Why high levels of "good cholesterol" might not be just that good for you

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One 67-year-old lady was once admitted with abnormally high levels of HDL, or high-density lipoprotein, the type which is considered protective against cardiovascular disease, but her arteries still had plaque potentially dangerous to her health. This paradoxical case has driven a scientific team which has decided to prove how high levels of HDL are not always a good signal for the cardiovascular health of an individual.

Actually, the whole concept of HDL may be even an opposite as the cholesterol system might be unable to collect all the fatty particles from our circulation, therefore leading to the development of plaque.

The normal role of HDL is to transfer the cholesterol from the arteries back to the liver, eliminating cholesterol from the body. This should somehow prevent the plaque development and increase the overall cardiovascular health, but drugs which increase HDL have simply flopped in the clinical trials while people who are genetically predisposed to high HDL levels haven’t shown any significant advantage when it comes to cardiovascular diseases.

All in all, a biochemist at the University of Washington, Seattle, Jay Heinecke, states that nothing is ever simple with HDL, as he has been studying it for years.

A recent issue in Science journal, has shown a study conducted by Daniel Rader, a lipidologist and geneticist at the University of Pennsylvania, and his team who have suggested that the HDL levels are not as important as the efficiency of cholesterol transfer from arteries to the liver.

His inspiration was a mouse model which was developed about 20 years ago by Monty Krieger, who has demonstrated that deletion of SCARB1 gene in mice increases the HDL levels but clogs the arteries with cholesterol. The cardiovascular issue was related to the disabled transportation of cholesterol of this group of mice.

SCARB1 gene is credited for producing a protein known as SR-B1, which eventually enables the process of cholesterol deposition. Mice without the SR-B1 protein have high levels of HDL with enormous amount of cholesterol, but insignificant efficiency to transport it to liver. Rader supposed that the same might be with humans, so he conducted a research which included a gene sequencing in 852 people with high levels of HDL.

A 67-year-old woman didn’t have the functioning SCARB1 gene copies, but showed enormously high HDL levels with plaque developed on the arteries. Eighteen other people had only one functional SCARB1 copy, instead of regular two, and most of these people had high HDL levels. A following detailed study of the selected nine people, including the aforementioned lady, has suggested that the abundant HDL wasn’t able to efficiently transport the cholesterol to the liver.

Even though HDL shows a good effect in vitro, the efficiency of HDL depends vastly on other genetic predispositions for the complete cholesterol transport. The further studies will surely show the role of HDL in cholesterol transport, as well as the other systems which are credited for the lipid transportation. However, high levels of HDL don’t necessarily mean that your arteries will be clean. Not at least for the time to come.

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