The increasing exploitation of nanomaterials including graphene-based materials necessitates a comprehensive evaluation of the potential effects of these materials on human health. However, although the interactions of nanomaterials with the immune system have been addressed, their impact on the microbiome of the host remains to be understood.
Graphene is an extremely thin material, a million times thinner than a human hair. It comprises a single layer of carbon atoms and is stronger than steel yet flexible, transparent, and electrically conductive. This makes it extremely useful in a multitude of applications, including in “smart” textiles equipped with wearable electronics and as a component of composite materials, to enhance the strength and conductivity of existing materials.
With the increased use of graphene-based nanomaterials comes a need to examine how these new materials affect the body. Nanomaterials are already known to impact on the immune system, and a few studies in recent years have shown that they can also affect the gut microbiome, the bacteria that naturally occur in the gastrointestinal tract.
The relationship between nanomaterial, gut microbiome and immunity has been the subject of the present study performed using zebrafish. The nanomaterial investigated was graphene oxide, which can be described as a relative of graphene that consists of carbon atoms along with atoms of oxygen. Unlike graphene, graphene oxide is soluble in water and of interest to medical research as, for example, a means of delivering drugs in the body.
In the study, the researchers exposed adult zebrafish to graphene oxide via the water and analyzed how it affects the composition of the microbiome. They used both normal fish and fish lacking a receptor molecule in their intestinal cells called the aryl hydrocarbon receptor, commonly abbreviated as AhR, a receptor for various endogenous and bacterial metabolites.
The researchers have also generated zebrafish larvae that completely lack a natural gut microbiome, which makes it possible to study the effects of individual microbiome components, in this case butyric acid (a fatty acid), which is secreted by certain types of gut bacteria. Butyric acid is known to be able to bind to AhR.
Doing this, the researchers found that the combination of graphene oxide and butyric acid gave rise to so-called type 2 immunity in the fish. The effect turned out to be dependent on the expression of AhR in the intestinal cells.
This type of immunity is normally seen as a response to parasitic infection. The interpretation is that the gut immune response can handle graphene oxide in a similar way to how it would handle a parasite.
Guotao Peng, Hanna M. Sinkko, Harri Alenius, Neus Lozano, Kostas Kostarelos, Lars Bräutigam, Bengt Fadeel. Graphene oxide elicits microbiome-dependent type 2 immune responses via the aryl hydrocarbon receptor. Nature Nanotechnology. Retrieved from : https://www.nature.com/articles/s41565-022-01260-8
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