances in the slow freezing cryopreservation of microencapsulated cells

Over the past few decades, the use of cell microencapsulation technology has been promoted for a wide range of applications as sustained drug delivery systems or as cells containing biosystems for regenerative medicine. However, difficulty in their preservation and storage has limited their availability to healthcare centers. Because the preservation in cryogenic temperatures poses many biological and biophysical challenges and that the technology has not been well understood, the slow cooling cryopreservation, which is the most used technique worldwide, has not given full measure of its full potential application yet. This review will discuss the different steps that should be understood and taken into account to preserve microencapsulated cells by slow freezing in a successful and simple manner. Moreover, it will review the slow freezing preservation of alginate-based microencapsulated cells and discuss some recommendations that the research community may pursue to optimize the preservation of microencapsulated cells, enabling the therapy translate from bench to the clinic.

Effect of trehalose on cryopreservation of pure peripheral blood stem cells

Stem cells are an important tool for the study of hematopoiesis. Despite developments in cryopreservation, post-thaw cell death remains a considerable problem. Cryopreservation protocol should limit cell damage due to freezing and ensure the recovery of the functional cell characteristics after thawing. Thus, the use of cryoprotectants is essential. In particular, the efficacy of trehalose has been reported for clinical purposes in blood stem cells. The aim of the current study was to establish an efficient method for biological research based on the use of trehalose, to cryopreserve pure peripheral blood stem cells. The efficacy of trehalose was assessed in vitro and the cell viability was evaluated. The data indicate that trehalose improves cell survival after thawing compared with the standard freezing procedure. These findings could suggest the potential for future trehalose application for research purposes in cell cryopreservation.

Trehalose, an easy, safe and efficient cryoprotectant for the parasitic protozoan Trypanosoma brucei

Trehalose, a non-permeating cryoprotective agent (CPA), has been documented as less toxic and highly efficient at cryopreserving different kinds of cells or organisms. In the present study, trehalose was evaluated for its application in cryopreservation of both Trypanosoma brucei procyclic and bloodstream form cells. The cryopreservation efficiency was determined by the motility of trypanosomes after thawing, as well as a subsequent recovery and infectivity assessment. The viability of trypanosomes from cultivation that were frozen in a serial concentrations of trehalose showed similar results to classical CPAs of glycerol and DMSO. Nevertheless, trypanosomes cryopreserved in 0.2M trehalose showed the best growth characteristic during subsequent cultivation. In addition, CPA cocktails with trehalose and permeating CPA glycerol or DMSO were developed and evaluated. Interestingly, trypanosomes in host (mouse) blood cryopreserved in 0.4M trehalose plus 5% glycerol showed higher infectivity than those preserved in trehalose/DMSO cocktails as well as individually. Further investigations showed that, in comparison with slow freezing at -80°C, flash freezing in liquid nitrogen provided better cryopreservation for bloodstream form cells than slow freezing. In conclusion, trehalose is an easy, safe and efficient CPA for cryopreservation of T. brucei and potentially for other protozoan species and cells.

Conditioned Medium from Placental Mesenchymal Stem Cells Reduces Oxidative Stress during the Cryopreservation of Ex Vivo Expanded Umbilical Cord Blood Cells

Background

The limited cell dose in umbilical cord blood (UCB) necessitates ex vivo expansion of UCB. Further, the effective cryopreservation of these expanded cells is important in widening their use in the clinics. During cryopreservation, cells experience oxidative stress due to the generation of reactive oxygen species (ROS). Conditioned medium from mesenchymal stem cells (MSCs-CM) has been shown to alleviate the oxidative stress during wound healing, Alzheimer’s disease and ischemic disease. This premise prompted us to investigate the influence of MSCs-CM during cryopreservation of expanded UCB cells.

Methodology/Principle findings

CM-was collected from cord/placental MSCs(C-MSCs-CM, P-MSC-CM). UCB CD34⁺cells were expanded as suspension cultures in serum free medium containing cytokines for 10 days. Cells were frozen with/without C-MSCs-CM and or P-MSCs-CM in the conventional freezing medium containing 20%FCS +10%DMSO using a programmable freezer and stored in liquid nitrogen. Upon revival, cells frozen with MSCs-CM were found to be superior to cells frozen in conventional medium in terms of viability, CD34⁺content and clonogenecity. Priming of revived cells for 48 hrs with MSCs-CM further improved their transplantation ability, as compared to those cultured without MSCs-CM. P-MSCs-CM radically reduced the oxidative stress in cryopreserved cells, resulting in better post thaw functionality of CD34⁺ cells than with C-MSCs-CM. The observed cryoprotective effect of MSCs-CM was primarily due to anti-oxidative and anti-apoptotic properties of the MSCs-CM and not because of the exosomes secreted by them.

Conclusions/Significance

Our data suggest that MSCs-CM can serve as a valuable additive to the freezing or the priming medium for expanded UCB cells, which would increase their clinical applicability.

Effect of Antioxidants and Apoptosis Inhibitors on Cryopreservation of Murine Germ Cells Enriched for Spermatogonial Stem Cells

Spermatogonial stem cells (SSCs) are germline stem cells that serve as the foundation of spermatogenesis to maintain fertility throughout a male’s lifetime. To treat male infertility using stem cell banking systems and transplantation, it is important to be able to preserve SSCs for long periods of time. Therefore, this study was conducted to develop an optimal cryopreservation protocol for SSCs using antioxidants and apoptosis inhibitors in freezing medium. No differences were observed compared to controls when SSCs were cryopreserved in the presence of apoptosis inhibitors by themselves. However, mouse germ cells cryopreserved in basal medium containing the antioxidant hypotaurine (14 mM) resulted in significantly greater proliferation potential and mitochondrial activity. Furthermore, treatment groups with combinations containing 200 mM trehalose and 14 mM hypotaurine showed higher proliferation rates compared to controls. In addition, several serum free conditions were evaluated for SSC cryopreservation. Treatment media containing 10% or 20% knockout serum replacement resulted in similar cryopreservation results compared to media containing FBS. SSC transplantation was also performed to confirm the functionality of SSCs frozen in 14 mM hypotaurine. Donor SSCs formed normal spermatogenic colonies and sperm in the recipient testis. These data indicate that inclusion of 14 mM hypotaurine in cryopreservation media is an effective way to efficiently cryopreserve germ cells enriched for SSCs and that knockout serum replacement can replace FBS in germ cell cryopreservation media.

Cryoprotective Effect of Disaccharides on Cord Blood Stem Cells with Minimal Use of DMSO

Umbilical cord blood (UCB) is an extremely attractive source of stem cells for the treatment of various benign and malignant hematological and non-hematological disorders. To facilitate the preservation of these stem cells, 10 % dimethylsulfoxide (DMSO) is widely used as cryoprotectant in cord blood banks. But it is found to be toxic at this concentration with the result of serious side effects in recipients after infusion of DMSO-cryopreserved cells. Evaluation of viability and functionality of cryopreserved hematopoietic stem cells is needed with either inclusion of nontoxic additives alone or with reduced DMSO concentration. We assessed the post thawing viability of UCB stem cells in the freezing medium containing disaccharides (sucrose or trehalose) alone and in combination with reduced amount i.e. 2 % DMSO by trypan blue staining. The functionally active progenitor cells content of the optimized media was then evaluated and compared with 5% DMSO by a colony forming unit assay using methylcellulose based media. The freezing solution containing 0.2 M trehalose with 2 % DMSO came out to be superior in the evaluation of viability and generation of hematopoietic colonies of erythroid and myeloid lineage than 5 % DMSO alone. While the percentage of viability was lower than 2 % DMSO, as observed in the medium containing 0.2 M trehalose or sucrose alone, with poor outcome of generation of myeloid lineage based colonies. Our study results suggest that trehalose (0.2M) with the inclusion of reduced concentration of DMSO(2%) can better replace 5%DMSO rather than complete removal of DMSO from the freezing medium.

Effect of sugar molecules on the cryopreservation of mouse spermatogonial stem cells

OBJECTIVE

To study the influence of sugars and establish a serum-free freezing method for the cryopreservation of spermatogonial stem cells (SSCs).

DESIGN

Animal study.

SETTING

University laboratory.

ANIMAL(S)

C57BL/6-TgEGFP, C57BL/6 mice.

INTERVENTION(S)

Germ cells enriched from testis cells were frozen using standard freezing medium containing sugars, including monosaccharides, disaccharides, and trisaccharides at 50, 100, and 200 mM, respectively. To study the feasibility of establishing a serum-free freezing method, fetal bovine serum was substituted with knockout serum replacement.

MAIN OUTCOME MEASURE(S)

Freeze-thawed germ cells were evaluated for recovery rate, proliferation capacity, and stem cell activity after transplantation to recipient testes.

RESULT(S)

Supplementation of freezing medium with 200 mM disaccharide is an effective method for cryopreservation of SSCs. Trehalose is the most effective cryoprotectant among all the sugars tested and only lactose was comparable to trehalose. Our proliferation and transplantation data show that serum-free freezing can be achieved in freezing medium supplemented with 200 mM trehalose, 10% knockout serum replacement, and 10% dimethyl sulfoxide (DMSO) for cryopreservation of SSCs.

CONCLUSION(S)

These findings raise the possibility of effectively banking frozen SSCs from various species, including humans, in a traditional serum-free medium for germ cell research and male infertility treatments.

Cryopreservation in trehalose preserves functional capacity of murine spermatogonial stem cells

Development of techniques to isolate, culture, and transplant human spermatogonial stem cells (SSCs) has the future potential to treat male infertility. To maximize the efficiency of these techniques, methods for SSC cryopreservation need to be developed to bank SSCs for extended periods of time. Although, it has been demonstrated that SSCs can reinitiate spermatogenesis after freezing, optimal cryopreservation protocols that maximize SSC proliferative capacity post-thaw have not been identified. The objective of this study was to develop an efficient cryopreservation technique for preservation of SSCs. To identify efficient cryopreservation methods for long-term preservation of SSCs, isolated testis cells enriched for SSCs were placed in medium containing dimethyl sulfoxide (DMSO) or DMSO and trehalose (50 mM, 100 mM, or 200 mM), and frozen in liquid nitrogen for 1 week, 1 month, or 3 months. Freezing in 50 mM trehalose resulted in significantly higher cell viability compared to DMSO at all thawing times and a higher proliferation rate compared to DMSO for the 1 week freezing period. Freezing in 200 mM trehalose did not result in increased cell viability; however, proliferation activity was significantly higher and percentage of apoptotic cells was significantly lower compared to DMSO after freezing for 1 and 3 months. To confirm the functionality of SSCs frozen in 200 mM trehalose, SSC transplantation was performed. Donor SSCs formed spermatogenic colonies and sperm capable of generating normal progeny. Collectively, these results indicate that freezing in DMSO with 200 mM trehalose serves as an efficient method for the cryopreservation of SSCs.

Preservation of stem cells

Adult stem cells (hematopoietic and mesenchymal) have demonstrated tremendous human therapeutic potential. Currently, human embryonic stem cells are used principally for understanding development and disease progression but also hold tremendous therapeutic potential. The ability to preserve stem cells is critical for their use in clinical and research applications. Preservation of cells permits the transportation of cells between sites, as well as completion of safety and quality control testing. Preservation also permits the development of a 'manufacturing paradigm' for cell therapies, thereby maximizing the number of products that can be produced at a given facility. in this article, we will review modes of preservation and the current status of preservation of hematopoietic, mesenchymal and human embryonic stem cells. Current and emerging issues in the area of stem cell preservation will also be described.

Polyunsaturated fatty acids confer cryoresistance on megakaryocytes generated from cord blood and also enhance megakaryocyte production from cryopreserved cord blood cells

BACKGROUND AIMS

Previous data have shown that the addition of docosahexanoic acid (DHA)/arachidonic acid (AA) has a beneficial effect on cytokine-mediated in vitro generation of megakaryocytes (MK) from umbilical cord blood (UCB).Cryopreservation forms an inherent part of UCB banking and MK progenitors are known to be very sensitive to the stresses of freezing. It is therefore imperative to generate functional cells from cryopreserved cells, and the generated cells need to be cryopreserved until used. In the present study, cryopreservation of ex vivo-expanded MK as well as MK generation from cryopreserved UCB samples was investigated.

METHODS

MK generated with or without DHA/AA were cryopreserved in freezing medium containing 10% dimethyl sulfoxide (DMSO). Freezing efficacy was tested by quantitating MK after revival. Cryopreserved CD34(+) cells were cultured with stem cell factor (SCF) and thrombopoietin (TPO), in the presence and absence of DHA/AA for 10 days, and then quantitated for MK. Results. We observed a 1.5-3-fold increase in MK numbers, their progenitor content and their expression of phenotypic markers and MK-related transcription factors. DHA/AA sets showed a 2-5-fold improved engraftment in NOD/SCID mice. These data showed that the beneficial effect of DHA/AA obtained during MK expansion was not altered after freezing stress. The enhancement in MK generation obtained from fresh cord blood (CB) cells was reproduced with comparable efficiency when we used cryopreserved CB samples.

CONCLUSIONS

Taken together, our data suggest that in vitro-generated DHA/AA MK survive cryoinjuries in a functionally better state. DHA/AA support a more efficient generation of MK from cryopreserved UCB.

Pharmacological inhibition of caspase and calpain proteases: a novel strategy to enhance the homing responses of cord blood HSPCs during expansion

Background

Expansion of hematopoietic stem/progenitor cells (HSPCs) is a well-known strategy employed to facilitate the transplantation outcome. We have previously shown that the prevention of apoptosis by the inhibition of cysteine proteases, caspase and calpain played an important role in the expansion and engraftment of cord blood (CB) derived HSPCs. We hypothesize that these protease inhibitors might have maneuvered the adhesive and migratory properties of the cells rendering them to be retained in the bone marrow for sustained engraftment. The current study was aimed to investigate the mechanism of the homing responses of CB cells during expansion.

Methodology/Principal Findings

CB derived CD34⁺ cells were expanded using a combination of growth factors with and without Caspase inhibitor -zVADfmk or Calpain 1 inhibitor- zLLYfmk. The cells were analyzed for the expression of homing-related molecules. In vitro adhesive/migratory interactions and actin polymerization dynamics of HSPCs were assessed. In vivo homing assays were carried out in NOD/SCID mice to corroborate these observations. We observed that the presence of zVADfmk or zLLYfmk (inhibitors) caused the functional up regulation of CXCR4, integrins, and adhesion molecules, reflecting in a higher migration and adhesive interactions in vitro. The enhanced actin polymerization and the RhoGTPase protein expression complemented these observations. Furthermore, in vivo experiments showed a significantly enhanced homing to the bone marrow of NOD/SCID mice.

Conclusion/Significance

Our present study reveals another novel aspect of the regulation of caspase and calpain proteases in the biology of HSPCs. The priming of the homing responses of the inhibitor-cultured HSPCs compared to the cytokine-graft suggests that the modulation of these proteases may help in overcoming the major homing defects prevalent in the expansion cultures thereby facilitating the manipulation of cells for transplant procedures.

Current development of bioreactors for extracorporeal bioartificial liver (Review)

The research and development of extracorporeal bioartificial liver is gaining pace in recent years with the introduction of a myriad of optimally designed bioreactors with the ability to maintain long-term viability and liver-specific functions of hepatocytes. The design considerations for bioartificial liver are not trivial; it needs to consider factors such as the types of cell to be cultured in the bioreactor, the bioreactor configuration, the magnitude of fluid-induced shear stress, nutrients' supply, and wastes' removal, and other relevant issues before the bioreactor is ready for testing. This review discusses the exciting development of bioartificial liver devices, particularly the various types of cell used in current reactor designs, the state-of-the-art culturing and cryopreservation techniques, and the comparison among many today's bioreactor configurations. This review will also discuss in depth the importance of maintaining optimal mass transfer of nutrients and oxygen partial pressure in the bioreactor system. Finally, this review will discuss the commercially available bioreactors that are currently undergoing preclinical and clinical trials.

Cryopreservation of amniotic fluid-derived stem cells using natural cryoprotectants and low concentrations of dimethylsulfoxide

Amniotic fluid-derived stem cells (AFSCs) are a potential cell source for therapeutic applications. They can be easily mass produced, cryopreserved and shipped to clinics for immediate use. However, one major obstacle to the manufacturing of clinical grade stem cells is the need for current good manufacturing practices for cryopreservation, storage, and distribution of these cells. Most current cryopreservation methods used for stem cells include the potentially toxic cryoprotectant (CPA) dimethylsulfoxide (Me(2)SO) in the presence of animal serum proteins that prevent direct use of these cells in human therapeutic applications. To avoid any potential cryoprotectant related complications, it will be essential to develop non-toxic CPAs or reduce CPA concentration in the freezing media used. In this study, we assessed the use of disaccharides, antioxidants and caspase inhibitors for cryopreservation of AFSCs in combination with a reduced concentration of Me(2)SO. The thawed cells were tested for viability with MTT assays and a growth curve was created to measure population doubling time. In addition, we performed flow cytometry analysis for cell surface antigens, RT-PCR for mRNA expression of stem cell markers, and assays to determine the myogenic differentiation potential of the cells. A statistically significant (p<0.05) increase in post-thawed cell viability in solutions containing trehalose, catalase and (Z)VAD-fmk with 5% Me(2)SO was observed. The solutions containing trehalose and catalase with 5% or 2.5% (v/v) Me(2)SO produced results similar to those for the control (10% (v/v) Me(2)SO and 30% FBS) in terms of culture growth, expression of cell surface antigens and mRNA expression of stem cell markers in AFSCs cryopreserved for a minimum of 3 weeks. Thus, AFSCs can be cryopreserved with 1/4 the standard Me(2)SO concentration with the addition of disaccharides, antioxidants and caspase inhibitors. The use of Me(2)SO at low concentrations in cell freezing solutions may support the development of clinical trials of AFSCs.

Expansion of cord blood CD34 cells in presence of zVADfmk and zLLYfmk improved their in vitro functionality and in vivo engraftment in NOD/SCID mouse

Background

Cord blood (CB) is a promising source for hematopoietic stem cell transplantations. The limitation of cell dose associated with this source has prompted the ex vivo expansion of hematopoietic stem and progenitor cells (HSPCs). However, the expansion procedure is known to exhaust the stem cell pool causing cellular defects that promote apoptosis and disrupt homing to the bone marrow. The role of apoptotic machinery in the regulation of stem cell compartment has been speculated in mouse hematopoietic and embryonic systems. We have consistently observed an increase in apoptosis in the cord blood derived CD34⁺ cells cultured with cytokines compared to their freshly isolated counterpart. The present study was undertaken to assess whether pharmacological inhibition of apoptosis could improve the outcome of expansion.

Methodology/Principal Findings

CB CD34⁺ cells were expanded with cytokines in the presence or absence of cell permeable inhibitors of caspases and calpains; zVADfmk and zLLYfmk respectively. A novel role of apoptotic protease inhibitors was observed in increasing the CD34⁺ cell content of the graft during ex vivo expansion. This was further reflected in improved in vitro functional aspects of the HSPCs; a higher clonogenicity and long term culture initiating potential. These cells sustained superior long term engraftment and an efficient regeneration of major lympho-myeloid lineages in the bone marrow of NOD/SCID mouse compared to the cells expanded with growth factors alone.

Conclusion/Significance

Our data show that, use of either zVADfmk or zLLYfmk in the culture medium improves expansion of CD34⁺ cells. The strategy protects stem cell pool and committed progenitors, and improves their in vitro functionality and in vivo engraftment. This observation may complement the existing protocols used in the manipulation of hematopoietic cells for therapeutic purposes. These findings may have an impact in the CB transplant procedures involving a combined infusion of unmanipulated and expanded grafts.

Hypothermic storage of hepatocytes used for bioartificial liver support system: current status and recent advances

The problem that high-quality hepatocytes are difficult to obtain restricts the use of bioartificial liver support system (BLASS) in clinical practice. Finding an effective way to preserve hepatocytes and constructing a "ready-to-use" hepatocyte bank would efficiently promote the development of the BLASS. Nowadays, the methods for hypothermic storage of hepatocytes could be classified into two types: conventional hypothermic storage at 4 °C or subzero nonfreezing storage, and cryopreservation at -80 °C or -196 °C. Each type of hypothermic storage method has its advantages and disadvantages. Many factors may affect the effect of hypothermic storage (cryopreservation), such as storage solution and cryoprotective agent. Although the precise mechanism underlying the death of hepatocytes during hypothermic storage is not well understood, numerous studies have indicated that apoptosis plays an important role in hypothermic storage injury.

Subzero nonfreezing storage of C3A hepatocytes for use in bioartificial liver support systems

AIM: To investigate whether subzero nonfreezing storage (-0.8 °C) is superior to conventional cold storage in preservation of C3A hepatocytes for use in bioartificial liver support systems.

METHODS: C3A hepatocytes suspended in University of Wisconsin (UW) solution were divided into three groups: subzero nonfreezing group (-0.8 °C), zero nonfreezing group (0 °C) and control group (4 °C). After 24, 48 and 72 hours of hypothermic storage, cell viability and apoptosis were detected by flow cytometry; intracellular adenosine triphosphate (ATP) content, lactate dehydrogenase (LDH) release, lactic acid production, urea synthesis and albumin secretion were determined; and cell morphological changes were observed.

RESULTS: Compared to the zero nonfreezing group and the control group, after 72 hours of hypothermic storage, the percentage of viable C3A hepatocytes was significantly higher (86.49% ± 2.80% vs 81.50% ± 2.83% and 77.83% ± 3.40%, respectively; both P < 0.05), and cell apoptosis rate was significantly lower (1.26% ± 0.84% vs 5.34% ± 1.20% and 9.16% ± 1.99%, respectively; both P < 0.05) in the subzero nonfreezing group. Lactic acid and LDH production was more significantly suppressed (lactic acid: 10.38 μg/10⁶ cells ± 1.40 μg/10⁶ cells vs 12.02 μg/10⁶ cells ± 1.64 μg/106 cells and 17.41 μg/10⁶ cells ± 2.40 μg/10⁶ cells; LDH: 80.10 U/L ± 11.10 U/L vs 120.04 U/L ± 14.32 U/L and 148.98 U/L ± 15.37 U/L, respectively; all P < 0.05), and the ability of hepatocytes to synthesize urea and secrete albumin was better maintained in the subzero nonfreezing group (both P < 0.05). Moreover, cells in the subzero nonfreezing storage group had lower death rate and better cellular morphology. A burr-like structure around the cell membrane and an intracellular vacuole-like structure were found in cells in the zero nonfreezing group and the control group, but not in the subzero nonfreezing group.

CONCLUSION: Subzero nonfreezing storage (-0.8 °C) of hepatocytes to construct a "ready-to-use" hepatocyte bank like the "blood bank" will efficiently promote the development of bioartificial liver support systems.

Evaluations of bioantioxidants in cryopreservation of umbilical cord blood using natural cryoprotectants and low concentrations of dimethylsulfoxide

Transplantation using hematopoietic stem cells from umbilical cord blood (UCB) is a life-saving treatment option for patients with select oncologic diseases, immunologic diseases, bone marrow failure, and others. Often this transplant modality requires cryopreservation and storage of hematopoietic stem cells (HSC), which need to remain cryopreserved in UCB banks for possible future use. The most widely used cryoprotectant is dimethylsulfoxide (Me(2)SO), but at 37 degrees C, it is toxic to cells and for patients, infusion of cryopreserved HSC with Me(2)SO has been associated with side effects. Freezing of cells leads to chemical change of cellular components, which results in physical disruption. Reactive oxygen species (ROS) generation also has been implicated as cause of damage to cells during freezing. We assessed the ability of two bioantioxidants and two disaccharides, to enhance the cryopreservation of UCB. UCB was processed and subjected to cryopreservation in solutions containing different concentrations of Me(2)SO, bioantioxidants and disaccharides. Samples were thawed, and then analysed by: flow cytometry analysis, CFU assay and MTT viability assay. In this study, our analyses showed that antioxidants, principally catalase, performed greater preservation of: CD34+ cells, CD123+ cells, colony-forming units and cell viability, all post-thawed, compared with the standard solution of cryopreservation. Our present studies show that the addition of catalase improved the cryopreservation outcome. Catalase may act on reducing levels of ROS, further indicating that accumulation of free radicals indeed leads to death in cryopreserved hematopoietic cells.

Optimisation of the cryopreservation of primary hepatocytes

The use of cryopreserved hepatocytes has increased in the last decade due to the improvement of the freezing and thawing methods and has even achieved acceptance by the U.S. Food and Drug Administration for use in drug-metabolising enzyme induction studies. This chapter provides an overview of the theories behind the process of cryopreservation and some of the most important advances which have led to the ability to cryopreserve hepatocytes, which when thawed retain functions similar to fresh cells. Parameters such as cell density, cryoprotectants and freezing media should be considered as well as storage conditions and thawing techniques. Special emphasis is placed on human hepatocytes but information for the cryopreservation of animal hepatocytes is also described. Finally, a suggested method for optimising cryopreservation method is outlined.

Comparison of University of Wisconsin and ET-Kyoto preservation solutions for the cryopreservation of primary human hepatocytes

Primary human hepatocytes are clinically used for transplantation or in bioartificial liver devices for the treatment of patients with liver failure. We aimed to assess whether an organ preservation solution containing trehalose, namely ET-Kyoto solution (ETK), could improve human liver cell viability when used for cryopreservation in comparison to the University of Wisconsin solution (UW). Our study showed beneficial effects of ETK when used in combination with other cryoprotectants on the viability of thawed hepatocytes. Indeed, no significant difference was seen between the viability of freshly isolated cells and cryopreserved cells when cryopreserved with ETK combined with other cryoprotectants. In contrast, a significant decrease of viability was observed in cells cryopreserved with UW or ETK combined with dimethysulfoxide (DMSO) only, or with UW combined with other cryoprotectants, compared to freshly isolated cells. No significant difference was observed between the four different groups of cryopreserved hepatocytes with regards to cell recovery rate or cell attachment after thawing. However, a significant decrease in cell metabolic activity was found in cells cryopreserved with UW 10% DMSO compared to the other groups. In conclusion, our study confirms the beneficial effect of ETK for the cryopreservation of human hepatocytes in combination with other cryoprotective agents.

Trehalose and trehalose-based polymers for environmentally benign, biocompatible and bioactive materials

Trehalose is a non-reducing disaccharide that is found in many organisms but not in mammals. This sugar plays important roles in cryptobiosis of selaginella mosses, tardigrades (water bears), and other animals which revive with water from a state of suspended animation induced by desiccation. The interesting properties of trehalose are due to its unique symmetrical low-energy structure, wherein two glucose units are bonded face-to-face by 1→1-glucoside links. The Hayashibara Co. Ltd., is credited for developing an inexpensive, environmentally benign and industrial-scale process for the enzymatic conversion of α-1,4-linked polyhexoses to α,α-d-trehalose, which made it easy to explore novel food, industrial, and medicinal uses for trehalose and its derivatives. Trehalose-chemistry is a relatively new and emerging field, and polymers of trehalose derivatives appear environmentally benign, biocompatible, and biodegradable. The discriminating properties of trehalose are attributed to its structure, symmetry, solubility, kinetic and thermodynamic stability and versatility. While syntheses of trehalose-based polymer networks can be straightforward, syntheses and characterization of well defined linear polymers with tailored properties using trehalose-based monomers is challenging, and typically involves protection and deprotection of hydroxyl groups to attain desired structural, morphological, biological, and physical and chemical properties in the resulting products. In this review, we will overview known literature on trehalose’s fascinating involvement in cryptobiology; highlight its applications in many fields; and then discuss methods we used to prepare new trehalose-based monomers and polymers and explain their properties.

Curcumin treatment enhances islet recovery by induction of heat shock response proteins, Hsp70 and heme oxygenase-1, during cryopreservation

Limited recovery of islets post-cryopreservation influences graft survival and transplantation efficiency during diabetes treatment. As curcumin, a potent antioxidant/radical scavenging compound, protects islets against beta cell toxins, we hypothesized that inclusion of curcumin during cryopreservation or during post-thaw culture or both may rescue islets from cryoinjury. To test the effect of curcumin inclusion on islet recovery murine islets were isolated by the collagenase digestion, cultured for 48 h, cryopreserved using dimethylsulphoxide as cryoprotectant -- with or without curcumin (10 microM) -- and then slow cooled to -40 degrees C before immersing them in liquid nitrogen for 7 days. Following rapid thawing with sucrose gradient and 24 h post-thaw culture -- in presence or absence of curcumin (10 microM) -- islet viability and functionality were determined. Islet recovery in curcumin treated groups was significantly higher than in groups where islets were cryopreserved without curcumin. Islets cryopreserved with curcumin also showed more intact islets as well as better morphology as compared to islets cryopreserved without curcumin. Curcumin treated islets also showed significant inhibition of ROS generation as compared to islets cryopreserved without curcumin. Glucose responsiveness and insulin secretion in islets cryopreserved with curcumin was equal to that of the freshly isolated islets as against islets cryopreserved without curcumin. Elevated level of Hsp 70 and HO-1 were observed in islets cryopreserved with curcumin and may contribute to curcumin-induced islet rescue. Hence, we conclude that inclusion of curcumin into cryopreservation medium inhibits ROS generation and corresponding islet damage and dysfunction.

Cryoprotective effects of d-allose on mammalian cells

D-allose, an aldo-hexose, is a rare sugar whose biological functions remain largely unclear. Recently, we demonstrated a novel inhibitory effect of D-allose on production of reactive oxygen species (ROS). Here, we focused on investigating cryoprotective effects of D-allose on cell viability. Mammalian cell lines including OVCAR-3 (human ovarian cancer), HeLa (human cervical cancer), HaCaT (human skin keratinocytes), HDF (human dermal fibroblasts) and NIH3T3 (murine fibroblasts) cells were frozen at -80 degrees C in culture media with various D-allose concentrations. Cells were allowed to recover for 24 h, 1 week or 1 month prior to survival assessment using the trypan blue dye exclusion test, when cell proliferation was evaluated by MTT assay. A beneficial protective role of D-allose on cell survival was found, similar to that of trehalose (disaccharide of glucose), a recognized cryoprotectant. The results suggest that D-allose as a sole additive may provide effective protection for mammalian cells during freezing. Practical studies now need to be performed with D-allose, for example to determine optimal freezing protocols and explore potential for preservation of tissues or organs at non-freezing temperatures.

Cell partitioning during the directional solidification of trehalose solutions

Previous studies have demonstrated that ice/cell interaction influences post thaw viability and specific cryoprotective agents can affect those interactions. Trehalose, a disaccharide, has been shown to have a protective benefit during conventional slow freezing. Existing theories have been put forth to explain the protective benefit of trehalose during desiccation and vitrification, but these theories do not explain the protective benefit observed during conventional freezing protocols. The overall objective of this investigation was to characterize cell/ice interactions in the presence of trehalose using non-planar freezing conditions. To that end, lymphoblasts suspended in phosphate buffered saline solution with various levels of trehalose (0, 10, 100, and 300 mM) were frozen on a directional solidification stage. The partitioning of cells into the interdendritic space or engulfment by an advancing dendrite was determined as a function of velocity and solution composition. For a given temperature gradient, the fraction of cells entrapped into the interdendritic region increased with increasing velocity. With small additions of trehalose (10 mM), the velocity at which cells were entrapped in the interdendritic region increased. At high trehalose concentrations (100, 300 mM), interface morphology was significantly different and cells were engulfed by the advancing interface. Dehydration of cells in the region shortly before and after the interface was significant and depended upon of the type of interaction experienced by the cell (entrapped vs. engulfed). These studies suggest that one potential mechanism for the action of trehalose involves changing the ice/cell interactions during conventional slow freezing.

Cryopreservation of primary human hepatocytes: the benefit of trehalose as an additional cryoprotective agent

Problems with the limited availability of human hepatocytes for cell transplantation may be overcome by efficient cryopreservation techniques and formation of appropriate cell banking. In this study we investigated the effect of the disaccharide trehalose on the cryopreservation of human hepatocytes. For analysis, liver cells were frozen in culture medium containing 10% dimethyl sulfoxide (DMSO) that was supplemented with varying concentrations of trehalose. During the postthawing culture period, viability, plating efficiency, total protein, cell proliferation, enzyme leakage, albumin and urea formation, as well as phase I and II metabolism were analyzed. In the pilot study, among the concentrations investigated, 0.2 M trehalose showed the best overall outcome. Compared to the use of DMSO alone, we found significant improvement in postthaw cell viability (62.9 +/- 13 vs. 46.9 +/- 11%, P < 0.01) and plating efficiency (41.5 +/- 18 vs. 17.6 +/- 13%, P < 0.01) in the trehalose group. The use of trehalose as an additive for cryopreserving human hepatocytes resulted in a significantly increased total protein level in the attached cells, higher secretion of albumin and a lower aspartate aminotransferase (AST) level after thawing. In conclusion, the use of trehalose as cryoprotective agent significantly improves the outcome of human hepatocyte cryopreservation.

Cryopreservation of hematopoietic and non-hematopoietic stem cells

Recent studies illustrate the potential for improving the cryopreservation of stem cells. Reduced DMSO concentrations in the cryopreservation medium, post thaw washing of cells and increased cell concentration have been actively studied. Standardization of cell processing has led to the study of liquid storage prior to cryopreservation, validation of mechanical (uncontrolled rate freezing) freezing, and cryopreservation bag failure. Finally, the need for the systematic study and optimization of preservation processes has not been fulfilled. As the sources and applications of stem cells (hematopoietic and non-hematopoietic) continue to be developed, the need for effective preservation methods will only grow.

Prevention of apoptosis as a possible mechanism behind improved cryoprotection of hematopoietic cells by catalase and trehalose

BACKGROUND

Our previous in vitro work has shown the usefulness of membrane stabilizers and antioxidants as additives in conventional freezing medium to freeze mouse and human hematopoietic cells. The present work was carried out using murine model to test the in vivo engraftment ability of mouse bone marrow frozen with (test cells) or without (control cells) addition of a combination of trehalose and catalase in the medium containing 10% dimethyl sulfoxide (DMSO).

METHODS

Viability, nucleated cell recovery, and progenitor content of revived cells were measured. Freezing efficacy was tested by in vivo assays like colony forming unit-spleen (CFU-S), pre-CFU-S, and short-term engraftment of frozen marrow in irradiated mice. Long-term engraftment ability of frozen marrow was assessed using a Ly5.1-Ly 5.2 chimera model. Levels of apoptosis and reactive oxygen species (ROS) generated in revived cells were estimated. The former by Annnexin V, TUNEL, and DNA laddering and the latter by DCFH-DA probe.

RESULTS

Our results show that the combination of catalase and trehalose with 10% DMSO improves freezing efficacy not only in terms of viability, cell recovery, and progenitor content but also by in vivo assays like CFU-S, pre-CFU-S, and short- and long-term engraftment. Both the level of apoptosis and ROS generation were considerably reduced in test set as compared to control set.

CONCLUSIONS

We conclude that inclusion of a combination of trehalose and catalase in conventional freezing medium leads to enhanced engraftment potential of cryopreserved mouse bone marrow cells probably by preventing apoptotic cell death. Our observation using animal model may have significant clinical implications.