Plasma Proprotein Convertase Subtilisin/kexin 9 Levels Research Articles

Predictive Value of Plasma PCSK9 Levels for Degree of Atherosclerosis and Major Adverse Cardiovascular and Cerebrovascular Events in Older Adult Patients with Non-Alcoholic Fatty Liver Disease.

This study investigated the influence of plasma proprotein convertase subtilisin/kexin 9 (PCSK9) levels on the degree of atherosclerosis and major adverse cardiovascular and cerebrovascular events (MACCE) in older adults with non-alcoholic fatty liver disease. The degree of atherosclerosis severity was assessed by the standard Gensini score quartile method. According to the degree of atherosclerosis, patients were divided into mild (0-24 points; n=84), moderate (25-53 points; n=86), and severe groups (≥54 points; n=84) and then categorized as MACCE (n=30) or non-MACCE (n=224) according to 6-month follow-up data. The patients' age, sex, smoking history, medical history, and early morning fasting venous blood, for measuring biochemical indexes, were collected. Clinical data were compared between groups and the relationship between Gensini scores and PCSK9 was evaluated. Compared with the mild group, the moderate and severe groups had higher high-sensitivity C-reactive protein(hs-CRP), PCSK9, triglycerides(TG), low-density lipoprotein cholesterol (LDL-C), and lipoprotein(a)[Lp(a)] levels and lower high-density lipoprotein cholesterol(HDL-C) levels (all P<0.05). Moreover, PCSK9 positively correlated with Gensini scores (r=0.657, P<0.01). The MACCE and non-MACCE groups had significantly different ages, statin use, Gensini scores, PCSK9, and LDL-C (all P<0.05). Multi-factorial Cox risk regression analysis showed the Gensini score (HR=1.018, 95% CI: 1.006~1.029) and PCSK9 (HR=1.147, 95% CI: 1.038~1.287) were independent risk factors for MACCE. The Gensini score and PCSK9 levels can be used as predictive indicators for the degree of illness and occurrence of MACCE in older NAFLD patients.

Impact of conventional lipid-lowering therapy on circulating levels of PCSK9: protocol for a systematic review and meta-analysis of randomised controlled trials

IntroductionConventional lipid-lowering agents, including statins, ezetimibe, fibrates, bile acid sequestrants, nicotinic acid, bempedoic acid and Omega-3, are essential to the management of dyslipidaemia. However, these agents have been shown to...

Association between PCSK9 Levels and Markers of Inflammation, Oxidative Stress, and Endothelial Dysfunction in a Population of Nondialysis Chronic Kidney Disease Patients.

Proprotein convertase subtilisin/kexin 9 (PCSK9) plays an important role in lipid metabolism while available literature regarding its involvement in the pathogenesis of atherosclerosis and in the expression of genes associated with apoptosis and inflammation is constantly increasing. Patients with chronic kidney disease (CKD) experience disproportionately increased cardiovascular morbidity and mortality due to dyslipidemia, accelerated atherosclerosis, inflammation, oxidative stress, and other risk factors. In the present cross-sectional study, we investigated the possible association of serum PCSK9 levels with markers of inflammation, oxidative stress, and endothelial damage in patients with CKD. Patients and Methods. Ninety-two patients with CKD stages II-ΙV (eGFR CKD-EPI 47.3 ± 25.7 ml/min/1.73 m2, mean age 66 years, 51 men) were included in the study. Plasma PCSK9 levels were correlated with comorbidities (arterial hypertension, diabetes mellitus, and history of cardiovascular disease), renal function indices (eGFR, proteinuria–UPR/24 h), lipid parameters (LDL-cholesterol, HDL-cholesterol, triglycerides, Lp(a), APO-A1, and APO-B), and soluble biomarkers of inflammation, oxidative stress, and endothelial damage (hs-CRP, fibrinogen, 8-epiPGF2a, ox-LDL, IL-6, TNF-α, sICAM-1, and sVCAM-1). Results. The mean plasma value of PCSK9 was 278.1 ng/ml. PCSK9 levels showed direct correlation with serum triglycerides (p = 0.03), Lp(a) (p = 0.01), and sICAM-1 levels (p = 0.03). There was no significant correlation between PCSK9 levels and indices of the renal function, other lipid profile parameters, inflammatory markers, or comorbidities. Multiple regression analysis showed a significant effect of Lp(a) on PCSK9 levels, and for each unit of higher Lp(a), an increase by 3.082 is expected (95% CI: 0.935-5.228, p = 0.006). At the same time, patients receiving statins are expected to have on average 63.8 ng/ml higher PCSK9 values compared to patients not receiving statins (95% CI: 14.6-113.5, p = 0.012). Conclusion. Plasma levels of PCSK9 in nondialysis CKD patients are correlated with endothelial dysfunction and lipid metabolism parameters. Statin intake increases PCSK9 levels significantly in this patient population. PCSK9 levels are not correlated with the severity of kidney disease. Major prospective studies are necessary to investigate the role of PCSK9 in the atherosclerotic cardiovascular outcome in CKD.

Efficacy and Safety of PCSK9 Inhibitors in Hypercholesterolemia Associated With Refractory Nephrotic Syndrome

IntroductionTreatment of hypercholesterolemia in refractory nephrotic syndrome remains a therapeutic challenge. There is not enough evidence supporting the efficacy of statins, and these drugs can be associated with an increased incidence of adverse effects. Herein we summarize our clinical experience with 12 patients suffering from refractory nephrotic syndrome with associated vascular disease and uncontrolled hypercholesterolemia despite treatment with statins who were treated with proprotein convertase subtilisin kexin 9 (PCSK9) inhibitors.MethodsTwelve adult patients with primary nephrotic syndrome refractory to multiple lines of immunosuppressive treatment who suffered from clinical atheromatous vascular disease were treated with PCSK9 inhibitors according to the prescription guidelines for secondary prevention of cardiovascular events. Eight patients with refractory nephrotic syndrome without vascular disease treated with atorvastatin comprised the control group.ResultsFour weeks after treatment with PCSK9 inhibitors, a statistically significant decrease in total cholesterol and low-density lipoprotein cholesterol (LDL-C) levels was observed without significant changes in serum albumin levels or proteinuria. The mean LDL-C decrease was 36.8% ± 4.9% mmol/L at 4 weeks and remained unchanged throughout the follow-up period. In the control group, there were no significant changes in the levels of total cholesterol or LDL-C during the follow-up period. At the diagnosis of nephrotic syndrome, plasma PCSK9 levels were 334 ± 40 ng/mL and correlated significantly with serum LDL-C levels (r = 0.49, P = 0.023). Six months after starting treatment with PCSK9 inhibitors, plasma PCSK9 levels were significantly reduced to values of 190 ± 36 ng/mL (P = 0.001) with a mean relative reduction of 42.3% ± 12.6%. No local adverse effects were seen at the injection site and no significant changes were seen in the levels of transaminase, creatine phosphokinase, or aldolase.ConclusionPCSK9 inhibitors may be an effective and safe alternative for the treatment of hypercholesterolemia associated with refractory nephrotic syndrome.

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

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. 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. 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. 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 is associated with mortality in patients with septic shock: data from the ALBIOS study

Pro-protein convertase subtilisin/kexin 9 (PCSK9) is a proenzyme primarily known to regulate low-density lipoprotein receptor re-uptake on hepatocytes. Whether PCSK9 can concurrently trigger inflammation or not remains unclear. Here, we investigated the potential association between circulating levels of PCSK9 and mortality in patients with severe sepsis or septic shock. Plasma PCSK9 levels at days 1, 2 and 7 were measured in 958 patients with severe sepsis or septic shock previously enrolled in the Albumin Italian Outcome Sepsis (ALBIOS) trial. Correlations between levels of PCSK9 and pentraxin 3 (PTX3), a biomarker of disease severity, were evaluated with ranked Spearman's coefficients. Cox proportional hazards models were used to assess the association of PCSK9 levels at day 1 with 28- and 90-day mortality. Median plasma PCSK9 levels were 278 [182-452] ngmL-1 on day 1. PCSK9 correlated positively with PTX3 at the three time-points, and patients with septic shock within the first quartile of PCSK9 showed higher levels of PTX3. Similar mortality rates were observed in patients with severe sepsis across PCSK9 quartiles. Patients with septic shock with lower PCSK9 levels on day 1 (within the first quartile) showed the highest 28- and 90-day mortality rate as compared to other quartiles. In our sub-analysis of the ALBIOS trial, we found that patients with septic shock presenting with lower plasma PCSK9 levels experienced higher mortality rate. Further studies are warranted to better evaluate the pathophysiological role of PCSK9 in sepsis.

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

Background and aimsTo 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 resultsIn 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. ConclusionsThese results suggest a pivotal role of adipose tissue and insulin resistance on PCSK9 homeostasis in severely obese patients.

PCSK9 is Increased in Cerebrospinal Fluid of Individuals With Alcohol Use Disorder.

Recent studies have shown that alcohol use affects the regulation and expression of proprotein convertase subtilisin/kexin 9 (PCSK9). While a major role of PCSK9 in hepatic function and lipid regulation has been clearly established, other pleiotropic effects remain poorly understood. Existing research suggests a positive association between PCSK9 expression in the brain and psychopathology, with increased levels of PCSK9 in the cerebrospinal fluid (CSF) of individuals with dementia and epigenetic modifications of PCSK9 associated with alcohol use disorder (AUD). In this study, we hypothesized that chronic alcohol use would increase PCSK9 expression in CSF. PCSK9 levels in CSF were measured in individuals with AUD (n=42) admitted to an inpatient rehabilitation program and controls (n=25). CSF samples in AUD were assessed at 2 time points, at day 5 and day 21 after admission. Furthermore, plasma samples were collected and measured from the individuals with AUD. PCSK9 in CSF was significantly increased in the AUD group at day 5 and day 21 compared to the controls (p<0.0001). Plasma PCSK9 levels were correlated positively with CSF PCSK9 levels in AUD (p=0.0493). Our data suggest that PCSK9 is elevated in the CSF of individuals with AUD, which may indicate a potential role of PCSK9 in AUD. Additional studies are necessary to further elucidate the functions of PCSK9 in the brain.

Plasma PCSK9 levels and lipoprotein distribution are preserved in carriers of genetic HDL disorders

Proprotein convertase subtilisin/kexin 9 (PCSK9), a protein regulating the number of cell-surface LDL receptors (LDLR), circulates partially associated to plasma lipoproteins. How this interaction alters PCSK9 plasma levels is still unclear. In the present study, we took advantage of the availability of a large cohort of carriers of genetic HDL disorders to evaluate how HDL defects affect plasma PCSK9 levels and its distribution among lipoproteins. Plasma PCSK9 concentrations were determined by ELISA in carriers of mutations in LCAT, ABCA1, or APOAI genes, and lipoprotein distribution was analyzed by FPLC. Carriers of one or two mutations in the LCAT gene show plasma PCSK9 levels comparable to that of unaffected family controls (homozygotes, 159.4 ng/mL (124.9;243.3); heterozygotes, 180.3 ng/mL (127.6;251.5) and controls, 190.4 ng/mL (146.7;264.4); P for trend = 0.33). Measurement of PCSK9 in plasma of subjects carrying mutations in ABCA1 or APOAI genes confirmed normal values. When fractionated by FPLC, PCSK9 peaked in a region between LDL and HDL in control subjects. In carriers of all HDL defects, lipoprotein profile shows a strong reduction of HDL, but the distribution of PCSK9 was superimposable to that of controls. In conclusion, the present study demonstrates that in genetically determined low HDL states plasma PCSK9 concentrations and lipoprotein distribution are preserved, thus suggesting that HDL may not be involved in PCSK9 transport in plasma.

Abstract 545: Evolocumab Alters LDL-cholesterol Levels but Not Glycemic Profile and Liver Lipids in Chow Fed and High fat/Cholesterol/Fructose Fed Golden Syrian Hamsters

Background: Beside its effect on LDL-cholesterol levels, proprotein convertase subtilisin/kexin9 (PCSK9) could also be linked to glucose metabolism and non-alcoholic fatty liver diseases. Here we evaluated whether Evolocumab (EVO), a monoclonal antibody targeting PCSK9, may alter glycemic profile and liver lipids in hamsters. Methods: Hamsters were maintained on either a control chow (CC) or high fat/cholesterol/fructose (HFCF) diet for 5 weeks. After 2 weeks of diet, hamsters were randomized into 2 groups, control or EVO at 30mg/kg s.c. once weekly for 3 weeks, to evaluate the effects on lipoprotein/glycemic profiles, and liver lipids. Results: When compared with CC diet, HFCF diet significantly increased total cholesterol and LDL-cholesterol levels by 87% and 102%. Hamsters fed the HFCF diet also showed higher HOMA-IR index of insulin resistance, higher blood glucose area under the curve (AUC) during an oral glucose tolerance test (OGTT), and higher liver lipids (triglycerides: +197%, total cholesterol: +421%, both p&lt;0.001 vs. CC). However, plasma PCSK9 levels were markedly reduced by 47% in HFCF fed hamsters (p&lt;0.001 vs. CC). As expected, treatment with EVO significantly increased hepatic LDL-receptor protein levels by 1.74-fold and reduced plasma LDL-cholesterol by up to 28% in CC fed hamsters (p&lt;0.01 vs. CC control). The LDL-cholesterol reduction was also observed in HFCF fed hamsters treated with EVO, but to a lesser extent (up to 16%). In both CC and HFCF fed hamsters, EVO did not alter fasting glycemia and plasma insulin levels. IN CC fed hamsters, EVO transiently reduced blood glucose levels by 15% at time 15 minutes (p&lt;0.01 vs. CC control) after an oral glucose load. However, EVO did not change blood glucose levels AUC or plasma insulin levels during the OGTT, in neither CC nor HFCF fed hamsters. As well, no change in liver lipids levels was observed in CC or HFCF fed hamsters treated with EVO. Conclusion: Our data indicate that diet-induced insulin resistance and liver steatosis in hamsters are not associated with elevated plasma PCSK9 levels, and are not altered by Evolocumab. Whether these results are specific to our hamster model and can translate to humans remains to be further investigated.

Plasma PCSK9 levels and lipoprotein distribution are preserved in patients with severe hypoalphalipoproteinemia

Aim: Proprotein convertase subtilisin/kexin 9 (PCSK9), a protein regulating the number of cell-surface low-density lipoprotein (LDL) receptors (LDL-R), circulates partially associated to LDL, high-density lipoproteins (HDL) and lipoprotein (a). How this interaction alters PCSK9 plasma levels is still unclear. In the present study, we investigated whether a condition of familial hypoalphalipoproteinemia (FHA), due to genetic mutations in LCAT, ABCA1 or APOAI genes, could alter PCSK9 levels and distribution among different lipoproteins.

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

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

Abstract 16404: CETP Inhibitor K-312 Lowers PCSK9 Expression and LDL Cholesterol Levels in vivo

Background: Despite potent LDL-cholesterol (LDL-C) therapies, substantial residual cardiovascular risk remains. Proprotein convertase subtilisin/kexin 9 (PCSK9) is a promising target for lowering LDL-C. We recently demonstrated that K-312, originally found as a cholesteryl ester transfer protein (CETP) inhibitor, decreased PCSK9 expression in vitro through the reduction of its promoter activity. The present study has further examined the underlying molecular mechanisms and in vivo effects of K-312 on PCSK9 levels using mass spectrometry. Methods and Results: CETP silencing by siRNA in the human hepatocyte cell line HepG2 did not compromise suppression of PCSK9 expression by K-312, indicating a mechanism independent of CETP inhibition. Transcription factors sterol-regulatory element binding protein (SREBP)-1 and SREBP-2 bind to the sterol regulatory element (SRE) of PCSK9 promoter when their precursor forms are cleaved into active forms. K-312 treatment decreased binding of SREBP-1 and SREBP-2 to SRE of the PCSK9 promoter (chromatin immunoprecipitation) and active forms of SREBP-1 and SREBP-2 (western blotting), suggesting the suppression of PCSK9 expression by K-312 involves SREBP-1 and SREBP-2. We then examined the effects of K-312 in cholesterol-fed New Zealand White rabbits administered either vehicle (N=7) or K-312 30 mg/kg (N=7) for 2 weeks. K-312 treatment decreased LDL-C (vehicle: 272.5 ± 42.2 mg/dl; K-312: 193.0 ± 36.5 mg/dl), increased HDL cholesterol (vehicle: 29.9 ± 3.7 mg/dl; K-312: 93.3 ± 14.7 mg/dl) and decreased PCSK9 mRNA levels in the liver by 63%. We further used two mass spectrometry-based approaches to measure PCSK9 levels in rabbit plasma: spectral counting and a novel high resolution (HR)-MS/MS quantification method. Immunoprecipitation of PCSK9 successfully enriched PCSK9 signal. Spectral counting and HR-MS/MS of PCSK9 peptides both demonstrated that K-312 treatment significantly decreased plasma PCSK9 levels by 76% (p&lt;0.01) and 60% (p&lt;0.05), respectively. Conclusion: K-312 may lower LDL cholesterol levels by suppressing CETP activity and PCSK9 expression, serving as a novel therapy for dyslipidemia and cardiovascular disease.

Loss of Plasma Proprotein Convertase Subtilisin/Kexin 9 (PCSK9) After Lipoprotein Apheresis

Lipoprotein apheresis (LA) reduces low-density lipoprotein (LDL) levels in patients with severe familial hypercholesterolemia (FH). We have recently reported that >30% of plasma proprotein convertase subtilisin/kexin 9 (PCSK9) is bound to LDL, thus we predicted that LA would also reduce plasma PCSK9 levels by removing LDL. Pre- and post-apheresis plasma from 6 patients with familial hypercholesterolemia on 3 consecutive treatment cycles was used to determine changes in PCSK9 levels. LA drastically reduced plasma LDL (by 77 ± 4%). Concomitantly, PCSK9 levels fell by 52 ± 5%, strongly correlating with the LDL drop (P=0.0322; r(2)=0.26), but not with decreases in triglyceride (49 ± 13%) or high-density lipoprotein levels (18 ± 2%). Levels of albumin, creatinine, and CK-MB did not show significant changes after LA. Similar to LDL, PCSK9 levels returned to pretreatment values between cycles (2-week intervals). Fractionation of pre- and post-apheresis plasma showed that 81 ± 11% of LDL-bound PCSK9 and 48 ± 14% of apolipoprotein B-free PCSK9 were removed. Separation of whole plasma, purified LDL, or the apolipoprotein B-free fraction through a scaled-down, experimental dextran sulfate cellulose beads column produced similar results. Our results show, for the first time, that modulation of LDL levels by LA directly affects plasma PCSK9 levels, and suggest that PCSK9 reduction is an additional benefit of LA. Because the loss of PCSK9 could contribute to the LDL-lowering effect of LA, then (1) anti-PCSK9 therapies may reduce frequency of LA in patients currently approved for therapy, and (2) LA and anti-PCSK9 therapies may be used synergistically to reduce treatment burden.

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

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

The unique role of proprotein convertase subtilisin/kexin 9 in cholesterol homeostasis

The LDL receptor (LDLR) plays an essential role in the regulation of plasma (LDL) cholesterol concentrations by virtue of its ability to clear plasma LDL. Down-regulation of the LDLR by proprotein convertase subtilisin/kexin 9 (PCSK9) has recently emerged as a regulatory mechanism that controls plasma LDL cholesterol concentrations. Studies in which PCSK9 is over-expressed in mice, have demonstrated that PCSK9, by enhancing hepatic LDLR degradation, decreases the availability of the LDLR for LDL uptake, resulting in increased plasma LDL cholesterol levels. However, PCSK9 has also recently been shown to mediate down-regulation of surface receptors other than the LDLR, suggesting that it may have much broader roles than initially thought.

Errata. PCSK9 function and physiology

PCSK9 has exploded onto center stage of plasma cholesterol metabolism, raising hopes for a new strategy to treat hypercholesterolemia. PCSK9 in a plasma protein that triggers increased degradation of the LDL receptor. Gain-of-function mutations in PCSK9 reduce LDL receptor levels in the liver, resulting in high levels of LDL cholesterol in the plasma and increased susceptibility to coronary heart disease. Loss-of-function mutations lead to higher levels of the LDL receptor, lower LDL cholesterol levels, and protection from coronary heart disease. Two papers in this issue of the Journal of Lipid Research exemplify the rapid pace of progress in understanding PCSK9 molecular interactions and physiology. Dr. Shilpa Pandit and coworkers from Merck Research Laboratories describe the functional basis for the hypercholesterolemia associated with gain-of-function missense mutations in PCSK9. Dr. Jay Horton's group at UT Southwestern describe the kinetics and metabolism of PCSK9 and the impact of PCSK9 on LDL receptors in the liver and adrenal gland.