Into The Heart originated July 2007, more information about High Density Lipoproteins Concentrations  will posted over the next few weeks.

HDL Removes Cholesterol from the Body

HDL is a protein enriched lipoprotein that has an important role in reverse cholesterol transport, or the transfer of cholesterol from extra-hepatic sites, including vascular macrophages to the liver for biliary excretion.

Although HDL and HDL-C are often used interchangeably, HDL refers to the liprotein particle and its properties. whereas, HDL-C refers to its measured level.

Several Important Proteins help Regulate the Process of Reverse Cholesterol Transport.

The initial step of cholesterol removal is mediated by the ATP binding protein ABCA1, which belongs to a family of proteins involved in the transfer of substrates across cell membranes.

The free cholesterol liberated from extra-hepatic cells is then moved to the HDL core following esterfication in plasma by lecithin cholesterol acyltransferase.

Apolipoprotein A-1 derived from both hepatic and intestinal sources, serves as a cofactor for this reaction.

Cholesterol carried by HDL may be removed from the circulation by transfer to lower-density lipoproteins in exchange for triglycerides.

This process is mediated by the cholesteryl ester transfer protein or by direct uptake by the liver or steroidgentic tissue via scavenger receptor B1.

Cholesterol entering the liver is converted to bile and bile acids and is ultimately excreted in the feces.

In general, higher HDL-concentrations, reflect a greater capacity to remove cholesterol and prevent blockages from developing in blood vessels.
HDL concentrations close to 60 mg/dL are optimal and protect the vascular wall.

HDL concentrations of 40 mg/dL are considered unhealthy because not enough cholesterol is being removed from the arteries.
Low HDL cholesterol is the most common lipoprotein abnormality in individuals with coronary heart disease and is predictive of subsequent coronary heart disease events, even when total cholesterol is within the desirable range.

Source:
Michael Miller MD
Director, Center for Preventive Cardiology
Dept of Medicine and Epidemiology
University of Maryland Medical Center, Baltimore.