Damages and stress responses in sperm cells and other germplasms during dehydration and storage at nonfreezing temperatures for fertility preservation

Long-term preservation of sperm, oocytes, and gonadal tissues at ambient temperatures has the potential to lower the costs and simplify biobanking in human reproductive medicine, as well as for the management of animal populations. Over the past decades, different dehydration protocols and long-term storage solutions at nonfreezing temperatures have been explored, mainly for mammalian sperm cells. Oocytes and gonadal tissues are more challenging to dehydrate so little to no progress have been made. Currently, the detrimental effects of the drying process itself are better characterized than the impact of long-term storage at nonfreezing temperatures. While structural and functional properties of germ cells can be preserved after dehydration, a long list of damages and stresses in nuclei, organelles, and cytoplasmic membranes have been reported and sometimes mitigated. Characterizing those damages and better understanding the response of germ cells and tissues to the stress of dehydration is fundamental. It will contribute to the development of optimal protocols while proving the safety of alternative storage options for fertility preservation. The objective of this review is to (1) document the types of damages and stress responses, as well as their mitigation in cells dried with different techniques, and (2) propose new research directions.

Long-term and short-term preservation strategies for tissue engineering and regenerative medicine products: state of the art and emerging trends

There is an ever-growing need of human tissues and organs for transplantation. However, the availability of such tissues and organs is insufficient by a large margin, which is a huge medical and societal problem. Tissue engineering and regenerative medicine (TERM) represent potential solutions to this issue and have therefore been attracting increased interest from researchers and clinicians alike. But the successful large-scale clinical deployment of TERM products critically depends on the development of efficient preservation methodologies. The existing preservation approaches such as slow freezing, vitrification, dry state preservation, and hypothermic and normothermic storage all have issues that somehow limit the biomedical applications of TERM products. In this review, the principles and application of these approaches will be summarized, highlighting their advantages and limitations in the context of TERM products preservation.

Desiccated cat spermatozoa retain DNA integrity and developmental potential after prolonged storage and shipping at non-cryogenic temperatures

PURPOSE

To evaluate the DNA integrity and developmental potential of microwave-dehydrated cat spermatozoa after storage at - 20 °C for different time periods and/or overnight shipping on dry ice.

METHODS

Epididymal spermatozoa from domestic cats were microwave-dehydrated on coverslips after trehalose exposure. Dried samples were either assessed immediately, stored for various duration at - 20 °C, or shipped internationally on dry ice before continued storage. Dry-stored spermatozoa were rehydrated before assessing DNA integrity (TUNEL assays) or developmental potential (injection into in vitro matured oocytes followed by in vitro embryo culture for up to 7 days).

RESULTS

Percentages of dried-rehydrated spermatozoa with intact DNA was not significantly affected (P > 0.05) by desiccation and short-term storage (range, 78.9 to 80.0%) but decreased (P < 0.05) with storage over 5 months (range, 71.0 to 75.2%) compared to fresh controls (92.6 ± 2.2%). After oocyte injection with fresh or dried-rehydrated spermatozoa (regardless of storage time), percentages of activation, pronuclear formation, and embryo development were similar (P > 0.05). Importantly, spermatozoa shipped internationally also retained the ability to support embryo development up to the morula stage.

CONCLUSION

Results demonstrated the possibility to sustain DNA integrity and developmental potential of spermatozoa by dry-preservation, even after long-term storage and long-distance shipment at non-cryogenic temperatures. While further studies are warranted, present results demonstrate that dry preservation can be a reliable approach for simple and cost-effective sperm biobanking or shipment.

Concise Review: Considering Optimal Temperature for Short-Term Storage of Epithelial Cells

Transplantation of novel tissue-engineered products using cultured epithelial cells is gaining significant interest. While such treatments can readily be provided at centralized medical centers, delivery to patients at geographically remote locations requires the establishment of suitable storage protocols. One important aspect of storage technology is temperature. This paper reviews storage temperature for above-freezing point storage of human epithelial cells for regenerative medicine purposes. The literature search uncovered publications on epidermal cells, retinal pigment epithelial cells, conjunctival epithelial cells, corneal/limbal epithelial cells, oral keratinocytes, and seminiferous epithelial cells. The following general patterns were noted: (1) Several studies across different cell types inclined toward 4 and 16°C being suitable short-term storage temperatures. Correspondingly, almost all studies investigating 37°C concluded that this storage temperature was suboptimal. (2) Cell death typically escalates rapidly following 7–10 days of storage. (3) The importance of the type of storage medium and its composition was highlighted by some of the studies; however, the relative importance of storage medium vs. storage temperature has not been investigated systematically. Although a direct comparison between the included investigations is not reasonable due to differences in cell types, storage media, and storage duration, this review provides an overview, summarizing the work carried out on each cell type during the past two decades.

Microwave- and Laser-Assisted Drying for the Anhydrous Preservation of Biologics

Dry preservation has become an attractive approach for the long-term storage of biologics. By removing water from the matrix to solidify the sample, refrigeration needs are reduced, and thus storage costs are minimized and shipping logistics greatly simplified. This chapter describes two energy deposition technologies, namely, microwave and laser systems, that have recently been used to enhance the rate and nature of solution densification for the purpose of anhydrous preservation of feline oocytes, sperm, and egg white lysozyme in trehalose glass. Several physical screening methodologies used to determine the suitability of an amorphous matrix for biopreservation are also introduced in this chapter.

Technologies and Applications Toward Preservation of Cells in a Dry State for Therapies

Cell-based therapeutics promise to transform the treatment of a wide range of diseases, many of which, up to this point, are incurable. During the past decade, an increasing number of cell therapies have been approved by government regulatory agencies in the United States, Europe, and Japan. Thousands of clinical trials based on live cell therapies are now taking place around the world. But most of these live cell therapies face temporal and/or spatial distances between manufacture and administration, posing a risk of degradation in potency. Cryopreservation has become the predominant biobanking approach to maintain the product's safety and efficacy during transportation and storage. However, the necessity of cryogenic shipment and storage could limit patient access to these emerging therapies and increase the costs of logistics. In the (bio)pharmaceutical industries, freeze-drying and desiccation are established preservation procedures for manufacturing small molecule drugs, liposomes, and monoclonal antibodies. Over the past two decades, there has been a growing body of research exploring the freeze-drying or drying of mammalian cells, with varying degrees of success. This article provides an overview of the technologies that were adopted or developed in these pioneering studies, paving the road toward the preservation of cell-based therapeutics in a dry state for biomanufacturing.

Preserving the Female Genome in Trehalose Glass at Supra-Zero Temperatures: The Relationship Between Moisture Content and DNA Damage in Feline Germinal Vesicles

Introduction

Maintaining a stable dry state is critical for long-term preservation of live biomaterials at suprazero temperatures. The objective of the study was to characterize the effect of moisture content on DNA integrity within the germinal vesicle (GV) of feline oocytes following dehydration and storage at 22-24 °C.

Methods

Using microwave-assisted drying, conditions that led to a predictable and stable moisture content in trehalose solutions were determined. To explore moisture content stability during storage, trehalose samples were dried for 15 min and stored in glass vials at 11 or 43% RH for 8 weeks. To examine whether this condition allowed proper storage of GVs, permeabilized cat oocytes were incubated in trehalose for 10 min and dried for 15 or 30 min. Oocytes then were rehydrated to assess DNA integrity either directly after drying or after 8 weeks of storage in an 11% RH environment. Raman spectroscopy was used to identify the states of dried samples during storage.

Results

Moisture content was stable during the storage period. There was no significant difference in DNA integrity between fresh and dried samples without storage. After 8 weeks of storage, DNA integrity was maintained in GVs dried for 30 min. Samples dried for 15 min and stored were compromised, suggesting crystallization of the preservation matrix during storage. Biostabilization was optimal when samples were directly processed to moisture contents consistent with storage in the glassy state.

Conclusion

Microwave-assisted drying processing and storage conditions were optimized to ensure stable long-term storage of structural and functional properties of genetic resources.

Light-assisted drying for anhydrous preservation of biological samples: optical characterization of the trehalose preservation matrix

Protein-based drugs have been developed to treat a variety of conditions and assays use immobilized capture proteins for disease detection. Freeze-drying is currently the standard for the preservation of proteins, but this method is expensive and requires lengthy processing times. Anhydrous preservation in a trehalose amorphous solid matrix offers a promising alternative to freeze-drying. Light assisted drying (LAD) is a processing method to create an amorphous trehalose matrix. Proteins suspended in a trehalose solution are dehydrated using near-infrared laser light. The laser radiation accelerates drying and as water is removed the trehalose forms a protective matrix. In this work, LAD samples are characterized to determine the crystallization kinetics of the trehalose after LAD processing and the distribution of amorphous trehalose in the samples. These characteristics influence the long-term stability of the samples. Polarized light imaging revealed that LAD processed samples are stable against crystallization during low-humidity storage at room temperature. Scanning white light interferometry and Raman spectroscopy indicated that trehalose was present across samples in an amorphous form. In addition, differential scanning microcalorimetry was used to measure the thermodynamic characteristics of the protein lysozyme after LAD processing. These results demonstrate that LAD does not change the properties of this protein.

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.

Development of a surface tension mediated technique for dry stabilization of mammalian cells

Dry state preservation at ambient temperatures (lyopreservation) is a biomimetic alternative to low temperature stabilization (cryopreservation) of biological materials. Lyopreservation is hypothesized to rely upon the creation of a glassy environment, which is commonly observed in desiccation-tolerant organisms. Non-uniformities in dried samples have been indicated as one of the reasons for instability in storage outcome. The current study presents a simple, fast, and uniform surface tension based technique that can be implemented for lyopreservation of mammalian cells. The technique involves withdrawing cells attached to rigid substrates to be submerged in a solution of lyoprotectant and then withdrawing the samples at a specific rate to an inert environment. This creates a uniform thin film of desiccated lyoprotectant due to sudden change of surface tension. The residual moisture contents at different locations in the desiccated film was quantified using a spatially resolved Raman microspectroscopy technique. Post-desiccation cellular viability and growth are quantified using fluorescent microscopy and dye exclusion assays. Cellular injury following desiccation is evaluated by bioenergetic quantification of metabolic functions using extracellular flux analysis and by a Raman microspectroscopic analysis of change in membrane structure. The technique developed here addresses an important bottleneck of lyoprocessing which requires the fast and uniform desiccation of cellular samples.

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.

Synergistic Development of Biochips and Cell Preservation Methodologies: A Tale of Converging Technologies

PURPOSE OF THE REVIEW

Over the past several decades, cryopreservation has been widely used to preserve cells during long term storage, but advances in stem cell therapies, regenerative medicine, and miniaturized cell-based diagnostics and sensors are providing new targets of opportunity for advancing preservation methodologies. The advent of microfluidics-based devices is an interesting case in which the technology has been used to improve preservation processing, but as the devices have evolved to also include cells, tissues, and simulated organs as part of the architecture, the biochip itself is a desirable target for preservation. In this review, we will focus on the synergistic co-development of preservation methods and biochip technologies, while identifying where the challenges and opportunities lie in developing methods to place on-chip biologics on the shelf, ready for use.

RECENT FINDINGS

Emerging studies are demonstrating that the cost of some biochips have been reduced to the extent that they will have high utility in point-of-care settings, especially in low resource environments where diagnostic capabilities are limited. Ice-free low temperature vitrification and anhydrous vitrification technologies will likely emerge as the preferred strategy for long-term preservation of bio-chips.

SUMMARY

The development of preservation methodologies for partially or fully assembled biochips would enable the widespread distribution of these technologies and enhance their application.

Effects of Water on Structure and Dynamics of Trehalose Glasses at Low Water Contents and its Relationship to Preservation Outcomes

Dry preservation of biologics in sugar glasses is regarded as a promising alternative to conventional cryopreservation. Evidence from various studies has suggested that there is a critical range of water content beyond which the viability of preserved biologics can be greatly compromised. In this study the viability of T-cells was determined as a function of end water content after microwave-assisted drying in trehalose solutions. Hydrogen-bonding and clustering phenomena in trehalose solutions of the same moisture content were also evaluated using molecular dynamics simulation. Post-rehydration viability decreased dramatically within the range of 0.1-1 gH2O/gdw. Molecular modeling revealed that as the water content approached 0.1 gH2O/gdw the matrix formed a large interconnected trehalose skeleton with a minimal number of bound water molecules scattered in the bulk. The diffusion coefficients of trehalose oxygen atoms most distant from the glycosidic linkage fluctuated around 7.5 × 10(-14) m(2)/s within the range of 0.02-0.1 gH2O/gdw and increased again to ~1.13 × 10(-13) m(2)/s at 0.01 gH2O/gdw and below due to the loss of water in the free volume between trehalose molecules. These insights can guide the optimal selection of final moisture contents to advance dry preservation methods.

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.

Advancing microwave technology for dehydration processing of biologics

Our prior work has shown that microwave processing can be effective as a method for dehydrating cell-based suspensions in preparation for anhydrous storage, yielding homogenous samples with predictable and reproducible drying times. In the current work an optimized microwave-based drying process was developed that expands upon this previous proof-of-concept. Utilization of a commercial microwave (CEM SAM 255, Matthews, NC) enabled continuous drying at variable low power settings. A new turntable was manufactured from Ultra High Molecular Weight Polyethylene (UHMW-PE; Grainger, Lake Forest, IL) to provide for drying of up to 12 samples at a time. The new process enabled rapid and simultaneous drying of multiple samples in containment devices suitable for long-term storage and aseptic rehydration of the sample. To determine sample repeatability and consistency of drying within the microwave cavity, a concentration series of aqueous trehalose solutions were dried for specific intervals and water content assessed using Karl Fischer Titration at the end of each processing period. Samples were dried on Whatman S-14 conjugate release filters (Whatman, Maidestone, UK), a glass fiber membrane used currently in clinical laboratories. The filters were cut to size for use in a 13 mm Swinnex(®) syringe filter holder (Millipore(™), Billerica, MA). Samples of 40 μL volume could be dehydrated to the equilibrium moisture content by continuous processing at 20% with excellent sample-to-sample repeatability. The microwave-assisted procedure enabled high throughput, repeatable drying of multiple samples, in a manner easily adaptable for drying a wide array of biological samples. Depending on the tolerance for sample heating, the drying time can be altered by changing the power level of the microwave unit.

Determination of the relaxation characteristics of sugar glasses embedded in microfiber substrates

Recently there has been considerable interest in developing sugar glasses that enable storage of biologics without refrigeration. Microfiber filter papers are good substrates for drying biologics in the presence of sugar glass-formers, providing for an even distribution of samples and an enhanced surface area for drying, but the opaqueness prevents macroscopic observation of the sample and can introduce complexities that impede physical characterization. Because drying kinetics and processing conditions can impact the relaxation dynamics (e.g., α- and β-relaxation), which can influence the efficacy of the glass as a stabilizer, methods are needed that can enable a determination of relaxation phenomena of sugar glasses in such complex environments. In this study we present a method which provides verification of the absence of crystallinity following drying on glass fiber filter paper and also enables the determination of relaxation characteristics of amorphous sugar compositions embedded within these filter substrates. Using material pockets to contain the sugar glass-embedded microfiber paper, the α-relaxation temperature, Tα, was determined as a function of the water content in trehalose and sucrose samples using Dynamic Mechanical Analysis (DMA). Results were verified by comparison with previous calorimetric and spectroscopic studies. The data also demonstrated the plasticizing effects of water, as Tα was shown to correlate with water content via a Gordon-Taylor-like relationship. Our findings validate a new approach for determining the relaxation characteristics of microfiber embedded sugar glasses, and offer new insights into the relaxation characteristics of glasses prepared by microwave-assisted drying on filter papers.

Somatic cells, stem cells, and induced pluripotent stem cells: how do they now contribute to conservation?

More than a decade has now passed since the birth of the first endangered species produced from an adult somatic cell reprogrammed by somatic cell nuclear transfer. At that time, advances made in domestic and laboratory animal species provided the necessary foundation for attempting cutting-edge technologies on threatened and endangered species. In addition to nuclear transfer, spermatogonial stem cell transplantation and induction of pluripotent stem cells have also been explored. Although many basic scientific questions have been answered and more than 30 wild species have been investigated, very few successes have been reported. The majority of studies document numerous obstacles that still need to be overcome to produce viable gametes or embryos for healthy offspring production. This chapter provides an overview of somatic cell and stem cell technologies in different taxa (mammals, fishes, birds, reptiles and amphibians) and evaluates the potential and impact of these approaches for animal species conservation.

Retention of structure and function of the cat germinal vesicle after air-drying and storage at suprazero temperature

The study explored a novel approach for preserving the maternal genome without the entire oocyte by air-drying the cat germinal vesicle (GV) in the presence of the disaccharide trehalose. Specifically, we examined GV structure and function after desiccation, storage at 4 °C (up to 32 wk), and rehydration including the ability to resume meiosis after injection into a fresh, conspecific cytoplast. In experiment 1, DNA integrity was similar to fresh controls after 1 and 4 wk storage in the presence of trehalose, but was more fragmented at later time points (especially after 32 wk). Nuclear envelope integrity was sustained in >90% of oocytes stored for 0, 4, or 16 wk regardless of protective treatment. In experiment 2, compacted, air-dried GVs were stored for 2 or 4 wk, rehydrated, and injected into fresh cytoplasts. After culture for 24 h in vitro, up to 73% of oocytes reconstructed with desiccated GVs preserved in trehalose resumed meiosis compared to 30% of those dried in the absence of the disaccharide. At each storage time point, trehalose presence during air-drying was advantageous for resumption of meiosis, with >20% of oocytes completing nuclear maturation to metaphase II. This demonstrates a potential for preserving the female genome using the GV alone and for multiple weeks after desiccation. Trehalose enhanced the process by retaining the ability of a dried and rehydrated GV to resume communication with the surrounding cytoplasm of the recipient oocyte to permit reaching metaphase II and likely sustain subsequent embryo development.

Isothermal vitrification methodology development for non-cryogenic storage of archival human sera

Biorepositories worldwide collect human serum samples and store them for future research. Currently, hundreds of biorepositories across the world store human serum samples in refrigerators, freezers, or liquid nitrogen without following any specific cryopreservation protocol. This method of storage is both expensive and potentially detrimental to the biospecimens. To decrease both cost of storage and the freeze/thaw stresses, we explored the feasibility of storing archival human serum samples at non-cryogenic temperatures using isothermal vitrification. When biospecimens are vitrified, biochemical reactions can be stopped, the specimen ceases to degrade, and macromolecules can be stabilized without requiring cryogenic storage. In this study, 0.2, 0.4, or 0.8M trehalose; 0, 0.005 or 0.01M dextran; and 0 or 10% (v/v) glycerol was added to human serum samples. The samples were either dried diffusively as sessile droplets or desiccated under vacuum after they are adsorbed onto glass microfiber filters. The glass transition temperatures (Tg) of the desiccated samples were measured by temperature-ramp Fourier Transform Infrared (FTIR) spectroscopy. Sera samples vitrified at 4±2°C when 0.8M trehalose and 0.01M dextran were added and the samples were vacuum dried for two hours. Western immunoblotting showed that vitrified serum proteins were minimally degraded when stored for up to one month at 4°C. About 80% of all proteins were recovered after storage at 4°C on glass microfiber filters, and recovery did not decrease with storage time. These results demonstrated the feasibility of long-term storage of vitrified serum at hypothermic (and non-cryogenic) temperatures.

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.

High-resolution intracellular viscosity measurement using time-dependent fluorescence anisotropy

A low-cost pulsed laser is used in conjunction with a homebuilt laser confocal-scanning epifluorescence microscope having submicron lateral and axial spatial resolution to determine cytoplasmic viscosity at specific intracytoplasmic locations in J774 mouse macrophage cells. Time-dependent fluorescence anisotropy measurements are made at each location and global deconvolution techniques are used to determine rotational correlation times. These rotational correlation times are related to the hydrated volume of 8-hydroxyperene-1,3,6-trisulfonic acid (HPTS) to calculate viscosity at specific points inside the cell. In the cytoplasmic areas measured, rotational correlation times of HPTS ranged from 0.186 ns to 0.411 ns, corresponding to viscosities ranging from 1.00 +/- 0.03 cP to 2.21+/- 0.05 cP.