Using a technique that enables them to study both early and advanced stages of arterial plaque buildup in the same mice, researchers at
Cedars-Sinai Medical Center found that an
antioxidant compound found in green tea leaves does not clear established plaque but does inhibit the development of new deposits.
Several components of green tea leaves are known to have natural properties that counteract the harmful effects of oxidation in the blood. In fact, the principal and most powerful of these catechins or flavonoids, EGCG (epigallocatechin-3-gallate), has been shown to provide some protection against the development of inflammation, tumors and the new blood vessels that support tumor growth.
Because of the antioxidant properties of the catechins in its leaves, tea also has been seen as a potential dietary intervention for cardiovascular diseases. Oxidation, which damages the inner surfaces of arteries and encourages the formation of plaque deposits, is believed to be one factor in the development of atherosclerosis.
In fact, antioxidants have been shown to protect against plaque formation in animal studies, but results in human trials have been disappointing. This has led researchers to wonder if failure in clinical trials might be due to the short duration of treatment, the use of the “wrong” antioxidant, or other factors such as the timing of the introduction of antioxidants. Theoretically, antioxidant therapy might be effective in human trials if it is started before atherosclerosis is established.
“Most animal experiments evaluating the effects of antioxidants are started when the animals are young, while randomized clinical trials typically enroll adult patients with varying stages of plaques,” said Kuang-Yuh Chyu, MD, PhD, cardiologist, first author of the article. “This discrepancy supports speculation that antioxidant treatment affects early but not later stages of plaque development.”
To test the theory, researchers at Cedars-Sinai’s Atherosclerosis Research Center studied the effects of a highly purified form of EGCG, provided for the study by Lipton® Tea, on two areas of blood vessels in mice that are genetically predisposed to rapid development of plaque. The mice were fed a high-cholesterol diet and at the age of 28 weeks the right common carotid artery was injured to induce new plaque formation. This enabled the researchers to determine the effect of EGCG on new plaque at the site of the injury as well as on established plaque in the aorta.
EGCG was injected once a day, five days a week after carotid artery injury, and animals were sacrificed three days, 21 days and 42 days after injury. Atherosclerotic development and benefits of treatment were measured in comparison to mice in a control group. In the mice that did not receive EGCG, plaque continued to build up at the carotid artery site. In treated mice, however, administration of EGCG significantly reduced new plaque formation. In fact, there was little difference in the size of the plaque after 42 days compared to 21 days. But treatment had no effect on established plaque.