Uremic toxicity and sclerostin in chronic kidney disease patients

Impact of Effectiveness of Physical Activity in a Virtual Environment on the Regulation of Sclerostin and Interleukin 6 Levels in Haemodialysis Patients

Background: Chronic kidney disease is a significant public health issue associated with reduced physical activity. This can lead to mineral and bone disorders and increased levels of inflammatory markers. One innovative solution that can significantly contribute to increasing patient motivation is the combination of physical training with virtual reality technology during haemodialysis sessions. The aim of this study is to comprehensively assess the impact of regular virtual reality-based physical activity on plasma sclerostin and interleukin 6 levels, as well as on physical performance and the level of physical activity in patients undergoing renal replacement therapy through haemodialysis. Methods: This study is a prospective cohort study. Patients included in the study were randomly assigned to two groups: the study group and the control group. The study group consisted of patients who were entrusted with the task of conducting training using the prototype of the NefroVR system. The duration of the study period for both the study and control groups was 3 months. Results: One hundred and two (102) patients with stage 5 chronic kidney disease who underwent haemodialysis as a renal replacement therapy participated in the study. Patients from the study group were characterized by higher physical activity compared to the control group. There was a significant difference in the level of IL-6 and SOST between the study and control groups in the second measurement. Conclusions: Regular physical activity, especially using approaches such as virtual reality, contributes to improving physical fitness and overall activity levels in patients undergoing haemodialysis. The study demonstrated that regular exercise may be associated with a reduction in inflammatory parameters and positive effects on bone metabolism in patients undergoing haemodialysis.

The AKI-to-CKD Transition: The Role of Uremic Toxins

After acute kidney injury (AKI), renal function continues to deteriorate in some patients. In a pro-inflammatory and profibrotic environment, the proximal tubules are subject to maladaptive repair. In the AKI-to-CKD transition, impaired recovery from AKI reduces tubular and glomerular filtration and leads to chronic kidney disease (CKD). Reduced kidney secretion capacity is characterized by the plasma accumulation of biologically active molecules, referred to as uremic toxins (UTs). These toxins have a role in the development of neurological, cardiovascular, bone, and renal complications of CKD. However, UTs might also cause CKD as well as be the consequence. Recent studies have shown that these molecules accumulate early in AKI and contribute to the establishment of this pro-inflammatory and profibrotic environment in the kidney. The objective of the present work was to review the mechanisms of UT toxicity that potentially contribute to the AKI-to-CKD transition in each renal compartment.

Sclerostin, Osteocytes, and Wnt Signaling in Pediatric Renal Osteodystrophy

The pathophysiology of chronic kidney disease-mineral and bone disorder (CKD-MBD) is not well understood. Specific factors secreted by osteocytes are elevated in the serum of adults and pediatric patients with CKD-MBD, including FGF-23 and sclerostin, a known inhibitor of the Wnt signaling pathway. The molecular mechanisms that promote bone disease during the progression of CKD are incompletely understood. In this study, we performed a cross-sectional analysis of 87 pediatric patients with pre-dialysis CKD and post-dialysis (CKD 5D). We assessed the associations between serum and bone sclerostin levels and biomarkers of bone turnover and bone histomorphometry. We report that serum sclerostin levels were elevated in both early and late CKD. Higher circulating and bone sclerostin levels were associated with histomorphometric parameters of bone turnover and mineralization. Immunofluorescence analyses of bone biopsies evaluated osteocyte staining of antibodies towards the canonical Wnt target, β-catenin, in the phosphorylated (inhibited) or unphosphorylated (active) forms. Bone sclerostin was found to be colocalized with phosphorylated β-catenin, which suggests that Wnt signaling was inhibited. In patients with low serum sclerostin levels, increased unphosphorylated "active" β-catenin staining was observed in osteocytes. These data provide new mechanistic insight into the pathogenesis of CKD-MBD and suggest that sclerostin may offer a potential biomarker or therapeutic target in pediatric renal osteodystrophy.

Serum sclerostin level is positively associated with endothelial dysfunction measured by digital thermal monitoring in patients with type 2 diabetes: A prospective cross-sectional study

Sclerostin and dickkopf-1 (DKK1), extracellular inhibitors of the canonical Wnt/β-catenin signaling pathway, have been associated with vascular aging and atherosclerosis. This study aimed to assess the correlation of sclerostin and DKK1 concentrations with endothelial function measured using vascular reactivity index (VRI) in patients with type 2 diabetes mellitus (T2DM). Fasting blood samples were collected from 100 patients with T2DM. Endothelial function and VRI were measured using digital thermal monitoring and circulating sclerostin and DKK1 levels by enzyme-linked immunosorbent assays. VRI values < 1.0, 1.0-1.9, and > 2.0 indicated poor, intermediate, and good vascular reactivity, respectively. Overall, 30, 38, and 32 patients had poor, intermediate, and good vascular reactivity, respectively. Older age, higher serum glycated hemoglobulin, urinary albumin-to-creatinine ratio, and sclerostin as well as lower hypertension prevalence, systolic blood pressure, and diastolic blood pressure (DBP) were associated with poor VRI. Multivariable forward stepwise linear regression analysis showed that DBP (β = 0.294, adjusted R2 change = 0.098, P < .001), log-glycated hemoglobin (β = -0.235, adjusted R2 change = 0.050, P = .002), log-urine albumin-to-creatinine ratio (β = -0.342, adjusted R2 change = 0.227, P < .001), and log-sclerostin level (β = -0.327, adjusted R2 change = 0.101, P < .001) were independently associated with VRI. Serum sclerostin, along with glycated hemoglobin and albumin-to-creatinine ratio, exhibited a negative correlation with VRI, while DBP showed a positive correlation with VRI. These factors can independently predict endothelial dysfunction in patients with T2DM.

Association between sclerostin levels and vascular outcomes in kidney transplantation patients

BACKGROUND

The impact of circulating sclerostin levels on vascular calcification has shown conflicting results depending on the target population and vascular anatomy. This study investigated the associations of sclerostin levels with vascular outcomes in kidney transplant patients.

METHODS

In a prospective observational study of the Korean Cohort Study for Outcome in Patients with Kidney Transplantation, 591 patients with serum sclerostin level data prior to transplantation were analyzed. The main predictor was the pre-transplant sclerostin level. Vascular outcomes were the abdominal aortic calcification score and brachial-ankle pulse wave velocity measured at pre-transplant screening and three and five years after kidney transplantation.

RESULTS

In linear regression analysis, sclerostin level positively correlated with changes in abdominal aortic calcification score between baseline and five years after kidney transplantation (coefficient of 0.73 [95% CI, 0.11-1.35] and 0.74 [95% CI, 0.06-1.42] for second and third tertiles, respectively, vs the first tertile). In a longitudinal analysis over five years, using generalized estimating equations, the coefficient of the interaction (sclerostin × time) was significant with a positive value, indicating that higher sclerostin levels were associated with faster increase in post-transplant abdominal aortic calcification score. Linear regression analysis revealed a positive association between pre-transplant sclerostin levels and changes in brachial-ankle pulse wave velocity (coefficient of 126.7 [95% CI, 35.6-217.8], third vs first tertile). Moreover, a significant interaction was identified between sclerostin levels and brachial-ankle pulse wave velocity at five years.

CONCLUSIONS

Elevated pre-transplant sclerostin levels are associated with the progression of post-transplant aortic calcifications and arterial stiffness.

Soluble guanylate cyclase agonist, isoliquiritigenin attenuates renal damage and aortic calcification in a rat model of chronic kidney failure

AIMS

Chronic kidney disease (CKD) is a growing fatal health problem worldwide associated with vascular calcification. Therapeutic approaches are limited with higher costs and poor outcomes. Adenine supplementation is one of the most relevant CKD models to human. Insufficient Nitric Oxide (NO)/ cyclic Guanosine Monophosphate (cGMP) signaling plays a key role in rapid development of renal fibrosis. Natural products display proven protection against CKD. Current study therefore explored isoliquiritigenin, a bioflavonoid extracted from licorice roots, potential as a natural activator for soluble Guanylate Cyclase (sGC) in a CKD rat model.

MATERIALS AND METHODS

60 male Wistar rats were grouped into Control group (n = 10) and the remaining rats received adenine (200 mg/kg, p.o) for 2 wk to induce CKD. They were equally sub-grouped into: Adenine untreated group and 4 groups orally treated by isoliquiritigenin low or high dose (20 or 40 mg/kg) with/without a selective sGC inhibitor, ODQ (1-H(1,2,4)oxadiazolo(4,3-a)-quinoxalin-1-one, 2 mg/kg, i.p) for 8 wk.

KEY FINDINGS

Long-term treatment with isoliquiritigenin dose-dependently and effectively amended adenine-induced chronic renal and endothelial dysfunction. It not only alleviated renal fibrosis and apoptosis markers but also aortic calcification. Additionally, this chalcone neutralized renal inflammatory response and oxidative stress. Isoliquiritigenin beneficial effects were associated with up-regulation of serum NO, renal and aortic sGC, cGMP and its dependent protein kinase (PKG). However, co-treatment with ODQ antagonized isoliquiritigenin therapeutic impact.

SIGNIFICANCE

Isoliquiritigenin seems to exert protective effects against CKD and vascular calcification by activating sGC, increasing cGMP and its downstream PKG.

Predictive markers in chronic kidney disease

Chronic kidney disease (CKD) is defined by gradual deterioration of the renal parenchyma and decline of functioning nephrons. CKD is now recognized as a distinct risk factor for cardiovascular disease (CVD). This risk rises in tandem with the decline in kidney function and peaks at the end-stage. It is important to identify individuals with CKD who are at a higher risk of advancing to end-stage renal disease (ESRD) and the beginning of CVD. This will enhance the clinical benefits and so that evidence-based therapy may be started at the initial stages for those individuals. A promising biomarker must represent tissue damage, and be easy to detect using non-invasive methods. Current CKD progression indicators have difficulties in reaching this aim. Hence this review presents an update on markers studied in the last decade, which help in the prediction of CKD progression such as neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, urinary liver-type fatty acid-binding protein, cystatin-C, asymmetric dimethylarginine, symmetric dimethylarginine, endotrophin, methylglyoxal, sclerostin, uric acid, and miRNA-196a. Additional research is needed to determine the predictive usefulness of these indicators in clinical samples for disease development. Their utility as surrogate markers need to be explored further for the early identification of CKD progression.

Role of Sclerostin in Cardiovascular Disease

Sclerostin is most recognized for its role in controlling bone formation but is also expressed in the heart, aorta, coronary, and peripheral arteries. This review summarizes research on sclerostin's role in cardiovascular disease. Rodent studies have found sclerostin to be expressed at sites of arterial calcification. In contrast, aortic sclerostin was reported to be downregulated in a mouse model of abdominal aortic aneurysm, and transgenic upregulation or administration of sclerostin was found to prevent abdominal aortic aneurysm and atherosclerosis formation. Sclerostin deficiency was reported to stimulate cardiac rupture in one rodent model. In humans, 7 of 11 studies reported a significant association between high serum sclerostin and high carotid intima media thickness. Ten of 15 studies reported a significant association between high serum sclerostin and severe arterial calcification. Twelve of 14 studies reported a significant association between high serum sclerostin and high arterial stiffness or atherosclerosis severity. Four of 9 studies reported a significant association between high serum sclerostin and high risk of cardiovascular events. A meta-analysis of randomized controlled trials suggested that administration of the sclerostin blocking antibody romosozumab did not significantly increase the risk of major adverse cardiovascular events (risk ratio, 1.14 [95% CI, 0.83-1.57]; P=0.54) or cardiovascular death (risk ratio, 0.92 [95% CI, 0.53-1.59]; P=0.71). Human genetic studies reported variants predisposing to low arterial sclerostin expression were associated with a high risk of cardiovascular events. Overall, past research suggests a cardiovascular protective role of sclerostin but findings have been inconsistent, possibly due to variations in study design, the unique populations and models studied, and the heterogeneous methods used.

Research progress on the relationship between IS and kidney disease and its complications

Indoxyl sulphate (IS) a representative uraemic toxin in the blood of patients with chronic kidney disease (CKD). Its accumulation may be closely related to CKD and the increasing morbidity and mortality of the disease's related complications. Timely and effective detection of the IS level and efficient clearance of IS may effectively prevent the progression of CKD and its related complications. Therefore, this article summarizes the research progress of IS related, including IS in CKD and its associated complications including chronic kidney disease, chronic kidney disease with cardiovascular disease, renal anemia, bone mineral metabolic disease and neuropsychiatric disorders, looking for IS accurate rapid detection methods, and explore the efficient treatment to reduce blood levels of indole phenol sulphate.

Chronic Kidney Disease-Mineral Bone Disease biomarkers in kidney transplant patients

Background:

Chronic Kidney Disease associated with Mineral Bone Disease (CKD-MBD) is frequent in kidney transplant patients. Post-transplantation bone disease is complex, especially in patients with pre-existing metabolic bone disorders that are further affected by immunosuppressive medications and changes in renal allograft function. Main biochemical abnormalities of mineral metabolism in kidney transplantation (KTx) include hypophosphatemia, hyperparathyroidism (HPTH), insufficiency or deficiency of vitamin D, and hypercalcemia.

Objective:

This review aimed to summarize the pathophysiology and main biomarkers of CKD-MBD in KTx.

Methods:

A comprehensive and non-systematic search in PubMed was independently made with an emphasis on biomarkers in mineral bone disease in KTx.

Results:

CKD-MBD can be associated with numerous factors including secondary HPTH, metabolic dysregulations before KTx, and glucocorticoids therapy in post-transplant subjects. Fibroblast growth factor 23 (FGF23) reaches normal levels after KTx with good allograft function, while calcium, vitamin D and phosphorus, ultimately, result in hypercalcemia, persistent vitamin D insufficiency, and hypophosphatemia respectively. As for PTH levels, there is an initial tendency of a significant decrease, followed by a raise due to secondary or tertiary HPTH. In regard to sclerostin levels, there is no consensus in the literature.

Conclusion:

KTx patients should be continuously evaluated for mineral homeostasis and bone status, both cases with successful kidney transplantation and those with reduced functionality. Additional research on CKD-MBD pathophysiology, diagnosis, and management is essential to guarantee long-term graft function, better prognosis, good quality of life, and reduced mortality for KTx patients.

Competitive blocking of LRP4-sclerostin binding interface strongly promotes bone anabolic functions

Induction of bone formation by Wnt ligands is inhibited when sclerostin (Scl), an osteocyte-produced antagonist, binds to its receptors, the low-density lipoprotein receptor-related proteins 5 or 6 (LRP5/6). Recently, it was shown that enhanced inhibition is achieved by Scl binding to the co-receptor LRP4. However, it is not clear if the binding of Scl to LRP4 facilitates Scl binding to LRP5/6 or inhibits the Wnt pathway in an LRP5/6-independent manner. Here, using the yeast display system, we demonstrate that Scl exhibits a stronger binding affinity for LRP4 than for LRP6. Moreover, we found stronger Scl binding to LRP6 in the presence of LRP4. We further show that a Scl mutant (SclN93A), which tightly binds LRP4 but not LRP6, does not inhibit the Wnt pathway on its own. We demonstrate that SclN93A competes with Scl for a common binding site on LRP4 and antagonizes Scl inhibition of the Wnt signaling pathway in osteoblasts in vitro. Finally, we demonstrate that 2 weeks of bi-weekly subcutaneous injections of SclN93A fused to the fragment crystallizable (Fc) domain of immunoglobulin (SclN93AFc), which retains the antagonistic activity of the mutant, significantly increases bone formation rate and enhances trabecular volumetric bone fraction, trabecular number, and bone length in developing mice. Our data show that LRP4 serves as an anchor that facilitates Scl-LRP6 binding and that inhibition of the Wnt pathway by Scl depends on its prior binding to LRP4. We further provide evidence that compounds that inhibit Scl-LRP4 interactions offer a potential strategy to promote anabolic bone functions.

Circulating miRNA-29b and Sclerostin Levels Correlate with Coronary Artery Calcification and Cardiovascular Events in Maintenance Hemodialysis Patients

Objective

Coronary artery calcification (CAC) is a common complication in end-stage renal disease (ESRD) patients undergoing maintenance hemodialysis (MHD), and the extent of CAC is a predominant predictor of cardiovascular outcomes in MHD patients. In this study, we sought to uncover the relationship between circulating miRNA-29b, sclerostin levels, CAC, and cardiovascular events (CVEs) in MHD patients.

Methods

This study recruited patients receiving MHD for at least three months in the Hainan General Hospital between January 2016 and June 2019, and all patients were followed up 24 months for CVEs. The serum level of sclerostin was determined by enzyme-linked immunosorbent assay (ELISA) and miRNA-29b expression by real-time qPCR (RT-qPCR). All patients received cardiac CT scans to evaluate CAC, and CAC scores were expressed in Agatston units. The MHD patients with CACs <100 were arranged into the CAC (<100) group, those with 100–400 CACs into the CAC (100–400) group, and those with CACs >400 into the CAC (>400) group. Net reclassification index (NRI) and integrated discrimination index (IDI) were calculated to assess the predictive performance of serum sclerostin level for the occurrence of CVEs.

Results

Compared with the CAC (<100) group, the CAC (>400) group had higher proportions of older patients, hypertension and diabetes mellitus patients, longer dialysis duration, higher mean arterial pressure (MAP), higher levels of high-sensitivity C-reactive protein (hs-CRP), alkaline phosphatase (ALP), and phosphate (P < 0.05). It was found that the CAC (100–400) and CAC (>400) groups exhibited higher serum levels of sclerostin but lower levels of miRNA-29b than the CAC (<100) group (P < 0.05) and the CAC (>400) group had a higher level of sclerostin and a lower level of miRNA-29b than the CAC (100–400) group (P < 0.05). The circulating level of miRNA-29b was negatively correlated with the serum level of sclerostin in MHD patients (r = −0.329, P < 0.01). The multivariate logistic regression analysis showed that hs-CRP, phosphate, sclerostin, and miRNA-29b were independent risk factors for CAC in MHD patients (P < 0.05, Table 2). ROC for prediction of CAC by sclerostin yielded 0.773 AUC with 95% CI 0.683–0.864 (P < 0.01). As depicted by Kaplan–Meier curves of CVE incidence in MHD patients according to median sclerostin (491.88 pg/mL) and median miRNA-29b (Ct = 25.15), we found that serum levels of sclerostin and miRNA-29b were correlated with the incidence of CVEs in MHD patients. When a new model was used to predict the incidence of CVEs, NRI 95% CI was 0.60 (0.16–1.03) (P < 0.05) and IDI 95% CI was 0.002 (−0.014 to 0.025) (P < 0.05), suggesting that sclerostin added into the old model could improve the prediction of the incidence of CVEs.

Conclusions

These data suggest that circulating miRNA-29b and sclerostin levels are correlated with CAC and incidence of CVEs in MHD patients. Higher sclerostin and lower miRNA-29b may serve as independent risk factors for the incidence of CVEs in MHD patients.

Cardiovascular Safety of Anti-Sclerostin Therapy in Chronic Kidney Disease

The significance of sclerostin for bone and cardiovascular health in patients with chronic kidney disease (CKD) is complex and incompletely understood. Experimental evidence suggests that anti-sclerostin therapy shows diminished efficacy on bone in the setting of CKD. Limited clinical evidence suggests that the osteoanabolic and anti-resorptive activity is attenuated, but hypocalcemia is more prevalent in patients with advanced CKD (eGFR < 30 mL/min) treated with anti-sclerostin (romosozumab) therapy as compared to patients without kidney disease. Furthermore, sclerostin is prominently expressed in uremic arteries. Whether the inhibition of sclerostin has adverse effects on cardiovascular health in CKD is currently unknown. This review summarizes the current understanding of the physiology and pathophysiology of sclerostin in CKD, with a focus on the cardiovascular safety of anti-sclerostin therapy in patients with or without CKD.

Wnt/β-catenin pathway proteins in end-stage renal disease

Aim: To delineate the association of end-stage renal disease (ESRD) and Wnt-proteins including the agonist R-spondin-1, the transducer β-catenin and the antagonists DKK1 and sclerostin. Materials & methods: Serum Wnt-pathway proteins levels were measured by ELISA in 60 ESRD patients and 30 normal controls. Results: DKK1 and sclerostin were significantly higher in ESRD than in controls, and β-catenin and the catenin + R-spondin-1/DKK1 + sclerostin ratio, reflecting the ratio of agonist and transducer on antagonists (AT/ANTA), were significantly lower in ESRD. Estimated glomerular filtration rate was significantly associated with DKK1 and sclerostin (inversely), β-catenin (positively) and the AT/ANTA ratio (r = 0.468, p < 0.001). Conclusion: Wnt/β-catenin pathway proteins show significant alterations in ESRD, indicating significantly increased levels of antagonists.

Supplemented Low-Protein Diet May Delay the Need for Preemptive Kidney Transplantation: A Nationwide Population-Based Cohort Study

BACKGROUND

Although several studies suggest the benefit of a low-protein diet supplemented with amino acids and keto acids (sLPD) in delaying the initiation of hemodialysis, evidence on whether these nutritional approaches could delay the timing of preemptive transplantation is lacking.

METHODS

Retrospective nationwide cohort study, from Taiwan's National Health Insurance Research Database. Patients having undergone a first preemptive kidney transplantation between 2001 and 2017 were identified and divided into two groups according to the presence of sLPD treatment or not. The primary outcome was the time between the diagnosis of advanced CKD and transplantation. Secondary outcomes were post-transplantation adverse events.

RESULTS

A total of 245 patients who received their first preemptive kidney transplantation were identified from the nationwide database; 63 of them had been on an sLPD prior to transplantation (sLPD group). The duration between the day of advanced CKD diagnosis and the day of transplantation was significantly longer in the sLPD group compared with the non-sLPD group (median duration: 345 vs. 220 days, p = 0.001). The risk of post-transplantation adverse events did not differ between the two groups.

CONCLUSIONS

Within the limits of its observational, retrospective design, this is the first study to suggest that nutritional management with sLPDs can safely delay the timing of preemptive kidney transplantation.

Meta-analysis of the association between sclerostin level and adverse clinical outcomes in patients undergoing maintenance haemodialysis

BACKGROUND

Studies regarding the relationship of sclerostin (Scl) with clinical outcomes in patients undergoing maintenance haemodialysis have yielded controversial findings. This meta-analysis was performed to investigate the predictive role of Scl in this patient population.

METHODS

Several electronic medical databases (e.g. PubMed, Embase, Web of Science and Cochrane Library) were searched for eligible studies through December 20, 2019. Summary hazard ratios (HRs) with 95% confidence intervals (CIs) were calculated based on Scr level (high or low) using a random or fixed effects model.

RESULTS

From among 641 initially screened publications, 16 eligible studies were included in this meta-analysis. A high Scl level was not associated with cardiovascular events [HR = 0.8 (95% CI, 0.42-1.35)] or all-cause mortality [HR = 0.93 (95% CI, 0.56-1.54)]. There was high heterogeneity, but no evidence of publication bias. Interestingly, a high Scl level was associated with reduced cardiovascular events [HR = 0.44 (95% CI, 0.29-0.69)] in the subgroup by shorter follow-up period or all-cause mortality [pooled HR = 0.58 (95% CI, 0.36-0.91)] by shorter dialysis vintage.

CONCLUSION

This meta-analysis indicated that a high Scl level did not predict total clinical outcomes in patients undergoing maintenance haemodialysis despite survival benefits in the subgroups. The predictive role of Scl in these patients should be further evaluated in large prospective studies.

Uremic Toxins Affecting Cardiovascular Calcification: A Systematic Review

Cardiovascular calcification is highly prevalent and associated with increased morbidity in chronic kidney disease (CKD). This review examines the impact of uremic toxins, which accumulate in CKD due to a failing kidney function, on cardiovascular calcification. A systematic literature search identified 41 uremic toxins that have been studied in relation to cardiovascular calcification. For 29 substances, a potentially causal role in cardiovascular calcification was addressed in in vitro or animal studies. A calcification-inducing effect was revealed for 16 substances, whereas for three uremic toxins, namely the guanidino compounds asymmetric and symmetric dimethylarginine, as well as guanidinosuccinic acid, a calcification inhibitory effect was identified in vitro. At a mechanistic level, effects of uremic toxins on calcification could be linked to the induction of inflammation or oxidative stress, smooth muscle cell osteogenic transdifferentiation and/or apoptosis, or alkaline phosphatase activity. For all middle molecular weight and protein-bound uremic toxins that were found to affect cardiovascular calcification, an increasing effect on calcification was revealed, supporting the need to focus on an increased removal efficiency of these uremic toxin classes in dialysis. In conclusion, of all uremic toxins studied with respect to calcification regulatory effects to date, more uremic toxins promote rather than reduce cardiovascular calcification processes. Additionally, it highlights that only a relatively small part of uremic toxins has been screened for effects on calcification, supporting further investigation of uremic toxins, as well as of associated post-translational modifications, on cardiovascular calcification processes.

Factors associated with sclerostin levels - A calcification inhibitor - In individuals with type 2 diabetes mellitus; Is autonomic neuropathy the missing link?

BACKGROUND

Sclerostin inhibits bone formation and its expression is upregulated in the vasculature during the arterial calcification process as a counterregulatory mechanism preventing further calcification. Lower extremity arterial calcification (LEAC) is common in neuropathic patients with type 2 diabetes (T2DM). Herein, we investigated for associations between plasma sclerostin levels and diabetic neuropathy as well as LEAC in subjects with T2DM.

METHODS

A total of 74 individuals with and 76 without T2DMwere recruited. Plasma sclerostin levels were measured by ELISA. Diagnosis of cardiac autonomic neuropathy (CAN) was based on the battery of the four autonomic tests, while of somatosensory peripheral neuropathy (DPN) on neuropathy symptom score and neuropathy disability score. LEAC was assessed with conventional ankle and foot x-rays.

RESULTS

Plasma sclerostin levels were higher in participants with LEAC vs. those without LEAC in both diabetes and non-diabetes cohorts (p = 0.035 and p = 0.003, respectively). In the diabetes cohort, patients with CAN, but not with DPN, had higher sclerostin levels when compared with those without CAN (p < 0.001). Multivariate analysis in the diabetes cohort demonstrated that sclerostin levels were associated positively with CAN and LEAC, while in the non-diabetes cohort there was a trend for a positive association with male gender and presence of LEAC.

CONCLUSION

Plasma sclerostin levels are increased in individuals with LEAC irrespectively of diabetes status. In addition, plasma sclerostin concentrations are associated independently with LEAC and CAN in people with T2DM.

Physical Activity versus Sclerostin and Interleukin 6 Concentration in Patients Receiving Renal Replacement Therapy by Hemodialysis

Introduction

Chronic kidney disease and renal replacement therapy are associated with reduced motor activity, which may result in the presence of mineral bone disorders and an increase in inflammation markers. The aim of the study was to assess the relationship between the performance of daily physical activity, expressed in the number of steps performed by patients undergoing hemodialysis and the concentration of selected biochemical parameters (SCL, IL-6).

Patients and Methods

The study group (B) involved 33 patients aged 59.8 ± 9.8 years from the dialysis station at the Department of Nephrology, Transplantology and Internal Medicine PUM. In group B, interventions considering an increase in physical activity expressed in the number of steps were introduced. Group C consisted of 30 people aged 54.9 (9.37), with GFR over 60 mL/min/1.73m. Physical activity was measured with pedometers. Anthropometric and biochemical parameters were assessed at baseline, after the third and sixth month of the study. Descriptive statistics, intergroup comparisons using Mann–Whitney U test and Spearman correlation analysis were performed. The level of significance was set at p≤0.005.

Results

A relationship between IL-6 concentration and the number of steps in group B after three months of intervention was demonstrated. In group C, the concentration of SCL and IL-6 decreased with the increase in the number of steps taken. Only in group C the waist circumference decreased with the increase of the number of steps performed.

Conclusion

Patients receiving renal replacement therapy by hemodialysis showed significantly lower physical activity compared to people without kidney disease. Performing bigger number of steps can lower interleukin 6 levels in hemodialysis patients.

Sclerostin is an independent risk factor for all-cause mortality in kidney transplant recipients

Background

Sclerostin is a hormone contributing to the bone-vascular wall cross talk and has been implicated in cardiovascular events and mortality in patients with chronic kidney disease (CKD). We analyzed the relationship between sclerostin and mortality in renal transplant recipients.

Methods

600 stable renal transplant recipients (367men, 233 women) were followed for all-cause mortality for 3 years. Blood and urine samples for analysis and clinical data were collected at study entry. We performed Kaplan–Meier survival analysis and Cox regression models considering confounding factors such as age, eGFR, cold ischemia time, HbA1c, phosphate, calcium, and albumin. Optimal cut-off values for the Cox regression model were calculated based on ROC analysis.

Results

Sixty-five patients died during the observation period. Nonsurvivors (n = 65; sclerostin 57.31 ± 30.28 pmol/L) had higher plasma sclerostin levels than survivors (n = 535; sclerostin 47.52 ± 24.87 pmol/L) (p = 0.0036). Kaplan–Meier curve showed that baseline plasma sclerostin concentrations were associated with all-cause mortality in stable kidney transplant recipients (p = 0.0085, log-rank test). After multiple Cox regression analysis, plasma levels of sclerostin remained an independent predictor of all-cause mortality (hazard ratio, 1.011; 95% CI 1.002–1.020; p = 0.0137).

Conclusions

Baseline plasma sclerostin is an independent risk factor for all-cause mortality in patients after kidney transplantation.

Electronic supplementary material

The online version of this article (10.1007/s10157-020-01956-y) contains supplementary material, which is available to authorized users.

Sclerostin and Vascular Pathophysiology

There is cumulating evidence for a contribution of Wnt signaling pathways in multiple processes involved in atherosclerosis and vascular aging. Wnt signaling plays a role in endothelial dysfunction, in the proliferation and migration of vascular smooth muscle cells (VSMCs) and intimal thickening. Moreover, it interferes with inflammation processes, monocyte adhesion and migration, as well as with foam cell formation and vascular calcification progression. Sclerostin is a negative regulator of the canonical Wnt signaling pathway and, accordingly, the consequence of increased sclerostin availability can be disruption of the Wnt signalling cascade. Sclerostin is becoming a marker for clinical and subclinical vascular diseases and several lines of evidence illustrate its role in the pathophysiology of the vascular system. Sclerostin levels increase with aging and persist higher in some diseases (e.g., diabetes, chronic kidney disease) that are known to precipitate atherosclerosis and enhance cardiovascular risk. Current knowledge on the association between sclerostin and vascular diseases is summarized in this review.

Should We Consider the Cardiovascular System While Evaluating CKD-MBD?

Cardiovascular (CV) disease is highly prevalent in the population with chronic kidney disease (CKD), where the risk of CV death in early stages far exceeds the risk of progression to dialysis. The presence of chronic kidney disease-mineral and bone disorder (CKD-MBD) has shown a strong correlation with CV events and mortality. As a non-atheromatous process, it could be partially explained why standard CV disease-modifying drugs do not provide such an impact on CV mortality in CKD as observed in the general population. We summarize the potential association of CV comorbidities with the older (parathyroid hormone, phosphate) and newer (FGF23, Klotho, sclerostin) CKD-MBD biomarkers.

Serum Sclerostin But Not DKK-1 Correlated with Central Arterial Stiffness in End Stage Renal Disease Patients

Sclerostin and dickkopf-1 (DKK1) played a role in the development of cardiovascular diseases and arterial stiffness in chronic kidney disease (CKD) patients but with controversial results of patients in end-stage renal disease (ESRD) including hemodialysis (HD) and peritoneal dialysis (PD). This study aimed to examine the association between the mode of dialysis or the values of sclerostin or DKK1 and carotid-femoral pulse wave velocity (cfPWV) in ESRD patients. There were 122 HD and 72 PD patients enrolled in this study. By a validated tonometry system, cfPWV was measured and then segregated patients into values of >10 m/s as the high central arterial stiffness (AS) group and values ≤ 10 m/s as the control group. Serum levels of sclerostin and DKK1 were measured using a commercial enzyme-linked immunosorbent assay kit. Possible risk factors for the development of AS were analyzed by logistic regression analysis. There were 21 (29.2%) of PD and 53 (43.4%) of HD in the high AS group. Compared to patients in the control group, those in the high AS group were older, had more comorbidities, had higher systolic blood pressure, and had higher serum levels of fasting glucose, C-reactive protein, and sclerostin. Levels of sclerostin (adjusted OR 1.012, 95% CI. 1.006–1.017, p = 0.0001) was found to be an independent predictor of high AS in ESRD patients by multivariate logistic regression analysis. Furthermore, receiver operating characteristic curve analysis showed the optimal cut-off values of sclerostin for predicting AS was 208.64 pmol/L (Area under the curve 0.673, 95% CI: 0.603–0.739, p < 0.001). This study showed that serum levels of sclerostin, but not DKK1 or mode of dialysis, to be a predictor for high central AS in ESRD patients.

Sclerostin within the chronic kidney disease spectrum

Sclerostin is sometimes presented as a promising biomarker in assessing bone health both in the general population and chronic kidney disease patients. However, it is still unclear whether it has any true added value compared to existing bone biomarkers in predicting bone turnover and/or bone density in chronic kidney disease patients. A wealth of papers has been published to evaluate the association between sclerostin and vascular calcifications development or even as prognostic biomarker for mortality, but often with conflicting results. Standardization and harmonization of analytical techniques is a prerequisite to advance clinical knowledge in sclerostin.

Assessment of Sclerostin and Interleukin 6 Levels and Selected Anthropometric Parameters in Patients Receiving Hemodialysis Replacement Therapy-Pilot Study

Background and Objectives: Chronic kidney disease (CKD) is an important public health problem associated with, e.g., progressive renal insufficiency, bone mineral disorders, and increased inflammatory marker levels. The objective of this study was to compare selected biochemical parameters and to evaluate potential correlations between selected anthropometric parameters and levels of sclerostin and interleukin 6 (IL-6) in blood plasma. Materials and Methods: The study group consisted of 34 patients aged 59.8 ± 9.8 years, receiving hemodialysis therapy. The control group consisted of 31 individuals aged 55.4 ± 9.37 years, presenting with GFR (glomerular filtration rate) of more than 60 mL/min/1.73 m2. Selected anthropometric and biochemical parameters were assessed at baseline, as well as 3 and 6 months into the study. Statistical analyses were performed using the Statistica 2014 software package (StatSoft, Inc.Tulsa, OK, USA). Analyses included descriptive statistics, intergroup comparisons using the Mann-Whitney U-test or the Kruskal-Wallis test, and Spearman's correlation analysis. The significance level was set at p ≤ 0.005. Results: At all measurement time points, i.e., at baseline, at month 3, and at month 6, the IL-6 levels in the study group were significantly higher than those in the control group. No correlations were observed in the study group between SCL or IL-6 levels and anthropometric parameters such as body weight, body mass index (BMI), or waist circumference. Conclusions: Patients receiving hemodialysis replacement therapy present with significantly higher levels of IL-6 in their blood. Anthropometric parameters (body weight, BMI, and waist circumference) have no impact on sclerostin and IL-6 levels in patients undergoing hemodialysis therapy. The results obtained are satisfactory, and the research will be continued.

Increased Sclerostin, but Not Dickkopf-1 Protein, Is Associated with Elevated Pulse Wave Velocity in Hemodialysis Subjects

BACKGROUND

Sclerostin and Dickkopf-1 (Dkk-1) proteins are inhibitors of the canonical Wnt/β-catenin bone pathway. Pilot data suggest that sclerostin may be involved in vascular changes in chronic kidney disease (CKD), but data on the effects of Dkk-1 are scarce. This is the first study investigating simultaneously the associations of sclerostin and Dkk-1 with arterial stiffness in hemodialysis patients.

METHODS

A total of 80 patients on chronic hemodialysis had carotid-femoral pulse wave velocity (PWV), central blood pressure (BP), and wave reflections evaluated with applanation tonometry (Sphygmocor) on a midweek non-dialysis day. Serum levels of sclerostin and Dkk-1 were measured with ELISA. A large set of demographic, comorbid, laboratory, and drug parameters were used in the analyses.

RESULTS

Subjects with PWV >9.5 m/s (high arterial stiffness group, n = 40) were older, had higher BMI, higher prevalence of hypertension, diabetes, and coronary heart disease, and higher peripheral systolic BP, central systolic BP, C-reactive protein, and serum sclerostin (p = 0.02), but similar Dkk-1, compared to subjects with low PWV. When dichotomizing the population by sclerostin levels, those with high sclerostin had higher PWV than patients with low sclerostin levels (10.63 ± 2.71 vs. 9.77 ± 3.13, p = 0.048). Increased sclerostin (>200 pg/mL) was significantly associated with increased PWV (>9.5 m/s; HR 2.778, 95% CI 1.123-6.868 per pg/mL increase); this association remained significant after stepwise adjustment for Dkk-1, intact parathyroid hormone, and calcium × phosphate product. In contrast, no association was noted between Dkk-1 and PWV (HR 1.000, 95% CI 0.416-2.403).

CONCLUSION

Serum sclerostin is associated with PWV independently of routine markers of CKD-MBD in hemodialysis patients. In contrast, Dkk-1 has no association with arterial stiffness and is not pathophysiologically involved in relevant vascular changes.

Correlation between sclerostin and Dickkopf-1 with aortic arterial stiffness in patients with type 2 diabetes: A prospective, cross-sectional study

BACKGROUND

Sclerostin and Dickkopf-1 are extracellular inhibitors of the canonical Wnt/β-catenin signalling pathway, which is implicated in the development of arterial stiffness. However, the correlation between aortic stiffness and sclerostin or Dickkopf-1 levels in patients with type 2 diabetes mellitus is unknown.

METHODS

Fasting blood samples were collected from 125 patients with type 2 diabetes mellitus. Aortic stiffness was measured by carotid-femoral pulse wave velocity, and high aortic stiffness was defined by a carotid-femoral pulse wave velocity of >10 m/s. The serum sclerostin and Dickkopf-1 concentrations were determined using commercially available enzyme-linked immunosorbent assays.

RESULTS

In total, 46 patients with type 2 diabetes mellitus (36.8%) had high levels of aortic stiffness. Compared to the control group without aortic stiffness, this group was significantly older, had higher systolic and diastolic blood pressures, had higher blood urea nitrogen, creatinine, urinary albumin-to-creatinine ratio and serum sclerostin levels, and had significantly lower high-density lipoprotein cholesterol levels and estimated glomerular filtration rates. After adjusting for confounders, serum sclerostin [odds ratio = 1.005 (1.002-1.007), p = 0.002] levels remained an independent predictor of aortic stiffness. Multivariate analysis showed that the serum sclerostin level ( β = 0.374, adjusted R² change = 0.221, p < 0.001) was positively associated with carotid-femoral pulse wave velocity.

CONCLUSION

Serum levels of sclerostin, but not Dickkopf-1, are positively correlated with carotid-femoral pulse wave velocity and independently predict aortic stiffness in patients with type 2 diabetes mellitus.

Association of Serum Sclerostin with Bone Sclerostin in Chronic Kidney Disease is Lost in Glucocorticoid Treated Patients

The osteocytic protein sclerostin inhibits bone turnover. Serum sclerostin rises early in chronic kidney disease (CKD), but if this reflects osteocyte sclerostin production is unclear, since sclerostin is also expressed in extra-skeletal tissue. Glucocorticoid treatment impacts on serum sclerostin, but the effect on the association between serum and bone sclerostin is unknown. We sought to determine whether serum sclerostin reflects bone sclerostin in different CKD stages and how this association is influenced by glucocorticoid treatment. In a cross-sectional analysis, we investigated serum sclerostin, bone sclerostin by immunohistochemistry, and bone histomorphometry in iliac crest bone biopsies from 43 patients with CKD 3-5D, including 14 dialysis patients and 22 transplanted patients (18 kidney, 4 other). Thirty-one patients were on glucocorticoid treatment at time of biopsy. Patients with low bone turnover (bone formation rate < 97 µm²/mm²/day; N = 13) had higher median serum sclerostin levels (224.7 vs. 141.7 pg/ml; P = 0.004) and higher bone sclerostin, expressed as sclerostin positive osteocytes per bone area (12.1 vs. 5.0 Scl+ osteocytes/B.Ar; P = 0.008), than patients with non-low bone turnover (N = 28). In linear regression analyses, correcting for age, gender, dialysis status and PTH, serum sclerostin was only associated with bone sclerostin in patients not treated with glucocorticoids (r² = 0.6, P = 0.018). For the first time, we describe that female CKD patients have higher median bone sclerostin than males (11.7 vs. 5.7 Scl+ osteocytes/B.Ar, P = 0.046), despite similar serum sclerostin levels and bone histo-morphometric parameters. We conclude that glucocorticoid treatment appears to disrupt the association of serum sclerostin with bone sclerostin in CKD.

WISP1 silencing confers protection against epithelial-mesenchymal transition of renal tubular epithelial cells in rats via inactivation of the wnt/β-catenin signaling pathway in uremia

Uremia can affect hepatic metabolism of drugs by regulating the clearance of drugs, but it has not been clarified whether gene silencing could modulate the epithelial-mesenchymal transition (EMT) process in uremia. Hence, we investigated the effect of WISP1 gene silencing on the renal tubular EMT in uremia through the wnt/β-catenin signaling pathway. Initially, microarray-based gene expression profiling of uremia was used to identify differentially expressed genes. Following the establishment of uremia rat model, serum creatinine, and urea nitrogen of rats were detected. Renal tubular epithelial cells (TECs) were transfected with shRNA-WISP1 lentivirus interference vectors and LiCI (the wnt/β-catenin signaling pathway activator) to explore the regulatory mechanism of WISP1 in uremia in relation to the wnt/β-catenin signaling pathway. Then, expression of WISP1, wnt2b, E-cadherin, α-SMA, c-myc, Cyclin D1, MMP-2, and MMP-9 was determined. Furthermore, TEC migration and invasion were evaluated. Results suggested that WISP1 and the wnt/β-catenin signaling pathway were associated with uremia. Uremic rats exhibited increased serum creatinine and urea nitrogen levels, upregulated WISPl, and activated wnt/β-catenin signaling pathway. Subsequently, WISP1 silencing decreased wnt2b, c-myc, Cyclin D1, α-SMA, MMP-2, and MMP-9 expression but increased E-cadherin expression, whereas LiCI treatment exhibited the opposite trends. In addition, WISP1 silencing suppressed TEC migration and invasion, whereas LiCI treatment promoted TEC migration and invasion. The findings indicate that WISP1 gene silencing suppresses the activation of the wnt/β-catenin signaling pathway, thus reducing EMT of renal TECs in uremic rats.

Serum levels of sclerostin as a potential biomarker in central arterial stiffness among hypertensive patients

BACKGROUND

Sclerostin is known to be a canonical Wnt/β-catenin signaling pathway inhibitor, while the Wnt/β-catenin signaling pathway is proposed to be involved in the development of arterial stiffness. This study aims to investigate the relationship between serum sclerostin levels and carotid-femoral pulse wave velocity (cfPWV) among hypertensive patients.

METHODS

Fasting blood samples were obtained from 105 hypertensive patients. Patients with cfPWV values of > 10 m/s were classified in the high arterial stiffness group, whereas those with cfPWV values of ≤10 m/s were assigned to the low arterial stiffness group. Serum sclerostin and Dickkopf-1 (DKK1) levels were quantified using commercially available enzyme-linked immunosorbent assays.

RESULTS

Thirty-six hypertensive patients (34.3%) who belonged to the high arterial stiffness group were generally older (p < 0.001), presented with lower estimated glomerular filtration rates (eGFR, p = 0.014), higher incidence of diabetes mellitus (p = 0.030), average systolic blood pressures (SBP, p = 0.013), pulse pressure (p = 0.026), serum creatinine levels (p = 0.013), intact parathyroid hormone levels (iPTH, p = 0.003), and sclerostin levels (p < 0.001) than their counterparts in the low arterial stiffness group. A multivariable logistic regression analysis identified sclerostin as an independent predictor of arterial stiffness in hypertensive patients (odds ratio, 1.042; 95% confidence interval (CI), 1.017-1.068; p = 0.001). Multivariable forward stepwise linear regression analysis also showed that serum sclerostin level (β = 0.255, adjusted R2 change: 0.146, p = 0.003) was positively associated with cfPWV values in patients with hypertension.

CONCLUSIONS

In this study, serum sclerostin level, but not DKK1, is found to be positively correlated with cfPWV values and is identified as an independent predictor of arterial stiffness in hypertensive patients after adjusting for significant confounders.

Associations of sclerostin with carotid artery atherosclerosis and all-cause mortality in Chinese patients undergoing maintenance hemodialysis

BACKGROUND

Previous clinical studies found inconsistent relationship between circulating sclerostin levels and treatment outcome in patients undergoing maintenance hemodialysis (MHD). Therefore, this study aimed to assess the associations of sclerostin with carotid artery atherosclerosis and all-cause mortality in Chinese patients undergoing MHD.

METHODS

This retrospective study assessed 84 patients undergoing MHD at the Nephrology Department of Beijing Hospital from January to April 2012, with a median follow-up of 61.2 months (range: 11.5 to 63 months). Carotid artery intima-media thicknesses (CIMTs) and atherosclerotic plaques were measured by B-mode Doppler ultrasound at baseline. Blood samples were collected for measuring serum sclerostin and soluble klotho (s-klotho) levels. The associations of sclerostin levels with carotid artery atherosclerosis was evaluated by correlation methods. Predictive factors of mortality were assessed by multivariate COX regression.

RESULTS

Baseline serum sclerostin averaged 162.01 pmol/L, with an interquartile range of 121.69 to 225.22 pmol/L, while CIMT values were 1.35 ± 0.39 mm. Carotid artery atherosclerotic plaques were detected in 68 subjects (81%). Subjects with sclerostin levels above the median value had higher CIMT (p = 0.038) and higher prevalence of atherosclerotic plaque (p = 0.025). During follow-up, 27 patients died; Kaplan-Meier curves indicated that subjects with high sclerostin levels (above the median value at baseline) had shorter survival (log rank p = 0.011). In multivariate COX regression analysis, serum sclerostin (HR, 1.095; 95% confidence interval [CI] 1.022-1.174, p = 0.010) and albumin (HR, 0.742; 95%CI 0.612-0.900, p = 0.002) levels were independent predictors of all-cause mortality.

CONCLUSIONS

Sclerostin is positively associated with CIMT. In addition, patients with low baseline serum sclerostin undergoing MHD show better survival.

Does a Supplemental Low-Protein Diet Decrease Mortality and Adverse Events After Commencing Dialysis? A Nationwide Cohort Study

Background: A beneficial effect of a ketoanalogue-supplemented low-protein diet (sLPD) in postponing dialysis has been demonstrated in numerous previous studies. However, evidence regarding its effect on long-term survival is limited. Our study assessed the long-term outcomes of patients on an sLPD after commencing dialysis. Methods: This retrospective study examined patients with new-onset end-stage renal disease with permanent dialysis between 2001 and 2013, extracted from Taiwan’s National Health Insurance Research Database. Patients who received more than 3 months of sLPD treatment in the year preceding the start of dialysis were extracted. The outcomes studied were all-cause mortality, infection rate, and major cardiac and cerebrovascular events (MACCEs). Results: After propensity score matching, the sLPD group (n = 2607) showed a lower risk of all-cause mortality (23.1% vs. 27.6%, hazard ratio (HR) 0.77, 95% confidence interval (CI) 0.70–0.84), MACCEs (19.2% vs. 21.5%, HR 0.86, 95% CI 0.78–0.94), and infection-related death (9.9% vs. 12.5%, HR 0.76, 95% CI 0.67–0.87) than the non-sLPD group did. Conclusion: We found that sLPD treatment might be safe without long-term negative consequences after dialysis treatment.

Circulating levels of sclerostin are associated with cardiovascular mortality

Cardiovascular diseases are a health problem throughout the world, especially in people with diabetes. The identification of cardiovascular disease biomarkers can improve risk stratification. Sclerostin is a modulator of the Wnt/β-catenin signalling pathway in different tissues, and it has recently been linked to vascular biology. The current study aimed to evaluate the relationship between circulating sclerostin levels and cardiovascular and non-cardiovascular mortality in individuals with and without type 2 diabetes. We followed up a cohort of 130 participants (mean age 56.8 years; 48.5% females; 75 with type 2 diabetes; 46 with prevalent cardiovascular disease) in which serum sclerostin levels were measured at the baseline. Time to death (both of cardiovascular and non-cardiovascular causes) was assessed to establish the relationship between sclerostin and mortality. We found that serum sclerostin concentrations were significantly higher in patients with prevalent cardiovascular disease (p<0.001), and independently associated with cardiovascular mortality (p = 0.008), showing sclerostin to be a stronger predictor of mortality than other classical risk factors (area under the curve = 0.849 vs 0.823). The survival analysis showed that an increase of 10 pmol/L in the serum sclerostin level resulted in a 31% increase in cardiovascular mortality. However, no significant association was observed between sclerostin levels and non-cardiovascular mortality (p = 0.346).

From these results, we conclude that high sclerostin levels are related to mortality due to cardiovascular causes. The clinical implication of these findings is based on the possible use of serum sclerostin as a new biomarker of cardiovascular mortality risk in order to establish preventive strategies.

Effect of uremic toxin-indoxyl sulfate on the skeletal system

Chronic kidney disease-mineral bone disorders (CKD-MBD) exhibit abnormalities in the circulating mineral levels, vitamin D metabolism, and parathyroid function that contribute to the formation of a bone lesion. The uremic toxin, indoxyl sulfate (IS), accumulates in the blood in cases of renal failure and leads to bone loss. The bone and renal responses to the action of the parathyroid hormone (PTH) are progressively decreased in CKD in spite of increasing PTH levels, a condition commonly called PTH resistance. There is a high prevalence of low bone turnover or adynamic bone disease in the early stages of CKD. This could be due to the inhibition of bone turnover, such as in PTH resistance, reduced active vitamin D levels, diabetes, aluminum, and, increased IS. With an increase in IS, there is a decrease in the osteoblast Wnt/b-catenin signaling and increase in the expression of Wnt signaling inhibitors, such as sclerostin and Dickkopf-1 (DKK1). Thus, a majority of early CKD patients exhibit deterioration of bone quality owing to the action of IS, this scenario could be termed uremic osteoporosis. However, this mechanism is complicated and not fully understood. With progressive deterioration in the renal function, IS accumulates along with persistent PTH secretion, potentially leading to high-turnover bone disease because high serum PTH levels have the ability of overriding peripheral PTH resistance and other inhibitory factors of bone formation. Finally, it leads to deterioration in bone quantity with prominent bone resorption in end stage renal disease. Uremic toxins adsorbents may decelerate oxidative stress and improve bone health in CKD patients. This review article focuses on IS and bone loss in CKD patients.

Role of Uremic Toxins for Kidney, Cardiovascular, and Bone Dysfunction

With decreasing kidney function, cardiovascular disease (CVD) and mineral bone disorders frequently emerge in patients with chronic kidney disease (CKD). For these patients, in addition to the traditional risk factors, non-traditional CKD-specific risk factors are also associated with such diseases and conditions. One of these non-traditional risk factors is the accumulation of uremic toxins (UTs). In addition, the accumulation of UTs further deteriorates kidney function. Recently, a huge number of UTs have been identified. Although many experimental and clinical studies have reported associations between UTs and the progression of CKD, CVD, and bone disease, these relationships are very complex and have not been fully elucidated. Among the UTs, indoxyl sulfate, asymmetric dimethylarginine, and p-cresylsulfate have been of particular focus, up until now. In this review, we summarize the pathophysiological influences of these UTs on the kidney, cardiovascular system, and bone, and discuss the clinical data regarding the harmful effects of these UTs on diseases and conditions.

Is Sclerostin Level Associated with Cardiovascular Diseases in Hemodialysis Patients?

BACKGROUND/AIMS

The objective of this study is to evaluate the relation between sclerostin, arterial stiffness, and cardiovascular events (CVE) in hemodialysis patients (HD).

METHODS

Sclerostin level and carotid-femoral pulse wave velocity (PWV) in 97 HD patients and sclerostin level in 40 controls were measured.

RESULTS

Sclerostin level was significantly higher in patients than in controls. Sclerostin associated positively with age, male gender, cardiovascular disease, statin use, BMI, and PWV while negatively with alkaline phosphatase, parathormone (PTH), Kt/V, cinacalcet and vitamin D use in univariable correlation analyses. Sclerostin associated positively with male gender and statin use but negatively with PTH in multivariate regression analyses. During observation, 30 fatal or nonfatal CVEs were observed. While univariate correlation analysis showed a positive association between PWV and sclerostin, there was no relation between the two in multivariate regression analysis.

CONCLUSION

Further studies are needed to understand the role of sclerostin in predicting PWV changes in HD patients.

Elevated levels of serum sclerostin are linked to adverse cardiovascular outcomes in peritoneal dialysis patients

PURPOSE

To investigate the correlation between elevated serum sclerostin levels and chronic kidney disease outcomes for patients receiving peritoneal dialysis (PD).

METHODS

We performed a prospective observational study in stable PD patients. Serum sclerostin levels were determined via enzyme immunoassay, and median levels of sclerostin were used to divide patients into high and low sclerostin groups. New-onset cardiovascular events (CVEs) and cardiovascular mortality were evaluated during a 6-year follow-up period.

RESULTS

Ninety-eight patients [mean age 52.5 ± 10.9 years, 49% males, 21.4% diabetic, median dialysis vintage 40.7 (range 17.9-72.2) months] were recruited. Compared with those in the low sclerostin group, patients in the high sclerostin group demonstrated higher levels of total-cholesterol, NT-proBNP, and osteoprotegerin (all P < 0.05). During the 6-year study period, 25 CVEs and 17 cardiovascular deaths occurred in the high sclerostin group, whereas 11 CVEs and four cardiovascular deaths occurred in the low sclerostin group. A Cox regression analysis determined that high sclerostin levels significantly increased the risk for CVEs (HR 2.475, 95% CI 1.116-5.489, P = 0.026) and cardiovascular death (HR 3.484, 95% CI1.134-10.706, P = 0.029), after multiple adjustments were made.

CONCLUSIONS

Our data suggest that high sclerostin levels may predict the onset of CVEs and cardiovascular mortality among PD patients.

Protein-bound toxins: has the Cinderella of uraemic toxins turned into a princess?

Chronic kidney disease (CKD) has emerged as a global public health problem. Although the incidence and prevalence of CKD vary from one country to another, the estimated worldwide prevalence is 8-16%. The complications associated with CKD include progression to end-stage renal disease (ESRD), mineral and bone disorders, anaemia, cognitive decline and elevated all-cause and cardiovascular (CV) mortality. As a result of progressive nephron loss, patients with late-stage CKD are permanently exposed to uraemic toxins. These toxins have been classified into three groups as a function of the molecular mass: small water-soluble molecules, middle molecules and protein-bound uraemic toxins. The compounds can also be classified according to their origin (i.e. microbial or not) or their protein-binding ability. The present review will focus on the best-characterized protein-bound uraemic toxins, namely indoxylsulfate (IS), indole acetic acid (IAA) and p-cresylsulfate (PCS, a cresol metabolite). Recent research suggests that these toxins accelerate the progression of CV disease, kidney disease, bone disorders and neurological complications. Lastly, we review therapeutic approaches that can be used to decrease toxin levels.

Interactions of sclerostin with FGF23, soluble klotho and vitamin D in renal transplantation

Relationships of Sclerostin, a bone anti-anabolic protein, with biomarkers of mineral bone disorders in chronic kidney disease are still unsettled, in particular in kidney transplant (KTR). In 80 KTR patients (31F/49M, 54.7±10.3 years) we studied the relationships of serum Sclerostin with eGFR, Calcium, Phosphate, Alkaline Phosphatase (AP), intact Parathyroid hormone (iPTH), soluble alpha-Klotho (sKlotho), intact Fibroblast Growth Factor 23 (iFGF23), 25-hydroxyvitamin D(25D) and 1,25-dihydroxyvitamin D (1,25D). Thirty healthy subjects (35.0±12.4 years, eGFR 109.1±14.1 ml /min/1,73m²) served as control for Sclerostin, iFGF23 and sKlotho. With a median eGFR of 46.3 mL/min/1.73m² (IQR, 36.2–58.3) our KTR had median Sclerostin levels of 23.7 pmol/L (IQR: 20.8–32.8), not different from controls (26.6 pmol/L, IQR: 22.0–32.2; p = n.s). Sclerostin correlated negatively with AP (r = -.251; p = 0.023) and positively with iFGF23 (r = .227; p = 0.017) and 25D (r = .214; p = 0.025). Age-adjusted multiple regression analysis identified AP and 1,25D as negative and 25D and sKlotho as positive best predictors of Sclerostin. No correlation was evident with eGFR. The negative correlation with AP confirms the direct anti-anabolic role of Sclerostin. The associations either negative or positive with iFGF23, sKlotho, and vitamin D metabolites suggest also a modulatory role in mineral homeostasis. In particular, the associations with iFGF23 (positive) and 1,25D (negative) underline the relevant inhibitory action of Sclerostin on vitamin D activation. In conclusion, Sclerostin levels in KTR are normal and influenced more by bone turnover than by eGFR. Its involvement with other hormones of mineral homeostasis (FGF23/Klotho and Vitamin D) is part of the sophisticated cross-talk between bone and the kidney.

Sclerostin is a possible candidate marker of arterial stiffness: Results from a cohort study in Catania

Osteoporosis and cardiovascular disease are worldwide public health issues. Recent evidence indicates a possible role of the canonical Wnt/β-catenin signalling pathway as a common mediator between these two diseases. The aim of the present study was to investigate the relationship between serum concentrations of sclerostin and Dkk1, two extracellular inhibitors of Wnt/β-catenin signalling, with carotid intima-media thickness (CIMT) and with arterial stiffness, evaluated by measuring the pulse wave velocity (PWV) in an ambulatory population of adults. To this aim, 67 subjects were recruited in the 'Atherosclerosis and osteoporosis: identification of common pathogenetic factors' investigation. Serum sclerostin levels correlated positively with CIMT (r=0.314, p=0.03) and inversely with the augmentation index, a marker of arterial stiffness (r=-0.286, p<0.05), whereas Dkk1 did not. Moreover, in a multivariate linear regression model, sclerostin [β -0.1472; p=0.0023; standard error (SE)=0.04620] was an independent predictor of PWV in the study subjects. Our study shows that, following adjustment for confounders, sclerostin is an independent predictor of arterial stiffness in an ambulatory population, whereas Dkk1 is not.

Molecular Abnormalities Underlying Bone Fragility in Chronic Kidney Disease

Prevention of bone fractures is one goal of therapy for patients with chronic kidney disease-mineral and bone disorder (CKD-MBD), as indicated by the Kidney Disease: Improving Global Outcomes guidelines. CKD patients, including those on hemodialysis, are at higher risk for fractures and fracture-related death compared to people with normal kidney function. However, few clinicians focus on this issue as it is very difficult to estimate bone fragility. Additionally, uremia-related bone fragility has a more complicated pathological process compared to osteoporosis. There are many uremia-associated factors that contribute to bone fragility, including severe secondary hyperparathyroidism, skeletal resistance to parathyroid hormone, and bone mineralization disorders. Uremia also aggravates bone volume loss, disarranges microarchitecture, and increases the deterioration of material properties of bone through abnormal bone cells or excess oxidative stress. In this review, we outline the prevalence of fractures, the interaction of CKD-MBD with osteoporosis in CKD patients, and discuss possible factors that exacerbate the mechanical properties of bone.

Hormonal and systemic regulation of sclerostin

The Wnt/β-catenin signaling pathway plays an essential role in osteoblast biology. Sclerostin is a soluble antagonist of Wnt/β-catenin signaling secreted primarily by osteocytes. Current evidence indicates that sclerostin likely functions as a local/paracrine regulator of bone metabolism rather than as an endocrine hormone. Nonetheless, circulating sclerostin levels in humans often reflect changes in the bone microenvironment, although there may be exceptions to this observation. Using existing assays, circulating sclerostin levels have been shown to be altered in response to both hormonal stimuli and across a variety of normal physiological and pathophysiological conditions. In both rodents and humans, parathyroid hormone provided either intermittently or continuously suppresses sclerostin levels. Likewise, most evidence from both human and animal studies supports a suppressive effect of estrogen on sclerostin levels. Efforts to examine non-hormonal/systemic regulation of sclerostin have in general shown less consistent findings or have provided associations rather than direct interventional information, with the exception of mechanosensory studies which have consistently demonstrated increased sclerostin levels with skeletal unloading, and conversely decreases in sclerostin with enhanced skeletal loading. Herein, we will review the existent literature on both hormonal and non-hormonal/systemic factors which have been studied for their impact on sclerostin regulation.

Sclerostin measurement in human disease: Validity and current limitations

Sclerostin a potent regulator of bone formation, is an antagonist of the Wnt-signaling pathway. The advent of assays to measure circulating sclerostin has enabled research to be performed with the aim to understand the potential role of circulating sclerostin as a pathophysiological marker in a variety of clinical settings. At this time, however, assays to measure circulating sclerostin are still relatively new and have not demonstrated consistent internal agreement in addition to which there are differences between serum and plasma levels. Nevertheless, measurement of sclerostin in the circulation has the potential to reflect the dynamics of bone formation with particular reference to situations in which osteocytes, the major source of circulating sclerostin, may be perturbed. Because of technical uncertainties regarding sclerostin assays that are currently available, circulating sclerostin measurements should be interpreted cautiously with attention to reference ranges for each assay and whether or not the measurement is made in serum or plasma.

Association of Circulating Wnt Antagonists With Severe Abdominal Aortic Calcification in Elderly Women

Context

There is great interest in the biology of vascular calcification. Wnt/β-catenin signaling is an important mediator of mineralization and may play a role in vascular calcification.

Objective

We assessed the association between circulating Wnt antagonists and abdominal aortic calcification (AAC) severity in elderly women.

Design

This was a cross-sectional analysis of the Calcium Intake Fracture Outcome Study.

Setting

The participants were recruited from the community-dwelling elderly population.

Participants

We examined 768 women aged over 70 years.

Interventions

We collected blood samples, and lateral spine images captured during bone density assessment were used to score AAC with a validated 24-point scale.

Main Outcome Measures

We tested the hypothesis that low Wnt antagonist levels of Dickkopf-1 (DKK1), secreted frizzled related protein 3 (sFRP3), and Wnt inhibitory factor 1 (WIF1) are associated with severe AAC (AAC24 score > 5).

Results

Severe AAC was present in 146 women (19%). Lower levels of DKK1, but not WIF1 and sFRP3, were associated with higher odds of severe AAC. Per standard deviation decrease in DKK1 was associated with increased multivariable-adjusted odds ratio (OR) of severe AAC [OR, 1.26; 95% confidence interval (CI), 1.04 to 1.52; P = 0.017]. In quartile analyses, the lowest and second-lowest quartiles of DKK1 had increased multivariable-adjusted odds of severe AAC vs the highest quartile (OR, 2.05; 95% CI, 1.18 to 3.56; P = 0.011 and OR, 1.83; 95% CI, 1.05 to 3.19; P = 0.035).

Conclusions

In elderly women, DKK1, but not sFRP3 or WIF1, is associated with severe AAC. This study supports the concept that Wnt/β-catenin signaling is an important regulator of vascular mineral metabolism and is independent of other risk factors.

Serum sclerostin level might be a potential biomarker for arterial stiffness in prevalent hemodialysis patients

AIM

To explore the relationship between circulating sclerostin levels and pulse wave velocity (PWV) in prevalent hemodialysis (HD) patients.

PATIENTS & METHODS

154 HD patients were enrolled and examined for serum sclerostin level, carotid-femoral pulse wave velocity (cf-PWV), abdominal artery calcification and calcaneus bone marrow density.

RESULTS

Serum sclerostin level was significantly elevated in patients with arterial stiffness. Univariate correlation showed serum sclerostin level significantly correlated with intact parathyroid hormone level, cf-PWV and calcaneus bone marrow density. Multiple linear regression analysis in patients with parathyroid hormone ≤300 pg/ml showed that pulse pressure, logAACs and serum sclerostin level were significant independent factors for cf-PWV.

CONCLUSION

Serum sclerostin level was significantly associated with PWV in prevalent HD patients without hyperparathyroidism.

Sclerostin Antibody Therapy for the Treatment of Osteoporosis: Clinical Prospects and Challenges

It is estimated that over 200 million adults worldwide have osteoporosis, a disease that has increasing socioeconomic impact reflected by unsustainable costs associated with disability, fracture management, hospital stays, and treatment. Existing therapeutic treatments for osteoporosis are associated with a variety of issues relating to use, clinical predictability, and health risks. Consequently, additional novel therapeutic targets are increasingly sought. A promising therapeutic candidate is sclerostin, a Wnt pathway antagonist and, as such, a negative regulator of bone formation. Sclerostin antibody treatment has demonstrated efficacy and superiority compared to other anabolic treatments for increasing bone formation in both preclinical and clinical settings. Accordingly, it has been suggested that sclerostin antibody treatment is set to achieve market approval by 2017 and aggressively compete as the gold standard for osteoporotic treatment by 2021. In anticipation of phase III trial results which may potentially signify a significant step in achieving market approval here, we review the preclinical and clinical emergence of sclerostin antibody therapies for both osteoporosis and alternative applications. Potential clinical challenges are also explored as well as ongoing developments that may impact on the eventual clinical application of sclerostin antibodies as an effective treatment of osteoporosis.

Sclerostin, TNF-alpha and Interleukin-18 Correlate and are Together with Klotho Related to Other Growth Factors and Cytokines in Haemodialysis Patients

Patients with chronic renal failure are known to have renal osteodystrophy (bone disease) and increased calcification of vessels. A new marker of bone disease, sclerostin, the two pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin-18 (IL-18), and the fibroblast growth factor-23 (FGF-23) receptor-associated marker Klotho were tested in 84 haemodialysis (HD) patients and in healthy controls. The patients had significantly higher levels of the three former markers than of the controls while Klotho was significantly higher in the controls. Low level, but significant, correlations were observed in the patient group when the levels of these four markers were compared to each other and to those of 5 cytokines and growth factors tested earlier; high-sensitive CRP (hsCRP), interleukin-6 (IL-6), hepatocyte growth factor (HGF), fibroblast growth factor-23 (FGF-23) and soluble urokinase plasminogen activator (suPAR). Ln sclerostin correlated positively to Ln hsTNF-alpha, Ln HGF and Ln suPAR. Ln hsTNF-alpha correlated positively to Ln sclerostin, Ln hsCRP, Ln IL-6, Ln FGF-23, Ln suPAR and Ln IL-18. Ln IL-18 correlated positively to Ln suPAR and Ln TNF-alpha. Ln Klotho correlated negatively to Ln hsCRP but did not correlate to Ln FGF-23. The markers studied here may be involved in the calcification of vessels seen in HD patients due to a combination of inflammation and bone disease. The mechanisms are still not fully known but may be of importance for future therapeutic possibilities in this group of patients.