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      Significant Association Between Bone-Specific Alkaline Phosphatase and Vascular Calcification of the Hand Arteries in Male Hemodialysis Patients

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          Abstract

          Background/Aims: Bone-specific alkaline phosphatase (BAP) hydrolyzes pyrophosphate, which inhibits vascular calcification. We examined association between serum BAP and vascular calcification of male hemodialysis patients. Methods: Hand roentgenography of 167 male maintenance hemodialysis patients was conducted, and visible vascular calcification of the hand arteries was evaluated. Serum levels of 3 bone formation markers (BAP, osteocalcin, and N-terminal propeptide of type I collagen) and 2 bone resorption markers (C-terminal telopeptide of type I collagen, and cross-linked N-telopeptide of type I collagen) were measured, along with serum intact parathyroid hormone (PTH). Results: Of 167 patients, visible vascular calcification was seen in 37 patients. Among the bone formation and resorption markers, serum BAP was significantly higher in patients with vascular calcification than in those without (p<0.05); although the other 5 serum bone markers were not significantly different between them. Multivariate logistic regression analyses revealed that log [BAP] was significantly associated with vascular calcification after adjustment for age, hemodialysis duration, presence of diabetes, log [intact PTH] and each of the other 5 bone markers (p<0.0001). Conclusions: Higher serum BAP, but not other bone markers, is significantly associated with the presence of vascular calcification in male hemodialysis patients.

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          Most cited references 27

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          Phosphate regulation of vascular smooth muscle cell calcification.

          Vascular calcification is a common finding in atherosclerosis and a serious problem in diabetic and uremic patients. Because of the correlation of hyperphosphatemia and vascular calcification, the ability of extracellular inorganic phosphate levels to regulate human aortic smooth muscle cell (HSMC) culture mineralization in vitro was examined. HSMCs cultured in media containing normal physiological levels of inorganic phosphate (1.4 mmol/L) did not mineralize. In contrast, HSMCs cultured in media containing phosphate levels comparable to those seen in hyperphosphatemic individuals (>1.4 mmol/L) showed dose-dependent increases in mineral deposition. Mechanistic studies revealed that elevated phosphate treatment of HSMCs also enhanced the expression of the osteoblastic differentiation markers osteocalcin and Cbfa-1. The effects of elevated phosphate on HSMCs were mediated by a sodium-dependent phosphate cotransporter (NPC), as indicated by the ability of the specific NPC inhibitor phosphonoformic acid, to dose dependently inhibit phosphate-induced calcium deposition as well as osteocalcin and Cbfa-1 gene expression. With the use of polymerase chain reaction and Northern blot analyses, the NPC in HSMCs was identified as Pit-1 (Glvr-1), a member of the novel type III NPCs. These data suggest that elevated phosphate may directly stimulate HSMCs to undergo phenotypic changes that predispose to calcification and offer a novel explanation of the phenomenon of vascular calcification under hyperphosphatemic conditions. The full text of this article is available at http://www.circresaha.org.
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            Progressive vascular calcification over 2 years is associated with arterial stiffening and increased mortality in patients with stages 4 and 5 chronic kidney disease.

            Vascular calcification is increasingly recognized as an important component of cardiovascular disease in chronic kidney disease. The objective of this study was to investigate prospectively the determinants, cardiovascular functional consequences, and survival associated with vascular calcification over 24 mo. A total of 134 patients (60 on hemodialysis, 28 on peritoneal dialysis, and 46 with stage 4 chronic kidney disease) were studied. Vascular calcification of the superficial femoral artery was assessed using multislice spiral computed tomography; pulse wave velocity; all medications and time-averaged biochemical parameters were recorded at baseline and 12 and 24 mo. A total of 101 patients remained at 24 mo. Progressive calcification was seen in 58 of 101 patients. Most (31 of 46) patients with an initial calcification score of zero did not develop calcification. The hemodialysis group demonstrated a greater degree of progression than patients who were on peritoneal dialysis or had stage 4 chronic kidney disease. Progressive calcification was associated with age, male gender, serum alkaline phosphatase, beta blockers, and lipid-lowering agents. Increases in vascular calcification correlated with increased arterial stiffness. Vascular calcification was present in 20 of 21 patients who died. Cox proportional hazard analysis identified change in calcification score, calcium intake from phosphate binders, and low albumin as risk factors for death. Patients with stages 4 and 5 chronic kidney disease and preexisting vascular calcification exhibit significantly increased calcification over 24 mo. Rapid progression of calcification is associated with arterial stiffness and mortality.
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              Upregulation of alkaline phosphatase and pyrophosphate hydrolysis: potential mechanism for uremic vascular calcification.

              Pyrophosphate is a potent inhibitor of medial vascular calcification where its level is controlled by hydrolysis via a tissue-nonspecific alkaline phosphatase (TNAP). We sought to determine if increased TNAP activity could explain the pyrophosphate deficiency and vascular calcification seen in renal failure. TNAP activity increased twofold in intact aortas and in aortic homogenates from rats made uremic by feeding adenine or by 5/6 nephrectomy. Immunoblotting showed an increase in protein abundance but there was no increase in TNAP mRNA assessed by quantitative polymerase chain reaction. Hydrolysis of pyrophosphate by rat aortic rings was inhibited about half by the nonspecific alkaline phosphatase inhibitor levamisole and was reduced about half in aortas from mice lacking TNAP. Hydrolysis was increased in aortic rings from uremic rats and all of this increase was inhibited by levamisole. An increase in TNAP activity and pyrophosphate hydrolysis also occurred when aortic rings from normal rats were incubated with uremic rat plasma. These results suggest that a circulating factor causes pyrophosphate deficiency by regulating TNAP activity and that vascular calcification in renal failure may result from the action of this factor. If proven by future studies, this mechanism will identify alkaline phosphatase as a potential therapeutic target.
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                Author and article information

                Journal
                KBR
                Kidney Blood Press Res
                10.1159/issn.1420-4096
                Kidney and Blood Pressure Research
                S. Karger AG
                1420-4096
                1423-0143
                2014
                November 2014
                16 September 2014
                : 39
                : 4
                : 299-307
                Affiliations
                aDepartment of Nephrology, Osaka City University Graduate School of Medicine, Osaka 545-8585; bShirasagi Hospital Kidney Center, Osaka 546-0002; cDepartment of Endocrinology, Metabolism and Molecular Medicine, Osaka City University Graduate School of Medicine, Osaka 545-8585, Japan
                Author notes
                *Eiji Ishimura, MD, PhD, Department of Nephrology, Osaka City University Graduate School of Medicine, 1-4-3, Asahi-machi, Abeno-ku, Osaka 545-8585 (Japan), Tel. +06-6645-3806, Fax +06-6645-3808, E-Mail ish@med.osaka-cu.ac.jp
                Article
                355807 Kidney Blood Press Res 2014;39:299-307
                10.1159/000355807
                25300371
                © 2014 S. Karger AG, Basel

                Open Access License: This is an Open Access article licensed under the terms of the Creative Commons Attribution-NonCommercial 3.0 Unported license (CC BY-NC) ( http://www.karger.com/OA-license), applicable to the online version of the article only. Distribution permitted for non-commercial purposes only. 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.

                Page count
                Pages: 9
                Categories
                Original Paper

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