Evidence from a randomized trial that simvastatin, but not ezetimibe, upregulates circulating PCSK9 levels

Geranylgeranyl isoprenoids and hepatic Rap1a regulate basal and statin-induced expression of PCSK9

LDL-C lowering is the main goal of atherosclerotic cardiovascular disease prevention, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition is now a validated therapeutic strategy that lowers serum LDL-C and reduces coronary events. Ironically, the most widely used medicine to lower cholesterol, statins, has been shown to increase circulating PCSK9 levels, which limits their efficacy. Here, we show that geranylgeranyl isoprenoids and hepatic Rap1a regulate both basal and statin-induced expression of PCSK9 and contribute to LDL-C homeostasis. Rap1a prenylation and activity is inhibited upon statin treatment, and statin-mediated PCSK9 induction is dependent on geranylgeranyl synthesis and hepatic Rap1a. Accordingly, treatment of mice with a small-molecule activator of Rap1a lowered PCSK9 protein and plasma cholesterol and inhibited statin-mediated PCSK9 induction in hepatocytes. The mechanism involves inhibition of the downstream RhoA-ROCK pathway and regulation of PCSK9 at the post-transcriptional level. These data further identify Rap1a as a novel regulator of PCSK9 protein and show that blocking Rap1a prenylation through lowering geranylgeranyl levels contributes to statin-mediated induction of PCSK9.

Geranylgeranyl Isoprenoids and Hepatic Rap1a Regulate Basal and Statin-Induced Expression of PCSK9

Low-density lipoprotein cholesterol (LDL-C) lowering is the main goal of atherosclerotic cardiovascular disease prevention, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition is now a validated therapeutic strategy that lowers serum LDL-C and reduces coronary events. Ironically, the most widely used medicine to lower cholesterol, statins, has been shown to increase circulating PCSK9 levels, which limits their efficacy. Here, we show that geranylgeranyl isoprenoids and hepatic Rap1a regulate both basal and statin induced expression of PCSK9 and contribute to LDL-C homeostasis. Rap1a prenylation and activity is inhibited upon statin treatment, and statin mediated PCSK9 induction is dependent on geranylgeranyl synthesis and hepatic Rap1a. Accordingly, treatment of mice with a small molecule activator of Rap1a lowered PCSK9 protein and plasma cholesterol and inhibited statin mediated PCSK9 induction in hepatocytes. The mechanism involves inhibition of the downstream RhoA-ROCK pathway and regulation of PCSK9 at the post transcriptional level. These data further identify Rap1a as a novel regulator of PCSK9 protein and show that blocking Rap1a prenylation through lowering geranylgeranyl levels contributes to statin-mediated induction of PCSK9.

PCSK9 Plasma Levels Are Associated with Mechanical Vascular Impairment in Familial Hypercholesterolemia Subjects without a History of Atherosclerotic Cardiovascular Disease: Results of Six-Month Add-On PCSK9 Inhibitor Therapy

Proprotein convertase subtilisin/kexin type-9 (PCSK9) is a key regulator of low-density lipoprotein (LDL) metabolism involved in the degradation of the low-density lipoprotein receptor (LDLR) through complex mechanisms. The PCSK9 plasma levels change according to lipid lowering therapy (LLT). Few data exist regarding the role of PCSK9 in vascular damage. We aimed to evaluate the impact of PCSK9 plasma levels on pulse wave velocity (PWV) and the effect of PCSK9 inhibitors (PCSK9-i) on circulating PCSK9 and PWV in a cohort of heterozygous familial hypercholesterolemia (HeFH) subjects. In a previous step, HeFH patients were enrolled and LLT was prescribed according to guidelines. Biochemical analyses and PWV assessment were performed at baseline (T0), after 6 months of high-efficacy statin plus ezetimibe (T1) and after 6 months of PCSK9-i (T2). The PCSK9 levels were evaluated in 26 selected HeFH subjects at the three time points and 26 healthy subjects served as controls for the reference value for PCSK9 plasma levels. The PWV values decreased at each time point in HeFH subjects after LLT starting (8.61 ± 2.4 m/s, −8.7%; p < 0.001 vs. baseline at T1, and 7.9 ± 2.1 m/s, −9.3%; p < 0.001 vs. both T1 and baseline) and it was correlated to PCSK9 (r = 0.411, p = 0.03). The PCSK9 levels increased on statin/EZE therapy (+42.8% at T1) while it decreased after PCSK9-i was started (−34.4% at T2). We noted a significant relationship between PCSK9 levels and PWV changes at T1 and T2. In conclusion, PCSK9 levels were associated with baseline PWV values in HeFH subjects; moreover, we found that PCSK9 level variations seemed to be correlated with PWV changes on LLT. A longer observation time and wider sample size are needed to assess the potential role of PCSK9 plasma levels on the vascular function and remodelling, and to clarify the effects of PCSK9-i in these pathways.

Supplementation with Octacosanol Affects the Level of PCSK9 and Restore Its Physiologic Relation with LDL-C in Patients on Chronic Statin Therapy

Dietary supplementation with sugar cane derivates may modulate low-density lipoprotein cholesterol (LDL-C) and proprotein convertase subtilisin/kexin type 9 (PCSK9) levels. The purpose of this study was to determine if dietary supplement (DS), containing Octacosanol (20 mg) and vitamin K2 (45 µg), could restore the disrupted physiologic relation between LDL-C and serum PCSK9. Double-blind, randomized, placebo-controlled, single-center study including 87 patients on chronic atorvastatin therapy was conducted. Eighty-seven patients were randomized to receive DS (n = 42) or placebo (n = 45), and followed for 13 weeks. Serum PCSK9 levels, lipid parameters and their relationship were the main efficacy endpoints. The absolute levels of PCSK9 and LDL-C were not significantly different from baseline to 13 weeks. However, physiologic correlation between % change of PCSK9 and % change of LDL-C levels was normalized only in the group of patients treated with DS (r = 0.409, p = 0.012). This study shows that DS can restore statin disrupted physiologic positive correlation between PCSK9 and LDL-C. Elevated PCSK9 level is an independent risk factor so controlling its rise by statins may be important in prevention of cardiovascular events.

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

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

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

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

Proprotein convertase subtilisin/kexin type 9 inhibitors and lipoprotein(a)-mediated risk of atherosclerotic cardiovascular disease: more than meets the eye?

PURPOSE OF REVIEW

Evidence continues to mount for elevated lipoprotein(a) [Lp(a)] as a prevalent, independent, and causal risk factor for atherosclerotic cardiovascular disease. However, the effects of existing lipid-lowering therapies on Lp(a) are comparatively modest and are not specific to Lp(a). Consequently, evidence that Lp(a)-lowering confers a cardiovascular benefit is lacking. Large-scale cardiovascular outcome trials (CVOTs) of inhibitory mAbs targeting proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9i) may address this issue.

RECENT FINDINGS

Although the ability of PCSK9i to lower Lp(a) by 15-30% is now clear, the mechanisms involved continue to be debated, with in-vitro and in-vivo studies showing effects on Lp(a) clearance (through the LDL receptor or other receptors) and Lp(a)/apolipoprotein(a) biosynthesis in hepatocytes. The FOURIER CVOT showed that patients with higher baseline levels of Lp(a) derived greater benefit from evolocumab and those with the lowest combined achieved Lp(a) and LDL-cholesterol (LDL-C) had the lowest event rate. Meta-analysis of ten phase 3 trials of alirocumab came to qualitatively similar conclusions concerning achieved Lp(a) levels, although an effect independent of LDL-C lowering could not be demonstrated.

SUMMARY

Although it is not possible to conclude that PCSK9i specifically lower Lp(a)-attributable risk, patients with elevated Lp(a) could derive incremental benefit from PCSK9i therapy.

PCSK9: from molecular biology to clinical applications

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

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

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

The interrelations between PCSK9 metabolism and cholesterol synthesis and absorption

Very few studies have investigated the interrelations between proprotein convertase subtilisin/kexin type 9 (PCSK9) metabolism, cholesterol synthesis, and cholesterol absorption. We aimed to address this issue in a large clinical trial of 245 patients with hypercholesterolemia. Serum lipids, PCSK9, lathosterol (cholesterol synthesis marker), campesterol, and sitosterol (cholesterol absorption markers) were measured before and 4-8 weeks after the start of treatment with PCSK9-antibodies (alirocumab or evolocumab). The patients had mean (standard error) LDL-cholesterol and PCSK9 concentrations of 3.87 (0.10) mmol/l and 356 (17) ng/ml, respectively. Eighty-four patients received no lipid-lowering pretreatment, 26 ezetimibe, 38 statins, and 97 ezetimibe + statins. Circulating PCSK9 increased in parallel with the potency of lipid-lowering pretreatment with circulating PCSK9 being highest in the ezetimibe + statin group (P < 0.001). Treatment with PCSK9-antibodies strongly decreased LDL-cholesterol, lathosterol, campesterol, and sitosterol (all P < 0.001) but hardly affected noncholesterol sterol to cholesterol ratios. Lipid-lowering pretreatment was not associated with the effects of PCSK9-antibodies on noncholesterol sterols (all P > 0.05). Summing up, circulating PCSK9 is increased by cholesterol synthesis and absorption inhibitors. Increased PCSK9 expression may partly explain the strong reductions of LDL-cholesterol achieved with PCSK9-antibodies after such pretreatment. On the other hand, treatment with PCSK9-antibodies does not significantly change the balance between cholesterol synthesis and absorption.

Simvastatin as a Potential Disease-Modifying Therapy for Patients with Parkinson's Disease: Rationale for Clinical Trial, and Current Progress

Many now believe the holy grail for the next stage of therapeutic advance surrounds the development of disease-modifying approaches aimed at intercepting the year-on-year neurodegenerative decline experienced by most patients with Parkinson’s disease (PD). Based on recommendations of an international committee of experts who are currently bringing multiple, potentially disease-modifying, PD therapeutics into long-term neuroprotective PD trials, a clinical trial involving 198 patients is underway to determine whether Simvastatin provides protection against chronic neurodegeneration. Statins are widely used to reduce cardiovascular risk, and act as competitive inhibitors of HMG-CoA reductase. It is also known that statins serve as ligands for PPARα, a known arbiter for mitochondrial size and number. Statins possess multiple cholesterol-independent biochemical mechanisms of action, many of which offer neuroprotective potential (suppression of proinflammatory molecules & microglial activation, stimulation of endothelial nitric oxide synthase, inhibition of oxidative stress, attenuation of α-synuclein aggregation, modulation of adaptive immunity, and increased expression of neurotrophic factors). We describe the biochemical, physiological and pharmaceutical credentials that continue to underpin the rationale for taking Simvastatin into a disease-modifying trial in PD patients. While unrelated to the Simvastatin trial (because this conducted in patients who already have PD), we discuss conflicting epidemiological studies which variously suggest that statin use for cardiovascular prophylaxis may increase or decrease risk of developing PD. Finally, since so few disease-modifying PD trials have ever been launched (compared to those of symptomatic therapies), we discuss the rationale of the trial structure we have adopted, decisions made, and lessons learnt so far.

Lipid Lowering Therapy and Circulating PCSK9 Concentration

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

Evolocumab for the treatment of hypercholesterolemia

INTRODUCTION

Evolocumab is a fully human monoclonal immunoglobulin G2 directed against human proprotein convertase subtilisin/kexin type 9 (PCSK9). It is administered by subcutaneous injection every 2 weeks or once monthly. Area covered: Herein, the authors discuss the rationale for inhibiting PCSK9 and describe the pharmacodynamics, pharmacokinetics and clinical trials with evolocumab. Evolocumab reduces low density lipoprotein cholesterol (LDL-C) levels by 50 to 60% in most patients with and without background treatment with statins or other lipid lowering agents. The safety profile appears satisfactory from the completed clinical studies and concerns regarding the risk of neurocognitive events have largely been dispelled. Expert opinion: The reduction of LDL-C with evolocumab to previously unattainable levels has resulted in a reduction in the composite cardiovascular event endpoint in the FOURIER trial and this is likely to impact on future lipid management guidelines. The clinical outcome data and excellent tolerability profile clearly support the use of evolocumab in patients at high cardiovascular risk, including those with heterozygous or homozygous familial hypercholesterolemia, who are unable to achieve LDL-C targets with statins with or without other lipid-lowering drugs. The high cost of evolocumab will restrict its use, however.

PCSK9 inhibitors - from discovery of a single mutation to a groundbreaking therapy of lipid disorders in one decade

Hypercholesterolemia is one of the main risk factors for coronary heart disease and significantly contributes to the high mortality associated with cardiovascular diseases. Statin therapy represents the gold standard in the reduction of low-density lipoprotein cholesterol concentration. Nevertheless, many patients still cannot achieve the recommended target levels, due to either inadequate effectiveness or intolerance of these drugs. Monoclonal antibodies that inhibit proprotein convertase subtilisin/kexin type 9 (PCSK9) have emerged as a promising option in lipid-lowering treatment. After confirmation of their efficacy and safety in clinical trials, evolocumab and alirocumab received approval from the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) for introduction into clinical practice. In this review, we present a history of the development and mechanisms of action, as well as the results of the most important studies concerning PCSK9 inhibitors.

Geranylgeraniol prevents the simvastatin-induced PCSK9 expression: Role of the small G protein Rac1

Statins are known to increase the plasma levels of proprotein convertase subtilisin kexin type 9 (PCSK9) through the activation of the sterol responsive element binding protein (SREBP) pathway due to the inhibition of cholesterol biosynthesis. In the present study, we explore a possible role of the prenylated proteins on the statin-mediated PCSK9 induction in Caco-2 cells. Simvastatin (40μM) induced both PCSK9 mRNA (10.7±3.2 fold) and protein (2.2±0.3 fold), after 24h incubation. The induction of PCSK9 mRNA was partially, but significantly, prevented by the co-incubation with mevalonate (MVA), farnesol (FOH) and geranylgeraniol (GGOH), while a complete prevention was observed on secreted PCSK9, evaluated by ELISA assay. Under the same experimental conditions, MVA, GGOH, but not FOH, prevented the activation of the PCSK9 promoter by simvastatin in a SRE-dependent manner. Simvastatin reduced by -35.7±15.2% the Rac1-GTP levels, while no changes were observed on RhoA- and Cdc42-GTP. This effect was prevented by MVA and GGOH. A Rac inhibitor, and N17Rac1 dominant negative mutant, significantly induced PCSK9 levels, and a suppression of Rac1 expression by siRNA, counteract the effect of simvastatin on the induction of PCSK9 mRNA. Finally, simvastatin, and Rac inhibitor inhibited the nuclear translocation of STAT3 and its knock-down by siRNA increased significantly the susceptibility of Caco-2 to simvastatin on PCSK9 expression. Taken together, the present study reveal a direct role of Rac1 on simvastatin-mediated PCSK9 expression via the reduction of STAT3 nuclear translocation.

The effects of additional ezetimibe treatment to baseline rosuvastatin on circulating PCSK9 among patients with stable angina

BACKGROUND

Blood lipid management is one of the effective strategies for coronary heart disease, and statins are the first-line lipid-lowering drugs. Low density lipoprotein cholesterol (LDL-C) drop brings about cardioprotective effects. Proprotein convertase subtilisin kexin type 9 (PCSK9) is known to increase LDL-C, thus hazarding LDL-C reduction-induced benefits. To date, how PCSK9 responds to various lipid-lowering strategies has not been fully clarified.

METHODS

This study involves patients with stable angina and aims to explore and clarify the short-term impacts of rosuvastatin and ezetimibe, alone or in combination, on circulating PCSK9. A total of 68 patients with stable angina were enrolled and 60 eligible patients were randomly assigned into 3 groups (20 subjects in each). Patients in different groups were treated for a period of 14 days with rosuvastatin 10 mg/d, ezetimibe 10 mg/d, and rosuvastatin 10 mg/d plus ezetimibe 10 mg/d, respectively. Concentrations of blood LDL-C and PCSK9 levels were measured at baseline and at the 14^th day after treatment.

RESULTS

Both rosuvastatin and ezetimibe could reduce the LDL-C levels, and rosuvastatin displayed a stronger cholesterol-lowering effect than ezetimibe. Moreover, when combined, they yielded even greater efficacy in lowering LDL-C, as compared with either rosuvastatin or ezetimibe mono-treatment (P<0.05). Rosuvastatin therapy (alone or combined with ezetimibe) caused significant rise in circulating PCSK9. Nevertheless, no significant growth of PCSK9 levels (P=0.558) was observed during ezetimibe treatment. At the 14^th day, no difference in PCKS9 levels was observed between the rosuvastatin group and the combination-therapy group (P=0.906).

CONCLUSIONS

Rosuvastatin plus ezetimibe therapy is more effective in reducing LDL-C levels as compared with either rosuvastatin or ezetimibe mono-medication. Meanwhile, such combination strategy does not further increase the levels of circulating PCSK9 compared to rosuvastatin mono-intervention, thus maintaining maximal clinical benefits from lipid-lowering.

Ezetimibe increases intestinal expression of the LDL receptor gene in dyslipidaemic men with insulin resistance

AIM

To gain further insight into intestinal cholesterol homeostasis in dyslipidaemic men with insulin resistance (IR) by examining the impact of treatment with ezetimibe on the expression of key genes involved in cholesterol synthesis and LDL receptor (R)-mediated uptake of lipoproteins.

METHODS

A total of 25 men with dyslipidaemia and IR were recruited to participate in this double-blind, randomized, crossover, placebo-controlled trial. Participants received 10 mg/day ezetimibe or placebo for periods of 12 weeks each. Intestinal gene expression was measured by quantitative PCR in duodenal biopsy samples collected by gastroduodenoscopy at the end of each treatment.

RESULTS

A total of 20 participants completed the protocol. Treatment with ezetimibe significantly increased intestinal LDLR (+16.2%; P = .01), 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoAR; +14.0%; P = .04) and acetyl-Coenzyme A acetyltransferase 2 (ACAT-2) mRNA expression (+12.5%; P = .03). Changes in sterol regulatory element-binding transcription factor 2 (SREBP-2) expression were significantly correlated with changes in HMG-CoAR (r = 0.55; P < .05), ACAT-2 (r = 0.69; P < .001) and proprotein convertase substilisin/kexin type 9 (PCSK9) expression (r = 0.45; P < .05).

CONCLUSIONS

These results show that inhibition of intestinal cholesterol absorption by ezetimibe increases expression of the LDLR gene, supporting the concept that increased LDL clearance with ezetimibe treatment occurs not only in the liver but also in the small intestine.

Proprotein convertase subtilisin kexin type 9 and high-density lipoprotein metabolism: experimental animal models and clinical evidence

Proprotein convertase subtilisin kexin type 9 (PCSK9) belongs to the proprotein convertase family. Several studies have demonstrated its involvement in the regulation of low-density lipoprotein (LDL) cholesterol levels by inducing the degradation of the LDL receptor (LDLR). However, experimental, epidemiologic, and pharmacologic data provide important evidence on the role of PCSK9 also on high-density lipoproteins (HDLs). In mice, PCSK9 regulates the HDL cholesterol (HDL-C) levels by the degradation of hepatic LDLR, thus inhibiting the uptake of apolipoprotein (Apo)E-containing HDLs. Several epidemiologic and genetic studies reported positive relationship between PCSK9 and HDL-C levels, likely by reducing the uptake of the ApoE-containing HDL particles. PCSK9 enhances also the degradation of LDLR's closest family members, ApoE receptor 2, very low-density lipoprotein receptor, and LDLR-related protein 1. This feature provides a molecular mechanism by which PCSK9 may affect HDL metabolism. Experimental studies demonstrated that PCSK9 directly interacts with HDL by modulating PCSK9 self-assembly and its binding to the LDLR. Finally, the inhibition of PCSK9 by means of monoclonal antibodies directed to PCSK9 (ie, evolocumab and alirocumab) determines an increase of HDL-C fraction by 7% and 4.2%, respectively. Thus, the understanding of the role of PCSK9 on HDL metabolism needs to be elucidated with a particular focus on the effect of PCSK9 on HDL-mediated reverse cholesterol transport.

Relationship Between Low-Density Lipoprotein Cholesterol, Free Proprotein Convertase Subtilisin/Kexin Type 9, and Alirocumab Levels After Different Lipid-Lowering Strategies

Background

Alirocumab undergoes target‐mediated clearance via binding of proprotein convertase subtilisin/kexin type 9 (PCSK9). Statins increase PCSK9 levels; the effects of nonstatin lipid‐lowering therapies are unclear. Every‐4‐weeks dosing of alirocumab may be appropriate for some patients in absence of background statin but is not yet approved.

Methods and Results

Low‐density lipoprotein cholesterol (LDL‐C), PCSK9, and alirocumab levels were assessed in subjects (LDL‐C >130 mg/dL, n=24/group) after a 4‐week run‐in taking oral ezetimibe, fenofibrate, or ezetimibe placebo, when alirocumab 150 mg every 4 weeks (days 1, 29, and 57) was added. Maximal mean LDL‐C reductions from day −1 baseline (prealirocumab) occurred on day 71 in all groups: alirocumab plus placebo, 47.4%; alirocumab plus ezetimibe, 56.6%; and alirocumab plus fenofibrate, 54.3%. LDL‐C reductions were sustained through day 85 with alirocumab plus placebo (47.0%); the duration of effect was slightly diminished at day 85 versus day 71 with ezetimibe (49.6%) or fenofibrate combinations (43.2%). Free PCSK9 concentrations were lowest at day 71 in all groups, then increased over time; by day 85, free PCSK9 concentrations were higher, and alirocumab levels lower, with alirocumab plus fenofibrate, and to a lesser extent alirocumab plus ezetimibe, versus alirocumab plus placebo.

Conclusions

Alirocumab 150 mg every 4 weeks produced maximal LDL‐C reductions of 47% in combination with placebo and 54% to 57% in combination with ezetimibe or fenofibrate. The oral lipid‐lowering therapies appear to increase PCSK9 levels, leading to increased alirocumab clearance. Although the duration of effect was modestly diminished with alirocumab plus ezetimibe/fenofibrate versus placebo, the effect was less than observed in trials with background statins, and it would not preclude the use of alirocumab every 4 weeks in patients taking these nonstatin lipid‐lowering therapies concomitantly.

Clinical Trial Registration

URL: http://www.Clinicaltrials.gov. Unique identifier: NCT01723735.

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.

The Central Role of Proprotein Convertase Subtilisin/Kexin Type 9 in Septic Pathogen Lipid Transport and Clearance

Microbial cell walls contain pathogenic lipids, including LPS in gram-negative bacteria, lipoteichoic acid in gram-positive bacteria, and phospholipomannan in fungi. These pathogen lipids are major ligands for innate immune receptors and figure prominently in triggering the septic inflammatory response. Alternatively, pathogen lipids can be cleared and inactivated, thus limiting the inflammatory response. Accordingly, biological mechanisms for sequestering and clearing pathogen lipids from the circulation have evolved. Pathogen lipids released into the circulation are initially bound by transfer proteins, notably LPS binding protein and phospholipid transfer protein, and incorporated into high-density lipoprotein particles. Next, LPS binding protein, phospholipid transfer protein, and other transfer proteins transfer these lipids to ApoB-containing lipoproteins, including low-density (LDL) and very-low-density lipoproteins and chylomicrons. Pathogen lipids within these lipoproteins and their remnants are then cleared from the circulation by the liver. Hepatic clearance involves the LDL receptor (LDLR) and possibly other receptors. Once absorbed by the liver, these lipids are then excreted in the bile. Recent evidence suggests pathogen lipid clearance can be modulated. Importantly, reduced proprotein convertase subtilisin/kexin type 9 activity increases recycling of the LDLR and thereby increases LDLR on the surface of hepatocytes, which increases clearance by the liver of pathogen lipids transported in LDL. Increased pathogen lipid clearance, which can be achieved by inhibiting proprotein convertase subtilisin/kexin type 9, may decrease the systemic inflammatory response to sepsis and improve clinical outcomes.

Increased Plasma PCSK9 Levels Are Associated with Reduced Endotoxin Clearance and the Development of Acute Organ Failures during Sepsis

PURPOSE

We have recently shown that PCSK9 reduces the clearance of endotoxin and is therefore a critical regulator of the innate immune response during infection. However, plasma PCSK9 levels during human sepsis and their relationship to outcomes are not known. Our objective was to determine the relationship between plasma PCSK9 levels and the rate of endotoxin clearance, and then correlate PCSK9 levels with the development of acute organ failures in a cohort of patients with sepsis.

METHODS

Using human hepatocyte cells, we determined the threshold at which PCSK9 is able to reduce Escherichia coli endotoxin uptake by cultured human hepatocytes. In a single-centre observational cohort at St. Paul's Hospital in Vancouver, Canada, we recruited 200 patients who activated our Emergency Department's sepsis protocol and measured plasma PCSK9 and lipid levels at triage and throughout the admission. Outcomes were the development of sepsis-induced cardiovascular or respiratory failure.

RESULTS

We reviewed the literature and determined that the normal human range of PCSK9 found in plasma is 170-220 ng/ml, while levels of 250 ng/ml and above reduced E. coli endotoxin clearance in cultured human hepatocytes. In septic patients, the median levels associated with new-onset respiratory and cardiovascular failure were 370 (250-500) and 380 (270-530) ng/ml, respectively, versus 270 (220-380) ng/ml in patients who did not go on to develop any organ failure (p = 0.003 and 0.005, respectively).

CONCLUSIONS

Plasma PCSK9 levels are greatly increased in sepsis. At normal levels, PCSK9 has no influence upon hepatocyte bacterial endotoxin clearance, but as levels rise, there is a progressive inhibition of clearance. During sepsis, PCSK9 levels are highly correlated with the development of subsequent multiple organ failure. Inhibition of PCSK9 activity is an attractive target for treating the spectrum of sepsis and septic shock.

Ancestry and other genetic associations with plasma PCSK9 response to simvastatin

OBJECTIVE

Statins stimulate transcription of proprotein convertase subtilisin/kexin type 9 (PCSK9), a negative regulator of the low-density lipoprotein receptor, thus blunting the cholesterol-lowering effects of statin treatment. Although there is interindividual variation in PCSK9 statin response, little is known about ancestral and other genetic factors that could contribute to this variation.

METHODS

We measured plasma PCSK9 levels before and after 6 weeks of treatment with 40 mg/day simvastatin in 901 participants of the Cholesterol and Pharmacogenetics clinical trial and tested phenotypic and genetic factors for correlation with PCSK9 statin response.

RESULTS

Statin-induced changes in plasma low-density lipoprotein cholesterol, total cholesterol, and apolipoprotein B were all significantly correlated with statin-induced changes in PCSK9. A detailed examination of the associations of genetic ancestry with PCSK9 statin response revealed that Ashkenazi Jews had smaller statin-induced increases in PCSK9 levels than other self-reported Caucasians (P=0.016). Using genomewide association analysis, we found that the 'G' minor allele of rs13064411 in the WD repeat domain 52 (WDR52) gene was significantly associated with greater statin-induced increases in plasma PCSK9 in Caucasians (P=8.2 × 10(-8)) in the Cholesterol and Pharmacogenetics trial.

CONCLUSION

Overall, these results suggest that genetic ancestry and the rs13064411 genotype contribute to interindividual variation in PCSK9 statin response in Caucasians.

Effect of statin therapy on plasma proprotein convertase subtilisin kexin 9 (PCSK9) concentrations: a systematic review and meta-analysis of clinical trials

AIMS

To evaluate the magnitude of the effect of statin therapy on plasma proprotein convertase subtilisin kexin 9 (PCSK9) levels through a systematic review and meta-analysis of clinical trials.

METHODS

A random-effects model (using DerSimonian-Laird method) and the generic inverse variance method were used for quantitative data synthesis. Heterogeneity was quantitatively assessed using the I(2) index. Sensitivity analyses were conducted using the one-study remove approach. Random-effects meta-regression was performed using an unrestricted maximum likelihood method to evaluate the association between statin-induced elevation of plasma PCSK9 concentrations with duration of treatment and magnitude of LDL cholesterol reduction.

RESULTS

A total of 15 clinical trials examining the effects of statin therapy on plasma PCSK9 levels were included. Meta-analysis of data from single-arm statin treatment arms [weighted mean difference (WMD) 40.72 ng/ml, 95% confidence interval (CI) 34.79, 46.65; p < 0.001] and randomized placebo-controlled trials (WMD 22.98 ng/ml, 95% CI 17.95, 28.01; p < 0.001) showed a significant increase in plasma PCSK9 concentrations after statin therapy, irrespective of the type of statin administered in either of the analyses (single-arm or randomized placebo-controlled trial). There was no significant elevation of plasma PCSK9 levels with statin/ezetimibe combination therapy compared with statin monotherapy (WMD 23.14 ng/ml, 95% CI -1.97, 48.25; p = 0.071); however, removal of one study in the meta-analysis yielded a significant result in the sensitivity analysis (WMD 31.41 ng/ml, 95% CI 7.86, 54.97; p = 0.009).

CONCLUSIONS

This meta-analysis suggests that statin therapy causes a significant increase in plasma PCSK9 concentrations.

The role of PCSK9 in intestinal lipoprotein metabolism: synergism of statin and ezetimibe

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a major role in the regulation of lipoprotein metabolism, mostly through control of low-density lipoprotein receptor degradation. Depletion of cellular cholesterol causes a compensatory increase in plasma PCSK9 levels, which can diminish the cholesterol-lowering power of statins and may lead to the overproduction of intestinal lipoproteins, mainly thorough the up regulation of microsomal triglyceride transfer protein and the Niemann-Pick C1-like 1 protein, the target of ezetimibe. Thus, ezetimibe therapy may counter this unwanted effect of statins, providing an additional theoretical rationale for combining the effect of ezetimibe on intestinal cholesterol absorption and that of statins on cholesterol synthesis.

Impact of Ezetimibe Alone or in Addition to a Statin on Plasma PCSK9 Concentrations in Patients with Type 2 Diabetes and Hypercholesterolemia: A Pilot Study

BACKGROUND AND AIM

The increase in proprotein convertase subtilisin/kexin type 9 (PCSK9) leads to low-density lipoprotein (LDL) receptor degradation. Statins significantly reduce LDL-cholesterol levels, but upregulate PCSK9. This study evaluated the effect of ezetimibe monotherapy or ezetimibe in combination with a statin on serum levels of PCSK9 in patients with type 2 diabetes and hypercholesterolemia.

METHODS

Ezetimibe treatment was given to ten patients with diabetes without statin therapy and ten patients with statin therapy. Plasma levels of PCSK9 were examined at baseline and 24 weeks after treatment.

RESULTS

At baseline, PCSK9 concentrations in patients with statin therapy were significantly higher than those in patients without statin use and in control subjects [median (25th-75th percentile) 411 (272-467) and 382 (356-453) ng/mL, respectively, p < 0.01]. After ezetimibe treatment for 24 weeks, LDL-cholesterol, triglyceride and remnant-like lipoprotein cholesterol were significantly decreased in both groups. However, PCSK9 concentration did not change compared with baseline measurements in both groups. The percentage change in LDL-cholesterol after ezetimibe therapy for 24 weeks was not correlated with the percentage change in PCSK9 concentration.

CONCLUSION

Ezetimibe may reduce LDL-cholesterol levels without affecting PCSK9 in patients with type 2 diabetes and hypercholesterolemia.

Serum proprotein convertase subtilisin/kexin type 9 concentration is not increased by plant stanol ester consumption in normo- to moderately hypercholesterolaemic non-obese subjects. The BLOOD FLOW intervention study

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates low-density lipoprotein (LDL) cholesterol (LDL-C) metabolism by targeting LDL receptors for degradation. Statins increase serum PCSK9 concentration limiting the potential of statins to reduce LDL-C, whereas ezetimibe, inhibitor of cholesterol absorption, has ambiguous effects on circulating PCSK9 levels. Plant stanols also reduce cholesterol absorption, but their effect on serum PCSK9 concentration is not known. Therefore, we performed a controlled, randomized, double-blind study, in which 92 normo- to moderately hypercholesterolaemic subjects (35 males and 57 females) consumed vegetable-oil spread 20 g/day enriched (plant stanol group, n=46) or not (control group, n=46) with plant stanols 3 g/day as ester for 6 months. Fasting blood samples were drawn at baseline and at the end of the study. Serum PCSK9 concentration was analysed with Quantikine Elisa Immunoassay, serum and lipoprotein lipids enzymatically and serum non-cholesterol sterols with GLC. At baseline, PCSK9 concentration varied from 91 to 716 ng/ml with a mean value of 278±11 (S.E.M.) ng/ml with no gender difference. It correlated with serum and LDL-C, serum triglycerides, age, body mass index (BMI) and plasma glucose concentration, but not with variables of cholesterol metabolism when adjusted to serum cholesterol. Plant stanols reduced LDL-C by 10% from controls (P<0.05), but PCSK9 levels were unchanged and did not differ between the groups. In conclusion, the present study demonstrated for the first time that inhibition of cholesterol absorption with plant stanol esters did not affect serum PCSK9 concentration. Thus, plant stanol esters provide an efficient dietary means to lower LDL-C without interfering with the PCSK9 metabolism and in this regard the LDL receptor-mediated cellular cholesterol uptake and removal.

Impacts of ezetimibe on PCSK9 in rats: study on the expression in different organs and the potential mechanisms

Background

Previous studies including our group have indicated the effects of ezetimibe on increased plasma proprotein convertase subtilisin/kexin type 9 (PCSK9) concentration, while the rapid expression in different organs and the potential molecular mechanisms for this impact have not been carefully evaluated.

Methods

Thirty rats were randomly divided into two groups (n = 15 for each), which were orally administrated with ezetimibe (10 mg/kg/day) or normal saline. Blood samples were obtained at day 3 after orally administration, and the PCSK9 levels were determined by ELISA. We further analyzed the mRNA expression of PCSK9, low-density lipoprotein receptor (LDLR), sterol regulator element-binding protein 2 (SREBP2), and hepatocyte nuclear factor 1 alpha (HNF-1α) by real-time PCR, as well as the protein expression by western blot, in liver, intestine and kidney respectively.

Results

Ezetimibe significantly increased plasma PCSK9 levels compared with control group, while there was no significant difference between the two groups with regard to lipid profile at day 3. Moreover, ezetimibe remarkably increased the expression of PCSK9, LDLR, SREBP2 and HNF-1α in liver. Enhanced expression of PCSK9, LDLR and SREBP2 protein were found in intestine and kidney, while no changes in the expression of HNF-1α were observed in intestine and kidney of rats with ezetimibe treatment.

Conclusions

The data demonstrated that ezetimibe increased PCSK9 expression through the SREBP2 and HNF-1α pathways in different organs, subsequently resulting in elevated plasma PCSK9 levels prior to the alterations of lipid profile in rats.

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

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

PCSK9 antibodies for the treatment of hypercholesterolemia

The serine protease proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low-density lipoprotein (LDL) receptor (LDLR) and directs it to lysosomes for intracellular degradation. This results in decreased numbers of LDLR available on the hepatic cell surface to bind LDL particles and remove them from the circulation and therefore to a subsequent increase in circulating LDL-cholesterol (LDL-C) plasma levels. Since 2003, when the role of PCSK9 in LDL-C metabolism was discovered, there have been major efforts to develop efficient and safe methods to inhibit it. Amongst those, monoclonal antibodies against PCSK9 are the furthest in development, with multiple phase 3 trials already published and with cardiovascular endpoint trials currently underway. Two fully human monoclonal antibodies, evolocumab (AMG 145) and alirocumab (REGN727/SAR236553), have been extensively studied in a wide range of subjects, such as those with statin intolerance, as an add-on to statin therapy, as a monotherapy and in patients with familial hypercholesterolemia. PCSK9 antibodies result in a consistent and robust decrease in LDL-C plasma levels ranging from 40% to 70%, either on top of statins or as a monotherapy. If the safety data from the on-going phase 3 trials remain as reassuring as the data available till now, PCSK9 antibodies will offer a novel, powerful therapeutic option to decrease LDL-C plasma levels and, hopefully, cardiovascular risk.

New therapies for reducing low-density lipoprotein cholesterol

Although the past 4 decades have been the most productive in transitioning from an low-density lipoprotein cholesterol (LDL-C) hypothesis to demonstration of clinical benefit, cardiovascular disease remains a major cause of mortality and morbidity. It is fortunate that most of the effective lipid-lowering drugs, the statins, have become generic and inexpensive. However, there remains a large unmet medical need for new and effective agents that are also well tolerated and safe, especially for patients unable to either tolerate statins or achieve optimal LDL-C on current therapies. It is likely that the agents discussed in this review will fill that need.

Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9): Lessons Learned from Patients with Hypercholesterolemia

BACKGROUND

Identification of the proprotein convertase subtilisin/kexin type 9 (PCSK9) as the third gene causing familial hypercholesterolemia (FH) and understanding its complex biology has led to the discovery of a novel class of therapeutic agents.

CONTENT

PCSK9 undergoes autocatalytic cleavage in the endoplasmic reticulum and enters the secretory pathway. The PCSK9 gene is under the regulatory control of sterol receptor binding proteins 1 and 2. Statins increase PCSK9 and this may modulate the response to this class of medications. In plasma, PCSK9 binds to the epidermal growth factor–like domain of the LDL receptor (LDL-R) on the cell and, once incorporated in the late endosomal pathway, directs the LDL-R toward lysosomal degradation rather than recycling to the plasma membrane. Thus, gain-of-function PCSK9 mutations lead to an FH phenotype, whereas loss-of-function mutations are associated with increased LDL-R–mediated endocytosis of LDL particles and lower LDL cholesterol in plasma. Inhibition of PCSK9 is thus an attractive therapeutic target. Presently, this is achieved by using monoclonal antibodies for allosteric inhibition of the PCSK9–LDL-R interaction. Phase 2 and 3 clinical trials in patients with moderate and severe hypercholesterolemia (including FH) show that this approach is safe and highly efficacious to lower LDL-C and lipoprotein(a).

SUMMARY

PCSK9 has other biological roles observed in vitro and in animal studies, including viral entry into the cell, insulin resistance, and hepatic tissue repair. Given the potential number of humans exposed to this novel class of medications, careful evaluation of clinical trial results is warranted.

PCSK9: a key modulator of cardiovascular health

Since the discovery of proprotein convertase subtilisin kexin 9 (PCSK9) in 2003, this PC has attracted a lot of attention from the scientific community and pharmaceutical companies. Secreted into the plasma by the liver, the proteinase K-like serine protease PCSK9 binds the low-density lipoprotein (LDL) receptor at the surface of hepatocytes, thereby preventing its recycling and enhancing its degradation in endosomes/lysosomes, resulting in reduced LDL-cholesterol clearance. Surprisingly, in a nonenzymatic fashion, PCSK9 enhances the intracellular degradation of all its target proteins. Rare gain-of-function PCSK9 variants lead to higher levels of LDL-cholesterol and increased risk of cardiovascular disease; more common loss-of-function PCSK9 variants are associated with reductions in both LDL-cholesterol and risk of cardiovascular disease. It took 9 years to elaborate powerful new PCSK9-based therapeutic approaches to reduce circulating levels of LDL-cholesterol. Presently, PCSK9 monoclonal antibodies that inhibit its function on the LDL receptor are evaluated in phase III clinical trials. This review will address the biochemical, genetic, and clinical aspects associated with PCSK9's biology and pathophysiology in cells, rodent and human, with emphasis on the clinical benefits of silencing the expression/activity of PCSK9 as a new modality in the treatment of hypercholesterolemia and associated pathologies.

Impact of currently prescribed lipid-lowering drugs on plasma PCSK9 concentration: single or in combination study in rats

Background

An emerging data suggested a significant impact of statins on PCSK9 concentration, while the rapid impacts of other lipid-lowering drugs such as ezetimibe and xuezhikang alone or in combination on PCSK9 and lipid profile have not been assessed. This study aims to investigate whether an enhanced PCSK9 concentration by single or combined therapy of lipid-lowering drugs currently used precedes the changes of lipid profile in rats.

Methods

Sixty-three rats were randomly divided into six groups and orally administrated with placebo (N = 13), ezetimibe 10 mg/kg daily, Xuezhikang 1200 mg/kg daily, ezetimibe 10 mg/kg plus Xuezhikang 1200 mg/kg daily, pitavastatin 10 mg/kg daily or pitavastatin 10 mg/kg plus ezetimibe 10 mg/kg daily for 3 days (N = 10 for each group respectively). Blood samples were obtained at day 3 after orally administration. Plasma PCSK9 levels were determined by ELISA and lipid profile were measured by enzymatic assay.

Results

Ezetimibe, Xuezhikang and pitavastatin alone and Xuezhikang plus ezetimibe as well as pitavastatin plus ezetimibe increased PCSK9 levels by 124%, 56%, 111%, 63% and 204% respectively (p < 0.05 compared with placebo). However, Xuezhikang plus ezetimibe did not enhance greater PCSK9 levels compared to monotherapy. Ezetimibe and pitavastatin in combination induced higher PCSK9 levels than pitavastatin monotherapy or co-therapy with ezetimibe plus Xuezhikang. There was no significant difference between any groups with regard to lipid profile levels at day 3 (P > 0.05).

Conclusions

Elevated PCSK9 concentration by ezetimibe, Xuezhikang and pitavastatin alone or in combination was found prior to the alterations of lipid profile in rats. Combination of Xuezhikang and ezetimibe significantly attenuated increase in PCSK9 compared to ezetimibe plus pitavastatin, suggesting that the former combination may be better than the latter in future clinical application.

[Hypolipidemic and pleiotropic effects of a combination of simvastatin and ezetimibe in patients with different types of hyperlipidemia]

The review considers trials dealing with the efficiency of combination hypolipidemic therapy with simvastatin and ezetimibe. Its synergistic potentiating effect can cause a considerable decrease in the level of total cholesterol, low-density lipoproteins, triglycerides, and C-reactive protein, which are important participants in the atherogenic process. This effect promotes the achievement of hypolipidemic therapeutic goals in many cases when this cannot be attained by high-dose statin monotherapy. The authors consider the results of trials of combination hypolipidemic therapy with simvastatin and ezetimibe performed as basic ones done in both previous and recent years.

Proprotein convertases subtilisin/kexin type 9, an enzyme turned escort protein: hepatic and extra hepatic functions

Proprotein Convertases Subtilisin/Kexin Type 9 (PCSK9) is a serine endoproteinase. Biosynthesized as a zymogen, it cleaves itself once, and then turns into an escort protein for transmembrane proteins, leading them into lysosomes for degradation. It is primarily produced and secreted by the liver. It attaches to the low-density lipoprotein receptor (LDLR) at the surface of hepatocytes and, after co-endocytosis, directs it into lysosomes where it is degraded. By downregulating LDLR, PCSK9 reduces hepatic clearance of LDL-cholesterol. Inborn or induced increase of this function causes hypercholesterolemia; its decrease causes hypocholesterolemia. This has been experimentally demonstrated ex vivo and in vivo, and corroborated by epidemiological studies associating PCSK9 genetic variations with plasma cholesterol levels. PCSK9 is now a proven target for inactivation in the treatment of hypercholesterolemia and associated atherosclerosis. However, it is still uncertain whether its severe or complete inactivation, combined with other predispositions, will be without undesirable side-effects. Some experimental data suggest that PCSK9 could contribute positively to the physiology of non-hepatic cells such as pancreatic islets β cells, adipocytes and macrophages, protecting them from excessive lipid uptake, in an endocrine, autocrine, or paracrine manner. Genetic variations that attenuate PCSK9 anti-LDLR activity are common in human populations. Their evolutionary significance still needs to be evaluated on the background of environmental pressures, such as infectious diseases, cold weather and famine, which have threatened survival and reproduction in the course of human prehistory and history.