P-230 Use of a novel in vivo biosensor to rapidly determine oocyte developmental competence
Authors: Barnes S , Kelly J , Noschka E , Kostecki R 
Published: July 2024

Abstract

Study question
Can a novel in vivo biosensor (IVOS) rapidly determine oocyte developmental competence?

Summary answer
Data collected with the IVOS biosensor can be used to determine oocyte developmental competence, observed as blastocyst development after in vitro embryo production.

What is known already
Methods allowing for rapid, non-invasive assessment of oocyte quality are limited. Subjective morphology is used for gamete selection, but cannot discern between cells with subcellular dysfunction. Metabolism is an accurate method to distinguish cellular quality, but current methods are not rapid, require highly artificial environments, or lack appropriate sensitivity. Extracellular indicators associated with metabolic output may correlate to inherent oocyte developmental potential and serve as a biomarker. A published in vivo biosensor (IVOS) which analyses REDOX homeostasis, an indicator of subcellular function, may be optimised to use at the cellular level to assess oocyte quality.

Study design, size, duration
Experiments were performed in South Australia using abattoir derived cumulus-oocytes complexes (COC) aspirated from ewe ovaries for in vitro embryo production. COCs were group matured then maintained individually after IVOS analysis to permit identification of oocyte measurements to embryo developmental endpoint. Methodology optimisation and experiments were performed in June 2023 and October 2023, respectively. A holding pipette was modified to permit compatibility with the IVOS system using a proprietary method.

Participants/materials, setting, methods
Matured COCs were denuded to the corona radiata and placed into an air-buffered medium for IVOS analysis. The holding pipette suctioned COCs prior to excitation (488nm) of extracellular molecules at the COC surface. Emission wavelengths (515-520nm) were retrieved for ten consecutive replicates. COCs were subsequently co-incubated with frozen-thawed ram semen. Presumptive zygotes were cleaned of cumulus cells and loose spermatozoa, cultured for seven days, and stained using Hoechst H33342 to obtain total cell number.

Main results and the role of chance
Embryos were graded into three categories: 1) did not display a blastocoel cavity (not blastocyst); 2) embryo displaying a blastocoel and total cell count below 50 (early blastocyst); and 3) embryo displaying a blastocoel with a total cell count above 50 (blastocyst). Standard deviation calculations for technical replicates of each COC (n = 32) were used to form an equation capable of distinguishing between groups based on developmental endpoint reached. From this equation, IVOS measurements were lower in oocytes reaching the early blastocyst stage compared to those which reached the blastocyst stage (P &lt; 0.001) or did not reach the blastocyst stage (P = 0.042). Data from oocytes that became full blastocysts were higher than those which did not become blastocysts (P = 0.031).

Limitations, reasons for caution
The technology used in this study has been tested on sheep oocytes using blastocyst development as a measure of developmental competence. Further research is required to determine if it is applicable to other species or reproductive outcomes such as pregnancy and live birth.

Wider implications of the findings
This study provides a new technology and optimised methodology to improve the selection of high-quality oocytes among gametes graded homogeneously using subjective morphology. It can be utilised with existing assisted reproductive technologies to possibly increase the success rate of these procedures.

Trial registration number
N/A