Vitamin A may help protect against colon cancer that is due to chronic bowel inflammation, according to findings of a recent study with mice.
In the study, “Normalizing Microbiota-Induced Retinoic Acid Deficiency Stimulates Protective CD8+ T Cell-Mediated Immunity in Colorectal Cancer,” published in the journal Immunity, researchers found that mice with colon cancer caused by inflammation had lower levels of retinoic acid, a compound made in the body from vitamin A. When these mice were treated with retinoic acid, tumor growth slowed.
Colon cancer is the second leading cause of cancer-related deaths in the United States. There is a “clear link” in humans between inflammatory bowel conditions, such as ulcerative colitis, and the development of colon (also known as bowel) cancer, according to Professor Edgar Engleman of Stanford University School of Medicine, and the study’s lead researcher.
“Retinoic acid has been known for years to be involved in suppressing inflammation in the intestine,” Engleman said in a news report. “We wanted to connect the dots and learn whether and how retinoic acid levels directly affect cancer development.”
Researchers investigated the levels of retinoic acid in mice with colon cancer that developed from bowel inflammation. The team also looked at tumor samples from patients with colon cancer, also derived from different forms of chronic bowel inflammation, including ulcerative colitis.
The results showed a retinoic acid deficiency in the bowels of the mice, and this effect was caused by bacteria driven inflammation, which also enhanced the break down of retinoic acid.
An interesting result was seen when the team treated the mice with the compound. When the levels increased, the growth of tumor cells were seen to slow down. This benefit was due to the activation of T-cells (killer cells), which are crucial immune system players that target cancer cells.
To further test the involvement of the retinoic acid, the researchers blocked its action, and tumor growth was seen to escalate.
Tumor samples from patients with colon cancer also showed alterations similar to those seen in the mice, with reduced levels of retinolic acid in the bowels. The researchers also found high levels of an enzyme that breaks down this compound in the patients, and those with the highest levels were also seen to have the poorest survival rate.
These findings reveal a link between bowel inflammation, retinolic acid deficiency, and colon cancer in mice and humans. But further studies are needed, according to Professor Alastair Watson, a Cancer Research UK specialist in colon cancer.
“The next challenge is to establish whether giving vitamin A to people with ulcerative colitis could reduce their risk of developing bowel cancer,” he said. “Less than one in 10 cases of bowel cancer are caused by ulcerative colitis, so a further challenge is to determine whether vitamin A also has a role to play in more common cases of the disease.”