Studies show apo A-I Milano gene transfer and antibody therapy cut atherosclerotic plaque

Presentations: American Heart Association Scientific Sessions 2005

Cardiology researchers at Cedars-Sinai Medical Center have found that a single injection of a harmless virus engineered to carry a beneficial, mutant gene enabled animals to manufacture their own supply of the gene’s protein product that protects against plaque buildup in blood vessels. As a result, the amount of plaque was significantly reduced, as was an immune reaction that can lead to plaque buildup and rupture, which can cause a blocked artery and heart attack or stroke.

The researchers will present their findings from this and other studies at the American Heart Association Scientific Sessions 2005 Nov. 13 through 16 in Dallas. They are pursuing a variety of approaches to interrupt the complex processes leading to plaque formation and rupture, seeking new ways to treat and even prevent atherosclerosis.

Apolipoprotein A-I (apo A-I) is a protein that becomes part of HDL, or “good” cholesterol. About 25 years ago, a family in northern Italy was found by Italian researchers to have a mutation in the gene responsible for making the protein. The mutant form (apo A-I Milano) appeared to protect its carriers from cardiovascular disease. In 1994, Cedars-Sinai researchers led by Prediman K. Shah, M.D., director of the Division of Cardiology and the Atherosclerosis Research Center, showed for the first time that intravenous injection of a genetically engineered form of the protein markedly reduced arterial plaque buildup in animals fed a high cholesterol diet. A series of subsequent studies in genetically engineered mice conducted in Shah’s laboratory confirmed the potent effects of apo A-I Milano protein on prevention and reversal of plaque build-up.

Based on the results of Shah’s studies, a clinical trial was conducted in humans with similar results. After five weeks of once-a-week injections, apo A-I Milano significantly shrank plaque in coronary arteries. The protein appeared to actually remove bad cholesterol, even from sites on arteries where plaque had accumulated.

“The initial studies and treatments were based on injection of the apo A-I Milano protein,” said Shah. “Now we are using not the protein, but the gene itself. We are putting the gene inside an innocuous virus and injecting the virus so that the body can produce its own supply of apo A-I Milano. One single injection of the gene, carried by the virus, markedly reduces plaque buildup in mice. Advantages of this approach are that we would not need to produce the protein in the laboratory and there would be no need for repeated injections, as there is with the protein. With the animal studies confirming the effectiveness of the gene therapy approach, it may be possible that human trials could begin within several years.”

The gene therapy also modulated an immune response that contributes to plaque buildup and rupture. When LDL (bad cholesterol) remains in the bloodstream, it becomes oxidized, which causes the release of a variety of chemicals that damage the blood vessel. In its attempt to repair the injury, the body floods the area with immune system cells called macrophages, which, along with LDL, infiltrate the blood vessel wall.

The result of this injury-repair cycle is the accumulation of plaque – lipids and macrophages covered by a fibrous cap. Plaques with a large lipid core, many inflammatory cells and a thin cap are especially vulnerable to rupture. If a plaque deposit ruptures, debris can block the flow of blood, but the bloodstream also can be blocked by the formation of a blood clot – the immune system’s attempt to heal the rupture.

With a growing understanding of the inflammatory processes involved in the development and threat of “vulnerable” plaque, researchers are looking for ways to limit the local immune response, and in animals receiving the apo A-I Milano gene, macrophage immunoreactivity was reduced by 36 percent and 54 percent, compared to two control groups.

A related study to be presented at the AHA meetings confirmed that transfer of the apo A-I Milano gene is more effective than transfer of the normal apo A-I gene in reducing atherosclerosis and plaque inflammation.

Cedars-Sinai researchers, collaborating with researchers from University of Lund in Sweden, will also describe an immunization technique in which antibodies that specifically target oxidized LDL was injected. An earlier study found that the antibody therapy could prevent plaque buildup, but this work documented that pre-existing plaque could be reduced by up to 50 percent in the animal model.

“The present study suggests that antibody treatment has the ability to rapidly and significantly reduce the extent of already present, advanced atherosclerotic lesions,” according to the research team. “Positive immunization with antibodies directed against oxidized LDL isotopes might constitute a future fast-acting therapy for patients at high risk for acute cardiovascular events.”