Interactions of Engineered Nanoparticles with Organs Protected by Internal Biological Barriers

Engineered nanomaterials may exert adverse effects on human health which, in turn, may be linked to their propensity to cross biological barriers in the body. Here, we will discuss available evidence based on in vivo studies for interactions of commercially relevant nanoparticles with critical internal barriers. The internal barriers at focus of this review are the blood-brain barrier (BBB), protecting the brain, the blood-testis barrier (BTB), protecting the male germ line, and the placenta, protecting the developing fetus. The route of exposure (pulmonary, gastrointestinal, intravenous, intraperitoneal, dermal), and the portal of entry of nanoparticles into the body, is of critical importance. Different physico-chemical properties, not only size, may determine the ability of nanoparticles to breach biological barriers; the situation is further compounded by the formation of a so-called corona of biomolecules on the surface of nanoparticles, the composition of which may vary depending on the route of exposure and the “history” of the nanoparticles as they translocate from one biological compartment to another. The relevance of nanoparticle interactions with internal biological barriers for their impact on the organs protected by these barriers is discussed.