Good Cholesterol, Bad Puzzle

So far, the cholesterol story has been a relatively simple one in which 8220;bad8221; low-density lipoprotein LDL cholesterol formed plaques that eventually blocked arteries, while 8220;good8221; high-density lipoprotein HDL cholesterol worked to carry away those deposits, explained Dr Jay Heinecke, a professor of medicine at the University of Washington, Seattle.

8220;But in the last few years, there has been growing evidence that HDL does other things,8221; he said. 8220;In particular, it may be inhibiting inflammation.8221;

Inflammation is the major villain in the new picture. Arteries are not only blocked because of the gradual growth of plaque. Instead, there comes a moment when plaque ruptures, causing a clot to form and block blood flow, Heinecke said. Proteins called proteases play a major role in these ruptures.

8220;What we found in HDL is a whole series of proteins that inhibit proteases,8221; Heinecke said, describing what he called the most detailed analysis to date of HDL8217;s protein composition. 8220;So, part of HDL8217;s protective effect is to prevent rupture.8221;

The Seattle analysis also found a lot of previously unrecognised HDL proteins, including 22 that play roles in cholesterol metabolism.

One finding of particular significance is that HDL protein composition can be different in people who have heart disease and those who do not, meaning that some of the supposedly 8220;good8221; HDL proteins are really bad.

8220;With LDL cholesterol it8217;s simple, the lower the better,8221; Heinecke said. 8220;With HDL, it8217;s much more complicated. The protein composition of people with and without heart disease is different.8221;

So, measuring blood levels of LDL and HDL cholesterol is not as predictive of cardiac risk, as has been assumed, Heinecke stressed. 8220;Protein composition in HDL cholesterol may be a better handle on whether someone is at risk,8221; he added.

Animal studies have found 8220;dysfunctional8221; HDL cholesterol, which works against coronary health, Heinecke said. 8220;It is proposed that the same thing is going on in humans,8221; he noted.

The finding of dysfunctional HDL proteins helps explain why a major pharmaceutical company ended work on an HDL-boosting drug when it was found to actually increase deaths and heart problems in a human trial.

A better understanding of the protein components of HDL could lead to more accurate tests for heart disease, Heinecke said. 8220;Most people who have heart attacks have normal levels of HDL, so the composition of the HDL may tell who is vulnerable,8221; he said. Future cardiac therapy may include LDL-lowering statins and new drugs aimed at the damaging components of HDL cholesterol, Heinecke said.

LOWDOWN ON LIPOPROTEINS

LDL bad Cholesterol

When too much Low-Density Lipoprotein circulates in blood, it accumulates in the inner walls of the arteries that feed the heart and brain. Together with other substances, it can form plaque, a thick, hard deposit that narrows the arteries and makes them less flexible. In case of a clot formation in these arteries, a heart attack or stroke can result.

HDL good Cholesterol

About one-fourth to one-third of blood cholesterol is carried by High-Density Lipoprotein. High levels of HDL seem to protect against heart attack, and low levels increase the risk of heart disease.

How to increase HDL

8226; Life style modification: Regular aerobic exercise, loss of excess weight and cessation of smoking

8226; Moderate alcohol consumption such as one drink a day also raises HDL cholesterol. When life style modifications are insufficient, medications are used. Some experts think that HDL tends to carry cholesterol away from the arteries and back to the liver, where it8217;s passed from the body. It is also believed that HDL removes excess cholesterol from arterial plaque, thus slowing its buildup.

8226; Even small increases in HDL cholesterol reduce the frequency of heart attacks. For each 1 mg/dl increase in HDL cholesterol there is a 2 to 4 reduction in the risk of coronary heart disease.