Dynamic assessment of human sperm DNA damage III: the effect of sperm freezing techniques

Effects of Slow Freezing and Vitrification of Human Semen on Post-Thaw Semen Quality and miRNA Expression

Semen cryopreservation has played an important role in medically assisted reproduction for decades. In addition to preserving male fertility, it is sometimes used for overcoming logistical issues. Despite its proven clinical usability and safety, there is a lack of knowledge of how it affects spermatozoa at the molecular level, especially in terms of non-coding RNAs. Therefore, we conducted this study, where we compared slow freezing and vitrification of good- and poor-quality human semen samples by analyzing conventional sperm quality parameters, performing functional tests and analyzing the expression of miRNAs. The results revealed that cryopreservation of normozoospermic samples does not alter the maturity of spermatozoa (protamine staining, hyaluronan binding), although cryopreservation can increase sperm DNA fragmentation and lower motility. On a molecular level, we revealed that in both types of cryopreservation, miRNAs from spermatozoa are significantly overexpressed compared to those in the native semen of normozoospermic patients, but in oligozoospermic samples, this effect is observed only after vitrification. Moreover, we show that expression of selected miRNAs is mostly overexpressed in native oligozoospermic samples compared to normozoospermic samples. Conversely, when vitrified normozoospermic and oligozoospermic samples were compared, we determined that only miR-99b-5p was significantly overexpressed in oligozoospermic sperm samples, and when comparing slow freezing, only miR-15b-5p and miR-34b-3p were significantly under-expressed in oligozoospermic sperm samples. Therefore, our results imply that cryopreservation of normozoospermic sperm samples can modulate miRNA expression profiles in spermatozoa to become comparable to those in oligozoospermic samples.

Sperm DNA Fragmentation after Cryopreservation and Sperm Selection Has No Implications for Clinical Pregnancies and Live Births after Intrauterine Insemination with Donor Sperm

Intrauterine insemination with donor sperm (IUI-D) requires multiple in vitro manipulations such as sperm selection and cryopreservation during which spermatozoa may be exposed to oxidative stress (OS) and other insults that may produce potential damage including sperm DNA fragmentation (SDF). High levels of SDF, referring to damage or breaks in the genetic material of sperm cells, are linked to an increased risk of reproductive failure. This retrospective, observational study set out to evaluate whether SDF assessment could predict clinical outcome in an IUI-D program, where sperm donors are selected on strict conventional semen parameters. A total of 18 donors and 106 recipients were matched for IUI-D. Out of 429 cycles, 100 (23.3%) resulted in clinical pregnancy. We counted 78 live births (18.2% of cycles), while 20 pregnancies ended in miscarriage (4.7% of cycles), 1 in extra-uterine pregnancy and 1 in stillbirth. Female age significantly influenced clinical pregnancy and miscarriage rates. SDF increased after cryopreservation (26.3 ± 14.5%; p < 0.001) and more so after post-thaw density gradient (34.9 ± 22.1%; p = 0.04) without affecting clinical pregnancy (OR [95% CI] 1.01 [0.99; 1.02]; p = 0.27), live birth (1.00 [0.99; 1.02]; p = 0.72) and miscarriage rates (1.02 [1.00; 1.05]; p = 0.08). The implications of our findings extend to a better selection of sperm donors and a better sperm preparation technique tailored to the donor semen's properties in order to maximize the chances of a favorable treatment outcome.

The Role of Selected Natural Biomolecules in Sperm Production and Functionality

Emerging evidence from in vivo as well as in vitro studies indicates that natural biomolecules may play important roles in the prevention or management of a wide array of chronic diseases. Furthermore, the use of natural compounds in the treatment of male sub- or infertility has been proposed as a potential alternative to conventional therapeutic options. As such, we aimed to evaluate the effects of selected natural biomolecules on the sperm production, structural integrity, and functional activity. At the same time, we reviewed their possible beneficial or adverse effects on male reproductive health. Using relevant keywords, a literature search was performed to collect currently available information regarding molecular mechanisms by which selected natural biomolecules exhibit their biological effects in the context of male reproductive dysfunction. Evidence gathered from clinical trials, in vitro experiments and in vivo studies suggest that the selected natural compounds affect key targets related to sperm mitochondrial metabolism and motion behavior, oxidative stress, inflammation, DNA integrity and cell death. The majority of reports emphasize on ameliorative, stimulating and protective effects of natural biomolecules on the sperm function. Nevertheless, possible adverse and toxic behavior of natural compounds has been indicated as well, pointing out to a possible dose-dependent impact of natural biomolecules on the sperm survival and functionality. As such, further research leading to a deeper understanding of the beneficial or adverse roles of natural compounds is necessary before these can be employed for the management of male reproductive dysfunction.

Protective Effect of Cerium Oxide Nanoparticles on Human Sperm Function During Cryopreservation

The generation of reactive oxygen species during cryopreservation of human sperm has negative effects on the consistency of the thawed sperm. The antioxidant properties of cerium oxide nanoparticles (CeO₂NPs) may be useful for reducing cryodamage in thawed sperm. This research was conducted to determine the effects of CeO₂NPs on the quality and function of human sperm after thawing. Samples of semen obtained from 20 normozoospermic individuals were allocated to the following four groups: fresh, frozen control (sperm not treated with CeO₂NPs), and those exposed to 0.1 μg/mL CeO₂NPs (CeO₂-0.1), 1 μg/mL CeO₂NPs (CeO₂-1), and 5 μg/mL CeO₂NPs (CeO₂-5). Sperm parameters of motility, viability, membrane integrity, DNA fragmentation, protamination, malondialdehyde (MDA) levels, mitochondria membrane potential, and morphology were evaluated after the freezing-thawing process. The results showed that 0.1 μg/mL CeO₂NPs significantly (p < 0.05) improved the following human sperm parameters after thawing: progressive (44.6% ± 1.14% vs. 36.2% ± 1.24%) and total motility (60.9% ± 2.5% vs. 51.3% ± 2.5%), viability (67.9% ± 1.5% vs. 58.1% ± 1.5%), membrane functionality (66.1% ± 1.85% vs. 55.4% ± 1.85%), DNA integrity (30.8% vs. 24.04%), and protamination (69.85% ± 2.09% vs. 57.2% ± 2.09%) compared with the frozen control group. We observed the lowest MDA levels in the CeO₂-0.1 (3.06 ± 0.25 nmol/mL), CeO₂-1 (3.1 ± 0.25 nmol/mL), and CeO₂-5 (3.08 ± 0.25 nmol/mL) groups compared with the frozen control group (3.72 ± 0.25). Different concentrations of CeO₂NPs did not significantly change sperm normal morphology and mitochondria activity (p < 0.05).

Social sperm freezing

Increased paternal age has been associated with lower fertility and higher genetic risk for the offspring. One way to prevent these consequences is to freeze sperm at a young age. Social sperm freezing could be developed in a way similar to social oocyte freezing. The main difference between freezing oocytes and sperm is that social sperm freezing is much less focussed on fertility preservation and much more on avoiding increased genetic risk. Contrary to what some people seem to believe, sperm freezing is more complicated than it looks at first sight. This article considers three practical aspects: freezing, storage and testing. It is concluded that the remedy (cryopreservation) may itself cause damage to the quality of the spermatozoon and to its genetic integrity, thus undoing the possible benefits in terms of fertility and health of offspring.