IL-1beta, TNF-alpha, TGF-beta, and bFGF expression in bone biopsies before and after parathyroidectomy

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.

Tumor necrosis factor-alpha is associated with mineral bone disorder and growth impairment in children with chronic kidney disease

BACKGROUND

Mineral and bone disorder (MBD) and growth impairment are common complications of pediatric chronic kidney disease (CKD). Chronic inflammation detrimentally affects bone health and statural growth in non-CKD settings, but the impact of inflammation on CKD-MBD and growth in pediatric CKD remains poorly understood. This study assessed associations between inflammatory cytokines with biomarkers of CKD-MBD and statural growth in pediatric CKD.

METHODS

This is a cross-sectional study of children with predialysis CKD stages II-V. Cytokines (IL-1b, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, TNF-α, interferon-γ), bone alkaline phosphatase (BAP), and procollagen type 1 N-terminal propeptide (P1NP) were measured at the same time as standard CKD-MBD biomarkers. Associations between cytokines, CKD-MBD biomarkers, and height z-score were assessed using linear regression analysis.

RESULTS

Among 63 children, 52.4% had stage 3 CKD, 76.2% non-glomerular CKD etiology, and 21% short stature. TNF-α was the only cytokine associated with parathyroid hormone (PTH) independent of glomerular filtration rate. After stratification by low, medium, and high TNF-α tertiles, significant differences in PTH, serum phosphorus, alkaline phosphatase, BAP, P1NP, and height z-score were found. In a multivariate analysis, TNF-α positively associated with phosphorus, PTH, and alkaline phosphatase and inversely associated with height z-score, independent of kidney function, age, sex, and active vitamin D analogue use.

CONCLUSIONS

TNF-α is positively associated with biomarkers of CKD-MBD and inversely associated with height z-score, indicating that inflammation likely contributes to the development of CKD-MBD and growth impairment in pediatric CKD. Prospective studies to definitively assess causative effects of inflammation on bone health and growth in children with CKD are warranted.

Parathyroid Hormone: A Uremic Toxin

Parathyroid hormone (PTH) has an important role in the maintenance of serum calcium levels. It activates renal 1α-hydroxylase and increases the synthesis of the active form of vitamin D (1,25[OH]₂D₃). PTH promotes calcium release from the bone and enhances tubular calcium resorption through direct action on these sites. Hallmarks of secondary hyperparathyroidism associated with chronic kidney disease (CKD) include increase in serum fibroblast growth factor 23 (FGF-23), reduction in renal 1,25[OH]₂D₃ production with a decline in its serum levels, decrease in intestinal calcium absorption, and, at later stages, hyperphosphatemia and high levels of PTH. In this paper, we aim to critically discuss severe CKD-related hyperparathyroidism, in which PTH, through calcium-dependent and -independent mechanisms, leads to harmful effects and manifestations of the uremic syndrome, such as bone loss, skin and soft tissue calcification, cardiomyopathy, immunodeficiency, impairment of erythropoiesis, increase of energy expenditure, and muscle weakness.

The Osteocyte as the New Discovery of Therapeutic Options in Rare Bone Diseases

Osteocytes are the most abundant (~95%) cells in bone with the longest half-life (~25 years) in humans. In the past osteocytes have been regarded as vestigial cells in bone, since they are buried inside the tough bone matrix. However, during the last 30 years it has become clear that osteocytes are as important as bone forming osteoblasts and bone resorbing osteoclasts in maintaining bone homeostasis. The osteocyte cell body and dendritic processes reside in bone in a complex lacuno-canalicular system, which allows the direct networking of osteocytes to their neighboring osteocytes, osteoblasts, osteoclasts, bone marrow, blood vessels, and nerves. Mechanosensing of osteocytes translates the applied mechanical force on bone to cellular signaling and regulation of bone adaptation. The osteocyte lacuno-canalicular system is highly efficient in transferring external mechanical force on bone to the osteocyte cell body and dendritic processes via displacement of fluid in the lacuno-canalicular space. Osteocyte mechanotransduction regulates the formation and function of the osteoblasts and osteoclasts to maintain bone homeostasis. Osteocytes produce a variety of proteins and signaling molecules such as sclerostin, cathepsin K, Wnts, DKK1, DMP1, IGF1, and RANKL/OPG to regulate osteoblast and osteoclast activity. Various genetic abnormality-associated rare bone diseases are related to disrupted osteocyte functions, including sclerosteosis, van Buchem disease, hypophosphatemic rickets, and WNT1 and plastin3 mutation-related disorders. Meticulous studies during the last 15 years on disrupted osteocyte function in rare bone diseases guided for the development of various novel therapeutic agents to treat bone diseases. Studies on genetic, molecular, and cellular mechanisms of sclerosteosis and van Buchem disease revealed a role for sclerostin in bone homeostasis, which led to the development of the sclerostin antibody to treat osteoporosis and other bone degenerative diseases. The mechanism of many other rare bone diseases and the role of the osteocyte in the development of such conditions still needs to be investigated. In this review, we mainly discuss the knowledge obtained during the last 30 years on the role of the osteocyte in rare bone diseases. We speculate about future research directions to develop novel therapeutic drugs targeting osteocyte functions to treat both common and rare bone diseases.

TGF-Beta Signaling in Bone with Chronic Kidney Disease

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

Bone marrow failure and extramedullary hematopoiesis in McCune-Albright syndrome

In fibrous dysplasia/McCune-Albright syndrome (FD/MAS), bone and bone marrow are, to varying degrees, replaced by fibro-osseous tissue typically devoid of hematopoietic marrow. Despite the extensive marrow replacement in severely affected patients, bone marrow failure is not commonly associated with FD/MAS. We present a 14-year-old girl with FD/MAS, who developed pancytopenia and extramedullary hematopoiesis (EMH) with no identified cause, in the setting of iatrogenic thyrotoxicosis and hyperparathyroidism. Pancytopenia, requiring monthly blood transfusions, persisted despite multiple strategies to correct these endocrinopathies. Due to worsening painful splenomegaly, likely as a result of sequestration, splenectomy was performed. Following splenectomy, pancytopenia resolved and patient has since been transfusion-independent. We report the first detailed case of bone marrow failure and EMH in FD/MAS. The etiology of marrow failure is likely multifactorial and related to the loss of marrow reserve due to extensive polyostotic FD, exacerbated by iatrogenic thyrotoxicosis and hyperparathyroidism. Mini Abstract: A patient with fibrous dysplasia developed bone marrow failure and extramedullary hematopoiesis. The etiology likely involved loss of hematopoetic marrow space and uncontrolled endocrinopathies. Splenectomy was therapeutic.

Osteocyte Protein Expression Is Altered in Low-Turnover Osteoporosis Caused by Mutations in WNT1 and PLS3

CONTEXT

Osteocytes express proteins that regulate bone remodeling and mineralization.

OBJECTIVE

To evaluate the relationship between osteocyte-specific protein expression and bone histology in patients with monogenic osteoporosis due to wingless integration site 1 (WNT1) or plastin 3 (PLS3) mutations.

DESIGN AND SETTING

Cross-sectional cohort study at a university hospital.

PARTICIPANTS

Six patients (four males; ages: 14 to 72 years) with a heterozygous WNT1 mutation and five patients (four males; ages: 9 to 70 years) with a heterozygous/hemizygous PLS3 mutation.

METHODS AND MAIN OUTCOME MEASURES

Immunohistochemistry was performed for fibroblast growth factor 23 (FGF23), dentin matrix protein 1 (DMP1), sclerostin, and phosphorylated (phospho-)β-catenin in iliac crest samples and compared with bone histomorphometry.

RESULTS

FGF23 expression in WNT1 patients was 243% that observed in PLS3 patients (P < 0.01). DMP1, sclerostin, and phospho-β-catenin expression did not differ between groups. Serum phosphate correlated inversely with FGF23 expression (r = -0.79, P = 0.01) and serum ionized calcium correlated inversely with sclerostin expression (r = -0.60, P = 0.05). Phospho-β-catenin expression correlated inversely with DMP1 expression (r = -0.88, P < 0.001), osteoid volume/bone volume (r = -0.68, P = 0.02), and bone formation rate (r = -0.78, P < 0.01). FGF23 expression did not correlate with DMP1 expression, sclerostin expression, or bone histomorphometry. Marrow adiposity was higher in WNT1 than in PLS3 patients (P = 0.04).

CONCLUSIONS

Mutations that disrupt WNT signaling and osteocytic mechanosensing affect osteocyte protein expression. Abnormal osteocyte function may play a role in the pathogenesis of monogenetic forms of osteoporosis.

Pharmacological Management of Secondary Hyperparathyroidism in Patients with Chronic Kidney Disease

Secondary hyperparathyroidism (SHPT) is a common complication of chronic kidney disease (CKD) and is part of the CKD-mineral bone disorder (CKD-MBD). SHPT is associated with increased risk of fracture and mortality; thus, SHPT control is recommended as kidney function declines. Effective SHPT management becomes more difficult once skeletal and cardiovascular adverse effects associated with severe SHPT have become established. However, interventional studies to lower parathyroid hormone (PTH) have so far shown inconsistent results in improving patient-centred outcomes such as mortality, cardiovascular events and fracture. Pharmacological treatment effect on PTH level is also inconsistent between pre-dialysis CKD and dialysis patients, which adds to the complexity of SHPT management. This review aims to give an overview on the pathophysiology, pharmacological and non-pharmacological treatment for SHPT in CKD including some of the limitations of current therapeutic options.

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

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

Anaemia in kidney disease: harnessing hypoxia responses for therapy

Improved understanding of the oxygen-dependent regulation of erythropoiesis has provided new insights into the pathogenesis of anaemia associated with renal failure and has led to the development of novel therapeutic agents for its treatment. Hypoxia-inducible factor (HIF)-2 is a key regulator of erythropoiesis and iron metabolism. HIF-2 is activated by hypoxic conditions and controls the production of erythropoietin by renal peritubular interstitial fibroblast-like cells and hepatocytes. In anaemia associated with renal disease, erythropoiesis is suppressed due to inadequate erythropoietin production in the kidney, inflammation and iron deficiency; however, pharmacologic agents that activate the HIF axis could provide a physiologic approach to the treatment of renal anaemia by mimicking hypoxia responses that coordinate erythropoiesis with iron metabolism. This Review discusses the functional inter-relationships between erythropoietin, iron and inflammatory mediators under physiologic conditions and in relation to the pathogenesis of renal anaemia, as well as recent insights into the molecular and cellular basis of erythropoietin production in the kidney. It furthermore provides a detailed overview of current clinical experience with pharmacologic activators of HIF signalling as a novel comprehensive and physiologic approach to the treatment of anaemia.

Role of TGF-β in a mouse model of high turnover renal osteodystrophy

Altered bone turnover is a key pathologic feature of chronic kidney disease-mineral and bone disorder (CKD-MBD). Expression of TGF-β1, a known regulator of bone turnover, is increased in bone biopsies from individuals with CKD. Similarly, TGF-β1 mRNA and downstream signaling is increased in bones from jck mice, a model of high-turnover renal osteodystrophy. A neutralizing anti-TGF-β antibody (1D11) was used to explore TGF-β's role in renal osteodystrophy. 1D11 administration to jck significantly attenuated elevated serum osteocalcin and type I collagen C-telopeptides. Histomorphometric analysis indicated that 1D11 administration increased bone volume and suppressed the elevated bone turnover in a dose-dependent manner. These effects were associated with reductions in osteoblast and osteoclast surface areas. Micro-computed tomography (µCT) confirmed the observed increase in trabecular bone volume and demonstrated improvements in trabecular architecture and increased cortical thickness. 1D11 administration was associated with significant reductions in expression of osteoblast marker genes (Runx2, alkaline phosphatase, osteocalcin) and the osteoclast marker gene, Trap5. Importantly, in this model, 1D11 did not improve kidney function or reduce serum parathyroid hormone (PTH) levels, indicating that 1D11 effects on bone are independent of changes in renal or parathyroid function. 1D11 also significantly attenuated high-turnover bone disease in the adenine-induced uremic rat model. Antibody administration was associated with a reduction in pSMAD2/SMAD2 in bone but not bone marrow as assessed by quantitative immunoblot analysis. Immunostaining revealed pSMAD staining in osteoblasts and osteocytes but not osteoclasts, suggesting 1D11 effects on osteoclasts may be indirect. Immunoblot and whole genome mRNA expression analysis confirmed our previous observation that repression of Wnt/β-catenin expression in bone is correlated with increased osteoclast activity in jck mice and bone biopsies from CKD patients. Furthermore, our data suggest that elevated TGF-β may contribute to the pathogenesis of high-turnover disease partially through inhibition of β-catenin signaling.

Serum transforming growth factor-beta levels in patients with vitamin D deficiency

BACKGROUND

Transforming growth factor-beta 1 (TGF-β1) contributes to tissue repair by promoting tissue fibrosis, and elevations have been reported in patients with bone marrow fibrosis. The aim of this study was to evaluate the relationship between TGF-β1 levels and vitamin D deficiency.

METHODS

All patients presenting to the outpatient Endocrinology and Metabolic Diseases clinic between June and September of 2008 were approached, and consenting patients who were deemed suitable candidates were enrolled. Hematological parameters were measured, along with serum levels of total and ionized calcium, phosphorus, parathyroid hormone, iron, folic acid vitamin B12 levels, 25 OH vitamin D3 (25OHD(3)) and TGF-β1.

RESULTS

A total of 132 patients were included in the study. Patients were divided into 4 groups based on levels of 25OHD(3) [group 1 (<5 ng/ml), 20 patients; group 2 (5-15 ng/ml), 38 patients; group 3 (16-30 ng/ml); and group 4 (>30 ng/ml), 28 patients]. TGF-β1 levels were higher in patients in group 1 compared to the other groups. Transforming growth factor-beta levels correlated negatively with vitamin D3 and positively with leukocyte count, platelet count, of MCV and MCH. Multiple regression analyses revealed TGF-β1 levels to be associated with 25OHD(3) as well as with platelet count.

CONCLUSIONS

Results of this study are suggestive of the presence of a significant relationship between TGF-β and vitamin D deficiency. Increased TGF-β1 and platelet count may be an early indicator of bone marrow fibrosis in patients with vitamin D deficiency.

Dietary-induced hyperparathyroidism affects serum and gingival proinflammatory cytokine levels in rats

BACKGROUND

Poor diet and inadequate nutrition are suggested to affect the periodontium as well as impair the systemic health. This study investigated the systemic and periodontal effects of dietary-induced hyperparathyroidism (dHPT) by evaluating serum and gingival proinflammatory cytokine levels.

METHODS

Twenty-four Sprague-Dawley rats were used in the study. dHPT was induced in 12 rats by calcium/phosphorus imbalance, and 12 rats were fed a standard diet (SD). Afterward, endotoxin-induced periodontitis was induced on the right mandibular molar teeth (mmt). Four study groups were created: dHPT + mmt without periodontitis (group 1), dHPT + mmt with periodontitis (group 2), SD + mmt with periodontitis (group 3), and SD + mmt without periodontitis (group 4). Interleukin (IL)-1beta and tumor necrosis factor-alpha (TNF-alpha) levels were measured by enzyme-linked immunosorbent assay to evaluate the proinflammatory cytokine profiles. Serum cytokines were analyzed in the blood samples collected prior to periodontitis induction, whereas gingival cytokines were analyzed in the gingival supernatants of the four groups.

RESULTS

Serum cytokines were higher in dHPT rats than in SD rats (P <0.001), with a positive correlation between parathormone and the cytokines (P <0.001). Gingival cytokines were highest in group 2 and lowest in group 4 (group 2 > group 3 > group 1) (P <0.001). There was a positive correlation between parathormone and the gingival cytokines in group 1 (P <0.001 for IL-1beta; P <0.01 for TNF-alpha).

CONCLUSION

The results suggested that increased serum proinflammatory cytokine production may be a complication of dHPT, and this may affect healthy and diseased periodontia by increasing gingival proinflammatory cytokine levels.

Gene clustering analysis in human osseous remodeling

BACKGROUND

Tentative bioinformatic predictions were performed to comprehend the complexity of the gene interaction networks of the T lymphocyte cell cycle and of human periodontitis. This study aims to identify and rank genes involved in osseous augmentation or bone remodeling to obtain groups with more numerous predicted associations called the leader gene clusters.

METHODS

An iterative search (consisting of a consecutive expansion-filtering loop) was performed for which only genes involved in a specific process were identified. For each gene, predicted associations with all other involved genes were obtained from a Web-available database (Search Tool for the Retrieval of Interacting Genes/Proteins) and the weighted number of links (WNL), given by the sum of only high-confidence predicted associations (results with a score > or =0.9), allowing gene ranking. Genes belonging to higher clustering classes were identified.

RESULTS

A total of 161 genes potentially involved in bone-volume augmentation and 128 genes connected with the bone-remodeling phenomenon were identified. For the bone-volume augmentation process, only one gene belonged to the leader gene group, whereas six other genes were classified as cluster B genes; for the bone-remodeling phenomenon, three leader genes were identified, whereas six other genes formed the cluster B group. No one gene belonged to leader gene clusters of both processes, whereas one gene of each higher cluster group belonged to the immediately lower cluster of the opposite process. Only three genes of the higher clusters were experimentally involved in both analyses.

CONCLUSIONS

A de novo identification was performed based on the data mining of leader genes involved in bone-volume augmentation or bone remodeling to acquire primeval information about their molecular basis and to plan future ad hoc targeted experiments. For several genes of the upper clusters, an active role in the bone processes was already known, but the present analysis suggested that they play a major role in the analyzed phenomena. The role of the transcription factors as leader genes and the numerous orphan genes (genes with WNL = 0) recovered probably attest to a lack of information regarding these processes, which could be further clarified through specific DNA microarray experiments.

Patterns of FGF-23, DMP1, and MEPE expression in patients with chronic kidney disease

Fibroblast growth factor 23 (FGF-23), dentin matrix protein 1 (DMP1), and matrix extracellular phosphoglycoprotein (MEPE) are skeletal proteins involved in the regulation of phosphate homeostasis and bone metabolism. Circulating FGF-23 levels are increased in patients with chronic kidney disease (CKD); however, FGF-23 skeletal expression and its regulation by DMP1 and MEPE have yet to be evaluated. Thus, expression of these three proteins was characterized by immunohistochemistry in 32 pediatric and young adult patients with CKD stages 2-5. When compared to normal controls, bone FGF-23 and DMP1 expression were increased in all stages of CKD; significant differences in bone FGF-23 and DMP1 expression were not detected between pre-dialysis CKD and dialysis patients. Bone MEPE expression in CKD did not differ from controls. FGF-23 was expressed in osteocyte cell bodies located at the trabecular periphery. DMP1 was widely expressed in osteocyte cell bodies and dendrites throughout bone. MEPE was also expressed throughout bone, but only in osteocyte cell bodies. Bone FGF-23 expression correlated directly with plasma levels of the protein (r=0.43, p<0.01) and with bone DMP1 expression (r=0.54, p<0.01) and expression of both proteins were inversely related to osteoid accumulation. Bone MEPE expression was inversely related to bone volume. In conclusion, skeletal FGF-23 and DMP1 expression are increased in CKD and are related to skeletal mineralization. The patterns of expression of FGF-23, MEPE, and DMP1 differ markedly in trabecular bone, suggesting that individual osteocytes may have specialized functions. Increases in bone FGF-23 and DMP1 expression suggest that osteocyte function is altered early in the course of CKD.

RANKL is a mediator of bone resorption in idiopathic hypercalciuria

BACKGROUND AND OBJECTIVES

This study aimed to determine the expression of osteoprotegerin, receptor activator of nuclear factor kappaB ligand, interleukin-1alpha, transforming growth factor-beta, and basic fibroblast growth factor in stone-forming patients with idiopathic hypercalciuria.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Immunohistochemical analysis was performed in undecalcified bone samples previously obtained from 36 transiliac bone biopsies of patients who had idiopathic hypercalciuria and whose histomorphometry had shown lower bone volume, increased bone resorption, and prolonged mineralization lag time.

RESULTS

Bone expression of receptor activator of nuclear factor kappaB ligand and osteoprotegerin was significantly higher in patients with idiopathic hypercalciuria versus control subjects. Transforming growth factor-beta immunostaining was lower in patients with idiopathic hypercalciuria than in control subjects and correlated directly with mineralization surface. Interleukin-1alpha and basic fibroblast growth factor staining did not differ between groups. Receptor activator of nuclear factor kappaB ligand bone expression was significantly higher in patients who had idiopathic hypercalciuria and exhibited higher versus normal bone resorption.

CONCLUSION

A higher expression of receptor activator of nuclear factor kappaB ligand in bone tissue suggests that increased bone resorption in patients with idiopathic hypercalciuria is mediated by receptor activator of nuclear factor kappaB ligand. Osteoprotegerin bone expression might have been secondarily increased in an attempt to counteract the actions of receptor activator of nuclear factor kappaB ligand. The low bone expression of transforming growth factor-beta could contribute to the delayed mineralization found in such patients.

Usefulness of a quick decalcification of bone sections embedded in methyl methacrylate[corrected]: an improved method for immunohistochemistry

Immunohistochemistry of undecalcified bone sections embedded in methyl methacrylate (MMA) is not commonly employed because of potential destruction of tissue antigenicity by highly exothermic polymerization. The aim of the present study was to describe a new technique in which a quick decalcification of bone sections embedded in MMA improves the results for immunohistochemistry. The quality of interleukin 1alpha (IL-1alpha) immunostaining according to the present method was better than the conventional one. Immunostaining for osteoprotegerin (OPG) and the receptor activator of NF-kappaB ligand (RANKL) in bone sections of chronic kidney disease patients with mineral bone disorders (CKD-MBD) was stronger than in controls (postmortem healthy subjects). The present study suggested that this method is easy, fast, and effective to perform both histomorphometry and immunohistochemistry in the same bone fragment, yielding new insights into pathophysiological aspects and therapeutic approaches in bone disease.

Osteoporosis and chronic kidney disease

Osteoporosis (OP), the most frequent bone disease affecting the general population, is associated with high fracture risk. Patients with impaired kidney function have bone and mineral disturbances leading to extraskeletal calcifications and complex changes in bone turnover that predispose them to increased fracture risk accompanied by increased morbidity and mortality. The combination of these two bone disorders seems to have an additive effect with regard to fracture risk and its outcome, so that appropriate diagnosis and treatment of this disorder should be of primary concern when approaching patients with kidney disease. Nevertheless, the clinical and laboratory diagnostic tools used to identify OP in the general population do not suit the requirement for detecting the complex bone and metabolic changes that occur with chronic kidney disease, leading to the lack of or the initiation of inappropriate therapy. This review will focus on the bone pathophysiologic processes involved in OP and renal osteodystrophy and address some of the problems associated with our current diagnostic tools and aspects of the therapeutic approaches.

Effect of parathyroidectomy on fluctuations in calcium transport between the blood and mineralized tissues of rats

Parathyroidectomy increases the degree of(45)Ca fluctuations between the blood and mineralized tissues (bones and teeth) in rats, which is associated with a decrease in 14C-glycine incorporation into bone proteins. Disturbances in Ca(2+)metabolism and transport during hyperparathyroidism are partly prevented by parathyroidectomy. It is mainly related to variations in the interaction of parathyroid hormone, calcitonin, 1.25(OH)2D3, and other bioactive substances, but not to initiation of mineralization with protein matrixes.

Osteoprotegerin and RANKL serum levels and their relationship with serum ghrelin in children with chronic renal failure and on dialysis

BACKGROUND

Osteoprotegerin (OPG) and receptor activator of the nuclear factor kappaB ligand (RANKL) constitute a complex system of mediators involved in the regulation of bone resorption process. Ghrelin, a growth hormone secretagogue, has been shown to modulate proliferation and differentiation of osteoblasts. The present study was carried out to evaluate the serum concentrations of OPG and sRANKL in children with chronic renal impairment (CRI) and on dialysis, and to establish a possible relationship between their serum levels and that of ghrelin.

METHODS

33 patients including 10 patients with CRI, 12 peritoneal dialysis (PD) and 11 hemodialysis (HD) patients and 22 healthy controls were enrolled into the study. OPG, sRANKL and ghrelin levels were studied with radioimmunoassay.

RESULTS

Serum OPG levels in CRI, PD and HD groups were significantly higher than the healthy controls (p = 0.002, p < 0.001, p < 0.001, respectively) whereas sRANKL levels were significantly lower than the healthy controls (p = 0.03, p = 0.01, p = 0.001, respectively). Ghrelin levels were significantly higher in CRI, PD and HD groups compared to healthy controls (p = 0.001, p < 0.001, p < 0.001, respectively). We observed a negative correlation between the sRANKL and OPG levels (r = -0.27, p = 0.04) as well as between sRANKL and ghrelin levels (r = -0.31, p = 0.02). OPG levels showed a positive correlation with ghrelin levels (r = 0.63, p < 0.001).

CONCLUSION

We found a lower RANKL bioactivity index in children with CRI and on dialysis. The mechanism and the role of elevated OPG and low sRANKL in uremia are unclear, but they might partly represent a compensatory mechanism to the negative balance of bone remodeling in renal bone disease in children. Additionally, we demonstrated for the first time that ghrelin and the RANKL/OPG system have a close relationship in CRF. Therefore, ghrelin may be of importance in mediating the effects of the RANKL/OPG system in renal bone disease.

Bone health in chronic kidney disease-mineral and bone disease

Chronic kidney disease (CKD) is accompanied by disturbances in calcium, phosphate, vitamin D, and parathyroid hormone (PTH) homeostasis that play an important role in the pathophysiology of renal bone disease. The increased cardiovascular morbidity and mortality observed among patients with CKD has recently been recognized to be associated with these disturbances in mineral metabolism. Thus, disturbances in mineral metabolism observed in renal failure results in a multisystem disorder, making the development of a standardized definition of these disorders a top priority. Therefore, the Board of Directors of Kidney Disease: Improving Global Outcomes proposed to define the broader category of mineral disorders associated with CKD as CKD-mineral and bone disorder (CKD-MBD). This newly proposed definition will include the disorders of mineral metabolism, bone histology (renal osteodystrophy), and the extraskeletal manifestations such as vascular calcification. This new definition and stratification of disease should result in improvement not only in the clinical management of patients but also will facilitate the interpretation and translation of clinical research. Renal osteodystrophy is now considered as 1 component of this disorder and will be defined as a morphologic alteration only, based on unification of the histomorphometric definitions that will include parameters of turnover, mineralization, and volume. An internationally accepted classification system will enable the consensus for bone biopsy evaluation as well as for the role of biomarkers. This article will focus on the newly proposed definitions of bone disease as part of CKD-MBD, based on the complex pathophysiologic process underlying bone disease in CKD stages 2 to 5.

Osteoporosis in hemodialysis patients revisited by bone histomorphometry: a new insight into an old problem

Osteoporosis in hemodialysis patients is associated with high morbidity and mortality and, although extensively studied by noninvasive methods, has never been assessed through bone biopsy. The aim of this study was to use histomorphometry to evaluate osteoporosis and identify factors related to its development in hemodialysis patients. We conducted a cross-sectional study involving 98 patients (35 women and 63 men; mean age: 48.4 +/- 13 years) on hemodialysis for 36.9 +/- 24.7 months. Patients were submitted to transiliac bone biopsy with double tetracycline labeling. The bone metabolism factors ionized calcium, phosphorus, bone alkaline phosphatase, deoxypyridinoline, intact parathyroid hormone, and 25(OH) vitamin D were evaluated, as were the bone remodeling cytokines osteoprotegerin (OPG), soluble receptor-activator of NF-kappabeta ligand (sRANKL) and tumor necrosis factor-alpha (TNF)alpha. Osteoporosis was defined as trabecular bone volume (BV/TV) greater than 1 s.d. below normal (men <17.4%; women <14.7%). Forty-five patients (46%) presented osteoporosis, which was correlated with white race. We found BV/TV to correlate with age, OPG/sRANKL ratio, TNFalpha levels, and length of amenorrhea. In multiple regression analysis adjusted for sex and age, length of amenorrhea, white race, and OPG/sRANKL ratio were independent determinants of BV/TV. Histomorphometric analysis demonstrated that osteoporotic patients presented normal eroded surface and low bone formation rate (BFR/BS). Osteoporosis is prevalent in hemodialysis patients. Low BFR/BS could be involved in its development, even when bone resorption is normal. Cytokines may also play a role as may traditional risk factors such as advanced age, hypogonadism, and white race.

Insuffizienzfrakturen in der Rheumatologie

Stress fractures occur as insufficiency fractures, with a prevalence of 0.8% in patients with rheumatological illness. The main sites of insufficiency fractures are the pelvis and sacrum, parts of the tibia and fibula that are close to the joints, and the calcaneus and hip. Since the painful symptoms overlap with the clinical picture of the painful joint diseases and because of the low sensitivity of conventional diagnostic X-ray, insufficiency fractures are not diagnosed directly or their diagnosis is delayed. The high sensitivity of computer tomography, skeletal scintigraphy and nuclear magnetic resonance imaging should be exploited in the diagnosis of insufficiency fractures. The case report presented describes insufficiency fractures of the distal right tibia and fibula in an elderly female patient with rheumatoid arthritis being treated with long-term glucocorticoids. In addition to advanced age, female gender, immobility and rheumatoid arthritis requiring long-term cortisone, there are further risk factors for insufficiency fractures: fluoride treatment over many years in the past, hypovitaminosis D3, renal failure. The DXA bone density values of the neck of the femur and the lumbar vertebrae do not show any osteoporosis, and the calcium concentration in the serum is low; phosphate is raised and parathormone is normal; osteocalcin, beta crosslaps and alkaline phosphatase are raised. Bone biopsy specimens taken from the iliac crest and the proximal femur and investigated for the purpose of differential diagnosis revealed renal osteopathy with secondary hyperparathyroidism and osteomalacia. In elderly patients with kidney failure, the possibility of renal osteopathy must be considered as the possible cause of reduced bone quality with a raised risk of insufficiency fractures, even when the parathormone levels are normal. In view of the frequency of osteopathies in rheumatological patients, osteology is of enormous significance in rheumatology.

Development of renal bone disease

Renal osteodystrophy (ROD) develops as the early stages of chronic renal failure (CRF) and covers a spectrum of bone changes observed in the uraemic patient, which extend from high remodelling bone disease (frequently known as osteitis fibrosa) to low turnover, or adynamic disease. Between these two extremes there are also cases of bone mineralization compromised in variable degrees, as is the case of 'mixed bone disease' and osteomalacia. The dynamic process of bone remodelling is compromised in CRF, and a positive or negative bone balance can be observed in uraemic patients. In addition to the classic modulators of bone remodelling, like parathyroid hormone, calcitriol and calcitonin, other factors were recently identified as significant modulators of osteoblast and osteoclast activation in uraemic patients. In fact, different cytokines and growth factors, acting at an autocrine or paracrine level, seem to play a relevant role in the bone and mineral changes observed in uraemia. Recently, observations have been made of the development of more sensitive and specific techniques to assay different biochemical markers of bone turnover and mineral metabolism. Analogously, new contributions of conventional bone histology, bone immunocytochemistry and molecular biology, which enabled the understanding of some etiopathogenic mechanisms of ROD, were observed.

Gene expression profiles give insight into the molecular pathology of bone in primary hyperparathyroidism

Global gene expression profiling has been used to study the molecular mechanisms of increased bone remodeling caused by PHPT. This disease is a model for chronic over-stimulation of target organs by PTH due to an inappropriate overproduction of the hormone. Hyperactivity of osteoblasts and osteoclasts lead to increased calcium and phosphate mobilization from the skeleton and hypercalcaemia. The ensemble of genes that alter expression and thus is responsible for the effects of chronic PTH stimulation is today largely unknown. The differentiated gene expression profiles revealed characteristic molecular disease modalities which define the bone remodeling abnormalities occurring in PTH dependent osteodystrophy. We analyzed mRNAs in transiliacal bone biopsies from 7 patients with PHPT using Affymetrix HG-U133A Gene Chips containing more than 22000 different probe sets. Similar analyses of the global transcriptional activity were repeated in a second bone biopsy from the same patient taken one year after surgery and reversal of disease parameters. Real time PCR was carried out on many genes for corroboration of the results. Out of more than 14500 different genes examined, 99 which were related to bone and extra-cellular matrix, showed altered expression. Of these were 85 up- and 14 down-regulated before operation. The majority of regulated genes represented structural and adhesion proteins, but included also proteases and protease regulators which promote resorption. Increased expressions of collagen type 1 and osteocalcin mRNAs in disease reflecting the PTH anabolic action were paralleled by increased concentrations of these proteins in serum. In addition, genes encoding transcriptional factors and their regulators as well as cellular signal molecules were up-regulated during disease. The identified genetic signature represents the first extensive description of the ensemble of bone and matrix related mRNAs, which are regulated by chronic PTH action. These results identify the molecular basis for this skeletal disease, and provide new insight into this clinical condition with potential bearing on future treatment.

Can hyperparathyroid bone disease be arrested or reversed?

Parathyroid hyperplasia, oversecretion of parathyroid hormone (PTH), and hyperparathyroid bone disease are characteristic features of chronic uremia; they develop early in the course of uremia and often in a progressive way. This review focuses on the potential for arrest or regression of hyperparathyroid-induced bone disease. For this purpose, the review addresses investigations that have used bone histology and not investigations that indirectly attempted to demonstrate changes in the skeleton by measurements of bone mineral density or laboratory indices of bone turnover, other than PTH. A prerequisite for inducing regression of the hyperparathyroid bone disease is a significant suppression of PTH secretion or reversal of hyperparathyroidism and uremia. It is concluded, on the basis of paired bone biopsy studies in patients with established hyperparathyroid bone disease, that bone histology can be improved or normalized after treatment that diminishes PTH levels. Oversuppression of PTH levels, however, might lead to adynamic bone disease.

Transforming growth factor beta1 and prostaglandin E2 concentrations are associated with bone formation markers in ulcerative colitis patients

Osteoporosis is a significant complication of a multifactoral etiology associated with inflammatory bowel disease. The aim of study was to evaluate the relationships between bone mineral density as well as bone turnover markers and inflammatory activity modulators (i.e., PGE2 and TGFbeta1) in ulcerative colitis (UC). Twenty-one active ulcerative colitis subjects and 14 healthy individuals were included into the study. We observed no significant differences in serum concentrations of osteoprotegerin and osteocalcin, as well as bone mineral density between UC patients and healthy individuals. Plasma concentrations of PGE2, TGFbeta1 and TNF-alpha were significantly higher in UC patients than in controls. Serum osteocalcin demonstrated a positive correlation with both serum PGE2 and plasma TGFbeta1. Moreover there was significant correlation between osteoprotegerin and TGFbeta1 as well as serum TNF-alpha concentrations. In conclusion a positive association between PGE2 and TGFbeta1 and bone formation markers-osteoprotegerin and osteocalcin, as well as a comparable BMD in UC patients and healthy individuals was shown. Our results may indicate that increase of PGE2 as well as TGFbeta1 concentrations may play a protective role against bone loss in ulcerative colitis patients.

Differential bone turnover in an angulated fracture model in the rat

We have developed a simple rat model of angulated tibial fracture which elicits substantial differences in bone formation and resorption within the same bone. In 35 rats the right mid-tibia was manually fractured and fixed with an intramedullary 17-gauge cannula needle. Twenty tibias were fixed in anterior angulation (27 +/- 5 degrees) and 15 in posterior angulation (31 +/- 5 degrees). Serial X-rays were taken over a 12-week period. All fractures healed completely within five weeks. In both groups, bone thickness was already significantly greater on the concave side than on the convex side at week 3 and remained so until the end of the experiment. The thickness on the convex side decreased dramatically within 3 to 5 weeks and gradually thereafter. For morphological analysis of bone mineralization, 3 rats from each group were given calcein and alizarin red injected at different time points up to 14 weeks. Maximum new bone formation was noted within the first 3 weeks. Over the ensuing weeks, new bone formation remained intense on the concave side, but it was virtually absent on the convex side. These results show that angulated fracture deformity reproducibly exhibits differential bone turnover, which can be exploited in research on local regulatory factors. To exemplify the utility of the model, an immunohistochemical study on two local markers was done. Callus tissue of five rats in the anterior angulation group at week 3 post-fracture was stained for the cytokine IL- 1beta, a stimulator of bone resorption, and the neuropeptide CGRP, an inhibitor of resorption, showing clear differences in positive staining between the concave and convex sides. Our in-vivo model offers a means of analyzing morphologically and quantitatively the differential expression and action of factors involved in local bone turnover.