High-Density Lipoprotein Dysfunction and Atherosclerotic Cardiovascular Disease: From Quantity to Quality.

High-density lipoprotein cholesterol (HDL-C) has long been inversely associated with atherosclerotic cardiovascular disease risk, but pharmacologic efforts to raise HDL-C have consistently failed to reduce cardiovascular events. This has shifted focus from HDL quantity to quality, emphasizing functional properties such as cholesterol efflux, antioxidative capacity, and anti-inflammatory activity. Dysfunctional HDL, often modified by oxidative and inflammatory processes mediated by myeloperoxidase, loses its ability to promote reverse cholesterol transport, support endothelial function, and suppress vascular inflammation. Advanced proteomic and lipidomic studies have revealed compositional remodeling that underlies HDL's functional heterogeneity and disease-specific signatures. Functional measures like cholesterol efflux capacity and cell-free HDL assays correlate more strongly with cardiovascular outcomes than static HDL-C levels, providing a more accurate index of vascular protection. Despite the promising therapies such as cholesterol ester transfer protein (CETP) inhibitors, niacin, and apolipoprotein A-I infusions (reconstituted high-density lipoprotein (CSL112)), none have yet demonstrated definitive event reduction. Future directions include standardizing HDL functional assays, prioritizing quality over concentration, and integrating HDL-targeted and metabolic therapies, including glucagon-like peptide-1 (GLP-1) receptor agonists and sodium-glucose transport 2 (SGLT2) inhibitors, to restore HDL's protective phenotype and redefine preventive cardiology.