Some pollutants made mice less friendly

The body’s endocrine system makes hormones. Like a band director’s baton, those hormones signal cells when and how to perform. But some chemicals can mimic — or sometimes block — the activity of these hormones. Like a fake band director, these hormone imposters might send out false directions. Many such hormone-like chemicals leach out of plastics, cosmetics, packaging materials and more. A mouse study now finds signs that some of these common pollutants indeed can issue false signals. In a recent study, overweight mice had lower social status than slimmer ones did. Lighter mice were more dominant. Faking out the body’s hormone sensors could alter biology in a host of ways. It might affect how the body develops. It might alter how an individual behaves. It could even increase an individual’s risk of disease. In the new study, the affected mice seemed to become anxious. The pollutants also altered the rate at which the mice grew. No one knows if the same thing is going on in people exposed to these common chemicals. But that’s one of the concerns that prompted the new research. Alexander Suvorov studies environmental health at the University of Massachusetts in Amherst. He had become curious about why rates of two brain disorders seem to be on the rise. The first is autism. It affects how someone experiences the world and interacts with it. The second condition is ADHD, or attention deficit hyperactivity disorder. People with ADHD have difficulty concentrating and staying still. Suvorov wanted to test in mice whether pollutants might cause or intensify behaviours typical of autism or ADHD. If the chemicals did, that might explain recent increases in the number of people diagnosed with the disorders. For its new study, Suvorov’s team exposed pregnant mice to high doses of one of three common chemicals. They were bisphenol S, BDE-47 and TBBPA. Bisphenol S is used in some clear plastics and papers used to make cash-register receipts. BDE-47 and TBBPA are flame-retardants. Companies no longer use BDE-47, though. Scientists suspect it may have harmful health effects in people. The dose of BDE-47 given to mice in the study was similar to the amount that studies have shown has accumulated in the bodies of humans, Suvorov says. And everyone is exposed to TBBPA. That’s because it is now one of the most widely used chemicals for making materials fire resistant. Each of the three chemicals can affect hormones. Scientists call such chemicals endocrine disruptors. For instance, BPS can work like a weak version of oestrogen. Mice were exposed to different levels of these chemicals in the womb. Later, as adults, the mice encountered a stranger mouse. Mice that had been exposed to a pollutant now moved more quickly around the stranger than unexposed animals did. This suggests the exposed animals felt anxious, Suvorov says. Indeed, mice exposed to these chemicals avoided the stranger mice and spent more time alone. In contrast, mice not exposed to any of the three chemicals sniffed strangers longer and acted friendlier. The new study also found that weight affected how social a mouse was. That is a measure of how comfortable it was around others of its kind. Heavier mice had a lower status. They tended to be less popular or attractive to others. Skinnier mice were more dominant. The scientists also found some hints that the chemicals they worked with could affect body weight. A bigger study is needed to confirm the new observations. But if they are confirmed, then these pollutants may have the ability to indirectly affect an individual’s social status. That could be very important, Suvorov says. “It has never been shown in animals before that having a higher body weight also means it will be subordinate,” that is, lower in rank or position. It is still too early to tell if people might respond similarly, Suvorov says. In fact, no data exist to show these chemicals have any effect on human behaviour. Still, the new tests have begun to probe what types of changes to look for in people. For instance, Suvorov wonders if exposures to such chemicals might slightly change how people interact. “Let’s imagine that everybody in our society is now 10 percent more aggressive,” he says. That small change would make little difference in one individual. But if everybody was affected, “then the whole society may function differently,” he says. Like the mice in the study, overweight people in many societies may be shunned or less popular, said Robert Schwartz. A retired doctor in Wake Forest, N.C., his work focused on hormone effects in children. But, Schwartz notes, people are exposed to many endocrine disruptors. They can be found throughout the environment and in our diets. So, he says, “It’s hard to say that at the lower levels that humans are exposed to, that these chemicals have significant effects.”

Science New, 14 September 2015 ; ;