Differential effects of butylated hydroxytoluene analogs on bull sperm subjected to cold-induced membrane stress

Butylated Hydroxytoluene (BHT) Improves the Post-Thaw Semen Quality in Low-Dose Sperm Cryopreservation in Murrah Buffalo Bull

BACKGROUND: Cryopreservation is an important technique for the long-term storage of semen for artificial insemination (AI). Buffalo spermatozoa are sensitive to cryopreservation procedures because of the presence of a high amount of polyunsaturated fatty acids in the plasma membrane. OBJECTIVE: To study the effect of different concentrations of BHT on the quality of Murrah buffalo bull semen for low-dose cryopreservation. MATERIAL AND METHODS: Semen was collected from four high fertile Murrah buffalo bulls (6 ejaculates each) using an artificial vagina. A total of 24 ejaculates were collected from each bull twice a week using an artificial vagina. Every sample was split into four parts: Control without additives; and three treatments with BHT at 0.5 mM, 1 mM or 2 mM. Semen was cryopreserved at low-dose sperm cryopreservation of 20, 15, 10 and 5 million sperm per aliquot after supplementation of BHT. Semen samples were evaluated for fresh, pre-freeze and post-thaw stages. RESULTS:There was a significant increase (p<0.05) in sperm quality parameters, such as progressive motility (%), viability (%), HOST response (%), acrosome integrity (%) and post-thaw motility, with the addition of 0.5-1 mM BHT. CONCLUSION: The addition of BHT in Murrah buffalo semen improves the low dose cryopreservation quality in a dose-dependent manner.

Post-thaw quality of ram sperm frozen with different concentrations of low-density lipoproteins associated with non-enzymatic antioxidants

The cryopreservation reduces ram sperm quality, decreasing the pregnancy rate of ewes inseminated with thawed sperm. Hence, we aimed to improve the post-thaw quality of ram sperm replacing egg yolk on Tris-Glucose extender with different concentrations of LDL (2 or 8%), associated with the addition of 10 mM non-enzymatic antioxidants (ascorbic acid, hydroxytoluene butylate, ascorbyl palmitate, and trehalose). Semen samples were collected from six rams, split into different treatments, and frozen. After thawing, kinematic (CASA), structural (propidium iodide and carboxyfluorescein diacetate) and functional (hypoosmotic test) sperm membrane integrity was assessed. Total motility, VCL, and LIN were also assessed in thawed samples during 3 h of incubation (38 °C). The results showed that hydroxytoluene butylate at 10 mM in Tris-Glucose extender with 8% LDL improved velocity parameters immediately post-thaw compared with Tris-Glucose egg yolk extender, as well as prevented the reduction of total motility and VCL after incubation. There was no benefit of adding ascorbic acid and trehalose. Moreover, for the first time, it was shown the motility impairment promoted by ascorbyl palmitate to ram sperm.

Effect of astaxanthin in extenders on sperm quality and functional variables of frozen-thawed boar semen

The aim of the study was to determine whether the presence of astaxanthin (ASX) protects boar spermatozoa against damage related to cryopreservation. Pooled ejaculates extended in Beltsville Thawing Solution (BTS) were used. Three experiments were conducted: 1) sperm samples were pre-incubated overnight (17 °C) with ASX (0, 0.5, 5, 15 μM) prior to freezing and then frozen using cooling and thawing extenders supplemented with ASX (0, 0.5, 5, 15 μM); 2) sperm samples were treated with ASX (0, 0.5, 5, 15 μM) only during overnight pre-incubation (17 °C) prior to cryopreservation; and 3) a thawing extender was supplemented with ASX (0, 0.5, 5, 15 μM). The groups were as follows: control (C; no treatment), ASX 1 (0.5 μM), ASX 2 (5 μM) and ASX 3 (15 μM). Total (TM) and progressive (PM) motility was analyzed using CASA, while sperm viability, reactive oxygen species generation, lipid peroxidation and apoptoticlike changes were analyzed using flow cytometry. Sperm variables were evaluated prior to freezing as well as 30 and 150 min after thawing. In Experiment 1, the values of TM and sperm viability post-thaw were less in the ASX 3 than C group. In Experiment 2, there was no effect of ASX on any of the sperm variables evaluated, while in Experiment 3, apoptotic-like changes were less in the ASX 1 than C group. In conclusion, there was a subtle beneficial effect on cryopreserved boar spermatozoa after addition of ASX to thawing media.

ADIÇÃO DE HIDROXITOLUENO BUTILADO (BHT) NO DILUIDOR ACP-106c PARA CONGELAÇÃO DE SÊMEN CANINO

Resumo: Este estudo foi realizado para determinar o efeito de hidroxitolueno butilado (BHT) sobre a qualidade do sêmen canino congelado e descongelado, utilizando o diluidor à base de água de coco em pó (ACP-106c). Para tanto, foram realizadas quinze coletas de sêmen provenientes de cinco cães. O sêmen obtido foi diluído em ACP-106c acrescido de glicerol e gema de ovo. As amostras foram então transferidas para tubos contendo diferentes concentrações de BHT (0; 0,5; 1,0 e 2,0 mM). Em seguida, as amostras foram envasadas, congeladas e armazenadas em nitrogênio líquido. O sêmen coletado foi avaliado in natura quanto aos seguintes parâmetros: coloração, volume da fração espermática, motilidade total, vigor, concentração, morfologia e funcionalidade de membrana espermática. Após uma semana, as amostras foram descongeladas e avaliadas por meio de análise computadorizada, como também foram realizadas análises da funcionalidade de membrana e da morfologia espermática. A motilidade progressiva no grupo BHT 2,0 mM foi significativamente superior (P < 0,05) do que a do grupo BHT 0 mM (27,6 ± 11,7% vs. 19,0 ± 9,5%, respectivamente). Em todos os demais parâmetros avaliados, não houve diferença entre os grupos testados. Portanto, conclui-se que a adição do BHT ao diluidor ACP-106c não afetou a qualidade do sêmen canino pós-descongelação.

Effect of butylated hydroxytoluene (BHT) on the cryopreservation of common carp (Cyprinus carpio) spermatozoa

The aim of the present study was to test the effects of butylated hydroxytoluene (BHT) on the cryopreservation of common carp spermatozoa. BHT is widely used in the cryopreservation of the spermatozoa of different animal species and successfully sustains the characteristics of spermatozoa during freezing and thawing, but it has not previously been used with fish. After sampling, common carp spermatozoa were diluted with an extender composed of modified Kurokura's extender, 10% DMSO, and 10% egg yolk containing 0.0001, 0.001, 0.01, 0.1, 1, 2.5, 5, or 10mM BHT and subsequently frozen in liquid nitrogen. The post-thaw spermatozoa characteristics (i.e., progressive motility percentage (%), duration of progressive motility (s), fertilization rate (%), and eyed-eggs rate (%)) were evaluated and compared with those of the control group. There were significant increases in the percentage of progressive motility and the duration of progressive motility at the concentrations of 0.1 and 0.001mM BHT (P<0.05). The duration of post-thawed spermatozoa progressive motility at 0.001mM BHT was significantly greater than that of the other groups (39.6±0.4s, P<0.05), and the fertilization rates and eyed-eggs rates were also higher following the 0.1 and 1mM BHT treatments. BHT at concentrations of more than 1mM caused sperm immobility during the preparatory stages of the sperm freezing. We concluded that 0.001-0.1mM BHT can be beneficial for the cryopreservation of common spermatozoa.

Effects of different concentrations of BHT on microscopic and oxidative parameters of Mahabadi goat semen following the freeze-thaw process

Oxidative damage to sperm is one of the main causes for decline in motility and fertility of frozen-thawed sperm. Thus, it is crucial to use cryoprotectant agents in extender in order to prevent lethal intracellular ice crystal formation. The present study aims to evaluate the effects of different concentrations of the antioxidant butylated hyroxytoluene (BHT) on sperm parameters post-thaw. Semen was diluted into five equal aliquots of extender containing different concentrations of BHT (0, 0.5, 1, 2 and 4mM), aspirated into 0.25 mL straws, and equilibrated at 5°C for 2h. After equilibration, straws were frozen in liquid nitrogen vapor and plunged into liquid nitrogen for storage. Sperm parameters, including motility and progressive motility, viability, membrane integrity, acrosome integrity and capacitation status, were assessed. Malondialdehiyde (MDA) and glutathione peroxidase (GSH-PX) activity were also evaluated after freezing-thawing. Results of this experiment show that addition of 1mM of BHT to the extender for freezing of goat semen can improve motility, progressive motility and viability (P<0.05) and reduce the MDA level (P<0.01). HOST (hypo-osmotic swelling test), acrosome integrity, capacitation status and GSH-PX were not affected by the concentrations of BHT (P>0.05). Therefore, we conclude that the optimum concentration of BHT for cryopreservation of goat semen is 1mM.

Survival and Fertility of Boar Spermatozoa After Freeze-Thawing in Extender Supplemented With Butylated Hydroxytoluene

This study evaluated the protective effect of butylated hydroxytoluene (BHT), a lipid-soluble antioxidant, against cryopreservation injuries to boar spermatozoa. In experiment 1, the lowest BHT concentrations able to reduce lipid peroxidation in boar spermatozoa were determined. Nine BHT concentrations (ranging from 0.025 to 3.2 mM) were evaluated, and the lowest (P <.05) production of malondialdehyde (MDA), as an indicator of lipid peroxidation, was obtained when BHT ranged from 0.2 to 1.6 mM. In experiment 2, sperm survivability was evaluated when BHT was added to a postthaw freezing extender by measuring the degree of sperm lipid peroxidation (using MDA production) and by measuring parameter such as motility, plasma membrane and acrosome integrity, and cell apoptosis. The ability of thawed spermatozoa to fertilize in vitro-matured oocytes and of embryos to develop to the blastocyst stage in vitro was also assessed. Pooled sperm-rich fractions collected from 3 mature Pietrain boars were frozen in 0.5-mL straws after dilution with lactose-egg yolk-glycerol-Orvus ES Paste extender supplemented with 0, 0.2, 0.4, 0.8, and 1.6 mM BHT. Postthaw sperm survival, evaluated 30 and 150 minutes after thawing, was higher in BHT-treated spermatozoa, being significant (P <.05) when the freezing extender was supplemented with 0.2, 0.4, and 0.8 mM BHT. The addition of BHT to the freezing extender resulted in a significant (P <.05) decrease in the MDA concentration in thawed spermatozoa, irrespective of the level of BHT used. BHT had no effect on oocyte cleavage rates, but the development to blastocyst was improved for embryos derived from spermatozoa frozen in extender supplemented with 0.4 mM BHT (16% vs 29% of blastocysts per total oocytes; P <.05). In conclusion, under the conditions tested in the present study, the addition of BHT to the freezing extender improved the overall efficiency of thawed boar spermatozoa.

Butylated hydroxytoluene inclusion in semen extender improves the post-thawed semen quality of Nili-Ravi buffalo (Bubalus bubalis)

The study was carried out to evaluate the potential impact of butylated hydroxytoluene (BHT) on the frozen-thawed semen quality of Nili-Ravi buffalo bulls. Ejaculated bull semen was extended in a Tris-citrate egg yolk extender containing various concentrations of BHT (0.5, 1.0, 2.0 and 3.0mM). Semen was frozen at -196 degrees C using 50 x 10(6) spermatozoa per 0.5 mL straws. Five straws from each treatment were thawed to assess the semen quality in terms of sperm motility, viability, plasma membrane integrity and acrosomal integrity. Post-thawed sperm motility was determined using a phase-contrast microscope. Viability, plasma membrane integrity and acrosomal integrity were evaluated by the supravital staining, hypo-osmotic swelling test and normal acrosomal reaction, respectively. The highest (P<0.05) motility, acrosomal integrity and hypo-osmotic swelling response of spermatozoa was achieved by addition of 1.0 and 2.0mM BHT to semen extender. However, highest (P<0.05) viability of spermatozoa was achieved by inclusion of 2.0mM BHT. The higher concentration of BHT (3.0mM) reduced the motility, acrosomal integrity, viability and hypo-osmotic swelling response of the spermatozoa compared to other concentration used. In conclusion, BHT when added in the semen extender can improve the semen quality of buffalo bulls.

Effect of butylated hydroxytoluene on bull spermatozoa frozen in egg yolk-citrate extender

Effect of butylated hydroxytoluene (BHT) on the quality of frozen-thawed Holstein bull sperm in egg yolk-citrate extender was evaluated. High quality semen samples were diluted in egg yolk-citrate extenders containing 0, 0.5, 1, 2 and 4 mM BHT and subsequently frozen in liquid nitrogen. Pre-freeze and post-thaw progressive motility, and live/dead ratio and acrosomal integrity of 200 sperm per slide, stained with Eosin-Nigrosin and Giemsa, were evaluated at 0, 2 and 4 h after thawing. There was a significant decrease in forward motility, livability and acrosomal integrity up to 4 h after thawing the frozen sperm. Upon thawing, sperm progressive motility at 1 mM BHT was significantly (P<0.001) higher (11%) than other groups, but percentages of live sperm and live sperm with intact acrosomes were higher at 0.5 mM BHT. BHT at 4 mM BHT caused a significant decrease in motility, livability and acrosomal integrity during preparatory stages of freezing sperm. It is concluded that 0.5-1.0 mM BHT can be beneficial for freezing Holstein bull spermatozoa in egg yolk-citrate diluent, when inseminated immediately after thawing.

Cholesterol-loaded cyclodextrins added to fresh bull ejaculates improve sperm cryosurvival1

Damage occurring to spermatozoa during cryopreservation results in a loss of motile cells and cells that are functionally normal, compared with fresh sperm samples. Treating bull sperm with cholesterol-loaded cyclodextrins (CLC) before cryopreservation results in increased sperm cryosurvival. However, in previous studies, CLC were always added to sperm samples that had been highly diluted. The aim of this study was to develop a procedure for adding CLC to whole bull ejaculates that would optimize sperm cryosurvival. Adding 2 or 4 mg of CLC/120 x 10(6) sperm to sperm samples ranging in concentration from 120 to 2,000 x 10(6) sperm/mL resulted in greater (17 to 28 percentage points; P < 05) numbers of live cells compared with control samples (no CLC treatment), regardless of the sperm concentration, except for samples at 120 x 10(6) sperm/mL treated with 4 mg of CLC. Incubating sperm with CLC at 23 or 37 degrees C before cryopreservation resulted in similar sperm cryosurvival. The cooling rate used to cryopreserve CLC-treated cells did not affect sperm cryosurvival. Finally, adding CLC to undiluted ejaculates (2 mg of CLC/120 x 10(6) sperm) resulted in greater percentages of live sperm compared with the control samples (62 vs. 45%; P < 0.05), although the percentages of motile sperm were similar for both CLC-treated and control samples (58%). In conclusion, bull sperm cryo-survival can be improved if spermatozoa are treated with CLC before freezing. In addition, CLC can be added to fresh ejaculates at either 23 or 37 degrees C. This technique is simple, practical, and can be easily integrated into current cryopreservation protocols.

Pellet-freezing of Damascus goat semen in a chemically defined extender

During the breeding season of goats (12 bucks and 64 does) in Egypt, five experiments were conducted using a chemically defined cryoextender (CDE) to investigate: (1) the influence of rates of semen dilution (1:2, 1:4 and 1:19) and methods of thawing of frozen semen pellets (dry thawing versus wet thawing) on sperm progressive motility (SPM), sperm acrosome abnormalities (SAA) and rate of lipid peroxidation in semen as measured by malonaldehyde (MAL) production, and (2) the effect of insemination of does in natural (n = 38) and cloprostenol-synchronized (n = 26) estrus with frozen semen on their kidding rates and prolificacy. Semen (two successive ejaculates/buck) was collected twice a week via an AV and only ejaculates of >2500 x 10(6) sperm/ml and 70% SPM were diluted in one step at 30 degrees C with the CDE, cooled to 5 degrees C over a 4h-period, frozen in the form of 0.30 ml pellets and stored in liquid nitrogen for 72 h. The results revealed that post-thaw SPM of semen diluted at a rate of 1:4 was significantly (P < 0.01) higher than that of semen diluted at the other rates. Dilution of semen at a rate of 1:19 (< or =151 x 10(6) sperm/ml) not only minimized (P < 0.01) pre-freeze and post-thaw SPM, but also augmented (P < 0.01) pre-freeze and post-thaw rates of lipid peroxidation as evidenced by the high level of MAL production and the ability of antioxidants (1mg/ml EDTA, 200 U/ml bovine liver catalase, 0.61 mg/ml reduced glutathione and 0.11 mg/ml sodium pyruvate) to restore (P < 0.01) pre-freeze and post-thaw SPM. Frozen semen pellets exposed to dry thawing had a greater percentage of SPM (P < 0.01) as well as lower values of SAA and MAL (P < 0.01) than those exposed to wet thawing. Although the kidding rates did not vary significantly among does in natural (55.26%) and synchronized (53.85%) estrus, a higher (P < 0.05) prolificacy was obtained after their insemination in natural (1.81+/-0.16) rather than in synchronized (1.22+/-0.11) estrus.

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.

Protection of boar spermatozoa from cold shock damage by 2-hydroxypropyl-beta-cyclodextrin

This study examined whether 2-hydroxypropyl-beta-cyclodextrin (HBCD) could play a role in protecting spermatozoa from cold shock, as judged by motility parameters, intact acrosomes, and membrane integrity. Motility parameters were assessed by a computer-assisted sperm motility analysis (CASA) system, and the acrosome and membrane integrity were evaluated by fluorescent staining with FlTC-labeled peanut agglutinin and SYBR-14 plus Propidium Iodide, respectively. The addition of HBCD to the BF5 extender significantly increased the percentages of spermatozoa with intact acrosomes and increased membrane integrity after cold shock. The motility, progressive motility, and progressive velocity of the cold-shocked spermatozoa in the presence of HBCD were significantly higher than in the absence of HBCD. In contrast, further supplement of HBCD with cholesterol-3-sulfate (a cholesterol analogue) resulted in a decrease in all the aforementioned criteria, suggesting that the ability of HBCD to protect spermatozoa from cold shock injury is blocked by saturating the cholesterol binding sites of HBCD. It is therefore concluded that HBCD protects spermatozoa against cold shock injury, possibly due to its ability to remove membrane cholesterol.

Storage of boar semen

The problems, aspects and methods of liquid storage and freeze-thawing of boar semen are discussed and a review is given on examination of spermatozoa by the recent fluorescent staining methods.

Fertilizing potential of mouse spermatozoa cryopreserved in a medium containing whole eggs

Experiments were conducted to improve survival of mouse spermatozoa through the cryopreservation process. In the first experiment, percentages of motile spermatozoa and fertilizing capacities of spermatozoa were evaluated when mouse spermatozoa were cryopreserved using three previously reported cryopreservation media: (1) 18% raffinose in 3% skim milk; (2) Tes/Tris medium containing 25% egg yolk and 1.25% glycerol; and (3) PBS containing 18% raffinose and 1.75% glycerol, each at three different cooling rates (-3, -10, and -50 degrees C/min). Spermatozoa frozen in the skim milk/raffinose medium exhibited the highest percentage of motile spermatozoa (39%) when cells were frozen at -10 degrees C/min (P<0.05). The second experiment evaluated the effects of modifying the Tes/Tris/egg yolk medium, comparing different concentrations of egg yolk, BSA, and sodium dodecyl sulfate. Reducing egg yolk from 25% of the medium volume to 5%, increased percentages of motile spermatozoa after cryopreservation from 29 to 36% (P<0.05). Addition of 1% BSA and sodium dodecyl sulfate to medium containing 5% egg yolk further improved percentages of motile spermatozoa after freezing. In the final experiment, 20% whole egg was substituted for 5% egg yolk and 1% BSA used in previous experiments and resulted in percentages of motile spermatozoa (51%) equal to that of the skim milk-raffinose medium. However, fertility rates were higher (68%) than for spermatozoa frozen in the skim milk-raffinose medium (P < 0.05) and were comparable to the fertility rates of fresh spermatozoa (77%; P>0.05). In conclusion, freezing mouse spermatozoa in a medium containing 20% whole egg, 0.035% sodium dodecyl sulfate, and 1.25% glycerol using a cooling rate of -10 degrees C/min preserves the motility and fertilization capacity of mouse spermatozoa.

Motility of ram spermatozoa during storage in a chemically-defined diluent containing antioxidants

The effects of five antioxidants--Vitamin E (VE), butylated hydroxyanisole (BHA), n-propyl gallate (n-PG), deferoxamine mesylate (Desferal) and catalase (EC 1 . 11 . 1 . 6)--on the maintenance of motility of ram spermatozoa in a chemically-defined ram semen diluent (RSD-1) have been evaluated. VE, n-PG and Desferal inhibited spermatozoal motility. The relative inhibition (i.e., ratio of change in % motility over 24 h between the treatment group and the corresponding control) at equimolar concentrations (100 microM) of Desferal, VE and n-PG were 1.6, 1.8 and 3.6 respectively. BHA had no effect at 10 microM but at lower concentrations, gave a slight improvement in motility in freshly diluted spermatozoal samples and in those stored for 1 day at 15 degrees C. The addition of catalase to RSD-1 was also ineffective in improving the motility of spermatozoa. The lack of beneficial effects of the tested antioxidants suggests that RSD-1 itself may destroy reactive oxygen species and the antioxidant activity of RSD-1 components requires further study.

Categorical data analysis of the effect on bull fertility of butylated hydroxytoluene addition to semen extenders prior to freezing

Butylated hydroxytoluene is an antioxidant that has antiviral properties and sustains sperm viability during freezing and thawing. A field trial involving 11 bulls and 19,000 AI was conducted to determine whether addition of .5 mM butylated hydroxytoluene to whole milk extender during seminal processing affected bull fertility as estimated by nonreturn rates generated by cows bred to the bulls. Effects of bull, batch of semen nested within bull, treatment, and month of AI were studied. Nonreturn rates were recorded for each month for every bull, batch of semen (ejaculates pooled on a given day), and treatment combination. Because some bulls had < 6 batches of semen, the original experimental design was reduced to two smaller designs. Categorical data analysis with maximum likelihood estimation was used for analysis of nonreturn rates. The results from three models were used to interpret the data. The nonreturn rates were approximately 73.9% for the butylated hydroxytoluene treatment and 74.1% for the control. In all models, bull effect was significant, but batch, month of AI, and treatment had no effect on bull fertility. Addition of .5 mM butylated hydroxytoluene to whole milk extender during semen processing did not affect bull nonreturn rates.

Effects of cryopreservation procedures on sperm membranes

Empirical approaches to semen cryopreservation have resulted in the production of young in a broad range of species. However, acceptable levels of fertility in most domestic animal species has not been achieved. In this review, an attempt has been made to describe the complexity of the sperm plasma membrane and the many steps in a cryopreservation procedure where membrane perturbations can occur. Improvement in sperm cryopreservation procedures will require a careful consideration of the complexity of the sperm plasma membrane, the interaction of its components and the influence of cooling, freezing and thawing on these interactions.