Scientists at the University of Illinois have found evidence that lifelong exposure to genistein, a bioactive component in soy foods, protects against colon cancer by repressing a signal that leads to accelerated growth of cells, polyps, and eventually malignant tumors. The study, funded by theNational Institutes of Health, University of IllinoisResearch Board, and the Illinois Soybean Association,will be published in an upcoming August 2013 issue of Carcinogenesis.[1]

Commenting on the results of the study, Hong Chen,Ph.D, (Photo) Professor of Food Science and Human Nutrition at the University of Illinois, said: “In our study, we report a change in the expression of three genes that control an important signaling pathway”.


Genistein decreased the expression of three genes and repressed this signaling process that is associated with abnormal cell growth and cancer development


The cells in the lining of the human gut turn over and are completely replaced weekly, she noted. “However, in 90% of colon cancer patients, an important growth-promoting signal is always switched ‘on’, leading to uncontrolled growth and malignancies. Our study suggests that the aberrantWntsignaling during the development of colon cancer can be regulated by soy-rich diets.”

“The good news is that a diet rich in soy genistein represses those signals through epigenetic modifications at the regulatory regions of those genes,” Yukun Zhang, a doctoral student in Chen’s laboratory, noted.

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Exposure
“Chronic exposure to genistein, a soy isoflavone, reduced the number of pre-cancerous lesions in the colons of laboratory rats exposed to a carcinogen by 40% and reduced Wnt signaling to normal levels,” Chen explained.

In their study, the scientists modeled lifetime exposure to soy by feeding pregnant rats and their offspring a diet containing soy protein isolate and a diet that contained genistein compound. At seven weeks of age, offspring rats were exposed to a carcinogen, and they continued eating either the soy protein or the genistein diet until they were 13 weeks old.

At that time, the researchers inspected the colons of rats in both soy groups and compared them to rats in a control group, noting the number and severity of tiny abnormal growths in each. They also compared Wnt signaling before and after the carcinogen to see whether either diet had any effect on its up-regulation.

In the genistein-fed animals, signaling levels were similar to rats that had not received the carcinogen.

“Genistein decreased the expression of three genes and repressed this signaling process that is associated with abnormal cell growth and cancer development,” Chen said.

Disease susceptibility
She said this shows that colon cancer is an epigenetic disease, meaning that dietary and environmental factors can influence genes to be switched ‘on’ or ‘off’ so you have a different pattern of gene expression, leading to a change in disease susceptibility.

“Interestingly,” Chen noted, “It has long been known that immigrants from Asia?where soy is traditionally a food staple?experience rising levels of colon cancer as they adopt the eating habits of the Western nations they now call home.” She added:”The genetic information you inherit from your parents is not the whole story. Our dietary choices, our exposure to environmental toxins, even our stress levels, affect the expression of those genes.”

Prostate cancer
An unrelated study by researchers at theCollege of Medicineat the University of Illinois published in the July 10, 2013 issue ofJAMA, The Journal of the American Medical Association, [2] showed that adding soy after surgery does not show any benefit. The authors of this study write that apossible explanation for the discrepancy seen in this study between previous results and their research is that soy may be protective against prostate cancer if consumption begins early in life but not once prostate cancer is already present.

For more information:
[1] Zhang Y, Li Q, Chen H. DNA methylation and histone modifications of Wnt genes by genistein during colon cancer development. Carcinogenesis. 2013 Aug;34(8):1756-63. doi: 10.1093/carcin/bgt129. Epub 2013 Apr 18. [Abstract][PubMed]
[2]Bosland MC, Kato I, Zeleniuch-Jacquotte A, Schmoll J, Rueter EE, Melamed J, et al. Effect of Soy Protein Isolate Supplementation on Biochemical Recurrence of Prostate Cancer After Radical ProstatectomyA Randomized Trial. JAMA. 2013;310(2):170-178. doi:10.1001/jama.2013.7842. [Abstract][PubMed]

Photo:Hong Chen,Ph.D, Professor of Food Science and Human Nutrition at theUniversity of Illinois. Photo Courtesy:University of Illinois.

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