Sperm membrane functionality in the dog assessed by flow cytometry

Comparing different sperm concentrations for optimizing cooled semen use in the dog

The use of shipping canine semen for artificial insemination has bloomed over the last 20 years. This allows for the spread of genetic material while overcoming geographical or time-related challenges. The optimal sperm concentration for cooled semen transport in the dog is unknown. Often canine semen is extended 1:3-5 vol:vol without standardized sperm concentrations for cooled shipment. We compared different sperm concentrations for cooled storage and hypothesized that lower concentrations would result in better semen quality. Semen was collected from healthy client-owned dogs (n = 8). Individual ejaculates were divided into a control aliquot (CON) extended 1:3 vol:vol with a commercial extender. The remaining sample was centrifuged and extended to 200 ×106 sperm/ml (C200), then serially diluted to 100, 50, and 25 ×106 sperm/ml concentrations (C100-C25). Aliquots were cooled for 24 h and then centrifuged and re-extended. Sperm concentration, plasma membrane integrity (PMI, %), motility (subjective total, STM; computer-assisted sperm analysis (CASA) total and progressive, TM, PM; %), and normal morphology (NM, %) were assessed in raw semen (T0), post-extension (T1), after 24 h of cooling (T2), and after processing at 24 h (T3). Cooling resulted in significant declines in STM and NM for all groups and in decreased PMI for CON and C25-50. After cooling (at T2), PMI was significantly lower for C25 compared with all the groups and higher for CON compared with C25-100 (p ≤ 0.038). Processing and re-extension after cooling further decreased the spermiogram parameters. At T3, PMI for CON was similar to C200 but significantly higher than C25-100, while C25 had the lowest PMI. For motility parameters and NM, C25 performed worse than all or most of the other groups. Comparing CON at T3 with C25-200 at T2, PMI, STM, and NM for CON were significantly lower than C25-200, C200, and C100-200, respectively. In conclusion, our results show that cooling canine semen for 24 h at 200 ×106 sperm/ml final concentration after processing or extending 1:3 vol:vol without centrifugation is preferred based on the highest PMI. If volume restrictions apply, processing raw semen and extending to the desired volume with higher sperm concentrations at the collection facility is superior to centrifugation and volume adjustment after 24 h of cooled storage.

Defining an Optimal Range of Centrifugation Parameters for Canine Semen Processing

Our objective was to determine a clinically relevant range of centrifugation parameters for processing canine semen. We hypothesized that higher gravitational (g) force and longer time of centrifugation would result in improved spermatozoa recovery rate (RR) but poorer semen quality. Cooled storage under standard shipping conditions was used as a stressor to evaluate long-term treatment effects. Individual ejaculates collected from 14 healthy dogs were split into six treatment groups (400 g, 720 g, and 900 g for 5 or 10 min). Sperm RR (%) was calculated post-centrifugation, and plasma membrane integrity (%, Nucleocounter^® SP-100™), total and progressive motility (%, subjective and computer-assisted sperm analysis), and morphology (%, eosin-nigrosin staining) were assessed on initial raw semen (T0), post-centrifugation (T1), and 24 h (T2) and 48 h (T3) after cooling. Sperm losses were minimal, and RRs were similar across treatment groups (median >98%, p ≥ 0.062). Spermatozoa membrane integrity was not different between centrifugation groups at any time point (p ≥ 0.38) but declined significantly during cooling (T1 vs. T2/T3, p ≤ 0.001). Similarly, total and progressive motility did not differ across treatments but declined in all groups from T1 to T3 (p ≤ 0.02). In conclusion, our study showed that centrifugation within a range of 400 g-900 g for 5-10 min is appropriate for processing canine semen.

Measurement of membrane integrity in canine spermatozoa using a fluorescent computer-assisted spermatozoal quantification method after SYBR-14/PI staining compared with manual counting after CFDA/PI staining

The aim of this study was to compare measurements of spermatozoal membrane status in dogs using computer-assisted spermatozoal quantification (CASQ) after staining with SYBR-14 and propidium iodide (PI) with manual counting after CFDA/PI staining. CASQ was performed on fresh (n = 11) and thawed cryopreserved canine semen (n = 91) using (1) a red long-pass (LP) filter on an untreated sample (membrane-disrupted spermatozoa, MDS count) and in a sample with all cellular membranes disrupted (total spermatozoal count, TC), (2) green LP filter for a TC and the red filter for an MDS count and (3) a green short-pass filter to obtain a membrane-intact spermatozoa (MIS) count and the red filter to obtain the MDS count, which were added to give a TC (red-green filter CASQ, n = 50). Spermatozoa were also stained with CFDA/PI, manually examined and classified as MIS or MDS. All measurements were performed in duplicate. The percentage of membrane-intact spermatozoa (MIS) was calculated. The percentage of progressively motile spermatozoa (PMS) was determined subjectively. The data were analysed to measure the agreement between the CASQ and CFDA/PI methods, repeatability of the methods and correlation between the MIS and PMS percentage. Compared with the CFDA/PI method, the agreement of MIS percentage with red filter CASQ was -12% to 34%, green LP filter CASQ -42% to 47% and red-green filter CASQ -23% to 29%. The repeatability of the CFDA/PI and red-green filter CASQ methods were the highest. The MIS and PMS percentages were always correlated (p < .05). Measurement of MIS percentage using red and red-green filter CASQ appeared to be the most reliable automated methods.

Cryopreservation effects on canine sperm morphometric variables and ultrastructure: Comparison between vitrification and conventional freezing

Semen cryopreservation is an increasingly demanded technique in canids, particularly in order to preserve and spread high genetic value material. Sperm vitrification may represent an interesting alternative to costly and time consuming conventional freezing. The objective of this study was to evaluate the effect of sperm vitrification on sperm morphometry and ultrastructure compared to conventional freezing. Pools of nine beagle dogs were both frozen and vitrified. Computerized morphological parameters (length, wide, area and perimeter) and sperm ultrastructure, using scanning and transmission microscopy, were analysed in both fresh and in thawed/warmed samples. There were no differences (p > 0.05) between post-thaw and fresh morphometric variables of the sperm heads. However, cluster analysis revealed that sperm-heads turned out to be smaller after thawing (p < 0.05) in two of the four subpopulations. Vitrification-warming process led to an overall increase in sperm-head size. Furthermore, the sperm head size increased after warming in two subpopulations (p < 0.05). In conclusion, the variations in the sperm head area depended on the cryopreservation procedure (conventional freezing or vitrification). Conventional freezing tended to decrease the head dimensions, at least in some subpopulations, and vitrification led to an overall increase in the sperm head size. Decondensation of chromatin and plasma membrane blebbing in the head region was observed by transmission electron microscopy in several vitrified sperm, which might explain the increase of head dimensions detected by CASA-Morph system.

Evaluation of Sperm Mitochondrial Function: A Key Organelle for Sperm Motility

Introduction: The role of nutraceuticals in the treatment of male infertility, especially in the “idiopathic form”, remains the subject of significant debate. Many antioxidants improve sperm motility but the exact mechanism by which they act is still unclear. Although several studies have shown a correlation between sperm motility and mitochondrial function, the effects of antioxidant therapy on mitochondrial membrane potential (MMP) are poorly studied. The first aim of this review was to evaluate the efficacy of antioxidants on mitochondrial function and, consequently, on sperm motility in male infertile patients. Material and Methods: we performed a systematic search of all randomized controlled and uncontrolled studies available in the literature that reported sperm motility and MMP at baseline and after antioxidant administration in-vivo and in-vitro in patients with idiopathic asthenozoospermia. Pubmed, MEDLINE, Cochrane, Academic One Files, Google Scholar and Scopus databases were used. Results: Unexpectedly, among 353 articles retrieved, only one study met our inclusion criteria and showed a significant effect of myoinositol on both MMP and sperm motility. We then summarized the main knowledge on anatomy and metabolism of sperm mitochondria, techniques allowing to assess sperm mitochondria function and its relationships with low sperm motility. Finally, we paid special attention to the effect of antioxidant/prokinetic molecules for the treatment of asthenozoospermia. Conclusions: This is the first systematic review that has attempted to evaluate the effects of antioxidants on MMP and sperm motility. Although results are not conclusive due to the dearth of studies, the close relationship between mitochondria and sperm motility is clear. The investigation of this correlation could provide valuable information to be exploited in clinical practice for the treatment of male infertility.

Effects from aging on semen quality of fresh and cryopreserved semen in Labrador Retrievers

Characteristics of frozen sperm associated with fertility and aging have not been fully determined in dogs. The aim of this study was to determine the relationship between fresh and post-thaw sperm quality, age, among the factors of motility, viability, morphology and oxidative stress in a group of fertile stud dogs with extensive breeding records and in dogs with reported subfertility problems. Sperm parameters from 39 fertile dogs were measured in fresh semen and frozen thawed semen. Additionally, frozen semen from 9 subfertile dogs was thawed and analyzed. Subfertile dogs were defined by referring veterinarians solely on the basis of owner history; breeding records were not available to this study. Evaluation included total motility (TM) and progressive motility (PM), average path velocity (VAP), viability, morphology and presence of sperm reactive oxygen species (ROS). Fertile males' ages ranged from 1 to 10 years, subfertile males' ages ranged from 4 to 14 years. All dogs were assigned to age groups according to age as young (1-3 years) middle (4-6 years) and senior (>7 years). The effect of sperm state (fresh vs. frozen-thawed), age, and fertility history (fertile vs. subfertile) on the measured endpoints were determined using a mixed effects model. TM showed a negative correlation with age in the frozen-thawed semen. Additionally, TM in fresh semen was higher in all age groups compared to post thaw semen (P < 0.05). PM was higher in all age dogs of fresh semen compared to frozen-thawed semen (P < 0.05). As such, TM and PM in post thaw semen statistically decreased compared to fresh semen regardless of age of stud male (P < 0.05). Differences in VAP were only observed between young and senior age groups in fresh semen (P < 0.05) while young and middle age dogs from fresh semen were different in all age groups for frozen-thawed semen (P < 0.05). ROS was higher in the young frozen-thawed semen compared to the young fresh semen (P < 0.05). When comparing TM, PM and VAP of fertile vs. subfertile dogs, middle aged fertile dogs are different from middle aged and senior subfertile dogs (P < 0.05). No differences were found in measures of ROS between fertile and subfertile. For sperm viability and morphology, differences were observed between all age groups of fertile dogs in comparison to all ages of subfertile dogs (P < 0.05). Sperm motility appeared to be the most affected parameter by freezing damage than any other parameter measured in this study, while we were not able to determine a significant association between ROS production and fertility status.

Sperm membrane integrity and stability after selection of cryopreserved ovine semen on colloidal solutions

The aim of this study was to evaluate the effect of four methods of sperm selection, on the integrity and stability of the plasma membrane, integrity of the acrosomal membrane and spermatic morphology in frozen/thawed ovine semen. Two types of colloidal silica: colloidal silica-silane and colloidal silica-polyvinylpyrrolidone (PVP), and two aliquots: 1 and 4 ml, were used for sperm selection. Probes FITC-PSA and PI were used to measure the integrity of the plasma and acrosomal membranes. Plasma membrane stability was measured, using fluorescent probes M540 and YOPRO1. Effective reduction in the incidence of spermatozoa with acrosomal pathologies was only achieved using 1 ml colloidal silica-silane. All methods were efficient in select viable and unreacted spermatozoa. Only methods using 1 ml of silica were efficient in decrease spermatozoa stained by PI (death). Methods using silica colloidal-silane were more efficient to decrease apoptotic cells after selection when compared to silica colloidal-PVP. In conclusion, sperm selection in colloidal silica-silane and colloidal silica-PVP improved sperm quality when compared to the controls. The method using 1 ml of colloidal silica-silane is the preferred method because its effectiveness and lower cost.

Use of the fluorescent dye tetramethylrhodamine methyl ester perchlorate for mitochondrial membrane potential assessment in human spermatozoa

Mitochondrial membrane potential (ΔΨm) is an indicator of sperm quality and its evaluation complements the standard semen analysis. The fluorescent dye JC-1 has been widely used to assess sperm ΔΨm; however, some problems have been detected under certain experimental conditions. Another fluorescent compound, tetramethylrhodamine methyl ester perchlorate (TMRM), has been used in somatic cells and bovine spermatozoa but not in human spermatozoa. TMRM accumulates in hyperpolarised mitochondria and the fluorescence intensity of this compound correlates with ΔΨm. Thus, the aim of this study was to evaluate and validate the usefulness of the fluorescent dye TMRM for measuring sperm ΔΨm. The results showed that TMRM accurately detects sperm populations displaying either high or low ΔΨm. Moreover, TMRM was able to measure sperm ΔΨm under the experimental conditions in which JC-1 had previously presented difficulties. Differences in ΔΨm according to sperm and semen quality were properly detected and a positive correlation between ΔΨm and conventional semen parameters was observed. Finally, a positive correlation was found between the ΔΨm measurement by TMRM and by the widely used JC-1. In conclusion, TMRM is a simple, time-effective method, easy to set in laboratories equipped with flow cytometry technology, and can accurately detect changes in ΔΨm with efficiency comparable to JC-1 without its limitations.

Effect of sperm pretreatment with sodium hydroxide and dithiothreitol on the efficiency of bovine intracytoplasmic sperm injection

The efficiency of intracytoplasmic sperm injection (ICSI) in bovines is lower than in other species due, in part, to a lack of optimal conditions for its implementation; this has hindered the achievement of high rates of embryonic development and the birth of live offspring. The aim of the present study was to evaluate the effects of pretreatment of bovine spermatozoa with NaOH and dithiothreitol (DTT) on the viability, plasma membrane integrity, DNA fragmentation and in vitro developmental potential of embryos generated by ICSI. Following pretreatment of spermatozoa with 5 mM DTT for 20 min and a low concentration of NaOH (1 mM for 60 min), there were fewer live and acrosome reacted spermatozoa (44% and 34%, respectively) than in the control group without treatment (82%). Spermatozoa subjected to higher alkali concentrations (10–50 mM) were mostly dead and reacted. However, pronuclear formation, cleavage, blastocyst rate and embryo quality did not differ between these pretreatment groups and the untreated control group. In conclusion, we have described, for the first time, the effects of NaOH treatment on bovine spermatozoa and subsequent in vitro embryonic development after ICSI, and have demonstrated that pretreatment of bovine spermatozoa with NaOH or DTT is not necessary for an appropriate in vitro embryo development in this species.

Customizing semen preservation protocols for individual dogs and individual species: sperm preservation beyond the state of the art

Sperm quality can be variable in morphometric and physiological attributes between males of different species, between males within species subtypes reared under different environmental conditions, between ejaculates of the same male or even between sperm populations within an ejaculate. Clinical semen evaluation is based on evaluation of whole ejaculates, which is not a chemically or physiologically well-defined entity, rather a collection of heterogeneous subpopulations giving different measurements and possessing different fertilizing potential. Identification of subpopulations with different motility patterns is important as well as characterizing the subtle structural changes underlying the motility differences observed. The ability to identify populations of sperm responding rapidly or failing to progress through the capacitation process may have clinical applications. Studies of lipid-phase fluidity of sperm membranes, mathematical modelling of membrane ion transport, role of modifying components and detergent-resistant microdomains are of particular interest. When customizing extenders to ejaculates from cryosensitive males or species, a thorough knowledge of species sperm membrane physiology and an assessment of the individual ejaculate's sperm populations are necessary. Structural differences have been found in sperm membranes between fox species with different cryosurvival potential of their spermatozoa. Supplementation of lipids and detergents in cryoextenders may influence membrane fluidity of the surviving spermatozoa in a species-dependent manner and influence capacitation. Immobilization of sperm prior to cryopreservation with subsequent slow release of sperm in the female genital tract may be a way to prolong the fertile life of sperm. In canids with a long oocyte maturation time, delayed capacitation may be beneficial.

Use of fluorescent stainings and flow cytometry for canine semen assessment

Over the last few decades, appreciable progress has been noted in canine semen assessment techniques. The common use of accurate and sensitive diagnostic methods, such as computer-assisted sperm analysis (CASA), flow cytometry and sperm penetration tests have become routine procedures in specialized andrology laboratories. Many fluorescent probes have been applied to the assessment of specific sperm characteristics in dogs. Flow cytometry enables the observation of cell characteristics such as size, shape and function of the spermatozoon, that can be revealed by a fluorochrome or fluorescent label. The analysis of events detected on dot plots gives accurate and highly reliable information on membrane integrity, acrosomal status, mitochondrial activity, capacitation status, lipid peroxidation, apoptosis and DNA damage. Despite the development of these modern and accurate tools, it is still questionable if the ideal method of semen evaluation, allowing predicting of the fertilizing potential of semen, has been established.

Assessment of sperm function parameters and DNA fragmentation in ejaculated alpaca sperm (Lama pacos) by flow cytometry

Flow cytometry has been shown to be an accurate and highly reproducible tool for the analysis of sperm function. The main objective of this study was to assess sperm function parameters in ejaculated alpaca sperm by flow cytometry. Semen samples were collected from six alpaca males and processed for flow cytometric analysis of sperm viability and plasma membrane integrity using SYBR-14⁄PI staining; acrosomal membrane integrity using FITC-conjugated Pisum Sativum Agglutinin⁄PI labelling; mitochondrial membrane potential (Δψm) by staining with JC-1 and DNA Fragmentation Index (DFI) by TUNEL. The results indicate that the mean value for sperm viability was 57 ± 8 %. Spermatozoa with intact acrosome membrane was 87.9 ± 5%, and viable sperm with intact acrosomal membrane was 46.8 ± 9%, high mitochondrial membrane potential (Δψm) was detected in 66.32 ± 9.51% of spermatozoa and mean DFI value was 0.91 ± 0.9%. The DFI was inversely correlated with high Δψm (p = 0.04; r = -0.41) and with plasma membrane integrity (p = 0.01; r = -0.47). To our knowledge, this is the first report of the assessment on the same sample of several parameters of sperm function in ejaculated alpaca sperm by flow cytometry.