Oxidative stress in OPU mares can delay embryo development in vitro

Abstract

The application of ovum pickup-intracytoplasmic sperm injection (OPU-ICSI) is well established for the commercial equine in vitro production (IVP). There is a marked individual mare effect on the OPU-ICSI outcome, but little is known about the influence of the mare's health conditions. This study aimed to determine a potential association between the concentrations of interleukin-6 (IL-6) and reactive oxygen metabolites (d-ROMs) in the serum of the donor mare on the efficiency of equine IVP. Just before OPU, a blood sample was collected from 28 Warmblood donor mares, that were subjected to a routine OPU-ICSI program. The serum concentrations of IL-6 and d-ROMs were photometrically assayed using the equine Nori® (Genorise Scientific, USA) and Diacron® (Diacron International, Italy) kits, respectively. The kinetics of blastocyst development and the blastocyst rate (blastocysts/injected oocytes) were recorded. For the blastocyst forming mares, Pearson's and Spearman's correlation coefficients were calculated between the blastocyst rate and the serum concentration of IL-6 and d-ROMs. The serum concentrations were also compared between mares yielding at least one and mares yielding no blastocyst or between mares with fast (at day 7-8 post ICSI) and slow (≥ day 9 post ICSI)growing blastocysts using the independent t-test or Mann-Whitney U-test. The average blastocyst formation rate was 24.68±5.16 % and the average concentrations of IL-6 and d-ROMs were 519.59±157.08 pg/mL and 171.30±4.55 carratelli units (UCARR), respectively. Serum concentrations of IL-6 and d-ROMs, respectively, were not significantly correlated with blastocyst formation rates and not markedly different between the blastocyst forming (552.68±235.18 pg/mL and 168.36±5.56 UCARR) and non-forming (468.47±179.99 pg/mL and 175.85±7.89 UCARR) mares. Serum concentrations of d-ROMs were significantly lower in mares with fast growing (148.10±8.13 UCARR) compared to those with slow growing blastocysts (179.41±4.89 UCARR; P= 0.003). Taken together, the serum concentration of IL-6 and d-ROMs are not associated with the mares’ ability to produce blastocysts after OPU-ICSI. Although it may be questioned whether a single sample is representative of the mare's health status, changes in serum metabolites related to oxidative stress at the time of oocyte retrieval may diminish the OPU-ICSI outcome via interfering with the embryonic development in mares. Funded by the Ministry of Higher Education of the Arab Republic of Egypt.