Sclerostin and Dickkopf-1 in renal osteodystrophy

Only bioactive forms of PTH (n-oxPTH and Met18(ox)-PTH) inhibit synthesis of sclerostin - evidence from in vitro and human studies

Sclerostin (SOST) is produced by osteocytes and is known as a negative regulator of bone homeostasis. Parathyroid hormone (PTH) regulates calcium, phosphate as well as vitamin D metabolism, and is a strong inhibitor of SOST synthesis in vitro and in vivo. PTH has two methionine amino acids (positions 8 and 18) which can be oxidized. PTH oxidized at Met18 (Met18(ox)-PTH) continues to be bioactive, whereas PTH oxidized at Met8 (Met8(ox)-PTH) or PTH oxidized at Met8 and Met18 (Met8, Met18(di-ox)-PTH) has minor bioactivity. How non-oxidized PTH (n-oxPTH) and oxidized forms of PTH act on sclerostin synthesis is unknown. The effects of n-oxPTH and oxidized forms of PTH on SOST gene expression were evaluated in UMR106 osteoblast-like cells. Moreover, we analyzed the relationship of SOST with n-oxPTH and all forms of oxPTH in 516 stable kidney transplant recipients using an assay system that can distinguish in clinical samples between n-oxPTH and the sum of all oxidized PTH forms (Met8(ox)-PTH, Met18(ox)-PTH, and Met8, Met18(di-ox)-PTH). We found that both n-oxPTH and Met18(ox)-PTH at doses of 1, 3, 20, and 30 nmol/L significantly inhibit SOST gene expression in vitro, whereas Met8(ox)-PTH and Met8, Met18(di-ox)-PTH only have a weak inhibitory effect on SOST gene expression. In the clinical cohort, multivariate linear regression showed that only n-oxPTH, but not intact PTH (iPTH) nor oxPTH, is independently associated with circulating SOST after adjusting for known confounding factors. In conclusion, only bioactive PTH forms such as n-oxPTH and Met18(ox)-PTH, inhibit SOST synthesis.

Application of artificial intelligence to chronic kidney disease mineral bone disorder

The global derangement of mineral metabolism that accompanies chronic kidney disease (CKD-MBD) is a major driver of the accelerated mortality for individuals with kidney disease. Advances in the delivery of dialysis, in the composition of phosphate binders, and in the therapies directed towards secondary hyperparathyroidism have failed to improve the cardiovascular event profile in this population. Many obstacles have prevented progress in this field including the incomplete understanding of pathophysiology, the lack of clinical targets for early stages of chronic kidney disease, and the remarkably wide diversity in clinical manifestations. We describe in this review a novel approach to CKD-MBD combining mathematical modelling of biologic processes with machine learning artificial intelligence techniques as a tool for the generation of new hypotheses and for the development of innovative therapeutic approaches to this syndrome. Clinicians need alternative targets of therapy, tools for risk profile assessment, and new therapies to address complications early in the course of disease and to personalize therapy to each individual. The complexity of CKD-MBD suggests that incorporating artificial intelligence techniques into the diagnostic, therapeutic, and research armamentarium could accelerate the achievement of these goals.

Bone and bone derived factors in kidney disease

Purpose of review: Mineral and bone disorder (MBD) is a prevalent complication in chronic kidney disease (CKD), significantly impacting overall health with multifaceted implications including fractures, cardiovascular events, and mortality. Despite its pervasive nature, effective treatments for CKD-MBD are lacking, emphasizing the urgency to advance understanding and therapeutic interventions. Bone metabolism intricacies, influenced by factors like 1,25 dihydroxy vitamin D, parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23), along with intrinsic osseous mechanisms, play pivotal roles in CKD. Skeletal abnormalities precede hormonal changes, persisting even with normalized systemic mineral parameters, necessitating a comprehensive approach to address both aspects. Recent findings: In this review, we explore novel pathways involved in the regulation of systemic mineral bone disease factors, specifically examining anemia, inflammation, and metabolic pathways. Special emphasis is placed on internal bone mechanisms, such as hepatocyte nuclear factor 4α, transforming growth factor-β1, and sclerostin, which play crucial roles in the progression of renal osteodystrophy. Summary: Despite advancements, effective treatments addressing CKD-MBD morbidity and mortality are lacking, necessitating ongoing research for novel therapeutic targets.

Potential Role of Bone Metabolism Markers in Kidney Transplant Recipients

BACKGROUND

The impact of treatments, suppressing the immune system, persistent hyperparathyroidism, and other risk factors on mineral and bone disorder (MBD) after kidney transplantation is well-known. However, there is limited knowledge about their effect on bone metabolism biomarkers. This study aimed to investigate the influence of kidney transplant on these markers, comparing them to patients undergoing hemodialysis and healthy individuals.

METHODS

In this cross-sectional study, three groups were included: kidney transplant patients (n = 57), hemodialysis patients (n = 26), and healthy controls (n = 31). Plasma concentrations of various bone metabolism biomarkers, including Dickkopf-related protein 1, osteoprotegerin, osteocalcin, osteopontin, sclerostin, and fibroblast growth factor 23, were measured. Associations between these biomarkers and clinical and laboratory data were evaluated.

RESULTS

A total of 114 patients participated. Transplant recipients had significantly lower levels of Dickkopf-related protein 1, osteoprotegerin, osteocalcin, osteopontin, sclerostin, and fibroblast growth factor 23 compared to hemodialysis patients. Alkaline phosphatase levels positively correlated with osteopontin (r = 0.572, p < 0.001), while fibroblast growth factor 23 negatively correlated with 25-hydroxyvitamin D (r = -0.531, p = 0.019). The panel of bone biomarkers successfully predicted hypercalcemia (area under the curve [AUC] = 0.852, 95% confidence interval [CI] = 0.679-1.000) and dyslipidemia (AUC = 0.811, 95% CI 0.640-0.982) in transplant recipients.

CONCLUSION

Kidney transplantation significantly improves mineral and bone disorders associated with end-stage kidney disease by modulating MBD markers and reducing bone metabolism markers, such as Dickkopf-related protein 1, osteoprotegerin, osteocalcin, osteopontin, and sclerostin. Moreover, the panel of bone biomarkers effectively predicted hypercalcemia and dyslipidemia in transplant recipients.

Effects of Multiwall Carbon Nanotubes on Premature Kidney Aging: Biochemical and Histological Analysis

Carbon nanotubes (CNTs) have gained much attention due to their superb properties, which make them promising options for the reinforcing composite materials with desirable mechanical properties. However, little is known about the linkage between lung exposure to nanomaterials and kidney disease. In this study, we compared the effects on the kidneys and aging for two different types of multiwall carbon nanotubes (MWCNTs): pristine MWCNTs (PMWCNTs) and acid-treated MWCNTs (TMWCNTs), with TMWCNTs being the preferred form for use as a composite material due to its superior dispersion properties. We used tracheal instillation and maximum tolerated dose (MTD) for both types of CNTs. MTD was determined as a 10% weight loss dose in a 3-month subchronic study, and the appropriate dosage for 1-year exposure was 0.1 mg/mouse. Serum and kidney samples were analyzed using ELISA, Western blot, and immunohistochemistry after 6 months and 1 year of treatment. PMWCNT-administered mice showed the activation of pathways for inflammation, apoptosis, and insufficient autophagy, as well as decreased serum Klotho levels and increased serum levels of DKK-1, FGF-23, and sclerostin, while TMWCNTs did not. Our study suggests that lung exposure to PMWCNTs can induce premature kidney aging and highlights a possible toxic effect of using MWCNTs on the kidneys in the industrial field, further highlighting that dispersibility can affect the toxicity of the nanotubes.

New Emerging Biomarkers for Bone Disease: Sclerostin and Dickkopf-1 (DKK1)

A healthy skeleton depends on a continuous renewal and maintenance of the bone tissue. The process of bone remodeling is highly controlled and consists of a fine-tuned balance between bone formation and bone resorption. Biochemical markers of bone turnover are already in use for monitoring diseases and treatment involving the skeletal system, but novel biomarkers reflecting specific biological processes in bone and interacting tissues may prove useful for diagnostic, prognostic, and monitoring purposes. The Wnt-signaling pathway is one of the most important pathways controlling bone metabolism and consequently the action of inhibitors of the pathway such as sclerostin and Dickkopf-related protein 1 (DKK1) have crucial roles in controlling bone formation and resorption. Thus, they might be potential markers for clinical use as they reflect a number of physiological and pathophysiological events in bone and in the cross-talk with other tissues in the human body. This review focuses on the clinical utility of measurements of circulating sclerostin and DKK1 levels based on preanalytical and analytical considerations and on evidence obtained from published clinical studies. While accumulating evidence points to clear associations with a number of disease states for the two markers, and thus, the potential for especially sclerostin as a biochemical marker that may be used clinically, the lack of standardization or harmonization of the assays still hampers the clinical utility of the markers.

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.

Bone Disease in Chronic Kidney Disease and Kidney Transplant

Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD) comprises alterations in calcium, phosphorus, parathyroid hormone (PTH), Vitamin D, and fibroblast growth factor-23 (FGF-23) metabolism, abnormalities in bone turnover, mineralization, volume, linear growth or strength, and vascular calcification leading to an increase in bone fractures and vascular disease, which ultimately result in high morbidity and mortality. The bone component of CKD-MBD, referred to as renal osteodystrophy, starts early during the course of CKD as a result of the effects of progressive reduction in kidney function which modify the tight interaction between mineral, hormonal, and other biochemical mediators of cell function that ultimately lead to bone disease. In addition, other factors, such as osteoporosis not apparently dependent on the typical pathophysiologic abnormalities resulting from altered kidney function, may accompany the different varieties of renal osteodystrophy leading to an increment in the risk of bone fracture. After kidney transplantation, these bone alterations and others directly associated or not with changes in kidney function may persist, progress or transform into a different entity due to new pathogenetic mechanisms. With time, these alterations may improve or worsen depending to a large extent on the restoration of kidney function and correction of the metabolic abnormalities developed during the course of CKD. In this paper, we review the bone lesions that occur during both CKD progression and after kidney transplant and analyze the factors involved in their pathogenesis as a means to raise awareness of their complexity and interrelationship.

Is Adynamic Bone Always a Disease? Lessons from Patients with Chronic Kidney Disease

Renal osteodystrophy (ROD) is a common complication of end-stage kidney disease that often starts early with loss of kidney function, and it is considered an integral part in management of patients with chronic kidney disease (CKD). Adynamic bone (ADB) is characterized by suppressed bone formation, low cellularity, and thin osteoid seams. There is accumulating evidence supporting increasing prevalence of ADB, particularly in early CKD. Contemporarily, it is not very clear whether it represents a true disease, an adaptive mechanism to prevent bone resorption, or just a transitional stage. Several co-players are incriminated in its pathogenesis, such as age, diabetes mellitus, malnutrition, uremic milieu, and iatrogenic factors. In the present review, we will discuss the up-to-date knowledge of the ADB and focus on its impact on bone health, fracture risk, vascular calcification, and long-term survival. Moreover, we will emphasize the proper preventive and management strategies of ADB that are pivotal issues in managing patients with CKD. It is still unclear whether ADB is always a pathologic condition or whether it can represent an adaptive process to suppress bone resorption and further bone loss. In this article, we tried to discuss this hard topic based on the available limited information in patients with CKD. More studies are needed to be able to clearly address this frequent ROD finding.

Clinical significance of serum levels of osteoproteherin and sclerostin in assessment of vascular calcification in chronic kidney disease stage 3–5

Aim. To clarify the mechanisms of the effect of osteoprotegerin (OPG) and sclerostin on vascular calcification and the state of the cardiovascular system in chronic kidney disease (CKD). Materials and methods. A total of 110 patients aged 18 to 65 years with CKD stages 35D were examined. OPG, sclerostin, intact parathyroid hormone, and serum troponin I were determined using the commercial "Enzyme-linked Immunosorbent Assay Kit for Sclerostin" from Cloude-Clone Corp. (USA) by enzyme-linked immunosorbent assay. Results. An increase in sclerostin and OPG levels was revealed, which significantly correlated with a decrease in glomerular filtration rate, as well as an increase in left ventricle myocardial mass index and peak systolic blood flow in the aortic arch. Conclusion. Changes in the regulation of bone-mineral metabolism, in which the proteins inhibitors of bone metabolism, OPG and sclerostin, as well as the interactive interaction between the vascular and skeletal systems, play a decisive role in the development of lesions of the cardiovascular system caused by vascular calcification in CKD.

Crosstalk between bone and other organs

Bone has long been considered as a silent organ that provides a reservoir of calcium and phosphorus, traditionally. Recently, further study of bone has revealed additional functions as an endocrine organ connecting systemic organs of the whole body. Communication between bone and other organs participates in most physiological and pathological events and is responsible for the maintenance of homeostasis. Here, we present an overview of the crosstalk between bone and other organs. Furthermore, we describe the factors mediating the crosstalk and review the mechanisms in the development of potential associated diseases. These connections shed new light on the pathogenesis of systemic diseases and provide novel potential targets for the treatment of systemic diseases.

Role of Fracture Risk Assessment Tool and Bone Turnover Markers in Predicting All-Cause and Cardiovascular Mortality in Hemodialysis Patients

Background

Fracture Risk Assessment Tool (FRAX) and bone turnover markers (BTMs) predict fractures in the general population. However, the role of FRAX and BTMs in predicting mortality remains uncertain in hemodialysis (HD) patients.

Methods

One hundred and sixty-four HD patients stratified by low or high risk of 10-year fracture probability using FRAX. High risk of fracture was defined as 10-year probability of hip fracture ≥3% or major osteoporotic fracture ≥20%. The association of high risk of fracture and BTMs with all-cause mortality and cardiovascular (CV) mortality were evaluated using multivariate-adjusted Cox regression analysis.

Results

Eighty-five (51.8%) patients were classified as high risk of fracture based on FRAX among 164 HD patients. During a mean follow-up period of 3.5 ± 1.0 years, there were 39 all-cause deaths and 23 CV deaths. In multivariate-adjusted Cox regression, high risk of fracture based on FRAX was independently associated with all-cause mortality [hazard ratio (HR): 2.493, 95% confidence interval (CI): 1.026–6.056, p = 0.044) but not with CV mortality (HR: 2.129, 95% CI: 0.677–6.700, p = 0.196). There were no associations between BTMs and mortality risk. Furthermore, lower geriatric nutritional risk index (GNRI) was significantly associated with increased CV mortality (HR: 0.888, 95% CI: 0.802–0.983, p = 0.022) after adjusting by confounding variables.

Conclusion

High risk of fracture using FRAX was an independent predictor of all-cause mortality in patients undergoing HD. FRAX, rather than BTMs, has an important role of prognostic significance in HD patients.

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.

Serum Sclerostin Level Is Negatively Associated with Bone Mineral Density in Hemodialysis Patients

Background and Objectives: Sclerostin and Dickkopf-1 (DKK1) modulate osteoblastogenesis, but their role in bone loss in hemodialysis (HD) patients is inconclusive. This study investigated relationships among lumbar bone mineral density (BMD), serum sclerostin, and DKK1 in HD patients. Materials and Methods: Blood samples were obtained from 75 HD patients. Dual-energy X-ray absorptiometry measured lumbar BMD of the lumbar vertebrae (L2−L4). Enzyme-linked immunosorbent assay revealed serum sclerostin and DKK1 concentrations. Results: There were 10 (13.3%), 20 (26.7%), and 45 (60%) patients defined as presenting with osteoporosis, osteopenia, or normal BMD, respectively. Age, alkaline phosphatase, urea reduction rate, fractional clearance index for urea, sclerostin level, and percentage of female patients are significantly negatively associated with the lumbar BMD and T-score, while the body mass index and waist circumference significantly positively associated with the lumbar BMD and T-score. Multivariate forward stepwise linear regression analysis indicated that serum sclerostin (β = −0.546, adjusted R2 change = 0.454; p < 0.001), age (β = −0.216, adjusted R2 change = 0.041; p = 0.007), and percentage of female HD patients (β = −0.288, adjusted R2 change = 0.072; p = 0.0018) were significantly negatively associated with lumbar BMD in HD patients. Conclusions: Advanced age, female gender, and serum sclerostin level, but not DKK1, were negatively associated with BMD in HD patients.

Could Bone Biomarkers Predict Bone Turnover after Kidney Transplantation?—A Proof-of-Concept Study

Aim: Bone disease after kidney transplant (KT) results from multiple factors, including previous bone and mineral metabolism disturbances and effects of transplant-related medications. New biomolecules have been recently associated with the development and progression of the chronic kidney disease–associated bone and mineral disorder (CKD-MBD). These include sclerostin and the soluble receptor activator of nuclear factor-kB ligand (sRANKL). Methods: To better understand the role of biomarkers in post-transplant bone disease, this study was designed to prospectively evaluate and correlate results from the histomorphometric analysis of bone biopsies after KT with emerging serum biomarkers of the CKD-MBD: sclerostin, Dickkopf-related protein 1 (Dkk-1), sRANKL and osteo-protegerin (OPG). Results: Our data shows a significant increase in plasma levels of bioactive sclerostin after KT accompanied by a significant reduction in plasma levels of Dkk-1, suggesting a promotion of the inhibition of bone formation by osteoblasts through the activation of these inhibitors of the Wnt signaling pathway. In addition, we found a significant increase in plasma levels of free sRANKL after KT accompanied by a significant reduction in plasma levels of its decoy receptor OPG, suggesting an enhanced bone resorption by osteoclasts mediated by this mechanism. Conclusions: Taken together, these results suggest that the loss of bone volume observed after KT could be explain mainly by the inhibition of bone formation mediated by sclerostin accompanied by an enhanced bone resorption mediated by sRANKL.

Serum sclerostin in acute kidney injury patients

BACKGROUND

Many of the mineral metabolite abnormalities encountered in chronic kidney disease (CKD) patients were found also associated with acute kidney injury (AKI). In the last decade, sclerostin was found to intimately affect bone mineral metabolism in CKD patients. Nothing is known about sclerostin in AKI.

OBJECTIVE

We looked for serum level of sclerostin in AKI patients in comparison to normal control subjects and if there is an impact on metabolic derangement, endothelial function or clinical outcome.

CASES AND METHODS

This is a cross sectional case control observational study of 219 AKI cases (group I) beside 219 age matched normal control subjects (group II). All cases of group I were in the intensive care because of sepsis; 86 had acute on CKD (group Ib), while 133 had de novo AKI (group Ia). All studied subjects underwent estimation of serum sclerostin, parathyroid hormone (PTH), 25 hydroxy vitamin D (25 OH vit D), fibroblast growth factor 23 (FGF23), C-reactive protein (CRP), interleukin 6 (IL6), Homeostatic Model Assessment for Insulin Resistance (Homa IR), beside the routine CBC, kidney and liver function tests, serum calcium, and phosphorus, and flow mediated vasodilation of brachial artery (FMD). Follow-up of group I cases was done till they recovered or passed away.

RESULTS

Serum sclerostin, PTH, FGF23, phosphorus, CRP, IL6, HOMA IR, creatinine, urea, uric acid, ALT, AST and white blood cell count (WBC) were significantly higher while serum calcium, 25 OH vit D, hemoglobin, platelet count and FMD were significantly lower in group I compared to group II (P<0.001 in all). On the other hand, there was no significant difference in serum sclerostin, PTH, FGfF23, 25 OH vit D, CRP, IL6, Homa IR and FMD between group Ia and Ib. Survivors were younger in age (median 55.5 vs. 60 years, P<0.04), had lower AST (30.5 vs. 58 units, P<0.001), had higher platelet count (206 vs 162×10⁹/L, P<0.001), otherwise, there was no significant difference in any of the other parameters between survivors and patients that were lost. Serum sclerostin had strong correlation with FGF23 in group I (r=0.99, P<0.001) and group II (r=1, P<0.001). Homa IR had positive correlation with serum sclerostin (r=0.148, P=0.014) and serum FGF23 (r=0.142, P=0.018) in group I.

CONCLUSION

Sclerostin is intimately related to FGF23. Sclerostin level increases in AKI patients. Both sclerostin and FGF23 might increase insulin resistance but have no impact on FMD. Neither sclerostin nor FGF23 interfere with AKI outcome.

Interrelationships Between Sclerostin, Secondary Hyperparathyroidism, and Bone Metabolism in Patients on Hemodialysis

CONTEXT

Sclerostin is an osteocyte-derived inhibitor of bone formation and is increased in kidney failure, but its role in the pathogenesis of renal bone disease remains unknown.

OBJECTIVE

We aimed to explore the association of serum sclerostin with bone metabolism in patients undergoing hemodialysis, with a particular focus on parathyroid hormone (PTH)-dependent and PTH-independent pathways.

METHODS

This cross-sectional and prospective cohort study included 654 patients undergoing hemodialysis at 10 facilities in Japan. We employed multivariable linear regression to explore whether sclerostin levels were associated with metacarpal bone mineral density (BMD), intact PTH, bone alkaline phosphatase (BAP), and tartrate-resistant acid phosphatase-5b (TRACP-5b). We employed mediation analyses to explore whether and to what extent the association of PTH with bone turnover markers is mediated by sclerostin. We also compared sclerostin levels between patients with and without previous or incident fractures.

RESULTS

The median sclerostin level in hemodialysis patients was 3- to 4-fold higher than that in healthy individuals. Higher sclerostin levels were associated with higher metacarpal BMD and lower levels of intact PTH, BAP, and TRACP-5b. However, the relationships of sclerostin with bone turnover markers were substantially attenuated after adjustment for PTH. Mediation analysis suggested that the effects of PTH on bone turnover markers were mainly direct rather than mediated by sclerostin. Sclerostin levels were not associated with previous or incident fractures.

CONCLUSION

These findings suggest that in patients undergoing dialysis, sclerostin has only a limited role in bone metabolism and may not mediate the effect of PTH on bone turnover.

The Relationship between Serum Sclerostin Levels and Bone Mineral Disorders and Vascular Calcification in Hemodialysis Patients

Background and aim of the study: Sclerostin is produced by osteocytes and has been shown to down-regulate the synthesis of many markers of bone formation by osteogenic cells. The aim of this study to investigate the relationship between serum sclerostin levels and bone mineral disorders and vascular calcification in hemodialysis patients (HD). Methods:This is a cross-sectional study of 70 patients with ESRD on regular HD for at least six months, Theodor Bilharz Research Institute, Giza, Egypt.Twenty-five subjects who matched the ages, genders, and demographics of the study patients were included as a control group.All patients and control groups included in the study underwent a full through history and clinical examination. Serum calcium, phosphorus, alkaline phosphatase and intact PTH (iPTH) levels were measured. Serum sclerostin was measured by an ELISA. Bone Mineral Densitometry Measurements BMD (g/cm2) was determined by dual-energy X-ray absorptiometry (DXA). CT scan was done to detect the presence or absence of vascular calcification and transthoracic echocardiogram to detect the presence or absence of  valvular calcification. Results:The mean seumscleostin levels was a statistically significant high in the HD patients when compared with the control group (156.8 ±121.4 Vs.29.38±0.84,  p =0.0001 ) and statistically significant high mean ALP in the HD patients when compared with the control group (147.2 ± 94.3      Vs.              38.8 ±23.4, p = 0.0001). The mean BMD  was statistically significant low in the HD patients when compared with the controls (0.839±0.086 g/ m2 Vs.1.306  ±0.153 g/ m2, p = 0.0001).The mean seumscleostin levels was statistically significant high in the HD patients with vascular and valvular  calcification  when compared with HD patients without calcification.Using spearman correlation coefficient analysis, there was  statistically significant negative correlations between serum sclerostin levels and iPTH(r=-0.362,   p =0.0021), ALP (r=-0.301, p =0.0114), and BMD (r=-0.469, p =0.0278 ), and there was a statistically significant positive correlation between serum sclerostin levels and phosphate(r=0.5829,  p =0.0001 ).Independent predictors of BMD in HD patients were determined using multi-variate regression analysis. Sclerostin levels, iPTH, ALP, and age  were found to be independent predictors of BMD. Conclusion: High sclerostin levels in patients with ESRD on HD were associated with high risk of vascular and valvularcalcification and were independent predictors of low BMD in such population.

New Insights to the Crosstalk between Vascular and Bone Tissue in Chronic Kidney Disease-Mineral and Bone Disorder

Vasculature plays a key role in bone development and the maintenance of bone tissue throughout life. The two organ systems are not only linked in normal physiology, but also in pathophysiological conditions. The chronic kidney disease–mineral and bone disorder (CKD-MBD) is still the most serious complication to CKD, resulting in increased morbidity and mortality. Current treatment therapies aimed at the phosphate retention and parathyroid hormone disturbances fail to reduce the high cardiovascular mortality in CKD patients, underlining the importance of other factors in the complex syndrome. This review will focus on vascular disease and its interplay with bone disorders in CKD. It will present the very late data showing a direct effect of vascular calcification on bone metabolism, indicating a vascular-bone tissue crosstalk in CKD. The calcified vasculature not only suffers from the systemic effects of CKD but seems to be an active player in the CKD-MBD syndrome impairing bone metabolism and might be a novel target for treatment and prevention.

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.

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.

Sclerostin and DKK1 circulating levels associate with low bone turnover in patients with chronic kidney disease Stages 3 and 4

BACKGROUND

Disordered mineral and bone metabolism is a common complication of chronic kidney disease (CKD). Bone biopsy remains the gold standard tool for evaluating renal osteodystrophy (ROD), but it is an invasive procedure. Despite a growing interest in the ability of newer bone biomarkers to discriminate between different forms of ROD, data on pre-dialysis patients are scarce.

METHODS

A cross-sectional study was conducted in a cohort of 56 patients with CKD Stages 3 and 4. Participants underwent a transiliac bone biopsy after a course of double tetracycline labelling. Circulating levels of Wnt signalling inhibitors sclerostin and Dickkopf-1 (DKK1), soluble receptor activator of nuclear factor-κB ligand (sRANKL) and osteoprotegerin were measured and correlated with histomorphometric analysis results.

RESULTS

Most patients had abnormal bone histology and low-turnover bone disease was the predominant form of ROD. Characteristics associated with high bone turnover were worse renal function, lower serum calcium and higher intact parathyroid hormone and fibroblast growth factor-23 levels. Patients with low bone turnover, on the other hand, presented with higher sclerostin along with lower DKK1 and sRANKL levels. In the multivariable logistic regression analysis, sclerostin and DKK1 levels were independently associated with low-turnover bone disease.

CONCLUSIONS

Our results suggest that circulating levels of Wnt signalling inhibitors sclerostin and DKK1 are predictive of low-turnover bone disease in patients not yet on dialysis. Further research is needed to assess the performance of these bone turnover biomarkers, compared with histomorphometric analysis, in the diagnosis and treatment monitoring of ROD.

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.

Hemodiafiltration Is Associated With Reduced Inflammation and Increased Bone Formation Compared With Conventional Hemodialysis in Children: The HDF, Hearts and Heights (3H) Study

Background

Patients on dialysis have a high burden of bone-related comorbidities, including fractures. We report a post hoc analysis of the prospective cohort study HDF, Hearts and Heights (3H) to determine the prevalence and risk factors for chronic kidney disease-related bone disease in children on hemodiafiltration (HDF) and conventional hemodialysis (HD).

Methods

The baseline cross-sectional analysis included 144 children, of which 103 (61 HD, 42 HDF) completed 12-month follow-up. Circulating biomarkers of bone formation and resorption, inflammatory markers, fibroblast growth factor-23, and klotho were measured.

Results

Inflammatory markers interleukin-6, tumor necrosis factor-α, and high-sensitivity C-reactive protein were lower in HDF than in HD cohorts at baseline and at 12 months (P < .001). Concentrations of bone formation (bone-specific alkaline phosphatase) and resorption (tartrate-resistant acid phosphatase 5b) markers were comparable between cohorts at baseline, but after 12-months the bone-specific alkaline phosphatase/tartrate-resistant acid phosphatase 5b ratio increased in HDF (P = .004) and was unchanged in HD (P = .44). On adjusted analysis, the bone-specific alkaline phosphatase/tartrate-resistant acid phosphatase 5b ratio was 2.66-fold lower (95% confidence interval, −3.91 to −1.41; P < .0001) in HD compared with HDF. Fibroblast growth factor-23 was comparable between groups at baseline (P = .52) but increased in HD (P < .0001) and remained unchanged in HDF (P = .34) at 12 months. Klotho levels were similar between groups and unchanged during follow-up. The fibroblast growth factor-23/klotho ratio was 3.86-fold higher (95% confidence interval, 2.15–6.93; P < .0001) after 12 months of HD compared with HDF.

Conclusion

Children on HDF have an attenuated inflammatory profile, increased bone formation, and lower fibroblast growth factor-23/klotho ratios compared with those on HD. Long-term studies are required to determine the effects of an improved bone biomarker profile on fracture risk and cardiovascular health.

Hyporesponsiveness or resistance to the action of parathyroid hormone in chronic kidney disease

Secondary hyperparathyroidism (SHPT) is an integral component of the chronic kidney disease-mineral and bone disorder (CKD-MBD). Many factors have been associated with the development and progression of SHPT but the presence of skeletal or calcemic resistance to the action of PTH in CKD has often gone unnoticed. The term hyporesponsiveness to PTH is currently preferred and, in this chapter, we will not only review the scientific timeline but also some of the molecular mechanisms behind. Moreover, the presence of resistance to the biological action of PTH is not unique in CKD since resistance to other hormones has also been described ("uremia as a receptor disease"). This hyporesponsiveness carries out important clinical implications since it explains, at least partially, not only the progressive nature of the pathogenesis of CKD-related PTH hypersecretion and parathyroid hyperplasia but also the increasing prevalence of adynamic bone disease in the CKD population. Therefore, we underline the importance of PTH control in all CKD stages, but not aiming to completely normalize PTH levels since a certain degree of SHPT may represent an adaptive clinical response. Future studies at the molecular level, i.e. on uremia or the recent description of the calcium-sensing receptor as a phosphate sensor, may become of great value beyond their significance to explain just the hyporesponsiveness to PTH in CKD.

Diagnosis and Management of Osteoporosis in Advanced Kidney Disease: A Review

Osteoporosis and fractures are common in persons with advanced chronic kidney disease (CKD) and on maintenance dialysis. Although the diagnosis of osteoporosis in this population can be difficult, imaging, especially with dual-energy x-ray absorptiometry (DXA), is helpful in identifying persons with CKD at the highest risk of fracture. Although blood biomarkers including parathyroid hormone and bone-specific alkaline phosphatase concentrations can aid in assessing bone turnover state, bone biopsy remains the gold standard in determining bone turnover in persons with advanced kidney disease and osteoporosis. With the increasing armamentarium of osteoporosis drugs, it now may be possible to prevent many fractures in advanced CKD. Unfortunately, data on these drugs are limited in persons with advanced CKD. Clinicians, aided by advances in imaging, biomarkers, and bone biopsy can now use these novel agents to target bone turnover abnormalities such as adynamic bone disease and high bone turnover disease. This review will discuss the most recent literature surrounding the diagnosis, management, and monitoring of osteoporosis and fractures in persons with advanced CKD or on maintenance dialysis.

Patterns of renal osteodystrophy one year after kidney transplantation

BACKGROUND

Renal osteodystrophy is considered common, but is not well characterized, in contemporary kidney transplant recipients. This study reports extensively on bone phenotype by bone histomorphometry, bone densitometry, and novel bone biomarkers 1 year after kidney transplantation.

METHODS

A transiliac bone biopsy and dual energy x-ray absorptiometry were performed in 141 unselected kidney transplant recipients in this observational cohort study. Blood and 24 hr urine samples were collected simultaneously.

RESULTS

Median age was 57 ± 11 years, 71% were men, and all were of Caucasian ethnicity. Bone turnover was normal in 71% of patients, low in 26%, and high in just four cases (3%). Hyperparathyroidism with hypercalcemia was present in 13% of patients, of which one had high bone turnover. Delayed bone mineralization was detected in 16% of patients, who were characterized by hyperparathyroidism (137 vs. 53 ρg/mL), a higher fractional excretion of phosphate (40 vs. 32%), and lower levels of phosphate (2.68 vs 3.18 mg/dL) and calcidiol (29 vs. 37 ng/mL) compared to patients with normal bone mineralization. Osteoporosis was present in 15-46% of patients, with the highest prevalence at the distal skeleton. The proportion of osteoporotic patients was comparable across categories of bone turnover and mineralization.

CONCLUSION

The majority of kidney transplant recipients, including patients with osteoporosis, have a normal bone turnover at 1-year post-transplant. Low bone turnover is seen in a substantial subset, while high bone turnover is rare. Vitamin D deficiency and hypophosphatemia represent potential interventional targets to improve bone health post-transplant.

Analysis of the Prevalence and Severity of Dysregulated Bone Mineral Homeostasis in Nondialyzed Chronic Kidney Disease Patients

Background Progressive loss of kidney function in chronic kidney disease (CKD) leads to altered mineral homeostasis, reflected by the imbalance in calcium and phosphorus, and has been associated with progression of renal failure.

Aims The aim of this study was to investigate CKD-mineral bone disorder (CKD-MBD)-associated candidate variables and its relationship with parathyroid hormone (PTH), as well as to quantify the prevalence of CKD-associated mineral disturbances in nondialyzed CKD patients.

Study Design, Materials, and Methods This cross-sectional analytical study included 124 CKD patients and 157 control participants. Blood samples were analyzed for serum total calcium, phosphorus, PTH, electrolytes, and other hematological/hemodynamic parameters by standard methods. Suitable descriptive statistics was used for different variables.

Results The 124 patients had a mean age of 50.2 ± 7.8 years with male to female ratio of 1.58; majority of patients had stage 3 CKD (40.32%), and the most common comorbid conditions were diabetes mellitus ( n = 78 [62.9%]) and hypertension ( n = 63 [50.8%]). A high prevalence of mineral metabolite abnormalities was observed in a patient cohort; overall prevalence of hyperparathyroidism was found in 57.25% patients, hypocalcemia in 61.29%, and hyperphosphatemia in 82.25% patients. Prevalence of abnormal homeostasis (with regard to total calcium, phosphate, and PTH) increased progressively with the severity of disease (analysis of variance; p < 0.05). Significant differences in the mean values of total calcium, phosphorus, alkaline phosphatase, and PTH were seen compared with healthy participants ( p < 0.0001). Furthermore, there was a significant positive correlation between serum PTH with serum phosphorous ( R 2: 0.33; p < 0.0001), serum creatinine ( R 2: 0.084; p < 0.0259), serum potassium ( R 2: 0.068; p < 0.0467), and a significant negative correlation with serum total calcium ( R 2: 0.37; p < 0.0001).

Conclusions CKD patients are at risk of or may already have developed secondary hyperparathyroidism apparent from PTH-linked derangements in mineral metabolism in predialysis CKD patients. These abnormalities start in early stages of CKD and worsen with disease progression. This accentuates the significance of early recognition of mineral bone disorder, understanding its pathophysiological consequences and scheduling necessary interventions/management strategies to protect the CKD patients from a plethora of complications.

Bone Quality in CKD Patients: Current Concepts and Future Directions - Part I

BACKGROUND

There is ample evidence that patients with CKD have an increased risk of osteoporotic fractures. Bone fragility is not only influenced by low bone volume and mass but also by poor microarchitecture and tissue quality. More emphasis has been given to the quantitative rather than qualitative assessment of bone health, both in general population and CKD patients. Although bone mineral density (BMD) is a very useful clinical tool in assessing bone strength, it may underestimate the fracture risk in CKD patients. Serum and urinary bone biomarkers have been found to be reflective of bone activities and predictive of fractures independently of BMD in CKD patients. Bone quality and fracture risk in CKD patients can be better assessed by utilizing new technologies such as trabecular bone score and high-resolution imaging studies. Additionally, invasive assessments such as bone histology and micro-indentation are useful counterparts in the evaluation of bone quality.

SUMMARY

A precise diagnosis of the underlying skeletal abnormalities in CKD patients is crucial to prevent further bone loss and fractures. We must consider bone quantity and quality abnormalities for management of CKD patients. Here in this part I, we are focusing on advances in bone quality diagnostics that are expected to help in proper understanding of the bone health in CKD patients.

KEY MESSAGES

Assessment of bone quality and quantity in CKD patients is essential. Both noninvasive and invasive techniques for the assessment of bone quality are available.

The Association of Urinary Sclerostin and Renal Magnesium Handling in Type 2 Diabetic Patients with Chronic Kidney Disease

INTRODUCTION

Sclerostin could enhance renal excretion of calcium (Ca) and phosphate (P). The association between sclerostin and magnesium (Mg) has not yet discovered. In patients with type 2 diabetes mellitus (T2DM) or chronic kidney disease (CKD), higher serum sclerostin and altered renal excretion of Ca, P, and Mg were detected. Therefore, we tried to evaluate if there was any association between sclerostin and fractional excretion of Ca, P, and Mg (FeCa, FeP, and FeMg) in T2DM with CKD.

METHODS

In this prospective cohort study, 43 T2DM patients without CKD or with CKD stage 1-5 were enrolled. Values of parameters, including serum and urine sclerostin, were collected at baseline and 6 months later. For baseline data, the Mann-Whitney U test, χ2 test, or Spearman's correlation were used. For multivariate repeated measurement analysis, generalized estimating equation (GEE) model was utilized.

RESULTS

Patients with lower estimated glomerular filtration rate had higher serum sclerostin, FeP, FeMg, and lower FeCa. By correlation analysis, serum sclerostin was negatively associated with FeCa (p = 0.02) and positively associated with FeP (p = 0.002). The urine sclerostin to creatinine ratio (Uscl/Ucre) was positively correlated with FeP (p = 0.007) and FeMg (p = 0.005). After multivariate analyses by GEE model, serum sclerostin was still inversely associated with FeCa, while Uscl/Ucre was significantly associated with FeMg. On the other hand, FeP lost its associations with serum sclerostin or Uscl/Ucre.

CONCLUSION

In our study population of T2DM patients with or without CKD, the inverse correlation between serum sclerostin and FeCa could not be explained by the calciuric effect of sclerostin. In addition, a newly discovered positive association between urinary sclerostin and FeMg indicated a possible role of urinary sclerostin in regulating renal Mg handling especially over distal convoluted tubules.

Serum sclerostin in acute kidney injury patients

BACKGROUND

Many of the mineral metabolite abnormalities encountered in chronic kidney disease (CKD) patients were found also associated with acute kidney injury (AKI). In the last decade, sclerostin was found to intimately affect bone mineral metabolism in CKD patients. Nothing is known about sclerostin in AKI.

OBJECTIVE

We looked for serum level of sclerostin in AKI patients in comparison to normal control subjects and if there is an impact on metabolic derangement, endothelial function or clinical outcome.

CASES AND METHODS

This is a cross sectional case control observational study of 219 AKI cases (group I) beside 219 age matched normal control subjects (group II). All cases of group I were in the intensive care because of sepsis; 86 had acute on CKD (group Ib), while 133 had de novo AKI (group Ia). All studied subjects underwent estimation of serum sclerostin, parathyroid hormone (PTH), 25 hydroxy vitamin D (25 OH vit D), fibroblast growth factor 23 (FGF23), C-reactive protein (CRP), interleukin 6 (IL6), Homeostatic Model Assessment for Insulin Resistance (Homa IR), beside the routine CBC, kidney and liver function tests, serum calcium, and phosphorus, and flow mediated vasodilation of brachial artery (FMD). Follow-up of group I cases was done till they recovered or passed away.

RESULTS

Serum sclerostin, PTH, FGF23, phosphorus, CRP, IL6, HOMA IR, creatinine, urea, uric acid, ALT, AST and white blood cell count (WBC) were significantly higher while serum calcium, 25 OH vit D, hemoglobin, platelet count and FMD were significantly lower in group I compared to group II (P<0.001 in all). On the other hand, there was no significant difference in serum sclerostin, PTH, FGfF23, 25 OH vit D, CRP, IL6, Homa IR and FMD between group Ia and Ib. Survivors were younger in age (median 55.5 vs. 60 years, P<0.04), had lower AST (30.5 vs. 58 units, P<0.001), had higher platelet count (206 vs 162×109/L, P<0.001), otherwise, there was no significant difference in any of the other parameters between survivors and patients that were lost. Serum sclerostin had strong correlation with FGF23 in group I (r=0.99, P<0.001) and group II (r=1, P<0.001). Homa IR had positive correlation with serum sclerostin (r=0.148, P=0.014) and serum FGF23 (r=0.142, P=0.018) in group I.

CONCLUSION

Sclerostin is intimately related to FGF23. Sclerostin level increases in AKI patients. Both sclerostin and FGF23 might increase insulin resistance but have no impact on FMD. Neither sclerostin nor FGF23 interfere with AKI outcome.

Phosphate and bone fracture risk in chronic kidney disease patients

In chronic kidney disease (CKD), phosphate homoeostasis plays a central role in the development of mineral and bone disorder (MBD) together with decreased serum calcium and elevated serum parathyroid hormone, fibroblast growth factor 23 and sclerostin levels. Today there are only a few data exploring the direct role of abnormal phosphate homoeostasis and hyperphosphataemia in the development of CKD-MBD. On the other hand, several studies have looked at the link between hyperphosphataemia and cardiovascular morbidity and mortality in CKD, but there is a lack of evidence to indicate that lowering phosphate levels improves cardiovascular outcomes in this population. Furthermore, the impact of liberalizing phosphate targets on CKD-MBD progression and bone fracture is currently not known. In this review we discuss the central role of phosphate in the pathogenesis of CKD-MBD and how it may be associated with fracture risk, both in hyper- and hypophosphataemia.

Hyporesponsiveness or resistance to the action of parathyroid hormone in chronic kidney disease

Secondary hyperparathyroidism (SHPT) is an integral component of the chronic kidney disease-mineral and bone disorder (CKD-MBD). Many factors have been associated with the development and progression of SHPT but the presence of skeletal or calcemic resistance to the action of PTH in CKD has often gone unnoticed. The term hyporesponsiveness to PTH is currently preferred and, in this chapter, we will not only review the scientific timeline but also some of the molecular mechanisms behind. Moreover, the presence of resistance to the biological action of PTH is not unique in CKD since resistance to other hormones has also been described ("uremia as a receptor disease"). This hyporesponsiveness carries out important clinical implications since it explains, at least partially, not only the progressive nature of the pathogenesis of CKD-related PTH hypersecretion and parathyroid hyperplasia but also the increasing prevalence of adynamic bone disease in the CKD population. Therefore, we underline the importance of PTH control in all CKD stages, but not aiming to completely normalize PTH levels since a certain degree of SHPT may represent an adaptive clinical response. Future studies at the molecular level, i.e. on uremia, or the recent description of the calcium-sensing receptor as a phosphate sensor, may become of great value beyond their significance to explain just the hyporesponsiveness to PTH in CKD.

Role of the RANK/RANKL/OPG and Wnt/β-Catenin Systems in CKD Bone and Cardiovascular Disorders

In the course of chronic kidney disease (CKD), alterations in the bone-vascular axis augment the risk of bone loss, fractures, vascular and soft tissue calcification, left ventricular hypertrophy, renal and myocardial fibrosis, which markedly increase morbidity and mortality rates. A major challenge to improve skeletal and cardiovascular outcomes in CKD patients requires a better understanding of the increasing complex interactions among the main modulators of the bone-vascular axis. Serum parathyroid hormone (PTH), phosphorus (P), calcium (Ca), fibroblast growth factor 23 (FGF23), calcidiol, calcitriol and Klotho are involved in this axis interact with RANK/RANKL/OPG system and the Wnt/β-catenin pathway. The RANK/RANKL/OPG system controls bone remodeling by inducing osteoblast synthesis of RANKL and downregulating OPG production and it is also implicated in vascular calcification. The complexity of this system has recently increased due the discovery of LGR4, a novel RANKL receptor involved in bone formation, but possibly also in vascular calcification. The Wnt/β-catenin pathway plays a key role in bone formation: when this pathway is activated, bone is formed, but when it is inhibited, bone formation is stopped. In the progression of CKD, a downregulation of the Wnt/β-catenin pathway has been described which occurs mainly through the not coincident elevations of sclerostin, Dickkopf1 (Dkk1) and the secreted Frizzled Related Proteins (sFRPs). This review analyzes the interactions of PTH, P, Ca, FGF23, calcidiol, calcitriol and Klotho with the RANKL/RANKL/OPG system and the Wnt/β-catenin, pathway and their implications in bone and cardiovascular disorders in CKD.

The Non-invasive Diagnosis of Bone Disorders in CKD

Abnormal bone metabolism is an integral part of the chronic kidney disease-mineral bone disorder (CKD-MBD). For several reasons, the difficult bone compartment was neglected for some time, but there has been renewed interest as a result of the conception of bone as a new endocrine organ, the increasing recognition of the cross-talk between bone and vessels, and, especially, the very high risk of osteoporotic fractures (and associated mortality) demonstrated in patients with CKD. Therefore, it has been acknowledged in different guidelines that action is needed in respect of fracture risk assessment and the diagnosis and treatment of osteoporosis in the context of CKD and CKD-MBD, even beyond renal osteodystrophy. These updated guidelines clearly underline the need to improve a non-invasive approach to these bone disorders in order to guide treatment decisions aimed at not only controlling CKD-MBD but also decreasing the risk of fracture. In this report, we review the current role of the most often clinically used or promising biochemical circulating biomarkers such as parathyroid hormone, alkaline phosphatases, and other biochemical markers of bone activity as alternatives to some aspects of bone histomorphometry. We also mention the potential role of classic and new imaging techniques for CKD patients. Information on many aspects is still scarce and heterogeneous, but many of us consider that it is indeed time for action, recognizing our definitely limited ability to base certain treatment decisions only on our current non-comprehensive knowledge.

Sclerostin and osteoprotegerin: new markers of chronic kidney disease mediated mineral and bone disease in children

Background Sclerostin and osteoprotegerin (OPG) are new markers of chronic kidney disease (CKD) mediated mineral bone disease (CKD-MBD) which were extensively evaluated in adult population. We aimed to evaluate the associations between serum levels of sclerostin/OPG and parameters of bone turnover and compare the serum levels of sclerostin/OPG in different stages of CKD in children. Methods 70 children with CKD stage 1-5, aged 2-21 years were examined. Serum levels of alkaline phosphatase (ALP), creatinine, total calcium, phosphorus , intact parathyroid hormone (iPTH) and vitamin D were measured. Serum sclerostin and OPG levels were measured in children with different levels of CKD stage and their association with bone turnover parameters were noted. Results We did not observe any significant correlation between serum levels of sclerostin and OPG and stages of CKD. A negative relationship was present between serum sclerostin and 25-OH vitamin D levels. Osteoprotegerin was positively and significantly correlated with ALP but serum sclerostin was negatively correlated with ALP. Conclusion Our study, which includes only children and adolescents with a growing skeleton under uremic conditions and excluding diabetes and atherosclerosis interference, is very valuable. We couldn't find any significant relationship between either sclerostin or OPG levels among different stages of CKD. Also our study demonstared a strong negative relationship between ALP and sclerostin levels and a strong positive relationship between ALP and OPG levels, reminding the importance of ALP levels to predict the bone-mineral status of the children with CKD.

The endocrine role of bone: Novel functions of bone-derived cytokines

Bone-derived cytokines refer to various proteins and peptides that are released from the skeleton and can distribute in organisms to regulate homeostasis by targeting many organs, such as the pancreas, brain, testicles, and kidneys. In addition to providing support and movement, many studies have disclosed the novel endocrine function of bone, and bone can modulate glucose and energy metabolism as well as phosphate metabolism by versatile bone-derived cytokines. However, this specific exoskeletonfunction of bone-derived cytokines in the regulation of homeostasis and the pathological response caused by skeletal dysfunction are still not very clear, and elucidation of the above mechanisms is of great significance for understanding the pathological processes of metabolic disorders and in the search for novel therapeutic measures for maintaining organ stability and physical fitness.

Osteoporosis in Patients with Chronic Kidney Diseases: A Systemic Review

Chronic kidney disease (CKD) is associated with the development of mineral bone disorder (MBD), osteoporosis, and fragility fractures. Among CKD patients, adynamic bone disease or low bone turnover is the most common type of renal osteodystrophy. The consequences of CKD-MBD include increased fracture risk, greater morbidity, and mortality. Thus, the goal is to prevent the occurrences of fractures by means of alleviating CKD-induced MBD and treating subsequent osteoporosis. Changes in mineral and humoral metabolism as well as bone structure develop early in the course of CKD. CKD-MBD includes abnormalities of calcium, phosphorus, PTH, and/or vitamin D; abnormalities in bone turnover, mineralization, volume, linear growth, or strength; and/or vascular or other soft tissue calcification. In patients with CKD-MBD, using either DXA or FRAX to screen fracture risk should be considered. Biomarkers such as bALP and iPTH may assist to assess bone turnover. Before initiating an antiresorptive or anabolic agent to treat osteoporosis in CKD patients, lifestyle modifications, such as exercise, calcium, and vitamin D supplementation, smoking cessation, and avoidance of excessive alcohol intake are important. Managing hyperphosphatemia and SHPT are also crucial. Understanding the complex pathogenesis of CKD-MBD is crucial in improving one's short- and long-term outcomes. Treatment strategies for CKD-associated osteoporosis should be patient-centered to determine the type of renal osteodystrophy. This review focuses on the mechanism, evaluation and management of patients with CKD-MBD. However, further studies are needed to explore more details regarding the underlying pathophysiology and to assess the safety and efficacy of agents for treating CKD-MBD.

The correlation between sclerostin and bone mineral density in renal transplant recipients

INTRODUCTION

Sclerostin is an anti-anabolic protein synthesized by osteocytes that may cause osteoporosis by inhibiting bone formation. The aim of our study was to investigate the correlation between sclerostin and bone mineral density (BMD) reduction in renal transplant recipients (RTRs) with more than 1 year after transplantation.

MATERIAL AND METHODS

This cross-sectional study was conducted on 80 patients (38 (47.5%) male/42 (52.5%) female) RTRs with a mean age of 44.68±10.39 years. Patients were compared with an age and sex-matched control group of 40 healthy individuals. BMD was measured by dual-energy X-ray absorptiometry. The levels of sclerostin were determined using enzyme-linked immunosorbent assay.

RESULTS

The mean sclerostin was 3.77±0.3pg/mL in patients and 3.81±0.21pg/mL in healthy individuals. The mean T score of femoral trochanter (FT) (FT-T), femoral neck (FN) (FN-T), lumbar vertebrae (L1-4) (L1-4-T) were -0.81±0.86, -1.08±1.09 and -0.8±1.2, respectively. The mean Z score of FT (FT-Z), FN (FN-Z), L1-4 (L1-4-Z) were -0.6±0.73, -0.32±0.9 and -0.54±1.13, respectively. FT-Z and L1-4-Z were lower in patients than healthy subjects (p=0.009, p=0.021 respectively). Serum creatinine (p<0.001), intact parathyroid hormone (p<0.001) were higher and phosphate (p<0.001), was lower in patients than healthy subjects. Patients with a log₁₀ sclerostin of >3.84pg/mL had higher FT-T (p=0.040), FT-Z, FN-T (p=0.018), FN-Z (p=0.006) than those with a log₁₀ sclerostin of ≤3.84pg/mL. There was a significant correlation between log₁₀ sclerostin and FN-T (r=-0.296, p=0.009) and FN-Z (r=-0.269, p=0.019). In linear regression analysis, high sclerostin was found to be correlated with male gender, lower FN-T and lower FN-Z independently of other risk factors.

CONCLUSION

The levels of sclerostin can predict reduction of proximal femur BMD and development of mineral and bone disorder in RTRs. There was no difference in sclerostin levels between RTRs and healthy individuals.

[Low serum Klotho level as a predictor of calcification of the heart and blood vessels in patients with CKD stages 2-5D]

Cardiovascular calcification (CVC) makes a significant contribution to the manifestation of cardiovascular complications in patients with chronic kidney disease. Early CVC markers are currently being actively studied to optimize cardio-renoprotective strategies. We performed a prospective comparative analysis of the following factors: FGF-23, a-Klotho, sclecrostin, phosphate, parathyroid hormone, the estimated glomerular filtration rate (eGFR), central systolic pressure as an independent determinant of CVC.

MATERIALS AND METHODS

The study included 131 patients with chronic kidney disease 25D st. Serum levels of FGF-23, Klotho, and sclerostin were evaluated using the ELISA method. Vascular augmentation (stiffness) indices, central arterial pressure (using the SphygmoCor device), calcification of heart valves and the degree of aortic calcification (aortic radiography) were also investigated. The observation period was 2 years.

RESULTS

According to the Spearman correlation analysis, the percent of calcification increase and the change in Klotho level are most related. According to ROC analysis, a decrease in serum levels of Klotho by 50 units or more is a significant predictor of an increase in aortic calcification of 50% or more with a sensitivity of 86% and a specificity of 77%. Using logistic regression analysis, it was found that a serum Klotho level 632 pg/L predicts an eGFR below a median level of 48 ml/min/1.73 m2 with a sensitivity of 85.5% and a specificity of 78.5%. Wherein OR 17.477 (CI 95% 8.04637.962; p0.001).

CONCLUSION

The factor most associated with CVC is Klotho. Decreased serum level of Klotho is a predictor of aortic calcification. In addition, the initial serum level of Klotho is a predictor of eGFR after 2 years.

Biomarkers in WNT1 and PLS3 Osteoporosis: Altered Concentrations of DKK1 and FGF23

Recent advancements in genetic research have uncovered new forms of monogenic osteoporosis, expanding our understanding of the molecular pathways regulating bone health. Despite active research, knowledge on the pathomechanisms, disease-specific biomarkers, and optimal treatment in these disorders is still limited. Mutations in WNT1, encoding a WNT/β-catenin pathway ligand WNT1, and PLS3, encoding X chromosomally inherited plastin 3 (PLS3), both result in early-onset osteoporosis with prevalent fractures and disrupted bone metabolism. However, despite marked skeletal pathology, conventional bone markers are usually normal in both diseases. Our study aimed to identify novel bone markers in PLS3 and WNT1 osteoporosis that could offer diagnostic potential and shed light on the mechanisms behind these skeletal pathologies. We measured several parameters of bone metabolism, including serum dickkopf-1 (DKK1), sclerostin, and intact and C-terminal fibroblast growth factor 23 (FGF23) concentrations in 17 WNT1 and 14 PLS3 mutation-positive subjects. Findings were compared with 34 healthy mutation-negative subjects from the same families. Results confirmed normal concentrations of conventional metabolic bone markers in both groups. DKK1 concentrations were significantly elevated in PLS3 mutation-positive subjects compared with WNT1 mutation-positive subjects (p < .001) or the mutation-negative subjects (p = .002). Similar differences were not seen in WNT1 subjects. Sclerostin concentrations did not differ between any groups. Both intact and C-terminal FGF23 were significantly elevated in WNT1 mutation-positive subjects (p = .039 and p = .027, respectively) and normal in PLS3 subjects. Our results indicate a link between PLS3 and DKK1 and WNT1 and FGF23 in bone metabolism. The normal sclerostin and DKK1 levels in patients with impaired WNT signaling suggest another parallel regulatory mechanism. These findings provide novel information on the molecular networks in bone. Extended studies are needed to investigate whether these biomarkers offer diagnostic value or potential as treatment targets in osteoporosis. © 2020 American Society for Bone and Mineral Research.

Klotho/FGF23 and Wnt Signaling as Important Players in the Comorbidities Associated with Chronic Kidney Disease

Fibroblast Growth Factor 23 (FGF23) and Klotho play an essential role in the regulation of mineral metabolism, and both are altered as a consequence of renal failure. FGF23 increases to augment phosphaturia, which prevents phosphate accumulation at the early stages of chronic kidney disease (CKD). This effect of FGF23 requires the presence of Klotho in the renal tubules. However, Klotho expression is reduced as soon as renal function is starting to fail to generate a state of FGF23 resistance. Changes in these proteins directly affect to other mineral metabolism parameters; they may affect renal function and can produce damage in other organs such as bone, heart, or vessels. Some of the mechanisms responsible for the changes in FGF23 and Klotho levels are related to modifications in the Wnt signaling. This review examines the link between FGF23/Klotho and Wnt/β-catenin in different organs: kidney, heart, and bone. Activation of the canonical Wnt signaling produces changes in FGF23 and Klotho and vice versa; therefore, this pathway emerges as a potential therapeutic target that may help to prevent CKD-associated complications.

A distinct bone phenotype in ADPKD patients with end-stage renal disease

Autosomal dominant polycystic kidney disease (ADPKD) is among the most common hereditary nephropathies. Low bone turnover osteopenia has been reported in mice with conditional deletion of the PKD1 and PKD2 genes in osteoblasts, and preliminary clinical data also suggest suppressed bone turnover in patients with ADPKD. The present study compared the bone phenotype between patients with end stage renal disease (ESRD) due to ADPKD and controls with ESRD due to other causes. Laboratory parameters of bone mineral metabolism (fibroblast growth factor 23 and sclerostin), bone turnover markers (bone alkaline phosphatase, tartrate-resistant acid phosphatase 5b) and bone mineral density (BMD, by dual energy x-ray absorptiometry, DXA) were assessed in 518 patients with ESRD, including 99 with ADPKD. Bone histomorphometry data were available in 71 patients, including 10 with ADPKD. Circulating levels of bone alkaline phosphatase were significantly lower in patients with ADPKD (17.4 vs 22.6 ng/mL), as were histomorphometric parameters of bone formation. Associations between ADPKD and parameters of bone formation persisted after adjustment for classical determinants including parathyroid hormone, age, and sex. BMD was higher in skeletal sites rich in cortical bone in patients with ADPKD compared to non-ADPKD patients (Z-score midshaft radius -0.04 vs -0.14; femoral neck -0.72 vs -1.02). Circulating sclerostin levels were significantly higher in ADPKD patients (2.20 vs 1.84 ng/L). In conclusion, patients with ESRD due to ADPKD present a distinct bone and mineral phenotype, characterized by suppressed bone turnover, better preserved cortical BMD, and high sclerostin levels.

Sclerostin in chronic kidney disease-mineral bone disorder think first before you block it!

Canonical Wnt signalling activity is a major player in physiological and adaptive bone metabolism. Wnt signalling is regulated by soluble inhibitors, with sclerostin being the most widely studied. Sclerostin's main origin is the osteocyte and its major function is blockade of osteoblast differentiation and function. Therefore, sclerostin is a potent inhibitor of bone formation and mineralization. Consequently, blocking sclerostin via human monoclonal antibodies (such as romosozumab) represents a promising perspective for the treatment of (postmenopausal) osteoporosis. However, sclerostin's physiology and the effects of sclerostin monoclonal antibody treatment are not limited to the skeleton. Specifically, the potential roles of sclerostin in chronic kidney disease (CKD) and associated pathologies covered by the term chronic kidney disease and mineral bone disorder (CKD-MBD), which also includes accelerated cardiovascular calcification, warrant specific attention. CKD-MBD is a complex disease condition in which sclerostin antibodies may interfere at different levels and influence the multiform interplay of hyperparathyroidism, renal osteodystrophy and vascular calcification, but the clinical sequelae remain obscure. The present review summarizes the potential effects of sclerostin blockade in CKD-MBD. We will address and summarize the urgent research targets that are being identified and that need to be addressed before a valid risk-benefit ratio can be established in the clinical setting of CKD.

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.

Bone biomarkers in de novo renal transplant recipients

Successful kidney transplantation (partly) corrects the physiologic and metabolic abnormalities driving chronic kidney disease - mineral and bone disorders. At the same time, renal transplant recipients are exposed to immunosuppressive agents that may affect bone metabolism. Bone biomarkers have been suggested as surrogates of or adjuncts to bone biopsy and imaging techniques to assess bone health and to classify risk of bone loss and fractures. Bone biomarkers may be classified as circulating factors that affect bone metabolism (commonly referred to as bone metabolism markers) or that reflect bone cell number and/or activity (commonly referred to as bone turnover markers). A growing body of evidence shows that successful renal transplantation has a major impact on both bone metabolism and bone turnover. Analytical issues, including the cross-reactivity with fragments, complicate the interpretation of bone biomarkers, especially in the setting of a rapid changing kidney function, as is the case after successful renal transplantation. Overall, bone turnover seems to decline following renal transplantation, but inter-individual variability is substantial. Preliminary evidence indicates that bone biomarkers may be useful in guiding mineral and bone therapy in renal transplant recipients.

Correlation between serum sclerostin level and bone density status in children on regular hemodialysis

Bone disease is frequently observed in chronic kidney disease (CKD) and increases a patient's risk for fracture. Sclerostin is an osteocyte-derived negative regulator of bone formation. We aimed to assess serum sclerostin level as a bone marker in children with CKD on regular hemodialysis (HD) and detect the association between this and bone density status. This cross-sectional comparative study was conducted on 25 children with CKD on HD and 25 age- and sex-matched healthy children, as controls. Their ages ranged from 4 to 18 years. Serum sclerostin levels were measured and dual-energy X-ray absorptiometry scan was performed in the same line with the traditional bone markers. There was a significant increase in serum sclerostin level in patients (1.754 ± 1.31 ng/mL) compared to controls (0.290 ± 0.074 ng/mL) with P = 0.001. Nine patients (36%) had low bone mineral density (BMD) with z score under -2.0, eight of whom had low BMD in both the neck of femur and lumbar spines. There was a significant increase in serum sclerostin levels in the patient-group with low BMD (2.38 ± 0.85 ng/mL) compared with patients with normal BMD (1.4 ± 0.98 ng/mL) (P = 0.001). A significant positive correlation was found between serum sclerostin level and alkaline phosphtase, parathormone with negative correlation with serum calcium. Sclerostin was 100% specific and sensitive in predicting CKD-mineral and bone disorder. Elevated sclerostin levels were consistent with low BMD and appear to be an independent predictor of reduced BMD in children on regular HD.