Stage-specific metabolomic changes in equine oviductal fluid: New insights into the equine fertilization environment

Glucose prevents the acquisition of the capacitated state in pig spermatozoa

BACKGROUND

Mammalian spermatozoa need to undergo a process named capacitation to be able to fertilize an oocyte. During their journey in the female tract, spermatozoa obtain energy while exposed to a changing environment containing a variety of metabolic substrates. The energy requirements for sperm capacitation are species-specific. In addition, the available energy source can hinder the process of sperm capacitation and eventually the acrosome reaction.

OBJECTIVES

To evaluate whether the metabolic substrates available in the in vitro sperm capacitation medium allow or interfere with the pig sperm capacitation process.

MATERIAL AND METHODS

The effect of different metabolic substrates on sperm capacitation process was evaluated by analyzing phosphorylation in the p32 protein; the acrosome reaction and the ATP intracellular content.

RESULTS

The presence of glucose in the in vitro capacitating medium diminishes, in a concentration-dependent manner, parameters associated with the capacitated status: induced acrosome exocytosis, plasma membrane destabilization, and protein tyrosine phosphorylation. Conversely, sperm incubation with pyruvate or lactate, either individually or in combination, allows the attainment of the capacitated status. Unexpectedly, pig spermatozoa incubated without any extracellular energy substrates or with a non-metabolizable substrate (l-glucose) for 4 h displayed similar sperm viability to the control and exhibited a capacitated phenotype. The capacitation-like phenotype observed in starved pig spermatozoa (absence of glucose, lactate, and pyruvate) was dependent on extracellular bicarbonate and calcium levels, and these spermatozoa exhibited lower intracellular ATP content compared to those not capacitated. Nevertheless, the intracellular content of calcium was not modified in comparison to the control.

DISCUSSION AND CONCLUSIONS

Our findings suggest that the metabolic substrates used to fuel pig sperm metabolism are important in achieving the capacitated status. The results of this work could be used to refine the capacitating medium employed in pig in vitro fertilization.

Preovulatory follicular fluid secretome added to in vitro maturation medium influences the metabolism of equine cumulus-oocyte complexes

BACKGROUND

In vitro embryo production is a highly demanded reproductive technology in horses, which requires the recovery (in vivo or post-mortem) and in vitro maturation (IVM) of oocytes. Oocytes subjected to IVM exhibit poor developmental competence compared to their in vivo counterparts, being this related to a suboptimal composition of commercial maturation media. The objective of this work was to study the effect of different concentrations of secretome obtained from equine preovulatory follicular fluid (FF) on cumulus-oocyte complexes (COCs) during IVM. COCs retrieved in vivo by ovum pick up (OPU) or post-mortem from a slaughterhouse (SLA) were subjected to IVM in the presence or absence of secretome (Control: 0 µg/ml, S20: 20 µg/ml or S40: 40 µg/ml). After IVM, the metabolome of the medium used for oocyte maturation prior (Pre-IVM) and after IVM (Post-IVM), COCs mRNA expression, and oocyte meiotic competence were analysed.

RESULTS

IVM leads to lactic acid production and an acetic acid consumption in COCs obtained from OPU and SLA. However, glucose consumption after IVM was higher in COCs from OPU when S40 was added (Control Pre-IVM vs. S40 Post-IVM: 117.24 ± 7.72 vs. 82.69 ± 4.24; Mean µM ± SEM; p < 0.05), while this was not observed in COCs from SLA. Likewise, secretome enhanced uptake of threonine (Control Pre-IVM vs. S20 Post-IVM vs. S40 Post-IVM: 4.93 ± 0.33 vs. 3.04 ± 0.25 vs. 2.84 ± 0.27; Mean µM ± SEM; p < 0.05) in COCs recovered by OPU. Regarding the relative mRNA expression of candidate genes related to metabolism, Lactate dehydrogenase A (LDHA) expression was significantly downregulated when secretome was added during IVM at 20-40 µg/ml in OPU-derived COCs (Control vs. S20 vs. S40: 1.77 ± 0.14 vs. 1 ± 0.25 vs. 1.23 ± 0.14; fold change ± SEM; p < 0.05), but not in SLA COCs.

CONCLUSIONS

The addition of secretome during in vitro maturation (IVM) affects the gene expression of LDHA, glucose metabolism, and amino acid turnover in equine cumulus-oocyte complexes (COCs), with diverging outcomes observed between COCs retrieved using ovum pick up (OPU) and slaughterhouse-derived COCs (SLA).

Nuclear Magnetic Resonance (NMR) Metabolomics: Current Applications in Equine Health Assessment

Metabolomics can allow for the comprehensive identification of metabolites within biological systems, at given time points, in physiological and pathological conditions. In the last few years, metabolomic analysis has gained popularity both in human and in veterinary medicine, showing great potential for novel applications in clinical activity. The aim of applying metabolomics in clinical practice is understanding the mechanisms underlying pathological conditions and the influence of certain stimuli (i.e., drugs, nutrition, exercise) on body systems, in the attempt of identifying biomarkers that can help in the diagnosis of diseases. Proton Nuclear Magnetic Resonance spectroscopy (1H-NMR) is well tailored to be used as an analytical platform for metabolites' detection at the base of metabolomics studies, due to minimal sample preparation and high reproducibility. In this mini-review article, the scientific production of NMR metabolomic applications to equine medicine is examined. The research works are very different in methodology and difficult to compare. Studies are mainly focused on exercise, reproduction, and nutrition, other than respiratory and musculoskeletal diseases. The available information on this topic is still scant, but a greater collection of data could allow researchers to define new reliable markers to be used in clinical practice for diagnostic and therapeutical purposes.

Characterization of preovulatory follicular fluid secretome and its effects on equine oocytes during in vitro maturation

In vitro maturation (IVM) of oocytes is clinically used in horses to produce blastocysts but current conditions used for horses are suboptimal. We analyzed the composition of equine preovulatory follicular fluid (FF) secretome and tested its effects on meiotic competence and gene expression in oocytes subjected to IVM. Preovulatory FF was obtained, concentrated using ultrafiltration with cut-off of 10 kDa, and stored at -80 °C. The metabolic and proteomic composition was analyzed, and its ultrastructural composition was assessed by cryo-transmission microscopy. Oocytes obtained post-mortem or by ovum pick up (OPU) were subjected to IVM in the absence (control) or presence of 20 or 40 μg/ml (S20 or S40) of secretome. Oocytes were then analyzed for chromatin configuration or snap frozen for gene expression analysis. Proteomic analysis detected 255 proteins in the Equus caballus database, mostly related to the complement cascade and cholesterol metabolism. Metabolomic analysis yielded 14 metabolites and cryo-transmission electron microscopy analysis revealed the presence of extracellular vesicles (EVs). No significant differences were detected in maturation rates among treatments. However, the expression of GDF9 and BMP15 significantly increased in OPU-derived oocytes compared to post-mortem oocytes (fold increase ± SEM: 9.4 ± 0.1 vs. 1 ± 0.5 for BMP15 and 9.9 ± 0.3 vs. 1 ± 0.5 for GDF9, respectively; p < 0.05). Secretome addition increased the expression of TNFAIP6 in S40 regardless of the oocyte source. Further research is necessary to fully understand whether secretome addition influences the developmental competence of equine oocytes.

Lactate as the sole energy substrate induces spontaneous acrosome reaction in viable stallion spermatozoa

BACKGROUND

Equine spermatozoa appear to differ from spermatozoa of other species in using oxidative phosphorylation preferentially over glycolysis. However, there is little information regarding effects of different energy sources on measured parameters in equine spermatozoa.

OBJECTIVE

To determine the effect of three individual energy substrates, glucose, pyruvate, and lactate, on motion characteristics, membrane integrity, and acrosomal status of stallion spermatozoa.

MATERIALS AND METHODS

Freshly ejaculated stallion spermatozoa were incubated with combinations of glucose (5 mm), pyruvate (10 mm), and lactate (10 mm) for 0.5 to 4 h. Response to calcium ionophore A23187 (5 μm) was used to evaluate capacitation status. Motility was evaluated using computer-assisted sperm analysis, and plasma membrane and acrosomal integrity were evaluated by flow cytometry.

RESULTS

Incubation with lactate alone for 2 h increased acrosomal sensitivity to A23187. Notably, incubation with lactate alone for 4 h induced a significant spontaneous increase in acrosome-reacted, membrane-intact (viable) spermatozoa, to approximately 50% of the live population, whereas no increase was seen with incubation in glucose or pyruvate alone. This acrosomal effect was observed in spermatozoa incubated at physiological pH as well as under alkaline conditions (medium pH approximately 8.5). Sperm motility declined concomitantly with the increase in acrosome-reacted spermatozoa. Sperm motility was significantly higher in pyruvate-only medium than in glucose or lactate. The addition of pyruvate to lactate-containing medium increased sperm motility but reduced the proportion of live acrosome-reacted spermatozoa in a dose-dependent fashion.

DISCUSSION

This is the first study to demonstrate that incubation with a specific energy substrate, lactate, is associated with spontaneous acrosome reaction in spermatozoa. The proportion of live, acrosome-reacted spermatozoa obtained is among the highest reported for equine spermatozoa.

CONCLUSION

These findings highlight the delicate control of key sperm functions, and may serve as a basis to increase our understanding of stallion sperm physiology.

Lactate-induced spontaneous acrosomal exocytosis as a method to study acrosome function in stallion sperm

Evaluation of acrosome function in stallion sperm is mostly based on the use of inducers of acrosomal exocytosis (AE), such as the calcium ionophore A23187 or progesterone. Recently, it has been reported that incubation of stallion sperm under presumed capacitating conditions (i.e., medium formulated with calcium, bicarbonate, and bovine serum albumin) using a lactate-only containing medium (Lac-MW) results in a high rate of spontaneous AE in viable sperm (AE/Viable). In the current study, we developed an alternative assay of acrosome function for stallion sperm following the incubation of sperm in a medium formulated only with lactate as an energy substrate (Lac-MW). In Experiment 1, freshly ejaculated stallion sperm was incubated with 10 μM A23187, Lac-MW, or Control, for up to 6 h under capacitating conditions. The percentages of motile sperm, viable sperm, total AE (Total AE), and AE in viable sperm (AE/Viable) were compared among treatment groups. Incubation in Lac-MW, but not with Control or A23187, resulted in a time-dependent increase in the percentage of AE/Viable, as determined by flow cytometry, particularly at 4 and 6 h of incubation (P < 0.05). In Experiment 2, freshly ejaculated sperm was incubated in Lac-MW for up to 6 h, and the occurrence of protein tyrosine phosphorylation and AE/Viable were determined. At 4h and 6h of incubation in Lac-MW, ∼40% of the sperm displayed a protein tyrosine phosphorylation immunofluorescence pattern that coincides with that recently associated with stallion sperm capacitation (i.e., immunofluorescence signal at the acrosome and midpiece). In Experiment 3, the rate of AE/Viable sperm was compared among freshly ejaculated, cool-stored, and frozen/thawed stallion sperm. Except at 2h incubation in Lac-MW, differences in mean AE/Viable among fresh, cool-stored, and frozen/thawed sperm were not observed (P > 0.05). In Experiment 4, the relationship between Total AE (A23187), or AE/Viable (Lac-MW), and in vivo fertility of 5 stallions was determined. A linear relationship was observed between mean AE/Viable and the per-cycle (r = 0.93; P < 0.05) and seasonal (r = 0.66; P < 0.05) pregnancy rates of five stallions used for artificial insemination with cool-stored semen. In Experiment 5, frozen/thawed sperm from subfertile Thoroughbred (TB) stallions, known to carry the susceptibility genotype for Impaired Acrosomal Exocytosis (IAE; FKBP6 A/A-A/A) was evaluated following incubation in Lac-MW. Sperm from subfertile TB stallions with IAE had lower mean AE/Viable, at both 4h and 6h incubation in Lac-MW, when compared to that of fertile control stallions (P < 0.05). Overall, the Lac-MW model validated in the current study may be a useful complementary assay to evaluate the ability of stallion sperm to physiologically undergo AE and to study stallion fertility potential. This acrosome function assay can be used to evaluate fresh, cool-stored, or frozen/thawed stallion sperm, and describes a strong linear relationship with in vivo-fertility of stallions used in artificial insemination programs.

Proteomic Differences Between the Ovulatory and Anovulatory Sides of the Mare's Follicular and Oviduct Fluid

The follicular fluid and oviduct fluid play major roles in oocyte maturation, sperm activation, and fertilization. To better understand the physiological environments for equine oocyte maturation and fertilization, here we conducted the proteome analysis and comparison on follicular fluids and oviduct fluids from the ovulatory side and the anovulatory side. The results showed that there is no significant difference between two side oviduct fluids, but a total of 71 differential abundance proteins (DAPs) were identified between two side follicular fluids, of which 9 are up-regulated and 62 are down-regulated in ovulatory side follicle fluid versus anovulatory side follicle fluid. As we expected, the function classification and enrichment results indicate that up- and down-regulated proteins are largely related to oocyte meiosis, maturation and ovulation. Noticeably, among 9 up-regulated DAPs in ovulatory side follicle fluid, as the DAP with the greatest fold change, PLA2G1B may be a newly discovered component that influences the efficacy of horse IVM/IVF. The current findings add to our knowledge of the in vivo conditions and regulation of equine reproduction, as well as the regulatory mechanism underpinning alternative ovulation.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

Metabolic profiling of preovulatory follicular fluid in jennies

Follicular fluid is formed from the transudation of theca and granulosa cells in the growing follicular antrum. Its main function is to provide an optimal intrafollicular microenvironment to modulate oocyte maturation. The aim of this study was to determine the metabolomic profile of preovulatory follicular fluid (PFF) in jennies. For this purpose, PFF was collected from 10 follicles of five jennies in heat. Then, PFF samples were analysed by nuclear magnetic resonance (NMR) and heteronuclear single quantum correlation (2D 1H/13C HSQC). Our study revealed the presence of at least 27 metabolites in the PFF of jennies (including common amino acids, carboxylic acids, amino acid derivatives, alcohols, saccharides, fatty acids, and lactams): 3-hydroxybutyrate, acetate, alanine, betaine, citrate, creatine, creatine phosphate, creatinine, ethanol, formate, glucose, glutamine, glycerol, glycine, hippurate, isoleucine, lactate, leucine, lysine, methanol, phenylalanine, proline, pyruvate, threonine, tyrosine, valine, and τ-methylhistidine. The metabolites found here have an important role in the oocyte development and maturation, since the PFF surrounds the follicle and provides it with the needed nutrients. Our results indicate a unique metabolic profile of the jennies PFF, as it differs from those previously observed in the PFF of the mare, a phylogenetically close species that is taken as a reference for establishing reproductive biotechnology techniques in donkeys. The metabolites found here also differ from those described in the TCM-199 medium enriched with fetal bovine serum (FBS), which is the most used medium for in vitro oocyte maturation in equids. These differences would suggest that the established conditions for in vitro maturation used so far may not be suitable for donkeys. By providing the metabolic composition of jenny PFF, this study could help understand the physiology of oocyte maturation as a first step to establish in vitro reproductive techniques in this species.

A stallion spermatozoon's journey through the mare's genital tract: In vivo and in vitro aspects of sperm capacitation

Conventional in vitro fertilization is not efficacious when working with equine gametes. Although stallion spermatozoa bind to the zona pellucida in vitro, these gametes fail to initiate the acrosome reaction in the vicinity of the oocyte and cannot, therefore, penetrate into the perivitelline space. Failure of sperm penetration most likely relates to the absence of optimized in vitro fertilization media containing molecules essential to support stallion sperm capacitation. In vivo, the female reproductive tract, especially the oviductal lumen, provides an environmental milieu that appropriately regulates interactions between the gametes and promotes fertilization. Identifying these 'fertilization supporting factors' would be a great contribution for development of equine in vitro fertilization media. In this review, a description of the current understanding of the interactions stallion spermatozoa undergo during passage through the female genital tract, and related specific molecular changes that occur at the sperm plasma membrane is provided. Understanding these molecular changes may hold essential clues to achieving successful in vitro fertilization with equine gametes.

Changes of sperm metabolites of Dezhou donkey after cryopreservation

Sperm cryopreservation technology has laid the foundation for promoting the popularity of artificial insemination in donkey reproduction, but the freeze-thaw process can cause sperm damage, and the viability of frozen sperm is greatly reduced, resulting in low insemination ability. Sperm metabolites play an important role in the freezing process of spermatozoa and have a major influence on the freezability of spermatozoa. The aim of this study was to explore the differential metabolites in donkey spermatozoa before and after cryopreservation by liquid chromatography tandem mass spectrometry (LC-MS/MS). We analysed ejaculate samples from male donkeys obtained before and after freezing and identified 1323 metabolites. Compared with fresh sperm (F), the metabolites of cryopreserved sperm (CRY) were significantly changed, and 570 metabolites were significantly different between the two groups (P < 0.05). Among them, 277 metabolites were higher in frozen sperm, while the opposite was true for 293 metabolites. These metabolites mainly include phospholipids, lysophospholipids, and amino acids., most of which are associated with oxidative stress and sperm capacitation. We describe significantly different metabolites before and after freezing that are significantly associated with decreased sperm motility postfreezing and can be used as biomarkers of decreased sperm motility postfreezing.

Metabolomic profiling of Dezhou donkey seminal plasma related to freezability

Donkeys are indispensable livestock in China because they have transport function and medicinal value. With the popularization of artificial insemination on donkeys, semen cryopreservation technology has gradually become a research hotspot. Seminal plasma is a necessary medium for transporting sperm and provides energy and nutrition for sperm. Seminal plasma metabolites play an important role in the process of sperm freezing, and also have an important impact on sperm motility and fertilization rate after freezing and thawing. In this study, liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was used to compare the metabolic characteristics of seminal plasma of high freezability (HF) and low freezability (LF) male donkeys. We identified 672 metabolites from donkey seminal plasma, of which 33 metabolites were significantly different between the two groups. Metabolites were identified and categorized according to their major chemical classes, including homogeneous non-metal compounds, nucleosides, nucleotides, and analogues, organosulphur compounds, phenylpropanoids and polyketide, organoheterocyclic compounds, organic oxygen compounds, benzenoids, organic acids and derivatives, lipids and lipid-like molecules, organooxygen compounds, alkaloids and derivatives, organic nitrogen compounds. The results showed that the contents of phosphatidylcholine, piceatannol and enkephalin in donkey semen of HF group were significantly higher than those of LF group (p < .05), while the contents of taurocholic and lysophosphatidic acid were significantly lower than those of LF group (p < .05). The different metabolites were mainly related to sperm biological pathway response and oxidative stress. These metabolites may be considered as candidate biomarkers for different fertility in jacks.

The Proteome of Equine Oviductal Fluid Varies Before and After Ovulation: A Comparative Study

Equine fertilization cannot be performed in the laboratory as equine spermatozoa do not cross the oocyte's zona pellucida in vitro. Hence, a more profound study of equine oviductal fluid (OF) composition at the pre-ovulatory and post-ovulatory stages could help in understanding what components are required to achieve fertilization in horses. Our work aimed to elucidate the proteomic composition of equine OF at both stages. To do this, OF was obtained postmortem from oviducts of slaughtered mares ipsilateral to a pre-ovulatory follicle (n = 4) or a recent ovulation (n = 4); the samples were kept at −80°C until analysis. After protein extraction and isobaric tags for relative and absolute quantification (iTRAQ) labeling, the samples were analyzed by nano-liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The analysis of the spectra resulted in the identification of a total of 1,173 proteins present in pre-ovulatory and post-ovulatory samples; among these, 691 were unique for Equus caballus. Proteins from post-ovulatory oviductal fluid were compared with the proteins from pre-ovulatory oviductal fluid and were categorized as upregulated (positive log fold change) or downregulated (negative log fold change). Fifteen proteins were found to be downregulated in the post-ovulatory fluid and 156 were upregulated in the post-ovulatory OF compared to the pre-ovulatory fluid; among the upregulated proteins, 87 were included in the metabolism of proteins pathway. The identified proteins were related to sperm–oviduct interaction, fertilization, and metabolism, among others. Our data reveal consistent differences in the proteome of equine OF prior to and after ovulation, helping to increase our understanding in the factors that promote fertilization and early embryo development in horses.

Culture protocols for horse embryos after ICSI: Effect of myo-inositol and time of media change

In vitro production of horse embryos via intracytoplasmic sperm injection (ICSI) is a useful clinical and research technique. Current rates of blastocyst production are typically sub-optimal, and few methods to increase the rate of equine blastocyst development have been reported. Factors that might improve blastocyst production in a horse embryo culture system were explored. Myo-inositol is found in the horse oviduct and improves blastocyst development in other species, thus Experiment 1 was conducted to assess the effect of 10 mM myo-inositol added to Day 0-5 embryo culture medium, using horse oocytes recovered by transvaginal aspiration. Experiment 2 was conducted to investigate effects of exclusion of a standard post-ICSI holding step (culture for 30-60 min in M199-based medium). Experiment 3 was conducted using oocytes recovered from abattoir-derived ovaries, to evaluate effects of earlier transition (Day 4 vs. Day 5) to the second-step medium and of media refreshment at different time points (Day 3 and/or Day 7) during embryo culture. In Experiments 1 and 2, there were no differences (P > 0.05) between groups in blastocyst development (Exp. 1, 36.7 % and 39.2 %; Exp. 2, 41.5 % and 44.6 %). In Experiment 3, blastocyst development was not different (P > 0.05) for embryos refreshed at both Day 3 and 7 (10.8 %) or only at Day 7 (26.6 %), or those transferred to second-step medium on Day 4 or Day 5 (20.6 % and 18.5 %). Knowledge of culture procedures compatible with blastocyst formation in vitro is valuable to laboratories starting to develop procedures for ICSI in horses.

Creatine Metabolism in Female Reproduction, Pregnancy and Newborn Health

Creatine metabolism is an important component of cellular energy homeostasis. Via the creatine kinase circuit, creatine derived from our diet or synthesized endogenously provides spatial and temporal maintenance of intracellular adenosine triphosphate (ATP) production; this is particularly important for cells with high or fluctuating energy demands. The use of this circuit by tissues within the female reproductive system, as well as the placenta and the developing fetus during pregnancy is apparent throughout the literature, with some studies linking perturbations in creatine metabolism to reduced fertility and poor pregnancy outcomes. Maternal dietary creatine supplementation during pregnancy as a safeguard against hypoxia-induced perinatal injury, particularly that of the brain, has also been widely studied in pre-clinical in vitro and small animal models. However, there is still no consensus on whether creatine is essential for successful reproduction. This review consolidates the available literature on creatine metabolism in female reproduction, pregnancy and the early neonatal period. Creatine metabolism is discussed in relation to cellular bioenergetics and de novo synthesis, as well as the potential to use dietary creatine in a reproductive setting. We highlight the apparent knowledge gaps and the research “road forward” to understand, and then utilize, creatine to improve reproductive health and perinatal outcomes.

A high glucose concentration during early stages of in vitro equine embryo development alters expression of genes involved in glucose metabolism

BACKGROUND

Equine embryos exhibit an unusual pattern of glucose tolerance in vitro and are currently cultured in hyperglycaemic conditions.

OBJECTIVE

Our main objective was to analyse the effect of different glucose concentrations on in vitro-produced equine embryo development and quality.

STUDY DESIGN

Experiments comparing in vitro and in vivo produced embryos.

METHODS

Oocytes (n = 641) were collected from post-mortem ovaries, matured in vitro and fertilised by intracytoplasmic sperm injection (ICSI). Embryo culture was divided from Day 0 to Day 4 and from Day 4 to Day 9 in three groups: 5-10 (5 and 10 mmol/L glucose respectively; n = 87); 5-17 (5 and 17.5 mmol/L; n = 66); and 10-17 (10 and 17.5 mmol/L; n = 117). A control group of 20 in vivo produced blastocysts was included. Cleavage and blastocyst rates were evaluated and embryos were snap-frozen for analysis of the relative mRNA expression of genes related to mitochondrial function, DNA methylation, apoptosis, glucose transport and metabolism.

RESULTS

No differences were observed in the cleavage or blastocyst rates among in vitro groups. Under high glucose conditions in vitro (10-17 group), BAX/BCL2 was higher, and PFKP, LDHA and COX2 were overexpressed compared to all other groups. The two groups with 5 mmol/L glucose concentration during the first culture stage (5-10 and 5-17) displayed similar patterns which differed to the 10-17 group.

MAIN LIMITATIONS

Conclusions related to embryo quality are based on gene expression patterns. Transfer of in vitro-produced embryos would reveal whether the observed differences improve embryo developmental competence.

CONCLUSIONS

Five mM glucose during the first days of culture seems to be preferable to avoid over-activation of embryonic glycolytic pathways. Further studies are necessary to determine whether this improves embryo developmental competence.

The Presence of D-Penicillamine during the In Vitro Capacitation of Stallion Spermatozoa Prolongs Hyperactive-Like Motility and Allows for Sperm Selection by Thermotaxis

Assisted reproductive technologies (ARTs) in the horse still yield suboptimal results in terms of pregnancy rates. One of the reasons for this is the lack of optimal conditions for the sperm capacitation in vitro. This study assesses the use of synthetic human tubal fluid (HTF) supplemented with D-penicillamine (HTF + PEN) for the in vitro capacitation of frozen/thawed stallion spermatozoa by examining capacitation-related events over 180 min of incubation. Besides these events, we explored the in vitro capacity of the spermatozoa to migrate by thermotaxis and give rise to a population of high-quality spermatozoa. We found that HTF induced higher levels of hyperactive-like motility and protein tyrosine phosphorylation (PTP) compared to the use of a medium commonly used in this species (Whitten's). Also, HTF + PEN was able to maintain this hyperactive-like motility, otherwise lost in the absence of PEN, for 180 min, and also allowed for sperm selection by thermotaxis in vitro. Remarkably, the selected fraction was enriched in spermatozoa showing PTP along the whole flagellum and lower levels of DNA fragmentation when compared to the unselected fraction (38% ± 11% vs 4.4% ± 1.1% and 4.2% ± 0.4% vs 11% ± 2% respectively, t-test p < 0.003, n = 6). This procedure of in vitro capacitation of frozen/thawed stallion spermatozoa in HTF + PEN followed by in vitro sperm selection by thermotaxis represents a promising sperm preparation strategy for in vitro fertilization and intracytoplasmic sperm injection in this species.

Study of the Metabolomics of Equine Preovulatory Follicular Fluid: A Way to Improve Current In Vitro Maturation Media

Production of equine embryos in vitro is currently a commercial technique and a reliable way of obtaining offspring. In order to produce those embryos, immature oocytes are retrieved from postmortem ovaries or live mares by ovum pick-up (OPU), matured in vitro (IVM), fertilized by intracytoplasmic sperm injection (ICSI), and cultured until day 8-10 of development. However, at best, roughly 10% of the oocytes matured in vitro and followed by ICSI end up in successful pregnancy and foaling, and this could be due to suboptimal IVM conditions. Hence, in the present work, we aimed to elucidate the major metabolites present in equine preovulatory follicular fluid (FF) obtained from postmortem mares using proton nuclear magnetic resonance spectroscopy (¹H-NMR). The results were contrasted against the composition of the most commonly used media for equine oocyte IVM: tissue culture medium 199 (TCM-199) and Dulbecco's modified eagle medium/nutrient mixture F-12 Ham (DMEM/F-12). Twenty-two metabolites were identified in equine FF; among these, nine of them are not included in the composition of DMEM/F-12 or TCM-199 media, including (mean ± SEM): acetylcarnitine (0.37 ± 0.2 mM), carnitine (0.09 ± 0.01 mM), citrate (0.4 ± 0.04 mM), creatine (0.36 ± 0.14 mM), creatine phosphate (0.36 ± 0.05 mM), fumarate (0.05 ± 0.007 mM), glucose-1-phosphate (6.9 ± 0.4 mM), histamine (0.25 ± 0.01 mM), or lactate (27.3 ± 2.2 mM). Besides, the mean concentration of core metabolites such as glucose varied (4.3 mM in FF vs. 5.55 mM in TCM-199 vs. 17.5 mM in DMEM/F-12). Hence, our data suggest that the currently used media for equine oocyte IVM can be further improved.