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Environmental Factor

May 2011

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NTP Peer Review Panel weighs in on Aloe vera extract, other compounds

By Ernie Hood
May 2011

Committee Chair John Cullen, V.M.D., Ph.D., left, of North Carolina State University, and NTP Deputy Program Director for Science Nigel Walker, Ph.D.

Committee Chair John Cullen, V.M.D., Ph.D., left, of North Carolina State University, and NTP Deputy Program Director for Science Nigel Walker, Ph.D., listened intently to one of the scientific presentations briefing the panel on the draft Technical Reports. (Photo courtesy of Steve McCaw)

Mary Boudreau, Ph.D.

Mary Boudreau, Ph.D., NCTR study scientist for the Aloe vera technical report, briefed the Peer Review Panel on the toxicology and carcinogenesis studies of Aloe vera administered in drinking water to rats and mice. (Photo courtesy of Steve McCaw)

Aloe vera plant

There are at least 420 different plant species of Aloe. Aloe vera specifically refers to the Aloe barbadensis Miller plant, which is the most common form used in Aloe-based products. An organic component in the outer leaf pulp of Aloe leaves, known as the latex, contains aloin. (Photo courtesy of NIEHS stock)

Fryer cooking french fries

Families can reduce their exposure to acrylamide by adopting a healthy, balanced eating plan that includes fruits and vegetables, lean meats, fish, and high-fiber grains. (Photo courtesy of NIEHS stock)

Don't throw out the aloe plant you keep to treat burns, but it might be time to reconsider if you consume certain commercial products containing Aloe vera, such as drinks, concentrates, capsules, powders, and flavorings.

In its April 5, 2011 meeting at NIEHS, the NTP Technical Reports Peer Review Panel agreed with the conclusions reached from two-year drinking water bioassays in rats and mice as presented in the draft NTP Technical Report (, which said, "There was clear evidence of carcinogenic activity of a non-decolorized whole leaf extract of Aloe vera in male and female F344/N rats based upon increased incidences of adenomas and carcinomas of the large intestine." Clear evidence is the highest designation in the four-point scale used by NTP to characterize levels of evidence for carcinogenic activity in the substances it evaluates. Watch the videos from NTP Speaks About Aloe Vera (

While previous NTP studies of dermal exposures (  Download Adobe Reader (2.8 MB) to Aloe vera in mice did not find a strong link with skin cancer, these newer studies showed that exposure via chronic ingestion in the water was associated with a high incidence of colon cancer in the rat.  The rat colon cancer shared morphological and molecular features with human colon cancer, the fourth most commonly diagnosed cancer and the second-leading cause of cancer-related deaths of people in the United States. In its oral form, Aloe vera is commonly marketed as an "herbal remedy" that is claimed to alleviate a variety of conditions, including cancer, arthritis, constipation, and gastrointestinal disorders. Since the Aloe vera extract is a dietary supplement, it has not been subjected to the same U.S. Food and Drug Administration (FDA) regulations as apply to drugs.

In collaboration with the FDA's National Center for Toxicological Research (NCTR), the NTP studied the non-decolorized extract processed from the whole leaf of the plant. That extract contains an anthraquinone called aloin, which may give the plant its laxative qualities.  Some anthraquionones have previously been shown to be carcinogenic. Many commercial preparations, it should be noted, run the whole leaf extract through a filtration process, decolorizing it and removing much of the aloin. However, according to the nomination of Aloe vera to the NTP testing process by the National Cancer Institute, the non-decolorized extract is still widely available, leading to potentially widespread exposure to aloin in the U.S. population.

The panel also agreed with the draft Technical Report (  Download Adobe Reader (2.3 MB) conclusions reporting clear evidence of carcinogenic activity in male and female mice and rats exposed to acrylamide in drinking water, with tumors formed at multiple sites. Acrylamide (  Download Adobe Reader (652 KB) is a chemical widely used in the manufacturing of papers, dyes, and other industrial products. It can be formed when certain foods are cooked at high temperatures, such as potatoes and grains processed to make French fries, toast, or potato chips. Cigarette smoke also contains acrylamide. To aid in its risk assessment concerning the compound, including potential actions to reduce human exposures, it was nominated by the FDA's Center for Food Safety and Applied Nutrition for study by the NTP and NCTR.

Finally, the panel also concurred with draft Technical Report conclusions on two other reports: toxicology and carcinogenesis studies of senna (  Download Adobe Reader (6.7 MB),  the active ingredient in frequently used over-the-counter laxatives and also as a flavoring agent, and toxicology  and carcinogenesis studies of transplacental exposure of several antiretroviral agents used singly or in combination to treat HIV.

The reviewers agreed that there was no evidence of carcinogenic activity of senna in the transgenic mouse models exposed to the compound. They also agreed with the variety of conclusions reached regarding transplacental exposures in mice to the drugs 3'-azido-3'-deoxythymidine (AZT), lamivudine (3TC), nevirapine (NVP), and nelfinavir nesylate (NFV). AZT was tested singly, in combination with 3TC, and both were used in combination with NVP or NFV, reflecting current "cocktail" HIV therapies. Among these combinations, there was some evidence of carcinogenic activity in male mice exposed to the mixture of AZT, 3TC, and NVP.

(Ernie Hood is a contract writer for the NIEHS Office of Communications and Public Liaison.)

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