Respiratory burst and NAD(P)H oxidase activity are involved in capacitation of cryopreserved bovine spermatozoa

Supplementation of Mito TEMPO and acetovanillone in semen extender improves freezability of buffalo spermatozoa

BACKGROUND

Oxidative stress is one of the leading factors responsible for poor post-thaw semen quality because of overproduction of reactive oxygen species (ROS) over neutralizing antioxidants present in semen. Mainly two ROS generation sites are present in spermatozoa, that is, mitochondria and plasma membrane. Therefore, the idea of targeting these specific sites for minimization of ROS production with the compounds having known mechanism of actions was built up as a core for this research.

OBJECTIVE

Present study was done to investigate the effects of Mito TEMPO and acetovanillone individually and in combination on freezability of buffalo spermatozoa.

MATERIALS AND METHODS

For the experiment, semen extender was supplemented with Mito TEMPO (50 μM), acetovanillone (50 μM), and a combination of Mito TEMPO + acetovanillone (50 μM+ 50 μM), designated as Group II, Group III, and Group IV, respectively. Control group without any supplementation was designated as Group I. A total of 24 ejaculates with individual progressive motility (IPM) of ≥70% were selected for the study. After final dilution, filling-sealing of straws, equilibration, and freezing were done as per the standard procedure. Semen samples were evaluated for IPM, plasma membrane integrity, lipid peroxidation, total antioxidant capacity (TAC), and cholesterol to phospholipids (C/P) ratio at both fresh and post-thaw stages. Evaluation of ROS, mitochondrial membrane potential (MMP), capacitation status (CTC assay), and in vitro fertility potential were conducted only on frozen-thawed samples.

RESULTS

The addition of Mito TEMPO (50 μM) and acetovanillone (50 μM) individually and in combination significantly (p < 0.05) improved post-thaw semen quality in terms of IPM, plasma membrane integrity, TAC, cholesterol content, C/P ratio, MMP, Chlortetracycline (CTC)-Full (F) pattern, and zona binding ability of buffalo spermatozoa, while significantly (p < 0.05) reduced ROS production, lipid peroxidation, and capacitation like changes as compared to the control group.

DISCUSSION

As Mito TEMPO acts as an SOD mimetic and also detoxifies ferrous iron at the mitochondria level, it aids in neutralization of excessive ROS production and minimizes oxidative stress-related damages that enhances the antioxidant potential of sperm mitochondria. Earlier studies also indicated improved post-thaw semen quality in 50 μM supplemented group. The improvement observed in acetovanillone (50 μM) group might be because of inhibition of Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase as this enzyme activation by various physical/chemical inducers during cryopreservation process leads to activation of CatSper channel resulting in calcium influx, premature capacitation, and acrosomal reaction like changes through activation of adenylate cyclase and cAMP/PKA-mediated tyrosine phosphorylation of sperm proteins. Acetovanillone also prevents NADPH oxidase-mediated inhibition of glutathione reductase activity, which has a vital role in protecting the structural and functional integrity of sperm plasma membrane.

CONCLUSION

Results indicated beneficial effects of supplementation of Mito TEMPO and acetovanillone on sperm freezability and individual supplementation was as efficient as the combination group for sustaining post-thaw semen quality.

Comparative evidence support better antioxidant efficacy of mitochondrial-targeted (Mitoquinone) than cytosolic (Resveratrol) antioxidant in improving in-vitro sperm functions of cryopreserved buffalo (Bubalus bubalis) semen

The present study compared the effect of mitochondria-targeted (Mitoquinone, MitoQ) and untargeted cytosolic antioxidant (Resveratrol, RESV) supplementation on lipid peroxidation (LPO) and in-vitro sperm functions of cryopreserved buffalo bull semen. To optimize additive's concentration, sperm pellet obtained from twenty-four ejaculates was supplemented with different concentrations of MitoQ (20 nM, 100 nM, 200 nM); and RESV (10 μM, 25 μM, 50 μM) against control in the extender. The post-thaw sperm motility, livability, and membrane integrity were higher (P < 0.05) in 200 nM MitoQ and 50 μM RESV than other concentrations used. In another experiment, sperm pellet from thirty-two ejaculates was supplemented with 200 nM MitoQ and 50 μM RESV in the extender. Pre-freeze and post-thaw progressive motility and livability were higher (P < 0.05) in MitoQ (200 nM) than RESV (50 μM) treatment. MitoQ supplementation improved post-thaw membrane integrity (CFDA-PI) higher (P < 0.05) than RESV, however, hypo-osmotic swelling response observed no improvement with RESV treatment. Post-thaw LPO rate was lower (P < 0.05) and Bovine cervical mucus penetration was higher (P < 0.05) in MitoQ than RESV treatment. In post-thaw semen, MitoQ showed higher (P < 0.05) proportion of acrosome intact (FITC-PNA), live non-apoptotic (P < 0.01) sperm with a higher reduction (P < 0.05) in membrane scrambling. MitoQ improved (P < 0.01) proportion of sperm with high Mitochondrial Membrane Potential and low LPO (P < 0.01) than RESV treatment. In conclusion, improvement in post-thaw in-vitro sperm functions and cryo-tolerance was more evident in MitoQ than RESV supplemented buffalo bull semen. Our study provides a better strategy to mitigate oxidative stress by enhancing mitochondrial antioxidant system with targeted antioxidants than cytosolic antioxidant supplementation.

Hyaluronic acid capacitation induces intracellular signals modulated by membrane-associated adenylate cyclase and tyrosine kinase involved in bovine in vitro fertilization

Heparin is the most commonly used in vitro capacitation inducer in the bovine. However, hyaluronic acid (HA) has been recently used for capacitation induction as well as for other reproductive biotechnologies, such as sperm selection and in vitro fertilization (IVF). Our aim was to induce sperm capacitation with heparin or HA in order to study mAC and TK intracellular signals and their relation with cleavage and blastocyst rates after IVF as well as with the oxidative status of the potential bovine embryos. 2,5-dideoxyadenosine and genistein were used as mAC and TK inhibitors, respectively. Sperm capacitation was analyzed using CTC technique, sperm plasma membrane and acrosome integrity were determined using trypan blue stain and differential interference contrast, and mitochondrial activity was evaluated using fluorochrome JC-1. Cleavage rate was analyzed 48h and blastocyst production 7-8 days after IVF, while cytosolic oxidative activity was determined using RedoxSensor Red CC-1 fluorochrome 7h after IVF. When mAC and TK inhibitors were added to sperm samples, only capacitation decreased significantly both in HA and heparin treated samples (P < 0.05), but plasma membrane and acrosome integrity percentages were not affected in any of these groups (P > 0.05). Sperm mitochondrial membrane potential only decreased in heparin treated samples in the presence of both inhibitors (P < 0.05). Oocytes activated with HA sperm treated samples with the addition of 2,5-dideoxyadenosine and genistein presented a lower cytosolic oxidative status than those activated with sperm treated with HA alone (P < 0.05). On the other hand, oocytes activated with heparin treated sperm samples presented a lower cytosolic oxidative status only in the presence of 2,5-dideoxyadenosine (P < 0.05). Therefore, mAC and TK present a differential participation in heparin and HA sperm induced capacitation and mitochondrial function as well as in IVF.

The Importance of Oxidative Stress in Determining the Functionality of Mammalian Spermatozoa: A Two-Edged Sword

This article addresses the importance of oxidative processes in both the generation of functional gametes and the aetiology of defective sperm function. Functionally, sperm capacitation is recognized as a redox-regulated process, wherein a low level of reactive oxygen species (ROS) generation is intimately involved in driving such events as the stimulation of tyrosine phosphorylation, the facilitation of cholesterol efflux and the promotion of cAMP generation. However, the continuous generation of ROS ultimately creates problems for spermatozoa because their unique physical architecture and unusual biochemical composition means that they are vulnerable to oxidative stress. As a consequence, they are heavily dependent on the antioxidant protection afforded by the fluids in the male and female reproductive tracts and, during the precarious process of insemination, seminal plasma. If this antioxidant protection should be compromised for any reason, then the spermatozoa experience pathological oxidative damage. In addition, situations may prevail that cause the spermatozoa to become exposed to high levels of ROS emanating either from other cells in the immediate vicinity (particularly neutrophils) or from the spermatozoa themselves. The environmental and lifestyle factors that promote ROS generation by the spermatozoa are reviewed in this article, as are the techniques that might be used in a diagnostic context to identify patients whose reproductive capacity is under oxidative threat. Understanding the strengths and weaknesses of ROS-monitoring methodologies is critical if we are to effectively identify those patients for whom treatment with antioxidants might be considered a rational management strategy.

Triphenyltin exposition induces spermatic parameter alters of Calomys laucha species

The present study aims to evaluate the influence of triphenyltin (TPT) exposure on reproductive physiology on Calomys laucha species, since this species inhabits regions susceptible to exposure to this contaminant. Animals exposed to the highest dose (10.0 mg/kg) presented signs of severe intoxication in only 7 days of exposure, demonstrating a higher sensitivity of this species to triphenyltin. The 10.0 mg TPT/kg dose was analyzed separately for short-term exposure and results suggest that exposure to this dose was severely detrimental to sperm activity. Among the main results obtained in the evaluation of sperm kinetics, a reduction in total motility was observed from the 0.5 mg TPT/kg group, accentuated according to the increase in the doses of TPT. In progressive motility, there was a decrease from the dose of 0.5 mg TPT/kg and maintained the plateau until the dose of 5.0 mg TPT/kg. It was also observed an increase in the distances and velocities average path, rectilinear and curvilinear in doses of 2.5 and 5.0 mg/kg. From the flow cytometry, evaluation a decrease in mitochondrial functionality was observed as the dose increased. Increased membrane fluidity was also observed from the 5.0 mg TPT/kg dose and the acrosome reaction presented higher values at doses of 0.5 and 5.0 mg TPT/kg. We can conclude that TPT causes impairment of the sperm activity, reducing it in individuals exposed in the adult phase.

Factors affecting staining to discriminate between bull sperm with greater and lesser mitochondrial membrane potential

The sperm mitochondrial membrane potential (MMP) is usually evaluated using the JC-1 dye. This study aimed to verify the effect of incubation temperature (25 °C or 38 °C), incubation time (10, 30, and 45 min), JC-1 stain concentration (0.2 μM, 2 μM, 8 μM, 12 μM), and the presence of glycerol (6.6% compared with 0%), on the capacity of the stain to discriminate between sperm with high mitochondrial membrane potential (hMMP) and low mitochondrial membrane potential (lMMP) in fresh and frozen bull sample by both flow cytometry and epifluorescence microscopy. The temperature (38 °C for 10 min) and the dye concentration (8 μM and 12 μM) resulted in a greater proportion of hMMP (P < .05). The incubation for 45 min at 38 °C resulted in a significant reduction of hMMP in samples stained with JC-1 dye at 8 μM and 12 μM (P < .01). A longer incubation time (45 min) and greater dye concentration (8 μM and 12 μM) resulted in an increased proportion of hMMP sperm in cryopreserved samples. Fresh sperm incubated with glycerol had a hMMP (P < .05). Data for the present study indicate that the optimal incubation temperature was 38 °C, with an incubation time differing between fresh (10-30 min) and cryopreserved sperm (at least 45 min). Furthermore, the JC-1 dye concentration used that could reliably detect the proportion of hMMP sperm was 2 μM in fresh samples, and at least 8 μM in cryopreserved sperm.

Reactive oxygen species as mediators of sperm capacitation and pathological damage

Oxidative stress plays a major role in the life and death of mammalian spermatozoa. These gametes are professional generators of reactive oxygen species (ROS), which appear to derive from three potential sources: sperm mitochondria, cytosolic L-amino acid oxidases, and plasma membrane Nicotinamide adenine dinucleotide phosphate oxidases. The oxidative stress created via these sources appears to play a significant role in driving the physiological changes associated with sperm capacitation through the stimulation of a cyclic adenosine monophosphate/Protein kinase A phosphorylation cascade, including the activation of Extracellular signal regulated kinase-like proteins, massive up-regulation of tyrosine phosphorylation in the sperm tail, as well as the induction of sterol oxidation. When generated in excess, however, ROS can induce lipid peroxidation that, in turn, disrupts membrane characteristics that are critical for the maintenance of sperm function, including the capacity to fertilize an egg. Furthermore, the lipid aldehydes generated as a consequence of lipid peroxidation bind to proteins in the mitochondrial electron transport chain, triggering yet more ROS generation in a self-perpetuating cycle. The high levels of oxidative stress created as a result of this process ultimately damage the DNA in the sperm nucleus; indeed, DNA damage in the male germ line appears to be predominantly induced oxidatively, reflecting the vulnerability of these cells to such stress. Extensive evaluation of antioxidants that protect the spermatozoa against oxidative stress while permitting the normal reduction-oxidation regulation of sperm capacitation is therefore currently being undertaken, and has already proven efficacious in animal models.

Progesterone causes metabolic changes involving aminotransferases and creatine kinase in cryopreserved bovine spermatozoa

Progesterone (P4) is capable of inducing acrosome reaction in many species. The objective of this study was to determine the activity of enzymes involved in metabolism that contribute to the redox state and supply energy for acrosome reaction in cryopreserved bull spermatozoa. To accomplish this aim, acrosome reaction was induced by P4 in capacitated and non-capacitated samples. Alanine and aspartate aminotransferases (ALT, AST) and creatine kinase (CK) activities were measured spectrophotometrically at 340 nm after acrosome reaction with P4. Oxygen consumption was measured polarographically. ALT and AST activities increased by the addition of P4 capacitated and non-capacitated samples. P4 addition provoked an increase in CK activity in non-capacitated spermatozoa compared to heparin capacitated spermatozoa with or without P4 addition. P4 increased oxygen consumption, the percentage of acrosome reacted spermatozoa as well as the absence of acrosome integrity in both capacitated and non-capacitated bovine spermatozoa, but oxygen consumption in P4 samples was significantly lower than in heparin capacitated spermatozoa (P<0.05). Acrosome reaction induction by P4 required different creatine kinase activity with the same oxygen consumption and transaminases level to maintain oxidative metabolism and redox state through reducing equivalents transfer between cytosolic and mitochondrial compartment. In conclusion, P4 induces a lower oxidative metabolism during acrosome reaction in bovine cryopreserved spermatozoa, compared to heparin induced capacitation process.

Sperm Proteome Maturation in the Mouse Epididymis

In mammals, transit through the epididymis, which involves the acquisition, loss and modification of proteins, is required to confer motility and fertilization competency to sperm. The overall dynamics of maturation is poorly understood, and a systems level understanding of the complex maturation process will provide valuable new information about changes occurring during epididymal transport. We report the proteomes of sperm collected from the caput, corpus and cauda segments of the mouse epididymis, identifying 1536, 1720 and 1234 proteins respectively. This study identified 765 proteins that are present in sperm obtained from all three segments. We identified 1766 proteins that are potentially added (732) or removed (1034) from sperm during epididymal transit. Phenotypic analyses of the caput, corpus and cauda sperm proteomes identified 60 proteins that have known sperm phenotypes when mutated, or absent from sperm. Our analysis indicates that as much as one-third of proteins with known sperm phenotypes are added to sperm during epididymal transit. GO analyses revealed that cauda sperm are enriched for specific functions including sperm-egg recognition and motility, consistent with the observation that sperm acquire motility and fertilization competency during transit through the epididymis. In addition, GO analyses revealed that the immunity protein profile of sperm changes during sperm maturation. Finally, we identified components of the 26S proteasome, the immunoproteasome, and a proteasome activator in mature sperm.

Dose-dependent short-term study of di-n-butyl phthalate on the testicular antioxidant system of Wistar rats

Di-n-butyl phthalate (DBP), a xenobiotic, is widely used in industries as a softener for polyvinyl chloride resins. The aim of the present study was to evaluate whether DBP induces oxidative stress in testes of Wistar rats. DBP at doses of 500, 1,000 and 1,500 mg/kg b.wt. (doses below LD50) was given orally for 7 days. After 24 hrs from the last dose, the animals were killed under ether anesthesia. Nonsignificant increase in testicular weight was observed. Histological studies indicated a dose-related degeneration of germinal, Leydig and Sertoli cells along with loss of spermatozoa in the lumen. The concentrations of malondialdehyde (TBARS), lipid hydroperoxides, water-soluble antioxidant capacity, glutathione-S-transferase, catalase and trace elements-zinc and copper increased while concentrations of total protein, lipid soluble antioxidant capacity, ascorbic acid, glutathione, total superoxide dismutase (SOD), Cu-ZnSOD, MnSOD, glutathione peroxidase, glutathione reductase and metallothionein decreased at all the dose levels. The data suggests that the cellular functions were adversely affected due to impairment of spermatogenesis indicative of oxidative stress as evident by altered antioxidative defense system which appears to mediate through hypothalamo-pituitary-gonadal axis. The spectrum of changes in testes reflects its susceptibility to phthalate even at low dose with the potential to interfere with critical reproductive function.

Mitochondria functionality and sperm quality

Although mitochondria are best known for being the eukaryotic cell powerhouses, these organelles participate in various cellular functions besides ATP production, such as calcium homoeostasis, generation of reactive oxygen species (ROS), the intrinsic apoptotic pathway and steroid hormone biosynthesis. The aim of this review was to discuss the putative roles of mitochondria in mammalian sperm function and how they may relate to sperm quality and fertilisation ability, particularly in humans. Although paternal mitochondria are degraded inside the zygote, sperm mitochondrial functionality seems to be critical for fertilisation. Indeed, changes in mitochondrial integrity/functionality, namely defects in mitochondrial ultrastructure or in the mitochondrial genome, transcriptome or proteome, as well as low mitochondrial membrane potential or altered oxygen consumption, have been correlated with loss of sperm function (particularly with decreased motility). Results from genetically engineered mouse models also confirmed this trend. On the other hand, increasing evidence suggests that mitochondria derived ATP is not crucial for sperm motility and that glycolysis may be the main ATP supplier for this particular aspect of sperm function. However, there are contradictory data in the literature regarding sperm bioenergetics. The relevance of sperm mitochondria may thus be associated with their role in other physiological features, particularly with the production of ROS, which in controlled levels are needed for proper sperm function. Sperm mitochondria may also serve as intracellular Ca²⁺ stores, although their role in signalling is still unclear.

Effect of several antioxidants on thawed ram spermatozoa submitted to 37°C up to four hours

Thawed ram spermatozoa were incubated at 37°C in the presence of dehydroascorbic acid (DHA), TEMPOL (TPL), N-acetyl-cysteine (NAC) and rutin (RUT), at 0.1 and 1 mm, in order to test their effects on sperm physiology. Cryopreserved spermatozoa from four rams were thawed, pooled, washed and incubated in TALP-Hepes with 1 mm or 0.1 mm of each antioxidant, performing a replicate with induced oxidative stress (Fe(2+) /ascorbate). Motility (CASA), viability and mitochondrial membrane potential (flow cytometry) were analysed at 2 and 4 h. Lipoperoxidation (MDA production), intracellular reactive oxygen species (ROS) and DNA status (TUNEL) were analysed at 4 h. Antioxidants, except DHA 0.1 mm, decreased motility and kinematic parameters, but had little effect on viability or mitochondrial activity. Except 1 mm DHA, the antioxidants reduced ROS at 4 h. Moreover, NAC 1 mm, rutin and TEMPOL reduced ROS and DNA damage in the presence of oxidative stress. N-acetyl-cysteine, rutin 1 mm and TEMPOL reduced lipoperoxidation in the presence of oxidative stress. However, DHA did not affect lipoperoxidation. At 1 mm, DHA increased DNA damage in the absence of oxidative stress. Dehydroascorbic acid effects could arise from spermatozoa having a low capacity for reducing it to ascorbic acid, and it may be tested in the presence of other antioxidants or reducing power. Future research should focus in testing whether the inhibition of motility observed for NAC, rutin and TEMPOL is reversible. These antioxidants might be useful at lower temperatures (refrigerated storage or cryopreservation) when their protective effects could be advantageous.

Acrosin activity regulation by protein kinase C and tyrosine kinase in bovine sperm acrosome exocytosis induced by lysophosphatidylcholine

Acrosin is an important proteolytic enzyme that is capable of hydrolysing the zona pellucida in bovine oocyte. Lysophosphatydic acid (LPA) derivated from lysophosphatidylcholine (LPC) is known to trigger the acrosome exocytosis. The present study was aimed at examining the acrosin activity variations in LPC-induced acrosome exocytosis and its regulation by tyrosine kinase, protein kinase C (PKC) and voltage-dependent calcium channels (VDCC) in spermatozoa previously capacitated with heparin or quercetin. The enzyme activities were spectrophotometrically measured using N-α-benzoyl-DL-arginine p-nitroanilide as an acrosin-specific substrate. The capacitation and acrosomal reaction were evaluated by chlorotetracycline assay, and the viability and acrosome integrity were evaluated by the trypan blue stain/differential interference contrast. It was observed that LPC induced acrosome exocytosis and increased the activity of acrosin in spermatozoa previously capacitated with heparin. In heparin/LPC-treated samples, it was observed that the inhibition of tyrosine kinase and PKC blocked the acrosome exocytosis and the acrosin activity (p < 0.05). Under these conditions, in heparin-capacitated spermatozoa, the LPC provokes an acrosin activity increase that is independent of calcium influx through VDCC Type L. In cryopreserved bovine spermatozoa, LPC might require modulation, mainly tyrosine kinase participation with respect to PKC activity to induce acrosome exocytosis and increase acrosin activity.

Effects of the seminal plasma zinc content and catalase activity on the semen quality of water buffalo (Bubalus bubalis) bulls

In order to determine zinc and catalase content of seminal plasma in the buffalo and to study their associations with the semen characteristics, 54 semen samples were collected from 10 buffalo bulls; semen volume and sperm concentration, gross and progressive motility and viability were evaluated, seminal plasma was then harvested by centrifugation and its zinc content was estimated by atomic absorption spectrophotometer and its catalase activity determined by using a commercial kit. The zinc content of the seminal plasma (Mean +/- SEM) was recorded as 154.40 +/- 1.74 mg L(-1), while, the mean catalase value was 32.00 +/- 0.42 U mL(-1). The mean zinc values was highly correlated with sperm progressive motility and viability and with catalase values (p = 0.000 for all) and also was associated with gross motility (p = 0.020) and negatively with abnormal morphology (p = 0.049). The catalase values were highly associated with sperm progressive motility, viability and zinc content (p = 0.000 for all) and was associated with sperm gross motility (p = 0.024). For further clarification of these correlations, the samples were categorized in three groups of excellent (Ex, >90% motile, n = 33), good (Go, 80-89% motile, n = 15) and moderate (Mo, <79% motile, n = 6) according to their percentage of sperm motility. The mean progressive motility in Ex group was 92.54 +/- 0.51%, in Go group was 81.66 +/- 0.62% and in Mo group was 71.66 +/- 1.05%. The mean zinc and catalase values were recorded as 161.07 +/- 1.63 mg L(-1) and 33.41 +/- 0.34 U mL(-1) in Ex, 146.70 +/- 1.91 mg L(-1) and 31.01 +/- 0.67 in Go and 136.42 +/- 4.97 mg L(-1) and 26.51 +/- 0.87 U mL(-1) in Mo groups. The mean zinc value in Ex group was highly associated with sperm motility, viability and catalase values, in Go group was associated with catalase values and highly associated with sperm abnormal morphology and in Mo group it was highly associations with catalase values only. The mean catalase value in Ex group, was highly associated with sperm motility and viability, in Go group was associated with zinc content and in Mo groups was highly associated with the zinc content. These results show that seminal plasma zinc and catalase content are correlated with semen characteristics and synergistically act to preserve motility and viability of the spermatozoa after ejaculation.

Heparin and quercitin generate differential metabolic pathways that involve aminotransferases and LDH-X dehydrogenase in cryopreserved bovine spermatozoa

Heparin and quercetin induce capacitation in spermatozoa through membrane receptor binding and inhibition of Ca-ATPase of the plasma membrane, respectively. Although capacitation is energy intensive, ammonia from amino acid metabolism can inhibit respiration and Krebs cycle activity. The objective was to determine activities of key enzymes in bull spermatozoa that contribute to the redox state and supply energy for capacitation. Malate dehydrogenase (MDH-NAD(+)), alanine and aspartate aminotransferases (ALT, AST), and lactate dehydrogenase-X (LDH-X) were measured spectrophotometrically (340 nm); mean (+/-S.D.) activities in control spermatozoa were 7.65+/-1.67, 0.45+/-0.05 and 0.74+/-0.14x10(-2)U/10(8) spermatozoa for MDH-NAD(+), ALT and AST, respectively, and were 2.83+/-0.66U/10(8) spermatozoa for LDH-X. Heparin decreased (P<0.05) activities of MDH-NAD(+), ALT, AST and LDH-X (78, 53, 66 and 66% of control levels, respectively); we inferred that amino acid catabolism was decreased. Quercetin decreased (P<0.05) activities of MDH-NAD(+) and ALT (60 and 49% of control levels), but activities of AST and LDH-X were not significantly different from controls; apparently maintenance of LDH-X activity supplied pyruvate for cellular metabolism. The proportion of capacitated spermatozoa in controls (8.5+/-1.73%) was substantially increased (P<0.05) by treatment with either heparin (36.2+/-4.5%) or quercetin (32.8+/-4.7%), there was no significant difference among groups for acrosomal integrity and sperm viability. In conclusion, heparin- or quercetin-induced capacitation affected different metabolic pathways that modulated the redox state and oxidative metabolism in cryopreserved bovine spermatozoa.