Nanoplastic particles damage neurons and may lead to anxiety-like behavior in offspring

  • 2022-08-18

Plastic is widely used in daily life, but it also brings serious environmental pollution and damages the health of animals and humans. Recently, a research team from the College of Animal Science and Technology and College of Veterinary Medicine of Huazhong Agricultural University published a research report in the journal Environment International (hereinafter referred to as the "Report"), "Simultaneous exposure of polystyrene microns and nanoparticles can cause damage to fetal thalamus by ROS mediated apoptosis." By exposing pregnant mice to plastic particles with different particle sizes and surface modifications, the report found that these plastic particles caused oxidative damage to fetal thalamic cells, leading to anxiety-like behavior in the offspring.

 

Previous studies have shown that annual global production of plastic has soared from 1.5 million tonnes in 1950 to 368 million tonnes in 2019. However, most plastic waste is difficult to recycle, causing serious pollution to farmland, waterways, oceans and other natural environments.

 

In addition, macromolecular plastics break down into microplastics (plastic particles with an average size of 1 nanometer to 5 microns) and nanoplastics (plastic particles with an average size of less than 1 nanometer) through mechanical wear, ultraviolet radiation, and biodegradation. Studies have found that microplastic and nanoplastic particles exist in a large number of natural environments such as atmosphere, water and soil. They can easily enter animals and humans through air, food, drinking water and so on, posing potential threats to animal and human health.


At present, the toxic effects of plastic-degrading particles on adult animals have been extensively reported in the literature, but their potential toxicity on fetal neural development remains unclear. In this context, the report deeply explored the effects of plastic particles on fetal neural development by exposing pregnant mice to plastic particles with different particle sizes and surface modifications, and using fluorescent labeling, genome sequencing, behavioral testing and other methods. The main findings are as follows:

 

1. The presence of microplastics promotes the entry of nanoplastics into the placenta and fetal thalamus


The report found that microplastics and nanoplastics ingested by pregnant rats were distributed in the stomach, large intestine, small intestine, uterus and placenta, while in the fetus, nanoplastics were detected in the chest, abdomen and brain.

 

In addition, when the mothers were exposed to a mixture of microplastics and nanoplastics, their fetuses accumulated more nanoparticles in their brains than when they were exposed to the nanoplastics alone.


Therefore, the report speculates that the presence of microplastics could help nanoplastics break down the maternal placental barrier and facilitate the entry of nanoplastics into the fetal brain.

 

2. Nanoplastics alter gene expression in fetal thalamus, causing oxidative damage and neuronal apoptosis


Thalamic tissue for the fetus by the transcriptome sequencing analysis, the report found that the main enrichment of differentially expressed genes induced by plastic particles against oxidative phosphorylation and gamma aminobutyric acid (GABA) synaptic related pathways, and the apoptosis induced by oxidative stress, and increase the intercellular space, can hinder the GABA neurotransmitter affect normal fetal thalamus gene expression.

  

The report found that exposure of maternal mice to plastic particles decreased the amount of glutamate decarboxylase 2 (a key enzyme in GABA synthesis) in the fetal thalamus, as did the level of total antioxidant capacity. Moreover, exposure to both microplastics and nanoplastics resulted in a further decrease in total antioxidant capacity levels compared with exposure to nanoparticles alone.

 

"These results suggest that nanoplastics inhibit fetal brain development, and that microplastics could promote more nanoparticles into the fetal brain, further enhancing the neurotoxicity of nanoplastics," the report said.

 

3. Nanoplastic induces more reactive oxygen species, leading to anxiety-like behavior in offspring, which can be alleviated by neutralizing reactive oxygen species


Fetal brains are rich in lipids but low in antioxidants, which may make them vulnerable to oxidative stress. Using high-throughput sequencing, the report found that the accumulation of nanoplastics in the body altered pathways associated with oxidative phosphorylation, inducing the production of more reactive oxygen species. However, excessive reactive oxygen species are harmful to neural tissue, which can inhibit the synthesis of GABA in the thalamus, reduce the release of GABA to the prefrontal cortex and amygdala (an important neural region for controlling emotion), and affect the body's regulation function of anxiety, thus causing anxiety-like behavior in offspring. Therefore, the report speculates that excessive production of reactive oxygen species induced by nanoplastics may be responsible for anxiety-like behavior in offspring.

  

Anxiety-like behaviour is a trigger for autism, depression, schizophrenia, Alzheimer's disease and Parkinson's disease, so the report suggests that exposure to nanoplastics increases the risk of neurological disorders in animals.

 

Since excessive reactive oxygen species are the cause of anxiety-like behavior, the report went on to explore whether adding antioxidants exogenously to mothers during pregnancy would attenuate plastic-particle-induced oxidative stress and anxiety-like behavior in offspring. The results showed that with antioxidant supplementation, the total antioxidant level in the thalamus of the fetus was increased, the rate of neuronal apoptosis was decreased, the levels of GABA transmitter in the prefrontal cortex and amygdala were increased, and anxiety-like behavior was reversed.

 

To sum up, the report found, polystyrene nanoparticles will be induced by oxidative damage, apoptosis inhibiting GABA synthesis, cause methods such as negative influence on fetal brain development, leading to the adult offspring appeared anxious behavior, increase the risk of neurological disorders, anxiety and adding antioxidants can reverse the sample. Therefore, the report states that the application of antioxidants would be a potential way to prevent human health from being threatened by plastic particles.

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