Beyond LDL-C lowering: distinct molecular sphingolipids are good indicators of proprotein convertase subtilisin/kexin type 9 (PCSK9) deficiency.

OBJECTIVES: Inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9) has been proposed to be a potential new therapeutic target for treatment of hypercholesterolaemia. However, little is known about the effects of PCSK9 inhibition on the lipidome. METHODS: We performed molecular lipidomic analyses of plasma samples obtained from PCSK9-deficient mice, and serum of human carriers of a loss-of-function variant in the PCSK9 gene (R46L). RESULTS: In both mouse and man, PCSK9 deficiency caused a decrease in several cholesteryl esters (CE) and short fatty acid chain containing sphingolipid species such as CE 16:0, glucosyl/galactosylceramide (Glc/GalCer) d18:1/16:0, and lactosylceramide (LacCer) d18:1/16:0. In mice, the changes in lipid concentrations were most prominent when animals were given regular chow diet. In man, a number of molecular lipid species was shown to decrease significantly even when LDL-cholesterol was non-significantly reduced by 10% only. Western diet attenuated the lipid lowering potency of PCSK9 deficiency in mice. CONCLUSIONS: Plasma molecular lipid species may be utilized for characterizing novel compounds inhibiting PCSK9 and as sensitive efficacy markers of the PCSK9 inhibition.

Lipidomics-based safety biomarkers for lipid-lowering treatments.

Recent data suggest that aggressive lipid-lowering treatment results in significant reductions of atherosclerotic complications, ie, strokes, heart attacks, or peripheral vascular diseases. Thus, more patients will be titrated to higher doses of statins in order to reach the aggressive targets of low-density lipoprotein- cholesterol reduction. However, aggressive treatment with high statin doses has increased the risk of statin-induced myopathy. The incidence of myopathy in cohort studies and in randomized trials has been low, supporting the good safety profile of statin drugs. However, muscle effects seem to be more frequent in clinical practice. Of all statin users, approximately 1% to 5% suffers from muscular symptoms caused by medication. This potentially reduces the compliance toward treatment and number of patients reaching their treatment targets due to withdrawal of therapy. Thus, novel biomarkers are needed for prediction or improved diagnoses of statin-induced side effects. This would potentially increase the quality of life of patients and improve treatment results. Using lipidomic analysis, we found that the plasma lipidomic changes following simvastatin treatment correlate with the muscle expression of the arachidonate 5-lipoxygenase-activating protein. Intriguingly, these results suggest that the plasma lipidomic profile may serve as a highly sensitive biomarker of statin-induced metabolic alterations in muscle and may thus allow us to identify patients who should be treated with a lower dose to prevent a possible toxicity.

Metabolomic strategies to identify tissue-specific effects of cardiovascular drugs.

BACKGROUND: The number of patients eligible for cardiovascular therapies in general is forecast to increase substantially in the coming decades. However, the current list of potential future cardiovascular blockbuster drugs is alarmingly short. There is thus a clear need for innovative strategies to increase the efficiency of drug development pipelines by establishing new sensitive biomarkers to monitor drug efficacy and safety in the context of complexity of lipoprotein metabolism targeted by the cardiovascular drugs. METHODS: Metabolomics is a discipline dedicated to the systematic study of small molecules in cells, tissues and biofluids. Since lipids (including cholesterol), as well as other metabolites, are key constituents of lipoprotein particles and are thus part of the complex lipoprotein metabolism that includes exchange of lipids and metabolites with peripheral tissues, cardiovascular drug safety and efficacy needs to be addressed in the context of systemic lipid metabolism. RESULTS/CONCLUSION: Metabolomics, lipidomics in particular, is expected to make an important impact on the discovery and development of cardiovascular therapies.

Apolipoprotein E activates the low-activity form of human phospholipid transfer protein.

Phospholipid transfer protein (PLTP) exists in a high-activity (HA-PLTP) and a low-activity form (LA-PLTP) in the circulation. LA-PLTP is associated with apoA-I while the HA-PLTP complex is enriched with apoE. To study the interaction of PLTP with apolipoproteins, we carried out surface plasmon resonance analyses. These demonstrated a concentration-dependent binding of recombinant human PLTP, which represents an active PLTP form, and LA-PLTP to apoE, apoA-I, and apoA-IV within a nanomolar K(D) range. To study whether LA-PLTP can be transformed into an active form, we incubated it in the presence of proteoliposomes containing apoE, apoA-I or apoA-IV. The apoE proteoliposomes induced a concentration-dependent activation of LA-PLTP. ApoA-IV proteoliposomes also activated LA-PLTP in a concentration-dependent manner, whereas apoA-I proteoliposomes had no such effect. These observations suggest that PLTP is capable of interacting with apoE, apoA-I, and apoA-IV, and that these interactions regulate PLTP-activity levels in plasma.

Active and low-active forms of serum phospholipid transfer protein in a normal Finnish population sample.

Human serum phospholipid transfer protein (PLTP) exists as a catalytically active (HA-PLTP) and a low-active (LA-PLTP) form. In this study, the association of PLTP activity and the concentrations of both forms with lipid and carbohydrate parameters were investigated. In a random Finnish population sample, serum PLTP concentration (n=250) was 6.56 +/- 1.45 mg/l, the mean lipoprotein-independent (PLTPexo) phospholipid transfer activity was 6.59 +/- 1.66 micromol/ml/h, and the mean lipoprotein-dependent (PLTPendo) activity was 1.37 +/- 0.29 micromol/ml/h. Of the serum PLTP concentration, approximately 46% was in a catalytically active form. HA-PLTP concentration correlated positively with serum PLTPexo activity (r=0.380, P <0.001), HDL cholesterol (r=0.291, P <0.001), and apolipoprotein A-I (r=0.187, P <0.01). Of the potential regulatory factors for PLTP, apolipoprotein E showed a weak positive correlation with serum PLTPexo (r=0.154, P <0.05) and PLTPendo (r=0.192, P <0.01) activity but not with PLTP concentration. Weak associations were also observed between PLTP parameters and determinants of glucose homeostasis (glucose, insulin, and homeostasis model assessment for insulin resistance). The present data on PLTP activity and concentration reveal novel connections of the two PLTP forms to lipid and carbohydrate metabolism.