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.

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.

Skeletal and mineral metabolic effects of risedronate in a rat model of high-turnover renal osteodystrophy

INTRODUCTION

High-turnover bone disease is a major consequence of SHPT and may explain the high risk for fracture in patients with advanced chronic kidney disease (CKD). Bisphosphonates suppress bone turnover and improve bone strength, but their effects have not been fully characterized in advanced CKD with severe SHPT. Bisphosphonates also increase 1,25-dihydroxyvitamin D levels in normal and uremic rats, but the underlying mechanism remains to be determined.

MATERIALS AND METHODS

We investigated the skeletal and mineral metabolic effects of RIS, a pyridinyl bisphosphonate, in rats with severe SHPT induced by 5/6 nephrectomy plus a high phosphate diet.

RESULTS

Nephrectomized rats developed severe SHPT, along with hyperphosphatemia, low 1,25-dihydroxyvitamin D, and markedly increased FGF23. Moreover, these rats exhibited characteristic features of high-turnover renal osteodystrophy, including increased indices of trabecular bone turnover, decreased cortical bone thickness, inferior cortical biomechanical properties, and a prominent increase in peritrabecular fibrosis. RIS treatment increased bone volume and partially attenuated trabecular bone remodeling, cortical bone loss, and mechanical properties, whereas it produced a marked improvement in peritrabecular fibrosis along with a corresponding decrease in osteogenic gene markers. RIS treatment also suppressed the elevation of FGF23, which was associated with increased 1,25-dihydroxyvitamin D.

CONCLUSIONS

In a rat model of severe SHPT, treatment with RIS partially attenuated histological manifestations of high-turnover bone disease. RIS treatment also suppressed the elevation of FGF23, which may explain the increased 1,25-dihydroxyvitamin D production during the treatment.

Adverse Effects of Autoclaved Diets on the Progression of Chronic Kidney Disease and Chronic Kidney Disease-Mineral Bone Disorder in Rats

BACKGROUND

Autoclaving rodent diets is common in laboratory animals, but autoclaving increases the formation of dietary advanced glycation end-products (AGE). We studied the effect of autoclaved (AC) diet alone or in combination with a diet high in bioavailable phosphorus on biochemistries of chronic kidney disease-mineral and bone disorder (CKD-MBD), intestinal gene expression, and oxidative stress.

METHODS

Male CKD rats (Cy/+) and normal littermates were fed 1 of 3 diets: AC 0.7% phosphorus grain-based diet for 28 weeks (AC); AC diet for 17 weeks followed by non-autoclaved (Non-AC) 0.7% phosphorus casein diet until 28 weeks (AC + Casein); or Non-AC diet for 16 weeks followed by a Non-AC purified diet until 30 weeks (Non-AC + Casein).

RESULTS

AC diets contained ~3× higher AGEs and levels varied depending on the location within the autoclave. Rats fed the AC and AC + Casein diets had higher total AGEs and oxidative stress, irrespective of kidney function. Kidney function was more severely compromised in CKD rats fed AC or AC + Casein compared to Non-AC + Casein. There was a disease-by-diet interaction for plasma phosphorus, parathyroid hormone, and c-terminal fibroblast growth factor-23, driven by high values in the CKD rats fed the AC + Casein diet. Compared to Non-AC + Casein, AC and AC + Casein-fed groups had increased expression of receptor of AGEs and intestinal NADPH oxidase dual oxidase-2, independent of kidney function.

CONCLUSIONS

Autoclaving rodent diets impacts the progression of CKD and CKD-MBD, highlighting the critical importance of standardizing diets in experiments.

International variation in the management of mineral bone disorder in patients with chronic kidney disease: Results from CKDopps

BACKGROUND AND OBJECTIVES

Chronic kidney disease (CKD) is commonly associated with mineral and bone metabolism disorders, but these are less frequently studied in non-dialysis CKD patients than in dialysis patients. We examined and described international variation in mineral and bone disease (MBD) markers and their treatment and target levels in Stage 3-5 CKD patients.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

Prospective cohort study of 7658 adult patients with eGFR <60mL/min/1.73m², excluding dialysis or transplant patients, participating in the Chronic Kidney Disease Outcomes and Practice Patterns Study (CKDopps) in Brazil, France, Germany, and the US. CKD-MBD laboratory markers included serum levels of phosphorus (P), calcium (Ca), intact parathyroid hormone (iPTH), and 25-hydroxyvitamin D (25-D). MBD treatment data included phosphate binders and vitamin D (nutritional and active). Nephrologist survey data were collected on target MBD marker levels.

RESULTS

Over two-thirds of the patients had MBD markers measured at time intervals in line with practice guidelines. P and iPTH increased and Ca decreased gradually from eGFR 60-20mL/min/1.73m² and more sharply for eGFR<20. 25-D showed no relation to eGFR. Nephrologist survey data indicated marked variation in upper target P and iPTH levels. Among patients with P>5.5mg/dL, phosphate binder use was 14% to 43% across the four countries. Among patients with PTH >300pg/mL, use of active (calcitriol and related analogs) vitamin D was 12%-51%, and use of any (active or nutritional) vitamin D was 60%-87%.

CONCLUSIONS

Although monitoring of CKD-MBD laboratory markers by nephrologists in CKDopps countries is consistent with guidelines, target levels vary notably and prescription of medications to treat abnormalities in these laboratory markers is generally low in these cross-sectional analyses. While there are opportunities to increase treatment of hyperphosphatemia, hyperparathyroidism, and vitamin D deficiency in advanced CKD, the effect on longer-term complications of these conditions requires study.

Parathyroid suppression therapy normalizes chronic kidney disease-induced elevations in cortical bone vascular perfusion: a pilot study

Interventions that alter PTH levels in an animal model of chronic kidney disease have effects on the perfusion of bone and bone marrow.

INTRODUCTION

Patients with chronic kidney disease (CKD) have accelerated bone loss, vascular calcification, and abnormal biochemistries, together contributing to an increased risk of cardiovascular disease and fracture-associated mortality. Despite evidence of vascular pathologies and dysfunction in CKD, our group has shown that cortical bone tissue perfusion is higher in a rat model of high-turnover CKD. The goal of the present study was to test the hypothesis that parathyroid hormone (PTH) suppressive interventions would normalize cortical bone vascular perfusion in the setting of CKD.

METHODS

In two separate experiments, 35-week-old CKD animals and their normal littermates underwent intra-cardiac fluorescent microsphere injection to assess the effect of 10 weeks of PTH suppression (Experiment 1: calcium supplementation, Experiment 2: calcimimetic treatment) on alterations in bone tissue perfusion.

RESULTS

In Experiment 1, CKD animals had serum blood urea nitrogen (BUN) and PTH levels significantly higher than NL (+ 182% and + 958%; p < 0.05). CKD+Ca animals had BUN levels that were similar to CKD, while PTH levels were significantly lower and comparable to NL. Both femoral cortex (+ 220%, p = 0.003) and tibial cortex (+ 336, p = 0.005) tissue perfusion were significantly higher in CKD animals when compared to NL; perfusion was normalized to those of NL in CKD+Ca animals. MicroCT analysis of the proximal tibia cortical porosity showed a trend toward higher values in CKD (+ 401%; p = 0.017) but not CKD+Ca (+ 111%; p = 0.38) compared to NL. Experiment 2, using an alternative method of PTH suppression, showed similar results as those of Experiment 1.

CONCLUSIONS

These data demonstrate that PTH suppression-based interventions normalize cortical bone perfusion in the setting of CKD.

[Osteoporosis and chronic kidney disease: review and new therapeutic strategies]

Osteoporosis affects a segment of the population in which Chronic Kidney Disease is also greatly represented. Nephropathic patients may present peculiar biochemical abnormalities related to Chronic Kidney Disease, defining the Mineral and Bone Disorder. This kind of anomalies, in the worst scenarios, configure the typical histomorphology patterns of Renal Osteodystrophy. Scientific Societies of Endocrinology have established therapy guidelines for patients with osteoporosis only based on the glomerular filtration rate and recommend avoiding the use of some drugs for the more advanced classes of nephropathy. However, there is no clear therapeutic approach for patients with advanced nephropathy and bone abnormalities. In this paper we propose a systematic review of the literature and present our proposal for managing patients with advanced nephropathy, based on eGFR and on presence of Mineral and Bone Disorder.

GFR-Specific versus GFR-Agnostic Cutoffs for Parathyroid Hormone and Fibroblast Growth Factor-23 in Advanced Chronic Kidney Disease

BACKGROUND

In the majority of patients with advanced chronic kidney disease (CKD), values of parathyroid hormone (PTH1-84) and fibroblast growth factor 23 (FGF-23) exceed the normal reference range, potentially as an appropriate adaptation to reduced glomerular filtration rate (GFR). We tested whether GFR-specific cutoffs for PTH1-84 and FGF-23 could better identify patients with inappropriately high PTH1-84 and FGF-23 for their degree of CKD and thereby improve prognostication of clinical outcomes compared to a uniform threshold.

METHODS

Prospective pan-Canadian cohort of 1,812 patients with mean estimated GFR (eGFR) 28.9 mL/min/1.73 m2 followed for a median of 52 months. Repeated log-rank tests were used to identify optimal cutoffs for PTH1-84 and FGF-23 within eGFR strata (<20, 20-29 and ≥30 mL/min/1.73 m2) that maximally differentiated high- and low-risk populations for (1) cardiovascular (CV) events (fatal or nonfatal myocardial infarction, coronary revascularization, stroke, heart failure) and (2) renal events (initiation of chronic renal replacement therapy). In multivariable models, we examined the association between -GFR-specific cutoffs and outcomes and compared their added prognostic value to existing uniform thresholds.

RESULTS

Risk-based cutoffs for PTH1-84 and FGF-23 increased in a graded fashion with decreasing eGFR. Among patients with eGFR <20 mL/min/1.73 m2, CV risk-based cutoffs for PTH1-84 and FGF-23 were 3.4 and 5.5 times the upper limit of normal, respectively, and reclassified 31.9 and 35.1% of patients when added to a multivariable base model for CV events. In contrast, the addition of PTH1-84 and FGF-23 to the base model using uniform cutoffs failed to reclassify such patients. Similar findings were demonstrated for renal outcomes.

CONCLUSION

GFR-specific risk-based cutoffs for PTH1-84 and FGF-23 may facilitate more meaningful risk stratification in advanced CKD than current GFR-agnostic reference ranges derived from healthy adults. This may be most applicable in those with severely reduced GFR.

Relationship between plasma levels of sclerostin, calcium-phosphate disturbances, established markers of bone turnover, and inflammation in haemodialysis patients

PURPOSE

Data concerning the relation between increased levels of circulating sclerostin (a physiological inhibitor of bone formation) and bone turnover in patients with chronic renal failure (CRF) are limited. Therefore, the aim of this study was to evaluate associations between plasma sclerostin levels and calcium-phosphate disturbances, markers of bone turnover as well as inflammation in haemodialysis (HD) patients.

METHODS

In plasma samples obtained in 150 stable HD patients (92 men) aged 40-70 years, levels of sclerostin, fibroblast growth factor (cFGF23), osteocalcin, the N-terminal propeptide of type I procollagen, C-terminal telopeptide of the alpha chain of type I collagen (β-CTx), and inflammatory markers (IL-6 and TNF-α) in addition to routine parameters (calcium, phosphorus, parathyroid hormone-iPTH, 25-OH-D, alkaline phosphatase) were measured.

RESULTS

Plasma sclerostin concentrations were significantly higher in HD men than women (2.61 vs. 1.88 ng/mL, p < 0.01). Patients with sclerostin levels above median were characterized by lower iPTH and IL-6, but higher cFGF23 and TNF-α (significantly only in men) concentrations. Plasma sclerostin concentration positively correlated with serum 25-OH-D (τ = 0.204), phosphorus (τ = 0.1482), and TNF-α (τ = 0.183) and inversely with iPTH (τ = - 0.255), alkaline phosphatase (τ = - 0.203), IL-6 (τ =- 0.201), and β-CTx (τ = - 0.099) levels. In multivariate regression analysis, variability of sclerostin levels was explained by sex and 25-OH-D and phosphorus levels.

CONCLUSIONS

Increased circulating sclerostin levels seem to reflect slower bone turnover in HD patients. Low levels of sclerostin are associated with vitamin D deficiency and good phosphates alignment.

[The prevention and treatment of vascular calcification.]

We had called the various bone disorder in chronic kidney disease(CKD)as a "ROD:renal osteodystrophy" until last decade. However the concept of ROD have changed into the chronic kidney disease-mineral and bone disease(CKD-MBD)within this decade. This concept is containing systemic disorder affected mortality. Vascular calcification is an independent risk factor for the development of cardiovascular disease and mortality. The best strategy to prevent and treat vascular calcification would consist of the CKD-MBD management. It is expected that the treatment of preventing directly vascular calcification to appear by finding the detailed mechanism in the future.

Skeletal status assessment by quantitative ultrasound and bone densitometry in children with different renal conditions

Two methods of skeletal status assessment-quantitative ultrasound (QUS) and densitometry (DXA)-were applied and compared in a group of children with different renal disorders. Skeletal assessments in children with different renal conditions should rather not be based on a single diagnostic tool. Lumbar spine DXA is very effective to reveal disturbances secondary to glucocorticoids, whereas total body DXA and QUS are both better in identification of disturbances related to decreased GFR.

INTRODUCTION

The aim of the study was to evaluate the skeletal status in children in different stages of chronic kidney disease (CKD) or treated with glucocorticoids, using either densitometry (DXA) or quantitative ultrasound (QUS) methods.

METHODS

Seventy-six subjects (27 girls/49 boys) at the mean age of 11.8 ± 4.0 years were enrolled to the reported study. They were divided into three subgroups: with normal glomerular filtration rate (GFR) but treated with glucocorticoids (GCs, n = 38), with decreased GFR (CKD 2-5, n = 26) and with normal GFR and without any bone-toxic treatment (CKD 1, n = 12). DXA scans were carried out at lumbar spine (LS) and at total body (TB), and quantitative ultrasound (QUS) imaging was done at hand phalanges. QUS results were compared to those obtained from 310 healthy matched controls.

RESULTS

The average Z-score for LS-BMD and TB-BMD was below zero in all the study subgroups. Neither were there any significant differences in the mean Z-score for LS among the subgroups. The mean Z-score for TB was significantly the lowest in the CKD 2-5 subgroup. The percentage of subjects with TB Z-score ≤ - 2.0 was the highest in the CKD 2-5 subgroup (69.2%), whereas the percentage of subjects with LS Z-score ≤ - 2.0 was the highest in the GC subgroup (23.7%). QUS results in CKD 2-5 were significantly lower than those in the controls, whereas the results, obtained in GC and CKD 1 subgroups, were similar to those in healthy subjects.

CONCLUSIONS

Skeletal status assessment in children and adolescents with different renal conditions should not be based on single diagnostic approach. DXA scanning, performed at lumbar spine, is potentially more appropriate to reveal disturbances secondary to long-term GC therapy, whereas TB-DXA is highly effective in the identification of skeletal disturbances related to decreased kidney function. QUS at hand phalanges seems to be a useful diagnostic means in CKD with diminished GFR but insufficient to detect GC-related disturbances.

Effects of Flaxseed Oil on Serum Bone Turnover Markers in Hemodialysis Patients: a Randomized Controlled Trial

INTRODUCTION

Chronic kidney disease-mineral and bone disorder is a common complication in hemodialysis patients. The present study was designed to investigate the effects of flaxseed oil, a rich source of plant omega-3 fatty acid alpha-linolenic acid, on serum markers of bone formation and resorption in hemodialysis patients.

MATERIALS AND METHODS

In this randomized controlled trial, 34 hemodialysis patients were randomly assigned to either the flaxseed oil or the control group. The patients in the flaxseed oil group received 6 g/d of flaxseed oil for 8 weeks, whereas the control group received 6 g/d of medium chain triglycerides oil. At baseline and the end of the 8th week, 7 mL of blood was obtained from each patient after a 12- to 14-hour fast and serum concentrations of osteocalcin, osteoprotegerin, N-telopeptide, and receptor activator of nuclear factor kappa B ligand were measured.

RESULTS

Serum N-telopeptide concentration decreased significantly up to 17% in the flaxseed oil group at the end of week 8, as compared to baseline (P < .01), and the reduction was significant in comparison with the control group. There were no significant differences between the two groups in the mean changes of serum osteocalcin, osteoprotegerin, or receptor activator of nuclear factor kappa B ligand.

CONCLUSIONS

This study indicates that daily consumption of 6 g/d of flaxseed oil may reduce bone resorption in hemodialysis patients.

Impact of Chronic Kidney Disease Mineral and Bone Disorder on Jaw and Alveolar Bone Metabolism: A Narrative Review

Chronic kidney disease (CKD) has become a worldwide public health problem. It is estimated that nearly 90% of patients with chronic renal failure manifest some symptoms of oral disease. With advances in medical treatment, CKD patients are living longer and require oral care. Chronic kidney disease is often accompanied by disturbances in mineral metabolism which are classified as their own clinical entity known as CKD-mineral and bone disorder (CKD-MBD). CKD-MBD affects all aspects of bone physiology: bone volume, bone turnover and bone mineralization. Jaw bones affected with CKD-MBD can have important clinical implications for the survival and osseointegration of dental implants, success of bone regeneration therapy, and increased risk of bone loss in patients with periodontitis or risk of bone fracture. Assessment of bone turnover is the most important diagnostic tool to monitor progression of CKD-MBD. Bone biomarkers and radiographical examination of bone density may be particularly useful to both, diagnosis and monitoring of bone turnover. Cone beam computed tomography (CBCT) as a reliable method with many advantages over other radiographic methods can be used for analysis of jaw bone micro-architectural changes and may be of a great help in bone quality determination in CKD-MBD.

[Update 2017 of the KDIGO guidelines on Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD). What are the real changes?]

Guidelines for the assessment, diagnosis and therapy of the alterations that characterize the CKD-MBD are an important support in the clinical practice of the nephrologist. Compared to the KDIGO guidelines published in 2009, the 2017 update made changes on some topics on which there was previously no strong evidence both in terms of diagnosis and therapy. The recommendations include the diagnosis of bone anomalies in CKD-MBD and the treatment of mineral metabolism abnormalities with particular regard to hyperphosphataemia, calcium levels, secondary hyperparathyroidism and anti-resorptive therapies. The Italian Study Group on Mineral Metabolism, in reviewing the 2017 recommendations, aimed to assess the weight of the evidence that led to this update. In fact, on some topics there has not been a substantial difference on the degree of evidence compared to the previous guidelines. The Italian Study Group emphasizes the points that may still reserve critical issues, including interpretation, and invites an evaluation that is articulated and personalized for each patient.

Klotho and activin A in kidney injury: plasma Klotho is maintained in unilateral obstruction despite no upregulation of Klotho biosynthesis in the contralateral kidney

In a new paradigm of etiology related to chronic kidney disease-mineral and bone disorder (CKD-MBD), kidney injury may cause induction of factors in the injured kidney that are released into the circulation and thereby initiate and maintain renal fibrosis and CKD-MBD. Klotho is believed to ameliorate renal fibrosis and CKD-MBD, while activin A might have detrimental effects. The unilateral ureter obstruction (UUO) model is used here to examine this concept by investigating early changes related to renal fibrosis in the obstructed kidney, untouched contralateral kidney, and vasculature which might be affected by secreted factors from the obstructed kidney, and comparing with unilateral nephrectomized controls (UNX). Obstructed kidneys showed early Klotho gene and protein depletion, whereas plasma Klotho increased in both UUO and UNX rats, indicating an altered metabolism of Klotho. Contralateral kidneys had no compensatory upregulation of Klotho and maintained normal expression of the examined fibrosis-related genes, as did remnant UNX kidneys. UUO caused upregulation of transforming growth factor-β and induction of periostin and activin A in obstructed kidneys without changes in the contralateral kidneys. Plasma activin A doubled in UUO rats after 10 days while no changes were seen in UNX rats, suggesting secretion of activin A from the obstructed kidney with potentially systemic effects on CKD-MBD. As such, increased aortic sclerostin was observed in UUO rats compared with UNX and normal controls. The present results are in line with the new paradigm and show very early vascular effects of unilateral kidney fibrosis, supporting the existence of a new kidney-vasculature axis.

The Effect of Extended Release Niacin on Markers of Mineral Metabolism in CKD

BACKGROUND AND OBJECTIVES

Niacin downregulates intestinal sodium-dependent phosphate transporter 2b expression and reduces intestinal phosphate transport. Short-term studies have suggested that niacin lowers serum phosphate concentrations in patients with CKD and ESRD. However, the long-term effects of niacin on serum phosphate and other mineral markers are unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglycerides: Impact on Global Health Trial was a randomized, double-blind, placebo-controlled trial testing extended release niacin in persons with prevalent cardiovascular disease. We examined the effect of randomized treatment with niacin (1500 or 2000 mg) or placebo on temporal changes in markers of mineral metabolism in 352 participants with eGFR<60 ml/min per 1.73 m2 over 3 years. Changes in each marker were compared over time between the niacin and placebo arms using linear mixed effects models.

RESULTS

Randomization to niacin led to 0.08 mg/dl lower plasma phosphate concentrations per year of treatment compared with placebo (P<0.01) and 0.25 mg/dl lower mean phosphate 3 years after baseline (3.32 versus 3.57 mg/dl; P=0.03). In contrast, randomization to niacin was not associated with statistically significant changes in plasma intact fibroblast growth factor 23, parathyroid hormone, calcium, or vitamin D metabolites over 3 years.

CONCLUSIONS

The use of niacin over 3 years lowered serum phosphorous concentrations but did not affect other markers of mineral metabolism in participants with CKD.

Two-year cortical and trabecular bone loss in CKD-5D: biochemical and clinical predictors

This prospective two-year study of patients on chronic dialysis measured changes in bone mineral density (BMD). Patients with higher baseline BMD and shorter dialysis vintage lost more bone. Treatment with anti-hypertensives acting on the central nervous system was protective against bone loss. Baseline serum levels of sclerostin and bone-specific alkaline phosphatase predicted bone loss.

INTRODUCTION

This prospective 2-year study of chronic kidney disease on dialysis (CKD-5D) patients assessed trabecular and cortical bone loss at the hip and spine and examined potential demographic, clinical, and serum biochemical predictors of bone loss.

METHODS

Eighty-nine CKD-5D patients had baseline, year 1, and year 2 bone mineral density (BMD) measurements using dual X-ray absorptiometry (DXA) and quantitative computed tomography (QCT); concurrent blood samples were drawn and clinical variables recorded. No study treatments occurred.

RESULTS

The 2-year total hip BMD change was - 5.9% by QCT and - 3.1% by DXA (p < 0.001). Spinal BMD was unchanged. QCT total hip cortical mass and volume decreased (- 7.3 and - 10.0%); trabecular volume increased by 5.9% (ps < 0.001). BMD changes did not vary with age, BMI, race, diabetes, smoking, or exercise. Patients with higher baseline BMD and shorter dialysis vintage lost more bone (p < 0.05). Vitamin D analogs and phosphate binders were not protective against bone loss; cinacalcet was protective by univariate but not by multivariable analysis. CNS-affecting antihypertensives were protective against loss of BMD, cortical mass, cortical volume (ps < 0.05) and trabecular mass (p = 0.007). These effects remained after adjustment. BSAP correlated with changes in BMD, cortical mass, and volume (p < 0.01) as did sclerostin (inversely).

CONCLUSIONS

There was severe cortical bone loss at the hip best recognized by QCT. Patients with shorter dialysis vintage and less pre-existing bone loss lost more bone, while treatment with CNS-acting antihypertensives was protective. BSAP and sclerostin were useful markers of bone loss.

Dental Manifestations of Pediatric Bone Disorders

PURPOSE OF REVIEW

Several bone disorders affecting the skeleton often are manifest in the maxillofacial region. This review presents the most common bone disorders in children and their dental-oral manifestations: fibrous dysplasia, Paget's disease, osteogenesis imperfecta, renal osteodystrophy, hypophosphatasia, and osteoporosis. The specific intraoral characteristics will reviewed in detail.

RECENT FINDINGS

Recent studies confirmed the close relationship between the mandible and the maxilla with the most prevalent systemic bone disorders in children. This review will help practitioners to integrate the oral health into the systemic health and improve the multidisciplinary approach of pediatric patients between medicine and dentistry.

Renal osteodystrophy in the obesity era: Is metabolic syndrome relevant?

BACKGROUND

Observational studies have shown a beneficial effect of obesity on bone health; however, most of those studies were not based on bone biopsies. Metabolic syndrome (MetS) could have an effect on bone remodeling. However, there are no data on the effects of MetS in the presence of renal osteodystrophy.

OBJECTIVE

The aim of this study was to investigate associations between MetS and renal osteodystrophy using the bone histomorphometric turnover-mineralization-volume (TMV) classification.

DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS

This observational cross-sectional study included 55 hemodialysis patients (28 women/27 men) who were evaluated for MetS and bone histomorphometry. Biochemical parameters included calcium, phosphorus, alkaline phosphatase, intact parathyroid hormone (iPTH), 25-hydroxyvitamin D, free serum leptin, fibroblast growth factor 23 (FGF23), intact osteocalcin, sclerostin (Scl), glucose, insulin, and thyroid hormones. Robust models of multivariate linear regressions were used for the statistical analyses.

RESULTS

Females had higher iPTH levels (1,143 vs. 358, p = 0.02). Patients with normal bone volume (BV/TV) had a higher prevalence of MetS (73.6% vs. 41.7%, p = 0.02) and higher serum phosphorus, C-terminal FGF23 and insulin levels. The multivariate regression analysis showed that low-density lipoprotein cholesterol (LDL) was positively correlated with bone formation rate (BFR/BS) and negatively associated with mineralization lag time. Bone volume was negatively associated with age but positively associated with MetS. Body mass index (BMI) was not correlated with any of the bone histomorphometric parameters.

CONCLUSION

Our results suggest that MetS is not a risk factor for low bone volume in hemodialysis patients. Furthermore, BMI alone was not related to bone volume in this population.

Association of Parameters of Mineral Bone Disorder with Mortality in Patients on Hemodialysis according to Level of Residual Kidney Function

BACKGROUND AND OBJECTIVES

The relationship between mineral and bone disorders and survival according to residual kidney function status has not been previously studied in patients on hemodialysis. We hypothesized that residual kidney function, defined by renal urea clearance, modifies the association between mineral and bone disorder parameters and mortality.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The associations of serum phosphorus, albumin-corrected calcium, intact parathyroid hormone, and alkaline phosphatase with all-cause mortality were examined across three strata (<1.5, 1.5 to <3.0, and ≥3.0 ml/min per 1.73 m2) of baseline residual renal urea clearance using Cox models adjusted for clinical characteristics and laboratory measurements in 35,114 incident hemodialysis patients from a large United States dialysis organization over the period of 2007-2011.

RESULTS

A total of 8102 (23%) patients died during the median follow-up of 1.3 years (interquartile range, 0.6-2.3 years). There was an incremental mortality risk across higher serum phosphorus concentrations, which was pronounced among patients with higher residual renal urea clearance (Pinteraction=0.001). Lower concentrations of serum intact parathyroid hormone were associated with higher mortality among patients with low residual renal urea clearance (i.e., <1.5 ml/min per 1.73 m2), whereas higher concentrations showed a higher mortality risk among patients with greater residual renal urea clearance (i.e., ≥1.5 ml/min per 1.73 m2; Pinteraction<0.001). Higher serum corrected total calcium and higher alkaline phosphatase concentrations consistently showed higher mortality risk (Ptrend<0.001 for both) irrespective of residual renal urea clearance strata (Pinteraction=0.34 and Pinteraction=0.53, respectively).

CONCLUSIONS

Residual kidney function modified the mortality risk associated with serum phosphorus and intact parathyroid hormone among incident hemodialysis patients. Future studies are needed to examine whether taking account for residual kidney function into the assessment of mortality risk associated with serum phosphorus and intact parathyroid hormone improves patient management and clinical outcomes in the hemodialysis population.

Vitamin D levels and other biochemical parameters of mineral bone disorders and their association with diastolic dysfunction and left ventricular mass in young nondiabetic adult patients with chronic kidney disease

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in patients with end-stage renal disease. Chronic kidney disease (CKD)-associated cardiovascular mortality is more prevalent in those with diastolic heart failure and is an early predictor, while increased left ventricular mass (LVM) is a strong independent risk factor. Hypovitaminosis D is extensively being studied as a nontraditional risk factor for CVD. The aim of the present study is to look at the association of Vitamin D and other parameters of mineral bone disorder (MBD) with diastolic dysfunction and LVM in nondiabetic young adult patients with CKD. This was a hospital-based, cross-sectional observational study. Groups I and II comprised nondiabetic predialysis CKD patients (stage 4 and 5) and healthy controls, respectively. Groups IA and IB comprised cases with and without diastolic dysfunction, respectively. Vitamin D level was measured by enhanced chemiluminescence method and intact parathyroid hormone (iPTH) by electrochemiluminescence method. Parameters for diastolic function and LVM were assessed by Doppler echocardiography, tissue Doppler imaging, and M-mode echocardiography. Vitamin D level was significantly lower in Group I as compared to Group II. Diastolic dysfunction was present in 48.8% of the cases and was significantly associated with serum phosphorus and calcium-phosphorous product, but not with Vitamin D level. A statistically significant positive correlation between LVM and iPTH was found in our study. Hyperphosphatemia and high calcium-phosphorous product can be a better early predictor of diastolic dysfunction than Vitamin D while secondary hyperpara-thyroidism with increased LVM may be a bad prognostic marker.

Circulating markers of bone turnover

Renal osteodystrophy is a feature of chronic kidney disease (CKD), with increasing prevalence as CKD progresses. This bone disease is responsible for major morbidity, including fractures, and a deterioration in the quality of life and its sequelae. Circulating biomarkers of renal osteodystrophy typically indicate bone turnover, but not other features of bone, like bone volume, mineralization, quality or strength. Bone turnover can be considered to be primarily a reflection of bone cell activity, in particular that of osteoblasts and osteoclasts. Since current treatments for bone disease usually target cellular activity, biomarkers are considered to be able to contribute to the decision-making for treatment and its follow-up. In CKD, one has to consider the impact of a diminished clearance of biomarkers or their altered metabolism, both potentially limiting its clinical use. Here, several aspects of the most frequently used biomarkers of bone turnover are reviewed, with an emphasis on the specific situation represented by CKD. This review is based on the overview lecture at the symposium held in Amsterdam, September 23, 2016: “The Bone In CKD”, organized by the CKD-MBD working group of ERA-EDTA.

Trajectories of CKD-MBD biochemical parameters over a 2-year period following diagnosis of secondary hyperparathyroidism: a pharmacoepidemiological study

OBJECTIVES

To define groups of patients according to the changes of biochemical parameters, that is, serum calcium, phosphate and parathyroid hormone (PTH), over a 2-year follow-up period using group-based multi-trajectory modeling (GBMM) among a cohort of dialysis patients with newly diagnosed secondary hyperparathyroidism (SHPT) (ie, PTH≥500 ng/L for the first time) and to compare their patient characteristics and treatments.

DESIGN

Pharmacoepidemiological study.

SETTING

In the 12 dialysis units located in the French region of Lorraine.

PARTICIPANTS

A total of 269 dialysis patients with newly diagnosed SHPT were prospectively included from December 2009 to May 2012 and followed-up for 2 years.

RESULTS

We identified four distinct trajectory groups: 'rapid PTH drop' experiencing a rapid and sharp decrease (over weeks) in PTH level associated with decreasing phosphate level within normal range (n=34; 12.7%), 'gradual PTH decrease' experiencing a gradual and continuous decrease (over months) in PTH level and maintaining phosphate at a middle level throughout the study (n=98; 36.4%), 'slow PTH decrease with high phosphate' experiencing a slow decrease in PTH level associated with a relatively high phosphate level (n=105; 39.0%) and 'uncontrolled SHPT' with high levels of PTH and phosphate throughout the study (n=32; 11.9%). Patients in the 'uncontrolled SHPT' group were significantly (p<0.00001) younger than patients in other groups. Kidney Disease Improving Global Outcomes (KDIGO) targets for PTH, phosphate and calcium were reached simultaneously for 14.9% of patients at baseline and 16.7% at the end of the study. Patients were given cinacalcet more frequently at months 3 and 6 in the 'rapid PTH drop' and at month 24 in the 'uncontrolled SHPT' groups.

CONCLUSIONS

Over 2 years following a new SHPT diagnosis, a younger age and a higher rate of alkaline phosphatase were associated to a continuous uncontrolled SHPT. Patients with the lowest PTH at the end of the follow-up tended to receive more often cinacalcet.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov number, NCT02888639, post results.

Cystatin C is Better than Serum Creatinine for Estimating Glomerular Filtration Rate to Detect Osteopenia in Chronic Kidney Disease Patients

PURPOSE

Recent studies have reported that loss of bone mass is associated with renal function decline and increased fracture risks in chronic kidney disease (CKD) patients. The aim of this study was to investigate the best estimated glomerular filtration rate (eGFR) equation to detect osteopenia in CKD patients.

MATERIALS AND METHODS

This was a cross-sectional study, and 780 patients aged 50 years or above were classified into normal bone mass or osteopenia groups according to the -1.0 of T-scores at total hip and femur neck. Comparisons of area under the receiver operating characteristic (ROC) curves (AUC) were performed to investigate significant differences among three eGFR formulas: Modification of Diet in Renal Disease, CKD-Epidemiology Collaboration (EPI) creatinine, and CKD-EPI cystatin C (CKD-EPI-Cys).

RESULTS

The mean age was 61 years old and the proportion of females was 37.3%. The total hip osteopenia group showed lower CKD-EPI-Cys eGFR levels (osteopenia group, 33.3±19.0 mL/min/1.73 m²; normal group, 48.1±26.2 mL/min/1.73 m², p<0.001). In multiple logistic regression analysis, CKD-EPI-Cys eGFR was independently associated with osteopenia at the total hip (per 1 mL/min/1.73 m² increase, odds ratio 0.98, 95% confidence interval 0.97-0.99, p=0.004) after adjusting for confounding variables. ROC curve analyses indicated that CKD-EPI-Cys shows the largest AUC for osteopenia at the total hip (AUC=0.678, all p<0.01) and the femur neck (AUC=0.665, all p<0.05).

CONCLUSION

Decreased renal function assessed by CKD-EPI-Cys equation correlates with osteopenia better than creatinine-based methods in CKD patients, and the CKD-EPI-Cys formula might be a useful tool to assess skeletal-related event risks.

[Update on recent progress in vitamin D research. The role of vitamin D in management of CKD-MBD.]

Vitamin D was originally discovered as a substance which alleviates rickets and studies revealed that vitamin D exerts pleiotropic effects. Vitamin D has a therapeutic effect on Chronic Kidney Disease(CKD)-associated bone lesion or secondary hyperparathyroidism. On the other hand, excessive vitamin D induces calcium and phosphate overload, resulting in vascular calcification and cardiovascular events. From the data so far, not all CKD patients can get the benefit of vitamin D. It is well indicated for CKD patients with vitamin D insufficiency, secondary parathyroidism, hypocalcemia, or low-turnover bone disease on the basis of avoiding calcium over load.

Osteoporosis in Patients with CKD: A Diagnostic Dilemma

Osteoporosis in patients with chronic kidney disease (CKD) is a complex problem, with diagnostic criteria and treatment plans often debated. The debate creates a practice dilemma for clinicians faced with an aging population and an increasing incidence of fragility fractures. This article discusses the dilemma as seen from the perspective of the nephrology clinician on differentiating osteoporosis from other bone mineral disorders in patients with progressive CKD in order to provide the most efficacious and safe care.

Phosphorus Regulation in Chronic Kidney Disease

Serum phosphorus levels stay relatively constant through the influence of multiple factors-such as parathyroid hormone, fibroblast growth factor 23, and vitamin D-on the kidney, bone, and digestive system. Whereas normal serum phosphorus ranges between 3 mg/dL to 4.5 mg/dL, large cross-sectional studies have shown that even people with normal kidney function are sometimes found to have levels ranging between 1.6 mg/dL and 6.2 mg/dL. While this may partially be due to diet and the factors mentioned above, total understanding of these atypical ranges of serum phosphorus remains uncertain. Risks for bone disease are high in people aged 50 and older, and this group comprises a large proportion of people who also have chronic kidney disease. Consuming diets low in calcium and high in phosphorus, especially foods with phosphate additives, further exacerbates bone turnover. Existing bone disease increases the risk for high serum phosphorus, and higher serum phosphorus has been associated with increased adverse events and cardiovascular-related mortality both in people with chronic kidney disease and in those with no evidence of disease. Once kidney function has deteriorated to end-stage disease (Stage 5), maintaining normal serum phosphorus requires dietary restrictions, phosphate-binding medications, and dialysis. Even so, normal serum phosphorus remains elusive in many patients with Stage 5 kidney disease, and researchers are testing novel targets that may inhibit intestinal transport of phosphorus to achieve better phosphate control. Protecting and monitoring bone health should also aid in controlling serum phosphorus as kidney disease advances.

Parathyroidectomy Increases Heart Rate Variability and Leptin Levels in Patients with Stage 5 Chronic Kidney Disease

BACKGROUND

In chronic kidney disease (CKD) patients, decreased heart rate variability (HRV) reflects impaired cardiac automatic nervous function and high risk of cardiovascular disease (CVD). Lower HRV in patients with severe secondary hyperparathyroidism (SHPT), a clinical manifestation of CKD-mineral and bone disorder (CKD-MBD), could be reversed by parathyroidectomy (PTX). It has been proved that leptin interacts with the autonomic nervous function. However, the associations between leptin and HRV in CKD patients and their longitudinal changes in SHPT patients after PTX are still unknown.

METHODS

This was a cross-sectional study including 141 stage 5 CKD patients, and a prospective study in 36 severe SHPT patients with PTX. HRV was measured by Holter and serum leptin was measured by ELISA. Serum leptin levels were adjusted for body mass index (BMI) and transformed using natural logarithm (lnleptin/BMI).

RESULTS

With a gradient of lnleptin/BMI across quartiles from Q1 to Q4 in CKD patients, HRV indices showed no differences among quartiles. Patients in Q1 group had higher mean 24 h heart rates, and lower ln(very low frequency) (lnVLF) than other quartiles, although there were no statistically significant difference. In multivariate stepwise regression, serum leptin/BMI was an independent predictor for low frequency/high frequency. HRV indices and lnleptin/BMI levels were increased in severe SHPT patients after PTX. Compared to other quartiles, SHPT patients in Q1 group had larger improvement of lnVLF after PTX.

CONCLUSION

Circulating leptin levels may be a novel treatment target to reduce CVD risk in advanced CKD-MBD patients.

[The expanding concept of CKD-MBD]

Almost seven years have passed since the publication of the KDIGO clinical practice guideline on chronic kidney disease-mineral and bone disorder(CKD-MBD). During this period, several new medications for osteoporosis that may be applicable to patients with CKD have become available. Clinical studies have also shown the utility of bone mineral density to assess fracture risk in CKD. These new data charges us with the task of reconciling the concept of renal osteodystrophy(ROD)and osteoporosis in CKD. This review summarize the recent advances in the management of bone disease in CKD and the key points raised during the discussion for the KDIGO guideline revision, and address the problems to be solved in future.

Important abnormalities of bone mineral metabolism are present in patients with coronary artery disease with a mild decrease of the estimated glomerular filtration rate

Chronic kidney disease (CKD)-mineral and bone disorder (MBD) is characterized by increased circulating levels of parathormone (PTH) and fibroblast growth factor 23 (FGF23), bone disease, and vascular calcification, and is associated with adverse outcomes. We studied the prevalence of mineral metabolism disorders, and the potential relationship between decreased estimated glomerular filtration rate (eGFR) and CKD-MBD in coronary artery disease patients in a cross-sectional study of 704 outpatients 7.5 ± 3.0 months after an acute coronary syndrome. The mean eGFR (CKD Epidemiology Collaboration formula) was 75.8 ± 19.1 ml/min/1.73 m(2). Our patients showed lower calcidiol plasma levels than a healthy cohort from the same geographical area. In the case of men, this finding was present despite similar creatinine levels in both groups and older age of the healthy subjects. Most patients (75.6 %) had an eGFR below 90 ml/min/1.73 m(2) (eGFR categories G2-G5), with 55.3 % of patients exhibiting values of 60-89 ml/min/1.73 m(2) (G2). PTH (r = -0.3329, p < 0.0001) and FGF23 (r = -0.3641, p < 0.0001) levels inversely correlated with eGFR, whereas calcidiol levels and serum phosphate levels did not. Overall, PTH levels were above normal in 34.9 % of patients. This proportion increased from 19.4 % in G1 category patients, to 33.7 % in G2 category patients and 56.6 % in G3-G5 category patients (p < 0.001). In multivariate analysis, eGFR and calcidiol levels were the main independent determinants of serum PTH. The mean FGF23 levels were 69.9 (54.6-96.2) relative units (RU)/ml, and 33.2 % of patients had FGF23 levels above 85.5 RU/ml (18.4 % in G1 category patients, 30.0 % in G2 category patients, and 59.2 % in G3-G5 category patients; p < 0.001). In multivariate analysis, eGFR was the main predictor of FGF23 levels. Increased phosphate levels were present in 0.7 % of the whole sample: 0 % in G1 category patients, 0.3 % in G2 category patients, and 2.8 % in G3-G5 category patients (p = 0.011). Almost 90 % of patients had calcidiol insufficiency without significant differences among the different degrees of eGFR. In conclusion, in patients with coronary artery disease there is a large prevalence of increased FGF23 and PTH levels. These findings have an independent relationship with decreased eGFR, and are evident at an eGFR of 60-89 ml/min/1.73 m(2). Then, mild decreases in eGFR must be taken in consideration by the clinician because they are associated with progressive abnormalities of mineral metabolism.

[Chronic Kidney Disease and Bone]

Both bone and kidney are members of the physiological network sharing a purpose of systemic mineral metabolism. In patients with chronic kidney disease whose kidney function is lost, the organ functions of other mineral metabolism network member including bone fail into uncontrollable due to dysregulated feedback system. This is the concept of Chronic Kidney Disease(related)- Mineral and Bone Disorder(CKD-MBD). However, the bone metabolic abnormalities in patients with chronic kidney disease cannot be explained merely by the framework of this mineral metabolism network. Although dialysis patients show several times higher hip fracture risk than general population, the main pathogenesis seems not to be their disordered mineral metabolism. We need to consider "uremic osteoporosis" characterized by deteriorated bone material properties due to uremic condition.

[Phosphate binders in renal patients: a point estimate from rationale, through evidences to the real world setting]

Phosphate binders represent a common intervention in renal patients affected by chronic kidney disease and mineral bone disorder (CKD-MBD). Although counteracting P overload through binders adoption is argued by a physiology-driven approach, the efficacy of this intervention on hard endpoints remains poorly evident. The inconsistencies between rationale and methodological weakness, concerning the clinical relevance of P binding in chronic kidney disease, will be herein discussed with special focus on the need of a multi-factorial treatment against CKD-MBD, which is currently more achievable due to the variety of P binders and the rapid evolution of nutritional therapy, dialysis techniques and nursing science.

Oral Manifestations of Chronic Kidney Disease and Renal Secondary Hyperparathyroidism: A Comparative Review

Recent epidemiological studies have demonstrated that significant associations exist between oral disease and diseases involving non-oral tissues. Occasionally, the roles may be reversed and the oral cavity can be severely affected by systemic disease originating in another part of the body. Renal secondary hyperparathyroidism is a common endocrinopathy that occurs as a consequence of chronic azotemic kidney disease. Renal osteodystrophy, the most dramatic clinical consequence of renal secondary hyperparathyroidism is uncommon, but can result in demineralization of maxillofacial bones, loosening of teeth, and pathological jaw fractures. The purpose of this report is to update the current understanding of the pathophysiology of this endocrine disease and to compare the oral manifestations of renal secondary hyperparathyroidism in humans and companion animals. A 50-year review of the veterinary literature was undertaken to examine the clinical presentation of renal osteodystrophy in dogs, and to determine what clinical consequences of renal secondary hyperparathyroidism have been reported in domestic cats.

Adynamic bone disease: from bone to vessels in chronic kidney disease

Adynamic bone disease (ABD) is a well-recognized clinical entity in the complex chronic kidney disease (CKD)-mineral and bone disorder. Although the combination of low intact parathyroid hormone (PTH) and low bone alkaline phosphatase levels may be suggestive of ABD, the gold standard for precise diagnosis is histomorphometric analysis of tetracycline double-labeled bone biopsies. ABD essentially is characterized by low bone turnover, low bone volume, normal mineralization, and markedly decreased cellularity with minimal or no fibrosis. ABD is increasing in prevalence relative to other forms of renal osteodystrophy, and is becoming the most frequent type of bone lesion in some series. ABD develops in situations with reduced osteoanabolic stimulation caused by oversuppression of PTH, multifactorial skeletal resistance to PTH actions in uremia, and/or dysregulation of Wnt signaling. All may contribute not only to bone disease but also to the early vascular calcification processes observed in CKD. Various risk factors have been linked to ABD, including calcium loading, ageing, diabetes, hypogonadism, parathyroidectomy, peritoneal dialysis, and antiresorptive therapies, among others. The relationship between low PTH level, ABD, increased risk fracture, and vascular calcifications may at least partially explain the association of ABD with increased mortality rates. To achieve optimal bone and cardiovascular health, attention should be focused not only on classic control of secondary hyperparathyroidism but also on prevention of ABD, especially in the steadily growing proportions of diabetic, white, and elderly patients. Overcoming the insufficient osteoanabolic stimulation in ABD is the ultimate treatment goal.

Decreased renal function in association with administration of 1,25-dihydroxyvitamin D3 to patients with stable, advanced renal failure

A controlled study of the effects of 1,25-dihydroxycholecalciferol (1,25[OH]2D3) and vitamin D3 (D3) was performed in 18 non-dialyzed patients with chronic renal failure (CRF) (creatinine clearance below 35 ml/min) and mild renal osteodystrophy. After 6 months observation of the spontaneous course, the patients were randomly allocated to 6 months oral treatment with either 1,25(OH)2D3 or D3 in initial daily doses of 1 and 100 microgram, respectively, combined with 0.5 g calcium (Calcium Sandoz). 1,25(OH)2D3 had a fast normalizing effect on the biochemical changes of calcium metabolism. D3 had similar, but less pronounced effects. The percent fall in creatinine clearance was greater during than before treatment in all patients on 1,25(OH)2D3 (p less than 0.01) and in 7 of 9 patients on D3 treatment (n.s.). Deterioration of renal function is a major limitation to clinical use of 1,25(OH)2D3 (and D3) in non-dialyzed patients with CRF. In fact, the decreased formation of 1,25(OH)2D3 seen in CRF might protect renal function through the abnormalities in mineral metabolism.

Renal osteodystrophy in early chronic renal failure

A bone histological investigation was performed in 20 mondialyzed patients with chronic renal failure and a glomerular filtration rate of 5.1--31.9 ml/min. Osteomalacia was the predominant pathological feature in 60% of the patients, mixed lesion of both osteomalacia and osteitis fibrosa in 30%, and osteitis fibrosa only was seen in 5% of the patients. Only 1 showed normal bone histology. Elevated plasma immunoreactive parathyroid hormone was found in only 1 patient out of 6. The beneficial effect of 1 alpha-hydroxycholecalciferol was recognized in 7 patients, but the drug induced relatively rapid growth of serum creatinine incidentally, when patients had more than 4 mg/dl of serum creatinine.

Effects of unfractionated heparin on renal osteodystrophy and vascular calcification in chronic kidney disease rats

Unfractionated heparin (UFH) is the most widely used anticoagulant in hemodialysis for chronic kidney disease (CKD) patients. Many studies have verified that UFH can induce bone loss in subjects with normal bone, but few have focused on its effect on renal osteodystrophy. We therefore investigated this issue in adenine-induced CKD rats. As CKD also impairs mineral metabolism systemically, we also studied the impacts of UFH on serum markers of CKD-mineral and bone disorder (CKD-MBD) and vascular calcification. We administered low and high doses of UFH (1U/g and 2U/g body weight, respectively) to CKD rats and compared them with CKD controls. At sacrifice, the serum markers of CKD-MBD did not significantly differ among the two UFH CKD groups and the CKD control group. The mean bone mineral densities (BMDs) of the total femur and a region of interest (ROI) constituted of trabecular and cortical bone were lower in the high-dose UFH (H-UFH) CKD group than in the CKD control group (P<0.05 and P<0.01, respectively). The BMD of the femoral ROI constituted of cortical bone did not differ between the H-UFH CKD group and the CKD control group. Histomorphometrical changes in the CKD rats indicated secondary hyperparathyroidism, and the femoral trabecular bone volume, but not cortical bone volume, significantly decreased with increasing UFH dose. The same decreasing trend was found in osteoblast parameters, and an increasing trend was found in osteoclast parameters; however, most differences were not significant. Moreover, no distinct statistical differences were found in the comparison of vascular calcium or phosphorus content among the CKD control group and the two UFH CKD groups. Therefore, we concluded that UFH could induce bone loss in CKD rats with secondary hyperparathyroidism, mainly by reducing the trabecular volume and had little effect on cortical bone volume. The underlying mechanism might involve inhibition of osteoblast activity and promotion of osteoclast activity by UFH. We did not find any effect of UFH on vascular calcification in CKD rats with secondary hyperparathyroidism.

Which vitamin D in CKD-MBD? The time of burning questions

Vitamin D is a common treatment against secondary hyperparathyroidism in renal patients. However, the rationale for the prescription of vitamin D sterols in chronic kidney disease (CKD) is rapidly increasing due to the coexistence of growing expectancies close to unsatisfactory evidences, such as (1) the lack of randomized controlled trials (RCTs) proving the superiority of any vitamin D sterol against placebo on patients centered outcomes, (2) the scanty clinical data on head to head comparisons between the multiple vitamin D sterols currently available, (3) the absence of RCTs confirming the crescent expectations on nutritional vitamin D pleiotropic effects even in CKD patients, (4) the promising effects of vitamin D receptors activators (VDRA) against proteinuria and myocardial hypertrophy in diabetic CKD cohorts, and (5) the conflicting data on the impact on mortality of VDRA versus calcimimetic centered regimens to control CKD-MBD. The present review arguments these issues focusing on the opened questions that nephrologists should consider dealing with the prescription of nutritional vitamin D or VDRA and with the choice of a VDRA versus a calcimimetic based regimen in CKD-MBD patients.

Modeling hepatic osteodystrophy in Abcb4 deficient mice

Hepatic osteodystrophy (HOD) denotes the alterations in bone morphology and metabolism frequently observed in patients with chronic liver diseases, in particular in case of cholestatic conditions. The molecular mechanisms underlying HOD are only partially understood. In the present study, we characterized the bone phenotypes of the ATP-binding cassette transporter B4 knockout mouse (Abcb4(-/-)), a well-established mouse model of chronic cholestatic liver disease, with the aim of identifying and characterizing a mouse model for HOD. Furthermore, we investigated the influence of vitamin D on bone quality in this model. The bone morphology analyses revealed reduced bone mineral contents as well as changes in trabecular bone architecture and decreased cortical bone densities in Abcb4(-/-) mice with severe liver fibrosis. We observed dysregulation of genes involved in bone remodeling (osteoprotegerin, osteocalcin, osteopontin) and vitamin D metabolism (7-dehydrocholesterol reductase, Gc-globulin, Cyp2r1, Cyp27a1) as well as alterations in calcium and vitamin D homeostasis. In addition, serum RANKL and TGF-β levels were increased in Abcb4(-/-) mice. Vitamin D dietary intervention did not restore the bone phenotypes of Abcb4(-/-) animals. We conclude that the Abcb4(-/-) mouse provides an experimental framework and a preclinical model to gain further insights into the molecular pathobiology of HOD and to study the systemic effects of therapeutic interventions.

The osteocyte in CKD: new concepts regarding the role of FGF23 in mineral metabolism and systemic complications

The identification of elevated circulating levels of the osteocytic protein fibroblast growth factor 23 (FGF23) in patients with chronic kidney disease (CKD), along with recent data linking these values to the pathogenesis of secondary hyperparathyroidism and to systemic complications, has changed the approach to the pathophysiology and treatment of disordered bone and mineral metabolism in renal failure. It now appears that osteocyte biology is altered very early in the course of CKD and these changes have implications for bone biology, as well as for progressive cardiovascular and renal disease. Since circulating FGF23 values are influenced by therapies used to treat secondary hyperparathyroidism, the effects of different therapeutic paradigms on FGF23 have important implications for mineral metabolism as well as for morbidity and mortality. Further studies are critically needed to identify the initial trigger for abnormalities of skeletal mineralization and turnover as well as the potential effects that current therapeutic options may have on osteocyte biology.

Searching the optimal PTH target range in children undergoing peritoneal dialysis: new insights from international cohort studies

The treatment of the mineral and bone disorder associated with chronic kidney disease (CKD-MBD) remains a major challenge in pediatric patients. The principal aims of therapeutic measures are not only to prevent the debilitating skeletal complications and to achieve normal growth but also to preserve long-term cardiovascular health. Serum parathyroid hormone (PTH) levels are used as a surrogate parameter of bone turnover. Whereas it is generally accepted that serum calcium and phosphate levels should be kept within the range for age, current pediatric consensus guidelines differ markedly with respect to the optimal PTH target range and operate on a limited evidence base. Recently, the International Pediatric Dialysis Network (IPPN) established a global registry collecting detailed clinical and biochemical information, including data relevant to CKD-MBD in children on chronic peritoneal dialysis (PD). This review highlights the current evidence basis regarding the optimal PTH target range in pediatric CKD patients, and re-assesses the current guidelines in view of the outcome data collected by the IPPN registry. Based on a comprehensive evaluation of CKD-MBD outcome measures in this global patient cohort, a PTH target range of 1.7-3 times the upper limit of normal (i.e. 100-200 pg/ml) appears reasonable in children undergoing chronic PD.

Relationship between aortic mineral elements and osteodystrophy in mice with chronic kidney disease

In chronic kidney disease (CKD), osteodystrophy and arterial calcification often coexist. However, arterial alterations have not been addressed in CKD unaccompanied by evidence of calcification. We investigated the association of phosphate (P) and calcium (Ca) accumulation in calcification-free aortas with CKD-induced osteodystrophy. Aortic accumulation of magnesium (Mg), an inhibitor of calcification, was also examined. Male mice aged 26 weeks with CKD characterized by hyperparathyroidism and hyperphosphatemia (Nx, n = 8) and age-matched healthy male mice (shams, n = 8) were sampled for blood, and thoracic vertebrae and aortas were harvested. Bone structure and chemicals were analyzed by microcomputed tomography and infrared microspectroscopy, respectively, and aortic accumulation of P, Ca, and Mg was evaluated by plasma-atomic emission spectrometry. Volume fractions of cortical and trabecular bones were smaller in Nx than in sham animals (P < 0.05), attributed to cortical thinning and reduction in trabecular number, respectively. Bone chemicals were not different between the groups. No calcification was found in either group, but P, Ca, and Mg contents were higher in Nx than in shams (P < 0.05). The mass ratio of Ca/P was lower in Nx than in shams (P < 0.05), but that of Mg/Ca and Mg/P was not different between the groups. Aortic P and Ca contents were inversely correlated with the volume fraction of cortical bone (P < 0.05). In conclusion, the relationship of osteodystrophy with aortic P and Ca accumulation suggests the existence of a bone-vascular axis, even in calcification-free arteries in CKD. The preservation of ratios of Mg/Ca and Mg/P despite CKD development might contribute to calcification resistance.

The consequences of chronic kidney disease on bone metabolism and growth in children

Growth retardation, decreased final height and renal osteodystrophy (ROD) are common complications of childhood chronic kidney disease (CKD), resulting from a combination of abnormalities in the growth hormone (GH) axis, vitamin D deficiency, hyperparathyroidism, hypogonadism, inadequate nutrition, cachexia and drug toxicity. The impact of CKD-associated bone and mineral disorders (CKD-MBD) may be immediate (serum phosphate/calcium disequilibrium) or delayed (poor growth, ROD, fractures, vascular calcifications, increased morbidity and mortality). In 2012, the clinical management of CKD-MBD in children needs to focus on three main objectives: (i) to provide an optimal growth in order to maximize the final height with an early management with recombinant GH therapy when required, (ii) to equilibrate calcium/phosphate metabolism so as to obtain acceptable bone quality and cardiovascular status and (iii) to correct all metabolic and clinical abnormalities that can worsen bone disease, growth and cardiovascular disease, i.e. metabolic acidosis, anaemia, malnutrition and 25(OH)vitamin D deficiency. The aim of this review is to provide an overview of the mineral, bone and vascular abnormalities associated with CKD in children in terms of pathophysiology, diagnosis and clinical management.

[Kidney and bone update : the 5-year history and future of CKD-MBD. About the guideline of the Japanese Society for Dialysis Therapy]

Disturbances in mineral and bone metabolism are prevalent in chronic kidney disease (CKD) and are an important cause of morbidity, decreased quality of life Accordingly, instead of the classic term "Renal Osteodystrophy (ROD) " , a new term, "CKD-Mineral and Bone Disorders (CKD-MBD) " , has been proposed as a systemic disorder. In 2012, new Japanese Society for Dialysis Therapy (JSDT) clinical practice guideline for CKD-MBD is intended to assist the practitioner caring for adults and children with CKD stages 3-5, on HD therapy, on PD therapy or with a kidney transplant.

[End stage of chronic kidney disease and metabolic acidosis]

Renal function disorder is inevitably associated with metabolic acidosis. An adult produces approximately 1 mmol of acids/kg of body weight every day (3 mmol/kg in children), derived from metabolization of proteins from food. Development of metabolic acidosis in patients with kidney disease is based on accumulation of acids and insufficient production of bicarbonates; alkaline loss represents a marginal issue here limited to patients with type II renal tubular acidosis only. The prevalence of this disorder increases with declining glomerular filtration (GFR) from 2% in patients with GFR 1.0-1.5 ml/s/1.73 m2 to 39% in patients with GFR < 0.3 ml/s/1.73 m2 or, alternatively, to 19% in patients with GFR 0.25-0.3 ml/s/1.73 m2. Notwithstanding the primary cause of the renal disease, declining GFR is associated with compensatory increase in ammoniac production in residual nephrons. This is an adaptive mechanism aimed at maintaining sufficient elimination of acids despite reduced volume of functional tissue. However, an increased ammoniac production simultaneously becomes a stimulus for activation of the complement via an alternative route and is thus one of the factors contributing, through this induced inflammation, to progression of tubular interstitial fibrosis that subsequently leads to further GFR reduction. Metabolic acidosis has a number of severe adverse effects on the organism, e.g. deterioration of kidney bone disease through stimulation of bone resorption and inhibition of bone formation, inhibition of vitamin D formation, increased muscle catabolism, reduced albumin production, glucose metabolism disorder, increased insulin resistance, reduced production of thyroid hormones, increased accumulation of β2-microglobulin etc. Non-interventional studies suggest that alkali supplementation may slow down progression of chronic nephropathies. However, this approach, safe and inexpensive, has not been widely implemented in clinical practice yet. With respect to dialyzed patients, abnormal levels of bicarbonates are associated with increased mortality. Both metabolic acidosis and alkalosis, rather regularly seen in a considerable number of patients, have a negative effect on patient survival. Alkali substitution from a dialysis solution is the main pillar of metabolic acidosis management in patients on hemo- as well as peritoneal dialysis. Available technologies allow individualization of the treatment and this should be observed.

Type 2 diabetes and bone fractures

PURPOSE OF REVIEW

To discuss current literature and hypotheses pertaining to the pathophysiology of increased bone fragility and fracture in men and women with type 2 diabetes mellitus.

RECENT FINDINGS

Despite high bone mineral density, studies have shown that men and women with type 2 diabetes mellitus (T2DM) are at increased risk for fracture. Complications of T2DM including retinopathy and autonomic dysfunction may contribute to bone fracture by increasing fall risk. Nephropathy may lead to renal osteodystrophy. Lean mass and potentially fat mass, may additionally contribute to skeletal health in diabetes. There is increasing acknowledgement that the marrow microenvironment is critical to efficient bone remodeling. Medications including thiazolidinediones and selective serotonin reuptake inhibitors may also impair bone remodeling by acting on mesenchymal stem cell differentiation and osteoblastogenesis. T2DM is associated with significant alterations in systemic inflammation, advanced glycation end-product accumulation and reactive oxygen species generation. These systemic changes may also directly and adversely impact the remodeling cycle and lead to bone fragility in T2DM, though more research is needed.

SUMMARY

Fracture is a devastating event with dismal health consequences. Identifying the extrinsic and intrinsic biochemical causes of bone fracture in T2DM will speed the discovery of effective strategies for fracture prevention and treatment in this at-risk population.