Balancing Altered Calcium Metabolism with Bone Health in Sarcoidosis.

Abnormal calcium metabolism in sarcoidosis patients can lead to hypercalcemia, hypercalciuria, and kidney stones. Hypercalcemia in sarcoidosis is usually due to increased activity of 1α-hydroxylase in macrophages of pulmonary granulomata, resulting in low levels of 25-hydroxyvitamin D and high levels of calcitriol. Vitamin D supplementation may be dangerous for some sarcoidosis patients and is recommended only for those with decreased 25-hydroxyvitamin D and reduced or normal calcitriol level. Diagnosis, treatment of osteoporosis, and maintenance of bone health are complex issues for sarcoidosis patients. An approach to diagnosis and treatment of bone fragility is presented.

RANKL cytokine enhances TNF-induced osteoclastogenesis independently of TNF receptor associated factor (TRAF) 6 by degrading TRAF3 in osteoclast precursors.

Cytokines, including receptor activator of nuclear factor κB ligand (RANKL) and TNF, induce increased osteoclast (OC) formation and bone loss in postmenopausal osteoporosis and inflammatory arthritides. RANKL and TNF can independently induce OC formation in vitro from WT OC precursors via TNF receptor-associated factor (TRAF) adaptor proteins, which bind to their receptors. Of these, only TRAF6 is required for RANKL-induced osteoclastogenesis in vitro However, the molecular mechanisms involved remain incompletely understood. Here we report that RANKL induced the formation of bone-resorbing OCs from TRAF6-/- OC precursors when cultured on bone slices but not on plastic. The mechanisms involved increased TNF production by TRAF6-/- OC precursors resulting from their interaction with bone matrix and release of active TGFß from the resorbed bone, coupled with RANKL-induced autophagolysosomal degradation of TRAF3, a known inhibitor of OC formation. Consistent with these findings, RANKL enhanced TNF-induced OC formation from TRAF6-/- OC precursors. Moreover, TNF induced significantly more OCs from mice with TRAF3 conditionally deleted in myeloid lineage cells, and it did not inhibit RANKL-induced OC formation from these cells. TRAF6-/- OC precursors that overexpressed TRAF3 or were treated with the autophagolysosome inhibitor chloroquine formed significantly fewer OCs in response to TNF alone or in combination with RANKL. We conclude that RANKL can enhance TNF-induced OC formation independently of TRAF6 by degrading TRAF3. These findings suggest that preventing TRAF3 degradation with drugs like chloroquine could reduce excessive OC formation in diseases in which bone resorption is increased in response to elevated production of these cytokines.

Current concepts regarding calcium metabolism and bone health in sarcoidosis.

PURPOSE OF REVIEW: Vitamin D supplementation is widespread used in the general population. In sarcoidosis, up to 50% of patients, especially postmenopausal women and those taking corticosteroids, show evidence of increased bone fragility. The purpose of this review is to provide an evidence-based rationale on how to treat sarcoidosis patients with bone health issues. RECENT FINDINGS: Evidence from observational studies show that decreased 25-hydroxy vitamin D is common in sarcoidosis. However, the great majority of sarcoidosis patents have normal or often elevated levels of 1,25-dihydroxy vitamin D (calcitriol), a marker associated with disease activity. High calcitriol levels may often be associated with hypercalcemia and hypercalcuria. The few interventional randomized controlled studies in the field, suggest that vitamin D supplementation may not be well tolerated because of hypercalcemia, moreover without substantial benefit on bone health and risk for fractures in these patients. SUMMARY: Vitamin D supplementation may be withheld in sarcoidosis patients with bone fragility, unless calcitriol levels are below normal limits. A treating scheme is proposed.

Calcium nephrolithiasis and bone demineralization: pathophysiology, diagnosis, and medical management.

PURPOSE OF REVIEW: To establish the relationship between calcium nephrolithiasis, bone densitometry scoring, and bone mineral density (BMD) loss according to bone turnover markers (BTMs) and urinary metabolites. RECENT FINDINGS: Patients with recurrent calcium nephrolithiasis and idiopathic fasting hypercalciuria (urinary calcium/creatinine ratio >0.11) are more likely to have BMD loss that may lead to osteopenia or osteoporosis. In these patients, BTMs may be used as a surrogate for both bone health and stone recurrence. Suspect higher lithogenic states when calcium stone formers have serum beta-crosslaps (resorptive marker) greater than 0.311 ng/ml, serum osteocalcin (formative marker) greater than 13.2 ng/ml, and beta-crosslaps/osteocalcin ratio greater than 0.024. SUMMARY: Patients with recurrent calcium nephrolithiasis and fasting hypercalciuria have a higher incidence of osteopenia and osteoporosis, measured by the dual-energy X-ray absorptiometry. These patients present not only with hypercalciuria and increased BTMs (mainly resorptive), but also up to 30% have hypocitraturia and increased urinary calcium/citrate ratio (>0.25). On the basis of these results, a diagnostic algorithm was created, classifying hypercalciurics according to their fasting calcium/creatinine and calcium/citrate ratio. Medical therapy for these patients is aimed at improving the dietary habits (normocalcemic, low salt, low animal protein diet), prescribing combinations of potassium citrate, thiazides, and bisphosphonates, and correcting bone and urinary abnormalities that may lower future skeletal and kidney stone risk.

Risk factors for developing mineral bone disease in phenylketonuric patients.

There is a compromised bone mass in phenylketonuria patients compared with normal population, but the mechanisms responsible are still a matter of investigation. In addition, tetrahydrobiopterin therapy is a new option for a significant proportion of these patients and the prevalence of mineral bone disease (MBD) in these patients is unknown. We conducted a cross-sectional observational study including 43 phenylketonuric patients. Bone densitometry, nutritional assessment, physical activity questionnaire, biochemical parameters, and molecular study were performed in all patients. Patients were stratified by phenotype, age and type of treatment. The MBD prevalence in phenylketonuria was 14%. Osteopenic and osteoporotic (n=6 patients) had an average daily natural protein intake significantly lower than the remaining (n=37) patients with PKU (14.33 ± 8.95 g vs 21.25 ± 20.85 g). Besides, a lower body mass index was found. There were no statistical differences in physical activity level, calcium, phosphorus and fat intake, and in phenylalanine, vitamin D, paratohormone, docosahexaenoic and eicosapentaenoic acid blood levels. Mutational spectrum was found in up to 30 different PAH genotypes and no relationship was established among genotype and development of MBD. None of the twelve phenylketonuric patients treated with tetrahydrobiopterin (27.9%), for an average of 7.1 years, developed MBD. Natural protein intake and blood levels of eicosapentaenoic acid were significantly higher while calcium intake was lower in these patients. This study shows that the decrease in natural protein intake can play an important role in MBD development in phenylketonuric patients. Therapy with tetrahydrobiopterin allows a more relaxed protein diet, which is associated with better bone mass.

Regulation of bone-renal mineral and energy metabolism: the PHEX, FGF23, DMP1, MEPE ASARM pathway.

More than 300 million years ago, vertebrates emerged from the vast oceans to conquer gravity and the dry land. With this transition, new adaptations occurred that included ingenious changes in reproduction, waste secretion, and bone physiology. One new innovation, the egg shell, contained an ancestral protein (ovocleidin-116) that likely first appeared with the dinosaurs and was preserved through the theropod lineage in modern birds and reptiles. Ovocleidin-116 is an avian homolog of matrix extracellular phosphoglycoprotein (MEPE) and belongs to a group of proteins called short integrin-binding ligand-interacting glycoproteins (SIBLINGs). These proteins are all localized to a defined region on chromosome 5q in mice and chromosome 4q in humans. A unifying feature of SIBLING proteins is an acidic serine aspartate-rich MEPE-associated motif (ASARM). Recent research has shown that the ASARM motif and the released ASARM peptide have regulatory roles in mineralization (bone and teeth), phosphate regulation, vascularization, soft-tissue calcification, osteoclastogenesis, mechanotransduction, and fat energy metabolism. The MEPE ASARM motif and peptide are physiological substrates for PHEX, a zinc metalloendopeptidase. Defects in PHEX are responsible for X-linked hypophosphatemic rickets (HYP). There is evidence that PHEX interacts with another ASARM motif containing SIBLING protein, dentin matrix protein-1 (DMP1). DMP1 mutations cause bone and renal defects that are identical with the defects caused by a loss of PHEX function. This results in autosomal recessive hypophosphatemic rickets (ARHR). In both HYP and ARHR, increased FGF23 expression plays a major role in the disease and in autosomal dominant hypophosphatemic rickets (ADHR), FGF23 half-life is increased by activating mutations. ASARM peptide administration in vitro and in vivo also induces increased FGF23 expression. FGF23 is a member of the fibroblast growth factor (FGF) family of cytokines, which surfaced 500 million years ago with the boney fish (i.e., teleosts) that do not contain SIBLING proteins. In terrestrial vertebrates, FGF23, like SIBLING proteins, is expressed in the osteocyte. The boney fish, however, are an-osteocytic, so a physiological bone-renal link with FGF23 and the SIBLINGs was cemented when life ventured from the oceans to the land during the Triassic period, approximately 300 million years ago. This link has been revealed by recent research that indicates a competitive displacement of a PHEX-DMP1 interaction by an ASARM peptide that leads to increased FGF23 expression. This review discusses the new discoveries that reveal a novel PHEX, DMP1, MEPE, ASARM peptide, and FGF23 bone-renal pathway. This pathway impacts not only bone formation, bone-renal mineralization, and renal phosphate homeostasis but also energy metabolism. The study of this new pathway is relevant for developing therapies for several diseases: bone-teeth mineral loss disorders, renal osteodystrophy, chronic kidney disease and bone mineralization disorders (CKD-MBD), end-stage renal diseases, ectopic arterial-calcification, cardiovascular disease renal calcification, diabetes, and obesity.

Longitudinal assessment of bone mineral density in children and adolescents with inflammatory bowel disease.

OBJECTIVES: Low bone mineral density (BMD) is recognized as a potential problem in children with inflammatory bowel disease (IBD). We aimed to describe the longitudinal development of BMD in a population of Swedish pediatric patients with IBD. METHODS: A total of 144 patients with IBD (93 males; 83 with ulcerative colitis [UC], 45 with Crohn disease [CD]) were examined with dual-energy x-ray absorptiometry at baseline. At follow-up 2 years later, 126 of the initial 144 patients were reexamined. BMD values are expressed as z scores. RESULTS: Children with UC and CD had significantly lower mean BMD z scores for the lumbar spine (LS) at baseline and after 2 years. The reduction in BMD was equally pronounced in patients with UC and CD, and neither group improved their z score during the follow-up period. Furthermore, significantly lower mean BMD z scores for the LS were found at baseline in boys (-1.1 SD, ±2.7 SD, P < 0.001), but not in girls (-0.0 SD, ±3.0 SD). This finding remained unchanged at follow-up. Subanalyses of the different age groups at baseline showed the lowest BMD values in the group of patients ages 17 to 19 years in boys (mean z score for the LS 1.59 SD, ±3.1 SD) and in girls (mean z score for the LS -3.40 SD, ±3.1 SD); however, at follow-up, these patients had improved their BMD significantly (mean change z score for the LS 1.00 SD, 95% CI 0.40-1.60; 1.90 SD, 95% CI 0.60-3.20). CONCLUSIONS: In this longitudinal study, the entire group of pediatric patients with IBD showed permanent decreases in their BMD z scores for the LS; however, our data indicate that afflicted children have the potential to improve their BMD by the time they reach early adulthood.

NHERF1 mutations and responsiveness of renal parathyroid hormone.

Impaired renal phosphate reabsorption, as measured by dividing the tubular maximal reabsorption of phosphate by the glomerular filtration rate (TmP/GFR), increases the risks of nephrolithiasis and bone demineralization. Data from animal models suggest that sodium-hydrogen exchanger regulatory factor 1 (NHERF1) controls renal phosphate transport. We sequenced the NHERF1 gene in 158 patients, 94 of whom had either nephrolithiasis or bone demineralization. We identified three distinct mutations in seven patients with a low TmP/GFR value. No patients with normal TmP/GFR values had mutations. The mutants expressed in cultured renal cells increased the generation of cyclic AMP (cAMP) by parathyroid hormone (PTH) and inhibited phosphate transport. These NHERF1 mutations suggest a previously unrecognized cause of renal phosphate loss in humans.

Managing bone health with zoledronic acid: a review of randomized clinical study results.

AIM: To systematically review randomized, controlled clinical trials for managing osteoporosis, cancer treatment-induced bone loss, and bone metastases from breast cancer using zoledronic acid (ZOL). METHOD: A systematic review of published literature and meeting abstracts was conducted to examine the efficacy of ZOL dosing strategies in clinical trials of osteoporosis, adjuvant therapy for breast cancer, and bone metastases from breast cancer. Bone resorption rates, tumor burden, skeletal health goals, and clinical data were considered when assessing ZOL in each setting. RESULTS: Dosing schedules vary between approved indications for osteoporosis and bone metastases and the investigational use in women receiving endocrine therapy for BC, taking into consideration the different levels of bone loss and tumor burden in each setting. Gradual bone loss in healthy postmenopausal women with osteopenia or osteoporosis can be prevented or treated with the approved biennial or annual ZOL (5 mg), respectively. Rapid bone loss in patients receiving adjuvant chemotherapy and/or endocrine therapy for early-stage BC and low tumor burden is managed in the clinical setting with ZOL 4 mg every 6 months. In patients with bone metastases, very high tumor burden, high bone resorption levels, and decreases in bone integrity are managed by the approved ZOL schedule (4 mg every 3-4 weeks) to prevent skeleton-related events. CONCLUSIONS: Dosing schedules are based on clinical evidence and vary depending on goals of therapy, rate of bone loss, and tumor burden. ZOL 5 mg every 12 months and every 24 months are approved for osteoporosis and osteopenia, respectively, whereas ZOL 4 mg every 6 months has been used during adjuvant endocrine therapy and ZOL 4 mg every 3-4 weeks is approved for managing bone metastases.

WNT/beta-catenin signaling is involved in regulation of osteoclast differentiation by human immunodeficiency virus protease inhibitor ritonavir: relationship to human immunodeficiency virus-linked bone mineral loss.

Untreated human immunodeficiency virus (HIV) infection is accompanied by reduced bone mineral density, which appears to be exacerbated by certain HIV protease inhibitors (PIs). The mechanisms leading to this apparent paradox, however, remain unclear. We have previously shown that, the HIV envelope glycoprotein gp120 used at levels similar those in plasmas of untreated HIV(+) patients, induced expression of the osteoclast (OC) differentiation factor RANKL in CD4+ T cells. In addition, the HIV PI ritonavir abrogated the interferon-gamma-mediated degradation of the RANKL nuclear adapter protein TRAF6, a physiological block to RANKL activity. Here, using oligonucleotide microarrays and quantitative polymerase chain reaction, we explored potential upstream mechanisms for these effects. Ritonavir, but not the HIV PIs indinavir or nelfinavir, up-regulated the production of transcripts for OC growth factors and the non-canonical Wnt Proteins 5B and 7B as well as activated promoters of nuclear factor-kappaB signaling, but suppressed genes involved in canonical Wnt signaling. Similarly, ritonavir blocked the cytoplasmic to nuclear translocation of beta-catenin, the molecular node of the Wnt signaling pathway, in association with enhanced beta-catenin ubiquitination. Exposure of OC precursors to LiCl, an inhibitor of the canonical Wnt antagonist GSK-3beta, suppressed OC differentiation, as did adenovirus-mediated overexpression of beta-catenin. These data identify, for the first time, a biologically relevant role for Wnt signaling via beta-catenin in isolated OC precursors and the modulation of Wnt signaling by ritonavir. The reversal of these ritonavir-mediated changes by interferon-gamma provides a model for possible intervention in this metabolic complication of HIV therapy.

Preproenkephalin (Penk) is expressed in differentiated osteoblasts, and its deletion in Hyp mice partially rescues their bone mineralization defect.

Although our understanding of the molecular mechanisms controlling osteoblast differentiation and function is steadily increasing, there are still many open questions, especially regarding the regulation of bone matrix mineralization. For instance, while there is hallmark evidence for the importance of the endopeptidase Phex, whose inactivation in Hyp mice or human patients causes X-linked hypophosphatemic rickets, it is still largely unknown how Phex controls bone mineralization since a physiological substrate for its endopeptidase activity has not been identified yet. Using a genome-wide expression analysis comparing primary calvarial osteoblasts, we have identified preproenkephalin (Penk) as a gene that is selectively expressed in mineralized cultures. Since a role of enkephalin in the regulation of bone remodeling has been suggested previously and since Leu-enkephalin is known to be cleaved by Phex, we analyzed whether Penk expression in osteoblasts is physiologically relevant. Through skeletal analysis of a Penk-deficient mouse model, we found that Penk expression is dispensable for bone development and remodeling since we could not detect any defect following nondecalcified bone histology and histomorphometry compared to wild-type littermates. When Penk was deleted in Phex-deficient Hyp mice, however, we observed a significant reduction of the osteoid enrichment at 24 weeks of age, whereas their disturbance of mineral homeostasis was not affected by the additional absence of the Penk gene. Taken together, our data provide the first in vivo analysis concerning the role of Penk in osteoblasts.

[Fractures and chronic renal insufficiency]. / La patologia fratturativa nei diversi gradi di insufficienza renale cronica.

Chronic renal insufficiency (CRI) causes important modifications in the metabolism of phosphorus and calcium, to which frequently resulting in serious disorders of the skeleton, including demineralization, reduction of the bone resistance and a higher risk of fractures. Renal osteodystrophy is the term used to describe these disorders; they are generally heterogeneous and are classified according to the state of bone turnover into secondary hyperparathyroidism, adynamic bone, and osteomalacia. The incidence of hip fractures in the patients with CRI is higher than in the general population. Hip fractures are an important cause of morbidity and mortality. The evaluation of the fracture risk in the patients with different degrees of CRI is problematic, in particular because of the difficulty in identifying fractures, especially vertebral ones. The instrumental index that best expresses the fracture risk in the general population is bone mineral density (BMD); however, the relationship between low BMD and CRI is disputed. Bone disorders in patients with CRI have in fact a multifactorial pathogenesis and low BMD is not the only risk factor for fractures. Besides densitometric evaluation, also that vertebral morphometric evaluation would be desirable in patients with CRI. The fracture risk increases progressively with the severity of chronic renal disease and it is especially high in patients with renal insufficiency in more advanced-stages CRI (creatinine clearance<15-20 mL/min). However, not only in patients with severe CRI undergoing dialysis, but also in those with milder renal disease is the risk of bone fractures high.

[Bone metabolism disturbances in anorexia nervosa]. / Zaburzenia metabolizmu kostnego w jadlowstrkcie psychicznym.

Osteoporosis is a frequent complications of anorexia nervosa (AN). The etiology of osteoporosis in AN is multifactorial. Multiaxial hormonal disturbances and chronic undernutrition cause decrease or the lack of increase of bone mineral density (BMD), expected in adolescence. Both processes result from increased resorption and insufficient bone formation and/or mineralization. Decreased BMD persist in adult patients with a history of AN in the adolescence. There are no guidelines concerning treatment of osteoporosis in AN. The authors present review of the literature concerning bone metabolism in AN.

Bone demineralization is improved by ivacaftor in patients with cystic fibrosis carrying the p.Gly551Asp mutation.

Low bone mineral density (BMD) is a common problem in adults with cystic fibrosis (CF), the etiology of which is multifactorial. In this study, we provide the first evidence that ivacaftor improves BMD in CF patients carrying the p.Gly551Asp mutation. Consistently, in vitro experiments with TNF-α-stimulated primary F508del-CFTR osteoblasts demonstrated that correction of p.Phe508del-CFTR markedly decreased RANKL protein production, a major factor of bone resorption. These clinical and fundamental observations suggest that rescue of mutated CFTR protein improves bone remodeling and support the link between CFTR and bone cell physiology. These findings represent a step forward in the development of potential new therapies for CF-related bone disease.

Increased EZH2 and decreased osteoblastogenesis during local irradiation-induced bone loss in rats.

Radiation therapy is commonly used to treat cancer patients but exhibits adverse effects, including insufficiency fractures and bone loss. Epigenetic regulation plays an important role in osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Here, we reported local bone changes after single-dose exposure to (137)CS irradiation in rats. Femur bone mineral density (BMD) and trabecular bone volume in the tibia were significantly decreased at 12 weeks after irradiation. Micro-CT results showed that tBMD, Tb.h and Tb.N were also significantly reduced at 12 weeks after irradiation exposure. ALP-positive OB.S/BS was decreased by 42.3% at 2 weeks after irradiation and was decreased by 50.8% at 12 weeks after exposure. In contrast to the decreased expression of Runx2 and BMP2, we found EZH2 expression was significantly increased at 2 weeks after single-dose (137)CS irradiation in BMSCs. Together, our results demonstrated that single-dose (137)CS irradiation induces BMD loss and the deterioration of bone microarchitecture in the rat skeleton. Furthermore, EZH2 expression increased and osteoblastogenesis decreased after irradiation. The underlying mechanisms warrant further investigation.

We can rebuild it: reconstructive solutions for structural urologic diseases.

Bladder augmentation and urinary diversion have become standard of care as surgical treatments for structural and functional disorders affecting the bladder, both in children and adults. With improved medical care, long-term survival of these patients is expected. Common medical problems that can occur such as metabolic side effects including acid-base imbalances and nutritional issues need to be anticipated and addressed. In addition, surgical problems caused by impaired urinary drainage, namely stones and urinary tract infections, and mechanical factors related to catheterizable channels and continence also may compound postoperative management. The risk of malignancy after bladder augmentation and substitution, and appropriate surveillance for this, remains to be clearly defined.

Long-term consequences of fracture of the lower leg: cross-sectional study and long-term longitudinal follow-up of bone mineral density in the hip after fracture of lower leg.

The purpose of this study was to investigate whether bone loss in the hip, occurring after a fracture of the lower leg, persists many years after the fracture. In a long-term follow-up we measured bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) of both hips and the lumbar spine in a group of 11 patients, 5 years after a fracture of the lower leg. These patients were part of an earlier study, evaluating bone loss in the hip, up to 1 year after fracture of the lower leg. In this follow-up study, 5 years after fracture, loss from baseline BMD in the trochanteric region of the ipsilateral hip was 4.7% (p=0.04), whereas after a year in this group there was a decrease of 12.5% from baseline. On the contralateral side, hardly any change occurred. In the ipsilateral femoral neck, 5 years after fracture, BMD decreased by 2.9% (p=0.10), after 1 year loss from baseline was 5.1%. In a cross-sectional study we examined the differences in BMD of both hips, measured by DXA, in a group of 19 elderly patients reporting a fracture of the lower leg, with a mean time of 9.3 years after fracture. In this study, we found a 4.7% lower BMD in the trochanteric region of the hip on the fractured side compared with the nonfractured side (p=0.006), and a 2.9% lower BMD in the femoral neck (p=0.25). We conclude that, after fracture of the lower leg, BMD in the ipsilateral hip decreases significantly, with maximal bone loss after 1 year. After 5 years recovery has occurred, but not to baseline. Thereafter, significant excess bone loss is still observed in the trochanteric region. This persisting lower BMD may lead to an increased risk of another fracture in later years.