Membrane permeability parameters for freezing of stallion sperm as determined by Fourier transform infrared spectroscopy

Cryopreservation of spermatozoa from black-and-gold howler monkeys (Alouatta caraya) using egg yolk-based or soy lecithin-based extenders

There are more than 200 species and subspecies of Neotropical Primates of which more than 40% are listed as threatened by the IUCN Red List of Threatened Species. Both in situ and ex situ conservation programs can benefit from the use of assisted reproductive technologies. The objective of this study was to evaluate, for the first time, cryopreservation techniques for Alouatta caraya semen. Semen samples were collected from five adult males, analyzed, and frozen in either Test-egg yolk or Test-soy lecithin-based extenders containing either 3 or 4% glycerol. Frozen-thawed samples were analyzed at 10, 40, and 80 min post-thaw. Egg yolk-based extenders were overall better than soy lecithin-based extenders. There was no significant difference between 3 and 4% glycerol in any of the parameters analyzed, however, 4% glycerol in egg yolk-based extender produced more favorable results for total motility, intact plasma membrane, lipid peroxidation, and DNA fragmentation index. This study brought novel information on semen characteristics and cryopreservation aspects for A. caraya, which can help shape future experiments to improve the outcome of frozen-thawed sperm for this and other species of Neotropical primates.

Cryopreservation of Yak Semen: A Comprehensive Review

An urgent need to boost the sustainability and efficiency of animal production exists, owing to the growing global population. Enhancing the global fertility of animals, especially cattle, is essential to ameliorate this issue. Artificial insemination and sperm cryopreservation have a considerable and favorable influence on the quantity and quality of the cattle produced. Sperm cryopreservation is crucial for livestock production because it promotes and accelerates genetic diversity and the worldwide dispersion of animals with enhanced genetics. Owing to the importance of cryobiology in reproductive technologies, researchers are developing new approaches, and they are testing cryoprotectant drugs to enhance sperm cryosurvival. However, the viability of sperm after freezing is low and widely varies across breeding yaks. These faults are crucial because they impede advances in reproductive biotechnology and the study of mammalian gametes at a fundamental level. Using chemicals, researchers have developed and enhanced various extenders with varying degrees of efficiency to reduce cryodamage and oxidative stress. In this article, we review the cryopreservation of yak semen, the development of extenders, the difficulties faced during cryopreservation, and the evaluation of semen quality using various methodologies. This review might be helpful for researchers exploring semen cryopreservation in the future, as demand for enhanced cryopreservation exists to boost the post-thaw viability and fertility of sperm.

The replacement of fresh egg yolk by lyophilized egg yolk in Tris-base extender in cryopreserved Boer and Saanen semen

Egg yolk is a common cryoprotectant that can be used as a semen extender to protect the spermatozoa from damage during cryopreservation. Therefore, the aim of this study was to investigate the efficacy of fresh and lyophilized egg yolk, as a Tris-base extender, on the quality of cryopreserved goat semen. Semen from ten rams of two different breeds (Boer and Saanen) was collected using an artificial vagina. Each ejaculate sample was divided into four equal aliquots, which contained 20% of the fresh egg yolk (a control group), and then 10%, 15%, and 20% of the lyophilized egg yolk as a Tris-base extender. Sperm motility and kinematic parameters were determined using a computer assisted semen analyzer (CASA). The results showed that the addition of 20% of the fresh egg yolk in Tris-base extender exhibited significantly higher progressive motility, progressive fast motility, distance curve line (DCL), and beat cross frequency (BCF) parameters in the post-thaw Boer and Saanen goat sperm when compared with the addition of 10%, 15%, and 20% of the lyophilized egg yolk. The percentage of total motility, and immotile parameters in the post-thaw Boer and Saanen goat sperm were not significantly different between the control and 10%, 15% as well as 20% of the lyophilized egg yolk groups. Moreover, the percentage of viability parameter in the Boer and Saanen goat sperm was not significantly different between the control and 10% of the lyophilized egg yolk group, but showed significant difference between the control group and 15% and 20% of the lyophilized egg yolk groups. Furthermore, the interaction between the two breeds was significantly different in terms of head activity (HAC), and straightness (STR) parameter. In conclusion, the treatment with 20% of fresh egg yolk in Tris-base extender is superior to the lyophilized egg yolk. However, an addition of 10% of the lyophilized egg yolk in Tris-base extender presented the percentage of total motility and viability parameters showing no difference with 20% of fresh egg yolk. Therefore, 10% of the lyophilized egg yolk in Tris-base extender provided detail of the lyophilized egg yolk protocol in cryopreserved goat semen as an example of an alternative extender to 20% of fresh egg yolk for situations where an animal's origin represents a microbiological risk.

Cryopreservation of human T lymphocytes under fast cooling with controlled ice nucleation in cryoprotective solutions of low toxicity

Cryopreservation of human T lymphocytes has become an essential tool for some cell-based immunotherapy. However, the cryopreservation procedure of the cells has not been systematically studied. In particular, the key factors of ice seeding and cryoprotective agents (CPA) driving the success of cryopreservation remain unclear. We systematically investigated the key factors, including cooling rate, ice-seeding temperature, CPA concentration, and types of CPA, during cryopreservation of human T lymphocytes with controlled ice nucleation. We found that ice seeding at below -10 °C could enable human T lymphocytes to be cooled at 90 °C min^-1 with high relative viability and recovery after rewarming, 94.9% and 90.2%, respectively, which are significantly higher than those without ice seeding (P < 0.001). After optimization, the concentration of dimethyl sulphoxide was as low as 2% (v/v) with relative viability and recovery of 95.4% and 100.8%, respectively, at the cooling rate of 90 °C min^-1 after ice seeding at -16 °C. The cryopreservation procedure developed in this study could facilitate the understanding of the mechanism for ice seeding and cell injury and offer a promising cryopreservation method with a high cooling rate and extremely low toxicity for extensive clinical application of immunotherapy.

Use of In Situ Fourier Transform Infrared Spectroscopy in Cryobiological Research

In this chapter, we describe how Fourier transform infrared spectroscopy (FTIR) can be applied in cryobiological research to study: structure and thermal properties of biomolecules in cells and tissues, physical properties of cryopreservation and freeze-drying formulations, and permeation of molecules into cells and tissues. An infrared spectrum gives information about characteristic molecular vibrations of specific groups in molecules, whereas the temperature dependence of specific infrared bands may reveal information about conformational and phase changes. Infrared spectroscopy is minimally invasive and does not require labeling, whereas spectra can be recorded in any physical state of a sample. Data acquisition and spectral processing procedures are described to study phase state changes of protective formulations, cell membrane phase behavior during freezing and drying, protein denaturation during heating, and permeation of protective molecules into tissues. The latter can be used to estimate incubation times needed to load tissues with sufficient amounts of protective agents for cryopreservation or freeze-drying.

Alteration of the lipid phase transition during mouse embryos freezing after in vitro culture with linoleic acid

Lipids significantly affect embryo cryopreservation in some mammalian species depending on the cell lipidome quantity and composition. One of the ways to study the relationship between lipid content and cryotolerance of cells is to study the effect of lipidome modification on laboratory mice. The objective of this research was to study how in vitro culture of mouse embryos with linoleic acid (LA) will affect lipid phase transition (LPT) during cooling and subsequent embryo development after cryopreservation. Embryos obtained in vivo at the 2-cell stage were cultured with 200 μM LA for 46 h up to the morula/blastocyst stage. Thereafter, one portion of embryos was slowly frozen to reveal the effect of LA on survival after cryopreservation, another portion was used to characterize the lipid composition and to determine the temperature of the LPT onset. Confocal fluorescence microscopy of Nile Red stained embryos showed a significant increase in lipid content of the LA treated group compared to the controls. Raman measurements showed that the onset of LPT in LA treated embryos is lower than in untreated ones: -5 °C vs +2 °C. However, these changes in the LPT onset did not affect the survival rates of embryos after cryopreservation. In summary, in vitro culture with LA changes the biophysical characteristics of embryos' lipidome and is realized in lower LPT onset, but this does not affect embryo survival after cryopreservation.

Principles Underlying Cryopreservation and Freeze-Drying of Cells and Tissues

Cryopreservation and freeze-drying can be used to preserve cells or tissues for prolonged periods. Vitrification, or ice-free cryopreservation, is an alternative to cryopreservation that enables cooling cells to cryogenic temperatures in the absence of ice. The processing pathways involved in (ice-free) cryopreservation and freeze-drying of cells and tissues, however, can be very damaging. In this chapter, we describe the principles underlying preservation of cells for which freezing and drying are normally lethal processes as well as for cells that are able to survive in a reversible state of suspended animation. Freezing results in solution effects injury and/or intracellular ice formation, whereas drying results in removal of (non-freezable) water normally bound to biomolecules, which is generally more damaging. Cryopreservation and freeze-drying require different types of protective agents. Different mechanistic modes of action of cryoprotective and lyoprotective agents are described including minimizing ice formation, preferential exclusion, water replacement, and vitrification. Furthermore, it is discussed how protective agents can be introduced into cells avoiding damage due to too large cell volume excursions, and how knowledge of cell-specific membrane permeability properties in various temperature regimes can be used to rationally design (ice-free) cryopreservation and freeze-drying protocols.

Raman spectroscopy evidence of lipid separation in domestic cat oocytes during freezing

Although lipid droplets are believed to play an important role in cryopreservation of mammalian embryos and oocytes, the effect of low temperatures on lipid droplets and related mechanisms of cryodamage are still obscure. Here, we provide Raman spectroscopy evidence of lipid separation inside the lipid droplets in domestic cat oocytes during slow freezing. It was shown that at -25 °C lipids coexist in two separated phase states inside lipid droplets. The scale of detected domains was a few micrometers size. We also found that under certain conditions these areas have a specific spatial distribution. Lipids with high melting temperatures are distributed near the surface of lipid droplets while fusible lipids are located deep inside. Raman spectroscopy was found to be a prospective approach to study inhomogeneity of lipid phase transition in cells and to reveal effects of this inhomogeneity on cryopreservation of biological cells.

Cryopreservation of primary cultures of mammalian somatic cells in 96-well plates benefits from control of ice nucleation

Cryopreservation of mammalian cells has to date typically been conducted in cryovials, but there are applications where cryopreservation of primary cells in multiwell plates would be advantageous. However excessive supercooling in the small volumes of liquid in each well of the multiwell plates is inevitable without intervention and tends to result in high and variable cell mortality. Here, we describe a technique for cryopreservation of adhered primary bovine granulosa cells in 96-well plates by controlled rate freezing using controlled ice nucleation. Inducing ice nucleation at warm supercooled temperatures (less than 5 °C below the melting point) during cryopreservation using a manual seeding technique significantly improved post-thaw recovery from 29.6% (SD = 8.3%) where nucleation was left uncontrolled to 57.7% (9.3%) when averaged over 8 replicate cultures (p < 0.001). Detachment of thawed cells was qualitatively observed to be more prevalent in wells which did not have ice nucleation control which suggests cryopreserved cell monolayer detachment may be a consequence of deep supercooling. Using an infra-red thermography technique we showed that many aliquots of cryoprotectant solution in 96-well plates can supercool to temperatures below −20 °C when nucleation is not controlled, and also that the freezing temperatures observed are highly variable despite stringent attempts to remove contaminants acting as nucleation sites. We conclude that successful cryopreservation of cells in 96-well plates, or any small volume format, requires control of ice nucleation.

Advances in Cryopreservation of Bull Sperm

Cryopreservation of semen and artificial insemination have an important, positive impact on cattle production, and product quality. Through the use of cryopreserved semen and artificial insemination, sperm from the best breeding bulls can be used to inseminate thousands of cows around the world. Although cryopreservation of bull sperm has advanced beyond that of other species, there are still major gaps in the knowledge and technology bases. Post-thaw viability of sperm is still low and differs significantly among the breeding bulls. These weaknesses are important because they are preventing advances both in fundamental science of mammalian gametes and reproductive biotechnology. Various extenders have been developed and supplemented with chemicals to reduce cryodamage or oxidative stress with varying levels of success. More detailed insights on sperm morphology and function have been uncovered through application of advanced tools in modern molecular and cell biology. This article provides a concise review of progress in the cryopreservation of bull sperm, advances in extender development, and frontiers using diverse techniques of the study of sperm viability. This scientific resource is important in animal biotechnology because with the advances in discovery of sperm fertility markers, there is an urgent need to improve post-thaw viability and fertility of sperm through enhanced cryopreservation for precision agriculture to produce food animals to ensure food security on the global scale.

Recombinant peptide reverses cryo-capacitation in ram sperm and improves in vitro fertilization

Semen cryopreservation is a very important technique for assisted reproduction; however, the cryopreservation process is harmful because it results in a reduction in sperm motility and viability, and leads to premature signals of capacitation, resulting in lesser than desirable fertility rates after artificial insemination. A fraction of seminal plasma, enriched in proteins that contain type II fibronectin domains (FNII) can reverse molecular indicators of cryo-capacitation. The beneficial effects of these proteins, however, depend on the relative abundance in seminal plasma. To create a safe additive for improving frozen sperm functionality, in the present study there was cloning and expression of a recombinant peptide containing four FNII domains (named TrxA-FNIIx4-His6) and evaluation of its effect after addition to frozen/thawed ram sperm. The cDNA for this protein was expressed in E. coli and after denaturation and re-naturalization of the protein, toxicity and binding capacity were assessed. By fluorescent labelling assessment, there was binding of the protein to the thawed sperm. At the two doses used (0.15 and 0.3 μM), TrxA-FNIIx4-His6 had the capacity to reverse the molecular indicators of cryo-capacitation as indicated by the reduction on phosphorylated substrates of PKA. Furthermore, the supplementation with this protein resulted in a normal capacitation process as evidenced by the increase in the in vitro fertilization rate when the greatest concentration of the protein was evaluated (73.25 ± 2.95; 40.13 ± 11.82 for 0.3 μM and control, respectively). There was no effect of protein supplementation on sperm objective motility compared to untreated sperm. In conclusion, the use of TrxA-FNIIx4-His6 is a promising biotechnological approach for cryopreserving ram sperm and maintaining sperm viability.

Factors Affecting the Membrane Permeability Barrier Function of Cells during Preservation Technologies

Cellular membranes are exposed to extreme conditions during the processing steps involved in cryopreservation (and freeze-drying) of cells. The first processing step involves adding protective agents. Exposing cells to protective agents causes fluxes of both water and solutes (i.e., permeating cryoprotective agents) across the cellular membrane, resulting in cell volume changes and possibly osmotic stress. In addition, protective molecules may interact with lipids, which may lead to membrane structural changes and permeabilization. After loading with protective agents, subsequent freezing exposes cells to severe osmotic and mechanical stresses, caused by extra and/or intracellular ice formation and a drastically increased solute concentration in the unfrozen fraction. Furthermore, cellular membranes undergo thermotropic and lyotropic phase transitions during cooling and freezing, which drastically alter the membrane permeability and its barrier function. In this article, it is shown that membrane permeability to water and solutes is dependent on the temperature, medium osmolality, types of solutes present, cell hydration level, and absence or presence of ice. Freezing most drastically alters the membrane permeability barrier function, which is reflected as a change in the activation energy for water transport. In addition, membranes become temporarily leaky during freezing-induced fluid-to-gel membrane phase transitions, resulting in the uptake of impermeable solutes.

Comparison of the Effects of Five Semen Extenders on the Quality of Frozen-Thawed Equine Epididymal Sperm

Cryopreservation of epididymal sperm allows the saving of genetic material in case of unexpected death or emergency castration. The aim of the present study was the comparison of five different combinations of extenders commercially available for equine frozen semen processing for cryopreservation of epididymal sperm. Epididymal sperm were harvested from gonads of 10 healthy stallions after routine castration by retrograde flush technique. Then, samples were split and diluted with (1) INRA96 + INRA Freeze, (2) BotuSemen + BotuCRIO, (3) EquiPlus + Gent Freeze, (4) EquiPlus + EquiPlus Freeze, and (5) Gent + Gent Freeze. Extenders 1 and 2 showed higher values for total and progressive motility after thawing compared with extender 4 (P < .05). Extender 3 was in between 1 and 2 (P > .05), and extender 5 resulted in the lowest values (P < .05). The subpopulation of viable frozen-thawed sperm with high mitochondrial membrane potential and low intracellular calcium content was higher using extender 1 compared with extenders 3, 4, and 5 (P < .05) and higher in extender 2 compared with extenders 4 and 5 immediately after thawing (P < .05). After 1 hour of incubation, this subpopulation yielded the highest values in extender 2 (P < .05). Immediately after thawing, extender 1 yielded higher values for percentage of DFI and mean DFI than extenders 3, 4, and 5 (P < .05). Following 1 hour of incubation after thawing, sperm processed with extender 1 resulted in the highest values for percentage of DFI and mean DFI (P < .05). Using extender 2, mean DFI values were lower than those in extender 1 and higher than the extenders 3, 4, and 5 (P < .05). The study revealed that according to the examined sperm quality parameters, freezing extenders (extender 1, extender 2) using low concentrations of glycerol either combined with or without methylformamide were beneficial for cryopreservation of stallion epididymal sperm. For processing of stallion epididymal sperm, an extender containing milk proteins (extenders 1-4) for initial dilution after sperm harvesting is preferable to an extender including egg yolk (extender 5).

Lipid Droplet Phase Transition in Freezing Cat Embryos and Oocytes Probed by Raman Spectroscopy

Embryo and oocyte cryopreservation is a widely used technology for cryopreservation of genetic resources. One limitation of cryopreservation is the low tolerance to freezing observed for oocytes and embryos rich in lipid droplets. We apply Raman spectroscopy to investigate freezing of lipid droplets inside cumulus-oocyte complexes, mature oocytes, and early embryos of a domestic cat. Raman spectroscopy allows one to characterize the degree of lipid unsaturation, the lipid phase transition from the liquid-like disordered to solid-like ordered state, and the triglyceride polymorphic state. For all cells examined, the average degree of lipid unsaturation is estimated as ∼1.3 (with ±20% deviation) double bonds per acyl chain. The onset of the lipid phase transition occurs in a temperature range from -10 to +4°C and does not depend on the cell type. Lipid droplets in cumulus-oocyte complexes are found to undergo abrupt lipid crystallization shifted in temperature from the ordering of the lipid conformational state. In the case of mature oocytes and early embryos obtained in vitro, the lipid crystallization is broadened. In the frozen state, lipid droplets inside cumulus-oocyte complexes have a higher content of triglyceride polymorphic β and β' phases than estimated for mature oocytes and early embryos. For the first time, to our knowledge, the temperature evolution of the phase state of lipid droplets is examined. Raman spectroscopy is proved to be a promising tool for in situ monitoring of the lipid phase state in a single embryo/oocyte during its freezing.

Freezability of Andalusian donkey (Equus asinus) spermatozoa: effect of extenders and permeating cryoprotectants

The aim of this study was to compare the effect of two semen extenders and four permeating cryoprotectants on post-thaw sperm quality of Andalusian donkeys. First, 32 ejaculates were pooled, split and frozen in either Gent B or INRA 96 with egg yolk and glycerol. Second, 12 pooled semen samples were simultaneously frozen in Gent B (glycerol) or Gent A containing ethylene glycol (EG; 1 or 1.5%) or dimethyl sulfoxide (DMSO; 1.5 or 2%). Finally, nine pooled samples were simultaneously cryopreserved in Gent A containing 1% EG (as control), dimethylformamide (DMFA; 1 or 2.5%) or a combination of 1% EG and 1.5% DMFA. Gent B yielded a higher (P<0.01) post-thaw sperm motility than modified INRA96. EG 1% increased the sperm membrane integrity (P<0.001), whereas DMSO affected sperm motility and membrane integrity (P<0.001). DMFA 2.5% yielded higher (P<0.001) values for sperm motility and membrane integrity. We concluded that Gent B improves in vitro post-thaw sperm quality of donkey spermatozoa, but the replacement of glycerol with 1% EG or 2.5% DMFA increased sperm protection against cryodamage. The use of DMSO for freezing donkey semen was unsuccessful and a toxic effect is suspected. These extenders should be included in the pre-freeze test for each donkey.

Stallion Sperm Cryopreservation Using Various Permeating Agents: Interplay Between Concentration and Cooling Rate

In this study, modeling and experimental approaches were used to investigate the interplay between cooling rate and protectant concentration for cryopreservation of stallion sperm. Glycerol (GLY), ethylene glycol (EG), dimethylformamide (DMF), propylene glycol (PG), and dimethyl sulfoxide (DMSO) were tested as cryoprotective agents (CPAs), using concentrations up to 1500 mM and cooling rates ranging from 5°C to 55°C min^-1. Modeling of the extent of sperm dehydration during freezing was done using previously determined values of the sperm membrane permeability to water to predict optimal cooling rates for cryopreservation. Sperm cryosurvival was experimentally determined through flow cytometric assessments on membrane intactness and using computer-assisted analysis of motility. Sperm could withstand exposure to 1500 mM concentrations prefreeze for all CPAs tested. The overall highest cryosurvival rates were obtained with DMF, followed by GLY and EG, whereas the use of PG and DMSO resulted in poor cryosurvival rates. Cryosurvival with DMF increased with increasing concentration, reaching a plateau at 500 mM, whereas for GLY and EG, an optimum concentration between 250 and 500 mM resulted in maximal survival. An optimal cooling rate was only observed at low CPA concentrations, whereas at higher concentrations, cryosurvival rates were not affected by the cooling rate. In the case of DMF, survival remained relatively high in the investigated range of concentrations and cooling rates, whereas with GLY and EG, a much narrower combination of CPA concentration and cooling rate resulted in optimal cryosurvival. Sperm cryopreserved with DMF showed altered motility characteristics indicating hyperactivation, which was not observed with GLY and EG. Optimal cooling rates that were predicted from calculated dehydration curves did not match experimentally determined optimal cooling rates.

Freezing-induced uptake of trehalose into mammalian cells facilitates cryopreservation

The aim of this study was to investigate if membrane-impermeable molecules are taken up by fibroblasts when exposing the cells to membrane phase transitions and/or freezing-induced osmotic forces. The membrane-impermeable fluorescent dye lucifer yellow (LY) was used to visualize and quantify uptake during endocytosis, and after freezing-thawing. In addition, trehalose uptake after freezing and thawing was studied. Fourier transform infrared spectroscopic studies showed that fibroblasts display a minor non-cooperative phase transition during cooling at suprazero temperatures, whereas cells display strong highly cooperative fluid-to-gel membrane phase transitions during freezing, both in the absence and presence of protectants. Cells do not show uptake of LY upon passing the suprazero membrane phase transition at 30-10°C, whereas after freezing and thawing cells show intracellular LY equally distributed within the cell. Both, LY and trehalose are taken up by fibroblasts after freezing and thawing with loading efficiencies approaching 50%. When using 250 mM extracellular trehalose during cryopreservation, intracellular concentrations greater than 100 mM were determined after thawing. A plot of cryosurvival versus the cooling rate showed a narrow inverted-'U'-shaped curve with an optimal cooling rate of 40°C min(-1). Diluting cells cryopreserved with trehalose in isotonic cell culture medium resulted in a loss of cell viability, which was attributed to intracellular trehalose causing an osmotic imbalance. Taken together, mammalian cells can be loaded with membrane-impermeable compounds, including the protective agent trehalose, by subjecting the cells to freezing-induced osmotic stress.

Mode of action of cryoprotectants for sperm preservation

Sperm cryopreservation facilitates storage and transport for use in artificial reproduction technologies. Cryopreservation processing, however, exposes cells to stress resulting in cellular damage compromising sperm function. Cryoprotective agents are needed to minimize cryopreservation injury, but at higher concentration they are toxic to cells. In this review, we describe cryoinjury mechanisms, and modes of action of different types of cryoprotective agents. Furthermore, measures are discussed how to minimize toxic effects caused by adding and removing cryoprotective agents. Cryoprotective agents can be divided into permeating and non-permeating agents. Permeating agents such as glycerol can move across cellular membranes and modulate the rate and extent of cellular dehydration during freezing-induced membrane phase transitions. Permeating protectants provide intracellular protection because they are preferentially excluded from the surface of biomolecules thereby stabilizing the native state. Non-permeating agents can be divided into osmotically active smaller molecules and osmotically inactive macromolecules. Both, permeating and non-permeating protectants form a protective glassy state during freezing preserving biomolecular and cellular structures. Freezing extenders for sperm contain salts, buffer compounds, sugars, proteins and lipids, and typically contain glycerol as the main permeating cryoprotective agent providing intracellular protection. Non-permeating protectants including sugars and proteins are used as bulking agents and to increase the glass transition temperature of the freezing extender. Ultra-heat-treated milk and egg yolk are frequently added as membrane modifying agents to enhance the inherent sperm cryostability. The protocol how to use and add cryoprotectants is a compromise between their beneficial and potentially detrimental effects.

Fourier transform infrared (FT-IR) study on cyanide induced biochemical and structural changes in rat sperm

In the recent years, great attention had been focused on cyanide toxicity because of its widespread use in industries and considered to be a ubiquitous pollutant in the environment. Therefore, the current study aimed to evaluate the toxic effect of cyanide on rat sperms at molecular level by using FT-IR technique. For this purpose, rats were randomly divided into four groups and treated with 0.0, 0.64, 1.2 and 3.2 mg kg^-1 body weight (BW) for the period of 90 days. The group treated with lower dose (0.64 mg kg^-1 BW) showed an insignificant change in all the peaks, except the peaks assigned to olefinic 000000000000 000000000000 000000000000 111111111111 000000000000 111111111111 000000000000 000000000000 000000000000 C-H, CH₂ asymmetric and CH₂ symmetric stretching vibration in the lipids. While, the groups treated with higher doses (1.2 and 3.2 mg kg^-1 BW) showed the significant decrease in the area under the peaks corresponds to different bio-molecules. In addition, spectral second derivative analysis showed the significant alteration in α-helix, turns, β-sheet, aggregated β-sheet and random coil structures in the proteins. In conclusion, the selected higher dosage of cyanide had caused significant decrease in the biochemical composition of rat sperms along with structural changes in the proteins. The FT-IR technique is an excellent tool used for the analysis of oxidative damage in the sperms.

Genotoxicity evaluation of environmental pollutants using analysis of nucleolar alterations

Nucleolar alterations resulting from the action of either chemical or physical agents can serve as important genotoxicity biomarkers. In this study, the efficiency of AgNOR banding technique to identify the presence of nucleoli in micronucleus and assess nucleolar alterations in aberrant cells of Allium cepa was evaluated. Seeds of this plant were exposed to both water samples from a river that receives untreated urban effluent and to the trifluralin herbicide (0.84 mg/L concentration), both analyzed in two different seasons (summer and winter seasons). Samples induced significant frequencies of chromosomal and nuclear aberrations and micronuclei, as observed in cells submitted to conventional chromosomal staining. The herbicide caused a significant increase in the number of nucleoli and micronuclei, interpreted as due to the elimination of excessive nucleolar material resulting from polyploidization. The use of the AgNOR technique enabled the identification of both the presence of the nucleolus in some micronuclei and the nucleolar organizer region (NOR) behavior of aberrant cells. The NOR-banding technique showed to be an efficient tool for studying the genotoxic effects caused by a xenobiotics and a complex environmental sample.

Heat shock protein A8 stabilizes the bull sperm plasma membrane during cryopreservation: Effects of breed, protein concentration, and mode of use

Heat shock protein A8 (HSPA8) is a highly conserved member of the Hsp70 family, which is expressed in oviductal cells, translocated into oviductal fluid, and becomes attached to the sperm surface during sperm transport. Previous research has shown that HSPA8 supports mammalian sperm viability during in vitro incubation at both 5 °C and body temperature. The present series of experiments was designed to explore the possibility that bovine recombinant HSPA8 might therefore protect bull spermatozoa during cryopreservation through its beneficial effects on the sperm plasma membrane. Soy-based cryopreservation media were used in these experiments. The effects of HSPA8 addition before freezing were examined at concentrations ranging from 0.2 to 6.4 μg/mL, whereas the effects of postthaw HSPA8 addition were tested between 0.2 and 12.8 μg/mL. When bull spermatozoa (from beef and dairy breeds) were frozen in the presence of HSPA8, beneficial but complex effects on postthaw viability were observed. Low HSPA8 concentrations (0.2 and 0.4 μg/mL) resulted in significantly reduced postthaw sperm viability, but concentrations above 0.8 μg/mL improved plasma membrane integrity. If HSPA8 was added to spermatozoa after thawing, outcomes were also biphasic and beneficial effects on viability were only seen if the HSPA8 concentration exceeded 3.2 μg/mL. Beneficial effects were significantly more apparent with beef rather than dairy breeds. When HSPA8 was used in combination with cholesterol-loaded cyclodextrin, spermatozoa from the beef breeds showed significantly lower apoptotic effects. This was not observed with the dairy breeds.

The protein tyrosine phosphorylation during in vitro capacitation and cryopreservation of mammalian spermatozoa

Before the process of fertilization, spermatozoa necessitate a period of residence in the female reproductive environment, and undergo a sequence of physiological and biochemical changes collectively referred to as capacitation. Accumulated evidences from several laboratories indicated that the protein tyrosine phosphorylation (PTP) is one of the most important intracellular signaling events regulating sperm function, and is a meaningful indicator of capacitation. Different factors that affect PTP are cholesterol efflux, influx of HCO3(-), increased intracellular Ca(2+), cAMP and reactive oxygen species (ROS). cAMP/PKA and extracellular signal regulated kinases (ERKs) are the known important signaling pathways primarily involved in PTP. Advanced proteomics approaches have revealed several proteins that undergo tyrosine phosphorylation during capacitation. Semen cryopreservation subjects spermatozoa to frequent stressors, which result in capacitation like changes (cryo-capacitation). The cryo-capacitated spermatozoa usually show different patterns of PTP than the normal in vitro capacitated spermatozoa. In the current manuscript, we have summarized some information about the proteins undergoing tyrosine phosphorylation during capacitation and the effect of cryopreservation on PTP as well as the possibilities to reduce the changes associated with cryopreservation process.

Localization and functional modification of L-type voltage-gated calcium channels in equine spermatozoa from fresh and frozen semen

It is well known that insemination of cryopreserved semen always results in lower fertility when compared with fresh semen, but there is an increased interest and demand for frozen equine semen by the major breeder associations because of the utility arising from semen already "on hand" at breeding time. In this article, we report that equine sperm cells express L-type voltage-gated calcium channels; their localization is restricted to sperm neck and to the principal piece of the tail in both fresh and frozen-thawed spermatozoa. We also studied the causes of cryoinjury at the membrane level focusing on the function of L-type calcium channels. We report that in cryopreserved spermatozoa the mean basal value of [Ca(2+)]i is higher than that of spermatozoa from fresh semen (447.130 vs. 288.3 nM; P < 0.001) and L-type channels function differently in response to their agonist and antagonist in relation to semen condition (fresh or frozen-thawed). We found that on addition of agonist to the culture medium, the increase in intracellular calcium concentrations ([Ca(2+)]i) was greater in frozen semen than in fresh semen (Δ[Ca(2+)]i = 124.59 vs. 16.04 nM; P < 0.001), whereas after the addition of antagonist the decrease in [Ca(2+)]i was lower in frozen semen than in fresh semen (Δ[Ca(2+)]i = 32.5 vs. 82.5 nM; P < 0.001). In this article, we also discuss the impact of cryopreservation on sperm physiology.

GMP cryopreservation of large volumes of cells for regenerative medicine: active control of the freezing process

Cryopreservation protocols are increasingly required in regenerative medicine applications but must deliver functional products at clinical scale and comply with Good Manufacturing Process (GMP). While GMP cryopreservation is achievable on a small scale using a Stirling cryocooler-based controlled rate freezer (CRF) (EF600), successful large-scale GMP cryopreservation is more challenging due to heat transfer issues and control of ice nucleation, both complex events that impact success. We have developed a large-scale cryocooler-based CRF (VIA Freeze) that can process larger volumes and have evaluated it using alginate-encapsulated liver cell (HepG2) spheroids (ELS). It is anticipated that ELS will comprise the cellular component of a bioartificial liver and will be required in volumes of ∼2 L for clinical use. Sample temperatures and Stirling cryocooler power consumption was recorded throughout cooling runs for both small (500 μL) and large (200 mL) volume samples. ELS recoveries were assessed using viability (FDA/PI staining with image analysis), cell number (nuclei count), and function (protein secretion), along with cryoscanning electron microscopy and freeze substitution techniques to identify possible injury mechanisms. Slow cooling profiles were successfully applied to samples in both the EF600 and the VIA Freeze, and a number of cooling and warming profiles were evaluated. An optimized cooling protocol with a nonlinear cooling profile from ice nucleation to -60°C was implemented in both the EF600 and VIA Freeze. In the VIA Freeze the nucleation of ice is detected by the control software, allowing both noninvasive detection of the nucleation event for quality control purposes and the potential to modify the cooling profile following ice nucleation in an active manner. When processing 200 mL of ELS in the VIA Freeze-viabilities at 93.4% ± 7.4%, viable cell numbers at 14.3 ± 1.7 million nuclei/mL alginate, and protein secretion at 10.5 ± 1.7 μg/mL/24 h were obtained which, compared well with control ELS (viability -98.1% ± 0.9%; viable cell numbers -18.3 ± 1.0 million nuclei/mL alginate; and protein secretion -18.7 ± 1.8 μg/mL/24 h). Large volume GMP cryopreservation of ELS is possible with good functional recovery using the VIA Freeze and may also be applied to other regenerative medicine applications.

Mitochondrial hydrogen peroxide and defective cholesterol efflux prevent in vitro fertilization by cryopreserved inbred mouse sperm

Recent advances in the cryopreservation of mouse sperm have resulted in dramatically improved in vitro fertilization (IVF) rates, but the biological mechanisms underlying the techniques remain unclear. Two different classes of compounds have been widely utilized to improve the IVF rates of cryopreserved mouse sperm: antioxidants and cyclodextrins. To determine how cryopreservation reduces mouse sperm IVF and how antioxidants and cyclodextrins mitigate this effect, we examined sperm function and oxidative damage after cryopreservation, with and without treatments, in mouse strains important for biomedical research. Our investigation revealed mouse strain-specific effects on IVF by modulation of oxidative stress and cholesterol efflux of cryopreserved sperm. Antioxidants improved IVF rates of C57Bl6/J cryopreserved mouse sperm by reducing hydrogen peroxide produced by sperm mitochondria and ameliorating peroxidative damage to the sperm acrosome. Enhancing cholesterol efflux with cyclodextrin restored capacitation-dependent sperm function and IVF after cryopreservation of C57Bl/6J, C57Bl/6N, and 129X1 mouse sperm. Our results highlight two accessible pathways for continued development of IVF techniques for mouse sperm and provide novel endpoints prognostic of IVF success. These insights may improve sperm cryopreservation methods of other mouse strains and species.

Osmotic stress and membrane phase changes during freezing of stallion sperm: mode of action of cryoprotective agents

The aim of this study was to determine how different membrane-permeable and -impermeable cryoprotective agents modulate tolerance of stallion sperm to osmotic stress and stabilize membranes during cryopreservation. Special emphasis was on hydroxyl ethylene starch (HES), which exposes cells to minimal osmotic stress due to its large molecular weight. Percentages of motile sperm post-thaw were found to be similar when glycerol, sucrose, and HES were used at their optimal concentrations. Percentages of plasma membrane intact sperm after return to isotonic medium were highest for HES. Fourier transform infrared spectroscopy studies were carried out to study subzero membrane phase and permeability behavior. Cryoprotectants were shown to decrease the initial rate of membrane dehydration during freezing, decrease the activation energy for water transport, and increase the total extent of freezing-induced dehydration. Freezing studies with liposomes as a model system showed that only the membrane-permeable cryoprotective agents glycerol and ethylene glycol protected membranes against leakage, whereas egg yolk, sucrose, and HES did not. Differential scanning calorimetry studies showed that sucrose and HES raise the glass transition temperature of the freezing extender and the difference in heat capacity associated with the glass transition. This indicates that these compounds enable formation of a stable glassy matrix at higher subzero temperatures. Sperm cryosurvival rates can be increased by combining different cryoprotectants with different protective functions; membrane permeable cryoprotective agents stabilize membranes and modulate the rate of cellular dehydration, whereas di- and polysaccharides increase the glass transition temperature and facilitate storage and handling at higher subzero temperatures.

Slow freezing coupled static magnetic field exposure enhances cryopreservative efficiency--a study on human erythrocytes

The aim of this study was to assess the cryoprotective effect of static magnetic fields (SMFs) on human erythrocytes during the slow cooling procedure. Human erythrocytes suspended in 20% glycerol were slowly frozen with a 0.4-T or 0.8-T SMF and then moved to a -80°C freezer for 24 hr. The changes in survival rate, morphology, and metabolites of the thawed erythrocytes were examined. To understand possible cryoprotective mechanisms of SMF, membrane fluidity and dehydration stability of SMF-exposed erythrocytes were tested. For each test, sham-exposed erythrocytes were used as controls. Our results showed that freezing coupled with 0.4-T or 0.8-T SMFs significantly increased the relative survival ratios of the frozen-thawed erythrocytes by 10% and 20% (p<0.001), respectively. The SMFs had no effect on erythrocyte morphology and metabolite levels. However, membrane fluidity of the samples exposed to 0.8-T SMF decreased significantly (p<0.05) in the hydrophobic regions. For the dehydration stability experiments, the samples exposed to 0.8-T SMF exhibited significantly lower (p<0.05) hemolysis. These results demonstrate that a 0.8-T SMF decreases membrane fluidity and enhances erythrocyte membrane stability to resist dehydration damage caused by slow cooling procedures.

The specific response to capacitating stimuli is a sensitive indicator of chilling injury in hypothermically stored boar spermatozoa

Boar spermatozoa are sensitive to storage temperatures below 15 °C. Chilling injury causes loss of motility and membrane integrity in a minority of cells, whereas the main population displays sublethal changes compromising fertility. In this study, changes of the response to capacitation conditions in hypothermically stored boar spermatozoa have been examined using a kinetic approach with well-defined test and control media. Ejaculates of seven boars were diluted in Beltsville Thawing Solution kept for 3 h at 22 °C or cooled to 17, 10 and 5 °C and stored for 24 and 96 h. At each time point, the standard sperm parameters motility and membrane integrity were evaluated. Subsequently, washed subsamples were incubated in capacitating and control medium before flow cytometric analysis of intracellular calcium content using the Fluo-3 probe and changes in phospholipid disorder using merocyanine. Kinetic changes of response parameters were monitored in viable (plasma membrane intact) cells. Chilling led to a loss of standard sperm quality traits in a minor subpopulation of cells, whereas storage length had no effect on these parameters. However, responses to incubation as determined by the loss of live cells with low intracellular calcium content showed marked changes in relation to storage conditions. The specific responsiveness to capacitation conditions decreased in close relation to storage temperature and length. In contrast, the merocyanine probe revealed to be limited to detect effects of hypothermic storage. Using Fourier transform infrared spectroscopy, no influence of chilling on membrane phase behaviour was found that might implicate decreased sperm function. In conclusion, assessment of response to capacitating media by monitoring intracellular calcium levels provides a sensitive measure for chilling injury in extended boar semen, and therefore, deserves implementation in hypothermic storage tests.

Sperm surface changes and physiological consequences induced by sperm handling and storage

Spermatozoa interact with their immediate environment and this contact remodels the sperm surface in preparation for fertilisation. These fundamental membrane changes will be critically covered in this review with special emphasis on the very specific surface destabilisation event, capacitation. This process involves very subtle and intricate modifications of the sperm membrane including removal of suppression (decapacitation) factors and changes in the lateral organisation of the proteins and lipids of the sperm surface. Processing of sperm for assisted reproduction (storage, sex-sorting, etc.) subjects spermatozoa to numerous stressors, and it is possible that this processing overrides such delicate processes resulting in sperm instability and cell damage. To improve sperm quality, novel mechanisms must be used to stabilise the sperm surface during handling. In this review, different types of membrane stress are considered, as well as novel surface manipulation methods to improve sperm stability.

Liposomes for cryopreservation of bovine sperm

In this study, the effect of various unilamellar liposomes on cryopreservation of bovine spermatozoa has been investigated. Liposomes were composed of saturated lipids with various acyl chain lengths: DSPC (18:0), DPPC (16:0), DMPC (14:0), or DLPC (12:0). Alternatively, liposomes were prepared using unsaturated egg phosphatidylcholine (EPC) or DOPC (18:1, neutral), alone or in combination with lipids with various head groups: DOPS (negatively charged), DOPG (negatively charged), and DOPE (neutral). Fourier transform infrared spectroscopy studies showed that bovine sperm membranes display a gradual phase transition from 10 to 24 (o)C. Phase transition temperatures of the liposomes varied from -20 to +53 (o)C. Sperm was incubated in the presence of liposomes for either 6 or 24 h at 4 °C prior to freezing. Postfreeze survival rates were determined based on the percentage of progressively motile cells as well as the percentage of acrosome- and plasma membrane-intact cells. With DOPC liposomes a postthaw progressive motility of 43% was obtained compared with 59% using standard egg yolk freezing extender. Postthaw progressive motility increased up to 52% using DOPC:DOPG (9:1) liposomes, whereas DOPC:DOPS or DOPC:DOPE liposomes did not increase survival compared with DOPC liposomes. Among the saturated lipids, only DMPC was found to increase cryosurvival, up to 44% based on progressive motility. DLPC liposomes caused a complete loss in cell viability, already prior to freezing, whereas DPPC and DSPC liposomes neither positively nor negatively affected cryosurvival. Taken together, the higher postthaw survival obtained with DOPC:DOPG liposomes as compared with DOPC liposomes can likely be attributed to increased liposome-sperm interactions between the charged phosphatidylglycerol groups and charged regions in the sperm membranes. Interestingly, the lipid phase state of the liposomes during preincubation is not the decisive factor for their cryoprotective action.