Nanoparticles disrupt the digestive system
By By Katherine Bourzac | 27 Feb 2012
Nanomaterials are commonly used as preservatives and whiteners in processed foods, but little is known about the potential long-term effects of these materials on the digestive system. Now a study of model nanoparticles in chicken and in a cell model of the human intestine suggests that ingesting these materials can interfere with iron absorption in the short term, and in the long term, leads to changes in the tissues lining the intestine.
Engineered nanoparticles are already in the food system, and may have unintended consequences, says Gretchen Mahler, an assistant professor of bioengineering at Binghamton University in New York.
Many studies of the potential health effects of nanoparticles have focused on acute exposures and serious injury or death. Subtler effects that may emerge over the long term are not well understood. Mahler worked with Michael Shuler, chair of the department of biomedical engineering at Cornell University, to test a model system for uncovering the effects of nanoparticles on the intestine.
The researchers focused on how the nanoparticles affect iron uptake. They exposed cell models and live chicken to polystyrene spheres 50 and 200 nanometres in diameter and with positive, negative, or neutral surface charges. Polystyrene is not found in food but it's easy to label the nanoparticles with fluorescent markers for imaging.
That made polystyrene nanoparticles an easy to use first test case for the Cornell model. Mahler says they used chicken because it's easier to perform surgery on them than, for example, small mice, and because previous studies have established that iron absorption in these fowl is a good model for human intake of the essential nutrient.
Chicken that were fed large doses of the nanoparticles over a short period of time absorbed less iron than birds that hadn't been exposed, and less than birds that were chronically exposed to the polystyrene particles. The in vitro models bore this out. High doses of the nanoparticles inhibited the cells' ability to transport iron.
Mahler says it's not clear what the mechanism is - there was no evidence of inflammation or other changes. ''We think the nanoparticles cause a mechanical disruption of iron-transport proteins,'' she says.
Over the long-term, the effects were almost the opposite. Chronic exposure to low doses of polystyrene nanoparticles led to changes in structure of the tissue lining the intestinal wall, increasing the surface area available to take up iron and other nutrients. And over time, chickens repeatedly exposed to low doses of the nanoparticles began taking up more iron than the others. Again, this was borne out in the in vitro models. This research is described in the journal Nature Nanotechnology.
Mahler says the researchers will now use the in vitro and chicken models to study nanoparticles found in food to determine whether these, too, affect iron uptake. Mahler says the group will look for effects on absorption of other essential nutrients, including zinc and fat-soluble vitamins.
The goal is to develop the in vitro system to the point where it can be used to rapidly pre-screen nanoparticles for potential ill effects, flagging some for further safety studies in animals. There's a tremendous amount of variation in the chemistry and structure of nanomaterials, and it's not practical to test every new permutation in animal studies to make sure it's safe.
Andre Nel, a professor of medicine at the University of California, Los Angeles, and the director of Center for the Environmental Implications of Nanotechnology, hopes that emerging high-throughput nanomaterials safety screens will help people developing nanomaterials ''put the safety of materials up front in the development process, rather than dealing with it retroactively.''
(Courtesy: Materials Research Society)
