Rajesh Movva

Laboratory Assessment of HDL Heterogeneity and Function

BACKGROUND Plasma concentrations of HDL cholesterol (HDL-C) and its major protein component apolipoprotein (apo) A-I are strongly inversely associated with cardiovascular risk, leading to the concept that therapy to increase HDL-C and apoA-I concentrations would be antiatherosclerotic and protective against cardiovascular events. The recent failure of the drug torcetrapib, a cholesteryl ester transfer protein inhibitor that substantially increased HDL-C concentrations, has brought focus on the issues of HDL heterogeneity and function as distinct from HDL-C concentrations. CONTENT This review addresses the current state of knowledge regarding assays of HDL heterogeneity and function and their relationship to cardiovascular disease. HDL is highly heterogeneous, with subfractions that can be identified on the basis of density, size, charge, and protein composition, and the concept that certain subfractions of HDL may be better predictors of cardiovascular risk is attractive. In addition, HDL has been shown to have a variety of functions that may contribute to its cardiovascular protective effects, including promotion of macrophage cholesterol efflux and reverse cholesterol transport and antiinflammatory and nitric oxide-promoting effects. SUMMARY Robust laboratory assays of HDL subfractions and functions and validation of the usefulness of these assays for predicting cardiovascular risk and assessing response to therapeutic interventions are critically important and of great interest to cardiovascular clinicians and investigators and clinical chemists.

Potent and Selective PPAR-α Agonist LY518674 Upregulates Both ApoA-I Production and Catabolism in Human Subjects With the Metabolic Syndrome

Objective—The study of PPAR-α activation on apoA-I production in humans has been limited to fibrates, relatively weak PPAR-α agonists that may have other molecular effects. We sought to determine the effect of a potent and highly specific PPAR-α agonist, LY518674, on apoA-I, apoA-II, and apoB-100 kinetics in humans with metabolic syndrome and low levels of HDL cholesterol (C). Methods and Results—Subjects were randomized to receive LY518674 (100 &mgr;g) once daily (n=13) or placebo (n=15) for 8 weeks. Subjects underwent a kinetic study using a deuterated leucine tracer to measure apolipoprotein production and fractional catabolic rates (FCR) at baseline and after treatment. LY518674 significantly reduced VLDL-C (−38%, P=0.002) and triglyceride (−23%, P=0.002) levels whereas LDL-C and HDL-C levels were unchanged. LY518674 significantly reduced VLDL apoB-100 (−12%, P=0.01) levels, attributable to an increased VLDL apoB-100 FCR with no change in VLDL apoB-100 production. IDL and LDL apoB-100 kinetics were unchanged. LY518674 significantly increased the apoA-I production rate by 31% (P<0.0001), but this was accompanied by a 33% increase in the apoA-I FCR (P=0.002), resulting in no change in plasma apoA-I. There was a 71% increase in the apoA-II production rate (P<0.0001) accompanied by a 25% increase in the FCR (P<0.0001), resulting in a significant increase in plasma apoA-II. Conclusions—Activation of PPAR-α with LY518674 (100 &mgr;g) in subjects with metabolic syndrome and low HDL-C increased the VLDL apoB-100 FCR consistent with enhanced lipolysis of plasma triglyceride. Significant increases in the apoA-I and apoA-II production rates were accompanied by increased FCRs resulting in no change in HDL-C levels. These data indicate a major effect of LY518674 on the production and clearance of apoA-I and HDL despite no change in the plasma concentration. The effect of these changes on reverse cholesterol transport remains to be determined.

Pharmacokinetic Interactions of the Microsomal Triglyceride Transfer Protein Inhibitor, Lomitapide, with Drugs Commonly Used in the Management of Hypercholesterolemia

To characterize the effects of two doses (10 and 60 mg) of lomitapide—a microsomal triglyceride transfer protein inhibitor approved as adjunct treatment to lower low‐density lipoprotein cholesterol levels in patients with homozygous familial hypercholesterolemia—on the pharmacokinetics of several lipid‐lowering therapies: atorvastatin, simvastatin, rosuvastatin, fenofibrate, ezetimibe, and niacin.

Laboratory assessment of HDL heterogeneity and function

BACKGROUND Plasma concentrations of HDL cholesterol (HDL-C) and its major protein component apolipoprotein (Apo) A-I are strongly inversely associated with cardiovascular risk, leading to the concept that therapy to increase HDL-C and ApoA-I concentrations would be antiatherosclerotic and protective against cardiovascular events. The recent failure of the drug torcetrapib, a cholesteryl ester transfer protein inhibitor that substantially increased HDL-C concentrations, has brought focus on the issues of HDL heterogeneity and function as distinct from HDL-C concentrations. CONTENT This review addresses the current state of knowledge regarding assays of HDL heterogeneity and function and their relationship to cardiovascular disease. HDL is highly heterogeneous, with subfractions that can be identified on the basis of density, size, charge, and protein composition, and the concept that certain subfractions of HDL may be better predictors of cardiovascular risk is attractive. In addition, HDL has been shown to have a variety of functions that may contribute to its cardiovascular protective effects, including promotion of macrophage cholesterol efflux and reverse cholesterol transport and antiinflammatory and nitric oxide-promoting effects. SUMMARY Robust laboratory assays of HDL subfractions and functions and validation of the usefulness of these assays for predicting cardiovascular risk and assessing response to therapeutic interventions are critically important and of great interest to cardiovascular clinicians and investigators and clinical chemists.

Oral Apolipoprotein A‐I Mimetic D‐4F Lowers HDL‐Inflammatory Index in High‐Risk Patients: A First‐in‐Human Multiple‐Dose, Randomized Controlled Trial

A single dose of the apolipoprotein (apo)A‐I mimetic peptide D‐4F rendered high‐density lipoprotein (HDL) less inflammatory, motivating the first multiple‐dose study. We aimed to assess safety/tolerability, pharmacokinetics, and pharmacodynamics of daily, orally administered D‐4F. High‐risk coronary heart disease (CHD) subjects added double‐blinded placebo or D‐4F to statin for 13 days, randomly assigned 1:3 to ascending cohorts of 100, 300, then 500 mg (n = 62; 46 men/16 women). D‐4F was safe and well‐tolerated. Mean ± SD plasma D‐4F area under the curve (AUC, 0–8h) was 6.9 ± 5.7 ng/mL*h (100 mg), 22.7 ± 19.6 ng/mL*h (300 mg), and 104.0 ± 60.9 ng/mL*h (500 mg) among men, higher among women. Whereas placebo dropped HDL inflammatory index (HII) 28% 8 h postdose (range, 1.25–0.86), 300–500 mg D‐4F effectively halved HII: 1.35–0.57 and 1.22–0.63, respectively (P < 0.03 vs. placebo). Oral D‐4F peptide dose predicted HII suppression, whereas plasma D‐4F exposure was dissociated, suggesting plasma penetration is unnecessary. In conclusion, oral D‐4F dosing rendered HDL less inflammatory, affirming oral D‐4F as a potential therapy to improve HDL function.