Sclerostin in chronic kidney disease-mineral bone disorder think first before you block it!

The mechanisms underlying acute myocardial infarction in chronic kidney disease patients undergoing hemodialysis

Cardiovascular disease (CVD) is a leading cause of death in chronic kidney disease (CKD). Hemodialysis is one of the main treatments for patients with end-stage kidney disease. Epidemiological data has shown that acute myocardial infarction (AMI) accounts for the main reason for death in patients with CKD under hemodialysis therapy. Immune dysfunction and changes in metabolism (including a high level of inflammatory cytokines, a disorder of lipid and mineral ion homeostasis, accumulation of uremic toxins et al.) during CKD can deteriorate stability of atherosclerotic plaque and promote vascular calcification, which are exactly the pathophysiological mechanisms underlying the occurrence of AMI. Meanwhile, the hemodialysis itself also has adverse effects on lipoprotein, the immune system and hemodynamics, which contribute to the high incidence of AMI in these patients. This review aims to summarize the mechanisms and further promising methods of prevention and treatment of AMI in CKD patients undergoing hemodialysis, which can provide an excellent paradigm for exploring the crosstalk between the kidney and cardiovascular system.

The Relationship between Sclerostin and Kidney Transplantation Mineral Bone Disorders: A Molecule of Controversies

Kidney transplantation is the most effective treatment option for most patients with end-stage kidney disease due to reduced mortality, decreased cardiovascular events and increased quality of life compared to patients treated with dialysis. However, kidney transplantation is not devoid of both acute and chronic complications including mineral bone disorders (MBD) which are already present in patients with chronic kidney disease (CKD) before kidney transplantation. The natural history of MBD after kidney transplantation is variable and new markers are needed to define MBD after kidney transplantation. One of these promising molecules is sclerostin. The main action of sclerostin is to inhibit bone formation and mineralization by blocking osteoblast differentiation and function. In kidney transplant recipients (KTRs), various studies have shown that sclerostin is associated with graft function, bone parameters, vascular calcification, and arterial stiffness although non-uniformly. Furthermore, data for inhibition of sclerostin with monoclonal antibody romosozumab for treatment of osteoporosis is available for general population but not in KTRs which osteoporosis is highly prevalent. In this narrative review, we have summarized the studies investigating the change of sclerostin before and after kidney transplantation, the relationship between sclerostin and laboratory parameters, bone metabolism and vascular calcification in the context of kidney transplantation. We also pointed out the uncertainties, explained the causes of divergent findings and suggest further potential study topics regarding sclerostin in kidney transplantation.

Current therapeutic approach of chronic kidney disease-mineral and bone disorder

Chronic kidney disease (CKD) has emerged as one of the leading noncommunicable diseases affecting >10% of the population worldwide. Bone and mineral disorders are a common complication among patients with CKD resulting in a poor life quality, high fracture risk, increased morbidity and cardiovascular mortality. According to Kidney Disease: Improving Global Outcomes, renal osteodystrophy refers to changes in bone morphology found in bone biopsy, whereas CKD-mineral and bone disorder (CKD-MBD) defines a complex of disturbances including biochemical and hormonal alterations, disorders of bone and mineral metabolism and extraskeletal calcification. As a result, the management of CKD-MBD should focus on the aforementioned parameters, including the treatment of hyperphosphatemia, hypocalcemia, abnormal PTH and vitamin D levels. Regarding the bone fragility fractures, osteoporosis and renal osteodystrophy, which constitute the bone component of CKD-MBD, anti-osteoporotic agents constitute the mainstay of treatment. However, a thorough elucidation of the CKD-MBD pathogenesis is crucial for the ideal personalized treatment approach. In this paper, we review the pathology and management of CKD-MBD based on the current literature with special attention to recent advances.

The Molecular Mechanisms Underlying the Systemic Effects Mediated by Parathormone in the Context of Chronic Kidney Disease

Chronic kidney disease (CKD) stands as a prominent non-communicable ailment, significantly impacting life expectancy. Physiopathology stands mainly upon the triangle represented by parathormone-Vitamin D-Fibroblast Growth Factor-23. Parathormone (PTH), the key hormone in mineral homeostasis, is one of the less easily modifiable parameters in CKD; however, it stands as a significant marker for assessing the risk of complications. The updated "trade-off hypothesis" reveals that levels of PTH spike out of the normal range as early as stage G2 CKD, advancing it as a possible determinant of systemic damage. The present review aims to review the effects exhibited by PTH on several organs while linking the molecular mechanisms to the observed actions in the context of CKD. From a diagnostic perspective, PTH is the most reliable and accessible biochemical marker in CKD, but its trend bears a higher significance on a patient's prognosis rather than the absolute value. Classically, PTH acts in a dichotomous manner on bone tissue, maintaining a balance between formation and resorption. Under the uremic conditions of advanced CKD, the altered intestinal microbiota majorly tips the balance towards bone lysis. Probiotic treatment has proven reliable in animal models, but in humans, data are limited. Regarding bone status, persistently high levels of PTH determine a reduction in mineral density and a concurrent increase in fracture risk. Pharmacological manipulation of serum PTH requires appropriate patient selection and monitoring since dangerously low levels of PTH may completely inhibit bone turnover. Moreover, the altered mineral balance extends to the cardiovascular system, promoting vascular calcifications. Lastly, the involvement of PTH in the Renin-Angiotensin-Aldosterone axis highlights the importance of opting for the appropriate pharmacological agent should hypertension develop.

Vascular calcification in peritoneal dialysis patients and its association with bone-derived molecules and bone histomorphometry

INTRODUCTION

Data regarding vascular calcification (VC) in contemporary peritoneal dialysis (PD) patients is scarce. Bone-vascular axis has been demonstrated in hemodialysis (HD). However, studies showing the link between bone disease and VC in PD patients are lacking. The role of sclerostin, dickkopf-related protein 1 (DKK-1), receptor activator for nuclear factor kB ligand and osteoprotegerin (OPG) in VC in PD remains to clarify.

MATERIALS AND METHODS

Bone biopsy was performed in 47 prevalent PD patients with histomorphometric analysis. Patients were submitted to pelvis and hands X-ray to evaluate VC using the Adragão score (AS). Relevant clinical and biochemical data was collected.

RESULTS

Thirteen patients (27.7%) had positive AS (AS≥1). Patients with VC were significantly older (58.9 vs. 50.4 years, p=0.011), had a lower dialysis dose (KT/V 2.0 vs. 2.4, p=0.025) and a higher glycosylated hemoglobin (7.2 vs. 5.4%, p=0.001). There was not any laboratorial parameter of mineral and bone disease used in clinical practice different between patients with or without VC. All diabetic patients had VC but only 8.1% of non-diabetic had VC (p<0.001). Patients with VC showed significantly higher erythrocyte sedimentation rate (ESR) (91.1 vs. 60.0mm/h, p=0.001), sclerostin (2250.0 vs. 1745.8pg/mL, p=0.035), DKK-1 (1451.6 vs. 1042.9pg/mL, p=0.041) and OPG levels (2904.9 vs. 1518.2pg/mL, p=0.002). On multivariate analysis, only ESR remained statistically significant (OR 1.07; 95% CI 1.01-1.14; p=0.022). Bone histomorphometric findings were not different in patients with VC. There was no correlation between bone formation rate and AS (r=-0.039; p=0.796).

CONCLUSION

The presence of VC was not associated with bone turnover and volume evaluated by bone histomorphometry. Inflammation and diabetes seem to play a more relevant role in VC in PD.

El diálogo oculto entre el hueso y los tejidos a través del remodelado óseo

El hueso es mucho más que un reservorio de calcio y fósforo. Su disposición lacuno-canalicular ofrece una importante vía de intercambio con la circulación y actualmente, el esqueleto se considera un gran órgano endocrino, con acciones que van más allá del control del balance fosfocálcico mediado por el factor fibroblástico 23 (FGF23). Paralelamente al efecto modulador de las adipoquinas sobre el remodelado óseo, diversas proteínas óseas, como la osteocalcina y la esclerostina, ejercen cierta acción contra-reguladora sobre el metabolismo energético, posiblemente en un intento de asegurar los enormes requerimientos energéticos del remodelado. En esta interacción del hueso con otros tejidos, especialmente el adiposo, participa la señalización canónica Wnt/β-catenina y por ello la esclerostina, una proteína osteocítica que inhibe esta señalización, emerge como un potencial biomarcador. Es más, su participación en diversas patologías le posiciona como diana terapéutica, existiendo un anticuerpo anti-esclerostina, recientemente aprobado en nuestro país para el tratamiento de la osteoporosis. Esta revisión aborda el carácter endocrino del hueso, el papel de la osteocalcina y, especialmente, el papel regulador y modulador de la esclerostina sobre remodelado óseo y la homeóstasis energética a través de su interacción con la señalización canónica Wnt/β-catenina, así como su potencial utilidad como biomarcador.

The hidden cross talk between bone and tissues through bone turnover

Bone is more than a reservoir of calcium and phosphorus. Its lacuno-canalicular arrangement provides an important pathway for exchange with circulation and currently, the skeleton is considered a large endocrine organ with actions that go beyond the control of calcium-phosphorus balance mediated by fibroblastic growth factor 23 (FGF23). Parallel to the modulating effect of adipokines on bone turnover, certain bone proteins, such as osteocalcin and sclerostin, play a counter-regulatory role on energy metabolism, probably in an attempt to ensure its high energy requirement for bone turnover. In this crosstalk between bone and other tissues, especially with adipose tissue, canonical Wnt/β-catenin signaling is involved and therefore, sclerostin, an osteocyte derived protein that inhibits this signalling, emerges as a potential biomarker. Furthermore, its involvement in diverse pathologic conditions supports sclerostin as a therapeutic target, with an anti-sclerostin antibody recently approved in our country for the treatment of osteoporosis. This review addresses the endocrine nature of bone, the role of osteocalcin, and specially, the regulatory and modulatory role of sclerostin on bone turnover and energy homeostasis through its inhibitory effect on canonical Wnt/β-catenin signaling, as well as its potential utility as a biomarker.

Romosozumab in osteoporosis: yesterday, today and tomorrow

Osteoporosis is a systemic bone disease characterized by low bone mass, microarchitectural deterioration, increased bone fragility, and fracture susceptibility. It commonly occurs in older people, especially postmenopausal women. As global ageing increases, osteoporosis has become a global burden. There are a number of medications available for the treatment of osteoporosis, categorized as anabolic and anti-resorptive. Unfortunately, there is no drugs which have dual influence on bone, while all drugs have limitations and adverse events. Some serious adverse events include jaw osteonecrosis and atypical femoral fracture. Recently, a novel medication has appeared that challenges this pattern. Romosozumab is a novel drug monoclonal antibody to sclerostin encoded by the SOST gene. It has been used in Japan since 2019 and has achieved promising results in treating osteoporosis. However, it is also accompanied by some controversy. While it promotes rapid bone growth, it may cause serious adverse events such as cardiovascular diseases. There has been scepticism about the drug since its inception. Therefore, the present review comprehensively covered romosozumab from its inception to its clinical application, from animal studies to human studies, and from safety to cost. We hope to provide a better understanding of romosozumab for its clinical application.

Pathophysiology of bone disease in chronic kidney disease: from basics to renal osteodystrophy and osteoporosis

Chronic kidney disease (CKD) is a highly prevalent disease that has become a public health problem. Progression of CKD is associated with serious complications, including the systemic CKD-mineral and bone disorder (CKD-MBD). Laboratory, bone and vascular abnormalities define this condition, and all have been independently related to cardiovascular disease and high mortality rates. The "old" cross-talk between kidney and bone (classically known as "renal osteodystrophies") has been recently expanded to the cardiovascular system, emphasizing the importance of the bone component of CKD-MBD. Moreover, a recently recognized higher susceptibility of patients with CKD to falls and bone fractures led to important paradigm changes in the new CKD-MBD guidelines. Evaluation of bone mineral density and the diagnosis of "osteoporosis" emerges in nephrology as a new possibility "if results will impact clinical decisions". Obviously, it is still reasonable to perform a bone biopsy if knowledge of the type of renal osteodystrophy will be clinically useful (low versus high turnover-bone disease). However, it is now considered that the inability to perform a bone biopsy may not justify withholding antiresorptive therapies to patients with high risk of fracture. This view adds to the effects of parathyroid hormone in CKD patients and the classical treatment of secondary hyperparathyroidism. The availability of new antiosteoporotic treatments bring the opportunity to come back to the basics, and the knowledge of new pathophysiological pathways [OPG/RANKL (LGR4); Wnt-ß-catenin pathway], also affected in CKD, offers great opportunities to further unravel the complex physiopathology of CKD-MBD and to improve outcomes.

Cardiovascular Calcification Heterogeneity in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) exhibit tremendously elevated risk for cardiovascular disease, particularly ischemic heart disease, due to premature vascular and cardiac aging and accelerated ectopic calcification. The presence of cardiovascular calcification associates with increased risk in patients with CKD. Disturbed mineral homeostasis and diverse comorbidities in these patients drive increased systemic cardiovascular calcification in different manifestations with diverse clinical consequences, like plaque instability, vessel stiffening, and aortic stenosis. This review outlines the heterogeneity in calcification patterning, including mineral type and location and potential implications on clinical outcomes. The advent of therapeutics currently in clinical trials may reduce CKD-associated morbidity. Development of therapeutics for cardiovascular calcification begins with the premise that less mineral is better. While restoring diseased tissues to a noncalcified homeostasis remains the ultimate goal, in some cases, calcific mineral may play a protective role, such as in atherosclerotic plaques. Therefore, developing treatments for ectopic calcification may require a nuanced approach that considers individual patient risk factors. Here, we discuss the most common cardiac and vascular calcification pathologies observed in CKD, how mineral in these tissues affects function, and the potential outcomes and considerations for therapeutic strategies that seek to disrupt the nucleation and growth of mineral. Finally, we discuss future patient-specific considerations for treating cardiac and vascular calcification in patients with CKD-a population in need of anticalcification therapies.

Serum Intact Fibroblast Growth Factor 23 Levels Are Negatively Associated with Bone Mineral Density in Chronic Hemodialysis Patients

(1) Background: Fibroblast growth factor 23 (FGF23) is predominantly secreted from bone and plays an important role in mineral balance in chronic kidney disease. However, the relationship between FGF23 and bone mineral density (BMD) in chronic hemodialysis (CHD) patients remains unclear. (2) Methods: This was a cross-sectional observational study that involved 43 stable outpatients on CHD. A linear regression model was used to determine risk factors for BMD. Measurements included serum hemoglobin, intact FGF23 (iFGF23), C-terminal FGF23 (cFGF23), sclerostin, Dickkopf-1, α-klotho, 1,25-hydroxyvitamin D, intact parathyroid hormone levels and dialysis profiles. (3) Results: Study participants had a mean age of 59.4 ± 12.3 years, and 65% were male. In the multivariable analysis, cFGF23 levels showed no significant associations with the BMD of the lumbar spine (p = 0.387) nor that of the femoral head (p = 0.430). However, iFGF23 levels showed a significant negative association with the BMD of the lumbar spine (p = 0.015) and that of the femoral neck (p = 0.037). (4) Conclusions: Among patients on CHD, higher serum iFGF23 levels, but not serum cFGF23 levels, were associated with lower BMD values of the lumbar spine and femoral neck. However, further research is required to validate our findings.

One-Year Romosozumab Treatment Followed by One-Year Denosumab Treatment for Osteoporosis in Patients on Hemodialysis: An Observational Study

There is limited evidence on the use of romosozumab (ROMO) in the treatment of osteoporosis in patients on hemodialysis (HD); thus, we aimed to investigate this topic. This prospective, observational, single-center cohort study included 13 prior osteoporosis treatment-naïve patients on HD with osteoporosis. They first received ROMO once monthly for 12 months (210 mg; subcutaneously once every month). Thereafter, they received denosumab (DENO) for an additional 12 months (60 mg; subcutaneously once every 6 months). We examined the incidence of new fractures; treatment safety; and temporal changes in the bone mineral density (BMD), bone metabolism markers, and vascular calcification. No new cases of fractures were noted. The median one-year percentage changes (from the baseline) in the BMDs at the lumbar spine (LS), total hip (TH), and femoral neck (FN) were + 9.0%, + 2.5%, and + 4.7%, respectively. These changes were maintained for 24 months. The corresponding relative changes from the baseline to 24 months thereafter were + 14.9%, + 5.4%, and + 6.5%, respectively. The percentage changes in TH BMD and FN BMD were negatively correlated with baseline BMD. Coronary artery and thoracic aorta calcification scores increased slightly from baseline to 12 months thereafter. However, fatal events (cardiovascular disease-associated and all-cause deaths) did not occur during ROMO treatment. Effectiveness of ROMO was better in patients who had severe osteoporosis with low TH BMD, low FN BMD, and high tartrate-resistant acid phosphatase 5b level at ROMO initiation.

[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.

Sclerostin is involved in osteogenic transdifferentiation of vascular smooth muscle cells in chronic kidney disease-associated vascular calcification with non-canonical Wnt signaling

Vascular calcification is prominent in patients with chronic kidney disease (CKD) and is a strong predictor of cardiovascular mortality in the CKD population. However, the mechanism underlying CKD-associated vascular calcification remains unclear. To identify potential therapeutic targets, a 5/6 nephrectomy rat model was established by feeding of a high-phosphorous diet as the CKD group and compared with sham group rats at 4 and 16 weeks. Sequencing analyses of the rat aorta revealed 643 upregulated and 1023 downregulated genes at 4 weeks, as well as 899 upregulated and 1185 downregulated genes at 16 weeks in the CKD group compared to the sham group. Bioinformatics analyses suggested that SOST (which encodes sclerostin) and Wnt signaling are involved in CKD-associated vascular calcification. Furthermore, protein-protein interactions analysis revealed interactions between SOST, WNT5A, and WNT5B, that involved runt-related transcription factor 2 (RUNX2) and transgelin (TAGLN). SOST was increased in CKD-associated vascular calcification following reduction of the Wnt signaling, including WNT5A and WNT5B, both in vivo and in vitro. TargetScan was used to predict the microRNAs (miRNAs) targeting WNT5A and WNT5B. The expression levels of miR-542-3p, miR-298-3p, miR-376b-5p, and miR-3568 were significantly reduced, whereas that of miR-742-3p was significantly increased in calcified rat aortic vascular smooth muscle cells (VSMCs). In CKD rat aortas, the expression of miR-542-3p, miR-298-3p, miR-376b-5p, miR-3568, miR-742-3p, and miR-22-5p were significantly reduced at both 4 and 16 weeks. Altogether, owing to several assessments, potentially diagnostic and prognostic biomarkers for improving common CKD diagnostic tools were identified in this study.

Abbreviations: BUN: blood urea nitrogen; CKD: chronic kidney disease; CKD-MBD: chronic kidney disease-mineral bone disorder; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GO: the Gene Ontology; HE: hematoxylin-eosin; HRP: horseradish peroxidase; KEGG: Kyoto Encyclopedia of Genes and Genomes; MiRNAs: microRNAs; PAS: periodic acid-Schiff; RUNX2: runt-related transcription factor 2; SCr: serum creatinine; STRING: the Search Tool for the Retrieval of Interacting Genes/Proteins; TAGLN: transgelin; VSMC: vascular smooth muscle cell.

Management of osteoporosis in patients with chronic kidney disease

Patients with CKD have a 4-fivefold higher rate of fractures. The incidence of fractures increases with deterioration of kidney function. The process of skeletal changes in CKD patients is characterized by compromised bone strength because of deterioration of bone quantity and/or quality. The fractures lead to a deleterious effect on the quality of life and higher mortality in patients with CKD. The pathogenesis of bone loss and fracture is complex and multi-factorial. Renal osteodystrophy, uremic milieu, drugs, and systemic diseases that lead to renal failure all contribute to bone damage in CKD patients. There is no consensus on the optimal diagnostic method of compromised bone assessment in patients with CKD. Bone quantity and mass can be assessed by dual-energy x-ray absorptiometry (DXA) or quantitative computed tomography (QCT). Bone quality on the other side can be assessed by non-invasive methods such as trabecular bone score (TBS), high-resolution bone imaging methods, and invasive bone biopsy. Bone turnover markers can reflect bone remodeling, but some of them are retained by kidneys. Understanding the mechanism of bone loss is pivotal in preventing fracture in patients with CKD. Several non-pharmacological and therapeutic interventions have been reported to improve bone health. Controlling laboratory abnormalities of CKD-MBD is crucial. Anti-resorptive therapies are effective in improving BMD and reducing fracture risk, but there are uncertainties about safety and efficacy especially in advanced CKD patients. Accepting the prevalent of low bone turnover in patients with advanced CKD, the osteo-anabolics are possibly promising. Parathyroidectomy should be considered a last resort for intractable cases of renal hyperparathyroidism. There is a wide unacceptable gap in osteoporosis management in patients with CKD. This article is focusing on the updated management of CKD-MBD and osteoporosis in CKD patients. Chronic kidney disease deteriorates bone quality and quantity. The mechanism of bone loss mainly determines pharmacological treatment. DXA and QCT provide information about bone quantity, but assessing bone quality, by TBS, high-resolution bone imaging, invasive bone biopsy, and bone turnover markers, can guide us about the mechanism of bone loss.

A pharmacovigilance analysis of FDA adverse event reporting system events for romosozumab

BACKGROUND

Romosozumab is a novel drug for the treatment of osteoporosis. The adverse reactions of romosozumab still need to be explored. The FDA Adverse Event Reporting System (FAERS) provides an enormous dataset for adverse events (AEs) analysis.

RESEARCH DESIGN AND METHODS

AEs registered in FAERS between January 2019 and December 2020 were collected for this study. The reporting odds ratio (ROR) method was applied to analyze the AEs of romosozumab. The number of AEs ≥4 cases and ROR value 95% confidence interval (CI) lower limit >1 was considered statistically significant.

RESULTS

A total of 4,413,695 AEs were collected for this study. There were 1,948 AEs related with romosozumab reported in FAERS. There are 1851 AEs including 17 system classifications after filtered. Injection site pain (ROR = 6.89, CI = 5.60, 8.48), cardiac failure (ROR = 12.62, CI = 9.85, 16.17), renal impairment (ROR = 9.11, CI = 6.98, 11.89), pneumonia (ROR = 1.53, CI = 1.10, 2.21), blood alkaline phosphatase increased (ROR = 14.60, CI = 9.28, 22.97) were possible AEs after romosozumab application.

CONCLUSIONS

Our study provides an adverse reaction warning for the clinical application of romosozumab and provides a real-world disproportionality analysis data support for the possible AEs of romosozumab.

Alkaline Phosphatase: An Old Friend as Treatment Target for Cardiovascular and Mineral Bone Disorders in Chronic Kidney Disease

Alkaline phosphatase (ALP) is an evolutionary conserved enzyme and widely used biomarker in clinical practice. Tissue-nonspecific alkaline phosphatase (TNALP) is one of four human isozymes that are expressed as distinct TNALP isoforms after posttranslational modifications, mainly in bone, liver, and kidney tissues. Beyond the well-known effects on bone mineralization, the bone ALP (BALP) isoforms (B/I, B1, B1x, and B2) are also involved in the pathogenesis of ectopic calcification. This narrative review summarizes the recent clinical investigations and mechanisms that link ALP and BALP to inflammation, metabolic syndrome, vascular calcification, endothelial dysfunction, fibrosis, cardiovascular disease, and mortality. The association between ALP, vitamin K, bone metabolism, and fracture risk in patients with chronic kidney disease (CKD) is also discussed. Recent advances in different pharmacological strategies are highlighted, with the potential to modulate the expression of ALP directly and indirectly in CKD–mineral and bone disorder (CKD-MBD), e.g., epigenetic modulation, phosphate binders, calcimimetics, vitamin D, and other anti-fracture treatments. We conclude that the significant evidence for ALP as a pathogenic factor and risk marker in CKD-MBD supports the inclusion of concrete treatment targets for ALP in clinical guidelines. While a target value below 120 U/L is associated with improved survival, further experimental and clinical research should explore interventional strategies with optimal risk–benefit profiles. The future holds great promise for novel drug therapies modulating ALP.

Sclerostin is a promising therapeutic target for oral inflammation and regenerative dentistry

Sclerostin is the protein product of the SOST gene and is known for its inhibitory effects on bone formation. The monoclonal antibody against sclerostin has been approved as a novel treatment method for osteoporosis. Oral health is one of the essential aspects of general human health. Hereditary bone dysplasia syndrome caused by sclerostin deficiency is often accompanied by some dental malformations, inspiring the therapeutic exploration of sclerostin in the oral and dental fields. Recent studies have found that sclerostin is expressed in several functional cell types in oral tissues, and the expression level of sclerostin is altered in pathological conditions. Sclerostin not only exerts similar negative outcomes on the formation of alveolar bone and bone-like tissues, including dentin and cementum, but also participates in the development of oral inflammatory diseases such as periodontitis, pulpitis, and peri-implantitis. This review aims to highlight related research progress of sclerostin in oral cavity, propose necessary further research in this field, and discuss its potential as a therapeutic target for dental indications and regenerative dentistry.

Sclerostin and DKK1 circulating levels associate with low bone turnover in patients with chronic kidney disease Stages 3 and 4

Background

Disordered mineral and bone metabolism is a common complication of chronic kidney disease (CKD). Bone biopsy remains the gold standard tool for evaluating renal osteodystrophy (ROD), but it is an invasive procedure. Despite a growing interest in the ability of newer bone biomarkers to discriminate between different forms of ROD, data on pre-dialysis patients are scarce.

Methods

A cross-sectional study was conducted in a cohort of 56 patients with CKD Stages 3 and 4. Participants underwent a transiliac bone biopsy after a course of double tetracycline labelling. Circulating levels of Wnt signalling inhibitors sclerostin and Dickkopf-1 (DKK1), soluble receptor activator of nuclear factor-κB ligand (sRANKL) and osteoprotegerin were measured and correlated with histomorphometric analysis results.

Results

Most patients had abnormal bone histology and low-turnover bone disease was the predominant form of ROD. Characteristics associated with high bone turnover were worse renal function, lower serum calcium and higher intact parathyroid hormone and fibroblast growth factor-23 levels. Patients with low bone turnover, on the other hand, presented with higher sclerostin along with lower DKK1 and sRANKL levels. In the multivariable logistic regression analysis, sclerostin and DKK1 levels were independently associated with low-turnover bone disease.

Conclusions

Our results suggest that circulating levels of Wnt signalling inhibitors sclerostin and DKK1 are predictive of low-turnover bone disease in patients not yet on dialysis. Further research is needed to assess the performance of these bone turnover biomarkers, compared with histomorphometric analysis, in the diagnosis and treatment monitoring of ROD.

Cardiovascular Safety of Anti-Sclerostin Therapy in Chronic Kidney Disease

The significance of sclerostin for bone and cardiovascular health in patients with chronic kidney disease (CKD) is complex and incompletely understood. Experimental evidence suggests that anti-sclerostin therapy shows diminished efficacy on bone in the setting of CKD. Limited clinical evidence suggests that the osteoanabolic and anti-resorptive activity is attenuated, but hypocalcemia is more prevalent in patients with advanced CKD (eGFR < 30 mL/min) treated with anti-sclerostin (romosozumab) therapy as compared to patients without kidney disease. Furthermore, sclerostin is prominently expressed in uremic arteries. Whether the inhibition of sclerostin has adverse effects on cardiovascular health in CKD is currently unknown. This review summarizes the current understanding of the physiology and pathophysiology of sclerostin in CKD, with a focus on the cardiovascular safety of anti-sclerostin therapy in patients with or without CKD.

Bone Quality in Chronic Kidney Disease Patients: Current Concepts and Future Directions - Part II

Background

Patients with chronic kidney disease (CKD) have an increased risk of osteoporotic fractures, which is due not only to low bone volume and mass but also poor microarchitecture and tissue quality. The pharmacological and nonpharmacological interventions detailed, herein, are potential approaches to improve bone health in CKD patients. Various medications build up bone mass but also affect bone tissue quality. Antiresorptive therapies strikingly reduce bone turnover; however, they can impair bone mineralization and negatively affect the ability to repair bone microdamage and cause an increase in bone brittleness. On the other hand, some osteoporosis therapies may cause a redistribution of bone structure that may improve bone strength without noticeable effect on BMD. This may explain why some drugs can affect fracture risk disproportionately to changes in BMD.

Summary

An accurate detection of the underlying bone abnormalities in CKD patients, including bone quantity and quality abnormalities, helps in institution of appropriate management strategies. Here in this part II, we are focusing on advancements in bone therapeutics that are anticipated to improve bone health and decrease mortality in CKD patients.

Key Messages

Therapeutic interventions to improve bone health can potentially advance life span. Emphasis should be given to the impact of various therapeutic interventions on bone quality.

Role of Vitamin K in CKD: Is Its Supplementation Advisable in CKD Patients?

BACKGROUND

Patients with CKD are at an increased risk of developing vascular calcification (VC) and bone complications which translate into a higher morbidity and mortality. The dephosphorylated and uncarboxylated matrix Gla protein (dp-ucMGP) is considered to be an indicator of vitamin K2 status and correlates with markers of VC. It is activated by γ-glutamyl carboxylase that converts inactive MGP into an active form, and vitamin K2 is a cofactor of this reaction. The active form of MGP is a known inhibitor of arterial wall calcification and plays an important role in bone turnover. Recent studies show poor vitamin K2 status in CKD patients. We aimed to review the literature for the association between vitamin K2 status and calcification and bone disease risk and the efficacy of vitamin K2 supplementation in CKD population.

SUMMARY

Most CKD patients, including those on renal replacement therapy, have vitamin K2 deficiency. The dp-ucMGP level, a marker of vitamin K2 status, is decreased by vitamin K2 supplementation in CKD patients, but there is no unequivocal proof that it influences arterial calcification progression and bone complications. Key Messages: CKD population are at risk of vitamin K deficiency. Supplementation of vitamin K2 is safe and improves the serum markers of its deficiency. There is lack of strong evidence that vitamin K2 supplementation slows progression of calcification or reduces the frequency of bone complications. More prospective studies are needed.

T-Cell Mediated Inflammation in Postmenopausal Osteoporosis

Osteoporosis is the most prevalent metabolic bone disease that affects half the women in the sixth and seventh decade of life. Osteoporosis is characterized by uncoupled bone resorption that leads to low bone mass, compromised microarchitecture and structural deterioration that increases the likelihood of fracture with minimal trauma, known as fragility fractures. Several factors contribute to osteoporosis in men and women. In women, menopause - the cessation of ovarian function, is one of the leading causes of primary osteoporosis. Over the past three decades there has been growing appreciation that the adaptive immune system plays a fundamental role in the development of postmenopausal osteoporosis, both in humans and in mouse models. In this review, we highlight recent data on the interactions between T cells and the skeletal system in the context of postmenopausal osteoporosis. Finally, we review recent studies on the interventions to ameliorate osteoporosis.

Role of the RANK/RANKL/OPG and Wnt/β-Catenin Systems in CKD Bone and Cardiovascular Disorders

In the course of chronic kidney disease (CKD), alterations in the bone-vascular axis augment the risk of bone loss, fractures, vascular and soft tissue calcification, left ventricular hypertrophy, renal and myocardial fibrosis, which markedly increase morbidity and mortality rates. A major challenge to improve skeletal and cardiovascular outcomes in CKD patients requires a better understanding of the increasing complex interactions among the main modulators of the bone-vascular axis. Serum parathyroid hormone (PTH), phosphorus (P), calcium (Ca), fibroblast growth factor 23 (FGF23), calcidiol, calcitriol and Klotho are involved in this axis interact with RANK/RANKL/OPG system and the Wnt/β-catenin pathway. The RANK/RANKL/OPG system controls bone remodeling by inducing osteoblast synthesis of RANKL and downregulating OPG production and it is also implicated in vascular calcification. The complexity of this system has recently increased due the discovery of LGR4, a novel RANKL receptor involved in bone formation, but possibly also in vascular calcification. The Wnt/β-catenin pathway plays a key role in bone formation: when this pathway is activated, bone is formed, but when it is inhibited, bone formation is stopped. In the progression of CKD, a downregulation of the Wnt/β-catenin pathway has been described which occurs mainly through the not coincident elevations of sclerostin, Dickkopf1 (Dkk1) and the secreted Frizzled Related Proteins (sFRPs). This review analyzes the interactions of PTH, P, Ca, FGF23, calcidiol, calcitriol and Klotho with the RANKL/RANKL/OPG system and the Wnt/β-catenin, pathway and their implications in bone and cardiovascular disorders in CKD.

The Non-invasive Diagnosis of Bone Disorders in CKD

Abnormal bone metabolism is an integral part of the chronic kidney disease-mineral bone disorder (CKD-MBD). For several reasons, the difficult bone compartment was neglected for some time, but there has been renewed interest as a result of the conception of bone as a new endocrine organ, the increasing recognition of the cross-talk between bone and vessels, and, especially, the very high risk of osteoporotic fractures (and associated mortality) demonstrated in patients with CKD. Therefore, it has been acknowledged in different guidelines that action is needed in respect of fracture risk assessment and the diagnosis and treatment of osteoporosis in the context of CKD and CKD-MBD, even beyond renal osteodystrophy. These updated guidelines clearly underline the need to improve a non-invasive approach to these bone disorders in order to guide treatment decisions aimed at not only controlling CKD-MBD but also decreasing the risk of fracture. In this report, we review the current role of the most often clinically used or promising biochemical circulating biomarkers such as parathyroid hormone, alkaline phosphatases, and other biochemical markers of bone activity as alternatives to some aspects of bone histomorphometry. We also mention the potential role of classic and new imaging techniques for CKD patients. Information on many aspects is still scarce and heterogeneous, but many of us consider that it is indeed time for action, recognizing our definitely limited ability to base certain treatment decisions only on our current non-comprehensive knowledge.

Osteoporosis and Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD): Back to Basics

Osteoporosis is defined as a skeletal disorder of compromised bone strength predisposing those affected to an elevated risk of fracture. However, based on bone histology, osteoporosis is only part of a spectrum of skeletal complications that includes osteomalacia and the various forms of renal osteodystrophy of chronic kidney disease-mineral and bone disorder (CKD-MBD). In addition, the label "kidney-induced osteoporosis" has been proposed, even though the changes caused by CKD do not qualify as osteoporosis by the histological diagnosis. It is clear, therefore, that such terminology may not be helpful diagnostically or in making treatment decisions. A new label, "CKD-MBD/osteoporosis" could be a more appropriate term because it brings osteoporosis under the official label of CKD-MBD. Neither laboratory nor noninvasive diagnostic investigations can discriminate osteoporosis from the several forms of renal osteodystrophy. Transiliac crest bone biopsy can make the diagnosis of osteoporosis by exclusion of other kidney-associated bone diseases, but its availability is limited. Recently, a classification of metabolic bone diseases based on bone turnover, from low to high, together with mineralization and bone volume, has been proposed. Therapeutically, no antifracture treatments have been approved by the US Food and Drug Administration for patients with kidney-associated bone disease. Agents that suppress parathyroid hormone (vitamin D analogues and calcimimetics) are used to treat hyperparathyroid bone disease. Antiresorptive and osteoanabolic agents approved for osteoporosis are being used off-label to treat CKD stages 3b-5 in high-risk patients. It has now been suggested that intermittent administration of parathyroid hormone as early as CKD stage 2 could be an effective management strategy. If confirmed in clinical trials, it could mitigate the retention of phosphorus and subsequently the rise in fibroblast growth factor 23 and may be beneficial for coexisting osteoporosis.

Sclerostin and Osteocalcin: Candidate Bone-Produced Hormones

In addition to its structural role, the skeleton serves as an endocrine organ that controls mineral metabolism and energy homeostasis. Three major cell types in bone - osteoblasts, osteoclasts, and osteocytes - dynamically form and maintain bone and secrete factors with systemic activity. Osteocalcin, an osteoblast-derived factor initially described as a matrix protein that regulates bone mineralization, has been suggested to be an osteoblast-derived endocrine hormone that regulates multiple target organs including pancreas, liver, muscle, adipose, testes, and the central and peripheral nervous system. Sclerostin is predominantly produced by osteocytes, and is best known as a paracrine-acting regulator of WNT signaling and activity of osteoblasts and osteoclasts on bone surfaces. In addition to this important paracrine role for sclerostin within bone, sclerostin protein has been noted to act at a distance to regulate adipocytes, energy homeostasis, and mineral metabolism in the kidney. In this article, we aim to bring together evidence supporting an endocrine function for sclerostin and osteocalcin, and discuss recent controversies regarding the proposed role of osteocalcin outside of bone. We summarize the current state of knowledge on animal models and human physiology related to the multiple functions of these bone-derived factors. Finally, we highlight areas in which future research is expected to yield additional insights into the biology of osteocalcin and sclerostin.

Uremic Toxins Affecting Cardiovascular Calcification: A Systematic Review

Cardiovascular calcification is highly prevalent and associated with increased morbidity in chronic kidney disease (CKD). This review examines the impact of uremic toxins, which accumulate in CKD due to a failing kidney function, on cardiovascular calcification. A systematic literature search identified 41 uremic toxins that have been studied in relation to cardiovascular calcification. For 29 substances, a potentially causal role in cardiovascular calcification was addressed in in vitro or animal studies. A calcification-inducing effect was revealed for 16 substances, whereas for three uremic toxins, namely the guanidino compounds asymmetric and symmetric dimethylarginine, as well as guanidinosuccinic acid, a calcification inhibitory effect was identified in vitro. At a mechanistic level, effects of uremic toxins on calcification could be linked to the induction of inflammation or oxidative stress, smooth muscle cell osteogenic transdifferentiation and/or apoptosis, or alkaline phosphatase activity. For all middle molecular weight and protein-bound uremic toxins that were found to affect cardiovascular calcification, an increasing effect on calcification was revealed, supporting the need to focus on an increased removal efficiency of these uremic toxin classes in dialysis. In conclusion, of all uremic toxins studied with respect to calcification regulatory effects to date, more uremic toxins promote rather than reduce cardiovascular calcification processes. Additionally, it highlights that only a relatively small part of uremic toxins has been screened for effects on calcification, supporting further investigation of uremic toxins, as well as of associated post-translational modifications, on cardiovascular calcification processes.

Osteoporosis in Patients with Chronic Kidney Diseases: A Systemic Review

Chronic kidney disease (CKD) is associated with the development of mineral bone disorder (MBD), osteoporosis, and fragility fractures. Among CKD patients, adynamic bone disease or low bone turnover is the most common type of renal osteodystrophy. The consequences of CKD-MBD include increased fracture risk, greater morbidity, and mortality. Thus, the goal is to prevent the occurrences of fractures by means of alleviating CKD-induced MBD and treating subsequent osteoporosis. Changes in mineral and humoral metabolism as well as bone structure develop early in the course of CKD. CKD-MBD includes abnormalities of calcium, phosphorus, PTH, and/or vitamin D; abnormalities in bone turnover, mineralization, volume, linear growth, or strength; and/or vascular or other soft tissue calcification. In patients with CKD-MBD, using either DXA or FRAX to screen fracture risk should be considered. Biomarkers such as bALP and iPTH may assist to assess bone turnover. Before initiating an antiresorptive or anabolic agent to treat osteoporosis in CKD patients, lifestyle modifications, such as exercise, calcium, and vitamin D supplementation, smoking cessation, and avoidance of excessive alcohol intake are important. Managing hyperphosphatemia and SHPT are also crucial. Understanding the complex pathogenesis of CKD-MBD is crucial in improving one's short- and long-term outcomes. Treatment strategies for CKD-associated osteoporosis should be patient-centered to determine the type of renal osteodystrophy. This review focuses on the mechanism, evaluation and management of patients with CKD-MBD. However, further studies are needed to explore more details regarding the underlying pathophysiology and to assess the safety and efficacy of agents for treating CKD-MBD.

The role of activin: the other side of chronic kidney disease-mineral bone disorder?

Chronic kidney disease-mineral bone disorder (CKD-MBD) plays a pivotal role in the excess of cardiovascular morbidity and mortality associated with CKD. There is now a growing awareness that pathways involved in CKD-MBD, like canonical Wnt signalling, are activated from the earliest stages of CKD, playing a role in the development of adynamic bone disease with unknown consequences on vasculature. These changes occur before the classic changes in mineral metabolism: secondary hyperparathyroidism, calcitriol deficiency and hyperphosphataemia. Furthermore, vascular calcification is frequently associated and evolves with decreased bone mineral density and deranged bone turnover, while bone and arterial mineralization share common pathways. Therefore, results of clinical trials focused on mineral bone disorder, aimed at preserving bone and cardiovascular health, are considered unsatisfactory. In order to identify more effective therapeutic strategies, it is necessary to clarify the pathways modulating the cross-talk between bone and vasculature and identify new mediators involved in the pathogenesis of CKD-MBD. Much attention has been paid recently to the role of the transforming growth factor-beta superfamily members in renal disease, and in particular of activin A (ActA). Preclinical studies demonstrate an upgrade of ActA signalling in kidney, skeleton, vasculature and heart during CKD. This supports the idea that an endocrine factor produced in the kidney during renal disease, in addition to promoting the progression of kidney damage, deranges other organs' homoeostasis and participates in CKD-MBD. In this review, we analyse the contribution of ActA to kidney fibrosis and inflammation as well as its role in the development of CKD-MBD.

Evaluating the cardiovascular safety of sclerostin inhibition using evidence from meta-analysis of clinical trials and human genetics

Inhibition of sclerostin is a therapeutic approach to lowering fracture risk in patients with osteoporosis. However, data from phase 3 randomized controlled trials (RCTs) of romosozumab, a first-in-class monoclonal antibody that inhibits sclerostin, suggest an imbalance of serious cardiovascular events, and regulatory agencies have issued marketing authorizations with warnings of cardiovascular disease. Here, we meta-analyze published and unpublished cardiovascular outcome trial data of romosozumab and investigate whether genetic variants that mimic therapeutic inhibition of sclerostin are associated with higher risk of cardiovascular disease. Meta-analysis of up to three RCTs indicated a probable higher risk of cardiovascular events with romosozumab. Scaled to the equivalent dose of romosozumab (210 milligrams per month; 0.09 grams per square centimeter of higher bone mineral density), the SOST genetic variants were associated with lower risk of fracture and osteoporosis (commensurate with the therapeutic effect of romosozumab) and with a higher risk of myocardial infarction and/or coronary revascularization and major adverse cardiovascular events. The same variants were also associated with increased risk of type 2 diabetes mellitus and higher systolic blood pressure and central adiposity. Together, our findings indicate that inhibition of sclerostin may elevate cardiovascular risk, warranting a rigorous evaluation of the cardiovascular safety of romosozumab and other sclerostin inhibitors.

The bone-vessel axis in chronic kidney disease: An update on biochemical players and its future role in laboratory medicine

Vascular wall calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD). In CKD, VC is more frequent and severe than in the general population and it is associated with increased cardiovascular mortality and morbidity. In the last years, laboratory and clinical evidence have drawn the attention to the relationship between bone disease and VC in CKD patients, leading to the concept of a bone-vessel or bone-vascular axis. It means that disorders of bone volume and bone turnover may influence the risk of VC and ultimately the high risk of cardiovascular mortality. In fact, a higher burden of VC has been associated to low bone volume and low bone turnover in hemodialysis (HD) patients with renal osteodystrophy characterized by histomorphometric evaluation of bone biopsies. The molecular mechanisms underlying the regulation of bone cells and vascular cells in CKD are poorly understood. In this review, we discuss relevant evidence linking bone disorders and VC in CKD and also rising molecular players involved in this bone-vascular axis. Indeed, accumulating data is available for two proposed systems: receptor activator for nuclear factor kB (RANK)/ RANK ligand (RANKL)/osteoprotegerin (OPG) system and inhibitors of Wnt signaling - mainly sclerostin. Although they are promising biochemical markers linking bone formation and bone reabsorption with VC, there is a long way to go as long evidence from laboratory studies is often divergent to the clinical data as will be discussed. Future prospective studies are needed in order to evaluate the role of these biochemical players as useful clinical markers for VC, bone volume and perhaps bone turnover.

The Role of Sclerostin in Bone and Ectopic Calcification

Sclerostin, a 22-kDa glycoprotein that is mainly secreted by the osteocytes, is a soluble inhibitor of canonical Wnt signaling. Therefore, when present at increased concentrations, it leads to an increased bone resorption and decreased bone formation. Serum sclerostin levels are known to be increased in the elderly and in patients with chronic kidney disease. In these patient populations, there is a high incidence of ectopic cardiovascular calcification. These calcifications are strongly associated with cardiovascular morbidity and mortality. Although data are still controversial, it is likely that there is a link between ectopic calcification and serum sclerostin levels. The main question, however, remains whether sclerostin exerts either a protective or deleterious role in the ectopic calcification process.

Sclerostin as Regulatory Molecule in Vascular Media Calcification and the Bone-Vascular Axis

Sclerostin is a well-known inhibitor of bone formation that acts on Wnt/β-catenin signaling. This manuscript considers the possible role of sclerostin in vascular calcification, a process that shares many similarities with physiological bone formation. Rats were exposed to a warfarin-containing diet to induce vascular calcification. Vascular smooth muscle cell transdifferentiation, vascular calcification grade, and bone histomorphometry were examined. The presence and/or production of sclerostin was investigated in serum, aorta, and bone. Calcified human aortas were investigated to substantiate clinical relevance. Warfarin-exposed rats developed vascular calcifications in a time-dependent manner which went along with a progressive increase in serum sclerostin levels. Both osteogenic and adipogenic pathways were upregulated in calcifying vascular smooth muscle cells, as well as sclerostin mRNA and protein levels. Evidence for the local vascular action of sclerostin was found both in human and rat calcified aortas. Warfarin exposure led to a mildly decreased bone and mineralized areas. Osseous sclerostin production and bone turnover did not change significantly. This study showed local production of sclerostin in calcified vessels, which may indicate a negative feedback mechanism to prevent further calcification. Furthermore, increased levels of serum sclerostin, probably originating from excessive local production in calcified vessels, may contribute to the linkage between vascular pathology and impaired bone mineralization.

Vitamin D-regulated osteocytic sclerostin and BMP2 modulate uremic extraskeletal calcification

We induced chronic kidney disease (CKD) with adenine in WT mice, mice with osteocyte-specific deletion of Cyp27b1, encoding the 25-hydroxyvitamin D 1(OH)ase [Oct-1(OH)ase-/-], and mice with global deletion of Cyp27b1 [global-1α(OH)ase-/-]; we then compared extraskeletal calcification. After adenine treatment, mice displayed increased blood urea nitrogen, decreased serum 1,25(OH)2D, and severe hyperparathyroidism. Skeletal expression of Cyp27b1 and of sclerostin and serum sclerostin all increased in WT mice but not in Oct-1α(OH)ase-/- mice or global-1α(OH)ase-/- mice. In contrast, skeletal expression of BMP2 and serum BMP2 rose in the Oct-1α(OH)ase-/- mice and in the global-1α(OH)ase-/- mice. Extraskeletal calcification occurred in muscle and blood vessels of mice with CKD and was highest in Oct-1α(OH)ase-/-mice. In vitro, recombinant sclerostin (100 ng/mL) significantly suppressed BMP2-induced osteoblastic transdifferentiation of vascular smooth muscle A7r5 cells and diminished BMP2-induced mineralization. Our study provides evidence that local osteocytic production of 1,25(OH)2D stimulates sclerostin and inhibits BMP2 production in murine CKD, thus mitigating osteoblastic transdifferentiation and mineralization of soft tissues. Increased osteocytic 1,25(OH)2D production, triggered by renal malfunction, may represent a "primary defensive response" to protect the organism from ectopic calcification by increasing sclerostin and suppressing BMP2 production.

Exercise Alleviates Osteoporosis in Rats with Mild Chronic Kidney Disease by Decreasing Sclerostin Production

Chronic kidney disease–mineral bone disorder (CKD–MBD), comprising mineral, hormonal, and bone metabolic imbalance, is a major CKD-related issue; it causes osteoporosis prevalence in CKD patients. Osteocyte-derived sclerostin inhibits the osteogenic Wnt/β-catenin signaling pathway; its levels rise when kidney function declines. Exercise modulates the physiological functions of osteocytes, potentially altering sclerostin production. It may aid bone and mineral electrolyte homeostasis in CKD. Mild CKD was induced in rats by partial nephrectomy. They were divided into: sham (no CKD), CKD, and CKD + exercise (8 weeks of treadmill running) groups. Micro-CT scanning demonstrated that the CKD + exercise-group rats had a higher bone mineral density (BMD) of the spine and femoral metaphysis and higher femoral trabecular bone volume than the CKD-group rats. Bone formation rates were not significantly different. The CKD + exercise-group rats had lower serum sclerostin (157.1 ± 21.1 vs 309 ± 38.1 pg/mL, p < 0.05) and CTX-1 (bone resorption marker) levels. Immunohistochemistry revealed higher tibial β-catenin concentrations in the CKD + exercise-group rats. Serum FGF-23, intact parathyroid hormone (iPTH), alkaline phosphatase (ALP), calcium, and phosphate levels showed no significant differences between these groups. Thus, exercise improves BMD and bone microstructure in mild CKD by inhibiting sclerostin production, but does not alter serum minerals.