Canzer-cola
Drinking soda led to colon tumors in mice
Scientists have found out that sweet carbonated water leads to colon cancer in mice, writes Sciencemag (The corn syrup in a soda a day can give mice bigger colon tumors) with reference to Science (Goncalves et al., High–fructose corn syrup enhances intestinal tumor growth in mice).
It is unclear whether humans react the same way as rodents, but the researchers who conducted the new work believe that their results could explain the recent increase in cases of colon cancer in young people and even point to ways to treat this disease.
"This is perhaps the most direct evidence that sugar, in addition to obesity, can contribute to the development of cancer. This is an example of what happens if you are predisposed to colon cancer and drink a can of Coca-Cola a day," says Princeton University biochemist Joshua Rabinovich, who was not involved in the study.
Sales of sweetened beverages soared in the 1980s when corn subsidies in the United States led to the introduction of cheap, high-fructose corn syrup, which flooded the market and replaced table sugar. Since then, the love of sweet soda has been blamed for the development of obesity and, indirectly, cancer. Obesity causes inflammation, which helps tumors grow. In particular, colon cancer is associated with overweight. But biochemist Lewis Cantley of Weill Cornell Medicine in New York and his then-postdoc Jihye Yun wondered if there was a more direct link between sugary drinks and cancer.
Together with other scientists, they studied mice by injecting into their stomachs about one tenth of a teaspoon of water containing 25% high-fructose corn syrup. In order to gain weight, this is not enough, although it is equivalent to almost a can of soda a day. Mice with the APC gene predisposing to the development of cancer were selected as a control group.
In mice consuming sugar, invasive tumors appeared after about 2 months. Tests with isotope–labeled glucose and fructose – two components of high-fructose corn syrup - showed that most of the fructose avoids its usual absorption pathway into the blood through the small intestine and instead goes straight to the colon, where tumor cells absorb it along with glucose.
Once inside the tumor cells, fructose is broken down by an enzyme called fructokinase (KHK), which lowers the energy level in the cell and triggers additional glucose metabolism to restore it. The researchers found that this glycolysis also leads to the formation of fats necessary for tumor cells to grow. In mice designed so that they lack the enzyme KHK, as well as APC, tumors grew no more than in control animals with AP C that did not receive corn syrup.
The researchers say that the results obtained in mice suggest that sugary drinks, including those containing table sugar (also a mixture of fructose and glucose), can accelerate the growth of precancerous polyps in people who would otherwise take decades to develop cancer. "Even a small amount of sugary drinks can shorten the time it takes for cancer to develop," says Yun, currently an associate professor at Baylor College of Medicine in Houston, Texas, where her lab helped complete the study.
"The experiments are well done and the results are convincing," says physiologist Luc Tappi from the University of Lausanne in Switzerland. But he and others warn that it is not yet clear how appropriate rodent experiments are for people who can reduce the effects of corn syrup by drinking carbonated water slowly or with food. "Does it moderately or slightly increase the risk? Or is it negligible compared to other factors that we know about?" says medical scientist Mark Herman from Duke University in Durham (North Carolina).
To answer this question, Cantlie's team hopes to study whether a low-sugar diet slows the growth of intestinal polyps in people genetically predisposed to their development. They also suggest that a KHK-inhibiting drug in clinical trials for liver obesity could potentially be added to standard medications as part of a clinical trial for the treatment of people with colon cancer.
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