Comparison of the microdrop and minimum volume cooling methods for vitrification of porcine in vitro-produced zygotes and blastocysts after equilibration in low concentrations of cryoprotectant agents

We compared the efficacy of the microdrop and minimum volume cooling (MVC) methods for the vitrification of in vitro-produced porcine zygotes and blastocysts after equilibration in low concentrations of cryoprotectant agents. Zygotes and blastocysts were equilibrated in 2% (v/v) ethylene glycol and 2% (v/v) propylene glycol for 13–15 min. Then, they were vitrified in a medium comprised of 17.5% ethylene glycol, 17.5% propylene glycol, 0.3 M sucrose, and 50 mg/ml polyvinylpyrrolidone either by either dropping them directly into liquid nitrogen (microdrop method) or placing them on Cryotop sheets in a minimum volume of medium and plunging into liquid nitrogen (MVC method). Both zygotes and blastocysts were successfully vitrified. For the vitrification of zygotes, the MVC and microdrop methods were equally effective; however, for blastocyst vitrification, MVC was superior. For both methods, the vitrification of zygotes produced higher-quality embryos than the vitrification of blastocysts.

Cryotolerance of porcine in vitro-produced blastocysts relies on blastocyst stage and length of in vitro culture prior to vitrification

The aim of our study was to assess whether the cryotolerance of in vitro-produced embryos could be influenced by the length of in vitro culture and size of blastocoel cavity before vitrification, using the pig as a model. For this purpose we analysed the cryoresistance and apoptosis rate of blastocysts at different stages of development as derived on Day 5 and 6 of in vitro culture. Blastocysts were subsequently vitrified, warmed and cultured for 24 h. Re-expansion rates were recorded at 3 and 24 h and total cell number and apoptotic cells were determined at 24 h. Day-6 blastocysts showed the highest rates of survival after warming, which indicates higher quality compared with Day-5 blastocysts. Higher re-expansion rates were observed for expanded blastocysts and those in the process of hatching when compared with early blastocysts. Total cell number and apoptotic cells were affected by blastocyst stage, vitrification–warming procedures and length of in vitro culture, as expanding and hatching–hatched blastocysts from Day 6 presented higher percentages of apoptotic cells than fresh blastocysts and blastocysts vitrified at Day 5. Our findings suggest that the cryotop vitrification method is useful for the cryopreservation of porcine blastocysts presenting a high degree of expansion, particularly when vitrification is performed after 6 days of in vitro culture. Furthermore, these results show that faster embryo development underlies higher blastocyst cryotolerance and provide evidence that blastocoel cavity expansion before vitrification is a reliable index of in vitro-produced embryo quality and developmental potential.

Comparative effects of adding β-mercaptoethanol or L-ascorbic acid to culture or vitrification-warming media on IVF porcine embryos

The aims of the present study were to; (1) determine the effects of supplementation with two antioxidants during in vitro culture (IVC) on embryo development and quality; and (2) test the effects of adding the antioxidants to vitrification-warming media on the cryotolerance of in vitro-produced (IVP) porcine blastocysts. In Experiment 1, presumptive zygotes were cultured without antioxidants, with 50 µM β-mercaptoethanol (β-ME) or with 100 µM L-ascorbic acid (AC). After culture, blastocyst yield, quality and cryotolerance were evaluated in each treatment group. In Experiment 2, survival rates (3 and 24 h), total cell number, apoptosis index and the formation of reactive oxygen species (ROS) in blastocysts vitrified-warmed with 100 µM AC or 50 µM β-ME or without antioxidants added to the vitrification medium were compared. Antioxidant addition during IVC had no effect on embryo development, total cell number or the apoptosis index, and culturing embryos in the presence of β-ME had no effects on cryotolerance. In contrast, ROS levels and survival rates after vitrification-warming were significantly improved in embryos cultured with AC. Furthermore, addition of AC into vitrification-warming media enhanced embryo survival and embryo quality after warming. In conclusion, our results suggest that supplementing culture or vitrification media with 100 µM AC improves the quality and cryosurvival of IVP porcine blastocysts.

Supplementing culture and vitrification-warming media with l-ascorbic acid enhances survival rates and redox status of IVP porcine blastocysts via induction of GPX1 and SOD1 expression

The present study sought to determine the effect of adding l-ascorbic acid (AC) to (1) in vitro culture medium and (2) vitrification and warming solutions on redox status and developmental ability and quality of IVP porcine embryos. In both experiments, embryo quality was analysed in terms of total cell number (TCN), DNA fragmentation, intracellular peroxide levels and expression of three oxidative stress-related genes: glutathione peroxidase 1 (GPX1), superoxide dismutase 1 (SOD1) and 2 (SOD2). In the first experiment, fresh blastocysts were found to upregulate SOD1 expression when cultured with medium supplemented 100 μM AC. No differences were found between culture groups in the other analysed parameters. In the second experiment, blastocysts cultured with or without AC were divided into two groups: vitrified and warmed with solutions containing 0 or 100 μM AC. Addition of AC during culture and vitrification-warming upregulated the expression of GPX1 and SOD1 genes, enhanced survival rates and decreased peroxide levels at 24h post-warming. In addition, peroxide levels were negatively correlated with relative GPX1- and SOD1-transcript abundances, whereas GPX1 was positively correlated with embryo survival at 24h post-warming. No effects of AC-supplementation were seen for TCN, DNA fragmentation or relative SOD2-transcript abundance in vitrified blastocysts. In conclusion, the addition of AC to culture and vitrification-warming media increases gene expression of antioxidant enzymes SOD1 and GPX1. This appears to improve redox balance and is suggested to ultimately enhance embryo cryosurvival.

Energy substrate influences the effect of the timing of the first embryonic cleavage on the development of in vitro-produced porcine embryos in a sex-related manner

In vitro culture conditions and certain events during the earliest stages of development are linked to embryonic survival, possibly in a sex-related manner. In vitro-produced (IVP) porcine embryos cultured with glucose (IVC-Glu) or pyruvate-lactate (IVC-PL) were tested for any relationship between the timing of the first embryonic cleavage and development and sex ratio. The embryos were assigned to IVC-Glu or IVC-PL groups and classified depending on the timing of their first cleavage: 24, 26, 30, and 48 hr post-insemination (hpi). They were cultured separately in vitro and evaluated for cleavage rate and pattern, blastocyst rate and stage, cell number, apoptosis, and sex ratio. Regardless of energy source, the percentage of two-cell stage and fragmented embryos at the time of their first cleavage was, respectively, higher and lower in early-cleaving embryos. Those embryos cleaved by 24 hpi developed to blastocysts at a higher rate (IVC-Glu: 37.90 ± 3.06%; IVC-PL: 38.73 ± 4.08%) than those cleaved between 30 and 48 hpi (IVC-Glu: 5.87 ± 3.02%; IVC-PL: 8.41 ± 3.50%). Furthermore, a shift toward males was seen among embryos first cleaved before 30 hpi, versus towards females among those cleaved later. The early-cleaving embryos, only from the IVC-PL group, had a higher proportion of expanded blastocysts (81.05 ± 6.54% vs. 13.33 ± 13.33%) with higher cell numbers than their late-cleaving counterparts. Moreover, a shift toward males only appeared at the blastocyst stage in IVC-PL embryos. These findings confirm that the timing of the first cleavage influences development of IVP porcine embryos in a sex-related manner, and it depends on the main energy source of the in vitro culture medium.