Serum level of the phosphaturic factor FGF23 is associated with abdominal aortic calcification in men: the STRAMBO study

Plasma FGF23 and the risk of stroke: the Northern Manhattan Study (NOMAS)

OBJECTIVE

To examine fibroblast growth factor 23 (FGF23) as a risk factor for incident stroke in a racially/ethnically diverse population-based urban cohort.

METHODS

Stroke-free Northern Manhattan Study participants with FGF23 measurements (n = 2,525) were followed for a mean of 12 (±5) years to detect incident strokes. We used Cox proportional hazards models to estimate the association of baseline FGF23 with incident total, ischemic, and hemorrhagic stroke.

RESULTS

Median FGF23 was 57 relative units (RU)/mL (interquartile range = 44-81 RU/mL). Each unit increase of natural log-transformed FGF23 conferred a 40% greater overall stroke risk after adjusting for estimated glomerular filtration rate and sociodemographic and vascular risk factors (hazard ratio = 1.4, 95% confidence interval 1.1-1.6, p = 0.004). Penalized spline analysis revealed a linear association with overall stroke risk at ≥90 RU/mL FGF23, compared with <90 RU/mL (hazard ratio = 1.5, 95% confidence interval = 1.2-2.1, p = 0.004). Greater FGF23 conferred a doubling of intracerebral hemorrhage (ICH) risk but no significant increased risk of ischemic stroke. The associations of elevated FGF23 levels with greater risks of overall stroke and ICH events were independent of phosphate and parathyroid hormone levels and were similar among participants without chronic kidney disease.

CONCLUSIONS

Elevated FGF23 was a risk factor for overall stroke and ICH events, in particular in a racially and ethnically diverse urban community, independent of chronic kidney disease.

Cardiovascular risk markers associated with arterial calcification in patients with chronic kidney disease Stages 3 and 4

Background

The contribution of pro-inflammatory markers to cardiovascular (CV) risk and vascular calcification in chronic kidney disease (CKD) remains largely to be elucidated. We investigated the association between plasma levels of several biomarkers and calcification volume in three different vascular beds in CKD Stages 3 and 4 patients.

Methods

This is a cross-sectional, exploratory study in patients with an estimated glomerular filtration rate (eGFR) ≥20 and ≤45 mL/min/1.73 m² and serum phosphorus ≥3.5 and <6.0 mg/dL enrolled in a previously published randomized, double blind, placebo-controlled single-centre trial. Ethylenediaminetetraacetic acid (EDTA) plasma samples were collected at baseline before patients received study medication and analysed for the presence of a number of biomarkers. Coronary artery calcium (CAC), thoracic aortic calcification (TAC) and abdominal aortic calcification (AAC) volumes were measured using standard electron-beam computed tomography protocols. Associations were adjusted for age, sex, smoking, body mass index, diabetes mellitus status, low-density lipoprotein cholesterol (LDL-C), systolic blood pressure and eGFR.

Results

Associations with CAC were found for β2-microglobulin (B2M), fibroblast growth factor 23 (FGF23), interleukin-8 (IL-8) and IL-18. AAC was associated with: B2M, FGF23 and IL-2 receptor alpha (IL-2 RA). TAC was associated with: B2M, FGF23, IL-2 RA, IL-18 and tumour necrosis factor receptor type I. For most of the analysed biomarkers, there were non-significant trends of associations with calcification.

Conclusions

This exploratory study found that elevated plasma levels of several inflammatory biomarkers are significantly associated with arterial calcification in CKD Stages 3 and 4 patients. A greater understanding of inflammation and calcification in CKD patients may help the development of CV risk-assessment algorithms for better management of these patients.

Fibroblast growth factor 23, the ankle-brachial index, and incident peripheral artery disease in the Cardiovascular Health Study

BACKGROUND

Fibroblast growth factor 23 (FGF23) has emerged as a novel risk factor for mortality and cardiovascular events. Its association with the ankle-brachial index (ABI) and clinical peripheral artery disease (PAD) is less known.

METHODS

Using data (N = 3143) from the Cardiovascular Health Study (CHS), a cohort of community dwelling adults >65 years of age, we analyzed the cross-sectional association of FGF23 with ABI and its association with incident clinical PAD events during 9.8 years of follow up using multinomial logistic regression and Cox proportional hazards models respectively.

RESULTS

The prevalence of cardiovascular disease (CVD) and traditional risk factors like diabetes, coronary artery disease, and heart failure increased across higher quartiles of FGF23. Compared to those with ABI of 1.1-1.4, FGF23 per doubling at baseline was associated with prevalent PAD (ABI < 0.9) although this association was attenuated after adjusting for CVD risk factors, and kidney function (OR 0.91, 95% CI 0.76-1.08). FGF23 was not associated with high ABI (>1.4) (OR 1.06, 95% CI 0.75-1.51). Higher FGF23 was associated with incidence of PAD events in unadjusted, demographic adjusted, and CVD risk factor adjusted models (HR 2.26, 95% CI 1.28-3.98; highest versus lowest quartile). The addition of estimated glomerular filtration and urine albumin to creatinine ratio to the model however, attenuated these findings (HR 1.46, 95% CI, 0.79-2.70).

CONCLUSIONS

In community dwelling older adults, FGF23 was not associated with baseline low or high ABI or incident PAD events after adjusting for confounding variables. These results suggest that FGF23 may primarily be associated with adverse cardiovascular outcomes through non atherosclerotic mechanisms.

Severe abdominal aortic calcification in older men is negatively associated with DKK1 serum levels: the STRAMBO study

CONTEXT

Experimental data show that dickkopf-1 (DKK1) may be involved in the regulation of arterial calcification. However, clinical data on the association between serum DKK1 levels and severity of abdominal aortic calcification (AAC) are scarce.

OBJECTIVE

Our aim was to determine the association between serum DKK1 concentration and AAC severity in men.

DESIGN

This is a cross-sectional analysis in the STRAMBO cohort.

SETTING

The cohort was recruited from the general population.

PARTICIPANTS

We examined 1139 male volunteers aged 20 to 87 years. No specific exclusion criteria were used.

INTERVENTIONS

We collected blood samples and assessed AAC severity on the lateral spine scans obtained by a Discovery A Hologic device using the semiquantitative Kauppila score.

MAIN OUTCOME MEASURES

We tested the hypothesis that low DKK1 levels are associated with AAC severity in men.

RESULTS

In men aged 20 to 60 years, serum DKK1 levels were not associated with other variables. In men aged 60 years and older, lower DKK1 levels were associated with higher odds of severe AAC (AAC score >5). After adjustment for confounders, odds of severe AAC increased with decreasing DKK1 levels (odds ratio = 1.42, 95% confidence interval = 1.13-1.79, P < .005) and was higher below vs above the median DKK1 level (odds ratio = 2.19, 95% confidence interval = 1.37-3.49, P < .005). Heavy smoking, hypertension, ischemic heart disease, and elevated levels of fibroblast growth factor 23 were associated with severe AAC significantly, independently of DKK1 and additively with low DKK1 levels.

CONCLUSION

In older men, lower serum DKK1 levels are associated with severe AAC regardless of age and other potential confounders.

Vascular calcification

PURPOSE OF REVIEW

This review presents new evidence related to molecular mechanisms involved in the process of cardiovascular calcification, as well as to discuss new biomarkers and novel therapeutic strategies related to vascular calcification in chronic kidney disease (CKD) patients.

RECENT FINDINGS

microRNAs have emerged as potential players in the genesis of osteo-chondrogenic transformation, depending on the stimulus and the localization of vascular calcification. The disturbances of the fibroblast growth factor-23 (FGF23)/alpha-Klotho (Klotho) axis observed in CKD appear to play an important role in CKD-associated vascular calcification. Numerous studies have identified circulating biomarkers potentially responsible for vascular calcification and have evaluated their link with this process. The respective role of these biomarkers is not yet elucidated. Beyond phosphate binders, modulation of calcium-sensing receptor and vitamin K supplementation come into sight as new potential strategies to prevent cardiovascular calcification.

CONCLUSION

A better understanding of the molecular mechanisms which are responsible for cardiovascular calcification have led to a better detection and more adequate follow-up of this pathologic process, as well as the identification of novel therapeutic targets. Whether these new insights will lead to improved care and better survival of CKD patients with cardiovascular calcification remains to be demonstrated.

Quantification of lower leg arterial calcifications by high-resolution peripheral quantitative computed tomography

Vascular calcifications and bone health seem to be etiologically linked via common risk factors such as aging and subclinical chronic inflammation. Epidemiologic studies have shown significant associations between low bone mineral density (BMD), fragility fractures and calcifications of the coronary arteries and the abdominal aorta. In the last decade, high-resolution peripheral quantitative computed tomography (HR-pQCT) has emerged as in-vivo research tool for the assessment of peripheral bone geometry, density, and microarchitecture. Although vascular calcifications are frequently observed as incidental findings in HR-pQCT scans, they have not yet been incorporated into quantitative HR-pQCT analyses. We developed a semi-automated algorithm to quantify lower leg arterial calcifications (LLACs), captured by HR-pQCT. The objective of our study was to determine validity and reliability of the LLAC measure. HR-pQCT scans were downscaled to a voxel size of 250μm. After subtraction of bone volumes from the scans, LLACs were detected and contoured by a semi-automated, dual-threshold seed-point segmentation. LLAC mass (in mg hydroxyapatite; HA) was calculated as the product of voxel-based calcification volume (mm(3)) and mean calcification density (mgHA/cm(3))/1000. To determine validity, we compared LLACs to coronary artery calcifications (CACs), as quantified by multi-detector computed tomography (MDCT) and Agatston scoring in forty-six patients on chronic hemodialysis. Moreover, we investigated associations of LLACs with age, time on dialysis, type-2 diabetes mellitus, history of stroke, and myocardial infarction. In a second step, we determined intra- and inter-reader reliability of the LLAC measure. In the validity study, LLACs were present (>0mgHA) in 76% of patients, 78% of patients had CACs (>0mgHA). Median LLAC was 6.65 (0.08-24.40)mgHA and median CAC as expressed by Agatston score was 266.3 (15.88-1877.28). We found a significant positive correlation between LLAC and CAC (rho=0.6; p<0.01). Dialysis patients with type-2 diabetes mellitus (DM; 35%) and history of stroke (13%) had higher median LLAC than patients without those conditions (DM 20.0 fold greater, p=0.006; Stroke 5.1 fold greater, p=0.047). LLAC was positively correlated with time on dialysis (rho=0.337, p=0.029), there was a trend towards a positive association of LLAC and age (rho=0.289, p=0.053). The reliability study yielded excellent intra- and inter-reader agreement of the LLAC measure (intra-reader ICC=0.999, 95% CI=0.998-1.000; inter-reader ICC=0.998, 95% CI=0.994-0.999). Our study indicates that the LLAC measure has good validity and excellent reliability. The use of HR-pQCT for the simultaneous evaluation of arterial calcifications, peripheral bone geometry, bone density, and bone microarchitecture should facilitate future research on osteo-vascular interactions and potential associations with cardiovascular events.

Calcimimetics and outcomes in CKD

In the past decade, several experimental studies demonstrated an inhibitory effect of calcimimetics on the progression of vascular calcification in animals with chronic kidney disease (CKD), in keeping with the expression of the calcium-sensing receptor (CaR) in vascular tissue. In addition, calcimimetics were also found to prevent the arterial remodeling caused by CKD and to slow the progression of atherosclerosis in uremic rats and mice, respectively. The mode of action of these CaR modulators could be both via a better control of secondary hyperparathyroidism and direct effects on the vessel wall. Two main clinical trials, ADVANCE and EVOLVE, recently evaluated in patients with CKD stage 5D the effects of the calcimimetic cinacalcet on the progression of vascular calcification and hard cardiovascular outcomes, respectively. Both trials missed their respective primary end point by intent-to-treat analysis although by other prespecified analyses, including adjustment for baseline characteristics, there was strong suggestive evidence in favor of reductions in risk, in agreement with numerous experimental studies. Further clinical trials are needed to settle this issue definitively.

Fibroblast growth factor-23 and the long-term risk of hospital-associated AKI among community-dwelling older individuals

BACKGROUND AND OBJECTIVES

AKI occurs frequently in older persons. Elevated circulating fibroblast growth factor-23 (FGF-23), a known marker of impaired mineral metabolism, may also reflect tubular dysfunction and risk of AKI. This study evaluated FGF-23 as well as traditional markers of kidney disease, namely urine albumin-to-creatinine ratio (UACR) and creatinine-cystatin C estimated GFR (eGFRCrCyC), as risk factors for AKI in elderly individuals.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Plasma FGF-23, UACR, and eGFRCrCyC were measured in 3241 community-dwelling elderly individuals in the Cardiovascular Health Study. Hospitalization for AKI was defined by International Classification of Diseases, Ninth Revision, Clinical Modification codes. Associations of each biomarker with AKI were evaluated using Cox proportional hazards models adjusted for demographics, cardiovascular risk factors, and biomarkers of kidney function.

RESULTS

The mean participant age was 78 years; 60% of participants were women and 16% were African American. The median (interquartile range) values of biomarkers were as follows: FGF-23, 70 RU/ml (53, 99); UACR, 8.88 mg/g (4.71, 20.47); and eGFRCrCyC, 71 ml/min per 1.73 m(2) (59, 83). Hospitalized AKI occurred in 119 participants over 10.0 years of median follow-up. In fully adjusted analyses, compared with the lowest quartiles, the highest quartiles of FGF-23 (≥100 RU/ml) and UACR (≥20.9 mg/g) were associated with AKI (FGF-23: hazard ratio [HR], 1.99; 95% confidence interval [95% CI], 1.04 to 3.80; and UACR: HR, 3.35; 95% CI, 1.83 to 6.13). Compared with the highest quartile, the lowest quartile of eGFRCrCyC (<57 ml/min per 1.73 m(2)) was associated with AKI with an HR of 2.15 (95% CI, 1.21 to 3.82).

CONCLUSIONS

FGF-23 adjusted for albuminuria, cardiovascular disease risk factors, and baseline eGFR is independently associated with a higher risk of AKI hospitalizations in community-dwelling elderly individuals. Further studies to understand the nature of this association are warranted.

Regulation of mineral metabolism by lithium

Lithium, an inhibitor of glycogen synthase kinase 3 (GSK3), is widely used for the treatment of mood disorders. Side effects of lithium include nephrogenic diabetes insipidus, leading to renal water loss. Dehydration has in turn been shown to downregulate Klotho, which is required as co-receptor for the downregulation of 1,25(OH)2D3 formation by fibroblast growth factor 23 (FGF23). FGF23 decreases and 1,25(OH)2D3 stimulates renal tubular phosphate reabsorption. The present study explored whether lithium influences renal Klotho expression, FGF23 serum levels, 1,25(OH)2D3 formation, and renal phosphate excretion. To this end, mice were analyzed after a 14-day period of sham treatment or of treatment with lithium (200 mg/kg/day subcutaneously). Serum antidiuretic hormone (ADH), FGF23, and 1,25(OH)2D3 concentrations were determined by ELISA or EIA, renal Klotho protein abundance and GSK3 phosphorylation were analyzed by Western blotting, and serum phosphate and calcium concentration by photometry. Lithium treatment significantly increased renal GSK3 phosphorylation, enhanced serum ADH and FGF23 concentrations, downregulated renal Klotho expression, stimulated renal calcium and phosphate excretion, and decreased serum 1,25(OH)2D3 and phosphate concentrations. In conclusion, lithium treatment upregulates FGF23 formation, an effect paralleled by substantial decrease of serum 1,25(OH)2D3, and phosphate concentrations and thus possibly affecting tissue calcification.

Associations among total and food additive phosphorus intake and carotid intima-media thickness--a cross-sectional study in a middle-aged population in Southern Finland

Background

Dietary phosphorus (P) intake in Western countries is 2- to 3-fold higher than recommended, and phosphate is widely used as a food additive in eg. cola beverages and processed meat products. Elevated serum phosphate concentrations have been associated with cardiovascular disease (CVD) risk factors and CVD itself in several studies in patients with renal dysfunction and in a few studies in the general population. Carotid intima-media thickness (IMT) is a CVD risk factor, thus the aim of the study was to determine if an association between dietary P, especially food additive phosphate (FAP), intake, and IMT exists.

Methods

Associations among total phosphorus (TP) and FAP intake and carotid IMT were investigated in a cross-sectional study of 37- to 47-year-old females (n = 370) and males (n = 176) in Finland. Associations among TP intake, FAP intake, and IMT were tested by analysis of covariance (ANCOVA) in quintiles (TP) and sextiles (FAP) using sex, age, low-density/high-density lipoprotein cholesterol ratio, smoking status, and IMT sonographer as covariates.

Results

No significant associations were present between TP or FAP intake and IMT (p > 0.05, ANCOVA), but in between-group comparisons some differences were found indicating higher IMT among subjects with higher P intake. When testing for a significant linear trend with contrast analysis, a positive trend was observed between energy-adjusted TP intake and IMT among all subjects (p = 0.039), and among females a tendency for a trend existed (p = 0.067). Among all subjects, a significant positive linear trend was also present between FAP intake and IMT (p = 0.022); this trend was also seen in females (p = 0.045). In males, no significant associations or trends were noted between TP or FAP intake and IMT (p > 0.05).

Conclusions

Our results indicate that a significant linear trend exists between energy-adjusted TP intake and FAP intake, and IMT among all subjects. Based on these results, high dietary P intake should be further investigated due to its potential association with adverse cardiovascular health effects in the general population.

Public health impact of dietary phosphorus excess on bone and cardiovascular health in the general population

This review explores the potential adverse impact of the increasing phosphorus content in the American diet on renal, cardiovascular, and bone health of the general population. Increasingly, studies show that phosphorus intakes in excess of the nutrient needs of a healthy population may significantly disrupt the hormonal regulation of phosphate, calcium, and vitamin D, which contributes to disordered mineral metabolism, vascular calcification, impaired kidney function, and bone loss. Moreover, large epidemiologic studies suggest that mild elevations of serum phosphate within the normal range are associated with cardiovascular disease (CVD) risk in healthy populations without evidence of kidney disease. However, few studies linked high dietary phosphorus intake to mild changes in serum phosphate because of the nature of the study design and inaccuracies in the nutrient composition databases. Although phosphorus is an essential nutrient, in excess it could be linked to tissue damage by a variety of mechanisms involved in the endocrine regulation of extracellular phosphate, specifically the secretion and action of fibroblast growth factor 23 and parathyroid hormone. Disordered regulation of these hormones by high dietary phosphorus may be key factors contributing to renal failure, CVD, and osteoporosis. Although systematically underestimated in national surveys, phosphorus intake seemingly continues to increase as a result of the growing consumption of highly processed foods, especially restaurant meals, fast foods, and convenience foods. The increased cumulative use of ingredients containing phosphorus in food processing merits further study given what is now being shown about the potential toxicity of phosphorus intake when it exceeds nutrient needs.

Fibroblast growth factor 23 is not associated with and does not induce arterial calcification

Elevated fibroblast growth factor 23 (FGF23) is associated with cardiovascular disease in patients with chronic kidney disease. As a potential mediating mechanism, FGF23 induces left ventricular hypertrophy; however, its role in arterial calcification is less clear. In order to study this, we quantified coronary artery and thoracic aorta calcium by computed tomography in 1501 patients from the Chronic Renal Insufficiency Cohort (CRIC) study within a median of 376 days (interquartile range 331-420 days) of baseline. Baseline plasma FGF23 was not associated with the prevalence or severity of coronary artery calcium after multivariable adjustment. In contrast, higher serum phosphate levels were associated with prevalence and severity of coronary artery calcium, even after adjustment for FGF23. Neither FGF23 nor serum phosphate were consistently associated with thoracic aorta calcium. We could not detect mRNA expression of FGF23 or its coreceptor, klotho, in human or mouse vascular smooth muscle cells, or normal or calcified mouse aorta. Whereas elevated phosphate concentrations induced calcification in vitro, FGF23 had no effect on phosphate uptake or phosphate-induced calcification regardless of phosphate concentration or even in the presence of soluble klotho. Thus, in contrast to serum phosphate, FGF23 is not associated with arterial calcification and does not promote calcification experimentally. Hence, phosphate and FGF23 promote cardiovascular disease through distinct mechanisms.

Fibroblast growth factor 23 is associated with carotid artery calcification in chronic kidney disease patients not undergoing dialysis: a cross-sectional study

Background

Fibroblast growth factor 23 (FGF23) is an important hormone in the regulation of phosphate metabolism. It is unclear whether FGF23 is associated with carotid artery calcification (CAAC) in predialysis patients. The present study aimed to clarify the relationship between FGF23 and CAAC in patients with chronic kidney disease (CKD) who were not on dialysis.

Methods

One-hundred ninety-five predialysis CKD patients were enrolled in this cross-sectional study. CAAC was assessed using multidetector computed tomography, and the prevalence of CAAC was examined. Intact FGF23 was measured in each patient. The risk factors for CAAC were evaluated using a logistic regression model.

Results

We found CAAC in 66% of the patients. The prevalence of CAAC significantly increased across CKD stages: it was 37% in CKD stages 1–2, 58% in stage 3; 75% in stage 4, and 77% in stage 5 (p < 0.01). In multivariate analysis, smoking, diabetes mellitus and log FGF23 were each identified as risk factors for CAAC. The study population was divided in quartiles of FGF23 levels. Compared with the lowest FGF23 quartile, each subsequent quartile had a progressively higher odds ratio (OR) for CAAC, adjusted for confounders (ORs [95% confidence interval] of 2.34 [0.78 to 7.31], 5.28 [1.56 to 19.5], and 13.6 [2.92 to 74.6] for the second, third, and fourth quartiles, respectively.

Conclusions

The prevalence of CAAC is increased with the decline in the kidney function. FGF23 is independently related to CAAC in patients with CKD who are not on dialysis.

Serum myostatin levels are negatively associated with abdominal aortic calcification in older men: the STRAMBO study

OBJECTIVE

To assess the association between abdominal aortic calcification (AAC) and serum levels of myostatin, a negative regulator of skeletal muscle mass, which has been implicated in the development of atherosclerotic lesions in mice.

DESIGN AND PATIENTS

We assessed AAC semiquantitatively from the lateral spine scans obtained using dual energy X-ray absorptiometry in 1071 men aged 20-87 years. Serum myostatin levels were measured by an immunoassay that detects all myostatin forms.

RESULTS

Total myostatin serum levels did not differ between men with or without self-reported ischemic heart disease, hypertension, or diabetes mellitus. Total serum myostatin levels were higher in men with higher serum calcium levels and lower in men with higher serum concentrations of highly sensitive C-reactive protein. Men with AAC had lower myostatin levels compared with men without AAC. Prevalence of AAC (AAC score > 0) was lower in the highest myostatin quartile compared with the three lower quartiles (P < 0.05). After adjustment for confounders, odds of AAC (AAC score > 0) were lower (OR=0.62; 95% confidence interval (95% CI), 0.45-0.85; P< 0.005) for the fourth myostatin quartile vs the three lower quartiles combined. In the sub-analysis of 745 men aged 60 years, the results were similar: AAC prevalence was lower in the highest myostatin quartile compared with the three lower quartiles combined (OR=0.54; 95% CI, 0.38-0.78; P<0.001).

CONCLUSIONS

In older men, total myostatin serum levels are inversely correlated with AAC. Further studies are needed to investigate mechanisms underlying this association and to assess utility of myostatin as a cardiovascular marker.

What's new in FGF23 research?

FGF23 is a hormone that regulates phosphate and vitamin D metabolism by binding to Klotho-fibroblast growth factor (FGF) receptor complex. Excess actions of FGF23 cause several kinds of hypophosphatemic diseases. The mechanism of overproduction of FGF23 in some of these diseases is becoming clear, whereas it is not yet completely understood. Several specific methods to inhibit FGF23 actions have been reported as candidates for new therapies for these FGF23-related hypophosphatemic diseases. On the other hand, many epidemiological studies indicated the association between high FGF23 levels and several adverse events in cardiovascular system, kidney, bone and mortality. FGF23 was recently shown to induce ventricular hypertrophy in a Klotho-independent manner. However, it is not yet shown whether this Klotho-independent action of FGF23 can explain all the results of epidemiological studies.