The bone-vessel axis in chronic kidney disease: An update on biochemical players and its future role in laboratory medicine

Understanding the Korean Dialysis Cohort for Mineral, Vascular Calcification, and Fracture (ORCHESTRA) Study: Design, Method, and Baseline Characteristics

INTRODUCTION

End-stage renal disease (ESRD) is a growing disease worldwide, including Korea. This is an important condition that affects patient outcome. To provide optimal management for mineral disturbance, vascular calcification, and bone disease in ESRD patients, the Korean dialysis cohort for mineral, vascular calcification, and fracture (ORCHESTRA) study was conducted by enrolling Korean dialysis patients.

METHODS

Sixteen university-affiliated hospitals and one Veterans' Health Service Medical Center participated in this study. This prospective cohort study enrolled approximately 900 consecutive patients on dialysis between May 2019 and January 2021. Enrolled subjects were evaluated at baseline for demographic information, laboratory tests, radiologic imaging, and bone mineral densitometry (BMD) scans. After enrollment, regular assessments of the patients were performed, and their biospecimens were collected according to the study protocol. The primary outcomes were the occurrence of major adverse cardiovascular events, invasive treatment for peripheral artery disease, and osteoporotic fractures. The secondary outcomes were hospitalization for cerebrovascular disease or progression of abdominal aortic calcification. Participants will be assessed for up to 3 years to determine whether primary or secondary outcomes occur.

RESULTS

Between May 2019 and January 2021, all participating centers recruited 900 consecutive dialysis patients, including 786 undergoing hemodialysis (HD) and 114 undergoing peritoneal dialysis (PD). The mean age of the subjects was 60.4 ± 12.3 years. Males accounted for 57.7% of the total population. The mean dialysis vintage was 6.1 ± 6.0 years. The HD group was significantly older, had a longer dialysis vintage, and more comorbidities. Overall, the severity of vascular calcification was higher and the level of BMD was lower in the HD group than in the PD group.

CONCLUSION

This nationwide, multicenter, prospective cohort study focused on chronic kidney disease-mineral and bone disorder and aimed to provide clinical evidence to establish optimal treatment guidelines for Asian dialysis patients.

Vascular calcification in peritoneal dialysis patients and its association with bone-derived molecules and bone histomorphometry

INTRODUCTION

Data regarding vascular calcification (VC) in contemporary peritoneal dialysis (PD) patients is scarce. Bone-vascular axis has been demonstrated in hemodialysis (HD). However, studies showing the link between bone disease and VC in PD patients are lacking. The role of sclerostin, dickkopf-related protein 1 (DKK-1), receptor activator for nuclear factor kB ligand and osteoprotegerin (OPG) in VC in PD remains to clarify.

MATERIALS AND METHODS

Bone biopsy was performed in 47 prevalent PD patients with histomorphometric analysis. Patients were submitted to pelvis and hands X-ray to evaluate VC using the Adragão score (AS). Relevant clinical and biochemical data was collected.

RESULTS

Thirteen patients (27.7%) had positive AS (AS≥1). Patients with VC were significantly older (58.9 vs. 50.4 years, p=0.011), had a lower dialysis dose (KT/V 2.0 vs. 2.4, p=0.025) and a higher glycosylated hemoglobin (7.2 vs. 5.4%, p=0.001). There was not any laboratorial parameter of mineral and bone disease used in clinical practice different between patients with or without VC. All diabetic patients had VC but only 8.1% of non-diabetic had VC (p<0.001). Patients with VC showed significantly higher erythrocyte sedimentation rate (ESR) (91.1 vs. 60.0mm/h, p=0.001), sclerostin (2250.0 vs. 1745.8pg/mL, p=0.035), DKK-1 (1451.6 vs. 1042.9pg/mL, p=0.041) and OPG levels (2904.9 vs. 1518.2pg/mL, p=0.002). On multivariate analysis, only ESR remained statistically significant (OR 1.07; 95% CI 1.01-1.14; p=0.022). Bone histomorphometric findings were not different in patients with VC. There was no correlation between bone formation rate and AS (r=-0.039; p=0.796).

CONCLUSION

The presence of VC was not associated with bone turnover and volume evaluated by bone histomorphometry. Inflammation and diabetes seem to play a more relevant role in VC in PD.

Serum OPG and RANKL Levels as Risk Factors for the Development of Cardiovascular Calcifications in End-Stage Renal Disease Patients in Hemodialysis

Cardiovascular calcifications (CVC) are frequently observed in chronic kidney disease (CKD) patients and contribute to their cardiovascular mortality. The aim of the present study was to investigate the impact of osteoprotegerin (OPG)/Receptor Activator of NF-κΒ (RANK)/RANK ligand (RANKL) pathway in the development and evolution of CVCs in hemodialysis patients. In total, 80 hemodialysis patients were assessed for the presence of vascular (abdominal aorta and muscular arteries) calcifications and results were correlated to serum OPG and RANKL levels and the OPG/RANKL ratio. Traditional cardiovascular risk factors and mineral bone disease parameters were also estimated. The presence of VCs was also evaluated 5 years after the initiation of the study, and results were correlated to the initial serum OPG levels. Age, diabetes mellitus, coronary artery disease and OPG levels (p < 0.001) were associated with VCs, whereas RANKL levels were not. Multivariate analysis though revealed that only OPG levels were significantly associated with abdominal aorta calcifications (p = 0.026), but they were not correlated with the progression of VCs. Serum OPG levels are positively and independently associated with VCs in HD patients, but not with their progression. RANKL levels did not show any associations, whereas further studies are needed to establish the significance of OPG/RANKL ratio.

Wnt/β-catenin pathway inhibitors, bone metabolism and vascular health in kidney transplant patients

BACKGROUND AND OBJECTIVES

Sclerostin, dickkopf-related protein 1 (DKK1), fibroblast growth factor-23 (FGF23) and α-klotho have been shown to play an important role in bone and vascular disease of chronic kidney disease. We aimed to evaluate the evolution of these bone markers in newly kidney transplanted patients, and whether they are associated with bone metabolism and vascular stiffness.

DESIGN, SETTING, PARTICIPANTS AND MEASUREMENTS

This is a longitudinal single-center observational cohort study. Circulating levels of Wnt/β-catenin pathway inhibitors (sclerostin, DKK1, FGF23 and α-klotho), arterial stiffness (carotid-femoral pulse-wave velocity (PWV), carotid-radial PWV, PWV ratio, augmented index) and bone parameters were assessed before (M0), and at 3 (M3) and 6 months (M6) after transplantation. Generalized estimating equations were conducted for comparative analyses between the three time points. We used a marginal structural model for repeated measures for the impact of changes in bone markers on the evolution of arterial stiffness. Multivariate linear regression analyses were performed for the associations between Wnt/β-catenin pathway inhibitors and mineral metabolism parameters.

RESULTS

We included 79 patients (70% male; median age of 53 (44-60) years old). The levels of sclerostin (2.06 ± 1.18 ng/mL at M0 to 0.88 ± 0.29 ng/mL at M6, p ≤ 0.001), DKK1 (364.0 ± 266.7 pg/mL at M0 to 246.7 ± 149.1 pg/mL at M6, p ≤ 0.001), FGF23 (5595 ± 9603 RU/mL at M0 to 137 ± 215 RU/mL at M6, p ≤ 0.001) and α-klotho (457.6 ± 148.6 pg/mL at M0 to 109.8 ± 120.7 pg/mL at M6, p < 0.05) decreased significantly after kidney transplant. Sclerostin and FGF23 were positively associated with carotid-femoral (standardized β = 0.432, p = 0.037 and standardized β = 0.592, p = 0.005) and carotid-radial PWV (standardized β = 0.259, p = 0.029 and standardized β = 0.242, p = 0.006) throughout the 6 months of follow-up. The nature of the associations between bone markers and bone metabolism parameters varies after kidney transplant.

CONCLUSIONS

The circulating levels of Wnt/β-catenin pathway inhibitors and α-klotho significantly decrease after kidney transplantation, while sclerostin and FGF23 levels might be associated with improvement of vascular stiffness and blood pressure.

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.

Etelcalcetide controls secondary hyperparathyroidism and raises sclerostin levels in hemodialysis patients previously uncontrolled with cinacalcet

INTRODUCTION

There is scarce clinical experience with etelcalcetide in patients with secondary hyperparathyroidism uncontrolled with cinacalcet. The effect of etelcalcetide on serum sclerostin levels remains to be clarified.

MATERIALS AND METHODS

Prospective cohort study in prevalent hemodialysis patients with uncontrolled sHPT under cinacalcet for at least 3 months, mean parathyroid hormone (PTH)>800pg/mL and calcium (Ca)>8.3mg/dL. Etelcalcetide 5mg IV/HD was initiated after cinacalcet washout. Levels of PTH, Ca, and phosphorus (Pi) followed monthly for 6 months. Plasma sclerostin levels measured before etelcalcetide treatment and after 6 months.

RESULTS

Thirty-four patients were enrolled, 19 (55.9%) male gender. Mean age 60.7 (± 12.3) years; median time on HD 82.5 (7-296) months and median cinacalcet dose was 180mg/week (Interquartile Range: 180-270). Serum Ca, Pi and PTH levels showed a significant reduction after etelcalcetide treatment from 8.8mg/dL, 5.4mg/dL and 1005pg/mL to 8.1mg/dL (p=0.08), 4.9mg/dL (p=0.01) and 702pg/mL (p<0.001), respectively. Median etelcalcetide dose remained at 5mg/HD. Plasma sclerostin concentration increased from 35.66pmol/L (IQR11.94-54.58) to 71.05pmol/L (IQR54.43-84.91) (p<0.0001).

CONCLUSION

Etelcalcetide improved sHPT control in this group of patients, previously under cinacalcet treatment, and significantly increased plasma sclerostin concentration. The impact of etelcalcetide treatment on sclerostin levels is a novel 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.

Vascular Calcification: New Insights Into BMP Type I Receptor A

Vascular calcification (VC) is a complex ectopic calcification process and an important indicator of increased risk for diabetes, atherosclerosis, chronic kidney disease, and other diseases. Therefore, clarifying the pathogenesis of VC is of great clinical significance. Numerous studies have shown that the onset and progression of VC are similar to bone formation. Members of the bone morphogenetic protein (BMP) family of proteins are considered key molecules in the progression of vascular calcification. BMP type I receptor A (BMPR1A) is a key receptor of BMP factors acting on the cell membrane, is widely expressed in various tissues and cells, and is an important “portal” for BMP to enter cells and exert their biological effect. In recent years, many discoveries have been made regarding the occurrence and treatment of ectopic ossification-related diseases involving BMP signaling targets. Studies have confirmed that BMPR1A is involved in osteogenic differentiation and that its high expression in vascular endothelial cells and smooth muscle cells can lead to vascular calcification. This article reviews the role of BMPR1A in vascular calcification and the possible underlying molecular mechanisms to provide clues for the clinical treatment of such diseases.

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.

Inspiration for the prevention and treatment of neuropsychiatric disorders: New insight from the bone-brain-axis

Bone is the main supporting structure of the body and the main organ involved in body movement and calcium and phosphorus metabolism. Recent studies have shown that bone is also a potential new endocrine organ that participates in the physiological and pathophysiological processes of the cardiovascular, digestive, and endocrine systems through various bioactive cytokines secreted by bone cells and bone marrow. Bone-derived active cytokines can also directly act on the central nervous system and regulate brain function and individual behavior. The bidirectional regulation of the bone-brain axis has gradually attracted attention in the field of neuroscience. This paper reviews the regulatory effects of bone-derived active cytokines and bone-derived cells on individual brain function and brain diseases, as well as the occurrence and development of related neuropsychiatric diseases. The central regulatory mechanism function is briefly introduced, which will broaden the scope for mechanistic research and help establish prevention and treatment strategies for neuropsychiatric diseases based on the bone-brain axis.

Understanding the Stony Bridge between Osteoporosis and Vascular Calcification: Impact of the FGF23/Klotho axis

A relationship between osteoporosis (OP) and vascular calcification (VC) is now proposed. There are common mechanisms underlying the regulation of them. Fibroblast growth factor- (FGF-) 23 and Klotho are hormones associated with the metabolic axis of osteovascular metabolism. Most recently, it was suggested that the FGF23-klotho axis is associated with increasing incidence of fractures and is potentially involved in the progression of the aortic-brachial stiffness ratio. Herein, we discussed the potential role of the FGF23/Klotho axis in the pathophysiology of OP and VC. We want to provide an update review in order to allow a better understanding of the potential role of the FGF23/Klotho axis in comorbidity of OP and VC. We believe that a better understanding of the relationship between both entities can help in proposing new therapeutic targets for reducing the increasing prevalence of OP and VC in the aging population.

Chronic Kidney Disease-Mineral and Bone Disorders: Pathogenesis and Management

The key players of the chronic kidney disease-mineral and bone disorders (CKD-MBD) are calcium, phosphate, PTH, FGF23, and the vitamin D hormonal system. The progressive reduction of kidney function greatly modifies the tightly interrelated mechanisms that control these parameters. As a result, important changes occur in the bone and mineral hormonal axis, leading to changes in bone turnover with relevant consequences in clinical outcomes, such as decrease in bone mass with increased bone fragility and bone fractures and increased vascular and valvular calcification, also with great impact in the cardiovascular outcomes. So far, the knowledge of the mineral and bone disorders in CKD and the increased variety of efficacious therapies should lead to a better prevention and management of CKD-MBD.

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.