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.

Several clinical laboratories assess sperm DNA fragmentation (sDF) in addition to semen analysis in male infertility diagnosis. Among tests evaluating sDF, TUNEL (Terminal deoxynucleotidyl transferase dUTP nick end labeling) and SCD (Sperm Chromatin Dispersion) are widely used. Our lab developed a modified version of TUNEL (TUNEL/PI) able to distinguish two sperm populations (PI Brighter and PI Dimmer) differently associated with sperm viability and reproductive outcomes. The aim of this study was to compare sDF levels detected by SCD and TUNEL/PI in the semen samples from 71 male subjects attending our Andrology Laboratory. Our results demonstrate that SCD is less sensitive in determining sDF compared to TUNEL/PI. The statistically significant positive correlation found between sDF evaluated by SCD and PI Dimmer (consisting of all dead spermatozoa) suggests that SCD mainly detects sDF in unviable spermatozoa. We confirmed that most spermatozoa detected by SCD are unviable by performing SCD after incubation in hypo-osmotic medium to discriminate viable and unviable cells in 52 samples. Such results might explain the lower ability of this test in discriminating couples having successful ART outcomes demonstrated in published metanalyses. Overall, our results indicate that SCD is less sensitive in evaluating sDF for diagnostic purposes.

Sperm preparation is a critical step in assisted reproduction, aiming to isolate spermatozoa with optimal characteristics and high fertilizing potential. Traditional sperm selection methods involve centrifugation, which may cause sperm damage. Microfluidic sperm sorting (MSS) offers an alternative approach, mimicking the female reproductive tract environment, avoiding centrifugation, and reducing manipulation and processing time. This study aims to compare the performance of MSS and Swim-up (SU) in 26 normozoospermic, 31 hyperviscous normozoospermic, 15 oligozoospermic, and 9 asthenozoospermic subjects. Semen samples were collected from male subjects undergoing routine semen analysis at Careggi University Hospital, Florence. Sperm selection was carried out using both SU and MSS. The parameters assessed included sperm motility, viability, concentration, kinematics, DNA fragmentation (sDF), chromatin compaction, and oxidative status. Both SU and MSS improved sperm characteristics compared to unselected samples. MSS isolated high-quality spermatozoa with lower sDF and higher chromatin compaction than SU, not only in normozoospermic samples but also in samples with semen defects like hyperviscosity, low concentration and/or motility, and high sDF. In conclusion, the use of microfluidics may enhance the chances of successful fertilization and improve reproductive outcomes, especially for individuals with compromised semen quality where conventional methods may fail.

Benzo(a)pyrene (BaP) is considered one of the most dangerous air pollutants for adverse health effects, including reproductive toxicity. It is found both in male and female reproductive fluids likely affecting spermatozoa after the selection process through cervical mucus, a process mimicked in vitro with the swim-up procedure. In vitro effects of BaP (1, 5, 10 µM) were evaluated both in unselected and swim-up selected spermatozoa after 3 and 24 h of incubation. BaP reduced total, progressive and hyperactivated motility and migration in a viscous medium both in swim-up selected and unselected spermatozoa. Viability was not significantly affected in swim-up selected but was reduced in unselected spermatozoa. In swim-up selected spermatozoa, increases in the percentage of spontaneous acrosome reaction and DNA fragmentation were observed after 24 h of incubation, whereas no differences between the control and BaP-treated samples were observed in caspase-3 and -7 activity, indicating no effects on apoptotic pathways. ROS species, evaluated by staining with CellROX^® Orange and Dihydroethidium, did not differ in viable spermatozoa after BaP treatment. Conversely, the percentage of unviable ROS-positive spermatozoa increased. Our study suggests that BaP present in male and female genital fluids may heavily affect reproductive functions of human spermatozoa.

Background: Sperm cryopreservation is recommended to preserve male fertility for cancer patients or other medical conditions at risk of sperm decline. Whether motility and viability recovery rates vary depending on the medical conditions requiring cryopreservation is poorly known. We report here on the 24-year experience of our semen bank. Methods: Motility and viability recovery rates were evaluated in 1973 collections from patients with various medical conditions and 67 collections from donors, and the results were related to basal semen quality. Results: Motility and viability recovery were highly related to basal semen quality and varied between cancer and non-cancer conditions, independently of the duration of cryopreservation and patient age. In samples with a sperm number below 2 × 10⁶/mL, recovery rates approximated to zero. The highest recovery rates were found in donor collections. Cut-off values for the recovery of at least 1% motile spermatozoa were established based on initial semen quality. Conclusions: Our results indicate that the occurrence of any pathological or medical condition resulted in lower recovery rates with respect to donors, indicating that intrinsic sperm characteristics drive susceptibility to cryodamage. Established cut-off values for motility recovery can be useful for patient counseling as well as for ART laboratories to decide the type of procedure.

Infertility is a widespread global problem, with a male factor contributing to approximately 40–50% of cases. Several studies have investigated the involvement of adipokines in reproductive functions, but only a few have investigated their role in the male reproductive component. Collectively, adipokines are present in human sperm and most of them are expressed in the male genital tract. Some authors report that adiponectin, in contrast with other adipokines such as resistin or chemerin, has a positive effect on spermatogenesis. Although the pathophysiological role of adipokines in sperm is not yet fully understood, they could influence sperm functionality and could be potential biomarkers of male fertility. High levels of sperm DNA fragmentation have been associated with several adverse reproductive outcomes, although studies have shown conflicting results. Another critical factor in male infertility is oxidative stress, which negatively affects sperm function and viability, also because it triggers DNA alterations, lipid peroxidation and alterations in protein expression, compromising fertilization potential. To better understand the correlation between sperm DNA fragmentation, adiponectin and oxidative stress and their role in clinical practice, we evaluated these parameters in the seminal plasma of males who presented to the infertility study center of Careggi University Hospital of Florence. By accurately evaluating these parameters and their possible correlation, it will be possible to personalize treatment for individual patients.