Prior posts have noted the adverse health impact of nanoparticles, and that they can cross the so-called blood-brain barrier. Now, animal tests suggest that they affect the function of arterioles, the vessels that connect arteries to capillaries (see Wikipedia- Arteriole).
Researchers exposed rats to airborne titanium dioxide spheres about 100 billionth of a meter across for hour hours on two consecutive days. As noted in prior posts, particles of this size are found in common materials, including sunscreens and cosmetics. The dose was not toxic, but sufficiently high to provide an understanding of the possible impacts of occupational exposures to such engineered materials and nanopollutants associated with mountaintop mining.
24 hours after the second exposure, the muscles of the rats were stimulated to contract, which in turn triggered arteriole dilation, increasing blood flow. Compared to rats breathing "clean" air, the vessel dilation was lessened. The diminished vessel relaxation is similar to that which elicits a muscle cramp, chest pain in the heart, or a transient stroke in the brain, noted the authors.
In another experiment the rates inhaled or ingested multiwalled carbon nanotubes (about 50 billionths of a meter across); such tubes are being examined for use in delivering drugs via the nose, mouth, or injection (as noted in prior posts). As with the nanospheres, the nanotubes made it more difficult for the arterioles to dilate. The nanotubes also exaggerated constriction when the body signaled the arterioles to reduce blood flow. The effects peaked about 24 hours after exposure to the particles; thereafter, responsiveness began to improve. However, even a week later, the vessels had not fully returned to normal.
The tests demonstrated that impairment did not require lung exposure; in these experiments, ingestion of nanotubes produced the most dramatic change in arteriole activity.
The researchers noted that these results mean that drug researchers need to consider how to nano-deliver a drug.
Information on these experiements and related investigations can be found at http://onlinelibrary.wiley.com/doi/10.1111/j.1549-8719.2011.00137.x/abstract;jsessionid=703A9FAC0F1D5EC7DFE07A1468E343E2.d02t02?userIsAuthenticated=false&deniedAccessCustomisedMessage. Also information can be found, once it is published, from the proceedings of the Society of Toxicology annual meeting, March 13, 2012, San Francisco, Abstracts 924, 925, 929, 930, 818, 819, 820, & 821.