High-density lipoprotein cholesterol, high-density lipoprotein particle size, and apolipoprotein A-I: significance for cardiovascular risk: the IDEAL and EPIC-Norfolk studies.

OBJECTIVES: This study was designed to assess the relationship of high-density-lipoprotein cholesterol (HDL-C), HDL particle size, and apolipoprotein A-I (apoA-I) with the occurrence of coronary artery disease (CAD), with a focus on the effect of very high values of these parameters.

BACKGROUND: High plasma levels of HDL-C and apoA-I are inversely related to the risk of CAD. However, recent data suggest that this relationship does not hold true for very high HDL-C levels, particularly when a preponderance of large HDL particles is observed.

METHODS: We conducted a post-hoc analysis of 2 prospective studies: the IDEAL (Incremental Decrease in End Points through Aggressive Lipid Lowering; n = 8,888) trial comparing the efficacy of high-dose to usual-dose statin treatment for the secondary prevention of cardiovascular events, and the EPIC (European Prospective Investigation into Cancer and Nutrition)-Norfolk case-control study, including apparently healthy individuals who did (cases, n = 858) or did not (control patients, n = 1,491) develop CAD during follow-up. In IDEAL, only HDL-C and apoA-I were available; in EPIC-Norfolk, nuclear magnetic resonance spectroscopy-determined HDL particle sizes were also available.

RESULTS: In the IDEAL study, higher HDL-C proved a significant major cardiac event risk factor following adjustment for age, gender, smoking, apoA-I, and apoB. A similar association was observed for HDL particle size in EPIC-Norfolk. Increased risk estimates were particularly present in the high ends of the distributions. In contrast, apoA-I remained negatively associated across the major part of its distribution in both studies.

CONCLUSIONS: When apoA-I and apoB are kept constant, HDL-C and HDL particle size may confer risk at very high values. This does not hold true for very high levels of apoA-I at fixed levels of HDL-C and apoB. These findings may have important consequences for assessment and treatment of CAD risk.