Maternal exposure to short-chain PFAS causes persistent memory problems in adult rats

Exposure to supposedly safer alternatives to traditional forever chemicals during pregnancy and nursing causes lasting memory and learning problems in adult rats. The animal research suggests that early contact with these synthetic compounds interferes with normal brain development. The study was published in Frontiers in Toxicology.

Per- and polyfluoroalkyl substances, universally known as PFAS, are highly stable synthetic chemicals characterized by extremely strong carbon-fluorine bonds. Manufacturers have used them since the 1940s to make products resist heat, oil, and water. These functional properties make them highly useful in nonstick cookware, food packaging, and waterproof clothing.

Because they break down very slowly, they accumulate in the environment and inside the human body. Older versions of these chemicals are typically composed of molecular chains featuring eight or more carbon atoms. Epidemiological studies have repeatedly linked prenatal exposure to these long-chain PFAS with adverse developmental outcomes, altering cognition and behavior in children.

In response to health and environmental concerns, manufacturers largely phased out these long-chain variants. They replaced them with short-chain varieties, which contain fewer carbon atoms and are purportedly eliminated from the human body more quickly. Two common chemical replacements in this category are GenX and perfluorobutanoic acid, widely known as PFBA.

Despite the widespread adoption of short-chain PFAS, experimental data regarding their safety during fetal and early life stages remains highly limited. Researchers from the University of Bologna and the Istituto Zooprofilattico Sperimentale delle Venezie designed an animal experiment to test whether early exposure to GenX and PFBA affects the mammalian brain. Lead researchers Luca Lorenzini and Marzia Moretti sought to understand how exposure during pregnancy and nursing might alter brain architecture and cognitive function well into adulthood.

Free daily newsletter

The researchers fed female rats a diet contaminated with either GenX or PFBA for thirty days before mating. The synthetic chemicals remained in the animals’ food supply throughout pregnancy and until their newborn pups were weaned. The doses were designed to fall beneath the threshold where acute physical toxicity is normally observed, mirroring the low but persistent exposure levels sometimes found in human water supplies.

After weaning, the offspring ate a standard diet free of any contamination. This design mirrors the way mammals experience placental and maternal milk transfer of chemicals. The scientists waited until the offspring reached adulthood, roughly twelve weeks after weaning, to evaluate their neurocognitive performance.

The researchers evaluated several behavioral domains before testing learning and memory. They placed the animals in a new, enclosed space to observe their natural movement patterns. Unexposed rats explored at a predictable pace, but rats exposed to the lowest doses of PFBA displayed unusually high levels of activity, traveling much longer distances.

The highest dose groups did not show this hyperactivity. This phenomenon, where low and high doses cause vastly different biological reactions, is a frequently observed feature of hormone-disrupting chemicals. The team also evaluated the animals’ motor coordination by having them walk on a rotating rod. None of the exposed groups experienced issues with basic physical balance.

To test learning and memory, the researchers placed the rats in a large pool of opaque water. The animals had to learn specific visual cues in the room to navigate toward a hidden submerged platform. This test evaluates spatial learning and relies heavily on a brain region called the hippocampus.

Rats exposed to high doses of GenX and PFBA during their early development struggled considerably with the task. They took longer to learn the location of the hidden platform than unexposed rats. When the researchers moved the platform to test cognitive flexibility, the exposed rats had great difficulty adapting to the new location.

These memory issues occurred despite an absence of the chemicals in the adult rat brains at the time of testing. Chemical analysis showed that GenX had completely exited the animals’ systems. While trace amounts of PFBA remained in some organs like the liver, the brain was largely clear of the chemical, ruling out the possibility of acute biological toxicity causing the memory failure.

Instead, the research team investigated how early exposure might have disrupted the physical construction of the developing brain. To do so, they cultured brain cells taken from fetal rats whose mothers were exposed to PFBA. The researchers observed these neurons under microscopes as they matured over three weeks in laboratory dishes.

When the researchers looked closely at the cultures after a week of maturation, the neurons from exposed animals appeared strangely overgrown, sprouting uncoordinated branches. By the third week, this early chaotic growth resulted in poorly developed structures. Normally, neurons generate long, specialized extensions to communicate, eventually forming connection points called synapses. The cells exposed to PFBA produced fewer connection points and expressed lower levels of proteins that are essential for stable synapse formation.

The team also examined the actual brains of the adult rats that underwent the behavioral testing. They specifically looked at the dentate gyrus, a section of the hippocampus responsible for generating new brain cells. In healthy adult animals, this region constantly produces and matures new neurons that help with memory formation and learning.

Adult rats exposed to high levels of PFBA and GenX showed clear abnormalities in this central brain area. The investigators noted an elevated presence of biological markers associated with unspecialized stem cells. At the same time, the affected rats exhibited a sharp decline in markers for maturing neurons.

This pattern points to a stall in the developmental process, where new cells fail to transition into fully functioning neurons. The researchers also analyzed the genetic activity within the hippocampus. They found distinct abnormalities in how the cells operated, particularly an increase in genes responsible for driving cellular inflammation.

Inflammation in the brain can disrupt normal cell-to-cell communication and hinder the survival of new neurons. The male rats exposed to GenX showed large elevations in multiple chemokines, which are immune signaling proteins. Female rats exposed to the chemicals also displayed similar, yet distinct, abnormal inflammatory signatures in their brain tissue.

The team also checked the animals’ circulating hormone levels, as hormones heavily influence brain development. The male rats exposed to high doses of either GenX or PFBA produced substantially lower levels of testosterone compared to unexposed animals. Female rats exposed to GenX experienced a similar drop in progesterone.

These altered hormonal states persisted for months after the exposure ended. Hormones like testosterone play a major role in keeping newly formed neurons alive in the hippocampus. The lack of these hormones might have amplified the cognitive problems observed in the affected rats.

While the findings clearly demonstrate the neurotoxic potential of short-chain PFAS in a rodent model, the researchers note certain limitations with their work. The team did not test hormone or chemical levels immediately after the rats finished nursing. Missing this data makes it difficult to separate the direct chemical toxicity on the infant brain from the indirect effects of maternal distress.

The study investigated only two short-chain PFAS variants out of thousands of similar synthetic compounds. The results achieved using GenX and PFBA might not apply to other members of the chemical family. Future experiments will need to examine varied short-chain compounds to determine if these developmental issues are a universal feature of the entire class.

Scaling these animal results directly to human beings also requires patience. Humans eliminate these compounds from their bodies at different rates than rodents. Evaluating how low-dose, chronic exposure affects human brain functioning will require targeted tracking of exposed populations over multiple decades.

The study, “Short-chain PFAS exposure during gestation and breastfeeding alters learning and memory in adulthood: possible mechanisms related to brain development,” was authored by Luca Lorenzini, Marzia Moretti, Claudia Zanardello, Federica Gallocchio, Vito A. Baldassarro, Alessandra Moressa, Lorenzo Zanella, Michele Sannia, Greta Foiani, Corinne Quadalti, Maura Cescatti, Valentina Burato, Margherita Soncin, Marzia Mancin, Luciana Giardino, Franco Mutinelli, Marta Vascellari, and Laura Calzà.\