"Nanoparticles can cause DNA damage across a cellular barrier."That's the title of a paper published in Nature Nanotechnology that inspired a number of ominous news headlines (two examples: Nanoparticles 'can damage DNA' and Nanoparticles can damage DNA at a distance: study). The stories that followed basically sang the same tune—that nanoparticles can damage our cells' genetic material even from a distance (a relatively short distance of four cells away). However, experts are speaking up in response to the media hype, and argue that this study should have never been covered in the news. This particular study has little relevance to human exposure risks, experts say, and it is deeply flawed in other ways
. At least one expert called the study "meaningless," however other scientists were more diplomatic and have pointed to a number of interesting questions the study raises that are worth pursuing.
In the study, researchers exposed a thin "barrier" of four layers of cancer cells to cobalt-chromium ions or particles. Cells close to the nanoparticles experienced signs of mitochondrial damage. But even cells on the other side of the barrier suffered some DNA damage, the team found, despite the fact that there was no evidence that the metals themselves moved through the cells to the other side of the barrier
. Interesting indeed, but experts are pointing out that this set-up is not entirely relevant to humans, or any living organism for that matter. The nanoparticles used in the study, cobalt-chromium particles, are not used in any medical treatments, but are used in larger pieces to make replacement hips.
Hundreds of thousands of people receive cobalt-chromium implants every year, and there has been no evidence of ill effects reported [New Scientist]
. Experts also point out that the experiment exposed cells to the nanoparticles at concentrations that were thousands of times higher than what would ever be seen in the body; remember the maxim that "the dose makes the poison." Finally, the cells used to construct the barrier are human cancer cells (BeWo cells for the jargon-minded) that have been adapted to life in the petri dish, so they aren't exactly like cells in the body. Artificial set up or not, if the nanoparticles didn't cross the barrier, then how was DNA damaged on the other side? The researchers suggested that the nanoparticles created a cascading chemical change.
This is the part that is likely to whet the appetites of other scientists in the field. It looks like the nanoparticles set off a series of signals within the cells of the barrier, that ultimately led to the release of DNA-damaging [molecules] through two specific channels at the edge of the barrier [The Great Beyond]. When the researchers then blocked these channels in a subsequent experiment
—poof!—the damage didn't happen.
The researchers who conducted the experiments have responded to the criticism by saying that they only intended to study how the nanoparticles would interact with the physical barrier; they say they didn't set out to conduct a realistic assessment of potential dangers posed by the particles. Hopefully, other research groups will set out to do just that. Scientists already suspect that nanoparticles can cause damage in some circumstances, and the need for more research is obvious.
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Image: Wikimedia Commons / Nandiyanto
