Polymeric cryoprotectants in the preservation of biological ultrastructure. III. Morphological aspects

Technology for Biobanking of Epididymal Spermatozoa from Patient with Obstructive Azoospermia: Case Report about Baby Born after Conventional Freezing Only with a Nonpermeable Cryoprotectant 360 kDa Polyvinylpyrrolidone

This publication reports, for the first time, the birth of a healthy child after intracytoplasmic sperm injection (ICSI) of motile spermatozoa after conventional ("slow") freezing of epididymal spermatozoa using 5% polyvinylpyrrolidone (PVP) of high molecular weight (360 kDa). Cryopreservation solution with 10% PVP was added to 30 µL of spermatozoa suspension in a 1:1 ratio, with a final PVP concentration of 5%. Then, polycarbonate capillaries for oocyte denudation with a diameter of 170 µm were filled with 60 µL of the resulting sperm suspension. After that, the capillaries were placed for 10 minutes at a height of 15 cm above liquid nitrogen and immersed into liquid nitrogen. To warm the spermatozoa, the capillaries were immersed in a water bath at a temperature of 40°C for 30 seconds. Oocyte fertilization was performed by ICSI. Zygotes were cultured in vitro for 5 days to the blastocyst stage. More than 100 spermatozoa were obtained after percutaneous epidydimal sperm aspiration, of which 80% were motile. After cryopreservation, storage for 3 months in liquid nitrogen, and thawing, 72% of the total sperm cells remained motile. Ten oocyte-cumulus complexes were found after follicle puncture, and eight metaphase II stage oocytes were fertilized using ICSI. After 18 hours, two pronuclei were found in seven (88%) of the oocytes. An analysis of the morphological characteristics of 5-day-old embryos showed that four (57%) of them reached the blastocyst stage. One embryo was transferred, and the remaining embryos were cryopreserved (vitrified). The onset of pregnancy was detected on the 14th day after embryo transfer, and one healthy girl (3300 g) was born at term.

New method for cryoprotectant-free freezing of human oligoasthenoteratozoospremic spermatozoa with high-molecular polymer

Data about cryoprotectant-free cryopreservation of human ICSI spermatozoa are limited. The aim of this investigation was to compare two technologies for cryopreservation of spermatozoa from men with oligoasthenoteratozoospermia: standard conventional freezing with 5% glycerol (freezing in glycerol) and cryoprotectant-free freezing with 5% high-molecular-weight (360 kDa) polyvinylpyrrolidone (PVP) (PVP-freezing). Capillaries with spermatozoa were cooled in vapor and then plunginged into liquid nitrogen. Head-, midpiece- and tail-abnormality of spermatozoa, mitochondrial membrane potential (MMP) and DNA fragmentation rates after cryopreservation were evaluated. After warming of spermatozoa, fertilization of oocytes (ICSI) was performed. It was detected the lower rate of morphological abnormalities of PVP-frozen spermatozoa in comparison with cells frozen with glycerol (34.6 ± 4.1% vs. 20.7 ± 4.7%, respectively) (P < 0.05). Quality of cells with high MMP after warming in spermatozoa frozen with glycerol was lower than in PVP-frozen spermatozoa (34.7 ± 4.2 vs. 54.5 ± 4.2%, respectively) (P < 0.05). It was established that the DNA fragmentation rate in PVP-frozen spermatozoa was significantly lower in comparison with spermatozoa frozen with glycerol (23.1 ± 2.5% vs. 38.8 ± 3.0%, respectively) (P < 0.05). After fertilization (ICSI) of oocytes, it was established that cleavage and blastulation rates were higher in oocytes after fertilization with PVP-frozen spermatozoa than with spermatozoa frozen with glycerol. Fertilization-, development to 8-blastomeres-, and blastocyst-rates were for PVP-frozen and spermatozoa frozen with glycerol, respectively: 94.4 ± 7.8 vs. 82.2 ± 6.2% (P > 0.1 with tendency to increasing), 90.0 ± 4.6 vs. 69.5 ± 5.1% (P < 0.05), and 45.4 ± 4.1% vs. 30.9 ± 3.3% (P < 0.05). It was concluded that permeable cryoprotectant-free freezing with 5% high-molecular-weight (360 kDa) polyvinylpyrrolidone can be applied successfully for cryopreservation of human oligoasthenoteratozoospremic spermatozoa.

A combination of hydroxypropyl cellulose and trehalose as supplementation for vitrification of human oocytes: a retrospective cohort study

PURPOSE

This study aimed to determine whether the new formulation of vitrification solutions containing a combination of hydroxypropyl cellulose (HPC) and trehalose does not affect outcomes in comparison with using conventional solutions made of serum substitute supplement (SSS) and sucrose.

METHODS

Ovum donation cycles were retrospectively compared regarding the solution used for vitrification and warming of human oocytes. The analysis included 218 cycles (N = 2532 oocytes) in the study group (HPC + trehalose) and 214 cycles (N = 2353 oocytes) in the control group (SSS + sucrose).

RESULTS

No statistical differences were found in ovarian stimulation parameters and baseline characteristics of donors and recipients. The survival rate was 91.3% (95% confidence interval (CI) = 89.8-92.9) in the HPC + trehalose group vs. 92.1% (95% CI = 90.4-93.7) in the SSS + sucrose group (NS). The implantation rate (42.8%, 95% CI = 37.7-47.9 vs. 41.2%, 95% CI = 36.0-46.4), clinical pregnancy rate (CPR) per transfer (60.7%, 95% CI = 53.9-67.5 vs. 56.4%, 95% CI = 49.3-63.5), and ongoing pregnancy rate (OPR) per transfer (48.5%, 95% CI = 41.5-55.5 vs. 46.3%, 95% CI = 39.2-53.4) were similar for patients who received either HPC + trehalose-vitrified oocytes or SSS + sucrose-vitrified oocytes. Statistical differences were found when analyzing blastocyst rate both per injected oocyte (30.2%, 95% CI = 28.3-32.1 vs. 24.1%, 95% CI = 22.3-25.9) and per fertilized oocyte (40.8%, 95%CI = 38.5-43.1 vs. 33.2%, 95% CI = 30.8-35.5) (P < 0.0001). Delivery rate was comparable between groups (37.2%, 95% CI = 30.8-46.6 vs. 36.9%, 95% CI = 30.4-43.4; NS).

CONCLUSIONS

Our data demonstrate that HPC and trehalose are suitable and safe substitutes for serum and sucrose. Therefore, the new commercial media can be used efficiently in the vitrification of human oocytes avoiding viral and endotoxin contamination risk.

Crystalline ice as a cryoprotectant: theoretical calculation of cooling speed in capillary tubes

It is generally assumed that vitrification of both cells and the surrounding medium provides the best preservation of ultrastructure of biological material for study by electron microscopy. At the same time it is known that the cell cytoplasm may provide substantial cryoprotection for internal cell structure even when the medium crystallizes. Thus, vitrification of the medium is not essential for good structural preservation. By contrast, a high cooling rate is an essential factor for good cryopreservation because it limits phase separation and movement of cellular components during freezing, thus preserving the native-like state. Here we present calculations of freezing rates that incorporate the effect of medium crystallization, using finite difference methods. We demonstrate that crystallization of the medium in capillary tubes may increase the cooling rate of suspended cells by a factor of 25-300 depending on the distance from the centre. We conclude that crystallization of the medium, for example due to low cryoprotectant content, may actually improve cryopreservation of some samples in a near native state.

Stereochemical studies of enzymic C-methylations

Samples of methionine carrying a chiral CHDT-group have been prepared from and degraded chemically to chiral acetic acid. With this powerful tool inversion mechanisms were detected for the methylations on sulphur, oxygen and carbon atoms in the biosynthesis of methionine, loganin and cyanocobalamin, respectively. Chirality of the methyl group of methionine is retained during formation of the C-24 methyl group in ergosterol biosynthesis. A stereochemical scheme for the unusual course of this reaction is presented and the current stage of experiments aimed at its verification is discussed.

Media alternatives for the collection, culture and freezing of mouse and cattle embryos

The replacement of biological products in media for the collection, culture and freezing of mammalian embryos was studied. To test the hypothesis that chemically defined surfactants can replace bovine serum albumin (BSA) or serum in embryo media, morula-stage mouse and cattle embryos were collected, cultured, and/or frozen in the surfactant compound, VF5. Collection efficiency of mouse and cattle embryos did not differ whether the medium contained serum or surfactant. In addition, morula-stage mouse and cattle embryos developed and hatched at similar rates in culture media containing either BSA or surfactant. Although the freeze/thaw survival and development in culture of bovine embryos was not significantly different in any of the media, there was a significantly lower hatching rate of mouse embryos frozen with serum or surfactant than with cryoprotectant alone or with cryoprotectant plus albumin-free serum. However, the absence of serum or surfactant in embryo freezing media resulted in embryo loss, presumably due to stickiness. The data suggest that serum can be replaced by a chemically defined surfactant in mouse and cattle embryo transfer systems for the collection, culturing and freezing of embryos. It is likely that the beneficial effects of serum are due to its surfactant properties.

Quick sampling and perpendicular cryosectioning of cell monolayers for the X-ray microanalysis of diffusible elements

A quick sampling and preparation method for freezing of cell monolayers is described. The cells are grown on a large Formvar film supported by a frame of polystyrene. A polyvinylpyrrolidone (PVP) solution is applied to one side of the film forming a flat disc when frozen with a pair of pliers precooled in liquid nitrogen. The PVP solution provides the specimen with sufficient strength and may be used as an elemental standard for absolute quantification if salts of known concentrations are added. Manipulation of the cells prior to freezing is thus restricted to a minimum, which eliminates possible harmful treatments like scraping and centrifugation. The procedure is quickly performed, the freezing being completed within 30 s of the cells having been removed from the culture well. The analytical results reveal low and stable Na:K ratios. Our results confirm that cells in vitro are comparable to cells in vivo with respect to elemental composition.

Biophysical chemical aspects of cellular cryobehavior

Freezing tolerance and resistance in nature are among the most important and challenging aspects of biochemical adaptation to extreme environments. Some biochemical strategies are known but their mechanism is still poorly understood. Cryopreservation of cells and tissues of sensitive organisms is still generally based on physical chemistry rather than on biophysical chemical mechanisms. This paper describes the main aspects of these problems and features new trends in their study.

Interactive effects of cryosolvents, ionic and macromolecular solutes on protein structures and functions

Surprisingly, cryosolvents may mimic the effects of ionic solutes on the structures and functions of macromolecular assemblages, showing additive or opposite effects depending on the respective concentrations. These interactive effects are hard to analyze precisely because they may result from so many possible contributions. However, studies on model systems clearly show the nature of the interactive effects and bring about useful information concerning the mechanism of action of cryosolvents and ions and the response of enzyme systems. Such results suggest new studies on the interaction of biopolymers and water and their possible impact on the cryobehavior of highly organized and living systems.

Application of X-ray microanalysis to cell suspensions of oil palm (Elaeis guineensis Jacq.)

X-ray microanalysis has been used to determine the elemental composition of oil-palm (Elaeis guineesis) cell suspensions without the use of cryoprotectants. Results based on individual cells were gathered over a typical growth cycle of 14 d. During the log phase (5-7 d) there is an increase in the number of cells containing high concentrations of both K (400 mmol kg(-1) dry weight) and P (400 mmol kg(-1) dry weight). Morphologically these cells had thin cell walls and were frequently joined to other cells (two to five cells per clump).

An ultrastructural study of cryofractured myocardial cells with special attention to the relationship between mitochondria and sarcoplasmic reticulum

A comparative study of various cryofracturing techniques has been conducted on the mammalian myocardial cell. Quench freezing of fresh or fixed tissue in melting Freon 22 resulted in severe cellular damage due to ice crystallization. Fixation with Karnovsky's fixative prior to quenching had no modifying effect on the size and distribution of the ice crystals. The crystals were orientated primarily in the direction of the long axis of the myofibrils, manifested as empty tube-like structures in the scanning electron microscope (SEM). Regular cross-bridging often seen at the Z-band levels indicated that ice crystals, at least in some portions of the cells, were confined within the sarcomere. Within the same cell the size of the ice crystals could vary considerably. Treatment of the tissue with polyvinylpyrrolidone (PVP) prior to rapid freezing had no noticeable cryoprotective effect. The surface of the thin layer of PVP surrounding the freeze dried tissue appeared amorphous in the SEM. However, the first evidence of ice crystallization was found a few micrometers under the surface. The freezing artefacts were completely circumvented if the cryofracturing was carried out on ethanol-impregnated or on critical point dried material. While the first method resulted in a smooth fracture plane passing through the cell structures, the intracellular fracture plane of the critical point dried material followed the surface of the cell organelles. Separation of the cell organelles caused by freezing or by critical point drying revealed thread-like structures extending from the mitochondrial surface. Re-examination of SEM-processed material in the transmission electron microscope (TEM) revealed that these structures were part of the sarcoplasmic reticulum (SR), and that a close contact between the SR and the outer mitochondrial membrane existed. TEM of conventional prepared material revealed that strands of electron-dense material, here named 'mito-reticular junctional fibres', bridged the narrow gap between the mitochondrial surface and the SR. It is suggested that these fibres have a specific anchoring function.

Developments in low-temperature biochemistry and biology

Though under most circumstances harmful changes are induced in cellular structures by subzero temperatures, conditions can be found under which such damage is avoided. Thus, in solution, biochemical reactions can be slowed and more easily analysed and many enzyme-substrate complexes can be stabilized and structurally analysed; in crystals, 'stop-action' pictures unveil the stereochemical changes along reaction pathways. The progressive 'solidification' of non-covalent bonds involved in protein structures should permit investigation of their dynamics. Studies at high pressures open the way to new investigations on 'activated' enzyme-substrate complexes and might permit the refinement of current concepts to a considerable degree, as a preliminary but decisive step towards a full description of enzyme mechanisms. The conditions of medium allowing such cryobiochemical studies fail to protect cellular structures against cold. Investigations of plasma membrane behaviour are now under way to determine processes leading to cryosensitivity or cryotolerance of cells.

Cryoultramicrotomy as a preparative method for x-ray microanalysis in pathology

The role of ion shifts in cell injury has become one of the most intriguing fields of application of X-ray microanalysis in pathology. In principle, cryo(ultra)-microtomy is the best preparative method for X-ray microanalysis of diffusible substances. In this review, the following points are discussed: the choice of freezing method and coolant, the use of high molecular weight polymer cryoprotectants and their possible physiological effects the choice of the cryosectioning temperature, and techniques for handling and transfer of sections. Experiences with the sectioning of cryoprotected tissue are presented. Finally, other preparative techniques for microanalysis are compared to cryoultramicrotomy.

Polyvinyl alcohol coating: an improvement of the freeze-fracture technique

A modification of the freeze-fracture technique, involving the coating of tissues with polyvinyl alcohol (Vinol) prior to freezing, is described. This results in substantial improvements over the more conventional method in which material is cryoprotected and frozen in buffered glycerol alone. The high vacuum is produced more rapidly and can be better than in the absence of vinol and the speed of replica recuperation is greatly increased.

Application of scanning electron microscopy to x-ray analysis of frozen-hydrated sections. I. Specimen handling techniques

X-ray microanalysis of frozen-hydrated tissue sections permits direct quantitative analysis of diffusible elements in defined cellular compartments. Because the sections are hydrated, elemental concentrations can be defined as wet-weight mass fractions. Use of these techniques should also permit determination of water fraction in cellular compartments. Reliable preparative techniques provide flat, smooth, 0.5 micrometers-thick sections with little elemental and morphological disruption. The specimen support and transfer system described permits hydrated sections to be transferred to the scanning electron microscope cold stage for examination and analysis without contamination or water loss and without introduction of extraneous x-ray radiation.

The x-ray microanalysis of frozen-hydrated sections in scanning electron microscopy: an evaluation

The present status of the technique to measure concentrations of electrolyte elements and dry mass in or approximately 1 mum thick frozen-hydrated sections of soft biological tissues with electron probe X-ray microanalysis in a scanning electron microscope is critically reviewed. The technique is to quench-freeze fresh specimens to less than -180 degrees C, cut approximately 1 mum thick hydrated cryosections ( less than or equal to -70 degrees C), transfer on to a cold stage (less than -170 degrees C) of a suitable microanalytical arrangement, obtain scanning transmission images to identify the cell and tissue compartments, locate an electron probe (several mum2 to 100 nm) on the areas of interest and collect X-ray quanta. The X-ray quanta collected with suitable spectrometers (WDS and EDS) and processed with a computer using a comprehensive programme based on continuum normalization procedures ('Hall' programme). The cryosections are analysed first in a hydrated state and second after dehydration within the microanalyser column to obtain directly elemental concentrations in muM kg-1 wet wt and muM kg-1 dry wt of the compartments identified under the beam. The local water-fractions are estimated and the elemental concentrations converted into muM 1(-1) water. In the past 7 years the technique has been applied to obtain fully quantitative information on Na, K, Cl, P, S, Ca and H2O in more than ten types of tissue.

Ultrastructural effects of the high molecular weight cryoprotectants Dextran and polyvinyl pyrrolidone on liver and brown adipose tissue in vitro

The ultrastructural changes caused by incubation of rat liver and brown fat in buffered solutions of high molecular weight cryoprotectives (Dextran and polyvinyl pyrrolidone) at high concentrations (up to 25% w/v) have been examined. Under appropriate conditions of incubation rather small qualitative changes were found. Hepatocytes showed some signs of plasmolysis. Evidence for the endocytosis of Dextran and polyvinyl pyrrolidone was obtained. Cryoultramicrotomy of unfixed, quench-frozen specimens after the same incubation procedures showed good cutting properties and only slight ice-crystal damage. Several of the larger tissue compartments were recognizable in such sections. Although high molecular weight cryoprotectants do penetrate cells by endocytosis (and these effects require further functional evaluation), the present observations provide further support for the idea that such compounds significantly improve the quench-freezing of biological specimens and offer a practical way forward for the preparation of material for X-ray microanalysis of diffusible elements.

Ultrastructure of red cells frozen with hydroxyethyl starch

The freeze fracture appearance of red cells frozen in the presence of varying concentrations of hydroxyethyl starch (HES) is described. A technique is used which allows examination of a small portion of cells from a larger unit. The frozen cells appear distorted probably as a result of osmotic dehydration but indicate no evidence of intracellular ice. The frozen mixture with HES has three phases--a particulate phase consisting of the concentrated HES (and other salts), a sculptured ice phase and the red cells. When the concentration of HES is increased, the particulate phase becomes more prominent and at 14% HES appears to surround nearly all cells. In cells frozen in saline alone and 4% HES, the cytoplasm in a majority of cells has numerous cavities and depressions. Since such units haemolyse badly when thawed, it is possible that these regions indicate structural damage. In contrast, those units frozen with 14% HES (in which nearly 85% of the cells survive freeze-thaw) possess cells which only infrequently have such regions in the cytoplasm.

Biological X-ray microanalysis

By means of X-ray microanalysis it is now practical to detect approximately 10(-19) g of an element in a static-probe analysis within an ultrathin section, with analytical spatial resolution in the range 20--30 nm. The main difficulties for biological microanalysis are connected not with sensitivity but with specimen preparation and beam damage. Careful cryopreparation, beginning with the quench-freezing of a small block of tissue, is essential even for determining the storage sites, or sites of binding in vivo, of physiologically active elements. In frozen-dried or frozen-hydrated sections of quench-frozen tissue, it is now possible to measure local mass fractions of diffusible as well as of bound elements.

New trends in cryoenzymology: I.-Supercooled aqueous solutions

A water in oil emulsion technique is proposed to investigate enzyme catalyzed reactions at sub-zero temperatures in the supercooled liquid state to avoid some reversible effects of the usual cosolvents on kinetics. Some results are listed: potentialities and technical problems of the procedure are discussed.

Cryo-ultramicrotomy and myofibrillar fine structure: a review

In the past, the techniques of electron microscopy and X-ray diffraction have both been very informative about the ultrastructure of the muscle myofibril But X-ray diffraction patterns are difficult to interpret unambiguously and until now specimen preservation in plastic embedded muscle has been sufficiently poor to make it difficult to use electron micrographs of muscle as a means of interpreting the available X-ray diffraction evidence. The possibility of using ultrathin sections of frozen muscle, in which the disruptive steps of chemical dehydration and plastic embedding can be avoided, promises to help to bridge the information gap between present X-ray and electron microscope results. For this reason we here review the application of the cryosectioning technique to muscle, we assess the technique in terms of the improvements in preservation which have so far been obtained and which might be expected and we discuss some of the many potential advantages and uses of this technique for studies of muscle ultrastructure and function. It is concluded that this technique should be developed vigorously since it promises to play a very important role in muscle research in the future.

Biological freezing and cryofixation

Freezing and freeze fixation are commonly used to achieve ultrastructural and biological preservation. Freezing in biological materials is complex because of their heterogeneous nature-water is unevenly distributed and the various domains are separated by semi-permeable membranes. Processes to be considered include: (1) osmotic gradients leading to redistribution of water, (2) nucleation and uncontrolled growth of ice crystals, (3) recrystallization of nucleated aqueous substrate. To avoid ultrastructural deformation in biological specimens cryofixatives are commonly employed. These are water soluble molecules, able to penetrate cell membranes (e.g. glycerol and dimethylsulphoxide). Interacting strongly with water, ions and bipolymers, they give rise to metabolic and physiological changes which render them useless for X-ray microprobe analytical studies. However, they can enable tissues to survive low temperature storage. Some plants and animals develop in vivo mechanisms which enable them to avoid or tolerate freezing. Alternative means of cryofixation have recently been developed. They rely on non-penetrating polymers of high and specific water binding capacity. These polymers enable the extracellular spaces to be vitrified rather than frozen. Such suppression of ice nuclei enables the cell contents to be maximally subcooled, resulting in the formation of nm dimension ice crystals. Since the polymers have a low osmotic activity and do not penetrate membranes, the interior of the cell is substantially undisturbed. Also hydrophilic polymers used as cryofixatives are physiologically less active than conventional cryoprotectants at equivalent weight concentrations, and th eir mechanical properties render them useful as matrices for cryosectioning.

Polymeric cryoprotectants in the preservation of biological ultrastructure. II. Physiological effects

A study has been made of the physiological effects of three non-penetrating polymeric cryoprotective agents on sixteen different plant and animal cells and tissues. The cryoprotectants, when used at concentrations at which they are effective in preventing ice-crystal formation, generally have a lower toxicity to cells and tissue than similar concentrations of glycerol. The relatively low toxicity of these substances suggests that they would be more suitable as cryoprotectants for morphological and analytical studies than the commonly used low molecular weight compounds.

Polymer cryoprotectants in the preservation of biological ultrastructure. I. Low temperature states of aqueous solutions of hydrophilic polymers

The solid states formed by vitrified and frozen aqueous solutions of some hydrophilic polymers, able to act as biological cryoprotectants, have been studied by differential scanning calorimetry and freeze fracture electron microscopy. Glass transitions, devitrification, recrystallization and melting behaviour of aqueous solutions of polyvinylpyrrolidone, hydroxyethyl starch and dextran have been established. The vitrified polymer solutions exhibit a characteristic microspheral morphology which is not induced by the quench cooling process but is an inherent feature of the solutions themselves.