Vincent Brandenburg

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

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.

Association between human fetuin-A and the metabolic syndrome: data from the Heart and Soul Study.

Background— Fetuin-A is a multifunctional hepatic secretory protein that inhibits the action of insulin in experimental animals. We evaluated the association between human serum fetuin-A and the metabolic syndrome (MetS) in a cohort of persons with coronary artery disease. Methods and Results— We defined MetS by the National Cholesterol Education Program criteria among 711 nondiabetic outpatients with coronary artery disease. The mean age was 67 years, and 82% were male. We divided participants into quartiles by serum fetuin-A concentrations. A total of 45% of participants (80 of 177) in the highest quartile of fetuin-A had MetS compared with 24% of participants (42 of 177) in the lowest quartile (odds ratio, 2.7; 95% confidence interval, 1.7 to 4.2; P<0.001). This association persisted after adjustment for potential confounding variables, including hypertension, body mass index, and inflammatory biomarkers (adjusted odds ratio, 2.0; 95% confidence interval, 1.1 to 3.5; P=0.02). Higher fetuin-A quartiles were also strongly and independently associated with higher low-density lipoprotein, non–high-density lipoprotein (HDL), and triglyceride concentrations and lower HDL concentrations (all P<0.01). Conclusions— Higher human fetuin-A concentrations are strongly associated with MetS and an atherogenic lipid profile. Future studies should evaluate whether fetuin-A predicts coronary artery disease risk.

Vitamin D deficiency is associated with sudden cardiac death, combined cardiovascular events, and mortality in haemodialysis patients

Aims Dialysis patients experience an excess mortality, predominantly of sudden cardiac death (SCD). Accumulating evidence suggests a role of vitamin D for myocardial and overall health. This study investigated the impact of vitamin D status on cardiovascular outcomes and fatal infections in haemodialysis patients. Methods and results 25-hydroxyvitamin D [25(OH)D] was measured in 1108 diabetic haemodialysis patients who participated in the German Diabetes and Dialysis Study and were followed up for a median of 4 years. By Cox regression analyses, we determined hazard ratios (HR) for pre-specified, adjudicated endpoints according to baseline 25(OH)D levels: SCD (n = 146), myocardial infarction (MI, n = 174), stroke (n = 89), cardiovascular events (CVE, n = 414), death due to heart failure (n = 37), fatal infection (n = 111), and all-cause mortality (n = 545). Patients had a mean age of 66 ± 8 years (54% male) and median 25(OH)D of 39 nmol/L (interquartile range: 28–55). Patients with severe vitamin D deficiency [25(OH)D of≤ 25 nmol/L] had a 3-fold higher risk of SCD compared with those with sufficient 25(OH)D levels >75 nmol/L [HR: 2.99, 95% confidence interval (CI): 1.39–6.40]. Furthermore, CVE and all-cause mortality were strongly increased (HR: 1.78, 95% CI: 1.18–2.69, and HR: 1.74, 95% CI: 1.22–2.47, respectively), all persisting in multivariate models. There were borderline non-significant associations with stroke and fatal infection while MI and deaths due to heart failure were not meaningfully affected. Conclusion Severe vitamin D deficiency was strongly associated with SCD, CVE, and mortality, and there were borderline associations with stroke and fatal infection. Whether vitamin D supplementation decreases adverse outcomes requires further evaluation.

Association of Fetuin-A With Mitral Annular Calcification and Aortic Stenosis Among Persons With Coronary Heart Disease. Data From the Heart and Soul Study

Background— Fetuin-A is a multifunctional hepatic secretory protein that inhibits dystrophic vascular and valvular calcification. Lower serum fetuin-A concentrations are associated with valvular calcification in persons with end-stage renal disease. Whether fetuin-A is associated with valvular calcification in other patient populations is unknown. Methods and Results— We evaluated the associations among serum fetuin-A concentrations, mitral annular calcification, and aortic stenosis in 970 ambulatory persons with coronary heart disease and without severe kidney disease. The presence or absence of mitral annular calcification and aortic stenosis was determined by transthoracic echocardiography. The subjects’ mean age was 66 years; 81% were men; 189 (20%) had mitral annular calcification; and 79 (8%) had aortic stenosis. Participants were categorized by tertiles of fetuin-A concentrations. Those within the highest fetuin-A tertile had significantly lower odds of mitral annular calcification compared with the lowest tertile (adjusted odds ratio, 0.47; 95% confidence interval, 0.29 to 0.77; P=0.002); this association was similar regardless of diabetes status (P for interaction=0.34). In contrast, the association of fetuin-A with aortic stenosis was modified by the presence or absence of diabetes mellitus (P for interaction=0.03). Among participants without diabetes, the highest fetuin-A tertile had a significantly lower odds of aortic stenosis compared with the lowest tertile (adjusted odds ratio, 0.37; 95% confidence interval, 0.15 to 0.92; P=0.03), whereas among participants with diabetes, no statistically significant association was observed between fetuin-A and aortic stenosis (adjusted odds ratio, 1.49; 95% confidence interval, 0.48 to 4.63; P=0.49). Conclusions— Among persons with coronary heart disease, we observed an inverse association of fetuin-A and mitral annular calcification. An inverse association also was observed between fetuin-A and aortic stenosis among participants without diabetes mellitus. Fetuin-A may represent an important inhibitor of dystrophic calcification in persons with coronary heart disease.

Circulating Nonphosphorylated Carboxylated Matrix Gla Protein Predicts Survival in ESRD

The mechanisms for vascular calcification and its associated cardiovascular mortality in patients with ESRD are not completely understood. Dialysis patients exhibit profound vitamin K deficiency, which may impair carboxylation of the calcification inhibitor matrix gla protein (MGP). Here, we tested whether distinct circulating inactive vitamin K-dependent proteins associate with all-cause or cardiovascular mortality. We observed higher levels of both desphospho-uncarboxylated MGP (dp-ucMGP) and desphospho-carboxylated MGP (dp-cMGP) among 188 hemodialysis patients compared with 98 age-matched subjects with normal renal function. Levels of dp-ucMGP correlated with those of protein induced by vitamin K absence II (PIVKA-II; r = 0.62, P < 0.0001). We found increased PIVKA-II levels in 121 (64%) dialysis patients, indicating pronounced vitamin K deficiency. Kaplan-Meier analysis showed that patients with low levels of dp-cMGP had an increased risk for all-cause and cardiovascular mortality. Multivariable Cox regression confirmed that low levels of dp-cMGP increase mortality risk (all-cause: HR, 2.2; 95% CI, 1.1 to 4.3; cardiovascular: HR, 2.7; 95% CI, 1.2 to 6.2). Furthermore, patients with higher vascular calcification scores showed lower levels of dp-cMGP. In 17 hemodialysis patients, daily supplementation with vitamin K2 for 6 weeks reduced dp-ucMGP levels by 27% (P = 0.003) but did not affect dp-cMGP levels. In conclusion, the majority of dialysis patients exhibit pronounced vitamin K deficiency. Lower levels of circulating dp-cMGP may serve as a predictor of mortality in dialysis patients. Whether vitamin K supplementation improves outcomes requires further study.

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

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.

Characterisation and potential diagnostic value of circulating matrix Gla protein (MGP) species

Matrix γ-carboxyglutamate (Gla) protein (MGP) is an important local inhibitor of vascular calcification, which can undergo two post-translational modifications: vitamin K-dependent γ-glutamate carboxylation and serine phosphorylation. While carboxylation is thought to have effects upon binding of calcium-ions, phosphorylation is supposed to affect the cellular release of MGP. Since both modifications can be exerted incompletely, various MGP species can be detected in the circulation. MGP levels were measured with two commercially available competitive and two novel sandwich assays in healthy controls, in patients with rheumatic disease, aortic valve disease, and end-stage renal disease, as well as in volunteers after vitamin K supplementation (VKS) and treatment with vitamin K antagonists (VKA). Major differences were found between the MGP assays, including significantly different behaviour with regard to vascular disease and the response to VKA and VKS. The dual-antibody assay measuring non-phosphorylated, non-carboxylated MGP (dp-ucMGP) was particularly sensitive for these changes and would be suited to assess the vascular vitamin K status. We conclude that the different assays for particular circulating MGP species allows the assessment of various aspects of the MGP system.

Ultrastructural Analysis of Vascular Calcifications in Uremia

Accelerated intimal and medial calcification and sclerosis accompany the increased cardiovascular mortality of dialysis patients, but the pathomechanisms initiating microcalcifications of the media are largely unknown. In this study, we systematically investigated the ultrastructural properties of medial calcifications from patients with uremia. We collected iliac artery segments from 30 dialysis patients before kidney transplantation and studied them by radiography, microcomputed tomography, light microscopy, and transmission electron microscopy including electron energy loss spectrometry, energy dispersive spectroscopy, and electron diffraction. In addition, we performed synchrotron x-ray analyses and immunogold labeling to detect inhibitors of calcification. Von Kossa staining revealed calcification of 53% of the arteries. The diameter of these microcalcifications ranged from 20 to 500 nm, with a core-shell structure consisting of up to three layers (subshells). Many of the calcifications consisted of 2- to 10-nm nanocrystals and showed a hydroxyapatite and whitlockite crystalline structure and mineral phase. Immunogold labeling of calcification foci revealed the calcification inhibitors fetuin-A, osteopontin, and matrix gla protein. These observations suggest that uremic microcalcifications originate from nanocrystals, are chemically diverse, and intimately associate with proteinaceous inhibitors of calcification. Furthermore, considering the core-shell structure of the calcifications, apoptotic bodies or matrix vesicles may serve as a calcification nidus.

Vitamin D status and clinical outcomes in incident dialysis patients: results from the NECOSAD study

BACKGROUND The majority of dialysis patients suffer from vitamin D deficiency, which might contribute to an adverse health outcome. We aimed to elucidate whether European dialysis patients with low 25-hydroxyvitamin D (25(OH)D) levels are at increased risk of mortality and specific fatal events. METHODS This was a prospective cohort study of incident dialysis patients in the Netherlands (the NECOSAD). We selected all patients with measured 25(OH)D at 12 months after the start of dialysis, the baseline for our study. By Cox regression analyses, we assessed the impact of 25(OH)D levels on short-term (6 months of follow-up) as well as longer-term mortality (3 years of follow-up). Associations of 25(OH)D levels with cardiovascular and non-cardiovascular mortality were also determined. RESULTS The data from 762 patients (39% females, age 59 ± 15 years, 25(OH)D = 18 ± 11 ng/mL) were available. Fifty-one and 213 patients died during a follow-up of 6 months and 3 years, respectively. After adjustments for possible confounders, the hazard ratio (HR) (with 95% CI) for mortality was 2.0 (1.0-3.8) for short-term and 1.5 (1.0-2.1) for longer-term mortality when comparing patients with 25(OH)D levels ≤ 10 ng/mL with those presenting with 25(OH)D levels > 10 ng/mL. Adjusted HRs for cardiovascular mortality were 2.7 (1.1-6.5) and 1.7 (1.1-2.7) for short- and longer-term mortality, respectively. For non-cardiovascular mortality, we observed no relevant association overall. The impact of 25(OH)D levels on clinical events was modified by parathyroid hormone (PTH) status, with low 25(OH)D levels meaningfully affecting outcomes only in patients with PTH levels above the median of 123 pmol/L. CONCLUSIONS Vitamin D deficiency in dialysis patients is associated with an adverse health outcome, in particular with short-term cardiovascular mortality. Intervention studies are urgently needed to evaluate whether vitamin D supplementation improves health outcomes of dialysis patients.

Progression of aortic calcification is associated with disorders of mineral metabolism and mortality in chronic dialysis patients

BACKGROUND Previous studies have shown that simple imaging methods may be useful for detection of vascular calcifications in dialysis patients. Based on annual, plain chest X-rays during follow-up on dialysis, we studied the associations of mineral metabolism with the presence and progression of aortic calcification. In addition, we assessed the impact of aortic calcification on mortality. METHODS Three hundred and eighty-four patients who started haemodialysis or peritoneal dialysis between 1997 and 2007 were included (age 61 ± 15 years, 64% male, 61% haemodialysis). Annual chest X-rays were screened for calcification in the aortic arch, and patients were categorized as having no, moderate or severe calcification. Progression was defined as an increase in calcification category during follow-up on dialysis. RESULTS At baseline, 96 (25%) patients had severe, 205 (53%) patients had moderate and 83 (22%) patients had no aortic calcification. For 237 of the 288 patients with no or moderate calcifications at baseline, X-rays were available for follow-up. During follow-up (mean 2.3 years), aortic calcification progressed in 71 patients (30%). We found that baseline plasma calcium > 9.5 mg/dL and iPTH > 300 pg/mL were associated with progression [odds ratios of 3.1, 95% confidence interval (1.2-8.2) and 4.4 (1.4-14.1), respectively]. Progression of aortic calcification was significantly associated with increased risk of all-cause mortality (hazard ratio: 1.9; 95% CI: 1.2-3.1) and cardiovascular mortality (hazard ratio: 2.7; 95% CI: 1.3-5.6). CONCLUSIONS Aortic calcification progressed in almost a third of the patients during dialysis. Hypercalcaemia and hyperparathyroidism were associated with an increased risk of progression. Progression of aortic calcification was significantly related to an increased mortality risk.