Urea influences amino acid turnover in bovine cumulus-oocyte complexes, cumulus cells and denuded oocytes, and affects in vitro fertilization outcome

Abstract

High-protein diets often lead to an increase in urea concentration in follicular fluid of dairy cows, which may reduce oocyte competence. In the present study, maturation media were supplemented with urea (0, 20, 40 mg/dl), and amino acids (AAs) turnover was evaluated in the 24-h spent media of specimens (cell types), bovine cumulus-oocyte complexes (COCs), cumulus cells (CCs), or denuded oocytes (DOs). The main effects of urea and cell type, and their interaction were significant on the individual turnover (expect threonine, glycine, and tyrosine) and total turnover, depletion, and appearance of AAs. The results showed a high level of urea and DOs increased the depletion of all AAs and that of essential and non-AAs, respectively. Sensitivity analysis revealed the highest sensitivity of isoleucine, lysine, and tryptophan to urea, especially in DOs. Principal component analysis (PCA) evaluated the strong correlations between the turnover of: (1) glutamine, aspartic acid or glycine, and developmental competence and fertilization of COCs; (2) serine, isoleucine, valine or glutamic acid, and cleavage rate of DOs; and (3) serine, glutamine, aspartic acid or alanine, and CCs viability. In conclusion, urea significantly changed the turnover of AAs by COCs, CCs and DOs, and reduced the subsequent developmental competence of bovine oocytes.

A multilevel analysis identifies the different relationships between amino acids and the competence of oocytes matured individually or in groups

“…Moreover, the depletion of AAs was the highest in urea-incubated COCs with greater depletion in non-cleaved COCs than in cleaved COCs using an individual-IVM culture. Recently, we observed a greater depletion of AAs and a decrease in oocyte competence in the presence of high urea levels in the group-IVM system 17 . Similarly, Hemmings et al reported that higher AA depletion is associated with a decrease in the developmental competence of oocytes in humans and bovines 18 , 19 .…”

“…We have previously reported that high urea levels not only increased the percentage of oocyte degeneration, but also decreased the in vitro viability of CCs and oviduct epithelial cells 16,17,39 . In this study, the addition of urea to the maturation medium increased the percentage of oocyte degeneration by day 3 after insemination.…”

“…1, Phase 1). The determination of AAs in the 24-h spent media (n = 17) and fresh maturation media (n = 6) was conducted using the HPLC method (HyperClone ODS C 18, 250 mm × 4.6 mm, 5 μm, Agilent 1100, Agilent Technologies, Waldbronn, Germany) based on our previous work 17 . HPLC was used at a flow rate of 1.2 ml/min with fluorescence detection after pre-column derivatization (with o-phthaldialdehyde, OPA).…”

“…Blood urea nitrogen (BUN) levels greater than 19 mg/dl are directly associated with decreased reproductive efficiency in healthy dairy cows 14 . A growing body of evidence supports the detrimental effect of high levels of urea on the competence of bovine oocytes, in vivo and in vitro 15 – 17 . Moreover, urea increases the consumption of AAs by CCs, denuded oocytes (DOs) and COCs 17 .…”

“…A growing body of evidence supports the detrimental effect of high levels of urea on the competence of bovine oocytes, in vivo and in vitro 15 – 17 . Moreover, urea increases the consumption of AAs by CCs, denuded oocytes (DOs) and COCs 17 . Hemmings et al reported a concomitant increase in AA consumption and a decrease in the developmental competence of bovine and human oocytes 18 , 19 .…”