April 15, 2005

Supplement’s ability to guard arteries studied

Featured Image

James May, M.D., left, and Anup Sabharwal, M.D., evaluate wave pulse forms by applanation tonography in a subject with hypercholesterolemia.
photo by Dana Johnson

Supplement’s ability to guard arteries studied

Vanderbilt University Medical Center researchers are conducting a study to examine whether alpha-lipoic acid, a commonly available over-the-counter dietary supplement consumed by many as an antioxidant, may have the ability to prevent high levels of cholesterol from damaging arteries.

“Most cholesterol-lowering prescription drugs are very effective at lowering cholesterol and preventing coronary heart disease,” said James M. May, M.D., professor of Medicine in the Division of Diabetes and Endocrinology. “However, they do not prevent all disease, and may cost as much as $100 a month.” The search is under way for other types of safe, effective, and lower-cost therapies to lessen damage to arteries due to accumulation of LDL cholesterol, otherwise known as “bad” cholesterol.

Alpha-lipoic acid is a relatively new antioxidant supplement. Scientists first discovered it in the 1950s, with the compound being recognized as an antioxidant in 1988. While alpha-lipoic acid has been the subject of research worldwide, there is still much to be learned about its actions.

Many health food stores and Internet sites that sell dietary supplements market alpha-lipoic acid as a treatment for age-related diseases such as heart disease, stroke, diabetes and cataracts. In fact, May says alpha-lipoic acid is commonly taken in many European countries as a treatment for a variety of aliments.

“Lipoic acid has been used for years in Germany as a treatment for pain associated with the neuropathy of diabetes,” May said. “At least in two clinical trials lipoic acid seems beneficial for this purpose. This is thought to be associated with its antioxidant properties, although this isn't known for sure.”

Further, a recently published study of patients with diabetes found that alpha-lipoic acid increased the ability of blood vessels to release nitric oxide and to relax blood vessels, which suggests that it can reverse the earliest sign of underlying vascular disease.

May and research collaborator Anup Sabharwal, M.D., clinical fellow in the Division of Diabetes, Endocrinology and Metabolism, are studying alpha-lipoic acid at two levels: in tissue culture cells and in humans. In the tissue culture studies, they are testing the ability of alpha-lipoic acid to prevent damage from oxidized lipids in cultured endothelial cells. These are cells that line all blood vessel walls, and are the first site of damage in atherosclerosis. The oxidized lipid used to stress the cells is oxidized human LDL, which is thought to play a major role in causing plaque buildup in human coronary disease. Results thus far show that alpha-lipoic acid clearly works as an antioxidant preventing damage to these cells, just as vitamin C would protect them from attack. If alpha-lipoic acid can protect these cells against such oxidant stress, then it may also do so in humans.

In the second phase of their research, May and Sabharwal are undertaking a study of people with high levels of cholesterol who may have some vascular damage that has not yet become apparent. The plan, according to May, “is to test the theory that alpha-lipoic acid supplements can promote a healthy vascular endothelium and limit inflammatory damage from high cholesterol levels.”

For the study, May and Sabharwal are seeking individuals ages 50-75 years of age who:

• Have an LDL cholesterol level of 160 mg/dl or greater (roughly a total cholesterol of 260 mg/dl),

• Aren't taking any cholesterol-lowering medications, and

• Don't have diagnosed coronary artery disease, or any other related diseases that would interfere with the ability to carefully monitor the actions of alpha-lipoic acid on the blood vessels.

Other exclusion criteria for the study include heart, kidney or liver disease, and other conditions known to cause oxidant stress such as smoking or diabetes mellitus. Women who can become pregnant, or who are lactating, are also excluded.

“We want to isolate a subset of the population who have high cholesterol, but do not have other risk factors that would require them to be on an oral cholesterol medication,” Sabharwal said. “This population of individuals would allow us the necessary 'window' for participation in the study, and to see whether lipoic acid can improve vascular health in hypercholesterolemic patients.”

The study includes four weeks of therapy with alpha-lipoic acid, a four-week period where patients receive a placebo, and a six-week “washout” period in between so participant's bodies can clear the compound between monitoring periods. The design of the study allows for the person to be his/her own control by receiving both alpha-lipoic acid and placebo.

May and Sabharwal will measure markers of inflammation, along with cholesterol levels both before and after receiving the compound and placebo. Measurements of C-reactive protein (CRP), PAI-1, and F-2 isoprostanes will be taken to further gauge the effects of alpha-lipoic acid. Also, the ability of the blood vessels to relax will be assessed using a new non-invasive technique that measures pressure changes in an artery in the arm. “This has proven to be a very sensitive measure of the presence of early, reversible, vascular changes due to high cholesterol,” says May.

For more information about enrollment in this study, please contact Anup Sabharwal, M.D., in the Division of Diabetes, Endocrinology and Metabolism at 936-1727.