Re-Release: Studying the relationship between cancer and fish oil

ALOX15 loss, which is common in colorectal tumors, impairs the cancer-preventative effects of fish oil.

About 19 million American adults consume dietary fish oil supplements.

These supplements, which primarily consist of omega-3 fatty acids, are widely used as a remedy for chronic diseases.

However, the effects of EPA and DHA supplementation on cancer risk have been inconsistent.

In a study, a team of researchers from the University of Michigan and University of Texas MD Anderson Cancer Center have shown that the gene ALOX15 is essential for helping EPA and DHA suppress colorectal cancer.

The results, published in Cellular and Molecular Gastroenterology and Hepatology, emphasize the need to screen for the presence of ALOX15 in cancer patients when developing preventative strategies using EPA and DHA supplements.

Large clinical studies focusing on the association between fish oil, EPA, DHA, and cancer have largely been inconclusive.

While some have shown that these supplements can reduce cancer risk, others have shown no benefit or even an increase in cancer incidence.

In the current study, researchers first compared the response of mice given a diet supplemented with fish oil to a control diet.

To their surprise, fish oil increased the number of colon tumors in mice exposed to chemicals that cause inflammation and accelerated colon tumor formation.

When DHA and EPA are consumed, they are broken down into molecules called resolvins that prevent chronic inflammation, key feature in cancer formation.

This metabolism of DHA and EPA depends on the enzyme ALOX15, which is usually turned off in various cancers.

The team tested whether mice lacking ALOX15 responded differently to fish oil supplements compared to control mice.

They found that the loss of ALOX15 increased colorectal tumors when the mice were fed fish oil, although the degree differed based on the type of omega-3 acid.

There were few tumors in mice that were fed EPA diets compared to DHA.

The commonly used forms of EPA and DHA include free fatty acids, ethyl esters, and triglycerides.

Lovasa, which contains the ethyl ester forms of EPA and DHA, is approved by the Food and Drug Administration to treat high levels of triglycerides in the blood.

Overall, Lovasa and the ethyl ester and free forms of EPA reduce the tumor numbers and volumes, especially when the mice contained ALOX15.

On the other hand, the different variants of DHA were unable to inhibit tumor development in mice lacking ALOX15.

The presence of ALOX15, however, reduced tumor growth.

Not all fish supplements are the same, said Ahmad Shariki, professor of internal medicine at the University of Michigan and a member of the Rogel Cancer Center.

It is also important to ask whether the person who's taking the supplement has the required enzymes to metabolize these products to prevent chronic inflammation and subsequently cancer development.

Although the reported results were from studies mostly done on animals, the findings suggest that having colon polyps without ALOX15 will make EPA and DHA less effective in stopping tumor growth.

Shiriki recommends that people talk to their physicians before they take fish oil supplements.

The team is now working on developing drugs that can help increase ALOX15 expression in cancer cells.