Where next with HDL assays?

Progressive, Qualitative, and Quantitative Alterations in HDL Lipidome from Healthy Subjects to Patients with Prediabetes and Type 2 Diabetes

Prediabetes is a clinically silent, insulin-resistant state with increased risk for the development of type 2 diabetes (T2D) and cardiovascular disease (CVD). Since glucose homeostasis and lipid metabolism are highly intersected and interrelated, an in-depth characterization of qualitative and quantitative abnormalities in lipoproteins could unravel the metabolic pathways underlying the progression of prediabetes to T2D and also the proneness of these patients to developing premature atherosclerosis. We investigated the HDL lipidome in 40 patients with prediabetes and compared it to that of 40 normoglycemic individuals and 40 patients with established T2D using Nuclear Magnetic Resonance (NMR) spectroscopy. Patients with prediabetes presented significant qualitative and quantitative alterations, potentially atherogenic, in HDL lipidome compared to normoglycemic characterized by higher percentages of free cholesterol and triglycerides, whereas phospholipids were lower. Glycerophospholipids and ether glycerolipids were significantly lower in prediabetic compared to normoglycemic individuals, whereas sphingolipids were significantly higher. In prediabetes, lipids were esterified with saturated rather than unsaturated fatty acids. These changes are qualitatively similar, but quantitatively milder, than those found in patients with T2D. We conclude that the detailed characterization of the HDL lipid profile bears a potential to identify patients with subtle (but still proatherogenic) abnormalities who are at high risk for development of T2D and CVD.

Early Signs of Atherogenic Features in the HDL Lipidomes of Normolipidemic Patients Newly Diagnosed with Type 2 Diabetes

Cardiovascular disease (CVD) is the major cause of death in patients with type-2 diabetes mellitus (T2DM), although the factors that accelerate atherosclerosis in these patients are poorly understood. The identification of the altered quantity and quality of lipoproteins, closely related to atherogenesis, is limited in routine to a pattern of high triglycerides and low HDL-cholesterol (HDL-C) and in research as dysfunctional HDLs. We used the emerging NMR-based lipidomic technology to investigate compositional features of the HDLs of healthy individuals with normal coronary arteries, drug-naïve; recently diagnosed T2DM patients with normal coronary arteries; and patients with recent acute coronary syndrome. Patients with T2DM and normal serum lipid profiles even at diagnosis presented significant lipid alterations in HDL, characterized by higher triglycerides, lysophosphatidylcholine and saturated fatty acids; and lower cholesterol, phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, plasmalogens and polyunsaturated fatty acids, an atherogenic pattern that may be involved in the pathogenesis of atherosclerosis. These changes are qualitatively similar to those found, more profoundly, in normolipidemic patients with established Coronary Heart Disease (CHD). We also conclude that NMR-based lipidomics offer a novel holistic exploratory approach for identifying and quantifying lipid species in biological matrixes in physiological processes and disease states or in disease biomarker discovery.

High-density lipoprotein: our elusive friend

PURPOSE OF REVIEW

Despite advances in the research on HDL composition (lipidomics and proteomics) and functions (cholesterol efflux and antioxidative capacities), the relationship between HDL compositional and functional properties is not fully understood. We have reviewed the recent literature on this topic and pointed out the difficulties which limit our understanding of HDL's role in cardiovascular disease (CVD).

RECENT FINDINGS

Though current findings strongly support that HDL has a significant role in CVD, the underlying mechanisms by which HDL mitigates CVD risk are not clear. This review focuses on studies that investigate the cell-cholesterol efflux capacity and the proteomic and lipidomic characterization of HDL and its subfractions especially those that analyzed the relationship between HDL composition and functions.

SUMMARY

Recent studies on HDL composition and HDL functions have greatly contributed to our understanding of HDL's role in CVD. A major problem in HDL research is the lack of standardization of both the HDL isolation and HDL functionality methods. Data generated by different methods often produce discordant results on the particle number, size, lipid and protein composition, and the various functions of HDL.

From HDL-cholesterol to HDL-function: cholesterol efflux capacity determinants

PURPOSE OF REVIEW

The validity of HDL-cholesterol (HDL-C) elevation as a therapeutic target has been questioned, in comparison to enhancing HDL functionality. Cholesterol efflux capacity (CEC) is an in-vitro assay that measures the ability of an individual's HDL to promote cholesterol efflux from cholesterol donor cells such as macrophages. CEC of HDL is a predictor of cardiovascular risk independent of HDL-C levels. However, molecular determinants of CEC and the effects of diseases and therapeutic interventions on CEC have not been completely defined.

RECENT FINDINGS

We review here recent findings on elevated HDL-C and disease risk, as well as determinants of CEC, from genetics and proteomics to pathophysiology and therapeutic interventions that contribute to our understanding of CEC as a biomarker of HDL functionality.

SUMMARY

Elevated HDL-C levels are not always protective against cardiovascular disease and mortality. CEC is a heritable trait, and genetic polymorphisms in genes involved in HDL and triglycerides metabolism are associated with CEC. Multiple HDL proteins correlate positively with CEC levels and inversely with noncalcified plaque burden. Differences in CEC assays that make comparisons between studies difficult are also emphasized. CEC should be measured in clinical trials of lipid-modifying and anti-inflammatory therapies to determine whether increases are cardioprotective.