Vitamin C Protects Porcine Oocytes From Microcystin-LR Toxicity During Maturation

Microcystin-LR in drinking water: An emerging role of mitochondrial-induced epigenetic modifications and possible mitigation strategies

Algal blooms are a serious menace to freshwater bodies all over the world. These blooms typically comprise cyanobacterial outgrowths that produce a heptapeptide toxin, Microcystin-LR (MC-LR). Chronic MC-LR exposure impairs mitochondrial-nuclear crosstalk, ROS generation, activation of DNA damage repair pathways, apoptosis, and calcium homeostasis by interfering with PC/MAPK/RTK/PI3K signaling. The discovery of the toxin's biosynthesis pathways paved the way for the development of molecular techniques for the early detection of microcystin. Phosphatase inhibition-based bioassays, high-performance liquid chromatography, and enzyme-linked immunosorbent tests have recently been employed to identify MC-LR in aquatic ecosystems. Biosensors are an exciting alternative for effective on-site analysis and field-based characterization. Here, we present a synthesis of evidence supporting MC-LR as a mitotoxicant, examine various detection methods, and propose a novel theory for the relevance of MC-LR-induced breakdown of mitochondrial machinery and its myriad biological ramifications in human health and disease.

Astaxanthin Alleviates Hepatic Lipid Metabolic Dysregulation Induced by Microcystin-LR

Microcystin-LR (MC-LR), frequently generated by cyanobacteria, has been demonstrated to raise the likelihood of liver disease. Few previous studies have explored the potential antagonist against MC-LR. Astaxanthin (ASX) has been shown to possess various beneficial effects in regulating lipid metabolism in the liver. However, whether ASX could alleviate MC-LR-induced hepatic lipid metabolic dysregulation is as yet unclear. In this work, the important roles and mechanisms of ASX in countering MC-LR-induced liver damage and lipid metabolic dysregulation were explored for the first time. The findings revealed that ASX not only prevented weight loss but also enhanced liver health after MC-LR exposure. Moreover, ASX effectively decreased triglyceride, total cholesterol, aspartate transaminase, and alanine aminotransferase contents in mice that were elevated by MC-LR. Histological observation showed that ASX significantly alleviated lipid accumulation and inflammation induced by MC-LR. Mechanically, ASX could significantly diminish the expression of genes responsible for lipid generation (Srebp-1c, Fasn, Cd36, Scd1, Dgat1, and Pparg), which probably reduced lipid accumulation induced by MC-LR. Analogously, MC-LR increased intracellular lipid deposition in THLE-3 cells, while ASX decreased these symptoms by down-regulating the expression of key genes in the lipid synthesis pathway. Our results implied that ASX played a crucial part in lipid synthesis and effectively alleviated MC-LR-induced lipid metabolism dysregulation. ASX might be developed as a novel protectant against hepatic impairment and lipid metabolic dysregulation associated with MC-LR. This study offers new insights for further management of MC-LR-related metabolic diseases.

The cytotoxicity of microcystin-LR: ultrastructural and functional damage of cells

Microcystin-LR (MC-LR) is a toxin produced by cyanobacteria, which is widely distributed in eutrophic water bodies and has multi-organ toxicity. Previous cytotoxicity studies have mostly elucidated the effects of MC-LR on intracellular-related factors, proteins, and DNA at the molecular level. However, there have been few studies on the adverse effects of MC-LR on cell ultrastructure and function. Therefore, research on the cytotoxicity of MC-LR in recent years was collected and summarized. It was found that MC-LR can induce a series of cytotoxic effects, including decreased cell viability, induced autophagy, apoptosis and necrosis, altered cell cycle, altered cell morphology, abnormal cell migration and invasion as well as leading to genetic damage. The above cytotoxic effects were related to the damage of various ultrastructure and functions such as cell membranes and mitochondria. Furthermore, MC-LR can disrupt cell ultrastructure and function by inducing oxidative stress and inhibiting protein phosphatase activity. In addition, the combined toxic effects of MC-LR and other environmental pollutants were investigated. This review explored the toxic targets of MC-LR at the subcellular level, which will provide new ideas for the prevention and treatment of multi-organ toxicity caused by MC-LR.

How Do Environmental Toxicants Affect Oocyte Maturation Via Oxidative Stress?

In mammals, oogenesis initiates before birth and pauses at the dictyate stage of meiotic prophase I until luteinizing hormone (LH) surges to resume meiosis. Oocyte maturation refers to the resumption of meiosis that directs oocytes to advance from prophase I to metaphase II of meiosis. This process is carefully modulated to ensure a normal ovulation and successful fertilization. By generating excessive amounts of oxidative stress, environmental toxicants can disrupt the oocyte maturation. In this review, we categorized these environmental toxicants that induce mitochondrial dysfunction and abnormal spindle formation. Further, we discussed the underlying mechanisms that hinder oocyte maturation, including mitochondrial function, spindle formation, and DNA damage response.

Attenuation of sodium arsenite mediated ovarian DNA damage, follicular atresia, and oxidative injury by combined application of vitamin E and C in post pubertal Wistar rats

Arsenic being a toxic metalloid ubiquitously persists in environment and causes several health complications including female reproductive anomalies. Epidemiological studies documented birth anomalies due to arsenic exposure. Augmented reactive oxygen species (ROS) generation and quenched antioxidant pool are foremost consequences of arsenic threat. On the contrary, Vitamin E (VE) and C (VC) are persuasive antioxidants and conventionally used in toxicity management. Present study was designed to explore the extent of efficacy of combined VE and VC (VEC) against Sodium arsenite (NaAsO2) mediated ovarian damage. Thirty-six female Wistar rats were randomly divided into three groups (Grs) and treated for consecutive 30 days; Gr I (control) was vehicle fed, Gr II (treated) was gavaged with NaAsO2 (3 mg/kg/day), Gr III (supplement) was provided with VE (400 mg/kg/day) & VC (200 mg/kg/day) along with NaAsO2. Marked histological alterations were evidenced by disorganization in oocyte, granulosa cells and zona pellucida layers in treated group. Considerable reduction of different growing follicles along with increased atretic follicles was noted in treated group. Altered activities ofΔ5 3β-Hydroxysteroid dehydrogenase and 17β-Hydroxysteroid dehydrogenase accompanied by reduced luteinizing hormone, follicle-stimulating hormone and estradiol levels were observed in treated animals. Irregular estrous cyclicity pattern was also observed due to NaAsO2 threat. Surplus ROS production affected ovarian antioxidant strata as evidenced by altered oxidative stress markers. Provoked oxidative strain further affects DNA status of ovary. However, supplementation with VEC caused notable restoration from such disparaging effects of NaAsO2 toxicities. Antioxidant and antiapoptotic attributes of those vitamins might be liable for such restoration.

Cardiac Toxicity Induced by Long-Term Environmental Levels of MC-LR Exposure in Mice

Cyanobacterial blooms are considered a serious global environmental problem. Recent studies provided evidence for a positive association between exposure to microcystin-LR (MC-LR) and cardiotoxicity, posing a threat to human cardiovascular health. However, there are few studies on the cardiotoxic effects and mechanisms of long-term low-dose MC-LR exposure. Therefore, this study explored the long-term toxic effects and toxic mechanisms of MC-LR on the heart and provided evidence for the induction of cardiovascular disease by MC-LR. C57BL/6 mice were exposed to 0, 1, 30, 60, 90, and 120 μg/L MC-LR via drinking water for 9 months and subsequently necropsied to examine the hearts for microstructural changes using H&E and Masson staining. The results demonstrated fibrotic changes, and qPCR and Western blots showed a significant up-regulation of the markers of myocardial fibrosis, including TGF-β1, α-SMA, COL1, and MMP9. Through the screening of signaling pathways, it was found the expression of PI3K/AKT/mTOR signaling pathway proteins was up-regulated. These data first suggested MC-LR may induce myocardial fibrosis by activating the PI3K/AKT/mTOR signaling pathway. This study explored the toxicity of microcystins to the heart and preliminarily explored the toxic mechanisms of long-term toxicity for the first time, providing a theoretical reference for preventing cardiovascular diseases caused by MC-LR.

Effects of Cyanobacterial Harmful Algal Bloom Toxin Microcystin-LR on Gonadotropin-Dependent Ovarian Follicle Maturation and Ovulation in Mice

BACKGROUND

Cyanobacterial harmful algal blooms (CyanoHABs) originate from the excessive growth or bloom of cyanobacteria often referred to as blue-green algae. They have been on the rise globally in both marine and freshwaters in recently years with increasing frequency and severity owing to the rising temperature associated with climate change and increasing anthropogenic eutrophication from agricultural runoff and urbanization. Humans are at a great risk of exposure to toxins released from CyanoHABs through drinking water, food, and recreational activities, making CyanoHAB toxins a new class of contaminants of emerging concern.

OBJECTIVES

We investigated the toxic effects and mechanisms of microcystin-LR (MC-LR), the most prevalent CyanoHAB toxin, on the ovary and associated reproductive functions.

METHODS

Mouse models with either chronic daily oral or acute intraperitoneal exposure, an engineered three-dimensional ovarian follicle culture system, and human primary ovarian granulosa cells were tested with MC-LR of various dose levels. Single-follicle RNA sequencing, reverse transcription-quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, immunohistochemistry (IHC), and benchmark dose modeling were used to examine the effects of MC-LR on follicle maturation, hormone secretion, ovulation, and luteinization.

RESULTS

Mice exposed long term to low-dose MC-LR did not exhibit any differences in the kinetics of folliculogenesis, but they had significantly fewer corpora lutea compared with control mice. Superovulation models further showed that mice exposed to MC-LR during the follicle maturation window had significantly fewer ovulated oocytes. IHC results revealed ovarian distribution of MC-LR, and mice exposed to MC-LR had significantly lower expression of key follicle maturation mediators. Mechanistically, in both murine and human granulosa cells exposed to MC-LR, there was reduced protein phosphatase 1 (PP1) activity, disrupted PP1-mediated PI3K/AKT/FOXO1 signaling, and less expression of follicle maturation-related genes.

DISCUSSION

Using both in vivo and in vitro murine and human model systems, we provide data suggesting that environmentally relevant exposure to the CyanoHAB toxin MC-LR interfered with gonadotropin-dependent follicle maturation and ovulation. We conclude that MC-LR may pose a nonnegligible risk to women's reproductive health by heightening the probability of irregular menstrual cycles and infertility related to ovulatory disorders. https://doi.org/10.1289/EHP12034.

MitoQ Protects Ovarian Organoids against Oxidative Stress during Oogenesis and Folliculogenesis In Vitro

Ovarian organoids, based on mouse female germline stem cells (FGSCs), have great value in basic research and are a vast prospect in pre-clinical drug screening due to their properties, but the competency of these in vitro-generated oocytes was generally low, especially, in vitro maturation (IVM) rate. Recently, it has been demonstrated that the 3D microenvironment triggers mitochondrial dysfunction during follicle growth in vitro. Therefore, therapies that protect mitochondria and enhance their function in oocytes warrant investigation. Here, we reported that exposure to 100 nM MitoQ promoted follicle growth and maturation in vitro, accompanied by scavenging ROS, reduced oxidative injury, and restored mitochondrial membrane potential in oocytes. Mechanistically, using mice granulosa cells (GCs) as a cellular model, it was shown that MitoQ protects GCs against H₂O₂-induced apoptosis by inhibiting the oxidative stress pathway. Together, these results reveal that MitoQ reduces oxidative stress in ovarian follicles via its antioxidative action, thereby protecting oocytes and granulosa cells and providing an efficient way to improve the quality of in vitro-generated oocytes.

Nonylphenol exposure-induced oocyte quality deterioration could be reversed by melatonin supplementation in mice

Nonylphenol (NP) belongs to the metabolites of commercial detergents, which acts as an environmental endocrine disruptor. NP is reported to have multiple toxicity including reproductive toxicity. In present study, we reported the protective effects of melatonin on the NP-exposed oocyte quality. We set up a mouse in vivo model of NP exposure (500 μg/L), by daily drinking and continued feeding for 4 weeks; and we gave a daily dose of melatonin (30 mg/kg) to the NP-exposed mice. Melatonin supplementation restores the development ability of oocytes exposed to NP, and this was due to the reduction of ROS level and DNA damage by melatonin. Melatonin could rescue aberrant mitochondria distribution, mitochondria membrane potential, which also was reflected by ATP content and mtDNA copy number. Moreover, melatonin could restore the RPS3 expression to ensure the ribosome function for protein synthesis, and reduced GRP78 protein level to protect against ER stress and ER distribution defects. We also found that vesicle protein Rab11 from Golgi apparatus was protected by melatonin at the spindle periphery of oocytes of NP-exposed mice, which further moderated LAMP2 for lysosome function. Our results indicate that melatonin protects oocytes from NP exposure through its effects on the reduction of oxidative stress and DNA damage, which might be through its amelioration on the organelles in mice.

Beneficial Effect of Selenium Doped Carbon Quantum Dots Supplementation on the in vitro Development Competence of Ovine Oocytes

Background

After the synthesis of selenium doped carbon quantum dots (Se/CDs) via a step-by-step hydrothermal synthesis method with diphenyl diselenide (DPDSe) as precursor, the beneficial effects of Se/CDs’ supplementation on the in vitro development competence of ovine oocytes were firstly investigated in this study by the assay of maturation rate, cortical granules’ (CGs) dynamics, mitochondrial activity, reactive oxygen species (ROS) production, epigenetic modification, transcript profile, and embryonic development competence.

Results

The results showed that the Se/CDs’ supplementation during the in vitro maturation (IVM) process not only enhanced the maturation rate, CGs’ dynamics, mitochondrial activity and embryonic developmental competence of ovine oocytes, but remarkably decreased the ROS production level of ovine oocytes. In addition, the expression levels of H3K9me3 and H3K27me3 in the ovine oocytes were significantly up-regulated after the Se/CDs’ supplementation, in consistent with the expression levels of 5mC and 5hmC. Moreover, 2994 up-regulated differentially expressed genes (DEGs) and 846 repressed DEGs were found in the oocytes after the Se/CDs’ supplementation. According to the analyses of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG), these DEGs induced by the Se/CDs’ supplementation were positively related to the progesterone mediated oocyte maturation and mitochondrial functions. And these remarkably up-regulated expression levels of DEGs related to oocyte maturation, mitochondrial function, and epigenetic modification induced by the Se/CDs’ supplementation further confirmed the beneficial effect of Se/CDs’ supplementation on the in vitro development competence of ovine oocytes.

Conclusion

The Se/CDs prepared in our study significantly promoted the in vitro development competence of ovine oocytes, benefiting the extended research about the potential applications of Se/CDs in mammalian breeding technologies.

Tea polyphenols alleviate the adverse effects of diabetes on oocyte quality

Maternal diabetes mellitus reduces oocyte quality, such as abnormalities of spindle assembly and chromosome segregation, mitochondrial dysfunction, decrease of fertilization rate, increase of ROS, and so on. So, it is important to research how to restore the decreased oocyte quality induced by maternal diabetes mellitus. Polyphenols are the most abundant bioactive components of green tea. It is reported that tea polyphenols have many health functions, for instance anti-oxidation, anti-inflammation, anti-obesity, and anti-diabetes. Thus, we hypothesize that tea polyphenols may play a crucial role in alleviating adverse effects of diabetes on oocyte quality. In the present study, we researched the effects of tea polyphenols on diabetic oocyte maturation in vitro. Compared with the control, oocytes from diabetic mice displayed a lower maturation rate and a higher frequency of spindle defects and chromosome misalignment. However, tea polyphenols significantly increased the oocyte maturation rate, and reduced the incidence of abnormal spindle assembly and chromosome segregation. Tea polyphenols also obviously decreased the reactive oxygen species (ROS) levels in diabetic oocytes, and increased the expression of antioxidant genes (Sod1 and Sod2). Abnormal mitochondrial membrane potential was also alleviated in diabetic oocytes, and the expression of genes regulating mitochondrial fusion (Opa1, Mfn1 and Mfn2) and fission (Drp1) was significantly increased while tea polyphenols were added. Meanwhile, tea polyphenols reduced DNA damage in diabetic oocytes which may be mediated by the increased expression of Rad51, related to DNA damage repair. Our results suggest that tea polyphenols would, at least partially, restore the adverse effects of diabetes mellitus on oocyte quality.

Grape Seed Proanthocyanidin Ameliorates FB1-Induced Meiotic Defects in Porcine Oocytes

Fumonisin B₁ (FB₁), as the most prevalent and toxic fumonisin, poses a health threat to humans and animals. The cytotoxicity of FB₁ is closely related to oxidative stress and apoptosis. The purpose of this study is to explore whether Grape seed proanthocyanidin (GSP), a natural antioxidant, could alleviate the meiotic maturation defects of oocytes caused by FB₁ exposure. Porcine cumulus oocyte complexes (COCs) were treated with 30 μM FB₁ alone or cotreated with 100, 200 and 300 μM GSP during in vitro maturation for 44 h. The results show that 200 μM GSP cotreatment observably ameliorated the toxic effects of FB₁ exposure, showing to be promoting first polar body extrusion and improving the subsequent cleavage rate and blastocyst development rate. Moreover, 200 μM GSP cotreatment restored cell cycle progression, reduced the proportion of aberrant spindles, improved actin distribution and protected mitochondrial function in FB₁-exposed oocytes. Furthermore, reactive oxygen species (ROS) generation was significantly decreased and the mRNA levels of CAT, SOD2 and GSH-PX were obviously increased in the 200 μM GSP cotreatment group. Notably, the incidence of early apoptosis and autophagy level were also significantly decreased after GSP cotreatment and the mRNA expression levels of BAX, CASPASE3, LC3 and ATG5 were markedly decreased, whereas BCL2 and mTOR were observably increased in the oocytes after GSP cotreatment. Together, these results indicate that GSP could exert significant preventive effects on FB₁-induced oocyte defects by ameliorating oxidative stress through repairing mitochondrial dysfunction.

Mogroside V Protects Porcine Oocytes From Lipopolysaccharide-Induced Meiotic Defects

Accumulating evidence has demonstrated that lipopolysaccharide (LPS) compromises female reproduction, especially oocyte maturation and competence. However, methods to protect oocyte quality from LPS-induced deterioration remain largely unexplored. We previously found that mogroside V (MV) can promote oocyte maturation and embryonic development. However, whether MV can alleviate the adverse effects of LPS exposure on oocyte maturation is unclear. Thus, in this study, we used porcine oocytes as a model to explore the effects of MV administration on LPS-induced oocyte meiotic defects. Our findings show that supplementation with MV protected oocytes from the LPS-mediated reduction in the meiotic maturation rate and the subsequent blastocyst formation rate. In addition, MV alleviated the abnormalities in spindle formation and chromosome alignment, decrease in α-tubulin acetylation levels, the disruption of actin polymerization, and the reductions in mitochondrial contents and lipid droplet contents caused by LPS exposure. Meanwhile, LPS reduced m⁶A levels in oocytes, but MV restored these epigenetic modifications. Furthermore, MV reduced reactive oxygen species (ROS) levels and early apoptosis in oocytes exposed to LPS. In summary, our study demonstrates that MV can protect oocytes from LPS-induced meiotic defects in part by reducing oxidative stress and maintaining m⁶A levels.