Genetic Engineering May Provide an End to Fat-Free Diets

A new study in mice raises an exciting prospect--that humans may one day be able to eat any kind of fat they want without raising their risk of heart disease.

"We deleted an enzyme in mice, and they could eat any type of fat and not get heart disease,” said Lawrence Rudel, Ph.D., a professor of comparative medicine at Wake Forest University (Winston-Salem, NC, USA). "If you're a mouse, it's great. Of course, we don't know yet if it will be the same in humans.”

Dr. Rudel's findings were published online May 2007 in the journal Arteriosclerosis, Thrombosis, and Vascular Biology. The study involved deleting a gene in the mice that causes production of ACAT2, an enzyme that changes the molecular structure of cholesterol so that it can be transported to the body's cells.

"Regardless of the type of fatty acid in the diet, even trans-fat, no atherosclerosis occurs if the ACAT2 enzyme isn't present,” said Dr. Rudel. "Our research in animals tells us that ACAT2 is a potential treatment target to protect people against heart disease.”

Groups of female mice with and without the ACAT2 gene were fed six different diets enriched with one of these types of fat: fish oil, flax seed oil, polyunsaturated fat from vegetable oil, saturated fat, trans-monounsaturated fat, and cis-monounsaturated fat, such as in olive oil. Fish oil, flax seed oil, and polyunsaturated fats are considered "healthy” fats. Saturated fat--found in meats, milk, and cheeses, coconut oil, palm oil, and palm kernel oil--is considered a major cause of high cholesterol.

There are two types of monounsaturated fatty acids, "cis” and "trans,” which are named according to their shapes. Trans-fatty acids are formed when vegetable oil is treated to make it less likely to go rancid and are found in many baked goods, fried foods, and potato chips. Cis monounsaturated fat is naturally occurring and is especially high in canola and olive oil. Recently, the U.S. Food and Drug Administration has required that levels of trans-fats be listed on food labels.

After 20 weeks on the diets, the mice that had the active ACAT2 enzyme and were fed saturated fat and both types of monounsaturated fat had higher levels of cholesterol and more atherosclerosis than the mice that were fed polyunsaturated fats. All of the mice without the ACAT2 enzyme were protected against atherosclerosis, which is the buildup of fatty deposits in the blood vessels that can lead to heart attacks and strokes.

"Regardless of the diet fed, the mice without ACAT2 were protected from atherosclerosis,” said Dr. Rudel. Eliminating ACAT2 did not interfere with the normal processing of cholesterol. ACAT2 is one of three enzymes that can alter cholesterol into a form that can be more easily carried in blood. Studies in both mice and monkeys show that when cholesterol is changed by ACAT2, it is more likely to build up in blood vessel walls and cause atherosclerosis.

Dr. Rudel hopes to get funding to repeat the study in monkeys. "If it works in monkeys, it would be proof of concept that it could work in humans,” he said. He also hopes the research will lead to a drug that can suppress the enzyme's actions in humans. At present, there is an agent that can block ACAT2, but it must be injected so is not quite as practical as a drug. He is collaborating with a pharmaceutical company that is working to find a compound that could be taken orally.

Scientists already know that humans produce ACAT2 in the liver and that women have lower levels than men. Recent studies have demonstrated hat estrogen can lower ACAT2 production, which may in part explain why women are less likely than men to get heart disease during their estrogen-producing years. "All of these findings tell us that a potential treatment for protecting against heart disease is a compound that decreases ACAT2 activity,” said Dr. Rudel.


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