Some HDL, or "good" cholesterol, may not protect against heart disease

A new study by Harvard School of Public Health (HSPH) researchers has found that a subclass of high-density lipoprotein (HDL) cholesterol, the so-called ''good'' cholesterol, may not protect against coronary heart disease (CHD) and in fact may be harmful.

This is the first study to show that a small protein, apolipoprotein C-III (apoC-III), that sometimes resides on the surface of HDL cholesterol may increase the risk of heart disease and that HDL cholesterol without this protein may be especially heart protective.

The study was published online in the Journal of the American Heart Association.

''This finding, if confirmed in ongoing studies, could lead to better evaluation of risk of heart disease in individuals and to more precise targeting of treatments to raise the protective HDL or lower the unfavorable HDL with apoC-III,'' said Frank Sacks, professor of cardiovascular disease prevention at HSPH and senior author of the study.

A high level of HDL cholesterol is strongly predictive of a low incidence of coronary heart disease (CHD). But trials of drugs that increase HDL cholesterol have not consistently shown decreases in CHD, leading to the hypothesis that HDL cholesterol may contain both protective and non-protective components.

ApoC-III, a proinflammatory protein, resides on the surface of some lipoproteins - both HDL and low-density lipoproteins, or LDL (''bad'') cholesterol. The researchers, led by Sacks and Majken Jensen, research associate in the Department of Nutrition at HSPH, examined whether the existence or absence of apoC-III on HDL cholesterol affected the ''good'' cholesterol's heart-protective qualities, and whether its existence could differentiate HDL cholesterol into two subclasses-those which protect against the risk of future heart disease and those which do not.