Luteinizing hormone depletes ascorbic acid in preovulatory follicles

Ascorbic acid protects the toxic effects of aflatoxin B1 on yak oocyte maturation

High-quality oocytes are a prerequisite for successful fertilization. Mammals feeding on aflatoxin-contaminated feed can cause reproductive toxicity, including follicular atresia, poor oocyte development and maturation, and aberrant epigenetic modifications of oocytes. In addition, the important role of ascorbic acid (AA) in reproductive biology has been confirmed, and AA is widely used as an antioxidant in cell culture. However, the toxic effects of aflatoxin B₁ (AFB₁ ) on yak oocytes and whether AA has protective effects remain unknown. In this study, we found that exposure to AFB₁ impedes meiotic maturation of oocytes, promotes apoptosis by triggering high levels of reactive oxygen species (ROS), and disrupts mitochondrial distribution and actin integrity, resulting in a decrease in the fertilization ability and parthenogenetic development ability of oocytes. In addition, these injuries changed the DNA methylation transferase transcription level of mature oocytes. After adding 50 μg/ml AA, the indices recovered to levels close to those of the control group. The results showed that AA could protect yak oocytes from the toxic effects of AFB₁ and improve the quality of oocytes.

Involvement of peroxiredoxin 2 in cumulus expansion and oocyte maturation in mice

Peroxiredoxin 2 (Prdx2), an antioxidant enzyme, is expressed in the ovary during the ovulatory process. The aim of the present study was to examine the physiological role of Prdx2 during ovulation using Prdx2-knockout mice and mouse cumulus-oocyte complex (COC) from WT mice. Two days of treatment of immature mice (21-23 days old) with equine chorionic gonadotrophin and followed by treatment with human chorionic gonadotrophin greatly impaired cumulus expansion and oocyte maturation in Prdx2-knockout but not wild-type mice. Treatment of COCs in culture with conoidin A (50µM), a 2-cys Prdx inhibitor, abolished epiregulin (EPI)-induced cumulus expansion. Conoidin A treatment also inhibited EPI-stimulated signal molecules, including signal transducer and activator of transcription-3, AKT and mitogen-activated protein kinase 1/2. Conoidin A treatment also reduced the gene expression of EPI-stimulated expansion-inducing factors (hyaluronan synthase 2 (Has2), pentraxin 3 (Ptx3), TNF-α induced protein 6 (Tnfaip6) and prostaglandin-endoperoxide synthase 2 (Ptgs2)) and oocyte-derived factors (growth differentiation factor 9 (Gdf9) and bone morphogenetic protein 15 (Bmp15)). Furthermore, conoidin A inhibited EPI-induced oocyte maturation and the activity of connexins 43 and 37. Together, these results demonstrate that Prdx2 plays a role in regulating cumulus expansion and oocyte maturation during the ovulatory process in mice, probably by modulating epidermal growth factor receptor signalling.

Decreased ascorbic acid biosynthesis in response to PMSG in the pre-pubertal female rat ovary

Ascorbic acid (AA) is known to be an important antioxidant serving as a cofactor in collagen synthesis, and thus facilitates follicular growth in the ovary. Many studies have shown that AA is synthesized in the liver and transported to other organs including ovary, however, there is no direct evidence of ascorbic acid synthesis in the ovary. Hence, we examined the expression pattern of different proteins (SMP30/GNL and GULO) involved in the AA synthesis in pre-pubertal rat, which showed significant expression of these proteins, suggesting the synthesis of AA in the ovary. Accumulation of AA in the ovary during follicular growth has been well demonstrated. However, the effect of Pregnant Mare Serum Gonadotropin (PMSG) on the AA synthesis in the ovary has not been studied in detail. Hence to decipher the effect, different doses of PMSG were injected subcutaneously into the pre-pubertal female rats, and ovarian AA level was measured after 48 h. A significant increase in AA content was observed in PMSG treated animal groups. Further, to understand the mechanism underlying ovarian AA accumulation, the expression levels of SMP30/GNL and GULO genes were measured. Expression of both the genes was significantly suppressed, which suggested a lowered AA synthesis in the PMSG treated rat ovary. For further understanding, mRNA expression of AA transporters SVCT1 and SVCT2 encoded by SLC23A1 and SLC23A2 genes respectively were measured, which showed increased level of SVCT1 expression. These observations suggested that the increased AA content might not be due to increased synthesis of AA within the ovary but possibly due to increased uptake from blood during the stimulation of follicular growth.

Ascorbic acid and CoQ10 ameliorate the reproductive ability of superoxide dismutase 1-deficient female mice†

Superoxide dismutase 1 suppresses oxidative stress within cells by decreasing the levels of superoxide anions. A dysfunction of the ovary and/or an aberrant production of sex hormones are suspected causes for infertility in superoxide dismutase 1-knockout mice. We report on attempts to rescue the infertility in female knockout mice by providing two antioxidants, ascorbic acid and/or coenzyme Q10, as supplements in the drinking water of the knockout mice after weaning and on an investigation of their reproductive ability. On the first parturition, 80% of the untreated knockout mice produced smaller litter sizes compared with wild-type mice (average 2.8 vs 7.3 pups/mouse), and supplementing with these antioxidants failed to improve these litter sizes. However, in the second parturition of the knockout mice, the parturition rate was increased from 18% to 44–75% as the result of the administration of antioxidants. While plasma levels of progesterone at 7.5 days of pregnancy were essentially the same between the wild-type and knockout mice and were not changed by the supplementation of these antioxidants, sizes of corpus luteum cells, which were smaller in the knockout mouse ovaries after the first parturition, were significantly ameliorated in the knockout mouse with the administration of the antioxidants. Moreover, the impaired vasculogenesis in uterus/placenta was also improved by ascorbic acid supplementation. We thus conclude that ascorbic acid and/or coenzyme Q10 are involved in maintaining ovarian and uterus/placenta homeostasis against insults that are augmented during pregnancy and that their use might have positive effects in terms of improving female fertility.

Vitamin C: the known and the unknown and Goldilocks

Vitamin C (Ascorbic Acid), the antiscorbutic vitamin, cannot be synthesized by humans and other primates, and has to be obtained from diet. Ascorbic acid is an electron donor and acts as a cofactor for fifteen mammalian enzymes. Two sodium-dependent transporters are specific for ascorbic acid, and its oxidation product dehydroascorbic acid is transported by glucose transporters. Ascorbic acid is differentially accumulated by most tissues and body fluids. Plasma and tissue vitamin C concentrations are dependent on amount consumed, bioavailability, renal excretion, and utilization. To be biologically meaningful or to be clinically relevant, in vitro and in vivo studies of vitamin C actions have to take into account physiologic concentrations of the vitamin. In this paper, we review vitamin C physiology; the many phenomena involving vitamin C where new knowledge has accrued or where understanding remains limited; raise questions about the vitamin that remain to be answered; and explore lines of investigations that are likely to be fruitful.

Hypoxia limits mouse follicle growth in vitro

Ovarian follicle culture is useful for elucidation of factors involved in the regulation of follicular function. We examined the effects of gas phase oxygen concentration, an oil overlay, serum type and medium supplementation with FSH, insulin-transferrin-selenium (ITS) and l-ascorbic acid on cultured preantral mouse follicle growth in a spherical, non-attached follicle culture system. Follicle growth in 5% oxygen was significantly (P < 0.01) inferior to growth in 20% oxygen in terms of follicle diameter. This was likely due to hypoxia, as evidenced by significantly (P < 0.05) increased follicle secretion of vascular endothelial growth factor (VEGF), a marker of cell hypoxia. Follicular growth was not (P > 0.05) affected by an oil overlay, ITS supplementation or serum type. Culture in medium with 5% mouse serum, 1 IU mL-1 FSH, 25 μg mL-1 l-ascorbic acid and 20% oxygen without an oil overlay supported the growth of follicles to a maximum diameter of 380 μm in 6 days. Compared with mature preovulatory mouse follicles in vivo that often have diameters >500 μm within the same time frame, in vitro-grown follicles clearly exhibit limited growth. Thus, adequate oxygenation is an essential factor in the process of optimising follicle growth.

Reactive oxygen and nitrogen species during meiotic resumption from diplotene arrest in mammalian oocytes

Mammalian ovary is metabolically active organ and generates by-products such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) on an extraordinary scale. Both follicular somatic cells as well as oocyte generate ROS and RNS synchronously and their effects are neutralized by intricate array of antioxidants. ROS such as hydrogen peroxide (H(2)O(2)) and RNS such as nitric oxide (NO) act as signaling molecules and modulate various aspects of oocyte physiology including meiotic cell cycle arrest and resumption. Generation of intraoocyte H(2)O(2) can induce meiotic resumption from diplotene arrest probably by the activation of adenosine monophosphate (AMP)-activated protein kinase A (PRKA)-or Ca(2+)-mediated pathway. However, reduced intraoocyte NO level may inactivate guanylyl cyclase-mediated pathway that results in the reduced production of cyclic 3',5'-guanosine monophosphate (cGMP). The reduced level of cGMP results in the activation of cyclic 3',5'-adenosine monophosphate (cAMP)-phosphodiesterase 3A (PDE3A), which hydrolyses cAMP. The reduced intraoocyte cAMP results in the activation of maturation promoting factor (MPF) that finally induces meiotic resumption. Thus, a transient increase of intraoocyte H(2)O(2) level and decrease of NO level may signal meiotic resumption from diplotene arrest in mammalian oocytes.

Stress stimulates AMP-activated protein kinase and meiotic resumption in mouse oocytes

This study examined the effects of three different cellular stresses on oocyte maturation in meiotically arrested mouse oocytes. Cumulus-cell enclosed oocytes (CEO) or denuded oocytes (DO) from immature, eCG-primed mice were cultured for 17-18 h in dbcAMP-containing medium plus increasing concentrations of the metabolic poison, sodium arsenite, or the free radical-generating agent, menadione. Alternatively, oocytes were exposed to osmotic stress by pulsing with sorbitol and returned to control inhibitory conditions for the duration of culture. Arsenite and menadione each dose-dependently induced germinal vesicle breakdown (GVB) in both DO and CEO. DO, but not CEO, pulsed for 60 min with 500 mM sorbitol were stimulated to resume maturation. The lack of effect in CEO suggests that the cumulus cells may be playing a protective role in osmotic stress-induced GVB. The AMP-activated protein kinase (PRKA; formerly known as AMPK) inhibitors, compound C and araA, completely blocked the meiosis-stimulating effects of all the tested stresses. Western blots showed that acetyl-CoA carboxylase, an important substrate of PRKA, was phosphorylated before GVB, supporting a role for PRKA in stress-induced maturation. Together, these data show that a variety of stresses stimulate GVB in meiotically arrested mouse oocytes in vitro and suggest that this effect is mediated through activation of PRKA.

Role of reactive oxygen species in gynecologic diseases

Free radicals derived from molecular oxygen and nitrogen are highly reactive metabolites called reactive oxygen species (ROS). Cells continuously produce free radicals and ROS as part of the metabolic process. They are involved in the various functions of the reproductive system. Antioxidants are enzymes or compounds that scavenge and reduce the presence of free radicals. Normally, a balance exists between concentrations of reactive oxygen species and antioxidant scavenging systems. The disruption of the delicate balance between pro- and antioxidants results in oxidative stress. Oxidative stress has been implicated in embryo fragmentation, DNA damage, apoptosis and poor pregnancy outcome. It has also been implicated in a large number of gynecologic diseases, such as endometriosis, pre-eclampsia and maternal diabetes. The use of antioxidants may be beneficial in combating the harmful effects of oxidative stress in many of these diseases. The present review outlines the importance of these species in the pathology of various gynecologic diseases. (Reprod Med Biol 2004; 3: 177 - 199).

Exposure to L-ascorbic acid or alpha-tocopherol facilitates the development of porcine denuded oocytes from metaphase I to metaphase II and prevents cumulus cells from fragmentation

It is known that alpha-tocopherol (vitamin E) and L-ascorbic acid (vitamin C) can modulate many biochemical processes intracellularly or extracellularly as antioxidants. The objective of the present study was to investigate the effects of alpha-tocopherol and L-ascorbic acid on porcine oocyte meiotic maturation, viability and the functions of cumulus cells. In two independent experiments, porcine oocytes with or free from cumulus cells were exposed to different levels of alpha-tocopherol (0, 10, 100 and 200 microM) or L-ascorbic acid (0, 50, 250 and 750 microM). Cumulus expansion, cumulus cell DNA fragmentation, meiotic maturation and degeneration of oocytes were assessed 48 h after in vitro culture. The results showed that: (1) neither alpha-tocopherol nor L-ascorbic acid influenced cumulus expansion but both prevented cumulus cell DNA fragmentation. (2) Alpha-tocopherol lowered the percentage of denuded oocytes (DOs) arrested at germinal vesicle stage (GV). Among the oocytes undergoing germinal vesicle breakdown (GVBD) proportion, fewer DOs treated by alpha-tocopherol were at metaphase I (MI) and more at metaphase II (MII). L-ascorbic acid caused lower percentage of DOs arrested at GV stage and higher percentage of DOs undergoing GVBD, especially at MII. The influences of alpha-tocopherol and L-ascorbic acid were not obvious in cumulus-enclosed oocytes (CEOs). (3) Both vitamins compromised the viability of CEOs and DOs. These results indicate that exposure to alpha-tocopherol or L-ascorbic acid promotes the development of porcine DOs from MI to MII and prevents cumulus cell DNA fragmentation at certain levels, especially 10 microM alpha-tocopherol or 250 microM L-ascorbic acid.

Organic hydroperoxide-induced chemiluminescence of follicular fluid and blood serum samples obtained from women pretreated for in vitro fertilization

The organic hydroperoxide-induced chemiluminescence of follicular fluid obtained from in vitro fertilized patients and its differently separated fractions were evaluated. Peroxidative stress causes a different photo-emission in the samples which alludes to some factors playing a role in the maintenance of the pro-oxidant/antioxidant balance. Interactions between the protein compounds of the samples and the organic hydroperoxide associate with formation of excited species contributing to the distinctive light emission processes. The technique offers a special re-interpretation of the scavenger state relating to the components of follicular fluid.

Eight-hydroxy-2'-deoxyguanosine in granulosa cells is correlated with the quality of oocytes and embryos in an in vitro fertilization-embryo transfer program

OBJECTIVE

To determine the effects of oxidative stress on the quality of oocytes and embryos, 8-hydroxy-2'-deoxyguanosine (8-OHdG) in granulosa cells was quantitatively studied during an in vitro fertilization and embryo transfer (IVF-ET) program.

DESIGN

Immunocytochemical staining of 8-OHdG in granulosa cells was quantitatively estimated using a charge-coupled device camera and analyzed using the National Institute of Health Image (NIH Image) freeware on a computer .

SETTING

Obstetrics and gynecology department in a university hospital.

PATIENT(S)

Ninety-six infertile couples undergoing IVF-ET treatment and intracytoplasmic sperm injection (IVF, n = 72; intracytoplasmic sperm injection, n = 24).

INTERVENTION(S)

Oocytes, granulosa cells, and follicular fluids were collected 35-36 hours after the administration of hCG.

MAIN OUTCOME MEASURE(S)

8-OHdG indices were obtained for mural [8-OHdG index (m)] and cumulus [8-OHdG index (c)] granulosa cells.

RESULT(S)

A negative correlation between the fertilization rate and both 8-OHdG indices (c and m) was found. The rate of production of good embryos also showed a negative correlation with the 8-OHdG index (m) and the 8-OHdG index (c). Negative correlations between the 8-OHdG index (c) and E2 levels in follicular fluid were observed. Endometriosis patients showed a higher 8-OHdG index (c) than did patients with other infertility causes, such as tubal, male factor, and unknown.

CONCLUSION(S)

Oxidative stress in granulosa cells lowered fertilization rates and subsequently led to a decrease in the quality of embryos. The quality of oocytes for endometriosis patients was impaired by the presence of 8-OHdG. This might be one causative factor in infertility in endometriosis patients.

Ascorbic acid supplement during luteal phase in IVF

PURPOSE

To evaluate the impact of ascorbic acid of different doses as additional support during luteal phase in infertility treatment by means of a prospective, randomized, placebo-controlled, group comparative, double-blind study.

METHODS

Voluntary daily oral intake of either ascorbic acid (1, 5, or 10 g/day) or Placebo for 14 days after follicle aspiration for IVF-ET procedure. Data was obtained on 620 cases of women, age <40 years, undergoing first IVF-embryo transfer cycles in two private outpatient infertility clinics. All women were stimulated by the same protocol. The mean age was 31.73 (+/- 4.4 SD) years.

RESULTS

No differences in clinical pregnancy rate and implantation rate were noted in statistical logistic regression analysis between the four intake groups.

CONCLUSIONS

There was no clinical evidence of any beneficial effect, as defined by main outcome measures, of ascorbic acid on IVF-ET. Our data suggest there is no obvious value of high dosed intake of vitamin C during luteal phase in infertility treatment.

Enhancement of developmental competence after in vitro fertilization of porcine oocytes by treatment with ascorbic acid 2-O-alpha-glucoside during in vitro maturation

The present study was conducted to examine the effect of ascorbic acid 2-O-alpha-glucoside (AA-2G), a stable ascorbate derivative, on the sustenance of cytoplasmic maturation responsible for subsequent developmental competence after in vitro fertilization of porcine oocytes. Cumulus-oocyte complexes were cultured for 44 h in North Carolina State University 37 medium supplemented with cysteine, gonadotropins, 10% (v:v) porcine follicular fluid, and 0-750 microM AA-2G. When oocytes were matured in the presence of 250 microM AA-2G, their ability to promote transformation of the sperm nucleus into the male pronucleus (MPN) was strongly enhanced after in vitro fertilization. Similarly, the presence of 25 microM beta-mercaptoethanol (ME) enhanced the degree of progression to MPN of penetrated sperm by associating with the increase in intracellular glutathione (GSH) content. Although the AA-2G treatment during oocyte maturation showed no influence on the GSH concentration, significantly higher levels of ascorbic acid (AsA) were detected in these oocytes than in those oocytes cultured without AA-2G (P < 0.05). The length of DNA migration encompassed by reactive oxygen species (ROS), generated by the hypoxanthine-xanthine oxidase system, was not increased in the oocytes treated with AA-2G, whereas ME treatment could not block the DNA damage by ROS. These findings indicate that AA-2G in maturation medium can potentiate the cellular protection of oocytes against oxidative stress by continuously supplying AsA. The proportion of development to the blastocyst stage after in vitro insemination was significantly increased in oocytes matured with AA-2G (P < 0.05), and this proportion showed no difference in comparison with that of oocytes treated with ME. These findings suggest that a critical concentration of intracellular AsA, supplied by AA-2G during in vitro maturation, plays an important role in supporting the cytoplasmic maturation responsible for developmental competence after fertilization by prevention of oxidative stress against porcine oocytes.