Analysis of "solution effects" injury: rabbit renal cortex frozen in the presence of dimethyl sulfoxide

Investigating the Solubility and Activity of a Novel Class of Ice Recrystallization Inhibitors

O-aryl-β-d-glucosides and N-alkyl-d-gluconamides are two classes of effective ice recrystallization inhibitors (IRIs), however their solubilities limit their use in cryopreservation applications. Herein, we have synthesized and assessed phosphonate analogues of small-molecule IRIs as a method to improve their chemical and physical properties. Four sodium phosphonate compounds 4–7 were synthesized and exhibited high solubilities greater than 200 mM. Their IRI activity was evaluated using the splat cooling assay and only the sodium phosphonate derivatives of α-methyl-d-glucoside (5-Na) and N-octyl-d-gluconamide (7-Na) exhibited an IC50 value less than 30 mM. It was found that the addition of a polar sodium phosphonate group to the alkyl gluconamide (1) and aryl glucoside (2) structure decreased its IRI activity, indicating the importance of a delicate hydrophobic/hydrophilic balance within these compounds. The evaluation of various cation-phosphonate pairs was studied and revealed the IRI activity of ammonium and its ability to modulate the IRI activity of its paired anion. A preliminary cytotoxicity study was also performed in a HepG2 cell line and phosphonate analogues were found to have relatively low cytotoxicity. As such, we present phosphonate small-molecule carbohydrates as a biocompatible novel class of IRIs with high solubilities and moderate-to-high IRI activities.

Principles of Ice-Free Cryopreservation by Vitrification

Vitrification is an alternative to cryopreservation by freezing that enables hydrated living cells to be cooled to cryogenic temperatures in the absence of ice. Vitrification simplifies and frequently improves cryopreservation because it eliminates mechanical injury from ice, eliminates the need to find optimal cooling and warming rates, eliminates the importance of differing optimal cooling and warming rates for cells in mixed cell type populations, eliminates the need to find a frequently imperfect compromise between solution effects injury and intracellular ice formation, and can enable chilling injury to be "outrun" by using rapid cooling without a risk of intracellular ice formation. On the other hand, vitrification requires much higher concentrations of cryoprotectants than cryopreservation by freezing, which introduces greater risks of both osmotic damage and cryoprotectant toxicity. Fortunately, a large number of remedies for the latter problem have been discovered over the past 35 years, and osmotic damage can in most cases be eliminated or adequately controlled by paying careful attention to cryoprotectant introduction and washout techniques. Vitrification therefore has the potential to enable the superior and convenient cryopreservation of a wide range of biological systems (including molecules, cells, tissues, organs, and even some whole organisms), and it is also increasingly recognized as a successful strategy for surviving harsh environmental conditions in nature. But the potential of vitrification is sometimes limited by an insufficient understanding of the complex physical and biological principles involved, and therefore a better understanding may not only help to improve present outcomes but may also point the way to new strategies that may be yet more successful in the future. This chapter accordingly describes the basic principles of vitrification and indicates the broad potential biological relevance of this alternative method of cryopreservation.

Cryopreservation of Rat and Monkey Liver Slices

A method for the long-term storage of liver slices by cryopreservation was developed. The viability of liver slices was determined by analysing the leakage of alanine aminotransferase, urea production, and the metabolism of testosterone. Rat liver slices were found to be optimally cryopreserved by exposure for 30 minutes to 12% dimethyl sulphoxide (v/v) at 2°C before freezing. Subsequent direct immersion in liquid nitrogen was more effective than a cooling rate of ±1°C/mmute, which reduced viability. Storage at a temperature of -80°C lowered viability compared to storage at -196°C.

These conditions for optimal cryopreservation were used to cryopreserve rat, rhesus monkey and cynomolgus monkey liver slices. The viability of these liver slices was maintained at: 74%, 86% and 85%, respectively, when alanine aminotransferase content was measured; 80%, 109% and 82%, respectively, when urea production was measured; and 109%, 60% and 85%, respectively, when the metabolism of testosterone was measured. Viability was maintained for at least one month. The results show that, by using the method presented here, liver slices from these species can be stored while maintaining viabilities similar to initial values. This method will facilitate the optimal use of liver slices and reduce the number of experimental animals used.

Effect of high DMSO concentration on albumin during freezing and vitrification

This is a light microscopy image taken of the frozen solution at −20 °C during equilibrium freezing. The freeze concentrate surrounding the ice crystals, comprises unfrozen water and solutes (DMSO and albumin). The bright rectangle is the IR aperture.

Physical and biological aspects of renal vitrification

Cryopreservation would potentially very much facilitate the inventory control and distribution of laboratory-produced organs and tissues. Although simple freezing methods are effective for many simple tissues, bioartificial organs and complex tissue constructs may be unacceptably altered by ice formation and dissolution. Vitrification, in which the liquids in a living system are converted into the glassy state at low temperatures, provides a potential alternative to freezing that can in principle avoid ice formation altogether. The present report provides a brief overview of the problem of renal vitrification. We report here the detailed case history of a rabbit kidney that survived vitrification and subsequent transplantation, a case that demonstrates both the fundamental feasibility of complex system vitrification and the obstacles that must still be overcome, of which the chief one in the case of the kidney is adequate distribution of cryoprotectant to the renal medulla. Medullary equilibration can be monitored by monitoring urine concentrations of cryoprotectant, and urine flow rate correlates with vitrification solution viscosity and the speed of equilibration. By taking these factors into account and by using higher perfusion pressures as per the case of the kidney that survived vitrification, it is becoming possible to design protocols for equilibrating kidneys that protect against both devitrification and excessive cryoprotectant toxicity.

Cryopreservation of complex systems: the missing link in the regenerative medicine supply chain

Transplantation can be regarded as one form of "antiaging medicine" that is widely accepted as being effective in extending human life. The current number of organ transplants in the United States is on the order of 20,000 per year, but the need may be closer to 900,000 per year. Cadaveric and living-related donor sources are unlikely to be able to provide all of the transplants required, but the gap between supply and demand can be eliminated in principle by the field of regenerative medicine, including the present field of tissue engineering through which cell, tissue, and even organ replacements are being created in the laboratory. If so, it could allow over 30% of all deaths in the United States to be substantially postponed, raising the probability of living to the age of 80 by a factor of two and the odds of living to 90 by more than a factor of 10. This promise, however, depends on the ability to physically distribute the products of regenerative medicine to patients in need and to produce these products in a way that allows for adequate inventory control and quality assurance. For this purpose, the ability to cryogenically preserve (cryopreserve) cells, tissues, and even whole laboratory-produced organs may be indispensable. Until recently, the cryopreservation of organs has seemed a remote prospect to most observers, but developments over the past few years are rapidly changing the scientific basis for preserving even the most difficult and delicate organs for unlimited periods of time. Animal intestines and ovaries have been frozen, thawed, and shown to function after transplantation, but the preservation of vital organs will most likely require vitrification. With vitrification, all ice formation is prevented and the organ is preserved in the glassy state below the glass transition temperature (T(G)). Vitrification has been successful for many tissues such as veins, arteries, cartilage, and heart valves, and success has even been claimed for whole ovaries. For vital organs, a significant recent milestone for vitrification has been the ability to routinely recover rabbit kidneys after cooling to a mean intrarenal temperature of about -45 degrees C, as verified by life support function after transplantation. This temperature is not low enough for long-term banking, but research continues on preservation below -45 degrees C, and some encouraging preliminary evidence has been obtained indicating that kidneys can support life after vitrification. Full development of tissue engineering and organ generation from stem cells, when combined with the ability to bank these laboratory-produced products, in theory could dramatically increase median life expectancy even in the absence of any improvements in mitigating aging processes on a fundamental level.

Vitrification of large tissues with dielectric warming: biological problems and some approaches to their solution

If large pieces of tissue and organs are to be successfully stored at low temperatures, some means must be found to minimize the disruption of extracellular structures by the ice that develops during conventional cryopreservation methods. The use of sufficiently high concentrations of cryoprotectant (CPA) to vitrify rather than freeze the tissue is a possible solution to this problem, and the retention of function of embryos and elastic arteries after vitrification suggests that some cells and tissues at least can withstand exposure to the high concentrations of CPA necessary for this process to occur. There are, however, additional problems in applying vitrifying techniques to bulky tissues and organs. These are related to the additional time required for tissue equilibration of CPA to occur and the consequences for toxic injury, the difficulty in achieving sufficiently rapid and uniform cooling rates to produce the required glassy state, and the even more rapid and uniform warming rates that are necessary to avoid devitrification. Non-uniformity of temperature will increase the risk of mechanical stresses and fractures developing in the glass during rapid warming. This paper reviews possible strategies and the progress that has been made in overcoming these problems. This will include the permeation of CPA mixtures into whole tissues and possibilities for reducing their toxicity by the inclusion of adjuncts such as ice inhibitors and sugars. The warming of tissues by dielectric heating is currently the only practical means by which sufficiently rapid rates can be achieved in bulky tissues given that the tolerable limits of CPA concentration will most likely be insufficient to prevent the development of ice nuclei during cooling. The biological effects of microwaves are reviewed and their effectiveness in producing the required uniformity in warming of tissue models of various shapes are discussed.

The technical feasibility of cryonics

Cryonic suspension is a method of stabilizing the condition of someone who is terminally ill so that they can be transported to the medical care facilities that will be available in the late 21st or 22nd century. There is little dispute that the condition of a person stored at the temperature of liquid nitrogen is stable, but the process of freezing inflicts a level of damage which cannot be reversed by current medical technology. Could this damage be reversed by future technology? We consider the limits of what medical technology should eventually be able to achieve (based on currently understood chemistry and physics) and whether the repair of frozen tissue is within those limits.

Studies on the mechanisms of mammalian cell killing by a freeze-thaw cycle: conditions that prevent cell killing using nucleated freezing

Normally a freeze-thaw cycle is a very efficient method of killing mammalian cells. However, this report describes conditions that prevent killing of cultured mammalian cells by nucleated freezing at -24 degrees C. Optimal protection from cell killing at -24 degrees C was obtained in isotonic solutions containing an organic cryoprotectant such as dimethyl sulfoxide (DMSO; 10%, v/v), a saccharide such as sucrose over a broad concentration range from 50 to 150 mM, and glucose. Glycerol was also an effective cryoprotectant but other organic solvents were ineffective, although in some cases they appeared to protect cell membranes, while not protecting other vital components. A wide variety of saccharide structures were effective at protecting cells from freeze-thaw killing, with trehalose being particularly effective. The degree of resistance to killing by a freeze-thaw cycle under these conditions varied widely among different cell lines. If toxicity of DMSO was responsible for this variability of cryoprotection, it must have been due to short-term, not longer term, toxicity of DMSO. Studies on the mechanism by which cells are protected from killing under these conditions indicated that neither vitrification of the medium nor the concentrating of components during freezing were involved. One model not eliminated by the mechanistic studies proposes that the organic solvent cryoprotectant component acts by fluidizing membranes under the thawing conditions, so that any holes produced by ice crystals propagating through membranes can reseal during the thawing process. In this model one of the mechanisms by which the saccharide component could act is by entering the cells and stabilizing vital intracellular components. Consistent with this, a freeze-thaw cycle promoted the uptake of labeled sucrose into cultured cells.

Some emerging principles underlying the physical properties, biological actions, and utility of vitrification solutions

Vitrification solutions are aqueous cryoprotectant solutions which do not freeze when cooled at moderate rates to very low temperatures. Vitrification solutions have been used with great success for the cryopreservation of some biological systems but have been less successful or unsuccessful with other systems, and more fundamental knowledge about vitrification solutions is required. The purpose of the present survey is to show that a general understanding of the physical behavior and biological effects of vitrification solutions, as well as an understanding of the conditions under which vitrification solutions are required, is gradually emerging. Detailed nonequilibrium phase diagram information in combination with specific information on the tolerance of biological systems to ice and to cryoprotectant at subzero temperatures provides a quantitative theoretical basis for choosing between vitrification and freezing. The vitrification behavior of mixtures of cryoprotective agents during cooling is predictable from the behavior of the individual agents, and the behavior of individual agents is gradually becoming predictable from the details of their molecular structures. Progress is continuing concerning the elucidation of mechanisms and cellular sites of toxicity and mechanisms for the reduction of toxicity. Finally, important new information is rapidly emerging concerning the crystallization of previously vitrified cryoprotectant solutions during warming. It appears that vitrification tendency, toxicity, and devitrification all depend on subtle variations in the organization of water around dissolved substances.

Variation of cooling rate and concentration of dimethyl sulfoxide on rabbit kidney function

Rabbit kidney function was assessed in vitro after cryoprotection with either 3 or 4 M dimethyl sulfoxide. The introduction and removal of the cryoprotectant was carried out in a stepwise progressive manner and the removal in a stepwise progressive manner with hypertonic mannitol solutions. This in vitro model can be shown to respond to various ischemic-like states resulting in poor or absent function. Active tubular transport can be demonstrated. It has been used by many authors as an intermediate step prior to the ultimate test of reimplant and contralateral nephrectomy. Variations in the rate of cooling at cryoprotection levels of 3 and 4 M dimethyl sulfoxide concentration (Me2SO) were carried out. In general, at 3 M concentration of Me2SO, creatinine clearance, sodium and glucose reabsorption are preserved with a fair degree of success after cooling to -10, -15, and -20 degrees C in our model, when the rate of cooling to these levels is 1.0 degree C/min. When a cooling rate of 0.5 degree C/min is used, renal function is significantly reduced whether the final temperature is -10, -15, or -20 degrees C. Control rabbit kidneys will tolerate 4 M concentration of Me2SO and give fairly good function. When cooled to -15 or -20 degrees C, there is poor function at 0.1 and 0.5 degrees C/min. Fair function is obtained at the rate of 1 degree C/min to -10 degrees C. Therefore, at cryoprotectant levels of 3 and 4 M Me2SO, kidney function as assayed by in vitro perfusion, is better when the cooling rate is 1.0 degree C/min.

Studies of capsule and capsular space of cat muscle spindles

The presence of hyaluronate in the capsular space of the cat muscle spindle was demonstrated using alcian blue staining at various pHs, the critical electrolyte concentration technique and hyaluronidase treatment. In spindles with intact capsules an extracellular marker, the dye Ruthenium Red, gained access to the capsular space through the gap in the sleeve region, but for a limited distance. In muscle spindles with the capsule nicked, the marker diffused into the capsular space in the equatorial region, revealing a dense network in this space which consisted of globular structures interconnected by thin filaments. Based on their thickness, these filaments were inferred to be hyaluronic acid, and the globular structures were inferred to be protein molecules. Longitudinal diffusion of the dye into the capsular space through the nicked site was limited. The limited diffusion is probably due to electrostatic binding of the dye, which is a hexavalent cation, to negatively charged glycosaminoglycan hyaluronate that is present in the space. The transcapsular potential was measured by use of glass micropipettes filled with 3 M-KCl. The value was 15 mV +/- 4 (average +/- S.D., n = 12; range, 10-20 mV) inside negative. The input resistance and capacitance of the capsule, measured with two independent electrodes, varied widely (1.3-8.0 M omega and 0.5-1.3 nF, n = 4) and the capsule showed marked delayed rectification to outward current pulses. [K+] in the space measured with K+-sensitive resin-filled glass micropipettes was a few millimolar higher than that in the bathing solution. The effects of [K+] and [Ca2+] on impulse activities were examined in spindles with intact capsules or with partially resected capsules. In spindles with intact capsules the effects of [K+] and [Ca2+] were significantly less or negligible compared with those in spindles with the capsule opened. Hyaluronidase (approximately 10(-4) g/ml) added to the bathing solution around nicked capsules significantly reduced both resting and stretch-induced impulse activities in 40-50 min. By this time the capsular space was completely collapsed. An increase in [K+] of the bathing solution from 3.5 to 6 or 8 mM restored these impulse activities. A similar restoring effect was also observed when [Ca2+] in the bathing solution was reduced.(ABSTRACT TRUNCATED AT 400 WORDS)

The relevance of cryoprotectant "toxicity" to cryobiology

Cryoprotective agents are essential for the cryopreservation of almost all biological systems. These additives, however, do not usually permit 100% survival after freezing and thawing, though from a theoretical point of view they should be able to fully suppress all known types of freezing injury. In view of the known biological and physicochemical effects of cryoprotectants, it is suggested that the toxicity of these agents is a key limiting factor in cryobiology. Not only does this toxicity prevent the use of fully protective levels of additive, but it may also be manifested in the form of cryoinjury over and beyond the cryoinjury due to classical causes. Evidence for this extra injury ("cryoprotectant-associated freezing injury") is reviewed. It is suggested that better suppression of toxicity is possible and will lead to advances in cryopreservation.

Ice-free cryopreservation of mouse embryos at -196 degrees C by vitrification

The failure of complex mammalian organs, such as the kidney, to function following freezing to low temperatures is thought to be due largely to mechanical disruption of the intercellular architecture by the formation of extracellular ice. Classical approaches to the avoidance of ice formation through the imposition of ultra-rapid cooling and warming rates or by gradual depression of the equilibrium freezing point during cooling to -80 degrees C have not been adequate. An alternative approach relies on the ability of highly concentrated aqueous solutions of cryoprotective agents to supercool to very low temperatures. At sufficiently low temperatures, these solutions become so viscous that they solidify without the formation of ice, a process termed vitrification. When embryo suspensions are cryopreserved using conventional procedures, this supercooling behaviour allows intracellular vitrification, even in the presence of extracellular ice. We have therefore used mouse embryos to examine the feasibility of obtaining high survival following vitrification of both the intra- and extracellular solutions and report here that in properly controlled conditions embryos seem to survive in high proportions after cryopreservation in the absence of ice.

The effect of cooling and warming rate on cortical cell function of glycerolized rabbit kidneys

Experiments previously reported (I.A. Jacobsen, D.E. Pegg, H. Starklint, J. Chemnitz, C.J. Hunt, P. Barfort, and M.P. Diaper, Cryobiology 19, 668, 1982) suggested that rabbit kidneys permeated with 2 M glycerol are least damaged during freezing and thawing if they are cooled very slowly (1 degree C/hr). Using similar techniques of glycerolization, cooling, storage at -80 degrees C, rewarming, and deglycerolization, active cell function in cortical tissue slices prepared from such kidneys has now been studied. Oxygen uptake, tissue K+/Na+ ratio after incubation, and slice/medium PAH ratio after incubation were measured. Kidneys cooled at 3.1 degree C/min and warmed at 4.2 degrees C/min gave poor results in the previous studies and the lowest levels of cell function in the present experiments. Kidneys cooled at 1 degree C/hr exhibited degrees of slice function that were dependent on warming rate: warming at 1 degree C/min was better than warming at either 1 degree C/hr or c.20 degrees C/min. These results refine the previously drawn conclusions, (loc cit) and indicate optimal cooling and warming rates for rabbit kidneys containing 2 M glycerol, in the region of 1 degree C/hr cooling and 1 degree C/min warming. These rates are much lower than have hitherto been used by others for any system. Some implications of these findings are discussed.

Factors influencing renal cryopreservation. I. Effects of three vehicle solutions and the permeation kinetics of three cryoprotectants assessed with rabbit cortical slices

A renal cortical slice model was used to assess the effects on viability of three vehicle solutions-Krebs-Henseleit (K-H), solution A, and RPS-2--at 25 degrees C. After 120 min incubation no differences in [K+]/[Na+] ratios were found. Tracer techniques were used to study the osmotic effects and permeation kinetics at 25 degrees C of three cryoprotectants (dimethyl sulfoxide (Me2SO), ethylene glycol, and glycerol) and the effect of the vehicle solution (K-H or RPS-2) on Me2SO kinetics. It was found that Me2SO was most permeable and ethylene glycol least, and that ethylene glycol had unusual effects which suggest that it may not act as a simple solute. Differences were found when Me2SO was introduced in K-H and RPS-2 that are believed to be related to the binding properties of Me2SO to cell constituents.

Analysis of "solution effects" injury. Equations for calculating phase diagram information for the ternary systems NaCl-dimethylsulfoxide-water and NaCl-glycerol-water

Slowly frozen cells are said to be subject to solution effects injury. An understanding of the mechanism of solution effects injury depends upon an understanding of the compositional changes brought about in the extracellular solution during the freezing process. To facilitate analysis of the mechanisms of freezing injury during slow cooling, empirical equations have been developed which permit a description of these changes in composition for the NaCl-dimethylsulfoxide-water ternary system and for the NaCl-glycerol-water ternary system. The equations describe the region of the phase diagram in which compositional changes are brought about only as a result of the precipitation of ice. The present phase diagram equations may be rearranged to give expression for composition variables such as water content, salt concentration, unfrozen fraction of the solution, etc., which may be employed in the analysis of the relationship between solution composition and solution effects injury.