Some per- and polyfluoroalkyl substances (PFAS) are poorly degradable and are also often called “perpetually chemicals.” They adversely affect health and might result in liver damage, obesity, hormonal disorders, and cancer. A research team from the Helmholtz Centre for Environmental Research (UFZ) has investigated the consequences of PFAS on the brain. Using a mixture of recent molecular biology methods and the zebrafish model, the researchers revealed the mechanism of motion and identified the genes involved. These genes are also present in humans. The test procedure developed on the UFZ might be used for the danger assessment of other neurotoxic chemicals. The study was recently published in Environmental Health Perspectives.
Due to their special properties — heat resistance, water and grease repellence, and high durability — PFAS are utilized in many on a regular basis products (e.g. cosmetics, outdoor clothing, and coated cookware). However it is precisely these properties that make them so problematic. “Because some PFAS are chemically stable, they accumulate within the environment and enter our bodies via air, drinking water, and food,” says UFZ toxicologist Prof Dr Tamara Tal. Even with careful consumption, it is almost not possible to avoid this group of drugs, which has been produced for the reason that Fifties and now includes hundreds of various compounds. “There may be an incredible need for research, especially relating to developing fast, reliable, and cost-effective test systems for assessing the risks of PFAS exposure,” says Tal. To date, the environmental and health consequences have been difficult to evaluate.
Of their current study, the researchers investigated how PFAS exposure affects brain development. To do that, they used the zebrafish model, which is ceaselessly utilized in toxicology research. One advantage of this model is that around 70% of the genes present in zebrafish (Danio rerio) are also present in humans. The findings from the zebrafish model can subsequently likely be transferred to humans. Of their experiments, the researchers exposed zebrafish to 2 substances from the PFAS group (PFOS and PFHxS), which have an identical structure. The researchers then used molecular biological and bioinformatic methods to research which genes within the brains of the fish larvae exposed to PFAS were disrupted in comparison with the control fish, which weren’t exposed. “Within the zebrafish exposed to PFAS, the peroxisome proliferator-activated receptor (ppar) gene group, which can also be present in a rather modified form in humans, was particularly lively,” says Sebastian Gutsfeld, PhD student on the UFZ and first writer of the study. “Toxicity studies have shown this to be the case in consequence of exposure to PFAS — albeit within the liver. We have now now also been in a position to exhibit this for the brain.”
But what consequences does an altered activity of the ppar genes triggered by PFAS exposure have for brain development and behavior of zebrafish larvae? The researchers investigated this in further studies using the zebrafish model. They used the CRISPR/Cas9 method, also often called gene scissors. “Using genetic scissors, we were in a position to selectively cut individual or several ppar genes and forestall them from functioning normally,” explains Gutsfeld. “We wanted to search out out which ppar genes are directly linked to a change in larval behaviour triggered by PFAS exposure.” Proof of the underlying mechanism was directly provided. In contrast to genetically unaltered zebrafish, the knockdown fish wherein the gene scissors were used shouldn’t show any behavioural changes after exposure to PFAS.
The 2 behavioural endpoints
In a single series of experiments, the researchers constantly exposed zebrafish to PFOS or PFHxS during their early developmental phase between day one and day 4 and in one other series of experiments only on day five. On the fifth day, the researchers then observed swimming behaviour. They used two different behavioural endpoints for this purpose. In a single endpoint, swimming activity was measured during a protracted dark phase. PFAS-exposed fish swam greater than fish not exposed to PFAS, whether constantly exposed to PFAS during brain development or shortly before the behaviour test. Interestingly, hyperactivity was only present when the chemical was around. When the researchers removed PFOS or PFHxS, hyperactivity subsided. Within the second endpoint, the startle response after a dark stimulus was measured. “In zebrafish exposed to PFOS for 4 days, we observed hyperactive swimming behaviour in response to the stimulus,” says Gutsfeld. In contrast, zebrafish only exposed to PFOS or PFHxS on the fifth day didn’t have a hyperactive startle response.
Based on these responses, the researchers conclude that PFOS exposure is related to abnormal consequences — particularly during sensitive developmental phases of the brain. Using knockdown zebrafish, the researchers identified two genes from the ppar group that mediate the behaviour triggered by PFOS.
“Because these genes are also present in humans, it is feasible that PFAS even have corresponding effects in humans,” concludes Tal. The scientists working with Tal want to research the neuroactive effects of other PFAS in future research projects and expand the tactic in order that it may possibly ultimately be used to evaluate the danger of chemicals within the environment, including PFAS.
