Cholesterol is a necessary part of all membranes. However, many people have too much cholesterol circulating through their system. Because cholesterol is virtually insoluble in water or blood, circulating cholesterol is carried by a number of different transport proteins. These proteins are classed by their densities. The highest density protein (HDL) transports cholesterol to the liver, where it can be broken down and eliminated. Low density lipoprotein (LDL) transports cholesterol from the liver back to other tissues. HDL-bound cholesterol is considered "good" cholesterol because it's on its way out of the body. LDL-bound cholesterol is considered "bad" cholesterol because it's staying in circulation.
LDL−bound cholesterol is considered "bad" cholesterol because it's staying in circulation.
Diet or medication can help lower total or LDL-bound cholesterol, but raising HDL-bound cholesterol has proven more difficult. This is where synthetic HDL may come into play.
The researchers describe synthetic HDL as a cholesterol sponge, capable of soaking up large amounts of cholesterol. In the body, this will hopefully transport excess cholesterol to the liver and out of harm's way, bringing the cholesterol of those with high levels down into the normal range. This won't happen tomorrow; synthetic HDL hasn't yet been tested on cells or anything that could be remotely described as living. But it will be.
All cholesterol transporting proteins are lipoproteins: molecules composed both of protein and lipid (not the cholesterol they transport). In designing their molecule, the researchers started with a gold core, layered on two lipids and finally, a protein called APOA1, the main protein component of natural HDL. Gold makes an ideal scaffolding because its size and shape can be easily tailored, and it's also non-toxic.
Synthetic HDL was created through collaboration between Northwestern's Feinberg School of Medicine and its chemistry department. The project was led by Chad A. Mirkin, professor of chemistry, medicine, and materials science and engineering, and Shad Thaxton, assistant professor of urology.
An article detailing the research is scheduled to appear in a future issue of the Journal of the American Chemical Society; an early, online version was published January 9, 2009 by the ACS on their website.