s for spicy food lovers; the active ingredient found in chili peppers - capsaicin - could reduce the risk of colorectal cancer, according to a new study published in The Journal of Clinical Investigation.The research team, including senior author Dr. Eyal Raz, professor of medicine at the University of California-San Diego School of Medicine, found that capsaicin activated a pain receptor called TRPV1 in mice, which reduced tumor development in their gut.
TRPV1 was first discovered in sensory neurons, the researchers say, where it protects the cells against potential damage from heat, acidity and spicy chemicals in the environment.
"Thus," says Dr. Raz. "TRPV1 was quickly described as a molecular 'pain receptor.' This can be considered to be its conventional function, which all takes place in the nervous system."
TRPV1 'suppresses intestinal tumors'
But in this latest study, Dr. Raz and colleagues found that epithelial cells in the intestines also express TRPV1 when stimulated by the epidermal growth factor receptor (EGFR) - a receptor crucial to cell growth in the intestines.
The researchers note that if EGFR signaling is impaired, this causes cell growth to become out of control, increasing the risk of tumor development.
The team's study revealed that when TRPV1 is activated by the EGFR, TRPV1 activates a "direct negative feedback" on the EGFR, which reduces growth of unwanted cells in the intestine and in turn, reduces the risk of tumor development.
The researchers genetically modified mice to be TRPV1-deficient, and found that they experienced a much higher rate of intestinal tumor growth, compared with mice who had an active form of TRPV1. This indicates, the team says, that TRPV1 usually works to suppress tumors in the intestines.
Furthermore, the team found that capsaicin appears to play a role in activating TRPV1.
The role of capsaicin against colorectal cancer
Capsaicin is the heat-generating ingredient in chili peppers that come from the Capsicum genus, such as jalapeño peppers. It is an irritant to mammals, including humans, causing a burning sensation when it comes into contact with body tissue.
As well as its obvious role in spicy foods, capsaicin is used in topical medications to relieve pain and is the active ingredient in pepper spray.
In their study, the team fed capsaicin to mice that were genetically susceptible to the development of multiple tumors in the gut.
They found that the component reduced tumor development in the mice by activating TRPV1 and extended their lifespan by more than 30%. In addition, such effects were boosted when combined with a COX-2 non-steroidal anti-inflammatory drug called celecoxib.
Commenting on their findings, the researchers say:
"Our data suggest that TRPV1 senses and regulates cell proliferation in the intestinal epithelium. [...] Our data also suggested that TRPV1 triggering by dietary administration of capsaicin suppressed intestinal tumorigenesis.
Based on these results, we propose that the administration of TRPV1 agonists in combination with a COX-2 inhibitor may prevent the adenoma-to-carcinoma sequence in humans."
Dr. Raz notes that TRPV1 mutations have previously been uncovered in molecular studies of human colorectal cancer samples, but as yet, there is no evidence suggesting that TRPV1 deficiency in humans increases the risk of colorectal cancer.
However, he stresses this association is something that needs to be addressed in future research.
