l-Carnitine Supplementation during In Vitro Maturation and In Vitro Culture Does not Affect the Survival Rates after Vitrification and Warming but Alters Inf-T and ptgs2 Gene Expression

Effect of the addition of IGF-1 during in vitro culture on the embryonic development speed from different crossbreed bovine embryos

Supplementation with insulin-like growth factor type 1 (IGF-1) during in vitro culture of bovine embryos has yielded mixed results, likely due to genetic variability among embryos. This work aimed to evaluate the effect of IGF-1 at two concentrations on the development speed embryos from primary F1 crossbreeds used in dual-purpose cattle farming in the Colombian low tropics. Specifically, we investigated the influence of IGF-1 and embryo breed on the blastocyst formation rate. Oocytes were sourced from non-pregnant cows: Bos taurus indicus (20 Brahman and 14 Gyr) and Bos taurus taurus (12 Holstein and 28 Romosinuano). Oocytes were fertilized with semen from specific bulls (Recoil for Holstein, Gabinete for Gyr, and UBER POI 1490 for Brahman). The resulting embryos from each crossbreed group were randomly distributed in three different cultured media with 50 ng/mL IGF-1, 100 ng/mL IGF-1, or no IGF-1 (control) for 7 days. Results showed that 50 ng/mL IGF-1 significantly increased embryo production by day 6 (25.9%±14.56%) compared to control (20.5%±11.84%) and 100 ng/mL IGF-1 (23.0%±9.54%) (p < 0.05). By day 7, both 50 ng/mL (42.6%±26.55%) and 100 ng/mL (49.7%±21.98%) IGF-1 groups exhibited significantly higher production rates compared to the control group (p < 0.001). The embryo breed also influenced development, with Gyr-Holstein (GxH) crossbreeds showing the highest production rates (p < 0.001). In conclusion, IGF-1 supplementation enhances in vitro embryo production, with the effect influenced by both breed and IGF-1 concentration. These findings suggest that breed-specific optimization of IGF-1 conditions is necessary to maximize embryonic development outcomes.

The Effect of Simulated Physiological Oocyte Maturation (SPOM) and L-Carnitine on Bovine Oocyte Developmental Competence

Background

Simulated Physiological Oocyte Maturation (SPOM) mimics in vitro the physiological events of oocyte maturation in the presence of cAMP modulators. These modulators increase the intracellular concentrations of cAMP, which inhibits the immediate resumption of meiosis and gives the oocyte more time to gain optimal developmental competence. In addition, L-carnitine helps to increase the energy supply of cells through the β-oxidation of fatty acids. This study aimed to investigate the effect of SPOM and L-carnitine supplementation during In Vitro Maturation (IVM) and In Vitro Culture (IVC) on the developmental competence of bovine oocytes.

Methods

Ovarian Cumulus Complexes (COCs) were cultured in the presence or absence of forskolin+IBMX during the first 2 hr of IVM (pre-IVM) with or without L-carnitine (LC) during IVM or IVC in six experimental groups as follows: I) pre-IVM (pre-IVM group), II) pre-IVM with L-carnitine supplementation during IVM (pre-IVM/LC group), III) L-carnitine supplementation during IVM (IVM/LC group), IV) L-carnitine supplementation during in vitro culture (IVC/LC group), V) pre-IVM+ IVC/LC group, and VI) no treatment during IVM and IVC (Control group). The cleavage and blastocyst rates, the blastocysts' total cells number, and the expression of Nanog, Bax, Oct4, Cdx2, and Ifnt genes in resulting blastocysts were assessed. To assess differences among experimental groups, a one-way analysis of variance was initially employed, followed by post hoc Fisher LSD. The difference between groups was considered statistically significant when p<0.05.

Results

The cleavage and blastocyst rates in the Pre-IVM and Pre-IVM/LC groups was higher than control group and other groups (p≤0.05) except for IVC/LC and IVM/LC groups, respectively. The number of blastocyst's Inner Cell Mass (ICM) in pre-IVM and Pre-IVM/LC groups as well as the ratio of ICM/TE were higher than control group (p<0.05). The expression of OCT4, CDX2, and IFNT increased in both the pre-IVM and pre-IVM/LC groups compared to the control group (p<0.05).

Conclusion

In conclusion, the application of SPOM-adapted IVM and L-carnitine during IVM of bovine oocyte improves the quantity and quality of the resulting embryos.

Factors affecting cryotolerance of mammalian oocytes

Cryopreservation of oocytes is an important tool for preserving genetic resources and for farm animals breeding. Processes taking place during vitrification affect oocytes and result in their reduced developmental capacity and lower fertilisation rates of cryopreserved oocytes. Further improvement in cryopreservation techniques is still required. Several authors already summarized the actual state and perspectives of oocyte cryopreservation as well as potential approaches to improve their development after thawing. The aim of this review is to specify factors affecting cryotolerance of mammalian oocytes, especially bovine in vitro matured oocytes, and to identify the areas, where more efforts were made to improve the success of oocyte cryopreservation. These factors include oocyte lipid content, membrane composition, mRNA protection, cytoskeleton stabilization and application of such potential stimulators of cell cryotolerance as antioxidants, growth factors or antifreeze proteins.

Impact of reducing lipid content during in vitro embryo production: A systematic review and meta-analysis

There is still no consensus regarding the role of lipid modulators during in vitro embryo production. Thus, we investigated how lipid reducers during the in vitro maturation of oocytes (IVM) or in vitro culture (IVC) of embryos impact their cryotolerance. A literature search was performed using three databases, recovering 43 articles for the systematic review, comprising 75 experiments (13 performed in IVM, 62 in IVC) and testing 13 substances. In 39 % of the experiments, an increase in oocyte and/or embryo survival after cryopreservation was reported, in contrast to 48 % exhibiting no effect, 5 % causing negative effects, and 8 % influencing in a dose-dependent manner. Of the 75 experiments extracted during IVM and IVC, 41 quantified the lipid content. Of those that reduced lipid content (n = 26), 50 % increased cryotolerance, 34 % had no effect, 8 % harmed oocyte/embryo survival, and 8 % had different results depending on the concentration used. Moreover, 28 out of the 43 studies were analyzed under a meta-analytical approach at the IVC stage in cattle. There was an improvement in the cryotolerance of bovine embryos when the lipid content was reduced. Forskolin, l-carnitine, and phenazine ethosulfate positively affected cryotolerance, while conjugated linoleic acid had no effect and impaired embryonic development. Moreover, fetal bovine serum has a positive impact on cryotolerance. SOF and CR1aa IVC media improved cryotolerance, while mSOF showed no effect. In conclusion, lipid modulators did not unanimously improve cryotolerance, especially when used in IVM, but presented positive effects on cryotolerance during IVC when reaching lipid reduction.

Associations of the Single Bovine Embryo Growth Media Metabolome with Successful Pregnancy

This study investigated whether metabolomic fingerprints of bovine embryo growth media improve the prediction of successful embryo implantation. In this prospective cohort study, the metabolome from in vitro-produced day 7 blastocysts with successful implantation (n = 11), blastocysts with failed implantation (n = 10), and plain culture media without embryos (n = 5) were included. Samples were analyzed using an AbsoluteIDQ® p180 Targeted Metabolomics Kit with LC-MS/MS, and a total of 189 metabolites were analyzed from each sample. Blastocysts that resulted in successful embryo implantation had significantly higher levels of methionine sulfoxide (p < 0.001), DOPA (p < 0.05), spermidine (p < 0.001), acetylcarnitine-to-free-carnitine ratio (p < 0.05), C2 + C3-to-free-carnitine ratio (p < 0.05), and lower levels of threonine (nep < 0.001) and phosphatidylcholine PC ae C30:0 (p < 0.001) compared to control media. However, when compared to embryos that failed to implant, only DOPA, spermidine, C2/C0, (C2 + C3)/C0, and PC ae C30:0 levels differentiated significantly. In summary, our study identifies a panel of differential metabolites in the culture media of bovine blastocysts that could act as potential biomarkers for the selection of viable blastocysts before embryo transfer.

Cumulus Cell and Oocyte Gene Expression in Prepubertal Gilts and Sows Identifies Cumulus Cells as a Prime Informative Parameter of Oocyte Quality

Cumulus cells (CCs) are pivotal during oocyte development. This study aimed to identify novel marker genes for porcine oocyte quality by examining the expression of selected genes in CCs and oocytes, employing the model of oocytes from prepubertal animals being of reduced quality compared to those from adult animals. Total RNA was extracted either directly after follicle aspiration or after in vitro maturation, followed by RT-qPCR. Immature gilt CCs accumulated BBOX1 transcripts, involved in L-carnitine biosynthesis, to a 14.8-fold higher level (p < 0.05) relative to sows, while for CPT2, participating in fatty acid oxidation, the level was 0.48 (p < 0.05). While showing no differences between gilt and sow CCs after maturation, CPT2 and BBOX1 levels in oocytes were higher in gilts at both time points. The apparent delayed lipid metabolism and reduced accumulation of ALDOA and G6PD transcripts in gilt CCs after maturation, implying downregulation of glycolysis and the pentose phosphate pathway, suggest gilt cumulus-oocyte complexes have inadequate ATP stores and oxidative stress balance compared to sows at the end of maturation. Reduced expression of BBOX1 and higher expression of CPT2 in CCs before maturation and higher expression of G6PD and ALDOA after maturation are new potential markers of oocyte quality.

L-carnitine enhances developmental potential of bovine oocytes matured under high lipid concentrations in vitro

Maternal obesity elevates non-esterified fatty acids (NEFA) follicular concentrations. Bovine cumulus-oocyte complexes (COCs) matured in vitro under high NEFA have altered metabolism and reduced quality. Systemically, obesity promotes altered mitochondrial metabolism linked to L-carnitine insufficiency. We hypothesized that L-carnitine supplementation during IVM of bovine COCs in the presence of high NEFA would lessen the negative effects of exposure to excessive lipids on embryonic development and oxidative stress. COCs were collected from abattoir ovaries and matured in four groups: CON (control), LC (3 mM L-carnitine), HN (high NEFA: 200uM oleic, 150uM palmitic and 75uM stearic acid), and HNLC (HN and LC). Mature oocytes were assayed for aerobic and anaerobic metabolism utilizing oxygen and pH microsensors or fertilized in vitro (D0). Cleavage (D3) and blastocyst (D7, D8) rates were assessed. D3 embryos with ≥ 4 cells were stained for cytosolic and mitochondrial ROS. D8 blastocysts were assayed for gene transcript abundance of metabolic enzymes. Oocyte metabolism was not affected by IVM treatment. D3 formation of embryos with ≥ 4 cells were lower in LC or HN than CON or HNLC; blastocyst rates were greater for CON and lower for HN than LC and HNLC. D3 embryo mitochondrial and cytosolic ROS were reduced in HNLC when compared to other groups. IVM in HN altered blastocyst gene transcript abundance when compared to CON, but not LC or HNLC. In conclusion, supplementation with L-carnitine protects oocytes exposed to high NEFA during IVM and improves their developmental competence, suggesting that high lipid exposure may lead to L-carnitine insufficiency in bovine oocytes.

Treatment of mouse cumulus-oocyte complexes with L-carnitine during vitrification and in vitro maturation affects maturation and embryonic developmental rate after parthenogenetic activation

The technique of oocyte vitrification remains a challenge in most animal species. The present study aimed to evaluate the effects of cumulus cell presence and L-carnitine (LC) treatment during vitrification of selected immature oocytes by brilliant cresyl blue (BCB) staining on maturation and embryonic developmental rate after parthenogenetic activation. Immature oocytes were obtained from C57BL/6 female mice ovaries and stained with BCB. The BCB⁺ cumulus-oocyte complexes (COCs) were then selected and random parts of COCs were denuded from cumulus cells (denuded oocytes: DOs). COCs and DOs were treated with/out LC (0.6 mg/ml) during vitrification and in vitro maturation (IVM) procedures. A number of non-vitrified COCs were also treated with LC during the IVM process (fresh group). Maturation rate, intracellular glutathione (GSH) contents, and developmental competence of oocytes were also examined. The GSH levels in vitrified DOs+LC and vitrified COCs+LC groups were significantly higher (p < 0.01) than untreated vitrified-warmed COCs and DOs. Maturation rate and blastocyst developmental rate were reduced after the vitrification-warming procedure compared with the fresh group. The vitrified COCs+LC group showed a higher percentage of mature oocytes and the ability to develop to blastocyst stage than the vitrified-warmed DOs group (p < 0.01). These data indicated that the presence of cumulus cells around the competent oocyte and LC treatment during vitrification and IVM procedure could improve parthenogenetic developmental competence of vitrified-warmed oocytes by increasing GSH levels and accelerating oocyte maturation.

Biological roles of l-carnitine in oocyte and early embryo development

Poor oocyte quality is responsible for female infertility. Multiple studies have been carried out to find supplements to enhance oocyte quality and mitigate infertility problems. l-carnitine and its derivatives have diverse roles in developing oocytes and early embryos. This review focuses on the in vitro and in vivo studies that using l-carnitine alone or in combination with other supplements for oocyte quality enhancement. The key roles of l-carnitine in oocyte quality and embryo growth were summarized, and the underlying mechanism was also elucidated. l-carnitine helps in the lipid metabolism process by controlling the transfer of fatty acids to mitochondria for β-oxidation. l-carnitine modulates glucose metabolism and enhances respiratory chain enzyme activity. Furthermore, it acts as an antioxidant to prevent oxidative damage and inhibit apoptosis, a signal in response to oxidative stress. Results show the potential of l-carnitine as a potential agent in assisted reproductive technology to improve oocyte quality and the subsequent embryonic development.

The role of L-carnitine in bovine embryo metabolism. A review of the effect of supplementation with a metabolic modulator on in vitro embryo production

Early embryo development is driven first by the maternal RNAs and proteins accumulated during the oocyte's cytoplasmic maturation and then after the embryo genome activation. In mammalian cells, ATP generation occurs via oxidative pathways or by glycolysis, whereas in embryonic stem cells, the consumption of glucose, pyruvate, lipids, and amino acids results in ATP synthesis. Although the bovine embryo has energy reserves in glycogen and lipids, the glycogen concentration is deficient. Conversely, lipids represent the most abundant energy reservoir of bovine embryos, where lipid droplets-containing triacylglycerols are the main fatty acid stores. Oocytes of many mammalian species contain comparatively high amounts of lipids stored as droplets in the ooplasm. L-carnitine has been described as a cofactor that facilitates the mobilization of fatty acids present in the oocyte's cytoplasm into the mitochondria to facilitate β-oxidation processes. However, the L-carnitine effects by addition to media in the in vitro produced embryos on the quality are highly disputed and contradictory by different researchers. This review's objective was to explore the effect that the addition of L-carnitine on culture media could have on the overall bovine embryo production in vitro, from the oocyte metabolism to the modulation of gene expression in the developing embryos.