O-102 From oocytes to embryos
Authors: Ptak G 
Published: July 2024

Abstract
Title: Oxidative stress and DNA damage in oocytes: clinical relevance and diagnosis
Study question: Is it possible to detect signs of oxidative stress (OS) in a living oocyte?
Summary answer: OS-driven changes in lipid profile can be detected in human oocytes.
What is known already: Oxidative stress and DNA damage are associated with increasing age of women. From all cellular molecules, lipids are most prone to OS-driven damage. DNA is more stable, so its damage may occur only later, probably as a result of cytoplasmic changes caused by damage to lipids and proteins. Initially, peroxidation of cellular lipids causes damage to lipid bilayers i.e. biological membranes and membranous organelles. Accumulation of lipid peroxidation products - toxic aldehydes - causes DNA damage and mutations. Screening of DNA damage in the oocyte is not feasible in human ART. However, oocyte lipid damage can be detected using live-cell label-free spectroscopies. So far, changes in the lipid profile of human oocytes have not been investigated. Here we propose the screening of lipid profile as a reliable method of evaluation of OS-driven damage of the oocyte.
Study design, size, duration: This study aims to thoroughly discuss effects of OS in female gamete. Special consideration is given to current limits in DNA damage detection and oocyte quality screening. Then, strategies to evaluate OS-driven damage of cellular components are proposed. Finally, obstacles and future perspectives in clinical diagnosis and treatment of OS-damaged oocytes are discussed.
Participants/materials, setting, methods: To investigate if it is possible to detect differences in oocyte LF, we examined a total of 48 GV oocytes derived from 26 women under 33 years of age and with no history of infertility, enrolled in an oocyte donation program. Furthermore, to evaluate the effect of lipid profile changes in oocytes on embryo development, 167 C57BL/6 mice were used. Modifications of cytoplasmic lipid droplets (LDs) profile in oocytes were evaluated by Coherent anti-stokes Raman Spectroscopy (CARS) and further validated by Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM). The influence of oocyte lipid changes on embryo development was verified using mouse model.
Main results and the role of chance: Here we show woman-age-dependent progressive changes in LF of oocytes consisting of increased LDs size, area and number, assessed by label-free imaging (CARS). LF variations in oocytes were detectable also within individual donors. We next confirmed woman-age-dependent changes in oocytes by demonstration of lipid peroxidation and composition changes (FTIR) and alterations of structural properties of lipid bilayers (TEM). Finally, using a mouse model we showed that LF changes in oocytes negatively affect preimplantation embryo development.
Limitations, reasons for caution: The idea of this study was to propose an original approach to assess the quality of oocytes based on changes in the lipid profile. The information presented should not be viewed as directly applicable, because human oocytes at the GV stage were assessed, and not at the MII stage.
Wider implications of the findings: Our findings highlight functional connections between lipids and other molecules building the oocyte, including DNA. Furthermore, this original study open the possibility to develop an innovative tool for oocyte assessment.
Study funding/competing interest(s): This research was funded by National Science Centre of Poland Grants 2021/41/B/NZ3/03507 and 2019/35/B/NZ4/03547.