Study shows how infections provoke tissues into becoming cancerous

Published on June 12, 2012 at 4:45 AM · No Comments

One of the biggest risk factors for liver, colon or stomach cancer is chronic inflammation of those organs, often caused by viral or bacterial infections. A new study from MIT offers the most comprehensive look yet at how such infections provoke tissues into becoming cancerous.

The study, which is appearing in the online edition of Proceedings of the National Academy of Sciences the week of June 11, tracked a variety of genetic and chemical changes in the livers and colons of mice infected with Helicobacter hepaticus, a bacterium similar to Helicobacter pylori, which causes stomach ulcers and cancer in humans.

The findings could help researchers develop ways to predict the health consequences of chronic inflammation, and design drugs to halt such inflammation.

"If you understand the mechanism, then you can design interventions," says Peter Dedon, an MIT professor of biological engineering. "For example, what if we develop ways to block or interrupt the toxic effects of the chronic inflammation?"

Dedon is one of four senior authors of the paper, along with Steven Tannenbaum, a professor of biological engineering and chemistry; James Fox, a professor of biological engineering and director of the Department of Comparative Medicine; and Gerald Wogan, a professor of biological engineering and chemistry. Lead author is Aswin Mangerich, a former MIT postdoc now at the University of Konstanz in Germany.

Too much of a good thing

For the past 30 years, Tannenbaum has led a group of MIT researchers dedicated to studying the link between chronic inflammation and cancer. Inflammation is the body's normal reaction to any kind of infection or damage, but when it goes on for too long, tissues can be damaged.

When the body's immune system detects pathogens or cell damage, it activates an influx of cells called macrophages and neutrophils. These cells' job is to engulf bacteria, dead cells and debris: proteins, nucleic acids and other molecules released by dead or damaged cells. As part of this process, the cells produce highly reactive chemicals that help degrade the bacteria.

"In doing this, in engulfing the bacteria and dumping these reactive chemicals on them, the chemicals also diffuse out into the tissue, and that's where the problem comes in," Dedon says.

If sustained over a long period, that inflammation can eventually lead to cancer. A recent study published in the journal The Lancet found that infections account for about 16 percent of new cancer cases worldwide.

Widespread damage

In the new MIT study, the researchers analyzed mice that were infected with H. hepaticus, which causes them to develop a condition similar to inflammatory bowel disease in humans. Over the course of 20 weeks, the mice developed chronic infections of the liver and colon, with some of the mice developing colon cancer.

Throughout the 20-week period, the researchers measured about a dozen different types of damage to DNA, RNA and proteins. They also examined tissue damage and measured which genes were turned on and off as the infection progressed. One of their key findings was that the liver and colon responded differently to infection.

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