Living the PCSK9 adventure: from the identification of a new gene in familial hypercholesterolemia towards a potential new class of anticholesterol drugs

Therapeutic PCSK9 targeting: Inside versus outside the hepatocyte?

As a major regulator of LDL receptor (LDLR) activity and thus of LDL-cholesterol (LDL-C) levels, proprotein convertase subtilisin/kexin type 9 (PCSK9) represents an obvious therapeutic target for lipid lowering. The PCSK9 inhibitors, alirocumab and evolocumab, are human monoclonal antibodies (mAbs) that act outside the cell by complexing circulating PCSK9 and thus preventing its binding to the LDLR. In contrast, inclisiran, a small interfering RNA (siRNA), inhibits hepatic synthesis of PCSK9, thereby resulting in reduced amounts of the protein inside and outside the cell. Both approaches result in decreased plasma LDL-C concentrations and improved cardiovascular outcomes. Marginally superior LDL-C reduction (≈ 60 %) is achieved with mAbs as compared to the siRNA (≈ 50 %); head-to-head comparisons are required to confirm between-class differences in efficacy. Both drug classes have shown variability in LDL-C lowering response between individuals in waterfall analyses. Whereas mAb-mediated inhibition leads to a compensatory increase in plasma PCSK9 levels, siRNA treatment reduces them. These agents differ in their pharmacokinetic and pharmacodynamic features, which may translate into distinct clinical opportunities under acute (e.g. acute coronary syndromes) as compared to chronic conditions. Both drug classes provide additional reduction in LDL-C levels (up to 50 %) beyond those achieved with statin therapy, facilitating attainment of guideline-recommended LDL-C goals in high and very high-risk patients. Additional PCSK9 inhibitors, including an oral macrocyclic peptide, a small PCSK9 binding protein and a novel small molecule, plus hepatic gene editing of PCSK9, are under development. This review critically appraises pharmacological strategies to target PCSK9 either inside or outside the cell.

The Effects of Statins, Ezetimibe, PCSK9-Inhibitors, Inclisiran, and Icosapent Ethyl on Platelet Function

This review aims to examine the complex interaction between dyslipidemia, platelet function, and related drug treatments. In particular, the manuscript provides an overview of the effects of major hypolipidemic drugs on platelet function. Indeed, growing evidence supports the view that statins, ezetimibe, PCSK9 inhibitors, inclisiran, and icosapent ethyl also act as antithrombotics. It is known that platelets play a key role not only in the acute phase of coronary syndromes but also in the early phase of atherosclerotic plaque formation. The goal of cholesterol-lowering therapy is to reduce cardiovascular events. The direct effects of cholesterol-lowering drugs are widely described in the literature. Lowering LDL-c (low-density lipoprotein cholesterol) by 1 mmol/L results in a 22-23% reduction in cardiovascular risk. Numerous studies have examined the direct antithrombotic effects of these drugs on platelets, endothelium, monocytes, and smooth muscle cells, and thus, potentially independent of blood LDL-cholesterol reduction. We reviewed in vitro and in vivo studies evaluating the complex interaction between hypercholesterolemia, hypertriglyceridemia, platelet function, and related drug treatments. First, we discussed the role of statins in modulating platelet activation. Discontinuation of statin therapy was associated with increased cardiovascular events with increased ox-LDL, P-selectin, and platelet aggregation. The effect of PCSK9-I (inhibitors of proprotein convertase subtilisin/kexin type 9, PCSK9 involved in the degradation of LDL receptors in the liver) was associated with a statistically significant reduction in platelet reactivity, calculated in P2Y12 reaction units (PRU), in the first 14 days and no difference at 30 days compared to placebo. Finally, in patients with hypertriglyceridemia, the REDUCE-IT study showed that icosapent ethyl (an ethyl ester of eicosapentaenoic acid that reduces triglyceride synthesis and improves triglyceride clearance) resulted in a 25% reduction in ischemic events and cardiovascular death. However, to date, there is not yet clear clinical evidence that the direct antithrombotic effects of the drugs may have a beneficial impact on outcomes independently from the reduction in LDL-C or triglycerides.

Identification of Potent Small-Molecule PCSK9 Inhibitors Based on Quantitative Structure-Activity Relationship, Pharmacophore Modeling, and Molecular Docking Procedure

The leading cause of atherosclerotic cardiovascular disease (ASCVD) is elevated low-density lipoprotein cholesterol (LDL-C). Proprotein convertase subtilisin/kexin type 9 (PCSK9) attaches to the domain of LDL receptor (LDLR), diminishing LDL-C influx and LDLR cell surface presentation in hepatocytes, resulting in higher circulating LDL-C levels. PCSK9 dysfunction has been linked to lower levels of plasma LDLC and a decreased risk of coronary heart disease (CHD). Herein, using virtual screening tools, we aimed to identify a potent small-molecule PCSK9 inhibitor in compounds that are currently being studied in clinical trials. We first performed chemical absorption, distribution, metabolism, excretion, and toxicity (ADMET) filtering of 9800 clinical trial compounds obtained from the ZINC 15 database using Lipinski's rule of 5 and achieved 3853 compounds. Two-dimensional (2D) quantitative structure-activity relationship (QSAR) was initiated by computing molecular descriptors and selecting important descriptors of 23 PCSK9 inhibitors. Multivariate calibration was performed with the partial least square regression (PLS) method with 18 compounds for training to design the QSAR model and 5 compounds for the test set to assess the model. The best latent variables (LV) (LV=6) with the lowest value of Root-Mean-Square Error of Cross-Validation (RMSECV) of 0.48 and leave-one-out cross-validation correlation coefficient (R2CV) = 0.83 were obtained for the QSAR model. The low RMSEC (0.21) with high R²cal (0.966) indicates the probability of fit between the experimental data and the calibration model. Using QSAR analysis of 3853 compounds, 2635 had a pIC50<1 and were considered for pharmacophore screening. The PHASE module (a complete package for pharmacophore modeling) designed the pharmacophore hypothesis through multiple ligands. The top 14 compounds (pIC50>1) were defined as active, whereas 9 (pIC50<1) were considered as an inactive set. Three five-point pharmacophore hypotheses achieved the highest score: DHHRR1, DHHRR2, and DHRRR1. The highest and best model with survival scores (5.365) was DHHRR1, comprising 1 hydrogen donor (D), 2 hydrophobic groups (H), and 2 rings of aromatic (R) features. We selected the molecules with a higher 1.5 fitness score (257 compounds) in pharmacophore screening (DHHRR1) for molecular docking screening. Molecular docking indicates that ZINC000051951669, with a binding affinity: of -13.2 kcal/mol and 2 H-bonds, has the highest binding to the PCSK9 protein. ZINC000011726230 with energy binding: -11.4 kcal/mol and 3 H-bonds, ZINC000068248147 with binding affinity: -10.7 kcal/mol and 1 H-bond, ZINC000029134440 with a binding affinity: -10.6 kcal/mol and 4 H-bonds were ranked next, respectively. To conclude, the archived molecules identified as inhibitory PCSK9 candidates, and especially ZINC000051951669 may therefore significantly inhibit PCSK9 and should be considered in the newly designed trials.

Circulating Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) is Associated with Disease Activity and Risk of Incident Cardiovascular Disease in Patients with Systemic Lupus Erythematosus

To study the relationship of serum PCSK9 and disease activity and major adverse cardiovascular events (MACEs) in systemic lupus erythematosus (SLE). Consecutive patients who fulfilled ≥ 4 ACR criteria for SLE and consented for a biomarker study in 2009-2013 were included. Stored serum samples were assayed for PCSK9. PCSK9 levels were correlated with SLE disease activity scores. Patients were divided into two groups according to the median PCSK9 level and new MACEs over time were evaluated. The effect of PCSK9 level on MACEs and mortality was studied by Cox regression, adjusted for confounders. A total of 539 SLE patients were studied (93% women, age 41.9 ± 14.0 years). The median PCSK9 level at baseline was 220 ng/ml. Patients with higher PCSK9 (≥ 220 ng/ml; n = 269) had significantly higher SLE disease activity index (SLEDAI) than those with lower PCSK9 (< 220 ng/ml; n = 270). PCSK9 levels were significantly higher in patients with active renal than active non-renal SLE, which in turn were significantly higher than those with inactive SLE or healthy controls. PCSK9 level correlated with SLEDAI in the overall population (ρ = 0.30; p < 0.001). Over 91.3 ± 18.6 months, 29 patients developed 31 MACEs and 40 patients succumbed (25% for vascular events). The cumulative incidence of MACEs at 5 years was 4.8% in the higher PCSK9 and 1.1% in the lower PCSK9 group (HR2.51[1.11-5.70]; p = 0.03). Cox regression revealed higher PCSK9 was significantly associated with MACEs (HR1.003[1.000-1.005] per ng/ml; p = 0.02) independent of age, sex, renal function, baseline disease activity score, traditional atherosclerotic risk factors, antiphospholipid antibody and the use of aspirin/warfarin, statins and immunosuppressive drugs. PCSK9 level was also independently associated with all-cause (HR1.002[1.000-1.004] per ng/ml; p = 0.03) and vascular mortality (HR1.004[1.000-1.007]; p = 0.04). We concluded that serum PCSK9 level correlates with SLE disease activity. Higher serum PCSK9 levels are associated with increased risk of cardiovascular events and mortality in SLE.

Genetic and molecular architecture of familial hypercholesterolemia

Atherosclerotic cardiovascular disease is the leading cause of death globally. Despite its important risk of premature atherosclerosis and cardiovascular disease, familial hypercholesterolemia (FH) is still largely underdiagnosed worldwide. It is one of the most frequently inherited diseases due to mutations, for autosomal dominant forms, in either of the LDLR, APOB, and PCSK9 genes or possibly a few mutations in the APOE gene and, for the rare autosomal forms, in the LDLRAP1 gene. The discovery of the genes implicated in the disease has largely helped to improve the diagnosis and treatment of FH from the LDLR by Brown and Goldstein, as well as the introduction of statins, to PCSK9 discovery in FH by Abifadel et al., and the very rapid availability of PCSK9 inhibitors. In the last two decades, major progress has been made in clinical and genetic diagnostic tools and the therapeutic arsenal against FH. Improving prevention, diagnosis, and treatment and making them more accessible to all patients will help reduce the lifelong burden of the disease.

Circulating PCSK9 Linked to Dyslipidemia in Lebanese Schoolchildren

In adults, elevated levels of circulating Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) have been associated with increased Low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), and worse cardiovascular outcomes. However, few studies analyzed the relation between PCSK9 and lipid parameters in pediatric populations. The aim of our study is to evaluate the distribution and the correlation of serum PCSK9 levels with lipid parameters in a sample of Lebanese school children. Using an immunofluorescence assay, we measured serum PCSK9 levels in 681 school children recruited from ten public and private Lebanese schools. We analyzed the association between PCSK9 and age, sex, Body Mass Index (BMI), and lipid parameters (total cholesterol (TC), LDL-C, TG, High-density lipoprotein cholesterol (HDL-C), non-HDL-C, and lipoprotein (a) (Lp(a)). Serum PCSK9 levels were significantly correlated with TC, LDL-C, and non-HDL-C (p value < 0.0001) but not with TG, HDL-C, and Lp(a). PCSK9 levels were also significantly higher in children with high TC, LDL-C, and non-HDL-C (p values = 0.0012, 0.0002, 0.001, respectively). No significant gender differences in PCSK9 were found. In addition, no significant associations between PCSK9 and both age and BMI percentiles were observed. In girls, no difference in PCSK9 values was observed according to menarche while in boys, testosterone levels were not significantly associated with PCSK9. Serum PCSK9 levels were significantly correlated with TC, LDL-C, and non-HDL-C levels. Further studies are needed to find if PCSK9 measurements have an additional value to predict future cardiovascular outcomes in pediatric populations.

The Emerging Roles of Intracellular PCSK9 and Their Implications in Endoplasmic Reticulum Stress and Metabolic Diseases

The importance of the proprotein convertase subtilisin/kexin type-9 (PCSK9) gene was quickly recognized by the scientific community as the third locus for familial hypercholesterolemia. By promoting the degradation of the low-density lipoprotein receptor (LDLR), secreted PCSK9 protein plays a vital role in the regulation of circulating cholesterol levels and cardiovascular disease risk. For this reason, the majority of published works have focused on the secreted form of PCSK9 since its initial characterization in 2003. In recent years, however, PCSK9 has been shown to play roles in a variety of cellular pathways and disease contexts in LDLR-dependent and -independent manners. This article examines the current body of literature that uncovers the intracellular and LDLR-independent roles of PCSK9 and also explores the many downstream implications in metabolic diseases.

A Systematic Approach to Assess the Activity and Classification of PCSK9 Variants

BACKGROUND

Gain of function (GOF) mutations of PCSK9 cause autosomal dominant familial hypercholesterolemia as they reduce the abundance of LDL receptor (LDLR) more efficiently than wild-type PCSK9. In contrast, PCSK9 loss of function (LOF) variants are associated with a hypocholesterolemic phenotype. Dozens of PCSK9 variants have been reported, but most remain of unknown significance since their characterization has not been conducted.

OBJECTIVE

Our aim was to make the most comprehensive assessment of PCSK9 variants and to determine the simplest approach for the classification of these variants.

METHODS

The expression, maturation, secretion, and activity of nine well-established PCSK9 variants were assessed in transiently transfected HEK293 cells by Western blot and flow cytometry. Their extracellular activities were determined in HepG2 cells incubated with the purified recombinant PCSK9 variants. Their binding affinities toward the LDLR were determined by solid-phase immunoassay.

RESULTS

LDLR expression increased when cells were transfected with LOF variants and reduced when cells were transfected with GOF variants compared with wild-type PCSK9. Extracellular activities measurements yielded exactly similar results. GOF and LOF variants had increased, respectively reduced, affinities for the LDLR compared with wild-type PCSK9 with the exception of one GOF variant (R218S) that showed complete resistance to inactivation by furin. All variants were expressed at similar levels and underwent normal maturation and secretion patterns except for two LOF and two GOF mutants.

CONCLUSIONS

We propose that transient transfections of HEK293 cells with a plasmid encoding a PCSK9 variant followed by LDLR expression assessment by flow cytometry is sufficient to reliably determine its GOF or LOF status. More refined experiments should only be used to determine the underlying mechanism(s) at hand.

PoLA/CFPiP/PCS/PSLD/PSD/PSH guidelines on diagnosis and therapy of lipid disorders in Poland 2021

In Poland there are still nearly 20 million individuals with hypercholesterolaemia, most of them are unaware of their condition; that is also why only ca. 5% of patients with familial hypercholesterolaemia have been diagnosed; that is why other rare cholesterol metabolism disorders are so rarely diagnosed in Poland. Let us hope that these guidelines, being an effect of work of experts representing 6 main scientific societies, as well as the network of PoLA lipid centers being a part of the EAS lipid centers, certification of lipidologists by PoLA, or the growing number of centers for rare diseases, with a network planned by the Ministry of Health, improvements in coordinated care for patients after myocardial infarction (KOS-Zawał), reimbursement of innovative agents, as well as introduction in Poland of an effective primary prevention program, will make improvement in relation to these unmet needs in diagnostics and treatment of lipid disorders possible.

Identification of a Variant in APOB Gene as a Major Cause of Hypobetalipoproteinemia in Lebanese Families

Familial hypobetalipoproteinemia (FHBL) is a codominant genetic disorder characterized by reduced plasma levels of low-density lipoprotein cholesterol and apolipoprotein B. To our knowledge, no study on FHBL in Lebanon and the Middle East region has been reported. Therefore, we conducted genetic studies in unrelated families and probands of Lebanese origin presenting with FHBL, in order to identify the causes of this disease. We found that 71% of the recruited probands and their affected relatives were heterozygous for the p.(Arg490Trp) variant in the APOB gene. Haplotype analysis showed that these patients presented the same mutant haplotype. Moreover, there was a decrease in plasma levels of PCSK9 in affected individuals compared to the non-affected and a significant positive correlation between circulating PCSK9 and ApoB levels in all studied probands and their family members. Some of the p.(Arg490Trp) carriers suffered from diabetes, hepatic steatosis or neurological problems. In conclusion, the p.(Arg490Trp) pathogenic variant seems a cause of FHBL in patients from Lebanese origin, accounting for approximately 70% of the probands with FHBL presumably as a result of a founder mutation in Lebanon. This study is crucial to guide the early diagnosis, management and prevention of the associated complications of this disease.

Monitoring of up to 15 years effects of lipoprotein apheresis on lipids, biomarkers of inflammation, and soluble endoglin in familial hypercholesterolemia patients

Background

Lipoprotein apheresis (LA) is considered as an add-on therapy for patients with familial hypercholesterolemia (FH). We aimed to analyze the data collected in the last 15 years from FH patients treated with LA, to elucidate the benefit of this procedure with respect to plasma lipids, biomarkers of inflammation, and endothelial dysfunction and soluble endoglin.

Results

14 patients (10 heterozygous FH patients (HeFH), 4 homozygous FH patients (HoFH)) were treated by long-term lipoprotein apheresis. Lipid levels were examined, and ELISA detected biomarkers of inflammation and soluble endoglin. Paired tests were used for intergroup comparisons, and a linear regression model served to estimate the influence of the number of days patients were treated with LA on the studied parameters. LA treatment was associated with a significant decrease of total cholesterol (TC), LDL-C, HDL-C, and apoB, in both HeFH and HoFH patients, after single apheresis and in a long-term period during the monitored interval of 15 years. Biomarkers of inflammation and endothelial dysfunction were reduced for soluble endoglin, hsCRP, and MCP-1, and sP-selectin after each procedure in some HeFH and HoFH patients.

Conclusions

LA treatment up to 15 years, reduced cholesterol levels, levels of biomarkers related to endothelial dysfunction, and inflammation not only after each procedure but also in the long-term evaluation in FH patients. We propose that long-term LA treatment improves lipid profile and endothelial dysfunction in familial hypercholesterolemia patients, suggesting a promising improvement in cardiovascular prognosis in most FH patients.

Single-Strand DNA-Like Oligonucleotide Aptamer Against Proprotein Convertase Subtilisin/Kexin 9 Using CE-SELEX: PCSK9 Targeting Selection

BACKGROUND

Proprotein convertase subtilisin/kexin 9 (PCSK9) serves a key regulatory function in the metabolism of low-density lipoprotein (LDL)-cholesterol (LDL-C) through interaction with the LDL receptor (LDLR) followed by its destruction that results in the elevation of the plasma levels of LDL-C. The aims of the present study were to separate and select a number of single-stranded DNA (ssDNA) aptamers against PCSK9 from a library pool (n > 10¹²) followed by their characterization.

METHODS

The aptamers obtained from the DNA-PCSK9 complexes which presented the highest affinity against PCSK9 were separated and selected using capillary electrophoresis evolution of ligands by exponential enrichment (CE-SELEX). The selected aptamers were amplified and cloned into a T/A vector. The plasmids from the positive clones were extracted and sequenced. The Mfold web server was used to predict the secondary structure of the aptamers.

RESULTS

Following three rounds of CE-SELEX, the identified anti-PCSK9 ssDNA aptamers, namely aptamer 1 (AP-1) and aptamer 2 (AP-2), presented half maximal inhibitory concentrations of 325 and 327 nM, lowest dissociation constants of 294 and 323 nM, and most negative Gibbs free energy values of - 9.17 and - 8.28 kcal/mol, respectively.

CONCLUSION

The results indicated that the selected aptamers (AP-1 and AP-2) induced potent inhibitory effects against PCSK9. Further in vivo studies demand to find out AP-1 and AP-2 aptamers as suitable candidates, instead of antibodies, for using in therapeutic purposes in patients with hypercholesterolemia and cardiovascular disease.

PCSK9: A Key Target for the Treatment of Cardiovascular Disease (CVD)

Proprotein convertase subtilisin/kexin type 9 (PCSK9), as a vital modulator of low-density lipoprotein cholesterol (LDL-C) , is raised in hepatocytes and released into plasma where it binds to LDL receptors (LDLR), leading to their cleavage. PCSK9 adheres to the epidermal growth factor-like repeat A (EGF-A) domain of the LDLR which is confirmed by crystallography. LDLR expression is adjusted at the transcriptional level through sterol regulatory element binding protein 2 (SREBP-2) and at the post translational stages, specifically through PCSK9, and the inducible degrader of the LDLR PCSK9 inhibition is an appealing new method for reducing the concentration of LDL-C. In this review the role of PCSK9 in lipid homeostasis was elucidated, the effect of PCSK9 on atherosclerosis was highlighted, and contemporary therapeutic techniques that focused on PCSK9 were summarized. Several restoration methods to inhibit PCSK9 have been proposed which concentrate on both extracellular and intracellular PCSK9, and they include blockage of PCSK9 production by using gene silencing agents and blockage of it's binding to LDLR through antibodies and inhibition of PCSK9 autocatalytic processes by tiny molecule inhibitors.

Long term follow-up of genetically confirmed patients with familial hypercholesterolemia treated with first and second-generation statins and then with PCSK9 monoclonal antibodies

BACKGROUND AND AIMS

In Italy, the clinical and genetic characteristics of familial hypercholesterolemia (FH) have been extensively assessed in various lipid clinics, although no studies on long-term cardiovascular outcomes in heterozygous patients (He-FH) have been conducted. This study evaluated the incidence of atherosclerotic cardiovascular disease (ASCVD) in He-FH before and after a long-term period of lipid-lowering treatments to ascertain the interference of other risk factors.

METHODS

A total of 294 genetically characterised He-FH subjects from 1989 to 2019 were retrospectively analysed. General characteristics, lipid profiles, ASCVD prevalence, and ultrasound carotid atherosclerosis assessment were evaluated. Primary end points were ASCVD outcomes and the percentage of patients reaching recommended LDL-C targets.

RESULTS

During follow-up, despite a significant improvement in plasma lipid profiles, the ESC/EAS 2016 and 2019 recommended LDL cholesterol (LDL-C) goals were attained in only a few patients treated with anti-PCSK9 monoclonal antibodies added to the maximum tolerated oral therapy with statins plus ezetimibe. Forty-seven subjects had an ASCVD event before starting lipid-lowering therapy (LLT). During follow-up (median 13 years) on LLT, 28 patients had a first ASCVD event and 16 had recurrent ASCVD. In basal conditions and during follow-up, higher LDL-C levels were associated with increased ASCVD risk (p < 0.001). Prevention of recurrent ASCVD events was recorded with a long-term reduction of LDL-C below 100 mg/dl with statins plus ezetimibe.

CONCLUSIONS

PCSK9 inhibition is the only therapeutic option to achieve LDL-C goals as recommended for He-FH and can prevent ASCVD events as reported in large clinical trials. Long-term treatment with statins and ezetimibe seems to be effective at preventing ASCVD recurrence when LDL-C is maintained below 130 and 100 mg/dL for primary and secondary prevention, respectively.

PCSK9 inhibitor effectively attenuates cardiometabolic impairment in obese-insulin resistant rats

Long-term high-fat diet consumption causes obese-insulin resistance and cardiac mitochondrial dysfunction, leading to impaired left ventricular (LV) function. Atorvastatin effectively improved lipid profiles in obese patients. However, inadequate reduction in low density lipoprotein cholesterol (LDL-C) level was found. Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor effectively reduced LDL-C levels. We hypothesized that this PCSK9 inhibitor has a greater efficacy in attenuating cardiometabolic impairments than atorvastatin in obese-insulin resistant rats. Female rats were fed with either a high fat or normal diet for 12 weeks. High fat diet fed rats (HFD) were then divided into 3 groups and were given vehicle, atorvastatin (40 mg/kg/day; s.c.), or PCSK9 inhibitor (4 mg/kg/day; s.c.) for additional 3 weeks. The metabolic parameters, cardiac and mitochondrial function and [Ca²⁺]_i transients were determined. HFD rats developed obese-insulin resistance as indicated by increased plasma insulin and HOMA index. Although high-fat diet fed rats treated with vehicle (HFV) rats had markedly impaired LV function as indicated by reduced %LVFS, impaired cardiac mitochondrial function, and [Ca²⁺]_i transient regulation, these impairments were attenuated in high-fat diet fed rats treated with atorvastatin (HFA) and high-fat diet fed rats treated with PCSK9 inhibitor (HFP) rats. However, these improvements were greater in HFP rats than HFA rats. Our findings indicated that the PCSK9 inhibitor exerted greater cardioprotection than atorvastatin through improved mitochondrial function in obese-insulin resistant rats.

PCSK9 inhibitor and atorvastatin reduce cardiac impairment in ovariectomized prediabetic rats via improved mitochondrial function and Ca2+ regulation

Post‐menopausal women have a higher risk of developing cardiometabolic dysfunction. Atorvastatin attenuates dyslipidaemia and cardiac dysfunction but it can have undesirable effects including increased risk of diabetes and myalgia. Currently, the proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor efficiently reduces low‐density lipoprotein cholesterol (LDL‐C) levels more effectively than atorvastatin. We have been suggested that PCSK9 inhibitor attenuated cardiometabolic impairment more effectively than atorvastatin in ovariectomized prediabetic rats. Female Wistar rats (n = 48) were fed a normal diet (ND) or high‐fat diet (HFD) for 12 weeks. Then, HFD rats were assigned to a sham‐operated (Sham) or ovariectomized (OVX) group. Six weeks after surgery, the OVX group was subdivided into 4 treatment groups: vehicle (HFOV), atorvastatin (HFOA) (40 mg/kg/day; s.c.), PCSK9 inhibitor (HFOP) (4 mg/kg/day; s.c.) and oestrogen (HFOE₂) (50 µg/kg/day; s.c.) for an additional 3 weeks. Metabolic parameters, cardiac and mitochondrial function, and [Ca²⁺]_i transients were evaluated. All HFD rats became obese‐insulin resistant. HFS rats had significantly impaired left ventricular (LV) function, cardiac mitochondrial function and [Ca²⁺]_i transient dysregulation. Oestrogen deprivation (HFOV) aggravated all of these impairments. Our findings indicated that the atorvastatin, PCSK9 inhibitor and oestrogen shared similar efficacy in the attenuation in cardiometabolic impairment in ovariectomized prediabetic rats.

Beyond cholesterol metabolism: The pleiotropic effects of proprotein convertase subtilisin/kexin type 9 (PCSK9). Genetics, mutations, expression, and perspective for long-term inhibition

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has a crucial role in lipid metabolism, particularly due to its function in low-density lipoprotein receptor degradation. Gain-of-function genetic mutations of PCSK9 result in autosomal dominant familial hypercholesterolemia, characterized by high levels of low-density lipoprotein cholesterol (LDL-C) and clinical signs of early atherosclerosis. In recent years, PCSK9 has become an important therapeutic target for cholesterol-lowering therapy. Particularly, its inhibition with monoclonal antibodies has shown excellent efficacy in decreasing LDL-C and reducing cardiovascular events. However, PCSK9, first identified in the brain, seems to be a ubiquitous protein with different tissue-specific functions also independent of cholesterol metabolism. Accordingly, it appears to be involved in the immune response, haemostasis, glucose metabolism, neuronal survival, and several other biological functions. This review provides a comprehensive overview of the genetics, biochemical structure, expression, and function of PCSK9 and discusses the potential implications of its long-term pharmacological inhibition.

Predicted loss and gain of function mutations in ACO1 are associated with erythropoiesis

Hemoglobin is the essential oxygen-carrying molecule in humans and is regulated by cellular iron and oxygen sensing mechanisms. To search for novel variants associated with hemoglobin concentration, we performed genome-wide association studies of hemoglobin concentration using a combined set of 684,122 individuals from Iceland and the UK. Notably, we found seven novel variants, six rare coding and one common, at the ACO1 locus associating with either decreased or increased hemoglobin concentration. Of these variants, the missense Cys506Ser and the stop-gained Lys334Ter mutations are specific to eight and ten generation pedigrees, respectively, and have the two largest effects in the study (EffectCys506Ser = -1.61 SD, CI95 = [-1.98, -1.35]; EffectLys334Ter = 0.63 SD, CI95 = [0.36, 0.91]). We also find Cys506Ser to associate with increased risk of persistent anemia (OR = 17.1, P = 2 × 10-14). The strong bidirectional effects seen in this study implicate ACO1, a known iron sensing molecule, as a major homeostatic regulator of hemoglobin concentration.

Efficacy and Safety of Alirocumab in Patients With Autosomal Dominant Hypercholesterolemia Associated With Proprotein Convertase Subtilisin/Kexin Type 9 Gain-of-Function or Apolipoprotein B Loss-of-Function Mutations

Autosomal dominant hypercholesterolemia results from mutations affecting the low-density lipoprotein receptor pathway, including proprotein convertase subtilisin/kexin type 9 (PCSK9) gain-of-function mutations (GoFm) and apolipoprotein B (APOB) loss-of-function mutations (LoFm). This study examined the long-term efficacy and safety of alirocumab in patients with PCSK9 GoFm and APOB LoFm who participated in the open-label extension to a Phase 2 double-blind study (NCT01604824). Of the 23 patients who completed the 14-week double-blind period and 8-week follow-up, 21 opted to continue in the open-label extension (PCSK9 GoFm, n = 15; APOB LoFm, n = 6). Patients received alirocumab 150 mg every 2 weeks from week 32 up to 3 years for PCSK9 GoFm and 2 years for APOB LoFm. Mean duration of alirocumab exposure was 129 weeks (median: 144 weeks). After initiation of alirocumab treatment, low-density lipoprotein cholesterol (LDL-C) decreased in both groups. At week 80, mean percent reduction in LDL-C from baseline was 58.0% and 47.1% for PCSK9 GoFm and APOB LoFm groups, respectively. Treatment-emergent adverse events were reported in 19 patients (90.5%); no patients discontinued treatment due to treatment-emergent adverse events. In patients with autosomal dominant hypercholesterolemia and elevated LDL-C levels despite receiving maximally tolerated lipid-lowering therapies, alirocumab 150 mg every 2 weeks resulted in clinically meaningful reductions in LDL-C, sustained through to 3 years and 2 years for patients with PCSK9 GoFm and APOB LoFm, respectively. Alirocumab was generally well tolerated with no unexpected safety concerns.

Dyslipidaemias and Cardiovascular Disease: Focus on the Role of PCSK9 Inhibitors

Genetic, experimental and clinical studies have consistently confirmed that inhibition of Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) can result in significant lowering of LDL-C and two fully human PCSK9 monoclonal antibodies have received regulatory approval for use in highrisk patients. Co-administration of PCSK9 with statins has resulted in extremely low LDL-C levels with excellent short-term safety profiles. While results from Phase III clinical trials provided significant evidence about the role of PCSK9 inhibitors in reducing cardiovascular event rates, their impact on mortality remains less clear. PCSK9 inhibitor therapy can be considered for high-risk patients who are likely to experience significant cardiovascular risk reduction.

Fragment-based design of small molecule PCSK9 inhibitors using simulated annealing of chemical potential simulations

PCSK9 is a protein secreted by the liver that binds to the low-density lipoprotein receptor (LDLR), causing LDLR internalization, decreasing the clearance of circulating LDL particles. Mutations in PCSK9 that strengthen its interactions with LDLR result in familial hypercholesterolemia (FH) and early onset atherosclerosis, while nonsense mutations of PCSK9 result in cardio-protective hypocholesterolemia. These observations led to PCSK9 inhibition for cholesterol lowering becoming a high-interest therapeutic target, with antibody drugs reaching the market. An orally-available small molecule drug is highly desirable, but inhibiting the PCSK9/LDLR protein-protein interaction (PPI) has proven challenging. Alternate approaches to finding good lead candidates are needed. Motivated by the FH mutation data on PCSK9, we found that modeling the PCSK9/LDLR interface revealed extensive electron delocalization between and within the protein partners. Based on this, we hypothesized that compounds assembled from chemical fragments could achieve the affinity required to inhibit the PCSK9/LDLR PPI if they were selected to interact with PCSK9 in a way that, like LDLR, also involves significant fractional charge transfer to form partially covalent bonds. To identify such fragments, Simulated Annealing of Chemical Potential (SACP) fragment simulations were run on multiple PCSK9 structures, using optimized partial charges for the protein. We designed a small molecule, composed of several fragments, predicted to interact at two sites on the PCSK9. This compound inhibits the PPI with 1 μM affinity. Further, we designed two similar small molecules where one allows charge delocalization though a linker and the other doesn’t. The first inhibitor with charge delocalization enhances LDLR surface expression by 60% at 10 nM, two orders of magnitude more potent than the EGF domain of LDLR. The other enhances LDLR expression by only 50% at 1 μM. This supports our conjecture that fragments can have surprisingly outsized efficacy in breaking PPI’s by achieving fractional charge transfer leading to partially covalent bonding.

Pharmacokinetic and pharmacodynamic assessment of alirocumab in patients with familial hypercholesterolemia associated with proprotein convertase subtilisin/kexin type 9 gain-of-function or apolipoprotein B loss-of-function mutations

BACKGROUND

Familial hypercholesterolemia is characterized by high levels of low-density lipoprotein cholesterol (LDL-C), and causes of familial hypercholesterolemia include apolipoprotein B (APOB) loss-of-function mutations (LOFm) and proprotein convertase subtilisin/kexin type 9 (PCSK9) gain-of-function mutations (GOFm).

OBJECTIVE

The aim of this study was to compare the pharmacokinetics and pharmacodynamics of alirocumab between patients with APOB LOFm vs PCSK9 GOFm.

METHODS

Patients (6 APOB LOFm and 17 PCSK9 GOFm carriers) with LDL-C ≥70 mg/dL on maximally tolerated lipid-lowering therapies received alirocumab 150 mg at Weeks 0, 2, 4, and 6, placebo at Week 8, alirocumab at Week 10, placebo at Weeks 12 and 14, then completed a follow-up period at Week 22.

RESULTS

At Week 8, mean ± standard error (SE) alirocumab concentration was lower in APOB LOFm carriers compared with PCSK9 GOFm carriers (12.12 ± 1.81 vs 16.74 ± 2.53 mg/L). APOB LOFm carriers had higher mean ± SE total PCSK9 (6.56 ± 0.73 mg/L) and lower mean ± SE free PCSK9 (0.025 ± 0.016 mg/L) at Week 8 compared with PCSK9 GOFm carriers (4.21 ± 0.35 and 0.11 ± 0.035 mg/L for total and free PCSK9, respectively). Despite this observed greater PCSK9 suppression, mean ± SE percent LDL-C reduction was lower in APOB LOFm (55.3 ± 1.0%) compared with PCSK9 GOFm carriers (73.1 ± 0.9%). Treatment-emergent adverse events occurred in 16 patients (94.1%) in the PCSK9 GOFm group and 5 patients (83.3%) in the APOB LOFm group.

CONCLUSIONS

Overall, PCSK9 inhibition with alirocumab results in clinically meaningful reductions in LDL-C in both APOB LOFm and PCSK9 GOFm carriers, although reductions were greater in the PCSK9 GOFm carriers. The results indicate a possible underlying contributor to hypercholesterolemia other than PCSK9 in patients with APOB LOFm.

CLINICAL TRIAL REGISTRATION

NCT01604824; clinicaltrials.gov.

Large-Scale Phenome-Wide Association Study of PCSK9 Variants Demonstrates Protection Against Ischemic Stroke

BACKGROUND

PCSK9 inhibition is a potent new therapy for hypercholesterolemia and cardiovascular disease. Although short-term clinical trial results have not demonstrated major adverse effects, long-term data will not be available for some time. Genetic studies in large biobanks offer a unique opportunity to predict drug effects and provide context for the evaluation of future clinical trial outcomes.

METHODS

We tested the association of the PCSK9 missense variant rs11591147 with predefined phenotypes and phenome-wide, in 337 536 individuals of British ancestry in the UK Biobank, with independent discovery and replication. Using a Bayesian statistical method, we leveraged phenotype correlations to evaluate the phenome-wide impact of PCSK9 inhibition with higher power at a finer resolution.

RESULTS

The T allele of rs11591147 showed a protective effect on hyperlipidemia (odds ratio, 0.63±0.04; P=2.32×10^-38), coronary heart disease (odds ratio, 0.73±0.09; P=1.05×10^-6), and ischemic stroke (odds ratio, 0.61±0.18; P=2.40×10^-3) and was associated with increased type 2 diabetes mellitus risk adjusted for lipid-lowering medication status (odds ratio, 1.24±0.10; P=1.98×10^-7). We did not observe associations with cataracts, heart failure, atrial fibrillation, and cognitive dysfunction. Leveraging phenotype correlations, we observed evidence of a protective association with cerebral infarction and vascular occlusion. These results explore the effects of direct PCSK9 inhibition; off-target effects cannot be predicted using this approach.

CONCLUSIONS

This result represents the first genetic evidence in a large cohort for the protective effect of PCSK9 inhibition on ischemic stroke and corroborates exploratory evidence from clinical trials. PCSK9 inhibition was not associated with variables other than those related to LDL (low-density lipoprotein) cholesterol, atherosclerosis, and type 2 diabetes mellitus, suggesting that other effects are either small or absent.

The Arg499His gain-of-function mutation in the C-terminal domain of PCSK9

BACKGROUND AND AIMS

Familial hypercholesterolemia (FH) is a monogenic disease characterized by high levels of low-density lipoprotein cholesterol and premature atherosclerotic cardiovascular disease. FH is caused by loss of function mutations in genes encoding LDL receptor (LDLR), and Apolipoprotein B (APOB) or gain of function (GOF) mutations in proprotein convertase subtilisin/kexin type 9 (PCSK9). In this study, we identified a novel variant in PCSK9, p.(Arg499His), located in the C-terminal domain, in two unrelated FH patients from Spain and Italy.

METHODS

We studied familial segregation and determined variant activity in vitro.

RESULTS

We determined PCSK9 expression, secretion and activity of the variant in transfected HEK293 cells; extracellular activity of the recombinant p.(Arg499His) PCSK9 variant in HEK 293 and HepG2 cells; PCSK9 affinity to the LDL receptor at neutral and acidic pH; the mechanism of action of the p.(Arg499His) PCSK9 variant by co-transfection with a soluble construct of the LDL receptor and by determining total PCSK9 intracellular accumulation when endosomal acidification is impaired and when an excess of soluble LDLr is present in the culture medium. Our results show high LDL-C concentrations and FH phenotype in p.(Arg499His) carriers. In vitro functional characterization shows that p.(Arg499His) PCSK9 variant causes a reduction in LDLr expression and LDL uptake. An intracellular activity for this variant is also shown when blocking the activity of secreted PCSK9 and by inhibiting endosomal acidification.

CONCLUSIONS

We demonstrated that p.(Arg499His) PCSK9 variant causes a direct intracellular degradation of LDLr therefore causing FH by reducing LDLr availability.

Implication of hypocholesterolemia in autism spectrum disorder and its associated comorbidities: A retrospective case-control study

Autism spectrum disorder (ASD) has been associated with low cholesterol levels in a limited number of studies. However, the prevalence of hypocholesterolemia as well as the degree of association with ASD remains to be elucidated. We therefore sought to investigate the lipid profiles of a group of French-Canadian ASD individuals. The medical records of 79 ASD individuals and 79 age and gender-matched healthy controls were retrospectively reviewed. The fasting lipid profiles including total cholesterol (TC), high-density lipoprotein, triglycerides, and low-density lipoprotein were extracted for individuals of both groups along with the following clinical data: anthropometric measurements, medication use and associated disorders. Lipid parameters were compared to age and gender-based normative population and categorized in centile groups. The prevalence of hypocholesterolemia was revealed to be more than threefold higher in ASD individuals as compared to the general population (23%; P = 0.005). The 25th centile was determined as a potential TC threshold that could best predict the ASD (odds ratio [OR] = 3.04; 95% confidence interval [CI]: 1.58-6.65; P < 0.001). This study identified specific ASD comorbidities associated with hypocholesterolemia: TC levels below the 10th centile were associated with a higher rate of ASD-associated intellectual disability (OR = 3.33; 95% CI: 1.26-8.00) and anxiety/depression (OR = 4.74; 95% CI: 1.40-15.73). Overall, these results support a potential association between hypocholesterolemia and ASD occurrence. Application of this study to larger populations is urging to provide more extensive data that may further elucidate the association between hypocholesterolemia and ASD. Autism Res 2019, 12: 1860-1869. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Association of autism spectrum disorder (ASD) with abnormally low levels of cholesterol (hypocholesterolemia) has been documented before. These studies were incomplete, and the conclusion remains speculative. Here, we reviewed the medical records of 79 French-Canadian ASD individuals and compared their total cholesterol (TC) levels to healthy individuals matched for age and gender. We observed four times more hypocholesterolemia in ASD than in the general population. Furthermore, low TC in ASD was associated with higher rates of ASD-associated intellectual disability and anxiety/depression. Our results support an association between hypocholesterolemia and ASD and open novel opportunities for the diagnosis and treatment of specific forms of ASD.

Structure and Function of Proprotein Convertase Subtilisin/kexin Type 9 (PCSK9) in Hyperlipidemia and Atherosclerosis

Background:

One of the important factors in Low-Density Lipoprotein (LDL) metabolism is the LDL receptor (LDLR) by its capacity to bind and subsequently clear cholesterol derived from LDL (LDL-C) in the circulation. Proprotein Convertase Subtilisin-like Kexin type 9 (PCSK9) is a newly discovered serine protease that destroys LDLR in the liver and thereby controls the levels of LDL in plasma. Inhibition of PCSK9-mediated degradation of LDLR has, therefore, become a novel target for lipid-lowering therapy.

Methods:

We review the current understanding of the structure and function of PCSK9 as well as its implications for the treatment of hyperlipidemia and atherosclerosis.

Results:

New treatments such as monoclonal antibodies against PCSK9 may be useful agents to lower plasma levels of LDL and hence prevent atherosclerosis.

Conclusion:

PCSK9's mechanism of action is not yet fully clarified. However, treatments that target PCSK9 have shown striking early efficacy and promise to improve the lives of countless patients with hyperlipidemia and atherosclerosis.

Low Density Lipoprotein (LDL) Cholesterol as a Causal Role for Atherosclerotic Disease: Potential Role of PCSK9 Inhibitors

Proprotein convertase subtilisin/kexin type 9 (PCSK9)-related discoveries of the turn of the century have translated into substantial novelty in dyslipidemia treatment in the last 5 years. With chronic preventable atherosclerotic cardiovascular diseases (ASCVD) representing an epidemic of morbidity and mortality worldwide, low-density lipoprotein cholesterol (LDL-c) reduction represents a public health priority. By overcoming two major statin-related issues, namely intolerance and ineffectiveness, PCSK9 inhibitors have offered a safe and effective option in selected clinical settings where LDL-c reduction is required. Herein, we recapitulate recent findings, clinical applications, and ASCVD prevention potential of PCSK9 inhibition, with focus on anti-PCSK9 monoclonal antibodies, evolocumab and alirocumab.

Implications of de novo mutations in guiding drug discovery: A study of four neuropsychiatric disorders

Recent studies have suggested an important role of de novo mutations (DNMs) in neuropsychiatric disorders. As DNMs are not subject to elimination due to evolutionary pressure, they are likely to have greater disruptions on biological functions. While a number of sequencing studies have been performed on neuropsychiatric disorders, the implications of DNMs for drug discovery remain to be explored. In this study, we employed a gene-set analysis approach to address this issue. Four neuropsychiatric disorders were studied, including schizophrenia (SCZ), autistic spectrum disorders (ASD), intellectual disability (ID) and epilepsy. We first identified gene-sets associated with different drugs, and analyzed whether the gene-set pertaining to each drug overlaps with DNMs more than expected by chance. We also assessed which medication classes are enriched among the prioritized drugs. We discovered that neuropsychiatric drug classes were indeed significantly enriched for DNMs of all four disorders; in particular, antipsychotics and antiepileptics were the most strongly enriched drug classes for SCZ and epilepsy respectively. Interestingly, we revealed enrichment of several unexpected drug classes, such as lipid-lowering agents for SCZ and anti-neoplastic agents. By inspecting individual hits, we also uncovered other interesting drug candidates or mechanisms (e.g. histone deacetylase inhibition and retinoid signaling) that might warrant further investigations. Taken together, this study provided evidence for the usefulness of DNMs in guiding drug discovery or repositioning.

Changes in circulating pro-protein convertase subtilisin/kexin type 9 levels - experimental and clinical approaches with lipid-lowering agents

Regulation of pro-protein convertase subtilisin/kexin type 9 (PCSK9) by drugs has led to the development of a still small number of agents with powerful activity on low-density lipoprotein cholesterol levels, associated with a significant reduction of cardiovascular events in patients in secondary prevention. The Further Cardiovascular Outcomes Research with PCSK9 Inhibition in Subjects with Elevated Risk (FOURIER) and Evaluation of Cardiovascular Outcomes After an Acute Coronary Syndrome During Treatment With Alirocumab (ODYSSEY OUTCOMES) studies, with the two available PCSK9 antagonists, i.e. evolocumab and alirocumab, both reported a 15% reduction in major adverse cardiovascular events. Regulation of PCSK9 expression is dependent upon a number of factors, partly genetic and partly associated to a complex transcriptional system, mainly controlled by sterol regulatory element binding proteins. PCSK9 is further regulated by concomitant drug treatments, particularly by statins, enhancing PCSK9 secretion but decreasing its stimulatory phosphorylated form (S688). These complex transcriptional mechanisms lead to variable circulating levels making clinical measurements of plasma PCSK9 for cardiovascular risk assessment a debated matter. Determination of total PCSK9 levels may provide a diagnostic tool for explaining an apparent resistance to PCSK9 inhibitors, thus indicating the need for other approaches. Newer agents targeting PCSK9 are in clinical development with a major interest in those with a longer duration of action, e.g. RNA silencing, allowing optimal patient compliance. Interest has been expanded to areas not only limited to low-density lipoprotein cholesterol reduction but also investigating other non-lipid pathways raising cardiovascular risk, in particular inflammation associated to raised high-sensitivity C-reactive protein levels, not significantly affected by the present PCSK9 antagonists.

Mipomersen and its use in familial hypercholesterolemia

INTRODUCTION

Familial Hypercholesterolemia (FH) is an inherited disorder characterized by a defect in the binding and internalization of low-density lipoprotein (LDL) particles, resulting in markedly elevated LDL levels and premature atherosclerosis. It is one of the most common inherited disorders of lipid metabolism. Many FH patients, especially those with homozygous FH do not reach LDL goals with traditional LDL therapies and may require additional, less often used, therapies. Areas covered: Mipomersen is an anti-sense oligonucleotide that prevents production of apolipoprotein B leading to decreased levels of very low-density lipoprotein (VLDL) and LDL. In this review the authors discuss the pharmacokinetics of the drug, the clinical trials evaluating its efficacy and safety, and risks and challenges associated with its clinical implementation. Its use as therapy for the treatment of FH is also discussed. Expert opinion: Mipomersen is approved for use only in homozygous FH. It has frequent adverse effects, such as injection site reactions, flu-like symptoms, and hepatoxicity. It is useful only in patients who have failed other therapies, and it faces competition from other medications that have more tolerable side effect profiles.

A New Strategy for Rapidly Screening Natural Inhibitors Targeting the PCSK9/LDLR Interaction In Vitro

The interaction between proprotein convertase subtilisin/kexin type 9 (PCSK9) and the low-density lipoprotein receptor (LDLR) is a promising target for the treatment of hyperc-holesterolemia. In this study, a new method based on competitive affinity and tag detection was developed, which aimed to evaluate potent natural inhibitors preventing the interaction of PCSK9/LDLR directly. Herein, natural compounds with efficacy in the treatment of hypercholesterolemia were chosen to investigate their inhibitory activities on the PCSK9/LDLR interaction. Two of them, polydatin (1) and tetrahydroxydiphenylethylene-2-O-glucoside (2), were identified as potential inhibitors for the PCSK9/LDLR interaction and were proven to prevent PCSK9-mediated LDLR degradation in HepG2 cells. The results suggested that this strategy could be applied for evaluating potential bioactive compounds inhibiting the interaction of PCSK9/LDLR and this strategy could accelerate the discovery of new drug candidates for the treatment of PCSK9-mediated hypercholesterolemia.

Determinants of Achieved LDL Cholesterol and "Non-HDL" Cholesterol in the Management of Dyslipidemias

PURPOSE OF REVIEW

The advent of combination therapy to provide LDL lowering beyond that achieved with statins necessitates the development of greater understanding of how drugs work together, what changes occur in key lipoprotein fractions, and what residual risk remains.

RECENT FINDINGS

Clinical trials of agents that, when added to statins, generate profound LDL lowering have been successful in reducing further the risk of cardiovascular disease. LDL cholesterol can be now decreased to unprecedented levels, so the focus of attention then shifts to other apolipoprotein B-containing, atherogenic lipoprotein classes such as lipoprotein(a) and remnants of the metabolism of triglyceride-rich particles. "Non-HDL cholesterol" is used increasingly (especially if measured in the non-fasting state) as a more comprehensive index of risk. Metabolic studies reveal how current drugs act in combination to achieve profound lipid lowering. However, care is needed in interpreting achieved LDLc and non-HDLc levels in the emerging treatment paradigm.

Advances in the field of proprotein convertase subtilisin kexin type 9 inhibitors

PURPOSE OF REVIEW

Proprotein convertase subtilisin kexin type 9 (PCSK9) inhibitors are promising therapies that inhibit the degradation of low-density lipoprotein (LDL) receptors in the hepatocyte and thus increase LDL cholesterol (LDL-C) uptake from the blood. This review summarizes main findings in the field of PCSK9 inhibitors, from basic mechanism to clinical studies, and aims to provide a contemporary and practical overview of the clinical implication and future directions with PCSK9 inhibitors.

RECENT FINDINGS

Monoclonal antibodies that inhibit PCSK9 reduce LDL-C levels by 40-70% across a wide range of patients with various LDL-C levels, and with different lipid-lowering regimens. These agents significantly reduce apolipoprotein B and lipoprotein (a), may have a potential role in plaque stabilization in acute coronary syndromes, and are safe and tolerable, even among statin-intolerant patients. Preliminary data with evolocumab and alirocumab demonstrate the potential reduction of cardiovascular (CV) events. These PCSK9 inhibitors were recently approved for clinical use, and recommended in the 2016 American College of Cardiology expert consensus document for nonstatin therapy for LDL-C lowering.

SUMMARY

PCSK9 inhibitors are novel promising therapies to reduce LDL-C. Ongoing phase 3 clinical trials with more than 70 000 high-risk patients will examine their safety and efficacy in reducing cardiovascular disease.

PCSK9 inhibitors: a non-statin cholesterol-lowering treatment option

Elevated low-density lipoprotein cholesterol (LDL-C) plays a major role in the development of atherosclerotic cardiovascular disease. Statins are the first-line treatment to lower LDL-C in patients with hypercholesterolemia; however, some high cardiovascular risk patients may have inadequate responses to statin therapy or are intolerant to statins, and may need additional and/or alternative non-statin therapies to further reduce their LDL-C levels. Monoclonal antibodies that inhibit proprotein convertase subtilisin/kexin type 9 (PCSK9), a key regulator of circulating LDL-C levels, have received considerable attention as promising non-statin therapeutic options for the management of hypercholesterolemia. This review provides a brief overview of the history and science of PCSK9 inhibitors, focusing on two PCSK9 monoclonal antibodies that have been approved by the US Food and Drug Administration: alirocumab and evolocumab. Recently released and forthcoming clinical trial data will be discussed, as well as the practical application of patient populations that may benefit from PCSK9 inhibitors. Finally, the recent expert recommendations regarding the use of PCSK9 inhibitors and other non-statin therapies to treat patients with inadequate LDL-C-lowering on statin therapy will be summarized.

Discovery of Flavonoids from Scutellaria baicalensis with Inhibitory Activity Against PCSK 9 Expression: Isolation, Synthesis and Their Biological Evaluation

Nine flavonoids were isolated and identified from a chloroform-soluble fraction of the roots of Scutellaria baicalensis through a bioactivity-guided fractionation using a proprotein convertase subtilisin/kexin type 9 (PCSK9) monitoring assay in HepG2 cells. All structures were established by interpreting the corresponding spectroscopic data and comparing measured values from those in the literature. All compounds were assessed for their ability to inhibit PCSK9 mRNA expression; compounds 1 (3,7,2'-trihydroxy-5-methoxy-flavanone) and 4 (skullcapflavone II) were found to suppress PCSK9 mRNA via SREBP-1. Furthermore, compound 1 was found to increase low-density lipoprotein receptor protein expression. Also, synthesis of compound 1 as a racemic mixture form (1a) was completed for the first time. Natural compound 1 and synthetic racemic 1a were evaluated for their inhibitory activities against PCSK9 mRNA expression and the results confirmed the stereochemistry of 1 was important.

New Sequencing technologies help revealing unexpected mutations in Autosomal Dominant Hypercholesterolemia

Autosomal dominant hypercholesterolemia (ADH) is characterized by elevated LDL-C levels leading to coronary heart disease. Four genes are implicated in ADH: LDLR, APOB, PCSK9 and APOE. Our aim was to identify new mutations in known genes, or in new genes implicated in ADH. Thirteen French families with ADH were recruited and studied by exome sequencing after exclusion, in their probands, of mutations in the LDLR, PCSK9 and APOE genes and fragments of exons 26 and 29 of APOB gene. We identified in one family a p.Arg50Gln mutation in the APOB gene, which occurs in a region not usually associated with ADH. Segregation and in-silico analysis suggested that this mutation is disease causing in the family. We identified in another family with the p.Ala3396Thr mutation of APOB, one patient with a severe phenotype carrying also a mutation in PCSK9: p.Arg96Cys. This is the first compound heterozygote reported with a mutation in APOB and PCSK9. Functional studies proved that the p.Arg96Cys mutation leads to increased LDL receptor degradation. This work shows that Next-Generation Sequencing (exome, genome or targeted sequencing) are powerful tools to find new mutations and identify compound heterozygotes, which will lead to better diagnosis and treatment of ADH.

Chemical modifications of nucleic acid drugs and their delivery systems for gene-based therapy

Gene-based therapy is one of essential therapeutic strategies for precision medicine through targeting specific genes in specific cells of target tissues. However, there still exist many problems that need to be solved, such as safety, stability, selectivity, delivery, as well as immunity. Currently, the key challenges of gene-based therapy for clinical potential applications are the safe and effective nucleic acid drugs as well as their safe and efficient gene delivery systems. In this review, we first focus on current nucleic acid drugs and their formulation in clinical trials and on the market, including antisense oligonucleotide, siRNA, aptamer, and plasmid nucleic acid drugs. Subsequently, we summarize different chemical modifications of nucleic acid drugs as well as their delivery systems for gene-based therapeutics in vivo based on nucleic acid chemistry and nanotechnology methods.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) Deficiency is Protective Against Venous Thrombosis in Mice

The effect of lipid lowering on the incidence of deep venous thrombosis (DVT) is controversial. The purpose of this study was to determine the effect of proprotein convertase subtilisin/kexin type 9 (PCSK9) deficiency on development of DVT in mice. Pcsk9 deficient (pcsk9 ^-/-) and wild-type (WT) littermates underwent partial inferior vena cava (IVC) ligation to induce venous thrombosis. 48 hours following IVC ligation, IVC thrombosis was evident in 60% of WT mice and 25% of pcsk9 ^-/- mice (p < 0.05). Analysis of IVC thrombosis revealed greater thrombus weight, length, myeloid cell recruitment, and more neutrophil extracellular trap formation (NETs) in WT compared to pcsk9 ^-/- mice. Intravital microscopy performed two hours following partial IVC ligation revealed that leukocyte firm attachment was increased in WT mice compared to mice undergoing a sham operation, however leukocyte attachment was reduced in pcsk9 ^-/- mice compared to WT mice. In conclusion, deficiency of PCSK9 is associated with protection from venous thrombosis. This protection is associated with reduced leukocyte recruitment and NET formation at the site of thrombosis.

PCSK9 Mutations in Familial Hypercholesterolemia: from a Groundbreaking Discovery to Anti-PCSK9 Therapies

PURPOSE OF REVIEW

In 2003, Abifadel et al. (Nat. Genet. 34:154-156, 2003) identified PCSK9, encoding proprotein convertase subtilisin/kexin type 9, as the third causal gene for autosomal dominant hypercholesterolemia. This review focuses on the main steps from this major breakthrough in familial hypercholesterolemia (FH) to the latest clinical trials with the anti-PCSK9 antibodies.

RECENT FINDINGS

The year 2015 was remarkable in cardiovascular disease through the field of cholesterol. Nearly 30 years after the discovery of statins, a new class of effective lipid-lowering drugs has emerged: the anti-PCSK9 antibodies. The discovery of the first gain-of-function mutations of PCSK9 in FH rapidly became the center of interest of researchers worldwide. Preclinical and clinical studies launched by pharmaceutical companies led to the first three anti-PCSK9 antibodies, two of which (evolocumab and alirocumab) reduce LDL cholesterol levels by 50-60% and received FDA and European Medicines Agency approvals in 2015 on top of statin therapy. Recently, results of the Further Cardiovascular Outcomes Research With PCSK9 Inhibition in Subjects With Elevated Risk (FOURIER) trial, the outcome trial of evolocumab over 2.2 years, showed a reduction of 15-20% in the risk of major cardiovascular outcomes in high-risk patients receiving statin therapy. Results of ODYSSEY OUTCOMES trial, evaluating the effect of alirocumab in 18,000 patients with established CVD are also eagerly awaited in 2018. The evolution of research on PCSK9, starting from the discovery of the first set of mutations in PCSK9 in FH in 2003, is an amazing example of successful translational research. It shows how rigorous and powered genetic analyses can lead to the discovery of a new class of lipid-lowering drugs that give hope in fighting high cholesterol levels and their cardiovascular complications.

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Zusammenfassung. Hypercholesterinämie ist einer der am umfassendsten dokumentierten modifizierbaren kardiovaskulären Risikofaktoren. Wir diskutieren die Grundpfeiler der medikamentösen Therapie bei Hypercholesterinämie in der Primär- und Sekundärprävention. Dabei stehen Indikation, klinisches Outcome und Verträglichkeit etablierter Therapien mit Statinen, Ezetimib und Fibraten sowie innovative Ansätze wie die Hemmung der PCSK9 im Fokus. Unser Übersichtsartikel befasst sich auch mit spezifischen Indikationen wie familiärer Hypercholesterinämie und Sekundärprävention bei Patienten mit kardiovaskulären Ereignissen sowie mit Therapieoptionen bei Patienten mit Statinintoleranz.

Potential role of lycopene in targeting proprotein convertase subtilisin/kexin type-9 to combat hypercholesterolemia

Proprotein convertase subtilisin/kexin type 9 (PCSK-9) is a serine protease of the proprotien convertase (PC) family that has profound effects on plasma low density lipoprotein cholesterol (LDL-C) levels, the major risk factor for coronary heart disease (CHD), through its ability to mediate LDL receptor (LDL-R) protein degradation and reduced recycling to the surface of hepatocytes. Thus, the current study was premeditated not only to evaluate the role of lycopene in targeting the inhibition of PCSK-9 via modulation of genes involved in cholesterol homeostasis in HFD rats but also to examine a correlation between HFD induced inflammatory cascades and subsequent regulation of PCSK-9 expression. Besides the effect of lycopene on hepatic PCSK-9 gene expression, PPI studies for PCSK-9-Lycopene complex and EGF-A of LDL-R were also performed via molecular informatics approach to assess the dual mode of action of lycopene in LDL-R recycling and increased removal of circulatory LDL-C. We for the first time deciphered that lycopene treatment significantly down-regulates the expression of hepatic PCSK-9 and HMGR, whereas, hepatic LDL-R expression was significantly up-regulated. Furthermore, lycopene ameliorated inflammation stimulated expression of PCSK-9 via suppressing the expression of inflammatory markers. The results from our molecular informatics studies confirmed that lycopene, while occupying the active site of PCSK-9 crystal structure, reduces the affinity of PCSK-9 to complex with EGF-A of LDL-R, whereas, atorvastatin makes PCSK-9-EGF-A complex formation more feasible than both of PCSK-9-EGF-A alone and Lycopene-PCSK-9-EGF-A complex. Based on above results, it can be concluded that lycopene exhibits potent hypolipidemic activities via molecular mechanisms that are either identical (HMGR inhibition) or distinct from that of statins (down-regulation of PCSK-9 mRNA synthesis). To the best of our knowledge, this is the first report that lycopene has this specific biological property. Being a natural, safer and alternative therapeutic agent, lycopene could be used as a complete regulator of cholesterol homeostasis and ASCVD.

Complexity of mechanisms among human proprotein convertase subtilisin-kexin type 9 variants

PURPOSE OF REVIEW

There are many reports of human variants in proprotein convertase subtilisin-kexin type 9 (PCSK9) that are either gain-of-function (GOF) or loss-of-function (LOF), with downstream effects on LDL cholesterol and cardiovascular disease (CVD) risk. However, data on particular mechanisms have only been minimally curated.

RECENT FINDINGS

GOF variants are individually ultrarare, affect all domains of the protein, act to reduce LDL receptor expression through several mechanisms, are a minor cause of familial hypercholesterolemia, have been reported mainly within families, have variable LDL cholesterol-raising effects, and are associated with increased CVD risk mainly through observational studies in families and small cohorts. In contrast, LOF variants can be either ultrarare mutations or relatively more common polymorphisms seen in populations, affect all domains of the protein, act to increase LDL receptor expression through several mechanisms, have variable LDL cholesterol-lowering effects, and have been associated with decreased CVD risk mainly through Mendelian randomization studies in epidemiologic populations.

SUMMARY

There is considerable complexity underlying the clinical concept of both LOF and GOF variants of PCSK9. But despite the underlying mechanistic heterogeneity, altered PCSK9 secretion or function is ultimately correlated with plasma LDL cholesterol level, which is also the driver of CVD outcomes.