Torcetrapib and atherosclerosis: what happened and where do we go from here?

Dysfunctional High-Density Lipoproteins in Type 2 Diabetes Mellitus: Molecular Mechanisms and Therapeutic Implications

High density lipoproteins (HDLs) are commonly known for their anti-atherogenic properties that include functions such as the promotion of cholesterol efflux and reverse cholesterol transport, as well as antioxidant and anti-inflammatory activities. However, because of some chronic inflammatory diseases, such as type 2 diabetes mellitus (T2DM), significant changes occur in HDLs in terms of both structure and composition. These alterations lead to the loss of HDLs' physiological functions, to transformation into dysfunctional lipoproteins, and to increased risk of cardiovascular disease (CVD). In this review, we describe the main HDL structural/functional alterations observed in T2DM and the molecular mechanisms involved in these T2DM-derived modifications. Finally, the main available therapeutic interventions targeting HDL in diabetes are discussed.

The Therapeutic Role of Niacin in Dyslipidemia Management

There is abundant epidemiologic evidence to support the independent, inverse relationship between low levels of high-density lipoprotein cholesterol (HDL-C) and incident cardiovascular (CV) risk, the clinical importance of which is underscored by the high prevalence of low HDL-C in populations with coronary heart disease (CHD), with or without elevated levels of low-density lipoprotein cholesterol (LDL-C). The National Cholesterol Education Program recommended that optimal treatment for high-risk patients includes both lowering LDL-C and non-HDL-C to risk stratified levels and raising HDL-C when it is <40 mg/dL, although no target level for the latter lipoprotein was suggested. Niacin is the most powerful agent currently available for raising low levels of HDL-C. It also induces significant reductions in triglycerides, lipoprotein(a), and LDL-C levels while also favorably altering LDL particle size and number. In the Coronary Drug Project, niacin treatment was associated with significant reductions in CV events and long-term mortality, similar to the reductions seen in the statin monotherapy trials. In combination trials, niacin plus a statin or bile acid sequestrant produces additive reductions in CHD morbidity and mortality and promotes regression of coronary atherosclerosis. Recently, 2 clinical outcome trials (Atherothrombosis Intervention in Metabolic Syndrome With Low HDL/High Triglycerides and Impact on Global Health Outcomes [AIM-HIGH] and Second Heart Protection Study [HPS-2 THRIVE]) failed to show a reduction in CV events in patients treated to optimally low levels of LDL-C. Despite favorable effects on HDL-C and triglycerides, these studies did not demonstrate incremental clinical benefit with niacin when added to simvastatin, although notable limitations were identified in each of these trials. Thus, there is insufficient evidence from clinical trials to recommend HDL-targeted therapy for additional event reduction at the present time. However, niacin should continue to be used as an adjuvant therapy for reducing atherogenic lipoprotein burden in patients who have not reached their risk stratified LDL-C and non-HDL-C targets.

Discovery of substituted biphenyl oxazolidinone inhibitors of cholesteryl ester transfer protein

Recently, there has been a strong interest in the ability to increase levels of high density lipoprotein-cholesterol (HDL-C). This interest stems from the hypothesis that such an elevation in HDL-C will decrease the likelihood of cardiovascular disease. Inhibition of cholesteryl ester transfer protein (CETP) has been shown to elevate HDL-C levels in human subjects. This letter describes the discovery of a novel and potent (<100 nM IC50 for the inhibition of CE transfer) CETP inhibitor scaffold containing an oxazolidinone core.

Novel therapies for increasing serum levels of HDL

The protectiveness of elevated HDL-C against CHD and its long-term sequelae is a subject of intense investigation throughout the world. HDL has the capacity to modulate a large number of atherogenic mechanisms, such as inflammation, oxidation, thrombosis, and cell proliferation. Among lipoproteins, HDL is also unique, in that it promotes the mobilization and clearance of excess lipid via the series of reactions collectively termed "reverse cholesterol transport." Numerous therapeutic agents are being developed in an attempt to modulate serum levels of HDL-C as well as its functionality. This article discusses the development of newer treatments targeted at raising HDL-C and HDL particle numbers to reduce residual risk in patients at risk for CHD.

High-density lipoprotein metabolism: potential therapeutic targets

It is well recognized that the lowering of low-density lipoprotein (LDL) cholesterol can substantially reduce coronary artery disease (CAD)-related morbidity and mortality. The prevention and management of CAD has chiefly focused on 1 component of the lipid profile: the reduction of LDL cholesterol. Yet, the majority of patients in both the primary and secondary prevention settings continue to experience significant residual risk for acute cardiovascular events even when their LDL cholesterol is lowered aggressively with combinations of lifestyle modification and pharmacologic intervention. As a result, there is increased focus on targeting and treating low serum levels of high-density lipoprotein (HDL) cholesterol in an effort to further reduce risk for cardiovascular events, including myocardial infarction, unstable angina, ischemic stroke, and death. Epidemiologically high serum levels of HDL cholesterol are associated with reduced risk for the development of atherosclerotic disease. HDL particles are believed to be antiatherogenic secondary to their capacity to drive reverse cholesterol transport and antagonize pathways of inflammation, thrombosis, and oxidation. HDL cholesterol can be quite challenging to raise in many individuals because of the large number of polymorphisms in the genes, enzymes, cell surface receptors, and apoproteins that regulate the serum concentrations, functionality, and patterns of metabolism of HDL particles This article reviews HDL metabolism and established as well as emerging therapeutic approaches to raising serum concentrations of this fascinating and complex lipoprotein.