HDL cholesterol’s carrying capacity lowers risk for atherosclerosis

The removing ability of high-density lipoprotein (HDL) cholesterol may be the secret behind apparently “good” cholesterol, according to a study published Dec. 18 in the New England Journal of Medicine.

It seems like a chicken and egg sort of question: Dallas Heart Study researchers were looking to understand if levels of high density lipoprotein (HDL) itself or its ability to ensure that cholesterol goes to the liver for disposal were what reduced a patient’s risk for cardiovascular disease.

To study it at a population level, Anand Rohatgi, MD, at the University of Texas Southwestern Medical Center in Dallas tapped the Dallas Heart Study cohort. They were able to obtain blood samples from 2,416 participants. A fluorescence-labeled agent was used to determine cholesterol efflux capacity -– its ability to carry cholesterol away. Follow-up occurred through a median of 9.4 years.

They found that increasing quartiles of cholesterol efflux capacity were only correlated with lipid levels, when examining traditional cardiovascular risk factors. These quartiles were defined by percentage of transported, marked material noted in the blood sample. The same was not true for actual HDL, where traditional risk factors, alcohol intake, and exercise activity explained a 35 percent variance in level.

Rohatgi et al noted that while HDL had an inverse association with atherosclerotic cardiovascular disease before adjustment, the correlation to traditional risk factors diminished its significance. They also found that HDL particle concentration was associated with an adjusted risk of 0.53 following attenuation for cardiovascular risk factors and HDL cholesterol levels.

A graded association was seen between risk for developing atherosclerotic cardiovascular disease and efflux capacity, as much as 0.44 from the fourth quartile to the first before adjustment and 0.33 after adjusting for traditional risks, HDL cholesterol levels and HDL particle concentration. In an estimated 10-year analysis where patients were stratified by cardiovascular risk, development of atherosclerosis in patients in the lowest risk efflux cohort was 0.25 and in the highest risk cohort, 0.36.

As efflux did not appear to relate to the amount of HDL cholesterol, nor to other traditional risk factors, Rohatgi et al suggested that the biological processes involved in HDL’s ability to carry cholesterol through the blood stream are independent of adiposity, insulin resistance or level of HDL cholesterol in the blood. However, they could not be definitive about why that would be nor whether the means to measure efflux used were part of what they were seeing, as currently this is a relatively new biomarker to be explored.

Still, Rohatgi et al suggested consideration of cholesterol efflux capacity in determining patient risk for atherosclerosis.