Reactive oxygen species signalling in the deterioration of quality of mammalian oocytes cultured in vitro: Protective effect of antioxidants

The in vitro fertilization (IVF) is the first choice of infertile couples worldwide to plan for conception. Besides having a significant advancement in IVF procedure, the success rate is still poor. Although several approaches have been tested to improve IVF protocol, minor changes in culture conditions, physical factors and/or drug treatment generate reactive oxygen species (ROS) in oocytes. Due to large size and huge number of mitochondria, oocyte is more susceptible towards ROS-mediated signalling under in vitro culture conditions. Elevation of ROS levels destabilize maturation promoting factor (MPF) that results in meiotic exit from diplotene as well as metaphase-II (M-II) arrest in vitro. Once meiotic exit occurs, these oocytes get further arrested at metaphase-I (M-I) stage or metaphase-III (M-III)-like stage under in vitro culture conditions. The M-I as well as M-III arrested oocytes are not fit for fertilization and limits IVF outcome. Further, the generation of excess levels of ROS cause oxidative stress (OS) that initiate downstream signalling to initiate various death pathways such as apoptosis, autophagy, necroptosis and deteriorates oocyte quality under in vitro culture conditions. The increase of cellular enzymatic antioxidants and/or supplementation of exogenous antioxidants in culture medium protect ROS-induced deterioration of oocyte quality in vitro. Although a growing body of evidence suggests the ROS and OS-mediated deterioration of oocyte quality in vitro, their downstream signalling and related mechanisms remain poorly understood. Hence, this review article summarizes the existing evidences concerning ROS and OS-mediated downstream signalling during deterioration of oocyte quality in vitro. The use of various antioxidants against ROS and OS-mediated impairment of oocyte quality in vitro has also been explored in order to increase the success rate of IVF during assisted reproductive health management.

Time elapsed between ovulation and insemination determines the quality of fertilized rat oocytes

Genetically modified rats are valuable models in human disease research. We recently developed an improved system for rat sperm cryopreservation and in vitro fertilization (IVF) that facilitates the efficient production and preservation of genetically modified rats. In the IVF procedure performed using frozen-thawed rat sperm, the IVF schedule is fixed to ensure timely hormone administration and oocyte collection. To enhance the flexibility of the IVF schedule, possible periods of postovulated rat oocytes with normal fertility and developmental abilities should be determined. Therefore, in this study, we examined the fertilization and developmental ability of incubated oocytes 1-13 h after oocyte collection at 9:00 AM. The fertilization rate decreased 7 h after oocyte collection, and abnormally fertilized oocytes appeared 10 h after oocyte collection. The developmental rate also decreased 7 h after oocyte collection; however, live pups were obtained from oocytes 12 h after oocyte collection. In summary, ovulated rat oocytes exhibited a high developmental ability after IVF for up to 4 h after oocyte collection.

Aging and oocyte competence: A molecular cell perspective

Follicular microenvironment is paramount in the acquisition of oocyte competence, which is dependent on two interconnected and interdependent processes: nuclear and cytoplasmic maturation. Extensive research conducted in human and model systems has provided evidence that those processes are disturbed with female aging. In fact, advanced maternal age (AMA) is associated with a lower chance of pregnancy and live birth, explained by the age-related decline in oocyte quality/competence. This decline has largely been attributed to mitochondria, essential for oocyte maturation, fertilization, and embryo development; with mitochondrial dysfunction leading to oxidative stress, responsible for nuclear and mitochondrial damage, suboptimal intracellular energy levels, calcium disturbance, and meiotic spindle alterations, that may result in oocyte aneuploidy. Nuclear-related mechanisms that justify increased oocyte aneuploidy include deoxyribonucleic acid (DNA) damage, loss of chromosomal cohesion, spindle assembly checkpoint dysfunction, meiotic recombination errors, and telomere attrition. On the other hand, age-dependent cytoplasmic maturation failure is related to mitochondrial dysfunction, altered mitochondrial biogenesis, altered mitochondrial morphology, distribution, activity, and dynamics, dysmorphic smooth endoplasmic reticulum and calcium disturbance, and alterations in the cytoskeleton. Furthermore, reproductive somatic cells also experience the effects of aging, including mitochondrial dysfunction and DNA damage, compromising the crosstalk between granulosa/cumulus cells and oocytes, also affected by a loss of gap junctions. Old oocytes seem therefore to mature in an altered microenvironment, with changes in metabolites, ribonucleic acid (RNA), proteins, and lipids. Overall, understanding the mechanisms implicated in the loss of oocyte quality will allow the establishment of emerging biomarkers and potential therapeutic anti-aging strategies. This article is categorized under: Reproductive System Diseases > Molecular and Cellular Physiology.

Importance of Antioxidant Supplementation during In Vitro Maturation of Mammalian Oocytes

The in vitro embryo production (IVEP) technique is widely used in the field of reproductive biology. In vitro maturation (IVM) is the first and most critical step of IVEP, during which, the oocyte is matured in an artificial maturation medium under strict laboratory conditions. Despite all of the progress in the field of IVEP, the quality of in vitro matured oocytes remains inferior to that of those matured in vivo. The accumulation of substantial amounts of reactive oxygen species (ROS) within oocytes during IVM has been regarded as one of the main factors altering oocyte quality. One of the most promising approaches to overcome ROS accumulation within oocytes is the supplementation of oocyte IVM medium with antioxidants. In this article, we discuss recent advancements depicting the adverse effects of ROS on mammalian oocytes. We also discuss the potential use of antioxidants and their effect on both oocyte quality and IVM rate.

Lycopene Reduces the In Vitro Aging Phenotypes of Mouse Oocytes by Improving Their Oxidative Status

Simple Summary

Ovulation is the process of oocyte release from the ruptured mature ovarian follicle into the oviduct. Fertilization usually occurs within 10 h post-ovulation in most mammals. If fertilization is delayed, the oocyte viability and quality will decrease, with many deteriorative changes in oocyte phenotype due to oxidative stress. This process is termed postovulatory aging. Postovulatory aging is a major problem that limits the success of many assisted reproductive technologies. Lycopene is a red carotenoid dye found within tomatoes and other fruits and vegetables. Lycopene has been reported to have a strong free-radical scavenging ability. our data showed beneficial effects of lycopene supplementation of in vitro maturation media during in vitro aging of mouse oocytes by reducing the oxidative stress damages that led to their apoptosis. The present study introduces lycopene as a natural supplement to reduce the postovulatory aging of mammalian oocytes.

Abstract

Postovulatory aging is a major problem that limits the success of many assisted reproductive technologies (ARTs). Oxidative stress is a leading cause of oocyte aging. This study investigated the effects of lycopene supplementation of in vitro maturation (IVM) medium during the aging of mouse oocytes on the oocytes’ morphology and oxidative stress status. Mouse cumulus-oocyte complexes (COCs) were collected and cultured in the IVM medium either for 17 h, (freshly matured oocytes), or for 48 h, (in vitro-aged oocytes), with or without lycopene. The rate of fragmented and degenerated oocytes and the oocyte levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), total antioxidant capacity (TAC), reduced glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD) were estimated and compared. Oocytes aged with 200 nM lycopene revealed significantly less fragmentation and degeneration, lower H₂O₂ and MDA levels, and higher TAC, GSH and SOD levels than those aged without lycopene. CAT levels were unchanged by lycopene treatment. Taken together, our data showed beneficial effects of lycopene during in vitro aging of mouse oocytes by reducing the oxidative stress damages that lead to their apoptosis. The present study introduces lycopene as a natural supplement to reduce the postovulatory aging-dependent abnormalities of mammalian oocytes.

In vivo and in vitro postovulatory aging: when time works against oocyte quality?

In mammalian species an optimal fertilization window during which successful fertilization occurs. In the majority of mammals estrus marks ovulation time and coincident with mating, thereby allowing the synchronized meeting in the fallopian tubes, between freshly ejaculated sperm and freshly ovulated oocytes. Conversely, women do not show natural visual signs of ovulation such that fertilization can occur hours later involving an aged oocyte and freshly ejaculated spermatozoa. During this time, the oocyte undergoes a rapid degradation known as “postovulatory aging” (POA). POA may become particularly important in the human-assisted reproductive technologies, as the fertilization of retrieved mature oocytes can be delayed due to increased laboratory workload or because of unforeseeable circumstances, like the delayed availability of semen samples. This paper is an updated review of the consequences of POA, either in vivo or in vitro, on oocyte quality with particular attention to modifications caused by POA on oocyte nuclear, cytoplasmic, genomic, and epigenetic maturation, and embryo development.

Involvement of nitric oxide during in vitro oocyte maturation, sperm capacitation and in vitro fertilization in pig

The importance of porcine species for meat production is undeniable. Due to the genetic, anatomical, and physiological similarities with humans, from a biomedical point of view, pig is considered an ideal animal model for the study and development of new therapies for human diseases. The in vitro production (IVP) of porcine embryos has become widespread as a result of these qualities and there is significant demand for these embryos for research purposes. However, the efficiency of porcine embryo IVP remains very low, which hinders its use as a model for research. The high degree of polyspermic fertilization is the main problem that affects in vitro fertilization (IVF) in porcine species. Furthermore, oocyte in vitro maturation (IVM) is another important step that could be related to polyspermic fertilization and low embryo production. The presence of nitric oxide synthase (NOS), the enzyme that produces nitric oxide (NO), has been detected in the oviduct, the ovary, the oocyte and the sperm cell of porcine species. Its functions include regulating oviductal activity, ovulation, acquisition of meiotic competence, oocyte activation, sperm capacitation, and gamete interaction. Therefore, in this review, we summarize the current knowledge on the role of NO/NOS system in each of the steps that lead to the production of porcine embryos in an in vitro environment, i.e. IVM, sperm capacitation, IVF, and embryo culture. We also discuss the possible ways in which the NO/NOS system could be used to enhance IVP of porcine embryos.

Inhibitory effects of astaxanthin on postovulatory porcine oocyte aging in vitro

Mammalian oocytes represent impaired quality after undergoing a process of postovulatory aging, which can be alleviated through various effective ways such as reagent treatment. Accumulating evidences have revealed the beneficial effects of astaxanthin (Ax) as a potential antioxidant on reproductive biology. Here, porcine matured oocytes were used as a model to explore whether Ax supplement can protect against oocyte aging in vitro and the underlying mechanism, and therefore they were cultured with or without 2.5 μM Ax for an additional 24 h. Aged oocytes treated with Ax showed improved yield and quality of blastocysts as well as recovered expression of maternal genes. Importantly, oxidative stress in aged oocytes was relieved through Ax treatment, based on reduced reactive oxygen species and enhanced glutathione and antioxidant gene expression. Moreover, inhibition in apoptosis and autophagy of aged oocyte by Ax was confirmed through decreased caspase-3, cathepsin B and autophagic activities. Ax could also maintain spindle organization and actin expression, and rescue functional status of organelles including mitochondria, endoplasmic reticulum, Golgi apparatus and lysosomes according to restored fluorescence intensity. In conclusion, Ax might provide an alternative for ameliorating the oocyte quality following aging in vitro, through the mechanisms mediated by its antioxidant properties.

Meiotic Instability Generates a Pathological Condition in Mammalian Ovum

Maintenance of metaphase-II (M-II) arrest in ovum is required to present itself as a right gamete for successful fertilization in mammals. Surprisingly, instability of meiotic cell cycle results in spontaneous exit from M-II arrest, chromosomal scattering and incomplete extrusion of second polar body (PB-II) without forming pronuclei so called abortive spontaneous ovum activation (SOA). It remains unclear what causes meiotic instability in freshly ovulated ovum that results in abortive SOA. We propose the involvement of various signal molecules such as reactive oxygen species (ROS), cyclic 3',5' adenosine monophosphate (cAMP) and calcium (Ca²⁺) in the induction of meiotic instability and thereby abortive SOA. These signal molecules through their downstream pathways modulate phosphorylation status and activity of cyclin dependent kinase (cdk1) as well as cyclin B1 level. Changes in phosphorylation status of cdk1 and its activity, dissociation and degradation of cyclin B1 destabilize maturation promoting factor (MPF). The premature MPF destabilization and defects in other cell cycle regulators possibly cause meiotic instability in ovum soon after ovulation. The meiotic instability results in a pathological condition of abortive SOA and deteriorates ovum quality. These ova are unfit for fertilization and limit reproductive outcome in several mammalian species including human. Therefore, global attention is required to identify the underlying causes in greater details in order to address the problem of meiotic instability in ova of several mammalian species icluding human. Moreover, these activated ova may be used to create parthenogenetic embryonic stem cell lines in vitro for the use in regenerative medicine.Graphical abstract.

L-carnitine prevents bovine oocyte aging and promotes subsequent embryonic development

L-carnitine (LC) is well known for its antioxidant activity. In this study, we explored the potential mechanistic effects of LC supplementation on aged bovine oocytes in vitro. We showed that in-vitro maturation could enhance the subsequent developmental capacity of aging oocytes, when supplemented with LC. After in vitro fertilization, the blastocyst formation rate in the aged oocytes post-LC treatment significantly increased compared to that in untreated aged oocytes (29.23 ± 2.20% vs. 20.90 ± 3.05%). Furthermore, after LC treatment, the level of intracellular reactive oxygen species in aged oocytes significantly decreased, and glutathione levels significantly increased, compared to those in untreated aged oocytes. Mitochondrial membrane potential, the percentage of early apoptotic oocytes, and caspase-3 activity were significantly reduced in LC-treated aged oocytes compared to those in untreated aged oocytes. Furthermore, during in vitro aging, the mRNA levels of the anti-apoptotic genes, Bcl-xl and survivin in LC-treated aged oocytes were significantly higher than those in untreated aged oocytes. Overall, these results indicate that at least in in vitro conditions, LC can prevent the aging of bovine oocytes and improve the developmental capacity of bovine embryo.

Reproductive competency and mitochondrial variation in aged Syrian hamster oocytes

The hamster is a useful model of human reproductive biology because its oocytes are similar to those in humans in terms of size and structural stability. In the present study we evaluated fecundity rate, ovarian follicular numbers, ova production, mitochondrial number, structure and function, and cytoplasmic lamellae (CL) in young (2-4 months) and old (12-18 months) Syrian hamsters (Mesocricetus auratus). Young hamsters had higher fertilisation rates and larger litters than old hamsters (100 vs 50% and 9.3±0.6 vs 5.5±0.6, respectively). Ovarian tissue from superovulated animals showed a 46% decrease in preantral follicles in old versus young hamsters. There was a 39% reduction in MII oocyte number in old versus young hamsters. Young ova had no collapsed CL, whereas old ova were replete with areas of collapsed, non-luminal CL. Eighty-nine per cent of young ova were expanded against the zona pellucida with a clear indentation at the polar body, compared with 58.64% for old ova; the remaining old ova had increased perivitelline space with no polar body indentation. Higher reactive oxygen species levels and lower mitochondrial membrane potentials were seen in ova from old versus young hamsters. A significant decrease in mitochondrial number (36%) and lower frequency of clear mitochondria (31%) were observed in MII oocytes from old versus young hamster. In conclusion, the results of the present study support the theory of oocyte depletion during mammalian aging, and suggest that morphological changes of mitochondria and CL in oocytes may be contributing factors in the age-related decline in fertility rates.

Melatonin improves the fertilization capacity and developmental ability of bovine oocytes by regulating cytoplasmic maturation events

Melatonin is a well-characterized antioxidant that has been successfully used to protect oocytes from reactive oxygen species during in vitro maturation (IVM), resulting in improved fertilization capacity and development ability. However, the mechanism via which melatonin improves oocyte fertilization capacity and development ability remains to be determined. Here, we studied the effects of melatonin on cytoplasmic maturation of bovine oocytes. In the present study, bovine oocytes were cultured in IVM medium supplemented with 0, 10^-7 , 10^-9 , and 10^-11  mol/L melatonin, and the cytoplasmic maturation parameters of MII oocytes after IVM were investigated, including redistribution of organelles (mitochondria, cortical granules [CGs], and endoplasmic reticulum [ER]), intracellular glutathione (GSH) and ATP levels, expression of endogenous antioxidant genes (Cat, Sod1, and GPx), and fertilization-related events (IP3R1 distribution and expression of CD9 and Juno). Our results showed that melatonin significantly improved the cytoplasmic maturation of bovine oocytes by improving the normal distribution of organelles, increasing intracellular GSH and ATP levels, enhancing antioxidant gene expression levels, and modulating fertilization-related events, all of which resulted in increased fertilization capacity and developmental ability. Meanwhile, melatonin also increased the mRNA and protein expression levels of the Tet1 gene and decreased the Dnmt1 gene mRNA and protein levels in bovine oocytes, indicating that melatonin regulates the expression of the detected genes via demethylation. These findings shed insights into the potential mechanisms by which melatonin improves oocyte quality during IVM.

Phenotypes of Aging Postovulatory Oocytes After Somatic Cell Nuclear Transfer in Mice

Oocytes rapidly lose their developmental potential after ovulation, termed postovulatory oocyte aging, and often exhibit characteristic phenotypes, such as cytofragmentation, abnormal spindle shapes, and chromosome misalignments. Here, we reconstructed mouse oocytes using somatic cell nuclear transfer (SCNT) to reveal the effect of somatic cell-derived nuclei on oocyte physiology during aging. Normal oocytes started undergoing cytofragmentation 24 hours after oocyte collection; however, this occurred earlier in SCNT oocytes and was more severe at 48 hours, suggesting that the transferred somatic cell nuclei affected oocyte physiology. We found no difference in the status of acetylated α-tubulin (Ac-Tub) and α-tubulin (Tub) between normal and SCNT aging oocytes, but unlike normal oocytes, aging SCNT oocytes did not have astral microtubules. Interestingly, aging SCNT oocytes displayed more severely scattered chromosomes or irregularly shaped spindles. Observations of the microfilaments showed that, in normal oocytes, there was a clear actin ring beneath the plasma membrane and condensed microfilaments around the spindle (the actin cap) at 0 hours, and the actin filaments started degenerating at 1 hour, becoming completely disrupted and distributed to the cytoplasm at 24 hours. By contrast, in SCNT oocytes, an actin cap formed around the transplanted nuclei within 1 hour of SCNT, which was still present at 24 hours. Thus, SCNT oocytes age in a similar but distinct way, suggesting that they not only contain nuclei with abnormal epigenetics but are also physiologically different.

The potential roles of c-Jun N-terminal kinase (JNK) during the maturation and aging of oocytes produced by a marine protostome worm

Previous investigations have indicated that c-Jun N-terminal kinase (JNK) regulates the maturation and aging of oocytes produced by deuterostome animals. In order to assess the roles of this kinase in a protostome, oocytes of the marine nemertean worm Cerebratulus were stimulated to mature and subsequently aged before being probed with phospho-specific antibodies against active forms of JNK and maturation-promoting factor (MPF). Based on blots of maturing oocytes, a 40-kD putative JNK is normally activated during germinal vesicle breakdown (GVBD), which begins at 30 min post-stimulation with seawater, whereas treating immature oocytes with JNK inhibitors downregulates both the 40-kD JNK signal and GVBD, collectively suggesting a 40-kD JNK may facilitate oocyte maturation. Along with this JNK activity, mature oocytes also exhibit high levels of MPF at 2 h post-stimulation. However, by ~6-8 h post-GVBD, mature oocytes lose the 40-kD JNK signal, and at ~20-30 h of aging, an ~48-kD phospho-JNK band arises as oocytes deactivate MPF and begin to lyse during a necroptotic-like mode of death. Accordingly, JNK inhibitors reduce the aging-related 48-kD JNK phosphorylation while maintaining MPF activity and retarding oocyte degradation. Such findings suggest that a 48-kD JNK may help deactivate MPF and trigger death. Possible mechanisms by which JNK activation either together with, or independently of, protein neosynthesis might stimulate oocyte degradation are discussed.

Treatment of allicin improves maturation of immature oocytes and subsequent developmental ability of preimplantation embryos

Allicin (AL) regulates the cellular redox, proliferation, viability, and cell cycle of different cells against extracellular-derived stress. This study investigated the effects of allicin treatment on porcine oocyte maturation and developmental competence. Porcine oocytes were cultured in medium supplemented with 0 (control), 0.01, 0.1, 1, 10 or 100 μM AL, respectively, during in vitro maturation (IVM). The rate of polar body emission was higher in the 0.1 AL-treated group (74.5% ± 2.3%) than in the control (68.0% ± 2.6%) (P < 0.1). After parthenogenetic activation, the rates of cleavage and blastocyst formation were significantly higher in the 0.1 AL-treated group than in the control (P < 0.05). The reactive oxygen species level at metaphase II did not significantly differ among all groups. In matured oocytes, the expression of both BAK and CASP3, and BIRC5 was significantly lower and higher, respectively, in the 0.1 AL-treated group than in the control. Similarly, the expression of BMP15 and CCNB1, and the activity of phospho-p44/42 mitogen-activated protein kinase (MAPK), significantly increased. These results indicate that supplementation of oocyte maturation medium with allicin during IVM improves the maturation of oocytes and the subsequent developmental competence of porcine oocytes.

Increased Intracellular Reactive Oxygen Species Mediates the Anti-Cancer Effects of WZ35 via Activating Mitochondrial Apoptosis Pathway in Prostate Cancer Cells

BACKGROUND

The limited treatment option for recurrent prostate cancer and eventual resistant to conventional chemotherapy drugs has fueled continued interest in finding new anti-neoplastic agents. WZ35, a chemical analog of curcumin, had been demonstrated to have high chemical stability and potential anticancer effects in gastric cancer cells. The present study aimed to investigate the anti-prostate cancer effects of WZ35 in vitro and in vivo as well as the underlying mechanism.

METHODS

Two prostate cancer cell lines RM-1 and DU145 were utilized to test the anti-cancer effects of WZ35 and the underlying mechanism. MTT assay was used to assess the cytotoxic effect of WZ35. Cell cycle distribution, apoptosis, alteration of ROS, and [Ca²⁺ ]_i level were evaluated using flow cytometry. Western blotting assay was applied to measure the levels of proteins associated with apoptosis and cell cycle. Immunofluorescence staining and Electron micrographs were used to evaluate activation of mitochondrial apoptosis pathway. Tumor models in nude mice were induced by injection of RM-1 prostate cancer cells to test the in vivo anticancer action of WZ35.

RESULTS

Our results showed that WZ35 treatment induced loss of cell viability, cell apoptosis, and G2/M cycle arrest in both RM-1 and DU145 cells, coupled with ROS overproduction, intracellular calcium surge, and activation of mitochondrial apoptosis pathway in RM-1 cells. Interestingly, all above changes induced by WZ35 were completely reversed by ROS blockage. In addition, prevention of [Ca²⁺ ]_i elevation by BAPTA/AM also inhibited activation of mitochondrial apoptosis pathway induced by WZ35. In vivo studies, WZ35 treatment significantly inhibited RM-1 homograft tumor growth along with increased ROS accumulation, mitochondrial disruption, and cell apoptosis in tumor tissues.

CONCLUSIONS

In conclusion, this work provides a novel anticancer candidate for the treatment of prostate cancer and demonstrated that increased ROS mediate the anti-cancer effects of WZ35 via activating mitochondrial apoptosis pathway. Importantly, this work also reveals that targeting ROS generation might be an effective strategy in human androgen-resistant prostate cancer treatment. Prostate 77:489-504, 2017. © 2016 Wiley Periodicals, Inc.

Effect and possible mechanisms of melatonin treatment on the quality and developmental potential of aged bovine oocytes

After reaching the metaphase II (MII) stage, unfertilised oocytes undergo a time-dependent process of quality deterioration referred to as oocyte aging. The associated morphological and cellular changes lead to decreased oocyte developmental potential. This study investigated the effect of exogenous melatonin supplementation on in vitro aged bovine oocytes and explored its underlying mechanisms. The levels of cytoplasmic reactive oxygen species and DNA damage response in bovine oocytes increased during in vitro aging. Meanwhile, maturation promoting factor activity significantly decreased and the proportion of morphologically abnormal oocytes significantly increased. Melatonin supplementation significantly decreased quality deterioration in aged bovine MII oocytes (P < 0.05). Additionally, it decreased the frequency of aberrant spindle organisation and cortical granule release during oocyte aging (P < 0.05). In the melatonin-supplemented group, mitochondrial membrane potential and ATP production were significantly increased compared with control. Furthermore, melatonin treatment significantly increased the speed of development of bovine oocytes to the blastocyst stage after in vitro fertilisation and significantly decreased the apoptotic rate in the blastocysts (P < 0.05). The expression of Bax and Casp3 in the blastocysts was significantly reduced after treatment with melatonin, whereas expression of Bcl2 significantly increased (P < 0.05). In conclusion, these findings suggest that supplementation of aged bovine oocytes with exogenous melatonin improves oocyte quality, thereby enhancing the developmental capacity of early embryos.

Effect of medium additives during liquid storage on developmental competence of in vitro matured bovine oocytes

Our aim was to improve the developmental competence of bovine oocytes during their liquid storage by using additives. In vitro matured oocytes were stored for 20 h at 25°C in HEPES buffered TCM 199 medium (base medium). After storage, in vitro embryo development after in vitro fertilization was compared to those of non-stored (control) ones. Addition of 10% (v/v) newborn calf serum or 10.27 mmol/L pyruvate alone to the base medium did not improve blastocyst formation rates in stored oocytes; however, their simultaneous addition significantly improved the rate compared with those stored in base medium (P < 0.05). Supplementation of the holding medium with dithiothreitol (DTT) at any concentrations did not improve embryo development from stored oocytes. Although supplementation with cyclosporine A (CsA) significantly reduced apoptosis and membrane damage rates during storage, it did not improve the developmental competence of oocytes. 1,2-bis(2-aminophenoxy) ethane N,N,N',N'-tetraacetic acid tetrakis-acetoxymethyl ester and ruthenium red had no effect on oocyte apoptotic rates. Blastocyst formation rates in all stored groups remained significantly lower than that of the control. In conclusion, pyruvate and serum had a synergic effect to moderate the reduction of oocyte quality during storage, whereas mitochondrial membrane pore inhibitor CsA and the antioxidant DTT did not affect their developmental competence.

Resveratrol protects PC12 cells against OGD/ R-induced apoptosis via the mitochondrial-mediated signaling pathway

In this study, we investigated the neuroprotective potential of resveratrol against oxygen glucose deprivation/reoxygenation (OGD/R)-induced apoptotic damages in well-differentiated PC12 cells and the underlying mechanisms. Cells were incubated under normal condition or OGD/R in the presence or absence of 10 μM resveratrol. Cell viability was determined with methyl-thiazolyl-tetrazolium (MTT) assay. Apoptotic ratio was determined with Hoechst 33342 staining and Annexin V-FITC/PI double staining. Oxidative stress was evaluated by measuring the intracellular reactive oxygen species (ROS), the mitochondrial superoxide, the malondialdehyde (MDA) content, and the activities of superoxide dismutase (SOD) and catalase (CAT). The intracellular calcium ([Ca2+]i) was estimated by Fluo-3/AM. The mitochondrial membrane potential (MMP) was evaluated by 5,5′,6,6′-tetrachloro-1,1,3,3′-tetraethyl-benzimidazolyl-carbocyanine iodide (JC-1) and rhodamine 123 (Rh123). The opening of mitochondrial permeability transition pore (MPTP) was determined by the Calcein/Co2+-quenching technique. The protein levels of cytochrome c, Bcl-2, Bax, cleaved caspase-9, and cleaved caspase-3 were detected by western blot analysis. The results showed that 10 μM resveratrol attenuated OGD/R-induced cell viability loss and cell apoptosis, which was associated with the decreases in the MDA content and the increases in the SOD and CAT activities. Furthermore, the accumulation of intracellular ROS and mitochondrial superoxide, disturbance of [Ca2+]i homeostasis, reduction of MMP, opening of MPTP, and release of mitochondrial cytochrome c observed in OGD/R-injured cells, which indicated a switch on the mitochondrial-mediated apoptotic pathway, were all reversed by resveratrol. These results suggest that resveratrol administration may play a neuroprotective role via modulating the mitochondrial-mediated signaling pathway in OGD/R-induced PC12 cell injury.

Increased level of reactive oxygen species persuades postovulatory aging-mediated spontaneous egg activation in rat eggs cultured in vitro

The present study was aimed to find out whether increased level of reactive oxygen species (ROS) particularity hydrogen peroxide (H2O2) could persuade postovulatory aging-mediated abortive spontaneous egg activation (SEA) in rat eggs cultured in vitro. For this purpose, ROS and H2O2 levels, mitochondria distribution and its membrane potential, p286-CaMK-II, Emi2, Thr-161 phophorylated cyclin-dependent protein kinase1 (Cdk1) as well as cyclin B1 levels, in vitro effects of 3-tert-butyl-4 hydroxy anisole (BHA), pentoxifylline and dibutyryl-adenosine 3',5'-cyclic monophosphate (db-cAMP) were analyzed during postovulatory aging-induced abortive SEA in vitro. Data of the present study suggest that postovulatory aging increased H2O2 levels, disturbed mitochondrial distribution pattern and mitochondrial membrane potential (MMP) in eggs. There was an significant increase of p286-CaMK-II level, while Emi2 level reduced significantly during egg aging in vitro. The reduced Emi2 level was associated with decreased Thr-161 phosphorylated cyclin-dependent kinase-1 (Cdk1) as well as cyclin B1 level in aged eggs that underwent abortive SEA. Further, supplementation of pentoxifylline, db-cAMP, and BHA protected postovulatory aging-mediated abortive SEA in concentration-dependent manner. These data suggest that postovulatory aging increased H2O2 levels, reduced MMP, and increased p286-CaMK-II. The increased p286-CaMK-II was associated with reduced Emi2 level and maturation-promoting factor levels during postovulatory aging-mediated abortive SEA. Drugs that elevate cAMP directly or indirectly and BHA protected postovulatory aging-mediated abortive SEA possibly by reducing ROS level in rat eggs cultured in vitro.

The effect of temperature during liquid storage of in vitro-matured bovine oocytes on subsequent embryo development

The aim of the present study was to optimize the temperature for the temporal storage of matured bovine oocytes. In vitro-matured bovine oocytes were preserved in HEPES-buffered TCM199 medium supplemented with 10% newborn calf serum at different temperatures (4 °C, 15 °C, 25 °C, and 38.5 °C) for 20 hours. Embryo development and blastocyst quality after in vitro fertilization, cytoplasmic ATP and glutathione levels in oocytes, and the frequency of apoptotic oocytes were compared among storage groups and a control group without storage. Among the storage groups, those at 25 °C and 38.5 °C showed the highest rates of blastocyst development (19.3% and 24.5%, respectively) compared with those stored at 4 °C and 15 °C (8.5% and 14.9%, respectively); however, blastocyst formation rates in all storage groups were lower than that in the control group (39.8%; P < 0.05). Storage at 38.5 °C and 15 °C was associated with reduced cell numbers in resultant blastocysts compared with the control and the 25 °C storage groups. Storage at 4 °C reduced metabolic activity of oocytes characterized by their lower ATP levels compared with the other groups. Storage for 20 hours significantly reduced the glutathione content in oocytes in all groups in a similar manner, irrespective of the temperature. Storage at 4 °C or 15 °C but not at 25 °C and 38.5 °C significantly increased the percentage of apoptotic oocytes compared with the control group. In conclusion, 25 °C was found to be the most suitable temperature for the temporal storage of matured bovine oocytes regarding both the developmental competence of oocytes and the quality of resultant blastocysts.

Age-associated potency decline in bovine oocytes is delayed by blocking extracellular Ca(2+) influx

Oocyte aging due to delayed fertilization is associated with declining quality and developmental potential. Intracellular calcium (Ca(2+)) concentration ([Ca(2+)]i) regulates oocyte growth, maturation, and fertilization and has also been implicated in aging. Using bovine oocytes, we tested the hypothesis that oocyte aging could be delayed by reducing [Ca(2+)]ivia blocking the influx of extracellular Ca(2+) or chelating ooplasmic free Ca(2+). After IVM, cumulus-oocyte complexes or denuded oocytes were cultured in medium supplemented with 1-octanol, phorbol 12-myristate 13-acetate, or 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis-acetoxymethyl ester (BAPTA-AM) to manipulate [Ca(2+)]i. Addition of 1-mM 1-octanol increased blastocyst development rates in the cumulus-oocyte complexes aged for 6 hours by IVF and for 6, 12, and 24 hours by parthenoactivation, and this effect was independent of the presence of cumulus cells. The intracellular levels of ATP, Glutathione, and Glutathione disulfide were not affected by 1-octanol, but [Ca(2+)]i was significantly decreased. When oocytes were cultured in Ca(2+)-free medium for 12 hours, the blastocyst development rate was greater and the beneficial effects of 1-octanol on oocyte aging were abolished. However, when the medium was supplemented with phorbol 12-myristate 13-acetate, [Ca(2+)]i increased and the blastocyst development rate decreased. Moreover, BAPTA-AM reduced [Ca(2+)]i and increased blastocyst development rates after IVF or parthenoactivation. We conclude that the age-associated developmental potency decline was delayed by blocking the influx of extracellular Ca(2+) or reducing ooplasmic free Ca(2+). 1-Octanol, BAPTA-AM, or Ca(2+)-free medium could be used to lengthen the fertilization windows of aged bovine oocytes.

Nitric oxide synthase (NOS) inhibition during porcine in vitro maturation modifies oocyte protein S-nitrosylation and in vitro fertilization

Nitric oxide (NO) is a molecule involved in many reproductive processes. Its importance during oocyte in vitro maturation (IVM) has been demonstrated in various species although sometimes with contradictory results. The objective of this study was to determine the effect of NO during IVM of cumulus oocyte complexes and its subsequent impact on gamete interaction in porcine species. For this purpose, IVM media were supplemented with three NOS inhibitors: NG-nitro-L-arginine methyl ester (L-NAME), NG-monomethyl-L-arginine (L-NMMA) and aminoguanidine (AG). A NO donor, S-nitrosoglutathione (GSNO), was also used. The effects on the cumulus cell expansion, meiotic resumption, zona pellucida digestion time (ZPdt) and, finally, on in vitro fertilization (IVF) parameters were evaluated. The oocyte S-nitrosoproteins were also studied by in situ nitrosylation. The results showed that after 42 h of IVM, AG, L-NAME and L-NMMA had an inhibitory effect on cumulus cell expansion. Meiotic resumption was suppressed only when AG was added, with 78.7% of the oocytes arrested at the germinal vesicle state (P<0.05). Supplementation of the IVM medium with NOS inhibitors or NO donor did not enhance the efficiency of IVF, but revealed the importance of NO in maturation and subsequent fertilization. Furthermore, protein S-nitrosylation is reported for the first time as a pathway through which NO exerts its effect on porcine IVM; therefore, it would be important to determine which proteins are nitrosylated in the oocyte and their functions, in order to throw light on the mechanism of action of NO in oocyte maturation and subsequent fertilization.

rAAV/ABAD-DP-6His attenuates oxidative stress-induced injury of PC12 cells

Our previous studies have revealed that amyloid β (Aβ)-binding alcohol dehydrogenase (ABAD) decoy peptide antagonizes Aβ42-induced neurotoxicity. However, whether it improves oxidative stress injury remains unclear. In this study, a recombinant adenovirus constitutively secreting and expressing Aβ-ABAD decoy peptide (rAAV/ABAD-DP-6His) was successfully constructed. Our results showed that rAAV/ABAD-DP-6His increased superoxide dismutase activity in hydrogen peroxide-induced oxidative stress-mediated injury of PC12 cells. Moreover, rAAV/ABAD-DP-6His decreased malondialdehyde content, intracellular Ca(2+) concentration, and the level of reactive oxygen species. rAAV/ABAD-DP-6His maintained the stability of the mitochondrial membrane potential. In addition, the ATP level remained constant, and apoptosis was reduced. Overall, the results indicate that rAAV/ABAD-DP-6His generates the fusion peptide, Aβ-ABAD decoy peptide, which effectively protects PC12 cells from oxidative stress injury induced by hydrogen peroxide, thus exerting neuroprotective effects.

Protein kinase RNA-like endoplasmic reticulum kinase (PERK)/calcineurin signaling is a novel pathway regulating intracellular calcium accumulation which might be involved in ventricular arrhythmias in diabetic cardiomyopathy

We previously found that endoplasmic reticulum (ER) stress was involved in ventricular arrhythmias in diabetic cardiomyopathy. The present study was aimed to investigate the possible mechanism. In the in vivo study, diabetes cardiomyopathy (DCM) was induced by streptozotocin (STZ) injection. Hemodynamic and plasma brain natriuretic peptide (BNP) detections were used to evaluate cardiac functions; ECG was used to assess the vulnerability to arrhythmias by recording ventricular arrhythmia events (VAEs). In the in vitro study, high-glucose incubation was employed to mimic the diabetic environment of myocytes. Immunofluorescent staining was used to investigate the nuclear factor of activated T cells (NFAT) nuclear translocation and (FK506-binding protein 12.6) FKBP12.6 disassociation. [(3)H]-ryanodine binding assay was implemented to assess the channel activity of ryanodine receptor. In both in vivo and in vitro studies, activity of calcineurin was determined by colorimetric method, and western blotting was used to detect protein expression levels. In the in vivo study, we found that inhibition of both of ER stress and PERK activation decreased the VAEs in DCM rats, accompanied by reduced activity of calcineurin in myocardial tissue. In the in vitro study, in high-glucose incubated myocytes, the depletion of PERK reduced activity of calcineurin, decreased NFAT translocation and FKBP12.6 disassociation from ryanodine receptor 2 (RyR2). Furthermore, PERK deletion also reduced RyR2 channel activity and consequently impaired intracellular calcium accumulation. We concluded that PERK/calcineurin-pathway was involved in intracellular calcium regulation in myocytes in diabetic heart, which might be the mechanism inducing arrhythmias in DCM.

Aging-related changes in in vitro-matured bovine oocytes: oxidative stress, mitochondrial activity and ATP content after nuclear maturation

The objective of this research was to clarify the aging-related changes in in vitro-matured bovine oocytes. Firstly, we examined the fertilization and embryonic development of bovine oocytes after 22 and 30–34 h of in vitro maturation (IVM). The oocytes after 30–34 h of IVM (penetrated by sperm at around 40 h after starting IVM) showed a lower developmental rate to blastocysts (P<0.01), although normal fertilization rates were similar regardless of IVM duration. In the next experiment, reactive oxygen species (ROS), mitochondrial activity and ATP content in oocytes after 20, 30 and 40 h of IVM were examined. The lowest level of ROS was found in the group subjected to 30 h of IVM. The mitochondrial activity and ATP content in the group subjected to 40 h of IVM were higher than in the group subjected to 20 h of IVM (P<0.01), and those in the group subjected to 30 h of IVM showed intermediate values. Thereafter, the mitochondrial activities at 3 days after in vitro fertilization in embryos derived from the oocytes subjected to 22 and 34 h of IVM were evaluated. In the group subjected to 34 h of IVM, high-polarized mitochondria were frequently observed at the periphery of blastomeres. The present results suggest that high mitochondrial activity observed in oocytes after prolonged IVM culture and localization of high-polarized mitochondria at the periphery of blastomeres during early embryonic development may be associated with the low developmental competence in aged bovine oocytes.