Omega-3 fatty acids have been linked to a wide-range of health benefits, including cardiovascular disease (CVD), good development of a baby during pregnancy, joint health, behaviour and mood, and certain cancers.
"It has been known for some time that omega-3 fatty acids can inhibit certain cancer cells. So, we were interested in determining whether these substances could inhibit liver cancer cells. If so, we also wanted to know by what mechanism this inhibition occurs," explained lead researcher Tong Wu, from the University of Pittsburgh School of Medicine.
Liver cancer is one of the rarer forms of the disease, accounting for about one per cent of all cancers. Worryingly, the risk of the disease increases with age, and rates have doubled since 1975, from two to four people per 100,000 people, according to Cancer Research UK.
The Pittsburgh scientists report the effects of omega 3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and the omega-6 fatty acid, arachidonic acid (AA), on liver cancer cells.
Both omega-3 fatty acids had a dose-dependent inhibitory effect, while the omega-6 acid had not effect, said the researchers.
Wu and colleagues found that DHA induced apoptosis, programmed cell death of the cancer cells, by promoting the splitting of a protein, called poly (ADP-Ribose) polymerase (PARP), which is considered a tell-tale marker of cell death.
Also, both DHA and EPA indirectly decreased the levels of a protein, beta-catein, which has been linked to tumour development.
"Beta-catenin is known to promote cell growth and also is implicated in tumor cell promotion. Therefore, our finding that omega-3 fatty acids can decrease levels of beta-catenin is further evidence that these compounds have the ability to interact on several points of pathways involved in tumor progression, said Wu.
A similar study was recently published on-line in the British Journal of Cancer (doi: 10.1038/sj.bjc.6603030), reporting the effects of EPA, DHA and AA, on the spread of human prostate cancer cell lines.
While both omega-3 fatty acids were reported to have beneficial effects on stopping the growth and spread of the prostate cancer cells, the omega-6 fatty acid was reported to produce a metabolite, prostaglandin E2, helped the spread of the prostate cancer cells to bone marrow cells.
The role of omega fatty acids in the prevention of cancer has received increased media attention in recent weeks after a British Medical Journal article published a meta-analysis reviewing the associations between omega-3 intake and the risk of heart disease, cancer and mortality.
The analysis reported that there was no indication that the fatty acids offered protection for any of the disease, conclusions that were rounded upon by industry groups.
Dr Ray Rice, a food scientist and technical adviser to the Omega 3 Group, a consortium of fish companies, hit back at the study, saying: "This report used a faulty technique. It is conceptually flawed and should not cause people to regard seafood as anything but tasty and nutritious."
The studies by Wu and colleagues are presented as abstracts numbers 2679 and 2680.