Retention of membrane charge attributes by cryopreserved-thawed sperm and zeta selection

Sperm selection in IVF: the long and winding road from bench to bedside

Spermatozoa wage battle to conquer fertilization but the traits needed to succeed remain elusive. The natural advantageous qualities that enable only a few selected sperm cells to reach the site of fertilization remain unknown. Although in vitro fertilization (IVF) facilitates the job of spermatozoa, a universally acceptable means of sperm selection is yet to be developed. No objective or reliable sperm quality indicators have been established and sperm selection is, to a great extent, based on subjective qualitative evaluation. The best method for sperm selection in IVF presents several challenges: intrinsic sperm qualities cannot be evaluated and the ideal endpoint for these studies is debatable. An ideal method for sperm selection in ART should be noninvasive and cost-effective, and allow the identification of high-quality spermatozoa and yield better outcomes in terms of pregnancy and live birth rates. This narrative review included 85 papers and focused on the new available methods and technologies that might shed some light on sperm selection in IVF. It discusses the available data on microfluidic devices, omics profiling, micronuclei studies, sperm plasma membrane markers, and other techniques, such as Magnetic Activated Cell Sorting (MACS), Raman micro-spectroscopy, and artificial intelligence systems. The new techniques herein reviewed offer fresh approaches to an old problem, for which a definite solution has yet to cross the bridge from bench to IVF clinics around the world, since clinical usefulness and application remain unproven.

DGC/Zeta as A New Strategy to Improve Clinical Outcome in Male Factor Infertility Patients following Intracytoplasmic Sperm Injection: A Randomized, Single-Blind, Clinical Trial

Objective

The aim of this blind randomised clinical trial study was to assess the clinical efficiency of combined density gradient centrifugation/Zeta (DGC/Zeta) sperm selection procedure compared to conventional DGC in infertile men candidates for intracytoplasmic sperm injection (ICSI). The literature shows that DGC/Zeta is more effective compared to DGC alone in selection of sperms with normal chromatin and improves the clinical outcome of the ICSI procedure. Therefore, this study re-evaluates the efficiency of DGC/Zeta in improving the clinical outcomes of ICSI in an independent clinical setting.

Materials and Methods

In this randomized, single-blind, clinical trial, a total of 240 couples with male factor infertility and at least one abnormal sperm parameter were informed regarding the study and 220 participated. Based on inclusion and exclusion criteria, 103 and 102 couples were randomly allocated into the DGC/Zeta and DGC groups, respectively. ICSI outcomes were followed and compared between the two groups.

Results

Although there was no significant difference in fertilization rate (P=0.67) between the DGC/Zeta and DGC groups, mean percentage of good embryo quality (P=0.04), good blastocysts quality (P=0.049), expanded blastocysts (P=0.007), chemical pregnancies (P=0.005) and clinical pregnancies (P=0.007) were significantly higher in the DGC/ Zeta group compared to DGC. In addition, implantation rate was insignificantly higher in DGC/Zeta compared to DGC (P=0.17).

Conclusion

This is the second independent study showing combined DGC/Zeta procedure improves ICSI outcomes, especially the pregnancy rate, compared to the classical DGC procedure and this is likely related to the improved quality of sperm selected by the DGC/Zeta procedure (Registration number: IRCT20180628040270N1).

Optimization of microelectrophoresis to select highly negatively charged sperm

PURPOSE

The sperm membrane undergoes extensive surface remodeling as it matures in the epididymis. During this process, the sperm is encapsulated in an extensive glycocalyx layer, which provides the membrane with its characteristic negative electrostatic charge. In this study, we develop a method of microelectrophoresis and standardize the protocol to isolate sperm with high negative membrane charge.

METHODS

Under an electric field, the percentage of positively charged sperm (PCS), negatively charged sperm (NCS), and neutrally charged sperm was determined for each ejaculate prior to and following density gradient centrifugation (DGC), and evaluated for sperm DNA damage, and histone retention. Subsequently, PCS, NCS, and neutrally charged sperm were selected using an ICSI needle and directly analyzed for DNA damage.

RESULTS

When raw semen was analyzed using microelectrophoresis, 94 % were NCS. In contrast, DGC completely or partially stripped the negative membrane charge from sperm resulting PCS and neutrally charged sperm, while the charged sperm populations are increased with an increase in electrophoretic current. Following DGC, high sperm DNA damage and abnormal histone retention were inversely correlated with percentage NCS and directly correlated with percentage PCS. NCS exhibited significantly lower DNA damage when compared with control (P < 0.05) and PCS (P < 0.05). When the charged sperm population was corrected for neutrally charged sperm, sperm DNA damage was strongly associated with NCS at a lower electrophoretic current.

CONCLUSION

The results suggest that selection of NCS at lower current may be an important biomarker to select healthy sperm for assisted reproductive treatment.

Sperm selection based on electrostatic charge

Charge is a fundamental property of all forms of matter that exhibit attraction or repulsion in the presence of another charged particle. This electrokinetic property occurs when the particles exhibiting a net negative or positive charge are subjected to an external electric field that exerts an electrostatic force between them. Sperm surface membranes exhibit varying levels of electrostatic potential that are proportional to the levels of sialic acid residue acquired on the cell surface during maturation. Electrostatic charge-based sperm separation is a recently developed technique that uses an electric field to isolate mature sperm with reduced levels of DNA fragmentation. Two methods for the separation of sperm based on electrostatic charge, the Zeta method and a commercially available electrophoretic method using the SpermSep Cell Sorter 10, are discussed in this chapter including a detailed protocol for sperm separation based on the Zeta method.

Sperm preparation: state-of-the-art--physiological aspects and application of advanced sperm preparation methods

For assisted reproduction technologies (ART), numerous techniques were developed to isolate spermatozoa capable of fertilizing oocytes. While early methodologies only focused on isolating viable, motile spermatozoa, with progress of ART, particularly intracytoplasmic sperm injection (ICSI), it became clear that these parameters are insufficient for the identification of the most suitable spermatozoon for fertilization. Conventional sperm preparation techniques, namely, swim-up, density gradient centrifugation and glass wool filtration, are not efficient enough to produce sperm populations free of DNA damage, because these techniques are not physiological and not modeled on the stringent sperm selection processes taking place in the female genital tract. These processes only allow one male germ cell out of tens of millions to fuse with the oocyte. Sites of sperm selection in the female genital tract are the cervix, uterus, uterotubal junction, oviduct, cumulus oophorus and the zona pellucida. Newer strategies of sperm preparation are founded on: (i) morphological assessment by means of 'motile sperm organelle morphological examination (MSOME)'; (ii) electrical charge; and (iii) molecular binding characteristics of the sperm cell. Whereas separation methods based on electrical charge take advantage of the sperm's adherence to a test tube surface or separate in an electrophoresis, molecular binding techniques use Annexin V or hyaluronic acid (HA) as substrates. Techniques in this category are magnet-activated cell sorting, Annexin V-activated glass wool filtration, flow cytometry and picked spermatozoa for ICSI (PICSI) from HA-coated dishes and HA-containing media. Future developments may include Raman microspectrometry, confocal light absorption and scattering spectroscopic microscopy and polarization microscopy.

Effects of advanced selection methods on sperm quality and ART outcome: a systematic review

BACKGROUND

Current routine semen preparation techniques do not inclusively target all intrinsic sperm characteristics that may impact the fertilization potential. In order to address these characteristics, several methods have been recently developed and applied to sperm selection. The objective of this study was to systematically review the literature describing these advanced sperm selection methods focusing on their anticipated benefits on sperm quality and assisted reproductive technique (ART) outcome.

METHODS

Systematic literature review was conducted by means of a Medline literature search. Sperm quality parameters assessed included: motility, morphology, viability, DNA integrity, apoptosis and maturity. ART outcomes assessed included: fertilization, embryo quality, pregnancy, abortion and live birth rates.

RESULTS

A total of 44 studies were identified describing four advanced sperm selection methods based on: (i) surface charge (electrophoresis and zeta potential), (ii) apoptosis (magnetic cell sorting and glass wool), (iii) membrane maturity (hyaluronic acid binding) and (iv) ultramorphology (high magnification). Selection of high-quality sperm including improvements in DNA integrity, resulted from the application of these methods. Fertilization and pregnancy rates showed improvement following some of the advanced sperm selection techniques.

CONCLUSIONS

While some of the advanced sperm selection methods are of value in specific clinical ART settings, others are in need of further evaluation. More clinical studies on safety and efficacy are needed before the implementation of advanced sperm selection methods could be universally recommended in ART.

Effects of cryopreservation on sperm parameters and ultrastructural morphology of human spermatozoa

PURPOSE

Cryopreservation of sperm is a widely used technique to maintain and protect the fertility in various occasions such as infertility and malignancy treatments. This study aims to reveal the effects of freezing and thawing on human spermatozoa.

MATERIALS AND METHODS

To evaluate the effects of freeze-thawing, semen samples were evaluated by light microscopy by means of morphology, motility and viability, by scanning and transmission electron microscopy for detailed ultrastructural changes.

RESULTS

After cryopreservation, a significant decrease in spermatozoa viability was observed (p < 0.01). Group a, b and c motility according to World Health Organization criteria decreased considerably (p < 0.05, p < 0.01, p < 0.05, respectively), whereas there was a substantial increase in group d motility. A strong correlation between rise in number of immotile spermatozoa and decrease in viability was also noted (r = -0.848, p < 0.01). Post-thaw light microscopic studies revealed a considerable decrease in rate of normal spermatozoa (p < 0.05). A considerable decline in the rate of normal sperm was also observed by TEM (p < 0.05). Statistically, acrosomal changes and subacrosomal swelling were found to be significantly increased (both p < 0.05), where the latter appears to be a novel finding in literature.

CONCLUSION

Cryopreservation has deleterious effects on spermatozoa, especially on plasmalemma, acrosomes and tails. Electron microscopy is the ultimate modality to investigate spermatogenic cells.