Polish researcher investigates whether bisphenol A negatively affects egg cells and embryo development

The researcher received a grant from the National Science Centre for this purpose.

Dr. Anna Ajduk, a professor at the Department of Embryology of the University of Warsaw, reminds in an interview with PAP that bisphenol A is an organic compound that is widely used in the production of various plastics.

'Due to its transparency, lightness and resistance to damage, bisphenol A is used in many everyday objects, such as plastic containers for storing food, plastic toys for children, metal cans (as coating for their inner surface). It is also a ingredient of cosmetics and dental fillings', the researcher says.

Mass production of this compound has contributed to its spread in the environment. 'BPA can be released from the materials for which it was used under the influence of changes in pH and temperature, and migrate to food, air, skin, saliva or blood', describes Dr. Ajduk. This compound enters the human body primarily with food.

Since it belongs to the xenoestrogens, synthetic compounds with oestrogen-like activity, it may interfere with the functioning of animal and human organisms, including the reproductive system.

The effect of BPA on reproductive functions and fertility is primarily studied in animal models. Research shows that this compound may adversely modify the functioning of the gonads, reduce the quality of reproductive cells, and even hinder the proper development of the foetus. Conclusions from human studies are not that clear - some studies show a correlation between increased concentrations of BPA in the body and reduced fertility, others do not.

'For me as a biologist, it seems very likely that a compound similar to oestrogen, one of the main sex hormones, can affect, for example, the process of formation and functioning of reproductive cells. That is why I decided to take a closer look at it', says Dr. Ajduk.

She mentions that for years she has been interested in the way in which oocytes react to fertilization - oscillatory changes in the concentration of calcium ions occur in them and last several hours. These changes are crucial for the initiation of embryo development.

'In my research, I focused on the effect of BPA on the ability of egg cells to produce these calcium oscillations', the biologist explains.

Earlier, in collaboration with Magdalena Najechalska, the researcher had shown that BPA at a concentration similar to that detected in the fluid of the ovarian follicles (that naturally surrounds the egg cells in the ovary) causes significant changes in the oscillation pattern of calcium ions generated in the egg cells at the time of conception. This research was the subject of Magdalena Najechalska's master's thesis.

Dr. Ajduk explains that calcium oscillations are extremely important for the initiation of embryonic development. They trigger a number of processes in the fertilized egg cell that determine its correct transformation into an embryo: they allow the completion of meiotic division and the initiation of mitotic divisions of the embryo, they initiate the creation of a block against polyspermy (penetration of more than one sperm into the egg cell - PAP), they regulate the functioning of mitochondria during fertilization and gene expression in the embryo.

The researchers also obtained data pointing to the possible molecular mechanism of action of BPA.

'These results made me consider further research on BPA important from the point of view of infertility treatment and very interesting for a biologist', emphasises Dr. Ajduk.

In the research project financed with the National Science Centre grant, the scientists will use mouse ova. 'The mouse is a proven model in research on the developmental and reproductive biology of mammals. Human ova are a much less accessible material and many experiments cannot be performed on them due to the legal regulations in force in Poland', the biologist explains.

BPA will be administered either in vitro, as an additive to the culture medium in which the egg cells will be kept, or in vivo - orally to mice. Researchers will use concentrations of BPA similar to those detected in ovarian follicle fluid (in vitro experiments), and the average daily dose of the compound taken by a human per body weight (in vivo experiments). A broad spectrum of molecular and cellular biology methods will be used in the experiments.

'We know from preliminary studies that BPA does indeed alter the pattern of calcium oscillations generated in the egg cells at the time of fertilization. In this way, this compound may disrupt or even prevent the development of the embryo, and thus negatively affect fertility. We want to verify this. We will also examine through which receptors and enzymes BPA affects egg cells', says Dr. Ajduk.

In her view, better understanding of these mechanisms could prevent the negative effects of BPA on eggs and fertility in the future. (PAP)

PAP - Science in Poland, Joanna Morga

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