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      Serum PCSK9 Levels Distinguish Individuals Who Do Not Respond to High-Dose Statin Therapy with the Expected Reduction in LDL-C

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          Abstract

          The purpose of the present report was to examine whether proprotein convertase subtilisin/kexin type 9 (PCSK9) levels differ in individuals who do not exhibit expected reductions in low density lipoprotein cholesterol (LDL-C) with statin therapy. Eighteen nonresponder subjects treated with 80 mg atorvastatin treatment for 6 months without substantial reductions in LDL-C (ΔLDL-C: 2.6 ± 11.4%) were compared to age- and gender-matched atorvastatin responders (ΔLDL-C: 50.7 ± 8.5%) and placebo-treated subjects (ΔLDL-C: 9.9 ± 21.5%). Free PCSK9 was marginally higher in nonresponders at baseline ( P = 0.07) and significantly higher in atorvastatin responders after 6 months of treatment ( P = 0.04). The change in free PCSK9 over 6 months with statin treatment was higher ( P < 0.01) in atorvastatin responders (134.2 ± 131.5 ng/mL post- versus prestudy) than in either the nonresponders (39.9 ± 87.8 ng/mL) or placebo subjects (27.8 ± 97.6 ng/mL). Drug compliance was not lower in the nonresponders as assessed by pill counts and poststudy plasma atorvastatin levels. Serum PCSK9 levels, both at baseline and in response to statin therapy, may differentiate individuals who do versus those who do not respond to statin treatment.

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          Decreased plasma cholesterol and hypersensitivity to statins in mice lacking Pcsk9.

          PCSK9 encodes proprotein convertase subtilisin/kexin type 9a (PCSK9), a member of the proteinase K subfamily of subtilases. Missense mutations in PCSK9 cause an autosomal dominant form of hypercholesterolemia in humans, likely due to a gain-of-function mechanism because overexpression of either WT or mutant PCSK9 reduces hepatic LDL receptor protein (LDLR) in mice. Here, we show that livers of knockout mice lacking PCSK9 manifest increased LDLR protein but not mRNA. Increased LDLR protein led to increased clearance of circulating lipoproteins and decreased plasma cholesterol levels (46 mg/dl in Pcsk9(-/-) mice versus 96 mg/dl in WT mice). Statins, a class of drugs that inhibit cholesterol synthesis, increase expression of sterol regulatory element-binding protein-2 (SREBP-2), a transcription factor that activates both the Ldlr and Pcsk9 genes. Statin administration to Pcsk9(-/-) mice produced an exaggerated increase in LDLRs in liver and enhanced LDL clearance from plasma. These data demonstrate that PCSK9 regulates the amount of LDLR protein in liver and suggest that inhibitors of PCSK9 may act synergistically with statins to enhance LDLRs and reduce plasma cholesterol.
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            Effect of statins on skeletal muscle function.

            Many clinicians believe that statins cause muscle pain, but this has not been observed in clinical trials, and the effect of statins on muscle performance has not been carefully studied. The Effect of Statins on Skeletal Muscle Function and Performance (STOMP) study assessed symptoms and measured creatine kinase, exercise capacity, and muscle strength before and after atorvastatin 80 mg or placebo was administered for 6 months to 420 healthy, statin-naive subjects. No individual creatine kinase value exceeded 10 times normal, but average creatine kinase increased 20.8±141.1 U/L (P<0.0001) with atorvastatin. There were no significant changes in several measures of muscle strength or exercise capacity with atorvastatin, but more atorvastatin than placebo subjects developed myalgia (19 versus 10; P=0.05). Myalgic subjects on atorvastatin or placebo had decreased muscle strength in 5 of 14 and 4 of 14 variables, respectively (P=0.69). These results indicate that high-dose atorvastatin for 6 months does not decrease average muscle strength or exercise performance in healthy, previously untreated subjects. Nevertheless, this blinded, controlled trial confirms the undocumented impression that statins increase muscle complaints. Atorvastatin also increased average creatine kinase, suggesting that statins produce mild muscle injury even among asymptomatic subjects. This increase in creatine kinase should prompt studies examining the effects of more prolonged, high-dose statin treatment on muscular performance. URL: http://www.clinicaltrials.gov. Unique identifier: NCT00609063.
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              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.
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                Author and article information

                Journal
                J Lipids
                J Lipids
                JL
                Journal of Lipids
                Hindawi Publishing Corporation
                2090-3030
                2090-3049
                2014
                17 July 2014
                : 2014
                : 140723
                Affiliations
                1Department of Cardiology, Henry Low Heart Center, Hartford Hospital, 85 Seymour Street, Hartford, CT 06102, USA
                2Department of Health Sciences, University of Hartford, 200 Bloomfield Avenue, West Hartford, CT 06117, USA
                3Department of Cardiology, Hartford Hospital, 85 Seymour Street, Hartford, CT 06102, USA
                4Department of Kinesiology, University of Connecitcut, 2095 Hillside Road, Unit 1110, Storrs, CT 06269, USA
                5Department of Kinesiology, University of Massachusetts Amherst, 110 Totman Building, 30 Eastman Lane, Amherst, MA 01003, USA
                6Regeneron Pharmaceuticals, Inc., 777 Old Saw Mill River Road, Tarrytown, NY 10591, USA
                7University of Connecticut School of Medicine, 263 Farmington Avenue, Farmington, CT 06030, USA
                Author notes

                Academic Editor: Maurizio Averna

                Article
                10.1155/2014/140723
                4127223
                44418520-1065-4ff8-9943-ef0b560549f5
                Copyright © 2014 Beth A. Taylor et al.

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 18 June 2014
                : 8 July 2014
                : 9 July 2014
                Categories
                Research Article

                Biochemistry
                Biochemistry

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