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Nanoparticles Impair Blood Vessel Function

Prior posts have noted the wide range of materials and consumer products in which nanoparticles are used, and also that nanoparticles can cross the so-called blood-brain barrier. New research, using animal models, suggests that such materials may impair blood vessel function.

Researchers exposed rats to airborne titanium dioxide nanoparticles (spheres 100 billionths of a meter across) for four hours on two consecutive days; this material appears in a range of products, including sunscreen and cosmetics. The pollutant doses, though not in a range considered toxic to the rats, were high enough to probe the possible effects of occupational exposures to such engineered materials and nano-pollutants associated with mountaintop mining. Twenty-four hours after the second day's exposure, the researchers stimulated the animals' muscles to contract. This triggers arteriole dilation, increasing blood flow. However, compared to changes witnessed in rats that had breathed only clean air, vessel dilation in those that had inhaled nanoparticles was impaired. This diminished vessel relaxation is similar to what elicits a muscle cramp, chest pain in the heart, or transient stroke in the brain, the researchers noted.

In another experiment, rats inhaled or ingested particles known as multi-walled carbon nanotubes. Made from rolled up sheets of carbon, these tubes are about 50 billionths of a meter across and are being explored for use in delivering drugs via the nose, mouth, or injections. As with the nanospheres, the nanotubes made it harder for arterioles to dilate. The nanotubes also exaggerated constriction when the body commanded arterioles to reduce blood flow. Effects peaked at about 24 hours after exposure to the particles, after which the arterioles' responsiveness began to improve. However, even a week later, the vessels hadn't fully returned to normal. Moreover, the findings showed that vessel impairments did not require lung exposures: In these experiments, ingested nanotubes produced the most dramatic change in arteriole reactivity.

Other researchers have recently reported preliminary evidence of toxic immune responses in animals and isolated cells to other nanoparticles being developed for releasing medicines. Taken together, researchers caution, these new data suggest that the method of delivery needs to be factored in to an evaluation of what is the best means to deliver medicines into the human body.

The studies are another indicator that nanomaterials need to be carefully considered. Like many advances in technology, there are tradeoffs in need of evaluation.

The studies have not been formally published, but were recently presented at the Society of Toxicology annual meeting in March 2012.

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