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      The Circulating Inactive Form of Matrix Gla Protein (ucMGP) as a Biomarker for Cardiovascular Calcification

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          Abstract

          Objective: Matrix γ-carboxyglutamate (Gla) protein (MGP) is a vitamin K-dependent protein and a strong inhibitor of vascular calcification. Vitamin K deficiency leads to inactive uncarboxylated MGP (ucMGP), which accumulates at sites of arterial calcification. We hypothesized that as a result of ucMGP deposition around arterial calcification, the circulating fraction of ucMGP is decreased. Here we report on the development of an ucMGP assay and the potential diagnostic utility of monitoring serum ucMGP levels. Methods and Results: An ELISA-based assay was developed with which circulating ucMGP can be determined. Serum ucMGP levels were measured in healthy subjects (n = 165) and in four patient populations; patients who underwent angioplasty (n = 30), patients with aortic stenosis (n = 25), hemodialysis patients (n = 52), and calciphylaxis patients (n = 10). All four patient populations had significantly lower ucMGP levels. In angioplasty patients and in those with aortic stenosis, some overlap was observed with the control population. However, in the hemodialysis and calciphylaxis populations, virtually all subjects had ucMGP levels below the normal adult range. Conclusion: Serum ucMGP may be used as a biomarker to identify those at risk for developing vascular calcification. This assay may become an important tool in the diagnosis of cardiovascular calcification.

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          Premature coronary-artery atherosclerosis in systemic lupus erythematosus.

          Premature coronary artery disease is a major cause of illness and death in patients with systemic lupus erythematosus, but little is known about the prevalence, extent, and causes of coronary-artery atherosclerosis. We used electron-beam computed tomography to screen for the presence of coronary-artery calcification in 65 patients with systemic lupus erythematosus (mean [+/-SD] age, 40.3+/-11.6 years) and 69 control subjects (mean age, 42.7+/-12.6 years) with no history of coronary artery disease. When calcification was detected, the extent was measured by means of the Agatston score. The frequency of risk factors for coronary artery disease was compared in patients and controls, and the relation between the patients' clinical characteristics and the presence or absence of coronary-artery calcification was examined. The two groups were similar with respect to age, race, and sex. Coronary-artery calcification was more frequent in patients with lupus (20 of 65 patients) than in control subjects (6 of 69 subjects) (P=0.002). The mean calcification score was 68.9+/-244.2 in the patients and 8.8+/-41.8 (P<0.001) in controls. Levels of total, high-density lipoprotein, and low-density lipoprotein cholesterol were not elevated in patients with lupus, but levels of triglycerides (P=0.02) and homocysteine (P<0.001) were. Among patients with lupus, measures of disease activity were similar in those with and those without coronary-artery calcification, but those with calcification were more likely to be older (P<0.001) and male (P=0.008). In patients with systemic lupus erythematosus, the prevalence of coronary-artery atherosclerosis is elevated and the age at onset is reduced. Early detection of atherosclerosis may provide an opportunity for therapeutic intervention. Copyright 2003 Massachusetts Medical Society
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            Prognostic value of coronary artery calcium screening in subjects with and without diabetes.

            The study was done to determine the interaction of coronary artery calcium and diabetes mellitus for prediction of all-cause death. Diabetes is a strong risk factor for coronary artery disease (CAD) and is associated with an elevated overall mortality. Electron beam tomography (EBT) provides information on the presence of subclinical atherosclerosis and may be useful for risk stratification. We followed 10,377 asymptomatic individuals (903 diabetic patients) referred for EBT imaging. Primary end point was all-cause mortality, and the average follow-up was 5.0 +/- 3.5 years. Cox proportional hazard models, with and without adjustment for other risk factors, were developed to predict all-cause mortality. Patients with diabetes had a higher prevalence of hypertension and smoking (p < 0.001) and were older. The average coronary calcium score (CCS) for subjects with and for those without diabetes was 281 +/- 567 and 119 +/- 341, respectively (p < 0.0001). Overall, the death rate was 3.5% and 2.0% for subjects with and without diabetes (p < 0.0001). In a risk-factor-adjusted model, there was a significant interaction of CCS with diabetes (p < 0.00001), indicating that, for every increase in CCS, there was a greater increase in mortality for diabetic than for nondiabetic subjects. However, patients suffering from diabetes with no coronary artery calcium demonstrated a survival similar to that of individuals without diabetes and no detectable calcium (98.8% and 99.4%, respectively, p = 0.5). Mortality from all causes is increased in asymptomatic patients with diabetes in proportion to the screening CCS. Nonetheless, subjects without coronary artery calcium have a low short-term risk of death even in the presence of diabetes mellitus.
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              Natural history of alkaptonuria.

              Alkaptonuria, caused by mutations in the HGO gene and a deficiency of homogentisate 1,2-dioxygenase, results in an accumulation of homogentisic acid (HGA), ochronosis, and destruction of connective tissue. There is no effective therapy for this disorder, although nitisinone inhibits the enzyme that produces HGA. We performed a study to delineate the natural history of alkaptonuria. We evaluated 58 patients with alkaptonuria (age range, 4 to 80 years), using clinical, radiographic, biochemical, and molecular methods. A radiographic scoring system was devised to assess the severity of spinal and joint damage. Two patients were treated with nitisinone for 10 and 9 days, respectively. Life-table analyses showed that joint replacement was performed at a mean age of 55 years and that renal stones developed at 64 years, cardiac-valve involvement at 54 years, and coronary-artery calcification at 59 years. Linear regression analysis indicated that the radiographic score for the severity of disease began increasing after the age of 30 years, with a more rapid increase in men than in women. Twenty-three new HGO mutations were identified. In a 51-year-old woman, urinary HGA excretion fell from 2.9 to 0.13 g per day after a 10-day course of nitisinone (7 days at a dose of 0.7 mg per day and 3 days at 2.8 mg per day). In a 59-year-old woman, urinary HGA fell from 6.4 g to 1.7 g per day after nine days of treatment with nitisinone (0.7 mg per day). Plasma tyrosine levels in these patients rose from approximately 1.1 mg per deciliter (60 micromol per liter) in both to approximately 12.8 mg per deciliter (700 micromol per liter) and 23.6 mg per deciliter (1300 micromol per liter), respectively, with no clinical signs or symptoms. The reported data on the natural history of alkaptonuria provide a basis for the evaluation of long-term therapies. Although nitisinone can reduce HGA production in humans with homogentisate 1,2-dioxygenase deficiency, the long-term safety and efficacy of this treatment require further evaluation. Copyright 2002 Massachusetts Medical Society
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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                2008
                August 2008
                10 April 2008
                : 45
                : 5
                : 427-436
                Affiliations
                aVitaK, bCardiovascular Research Institute CARIM, and cDepartment of Human Biology NUTRIM, Maastricht University, Maastricht, The Netherlands; Departments of dCardiology and eNephrology and Clinical Immunology, RWTH University Hospital Aachen, Aachen, fKuratorium für Heimdialyse, Dialysis Center, Würselen, Germany
                Article
                124863 J Vasc Res 2008;45:427–436
                10.1159/000124863
                18401181
                24fe3fa6-e7e1-45de-9457-b648d5380e9b
                © 2008 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                History
                : 18 August 2007
                : 29 November 2007
                Page count
                Figures: 5, Tables: 3, References: 41, Pages: 10
                Categories
                Research Paper

                General medicine,Neurology,Cardiovascular Medicine,Internal medicine,Nephrology
                Extracellular matrix,Vitamin K,Matrix Gla protein,Arteries,Calcification,Atherosclerosis

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