A New Lipid to Assess Heart Disease Risk

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Predicting cardiac events in progressing coronary artery disease with plasma ceramides

Heart disease is the most common cause of death in the United States and has been for more than 50 years.1 Ironically, heart disease is very treatable by highly effective preventive therapies including drugs, diet and exercise. Tragically, the first sign of heart disease is often a heart attack.2  Consequently, there is an ongoing search for risk factors to help identify and treat patients prior to symptomatic heart disease.

Traditional risk factors of heart disease include elevated body mass index, high blood pressure (hypertension), tobacco smoking and increased blood cholesterol. Most risk factors are related to atherosclerosis—the buildup of plaque in the walls of blood vessels. Atherosclerosis narrows arteries depriving downstream tissues of oxygen and nutrients. A heart attack—myocardial infarction (MI) is the result of atherosclerosis in the coronary arteries.

AL-Feb-CARDIOLOGY-Figure

Figure 1. Ceramides are associated with multiple atherosclerosis pathways. A) Ceramides increase LDL vascular infiltration and promote LDL aggregation within the intima. B) Ceramide synthesis increases in response to inflammatory cytokines. C) Atherosclerotic plaque is enriched with ceramide. D) Ceramides increase platelet activation and disrupt endothelial nitric oxide signaling.

Atherosclerosis begins when lipoproteins infiltrate the vascular intima, drawing monocytes across the endothelium (Figure 1). Phagocytosis of lipoproteins by monocytes creates lipid-bloated foam-cells, which release cytokines and effector molecules that promote myocyte migration while upregulating endothelial cell adhesion and platelet activation proteins and disrupting vasodilation mechanisms.

Plasma Ceramides: A Multifaceted Risk Marker

Current guideline-endorsed biomarkers are narrowly focused on circulating cholesterol and non-specific inflammatory markers. However, atherosclerosis is a complex pathophysiological disease involving dyslipidemia, inflammation, endothelial dysfunction, and platelet activation. Basic science has demonstrated associations between each of these mechanisms and plasma ceramides (Figure 1).

Ceramides are complex lipids that play a central role in cell membrane integrity, cellular stress response, inflammatory signaling and apoptosis. Synthesis of ceramides from saturated fats and sphingosine occurs in all tissues. Ceramides accumulate in tissues not suited for fat storage during dyslipidemia and caloric excess.

Low-density lipoprotein (LDL), infamous as the carrier of “bad” cholesterol, also transports ceramides in the blood. Ceramides promote LDL infiltration into the vessel wall, and LDL within arterial plaque is enriched 50-fold with ceramides.3,4 The inflammatory cytokines interferon-γ, tumor necrosis factor-α (TNFα), and interleukin-1ß all stimulate ceramide synthesis.5 Finally, ceramides are implicated in platelet activation and endothelial dysfunction via uncoupling of nitric oxide signaling pathways.6

Ceramides Predict Clinical Outcomes

Untargeted metabolomic analysis of patients with angiography confirmed atherosclerosis identified three plasma ceramides as significantly linked to cardiovascular mortality within three years.7 The association was independent of age, sex, body-mass index, smoking status, statin use, triglycerides, or LDL cholesterol. Additional predictive value was found when ceramides were normalized to ceramide 24:0, a highly abundant plasma ceramide not influenced by heart disease.

Independent studies performed at Mayo Clinic demonstrated that targeted measurement of these ceramides could be performed with accuracy and precision suitable for clinical application. The clinical utility of these ceramides for predicting risk of cardiovascular disease was confirmed in a cohort of patients undergoing coronary angiography.8

Additional reports using the targeted measurement approach have repeatedly verified that plasma ceramides are strong predictors of heart attack, stroke, or heart disease related death within one to five years.7,9 Risk conferred by plasma ceramides is independent of traditional risk factors including age, sex, body-mass index, smoking status, and blood cholesterol. Additionally, ceramides remained significant after adjusting for other markers such as C-reactive protein (CRP), apolipoprotein B (ApoB), and lipoprotein associated phospholipase A2 (Lp-PLA2).

Interpreting Elevated Ceramides

New risk factors for heart disease are proposed regularly. When evaluating the potential of a new risk factor, several factors must be considered. First, does the new risk marker provide new information independent of established risk factors? Plasma ceramides are able to stratify risk among patients even after adjustment for multiple traditional and contemporary risk factors.

A second consideration for new biomarkers is clinical application. Three plasma ceramides and their ratios to a fourth ceramide were found to be predictive of disease. Thus, there are a total of six results all predictive of cardiovascular disease. While this may be intriguing on an academic level, it allows for the potential of confusion in clinical practice. This prompted development of a ceramide risk score.9

The ceramide risk score incorporates the values from all six ceramide results into a clearly defined risk category. One or two points are added to the score for each result above the median or the third quartile, respectively. Thus, the potential risk attributable to ceramides is summarized on a 12-point scale. Applying the ceramide risk score to two large observational studies (>1,500 each) revealed that patients with a score of 10-12 had a four- to six-fold increase in risk of events compared to patients with a score ≤2 points.9

Ceramides Are Modifiable

Finally, a biomarker is only useful in the clinic when it is able to guide effective interventions. A significant decrease in plasma ceramides was observed among subjects taking simvastatin (alone or in combination with ezetimibe), rosuvastatin.7,10 Caloric restriction and aerobic exercise have also been shown to reduce plasma ceramides.11 Randomized clinical trials with pharmaceuticals specifically able to modify ceramides have not been reported. However, the data are promising in that therapies already known to be effective at reducing risk of heart disease are also able to modify plasma ceramide concentrations.

Disclosure: Mayo Medical Laboratories, the global reference laboratory for Mayo Clinic, offers laboratory testing for plasma ceramides on a service basis. Neither Dr. Meeusen nor his laboratory benefit financially from this testing.


References

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Jeffrey W. Meeusen, PhD

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