Probiotics vs. plastics: Review highlights protective effects against polystyrene toxicity

12 Jul 2023 --- Researchers have found that probiotics may overcome some toxicities associated with polystyrene nano- and microplastics in humans in a recent review. These particles increasingly make their way through the food chain and are absorbed through the gut. However, the authors caution probiotics’ health benefits need to be validated in clinical studies. 

The authors note that nanoplastics (smaller than 0.1 µm) and microplastics (smaller than 5 mm) made of polystyrene can be toxic to humans when ingested.

Such particles often enter the gastrointestinal (GI) tract, which can have adverse effects such as disturbances in the intestinal flora, mutagenicity, cytotoxicity, reproductive toxicity, neurotoxicity and aggravated oxidative stress. 

Although the researchers found various reports on probiotics’ protective effects on organs such as the GI tract, limited information is available on how these organisms may protect against polystyrene toxicity in humans or animals. 

According to the authors, nano- and microplastics have been shown to induce microbial dysbiosis in the gut, nose and lungs. This is characterized by a decrease in microbial diversity and an increase in inflammatory species. 

Protective effects of probiotics
The study, published in Frontiers in Nutrition, states that “probiotic bacteria could be considered for both prevention and treatment.” 

Adverse effects associated with ingested plastic particles include disturbances in the intestinal flora, neurotoxicity and aggravated oxidative stress.The review includes several studies that find probiotics can adsorb heavy metals and bind to molecules and toxins like benzo[a]pyrene, mycotoxins and phthalates. At the same time, some were able to degrade a common plastic ingredient, bisphenol A (BPA). 

For example, in a study on rats, probiotics reduced apoptosis (cell death) and oxidative damage caused by BPA and phthalates in the pancreas.

Although the exact mechanism of how probiotics can protect the hematological system – bone marrow and the cells it produces – from plastic particles’ toxic effects is unclear, the authors suggest probiotics can produce specific small molecule metabolites or drive signals that help an organism boost its immune response or suppress inflammatory responses. 

They refer to studies that reported probiotic strains can modulate the gut microbiome and normalize immune response to prevent and manage intestinal dysfunction. 

The authors also note that probiotic microorganisms may interact with polystyrene particles to modify their toxic effects on different tissues. For example, probiotics can block mercury absorption in the gut while increasing iron absorption and other minerals. 

Toxicity of polystyrene particles 
How polystyrene particles affect cells depends on their size and concentration, exposure duration, and the type of organism or cells exposed to the particles. Most studies reviewed in the article investigated toxic effects on fish or mice, with a few looking at human cells. 

Among others, studies found these particles have possible genotoxic, immunotoxic, neurotoxic, hematotoxicity and reproductive toxicity effects. They can also lead to oxidative damage and increase inflammation. 

For example, in the nervous system of mice, particles may alter the level of neurotransmitters, which in turn could affect stress responses and behavior. A different study found that DNA molecules of grass carp exposed to polystyrene nanoplastics were damaged by direct interaction between particles and the DNA or increased production of free radicals. 

Several studies looked at the cytotoxicity of polystyrene particles – causing cell damage or death – but results varied from finding no effects to particles physically rupturing cell membranes. 

The review includes studies that find probiotics can adsorb heavy metals and bind to molecules and toxins.The study’s authors note that the global use of plastics is increasing annually. Earlier research reported that plastics were detected in most categories of consumed foods, drinking water and human feces. Plastic particles can also potentially transfer from soil into food webs according to researchers. 

Moreover, airborne micro- and nanoplastics have been found to cause human health hazards along the respiratory tract, from irritation to the onset of cancer with chronic exposure. 

Beyond the gut
Research on probiotics’ health benefits and product innovations is expanding beyond gut health, moving into probiotics for mental health, immunity, eye and skin health. 

At the same time, nutrition brands highlight a sustained demand for products that target the gut-brain axis – the bidirectional communication system between the human digestive system and the brain – as research builds a better understanding of the links between the intestinal microflora and other health areas.

According to the review’s authors, clinical trials highlight that probiotics can restore gut and microbial diversity, thus reducing side effects caused by diseases or medical treatment. 

Other studies found that certain probiotics could improve liver function, protect kidney function, improve cognitive function and motor responses in patients with Parkinson’s disease and improve fertility in patients with polycystic ovary syndrome by reducing inflammation. 

A probiotic from Swedish company BioGaia has recently been found to increase the human body’s immunity response to COVID-19.

By Jolanda van Hal