Lipoproteins and Heart Attacks Lipoproteins

Lipoproteins and Heart Attacks

Lipoproteins are cholesterol substances which have both beneficial and harmful effects on the body. HDL's, or high-density lipids, are used by the body to scour the blood vessels and clean them of LDL's, or low-density lipids, which can cause harm in the blood vessels.

LDL's can cause heart attacks in several ways. The newest research has shown that vulnerable plaque is composed largely of LDL's (Naghavi). Although the complete etiology is not known, it appears that an injury to a blood vessel causes the aggregation of platelets and white blood cells at the lesion on a blood vessel. This lesion normally occurs in the medial area -- the middle layer of the blood vessel which is composed mainly of smooth muscle cells. As white blood cells rush to the area, platelets begin their thrombocytic cascade to cover the lesion with a "thin cap," which protects the lesion from further injury. Part of the process of injury healing produces LDL's, which form the "fatty core" of the vulnerable plaque. As the plaque builds, a traumatic event can occur which breaks the surface of the lesion, releases LDL's and causes a thrombolytic cascade which ends in a "silent" heart attack. Such heart attacks can be fatal, and account for about 35% of all heart attacks. These are the myocardial infarctions (M.I.'s) which can occur in people who are otherwise healthy, demonstrating no symptoms of angina or other stress, but fall to a massive heart attack within a very short period of time.

LDL's are also a sign of the body's overproduction of cholesterol. The liver generally converts proteins, fats and especially starches and sugars to glucose in order to give energy to the cells in a so-called "glucose-insulin cycle." If the liver encounters more food materials than the body can use at the time, it converts the extra food into fat, which can then be stored in the liver, in the fat cells, and circulate in the blood. The extra circulating cholesterol, especially the LDL's, are a sign that either (1) the person is eating too much, (2) the person is not exercising enough to "burn" the food that he/she eats, or both.

A surplus of LDL's results in a build-up of plaque in the arteries around the body (not just the heart). They can coat the cardiac, peripheral vascular and brain arteries with relatively eccentric plaque, building up over a period of time to create a reduced blood flow.