Reduction of centrifugation force in discontinuous percoll gradients increases in vitro fertilization rates without reducing bovine sperm recovery

Sperm Motility of Mice under Simulated Microgravity and Hypergravity

For deep space exploration, reproductive health must be maintained to preserve the species. However, the mechanisms underlying the effect of changes in gravity on male germ cells remain poorly understood. The aim of this study was to determine the effect of simulated micro- and hypergravity on mouse sperm motility and the mechanisms of this change. For 1, 3 and 6 h, mouse sperm samples isolated from the caudal epididymis were subjected to simulated microgravity using a random position machine and 2g hypergravity using a centrifuge. The experimental samples were compared with static and dynamic controls. The sperm motility and the percentage of motile sperm were determined using microscopy and video analysis, cell respiration was determined by polarography, the protein content was assessed by Western blotting and the mRNA levels were determined using qRT-PCR. The results indicated that hypergravity conditions led to more significant changes than simulated microgravity conditions: after 1 h, the speed of sperm movement decreased, and after 3 h, the number of motile cells began to decrease. Under the microgravity model, the speed of movement did not change, but the motile spermatozoa decreased after 6 h of exposure. These changes are likely associated with a change in the structure of the microtubule cytoskeleton, and changes in the energy supply are an adaptive reaction to changes in sperm motility.

Cushioned centrifugation during sperm selection increases the fertilization and cleavage rates of cattle embryos produced in vitro

This study was conducted to evaluate the effect of utilization of an iodixanol-based solution as a cushioning method during the sperm selection utilizing discontinuous Percoll gradient centrifugation in in vitro production (IVP) of cattle embryos. In Experiment I, all aliquots of thawed semen were subjected to sperm selection using the same discontinuous Percoll® gradients, except for the following four conditions: presence of cushioning solution (Cushion Fluid, Minitube) during the first centrifugation process (C1), presence of cushioning solution during the second centrifugation process (C2), inclusion of cushioning solution in both centrifugation steps (C1-2), and no addiction of cushioning solution (C; control group). Recovery rates, sperm kinetics, and reactive oxygen species (ROS) production were evaluated. In Experiment II, sperm cells were processed using sperm selection conditions C and C1, and fertilization rates and embryonic development kinetics were compared between experimental groups. With use of condition C1, there was improvement in fertilization and cleavage rates when compared to use of condition C (56.4% compared with 45.5% and 80.0% compared 64.7%, respectively). In conclusion, results indicate the use of a cushioning solution during sperm selection positively affects the developmental potential of embryos.

Effects of selection by the Percoll density gradient method on motility, mitochondrial membrane potential and fertility in a subpopulation of Atlantic salmon (Salmo salar) testicular spermatozoa

The aim of this study was to evaluate effects of selection using the Percoll density gradient method on motility, mitochondrial membrane potential (ΔΨMit) and fertility in a subpopulation of testicular spermatozoa obtained from Atlantic salmon (Salmo salar). Samples were divided into three groups: Control (C), T1 (45/90 % Percoll®) and T2 (45/60 % Percoll®). Sperm motility was evaluated using CASA (Computer-Assisted Sperm Analysis), ΔΨMit using flow cytometry, and fertility evaluating whether cleavage of fertilised eggs had occurred after 16 h of incubation at 10 °C. Results indicate that motility was greater in T1 (92 ± 2.91 %) and T2 (89 ± 2.88 %) than in the Control (83.2 ± 2.04 %). The percentage of ΔΨMit was 88.3 ± 0.58 % and 85 ± 2% for T1 and T2, respectively, compared to 35 ± 6.24 % for the control. The fertility rates were 76 ± 9.1 % and 70 ± 8.1 % for T1 and T2, respectively, compared with 66 ± 12 % for the control. The kinetic characteristics for T1 were curvilinear velocity (VCL): 92.44 ± 21.12 μm/s, average path velocity (VAP): 85.87 ± 21.83 μm/s; and for T2 VCL was 78.69 ± 17.63 μm/s and VAP was 73.62 ± 17.08 μm/s. The results indicate sperm motility and ΔΨMit were greater in T1 and T2 compared with the control (P < 0.05). Similarly, there was an increase in the fertilisation rate compared to the control. The results from this study are the first where sperm quality variables were evaluated for Salmo salar testicular sperm using the Percoll® density gradient method.

Sperm enrichment from poor semen samples by double density gradient centrifugation in combination with swim-up for IVF cycles

Sperm preparation in IVF cycles using density gradient centrifugation (DGC) in combination with swim-up (SU) has been widely adopted in reproductive centres worldwide. It is a fact that the sperm recovery rate following one DGC from poor semen samples (showing liquefaction defects/containing too many unresolvable clots or rare sperm) is relatively low. Our results showed that double DGC (DDGC) is effective at increasing the sperm recovery rate from poor semen samples. However, DDGC may increase the mechanical stress of sperm, thereby potentially impairing embryo development. Therefore, it is necessary to evaluate the safety of using sperm prepared by DDGC/SU for IVF cycles. In this study, we retrospectively analysed the data generated from a total of 529 IVF cycles (from June 2017 to June 2018), and these IVF cycles contributed 622 transfer cycles (from June 2017 to December 2018) in Changzhou Maternal and Child Health Care Hospital. Of them, 306 IVF cycles and the related 355 transfer cycles (normal semen samples prepared by DGC/SU) were set as the normal group, while 223 IVF cycles and the related 267 transfer cycles (poor semen prepared by DDGC/SU) were set as the observation group. The main outcome measures, including the normal fertilization rate, top D3 embryo formation rate, blastocyte formation rate, clinical pregnancy rate and live birth rate, birth weight and duration of pregnancy, were compared between the two groups. Compared to semen in the DGC/SU group, semen in the DDGC/SU group showed increased levels of the DNA fragmentation index (DFI) and reduced sperm concentration, percentage of progressive motility (PR) sperm, and percentage of normal morphology sperm. The indicators reflecting in vitro embryo development and clinical outcomes were similar in the DGC/SU group and DDGC/SU group, including the normal fertilization rate, top D3 embryo formation rate, blastocyte formation rate, pregnancy rate, implantation rate, spontaneous abortion rate, live birth rate, birth weight and duration of pregnancy. Furthermore, we found that the 1PN zygote formation rate was significantly lower in the DDGC/SU group than that in the DGC/SU group. We concluded that oocytes fertilized by sperm from poor semen samples separated by DDGC/SU achieved the same outcomes as oocytes fertilized by sperm from normal semen separated by DGC/SU, suggesting that DDGC/SU is an effective and safe method of sperm enrichment for poor semen samples in IVF. The main contribution of the present study is the verification of the effectiveness of DDGC/SU in improving sperm recovery from poor semen samples and the safety of using sperm prepared by DDGC/SU for IVF.

Chlorogenic acid improves the quality of boar semen processed in Percoll

This study aimed to evaluate if the addition of chlorogenic acid (ChA) to semen extenders improves the quality of cooled boar semen processed in Percoll. The experimental design was randomized blocks (ejaculates) in a 2×3 factorial (with or without Percoll, and three antioxidant systems: a negative control, without supplementation, a positive control – vitamin E, and ChA), totaling six treatments and 12 repetitions. ChA and vitamin E (VE) were added at 4.5 mg/ml and 400 μg/ml in extender, respectively. At 0, 48 and 72h of storage at 15ºC, 80 ml insemination doses each containing 2.0 billion sperm cells were submitted to centrifugation in Percoll. The use of Percoll impaired (P<0.01) all motility patterns but decreased (P<0.01) the number of abnormal cells at 0, 48 and 72h of storage. Both VE and ChA improved (P<0.05) the total motility after Percoll processing, but only in semen stored for 48h. The same effect was not observed (P>0.05) in semen stored for 72h. ChA improved (P<0.05) the total motility of the semen stored for 72h, but this effect was not observed (P>0.05) when the semen was processed in Percoll. The antioxidants had no effect (P>0.05) on the viability and integrity of the acrosome, but ChA reduced (P<0.05) the number of abnormal cells at 0h, while VE increased the number of abnormal cells in semen stored for 72h, independent of the use of Percoll. There was no effect (P>0.05) of antioxidants or Percoll on the concentration of malondialdehyde in seminal plasma. The use of Percoll had no effect (P>0.05) on the cholesterol efflux, but ChA increased (P<0.05) this parameter at 0h and reduced (P<0.05) in the semen stored for 72h not processed with Percoll. In conclusion, the addition of ChA to semen extenders improved the quality of boar semen processed or not in Percoll.

Exposing dairy bulls to high temperature-humidity index during spermatogenesis compromises subsequent embryo development in vitro

The possible impact of natural heat stress on animal fertility is currently a major concern for breeding companies. Here, we aimed to address this concern by determining the effects of natural heat stress on the fertility of Holstein bulls located in the Netherlands. Semen samples were collected from six bulls at two locations in March 2016 (low temperature-humidity index (THI) group; maximum THI of 51.8 and 55 at their respective locations) or August (high THI group; maximum THI of 77.9 and 80.5 during meiotic and spermiogenic stages of spermatogenesis, 42 to 14 days prior to semen collection). The effect of heat stress on semen quality was assessed by sperm morphology, motility, reactive oxygen species production, lipid peroxidation, viability, and DNA fragmentation. Moreover, we evaluated the development of embryos generated in vitro by low and high THI semen, and determined inner cell mass/trophectoderm ratio, apoptotic cell ratio, and embryonic gene expression in day-8 blastocysts. An increase in cell death (propidium iodide-positive cells; P = 0.039) was observed in the high THI group (31.5%) compared to the low THI group (27.6%). Moreover, a decrease (P < 0.001) was observed in the total blastocyst rates at day 7 post-insemination (15.3 vs 20.9%) and day 8 (23.2 vs 29.6%) in the high THI compared to the low THI group, respectively. There were no differences in the relative abundance of candidate transcripts examined. In conclusion, sperm samples from dairy bulls obtained during a period with higher THI had reduced viability and led to a decrease in blastocyst development and delayed hatching, compared to semen collected during a period with low THI.

Mini-percoll gradient may be used for frozen-thawed sperm selection in sheep

ABSTRACT This study evaluated the effect of increasing centrifugal force and reducing centrifugation time and volume in Percoll protocols on ram sperm parameters. Commercial semen of Santa Inês rams were used and five treatments were performed: traditional Percoll and mini-Percoll (MP) techniques (I- 5000 x g, 5min; II- 2500 x g, 5min; III- 1250 x g, 5min; IV- 700 x g, 10min). At post-thawing (PT) and post-selection protocols (0h), samples were assessed for spermatozoa recovery rate, motility, plasma membrane (PM) integrity, sperm capacitation and morphology and incubated at 37 C for 1, 2 and 3h. The sperm recovery rate averaged 9.1±1.4%, and most motility parameters were similar (P> 0.05) among protocols. VCL (µm/s) was higher (P< 0.05) after MP-II, III and IV (66.1±4.5) than traditional Percoll (46.3±4.9). Capacitation status and PM integrity were similar (P> 0.05) among treatments. For the first time, we have demonstrated the reduction of the gradient volume and centrifugation time associated with an increase on centrifugation force at Percoll can be successfully used for frozen-thawed ram sperm selection. MP may be used instead of traditional Percoll, decreasing costs and semen handling time.

Mercury at environmental relevant levels affects spermatozoa function and fertility capacity in bovine sperm

Over the last several years human sperm quality was found to be significantly reduced and the role environmental contaminants play in this phenomenon remain to be determined. Mercury (Hg) is one of the most widespread contaminants; however the correlation between metal exposure and adverse consequences on human and animals fertility are not completely established. The aim of this study was to determine the effects of direct exposure to inorganic Hg on male gametes using spermatozoa (bovine sperm) which characteristically resemble human sperm. Sperm were divided and incubated for 0.5, 1 or 2 h at low levels of Hg: i) Control: without exposure; ii) Hg8 nM: mercury chloride (HgCl₂) at 8 nM and iii) Hg8 μM: HgCl₂ at 8 μM. Sperm kinetics, morphology, sperm membrane integrity, and in vitro fertilization were assessed. In addition the levels of reactive oxygen species (ROS), lipid peroxidation and total antioxidant capacity were measured. Hg exposure for 2 h impaired sperm morphology and membrane integrity as well as kinetic parameters including curvilinear velocity and straight-line velocity, which are needed for fertilization as evidenced by the reduced fertilization rate in 8 μM Hg-treated gametes. Hg enhanced oxidative stress in male sperm as reflected by elevated levels of ROS and lipid peroxidation and decreased antioxidant capacity. Data demonstrated that low levels of Hg when incubated with spermatozoa are sufficient to increase oxidative stress, adversely affect sperm quality parameters, subsequently impairing sperm fertility capacity.

Sperm selection methods in the 21st century

Natural sperm selection in humans is a rigorous process resulting in the highest quality sperm reaching, and having an opportunity to fertilize, the oocyte. Relative to other mammalian species, the human ejaculate consists of a heterogeneous pool of sperm, varying in characteristics such as shape, size, and motility. Semen preparation in assisted reproductive technologies (ART) has long been performed using either a simple swim-up method or density gradients. Both methodologies provide highly motile sperm populations; however neither replicates the complex selection processes seen in nature. A number of methods have now been developed to mimic some of the natural selection processes that exist in the female reproductive tract. These methods attempt to select a better individual, or population of, spermatozoa when compared to classical methods of preparation. Of the approaches already tested, platforms based upon sperm membrane markers, such as hyaluronan or annexin V, have been used to either select or deselect sperm with varied success. One technology that utilizes the size, motility, and other characteristics of sperm to improve both semen analysis and sperm selection is microfluidics. Here, we sought to review the efficacy of both available and emerging techniques that aim to improve the quality of the sperm pool available for use in ART.

Non-invasive nuclear magnetic resonance analysis of male and female embryo metabolites during in vitro embryo culture

INTRODUCTION

In the past 20+ years, several studies of bovine embryo production showed how the ratio of male to female embryos changes if embryos are made in vivo or in vitro. It is known that in in vitro systems, the sex ratio is in favor of males when there are high levels of glucose, and favors females when the principal energetic substrate is one other than glucose, like citrate.

OBJECTIVES

The aim of this study was to evaluate the embryo metabolism during three important periods of in vitro development: the early development (from day 1 until day 3), the middle of culture (day 3 until day 5), and later development (day 5 until day 7).

METHODS

To obtain this information we evaluated the spent medium from each time period by ¹H NMR.

RESULTS

Our results confirm that embryo metabolism is different between sexes. The new information obtained by identifies markers that we can use to predict the embryo sex.

CONCLUSION

These results open a new, non-invasive method to evaluate sex of the embryos before the transfer. In the first period of embryo culture, valine concentration is good indicator (66.7% accurate), while in the last phase of culture, pyruvate depletion is the best marker (64% accurate) to evaluate the sex of the embryo.

Integration of microfluidics in animal in vitro embryo production

The in vitro production of livestock embryos is central to several areas of animal biotechnology. Further, the use of in vitro embryo manipulation is expanding as new applications emerge. ARTs find direct applications in increasing genetic quality of livestock, producing transgenic animals, cloning, artificial insemination, reducing disease transmission, preserving endangered germplasm, producing chimeric animals for disease research, and treating infertility. Whereas new techniques such as nuclear transfer and intracytoplasmic sperm injection are now commonly used, basic embryo culture procedures remain the limiting step to the development of these techniques. Research over the past 2 decades focusing on improving the culture medium has greatly improved in vitro development of embryos. However, cleavage rates and viability of these embryos is reduced compared with in vivo indicating that present in vitro systems are still not optimal. Furthermore, the methods of handling mammalian oocytes and embryos have changed little in recent decades. While pipetting techniques have served embryology well in the past, advanced handling and manipulation technologies will be required to efficiently implement and commercialize the basic biological advances made in recent years. Microfluidic systems can be used to handle gametes, mature oocytes, culture embryos, and perform other basic procedures in a microenvironment that more closely mimic in vivo conditions. The use of microfluidic technologies to fabricate microscale devices has being investigated to overcome this obstacle. In this review, we summarize the development and testing of microfabricated fluidic systems with feature sizes similar to the diameter of an embryo for in vitro production of pre-implantation mammalian embryos.

Gradient sperm selection for reproductive techniques in cattle: Is Isolate a suitable replacement for Percoll?

In assisted reproductive techniques, it is essential to perform a sperm selection to obtain spermatozoa with high motility and membrane integrity for in vitro fertilisation (IVF) and high-DNA integrity for intracytoplasmic sperm injection (ICSI). In this study, we evaluated whether Isolate^® was a suitable substitute for Percoll^® for assisted reproductive techniques. Commercial cryopreserved bovine semen was used after selection in both gradients, and plasma and acrosome membrane integrity, reactive oxygen species (ROS) levels, DNA integrity and mitochondrial membrane potential (ΔΨm) were assessed by flow cytometry. Motility parameters were also evaluated by CASA system. A similar percentage of spermatozoa with intact plasma membrane, acrosome integrity and high ΔΨm was observed in both sperm selection methods, but only Percoll^® showed higher percentage of spermatozoa with intact plasma and acrosome membrane compared to the post-thawing group. No differences were observed in the motility, ROS, DNA fragmentation and on the in vitro embryo production in all experimental groups. In conclusion, the selection of bovine spermatozoa with Isolate^® generates spermatozoa with similar quality parameters and embryonic development compared to Percoll^® providing a suitable alternative sperm selection method for assisted reproductive techniques in this species.

Improvement of bovine semen quality by removal of membrane-damaged sperm cells with DNA aptamers and magnetic nanoparticles

In cattle, cryopreservation of semen and sex-sorting kill up to 50% of spermatozoa and decrease the success of assisted insemination (AI). Therefore, significant efforts are being carried out to improve the quality of semen prior to AI. In this work we used the Cell-SELEX technique to select single strand DNA aptamers able to recognize with high affinity and specificity damaged sperm cells generated by heat-treatment. We first isolated aptamers with a conserved two motifs of 6 nucleotides of length that bind to the membrane of heat-treated spermatozoa. Then, we used synthetic biotin-labeled aptamers containing the conserved motif to recognize membrane-damaged cells and separate them from viable cells by the use of avidin-coated superparamagnetic iron oxide nanoparticles (SPION). This procedure improved the quality of semen by significantly increasing the percentage of healthy sperm cells without affecting the rate of blastocyst cleavage. This technique was successfully applied to both unsorted and sex-sorted sperm suspension.