P-227 Exposure to triclosan modifies oocyte development and embryo metabolism
Authors: Papachristofi V , Rotchell J.M , Sturmey R.G 
Published: June 2022

Abstract

Study question
Does the endocrine disruptor, triclosan, affect the function of cumulus-oocyte-complexes (COCs), and if so, do these effects persist in early embryo developmental competence and metabolism?

Summary answer
Triclosan caused COCs to i) increase progesterone secretion, ii) switch from releasing to consuming pyruvate, and iii) produce fewer blastocysts that were iv) metabolically compromised.

What is known already
Triclosan (TCS) is used widely as an antimicrobial agent in a range of consumer healthcare products, including hand sanitiser, toothpastes, soaps, and shampoos. Its prevalent use has led to accumulation in the environment and human exposure. Indeed, TCS has been identified in a range of bodily fluids. It is classed as an endocrine-disrupting chemical and there are reports of its detrimental impact on the vertebrate reproductive system. However, the direct effects of TCS on mammalian Cumulus-Oocyte-Complexes’ (COCs) function and subsequent development of the embryo remains unknown.

Study design, size, duration
COCs, isolated from abattoir-derived bovine ovaries on 5 independent occasions, were exposed of two environmentally-relevant doses of TCS (10nM and 1nM) during in vitro maturation. The TCS-exposed COCs were subsequently fertilised in vitro without further TCS addition, and the cleavage and blastocyst rate were recorded on Day 2 and Day 7/Day 8, respectively. The resulting blastocysts were collected and further cultured individually for 24 hours, and depletion/release of key-metabolites quantified.

Participants/materials, setting, methods
In vitro production was performed for the maturation of the bovine oocytes and the embryo culture. The production of steroid hormones (17b-estradiol and progesterone) during IVM was determined by ELISA. The concentrations of glucose, pyruvate, lactate during IVM and blastocyst formation were quantified in the spent media using microfluorometric assays.

Main results and the role of chance
TCS at 1nM had a significant impact on steroidogenesis during COCs in vitro maturation; progesterone production was significantly higher compared to control group (4.784 ±1.69 vs 2.85 ±0.83 pg/hour/COCs, p = 0.035; n = 5), although oestrogen release was not affected. In addition, there was a dramatic shift in pyruvate metabolism. Over the course of in vitro maturation, COCs exposed to TCS depleted pyruvate from the culture media regardless of the administrated dose whilst net pyruvate concentration increased in the medium of COCs in the control groups.
The cleavage rate of bovine embryos produced from TCS-exposed COCs was not significantly different to control group. However, COCs-exposed to 1nM TCS produced significantly fewer blastocysts (12.22% vs 29.11% n = 5; p = 0.02). Those blastocysts that did originate from COCs treated with TCS depleted significantly more pyruvate from the culture media compared to controls, regardless of TCS dose (19.86 ±10.54 vs 10.12 ±12.5 pmol/hour/embryo, p = 0.011 and 21.41 ±10.08 vs 10.12 ±12.5 pmol/hour/embryo, p = 0.002, TCS-10nM and TCS-1nM compared to Control, respectively). Additionally, while glucose depletion did not differ, the lactate release from blastocysts derived from COCs exposed to 10nM TCS was approximately halved compared to controls (15.20 ±14.59 vs 31.83 ±22.73 pmol/hour/embryo p = 0.0054).

Limitations, reasons for caution
The origin of the ovaries may be a limitation since they came from animals at different stages of estrous cycle. Furthermore, pre-exposure to TCS prior to animal slaughter cannot be discounted. Finally, these observations were made in an animal model in a laboratory setting which may differ from natural exposure.

Wider implications of the findings
TCS modifies oocyte maturation, developmental competence, and metabolic activity of resulting embryos. The differences in pyruvate metabolism and steroidogenesis point to altered mitochondrial function. These data indicate that TCS directly modulates oocyte and embryo physiology which may relate to fertility in domestic livestock species and may be extrapolated to humans.

Trial registration number
not applicable