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Nanomaterials in consumer and healthcare products can pass from the bloodstream to the brain side of a blood-brain barrier model with varying ease depending on their shape – creating potential neurological impacts that could be to be expected. both positive and negative, a new study reveals.
Scientists have found that metal-based nanomaterials such as silver and zinc oxide can cross an in vitro model of the “blood-brain barrier” (BBB) as particles and dissolved ions, which which negatively affects the health of astrocyte cells, which control neurological responses.
But the researchers also believe their discovery will help design safer nanomaterials and could open up new avenues for targeting hard-to-reach places when treating brain diseases.
Publish its findings today in PNAS, an international team of researchers has discovered that the physicochemical properties of metallic nanomaterials influence their efficiency in penetrating the in vitro model of the blood-brain barrier and their potential levels of toxicity in the brain.
A higher concentration of certain forms of silver nanomaterials and zinc oxide can interfere with cell growth and lead to increased permeability of BBB, which can lead to BBB allowing the brain easier access to these compounds.
BBB plays a vital role in brain health by restricting the passage of various chemicals and foreign molecules into the brain from surrounding blood vessels.
The integrity of the altered BBB compromises the health of the central nervous system and increased permeability to foreign substances can eventually cause brain damage (neurotoxicity).
Study co-author Iseult Lynch, professor of environmental nanosciences at the University of Birmingham, said: “We have discovered that nanomaterials of silver and zinc oxide, which are widely used in various products of daily consumption and health care, have gone through our in vitro BBB model, in the form of particles and dissolved ions.
“Variations in shape, size and chemical composition can dramatically influence the penetration of nanomaterials through the blood-brain barrier (in vitro). This is of paramount importance for the personalized medical application of nanomaterials – for example targeted delivery systems, bio-imaging and assessment of possible risks associated with each type of metallic nanomaterial. “
BBB is a physical barrier made up of a tight layer of endothelial cells surrounding the brain that separates the blood from the cerebrospinal fluid allowing the transfer of oxygen and essential nutrients but preventing the access of most molecules.
Recent studies have revealed that nanomaterials such as zinc oxide can accumulate on the brain side of BBB in vitro in altered states that can affect neurological activity and brain health. Nanomaterials inhaled, ingested and applied through the skin can enter the bloodstream and a small fraction of them can pass through the BBB, impacting the central nervous system.
Researchers synthesized a library of metallic nanomaterials with different compositions, sizes, and particle shapes – assessing their ability to enter BBB using an in vitro BBB model, followed by an assessment of their behavior and their future in and beyond the BBB model.
Understanding the behavior of these materials after crossing the blood-brain barrier is essential to assess the neurological effects resulting from their involuntary entry into the brain. The potential for neurotoxicity is greater in some materials than in others, due to the different ways in which their shapes allow them to move and be transported. “
Zhiling Guo, co-author, researcher, University of Birmingham
The research team tested different sizes of cerium oxide and iron oxide, as well as zinc oxide and four different shapes of silver – spherical (Ag NS), disc-shaped (Ag ND ), rod-shaped (Ag NR) and nanowires (Ag NW).
Zinc oxide slid through the BBB in vitro with the greatest ease. The researchers found that spherical and disc-shaped silver nanomaterials underwent different dissolution regimes – gradually turning into silver-sulfur compounds within the BBB, creating “easier” entry pathways.
Zinc oxide is used as a bulking agent and as a colorant. In over-the-counter pharmaceuticals, it’s used as a skin protector and sunscreen – reflecting and diffusing UV rays to help reduce or prevent sunburn and premature aging of the skin. The silver is used in cosmetics and skin care products such as anti-aging creams.
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