Plasma Proprotein Convertase Subtilisin/kexin Type 9 Research Articles

RETRACTED: Plasma PCSK9 Levels and Clinical Outcomes in the TNT (Treating to New Targets) Trial: A Nested Case-Control Study

The purpose of this study was to investigate whether high levels of circulating proprotein convertase subtilisin kexin type 9 (PCSK9) would increase cardiovascular risk in statin-treated patients. Statins activate low-density lipoprotein (LDL) receptor gene expression, thus lowering plasma LDL levels. But statins also activate the expression of PCSK9, a secreted inhibitor of the LDL receptor, thereby limiting their beneficial effects. We have measured the plasma PCSK9 levels of 1,613 patients with stable coronary heart disease enrolled in the Treating to New Targets study, a randomized trial that compared the efficacy of high- versus low-dose atorvastatin. After a run-in period with atorvastatin 10 mg daily, patients were randomized to either continue with 10 mg or be up-titrated to 80 mg of atorvastatin, and followed during 5 years for major cardiovascular events (MCVEs). Circulating PCSK9 levels measured at randomization were predictive of clinical outcomes in the group randomized to remain on atorvastatin 10 mg (p = 0.039), but not in the group that intensified atorvastatin treatment to 80 mg (p = 0.24). Further, PCSK9 levels measured 1 year post-randomization did not change upon increase of the statin dose. PCSK9 levels predict cardiovascular events in patients treated with low-dose atorvastatin. (A Study to Determine the Degree of Additional Reduction in CV Risk in Lowering LDL Below Minimum Target Levels [TNT]; NCT00327691).

Serum levels of proprotein convertase subtilisin/kexin type 9 in subjects with familial hypercholesterolemia indicate that proprotein convertase subtilisin/kexin type 9 is cleared from plasma by low-density lipoprotein receptor–independent pathways

Secreted proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low-density lipoprotein receptor (LDLR) at the cell surface and disrupts the normal recycling of the LDLR. When human PCSK9 is injected into LDLR-deficient mice, PCSK9 is still rapidly cleared by the liver. This finding may suggest that PCSK9 is physiologically also cleared by receptors other than the LDLR. An alternative explanation could be that PCSK9 has undergone modifications during purification and is cleared by scavenger receptors on liver endothelial sinusoidal cells when injected into mice. If the only mechanism for clearing PCSK9 in humans is through the LDLR, one would expect that differences in the number of LDLRs would affect the plasma levels of low-density lipoprotein cholesterol (LDLC) and PCSK9 in a similar fashion. In this study, levels of LDLC and PCSK9 were measured in familial hypercholesterolemia (FH) homozygotes, FH heterozygotes, and normocholesterolemic subjects. The ratio between the levels of LDLC and PCSK9 was 1.7-fold higher in FH heterozygotes and 3-fold higher in FH homozygotes than in the normocholesterolemic subjects. Thus, defective LDLRs have a greater impact on the levels of LDLC than on the levels of PCSK9. By assuming that the rate of PCSK9 synthesis is similar in the 3 groups, this finding suggests that in humans, plasma PCSK9 is also cleared by LDLR-independent mechanisms.

Plasma Lipoprotein-associated Phospholipase A2 Is Inversely Correlated with Proprotein Convertase Subtilisin-kexin Type 9

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) is a pro-atherogenic phospholipase A(2), which is predominantly complexed to low-density lipoprotein (LDL) particles. Proprotein convertase subtilisin-kexin type 9 (PCSK9) provides a key step in LDL metabolism by stimulating LDL receptor degradation. We determined relationships between plasma PCSK9 and Lp-PLA(2) mass. Lp-PLA(2) mass (turbidimetric immunoassay), PCSK9 (enzyme-linked immunosorbent assay) and (apo) lipoproteins were measured in 53 nondiabetic subjects (27 women) with body mass index <30 kg/m(2). Lp-PLA(2) and PCSK9 levels were both correlated positively with LDL cholesterol and non-high-density lipoprotein (HDL) cholesterol (r = 0.330 to r = 0.382, p ≤0.02). Remarkably, Lp-PLA(2) was inversely related to PCSK9 (r = -0.388, p = 0.004). The Lp-PLA(2)/apolipoprotein B ratio, as a measure of the Lp-PLA(2) content in apolipoprotein B-containing lipoproteins, was also inversely correlated with PCSK9 (r = -0.575, p <0.001). The inverse relationships of Lp-PLA(2) (p = 0.023) and the Lp-PLA(2)/apolipoprotein B ratio (p = 0.001) with PCSK9 levels remained significant after controlling for age, gender, triglycerides and HDL cholesterol. Despite increasing effects on LDL cholesterol, higher PCSK9 levels are unlikely to confer impaired Lp-PLA(2) metabolism. We propose to evaluate the possible influence of PCSK9 inhibiting strategies on Lp-PLA(2) regulation and vice versa to determine effects of Lp-PLA(2) inhibitors on the PCSK9 pathway.

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

The aim of the present study was to investigate the relationship between circulating PCSK9 (proprotein convertase subtilisin kexin type9) and FCHL (familial combined hyperlipidaemia) and, when positive, to determine the strength of its heritability. Plasma PCSK9 levels were measured in FCHL patients (n=45), NL (normolipidaemic) relatives (n=139) and their spouses (n=72). In addition, 11 FCHL patients were treated with atorvastatin to study the response in PCSK9 levels. PCSK9 levels were higher in FCHL patients compared with NL relatives and spouses: 96.1 compared with 78.7 and 82.0ng/ml (P=0.004 and P=0.002 respectively). PCSK9 was significantly associated with both TAG (triacylglycerol) and apolipoprotein B levels (P<0.001). The latter relationship was accounted for by LDL (low-density lipoprotein)-apolipoprotein B (r=0.31, P=0.02), not by VLDL (very-low-density lipoprotein)-apolipoprotein B (r=0.09, P=0.49) in a subgroup of subjects (n=59). Heritability calculations for PCSK9 using SOLAR and FCOR software yielded estimates of 67-84% respectively (P<0.0001). PCSK9 increased from 122 to 150ng/ml in 11 FCHL patients treated with atorvastatin (40mg) once daily for 8weeks (P=0.018). In conclusion, plasma PCSK9 is a heritable trait associated with both FCHL diagnostic hallmarks. These results, combined with the significant rise in PCSK9 levels after statin therapy, warrant further studies in order to unravel the exact role of PCSK9 in the pathogenesis and treatment of this highly prevalent genetic dyslipidaemia.

135 RIP2 LINKS IMMUNE SIGNALING AND SUBENDOTHELIAL LIPID ACCUMULATION BY REGULATING TLR4-DEPENDENT LIPID UPTAKE IN MACROPHAGES

Gain-of-function mutations within proprotein convertase subtilisin kexin type 9 (PCSK9) are linked to familial autosomal dominant hypercholesterolaemia, a disease characterized by elevated plasma concentrations of cholesterol associated with low-density lipoproteins (LDLs). Conversely, PCSK9 loss-of-function mutations result in low levels of LDL cholesterol (LDLC) and protect against coronary heart disease. Although compelling evidence indicates that PCSK9 impairs the LDLR pathway, its role in cholesterol metabolism remains incompletely defined. In the past two years, several new biochemical findings, including the PCSK9 crystal structure and the identification of several transcriptional repressors, were reported. Moreover, new clinical and epidemiological data have revealed the correlation between plasma PCSK9 concentrations and LDLC levels.

Plasma proprotein convertase subtilisin kexin type 9 is not altered in subjects with impaired glucose metabolism and type 2 diabetes mellitus, but its relationship with non-HDL cholesterol and apolipoprotein B may be modified by type 2 diabetes mellitus: The CODAM study

ObjectiveType 2 diabetes mellitus (T2DM) is associated with elevated plasma apolipoprotein B and triglycerides levels, reduced HDL cholesterol and the presence of small-dense LDL particles. The present study was conducted to investigate the role of plasma proprotein convertase subtilisin kexin type 9 (PCSK9) levels, a regulator of LDL-receptor expression, in the occurrence of diabetic dyslipidemia. MethodsPlasma PCSK9 was measured in a cohort of subjects with normal glucose metabolism (NGM; n=288), impaired glucose metabolism (IGM; n=121) and type 2 diabetes mellitus (T2DM; n=139) to study whether its relation with plasma apolipoprotein B, triglycerides, total cholesterol, non-HDL cholesterol, LDL cholesterol and HDL cholesterol differed by levels of glucose metabolism status. ResultsPlasma PCSK9 levels were not different between the three groups (82, 82 and 80ng/mL in NGM, IGM and T2DM, respectively). PCSK9 was positively associated with total cholesterol, non-HDL cholesterol, LDL cholesterol, apolipoprotein B and triglycerides levels in all subgroups. The regression slopes for the associations with non-HDL cholesterol were steeper among individuals with T2DM than with NGM (β=0.016 versus β=0.009, p-interaction=0.05). Similar results were obtained for the relation with apolipoprotein B (β=0.004 versus β=0.002, p-interaction=0.09). ConclusionsAlthough glucose metabolism status per se is not associated with plasma PCSK9 levels, the presence of T2DM may modify the relation between plasma PCSK9 and non-HDL cholesterol and apolipoprotein B. These observations should be regarded as hypothesis generating for further studies aimed at elucidating the role of PCSK9 in the pathogenesis and treatment of diabetic dyslipidemia.

Comparison of effects of bezafibrate and fenofibrate on circulating proprotein convertase subtilisin/kexin type 9 and adipocytokine levels in dyslipidemic subjects with impaired glucose tolerance or type 2 diabetes mellitus: Results from a crossover study

BackgroundBezafibrate and fenofibrate show different binding properties against peroxisome proliferator-activated receptor subtypes, which could cause different clinical effects on circulating proprotein convertase subtilisin/kexin type 9 (PCSK9) levels and on various metabolic markers. MethodsAn open, randomized, four-phased crossover study using 400mg of bezafibrate or 200mg of fenofibrate was performed. Study subjects were 14 dyslipidemia with impaired glucose tolerance or type 2 diabetes mellitus (61±16 years, body mass index (BMI) 26±3kg/m2, total cholesterol (TC) 219±53mg/dL, triglyceride (TG) 183±83mg/dL, high-density lipoprotein-cholesterol (HDL-C) 46±8mg/dL, fasting plasma glucose 133±31mg/dL and HbA1c 6.2±0.8%). Subjects were given either bezafibrate or fenofibrate for 8 weeks, discontinued for 4 weeks and then switched to the other fibrate for 8 weeks. Circulating PCSK9 levels and other metabolic parameters, including adiponectin, leptin and urine 8-hydroxy-2′-deoxyguanosine (8-OHdG) were measured at 0, 8, 12 and 20 weeks. ResultsPlasma PCSK9 concentrations were significantly increased (+39.7% for bezafibrate and +66.8% for fenofibrate, p<0.001) in all patients except for one subject when treated with bezafibrate. Both bezafibrate and fenofibrate caused reductions in TG (−38.3%, p<0.001 vs. −32.9%, p<0.01) and increases in HDL-C (+18.0%, p<0.001 vs. +11.7%, p<0.001). Fenofibrate significantly reduced serum cholesterol levels (TC, −11.2%, p<0.01; non-HDL-C, −17.3%, p<0.01; apolipoprotein B, −15.1%, p<0.01), whereas bezafibrate significantly improved glucose tolerance (insulin, −17.0%, p<0.05) and metabolic markers (γ-GTP, −38.9%, p<0.01; adiponectin, +15.4%, p<0.05; urine 8-OHdG/Cre, −9.5%, p<0.05). ConclusionBoth bezafibrate and fenofibrate increased plasma PCSK9 concentrations. The addition of a PCSK9 inhibitor to each fibrate therapy may achieve beneficial cholesterol lowering along with desirable effects of respective fibrates.

The Correlation between Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) and Insulin Resistance and the Components of Atherogenic Lipoprotein Phenotype in Males with Central Obesity

BACKGROUND: Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) promotes the degradation of LDL receptor in hepatocytes. in vitro studies have proven that insulin increases the expression of PCSK9. Insulin resistance, a common condition in central obesity is characterized by dyslipidemia called Atherogenic Lipoprotein Phenotype (ALP). This study aimed to investigate the correlation between insulin resistance (HOMA-IR) and PCSK9, and to analyze whether this condition is related to the development of ALP in central obesity.METHODS: This is an observational study with crosssectional design. The subjects consisted of 62 male adults with central obesity, aged 30-60 years old. ELISA was used to measure plasma PSCK9.RESULTS: The mean plasma PCSK9 concentration of the samples was 283.7 ng/mL. PCSK9 had positive linear correlation with HOMA-IR (r=0.225, p=0.045) and Apo B (r=0.245, p=0.055). After controlling of HOMA-IR, PCSK9 had positive linear correlation with triglycerides (r=0.352, p=0.045). In population with HOMA-IR &gt;2, crosstabs analysis showed that PCSK9 had significant correlation with triglycerides and Apo B with an odd ratio of 6,125 (r=0.376, p=0.037). Triglyceride showed significant negative correlation with HDL cholesterol and ratio of LDL/Apo B, but neither HOMA-IR nor PCSK9 did.CONCLUSION: In males with central obesity, PCSK9 is one of the factors mediating the occurence of ALP in insulin resistance.KEYWORDS: PCSK9, insulin resistance, atherogenic lipoprotein phenotype

Fasting reduces plasma proprotein convertase, subtilisin/kexin type 9 and cholesterol biosynthesis in humans

Proprotein convertase, subtilisin/kexin type 9 (PCSK9), a key regulator of plasma LDL-cholesterol (LDL-c) and cardiovascular risk, is produced in liver and secreted into plasma where it binds hepatic LDL receptors (LDLR), leading to their degradation. PCSK9 is transcriptionally activated by sterol response element-binding protein (SREBP)-2, a transcription factor that also activates all genes for cholesterol synthesis as well as the LDLR. Here we investigated the relationship between plasma PCSK9 levels and the lathosterol-to-cholesterol ratio, a marker of cholesterol biosynthesis, in 18 healthy subjects during a 48 h fast. In all individuals, plasma PCSK9 levels declined steadily during the fasting period, reaching a nadir at 36 h that was ∼58% lower than levels measured in the fed state (P < 0.001). Similarly, the lathosterol-to-cholesterol ratio declined in parallel with plasma PCSK9 concentrations during the fast, reaching a nadir at 36 h that was ∼28% lower than that measured in the fed state (P = 0.024). In summary, fasting has a marked effect on plasma PCSK9 concentrations, which is mirrored by measures of cholesterol synthesis in humans. Inasmuch as cholesterol synthesis and PCSK9 are both regulated by SREBP-2, these results suggest that plasma PCSK9 levels may serve as a surrogate marker of hepatic SREBP-2 activity in humans.

Beyond LDL Cholesterol, a New Role for PCSK9

Elevated low-density lipoprotein cholesterol (LDLC) levels in the plasma is the most important causative factor of atherosclerosis and associated ischemic cardiovascular diseases. The LDL receptor (LDLR) is the preferential pathway through which LDLs are cleared from the circulation. LDLs bound to the LDLR are internalized into clathrin-coated pits and subsequently undergo lysosomal degradation, whereas the LDLR is recycled back to the plasma membrane. See accompanying article on page 1333 Familial hypercholesterolemia (FH) is an autosomal dominant disorder associated with elevated LDL levels and premature coronary heart disease. FH is caused primarily by mutations of the LDLR or of apolipoprotein B100 (apoB100), the protein component of LDL that interacts with the LDLR. In 2003, “gain of function” mutations on a newly identified gene, proprotein convertase subtilisin/kexin type 9 ( PCSK9), were associated with FH. In 2005, a causative association was established between “loss of function” mutations in PCSK9 and low LDLC levels in 2% of the African-American population. The coronary heart disease risk in these individuals was reduced by 88%. As a result of these landmark studies (reviewed in Reference 1), PCSK9 became the subject of intensive research to discover the underlying mechanisms. PCSK9 is a serine protease mainly expressed in the liver and the intestine. It acts by reducing the amount of LDLR in hepatocytes. This was demonstrated in vitro and in mouse models …

Association between plasma PCSK9 and gamma-glutamyl transferase levels in diabetic patients

Background Proprotein convertase subtilisin kexin type 9 (PCSK9) is a secreted proprotein convertase acting as a natural inhibitor of the low-density lipoprotein (LDL) receptor. Here, we prospectively investigated the relationship between the circulating levels of PCSK9 and metabolic parameters in 117 diabetic patients. Results Plasma PCSK9 level was significantly higher in type 2 than in type 1 diabetes ( P = 0.04), in diabetic patients under statins ( P < 10 −4) and in those with macrovascular complications ( P = 0.002). Univariable regression analysis revealed that plasma PCSK9 level correlated positively with age ( P = 0.003), body mass index ( P = 0.04), systolic blood pressure (SBP) ( P = 0.01), gamma-glutamyl transferase (GGT) levels ( P = 0.0002) and statin treatment ( P = 0.001). In a multivariable linear regression analysis, PCSK9 correlated positively with GGT level ( β = 21.91, P = 0.0019) after adjustment for gender, age, type of diabetes, statin treatment, BMI, SBP and HbA1c. Conclusion PCSK9 level was independently associated with GGT level in diabetic patients, suggesting potential interaction between PCSK9 and liver function.

Healthy Individuals Carrying the PCSK9 p.R46L Variant and Familial Hypercholesterolemia Patients Carrying PCSK9 p.D374Y Exhibit Lower Plasma Concentrations of PCSK9

We measured plasma PCSK9 concentrations in healthy men with a PCSK9 (proprotein convertase subtilisin/kexin type 9) loss-of-function variant (p.R46L), in statin-treated patients with a clinical diagnosis of familial hypercholesterolemia (FH) and carrying a PCSK9 gain-of-function mutation (p.D374Y), and in statin-treated patients with FH due to different genetic causes. PCSK9 was measured with a previously described ELISA. In 81 healthy middle-aged Caucasian men, the PCSK9 concentration was significantly associated with the concentrations of total cholesterol (r = 0.42; P < 0.0001), LDL cholesterol (r = 0.34; P = 0.01), and triglycerides (r = 0.25; P = 0.02). In p.R46L carriers, mean (SD) concentrations of PCSK9 were 15% lower than in RR individuals [65.5 microg/L (21.6 microg/L) vs 77.5 microg/L (18.2 microg/L); P = 0.03]. In patients with the p.D374Y variant (n = 7), the mean PCSK9 concentration was significantly lower than in the combined group of patients with an LDLR (low density lipoprotein receptor) mutation (n = 25), an APOB [apolipoprotein B (including Ag(x) antigen)] variant encoding p.R3527Q (n = 6), or no detectable mutation (n = 14) [96.4 microg/L (42.5 microg/L) vs 151.6 microg/L (69.6 microg/L); P = 0.02]. Two of the 14 patients with no mutation had PCSK9 concentrations below the mean for p.D374Y carriers; sequencing of the PCSK9 gene and promoter revealed no mutations. Among 409 FH patients, we identified 6 carriers of the promoter variant -287G>A (1.5%), a frequency similar to that (1.0%) previously reported for 2772 healthy men in the UK. In neither group was the -287G>A variant associated with differences in lipid traits. The loss-of-function p.R46L variant is associated with the expected lower concentrations of circulating PCSK9; the gain-of-function p.D374Y mutation is also associated with lower concentrations, presumably because of the higher affinity of this variant for the LDL receptor and its more rapid clearance. In treated FH patients, a low plasma PCSK9 concentration does not appear to be a useful screening tool for identifying novel PCSK9 mutations.

Plasma Proprotein Convertase Subtilisin/Kexin Type 9: A Marker of LDL Apolipoprotein B-100 Catabolism?

Experimental studies suggest that proprotein convertase subtilisin/kexin type 9 (PCSK9) is an important regulator of LDL metabolism because of its ability to facilitate degradation of the LDL receptor. We investigated the association between plasma PCSK9 concentration and LDL apolipoprotein B-100 (apo B-100) metabolism in men with a wide range of body mass index values. We used GC-MS to study the kinetics of LDL apo B-100 after intravenous administration of deuterated leucine and analyzed the data by compartmental modeling. The plasma PCSK9 concentration was measured by ELISA. Univariate regression analysis revealed the plasma PCSK9 concentration to be significantly and positively correlated with cholesterol (r = 0.543; P = 0.011), LDL cholesterol (r = 0.543; P = 0.011), apo B-100 (r = 0.548; P = 0.010), and LDL apo B-100 concentrations (r = 0.514; P = 0.023), and inversely correlated with the LDL apo B-100 fractional catabolic rate (FCR) (r = -0.456; P = 0.038). The association between plasma PCSK9 concentration and the LDL apo B-100 FCR remained statistically significant after adjusting for age, obesity, plasma insulin, homeostasis model assessment score, and dietary energy; however, this association had borderline significance after adjusting for plasma lathosterol. In men, variation in plasma PCSK9 concentration influences the catabolism of LDL apo B-100. This finding appears to be independent of obesity, insulin resistance, energy intake, and age.

PCSK9 Dominant Negative Mutant Results in Increased LDL Catabolic Rate and Familial Hypobetalipoproteinemia

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a central player in the regulation of cholesterol homeostasis, increasing the low-density lipoprotein (LDL) receptor degradation. Our study aimed at exploring the pathogenic consequences in vivo and in vitro of a PCSK9 prodomain mutation found in a family with hypobetalipoproteinemia (FHBL). A white 49-year-old diabetic man had profound FBHL (LDLC: 16 mg/dL) whereas his daughter and sister displayed a milder phenotype (LDLC 44 mg/dL and 57 mg/dL, respectively), all otherwise healthy with a normal liver function. A monoallelic PCSK9 double-mutant R104C/V114A cosegregated with FBHL, with no mutation found at other FHBL-causing loci. A dose-effect was also found in FBHL relatives for plasma APOB and PCSK9 (very-low to undetectable in proband, approximately 50% decreased in sister and daughter) and LDL catabolic rate (256% and 88% increased in proband and daughter). Transient transfection in hepatocytes showed severely impaired processing and secretion of the double mutant which acted as a dominant negative over secretion of wild-type PCSK9. These results show that heterozygous PCSK9 missense mutations may associate with profound hypobetalipoproteinemia and constitute the first direct evidence in human that decrease of plasma LDLC concentrations associated to PCSK9 LOF mutations are attributable to an increased clearance rate of LDL.

Plasma PCSK9 Is Associated with Age, Sex, and Multiple Metabolic Markers in a Population-Based Sample of Children and Adolescents

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a protein convertase that posttranslationally promotes the degradation of the low-density lipoprotein receptor (LDLR) in hepatocytes and increases plasma LDL cholesterol (LDL-C). Heterozygote gain-of-function mutations of PCSK9 are associated with the familial hypercholesterolemia phenotype, whereas loss-of-function variants are associated with reduced LDL-C concentrations and lower coronary risk. Plasma PCSK9 correlates with body mass index, triglyceridemia, total cholesterol, and LDL-C in adults, but no data are available in youth. We studied 1739 French Canadian youth ages 9, 13, and 16 years who participated in the Quebec Child and Adolescent Health and Social Survey, a province-wide school-based survey conducted in 1999. An ELISA assay was used to measure plasma PSCK9. The mean (SD) plasma PCSK9 concentration was 84.7 (24.7) microg/L in the sample. In boys, plasma PCSK9 decreased with age, whereas the inverse was true for girls. There were statistically significant positive associations between PCSK9 and fasting glucose, insulin, and HOMA-IR (homeostasis model assessment of insulin resistance). In multivariable analysis, a 10% higher fasting insulin was associated with a 1%-2% higher PCSK9 in both sexes. There were also positive associations between PCSK9 and total cholesterol, LDL-C, and triglycerides, as well as with HDL-C and apolipoproteins A1 and B. PCSK9 is associated with age, sex, and multiple metabolic markers in youth. A novel finding is that PCSK9 is associated with fasting insulinemia, which suggests that PCSK9 could play a role in the development of dyslipidemia associated with the metabolic syndrome. .

Function and distribution of circulating human PCSK9 expressed extrahepatically in transgenic mice

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is predominantly expressed in liver and regulates cholesterol metabolism by down regulating liver LDL receptor (LDLR) proteins. Here we report transgenic overexpression of human PCSK9 in kidney increased plasma levels of PCSK9 and subsequently led to a dramatic reduction in liver LDLR proteins. The regulation of LDLR by PCSK9 displayed tissue specificity, with liver being the most responsive tissue. Even though the PCSK9 transgene was highly expressed in kidney, LDLR proteins were suppressed to a lower extent in this tissue than in liver. Adrenal LDLR proteins were not regulated by elevated plasma PCSK9. hPCSK9 transgene expression and subsequent reduction of liver LDLR led to increases in plasma total cholesterol, LDL cholesterol, and ApoB, which were further increased by a high-fat, high-cholesterol diet. We also observed that the size distribution of hPCSK9 in transgenic mouse plasma was heterogeneous. In chow-fed mice, the majority of PCSK9 proteins were in free forms; however, feeding a high-fat, high-cholesterol diet resulted in a shift of hPCSK9 distribution toward larger complexes. PCSK9 distribution in human plasma also exhibited heterogeneity and individual variability in the percentage of PCSK9 in free form and in large complexes. We provide strong evidence to support that human PCSK9 proteins secreted from extrahepatic tissue are able to promote LDLR degradation in liver and increase plasma LDL. Our data also suggest that LDLR protein regulation by PCSK9 has tissue specificity, with liver being the most responsive tissue.

Therapeutic RNAi targeting PCSK9 acutely lowers plasma cholesterol in rodents and LDL cholesterol in nonhuman primates

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates low density lipoprotein receptor (LDLR) protein levels and function. Loss of PCSK9 increases LDLR levels in liver and reduces plasma LDL cholesterol (LDLc), whereas excess PCSK9 activity decreases liver LDLR levels and increases plasma LDLc. Here, we have developed active, cross-species, small interfering RNAs (siRNAs) capable of targeting murine, rat, nonhuman primate (NHP), and human PCSK9. For in vivo studies, PCSK9 and control siRNAs were formulated in a lipidoid nanoparticle (LNP). Liver-specific siRNA silencing of PCSK9 in mice and rats reduced PCSK9 mRNA levels by 50-70%. The reduction in PCSK9 transcript was associated with up to a 60% reduction in plasma cholesterol concentrations. These effects were shown to be mediated by an RNAi mechanism, using 5'-RACE. In transgenic mice expressing human PCSK9, siRNAs silenced the human PCSK9 transcript by >70% and significantly reduced PCSK9 plasma protein levels. In NHP, a single dose of siRNA targeting PCSK9 resulted in a rapid, durable, and reversible lowering of plasma PCSK9, apolipoprotein B, and LDLc, without measurable effects on either HDL cholesterol (HDLc) or triglycerides (TGs). The effects of PCSK9 silencing lasted for 3 weeks after a single bolus i.v. administration. These results validate PCSK9 targeting with RNAi therapeutics as an approach to specifically lower LDLc, paving the way for the development of PCSK9-lowering agents as a future strategy for treatment of hypercholesterolemia.

Plasma PCSK9 preferentially reduces liver LDL receptors in mice

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that regulates the expression of LDL receptor (LDLR) protein. Gain-of-function mutations in PCSK9 cause hypercholesterolemia, and loss-of-function mutations result in lower plasma LDL-cholesterol. Here, we investigate the kinetics and metabolism of circulating PCSK9 relative to tissue levels of LDLRs. The administration of recombinant human PCSK9 (32 microg) to mice by a single injection reduced hepatic LDLRs by approximately 90% within 60 min, and the receptor levels returned to normal within 6 h. The half-life of the PCSK9 was estimated to be approximately 5 min. Continuous infusion of PCSK9 (32 microg/h) into wild-type mice caused a approximately 90% reduction in hepatic LDLRs within 2 h and no associated change in the level of LDLR in the adrenals. Parallel studies were performed using a catalytically inactive form of PCSK9, PCSK9(S386A), and similar results were obtained. Infusion of PCSK9(D374Y), a gain-of-function mutation, resulted in accelerated clearance of the mutant PCSK9 and a greater reduction in hepatic LDLRs. Combined, these data suggest that exogenously administrated PCSK9 in plasma preferentially reduces LDLR protein levels in liver at concentrations found in human plasma and that PCSK9's action on the LDLR is not dependent on catalytic activity in vivo.

Plasma PCSK9 Concentrations Correlate with LDL and Total Cholesterol in Diabetic Patients and Are Decreased by Fenofibrate Treatment

Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes the degradation of the LDL receptor (LDLr) in hepatocytes, and its expression in mouse liver has been shown to decrease with fenofibrate treatment. We developed a sandwich ELISA using recombinant human PCSK9 protein and 2 affinity-purified polyclonal antibodies directed against human PCSK9. We measured circulating PCSK9 concentrations in 115 diabetic patients from the FIELD (Fenofibrate Intervention and Event Lowering in Diabetes) study before and after fenofibrate treatment. We found that plasma PCSK9 concentrations correlate with total (r = 0.45, P = 0.006) and LDL (r = 0.54, P = 0.001) cholesterol but not with triglycerides or HDL cholesterol concentrations in that cohort. After 6 weeks of treatment with comicronized fenofibrate (200 mg/day), plasma PCSK9 concentrations decreased by 8.5% (P = 0.041 vs pretreatment). This decrease correlated with the efficacy of fenofibrate, as judged by a parallel reduction in plasma triglycerides (r = 0.31, P = 0.015) and LDL cholesterol concentrations (r = 0.27, P = 0.048). We conclude that this decrease in PCSK9 explains at least in part the LDL cholesterol-lowering effects of fenofibrate. Fenofibrate might be of interest to further reduce cardiovascular risk in patients already treated with a statin.

GENDER DIFFERENCES IN RISK FACTOR CONTROL OF PATIENTS ON LIPID LOWERING DRUGS, A NATIONAL PRIMARY HEALTH CARE STUDY

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is highly expressed in the kidney, where its function remains unclear. In vitro data suggested that PCSK9 could impair the trafficking of the epithelial Na channel (ENaC). Here, we aimed at determining the consequences of PCSK9-deficiency on blood pressure, sodium balance and ENaC function in vivo in mice.Blood pressure was measured using non-invasive tail-cuff system or radiotelemetry under basal conditions in male and female PCSK9+/+ and PCSK9−/− mice, as well as in models of hypertension: l-NAME (2 mg/kg/day), angiotensin II (1 mg/kg/day) and deoxycorticosterone acetate (DOCA)-salt in male mice only. Plasma and urine electrolytes (Na+, K+, Cl−) were collected under basal conditions, after DOCA-salt and amiloride treatment. Renal expression of ENaC subunits was assessed by western blotting.PCSK9-deficiency did not alter both basal blood pressure and its increase in salt-insensitive (l-NAME) and salt-sensitive (Ang-II and DOCA-salt) hypertension models. Plasma PCSK9 concentrations were increased by 2.8 fold in DOCA-salt-induced hypertension. The relative expression of the cleaved, active, 30-kDa αENaC subunit was significantly increased by 32% in kidneys of PCSK9−/− mice under basal, but not under high-Na+ diet or DOCA-salt conditions. Amiloride increased urinary Na+ excretion to similar level in both genotypes, indicating that ENaC activity was not affected by PCSK9-deficiency.Despite an increase of cleaved αENaC under basal condition, PCSK9−/− mice display normal sodium balance and blood pressure regulation. Altogether, these data are reassuring regarding the development of PCSK9 inhibitors in hypercholesterolemia.