Apolipoprotein B100 metabolism in autosomal-dominant hypercholesterolemia related to mutations in PCSK9

Characterization of lipoproteins and associated lipidome in very preterm infants: a pilot study

BACKGROUND

Preterm birth is associated with higher risks of suboptimal neurodevelopment and cardiometabolic disease later in life. Altered maternal-fetal lipid supply could play a role in such risks. Our hypothesis was that very preterm infants born with very low birth weight (VLBW) have altered lipidome and apolipoprotein profiles, compared with term infants.

METHODS

Seven mothers of VLBW infants born at <32 GA and 8 full-term mother-infant dyads were included. Cholesterol and triglycerides in lipoproteins were determined in maternal plasma and in the two blood vessels of the umbilical cord (vein (UV) and artery (UA)) following FPLC isolation. Apolipoprotein concentrations in lipoproteins and plasma lipidomic analysis were performed by LC-MS/MS.

RESULTS

We found higher cholesterol and VLDL-cholesterol in UV and UA and lower apolipoprotein A-I in HDL2 in UV in preterm neonates. Phosphatidylcholine (PC) containing saturated and monounsaturated fatty acids and specific sphingomyelin species were increased in UV and UA, whereas PC containing docosahexaenoic acid (DHA) was reduced in UV of VLBW neonates.

CONCLUSIONS

Lower DHA-PC suggests a lower DHA bioavailability and may contribute to the impaired neurodevelopment. Altered HDL-2, VLDL, and sphingomyelin profile reflect an atherogenic risk and increased metabolic risk at adulthood in infants born prematurely.

IMPACT

Lower ApoA-I in HDL2, and increased specific sphingomyelin and phosphatidylcholine containing saturated and monounsaturated fatty acid could explain the accumulation of cholesterol in umbilical vein in VLBW preterm neonates. Decreased phosphatidylcholine containing DHA suggest a reduced DHA availability for brain development in VLBW preterm infants. Characterization of alterations in fetal lipid plasma and lipoprotein profiles may help to explain at least in part the causes of the elevated cardiovascular risk known in people born prematurely and may suggest that a targeted nutritional strategy based on the composition of fatty acids carried by phosphatidylcholine may be promising in infants born very early.

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.

New Trends and Therapies for Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is associated with an elevated risk of atherosclerosis. The finding of monogenic defects indicates higher atherosclerotic risk in comparison with hypercholesterolemia of other etiologies. However, in heterozygous FH, cardiovascular risk is heterogeneous and depends not only on high cholesterol levels but also on the presence of other biomarkers and genes. The development of atherosclerosis risk scores specific for heterozygous FH and the use of subclinical coronary atherosclerosis imaging help with identifying higher-risk individuals who may benefit from further cholesterol lowering with PCSK9 inhibitors. There is no question about the extreme high risk in homozygous FH, and intensive LDL-cholesterol-lowering therapy must be started as soon as possible. These patients have gained life free of events in comparison with the past, but a high atherosclerosis residual risk persists. Furthermore, there is also the issue of aortic and supra-aortic valve disease development. Newer therapies such as inhibitors of microsomal transfer protein and angiopoietin-like protein 3 have opened the possibility of LDL-cholesterol normalization in homozygous FH and may provide an alternative to lipoprotein apheresis for these patients. Gene-based therapies may provide more definite solutions for lowering high LDL cholesterol and consequent atherosclerosis risk for people with FH.

The role of PCSK9 in NAFLD/NASH and therapeutic implications of PCSK9 inhibition

INTRODUCTION

There are inconsistent findings regarding the effect of lipid-lowering agents on nonalcoholic fatty liver disease (NAFLD). Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) is an important player in cholesterol homeostasis and intracellular lipogenesis, and PCSK9 inhibitors (PCSK9-i) have been found to be efficient for pharmacological management of hyperlipidemia.

AREAS COVERED

Whether PCSK9 (itself) or PCSK9-i affects NAFLD is still disputed. To address this question, we review published preclinical and clinical studies providing evidence for the role of PCSK9 in and the effect of PCSK9-I on the development and pathogenesis of NAFLD.

EXPERT OPINION

The current evidence from a landscape of preclinical and clinical studies examining the role of PCSK9 in NAFLD shows controversial results. Preclinical studies indicate that PCSK9 associates with NAFLD and nonalcoholic steatohepatitis (NASH) progression in opposite directions. In humans, it has been concluded that the severity of hepatic steatosis affects the correlation between circulating PCSK9 and liver fat content in humans, with a possible impact of circulating PCSK9 in the early stages of NAFLD, but not in the late stages. However, data from clinical trials with PCSK9-i reassure to the safety of these agents, although real-life long-term evidence is needed.

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

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

Proprotein Convertase Subtilisin/Kexin Type 9 Inhibitors Use for Atherogenic Dyslipidemia in Solid Organ Transplant Patients

Dyslipidemia is a widespread risk factor in solid organ transplant patients, due to many reasons, such as the use of immunosuppressive drugs, with a consequent increase in cardiovascular diseases in this population. PCSK9 is an enzyme mainly known for its role in altering LDL levels, consequently increasing cardiovascular risk. Monoclonal antibody PCSK9 inhibitors demonstrated remarkable efficacy in the general population in reducing LDL cholesterol levels and preventing cardiovascular disease. In transplant patients, these drugs are still poorly used, despite having comparable efficacy to the general population and giving fewer drug interactions with immunosuppressants. Furthermore, there is enough evidence that PCSK9 also plays a role in other pathways, such as inflammation, which is particularly dangerous for graft survival. In this review, the current evidence on the function of PCSK9 and the use of its inhibitors will be discussed, particularly in transplant patients, in which they may provide additional benefits.

Unravelling lipoprotein metabolism with stable isotopes: tracing the flow

Dysregulated lipoprotein metabolism is a major cause of atherosclerotic cardiovascular disease (ASCVD). Use of stable isotope tracers and compartmental modelling have provided deeper understanding of the mechanisms underlying lipid disorders in patients at high risk of ASCVD, including familial hypercholesterolemia (FH), elevated lipoprotein(a) [Lp(a)] and metabolic syndrome (MetS). In patients with FH, deficiency in low-density lipoprotein (LDL) receptor activity not only impairs the catabolism of LDL, but also induces hepatic overproduction and decreases catabolism of triglyceride-rich lipoproteins (TRLs). Patients with elevated Lp(a) are characterized by increased hepatic secretion of Lp(a) particles. Atherogenic dyslipidemia in MetS patients relates to a combination of overproduction of very-low density lipoprotein-apolipoprotein (apo) B-100, decreased catabolism of apoB-100-containing particles, and increased catabolism of high-density lipoprotein-apoA-I particles, as well as to impaired clearance of TRLs in the postprandial state. Kinetic studies show that weight loss, fish oils, statins and fibrates have complementary modes of action that correct atherogenic dyslipidemia. Defining the kinetic mechanisms of action of proprotein convertase subtilisin/kexin type 9 and angiopoietin-like 3 inhibitors on lipid and lipoprotein mechanism in dyslipidemic subjects will further our understanding of these therapies in decreasing the development of ASCVD. "Everything changes but change itself. Everything flows and nothing remains the same... You cannot step twice into the same river, for other waters and yet others go flowing ever on." Heraclitus (c.535- c. 475 BCE).

LDL-cholesterol and PCSK9 in patients with familial hypercholesterolemia: influence of PCSK9 variants under lipid-lowering therapy

Background

Familial hypercholesterolemia (FH), an autosomal dominant genetic disease with the elevated levels of low‐density lipoprotein (LDL) cholesterol (LDL‐C), increases the risk of coronary artery disease (CAD). The proprotein convertase subtilisin/kexin type 9 (PCSK9) gene is associated with FH. There is a positive relationship between circulating LDL‐C and PCSK9 levels, a potential CAD condition, without lipid‐lowering therapy (LLT); however, we do not know whether their correlation exists in FH patients under LLT.

Methods

This study compared the correlation of PCSK9 variants among patients with FH under LLT (n = 70; mean age, 53 years; male, 63%). LDLR, PCSK9 and APOB variants were analyzed using next‐generation sequencing.

Results

The LDL‐C and PCSK9 levels in patients with gain‐of‐function (GOF) variants of PCSK9 (n = 7) were mostly similar to those in patients with LDLR variants (n = 17) or variant‐negative patients (n = 46). A significant positive correlation was observed between LDL‐C and PCSK9 levels in patients with GOF variants of PCSK9 (r = 0.79, p = 0.04), but not in patients with LDLR variants or variant‐negative patients.

Conclusion

The LDL‐C‐PCSK9 correlation is suggested to be retained in FH patients with GOF variants of PCSK9 even under LLT, and these variants can be used as molecular markers for additional treatment with statins in FH patients.

The PCSK9 discovery, an inactive protease with varied functions in hypercholesterolemia, viral infections, and cancer

In 2003, the sequences of mammalian proprotein convertase subtilisin/kexin type 9 (PCSK9) were reported. Radiolabeling pulse-chase analyses demonstrated that PCSK9 was synthesized as a precursor (proPCSK9) that undergoes autocatalytic cleavage in the endoplasmic reticulum into PCSK9, which is then secreted as an inactive enzyme in complex with its inhibitory prodomain. Its high mRNA expression in liver hepatocytes and its gene localization on chromosome 1p32, a third locus associated with familial hypercholesterolemia, other than LDLR or APOB, led us to identify three patient families expressing the PCSK9 variants S127R or F216L. Although Pcsk9 and Ldlr were downregulated in mice that were fed a cholesterol-rich diet, PCSK9 overexpression led to the degradation of the LDLR. This led to the demonstration that gain-of-function and loss-of-function variations in PCSK9 modulate its bioactivity, whereby PCSK9 binds the LDLR in a nonenzymatic fashion to induce its degradation in endosomes/lysosomes. PCSK9 was also shown to play major roles in targeting other receptors for degradation, thereby regulating various processes, including hypercholesterolemia and associated atherosclerosis, vascular inflammation, viral infections, and immune checkpoint regulation in cancer. Injectable PCSK9 monoclonal antibody or siRNA is currently used in clinics worldwide to treat hypercholesterolemia and could be combined with current therapies in cancer/metastasis. In this review, we present the critical information that led to the discovery of PCSK9 and its implication in LDL-C metabolism. We further analyze the underlying functional mechanism(s) in the regulation of LDL-C, as well as the evolving novel roles of PCSK9 in both health and disease states.

Obesity-related genetic determinants of stroke

As obesity, circulating lipids and other vascular/metabolic factors influence the risk of stroke, we examined if genetic variants associated with these conditions are related to risk of stroke using a case-control study in Galicia, Spain. A selection of 200 single-nucleotide polymorphisms previously found to be related to obesity, body mass index, circulating lipids, type 2 diabetes, heart failure, obesity-related cancer and cerebral infarction were genotyped in 465 patients diagnosed with stroke and 480 population-based controls. An unsupervised Lasso regression procedure was carried out for single-nucleotide polymorphism selection based on their potential effect on stroke according to obesity. Selected genotypes were further analysed through multivariate logistic regression to study their association with risk of stroke. Using unsupervised selection procedures, nine single-nucleotide polymorphisms were found to be related to risk of stroke overall and after stratification by obesity. From these, rs10761731, rs2479409 and rs6511720 in obese subjects [odds ratio (95% confidence interval) = 0.61 (0.39-0.95) (P = 0.027); 0.54 (0.35-0.84) (P = 0.006) and 0.42 (0.22-0.80) (P = 0.0075), respectively], and rs865686 in non-obese subjects [odds ratio (95% confidence interval) = 0.67 (0.48-0.94) (P = 0.019)], were independently associated with risk of stroke after multivariate logistic regression procedures. The associations between the three single-nucleotide polymorphisms found to be associated with stroke risk in obese subjects were more pronounced among females; for rs10761731, odds ratios among obese males and females were 1.07 (0.58-1.97) (P = 0.84), and 0.31 (0.14-0.69) (P = 0.0018), respectively; for rs2479409, odd ratios were 0.66 (0.34-1.27) (P = 0.21), and 0.49 (0.24-0.99) (P = 0.04), for obese males and females, respectively; the stroke-rs6511720 association was also slightly more pronounced among obese females, odds ratios were 0.33 (0.13-0.87) (P = 0.022), and 0.28 (0.09-0.85) (P = 0.02) for obese males and females, respectively. The rs865686-stroke association was more pronounced among non-obese males [odds ratios = 0.61 (0.39-0.96) (P = 0.029) and 0.72 (0.42-1.22) (P = 0.21), for non-obese males and females, respectively]. A combined genetic score of variants rs10761731, rs2479409 and rs6511720 was highly predictive of stroke risk among obese subjects (P = 2.04 × 10^-5), particularly among females (P = 4.28 × 10^-6). In summary, single-nucleotide polymorphisms rs1076173, rs2479409 and rs6511720 were found to independently increase the risk of stroke in obese subjects after adjustment for established risk factors. A combined score with the three genomic variants was an independent predictor of risk of stroke among obese subjects in our population.

PCSK9: A Multi-Faceted Protein That Is Involved in Cardiovascular Biology

Pro-protein convertase subtilisin/kexin type 9 (PCSK9) is secreted mostly by hepatocytes and to a lesser extent by the intestine, pancreas, kidney, adipose tissue, and vascular cells. PCSK9 has been known to interact with the low-density lipoprotein receptor (LDLR) and chaperones the receptor to its degradation. In this manner, targeting PCSK9 is a novel attractive approach to reduce hyperlipidaemia and the risk for cardiovascular diseases. Recently, it has been recognised that the effects of PCSK9 in relation to cardiovascular complications are not only LDLR related, but that various LDLR-independent pathways and processes are also influenced. In this review, the various LDLR dependent and especially independent effects of PCSK9 on the cardiovascular system are discussed, followed by an overview of related PCSK9-polymorphisms and currently available and future therapeutic approaches to manipulate PCSK9 expression.

Critical Role of LOX-1-PCSK9 Axis in the Pathogenesis of Atheroma Formation and Its Instability

Cardiovascular disease (CVD) is a major contributor to annual deaths globally. Atherosclerosis is a prominent risk factor for CVD. Although significant developments have been recently made in the prevention and treatment, the molecular pathology of atherosclerosis remains unknown. Interestingly, the recent discovery of proprotein convertase subtilisin/kexin type 9 (PCSK9) introduced a new avenue to explore the molecular pathogenesis and novel management strategies for atherosclerosis. Initial research focussed on the PCSK9-mediated degradation of low density lipoprotein receptor (LDLR) and subsequent activation of pro-inflammatory pathways by oxidised low density lipoprotein (ox-LDL). Recently, PCSK9 and lectin-like oxidised low-density lipoprotein receptor-1 (LOX-1) were shown to positively amplify each other pro-inflammatory activity and gene expression in endothelial cells, macrophages and vascular smooth muscle cells. In this literature review, we provide insight into the reciprocal relationship between PCSK9 and LOX-1 in the pathogenesis of atheroma formation and plaque instability in atherosclerosis. Further understanding of the LOX-1-PCSK9 axis possesses tremendous translational potential to design novel management approaches for atherosclerosis.

Proprotein Convertase Subtilisin/Kexin Type 9: A View beyond the Canonical Cholesterol-Lowering Impact

Proprotein convertase subtilisin/kexin type 9 (PCSK9), mainly synthetized and released by the liver, represents one of the key regulators of low-density lipoprotein cholesterol. Although genetic and interventional studies have demonstrated that lowering PCSK9 levels corresponds to a cardiovascular benefit, identification of non-cholesterol-related processes has emerged since its discovery. Besides liver, PCSK9 is also expressed in many tissues (eg, intestine, endocrine pancreas, and brain). The aim of the present review is to describe and discuss PCSK9 pathophysiology and possible non-lipid-lowering effects whether already extensively characterized (eg, inflammatory burden of atherosclerosis, triglyceride-rich lipoprotein metabolism, and platelet activation), or to be unraveled (eg, in adipose tissue). The identification of novel transcriptional factors in the promoter region of human PCSK9 (eg, ChREBP) characterizes new mechanisms explaining how controlling intrahepatic glucose may be a therapeutic strategy to reduce cardiovascular risk in type 2 diabetes. Finally, the evidence describing PCSK9 as involved in cell proliferation and apoptosis raises the possibility of this protein being involved in cancer risk.

Inclisiran: A Novel Agent for Lowering Apolipoprotein B-Containing Lipoproteins

ABSTRACT

Hypercholesterolemia is a leading cause of cardiovascular morbidity and mortality. Accordingly, efforts to lower apolipoprotein B-containing lipoproteins in plasma are the centerpiece of strategies for cardiovascular prevention and treatment in primary and secondary management. Despite the importance of this endeavor, many patients do not achieve appropriate low density lipoprotein cholesterol (LDL-C) and non-high density lipoprotein cholesterol (non-HDL-C) goals, even among those who have experienced atherosclerotic cardiovascular disease (ASCVD). The development of new LDL-C-lowering medications with alternative mechanisms of action will facilitate improved goal achievement in high risk patients. Inclisiran is a novel small interfering ribonucleic acid (siRNA)-based drug that is experimental in the US and approved for clinical use in the EU. It lowers LDL-C and other apolipoprotein B-containing lipoproteins by reducing production of Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9), a protein that normally contributes to LDL-receptor (LDLR) degradation, thereby increasing LDLR density and recycling in hepatocytes. Although the lipid-lowering efficacy of inclisiran is comparable to results achieved with PCSK9-blocking monoclonal antibodies (PCSK9i) (alirocumab and evolocumab), there are several important differences between the two drug classes. First, inclisiran reduces levels of PCSK9 both intracellularly and extracellularly by blocking translation of and degrading PCSK9 messenger RNA. Second, the long biological half-life of inclisiran produces sustained LDL-C-lowering with twice yearly dosing. Third, although PCSK9i drugs are proven to reduce ASCVD events, clinical outcomes trials with inclisiran are still in progress. In this manuscript, we review the clinical development of inclisiran, its mechanism of action, lipid-lowering efficacy, safety and tolerability, and potential clinical role of this promising new agent.

Circulating Proprotein Convertase Subtilisin/Kexin Type 9 Levels and Cardiometabolic Risk Factors: A Population-Based Cohort Study

Aims: To evaluate the prospective association of circulating PCSK9 levels with the cardiometabolic risk profiles (high LDL-cholesterol, high triglycerides, low HDL-cholesterol, hypertension, type 2 diabetes, and metabolic syndrome).

Methods: A population-based prospective study was conducted among 7,104 Chinese individuals (age 56.2 ± 7.5 years; 32.0% men). Circulating PCSK9 levels were measured using ELISA.

Results: Circulating PCSK9 levels were higher in women than men (286.7 ± 90.1 vs. 276.1 ± 86.4 ng/ml, p < 0.001). And circulating PCSK9 was positively correlated with LDL-cholesterol, total cholesterol, and triglycerides both in men and women (all p < 0.001). The positive correlation between PCSK9 and waist circumference, fasting glucose, insulin resistance, systolic blood pressure, diastolic blood pressure and C-reactive protein (all p < 0.01) was observed in women only. According to Cox regression analysis, circulating PCSK9 was positively associated with incidence of high LDL-cholesterol both in men (HR 1.33, 95% CI 1.09–1.65, p < 0.001) and women (HR 1.36, 95% CI 1.12–1.69, p < 0.001). Moreover, PCSK9 was significantly associated with incident high triglycerides (HR 1.31, 95% CI 1.13–1.72, p < 0.001), hypertension (HR 1.28, 95% CI 1.08–1.53, p = 0.011), type 2 diabetes (HR 1.34, 95% CI 1.09–1.76, p = 0.005), and metabolic syndrome (HR 1.30, 95% CI 1.11–1.65, p = 0.009) per SD change in women only. No statistically significant association was observed between circulating PCSK9 and incidence of low HDL-cholesterol (p > 0.1).

Conclusions: Elevated circulating PCSK9 was significantly associated with cardiometabolic risk factors and independently contributed to the prediction of cardiometabolic risks in women.

Lipoprotein metabolism in familial hypercholesterolemia

Familial hypercholesterolemia (FH) is one of the most common genetic disorders in humans. It is an extremely atherogenic metabolic disorder characterized by lifelong elevations of circulating LDL-C levels often leading to premature cardiovascular events. In this review, we discuss the clinical phenotypes of heterozygous and homozygous FH, the genetic variants in four genes (LDLR/APOB/PCSK9/LDLRAP1) underpinning the FH phenotype as well as the most recent in vitro experimental approaches used to investigate molecular defects affecting the LDL receptor pathway. In addition, we review perturbations in the metabolism of lipoproteins other than LDL in FH, with a major focus on lipoprotein (a). Finally, we discuss the mode of action and efficacy of many of the currently approved hypocholesterolemic agents used to treat patients with FH, with a special emphasis on the treatment of phenotypically more severe forms of FH.

New Insights Into the Regulation of Lipoprotein Metabolism by PCSK9: Lessons From Stable Isotope Tracer Studies in Human Subjects

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a convertase enzyme mostly produced by the liver. It is a key regulator of LDL metabolism because of its ability to enhance degradation of the LDL receptor. PCSK9 also regulates the metabolism of lipoprotein(a) [Lp(a)] and triglyceride-rich lipoproteins (TRLs). Its key role in modulating atherosclerotic cardiovascular disease (ASCVD) is supported by genetic studies and clinical outcome trials. Kinetic studies provide mechanistic insight into the role of PCSK9 in regulating the physiology and pathophysiology of plasma lipids and lipoproteins. Kinetic data have demonstrated that plasma PCSK9 concentration is inversely associated with the clearance of LDL in men. Gain-of-function mutations of PCSK9 markedly increase plasma LDL-cholesterol concentrations due to impaired LDL-apoB catabolism. Conversely, PCSK9 deficiency results in low LDL-cholesterol associated with enhanced LDL-apoB clearance. Inhibition of PCSK9 with monoclonal antibodies (such as evolocumab or alirocumab) lowers plasma LDL-cholesterol and apoB levels chiefly by upregulating the catabolism of LDL particles in healthy individuals. As monotherapy, PCSK9 inhibitor reduced Lp(a) concentrations by decreasing the production rate. However, as combination therapy, it reduced the plasma concentration of Lp(a) by increasing the fractional catabolism of Lp(a) particles. In statin-treated patients with high Lp(a), PCSK9 inhibition lowers plasma Lp(a) concentrations by accelerating the catabolism of Lp(a) particles. The effect of PCSK9 inhibition on TRL metabolism has been studied in healthy individuals and in patients with type 2 diabetes. These findings suggest that PCSK9 appears to play a less important role in TRL than LDL metabolism. Kinetic studies of PCSK9 inhibition therapy on lipoprotein metabolism in diverse high risk patient populations (such as familial hypercholesterolemia) and new therapeutic combination also merit further investigation.

Association of APOA1-75G/A and +83C/T polymorphic variation with acute coronary syndrome patients in Kashmir (India)

Introduction: Acute coronary syndrome (ACS) comes under the ambit of cardiovascular disease.APOA-1 gene plays a vital role in lipid metabolism and has been observed to have plausible role in ACS. This cross sectional case-control study was conducted to evaluate association between APOA 1-75G/A(rs1799837), +83C/T (rs5069) genotypes and risk for ACS. Methods: The current case-control study that included confirmed 90 ACS cases and 150 healthy controls were genotyped for APOA 1-75 G/A and +83 C/T by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLF) method. Results: APOA 1-75G/A distribution of genotypes/alleles among cases and controls was seen proportionally same with no association to ACS (P = 0.5). APOA 1+83 C/T variants showed protective effect with ACS where variant TT genotype presented more in controls (12%) than cases (1.6%) (P = 0.004) and likewise variant 'T' allele was found more in controls than ACS cases (9.4% vs.28.5% respectively: P < 0.05). Further, significantly high difference of CT genotype was seen among cases and controls 15% vs. 33% respectively (P = 0.002). The overall distribution of different haplotypes showed a marked difference in GT when compared with GC between cases and controls (P = 0.0001). Conclusion: The study shows that TT genotype and variant T allele of APOA 1 +83 C/T depicted a protective role with respect to ACS whereas APOA 1-75G>A showed no relation. Haplotype GT was observed to significantly over-represent in controls with its protective effect in ACS as against wild type haplotype GC.

Impact of bariatric surgery-induced weight loss on circulating PCSK9 levels in obese patients

BACKGROUND AND AIMS

To investigate the effect of obesity and bariatric-induced weight loss on circulating levels of proprotein convertase subtilisin/kexin 9 (PCSK9) in severely obese patients.

METHODS AND RESULTS

In this non-randomized interventional study, we enrolled 36 severely obese patients (BMI 43.7 ± 5.6 kg/m²), of which 20 underwent bariatric surgery, and 12 nonobese healthy controls. An oral glucose tolerance test (75-g OGTT) was performed in 31 of these obese patients at baseline (T0) and in 14 patients at 6 months after bariatric surgery (T6) to assess plasma glucose, insulin and PCSK9 levels. Plasma PCSK9 levels were also measured in 18 of these obese patients at T0 during a 2-h hyperinsulinemic-euglycemic clamp (HEC). At T0, PCSK9 levels were higher in obese patients than in controls (274.6 ± 76.7 ng/mL vs. 201.4 ± 53.3 ng/mL) and dropped after bariatric surgery (T6; 205.5 ± 51.7 ng/mL) along with BMI (from 44.1 ± 5.9 kg/m² to 33.1 ± 5.6 kg/m²). At T6, there was also a decrease in plasma glucose (T0 vs. T6: 6.0 ± 1.8 vs. 5.0 ± 0.5 mmol/L) and insulin (15.7 ± 8.3 vs. 5.4 ± 2.1 mU/L) levels. At T0, plasma PCSK9 levels decreased during OGTT in obese patients, reaching a nadir of 262.0 ± 61.4 ng/mL at 120 min with a hyperinsulinemic peak of 75.1 ± 40.0 mU/L, at 60 min. Similarly, at T0 insulin infusion during 2-h HEC acutely reduced plasma PCSK9 levels in obese patients. The aforementioned OGTT-induced changes in plasma PCSK9 levels were not observed neither in nonobese healthy controls nor in obese patients after bariatric-surgery weight loss.

CONCLUSIONS

These results suggest a pivotal role of adipose tissue and insulin resistance on PCSK9 homeostasis in severely obese patients.

Progress and prospects of biological approaches targeting PCSK9 for cholesterol-lowering, from molecular mechanism to clinical efficacy

INTRODUCTION

Cardiovascular disorders are one of the leading causes of mortality and morbidity worldwide. Recent advances showed a promising role of proprotein convertase subtilisin/kexin type 9 (PCSK9) as a critical player in regulating plasma LDL levels and lipid metabolism.

AREAS COVERED

This review addresses the molecular functions of PCSK9 with a vision on the clinical progress of utilizing monoclonal antibodies and other biological approaches to block PCSK9 activity. The successful clinical trials with monoclonal antibodies are reviewed. Recent advances in (pre)clinical trials of other biological approaches, such as small interfering RNAs, are also discussed.

EXPERT OPINION

Discovery of PCSK9 and clinical use of its inhibitors to manage lipid metabolism is a step forward in hypolipidaemic therapy. A better understanding of the molecular activity of PCSK9 can help to identify new approaches in the inhibition of PCSK9 expression/activity. Whether if PCSK9 plays a role in other cardiometabolic conditions may provide grounds for further development of therapies.

Research progress on alternative non-classical mechanisms of PCSK9 in atherosclerosis in patients with and without diabetes

The proprotein convertase subtilisin/kexin type 9 (PCSK9) acts via a canonical pathway to regulate circulating low-density lipoprotein-cholesterol (LDL-C) via degradation of the LDL receptor (LDLR) on the liver cell surface. Published research has shown that PCSK9 is involved in atherosclerosis via a variety of non-classical mechanisms that involve lysosomal, inflammatory, apoptotic, mitochondrial, and immune pathways. In this review paper, we summarized these additional mechanisms and described how anti-PCSK9 therapy exerts effects through these mechanisms. These additional pathways further illustrate the regulatory role of PCSK9 in atherosclerosis and offer an in-depth interpretation of how the PCSK9 inhibitor exerts effects on the treatment of atherosclerosis.

VLDL (Very-Low-Density Lipoprotein)-Apo E (Apolipoprotein E) May Influence Lp(a) (Lipoprotein [a]) Synthesis or Assembly

Objective:

To clarify the association between PCSK9 (proprotein convertase subtilisin/kexin type 9) and Lp(a) (lipoprotein [a]), we studied Lp(a) kinetics in patients with loss-of-function and gain-of-function PCSK9 mutations and in patients in whom extended-release niacin reduced Lp(a) and PCSK9 concentrations.

Approach and Results:

Six healthy controls, 9 heterozygous patients with familial hypercholesterolemia (5 with low-density lipoprotein receptor [ LDLR ] mutations and 4 with PCSK9 gain-of-function mutations) and 3 patients with heterozygous dominant-negative PCSK9 loss-of-function mutations were included in the preliminary study. Eight patients were enrolled in a second study assessing the effects of 2 g/day extended-release niacin. Apolipoprotein kinetics in VLDL (very-low-density lipoprotein), LDL (low-density lipoprotein), and Lp(a) were studied using stable isotope techniques. Plasma Lp(a) concentrations were increased in PCSK9 -gain-of-function and familial hypercholesterolemia- LDLR groups compared with controls and PCSK9 -loss-of-function groups (14±12 versus 5±4 mg/dL; P =0.04), but no change was observed in Lp(a) fractional catabolic rate. Subjects with PCSK9 -loss-of-function mutations displayed reduced apoE (apolipoprotein E) concentrations associated with a VLDL-apoE absolute production rate reduction. Lp(a) and VLDL-apoE absolute production rates were correlated ( r =0.50; P <0.05). ApoE-to-apolipoprotein (a) molar ratios in Lp(a) increased with plasma Lp(a) ( r =0.96; P <0.001) but not with PCSK9 levels. Extended-release niacin-induced reductions in Lp(a) and VLDL-apoE absolute production rate were correlated ( r =0.83; P =0.015). In contrast, PCSK9 reduction (−35%; P =0.008) was only correlated with that of VLDL-apoE absolute production rate ( r =0.79; P =0.028).

Conclusions:

VLDL-apoE production could determine Lp(a) production and/or assembly. As PCSK9 inhibitors reduce plasma apoE and Lp(a) concentrations, apoE could be the link between PCSK9 and Lp(a).

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.

Efficacy and safety of proprotein convertase subtilisin/kexin 9 inhibitors in people with diabetes and dyslipidaemia

Diabetic dyslipidaemia, characterized by quantitative, qualitative and kinetic changes in all major circulating lipids, contributes to the increased cardiovascular risk in patients with type 2 diabetes mellitus (T2DM). A promising therapeutic avenue is the inhibition of the proprotein convertase subtilisin kexin 9 (PCSK9) with human monoclonal antibodies (mAbs) that potently reduce plasma low-density lipoprotein cholesterol (LDL-C) levels on top of statin treatment. The aim of this review is to evaluate the efficacy of PCSK9 inhibitors to lower the residual cardiovascular risk of T2DM patients and to discuss the safety of PCSK9 inhibition in these patients. PCSK9 inhibitors potently lower plasma LDL-C levels in T2DM patients and reduce risk for the development of cardiovascular disease. Anti-PCSK9 mAbs are generally not more or less effective in T2DM patients compared to a general high-risk population. Nevertheless, due to their higher cardiovascular risk, the absolute risk reduction of major cardiovascular events is more significant in T2DM patients. This suggests that treatment of T2DM patients with anti-PCSK9 mAbs could be attractive from a cost-effectiveness perspective. Treatment with anti-PCSK9 mAbs did not result in significant treatment-emergent adverse effects. While genetic studies suggest a potential link between PCSK9 inhibition and glucose homeostasis, anti-PCSK9 mAbs did not worsen glycaemic control in T2DM patients, but their safety should be verified after a longer-term follow-up.

PCSK9 positively correlates with plasma sdLDL in community-dwelling population but not in diabetic participants after confounder adjustment

This study aimed to investigate the relationship between plasma proprotein convertase subtilisin kexin 9 (PCSK9) and small dense low-density lipoprptein (sdLDL) in diabetic and non-diabetic participants in a community-dwelling cohort.The plasma levels of PCSK9 and sdLDL were detected in 1766 participants (median age: 61.40 years; 733 males vs 1033 females; 383 diabetic vs 1383 non-diabetic patients) from the Pingguoyuan community of Beijing, China.Results showed that Pearson correlation analysis revealed a positive correlation between PCSK9 and sdLDL (r = 0.263, P < .001). Multiple linear regression analysis showed a significant positive correlation between plasma PCSK9 and sdLDL in the whole population study. sdLDL was used as the dependent variable, and the potential cofounders were adjusted. However, any independent relationship was not observed between circulating PCSK9 and sdLDL in the diabetic subpopulation (r = 0.269, P < .05, β = 9.591, P > .05).Thus, there is a positive correlation between plasma PCSK9 and sdLDL in a community-dwelling cohort, but not in type 2 diabetic subpopulation, after confounder adjustment.

A review on coronary artery disease, its risk factors, and therapeutics

Coronary artery disease (CAD) is one of the major cardiovascular diseases affecting the global human population. This disease has been proved to be the major cause of death in both the developed and developing countries. Lifestyle, environmental factors, and genetic factors pose as risk factors for the development of cardiovascular disease. The prevalence of risk factors among healthy individuals elucidates the probable occurrence of CAD in near future. Genome-wide association studies have suggested the association of chromosome 9p21.3 in the premature onset of CAD. The risk factors of CAD include diabetes mellitus, hypertension, smoking, hyperlipidemia, obesity, homocystinuria, and psychosocial stress. The eradication and management of CAD has been established through extensive studies and trials. Antiplatelet agents, nitrates, β-blockers, calcium antagonists, and ranolazine are some of the few therapeutic agents used for the relief of symptomatic angina associated with CAD.

Inhibiting PCSK9 - biology beyond LDL control

Clinical trials have unequivocally shown that inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9) efficaciously and safely prevents cardiovascular events by lowering levels of LDL cholesterol. PCSK9 in the circulation is derived mainly from the liver, but the protein is also expressed in the pancreas, the kidney, the intestine and the central nervous system. Although PCSK9 modulates cholesterol metabolism by regulating LDL receptor expression in the liver, in vitro and in vivo studies have suggested that PCSK9 is involved in various other physiological processes. Although therapeutic PCSK9 inhibition could theoretically have undesired effects by interfering with these non-cholesterol-related processes, studies of individuals with genetically determined reduced PCSK9 function and clinical trials of PCSK9 inhibitors have not revealed clinically meaningful adverse consequences of almost completely eradicating PCSK9 from the circulation. The clinical implications of PCSK9 functions beyond lipid metabolism in terms of wanted or unwanted effects of therapeutic PCSK9 inhibition therefore appear to be limited. The objective of this Review is to describe the physiological role of PCSK9 beyond the LDL receptor to provide a rational basis for monitoring the effects of PCSK9 inhibition as these drugs gain traction in the clinic.

Targeted sequencing in patients with clinically diagnosed hereditary lipid metabolism disorder and acute coronary syndrome

The actual prevalence of genetic variants causing familial hypercholesterolemia (FH) in every population remains unknown. The aim of this work was to determine the spectrum of pathogenic variants in patients with acute coronary syndrome (ACS) and clinically diagnosed FH using targeted sequencing. We selected 38 patients with ACS from the sample of 2,081 participants of two multicenter observational studies (2004–2007; 2014–2016) who had a clinical diagnosis of FH based on the Dutch Lipid Clinic Network score and Simon Broome criteria. The men and women included in the study were ≤ 55 and ≤ 60 years of age, respectively. Molecular genetic screening was done by targeted next-generation sequencing. We started by sequencing 3 genes associated with FH, including LDLR, APOB, and PCSK9. If no relevant variants were detected, the panel was expanded. Of 38 patients, 24 (63.2%) were shown to have mutations that could cause clinical manifestations of FH and premature coronary artery disease. All patients were heterozygous carriers. Mutations were detected in three “classic” genes LDLR, APOB, and PCSK9 associated with FH, as well as in other genes involved in lipid metabolism, such as APOE, ABCA1, ABCG5, ABCG8, LPL, ANGPTL3, and MTTP. Five variants detected in our study sample had not been described previously: the pathogenic p.Val273_Cys313del variant of the LDLR gene, the likely pathogenic p.Arg160His variant in the APOE gene, two variants of uncertain significance p.Glu612Lys and c.*415G>A in the PCSK9 gene, and the mutant variant p.Ala776Ser in the LDLR gene. We conclude that the use of clinical diagnostic criteria in patients with ACS and FH enables identification of carriers of both “classic” mutations associated with FH and rare genetic variants that can be phenotypically expressed as FH.

Beyond LDL: What Role for PCSK9 in Triglyceride-Rich Lipoprotein Metabolism?

Elevated plasma triglyceride (TG) levels are an independent risk factor for cardiovascular disease (CVD). Proprotein convertase subtilisin-kexin 9 (PCSK9) - a protein therapeutically targeted to lower plasma cholesterol levels - might regulate plasma TG-rich lipoprotein (TRL) levels. We provide a timely and critical review of the current evidence for a role of PCSK9 in TRL metabolism by assessing the impact of PCSK9 gene variants, by reviewing recent clinical data with PCSK9 inhibitors, and by describing the potential mechanisms by which PCSK9 might regulate TRL metabolism. We conclude that the impact of PCSK9 on TRL metabolism is relatively modest, especially compared to its impact on cholesterol metabolism.

PCSK9: From Basic Science Discoveries to Clinical Trials

Unknown 15 years ago, PCSK9 (proprotein convertase subtilisin/kexin type 9) is now common parlance among scientists and clinicians interested in prevention and treatment of atherosclerotic cardiovascular disease. What makes this story so special is not its recent discovery nor the fact that it uncovered previously unknown biology but rather that these important scientific insights have been translated into an effective medical therapy in record time. Indeed, the translation of this discovery to novel therapeutic serves as one of the best examples of how genetic insights can be leveraged into intelligent target drug discovery. The PCSK9 saga is unfolding quickly but is far from complete. Here, we review major scientific understandings as they relate to the role of PCSK9 in lipoprotein metabolism and atherosclerotic cardiovascular disease and the impact that therapies designed to inhibit its action are having in the clinical setting.

Kinetics of plasma apolipoprotein E isoforms by LC-MS/MS: a pilot study

Human apoE exhibits three major isoforms (apoE2, apoE3, and apoE4) corresponding to polymorphism in the APOE gene. Total plasma apoE concentrations are closely related to these isoforms, but the underlying mechanisms are unknown. We aimed to describe the kinetics of apoE individual isoforms to explore the mechanisms for variable total apoE plasma concentrations. We used LC-MS/MS to discriminate between isoforms by identifying specific peptide sequences in subjects (three E2/E3, three E3/E3, and three E3/E4 phenotypes) who received a primed constant infusion of ²H₃-leucine for 14 h. apoE concentrations and leucine enrichments were measured hourly in plasma. Concentrations of apoE2 were higher than apoE3, and concentrations of apoE4 were lower than apoE3. There was no difference between apoE3 and apoE4 catabolic rates and between apoE2 and apoE3 production rates (PRs), but apoE2 catabolic rates and apoE4 PRs were lower. The mechanisms leading to the difference in total plasma apoE concentrations are therefore related to contrasted kinetics of the isoforms. Production or catabolic rates are differently affected according to the specific isoforms. On these grounds, studies on the regulation of the involved biochemical pathways and the impact of pathological environments are now warranted.

Proprotein Convertase Subtilisin-Kexin type-9 (PCSK9) and triglyceride-rich lipoprotein metabolism: Facts and gaps

After more than a decade of intense investigation, Pro-protein Convertase Subtilisin-Kexin type 9 (PCSK9) remains a hot topic of research both at experimental and clinical level. Interestingly PCSK9 is expressed in different tissues suggesting the existence of additional function(s) beyond the modulation of the Low-Density Lipoprotein (LDL) receptor in the liver. Emerging data suggest that PCSK9 might play a role in the modulation of triglyceride-rich lipoprotein (TGRL) metabolism, mainly Very Low-Density Lipoproteins (VLDL) and their remnants. In vitro, PCSK9 affects TGRLs production by intestinal cells as well as the catabolism of LDL receptor homologous and non-homologous targets such as VLDL receptor, CD36 and ApoE2R. However, the in vivo relevance of these findings is still debated. This review aims at critically discussing the role of PCSK9 on TGRLs metabolism with a major focus on the impact of its genetic and pharmacological modulation on circulating lipids and lipoproteins beyond LDL.

Impact of protease inhibitors on circulating PCSK9 levels in HIV-infected antiretroviral-naive patients from an ongoing prospective cohort

OBJECTIVE

The study aims to assess the association between proprotein convertase subtilisin/kexin type 9 (PCSK9), a major regulator of LDL cholesterol (LDL-C) homeostasis, and HIV-related dyslipidaemia in a cohort of HIV-positive (HIV+) patients under protease inhibitors.

METHODS

Plasma PCSK9 levels were measured in 103 HIV+ patients before and after initiating protease inhibitor-based antiretroviral therapy (ART), and in 90 HIV-negative controls matched for age and sex. PCSK9 was measured by ELISA. HIV+ patients who were not virologically suppressed at follow-up or were on lipid-lowering therapy were excluded.

RESULTS

In HIV+ (median age 36 years; 77.7% men), PCSK9 levels did not increase after protease inhibitor exposure (median 14 months) (279.5 ng/ml before, 289.6 ng/ml after; P = 0.49) and were significantly elevated versus controls at all timepoints (adjusted P value before and after: <0.05). After protease inhibitor initiation, total cholesterol, LDL-C and HDL cholesterol levels increased, but LDL-C remained lower versus controls. At baseline, PCSK9 levels were positively associated with immunodeficiency and the severity of HIV disease [HIV-1 viral load (P = 0.01), CD4 T-cell count <200/μl, P = 0.002], stage C HIV disease (P = 0.0002). In protease inhibitor-treated patients, PCSK9 levels were no longer associated with HIV-related factors but with total cholesterol (P = 0.0006), LDL-C (P = 0.01), HDL cholesterol (P = 0.01), triglycerides (P = 0.05) and glycaemia (P = 0.006).

CONCLUSION

PSCK9 levels are elevated in HIV+ patients. In ART-naive patients, the relationship between PCSK9 levels and infection severity suggests an effect of HIV disease. After initiating protease inhibitor-containing ART in virologically suppressed patients, PCSK9 levels were associated with dyslipidaemia similar to controls.

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.

siRNA-mediated inhibition of SREBP cleavage-activating protein reduces dyslipidemia in spontaneously dysmetabolic rhesus monkeys

BACKGROUND

SREBP cleavage-activating protein (SCAP) is a cholesterol binding endoplasmic reticulum (ER) membrane protein that is required to activate SREBP transcription factors. SREBPs regulate genes involved in lipid biosynthesis. They also influence lipid clearance by modulating the expression of LDL receptor (LDLR) and proprotein convertase subtilisin/kexin type 9 (PCSK9) genes. Inhibiting SCAP decreases circulating PCSK9, triglycerides (TG), and LDL-cholesterol (LDL-C), both in vitro and in vivo. Type 2 diabetics with dyslipidemia are at high risk for cardiovascular diseases. These patients present a unique pathophysiological lipid profile characterized by moderately elevated LDL-C, elevated TG and reduced HDL-cholesterol (HDL-C). The spontaneous dysmetabolic rhesus monkey model (DysMet RhM) recapitulates this human dyslipidemia and therefore is an attractive preclinical model to evaluate SCAP inhibition as a therapy for this disease population. The objective to of this study was to assess the effect of SCAP inhibition on the lipid profile of DysMet RhM.

METHOD

We assessed the effect of inhibiting hepatic SCAP on the lipid profile of DysMet RhM using an siRNA encapsulated lipid nanoparticle (siRNA-LNP).

RESULTS

The SCAP siRNA-LNP significantly reduced LDL-C, PCSK9 and TG in DysMet RhM; LDL-C was reduced by ≥20%, circulating PCSK9 by 30-40% and TG by >25%. These changes by the SCAP siRNA-LNP agree with the predicted effect of SCAP inhibition and reduced SREBP tone on these endpoints.

CONCLUSION

These data demonstrate that a SCAP siRNA-LNP improved the lipid profile in a clinically relevant preclinical disease model and provide evidence for SCAP inhibition as a therapy for diabetic dyslipidemic patients.

Monoclonal Antibodies for Lipid Management

In recent years, biochemical and genetic studies have identified proprotein convertase subtilisin/kexin type 9 (PCSK9) as a major mediator of low-density lipoprotein cholesterol (LDL-c) levels and thereby a potential novel target for reducing risk of coronary heart disease (CHD). These observations led to the development of PCSK9 inhibitors, which lower LDL-c levels more than any other non-invasive lipid-lowering therapy presently available. The PCSK9 inhibitors furthest along in clinical trials are subcutaneously injected monoclonal antibodies. These PCSK9 inhibitors have demonstrated LDL-c-lowering efficacy with acceptable safety in phase III clinical trials and may offer a useful therapy in addition to maximally tolerated HMG-CoA reductase inhibitors (statins) in certain patient groups. Longer-term data are required to ensure sustained efficacy and safety of this new class of medications. This review provides an overview of the biology, genetics, development, and clinical trials of monoclonal antibodies designed to inhibit PCSK9.

Nutritional and Lipid Modulation of PCSK9: Effects on Cardiometabolic Risk Factors

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a serine protease involved in the regulation of LDL receptor (LDLR) expression and apolipoprotein B lipoprotein cholesterol metabolism. Hepatic PCSK9 protein expression, activity, and secretion have been shown to affect cholesterol homeostasis. An upregulation of hepatic PSCK9 protein leads to increased LDLR degradation, resulting in decreased uptake of apoB lipoproteins and a consequent increase in the plasma concentration of these lipoproteins, including LDL and chylomicron remnants. Hence, PCSK9 has become a novel target for lipid-lowering therapies. The aim of this review is to outline current findings on the metabolic and dietary regulation of PCSK9 and effects on cholesterol, apoB lipoprotein metabolism, and cardiovascular disease (CVD) risk. PCSK9 gene and protein expression have been shown to be regulated by metabolic status and the diurnal pattern. In the fasting state, plasma PCSK9 is reduced via modulation of the nuclear transcriptional factors, including sterol regulatory element-binding protein (SREBP) 1c, SREBP2, and hepatocyte nuclear factor 1α. Plasma PCSK9 concentrations are also known to be positively associated with plasma insulin and homeostasis model assessment of insulin resistance, and appear to be regulated by SREBP1c independently of glucose status. Plasma PCSK9 concentrations are stable in response to high-fat or high-protein diets in healthy individuals; however, this response may differ in altered metabolic conditions. Dietary n-3 polyunsaturated fatty acids have been shown to reduce plasma PCSK9 concentration and hepatic PCSK9 mRNA expression, consistent with their lipid-lowering effects, whereas dietary fructose appears to upregulate PCSK9 mRNA expression and plasma PCSK9 concentrations. Further studies are needed to elucidate the mechanisms of how dietary components regulate PCSK9 and effects on cholesterol and apoB lipoprotein metabolism, as well as to delineate the clinical impact of diet on PCSK9 in terms of CVD risk.

PCSK9 and Atherosclerosis - Lipids and Beyond

Even though it is only a little over a decade from the discovery of proprotein convertase subtilisin/kexin type 9 (PCSK9) as a plasma protein that associates with both high and low cholesterol syndromes, a rich body of knowledge has developed, and drugs inhibiting this target have been approved in many markets. While the majority of research in recent years has focused on the impact of therapeutic antagonism of this molecule, important lines of investigation have emerged characterizing its unique physiology as it relates to cholesterol metabolism and atherosclerosis. The PCSK9 story is unfolding rapidly but is far from complete. One chapter that is of particular interest is the possible direct link between PCSK9 and atherosclerosis. This review specifically examines this relationship drawing from data produced from experimental models of plaque biology and inflammation, atherosclerosis imaging studies, and observational epidemiology.

Association and differences in genetic polymorphisms in PCSK9 gene in subjects with lacunar infarction in the Han and Uygur populations of Xinjiang Uygur Autonomous Region of China

Polymorphisms in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene are associated with severe hypercholesterolemia and stroke. Here, we investigated the relationship between single nucleotide polymorphisms in PCSK9 and stroke in 237 patients with lacunar infarction in the Uygur and Han populations in Xinjiang Uygur Autonomous Region of China. Using the SNaPshot single-base terminal extension method, four PCSK9 gene polymorphisms were analyzed. We found a significantly strong relationship between the PCSK9 rs17111503 (G > A) polymorphism and increased susceptibility to lacunar infarction by variant homozygote comparison, and using the dominant and recessive models in the Han population but not in the Uygur population. Low triglyceride levels were found in AA carriers (rs17111503, G > A) in the Han population but not in the Uygur population. Association analysis revealed that the rs17111503 (G > A) polymorphism was not significantly associated with smoking, alcohol drinking, history of hypertension or diabetes in the Han or Uygur lacunar infarction patients. rs11583680, rs483462 and rs505151 were not associated with risk of lacunar infarction in the Han or Uygur populations. Our findings suggest that the PCSK9 rs17111503 (G > A) polymorphism is associated with susceptibility to lacunar infarction in the Han population but not in the Uygur population.

Triglycerides Revisited to the Serial

This review discusses the role of triglycerides (TGs) in the normal cardiovascular system as well as in the development and clinical manifestation of cardiovascular diseases. Regulation of TGs at the enzymatic and genetic level, in addition to their possible relevance as preclinical and clinical biomarkers, is discussed, culminating with a description of available and emerging treatments. Due to the high complexity of the subject and the vast amount of material in the literature, the objective of this review was not to exhaust the subject, but rather to compile the information to facilitate and improve the understanding of those interested in this topic. The main publications on the topic were sought out, especially those from the last 5 years. The data in the literature still give reason to believe that there is room for doubt regarding the use of TG as disease biomarkers; however, there is increasing evidence for the role of hypertriglyceridemia on the atherosclerotic inflammatory process, cardiovascular outcomes, and mortality.

Effects of PCSK9 Inhibition With Alirocumab on Lipoprotein Metabolism in Healthy Humans

Supplemental Digital Content is available in the text.

Background:

Alirocumab, a monoclonal antibody to proprotein convertase subtilisin/kexin type 9 (PCSK9), lowers plasma low-density lipoprotein (LDL) cholesterol and apolipoprotein B100 (apoB). Although studies in mice and cells have identified increased hepatic LDL receptors as the basis for LDL lowering by PCSK9 inhibitors, there have been no human studies characterizing the effects of PCSK9 inhibitors on lipoprotein metabolism. In particular, it is not known whether inhibition of PCSK9 has any effects on very low-density lipoprotein or intermediate-density lipoprotein (IDL) metabolism. Inhibition of PCSK9 also results in reductions of plasma lipoprotein (a) levels. The regulation of plasma Lp(a) levels, including the role of LDL receptors in the clearance of Lp(a), is poorly defined, and no mechanistic studies of the Lp(a) lowering by alirocumab in humans have been published to date.

Methods:

Eighteen (10 F, 8 mol/L) participants completed a placebo-controlled, 2-period study. They received 2 doses of placebo, 2 weeks apart, followed by 5 doses of 150 mg of alirocumab, 2 weeks apart. At the end of each period, fractional clearance rates (FCRs) and production rates (PRs) of apoB and apo(a) were determined. In 10 participants, postprandial triglycerides and apoB48 levels were measured.

Results:

Alirocumab reduced ultracentrifugally isolated LDL-C by 55.1%, LDL-apoB by 56.3%, and plasma Lp(a) by 18.7%. The fall in LDL-apoB was caused by an 80.4% increase in LDL-apoB FCR and a 23.9% reduction in LDL-apoB PR. The latter was due to a 46.1% increase in IDL-apoB FCR coupled with a 27.2% decrease in conversion of IDL to LDL. The FCR of apo(a) tended to increase (24.6%) without any change in apo(a) PR. Alirocumab had no effects on FCRs or PRs of very low-density lipoproteins-apoB and very low-density lipoproteins triglycerides or on postprandial plasma triglycerides or apoB48 concentrations.

Conclusions:

Alirocumab decreased LDL-C and LDL-apoB by increasing IDL- and LDL-apoB FCRs and decreasing LDL-apoB PR. These results are consistent with increases in LDL receptors available to clear IDL and LDL from blood during PCSK9 inhibition. The increase in apo(a) FCR during alirocumab treatment suggests that increased LDL receptors may also play a role in the reduction of plasma Lp(a).

Clinical Trial Registration:

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01959971.