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Experts Criticize Nanoparticle Study
6 November 2009 (All day)
The headlines are laced with fear. "Nanoparticles 'can damage DNA.'" "Nanoparticle Safety Looking More Complicated." "Nanoparticles Indirect Threat to DNA." All seem to suggest that a new study, released yesterday, has found that nanoscale materials, used in everything from medical imaging to cancer treatment, can damage genetic material in our bodies, feeding public fears. But this particular study has little relevance to human exposure risks, experts say, and it is deeply flawed in other ways. "I think it's a meaningless study, to be blunt" says Günter Oberdörster, a nanotoxicologist at the University of Rochester in New York state.
Oberdörster and others agree that some concerns over nanoparticles are valid. These particles, 1 to 100 nanometers in size, are made from a wide variety and combination of elements. Their small size gives them unique optical, electrical, and chemical properties, raising concerns that they might have unforeseen effects in the body. And a variety of studies with animal models has shown that nanoparticles can trigger damage in living tissues (Science, 18 June 2004, p. 1732).
But the new work was narrower. Charles Patrick Case, an orthopedic specialist at the University of Bristol in the United Kingdom, and a raft of colleagues reported yesterday online in Nature Nanotechnology that cobalt-chromium particles--a smaller version of the metal alloy that is widely used in replacement joints--can damage distant cells in a specially-designed cell culture.
Case's team 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. Further studies suggested that damage to cells in the barrier triggered a chemical cascade that affected the neighboring cells, Case says.
In the paper, Case and colleagues suggest that, based on the results, nanoparticles used in a clinical setting might need to be evaluated for such unforeseen effects. "The potential damage to tissues located behind cell barriers needs to be considered when using nanoparticles for targeting disease states," the team writes. The point was further emphasized in a press release put out by Nature Nanotechnology this week: "These findings suggest that direct and indirect effects of nanoparticles on cells are equally crucial when considering the potential risks of their use in nanomedicine."
That's the kind of language that scares and confuses the public, says toxicologist Andre Nel of the University of California, Los Angeles. Especially, he and others say, when there's no evidence that the findings translate to people.
What's more, there are other reasons why the study isn't applicable to human health, says Andrew Maynard, chief scientist for the Woodrow Wilson International Center for Scholars' Project on Emerging Nanotechnologies in Washington, D.C. For starters, Maynard and others point out that Case's team exposed cells to metal particles at a concentration thousands of times higher than could be expected to occur in the body. "They forget completely that it's the dose that makes a poison and a mechanism of action," Oberdörster says. Even though the group found that micron-sized metal particles and metal ions also damage DNA, they focused primarily on nanoparticles. "The effects don't seem to be nanoparticle specific," Maynard points out.
In a press conference called to discuss the paper's results yesterday, Case said his team didn't set out to draw conclusions about the effects the metals may have in the body. Rather, he said, the study was designed to ask the more fundamental question of whether a physical barrier of cells would indeed act as a barrier to prevent damage to cells on the other side.
Such careful interpretations are often lost in news coverage and efforts by journals to promote coverage of particular papers, however. Nature Nanotechnology not only highlighted the paper in a news release but also organized the press conference, drawing additional attention to the study. "The danger is they created the controversy by giving it this attention," Maynard says. Nel points out that this is a regular occurrence in the nanotechnology area because the field is hot and it plays into peoples' fears about new technology. "We need to be much more careful in interpreting these results," Oberdörster says.