L-carnitine treatment during oocyte maturation improves in vitro development of cloned pig embryos by influencing intracellular glutathione synthesis and embryonic gene expression

Zinc supplementation during in vitro maturation increases the production efficiency of cloned pigs

Zinc supplementation (0.8 µg/ml) in in vitro maturation (IVM) medium significantly enhances oocyte quality. In this study, we compared the development of somatic cell nuclear transfer (SCNT) embryos produced from conventional IVM (control) and zinc-supplemented IVM oocytes. A total of 1206 and 890 SCNT embryos were produced using control and zinc-supplemented oocytes, respectively, and then were transferred to 11 and 8 recipients, respectively. Five control recipients and three zinc-supplemented recipients became pregnant. Two live piglets and eight mummies were born from two control recipients, and ten live piglets and six stillborn piglets were born from three zinc-supplemented recipients. The production efficiency significantly increased in the zinc-supplemented group (0.33% vs. 3.02%). This report suggests that zinc supplementation in IVM medium improved the production efficiency of cloned pigs.

Effect of Acteoside as a Cell Protector to Produce a Cloned Dog

Somatic cell nuclear transfer (SCNT) is a well-known laboratory technique. The principle of the SCNT involves the reprogramming a somatic nucleus by injecting a somatic cell into a recipient oocyte whose nucleus has been removed. Therefore, the nucleus donor cells are considered as a crucial factor in SCNT. Cell cycle synchronization of nucleus donor cells at G0/G1 stage can be induced by contact inhibition or serum starvation. In this study, acteoside, a phenylpropanoid glycoside compound, was investigated to determine whether it is applicable for inducing cell cycle synchronization, cytoprotection, and improving SCNT efficiency in canine fetal fibroblasts. Primary canine fetal fibroblasts were treated with acteoside (10, 30, 50 μM) for various time periods (24, 48 and 72 hours). Cell cycle synchronization at G0/G1 stage did not differ significantly with the method of induction: acteoside treatment, contact inhibition or serum starvation. However, of these three treatments, serum starvation resulted in significantly increased level of reactive oxygen species (ROS) (99.5 ± 0.3%) and apoptosis. The results also revealed that acteoside reduced ROS and apoptosis processes including necrosis in canine fetal fibroblasts, and improved the cell survival. Canine fetal fibroblasts treated with acteoside were successfully arrested at the G0/G1 stage. Moreover, the reconstructed embryos using nucleus donor cells treated with acteoside produced a healthy cloned dog, but not the embryos produced using nucleus donor cells subjected to contact inhibition. In conclusion, acteoside induced cell cycle synchronization of nucleus donor cells would be an alternative method to improve the efficiency of canine SCNT because of its cytoprotective effects.

Effects of L-carnitine against H2O2-induced oxidative stress in grass carp ovary cells (Ctenopharyngodon idellus)

This study was designed in vitro to investigate the effects of L-carnitine against H2O2-induced oxidative stress in a grass carp (Ctenopharyngodon idellus) ovary cell line (GCO). GCO cells were pre-treated with different concentrations of L-carnitine, followed by incubation with 2.5 mM H2O2 for 1 h to induce oxidative damage. The results indicated that adding L-carnitine at concentrations of 0.01-1 mM into the medium for 12 h significantly increased cell viability. Pre-treatment with L-carnitine at concentrations of 0.1-5 mM for 12 h significantly inhibited 2.5 mM H2O2-induced cell viability loss. The significant decreases in the level of reactive oxygen species and cell apoptosis were observed in 0.5 mM L-carnitine group compared to the H2O2 group. Malondialdehyde values of all of the L-carnitine groups were significantly lower than those of the H2O2 group, while total glutathione levels of all of the L-carnitine groups were significantly higher than of the H2O2 group. The activity of antioxidant enzymes, such as total superoxide dismutase (0.1 and 0.5 mM L-carnitine), catalase (0.5 mM L-carnitine) and γ-glutamyl cysteine synthetase (0.5 and 1 mM L-carnitine), was significantly increased. In addition, pre-treatment of L-carnitine in GCO cells exposed to 2.5 mM H2O2 significantly increased the mRNA expression of copper, zinc superoxide dismutase, catalase (0.5 mM L-carnitine), glutamate cysteine ligase catalytic subunit (0.1-1 mM) and glutathione peroxidase (0.1 mM L-carnitine). In conclusion, L-carnitine promotes GCO cell growth and improves antioxidant function, it plays a protective role against oxidative stress induced by H2O2 in GCO cells, and the appropriate supplemental amount of L-carnitine is 0.1-1 mM.

Cilostazol Improves Developmental Competence of Pig Oocytes by Increasing Intraoocyte Cyclic Adenosine Monophosphate Level and Delaying Meiotic Resumption

Cilostazol (CLZ) is a cyclic adenosine monophosphate (cAMP) modulator that influences the steady state of the meiotic stage. This study was conducted to determine the effects of CLZ treatment during in vitro maturation (IVM) on developmental competence of pig oocytes. Immature oocytes were exposed to 0 (control), 0.5, 2 and 4 μm CLZ during the first 22 h of IVM. Nuclear maturation, intraoocyte glutathione content and embryo cleavage after parthenogenesis (PA) and somatic cell nuclear transfer (SCNT) were not influenced by CLZ at any concentrations. However, 4 μm CLZ significantly (p < 0.05) improved blastocyst formation after PA (52.1% vs 38.7-46.0%) and SCNT relative to other concentrations (40.8% vs 25.0-30.7%). The mean cell numbers of SCNT blastocysts were significantly increased by 4 μm CLZ compared to the control (42.6 cells vs 35.3 cells/blastocyst). CLZ treatment significantly increased the intraoocyte cAMP level and effectively arrested oocytes at the germinal vesicle (GV) and GV break down stages compared to the control (74.5% vs 45.4%). Our results demonstrated that improved developmental competence of PA and SCNT pig embryos occurred via better synchronization of nuclear and cytoplasmic maturation induced by increased cAMP and delayed meiotic resumption after CLZ treatment.

Rapamycin treatment during in vitro maturation of oocytes improves embryonic development after parthenogenesis and somatic cell nuclear transfer in pigs

This study was conducted to investigate the effects of rapamycin treatment during in vitro maturation (IVM) on oocyte maturation and embryonic development after parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT) in pigs. Morphologically good (MGCOCs) and poor oocytes (MPCOCs) were untreated or treated with 1 nM rapamycin during 0-22 h, 22-42 h, or 0-42 h of IVM. Rapamycin had no significant effects on nuclear maturation and blastocyst formation after PA of MGCOCs. Blastocyst formation after PA was significantly increased by rapamycin treatment during 22-42 h and 0-42 h (46.6% and 46.5%, respectively) relative to the control (33.3%) and 0-22 h groups (38.6%) in MPCOCs. In SCNT, blastocyst formation tended to increase in MPCOCs treated with rapamycin during 0-42 h of IVM relative to untreated oocytes (20.3% vs. 14.3%, 0.05 < p < 0.1), while no improvement was observed in MGCOCs. Gene expression analysis revealed that transcript abundance of Beclin 1 and microtubule-associated protein 1 light chain 3 mRNAs was significantly increased in MPCOCs by rapamycin relative to the control. Our results demonstrated that autophagy induction by rapamycin during IVM improved developmental competence of oocytes derived from MPCOCs.

Effect of L-carnitine supplementation on maturation and early embryo development of immature mouse oocytes selected by brilliant cresyle blue staining

PURPOSE

The present study was designed to investigate the effect of L-carnitine treatment during IVM on nuclear and cytoplasmic maturation of immature oocytes selected by Brilliant Cresyle Blue (BCB) staining, and their subsequent developmental competence.

MATERIALS & METHODS

Compact cumulus-oocyte complexes (COCs) were collected from NMRI mice ovaries and stained with BCB staining. BCB+ (colored cytoplasm) oocytes were then cultured in tissue culture medium (TCM) 199 with 0.0, 0.3 and 0.6 mg/ml L-carnitine.

RESULTS

The both L-carnitine concentrations significantly increased the intracellular glutathione (P<0.001), nuclear maturation (P<0.01) and expression levels of cyclin-dependent kinase1 (CDK1) (P<0.05). Moreover, treated oocytes with 0.6 mg/ml L-carnitine showed increased (P < 0.05) expression of mitogen-activated protein kinase1 (MAPK1) mRNA. Also, adding L-carnitine (0.6 mg/ml) to IVM medium significantly increased the cleavage rate (P<0.05). The blastocyst development rate (BDR) in the both L-carnitine treated groups was significantly higher (P<0.001) than the control group. L-carnitine had no significant effect on total blastocyst cell numbers.

CONCLUSIONS

These data indicated that L-carnitine supplementation during IVM of immature BCB+ oocytes improved preimplantation developmental competence of oocytes after IVF, probably by accelerating cytoplasmic and nuclear maturation of oocytes. It may provide a novel approach to improving ART outcomes in infertile couples.

The evolution of porcine embryo in vitro production

The in vitro production of porcine embryos has presented numerous challenges to researchers over the past four decades. Some of the problems encountered were specific to porcine gametes and embryos and needed the concerted efforts of many to overcome. Gradually, porcine embryo in vitro production systems became more reliable and acceptable rates of blastocyst formation were achieved. Despite the significant improvements, the problem of polyspermic fertilization has still not been adequately resolved and the embryo in vitro culture conditions are still considered to be suboptimal. Whereas early studies focused on increasing our understanding of the reproductive processes involved, the technology evolved to the point where in vitro-matured oocytes and in vitro-produced embryos could be used as research material for developing associated reproductive technologies, such as SCNT and embryo cryopreservation. Today, the in vitro procedures used to mature oocytes and culture embryos are integral to the production of transgenic pigs by SCNT. This review discusses the major achievements, advances, and knowledge gained from porcine embryo in vitro production studies and highlights the future research perspectives of this important technology.

Fatty acid metabolism during maturation affects glucose uptake and is essential to oocyte competence

Fatty acid β-oxidation (FAO) is essential for oocyte maturation in mice. The objective of this study was to determine the effect of etomoxir (a FAO inhibitor; 100 μM), carnitine (1 mM), and palmitic acid (1 or 100 μM) during maturation on metabolism and gene expression of the oocyte and cumulus cells, and subsequent embryo development in the mouse. Carnitine significantly increased embryo development, while there was a decrease in development following maturation with 100 μM palmitic acid or etomoxir (P<0.05) treatment. Glucose consumption per cumulus-oocyte complex (COC) was decreased after treatment with carnitine and increased following etomoxir treatment (P<0.05). Intracellular oocyte lipid content was decreased after carnitine or etomoxir exposure (P<0.05). Abundance of Slc2a1 (Glut1) was increased after etomoxir treatment in the oocyte and cumulus cells (P<0.05), suggesting stimulation of glucose transport and potentially the glycolytic pathway for energy production when FAO is inhibited. Abundance of carnitine palmitoyltransferase 2 (Cpt2) tended to increase in oocytes (P=0.1) after treatment with 100 μM palmitic acid and in cumulus cells after exposure to 1 μM palmitic acid (P=0.07). Combined with carnitine, 1 μM palmitic acid increased the abundance of Acsl3 (P<0.05) and Cpt2 tended to increase (P=0.07) in cumulus cells, suggesting FAO was increased during maturation in response to stimulators and fatty acids. In conclusion, fatty acid and glucose metabolism are related to the mouse COC, as inhibition of FAO increases glucose consumption. Stimulation of FAO decreases glucose consumption and lipid stores, positively affecting subsequent embryo development, while an overabundance of fatty acid or reduced FAO negatively affects oocyte quality.

Lipids and oocyte developmental competence: the role of fatty acids and β-oxidation

Metabolism and ATP levels within the oocyte and adjacent cumulus cells are associated with quality of oocyte and optimal development of a healthy embryo. Lipid metabolism provides a potent source of energy and its importance during oocyte maturation is being increasingly recognised. The triglyceride and fatty acid composition of ovarian follicular fluid has been characterised for many species and is influenced by nutritional status (i.e. dietary fat, fasting, obesity and season) as well as lactation in cows. Lipid in oocytes is a primarily triglyceride of specific fatty acids which differ by species, stored in distinct droplet organelles that re-localise during oocyte maturation. The presence of lipids, particularly saturated vs unsaturated fatty acids, in in vitro maturation systems affects oocyte lipid content as well as developmental competence. Triglycerides are metabolised by lipases that have been localised to cumulus cells as well as oocytes. Fatty acids generated by lipolysis are further metabolised by β-oxidation in mitochondria for the production of ATP. β-oxidation is induced in cumulus–oocyte complexes (COCs) by the LH surge, and pharmacological inhibition of β-oxidation impairs oocyte maturation and embryo development. Promoting β-oxidation with l-carnitine improves embryo development in many species. Thus, fatty acid metabolism in the mammalian COC is regulated by maternal physiological and in vitro environmental conditions; and is important for oocyte developmental competence.

Regulation of fatty acid oxidation in mouse cumulus-oocyte complexes during maturation and modulation by PPAR agonists

Fatty acid oxidation is an important energy source for the oocyte; however, little is known about how this metabolic pathway is regulated in cumulus-oocyte complexes. Analysis of genes involved in fatty acid oxidation showed that many are regulated by the luteinizing hormone surge during in vivo maturation, including acyl-CoA synthetases, carnitine transporters, acyl-CoA dehydrogenases and acetyl-CoA transferase, but that many are dysregulated when cumulus-oocyte complexes are matured under in vitro maturation conditions using follicle stimulating hormone and epidermal growth factor. Fatty acid oxidation, measured as production of ³H₂O from [³H]palmitic acid, occurs in mouse cumulus-oocyte complexes in response to the luteinizing hormone surge but is significantly reduced in cumulus-oocyte complexes matured in vitro. Thus we sought to determine whether fatty acid oxidation in cumulus-oocyte complexes could be modulated during in vitro maturation by lipid metabolism regulators, namely peroxisome proliferator activated receptor (PPAR) agonists bezafibrate and rosiglitazone. Bezafibrate showed no effect with increasing dose, while rosiglitazone dose dependently inhibited fatty acid oxidation in cumulus-oocyte complexes during in vitro maturation. To determine the impact of rosiglitazone on oocyte developmental competence, cumulus-oocyte complexes were treated with rosiglitazone during in vitro maturation and gene expression, oocyte mitochondrial activity and embryo development following in vitro fertilization were assessed. Rosiglitazone restored Acsl1, Cpt1b and Acaa2 levels in cumulus-oocyte complexes and increased oocyte mitochondrial membrane potential yet resulted in significantly fewer embryos reaching the morula and hatching blastocyst stages. Thus fatty acid oxidation is increased in cumulus-oocyte complexes matured in vivo and deficient during in vitro maturation, a known model of poor oocyte quality. That rosiglitazone further decreased fatty acid oxidation during in vitro maturation and resulted in poor embryo development points to the developmental importance of fatty acid oxidation and the need for it to be optimized during in vitro maturation to improve this reproductive technology.

A requirement for fatty acid oxidation in the hormone-induced meiotic maturation of mouse oocytes

We have previously shown that fatty acid oxidation (FAO) is required for AMP-activated protein kinase (PRKA)-induced maturation in vitro. In the present study, we have further investigated the role of this metabolic pathway in hormone-induced meiotic maturation. Incorporating an assay with (3)H-palmitic acid as the substrate, we first examined the effect of PRKA activators on FAO levels. There was a significant stimulation of FAO in cumulus cell-enclosed oocytes (CEO) treated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) and RSVA405. In denuded oocytes (DO), AICAR stimulated FAO only in the presence of carnitine, the molecule that facilitates fatty acyl CoA entry into the mitochondria. The carnitine palmitoyltransferase 1 activator C75 successfully stimulated FAO in CEO. All three of these activators trigger germinal vesicle breakdown. Meiotic resumption induced by follicle-stimulating hormone (FSH) or amphiregulin was completely inhibited by the FAO inhibitors etomoxir, mercaptoacetate, and malonyl CoA. Importantly, FAO was increased in CEO stimulated by FSH and epidermal growth factor, and this increase was blocked by FAO inhibitors. Moreover, compound C, a PRKA inhibitor, prevented the FSH-induced increase in FAO. Both carnitine and palmitic acid augmented hormonal induction of maturation. In a more physiological setting, etomoxir eliminated human chorionic gonadotropin (hCG)-induced maturation in follicle-enclosed oocytes. In addition, CEO and DO from hCG-treated mice displayed an etomoxir-sensitive increase in FAO, indicating that this pathway was stimulated during in vivo meiotic resumption. Taken together, our data indicate that hormone-induced maturation in mice requires a PRKA-dependent increase in FAO.