Monday, August 12, 2013

Chemicals That Promote Obesity Down the Generations

Air Date: Week of August 9, 2013

Diet and exercise are seen as the key factors that cause obesity, but new research suggests that certain chemicals called obesogens contribute to the global weight problem. Bruce Blumberg, professor of developmental and cell biology at the University of California at Irvine tells host Steve Curwood that the effects of an obesogenic chemical he studied seem to persist for several generations.


BLUMBERG: An obesogen, according to us, is a chemical that somehow causes the body to store more fat. And it can do that by making more fat cells, by putting more fat into those cells, or can do that indirectly by changing how the metabolism works or by making you hungrier, or by making you less able to sense that you’ve had enough to eat.

CURWOOD: Bruce Blumberg is a professor of Developmental Biology at UC Irvine. And here’s the startling part of his research. Not only has his team confirmed earlier work showing that certain persistent organic pollutants can act as obesegens, they have found that initial exposures can echo down through at least three generations to make animals fat. This study used the chemical TBT – tributyltin --which was widely used as anti-fouling paint until a few years ago.

BLUMBERG: So we exposed pregnant mice to very low doses of tributyltin, and we knew from our previous work that would give us an effect on the babies that were so exposed - that would be - we would call that the F-1 generation. And we asked the question what happens if we bred those babies and the babies of those babies and checked whether there were subsequent effects.

CURWOOD: And what happened?

BLUMBERG: So what we found is that the effects persisted in the grandchildren and greatgrandchildren. And that some of the effects were actually stronger in the greatgrandchildren who had never been exposed.


CURWOOD: Now this study is lab mice, how well do you think these findings might translate to humans?

BLUMBERG: 100 percent.

CURWOOD: Really?

BLUMBERG: The reason I say that is because tributyltin - TBT - works through a hormone receptor called PPAR gamma. And we know there are pharmaceutical drugs that target that same receptor that make people fat. So if I have a chemical tributyltin that activates the same receptor, you would expect the same effect.


CURWOOD: One of the most startling things that’s in your report is your citation of a study that showed eight different species of animals including pets, laboratory animals, and feral rats, living in proximity to humans have become obese in parallel with the human obesity epidemic. And the odds of this being a coincidence was something like 10 million to 1 against.

Dr. Bruce Blumberg (photo: Bruce Blumberg)

BLUMBERG: 10 million to 1. Yes.

BLUMBERG: You can make the argument, if you talk to...the mainstream obesity community will make the argument that it’s all about diet and exercise, calories in and calories out. And I don’t see how you can explain the increase in obesity of animals, including wild animals, by calories in and calories out. It’s got to be something else. It has to be the nature of the calories. It has to be a chemical, an environmental factor, to which they’re exposed to now, that they were not previously exposed to, that underlies that.

CURWOOD: So who’s most susceptible to tributyltin exposure?

BLUMBERG: Tributyltin will make animals and humans fat at any stage of life. We’re particularly concerned with prenatal exposures because that’s where you have the capability to have transgenerational effects. You won’t cause, or we don’t believe that you will...exposing an adult will cause transgenerational effects on their offspring. But we know from our experiments, that exposing embryos to a chemical like tributyltin will cause transgenerational effects.


BLUMBERG: It says to me that the most important way that we can change obesity is not by treating obese people, but by preventing them from becoming obese in the first place, by preventing these exposures, which can include chemical exposures, but it can also include exposures to improper diet. There’s a fair bit of data that says exposing mom to a high fat or junk food diet makes the babies prefer that kind of food. There’s some kind of a programming event that’s not well understood that’s going on there. So it’s not just chemical exposures. Chemical exposures and dietary factors, and the nature of diet early in life, is the area that needs to be addressed to make inroads into solving this obesity problem that we face today.


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