It appears that in some cases, high-density lipoprotein (HDL) cholesterol, the so-called "good" cholesterol, does not protect against heart diseases, and may even be harmful. A new study suggests a subclass of HDL that carries a particular protein is bad for the heart. Previous studies have shown that high levels of HDL cholesterol are strongly linked to low risk of heart disease. Now, researchers have found that when the surface of HDL cholesterol bears a small protein called apolipoprotein C-III (apoC-III), there is an increase in the risk of heart disease, and when it is absent, HDL cholesterol is especially heart protective. ApoC-III is a proinflammatory protein that resides on the surface of some lipoproteins, including HDL and LDL (low-density lipoprotein, or "bad") cholesterol.
Researchers wanted to see whether apoC-III made a difference to the heart-protective qualities of HDL cholesterol: they wondered if there were two subclasses of HDL cholesterol, one that protected against heart disease and one that did not, depending on the presence of apoC-III. They compared the blood samples in several different ways: they looked at total HDL, HDL with apoC-III, and HDL without apoC-III, and assessed these concentrations against coronary heart disease (CHD) risk. They also adjusted the results so as to eliminate, as far as possible, effects from other factors that impact CHD risk, such as age, smoking status, diet and lifestyle.
The results showed that after taking these potential influencers into account, two subclasses of HDL cholesterol appear to have opposite effects on risk of CHD in men and women. The researchers suggest rather than simply measuring total HDL, it might be better to measure HDL with and without apoC-III to provide a more reliable gauge of heart disease risk, or the protective capacity of HDL.
