Reactive oxygen species and boar sperm function

Porcine sperm capacitation involves tyrosine phosphorylation and activation of aldose reductase

Mammalian sperm must be activated in the tubal isthmus through capacitation to induce the acrosome reaction and subsequent fertilization. Although the molecular mechanisms involved in capacitation have yet to be fully elucidated, increased concentrations of reactive oxygen species (ROS) and the extent of tyrosine phosphorylation of proteins have been suggested to play central roles in the completion of capacitation. In this study, aldose reductase was for the first time identified as one of the tyrosine-phosphorylated proteins involved in the capacitation of porcine cauda epididymal sperm. Both tyrosine phosphorylation and activity of aldose reductase associated with the particulate fraction of sperm cells were significantly enhanced during capacitation. Alrestatin, a membrane-permeable and specific inhibitor of aldose reductase, plays a role in the inhibition of aldose reductase activity, elevation of intracellular levels of ROS, and induction of hyperactivated motility, all at similar dose dependencies. Alrestatin canceled both the increase in the tyrosine phosphorylation of aldose reductase and the decrease in the glutathione levels in sperm-induced during capacitation. The hyperactivated motility was induced to a higher extent in the presence of glucose than in the presence of fructose. These results indicate that aldose reductase plays an important role in induction of hyperactivation and capacitation of sperm through the elevation of ROS in sperm cells. Furthermore, aldose reductase was shown to be added to sperm during transit through the epididymis, suggesting that aldose reductase is one of the key proteins that support the functional maturation of sperm.

Boar sperm cryosurvival is better after exposure to seminal plasma from selected fractions than to those from entire ejaculate

Boar bulk ejaculates are now being collected instead of usual sperm-rich fractions (SRF) for artificial insemination purpose. The present study evaluated the influence of holding boar sperm samples before freezing surrounded in their own seminal plasma (SP), from either fractions/portions or the entire ejaculate, on post-thawing sperm quality and functionality. Ejaculates collected as bulk (BE) or as separate (first 10 mL of SRF [P1] and rest of SRF [P2]) from 10 boars were held 24h at 15-17°C and then frozen. Some bulk ejaculate samples were frozen immediately after collections as Control. In addition, epididymal sperm samples from the same 10 boars were collected post-mortem and extended in SP from P1 (EP1), P2 (EP2) and post SRF (EP3), and also held 24h before freezing for a better understanding of the influence of SP on boar sperm cryopreservation. The sperm quality (motility, evaluated by CASA, and viability, evaluated by flow cytometry) and functionality (flow cytometry assessment of plasma membrane fluidity, mitochondrial membrane potential and intracellular generation of reactive oxygen species [ROS] in viable sperm) were evaluated at 30, 150 and 300 min post-thaw. Post-thawing sperm quality and functionality of P1 and P2 were similar but higher (p < 0.01) than BE samples. Control samples showed higher (p < 0.01) post-thaw sperm quality and functionality than BE samples. Post-thawing sperm quality and functionality of EP1 and EP2 were similar but higher (p < 0.05) than EP3. These results showed that boar sperm from BE are more cryosensitive than those from the SRF, particularly when held 24h before freezing, which would be attributable to the cryonegative effects exerted by the SP from post SRF.

Superoxide dismutase: a predicting factor for boar semen characteristics for short-term preservation

Superoxide dismutase (SOD), total antioxidant capacity (TAC), and thiobarbituric acid reactive substances (TBARS) in seminal plasma were evaluated on the basis of receiver operating characteristics (ROC) analysis as predictors for distinguishing satisfactory from unsatisfactory boar semen samples after storage. SOD on day 0 correlated significantly with progressive motility (r=-0.686; P<0.05) and viability (r=-0.513; P<0.05) after storage; TBARS correlated only with motility (r=-0.480; P<0.05). Semen samples that, after 3 days of storage, fulfilled all criteria for semen characteristics (viability>85%, motility>70%, progressive motility>25%, and normal morphology>50%) had significantly lower SOD levels on the day 0 than those with at least one criterion not fulfilled (P<0.05) following storage. SOD levels of less than 1.05 U/mL predicted with 87.5% accuracy that fresh semen will suit the requirements for satisfactory semen characteristics after storage, while semen with SOD levels higher than 1.05 U/mL will not fulfill with 100% accuracy at least one semen characteristic after storage. These results support the proposal that SOD in fresh boar semen can be used as a predictor of semen quality after storage.

Identification of peroxiredoxin-5 in bovine cauda epididymal sperm

Developing spermatozoa require a series of posttesticular modifications within the luminal environment of the epididymis to achieve maturation; this involves several surface modifications including changes in plasma membrane lipids, proteins, carbohydrates, and alterations in the outer acrosomal membrane. Epididymal maturation can therefore allow sperm to gain forward motility and fertilization capabilities. The objective of this study was to identify maturation-dependent protein(s) and to investigate their role with the production of functionally competent spermatozoa. Lectin blot analyses of caput and cauda sperm plasma membrane fractions identified a 17.5 kDa wheat germ agglutinin (WGA)-binding polypeptide present in the cauda sperm plasma membrane not in the caput sperm plasma membrane. Among the several WGA-stained bands, the presence of a 17.5 kDa WGA-binding polypeptide band was detected only in cauda epididymal fluid not in caput epididymal fluid suggesting that the 17.5 kDa WGA-binding polypeptide is secreted from the cauda epididymis and binds to the cauda sperm plasma membrane during epididymal transit. Proteomic identification of the 17.5 kDa polypeptide yielded 13 peptides that matched the sequence of peroxiredoxin-5 (PRDX5) protein (Bos Taurus). We propose that bovine cauda sperm PRDX5 acts as an antioxidant enzyme in the epididymal environment, which is crucial in protecting the viable sperm population against the damage caused by endogeneous or exogeneous peroxide.

Seminal plasma applied post-thawing affects boar sperm physiology: a flow cytometry study

Cryopreservation induces extensive biophysical and biochemical changes in the sperm. In the present study, we used flow cytometry to assess the capacitation-like status of frozen-thawed boar spermatozoa and its relationship with intracellular calcium, assessment of membrane fluidity, modification of thiol groups in plasma membrane proteins, reactive oxygen species (ROS) levels, viability, acrosomal status, and mitochondrial activity. This experiment was performed to verify the effect of adding seminal plasma on post-thaw sperm functions. To determine these effects after cryopreservation, frozen-thawed semen from seven boars was examined after supplementation with different concentrations of pooled seminal plasma (0%, 10%, and 50%) at various times of incubation from 0 to 4 hours. Incubation caused a decrease in membrane integrity and an increase in acrosomal damage, with small changes in other parameters (P > 0.05). Although 10% seminal plasma showed few differences with 0% (ROS increase at 4 hours, P < 0.05), 50% seminal plasma caused important changes. Membrane fluidity increased considerably from the beginning of the experiment, and ROS and free thiols in the cell surface increased by 2 hours of incubation. By the end of the experiment, viability decreased and acrosomal damage increased in the 50% seminal plasma samples. The addition of 50% of seminal plasma seems to modify the physiology of thawed boar spermatozoa, possibly through membrane changes and ROS increase. Although some effects were detrimental, the stimulatory effect of 50% seminal plasma could favor the performance of post-thawed boar semen, as showed in the field (García JC, Domínguez JC, Peña FJ, Alegre B, Gonzalez R, Castro MJ, Habing GG, Kirkwood RN. Thawing boar semen in the presence of seminal plasma: effects on sperm quality and fertility. Anim Reprod Sci 2010;119:160-5).

The relationship between feed efficiency traits and fertility in young beef bulls

Awda, B. J., Miller, S. P., Montanholi, Y. R., Vander Voort, G., Caldwell, T., Buhr, M. M. and Swanson, K. C. 2013. The relationship between feed efficiency traits and fertility in young beef bulls. Can. J. Anim. Sci. 93: 185–192. Great efforts have been taken in recent years for improving feed efficiency in beef cattle. Despite there being several studies on biological factors associated with this trait, little is known about the potential relationships between fertility and feed efficiency in beef cattle. The objective of this study was to examine the relationship between feed efficiency traits and bull fertility traits [sperm motility, viability and scrotal circumference (SC)]. From a total of 328 crossbred beef bulls that were subjected to a performance test (112 d in each of 6 yr), SC was measured and semen collected from 110 bulls using the electroejaculation method (average age±SE=417±2.5 d). Sperm were extended, cooled, and frozen in liquid nitrogen. Two residual feed intake (RFI) measures were considered with different prediction models for dry matter intake (DMI), RFIKoch included size and growth rate and RFIbkft included the additional adjustment for backfat thickness (BKFT). Sperm viability, motility and progressive motility of the 10 bulls with the greatest RFIKoch (Hi-RFIKoch) were greater than those of the 10 bulls with the lowest RFIKoch (Lo-RFIKoch; P<0.05, 0.01, and 0.05, respectively). Sperm motility (P<0.01), progressive motility and SC (P<0.05) of the 10 bulls with the greatest RFIbkft (Hi-RFIbkft) were greater than those of the 10 bulls with the lowest RFIbkft (Lo-RFIbkft). In summary, these data indicate that young beef bulls with greater feed efficiency have decreased sperm motility, sperm viability and SC, which is an undesirable effect of selection for improved feed efficiency that needs to be addressed through multiple trait selection.

Reduced glutathione and procaine hydrochloride protect the nucleoprotein structure of boar spermatozoa during freeze–thawing by stabilising disulfide bonds

One important change the head of boar spermatozoa during freeze–thawing is the destabilisation of its nucleoprotein structure due to a disruption of disulfide bonds. With the aim of better understanding these changes in frozen–thawed spermatozoa, two agents, namely reduced glutathione (GSH) and procaine hydrochloride (ProHCl), were added at different concentrations to the freezing media at different concentrations and combinations over the range 1–2 mM. Then, 30 and 240 min after thawing, cysteine-free residue levels of boar sperm nucleoproteins, DNA fragmentation and other sperm functional parameters were evaluated. Both GSH and ProHCl, at final concentrations of 2 mM, induced a significant (P < 0.05) increase in the number of non-disrupted sperm head disulfide bonds 30 and 240 min after thawing compared with the frozen–thawed control. This effect was accompanied by a significant (P < 0.05) decrease in DNA fragmentation 240 min after thawing. Concomitantly, 1 and 2 mM GSH, but not ProHCl at any of the concentrations tested, partially counteracted the detrimental effects caused by freeze–thawing on sperm peroxide levels, motility patterns and plasma membrane integrity. In conclusion, the results show that both GSH and ProHCl have a stabilising effect on the nucleoprotein structure of frozen–thawed spermatozoa, although only GSH exerts an appreciable effect on sperm viability.

Proteomic analysis of boar spermatozoa and quantity changes of superoxide dismutase 1, glutathione peroxidase, and peroxiredoxin 5 during epididymal maturation

Mammalian spermatozoa and their various proteins undergo various modifications during maturation in the epididymis. To characterize proteins that change in quantity during this maturational process, boar spermatozoa were collected from various regions of the epididymis, and extracts were analyzed by two-dimensional gel electrophoresis (2-DE). A number of proteins were identified as changing in quantity, and MALDI-MS analysis revealed that superoxide dismutase 1 (SOD1) from the acrosomal proteins of spermatozoa, and glutathione peroxidase (GPX) and peroxiredoxin 5 from the membranous fraction increased during the epididymal transit of spermatozoa. These proteins are antioxidants that remove reactive oxygen species (ROS); they are presumed to protect spermatozoa during epididymal transit and storage. Western blot analysis of SOD1, GPX and peroxiredoxin 5 showed that these protein levels increased as the spermatozoa traveled from the caput to the cauda epididymis. Activity analysis showed that total SOD activity also increased. Therefore, we conclude that several antioxidant proteins increase during the transit of boar spermatozoa through the epididymis, ultimately contributing to the maturation and/or survival of sperm.

Oxidative stress in zebrafish (Danio rerio) sperm

Laboratories around the world have produced tens of thousands of mutant and transgenic zebrafish lines. As with mice, maintaining all of these valuable zebrafish genotypes is expensive, risky, and beyond the capacity of even the largest stock centers. Because reducing oxidative stress has become an important aspect of reducing the variability in mouse sperm cryopreservation, we examined whether antioxidants might improve cryopreservation of zebrafish sperm. Four experiments were conducted in this study. First, we used the xanthine-xanthine oxidase (X-XO) system to generate reactive oxygen species (ROS). The X-XO system was capable of producing a stress reaction in zebrafish sperm reducing its sperm motility in a concentration dependent manner (P<0.05). Second, we examined X-XO and the impact of antioxidants on sperm viability, ROS and motility. Catalase (CAT) mitigated stress and maintained viability and sperm motility (P>0.05), whereas superoxide dismutase (SOD) and vitamin E did not (P<0.05). Third, we evaluated ROS in zebrafish spermatozoa during cryopreservation and its effect on viability and motility. Methanol (8%) reduced viability and sperm motility (P<0.05), but the addition of CAT mitigated these effects (P>0.05), producing a mean 2.0 to 2.9-fold increase in post-thaw motility. Fourth, we examined the effect of additional cryoprotectants and CAT on fresh sperm motility. Cryoprotectants, 8% methanol and 10% dimethylacetamide (DMA), reduced the motility over the control value (P<0.5), whereas 10% dimethylformamide (DMF) with or without CAT did not (P>0.05). Zebrafish sperm protocols should be modified to improve the reliability of the cryopreservation process, perhaps using a different cryoprotectant. Regardless, the simple addition of CAT to present-day procedures will significantly improve this process, assuring increased and less variable fertilization success and allowing resource managers to dependably plan how many straws are needed to safely cryopreserve a genetic line.

Detrimental effects of non-functional spermatozoa on the freezability of functional spermatozoa from boar ejaculate

In the present study, the impact of non-functional spermatozoa on the cryopreservation success of functional boar spermatozoa was evaluated. Fifteen sperm-rich ejaculate fractions collected from five fertile boars were frozen with different proportions of induced non-functional sperm (0--native semen sample-, 25, 50 and 75% non-functional spermatozoa). After thawing, the recovery of motile and viable spermatozoa was assessed, and the functional of the spermatozoa was evaluated from plasma membrane fluidity and intracellular reactive oxygen species (ROS) generation upon exposure to capacitation conditions. In addition, the lipid peroxidation of the plasma membrane was assessed by the indirect measurement of malondialdehyde (MDA) generation. The normalized (with respect to a native semen sample) sperm motility (assessed by CASA) and viability (cytometrically assessed after staining with Hoechst 33342, propidium iodide and fluorescein-conjugated peanut agglutinin) decreased (p<0.01) as the proportion of functional spermatozoa in the semen samples before freezing decreased, irrespective of the semen donor. However, the magnitude of the effect differed (p<0.01) among boars. Moreover, semen samples with the largest non-functional sperm subpopulation before freezing showed the highest (p<0.01) levels of MDA after thawing. The thawed viable spermatozoa of semen samples with a high proportion of non-functional spermatozoa before freezing were also functionally different from those of samples with a low proportion of non-functional spermatozoa. These differences consisted of higher (p<0.01) levels of intracellular ROS generation (assessed with 5-(and-6) chloromethyl-20,70-dichlorodihydrofluorescein diacetate acetyl ester; CM-H(2)DCFDA) and increased (p<0.01) membrane fluidity (assessed with Merocyanine 540). These findings indicate that non-functional spermatozoa in the semen samples before freezing negatively influence the freezability of functional spermatozoa.

Differences in the ability of spermatozoa from individual boar ejaculates to withstand different semen-processing techniques

The present study aimed to evaluate the ability of spermatozoa from individual boar ejaculates to withstand different semen-processing techniques. Eighteen sperm-rich ejaculate samples from six boars (three per boar) were diluted in Beltsville Thawing Solution and split into three aliquots. The aliquots were (1) further diluted to 3×10(7) sperm/mL and stored as a liquid at 17°C for 72 h, (2) frozen-thawed (FT) at 1×10(9) sperm/mL using standard 0.5-mL straw protocols, or (3) sex-sorted with subsequent liquid storage (at 17°C for 6 h) or FT (2×10(7) sperm/mL using a standard 0.25-mL straw protocol). The sperm quality was evaluated based on total sperm motility (the CASA system), viability (plasma membrane integrity assessed using flow cytometry and the LIVE/DEAD Sperm Viability Kit), lipid peroxidation (assessed via indirect measurement of the generation of malondialdehyde (MDA) using the BIOXYTECH MDA-586 Assay Kit) and DNA fragmentation (sperm chromatin dispersion assessed using the Sperm-Sus-Halomax(®) test). Data were normalized to the values assessed for the fresh (for liquid-stored and FT samples) or the sorted semen samples (for liquid stored and the FT sorted spermatozoa). All of the four sperm-processing techniques affected sperm quality (P<0.01), regardless of the semen donor, with reduced percentages of motile and viable sperm and increased MDA generation and percentages of sperm with fragmented DNA. Significant (P<0.05) inter-boar (effect of boars within each semen-processing technique) and intra-boar (effect of semen-processing techniques within each boar) differences were evident for all of the sperm quality parameters assessed, indicating differences in the ability of spermatozoa from individual boars to withstand the semen-processing techniques. These results are the first evidence that ejaculate spermatozoa from individual boars can respond in a boar-dependent manner to different semen-processing techniques.

Identification of hypoxic-responsive proteins in cucumber roots using a proteomic approach

To elaborate the mechanisms of response of cucumber (Cucumis sativus L. cv.) seedlings to hypoxic stress, plants were grown under either normoxic conditions or hypoxic stress. As expected, plant biomass was significantly reduced under hypoxic stress. Proteomic profiles of cucumber roots were studied at 72 h after treatment; 316 and 425 protein spots were detected on polyacrylamide gels from normoxic and hypoxic-treated plants, respectively. Compared with normoxic-treated plants, protein abundance of 22 proteins was significantly upregulated while protein abundance of 12 proteins decreased in the hypoxic-treated plants. Twenty one of the proteins whose abundance was altered were identified by MALDI-TOF/TOF MS analysis, and categorized into classes corresponding to energy and metabolism proteins, transcription factor proteins, defense stress proteins, structural proteins and regulatory proteins. Under hypoxic stress, glycolysis was induced; energy was channeled to primary metabolism, while secondary pathways and nitrogen metabolism pathways were inhibited. Cucumber plants scavenged reactive oxygen species by antioxidase, and increased Acyl-[acyl-carrier-protein] desaturase which defend against reactive oxygen species damage to plant cell structure. This study provides insight that may facilitate a better understanding of the response mechanisms of cucumber plant to hypoxic stress.

Cysteine addition on short-term cooled boar semen preservation and its relationship with swine field fertility

Artificial insemination is routinely used in the swine industry to reduce the costs of production through to increase the efficiency of the refrigerated boar semen process. The objective of this study was to evaluate the effect of different levels of cysteine (CYS) added to the Beltsville Thawing Solution (BTS) extender semen during cooling for up to 72 hours. Ejaculated from three boars were collected with the gloved-hand technique and semen aliquots were diluted in BTS as follow: BTS only (BTS), BTS + 0.1mM cysteine (CYS0.1), BTS + 0.5mM cysteine (CYS0.5), BTS + 1.0mM cysteine (CYS1.0), BTS + 2.5mM cysteine (CYS2.5), BTS + 5.0mM cysteine (CYS5.0), BTS + 10.0mM cysteine (CYS10.0), and BTS + 20.0mM cysteine (CYS20.0). Evaluation of sperm integrity were analyzed using 0.5mg/ml propidium iodide (plasma membrane), 100µg/ml isothiocynate-conjugated Pisum sativun agglutinin (acrosomal membrane) and 153µM 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl carbocyanine iodide (mitochondria potential) after semen dilution at specific times (0, 24, 48 and 72 hours). Additionally, we also evaluated the effects of 5.0 mM CYS addition in the BTS extender on the maintenance of sperm quality and their influence on fertility in the swine production. After artificial insemination, animals were evaluated based on the estrous return and the number of piglet's born. Cysteine at concentrations of 10.0 and 20.0mM resulted in more pronounced reductions even at the time zero. Semen viability decreased to levels below 10% at these high levels of CYS in the first 24 hour of storage at 17ºC. At the end of the storage time, less than 65% of sperm cells had intact plasma membrane in all groups. The sperm viability decreased significantly when the semen was added at high concentrations of CYS (time "0"; CYS10.0 and CYS20.0; p<0.05), when compared to the other CYS concentrations. The BTS (10.20±0.39) treated group showed a lower rate of estrus return when compared to other (BTSCYS; 86.05±039), and it showed also the highest total number of piglets borne per treatment (12.71±3.38 vs. 9.00±3.38, respectively). In conclusion, the addition of CYS in the BTS semen extender did not maintain spermatic viability of boar cooled spermatozoa and it results in a higher percentage of return to estrus and lower number of piglets borne.

Effect of the addition of beta-mercaptoethanol to a thawing solution supplemented with caffeine on the function of frozen-thawed boar sperm and on the fertility of sows after artificial insemination

We have reported that artificial insemination (AI) with frozen-thawed boar semen supplemented with caffeine increased the number of uterine sperm by inhibiting the migration of polymorphonuclear leukocytes (PMNs) into the uterine lumen, thereby improving the fertility of gilts and sows. The objective of the present study was to examine the effects of the addition of the antioxidant beta-mercaptoethanol (bME) and caffeine to the thawing solution on the function of frozen-thawed sperm, on the phagocytic activity of PMNs for sperm, and on the fertility of sows after AI. When frozen-thawed sperm were cultured in the presence of 25 or 50 μm bME, sperm capacitation and spontaneous acrosome reactions were inhibited (P < 0.01). There was no effect of bME on phagocytic activity of PMNs for sperm in vitro. When hormonally treated (400 IU of equine chorionic gonadotropin + 200 IU of human chorionic gonadotropin) weaned sows experienced a single intrauterine insemination with frozen-thawed sperm (25 × 10(8) sperm per 50 ml dose) 40 h after subsequent hCG administration, pregnancy and farrowing rates were unaffected by the addition of 50 μm bME (pregnancy rate, 20 vs 21% in controls; farrowing rate, 20 vs 21%; n = 15 and 14, respectively). However, litter size tended to be higher than in the presence of 50 μm bME compared to its absence (10.0 ± 1.0 vs 5.7 ± 1.5, respectively; P < 0.07). Thus, the addition of bME to the thawing solution containing caffeine could be of benefit for improving the function of frozen-thawed sperm without influencing the phagocytic activity of PMNs for sperm. Although there were no statistically significant effects of bME on pregnancy or farrowing rates, the litter size tended to be higher in the sows subjected to a fixed-time single AI treatment with synchronized ovulation.

Expression of E-cadherin and α-catenin in a varicocele-induced infertility rat model

The roles of E-cadherin and α-catenin were evaluated in the development of varicocele-induced infertility. Analysis of the association between the expression of E-cadherin/α-catenin and clinical/pathological parameters was performed. Thirty 10-week-old male rats (experimental group) were used for the experiments; the left renal vein was ligated to form a varicocele. The abdomen was incised in 30 rats (control group) and no procedure was performed on 10 rats (baseline group). The weights of the left testis, serum reactive oxygen species (ROS), testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and degenerative changes in the seminiferous tubules after 4 and 8 weeks were recorded. The expression of E-cadherin and α-catenin was evaluated by immunohistochemical (IHC) staining and Western blot analysis. The ROS increased in the 8-week experimental group, compared with the baseline and control groups (P < 0.001 for both). Additionally, FSH significantly increased in the 4- and 8-week experimental group compared with the control groups (P = 0.013 and P = 0.032, respectively). The ratio of degenerative changes in the seminiferous tubules of the experimental groups increased. The IHC staining showed that the expression of E-cadherin and α-catenin decreased in the 4- and 8-week experimental groups. Similar to the IHC staining, the experimental group had decreased reactivity on Western blot analysis. The expression of E-cadherin and α-catenin was significantly associated with the ROS and degenerative changes in the seminiferous tubules. The results of this study suggest that damage to the blood-testis barrier (BTB) is associated with varicocele-induced male infertility, and that ROS may cause damage to the BTB.

Changes in sperm membrane and ROS following cryopreservation of liquid boar semen stored at 15 °C

Boar semen is occasionally transferred to different locations in liquid form at 15 °C for cryopreservation. However, the use of frozen boar semen is limited due to the high susceptibility of boar sperm to cold shock. The aim of this study was to help improve the quality of frozen boar semen by determining the changes in sperm membrane and ROS during the cryopreservation processes of 15 °C-stored boar semen. Semen was collected from ten Duroc boars and transferred to our laboratory in liquid form stored at 15 °C. After cooling to 5 °C and freezing-thawing, conventional sperm parameters (total motility, progressive motility, and normal morphology), plasma membrane integrity, acrosomal membrane status, and intracellular ROS were evaluated. Sperm function, as assessed by conventional parameters, was unaffected by cooling but was decreased by freezing-thawing (P<0.05). However, the cooling and freezing-thawing processes led to damages in the sperm plasma membrane, and the cooling process caused increase in mean PNA (peanut agglutinin)-fluorescence intensity in viable acrosome-intact sperm (P<0.05). In ROS evaluation, the cooling process decreased intracellular (·)O(2) and H(2)O(2) in viable sperm (P<0.05), while the freezing-thawing process increased intracellular H(2)O(2) (P<0.05) without change in intracellular (·)O(2) in viable sperm. Our results suggest that, in liquid boar semen stored at 15 °C, cooling may be primarily responsible for the destabilization of sperm membranes in viable sperm, while freezing-thawing may induce reductions in sperm function with increase in membrane damage and H(2)O(2).

Methods for evaluating the potency and efficacy of antioxidants

PURPOSE OF REVIEW

The aim of this article is to present a brief panorama of the most widely used methods and of new analytical approaches for evaluating antioxidant capacity and to discuss them in terms of advantages and drawbacks.

RECENT FINDINGS

To date, many in-vitro tests are available from the chemical assay performed in a homogenous solution such as oxygen radical antioxidant capacity assay to more complex cell-based methods using exogenic probes to detect oxidation. In complement to these existing methods, novel approaches have recently been developed such as the conjugated autoxidizable triene assay implemented in emulsions and using tung oil as ultraviolet probe.

SUMMARY

The complexity and diverse range of research topics investigated have led to the development of a multitude of tests, but unfortunately none of them are universal. Thus, one of the major challenges is to know which method is best suited for a particular application.

The HSP90AA1 sperm content and the prediction of the boar ejaculate freezability

In a previous study we reported that the immunolabelling of GLUT3, HSP90AA1, and Cu/ZnSOD proteins on boar sperm did not show differences between good and poor freezability ejaculates, in terms of a qualitative analysis based on location and reactivity of these proteins at 17 degrees C and at 240 min post-thaw. Since predicting the ejaculate freezability is considerably important in sperm cryopreservation procedures, the objective of the present study was to quantify the expression of these three proteins in good and poor freezability ejaculates. For this purpose, 10 ejaculates from 9 Piétrain boars were cryopreserved and their sperm quality assessed in the three main steps of the freezing process (17 degrees C, 5 degrees C, and 240 min post-thaw). After this assessment, the 10 ejaculates were clustered for freezability on the basis of their sperm progressive motility and membrane integrity at 240 min post-thaw. From the whole ejaculates, only four good and four poor freezability ejaculates displaying the most divergent values were selected for a western blot assay using sperm samples coming from the three mentioned freezing steps. Protein levels through densitometry were significantly different between good and poor freezability ejaculates for Cu/ZnSOD at 240 min post-thaw (P <or= 0.01) and for HSP90AA1 at 17 degrees C and 5 degrees C (P <or= 0.05). This last finding claims the introduction of tests based on molecular markers in spermatozoa to accurately predict the freezability of ejaculates in order to promote the use of frozen semen on artificial insemination programmes.

Extracellular signal-regulated kinases (ERKs) pathway and reactive oxygen species regulate tyrosine phosphorylation in capacitating boar spermatozoa

The extracellular signal-regulated kinase (ERK) family of the mitogen-activated protein kinase (MAPK) pathway is identified for the first time in boar sperm and is associated with capacitation and tyrosine phosphorylation (tyr-P). Reactive oxygen species (ROS) modulate this signal transduction. Western immunoblotting detected the ERK pathway components RAF1, MEK1/2, and ERK1/2 in extracts from fresh boar spermatozoa and determined that their phosphoprotein profiles differed in a capacitation-dependent fashion. Capacitation was accompanied by appearance of two new ERKs (158 and 161 kDa) and disappearance of others. Capacitation was verified with increased tyr-P, which was inhibited by a 30-min pre-exposure of fresh boar sperm to a xanthine/xanthine oxidase ROS-generating system prior to the capacitating incubation; ROS pre-exposure also affected the phosphorylation of RAF1, MEK1/2, and ERK1/2. Preincubating sperm with inhibitors of the ERK components with or without the ROS generator affected subsequent capacitation. Inhibiting ERK1/2 inhibited tyr-P of capacitated boar spermatozoa proteins of 172, 97, and 66 kDa (P ≤ 0.04); with ROS, this inhibition increased (P < 0.002) and tyr-P of 111 kDa declined (P < 0.028). Pre-exposure to ROS plus MEK1/2 inhibitor prevented capacitation-induced tyr-P of proteins of 187 (P < 0.01) and 112 kDa (P < 0.04) versus capacitation with or without ROS. Therefore, ERK1/2 components of the MAPK pathway significantly regulate boar sperm capacitation, and RAF1 and MEK1/2 may have some lesser influence through crosstalk with different pathways. ROS affect RAF1, MEK1/2, and ERK1/2 and could influence the sequential events of boar sperm capacitation.

Osmotic stress induces oxidative cell damage to rhesus macaque spermatozoa

Cryopreservation introduces extreme temperature and osmolality changes that impart lethal and sublethal effects on spermatozoa survival. Additionally, evidence indicates that the osmotic stress induced by cryopreservation causes oxidative stress to spermatozoa as well. Our objective was to determine the effect of reactive oxygen species (ROS) on rhesus macaque (Macaca mulatta) sperm function and to determine whether osmotic stress elicits the production of ROS. In the first experiment, the xanthine-xanthine oxidase (X-XO) system was used to generate the ROS superoxide anion (O(2)(-.)) and hydrogen peroxide (H(2)O(2)) in the presence or absence of the ROS scavengers superoxide dismutase and catalase, respectively. In the second experiment, osmotic stress was introduced by incubation of spermatozoa in a series of anisosmotic media ranging from 100 to 1000 mOsmol/kg in the presence or absence of the antioxidant alpha-tocopherol. Treatment with the X-XO system resulted in a significant increase in the generation of O(2)(-.) and H(2)O(2) that was detectable using flow cytometry. The ROS generated by the X-XO system was dose dependent, and as the concentration of ROS increased, motility decreased and lipid peroxidation increased while no affect was observed on viability. Incubation of spermatozoa in anisosmotic media also resulted in an increase in O(2)(-.) generation and lipid peroxidation that was significantly decreased in the presence of the powerful antioxidant alpha-tocopherol. These results clearly indicate that osmotic stress causes oxidative stress in rhesus macaque spermatozoa, which strongly supports the hypothesis that cryopreservation-induced osmotic stress may lead to oxidative cell damage.

Manganese provides antioxidant protection for sperm cryopreservation that may offer new consideration for clinical fertility

Reactive oxygen species (ROS) are generated by sperm metabolism. While, ROS are required for maturation, capacitation and acrosome reaction, they also modify many peroxidable cellular compounds. There is production of ROS during cryopreservation and frozen spermatozoa are highly sensitive to lipid peroxidation (LPO). Antioxidants exert a protective effect on the plasma membrane of frozen bovine sperm preserving both metabolic activity and cellular viability. Manganese (Mn(++)) is proved to be a chain breaking antioxidant in biological system. Therefore, we examined the role of (Mn(++)) during cryopreservation of cattle bull semen. Semen was divided into four parts and cryopreserved in egg-yolk-citrate extender + glycerol (EYC-G), EYC-G + 100 microM of Mn(++), EYC-G + 150 microM of Mn(++) and EYC-G + 200 microM of Mn(++). After four hours of cooling and 24 hrs of freezing, the spermatozoa were examined for percentage motility, Hypo-osmotic swelling (HOS), LPO and protein leakage. Addition of manganese to the semen during cryopreservation showed a protective effect and accounted for an increase in semen quality parameters [percentage motility, HOS percent and decrease in malondialdehyde (MDA) production and protein leakage]. The effect of manganese on motility and HOS was non-significant (p < 0.05) in cooled spermatozoa but significant with 150 microM of Mn(++) in frozen-thawed spermatozoa. MDA production and protein leakage decreased to a significant and maximum level (p < 0.05) on addition of 200 microM of manganese. The addition of manganese to EYC-G dilutor will improve the quality/fertility of semen, which will result in improvement of in vitro fertilization and artificial insemination success rate.