Study on the relationship of serum fetuin-A concentration with aortic stiffness in patients on dialysis

Diabetes mellitus modifies the association between chronic kidney disease-mineral and bone disorder biomarkers and aortic stiffness in peritoneal dialysis patients

This study aimed to investigate the relationship of four chronic kidney disease-mineral and bone disorder (CKD-MBD) biomarkers, including intact parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), soluble klotho, and fetuin-A, with aortic stiffness in peritoneal dialysis (PD) patients, comparing those with and without diabetes mellitus (DM). A total of 213 patients (mean age 58 ± 14 years; 81 (38.0%) patients with DM) were enrolled. Their aortic pulse wave velocity (PWV) was measured using pressure applanation tonometry, while serum intact PTH, FGF23, α-klotho, and fetuin-A levels were measured using enzyme-linked immunosorbent assay. Overall, patients with DM had higher aortic PWV than those without (9.9 ± 1.8 vs. 8.6 ± 1.4 m/s, p < 0.001). Among the four CKD-MBD biomarkers, FGF23 levels were significantly lower in DM group (462 [127-1790] vs. 1237 [251-3120] pg/mL, p = 0.028) and log-FGF23 independently predicted aortic PWV in DM group (β: 0.61, 95% confidence interval: 0.06-1.16, p = 0.029 in DM group; β: 0.10, 95% confidence interval: - 0.24-0.45, p = 0.546 in nonDM group; interaction p = 0.016). In conclusion, the association between FGF23 and aortic PWV was significantly modified by DM status in PD patients.

Role of smooth muscle cells in vascular calcification: implications in atherosclerosis and arterial stiffness

Vascular calcification is associated with a significant increase in all-cause mortality and atherosclerotic plaque rupture. Calcification has been determined to be an active process driven in part by vascular smooth muscle cell (VSMC) transdifferentiation within the vascular wall. Historically, VSMC phenotype switching has been viewed as binary, with the cells able to adopt a physiological contractile phenotype or an alternate ‘synthetic’ phenotype in response to injury. More recent work, including lineage tracing has however revealed that VSMCs are able to adopt a number of phenotypes, including calcific (osteogenic, chondrocytic, and osteoclastic), adipogenic, and macrophagic phenotypes. Whilst the mechanisms that drive VSMC differentiation are still being elucidated it is becoming clear that medial calcification may differ in several ways from the intimal calcification seen in atherosclerotic lesions, including risk factors and specific drivers for VSMC phenotype changes and calcification. This article aims to compare and contrast the role of VSMCs in driving calcification in both atherosclerosis and in the vessel media focusing on the major drivers of calcification, including aging, uraemia, mechanical stress, oxidative stress, and inflammation. The review also discusses novel findings that have also brought attention to specific pro- and anti-calcifying proteins, extracellular vesicles, mitochondrial dysfunction, and a uraemic milieu as major determinants of vascular calcification.

Supplementary nutrients for prevention of vascular calcification in patients with chronic kidney disease

Vascular calcification (VC) and malnutrition associated with cardiovascular disease are common in patients with chronic kidney disease (CKD) treated with dialysis. VC, which reflects vascular aging, and malnutrition are also encountered in the non-CKD elderly population. This similarity of clinical findings suggests that the progression of CKD is related to aging and the existence of a causal relationship between VC and malnutrition. To retard renal progression, a low- or very-low-protein diet is usually recommended for CKD patients. Dietary education may induce malnutrition and deficiency of important nutrients, such as vitamins K and D. Menaquinone-7, a type of vitamin K2, is under investigation for inhibiting VC in elderly patients without CKD, as well as for prevention of VC in patients with CKD. Nutritional vitamin D, such as cholecalciferol, may be considered to decrease the required dose of active vitamin D, which increases the risk of VC due to increased calcium and phosphate loads. Omega-3 fatty acids are important nutrients and their ability to inhibit VC needs to be evaluated in clinical trials. This review focuses on the ability of supplementary nutrients to prevent VC in patients with CKD, in whom dietary restriction is essential.

Long-term follow-up of biomarkers of vascular calcification after switch from traditional hemodialysis to online hemodiafiltration

Rapid progression of vascular calcification (VC) in hemodialysis (HD) patients is caused by several factors including inflammation and an imbalance between active inducers and inhibitors of VC. Growing evidence shows that online hemodiafiltration (ol-HDF), a combination of diffusive and convective solute transport, has positive effects on the uremic environment that affects patients on dialysis. However, we recently reported that serum 25-hydroxyvitamin D (25(OH)D) decreased after a switch from HD to ol-HDF. As a consequence of this finding, the present study was undertaken to investigate if inducers and inhibitors of VC (i.e. the inactive matrix Gla protein fractions dp-ucMGP and t-ucMGP, fetuin-A, Gla-rich protein (GRP), osteopontin (OPN), bone-specific alkaline phosphatase (BALP), and osteoprotegerin (OPG)) also are affected by ol-HDF. This non-comparative prospective study comprised 35 prevalent patients who were investigated 6, 12, and 24 months after their switch from HD to ol-HDF. Most patients had increased levels of the calcification inhibitors OPN and OPG; and of the inactive calcification inhibitor dp-ucMGP during the study period irrespective of the dialysis modality. BALP and t-ucMGP were mostly within the reference interval, but fetuin-A was mostly below the reference interval during the study period. OPN was significantly associated with BALP and parathyroid hormone, r = 0.62 and r = 0.65 (p < .001), respectively. In conclusion, in contrast to decreased 25(OH)D levels, no differences were found for any of the measured biomarkers of VC following the switch from HD to ol-HDF. Further studies are needed to elucidate how these biomarkers can contribute to calcification risk assessment.

Arterial stiffness in end-stage renal disease-pathogenesis, clinical epidemiology, and therapeutic potentials

Arterial stiffness is an important risk factor for cardiovascular morbidity and mortality in patients with end-stage renal disease (ESRD). Arterial stiffness aggravates cardiovascular risk via multiple pathways, such as augmentation of aortic systolic pressure, subendocardial hypoperfusion, and excess pulsatile energy transmission from macro- to microcirculation. Pathogenesis of the arteriosclerotic process in ESRD is complex and not yet fully understood. Several factors unique to ESRD, such as mineral metabolism disturbances, vascular calcifications, formation of advanced glycation end-products, and acute and chronic volume overload, are proposed to play a particular role in the progression of arteriosclerosis in ESRD. As these and other mechanistic pathways of arterial stiffening in ESRD are elucidated, there is hope that this knowledge will be translated into novel therapeutic interventions targeting arterial stiffness. In the meantime, blood pressure (BP) lowering via strict volume control and appropriate use of antihypertensive drugs is a fundamental step in reversing accelerated arterial stiffening and modifying the cardiovascular risk profile of ESRD patients. In this article, we review the pathogenesis, clinical epidemiology, and therapies targeting arterial stiffness in ESRD, discussing recent advances and high-priority goals of future research in these important areas.

Vascular Smooth Muscle Cells and Arterial Stiffening: Relevance in Development, Aging, and Disease

The cushioning function of large arteries encompasses distension during systole and recoil during diastole which transforms pulsatile flow into a steady flow in the microcirculation. Arterial stiffness, the inverse of distensibility, has been implicated in various etiologies of chronic common and monogenic cardiovascular diseases and is a major cause of morbidity and mortality globally. The first components that contribute to arterial stiffening are extracellular matrix (ECM) proteins that support the mechanical load, while the second important components are vascular smooth muscle cells (VSMCs), which not only regulate actomyosin interactions for contraction but mediate also mechanotransduction in cell-ECM homeostasis. Eventually, VSMC plasticity and signaling in both conductance and resistance arteries are highly relevant to the physiology of normal and early vascular aging. This review summarizes current concepts of central pressure and tensile pulsatile circumferential stress as key mechanical determinants of arterial wall remodeling, cell-ECM interactions depending mainly on the architecture of cytoskeletal proteins and focal adhesion, the large/small arteries cross-talk that gives rise to target organ damage, and inflammatory pathways leading to calcification or atherosclerosis. We further speculate on the contribution of cellular stiffness along the arterial tree to vascular wall stiffness. In addition, this review provides the latest advances in the identification of gene variants affecting arterial stiffening. Now that important hemodynamic and molecular mechanisms of arterial stiffness have been elucidated, and the complex interplay between ECM, cells, and sensors identified, further research should study their potential to halt or to reverse the development of arterial stiffness.

Hyperphosphatemia. The hidden killer in chronic kidney disease

Hyperphosphatemia is a major cause of morbidity and mortality in patients with chronic kidney disease. The association between hyperphosphatemia and increased risk of death from cardiovascular disease/vascular calcification has been well established for a long time. This review explores the new aspects of pathogenesis of vascular calcification, as demonstrated by recent advances showing a recognized regulating role of phosphorus in vascular smooth muscle cell calcification. This novel mechanism may help in finding a new pharmacological therapy to reduce, or prevent blood vessel calcification. Furthermore, recent experimental and clinical studies involved in the treatment of hyperphosphatemia are reviewed in this article.

Arterial Stiffness: A Novel Risk Factor for Kidney Injury Progression?

Arterial stiffness is typical feature of vascular remodeling in chronic kidney disease (CKD). Increased arterial stiffness raises flow and pressure pulsatility and is considered the principle pathogenic mechanism of isolated systolic hypertension, left ventricular hypertrophy, and congestive heart failure. Apart from the impact of arterial stiffness on left ventricular afterload, downstream transmission of pressure pulsatility to the level of microcirculation is suggested to promote injury of other susceptible organs. This may be of particular importance for kidney injury progression, since passive renal perfusion along with low resistance and input impedance in renal microvessels make kidneys particularly vulnerable to the damaging effect of systemic pulsatile pressure. Recent studies have provided evidence that arterial stiffness culminates in elevated pulsatility and resistance in renal microvasculature, promoting structural damage of small intra-renal arterioles. Further, prospective observational studies have shown that reduced aortic compliance is closely associated with the annual rate of renal function decline and represents independent predictor of kidney injury progression to end-stage renal disease among patients with CKD. This article provides insights into the cross-talk between macrocirculation and renal microcirculation and summarizes the currently available clinical evidence linking increased arterial stiffness with kidney disease progression.

The role of fetuin-A in mineral trafficking and deposition

Calcium and phosphate are the principle ions involved in the deposition of mineral in the human body. Inhibitors of mineralisation are essential for the prevention of ectopic mineral precipitation and deposition. In the past decade, through in vitro, in vivo and clinical observation studies, we have come to appreciate the importance of fetuin-A (Fet-A), a circulating glycoprotein, in preventing ectopic calcium phosphate mineralisation. Moreover, the detection of Fet-A-containing mineral complex, termed calciprotein particles (CPPs), has provided new ways to assess an individual's calcific risk. The pathophysiological significance of CPPs in disease states is yet to be defined, but it provides an exciting avenue to further our understanding of the development of ectopic mineralisation.

The serum protein fetuin-B is involved in the development of acute myocardial infarction

Fetuin-B was one of highly expressed serum proteins in AMI compared with stable angina. This protein affected vascular plaque-stabilizing components in monocytes, macrophages and vascular smooth muscle cells. Fetuin-B may be a possible contributor to AMI.

Vascular calcification: from pathophysiology to biomarkers

The link between vascular calcification (VC) and increased mortality is now well established. Over time, as clinical importance of this phenomenon has begun to be fully considered, scientists have highlighted more and more physiopathological mechanisms and signaling pathways that underlie VC. Several conditions such as diabetes, dyslipidemia and renal diseases are undoubtedly identified as predisposing factors. But even if the process is better understood, many questions still remain unanswered. This review briefly develops the various theories that attempt to explain mineralization genesis. Nonetheless, the main purpose of the article is to provide a profile of the various existing biomarkers of VC. Indeed, in the past years, a lot of inhibitors and promoters, which form a dense and interconnected network, were identified. Given importance to assess and control mineralization process, a focusing on accumulated knowledge of each marker seemed to be necessary. Therefore, we tried to define their respective role in the physiopathology and how they can contribute to calcification risk assessment. Among these, Klotho/fibroblast growth factor-23, fetuin-A, Matrix Gla protein, Bone morphogenetic protein-2, osteoprotegerin, osteopontin, osteonectin, osteocalcin, pyrophosphate and sclerostin are specifically discussed.

A current understanding of vascular calcification in CKD

Patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD) have significant cardiovascular morbidity and mortality that is in part due to the development of vascular calcification. Vascular calcification is an active, highly regulated process that shares many similarities with normal bone formation. New discoveries related to extracellular vesicles, microRNAs, and calciprotein particles continue to reveal the mechanisms that are involved in the initiation and progression of vascular calcification in CKD. Further innovations in these fields are critical for the development of biomarkers and therapeutic options for patients with CKD and ESRD.

Serum osteoprotegerin is associated with vascular stiffness and the onset of new cardiovascular events in hemodialysis patients

BACKGROUND/AIMS

Osteoprotegerin (OPG) and fetuin-A are vascular calcification regulators that may be related to high cardiovascular (CV) mortality in hemodialysis (HD) patients. We evaluated the relationship between OPG, fetuin-A, and pulse wave velocity (PWV), a marker of vascular stiffness, and determined whether OPG and fetuin-A were independent predictors of CV events in HD patients.

METHODS

We conducted a prospective observational study in 97 HD patients. OPG and fetuin-A were measured at baseline and arterial stiffness was evaluated by PWV. All patients were stratified into tertiles according to serum OPG levels.

RESULTS

A significant trend was observed across increasing serum OPG concentration tertiles for age, HD duration, systolic blood pressure, cholesterol, triglycerides, and PWV. Multiple linear regression analysis revealed that diabetes (β = 0.430, p = 0.000) and OPG levels (β = 0.308, p = 0.003) were independently associated with PWV. The frequency of new CV events was significantly higher in the upper OPG tertiles compared with those in the lower OPG tertiles. In Cox proportional hazards analysis, upper tertiles of OPG levels were significantly associated with CV events (hazard ratio = 4.536, p = 0.011).

CONCLUSIONS

Serum OPG, but not fetuin-A, levels were closely associated with increased vascular stiffness, and higher OPG levels may be independent predictors of new CV events in HD patients.

Effect of serum FGF-23, MGP and fetuin-A on calcium-phosphate metabolism in maintenance hemodialysis patients

This study was aimed to explore the role of serum fibroblast growth factor (FGF)-23, matrix Gla protein (MGP) and fetuin-A in the calcium-phosphate metabolism and their predicting value in coronary artery calcification in maintenance hemodialysis (MHD) patients. This study included 64 patients who receive hemodialysis in our hospital. The serum FGF-23, MGP and fetuin-A were analyzed by enzyme-linked immunosorbent assay (ELlSA). Coronary artery calcification score (CACS) was evaluated by coronary artery computed tomography scan. The 64 patients (30 males, 34 females, 60.6 ± 11.3 years of age) received an average dialysis vintage of 6.88 ± 2.94 years. We divided the CACS into three levels, and 13 (20.31%), 16 (25%), and 35 (54.69%) exhibited a CACS of 0-100, 100-400, and >400, respectively. Dialysis vintage, serum FGF-23, fetuin-A, phosphorus and high-density lipoprotein-C levels were identified as independent variables of CACS by stepwise multiple regression analysis. The area under receiver operating characteristic curve indicated that serum FGF-23 and fetuin-A were useful for identifying CAC in MHD patients. The cut-off value corresponding to the highest Youden's index was serum FGF-23 ≥ 256 pg/mL and fetuin-A ≤ 85 μg/mL, which was defined as the optimal predictors of CAC. Different combinations of serum FGF-23 and fetuin-A in parallel or in series effectively boosted the identification of CAC. The incidence of CAC is high in MHD patients. Serum FGF-23 and fetuin-A levels are closely correlated with CAC.

Associations of serum fetuin-A levels with insulin resistance and vascular complications in patients with type 2 diabetes

OBJECTIVE

We examined the relationship between serum fetuin-A, insulin resistance (IR), metabolic syndrome (MS) and vascular complications including cardiac autonomic neuropathy (CAN) in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 172 T2DM patients were recruited and evaluated for diabetic microangiopathies (nephropathy, retinopathy and peripheral neuropathy) including CAN. Serum fetuin-A levels were measured by enzyme-linked immunosorbent assay (ELISA), and the IR was assessed by the index of homeostasis model [homeostasis model assessment-insulin resistance (HOMA-IR)]. Atherosclerotic burden was assessed by ankle-brachial index (ABI) and brachial-ankle pulse wave velocity (baPWV).

RESULTS

Serum fetuin-A levels showed significant positive correlations with HOMA-IR (r = 0.196, p = 0.022), and the mean levels of HOMA-IR were significantly increased progressively across fetuin-A tertiles (p for trend = 0.044). Serum fetuin-A showed significant positive correlations with baPWV, systolic blood pressure (BP), total cholesterol, triglycerides, serum fasting c-peptide and negative correlations with ABI. Serum fetuin-A levels were also negatively correlated with serum adiponectin and positively correlated with serum tumour necrosis factor-α (TNF-α). The mean levels of serum fetuin-A were not significantly different according to the presence of each microangiopathies including CAN. Also, the mean levels of serum fetuin-A were not different between patients with MS and without MS.

CONCLUSIONS

This present study showed that levels of serum fetuin-A are significantly associated with IR and arterial stiffness assessed by baPWV, while there are no associations with each microangiopathies in patients with T2DM.

Associations of fetuin-A and osteoprotegerin with arterial stiffness and early atherosclerosis in chronic hemodialysis patients

BACKGROUND

Cardiovascular morbidity and mortality remains excessive in patients with chronic kidney disease. The association of vascular changes with regulators of extraosseous calcification in this patient population is still under investigation. The aim of the present study was to investigate the associations of the calcification inhibitor fetuin-A, and the anti-osteoclastic factor osteoprotegerin (OPG) with vascular pathology in chronic hemodialysis patients.

METHODS

In this cross-sectional study including 81 stable chronic hemodialysis patients, we measured carotid-to-femoral pulse wave velocity (cfPWV) with applanation tonometry, reflecting arterial stiffness, and common carotid intima-media thickness (ccIMT), a surrogate of early atherosclerosis, as well as serum levels of fetuin-A and OPG. Co-morbidities, traditional cardiovascular risk factors, inflammatory markers and mineral-bone disease serology parameters were also recorded.

RESULTS

cfPWV correlated inversely with fetuin-A (r=-0.355, p=0.001) and positively with OPG (r=0.584, p<0.001). In multilinear regression analysis including age, gender, diabetes, cardiovascular disease, hypertension, pulse pressure, LDL, logCRP, both fetuin-A and OPG were independently associated with cfPWV (p=0.024 and p=0.041 respectively). ccIMT was negatively associated with fetuin-A (r=-0.312, p=0.005) and positively with OPG (r=0.521, p<0.0001); however these associations lost statistical significance after adjustment for age.

CONCLUSION

In chronic hemodialysis patients both fetuin-A and OPG levels are independently associated with arterial stiffness but not with early atherosclerotic vascular changes.

Utilization of UV absorbance for estimation of phosphate elimination during hemodiafiltration

BACKGROUND

Phosphate is an important factor in explaining the high progress of vascular calcification among dialysis patients. Today, phosphate concentration is measured in plasma on a regular basis. The aim of this study was to find out if it is possible to estimate total removed phosphate (TRp) in spent dialysate utilizing UV absorbance during hemodiafiltration.

METHODS

Eleven patients were monitored online with UV absorbance at 297 nm, three times during one week each (n = 33). Dialysate samples were taken at different times during treatment and from a collection tank to chemically determine phosphate concentrations. Two mathematical models (UVIND and UVGROUP) were tested to estimate TRp with supervision by UV absorbance and compared with TRp measured in the tank (reference).

RESULTS

High correlation between UV absorbance and phosphate concentration for each single patient and lower for the whole group together was found. TRp was (mean ± SD) 30.7 ± 7.3 mmol for the reference and 30.8 ± 8.2 and 29.1 ± 5.2 mmol for UVIND and UVGROUP, respectively (p > 0.05).

CONCLUSION

This study demonstrates a novel possibility to estimate TRp based on linear relationship between online monitoring of UV absorbance and concentration of phosphate in spent dialysate.

Arterial stiffness, vascular calcification and bone metabolism in chronic kidney disease

Patients with chronic kidney disease (CKD) have an extremely poor cardiovascular outcome. Arterial stiffness, a strong independent predictor of survival in CKD, is connected to arterial media calcification. A huge number of different factors contribute to the increased arterial calcification and stiffening in CKD, a process which is in parallel with impaired bone metabolism. This coincidence was demonstrated to be part of the direct inhibition of calcification in the vessels, which is a counterbalancing effect but also leads to low bone turnover. Due to the growing evidence, the definition of “CKD mineral bone disorder” was created recently, underlining the strong connection of the two phenomena. In this review, we aim to demonstrate the mechanisms leading to increased arterial stiffness and the up-to date data of the bone-vascular axis in CKD. We overview a list of the different factors, including inhibitors of bone metabolism like osteoprotegerin, fetuin-A, pyrophosphates, matrix Gla protein, osteopontin, fibroblast growth factor 23 and bone morphogenic protein, which seem to play role in the progression of vascular calcification and we evaluate their connection to impaired arterial stiffness in the mirror of recent scientific results.

A brief review of external mass balance and internal calcium redistribution in dialysis patients--is calcium a uremic toxin?

Recent debates between 2 schools of thought on calcium mass balance in dialysis patients and its relevance to disease--one emphasizing external calcium mass balance, and the other, internal calcium redistribution--have created controversy. Due to decreased ability to excrete calcium and loss of endocrine function by the kidney, patients suffering from chronic kidney disease, particularly when requiring dialysis, demonstrate varying degrees of positive or negative calcium balance, vitamin D deficiency, and secondary hyperparathyroidism. Consequently, patients are prone to bone demineralization, with diminished bone strength, and are thus prone to fractures that substantially worsen morbid outcomes in this population. However, intra- and interdialytic positive calcium mass balance creates complications of a different kind, which include the occurrence of vascular and cardiac disease and reduced survival. This review aims to shed light on the mechanisms of and relationships between external calcium mass balance and internal calcium redistribution and their consequences. It also discusses the potential to improve current regimens by means of diffusive and convective calcium mass transfer for the achievement of neutral calcium mass balance.

Fetuin-A, inflammation, and coronary artery calcification in hemodialysis patients

Hemodialysis patients have extremely increased cardiovascular mortality. Vascular calcification, inflammation, and low serum fetuin-A levels are implicated for increased mortality. In this study, relationship between coronary artery calcification, inflammation, and serum fetuin-A levels were investigated. Seventy-eight hemodialysis patients (38 male, 40 female, mean age: 52±14.5 years) were included. All patients were on dialysis for more than 6 months. Coronary artery calcium scores (CACS) are determined by electron-beam computed tomography. Serum CRP, IL-1β, IL-6, TNF-α, and serum fetuin-A levels were measured. Mean CACS value was 488.5±94.5. Serum fetuin-A levels were negatively correlated with CACS (r:–0.30, P=0.009). Patients are divided into two groups according to total CACS value; group 1 (CACS<10), group 2 (CACS≥10). There was a statistically significance difference in fetuin-A levels between CACS group 1 and group 2 (P=0.001). In this study, serum fetuin-A levels were associated with total CACS. This Fetuin-A may play a role in increased mortality in this group of patients via facilitating CAC.

Novel biomarkers do not correlate with severity of vascular stiffness in CKD patients with severe co-morbid disease

BACKGROUND/AIMS

Novel biomarkers may help explain the pathobiology of vascular disease in chronic kidney disease, and thus set the stage for identification of therapeutic targets, potential reversibility, and improved outcomes in this population.

METHODS

124 subjects with GFR <60 ml/min or on renal replacement therapy underwent measurement of inflammatory, vascular and cardiac biomarkers as well as aortic pulse wave velocity (PWV) testing. A subset of patients (n = 60) had repeat PWV measured at 6 months.

RESULTS

Thirty-four percent of the patients were diabetic, and 50% had a history of cardiovascular disease or congestive heart failure. Median PWV was 9.8 (IQR 8.3-12.7) m/s. No significant correlations between the measured biomarkers and baseline PWV was observed. An increase in PWV (>1.5 m/s) over 6 months was observed in those subjects with diabetes, a higher brain natriuretic peptide level, lower cholesterol and lower phosphate level. Age (HR 1.086, p = 0.0028), fetuin (0.024, p = 0.0448), and interleukin-10 (top tertile HR 4.720, p = 0.0359) were associated with mortality.

CONCLUSIONS

In this cohort of patients with chronic kidney disease and diabetes and/or heart disease, we were unable to demonstrate that select biomarkers can inform processes leading to vascular disease. Biomarkers do appear to have utility in predicting future events in this population.

Fetuin-mineral complex reflects extraosseous calcification stress in CKD

Fetuin-A is an important inhibitor of extraosseous calcification, but some of the studies that used ELISAs did not identify a significant relationship between serum fetuin-A levels and vascular calcification in patients with chronic kidney disease (CKD). Here, we used centrifugation to separate a fetuin-mineral complex (FMC) composed of fetuin-A, fibrinogen, fibronectin-1, and calcium from the serum of hemodialysis patients. In addition, we analyzed serum fetuin-A levels of 73 patients with diabetes and CKD (predialysis) after centrifugation. Fetuin-A concentrations were significantly lower in supernatants than in serum from patients at any stage of CKD, indicating systemic circulation of FMC in these patients. With greater severity of CKD, the contribution of FMC to total fetuin-A increased. Despite the absence of a correlation between serum fetuin-A and coronary artery calcification scores (CACS), supernatant fetuin-A negatively correlated with CACS and the extent to which centrifugation reduced fetuin-A (reduction ratio [RR]) positively correlated with CACS. In a longitudinal study of 12 hemodialysis patients with secondary hyperparathyroidism, parathyroidectomy and cinacalcet therapy each significantly reduced the RR without changing supernatant fetuin-A levels after 1 month, suggesting a reduction in FMC. Moreover, the magnitude of cinacalcet-induced reduction in parathyroid hormone correlated with the decrease in RR but not with changes in serum or supernatant fetuin-A. These data suggest that a quantitative measure of FMC, not supernatant or serum fetuin-A as measured in previous studies, reflects extraosseous calcification stress.

Factors associated with increased pulse wave velocity in peritoneal dialysis patients

Elevated pulse wave velocity (PWV) reflects increased arterial stiffness. Several studies have investigated PWV in peritoneal dialysis (PD) patients, but direct comparisons with healthy controls were not done. The potential influence of peritoneal transport characteristics on arterial stiffness in PD patients was suggested in recent studies. The aims of this study were to compare PWV in PD patients and healthy volunteers, and to investigate factors associated with increased PWV. The carotid-femoral PWV was measured in 28 PD patients and 28 healthy controls, matched for age and gender. A peritoneal equilibration test (PET) was performed in all PD patients. Based on the PET, patients were classified as: high transporters (H) (n=8), high-average (HA) (n=12), low-average (LA) (n=6), and low transporters (L) (n=2). Six of the PD patients were diabetic. PWV was significantly higher in the PD patients than in the controls (9,9±2,4 vs. 8,0±0,9; p=0,0004). In the PD group, PWV was higher in H/HA than in L/LA patients (10,4 ± 2,5 vs. 8,6 ± 1,0; p=0,008), but all the diabetic patients were in the H/HA group. PWV was significantly higher in diabetic than in non-diabetic PD patients (12,8 ± 2,0 vs. 9,1 ± 1,7; p=0,004). In the PD patients, significant positive correlations were found between PWV and: age, pulse pressure, Kt/V, and duration of PD therapy. In conclusion, the carotid-femoral PWV is elevated in peritoneal dialysis patients. Increased PWV in PD patients is associated with age, diabetic status, and longer duration of PD therapy, but not with this type of peritoneal transport.

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.

Factors associated with aortic stiffness and its change over time in peritoneal dialysis patients

BACKGROUND

An increase in aortic stiffness, as reflected by an increase in pulse wave velocity (PWV), is an important predictor of cardiovascular mortality in dialysis patients. Decreased serum concentration of calcification inhibitor, such as fetuin-A, is inversely related to mortality in haemodialysis patients. Our aim is to investigate the factors associated with aortic stiffness and its change over time in peritoneal dialysis (PD) patients.

METHODS

As a prospective observational study, we analysed 67 PD patients, aged 50 ± 14 years (mean ± SD) and with dialysis duration of 26 (5-58) months (median, interquartile range). At baseline, age, mean arterial pressure (MAP), left ventricular mass (LVM) index, diabetes, serum albumin, calcium (Ca), phosphorus (P) and intact parathyroid hormone (iPTH), uric acid, total bilirubin, high-sensitivity C-reactive protein (hsCRP), fetuin-A, and residual renal function were included in association analysis with aortic stiffness represented by heart-to-femoral PWV (hfPWV). We also evaluated simple vascular calcification score (SVCS) with plain radiograph of the pelvis and both hands. PWV was measured both at baseline and at 1 year. Change of aortic stiffness was determined by △PWV (difference between 1-year PWV and baseline PWV). Time-averaged concentrations were used to evaluate the relation between biologic markers and changes of aortic stiffness.

RESULTS

hfPWV was 1022 ± 276 cm/s at baseline, and hfPWV determined at 1 year was 1069 ± 317 cm/s. Mean serum fetuin-A concentration was 0.34 ± 0.08 g/L. At baseline, aortic PWV positively correlated with age, smoking status, diabetes, MAP, total cholesterol and LDL cholesterol. On the other hand, aortic PWV inversely correlated with fetuin-A, log PTH, haemoglobin and albumin. In a multiple regression model, association of serum fetuin-A (β = -0.329, P = 0.003) with aortic PWV remained significant, along with age (β = 0.512, P < 0.001), MAP (β = 0.215, P = 0.047) and log PTH (β = -0.269, P = 0.025). At follow-up, △MAP (β = 0.500, P < 0.001) and time-averaged TG (aTG) (β = 0.259 P = 0.019) were determinants of △PWV.

CONCLUSIONS

For our PD patients, serum fetuin-A was an independent determinant of aortic stiffness, as well as age, MAP and log PTH. Although 1 year is not sufficient to observe the change of aortic stiffness, some patients exhibited >15% increase of PWV during this period. △MAP and aTG were factors affecting the change of PWV. Follow-up over a longer period is necessary to elucidate factors that determine changes of aortic stiffness over time from PD patients.

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.

Fetuin-A is an independent determinant of change of aortic stiffness over 1 year in non-diabetic patients with CKD stages 3 and 4

BACKGROUND

Vascular calcification is highly prevalent in chronic kidney disease (CKD) patients. This calcification leads to arterial stiffening. Fetuin-A is an endogenous inhibitor of vascular calcification and has been associated with arterial stiffness and mortality in dialysis patients. We tested the relationship between fetuin-A and change in arterial stiffness in CKD stages 3 and 4.

METHODS

We measured fetuin-A concentrations in 92 patients with CKD stages 3 and 4 and studied the association with clinical, biochemical and vascular parameters including arterial stiffness measured by carotid-femoral pulse wave velocity (PWV) at 0 and 12 months.

RESULTS

Fetuin-A was significantly lower in the non-diabetic group (n = 73) compared to the diabetic group (n = 19, P = 0.018). There was a significant interaction between diabetic status and fetuin-A concentration. Univariate analysis of the non-diabetic group showed association between change in aortic stiffness over 1 year with fetuin-A (r = -0.481, P < 0.0001) and systolic blood pressure (r = 0.389, P = 0.001) and baseline PWV (r = 0.240, P = 0.041). In multivariate analysis, fetuin-A, systolic blood pressure and baseline PWV independently predicted change in carotid-femoral PWV at 1 year (beta = -0.355, P = or< 0.001; beta = 0.426, P < 0.001; and beta = -0.383, P < 0.001, respectively; model R(2) = 0.455).

CONCLUSIONS

In patients with non-diabetic CKD stages 3 and 4, fetuin-A is an independent risk factor for progressive arterial stiffness.

The physiologic development of fetuin-a serum concentrations in children

Fetuin-A prevents tissue calcification by forming soluble complexes with calcium and phosphate. A pathological depletion of serum fetuin-A has been observed in children on dialysis or after renal transplantation but knowledge on physiologic age-related changes in serum fetuin-A is limited. We prospectively evaluated serum fetuin-A in 133 infants and children, ranging from very low birth weight infants to adolescents. Highest serum fetuin-A levels were present between 23 and 30 wk of gestation (1 +/- 0.33 mg/mL). Thereafter, the values decreased. This decrease was linked to biological rather than chronological age. At 32 to 36 and 37 to 40 wk of gestation, the serum fetuin-A concentration was 0.63 +/- 0.26 and 0.63 +/- 0.21 mg/mL, respectively. Thereafter, the concentrations remained stable until adolescence at 0.58 +/- 0.12 mg/mL. Intercurrent infections were associated with a transient decrease of serum fetuin-A levels. The high serum fetuin-A concentrations in preterm children suggest that fetuin-A is of high physiologic impact for the fetal and the preterm-born organism, showing extensive tissue formation. This might point to a new mechanism contributing to organ damage in these patients, comparable with children on dialysis.

Elevated osteoprotegerin is associated with all-cause mortality in CKD stage 4 and 5 patients in addition to vascular calcification

BACKGROUND

Cardiovascular disease is the leading cause of death in the chronic kidney disease (CKD) population. The mechanisms of vascular damage are not fully understood. The objective of this study was to prospectively investigate the importance of novel mediators of vascular damage, in conjunction with vascular calcification (VC), on survival.

METHODS

A total of 134 subjects [60 haemodialysis (HD), 28 peritoneal dialysis (PD) and 46 CKD stage 4] were studied. All survivors completed 40 months of follow-up. VC was measured using multi-slice spiral CT of the superficial femoral artery. Circulating osteoprotegerin (OPG), Fetuin-A and high sensitivity C-reactive protein (hs-CRP) were measured in addition to standard clinical biochemical analysis.

RESULTS

After a 40-month follow-up, 31 patients had died (27 men and 4 women). Of 31 subjects, 31 had evidence of significant VC. The majority of deaths were in the HD group (48%), 36% were PD subjects and 16% were CKD subjects. The outcome of interest was survival at the end of follow-up. Multivariate logistical regression analysis revealed male gender [OR 8.06 (1.34-48.450) P = 0.02], OPG >25 pmol/L [OR 5.31(1.35-20.88) P = 0.02] and hypoalbuminaemia [OR 0.26 (0.12-0.56) P < 0.01], were associated with increased odds of death.

CONCLUSION

We have previously reported that VC and low albumin predict death in CKD stages 4 and 5 over a 2-year follow-up period. These data show that OPG, independent of CRP, is also associated with a negative outcome. The mechanisms remain to be elucidated; however, it is likely that they are associated with vascular damage through mechanisms in addition to VC.

The circulating calcification inhibitors, fetuin-A and osteoprotegerin, but not matrix Gla protein, are associated with vascular stiffness and calcification in children on dialysis

BACKGROUND

Vascular calcification occurs in the majority of patients with chronic kidney disease, but a subset of patients does not develop calcification despite exposure to a similar uraemic environment. Physiological inhibitors of calcification, fetuin-A, osteoprotegerin (OPG) and undercarboxylated-matrix Gla protein (uc-MGP) may play a role in preventing the development and progression of ectopic calcification, but there are scarce and conflicting data from clinical studies.

METHODS

We measured fetuin-A, OPG and uc-MGP in 61 children on dialysis and studied their associations with clinical, biochemical and vascular measures.

RESULTS

Fetuin-A and OPG were higher and uc-MGP lower in dialysis patients than controls. In controls, fetuin-A and OPG increased with age. Fetuin-A showed an inverse correlation with dialysis vintage (P = 0.0013), time-averaged serum phosphate (P = 0.03) and hs-CRP (P = 0.001). Aortic pulse wave velocity (PWV) and augmentation index showed a negative correlation with fetuin-A while a positive correlation was seen with PWV and OPG. Patients with calcification had lower fetuin-A and higher OPG than those without calcification. On multiple linear regression analysis Fetuin-A independently predicted aortic PWV (P = 0.004, beta = -0.45, model R(2) = 48%) and fetuin-A and OPG predicted cardiac calcification (P = 0.02, beta = -0.29 and P = 0.014, ss = 0.33, respectively, model R(2) = 32%).

CONCLUSIONS

This is the first study to define normal levels of the calcification inhibitors in children and show that fetuin-A and OPG are associated with increased vascular stiffness and calcification in children on dialysis. Higher levels of fetuin-A in children suggest a possible protective upregulation of fetuin-A in the early stages of exposure to the pro-calcific and pro-inflammatory uraemic environment.

IL-18 is involved in vascular injury in end-stage renal disease patients

BACKGROUND

The role of interleukin (IL)-6 and IL-18 in induction of the inflammatory reaction underlying arteriosclerosis, and protective effect of an anti-inflammatory cytokine IL-10 in this process, have been confirmed by experimental and clinical observations. A systemic inflammatory reaction marker, C-reactive protein (CRP), is known to be associated with the induction of IL-6 and IL-18 release. The chronic inflammatory state associated with renal insufficiency contributes to acceleration of arteriosclerosis, reflected by decreased elasticity which can be measured with aortal pulse wave velocity (PWV). It is well known that chronic kidney disease (CKD) is associated with the chronic inflammatory process, as evidenced by increase in CRP and IL-6 level. It also results in a drop of fetuin-A concentration which is the calcification inhibitor negatively regulated by inflammation. Part of the derangements associated with the progressive renal failure is also the rise of activated monocyte pool, which among others produces IL-18. The aim of the present study was to evaluate, through measurements of CRP, fetuin-A and aortal pulse wave velocity (aoPWV), whether IL-6 and IL-18 affect the arterial wall of CKD patients as a part of general inflammatory process or locally, through their effect on the arterial lesion development. Materials and methods. The study was performed in a group of 102 patients with stage V CKD (73 treated with haemodialysis and 29 treated with continuous ambulatory peritoneal dialysis) (CKD5 group) and in 30 healthy controls. We measured serum high-sensitivity C-reactive protein (hs-CRP), fetuin-A, IL-6, IL-18, IL-10 (ELISA) and others (haemoglobin level, white blood cell count, serum calcium, phosphate, calcium-phosphate product, albumin, fibrinogen, cholesterol, high-density lipoprotein (HDL), triglycerides and parathormone). ECG-gated carotid and femoral artery waveforms were recorded and analysed.

RESULTS

Serum levels of hs-CRP, IL-6, IL-10 and IL-18 were higher and fetuin-A levels were lower in the CKD5 group than in controls [6.4 (0.6-22.3) mg/dl versus 2.5 (0.5-5.2) mg/dl; 8.29 pg/ml (0.96-74.48)] versus 2.78 (7.91-0.77) pg/ml; 6.5 (3.7-29.7) pg/ml versus 4.1 (3.8-7.2) pg/ml; 254.4 (468.8-47.5) pg/ml versus 89.3 (91.3-27.5) pg/ml]. The aoPWV was higher in the CKD5 group patients than in the control group (9.4 +/- 1.75 m/s versus 7.76 +/- 1.67 m/s; P < 0.05, respectively). Serum fetuin-A level was negatively associated with hs-CRP and IL-6 but not with IL-18 or IL-10. The aoPWV positively correlated with hs-CRP (r = 0.246; P < 0.05), IL-6 and IL-18 (r = 0.220; P < 0.05) and negatively correlated with fetuin-A (r = -0.204; P < 0.05). No relationship between IL-10 and aoPWV was found. In a multiple regression analysis model respecting inflammatory markers the influence of hs-CRP, IL-18 and fetuin-A on aoPWV remained significant.

CONCLUSIONS

The novel observations in the present study are the data indicating that the distinctive contribution of IL-18, but not IL-6, to the arteriosclerosis occurrence in CKD patients, is independent from CRP, fetuin A or other factors involved in the general inflammatory process.

Is fetuin-A/alpha2-Heremans-Schmid glycoprotein associated with the metabolic syndrome in patients with chronic kidney disease?

INTRODUCTION

Components of the metabolic syndrome are highly prevalent in chronic kidney disease (CKD) patients--some of which paradoxically appear to predict an improved outcome in this population. We hypothesized that the circulating calcification inhibitor fetuin-A/AHSG, which is also a natural inhibitor of the tyrosine kinase insulin receptor, could be one factor explaining the association between increased fat mass and a survival advantage in CKD and thus conducted an explorational study to provide preliminary data to support further research into this hypothesis.

PATIENTS AND METHODS

In a cross-sectional study, we evaluated 198 CKD stage 5 patients (GFR 6.8 +/- 0.2 ml/min; 62% males, mean age 52 +/- 1 years) close to the start of renal replacement therapy. We studied circulating AHSG (ELISA) and two common functional AHSG gene polymorphisms (at amino acids Thr248Met (C-T) and Thr256Ser (C-G) using Pyrosequencing) and related these to multiple components of the metabolic syndrome.

RESULTS

Median circulating AHSG was lower (p < 0.01) in type-2 (0.22 g/l) and type-1 (0.16 g/l) diabetics as compared to non-diabetic CKD-5 patients (0.24 g/l). AHSG correlated with both total and truncal fat mass in type-2 diabetics (rho 0.37 and 0.39; p < 0.001, respectively), but not in type-1 diabetics or non-diabetics. Both SNPs significantly influenced circulating levels of AHSG, and were also associated with significant differences in serum triglycerides and HDL cholesterol. Furthermore, there were significant differences in the prevalence of metabolic syndrome criteria between the AHSG Thr256Ser (C-G) genotype groups, with a more atherogenic lipid profile in AHSG high producers (Thr/Thr homozygotes). In multivariate analysis, the association between circulating AHSG and fat mass remained significant also after adjustment for age, gender, inflammation (CRP >10 mg/l), and AHSG genotype.

CONCLUSIONS

The present, explorational, study supports further, mechanistic, studies into a physiological link between AHSG and body fat mass in patients with CKD. As we observed an association between higher fat mass and elevated AHSG levels, these preliminary results may form the basis of further study to establish if the observed associations may be one reason why obesity has been reported to constitute a survival advantage in CKD.