Omega-3 fatty acids -fats commonly found in fish oil â€“ were shown several years ago to prevent retinopathy, a major form of blindness, in a mouse model of the disease. A follow-up study now reveals exactly how omega-3â€²s provide protection, and provides reassurance that widely used COX-inhibiting drugs like aspirin and NSAIDs donâ€™t negate their benefit. The findings also suggest that omega-3â€²s may be beneficial in diabetes.
Retinopathy â€“ an eye disease caused by the proliferation of tortuous, leaky blood vessels in the retina â€“ is a leading cause of blindness, affecting 4.1 million Americans with diabetes (a number expected to double over the next 15 years) and many premature infants. Another 7 million-plus Americans have age-related macular degeneration (AMD); this too will increase as the population ages. The most common â€œwetâ€ form of AMD is also caused by abnormal blood vessel growth.
The ability to prevent these â€œneovascularâ€ eye diseases with omega-3 fatty acids could provide tremendous cost savings, says Childrenâ€™s ophthalmologist Lois Smith, senior investigator on the study. â€œThe cost of omega-3 supplementation is about $10 a month, versus up to $4,000 a month for anti-VEGF therapy,â€ she says, referring to drugs such as Macugen and Lucentis used in AMD and diabetic retinopathy. â€œOur new findings give us new information on how omega-3s work that makes them an even more promising option.â€
Omega-3 fatty acids, highly concentrated in the retina, are often lacking in Western diets, which tend to be higher in omega-6 fatty acids. In Smithâ€™s previous study, mice fed diets rich in omega-3 fatty acids by Smithâ€™s team had nearly 50 percent less pathologic vessel growth in the retina than mice fed omega-6-rich diets. Smith and colleagues further showed that the omega-3 diet decreased inflammatory messaging in the eye.
In the new study, they document another protective mechanism: a direct effect on blood vessel growth (angiogenesis) that selectively promotes the growth of healthy blood vessels and inhibits the growth of abnormal vessels.
In addition, Smith and colleagues isolated the specific compound from omega-3 fatty acids that has these beneficial effects in mice (a metabolite of the omega-3 fatty acid DHA, known as 4-HDHA), and the enzyme that produces it (5-lipoxygenase, or 5-LOX). They showed that COX enzymes are not involved in omega-3 breakdown, suggesting that aspirin and NSAIDs â€“ taken by millions of Americans â€” will not interfere with omega-3 benefits.
â€œThis is important for people with diabetes, who often take aspirin to prevent heart disease, and also for elderly people with AMD who have a propensity for heart disease,â€ says Smith. (One drug used for asthma, zileuton, does interfere with 5-LOX, however.)
Finally, the study demonstrated that 5-LOX acts by activating the PPAR-gamma receptor, the same receptor targeted by â€œglitazoneâ€ drugs such as Avandia, taken by patients with type 2 diabetes to increase their sensitivity to insulin. Since these drugs also increase the risk for heart disease, boosting omega-3 intake through diet or supplements might be a safer way to improve insulin sensitivity in patients with diabetes or pre-diabetes. â€œThere needs to be a good clinical study in diabetes,â€ Smith says.