Survival of Desiccated Mammalian Cells: Beneficial Effects of Isotonic Media

Molecular simulation on the interaction between trehalose and asymmetric lipid bilayer mimicking the membrane of human red blood cells

Trehalose is widely acknowledged for its ability to stabilize plasma membranes during dehydration. However, the exact mechanism by which trehalose interacts with lipid bilayers remains presently unclear. In this study, we conducted atomistic molecular dynamic simulations on asymmetric model bilayers that mimic the membrane of human red blood cells at various trehalose and water contents. We considered three different hydration levels mimicking the full hydration to desiccation scenarios. Results indicate that the asymmetric distribution of lipids did not significantly influence the computed structural characteristics at full and low hydration. At dehydration, however, the order parameter obtained from the symmetric bilayer is significantly higher compared to those obtained from asymmetric ones. Analysis of hydrogen bonds revealed that the protective ability of trehalose is well described by the water replacement hypothesis at full and low hydration, while at dehydration other interaction mechanisms associated with trehalose exclusion from the bilayer may involve. In addition, we found that trehalose exclusion is not attributed to sugar saturation but rather to the reduction in hydration levels. It can be concluded that the protective effect of trehalose is not only related to the hydration level of the bilayer, but also closely tied to the asymmetric distribution of lipids within each leaflet.

DMSO as new, counterintuitive excipient for freeze-drying human keratinocytes

DMSO is widely used as powerful cryoprotectant for the storage and transport of frozen cells. Beyond this established application of DMSO, we could now show that it has also promising lyoprotectant effects in the field of lyophilisation of therapeutic cells. Freeze-drying of HaCaT keratinocytes in 10% HES, 5% HE and in presence of DMSO led to an increase in cell membrane integrity from 25.3 ± 2.7 % without DMSO to 41.4 ± 4.3 % with 2% DMSO, as determined by trypan blue exclusion. Interruption of the lyophilisation cycle at different sampling points showed a rapid decrease of cell membrane integrity below a critical residual moisture content. DMSO was able to stabilise cell membranes below this moisture level up to a final residual moisture content of less than 1%. Furthermore, DMSO increased the total protein content of cells after freeze-drying and subsequent SDS PAGE analysis indicated that certain abundant proteins were better preserved with the use of DMSO. Owed to its low vapour pressure, a significant part of DMSO is not removed during freeze-drying and remains as plasticiser in the lyophilised cake. However, a T_g above 60°C for 2% DMSO indicates that samples can still be stored at temperatures of 2-8°C. Also, no macroscopic or microscopic collapse can be observed by SEM or BET measurements and DMSO addition leads even to more elegant cakes with reduced cake cracking. With a better preservation of cell membranes and cellular structures, DMSO can contribute to the still unsolved problem of freeze-drying cells of higher complexity.

Current Approaches of Preservation of Cells During (freeze-) Drying

The widespread application of therapeutic cells requires a successful stabilization of cells for the duration of transport and storage. Cryopreservation is currently considered the gold standard for the storage of active cells; however, (freeze-) drying cells could enable higher shelf life stability at ambient temperatures and facilitate easier transport and storage. During (freeze-) drying, freezing, (primary and secondary) drying and also the reconstitution step pose the risk of potential cell damage. To prevent these damaging processes, a wide range of protecting excipients has emerged, which can be classified, according to their chemical affiliation, into sugars, macromolecules, polyols, antioxidants and chelating agents. As many excipients cannot easily permeate the cell membrane, researchers have established various techniques to introduce especially trehalose intracellularly, prior to drying. This review aims to summarize the main damaging mechanisms during (freeze-) drying and to introduce the most common excipients with further details on their stabilizing properties and process approaches for the intracellular loading of excipients. Additionally, we would like to briefly explain recently discovered advantages of drying microorganisms, sperm, platelets, red blood cells, and eukaryotic cells, paying particular attention to the drying technique and residual moisture content.

Dry biobanking as a conservation tool in the Anthropocene

Species are going extinct at an alarming rate, termed by some as the sixth mass extinction event in the history of Earth. Many are the causes for this but in the end, all converge to one entity - humans. Since we are the cause, we also hold the key to making the change. Any change, however, will take time, and for some species this could be too long. While working on possible solutions, we also have the responsibility to buy time for those species on the verge of extinction. Genome resource banks, in the form of cryobanks, where samples are maintained under liquid nitrogen, are already in existence but they come with a host of drawbacks. Biomimicry - innovation inspired by Nature, has been a huge source for ideas. Searching methods that Nature utilizes to preserve biological systems for extended periods of time, we realize that drying rather than freezing is the method of choice. We thus argue here in favor of preserving at least part of the samples from critically endangered species in dry biobanks, a much safer, cost-effective, biobanking approach.

A technique for lyopreservation of Clostridium ljungdahlii in a biocomposite matrix for CO absorption

A system capable of biocatalytic conversion of distributed sources of single carbon gases such as carbon monoxide into hydrocarbons can be highly beneficial for developing commercially viable biotechnology applications in alternative energy. Several anaerobic bacterial strains can be used for such conversion. The anaerobic carbon monoxide-fixing bacteria Clostridium ljungdahlii OTA1 is a model CO assimilating microorganism that currently requires cryogenic temperature for storage of the viable strains. If these organisms can be stabilized and concentrated in thin films in advanced porous materials, it will enable development of high gas fraction, biocomposite absorbers with elevated carbon monoxide (CO) mass transfer rate, that require minimal power input and liquid, and demonstrate elevated substrate consumption rate compared to conventional suspended cell bioreactors. We report development of a technique for dry-stabilization of C. ljungdahlii OTA1 on a paper biocomposite. Bacterial samples coated onto paper were desiccated in the presence of trehalose using convective drying and stored at 4°C. Optimal dryness was ~1g H₂O per gram of dry weight (g_DW). CO uptake directly following biocomposite rehydration steadily increases over time indicating immediate cellular metabolic recovery. A high-resolution Raman microspectroscopic hyperspectral imaging technique was employed to spatially quantify the residual moisture content. We have demonstrated for the first time that convectively dried and stored C. ljungdahlii strains were stabilized in a desiccated state for over 38 days without a loss in CO absorbing reactivity. The Raman hyperspectral imaging technique described here is a non-invasive characterization tool to support development of dry-stabilization techniques for microorganisms on inexpensive porous support materials. The present study successfully extends and implements the principles of dry-stabilization for preservation of strictly anaerobic bacteria as an alternative to lyophilization or spray drying that could enable centralized biocomposite biocatalyst fabrication and decentralized bioprocessing of CO to liquid fuels or chemicals.

Dry Preservation of Spermatozoa: Considerations for Different Species

The current gold standard for sperm preservation is storage at cryogenic temperatures. Dry preservation is an attractive alternative, eliminating the need for ultralow temperatures, reducing storage maintenance costs, and providing logistical flexibility for shipping. Many seeds and anhydrobiotic organisms are able to survive extended periods in a dry state through the accumulation of intracellular sugars and other osmolytes and are capable of returning to normal physiology postrehydration. Using techniques inspired by nature's adaptations, attempts have been made to dehydrate and dry preserve spermatozoa from a variety of species. Most of the anhydrous preservation research performed to date has focused on mouse spermatozoa, with only a small number of studies in nonrodent mammalian species. There is a significant difference between sperm function in rodent and nonrodent mammalian species with respect to centrosomal inheritance. Studies focused on reproductive technologies have demonstrated that in nonrodent species, the centrosome must be preserved to maintain sperm function as the spermatozoon centrosome contributes the dominant nucleating seed, consisting of the proximal centriole surrounded by pericentriolar components, onto which the oocyte's centrosomal material is assembled. Preservation techniques used for mouse sperm may therefore not necessarily be applicable to nonrodent spermatozoa. The range of technologies used to dehydrate sperm and the effect of processing and storage conditions on fertilization and embryogenesis using dried sperm are reviewed in the context of reproductive physiology and cellular morphology in different species.

Resilience of oocyte germinal vesicles to microwave-assisted drying in the domestic cat model

The ability to compact and inject the cat germinal vesicle (GV) into a recipient cytoplast allows exploration of a new fertility preservation strategy that avoids whole oocyte freezing. The objective of the present study was to understand the impact of water loss and storage time on GV DNA integrity. Immature cat oocytes were exposed to 1.5 M trehalose for 10 min before microwave-assisted dehydration for 0, 5, 10, 15, 20, 25, 30, or 40 min. Oocytes then were rehydrated to assess chromatin configuration and the incidence of DNA fragmentation (TUNEL assay). The moisture content progressively decreased (p<0.05) from 1.7 to 0.1 gH2O/gDW over the first 30 min, but did not decrease further (p>0.05) after 40 min. Chromatin configuration was unaffected (p>0.05) over time. The percentage of GVs with DNA fragmentation was unaltered (p>0.05) from 0 to 30 min of treatment (range, 6.1%-12%), but increased (p<0.05) to 32.5% after 40 min. Next, the influence of storage at two different supra-zero temperatures after 30 min of drying was investigated. Oocyte-loaded, microwave-treated filters were individually sealed in Dri-Shield moisture barrier bags and stored at 4°C or ambient temperature for 0 to 8 weeks. Moisture contents gradually decreased (p<0.05) from 0.12 to 0.10 gH2O/gDW after 8 weeks of storage at 4°C or ambient temperature. The percentage of GVs with DNA fragmentation more than doubled (p<0.05) from 0 (14.3%) to 2 days (30.0%-33.0%), but remained stable (p>0.05) thereafter (1 through 4 weeks, 25.0%-35.0%). Collective results demonstrate the feasibility of using microwave processing to dehydrate the mammalian GV to a moisture content that is nonlethal and enables nonfrozen storage, an alternative approach for preserving the maternal genome at cool or ambient temperature.

Dry state preservation of nucleated cells: progress and challenges

Effective stabilization of nucleated cells for dry storage would be a transformative development in the field of cell-based biosensors and biotechnologic devices, as well as regenerative medicine and other areas in which stem cells have clinical utility. Ultimately, the tremendous promise of cell-based products will only be fully realized when stable long-term storage becomes available without the use of liquid nitrogen and bulky, energetically expensive freezers. Significant progress has been made over the last 10 years toward this goal, but obstacles still remain. Loading cells with the protective disaccharide trehalose has been achieved by several different techniques and has been shown to increase cell survival at low water contents. Likewise, the protective effect of heat shock proteins and other compounds have also been explored alone and in combination with trehalose. In some cases, the benefit of these molecules is seen not initially upon rehydration, but over time during cellular recovery. Other considerations, such as inhibiting apoptosis and utilizing isotonic buffer conditions have also provided stepwise increases in cell viability and function following drying and rehydration. In all these cases, however, a low level of residual water is required to achieve viability after rehydration. The most significant remaining challenge is to protect nucleated cells such that this residual water can be safely removed, thus allowing vitrification of intra- and extracellular trehalose and stable dry state storage at room temperature.

Design of novel cell penetrating peptides for the delivery of trehalose into mammalian cells

Stabilization of cells in a desiccated state can significantly simplify the storage and transportation and save expenses for clinical applications. Introduction of the impermeable disaccharide, trehalose, into cells is an important step to improve the desiccation tolerance of cells. In this study, a novel cell penetrating peptide, KRKRWHW, was developed based on molecular simulations. The peptide exhibited little cytotoxicity and high penetrating efficiency into mammalian cells. The cell viability of mouse embryonic fibroblasts (MEFs) after the incubation with various concentrations of KRKRWHW from 0.01mM to 5mM at 37°C for 4h was maintained at around 100%. The peptide was able to penetrate into MEFs within 1h at 37°C with an efficiency of around 90% at 0.1mM. Trehalose, as a cargo coupled with the peptide of KRKRWHW through hydrogen bond and π-π bond, was successfully loaded into the MEFs. This novel peptide provides a novel approach for the delivery of trehalose into mammalian cells.

Late embryogenesis abundant proteins protect human hepatoma cells during acute desiccation

Expression of late embryogenesis abundant (LEA) proteins is highly correlated with desiccation tolerance in anhydrobiotic animals, selected land plants, and bacteria. Genes encoding two LEA proteins, one localized to the cytoplasm/nucleus (AfrLEA2) and one targeted to mitochondria (AfrLEA3m), were stably transfected into human HepG2 cells. A trehalose transporter was used for intracellular loading of this disaccharide. Cells were rapidly and uniformly desiccated to low water content (<0.12 g H(2)O/g dry weight) with a recently developed spin-drying technique. Immediately on rehydration, control cells without LEA proteins or trehalose exhibited 0% membrane integrity, compared with 98% in cells loaded with trehalose and expressing AfrLEA2 or AfrLEA3m; surprisingly, AfrLEA3m without trehalose conferred 94% protection. Cell proliferation across 7 d showed an 18-fold increase for cells dried with AfrLEA3m and trehalose, compared with 27-fold for nondried controls. LEA proteins dramatically enhance desiccation tolerance in mammalian cells and offer the opportunity for engineering biostability in the dried state.

Xeroprotectants for the stabilization of biomaterials

With the advancement of science and technology, it is crucial to have effective preservation methods for the stable long-term storage of biological material (biomaterials). As an alternative to cryopreservation, various techniques have been developed, which are based on the survival mechanism of anhydrobiotic organisms. In this sense, it has been found that the synthesis of xeroprotectants can effectively stabilize biomaterials in a dry state. The most widely studied xeroprotectant is trehalose, which has excellent properties for the stabilization of certain proteins, bacteria, and biological membranes. There have also been attempts to apply trehalose to the stabilization of eukaryotic cells but without conclusive results. Consequently, a xeroprotectant or method that is useful for the stable drying of a particular biomaterial might not necessarily be suitable for another one. This article provides an overview of recent advances in the use of new techniques to stabilize biomaterials and compare xeroprotectants with other more standard methods.

Trehalose transporter from African chironomid larvae improves desiccation tolerance of Chinese hamster ovary cells

Dry preservation has been explored as an energy-efficient alternative to cryopreservation, but the high sensitivity of mammalian cells to desiccation stress has been one of the major hurdles in storing cells in the desiccated state. An important strategy to reduce desiccation sensitivity involves use of the disaccharide trehalose. Trehalose is known to improve desiccation tolerance in mammalian cells when present on both sides of the cell membrane. Because trehalose is membrane impermeant the development of desiccation strategies involving this promising sugar is hindered. We explored the potential of using a high-capacity trehalose transporter (TRET1) from the African chironomid Polypedilum vanderplanki[21] to introduce trehalose into the cytoplasm of mammalian cells and thereby increase desiccation tolerance. When Chinese hamster ovary cells (CHO) were stably transfected with TRET1 (CHO-TRET1 cells) and incubated with 0.4M trehalose for 4h at 37°C, a sevenfold increase in trehalose uptake was observed compared to the wild-type CHO cells. Following trehalose loading, desiccation tolerance was investigated by evaporative drying of cells at 14% relative humidity. After desiccation to 2.60g of water per gram dry weight, a 170% increase in viability and a 400% increase in growth (after 7days) was observed for CHO-TRET1 relative to control CHO cells. Our results demonstrate the beneficial effect of intracellular trehalose for imparting tolerance to partial desiccation.

Cryopreservation of spin-dried mammalian cells

This study reports an alternative approach to achieve vitrification where cells are pre-desiccated prior to cooling to cryogenic temperatures for storage. Chinese Hamster Ovary (CHO) cells suspended in a trehalose solution were rapidly and uniformly desiccated to a low moisture content (<0.12 g of water per g of dry weight) using a spin-drying technique. Trehalose was also introduced into the cells using a high-capacity trehalose transporter (TRET1). Fourier Transform Infrared Spectroscopy (FTIR) was used to examine the uniformity of water concentration distribution in the spin-dried samples. 62% of the cells were shown to survive spin-drying in the presence of trehalose following immediate rehydration. The spin-dried samples were stored in liquid nitrogen (LN(2)) at a vitrified state. It was shown that following re-warming to room temperature and re-hydration with a fully complemented cell culture medium, 51% of the spin-dried and vitrified cells survived and demonstrated normal growth characteristics. Spin-drying is a novel strategy that can be used to improve cryopreservation outcome by promoting rapid vitrification.

Rhesus macaque blastocysts resulting from intracytoplasmic sperm injection of vacuum-dried spermatozoa

BACKGROUND

Sperm desiccation is an attractive approach for sperm preservation. In this study, we examined the feasibility and efficiency of intracytoplasmic sperm injection using vacuum-dried rhesus macaque sperm in CZB medium supplemented with 10% fetal bovine serum.

METHODS

A total of 109 MII oocytes were injected with 69 fresh ejaculated sperm and 40 vacuum-dried sperm.

RESULTS

Cleavage occurred in 97% of oocytes injected with fresh, motile sperm and in 88% of oocytes injected with vacuum-dried sperm. Of the cleaved oocytes, 68% fresh sperm-injected oocytes and 74% of dried sperm-injected oocytes developed to the compact morula stage. Blastocyst development was comparable between fresh-injected (16%) and vacuum-dried-injected (17%) oocytes. Differences between treatment groups were not significant. Transmission electron microscopic observation of the blastocysts indicated no detectable differences between fresh sperm and dried sperm-derived embryos.

CONCLUSIONS

We conclude that vacuum-dried rhesus macaque sperm are capable of inducing fertilization and development of pre-implantation embryos when sperm were dried under vacuum and microinjected into normal viable oocytes.

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.

Naturally occurring and stress induced tubular structures from mammalian cells, a survival mechanism

Background

Tubular shaped mammalian cells in response to dehydration have not been previously reported. This may be due to the invisibility of these cells in aqueous solution, and because sugars and salts added to the cell culture for manipulation of the osmotic conditions inhibit transformation of normal cells into tubular shaped structures.

Results

We report the transformation of normal spherical mammalian cells into tubular shaped structures in response to stress. We have termed these transformed structures 'straw cells' which we have associated with a variety of human tissue types, including fresh, post mortem and frozen lung, liver, skin, and heart. We have also documented the presence of straw cells in bovine brain and prostate tissues of mice. The number of straw cells in heart, lung tissues, and collapsed straw cells in urine increases with the age of the mammal. Straw cells were also reproduced in vitro from human cancer cells (THP1, CACO2, and MCF7) and mouse stem cells (D1 and adipose D1) by dehydrating cultured cells. The tubular center of the straw cells is much smaller than the original cell; houses condensed organelles and have filamentous extensions that are covered with microscopic hair-like structures and circular openings. When rehydrated, the filaments uptake water rapidly. The straw cell walls, have a range of 120 nm to 200 nm and are composed of sulfated-glucose polymers and glycosylated acidic proteins. The transformation from normal cell to straw cells takes 5 to 8 hr in open-air. This process is characterized by an increase in metabolic activity. When rehydrated, the straw cells regain their normal spherical shape and begin to divide in 10 to 15 days. Like various types of microbial spores, straw cells are resistant to harsh environmental conditions such as UV-C radiation.

Conclusion

Straw cells are specialized cellular structures and not artifacts from spontaneous polymerization, which are generated in response to stress conditions, like dehydration. The disintegrative, mobile, disruptive and ubiquitous nature of straw cells makes this a possible physiological process that may be involved in human health, longevity, and various types of diseases such as cancer.

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.

Desiccation Response of Mammalian Cells: Anhydrosignaling

Dehydration through evaporation, or air drying, is expected to have both similarities and differences to osmostress. Both stresses involve water loss, but the degree of dehydration will ultimately be more severe during desiccation. Despite the severity of desiccation stress, there are examples of organisms that can survive almost complete water loss, including resurrection plants and plant seeds, certain invertebrates among the nematodes, brine shrimps, tardigrades and bdelloid rotifers, and many microorganisms, including bakers' yeast. During desiccation, these organisms enter a state of suspended animation, a process known as anhydrobiosis ("life without water"). For other organisms, desiccation is lethal, but there is considerable interest in using what is known about anhydrobiosis to confer desiccation tolerance on sensitive cell types, such as mammalian cells. Success with this approach, which we have termed anhydrobiotic engineering, will require a more complete knowledge of the mechanisms of desiccation tolerance and the sensing and response of nontolerant organisms to extreme dehydration. With this goal in mind, we have attempted to characterize the response of human tissue culture cells to desiccation and to compare this response with osmotic upshift. This chapter describes some of the methods used to begin to uncover the response to evaporative water loss in human cell cultures.

Engineering complex tissues

This article summarizes the views expressed at the third session of the workshop "Tissue Engineering--The Next Generation," which was devoted to the engineering of complex tissue structures. Antonios Mikos described the engineering of complex oral and craniofacial tissues as a "guided interplay" between biomaterial scaffolds, growth factors, and local cell populations toward the restoration of the original architecture and function of complex tissues. Susan Herring, reviewing osteogenesis and vasculogenesis, explained that the vascular arrangement precedes and dictates the architecture of the new bone, and proposed that engineering of osseous tissues might benefit from preconstruction of an appropriate vasculature. Jennifer Elisseeff explored the formation of complex tissue structures based on the example of stratified cartilage engineered using stem cells and hydrogels. Helen Lu discussed engineering of tissue interfaces, a problem critical for biological fixation of tendons and ligaments, and the development of a new generation of fixation devices. Rita Kandel discussed the challenges related to the re-creation of the cartilage-bone interface, in the context of tissue engineered joint repair. Frederick Schoen emphasized, in the context of heart valve engineering, the need for including the requirements derived from "adult biology" of tissue remodeling and establishing reliable early predictors of success or failure of tissue engineered implants. Mehmet Toner presented a review of biopreservation techniques and stressed that a new breakthrough in this field may be necessary to meet all the needs of tissue engineering. David Mooney described systems providing temporal and spatial regulation of growth factor availability, which may find utility in virtually all tissue engineering and regeneration applications, including directed in vitro and in vivo vascularization of tissues. Anthony Atala offered a clinician's perspective for functional tissue regeneration, and discussed new biomaterials that can be used to develop new regenerative technologies.

Moisture sorption characteristics and thermophysical properties of trehalose-PBS mixtures

The goal of the study was to quantify the thermophysical properties and the moisture sorption characteristics of the trehalose-PBS (phosphate-buffered saline) from the desiccation preservation perspective. A moisture sorption study was undertaken to determine the desorption isotherms of the trehalose-PBS mixtures. The Brunauer, Emmett, and Teller (BET)-equation and the Guggenheim, Anderson, and de Boer equation were used to quantify the desorption data. The glass transition temperature of the mixtures of trehalose-PBS, equilibrated at different relative humidities was studied using a differential scanning calorimeter. Fourier transform infrared spectroscopy was used to study the molecular interaction between the trehalose and PBS mixtures. The results showed that the addition of PBS to the trehalose mixture causes a shift from the type II isotherm to a type III isotherm (characterized by BET equation) which may have detrimental effect on cell desiccation. The results showed that an increase in PBS mass fraction in the trehalose-PBS mixture causes a decrease in the glass transition temperature (Tg) of the mixture and also a decrease in the hydrogen bonding capacity of the trehalose glasses. The addition of PBS to trehalose posed some challenges and should be subject to further optimization to use it in desiccation preservation of biologics.

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.

Forced and natural convective drying of trehalose/water thin films: implication in the desiccation preservation of Mammalian cells

Trehalose is believed to offer desiccation protection to mammalian cells by forming stable glassy matrices. The goal of the current study was to explore the desiccation kinetics of thin films of trehalose-water solution under forced and natural convective conditions and to investigate the thermophysical state of mammalian cells at the bottom of the thin film. We developed a finite difference model based on the mass and energy conservation equations coupled to the water transport model from the cells. The boundary conditions were obtained from correlations or experimental measurements and the Gordon-Taylor equation was used to predict the glass transition temperature at every location. Results indicated that there are three distinct regimes for drying for both forced and natural convection, characterized by the slope of the moisture content plot as a function of time. Our results also indicate that the surface of the solution reached the glassy state in less than 10 min for the Reynolds (forced) numbers explored and approximately 30 min for some Rayleigh (natural convective) numbers; however, significant water was trapped at this instant. Larger drying force hastened quicker glass formation but trapped more water. The numerical model was capable of predicting the drying kinetics for the dilute region accurately, but deviated while predicting the other regimes. Based on these experimental validations of the model, the osmotic response of different cells located at the bottom of the solution with orders of magnitude difference in their membrane permeability (Lp) was predicted. The results suggested that extracellular glass formed around cells at the bottom of a trehalose-water solution by the propagation of glass into the solution; however it takes more than an order of magnitude time (approximately 7 min to >100 min for forced convective drying) to remove sufficient water to form glass around cells from the time when the first surface glass is formed. This is attributed to low diffusivity of water through the glass. In addition, the water transport from the glassy matrix could be either diffusion or Lp limited. For diffusion-limited transport, lowering the film thickness at the beginning of drying by half almost lowers the drying time by an order of magnitude. In summary, the optimal design of convective desiccation protocols requires accounting for the size of the cell, their membrane permeability (Lp) and the starting thickness of the solution.

Dry storage of sperm: applications in primates and domestic animals

Cryopreservation of spermatozoa, oocytes and embryos, as well as somatic cells or cell lines for cloning from cells, are all options for the long-term storage of unique genotypes and endangered species. Spermatozoal cryopreservation and storage currently require liquid nitrogen or ultralow refrigeration-based methods for long- or short-term storage, which requires routine maintenance and extensive space requirements. The preservation of stem cells also has strict requirements for long-term storage to maintain genetic integrity. Dessicated (lyopreserved) sperm and stem cells will provide an unprecedented type of long-term storage without the need for expensive and burdensome cryogenic conditions. Experiments were conducted to determine an effective intracellular concentration of the lyoprotectant trehalose. High-pressure liquid chromatography studies revealed that trehalose can be incorporated into mature sperm cells as well as spermatogonial stem cells from rhesus monkeys. In addition, using fourier transform infrared spectroscopy, we determined that thermotropic phase transitions for fresh ejaculates from rhesus monkey and stallion sperm occurred at 10-15, 33-37 and 55-59 degrees C. Preliminary studies in our laboratory have indicated that spermatogonial stem cells can be dried to <3 g g(-1) water and maintain viability following rehydration. Studies in our laboratory have provided preliminary results suggesting that the desiccated storage of sperm and spermatogonial stem cells may be a viable alternative to conventional cryopreservation.

Trehalose uptake through P2X7 purinergic channels provides dehydration protection

The tetra-anionic form of ATP (ATP4-) is known to induce monovalent and divalent ion fluxes in cells that express purinergic P2X7 receptors and with sustained application of ATP it has been shown that dyes as large as 831 Da can permeate the cell membrane. The current study explores the kinetics of loading alpha,alpha-trehalose (342 Da) into ATP stimulated J774.A1 cells, which are known to express the purinergic P2X7 receptor. Cells that were incubated at 37 degrees C in a 50 mM phosphate buffer (pH 7.0) containing 225 mM trehalose and 5 mM ATP, were shown to load trehalose linearly over time. Concentrations of approximately 50 mM were reached within 90 min of incubation. Cells incubated in the same solution at 4 degrees C loaded minimally, consistent with the inactivity of the receptor at low temperatures. However, extended incubation at 37 degrees C (>60 min) resulted in zero next-day survival, with adverse effects appearing even with incubation periods as short as 30 min. By using a two-step protocol with a short time period at 37 degrees C to allow pore formation, followed by an extended loading period on ice, cells could be loaded with up to 50 mM trehalose while maintaining good next day recovery (49 +/- 12% by Trypan blue exclusion, 56 +/- 20% by alamarBlue assay). Cells porated by this method and allowed an overnight recovery period exhibited improved dehydration tolerance suggesting a role for ATP poration in the anhydrous preservation of cells.

Biopreservation of red blood cells: past, present, and future

Preservation and long-term storage of red blood cells (RBCs) is needed to ensure a readily available, safe blood supply for transfusion medicine. Effective preservation procedures are required at various steps in the production of a RBC product including testing, inventory, quality control, and product distribution. Biopreservation is the process of maintaining the integrity and functionality of cells held outside the native environment for extended storage times. The biopreservation of RBCs for clinical use can be categorized based on the techniques used to achieve biologic stability and ensure a viable state after long-term storage. This paper will review the history, science, current practices, and emerging technologies of current RBC biopreservation approaches: hypothermic storage, cryopreservation, and lyophilization.

A small stress protein acts synergistically with trehalose to confer desiccation tolerance on mammalian cells

The ability to desiccate mammalian cells while maintaining a high degree of viability would be very important in many areas of biological science, including tissue engineering, cell transplantation, and biosensor technologies. Certain proteins and sugars found in animals capable of surviving desiccation might aid this process. We report here that human embryonic kidney (293H) cells transfected with the gene for the stress protein p26 from Artemia and loaded with trehalose showed a sharp increase in survival during air-drying. Further, we find vacuum-drying greatly improved the ability of the cells to survive, and that the physical shape and structure of the cellular sample had a large influence on recovery following rehydration. Cells suspended in a rounded droplet survived desiccation markedly better than those spread as a thin film. Finally, we used alamarBlue to monitor cellular metabolism and Hema 3 to assess colony formation after vacuum-drying. AlamarBlue fluorescence indicated that the transfected 293H cells expressing p26 (E11'L) grew much better than the control 293H cells. In fact, immediate survival and colony formation in E11'L cells increased as much as 34-fold compared with control cells when the samples were dried to a water content of 0.2 g H2O/g dry weight, as measured by gravimetric analysis. These results indicate that p26 improves cell survival following drying and rehydration, and suggest that dry storage of mammalian cells is a likely possibility in the future.

Functional engineered channels and pores (Review)

Significant progress has been made in membrane protein engineering over the last 5 years, based largely on the re-design of existing scaffolds. Engineering techniques that have been employed include direct genetic engineering, both covalent and non-covalent modification, unnatural amino acid mutagenesis and total synthesis aided by chemical ligation of unprotected fragments. Combinatorial mutagenesis and directed evolution remain, by contrast, underemployed. Techniques for assembling and purifying heteromeric multisubunit pores have been improved. Progress in the de novo design of channels and pores has been slower. But, we are at the beginning of a new era in membrane protein engineering based on the accelerating acquisition of structural information, a better understanding of molecular motion in membrane proteins, technical improvements in membrane protein refolding and the application of computational approaches developed for soluble proteins. In addition, the next 5 years should see further advances in the applications of engineered channels and pores, notably in therapeutics and sensor technology.

Prediction of the glass transition temperature of water solutions: comparison of different models

The glass transition temperature (Tg) of a sample is an important parameter that determines its stability during storage. While Tg can be measured by a variety of methods, it is a time-consuming procedure, especially if the sample is to be kept at subzero temperatures, in anhydrous conditions, or if sampling a portion of the specimen for analysis is cumbersome. Hence, predicting rather than directly measuring Tg as a function of the content of the constituents of a blend, mixture, or solution can be a powerful tool. Two main models for predicting Tg have been proposed: Couchman-Karasz (C-K) and Gordon-Taylor (G-T) formalisms. However, many aspects of both are theoretical/terminological in nature, and substantial controversy exists about the various experimental approaches to measuring Tg as well. Here, we compare C-K and G-T formalisms, as well as related problems that arise from the variety of definitions and methods of measuring Tg. Water-trehalose solutions are used as an example for application of the analysis. However, the same conclusions can be expanded to any other solutions so thermodynamical parameters (Tg, DeltaCp, and k) of 20 other commonly used solutes are provided. Practical pitfalls related to determining water content, including experimental data on thermal gravimetry, are also discussed.

Measurement of trehalose loading of mammalian cells porated with a metal-actuated switchable pore

Efforts to improve the tolerance of mammalian cells to desiccation have focused on the role that sugars have in protecting cells from lethal injury. Among the key determinants of desiccation tolerance is the intracellular trehalose concentration, and thus quantifying the amount and rate of trehalose accumulation has now become very critical to the success of these desiccation approaches. We introduced trehalose into 3T3 fibroblasts, human keratinocytes, and rat hepatocytes using a genetically engineered mutant of the pore-forming alpha-hemolysin from Staphylococcus aureus. Manipulating the extracellular Zn(2+) concentration selectively opens and closes this pore ( approximately 2 nm) and enables controlled loading of cells with sugars. We quantified intracellular trehalose using gas chromatography-mass spectroscopy (GC-MS) to examine the trimethylsilyl derivative of intracellular trehalose. Using the GC-MS method, we demonstrate that the switchable characteristics of H5 alpha-hemolysin permit controlled loading of the high concentrations of trehalose (up to 0.5 M) necessary for engineering desiccation tolerance in mammalian cells.