Unravelling the functional significance of PCSK9

Biological Mechanisms and Related Natural Inhibitors of CD36 in Nonalcoholic Fatty Liver

Non-alcoholic fatty liver disease (NAFLD), a spectrum of liver disorders from non-alcoholic fatty liver (NAFL) to the more severe non-alcoholic steatohepatitis (NASH), is the leading etiology of chronic liver disease and its global prevalence is increasing. Hepatic steatosis, a condition marked by an abnormal buildup of triglycerides in the liver, is the precursor to NAFLD. Differentiated cluster 36 (CD36), a scavenger receptor class B protein, is a membrane receptor that recognizes multiple lipid and non-lipid ligands. It is generally agreed that CD36 contributes significantly to hepatic steatosis by taking part in fatty acid uptake as well as triglyceride storage and secretion. While there has not been any conclusive research on how CD36 inhibitors prevent NAFLD from progressing and no clinically approved CD36 inhibitors are currently available for use in NAFLD, CD36 remains a target worthy of further investigation in NAFLD. In recent years, the potential role of natural products acting through CD36 in treating non-alcoholic fatty liver disease has attracted much attention. This paper offers an overview of the pathogenesis of CD36 in NAFLD and summarizes some of the natural compounds or extracts that are currently being investigated for modulating NAFLD via CD36 or the CD36 pathway, providing an alternative approach to the development of CD36-related drugs in NAFLD.

FH through the retrospectoscope

After training as a gastroenterologist in the UK, the author became interested in lipidology while he was a research fellow in the USA and switched careers after returning home. Together with Nick Myant, he introduced the use of plasma exchange to treat familial hypercholesterolemia (FH) homozygotes and undertook non-steady state studies of LDL kinetics, which showed that the fractional catabolic rate of LDL remained constant irrespective of pool size. Subsequent steady-state turnover studies showed that FH homozygotes had an almost complete lack of receptor-mediated LDL catabolism, providing in vivo confirmation of the Nobel Prize-winning discovery by Goldstein and Brown that LDL receptor dysfunction was the cause of FH. Further investigation of metabolic defects in FH revealed that a significant proportion of LDL in homozygotes and heterozygotes was produced directly via a VLDL-independent pathway. Management of heterozygous FH has been greatly facilitated by statins and proprotein convertase subtilisin/kexin type 9 inhibitors but remains dependent upon lipoprotein apheresis in homozygotes. In a recent analysis of a large cohort treated with a combination of lipid-lowering measures, survival was markedly enhanced in homozygotes in the lowest quartile of on-treatment serum cholesterol. Emerging therapies could further improve the prognosis of homozygous FH; whereas in heterozygotes, the current need is better detection.

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.

Widening the spectrum of genetic testing in familial hypercholesterolaemia: Will it translate into better patient and population outcomes?

Familial hypercholesterolaemia (FH) is caused by pathogenic variants in LDLR, APOB or PCSK9. Impaired low-density lipoprotein (LDL) receptor function leads to decreased LDL catabolism and premature atherosclerotic cardiovascular disease (ASCVD). Thousands of LDLR variants are known, but assignation of pathogenicity requires accurate phenotyping, family studies and assessment of LDL receptor function. Precise, genetic diagnosis of FH using targeted next generation sequencing allows for optimal treatment, distinguishing FH from pathogenically distinct disorders requiring different treatment. Polygenic hypercholesterolaemia resulting from an accumulation of LDL cholesterol-raising single nucleotide polymorphisms (SNPs) could also be suspected by this approach. Similarly, ASCVD risk could be estimated by broader sequencing of cholesterol and non-cholesterol-related genes. Both of these areas require further research. The clinical management of FH, focusing on the primary or secondary prevention of ASCVD, has been boosted by PCSK9 inhibitor therapy. The efficacy of PCSK9 inhibitors in homozygous FH may be partly predicted by the LDLR variants. While expanded genetic testing in FH is clinically useful in providing an accurate diagnosis and enabling cost-effective testing of relatives, further research is needed to establish its value in improving clinical outcomes.

Inhibition of intestinal glucose transport by polyphenols: a mechanism for indirect attenuation of cholesterol absorption?

Cholesterol uptake and chylomicron synthesis are promoted by increasing glucose concentrations in both healthy and diabetic individuals during the postprandial phase. The goal of this study was to test whether acute inhibition of glucose uptake could impact cholesterol absorption in differentiated human intestinal Caco-2 cells. As expected, high glucose upregulated intestinal cholesterol metabolism promoting its uptake and incorporation in lipoproteins. This was accompanied by an increase in the gene expression of Niemann-Pick C1 Like 1 and proprotein convertase subtillisin/kexin type 9. Cholesterol uptake was attenuated by acute inhibition of glucose absorption by cytochalasin B, by a chamomile extract and by one of its main constituent polyphenols, apigenin 7-O-glucoside; however, chylomicron secretion was only reduced by the chamomile extract. These data support a potential indirect role for bioactives in modulating intestinal lipid pathways through effects on intestinal glucose uptake. This working hypothesis warrants further testing in an in vivo setting such as in hypercholesterolaemic or prediabetic individuals.

Emerging role of proprotein convertase subtilisin/kexin type-9 (PCSK-9) in inflammation and diseases

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is most recognized serine protease for its role in cardiovascular diseases (CVD). PCSK9 regulates plasma low-density lipoprotein cholesterol (LDL-C) levels by selectively targeting hepatic LDL receptors (LDLR) for degradation, thereby serving as a potential therapeutic target for CVD. New pharmacological agents under development aim to lower the risk of CVD by inhibiting PCSK9 extracellularly, although secondary effects of this approach are not yet studied. Here we review the history of PCSK9 and rationale behind developing inhibitors for CVD. Importantly, we summarized the studies investigating the role and impact of modulated PCSK9 levels in inflammation, specifically in sepsis, rheumatoid arthritis and other chronic inflammatory conditions. Furthermore, we summarized studies that investigated the interactions of PCSK9 with pro-inflammatory pathways, such as scavenger receptor CD36 and thrombospondin 1 (TSP-1) in inflammatory diseases. This review highlights the conflicting role that PCSK9 plays in different inflammatory disease states and postulates that any unwanted effects of PCSK9 inhibition in early clinical testing should critically be examined.

In vivo genome and base editing of a human PCSK9 knock-in hypercholesterolemic mouse model

Background

Plasma concentration of low-density lipoprotein (LDL) cholesterol is a well-established risk factor for cardiovascular disease. Inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9), which regulates cholesterol homeostasis, has recently emerged as an approach to reduce cholesterol levels. The development of humanized animal models is an important step to validate and study human drug targets, and use of genome and base editing has been proposed as a mean to target disease alleles.

Results

To address the lack of validated models to test the safety and efficacy of techniques to target human PCSK9, we generated a liver-specific human PCSK9 knock-in mouse model (hPCSK9-KI). We showed that plasma concentrations of total cholesterol were higher in hPCSK9-KI than in wildtype mice and increased with age. Treatment with evolocumab, a monoclonal antibody that targets human PCSK9, reduced cholesterol levels in hPCSK9-KI but not in wildtype mice, showing that the hypercholesterolemic phenotype was driven by overexpression of human PCSK9. CRISPR-Cas9-mediated genome editing of human PCSK9 reduced plasma levels of human and not mouse PCSK9, and in parallel reduced plasma concentrations of total cholesterol; genome editing of mouse Pcsk9 did not reduce cholesterol levels. Base editing using a guide RNA that targeted human and mouse PCSK9 reduced plasma levels of human and mouse PCSK9 and total cholesterol. In our mouse model, base editing was more precise than genome editing, and no off-target editing nor chromosomal translocations were identified.

Conclusions

Here, we describe a humanized mouse model with liver-specific expression of human PCSK9 and a human-like hypercholesterolemia phenotype, and demonstrate that this mouse can be used to evaluate antibody and gene editing-based (genome and base editing) therapies to modulate the expression of human PCSK9 and reduce cholesterol levels. We predict that this mouse model will be used in the future to understand the efficacy and safety of novel therapeutic approaches for hypercholesterolemia.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0624-2) contains supplementary material, which is available to authorized users.

In vivo genome and base editing of a human PCSK9 knock-in hypercholesterolemic mouse model

BACKGROUND

Plasma concentration of low-density lipoprotein (LDL) cholesterol is a well-established risk factor for cardiovascular disease. Inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9), which regulates cholesterol homeostasis, has recently emerged as an approach to reduce cholesterol levels. The development of humanized animal models is an important step to validate and study human drug targets, and use of genome and base editing has been proposed as a mean to target disease alleles.

RESULTS

To address the lack of validated models to test the safety and efficacy of techniques to target human PCSK9, we generated a liver-specific human PCSK9 knock-in mouse model (hPCSK9-KI). We showed that plasma concentrations of total cholesterol were higher in hPCSK9-KI than in wildtype mice and increased with age. Treatment with evolocumab, a monoclonal antibody that targets human PCSK9, reduced cholesterol levels in hPCSK9-KI but not in wildtype mice, showing that the hypercholesterolemic phenotype was driven by overexpression of human PCSK9. CRISPR-Cas9-mediated genome editing of human PCSK9 reduced plasma levels of human and not mouse PCSK9, and in parallel reduced plasma concentrations of total cholesterol; genome editing of mouse Pcsk9 did not reduce cholesterol levels. Base editing using a guide RNA that targeted human and mouse PCSK9 reduced plasma levels of human and mouse PCSK9 and total cholesterol. In our mouse model, base editing was more precise than genome editing, and no off-target editing nor chromosomal translocations were identified.

CONCLUSIONS

Here, we describe a humanized mouse model with liver-specific expression of human PCSK9 and a human-like hypercholesterolemia phenotype, and demonstrate that this mouse can be used to evaluate antibody and gene editing-based (genome and base editing) therapies to modulate the expression of human PCSK9 and reduce cholesterol levels. We predict that this mouse model will be used in the future to understand the efficacy and safety of novel therapeutic approaches for hypercholesterolemia.

Spontaneous severe hypercholesterolemia and atherosclerosis lesions in rabbits with deficiency of low-density lipoprotein receptor (LDLR) on exon 7

Rabbits (Oryctolagus cuniculus) have been the very frequently used as animal models in the study of human lipid metabolism and atherosclerosis, because they have similar lipoprotein metabolism to humans. Most of hyperlipidemia and atherosclerosis rabbit models are produced by feeding rabbits a high-cholesterol diet. Gene editing or knockout (KO) offered another means of producing rabbit models for study of the metabolism of lipids and lipoproteins. Even so, apolipoprotein (Apo)E KO rabbits must be fed a high-cholesterol diet to induce hyperlipidemia. In this study, we used the CRISPR/Cas9 system anchored exon 7 of low-density lipoprotein receptor (LDLR) in an attempt to generate KO rabbits. We designed two sgRNA sequences located in E7:g.7055-7074 and E7:g.7102-7124 of rabbit LDLR gene, respectively. Seven LDLR-KO founder rabbits were generated, and all of them contained biallelic modifications. Various mutational LDLR amino acid sequences of the 7 founder rabbits were subjected to tertiary structure modeling with SWISS-MODEL, and results showed that the structure of EGF-A domain of each protein differs from the wild-type. All the founder rabbits spontaneously developed hypercholesterolemia and atherosclerosis on a normal chow (NC) diet. Analysis of their plasma lipids and lipoproteins at the age of 12 weeks revealed that all these KO rabbits exhibited markedly increased levels of plasma TC (the highest of which was 1013.15 mg/dl, 20-fold higher than wild-type rabbits), LDL-C (the highest of which was 730.00 mg/dl, 35-fold higher than wild-type rabbits) and TG accompanied by reduced HDL-C levels. Pathological examinations of a founder rabbit showed prominent aortic atherosclerosis lesions and coronary artery atherosclerosis.In conclusion, we have reported the generation LDLR-KO rabbit model for the study of spontaneous hypercholesterolemia and atherosclerosis on a NC diet. The LDLR-KO rabbits should be a useful rabbit model of human familial hypercholesterolemia (FH) for the simulations of human primary hypercholesterolemia and such models would allow more exact research into cardio-cerebrovascular disease.

Small molecule modulators of PCSK9 - A literature and patent overview

Proprotein convertase subtilisin kexin like type 9 (PCSK9) has since its discovery been a key protein target for the modulation of LDL cholesterol. The interest in PCSK9 has grown even more with the positive clinical trial outcomes in cardiovascular disease recently reported for two PCSK9 antibodies. Currently, there are no PCSK9 small molecule programs active in clinical development. However, there has been a steady increase in publications and patent applications within the PCSK9 small molecule field. This digest will provide a summary of small molecule and peptide PCSK9 modulators reported both in scientific journals and in patent applications, most of them originating from the last 3-4 years. As such, this digest will serve as an introduction to the field and assist further identification and discovery of small molecule PCSK9 modulators.

PCSK9 in context: A contemporary review of an important biological target for the prevention and treatment of atherosclerotic cardiovascular disease

The identification of the critical role of proprotein convertase subtilisin/kexin type 9 (PCSK9) has rapidly led to the development of PCSK9 inhibition with monoclonal antibodies (mAbs). PCSK9 mAbs are already in limited clinical use and are the subject of major cardiovascular outcomes trials, which, if universally positive, could see much wider clinical application of these agents. Patients with familial hypercholesterolaemia are the most obvious candidates for these drugs, but other patients with elevated cardiovascular risk, statin intolerance or hyperlipoproteinaemia(a) may also benefit. PCSK9 mAbs, administered once or twice monthly, reduce LDL cholesterol levels by 50% to 70%, and appear to be safe and acceptable to patients over at least 2 years of treatment; however, treatment-emergent adverse effects are not always identified in clinical trials, as well-evidenced by statin myopathy. Inclisiran is a promising RNA-based therapy that promotes the degradation of PCSK9 mRNA transcripts and has similar efficacy to mAbs, but with a much longer duration of action. The cost-effectiveness and long-term safety of therapies targeted at inhibiting PCSK9 remain to be demonstrated if they are to be used widely in coronary prevention.

Increased half-life and enhanced potency of Fc-modified human PCSK9 monoclonal antibodies in primates

Blocking proprotein convertase subtilisin kexin type 9 (PCSK9) binding to low-density lipoprotein receptor (LDLR) can profoundly lower plasma LDL levels. Two anti-PCKS9 monoclonal antibodies (mAbs), alirocumab and evolocumab, were approved by the FDA in 2015. The recommended dose is 75 mg to 150 mg every two weeks for alirocumab and 140mg every two weeks or 420 mg once a month for evolocumab. This study attempted to improve the pharmacokinetic properties of F0016A, an IgG1 anti-PCKS9 mAb, to generate biologically superior molecules. We engineered several variants with two or three amino acid substitutions in the Fc fragment based on prior knowledge. The Fc-modified mAbs exhibited increased binding to FcRn, resulting in prolonged serum half-life and enhanced efficacy in vivo. These results demonstrate that Fc-modified anti-PCKS9 antibodies may enable less frequent or lower dosing of antibodies by improved recycling into the blood.

High Serum PCSK9 Is Associated With Increased Risk of New-Onset Diabetes After Transplantation in Renal Transplant Recipients

OBJECTIVE

New-onset diabetes after transplantation (NODAT) is a major complication in renal transplant recipients (RTRs). Cholesterol metabolism has been linked to diabetes development. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is crucial in LDL receptor regulation. Its association with NODAT is unknown. We prospectively determined the association between serum PCSK9 levels and NODAT development and then with all-cause mortality, cardiovascular mortality, and renal graft failure.

RESEARCH DESIGN AND METHODS

In a university setting, nondiabetic RTRs recruited between 2001 and 2003 with a functional graft for ≥1 year were eligible. Serum PCSK9 was measured by ELISA. Cox proportional hazards analysis was used to assess the association of PCSK9 with the development of NODAT, all-cause mortality, cardiovascular mortality, and graft failure.

RESULTS

In 453 RTRs (age 51 ± 12 years, 56% male; 6.1 [2.7-11.7] years after transplantation), serum PCSK9 was 107.1 ± 43.4 μg/L. During a median follow-up of 10 years, 70 RTRs developed NODAT, 123 died, and 59 developed graft failure. NODAT occurred more frequently in the upper PCSK9 tertile (23%) versus the lowest two PCSK9 tertiles (12%; P < 0.001). In crude Cox regression analyses, PCSK9 was significantly associated with development of NODAT (hazard ratio 1.34 [95% CI 1.10-1.63]) per SD change (P = 0.004). This association remained independent of adjustment for potential confounders, including statin use. PCSK9 was not associated with all-cause mortality, cardiovascular mortality, or graft failure.

CONCLUSIONS

Circulating PCSK9 is associated with NODAT in RTRs. The PCSK9 pathway may contribute to the pathogenesis of NODAT.

Predicting proprotein convertase subtilisin kexin type-9 loss of function mutations using plasma PCSK9 concentration

BACKGROUND

Low plasma proprotein convertase subtilisin kexin type-9 (PCSK9) concentration has been associated with loss of function (LOF) PCSK9 mutations in several studies. However, the current standard for detection of these LOF mutations is through gene sequencing. Gene sequencing is labor intensive and expensive. Identifying a simple test to help predict PCSK9 LOF mutations would help to better target subjects requiring gene sequencing.

OBJECTIVES

Determine the diagnostic accuracy of plasma PCSK9 concentration in detecting PCSK9 LOF mutations using genotyping as the gold standard.

METHODS

We carried out a retrospective analysis of 1412 French-Canadian participants of the Quebec Child and Adolescent Health and Social Survey who had been screened for the PCSK9 R46L and Leucine insertion (InsLEU) LOF mutations by genotyping. Their plasma PCSK9 concentrations were measured using a well-described enzyme-linked immunosorbent assay. We used the Youden index to determine the optimal cutoff for PCSK9 concentration to predict mutation status. We further investigated the use of low-density lipoprotein cholesterol (LDL-C) concentration in combination with plasma PCSK9 concentration to refine the prediction of mutation status.

RESULTS

Plasma PCSK9 had a moderate accuracy (area under the curve, 0.71) in detecting the PCSK9 R46L mutation with a sensitivity of 71% and specificity of 70% at cutoff of 70 ng/mL. Combining PCSK9 and LDL-C increased the diagnostic accuracy for the detection of the R46L mutation (area under the curve, 0.75). However, plasma PCSK9 concentration was no better than chance at detecting PCSK9 InsLEU mutation.

CONCLUSION

This analysis suggests that plasma PCSK9 combined with LDL-C concentrations might be useful to predict certain PCSK9 LOF mutations such as the R46L mutation but may fail to predict others such as the InsLEU mutation.

A Phase I Randomized Study of a Specifically Engineered, pH-Sensitive PCSK9 Inhibitor RN317 (PF-05335810) in Hypercholesterolemic Subjects on Statin Therapy

This phase I study assessed the safety, tolerability, pharmacokinetics, and pharmacodynamics of RN317 (PF-05335810), a specifically engineered, pH-sensitive, humanized proprotein convertase subtilisin kexin type 9 (PCSK9) monoclonal antibody, in hypercholesterolemic subjects (low-density lipoprotein cholesterol (LDL-C) ≥ 80 mg/dl) 18-70 years old receiving statin therapy. Subjects were randomized to: single-dose placebo, RN317 (subcutaneous (s.c.) 0.3, 1, 3, 6, or intravenous (i.v.) 1, 3, 6 mg/kg), or bococizumab (s.c. 1, 3, or i.v. 1 mg/kg); or multiple-dose RN317 (s.c. 300 mg every 28 days; three doses). Of 133 subjects randomized, 127 completed the study. RN317 demonstrated a longer half-life, greater exposure, and increased bioavailability vs. bococizumab. RN317 was well tolerated, with no subjects discontinuing because of treatment-related adverse events. RN317 lowered LDL-C by up to 52.5% (day 15) following a single s.c. dose of 3.0 mg/kg vs. a maximum of 70% with single-dose bococizumab s.c. 3.0 mg/kg. Multiple dosing of RN317 produced LDL-C reductions of ∼50%, sustained over an 85-day dosing interval.

PCSK9 inhibitors in the prevention of cardiovascular disease

Reducing plasma levels of low-density lipoprotein cholesterol (LDL-C) remains the cornerstone in the primary and secondary prevention of cardiovascular disease. However, lack of efficacy and adverse effects mean that a substantial proportion of patients fail to achieve acceptable LDL-C levels with currently available lipid-lowering drugs. Over the last decade, inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a promising therapeutic strategy to reduce residual cardiovascular disease risk. Binding of PCSK9 to the LDL receptor targets the receptor for lysosomal degradation. The recognition that inhibition of PCSK9 increases LDL receptor activity has led to the development of a number of approaches to directly target PCSK9. Numerous monoclonal antibodies against PCSK9 are currently being evaluated in phase 3 trials, involving various patient categories on different background lipid-lowering therapies. Current evidence shows reductions in LDL-C levels of up to 70 % may be achieved with PCSK9 inhibition, independent of background statin therapy. This review examines the most recent evidence and future prospects for the use of PCSK9 inhibitors in the prevention of cardiovascular disease.

Leptin decreases the expression of low-density lipoprotein receptor via PCSK9 pathway: linking dyslipidemia with obesity

Background

Previous studies have suggested that people with obesity showed elevated serum levels of leptin as well as lipid dysfunction and proprotein convertase subtilisin/kexin type 9 (PCSK9) played an important role in the regulation of lipid metabolism recently. The aim of this study was to determine if leptin participated in regulating the uptake of low-density lipoproteins (LDL) in hepatocytes via PCSK9.

Methods

HepG2 cells were treated with human recombinant leptin. The impact of leptin on cellular low density lipoprotein receptor (LDLR) and PCSK9 protein levels was determined by Western blot. Dil-LDL uptake assay was performed to examine the LDLR function. Specific small interfering RNAs (siRNAs) were used to interfere the expressions of target proteins.

Results

The expression of LDLR and LDL uptake could be significantly down-regulated by leptin treatment while the expressions of PCSK9 and hepatocyte nuclear factor 1α (HNF1α) were enhanced in HepG2 cells. Furthermore, inhibition of PCSK9 or HNF1α expression by siRNAs rescued the reduction of LDLR expression and LDL uptake by leptin. We found that leptin activated the p38 mitogen-activated protein kinase (p38MAPK) signaling pathway. Moreover, the changes of the expressions of HNF1α, PCSK9, LDLR, and LDL uptake induced by leptin could be blocked by p38MAPK inhibitor (SB203580). Additionally, leptin attenuated the up-regulation of LDLR caused by atorvastatin in HepG2 cells.

Conclusions

These findings indicated firstly that leptin reduced LDLR levels in hepatocyte via PCSK9 pathway, suggesting that PCSK9 might be a alternative target for dyslipidemia in the obesity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1032-4) contains supplementary material, which is available to authorized users.

Positive correlation between plasma PCSK9 and tissue factors levels in patients with angiographically diagnosed coronary artery disease and diabetes mellitus

BACKGROUND

Pro-protein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that influences plasma levels of low-density lipoprotein cholesterol (LDL-C). Both oxidized LDL and tissue factor (TF) contributed to the development of prothrombotic state. The present study aims to explore the relationship between plasma level of PCSK9 and that of TF in patient with coronary artery disease (CAD).

METHODS

From July 2013 to March 2014, we enrolled 197 consecutive patients who underwent coronary angiography because of suspected CAD at Beijing Anzhen Hospital in this study. All patients had no history of using lipid-lowering medication. Of these 197 patients (131 male and 66 female, mean age 56.9 ± 11.8 years), 81 had angiographically diagnosed CAD. Clinical data were collected. Plasma PCSK9 and TF were measured using enzyme-linked immunosorbent assay (ELISA). Levels of plasma PCSK9 and TF were compared and their correlation analyzed among different patient groups.

RESULTS

Both plasma levels of PCSK9 (279.8 ± 60.4 µg/L vs. 216.5 ± 45.3 µg/L, P < 0.01) and TF (156.4 ± 26.6 µg/mL vs. 112.1 ± 38.3 µg/L, P < 0.01) were significantly higher in patients with CAD, as compared with those without CAD. Correlation analysis showed plasma level of PCSK9 was significantly correlated with that of TF in both patients with and without CAD. However, multivariate regression analysis after adjustment for age, gender, smoking, alcohol, hypertension and hyperlipidemia showed that only in CAD patients with type 2 diabetes mellitus, there was significant positive correlation between plasma levels of PCSK9 and TF (β = 0.353, P < 0.01).

CONCLUSIONS

The plasma level of PCSK9 is independently and positively associated with that of TF in CAD patients with diabetes mellitus, but not in those without diabetes mellitus. Further study is needed to investigate the underlying mechanism.

Targeting PCSK9 as a promising new mechanism for lowering low-density lipoprotein cholesterol

Statins and other lipid-lowering drugs have dominated the market for many years for achievement of recommended levels of low-density lipoprotein cholesterol (LDL-C). However, a substantial number of high-risk patients are unable to achieve the LDL-C goal. Proprotein convertase subtilisin/kexin 9 (PCSK9) has recently emerged as a new, promising key therapeutic target for hypercholesterolemia. PCSK9 is a protease involved in chaperoning the low-density lipoprotein receptor to the process of degradation. PCSK9 inhibitors and statins effectively lower LDL-C. The PCSK9 inhibitors decrease the degradation of the LDL receptors, whereas statins mainly interfere with the synthetic machinery of cholesterol by inhibiting the key rate limiting enzyme, the HMG CoA reductase. PCSK9 inhibitors are currently being developed as monoclonal antibodies for their primary use in lowering LDL-C. They may be especially useful for patients with homozygous familial hypercholesterolemia, who at present receive minimal benefit from traditional statin therapy. The monoclonal antibody PCSK9 inhibitors, recently granted FDA approval, show the most promising safety and efficacy profile compared to other, newer LDL-C lowering therapies. This review will primarily focus on the safety and efficacy of monoclonal antibody PCSK9 inhibitors in comparison to statins. The review will also address new, alternative PCSK9 targeting drug classes such as small molecules, gene silencing agents, apolipoprotein B antisense oligonucleotides, and microsomal triglyceride transfer protein inhibitors.

Plasma proprotein convertase subtilisin/kexin type 9 is associated with Lp(a) in type 2 diabetic patients

AIM

Recent in vitro researches have shown that plasma Lp(a) can be reduced using a proprotein convertase subtilisin/kexin type 9 (PCSK9)-inhibitory monoclonal antibody. In our clinical study we tried to investigate the association between plasma Lp(a) and PCSK9 in Type 2 diabetic patients with elevated plasma Lp(a), and to check whether such an association would be related to LDL-receptor (LDL-R) levels.

METHODS

Plasma PCSK9 and LDL-R concentrations were measured by sandwich ELISA methods using recombinant human PCSK9 protein and LDL-R protein as standards in a cohort with type 2 diabetic patients (n=50) compared to an age- and sex-matched control group (n=50). Both clinical and biochemical parameters were determined in all patients.

RESULTS

Plasma PCSK9 level was significantly elevated in T2DM patients compared to controls (44.61±14.44 and 33.22±11.79ng/mL, respectively, P<0.0001). However LDL-R levels did not differ between the two groups. Remarkably, plasma PCSK9 levels were positively correlated with Lp(a) levels in whole population (r=+0.227, P=0.03) as well as in T2DM group (r=+0.398, P=0.0061) but not in control group. Multiple linear regression analysis showed that plasma Lp(a) levels were independently associated to those of PCSK9.

CONCLUSION

Lp(a) has been proposed as a contributing factor to the accelerated development of macrovascular complications in T2DM. Its synergic effect with PCSK9 may explain the enhanced atherogenicity in T2DM patients.

Recent advances in the understanding and care of familial hypercholesterolaemia: significance of the biology and therapeutic regulation of proprotein convertase subtilisin/kexin type 9

Familial hypercholesterolaemia (FH) is an autosomal co-dominant disorder that markedly raises plasma low-density lipoprotein-cholesterol (LDL-C) concentration, causing premature atherosclerotic coronary artery disease (CAD). FH has recently come under intense focus and, although there is general consensus in recent international guidelines regarding diagnosis and treatment, there is debate about the value of genetic studies. Genetic testing can be cost-effective as part of cascade screening in dedicated centres, but the full mutation spectrum responsible for FH has not been established in many populations, and its use in primary care is not at present logistically feasible. Whether using genetic testing or not, cholesterol screening of family members of index patients with an abnormally raised LDL-C must be used to determine the need for early treatment to prevent the development of CAD. The metabolic defects in FH extend beyond LDL, and may affect triacylglycerol-rich and high-density lipoproteins, lipoprotein(a) and oxidative stress. Achievement of the recommended targets for LDL-C with current treatments is difficult, but this may be resolved by new drug therapies. Lipoprotein apheresis remains an effective treatment for severe FH and, although expensive, it costs less than the two recently introduced orphan drugs (lomitapide and mipomersen) for homozygous FH. Recent advances in understanding of the biology of proprotein convertase subtilisin/kexin type 9 (PCSK9) have further elucidated the regulation of lipoprotein metabolism and led to new drugs for effectively treating hypercholesterolaemia in FH and related conditions, as well as for treating many patients with statin intolerance. The mechanisms of action of PCSK9 inhibitors on lipoprotein metabolism and atherosclerosis, as well as their impact on cardiovascular outcomes and cost-effectiveness, remain to be established.

Low-normal thyroid function and novel cardiometabolic biomarkers

The concept is emerging that low-normal thyroid function, i.e., either higher thyroid-stimulating hormone or lower free thyroxine levels within the euthyroid reference range, could contribute to the development of atherosclerotic cardiovascular disease. It is possible that adverse effects of low-normal thyroid function on cardiovascular outcome may be particularly relevant for specific populations, such as younger people and subjects with high cardiovascular risk. Low-normal thyroid function probably relates to modest increases in plasma total cholesterol, low density lipoprotein cholesterol, triglycerides and insulin resistance, but effects on high density lipoprotein (HDL) cholesterol and non-alcoholic fatty liver disease are inconsistent. Low-normal thyroid function may enhance plasma cholesteryl ester transfer, and contribute to an impaired ability of HDL to inhibit oxidative modification of LDL, reflecting pro-atherogenic alterations in lipoprotein metabolism and HDL function, respectively. Low-normal thyroid function also confers lower levels of bilirubin, a strong natural anti-oxidant. Remarkably, all these effects of low-normal thyroid functional status appear to be more outspoken in the context of chronic hyperglycemia and/or insulin resistance. Collectively, these data support the concept that low-normal thyroid function may adversely affect several processes which conceivably contribute to the pathogenesis of atherosclerotic cardiovascular disease, beyond effects on conventional lipoprotein measures.

Familial combined hyperlipidemia: from molecular insights to tailored therapy

PURPOSE OF REVIEW

This review presents recent basic and clinical developments in familial combined hyperlipidemia (FCHL).

RECENT FINDINGS

A variety of experiments have contributed to the elucidation of this complex disease. They consist of dynamic and gene expression studies in adipocytes, confirming the role of dysfunctional adipose tissue in the pathogenesis of FCHL and identifying potential new pathways, such as complement activation. Whole exome sequencing and classical linkage studies in FCHL pedigrees, some conducted with new traits (e.g. plasma proprotein convertase subtilisin/kexin type 9 [PCSK9] and phospholipid transfer protein activity), have revealed new genes of interest, among which SLC25A40 and LASS4. Finally, gene expression studies in liver biopsies and liver cell culture experiments have gained further insight in the role of upstream stimulatory factor 1, one of the most replicated genes in FCHL, in its pathogenesis.On the basis of these observations and recent phase II clinical trials, PCSK9 antagonizing is the most promising lipid-lowering therapy to be added to our current arsenal of statins and fibrates in FCHL treatment.

SUMMARY

Ongoing basic research provides a steady growth in our knowledge on the genes that are involved in FCHL as well as their metabolic function(s). This field of research may be enhanced when data are expanded and integrated for systems biology approaches. Our growing insights in the cause of FCHL allow for better, targeted treatment of dyslipidemia and prevention of cardiovascular complications.

Circulating PCSK9 is a strong determinant of plasma triacylglycerols and total cholesterol in homozygous carriers of apolipoprotein ε2

Plasma PCSK9, an important determinant of LDL-receptor degradation, is strongly related to total cholesterol and triacylglycerol levels in homozygous carriers of the apolipoprotein ε2 allele. This observation provides new insight into the pathogenesis of type III hyperlipidaemia and its treatment.

Plasma proprotein convertase subtilisin kexin type 9 levels are related to markers of cholesterol synthesis in familial combined hyperlipidemia

BACKGROUND AND AIMS

Two recent independent studies showed that patients with familial combined hyperlipidemia (FCHL) have elevated plasma levels of proprotein convertase subtilisin kexin type 9 (PCSK9) and markers of cholesterol synthesis. Both PCSK9 expression and cholesterol synthesis are downstream effects of hepatic activation of sterol regulatory element binding protein 2 (SREBP2). The present study was conducted to study the relationship between plasma PCSK9 and markers of cholesterol synthesis in FCHL.

METHODS AND RESULTS

Markers of cholesterol synthesis (squalene, desmosterol, lathosterol), cholesterol absorption (campesterol, sitosterol, cholestanol) and PCSK9 were measured in plasma of FCHL patients (n = 103) and their normolipidemic relatives (NLR; n = 240). Plasma PCSK9, lathosterol and desmosterol levels were higher in FCHL patients than their NLR (p < 0.001, age and sex adjusted). Heritability calculations demonstrated that 35% of the variance in PCSK9 levels could be explained by additive genetic effects (p < 0.001). Significant age- and sex-adjusted correlations were observed for the relationship between PCSK9 and lathosterol, both unadjusted and adjusted for cholesterol, in the overall FCHL population (both p < 0.001). Multivariate regression analyses, with PCSK9 as the dependent variable, showed that the regression coefficient for FCHL status decreased by 25% (from 0.8 to 0.6) when lathosterol was included. Nevertheless, FCHL status remained an independent contributor to plasma PCSK9 (p < 0.001).

CONCLUSIONS

The present study confirms the previously reported high and heritable PCSK9 levels in FCHL patients. Furthermore, we now show that high PCSK9 levels are, in part, explained by plasma lathosterol, suggesting that SREBP2 activation partly accounts for elevated PCSK9 levels in FCHL.

The promises of PCSK9 inhibition

PURPOSE OF REVIEW

In the past 10 years, the LDL receptor inhibitor proprotein convertase subtilisin kexin type 9 (PCSK9) has emerged as a validated target for lowering plasma LDL cholesterol levels. Here we review the most recent reports on PCSK9 out of a total of 500 publications published in print or online before March 2013 and indexed on PubMed.

RECENT FINDINGS

All published in 2012, phase I and II clinical trials demonstrate that fully human monoclonal antibodies targeting PCSK9 dramatically reduce LDL-C and enable patients to reach their target goals, without severe or serious safety issues.

SUMMARY

This review summarizes the discovery of PCSK9, its original mode of action as a secreted inhibitor of the LDL receptor, as well as its genetic regulation by statins. We then focus on the major results from the 2012 phase I and II PCSK9 inhibitor clinical trials. We also review the recent in-vivo studies demonstrating the potential cardiovascular benefits of long-term PCSK9 inhibition and discuss its potential side-effects.

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

OBJECTIVES

Inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9) has been proposed to be a potential new therapeutic target for treatment of hypercholesterolaemia. However, little is known about the effects of PCSK9 inhibition on the lipidome.

METHODS

We performed molecular lipidomic analyses of plasma samples obtained from PCSK9-deficient mice, and serum of human carriers of a loss-of-function variant in the PCSK9 gene (R46L).

RESULTS

In both mouse and man, PCSK9 deficiency caused a decrease in several cholesteryl esters (CE) and short fatty acid chain containing sphingolipid species such as CE 16:0, glucosyl/galactosylceramide (Glc/GalCer) d18:1/16:0, and lactosylceramide (LacCer) d18:1/16:0. In mice, the changes in lipid concentrations were most prominent when animals were given regular chow diet. In man, a number of molecular lipid species was shown to decrease significantly even when LDL-cholesterol was non-significantly reduced by 10% only. Western diet attenuated the lipid lowering potency of PCSK9 deficiency in mice.

CONCLUSIONS

Plasma molecular lipid species may be utilized for characterizing novel compounds inhibiting PCSK9 and as sensitive efficacy markers of the PCSK9 inhibition.

PCSK9 plays a significant role in cholesterol homeostasis and lipid transport in intestinal epithelial cells

OBJECTIVES

The proprotein convertase subtillisin/kexin type 9 (PCSK9) regulates cholesterol metabolism via degradation of low-density lipoprotein receptor (LDLr). Although PCSK9 is abundantly expressed in the intestine, limited data are available on its functions. The present study aims at determining whether PCSK9 plays important roles in cholesterol homeostasis and lipid transport in the gut.

METHODS AND RESULTS

Caco-2/15 cells were used allowing the exploration of the PCSK9 secretory route through the apical and basolateral compartments corresponding to intestinal lumen and serosal circulation, respectively. The output of PCSK9 occurred through the basolateral membrane, a site characterized by the location of LDLr. Co-immunoprecipitation studies indicated an association between PCSK9 and LDLr. Addition of purified recombinant wild type and D374Y gain-of function PCSK9 proteins to the basolateral medium was followed by a decrease in LDLr concomitantly with the accumulation of both forms of PCSK9. Furthermore, the latter caused a significant enhancement in cholesterol uptake also evidenced by a raised protein expression of cholesterol transporters NPC1L1 and CD36 without changes in SR-BI, ABCA1, and ABCG5/G8. Moreover, exogenous PCSK9 altered the activity of HMG-CoA reductase and acylcoenzyme A: cholesterol acyltransferase, and was able to enhance chylomicron secretion by positively modulating lipids and apolipoprotein B-48 biogenesis. Importantly, PCSK9 silencing led to opposite findings, which validate our data on the role of PCSK9 in lipid transport and metabolism. Moreover, PCSK9-mediated changes persisted despite LDLr knockdown.

CONCLUSIONS

These findings indicate that, in addition to its effect on LDLr, PCSK9 modulates cholesterol transport and metabolism, as well as production of apo B-containing lipoproteins in intestinal cells.

Adiposity blunts the positive relationship of thyrotropin with proprotein convertase subtilisin-kexin type 9 levels in euthyroid subjects

BACKGROUND

Effects of thyroid function status on lipoprotein metabolism may extend into the euthyroid range. Low-density lipoprotein (LDL) metabolism is governed by proprotein convertase subtilisin-kexin type 9 (PCSK9), which down-regulates LDL receptor expression, resulting in higher LDL cholesterol (LDL-C). Here, we tested whether plasma PCSK9 correlates with thyroid function in nonobese and obese euthyroid subjects.

METHODS

We assessed the extent to which plasma PCSK9 is determined by thyrotropin (TSH) in 74 euthyroid subjects (31 women; TSH between 0.5 and 4.0 mU/L and free thyroxine [FT4] between 11.0 and 19.5 pM) with varying degrees of obesity (body mass index [BMI] ranging from 20.2 to 40.4 kg/m(2)).

RESULTS

TSH, FT4, PCSK9, non-high-density lipoprotein cholesterol (non-HDL-C), LDL-C, and apolipoprotein B (apoB) levels were not different between 64 nonobese subjects (BMI<30 kg/m(2)) and 10 obese subjects (BMI≥30 kg/m(2); p>0.20 for each). PCSK9 correlated positively with TSH in nonobese subjects (r=0.285, p=0.023). In contrast, PCSK9 was not associated positively with TSH in obese subjects (r=-0.249, p=0.49). The relationship of PCSK9 with TSH was different between nonobese and obese subjects when taking age, sex, FT4, and the presence of anti-thyroid antibodies into account (multiple linear regression analysis: β=-0.320, p=0.012 for the interaction term between the presence of obesity and TSH on PCSK9), and was also modified by BMI as a continuous trait (β=-0.241, p=0.062 for the interaction term between BMI and TSH on PCSK9). Non-HDL-C, LDL-C, and apoB levels were dependent on PCSK9 in nonobese subjects (p≤0.01 for each), but not in obese subjects (p>0.50), Accordingly, BMI interacted negatively with PCSK9 on non-HDL-C (p=0.028) and apoB (p=0.071).

CONCLUSIONS

This study suggests that circulating PCSK9 levels correlate with thyroid function even in the normal range. This relationship appears to be blunted by obesity. Thyroid functional status may influence cholesterol metabolism through the PCSK9 pathway.

Proprotein convertase subtilisin/kexin type 9 inhibition

PURPOSE OF REVIEW

There are now ample data that demonstrate that inhibition of PCSK9 (proprotein convertase subtilisin/kexin type 9) can safely lower LDL cholesterol synergistically with statins. Considering that PCSK9 was first identified less than a decade ago, the last few years have shown rapid and remarkable advancements in our understanding and knowledge of the structure and function of PCSK9.

RECENT FINDINGS

Therapeutic developments have not lagged far behind with some monoclonal antibodies currently entering phase III trials. Of the many approaches to PCSK9 inhibition, these compounds are the furthest advanced in their clinical development while small molecule oral inhibitors seem a distant prospect.

SUMMARY

This review summarizes the discovery and history of PCSK9 and in particular its mode of action as an inhibitor of the LDL receptor. It also recapitulates key studies that have demonstrated the potential of inhibiting PCSK9 to further decrease LDL-cholesterol levels safely and synergistically with statins. Finally, we review the strategies that are currently in development to inhibit PCSK9, with a special emphasis on the spectacular results from recent phase-I and phase-II clinical trials.

Proprotein convertase subtilisin-kexin type 9 is elevated in proteinuric subjects: relationship with lipoprotein response to antiproteinuric treatment

OBJECTIVE

LDL-receptor deficiency may provide a mechanism which contributes to atherogenic lipoprotein abnormalities in experimental nephrosis and in humans with glomerular proteinuria. The proprotein convertase subtilisin-kexin type 9 (PCSK9) pathway plays a key role in lipoprotein metabolism by promoting LDL-receptor degradation. We tested whether plasma PCSK9 is elevated in proteinuric states, and determined relationships of PCSK9 with lipoprotein responses to proteinuria reduction.

METHODS

Thirty-nine kidney patients (e-GFR 61 ± 29 mL/min/1.73 m(2), proteinuria 1.9 [0.9-3.3] g/day; 19 on statin treatment) were studied during 2 randomized double-blind 6-week periods on either lisinopril (40 mg/day) and a regular sodium diet (194 ± 49 mmol Na+/day; baseline treatment) or lisinopril plus valsartan (320 mg/day) and a low sodium diet (102 ± 52 mmol Na(+)/day; maximal treatment), and compared to age- and sex-matched controls. Maximal treatment decreased proteinuria to 0.5 [0.3-1.1] g/day (P < 0.001).

RESULTS

Plasma PCSK9 was increased at baseline in proteinuric subjects (213 [161-314] vs. 143 [113-190] ug/L in controls, P ≤ 0.001), irrespective of statin use, e-GFR and BMI. PCSK9 correlated with proteinuria at baseline (R = 0.399, P = 0.018) and at maximal antiproteinuric treatment (R = 0.525, P = 0.001), but did not decrease during proteinuria reduction (P = 0.84). Individual changes in total cholesterol (R = 0.365, P = 0.024), non-HDL cholesterol (R = 0.333, P = 0.041), and LDL cholesterol (R = 0.346, P = 0.033) were correlated positively with individual PCSK9 responses. PCSK9 at baseline independently predicted the total/HDL cholesterol ratio response to treatment (P = 0.04).

CONCLUSION

Plasma PCSK9 was elevated in proteinuria, predicted lipoprotein responses to proteinuria reduction but remained unchanged after proteinuria reduction. Inhibition of the PCSK9 pathway may provide a novel treatment strategy in proteinuric subjects.

The PCSK9 decade

PCSK9 proprotein convertase subtilisin/kexin type (PCSK9) is a crucial protein in LDL cholesterol (LDL-C) metabolism by virtue of its pivotal role in the degradation of the LDL receptor. In recent years, both in vitro and in vivo studies have greatly supplemented our understanding of the (patho)physiological role of PCSK9 in human biology. In the current review, we summarize studies published or in print before May 2012 concerning the physiological role of PCSK9 in cholesterol metabolism. Moreover, we briefly describe the clinical phenotypes encountered in carriers of mutations in the gene encoding PCSK9. As PCSK9 has emerged as a novel target for LDL-C lowering therapy, methods to inhibit PCSK9 will also be reviewed. Initial data from investigations of PCSK9 inhibition in humans are promising and indicate that PCSK9 inhibition may be a viable new therapeutic option for the treatment of dyslipidemia and associated cardiovascular diseases.

Screening for familial hypercholesterolaemia

Familial hypercholesterolaemia (FH) is an autosomal dominant disorder characterised by increased plasma concentrations of low density lipoprotein (LDL) cholesterol leading to atherosclerosis and premature coronary heart disease (CHD) and death. The clinical diagnosis of FH is based on a personal and family history, physical examination findings and LDL-cholesterol concentrations. FH is primarily caused by mutations in the LDL-receptor gene (LDLR), and less frequently by mutations in genes for APOB and the more recently identified PCSK9. Lifestyle modification and pharmacotherapy can delay or prevent the onset of CHD in FH. It is estimated that only 20% of cases have been diagnosed in Australia and that the majority are inadequately treated. Screening options for FH include population screening (of children or adults), targeted screening of patients with premature CHD and their relatives, or opportunistic screening such as flagging laboratory lipid reports. Cascade screening, a form of targeted screening, is an ethically acceptable, cost-effective strategy for the identification of FH. However, for screening to be successful, medical practitioners need to be aware of the signs and diagnosis of FH and the benefits of early treatment.

Novel LDL-oriented pharmacotherapeutical strategies

Elevated levels of low-density cholesterol (LDL-C) are highly correlated with increased risk of cardiovascular diseases (CVD). Thus, current guidelines have recommended progressively lower LDL-C for cholesterol treatment and CVD prevention as the primary goal of therapy. Even so, some patients in the high risk category fail to achieve recommended LDL-C targets with currently available medications. Thereby, additional pharmaceutical strategies are urgently required. In the review, we aim to provide an overview of both current and emerging LDL-C lowering drugs. As for current available LDL-C lowering agents, attentions are mainly focused on statins, niacin, bile acid sequestrants, ezetimibe, fibrates and omega-3 fatty acids. On the other hand, the emerging drugs differ from mechanisms are including: intervention of cholesterol biosynthesis downstream enzyme (squalene synthase inhibitors), inhibition of lipoprotein assembly (antisense mRNA inhibitors of apolipoprotein B and microsomal transfer protein inhibitors), enhanced lipoprotein clearance (proprotein convertase subtilisin kexin type 9, thyroid hormone analogues), inhibition of intestinal cholesterol absorption (Niemann-Pick C1-like 1 protein and acyl coenzyme A:cholesterol acyltransferase inhibitors) and interrupting enterohepatic circulation (apical sodium-dependent bile acid transporter inhibitors). Several ongoing agents are in their different stages of clinical trials, in expectation of promising antihyperlipidemic drugs. Therefore, alternative drugs monotherapy or in combination with statins will be sufficient to reduce LDL-C concentrations to optimal levels, and a new era for better LDL-C managements is plausible.

Plasma proprotein convertase subtilisin kexin type 9 is a heritable trait of familial combined hyperlipidaemia

The aim of the present study was to investigate the relationship between circulating PCSK9 (proprotein convertase subtilisin kexin type 9) and FCHL (familial combined hyperlipidaemia) and, when positive, to determine the strength of its heritability. Plasma PCSK9 levels were measured in FCHL patients (n=45), NL (normolipidaemic) relatives (n=139) and their spouses (n=72). In addition, 11 FCHL patients were treated with atorvastatin to study the response in PCSK9 levels. PCSK9 levels were higher in FCHL patients compared with NL relatives and spouses: 96.1 compared with 78.7 and 82.0 ng/ml (P=0.004 and P=0.002 respectively). PCSK9 was significantly associated with both TAG (triacylglycerol) and apolipoprotein B levels (P<0.001). The latter relationship was accounted for by LDL (low-density lipoprotein)–apolipoprotein B (r=0.31, P=0.02), not by VLDL (very-low-density lipoprotein)–apolipoprotein B (r=0.09, P=0.49) in a subgroup of subjects (n=59). Heritability calculations for PCSK9 using SOLAR and FCOR software yielded estimates of 67–84% respectively (P<0.0001). PCSK9 increased from 122 to 150 ng/ml in 11 FCHL patients treated with atorvastatin (40 mg) once daily for 8 weeks (P=0.018). In conclusion, plasma PCSK9 is a heritable trait associated with both FCHL diagnostic hallmarks. These results, combined with the significant rise in PCSK9 levels after statin therapy, warrant further studies in order to unravel the exact role of PCSK9 in the pathogenesis and treatment of this highly prevalent genetic dyslipidaemia.

A new method for measurement of total plasma PCSK9: clinical applications

The proprotein convertase subtilisin kexin-9 (PCSK9) circulates in plasma as mature and furin-cleaved forms. A polyclonal antibody against human PCSK9 was used to develop an ELISA that measures total plasma PCSK9 rather than only the mature form. A cross-sectional study evaluated plasma levels in normal (n = 254) and hypercholesterolemic (n = 200) subjects treated or untreated with statins or statin plus ezetimibe. In controls, mean plasma PCSK9 (89.5 +/- 31.9 ng/ml) correlated positively with age, total cholesterol, LDL-cholesterol (LDL-C), triglycerides, and fasting glucose. Sequencing PCSK9 from individuals at the extremes of the normal PCSK9 distribution identified a new loss-of-function R434W variant associated with lower levels of circulating PCSK9 and LDL-C. In hypercholesterolemic subjects, PCSK9 levels were higher than in controls (99.3 +/- 31.7 ng/ml, P < 0.04) and increased in proportion to the statin dose, combined or not with ezetimibe. In treated patients (n = 139), those with familial hypercholesterolemia (FH; due to LDL receptor gene mutations) had higher PCSK9 values than non-FH (147.01 +/- 42.5 vs. 127.2 +/- 40.8 ng/ml, P < 0.005), but LDL-C reduction correlated positively with achieved plasma PCSK9 levels to a similar extent in both subsets (r = 0.316, P < 0.02 in FH and r = 0.275, P < 0.009 in non-FH). The detection of circulating PCSK9 in both FH and non-FH subjects means that this assay could be used to monitor response to therapy in a wide range of patients.

Longitudinal association of PCSK9 sequence variations with low-density lipoprotein cholesterol levels: the Coronary Artery Risk Development in Young Adults Study

BACKGROUND

Mutations of PCSK9 are associated cross-sectionally with plasma low-density lipoprotein cholesterol (LDL-C) levels, but little is known about their longitudinal association with LDL-C levels from young adulthood to middle age.

METHODS AND RESULTS

We investigated the associations of 6 PCSK9 variants with LDL-C over 20 years in 1750 blacks and 1828 whites from the Coronary Artery Risk Development In Young Adults study. Generalized estimating equations were used to assess longitudinal differences in LDL-C levels between genotype categories. For blacks, LDL-C levels at age 18 were significantly lower (P<0.001) among those with 3 genetic variants (L253F, C679X, and Y142X; 81.5 mg/dL) and A443T (95.5 mg/dL) compared with noncarriers (109.6 mg/dL). The difference in LDL-C levels from noncarriers tended to widen for those with the 3 variants only, by 0.24 mg/dL per year of age (P=0.14). For whites with the R46L variant, compared with noncarriers, LDL-C levels at age 18 were significantly lower (84.4 mg/dL versus 100.9 mg/dL; P<0.001), and the increase in LDL-C with age was similar to noncarriers. The 3 genetic variants and the A443T variant in black men were associated with lower carotid intima-media thickness and lower prevalence of coronary calcification measured at ages 38 to 50.

CONCLUSIONS

Our results suggest that participants with several genetic variants of PCSK9 have persistently lower serum LDL-C levels than noncarriers from ages 18 to 50. Such long-term reduction in LDL-C levels is associated with reduced subclinical atherosclerosis burden in black men.

Regulation of the proprotein convertase subtilisin/kexin type 9 in intestinal epithelial cells

Proprotein convertase subtilisin/kexin type 9 (PCSK9) posttranslationally promotes the degradation of the low-density lipoprotein receptor (LDLr) in hepatocytes and increases plasma LDL cholesterol. It is not clear, however, whether PCSK9 plays a role in the small intestine. Here, we characterized the patterns of variations of PCSK9 and LDLr in fully differentiated Caco-2/15 cells as a function of various potential effectors. Cholesterol (100 microM) solubilized in albumin or micelles significantly downregulated PCSK9 gene (30%, P<0.05) and protein expression (50%, P<0.05), surprisingly in concert with a decrease in LDLr protein levels (45%, P<0.05). Cells treated with 25-hydroxycholesterol (50 microM) also displayed significant reduction in PCSK9 gene (37%, P<0.01) and protein (75% P<0.001) expression, whereas LDLr showed a decrease at the gene (30%, P<0.05) and protein (57%, P<0.01) levels, respectively. The amounts of PCSK9 mRNA and protein in Caco-2/15 cells were associated to the regulation of 3-hydroxy-3-methylglutaryl-CoA reductase and sterol regulatory element binding protein-2 (SREBP-2) that can transcriptionally activate PCSK9 via sterol-regulatory elements located in its proximal promoter region. On the other hand, depletion of cholesterol content by hydroxypropyl-beta-cyclodextrin upregulated PCSK9 transcripts (20%, P<0.05) and protein mass (540%, P<0.001), in parallel with SREBP-2 protein levels. The addition of bile acids (BA) taurocholate and deoxycholate to the apical culture medium lowered PCSK9 gene expression (25%, P<0.01) and raised PCSK9 protein expression (30%, P<0.01), respectively, probably via the modulation of farnesoid X receptor. Furthermore, unconjugated and conjugated BA exhibited different effects on PCSK9 and LDLr. Altogether, these data indicate that intestinal PCSK9 is highly modulated by sterols and emphasize the distinct effects of BA species.