Skip Navigation
American College of Physicians Logo
  • Subscribe
  • Submit a Manuscript
  • Sign In
    Sign in below to access your subscription for full content
    INDIVIDUAL SIGN IN
    Sign In|Set Up Account
    You will be directed to acponline.org to register and create your Annals account
    INSTITUTIONAL SIGN IN
    Open Athens|Shibboleth|Log In
    Annals of Internal Medicine
    SUBSCRIBE
    Subscribe to Annals of Internal Medicine.
    You will be directed to acponline.org to complete your purchase.
Annals of Internal Medicine Logo Menu
  • Latest
  • Issues
  • Channels
  • CME/MOC
  • In the Clinic
  • Journal Club
  • Web Exclusives
  • Author Info
Advanced Search
  • ‹ PREV ARTICLE
  • This Issue
  • NEXT ARTICLE ›
Original Research |18 May 2010

The Associations of Fibroblast Growth Factor 23 and Uncarboxylated Matrix Gla Protein With Mortality in Coronary Artery Disease: The Heart and Soul Study Free

Benjamin D. Parker, MD; Leon J. Schurgers, PhD; Vincent M. Brandenburg, MD; Robert H. Christenson, PhD; Cees Vermeer, PhD; Markus Ketteler, MD; Michael G. Shlipak, MD, MPH; Mary A. Whooley, MD; Joachim H. Ix, MD, MAS

Benjamin D. Parker, MD

Leon J. Schurgers, PhD

Vincent M. Brandenburg, MD

Robert H. Christenson, PhD

Cees Vermeer, PhD

Markus Ketteler, MD

Michael G. Shlipak, MD, MPH

Mary A. Whooley, MD

Joachim H. Ix, MD, MAS

Article, Author, and Disclosure Information
Author, Article, and Disclosure Information
Grant Support: By a Hypertension Training Grant (T32 HL007261) through the National Heart, Lung, and Blood Institute (NHLBI) (Dr. Parker), an American Heart Association Fellow-to-Faculty transition grant, and the NHLBI (grant R01HL096851, Dr. Ix). The Heart and Soul Study was supported by the Department of Veterans Epidemiology Merit Review Program; the Department of Veterans Affairs Health Services Research and Development service; the NHLBI (grant R01 HL079235); the American Federation for Aging Research (Paul Beeson Scholars Program); the Robert Wood Johnson Foundation (Generalist Physician Faculty Scholars Program); and the Ischemia Research and Education Foundation. Dr. Ix had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Potential Conflicts of Interest: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M09-1886.
Reproducible Research Statement:Study protocol: Available at http://dgim.ucsf.edu/heartandsoulstudy/index.html. Statistical code: Available from Dr. Ix (e-mail, joeix@ucsd.edu). Data set: Restricted access; see http://dgim.ucsf.edu/heartandsoulstudy/index.html.
Corresponding Author: Joachim H. Ix, MD, MAS, Division of Nephrology and Hypertension, Department of Medicine, University of California, San Diego, and Veterans Affairs San Diego Healthcare System, 3350 La Jolla Village Drive, Mail Code 111-H, San Diego, CA 92161; e-mail, joeix@ucsd.edu.
Current Author Addresses: Drs. Parker and Ix: Division of Nephrology and Hypertension, University of California, San Diego, and Veterans Affairs San Diego Healthcare System, 3350 La Jolla Village Drive, Mail Code 111-H, San Diego, CA 92161.
Dr. Schurgers: Department of Biochemistry, University of Maastricht, PO Box 616, 6200 MD Maastricht, the Netherlands.
Dr. Brandenburg: Department of Nephrology and Clinical Immunology, University Hospital Aachen, Pauwelsstraße 30, D-52057 Aachen, Germany.
Dr. Christenson: Clinical Pathology, University of Maryland Medical Center, 22 South Greene Street, Baltimore, MD 21201.
Dr. Vermeer: VitaK BV, Maastricht University, BioPartner Center Maastricht, Oxfordlaan 70 6229 EV Maastricht, the Netherlands.
Dr. Ketteler: Nephrologische Klinik, Klinikum Coburg, Ketschendorfer Strasse 33, 96450 Coburg, Germany.
Drs. Shlipak and Whooley: Veterans Affairs Medical Center (111A1), 4150 Clement Street, San Francisco, CA 94121.
Author Contributions: Conception and design: J.H. Ix.
Analysis and interpretation of the data: B.D. Parker, L.J. Schurgers, V.M. Brandenburg, R.H. Christenson, C. Vermeer, M. Ketteler, M.G. Shlipak, M.A. Whooley, J.H. Ix.
Drafting of the article: B.D. Parker, J.H. Ix.
Critical revision of the article for important intellectual content: B.D. Parker, L.J. Schurgers, V.M. Brandenburg, R.H. Christenson, C. Vermeer, M. Ketteler, M.G. Shlipak, M.A. Whooley, J.H. Ix.
Final approval of the article: B.D. Parker, L.J. Schurgers, V.M. Brandenburg, R.H. Christenson, C. Vermeer, M. Ketteler, M.G. Shlipak, M.A. Whooley, J.H. Ix.
Provision of study materials or patients: L.J. Schurgers, V.M. Brandenburg, R.H. Christenson, C. Vermeer, M. Ketteler, M.A. Whooley.
Statistical expertise: B.D. Parker, M.G. Shlipak, J.H. Ix.
Obtaining of funding: L.J. Schurgers, V.M. Brandenburg, C. Vermeer, M.A. Whooley, J.H. Ix.
Administrative, technical, or logistic support: B.D. Parker, J.H. Ix.
Collection and assembly of data: L.J. Schurgers, V.M. Brandenburg, R.H. Christenson, C. Vermeer, M. Ketteler, M.A. Whooley, J.H. Ix.
  • From University of California, San Diego, and Veterans Affairs San Diego Healthcare System, San Diego, and University of California, San Francisco, and San Francisco Veterans Affairs Medical Center, San Francisco, California; VitaK and Cardiovascular Research Institute, Maastricht University, Maastricht, the Netherlands; University Hospital of the Rheinisch-Westfälische Technische Hochschule, Aachen, Germany; University of Maryland, Baltimore, Maryland; and Klinikum Coburg, Coburg, Germany.
×
  • ‹ PREV ARTICLE
  • This Issue
  • NEXT ARTICLE ›
Jump To
  • Full Article
  • FULL ARTICLE
  • FULL ARTICLE
    • Abstract
    • Methods
    • Results
    • Discussion
      1. References
    • Appendix
  • Figures
  • Tables
  • Supplements
  • Audio/Video
  • Summary for Patients
  • Clinical Slide Sets
  • CME / MOC
  • Comments
  • Twitter Link
  • Facebook Link
  • Email Link
More
  • LinkedIn Link
  • CiteULike Link

Abstract

Background:

Fibroblast growth factor 23 (FGF23), uncarboxylated matrix Gla protein (ucMGP), and fetuin-A are regulators of mineral metabolism and inhibitors of vascular calcification. Whether circulating levels of each are associated with cardiovascular disease (CVD) events or mortality in populations without end-stage renal disease is unknown.

Objective:

To evaluate the associations of FGF23, ucMGP, and fetuin-A with mortality and CVD events.

Design:

Observational study.

Setting:

12 outpatient clinics in the San Francisco Bay area.

Patients:

833 outpatients with stable coronary artery disease (CAD), recruited from 11 September 2000 to 20 December 2002.

Measurements:

Fibroblast growth factor 23, ucMGP, and fetuin-A concentrations were measured at baseline. Participants were followed until 1 December 2008 for mortality and CVD events.

Results:

During a median follow-up of 6.0 years, 220 participants died and 182 had CVD events. Compared with participants with FGF-23 levels in the lowest tertile, those in the highest tertile had 2-fold greater risk for mortality (hazard ratio [HR], 2.15 [95% CI, 1.43 to 3.24]) and CVD events (HR, 1.83 [CI, 1.15 to 2.91]) after adjustment for traditional CVD risk factors, C-reactive protein levels, and kidney function. The highest ucMGP tertile was associated with lower mortality risk (HR, 0.48 [CI, 0.31 to 0.75]) and showed a nonsignificant trend toward lower CVD event risk by tertile analysis (HR, 0.65 [CI, 0.40 to 1.05])—an association that was significant when modeled continuously (P = 0.029). No significant association of fetuin-A with mortality (HR, 0.84 [CI, 0.55 to 1.27]) or CVD events (HR, 0.99 [CI, 0.64 to 1.55]) was observed.

Limitation:

Participants had prevalent CAD.

Conclusion:

In outpatients with stable CAD, higher FGF23 and lower ucMGP levels are independently associated with mortality and CVD events.

Primary Funding Source:

American Heart Association.

Editors' Notes

Context

  • Other investigators recently identified novel regulators of mineral metabolism, which have been associated with cardiovascular disease and mortality in patients with end-stage renal disease.

Contribution

  • The authors studied 833 persons and found that those with higher levels of fibroblast growth factor 23 and lower levels of uncarboxylated matrix Gla protein had higher cardiovascular disease event rates and mortality after adjustment for traditional risk factors, C-reactive protein levels, and kidney function.

Caution

  • All study participants had coronary artery disease.

Implication

  • Better understanding of these relationships might lead to new therapies for cardiovascular disease.

—The Editors
People with cardiovascular disease (CVD) are at high risk for recurrent CVD events and mortality (1), and many traditional CVD risk factors are not strongly associated with CVD events in this setting (2, 3). New insights into mechanisms for recurrent events might ultimately provide novel therapeutic targets or prevention strategies.
Abnormalities in mineral metabolism are associated with CVD risk in the general population. For example, higher phosphorus levels promote arterial calcification in vitro (4, 5) and are associated with coronary artery calcification and CVD events in the general population, even among persons with normal kidney function (6–9). Similarly, lower serum vitamin D levels and higher serum intact parathyroid hormone levels are associated with CVD events in the general population (10, 11). Recently, several novel regulators of arterial calcification, including fibroblast growth factor 23 (FGF23), uncarboxylated matrix Gla protein (ucMGP), and fetuin-A, have been identified. Yet, the relationship of circulating levels of these proteins with CVD events and mortality is unknown.
Fibroblast growth factor 23 is a bone-derived protein that promotes renal phosphorus wasting and inhibits conversion of 25-hydroxyvitamin D to the active 1,25-dihydroxyvitamin D form (12–16). Studies of mice have suggested that elevated FGF23 levels may reflect a response to dietary phosphorus burden and serve as a marker of arterial calcification (17). Matrix Gla protein (MGP) is produced by chondrocytes and vascular smooth-muscle cells and prevents arterial calcification through local effects in the arterial wall (18–21). Its precursor form is ucMGP, which has affinity for hydroxyapatite and may be depleted from blood in the setting of arterial calcification. Therefore, low serum levels may be a marker of vascular disease (22). Fetuin-A is a liver-secreted protein that complexes with calcium and phosphorus in circulation and prevents the precipitation of these minerals from serum (23, 24). In mice, knockouts of genes encoding FGF23, ucMGP, or fetuin-A result in arterial or soft-tissue calcification or both (24–26). In humans, FGF23 and fetuin-A have been most extensively studied in cohorts with end-stage renal disease (ESRD), where higher FGF23 and lower fetuin-A levels are associated with mortality and CVD events (27–30). Although the temporal association of ucMGP with mortality is uncertain, patients with ESRD or atherosclerosis have lower ucMGP levels than healthy controls (31–34). Because these 3 proteins have complementary biological functions, we measured blood levels of all 3 and evaluated associations with mortality and CVD events in an ambulatory cohort with prevalent coronary artery disease (CAD) and a spectrum of kidney function from normal to moderate chronic kidney disease. On the basis of directions of association observed in cohorts with ESRD, we hypothesized that higher FGF23, lower ucMGP, and lower fetuin-A levels would each be associated with higher CVD events and mortality, independent of traditional CVD risk factors, kidney function, and one another.

Methods

Study Participants

The Heart and Soul Study is an observational study designed to investigate the influence of psychosocial factors on the progression of CVD. Methods are described elsewhere (35). In brief, participants were recruited from outpatient clinics in the San Francisco Bay area if they met at least one of the following inclusion criteria: history of myocardial infarction (MI); angiographic evidence of greater than 50% stenosis in 1 or more coronary vessels; evidence of exercise-induced ischemia by treadmill or nuclear testing; and history of coronary revascularization or documented diagnosis of CAD by an internist or cardiologist. Participants were excluded if they could not walk 1 block, had MI within the past 6 months, or were likely to move out of the area within 3 years. The study protocol was approved by the institutional review boards of participating institutions. All participants provided written informed consent. From September 2000 to December 2002, a total of 1024 participants enrolled and had a baseline study appointment.

Measurements

Predictor Variables

Fasting (12-hour) serum and plasma samples were obtained at the baseline visit, frozen at −70 °C, and later used for measurement of FGF23 (in 2007), ucMGP (in 2007), and fetuin-A (in 2004). Blood levels of each were measured twice in each participant, and results were averaged (the 4 includes measurement details).

Outcome Variables

From the baseline examination to 1 December 2008, we conducted annual telephone interviews with participants (or their proxies), inquiring about hospitalizations, cardiac procedures, or death. Two independent, blinded adjudicators reviewed all events, medical records, electrocardiography results, death certificates, and coroner's reports. In the event of disagreement, the adjudicators conferred, reconsidered their classification, and requested consultation from a third blinded adjudicator, as necessary.
We considered the composite of MI, stroke, transient ischemic attack, or heart failure as a CVD event. Myocardial infarction was defined by cardiac biomarkers, electrocardiography results, and cardiac symptoms or signs according to the American Heart Association criteria (36). We defined “stroke” as a new neurologic deficit not secondary to brain trauma, tumor, infection, or other cause. Transient ischemic attack was defined as a focal neurologic deficit (in the absence of head trauma) lasting more than 30 seconds and no longer than 24 hours, with rapid symptom evolution to the maximal level of deficit in less than 5 minutes and with subsequent complete resolution. We defined “heart failure” as hospitalization for a clinical syndrome involving at least 2 of the following changes from usual status: paroxysmal nocturnal dyspnea, orthopnea, elevated jugular venous pressure, pulmonary rales, third heart sound, and cardiomegaly or pulmonary edema on chest radiography. Mortality was determined by death certificates and coroner's reports.

Other Measurements

We determined age, sex, race or ethnicity, and smoking status by questionnaire. We instructed participants to bring their medication bottles to the baseline appointment, and study personnel recorded medications. Waist-to-hip ratio was calculated after measuring waist circumference midway between the lower rib margin and iliac crest and hip circumference at the level of the greater trochanters. We determined prevalent hypertension and diabetes by questionnaire. Systolic and diastolic blood pressures were measured after 5 minutes of rest in the supine position. We calculated estimated glomerular filtration rate (GFR) by incorporating creatinine concentrations, age, sex, and race in the abbreviated (4-variable) Modification of Diet in Renal Disease Study equation (37). High-sensitivity C-reactive protein levels were measured with the Roche assay (Indianapolis, Indiana) and the Beckman Extended Range assay (Galway, Ireland) (38). We measured total cholesterol, high-density lipoprotein cholesterol, calcium, and phosphorus levels by using standard clinical chemistry analyzers. Participants had transthoracic echocardiography at baseline, which we used to measure left ventricular ejection fraction. We did a symptom-limited, graded exercise treadmill test according to the standard Bruce protocol and defined peak exercise capacity as total number of metabolic equivalent tasks achieved.

Statistical Analysis

We excluded 5 participants (<1%) who were missing outcome data and 186 participants (18%) who did not have baseline blood specimens for measurement of fetuin-A, ucMGP, or FGF23, resulting in a final sample size of 833 participants. Compared with those of excluded participants, demographic characteristics and event rates were similar among participants who were retained in this analysis (Appendix Table 1). For descriptive statistics, we compared demographic and clinical variables among participants with and without CVD events or mortality during follow-up by using the t test or the Kruskal–Wallis test for continuous variables and the chi-square test or Fisher exact test for categorical variables, as appropriate. We used graphical methods to determine the distribution of FGF23, ucMGP, and fetuin-A in the study sample. Linear regression was used to compare associations of FGF23, ucMGP, and fetuin-A with calcium, phosphorus, and other baseline cardiovascular risks.

Appendix Table 1.

Comparison of Variables in Persons Excluded Because of Missing Measurements

Appendix Table 1.
We elected to evaluate tertiles of each protein as our primary predictor variables. The lowest tertile served as the reference category. Because the functional form was fairly linear for each, we also evaluated each protein on a continuous scale, to minimize the chance of a type II error. We used Kaplan–Meier curves to evaluate unadjusted time to events and Cox proportional hazards models to evaluate adjusted associations of each novel mineral regulator with CVD events and mortality. Three sequential models were developed: one adjusted for age, sex, and race; one adjusted for age, sex, race and other CVD risk factors (smoking, hypertension, diabetes, waist-to-hip ratio, systolic and diastolic blood pressures, total and high-density lipoprotein cholesterol levels, estimated GFR, C-reactive protein level, ejection fraction, peak exercise capacity, and medications used [Table 1 ]); and one adjusted for the CVD risk factors plus serum calcium, phosphorus, and the other 2 novel mineral regulators, because we considered it possible that the association of each novel mineral regulator might be mediated through calcium, phosphorus, or the other 2 novel mineral regulators. We assessed proportional hazards assumptions by visually inspecting log-minus-log plots and plots of Schoenfeld residuals versus survival time. No evidence of violation was observed. We used multiplicative interaction terms to evaluate effect modification by diabetes status and for the presence or absence of chronic kidney disease (estimated GFR <60 mL/min per 1.73 m2 vs. ≥60 mL/min per 1.73 m2). Analyses were done using Stata Statistical Software, version 9.2 (StataCorp, College Station, Texas).

Table 1.

Baseline Characteristics of Participants With and Without Events

Table 1.

Role of the Funding Source

The Heart and Soul Study was supported by the Department of Veterans Epidemiology Merit Review Program; Department of Veterans Affairs Health Services Research and Development service; National Heart, Lung, and Blood Institute; American Federation for Aging Research; Robert Wood Johnson Foundation; and Ischemia Research and Education Foundation. This ancillary study was supported by the American Heart Association and the National Heart, Lung, and Blood Institute. The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, approval, or decision to submit the manuscript for review.

Results

Among the 833 participants, the mean age was 67 years (SD, 11), 81% were men, 40% were nonwhite, 22% had moderate chronic kidney disease (estimated GFR <60 mL/min per 1.73 m2), and 27% had type 2 diabetes mellitus. Cardiovascular disease events occurred among 182 individuals during 3913 person-years of follow-up (median, 5.2 years), and 220 deaths occurred during 4360 person-years of follow-up (median, 6.0 years). Participants who had events were older; were more frequently men; were more likely to be receiving an angiotensin-converting enzyme inhibitor or angiotensin-receptor blocker and anticoagulants; and had lower peak exercise capacity, lower ejection fraction, greater waist-to-hip ratio, greater prevalence of diabetes, lower estimated GFR and high-density lipoprotein cholesterol levels, and higher C-reactive protein levels (Table 1).
The distribution of FGF23 was right-skewed, with a median of 43.1 RU/mL (interquartile range, 28.9 to 72.3 RU/mL), so the variable was natural log–transformed to approximate a normal distribution. The distributions of ucMGP and fetuin-A were approximately normal with means of 3290 nM (SD, 1178) and 0.65 g/L (SD, 0.14), respectively (Appendix Figure). After adjustment for age, sex, race, and estimated GFR, associations of mineral regulators with calcium, phosphorus, and one another demonstrated that a higher FGF23 level was strongly associated with phosphorus and weakly associated with calcium and that a higher ucMGP level was associated with a higher fetuin-A level (Appendix Table 2). The association of each novel mineral regulator with major demographic variables and traditional CVD risk factors varied by risk factor (Appendix Table 3), but persons with diabetes had higher levels of each of the 3 mineral regulators.
Appendix Figure.
Distribution of FGF23*, ucMGP, and fetuin-A levels among 833 participants with coronary artery disease.

FGF23 = fibroblast growth factor 23; ucMGP = uncarboxylated matrix Gla protein.

* 16 participants with FGF23 levels >480 RU/mL (range, 529 to 3150 RU/mL) were not included because of space limitations.

Appendix Table 2.

Association of Calcium and Phosphorus With ln-FGF23, ucMGP, and Fetuin-A Levels

Appendix Table 2.

Appendix Table 3.

Association Between Baseline Factors and ln-FGF23, ucMGP, and Fetuin-A Levels

Appendix Table 3.
Both higher FGF23 and lower ucMGP levels were associated with greater risk for mortality and CVD events in Kaplan–Meier analysis. In contrast, fetuin-A levels were not associated with either outcome (Figure). Table 2 shows the adjusted associations of each novel mineral regulator with CVD events and mortality. Compared with participants in the lowest FGF23 tertile, those in the highest tertile had approximately 3-fold greater risk for CVD events and mortality in models adjusted for age, sex, and race. Additional adjustment for traditional CVD risk factors, kidney function, C-reactive protein level, ejection fraction, peak exercise capacity, and medication use (multivariate model 1) attenuated this association; however, the highest tertile remained associated with an approximately 2-fold greater risk for either outcome. When FGF23 was evaluated as a continuous predictor, each doubling in FGF23 level was associated with a 41% higher mortality risk and 24% higher CVD event risk. Further adjustment for ucMGP, fetuin-A, calcium, and phosphorus produced essentially unaltered associations. Table 3 shows the associations of FGF23 with the individual components of the composite CVD event outcome, in which associations were qualitatively strongest for heart failure and stroke or transient ischemic attack.
Figure.
Unadjusted event-free survival, by tertiles of FGF23, ucMGP, and fetuin-A.

CVD = cardiovascular disease; FGF23 = fibroblast growth factor 23; ucMGP = uncarboxylated matrix Gla protein.

Table 2.

Association of FGF23, ucMGP, and Fetuin-A Levels With All-Cause Mortality or CVD Events

Table 2.

Table 3.

HRs for Individual Events per Change in FGF23, ucMGP, or Fetuin-A Level

Table 3.
Serum ucMGP levels were also associated with mortality risk, but in the opposite direction. Compared with participants in the lowest ucMGP tertile, participants in the highest tertile had approximately 50% lower risk for mortality in models adjusted for age, sex, and race (Table 2). This association remained after adjustment for traditional CVD risk factors, kidney function, C-reactive protein level, ejection fraction, peak exercise capacity, and medication use. The association of ucMGP with CVD events was in the same direction but of lesser magnitude. When ucMGP was evaluated as a continuous predictor variable, each 1000-nM higher ucMGP level was associated with a 22% lower risk for mortality and a 16% lower risk for CVD events. Further adjustment for FGF23, fetuin-A, calcium, and phosphorus had little effect on these associations. Among the components of the composite CVD outcome, MI risk was qualitatively more strongly associated with lower ucMGP levels (Table 3).
Compared with participants in the lowest fetuin-A tertile, participants in the highest tertile were not at statistically significantly higher risk for either CVD events or mortality. When fetuin-A was evaluated as a continuous predictor variable, its associations with mortality and CVD events were near unity (Tables 2 and 3).
We evaluated whether these associations were modified by diabetes or chronic kidney disease status. Association of all 3 mineral regulators with mortality or CVD events was similar, regardless of the presence or absence of chronic kidney disease (P ≥ 0.41 for interaction in multivariate model 1 for all). With the exception of the association of ucMGP with mortality, results were also similar in persons with or without diabetes (P ≥ 0.41 for interaction for all). The association of ucMGP with mortality was limited to participants without diabetes (P = 0.035 for interaction). In these persons (n = 610), each 1000-nM higher ucMGP level was associated with 33% lower mortality risk (hazard ratio, 0.67 [95% CI, 0.56 to 0.81]; P < 0.001), whereas there was no significant association of ucMGP with mortality in 221 participants with diabetes (hazard ratio, 1.10 [CI, 0.85 to 1.41]; P = 0.47).

Discussion

We demonstrate that among persons with stable CAD and a range of kidney function from normal to moderate chronic kidney disease, higher FGF23 levels and lower ucMGP levels are associated with mortality and CVD events, independent of one another, traditional CVD risk factors, kidney function, and C-reactive protein levels. In contrast, fetuin-A levels were not statistically significantly associated with mortality or CVD events.
Higher FGF23 levels are associated with higher mortality in cohorts with ESRD (30). However, to our knowledge, the association of FGF23 with mortality and CVD events in other settings has not previously been evaluated. The mechanisms responsible for this association are uncertain, but several possibilities exist. Fibroblast growth factor 23, an endocrine regulator of phosphorus metabolism, may be a marker of higher time-averaged serum phosphorus levels, and by extension, FGF23 may be a marker of vascular calcification. We and others (30) have demonstrated that higher FGF23 levels are associated with higher serum phosphorus levels, and others have shown that higher serum phosphorus levels are associated with vascular calcification and CVD events in community-living samples with and without severe kidney disease (7–9, 39). However, in our study and in a previous study among patients with ESRD, the associations of FGF23 with mortality were independent of serum phosphorus levels measured at one point in time. It may be that a single serum phosphorus measurement does not accurately represent cumulative phosphorus burden, given the high intraindividual biological variability in serum phosphorus levels when measured repeatedly over time (40). Because active vitamin D regulates the renin–angiotensin axis (41) and proliferation of cardiomyocytes (42), FGF23 may also affect the cardiovascular system through its inhibition of vitamin D activation (43). Fibroblast growth factor 23 is associated with left ventricular hypertrophy (44, 45), a relation that may be explained by the previously mentioned mechanisms, but it is also possible that FGF23 may influence cardiac remodeling through other mechanisms (46–48). Future studies that elucidate potential direct or indirect effects of FGF23 are required to determine these mechanisms.
To our knowledge, the relationship of ucMGP with mortality has not previously been demonstrated in any setting. Vascular smooth-muscle cells produce MGP, and vitamin K–dependent posttranslational activation produces carboxylated MGP, a locally acting and potent inhibitor of arterial calcification (18, 19, 25). Its precursor, ucMGP, accumulates in arteries near calcium deposits (22)—a process that may lower its blood concentration. Persons with ESRD, calcific uremic arteriolopathy, or cardiac valvular calcification have lower blood ucMGP levels than healthy control participants (31, 32), and ucMGP is inversely correlated with coronary artery calcification (33). The present analysis is novel in demonstrating that a lower ucMGP level is associated with mortality in persons with CAD, and that this association was limited to persons without diabetes. The mechanisms responsible for the effect modification by diabetes are uncertain, but the absence of diabetes may reflect a different underlying biology predisposing to ectopic calcification. We have shown previously that a lower ucMGP level was independently associated with cardiac valve calcification. This association, however, was also limited to persons without diabetes (49).
Synthesized by the liver and secreted into blood, fetuin-A is a circulating inhibitor of arterial calcification that increases the solubility of hydroxyapatite precursors in the bloodstream, reminiscent of mechanisms through which apolipoproteins increase the solubility of lipids (50). In cohorts with ESRD, lower fetuin-A levels have consistently been associated with higher mortality risk (27–29). Whether similar associations extend to nondialysis cohorts is uncertain. In persons with stage 3 or 4 chronic kidney disease, we observed no association of fetuin-A levels with all-cause or CVD mortality (51). Similarly, we observed no association of fetuin-A levels with mortality or CVD events among persons with normal to near-normal kidney function. Studies by other investigators in cohorts without ESRD have provided conflicting results. In 1 study, lower fetuin-A levels were associated with mortality among patients hospitalized with acute MI (52), whereas another study reported that higher fetuin-A levels were associated with MI in a community-living cohort (53). In cohorts with ESRD, fetuin-A has been suggested as a negative acute-phase reactant (27–29), but this association is not consistently observed in other settings (51, 54). In our analysis, we found no statistically significant association between fetuin-A and C-reactive protein levels after correction for other cardiovascular risks and estimated GFR (55). The reasons for conflicting results between ESRD cohorts and other settings remain uncertain. Because persons with ESRD have a high prevalence and severity of vascular calcification and frequently have calcium and phosphorus levels well outside the normal laboratory ranges, we hypothesize that this extreme phenotype may be required to observe the association of low fetuin-A levels with CVD events. Finally, although higher fetuin-A levels have also been associated with insulin resistance and risk for type 2 diabetes mellitus (56), the association of fetuin-A with CVD events and mortality in our study was similar among participants with or without diabetes.
Our study has important limitations. Parathyroid hormone and vitamin D levels were not measured, and whether participants used calcium or vitamin D supplements and bisphosphonates is unknown. All participants had prevalent CAD, and most were older men. Results may differ in younger persons, women, and persons without CAD. Although most deaths in older persons with prevalent CAD are related to cardiovascular events (1), the associations between FGF23 and ucMGP levels with mortality may also reflect noncardiovascular events, and the causes of death were not specifically adjudicated in our study. Heart failure was considered an ischemic event in this cohort with prevalent CAD, yet some heart failure events may have been nonischemic in origin. For the association of fetuin-A and events, our sample size was limited to 833 persons, and it is possible that a true association was missed or that results may differ with other assays; the results should be interpreted within the confines of the 95% CIs.
In conclusion, higher FGF23 and lower ucMGP levels are each associated with mortality and CVD events in outpatients with stable CAD. These findings need to be replicated in independent populations, but they add to the growing body of literature demonstrating that abnormalities in mineral metabolism may identify persons at greater risk for CVD events and death. Because in vitro and animal studies demonstrate that these pathways influence arterial calcification, future studies determining the exact mechanisms may ultimately provide novel therapies for primary or secondary prevention of CVD.

References

  1. Lloyd-Jones
    D
    ,  
    Adams
    R
    ,  
    Carnethon
    M
    ,  
    DeSimone
    G
    ,  
    Ferguson
    TB
    ,  
    Flegal
    K
    .  
    et al.
    American Heart Association Statistics Committee and Stroke Statistics Subcommittee
    Heart disease and stroke statistics—2009 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee.
    Circulation
    2009
    119
    21
    181
    PubMed
    CrossRef
  2. Schlant
    RC
    ,  
    Forman
    S
    ,  
    Stamler
    J
    ,  
    Canner
    PL
    .  
    The natural history of coronary heart disease: prognostic factors after recovery from myocardial infarction in 2789 men. The 5-year findings of the coronary drug project.
    Circulation
    1982
    66
    401
    14
    PubMed
  3. Vittinghoff
    E
    ,  
    Shlipak
    MG
    ,  
    Varosy
    PD
    ,  
    Furberg
    CD
    ,  
    Ireland
    CC
    ,  
    Khan
    SS
    .  
    et al.
    Heart and Estrogen/progestin Replacement Study Research Group
    Risk factors and secondary prevention in women with heart disease: the Heart and Estrogen/progestin Replacement Study.
    Ann Intern Med
    2003
    138
    81
    9
    PubMed
  4. Steitz
    SA
    ,  
    Speer
    MY
    ,  
    Curinga
    G
    ,  
    Yang
    HY
    ,  
    Haynes
    P
    ,  
    Aebersold
    R
    .  
    et al.
    Smooth muscle cell phenotypic transition associated with calcification: upregulation of Cbfa1 and downregulation of smooth muscle lineage markers.
    Circ Res
    2001
    89
    1147
    54
    PubMed
  5. Jono
    S
    ,  
    McKee
    MD
    ,  
    Murry
    CE
    ,  
    Shioi
    A
    ,  
    Nishizawa
    Y
    ,  
    Mori
    K
    .  
    et al.
    Phosphate regulation of vascular smooth muscle cell calcification.
    Circ Res
    2000
    87
    e10
    7
    PubMed
  6. Foley
    RN
    ,  
    Collins
    AJ
    ,  
    Ishani
    A
    ,  
    Kalra
    PA
    .  
    Calcium-phosphate levels and cardiovascular disease in community-dwelling adults: the Atherosclerosis Risk in Communities (ARIC) Study.
    Am Heart J
    2008
    156
    556
    63
    PubMed
  7. Dhingra
    R
    ,  
    Sullivan
    LM
    ,  
    Fox
    CS
    ,  
    Wang
    TJ
    ,  
    D'Agostino
    RB
    Sr
    ,  
    Gaziano
    JM
    .  
    et al.
    Relations of serum phosphorus and calcium levels to the incidence of cardiovascular disease in the community.
    Arch Intern Med
    2007
    167
    879
    85
  8. Tonelli
    M
    ,  
    Sacks
    F
    ,  
    Pfeffer
    M
    ,  
    Gao
    Z
    ,  
    Curhan
    G
    .  
    Cholesterol And Recurrent Events Trial Investigators
    Relation between serum phosphate level and cardiovascular event rate in people with coronary disease.
    Circulation
    2005
    112
    2627
    33
    PubMed
  9. Foley
    RN
    ,  
    Collins
    AJ
    ,  
    Herzog
    CA
    ,  
    Ishani
    A
    ,  
    Kalra
    PA
    .  
    Serum phosphorus levels associate with coronary atherosclerosis in young adults.
    J Am Soc Nephrol
    2009
    20
    397
    404
    PubMed
  10. Dobnig
    H
    ,  
    Pilz
    S
    ,  
    Scharnagl
    H
    ,  
    Renner
    W
    ,  
    Seelhorst
    U
    ,  
    Wellnitz
    B
    .  
    et al.
    Independent association of low serum 25-hydroxyvitamin d and 1,25-dihydroxyvitamin d levels with all-cause and cardiovascular mortality.
    Arch Intern Med
    2008
    168
    1340
    9
    PubMed
  11. Hagström
    E
    ,  
    Hellman
    P
    ,  
    Larsson
    TE
    ,  
    Ingelsson
    E
    ,  
    Berglund
    L
    ,  
    Sundström
    J
    .  
    et al.
    Plasma parathyroid hormone and the risk of cardiovascular mortality in the community.
    Circulation
    2009
    119
    2765
    71
    PubMed
  12. Antoniucci
    DM
    ,  
    Yamashita
    T
    ,  
    Portale
    AA
    .  
    Dietary phosphorus regulates serum fibroblast growth factor-23 concentrations in healthy men.
    J Clin Endocrinol Metab
    2006
    91
    3144
    9
    PubMed
  13. Burnett
    SM
    ,  
    Gunawardene
    SC
    ,  
    Bringhurst
    FR
    ,  
    Jüppner
    H
    ,  
    Lee
    H
    ,  
    Finkelstein
    JS
    .  
    Regulation of C-terminal and intact FGF-23 by dietary phosphate in men and women.
    J Bone Miner Res
    2006
    21
    1187
    96
    PubMed
  14. Gutierrez
    O
    ,  
    Isakova
    T
    ,  
    Rhee
    E
    ,  
    Shah
    A
    ,  
    Holmes
    J
    ,  
    Collerone
    G
    .  
    et al.
    Fibroblast growth factor-23 mitigates hyperphosphatemia but accentuates calcitriol deficiency in chronic kidney disease.
    J Am Soc Nephrol
    2005
    16
    2205
    15
    PubMed
  15. Shimada
    T
    ,  
    Kakitani
    M
    ,  
    Yamazaki
    Y
    ,  
    Hasegawa
    H
    ,  
    Takeuchi
    Y
    ,  
    Fujita
    T
    .  
    et al.
    Targeted ablation of Fgf23 demonstrates an essential physiological role of FGF23 in phosphate and vitamin D metabolism.
    J Clin Invest
    2004
    113
    561
    8
    PubMed
  16. Shimada
    T
    ,  
    Mizutani
    S
    ,  
    Muto
    T
    ,  
    Yoneya
    T
    ,  
    Hino
    R
    ,  
    Takeda
    S
    .  
    et al.
    Cloning and characterization of FGF23 as a causative factor of tumor-induced osteomalacia.
    Proc Natl Acad Sci U S A
    2001
    98
    6500
    5
    PubMed
  17. El-Abbadi
    MM
    ,  
    Pai
    AS
    ,  
    Leaf
    EM
    ,  
    Yang
    HY
    ,  
    Bartley
    BA
    ,  
    Quan
    KK
    .  
    et al.
    Phosphate feeding induces arterial medial calcification in uremic mice: role of serum phosphorus, fibroblast growth factor-23, and osteopontin.
    Kidney Int
    2009
    75
    1297
    307
  18. Boström
    K
    ,  
    Tsao
    D
    ,  
    Shen
    S
    ,  
    Wang
    Y
    ,  
    Demer
    LL
    .  
    Matrix GLA protein modulates differentiation induced by bone morphogenetic protein-2 in C3H10T1/2 cells.
    J Biol Chem
    2001
    276
    14044
    52
  19. Zebboudj
    AF
    ,  
    Shin
    V
    ,  
    Boström
    K
    .  
    Matrix GLA protein and BMP-2 regulate osteoinduction in calcifying vascular cells.
    J Cell Biochem
    2003
    90
    756
    65
    PubMed
  20. Reynolds
    JL
    ,  
    Joannides
    AJ
    ,  
    Skepper
    JN
    ,  
    McNair
    R
    ,  
    Schurgers
    LJ
    ,  
    Proudfoot
    D
    .  
    et al.
    Human vascular smooth muscle cells undergo vesicle-mediated calcification in response to changes in extracellular calcium and phosphate concentrations: a potential mechanism for accelerated vascular calcification in ESRD.
    J Am Soc Nephrol
    2004
    15
    2857
    67
    PubMed
  21. Murshed
    M
    ,  
    Schinke
    T
    ,  
    McKee
    MD
    ,  
    Karsenty
    G
    .  
    Extracellular matrix mineralization is regulated locally; different roles of two gla-containing proteins.
    J Cell Biol
    2004
    165
    625
    30
    PubMed
  22. Schurgers
    LJ
    ,  
    Teunissen
    KJ
    ,  
    Knapen
    MH
    ,  
    Kwaijtaal
    M
    ,  
    vanDiest
    R
    ,  
    Appels
    A
    .  
    et al.
    Novel conformation-specific antibodies against matrix gamma-carboxyglutamic acid (Gla) protein: undercarboxylated matrix Gla protein as marker for vascular calcification.
    Arterioscler Thromb Vasc Biol
    2005
    25
    1629
    33
    PubMed
  23. Heiss
    A
    ,  
    DuChesne
    A
    ,  
    Denecke
    B
    ,  
    Grötzinger
    J
    ,  
    Yamamoto
    K
    ,  
    Renné
    T
    .  
    et al.
    Structural basis of calcification inhibition by alpha 2-HS glycoprotein/fetuin-A. Formation of colloidal calciprotein particles.
    J Biol Chem
    2003
    278
    13333
    41
    PubMed
  24. Schafer
    C
    ,  
    Heiss
    A
    ,  
    Schwarz
    A
    ,  
    Westenfeld
    R
    ,  
    Ketteler
    M
    ,  
    Floege
    J
    .  
    et al.
    The serum protein alpha 2-Heremans-Schmid glycoprotein/fetuin-A is a systemically acting inhibitor of ectopic calcification.
    J Clin Invest
    2003
    112
    357
    66
    PubMed
  25. Luo
    G
    ,  
    Ducy
    P
    ,  
    McKee
    MD
    ,  
    Pinero
    GJ
    ,  
    Loyer
    E
    ,  
    Behringer
    RR
    .  
    et al.
    Spontaneous calcification of arteries and cartilage in mice lacking matrix GLA protein.
    Nature
    1997
    386
    78
    81
    PubMed
  26. Sitara
    D
    ,  
    Razzaque
    MS
    ,  
    St-Arnaud
    R
    ,  
    Huang
    W
    ,  
    Taguchi
    T
    ,  
    Erben
    RG
    .  
    et al.
    Genetic ablation of vitamin D activation pathway reverses biochemical and skeletal anomalies in Fgf-23-null animals.
    Am J Pathol
    2006
    169
    2161
    70
    PubMed
  27. Hermans
    MM
    ,  
    Brandenburg
    V
    ,  
    Ketteler
    M
    ,  
    Kooman
    JP
    ,  
    van der Sande
    FM
    ,  
    Boeschoten
    EW
    .  
    et al.
    Netherlands cooperative study on the adequacy of Dialysis (NECOSAD)
    Association of serum fetuin-A levels with mortality in dialysis patients.
    Kidney Int
    2007
    72
    202
    7
    PubMed
  28. Ketteler
    M
    ,  
    Bongartz
    P
    ,  
    Westenfeld
    R
    ,  
    Wildberger
    JE
    ,  
    Mahnken
    AH
    ,  
    Böhm
    R
    .  
    et al.
    Association of low fetuin-A (AHSG) concentrations in serum with cardiovascular mortality in patients on dialysis: a cross-sectional study.
    Lancet
    2003
    361
    827
    33
    PubMed
  29. Wang
    AY
    ,  
    Woo
    J
    ,  
    Lam
    CW
    ,  
    Wang
    M
    ,  
    Chan
    IH
    ,  
    Gao
    P
    .  
    et al.
    Associations of serum fetuin-A with malnutrition, inflammation, atherosclerosis and valvular calcification syndrome and outcome in peritoneal dialysis patients.
    Nephrol Dial Transplant
    2005
    20
    1676
    85
    PubMed
  30. Gutiérrez
    OM
    ,  
    Mannstadt
    M
    ,  
    Isakova
    T
    ,  
    Rauh-Hain
    JA
    ,  
    Tamez
    H
    ,  
    Shah
    A
    .  
    et al.
    Fibroblast growth factor 23 and mortality among patients undergoing hemodialysis.
    N Engl J Med
    2008
    359
    584
    92
    PubMed
  31. Cranenburg
    EC
    ,  
    Vermeer
    C
    ,  
    Koos
    R
    ,  
    Boumans
    ML
    ,  
    Hackeng
    TM
    ,  
    Bouwman
    FG
    .  
    et al.
    The circulating inactive form of matrix Gla Protein (ucMGP) as a biomarker for cardiovascular calcification.
    J Vasc Res
    2008
    45
    427
    36
    PubMed
  32. Hermans
    MM
    ,  
    Vermeer
    C
    ,  
    Kooman
    JP
    ,  
    Brandenburg
    V
    ,  
    Ketteler
    M
    ,  
    Gladziwa
    U
    .  
    et al.
    Undercarboxylated matrix GLA protein levels are decreased in dialysis patients and related to parameters of calcium-phosphate metabolism and aortic augmentation index.
    Blood Purif
    2007
    25
    395
    401
    PubMed
  33. Cranenburg
    EC
    ,  
    Brandenburg
    VM
    ,  
    Vermeer
    C
    ,  
    Stenger
    M
    ,  
    Mühlenbruch
    G
    ,  
    Mahnken
    AH
    .  
    et al.
    Uncarboxylated matrix Gla protein (ucMGP) is associated with coronary artery calcification in haemodialysis patients.
    Thromb Haemost
    2009
    101
    359
    66
    PubMed
  34. Schurgers
    LJ
    ,  
    Teunissen
    KJ
    ,  
    Knapen
    MH
    ,  
    Geusens
    P
    ,  
    van der Heijde
    D
    ,  
    Kwaijtaal
    M
    .  
    et al.
    Characteristics and performance of an immunosorbent assay for human matrix Gla-protein.
    Clin Chim Acta
    2005
    351
    131
    8
  35. Whooley
    MA
    ,  
    deJonge
    P
    ,  
    Vittinghoff
    E
    ,  
    Otte
    C
    ,  
    Moos
    R
    ,  
    Carney
    RM
    .  
    et al.
    Depressive symptoms, health behaviors, and risk of cardiovascular events in patients with coronary heart disease.
    JAMA
    2008
    300
    2379
    88
  36. Luepker
    RV
    ,  
    Apple
    FS
    ,  
    Christenson
    RH
    ,  
    Crow
    RS
    ,  
    Fortmann
    SP
    ,  
    Goff
    D
    .  
    et al.
    AHA Council on Epidemiology and Prevention
    Case definitions for acute coronary heart disease in epidemiology and clinical research studies: a statement from the AHA Council on Epidemiology and Prevention; AHA Statistics Committee; World Heart Federation Council on Epidemiology and Prevention; the European Society of Cardiology Working Group on Epidemiology and Prevention; Centers for Disease Control and Prevention; and the National Heart, Lung, and Blood Institute.
    Circulation
    2003
    108
    2543
    9
  37. Levey
    AS
    ,  
    Bosch
    JP
    ,  
    Lewis
    JB
    ,  
    Greene
    T
    ,  
    Rogers
    N
    ,  
    Roth
    D
    .  
    A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Modification of Diet in Renal Disease Study Group.
    Ann Intern Med
    1999
    130
    461
    70
  38. Whooley
    MA
    ,  
    Caska
    CM
    ,  
    Hendrickson
    BE
    ,  
    Rourke
    MA
    ,  
    Ho
    J
    ,  
    Ali
    S
    .  
    Depression and inflammation in patients with coronary heart disease: findings from the Heart and Soul Study.
    Biol Psychiatry
    2007
    62
    314
    20
  39. Kestenbaum
    B
    ,  
    Sampson
    JN
    ,  
    Rudser
    KD
    ,  
    Patterson
    DJ
    ,  
    Seliger
    SL
    ,  
    Young
    B
    .  
    et al.
    Serum phosphate levels and mortality risk among people with chronic kidney disease.
    J Am Soc Nephrol
    2005
    16
    520
    8
  40. Chonchol
    M
    ,  
    Dale
    R
    ,  
    Schrier
    RW
    ,  
    Estacio
    R
    .  
    Serum phosphorus and cardiovascular mortality in type 2 diabetes.
    Am J Med
    2009
    122
    380
    6
    PubMed
  41. Li
    YC
    ,  
    Kong
    J
    ,  
    Wei
    M
    ,  
    Chen
    ZF
    ,  
    Liu
    SQ
    ,  
    Cao
    LP
    .  
    1,25-Dihydroxyvitamin D(3) is a negative endocrine regulator of the renin-angiotensin system.
    J Clin Invest
    2002
    110
    229
    38
    PubMed
  42. O'Connell
    TD
    ,  
    Berry
    JE
    ,  
    Jarvis
    AK
    ,  
    Somerman
    MJ
    ,  
    Simpson
    RU
    .  
    1,25-Dihydroxyvitamin D3 regulation of cardiac myocyte proliferation and hypertrophy.
    Am J Physiol
    1997
    272
    H1751
    8
    PubMed
  43. Liu
    S
    ,  
    Quarles
    LD
    .  
    How fibroblast growth factor 23 works.
    J Am Soc Nephrol
    2007
    18
    1637
    47
    PubMed
  44. Gutiérrez
    OM
    ,  
    Januzzi
    JL
    ,  
    Isakova
    T
    ,  
    Laliberte
    K
    ,  
    Smith
    K
    ,  
    Collerone
    G
    .  
    et al.
    Fibroblast growth factor 23 and left ventricular hypertrophy in chronic kidney disease.
    Circulation
    2009
    119
    2545
    52
    PubMed
  45. Mirza
    MA
    ,  
    Larsson
    A
    ,  
    Melhus
    H
    ,  
    Lind
    L
    ,  
    Larsson
    TE
    .  
    Serum intact FGF23 associate with left ventricular mass, hypertrophy and geometry in an elderly population.
    Atherosclerosis
    2009
    207
    546
    51
    PubMed
  46. Detillieux
    KA
    ,  
    Sheikh
    F
    ,  
    Kardami
    E
    ,  
    Cattini
    PA
    .  
    Biological activities of fibroblast growth factor-2 in the adult myocardium.
    Cardiovasc Res
    2003
    57
    8
    19
    PubMed
  47. Takeshita
    K
    ,  
    Fujimori
    T
    ,  
    Kurotaki
    Y
    ,  
    Honjo
    H
    ,  
    Tsujikawa
    H
    ,  
    Yasui
    K
    .  
    et al.
    Sinoatrial node dysfunction and early unexpected death of mice with a defect of klotho gene expression.
    Circulation
    2004
    109
    1776
    82
    PubMed
  48. Yu
    X
    ,  
    Ibrahimi
    OA
    ,  
    Goetz
    R
    ,  
    Zhang
    F
    ,  
    Davis
    SI
    ,  
    Garringer
    HJ
    .  
    et al.
    Analysis of the biochemical mechanisms for the endocrine actions of fibroblast growth factor-23.
    Endocrinology
    2005
    146
    4647
    56
    PubMed
  49. Parker BD, Schurgers LJ, Vermeer C, Schiller NB, Whooley MA, Ix JH. The association of uncarboxylated matrix Gla protein with mitral annular calcification differs by diabetes status: the Heart and Soul Study. Atherosclerosis. 2010. [Forthcoming].
  50. Price
    PA
    ,  
    Lim
    JE
    .  
    The inhibition of calcium phosphate precipitation by fetuin is accompanied by the formation of a fetuin-mineral complex.
    J Biol Chem
    2003
    278
    22144
    52
    PubMed
  51. Ix
    JH
    ,  
    Shlipak
    MG
    ,  
    Sarnak
    MJ
    ,  
    Beck
    GJ
    ,  
    Greene
    T
    ,  
    Wang
    X
    .  
    et al.
    Fetuin-A is not associated with mortality in chronic kidney disease.
    Kidney Int
    2007
    72
    1394
    9
    PubMed
  52. Lim
    P
    ,  
    Collet
    JP
    ,  
    Moutereau
    S
    ,  
    Guigui
    N
    ,  
    Mitchell-Heggs
    L
    ,  
    Loric
    S
    .  
    et al.
    Fetuin-A is an independent predictor of death after ST-elevation myocardial infarction.
    Clin Chem
    2007
    53
    1835
    40
  53. Weikert
    C
    ,  
    Stefan
    N
    ,  
    Schulze
    MB
    ,  
    Pischon
    T
    ,  
    Berger
    K
    ,  
    Joost
    HG
    .  
    et al.
    Plasma fetuin-a levels and the risk of myocardial infarction and ischemic stroke.
    Circulation
    2008
    118
    2555
    62
    PubMed
  54. Hennige
    AM
    ,  
    Staiger
    H
    ,  
    Wicke
    C
    ,  
    Machicao
    F
    ,  
    Fritsche
    A
    ,  
    Häring
    HU
    .  
    et al.
    Fetuin-A induces cytokine expression and suppresses adiponectin production.
    PLoS One
    2008
    3
    1765
    PubMed
  55. Ix
    JH
    ,  
    Chertow
    GM
    ,  
    Shlipak
    MG
    ,  
    Brandenburg
    VM
    ,  
    Ketteler
    M
    ,  
    Whooley
    MA
    .  
    Association of fetuin-A with mitral annular calcification and aortic stenosis among persons with coronary heart disease: data from the Heart and Soul Study.
    Circulation
    2007
    115
    2533
    9
    PubMed
  56. Ix
    JH
    ,  
    Wassel
    CL
    ,  
    Kanaya
    AM
    ,  
    Vittinghoff
    E
    ,  
    Johnson
    KC
    ,  
    Koster
    A
    .  
    et al.
    Health ABC Study
    Fetuin-A and incident diabetes mellitus in older persons.
    JAMA
    2008
    300
    182
    8
    PubMed
  57. Jonsson
    KB
    ,  
    Zahradnik
    R
    ,  
    Larsson
    T
    ,  
    White
    KE
    ,  
    Sugimoto
    T
    ,  
    Imanishi
    Y
    .  
    et al.
    Fibroblast growth factor 23 in oncogenic osteomalacia and X-linked hypophosphatemia.
    N Engl J Med
    2003
    348
    1656
    63
    PubMed
  58. Cranenburg
    EC
    ,  
    Vermeer
    C
    ,  
    Koos
    R
    ,  
    Boumans
    ML
    ,  
    Hackeng
    TM
    ,  
    Bouwman
    FG
    .  
    et al.
    The circulating inactive form of matrix Gla Protein (ucMGP) as a biomarker for cardiovascular calcification.
    J Vasc Res
    2008
    45
    427
    36
    PubMed
  59. Hermans
    MM
    ,  
    Brandenburg
    V
    ,  
    Ketteler
    M
    ,  
    Kooman
    JP
    ,  
    van der Sande
    FM
    ,  
    Gladziwa
    U
    .  
    et al.
    Study on the relationship of serum fetuin-A concentration with aortic stiffness in patients on dialysis.
    Nephrol Dial Transplant
    2006
    21
    1293
    9
    PubMed
  60. Hermans
    MM
    ,  
    Brandenburg
    V
    ,  
    Ketteler
    M
    ,  
    Kooman
    JP
    ,  
    van der Sande
    FM
    ,  
    Boeschoten
    EW
    .  
    et al.
    Netherlands cooperative study on the adequacy of Dialysis (NECOSAD)
    Association of serum fetuin-A levels with mortality in dialysis patients.
    Kidney Int
    2007
    72
    202
    7
    PubMed

Appendix

Plasma FGF23 concentrations were measured by using a C-terminal human enzyme-linked immunosorbent assay (Immunotopics, San Clemente, California) (57). This assay recognizes 2 epitopes on the C-terminal side cleavage site and thus recognizes both full-length FGF23 and C-terminal cleavage fragments of FGF-23. The intra-assay coefficient of variation was 5.0%; the interassay coefficient of variation was 9.9% at a concentration of 36.4 RU/mL and 12.6% at a level 379 RU/mL. Serum ucMGP (nM) was measured by using a competitive enzyme-linked immunosorbent assay developed at VitaK BV, Maastricht University, Maastricht, the Netherlands (58). The assay detects both phosphorylated and nonphosphorylated ucMGP. The lower limit of detection is 98 nM. The intra-assay and interassay coefficients of variation were 6% and 11%, respectively, Fetuin-A was measured by a nephelometric assay (59). This assay uses the same high-specificity antibody as commercially available enzyme-linked immunosorbent assays and has been used in a previous analysis showing an association between fetuin-A and mortality in hemodialysis patients (60). The assay ranges from 0.05 to 3.5 g/L. The intra-assay coefficient of variation was 7.7%, and the interassay coefficient of variation was 8.1%.
Appendix Figure.
Distribution of FGF23*, ucMGP, and fetuin-A levels among 833 participants with coronary artery disease.

FGF23 = fibroblast growth factor 23; ucMGP = uncarboxylated matrix Gla protein.

* 16 participants with FGF23 levels >480 RU/mL (range, 529 to 3150 RU/mL) were not included because of space limitations.

Figure.
Unadjusted event-free survival, by tertiles of FGF23, ucMGP, and fetuin-A.

CVD = cardiovascular disease; FGF23 = fibroblast growth factor 23; ucMGP = uncarboxylated matrix Gla protein.

Appendix Table 1.

Comparison of Variables in Persons Excluded Because of Missing Measurements

Appendix Table 1.

Table 1.

Baseline Characteristics of Participants With and Without Events

Table 1.

Appendix Table 2.

Association of Calcium and Phosphorus With ln-FGF23, ucMGP, and Fetuin-A Levels

Appendix Table 2.

Appendix Table 3.

Association Between Baseline Factors and ln-FGF23, ucMGP, and Fetuin-A Levels

Appendix Table 3.

Table 2.

Association of FGF23, ucMGP, and Fetuin-A Levels With All-Cause Mortality or CVD Events

Table 2.

Table 3.

HRs for Individual Events per Change in FGF23, ucMGP, or Fetuin-A Level

Table 3.

Clinical Slide Sets

Terms of Use

The In the Clinic® slide sets are owned and copyrighted by the American College of Physicians (ACP). All text, graphics, trademarks, and other intellectual property incorporated into the slide sets remain the sole and exclusive property of the ACP. The slide sets may be used only by the person who downloads or purchases them and only for the purpose of presenting them during not-for-profit educational activities. Users may incorporate the entire slide set or selected individual slides into their own teaching presentations but may not alter the content of the slides in any way or remove the ACP copyright notice. Users may make print copies for use as hand-outs for the audience the user is personally addressing but may not otherwise reproduce or distribute the slides by any means or media, including but not limited to sending them as e-mail attachments, posting them on Internet or Intranet sites, publishing them in meeting proceedings, or making them available for sale or distribution in any unauthorized form, without the express written permission of the ACP. Unauthorized use of the In the Clinic slide sets will constitute copyright infringement.

This feature is available only to Registered Users

Subscribe/Learn More
Submit a Comment

2 Comments

Edward R Smith

Brighton & Sussex University Hospitals NHS Trust

May 26, 2010

Important differences in Fetuin-A measurement

TO THE EDITOR:

In their recent article (1), Parker and colleagues report finding no significant association between fetuin-A levels and mortality in a cohort with prevalent coronary artery disease. Our understanding of fetuin-A biology is greatly undermined by the lack of agreement between different methods of measurement. It is particularly important therefore that method descriptions are unambiguous. The authors comment that their nephelometric fetuin-A assay "uses the same high-specificity antibody as commercially available enzyme-linked immunosorbent assays". It is unclear to which commercially available ELISAs they are referring; the two most widely-used commercial kits not only use different antisera to one another but also employ a sandwich format with two different antibodies that recognise spatially distinct molecular epitopes. This statement implies a degree of equality with other methods that we have found not to be the case (2). The authors justify the use of this method with reference to a previous study, in which use of the same fetuin-A assay demonstrated an association between fetuin-A levels and mortality in haemodialysis patients (3). However, it does not necessarily follow that this method is powered to detect significant associations in other settings, which may be masked by a lack of specificity to the biologically relevant fraction.

The poor agreement between commercial assays for fetuin-A does not represent a mere analytical nuance, but has critical implications for observations derived from their measurements. For example, in a cohort of patients with mild-to-moderate chronic kidney disease (CKD), we recently showed that fetuin-A was an independent predictor of progressive aortic stiffness (4), a vascular parameter known to be predictive of cardiovascular events and mortality. This relationship was lost, even in simple bivariate correlation, using fetuin-A measurements made with an alternative assay. Our experiments suggest that the lack of agreement in both CKD as well as non-CKD settings, reflects variation in antibody specificity for different glycosylated forms of fetuin-A (2). Although the authors of the present study rightly acknowledge that "results may differ with other assays" it remains a relatively unappreciated point that differences in antibody specificity to different modified forms of the same protein (a heterogeneous mixture) can mask potentially important associations. In the case of fetuin-A, we wonder if the investigators have considered further study using alternative methodology.

References

1. Parker BD, Schurgers LJ, Brandenburg VM, Christenson RH, Vermeer C, Ketteler M, et al. The associations of fibroblast growth factor 23 and uncarboxylated matrix gla protein with mortality in coronary artery disease. Ann Intern Med. 2010;152:640-8.

2. Smith ER, Ford ML, Tomlinson LA, Rocks BF, Rajkumar C, Holt SG. Poor agreement between commercial ELISAs for plasma fetuin-A: an effect of protein glycosylation? Clin Chim Acta 2010;[in press].

3. Hermans MM, Brandenburg V, Ketteler M, Kooman JP, van der Sande FM, Boeschoten EW, et al; Netherlands cooperative study on the adequacy of Dialysis (NECOSAD). Association of serum fetuin-A levels with mortality in dialysis patients. Kidney Int. 2007;72:202-7.

4. Ford ML, Tomlinson LA, Smith ER, Rajkumar C, Holt SG. Fetuin-A is an independent determinant of change of aortic stiffness over 1 year in non-diabetic patients with CKD stages 3 and Nephrol Dial Transplant. 2010;[in press].

Conflict of Interest:

None declared

Joachim H. Ix

University of California San Diego, and Veterans Affairs San Diego Healthcare System

August 3, 2010

In Response to Smith and Holt

Vincent M. Brandenburg, Benjamin D. Parker, and Joachim H. Ix

From the Department of Cardiology, University Hospital of the RWTH Aachen, Aachen, Germany (V.M.B), and the Department of Medicine, Division of Nephrology (B.D.P, J.H.I), and Department of Family and Preventive Medicine (J.H.I), University of California, San Diego; the Veterans Affairs San Diego Healthcare System (B.D.P, J.H.I), San Diego, California

We appreciate Drs. Smith and Holt's insightful comments about the importance of assay characteristics and we agree that associations between particular measurements and outcome might be influenced by the assay. Moreover, test specificty and reliability might depend upon factors present in the participants and specimens being evaluated.

We used a fetuin-A assay developed by our group in Aachen, Germany; an assay that is not commercially available. This assay has been described in greater detail in our prior publications(1) and was used initially to demonstrate the associations of fetuin-A with mortality in ESRD patients.(2) We evaluated the nephelometric method for AHSG serum measurement in a side-by side comparison with immunoblot analysis to exclude cross-reactivity of the antibodies with other serum proteins and proteolyitc fragments of fetuin-A. Final serum fetuin-A concentrations were calculated by regression analysis of a serial dilution curve obtained from standard serum. For comparison and reliability testing, a control solution of purified serum fetuin-A powder (Boehringer Mannheim GmbH, Mannheim, Dade-Behrging, Marburg, Germany) was prepared. For both methods, we used the polyclonal rabbit anti-human Fetuin-A antibody that does not cross-react with fetuin-B.

In regards to similarity in findings with other groups and assays, we have demonstrated that higher fetuin-A levels were associated with the metabolic syndrome,(1) and diabetes using this assay.(3) Moreover, we have demonstrated that lower fetuin-A levels were associated with aortic stenosis; an association that was present only in non-diabetic participants.(4) These data are similar to recent findings from Drs. Smith and Holt's group using the Biovendor fetuin-A assay, where lower fetuin-A levels were associated with progression of arterial stiffness (potentially a consequence of greater arterial calcium deposition); an association that was also limited to individuals without diabetes.(5) Nonetheless, we are uncertain of the correlation of our assay with that from Biovendor. We agree that future studies with multiple assays may be useful to demonstrate their correlations one to another, and to determine which may have the strongest associations with arterial calcification, arterial stiffness, and CVD events in different settings.

REFERENCES:

1. Ix JH, Shlipak MG, Brandenburg VM, Ali S, Ketteler M, Whooley MA. Association between human fetuin-A and the metabolic syndrome: data from the Heart and Soul Study. Circulation. Apr 11 2006;113(14):1760-1767.

2. Ketteler M, Bongartz P, Westenfeld R, et al. Association of low fetuin- A (AHSG) concentrations in serum with cardiovascular mortality in patients on dialysis: a cross-sectional study. Lancet. Mar 8 2003;361(9360):827- 833.

3. Parker BD, Schurgers LJ, Brandenburg VM, et al. The associations of fibroblast growth factor 23 and uncarboxylated matrix Gla protein with mortality in coronary artery disease: the Heart and Soul Study. Ann Intern Med. May 18;152(10):640-648.

4. Ix JH, Chertow GM, Shlipak MG, Brandenburg VM, Ketteler M, Whooley MA. Association of fetuin-A with mitral annular calcification and aortic stenosis among persons with coronary heart disease: data from the Heart and Soul Study. Circulation. May 15 2007;115(19):2533-2539.

5. Ford ML, Tomlinson LA, Smith ER, Rajkumar C, Holt SG. Fetuin-A is an independent determinant of change of aortic stiffness over 1 year in non- diabetic patients with CKD stages 3 and 4. Nephrol Dial Transplant. Jun;25(6):1853-1858.

Conflict of Interest:

None declared

PDF
Not Available
Citations
Citation

Parker BD, Schurgers LJ, Brandenburg VM, Christenson RH, Vermeer C, Ketteler M, et al. The Associations of Fibroblast Growth Factor 23 and Uncarboxylated Matrix Gla Protein With Mortality in Coronary Artery Disease: The Heart and Soul Study. Ann Intern Med. ;152:640–648. doi: 10.7326/0003-4819-152-10-201005180-00004

Download citation file:

  • Ris (Zotero)
  • EndNote
  • BibTex
  • Medlars
  • ProCite
  • RefWorks
  • Reference Manager

© 2019

×
Permissions

Published: Ann Intern Med. 2010;152(10):640-648.

DOI: 10.7326/0003-4819-152-10-201005180-00004

0 Citations

See Also

Markers of Mineral Metabolism and Cardiovascular Disease
Important Differences in Measurement of Fetuin-A
Important Differences in Measurement of Fetuin-A
View MoreView Less

Related Articles

Update in Women's Health: Evidence Published in 2016
Annals of Internal Medicine; 166 (7): W48-W52
Heart: A Physiologic and Clinical Study of Cardiovascular Diseases.
Annals of Internal Medicine; 31 (6): 1133-1134
Postmenopausal Hormone Replacement Therapy and the Primary Prevention of Cardiovascular Disease
Annals of Internal Medicine; 137 (4): 273-284
Update in General Internal Medicine
Annals of Internal Medicine; 143 (3): 212-221
View MoreView Less

Journal Club

Review: Non–calcium-based phosphate binders reduce mortality compared with calcium-based binders in CKD
Annals of Internal Medicine; 159 (10): JC2
Review: Folic acid may reduce risk for CVD and stroke, and B-vitamin complex may reduce risk for stroke
Annals of Internal Medicine; 169 (8): JC44
In type 2 diabetes with CVD and kidney disease, empagliflozin reduced mortality and hospitalization
Annals of Internal Medicine; 168 (10): JC52
In stable CVD, rivaroxaban plus aspirin reduced CV events and increased bleeding compared with aspirin alone
Annals of Internal Medicine; 167 (10): JC52
View MoreView Less

Related Point of Care

Acute Kidney Injury
Annals of Internal Medicine; 167 (9): ITC66-ITC80
Chronic Kidney Disease
Annals of Internal Medicine; 162 (11): ITC1
Chronic Kidney Disease
Annals of Internal Medicine; 150 (3): ITC2-1
View MoreView Less

Related Topics

Cardiology
Coronary Heart Disease
Prevention/Screening

Cardiology, Coronary Heart Disease, Prevention/Screening.

PubMed Articles

Universal Electrocardiographic Screening for Long QT Syndrome in Hospitalized Neonates.
Am J Perinatol 2019.
Metabolic Costs During Backward Running with Body Weight Support.
Int J Sports Med 2019.
View More

Results provided by: PubMed

CME/MOC Activity Requires Users to be Registered and Logged In.
Sign in below to access your subscription for full content
INDIVIDUAL SIGN IN
Sign In|Set Up Account
You will be directed to acponline.org to register and create your Annals account
Annals of Internal Medicine
CREATE YOUR FREE ACCOUNT
Create Your Free Account|Why?
To receive access to the full text of freely available articles, alerts, and more. You will be directed to acponline.org to complete your registration.
×
The Comments Feature Requires Users to be Registered and Logged In.
Sign in below to access your subscription for full content
INDIVIDUAL SIGN IN
Sign In|Set Up Account
You will be directed to acponline.org to register and create your Annals account
Annals of Internal Medicine
CREATE YOUR FREE ACCOUNT
Create Your Free Account|Why?
To receive access to the full text of freely available articles, alerts, and more. You will be directed to acponline.org to complete your registration.
×
link to top

Content

  • Home
  • Latest
  • Issues
  • Channels
  • CME/MOC
  • In the Clinic
  • Journal Club
  • Web Exclusives

Information For

  • Author Info
  • Reviewers
  • Press
  • Readers
  • Institutions / Libraries / Agencies
  • Advertisers

Services

  • Subscribe
  • Renew
  • Alerts
  • Current Issue RSS
  • Latest RSS
  • In the Clinic RSS
  • Reprints & Permissions
  • Contact Us
  • Help
  • About Annals
  • About Mobile
  • Patient Information
  • Teaching Tools
  • Annals in the News
  • Share Your Feedback

Awards and Cover

  • Personae (Cover Photo)
  • Junior Investigator Awards
  • Poetry Prize

Other Resources

  • ACP Online
  • Career Connection
  • ACP Advocate Blog
  • ACP Journal Wise

Follow Annals On

  • Twitter Link
  • Facebook Link
acp link acp
silverchair link silverchair

Copyright © 2019 American College of Physicians. All Rights Reserved.

Print ISSN: 0003-4819 | Online ISSN: 1539-3704

Privacy Policy

|

Conditions of Use

This site uses cookies. By continuing to use our website, you are agreeing to our privacy policy. | Accept
×

You need a subscription to this content to use this feature.

×
PDF Downloads Require Access to the Full Article.
Sign in below to access your subscription for full content
INDIVIDUAL SIGN IN
Sign In|Set Up Account
You will be directed to acponline.org to register and create your Annals account
INSTITUTIONAL SIGN IN
Open Athens|Shibboleth|Log In
Annals of Internal Medicine
PURCHASE OPTIONS
Buy This Article|Subscribe
You will be redirected to acponline.org to sign-in to Annals to complete your purchase.
CREATE YOUR FREE ACCOUNT
Create Your Free Account|Why?
To receive access to the full text of freely available articles, alerts, and more. You will be directed to acponline.org to complete your registration.
×
Access to this Free Content Requires Users to be Registered and Logged In. Please Choose One of the Following Options
Sign in below to access your subscription for full content
INDIVIDUAL SIGN IN
Sign In|Set Up Account
You will be directed to acponline.org to register and create your Annals account
Annals of Internal Medicine
CREATE YOUR FREE ACCOUNT
Create Your Free Account|Why?
To receive access to the full text of freely available articles, alerts, and more. You will be directed to acponline.org to complete your registration.
×