04 April 2012

Exposure to Arsenic Can Turn Normal Stem Cells to Cancer Stem Cells

Arsenic is a natural element that is present in soil and minerals. It is both toxic and potentially carcinogenic. Prolonged exposure to arsenic can cause health problems even death. Non-cancer effects can include thickening and discoloration of the skin, stomach pain, nausea, vomiting; diarrhea; numbness in hands and feet; partial paralysis; and blindness. Arsenic has been linked to cancer of the bladder, lungs, skin, kidney, nasal passages, liver, and prostate.

Organic and inorganic forms of arsenic can be found in soil and ground water, and as a result, small amounts may be found in certain food and beverage products. Arsenic-based pesticides were commonly used in United States agricultural production up until 1970, when more effective substances became available. As a result, trace levels of organic and inorganic forms of arsenic can be detected in some agricultural settings, which may lead to small amounts of arsenic in certain foods and beverages.

In the periodic table, Arsenic is a semi-metal element. It is odorless and tasteless. Arsenic enters drinking water supplies from natural deposits in the earth or from agricultural and industrial practices. There are also reports that brown rice, apple juice and chicken meat may also contain high levels of arsenic.

Arsenic turns stem cells cancerous, spurring tumor growth

Researchers at the National Institutes of Health have discovered how exposure to arsenic can turn normal stem cells into cancer stem cells and spur tumor growth. Inorganic arsenic, which affects the drinking water of millions of people worldwide, has been previously shown to be a human carcinogen. A growing body of evidence suggests that cancer is a stem-cell based disease. Normal stem cells are essential to normal tissue regeneration, and to the stability of organisms and processes. But cancer stem cells are thought to be the driving force for the formation, growth, and spread of tumors.

Michael Waalkes, Ph.D., and his team at the National Toxicology Program Laboratory, National Institute of Environmental Health Sciences, part of NIH, had shown previously that normal cells become cancerous when they are treated with inorganic arsenic. This new study shows that when these cancer cells are placed near, but not in contact with normal stem cells, the normal stem cells very rapidly acquire the characteristics of cancer stem cells. It demonstrates that malignant cells are able to send molecular signals through a semi-permeable membrane, where cells can't normally pass, and turn the normal stem cells into cancer stem cells.

Video: Arsenic Mitigation

"This paper shows a different and unique way that cancers can expand by recruiting nearby normal stem cells and creating an overabundance of cancer stem cells," said Waalkes. "The recruitment of normal stem cells into cancer stem cells could have broad implications for the carcinogenic process in general, including tumor growth and metastases."

This reveals a potentially important aspect of arsenic carcinogenesis and may help explain observances by researchers working with arsenic that arsenic often causes multiple tumors of many types to form on the skin or inside the body. The paper is online in Environmental Health Perspectives.

Waalkes' lab started working with stem cells about five years ago. The researchers used a prostate stem cell line, not embryonic stem cells.

"Using stem cells to answer questions about disease is an important new growing area of research. Stem cells help to explain a lot about carcinogenesis, and it is highly likely that stem cells are contributing factors to other chronic diseases," Waalkes said.

Stem cells are unique in the body. They stay around for a long time and are capable of dividing and renewing themselves. "Most cancers take 30 or 40 years to develop," said Linda Birnbaum, Ph.D., director of NIEHS and NTP. "It makes sense that stem cells may play a role in the developmental basis of adult disease. We know that exposures to toxicants during development and growth can lead to diseases later in life."

Next, the laboratory team will look to see if this finding is unique to arsenic or if it is applicable to other organic and inorganic carcinogens.


NIH/National Institute of Environmental Health Sciences
National Toxicology Program Laboratory
Environmental Health Perspectives
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