Toxic materials hitchhike into cells on nanoparticles.

Jan 07, 2009

Bastian, S, W Busch, D Kuhnel, A Springer, T Meibner, R Holke, S Scholz, M Iwe, W Pompe, M Gelinsky, A Potthoff, V Richter, H Ikonomidou and K Shirmer. 2008. Toxicity of tungsten carbide and cobalt-doped tungsten carbide nanoparticles in mammalian cells in vitro. Environmental Health Perspectives doi:10.1289/ehp.0800121.

Synopsis by Stacey L. Harper

Toxicants that cannot enter cells on their own can get in and hurt them when they are bound in nanoparticles, those very, very small materials now widely used in a range of consumer products.

Catching a ride on nanoparticles is a newly discovered way for harmful substances to get inside living cells. While health effects in people are not yet known, the cell injury reported in this new study raises concern for workers who make the nanoparticles and consumers who use them.

It also shows how important it is to test each type of nanoparticle and its altered variety for health effects.

Surprisingly, it was not the nanoparticle by itself -- tungsten carbide -- that caused an adverse effect on the cells tested but the cobalt metal intentially added to it to bolster the materials performance. This study revealed that when cobalt was combined with  tungsten carbide in a nanoparticulate form, cobalt entered into living mammal cells and disrupted normal cell functions.

Very, very small materials called nanoparticles are made and used in a variety of consumer goods and manufacturing processes. The materials contain several atoms built into various shapes -- balls, tubes, boxes -- and measure less than 100 nanometers in size. (A nanometer is one billionth of a meter.) Their small size gives them special properties not found in larger versions of the same metals and materials.

Tungsten carbide nanoparticles are being tested for use in hard metals.

Cobalt is often mixed with hard metals to improve the toughness and strength of materials. Occupational exposure to cobalt-containing dust has been associated with asthma and lung cancer.

Alone, the tungsten carbide nanoparticles were not toxic to human lung, skin or intestinal cells or rat brain cells.  When ionic cobalt was added to the solution of tungsten carbide nanoparticles, the solution was not toxic to the cells either.  However, when cobalt was incorporated into the tungsten carbide nanoparticle by a process called doping, the combined materials affected the cells.

The resulting cell death with the tungsten-cobalt nanoparticle was higher than would be expected based on the levels of cobalt used. Intestinal and skin cells were hardest hit.

The researchers propose that the cobalt becomes more readily available to cells by hitchhiking on the nanoparticles, which are known to cross into cells. Referred to as a “trojan horse,” the nanoparticle acts as a carrier for toxic ions into cells.