P-580 Benzophenone interrupted maturation of oocytes in vitro by promoting mitochondrial activity and inflammatory response in mice
Authors: Kang I , Koo M , Lee W , Lee J 
Published: July 2024

Abstract

Study question
As an endocrine disrupting chemical, does benzophenone affect the competency of oocytes?

Summary answer
Benzophenone interfered with the in vitro maturation of oocytes and increased the number of mitochondria in oocytes by inducing of inflammatory response.

What is known already
Benzophenone (BP) is the organic compound used in ultraviolet (UV) filters due to its ability to absorb UV radiations and the applications of BP have a wide range in commercial/industrial products such as sunscreens, shampoos, lipsticks, food packaging, and plastics. However, BP is suspected to be an endocrine disrupting chemical (EDC) that can cause adverse effects on the endocrine system by mimicking or blocking the response of hormones in the body.

Study design, size, duration
Intraperitoneal injection of pregnant mare serum gonadotropin was performed at 7-week-old female ICR mice for acquire the number of available cumulus-oocyte-complexes (COCs). After 46 hours post injection, COCs were harvested from antrum follicles in the ovary and cultured in in-vitro maturation medium for 16 hours. After that, oocytes were retrieved.

Participants/materials, setting, methods
During in vitro maturation, BP was treated at COCs and Metaphase II (MII) oocytes were separated from retrieved oocytes. Intracellular tubulin of MII oocytes was stained for spindle alignment and their mitochondria were quantified by Mito-tracker and quantitative PCR (qPCR). Also, the expression levels of inflammation-related genes were confirmed by reverse transcription-qPCR.

Main results and the role of chance
In the present study, MII rates (MII/total oocyte) of each group were 77.50% of control, 79.17% of 1 μM BP, 68.10% of 10 μM BP, and 59.35% of 100 μM BP. Compared with the control group, the MII rate were significantly reduced at 100 μM of BP-treated group. We evaluated the morphology of meiotic spindle in MII oocytes with well-organized tubulin fibers and tightly aligned chromosomes. Abnormal morphology of spindle and chromosomal misalignment were found in the oocytes from BP-treated group. Because it has been known that having the optimal number of functional mitochondria is important for the maturation of oocytes, mitochondrial DNA (mtDNA) copy number and the distribution of mitochondria were confirmed in retrieved MII oocytes. There was a significant 4.2-fold increase in the number of mtDNA copies in 100 μM BP treatment group compared to the control group. Also, the number of activated mitochondria was raised when BP was treated, which was assessed using Mitotracker. Additionally, levels of inflammation-related genes (IL-1β, IL-6) were elevated in BP treatment groups.

Limitations, reasons for caution
Oocytes used in this study were collected from mice, not human. And since in vitro fertilization did not perform by using the MII oocytes, we couldn’t confirm whether BP-treated MII oocytes were capable of fertilization.

Wider implications of the findings
As industries evolve, novel chemicals, including EDCs, are being developed, used, and exposed to humans. Therefore, we need to understand the effects of these chemicals and assess their reproductive toxicity. Collectively, we suggest that BP causes an inflammatory response which activate mitochondria and has detrimental effects on the oocyte’s maturation.

Trial registration number
not applicable