Evidence of melatonin synthesis in the cumulus oocyte complexes and its role in enhancing oocyte maturation in vitro in cattle

The effects of melatonin on bovine uniparental embryos development in vitro and the hormone secretion of COCs

Melatonin is a unique multifunctional molecule that mediates reproductive functions in animals. In this study, we investigated the effects of melatonin on bovine parthenogenetic and androgenetic embryonic development, oocyte maturation, the reactive oxygen species (ROS) levels in parthenogenetic and androgenetic embryos and cumulus—oocyte complexes (COCs) hormone secretion with melatonin supplementation at four concentrations (0, 10, 20, and 30 pmol/mL), respectively. The results showed that melatonin significantly promoted the rates of bovine parthenogenetic and androgenetic embryonic cleavage and morula and blastocysts development (P < 0.05). The rate of cleavage was higher in the androgenetic embryo than that in the parthenogenetic embryo. Compared with the parthenogenetic embryos, the androgenetic embryos had a poor developmental competence from morula to blastocyst stage. Moreover, the levels of ROS were significantly lower in the parthenogenetic and androgenetic embryoes with melatonin-treated group than that of the control group (P < 0.05). Melatonin supplemented significantly increased the maturation rate of oocyte in vitro (P < 0.05). More importantly, melatonin significantly promoted the secretion of progesterone and estradiol by COCs (P < 0.05). To reveal the regulatory mechanism of melatonin on steroids synthesis, we found that steroidogenic genes (CYP11A1, CYP19A1 and StAR) were upregulated, suggesting that melatonin regulated estradiol and progesterone secretion through mediating the expression of steroidogenic genes (CYP11A1, CYP19A1 and StAR). In addition, MT1 and MT2 were identified in bovine early parthenogenetic and androgenetic embryos using western blot. It could be concluded that melatonin had beneficial effects on bovine oocyte in vitro maturation, COC hormone secretion, early development of subsequent parthenogenetic and androgenetic embryos. It is inferred that melatonin could be used to enhance the efficiency of in vitro developed embryos.

Addition of insulin-like growth factor I to the maturation medium of bovine oocytes subjected to heat shock: effects on the production of reactive oxygen species, mitochondrial activity and oocyte competence

This study was performed to investigate the effects of insulin-like growth factor-I (IGF-I) addition to in vitro maturation (IVM) medium on apoptosis, mitochondrial membrane potential, ROS production, and developmental competence of bovine oocytes subjected to heat shock. Two temperatures (conventional: 24 h at 38.5°C, or heat shock: 12 h at 41°C followed by 12 h at 38.5°C) and 3 IGF-I concentrations (0, 25, and 100 ng/mL) were tested during IVM. The oocytes were then fertilized in vitro, and the presumptive zygotes were cultured until reaching the blastocyst stage. There was no interaction between temperature and IGF-I concentration for any variable evaluated (P > 0.05). The addition of IGF-I did not alter the proportion of nuclear maturation, TUNEL-positive oocytes and caspase-3 activity, or blastocyst proportion on Days 7 and 8 post-fertilization. Furthermore, the total number of cells and the number of cells in the inner cell mass (ICM) in the blastocyst were not altered (P > 0.05). However, IGF-I increased (P < 0.05) the mitochondrial membrane potential and the production of ROS in oocytes and decreased (P < 0.05) the proportion of apoptotic cells in the ICM in blastocysts. Heat shock increased (P < 0.05) the proportion of TUNEL-positive oocytes and ROS production and reduced (P < 0.05) the mitochondrial membrane potential. Moreover, heat shock increased (P < 0.05) the apoptosis proportion in the ICM cells. In conclusion, supplementing IVM medium with IGF-I may increase the mitochondrial membrane potential and ROS production in oocytes and decrease apoptosis in the ICM in blastocysts. Heat shock for 12 h compromised oocyte developmental competence and increased apoptosis within the ICM cells of the blastocysts.

Beneficial Effects of Melatonin on the In Vitro Maturation of Sheep Oocytes and Its Relation to Melatonin Receptors

(1) Background: The binding sites of melatonin, as a multifunctional molecule, have been identified in human, porcine, and bovine samples. However, the binding sites and mechanisms of melatonin have not been reported in sheep; (2) Methods: Cumulus–oocyte complexes (COCs) were cultured in TCM-199 supplemented with melatonin at concentrations of 0, 10⁻³, 10⁻⁵, 10⁻⁷, 10⁻⁹, and 10⁻¹¹ M. Melatonin receptors (MT1 and MT2) were evaluated via immunofluorescence and Western blot. The effects of melatonin on cumulus cell expansion, nuclear maturation, embryo development, and related gene (GDF9, DNMT1, PTX3, HAS2, and EGFR) expression were investigated. The level of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were evaluated in oocytes and cumulus, respectively; (3) Results: Both MT1 and MT2 were expressed in oocytes, cumulus cells, and granulosa cells. Melatonin with a concentration of 10⁻⁷ M significantly enhanced the rates of nuclear maturation, cumulus cells expansion, cleavage, and blastocyst. Melatonin enhanced the expression of BMP15 in oocytes and of PTX3, HAS2, and EGFR in cumulus cells. Melatonin decreased the cAMP level of oocytes but enhanced the cGMP level in oocytes and cumulus cells; (4) Conclusion: The higher presence of MT1 in GV cumulus cells and the beneficial effects of melatonin indicated that its roles in regulating sheep oocyte maturation may be mediated mainly by the MT1 receptor.

Effect of lipopolysaccharide on developmental competence of oocytes

In postpartum dairy cows, lipopolysaccharide (LPS) derived from gram-negative bacteria such as Escherichia coli causes uterine inflammation resulting in low fertility. The aim of this study was to determine the effect of LPS on the developmental competence of bovine oocytes in vitro. LPS perturbed the nuclear maturation of bovine oocytes by inhibiting meiotic progression. Although LPS did not affect the copy number of mitochondrial DNA, it decreased mitochondrial membrane potential in matured oocytes. LPS inhibited mitochondrial redistribution throughout the cytoplasm. Oocytes matured under LPS treatment showed decreased development to the blastocyst stage. Moreover, the trophoblast cell number of blastocysts was significantly lower when the oocytes were matured in the presence of LPS. Our findings suggest that LPS might impair the nuclear and cytoplasmic maturation of oocytes and obstruct subsequent embryonic development in dairy cows.

Effects of melatonin on maturation, histone acetylation, autophagy of porcine oocytes and subsequent embryonic development

Melatonin (MLT) is an endogenous hormone with roles in animal germ cell development. However, the effect of MLT on porcine oocyte maturation and its underlying mechanisms remain largely unknown. Here, we investigated the effects of exogenous MLT on oocyte maturation, histone acetylation, autophagy and subsequent embryonic development. We found that 1 nmol/L MLT supplemented in maturation medium was the optimal concentration to promote porcine oocyte maturation and subsequent developmental competence and quality of parthenogenetic embryos. Interestingly, the beneficial effects of 1 nmol/L MLT treatment on porcine oocyte maturation and embryo development were mainly attributed to the first half period of in vitro maturation. Simultaneously, MLT treatment could also improve maturation of small follicle-derived oocytes, morphologically poor (cumulus cell layer ≤1) and even artificially denuded oocytes and their subsequent embryo development. Furthermore, MLT treatment not only could decrease the levels of H3K27ac and H4K16ac in metaphase II (MII) oocytes, but also could increase the expression abundances of genes associated with cumulus cell expansion, meiotic maturation, histone acetylation and autophagy in cumulus cells or MII oocytes. These results indicate that MLT treatment can facilitate porcine oocyte maturation and subsequent embryonic development probably, through improvements in histone acetylation and autophagy in oocytes.

Interaction of melatonin and gonadotropin-inhibitory hormone on the zebrafish brain-pituitary-reproductive axis

Circadian cycles and photoperiod are known to influence reproductive physiology in several animals. Neuropeptides, such as gonadotropin-inhibitory hormone (GNIH) and gonadotropin-releasing hormone (GNRH), are influenced by melatonin in birds and mammals. The present study demonstrates the role of melatonin in oocyte maturation in the zebrafish (Danio rerio), via the brain-pituitary-reproductive axis, under different photic conditions. Melatonin was significantly higher both in the whole brain and ovary under continuous dark (DD) compared to continuous light (LL) conditions. Transcription of gnih in the brain was high in LL, but low in DD; similarly, melatonin exogenous treatment reduced gnih in cultured brain in a dose-dependent manner. Expression of gnrh3, however, was high in both continuous photic conditions (DD and LL), whereas fshb and lhb were high only during DD. kiss2, another neuropeptide, was high in LL, but kiss1 remain unchanged among the conditions. At the gonad level, expression of fshr, lhcgr, mtnr1aa, and mtnr1ab tracked with the expression of their respective ligand in DD and LL. The expression of mprb is high in DD ovary, although intra-ovarian growth factors (tgfb1a and bmp15) were low. The measured increased percentages of germinal vesicle breakdown, expression of Cyclin B1, and reduced Cdc2p34 phosphorylation are consistent with increased maturation in the dark. Our study thus links melatonin to the inhibition of gnih in the brain-pituitary-reproductive axis of zebrafish in response to photic conditions.

Melatonin MT₁ and MT₂ Receptors in the Ram Reproductive Tract

Some melatonin functions in mammals are exerted through MT₁ and MT₂ receptors. However, there are no reports of their presence in the reproductive tract of the ram, a seasonal species. Thus, we have investigated their existence in the ram testis, epididymis, accessory glands and ductus deferens. Real-time polymerase chain reaction (qPCR) revealed higher levels of m-RNA for both receptors in the testis, ampulla, seminal vesicles, and vas deferens, than in the other organs of the reproductive tract (p < 0.05). Western blot analyses showed protein bands compatible with the MT₁ in the testis and cauda epididymis, and for the MT₂ in the cauda epididymis and deferent duct. Immunohistochemistry analyses revealed the presence of MT₁ receptors in spermatogonias, spermatocytes, and spermatids, and MT₂ receptors in the newly-formed spermatozoa in the testis, whereas both receptors were located in the epithelial cells of the ampulla, seminal vesicles, and ductus deferens. Indirect immunofluorescence showed significant differences in the immunolocation of both receptors in spermatozoa during their transit in the epididymis. In conclusion, it was demonstrated that melatonin receptors are present in the ram reproductive tract. These results open the way for new studies on the molecular mechanism of melatonin and the biological significance of its receptors.

Adição da proteína específica do oviduto de porcas (pOSP) e da melatonina em meios de maturação e o efeito na clivagem in vitro de embriões suínos

RESUMO No presente estudo, utilizou-se a melatonina e a proteína específica do oviduto (pOSP) nos meios de maturação in vitro. Foram avaliadas a expansão do complexo cumulus-ovócito (CCOs), as concentrações intracelulares de espécies reativas de oxigênio (ROS) e o desenvolvimento embrionário nos diferentes grupos (C = controle; T1 = somente com melatonina; T2 = com melatonina e pOSP e T3 somente com pOSP). No tocante à expansão do CCOs, houve diferença (P<0,05) dos valores obtidos no grupo C em relação aos valores médios dos grupos T1, T2 e T3, porém não houve diferença entre os valores obtidos nos tratamentos (P>0,05). Na dosagem de ROS, não houve diferença entre os valores médios obtidos no grupo C (26,4±10,9) e o valor verificado no grupo T1 (23,4±7,8), porém no grupo T2 (21,3±9,7) o valor médio mostrou-se satisfatório em relação ao valor do grupo C. No entanto, o valor médio do grupo T3 (16,6±10,5) foi o que demonstrou resultado mais satisfatório quando comparado aos demais grupos (P<0,05). A produção de embriões foi avaliada por meio da taxa de clivagem. Não houve diferença (P>0,05) entre os valores obtidos entre o grupo C (48,9 %) e os valores verificados nos grupos T1 (51,5 %), T2 (50 %), T3 (57,7 %), nem destes entre si. Este estudo permitiu concluir que a proteína específica do oviduto recombinante e a melatonina foram eficientes em melhorar a expansão dos CCOs. Além disso, as células tratadas com pOSP mostraram-se com menor quantidade de ROS, podendo a pOSP ser considerada um antioxidante proteico.

Modification of embryonic resistance to heat shock in cattle by melatonin and genetic variation in HSPA1L

The objectives were to test whether (1) melatonin blocks inhibition of embryonic development caused by heat shock at the zygote stage, and (2) the frequency of a thermoprotective allele for HSPA1L is increased in blastocysts formed from heat-shocked zygotes as compared with blastocysts from control zygotes. It was hypothesized that melatonin prevents effects of heat shock on development by reducing accumulation of reactive oxygen species (ROS) and that embryos inheriting the thermoprotective allele of HSPA1L would be more likely to survive heat shock. Effects of 1 µM melatonin on ROS were determined in experiments 1 and 2. Zygotes were cultured at 38.5 or 40°C for 3 h in the presence of CellROX reagent (ThermoFisher Scientific, Waltham, MA). Culture was in a low [5% (vol/vol)] oxygen (experiment 1) or low or high [21% (vol/vol)] oxygen environment (experiment 2). Heat shock and high oxygen increased ROS; melatonin decreased ROS. Development was assessed in experiments 3 and 4. In experiment 3, zygotes were cultured in low oxygen ± 1 µM melatonin and exposed to 38.5 or 40°C for 12 h (experiment 1) beginning 8 h after fertilization. Melatonin did not protect the embryo from heat shock. Experiment 4 was performed similarly except that temperature treatments (38.5 or 40°C, 24 h) were performed in a low or high oxygen environment (2×2 × 2 factorial design with temperature, melatonin, and oxygen concentration as main effects), and blastocysts were genotyped for a deletion (D) mutation (C→D) in the promoter region of HSPA1L associated with thermotolerance. Heat shock decreased percent of zygotes developing to the blastocyst stage independent of melatonin or oxygen concentration. Frequency of genotypes for HSPA1L was affected by oxygen concentration and temperature, with an increase in the D allele for blastocysts that developed in high oxygen and following heat shock. It was concluded that (1) lack of effect of melatonin or oxygen concentration on embryonic development means that the negative effects of heat shock on the zygote are not mediated by ROS, (2) previously reported effect of melatonin on fertility of heat-stressed cows might involve actions independent of the antioxidant properties of melatonin, and (3) the deletion mutation in the promoter of HSPA1L confers protection to the zygote from heat shock and high oxygen. Perhaps, embryonic survival during heat stress could be improved by selecting for thermotolerant genotypes.

Effects of melatonin on oocyte maturation in PCOS mouse model

The purpose of oocyte in vitro maturation is generation of mature oocytes that could support future development. Efforts have been made to enhance oocyte developmental competence by developing optimal culture conditions. The present study is conducted to determine melatonin effects on quality of polycystic ovarian syndrome (PCOS) oocytes when it has been added during in vitro maturation, and immature oocytes were cultured in defined conditioned medium with and without different melatonin concentrations. Melatonin could significantly improve nuclear maturation of PCOS oocytes (81.1% vs. 56.3%, P < 0.05 were achieved with 10^-6 mol/L concentration). Cleavage rate was significantly higher in 10^-5 mol/L concentration compared to untreated oocytes in PCOS (54% vs. 35%, respectively) and it was significantly higher with 10^-6 mol/L concentration in the control group, 55% versus 38%, compared to untreated oocytes. This study showed that melatonin has the potential to induce oocyte nuclear maturation and guarantee fertilization potential. © 2016 Japanese Society of Animal Science.

Effect of melatonin on maturation capacity and fertilization of Nili-Ravi buffalo (Bubalus bubalis) oocytes

This study evaluated the effect of melatonin supplementation of in vitro maturation media on in vitro maturation (IVM) and in vitro fertilization (IVF) rate of buffalo oocytes. Cumulus oocytes complexes (COCs) were aspirated from follicles of 2-8 mm diameter. In experiment I, COCs were matured in IVM medium supplemented with 0 (control), 250, 500, and 1000 μM melatonin for 22-24 hours in CO₂ incubator at 38.5°C with 5% CO₂ and at 95% relative humidity. The maturation rate did not differ in media supplemented with melatonin at 250 μM, 500 μM, 1000 μM and control (0 μM). In experiment II, the matured oocytes were fertilized in 50 μl droplets of Tyrode’s Albumin Lactate Pyruvate (TALP) medium having 10 ug/ml heparin for sperm (2 million/ml) capacitation. The fertilization droplets were then kept for incubation at 5% CO₂, 39°C and at 95% relative humidity for 18 hours. The fertilization rate was assessed by sperm penetration and pronuclear formation. Fertilization rate was improved when maturation medium was supplemented with 250 μM melatonin compared to control. In conclusion, melatonin supplementation to serum free maturation media at 250 μM improved the fertilization rate of buffalo oocytes.

Melatonin modulates the functions of porcine granulosa cells via its membrane receptor MT2 in vitro

Melatonin (N-acetyl-5-methoxytryptamine) is documented as a hormone involved in the circadian regulation of physiological and neuroendocrine function in mammals. Herein, the effects of melatonin on the functions of porcine granulosa cells in vitro were investigated. Porcine granulosa cells were cultivated with variable concentrations of melatonin (0, 0.001, 0.01, 0.1, 1.0, and 10ng/mL) for 48h. Melatonin receptor agonist (IIK7) and antagonist (Luzindole, 4P-PDOT) were used to further examine the action of melatonin. The results showed optimum cell viability and colony-forming efficiency of porcine granulosa cells at 0.01ng/mL melatonin for 48-h incubation period. The percentage of apoptotic granulosa cells was significantly reduced by 0.01 and 0.1ng/mL melatonin within the 48-h incubation period as compared with the rest of the treatments. Estradiol biosynthesis was significantly stimulated by melatonin supplementation and suppressed for the progesterone secretion; the minimum ratio of progesterone to estradiol was 1.82 in 0.01ng/mL melatonin treatment after 48h of cultivation. Moreover, the expression of BCL-2, CYP17A1, CYP19A1, SOD1, and GPX4 were up-regulated by 0.01ng/mL melatonin or combined with IIK7, but decreased for the mRNA levels of BAX, P53, and CASPASE-3, as compared with control or groups treated with Luzindole or 4P-PDOT in the presence of melatonin. In conclusion, the study demonstrated that melatonin mediated proliferation, apoptosis, and steroidogenesis in porcine granulosa cells predominantly through the activation of melatonin receptor MT2 in vitro, which provided evidence of the beneficial role of melatonin as well as its functional mechanism in porcine granulosa cells in vitro.

Effects of Two Types of Melatonin-Loaded Nanocapsules with Distinct Supramolecular Structures: Polymeric (NC) and Lipid-Core Nanocapsules (LNC) on Bovine Embryo Culture Model

Melatonin has been used as a supplement in culture medium to improve the efficiency of in vitro produced mammalian embryos. Through its ability to scavenge toxic oxygen derivatives and regulate cellular mRNA levels for antioxidant enzymes, this molecule has been shown to play a protective role against damage by free radicals, to which in vitro cultured embryos are exposed during early development. In vivo and in vitro studies have been performed showing that the use of nanocapsules as active substances carriers increases stability, bioavailability and biodistribution of drugs, such as melatonin, to the cells and tissues, improving their antioxidant properties. These properties can be modulated through the manipulation of formula composition, especially in relation to the supramolecular structures of the nanocapsule core and the surface area that greatly influences drug release mechanisms in biological environments. This study aimed to evaluate the effects of two types of melatonin-loaded nanocapsules with distinct supramolecular structures, polymeric (NC) and lipid-core (LNC) nanocapsules, on in vitro cultured bovine embryos. Embryonic development, apoptosis, reactive oxygen species (ROS) production, and mRNA levels of genes involved in cell apoptosis, ROS and cell pluripotency were evaluated after supplementation of culture medium with non-encapsulated melatonin (Mel), melatonin-loaded polymeric nanocapsules (Mel-NC) and melatonin-loaded lipid-core nanocapsules (Mel-LNC) at 10⁻⁶, 10⁻⁹, and 10⁻¹² M drug concentrations. The highest hatching rate was observed in embryos treated with 10⁻⁹ M Mel-LNC. When compared to Mel and Mel-NC treatments at the same concentration (10⁻⁹ M), Mel-LNC increased embryo cell number, decreased cell apoptosis and ROS levels, down-regulated mRNA levels of BAX, CASP3, and SHC1 genes, and up-regulated mRNA levels of CAT and SOD2 genes. These findings indicate that nanoencapsulation with LNC increases the protective effects of melatonin against oxidative stress and cell apoptosis during in vitro embryo culture in bovine species.

Mitochondria Synthesize Melatonin to Ameliorate Its Function and Improve Mice Oocyte's Quality under in Vitro Conditions

The physiology of oocyte in vitro maturation remains elusive. Generally, the oocytes have a very low maturation rate under in vitro conditions. In the current study, we found that melatonin promotes the maturation of oocytes in which mitochondria play a pivotal role. It was identified that; (1) mitochondria are the major sites for melatonin synthesis in oocytes and they synthesize large amounts of melatonin during their maturation; (2) melatonin improves mitochondrial function by increased mtDNA copy, mitochondrial membrane potential (ΔΨ_m) and mitochondrial distribution and ATP production in oocytes; (3) the meiotic spindle assembly is enhanced; (4) melatonin reduces ROS production and inhibits 8-oxodG formation, thereby protecting potential DNA mutation from oxidative damage. As a result, melatonin improves the quality of oocytes, significantly accelerates the developmental ability of IVF embryo. The results provide novel knowledge on the physiology of oocyte’s maturation, especially under in vitro conditions.

Effects of melatonin during IVM in defined medium on oocyte meiosis, oxidative stress, and subsequent embryo development

Melatonin may have beneficial effects when used in oocyte maturation and embryo development culture. The effect of melatonin during IVM on meiosis resumption and progression in bovine oocytes and on expression of antioxidant enzymes, nuclear fragmentation and free radicals, as well as on embryo development were assessed. Cumulus-oocyte complexes were matured in vitro with melatonin (10(-9) and 10(-6) M), FSH (positive control), or without hormones (negative control) in defined medium. Maturation rates were evaluated at 6, 12, 18, and 24 hours. Transcripts for antioxidant enzymes (CuZnSOD, MnSOD, and glutathione peroxidase 4 (GPX4)) in oocytes and cumulus cells, nuclear fragmentation in cumulus cells (TUNEL) and reactive oxygen species levels in oocytes (carboxy-H2 difluorofluorescein diacetate) were determined at 24 hours IVM. Effect of treatments on embryo development was determined after in vitro fertilization and culture. At 12 hours, meiosis resumption rates in FSH and melatonin-treated groups were similar (69.6%-81.8%, P > 0.05). At 24 hours, most oocytes were in metaphase II, with FSH showing highest rates (90.0%, P < 0.05) compared with the other groups (51.6%-69.1%, P > 0.05). In cumulus cells, MnSOD expression was higher in FSH group (P < 0.05) whereas Cu,ZnSOD transcripts were more abundant in melatonin group (10(-6)M; P < 0.05). Nuclear fragmentation in cumulus cells was highest in controls (37.4%/10,000 cells; P < 0.05) and lower in FSH and 10(-6)M melatonin (29.4% and 25.6%/10,000 cells, respectively). Reactive oxygen species levels were lower in oocytes matured with 10(-6)M melatonin than in control and FSH groups (P < 0.05). Embryo development from oocytes matured only with melatonin was similar to those matured in complete medium (P > 0.05). In conclusion, although melatonin during IVM in a defined medium does not stimulate nuclear maturation progression it does stimulate meiosis resumption and such treated oocytes support subsequent embryo development. Melatonin also shows cytoprotective effects on cumulus-oocyte complexes.

Melatonin delivery by nanocapsules during in vitro bovine oocyte maturation decreased the reactive oxygen species of oocytes and embryos

In this work, a promising approach to increase the advantageous properties of melatonin through its encapsulation into lipid-core nanocapsules (LNC) was examined. Oocytes were treated during in vitro maturation with non-encapsulated melatonin (Mel), melatonin-loaded lipid-core nanocapsules (Mel-LNC), and unloaded LNC. Cytotoxicity, meiotic maturation rate, development to the blastocyst stage, reactive oxygen species (ROS) and glutathione levels, mean cell number and apoptotic cell/blastocyst, and mRNA quantification were evaluated. Both Mel and Mel-LNC enhanced in vitro embryo production, however, Mel-LNC proved to be more effective at decreasing ROS levels and the apoptotic cell number/blastocyst, increasing the cleavage and blastocyst rates, up-regulating the GPX1 and SOD2 genes, and down-regulating the CASP3 and BAX genes. Mel-LNC could penetrate into oocytes and remain inside the cells until they reach the blastocyst stage. In conclusion, when melatonin was encapsulated in LNC and applied during in vitro oocyte maturation, some quality aspects of the blastocysts were improved.

Melatonin inhibits paraquat-induced cell death in bovine preimplantation embryos

Preimplantation embryos are sensitive to oxidative stress-induced damage that can be caused by reactive oxygen species (ROS) originating from normal embryonic metabolism and/or the external surroundings. Paraquat (PQ), a commonly used pesticide and potent ROS generator, can induce embryotoxicity. The present study aimed to investigate the effects of melatonin on PQ-induced damage during embryonic development in bovine preimplantation embryos. PQ treatment significantly reduced the ability of bovine embryos to develop to the blastocyst stage, and the addition of melatonin markedly reversed the developmental failure caused by PQ (20.9% versus 14.3%). Apoptotic assay showed that melatonin pretreatment did not change the total cell number in blastocysts, but the incidence of apoptotic nuclei and the release of cytochrome c were significantly decreased. Using real-time quantitative polymerase chain reaction analysis, we found that melatonin pre-incubation significantly altered the expression levels of genes associated with redox signaling, particularly by attenuating the transcript level of Txnip and reinforcing the expression of Trx. Furthermore, melatonin pretreatment significantly reduced the expression of the pro-apoptotic caspase-3 and Bax, while the expression of the anti-apoptotic Bcl-2 and XIAP was unaffected. Western blot analysis showed that melatonin protected bovine embryos from PQ-induced damage in a p38-dependent manner, but extracellular signal-regulated kinase (ERK) and c-JUN N-terminal kinase (JNK) did not appear to be involved. Together, these results identify an underlying mechanism by which melatonin enhances the developmental potential of bovine preimplantation embryos under oxidative stress conditions.

Melatonin inhibits apoptosis and improves the developmental potential of vitrified bovine oocytes

Vitrification of oocytes has been shown to be closely associated with increased levels of reactive oxygen species (ROS) and apoptotic events. However, little information is available the effect of melatonin on the ROS levels and apoptotic events in vitrified oocytes. Therefore, we studied the effect of melatonin on ROS and apoptotic events in vitrified bovine oocytes by supplementing vitrification solution or in vitro maturation (IVM) and vitrification solution with 10(-9) m melatonin. We analyzed the ROS, mitochondrial Ca(2+) (mCa(2+) ) and membrane potential (ΔΨm), externalization of phosphatidylserine (PS), caspase-3 activation, DNA fragmentation, mRNA expression levels of Bax and Bcl2 l1, and developmental potential of vitrified bovine oocytes. Vitrified bovine oocytes exhibited increased levels of ROS, mCa(2+) , Bax mRNA, and caspase-3 protein and higher rates of PS externalization and DNA fragmentation, and decreased ΔΨm and Bcl2 l1 mRNA expression level. However, melatonin supplementation in vitrification solution or IVM and vitrification solution significantly decreased the levels of ROS, mCa(2+) , Bax mRNA expression, and caspase-3 protein, and PS externalization and DNA fragmentation rates, and increased the ΔΨm and Bcl2 l1 mRNA expression level in vitrified oocytes, resulting in an increased developmental ability of vitrified bovine oocytes after parthenogenetic activation. The developmental ability of vitrified oocytes with melatonin supplementation in IVM and vitrification solution was similar to that of fresh ones. This study showed that supplementing the IVM and vitrification medium or vitrification medium with 10(-9) m melatonin significantly decreased the ROS level and inhibited apoptotic events of vitrified bovine oocytes, consequently increasing their developmental potential.

Evidence of melatonin synthesis in the ram reproductive tract

Melatonin is a ubiquitous molecule found in a wide range of fluids, one of them being ram seminal plasma, in which it can reach higher concentrations than those found in blood, suggesting an extrapineal secretion by the reproductive tract. In order to identify the source of the melatonin found in ram seminal plasma, we first tried to determine whether the melatonin levels were maintained during the day. For this purpose, melatonin concentrations were measured in seminal plasma obtained from first ejaculates of six rams at 6:00 a.m. in total darkness, at 10:00 a.m. and at 14:00 p.m. The melatonin concentration was higher (p < 0.05) in ejaculates collected at 6:00 a.m. than at 10:00 and 14:00. There was no statistical difference between the latter. To further corroborate an extrapineal secretion of melatonin, the presence of the two key enzymes involved in melatonin synthesis, arylalkylamine-N-acetyltransferase (AANAT) and N-acetylserotonin-O-methyltransferase (ASMT) was analyzed by RT-PCR, q-PCR and Western-blot in ram testes, epididymis, and accessory glands. The RT-PCR showed the presence of the m-RNA codifying both AANAT and ASTM in all the tissues under study, but the q-PCR and Western-blot revealed that gene expression of these enzymes was significantly higher in the testis (p < 0.05). Immunohistochemistry confirmed the presence of AANAT and ASMT in the testis and revealed that they were found in the Leydig cells, spermatocytes, and spermatids. Also, measurable levels of melatonin were found in testicular tissue and the tail of the epididymis. In conclusion, our study indicates that the testes are one of the likely sources of the high levels of melatonin found in ram seminal plasma, at least during the day.

Melatonin protects porcine oocyte in vitro maturation from heat stress

Melatonin is a pleiotropic molecule which plays an important role in animal reproductive activities. Because of the increased global warming, the impact of heat stress (HS) on stockbreeding has become an inevitable issue to be solved. To investigate the potential effects of melatonin on the in vitro maturation of porcine oocyte under the HS, a HS model for porcine oocyte maturation has been used in this study and the different concentrations of melatonin (10(-6) -10(-9)  m) were also tested for their protective effects on oocytes. The polar body rate, the index of the nuclear maturation of the oocytes, and the cleavage rate as well as the blastocyst rate were measured to evaluate the developmental competence of the oocytes after parthenogenetic activation (PA). The results showed that HS [in vitro maturation (IVM) 20-24 hr, 42°C] significantly reduced the polar body rate of oocytes and the blastocyte rate of porcine PA embryos, while melatonin (10(-7)  m) application not only improved polar body rate and blastocyte rate, but also preserved the normal levels of steroid hormone which is disrupted by HS. The presence of melatonin (10(-7)  m) during the oocyte maturation under the HS reduced reactive oxygen species (ROS) formation, enhanced glutathione (GSH) production, inhibited cell apoptosis, and increased the gene expressions of SIRT1, AKT2, and Polg2. Importantly, the endogenously occurring melatonin of cumulus-oocyte complexes was significantly induced by HS. The results indicated that melatonin application effectively protected the oocytes from HS. These observations warranted the further studies in vivo regarding to improve the reproductive activities of animals under the global warming environment.

Effect of cortisol on bovine oocyte maturation and embryo development in vitro

Glucocorticoids (GCs) are important mediators of key cellular events. Herein, we investigated the effect of adding cortisol to the IVM medium on the acquisition of developmental competency in bovine oocytes. Cortisol (0.01, 0.1, or 1 μg/mL) had no effect on cleavage rates or cell numbers of resulting blastocysts; however, supplementation with 0.1 μg/mL during IVM increased blastocyst rates of in vitro-fertilized bovine oocytes as compared to untreated controls (41 ± 10% vs. 21 ± 1.2%, P < 0.05, respectively). This concentration was chosen to assess changes in the relative expression of potential GC target genes. Oocytes matured in the presence of cortisol and their corresponding cumulus cells did not show changes in expression for genes analyzed as compared to untreated controls. Notably, blastocysts from oocytes matured in cortisol-supplemented medium expressed higher relative levels of glucose transporter 1 (GLUT1), fatty acid synthase (FASN), and heat shock protein 70 (HSP70). This study supports a role for cortisol in the acquisition of bovine oocyte competence. This is evidenced by increased blastocyst development rates and presumably related to elevated embryonic transcripts with roles in glucose and lipid metabolism, as well as the cellular response to stress.

Daily differential expression of melatonin-related genes and clock genes in rat cumulus-oocyte complex: changes after pinealectomy

This study investigated the maturational stage (immature and mature ovaries) differences of mRNA expression of melatonin-forming enzymes (Aanat and Asmt), melatonin membrane receptors (Mt1 and Mt2) and putative nuclear (Rorα) receptors, and clock genes (Clock, Bmal1, Per1, Per2, Cry1, Cry2) in cumulus-oocyte complexes (COC) from weaning Wistar rats. We also examined the effects of pinealectomy and of melatonin pharmacological replacement on the daily expression of these genes in COC. qRT-PCR analysis revealed that in oocytes, the mRNA expression of Asmt, Mt2, Clock, Bmal1, Per2, and Cry1 were higher (P < 0.05) in immature ovaries than in the mature ones. In cumulus cells, the same pattern of mRNA expression for Asmt, Aanat, Rorα, Clock, Per1, Cry1, and Cry2 genes was observed. In oocytes, pinealectomy altered the daily mRNA expression profiles of Asmt, Mt1, Mt2, Clock, Per1, Cry1, and Cry2 genes. In cumulus cells, removal of the pineal altered the mRNA expression profiles of Mt1, Mt2, Rorα, Aanat, Asmt, Clock, Bmal1, Per2, Cry1, and Cry2 genes. Melatonin treatment partially or completely re-established the daily mRNA expression profiles of most genes studied. The mRNA expression of melatonin-related genes and clock genes in rat COC varies with the maturational stage of the meiotic cellular cycle in addition to the hour of the day. This suggests that melatonin might act differentially in accordance with the maturational stage of cumulus/oocyte complex. In addition, it seems that circulating pineal melatonin is very important in the design of the daily profile of mRNA expression of COC clock genes and genes related to melatonin synthesis and action.

Genomewide association study of reproductive efficiency in female cattle

Reproductive efficiency is of economic importance in commercial beef cattle production, as failure to achieve pregnancy reduces the number of calves marketed per cow exposed. Identification of genetic markers with predictive merit for reproductive success would facilitate early selection of sires with daughters having improved reproductive rate without increasing generation intervals. To identify regions of the genome harboring variation affecting reproductive success, we applied a genomewide association study (GWAS) approach based on the >700,000 SNP marker assay, using a procedure based on genotyping multianimal pools of DNA to increase the number of animals that could be genotyped with available resources. Cows from several populations were classified according to reproductive efficiency, and DNA was pooled within population and phenotype prior to genotyping. Populations evaluated included a research population at the U.S. Meat Animal Research Center, 2 large commercial ranch populations, and a number of smaller populations (<100 head) across the United States. We detected 2 SNP with significant genomewide association (P ≤ 1.49 × 10(-7)), on BTA21 and BTA29, 3 SNP with suggestive associations (P ≤ 2.91 × 10(-6)) on BTA5, and 1 SNP with suggestive association each on BTA1 and BTA25. In addition to our novel findings, we confirmed previously published associations for SNP on BTA-X and all autosomes except 3 (BTA21, BTA22, and BTA28) encompassing substantial breed diversity including Bos indicus and Bos taurus breeds. The study identified regions of the genome associated with reproductive efficiency, which are being targeted for further analysis to develop robust marker systems, and demonstrated that DNA pooling can be used to substantially reduce the cost of GWAS in cattle.

Melatonin: shedding light on infertility?--A review of the recent literature

In recent years, the negative impact of oxidative stress on fertility has become widely recognised. Several studies have demonstrated its negative effect on the number and quality of retrieved oocytes and embryos following in-vitro fertilisation (IVF). Melatonin, a pineal hormone that regulates circadian rhythms, has also been shown to exhibit unique oxygen scavenging abilities. Some studies have suggested a role for melatonin in gamete biology. Clinical studies also suggest that melatonin supplementation in IVF may lead to better pregnancy rates. Here we present a critical review and summary of the current literature and provide suggestions for future well designed clinical trials.

Beneficial effects of melatonin on bovine oocytes maturation: a mechanistic approach

This study was performed to investigate the effect of melatonin on bovine oocyte maturation and subsequent embryonic development in vitro. The endogenous melatonin concentration in bovine follicular fluid is approximately 10(-11) M. To examine the potential beneficial effects of melatonin on bovine oocyte maturation in vitro, germinal vesicle (GV) oocytes were incubated with different concentrations of melatonin (10(-11), 10(-9), 10(-7), 10(-5), 10(-3) M). Melatonin supplementation at suitable concentrations significantly promoted oocyte maturation. The development of embryos and the mean cell number/blastocyst produced after in vitro fertilization were remarkably improved. The most effective melatonin concentrations obtained from the studies ranged from 10(-9) to 10(-7) M. The expression of melatonin receptor MT1 and MT2 genes was identified in cumulus cells, granulosa cells, and oocytes using reverse transcription PCR, immunofluorescence, and Western blot. The mechanistic studies show that the beneficial effects of melatonin on bovine oocyte maturation are mediated via melatonin membrane receptors as the melatonin receptor agonist (IIK7) promotes this effect while the melatonin receptor antagonist (luzindole) blocks this action. Mechanistic explorations revealed that melatonin supplementation during bovine oocyte maturation significantly up-regulated the expressions of oocyte maturation-associated genes (GDF9, MARF1, and DNMT1a) and cumulus cells expansion-related gene (PTX3, HAS1/2) and that LHR1/2, EGFR are involved in signal transduction and epigenetic reprogramming. The results obtained from the studies provide new information regarding the mechanisms by which melatonin promotes bovine oocyte maturation in vitro and provide an important reference for in vitro embryo production of bovine and the human-assisted reproductive technology.

Melatonin counteracts BMP-6 regulation of steroidogenesis by rat granulosa cells

The ovarian bone morphogenetic protein (BMP) system is a physiological inhibitor of luteinization in growing ovarian follicles. BMP-6, which is expressed in oocytes and granulosa cells of healthy follicles, specifically inhibits FSH actions by suppressing adenylate cyclase activity. In the present study, we studied the role of melatonin in ovarian steroidogenesis using rat primary granulosa cells of immature female rat ovaries by focusing on the interaction with BMP-6 activity. Treatment with melatonin had no direct effect on FSH-induced progesterone or estradiol production by granulosa cells, and the results were not affected by the presence of co-cultured oocytes. In addition, synthesis of cAMP by granulosa cells was not significantly altered by melatonin treatment. To elucidate the interaction between activities of melatonin and BMPs, the effect of melatonin treatment on suppression of progesterone synthesis by BMP-6 was investigated. Interestingly, the inhibitory effect of BMP-6 on FSH-induced progesterone production was impaired by co-treatment with melatonin. Granulosa cells express higher levels of MT1 than MT2, and BMP-6 had no significant effect on MT1 expression in granulosa cells. However, BMP-6-induced Smad1/5/8 phosphorylation and Id-1 transcription were suppressed by melatonin, suggesting that melatonin has an inhibitory effect on BMP receptor signaling in granulosa cells. Although the expression levels of ALK-2, -6, ActRII and BMPRII were not affected by melatonin, inhibitory Smad6, but not Smad7, expression was upregulated by melatonin. Thus, melatonin plays a role in the regulation of BMP-6 signal intensity for controlling progesterone production in the ovary. These findings suggest that the effect of melatonin on maintenance of ovarian function is, at least in part, due to the regulation of endogenous BMP activity in granulosa cells.

Melatonin and the circadian system: contributions to successful female reproduction

OBJECTIVE

To summarize the role of melatonin and circadian rhythms in determining optimal female reproductive physiology, especially at the peripheral level.

DESIGN

Databases were searched for the related English-language literature published up to March 1, 2014. Only papers in peer-reviewed journals are cited.

SETTING

Not applicable.

PATIENT(S)

Not applicable.

INTERVENTION(S)

Melatonin treatment, alterations of the normal light:dark cycle and light exposure at night.

MAIN OUTCOME MEASURE(S)

Melatonin levels in the blood and in the ovarian follicular fluid and melatonin synthesis, oxidative damage and circadian rhythm disturbances in peripheral reproductive organs.

RESULT(S)

The central circadian regulatory system is located in the suprachiasmatic nucleus (SCN). The output of this master clock is synchronized to 24 hours by the prevailing light-dark cycle. The SCN regulates rhythms in peripheral cells via the autonomic nervous system and it sends a neural message to the pineal gland where it controls the cyclic production of melatonin; after its release, the melatonin rhythm strengthens peripheral oscillators. Melatonin is also produced in the peripheral reproductive organs, including granulosa cells, the cumulus oophorus, and the oocyte. These cells, along with the blood, may contribute melatonin to the follicular fluid, which has melatonin levels higher than those in the blood. Melatonin is a powerful free radical scavenger and protects the oocyte from oxidative stress, especially at the time of ovulation. The cyclic levels of melatonin in the blood pass through the placenta and aid in the organization of the fetal SCN. In the absence of this synchronizing effect, the offspring may exhibit neurobehavioral deficits. Also, melatonin protects the developing fetus from oxidative stress. Melatonin produced in the placenta likewise may preserve the optimal function of this organ.

CONCLUSION(S)

Both stable circadian rhythms and cyclic melatonin availability are critical for optimal ovarian physiology and placental function. Because light exposure after darkness onset at night disrupts the master circadian clock and suppresses elevated nocturnal melatonin levels, light at night should be avoided.

Melatonin enhances the in vitro maturation and developmental potential of bovine oocytes denuded of the cumulus oophorus

This study was designed to determine the effect of melatonin on the in vitro maturation (IVM) and developmental potential of bovine oocytes denuded of the cumulus oophorus (DOs). DOs were cultured alone (DOs) or with 10-9 M melatonin (DOs + MT), cumulus-oocyte complexes (COCs) were cultured without melatonin as the control. After IVM, meiosis II (MII) rates of DOs, and reactive oxygen species (ROS) levels, apoptotic rates and parthenogenetic blastocyst rates of MII oocytes were determined. The relative expression of ATP synthase F0 Subunit 6 and 8 (ATP6 and ATP8), bone morphogenetic protein 15 (BMP-15) and growth differentiation factor 9 (GDF-9) mRNA in MII oocytes and IFN-tau (IFN-τ), Na+/K+-ATPase, catenin-beta like 1 (CTNNBL1) and AQP3 mRNA in parthenogenetic blastocysts were quantified using real-time polymerase chain reaction (PCR). The results showed that: (1) melatonin significantly increased the MII rate of DOs (65.67 ± 3.59 % vs. 82.29 ± 3.92%; P < 0.05), decreased the ROS level (4.83 ± 0.42 counts per second (c.p.s) vs. 3.78 ± 0.29 c.p.s; P < 0.05) and apoptotic rate (36.99 ± 3.62 % vs. 21.88 ± 2.08 %; P < 0.05) and moderated the reduction of relative mRNA levels of ATP6, ATP8, BMP-15 and GDF-9 caused by oocyte denudation; (2) melatonin significantly increased the developmental rate (24.17 ± 3.54 % vs. 35.26 ± 4.87%; P < 0.05), and expression levels of IFN-τ, Na+/K+-ATPase, CTNNBL1 and AQP3 mRNA of blastocyst. These results indicated that melatonin significantly improved the IVM quality of DOs, leading to an increased parthenogenetic blastocyst formation rate and quality.

Role of melatonin on production and preservation of gametes and embryos: a brief review

The aim of this brief review is to clarify the role of melatonin in the production and preservation of mammalian gametes and embryos. Melatonin is an indoleamine synthesized from tryptophan in the pineal gland and other organs that operates as a hypothalamic-pituitary-gonadal axis modulator and regulates the waxing and waning of seasonal reproductive competence in photoperiodic mammals. A major function of the melatonin rhythm is to transmit information about the length of the daily photoperiod to the circadian and circannual systems in order to provide time-of-day and time-of-year information, respectively, to the organism. Melatonin is also a powerful antioxidant and anti-apoptotic agent, which is due to its direct scavenging of toxic oxygen derivatives and its ability to reduce the formation of reactive species. Mammalian gametes and embryos are highly vulnerable to oxidative stress due to the presence of high lipid levels; during artificial breeding procedures, these structures are exposed to dramatic changes in the microenvironment, which have a direct bearing on their function and viability. Free radicals influence the balance between oxidation-reduction reactions, disturb the transbilayer-phospholipid asymmetry of the plasma membrane and enhance lipid peroxidation. Melatonin, due to its amphiphilic nature, is undoubtedly useful in tissues by protecting them from free radical-mediated oxidative damage and cellular death. The supplementation of melatonin to semen extender or culture medium significantly improves sperm viability, oocyte competence and blastocyst development in vitro.

Clinical relevance of melatonin in ovarian and placental physiology: a review

Within the last decade, the synthesis of melatonin in and its functions at the level of the peripheral reproductive organs has come into better focus. Melatonin is produced at several reproductive organ sites, e.g., the oocyte, ovarian follicular cells and the placental cytotrophoblasts. Moreover, these cells also contain membrane receptors for this indoleamine. In addition, via the free radical scavenging activity of melatonin and its metabolites, oxidative stress is reduced in all reproductive organ cells ensuring their optimal function. Enhancement of oocyte maturation and preservation of oocyte quality may be major functions of melatonin. Oocyte damage reduces successful fertilization and the development of a healthy fetus. The findings that melatonin protects the oocyte from toxic oxygen species have implications for improving the outcome of in vitro fertilization-embryo transfer procedures, as already shown in two published reports. Some actions of melatonin in the placenta may be context specific. Thus, melatonin is believed to function in the maintenance of optimal placental homeostasis by deferring apoptosis of villous cytotrophoblasts, while protecting syncytiotrophoblasts from oxidative damage. Melatonin reduces oxidative damage in the placenta and may improve hemodynamics and nutrient transfer at the placental-uterine interface. The use of melatonin to treat preeclampsia should also be considered.

Melatonin modulates the expression of BCL-xl and improve the development of vitrified embryos obtained by IVF in mice

PURPOSE

Antioxidant and anti-apoptotic effects of melatonin on development of in vitro fertilization (IVF)/vitrified two-cell mouse embryos were evaluated in this study.

METHODS

The IVF two-cell embryos were vitrified by cryotop, and were cultured in KSOM medium in different concentrations of melatonin (10(-6), 10(-9), 10(-12) M) and without melatonin. The blastocyst cell number, apoptotic cells and glutathione (GSH) level were evaluated by differential, TUNEL and cell tracker blue staining, respectively. The expression of Bax and Bcl-xl genes was evaluated by qPCR. The expression of melatonin receptors (Mtnr1a and Mtnr1b) in mouse 2-cell embryos and blastocysts was evaluated by RT-PCR.

RESULTS

Melatonin increased the rate of cleavage and blastulation at 10(-12) M concentration (p < 0.05). The number of trophectoderm and inner cell mass showed a significant increase (p < 0.05) in 10(-9) M melatonin. The 10(-9) M and 10(-12) M melatonin treatments significantly reduced (p < 0.05) the apoptotic index. The significant increase in the expression of Bcl-xl observed at 10(-9) M concentration however, reduced expression of Bax was not statistically significant. The levels of GSH in 10(-9) and 10(-12) M groups were significantly improved relative to the control group (p < 0.05). The Mtnr1a was expressed in 2-cell embryos and blastocysts in all groups, but the expression of Mntr1b was not detected.

CONCLUSION

Melatonin may have a special role against oxidative stress in protection of IVF/vitrified embryos.

Peripheral reproductive organ health and melatonin: ready for prime time

Melatonin has a wide variety of beneficial actions at the level of the gonads and their adnexa. Some actions are mediated via its classic membrane melatonin receptors while others seem to be receptor-independent. This review summarizes many of the published reports which confirm that melatonin, which is produced in the ovary, aids in advancing follicular maturation and preserving the integrity of the ovum prior to and at the time of ovulation. Likewise, when ova are collected for in vitro fertilization-embryo transfer, treating them with melatonin improves implantation and pregnancy rates. Melatonin synthesis as well as its receptors have also been identified in the placenta. In this organ, melatonin seems to be of particular importance for the maintenance of the optimal turnover of cells in the villous trophoblast via its ability to regulate apoptosis. For male gametes, melatonin has also proven useful in protecting them from oxidative damage and preserving their viability. Incubation of ejaculated animal sperm improves their motility and prolongs their viability. For human sperm as well, melatonin is also a valuable agent for protecting them from free radical damage. In general, the direct actions of melatonin on the gonads and adnexa of mammals indicate it is an important agent for maintaining optimal reproductive physiology.

Effect of mouse cumulus cells on the in vitro maturation and developmental potential of bovine denuded germinal vesicle oocytes

We investigated the effect mouse cumulus cells (mCCs) on the in vitro maturation (IVM) and developmental potential of bovine denuded germinal vesicle oocytes (DOs). Cumulus–oocyte complexes (COCs), DOs and DOs cocultured with either mCCs (DOs + mCCs) or bovine cumulus cells (bCCs; DOs + bCCs) were subjected to IVM. The meiosis II (MII) rates of DOs, glutathione (GSH) contents, zona pellucida (ZP) hardening and parthenogenetic blastocyst rates of MII oocytes were determined. The relative expression levels of bone morphogenetic protein 15 (BMP-15) and growth differentiation factor 9 (GDF-9) in MII oocytes were measured using quantitative real-time polymerase chain reaction (PCR). mCCs significantly increased the MII rate of DOs from 53.5 ± 3.58% to 69.67 ± 4.72% (p < 0.05) but had no effect on the GSH content (2.17 ± 0.31 pmol/oocyte with mCCs, 2.14 ± 0.53 pmol/oocyte without mCCs). For the DOs + mCCs group, the BMP-15 and GDF-9 expression levels were significantly higher and the ZP dissolution time was significantly lower (162.49 ± 12.51 s) than that of the DOs group (213.95 ± 18.87 s; p < 0.05). The blastocyst rate of the DOs + mCCs group (32.56 ± 4.94%) was similar to that of the DOs group (31.75 ± 3.65%) but was significantly lower than that of the COCs group (43.52 ± 5.37%; p < 0.05). In conclusion, mCCs increased the MII rate of DOs and expression of certain genes in MII oocytes, and decreased the ZP hardening of MII oocytes, but could not improve their GSH content or developmental potential.

Interaction between melatonin and follicle-stimulating hormone promotes in vitro development of caprine preantral follicles

The aim of this study was to investigate the effects of melatonin and follicle-stimulating hormone (FSH) on the in vitro culture of goat preantral follicles. Ovarian fragments were cultured for 7 d in α-minimum essential medium (α-MEM(+)) containing melatonin (100, 250, 500, or 1,000 pM), FSH (50 ng/mL), or a combination of the 2 hormones and further analyzed by histology and transmission electron and fluorescent microscopy. The results showed that after 7 d of culture, tissues cultured in α-MEM(+) alone or supplemented with FSH alone, melatonin (500 and 1,000 pM), or the combination of FSH and melatonin (1,000 pM) maintained percentages of normal preantral follicles similar to the fresh control. In contrast to the noncultured tissues, the percentage of developing follicles was increased under all culture conditions after 7 d (P < 0.05). The addition of 1,000 pM melatonin associated with FSH to the culture medium increased follicular and oocyte diameters compared with α-MEM(+) alone after 7 d of culture (P < 0.05). Ultrastructural and fluorescent analyses confirmed the integrity of follicles cultured with 1,000 pM of melatonin plus FSH for 7 d. In conclusion, this study demonstrated that the interaction between melatonin and FSH maintains ultrastructural integrity and stimulates further growth of cultured caprine preantral follicles.

MT3 melatonin binding site, MT1 and MT2 melatonin receptors are present in oocyte, but only MT1 is present in bovine blastocyst produced in vitro

BACKGROUND

Melatonin inclusion into in vitro oocyte maturation (IVM) protocols has been suggested because it possesses a powerful free radical scavenger capability that improves the quality of the oocyte used in in vitro embryo production (IVP). The aim of our study was to investigate the presence of melatonin membrane receptors (MT1and MT2) and MT3, which is the melatonin binding site of NQO2 enzyme, in both oocytes and hatched blastocysts to consider an additional subcellular mechanism responsible for the effects of melatonin on IVP.

METHODS

The presence of the high affinity melatonin receptors was investigated through an autoradiographic binding assay, using the non-permeable ligand [125I]-iodomelatonin (17 pM) in embryos. The kind of melatonin site was investigated in oocytes and embryos by immunocytochemistry. In vitro fertilized bovine embryos produced from in vitro maturated oocytes supplemented with melatonin (0.0001 to 1000 nM) were analysed to determine their cleavage and blastocyst formation rates.

RESULTS

The [125I]-iodomelatonin (17 pM) binding in blastocysts was blocked by pre-incubation with melatonin (30000 nM), showing the presence of the high affinity melatonin receptors. MT1, MT2 and NQO2 immunoreactivity was observed in oocytes. MT1 immunoreactivity was observed in hatched blastocysts, however MT2 and NQO2 were not observed in this embryonic stage. Melatonin (pM) triggered significant difference in both cleavage and blastocysts formation rates.

CONCLUSIONS

The high affinity MT1 melatonin receptor must be taking part in IVM events; furthermore it is the first melatonin receptor to appear during bovine embryo development in vitro.

Does supplementation of in-vitro culture medium with melatonin improve IVF outcome in PCOS?

Human pre-ovulatory follicular fluid (FF) contains a higher concentration of melatonin than serum. The aim of this study was to evaluate the effect of melatonin supplementation of culture medium on the clinical outcomes of an in-vitro maturation (IVM) IVF-embryo transfer programme for patients with polycystic ovarian syndrome (PCOS). Melatonin concentrations in the culture media of granulosa cells (GC) or cumulus-oocyte-complexes (COC) were measured and the clinical outcomes after using IVM media with or without melatonin were analysed. In the culture media of GC or COC, melatonin concentrations gradually increased. When human chorionic gonadotrophin priming protocols were used, implantation rates in the melatonin-supplemented group were higher than those of the non-supplemented control group (P<0.05). Pregnancy rates were also higher, although not significantly. The findings suggest that the addition of melatonin to IVM media may improve the cytoplasmic maturation of human immature oocytes and subsequent clinical outcomes. It is speculated that follicular melatonin may be released from luteinizing GC during late folliculogenesis and that melatonin supplementation may be used to improve the clinical outcomes of IVM IVF-embryo transfer. Melatonin is primarily produced by the pineal gland and regulates a variety of important central and peripheral actions related to circadian rhythms and reproduction. Interestingly, human pre-ovulatory follicular fluid contains a higher concentration of melatonin than serum. However, in contrast to animal studies, the direct role of melatonin on oocyte maturation in the human system has not yet been investigated. So, the aim of the study was to evaluate the effect of melatonin supplementation of culture medium on the clinical outcome of an in-vitro maturation (IVM) IVF-embryo transfer programme for PCOS patients. The melatonin concentrations in culture medium of granulosa cells (GC) or cumulus-oocyte-complexes (COC) were measured and the clinical outcomes of IVM IVF-embryo transfer using IVM medium alone or supplemented with melatonin were analysed. In the culture media of GC or COC, the melatonin concentration gradually increased. With human chorionic gonadotrophin priming, the pregnancy and implantation rates in the melatonin-supplemented group were higher than those of the non-supplemented control (P<0.05). Our findings suggest that follicular melatonin is released from luteinizing GC during late folliculogenesis and plays a positive role in oocyte maturation. Therefore, addition of melatonin into IVM medium may improve cytoplasmic maturation of human immature oocytes and subsequent clinical outcomes.

Follicular fluid supplementation during in vitro maturation promotes sperm penetration in bovine oocytes by enhancing cumulus expansion and increasing mitochondrial activity in oocytes

The aim of this study was to examine the effects of bovine follicular fluid (bFF) on mitochondrial activity in in vitro-matured (IVM) oocytes and to assess its importance for fertilisation and embryo development. Bovine follicular oocytes were subjected to IVM in medium supplemented either with polyvinylpyrrolidone, bovine serum albumin, calf serum or bFF. Nuclear maturation, cumulus expansion, mitochondrial distribution and ATP content in oocytes were compared between groups along with subsequent in vitro fertilisation (IVF) and embryo development. Compared with other supplements, bFF generated significantly enhanced re-distribution of active mitochondria in oocytes and this effect was associated with elevated intracellular ATP content. Furthermore, bFF significantly improved cumulus expansion, which was associated with improved fertilisation rates when cumulus-enclosed oocytes were subjected to IVF; however, its promoting effect was neutralised when denuded oocytes were inseminated. Elevating ATP content in oocytes by bFF did not affect maturation or embryo development but promoted fertilisation when mitochondrial electron transport was blocked in oocytes before IVF by Rotenone. In conclusion, supplementation of IVM medium with bFF promotes sperm penetration both by the improvement of cumulus expansion and by enhancing ATP levels in oocytes, which maintains their ability to be fertilised after mitochondrial stress.