Exploration of PCSK9 as a Cardiovascular Risk Factor

Assessment of serum proprotein convertase subtilisin/kexin type 9 in pediatric sepsis syndrome

Sepsis is a life-threatening condition that arises when the body's response to infection causes injury to its tissues and organs. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is an enzyme released in response to the drop in cholesterol level occurring in sepsis. Our study aimed to evaluate the prognostic role of serum Proprotein convertase subtilisin/kexin type 9 (PCSK9) level in children with sepsis and severe sepsis. Sixty children were included in this study. They were divided into two groups: 30 children in the sepsis group and 30 in the severe sepsis group. Another 30 apparently healthy children were included as a control group. Blood samples were withdrawn from all included children for complete blood count (CBC), renal function tests (RFT), liver function tests (LFT), LDL-cholesterol (LDL-C), blood culture, and serum PCSK9. In this study, PCSK9 and LDL-C were higher in the two sepsis groups than in the control group (p < 0.05). They were also higher in the severe sepsis group than the sepsis group and in the non-survivors than in the survivors (p < 0.05). PCSK9 was positively correlated with length of hospital stay in surviving children (r = 0.67, p = 0.001) and had predicted significant hematological dysfunction (adjusted B =  - 96.95, p = 0.03). In conclusion, the PCSK9 assay can be used as a biomarker for bad prognosis in children suffering from clinical sepsis.

One-Year Effects of High-Intensity Statin on Bioactive Lipids: Findings From the JUPITER Trial

BACKGROUND

Statin effects extend beyond low-density lipoprotein cholesterol reduction, potentially modulating the metabolism of bioactive lipids (BALs), crucial for biological signaling and inflammation. These bioactive metabolites may serve as metabolic footprints, helping uncover underlying processes linked to pleiotropic effects of statins and yielding a better understanding of their cardioprotective properties. This study aimed to investigate the impact of high-intensity statin therapy versus placebo on plasma BALs in the JUPITER trial (Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin; NCT00239681), a randomized primary prevention trial involving individuals with low-density lipoprotein cholesterol <130 mg/dL and high-sensitivity C-reactive protein ≥2 mg/L.

METHODS

Using a nontargeted mass spectrometry approach, over 11 000 lipid features were assayed from baseline and 1-year plasma samples from cardiovascular disease noncases from 2 nonoverlapping nested substudies: JUPITERdiscovery (n=589) and JUPITERvalidation (n=409). The effect of randomized allocation of rosuvastatin 20 mg versus placebo on BALs was examined by fitting a linear regression with delta values (∆=year 1-baseline) adjusted for age and baseline levels of each feature. Significant associations in discovery were analyzed in the validation cohort. Multiple comparisons were adjusted using 2-stage overall false discovery rate.

RESULTS

We identified 610 lipid features associated with statin randomization with significant replication (overall false discovery rate, <0.05), including 26 with annotations. Statin therapy significantly increased levels of 276 features, including BALs with anti-inflammatory activity and arterial vasodilation properties. Concurrently, 334 features were significantly lowered by statin therapy, including arachidonic acid and proinflammatory and proplatelet aggregation BALs. By contrast, statin therapy reduced an eicosapentaenoic acid-derived hydroxyeicosapentaenoic acid metabolite, which may be related to impaired glucose metabolism. Additionally, we observed sex-related differences in 6 lipid metabolites and 6 unknown features.

CONCLUSIONS

Statin allocation was significantly associated with upregulation of BALs with anti-inflammatory, antiplatelet aggregation and antioxidant properties and downregulation of BALs with proinflammatory and proplatelet aggregation activity, supporting the pleiotropic effects of statins beyond low-density lipoprotein cholesterol reduction.

Effects of PCSK9 on thrombosis and haemostasis in a variety of metabolic states: Lipids and beyond (Review)

Proprotein convertase subtilisin kexin type 9 (PCSK9) inhibitors are widely recognised as being able to induce a potent reduction in low‑density lipoprotein‑cholesterol. An increasing number of studies have suggested that PCSK9 also influences the haemostatic system by altering platelet function and the coagulation cascade. These findings have significant implications for anti‑PCSK9 therapy in patients with specific coagulation conditions, including expanded indications, dose adjustments and drug interactions. The present review summarises the changes in PCSK9 levels in individuals with liver diseases, chronic kidney diseases, diabetes mellitus, cancer and other disease states, and discusses their impact on thrombosis and haemostasis. Furthermore, the structure, effects and regulatory mechanisms of PCSK9 on platelets, coagulation factors, inflammatory cells and endothelial cells during coagulation and haemostasis are described.

Association of serum PCSK9 levels with platelet function in patients with acute coronary syndromes

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates low-density lipoprotein (LDL) homeostasis and plays a key role in acute coronary syndrome (ACS). The cardioprotective effect of PCSK9 inhibition extends beyond LDL cholesterol reduction, involving regulation of platelet function by not yet unraveled mechanisms. Oxidized-LDL (ox-LDL) is increased during ACS and induces platelet activation via binding to platelet surface. We will evaluate serum PCSK9 and its correlation with platelet reactivity and platelet-ox-LDL binding in Chinese ACS patients.

METHOD AND DESIGN

In this pilot cross-sectional study, we will enroll 115 Chinese participants aged 30 to 75 years with ACS. Blood sample will be obtained after the first maintenance dose of aspirin and clopidogrel during morning time. Serum PCSK9 will be measured by an enzyme-linked immunoadsorbent assay. Platelet reactivity will be assessed by; Platelet activation (P-selectin and GPIIbIIIa expression using flow cytometry) and; Platelet aggregation using light transmission aggregometry in response to various stimuli. On-treatment platelet reactivity is measured by adenosine diphosphate-induced platelet aggregation. Binding of ox-LDL to platelet will be evaluated by flow cytometry. Spearman correlations will be used to determine association of serum PCSK9 with platelet functional parameters and platelet-ox-LDL binding. Additionally, continuous PCSK9 levels will be categorized into tertiles of equal size to investigate its association with on-treatment platelet reactivity.

DISCUSSION

This study will reveal possible relationship between serum PCSK9 and platelet reactivity in the setting of ACS which may shed light on therapeutic potential in platelet inhibition by targeting PCSK9. The study will also explore the association of serum PCSK9 and platelet-ox-LDL binding, an important mechanism for platelet-LDL interplay, to provide mechanistic insight into PCSK9-mediated regulation of platelet reactivity.

Drug-Drug Interaction between Antiplatelet Therapy and Lipid-Lowering Agents (Statins and PCSK9 Inhibitors)

Lipid-lowering agents and antiplatelet drugs are guideline-recommended standard treatment for secondary prevention of acute thrombotic events in patients with increased cardiovascular risk. Aspirin is the most frequently used antiplatelet drug, either alone or in combination with other antiplatelet agents (P2Y₁₂ inhibitors), while statins are first-line treatment of hypercholesterolemia. The well-established mode of action of aspirin is inhibition of platelet-dependent thromboxane formation. In addition, aspirin also improves endothelial oxygen defense via enhanced NO formation and inhibits thrombin formation. Low-dose aspirin exerts in addition anti-inflammatory effects, mainly via inhibition of platelet-initiated activation of white cells.Statins inhibit platelet function via reduction of circulating low-density lipoprotein-cholesterol (LDL-C) levels and a more direct inhibition of platelet function. This comprises inhibition of thromboxane formation via inhibition of platelet phospholipase A₂ and inhibition of (ox)LDL-C-mediated increases in platelet reactivity via the (ox)LDL-C receptor (CD36). Furthermore, statins upregulate endothelial NO-synthase and improve endothelial oxygen defense by inhibition of NADPH-oxidase. PCSK9 antibodies target a serine protease (PCSK9), which promotes the degradation of the LDL-C receptor impacting on LDL-C plasma levels and (ox)LDL-C-receptor-mediated signaling in platelets similar to but more potent than statins.These functionally synergistic actions are the basis for numerous interactions between antiplatelet and these lipid-lowering drugs, which may, in summary, reduce the incidence of atherothrombotic vascular events.

Pleiotropic Effects of PCSK9: Focus on Thrombosis and Haemostasis

The proprotein convertase subtilisin/keying 9 (PCSK9) is a serine protease that has gained importance in recent years as a drug target, mainly due to its effect on cholesterol metabolism in promoting the degradation of the low-density lipoprotein receptor (LDLR). However, this protease may also play an important role in lipid-independent reactions, including the process of thrombogenesis. Considering this, we reviewed the effects and implications of PCSK9 on platelet function and blood coagulation. PCSK9 knockout mice exhibited reduced platelet activity and developed less agonist-induced arterial thrombi compared to the respective control animals. This is in line with known research that elevated blood levels of PCSK9 are associated with an increased platelet reactivity and total number of circulating platelets in humans. Moreover, PCSK9 also has an effect on crucial factors of the coagulation cascade, such as increasing factor VIII plasma levels, since the degradation of this blood clotting factor is promoted by the LDLR. The aforementioned pleiotropic effects of the PCSK9 are important to take into account when evaluating the clinical benefit of PCSK9 inhibitors.

PCSK9 Promotes Cardiovascular Diseases: Recent Evidence about Its Association with Platelet Activation-Induced Myocardial Infarction

Cardiovascular diseases are the leading cause of death worldwide, with the majority of the cases being heart failure due to myocardial infarction. Research on cardiovascular diseases is currently underway, particularly on atherosclerosis prevention, to reduce the risk of myocardial infarction. Proprotein convertase subtilisin/kexin type 9 (PCSK9) has been reported to play a role in lipid metabolism, by enhancing low-density lipoprotein (LDL) receptor degradation. Therefore, PCSK9 inhibitors have been developed and found to successfully decrease LDL plasma levels. Recent experimental studies have also implicated PCSK9 in platelet activation, having a key role during atherosclerosis progression. Although numerous studies have addressed the role of PCSK9 role in controlling hypercholesterolemia, studies and discussions exploring its involvement in platelet activation are still limited. Hence, here, we address our current understanding of the pathophysiological process involved in atherosclerosis-induced myocardial infarction (MI) through platelet activation and highlight the molecular mechanisms used by PCSK9 in regulating platelet activation. Undoubtedly, a deeper understanding of the relationship between platelet activation and the underlying molecular mechanisms of PCSK9 in the context of MI progression will provide a new strategy for developing drugs that selectively inhibit the most relevant pathways in cardiovascular disease progression.

PCSK9 inhibition could be effective for acute myocardial infarction

In this review, we will explore the role of PCSK9 and inhibition of PCSK9 in patients after acute myocardial infarction (MI). Despite the implementation of evidence-based therapies to improve outcomes, mortality at one-year remains at 12-15% and the need to further reduce complications related to MI persists. Mechanistic and epidemiologic studies suggest that the naturally occurring PCSK9 protein increases coronary plaque vulnerability through several pathways, including pro-inflammatory LDL-C oxidation and direct modification of plaque composition. PCSK9 inhibitors are a class of drugs with proven efficacy in patients with recent MI. The latest guidelines recommend the use of PCSK9 in patients with recent MI early in the process of care to reduce LDL-C values and associated morbidity. The use of PCSK9 inhibition could be beneficial for mortality reduction after an acute MI and should be tested in an appropriately powered randomized controlled trial.

Inhibitors of Protein Convertase Subtilisin/Kexin 9 (PCSK9) and Acute Coronary Syndrome (ACS): The State-of-the-Art

Acute Coronary Syndrome (ACS) remains one of the most frequent causes of morbidity and mortality in the world. Although the age- and gender-adjusted incidence of ACS is decreasing, the mortality associated with this condition remains high, especially 1-year after the acute event. Several studies demonstrated that PCSK9 inhibitors therapy determine a significant reduction of major adverse cardiovascular events (MACE) in post-ACS patients, through a process of plaque modification, by intervening in lipid metabolism and platelet aggregation and finally determining an improvement in endothelial function. In the EVACS (Evolocumab in Acute Coronary Syndrome) study, evolocumab allows >90% of patients to achieve LDL-C < 55 mg/dL according to ESC/EAS guidelines compared to 11% of patients who only receive statins. In the EVOPACS (EVOlocumab for Early Reduction of low-density lipoprotein (LDL)-cholesterol Levels in Patients With Acute Coronary Syndromes) study, evolocumab determined LDL levels reduction of 40.7% (95% CI: 45.2 to 36.2; p < 0.001) and allowed 95.7% of patients to achieve LDL levels <55 mg/dL. In ODYSSEY Outcome trial, alirocumab reduced the overall risk of MACE by 15% (HR = 0.85; CI: 0.78-0.93; p = 0.0003), with a reduced risk of all-cause mortality (HR = 0.85; CI: 0.73-0.98: nominal p = 0026), and fewer deaths for coronary heart disease (CHD) compared to the control group (HR = 0.92; CI: 0.76-1.11; p = 0.38). The present review aimed at describing the beneficial effect of PCSK9 inhibitors therapy early after ACS in reducing LDL circulating levels (LDL-C) and the risk of major adverse cardiovascular events, which was very high in the first year and persists higher later after the acute event.

Coming Back to Physiology: Extra Hepatic Functions of Proprotein Convertase Subtilisin/Kexin Type 9

Neuronal apoptosis regulated convertase-1 (NARC-1), now mostly known as proprotein convertase subtilisin/kexin type 9 (PCSK9), has received a lot of attention due to the fact that it is a key regulator of the low-density lipoprotein (LDL) receptor (LDL-R) and is therefore involved in hepatic LDL clearance. Within a few years, therapies targeting PCSK9 have reached clinical practice and they offer an additional tool to reduce blood cholesterol concentrations. However, PCSK9 is almost ubiquitously expressed in the body but has less well-understood functions and target proteins in extra hepatic tissues. As such, PCSK9 is involved in the regulation of neuronal survival and protein degradation, it affects the expression of the epithelial sodium channel (ENaC) in the kidney, it interacts with white blood cells and with cells of the vascular wall, and it modifies contractile activity of cardiomyocytes, and contributes to the regulation of cholesterol uptake in the intestine. Moreover, under stress conditions, signals from the kidney and heart can affect hepatic expression and thereby the plasma concentration of PCSK9 which then in turn can affect other target organs. Therefore, there is an intense relationship between the local (autocrine) and systemic (endocrine) effects of PCSK9. Although, PCSK9 has been recognized as a ubiquitously expressed modifier of cellular function and signaling molecules, its physiological role in different organs is not well-understood. The current review summarizes these findings.

PCSK9 (Proprotein Convertase Subtilisin/Kexin 9) Enhances Platelet Activation, Thrombosis, and Myocardial Infarct Expansion by Binding to Platelet CD36

BACKGROUND

PCSK9 (proprotein convertase subtilisin/kexin 9), mainly secreted by the liver and released into the blood, elevates plasma low-density lipoprotein cholesterol by degrading low-density lipoprotein receptor. Pleiotropic effects of PCSK9 beyond lipid metabolism have been shown. However, the direct effects of PCSK9 on platelet activation and thrombosis, and the underlying mechanisms, as well, still remain unclear.

METHODS

We detected the direct effects of PCSK9 on agonist-induced platelet aggregation, dense granule ATP release, integrin αIIbβ3 activation, α-granule release, spreading, and clot retraction. These studies were complemented by in vivo analysis of FeCl₃-injured mouse mesenteric arteriole thrombosis. We also investigated the underlying mechanisms. Using the myocardial infarction (MI) model, we explored the effects of PCSK9 on microvascular obstruction and infarct expansion post-MI.

RESULTS

PCSK9 directly enhances agonist-induced platelet aggregation, dense granule ATP release, integrin αIIbβ3 activation, P-selectin release from α-granules, spreading, and clot retraction. In line, PCSK9 enhances in vivo thrombosis in a FeCl₃-injured mesenteric arteriole thrombosis mouse model, whereas PCSK9 inhibitor evolocumab ameliorates its enhancing effects. Mechanism studies revealed that PCSK9 binds to platelet CD36 and thus activates Src kinase and MAPK (mitogen-activated protein kinase)-extracellular signal-regulated kinase 5 and c-Jun N-terminal kinase, increases the generation of reactive oxygen species, and activates the p38MAPK/cytosolic phospholipase A2/cyclooxygenase-1/thromboxane A₂ signaling pathways downstream of CD36 to enhance platelet activation, as well. Using CD36 knockout mice, we showed that the enhancing effects of PCSK9 on platelet activation are CD36 dependent. It is important to note that aspirin consistently abolishes the enhancing effects of PCSK9 on platelet activation and in vivo thrombosis. Last, we showed that PCSK9 activating platelet CD36 aggravates microvascular obstruction and promotes MI expansion post-MI.

CONCLUSIONS

PCSK9 in plasma directly enhances platelet activation and in vivo thrombosis, and MI expansion post-MI, as well, by binding to platelet CD36 and thus activating the downstream signaling pathways. PCSK9 inhibitors or aspirin abolish the enhancing effects of PCSK9, supporting the use of aspirin in patients with high plasma PCSK9 levels in addition to PCSK9 inhibitors to prevent thrombotic complications.

PCSK9 Regulates Nox2-Mediated Platelet Activation via CD36 Receptor in Patients with Atrial Fibrillation

Background: High levels of proprotein convertase subtilisin/kexin 9 (PCSK9) is predictive of cardiovascular events (CVEs) in atrial fibrillation (AF). We hypothesized that PCSK9 may directly induce platelet activation (PA). Methods: We measured platelet aggregation, recruitment, Thromboxane B2 (TxB2) formation and soluble P-selectin levels as markers of PA and soluble Nox2-derived peptide (sNox2-dp), H₂O₂, isoprostanes and oxidized Low-Density-Lipoprotein (oxLDL) to analyze oxidative stress (OS) in 88 patients having PCSK9 values < (n = 44) or > (n = 44) 1.2 ng/mL, balanced for age, sex and cardiovascular risk factors. Furthermore, we investigated if normal (n = 5) platelets incubated with PCSK9 (1.0–2.0 ng/mL) alone or with LDL (50 µg/mL) displayed changes of PA, OS and down-stream signaling. Results: PA and OS markers were significantly higher in patients with PCSK9 levels > 1.2 ng/mL compared to those with values < 1.2 ng/mL (p < 0.001). Levels of PCSK9 significantly correlated with markers of PA and OS. Platelets incubation with PCSK9 increased PA, OS and p38, p47 and Phospholipase A2 (PLA2) phosphorylation. These changes were amplified by adding LDL and blunted by CD36 or Nox2 inhibitors. Co-immunoprecipitation analysis revealed an immune complex of PCSK9 with CD36. Conclusions: We provide the first evidence that PCSK9, at concentration found in the circulation of AF patients, directly interacts with platelets via CD36 receptor and activating Nox2: this effect is amplified in presence of LDL.

Ticagrelor suppresses oxidized low‑density lipoprotein‑induced endothelial cell apoptosis and alleviates atherosclerosis in ApoE‑/‑ mice via downregulation of PCSK9

Although ticagrelor has been demonstrated to possess an anti-atherosclerosis (AS) effect, its underlying mechanism remains unclear. In the present study, it was investigated whether ticagrelor reduces oxidized low-density lipoprotein (ox-LDL)-induced endothelial cell apoptosis, an initial step for the development of AS, and alleviates AS in apolipoprotein-E-deficient (ApoE^−/−) mice by inhibiting the expression of proprotein convertase subtilisin/kexin type 9 (PCSK9). The human endothelial cell line EAhy926 was treated with ox-LDL, ox-LDL + ticagrelor (40 µmol/l) and ox-LDL + ticagrelor (60 µmol/l) for 24 h. Cell apoptosis was detected using Annexin V-fluorescein isothiocyanate/propidium iodide staining. The expression levels of PCSK9, apoptosis-associated proteins and signaling pathways were determined by reverse transcription-quantitative polymerase chain reaction and western blotting. ApoE^−/− mice fed a high-fat diet were used to induce an AS model. After 20 weeks, ApoE^−/− mice were randomly assigned to receive saline or ticagrelor intragastrically for 10 days. The formation of atherosclerotic plaques was detected by hematoxylin and eosin staining. The expression of PCSK9 in the arterial tissues was measured by immunohistochemistry. The results demonstrated that treatment with ticagrelor was able to decrease ox-LDL-induced apoptosis in a concentration-dependent manner (40 µmol/l vs. ox-LDL, 17.58±2.66 vs. 27.25±5.54%; 60 µmol/l vs. ox-LDL, 12.26±1.54 vs. 27.25±5.54%). The mRNA and protein expression level of PCSK9 significantly decreased following treatment with ticagrelor, accompanied with upregulation of B-cell lymphoma (Bcl) 2 and downregulation of Bcl-2 associated X, apoptosis regulator, caspase-3, p38, phosphorylated-(p) p38, p-c-Jun N-terminal kinases (JNK), p-extracellular signal-regulated kinases and the ratio of p-JNK to JNK. Histological analysis of arterial tissues revealed ticagrelor markedly decreased the atherosclerotic plaque area and inhibited the expression of PCSK9. The present results suggested that ticagrelor may alleviate AS via downregulation of PCSK9-mediated endothelial cell apoptosis, which may be JNK-dependent.