The effects of a glyphosate-based herbicide on the bovine gametes during an in vitro embryo production model

Roundup® (R), while it is the most used herbicide globally, and its residues are ubiquitous in urban and suburban areas, its impact on vertebrates' safety remains highly debated. Here, in three in vitro experiments, we investigated the effects of a very low dose (1 ppm) of R on the fertilization capacity and embryo development in cattle. In the first experiment, frozen-thawed bull semen exposed to R for 1 h exhibited reduced motility parameters but unaffected fertilization ability. However, after in vitro fertilization, the rates of embryo formation were significantly lower compared to the untreated controls. In the second experiment, oocytes exposed to R during in vitro maturation showed reduced cleavage rates, and the embryo yield on days 7, 8, and 9 of embryo culture was significantly lower than that of the controls. In the third experiment, oocytes were matured in the presence of R and in a medium containing both R and Zinc, chosen to offer antioxidant protection to the oocytes. Day-7 blastocysts were analyzed for the expression of genes associated with oxidative stress, apoptosis, and epigenetic reprogramming. Exposure to R markedly suppressed embryo formation rates compared to the controls. The combination of R with Zinc restored the blastocyst yield, which on days 8 and 9 was comparable to that of the controls and higher than the groups exposed only to R on all days. The gene expression analysis revealed that R promotes oxidative stress development, triggers apoptosis, and induces epigenetic changes in developing embryos, while zinc presence alleviates these adverse effects of R. These findings imply that even at very low doses, R could be highly toxic, leading to functional abnormalities in both gametes, potentially affecting fertility in both genders.

The activity of three glycosidases (β-Ν-acetyloglucosaminidase, α-mannosidase, and β-galactosidase) in the follicular fluid and in the maturation medium affects bovine oocyte maturation

We studied the role of follicular fluid's (FF) glycosidase (α-mannosidase [α-ΜΑΝ], β-Ν-acetyloglucosaminidase [NAGASE], β-galactosidase [β-GAL]) activity during IVM of bovine oocytes. Oocytes were allocated into two groups according to the follicular size (small follicle [SF]: 2-5 mm, large follicle [LF]: >5-8 mm). In experiment 1, cumulus-oocyte complexes (COCs) quality was evaluated according to morphologic criteria (grades A, B-C, D); oocyte (n = 801) nuclear maturation was assessed after 24 hours of incubation. Bovine embryos were produced in vitro in groups (experiment 2, n = 1503 oocytes) or individually (experiment 3, n = 50 oocytes). More grade-A and -BC COCs were collected from SF and LF groups, respectively (P < 0.05). Maturation rate (experiment 1) and cleavage rate (experiments 2 and 3) were similar in SF and LF groups. Activity of all glycosidases in FF was higher (P < 0.05) in SF group than in LF group, whereas in maturation medium of SF group it was, overall, significantly lower than in that of LF (experiments 2 and 3). In FF of SF group, NAGASE positively associated with grade-A oocytes and negatively with BC oocytes; increased β-GAL was associated with degenerated oocytes. Cleavage rate in LF group, related negatively to NAGASE and positively to α-MAN in maturation medium. These results indicate that during maturation, COCs release NAGASE and consume β-GAL, but differences probably exist between individual and group maturation.

112 EFFECTS OF GUAIAZULENE ON IN VITRO CULTURE OF BOVINE ZYGOTES, AND ON mRNA TRANSCRIPTS RELATED TO EMBRYO QUALITY

We have previously shown that follicular and oviductal fluid provide greater total protection against lipid peroxidation than the respective media used for the in vitro embryo production. Reactive oxygen species (ROS) production has been implicated as a major cause for the reduced in vitro bovine embryo production; it is believed that they participate in meiotic arrest of oocytes, embryonic block and cell death. The aim of this study was to determine whether guaiazulene (G), an exogenous antioxidant, added in the post fertilization culture medium would affect the early embryo development and the quality of the produced blastocysts in terms of mRNA expression of several important genes. In a previous study we had shown that media modified with 0.01 mm of G provided the same antioxidant protection as the respective in vivo environments (i.e. the follicular and the oviductal fluid). Bovine cumulus–oocyte complexes (COC) were aspirated from ovaries derived from slaughtered cows and matured in groups of 50 in 500 μL in TCM199 with 10% fetal calf serum and 10 ng mL–1 Epidermal Growth factor at 39°C in an atmosphere of 5% CO2 in air and maximum humidity. Twenty-four hours later matured oocytes were inseminated with frozen/thawed bull semen and co-incubated in the same conditions as maturation. Presumptive zygotes were divided into 4 groups and cultured in groups of 25 in 25 μL of SOF with 5% FCS (Control–, n = 355), supplemented with 0.01 mm of G (n = 344) or 0.1 mm of G (n = 345) or 0.05% DMSO – the G diluent–(Control+, n = 347) at 39°C in an atmosphere of 5% CO2, 5% O2 and maximum humidity. Blastocyst yield was recorded on Days 6, 7, 8 and 9; Day 7 blastocysts from each group were snap frozen and stored at –80°C for mRNA extraction. Quantification of transcripts for aldose reductase mRNA (AKRIBI), prostaglandin G/H synthase-2 (PGHS-2, COX-2), glyceraldehyde 3-phosphate dehydrogenase (GADPH), facilitated glucose/fructose transporter, member 5 (GLUT-5) genes related to metabolism, glutathione peroxidase 1 (GPX1), glucose-6-phosphate dehydrogenase (G6PD) antioxidant enzymes and placenta-specific 8 (PLAC8) related to implantation was carried out by real-time quantitative RT-PCR. Data for embryo development and on transcript abundance were analyzed by chi square and ANOVA, respectively. Cleavage rate tended to be higher in 0.01 mm group than in Control– (77.87% v. 71.41%, P = 0.07). Barring that, no other differences were detected in cleavage rate (Control+: 71.32%; 0.1 mm: 72.75%) or in the overall blastocyst yield on Day 9 (Control–: 25.50%; Control+: 26.71%; 0.1 mm: 25.75%; 0.01 mm: 29.58%). The relative abundance of genes studied varied among groups, but these differences were not significant. We infer that under the current culture conditions, G as an antioxidant has no serious direct effect on early embryo development or on embryo quality at least on the mRNA transcripts studied. Further studies using the same antioxidant in different atmospheric conditions are planed. ED and GSA were sponsored by COST (FAO702) and OECD fellowships, respectively.