Should We Take High-Density Lipoprotein Cholesterol Levels at Face Value?

The inverse correlation between high-density lipoprotein (HDL) levels and cardiovascular disease has driven several investigators to target the increase in this lipoprotein to prevent atherosclerosis and its complications. However, many reports have demonstrated that the use of HDL cholesterol (HDL-C) levels as a means to prevent and treat atherosclerosis has mainly resulted in negative outcomes. These findings may help to increase our knowledge of HDL metabolism and its protective effect.

There is evidence that the mechanism by which HDL-C levels are raised has a great impact on cardiovascular outcomes. When the increase in HDL-C levels is secondary to greater synthesis, a strong beneficial effect in the prevention of cardiovascular diseases is observed. Even small increases in HDL-C levels induce a marked reduction in cardiovascular events; this has been observed during treatment with fibrates. In contrast, when the increase in HDL-C levels is secondary to a reduction in HDL catabolism, unexpectedly, the opposite effects are usually noted. Even dramatic increases in HDL-C levels are not associated with better cardiovascular outcomes. In fact, these increases have been related to a greater number of cardiovascular-related deaths. This became clear from the results of trials that tested inhibitors of cholesteryl ester transfer protein (CETP). We suggest that increases in reverse cholesterol transport are more important than HDL-C levels. Strong evidence is provided by individuals that express apolipoprotein (apo)A-I Milano. These individuals have extremely low HDL-C levels due to greater catabolism of the lipoprotein. However, reverse cholesterol transport is increased in these individuals and, as a consequence, they have a low incidence of cardiovascular diseases.

We reinforce that, in clinical practice, the currently recommended levels of HDL-C should still be a major target to be aimed for. However, in the research field, we emphasize the need to look for other methods to improve reverse cholesterol transport, irrespective of HDL-C levels.