L-proline as a novel additive to cryopreservation media improved post-thaw quality of human spermatozoon via reducing oxidative stress

Sperm chromatin: Evaluation, epigenetic signatures and relevance for embryo development and assisted reproductive technology outcomes

Sperm chromatin is distinct from somatic cell chromatin, as a result of extensive remodeling during the final stages of spermatogenesis. In this process, the majority of histones is replaced with protamines. The chromatin is consequently highly condensed and inert, which facilitates protection of the DNA. The sperm epigenomic landscape is shaped by histone retention, histone and protamine modification, DNA methylation, and RNAs. In recent years, sperm chromatin integrity and its epigenetic marks have been increasingly studied, and the constitution of sperm chromatin is steadily being uncovered. This growing body of research prompts assessment of the frequently overlooked involvement of sperm in fertility and embryonic development. Moreover, numerous endogenous and exogenous factors are known to affect sperm chromatin, which may in turn impact the reproductive success. Concerns have been raised about the effects of assisted reproductive technology (ART) on the sperm epigenome, embryonic development and offspring health. This review examines the structure and epigenetic signatures of sperm chromatin in the context of fertility and early embryonic development. Additionally, sperm chromatin evaluation and causes of aberrant integrity are outlined. Building on the knowledge discussed in the current review, future research should aim to elucidate the intricate relationship between all aspects of sperm chromatin and embryo development. This could lead to the uncovering of new targets for treating infertility, as well as the acquisition of much needed insights into the possible reciprocal association between ART and sperm chromatin integrity.

Microplate-Based Cryopreservation of Adherent-Cultured Human Cell Lines Using Amino Acids and Proteins

With the progression of regenerative medicine and cell therapy, the importance of cryopreservation techniques for cultured cells continues to rise. Traditional cryoprotectants, such as dimethyl sulfoxide and glycerol, are effective in cryopreserving suspended cells, but they do not demonstrate sufficient efficacy for two-dimensional (2D)-cultured cells. In the past decade, small molecules and polymers have been studied as cryoprotectants. Some L-amino acids have been reported to be natural and biocompatible cryoprotectants. However, the cryoprotective effects of D-amino acids have not been investigated for such organized cells. In the present study, the cryoprotective effects of D- and L-amino acids and previously reported cryoprotectants were assessed using HepG2 cells cultured on a microplate without suspending the cells. d-Proline had the highest cryoprotective effect on 2D-cultured cells. The composition of the cell-freezing solution and freezing conditions were then optimized. The d-proline-containing cell-freezing solution also effectively worked for other cell lines. To minimize the amount of animal-derived components, fetal bovine serum in the cell freezing solution was substituted with bovine serum albumin and StemFit (a commercial supplement for stem cell induction). Further investigations on the mechanism of cryopreservation suggested that d-proline protected enzymes essential for cell survival from freeze-induced damage. In conclusion, an effective and xeno-free cell-freezing solution was produced using d-proline combined with dimethyl sulfoxide and StemFit for 2D-cultured cells.

L-Proline: A Promising Tool for Boosting Cryotolerance and Fertilizing Ability of Cryopreserved Sperm in Animals

Sperm cryopreservation technology significantly contributes to the safeguarding of genetic resources, particularly for endangered species, and supports the use of artificial insemination in domestic animals. Therefore, cryopreservation can negatively affect sperm health and function leading to reduce the freezing ability and fertility potential. Therefore, it is essential to prioritize the improvement of cryotolerance in cryopreserved sperm to enhance reproductive efficiency and ensure sustainability in livestock herds. The main reason for sperm dysfunction after thawing may be related to the excessive amount of oxidative stress (OS) produced during cryopreservation. Scientists have different ways for counteracting this OS including the use of plant extracts, enzymes, minerals, anti-freezing proteins, and amino acids. Recently, one such amino acid is L-proline (LP), which has multiple roles such as osmotic and OS defense, nitrogen, and carbon metabolism, as well as cell survival and signaling. LP has been found in seminal plasma and has recently been added to the freezing extender to improve the various post-thaw parameters of sperm. This improvement is related to the ability of LP to reduce the OS, sustain the plasma membrane and to act as an osmoregulatory agent. Moreover, LP can suppress cell apoptosis by modulating intracellular redox in sperm. This review addresses the ongoing research on the addition of L-proline as an osmoregulatory agent in freezing extenders to increase the cryotolerance of animal spermatozoa to freeze-thaw.

Advances in Cryopreservatives: Exploring Safer Alternatives

Cryopreservation of cells, tissues, and organs is widely used in the biomedical and research world. There are different cryopreservatives that are used for this process; however, many of them, such as DMSO, are used despite the problems they present, mainly due to the toxicity it presents to certain types of samples. The aim of this Review is to highlight the different types of substances used in the cryopreservation process. It has been shown that some of these substances are well-known, as in the case of the families of alcohols, sugars, sulfoxides, etc. However, in recent years, other compounds have appeared, such as ionic liquids, deep eutectic solvents, or certain polymers, which open the door to new cryopreservation methods and are also less toxic to frozen samples.

Effect of L-proline on sperm quality during cryopreservation of boar semen

L-proline has been reported to be useful in semen cryopreservation. However, its use has rarely been reported in the freezing of boar semen. The objective of this study was to evaluate the effects of different concentrations of L-proline (0, 10, 30, 50, and 90 mM) on the quality of boar semen after freezing and thawing. Semen samples from boars (n = 6) were frozen using freezing extenders with added concentrations of L-proline. Total sperm motility, progressive motility, survival time at 37 °C, acrosome integrity, mitochondrial activity, DNA integrity, the content of the lipid peroxidation product malondialdehyde (MDA), total antioxidant capacity (T-AOC) and, expression levels of apoptosis protein (cleaved caspase 3 and Bax) were evaluated after thawing. The results showed that total sperm viability (73.96% vs. 63.58%) and progressive motility (56.88% vs. 47.26%) after thawing were significantly higher in the 10 mM L-proline treatment group than in the control group. The survival time at 37 °C and the total motility of sperm in the 10 mM group within one hour after thawing were significantly higher than in the control group. Acrosome integrity and mitochondrial activity of sperm in the 10 mM group were significantly higher than those in the control, 50 mM, and 90 mM groups. The DNA integrity rate in the 10 mM group was significantly higher than in the control group. The L-proline treatment did not affect sperm MDA content or T-AOC. The expression levels of apoptosis protein (cleaved caspase 3 and Bax) in the 10 mM L-proline supplemented group were lower than those in the control group. In conclusion, the freezing extender containing 10 mM L-proline improved semen quality after freezing and thawing and thus would be a useful reagent for boar semen cryopreservation.

Combined addition of L-carnitine and L-proline improves cryopreservation of dairy goat semen

Cryopreservation of semen renders artificial insemination easier and cheaper compared to use of fresh semen. However, the cellular oxidative stress, toxicity of cryoprotectants, and osmotic imbalance may lead to a decline in semen quality and fertilization ability during the process of cryopreservation. L-carnitine and L-proline have been demonstrated to possess effective antioxidant properties in cryopreservation, with the latter also exhibiting excellent permeability and thus being utilized as a permeable cryoprotectant in the field. The aim of this study was to investigate the effects of LC and LP on cryopreservation of semen of dairy goats. After thawing, sperm motility, membrane integrity, and acrosome integrity rate of cryopreserved semen treated with LC (50 mM) were significantly higher compared to the untreated control samples. Based on this premise, we conducted experiments to assess the cryoprotective efficacy of different concentrations of LP. The findings demonstrated that the inclusion of 50 mM LP resulted in improved sperm motility compared to other concentrations. Furthermore, the levels of damaging reactive oxygen species and the malonyldialdehyde marker for oxidative stress were significantly lower in goat semen treated with these concentrations of LC and LP compared to semen exposed to other treatments. Semen treated with LC and LP also exhibited good fertilization ability during both in vitro fertilization and artificial insemination. Thus, LC (50 mM) and LP (50 mM) improve cryoprotection of dairy goat sperm which suggests that addition of these compounds will be highly beneficial to the development of dairy goat breeding.

The influence of L-proline and fulvic acid on oxidative stress and semen quality of buffalo bull semen following cryopreservation

BACKGROUND

This study investigates the effects of cryopreservation and supplementation of Azeri water buffalo's semen with proline (Lp) and fulvic acid (FA).

OBJECTIVES

Therefore, this study aimed to assess motility parameters, sperm viability, oxidative stress parameters, and DNA damage to detect the optimum concentrations of Lp and FA for buffalo semen cryopreservation.

METHODS

Thirty semen samples of three buffalo bulls were diluted in Tris-egg yolk extender and divided into 12 equal groups including control (C), Lp-10, Lp-20, Lp-40, Lp-60, Lp-80 (containing 10, 20, 40, 60, 80 mM L-proline, respectively), FA-0.2, FA-0.5, FA-0.8, FA-1.1, FA-1.4 and FA-1.7 (containing 0.2%, 0.5%, 0.8%, 1.1%, 1.4% and 1.7% fulvic acid, respectively).

RESULTS

The velocity parameters, TM and PM were improved by FA-1.7, FA-1.4, Lp-40 and Lp-60 groups compared to the C group but no significant difference was found regarding the amplitude of lateral head displacement and straightness compared to the control groups. The percentage of sperm viability and PMF were increased by FA-1.7, FA-1.4, FA-1.1, Lp-40 and Lp-60 groups compared to C group, while in terms of sperm DNA damage FA-1.7, FA-1.4, FA-1.1, Lp-10, Lp-20, Lp-40 and Lp-60 groups showed better results compared to C group. The results also showed that FA-1.7, FA-1.4, FA-1.1, Lp-20, Lp-40 and Lp-60 groups could improve TAC, SOD, GSH and decrease MDA levels. Also, FA-1.7, FA-1.4, Lp-20 and Lp-40 groups could improve GPx levels but just FA-1.7, and Lp-40 groups could improve CAT levels compared to C group.

CONCLUSIONS

Thus, it can be concluded that L-proline and fulvic acid supplementations can improve the quality parameters of post-thawed buffalo bull semen.

Characterization of freezability-associated metabolites in boar semen

Sperm cryopreservation maintains the diversities of porcine genetic resources and improves utilization efficiency of boar semen in artificial insemination practices. Freezability of boar semen presents remarkable differences among individuals. However, metabolic markers for boar semen freezability in both sperm and seminal plasma largely remain unknown. The present study thus aims to determine differences in metabolites of sperm and seminal plasma between poor (PF) and good (GF) freezability semen from a Chinese native pig and screen potential markers for semen freezability. A total of 72,048 metabolites in sperm and 66,551 metabolites in seminal plasma were identified by liquid chromatography-mass spectrometry, respectively. The proportion of lipid molecules among all metabolites in both sperm and seminal plasma was the maximum regardless of negative or positive mode. Furthermore, we identified 21 differentially expressed metabolites (DEMs) in sperm and 185 DEMs in seminal plasma between PF and GF group. Additionally, clustering analysis showed that DEMs in sperm and seminal plasma exhibited significant changes between PF and GF group. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that DEMs in sperm were mainly enriched in metabolic pathways of amino acids and caffeine. DEMs in seminal plasma were associated with AMPK and cAMP signaling pathways. Taken together, these results demonstrate that sperm and seminal plasma of native pigs present differential metabolome between PF and GF semen.

Sperm cryopreservation: current status and future developments

The cryopreservation of spermatozoa is an important reproductive technology for the preservation of fertility in man and animals. Since the serendipitous discovery of glycerol as an effective cryoprotectant in 1947, sperm cryopreservation has undergone many changes in terms of the freezing methods employed, the rates at which samples are frozen and thawed, and the media used to preserve sperm functionality and DNA integrity. An extensive literature survey has been conducted addressing the cryoprotectants employed for both animal and human semen and the freezing protocols utilised. The results indicate that glycerol remains the dominant cryoprotective agent, usually incorporated into a balanced salt solution containing energy substrates, buffers, osmolytes and protein in the form of human serum albumin (human) or skimmed milk (animal). Realisation that some of the damage observed in cryostored cells involves the generation of reactive oxygen species during the thawing process, has prompted many studies to assess the relative merits of incorporating antioxidants into the cryopreservation media. However, in the absence of systematic comparisons, there is currently no consensus as to which antioxidant combination might be the most effective. Utilising our fundamental understanding of cryodamage to optimise cryopreservation protocols for each species will be important in the future.

Beneficial Effect of Proline Supplementation on Goat Spermatozoa Quality during Cryopreservation

Sperm cryopreservation contributes to the extensive utilization of artificial insemination (AI) in the daily livestock industry. However, due to the presence of few sperm with good biological function in post-thaw goat sperm, its use has been limited for AI purposes. Hence, its improvement has been the focus of many research studies. This study aimed to investigate the effects of proline supplementation of the freezing medium on goat sperm. The goat semen was cryopreserved with freezing medium supplementation of different concentrations of proline (0, 0.5, 1, 2 and 4 mM). The post-thaw sperm motility patterns, membrane integrity, acrosome integrity, lipid peroxidation (LPO) levels, malondialdehyde (MDA) levels, total antioxidant capacity (T-AOC), proline dehydrogenase (PRODH) activity, superoxide dis-mutase (SOD) activity, glutathione (GSH) levels and GSH/GSSG were evaluated. Likewise, the expression and immunofluorescent localization of PRODH in post-thaw goat sperm was also detected. It was observed that addition of 2 mM proline to the freezing medium significantly enhanced post-thaw goat sperm total motility, progressive motility, straight-linear velocity (VSL), curvilinear velocity (VCL), average path velocity (VAP), straightness (STR), linearity (LIN), membrane integrity and acrosome integrity. Interestingly, PRODH was expressed in post-thaw goat sperm, especially in the post-acrosome and sperm tail. Addition of 2 mM proline also significantly increased the post-thaw sperm PRODH activity compared to the control. Moreover, post-thaw goat sperm LPO levels and MDA levels were reduced by supplementation of 2 mM proline. Furthermore, compared to the control, the values of post-thaw goat sperm T-AOC, SOD activity, GSH level and GSH/GSSG were also significantly increased in 2 mM proline treatment. Reduction of post-thaw goat sperm apoptosis in 2 mM proline treatment was also observed as the levels of Caspase3 and Caspase9 were decreased by the supplementation with 2 mM proline. These observations suggest that the addition of 2 mM proline to the freezing medium increased post-thaw goat sperm quality by reducing oxidative stress during cryopreservation. These findings also provide novel insights into the use of proline as an efficient additive to enhance post-thaw goat sperm quality during cryopreservation.

The Effect of Semen Cryopreservation Process on Metabolomic Profiles of Turkey Sperm as Assessed by NMR Analysis

Semen cryopreservation represents the main tool for preservation of biodiversity; however, in avian species, the freezing−thawing process results in a sharp reduction in sperm quality and consequently fertility. Thus, to gain a first insight into the molecular basis of the cryopreservation of turkey sperm, the NMR-assessed metabolite profiles of fresh and frozen−thawed samples were herein investigated and compared with sperm qualitative parameters. Cryopreservation decreased the sperm viability, mobility, and osmotic tolerance of frozen−thawed samples. This decrease in sperm quality was associated with the variation in the levels of some metabolites in both aqueous and lipid sperm extracts, as investigated by NMR analysis. Higher amounts of the amino acids Ala, Ile, Leu, Phe, Tyr, and Val were found in fresh than in frozen−thawed sperm; on the contrary, Gly content increased after cryopreservation. A positive correlation (p < 0.01) between the amino acid levels and all qualitative parameters was found, except in the case of Gly, the levels of which were negatively correlated (p < 0.01) with sperm quality. Other water-soluble compounds, namely formate, lactate, AMP, creatine, and carnitine, turned out to be present at higher concentrations in fresh sperm, whereas cryopreserved samples showed increased levels of citrate and acetyl-carnitine. Frozen−thawed sperm also showed decreases in cholesterol and polyunsaturated fatty acids, whereas saturated fatty acids were found to be higher in cryopreserved than in fresh sperm. Interestingly, lactate, carnitine (p < 0.01), AMP, creatine, cholesterol, and phosphatidylcholine (p < 0.05) levels were positively correlated with all sperm quality parameters, whereas citrate (p < 0.01), fumarate, acetyl-carnitine, and saturated fatty acids (p < 0.05) showed negative correlations. A detailed discussion aimed at explaining these correlations in the sperm cell context is provided, returning a clearer scenario of metabolic changes occurring in turkey sperm cryopreservation.