Removal of plasma mature and furin-cleaved proprotein convertase subtilisin/kexin 9 by low-density lipoprotein-apheresis in familial hypercholesterolemia: development and application of a new assay for PCSK9

Serum mature and furin-cleaved proprotein convertase subtilisin/kexin type 9 levels and their association with cardiovascular events in statin-treated patients with cardiovascular disease

BACKGROUND AND AIMS

Previous studies have not found a consistent association between circulating proprotein convertase subtilisin/kexin type 9 (PCSK9) levels and the risk of cardiovascular events partly due to measurement methods that cannot distinguish between uncleaved and furin-cleaved forms of PCSK9.

METHODS

This is a prespecified sub-study of the REAL-CAD study which is a prospective, multicenter, randomized trial to compare high- versus low-dose statin in patients with stable coronary artery disease (CAD). The primary endpoint was major adverse cerebrovascular and cardiovascular events (MACCE) defined as a composite of cardiovascular death, nonfatal myocardial infarction, nonfatal ischemic stroke, or unstable angina requiring emergency hospitalization. In this case-cohort study, serum mature (uncleaved) and furin-cleaved PCSK9 levels obtained at 6 months after randomization were measured among 426 participants who developed MACCE (cases) and 1,478 randomly selected participants (sub-cohort).

RESULTS

From 1,478 patients in the sub-cohort, the Cox proportional hazards models with a pseudolikelihood method for case-cohort design revealed that the risk of the primary endpoint in patients with the highest quartile of mature PCSK9 levels was similar to that in the lowest quartile (hazard ratio [HR] 0.809; 95% confidence intervals [CI], 0.541-1.209). Similarly, the HR for the highest to lowest quartiles of furin-cleaved PCSK9 was 0.948 (95% CI, 0.645-1.392) (P = 0.784). Compared to the lowest quartile, neither serum mature nor furin-cleaved PCSK9 levels predicted MACCE.

CONCLUSIONS

In a large-scale secondary prevention cohort, serum mature and furin-cleaved PCSK9 levels did not provide useful information for predicting future cardiovascular events in statin-treated patients with stable CAD.

Updated evidence of beneficial effect of LDL apheresis for refractory nephrotic syndrome due to a variety of causative diseases for nationwide and global approval

Low-density lipoprotein apheresis (LDL-A) therapy has shown reasonable efficacy in treating nephrotic syndrome (NS) refractory to initial drug therapy and has been covered by National Health Insurance for the indication of drug-resistant focal segmental glomerulosclerosis (FSGS) since 1992 in Japan and has contributed to liberating substantial number of patients of this disease from entering into end-stage renal disease by easier practical application in actual clinical settings. Subsequently, various beneficial evidence of this treatment has accumulated on those other than FSGS, however, due to the limitation of covered disease insurance only for FSGS, patients with diseases other than FSGS are unlikely to benefit from this treatment in practice. This review summarizes the therapeutic evidence of the beneficial effect of LDL-A accumulated to date and the mechanisms of action analyzed from multifaceted perspectives. examines the applicability of expanding insurance coverage for diseases other than FSGS.

Relationship between Serum Proprotein Convertase Subtilisin/Kexin Type 9 Concentration and Prevalence of Coronary Artery Calcium in a Community-Based Sample of Japanese Men

AIMS

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a promising new target for reducing low-density lipoprotein cholesterol (LDL-C) and cardiovascular events in high-risk patients. However, the influence of circulating PCSK9 concentration on atherosclerotic plaque formation in the general population remains unknown. We assessed the relationship between serum PCSK9 concentration and coronary artery calcium (CAC) prevalence in the general population.

METHODS

Community-dwelling Japanese men (n=622) aged 46-82 years without a history of cardiovascular disease and lipid-lowering medications were included. Serum PCSK9 concentration and CAC score were measured using the Agatston method, and the multivariable analysis was used to assess their association. CAC was defined as an Agatston score of ＞10. We conducted further analysis stratified by age (＜60, 60-69, and ≥ 70 years).

RESULTS

The average age, LDL-C, and median serum PCSK9 concentration were 68 years, 122 mg/dL, and 240 ng/mL, respectively. After multivariable adjustment for traditional cardiovascular risk factors, no significant association was observed between serum PCSK9 concentration and CAC prevalence (adjusted relative risk [aRR] 1.05, 95% confidence interval [CI] 0.97-1.13). With age stratification, serum PCSK9 concentration was significantly associated with CAC prevalence in men aged ＜60 years (aRR 1.38, 95% CI 1.01-1.88) but not in men aged 60-69 years (aRR 0.96, 95% CI 0.85-1.10) or ≥ 70 years (aRR 1.08, 95% CI 0.99-1.19).

CONCLUSIONS

A higher serum PCSK9 concentration was associated with a higher CAC prevalence in men aged ＜60 years, which was independent of traditional cardiovascular risk factors.

The circulating furin-cleaved/mature PCSK9 ratio has a potential prognostic significance in statin-naïve patients with acute ST elevation myocardial infarction

Background and aims

Proprotein convertase subtilisin/kexin type 9 (PCSK9) circulates as mature and furin-cleaved forms, but their biological functions are uncertain. We investigated whether their levels associate with prognosis in patients with acute ST elevation myocardial infarction (STEMI).

Methods

We enrolled 160 statin-naïve patients with acute STEMI and followed for 3 years. PCSK9 subtype levels were determined by an enzyme-linked immunosorbent assay before and at five timepoints up to 48 h after emergent coronary intervention. The occurrence of coronary and cardiac events was compared between subjects stratified by the PCSK9 level.

Results

One hundred and twenty-six patients completed 3 years of follow-up. In the acute phase, both PCSK9 subtype levels decreased, and thereafter increased from 6 to 48 h (mature: from 198 ± 67 to 334 ± 116 ng/mL, furin-cleaved: from 20 ± 7 to 39 ± 16 ng/mL, both p < 0.01). Major cardiac events occurred in 46 patients. The furin-cleaved/mature PCSK9 ratio at 48 h after coronary intervention predicted the likelihood of experiencing of events; patients in the third tertile had lower event-free survival than those in the first and second tetiles in Kaplan-Meier analysis (p = 0.004). Multivariate Cox regression analysis revealed that this ratio had a greater impact (HR: 1.92; 95% CI: 1.06-3.45, p = 0.03) on events than other known atherosclerosis risk factors.

Conclusions

The furin-cleaved/mature PCSK9 ratio was associated with 3-year cardiovascular events in statin-naïve patients with acute STEMI, suggesting a potential link between furin cleavage process of PCSK9 and its effect on prognosis. (249 words).

Pathogenic gain-of-function mutations in the prodomain and C-terminal domain of PCSK9 inhibit LDL binding

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a secreted protein that binds and mediates endo-lysosomal degradation of low-density lipoprotein receptor (LDLR), limiting plasma clearance of cholesterol-rich LDL particles in liver. Gain-of-function (GOF) point mutations in PCSK9 are associated with familial hypercholesterolemia (FH). Approximately 30%–40% of PCSK9 in normolipidemic human plasma is bound to LDL particles. We previously reported that an R496W GOF mutation in a region of PCSK9 known as cysteine-histidine–rich domain module 1 (CM1) prevents LDL binding in vitro [Sarkar et al., J. Biol. Chem. 295 (8), 2285–2298 (2020)]. Herein, we identify additional GOF mutations that inhibit LDL association, localized either within CM1 or a surface-exposed region in the PCSK9 prodomain. Notably, LDL binding was nearly abolished by a prodomain S127R GOF mutation, one of the first PCSK9 mutations identified in FH patients. PCSK9 containing alanine or proline substitutions at amino acid position 127 were also defective for LDL binding. LDL inhibited cell surface LDLR binding and degradation induced by exogenous PCSK9-D374Y but had no effect on an S127R-D374Y double mutant form of PCSK9. These studies reveal that multiple FH-associated GOF mutations in two distinct regions of PCSK9 inhibit LDL binding, and that the Ser-127 residue in PCSK9 plays a critical role.

Pharmacological rationale for the very early treatment of acute coronary syndrome with monoclonal antibodies anti-PCSK9

Immediate and aggressive lipid lowering therapies after acute coronary syndromes (ACS) and percutaneous coronary interventions (PCI) are supported by the ESC/EAS dyslipidemia guidelines, recommending the initiation of high-intensity statin therapy within the first 1-4 days of hospitalization. However, whether non statin lipid-lowering agents, added to statin treatment, could produce a further reduction in the risk of major adverse cardiovascular events (MACE) is still unknown. Thus, the efficacy of early treatment post-ACS with monoclonal antibodies (mAbs) anti PCSK9, evolocumab and alirocumab, is under investigation. The rationale to explore the rapid and aggressive pharmacological intervention with PCSK9 mAbs is supported by at least five confirmatory data in ACS: 1) circulating PCSK9 levels are raised during ACS 2) PCSK9 may stimulate platelet reactivity, this last being pivotal in the recurrence of ischemic events; 3) PCSK9 is associated with intraplaque inflammation, macrophage activation and endothelial dysfunction; 4) PCSK9 concentrations are associated with inflammation in the acute phase of ACS; and 5) statins raise PCSK9 levels promptly and, at times, dramatically. In this scenario, appropriate pharmacodynamic characteristics of anti PCSK9 therapies are a prerequisite for an effective response. Monoclonal antibodies act on circulating PCSK9 with a direct and rapid binding by blocking the interaction with the low-density lipoprotein receptor (LDLR). Evolocumab and alirocumab show a very rapid (within 4 h) and effective suppression of circulating unbound PCSK9 (- 95 % ÷ - 97 %). This inhibition results in a significant reduction of LDL-cholesterol (LDL-C) after 48 h (- 35 %) post injection with a full effect after 7-10 days (55-75 %). The complete and swift inhibitory action by evolocumab and alirocumab could have a potential clinical impact in ACS patients, also considering their potential inhibition of PCSK9 within the atherosclerotic plaque. Thus, administration of evolocumab or alirocumab is effective in lowering LDL-C levels in ACS, although the efficacy to prevent further cardiovascular (CV) events is still undetermined. The answer to this question will be provided by the ongoing clinical trials with evolocumab and alirocumab in ACS. In the present review we will discuss the pharmacological and biological rationale supporting the potential use of PCSK9 mAbs in ACS patients and the emerging evidence of evolocumab and alirocumab treatment in this clinical setting.

PCSK9 is minimally associated with HDL but impairs the anti-atherosclerotic HDL effects on endothelial cell activation

Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) regulates the cell-surface localization of LDL receptors in hepatocytes and is associated with LDL and lipoprotein(a) [Lp(a)] uptake, reducing blood concentrations. However, the connection between PCSK9 and HDL is unclear. Here, we investigated the association of plasma PCSK9 with HDL subpopulations and examined the effects of PCSK9 on the atheroprotective function of HDL. We examined the association of PCSK9 with HDL in apoB-depleted plasma by ELISA, native PAGE, and immunoblotting. Our analyses showed that upon apoB-depletion, total circulating PCSK9 levels were 32% of those observed in normolipidemic plasma, and only 6% of PCSK9 in the apoB-depleted plasma, including both the mature and furin-cleaved forms, was associated with HDL. We also show human recombinant PCSK9 abolished the capacity of reconstituted HDL to reduce the formation of ROS in endothelial cells, while a PCSK9-blocking antibody enhanced the capacity of human HDL (in apoB-depleted plasma) to reduce ROS formation in endothelial cells and promote endothelial cell migration. Overall, our findings suggest that PCSK9 is only minimally associated with HDL particles, but PCSK9 in apoB-depleted plasma can affect the atheroprotective properties of HDL related to preservation of endothelial function. This study contributes to the elucidation of the pathophysiological role of plasma PCSK9 and highlights further the anti-atherosclerotic effect of PCSK9 inhibition.

How Can We Identify Very High-Risk Heterozygous Familial Hypercholesterolemia?

Heterozygous familial hypercholesterolemia (HeFH) is a genetic disorder that elevates low-density lipoprotein cholesterol and increases the risk of premature atherosclerotic cardiovascular disease (ASCVD). However, despite their atherogenic lipid profiles, the cardiovascular risk of HeFH varies in each individual. Their variety of phenotypic features suggests the need for better risk stratification to optimize their therapeutic management. The current review summarizes three potential approaches, including (1) definition of familial hypercholesterolemia (FH)-related risk scores, (2) genetic analysis, and (3) biomarkers. The International Atherosclerosis Society has recently proposed a definition of severe FH to identify very high-risk HeFH subjects according to their clinical characteristics. Furthermore, published studies have shown the association of FH-related genetic phenotypes with ASCVD, which indicates the genetic analysis's potential to evaluate individual cardiovascular risks. Biomarkers reflecting disease activity have been considered to predict the formation of atherosclerosis and the occurrence of ASCVD in HeFH subjects. Incorporating these risk stratifications will be expected to allocate adequate intensity of lipid-lowering therapies in HeFH subjects, which ultimately improves cardiovascular outcomes.

Differential Effects of DPP-4 Inhibitors, Anagliptin and Sitagliptin, on PCSK9 Levels in Patients with Type 2 Diabetes Mellitus who are Receiving Statin Therapy

Aim: Proprotein convertase subtilisin/kexin type 9 (PCSK9) degrades the low-density lipoprotein (LDL) receptor, leading to hypercholesterolemia and cardiovascular risk. Treatment with a statin leads to a compensatory increase in circulating PCSK9 level. Anagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, was shown to decrease LDL cholesterol (LDL-C) levels to a greater extent than that by sitagliptin, another DPP-4 inhibitor, in the Randomized Evaluation of Anagliptin versus Sitagliptin On low-density lipoproteiN cholesterol in diabetes (REASON) trial. We investigated PCSK9 concentration in type 2 diabetes mellitus (T2DM) and the impact of treatment with anagliptin or sitagliptin on PCSK9 level as a sub-analysis of the REASON trial.

Methods: PCSK9 concentration was measured at baseline and after 52 weeks of treatment with anagliptin ( n =122) or sitagliptin ( n =128) in patients with T2DM who were receiving statin therapy. All of the included patients had been treated with a DPP-4 inhibitor prior to randomization.

Results: Baseline PCSK9 level was positively, but not significantly, correlated with LDL-C and was independently associated with platelet count and level of triglycerides. Concomitant with reduction of LDL-C, but not hemoglobin A1c (HbA1c), by anagliptin, PCSK9 level was significantly increased by treatment with sitagliptin (218±98 vs. 242±115 ng/mL, P =0.01), but not anagliptin (233±97 vs. 250±106 ng/mL, P =0.07).

Conclusions: PCSK9 level is independently associated with platelet count and level of triglycerides, but not LDL-C, in patients with T2DM. Anagliptin reduces LDL-C level independent of HbA1c control in patients with T2DM who are on statin therapy possibly by suppressing excess statin-mediated PCSK9 induction and subsequent degradation of the LDL receptor.

Circulating Furin-Cleaved Proprotein Convertase Subtilisin/Kexin Type 9 Concentration Predicts Future Coronary Events in Japanese Subjects

Background

Proprotein convertase subtilisin/kexin type 9 (PCSK9) circulates as mature and furin-cleaved forms, which differ in their properties to degrade low-density lipoprotein (LDL) receptors.

Objectives

In this study, we sought to investigate whether PCSK9 subtypes associate with atherosclerotic cardiovascular events.

Methods

We investigated 1,436 statin-naive Japanese subjects without any cardiovascular disease in the Suita Study, an epidemiologic Japanese cohort study. Total, mature, and furin-cleaved PCSK9 levels were measured by means of enzyme-linked immunosorbent assay. The occurrence of coronary and stroke events were compared in subjects stratified by PCSK9 level tertile.

Results

Total, mature, and furin-cleaved PCSK9 levels were associated with non–high-density lipoprotein cholesterol (all P < 0.001) and systolic blood pressure (P = 0.001, P = 0.004, and P < 0.001, respectively). Furthermore, only furin-cleaved PCSK9 level was correlated to high-sensitivity C-reactive protein (hs-CRP) (P < 0.001). During the 13.6-year observational period, furin-cleaved PCSK9 level predicted a greater likelihood of experiencing coronary events (tertile 2: hazard ratio [HR]: 2.84 [95% confidence interval [CI]: 1.21-6.65; P = 0.01]; tertile 3: HR: 2.81 [95% CI: 1.17-6.74; P = 0.02]), but not stroke (tertile 2: HR: 1.31 [95% CI: 0.72-2.40; P = 0.36]; tertile 3: HR: 1.27 [95% CI: 0.68-2.38; P = 0.44]). Total and mature PCSK9 levels were not associated with coronary events (total PCSK9: tertile 2: HR: 1.35 [95% CI: 0.68-2.68; P = 0.39]; tertile 3: HR: 1.13 [95% CI: 0.54-2.34; P = 0.73]; mature PCSK9: tertile 2: HR: 1.02 [95% CI: 0.52-2.02; P = 0.93]; tertile 3: HR: 0.96 [95% CI: 0.47-1.95; P = 0.92]) and stroke events (total PCSK9: tertile 2: HR: 0.90 [95% CI: 0.50-1.61; P = 0.72]; tertile 3: HR: 0.99 [95% CI:0.54-1.80; P = 0.97]; mature PCSK9: tertile 2: HR: 0.86 [95% CI: 0.47-1.57; P = 0.63]; tertile 3: HR: 1.11 [95% CI: 0.61-1.99; P = 0.72]), respectively.

Conclusions

Furin-cleaved but not total and mature PCSK9 was associated with both LDL cholesterol and hs-CRP and predicted future coronary events in the primary prevention settings. Our findings provide pathophysiological insights into the properties of PCSK9 subtypes in association with coronary events.

PCSK9 Inhibitors and Cardiovascular Disease: Impact on Cardiovascular Outcomes

Cardiovascular Disease (CVD) remains the leading cause of morbidity and mortality in the western world. Hypolipidemic drugs have long been used for the primary and secondary prevention of heart disease. However, the high frequency of recurrent events in patients despite hypolipidemic therapy has increased the need for new more targeted therapeutic approaches. Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors are monoclonal antibodies to the PCSK9 gene and represent a new class of drugs that have been shown to further decrease LDL-C when administered as a monotherapy or in combination with statins. In addition to LDL reduction, PCSK9 inhibitors are shown to decrease apolipoprotein B and lipoprotein (a) levels without major adverse effects. Whether or not PCSK9 inhibitors can actually reduce the incidence of cardiovascular events and ameliorate CVD prognosis is yet to be clarified. This review summarizes recent literature on the safety and efficacy of PCSK9 inhibitors on CVD outcome and its potential role in the management of patients with high-risk cardiovascular disease.

Circulating Mature PCSK9 Level Predicts Diminished Response to Statin Therapy

Background Statin-mediated efficacy of lowering low-density lipoprotein (LDL) cholesterol varies in each individual, and its diminished response is associated with worse outcomes. However, there is no established approach to predict hyporesponse to statins. PCSK9 (proprotein convertase subxilisin/kexin type 9) is a serine-protease associated with LDL metabolism, which circulates as mature and furin-cleaved PCSK9. Since mature PCSK9 more potently degrades the LDL receptor, its evaluation may enable the identification of statin hyporesponders. Methods and Results We analyzed 101 statin-naive patients with coronary artery disease who commenced a statin. PCSK9 subtypes at baseline and 1 month after statin use were measured by ELISA. Hyporesponse to statins was defined as a percent reduction in LDL cholesterol <15%. The relationship between each PCSK9 subtype level and hyporesponse to statins was investigated. Statins significantly lowered LDL cholesterol level (percent reduction, 40%±21%), whereas 11% of study participants exhibited a hyporeseponse to statins. Multivariable logistic regression analysis demonstrated that baseline mature PCSK9 level was an independent predictor for hyporesponse to statins even after adjusting clinical characteristics (mature PCSK9 per 10-ng/mL increase: odds ratio [OR], 1.12; 95% CI, 1.01-1.24 [P=0.03]), whereas furin-cleaved level was not (per 10-ng/mL increase: OR, 1.37; 95% CI, 0.73-2.58 [P=0.33]). Receiver operating characteristic curve analysis identified mature PCSK9 level of 228 ng/mL as an optimal cutoff to predict hyporesponse to statins (area under the curve, 0.73 [sensitivity, 0.91; specificity, 0.56]). Conclusions Baseline mature PCSK9 level >228 ng/mL is associated with hyporesponse to statins. This finding suggests that mature PCSK9 might be a potential determinant of hyporesponse to statins.

Dyslipidemia and cardiovascular health in childhood nephrotic syndrome

Children with steroid-resistant nephrotic syndrome (SRNS) are exposed to multiple cardiovascular risk factors predisposing them to accelerated atherosclerosis. This risk is negligible in steroid-sensitive nephrotic syndrome, but a substantial proportion of children with SRNS progress to chronic kidney disease, exacerbating the already existing cardiovascular risk. While dyslipidemia is an established modifiable risk factor for cardiovascular disease in adults with NS, it is uncertain to what extent analogous risks exist for children. There is increasing evidence of accelerated atherosclerosis in children with persistently high lipid levels, especially in refractory NS. Abnormalities of lipid metabolism in NS include hypertriglyceridemia and hypercholesterolemia due to elevated apolipoprotein B-containing lipoproteins, decreased lipoprotein lipase and hepatic lipase activity, increased hepatic PCSK9 levels, and reduced hepatic uptake of high-density lipoprotein. Existing guidelines for the management of dyslipidemia in children may be adapted to target lower lipid levels in children with NS, but they will most likely require both lifestyle modifications and pharmacological therapy. While there is a lack of data from randomized controlled trials in children with NS demonstrating the benefit of lipid-lowering drugs, therapies including statins, bile acid sequestrants, fibrates, ezetimibe, and LDL apheresis have all been suggested and/or utilized. However, concerns with the use of lipid-lowering drugs in children include unclear side effect profiles and unknown long-term impacts on neurological development and puberty. The recent introduction of anti-PCSK9 monoclonal antibodies and other therapies targeted to the molecular mechanisms of lipid transport disrupted in NS holds promise for the future treatment of dyslipidemia in NS.

A transient amphipathic helix in the prodomain of PCSK9 facilitates binding to low-density lipoprotein particles

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a ligand of low-density lipoprotein (LDL) receptor (LDLR) that promotes LDLR degradation in late endosomes/lysosomes. In human plasma, 30–40% of PCSK9 is bound to LDL particles; however, the physiological significance of this interaction remains unknown. LDL binding in vitro requires a disordered N-terminal region in PCSK9's prodomain. Here, we report that peptides corresponding to a predicted amphipathic α-helix in the prodomain N terminus adopt helical structure in a membrane-mimetic environment. This effect was greatly enhanced by an R46L substitution representing an atheroprotective PCSK9 loss-of-function mutation. A helix-disrupting proline substitution within the putative α-helical motif in full-length PCSK9 lowered LDL binding affinity >5-fold. Modeling studies suggested that the transient α-helix aligns multiple polar residues to interact with positively charged residues in the C-terminal domain. Gain-of-function PCSK9 mutations associated with familial hypercholesterolemia (FH) and clustered at the predicted interdomain interface (R469W, R496W, and F515L) inhibited LDL binding, which was completely abolished in the case of the R496W variant. These findings shed light on allosteric conformational changes in PCSK9 required for high-affinity binding to LDL particles. Moreover, the initial identification of FH-associated mutations that diminish PCSK9's ability to bind LDL reported here supports the notion that PCSK9-LDL association in the circulation inhibits PCSK9 activity.

A Healthy Family of Familial Hypobetalipoproteinemia Caused by a Protein-truncating Variant in the PCSK9 Gene

We present the first case of a Japanese patient with familial hypobetalipoproteinemia (FHBL) caused by a protein-truncating variant in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene. A 34-year-old woman was referred to our hospital due to her low low-density lipoprotein (LDL)-cholesterolemia (34 mg/dL). She did not have any secondary causes of hypobetalipoproteinemia. Her father and her younger sister also exhibited low LDL cholesterol levels. We identified a protein-truncating variant in the PCSK9 gene (c.1090_1091del/p.Pro364ArgfsTer62) among them. None of them exhibited atherosclerotic cardiovascular diseases nor any other complications associated with low LDL cholesterol, including fatty liver, neurocognitive disorders, or cerebral hemorrhaging.

Apolipoprotein(a) phenotype determines the correlations of lipoprotein(a) and proprotein convertase subtilisin/kexin type 9 levels in patients with potential familial hypercholesterolemia

BACKGROUND AND AIMS

The aim of this study is to investigate the relation between lipoprotein(a) [Lp(a)] and proprotein convertase subtilisin/kexin type 9 (PCSK9) concentrations, and their complex, in patients with potential familial hypercholesterolemia (FH), depending on apo(a) phenotype.

METHODS

The study included 205 patients with total cholesterol (TC) > 7.5 mmol/L and/or low density lipoprotein cholesterol (LDL-C)>4.9 mmol/L, 32 (15%) patients suffered from ischemic heart disease (IHD), 64 were taking statins. The diagnosis of FH was estimated according to the Dutch Lipid Clinics Network criteria. Lipid parameters, apoB-containing lipoprotein subfractions, Lp(a), PCSK9, Lp(a)-PCSK9 complex levels and apo(a) phenotype were determined. Depending on the apo(a) phenotype, all patients were divided into 2 groups: with high molecular weight (HMW) (n = 145) and low molecular weight (LMW) (n = 60) apo(a) phenotype.

RESULTS

The groups were comparable by all major clinical characteristics and biochemical parameters. In the whole group, PCSK9 concentration correlated with age, statins intake, Lp(a), TC and TG levels. Correlation between Lp(a) and PCSK9 levels was found only in the LMW apo(a) phenotype group independently of statins intake (r = 0.46, p < 0.001). Associations between Lp(a)-PCSK9 complex and large subfractions of intermediate (r = 0.30) and low-density lipoproteins (r = 0.30, p < 0.05 for both) were observed, with more significance in group 2 (r = 0.59, p < 0.005 and r = 0.40, p < 0.05, respectively).

CONCLUSIONS

In patients with potential familial hypercholesterolemia, positive correlations between concentrations of Lp(a) and PCSK9, as well as of Lp(a)-PCSK9 plasma complex with large subfractions of intermediate and low-density lipoproteins (IDL-1 and LDL-C), were determined by the LMW apo(a) phenotype.

PCSK9: from molecular biology to clinical applications

Proprotein convertase subtilisin kexin 9 (PCSK9) is a serine protease with a key role in regulating plasma low-density lipoprotein (LDL) concentration. Since its discovery via parallel molecular biology and clinical genetics studies in 2003, work to characterize PCSK9 has shed new light on the life-cycle of the low-density lipoprotein receptor and the molecular basis of familial hypercholesterolaemia. These discoveries have also led to the advent of the PCSK9 inhibitors, a new generation of low-density lipoprotein cholesterol (LDL-C) lowering drugs. Clinical trials have shown these agents to be both safe and capable of unprecedented reductions in LDL-C, and it is hoped they may herald a new era of cardiovascular disease prevention. As such, the still evolving PCSK9 story serves as a particularly successful example of translational medicine. This review provides a summary of the principal PCSK9 research findings, which underpin our current understanding of its function and clinical relevance.

Familial Hypercholesterolemia and Lipoprotein Apheresis

Lipoprotein apheresis has been developed as the treatment for refractory familial hypercholesterolemia (FH) to remove low-density lipoprotein (LDL), which is the main pathogenic factor. Currently, three procedures are available in Japan, including the plasma exchange, double-membrane filtration, and selective LDL adsorption. Selective LDL adsorption, which was developed in Japan, has been one of the most common treatment methods in the world. Lipoprotein apheresis enabled the prevention of atherosclerosis progression even in homozygous FH (HoFH) patients. However, in our observational study, HoFH patients who started lipoprotein apheresis in adulthood had a poorer prognosis than those who started in childhood. Therefore, HoFH patients need to start lipoprotein apheresis as early as possible. Although the indication for lipoprotein apheresis in heterozygous FH (HeFH) patients has been decreasing with the advent of strong statins, our observational study showed that HeFH patients who discontinued lipoprotein apheresis had a poorer prognosis than patients who continued apheresis therapy. These results suggest that it is beneficial for very-high-risk HeFH patients to be treated by lipoprotein apheresis even if their LDL cholesterol is controlled well by lipid-lowering agents. Since launching a new class of lipid-lowering agents, proprotein convertase subtilisin/kexin type 9 (PCSK9) antibody and microsome triglyceride transfer protein inhibitors, the indication for lipoprotein apheresis in FH has been changing. However, despite the development of these drugs, lipoprotein apheresis is still an option with a high therapeutic effect for FH patients with severe atherosclerotic cardiovascular disease.

Changes in serum LDL, PCSK9 and microRNA-122 in patients with chronic HCV infection receiving Daclatasvir/Asunaprevir

The present study evaluated the changes in lipid profile, and the associations between serum protein convertase subtilisin/kexin 9 (PCSK9), microRNA (miR)122 and low-density lipoprotein variation following treatment of hepatitis C virus (HCV) genotype 1b infection with Daclatasvir/Asunaprevir. A total of 39 patients with HCV genotype 1b infection with chronic hepatitis received a 24-week treatment regimen of Daclatasvir/Asunaprevir. Laboratory data were obtained for each subject every 4 weeks during treatment and every 12 weeks after treatment. Serum miR122 and PCSK9 were measured at the start of treatment (week 0), end of treatment (week 24), 4 weeks after the end of treatment (week 28), 12 weeks after the end of treatment (week 36) and 28 weeks after the end of treatment (week 52). LDL was increased at week 4 after the start of treatment to week 52. The increased LDL/HDL ratio at week 52 compared with week 4 was also associated with relative miR122 at week 52. At week 4, PCSK9-active form (A) was lower than that at other time points, and PCSK9-inactive form (I) exhibited the greatest increase. At week 52, PCSK9-A was higher than that during treatment, but PCSK9-I level at week 52 did not markedly differ from that any time point except for week 4. Relative miR122 at week 4 was associated with increased PCSK9-A at weeks 36 and 52 from the start of DAA. In summary, treatment of HCV with Daclatasvir/Asunaprevir resulted in elevated LDL, and relative miR122 and PCSK9-A levels in serum appeared to have some association with LDL increase.

Association between circulating proprotein convertase subtilisin/kexin type 9 levels and prognosis in patients with severe chronic kidney disease

Background

Chronic kidney disease is a risk factor for premature development of coronary atherosclerosis and mortality. A high level of proprotein convertase subtilisin/kexin type 9 (PCSK9) is a recently recognized cardiovascular risk factor and has become the target of effective inhibitory treatment. In 167 kidney transplantation candidates, we aimed to: (i) compare levels of PCSK9 with those of healthy controls, (ii) examine the association between levels of PCSK9 and low-density lipoprotein cholesterol (LDL-c) and the degree of coronary artery disease (CAD) and (iii) evaluate if levels of PCSK9 predict major adverse cardiac events (MACE) and mortality.

Methods

Kidney transplant candidates (n = 167) underwent coronary computed tomography angiography (CCTA) and invasive coronary angiography (ICA) before transplantation. MACE and mortality data were extracted from the Western Denmark Heart Registry, a review of patient records and patient interviews. A group of 79 healthy subjects were used as controls.

Results

Mean PCSK9 levels did not differ between healthy controls and kidney transplant candidates. In patients not receiving lipid-lowering therapy, PCSK9 correlated positively with LDL-c (rho = 0.24, P &lt; 0.05). Mean PCSK9 was similar in patients with and without obstructive CAD at both CCTA and ICA. In a multiple regression analysis, PCSK9 was associated with neither LDL-c (β=−6.45, P = 0.44) nor coronary artery calcium score (β=2.17, P = 0.84). During a follow-up of 3.7 years, PCSK9 levels were not associated with either MACE or mortality.

Conclusions

The ability of PCSK9 levels to predict cardiovascular disease and prognosis does not seem to apply to a cohort of kidney transplant candidates.

Plasma proprotein-convertase-subtilisin/kexin type 9 (PCSK9) and cardiovascular events in type 2 diabetes

AIM

To investigate whether plasma concentrations of proprotein-convertase-subtilisin/kexin type 9 (PCSK9) were associated with cardiovascular (CV) events in two cohorts of patients with type 2 diabetes mellitus.

METHODS

We considered patients from the DIABHYCAR (n = 3137) and the SURDIAGENE (n = 1468) studies. Baseline plasma PCSK9 concentration was measured using an immunofluorescence assay. In post hoc, but preplanned, analyses we assessed the relationship between PCSK9 and the following endpoints: (1) a combined endpoint of major CV events: CV death, non-fatal myocardial infarction (MI), stroke and heart failure-related hospital admission; (2) a composite of all CV events: MI, stroke, heart failure-related hospital admission, coronary/peripheral angioplasty or bypass, CV death; (3) MI; (4) stroke/transient ischaemic attack (TIA); and (5) CV death.

RESULTS

In the DIABHYCAR study, plasma PCSK9 tertiles were associated with the incidence of MI, all CV events and stroke/TIA (P for trend <.05). In adjusted Cox analysis, plasma PCSK9 was associated, independently of classic risk factors, with the incidence of major CV events (hazard ratio [HR] for 1-unit increase of log[PCSK9] 1.28 [95% confidence interval {CI} 1.06-1.55]), the incidence of MI (HR 1.66 [95% CI 1.05-2.63]), and the incidence of all CV events (HR 1.22 [95% CI 1.04-1.44]), but not with CV death. Plasma PCSK9 was not associated with the incidence of CV disease in the participants of the SURDIAGENE study with high CV risk treated with statins and insulin.

CONCLUSIONS

We found that PCSK9 was inconsistently associated with CV events in populations with type 2 diabetes. The association may depend on the level of CV risk and the background treatment.

Lipid Lowering Therapy and Circulating PCSK9 Concentration

Hypercholesterolemia, particularly an increase in low-density lipoprotein cholesterol (LDL-C) levels, contributes substantially to the development of coronary artery disease and the risk for cardiovascular events. As the first-line pharmacotherapy, statins have been shown to reduce both LDL-C levels and cardiovascular events. However, despite intensive statin therapy, a sizable proportion of statin-treated patients are unable to achieve the recommended target LDL-C levels, and not all patients can avoid future cardiovascular events. Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a key role in cholesterol homeostasis by enhancing the degradation of hepatic low-density lipoprotein receptor (LDLR). Owing to its importance in lipid metabolism, PCSK9 has emerged as a novel pharmacological target for lowering LDL-C levels. In this review, the potential role of circulating PCSK9 as a new biomarker of lipid metabolism is described. Next, previous studies evaluating the effects of lipid-modifying pharmacological agents, particularly statins, on circulating PCSK9 concentrations are summarized. Statins decrease hepatic intracellular cholesterol, resulting in increased LDLRs as well as increased PCSK9 protein. There is a clear dose-response effect of statin treatment on PCSK9 level, as increasing doses of statins also increase the level of circulating PCSK9. Finally, the available therapeutic strategies to inhibit PCSK9 are present. Monoclonal antibodies against PCSK9, in combination with statins, are one of the most promising and novel approaches to achieve further reduction of LDL-C levels and reduce the risk of cardiovascular events.

Threshold Effects of Circulating Angiopoietin-Like 3 Levels on Plasma Lipoproteins

CONTEXT

Angiopoietin-like 3 (ANGPTL3) deficiency in plasma due to loss-of-function gene mutations results in familial combined hypobetalipoproteinemia type 2 (FHBL2) in homozygotes. However, the lipid phenotype in heterozygotes is much milder and does not appear to relate directly to ANGPTL3 levels. Furthermore, the low-density lipoprotein (LDL) phenotype in carriers of ANGPTL3 mutations is unexplained.

OBJECTIVE

To determine whether reduction below a critical threshold in plasma ANGPTL3 levels is a determinant of lipoprotein metabolism in FHBL2, and to determine whether proprotein convertase subtilisin kexin type 9 (PCSK9) is involved in determining low LDL levels in this condition.

DESIGN

We studied subjects from 19 families with ANGPTL3 mutations and subjects with familial combined hypobetalipoproteinemia type 1 (FHBL1) due to truncated apolipoprotein B (apoB) species.

RESULTS

First, total cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, and HDL and LDL particle concentration correlated with plasma ANGPTL3 levels but only when the latter was <25% of normal (<60 ng/dL). Second, the very low-density lipoprotein particle concentration correlated strongly with plasma ANGPTL3 when the latter was <58% of normal. Third, both FHBL1 and FHBL2 subjects showed low levels of mature and LDL-bound PCSK9 and higher levels of its furin-cleaved form. Finally, LDL-bound PCSK9 is protected from cleavage by furin and binds to the LDL receptor more strongly than apoB-free PCSK9.

CONCLUSIONS

Our results suggest that the hypolipidemic effects of ANGPTL3 mutations in FHBL2 are dependent on a threshold of plasma ANGPTL3 levels, with differential effects on various lipoprotein particles. The increased inactivation of PCSK9 by furin in FHBL1 and FHBL2 is likely to cause increased LDL clearance and suggests novel therapeutic avenues.

PCSK9 inhibition in the management of familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a frequent hereditary metabolic disease characterized by high serum low-density lipoprotein (LDL) cholesterol concentration and premature atherosclerotic cardiovascular disease (ASCVD). The discovery of the LDL receptor as one of the causative genes of FH enabled us to understand the pathophysiology of FH and paved the way for developing statins. Similar to LDL receptor, discovery of proprotein convertase subtilisin/kexin type 9 (PCSK9) also created an opportunity for developing its inhibitors. Since PCSK9 degrades LDL receptor protein, inhibiting PCSK9 will be an effective strategy. Evolocumab and alirocumab, anti-PCSK9 antibodies that inhibit binding between PCSK9 and LDL receptors, are now available in Japan. Adding an anti-PCSK9 antibody to standard therapy with statin alone or statin combined with ezetimibe further reduced serum LDL cholesterol levels by around 60% and they significantly decrease cardiovascular event incidence as compared with placebo. Additionally, the strong LDL cholesterol lowering effect of anti-PCSK9 antibody therapies has reportedly enabled the frequency of lipoprotein apheresis to be reduced or to be discontinued. As alternative strategies against PCSK9, antisense oligonucleotide agents that inhibit PCSK9 protein synthesis as well as a small interfering (or short interference) RNA (siRNA) for PCSK9 are also being developed. While relatively high cost can be given as a problem, PCSK9 inhibitors are able to reduce LDL cholesterol dramatically even in FH patients who could not achieve targets until now. To ensure that these drugs are given to the patients who really need them, it is necessary to raise the diagnosis rate and family screening has to be more actively conducted. Finally, it has been reported that PCSK9 is expressed not only in hepatocytes but also in other cells such as epithelial cells in small intestine and vascular smooth muscle cells in atherosclerotic plaque. Further research regarding extra-hepatic pathophysiology of PCSK9 is expected.

The complexity of lipoprotein (a) lowering by PCSK9 monoclonal antibodies

Since 2012, clinical trials dedicated to proprotein convertase subtilisin kexin type 9 (PCSK9) inhibition with monoclonal antibodies (mAbs) have unambiguously demonstrated robust reductions not only in low-density lipoprotein (LDL) cholesterol (LDL-C) but also in lipoprotein (a) [Lp(a)] levels. The scientific literature published prior to those studies did not provide any evidence for a link between PCSK9 and Lp(a) metabolism. More recent investigations, either in vitro or in vivo, have attempted to unravel the mechanism(s) by which PCSK9 mAbs reduce circulating Lp(a) levels, with some showing a specific implication of the LDL receptor (LDLR) in Lp(a) clearance whereas others found no significant role for the LDLR in that process. This elusive pathway appears clearly distinct from that of the widely prescribed statins that also enhance LDLR function but do not lower circulating Lp (a) levels in humans. So how does PCSK9 inhibition with mAbs reduce Lp(a)? This still remains to be established.

Development of proprotein convertase subtilisin/kexin type 9 inhibitors and the clinical potential of monoclonal antibodies in the management of lipid disorders

The aim of this manuscript is to review available data to evaluate the present status of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors in the treatment of hypercholesterolemia. Relevant literature since 2003 is reviewed. The effectiveness of PCSK9 inhibitors in lowering low-density lipoprotein cholesterol and other atherogenic lipid fractions was studied in various Phase 2 and Phase 3 trials of Alirocumab, Evolocumab, and Bococizumab. The results of published long-term ODYSSEY and OSLER studies are summarized. There have been three excellent meta-analysis studies on PCSK9 inhibitors which are outlined. The complex problem of cost-effectiveness was carefully evaluated by the Institute for Clinical and Economic Review (ICER). The draft report (ICER-2015) is summarized herewith. The cardiovascular outcome trials with Evolocumab (FOURIER), Alirocumab (ODYSSEY OUTCOME) and Bococizumab (SPIRE-1 and SPIRE-2) are the ongoing clinical trials, and their results are expected in 2017-2018. The search for new cost-effective analogs of PCSK9 inhibitors is ongoing.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors: Present perspectives and future horizons

AIMS

Our comprehensive review highlights the drug development and pharmacogenomics leading to the recent approval of PCSK9 inhibitors. We also review the anticipated future advances into the uses of PCSK9 inhibition.

BACKGROUND

Despite the present advances in pharmacotherapy, atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of mortality worldwide. Low density lipoprotein-cholesterol (LDL-C) lowering is the primary target for ASCVD risk reduction, showing demonstrable benefits in mortality. However, 70% of events occur even in the presence of statins. This residual risk may be approached with additional LDL-C reduction. Statin intolerance is a common clinical concern affecting adherence and the benefit with statins. There is also significant variation of individual lipid-lowering. Following rapid development, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors have progressed from genetic observations, to mechanistic studies, to closer realization of the goal of CVD risk reduction. This review discusses the science behind PCSK9 inhibition, evidence of trials involving efficacy and safety, and reflections of its present and future role in clinical care, especially in high-risk patients with ASCVD, persons with suboptimal responses to statins and familial hyperlipidemia. Monoclonal antibodies have demonstrated LDL-C lowering of up to 57% as monotherapy and up to 73% when added to statins. Statins have limited efficacy in reduction of LDL-C due to an increased number of LDL-receptors. Elevated lipoprotein (a) levels may also be significantly lowered by PCSK9i. The journey from discovery to PSCK9 target validation took less than five years, and development and approval of therapeutic modalities for PCSK9 inhibitors happened over the next seven. This review highlights the drug development and pharmacogenomics leading to the recent approval of two agents, alirocumab and evolocumab, with a third bococizumab, and other novel approaches to the pathway pending.

DATA SYNTHESIS

We searched MEDLINE database via Pubmed for reviews, research publications and relevant trials available on PCSK9 inhibition.

CONCLUSION

Despite decades of medical advances, ASCVD remains one of the major causes of morbidity and mortality worldwide. Statin use has multiplied since the validation of LDL hypothesis, however, it is undeniable a more effective and well-tolerated agent is needed in significant number or patients. With the arrival of the era of unprecedented CV protection with PCSK9 inhibition, this exciting new therapy holds a pivotal promise as the future of lipid management. The data available already indicate safety, tolerability and superb efficacy of these agents, which are already changing contemporary cholesterol management. The rapid translation of innovative basic science research into drug development may lead to CV outcomes reduction and confirm that this pathway will become prominently utilized.

Correlation between serum levels of proprotein convertase subtilisin/kexin type 9 (PCSK9) and atherogenic lipoproteins in patients with coronary artery disease

Background

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key regulator of serum low-density lipoprotein (LDL) cholesterol levels. Recently, PCSK9 has additionally been related to metabolic risk factors such as the levels of triglycerides, apolipoprotein B (apoB), insulin, and glucose, as well as body mass index. The purpose of this study was to investigate correlations between serum levels of PCSK9 and apoB-containing atherogenic lipoproteins in patients with coronary artery disease (CAD).

Methods

Serum levels of PCSK9 and lipoprotein(a) [Lp(a)]; small, dense LDL; and oxidized LDL were measured in 101 patients with CAD who were not receiving lipid-lowering therapy.

Results

Serum hetero-dimer PCSK9 levels were positively correlated with serum levels of Lp(a) (r = 0.195, p = 0.05); small, dense LDL (r = 0.336, p = 0.0006); and oxidized LDL (r = 0.268, p = 0.008). Multivariate regression analyses showed that serum hetero-dimer PCSK9 was a significant predictor of serum levels of Lp(a) (β = 0.235, p = 0.01); small, dense LDL (β = 0.143, p = 0.03); and oxidized LDL (β = 0.268, p = 0.008).

Conclusions

Serum PCSK9 levels were positively correlated with serum levels of Lp(a); small, dense LDL; and oxidized LDL in patients with CAD. This suggests that the interaction between serum PCSK9 and apoB-containing lipoproteins plays a role in establishing the atherosclerotic status of patients.

Trial registration

UMIN Clinical Trials Registry, UMIN ID: C000000311.

Biology of proprotein convertase subtilisin kexin 9: beyond low-density lipoprotein cholesterol lowering

Proprotein convertase subtilisin kexin 9 (PCSK9) is a key regulator of low-density lipoprotein receptor levels and LDL-cholesterol levels. Loss-of-function mutations in PCSK9 gene are associated with hypocholesterolaemia and protection against cardiovascular disease, identifying PCSK9 inhibition as a valid therapeutic approach to manage hypercholesterolaemia and related diseases. Although PCSK9 is expressed mainly in the liver, it is present also in other tissues and organs with specific functions, raising the question of whether a pharmacological inhibition of PCSK9 to treat hypercholesterolaemia and associated cardiovascular diseases might be helpful or deleterious in non-hepatic tissues. For example, PCSK9 is expressed in the vascular wall, in the kidneys, and in the brain, where it was proposed to play a role in development, neurocognitive process, and neuronal apoptosis. A link between PCSK9 and immunity was also proposed as both sepsis and viral infections are differentially affected in the presence or absence of PCSK9. Despite the increasing number of observations, the debate on the exact roles of PCSK9 in extrahepatic tissues is still ongoing, and as very effective drugs that inhibit PCSK9 have become available to the clinician, a better understanding of the biological roles of PCSK9 is warranted.

Independent Link Between Levels of Proprotein Convertase Subtilisin/Kexin Type 9 and FABP4 in a General Population Without Medication

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to and degrades the low-density lipoprotein (LDL) receptor, leading to hypercholesterolemia and cardiovascular risk. Fatty acid binding protein 4 (FABP4/adipocyte FABP/aP2) is secreted from adipocytes in association with lipolysis, and circulating FABP4 has been reported to act as an adipokine for the development of insulin resistance and atherosclerosis. Elevated serum FABP4 level is associated with obesity, insulin resistance, dyslipidemia, and atherosclerosis. In this study, we examined the association between circulating levels of FABP4 and PCSK9 in a general population. A total of 265 subjects (male/female: 98/167) who were not on medication were recruited from subjects of the Tanno-Sobetsu Study, and concentrations of FABP4 and PCSK9 were measured. The level of FABP4, but not that of PCSK9, showed a gender difference, being higher in women than in men. FABP4 level was independently associated with gender, adiposity, renal dysfunction, and levels of cholesterol and PCSK9. There was a significant and gender-different correlation between PCSK9 level and age: negatively in men (r = -0.250, p = 0.013) and positively in women (r = 0.183, p = 0.018). After adjustment of age, gender, and LDL cholesterol level, PCSK9 level was positively and independently correlated with FABP4 concentration. In conclusion, PCSK9 level is differentially regulated by gender during aging. Circulating FABP4 is independently associated with the PCSK9 level, suggesting that elevation of FABP4 level as an adipokine leads to dyslipidemia through increased PCSK9 level and subsequent degradation of the LDL receptor.

PCSK9 Association With Lipoprotein(a)

RATIONALE

Lipoprotein(a) [Lp(a)] is a highly atherogenic low-density lipoprotein-like particle characterized by the presence of apoprotein(a) [apo(a)] bound to apolipoprotein B. Proprotein convertase subtilisin/kexin type 9 (PCSK9) selectively binds low-density lipoprotein; we hypothesized that it can also be associated with Lp(a) in plasma.

OBJECTIVE

Characterize the association of PCSK9 and Lp(a) in 39 subjects with high Lp(a) levels (range 39-320 mg/dL) and in transgenic mice expressing either human apo(a) only or human Lp(a) (via coexpression of human apo(a) and human apolipoprotein B).

METHODS AND RESULTS

We show that PCSK9 is physically associated with Lp(a) in vivo using 3 different approaches: (1) analysis of Lp(a) fractions isolated by ultracentrifugation; (2) immunoprecipitation of plasma using antibodies to PCSK9 and immunodetection of apo(a); (3) ELISA quantification of Lp(a)-associated PCSK9. Plasma PCSK9 levels correlated with Lp(a) levels, but not with the number of kringle IV-2 repeats. PCSK9 did not bind to apo(a) only, and the association of PCSK9 with Lp(a) was not affected by the loss of the apo(a) region responsible for binding oxidized phospholipids. Preferential association of PCSK9 with Lp(a) versus low-density lipoprotein (1.7-fold increase) was seen in subjects with high Lp(a) and normal low-density lipoprotein. Finally, Lp(a)-associated PCSK9 levels directly correlated with plasma Lp(a) levels but not with total plasma PCSK9 levels.

CONCLUSIONS

Our results show, for the first time, that plasma PCSK9 is found in association with Lp(a) particles in humans with high Lp(a) levels and in mice carrying human Lp(a). Lp(a)-bound PCSK9 may be pursued as a biomarker for cardiovascular risk.

Circulating Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Predicts Future Risk of Cardiovascular Events Independently of Established Risk Factors

BACKGROUND

The secreted protein proprotein convertase subtilisin/kexin type 9 (PCSK9) is a promising new target for lowering plasma low-density lipoprotein cholesterol and preventing cardiovascular disease (CVD). The relationship between circulating PCSK9 and incident CVD in the general population is unknown. We investigated whether serum PCSK9 concentration is associated with incident CVD in a prospective cohort study of 4232 men and women 60 years of age at the time of recruitment.

METHODS AND RESULTS

Incident CVD was recorded by matching to national registries. After 15 years of follow-up, a total of 491 incident events (fatal and nonfatal myocardial infarctions, unstable angina, deaths from coronary heart disease, fatal and nonfatal ischemic strokes) were recorded. Cox proportional hazards model was used to calculate hazard ratios with 95% confidence intervals. Baseline serum PCSK9 concentration predicted incident CVD; concentration in quartile 4 compared with quartile 1 was associated with a hazard ratio of 1.69 (95% confidence interval, 1.30-2.19) after adjustment for sex. Further adjustment for low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, lipoprotein(a), triglycerides, hypertension, diabetes mellitus, smoking, overweight, obesity, physical inactivity, and statin use resulted in a decrease in the hazard ratio to 1.48 (95% confidence interval, 1.12-1.95).

CONCLUSIONS

Serum PCSK9 concentration is associated with future risk of CVD even after adjustments for established CVD risk factors. Further studies are needed to confirm this observation.

Effects of Statin Therapy on Plasma Proprotein Convertase Subtilisin/kexin Type 9 and Sortilin Levels in Statin-Naive Patients with Coronary Artery Disease

AIM

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key regulator of serum low-density lipoprotein (LDL) cholesterol levels, and sortilin is linked to lipoprotein metabolism. Although statin therapy increases PCSK9 levels, effects of this therapy on plasma sortilin levels have not been evaluated. The purpose of the present study was to examine the effects of statins on plasma PCSK9 and sortilin levels, and association of statin-induced increase in PCSK9 levels with sortilin.

METHODS

Serum lipid levels and plasma PCSK9 and sortilin levels were measured at baseline and 8 months after statin therapy in 90 statin-naive patients with coronary artery disease (CAD). Pitavastatin 4 mg/day was used to treat 44 patients and pravastatin 20 mg/day to treat the remaining 46 patients.

RESULTS

For both statin groups, significant increases in hetero-dimer PCSK9 levels (pitavastatin: 31%, p＜0.0001; pravastatin: 34%, p=0.03) and decreases in sortilin levels (pitavastatin: －8%, p=0.02; pravastatin: －16%, p=0.002) were observed. Although a reduction in LDL cholesterol was greater in the pitavastatin group than in the pravastatin group, no significant differences were observed in percentage changes in hetero-dimer PCSK9 and sortilin levels. A significant positive correlation was observed between percentage changes in hetero-dimer PCSK9 levels and those in sortilin levels (pitavastatin: r=0.359, p=0.02; pravastatin: r=0.276, p=0.06).

CONCLUSIONS

Use of pitavastatin and pravastatin increased plasma PCSK9 and decreased sortilin levels. Statin-induced increases in PCSK9 were associated with changes in sortilin in statin-naive patients with CAD.

Proprotein convertase subtilisin/kexin 9 V4I variant with LDLR mutations modifies the phenotype of familial hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) is caused by mutations in the genes encoding low-density lipoprotein receptor (LDLR), apolipoprotein B, or proprotein convertase subtilisin/kexin 9 (PCSK9). However, FH shows variability of the clinical phenotype modified by other genetic variants or environmental factors.

OBJECTIVE

Our objective was to determine the distribution of PCSK9 variants in Japanese FH heterozygotes and to clarify whether those variants and the combination of those variants and LDLR mutations modify the clinical phenotypes.

METHODS

A direct sequence analysis was performed for all 18 exons of LDLR gene and 12 exons of PCSK9 gene in 269 clinically diagnosed FH heterozygotes. The serum lipid levels of the carriers of each variant were compared to those of noncarriers. We also assessed Achilles tendon xanthoma and the prevalence of coronary artery disease (CAD) in the patients aged ≥30 years.

RESULTS

Eleven PCSK9 variants were detected. There were 4 frequent PCSK9 variants: L21_22insL, A53 V, V4I, and E32 K. The PCSK9 L21_22insL and A53 V were in linkage disequilibrium with each other. There were no significant differences in serum lipids levels and the prevalence of CAD at the age of ≥ 30 years between PCSK9 V4I, L21_22insL/A53 V, or E32 K variant carriers and noncarriers without LDLR mutations. In the patients carrying LDLR mutations and aged ≥ 30 years, the additional PCSK9 V4I variant was linked to a significantly increased prevalence of CAD in accord with the elevation of the LDL-cholesterol level.

CONCLUSIONS

The addition of the PCSK9 V4I was suggested to modify the phenotype of patients carrying LDLR mutations by affecting their LDLR metabolism.

Lipoprotein apheresis: present and future uses

PURPOSE OF REVIEW

For the past 40 years, apheresis, in particular, lipoprotein apheresis, has been the therapy of choice to lower LDL-C for familial hypercholesterolemia patients with uncontrolled dyslipidemia and cardiovascular disease. With the advent of recent and future lipid-modifying agents and their ability to lower LDL-C, the question arises on what will be the future of lipoprotein apheresis.

RECENT FINDINGS

Lipoprotein apheresis lowers not only plasma levels of apolipoprotein B lipoproteins but also markers of vascular inflammation and blood rheology. Other vascular diseases, not necessarily associated with familial hypercholesterolemia, such as nephrotic syndrome and peripheral arterial disease have profited from lipoprotein apheresis therapy. In 2013, the Food and Drug Administration approved lipoprotein apheresis therapy for patients with focal segmental glomerulosclerosis. Since 2010, the German healthcare ministry has approved lipoprotein apheresis therapy for patients with an elevated lipoprotein(a) and ongoing cardiovascular disease irrespective of LDL-C levels.

SUMMARY

Recent and future lipid-modifying therapies will most likely reduce the practice of lipoprotein apheresis therapy for familial hypercholesterolemia patients. Future implications for lipoprotein apheresis will involve vascular diseases that are at present lacking clinically effective therapy, whereas acute and chronic reductions of lipids, vascular inflammation, and/or rheology may improve the clinical outcome.

Molecular and cellular function of the proprotein convertase subtilisin/kexin type 9 (PCSK9)

The proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a promising treatment target to lower serum cholesterol, a major risk factor of cardiovascular diseases. Gain-of-function mutations of PCSK9 are associated with hypercholesterolemia and increased risk of cardiovascular events. Conversely, loss-of-function mutations cause low-plasma LDL-C levels and a reduction of cardiovascular risk without known unwanted effects on individual health. Experimental studies have revealed that PCSK9 reduces the hepatic uptake of LDL-C by increasing the endosomal and lysosomal degradation of LDL receptors (LDLR). A number of clinical studies have demonstrated that inhibition of PCSK9 alone and in addition to statins potently reduces serum LDL-C concentrations. This review summarizes the current data on the regulation of PCSK9, its molecular function in lipid homeostasis and the emerging evidence on the extra-hepatic effects of PCSK9.

On the function and homeostasis of PCSK9: reciprocal interaction with LDLR and additional lipid effects

Proprotein convertase subtilisin kexin type 9 (PCSK9) is a circulatory ligand that terminates the lifecycle of the low-density lipoprotein (LDL) receptor (LDLR) thus affecting plasma LDL-cholesterol (LDL-C) levels. Recent evidence shows that in addition to the straightforward mechanism of action, there are more complex interactions between PCSK9, LDLR and plasma lipoprotein levels, including: (a) the presence of both parallel and reciprocal regulation of surface LDLR and plasma PCSK9; (b) a correlation between PCSK9 and LDL-C levels dependent not only on the fact that PCSK9 removes hepatic LDLR, but also due to the fact that up to 40% of plasma PCSK9 is physically associated with LDL; and (c) an association between plasma PCSK9 production and the assembly and secretion of triglyceride-rich lipoproteins. The effect of PCSK9 on LDLR is being successfully utilized toward the development of anti-PCSK9 therapies to reduce plasma LDL-C levels. Current biochemical research has uncovered additional mechanisms of action and interacting partners for PCSK9, and this opens the way for a more thorough understanding of the regulation, metabolism, and effects of this interesting protein.