Dietary fish oil may be a cancer chemopreventive agent

Researchers now suggest that fish oil may have the potential to be developed as a cancer chemopreventive agent. Environmental carcinogens termed polycyclic aromatic hydrocarbons can bind to DNA to form DNA adducts (additional products), which may in turn lead to mutations in critical genes, causing cancer. They found a reduced level of DNA adducts in animals treated with fish oil.

Epidemiological data have shown that smokers who had higher levels of DNA adducts in white blood cells were 3 times more likely to be diagnosed with lung cancer after 1-13 years than smokers with lower adduct levels.Therefore, reduction of DNA adduct levels may decrease tumor risk.

Fish oil has multiple health benefits including lack of toxicity and side effects. The team of  researchers from Texas A&M University, University of Texas, Austin and Baylor College of Medicine  discovered that dietary fish oil decreased liver PAH-DNA adducts in mice by 33% to 49% when treated with PAH.

The research results were published recently in the open access journal PLoS ONE.

The scientists fed male mice with 11.5% fish oil or corn oil diet for 30 days. The animals were then exposed to seven cancer causing PAHs including benzo(a)pyrene via a single intraperitoneal injection. Animals were euthanized at 1, 3, or 7d after treatment and levels of DNA adducts in the mice were determined.

Fish Oil Cancer DNA Adduct
Comparison of the levels of total DNA adducts in liver of mice between two diet groups. CO, corn oil; FO, fish oil. 

The results showed that the levels of total liver DNA adducts were significantly decreased in fish oil groups compared to corn oil groups in both low and high dose groups. Total adduct levels in the high dose PAH groups were significantly less in the fish oil at 7 d.  Animals treated with the low dose (2.5 fold lower) PAHs also displayed similar trends.

Fish oil significantly enhanced the expression of a gene involved in PAH metabolism (Cyp1a1) in both the high and low dose PAH groups. Animals, belonging to the fish oil group, that were treated with low dose of PAHs, showed high levels of Gstt1 (a gene involved in PAH metabolism and antioxidation) compared to those of the corn oil group.

fish oil reduce cancer DNA adduct
Histological changes in liver of mice treated with carcinogenic PAHs for both fish oi and corn oil diet groups. Seven days after treatment of carcinogenic PAH mixture, focal hemorrhage and tissue necrosis were present in dietary corn oil group of high dose PAHs (Panel B). Only mild histological changes were displayed in dietary fish oil group (D).

Histological observations at 7 days after PAH treatment indicated that fish oil played a hepatoprotective role. Dietary fish oil may block the formation of DNA adducts by detoxification of PAHs.

“Our results suggest that fish oil has a potential to be developed as a cancer chemopreventive agent that could be applied in high risk populations who are exposed to environmental PAH carcinogens including cigarette smokers,” said the authors.

Science news reference: 

Guo-Dong Zhou, Huiping Zhu, Tracie D. Phillips, Jianbo Wang, Shi-Zhou Wang, Fen Wang, Brad A. Amendt, Xanthi I. Couroucli, Kirby C. Donnelly, Bhagavatula Moorthy. (2011) Effects of Dietary Fish Oil on the Depletion of Carcinogenic PAH-DNA Adduct Levels in the Liver of B6C3F1 Mouse. PLoS ONE 6(10): e26589. doi:10.1371/journal.pone.0026589.