You may have seen wounded skin regenerate, and chances are you’re familiar with the fascinating stages of development a fetus goes through before it becomes a baby. Cell division or mitosis is involved in both cases. Mitosis is the process by which a parent cell divides into two identical daughter cells equipped with the same genetic information.
In cancer, regulation of this important process goes awry and the cells reproduce uncontrollably, leading to the formation of a tumor or neoplasm (from Greek, neo “new”, and plasm “formation”).
Cells get the energy they need to survive, divide, and repair by metabolizing foods. ROS, which stands for reactive oxygen species, are produced as a result of normal cellular metabolism. The build-up of these highly reactive molecules in cells may cause damage to the structures of the main biomolecules (DNA, RNA, proteins, and lipids), which can result in a variety of diseases. As with yin and yang, our bodies possess antioxidant systems responsible for maintaining the balance between antioxidants and ROS to preserve the redox status of the cell.
Cancer cells demand a great amount of energy to divide and proliferate, much more so than normal cells. Therefore, they metabolize (absorb, synthesize, store, and release) lipids at an accelerated rate. Cancer cells also exhibit increased levels of ROS, a condition that overwhelms their antioxidant capacity. This is known as oxidative stress, and it inevitably promotes tumor growth.
Colorectal cancer is the third most common type of cancer in men and women around the world. So much so that the estimated incidence of this disease in 2012 was 1.36 million people.
From Problem to Action
Given this situation, several research areas of interest focused on the prevention and treatment of cancer are being explored. A trend towards the study of foods fortified with beneficial substances, such as antioxidants, has been observed in recent years. Bioavailability of these compounds is greater when they are derived from natural sources and taken in organic form.
In this sense, selenium is classified as a microelement. The recommended daily intake for adults with an average weight of 70 kilograms (154 pounds) is 55 µg. An adequate intake of selenium helps activate antioxidant enzymes (proteins that catalyze chemical reactions in living organisms), such as glutathione peroxidase (GPx) and thioredoxin reductase (TrxR). They both have selenium atoms in their structure, so increased intake of selenium through diet leads to increased activity of both enzymes.
Foods such as grains, red meat, fish and shellfish, Brazil nuts, and broccoli are remarkable sources of selenium. However, the selenium content of food varies proportionally based on soil nutrient concentration. Deficiency in selenium intake increases the risk of developing several types of cancer.
The cancer-fighting potential of selenium has been demonstrated through several studies, according to which administration of this mineral in supranutritional amounts (that is, exceeding the recommended intake of 200 µg/day) reduces cancer cell growth and proliferation. On the other hand, pushing selenium intake beyond 350 µg has been shown to produce toxic effects. In spite of this, biofortification of foods with selenium provides a means to increase nutrient content and promote intake in selenium-deficient populations.
Experts from the Tec de Monterrey Functional Nutrition and NutriOmics Research Group conducted a study to assess the effect of a supranutritional selenium diet on tumor growth inhibition in mice inoculated with colon cancer cells and fed chickpea sprouts enriched with selenium upon germination.
During the four-day germination period in selenium-enriched soak waters, the chickpeas accumulated selenium as follows: the mineral replaced the sulfur atoms in two sulfur-containing amino acids found in chickpeas, methionine and cysteine, and this reaction led to the formation of seleno-amino acids: selenomethionine and selenocysteine, which are well-known for their cancer-fighting potential.
Additionally, chickpea germination resulted in increased concentration of phenolic compounds, especially the so-called isoflavonoids, which are also known for their antioxidant and cancer-fighting properties. To test the cancer-fighting and antioxidant activity of these two types of compounds, alone or in combination, different diets with varying amounts of both substances were prepared.
The mice were fed for three weeks, and they were then inoculated on the back portion of their bodies with cancer cells. Afterward, they were fed three more weeks for data collection. The progression of tumor growth was assessed using fluorescent technology.
In mice fed high selenium diets, both with and without isoflavonoids, tumor size turned out to be 40 percent smaller than in the control group. Increased selenium intake was associated with increased activity of selenoenzymes glutathione peroxidase and thioredoxin reductase, with improvements of 122% and 69%, respectively. Mice fed selenium-enriched chickpeas exhibited cholesterol, triglycerides, LDL, and HDL levels similar to those observed in healthy mice. In contrast, selenium-deficient diets were associated with very low levels of these parameters.
These findings confirm the chemopreventive effect of a selenium-rich diet. In summary, we propose that one of the main mechanisms by which selenium in chickpea sprouts suppresses cancer cell growth and proliferation involves increased antioxidant activity of selenoenzymes. By exerting a protective effect on the stability of lipidic compounds, selenoenzymes cut off the energy supply cancer cells so need to fuel their accelerated growth and proliferation. However, more detailed research is needed to further clarify the molecular mechanism behind the cancer-fighting activity of selenium.
In the near future, the research group at Tec de Monterrey expects highly nutritious, selenium-enriched foods, such as chickpeas, to be available in the market for use as a dietary means to lower the risk of developing colon cancer and to extend the life expectancy of thousands of people. However, this will pose challenges in terms of marketing and intake supervision.
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