EVALUATION OF DMSO TRANSPORT IN HUMAN ARTICULAR CARTILAGE: VEHICLE SOLUTIONS AND EFFECTS ON CELL FUNCTION

Osteochondral allografting techniques are limited by the availability of suitable donor tissue; there is an urgent need for effective cryopreservation. A fundamental requirement is the need to establish initial conditions of exposure to cryoprotectant that the chondrocytes will tolerate and that load the tissue with an adequate concentration of cryoprotectant. Three vehicle solutions to transport DMSO into the tissue were studied. Knee joints were obtained from deceased donors with appropriate consent. Whole condyles were treated with 20% w/w DMSO in each of three vehicle solutions and chondrocyte function and tissue CPA content measured. The results showed that exposure to 20% DMSO in each vehicle solution for 2 hours at 0 degrees C was tolerated without loss of GAG synthetic activity. It was observed that penetration of DMSO increased little after 1 hour of CPA exposure at 0 degrees C but the final tissue concentration of CPA was markedly lower than that in the medium.

[Permeability of isolated rat hepatocyte plasma membranes for molecules of dimethyl sulfoxide]

We have studied permeability of isolated rat hepatocyte membranes for molecules of dimethyl sulfoxide (DMSO) at different hypertonicity of a cryoprotective medium. The permeability coefficient of hepatocyte membranes κ1 for DMSO molecules was shown to be the differential function of osmotic pressure between a cell and an extracellular medium. Ten-fold augmentation of DMSO concentration in the cryoprotective medium causes the decrease of permeability coefficients κ1 probably associated with the increased viscosity in membrane-adjacent liquid layers as well as partial limitations appeared as a result of change in cell membrane shape after hepatocyte dehydration. We have found out that in aqueous solutions of NaCl (2246 mOsm/l) and DMSO (2250 mOsm/l) the filtration coefficient L(p) in the presence of a penetrating cryoprotectant (L(pDMSO) = (4.45 ± 0.04) x 10(-14) m3/Ns) is 3 orders lower compared to the case with electrolyte (L(pNaCl) = (2.25 ± 0.25) x 10(-11) m3/Ns). This phenomenon is stipulated by the cross impact of flows of a cryoprotectant and water at the stage of cell dehydration. Pronounced lipophilicity of DMSO, geometric parameters of its molecule as well as the presence of large aqueous pores in rat hepatocyte membranes allow of suggesting the availability of two ways of penetrating this cryoprotectant into the cells by non-specific diffusion through membrane lipid areas and hydrophilic channels.

Analytical optimal controls for the state constrained addition and removal of cryoprotective agents

Cryobiology is a field with enormous scientific, financial, and even cultural impact. Successful cryopreservation of cells and tissues depends on the equilibration of these materials with high concentrations of permeating chemicals (CPAs) such as glycerol or 1,2 propylene glycol. Because cells and tissues are exposed to highly anisosmotic conditions, the resulting gradients cause large volume fluctuations that have been shown to damage cells and tissues. On the other hand, there is evidence that toxicity to these high levels of chemicals is time dependent, and therefore it is ideal to minimize exposure time as well. Because solute and solvent flux is governed by a system of ordinary differential equations, CPA addition and removal from cells is an ideal context for the application of optimal control theory. Recently, we presented a mathematical synthesis of the optimal controls for the ODE system commonly used in cryobiology in the absence of state constraints and showed that controls defined by this synthesis were optimal. Here we define the appropriate model, analytically extend the previous theory to one encompassing state constraints, and as an example apply this to the critical and clinically important cell type of human oocytes, where current methodologies are either difficult to implement or have very limited success rates. We show that an enormous increase in equilibration efficiency can be achieved under the new protocols when compared to classic protocols, potentially allowing a greatly increased survival rate for human oocytes and pointing to a direction for the cryopreservation of many other cell types.

[DNA damage by active oxygen species in cryopreservation and the antioxydative properties of cryoprotectants]

Several disorders in the DNA structure in the cells of vertebrate and invertebrate animals, plant and algae are reviewed. Some causes of the DNA disorders, the reactive oxygen species, especially, are discussed. Some data are shown, that the common used cryoprotectants such as dimethylsulfoxide, glycerol, methanol, sucrose and albumin, are OH* scavengers. Some seldom used cryoprotectors, which scavenges several forms of active oxygen, are described. It is supposed that the antioxidant properties of the cryoprotectors are essential for their mechanism of action.

Myocyte enhancer factor 2c, an osteoblast transcription factor identified by dimethyl sulfoxide (DMSO)-enhanced mineralization

Rapid mineralization of cultured osteoblasts could be a useful characteristic in stem cell-mediated therapies for fracture and other orthopedic problems. Dimethyl sulfoxide (DMSO) is a small amphipathic solvent molecule capable of stimulating cell differentiation. We report that, in primary human osteoblasts, DMSO dose-dependently enhanced the expression of osteoblast differentiation markers alkaline phosphatase activity and extracellular matrix mineralization. Furthermore, similar DMSO-mediated mineralization enhancement was observed in primary osteoblast-like cells differentiated from mouse mesenchymal cells derived from fat, a promising source of starter cells for cell-based therapy. Using a convenient mouse pre-osteoblast model cell line MC3T3-E1, we further investigated this phenomenon showing that numerous osteoblast-expressed genes were elevated in response to DMSO treatment and correlated with enhanced mineralization. Myocyte enhancer factor 2c (Mef2c) was identified as the transcription factor most induced by DMSO, among the numerous DMSO-induced genes, suggesting a role for Mef2c in osteoblast gene regulation. Immunohistochemistry confirmed expression of Mef2c in osteoblast-like cells in mouse mandible, cortical, and trabecular bone. shRNAi-mediated Mef2c gene silencing resulted in defective osteoblast differentiation, decreased alkaline phosphatase activity, and matrix mineralization and knockdown of osteoblast specific gene expression, including osteocalcin and bone sialoprotein. A flow on knockdown of bone-specific transcription factors, Runx2 and osterix by shRNAi knockdown of Mef2c, suggests that Mef2c lies upstream of these two important factors in the cascade of gene expression in osteoblasts.

The effect of Tween 80 on eggshell permeabilization in Galleria mellonella (L.) (Lepidoptera, Pyralidae)

The development of a species-specific protocol for dechorionation and permeabilization of insect eggs is a necessary prerequisite to cryopreserve the embryos. Here we tested different procedures based on heptane or the surfactant Tween 80 as an alternative to alkane, evaluating their efficacy and toxicity on the early (24 h post-oviposition) and late (75 h post-oviposition) stage embryos. Heptane efficiently permeabilized the eggs of G. mellonella but the hatching rate ranged from 0.1 to 4.2 percent in the early stage and from 4.3 to 11.2 percent in the late stage. The embryos treated with 1.25 percent NaOCl + 0.08 percent Tween 80 for 2 min showed the same shrinkage and reswelling percentages as eggs exposed to heptane for 10 sec, with a significantly higher hatching percentage in the early (68.2 +/- 1.5 percent) and late stages (22.4 +/- 3.7 percent). Thus, 0.08 percent Tween 80 allows sufficient permeabilization of G. mellonella embryos without the high toxicity of alkane.

Microfluidics for cryopreservation

Minimizing cell damage throughout the cryopreservation process is critical to enhance the overall outcome. Osmotic shock sustained during the loading and unloading of cryoprotectants (CPAs) is a major source of cell damage during the cryopreservation process. We introduce a microfluidic approach to minimize osmotic shock to cells during cryopreservation. This approach allows us to control the loading and unloading of CPAs in microfluidic channels using diffusion and laminar flow. We provide a theoretical explanation of how the microfluidic approach minimizes osmotic shock in comparison to conventional cryopreservation protocols via cell membrane transport modeling. Finally, we show that biological experiments are consistent with the proposed mathematical model. The results indicate that our novel microfluidic-based approach improves post-thaw cell survivability by up to 25% on average over conventional cryopreservation protocols. The method developed in this study provides a platform to cryopreserve cells with higher viability, functionality, and minimal inter-technician variability. This method introduces microfluidic technologies to the field of biopreservation, opening the door to future advancements at the interface of these fields.

Influence of exposure to vitrification solutions on 2-cell mouse embryos: II. Osmotic effects or chemical toxicity?

In the companion paper (CryoLetters, 2007, 28:403-408), we reported effects of exposure of two-cell mouse embryos to vitrification solutions containing different vitrificants (EG, PG and DMSO) on the intracellular potassium and sodium content. We also compared exposure of 30% (v:v) ethylene glycol for 1.5 min to the similar experiments with 3-min exposure reported previously (CryoLetters, 2006, 27:87-98). In all experiments, four step protocols (2 steps of addition and 2 steps of washing) were used. Here we present mathematical modeling of the cell osmotic response using the relativistic permeability (RP) approach, which allows calculation of the osmotic curves without using simulation software but by direct calculations of the cell volume, intracellular concentration, and amount of the permeable vitrificants (Cryobiology, 2006, 53:402-3). Magnitude of the maximum cell volume excursion and other important osmotic characteristics were calculated for each step of the protocol, and the results of the mathematical modeling were superimposed onto the experimental data reported and discussed in the companion paper. The osmotic damage vs. specific chemical toxicity of the vitrificants as the major cause of the elemental disturbance of intracellular potassium and sodium content are discussed.

Raman microscopy of porcine inner retinal layers from the area centralis

PURPOSE

To characterize the Raman spectra of porcine inner retinal layers, specifically, the inner nuclear, inner plexiform, ganglion cell, and nerve fiber layers.

METHODS

Raman microscopy was employed at three excitation wavelengths, 785, 633, and 514 nm to measure Raman spectra in a high resolution grid across the inner layers of 4% paraformaldehyde cryoprotected porcine retina. Multivariate statistics were used to summarize the principal spectral signals within those layers and to map the distribution of each of those signals.

RESULTS

The detected Raman scattering was dominated by a signal characteristic of the protein population present in each layer. As expected, a significant nucleotide contribution was observed in the inner nuclear layer, while the inner plexiform layer displayed a minor contribution from fatty acid based lipid, which would be characteristic of the axonal and synaptic connection resident in this layer. Blood vessels were readily characterized by their distinct heme-derived spectral signature, which increased at 633 and 514 nm excitation compared to 785 nm. Discrete isolated nucleotide signals were identified in the ganglion cell layer, while the nerve fiber layer exhibited a homogenous profile, which is indicative of its broadly uniform axonal and cytoplasmic Muller cell components.

CONCLUSIONS

The present study demonstrated the potential of Raman microscopy as a tool to study the biochemical composition of pathologically normal retina. Specifically, the method allowed a unique method of analyzing the network of neurons involved in relaying information from the photoreceptor population to the ganglion cell derived nerve fiber layer. The study has demonstrated the ability of Raman microscopy to generate simultaneously information on a range of specific biochemical entities within the stratified normal retina.

Cytotoxicity of Dimethylacetamide and Pharmacokinetics in Children Receiving Intravenous Busulfan

Purpose

To assess the cytotoxicity and the exposure of N,N-dimethylacetamide (DMA) in children during high-dose therapy with an intravenous (IV) formulation of busulfan containing the potentially hepatotoxic and neurotoxic DMA as a solvent.

Patients and Methods

Eighteen children aged 0.9 to 17.3 years (median age, 4.0 years) received IV busulfan in 15 doses of 0.7 to 1.0 mg/kg busulfan containing overall DMA amounts of between 5 mmol (437 mg) and 70.5 mmol (6,142 mg) per dose. Plasma concentrations of DMA and busulfan were quantified and analyzed using nonlinear mixed-effects modeling. Four different leukemic cell lines were incubated with DMA, and cytotoxicity was assessed in comparison with busulfan as well as in a combination reflecting the ratio in the formulation.

Results

Maximal plasma concentrations of DMA up to 3.09 mmol/L were observed. No accumulation of the solvent occurred. Instead, the trough levels decreased over the 4 treatment days. The population pharmacokinetic analysis revealed a clearance of 86.9 mL h−1kg−1± 27% that increased to 298 mL h−1kg−1on the fourth day and a volume of distribution of 469 mL kg ± 22% (population mean ± interindividual variability). DMA volume of distribution correlated with the volume of distribution of busulfan. The cytotoxicity of DMA in vitro was 3 orders of magnitude lower than that of busulfan. No synergism was observed.

Conclusion

The lack of accumulation of DMA confirms that there is no safety concern related to the DMA content in this IV busulfan formulation. The contribution of DMA to the antileukemic effect of the formulation seems to be limited.

Significant variability among bulls in the sperm membrane permeability for water and glycerol: Possible implications for semen freezing protocols for individual males

The aim of this study was to test the hypothesis that bulls have significant intra-individual differences in the hydraulic conductivity (L(p)) and permeability coefficient for glycerol (P(s)) of the sperm cell membrane. The permeability parameters were determined at 22, 10, and 0 degrees C of sperm from 7 Holstein Frisian artificial insemination (AI) bulls, using four ejaculates per bull. A stopped-flow approach was applied to provide temporal resolution sufficient to measure rapid cell volume changes under anisosmotic conditions in the absence or presence of glycerol. This technique utilizes a concentration-dependent self-quenching entrapped fluorophore. The resulting cell volume changes were used in three-parameter fitting calculations to compute L(p) in the absence glycerol, and L(p) in the presence of glycerol (L(p)(gly)) and P(s). Averaged over all bulls, L(p) in the absence of glycerol was 0.28+/-0.01, 0.15+/-0.01 and 0.10+/-0.01 microm min(-1)atm(-1) (mean+/-SD) at 22, 10 and 0 degrees C, respectively, yielding an Arrhenius activation energy (E(a)) of 7.39 kcal/mol. The average L(p)(gly) value at 22 degrees C, was 3.8 times lower than L(p) in the absence of glycerol (P<0.05). L(p)(gly), P(s), and the reflection coefficient (sigma) at 22 degrees C were 0.073+/-0.015 microm min(-1)atm(-1), 0.80+/-0.33 x 10(-3)cm min(-1), and 0.92+/-0.10 (mean+/-SD), respectively. Subsequent experiments were performed at 10 and 0 degrees C. Activation energies for L(p)(gly) and P(s) were 10.08 and 8.77 kcal/mol, respectively. The significant differences between individual bulls in L(p) and P(s) indicate that individual males may require individual adjustments of the cooling protocol. Application of these data in a theoretical model to simulate the osmotic events during freezing resulted in predicted optimal cooling rates in the range of published empirical values.

Nonmetabolizable glucose compounds impart cryotolerance to primary rat hepatocytes

We herein report a novel method for the cryopreservation of hepatocytes using a non-metabolizable glucose derivative in an attempt to mimic the natural cryoprotective adaptations observed in freeze-tolerant frogs. Primary rat hepatocytes were loaded with 3-O-methyl glucose (3OMG) through endogenous glucose transporters without evident toxicity. The 3OMG-loaded hepatocytes were then frozen in a controlled rate freezer down to -80 degrees C and stored in liquid nitrogen at -196 degrees C. Hepatocytes cryopreserved with a relatively small amount of intracellular 3OMG (<0.2 M) showed high post-thaw viability and maintained long-term hepatospecific functions, including synthesis, metabolism, and detoxification. Metabolite uptake and secretion rates were also largely preserved in the cryopreserved hepatocytes. This is the first study to demonstrate the use of the non-metabolizable glucose derivative 3OMG in hepatocyte cryopreservation.

[Regularity of sugar-uptake in human red blood cells]

Lyophilization of human red blood cells has important significance in clinical application. Some sugars, especially trehalose, can be more tolerant of some organism or cells to dry environments, But, how to bring sugars into cells is a challenge. This study was aimed to investigate the regularity of sugar-uptake in human red blood cells. The absorption rate of trehalose and glucose in red blood cells, free hemoglobin level and erythrocyte deformation index were determined at different incubation temperature (4, 25 and 37 degrees C), different sugar concentration (0, 0.2, 0.4, 0.6, 0.8 and 1 mol/L) and different incubation time (1, 3, 5, 7 and 9 hours). The results showed that with increase of temperature and extracellular sugar concentration, the uptake of sugar in red blood cells also increased, the intracellular trehalose and glucose concentrations were over 30 mmol/L and 40 mmol/L respectively. The effects of incubation time on uptake of trehalose and glucose were different. With prolonging of incubation time, the uptake of trehalose showed firstly increase and then decrease, however, the uptake of glucose showed a constant increase. But the loading process had side-effect on free hemoglobin and maximum deformation index (MAXDI) of red blood cells, especially for trehalose, which mainly come from high osmotic pressure. It is concluded that the uptake of sugars in red blood cells is closely dependent on incubation temperature, extracellular sugar concentration and incubation time. In certain condition, the efficiency of sugar uptake is very high, but this process also damages red blood cells so as to affect the application of sugars in lyophilization of red blood cells. The research in the future should focus on how to deal with the relation between cell injury and uptake efficiency of sugar in red blood cells.

Permeability of ovine primordial follicles to different cryoprotectants

OBJECTIVE

To determine the behavior of isolated primordial follicles that were exposed to different concentrations of dimethyl sulfoxide (DMSO), ethylene glycol (EG), propylene glycol (PROH), and glycerol (GLY).

DESIGN

Isolated primordial follicles were exposed to the cryoprotectant (CPA) solution and photographed to calculate their volume at different periods of exposure.

SETTING

Laboratorio Renzo Giuliani, University of Florence, Italy.

ANIMAL(S)

Lambs, 30-40 days old.

INTERVENTION(S)

Isolation of primordial follicles and subsequent exposure to CPA.

MAIN OUTCOME MEASURE(S)

Follicular volume.

RESULT(S)

At 2 minutes of CPA exposure, all follicles appeared to be shrunken. At approximately 5 minutes, shrinkage ceased, and follicles started to swell, absorbing the CPA and water to maintain osmotic equilibrium. When DMSO was tested, follicular dehydration in all concentrations did not exceed 17%; with PROH and EG, it reached 33% and 27%, respectively. The highest degree of dehydration (48%) was seen with GLY. In almost all tested concentrations, follicular shrinkage occurred up to 5 minutes.

CONCLUSION(S)

Volume changes in isolated primordial follicles can fluctuate according to the CPA used and its concentration.

Permeability of mouse oocytes and embryos at various developmental stages to five cryoprotectants

To assess the permeability of mouse oocytes and embryos, matured oocytes and embryos at various stages of development were placed in five cryoprotectant solutions at 25 C for 25 min. From the cross-sectional areas of the oocytes/embryos, the relative change in volume was analyzed. In oocytes, shrinkage was least extensive and recovery was quickest in the propylene glycol solution, showing that propylene glycol permeates the oocytes most rapidly. Dimethyl sulfoxide, acetamide, and ethylene glycol permeated the oocytes slightly more slowly than propylene glycol. The oocytes in glycerol shrunk extensively and then expanded marginally, indicating slow permeation. The volume changes of 1-cell and 2-cell embryos were similar to those of oocytes, showing little change in permeability. In 8-cell embryos, the volume recovered much faster than in the earlier stages especially in glycerol and acetamide. In morulae, the volume recovery was much faster in glycerol and in ethylene glycol; in ethylene glycol, the extent of shrinkage was small and the recovery was fast, indicating an extremely rapid permeation. Although the permeability of oocytes/embryos generally increased as embryo development proceeded, the degree of increase varied greatly among the cryoprotectants. Interestingly, the volume change in propylene glycol was virtually unaffected by the stage of development. Such information will be valuable for determining a suitable protocol for the cryopreservation of oocytes/embryos at different stages of development.

Changes in sucrose and glycerol content in garlic shoot tips during freezing using PVS3 solution

Changes in moisture content (MC), sucrose and glycerol concentration in garlic shoot tips were monitored during loading and unloading with PVS3 solution. Upon PVS3 treatment, shoot tip MC decreased rapidly and sucrose and glycerol concentrations increased rapidly during the first 30 min. Sucrose and glycerol concentrations increased more slowly thereafter. Shoot tip MC in after PVS3 treatment was affected by their size, but not by sucrose concentration of the preculture medium. As the size of shoot tips increased, so their MC increased after PVS3 treatment. However, sucrose and glycerol concentrations decreased after PVS3 incubation, and concentrations in dehydrated shoot tips were much lower than those measured in non-air dried controls. During unloading with 1.2 M sucrose medium, shoot tip MC increased rapidly during the first 10 min, whereas glycerol concentration decreased steadily over 90 min. Loading and unloading of PVS3 solution in garlic shoot tips follows the principle of solute bulk flow.

Predicted permeability parameters of human ovarian tissue cells to various cryoprotectants and water

This study presents a generic numerical model to simulate the coupled solute and solvent transport in human ovarian tissue sections during addition and removal of chemical additives or cryoprotective agents (CPA). The model accounts for the axial and radial diffusion of the solute (CPA) as well as axial convection of the CPA, and a variable vascular surface area (A) during the transport process. In addition, the model also accounts for the radial movement of the solvent (water) into and out of the vascular spaces. Osmotic responses of various cells within an human ovarian tissue section are predicted by the numerical model with three model parameters: permeability of the tissue cell membrane to water (L(p)), permeability of the tissue cell membrane to the solute or CPA (omega) and the diffusion coefficient of the solute or CPA in the vascular space (D). By fitting the model results with published experimental data on solute/water concentrations within an human ovarian tissue section, I was able to determine the permeability parameters of ovarian tissue cells in the presence of 1.5M solutions of each of the following: dimethyl sulphoxide (DMSO), propylene glycol (PROH), ethylene glycol (EG), and glycerol (GLY), at two temperatures (4 degrees C and 27 degrees C). Modeling Approach 1: Assuming a constant value of solute diffusivity (D = 1.0 x 10(-9) m(2)/sec), the best fit values of L(p) ranged from 0.35 x 10(-14) to 1.43 x 10(-14) m(3)/N-sec while omega ranged from 2.57 x 10(-14) to 70.5 x 10(-14) mol/N-sec. Based on these values of L(p) and omega, the solute reflection coefficient, sigma defined as sigma = 1-omega v(CPA)/L(P) ranged from 0.9961 to 0.9996. Modeling Approach 2: The relative values of omega and sigma from our initial modeling suggest that the embedded ovarian tissue cells are relatively impermeable to all the CPAs investigated (or omega approximately 0 and sigma approximately 1.0). Consequently the model was modified and used to predict the values of L(p) and D assuming omega = 0 and sigma = 1.0. The best fit values of L(p) ranged from 0.44 x 10(-14) to 1.2 x 10(-14) m(3)/N-sec while D ranged from 0.85 x 10(-9) to 2.08 x 10(-9) m(2)/sec. Modeling Approach 3: Finally, the best fit values of D from modeling approach 2 were incorporated into model 1 to re-predict the values of L(p) and omega. It is hoped that the ovarian tissue cell parameters reported here will help to optimize chemical loading and unloading procedures for whole ovarian tissue sections and consequently, tissue cryopreservation procedures.

Betaine and carnitine uptake systems in Listeria monocytogenes affect growth and survival in foods and during infection

AIMS

To establish the relative importance of the osmo- and cryoprotective compounds glycine betaine and carnitine, and their transporters, for listerial growth and survival, in foods and during infection.

METHODS AND RESULTS

A set of Listeria monocytogenes mutants with single, double and triple mutations in the genes encoding the principal betaine and carnitine uptake systems (gbu, betL and opuC, respectively) was used to determine the specific contribution of each transporter to listerial growth and survival. Food models were chosen to represent high-risk foods of plant and animal origin i.e. coleslaw and frankfurters, which have previously been linked to major human outbreaks of listeriosis. BALB/c mice were used as an in vivo model of infection. Interestingly, while betaine appeared to confer most protection in foods, the hierarchy of transporter importance differs depending on the food type: Gbu>BetL>OpuC for coleslaw, as opposed to Gbu>OpuC>BetL in frankfurters. By contrast in the animal model, OpuC and thus carnitine, appears to play the dominant role, with the remaining systems contributing little to the infection process.

CONCLUSIONS

This study demonstrates that the individual contribution of each system appears dependent on the immediate environment. In foods Gbu appears to play the dominant role, while during infection OpuC is most important.

SIGNIFICANCE AND IMPACT OF THE STUDY

It is envisaged that this information may ultimately facilitate the design of effective control measures specifically targeting this pathogen in foods and during infection.

Measurement of the chondrocyte membrane permeability to Me2SO, glycerol and 1,2-propanediol

The addition of cryopreservative agents (CPAs) to chondrocytes and natural and engineered cartilage is critical to protect the cells and tissues from freezing damage during cryopreservation, but this may cause cell damage, e.g. by osmotic shock. The damage could be minimized by the control of the cell volume excursion with the knowledge of cell membrane permeability. In this study, the cell volume responses of chondrocytes to three commonly used CPAs were evaluated using a perfusion microscope stage. The osmotic response of chondrocytes was measured to the perfusion with 1.4 M dimethyl sulfoxide (Me2SO), 1,2-propanediol and glycerol at 21 degrees C. Cell volumes and their transients were determined with image analysis. The cell membrane permeability parameters, including the hydraulic conductivity (Lp), the CPA permeability (omega) and the reflection coefficients (sigma) in the Kedem-Katchalsky (K-K) model, and the Lp and omega in the two-parameter model were determined. The correlated K-K parameters at 21 degrees C were Lp=0.166 +/- 0.035, 0.149 +/- 0.061, 0.212 +/- 0.041 microm/min atm, omega=(7.630 +/- 0.174) x 10(-2), (1.428 +/- 0.627) x 10(-2), (2.744 +/- 0.775) x 10(-2) microm/s and sigma=0.91 +/- 0.09, 0.82 +/- 0.11, 0.88 +/- 0.10 for Me(2)SO, glycerol and 1,2-propanediol, respectively. For the two-parameter model, the parameter values were Lp=0.163 +/- 0.040, 0.128 +/- 0.031, 0.169 +/- 0.025 microm/min atm, omega=(7.881 +/- 0.178) x 10(-2), (1.529 +/- 0.525) x 10(-2), (3.716 +/- 0.493) x 10(-2) microm/s for Me2SO, glycerol and 1,2-propanediol, respectively. No significant difference in the predictions of cell volume excursion during CPA addition was observed when using either the K-K model or the two-parameter model and it was hence advised to adopt the simple two-parameter model in the evaluation. The measured parameters can be used to optimise the CPA addition and removal protocols to maximize the cell survival during cryopreservation.

Cryopreservation of human embryos using ethylene glycol in controlled slow freezing

BACKGROUND

Ethylene glycol (EG) has been successfully used as a cryoprotectant for vitrification of mammalian formula embryos (including human embryos) due to its low formula weight and high permeation into cells compared with other cryoprotectants, including propylene glycol (PROH). This study was carried out to evaluate the permeation and toxicity of EG and to investigate the effects of its use in a slow-freezing protocol on post-thaw development of mouse embryos and on pregnancy outcome of frozen human embryos.

METHODS

Spare human embryos after embryo transfer were cryopreserved using 1.5 mol/l EG or PROH using a slow-freezing protocol which had been tested previously in mouse experiments.

RESULTS

The post-thaw survival rate of human embryos in the EG group (80.6%) was significantly higher than that in the PROH group (65.2%, P < 0.05). The implantation and clinical pregnancy rates of human embryos in the EG group (20.3 and 46.9%) were significantly higher than those in the PROH group (7.5 and 24.6%, P < 0.05).

CONCLUSIONS

Ethylene glycol may be a good substitute for PROH to cryopreserve human embryos using a slow-freezing protocol.

Permeability characteristics and osmotic sensitivity of rhesus monkey (Macaca mulatta) oocytes

BACKGROUND

Permeability characteristics and sensitivity to osmotic shock are principal parameters that are important to derive procedures for the successful cryopreservation of mammalian oocytes.

METHODS AND RESULTS

The osmotically inactive volume of rhesus monkey oocytes was determined by measuring their volumes in the presence of hypertonic solutions of sucrose from 0.2 to 1.5 mol/l, compared with their volume in isotonic TALP-HEPES solution. Boyle-van't Hoff plots at infinite osmolality indicated that the non-osmotic volumes of immature and mature oocytes were 20 and 17% respectively. Osmotic responses of oocytes exposed to 1.0 mol/l solutions of glycerol, dimethylsulphoxide (DMSO) and ethylene glycol (EG) were determined. Rhesus monkey oocytes appeared to be less permeable to glycerol than to DMSO or to EG. Sensitivity of oocytes to osmotic shock was determined by exposing them to various solutions of EG (0.1 to 5.0 mol/l) and then abruptly diluting them into isotonic medium. Morphological survival, as measured by membrane integrity, of oocytes diluted out of EG depended significantly on the concentration of EG (P < 0.01).

CONCLUSION

Determination of permeability characteristics and sensitivity to osmotic shock of rhesus oocytes will aid in the derivation of procedures for their cryopreservation.

Analytical solution for the extremums of cell water volume and cell volume using a two-parameter model

Based on a two-parameter model [Cryobiology 37 (1998) 271-289], the analytical solution for the extremums of cell water volume and cell volume for a two-solute system are obtained. Compared with the numerical solution, the analytical solution offers an accurate but simple choice. The approximate solution [Cryobiology 40 (2000) 64-83] for the extremum of cell water volume is also discussed, the reason for the deviation is presented.

Canine RBC osmotic tolerance and membrane permeability

The objective of this study was to determine the cryobiological characteristics of canine red blood cells (RBC). These included the hydraulic conductivity (L(p)), the permeability coefficients (P(s)) of common cryoprotectant agents (CPAs), the associated reflection coefficient (sigma), the activation energies (E(a)) of L(p) and P(s) and the osmotic tolerance limits. By using a stopped-flow apparatus, the changes of fluorescence intensity emitted by intracellularly entrapped 5-carboxyfluorescein diacetate (CFDA) were recorded when cells were experiencing osmotic volume changes. After the determination of the relationship between fluorescence intensity and cell volume, cell volume changes were calculated. These volume changes were used in three-parameter fitting calculations to determine the values of L(p), P(s), and sigma for common CPAs. These volume measurements and data analyses were repeated at three different temperatures (22, 14, 7 degrees C). Using the Arrhenius equation, the activation energies of L(p) and P(s) in the presence of CPAs were determined. The osmotic tolerance limits for canine RBC were determined by measuring the percentage of free hemoglobin in NaCl solutions with various osmolalities compared to that released by RBC incubated in double distilled water. The upper and lower osmotic tolerance limits were found to be 150mOsm (1.67V(iso)) and 1200mOsm (0.45V(iso)), respectively. These parameters were then used to calculate the amount of non-permeating solute needed to keep cell volume excursions within the osmotic tolerance limits during CPA addition and removal.

The point of maximum cell water volume excursion in case of presence of an impermeable solute

A relativistic permeability model of cell osmotic response (Cryobiology 40:64-83; 41:366-367) is applied to a two-solute system with one impermeable solute. The use of the normalized water volume (w), and the amount of intracellular permeable solute (x), which is the product of the water volume and intracellular osmolality (y), as the main variables allowed us to obtain a homogeneous differential equation dx(Delta)/dw(Delta)=f(x(Delta)/w(Delta)), where w(Delta)=w-w(f), x(Delta)=x-x(f), and f refers to the final (equilibrium) values. The solution of this equation is an explicit function, w(Delta)=g(x(Delta)), which is given in the text. This approach allows us to obtain an analytical (exact) expression of the water volume at the moment of the maximum excursion (water extremum w(m)). Results are compared with numeration of basic osmotic equations and with approximation given in (Cryobiology 40:64-83). Assumption that, dw/dt approximately 0 gives good approximations of the kinetics of water and permeable CPA after the point of maximum volume excursion (the slow phase of osmotic response). Practical aspects of the relativistic permeability approach are also discussed.

The effect of cryoprotectants on the physical properties of large liposomes containing sodium diclofenac

Large liposomes (1-10 microm) containing sodium diclofenac were prepared and lyophilized using lactose or mannitol (7.5% in respect to the lipid content) as cryoprotectants. The physical studies of liposomes were performed during 30 days of storage in a dry or resuspended form. Lyophilization of large liposomes and storage in the dry form at 5 degrees C increases their physical stability. Lactose is a cryoprotectant which does not influence changes of properties of liposomes regarding their size, encapsulation efficacy and release rate. Large liposomes lyophilized in the presence of mannitol tend to increase in size and encapsulation efficacy, but the lipid bilayers are stabilized and less permeable to the drug.

Osmotic and cryoprotectant permeation characteristics of islet cells isolated from the newborn pig pancreas

The development of effective protocols for the low-temperature banking of pancreatic islets is an important step in islet transplantation for the treatment of type I diabetes mellitus. We have been exploring the use of islets from the newborn pig as an alternative source of tissue for transplantation. Current cryopreservation protocols are empirically derived, but may be optimized by modeling osmotic responses during the cryopreservation process. This study determined the osmotic and cryoprotectant permeability parameters of cells isolated from the pancreas of newborn pigs. Key parameters are: the osmotically inactive fraction of cell volume, hydraulic conductivity, the permeability coefficients of dimethyl sulfoxide (DMSO) and ethylene glycol (EG) at varying temperatures, and the activation energies of these transport processes. Newborn pig islets were dispersed into single cells and kinetic and equilibrium cell volumes were recorded during osmotic excursions using an electronic particle counter interfaced to a computer. Data were fitted to theoretical descriptions of the osmotic responses of cells, based on the Kedem-Katchalsky approach. The hydraulic conductivity (Lp) in the absence of cryoprotectant was calculated as 0.050 +/- 0.005, 0.071 +/- 0.006, and 0.300 +/- 0.016 microm/min/atm at 4 degrees C, 10 degrees C, and 22 degrees C, respectively (mean +/- SEM, n = 7, 6, or 9). These values give an activation energy value of 16.69 kcal/mol when put into an Arrhenius plot. The solute permeability (Ps) values for 1 M DMSO were 0.89 +/- 0.12, 1.86 +/- 0.28, and 5.33 +/- 0.26 microm/min at 4 degrees C, 10 degrees C, and 22 degrees C, respectively (n = 11, 8, or 10) giving an activation energy of 15.98 kcal/mol. The Lp values for cells exposed to 1 M DMSO were 0.071 +/- 0.006, 0.084 +/- 0.008, and 0.185 +/- 0.014 microm/min/atm at 4 degrees C, 10 degrees C, and 22 degrees C, respectively. The activation energy for these values was 8.95 kcal/mol. The Ps values for 2 M DMSO were 1.11 +/- 0.13, 1.74 +/- 0.19, and 7.68 +/- 0.12 microm/min for the same temperatures, with a calculated activation energy of 17.89 kcal/mol. The Lp values in the presence of 2 M DMSO were 0.070 +/- 0.006, 0.085 +/- 0.008, and 0.192 +/- 0.009 microm/min/atm at 4 degrees C, 10 degrees C, and 22 degrees C, respectively, with an activation energy of 9.40 kcal/mol. Solutions of 1 M EG gave Ps values of 1.01 +/- 0.13, 1.45 +/- 0.25, and 4.90 +/- 0.48 microm/min at the three test temperatures. The resulting activation energy was 14.60 kcal/mol. The corresponding Lp values were 0.071 +/- 0.007, 0.068 +/- 0.006, and 0.219 +/- 0.012 microm/min/atm with an activation energy of 10.96 kcal/mol. The solute permeabilities in the presence of 2 M EG for newborn pig islet cells were 1.03 +/- 0.15, 1.42 +/- 0.23, and 5.56 +/- 0.22 microm/min; the activation energy was 15.70. The Lp values for cells in the presence of 2 M EG were 0.068 +/- 0.008, 0.071 +/- 0.006, and 0.225 +/- 0.010 microm/min/atm; the activation energy for these values was 11.49 kcal/mol. These key cryobiological parameters permit the mathematical modeling of osmotic responses of intact islets during the cryopreservation process, which may lead to further improvements in the low temperature storage of islets from newborn pigs.

Modeling of cryopreservation of engineered tissues with one-dimensional geometry

Long-term storage of engineered bio-artificial tissues is required to ensure the off-the-shelf availability to clinicians due to their long production cycle. Cryopreservation is likely the choice for long-term preservation. Although the cryopreservation of cells is well established for many cell types, cryopreservation of tissues is far more complicated. Cells at different locations in the tissue could experience very different local environmental changes, i.e., the change of concentration of cryoprotecting chemicals (CPA) and temperature, during the addition/removal of CPA and cooling/warming, which leads to nonuniformity in cell survival in the tissue. This is due to the limitation of mass and heat transfer within the tissue. A specific aim of cryopreservation of tissue is to ensure a maximum recovery of cells and their functionality throughout a tissue. Cells at all locations should be protected adequately by the CPA and frozen at rates conducive to survival. It is hence highly desirable to know the cell transient and final states during cryopreservation within the whole tissue, which can be best studied by mathematical modeling. In this work, a model framework for cryopreservation of one-dimensional artificial tissues is developed on the basis of solving the coupled equations to describe the mass and heat transfer within the tissue and osmotic transport through the cell membrane. Using an artificial pancreas as an example, we carried out a simulation to examine the temperature history, cell volume, solute redistribution, and other state parameters during the freezing of the spherical heterogeneous construct (a single bead). It is found that the parameters affecting the mass transfer of CPA in tissue and through the cell membrane and the freezing rate play dominant roles in affecting the cell volume transient and extracellular ice formation. Thermal conductivity and extracellular ice formation kinetics, on the other hand, have little effect on cell transient and final states, as the heat transfer rate is much faster than mass diffusion. The outcome of such a model study can be used to evaluate the construct design on its survivability during cryopreservation and to select a cryopreservation protocol to achieve maximum cell survival.

HPLC simultaneous determination of glycerol and mannitol in human tissues for forensic analysis

A method for simultaneous determination of glycerol and mannitol in various human tissues was devised and for this we used high-performance liquid chromatography (HPLC). Specimens were homogenized in a mixture of chloroform and methanol, phosphate buffer (pH 7.0) and pentaerythritol (IS) solution. After centrifugation, an aliquot of the aqueous layer was evaporated to dryness and derivatized with p-nitrobenzoyl chloride at 50 degrees C for 1h, then applied to HPLC with analytical conditions of: column, CAPCELL PAK C18 MG (250 mm x 3.0 mm i.d., 5 microm, Shiseido Co. Ltd., Tokyo, Japan); column temperature, 1-2 degrees C; mobile phase, 75% acetonitrile-distilled water containing 0.05% trifluoroacetic acid, 0.05% heptafluoro-n-butyric acid and 0.1% triethylamine; flow rate, 0.5 ml/min; wavelength, 260 nm. Calibration curves for both substances were linear in concentration ranges from 1 to 500 microg/0.1g and correlation coefficients exceeded 0.99. The relative standard deviation (R.S.D.) of the method was evaluated at concentrations of 10 and 100 microg/0.1g, and ranged from 0.84 to 10.6%. Using this method, we determined the regional distribution levels of glycerol and mannitol in various tissues from an autopsied brain dead man.

Osmotic sensitivity of canine spermatozoa

The objective of this study was to determine osmotic tolerance of canine spermatozoa. The study comprised three experiments: (1) spermatozoa suspended either in an egg yolk-citrate (EYC) extender or in Kenney skim milk extender were exposed to NaCl solutions ranging from 290 to 1500 mOsm; (2) spermatozoa suspended in EYC were exposed to 550 to 1500 mOsm solutions of glucose, galactose, or fructose; and (3) spermatozoa suspended in EYC or glucose-bovine serum albumin (G-BSA) were exposed to 0.6 M (approximately 900 mOsm) or 1.2 M (approximately 1600 mOsm) solutions of glycerol, ethylene glycol (EG), or dimethyl sulfoxide (Me(2)SO). In all experiments, motility and membrane integrity of spermatozoa were assessed after they were diluted into isotonic medium at 37 degrees C. Exposure of canine spermatozoa to solutions of either NaCl or monosaccharides at osmolalities >500 mOsm caused a significant reduction of motility (P<0.01). Motility of spermatozoa was more affected by osmotic stress than their membrane integrity. Osmotic sensitivity of canine spermatozoa was dependent on the type of extender; spermatozoa suspended in the Kenney extender were more resistant to osmotic stress than those suspended in the EYC extender. Despite their sensitivity to exposure to high concentrations of nonpermeating agents, canine spermatozoa were rather resistant to exposure to glycerol and EG. However, Me(2)SO was toxic to canine spermatozoa; motility was substantially reduced after spermatozoa were exposed to 0.6 M Me(2)SO. The type of extender also affected the sensitivity of canine spermatozoa to Me(2)SO; spermatozoa suspended in the EYC extender were more resistant than those suspended in G-BSA. It was concluded that canine spermatozoa are sensitive to osmotic stress, but are tolerant to shrinking and swelling caused by exposure to permeating cryoprotectants.

Differential scanning calorimetry studies of intraembryonic freezing and cryoprotectant penetration in zebrafish (Danio rerio) embryos

Nucleation temperatures of intraembryonic water and cryoprotectant penetration in zebrafish embryos were studied using differential scanning calorimetry. The effects of embryo developmental stage, dechorionation, partial removal of yolk, cooling rate, and cryoprotectant treatment on the temperatures of intraembryonic freezing were investigated. Embryo stages were found to have a significant effect on the nucleation temperatures of intact embryos. Freeze onset temperatures of -11.9 +/- 1.5, -15.6 +/- 0.3, and -20.5 +/- 0.1 degrees C were obtained for intact embryos at 6-somite, prim-6, and high-pec stages, respectively. After dechorionation, the freeze onset temperatures of intraembryonic water shifted to significantly lower temperatures, being -23.5 +/- 0.8, -18.7 +/- 0.7, -24.9 +/- 0.8 degrees C for 6-somite, prim-6, and high-pec stages, respectively. Yolk-reduced high-pec stage embryos showed significantly lower nucleation temperatures with an average onset at -27.9 +/- 0.4 degrees C. The effect of cryoprotectant treatment on the nucleation temperatures of intraembryonic water varies among different embryo stages and different cryoprotectants. Thirty-minute treatment with 2 M methanol significantly decreased the nucleation temperatures of dechorionated 6-somite embryos whilst no temperature decrease was observed for prim-6 or yolk-reduced high-pec embryos. Thirty-minute exposure to 1 M propylene glycol did not significantly affect the nucleation temperatures of dechorionated 6-somite, prim-6, or yolk-reduced high-pec embryos. In order to increase the permeability of embryos to cryoprotectants, the yolk sacs of dechorionated embryos at 6-somite or prim-6 embryos were punctured with a sharp micro-needle before exposure to cryoprotectants. The punctured prim-6 embryos showed significantly lower temperatures of intraembryonic freezing after 30 min of exposure to 2 M methanol following the multi-punctures. The nucleation temperatures of punctured 6-somite or prim-6 embryos were also decreased significantly after exposure to 1 M propylene glycol for 30 min. These results suggested that in intact embryos, intraembryonic freezing appeared to be seeded by the external ice in the perivitelline fluid and that in dechorionated embryos (in the absence of external water) intraembryonic freezing was more likely a consequence of heterogeneous nucleation. Methanol was demonstrated to show a limited degree of penetration into prim-6 stage embryos, but it did not penetrate later-stage embryos such as prim-6 and yolk-reduced high-pec. No propylene glycol permeation was observed for embryos at all stages. However, multi-punctures of yolk resulted in the permeation of both cryoprotectants into prim-6 embryos and propylene glycol permeation into 6-somite embryos. These findings may have important implications in overcoming the problem associated with the low membrane permeability of zebrafish embryos to cryoprotectants.

Hepatic uptake of solutes from the preservation solution during hypothermic storage: a (1)H NMR study in rat liver

The hepatic uptake of histidine and carnosine (histidyl-alanine), used as buffer agents in four preservation solutions, was studied during 24-h hypothermic storage of rat livers by use of (1)H nuclear magnetic resonance (NMR) spectroscopy. Results demonstrated that there was a progressive, concentration-linked passive diffusion of histidine into liver tissues throughout the storage period. A similar inward diffusion of carnosine was also noted. Of the carbohydrate osmotic buffers in the preservation solutions, mannitol permeated the liver tissues to a greater degree and more rapidly than raffinose after the flushing with equivalent concentrations and storage at hypothermia. In general, many solutes from preservation solutions will increasingly penetrate the hepatic inter- and intracellular spaces during extended hypothermic preservation and (1)H NMR spectroscopy is one technique that can assist in the identification of these changes.

Algae permeability to Me(2)SO from -3 to 23 degrees C

Biphasic transport of water and dimethyl sulfoxide (Me(2)SO), a common cryoprotective agent (CPA), in algal cells was induced and measured on a cryoperfusion stage. A two-step experimental protocol provided data for the volumetric response of Chlorococcum (C.) texanum to impermeable and permeable solutes. First, the cells were exposed to a 500-mOsm sucrose solution, causing immediate shrinkage of the cell to a minimum equilibrium volume. Then an isoosmotic 200-mOsm/300-mOsm CPA/sucrose solution was introduced to the cells, resulting in increased cell volume to a new equilibrium state. Experiments were conducted at temperatures between -3 and 23 degrees C. Cell volumes were measured off-line by computer analysis of video images. A network thermodynamic model was fit to the transient volume data to determine permeabilities of C. texanum to water and Me(2)SO over the full temperature range, and results were calculated with two numeric methods. Biphasic transport was found to be slower at colder temperatures, with water entering the cell faster than Me(2)SO. Experimental results were also compared with data from similar experiments using methanol (MeOH) as the CPA. MeOH influx was calculated to be a magnitude larger than that of water. Additionally, MeOH permeability was at least three orders of magnitude greater than Me(2)SO permeability, and the difference in these solute permeabilities increased as temperature decreased.

Freeze-drying of polycaprolactone and poly(D,L-lactic-glycolic) nanoparticles induce minor particle size changes affecting the oral pharmacokinetics of loaded drugs

The present study was geared at identifying the conditions to stabilize poly (D,L-lactic-glycolic) (PLGA) and polycaprolactone (PCL) nanoparticles (NP) by freeze-drying with several cryoprotective agents. Differential scanning calorimetry and freeze-thawing studies were used to optimize the lyophilization process. These studies showed that all samples were totally frozen at -45 degrees C and evidenced the necessity of adding sucrose, glucose, trehalose or gelatine to preserve the properties of NP regardless of the freezing procedure. However, only 20% sucrose and 20% glucose exerted an acceptable lyoprotective effect on PLGA and PCL NP, respectively. Nonetheless, the final to initial size ratios ( approximately 1.5) indicated that particle size was slightly affected in both cases. In vivo studies with CyA-loaded PCL NP whose sizes matched those obtained after NP preparation (100 nm) and after being lyophilized (160 nm) showed that the changes of particle size might have some relevance on drug pharmacokinetics. The MRT was significantly (P<0.05) modified after an oral CyA dose of 5 mg/kg and the treatment with 160-nm sized CyA-loaded NP produced a higher drug partition into the liver of Wistar rats potentially affecting the toxic and immunosuppressive profile of the drug. Therefore, although the particle size changes induced by NP lyophilization were slight, they need to be carefully evaluated and cannot be neglected.

Dermal absorption of N,N-dimethylacetamide in human volunteers

OBJECTIVES

We investigated the potential for the dermal absorption of N,N-dimethylacetamide (DMAC: CAS No. 127-19-5) vapor, the biological half-life of N-methylacetamide (NMAC) in urine as the biological exposure item of DMAC, and the adjustment method for urinary concentrations.

METHODS

Twelve healthy male volunteers (mean age 25.2 years, range 21-43 years) were exposed to DMAC for 4 h on two occasions at intervals of 96 h or above. Each volunteer sat inside a whole-body-type exposure chamber for the dermal exposure experiment or outside the chamber for the inhalation exposure experiment. The temperature and relative humidity in the chamber were controlled at approximately 26 degrees C and 40% in order to keep the skin (90% naked) of the volunteers dry. DMAC concentrations were 6.1 +/- 1.3 ppm for dermal exposure and 6.1 +/- 1.3 ppm for inhalation exposure. Urine samples were collected from 0 h through 36 h and at 48 h and 72 h after the exposure. Extrapolations from exposure concentrations for 4 h to 10 ppm for 8 h were performed.

RESULTS

Mean dermal absorption was estimated to be 40.4% of the total DMAC uptake. The biological half-lives of urinary NMAC were 9.0 +/- 1.4 h and 5.6 +/- 1.3 h via skin and lung, respectively. Mean NMAC in urine just after 5 consecutive workdays (8 h/day) at 10 ppm DMAC exposure was assumed to be 33.7 mg/g x Cr (18.6-70.0 mg/g x Cr). Creatinine-adjusted NMAC concentration in urine for each volunteer within 12 h after the exposure was more closely correlated with the total excretion amount of NMAC up to 36 h than with urinary-volume-adjusted or specific-gravity-adjusted NMAC concentration in both the dermal and inhalation exposure experiments.

CONCLUSIONS

DMAC vapor was significantly absorbed through the skin. Estimated NMAC values indicate that 20 mg/g x Cr NMAC seems to be appropriate as the biological exposure index.

Preservation of frozen yeast cells by trehalose

Two different methods commonly used to preserve intact yeast cells-freezing and freeze-drying-were compared. Different yeast cells submitted to these treatments were stored for 28 days and cell viability assessed during this period. Intact yeast cells showed to be less tolerant to freeze-drying than to freezing. The rate of survival for both treatments could be enhanced by exogenous trehalose (10%) added during freezing and freeze-drying treatments or by a combination of two procedures: a pre-exposure of cells to 40 degrees C for 60 min and addition of trehalose. A maximum survival level of 71.5 +/- 6.3% after freezing could be achieved at the end of a storage period of 28 days, whereas only 25.0 +/- 1.4% showed the ability to tolerate freeze-drying treatment, if both low-temperature treatments were preceded by a heat exposure and addition of trehalose to yeast cells. Increased survival ability was also obtained when the pre-exposure treatment of yeast cells was performed at 10 degrees C for 3 h and trehalose was added: these treatments enhanced cell survival following freezing from 20.5 +/- 7. 7% to 60.0 +/- 3.5%. Although both mild cold and heat shock treatments could enhance cell tolerance to low temperature, only the heat treatment was able to increase the accumulation of intracellular trehalose whereas, during cold shock exposure, the intracellular amount of trehalose remained unaltered. Intracellular trehalose levels seemed not to be the only factor contributing to cell tolerance against freezing and freeze-drying treatments; however, the protection that this sugar confers to cells can be exerted only if it is to be found on both sides of the plasma membrane.

A network thermodynamic model of kidney perfusion with a cryoprotective agent

A network thermodynamic model has been devised to describe the coupled movement of water and a permeable additive within a kidney during perfusion under the combined action of diffusive, hydrodynamic, and mechanical processes. The model has been validated by simulating perfusions with Me2SO, glycerol, and sucrose and comparing predicted weight and vascular resistance with experimental results obtained by Pegg (1993). The flows of CPA, water, colloid, and cellular impermeants are governed by a combination of the individual osmotic potential and pressure differences between compartments of the kidney, the viscoelastic behavior of the tissue, and the momentum transferred between the flows. The model developed in this study presents an analytical tool for understanding the dynamics of the perfused kidney system and for modifying perfusion protocols to minimize the changes in cell volume, internal pressure build-up, and increases in vascular resistance that currently present barriers to the successful perfusion of organs.

Water and cryoprotectant permeability characteristics of isolated human and canine pancreatic islets

Cryopreservation allows accumulation of the necessary islet transplantable mass as well as adequate time for tissue typing and infectious disease screening. Cryopreservation protocols may be optimized by modeling the osmotically induced volume excursions that occur during the addition and removal of cryoprotective agents (CPAs). To that end, three transport parameters were measured at 22 degrees C in canine and human islets isolated by collagenase digestion and euroficoll purification: (i) the apparent hydraulic conductivity (Lp), (ii) the permeability coefficient of the CPA (Ps), and (iii) the associated reflection coefficient (sigma). The parameters were determined by volumetric analysis of islets upon abrupt exposure to 1, 2, and 3 M dimethyl sulfoxide (DMSO), ethylene glycol (EG), glycerol (GLY), and propylene glycol (PG). The parameters were calculated using the Kedem-Katchalsky theory to describe islet volume excursion kinetics (assuming islets to be single equivalent osmotic units with the same volume and surface area of the actual islet) and a three-parameter curve fit was performed using the Marquardt-Levenberg method. It was determined that the permeability characteristics of pancreatic islets are species specific, and based upon the measured parameters, the highest Ps values for canine islets were observed following exposure to 2 M EG, and the highest Ps values for human islets were observed following exposure to 2 M PG. The permeability parameters were analyzed adjusting for islet radius using ANCOVA procedures to acquire least square means. For canine islets exposed to 2 M EG these values were determined to be 0.936 microm/min/atm, 2.47 microm/s, and 0.90 (for Lp, Ps, and phi, respectively) and for human islets exposed to 2 M PG the values were determined to be 1.56 microm/min/atm, 3.48 microm/s, and 0.85 (for Lp, Ps, and sigma, respectively). These parameters were used in a model to calculate osmotically induced islet volumetric response upon addition/dilution of the optimum CPAs, taking into consideration critical volume excursion limits at which irreversible damage occurs.

Hydraulic conductivity (Lp) and its activation energy (Ea), cryoprotectant agent permeability (Ps) and its Ea, and reflection coefficients (sigma) for golden hamster individual pancreatic islet cell membranes

Long-term cryopreservation of islets of Langerhans would be advantageous to a clinical islet transplantation program. Fundamental cryobiology utilizes knowledge of basic biophysical characteristics to increase the understanding of the preservation process and possibly increase survival rate. In this study several of these previously unreported characteristics have been determined for individual islet cells isolated from Golden hamster islets. Using an electronic particle counting device and a temperature control apparatus, dynamic volumetric response of individual islet cells to anisosmotic challenges of 1.5 M dimethyl sulfoxide (DMSO) and 1.5 M ethylene glycol (EG) were recorded at four temperatures (8, 22, 28, and 37 degreesC). The resulting curves were fitted using Kedem and Katchalsky equations which describe water flux and cryoprotectant agent (CPA) flux based on hydraulic conductivity (Lp), CPA permeability (Ps), and reflection coefficient (final sigma) for the membrane. For Golden hamster islet cells, Lp, Ps, and final sigma for DMSO at 22 degreesC were found to be 0.23 +/- 0.06 microm/min/atm, 0.79 +/- 0.32 x 10(-3) cm/min, and 0.55 +/- 0.37 (n = 11) (mean +/- SD), respectively. For EG at 22 degreesC, Lp equaled 0.23 +/- 0.06 microm/min/atm, Ps equaled 0.63 +/- 0.20 x 10(-3) cm/min, and final sigma was 0.75 +/- 0.17 (n = 9). Arrhenius plots (ln Lp or ln Ps versus 1/temperature (K)) were created by adding the data from the other three temperatures and the resulting linear regression yielded correlation coefficients (r) of 0.99 for all four plots (Lp and Ps for both CPAs). Activation energies (Ea) of Lp and Ps were calculated from the slopes of the regressions. The values for DMSO were found to be 12.43 and 18.34 kcal/mol for Lp and Ps (four temperatures, total n = 52), respectively. For EG, Ea of Lp was 11.69 kcal/mol and Ea of Ps was 20.35 kcal/mol (four temperatures, total n = 58).

Membrane permeability modeling: Kedem-Katchalsky vs a two-parameter formalism

The analysis of experiments for the purpose of determining cell membrane permeability parameters is often done using the Kedem-Katchalsky (KK) formalism (1958). In this formalism, three parameters, the hydraulic conductivity (Lp), the solute permeability (Ps), and a reflection coefficient (final sigma), are used to characterize the membrane. Sigma was introduced to characterize flux interactions when water and solute (cryoprotectant) cross the membrane through a common channel. However, the recent discovery and characterization of water channels (aquaporins) in biological membranes reveals that aquaporins are highly selective for water and do not typically cotransport cryoprotectants. In this circumstance, sigma is a superfluous parameter, as pointed out by Kedem and Katchalsky. When sigma is unneeded, a two-parameter model (2P) utilizing only Lp and Ps is sufficient, simpler to implement, and less prone to spurious results. In this paper we demonstrate that the 2P and KK formalism yield essentially the same result (Lp and Ps) when cotransporting channels are absent. This demonstration is accomplished using simulation techniques to compare the transport response of a model cell using a KK or 2P formalism. Sigma is often misunderstood, even when its use is appropriate. It is discussed extensively here and several simulations are used to illustrate and clarify its meaning. We also discuss the phenomenological nature of transport parameters in many experiments, especially when both bilayer and channel transport are present.

Network thermodynamic model of coupled transport in a multicellular tissue--the islet of Langerhans

Network thermodynamic modeling via bond graphs was used to describe the water and cryoprotectant additive (CPA) transport in a multicellular tissue. The model is presented as a tool to understand the osmotic behavior of the islets of Langerhans when exposed to ternary aqueous solutions containing an electrolyte and a CPA. It accounts for the effects of the location of cells within the tissue and an interstitial matrix, plus differential permeabilities to water and CPA. The interstitial matrix was assumed to be a porous medium able to store the chemical species being transported. Controlled osmotic stress experiments were conducted on isolated rat pancreas islets to measure the transient volumetric response to step-wise changes in dimethyl sulfoxide, Me2SO, concentration. The model provides a tool for predicting the transient volumetric response of peripheral and interior cells and of interstitial tissue, as well as the build up of solute concentration, during addition and removal of CPAs and freezing and thawing protocols. Inverse solution methods were applied to determine values for standard cell membrane permeability parameters Lp, omega and sigma as well as for the interstitial flow conductivities Kw and Kp'.

Response of a liver tissue slab to a hyperosmotic sucrose boundary condition: microscale cellular and vascular level effects

Transport of a non-permeating CPA in liver tissue was studied by experimental and theoretical techniques. The system consisted of a 20 mm x 15 mm x 500 microns (thick) slab of liver tissue which was exposed to culture media and hyperosmotic sucrose (0.3 or 0.6 M) at the boundary. The volumetric changes of cell and vascular spaces within the tissue slab at 125 microns from one of the symmetric boundaries was studied by slam freezing followed by freeze substitution microscopy. The experimental data was then theoretically investigated using two models; one based on an effective diffusion coefficient for sucrose, and another which incorporated the convective flux of water out of the cells (and the tissue) while sucrose diffuses in. We estimate the effective diffusion of sucrose as 16-33% of the actual diffusivity of sucrose in bulk water. The role of convection of water out of the tissue is against the flow of sucrose and appears to be important in reducing the effective diffusivity of the sucrose. The role of vascular compliance, porosity and tortuosity are also discussed with respect to our results.

Membrane permeability characteristics of metaphase II mouse oocytes at various temperatures in the presence of Me2SO

In this study, the hydraulic conductivity (Lp), Me2SO permeability (PMe2SO), and the reflection coefficients (sigma) and their activation energies were determined for Metaphase II (MII) mouse oocytes by exposing them to 1.5 M Me2SO at temperatures of 30, 20, 10, 3, 0, and -3 degrees C. These data were then used to calculate the intracellular concentration of Me2SO at given temperatures. Individual oocytes were immobilized using a holding pipette in 5 microliters of an isosmotic PBS solution and perfused with precooled or prewarmed 1.5 M Me2SO solutions. Oocyte images were video recorded. The cell volume changes were calculated from the measurement of the diameter of the oocytes, assuming a spherical shape. The initial volume of the oocytes in the isoosmotic solution was considered 100%, and relative changes in the volume of the oocytes after exposure to the Me2SO were plotted against time. Mean (means +/- SEM) Lp values in the presence of Me2SO were (LpMe2SO) at 30, 20, 10, 3, 0 and -3 degrees C were determined to be 1.07 +/- 0.03, 0.40 +/- 0.02, 0.18 +/- 0.01, 7.60 x 10(-2) +/- 0.60 x 10(-2), 5.29 x 10(-2) +/- 0.40 x 10(-2), and 3.69 x 10(-2) +/- 0.30 x 10(-2) microns/min/atm, respectively. The PMe2SO values were 3.69 x 10(-3) +/- 0.3 x 10(-3), 1.07 x 10(-3) +/- 0.1 x 10(-3), 2.75 x 10(-4), +/- 0.15 x 10(-4), 7.83 x 10(-5) +/- 0.50 x 10(-5), 5.24 x 10(-5) +/- 0.50 x 10(-5), and 3.69 x 10(-5) +/- 0.40 x 10(-5) cm/min, respectively. The sigma values were 0.70 +/- 0.03, 0.77 +/- 0.04, 0.81 +/- 0.06, 0.91 +/- 0.05, 0.97 +/- 0.03, and 1 +/- 0.04, respectively. The estimated activation energies (Ea) for LpMe2SO, and PMe2SO, and sigma were 16.39, 23.24, and -1.75 Kcal/mol, respectively. These data may provide the fundamental basis for the development of more optimal cryopreservation protocols for MII mouse oocytes.

Plasma concentrations and pharmacokinetics of dimethylsulfoxide and its metabolites in patients undergoing peripheral-blood stem-cell transplants

PURPOSE

Dimethylsulfoxide (DMSO) is used to cryopreserve hematopoietic stem cells and is obligatorily infused into patients who receive stem-cell transplants. This study characterized the plasma concentrations and pharmacokinetics of DMSO and its metabolites in patients who underwent peripheral-blood stem-cell transplants.

MATERIALS AND METHODS

Plasma concentrations of DMSO, dimethylsulfone (DMSO2), and dimethylsulfide (DMSH2) were assessed in 10 patients who underwent autologous transplants with stem cells, cryopreserved in 10% DMSO (vol/vol). Blood was sampled at multiple times after the stem-cell infusion. Urine was pooled during the 24 hours postinfusion. DMSO, DMSO2, and DMSH2 were assayed simultaneously by gas chromatography. A one-compartment model with saturable elimination proved most suitable for fitting plasma DMSO concentration-versus-time data.

RESULTS

Stem-cell volumes infused ranged between 180 and 585 mL (254 to 824 mmol DMSO). Infusions lasted between 20 and 120 minutes. Peak plasma DMSO concentrations were 19.1 +/- 6.3 mmol/L (mean +/- SD). Pharmacokinetic parameters for volume of the central compartment (Vc), maximum velocity (Vmax), and Michaels-Menten constant (Km) were 37.3 +/- 17 L, 0.99 +/- 0.57 mmol/L/h, and 5.2 +/- 5.0 mmol/L, respectively. Plasma DMSO2 concentrations increased during the first 24 hours, plateaued at 4.4 +/- 1.2 mmol/L, and remained there until 48 hours (the last sample). DMSH2 concentrations were at steady-state by 5 minutes and remained between 3 and 5 mmol/L for 48 hours. Urinary excretion of DMSO and DMSO2 accounted for 44% +/- 4% and 4% +/- 1%, respectively, of the administered DMSO dose. Renal clearance of DMSO was 14.1 +/- 3.4 mL/min.

CONCLUSION

These data (1) document plasma concentrations of DMSO and metabolites in patients following peripheral-blood stem-cell transplants; (2) allow consideration of potential effects of these concentrations on stem-cell engraftment and drug-drug interactions; and (3) can facilitate a concentration-guided phase I trial of DMSO.

Permeation of human ovarian tissue with cryoprotective agents in preparation for cryopreservation

The recent improvements in the treatment of cancer by chemo- and radiotherapy have led to a significant increase in the survival rates of patients with malignant disease, but at the expense of distressing side effects. One major problem, especially for younger patients, is that aggressive therapy destroys a significant proportion of the follicular population, which can result in either temporary or permanent infertility. Freeze-banking pieces of ovarian cortex prior to treatment is one strategy for preserving fecundity. When the patient is in remission, fertility could, theoretically, be restored by autografting the thawed tissue at the orthotopic site or by growing isolated follicles to maturity in vitro. Recent studies have found good follicular survival in frozen-thawed human ovarian tissue but to optimize the process an effective cryopreservation method needs to be developed. An essential part of such a technique is to permeate the tissue with a cryoprotectant to minimize ice formation and the extent of this equilibration is an important determinant of post-thaw cellular survival. In the current study, we have investigated the diffusion of four cryoprotective agents into human tissue at both 4 degrees C and 37 degrees C. We have also studied the effect of adding different concentrations of the non penetrating cryoprotective agent, sucrose, to the freezing media using the release of lactate dehydrogenase as a measure of its protective effect. At 4 degrees C propylene glycol and glycerol penetrated the tissue significantly slower than either ethylene glycol or dimethyl sulphoxide. At the higher temperature of 37 degrees C all four cryoprotectants penetrated at a faster rate, however concern about enhanced toxicity prevents the use of these conditions in practice. Thus, the results suggest that the best method of preparing tissue for freezing is exposure for 30 min to 1.5 M solutions of ethylene glycol or dimethyl sulphoxide at 4 degrees C; this achieved a mean tissue concentration that was almost 80% that of the bathing solution. We also report that the addition of low concentrations of sucrose to the freezing medium does not have a significant protective effect against freezing injury.

Measurement of cryoprotective solvent penetration into intact organ tissues using high-field NMR microimaging

Existing methods are not able to monitor accurately the penetration of cryoprotective solvents (CPS) into intact tissues. In this study, NMR imaging is shown to be a noninvasive nondestructive way to measure penetration rates and effective diffusion coefficients of Me2SO into samples of rat kidney and rat liver tissues. This new method is unique in that the measurements obtained are not averaged over the entire tissue volume but may be made at any site in the tissue. Measurements of penetration rates yield values which are similar to literature values, and the effective diffusion coefficients fall within the expected range. The images also suggest an explanation of why CPSs fail to completely protect organs from freezing damage.

Injury and protection in split-thickness skin after very rapid cooling and warming

The ability of low glycerol concentrations and high cooling and warming rates to optimize the survival of frozen/thawed split-thickness porcine skin was investigated. 1H nuclear magnetic resonance spectroscopy was used to measure the diffusion kinetics of glycerol in skin at 4, 12, and 22 degrees C. Equilibrium concentrations were 44 to 69% of the external bathing medium. Rate constants for glycerol diffusion (D/l2) were calculated from the uptake data using a plane sheet model and a least squares method and were independent of external glycerol concentrations: D/l2 = 3.84 x 10(-4) 8-1 at 4 degrees C with an activation energy of 11.2 +/- 4.3 kcal/mol. Skin was cooled rapidly (-5100 degrees C/min) after different times of glycerol permeation at 4 or 22 degrees C, and survival was assessed after warming (+5400 degrees C/min) by an oxygen consumption assay. Recovery of aerobic activity increased in a concentration-dependent manner, and reached 100% after a 10-min exposure to 2 M glycerol at 4 degrees C or 3 min at 22 degrees C, for an uptake of 1.1 M glycerol. Light micrographs of freeze-substituted skin showed a glycerol-dependent decrease in the nucleation and growth of ice in the dermis and epidermis after rapid cooling. A 5-mm exposure to 2 M glycerol at 22 degrees C resulted in the elimination of all observable epidermal ice, except for extremely small ice crystals (< or = 0.5 micron diameter) in the intercellular spaces and in few nuclei, and complete preservation of the fibrous structure of dermal collagen bundles. This cryoprotective mechanism has the potential to offer complete protection of both dermal and viable epidermal targets of freeze/thaw injury and may be applicable to other thin, membranous tissues.

The determination of membrane permeability coefficients of canine pancreatic islet cells and their application to islet cryopreservation

Sufficient numbers of pancreatic islets for successful allotransplantation can be achieved by storing and then pooling islets from several donors. Optimal MHC matching and infectious disease screening also require long-term storage of islets, and cryopreservation is currently the only practical approach. Cryopreservation protocols may be optimized by modeling the changes in cell volume and the associated damage incurred during cryoprotectant addition and dilution and during cooling and warming. The objective of the present work was to determine the following biophysical parameters of canine islet cells; the osmotically inactive cell volume (Vb), hydraulic conductivity (Lp), cryoprotectant permeability coefficient (Ps), and the reflection coefficient sigma. A determination of these parameters allows the simulation of cell responses using computer models. Islets were isolated by collagenase digestion and Euro-Ficoll purification. After 24 h culture, islets were dissociated into single cells using trypsin and 2 mM EGTA. The kinetic change in cell volume as a function of time after exposure to 2 M dimethyl sulfoxide (Me2SO) was measured using an electronic particle counter at 22, 5, and -3 degrees C. At -11 degrees C, cells were preloaded with 1 M Me2SO and exposed to 4 M Me2SO to prevent the formation of ice in the working solution. Kedem-Katchalsky theory was used to describe the cell volume change kinetics, and a three-parameter curve fitting was performed using the Marquardt-Levenberg method to determine Lp, Ps, and sigma values. The Lp was determined to be 0.19 +/- 0.05, 0.037 +/- 0.005, 0.020 +/- 0.003, and 0.013 +/- 0.005 micron.min-1.atm-1 (mean +/- SD) at 22, 5, -3, and -11 degrees C, respectively. The Ps values were 1.05 +/- 0.50, 0.15 +/- 0.04, 0.096 +/- 0.028, and 0.067 +/- 0.029 x 10(-3) cm.min-1 at 22, 5, -3, and -11 degrees C, respectively. The sigma values were 0.81 +/- 0.16, 0.91 +/- 0.09, 0.80 +/- 0.21, and 0.98 +/- 0.04 at 22, 5, -3, and -11 degrees C, respectively. The temperature dependence or activation energy of Lp and Ps was calculated, using the Arrhenius equation, to be 12.7 and 13.5 kcal.mol-1, respectively. These permeability parameters were used to calculate cell water loss and the likelihood of lethal intracellular freezing during cooling, as well as both water flux and solute concentration gradients across the cell membrane during warming.

Quantitative measurement of cell membrane transport: technology and applications

The transport of water and cryoprotective chemicals across cell membranes plays an absolutely fundamental role in the outcome of cryopreservation processing. The diversity of cell types as well as the remarkable range of perturbations that cells are subjected to as part of cryopreservation practices generate many interesting research questions. Simply stated, the extreme conditions typical of cryopreservation protocols extend the limits of membrane transport inquiry well beyond that considered in "normal" cell physiology. This paper provides a brief review of methods which have been used for measuring membrane transport properties, especially those methods developed during the past decade which allow us to measure coupled and uncoupled membrane transport properties of water and cryoprotective agents for individual cells in terms of classical Kedem-Katchalsky membrane transport theory. Representative results obtained from these new technologies will be offered to illustrate their utility and relevance to membrane transport issues arising in cryopreservation practice. Engineers have made significant contributions to this area of research primarily in terms of device development and the application of inverse methods to estimate membrane transport properties.

Chill sensitivity and cryoprotectant permeability of dechorionated zebrafish embryos, Brachydanio rerio

The zebrafish (Brachydanio rerio) was used as a model for basic studies of the chilling sensitivity, permeability and toxicity of cryoprotectants. In both intact and dechorionated embryos, early-stage embryos (1.25, 1.5, 1.75, and 2 h) were more susceptible (P < 0.05) to chilling injury at 0 degrees C than late-stage embryos (50, 75, and 100% epiboly and three-somite stage). Moreover, enzymatic removal of the chorion did not alter (P > 0.05) this pattern of sensitivity to chilling. Eight-hour zebrafish embryos tolerated short-term exposures to temperatures ranging from 4 to 23 degrees C for 3.5 h with no detrimental developmental effects. The permeability of dechorionated embryos to cryoprotectants was examined by measuring the kinetics of volumetric change at various developmental stages (16 cells to six somites or ca. 1.25 to 14 h postfertilization) at 28.5 degrees C. The dechorionated zebrafish embryo is composed of two complex cellular compartments (i.e., a large yolk and the developing blastoderm). From 40 to 100% epiboly, the volumes of yolk and blastoderm remained constant, ca. 82 and 18%, respectively. However, these volumes changed rapidly after epiboly. For example, at the six-somite stage, the yolk composed 61% of the total volume, whereas the blastoderm composed 39%. When three- and six-somite embryos were placed in 1.5 and 2.0 M cryoprotectants (dimethyl sulfoxide and propylene glycol), osmometric measurement of volume changes indicated no permeation of the cryoprotectants. However, some permeation was observed for six-somite embryos immersed in a 2.0 M methanol solution, but not for 3-somite embryos. For up to 30 min at room temperature, these cryoprotectant solutions were toxic to zebrafish embryos; however, 1.5 M glycerol and ethylene glycol solutions were. We conclude that the complex nature of the zebrafish embryo reduces the effectiveness and predictive value of light microscopical measurements for cryoprotectant permeability studies.