L-proline: a highly effective cryoprotectant for mouse oocyte vitrification

Molecular modelling studies reveal cryoprotective mechanism of L-Proline during the frozen storage of shrimp (Litopenaeus vannamei)

This study aimed to investigate the cryoprotective properties of proline (1% and 3% (w/v)) on shrimp. The cryoprotective mechanism was studied using physico-chemical experiments and molecular simulations. Proline had a notable positive impact on the thawing loss and texture of shrimp in comparison to the control. The denaturation of myosin in frozen shrimp was delayed by proline. Microscopy analysis demonstrated that proline effectively lowered the harm caused by ice crystals to shrimp muscle. Molecular simulations indicated that proline potentially exerted a cryoprotective effect primarily through the "water substitution" and "glassy state" hypotheses. Proline formed hydrogen bonds with myosin to replace the water molecules around myosin. Additionally, proline interacted with water molecules to form a glassy state, impeding the growth of ice crystals. Consequently, the stability of shrimp myosin was enhanced during freezing. In conclusion, proline demonstrated promise as an efficacious cryoprotectant for aquatic products.

Vitrification of Mammalian Oocytes: Recent Studies on Mitochondrial Dysfunction

Vitrification of reproductive cells is definitely essential and integral in animal breeding, as well as in assisted reproduction. However, issues accompanied with this technology such as decreased oocyte competency and relatively low embryo survival rates appear to be a tough conundrum that has long perplexed us. As significant organelles in cell metabolism, mitochondria play pivotal roles in numerous pathways. Nonetheless, extensive evidence has demonstrated that vitrification can seriously impair mitochondrial function in mammalian oocytes. Thus, in this article, we summarize the current progress in oocyte vitrification and particularly outline the common mitochondrial abnormalities alongside subsequent injury cascades seen in mammalian oocytes following vitrification. Based on existing literature, we tentatively come up with the potential mechanisms related to mitochondrial dysfunction and generalize efficacious ways which have been recommended to restore mitochondrial function.

Proline and Proline Analogues Improve Development of Mouse Preimplantation Embryos by Protecting Them against Oxidative Stress

The culture of embryos in the non-essential amino acid L-proline (Pro) or its analogues pipecolic acid (PA) and L-4-thiazolidine carboxylic acid (L4T) improves embryo development, increasing the percentage that develop to the blastocyst stage and hatch. Staining of 2-cell and 4-cell embryos with tetramethylrhodamine methyl ester and 2',7'-dichlorofluorescein diacetate showed that the culture of embryos in the presence of Pro, or either of these analogues, reduced mitochondrial activity and reactive oxygen species (ROS), respectively, indicating potential mechanisms by which embryo development is improved. Inhibition of the Pro metabolism enzyme, proline oxidase, by tetrahydro-2-furoic-acid prevented these reductions and concomitantly prevented the improved development. The ways in which Pro, PA and L4T reduce mitochondrial activity and ROS appear to differ, despite their structural similarity. Specifically, the results are consistent with Pro reducing ROS by reducing mitochondrial activity while PA and L4T may be acting as ROS scavengers. All three may work to reduce ROS by contributing to the GSH pool. Overall, our results indicate that reduction in mitochondrial activity and oxidative stress are potential mechanisms by which Pro and its analogues act to improve pre-implantation embryo development.

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.

Chiral Materials: Progress, Applications, and Prospects

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Melatonin Protects Mitochondrial Function and Inhibits Oxidative Damage against the Decline of Human Oocytes Development Caused by Prolonged Cryopreservation

Melatonin (MT) can improve the effect of cryopreservation on oocytes by suppressing oxidative stress and maintaining the permeability of the oolemma. In this study, MT was firstly applied to human oocytes' cryopreservation to explore the effect of prolonged cryopreservation on developmental competence and its role. Collected in vitro-matured human oocytes were cryopreserved in MT-containing or MT-free medium for 0 and 6 months; after warming, viable oocytes were assessed for developmental viability, intracellular protein expression, mitochondrial function, and oxidation-antioxidant system. Meanwhile, fresh oocytes were set as the control. The results showed that with the extension of cryopreservation time, the developmental competence of oocytes gradually declined, accompanied by the down-regulation of most mitochondrial function-related proteins, the reduction in ATP and GSH production, the increase in ROS accumulation, and the aggravation of the imbalance of ROS/GSH in oocytes. However, the participation of MT seemed to effectively mitigate these negative effects. Therefore, we speculate that melatonin may maintain normal ATP production and ROS/GSH balance in cryopreserved oocytes by protecting mitochondrial function and inhibiting oxidative damage, thereby effectively maintaining the developmental competence of human oocytes in prolonged cryopreservation.

Oxidative Stress and Oocyte Cryopreservation: Recent Advances in Mitigation Strategies Involving Antioxidants

Oocyte cryopreservation is widely used in assisted-reproductive technology and animal production. However, cryopreservation not only induces a massive accumulation of reactive oxygen species (ROS) in oocytes, but also leads to oxidative-stress-inflicted damage to mitochondria and the endoplasmic reticulum. These stresses lead to damage to the spindle, DNA, proteins, and lipids, ultimately reducing the developmental potential of oocytes both in vitro and in vivo. Although oocytes can mitigate oxidative stress via intrinsic antioxidant systems, the formation of ribonucleoprotein granules, mitophagy, and the cryopreservation-inflicted oxidative damage cannot be completely eliminated. Therefore, exogenous antioxidants such as melatonin and resveratrol are widely used in oocyte cryopreservation to reduce oxidative damage through direct or indirect scavenging of ROS. In this review, we discuss analysis of various oxidative stresses induced by oocyte cryopreservation, the impact of antioxidants against oxidative damage, and their underlying mechanisms. We hope that this literature review can provide a reference for improving the efficiency of oocyte cryopreservation.

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.

Proline-based solution maintains cell viability and stemness of canine adipose-derived mesenchymal stem cells after hypothermic storage

Transportation of mesenchymal stem cells (MSCs) under hypothermic conditions in 0.9% normal saline solution (NSS) might increase cell death and alter the stemness of MSCs. The present study aimed to evaluate the effect of proline-based solution (PL-BS) on cell viability and the stemness of newly established canine adipose-derived mesenchymal stem cells (cAD-MSCs) under hypothermic conditions. Characterized cAD-MSCs were stored in 1, 10, and 100 mM PL-BS or NSS at 4°C for 6, 9, and 12 hours prior to an evaluation. The results demonstrated that storage in 1 mM PL-BS for 6 hours decreased cell apoptosis and proliferation ability, but improved cell viability and mitochondrial membrane potential. cAD-MSCs maintained their high expression of CD44 and CD90, but had a low expression of CD34 and MHC class II. Trilineage differentiation ability of cAD-MSCs was not affected by storage in 1 mM PL-BS. Gene expression analysis demonstrated that immunomodulatory genes, including IDO, HGF, PGE-2, and IL-6, were upregulated in cAD-MSCs stored in 1 mM PL-BS. In conclusion, PL-BS can be effectively applied for storing cAD-MSCs under hypothermic conditions. These findings provide a new solution for effective handling of cAD-MSCs which might be promising for clinical applications.

Cryoprotective Metabolites Are Sourced from Both External Diet and Internal Macromolecular Reserves during Metabolic Reprogramming for Freeze Tolerance in Drosophilid Fly, Chymomyza costata

Many cold-acclimated insects accumulate high concentrations of low molecular weight cryoprotectants (CPs) in order to tolerate low subzero temperatures or internal freezing. The sources from which carbon skeletons for CP biosynthesis are driven, and the metabolic reprogramming linked to cold acclimation, are not sufficiently understood. Here we aim to resolve the metabolism of putative CPs by mapping relative changes in concentration of 56 metabolites and expression of 95 relevant genes as larvae of the drosophilid fly, Chymomyza costata transition from a freeze sensitive to a freeze tolerant phenotype during gradual cold acclimation. We found that C. costata larvae may directly assimilate amino acids proline and glutamate from diet to acquire at least half of their large proline stocks (up to 55 µg per average 2 mg larva). Metabolic conversion of internal glutamine reserves that build up in early diapause may explain the second half of proline accumulation, while the metabolic conversion of ornithine and the degradation of larval collagens and other proteins might be two additional minor sources. Next, we confirm that glycogen reserves represent the major source of glucose units for trehalose synthesis and accumulation (up to 27 µg per larva), while the diet may serve as an additional source. Finally, we suggest that interconversions of phospholipids may release accumulated glycero-phosphocholine (GPC) and -ethanolamine (GPE). Choline is a source of accumulated methylamines: glycine-betaine and sarcosine. The sum of methylamines together with GPE and GPC represents approximately 2 µg per larva. In conclusion, we found that food ingestion may be an important source of carbon skeletons for direct assimilation of, and/or metabolic conversions to, CPs in a diapausing and cold-acclimated insect. So far, the cold-acclimation- linked accumulation of CPs in insects was considered to be sourced mainly from internal macromolecular reserves.

Efficient Citrus (Citrus unshiu) Byproduct Extract-Based Approach for Lactobacillus sakei WiKim31 Shelf-Life Extension

Lactic acid bacteria produce various bioactive compounds widely used in human healthcare. However, studies on cryoprotective agents for the efficient storage of lactic acid bacteria after freeze-drying are still lacking. Here, we report the shelf-life extension effects of a highly efficient and eco-friendly cryoprotective agent and a cold adaptation method on Lactobacillus sakei WiKim31. Cold adaptation of L. sakei WiKim31 increased exopolysaccharide expression in response to abiotic stress. As a possible cryoprotective agent, the citrus byproduct (CP) contains a variety of sugars, amino acids, and cations, exhibiting high antioxidant activity. L. sakei WiKim31 powders formulated with CP or a mixture of soy powder (SP) and CP exhibited high cell viability at 58.3 and 76.3%, respectively, after 56 days of storage. These results indicate that CP can be efficiently used as a novel cryoprotective agent either alone or in combination with SP to improve the storage conditions of L. sakei WiKim31 and preserve it longer.

Redox Regulation and Oxidative Stress in Mammalian Oocytes and Embryos Developed In Vivo and In Vitro

Oocytes and preimplantation embryos require careful regulation of the redox environment for optimal development both in vivo and in vitro. Reactive oxygen species (ROS) are generated throughout development as a result of cellular metabolism and enzyme reactions. ROS production can result in (i) oxidative eustress, where ROS are helpful signalling molecules with beneficial physiological functions and where the redox state of the cell is maintained within homeostatic range by a closely coupled system of antioxidants and antioxidant enzymes, or (ii) oxidative distress, where excess ROS are deleterious and impair normal cellular function. in vitro culture of embryos exacerbates ROS production due to a range of issues including culture-medium composition and laboratory culture conditions. This increase in ROS can be detrimental not only to assisted reproductive success rates but can also result in epigenetic and genetic changes in the embryo, resulting in transgenerational effects. This review examines the effects of oxidative stress in the oocyte and preimplantation embryo in both the in vivo and in vitro environment, identifies mechanisms responsible for oxidative stress in the oocyte/embryo in culture and approaches to reduce these problems, and briefly examines the potential impacts on future generations.

Nomogram to predict pregnancy outcomes of emergency oocyte freeze-thaw cycles

Background:

Existing clinical prediction models for in vitro fertilization are based on the fresh oocyte cycle, and there is no prediction model to evaluate the probability of successful thawing of cryopreserved mature oocytes. This research aims to identify and study the characteristics of pre-oocyte-retrieval patients that can affect the pregnancy outcomes of emergency oocyte freeze-thaw cycles.

Methods:

Data were collected from the Reproductive Center, Peking University Third Hospital of China. Multivariable logistic regression model was used to derive the nomogram. Nomogram model performance was assessed by examining the discrimination and calibration in the development and validation cohorts. Discriminatory ability was assessed using the area under the receiver operating characteristic curve (AUC), and calibration was assessed using the Hosmer–Lemeshow goodness-of-fit test and calibration plots.

Results:

The predictors in the model of “no transferable embryo cycles” are female age (odds ratio [OR] = 1.099, 95% confidence interval [CI] = 1.003–1.205, P = 0.0440), duration of infertility (OR = 1.140, 95% CI = 1.018–1.276, P = 0.0240), basal follicle-stimulating hormone (FSH) level (OR = 1.205, 95% CI = 1.051–1.382, P = 0.0084), basal estradiol (E2) level (OR = 1.006, 95% CI = 1.001–1.010, P = 0.0120), and sperm from microdissection testicular sperm extraction (MESA) (OR = 7.741, 95% CI = 2.905–20.632, P < 0.0010). Upon assessing predictive ability, the AUC for the “no transferable embryo cycles” model was 0.799 (95% CI: 0.722–0.875, P < 0.0010). The Hosmer–Lemeshow test (P = 0.7210) and calibration curve showed good calibration for the prediction of no transferable embryo cycles. The predictors in the cumulative live birth were the number of follicles on the day of human chorionic gonadotropin (hCG) administration (OR = 1.088, 95% CI = 1.030–1.149, P = 0.0020) and endometriosis (OR = 0.172, 95% CI = 0.035–0.853, P = 0.0310). The AUC for the “cumulative live birth” model was 0.724 (95% CI: 0.647–0.801, P < 0.0010). The Hosmer–Lemeshow test (P = 0.5620) and calibration curve showed good calibration for the prediction of cumulative live birth.

Conclusions:

The predictors in the final multivariate logistic regression models found to be significantly associated with poor pregnancy outcomes were increasing female age, duration of infertility, high basal FSH and E2 level, endometriosis, sperm from MESA, and low number of follicles with a diameter >10 mm on the day of hCG administration.

Cryopreservation of NK and T Cells Without DMSO for Adoptive Cell-Based Immunotherapy

Dimethylsufoxide (DMSO) being universally used as a cryoprotectant in clinical adoptive cell-therapy settings to treat hematological malignancies and solid tumors is a growing concern, largely due to its broad toxicities. Its use has been associated with significant clinical side effects-cardiovascular, neurological, gastrointestinal, and allergic-in patients receiving infusions of cell-therapy products. DMSO has also been associated with altered expression of natural killer (NK) and T-cell markers and their in vivo function, not to mention difficulties in scaling up DMSO-based cryoprotectants, which introduce manufacturing challenges for autologous and allogeneic cellular therapies, including chimeric antigen receptor (CAR)-T and CAR-NK cell therapies. Interest in developing alternatives to DMSO has resulted in the evaluation of a variety of sugars, proteins, polymers, amino acids, and other small molecules and osmolytes as well as modalities to efficiently enable cellular uptake of these cryoprotectants. However, the DMSO-free cryopreservation of NK and T cells remains difficult. They represent heterogeneous cell populations that are sensitive to freezing and thawing. As a result, clinical use of cryopreserved cell-therapy products has not moved past the use of DMSO. Here, we present the state of the art in the development and use of cryopreservation options that do not contain DMSO toward clinical solutions to enable the global deployment of safer adoptively transferred cell-based therapies.

The Multifaceted Roles of Proline in Cell Behavior

Herein, we review the multifaceted roles of proline in cell biology. This peculiar cyclic imino acid is: (i) A main precursor of extracellular collagens (the most abundant human proteins), antimicrobial peptides (involved in innate immunity), salivary proteins (astringency, teeth health) and cornifins (skin permeability); (ii) an energy source for pathogenic bacteria, protozoan parasites, and metastatic cancer cells, which engage in extracellular-protein degradation to invade their host; (iii) an antistress molecule (an osmolyte and chemical chaperone) helpful against various potential harms (UV radiation, drought/salinity, heavy metals, reactive oxygen species); (iv) a neural metabotoxin associated with schizophrenia; (v) a modulator of cell signaling pathways such as the amino acid stress response and extracellular signal-related kinase pathway; (vi) an epigenetic modifier able to promote DNA and histone hypermethylation; (vii) an inducer of proliferation of stem and tumor cells; and (viii) a modulator of cell morphology and migration/invasiveness. We highlight how proline metabolism impacts beneficial tissue regeneration, but also contributes to the progression of devastating pathologies such as fibrosis and metastatic cancer.

Development of Optimized Vitrification Procedures Using Closed Carrier System to Improve the Survival and Developmental Competence of Vitrified Mouse Oocytes

The open carrier system (OC) is used for vitrification due to its high efficiency in preserving female fertility, but concerns remain that it bears possible risks of cross-contamination. Closed carrier systems (CC) could be an alternative to the OC to increase safety. However, the viability and developmental competence of vitrified/warmed (VW) oocytes using the CC were significantly lower than with OC. We aimed to improve the efficiency of the CC. Metaphase II oocytes were collected from mice after superovulation and subjected to in vitro fertilization after vitrification/warming. Increasing the cooling/warming rate and exposure time to cryoprotectants as key parameters for the CC effectively improved the survival rate and developmental competence of VW oocytes. When all the conditions that improved the outcomes were applied to the conventional CC, hereafter named the modified vitrification/warming procedure using CC (mVW-CC), the viability and developmental competence of VW oocytes were significantly improved as compared to those of VW oocytes in the CC. Furthermore, mVW-CC increased the spindle normality of VW oocytes, as well as the cell number of blastocysts developed from VW oocytes. Collectively, our mVW-CC optimized for mouse oocytes can be utilized for humans without concerns regarding possible cross-contamination during vitrification in the future.

In Vitro Fertilisation of Mouse Oocytes in L-Proline and L-Pipecolic Acid Improves Subsequent Development

Exposure of oocytes to specific amino acids during in vitro fertilisation (IVF) improves preimplantation embryo development. Embryos fertilised in medium with proline and its homologue pipecolic acid showed increased blastocyst formation and inner cell mass cell numbers compared to embryos fertilised in medium containing no amino acids, betaine, glycine, or histidine. The beneficial effect of proline was prevented by the addition of excess betaine, glycine, and histidine, indicating competitive inhibition of transport-mediated uptake. Expression of transporters of proline in oocytes was investigated by measuring the rate of uptake of radiolabelled proline in the presence of unlabelled amino acids. Three transporters were identified, one that was sodium-dependent, PROT (SLC6A7), and two others that were sodium-independent, PAT1 (SLC36A1) and PAT2 (SLC36A2). Immunofluorescent staining showed localisation of PROT in intracellular vesicles and limited expression in the plasma membrane, while PAT1 and PAT2 were both expressed in the plasma membrane. Proline and pipecolic acid reduced mitochondrial activity and reactive oxygen species in oocytes, and this may be responsible for their beneficial effect. Overall, our results indicate the importance of inclusion of specific amino acids in IVF medium and that consideration should be given to whether the addition of multiple amino acids prevents the action of beneficial amino acids.

L-Proline Activates Mammalian Target of Rapamycin Complex 1 and Modulates Redox Environment in Porcine Trophectoderm Cells

L-proline (proline) is a key regulator of embryogenesis, placental development, and fetal growth. However, the underlying mechanisms that support the beneficial effects of proline are largely unknown. This study used porcine trophectoderm cell line 2 (pTr2) to investigate the underlying mechanisms of proline in cell proliferation and redox homeostasis. Cells were cultured in the presence of 0, 0.25, 0.50, or 1.0 mmol/L proline for an indicated time. The results showed that 0.5 and 1.0 mmol/L proline enhanced cell viability. These effects of proline (0.5 mmol/L) were accompanied by the enhanced protein abundance of p-mTORC1, p-p70S6K, p-S6, and p-4E-BP1. Additionally, proline dose-dependently enhanced the mRNA expression of proline transporters [solute carrier family (SLC) 6A20, SLC36A1, SLC36A2, SLC38A1, and SLC38A2], elevated proline concentration, and protein abundance of proline dehydrogenase (PRODH). Furthermore, proline addition (0.25 or 0.5 mmol/L) resulted in lower abundance of p-AMPKα when compared with a control. Of note, proline resulted in lower reactive oxygen species (ROS) level, upregulated mRNA expression of the catalytic subunit of glutamate–cysteine ligase (GCLC) and glutathione synthetase (GSS), as well as enhanced total (T)-GSH and GSH concentration when compared with a control. These data indicated that proline activates themTORC1 signaling and modulates the intracellular redox environment via enhancing proline transport.

Optical cryomicroscopy and differential scanning calorimetry of buffer solutions containing cryoprotectants

In the pharmaceutical industry, cryoprotectants are added to buffer formulations to protect the active pharmaceutical ingredient from freeze- and thaw damage. We investigated the freezing and thawing of aqueous sodium citrate buffer with various cryoprotectants, specifically amino acids (cysteine, histidine, arginine, proline and lysine), disaccharides (trehalose and sucrose), polyhydric alcohols (glycerol and mannitol) and surfactants (polysorbate 20 and polysorbate 80). Hereby, we employed optical cryomicroscopy in combination with differential scanning calorimetry in the temperature range to -80 °C. The effect of cryoprotectants on the morphology of the ice crystals, the glass transition temperature and the initial melting temperature is presented. Some of the cryoprotectants have a significant impact on ice crystal size. Disaccharides restrict ice crystal growth, whereas surfactants and glycerol allow ice crystals to increase in size. Cysteine and mannitol cause dehydration after thawing. Either one or two glass transition temperatures were detected, where arginine, surfactants, glycerol, proline and lysine suppress the second, implying a uniform freeze-concentrated solution. The initial melting temperature of pure buffer solution can be shifted up by adding mannitol, both disaccharides and both surfactants; but down by glycerol, proline and lysine.

L-Proline: An Effective Agent for Frozen and Post-thawed Donkey Semen Storage

The aim of this study was to evaluate the effects of L-proline on the extender quality of frozen and post-thawed jackass semen. Jackass (n = 6) semen samples were collected and cryopreserved in gradient concentrations (0-80 mM) of L-proline in extenders; post-thawed semen samples were cultured in L-proline medium for 10 hours at 37°C. For cryopreservation experiment I, the motile parameters, mitochondrial membrane potential (MMP), and plasma membrane, acrosome, and chromatin structure integrities of post-thawed semen were assessed. For culture experiment II, additional ROS contents were analyzed after incubation. For the fertility trial, jennies (n = 135) were divided into group I (30 mM L-proline in cryopreservation extender), group II (40 mM L-proline in culture medium), and the control. Pregnancy was diagnosed using an ultrasound scanner 30 days after ovulation. The results of experiment I showed that, motile parameters and acrosome and chromatin structure integrities of groups I and 40 mM were significantly higher than the control (P < .05). MMP of group I was significantly higher than the control and 40 mM groups (P < .05). In experiment II, after 4 hours of incubation, motile parameters, MMP, and DNA integrity in group II were significantly higher than the control (P < .05). Additionally, 40 and 80 mM L-proline in culture medium significantly reduced ROS accumulation after 4 and 10 hours of incubation (P < .05). Pregnancy rates of the control and groups I and II were 28.85%, 40%, and 36.84%, respectively. In conclusion, the extenders containing 30 to 40 mM L-proline improved both qualities of frozen and post-thawed semen, and it will be a beneficial agent for donkey frozen spermatozoa or post-thawed semen storage.

Incomplete proline catabolism drives premature sperm aging

Infertility is an increasingly common health issue, with rising prevalence in advanced parental age. Environmental stress has established negative effects on reproductive health, however, the impact of altering cellular metabolism and its endogenous reactive oxygen species (ROS) on fertility remains unclear. Here, we demonstrate the loss of proline dehydrogenase, the first committed step in proline catabolism, is relatively benign. In contrast, disruption of alh-6, which facilitates the second step of proline catabolism by converting 1-pyrroline-5-carboxylate (P5C) to glutamate, results in premature reproductive senescence, specifically in males. The premature reproductive senescence in alh-6 mutant males is caused by aberrant ROS homeostasis, which can be countered by genetically limiting the first committed step of proline catabolism that functions upstream of ALH-6 or by pharmacological treatment with antioxidants. Taken together, our work uncovers proline metabolism as a critical component of normal sperm function that can alter the rate of aging in the male reproductive system.

Melatonin alleviates the deterioration of oocytes and hormonal disorders from mice subjected to glyphosate

Glyphosate (Gly) is the herbicide widely used in agricultural fields and landscaping. Mammalian exposure to glyphosate could cause neurotoxicity, blood, liver, kidney, endocrine, reproductive, genetic and other toxic effects. Melatonin (MT) is a neuroendocrine hormone secreted mainly by the pineal gland. It is unknown whether MT can improve reproductive defects and hormonal disorders in mice exposed to Gly. In this study, mice were exposed to 250 and 500 mg/kg Gly by intragastric administered and 15 mg/kg MT was treated via intraperitoneal injection for 7 days. Our results shown that the weight gain of mice, the ovarian coefficient and the ATP content in the ovaries were decreased significantly. Gly-treated oocytes showed that the first polar body extrusion failed, the level of oxidative stress increased, and the mitochondrial membrane potential (MMP) decreased. Subsequently, our results showed that increased expression level of BAX protein, reduced expression of BCL-2 protein, ATG12 and LC3 protein expression increased in ovaries after Gly treatment. At the same time, Gly exposure led to abnormal expression of Hypothalamic-Pituitary-Thyroid (HPT) axis-related genes and disrupted hormone homeostasis. After the injection of 15 mg/kg MT, the oocytes showed decreased oxidative stress level, increased mitochondrial membrane potential, incremental ATP content in the ovaries and the hormone levels were approached to the control group. Thus, our results demonstrated that melatonin can improve oocyte quality and maintain hormone homeostasis in mice exposed to glyphosate.

Effects of vitrification and cryostorage duration on single-cell RNA-Seq profiling of vitrified-thawed human metaphase II oocytes

Oocyte cryopreservation is widely used for clinical and social reasons. Previous studies have demonstrated that conventional slow-freezing cryopreservation procedures, but not storage time, can alter the gene expression profiles of frozen oocytes. Whether vitrification procedures and the related frozen storage durations have any effects on the transcriptomes of human metaphase II oocytes remain unknown. Four women (30-32 years old) who had undergone IVF treatment were recruited for this study. RNA-Seq profiles of 3 fresh oocytes and 13 surviving vitrified-thawed oocytes (3, 3, 4, and 3 oocytes were cryostored for 1,2, 3, and 12 months) were analyzed at a single-cell resolution. A total of 1987 genes were differentially expressed in the 13 vitrified-thawed oocytes. However, no differentially expressed genes were found between any two groups among the 1-, 2-, 3-, and 12-month storage groups. Further analysis revealed that the aberrant genes in the vitrified oocytes were closely related to oogenesis and development. Our findings indicated that the effects of vitrification on the transcriptomes of mature human oocytes are induced by the procedure itself, suggesting that long-term cryostorage of human oocytes is safe.

Impacts of trehalose and l-proline on the thermodynamic nonequilibrium phase change and thermal properties of normal saline

Understanding the phase change behavior and thermal properties of cryoprotective agents (CPAs) in biological solutions is essential for enhancing the success of cryopreservation and biobanking. In this study, the phase change behavior and thermal properties of normal saline added with trehalose or l-proline were investigated using differential scanning calorimeter (DSC) and cryomicroscope during freezing and warming. The addition of trehalose or l-proline can eliminate the eutectic formation in normal saline. Trehalose had significantly lower latent heat release than l-proline does at a high concentration of 1 M (P < 0.05), while unfrozen water content of trehalose is significantly lower than that of l-proline at all the concentrations (P < 0.05). It was also found that addition of 0.2 M, 0.3 M and 1 M trehalose can achieve partial vitrification in normal saline and that the glass transition temperature rises along with the increase in concentrations of trehalose. However, no vitrification was observed in normal saline with l-proline at any concentrations. Besides, rates of ice crystal growth in normal saline added with trehalose are slower than those in normal saline with l-proline at the same concentrations. These results suggest that both trehalose and l-proline can act as CPAs by avoiding eutectic formation and inhibiting ice formation in normal saline for cell cryopreservation. It could be useful for CPA selection and designing in the future.

Bioinspired l-Proline Oligomers for the Cryopreservation of Oocytes via Controlling Ice Growth

Various types of cells are routinely cryopreserved in modern regenerative and cell-based medicines. For instance, the oocyte is one of the most demanding cells to be cryopreserved in genetic engineering and human-assisted reproductive technology (ART). However, the usage of cryopreserved oocytes in ART clinics is still limited mainly because of the unstable survival rate. This is due to the fact that oocytes are more prone to be damaged by ice crystals in comparison to other cells, as oocytes are larger in size and surface area. Meanwhile, oocytes contain more water, and thus, ice crystals are easier to form inside the cells. Currently, to avoid injury by the formed ice crystals, cryopreservation (CP) of oocytes has to use large amounts of small molecules as cryoprotectants such as dimethyl sulfoxide (DMSO) and ethylene glycol (EG), which can permeate into the cell and prevent ice formation inside. However, these molecules are chemically and epigenetically toxic to cells. Therefore, great efforts have been focused on reducing the amount of DMSO and EG used for oocyte CP. In nature, the antifreeze (glyco)proteins (AFGPs) locate extracellularly with the ability to protect living organisms from freezing damage via controlling ice growth. Inspired by this, biocompatible and nontoxic L-proline oligomers (L-Pro_n), which have the same polyproline II helix structure as that of AFGPs, are first employed for the CP of oocytes. The experimental results reveal that L-Pro₈ has a profound activity in inhibiting ice growth as that of AFGP8. Also, by the addition of 50 mM L-Pro₈, the amount of DMSO and EG can be greatly reduced by ca. 1.8 M for oocyte CP; moreover, the survival rate of the cryopreserved oocytes is increased up to 99.11%, and the coefficient of variance of the survival rate is decreased from 7.47 to 2.15%. These results mean that almost all oocytes can survive after CP with our method; importantly, the mitochondrial function as a critical criterion for the quality of the frozen-thawed oocytes is also improved. It is proposed that with the addition of L-Pro₈, the extracellular ice growth is slowed down, which prevents the direct injuries of cells by large ice crystals and the accompanying osmotic pressure increase. As such, this work is not only significant for meeting the ever-increasing demand by the ART clinics but also gives guidance for designing materials in controlling ice growth during CP of other cells and tissues.

Effects of mPEG-DSPE/corannulene or perylene nanoparticles on the ovary and oocyte

Corannulene (Cor) is a polycyclic aromatic hydrocarbon (PHA) whose molecular structure is three dimensional with a unique bowl-like structure and surface charge. Perylene (Per) is similar to corannulene, with 20π electrons in its fragrance system, but it is a planar structure. Although scientists in various fields have been extensively investigating corannulene, the toxicological evaluation on organisms and its possible mechanisms remain unclear. Our objective is to investigate the toxic effects of corannulene and perylene on ovaries and oocytes. First, corannulene and perylene were wrapped with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol)] (mPEG-DSPE) to form mPEG-DSPE/corannulene nanoparticles (mP-D/CoNps) and mPEG-DSPE/perylene nanoparticles (mP-D/PeNps), which enhanced their water solubility and biocompatibility. Then, the toxic effects of mP-D/CoNps or mP-D/PeNps on the quality of mouse oocytes and their possible mechanisms were studied in vivo. Our results indicated that mP-D/CoNps or mP-D/PeNps affected the first polar body extrusion of oocytes, increased the number of primordial follicles in the ovary, altered mitochondrial membrane potentials, induced oxidative stress and led to autophagy and apoptosis.

Corannulene (Cor) is a polycyclic aromatic hydrocarbon (PHA) whose molecular structure is three dimensional with a unique bowl-like structure and surface charge.

L-proline feeding for augmented freeze tolerance of Camponotus japonicus Mayr

The successful cryopreservation of organs is a strong and widespread demand around the world but faces great challenges. The mechanisms of cold tolerance of organisms in nature inspirit researchers to find new solutions for these challenges. Especially, the thermal, mechanical, biological and biophysical changes during the regulation of freezing tolerance process should be studied and coordinated to improve the cryopreservation technique and quality of complex organs. Here the cold tolerance of the Japanese carpenter ants, Camponotus japonicus Mayr, was greatly improved by using optimal protocols and feeding on L-proline-augmented diets for 5 days. When cooling to -27.66 °C, the survival rate of frozen ants increased from 37.50% ± 1.73% to 83.88% ± 3.67%. Profiling of metabolites identified the concentration of whole-body L-proline of ants increased from 1.78 to 4.64 ng g^-1 after 5-day feeding. High L-proline level, together with a low rate of osmotically active water and osmotically inactive water facilitated the prevention of cryoinjury. More importantly, gene analysis showed that the expression of ribosome genes was significantly up-regulated and played an important role in manipulating freezing tolerance. To the best of our knowledge, this is the first study to link genetic variation to the enhancement of ants' cold tolerance by feeding exogenous cryoprotective compound. It is worth noting that the findings provide the theoretical and technical foundation for the cryopreservation of more complex tissues, organs, and living organisms.

Using natural honey as an anti-oxidant and thermodynamically efficient cryoprotectant in embryo vitrification

Embryo cryopreservation is a common practice in reproductive biology and infertility treatments. Despite major improvements over years, the cryoprotectant solutions are still a major source of concern, mostly due to their chemical toxicity and suboptimal protection against cryoinjuries. In this work, we introduced natural honey as a non-permeating cryoprotectant to replace traditionally used sucrose in embryo vitrification. The proposed media were compared with conventional ones by evaluating vitrified/warmed mouse embryos based on their re-expansion, hatching rate and transcription pattern of selected genes involved in heat-shock response, apoptosis and oxidative stress. Despite the similar high re-expansion rate, molecular fingerprint of the cryopreservation is remarkably reduced when honey is used instead of sucrose. The biological response of the proposed media was explained from a fundamental point of view using antioxidant analysis, DSC and GC techniques. It was found that the proposed honey-based medium is less thermodynamically prone to ice formation, which along with its antioxidant capacity can control the production of oxygen radicals and minimize the stress-induced transcriptional response. Furthermore, this work tries to correlate the physico-chemical properties of the vitrification solutions with the cellular and molecular aspects of the cryopreservation and proposes the application of natural cryoprotectants in cryobiology.

The roles of reactive oxygen species and antioxidants in cryopreservation

Cryopreservation has facilitated advancement of biological research by allowing the storage of cells over prolonged periods of time. While cryopreservation at extremely low temperatures would render cells metabolically inactive, cells suffer insults during the freezing and thawing process. Among such insults, the generation of supra-physiological levels of reactive oxygen species (ROS) could impair cellular functions and survival. Antioxidants are potential additives that were reported to partially or completely reverse freeze-thaw stress-associated impairments. This review aims to discuss the potential sources of cryopreservation-induced ROS and the effectiveness of antioxidant administration when used individually or in combination.

Anti-apoptotic Regulation Contributes to the Successful Nuclear Reprogramming Using Cryopreserved Oocytes

Cryopreservation has a negative effect on the quality of oocytes and may be closely associated with increased levels of reactive oxygen species (ROS) and apoptotic events. The purpose of the present study was to evaluate the detrimental effects on the developmental competence of somatic cell nuclear transferred (SCNT) mouse embryos using vitrified (cryopreserved) oocytes and to evaluate the recovery effects of melatonin on cryo-damage in cloned embryos. Development of SCNT embryos using cryopreserved oocyte cytoplasm (SCNT-CROC) was inferior to those using fresh cytoplasm (SCNT-FOC). Using RNA-sequencing analysis, we found upregulation of eight pro-apoptotic-related genes (Cyct, Dapk2, Dffb, Gadd45g, Hint2, Mien1, P2rx7, and Pmaip) in the SCNT-CROC group. Furthermore, the addition of melatonin, an agent that reduces apoptosis and ROS production, enhanced blastocyst formation rates in the SCNT-CROP group when compared with the melatonin-untreated group. Additionally, melatonin treatment increased the derivation efficiency of pluripotent stem cells from cloned embryos using cryopreserved oocyte.

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Cloned mouse embryos using cryopreserved oocytes have shown increased apoptosis

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The addition of melatonin reduces apoptosis and ROS production

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Melatonin enhances development of the SCNT embryos using cryopreserved oocytes

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This system will be helpful in the derivation and application of human SCNT-ESC line

Exploring the Potential of Biocompatible Osmoprotectants as Highly Efficient Cryoprotectants

Cryoprotectants (CPAs) are critical to successful cryopreservation because they can protect cells from cryoinjuries. Because of the limitations of current CPAs, especially the toxicity, the search for new effective CPAs is attracting increasing attention. In this work, we reported that natural biocompatible osmoprotectants, which could protect cells from osmotic injury in various biological systems, might also be ideal candidates for CPAs. Three representative biocompatible osmoprotectants (proline, glycine, and taurine) were tested and compared. It was found that, aside from presenting a different ability to prevent osmotic injury, these biocompatible osmoprotectants also possessed a different ability to inhibit ice formation and thus mitigate intra-/extracellular ice injury. Because of the strongest ability to prevent the two types of injuries, we found that proline performed the best in cryopreserving five different types of cells. Moreover, the natural osmoprotectants are intrinsically biocompatible with the cells, superior to the current state-of-the-art CPA, dimethyl sulfoxide (DMSO), which is a toxic organic solvent. This work opens a new window of opportunity for DMSO-free cryopreservation, and sheds light on the applications of osmoprotectants in cryoprotection, which may revolutionize the current cryopreservation technologies.