Nanotech News

November 21, 2005

Characterizing How Carbon Nanotubes Can Damage Cells

Researchers have noted that cells can accumulate toxic levels of certain types of carbon nanotubes, particularly so-called multi-walled carbon nanotubes (MWCNTs), which are essentially a nanotube surrounded by another nanotube which is surrounded by another nanotube. The observation that high intracellular levels of certain types of carbon nanotubes has raised some cause regarding the safety of nanotubes for biomedical applications, prompting researchers to look for ways of minimizing any toxicity (see story) and to better understand why these nanostructures can be toxic.

To address this question of why nanotubes are toxic, a multi-institutional team, funded in part by the National Cancer Institute and led by Fanqing Chen, Ph.D., of Lawrence Berkeley National Laboratory and the University of California at San Francisco Comprehensive Cancer Center, followed how exposure to MWCNTs affected gene expression in human skin cells growing in a cell culture. The investigators used a commercially available whole-genome expression chip and robotic processing equipment to monitor gene expression in these two cell types. The researchers chose to study skin cells because skin is the tissue most likely to receive exposure to nanomaterials during their manufacture.

Discussing their work in the journal Nano Letters, the investigators found that treating human skin cells with MWCNTs resulted in profound changes in gene expression. Though gene expression patterns differed depending on the dose of MWCNTs a cell received, there was no apparent correlation between nanotube dose and the change in expression of specific genes. The researchers did note, though, that exposure to a particular level of MWCNTs affected distinct biochemical pathways. Similar types of changes are seen when cells are exposed to low and high levels of other toxins.

The investigators determined that exposure to low levels of MWCNTs affected the expression of genes involved in general cell growth and metabolism. At high doses, genes involved in inflammation and immune response were turned on in a manner characteristic of when a cell is fighting a viral infection. The researchers also noted that gene expression changes were greatly reduced when cells were treated with multi-walled carbon nanoparticles that resemble onions in their layered structured. The investigators concluded that the structure of a given nanomaterial plays a significant role in determining toxicity.

This work is detailed in a paper titled, "Molecular characterization of the cytotoxic mechanism of multiwall carbon nanotubes and nano-onions on human skin fibroblast." Investigators from the University of Kentucky and Affymetrix, Inc. also participated in this study. This paper was published online in advance of print publication. An abstract is available at the journal's website.
View abstract.