Fertility of bull spermatozoa frozen in whole milk extender with trehalose, taurine, or blood serum

Ultra-Rapid Freezing Using Droplets Immersed into Liquid Nitrogen in Bull Sperm: Evaluation of Two Cryoprotective Disaccharides and Two Warming Temperatures

The present study analyzes the effects of different disaccharide concentrations and two thawing temperatures on the characteristics of ultrarapid frozen (URF) bovine sperm, compared with conventional slow-frozen (CF) sperm. For URF sperm, samples were diluted in media comprising 2% bovine serum albumin (BSA) and various nonpermeable cryoprotectants. Five groups were compared: control (without cryoprotectant), sucrose 0.15 M, sucrose 0.3 M, trehalose 0.15 M, and trehalose 0.3 M. In addition, the influence of warming temperatures, 37°C and 65°C, was analyzed. The aspect of different diluents (by drops) immersed in liquid nitrogen was also evaluated. Sperm quality was assessed by measuring motility, viability, acrosome status, and membrane lipid peroxidation (LPO). Moreover, the cryoresistance rate (CR) was determined. The drops immersed in liquid nitrogen showed that crystallization occurred, but not vitrification. CF sperm exhibited significantly higher scores for total motility (TM) and progressive motility (PM), viability, and acrosome integrity, in contrast with URF samples. Cryoprotectants for URF sperm showed a significant (p ≤ 0.05) influence on the TM and PM, viability, acrosome integrity, and CR, but not on LPO. Sperm viability was reduced after ultrarapid freezing, and the control samples were observed to have significantly lower values than those treated with disaccharides. Samples supplemented with 0.3 M sucrose exhibited higher LPO when they were thawed at 37°C. In short, a limited number of spermatozoa were able to maintain their motility and other functional attributes after ultrarapid freezing, but disaccharides showed a moderate protective effect. Samples with trehalose and sucrose at 0.15 and 0.3 M, respectively, showed higher sperm quality than samples containing only BSA. In sum, the function of spermatozoa was moderately maintained when disaccharides were used for ultrarapid freezing, although motility was significantly reduced. In addition, thawing temperatures did not modify the sperm values, suggesting that the easier procedure, that is, 37°C for 30 seconds, can be used.

Optimizing Bull Semen Cryopreservation Media Using Multivariate Statistics Approaches

Cryo-injury reduces post-thaw semen quality. Extender components play a protective role, but existing experimental approaches do not elucidate interactions among extender components, semen samples, and post-thaw quality. To identify optimal concentrations for 12 extender ingredients, we ran 122 experiments with an I-optimal completely random design using a large dataset from our previous study. We obtained a maximum predicted total motility of 70.56% from an I-optimal design and 73.75% from a Monte Carlo simulation. Individual bull variations were significant and interacted with extenders independently. 67% of bulls reliably preferred extender formulations to reach maximum motility. Multifactor analysis suggests that some antioxidants may offer superior protection over others. Partial least squares path modeling (PLS-PM) found the highest positive loadings for glutathione in the antioxidant class, glycerol in the CPA class, and fructose in the basic compounds class. The optimal ranges for milk, water, and ethylene glycol were extremely narrow. Egg yolk, cholesterol-loaded cyclodextrin, and nerve growth factor had medium-loading impacts. PLS-PM showed that CPA, osmoregulators, and basic components were the most efficient contributors to motility, while the antioxidant and extracellular protectant classes had less efficiency. Thus, ingredients, concentrations, and interactions of extender compounds are critical to extender formulation, especially when using multiple compounds with the same function.

New approaches for long-term conservation of rooster spermatozoa

In contrast to the livestock industry, sperm cryopreservation has not yet been successfully established in the poultry industry. This is because poultry sperm cells have a unique shape and membrane fluidity, differing from those of livestock sperm. The objective of this review is to discuss the cellular and molecular characteristics of rooster spermatozoa as a cause for their generally low freezability. Furthermore, here, we discuss novel developments in the field of semen extenders, cryoprotectants, and freezing processes, all with the purpose of increasing the potential of rooster sperm cryopreservation. Currently, it is very important to improve cryopreservation of rooster sperm on a global scale for the protection of gene resources due to the incidence of epidemics such as avian influenza.

Effects of Taurine on Sperm Quality during Room Temperature Storage in Hu Sheep

Simple Summary

Hu sheep sperm is highly susceptible to ROS during storage at room temperature. It is very important to use an antioxidant to ameliorate oxidative damage. Tau is an important amino acid peptide antioxidant with a wide range of biological effects. It can effectively scavenge free radicals, regulate reproductive function, improve immunity, and enhance its antioxidant capacity. However, the effects of Tau in the preservation of Hu sheep semen at room temperature are unclear. Therefore, Tau was added to Hu sheep semen preserved at room temperature to explore its effect on semen. The results showed that adding an appropriate concentration of Tau had a positive effect on Hu sheep semen preserved at room temperature; in particular, 20 mM Tau performed best.

Abstract

The present study aimed to investigate whether the presence of Tau protected Hu sheep sperm from ROS stress during storage at room temperature. The semen was diluted with extender (Tris-based) at room temperature, supplemented with different concentrations of Tau (0, 10, 20, 40, 80, or 100 mM), and stored at 15 °C. Sperm quality parameters (sperm progressive motility, kinetic parameters, plasma membrane integrity rate, acrosome integrity rate, and MMP) and antioxidant parameters (ROS, MDA, SOD, CAT, and T-AOC) were evaluated during the preservation of semen. The addition of Tau, especially at a concentration of 20 mM, exerted positive effects on sperm quality parameters and antioxidant parameters compared to the sperm without Tau treatment (control group). The addition of Tau, especially at a concentration of 100 mM, exerted negative effects on sperm quality parameters and antioxidant parameters compared to the control group. Interestingly, the results indicated that the sperm acrosome integrity rate did not change during storage time. In conclusion, the addition of Tau to sperm preserved at room temperature can enhance the antioxidant ability of sperm, reduce the LPO on the 5th day, and improve the quality of semen preserved at room temperature. These results implied that Tau had potential to enhance Hu sheep sperm reproductive performance.

Milk proteins interact with goat Binder of SPerm (BSP) proteins and decrease their binding to sperm

Seminal plasma Binder of SPerm (BSP) proteins bind to sperm at ejaculation and promote capacitation. When in excess, however, BSP proteins damage the sperm membrane. It has been suggested that milk components of semen extenders associate with BSP proteins, potentially protecting sperm. Thus, this study was conducted to investigate if milk proteins interact with BSP proteins and reduce BSP binding to goat sperm. Using gel filtration chromatography, milk was incubated with goat seminal plasma proteins and loaded onto columns with and without calcium. Milk was also fractionated into parts containing mostly whey proteins or mostly caseins, incubated with seminal plasma proteins and subjected to gel filtration. Eluted fractions were evaluated by immunoblot using anti-goat BSP antibodies, confirming milk protein-BSP protein interactions. As determined by ELISA, milk proteins coated on polystyrene wells bound to increasing of goat BSP proteins. Far-western dot blots confirmed that BSP proteins bound to caseins and β-lactoglobulin in a concentration-dependent manner. Then, cauda epididymal sperm from five goats was incubated with seminal plasma; seminal plasma followed by milk; and milk followed by seminal plasma. Sperm membrane proteins were extracted and evaluated by immunoblotting. The pattern of BSP binding to sperm membrane proteins was reduced by 59.3 % when epididymal sperm were incubated with seminal plasma and then with skimmed milk (p < 0.05). When epididymal sperm were treated with milk followed by seminal plasma, coating of sperm with BSP proteins was not significantly reduced (57.6 %; p > 0.05). In conclusion, goat BSP proteins have an affinity for caseins and whey proteins. Milk reduces BSP binding to goat sperm, depending whether or not sperm had been previously exposed to seminal plasma. Such events may explain the protective effect of milk during goat sperm preservation.

Interaction of milk proteins and Binder of Sperm (BSP) proteins from boar, stallion and ram semen

BACKGROUND

Mammalian semen contains a family of closely related proteins known as Binder of SPerm (BSP proteins) that are added to sperm at ejaculation. BSP proteins extract lipids from the sperm membrane thereby extensively modifying its composition. These changes can ultimately be detrimental to sperm storage. We have demonstrated that bovine BSP proteins interact with major milk proteins and proposed that this interaction could be the basis of sperm protection by milk extenders. In the present study, we investigated if homologous BSP proteins present in boar, stallion and ram seminal plasma display a similar affinity for the milk proteins in order to assess whether the mechanism of sperm protection by milk for these species could be general.

METHODS

Skim milk was incubated with seminal plasma proteins (boar, stallion and ram), chromatographed on a Sepharose CL-4B column and protein fractions were analyzed by immunoblotting.

RESULTS

Boar, stallion and ram BSP proteins displayed affinity for a milk protein fraction (F1) mainly composed of α-lactalbumin, β-lactoglobulin, and κ-casein. They also had affinity for another milk protein fraction (F2) composed mostly of casein micelles. However, stallion BSP showed higher affinity for the fraction (F1).

CONCLUSIONS

These results further extend our view that the association of BSP proteins with milk proteins could be a general feature of the mechanism of mammalian sperm protection by milk to prevent detrimental effect of prolonged exposure of sperm to seminal plasma.

Effects of glycerol and sugar mixing temperature on the morphologic and functional integrity of cryopreserved ram sperm

Sperm deep freezing procedures for ram semen have considerable variations regarding the steps being employed for cooling, freezing, and addition of cryoprotectants. In this work, we evaluated the effects of the addition of glycerol and/or the disaccharides sucrose and trehalose to hypertonic diluents either before or after cooling from 30 °C to 5 °C in Merino Australian ram semen cryopreservation. Using optical and transmission electron microscopy techniques, we assessed that glycerol was beneficial to the cooling process independently of its addition at 30 °C or 5 °C in terms of sperm membrane integrity in different regions of the plasma membrane (acrosomal region, 14.5% higher integrity; postacrosomal region, 8.0% higher integrity [P < 0.01]; hypoosmotic swelling test [HOST], 10.8% higher integrity [P < 0.001]). Disaccharides were necessary for a better cryopreservation in liquid nitrogen, and the best procedure was their addition after cooling at 5 °C (12% higher sperm motility [P < 0.001]; 8% higher acrosome integrity, [P < 0.05]; 9.5% higher plasma membrane integrity assessed by HOST [P < 0.001]). Trehalose showed a greater preservation cryoprotectant capacity than sucrose, as indicated by sperm motility after thawing (8.1% greater [P < 0.01]) and by the integrity of the intermediate piece (20% greater [P < 0.05]). From these results, we conclude that the best procedure for ram semen cryopreservation in hypertonic disaccharide-containing diluents is the addition of glycerol and trehalose after the cooling process, at 5 °C.

Absence of beneficial effects on rabbit sperm cell cryopreservation by several antioxidant agents

The generation of reactive oxygen species associated with cryopreservation could be responsible for mammalian sperm damage and the limitable value of stored semen in artificial insemination. The aim of this study was to assess several antioxidant agents supplemented in a commercial freezing extender (Gent B®) in order to improve post-thaw rabbit sperm quality. Ejaculates of 26 New Zealand White rabbit bucks were collected, evaluated and frozen using a conventional protocol. Antioxidant agents were tested at different concentrations: bovine serum albumin (BSA; 5, 30 or 60 mg/ml), retinol (RO; 50, 100 or 200 μM) and retinyl (RI; 0.282 or 2.82 μg/ml). Per cent viability, morphological abnormalities and intact acrosomes were determined using eosin-nigrosin staining. Motility and progressivity were analyzed by computer-assisted sperm analysis (CASA). In general, all sperm quality parameters were negatively affected by the cryopreservation process, the largest effect seen was for total motility. The addition of antioxidant agents did not improve thaw sperm quality. Furthermore, for RI groups a significant decrease in sperm quality parameters was recorded. In conclusion, rabbit sperm quality is negatively affected by the cryopreservation process. To our knowledge this report is the first using these antioxidants to supplement rabbit freezing extender. BSA and RO at concentrations used in the study did not improve sperm quality parameters after thawing, whereas RI supplementation appeared to be toxic. More studies are required to find the appropriate antioxidants necessary and their most effective concentrations to improve rabbit post-thaw sperm quality.

Effect of Addition of Taurine on the Liquid Storage (5°C) of Mithun (Bos frontalis) Semen

The present study was undertaken to assess the effect of taurine on sperm motility, viability, total sperm abnormalities, acrosomal and plasma membrane integrity, enzymatic profiles such as reduced glutathione (GSH), glutathione peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT), and biochemical profiles such as cholesterol efflux and malondialdehyde (MDA) production. A total of 50 ejaculates were collected twice a week from 8 mithun bulls, and semen was split into 4 equal aliquots and diluted with the TEYC extender. Group 1: semen was without additives (control); groups 2 to 4: semen was diluted with 25 mM, 50 mM, and 100 mM of taurine, respectively. Seminal parameters and enzymatic and biochemical profiles were assessed at 5°C. Inclusion of taurine into diluent resulted in significant (P < 0.05) decreases in percentages of dead spermatozoa, abnormal spermatozoa, and acrosomal abnormalities after liquid storage compared with the control group. Additionally, taurine at 50 mM has significant improvement in quality of mithun semen than taurine at 25 or 100 mM stored in in vitro at 5°C. It was concluded that the possible protective effects of taurine on sperm parameters are from enhancing the function of antioxidant enzymes, preventing efflux of cholesterol from cell membranes and decreased MDA production.

John JC. The generation of live offspring from vitrified oocytes

Oocyte cryopreservation is extremely beneficial for assisted reproductive technologies, the treatment of infertility and biotechnology and offers a viable alternative to embryo freezing and ovarian grafting approaches for the generation of embryonic stem cells and live offspring. It also offers the potential to store oocytes to rescue endangered species by somatic cell nuclear transfer and for the generation of embryonic stem cells to study development in these species. We vitrified mouse oocytes using a range of concentrations of trehalose (0 to 0.3 M) and demonstrated that 0.1 and 0.3 M trehalose had similar developmental rates, which were significantly different to the 0.2 M cohort (P<0.05). As mitochondria are important for fertilisation outcome, we observed that the clustering and distribution of mitochondria of the 0.2 M cohort were more affected by vitifrication than the other groups. Nevertheless, all 3 cohorts were able to develop to blastocyst, following in vitro fertilisation, although developmental rates were better for the 0.1 and 0.3 M cohorts than the 0.2 M cohort (P<0.05). Whilst blastocysts gave rise to embryonic stem-like cells, it was apparent from immunocytochemistry and RT-PCR that these cells did not demonstrate true pluripotency and exhibited abnormal karyotypes. However, they gave rise to teratomas following injection into SCID mice and differentiated into cells of each of the germinal layers following in vitro differentiation. The transfer of 2-cell embryos from the 0.1 and 0.3 M cohorts resulted in the birth of live offspring that had normal karyotypes (9/10). When 2-cell embryos from vitrified oocytes underwent vitrification, and were thawed and transferred, live offspring were obtained that exhibited normal karyotypes, with the exception of one offspring who was larger and died at 7 months. We conclude that these studies highlight the importance of the endometrial environment for the maintenance of genetic stability and thus the propagation of specific genetic traits.

Activation and expression of urokinase-type plasminogen activator are modulated by freezing/thawing process through activation of redox signal pathway in primary porcine endometrial cells

Plasminogen activators (PAs) play a pivotal role in a variety of uterine physiologies, such as endometrial function, trophoblast invasion, and implantation process, but its alteration in expression or activity during cryopreservation of primary uterine cells has received little attention. In this study, we investigated whether PA expression and activity were modulated in first passage primary porcine uterus endometrial epithelium cells (PUEECs) treated with or without a freezing-thawing procedure. Western blotting and zymographic analysis showed that uPA expression and activity increased significantly in frozen-thawed PUEECs in a passage-dependent manner as compared to freshly prepared control cells. Moreover, intracellular reactive oxygen species (ROS) were increased by freezing-thawing and longer culturing, and were more prominent in frozen-thawed PUEECs than in control cells. However, the increase in both uPA expression and activity was greatly reduced or alleviated by treatment with either ROS scavenger N-acetylcysteine or extracellular signal-regulated kinase (ERK) inhibitor PD98059. These results suggest that ROS/ERK-mediated uPA activation may be an important factor in cryo-damage of primary uterine cells.

Semen collection, characterisation and artificial insemination in the beluga (Delphinapterus leucas) using liquid-stored spermatozoa

Ejaculates were collected from a beluga (Delphinapterus leucas) to gain an understanding of sperm biology and develop a short-term sperm preservation method for use in artificial insemination (AI). Ejaculate parameters and biochemistry, semen production and serum testosterone concentrations of an adult male were characterised for 21 months. Sperm viability, acrosome integrity and morphology did not change (P > 0.05) but ejaculate volume, sperm concentration and total spermatozoa per ejaculate were higher (P < 0.05) from January to June than from July to December. Peak testosterone concentrations (P < 0.05) were observed from October to April (8.0 ± 1.6 ng mL–1). The effects of hyaluronic acid (HA), antioxidants, storage temperature and time on in vitro sperm characteristics were examined. Motility parameters and viability were improved (P < 0.05) when semen was stored at 5°C compared with 21°C. During the first 24 h of storage sperm agglutination was absent only at 5°C in the presence of HA. A nulliparous 28-year-old female was inseminated endoscopically with liquid-stored semen. A pregnancy and birth of a calf was achieved following AI for the first time in this species, thereby validating both the AI technique and the fertility of beluga spermatozoa after chilled storage in a specialised diluent.

Effects of Bovine Serum Albumin and Trehalose in Semen Diluents for Improvement of Frozen-Thawed Ram Spermatozoa

In this study, two following experiments were performed to improve post-thaw motility and viability of frozen-thawed ram spermatozoa. We examined i) the effects of different concentrations of bovine serum albumin (0, 0.3, 1, 5, 10 and 15% BSA) in semen diluents lacking egg yolk and ii) the effects of four semen diluents, fructose (F: control) and trehalose (T) in semen diluents containing egg yolk, 15% BSA in semen diluents without egg yolk (BSA), and modified phosphate buffered saline (m-PBS). Frozen-thawed spermatozoa were examined for progressive sperm motility, viability, morphological abnormality, sperm tail swelling test, and sperm acrosome integrity. In Experiment 1, the rates of sperm motility immediately after thawing (0 h) were significantly (P<0.05) higher in the 10 and 15% BSA groups (55.0 +/- 2.9 and 58.3 +/- 6.7%, respectively) than in the positive control (F) group (41.7 +/- 4.4%). The rate of sperm viability in the negative control (0% BSA) group (80.2 +/- 3.3%) was significantly (P<0.05) lower than in the positive control (F) group (89.8 +/- 1.5%), but when compared with the F group, no significant differences were found among the 0.3, 1, 5, 10 and 15% BSA groups at 0 h. The rates of sperm morphological abnormality of the 10 and 15% BSA groups (6.5 +/- 1.3 and 6.3 +/- 1.1%, respectively) were significantly (P<0.05) lower at 0 h than that in the 1% BSA group (16.3 +/- 5.2%). In Experiment 2, T addition improved (P<0.05) the post-thaw motility compared with the F and BSA groups. Furthermore, at 3 and 6 h, the post-thaw motility of the T group (36.3 +/- 2.4 and 25.0 +/- 2.0%, respectively) was significantly (P<0.05) higher than in the BSA (26.3 +/- 2.4 and 18.8 +/- 1.3%, respectively) and F (28.8 +/- 3.8 and 18.8 +/- 2.4%, respectively) groups. The post-thaw sperm motility and viability in the m-PBS group were significantly (P<0.05) lower than those of the control (F), T, and BSA groups throughout all observation points. These results indicate that 10 and 15% BSA can be substituted for egg-yolk for ram semen diluent and that the addition of trehalose enhances motility and viability of ram spermatozoa after freezing and thawing.

Effect of semen thaw method on conception rate in four large commercial dairy heifer herds

Semen processed with procedures intended to permit a flexible thaw method is used to breed millions of cows yearly. One method of thawing straws, the "pocket thaw" is used extensively with semen prepared with these procedures. Published field data is lacking for thaw method comparisons with semen processed to permit flexible-thawing. The objective of the present study was to measure the effect of semen thaw method (warm-water or pocket thaw) over all seasons and its interaction with herds, inseminators, straw package size, and sperm number on conception rate in commercial dairy heifer herds using semen processed with procedures historically optimized for success with flexible-thawing. Professional inseminators performed 11,215 services over a 16-month period in four large herds, achieving a 67.6% conception rate. Thaw method was alternated weekly. Thaw effect on conception status, determined by 70 days non-return rate, was estimated by a generalized linear mixed model. Neither thaw method nor number of sperm per straw significantly affected probability of conception (P=0.658 and 0.769, respectively). No interactions of thaw method with herd, sperm number, season, straw size, and straw size by season were detected (P=0.297, 0.526, 0.365, 0.723, and 0.824, respectively). Bull, herd, inseminator within herd, year, season, and straw size affected conception rate (P=0.002, 0.000, 0.000, 0.000, 0.000, and 0.014, respectively). In conclusion, for semen processed with procedures that permit flexible-thawing, thaw method (pocket thaw versus warm-water thaw) did not affect conception rate under commercial conditions and with routine semen handling methods.

Effects of egg yolk during the freezing step of cryopreservation on the viability of goat spermatozoa

Four experiments were conducted to investigate the effects of egg yolk during the freezing step of cryopreservation (namely, the process except for the cooling step), on the viability of goat spermatozoa. The effects of egg yolk on sperm motility and acrosome integrity during the freezing step were investigated in Experiment 1. Spermatozoa diluted with Tris-citric acid-glucose (TCG) solution containing 20% (v/v) egg yolk were cooled to 5 degrees C, washed, and then frozen in TCG with egg yolk (TCG-Y), TCG without egg yolk (TGG-NY), 0.370 M trehalose with egg yolk (TH-Y), or trehalose without egg yolk (TH-NY). All extenders contained glycerol. In frozen-thawed spermatozoa, the inclusion of egg yolk in the freezing extenders increased (P<0.05) percentages of motile sperm, progressively motile sperm, and the recovery rate (ratio of post-thaw to pre-freeze values), but decreased (P<0.05) acrosomal integrity. Moreover, extenders with trehalose had better (P<0.05) post-thaw sperm viability. In Experiment 2, the effects of egg yolk on acrosome status before and after freezing were studied. Egg yolk significantly decreased the proportion of intact acrosomes before freezing, leading to fewer (P<0.05) intact acrosomes post-thaw and lower (P<0.05) recovery rates for intact acrosomes. In Experiment 3, including sodium dodecyl sulfate (SDS) in a diluent containing egg yolk tended to preserve the acrosome compared with the egg yolk containing diluent free of SDS, however, spermatozoa had a lower (P<0.05) proportion of intact acrosomes than those in a yolk-free diluent. However, after cooling, spermatozoa were diluted with a glycerolated extender containing egg yolk. Therefore, the objective of Experiment 4 was to explore whether the egg yolk or glycerol was responsible for the reduced intact acrosome percentage. In this experiment, after cooling and washing the spermatozoa were diluted in TCG with glycerol and/or egg yolk. The combination of glycerol and egg yolk in the extender reduced (P<0.05) the proportion of intact acrosomes compared with egg yolk or glycerol alone. In conclusion, the inclusion of egg yolk significantly improved sperm motility, indicating its beneficial effects during the freezing step of cryopreservation; trehalose appeared to synergistically increase its cryoprotective effects. Furthermore, although neither glycerol nor egg yolk per se affected the proportion of intact acrosomes, the combination of the two significantly reduced the proportion of acrosome-intact spermatozoa.

Effects of the supplementation of trehalose extender containing egg yolk with sodium dodecyl sulfate on the freezability of goat spermatozoa

Two experiments were conducted to determine the effect of sodium dodecyl sulfate (SDS) added to a trehalose-egg yolk extender on the cryopreservation of goat spermatozoa. In Experiment 1, semen from four goats was frozen in trehalose extender (osmolality = 370, pH = 7) containing 4 and 20% (v/v) glycerol and egg yolk, respectively, and 0.035-0.2% SDS. After thawing, sperm motility and acrosome integrity were assessed using a computer-assisted sperm analysis (CASA) system and fluorescein isothiocyanate-conjugated peanut agglutinin (FITC-PNA). Both motility and progressive motility were improved (P < 0.05) by increasing the concentration of SDS in the trehalose-egg yolk extender, with the best results obtained with SDS at 0.1% (80.0 +/- 1.5% and 65.0 +/- 1.7%, respectively). There were no significant differences in path velocity when spermatozoa were frozen in a diluent containing 0.035, 0.05, 0.075, or 0.1% SDS, but path velocity decreased significantly with 0.2% SDS. The percentage of acrosome-intact sperm were highest (P < 0.05) when 0.05% (74.0 +/- 1.1) and 0.075% (70.0 +/- 1.2) SDS were used. In Experiment 2, the effect of diluent storage time (6, 24, or 48 h) before freezing on the cryoprotective effect of SDS was investigated. Prolonged storage of the diluent had slight cryoprotective effects when 0.2% SDS is used, while motility and the acrosome integrity of the cryopreserved spermatozoa improved slightly when the extender was stored for 48 h at 5 degrees C before use. In conclusion, goat sperm freezability was significantly improved when sperm were frozen in a trehalose-egg yolk extender containing an adequate concentration of SDS.

Trehalose-enhanced fluidity of the goat sperm membrane and its protection during freezing

In an attempt to find a suitable freezing method for goat semen, two experiments were conducted to study the influence of trehalose on the cryopreservation of goat spermatozoa. In experiment 1, goat spermatozoa were frozen in trehalose extender (0.375 M) alone (100%) or at different combinations of trehalose with Tris-citric acid-glucose (TCG) extender (0%, 25%, 50%, 75%). Final concentrations of 20% (v:v) egg yolk and 4% (v:v) glycerol were employed in the extenders (osmolality = 370, pH = 7). Sperm motility was assessed using a computer-assisted sperm analysis system and acrosome integrity was assessed using fluorescein isothiocyanate-labeled peanut agglutinin (FITC-PNA). The sperm-motility parameters improved significantly by increasing the concentration of trehalose (P < 0.05) and significantly high recovery rates for the motility parameters were also achieved by a high concentration of trehalose (P < 0.05). Motility of the frozen-thawed spermatozoa after a 3-h incubation improved significantly with increasing concentrations of trehalose in the extender (P < 0.05). The 75% and 100% trehalose extenders yielded a significant increase in the percentage of spermatozoa with intact acrosome (P < 0.05). In experiment 2, merocyanine 540/Yo-Pro staining was used to study the influence of trehalose on membrane fluidity compared with that of sucrose and TCG. Percentage of cells with high merocyanine fluorescence was significantly higher in spermatozoa treated with trehalose than sucrose or TCG (P < 0.05), indicating a significantly highest membrane fluidity of sperm samples extended with trehalose solution. We thus conclude that the substitution of a Tris-citric acid diluent composition with trehalose significantly improves the freezability of goat spermatozoa. Furthermore, the cryoprotective effects of trehalose observed in this study may be due to enhanced sperm membrane fluidity before freezing.

Cryopreservation and post-thawed fertility of ram semen frozen in different trehalose concentrations

We evaluated freeze-thawing tolerance of heterospermic ram spermatozoa (Pampinta breed) in a base diluent (Tris, citric acid, fructose, egg yolk, glycerol) with the addition of different trehalose concentrations (0-400 mOsm). We chose sperm motility, acrosome integrity and hypo-osmotic swelling test as parameters to evaluate cryopreservation capacity. We obtained the best results for 50 and 100 mOsm trehalose-supplemented extenders, with values (referred to fresh semen values) of 65% for motility, 75% for acrosome integrity and 50% for hypo-osmotic swelling test, while freeze-thawing tolerance diminished significantly for 200 and 400 mOsm of the disaccharide. Fertility values measured at lambing were 47.1 and 44.6% (2 consecutive years), using semen cryopreserved in 100 mOsm trehalose-containing diluent, which is 2.5 times greater than those obtained with the base diluent (18.5 and 14.5%). We conclude that the membrane-protecting disaccharide trehalose confers a greater cryoprotective capacity to the base extender, when added up to 100 mOsm. This action is reflected in the different sperm membranes, the motile activity and in vivo fertility.

Islet cryopreservation: improved recovery following taurine pretreatment

Simple and efficient freezing methods with maximal postthawing recovery form the basis of ideal cryopreservation. Taurine (2-amino ethanesulfonic acid), an end-product of sulphur amino acid metabolism, is one of the most abundant free amino acids in the body. The membrane stabilizing, free radical scavenging, and osmoregulatory roles of taurine have been well documented. We studied the effect of physiological and supra-physiological concentrations (0.3 and 3.0 mM) of taurine on islet cryopreservation. Islet viability on cryopreservation was significantly improved in both the taurine-treated groups (91.9 +/- 2.3% in 0.3 mM and 94.6 +/- 1.58% in 3.0 mM group, p < 0.05) compared with the controls (85.7 +/- 3.4%). Loss of peripheral islet cells was highly reduced in the taurine group, as examined under phase contrast and quantified by islet morphometric analysis (p < 0.05) using a digital image analysis system. Taurine-treated islets showed significant reduction in lipid peroxidation (0.905 and 0.848 nM MDA/microg protein for 0.3 and 3.0 mM taurine, respectively, p < 0.05) compared with control (1.307 nM MDA/microg protein) islets. In all, 500 islet equivalents (IE) of treated or control group islets were transplanted to BALB/c mice rendered diabetic with STZ. All animals showed a normal glucose clearance following a glucose load. Graft functionality was confirmed by normoglycemia (fasting plasma glucose: fpg < 150 mg/dl) after transplantation and reappearing hyperglycemia (fpg > 200 mg/dl) following removal of the graft. Suboptimal islet transplantation using 250 IE suggests that the grafted islet mass was inadequate for diabetes reversal. In addition, no significant differences were observed in the islet insulin content between the three groups following cryopreservation of the islets at -196 degrees C. Our studies indicate that taurine pretreatment and its continued presence during islet cryopreservation improves the postthawing viable recovery of islets.

Production of reactive oxygen species by spermatozoa undergoing cooling, freezing, and thawing

In the present study, we provide evidence for the production of reactive oxygen species (ROS) during cryopreservation of bovine spermatozoa. Cooling and thawing of spermatozoa cause an increase in the generation of superoxide radicals. Although nitric oxide production remains unaltered during sperm cooling from 22-4 degrees C, a sudden burst of nitric oxide radicals is observed during thawing. Increase in lipid peroxidation levels have been observed in frozen/thawed spermatozoa and appears to be associated with a reduction in sperm membrane fluidity as detected by spin labeling studies. The data presented provide strong evidence that oxygen free radicals are produced during freezing and thawing of bovine spermatozoa and suggest that these reactive oxygen species may be a cause for the decrease in sperm function following cryopreservation. Mol. Reprod. Dev. 59: 451-458, 2001.

Storage of bovine semen in liquid and frozen state

This review describes the historical and current methods used for storage of bovine semen. The essential physiological differences between liquid and frozen semen, their relative advantages and disadvantages are addressed, and the current state of technology, the procedures used, their merits and future possibilities are also discussed.

Protection from cell death in cultured human fetal pancreatic cells

Endocrine cells from the human fetal pancreas will proliferate in vitro on extracellular matrix but lose hormone expression, and redifferentiation requires removal of the expanded cells from the matrix and reaggregation into cell aggregates. However, extensive cell death occurs during manipulation and culture. The mechanism of cell death was examined at each stage throughout the process under different experimental conditions to determine optimal protocols to increase cell viability. During shipment, the addition of trehalose to the media to prevent necrosis increased yield 17-fold, while during culture as islet-like cell clusters the apoptosis inhibitor Z-VAD increased yield 1.8-fold. Following disruption of cell matrix interactions and reaggregation, there was marked evidence of apoptotic bodies by the TUNEL assay. Addition of nicotinamide or Z-VAD, or removal of arginine from the media during reaggregation, reduced the number of apoptotic bodies and the effect was additive. However, a combination of treatments was necessary to significantly increase the yield of viable cells. We conclude that cell death of human fetal pancreatic tissue in culture results from both necrosis and apoptosis and that understanding the mechanisms at the cellular level will lead to protocols that will improve cell viability and promote beta-cell growth.

Effect of trehalose and EDTA on cryoprotective action of ram semen diluents

To obtain better ram semen extenders for artificial insemination (AI), we developed effective trehalose-containing hypertonic diluents. The cryoprotective action of trehalose has been explained by its dehydrating activity and interaction with cell membranes. Accordingly, we tested the cryopreserving capacity of different combinations of a Salamon's modified plus trehalose extender with EDTA. Evaluations were based on the percentage of motile spermatozoa and acrosome integrity, measured after thawing and after a 4-h post-thaw resistance test at 37 degrees C. We conclude that the combination of trehalose plus EDTA confers the highest cryopreserving activity tested, not only for freeze-thawing but also for post-thawing resistance, possibly by removing calcium from the medium thereby preventing cation competition with trehalose for membrane-binding sites.

Liquids storage (5 degrees C) of ram semen in different diluents

This study examined the effects of three diluents--skim milk (M), TesT (TE) and Tris-trehalose (TR)--on quality of ram semen stored at 5 degrees C over a long term. Percentage of motile spermatozoa (PM), motility score (MS), percentage of intact acrosomes (PIA), and percentage of swollen spermatozoa under hypoosmotic conditions (PS) were assessed after cooling and every 24 h up to day 16. There was a significant effect (p < .01) of diluent type in the conservation rates after cooling for PM. The TR diluent achieved greater values (94.7 +/- 1.36%) than TE (82.4 +/- 3.08%), while M showed an intermediate value (89.3 +/- 2.17%). In relation to time of storage, TR diluent showed the highest PM values up to day 12, but differed (p < .05) from TE medium only until day 4. The TR extender maintained a PM > 50% up to day 8, while TE and M were greater than 50% up to day 5. Skim milk maintained progressive movement of sperm cells for longer (MS = 3 until day 5) than the other diluents. There were no significant differences in PIA among the 3 media during the first 6 days of storage (except in day 2), and M showed the lowest value afterward. There was no significant extender effect on PS for the first 3 days, but after day 6 diluent M also showed the lowest values of this variable.

Sperm numbers inseminated in dairy cattle and nonreturn rates revisited

Three experiments were conducted to test fertility when sperm numbers per insemination ranged from 10 x 10(6) to 40 x 10(6) total sperm. All semen was from Holstein bulls that were on a regular schedule of semen collection. The semen was extended with heated homogenized whole milk, cooled, glycerolated, and frozen according to standard procedures. Semen was distributed to a large group of inseminators to minimize differential field effects on treatment. All experiments were a randomized block design, including a split plot in Experiment 2. In Experiment 1, data for 31,399 first inseminations distributed among treatments of 20 x 10(6), 25 x 10(6), 30 x 10(6), and 40 x 10(6) total sperm resulted in 69.8, 70.0, 70.1, and 70.1% nonreturns at 59 d, respectively. In Experiment 2, data for 18,197 first inseminations divided over treatments of 12 x 10(6), 16 x 10(6), and 20 x 10(6) total sperm resulted in 70.2, 72.4, and 70.8% nonreturns at 59 d, respectively. In Experiment 3, 38,890 first inseminations distributed over treatments of 10 x 10(6), 13 x 10(6), 16 x 10(6), and 20 x 10(6) total sperm resulted in 70.5, 72.2, 73.1, and 71.5% nonreturns at 59 d, respectively. Bull nonreturns ranged from 64 to 76% in the three trials. These results indicate that, under good conditions, total sperm numbers per straw can be reduced to 10 x 10(6) total sperm with a reduction of nonreturn rates at 59 d, for most bulls, of about 1 percentage unit from the maximum when professional inseminators are use.

Cryopreservation of rabbit spermatozoa using acetamide in combination with trehalose and methyl cellulose

Glycerol is not an effective cryoprotectant for rabbit spermatozoa; therefore, rabbit spermatozoa were used as a model for developing cryopreservation procedures for other cell types which also freeze poorly when glycerol is used as the cryoprotectant. Experiments were conducted to 1) compare several published protocols for cryopreserving rabbit spermatozoa; 2) determine if removal of seminal granules, required for flow cytometry analysis, affects the motility of rabbit spermatozoa; and 3) determine if using a combination of cell permeating cryoprotectants (acetamide) with cell nonpermeating cryoprotectants (trehalose and methyl cellulose; MC), can increase the recovery of viable rabbit spermatozoa after cryopreservation. Media containing acetamide as a cryoprotectant were found to be most effective for rabbit spermatozoa. The cryoprotectants ethylene glycol, dimethylsulfoxide and glycerol were not effective for cryopreserving rabbit spermatozoa. Second, rabbit spermatozoa could be centrifuged through a Percoll gradient composed of equal volumes of Prcoll and a HEPES-buffered sperm medium. This centrifugation removed all seminal granules without affecting the percentage of motile spermatozoa after initial sperm dilution (85 vs 74%) or after cryopreservation (35 vs 30%), when sperm were either centrifuged or not centrifuged, respectively. The substitution of trehalose in the cryopreservation medium for raffinose did not improve recovery of motile cells following cryopreservation (P > 0.05). However, addition of MC resulted in higher percentages of motile sperm after cryopreservation (43 vs 31%; P < 0.05). In addition, sperm viability and acrosomal integrity were simultaneously evaluated using flow cytometry. The addition of both trehalose and MC to media containing acetamide resulted in higher percentages of live acrosome-intact cells than acetamide alone (53 vs 37%; P < 0.05). These results indicate that a combination of permeating and nonpermeating cryoprotectants (acetamide, trehalose and MC) were more effective in preserving rabbit spermatozoa than acetamide alone and that analyzing multiple sperm characteristics, by flow cytometry, can assess sperm damage not detected by analyzing sperm motion characteristics.

In vitro study of the protective effect of trehalose and dextran during freezing of human red blood cells in liquid nitrogen

Two nonpermeant cryoprotectants, the disaccharide trehalose and the polymeric carbohydrate (dextran, 40 kDa), were assessed as substitutes for glycerol in the cryopreservation of human red blood cells (RBC). The agents were evaluated by measuring the percentage of RBC recovery (total of free hemoglobin after freezing) and by evaluating the erythrocyte state after freezing. Ninety percent of the red cells were recovered after freezing in 30% (w/v) dextran in liquid nitrogen, which is very close to the recovery obtained in 35. 5% (w/v) glycerol (92%). The activities of pyruvate kinase and glucose-6-phosphate dehydrogenase of RBCs frozen and thawed with dextran were not modified, and the 2,3-diphosphoglycerate was reduced by 26%, but remained within normal values. ATP was reduced by 56%. The erythrocyte membrane integrity, evaluated by its osmotic fragility, was not altered, and the RBCs protected by dextran retained their normal discoid shape without the formation of microvesicles. The 24-h hemolysis of the washed red cells after storage at 4 degrees C was 7%. These results suggest that dextran protects red blood cells during freezing in liquid nitrogen, but that some effort is still needed to limit the drop of ATP concentration. One of the main advantages of dextran is that it does not penetrate the RBCs and requires less washing than glycerol.