Cryopreservation of cultured skin cells

Insights on Cryopreserved Sheep Fibroblasts by Cryomicroscopy and Gene Expression Analysis

Cryopreservation includes a set of techniques aimed at storing biological samples and preserving their biochemical and functional features without any significant alterations. This study set out to investigate the effects induced by cryopreservation on cultured sheepskin fibroblasts (CSSF) through cryomicroscopy and gene expression analysis after subsequent in vitro culture. CSSF cells were cryopreserved in a cryomicroscope (CM) or in a straw programmable freezer (SPF) using a similar thermal profile (cooling rate -5°C/min to -120°C, then -150°C/min to -196°C). CSSF volume and intracellular ice formation (IIF) were monitored by a CM, while gene expression levels were investigated by real-time polymerase chain reaction in SPF-cryopreserved cells immediately after thawing (T0) and after 24 or 48 hours (T24, T48) of post-thaw in vitro culture. No significant difference in cell viability was observed at T0 between CM and SPF samples, while both CM and SPF groups showed lower viability (p < 0.05) compared to the untreated control group. Gene expression analysis of cryopreserved CSSF 24 and 48 hours post-thawing showed a significant upregulation of the genes involved in protein folding and antioxidant mechanisms (HPS90b and SOD1), while a transient increase (p < 0.05) in the expression levels of OCT4, BCL2, and GAPDH was detected 24 hours post-thawing. Overall, our data suggest that cryostored CSSF need at least 24 hours to activate specific networks to promote cell readaptation.

Comparison of different cooling rates for fibroblast and keratinocyte cryopreservation

Easy, cost-effective and reliable cryopreservation protocols are crucial for the successful and effective application of tissue engineering. Several different protocols are in use, but no comprehensive comparisons across different machine-based and manual methods have been made. Here, we compare the effects of different cooling rates on the post-thaw survival and proliferative capacity of two basic cell lines for skin tissue engineering fibroblasts and keratinocytes, cultured and frozen in suspension or as a monolayer. We demonstrate that effectiveness of cryopreservation cannot be reliably determined immediately after thawing: the results at this stage were not indicative of cell growth in culture 3 days post-thaw. Cryopreservation of fibroblasts in an adherent state greatly diminishes their subsequent growth potential. This was not observed when freezing in suspension. In keratinocytes, however, adherent freezing is as effective as freezing in suspension, which could lead to significant cost and labour savings in a tissue-engineering environment. The 'optimal' cryopreservation protocol depends on cell type and intended use. Where time, ease and cost are dominant factors, the direct freezing into a nitrogen tank (straight freeze) approach remains a viable method. The most effective solution across the board, as measured by viability 3 days post-thaw, was the commonly used, freezing container method. Where machine-controlled cryopreservation is deemed important for tissue-engineering Good Manufacturing Practice, we present results using a portfolio of different cooling rates, identifying the 'optimal' protocol depending on cell type and culture method. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of different freezing rates during cryopreservation of rat mesenchymal stem cells using combinations of hydroxyethyl starch and dimethylsulfoxide

Background

Mesenchymal stem cells (MSCs) are increasingly used as therapeutic agents as well as research tools in regenerative medicine. Development of technologies which allow storing and banking of MSC with minimal loss of cell viability, differentiation capacity, and function is required for clinical and research applications. Cryopreservation is the most effective way to preserve cells long term, but it involves potentially cytotoxic compounds and processing steps. Here, we investigate the effect of decreasing dimethyl sulfoxide (DMSO) concentrations in cryosolution by substituting with hydroxyethyl starch (HES) of different molecular weights using different freezing rates. Post-thaw viability, phenotype and osteogenic differentiation capacity of MSCs were analysed.

Results

The study confirms that, for rat MSC, cryopreservation effects need to be assessed some time after, rather than immediately after thawing. MSCs cryopreserved with HES maintain their characteristic cell surface marker expression as well as the osteogenic, adipogenic and chondrogenic differentiation potential. HES alone does not provide sufficient cryoprotection for rat MSCs, but provides good cryoprotection in combination with DMSO, permitting the DMSO content to be reduced to 5%. There are indications that such a combination would seem useful not just for the clinical disadvantages of DMSO but also based on a tendency for reduced osteogenic differentiation capacity of rat MSC cryopreserved with high DMSO concentration. HES molecular weight appears to play only a minor role in its capacity to act as a cryopreservation solution for MSC. The use of a ‘straight freeze’ protocol is no less effective in maintaining post-thaw viability of MSC compared to controlled rate freezing methods.

Conclusion

A 5% DMSO / 5% HES solution cryopreservation solution using a ‘straight freeze’ approach can be recommended for rat MSC.

Fibroblast cell line establishment, cryopreservation and interspecies embryos reconstruction in red panda (Ailurus fulgens)

In evolution, the red panda (Ailurus fulgens) plays a pivotal role in the higher level phylogeny of arctoides carnivore mammals. The red panda inhabits certain Asian countries only and its numbers are decreasing. Therefore, the development of feasible ways to preserve this species is necessary. Genetic resource cryopreservation and somatic cell nuclear transfer (SCNT) have been used extensively to rescue this endangered species. The present study describes the establishment, for the first time, of a red panda ear fibroblast cell line, which was then cryopreserved, thawed and cultured. Through micromanipulation, interspecies embryos were reconstructed using the cryopreserved–thawed fibroblasts of the red panda as the donor and rabbit oocytes as recipients. A total of 194 enucleated rabbit oocytes were reconstructed with red panda ear fibroblasts; enucleated oocytes were activated without fusion as the control. The results show that the fibroblast cell line was established successfully by tissue culture and then cryopreserved in liquid nitrogen. Supplementation with 20% fetal bovine serum and 8% dimethyl sulphoxide in basic medium facilitated the cryopreservation. The interspecies embryos were successfully reconstructed. The cleavage, morulae and blastocyst rates after in vitro culture were 71, 47 and 23% (31/194), respectively. This study indicated that a somatic cell line could be established and cryopreserved from red panda and that rabbit cytoplast supports mitotic cleavage of the red panda karyoplasts and is capable of reprogramming the nucleus to achieve blastocysts.

Cryo-injury and biopreservation

Mammalian cells appear to be naturally tolerant to cold temperatures, but the formation of ice when cells are cooled leads to a variety of damaging effects. The study of cryo-injury, therefore, becomes the study of when and how ice is formed both inside and outside the cell during cooling. Protectant chemicals are used to control or prevent ice formation in many preservation protocols, but these chemical themselves tend to be damaging. Cooling and warming rates also strongly affect the amount and location of ice that is formed. Through careful modification of these parameters successful cold preservation techniques for many cell types have been developed, but there are many more cell types that have defied preservation techniques, and the extension of cell-based techniques to tissues and whole organs has been very limited. There are many aspects to the damaging effects of ice in cells that are still poorly understood. In this brief article we review our current understanding of cellular injury and highlight the aspects of cellular injury during cryopreservation that are still poorly understood.

The possibility of long-term cryopreservation of cultured dermal substitute

Allogeneic cultured dermal substitute (CDS) was prepared by cultivating fibroblasts on a two-layered spongy matrix of hyaluronic acid (HA) and atelo-collagen (Col). CDS can be cryopreserved and transported to other hospitals in a frozen state. To evaluate cell viability, cell growth, and release of VEGF after long-term cryopreservation, the CDS was cryopreserved at -85 degrees C or -152 degrees C for a given period. We measured cell viability immediately after thawing and cell growth in CDS that was recultured for 1 week after thawing. In addition, the amount of vascular endothelial growth factor (VEGF) released from CDS that was recultured for 1 week after thawing was measured. The cell viability and cell growth of control CDS that was thawed within 3 weeks after freezing was 56.2% and 132.7%, respectively. The cell viability and cell growth of the CDS that was cryopreserved at -85 degrees C for 6 months was 43.4% and 119.7%, respectively. When cryopreserved at -152 degrees C for 1 year, the cell viability and cell growth was 52.0% and 110.8%, respectively. These values were comparable to those of the control. The amount of VEGF released from CDS cryopreserved at -85 degrees C for 6 months (491.0 pg/mL) or at -152 degrees C for 1 year (586.8 pg/mL) was comparable to that of the control CDS (587.3 pg/mL). In contrast, the amounts of VEGF released from CDS cryopreserved at -85 degrees C for 1 year (322.5 pg/mL) or at -152 degrees C for 2 years (210.8 pg/mL) were low, with a marked decrease in cell viability and cell growth. These findings suggest that CDS cryopreserved at -85 degrees C for 6 months or at -152 degrees C for 1 year maintains sufficient cell viability and the ability to proliferate and release a significant amount of VEGF. The release of VEGF from CDS after long-term cryopreservation is a useful therapeutic effect, and is important for clinical use.

Guidelines on processing and clinical use of skin allografts

Processing methods used for banking of skin for subsequent therapeutic use depend on whether the skin is to retain viability or not. For viable skin grafts, sterilisation techniques cannot be applied, however antibiotics and antimycotics may be used to disinfect the tissue with respect to bacteria and fungi. Nevertheless, strict standards are applied to avoid disease transmission from donor to recipient involving donor medical history, donor testing for viral diseases, aseptic retrieval and processing, and control of storage temperature. Cryopreservation is the preferred method for long term storage of viable skin grafts. If viability is not required, then additional long term preservation methods may be used including deep-freezing, freeze-drying or high concentration solute preservation. All three methods work by reducing water activity. In addition it is possible to apply certain sterilisation techniques that have been shown not to damage the tissue. It is important that sterilisation methods are validated in accordance with precise definitions of sterilisation, and for the initial levels of "bioburden" expected to be present immediately prior to application of the sterilisation method. The application of improved and refined methodologies in accordance with defined standards has ensured improved graft performance while reducing risk to the recipient.

Effects of vitamin E supplementation on intracellular antioxidant enzyme production in adolescents with type 1 diabetes and early microangiopathy

Defective intracellular antioxidant enzyme production (IAP) has been demonstrated in adults with diabetic nephropathy. To evaluate the effects on IAP of vitamin E administration in adolescents with type 1 diabetes and early signs of microangiopathy, 12 adolescents (aged 11-21 y; diabetes duration 10-18) were studied. Eight had retinopathy [background (four), preproliferative (three), or proliferative (one)], four had persistent microalbuminuria, and seven had both. Skin fibroblasts were obtained by biopsies and cultured in Dulbecco's modified Eagle's medium. CuZn superoxide dismutase (SOD), MnSOD, catalase (CAT), and glutathione-peroxidase (GPX) activity and mRNA expression were measured before and after 3 mo of synthetic vitamin E supplementation (600 mg twice daily); on both occasions, IAP was evaluated at different ex vivo glucose concentrations (5 and 22 mM). Ten adolescents with type 1 diabetes (aged 12-20 y) without angiopathy and eight healthy volunteers (aged 15-22 y) participated as control subjects. Vitamin E serum levels were measured throughout the study. In normal glucose concentrations, CuZnSOD, MnSOD, CAT, and GPX activity and mRNA expression were not different among the groups. In high glucose, CuZnSOD activity and mRNA increased similarly in all groups [angiopathics: 0.96 +/- 0.30 U/mg protein; 9.9 +/- 3.2 mRNA/glyceraldehyde-3-phosphate dehydrogenase). CAT and GPX activity and mRNA did not increase in high glucose only in adolescents with angiopathy (0.35 +/- 0.09; 4.2 +/- 0.1 and 0.52 +/- 0.14; 2.4 +/- 0.9, respectively). MnSOD did not change in any group. Vitamin E supplementation had no effect on any enzymatic activity and mRNA in both normal and hyperglycemic conditions. Adolescents with early signs of diabetic angiopathy have defective IAP and activity, which are not modified by vitamin E.

Development of a cultured dermal substitute composed of a spongy matrix of hyaluronic acid and atelo-collagen combined with fibroblasts: cryopreservation

An allogeneic cultured dermal substitute (CDS) was prepared by cultivating fibroblasts on a two-layered spongy matrix of hyaluronic acid (HA) and atelo-collagen (Col). The ability of fibroblasts to secrete cytokines is dependent on the conditions of freezing and thawing. The first experiment was designed to investigate the effects of supplements in a cryoprotective medium, that is, dimethylsulfoxide (DMSO), glycerol, and fetal bovine serum (FBS). In each experiment we measured the cell viability after thawing and the cell growth in CDS recultured after thawing. In addition, the amount of vascular endothelial growth factor (VEGF) released from the CDS recultured for one week after thawing was measured. The highest values of cell viability, cell growth, and the amount of VEGF released were obtained when CDS was frozen in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% DMSO and 40% FBS, and then thawed quickly in a water bath at 37 degrees C. However, due to the high cost of FBS, in clinical applications CDS is usually frozen in DMEM supplemented with 10% DMSO and 20% FBS. In practice, however, physicians often cannot use CDS immediately after thawing, depending on clinical conditions. Therefore, in the second experiment we investigated cell viability at different time points after thawing. In addition, we investigated cell growth and the amount of VEGF released from fibroblasts in CDS at different time points after thawing under different conditions, and after further reculturing for one week. We recommend that CDS be rinsed with lactated Ringer's solution immediately after thawing, and that it be used within 4 h after thawing.

The role of frozen storage in preserving adipose tissue obtained by suction-assisted lipectomy for repeated fat injection procedures

BACKGROUND

The injection of autologous free fat obtained by suction-assisted lipectomy for the correction of soft tissue defects is a common procedure in plastic surgery. However, unpredictable partial absorption of the injected fat often necessitates repeated procedures.

OBJECTIVE

To examine the role of frozen storage as a means of preserving the fat obtained by suction-assisted lipectomy for repeated procedures.

METHODS

Human adipose tissue obtained by suction-assisted lipectomy was stored in a domestic refrigerator at -18 degrees C for 2 weeks. After thawing, the fat was injected into nude mice. In the control group, the fat was injected immediately after the harvesting procedure. Grafts were dissected out and compared 15 weeks postinjection.

RESULTS

Injected fat survived in both study and control groups. No significant differences were found between fat graft weight and volume, or in any of the histologic parameters examined.

CONCLUSION

Fat obtained by suction-assisted lipectomy may be preserved for future use by freezing.

A theoretical model of intracellular devitrification

Devitrification of the intracellular solution can cause significant damage during warming of cells cryopreserved by freezing or vitrification. Whereas previous theoretical investigations of devitrification have not considered the effect of cell dehydration on intracellular ice formation, a new model which couples membrane-limited water transport equations, classical nucleation theory, and diffusion-limited crystal growth theory is presented. The model was used to explore the role of cell dehydration in devitrification of human keratinocytes frozen in the presence of glycerol. Numerical simulations demonstrated that water transport during cooling affects subsequent intracellular ice formation during warming, correctly predicting observations that critical warming rate increases with increasing cooling rate. However, for cells with a membrane transport activation energy less than approximately 50 kJ/mol, devitrification was also affected by cell dehydration during warming, leading to a reversal of the relationship between cooling rate and critical warming rate. Thus, for low warming rates (less than 10 degrees C/min for keratinocytes), the size and total volume fraction of intracellular ice crystals forming during warming decreased with decreasing warming rate, and the critical warming rate decreased with increasing cooling rate. The effects of water transport on the kinetics of intracellular nucleation and crystal growth were elucidated by comparison of simulations of cell warming with simulations of devitrification in H(2)O-NaCl-glycerol droplets of constant size and composition. These studies showed that the rate of intracellular nucleation was less sensitive to cell dehydration than was the crystal growth rate. The theoretical methods presented may be of use for the design and optimization of freeze-thaw protocols.

Variation of the HES concentration for the cryopreservation of keratinocytes in suspensions and in monolayers

It has recently been shown that keratinocytes, both in suspension and in monolayers, can be successfully cryopreserved with hydroxyethyl starch (HES) (6, 9). HES is a nontoxic biodegradable macromolecule which is clinically approved as a plasma expander and which has already been used for the cryopreservation of red blood cells (10, 11). In this study we varied the HES concentration between 0 and 10 wt% in 2% steps for suspended cells and between 0, 4, 6, 8, and 10 wt% for monolayer cells in order to determine the effect on the survival rate and metabolic activity after cryopreservation. The experiments with the suspended cells were performed both with and without NCS. Cryopreserved keratinocytes can be transplanted onto patients for the treatment of deep dermal burns and leg ulcers. In this study, we achieved a survival rate of 80% for the suspended cells (10 wt% HES, 3 degrees C/min) and a survival rate of even 88% when the cells were cryopreserved as a monolayer using the same parameters. The addition of NCS did not improve the results for the suspended cells significantly.

Long-term viability of cryopreserved cultured epithelial grafts

Human cultured epithelial grafts are frozen for long-term preservation. To assess the viability of these stored grafts, their cell survival rate and colony-forming efficiency of grafts cryopreserved at -135 degrees C and at -80 degrees C were followed over time. Flow cytometry showed that the cell survival rate of the grafts cryopreserved at -135 degrees C for 1 month, 6 months and 1 year averaged 89.3%, 61.7% and 61.6%. Cryopreservation at -80 degrees C maintained cell survival rate as well for 1 month, but after 6 months of cryopreservation survival was reduced at -80 degrees C (35.2%) compared with that of -135 degrees C. In histological examination, the cell structure and basal layer were very well preserved after 6 months of storage at -135 degrees C, but not at -80 degrees C. Cell survival rate at -135 degrees C was also assessed by colony-forming efficiency. Colony-forming efficiency of the grafts cryopreserved for 1 month, 6 months and 1 year averaged 66.1%, 58.5% and 55.1% of control (noncryopreserved) grafts. These findings suggest that, even when cultured epithelial grafts are subjected to long-term cryopreservation, cell viability remains sufficient, reculturing is possible, and that graft banking could be used for clinical applications.

Cryopreservation of keratinocytes in a monolayer

The cryopreservation of cells in tissues is one of the major challenges in current cryobiology, especially with regard to the progressively increasing field of tissue engineering. It is very questionable whether protocols which were developed for the cryopreservation of isolated cells are also applicable for cells in more complex structures, such as tissues. As a starting point toward cryopreservation of these three-dimensional structures, the aim of this study was to find an optimum cryopreservation protocol for keratinocytes in a monolayer (two-dimensional structure). These epidermal cells can be transplanted as a monolayer grown on an appropriate matrix for the treatment of deep-dermal burns and leg ulcers. The successful cryopreservation of such transplants would offer the advantage of long-term storage and immediate availability of the transplant. In our study, the variables investigated were the cryoprotective solution and the cooling rate. In order to find a nontoxic cryoprotective agent (CPA) which could be transplanted without an additional washing step, we included hydroxyethyl starch (HES) as a possible CPA in our experimental protocol with the commonly used CPAs Me(2)SO, glycerol, and ethylene glycol. For the evaluation, the cell survival rate was determined by dye exclusion (trypan blue) and the cell metabolism was investigated by cell activity assay (alamarBlue). In conclusion, the cryopreservation protocol with 10 wt.-% HES resulted not only in the highest survival rate (72%) but also in the highest metabolic activity of the cells after thawing; comparable values for the other CPAs were: Me(2)SO, 48%; glycerol, 8%; and ethylene glycol, 10%.

Quality issues in skin banking: a review

Over the last decade the concept of quality in healthcare has gained increasing prominence, not least in the field of skin and tissue banking. This was brought into sharp focus by the appearance of HIV, however, over the decade other viruses have also gained notoriety, e.g. Hepatitis C. The risk of cross infection has been the major factor driving tissue and blood banking towards ever improving standards of quality, which have been reinforced by national legislation and regulations, and professional standards. This has also provided an opportunity to consider other aspects of skin banking that might also affect quality and to offer standards or guidelines to optimise these aspects. The purpose of this review is to highlight these various quality issues in order to allow surgeons to make informed choices and decisions regarding their sources and uses of skin allografts.

Long-term storage of tissues by cryopreservation: critical issues

The technique of cryopreservation (maintenance of biological samples in a state of 'suspended animation' at cryogenic temperatures), its potential use in tissue engineering applications and current obstacles to the development of effective cryopreservation methods for tissues are reviewed. A didactic overview of the principles of cryobiology and the methodology of cryopreservation is given, with emphasis on the processes of injury to cells during freezing and thawing, and how these are related to the physicochemical and biophysical changes occurring during cryopreservation. Critical issues relevant to the application of cryopreservation methods to tissues are then addressed, including heat and mass transfer limitations in these bulk systems, intrinsic differences between isolated and cultured cells, and mechanisms of freezing injury unique to tissue systems.

Expression of differentiation markers in human adult keratinocytes cultured in submerged conditions

A number of studies have shown that human keratinocytes cultured in submerged conditions with non-delipidized serum do not express the major differentiation markers, i.e. 67 kDa keratin, ceramides, and lanosterol. However, they were mostly performed with neonatal or juvenile keratinocytes after a few passages, and not all the markers were analyzed in parallel. In this study, we compared the expression of several differentiation markers in preconfluent and postconfluent adult breast keratinocytes in primary and secondary cultures before and after cryopreservation. When primary cultures reached confluence, the 67 kDa keratin was synthesized, transglutaminase activity was increased, and, although overall lipid synthesis dropped, both lanosterol and free fatty acids contents were augmented. The same pattern was observed in postconfluent subcultures at Passage 2; however decreased overall lipid synthesis was more pronounced. Cryopreservation of keratinocytes just after isolation or after a few days in culture did not result in the loss of expression of these specific epidermic markers. Thus, adult breast keratinocytes in postconfluent submerged cultures represent an in vitro model that possesses various features of the normal epidermis, even after cryopreservation.