Markers of bone metabolism are affected by renal function and growth hormone therapy in children with chronic kidney disease

Growth hormone in pediatric chronic kidney disease: more than just height

Recombinant human growth hormone therapy, which was introduced in the 1980s, is now routine for children with advanced chronic kidney disease (CKD) who are exhibiting growth impairment. Growth hormone usage remains variable across different centers, with some showing low uptake. Much of the focus on growth hormone supplementation has been on increasing height because of social and psychological effects of short stature. There are, however, numerous other changes that occur in CKD that have not received as much attention but are biologically important for pediatric growth and development. This article reviews the current knowledge about the multisystem effects of growth hormone therapy in pediatric patients with CKD and highlights areas where additional clinical research is needed. We also included clinical data on children and adults who had received growth hormone for other indications apart from CKD. Ultimately, having robust clinical studies which examine these effects will allow children and their families to make more informed decisions about this therapy.

Chronic kidney disease mineral bone disorder in childhood and young adulthood: a 'growing' understanding

Chronic kidney disease (CKD) mineral and bone disorder (MBD) comprises a triad of biochemical abnormalities (of calcium, phosphate, parathyroid hormone and vitamin D), bone abnormalities (turnover, mineralization and growth) and extra-skeletal calcification. Mineral dysregulation leads to bone demineralization causing bone pain and an increased fracture risk compared to healthy peers. Vascular calcification, with hydroxyapatite deposition in the vessel wall, is a part of the CKD-MBD spectrum and, in turn, leads to vascular stiffness, left ventricular hypertrophy and a very high cardiovascular mortality risk. While the growing bone requires calcium, excess calcium can deposit in the vessels, such that the intake of calcium, calcium- containing medications and high calcium dialysate need to be carefully regulated. Normal physiological bone mineralization continues into the third decade of life, many years beyond the rapid growth in childhood and adolescence, implying that skeletal calcium requirements are much higher in younger people compared to the elderly. Much of the research into the link between bone (de)mineralization and vascular calcification in CKD has been performed in older adults and these data must not be extrapolated to children or younger adults. In this article, we explore the physiological changes in bone turnover and mineralization in children and young adults, the pathophysiology of mineral bone disease in CKD and a potential link between bone demineralization and vascular calcification.

Changes in bone biomarkers in response to different dosing regimens of cholecalciferol supplementation in children with chronic kidney disease

BACKGROUND

The effect of different dosing regimens of cholecalciferol supplementation on bone biomarkers has not been studied in children with chronic kidney disease (CKD).

METHODS

This is a post hoc analysis of a multi-center randomized controlled trial which included children with CKD stages 2-4 with vitamin D deficiency (25-hydroxy vitamin D (25OHD) < 30 ng/ml) randomized 1:1:1 to receive an equivalent dose of oral cholecalciferol as daily, weekly or monthly treatment. Markers of bone formation (bone alkaline phosphatase (BAP), procollagen I N terminal peptide (PINP)), bone resorption (tartarate-resistant acid phosphatase 5b (TRAP), C terminal telopeptide (CTX)), and osteocyte markers (intact fibroblast growth factor 23 (iFGF23), sclerostin) and soluble klotho were measured at baseline and after 3 months of intensive replacement therapy. The change in biomarkers and ratio of markers of bone formation to resorption were compared between treatment arms. BAP and TRAP were expressed as age- and sex-specific z-scores.

RESULTS

25OHD levels increased with cholecalciferol supplementation, with 85% achieving normal levels. There was a significant increase in the BAP/TRAP ratio (p = 0.04), iFGF23 (p = 0.004), and klotho (p = 0.002) with cholecalciferol therapy, but this was comparable across all three therapy arms. The BAPz was significantly higher in the weekly arm (p = 0.01). The change in 25OHD (Δ25OHD) inversely correlated with ΔPTH (r =  - 0.4, p < 0.001).

CONCLUSIONS

Although cholecalciferol supplementation was associated with a significant increase in bone formation, the three dosing regimens of cholecalciferol supplementation have a comparable effect on the bone biomarker profile, suggesting that they can be used interchangeably to suit the patient's needs and optimize adherence to therapy. A higher resolution version of the Graphical abstract is available as Supplementary information.

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.

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.

Vitamin D and Glomerulonephritis

Vitamin D presents a plethora of different functions that go beyond its role in skeletal homeostasis. It is an efficient endocrine regulator of the Renin–Angiotensin–Aldosterone System (RAAS) and erythropoiesis, exerts immunomodulatory effects, reduces the cardiovascular events and all-cause mortality. In Chronic Kidney Disease (CKD) patients, Vitamin D function is impaired; the renal hydrolyzation of its inactive form by the action of 1α-hydroxylase declines at the same pace of reduced nephron mass. Moreover, Vitamin D major carrier, the D-binding protein (DBP), is less represented due to Nephrotic Syndrome (NS), proteinuria, and the alteration of the cubilin–megalin–amnionless receptor complex in the renal proximal tubule. In Glomerulonephritis (GN), Vitamin D supplementation demonstrated to significantly reduce proteinuria and to slow kidney disease progression. It also has potent antiproliferative and immunomodulating functions, contributing to the inhibitions of kidney inflammation. Vitamin D preserves the structural integrity of the slit diaphragm guaranteeing protective effects on podocytes. Activated Vitamin D has been demonstrated to potentiate the antiproteinuric effect of RAAS inhibitors in IgA nephropathy and Lupus Nephritis, enforcing its role in the treatment of glomerulonephritis: calcitriol treatment, through Vitamin D receptor (VDR) action, can regulate the heparanase promoter activity and modulate the urokinase receptor (uPAR), guaranteeing podocyte preservation. It also controls the podocyte distribution by modulating mRNA synthesis and protein expression of nephrin and podocin. Maxalcalcitol is another promising alternative: it has about 1/600 affinity to vitamin D binding protein (DBP), compared to Calcitriol, overcoming the risk of hypercalcemia, hyperphosphatemia and calcifications, and it circulates principally in unbound form with easier availability for target tissues. Doxercalciferol, as well as paricalcitol, showed a lower incidence of hypercalcemia and hypercalciuria than Calcitriol. Paricalcitol demonstrated a significant role in suppressing RAAS genes expression: it significantly decreases angiotensinogen, renin, renin receptors, and vascular endothelial growth factor (VEGF) mRNA levels, thus reducing proteinuria and renal damage. The purpose of this article is to establish the Vitamin D role on immunomodulation, inflammatory and autoimmune processes in GN.

An innovative and cost-effective way to estimate alkaline phosphatase activity in in vitro cellular model systems

Alkaline phosphatase is an enzyme that converts para-nitrophenyl phosphate to para-nitrophenol (yellow coloured) in 2-amino, 2-methyl, 1-propanol buffer at pH 10.5. However, when this protocol is applied to the in vitro cellular model systems to estimate alkaline phosphatase activity, it tends to generate clumps of genomic DNA, leading to inaccurate pipetting for protein estimation. The aim of the study was to introduce minor modifications in the existing protocol to make it simple, cost-effective, with minimal labor-intensive procedures while estimating alkaline phosphatase activity in cellular model systems. The genomic DNA clumps were dissolved by depurination (adding 0.2 N HCl) and fragmentation (adding 0.2 N NaOH) during enzyme estimation. Moreover, these minor modifications have been standardized and optimized extensively by using serum samples (rich source of alkaline phosphatase), hFOB/ER9 (human Fetal osteoblastic cell) and HepG2 cells. Our results suggest that the modification incorporated in previously published method was robust enough to estimate ALP activity and protein concentration accurately. There was no significant variation in ALP activity estimated after modification (P > 0.05). This innovative approach could be beneficial for a researcher by providing an easy, cost effective and less labor-intensive solution for estimation of enzymatic activity in cellular model systems.

Serum and Urinary Osteocalcin in Healthy 7- to 19-Year-Old Finnish Children and Adolescents

Children and adolescents have high bone turnover marker (BTM) levels due to high growth velocity and rapid bone turnover. Pediatric normative values for BTMs reflecting bone formation and resorption are vital for timely assessment of healthy bone turnover, investigating skeletal diseases, or monitoring treatment outcomes. Optimally, clinically feasible measurement protocols for BTMs would be validated and measurable in both urine and serum. We aimed to (a) establish sex- and age-specific reference intervals for urinary and serum total and carboxylated osteocalcin (OC) in 7- to 19-year-old healthy Finnish children and adolescents (n = 172), (b) validate these against standardized serum and urinary BTMs, and (c) assess the impact of anthropometry, pubertal status, and body composition on the OC values. All OC values in addition to other BTMs increased with puberty and correlated with pubertal growth, which occurred and declined earlier in girls than in boys. The mean serum total and carboxylated OC and urinary OC values and percentiles for sex-specific age categories and pubertal stages were established. Correlation between serum and urinary OC was weak, especially in younger boys, but improved with increasing age. The independent determinants for OC varied, the urinary OC being the most robust while age, height, weight, and plasma parathyroid hormone (PTH) influenced serum total and carboxylated OC values. Body composition parameters had no influence on any of the OC values. In children and adolescents, circulating and urinary OC reflect more accurately growth status than bone mineral density (BMD) or body composition. Thus, validity of OC, similar to other BTMs, as a single marker of bone turnover, remains limited. Yet, serum and urinary OC similarly to other BTMs provide a valuable supplementary tool when assessing longitudinal changes in bone health with repeat measurements, in combination with other clinically relevant parameters.

Serum indoxyl sulfate concentrations associate with progression of chronic kidney disease in children

The uremic toxins indoxyl sulfate (IS) and p-cresyl sulfate (pCS) accumulate in patients with chronic kidney disease (CKD) as a consequence of altered gut microbiota metabolism and a decline in renal excretion. Despite of solid experimental evidence for nephrotoxic effects, the impact of uremic toxins on the progression of CKD has not been investigated in representative patient cohorts. In this analysis, IS and pCS serum concentrations were measured in 604 pediatric participants (mean eGFR of 27 ± 11 ml/min/1.73m2) at enrolment into the prospective Cardiovascular Comorbidity in Children with CKD study. Associations with progression of CKD were analyzed by Kaplan-Meier analyses and Cox proportional hazard models. During a median follow up time of 2.2 years (IQR 4.3-0.8 years), the composite renal survival endpoint, defined as 50% loss of eGFR, or eGFR <10ml/min/1.73m2 or start of renal replacement therapy, was reached by 360 patients (60%). Median survival time was shorter in patients with IS and pCS levels in the highest versus lowest quartile for both IS (1.5 years, 95%CI [1.1,2.0] versus 6.0 years, 95%CI [5.0,8.4]) and pCS (1.8 years, 95%CI [1.5,2.8] versus 4.4 years, 95%CI [3.4,6.0]). Multivariable Cox regression disclosed a significant association of IS, but not pCS, with renal survival, which was independent of other risk factors including baseline eGFR, proteinuria and blood pressure. In this exploratory analysis we provide the first data showing a significant association of IS, but not pCS serum concentrations with the progression of CKD in children, independent of other known risk factors. In the absence of comorbidities, which interfere with serum levels of uremic toxins, such as diabetes, obesity and metabolic syndrome, these results highlight the important role of uremic toxins and accentuate the unmet need of effective elimination strategies to lower the uremic toxin burden and abate progression of CKD.

Relationship between GFR, intact PTH, oxidized PTH, non-oxidized PTH as well as FGF23 in patients with CKD

Fibroblast growth factor 23 (FGF23) and parathyroid hormone (PTH) are regulators of renal phosphate excretion and vitamin D metabolism. In chronic kidney disease (CKD), circulating FGF23 and PTH concentrations progressively increase as renal function declines. Oxidation of PTH at two methionine residues (positions 8 and 18) causes a loss of function. The impact of n-oxPTH and oxPTH on FGF23 synthesis, however, and how n-oxPTH and oxPTH concentrations are affected by CKD, is yet unknown. The effects of oxidized and non-oxidized PTH 1-34 on Fgf23 gene expression were analyzed in UMR106 osteoblast-like cells. Furthermore, we investigated the relationship between n-oxPTH and oxPTH, respectively, with FGF23 in two independent patients' cohorts (620 children with CKD and 600 kidney transplant recipients). While n-oxPTH stimulated Fgf23 mRNA synthesis in vitro, oxidation of PTH in particular at Met8 led to a markedly weaker stimulation of Fgf23. The effect was even stronger when both Met8 and Met18 were oxidized. In both clinical cohorts, n-oxPTH-but not oxPTH-was significantly associated with FGF23 concentrations, independent of known confounding factors. Moreover, with progressive deterioration of kidney function, intact PTH (iPTH) and oxPTH increased substantially, whereas n-oxPTH increased only moderately. In conclusion, n-oxPTH, but not oxPTH, stimulates Fgf23 gene expression. The increase in PTH with decreasing GFR is mainly due to an increase in oxPTH in more advanced stages of CKD.

Bone and Mineral Metabolism in Children with Nephropathic Cystinosis Compared with other CKD Entities

CONTEXT

Children with nephropathic cystinosis (NC) show persistent hypophosphatemia, due to Fanconi syndrome, as well as mineral and bone disorders related to chronic kidney disease (CKD); however, systematic analyses are lacking.

OBJECTIVE

To compare biochemical parameters of bone and mineral metabolism between children with NC and controls across all stages of CKD.

DESIGN

Cross-sectional multicenter study.

SETTING

Hospital clinics.

PATIENTS

Forty-nine children with NC, 80 CKD controls of the same age and CKD stage.

MAIN OUTCOME MEASURES

Fibroblast growth factor 23 (FGF23), soluble Klotho, bone alkaline phosphatase (BAP), tartrate-resistant acid phosphatase 5b (TRAP5b), sclerostin, osteoprotegerin (OPG), biochemical parameters related to mineral metabolism, and skeletal comorbidity.

RESULTS

Despite Fanconi syndrome medication, NC patients showed an 11-fold increased risk of short stature, bone deformities, and/or requirement for skeletal surgery compared with CKD controls. This was associated with a higher frequency of risk factors such as hypophosphatemia, hypocalcemia, low parathyroid hormone (PTH), metabolic acidosis, and a specific CKD stage-dependent pattern of bone marker alterations. Pretransplant NC patients in mild to moderate CKD showed a delayed increase or lacked an increase in FGF23 and sclerostin, and increased BAP, TRAP5b, and OPG concentrations compared with CKD controls. Post-transplant, BAP and OPG returned to normal, TRAP5b further increased, whereas FGF23 and PTH were less elevated compared with CKD controls and associated with higher serum phosphate.

CONCLUSIONS

Patients with NC show more severe skeletal comorbidity associated with distinct CKD stage-dependent alterations of bone metabolism than CKD controls, suggesting impaired mineralization and increased bone resorption, which is only partially normalized after renal transplantation.

Isolated nocturnal and isolated daytime hypertension associate with altered cardiovascular morphology and function in children with chronic kidney disease: findings from the Cardiovascular Comorbidity in Children with Chronic Kidney Disease study

INTRODUCTION

Prevalence of isolated nocturnal hypertension (INH) and isolated daytime hypertension (IDH) is around 10% in adults. Data in children, especially in chronic kidney disease (CKD), are lacking. The aim of this cross-sectional multicenter cohort study was to define the prevalence of INH and IDH and its association with cardiovascular morphology and function, that is, pulse wave velocity (PWV), carotid intima-media thickness (cIMT), or left ventricular mass index (LVMI) in children with CKD.

METHODS

Ambulatory blood pressure (BP) monitoring profiles were analyzed in 456 children with CKD stages III-V participating in the Cardiovascular Comorbidity in Children with Chronic Kidney Disease Study (64.3% males, 71.3% congenital anomaly of the kidney and urinary tract, age 12.5 ± 3.2 years, estimated glomerular filtration rate 29 ± 12 ml/min per 1.73 m). Baseline PWV, cIMT, and LVMI were compared in normotension, INH, IDH, or sustained 24-h hypertension.

RESULTS

Prevalence of sustained hypertension was 18.4%, of INH 13.4%, and of IDH 3.7%. PWV SDS (SD score) and cIMT SDS were significantly higher in sustained hypertension and INH, and PWV SDS was significantly higher in IDH, compared with normotension. LVMI was significantly increased in sustained hypertension, but not in INH or IDH. Determinants of INH were smallness for gestational age, older age, higher height SDS and parathyroid hormone, and shorter duration of CKD. In logistic regression analysis, day/night-time hypertension or ambulatory BP monitoring pattern (normal, INH, IDH, sustained hypertension) were independently associated with cardiovascular outcome measures: elevated night-time BP was associated with increased cIMT, PWV, and left ventricular hypertrophy; INH was associated with cIMT.

CONCLUSION

INH is present in almost one out of seven children with predialysis CKD; INH and nocturnal hypertension in general are associated with alterations of arterial morphology and function.

Assessing bone mineralisation in children with chronic kidney disease: what clinical and research tools are available?

Mineral and bone disorder in chronic kidney disease (CKD-MBD) is a triad of biochemical imbalances of calcium, phosphate, parathyroid hormone and vitamin D, bone abnormalities and soft tissue calcification. Maintaining optimal bone health in children with CKD is important to prevent long-term complications, such as fractures, to optimise growth and possibly also to prevent extra-osseous calcification, especially vascular calcification. In this review, we discuss normal bone mineralisation, the pathophysiology of dysregulated homeostasis leading to mineralisation defects in CKD and its clinical consequences. Bone mineralisation is best assessed on bone histology and histomorphometry, but given the rarity with which this is performed, we present an overview of the tools available to clinicians to assess bone mineral density, including serum biomarkers and imaging such as dual-energy X-ray absorptiometry and peripheral quantitative computed tomography. We discuss key studies that have used these techniques, their advantages and disadvantages in childhood CKD and their relationship to biomarkers and bone histomorphometry. Finally, we present recommendations from relevant guidelines-Kidney Disease Improving Global Outcomes and the International Society of Clinical Densitometry-on the use of imaging, biomarkers and bone biopsy in assessing bone mineral density. Given low-level evidence from most paediatric studies, bone imaging and histology remain largely research tools, and current clinical management is guided by serum calcium, phosphate, PTH, vitamin D and alkaline phosphatase levels only.

Strategies for Optimizing Growth in Children With Chronic Kidney Disease

Growth failure is a hallmark in children with chronic kidney disease (CKD). Therefore, early diagnosis and adequate management of growth failure is of utmost importance in these patients. The risk of severe growth retardation is the higher the younger the child is, which places an additional burden on patients and their families and hampers the psychosocial integration of these children. Careful monitoring of growth, and effective interventions are mandatory to prevent and treat growth failure in children with CKD at all ages and all stages of kidney failure. Early intervention is critical, as all therapeutic interventions are much more effective if they are started prior to the initiation of dialysis. Prevention and treatment of growth failure focuses on: (i) preservation of renal function, e.g., normalization of blood pressure and proteinuria by use of inhibitors of the renin-angiotensin aldosterone system, (ii) adequate energy intake, including tube feeding or gastrostomy in case of persisting malnutrition, (iii) substitution of water and electrolytes, especially in children with renal malformation, (iv) correction of metabolic acidosis, (v) control of parathyroid hormone levels within the CKD-dependent target range, (vi) use of recombinant human growth hormone in cases of persistent growth failure, and, (vii) early/preemptive kidney transplantation using steroid-minimizing immunosuppressive protocols in children with end-stage CKD. This review discusses these measures based on recent guidelines.

Indoxyl sulfate associates with cardiovascular phenotype in children with chronic kidney disease

BACKGROUND

Cardiovascular disease is the leading cause of death in children with chronic kidney disease (CKD). Serum levels of gut-derived uremic toxins increase with deterioration of kidney function and are associated with cardiac comorbidities in adult CKD patients.

METHODS

Indoxyl sulfate (IS) and p-cresyl sulfate (pCS) were measured by high-performance liquid chromatography in serum of children participating in the Cardiovascular Comorbidity in Children with CKD (4C) Study. Results were correlated with measurements of the carotid intima-media thickness (cIMT), central pulse wave velocity (PWV), and left ventricular mass index (LVMI) in children aged 6-17 years with initial eGFR of 10-60 ml/min per 1.73 m².

RESULTS

The median serum levels of total IS and of pCS, measured in 609 patients, were 5.3 μmol/l (8.7) and 17.0 μmol/l (21.6), respectively. In a multivariable regression model, IS and pCS showed significant positive associations with urea and negative associations with eGFR and uric acid. Furthermore, positive associations of pCS with age, serum albumin, and non-Mediterranean residency and a negative association with glomerular disease were observed. By multivariable regression analysis, only IS was significantly associated with a higher cIMT SDS at baseline and progression of PWV SDS within 12 months, independent of other risk factors.

CONCLUSIONS

Serum levels of gut-derived uremic toxins IS and pCS correlated inversely with eGFR in children. Only IS was significantly associated with surrogate markers of cardiovascular disease in this large pediatric CKD cohort.

Effects of nutritional vitamin D supplementation on markers of bone and mineral metabolism in children with chronic kidney disease

Background

We investigated the effects of nutritional vitamin D supplementation on markers of bone and mineral metabolism, i.e. serum levels of fibroblast growth factor 23 (FGF23), Klotho, bone alkaline phosphatase (BAP) and sclerostin, in two cohorts with chronic kidney disease (CKD).

Methods

In all, 80 vitamin D-deficient children were selected: 40 with mild to moderate CKD from the ERGO study, a randomized trial of ergocalciferol supplementation [estimated glomerular filtration rate (eGFR) 55 mL/min/1.73 m2], and 40 with advanced CKD from the observational Cardiovascular Comorbidity in Children with Chronic Kidney Disease (4C) study (eGFR 24 mL/min/1.73 m2). In each study, vitamin D supplementation was started in 20 children and 20 matched children not receiving vitamin D served as controls. Measures were taken at baseline and after a median period of 8 months. Age- and gender-related standard deviation scores (SDSs) were calculated.

Results

Before vitamin D supplementation, children in the ERGO study had normal FGF23 (median 0.31 SDS) and BAP (-0.10 SDS) but decreased Klotho and sclerostin (-0.77 and -1.04 SDS, respectively), whereas 4C patients had increased FGF23 (3.87 SDS), BAP (0.78 SDS) and sclerostin (0.76 SDS) but normal Klotho (-0.27 SDS) levels. Vitamin D supplementation further increased FGF23 in 4C but not in ERGO patients. Serum Klotho and sclerostin normalized with vitamin D supplementation in ERGO but remained unchanged in 4C patients. BAP levels were unchanged in all patients. In the total cohort, significant effects of vitamin D supplementation were noted for Klotho at eGFR 40-70 mL/min/1.73 m2.

Conclusions

Vitamin D supplementation normalized Klotho and sclerostin in children with mild to moderate CKD but further increased FGF23 in advanced CKD.

Vigier R, Zustin J, Haffner D. Management of bone disease in cystinosis: Statement from an international conference

Cystinosis is an autosomal recessive storage disease due to impaired transport of cystine out of lysosomes. Since the accumulation of intracellular cystine affects all organs and tissues, the management of cystinosis requires a specialized multidisciplinary team consisting of pediatricians, nephrologists, nutritionists, ophthalmologists, endocrinologists, neurologists' geneticists, and orthopedic surgeons. Treatment with cysteamine can delay or prevent most clinical manifestations of cystinosis, except the renal Fanconi syndrome. Virtually all individuals with classical, nephropathic cystinosis suffer from cystinosis metabolic bone disease (CMBD), related to the renal Fanconi syndrome in infancy and progressive chronic kidney disease (CKD) later in life. Manifestations of CMBD include hypophosphatemic rickets in infancy, and renal osteodystrophy associated with CKD resulting in bone deformities, osteomalacia, osteoporosis, fractures, and short stature. Assessment of CMBD involves monitoring growth, leg deformities, blood levels of phosphate, electrolytes, bicarbonate, calcium, and alkaline phosphatase, periodically obtaining bone radiographs, determining levels of critical hormones and vitamins, such as thyroid hormone, parathyroid hormone, 25(OH) vitamin D, and testosterone in males, and surveillance for nonrenal complications of cystinosis such as myopathy. Treatment includes replacement of urinary losses, cystine depletion with oral cysteamine, vitamin D, hormone replacement, physical therapy, and corrective orthopedic surgery. The recommendations in this article came from an expert meeting on CMBD that took place in Salzburg, Austria, in December 2016.

C-type natriuretic peptide attenuates renal osteodystrophy through inhibition of FGF-23/MAPK signaling

Renal osteodystrophy (ROD) occurs as early as chronic kidney disease (CKD) stage 2 and seems ubiquitous in almost all pediatric patients with CKD stage 5. Fibroblast growth factor (FGF)-23, a bone-derived endocrine regulator of phosphate homeostasis, is overexpressed in CKD and disturbs osteoblast differentiation and matrix mineralization. In contrast, C-type natriuretic peptide (CNP) acts as a potent positive regulator of bone growth. In the present study, we infused CNP into uremic rats and observed whether CNP could attenuate ROD through the inhibition of FGF-23 cascades. In uremic rats, CNP administration significantly alleviated renal dysfunction, calcium phosphate metabolic disorders, hypovitaminosis D, secondary hyperparathyroidism, the decrease in bone turnover markers and retarded bone pathological progression. More importantly, within FGF-23/mitogen-activated protein kinase (MAPK) signaling, the fibroblast growth factor receptor-1, Klotho and alternative (STAT-1/phospho-STAT-1) elements were upregulated by CNP, whereas FGF-23, RAF-1/phospho-RAF-1, and downstream (ERK/phospho-ERK and P38/phospho-P38) elements were paradoxically underexpressed in bone tissue. Therefore, CNP exerts a therapeutic effect on ROD through inhibition of FGF-23/MAPK signaling at the RAF-1 level.

Twenty years of growth hormone treatment in dialyzed children in Poland-Results of national multicenter study

PURPOSE

The aim of the study was to analyze the effect of recombinant human growth hormone (rhGH) therapy and to establish factors influencing growth rate in dialyzed children in Poland.

METHODS

We retrospectively analyzed medical records of 81 children with end-stage renal disease (ESRD) on chronic dialysis treated with rhGH for ≥12 months between 1994 and 2014. The following data were recorded: cause of ESRD, dialysis modality, age at the dialysis and rhGH initiation [years]. In addition, growth [cm], [standard deviation score - SDS], body mass index [SDS], skeletal age [years], bone mineral density [SDS], hemoglobin, total protein, albumin, urea, creatinine, calcium, phosphorus, calcium phosphorus product, PTH, and alkaline phosphatase were measured at the baseline and after 12 months.

RESULTS

Growth velocity in 81 children during one-year rhGH treatment was 7.33 ± 2.63 cm (ΔSDS 0.36 ± 0.43). Height SDS increased significantly (-3.31 ± 1.12 vs. -2.94 ± 1.15, p < 0.001). Children on peritoneal dialysis (PD) (n = 51) were younger than children on hemodialysis (HD) (n = 30) (9.92 ± 3.72 vs. 12.32 ± 3.11 years, p = 0.003). ΔSDS did not differ between PD and HD children (0.40 ± 0.33 vs. 0.30 ± 0.47, p = 0.311). Growth velocity (ΔSDS) correlated with age at dialysis initiation (r=-0.30, p = 0.009), age at rhGH treatment initiation (r=-0.35, p = 0.002), skeletal age (r=-0.36, p = 0.002), BMI SDS (r=-0.27, p = 0.019), and PTH (r=-0.27, p = 0.017). No correlation between growth velocity and other parameters was observed.

CONCLUSIONS

Treatment with rhGH in children with ESRD is effective and safe irrespective of dialysis modality. Early initiation of rhGH therapy is a crucial factor determining response to the treatment in children with ESRD.

Cardiovascular risk in children and adolescents with end stage renal disease

OBJECTIVES

To evaluate cardiovascular involvement in children and adolescents with End Stage Renal Disease (ESRD) and to characterize the main risk factors associated with this outcome.

METHODS

Cross-sectional study of 69 children and adolescents at renal transplantation and 33 healthy individuals matched by age and gender. The study outcomes were left ventricular mass z-score (LVMZ) and carotid artery intima-media thickness (CIMT). The potential risk factors considered were age, gender, CKD etiology, use of oral vitamin D and calcium-based phosphate binders, systolic and diastolic blood pressure, body mass index z-score, time since diagnosis, dialysis duration, serum levels of ionic calcium, phosphorus, parathyroid hormone, fibroblast growth factor (FGF 23), uric acid, homocysteine, cholesterol, triglycerides, C-reactive protein (CRP), vitamin D and hemoglobin.

RESULTS

In the multivariate analysis, the factors associated with LVMZ were dialysis duration, age, systolic blood pressure, serum hemoglobin and HDL cholesterol levels. Regarding CIMT, in the multivariate analysis, systolic blood pressure was the only factor associated with the outcome.

CONCLUSION

Children exhibited important cardiovascular involvement at the time of the renal transplantation. Both of the studied outcomes were independently associated with systolic blood pressure. For this reason, controlling blood pressure seems to be the main therapy to minimize cardiovascular involvement in children with ESRD.

Fibroblast growth factor-23 may serve as a novel biomarker for renal osteodystrophy progression

The purpose of the present study was to determine whether fibroblast growth factor (FGF)‑23 could serve as a novel biomarker for renal osteodystrophy (ROD) progression. A rat model of ROD was induced by left nephrectomy plus intravenous injection of Adriamycin. Serum FGF‑23 was determined using an enzyme‑linked immunosorbent assay. Serum level and bone expression of FGF‑23 were both significantly elevated in the ROD group at 24 h post‑surgery. Serum FGF‑23 was negatively correlated with calcium, phosphate, 25‑hydroxyvitamin D, conventional bone biomarkers and bone collagen X. More importantly, serum FGF‑23 was significantly associated with abnormalities in bone formation rate, osteoblasts, osteoclasts, trabecular volume thickness and osteoid volume. Therefore, FGF‑23 may serve as a novel biomarker for ROD.

Analysis of Circulating Mediators of Bone Remodeling in Prader-Willi Syndrome

We tested the hypothesis that the levels of bone remodeling mediators may be altered in Prader-Willi syndrome (PWS). We assessed RANKL, OPG, sclerostin, DKK-1 serum levels, and bone metabolism markers in 12 PWS children (7.8 ± 4.3 years), 14 PWS adults (29.5 ± 7.2 years), and 31 healthy controls matched for sex and age. Instrumental parameters of bone mineral density (BMD) were also evaluated. Lumbar spine BMD Z-scores were reduced in PWS children (P < 0.01), reaching osteopenic levels in PWS adults. PWS patients showed lower 25(OH)-vitamin D serum levels than controls (P < 0.001). Osteocalcin was increased in PWS children but reduced in adults respect to controls (P < 0.005 and P < 0.01, respectively). RANKL levels were higher in both pediatric and PWS adults than controls (P < 0.004), while OPG levels were significantly reduced (P < 0.004 and P < 0.006, respectively). Sclerostin levels were increased in children (P < 0.04) but reduced in adults compared to controls (P < 0.01). DKK-1 levels did not show significant difference between patients and controls. In PWS patients, RANKL, OPG, and sclerostin significantly correlated with metabolic and bone instrumental parameters. Consistently, with adjustment for age, multiple linear regression analysis showed that BMD and osteocalcin were the most important predictors for RANKL, OPG, and sclerostin in children, and GH and sex steroid replacement treatment in PWS adults. We demonstrated the involvement of RANKL, OPG, and sclerostin in the altered bone turnover of PWS subjects suggesting these molecules as markers of bone disease and new potential pharmacological targets to improve bone health in PWS.

Evidence for Bone and Mineral Metabolism Alterations in Children With Autosomal Dominant Polycystic Kidney Disease

CONTEXT

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disease. Hypophosphatemia was demonstrated in adult patients with preserved renal function, together with high fibroblast growth factor 23 (FGF23) and low soluble Klotho levels. The latter explained the relative FGF23 hyporesponsiveness in this cohort.

OBJECTIVE

Evaluating phosphate and bone mineral metabolism in children with ADPKD compared with what is known in adult ADPKD patients.

DESIGN

Observational cross-sectional study.

SETTING

Multicenter study via ambulatory care in tertiary centers.

PARTICIPANTS

Ninety-two children with ADPKD (52 males; mean ± standard deviation age, 10.2 ± 5.0 years) and 22 healthy controls (HCs, 10 males; mean ± standard deviation age, 10.3 ± 4.1 years).

MAIN OUTCOME MEASURES

The predictor was early ADPKD stage. Bone mineral metabolism and renal phosphate handling were the main outcome measures. Performed measurements were serum phosphate, tubular maximum phosphorus reabsorption per glomerular filtration rate, FGF23, soluble Klotho, sclerostin, and bone alkaline phosphatase.

RESULTS

ADPKD children had significantly lower serum phosphate levels compared with HC. Low tubular maximum phosphorus reabsorption per glomerular filtration rate was observed in 24% of patients, although not significantly different from HC. Serum FGF23 and soluble Klotho levels were comparable between patients and HC. In addition, we showed decreased bone alkaline phosphatase levels in ADPKD children, suggesting suppressed bone formation.

CONCLUSIONS

This report demonstrates hypophosphatemia and suppressed bone formation in a pediatric ADPKD cohort, with preserved renal function, compared with HC. Although FGF23 levels were not different from controls, they should be considered inappropriate, given the concomitant hypophosphatemia. Further studies are required to elucidate underlying pathophysiology and potential clinical consequences.

Protecting Bone Health in Pediatric Rheumatic Diseases: Pharmacological Considerations

Bone health in children with rheumatic conditions may be compromised due to several factors related to the inflammatory disease state, delayed puberty, altered life style, including decreased physical activities, sun avoidance, suboptimal calcium and vitamin D intake, and medical treatments, mainly glucocorticoids and possibly some disease-modifying anti-rheumatic drugs. Low bone density or even fragility fractures could be asymptomatic; therefore, children with diseases of high inflammatory load, such as systemic onset juvenile idiopathic arthritis, juvenile dermatomyositis, systemic lupus erythematosus, and those requiring chronic glucocorticoids may benefit from routine screening of bone health. Most commonly used assessment tools are laboratory testing including serum 25-OH-vitamin D measurement and bone mineral density measurement by a variety of methods, dual-energy X-ray absorptiometry as the most widely used. Early disease control, use of steroid-sparing medications such as disease-modifying anti-rheumatic drugs and biologics, supplemental vitamin D and calcium, and promotion of weight-bearing physical activities can help optimize bone health. Additional treatment options for osteoporosis such as bisphosphonates are still controversial in children with chronic rheumatic diseases, especially those with decreased bone density without fragility fractures. This article reviews common risk factors leading to compromised bone health in children with chronic rheumatic diseases and discusses the general approach to prevention and treatment of bone fragility.

Serum sclerostin levels in renal cell carcinoma patients with bone metastases

Sclerostin has been proposed as a potent inhibitor of bone formation. Sclerostin antibodies are under clinical development to treat osteoporosis and metastatic bone disease. Serum sclerostin level is elevated in multiple myeloma, an osteolytic malignancy, where it might serve as predictive marker for the use of sclerostin-directed antibodies. As renal cell carcinoma (RCC) patients often present with osteolytic metastases, we aimed to investigate serum sclerostin levels in RCC patients. Our study included 53 RCC patients (19 with bone metastases, 25 with visceral metastases and 9 with localized disease) and 53 age- and gender-matched non-osteoporotic controls. Frozen serum samples were subjected to sclerostin quantitative sandwich ELISA. The mean serum sclerostin levels of RCC patients and controls were 45.8 pmol/l and 45.1 pmol/l, respectively (p = 0.86). Analysis of variance showed no difference between the subgroups of RCC patients with regard to visceral or bone metastases or localized disease (p = 0.22). There was no significant association between eGFR (estimated glomerular filtration rate) and serum sclerostin levels in RCC patients (r = 0.05; p = 0.74) and controls (r = 0.06; p = 0.68). Our results indicate that serum sclerostin levels appear not to be a valuable biomarker to assess the occurrence of bone metastases in RCC patients.

Growth hormone therapy in children with CKD after more than two decades of practice

This review focuses on the evidence for the efficacy and safety of recombinant human growth hormone (rhGH) therapy in children with all stages of chronic kidney disease (CKD) and at all ages. It describes the improving height prognosis for our patients both with and without rhGH; explains the underlying hormonal abnormalities that provide the rationale for rhGH use in CKD and the endocrine changes that accompany treatment; and views on who warrants treatment, with what dose, and how long for.