Morphological sperm defects analyzed by light microscopy and transmission electron microscopy and their correlation with sperm motility

Human Sperm Head Vacuoles Are Related to Nuclear-Envelope Invaginations

Nuclear vacuoles are specific structures present on the head of the human sperm of fertile and non-fertile men. Human sperm head vacuoles have been previously studied using motile sperm organelle morphology examination (MSOME) and their origin related to abnormal morphology, abnormal chromatin condensation and DNA fragmentation. However, other studies argued that human sperm vacuoles are physiological structures and consequently, to date, the nature and origin of the nuclear vacuoles remains to be elucidated. Here, we aim to define the incidence, position, morphology and molecular content of the human sperm vacuoles using transmission electron microscopy (TEM) and immunocytochemistry techniques. The results showed that ~50% of the analyzed human sperm cells (n = 1908; 17 normozoospermic human donors) contained vacuoles mainly located (80%) in the tip head region. A significant positive correlation was found between the sperm vacuole and nucleus areas. Furthermore, it was confirmed that nuclear vacuoles were invaginations of the nuclear envelope from the perinuclear theca and containing cytoskeletal proteins and cytoplasmic enzyme, discarding a nuclear or acrosomal origin. According to our findings, these human sperm head vacuoles are cellular structures originating from nuclear invaginations and contain perinuclear theca (PT) components, allowing us to define a new term of 'nuclear invaginations' rather than 'nuclear vacuoles'.

Ultra-structural analysis of human spermatozoa by aperture scanning near-field optical microscopy

Scanning near-field optical microscopy (SNOM) represents a potential candidate for investigation of ultrastructure in human spermatozoa. It is a noninvasive optical technique that offers two main advantages: minimal sample preparation and simultaneous topographical and optical images acquisition with a spatial resolution beyond the diffraction limit. This enables the combination of surface characterization and information from the inner cellular organization in a single acquisition providing an immediate and comprehensive analysis of the cellular portions. In this work spermatozoa are immobilized on poly-L-lysine coated coverslips, fixed according to a standard protocol and imaged by aperture-SNOM in air. In the SNOM images, all peculiar sperm portions show well-resolved optical features, which exhibit good similarities with the structures revealed in transmission electron microscopy images, as compared with literature data. The optical features of anomalous spermatozoa are clearly different as respect with those observed for healthy ones. This analysis reveals the potentialities of SNOM and opens to its application to high-resolution analysis of sperm morphological alterations, which might be relevant in reproductive medicine.

Micromorphological and ultrastructural description of spermatozoa from squirrel monkeys (Saimiri collinsi Osgood, 1916)

Saimiri collinsi is used as an animal model in biotechnology research for conservation of species from the genus Saimiri. However, the development of biotechnologies depends on a proper knowledge of the sperm morphology to understand the basic aspects of sperm physiology, as potential male fertility depends on different cellular sperm structures. With this purpose, this study characterized the micromorphological and ultrastructural characteristics of squirrel monkeys (Saimiri collinsi) sperm using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM electromyography revealed that a normal Saimiri collinsi sperm measures 71.7 ± 0.7 μm with lateral tail insertion, a paddle-shaped flattened head and an acrosome occupying most of the head. TEM also showed that the middle piece is characterized by a central 9 + 2 microtubule axoneme surrounded by nine dense fibres, and that the mitochondria were juxtaposed, forming the mitochondrial sheath. Here we provide the first micromorphological and ultrastructure description of S. collinsi sperm.

An illustration of human sperm morphology and their functional ability among different group of subfertile males

Condensed sperm chromatin is a prerequisite for natural fertilization. Some reports suggested the prevalence of chromatin condensation defects in teratozoospermia cases with head anomalies; conversely, earlier studies exemplified its occurrence in morphologically normal spermatozoa too. The aim of this study was to compare the condensation defects in correlation with head anomalies among different groups of subfertile males and its impact on the rate of fertilization in assisted reproduction procedures. Ultrastructure analysis of spermatozoa through scanning electron microscopy and atomic force microscopy could facilitate an in-depth evaluation of sperm morphology. Nuclear condensation defects (%) in spermatozoa were analyzed in 666 subjects, and its effect on the rate of fertilization was analyzed in 116 IVF and 90 intracytoplasmic sperm injection cases. There was no correlation of condensation defects with head anomalies (%). Student's t-test showed no significant changes in mean values of condensation defects in abnormal semen samples in comparison with the normal group. Condensation defects were observed in normal spermatozoa too, which was negatively associated with the rate of fertilization in IVF (p < 0.01), but intracytoplasmic sperm injection outcome remained unaffected. Ultrastructure study revealed sperm morphological features in height, amplitude, and three-dimensional views in atomic force microscopy images presenting surface topography, roughness property of head, and compact arrangement of mitochondria over axoneme with height profile at nanoscale. In pathological forms, surface roughness and nuclear thickness were marked higher than the normal spermatozoa. Thus, percentage of normal spermatozoa with condensation defects could be a predictive factor for the rate of fertilization in IVF. From diverse shapes of nucleus in AFM imaging, it could be predicted that defective nuclear shaping might be impeding the activity of some proteins/ biological motors, those regulate the proper Golgi spreading over peri-nuclear theca.

Adapted methods for scanning electron microscopy (SEM) in assessment of human sperm morphology

Infertility is a widespread problem, and in some cases, the routine basic semen analysis is not sufficient to detect the cause of male infertility. The use of the scanning electron microscope (SEM) could provide a detailed insight into spermatozoa morphology, but it requires specific sample preparation techniques. The purpose of this study was to select, adjust, and optimize a method for the preparation of spermatozoa samples prior to SEM analysis, and to establish the protocol required for its use in clinical practice. We examined sperm samples of 50 men. The samples were fixed with modified iso-osmolar aldehyde solution followed by osmium post-fixation. In the first method, dehydration of the cells and subsequent critical point drying (CPD) were performed on a coverslip. In the second method, the samples were dehydrated in centrifuge tubes; hexamethyldisilazane (HMDS) was used as a drying agent instead of CPD, and the samples were air-dried. The third procedure was based on a membrane filter. The samples were dehydrated and dried with HMDS in a Gooch crucible, continuously, without centrifugation or redispersion of the sample. Our results showed that the fixation with modified iso-osmolar aldehyde solution followed by osmium post-fixation, and combined with dehydration and CPD on a coverslip, is the most convenient procedure for SEM sample preparation. In the case of small-size samples or low sperm concentration, dehydration and drying with HMDS on the membrane filter enabled the best reliability, repeatability, and comparability of the results. The presented procedures are suitable for routine use, and they can be applied to confirm as well as to correct a diagnosis.

Combination of density gradient centrifugation and swim-up methods effectively decreases morphologically abnormal sperms

Density gradient centrifugation (DGC) and swim-up techniques have been reported for semen preparation in assisted reproductive techniques in humans. We investigated whether semen preparation using a combination of DGC and swim-up techniques could effectively decrease morphologically abnormal human sperms at the ultrastructural level. Semen samples were obtained from 16 infertile males and fractionated by swim-up following DGC. Ultrastructural abnormalities of sperms obtained from original semen, lower layer of swim-up following DGC, and upper layer of swim-up following DGC were analyzed by transmission electron microscopy. The correlation among ultrastructural head abnormality in sperms from the upper layer of swim-up, fertilization in in vitro fertilization, and pregnancy after embryo transfer was also investigated. Furthermore, sperms with DNA fragmentation in the samples processed via a combination of DGC and swim-up was assessed in a sperm chromatin structure assay. Ultrastructural abnormalities in sperm heads and tails in the upper layer after swim-up following DGC was the lowest among the three groups. Sperms with nuclear vacuoles were the most difficult to eliminate using a combination of DGC and swim-up in all types of head abnormalities. A negative correlation was confirmed between the fertilization rates of intracytoplasmic sperm injection and head abnormality of sperms obtained from the upper layer of the swim-up following DGC. Sperms with DNA fragmentation were effectively decreased using the combination of two techniques. In conclusion, the combination of DGC and swim-up effectively decreased the number of sperms with ultrastructural abnormalities both in the head and in the tail. However, sperms with ultrastructural abnormalities that cannot be completely decreased using a combination of DGC and swim-up may impair fertilization in some cases of intracytoplasmic sperm injection.

The importance of transmission electron microscopy analysis of spermatozoa: Diagnostic applications and basic research

This review is aimed at discussing the role of ultrastructural studies on human spermatozoa and evaluating transmission electron microscopy as a diagnostic tool that can complete andrology protocols. It is clear that morphological sperm defects may explain decreased fertilizing potential and acquire particular value in the field of male infertility. Electron microscopy is the best method to identify systematic or monomorphic and non-systematic or polymorphic sperm defects. The systematic defects are characterized by a particular anomaly that affects the vast majority of spermatozoa in a semen sample, whereas a heterogeneous combination of head and tail defects found in variable percentages are typically non-systematic or polymorphic sperm defects. A correct diagnosis of these specific sperm alterations is important for choosing the male infertility's therapy and for deciding to turn to assisted reproduction techniques. Transmission electron microscopy (TEM) also represents a valuable method to explore the in vitro effects of different compounds (for example drugs with potential spermicidal activity) on the morphology of human spermatozoa. Finally, TEM used in combination with immunohistochemical techniques, integrates structural and functional aspects that provide a wide horizon in the understanding of sperm physiology and pathology.

ABBREVIATIONS

transmission electron microscopy: TEM; World Health Organization: WHO; light microscopy: LM; motile sperm organelle morphology examination: MSOME; intracytoplasmic morphologically selected sperm injection: IMSI; intracytoplasmic sperm injection: ICSI; dysplasia of fibrous sheath: DFS; primary ciliary dyskinesia: PCD; outer dense fibers: ODF; assisted reproduction technologies: ART; scanning electron microscopy: SEM; polyvinylpirrolidone: PVP; tert-butylhydroperoxide: TBHP.

Use of density centrifugation for delayed cryopreservation of stallion sperm: perform sperm selection directly after collection or after storage?

Equipment for cryopreservation of stallion sperm is not always available. In such cases, diluted semen can be shipped to a facility for later cryopreservation. The aim of this study was to evaluate if selection of sperm via density centrifugation yields higher survival rates when cryopreservation is to be delayed (i.e. carried out after 1 day of storage at 5°C). Two-layer iodixanol as well as single-layer Androcoll density centrifugation were tested and compared with samples prepared with standard centrifugation. Special emphasis was placed on comparing centrifugation on the day of semen collection with centrifugation after 1-day refrigerated storage. Sperm morphology and motility as well as membrane and chromatin integrity were evaluated before and after centrifugation. Sperm motility and membrane integrity were also assessed after cryopreservation. It was found that both two- and single-layer density centrifugation processing resulted in higher percentages of morphologically normal and motile sperm with higher membrane and chromatin integrity, as compared to standard centrifugation or diluted samples. Differences were only in the order of magnitude of 5%. Recovery rates after density centrifugation were only approximately 30-40%. When cryopreservation was carried out after 1-day refrigerated storage, centrifugation processing of sperm directly after semen collection resulted in higher percentages of plasma membrane intact sperm post-thaw as compared to performing centrifugation processing of stored sperm just prior to cryopreservation. No significant differences in progressively motile sperm post-thaw were seen. Taken together, for delayed cryopreservation, it is best to perform density centrifugation directly after collection rather than immediately prior to cryopreservation.

Evaluation of morphological criteria of sperm quality before in vitro fertilization and intracytoplasmic sperm injection

The quality of sperm has a direct influence on the fertilization and developmental competence of embryos. In the literature we did not find defined criteria for evaluation of normal sperm parameters in various species of domestic mammals. Therefore we attempted to review evaluation of criteria of morphologically normal human sperm and their abnormalities. All sperm cells observed in the stained sample are classified as normal or abnormal. Any abnormalities in morphology of sperm have a negative effect on the outcome in in vitro fertilization and intracytoplasmic sperm injection. Abnormal sperm are categorized into subgroups according to the observed defects (concerning the head and/or midpiece and/or tail). Most morphologically abnormal sperm have multiple defects. This article can be considered as guideline for the manual of sperm quality evaluation in different species of domestic mammals.

The Effects of Smoking and Alcohol Intake on Sperm Quality: Light and Transmission Electron Microscopy Findings

Objective:

To evaluate the effects of alcohol consumption and cigarette smoking on sperm quality using transmission electron microscopy and light microscopy.

Methods:

Semen samples were collected from 62 healthy men. The subjects were classified according to alcohol consumption and smoking status. Semen analysis was performed according to World Health Organization criteria. Transmission electron microscopy was used to examine sperm ultrastructure.

Results:

Heavy smoking (> 20 cigarettes/day) was associated with a decreased sperm count. Moderate/high alcohol consumption (≥15.4 g/day) was associated with an increase in morphologically abnormal sperm. Transmission electron microscopy revealed no effect of smoking on sperm ultrastructure. Alcohol consumption resulted in significant increases in morphologically abnormal nuclei and plasma membranes.

Conclusions:

Heavy smoking was associated with decreased sperm counts and alcohol consumption was associated with increased numbers of morphologically abnormal sperm.

Light, polarizing, and transmission electron microscopy: three methods for the evaluation of sperm quality

Semen from 33 patients were evaluated by light microscopy (LM) obtaining sperm concentration, percent motility, percentage of sperm with normal morphology (PAP staining), and percentage of dead sperm (Eosin Y stained). The samples were observed by polarizing microscopy (PM), that evaluates sperm morphology and the viability by birefringence of organelles, and it provides a PM index (percentage of birefringent, viable, motile sperm) and a percentage of dead, non-birefringent sperm. Sperm were processed for transmission electron microscopy (TEM) and TEM data were elaborated with a mathematical formula able to provide a fertility index (FI, number of sperm free of structural defects) and percentages of sperm immaturity and necrosis (dead sperm). To test the reliability of these techniques, the values of normal acrosome, nucleus, midpiece, and tail and the presence of cytoplasmic residues obtained with the three methods were compared. With the exception of cytoplasmic residues (P = 0.40), significant differences in the evaluation of each organelle were observed and TEM analysis resulted as the most stringent screening. In addition, relationships among relevant sperm variables were investigated. Motility showed positive correlations with the percentage of normal tail, midpiece, and PM index (P < 0.01), but it exhibited negative correlations with indices of sperm death (non-birefringent sperm: P < 0.05; percentage of eosin Y stained sperm: P < 0.05; necrosis: P < 0.01), which were positively correlated with each other (P < 0.01). Positive correlations were found between indices expressing normal sperm morphology: FI with PM index (P < 0.01) and with the percentage of normal sperm (PAP staining) (P < 0.01), which in turn were correlated with the PM index (P < 0.001). Sperm immaturity showed positive correlations (P < 0.01) with the presence of cytoplasmic residues detected with the three methods. In conclusion, LM, PM, and TEM are reliable techniques in evaluating sperm quality. PM appears to offer several advantages 'midway' between LM and TEM and it should be considered in sperm analysis.

Protective effects of grape seed procyanidin extract against nickel sulfate-induced apoptosis and oxidative stress in rat testes

This study determined whether nickel sulfate (Ni)-induced reproductive damage occurs via apoptosis and oxidative stress and to examine the expression of Bax and c-kit and their effects on Ni exposure. The study also explored the protective effects of grape seed proanthocyanidin extract (GSPE) against Ni toxicity in the testes. Wistar rats were treated with normal saline, Ni alone (1.25, 2.5, and 5 mg/kg/day), and Ni (2.5 mg/kg/day) plus GSPE (50 and 100 mg/kg/day). After 30 days, Ni significantly decreased sperm motility and the percentage of S-phase cells and enhanced testicular apoptosis in the 2.5 and 5 mg groups. The levels of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and nitric oxide (NO) significantly increased. The decreased activity of glutathione peroxidase and catalase in the Ni groups showed that Ni could increase oxidative stress, especially at 2.5 and 5 mg. Western blot analysis showed that the expression of Bax protein and c-kit increased in 2.5 and 5 mg Ni groups compared with controls. Conversely, these changes were partially attenuated in rats simultaneously administered GSPE, especially in the 100 mg group. These results demonstrate the following: (1) Ni exhibits reproductive toxicity in rats by decreasing sperm at concentrations of 2.5 and 5 mg; (2) intratesticular apoptosis, oxidative stress, and c-kit overexpression play pivotal roles in reproductive damage induced by Ni; and (3) GSPE enhances sperm motility by down-regulating c-kit expression and offsetting the apoptosis and oxidative stress induced by Ni by directly decreasing MDA and NO, scavenging H₂O₂, and down-regulating Bax expression.