Co-incubation of spermatozoa with human follicular fluid reduces sperm DNA fragmentation by mitigating DNase activity in the seminal plasma

Extend the Survival of Human Sperm In Vitro in Non-Freezing Conditions: Damage Mechanisms, Preservation Technologies, and Clinical Applications

Preservation of human spermatozoa in vitro at normothermia or hypothermia maintaining their functions and fertility for several days plays a significant role in reproductive biology and medicine. However, it is well known that human spermatozoa left in vitro deteriorate over time irreversibly as the consequence of various stresses such as the change of osmolarity, energy deficiency, and oxidative damage, leading to substantial limitations including the need for semen examinations, fertility preservation, and assisted reproductive technology. These problems may be addressed with the aid of non-freezing storage techniques. The main and most effective preservation strategies are the partial or total replacement of seminal plasma with culture medium, named as extenders, and temperature-induced metabolic restriction. Semen extenders consist of buffers, osmolytes, and antioxidants, etc. to protect spermatozoa against the above-mentioned adverse factors. Extended preservation of human spermatozoa in vitro has a negative effect on sperm parameters, whereas its effect on ART outcomes remains inconsistent. The storage duration, temperature, and pre-treatment of semen should be determined according to the aims of preservation. Advanced techniques such as nanotechnology and omics have been introduced and show great potential in the lifespan extension of human sperm. It is certain that more patients will benefit from it in the near future. This review provided an overview of the current knowledge and prospects of prolonged non-freezing storage of human sperm in vitro.

DNase activity in human seminal plasma and follicular fluid and its inhibition by follicular fluid chelating agents

RESEARCH QUESTION

What is the mechanism by which human follicular fluid inhibits seminal plasma DNase activity?

DESIGN

Human genomic DNA was incubated with human follicular fluid and seminal plasma (reaction mixture) under different experimental conditions; increasing volumes of human follicular fluid; proteinase K digested or heat inactivated human follicular fluid; and the addition of Ca²⁺ or Mg²⁺ to the reaction mixture.

RESULTS

Increasing volume of human follicular fluid resulted in a dose-dependent inhibition of seminal plasma DNase activity. Inhibition was not caused by proteins in the human follicular fluid as digestion with proteinase K or heat inactivation of human follicular fluid failed to abolish its inhibitory effect. Addition of divalent cations resulted in a reversion of the inhibitory effect, providing evidence that human follicular fluid inhibition of seminal plasma DNase activity seems to be mediated by a compound with chelating activity. Furthermore, incubation of genomic DNA with human follicular fluid in the presence of divalent cations served to elicit the existence of DNase activity.

CONCLUSIONS

Human follicular fluid seems to contain a molecule or molecules with chelating capacity that inhibits DNase activity of both follicular fluid and seminal plasma. Our findings provide new insight to understanding sperm preservation and the physiology of fertilization biology.

Microencapsulation of human spermatozoa increases membrane stability and DNA longevity

The microencapsulation of spermatozoa offers potential benefits for maintaining sperm survival in vitro. The technique has also resulted in the production of offspring in several domestic animal species, but as yet, it has not been successfully applied in human reproductive medicine. This study examined the effect of alginic acid microencapsulation on human sperm membrane integrity (viability) and sperm DNA fragmentation (SDF) following storage for 24 hr at 37°C. The cumulative sperm viability (Log-rank, Mantel-Cox; Chi-square = 114.95, p = .000) and cumulative sperm DNA fragmentation (Log-rank, Mantel-Cox; Chi-square = 187.86, p = .000) of encapsulated spermatozoa were substantially improved when compared to control spermatozoa. Significant differences in the dynamic behaviour of different individuals were only apparent for sperm viability in microencapsulated samples (p = .021) while no significant differences were observed in control spermatozoa (p = .245); the equivalent comparison for SDF showed no differences (control p = .320; microencapsulated p = .432). We present potential scenarios for the use of microencapsulated human spermatozoa in reproductive medicine.