Effect of different glycerol concentrations on phosphatidylserine translocation and mitochondrial membrane potential in chilled boar spermatozoa

Cold-induced damage in boar sperm cooled to 5°C in Lactose Egg Yolk (LEY) medium with different Glycerol concentrations

Boar sperm is highly susceptible to cold damage. When temperature drops to 5°C, the plasmatic membrane is destabilized. The freezing process causes a reduction of the fertility window because frozen/thawed boar sperm has less survivability. The aim of this work was to analyze the effect on sperm characteristics and response to capacitation stimuli of cooling to 5°C using a controlled protocol. Also, we evaluated if the addition of Glycerol 2% or 3% at 5°C was able to modify these parameters. For this purpose, we assessed motility, plasmatic membrane integrity and acrosomal membrane status. Capacitation was induced using Tyrode´s capacitating medium (TCM) and assessed by chlortetracycline stain and induction of acrosomal reaction with Progesterone. Motility patterns were analyzed using a CASA system. These tests were performed at three different points of the freezing curve: 37°C; 17°C and 5°C. Response to TCM vs TBM was only significant at 37°C. While at 37°C and 17°C capacitated sperm was below 20%, at 5°C reached 50% both in the TBM and TCM. CASA analysis showed that spermatozoa exposed to TCM had higher LIN and WOB than those in TBM. All parameters were similar in the Glycerol concentrations studied. These results suggest that the chilling process may be causing an effect similar to cryocapacitation along the cooling curve, starting subtle at 17°C and reaching 50% of the sperm population at 5°C, being independent of Glycerol concentration.

Kojic acid inhibits pig sperm apoptosis and improves capacitated sperm state during liquid preservation at 17°C

The parameters of sperm apoptosis and capacitation during liquid storage at 17°C can indicate the quality of pig sperm and the potential development of early embryos. However, the effect of kojic acid (KA) on semen preservation and its mechanism has not been fully understood. In this study, we discovered that adding KA to the diluent improved the antioxidant capacity of sperm mitochondria, maintained the normal structure of sperm mitochondria, and reduced sperm apoptosis. Western blot analysis revealed that KA prevented the release of Cytochrome c from mitochondria to the cytoplasm, reduced the expression of pro-apoptosis proteins cleaved Caspase-3 and cleaved Caspase-9, and increased the expression of the antiapoptosis protein Bcl-XL. Furthermore, KA also enhanced the motility parameters, oxidative phosphorylation level, adenosine triphosphate level, and protein tyrosine phosphorylation of capacitated sperm, while preserving the acrosome integrity and plasma membrane integrity of capacitated sperm. In conclusion, this study offers new insights into the molecular mechanism of how KA inhibits porcine sperm apoptosis and improves capacitated sperm parameters. Additionally, it suggests that KA can serve as an alternative to antibiotics.

Is glycerol a good cryoprotectant for sperm cells? New exploration of its toxicity using avian model

Glycerol is a cryoprotectant used widely for the cryopreservation of animal sperm, but it is linked to a decrease in fertility. The mechanism underlying the negative effects of glycerol remains unclear. Therefore, in this study, we aimed to gain a better understanding by using the chicken model. First, we investigated the impact of increasing the concentration of glycerol during insemination on hen fertility. Our findings revealed that 2% glycerol resulted in partial infertility, while 6% glycerol led to complete infertility. Subsequently, we examined the ability of sperm to colonize sperm storage tubules (SST) during in vivo insemination and in vitro incubation. The sperm used in the experiment were stained with Hoechst and contained 0, 2, or 6% glycerol. Furthermore, we conducted perivitelline membrane lysis tests and investigated sperm motility, mitochondrial function, ATP concentration, membrane integrity, and apoptosis after 60 min of incubation with different glycerol concentrations (0%, 1%, 2%, 6%, and 11%) at two temperatures to simulate pre-freezing (4 °C) and post-insemination (41 °C) conditions. Whereas 2% glycerol significantly reduced 50% of sperm containing SST, 6% glycerol completely inhibited SST colonization in vivo. On the other hand, in vitro incubation of sperm with SST revealed no effect of 2% glycerol, and 6% glycerol showed only a 17% reduction in sperm-filled SST. Moreover, glycerol reduced sperm-egg penetration rates and also affected sperm motility, bioenergetic metabolism, and cell death at 4 °C. These effects were observed when the concentration of glycerol exceeded 6%. Furthermore, at 41 °C, glycerol caused even greater damage, particularly in terms of reducing sperm motility. These data altogether reveal important effects of glycerol on sperm biology, sperm migration, SST colonization, and oocyte penetration. This suggests that glycerol plays a role in reducing fertility and presents opportunities for improving sperm cryopreservation.

Research of the survival of a consortium of Zygosaccharomyces kombuchaensis yeast and Gluconoacetobacter xylinus bacteria during frozen storage using various protective media

In the present study the survival of the consortium of yeast and bacteria using protective media was investigated. The protective medium consisting of 1 % gelatin, 5 % monosodium glutamate and 5 % sucrose provides the best preservation of living cells of the consortium and allows stabilization of cells for up to 100 days at storage temperatures from -2 °C to -10 °C. The projective medium consisting of 1 % gelatin and 10 % sucrose provides effective storage of the cells at t=-2 °C for 100 days; t=-5 °C – 80 days; t=-10 °C – 60 days. The projective medium of skimmed milk and 7.5 % glucose ensures effective storage of the cells of the consortium at t=-2 °C for 100 days; t=-5 °C – 80 days; t=-10 °C – 80 days. The information obtained is interesting for following researches of the development of technologies for the bioconversion of plant materials.