Sep 18 (HeartCenterOnline) - Researchers have identified a substance within the proteins that carry cholesterol through the blood that may encourage the accumulation of body fat. According to a study published in the September 11, 2001 issue of Circulation, a substance called apolipoprotein A-II (apoA-II) not only promotes the accumulation of fat around the abdomen, but also may keep the body from processing large VLDLs (very-low density lipoproteins), a dangerous form of cholesterol.

Apolipoproteins are the nonfat portions of lipoproteins (proteins that carry cholesterol and triglycerides through the blood). They are classified by their functions into five groups: B100, A1, A2, B and E. Some also have subgroups. Apolipoproteins attach to specific enzymes found on cell membranes and transport lipoproteins to their sites of metabolism.

According to the report in Circulation, apoA-II is a major structural protein of HDLs (high-density lipoproteins) found in plasma, the liquid part of blood in which blood cells are suspended. However, little is actually known about the function of apoA-II. Researchers did not speculate on the implications of these findings.

Cholesterol is a fat-like substance (lipid). It is either produced in the liver or consumed by eating animal products such as meat, eggs or dairy products. The body uses cholesterol to assist in the manufacture of hormones or vitamin D, to build cell walls and to produce bile, which breaks down other fats. It is carried through the bloodstream by lipoproteins.

Lipoproteins are proteins that wrap around both cholesterol and other fatty materials and transport them through the bloodstream. High-density lipoproteins (HDLs) move easily through the blood and are actually beneficial to the body, earning the nickname "good cholesterol." They are stable and do not stick to artery walls. They help to prevent heart disease by carrying cholesterol away from the arteries and back to the liver, where the process of their removal from the body begins.

Low-density lipoproteins (LDLs) contain more fat and less protein than HDLs, are unstable; and tend to fall apart. Rather than being removed from the body by the liver, they stick to artery walls and contribute to plaque build-up. This can eventually lead to hardened arteries (atherosclerosis) or coronary artery disease. Therefore, high levels of LDLs are strongly associated with increased risk for heart disease.

Cholesterol may travel in very low-density lipoproteins (VLDLs) or another type of lipoprotein called chylomicrons (which are rich in triglycerides). VLDLs are considered to be the most dangerous form of lipoprotein. They carry the least amount of protein and the most amount of fat. They also stick to arterial walls and contribute to plaque build- up.

More information can be found by visiting the following HeartCenterOnline topic centers and encyclopedia articles:
Cholesterol & Your Health
The Cholesterol Center
The Weight & Obesity Center

Other news articles of interest can be found at the following links:
Racial differences in LDL cholesterol size (Jul 13, 2001)
Sleep apnea linked to Alzheimer's gene (Jun 13, 2001)
Study finds genetic link to high cholesterol (Apr 13, 2001)
Gene influences alcohol's effect on cholesterol (Apr 6, 2001)
Gene variant linked to higher heart disease risk (Jan 29, 2001)

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