Chronic kidney disease and the skeleton

Crosstalk between kidney and bones: New perspective for modulating osteoporosis

Growing evidence indicates an interesting interplay between kidney and bone. The pathophysiological condition of the skeletal system is intricately associated with the normal functioning of the kidneys. This relationship is modulated by various factors, including calcium and phosphate, 1-α-hydroxylase, erythropoietin (EPO), klotho, fibroblast growth factor 23 (FGF23), bone morphogenetic protein-7 (BMP-7), and extracellular vesicles (EVs). These interactions are notably evident in conditions such as chronic kidney disease with bone mineral density (CKD-BMD), renal osteodystrophy (ROD), and osteoporosis (OP). Furthermore, innovative methodologies such as cell co-culture, organ-on-a-chip, single-cell sequencing, and spatial transcriptomics are highlighted as instrumental in advancing the study of inter-organ interactions. This review, grounded in the pathogenesis, diagnostic and therapeutic modalities, and pharmacological treatments of OP, synthesizes evidence from molecular biology to clinical perspectives. It aims to establish a foundation for the development of more complex and physiologically relevant in vitro models and to propose potential therapeutic strategies.

Impact of elevated sclerostin levels on bone resorption : unravelling structural changes and mineral metabolism disruption

Aims

The physiological function of sclerostin remains unknown. Sclerostin is synthesized by osteocytes and operates by inhibiting the Wnt/β-catenin pathway. Similarly, it is well established that low levels of sclerostin lead to enhanced bone formation and reduced calciuria, and that high levels of sclerostin are associated with osteoporosis.

Methods

The impact of high levels of recombinant sclerostin on bone and mineral metabolism parameters was analyzed in this study. In male healthy rats, the effects of three elevated doses of sclerostin over a 14-day period were studied, involving bone histomorphometry, micro-CT (μCT), immunohistochemistry, and analysis of mineral metabolism parameters.

Results

Although there was increased bone formation, high doses of sclerostin led to a higher reduction in trabecular bone volume due to a significant increase in bone resorption through the direct activation of osteoclastogenesis. In vitro, sclerostin promoted the differentiation of bone marrow stem cells into osteoclasts. Bone resorption, as measured by tartrate-resistant acid phosphatase (TRAP) activity, was excessive in trabecular, cortical, and subchondral bone. Similarly, high doses of sclerostin increased the number of hypertrophic chondrocytes, consequently expanding the growth plate area. At the cortical level, positive TRAP staining could be observed, suggestive of osteocytic osteolysis and trabecularization of cortical bone. The increased bone resorption resulted in a substantial rise in the urinary excretion of phosphorus and calcium, accompanied by elevated levels of FGF23 and a significant decrease in parathyroid hormone (PTH).

Conclusion

These findings suggest that elevated levels of sclerostin promote bone resorption through the activation of osteoclasts and the generation of osteocytic osteolysis, resulting in increased calciuria, phosphaturia, and changes in mineral metabolism.

Assessment of Vertebral Bone Marrow Perfusion, Fat/Water Content, and Trabecular Bone Changes Using Multimodal MRI and Micro-CT in a Rat Model of Chronic Kidney Disease

Background

Disturbances in calcium and phosphorus homeostasis resulting from chronic kidney disease (CKD) may lead to atherosclerotic changes in blood vessels, potentially altering bone marrow perfusion. Our study aimed to investigate vertebral bone marrow perfusion using dynamic contrast-enhanced (DCE) MRI with a pharmacokinetic model. We also measured possible changes in water and fat content and bony trabeculae using T2* quantification, MR spectroscopy (MRS), and microcomputed tomography (μCT).

Methods

Twelve rats were randomly separated into a normal control group and a CKD (5/6 nephrectomy) group. Their lumbar spines were imaged, with monitoring of the L5 vertebral body conducted at 0, 8, 16, 30, and 43 weeks. After Week 43, all rats were sacrificed, and histologic changes were correlated with MRI and μCT results.

Results

The CKD group demonstrated significantly lower A and k el values (p < 0.05), significantly increased T2* values (p < 0.05), significantly decreased fat content and trabeculation (p < 0.05), sinusoidal dilatation, and decreased adipocytes in the vertebral bone marrow.

Conclusion

Using quantitative MRI and μCT to assess CKD-related arthropathy of the vertebral body is feasible. Lumbar spine bone marrow perfusion deficiency in experimental CKD may be associated with decreased fat content, increased water content, and sparse trabeculation.

Multi-omics analysis of kidney, bone and bone marrow explored potential mechanisms of Erzhi Wan against osteoporosis with kidney-Yin deficiency

Osteoporosis (OP) is a metabolic bone disease that can lead to major health challenges. The theory of Traditional Chinese medicine believes that kidney-Yin deficiency (KYD) is the main cause of postmenopausal osteoporosis. This study was aimed to investigate the effect of EZW on anti-osteoporosis with KYD, and explore potential mechanisms from the perspective of the kidney, bone and bone marrow through analysis of metabolomics and proteomics. The model of OP with KYD was established by rats treated with bilateral ovariectomy (OVX), and then given intragastric administration of thyroid and reserpine to induce. Micro-CT was applied to determine the microstructures of bone. Serum levels associated with bone turnover markers and kidney-Yin deficiency were detected by enzyme-linked immunosorbent (ELISA) assay. The differential metabolites in the kidney, bone and bone marrow were analyzed by metabolomics. The differentially expressed proteins in these three tissues were detected via proteomics. The findings suggested that EZW could alleviate a variety of metabolites and proteins among the kidney, bone and bone marrow, primarily in amino acid metabolism, carbohydrate metabolism, nucleotide metabolism and lipid metabolism, thus leading to improvements of OP with KYD, which provided theoretical basis for clinical treatment of EZW on OP with KYD.

Dental implant considerations in patients with systemic diseases: An updated comprehensive review

BACKGROUND

Various medical conditions and the drugs used to treat them have been shown to impede or complicate dental implant surgery. It is crucial to carefully monitor the medical status and potential post-operative complications of patients with systemic diseases, particularly elderly patients, to minimize the risk of health complications that may arise.

AIM

The purpose of this study was to review the existing evidence on the viability of dental implants in patients with systemic diseases and to provide practical recommendations to achieve the best possible results in the corresponding patient population.

METHODS

The information for our study was compiled using data from PubMed, Scopus, Web of Science and Google Scholar databases and searched separately for each systemic disease included in our work until October 2023. An additional manual search was also performed to increase the search sensitivity. Only English-language publications were included and assessed according to titles, abstracts and full texts.

RESULTS

In total, 6784 studies were found. After checking for duplicates and full-text availability, screening for the inclusion criteria and manually searching reference lists, 570 articles remained to be considered in this study.

CONCLUSION

In treating patients with systemic conditions, the cost-benefit analysis should consider the patient's quality of life and expected lifespan. The success of dental implants depends heavily on ensuring appropriate maintenance therapy, ideal oral hygiene standards, no smoking and avoiding other risk factors. Indications and contraindications for dental implants in cases of systemic diseases are yet to be more understood; broader and hardcore research needs to be done for a guideline foundation.

Chronic Kidney Disease in Patients with Hip Fracture: Prevalence and Outcomes

Objective. Although the association between chronic kidney disease (CKD) and osteoporotic fractures is well established, data on CKD combined with hip fracture (HF) are scarce and controversial. We aimed to assess in patients with HF the prevalence of CKD, its impact on hospital mortality and length of stay (LOS) and to determine the prognostic value of CKD to predict hospital outcomes. Methods. Prospectively collected clinical data were analysed in 3623 consecutive HF patients aged ≥65 years (mean age 83.4 ± 7.50 [standard deviation] years; 74.4% females). Results. CKD among older patients with HF is highly prevalent (39.9%), has different clinical characteristics, a 2.5-fold higher mortality rate, and 40% greater risk of prolonged LOS. The strongest risk for a poor outcome was advanced age (>80 years). The risk of death substantially increases in combination with chronic disorders, especially coronary artery disease, anaemia, hyperparathyroidism, and atrial fibrillation; models based only on three variables—CKD stage, age >80, and presence of a specific chronic condition—predicted in-hospital death with good discrimination capability (AUC ≥ 0.700) and reasonable accuracy, the number needed to predict ranged between 5.7 and 14.5. Only 12% of HF patients received osteoporotic drugs prefracture. Conclusion. In HF patients with CKD, the risk of adverse outcomes largely increases in parallel with worsening kidney function and, especially, in combination with comorbidities; models based on three admission variables predict a fatal outcome. Assessment of renal function is essential to preventing osteoporotic fractures.

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

Development of an injectable chitosan-based hydrogel containing nano-hydroxy-apatite and alendronate for MSC-based therapy

BACKGROUND

The combination of cells and biomaterials has become a powerful approach to regenerative medicine in recent years. Understanding the in-vitro interactions between cells and biomaterials is crucial for the success of regenerative medicine.

AIM

In this study, we developed an AD-pectin/chitosan/nano-crystalline cellulose scaffold with nano-hydroxy-apatite (n-HAP) and alendronate (ALN). The second step was to evaluate its effect on the immunomodulatory properties and biological behaviors of seeded adipose-derived mesenchymal stem cells (ADSCs) for bone tissue repair.

MATERIAL AND METHOD

After preparing and evaluating the characterization tests of the new combined n-HAP scaffold, we established different culture conditions to evaluate ADSC growth on this scaffold with or without ALN. The main assays were MTT assay, RT-PCR, and ELISA.

RESULTS

Our data regarding characterization tests (including SEM, TGA, FTIR, gelation time, swelling ratio, rheology and degradation tests) of ALN-loaded n-HAP scaffold showed the proper stability and good mechanical status of the scaffold. ADSC proliferation and viability increased in the presence of the scaffold compared with other conditions. Moreover, our data demonstrated increased gene expression and protein levels of anti-inflammatory TGF-β, HGF, and IDO cytokines in the presence of the ALN-loaded n-HAP scaffold, indicating the increased immunosuppressive activity of ADSCs in vitro.

CONCLUSION

This study demonstrates the promising abilities of the ALN-loaded n-HAP scaffold to increase the proliferation, viability, and immunomodulatory capacity of ADSCs, elucidating new aspects of cell-material interactions that can be used for bone tissue regeneration/repair, and paving the path of future research in developing new approaches for MSC- based therapy.

Severe Hypocalcemia With Denosumab Among Older Female Dialysis-Dependent Patients

Importance

Dialysis-dependent patients experience high rates of morbidity from fractures, yet little evidence is available on optimal treatment strategies. Chronic kidney disease-mineral and bone disorder is nearly universal in dialysis-dependent patients, complicating diagnosis and treatment of skeletal fragility.

Objective

To examine the incidence and comparative risk of severe hypocalcemia with denosumab compared with oral bisphosphonates among dialysis-dependent patients treated for osteoporosis.

Design, Setting, and Participants

Retrospective cohort study of female dialysis-dependent Medicare patients aged 65 years or older who initiated treatment with denosumab or oral bisphosphonates from 2013 to 2020. Clinical performance measures including monthly serum calcium were obtained through linkage to the Consolidated Renal Operations in a Web-Enabled Network database.

Exposures

Denosumab, 60 mg, or oral bisphosphonates.

Main Outcomes and Measures

Severe hypocalcemia was defined as total albumin-corrected serum calcium below 7.5 mg/dL (1.88 mmol/L) or a primary hospital or emergency department hypocalcemia diagnosis (emergent care). Very severe hypocalcemia (serum calcium below 6.5 mg/dL [1.63 mmol/L] or emergent care) was also assessed. Inverse probability of treatment-weighted cumulative incidence, weighted risk differences, and weighted risk ratios were calculated during the first 12 treatment weeks.

Results

In the unweighted cohorts, 607 of 1523 denosumab-treated patients and 23 of 1281 oral bisphosphonate-treated patients developed severe hypocalcemia. The 12-week weighted cumulative incidence of severe hypocalcemia was 41.1% with denosumab vs 2.0% with oral bisphosphonates (weighted risk difference, 39.1% [95% CI, 36.3%-41.9%]; weighted risk ratio, 20.7 [95% CI, 13.2-41.2]). The 12-week weighted cumulative incidence of very severe hypocalcemia was also increased with denosumab (10.9%) vs oral bisphosphonates (0.4%) (weighted risk difference, 10.5% [95% CI, 8.8%-12.0%]; weighted risk ratio, 26.4 [95% CI, 9.7-449.5]).

Conclusions and Relevance

Denosumab was associated with a markedly higher incidence of severe and very severe hypocalcemia in female dialysis-dependent patients aged 65 years or older compared with oral bisphosphonates. Given the complexity of diagnosing the underlying bone pathophysiology in dialysis-dependent patients, the high risk posed by denosumab in this population, and the complex strategies required to monitor and treat severe hypocalcemia, denosumab should be administered after careful patient selection and with plans for frequent monitoring.

The Pathophysiology, Identification and Management of Fracture Risk, Sublesional Osteoporosis and Fracture among Adults with Spinal Cord Injury

BACKGROUND

The prevention of lower extremity fractures and fracture-related morbidity and mortality is a critical component of health services for adults living with chronic spinal cord injury (SCI).

METHODS

Established best practices and guideline recommendations are articulated in recent international consensus documents from the International Society of Clinical Densitometry, the Paralyzed Veterans of America Consortium for Spinal Cord Medicine and the Orthopedic Trauma Association.

RESULTS

This review is a synthesis of the aforementioned consensus documents, which highlight the pathophysiology of lower extremity bone mineral density (BMD) decline after acute SCI. The role and actions treating clinicians should take to screen, diagnose and initiate the appropriate treatment of established low bone mass/osteoporosis of the hip, distal femur or proximal tibia regions associated with moderate or high fracture risk or diagnose and manage a lower extremity fracture among adults with chronic SCI are articulated. Guidance regarding the prescription of dietary calcium, vitamin D supplements, rehabilitation interventions (passive standing, functional electrical stimulation (FES) or neuromuscular electrical stimulation (NMES)) to modify bone mass and/or anti-resorptive drug therapy (Alendronate, Denosumab, or Zoledronic Acid) is provided. In the event of lower extremity fracture, the need for timely orthopedic consultation for fracture diagnosis and interprofessional care following definitive fracture management to prevent health complications (venous thromboembolism, pressure injury, and autonomic dysreflexia) and rehabilitation interventions to return the individual to his/her pre-fracture functional abilities is emphasized.

CONCLUSIONS

Interprofessional care teams should use recent consensus publications to drive sustained practice change to mitigate fracture incidence and fracture-related morbidity and mortality among adults with chronic SCI.

A Primer in Precision Nephrology: Optimizing Outcomes in Kidney Health and Disease through Data-Driven Medicine

This year marks the 63rd anniversary of the International Society of Nephrology, which signaled nephrology's emergence as a modern medical discipline. In this article, we briefly trace the course of nephrology's history to show a clear arc in its evolution-of increasing resolution in nephrological data-an arc that is converging with computational capabilities to enable precision nephrology. In general, precision medicine refers to tailoring treatment to the individual characteristics of patients. For an operational definition, this tailoring takes the form of an optimization, in which treatments are selected to maximize a patient's expected health with respect to all available data. Because modern health data are large and high resolution, this optimization process requires computational intervention, and it must be tuned to the contours of specific medical disciplines. An advantage of this operational definition for precision medicine is that it allows us to better understand what precision medicine means in the context of a specific medical discipline. The goal of this article was to demonstrate how to instantiate this definition of precision medicine for the field of nephrology. Correspondingly, the goal of precision nephrology was to answer two related questions: ( 1 ) How do we optimize kidney health with respect to all available data? and ( 2 ) How do we optimize general health with respect to kidney data?

Skeletal Muscle Complications in Chronic Kidney Disease

PURPOSE OF REVIEW

To provide an overview of the recent literature investigating the pathophysiology of skeletal muscle changes, interventions for skeletal muscle, and effects of exercise in chronic kidney disease (CKD).

RECENT FINDINGS

There are multiple CKD-related changes that negatively impact muscle size and function. However, the variability in the assessment of muscle size, in particular, hinders the ability to truly understand the impact it may have in CKD. Exercise interventions to improve muscle size and function demonstrate inconsistent responses that warrant further investigation to optimize exercise prescription. Despite progress in the field, there are many gaps in the knowledge of the pathophysiology of sarcopenia of CKD. Identifying these gaps will help in the design of interventions that can be tested to target muscle loss and its consequences such as impaired mobility, falls, and poor quality of life in patients with CKD.

[Nephrological management and drug dosing in patients with rheumatic diseases and renal insufficiency]

BACKGROUND

In patients with inflammatory rheumatic diseases and renal insufficiency there are two challenges for physicians: to adapt the antirheumatic medication to the renal function and to carry out a nephroprotective treatment that prevents long-term deterioration of renal function and reduces the elevated cardiovascular risk.

METHODS

A literature search (in PubMed) was carried out and the current state of knowledge on nephroprotective treatment strategies and the treatment of rheumatic diseases in the presence of renal insufficiency was collated, evaluated and summarized.

RESULTS

Lifestyle interventions, especially the cessation of smoking and drug treatment strategies form the basis of nephroprotection including the control of diabetes mellitus with metformin, sodium glucose transporter 2 (SGLT2) inhibitors, glucagon-like peptide 1 (GLP1) analogues and control of hypertension with blockade of the renin-angiotensin-aldosterone system (RAAS), hyperlipidemia, hyperphosphatemia and metabolic acidosis. The SGLT2 inhibitors are also effective for nondiabetic nephropathy. The elevated cardiovascular risk is further reduced by effective control of inflammatory rheumatic activity. Numerous conventional disease modifying antirheumatic drugs, especially methotrexate and the Janus kinase (JAK) inhibitors baricitinib and filgotinib, must mostly be adapted to the renal function. In contrast, biologics can be given in standard doses with the exception of anakinra. The increased cardiovascular risk currently limits the use of tofacitinib in patients with renal insufficiency.

CONCLUSION

The antirheumatic medication should be modified and a complex nephroprotective treatment concept is mandatory in the management of patients with rheumatic disease and renal insufficiency, that in the best-case scenario can be guaranteed by a close interdisciplinary cooperation of rheumatologists and nephrologists.

Renal osteodystrophy: A historical review of its origins and conceptual evolution

Long considered an inert supporting framework, bone studies went neglected until the 17th century when they began as descriptive microscopic studies of structure which over time progressed into that of chemistry and physiology. It was in the mid-19th century that studies evolved into an inquisitive discipline which matured into the experimental investigation of bone in health and disease in the 20th century, and ultimately that of molecular studies now deciphering the genetic language of bone biology. These fundamental studies were catalyzed by increasing clinical interest in bone disease. The first bone disease to be identified was rickets in 1645. Its subsequent connection to albuminuric patients reported in 1883 later became renal osteodystrophy in 1942, launching studies that elucidated the functions of vitamin D and parathyroid hormone and their role in the altered calcium and phosphate metabolism of the disease. Studies in osteoporosis and renal osteodystrophy have driven most recent progress benefitting from technological advances in imaging and the precision of evaluating bone turnover, mineralization, and volume. This review exposes the progress of bone biology from a passive support structure to a dynamically regulated organ with vital homeostatic functions whose understanding has undergone more revisions and paradigm shifts than that of any other organ.

The impact of chronic kidney disease and dialysis therapy on outcomes of elderly patients with hip fractures: A systematic review and meta-analysis

BACKGROUND AND AIMS

Hip fractures are a commonly occurring comorbidity in patients with chronic kidney disease. To evaluate the comparative rates of post-operative complications, revision surgery, and mortality after hip fracture surgery in chronic kidney disease patients undergoing hemodialysis.

METHODS

A systematic search of the academic literature was performed according to the PRISMA guidelines across five databases: Web of Science, EMBASE, CENTRAL, Scopus, and MEDLINE. A random-effect meta-analysis was conducted to evaluate the overall comparative risks of post-operative complications in chronic kidney disease patients.

RESULTS

Out of 993 studies, 11 eligible studies were included in the review, with a total of 72618 chronic kidney disease patients (mean age: 75.3  ±  3.0 years), and 50566 healthy controls (75.3  ±  2.6 years). Meta-analysis revealed a higher risk of post-operative complications (Odd's ratio: 1.76), revision surgeries (1.69), and mortality-related outcomes (2.47) after hip fracture surgery in chronic kidney disease patients undergoing hemodialysis as compared to chronic kidney disease patients not undergoing hemodialysis.

CONCLUSION

We report higher risks of post-operative complications, revision surgery, and mortality in chronic kidney disease patients undergoing hemodialysis as compared to chronic kidney disease patients not undergoing hemodialysis.

Data Mining and Network Pharmacology Analysis of Kidney-Tonifying Herbs on the Treatment of Renal Osteodystrophy Based on the Theory of "Kidney Governing Bones" in Traditional Chinese Medicine

Background

Renal osteodystrophy (ROD) secondary to chronic kidney disease is closely associated with osteoporosis and fractures. Based on the theory of “kidney governing bones” in traditional Chinese medicine (TCM), treating bone diseases from the perspective of the kidney has become a basic principle of treating ROD. However, there are many kidney-tonifying herbs and their mechanisms of treating ROD are not clear. Therefore, our study intends to use data mining and network pharmacology to study the commonly used kidney-tonifying herbs, as well as their active ingredients and mechanisms of treating ROD.

Methods

We established a clinical ROD database by searching PubMed, CNKI, and other databases and screened out a core herbal combination of treating ROD. Furthermore, by using databases such as Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform and GeneCards, we obtained active ingredients and targets of the core herbal combination and ROD targets. The STRING website and Cytoscape software were then used to obtain information on key active ingredients and key targets. Finally, we conducted GO and KEGG analyses using the Metascape website and molecular docking using the AutoDock Vina software.

Results

Our study eventually included 58 prescriptions and 116 herbs of treating ROD. Through data mining, we found that yin-yang-huo, du-zhong, and bu-gu-zhi (YDB) constituted a core herbal combination to treat ROD. Network pharmacology showed that YDB mainly acted on targets such as estrogen receptor alpha through active ingredients such as quercetin by mitogen-activated protein kinase and other signaling pathways.

Conclusion

Many ingredients, targets, and pathways are involved in the treatment of YDB for ROD. Specifically, the flavonoids contained in YDB have great potential for ROD treatment.

Risk factors for lower bone mineral density in older adults with type 1 diabetes: a cross-sectional study

BACKGROUND

Type 1 diabetes is associated with lower bone mineral density (BMD) and increased fracture risk, but little is known regarding the effects of diabetes-related factors on BMD. We assessed whether these factors are associated with lower hip BMD among older adults with type 1 diabetes.

METHODS

This cross-sectional study was embedded in a long-term observational study, the Epidemiology of Diabetes Interventions and Complications study (EDIC), a cohort of participants with type 1 diabetes, who were originally enrolled in the Diabetes Control and Complications Trial (DCCT), and were followed-up for more than 30 years at 27 sites in the USA and Canada. All active EDIC participants were eligible except if they were pregnant, weighed above the dual-energy x-ray absorptiometry (DXA) scanner limit, had an implanted neurostimulator, or were not willing to participate. The primary study outcome was total hip BMD. Hip, spine, and radius BMD and trabecular bone score (TBS) were measured with DXA at an annual EDIC visit (2017-19). Time-weighted mean HbA_1c, kidney disease, and peripheral neuropathy were measured annually during EDIC, and retinopathy was measured every 4 years. Skin intrinsic fluorescence, a measure of advanced glycation end products (AGEs), and cardiac autonomic neuropathy were assessed once (2009-10) during EDIC.

FINDINGS

1147 of the 1441 participants who were enrolled in the DCCT trial remained active EDIC participants at the start of this cross-sectional study. Between Sept 20, 2017, and Sept 19, 2019, 1094 of 1147 participants were screened for the EDIC Skeletal Health study. 1058 participants completed at least one of a set of DXA scans and were included in the analysis. 47·8% were women and 52·2% were men, 96·6% were White and 3·4% were of other race or ethnicity. The mean age of participants was 59·2 years (SD 6·7). Higher mean HbA_1c, higher skin intrinsic fluorescence, and kidney disease (but not retinopathy or neuropathy) were independently associated with a lower total hip BMD. Total hip BMD differed by -10·7 mg/cm² (95% CI -19·6 to -1·7) for each 1% increase in mean HbA_1c, -20·5 mg/cm² (-29·9 to -11·0) for each 5 unit higher skin intrinsic fluorescence, and -51·7 mg/cm² (-80·6 to -22·7) in the presence of kidney disease. Similar associations were found for femoral neck and ultra-distal radius BMD, but not for lumbar spine BMD or TBS.

INTERPRETATION

Poorer glycaemic control, AGE accumulation, and kidney disease are independent risk factors for lower hip BMD in older adults with type 1 diabetes. Maintenance of glycaemic control and prevention of kidney disease might reduce bone loss and ultimately fractures in this population. Osteoporosis screening might be particularly important in people with these risk factors. Further research to identify AGE blockers could benefit skeletal health.

FUNDING

National Institute of Diabetes and Digestive and Kidney Disease.

Cervical Fusion-Requiring Mineral and Bone Disorder Disguised as Osteoporosis in a Chronic Kidney Disease Patient on Hemodialysis: A Case Report

Bony deformities and fragility fractures in end-stage renal disease (ESRD) patients on long-term hemodialysis can be caused by either osteoporosis or chronic kidney disease-mineral and bone disorder (CKD-MBD). Correct identification of the underlying mechanism is critical since the treatment methods differ, and one treatment approach could negatively affect the other. Cervical kyphosis, severe enough to require immediate surgical treatment, can be caused by uncontrolled CKD-MBD, albeit in limited cases. This report presents the case of a 61-year-old female with an 11-year history of hemodialysis treatment and severe cervical kyphosis with myelopathy, which required 2-stage spinal surgeries. Our report calls for a careful diagnostic approach in ESRD patients with skeletal disorders, the points to consider before calcium replacement, and early detection of fragility fractures in them. Moreover, early mobilization and weight-bearing after the surgical procedure may lead to better neurological and functional improvements.

Diosmin, a citrus fruit-derived phlebotonic bioflavonoid protects rats from chronic kidney disease-induced loss of bone mass and strength without deteriorating renal function

Kidney Disease: Improving Global Outcomes (KDIGO) 2017 Clinical Practice Guideline recommended treatment decisions for patients with chronic kidney disease (CKD) with osteoporosis and/or high risk of fracture. Bisphosphonates, the first-line...

Characterization of Primary Cilia in Osteoblasts Isolated From Patients With ADPKD and CKD

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of chronic kidney disease (CKD) and leads to a specific type of bone disease. The primary cilium is a major cellular organelle implicated in the pathophysiology of ADPKD caused by mutations in polycystin-1 (PKD1) and polycystin-2 (PKD2). In this study, for the first time, cilia were characterized in primary preosteoblasts isolated from patients with ADPKD. All patients with ADPKD had low bone turnover and primary osteoblasts were also obtained from patients with non-ADPKD CKD with low bone turnover. Image-based immunofluorescence assays analyzed cilia using standard markers, pericentrin, and acetylated-α-tubulin, where cilia induction and elongation were chosen as relevant endpoints for these initial investigations. Osteoblastic activity was examined by measuring alkaline phosphatase levels and mineralized matrix deposition rates. It was found that primary cilia can be visualized in patient-derived osteoblasts and respond to elongation treatments. Compared with control cells, ADPKD osteoblasts displayed abnormal cilia elongation that was significantly more responsive in cells with PKD2 nontruncating mutations and PKD1 mutations. In contrast, non-ADPKD CKD osteoblasts were unresponsive and had shorter cilia. Finally, ADPKD osteoblasts showed increased rates of mineralized matrix deposition compared with non-ADPKD CKD. This work represents the first study of cilia in primary human-derived osteoblasts from patients with CKD and patients with ADPKD who have normal kidney function, offering new insights as bone disease phenotypes are not well recapitulated in animal models. These data support a model whereby altered cilia occurs in PKD-mutated osteoblasts, and that ADPKD-related defects in bone cell activity and mineralization are distinct from adynamic bone disease from patients with non-ADPKD CKD. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Renal Proximal Tubule Cell Cannabinoid-1 Receptor Regulates Bone Remodeling and Mass via a Kidney-to-Bone Axis

The renal proximal tubule cells (RPTCs), well-known for maintaining glucose and mineral homeostasis, play a critical role in the regulation of kidney function and bone remodeling. Deterioration in RPTC function may therefore lead to the development of diabetic kidney disease (DKD) and osteoporosis. Previously, we have shown that the cannabinoid-1 receptor (CB1R) modulates both kidney function as well as bone remodeling and mass via its direct role in RPTCs and bone cells, respectively. Here we employed genetic and pharmacological approaches that target CB1R, and found that its specific nullification in RPTCs preserves bone mass and remodeling both under normo- and hyper-glycemic conditions, and that its chronic blockade prevents the development of diabetes-induced bone loss. These protective effects of negatively targeting CB1R specifically in RPTCs were associated with its ability to modulate erythropoietin (EPO) synthesis, a hormone known to affect bone mass and remodeling. Our findings highlight a novel molecular mechanism by which CB1R in RPTCs remotely regulates skeletal homeostasis via a kidney-to-bone axis that involves EPO.

Kidney Disease Progression Does Not Decrease Intestinal Phosphorus Absorption in a Rat Model of Chronic Kidney Disease-Mineral Bone Disorder

The Cy/+ rat has been characterized as a progressive model of chronic kidney disease-mineral bone disorder (CKD-MBD). We aimed to determine the effect of kidney disease progression on intestinal phosphorus absorption and whole-body phosphorus balance in this model. A total of 48 Cy/+ (CKD) and 48 normal littermates (NL) rats were studied at two ages: 20 weeks and 30 weeks, to model progressive kidney function decline at approximately 50% and 20% of normal kidney function. Sodium-dependent and sodium-independent intestinal phosphorus absorption efficiency were measured by the in situ jejunal ligated loop method using 33 P radioisotope. Our results show that CKD rats had slightly higher sodium-dependent phosphorus absorption compared to NL rats, and absorption decreased from 20 to 30 weeks. These results are in contrast to plasma 1,25OH2 D, which was lower in CKD rats. Gene expression of the major intestinal phosphorus transporter, NaPi-2b, was not different between CKD and NL rats in the jejunum but was lower in CKD rats versus NL rats in the duodenum. Jejunal ligated loop phosphorus absorption results are consistent with percent net phosphorus absorption results obtained from metabolic balance: higher net percent phosphorus absorption values in CKD rats compared with NL, and lower values in 30-week-olds compared with 20-week-olds. Phosphorus balance was negative (below zero) in CKD rats, significantly lower in 30-week-old rats compared with 20-week-old rats, and lower in CKD rats compared with NL rats at both ages. These results demonstrate no reduction in intestinal phosphorus absorption with progression of CKD despite lower 1,25OH2 D status when assessed by an in situ ligated loop test, which is in contrast to the majority of in vitro studies, and if confirmed in further studies, could challenge the physiological relevance of in vitro findings. © 2019 American Society for Bone and Mineral Research.

Kidney function and its association to imminent, short- and long-term fracture risk-a longitudinal study in older women

Reduced kidney function is associated with an increased fracture risk, although the relationship between an age-related decline and fractures needs further investigation. We followed kidney function and fracture risk for 10 years. A mild-moderate decline in kidney function was associated with fracture, but not in advanced age.

INTRODUCTION

With age, kidney function declines. Though well known that chronic kidney disease is associated with increased fracture risk, the extent to which the typical age-related decline contributes is unclear. In the OPRA cohort, a longitudinal study of older non-selected women, we investigated the association between kidney function and fracture.

METHODS

Cystatin C-based kidney function estimates were available at age 75 (n = 981) and 80 (n = 685). Women were categorized by kidney function: normal (CKD stages 1 and 2), mild-moderate (3a), poor (3b-5), and imminent, short- and long-term fracture risk investigated. BMD measurements and kidney function for risk prediction were also evaluated; women were categorized by both reduced kidney function (stages 3-5) and osteoporosis status.

RESULTS

In the short term, 2-3 years, mild-moderate kidney dysfunction was associated with the highest risk increase: osteoporotic fractures (2 years HRadj 2.21, 95% CI 1.27-3.87) and also up to 5 years (between 75 and 80 years) (HRadj 1.51, 1.04-2.18). Hip fracture risk was similarly increased. This association was not observed from age 80 nor for women with poorest kidney function. Reduced kidney function was associated with higher risk even without osteoporosis (osteoporotic fracture; HRadj 1.66, 1.08-2.54); risk increased by having both osteoporosis and reduced function (HRadj 2.53, 1.52-4.23).

CONCLUSION

Older women with mild-moderate reduction of kidney function are at increased risk of fractures, but not those with the worst function. Our findings furthermore confirm the value of osteoporosis assessment and it is possible that in this age group, age-related decline of kidney function has limited contribution compared with BMD.

Skeletal levels of bisphosphonate in the setting of chronic kidney disease are independent of remodeling rate and lower with fractionated dosing

BACKGROUND

Chronic kidney disease (CKD) results in a dramatic increase in skeletal fracture risk. Bisphosphates (BP) are an effective treatment for reducing fracture risk but they are not recommended in advanced CKD. We have recently shown higher acute skeletal accumulation of fluorescently-tagged zoledronate (ZOL) in the setting of CKD but how this accumulation is retained/lost over time is unclear. Furthermore, it is unknown if alternative dosing approaches can modulate accumulation in the setting of CKD.

METHODS

To address these two questions normal (NL) and Cy/+ (CKD) rats were divided into control groups (no dosing), a single dose of a fluorescent-tagged ZOL (FAM-ZOL), a single dose of non-labelled zoledronate (ZOL) or ten weekly doses of FAM-ZOL each at 1/10th the dose of the single dose group. Half of the CKD animals in each group were provided water with 3% calcium in drinking water (CKD + Ca) to suppress PTH and remodeling. At 30 or 35 weeks of age, serum, tibia, ulna, radius, vertebra, femora, and mandible were collected and subjected to assessment methods including biochemistry, dynamic histomorphometry and multi-spectral fluorescence levels (using IVIS SpectrumCT).

RESULTS

FAM-ZOL did not significantly reduce bone remodeling in either NL or CKD animals while Ca supplementation in CKD produced remodeling levels comparable to NL. At five- and ten-weeks post-dosing, both CKD and CKD + Ca groups had higher levels of FAM-ZOL in most, but not all, skeletal sites compared to NL with no difference between the two CKD groups suggesting that the rate of remodeling did not affect skeletal retention of FAM-ZOL. Fractionating the FAM-ZOL into ten weekly doses led to 20-32% less (p < 0.05) accumulation/retention of compound in the vertebra, radius, and ulna compared to administration as a single dose.

CONCLUSIONS

The rate of bone turnover does not have significant effects on levels of FAM-ZOL accumulation/retention in animals with CKD. A lower dose/more frequent administration paradigm results in lower levels of accumulation/retention over time. These data provide information that could better inform the use of bisphosphonates in the setting of CKD in order to combat the dramatic increase in fracture risk.

Clinical and translational pharmacology of the cathepsin K inhibitor odanacatib studied for osteoporosis

Cathepsin K (CatK) is a cysteine protease abundantly expressed by osteoclasts and localized in the lysosomes and resorption lacunae of these cells. CatK is the principal enzyme responsible for the degradation of bone collagen. Odanacatib is a selective, reversible inhibitor of CatK at subnanomolar potency. The pharmacokinetics of odanacatib have been extensively studied and are similar in young healthy men, postmenopausal women and elderly men, and were qualitatively similar throughout Phase 1 development and in-patient studies. Following 3 weeks of 50 mg once weekly dosing the geometric mean area under the curve from 0 to 168 hours was 41.1 μM h, the concentration at 168 hours was 126 nM and the harmonic mean apparent terminal half-life was 84.8 hr. Odanacatib exposure increased in a less than dose proportional manner due to solubility limited absorption. It is estimated that approximately 70% of the absorbed dose of odanacatib is eliminated via metabolism, 20% is excreted as unchanged drug in the bile or faeces, and 10% is excreted as unchanged drug in the urine. The systemic clearance was low (approximately 13 mL/min). Odanacatib decreases the degradation of bone matrix proteins and reduces the efficiency of bone resorption with target engagement confirmed by a robust decrease in serum C-telopeptides of type 1 collagen (approximately 60%), urinary aminoterminal crosslinked telopeptides of type 1 collagen to creatinine ratio (approximately 50%) and total urine deoxypyridinoline/Cr (approximately 30%), with an increase in serum cross-linked carboxy-terminal telopeptide of type 1 collagen (approximately 55%). The 50-mg weekly dosing regimen evaluated in Phase 3 achieved near maximal reduction in bone resorption throughout the treatment period. The extensive clinical programme for odanacatib, together with more limited clinical experience with other CatK inhibitors (balicatib and ONO-5334), provides important insights into the clinical pharmacology of CatK inhibition and the potential role of CatK in bone turnover and mineral homeostasis. Key findings include the ability of this mechanism to: (i) provide sustained reductions in resorption markers, increases in bone mineral density, and demonstrated fracture risk reduction; (ii) be associated with relative formation-sparing effects such that sustained resorption reduction is achieved without accompanying meaningful reductions in bone formation; and (iii) lead to increases in osteoclast number as well as other osteoclast activity (including build-up of CatK enzyme), which may yield transient increases in resorption following treatment discontinuation and the potential for nonmonotonic responses at subtherapeutic doses.

Skeletal accumulation of fluorescently tagged zoledronate is higher in animals with early stage chronic kidney disease

This work examines the skeletal accumulation of fluorescently tagged zoledronate in an animal model of chronic kidney disease. The results show higher accumulation in 24-h post-dose animals with lower kidney function due to greater amounts of binding at individual surfaces.

INTRODUCTION

Chronic kidney disease (CKD) patients suffer from increased rates of skeletal-related mortality from changes driven by biochemical abnormalities. Bisphosphonates are commonly used in reducing fracture risk in a variety of diseases, yet their use is not recommended in advanced stages of CKD. This study aimed to characterize the accumulation of a single dose of fluorescently tagged zoledronate (FAM-ZOL) in the setting of reduced kidney function.

METHODS

At 25 weeks of age, FAM-ZOL was administered to normal and CKD rats. Twenty-four hours later, multiple bones were collected and assessed using bulk fluorescence imaging, two-photon imaging, and dynamic histomorphometry.

RESULTS

CKD animals had significantly higher levels of FAM-ZOL accumulation in the proximal tibia, radius, and ulna, but not in lumbar vertebral body or mandible, based on multiple measurement modalities. Although a majority of trabecular bone surfaces were covered with FAM-ZOL in both normal and CKD animals, the latter had significantly higher levels of fluorescence per unit bone surface in the proximal tibia.

CONCLUSIONS

These results provide new data regarding how reduced kidney function affects drug accumulation in rat bone.

Hypocalcemia and bone mineral density changes following denosumab treatment in end-stage renal disease patients: a meta-analysis of observational studies

The incidence of hypocalcemia and bone mineral density (BMD) changes in end-stage renal disease (ESRD) patients on denosumab remains unclear. We performed this meta-analysis to assess the incidence of denosumab-associated hypocalcemia and effects of denosumab on BMD in ESRD patients. A literature search was conducted using MEDLINE, EMBASE, and Cochrane Database from inception through November 2017 to identify studies evaluating incidence of denosumab-associated hypocalcemia and changes in serum calcium, phosphate, alkaline phosphatase (ALP), parathyroid hormone (PTH), and BMD from baseline to post-treatment course of denosumab in ESRD patients. Study results were pooled and analyzed using a random-effect model. The protocol for this meta-analysis is registered with PROSPERO (International Prospective Register of Systematic Reviews; no. CRD42017081074). Six observational studies with a total of 84 ESRD patients were enrolled. The pooled estimated incidence of hypocalcemia during denosumab treatment was 42% (95% CI 29-55%, I² = 0%). Hypocalcemia occurred approximately 7 to 20 days after the first dose and reached nadir of low calcium levels in the first 2 weeks up to 2 months. However, there were no significant changes in serum calcium or phosphate from baseline to post-treatment course (≥ 3 months after treatment) with mean differences [MDs] of 0.20 mg/dL (95% CI, - 0.30 to 0.69 mg/dL) and - 0.10 mg/dL (95% CI, - 0.70 to 0.49 mg/dL). There were significant reductions in ALP and PTH levels with standardized mean differences (SMDs) of - 0.65 (95% CI - 1.13 to - 0.16) and - 1.89 (95% CI - 3.44 to - 0.34), respectively. There were significant increases in T-scores with MDs of 0.39 (95% CI 0.10 to 0.69) and 0.79 (95% CI 0.60 to 0.98) for lumbar spine and femoral neck, respectively. Our study demonstrates the estimated incidence of denosumab-associated hypocalcemia in dialysis patients of 42%. From baseline to post-treatment course, although there are no differences in serum calcium and phosphate, our findings suggest significant reductions in ALP and PTH and a significant increase in BMD. Currently, denosumab should not be considered as the treatment of choice in ESRD patients until more safety and efficacy data are available.

Osteoporosis, bone mineral density and CKD-MBD complex (I): Diagnostic considerations

Osteoporosis (OP) and chronic kidney disease (CKD) independently influence bone and cardiovascular health. A considerable number of patients with CKD, especially those with stages 3a to 5D, have a significantly reduced bone mineral density leading to a high risk of fracture and a significant increase in associated morbidity and mortality. Independently of classic OP related to age and/or gender, the mechanical properties of bone are also affected by inherent risk factors for CKD ("uraemic OP"). In the first part of this review, we will analyse the general concepts regarding bone mineral density, OP and fractures, which have been largely undervalued until now by nephrologists due to the lack of evidence and diagnostic difficulties in the context of CKD. It has now been proven that a reduced bone mineral density is highly predictive of fracture risk in CKD patients, although it does not allow a distinction to be made between the causes which generate it (hyperparathyroidism, adynamic bone disease and/or senile osteoporosis, etc.). Therefore, in the second part, we will analyse the therapeutic indications in different CKD stages. In any case, the individual assessment of factors which represent a higher or lower risk of fracture, the quantification of this risk (i.e. using tools such as FRAX^®) and the potential indications for densitometry in patients with CKD could represent an important first step pending new clinical guidelines based on randomised studies which do not exclude CKD patients, all the while avoiding therapeutic nihilism in an area of growing importance.

Is there a practical role for bone biopsy in chronic kidney disease?

Bone biopsy is currently the only means to accurately assess renal osteodystrophy and responses to therapeutic interventions. With sedation, the technique is relatively painless, and complications are uncommon. Bone biopsy should be considered when the aetiology of symptoms or biochemical abnormalities is in question, and results may lead to changes in therapy. Although it remains prudent to use antiresorptive drugs cautiously in patients with chronic kidney disease (CKD) stages 3a-4 and low bone mineral density, bone biopsy may not be warranted before commencing therapy in these patients. Histomorphometric indices adopted for bone biopsy assessment are turnover (T), mineralisation (M) and volume (V). Often, only measurements of trabecular bone are reported; however, marked cortical changes are common in CKD and may be critical to bone structure and integrity. MicroCT of bone biopsies can rapidly assess static parameters and provides information on the cortical and trabecular compartments that may influence management. Limitations of bone biopsy include the time required for pre-biopsy tetracycline labelling and sample processing, and a paucity of facilities to process and report samples. Patients with CKD may not respond predictably to treatments, and because the biopsy sample is illustrative of activity at only one skeletal site and one point in time, assessment of real-time laboratory trends is always required. Optimally, we need a non-invasive 'virtual bone biopsy' that provides information for initiating and monitoring therapy. However, bone biopsy is the current standard by which the accuracy of investigational imaging techniques, hormonal values and biochemical turnover markers are judged.

Use of dual energy X-ray absorptiometry, the trabecular bone score and quantitative computed tomography in the evaluation of chronic kidney disease-mineral and bone disorders

In subjects with chronic kidney disease (CKD) who suffer a minimal trauma fracture, the problem is to differentiate between osteoporosis and the various forms of renal bone disease associated with CKD-mineral and bone disorder. This problem is exacerbated by the fact that renal osteodystrophy may coexist with osteoporosis. The World Health Organization's bone mineral density (BMD) criteria for osteopenia ( -2.5 < T-score < -1.0) and osteoporosis (a T-score ≤ -2.5) may be used in patients with CKD stages 1-3. In CKD stages 4-5, BMD by dual-energy X-ray absorptiometry (DXA) is less predictive and may underestimate fracture risk. The development of absolute fracture risk (AFR) algorithms, such as FRAX® and the Garvan absolute fracture risk calculator, to predict risk of fracture over a given time (usually 10 years) aims to incorporate non-BMD risk factors into the clinical assessment. FRAX® has been shown to be useful to assess fracture risk in CKD but may underestimate fracture risk in advanced CKD. The trabecular bone score is a measure of grey scale homogeneity obtained from spine DXA, which correlates to trabecular microarchitecture and is an independent risk factor for fracture. Recent data demonstrate the potential utility of the trabecular bone score adjustment of AFR through the FRAX® algorithm in subjects with CKD. Parameters of bone microarchitecture using peripheral quantitative computed tomography (pQCT) or high-resolution pQCT are also able to discriminate fracture status in subjects with CKD. However, there are at present no convincing data that the addition of pQCT or high-resolution pQCT parameters to DXA BMD improves fracture discrimination. More advanced estimates of bone strength derived from measurements of micro-architecture, by QCT-derived finite element analysis may be incorporated into AFR algorithms in the future.

Augmented Fibroblast Growth Factor-23 Secretion in Bone Locally Contributes to Impaired Bone Mineralization in Chronic Kidney Disease in Mice

Chronic kidney disease-mineral and bone disorder (CKD-MBD) is a systemic disorder of mineral and bone metabolism caused by CKD. Impaired bone mineralization together with increased bony secretion of fibroblast growth factor-23 (FGF23) are hallmarks of CKD-MBD. We recently showed that FGF23 suppresses the expression of tissue nonspecific alkaline phosphatase (TNAP) in bone cells by a Klotho-independent, FGF receptor-3-mediated signaling axis, leading to the accumulation of the mineralization inhibitor pyrophosphate. Therefore, we hypothesized that excessive FGF23 secretion may locally impair bone mineralization in CKD-MBD. To test this hypothesis, we induced CKD by 5/6 nephrectomy in 3-month-old wild-type (WT) mice and Fgf23^-/-/VDR^Δ/Δ (Fgf23/VDR) compound mutant mice maintained on a diet enriched with calcium, phosphate, and lactose. Eight weeks postsurgery, WT CKD mice were characterized by reduced bone mineral density at the axial and appendicular skeleton, hyperphosphatemia, secondary hyperparathyroidism, increased serum intact Fgf23, and impaired bone mineralization as evidenced by bone histomorphometry. Laser capture microdissection in bone cryosections showed that both osteoblasts and osteocytes contributed to the CKD-induced increase in Fgf23 mRNA abundance. In line with our hypothesis, osteoblastic and osteocytic activity of alkaline phosphatase was reduced, and bone pyrophosphate concentration was ~2.5-fold higher in CKD mice, relative to Sham controls. In Fgf23/VDR compound mice lacking Fgf23, 5/6-Nx induced secondary hyperparathyroidism and bone loss. However, 5/6-Nx failed to suppress TNAP activity, and bone pyrophosphate concentrations remained unchanged in Fgf23/VDR CKD mice. Collectively, our data suggest that elevated Fgf23 production in bone contributes to the mineralization defect in CKD-MBD by auto-/paracrine suppression of TNAP and subsequent accumulation of pyrophosphate in bone. Hence, our study has identified a novel mechanism involved in the pathogenesis of CKD-MBD.

Review on the Utility of Trabecular Bone Score, a Surrogate of Bone Micro-architecture, in the Chronic Kidney Disease Spectrum and in Kidney Transplant Recipients

Chronic kidney disease (CKD) is defined as abnormalities of kidney structure or function, present for >3 months, with implications for, among others, bone health. Advanced stages of CKD have an increased risk of fragility fractures. Trabecular bone score (TBS) is a relatively new gray-level textural parameter, which provides information on bone microarchitecture and has been shown to be a good predictor of fragility fractures independently of bone density and clinical risk factors. We aimed to review the scientific literature on TBS and its utility along the CKD spectrum and in kidney transplant recipients. In total, eight articles had investigated this topic: one article in patients with reduced kidney function, two in patients on hemodialysis, and five in kidney transplant recipients. In general, all the studies had shown an association between lower values of TBS and reduced kidney function; or lower TBS values among the hemodialysis or kidney transplant patients compared to healthy controls. Moreover, TBS was shown to be a good and independent predictor of fragility fractures in patients with CKD or who underwent kidney transplantation. TBS postulates itself as a valuable marker to be used in clinical practice as an assessor of bone microarchitecture and fracture risk predictor in these specific populations. However, evidence is to some extent limited and larger follow-up case-control studies would help to further investigate the TBS utility in the management of bone health damage and increased fracture risk in patients with CKD or kidney transplant.

Bone Turnover Status: Classification Model and Clinical Implications

Aim: To develop a practical model for classification bone turnover status and evaluate its clinical usefulness. Methods: Our classification of bone turnover status is based on internationally recommended biomarkers of both bone formation (N-terminal propeptide of type1 procollagen, P1NP) and bone resorption (beta C-terminal cross-linked telopeptide of type I collagen, bCTX), using the cutoffs proposed as therapeutic targets. The relationships between turnover subtypes and clinical characteristic were assessed in1223 hospitalised orthogeriatric patients (846 women, 377 men; mean age 78.1±9.50 years): 451(36.9%) subjects with hip fracture (HF), 396(32.4%) with other non-vertebral (non-HF) fractures (HF) and 376 (30.7%) patients without fractures. Resalts: Six subtypes of bone turnover status were identified: 1 - normal turnover (P1NP>32 μg/L, bCTX≤0.250 μg/L and P1NP/bCTX>100.0[(median value]); 2- low bone formation (P1NP ≤32 μg/L), normal bone resorption (bCTX≤0.250 μg/L) and P1NP/bCTX>100.0 (subtype2A) or P1NP/bCTX<100.0 (subtype 2B); 3- low bone formation, high bone resorption (bCTX>0.250 μg/L) and P1NP/bCTX<100.0; 4- high bone turnover (both markers elevated ) and P1NP/bCTX>100.0 (subtype 4A) or P1NP/bCTX<100.0 (subtype 4B). Compared to subtypes 1 and 2A, subtype 2B was strongly associated with nonvertebral fractures (odds ratio [OR] 2.0), especially HF (OR 3.2), age>75 years and hyperparathyroidism. Hypoalbuminaemia and not using osteoporotic therapy were two independent indicators common for subtypes 3, 4A and 4B; these three subtypes were associated with in-hospital mortality. Subtype 3 was associated with fractures (OR 1.7, for HF OR 2.4), age>75 years, chronic heart failure (CHF), anaemia, and history of malignancy, and predicted post-operative myocardial injury, high inflammatory response and length of hospital stay (LOS) above10 days. Subtype 4A was associated with chronic kidney disease (CKD), anaemia, history of malignancy and walking aids use and predicted LOS>20 days, but was not discriminative for fractures. Subtype 4B was associated with fractures (OR 2.1, for HF OR 2.5), age>75 years, CKD and indicated risks of myocardial injury, high inflammatory response and LOS>10 days. Conclusions: We proposed a classification model of bone turnover status and demonstrated that in orthogeriatric patients altered subtypes are closely related to presence of nonvertebral fractures, comorbidities and poorer in-hospital outcomes. However, further research is needed to establish optimal cut points of various biomarkers and improve the classification model.

Dental implant treatment for renal failure patients on dialysis: a clinical guideline

Chronic kidney disease (CKD) is a worldwide public health problem that is growing in prevalence and is associated with severe complications. During the progression of the disease, a majority of CKD patients suffer oral complications. Dental implants are currently the most reliable and successful treatment for missing teeth. However, due to complications of CKD such as infections, bone lesions, bleeding risks, and altered drug metabolism, dental implant treatment for renal failure patients on dialysis is more challenging. In this review, we have summarized the characteristics of CKD and previous publications regarding dental treatments for renal failure patients. In addition, we discuss our recent research results and clinical experience in order to provide dental implant practitioners with a clinical guideline for dental implant treatment for renal failure patients undergoing hemodialysis.

Chronic kidney disease and vitamin D metabolism in human bone marrow-derived MSCs

Vitamin D that is synthesized in the skin or is ingested undergoes sequential steps of metabolic activation via a cascade of cytochrome P450 enzymatic hydroxylations in the liver and kidney to produce 1α,25-dihydroxyvitamin D (1α,25(OH)2 D). There are many tissues that are able to synthesize 1α,25(OH)2 D, but the biological significance of extrarenal hydroxylases is unresolved. Human marrow-derived mesenchymal stem cells (marrow stromal cells, hMSCs) give rise to osteoblasts, and their differentiation is stimulated by 1α,25(OH)2 D. In addition to being targets of 1α,25(OH)2 D, hMSCs can synthesize it; on the basis of those observations, we further examined the local autocrine/paracrine role of vitamin D metabolism in osteoblast differentiation. Research with hMSCs from well-characterized subjects provides an innovative opportunity to evaluate the effects of clinical attributes on the regulation of hMSCs. Like the renal 1α-hydroxylase, the enzyme in hMSCs is constitutively decreased with age and chronic kidney disease (CKD); both are regulated by PTH1-34, insulin-like growth factor 1, calcium, 1α,25(OH)2 D, 25(OH)D, and fibroblast growth factor 23. CKD is associated with impaired renal biosynthesis of 1α,25(OH)2 D, low bone mass, and increased fracture risk. Studies with hMSCs from CKD patients or aged subjects indicate that circulating 25(OH)D may have an important role in osteoblast differentiation on vitamin D metabolism and action in hMSCs.

Efficacy and safety of osteoporosis medications in a rat model of late-stage chronic kidney disease accompanied by secondary hyperparathyroidism and hyperphosphatemia

This study showed that bisphosphonate was safe and effective for the treatment of bone disorders in stage 4 chronic kidney disease (CKD) rats. Intermittent teriparatide therapy showed an anabolic action on bone even under secondary hyperparathyroidism conditions without having an adverse effect on mineral metabolism in late-stage CKD.

INTRODUCTION

Patients with late-stage CKD are at high risk for fragility fractures. However, there are no consensus on the efficacy and safety of osteoporosis medications for patients with late-stage CKD. In the present study, we aimed to examine the efficacy and safety of alendronate (ALN) and teriparatide (TPD) for treating bone disorder in late-stage CKD with pre-existing secondary hyperparathyroidism using a rat model of CKD.

METHODS

Male 10-week-old Sprague-Dawley rats were subjected to a 5/6 nephrectomy or sham surgery and randomized into the following four groups: sham, vehicle (saline subcutaneous (sc) daily), ALN (50 μg/kg sc daily), and TPD (40 μg/kg sc daily). Medications commenced at 24 weeks of age and continued for 4 weeks. Micro-computed tomography, histological analysis, infrared spectroscopic imaging, and serum assays were performed.

RESULTS

Nephrectomized rats developed hyperphosphatemia, secondary hyperparathyroidism (SHPT), and high creatinine, equivalent to CKD stage 4 in humans. ALN suppressed the bone turnover and increased the degree of mineralization in cortical bone, resulting in an improvement in the mechanical properties. TPD further increased the bone turnover and significantly increased the degree of mineralization, micro-geometry, and bone volume, resulting in a significant improvement in the mechanical properties. Both ALN and TPD had no adverse effect on renal function and mineral metabolism.

CONCLUSIONS

BP is safe and effective for the treatment of bone disorders in stage 4 CKD rats. Intermittent TPD therapy showed an anabolic action on bone even under SHPT conditions without having an adverse effect on mineral metabolism in late-stage CKD.

Does the OPG/RANKL system contribute to the bone-vascular axis in chronic kidney disease? A systematic review

Vascular calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD) and is strongly associated with cardiovascular mortality and morbidity. Accumulating evidence over the past decade has challenged the hypothesis of close interaction between bone and VC what raises the possibility of a common underlying pathophysiological mechanism. Lately, bone regulatory proteins such as: osteoprotegerin (OPG) and Receptor Activator for Nuclear Factor κB Ligand (RANKL) has attracted attention of researchers as a possible key mediators of bone-vascular calcification imbalance. The literature search was carried out using the MEDLINE/PubMed database and a combination of keywords and MeSH terms, and only papers published since January 2005 to July 2016 were selected. The search resulted in 562 potential articles. After selection according to the eligibility criteria, 107 studies fulfilled were included (102 full texts and 5 was case reports). OPG and RANKL plays essential role in the regulation of bone metabolism and may be regarded as a possible link between VC, bone and mineral metabolism in CKD patients. Further studies are required to determine the diagnostic significance of these proteins in evaluation of progression and severity of VC process in CKD patients. Finally, the efficacy and safety, especially in regard to VC, of anti-RANKL therapy in CKD patients requires well-designed prospective, randomized trials.

The role of bone biopsy for the diagnosis of renal osteodystrophy: a short overview and future perspectives

Chronic kidney disease (CKD) patients present specific bone and mineral metabolism disturbances, which account for important morbidity and mortality. The term renal osteodystrophy, classically used for the nomination of CKD-associated bone disorder, has been limited to the histologic description of bone lesions, requiring the use of bone biopsy. Biochemical markers and imaging tools do not adequately predict the complex bone changes that are observed in renal osteodystrophy. Parathyroid hormone, which is a universally used biomarker of bone turnover in clinical practice, lacks specificity and sensitivity. Therefore, tetracycline double-labelled transiliac bone biopsy, with bone histology and histomorphometric evaluation, remains the best clinical tool to discriminate bone turnover and to evaluate the other dimensions of renal osteodystrophy. This review will focus on the value of classic bone histomorphometric analysis of trabecular bone in CKD patients and unfold new perspectives of this diagnostic tool, including cortical bone evaluation and bone tissue immunohistochemistry.

Oral Tori in Chronic Peritoneal Dialysis Patients

BACKGROUND

The pathogenesis of oral tori has long been debated and is thought to be the product of both genetic and environmental factors, including occlusal forces. Another proposed mechanism for oral tori is the combination of biomechanical forces, particularly in the oral cavity, combined with cortical bone loss and trabecular expansion, as one might see in the early stages of primary hyperparathyroidism. This study investigated the epidemiology of torus palatinus (TP) and torus mandibularis (TM) in peritoneal dialysis patients, and analyzed the influences of hyperparathyroidism on the formation of oral tori.

METHOD

In total, 134 peritoneal dialysis patients were recruited between July 1 and December 31, 2015 for dental examinations for this study. Patients were categorized into two subgroups based on the presence or absence of oral tori. Demographic, hematological, biochemical, and dialysis-related data were obtained for analysis.

RESULTS

The prevalence of oral tori in our sample group was high at 42.5% (57 of 134), and most patients with oral tori were female (61.4%). The most common location of tori was TP (80.7%), followed by TP and TM (14.0%), then TM (5.3%). All 54 TP cases were at the midline, and most were <2 cm (59.3%), flat (53.7%), and located in the premolar region (40.7%). Of the 11 TM cases, all were bilateral and symmetric, mostly <2 cm (81.9%), lobular (45.4%), and located at premolar region (63.6%). Interestingly, patients with oral tori had slightly lower serum levels of intact parathyroid hormones than those without oral tori, but the difference was not statistically significant (317.3±292.0 versus 430.1±492.6 pg/mL, P = 0.126). In addition, patients with oral tori did not differ from patients without tori in inflammatory variables such as serum high sensitivity C-reactive protein levels (6.6±8.2 versus 10.3±20.2 mg/L, P = 0.147) or nutritional variables such as serum albumin levels (3.79±0.38 versus 3.77±0.45 g/dL, P = 0.790). Furthermore, there were no differences between patients with and without oral tori in dialysis adequacy (weekly Kt/Vurea, 2.14±0.39 versus 2.11±0.33, P = 0.533; weekly creatinine clearance rate, 59.31±17.58 versus 58.57±13.20 L/1.73 m2, P = 0.781), or peritoneal membrane transporter characteristics (P = 0.098).

CONCLUSION

Secondary hyperparathyroidism does not contribute to the formation of tori in peritoneal dialysis patients. Further studies are warranted.