Associate editor: M.J. Chapman
Remnant cholesterol as a cause of ischemic heart disease: Evidence, definition, measurement, atherogenicity, high risk patients, and present and future treatment

https://doi.org/10.1016/j.pharmthera.2013.11.008Get rights and content

Abstract

This review focuses on remnant cholesterol as a causal risk factor for ischemic heart disease (IHD), on its definition, measurement, atherogenicity, and levels in high risk patient groups; in addition, present and future pharmacological approaches to lowering remnant cholesterol levels are considered.

Observational studies show association between elevated levels of remnant cholesterol and increased risk of cardiovascular disease, even when remnant cholesterol levels are defined, measured, or calculated in different ways. In-vitro and animal studies also support the contention that elevated levels of remnant cholesterol may cause atherosclerosis same way as elevated levels of low-density lipoprotein (LDL) cholesterol, by cholesterol accumulation in the arterial wall. Genetic studies of variants associated with elevated remnant cholesterol levels show that an increment of 1 mmol/L (39 mg/dL) in levels of nonfasting remnant cholesterol associates with a 2.8-fold increased risk of IHD, independently of high-density lipoprotein cholesterol levels. Results from genetic studies also show that elevated levels of remnant cholesterol are causally associated with both low-grade inflammation and IHD. However, elevated levels of LDL cholesterol are associated with IHD, but not with low-grade inflammation. Such results indicate that elevated LDL cholesterol levels cause atherosclerosis without a major inflammatory component, whereas an inflammatory component of atherosclerosis is driven by elevated remnant cholesterol levels.

Post-hoc subgroup analyses of randomized trials using fibrates in individuals with elevated triglyceride levels, elevated remnant cholesterol levels, show a benefit of lowering triglycerides or remnant cholesterol levels; however, large randomized trials with the primary target of lowering remnant cholesterol levels are still missing.

Section snippets

Introduction including definition

Ischemic heart disease (IHD) is a leading cause of morbidity and mortality worldwide. An important risk factor for IHD is elevated levels of low-density lipoprotein (LDL) cholesterol, but even after lowering of LDL cholesterol to recommended levels, there is a considerable residual risk of IHD. Some of this residual risk may be explained by elevated remnant cholesterol levels (Chapman et al., 2011).

Lipoproteins transport water-insoluble triglycerides and cholesterol between tissues and organs

Remnant cholesterol levels and observational risk of ischemic heart disease

Large observational studies, and meta-analyses thereof, have shown that elevated triglycerides are associated with increased risk of cardiovascular disease (Austin, 1991, Chapman et al., 2011, Di Angelantonio et al., 2009, Freiberg et al., 2008, Hokanson and Austin, 1996, Nordestgaard et al., 2007, Varbo, Benn, Tybjaerg-Hansen and Nordestgaard, 2013); however, the association of elevated remnant cholesterol levels with cardiovascular disease risk is not as thoroughly studied. Although there has

Remnant cholesterol, genetic variation, and causal risk of ischemic heart disease

Plasma levels of remnant cholesterol (and likewise triglycerides) are partly genetically determined by common and rare genetic variants (Hegele et al., 2009, Johansen, Kathiresan and Hegele, 2011, Johansen, Wang, et al., 2011, Yuan et al., 2007), and partly determined by lifestyle factors such as diet, obesity, alcohol intake, and physical activity (Chapman et al., 2011). Several rare genetic variants are known to influence levels of triglycerides, and thus remnant cholesterol levels, such as

Measurement of remnant cholesterol

Separation of lipoproteins into different classes was first done by ultracentrifugation in the 1940's (Gofman et al., 1956). Since then, assays for measuring remnants using different methods have been developed (Hanada et al., 2012, Havel, 2000, Nakajima et al., 1993, Nakajima et al., 2011, Ooi and Nordestgaard, 2011). However, as lipoprotein remnants are different both in composition of lipids and apolipoproteins as a result of different stages of triglyceride lipolysis and exchange of

Atherogenicity of elevated remnant cholesterol

Mechanistically, the explanation for a causal effect of elevated levels of nonfasting remnant cholesterol on increased risk of IHD likely is simple and straight forward, that is, that remnant cholesterol, like LDL cholesterol, enter and is trapped in the intima of the arterial wall (Nordestgaard et al., 1992, Nordestgaard et al., 1995, Shaikh et al., 1991), leading to accumulation of intimal cholesterol, atherosclerosis and ultimately IHD (Fig. 5).

Different sizes of lipoproteins presumably play

Remnant cholesterol levels in high risk patient groups

The most common cause of elevated remnant cholesterol and triglycerides is obesity (Table 1). Likewise, poorly controlled diabetes mellitus and excessive alcohol intake are common causes of elevated remnant cholesterol levels. In some women, high estrogen levels, either endogenous during pregnancy or from exogenous sources like oral contraceptives or hormone replacement therapy, can lead to high triglycerides, and possibly high remnant cholesterol levels. Kidney and liver diseases, and a number

Lowering of remnant cholesterol levels using current approaches

In a recent consensus document (Chapman et al., 2011), therapeutic targeting of triglycerides ≥1.7 mmol/L (≥150 mg/dL) was recommended in patients at high risk of cardiovascular disease after lowering of LDL cholesterol below recommended levels, which includes lowering of remnant cholesterol. Elevated levels of remnant cholesterol can be lowered by lifestyle changes and by pharmacological therapy. Lifestyle changes that effectively lower remnant cholesterol levels include weight reduction (the

Future pharmacological approaches to lowering remnant cholesterol levels

Given the documented causal association between elevated levels of remnant cholesterol and increased risk of IHD (Jorgensen et al., 2013, Varbo, Benn, Tybjaerg-Hansen, Jorgensen, et al., 2013, Varbo, Benn, Tybjaerg-Hansen and Nordestgaard, 2013), and the lack of well documented effect in reducing IHD risk in those with elevated remnant cholesterol levels with statins, fibrates, and/or niacin, there is a clear need for new therapies to reduce remnant cholesterol as add on therapy to statins or

Conclusions and perspectives

In conclusion, evidence from observational studies, in-vitro and animal studies, and from genetic studies all support a causal association between elevated levels of remnant cholesterol and increased risk of IHD; however, even though post-hoc subgroup analyses of randomized trials using fibrates showed a benefit of lowering triglycerides or remnant cholesterol levels, large randomized clinical intervention trials with the primary target of lowering remnant cholesterol levels are still missing.

Funding sources

The research of AV, MB and BGN are supported by The Danish Council for Independent Research, Medical Sciences (FSS), The Danish Heart Foundation, Herlev Hospital, Copenhagen University Hospital, Copenhagen County Foundation, and Chief Physician Johan Boserup and Lise Boserup's Fund, Denmark.

Conflict of interest disclosures

BGN has received lecture and/or consultancy honoraria from Omthera, Sanofi-Aventis/Regeneron, Aegerion, AstraZeneca, Amgen, and ISIS Pharmaceuticals. AV and MB have no conflicts of interest.

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