Early renal impairment affects hormonal regulators of calcium and bone metabolism and Wnt signalling and the response to vitamin D supplementation in healthy older adults

Bone and renal metabolism are regulated by common factors and there is extensive cross-talk between these organs (the 'renal-bone-axis'). Ageing is associated with physiological changes including reduced bone mass, renal function and tissue sensitivity to regulatory hormones, impacting the renal-bone axis. We aimed to investigate the influence of estimated Glomerular Filtration Rate (eGFR) on plasma concentrations of vitamin D metabolites, Wnt signalling and bone metabolism in a dose ranging vitamin D₃ RCT (12,000 IU, 24,000 IU, 48,000 IU/month for 1 year; n = 379, >70 y) with a baseline eGFR > 30 mL/min/1.73 m². Participants were categorised on basis of eGFR (≥60 or mL/min/1.73 m²) based on 5 commonly used algorithms for eGFR. Differences between eGFR categories were tested with ANCOVA. Before supplementation commenced, a lower eGFR was associated with significantly higher concentrations of c-terminal and intact Fibroblast Growth Factor-23 (cFGF23; iFGF23), intact Parathyroid Hormone (iPTH) and Sclerostin (SOST) and lower Klotho, 1,25-dihydroxy Vitamin D (1,25(OH)₂D) and Dickkopf-related Protein 1 (DKK1) concentrations. Differences between eGFR groups in 25-hydroxy Vitamin D (25(OH)D), 24,25-dihydroxy Vitamin D (24,25(OH)₂D) and iPTH were only detected with eGFR based on Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Modification in Diet for Renal Disease (MDRD-4) algorithms. Differences in Bone Mineral Density and Content (BMD; BMC) and bone turnover markers were detected only with Cockcroft-Gault (CG). Pre- and post- supplementation comparisons showed differences in the response to supplementation by eGFR group. Plasma 25(OH)D, 24,25(OH)₂D, 1,25(OH)₂D and DKK1 increased and iPTH and C-terminal telopeptide (CTX) decreased in both groups. Plasma iFGF23, bone specific alkaline phosphatase (BAP) and Procollagen 1 intact N-terminal Propeptide (PINP) increased and phosphate decreased only in the group with eGFR ≥ 60 mL/min/1.73 m². Findings were largely consistent across all eGFR algorithms. Post-supplementation, cFGF23, iFGF23, iPTH and SOST remained significantly higher in the lower eGFR group. Plasma 1,25(OH)₂D and Klotho did no longer differ between eGFR groups. This was found for all eGFR algorithms, with the exception of iPTH and iFGF23, which were not significantly different with eGFR based on CG. Differences in BMD and BMC were detected with CKD-EPI-creatinine and MDRD-4 but not GC. This study showed that even a moderate decline in eGFR is associated with alterations in vitamin D metabolism, Wnt signalling and bone turnover markers. Renal function influenced the response to vitamin D supplementation. Supplementation increased Vitamin D metabolites in the group with moderate renal impairment to concentrations comparable to those found in the group with normal renal function. However, although CTX decreased, an increase in bone formation markers was not found in the group with eGFR 60 mL/min/1.73 m². In conclusion, vitamin D supplementation had beneficial effects on markers of the renal-bone axis in older people with both normal and impaired renal function.

Updates in the chronic kidney disease-mineral bone disorder show the role of osteocytic proteins, a potential mechanism of the bone-Vascular paradox, a therapeutic target, and a biomarker

The chronic kidney disease-mineral bone disorder (CKD-MBD) is a complex multi-component syndrome occurring during kidney disease and its progression. Here, we update progress in the components of the syndrome, and synthesize recent investigations, which suggest a potential mechanism of the bone-vascular paradox. The discovery that calcified arteries in chronic kidney disease inhibit bone remodeling lead to the identification of factors produced by the vasculature that inhibit the skeleton, thus providing a potential explanation for the bone-vascular paradox. Among the factors produced by calcifying arteries, sclerostin secretion is especially enlightening. Sclerostin is a potent inhibitor of bone remodeling and an osteocyte specific protein. Its production by the vasculature in chronic kidney disease identifies the key role of vascular cell osteoblastic/osteocytic transdifferentiation in vascular calcification and renal osteodystrophy. Subsequent studies showing that inhibition of sclerostin activity by a monoclonal antibody improved bone remodeling as expected, but stimulated vascular calcification, demonstrate that vascular sclerostin functions to brake the Wnt stimulation of the calcification milieu. Thus, the target of therapy in the chronic kidney disease-mineral bone disorder is not inhibition of sclerostin function, which would intensify vascular calcification. Rather, decreasing sclerostin production by decreasing the vascular osteoblastic/osteocytic transdifferentiation is the goal. This might decrease vascular calcification, decrease vascular stiffness, decrease cardiac hypertrophy, decrease sclerostin production, reduce serum sclerostin and improve skeletal remodeling. Thus, the therapeutic target of the chronic kidney disease-mineral bone disorder may be vascular osteoblastic transdifferentiation, and sclerostin levels may be a useful biomarker for the diagnosis of the chronic kidney disease-mineral bone disorder and the progress of its therapy.

Relationships between Sclerostin, Leptin and Metabolic Parameters in Non-Dialysis Chronic Kidney Disease Males

Sclerostin is an inhibitor of the Wnt-beta-catenin pathway. The relationship between sclerostin and adipose tissue or between sclerostin and nutritional status has been the subject of research interest in the last decade. Sclerostin concentrations are elevated in patients with chronic kidney disease (CKD). Leptin is an adipocytokine which inhibits food intake by stimulating the satiety center in the hypothalamus. Leptin concentrations rise with the reduction of eGFR (glomerular filtration rate). The aim of this study was to investigate the possible association between sclerostin and leptin, between sclerostin and selected poor prognostic factors of CKD progression, and between sclerostin and nutritional parameters in non-dialysis CKD male patients. 101 men with non-dialysis CKD stage 3-5 were included in the study. Bioimpedance spectroscopy (BIS) was used to measure body composition. Blood samples were drawn to measure the serum concentrations of sclerostin, leptin, creatinine, hemoglobin (Hgb), parathormone (PTH), inflammatory markers, and markers of nutritional status. We also measured homeostatic model assessment of insulin resistance (HOMA-IR) as well as blood pressure. We observed a significant, positive relationship between sclerostin and age, leptin, and glycated hemoglobin (HgbA1c) concentrations. A significant, negative association was observed between sclerostin and eGFR. Sclerostin is associated with leptin in non-dialysis CKD male patients. Sclerostin is also related to metabolic disturbances such as hyperglycemia in this population.

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.

Caloric restriction: Anti-inflammatory and antioxidant mechanisms against epileptic seizures

Caloric restriction (CR) possesses different cellular mechanisms. Though there are still gaps in the literature regarding its plausible beneficial effects, the suggestion that this alternative therapy can improve the inflammatory and antioxidant response to control epileptic seizures is explored throughout this study. Epilepsy is the second most prevalent neurodegenerative disease in the world. However, the appropriate mechanisms for it to be fully controlled are still unknown. Neuroinflammation and oxidative stress promote epileptic seizures' appearance and might even aggravate them. There is growing evidence that caloric restriction has extensive anti-inflammatory and antioxidant properties. For instance, nuclear factor erythroid 2-related factor 2 (Nrf2) and all-trans retinoic acid (ATRA) have been proposed to induce antioxidant processes and ulteriorly improve the disease progression. Caloric restriction can be an option for those patients with refractory epilepsy since it allows for anti-inflammatory and antioxidant properties to evolve within the brain areas involved.

Influence of Renal Function on Pharmacokinetics, Pharmacodynamics, and Safety of a Single Dose of Romosozumab

We evaluated the pharmacokinetics, pharmacodynamics, and safety of a single subcutaneous dose of romosozumab 210 mg, a monoclonal antibody against sclerostin, in an open-label, parallel-group study in participants with severe (stage 4) renal impairment (RI; n = 8) or end-stage renal disease requiring hemodialysis (ESRD-RH; n = 8), or healthy participants with normal renal function (n = 8). Compared with the group with normal renal function, the mean romosozumab exposure was 31% and 43% higher as measured by C_max and AUC, respectively, in the severe RI group and similar to those in the ESRD-RH group. For all 3 groups, the maximum mean percent increase in procollagen type 1 N terminal propeptide (P1NP) and decrease in serum C-telopeptide (sCTX) levels from baseline were observed on day 15. Changes in P1NP and sCTX were of similar patterns in all 3 groups. The single dose of romosozumab 210 mg was well tolerated. Adverse events (AEs) were reported for 13 patients (7 patients with severe RI and 6 with ESRD-RH), with no deaths, AEs, or serious AEs leading to withdrawal. The incidence of subjects with postbaseline transient decreases in serum calcium (severe RI, n = 1; ESRD-RH, n = 5) and increases in intact parathyroid hormone (severe RI, n = 7; ESRD-RH, n = 7; healthy, n = 3) were greater in severe RI and ESRD-RH groups than in the healthy group. All reported events of hypocalcemia (severe RI, n = 1; ESRD-RH, n = 4) were asymptomatic. These results support the use of romosozumab without dose adjustment in patients with severe RI or ESRD-RH. This article is protected by copyright. All rights reserved.

Muscle-bone axis in children with chronic kidney disease: current knowledge and future perspectives

Bone and muscle tissue are developed hand-in-hand during childhood and adolescence and interact through mechanical loads and biochemical pathways forming the musculoskeletal system. Chronic kidney disease (CKD) is widely considered as both a bone and muscle-weakening disease, eventually leading to frailty phenotype, with detrimental effects on overall morbidity. CKD also interferes in the biomechanical communication between two tissues. Pathogenetic mechanisms including systemic inflammation, anorexia, physical inactivity, vitamin D deficiency and secondary hyperparathyroidism, metabolic acidosis, impaired growth hormone/insulin growth factor 1 axis, insulin resistance, and activation of renin-angiotensin system are incriminated for longitudinal uncoordinated loss of bone mineral content, bone strength, muscle mass, and muscle strength, leading to mechanical impairment of the functional muscle-bone unit. At the same time, CKD may also interfere in the biochemical crosstalk between the two organs, through inhibiting or stimulating the expression of certain osteokines and myokines. This review focuses on presenting current knowledge, according to in vitro, in vivo, and clinical studies, concerning the pathogenetic pathways involved in the muscle-bone axis, and suggests approaches aimed at preventing bone loss and muscle wasting in the pediatric population. Novel therapeutic targets for preserving musculoskeletal health in the context of CKD are also discussed.

Urinary metabolomics analysis to reveal metabolic mechanism of guanxinning injection on heart failure with renal dysfunction

Consistently, the multiple heart-kidney interactions make pharmaceutical research for cardiorenal syndrome difficult and complex. Guanxinning Injection (GXN) has been reported to provide unique advantage for treating cardiac and renal diseases compared to typical monotherapies. However, the protection mechanism of GXN is largely unknown. This study explored the acting mechanism of GXN on heart failure with renal dysfunction from a metabolic perspective. Transverse aortic constriction (TAC) surgery was performed on C57/BL/6 mice to induce heart failure with renal dysfunction. Using telmisartan as a positive control, GXN treatment was applied during the 12th to 16th week after TAC. Cardiac function and structure were examined using M-mode echocardiography, and renal function was evaluated via representative biochemical parameters and hematoxylin-eosin staining. Moreover, untargeted metabolomic analyses of urine were conducted to screen for differential substances associated with the cardiorenal protection effect of GXN. As a result, GXN provided good cardioprotective effects on left ventricular ejection fraction elevation, fractional shortening, internal diastolic, and mass maintenance. GXN also reduced TAC-induced elevation of blood urea nitrogen, and serum Cystatin C and relieved kidney pathological damage. Metabolomic analyses identified 21 differential metabolites in the TAC model group. Ten metabolites involving the metabolic pathways of carnitine synthesis, valine, leucine and isoleucine degradation, and glutamate metabolism, taurine and hypotaurine metabolism, tryptophan metabolism, arginine and proline metabolism, and purine metabolism were restored by GXN. The main cardiorenal protection mechanism of GXN was found to be related to energy metabolism and oxidative stress. Taken together, this study provides the first evidence of the metabolic protection mechanism of GXN on heart failure with renal dysfunction for the first time and provides a research basis for the application of GXN in CRS-2 pharmaceuticals.

Relation of Wnt Signaling Pathway Inhibitors (Sclerostin and Dickkopf-1) to Left Ventricular Mass Index in Maintenance Hemodialysis Patients

BACKGROUND

Left ventricular hypertrophy (LVH) is common in hemodialysis (HD) patients. It predicts poor prognosis. Several inhibitors regulate Wnt canonical pathways like Dickkopf-related protein-1 (Dkk-1) and sclerostin.

OBJECTIVES

To investigate the relationship between serum sclerostin, Dkk-1, left ventricular mass (LVM), and LVM index (LVMI) in HD patients.

METHODS

This is a cross-sectional study including 65 HD patients in our HD unit. Patients were divided into two groups according to LVMI (group 1 with LVMI < 125 gm/m2 (N = 29) and group 2 with LVMI > 125 gm/m2 (N = 36)). Echocardiographic evaluation of the LVM, aortic, and mitral valves calcification (AVC and MVC) was done. Serum levels of sclerostin and Dkk-1 and patients' clinical and biochemical data were recorded.

RESULTS

Group 2 showed significantly higher age, blood pressure, AVC, and MVC and significantly lower hemoglobin, sclerostin, and Dkk-1 levels. LVM and LVMI had a significant linear negative correlation to both serum sclerostin and Dkk-1 (r = -0.329 and -0.257, P=0.01 and 0.046 for LVM; r = -0.427 and -0.324, P=0.001 and 0.012 for LVMI, resp.). Serum Dkk-1 was an independent negative indicator for LVM and LVMI in multiple regression analyses (P=0.003 and 0.041 with 95% CI = -0.963 to -0.204 and -0.478 to -0.010, resp.).

CONCLUSION

Serum sclerostin and Dkk-1 were significantly lower in HD patients with increased LVMI > 125 gm/m2, and both had a significant linear negative correlation with LVM and LVMI. Dkk-1 was a significant negative independent indicator for LVM and LVMI in HD patients.

Transcriptomics: a Solution for Renal Osteodystrophy?

PURPOSE OF REVIEW

The molecular mechanisms of the bone disease associated with chronic kidney disease (CKD), called renal osteodystrophy (ROD), are poorly understood. New transcriptomics technologies may provide clinically relevant insights into the pathogenesis of ROD. This review summarizes current progress and limitations in the study and treatment of ROD, and in transcriptomics analyses of skeletal tissues.

RECENT FINDINGS

ROD is characterized by poor bone quality and strength leading to increased risk of fracture. Recent studies indicate permanent alterations in bone cell populations during ROD. Single-cell transcriptomics analyses, successful at identifying specialized cell subpopulations in bone, have not yet been performed in ROD. ROD is a widespread poorly understood bone disease with limited treatment options. Transcriptomics analyses of bone are needed to identify the bone cell subtypes and their role in the pathogenesis of ROD, and to develop adequate diagnosis and treatment strategies.

Sclerostin Antibody Treatment Increases Bone Mass and Normalizes Circulating Phosphate Levels in Growing Hyp Mice

X-linked hypophosphatemia (XLH), caused by a loss-of-function mutation in the phosphate regulating gene with homology to endopeptidase located on the X chromosome (PHEX), is the most common form of vitamin D-resistant rickets. Loss of functional PHEX results in elevated fibroblast growth factor 23 (FGF23) levels, impaired phosphate reabsorption, and inhibited skeletal mineralization. Sclerostin, a protein produced primarily in osteocytes, suppresses bone formation by antagonizing Wnt signaling and is reported to be elevated in XLH patients. This study used the Hyp mouse model to investigate sclerostin's role in the pathophysiology of XLH by evaluating the use of a monoclonal antibody to sclerostin in a mouse model of XLH, the Hyp mouse. Male and female wild-type and Hyp littermates were injected with 25 mg/kg of vehicle or sclerostin antibody (Scl-Ab) twice weekly, beginning at 4 weeks of age and euthanized at 8 weeks of age. Scl-Ab treatment increased serum phosphate levels and suppressed circulating levels of intact FGF23 in treated wild-type and Hyp mice of both sexes. Cortical area, trabecular bone volume fraction (BV/TV), metaphyseal apparent density, and the peak load increased with Scl-Ab treatment in both sexes. This short-term treatment study suggests that Scl-Ab treatment can effectively improve some of the pathologies associated with XLH, including normalization of phosphate, and that sclerostin may play a role in regulating FGF23 and phosphate metabolism in XLH. © 2019 American Society for Bone and Mineral Research.

Bone-Vascular Axis in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) are at increased risk of osteoporosis and vascular calcification. Bone demineralization and vascular mineralization go often hand in hand in CKD, similar to as in the general population. This contradictory association is independent of aging and is commonly referred to as the "calcification paradox" or the bone-vascular axis. Various common risk factors and mechanisms have been identified. Alternatively, calcifying vessels may release circulating factors that affect bone metabolism, while bone disease may infer conditions that favor vascular calcification. The present review focuses on emerging concepts and major mechanisms involved in the bone-vascular axis in the setting of CKD. A better understanding of these concepts and mechanisms may identify therapeutics able to target and exert beneficial effects on bone and vasculature simultaneously.

Sclerostin: a new biomarker of CKD-MBD

The causes of the increased cardiovascular risk associated with kidney diseases partly reside in the chronic kidney disease-mineral bone disorder (CKD-MBD) syndrome. Three cardiovascular risk factors [hyperphosphatemia, vascular calcification, and elevated fibroblast growth factor 23 (FGF23)] levels have been discovered within the CKD-MBD over the last decades. In addition, sclerostin is recently presented as a new bone and vascular disease biomarker. This 22-kDa glycoprotein, secreted mainly by osteocytes, is a soluble inhibitor of the canonical Wnt pathway that has a pivotal role in bone biology and turnover. CKD patients are reported with higher levels of sclerostin, and levels decrease during dialysis. Sclerostin is associated with vascular calcification and CV risk in CKD, although data are still controversial. The question whether serum sclerostin has protective or deleterious role in CKD-MBD pathophysiology, and therefore in cardiovascular risk and overall mortality, is still open and needs to be answered. The standardization of assays and the establishment of a clear cut-off values when sclerostin starts to switch from physiological to pathophysiological role have to be another important step. Further research is needed also to define its relationship with other CKD-MBD biomarkers for future diagnostic and therapeutic strategies.

Phosphate binders for preventing and treating chronic kidney disease-mineral and bone disorder (CKD-MBD)

BACKGROUND

Phosphate binders are used to reduce positive phosphate balance and to lower serum phosphate levels for people with chronic kidney disease (CKD) with the aim to prevent progression of chronic kidney disease-mineral and bone disorder (CKD-MBD). This is an update of a review first published in 2011.

OBJECTIVES

The aim of this review was to assess the benefits and harms of phosphate binders for people with CKD with particular reference to relevant biochemical end-points, musculoskeletal and cardiovascular morbidity, hospitalisation, and death.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 12 July 2018 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) or quasi-RCTs of adults with CKD of any GFR category comparing a phosphate binder to another phosphate binder, placebo or usual care to lower serum phosphate. Outcomes included all-cause and cardiovascular death, myocardial infarction, stroke, adverse events, vascular calcification and bone fracture, and surrogates for such outcomes including serum phosphate, parathyroid hormone (PTH), and FGF23.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion and extracted study data. We applied the Cochrane 'Risk of Bias' tool and used the GRADE process to assess evidence certainty. We estimated treatment effects using random-effects meta-analysis. Results were expressed as risk ratios (RR) for dichotomous outcomes together with 95% confidence intervals (CI) or mean differences (MD) or standardised MD (SMD) for continuous outcomes.

MAIN RESULTS

We included 104 studies involving 13,744 adults. Sixty-nine new studies were added to this 2018 update.Most placebo or usual care controlled studies were among participants with CKD G2 to G5 not requiring dialysis (15/25 studies involving 1467 participants) while most head to head studies involved participants with CKD G5D treated with dialysis (74/81 studies involving 10,364 participants). Overall, seven studies compared sevelamer with placebo or usual care (667 participants), seven compared lanthanum to placebo or usual care (515 participants), three compared iron to placebo or usual care (422 participants), and four compared calcium to placebo or usual care (278 participants). Thirty studies compared sevelamer to calcium (5424 participants), and fourteen studies compared lanthanum to calcium (1690 participants). No study compared iron-based binders to calcium. The remaining studies evaluated comparisons between sevelamer (hydrochloride or carbonate), sevelamer plus calcium, lanthanum, iron (ferric citrate, sucroferric oxyhydroxide, stabilised polynuclear iron(III)-oxyhydroxide), calcium (acetate, ketoglutarate, carbonate), bixalomer, colestilan, magnesium (carbonate), magnesium plus calcium, aluminium hydroxide, sucralfate, the inhibitor of phosphate absorption nicotinamide, placebo, or usual care without binder. In 82 studies, treatment was evaluated among adults with CKD G5D treated with haemodialysis or peritoneal dialysis, while in 22 studies, treatment was evaluated among participants with CKD G2 to G5. The duration of study follow-up ranged from 8 weeks to 36 months (median 3.7 months). The sample size ranged from 8 to 2103 participants (median 69). The mean age ranged between 42.6 and 68.9 years.Random sequence generation and allocation concealment were low risk in 25 and 15 studies, respectively. Twenty-seven studies reported low risk methods for blinding of participants, investigators, and outcome assessors. Thirty-one studies were at low risk of attrition bias and 69 studies were at low risk of selective reporting bias.In CKD G2 to G5, compared with placebo or usual care, sevelamer, lanthanum, iron and calcium-based phosphate binders had uncertain or inestimable effects on death (all causes), cardiovascular death, myocardial infarction, stroke, fracture, or coronary artery calcification. Sevelamer may lead to constipation (RR 6.92, CI 2.24 to 21.4; low certainty) and lanthanum (RR 2.98, CI 1.21 to 7.30, moderate certainty) and iron-based binders (RR 2.66, CI 1.15 to 6.12, moderate certainty) probably increased constipation compared with placebo or usual care. Lanthanum may result in vomiting (RR 3.72, CI 1.36 to 10.18, low certainty). Iron-based binders probably result in diarrhoea (RR 2.81, CI 1.18 to 6.68, high certainty), while the risks of other adverse events for all binders were uncertain.In CKD G5D sevelamer may lead to lower death (all causes) (RR 0.53, CI 0.30 to 0.91, low certainty) and induce less hypercalcaemia (RR 0.30, CI 0.20 to 0.43, low certainty) when compared with calcium-based binders, and has uncertain or inestimable effects on cardiovascular death, myocardial infarction, stroke, fracture, or coronary artery calcification. The finding of lower death with sevelamer compared with calcium was present when the analysis was restricted to studies at low risk of bias (RR 0.50, CI 0.32 to 0.77). In absolute terms, sevelamer may lower risk of death (all causes) from 210 per 1000 to 105 per 1000 over a follow-up of up to 36 months, compared to calcium-based binders. Compared with calcium-based binders, lanthanum had uncertain effects with respect to all-cause or cardiovascular death, myocardial infarction, stroke, fracture, or coronary artery calcification and probably had reduced risks of treatment-related hypercalcaemia (RR 0.16, CI 0.06 to 0.43, low certainty). There were no head-to-head studies of iron-based binders compared with calcium. The paucity of placebo-controlled studies in CKD G5D has led to uncertainty about the effects of phosphate binders on patient-important outcomes compared with placebo.It is uncertain whether the effects of binders on clinically-relevant outcomes were different for patients who were and were not treated with dialysis in subgroup analyses.

AUTHORS' CONCLUSIONS

In studies of adults with CKD G5D treated with dialysis, sevelamer may lower death (all causes) compared to calcium-based binders and incur less treatment-related hypercalcaemia, while we found no clinically important benefits of any phosphate binder on cardiovascular death, myocardial infarction, stroke, fracture or coronary artery calcification. The effects of binders on patient-important outcomes compared to placebo are uncertain. In patients with CKD G2 to G5, the effects of sevelamer, lanthanum, and iron-based phosphate binders on cardiovascular, vascular calcification, and bone outcomes compared to placebo or usual care, are also uncertain and they may incur constipation, while iron-based binders may lead to diarrhoea.

TGF-Beta Signaling in Bone with Chronic Kidney Disease

Transforming growth factor (TGF)-β signaling is not only important in skeletal development, but also essential in bone remodeling in adult bone. The bone remodeling process involves integrated cell activities induced by multiple stimuli to balance bone resorption and bone formation. TGF-β plays a role in bone remodeling by coordinating cell activities to maintain bone homeostasis. However, mineral metabolism disturbance in chronic kidney disease (CKD) results in abnormal bone remodeling, which leads to ectopic calcification in CKD. High circulating levels of humoral factors such as parathyroid hormone, fibroblast growth factor 23, and Wnt inhibitors modulate bone remodeling in CKD. Several reports have revealed that TGF-β is involved in the production and functions of these factors in bone. TGF-β may act as a factor that mediates abnormal bone remodeling in CKD.

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.

Role of the Wnt/β-Catenin Pathway in Renal Osteodystrophy

Vascular calcification and bone fragility are common and interrelated health problems that affect chronic kidney disease (CKD) patients. Bone fragility, which leads to higher risk of fracture and mortality, arises from the abnormal bone remodeling and mineralization that are seen in chronic kidney disease. Recently, sclerostin and Dickkopf-related protein 1 were suggested to play a significant role in CKD-related bone disease as they are known inhibitors of the Wnt pathway, thus preventing bone formation. This review focuses on new knowledge about the Wnt pathway in bone, how its function is affected by chronic kidney disease and how this affects bone structure. Expression of components and inhibitors of the Wnt pathway has been shown to be affected by the loss of kidney function, and a better understanding of the bone effects of Wnt pathway inhibitors could allow the development of new therapies to prevent bone fragility in this population.

The chronic kidney disease - Mineral bone disorder (CKD-MBD): Advances in pathophysiology

The causes of excess cardiovascular mortality associated with chronic kidney disease (CKD) have been attributed in part to the CKD-mineral bone disorder syndrome (CKD-MBD), wherein, novel cardiovascular risk factors have been identified. New advances in the causes of the CKD-MBD are discussed in this review. They demonstrate that repair and disease processes in the kidneys release factors to the circulation that cause the systemic complications of CKD. The discovery of WNT inhibitors, especially Dickkopf 1 (Dkk1), produced during renal repair as participating in the pathogenesis of the vascular and skeletal components of the CKD-MBD implied that additional pathogenic factors are critical. This lead to the discovery that activin A is a second renal repair factor circulating in increased levels during CKD. Activin A derives from peritubular myofibroblasts of diseased kidneys, wherein it stimulates fibrosis, and decreases tubular klotho expression. Activin A binds to the type 2 activin A receptor, ActRIIA, which is variably affected by CKD in the vasculature. In diabetic/atherosclerotic aortas, specifically in vascular smooth muscle cells (VSMC), ActRIIA signaling is inhibited and contributes to CKD induced VSMC dedifferentiation, osteogenic transition and neointimal atherosclerotic calcification. In nondiabetic/nonatherosclerotic aortas, CKD increases VSMC ActRIIA signaling, and vascular fibroblast signaling causing the latter to undergo osteogenic transition and stimulate vascular calcification. In both vascular situations, a ligand trap for ActRIIA prevented vascular calcification. In the skeleton, activin A is responsible for CKD stimulation of osteoclastogenesis and bone remodeling increasing bone turnover. These studies demonstrate that circulating renal repair and injury factors are causal of the CKD-MBD and CKD associated cardiovascular disease.

[Sucroferric oxyhydroxide, a novel iron-based phosphate binder. Which current use in dialysis patients?]

International guidelines suggest lowering elevated phosphorus level to the normal range in patients on dialysis. Among the phosphate-lowering strategies, phosphate binder is frequently used in addition to dietary phosphate restriction and an adequate dialysis strategy. However, serum phosphate concentration higher than 1.78mmol/L is observed in more than 40% of patients justifying the quest for new drugs. Sucroferric oxyhydroxide is one of the new iron-based agents and is available in France since May 2016. A recent international multicentre study showed this new drug to be as efficacious and non-inferior to sevelamer carbonate in magnitude of serum phosphate control. The serum phosphorus-lowering effect was maintained over 1year. When compared to carbonate sevelamer, the pill-burden was half with sucroferric oxyhydroxide because of its high phosphate binding capacity. As previously shown by experimental studies, no risk of iron accumulation was observed since iron absorption is negligible. Discolored feces and diarrhea were fairly frequent side effects. When diarrhea subsides, the tolerability of this new phosphate binder is excellent on a long-term basis.

Ligand trap of the activin receptor type IIA inhibits osteoclast stimulation of bone remodeling in diabetic mice with chronic kidney disease

Dysregulation of skeletal remodeling is a component of renal osteodystrophy. Previously, we showed that activin receptor signaling is differentially affected in various tissues in chronic kidney disease (CKD). We tested whether a ligand trap for the activin receptor type 2A (RAP-011) is an effective treatment of the osteodystrophy of the CKD-mineral bone disorder. With a 70% reduction in the glomerular filtration rate, CKD was induced at 14 weeks of age in the ldlr-/- high fat-fed mouse model of atherosclerotic vascular calcification and diabetes. Twenty mice with CKD, hyperphosphatemia, hyperparathyroidism, and elevated activin A were treated with RAP-011, wherease 19 mice were given vehicle twice weekly from week 22 until the mice were killed at 28 weeks of age. The animals were then evaluated by skeletal histomorphometry, micro-computed tomography, mechanical strength testing, and ex vivo bone cell culture. Results in the CKD groups were compared with those of the 16 sham-operated ldlr-/- high fat-fed mice. Sham-operated mice had low-turnover osteodystrophy and skeletal frailty. CKD stimulated bone remodeling with significant increases in osteoclast and osteoblast numbers and bone resorption. Compared with mice with CKD and sham-operated mice, RAP-011 treatment eliminated the CKD-induced increase in these histomorphometric parameters and increased trabecular bone fraction. RAP-011 significantly increased cortical bone area and thickness. Activin A-enhanced osteoclastogenesis was mediated through p-Smad2 association with c-fos and activation of nuclear factor of activated T cells c1 (NFATc1). Thus, an ActRIIA ligand trap reversed CKD-stimulated bone remodeling, likely through inhibition of activin-A induced osteoclastogenesis.

Ligand trap for the activin type IIA receptor protects against vascular disease and renal fibrosis in mice with chronic kidney disease

The causes of cardiovascular mortality associated with chronic kidney disease (CKD) are partly attributed to the CKD-mineral bone disorder (CKD-MBD). The causes of the early CKD-MBD are not well known. Our discovery of Wnt (portmanteau of wingless and int) inhibitors, especially Dickkopf 1, produced during renal repair as participating in the pathogenesis of the vascular and skeletal components of the CKD-MBD implied that additional pathogenic factors are critical. In the search for such factors, we studied the effects of activin receptor type IIA (ActRIIA) signaling by using a ligand trap for the receptor, RAP-011 (a soluble extracellular domain of ActRIIA fused to a murine IgG-Fc fragment). In a mouse model of CKD that stimulated atherosclerotic calcification, RAP-011 significantly increased aortic ActRIIA signaling assessed by the levels of phosphorylated Smad2/3. Furthermore, RAP-011 treatment significantly reversed CKD-induced vascular smooth muscle dedifferentiation as assessed by smooth muscle 22α levels, osteoblastic transition, and neointimal plaque calcification. In the diseased kidneys, RAP-011 significantly stimulated αklotho levels and it inhibited ActRIIA signaling and decreased renal fibrosis and proteinuria. RAP-011 treatment significantly decreased both renal and circulating Dickkopf 1 levels, showing that Wnt activation was downstream of ActRIIA. Thus, ActRIIA signaling in CKD contributes to the CKD-MBD and renal fibrosis. ActRIIA signaling may be a potential therapeutic target in CKD.

Fractures in chronic kidney disease: pursuing the best screening and management

PURPOSE OF REVIEW

Osteoporotic fractures are common and cause increased sickness and death. Men and women with chronic kidney disease (CKD) are at particularly high risk of osteoporotic fractures. Currently, however, there are no guidelines concerning noninvasive methods to assess fracture risk in CKD. Further, approved treatments to prevent fractures in otherwise healthy men and women are only recommended for use with caution in those with CKD. This review focuses on the recent data that support the use of noninvasive methods to assess fracture risk in CKD and highlights new therapies that could be used in fracture prevention in CKD.

RECENT FINDINGS

Data from prospective studies demonstrate that low bone mineral density predicts fracture in CKD patients. Post-hoc analyses demonstrate that agents approved for the treatment of postmenopausal osteoporosis (bisphosphonates, denosumab and teriparatide) when given to those with CKD are well tolerated and potentially efficacious with respect to fracture risk reduction.

SUMMARY

To date, patients, and nephrologists taking care of them, have largely ignored fracture risk assessment and treatment in CKD. This should change given recent data. Further studies are needed, specifically bone histomorphometric studies, which will increase our understanding of CKD-mineral bone disease (MBD) pathophysiology, and randomized clinical trials of therapy in patients with CKD.

Sclerostin, Osteocytes, and Chronic Kidney Disease - Mineral Bone Disorder

Osteocytes respond to kidney damage by increasing production of secreted factors important to bone and mineral metabolism. These circulating proteins include the antianabolic factor, sclerostin, and the phosphaturic hormone, fibroblast growth factor 23 (FGF23). Elevated sclerostin levels correlate with increased FGF23, localized reduction in Wnt/β-catenin signaling in the skeleton and reduced osteoblast differentiation/activity. Decreased Wnt/β-catenin signaling occurs regardless of the overall changes in bone formation rates, suggesting that a reduction in the anabolic response may be a common feature of renal bone disorders but additional mechanisms may contribute to the diversity of osteodystrophy phenotypes. Recent preclinical studies support this hypothesis, as treatment with antisclerostin antibodies improved bone quality in the context of low but not high turnover renal osteodystrophy. Sclerostin also appears in the circulation suggesting additional roles outside the skeleton in normal and disease states. In patients with chronic kidney disease (CKD), serum levels are elevated several fold relative to healthy individuals. Emerging data suggest that these changes are associated with increased fracture rates but the relationship between sclerostin and cardiovascular disease is unclear. Additional epidemiologic studies that examine stage specific and patient sub-populations are needed to assess whether sclerostin elevations influence comorbidities associated with CKD.

Pathophysiology of the chronic kidney disease-mineral bone disorder

PURPOSE OF REVIEW

The causes of excess cardiovascular mortality associated with chronic kidney disease (CKD) have been attributed in part to the CKD-mineral bone disorder syndrome (CKD-MBD), wherein, novel cardiovascular risk factors have been identified. The causes of the CKD-MBD are not well known and they will be discussed in this review

RECENT FINDINGS

The discovery of WNT (portmanteau of wingless and int) inhibitors, especially Dickkopf 1, produced during renal repair and participating in the pathogenesis of the vascular and skeletal components of the CKD-MBD implied that additional pathogenic factors are critical, leading to the finding that activin A is a second renal repair factor circulating in increased levels during CKD. Activin A derives from peritubular myofibroblasts of diseased kidneys, where it stimulates fibrosis, and decreases tubular klotho expression. The type 2 activin A receptor, ActRIIA, is decreased by CKD in atherosclerotic aortas, specifically in vascular smooth muscle cells (VSMC). Inhibition of activin signaling by a ligand trap inhibited CKD induced VSMC dedifferentiation, osteogenic transition and atherosclerotic calcification. Inhibition of activin signaling in the kidney decreased renal fibrosis and proteinuria.

SUMMARY

These studies demonstrate that circulating renal repair factors are causal for the CKD-MBD and CKD associated cardiovascular disease, and identify ActRIIA signaling as a therapeutic target in CKD that links progression of renal disease and vascular disease.

Use of sevelamer in chronic kidney disease: beyond phosphorus control

Sevelamer is a non-calcium phosphate binder used in advanced chronic kidney disease (CKD) and in dialysis for hyperphosphataemia control. Several experimental, observational studies and clinical trials have shown that sevelamer has pleiotropic effects, beyond hyperphosphataemia control, including actions on inflammation, oxidative stress, lipid profile and atherogenesis, vascular calcification, endothelial dysfunction and the reduction of several uremic toxins. This is the biological basis for its global effect on cardiovascular morbidity and mortality in patients with chronic kidney disease. This review focuses on these pleiotropic actions of sevelamer and their impact on cardiovascular health, with the experience published after more than ten years of clinical expertise.

Sclerostin and DKK1: new players in renal bone and vascular disease

For more than a decade, the Wnt-β-catenin pathway has been the focus of intense basic and clinical research in the bone field because of its importance in skeletal development and maintenance of bone mass. Wnt activation increases bone formation and decreases bone resorption. The Wnt-β-catenin signaling pathway is tightly regulated by several inhibitors, among which Dickkopf-related protein 1 (DKK1) and sclerostin have been most comprehensively studied. Mounting evidence indicates that a disturbed Wnt-β-catenin signaling is also implicated in the pathogenesis of the chronic kidney disease-associated bone and mineral disorder (CKD-MBD) and affects its various components. DKK1 and sclerostin, more specifically, may be involved in the intense cross-talk between the kidneys, vasculature, and bone. Studies exploring clinical correlates of circulating sclerostin and DKK1 levels so far yielded conflicting results. Biological variability and analytical issues account at least partly for this inconsistency. Antibodies neutralizing Wnt inhibitors may be an appealing strategy to prevent or treat CKD-MBD. Caution is however warranted as sclerostin not only opposes mineralization in the bone but possibly also in the vasculature. Additional studies are required to define determinants of Wnt inhibitors in CKD and to evaluate the efficacy and safety of recently introduced pharmaceuticals targeting these inhibitors.

Sclerostin and CKD-MBD

Declining kidney function is associated with sequential systemic changes in mineral homeostasis leading to pathologic alterations in the cardiovascular system and the skeleton. One of the earliest changes in response to renal injury is the increased osteocyte production of secreted factors including the anti-anabolic protein, sclerostin. Elevated sclerostin is associated with reduced Wnt/β-catenin signaling in bone and decreased osteoblast differentiation/activity. Agents that directly or indirectly inhibit β-catenin signaling have differential skeletal effects suggesting additional mechanisms contribute to the diversity of renal osteodystrophies. Similarly, Wnt/β-catenin activation in smooth muscle cells contributes to cardiovascular calcification yet emerging data suggests that this pathway may also be protective when elevated in neighboring tissues. The ongoing epidemiology studies examining the relationship between circulating sclerostin and cardiovascular disease, particularly those that investigate stage specific and/or patient sub-populations, will be useful in understanding the overall contributions of this pathway, its antagonist sclerostin, and the progression of CKD-MBD.

Sevelamer carbonate: a review in hyperphosphataemia in adults with chronic kidney disease

Sevelamer carbonate (Renvela(®)), a buffered form of sevelamer hydrochloride (Renagel(®)), is an orally administered non-absorbed phosphate-binding anion exchange resin used in the treatment of hyperphosphataemia in chronic kidney disease (CKD). In the EU, sevelamer carbonate is approved in adult CKD patients who require dialysis and in those who do not require dialysis with serum phosphate levels ≥ 1.78 mmol/L, whereas in the USA sevelamer carbonate is approved in adult CKD patients who require dialysis. Sevelamer carbonate and sevelamer hydrochloride achieved similar reductions in serum phosphate levels in randomized comparative trials in patients with CKD receiving haemodialysis; sevelamer carbonate also reduced serum phosphate levels in noncomparative studies in CKD patients not requiring dialysis. The most common adverse events with sevelamer carbonate are gastrointestinal in nature. Sevelamer has pleiotropic effects, such as improving the serum lipid profile and attenuating endothelial and cardiovascular risk factors in CKD. All formulations of sevelamer have markedly higher acquisition costs than calcium-based phosphate binders. Cost-effectiveness analyses focusing specifically on sevelamer carbonate have not been conducted, and those based on clinical trial data with sevelamer hydrochloride have provided both favourable and unfavourable results compared with calcium-based phosphate binders, reflecting heterogeneity between modelled analyses in terms of data sources, assumptions, comparators, geographical regions, type of costs included and other factors. Although well-designed studies evaluating the impact of phosphate binders on hard clinical endpoints appear to be warranted, sevelamer carbonate may be particularly useful for the treatment of patients at risk of metabolic acidosis (offering advantages over sevelamer hydrochloride in this regard) and for individuals requiring treatment with a phosphate binding agent that does not contain aluminium or calcium.

Associations between the levels of sclerostin, phosphate, and fibroblast growth factor-23 and treatment with vitamin D in hemodialysis patients with low intact PTH level

Serum sclerostin levels could be closely associated with serum phosphate and fibroblast growth factor-23 levels in hemodialysis patients with low intact parathyroid hormone (PTH) levels. Further study is required to indicate whether these close associations are present in patients with spontaneously low PTH levels without any vitamin D treatment.

INTRODUCTION

Intact parathyroid hormone (iPTH) is involved in the interaction between sclerostin and phosphate/fibroblast growth factor-23 (FGF23) in animal models. However, their relationship in patients on hemodialysis (HD) is unclear.

METHODS

Data of 102 HD patients were collected regarding clinical and laboratory parameters and mineral bone disorder medications. The patients were divided into subgroups according to the iPTH level (A, <70 pg/mL; B, 70-150 pg/mL; C, 150-300 pg/mL; and D, ≥ 300 pg/mL).

RESULTS

The sclerostin level was significantly and positively correlated with phosphate and log of FGF23 levels in subgroups A, B, and combined A and B. Multiple linear regression analysis in the combined A and B subgroup revealed that male sex (t = 3.24, P = 0.01; 95% confidence interval [CI] 11.78 to 50.43) and phosphate level (t = 2.13, P = 0.04; 95% CI, 1.08 to 36.91) were independent factors for serum sclerostin level. The log of serum FGF23 level (t = 1.90, P = 0.06, 95% CI -1.85 to 63.50) appeared to be an important factor for serum sclerostin level. The frequency of patients using vitamin D treatment was not significantly different among subgroups A (93.1%), B (88.0%), C (85.2%), and D (90.5%).

CONCLUSION

Serum sclerostin levels were associated with serum phosphate and FGF23 levels in patients with low iPTH levels. Further study is required to indicate whether these close associations are present in patients with spontaneously low iPTH levels without vitamin D treatment.

Serum sclerostin is an independent predictor of mortality in hemodialysis patients

Background

Sclerostin (Scl) has recently emerged as a novel marker of bone remodeling and vascular calcification. However, whether high circulating Scl is also a risk factor for death is not well established. The purpose of this study was to test whether serum Scl would be associated with mortality.

Methods

we measured serum Scl in a hemodialysis patients’ cohort, which was followed during a ten-year period. Competing risk regression models were applied, as during the follow-up, patients were exposed to both events kidney transplant and death.

Results

Ninety-one patients aged 42.3 ± 18.8 years (55% of male gender, 15% of diabetes) were included. During the follow-up, 32 patients underwent kidney transplant and 26 patients died. Non-survivals presented higher FGF23, higher Scl and lower creatinine. There was an association between all-cause mortality and higher Scl (HR = 2.2), higher age (HR = 1.04) and presence of diabetes (HR = 2.27), by competing risk analyses. Even including potential markers of mortality, as creatinine, FGF 23, and gender, Scl, age and diabetes remained significantly related to higher mortality.

Conclusion

Serum Scl is an independent predictor of mortality in dialysis patients. However, whether clinical interventions to modulate Scl would be able to improve these patients survival needs to be determined.

Uremic toxicity and sclerostin in chronic kidney disease patients

BACKGROUND AND AIMS

Sclerostin is a circulating inhibitor of the Wnt/β-catenin pathway and may have a role in chronic kidney disease (CKD)-mineral and bone disorder. Blood sclerostin levels are known to be elevated in patients undergoing maintenance dialysis. The aims of the present study were to evaluate sclerostin levels in patients at different CKD stages and study potential associations between sclerostin levels and (i) biochemical parameters that are disturbed in CKD, (ii) markers of vascular disease and (iii) mortality.

METHODS

One hundred and forty patients at CKD stages 2-5D were included in the present study. Routine clinical biochemistry tests and assays for sclerostin, protein-bound uremic toxins (indoxylsulphate [IS] and p-cresyl sulphate [PCS]) and the toxin β2 microglobulin (β2M) were performed. Aortic and coronary calcification and arterial stiffness were assessed by multislice spiral computed tomography and pulse wave velocity measurements. The enrolled patients were prospectively monitored for mortality.

RESULTS

Sclerostin levels were found to be elevated in CKD patients (especially those on hemodialysis). Furthermore, sclerostin levels were positively correlated with inflammation markers, phosphate, fibroblast growth factor 23, IS, PCS, β2M and arterial stiffness. A multivariate linear regression analysis indicated that sclerostin levels were independently associated with IS, PCS and β2M levels. Elevated serum sclerostin appeared to be associated with mortality (independently of age and inflammation). However, this association disappeared after adjustment for a propensity score including age, phosphate, interleukin-6, CKD stage and PCS.

CONCLUSION

Our results indicate that sclerostin levels are elevated in CKD patients and are associated with inflammation, vascular lesions, uremia and (potentially) mortality.

Vascular calcification and renal bone disorders

At the early stage of chronic kidney disease (CKD), the systemic mineral metabolism and bone composition start to change. This alteration is known as chronic kidney disease-mineral bone disorder (CKD-MBD). It is well known that the bone turnover disorder is the most common complication of CKD-MBD. Besides, CKD patients usually suffer from vascular calcification (VC), which is highly associated with mortality. Many factors regulate the VC mechanism, which include imbalances in serum calcium and phosphate, systemic inflammation, RANK/RANKL/OPG triad, aldosterone, microRNAs, osteogenic transdifferentiation, and effects of vitamins. These factors have roles in both promoting and inhibiting VC. Patients with CKD usually have bone turnover problems. Patients with high bone turnover have increase of calcium and phosphate release from the bone. By contrast, when bone turnover is low, serum calcium and phosphate levels are frequently maintained at high levels because the reservoir functions of bone decrease. Both of these conditions will increase the possibility of VC. In addition, the calcified vessel may secrete FGF23 and Wnt inhibitors such as sclerostin, DKK-1, and secreted frizzled-related protein to prevent further VC. However, all of them may fight back the inhibition of bone formation resulting in fragile bone. There are several ways to treat VC depending on the bone turnover status of the individual. The main goals of therapy are to maintain normal bone turnover and protect against VC.

CKD-induced wingless/integration1 inhibitors and phosphorus cause the CKD-mineral and bone disorder

In chronic kidney disease, vascular calcification, renal osteodystrophy, and phosphate contribute substantially to cardiovascular risk and are components of CKD-mineral and bone disorder (CKD-MBD). The cause of this syndrome is unknown. Additionally, no therapy addresses cardiovascular risk in CKD. In its inception, CKD-MBD is characterized by osteodystrophy, vascular calcification, and stimulation of osteocyte secretion. We tested the hypothesis that increased production of circulating factors by diseased kidneys causes the CKD-MBD in diabetic mice subjected to renal injury to induce stage 2 CKD (CKD-2 mice). Compared with non-CKD diabetic controls, CKD-2 mice showed increased renal production of Wnt inhibitor family members and higher levels of circulating Dickkopf-1 (Dkk1), sclerostin, and secreted klotho. Neutralization of Dkk1 in CKD-2 mice by administration of a monoclonal antibody after renal injury stimulated bone formation rates, corrected the osteodystrophy, and prevented CKD-stimulated vascular calcification. Mechanistically, neutralization of Dkk1 suppressed aortic expression of the osteoblastic transcription factor Runx2, increased expression of vascular smooth muscle protein 22-α, and restored aortic expression of klotho. Neutralization of Dkk1 did not affect the elevated plasma levels of osteocytic fibroblast growth factor 23 but decreased the elevated levels of sclerostin. Phosphate binder therapy restored plasma fibroblast growth factor 23 levels but had no effect on vascular calcification or osteodystrophy. The combination of the Dkk1 antibody and phosphate binder therapy completely treated the CKD-MBD. These results show that circulating Wnt inhibitors are involved in the pathogenesis of CKD-MBD and that the combination of Dkk1 neutralization and phosphate binding may have therapeutic potential for this disorder.

Effects of dietary phosphate on adynamic bone disease in rats with chronic kidney disease--role of sclerostin?

High phosphate intake is known to aggravate renal osteodystrophy along various pathogenetic pathways. Recent studies have raised the possibility that dysregulation of the osteocyte Wnt/β-catenin signaling pathway is also involved in chronic kidney disease (CKD)-related bone disease. We investigated the role of dietary phosphate and its possible interaction with this pathway in an experimental model of adynamic bone disease (ABD) in association with CKD and hypoparathyroidism. Partial nephrectomy (Nx) and total parathyroidectomy (PTx) were performed in male Wistar rats. Control rats with normal kidney and parathyroid function underwent sham operations. Rats were divided into three groups and underwent pair-feeding for 8 weeks with diets containing either 0.6% or 1.2% phosphate: sham 0.6%, Nx+PTx 0.6%, and Nx+PTx 1.2%. In the two Nx+PTx groups, serum creatinine increased and blood ionized calcium decreased compared with sham control group. They also presented hyperphosphatemia and reduced serum parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) levels. Fractional urinary excretion of phosphate increased in Nx+PTx 1.2% rats despite lower PTH and FGF23 levels than in sham group. These biochemical changes were accompanied by a decrease in bone formation rates. The Nx+PTx 1.2% group had lower bone volume (BV/TV), higher osteoblast and osteocyte apoptosis, and higher SOST and Dickkopf-1 gene expression than the Nx+PTx 0.6% group. Nx+PTx 0.6% rat had very low serum sclerostin levels, and Nx+PTx 1.2% had intermediate sclerostin levels compared with sham group. Finally, there was a negative correlation between BV/TV and serum sclerostin. These results suggest that high dietary phosphate intake decreases bone volume in an experimental model of CKD-ABD, possibly via changes in SOST expression through a PTH-independent mechanism. These findings could have relevance for the clinical setting of CKD-ABD in patients who low turnover bone disease might be attenuated by optimal control of phosphate intake and/or absorption.