Sperm cryopreservation: current status and future developments

Incorporating olive (Olea europaea L) fruit extracts in a tris-based extender improves buffalo semen cryotolerance by reducing oxidative stress

This work aimed to evaluate whether supplementing the freezing extender with olive fruit extract (OFE) would improve the antioxidant defense of buffalo sperm, resulting in improved post-thaw semen quality. Ejaculates (two per 16 Murrah buffalo bulls) were split into four aliquots that were diluted in an extender supplemented with different doses of OFE (0, D50, D100, and D150, based on µM concentrations of hydroxytyrosol, the most represented polyphenol) and frozen according to standard procedures. At thawing, sperm motility, kinetics, viability, acrosome integrity, and membrane functionality were evaluated. Based on the dose-response results, biological antioxidant potential (BAP) and reactive oxygen metabolites (ROMs) were assessed after thawing in D50 and control groups. The pre-freezing supplementation of the extender with D50 OFE showed higher (P < 0.05) total and progressive sperm motility, as well as straight-line velocity compared to the control. Treatment with D50 OFE of buffalo semen also improved (P < 0.01) post-thaw sperm viability, membrane functionality, and acrosome integrity compared to the control. The enrichment of the extender with D50 OFE increased (P < 0.01) the post-thaw BAP and reduced (P < 0.05) the ROMs levels. The highest concentration tested (D150 OFE) negatively affected (P < 0.05) total and progressive motility, and the percentage of sperm with functional membranes and intact acrosomes, compared to the control. In conclusion, low doses of OFE added to the extender significantly improved post-thawing buffalo semen quality by protecting the spermatozoa from cryopreservation-induced oxidative stress. Further studies should investigate its effectiveness on in vivo and in vitro fertility, for potential commercial applications.

The Influence of Cryopreservation on Sperm Morphology and Its Implications in Terms of Fractions of Higher-Quality Sperm

Background/Objectives: Male infertility is a significant global health issue, comprising approx. 50% of all infertility cases. Semen cryopreservation, a critical component of assisted reproductive technologies (ARTs), is a method commonly used in a wide range of situations, including gonadotoxic treatments such as radiation or chemotherapy, hazardous occupational exposures, and various medical conditions. Although historically viewed as potentially damaging to sperm, recent findings suggest that cryopreservation, when performed with appropriate techniques, may in fact enhance semen quality by improving the proportion of healthy spermatozoa, particularly in terms of their morphological parameters. The aim of this study was to evaluate the impact of cryopreservation on sperm morphology and viability, utilizing advanced morphological assessments pre- and post-freezing. Methods: Semen samples were collected from 97 patients undergoing infertility treatment at the KRIOBANK clinic (Białystok, Poland). The semen was liquefied and prepared in the form of slides. Sperm morphology was then assessed using an OLYMPUS BX40 microscope at 60× magnification. Results: The findings of the study revealed significant improvements in sperm morphology, with increased percentages of normal sperm and reductions in deformation indices post-thaw. Conclusions: The findings indicate that optimized cryopreservation protocols may support the selection of higher-quality sperm, offering valuable benefits for ART applications. These results challenge certain past assumptions regarding the impact of cryopreservation and underscore the need for refined freezing techniques to maintain and potentially enhance semen quality for reproductive use.

Evaluation of the effect of lecithin and nanolecithin in repairing membrane damage, maintaining membrane integrity, and improving human sperm function in the freezing-thawing process

PURPOSE

Our study aimed to evaluate the effects of lecithin nanoparticles on sperm quality during cryopreservation.

METHODS

In phase one, sperm-freezing media were prepared with lecithin concentrations (0.5%, 1%, and 2%) and lecithin nanoparticles of various sizes (50-100, 100-200, and ≥ 200 nm). Post-thaw, sperm motility, viability, mitochondrial membrane potential (MMP), lipid peroxidation (measured by malondialdehyde, MDA), and DNA fragmentation were evaluated. In phase two, the acrosomal reaction was assessed in the best and worst-performing groups from phase one. DiI labeling detected interactions between lecithin nanoparticles and the sperm membrane. Field emission scanning electron microscopy (FESEM) examined the sperm membrane's surface structure and lecithin binding sites. Atomic force microscopy (AFM) assessed height differences in the sperm surface layer in the best-performing group from phase one.

RESULTS

The group treated with 1% lecithin nanoparticles (50-100 nm) showed significantly increased viability post-thaw compared to other groups, with reduced DNA fragmentation and MDA levels. While motility significantly decreased in all groups compared to before freezing levels, lower concentrations, and smaller particle sizes yielded better results. MMP also significantly decreased across all groups with no significant differences. The acrosomal reaction significantly decreased with 1% lecithin nanoparticles (50-100 nm) compared to the 2% (≥ 200 nm) group. DiI-labeled nanoparticles and FESEM revealed that lecithin nanoparticles primarily bound to and infiltrated the sperm membrane, particularly in the head and postacrosomal regions.

CONCLUSIONS

Lecithin nanoparticles effectively bind to the sperm membrane, protecting it during the freeze-thaw process and improving sperm viability.

Current State and Challenges of Tissue and Organ Cryopreservation in Biobanking

Recent years have witnessed significant advancements in the cryopreservation of various tissues and cells, yet several challenges persist. This review evaluates the current state of cryopreservation, focusing on contemporary methods, notable achievements, and ongoing difficulties. Techniques such as slow freezing and vitrification have enabled the successful preservation of diverse biological materials, including embryos and ovarian tissue, marking substantial progress in reproductive medicine and regenerative therapies. These achievements highlight improved post-thaw survival and functionality of cryopreserved samples. However, there are remaining challenges such as ice crystal formation, which can lead to cell damage, and the cryopreservation of larger, more complex tissues and organs. This review also explores the role of cryoprotectants and the importance of optimizing both cooling and warming rates to enhance preservation outcomes. Future research priorities include developing new cryoprotective agents, elucidating the mechanisms of cryoinjury, and refining protocols for preserving complex tissues and organs. This comprehensive overview underscores the transformative potential of cryopreservation in biomedicine, while emphasizing the necessity for ongoing innovation to address existing challenges.

Exploring the full potential of sperm function with nanotechnology tools

Sperm quality is essential to guarantee the success of assisted reproduction. However, selecting high-quality sperm and maintaining it during (cryo)preservation for high efficiency remains challenging in livestock reproduction. A comprehensive understanding of sperm biology allows for better assessment of sperm quality, which could replace conventional sperm analyses used today to predict fertility with low accuracy. Omics approaches have revealed numerous biomarkers associated with various sperm phenotypic traits such as quality, survival during storage, freezability, and fertility. At the same time, nanotechnology is emerging as a new biotechnology with high potential for use in preparing sperm intended to improve reproduction in livestock. The unique physicochemical properties of nanoparticles make them exciting tools for targeting (e.g., sperm damage and sexing) and non-targeting bioapplications. Recent advances in sperm biology have led to the discovery of numerous biomarkers, making it possible to target specific subpopulations of spermatozoa within the ejaculate. In this review, we explore potential biomarkers associated with sperm phenotypes and highlight the benefits of combining these biomarkers with nanoparticles to further improve sperm preparation and technology.

Supplementation of sperm cryopreservation media with H2S donors enhances sperm quality, reduces oxidative stress, and improves in vitro fertilization outcomes

Cryopreservation of sperm can cause oxidative stress and damage, leading to decreased different functional parameters and fertilization potential. In this study, we evaluated two types of H2S donors: NaHS, a fast-releasing donor, and GYY4137, a slow-releasing donor during cryopreservation of goat sperm. Initially, we determined that 1.5 and 3 μM NaHS, and 15 and 30 μM GYY4137 are optimal concentrations that improved different sperm functional parameters including motility, viability, membrane integrity, lipid peroxidation, and ROS production during incubation at 38.5 °C for 90 min. We subsequently evaluated the impact of the optimal concentration of NaHS and GYY4137 supplementation on various functional parameters following thawing during cryopreservation. Our data revealed that supplementation of extender improved different parameters including post-thaw sperm motility, viability, membrane integrity, and reduced DNA damage compared to the frozen-thawed control group. The supplementation also restored the redox state, decreased lipid peroxidation, and improved mitochondrial membrane potential in the thawed sperm. Finally, we found that supplementation of the extender with NaHS and GYY4137 enhanced IVF outcomes in terms of blastocyst rate and quality of blastocysts. Our results suggest that both donors can be applied for cryopreservation as antioxidants to improve sperm quality and IVF outcomes of frozen-thawed goat sperm.

A Pilot Analysis of Whole Transcriptome of Human Cryopreserved Sperm

Sperm cryopreservation is a procedure widely used to store gametes for later use, to preserve fertility in patients prior to gonadotoxic treatments or surgery, and for sperm donation programs. The purpose of the study was to assess the impact of cryopreservation on human sperm transcriptome. Semen samples were collected from 13 normospermic men. Each sample was divided into two aliquots. The total RNA was immediately extracted from one aliquot. The second aliquot was frozen and total RNA was extracted after a week of storage in liquid nitrogen. The RNA samples were randomized in four pools, each of six donors, and analyzed by microarrays. The paired Significance Analysis of Microarray was performed. We found 219 lower abundant transcripts and 28 higher abundant transcripts in cryopreserved sperm than fresh sperm. The gene ontology analysis disclosed that cryopreservation alters transcripts of pathways important for fertility (i.e., spermatogenesis, sperm motility, mitochondria function, fertilization, calcium homeostasis, cell differentiation, and early embryo development), although the increase of some transcripts involved in immune response can compensate for the harmful effects of freezing.

Addition of Vitamin C Mitigates the Loss of Antioxidant Capacity, Vitality and DNA Integrity in Cryopreserved Human Semen Samples

Cryopreservation of human spermatozoa is a necessity for males suffering from infertility who cannot produce fresh semen for insemination. However, current ART cryopreservation protocols are associated with losses of sperm motility, vitality and DNA integrity, which are thought to be linked to the induction of oxidative damage and the toxic properties of commercial cryoprotectants (CPAs). Preventing or mitigating these losses would be hugely beneficial to sperm survival during ART. Therefore, in this in vitro investigation, lipid peroxidation, production of reactive oxygen species, movement characteristics, antioxidant capacity, vitality, and DNA integrity were examined in semen samples both pre- and post-cryopreservation with CPA supplementation. The findings revealed a 50% reduction in antioxidant capacity with CPA addition, which was accompanied by significant increases in generation of reactive oxygen species and formation of lipid aldehydes. These changes were, in turn, correlated with reductions in sperm viability, motility and DNA integrity. Antioxidant supplementation generated bell-shaped dose-response curves with both resveratrol and vitamin C, emphasising the vulnerability of these cells to both oxidative and reductive stress. At the optimal dose, vitamin C was able to significantly enhance vitality and reduce DNA damage recorded in cryopreserved human spermatozoa. An improvement in sperm motility did not reach statistical significance, possibly because additional pathophysiological mechanisms limit the potential effectiveness of antioxidants in rescuing this aspect of sperm function. The vulnerability of human spermatozoa to reductive stress and the complex nature of sperm cryoinjury will present major challenges in creating the next generation of cryoprotective media.

Cryopreservation of black seabream (Acanthopagrus schlegelii) sperm

In recent years, biotechnology has had a significant impact on the aquaculture industry, particularly in the field of breeding. Molecular selection breeding has emerged as a novel approach to breeding. Reducing the cost of genetic information for individuals with desirable traits after breeding has become an important research direction. Cryopreservation technology allows bypassing time and space constraints in genetic breeding, simplifying broodstock management. This study presents a detailed cryopreservation method for black seabream sperm, evaluating extender type, glucose concentration, cryoprotectant type and concentration, sperm-dilution ratio, and cooling protocols. Sperm motility parameters were analyzed using computer-assisted sperm analysis (CASA) before and after two days of freezing. This involved using an RS solution with a glucose concentration of 15 g/L and adding a 5% final concentration of EG as the sperm cryoprotectant. After mixing the sperm and solution at a ratio of 1:2, we subjected it to 5 min fumigation at 5 cm above the liquid nitrogen surface before plunging it into the nitrogen. Sperm motility reached 85.46 ± 7.32% after two days. Various enzymatic activities showed changes over 20 days post-cryopreservation. This improved cryopreservation protocol for black seabream sperm is beneficial for genetic breeding and reproduction and provides reference for studying the cryodamage mechanisms of black seabream sperm.

Cryopreservation of Human Spermatozoa: Functional, Molecular and Clinical Aspects

Cryopreservation is an expanding strategy to allow not only fertility preservation for individuals who need such procedures because of gonadotoxic treatments, active duty in dangerous occupations or social reasons and gamete donation for couples where conception is denied, but also for animal breeding and preservation of endangered animal species. Despite the improvement in semen cryopreservation techniques and the worldwide expansion of semen banks, damage to spermatozoa and the consequent impairment of its functions still remain unsolved problems, conditioning the choice of the technique in assisted reproduction procedures. Although many studies have attempted to find solutions to limit sperm damage following cryopreservation and identify possible markers of damage susceptibility, active research in this field is still required in order to optimize the process. Here, we review the available evidence regarding structural, molecular and functional damage occurring in cryopreserved human spermatozoa and the possible strategies to prevent it and optimize the procedures. Finally, we review the results on assisted reproduction technique (ARTs) outcomes following the use of cryopreserved spermatozoa.