Original Research Article

Factorial Effects of Evolocumab and Atorvastatin on Lipoprotein MetabolismClinical Perspective

Gerald F. Watts, Dick C. Chan, Ricardo Dent, Ransi Somaratne, Scott M. Wasserman, Rob Scott, Sally Burrows, P. Hugh R. Barrett
https://doi.org/10.1161/CIRCULATIONAHA.116.025080
Circulation. 2017;135:338-351
Originally published December 9, 2016

Jump to

Abstract

Background: Monoclonal antibodies against proprotein convertase subtilisin kexin type 9 (PCSK9), such as evolocumab, lower plasma low-density lipoprotein (LDL)-cholesterol concentrations. Evolocumab is under investigation for its effects on cardiovascular outcomes in statin-treated, high-risk patients. The mechanism of action of PCSK9 monoclonal antibodies on lipoprotein metabolism remains to be fully evaluated. Stable isotope tracer kinetics can effectively elucidate the mode of action of new lipid-regulating pharmacotherapies.

Methods: We conducted a 2-by-2 factorial trial of the effects of atorvastatin (80 mg daily) and subcutaneous evolocumab (420 mg every 2 weeks) for 8 weeks on the plasma kinetics of very-low-density lipoprotein (VLDL)–apolipoprotein B-100 (apoB), intermediate-density lipoprotein–apoB, and LDL-apoB in 81 healthy, normolipidemic, nonobese men. The kinetics of apoB in these lipoproteins was studied using a stable isotope infusion of D3-leucine, gas chromatography/mass spectrometry, and multicompartmental modeling.

Results: Atorvastatin and evolocumab independently accelerated the fractional catabolism of VLDL-apoB (P<0.001 and P.032, respectively), intermediate-density lipoprotein–apoB (P=0.021 and P=.002, respectively), and LDL-apoB (P<0.001, both interventions). Evolocumab but not atorvastatin decreased the production rate of intermediate-density lipoprotein–apoB (P=0.043) and LDL-apoB (P<0.001), which contributed to the reduction in the plasma pool sizes of these lipoprotein particles. The reduction in LDL-apoB and LDL-cholesterol concentrations was significantly greater with combination versus either monotherapy (P<0.001). Whereas evolocumab but not atorvastatin lowered the concentration of free PCSK9, atorvastatin lowered the lathosterol/campesterol ratio (a measure of cholesterol synthesis/absorption) and apoC-III concentration. Both interventions decreased plasma apoE, but neither significantly altered lipoprotein lipase and cholesteryl ester protein mass or measures of insulin resistance.

Conclusions: In healthy, normolipidemic subjects, evolocumab decreased the concentration of atherogenic lipoproteins, particularly LDL, by accelerating their catabolism. Reductions in intermediate-density lipoprotein and LDL production also contributed to the decrease in LDL particle concentration with evolocumab by a mechanism distinct from that of atorvastatin. These kinetic findings provide a metabolic basis for understanding the potential benefits of PCSK9 monoclonal antibodies incremental to statins in on-going clinical end point trials.

Clinical Trial Registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02189837.

Introduction

Editorial, see p 363

Elevated low-density lipoprotein (LDL)-cholesterol is a major cause of atherosclerotic cardiovascular disease.1 The plasma concentration of LDL-cholesterol is physiologically and tightly regulated by the sequential delipidation of triglyceride-rich lipoproteins (TRLs) that originate in the liver and by the functional activity of hepatic LDL receptors (LDLRs),2 which internalize apolipoprotein B-100 (apoB)–containing LDL particles. The homeostasis of these lipoproteins is fundamental to understanding the dyslipidemias and its regulation is the principal target of effective pharmacotherapies.3,4 The major advances in our present knowledge of the physiology, pathophysiology, and therapeutic control of human lipoprotein metabolism has relied on the application of stable isotope tracer and multicompartmental modeling methods.3,4

Proprotein convertase subtilisin kexin type 9 (PCSK9) is a secretory protease, expressed mainly in liver, that enhances intracellular degradation of hepatic cell surface receptors involved in lipid and lipoprotein metabolism.5 PCSK9 regulates cholesterol homeostasis via LDLR activity,5 and its functional genetic variants can influence atherosclerotic cardiovascular disease.5,6 Both PCSK9 and LDLRs are transcriptionally coregulated by sterol regulatory element–binding protein-2 in response to intracellular cholesterol.5 The key physiological role of PCSK9 provides the scientific basis for the development of specific inhibitors of this protease for treating dyslipidemias that perturb the metabolism of LDL particles.5,6

PCSK9 inhibition with monoclonal antibodies (mAbs) blocks the extracellular interaction of PCSK9 with the LDLR,6,7 and profound LDL-cholesterol lowering has been consistently reported in hypercholesterolemic patients, with implications for the prevention of atherosclerotic cardiovascular disease.6,7 However, the precise mechanism of action of PCSK9 mAbs on lipoprotein metabolism in humans remains to be demonstrated. Whereas experimental data suggest a major effect in increasing LDL clearance via the LDLR pathway,5–7 PCSK9 inhibition can lower both hepatic apoB secretion and production of LDL particles and may possibly also increase clearance of TRLs,5 but these mechanisms are less well recognized and remain to be confirmed in humans.

Statins inhibit 3-hydroxy-3-methylglutaryl-coenzyme A reductase, which decreases intracellular free cholesterol and stimulates expression of sterol regulatory element–binding protein-2 and LDLR activity.8 This lowers plasma LDL particle concentration by accelerating hepatic clearance but is counterbalanced by increased secretion of PCSK9.7,9 Statins may also lower production of apoB and enhance clearance of TRLs,4 but these mechanisms are less well accepted.

Whereas statins increase hepatic secretion of PCSK9 dose dependently,7 PCSK9 inhibition may not synergistically lower LDL-cholesterol in hypercholesterolemic patients,7 in whom there may be a limit to the upregulation of LDLRs. Whether this also applies to normocholesterolemic individuals with fully functional LDLRs is unclear. This question may be particularly relevant to understanding the pharmacodynamics of LDL-cholesterol reduction with combination therapy at low plasma concentrations of LDL-cholesterol.6,7

Therefore, we investigated the independent and combined effects of decreasing cholesterol synthesis with atorvastatin and inhibiting PCSK9 activity with evolocumab on apoB kinetics in normocholesterolemic men by using a factorial study design. We hypothesized that, via different mechanisms of action, atorvastatin and evolocumab independently and additively improve apoB metabolism, with particular enhancement in LDL particle catabolism.

Methods

Subjects

We studied healthy, normolipidemic men aged 18 to 65 years with fasting plasma LDL-cholesterol of ≥2.5 and <4.9 mmol/L and triglycerides of <1.7 mmol/L, Framingham Risk Score ≤10%, and body mass index of 18 to 32 kg/m2. None had diabetes mellitus; familial hypercholesterolemia; hypertension; or cardiovascular, renal, hepatic, thyroid, musculoskeletal, psychiatric, or other medical disorders; abnormal liver or muscle enzymes; alcohol or substance abuse; nor were taking medications affecting lipid metabolism. All were consuming isocaloric diets and took light-to-moderate exercise. The study was approved by a national ethics committee (Bellberry Ltd, Eastwood, South Australia); all subjects provided informed consent.

Study Design and Clinical Protocol

Eligible subjects entered a randomized, double-blind, placebo-controlled, two-by-two factorial design, intervention trial involving a 7-day run-in period, during which dietary intake, exercise, and body weight were stable. Subjects were randomly assigned (1:1:1:1) to 1 of the 4 treatment groups for 8 weeks: placebo subcutaneous (SC) every 2 weeks (Q2W) and oral placebo once a day (QD; placebo); placebo SC Q2W and oral atorvastatin 80 mg QD (atorvastatin); SC evolocumab 420 mg Q2W and oral placebo QD (evolocumab); or SC evolocumab 420 mg Q2W and oral atorvastatin 80 mg QD (evolocumab/atorvastatin); the dose regimens of atorvastatin and evolocumab were selected to achieve maximal inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and PCSK9 activities, respectively, and hence to provide the best test of our experimental hypothesis. Study visits were every 2 weeks for evolocumab dosing, treatment adherence assessment, laboratory testing, and safety measurements.

Subjects were admitted to the site metabolic ward after a 14-hour fast at the end of the run-in period (baseline study) and 7 days after the final SC dose of evolocumab or placebo, during which they continued with the oral placebo or atorvastatin. Subjects were studied in a semirecumbent position and allowed to drink only water. Venous blood was collected for laboratory measurements, and plasma volume was determined by multiplying body weight by 0.045.

A single bolus of D3-leucine (5 mg/kg of body weight) was administered intravenously within a 2-minute period into an antecubital vein. Blood samples were taken at baseline and at 5, 10, 20, 30, and 40 minutes and at 1, 1.5, 2, 2·5, 3, 4, 5, 6, 8, and 10 hours after injection of the isotope.9,10 Subjects were then given a snack and discharged home. Additional fasting blood samples were collected in the morning on the following 4 days of the same week (ie, at 24, 48, 72, and 96 hours after injection of the isotope).

Isolation and Measurement of Isotopic Enrichment of Very-Low-Density Lipoprotein–apoB, Intermediate-Density Lipoprotein–apoB, and LDL-apoB

Very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and LDL were isolated from 3.5 mL of plasma by sequential ultracentrifugation (Optima XL-100K, Beckman Coulter) at densities of 1.006, 1.019, and 1.063 g/mL, respectively. To avoid interference of lipoprotein (a) [Lp(a)]–apoB with the measurement of LDL-apoB, we removed Lp(a) from plasma before ultracentrifugation by using a immunomagnetic isolation method (Dynabeads Protein G, Life Technologies) with beads coated with a goat polyclonal antibody (immunoglobulin G) to human Lp(a) (Advy Chemical Ltd). The procedures for isopropanol precipitation, delipidation, hydrolysis, and derivatization of apoB to the oxazolinone derivative were described previously.3,9,11 Plasma-free leucine was also isolated by cation-exchange chromatography using AG 50 W-X8 resin (BioRad) after removing plasma proteins with 60% perchloric acid. Isotopic enrichment was determined by using gas chromatography/mass spectrometry with selected ion monitoring of samples at a mass to charge ratio (m/z) of 212 and 209 and negative ion chemical ionization. Tracer enrichments were derived from isotopic ratios for each sample.

Quantification of apoB and Other Analytes

Plasma samples were combined from 5 time points (0, 1, 3, 8, and 24 hours) to yield 3 pooled VLDL, IDL, and LDL samples per subject study (3.5 mL of plasma), as previously described.3,9,10 ApoB in VLDL, IDL, and LDL fractions from the pooled plasma samples was isolated and determined by a modified Lowry method,9,10 with an interassay imprecision of <5%. All routine lipid, lipoprotein, and apo analyses were assayed in serum samples by Medpace Reference Laboratories according to the Centers for Disease Control and Prevention Lipid Standardization Program. Triglyceride and cholesterol were measured with enzymatic colorimetric tests (Olympus AU2700 or AU5400 Analyzer, Olympus), with calibration directly traceable to Centers for Disease Control and Prevention reference procedures. ApoB-containing lipoproteins were precipitated with dextran sulfate, and high-density lipoprotein–cholesterol was measured in the supernatant. Calculated LDL-cholesterol was derived by using the Friedewald formula. LDL-cholesterol was also measured by preparative ultracentrifugation at the Lipid Core Laboratory. ApoA-I and apoB were measured by immunonephelometry (Dade Behring BNII nephelometer, Siemens Healthcare Diagnostics) and Lp(a) by immunoturbidimetry (Denka Seiken Co Ltd, Lp(a) assay, Polymedco). Plasma apoA-V (US Biological), apoC-III (Assay Pro), apoE (R & D Systems), lipoprotein lipase (Cusabio), and cholesteryl ester transfer protein (Cell Biolabs, Inc) concentrations were determined using enzyme-linked immunosorbent assay; free PCSK9 concentration was assayed by a quantitative enzyme-linked immunosorbent assay method (PPD Bioanalytical Laboratory).12 Plasma lathosterol and campesterol concentrations were assayed by using gas-liquid chromatography and gas chromatography/mass spectrometry (Boston Heart Diagnostics),9–11 from which the relative ratios and individual cholesterol ratios were estimated as indices of cholesterol synthesis and absorption. Plasma insulin was measured by chemiluminescent microparticle immunoassay, and glucose was measured by the hexokinase method (Abbott Diagnostics). Insulin sensitivity was estimated by the homeostasis model assessment score as fasting insulin (mU/L)×glucose (mmol/L)/22.5. Routine chemistry (aminotransferases, creatine kinase, electrolytes, and creatinine) and hematology tests were performed in the central laboratory (Covance Pt Ltd).

Model of apoB Metabolism and Calculation of Kinetic Parameters

The details and assumptions of the model were previously described.3,9,10 In brief, compartments 1 to 4 describe plasma leucine kinetics. These are connected to an intrahepatic compartment (compartment 5) that accounts for the synthesis and secretion of apoB into plasma. Compartments 6 and 7 describe the kinetics of VLDL-apoB. Plasma IDL kinetics is described by compartment 8. Compartment 9 describes plasma LDL, and compartment 10 is an extravascular LDL compartment. VLDL-apoB, IDL-apoB, and LDL-apoB metabolic parameters (fractional catabolic rate [FCR], production rate, and conversion rate) were derived following an optimal fit of the model to the plasma leucine, VLDL-apoB, IDL-apoB, and LDL-apoB enrichment data.3,9,10

Statistical Analyses

All analyses were performed using STATA 12 (StataCorp. 2011. Stata Statistical Software: Release 13). Variables were log-transformed to normalize distributions. Main effects of treatment (ie, isolated effect of 1 treatment irrespective of effect of second treatment) and interactive effects of treatment (ie, effect of combination treatment not predicted by the main effects of each treatment) were assessed by maximum-likelihood random-effects regression models. The models contained 3-way interactions of time, atorvastatin, and evolocumab. If the 3-way interaction of atorvastatin, evolocumab, and time was not statistically significant, then only the main effects (time-atorvastatin and time-evolocumab) were included in the model. When the interaction (atorvastatin-evolocumab-time) was identified (ie, P<0.05), 6 comparisons were made among the 4 groups (placebo, atorvastatin, evolocumab, evolocumab/atorvastatin) using random-effects regression models, with a Holm-Bonferroni test (step-down procedure) to adjust for multiple comparisons between groups. Because the postintervention PCSK9 values were below the lower detection limit, random-effects Tobit regression analysis was used to examine the effect of atorvastatin and evolocumab on plasma PCSK9 concentrations. Changes in variables with interventions relative to baseline were described as ratio of geometric means (post/preintervention) and as percentages. Associations between the changes in apoB kinetics and other metabolites were examined by using linear regression and Spearman/Pearson correlations. Statistical significance was defined at the 5% level.

Results

Of 245 subjects screened, 89 were eligible and were randomly assigned to either placebo (n=22), atorvastatin (n=23), evolocumab (n=23), or evolocumab/atorvastatin (n=21); one in each group withdrew consent before receiving study drugs (see Consort Diagram, Figure 1). Eighty-one (95%) of 85 subjects completed the study: 3 withdrew consent before completing the protocol, and 1 evolocumab/atorvastatin subject withdrew consent following a serious adverse event of marked increases in liver and muscle enzymes.

Figure 1.
Figure 1.

CONSORT diagram. Disposition of the subjects in the study. Q2W indicates once every 2 weeks; QD, once daily; and SC, subcutaneous.

The subjects who completed the study were on average 31 years old, lean, normolipidemic, normoglycemic, and normotensive, with well-balanced characteristics among treatment groups (Table 1). Tablet and syringe administration counts confirmed 100% compliance with randomized treatments.

View this table:
Table 1.

Clinical and Biochemical Characteristics of the 81 Subjects at Baseline

There was a significant interaction between atorvastatin and evolocumab in lowering cholesterol concentration (P=0.034), with significant decreases (P<0.001) with evolocumab/atorvastatin (–58%), atorvastatin (–33%), and evolocumab (–37%) therapies compared with placebo (Table 2, online-only Data Supplement Table IA). There were also significant interactions between atorvastatin and evolocumab in lowering LDL-cholesterol and total apoB concentrations (P=0.001 and P=0.017, respectively; online-only Data Supplement Figure I, online-only Data Supplement Table IB and IC), with the percentage reductions with evolocumab (–59% and –51%, respectively) being significantly greater than with atorvastatin (–47% and –38%, respectively); the reductions with combination therapy (–86% and –76%, respectively) were also significantly greater in comparison with either monotherapy. There were significant effects of atorvastatin in lowering triglycerides (–23%, PME=0.001), apoC-III (–18%, PME=0.009), and apoE (–28%, PME<0.001) concentrations and of evolocumab in raising high-density lipoprotein–cholesterol (+9%, PME<0.001) and lowering apoE (–27%, PME<0.001) and Lp(a) (–25%, PME=0·002). The ratio of LDL-cholesterol/apoB fell significantly with atorvastatin (–19%, PME<0.001) and evolocumab (–20%, PME<0.001). There were no significant effects on apo A-V, lipoprotein lipase, or cholesteryl ester transfer protein mass concentrations.

View this table:
Table 2.

Effect of the Interventions on Plasma Lipid, Lp, apo, LPL, and CETP Concentrations in the Subjects

There were significant effects (PME<0.005) of both atorvastatin and evolocumab in lowering lathosterol and of evolocumab in lowering campesterol. Because the reductions in the plasma concentrations of both of these noncholesterol sterols reflect, in part, the reductions in the apoB-containing lipoproteins in which they are transported in plasma, we estimated the corresponding lathosterol/cholesterol, campesterol/cholesterol, and lathosterol/campesterol ratios, as in other studies.9,11,13 There were significant effects (PME<0.001) of atorvastatin but not evolocumab in lowering the lathosterol/cholesterol (–68%) and lathosterol/campesterol ratios (–79%) and in raising the campesterol/cholesterol ratio (+52%), implying a reduction in cholesterol synthesis and an increase in cholesterol absorption, respectively. There were no significant changes in glucose and insulin concentrations with either intervention. There were significant effects (PME<0.001) of atorvastatin in increasing (+41%) and of evolocumab in decreasing (–98%) plasma-free PCSK9 levels (Table 3). There were no significant group changes in body weight and blood pressure.

View this table:
Table 3.

Effect of the Interventions on Plasma Lathosterol, Campesterol, Glucose, Insulin Concentrations, HOMA Score, and PCSK9 Levels in the Subjects

Atorvastatin significantly lowered the plasma pool sizes of VLDL-apoB (–26%, PME=0·001) and IDL-apoB (–26%, PME<0.001; Figure 2A and 2B) and increased the corresponding FCRs (VLDL-apoB, +40%, PME<0.001; IDL-apoB, +27%, PME=0.002, respectively; Figure 3A and 3B). Evolocumab also significantly lowered the pool sizes of VLDL-apoB (–28%, PME=0.001) and IDL-apoB (–39%, PME<0.001; Figure 1A and 1B) and increased the corresponding FCRs (VLDL-apoB, +23%, PME=0·032; IDL-apoB, +37%, PME=0.002, respectively; Figure 3A and 3B). Neither intervention altered the production of VLDL-apoB, but, in contrast to atorvastatin, evolocumab significantly lowered the production of IDL-apoB (–16%, PME=0.043; Table 4, Figure 3C and 3D).

View this table:
Table 4.

Effect of the Interventions on VLDL, IDL, and LDL apoB-100 Metabolism in the Subjects

Figure 2.
Figure 2.

ApoB Pool Size in VLDL, IDL, and LDL. A, Ratio of geometric means (post/preintervention) for individual effects of placebo, atorvastatin, evolocumab, and atorvastatin plus evolocumab on apoB pool size in VLDL, IDL, and LDL. B, ratio of geometric means (post/preintervention) for main effects of atorvastatin and evolocumab on apoB pool size in VLDL and IDL and ratio of geometric means (post/preintervention) for atorvastatin and evolocumab effects on apoB pool size in LDL. Because of a statistical 3-way interaction (time-atorvastatin-evolocumab) between groups, changes in LDL-apoB pool size were analyzed by maximum-likelihood random-effects regression model; main effects of interventions (time-atorvastatin and time-evolocumab) on VLDL-apoB and IDL-apoB pool size were analyzed by maximum-likelihood random-effects regression models. *P<0.001 in comparison with placebo, atorvastatin, and evolocumab. †P<0.001 in comparison with placebo and P=0·041 in comparison with atorvastatin. ‡P<0.001 in comparison with placebo. apoB indicates apolipoprotein B; CI, confidence interval; IDL, intermediate-density lipoprotein; LDL, low-density lipoprotein; and VLDL, very-low-density lipoprotein.

Figure 3.
Figure 3.

FCR and PR of apoB in VLDL, IDL, and LDL. Ratio of geometric means (post/preintervention) for individual effects of placebo, atorvastatin, evolocumab, and atorvastatin plus evolocumab on fractional catabolic rate (FCR) of apoB in VLDL, IDL, and LDL (A); with ratio of geometric means (post/preintervention) for main effects of atorvastatin and evolocumab on the corresponding FCRs (B); and ratio of geometric means (post/preintervention) for individual treatment effects on production rate (PR) of apoB from VLDL to IDL and from IDL to LDL and on total PR of LDL-apoB (C); with ratio of geometric means (post/preintervention) for main effects of atorvastatin and evolocumab on the corresponding PRs of apoB (D). Main effects of interventions were analyzed by maximum-likelihood random-effects regression models. apoB indicates apolipoprotein B; CI, confidence interval; IDL, intermediate-density lipoprotein; LDL, low-density lipoprotein; and VLDL, very low–density lipoprotein.

There was a statistically significant interaction between atorvastatin and evolocumab on the pool size of LDL-apoB (Table 4, Figure 2A, online-only Data Supplement Table ID), with the reduction with combination therapy (–85%) being significantly greater (P<0.001) in comparison with placebo and both monotherapies. Atorvastatin significantly increased the FCR of LDL-apoB (+95%, PME<0.001; Figure 3A and 3B), with no significant effect on LDL-apoB production rate (Figure 3C and 3D). Evolocumab significantly increased the FCR (+106%, PME<0.001; Figure 3A and 3B) and lowered the production rate (–30%, PME<0·001; Figure 3C and 3D) of LDL-apoB and decreased the production (or transport) rate of apoB from VLDL to IDL (–19%, PME=0.038) and from IDL to LDL (–31%, PME=0.001; Table 4, Figure 3C and 3D). There were no significant effects of interventions on direct hepatic secretion rates of IDL-apoB and LDL-apoB.

In the 3 intervention groups combined, the reductions in VLDL-apoB, IDL-apoB, and LDL-apoB pool sizes were significantly correlated with the corresponding increases in FCRs (r=–0·51, P<0.001 for VLDL; r=–0·49, P<0.001 for IDL; r=–0·48, P<0.001 for LDL). In multivariable regression, the increase in LDL-apoB FCR (standardized β-coefficient –0.442, P<0.001) and the reduction in LDL-apoB production rate (standardized β-coefficient 0.596, P<0.001) were independent predictors of the decrease in LDL-apoB pool size. The increase in VLDL-apoB FCR was only significantly correlated with the fall in plasma apoC-III (r=–0·34, P=0.008); increases in LDL-apoB FCR were inversely correlated with the lathosterol/campesterol ratio (r=–0·35, P=0.006).

The overall rates of adverse events were similar among the groups, although they were reported with greater frequency in the active intervention groups (70.0%–86.4%) than with placebo (52.4%; online-only data Supplement Table II). There was 1 serious adverse event of marked but asymptomatic elevations in plasma aminotransferases (peak alanine transaminase 86×, aspartate transaminase 52× upper limit of normal [ULN]), and creatine kinase (peak=19× ULN) in the evolocumab/atorvastatin group related to acute, excessive consumption of alcohol, strenuous activity, and concomitant use of paracetamol. The subject withdrew from the study and had spontaneous resolution of abnormal to normal values 4 weeks after cessation of treatment. Headache was reported more frequently in subjects receiving active treatments (22.7%–36.4%) than in those in the placebo group (9.5%), as was nausea (9.1%–13.6% versus 4.8%, respectively). Potential injection-site reactions were seen in 2 subjects in the atorvastatin group (9.1%) and in 1 subject in the evolocumab/atorvastatin group (5.0%) in comparison with none in the other groups. Muscle-related adverse events were seen in 3 subjects in each of the atorvastatin (13.6%) and evolocumab/atorvastatin groups (15.0%) in comparison with 1 subject in the placebo group (4.8%) and in the evolocumab group. Elevations of >3× ULN in hepatic aminotransferases were reported in 1 subject each in the atorvastatin groups (4.8%) in comparison with no subjects in the evolocumab or placebo groups. Elevations in plasma creatine kinase of >5× ULN were seen in 2 subjects in each of the groups receiving atorvastatin (9.1%–10%) in comparison with 1 subject in the evolocumab group (4.5%) and none in the placebo group. There were no deaths, cardiovascular events, or hospitalizations.

Discussion

This is the first and most comprehensive investigation of the effects of inhibiting PCSK9 and cholesterol synthesis on the kinetics of apoB-containing lipoproteins in humans. In normolipidemic subjects, maximal dose regimens of atorvastatin and evolocumab independently increased the catabolism of all apoB-containing lipoproteins by separate mechanisms that most likely involve enhanced activity of the hepatic LDLR superfamily. Whereas each intervention accelerated the catabolism of VLDL-apoB, IDL-apoB, and LDL-apoB, evolocumab alone decreased the production of IDL-apoB and LDL-apoB.

The effects of pharmacotherapies on lipoprotein kinetics have been undertaken mostly in patients with dyslipoproteinemia.3,4 We selected normolipidemic subjects to investigate the metabolic consequences of inhibiting cholesterol synthesis and PCSK9 in the setting of physiological apoB transport and a fully functional LDLR pathway. Although we did not strictly test for gene variants in this pathway, the physiological and highly responsive FCR of LDL-apoB of our subjects evidently implies that their LDLR function was normal. Under physiological conditions, LDLR recycling within hepatocytes is regulated intracellularly by free cholesterol and extracellularly by PCSK9.5 That evolocumab and atorvastatin increased the catabolism of LDL-apoB is consistent with their primary effects in inhibiting circulating free PCSK9 and de novo cholesterol synthesis (reflected by the plasma lathosterol/cholesterol ratio),5,7,9,13,14 respectively, both of which increase hepatic LDLR function.5,8,14 These primary mechanisms were confirmed by our findings of significant reductions in serum-free PCSK9 levels and the lathosterol/cholesterol ratio, respectively.7,13

That the increase in catabolism of LDL-apoB was comparable between evolocumab and atorvastatin implies that maximal increase in LDLR recycling, because of complete inhibition of PCSK9, and potent upregulation of the LDLR, because of inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, have equivalent and independent effects on hepatic LDLR function. Accordingly, the enhancing effect of combination therapy on the catabolism of LDL suggests that the primary mechanism of action of both agents can independently increase LDLR activity,7,8,14 with further lowering of LDL-apoB and LDL-cholesterol even within a lower range of plasma LDL concentrations. Evolocumab also uniquely decreased the plasma transport of apoB and, hence, the production and concentration of LDL-apoB. Although the marked increase in LDL-apoB FCR led to a fall in LDL-apoB pool size with the treatments, LDL-apoB production was the more important predictor of the change in pool size in regression analyses. This suggests that, in response to the interventions, a balancing feedback mechanism determines the final, steady-state concentration of LDL-apoB in plasma.3,4,15 Accordingly, this could explain why the profound increase in fractional catabolism of LDL-apoB with combination therapy was not paralleled by a commensurate fall in pool size. That LDL size, as reflected by the LDL-cholesterol/apoB ratio, fell with both interventions is consistent with cholesterol depletion of LDL particles.16 This refutes the notion that accelerated catabolism of LDL-apoB involves an increase in size-related affinity of particles for the LDLR. An impact of the interventions on the intrahepatic oxysterol pool with subsequent activation of the liver-X receptor and increased catabolism of the inducible degradator of the LDLR is another possible mechanism that merits further investigation.17,18

We confirm our previous studies that atorvastatin enhances the fractional catabolism of LDL in humans.4 As in those studies, we found no effect of either evolocumab or atorvastatin in decreasing hepatic secretion of apoB, despite our subjects not being insulin resistant. Our findings suggest that a marked increase in LDLR functionality or reduction in the availability of intracellular cholesterol does not limit the secretion of apoB by the liver. Although we previously showed that low-dose simvastatin decreased the hepatic secretion of apoB in normolipidemic subjects,19 our present data suggest that a much greater activation of the LDLR pathway and commensurate catabolism of apoB with high-potency atorvastatin or with evolocumab may attenuate such an effect. This may entail a nonspecific balancing feedback mechanism that may also overcome the impact of increased hepatic LDLR activity on newly secreted apoB.15,20 Although PCSK9 gene variants can affect hepatic secretion of apoB in humans,21,22 the experimental evidence supporting a role of PCSK9 in the assembly and secretion of apoB is less clear.5 Our kinetic findings concur with data showing that subjects with missense, loss-of-function mutations in PCSK9 have profound hypocholesterolemia because of the accelerated catabolism of LDL particles. Although we did not measure hepatic LDLR function directly in our study, the FCR of LDL-apoB is well known to be inversely correlated with LDLR activity.23

The differential effects of atorvastatin and evolocumab on the intravascular production of LDL-apoB are noteworthy. The explanation for the reduction in LDL-apoB production with evolocumab as opposed to atorvastatin could relate to greater enhancement in the direct hepatic uptake of IDL-apoB, the precursor of LDL-apoB, and to the absence of an effect on the lipolysis of TRLs with evolocumab, as reflected by the lack of significant changes in the plasma concentrations of apoA-V, apoC-III, and lipoprotein lipase. Measurement of lipoprotein lipase and hepatic lipase activities in postheparin plasma may provide a more precise mechanism of action of evolocumab and atorvastatin on intravascular lipolysis of TRLs, particularly in respect to the differential reductions in the transport rate of apoB from VLDL to IDL and from IDL to LDL with evolocumab. By contrast to PCSK9 inhibitors, statins decrease the biliary excretion of cholesterol and potentially increase the fractional enterocytic absorption of cholesterol,24,25 consistent with the significant elevation in campesterol seen with atorvastatin in our study25; such a response could in turn offset the effect of decreased cholesterol synthesis on the production and catabolism of apoB.2,26 Although evolocumab decreased the plasma lathosterol and campesterol levels alone, it did not alter the ratios of lathosterol to cholesterol, campesterol to cholesterol, and lathosterol to campesterol. Hence, the increase in LDL-apoB catabolism with evolocumab was likely to be driven chiefly by the effect of PCSK9 inhibition on LDL receptor recycling and activity.

The LDLR, a member of a superfamily of hepatic receptors, clears TRLs from plasma. VLDL and LDLR-related protein receptors recognize TRL remnants via the ligand apoE, but this requires initial lipolysis of nascent particles by lipoprotein and hepatic lipases.27,28 ApoC-III also potently regulates the lipolysis of TRLs and hepatic uptake of remnant lipoproteins.29 We have consistently demonstrated that statins increase the catabolism of TRL remnants,4,30 which may partly entail a peroxisome proliferator–activated receptor-α agonist effect that decreases expression of apoC-III.31 By contrast to the LDLR, the expression of VLDLRs is not sensitive to the sterol content of hepatocytes.27 It is possible that the significant fall in plasma apoC-III with atorvastatin partly accounts for the associated increase in catabolism of VLDL and IDL in our study.4,29 That no reduction apoC-III was seen with evolocumab implies that the clearance of TRLs may relate exclusively to a direct receptor-mediated mechanism,3,4,29 which is of sufficient magnitude to decrease the intravascular production of both IDL-apoB and LDL-apoB.

Beyond the LDLR, experimental evidence suggests that PCSK9 is involved in the regulation and intracellular degradation of other lipoprotein receptors, including VLDLR and LDLR-related protein.5,31 However, these are less sensitive to the effects of PCSK9 than the LDLR.5,31 The apparently less potent effect of evolocumab than atorvastatin in accelerating the catabolism of VLDL particles and lowering plasma triglyceride concentrations is compatible with the lack of significant reduction in apoC-III and less effective upregulation of the VLDLR with evolocumab.3,4,29 The statistically significant effects of both interventions on the catabolism of VLDL-apoB and IDL-apoB are also consistent with different mechanisms of action on the corresponding hepatic receptors. The extent to which reduction in plasma apoE levels with both agents increases the catabolism of TRLs merits further investigation.32,33

The strengths of our study include the largest sample size for this type of investigation and the use of well-validated metabolic methods.3,4 We also studied only men to offset potential confounding effects of estrogens, either during the menstrual cycle or related to the menopause, on lipid metabolism within a normolipidemic range. However, it is likely that similar overall findings would apply to women with fully functional LDL receptor activity.2 The selection of healthy, nonobese, insulin-sensitive, normolipidemic subjects ensured that the LDLR pathway was fully functional and plasma apoB transport physiological. The factorial design enhanced the cost efficiency of the investigation, the sample size being based on postulated main effects of atorvastatin and evolocumab on the fractional catabolism of LDL-apoB. However, we might have lacked statistical power to detect small effects of either intervention on VLDL-apoB production and of atorvastatin alone on IDL-apoB and LDL-apoB production.

The safety profile of evolocumab was compatible with phase 2 and 3 studies and a meta-analysis of published trials with PCSK9 mAbs.34 A duration of intervention of 8 weeks is insufficient to fully assess the benefit-to-risk ratio of long-term therapy. The regimen of evolocumab we used was intended to achieve maximal inhibition of PCSK9 activity and has not been previously tested in, and is not approved for, nonfamilial hypercholesterolemic populations. Our study accordingly provides valuable short-term safety data in healthy individuals.

Whether our principal findings apply to pre- or postmenopausal women, to subjects with apoB transport defects, and to more extended periods of treatment with different dose regimens remains to be formally tested. We anticipate that the lipoprotein kinetic changes apply to other PCSK9 mAbs,6,7 provided that the dosing regimen is sufficient to substantially inhibit the plasma concentration of free PCSK9 and its interaction with hepatic lipoprotein receptors.5 Beyond accelerating catabolism, the reduction in production of apoB seen with our PCSK9 mAb regimen could have a specific therapeutic advantage and remains to be further evaluated clinically. Specifically, the reduced production of IDL and LDL-apoB may not apply to patients who have impaired activity of hepatic receptors, such as those with multigenic or autosomal dominant hypercholesterolemia with higher plasma concentration of LDL-cholesterol, particularly on high-intensity statin therapy.35 Accordingly, future studies should investigate the postabsorptive and postprandial effects of evolocumab on lipoprotein kinetics in subjects with atherogenic dyslipidemia, including those with type 2 diabetes mellitus, the metabolic syndrome, and familial hypercholesterolemia.35–37

Tracer kinetics underpin our knowledge of the in vivo physiology and pathophysiology of plasma lipids and lipoproteins.2–4 These dynamic studies provide unique data for understanding the modes of action and efficacy of lipid-regulating therapies in humans and can therefore bear significantly on best clinical practice and the prevention and treatment of atherosclerotic cardiovascular disease.3,4 Although strictly an interventional investigation of normal lipoprotein physiology, our findings proffer fundamental mechanisms that could underpin the outcomes of previous and future clinical trials using PCSK9 mAbs.6

Acknowledgments

The authors thank Janice Carlson, PhD (of Amgen Inc), and Gurpreet Kaur, PhD, of Cactus Communications (on behalf of Amgen Inc) for editorial support. All authors had full access to all the data in the study and take responsibility for its integrity and the data analysis.

Sources of Funding

This study was funded by Amgen Inc.

Disclosures

Dr Watts has received honoraria for advisory boards and speakers bureau or research grants from Amgen Inc., Sanofi, Regeneron, Kowa, and Genfit. Drs Chan and Barrett have no disclosures. Drs Dent, Somaratne, Wasserman, and Scott are current or former employees of Amgen Inc.

Footnotes

  • Received August 23, 2016.
  • Accepted November 23, 2016.

References

  1. 1.↵
    1. Catapano AL,
    2. Graham I,
    3. De Backer G,
    4. Wiklund O,
    5. Chapman MJ,
    6. Drexel H,
    7. Hoes AW,
    8. Jennings CS,
    9. Landmesser U,
    10. Pedersen TR,
    11. Reiner Ž,
    12. Riccardi G,
    13. Taskinen MR,
    14. Tokgozoglu L,
    15. Verschuren WM,
    16. Vlachopoulos C,
    17. Wood DA,
    18. Zamorano JL.
    2016 ESC/EAS guidelines for the management of dyslipidaemias: The Task Force for the Management of Dyslipidaemias of the European Society of Cardiology (ESC) and European Atherosclerosis Society (EAS). Atherosclerosis. 2016;253:281–344.
    OpenUrl
  2. 2.↵
    1. Dietschy JM,
    2. Turley SD,
    3. Spady DK.
    Role of liver in the maintenance of cholesterol and low density lipoprotein homeostasis in different animal species, including humans. J Lipid Res. 1993;34:1637–1659.
    OpenUrlPubMed
  3. 3.↵
    1. Barrett PH,
    2. Chan DC,
    3. Watts GF.
    Thematic review series: patient-oriented research. Design and analysis of lipoprotein tracer kinetics studies in humans. J Lipid Res. 2006;47:1607–1619. doi: 10.1194/jlr.R600017-JLR200.
    OpenUrlAbstract/FREE Full Text
  4. 4.↵
    1. Chan DC,
    2. Barrett PH,
    3. Watts GF.
    The metabolic and pharmacologic bases for treating atherogenic dyslipidaemia. Best Pract Res Clin Endocrinol Metab. 2014;28:369–385. doi: 10.1016/j.beem.2013.10.001.
    OpenUrlCrossRef
  5. 5.↵
    1. Seidah NG,
    2. Awan Z,
    3. Chrétien M,
    4. Mbikay M.
    PCSK9: a key modulator of cardiovascular health. Circ Res. 2014;114:1022–1036. doi: 10.1161/CIRCRESAHA.114.301621.
    OpenUrlAbstract/FREE Full Text
  6. 6.↵
    1. Giugliano RP,
    2. Sabatine MS.
    Are PCSK9 inhibitors the next breakthrough in the cardiovascular field? J Am Coll Cardiol. 2015;65:2638–2651. doi: 10.1016/j.jacc.2015.05.001.
    OpenUrlFREE Full Text
  7. 7.↵
    1. Stein EA,
    2. Raal F.
    Reduction of low-density lipoprotein cholesterol by monoclonal antibody inhibition of PCSK9. Annu Rev Med. 2014;65:417–431. doi: 10.1146/annurev-med-022613-090402.
    OpenUrlCrossRefPubMed
  8. 8.↵
    1. Grundy SM.
    Statins: definitive translational research. Mol Med. 2014;20(suppl 1):S20–S23. doi: 10.2119/molmed.2014.00194.
    OpenUrl
  9. 9.↵
    1. Ooi EM,
    2. Barrett PH,
    3. Chan DC,
    4. Nestel PJ,
    5. Watts GF.
    Dose-dependent effect of rosuvastatin on apolipoprotein B-100 kinetics in the metabolic syndrome. Atherosclerosis. 2008;197:139–146. doi: 10.1016/j.atherosclerosis.2007.03.004.
    OpenUrlCrossRefPubMed
  10. 10.↵
    1. Chan DC,
    2. Watts GF,
    3. Barrett PH,
    4. Mori TA,
    5. Beilin LJ,
    6. Redgrave TG.
    Mechanism of action of a 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitor on apolipoprotein B-100 kinetics in visceral obesity. J Clin Endocrinol Metab. 2002;87:2283–2289. doi: 10.1210/jcem.87.5.8455.
    OpenUrlCrossRefPubMed
  11. 11.↵
    1. Watts GF,
    2. Barrett PH,
    3. Ji J,
    4. Serone AP,
    5. Chan DC,
    6. Croft KD,
    7. Loehrer F,
    8. Johnson AG.
    Differential regulation of lipoprotein kinetics by atorvastatin and fenofibrate in subjects with the metabolic syndrome. Diabetes. 2003;52:803–811.
    OpenUrlAbstract/FREE Full Text
  12. 12.↵
    1. Colbert A,
    2. Umble-Romero A,
    3. Prokop S,
    4. Xu R,
    5. Gibbs J,
    6. Pederson S.
    Characterization of a quantitative method to measure free proprotein convertase subtilisin/kexin type 9 in human serum. MAbs. 2014;6:1103–1113. doi: 10.4161/mabs.28719.
    OpenUrlCrossRefPubMed
  13. 13.↵
    1. Kempen HJ,
    2. Glatz JF,
    3. Gevers Leuven JA,
    4. van der Voort HA,
    5. Katan MB.
    Serum lathosterol concentration is an indicator of whole-body cholesterol synthesis in humans. J Lipid Res. 1988;29:1149–1155.
    OpenUrlAbstract
  14. 14.↵
    1. Grundy SM.
    HMG-CoA reductase inhibitors for treatment of hypercholesterolemia. N Engl J Med. 1988;319:24–33. doi: 10.1056/NEJM198807073190105.
    OpenUrlCrossRefPubMed
  15. 15.↵
    1. Csete ME,
    2. Doyle JC.
    Reverse engineering of biological complexity. Science. 2002;295:1664–1669. doi: 10.1126/science.1069981.
    OpenUrlAbstract/FREE Full Text
  16. 16.↵
    1. Campos H,
    2. Arnold KS,
    3. Balestra ME,
    4. Innerarity TL,
    5. Krauss RM.
    Differences in receptor binding of LDL subfractions. Arterioscler Thromb Vasc Biol. 1996;16:794–801.
    OpenUrlAbstract/FREE Full Text
  17. 17.↵
    1. Dong B,
    2. Wu M,
    3. Cao A,
    4. Li H,
    5. Liu J.
    Suppression of Idol expression is an additional mechanism underlying statin-induced up-regulation of hepatic LDL receptor expression. Int J Mol Med. 2011;27:103–110. doi: 10.3892/ijmm.2010.559.
    OpenUrlPubMed
  18. 18.↵
    1. Sasaki M,
    2. Terao Y,
    3. Ayaori M,
    4. Uto-Kondo H,
    5. Iizuka M,
    6. Yogo M,
    7. Hagisawa K,
    8. Takiguchi S,
    9. Yakushiji E,
    10. Nakaya K,
    11. Ogura M,
    12. Komatsu T,
    13. Ikewaki K.
    Hepatic overexpression of idol increases circulating protein convertase subtilisin/kexin type 9 in mice and hamsters via dual mechanisms: sterol regulatory element-binding protein 2 and low-density lipoprotein receptor-dependent pathways. Arterioscler Thromb Vasc Biol. 2014;34:1171–1178. doi: 10.1161/ATVBAHA.113.302670.
    OpenUrlAbstract/FREE Full Text
  19. 19.↵
    1. Watts GF,
    2. Naoumova RP,
    3. Kelly JM,
    4. Riches FM,
    5. Croft KD,
    6. Thompson GR.
    Inhibition of cholesterogenesis decreases hepatic secretion of apoB-100 in normolipidemic subjects. Am J Physiol. 1997;273(3 pt 1):E462–E470.
    OpenUrl
  20. 20.↵
    1. Blasiole DA,
    2. Oler AT,
    3. Attie AD.
    Regulation of ApoB secretion by the low density lipoprotein receptor requires exit from the endoplasmic reticulum and interaction with ApoE or ApoB. J Biol Chem. 2008;283:11374–11381. doi: 10.1074/jbc.M710457200.
    OpenUrlAbstract/FREE Full Text
  21. 21.↵
    1. Ouguerram K,
    2. Chetiveaux M,
    3. Zair Y,
    4. Costet P,
    5. Abifadel M,
    6. Varret M,
    7. Boileau C,
    8. Magot T,
    9. Krempf M.
    Apolipoprotein B100 metabolism in autosomal-dominant hypercholesterolemia related to mutations in PCSK9. Arterioscler Thromb Vasc Biol. 2004;24:1448–1453. doi: 10.1161/01.ATV.0000133684.77013.88.
    OpenUrlAbstract/FREE Full Text
  22. 22.↵
    1. Cariou B,
    2. Ouguerram K,
    3. Zaïr Y,
    4. Guerois R,
    5. Langhi C,
    6. Kourimate S,
    7. Benoit I,
    8. Le May C,
    9. Gayet C,
    10. Belabbas K,
    11. Dufernez F,
    12. Chétiveaux M,
    13. Tarugi P,
    14. Krempf M,
    15. Benlian P,
    16. Costet P.
    PCSK9 dominant negative mutant results in increased LDL catabolic rate and familial hypobetalipoproteinemia. Arterioscler Thromb Vasc Biol. 2009;29:2191–2197. doi: 10.1161/ATVBAHA.109.194191.
    OpenUrlAbstract/FREE Full Text
  23. 23.↵
    1. Bilheimer DW,
    2. Stone NJ,
    3. Grundy SM.
    Metabolic studies in familial hypercholesterolemia. Evidence for a gene-dosage effect in vivo. J Clin Invest. 1979;64:524–533. doi: 10.1172/JCI109490.
    OpenUrlCrossRefPubMed
  24. 24.↵
    1. Duane WC,
    2. Hunninghake DB,
    3. Freeman ML,
    4. Pooler PA,
    5. Schlasner LA,
    6. Gebhard RL.
    Simvastatin, a competitive inhibitor of HMG-CoA reductase, lowers cholesterol saturation index of gallbladder bile. Hepatology. 1988;8:1147–1150.
    OpenUrlCrossRefPubMed
  25. 25.↵
    1. Watts GF,
    2. Chan DC,
    3. Barrett PH,
    4. O’Neill FH,
    5. Thompson GR.
    Effect of a statin on hepatic apolipoprotein B-100 secretion and plasma campesterol levels in the metabolic syndrome. Int J Obes Relat Metab Disord. 2003;27:862–865. doi: 10.1038/sj.ijo.0802287.
    OpenUrlCrossRefPubMed
  26. 26.↵
    1. Thompson GR,
    2. Naoumova RP,
    3. Watts GF.
    Role of cholesterol in regulating apolipoprotein B secretion by the liver. J Lipid Res. 1996;37:439–447.
    OpenUrlAbstract
  27. 27.↵
    1. Krieger M,
    2. Herz J.
    Structures and functions of multiligand lipoprotein receptors: macrophage scavenger receptors and LDL receptor-related protein (LRP). Annu Rev Biochem. 1994;63:601–637. doi: 10.1146/annurev.bi.63.070194.003125.
    OpenUrlCrossRefPubMed
  28. 28.↵
    1. Mahley RW,
    2. Ji ZS.
    Remnant lipoprotein metabolism: key pathways involving cell-surface heparan sulfate proteoglycans and apolipoprotein E. J Lipid Res. 1999;40:1–16.
    OpenUrlAbstract/FREE Full Text
  29. 29.↵
    1. Ooi EM,
    2. Barrett PH,
    3. Chan DC,
    4. Watts GF.
    Apolipoprotein C-III: understanding an emerging cardiovascular risk factor. Clin Sci (Lond). 2008;114:611–624. doi: 10.1042/CS20070308.
    OpenUrlCrossRefPubMed
  30. 30.↵
    1. Chan DC,
    2. Watts GF,
    3. Ooi EM,
    4. Ji J,
    5. Johnson AG,
    6. Barrett PH.
    Atorvastatin and fenofibrate have comparable effects on VLDL-apolipoprotein C-III kinetics in men with the metabolic syndrome. Arterioscler Thromb Vasc Biol. 2008;28:1831–1837. doi: 10.1161/ATVBAHA.108.170530.
    OpenUrlAbstract/FREE Full Text
  31. 31.↵
    1. Poirier S,
    2. Mayer G,
    3. Benjannet S,
    4. Bergeron E,
    5. Marcinkiewicz J,
    6. Nassoury N,
    7. Mayer H,
    8. Nimpf J,
    9. Prat A,
    10. Seidah NG.
    The proprotein convertase PCSK9 induces the degradation of low density lipoprotein receptor (LDLR) and its closest family members VLDLR and ApoER2. J Biol Chem. 2008;283:2363–2372. doi: 10.1074/jbc.M708098200.
    OpenUrlAbstract/FREE Full Text
  32. 32.↵
    1. Curtiss LK,
    2. Boisvert WA.
    Apolipoprotein E and atherosclerosis. Curr Opin Lipidol. 2000;11:243–251.
    OpenUrlCrossRefPubMed
  33. 33.↵
    1. Ooi EM,
    2. Ng TW,
    3. Watts GF,
    4. Chan DC,
    5. Barrett PH.
    Effect of fenofibrate and atorvastatin on VLDL apoE metabolism in men with the metabolic syndrome. J Lipid Res. 2012;53:2443–2449. doi: 10.1194/jlr.P029223.
    OpenUrlAbstract/FREE Full Text
  34. 34.↵
    1. Stein EA,
    2. Giugliano RP,
    3. Koren MJ,
    4. Raal FJ,
    5. Roth EM,
    6. Weiss R,
    7. Sullivan D,
    8. Wasserman SM,
    9. Somaratne R,
    10. Kim JB,
    11. Yang J,
    12. Liu T,
    13. Albizem M,
    14. Scott R,
    15. Sabatine MS
    ; PROFICIO Investigators. Efficacy and safety of evolocumab (AMG 145), a fully human monoclonal antibody to PCSK9, in hyperlipidaemic patients on various background lipid therapies: pooled analysis of 1359 patients in four phase 2 trials. Eur Heart J. 2014;35:2249–2259. doi: 10.1093/eurheartj/ehu085.
    OpenUrlAbstract/FREE Full Text
  35. 35.↵
    1. Rashid S,
    2. Tavori H,
    3. Brown PE,
    4. Linton MF,
    5. He J,
    6. Giunzioni I,
    7. Fazio S.
    Proprotein convertase subtilisin kexin type 9 promotes intestinal overproduction of triglyceride-rich apolipoprotein B lipoproteins through both low-density lipoprotein receptor-dependent and -independent mechanisms. Circulation. 2014;130:431–441. doi: 10.1161/CIRCULATIONAHA.113.006720.
    OpenUrlAbstract/FREE Full Text
  36. 36.↵
    1. Ooi EM,
    2. Barrett PH,
    3. Watts GF.
    The extended abnormalities in lipoprotein metabolism in familial hypercholesterolemia: developing a new framework for future therapies. Int J Cardiol. 2013;168:1811–1818. doi: 10.1016/j.ijcard.2013.06.069.
    OpenUrlCrossRefPubMed
  37. 37.↵
    1. Druce I,
    2. Abujrad H,
    3. Ooi T.
    PCSK9 and triglyceride-rich lipoprotein metabolism. J Biomed Res. 2015;29:429–436.
    OpenUrl

Clinical Perspective

What Is New?

  • This is the largest and most robust stable isotope tracer study of the effect of inhibiting proprotein convertase subtilisin kexin type 9 and cholesterol synthesis on lipoprotein metabolism in humans.

  • In healthy subjects, high-dose atorvastatin and evolocumab independently accelerated the catabolism of very-low-density, intermediate-density, and low-density lipoprotein particles.

  • Evolocumab but not atorvastatin decreased the production of intermediate-density lipoprotein and low-density lipoprotein.

  • This explained the greater reduction in plasma concentrations of low-density lipoprotein particles with evolocumab than with atorvastatin and the greater efficacy of combination therapy than monotherapy in lowering the plasma concentration of the apolipoprotein B-100–containing lipoprotein particles.

What Are the Clinical Implications?

  • Evolocumab, a monoclonal antibody against proprotein convertase subtilisin kexin type 9, lowers the plasma concentrations of atherogenic apolipoprotein B-100–containing lipoproteins by accelerating catabolism and reducing production of these particles, even in subjects with a normal plasma lipid profile.

  • High-dose atorvastatin also accelerates catabolism but does not lower production of these lipoproteins, implying that, even at lower plasma lipid levels, both agents have complementary modes of action.

  • The mechanisms described may apply to individuals with milder forms of dyslipidemias, but need further investigation in those with familial hypercholesterolemia.

  • The findings proffer potential new mechanisms for understanding the outcomes of ongoing clinical trials using proprotein convertase subtilisin kexin type 9 inhibitors.

View Abstract

This Issue

Jump to

Article Tools

Share this Article

  • Email
  • Factorial Effects of Evolocumab and Atorvastatin on Lipoprotein MetabolismClinical Perspective
    Gerald F. Watts, Dick C. Chan, Ricardo Dent, Ransi Somaratne, Scott M. Wasserman, Rob Scott, Sally Burrows and P. Hugh R. Barrett
    Circulation. 2017;135:338-351, originally published December 9, 2016
    https://doi.org/10.1161/CIRCULATIONAHA.116.025080
    del.icio.us logo Digg logo Reddit logo Twitter logo CiteULike logo Facebook logo Google logo Mendeley logo

Related Articles

Cited By...

Subjects