Brain damage: Caused by plasticisers?

The plasticisers contained in many everyday objects can impair important brain functions in humans; warn biologists in a recent article from "Communications Biology".

Bisphenols impair communication between nerve cells

The plasticisers contained in many everyday objects can impair important brain functions in humans. Biologists from the University of Bayreuth, Germany (Universität Bayreuth) warn of this danger in an article published in "Communications Biology".

As the study shows, the signal transmission between nerve cells in fish brains is already disturbed by small amounts of the plasticisers bisphenol A and bisphenol S. The researchers consider it very likely that similar damage can also occur in the brains of adult humans. They therefore call for an accelerated development of alternative plasticisers that do not pose a risk to the central nervous system.

Bisphenols are plasticisers that are found in a large number of plastic products worldwide - for example, in food packaging, plastic tableware, drinking bottles, toys, tooth fillings or baby dummies. In recent years, numerous health risks have already been uncovered, especially from bisphenol A (BPA). The Bayreuth research team led by Dr. Peter Machnik at the Chair of Animal Physiology (Prof. Dr. Stefan Schuster) has for the first time investigated the effects of plasticisers on signal transmission between nerve cells in the adult brain. The study covers not only BPA, but also bisphenol S (BPS), which is often considered less harmful to health.

Permanent damage to the nervous system

The harmful effects on the brain mainly affect the delicate balance of different nerve functions: Some brain cells transmit signals that trigger a state of excitation in downstream cells; other brain cells in turn have the function of inhibiting downstream cells. Only when both functions are coordinated is the central nervous system intact. "It is known that numerous disorders in the nervous system of vertebrates are triggered by the fact that excitation signals and inhibition signals are not or only inadequately coordinated. It is all the more alarming that the plasticisers BPA and BPS significantly impair precisely this coordination," explains Dr Peter Machnik, one of the study’s authors.

"It surprised us how many vital brain functions in fish are weakened by the plasticisers used across numerous industries. This damage, as we were able to show, does not occur immediately. But when the brain cells are exposed to small amounts of BPA or BPS for a month, the damage is unmistakable," says Elisabeth Schirmer, a Bayreuth University doctoral student and study co-author. It turns out that the plasticisers influence the action potential of brain cells. They change the chemical and electrical signal transmissions through the synapses. In addition, they disrupt the circuits that are important for the perception and processing of acoustic and visual stimuli.

Studies on Mauthner cells in goldfish

The discovery of the damage caused by plasticisers came from detailed investigations on living goldfish. The focus was on the two largest nerve cells in the fish's brain, the Mauthner cells. This is where all sensory stimuli converge, which must be processed quickly and in a precisely coordinated manner when predators approach. In this case, the Mauthner cells trigger life-saving escape reactions. Due to this function, which is essential for survival, they have developed a pronounced robustness in the course of evolution. Mauthner cells are able to ward off damaging influences to a certain extent or to compensate for them afterwards. It is therefore all the more significant that plasticisers are capable of causing considerable damage to these cells.

Transferability of the results to humans

"The findings obtained from studies on fish brains justify the assessment that BPA and BPS can also cause serious damage to the brains of adult humans. Against this background, it is urgent that science and industry develop new plasticisers that can replace these bisphenols and are harmless to health," says Dr Peter Machnik. Prof. Dr. Stefan Schuster adds: "The efficiency of the research techniques we used in our study can be of valuable aid in the development of alternative plasticisers. These techniques make it possible to quickly and inexpensively test how substances being considered for this purpose affect brain cells."

Elisabeth Schirmer, Stefan Schuster, Peter Machnik: Bisphenols exert detrimental effects on neuronal signalling in mature vertebrate brains. Communications Biology (2021)

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