Reversal of the adynamic bone disorder and decreased vascular calcification in chronic kidney disease by sevelamer carbonate therapy

Mild Chronic Kidney Disease Associated with Low Bone Formation and Decrease in Phosphate Transporters and Signaling Pathways Gene Expression

The initial phases of molecular and cellular maladaptive bone responses in early chronic kidney disease (CKD) remain mostly unknown. We induced mild CKD in spontaneously hypertensive rats (SHR) by either causing arterial hypertension lasting six months (sham-operated rats, SO6) or in its' combination with 3/4 nephrectomy lasting two and six months (Nx2 and Nx6, respectively). Sham-operated SHRs (SO2) and Wistar Kyoto rats (WKY2) with a two-month follow-up served as controls. Animals were fed standard chow containing 0.6% phosphate. Upon follow-up completion in each animal, we measured creatinine clearance, urine albumin-to-creatinine ratio, renal interstitial fibrosis, inorganic phosphate (Pi) exchange, intact parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), Klotho, Dickkopf-1, sclerostin, and assessed bone response by static histomorphometry and gene expression profiles. The mild CKD groups had no increase in renal Pi excretion, FGF23, or PTH levels. Serum Pi, Dickkopf-1, and sclerostin were higher in Nx6. A decrease in trabecular bone area and osteocyte number was obvious in SO6. Nx2 and Nx6 had additionally lower osteoblast numbers. The decline in eroded perimeter, a resorption index, was only apparent in Nx6. Significant downregulation of genes related to Pi transport, MAPK, WNT, and BMP signaling accompanied histological alterations in Nx2 and Nx6. We found an association between mild CKD and histological and molecular features suggesting lower bone turnover, which occurred at normal levels of systemic Pi-regulating factors.

Mouse Models of Mineral Bone Disorders Associated with Chronic Kidney Disease

Patients with chronic kidney disease (CKD) inevitably develop mineral and bone disorders (CKD–MBD), which negatively impact their survival and quality of life. For a better understanding of underlying pathophysiology and identification of novel therapeutic approaches, mouse models are essential. CKD can be induced by surgical reduction of a functional kidney mass, by nephrotoxic compounds and by genetic engineering specifically interfering with kidney development. These models develop a large range of bone diseases, recapitulating different types of human CKD–MBD and associated sequelae, including vascular calcifications. Bones are usually studied by quantitative histomorphometry, immunohistochemistry and micro-CT, but alternative strategies have emerged, such as longitudinal in vivo osteoblast activity quantification by tracer scintigraphy. The results gained from the CKD–MBD mouse models are consistent with clinical observations and have provided significant knowledge on specific pathomechanisms, bone properties and potential novel therapeutic strategies. This review discusses available mouse models to study bone disease in CKD.

Is Adynamic Bone Always a Disease? Lessons from Patients with Chronic Kidney Disease

Renal osteodystrophy (ROD) is a common complication of end-stage kidney disease that often starts early with loss of kidney function, and it is considered an integral part in management of patients with chronic kidney disease (CKD). Adynamic bone (ADB) is characterized by suppressed bone formation, low cellularity, and thin osteoid seams. There is accumulating evidence supporting increasing prevalence of ADB, particularly in early CKD. Contemporarily, it is not very clear whether it represents a true disease, an adaptive mechanism to prevent bone resorption, or just a transitional stage. Several co-players are incriminated in its pathogenesis, such as age, diabetes mellitus, malnutrition, uremic milieu, and iatrogenic factors. In the present review, we will discuss the up-to-date knowledge of the ADB and focus on its impact on bone health, fracture risk, vascular calcification, and long-term survival. Moreover, we will emphasize the proper preventive and management strategies of ADB that are pivotal issues in managing patients with CKD. It is still unclear whether ADB is always a pathologic condition or whether it can represent an adaptive process to suppress bone resorption and further bone loss. In this article, we tried to discuss this hard topic based on the available limited information in patients with CKD. More studies are needed to be able to clearly address this frequent ROD finding.

Effects of Phosphate Binders on Bone Biomarkers and Bone Density in Hemodialysis Patients

BACKGROUNDS

The incidences of osteoporosis, fracture, and vascular calcification increase concordantly with the progression of chronic kidney disease (CKD). CKD-mineral bone disease (CKD-MBD) induced by hyperphosphatemia is a major pathophysiologic mechanism. The effects of phosphate binders on bone turnover biomarkers and bone mineral density (BMD) in hemodialysis patients are still inconclusive. Our aim is to demonstrate the effects of these phosphate binders on different aspects of CKD-MBD.

METHODS

We conducted a prospective cohort of 65 hemodialysis patients to investigate the effect of 12-month monotherapy of phosphate binders composing calcium-based phosphate binders (CPB) or non-calcium-based phosphate binders (NCPB), including sevelamer and lanthanum, on bone turnover biomarkers and BMD changes. The performance of bone turnover biomarkers to predict low BMD was attentively determined.

RESULTS

When compared with CPB, NCPB use was associated with higher levels of bone turnover biomarkers. NCPB was also associated with lower BMD at lumbar and distal radius. Total procollagen type 1 N-terminal propeptide (P1NP), bone-specific alkaline phosphatase (BALP), and tartrate-resistant acid phosphatase 5b (TRAP5b) provided the best performance for diagnosing low BMD in hemodialysis patients.

CONCLUSIONS

Switching from CPB to NCPB might increase bone biomarkers and prevent the development of adynamic bone disease. On the contrary, NCPB should be cautiously used in hemodialysis patients who already had low BMD. P1NP, BALP, and TRAP5b could be used to guide the appropriate management, including anti-resorptive and anabolic medications, and predict low BMD in hemodialysis patients treated with phosphate binders. This article is protected by copyright. All rights reserved.

Adynamic bone disease: Revisited

The bone and mineral disorders form an integral part of the management of a chronic kidney disease (CKD) patient. Amongst various types of bone pathologies in chronic kidney disease-mineral bone disorder (CKD-MBD), the prevalence of adynamic bone disease (ABD) is increasing. The present review discusses the updated pathophysiology, risk factors, and management of this disorder.

Nitroxyl Radical as a Theranostic Contrast Agent in Magnetic Resonance Redox Imaging

Significance:In vivo assessment of paramagnetic and diamagnetic conversions of nitroxyl radicals based on cyclic redox mechanism can be an index of tissue redox status. The redox mechanism of nitroxyl radicals, which enables their use as a normal tissue-selective radioprotector, is seen as being attractive on planning radiation therapy. Recent Advances:In vivo redox imaging using nitroxyl radicals as redox-sensitive contrast agents has been developed to assess tissue redox status. Chemical and biological behaviors depending on chemical structures of nitroxyl radical compounds have been understood in detail. Polymer types of nitroxyl radical contrast agents and/or nitroxyl radical-labeled drugs were designed for approaching theranostics. Critical Issues: Nitroxyl radicals as magnetic resonance imaging (MRI) contrast agents have several advantages compared with those used in electron paramagnetic resonance (EPR) imaging, while support by EPR spectroscopy is important to understand information from MRI. Redox-sensitive paramagnetic contrast agents having a medicinal benefit, that is, nitroxyl-labeled drug, have been developed and proposed. Future Directions: A development of suitable nitroxyl contrast agent for translational theranostic applications with high reaction specificity and low normal tissue toxicity is under progress. Nitroxyl radicals as redox-sensitive magnetic resonance contrast agents can be a useful tool to detect an abnormal tissue redox status such as disordered oxidative stress. Antioxid. Redox Signal. 36, 95-121.

Sevelamer Attenuates Bioprosthetic Heart Valve Calcification

Objective: Sevelamer hydrochloride is a phosphate binder used to treat hyperphosphatemia in chronic kidney disease (CKD) patients that can reduce valvular and vascular calcification. The aim of this study was to examine the effects of sevelamer treatment on calcification in bioprosthetic heart valves (BHVs).

Methods: Wister rats were randomly divided into three groups according to sevelamer intake and implantation (sham–sham operation; implant–implantation and normal diet, implant+S implantation, and sevelamer diet). Two kinds of BHVs—bovine pericardium treated with glutaraldehyde (GLUT) or non-GLUT techniques—were implanted in rat dorsal subcutis at 4 weeks. After implantation, sevelamer was administered to the implant+S group. The animals were executed at days 0 (immediately after implantation), 7, 14, 28, and 56. Calcium levels were determined by atomic absorption spectroscopy and von Kossa staining. Serum biochemistry analysis, Western blotting, real-time quantitative polymerase chain reaction, alkaline phosphatase activity measurement, histopathologic analysis, immunohistochemistry, and enzyme-linked immunosorbent assay were conducted to identify the anti-calcification mechanism of sevelamer.

Results: Non-GLUT crosslinking attenuates BHV calcification. Serum phosphate and calcium remained unreactive to sevelamer after a 14-day treatment. However, the mean calcium level in the implant+S group was significantly decreased after 56 days. In addition, the PTH level, inflammatory cell infiltration, system and local inflammation, and expression of Bmp2, Runx2, Alp, IL-1β, IL-6, and TNF-α were significantly reduced in the implant+S group.

Conclusion: Sevelamer treatment significantly attenuated the calcification of BHVs and had anti-inflammation effects that were independent from serum calcium and phosphate regulation. Thus, sevelamer treatment might be helpful to improve the longevity of BHVs.

Adynamic bone disease: Revisited

The bone and mineral disorders form an integral part of the management of a chronic kidney disease (CKD) patient. Amongst various types of bone pathologies in chronic kidney disease-mineral bone disorder (CKD-MBD), the prevalence of adynamic bone disease (ABD) is increasing. The present review discusses the updated pathophysiology, risk factors, and management of this disorder.

Oxidative stress contributes to vascular calcification in patients with chronic kidney disease

Vascular calcification (VC) is a major cause of mortality in patients with chronic kidney disease (CKD). While elevations in serum phosphorus contribute to VC, we provide evidence here for a major role of oxidative stress (OS) in VC pathogenesis without an apparent increase in serum phosphorus in early CKD. In a rat model for stage 5 CKD (CKD5), we observed 1) robust increases of VC and OS, 2) significant reductions of smooth muscle 22 alpha (SM22α) and calponin, and 3) upregulations in Runt-related transcription factor 2 (RUNX2) and collagen I in vascular smooth muscle cells (VSMCs). Inhibition of OS using MnTMPyP dramatically reduced these events without normalization of hyperphosphatemia. In CKD5 patients with VC (n = 11) but not in those without VC (n = 13), OS was significantly elevated. While the serum levels of calcium and phosphate were not altered in the animal model for early stage CKD (ECKD), OS, VC, SM22α, calponin, RUNX2, collagen I and NADPH oxidase 1 (NOX1) in VSMCs were all significantly changed. More importantly, serum (5%) derived from patients with ECKD (n = 30) or CKD5 (n = 30) induced SM22α and calponin downregulation, and RUNX2, collagen I, NOX1 upregulation along with a robust elevation of OS and calcium deposition in primary rat VSMCs. These alterations were all reduced by MnTMPyP, ML171 (a NOX1 inhibitor), and U0126 (an inhibitor of Erk signaling). Collectively, we provide a comprehensive set of evidence supporting an important role of OS in promoting VC development in CKD patients (particularly in those with ECKD); this was at least in part through induction of osteoblastic transition in VSMCs which may involve the Erk singling. Our research thus suggests that reductions in OS may prevent VC in CKD patients.

Sclerostin: a new biomarker of CKD-MBD

The causes of the increased cardiovascular risk associated with kidney diseases partly reside in the chronic kidney disease-mineral bone disorder (CKD-MBD) syndrome. Three cardiovascular risk factors [hyperphosphatemia, vascular calcification, and elevated fibroblast growth factor 23 (FGF23)] levels have been discovered within the CKD-MBD over the last decades. In addition, sclerostin is recently presented as a new bone and vascular disease biomarker. This 22-kDa glycoprotein, secreted mainly by osteocytes, is a soluble inhibitor of the canonical Wnt pathway that has a pivotal role in bone biology and turnover. CKD patients are reported with higher levels of sclerostin, and levels decrease during dialysis. Sclerostin is associated with vascular calcification and CV risk in CKD, although data are still controversial. The question whether serum sclerostin has protective or deleterious role in CKD-MBD pathophysiology, and therefore in cardiovascular risk and overall mortality, is still open and needs to be answered. The standardization of assays and the establishment of a clear cut-off values when sclerostin starts to switch from physiological to pathophysiological role have to be another important step. Further research is needed also to define its relationship with other CKD-MBD biomarkers for future diagnostic and therapeutic strategies.

Ischemic Colitis in Association with Sevelamer Crystals

Sevelamer is an important drug used to lower serum phosphate levels in advanced kidney disease and in patients on dialysis. This drug is generally well tolerated but some patients report mild gastrointestinal distress as a side effect. Although regulatory agencies, such as Food and Drug Administration, list bowel ischemia and necrosis as potential and rare side effects, there are few case reports describing these adverse effects. We present a 35-year-old HIV patient with end-stage renal disease on hemodialysis who developed colonic hemorrhage and perforation. Imaging showed ischemic gangrene of bowel wall. Histopathology was consistent with transmural ischemic necrosis with deposition of fibrin thrombi and sevelamer crystals.

Management Practice, and Adherence and Its Contributing Factors among Patients with Chronic Kidney Disease at Tikur Anbessa Specialized Hospital: A Hospital Based Cross-Sectional Study

The objective of this study was to assess the management practice, medication adherence, and factors affecting medication adherence in CKD patients at Tikur Anbessa Specialized Hospital (TASH). Methods. A cross-sectional study was conducted at the nephrology clinic of TASH. A total of 256 CKD (stages 1 and 2=50, stage 3=88, stage 4=55, and stage 5=63) patients were recruited through systematic random sampling. Data were collected from medical records and interviewing patients. The rate of adherence was determined using 8-item Morisky medication adherence scale. The data were analyzed using SPSS version 20.0 statistical software. Univariate and multivariate binary logistic regression were used to investigate the potential predictors of medication nonadherence. Results. About 57.3% of diabetes mellitus with hypertension were treated with combination of insulin and ACEI based regimens. Other cardiovascular comorbidities were predominantly treated with Acetyl Salicylic Acid in combination with β-blocker. Only 61.3% (stages 1 and 2=70%, stage 3=73.9%, stage 4=54.5%, and stage 5=43%) of the study population were adherent to their treatment regimens. Forgetfulness (79.8%) was the major reason for medication nonadherence. Patients who had an average and high monthly income were 4.14 (AOR=4.14, 95% CI: 1.45-11.84, p=0.008) and 6.17 times (AOR=6.17, 95% CI: 1.02-37.46, p=0.048) more likely to adhere as compared to those who had very low income. Patients who were prescribed with ≥5 drugs were 0.46 times (AOR= 0.54, 95% CI: 0.27-1.10, p=0.049) less likely to adhere compared to their counterpart. Patients who were students, drivers, or teachers working in private school were about 7.46 times (AOR=7.46, 95% CI: 1.49-37.26, p=0.014) more likely to adhere compared with patients who were farmers. Conclusion. Insulin and ACEIs based regimens were the most frequently used regimens in the treatment of diabetes mellitus and hypertension comorbidities. Very low income, increased number of prescribed medications, and being a farmer were the predictors of medication nonadherence.

Management practice, and adherence and its contributing factors among patients with chronic kidney disease at Tikur Anbessa Specialized Hospital: A hospital-based cross-sectional study

INTRODUCTION

Chronic kidney disease (CKD) has a complicated interrelationship with other diseases and major risk factor for cardiovascular disease. Therapeutic management for CKD patients is complicated due to co-morbidities and dominant risk factors of CKD. Non-adherence to treatment is an increasing problem for patients with CKD and it has not been extensively studied in patients with CKD. Hence, the present study was carried out to assess the management practice, medication adherence and factors affecting medication adherence in CKD patients at Tikur Anbessa Specialized Hospital (TASH).

METHODS

A hospital-based cross-sectional study was conducted at the nephrology clinic of TASH. A total of 256 patients were recruited through systematic random sampling. Data were collected from medical records and interviewing patients. The degree of adherence was determined using eight-item Morisky Medication Adherence Scale. The data were entered into Epi Info 7.2.2.2 and analyzed using SPSS version 20.0 statistical software. Descriptive statistics such as frequency, percent, mean and standard deviation were used to summarize patients' baseline characteristics. Univariable and multivariable binary logistic regression were used to investigate the potential predictors of medication non-adherence.

RESULTS

About 55% patients with hypertension only were treated with non-angiotensin converting enzyme inhibition based regimens; 57.3% of diabetes mellitus with hypertension treated with combination of insulin and ACEI based regimens. About three-fourth of patients with anemia and osteodystrophy complications were treated with iron preparations and calcium based phosphate binder. Only 61.3% of the study population were adherent to their treatment regimens. Forgetfulness (79.8%) was the major reason for medication non-adherence. Patients who had an average and high monthly income were 4.14 (AOR = 4.14, 95% CI: 1.45-11.84, p = 0.008) and 6.17 times (AOR = 6.17, 95% CI: 1.02-37.46, p = 0.048) more likely to adhere as compared to those who had very low income. Patients who were prescribed with ≥5 drugs were 0.46 times (AOR = 0.54, 95% CI: 0.27-1.10, p = 0.049) less likely to adhere compared to their counterpart. Patients who were students, drivers, teachers working in private school were about 7.46 times (AOR = 7.46, 95% CI: 1.49-37.26, p = 0.014) more likely to adhere compared with patients who were farmers.

CONCLUSION

Insulin and ACEIs based regimens were the most frequently used regimens in the treatment of diabetes mellitus and hypertension co-morbidities. Very low income, increased number of prescribed medications and being a farmer were the predictors of medication non-adherence.

Arterial Calcification in Diabetes Mellitus: Preclinical Models and Translational Implications

Diabetes mellitus increasingly afflicts our aging and dysmetabolic population. Type 2 diabetes mellitus and the antecedent metabolic syndrome represent the vast majority of the disease burden-increasingly prevalent in children and older adults. However, type 1 diabetes mellitus is also advancing in preadolescent children. As such, a crushing wave of cardiometabolic disease burden now faces our society. Arteriosclerotic calcification is increased in metabolic syndrome, type 2 diabetes mellitus, and type 1 diabetes mellitus-impairing conduit vessel compliance and function, thereby increasing the risk for dementia, stroke, heart attack, limb ischemia, renal insufficiency, and lower extremity amputation. Preclinical models of these dysmetabolic settings have provided insights into the pathobiology of arterial calcification. Osteochondrogenic morphogens in the BMP-Wnt signaling relay and transcriptional regulatory programs driven by Msx and Runx gene families are entrained to innate immune responses-responses activated by the dysmetabolic state-to direct arterial matrix deposition and mineralization. Recent studies implicate the endothelial-mesenchymal transition in contributing to the phenotypic drift of mineralizing vascular progenitors. In this brief overview, we discuss preclinical disease models that provide mechanistic insights-and point to challenges and opportunities to translate these insights into new therapeutic strategies for our patients afflicted with diabetes mellitus and its arteriosclerotic complications.

Persistence of Vascular Calcification after Reversal of Uremia

The extent to which vascular calcification is reversible and the possible mechanisms are unclear. To address this, calcified aortas from uremic mice were transplanted orthotopically into normal mice, and the calcium content, histology, and minerals of the allografts were compared with the nontransplanted donor aorta. Calcium content decreased immediately after transplantation but remained constant thereafter, with 68% ± 12% remaining after 34 weeks. X-ray diffraction showed the presence of apatite in both donor aortas and allografts. Osteoclasts were absent in the allografts and there was no expression of the macrophage marker CD11b, the osteoclast marker tartrate-resistant acid phosphatase, or carbonic anhydrase II. The initial loss of calcium was less in heavily calcified aortas and was associated with an increase in the Ca/P ratio from 1.49 to 1.63, consistent with a loss of nonapatitic calcium. The results indicate that vascular calcification persists after reversal of uremia, because of a lack of active resorption of apatite. This failure to resorb established calcifications may contribute to the severity of vascular calcification and suggests that therapy should be aimed at prevention.

Early diagnosis of atherosclerosis with panoramic radiographs: a review

Carotid artery disease has been linked with cerebral vascular accident, also known as stroke, cerebral hemorrhage, or cerebral ischemia. It is caused by narrowing or obstruction of arteries in the neck (the carotid arteries) that are responsible for transporting blood from the aorta to the brain. Panoramic radiographs are used in dentistry to show both dental arches as a supplement to the clinical dental examination. The objective of this study is to highlight the importance of panoramic radiographs for diagnosis of arterial disease, by means of a bibliographic review. The PubMed database was searched using the keywords “atherosclerosis” and “panoramic”, with the filters “last 5 years” and “humans”. Twenty articles were identified, six of which were chosen for this study because they were open access. The review concluded that panoramic radiographs enable early diagnosis of carotid artery calcification, resulting in earlier interventions, and offer an accessible cost.

Phosphate Binding with Sevelamer Preserves Mechanical Competence of Bone Despite Acidosis in Advanced Experimental Renal Insufficiency

Introduction

Phosphate binding with sevelamer can ameliorate detrimental histomorphometric changes of bone in chronic renal insufficiency (CRI). Here we explored the effects of sevelamer-HCl treatment on bone strength and structure in experimental CRI.

Methods

Forty-eight 8-week-old rats were assigned to surgical 5/6 nephrectomy (CRI) or renal decapsulation (Sham). After 14 weeks of disease progression, the rats were allocated to untreated and sevelamer-treated (3% in chow) groups for 9 weeks. Then the animals were sacrificed, plasma samples collected, and femora excised for structural analysis (biomechanical testing, quantitative computed tomography).

Results

Sevelamer-HCl significantly reduced blood pH, and final creatinine clearance in the CRI groups ranged 30%-50% of that in the Sham group. Final plasma phosphate increased 2.4- to 2.9-fold, and parathyroid hormone 13- to 21-fold in CRI rats, with no difference between sevelamer-treated and untreated animals. In the femoral midshaft, CRI reduced cortical bone mineral density (-3%) and breaking load (-15%) (p<0.05 for all versus Sham), while sevelamer increased bone mineral density (+2%) and prevented the deleterious changes in bone. In the femoral neck, CRI reduced bone mineral density (-11%) and breaking load (-10%), while sevelamer prevented the decrease in bone mineral density (+6%) so that breaking load did not differ from controls.

Conclusions

In this model of stage 3–4 CRI, sevelamer-HCl treatment ameliorated the decreases in femoral midshaft and neck mineral density, and restored bone strength despite prevailing acidosis. Therefore, treatment with sevelamer can efficiently preserve mechanical competence of bone in CRI.

Ligand trap of the activin receptor type IIA inhibits osteoclast stimulation of bone remodeling in diabetic mice with chronic kidney disease

Dysregulation of skeletal remodeling is a component of renal osteodystrophy. Previously, we showed that activin receptor signaling is differentially affected in various tissues in chronic kidney disease (CKD). We tested whether a ligand trap for the activin receptor type 2A (RAP-011) is an effective treatment of the osteodystrophy of the CKD-mineral bone disorder. With a 70% reduction in the glomerular filtration rate, CKD was induced at 14 weeks of age in the ldlr-/- high fat-fed mouse model of atherosclerotic vascular calcification and diabetes. Twenty mice with CKD, hyperphosphatemia, hyperparathyroidism, and elevated activin A were treated with RAP-011, wherease 19 mice were given vehicle twice weekly from week 22 until the mice were killed at 28 weeks of age. The animals were then evaluated by skeletal histomorphometry, micro-computed tomography, mechanical strength testing, and ex vivo bone cell culture. Results in the CKD groups were compared with those of the 16 sham-operated ldlr-/- high fat-fed mice. Sham-operated mice had low-turnover osteodystrophy and skeletal frailty. CKD stimulated bone remodeling with significant increases in osteoclast and osteoblast numbers and bone resorption. Compared with mice with CKD and sham-operated mice, RAP-011 treatment eliminated the CKD-induced increase in these histomorphometric parameters and increased trabecular bone fraction. RAP-011 significantly increased cortical bone area and thickness. Activin A-enhanced osteoclastogenesis was mediated through p-Smad2 association with c-fos and activation of nuclear factor of activated T cells c1 (NFATc1). Thus, an ActRIIA ligand trap reversed CKD-stimulated bone remodeling, likely through inhibition of activin-A induced osteoclastogenesis.

Calcium Homeostasis in Health and in Kidney Disease

Calcium is an important ion in cell signaling, hormone regulation, and bone health. Its regulation is complex and intimately connected to that of phosphate homeostasis. Both ions are maintained at appropriate levels to maintain the extracellular to intracellular gradients, allow for mineralization of bone, and to prevent extra skeletal and urinary calcification. The homeostasis involves the target organs intestine, parathyroid glands, kidney, and bone. Multiple hormones converge to regulate the extracellular calcium level: parathyroid hormone, vitamin D (principally 25(OH)D or 1,25(OH)2D), fibroblast growth factor 23, and α-klotho. Fine regulation of calcium homeostasis occurs in the thick ascending limb and collecting tubule segments via actions of the calcium sensing receptor and several channels/transporters. The kidney participates in homeostatic loops with bone, intestine, and parathyroid glands. Initially in the course of progressive kidney disease, the homeostatic response maintains serum levels of calcium and phosphorus in the desired range, and maintains neutral balance. However, once the kidneys are no longer able to appropriately respond to hormones and excrete calcium and phosphate, positive balance ensues leading to adverse cardiac and skeletal abnormalities. © 2016 American Physiological Society. Compr Physiol 6:1781-1800, 2016.

Sigmoid colon diverticula perforation associated with sevelamer hydrochloride administration: A case report

Introduction

Sevelamer is an anion exchange resin used to treat hyperphosphatemia. A common adverse effect of sevelamer is constipation. According to a review of the available literature, colon perforation associated with this resin agent was less common.

Presentation of case

A 66-year-old man complaining of lower abdominal pain was transferred to our hospital. The patient had been undergoing hemodialysis for chronic renal failure due to rapidly progressive glomerulonephritis, and had been receiving sevelamer hydrochloride 4.5 g/day for 8years as treatment for hyperphosphatemia. Abdominal computed tomography revealed ascites, free air in the abdominal cavity, multiple diverticula of the sigmoid colon, as well as increased fat tissue surrounding the sigmoid colon. We diagnosed colonic perforation and performed emergency surgery, which revealed a 5 × 5 mm perforation in the sigmoid colon surrounded with soft stool. Histopathologically, sevelamer crystals were detected at the perforation site.

Discussion

We theorize that physical stimulation by sevelamer crystals contributed to colon perforation at the already vulnerable diverticulum site.

Conclusion

When sevelamer is administered to patients with hemodialysis, the risk of intestinal perforation should be considered.

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Sevelamer may contribute to colonic perforation in hemodialysis patients.

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Our patient underwent resection of a perforated portion of sigmoid colon.

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Histopathologically, sevelamer crystals were detected at the site of perforation.

Skeletal inflammation and attenuation of Wnt signaling, Wnt ligand expression, and bone formation in atherosclerotic ApoE-null mice

ApoE-null (ApoE-KO) mice fed a high-fat diet (HFD) develop atherosclerosis, due in part to activation of vascular inflammation by oxidized low-density lipoprotein. Since bone loss also occurs in these mice, we used them to investigate the impact of oxidized lipids on bone homeostasis and to search for underlying pathogenic pathways. Four-month-old female ApoE-KO mice fed a HFD for three months exhibited increased levels of oxidized lipids in bone, as well as decreased femoral and vertebral trabecular and cortical bone mass, compared with ApoE-KO mice on normal diet. Despite HFD-induced increase in expression of Alox15, a lipoxygenase that oxidizes LDL and promotes atherogenesis, global deletion of this gene failed to ameliorate the skeletal impact of HFD. Osteoblast number and function were dramatically reduced in trabecular and cortical bone of HFD-fed mice, whereas osteoclast number was modestly reduced only in trabecular bone, indicating that an imbalance in favor of osteoclasts was responsible for HFD-induced bone loss. These changes were associated with decreased osteoblast progenitors and increased monocyte/macrophages in the bone marrow as well as increased expression of IL-1β, IL-6, and TNF. HFD also attenuated Wnt signaling as evidenced by reduced expression of Wnt target genes, and it decreased expression of pro-osteoblastogenic Wnt ligands. These results suggest that oxidized lipids decrease bone mass by increasing anti-osteoblastogenic inflammatory cytokines and decreasing pro-osteoblastogenic Wnt ligands.

Ligand trap for the activin type IIA receptor protects against vascular disease and renal fibrosis in mice with chronic kidney disease

The causes of cardiovascular mortality associated with chronic kidney disease (CKD) are partly attributed to the CKD-mineral bone disorder (CKD-MBD). The causes of the early CKD-MBD are not well known. Our discovery of Wnt (portmanteau of wingless and int) inhibitors, especially Dickkopf 1, produced during renal repair as participating in the pathogenesis of the vascular and skeletal components of the CKD-MBD implied that additional pathogenic factors are critical. In the search for such factors, we studied the effects of activin receptor type IIA (ActRIIA) signaling by using a ligand trap for the receptor, RAP-011 (a soluble extracellular domain of ActRIIA fused to a murine IgG-Fc fragment). In a mouse model of CKD that stimulated atherosclerotic calcification, RAP-011 significantly increased aortic ActRIIA signaling assessed by the levels of phosphorylated Smad2/3. Furthermore, RAP-011 treatment significantly reversed CKD-induced vascular smooth muscle dedifferentiation as assessed by smooth muscle 22α levels, osteoblastic transition, and neointimal plaque calcification. In the diseased kidneys, RAP-011 significantly stimulated αklotho levels and it inhibited ActRIIA signaling and decreased renal fibrosis and proteinuria. RAP-011 treatment significantly decreased both renal and circulating Dickkopf 1 levels, showing that Wnt activation was downstream of ActRIIA. Thus, ActRIIA signaling in CKD contributes to the CKD-MBD and renal fibrosis. ActRIIA signaling may be a potential therapeutic target in CKD.

Peritoneal delivery of sodium pyrophosphate blocks the progression of pre-existing vascular calcification in uremic apolipoprotein-E knockout mice

Chronic kidney disease (CKD) is generally associated with disturbances of mineral and bone metabolism. They contribute to the development of vascular calcification (VC), a strong, independent predictor of cardiovascular risk. Pyrophosphate (PPi), an endogenous inhibitor of hydroxyapatite formation, has been shown to slow the progression of VC in uremic animals. Since in patients with CKD treatment is usually initiated for already existing calcifications, we aimed to compare the efficacy of PPi therapy with that of the phosphate binder sevelamer, using a uremic apolipoprotein-E knockout mouse model with advanced VCs. After CKD creation or sham surgery, 12-week-old female mice were randomized to one sham group and four CKD groups (n = 18-19/group). Treatment was initiated 8 weeks after left nephrectomy allowing prior VC development. Uremic groups received either intraperitoneal PPi (high dose, 1.65 mg/kg or low dose, 0.33 mg/kg per day), oral sevelamer (3 % in diet), or placebo treatment for 8 weeks. Both intima and media calcifications worsened with time in placebo-treated CKD mice, based on both quantitative image analysis and biochemical measurements. Progression of calcification between 8 and 16 weeks was entirely halted by PPi treatment, as it was by sevelamer treatment. PPi did not induce consistent bone histomorphometry changes. Finally, the beneficial vascular action of PPi probably involved mechanisms different from that of sevelamer. Further studies are needed to gain more precise insight into underlying mechanisms and to see whether PPi administration may also be useful in patients with CKD and VC.

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

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

Sevelamer carbonate: a review in hyperphosphataemia in adults with chronic kidney disease

Sevelamer carbonate (Renvela(®)), a buffered form of sevelamer hydrochloride (Renagel(®)), is an orally administered non-absorbed phosphate-binding anion exchange resin used in the treatment of hyperphosphataemia in chronic kidney disease (CKD). In the EU, sevelamer carbonate is approved in adult CKD patients who require dialysis and in those who do not require dialysis with serum phosphate levels ≥ 1.78 mmol/L, whereas in the USA sevelamer carbonate is approved in adult CKD patients who require dialysis. Sevelamer carbonate and sevelamer hydrochloride achieved similar reductions in serum phosphate levels in randomized comparative trials in patients with CKD receiving haemodialysis; sevelamer carbonate also reduced serum phosphate levels in noncomparative studies in CKD patients not requiring dialysis. The most common adverse events with sevelamer carbonate are gastrointestinal in nature. Sevelamer has pleiotropic effects, such as improving the serum lipid profile and attenuating endothelial and cardiovascular risk factors in CKD. All formulations of sevelamer have markedly higher acquisition costs than calcium-based phosphate binders. Cost-effectiveness analyses focusing specifically on sevelamer carbonate have not been conducted, and those based on clinical trial data with sevelamer hydrochloride have provided both favourable and unfavourable results compared with calcium-based phosphate binders, reflecting heterogeneity between modelled analyses in terms of data sources, assumptions, comparators, geographical regions, type of costs included and other factors. Although well-designed studies evaluating the impact of phosphate binders on hard clinical endpoints appear to be warranted, sevelamer carbonate may be particularly useful for the treatment of patients at risk of metabolic acidosis (offering advantages over sevelamer hydrochloride in this regard) and for individuals requiring treatment with a phosphate binding agent that does not contain aluminium or calcium.

Sevelamer revisited: pleiotropic effects on endothelial and cardiovascular risk factors in chronic kidney disease and end-stage renal disease

Endothelial dysfunction underlies multiple cardiovascular consequences of chronic kidney disease (CKD) and antecedent diabetes or hypertension. Endothelial insults in CKD or end-stage renal disease (ESRD) patients include uremic toxins, serum uric acid, hyperphosphatemia, reactive oxygen species, and advanced glycation endproducts (AGEs). Sevelamer carbonate, a calcium-free intestinally nonabsorbed polymer, is approved for hyperphosphatemic dialysis patients in the US and hyperphosphatemic stage 3-5 CKD patients in many other countries. Sevelamer has been observed investigationally to reduce absorption of AGEs, bacterial toxins, and bile acids, suggesting that it may reduce inflammatory, oxidative, and atherogenic stimuli in addition to its on-label action of lowering serum phosphate. Some studies also suggest that noncalcium binders may contribute less to vascular calcification than calcium-based binders. Exploratory sevelamer carbonate use in patients with stages 2-4 diabetic CKD significantly reduced HbA1c, AGEs, fibroblast growth factor (FGF)-23, and total and low-density lipoprotein (LDL) cholesterol versus calcium carbonate; inflammatory markers decreased and defenses against AGEs increased. Sevelamer has also been observed to reduce circulating FGF-23, potentially reducing risk of left ventricular hypertrophy. Sevelamer but not calcium-based binders in exploratory studies increases flow-mediated vasodilation, a marker of improved endothelial function, in patients with CKD. In contrast, lanthanum carbonate and calcium carbonate effects on FMV did not differ in hemodialysis recipients. The recent independent-CKD randomized trial compared sevelamer versus calcium carbonate in predialysis CKD patients (investigational in the US, on-label in European participants); sevelamer reduced 36-month mortality and the composite endpoint of mortality or dialysis inception. Similarly, independent-HD in incident dialysis patients showed improved survival with 24 months of sevelamer versus calcium-based binders. This review discusses recent exploratory evidence for pleiotropic effects of sevelamer on endothelial function in CKD or ESRD. Endothelial effects of sevelamer may contribute mechanistically to the improved survival observed in some studies of CKD and ESRD patients.

[Pleiotropic effects of sevelamer: a model of intestinal tract chelating agent]

The number of patients with chronic kidney disease (CKD) with its associated complications has increased dramatically worldwide in recent years. Therefore, many experimental and clinical studies have examined over the last decade the mechanisms involved, in order to explain the sharp increase in cardiovascular mortality. Hyperphosphatemia is a major problem in these patients especially at advanced stages of CKD, and it is associated with cardiovascular and mineral complications in these patients. Sevelamer is a phosphate binder that allows a better control of hyperphosphatemia, like other phosphate binder agents, but it has additional pleiotropic effects such as correcting certain abnormalities of lipid metabolism and clearance of several uremic toxins. These effects of sevelamer, restricted to the intestinal lumen, underline the importance of intestinal pathway in CKD and open the way to new therapeutic strategies for the management of the CKD and its complications.

CKD-induced wingless/integration1 inhibitors and phosphorus cause the CKD-mineral and bone disorder

In chronic kidney disease, vascular calcification, renal osteodystrophy, and phosphate contribute substantially to cardiovascular risk and are components of CKD-mineral and bone disorder (CKD-MBD). The cause of this syndrome is unknown. Additionally, no therapy addresses cardiovascular risk in CKD. In its inception, CKD-MBD is characterized by osteodystrophy, vascular calcification, and stimulation of osteocyte secretion. We tested the hypothesis that increased production of circulating factors by diseased kidneys causes the CKD-MBD in diabetic mice subjected to renal injury to induce stage 2 CKD (CKD-2 mice). Compared with non-CKD diabetic controls, CKD-2 mice showed increased renal production of Wnt inhibitor family members and higher levels of circulating Dickkopf-1 (Dkk1), sclerostin, and secreted klotho. Neutralization of Dkk1 in CKD-2 mice by administration of a monoclonal antibody after renal injury stimulated bone formation rates, corrected the osteodystrophy, and prevented CKD-stimulated vascular calcification. Mechanistically, neutralization of Dkk1 suppressed aortic expression of the osteoblastic transcription factor Runx2, increased expression of vascular smooth muscle protein 22-α, and restored aortic expression of klotho. Neutralization of Dkk1 did not affect the elevated plasma levels of osteocytic fibroblast growth factor 23 but decreased the elevated levels of sclerostin. Phosphate binder therapy restored plasma fibroblast growth factor 23 levels but had no effect on vascular calcification or osteodystrophy. The combination of the Dkk1 antibody and phosphate binder therapy completely treated the CKD-MBD. These results show that circulating Wnt inhibitors are involved in the pathogenesis of CKD-MBD and that the combination of Dkk1 neutralization and phosphate binding may have therapeutic potential for this disorder.

Early chronic kidney disease-mineral bone disorder stimulates vascular calcification

The chronic kidney disease-mineral and bone disorder (CKD-MBD) syndrome is an extremely important complication of kidney diseases. Here we tested whether CKD-MBD causes vascular calcification in early kidney failure by developing a mouse model of early CKD in a background of atherosclerosis-stimulated arterial calcification. CKD equivalent in glomerular filtration reduction to human CKD stage 2 stimulated early vascular calcification and inhibited the tissue expression of α-klotho (klotho) in the aorta. In addition, osteoblast transition in the aorta was stimulated by early CKD as shown by the expression of the critical transcription factor Runx2. The ligand associated with the klotho-fibroblast growth factor receptor complex, FGF23, was found to be expressed in the vascular media of sham-operated mice. Its expression was decreased in early CKD. Increased circulating levels of the osteocyte-secreted proteins, FGF23, and sclerostin may have been related to increased circulating klotho levels. Finally, we observed low-turnover bone disease with a reduction in bone formation rates more than bone resorption. Thus, the CKD-MBD, characterized by cardiovascular risk factors, vascular calcification, increased circulating klotho, FGF23 and sclerostin levels, and low-turnover renal osteodystrophy, was established in early CKD. Early CKD caused a reduction of vascular klotho, stimulated vascular osteoblastic transition, increased osteocytic secreted proteins, and inhibited skeletal modeling producing the CKD-MBD.

Phosphate: an old bone molecule but new cardiovascular risk factor

Phosphate handling in the body is complex and involves hormones produced by the bone, the parathyroid gland and the kidneys. Phosphate is mostly found in hydroxyapatite. however recent evidence suggests that phosphate is also a signalling molecule associated with bone formation. Phosphate balance requires careful regulation of gut and kidney phosphate transporters, SLC34 transporter family, but phosphate signalling in osteoblasts and vascular smooth muscle cells is likely mediated by the SLC20 transporter family (PiT1 and PiT2). If not properly regulated, phosphate imblanace could lead to mineral disorders as well as vascular calcification. In chronic kidney disease-mineral bone disorder, hyperphosphataemia has been consistently associated with extra-osseous calcification and cardiovascular disease. This review focuses on the physiological mechanisms involved in phosphate balance and cell signalling (i.e. osteoblasts and vascular smooth muscle cells) as well as pathological consequences of hyperphosphataemia. Finally, conventional as well as new and experimental therapeutics in the treatment of hyperphosphataemia are explored.

High serum phosphorus and FGF 23 levels are associated with progression of coronary calcifications

BACKGROUND

Coronary calcifications (CC) portend increased mortality in adults receiving hemodialysis (HD), however the risk factors associated with CC progression are not well known in pediatric patients. Our previous cross-sectional studies demonstrated high CC prevalence (31 %) in pediatric patients, which were significantly associated with high serum phosphorus (P), fibroblast growth factor 23 (FGF) levels, dialysis vintage, and low cholesterol. The current study was undertaken to determine and elucidate CC progression in pediatric HD patients.

METHODS

A 1-year prospective longitudinal study of 16 pediatric patients (ten male; mean age, 16.9 ± 3 years; range, 10.1-20.4 years) receiving chronic HD was conducted.

RESULTS

CC were observed in five of 16 (31.3 %) patients on baseline computed tomogram (CT) scan; 14/16 patients underwent 1-year CT. All patients with initial CC who completed CT at 1 year (3/5) progressed; one patient had new CC and none of the patients had resolved CC. Mean Agatston score increased from 23.4 ± 18.06 HU (baseline) to 169 ± 298.9 HU. Patients with CC progression had higher mean serum P (8.6 ± 1.8 mg/dl vs. 6.3 ± 1.1 mg/dl, p = 0.015) and FGF 23 levels (3,994 ± 860.5 pg/ml vs. 2,327 ± 1,206.4 pg/ml, p = 0.028). Serum P and FGF 23 levels were positively correlated with final Agatston scores (R = 0.65, p = 0.01 for serum P and R = 0.54, p = 0.045 for FGF 23) and change in Agatston scores (R = 0.65, p = 0.01 for serum P and R = 0.52, p = 0.048 for FGF 23).

CONCLUSIONS

Our study shows that CC is progressive in pediatric patients receiving HD and that increased serum P and FGF 23 levels are associated with this progression.

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

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

Metformin inhibits vascular calcification in female rat aortic smooth muscle cells via the AMPK-eNOS-NO pathway

Metformin exhibits diverse protective effects against diabetic complications, such as bone loss. Here, we investigated the effect of metformin on vascular calcification, another type 2 diabetes complication. In female rat aortic smooth muscle cells (RASMCs), we observed that metformin significantly alleviated β-glycerophosphate-induced Ca deposition and alkaline phosphatase activity, corresponding with reduced expression of some specific genes in osteoblast-like cells, including Runx2 and bone morphogenetic protein-2, and positive effects on α-actin expression, a specific marker of smooth muscle cells. Mechanistic analysis showed that phosphorylation levels of both AMP-activated protein kinase (AMPK) and endothelial nitric oxide synthase (eNOS) were increased with NO overproduction. After inhibition of either AMPK or eNOS with the pharmacologic inhibitors, compound C or Nω-Nitro-L-arginine methyl ester, NO production was lowered and metformin-meditated vascular protection against β-glycerophosphate-induced Ca deposition was removed. Our results support that metformin prevents vascular calcification via AMPK-eNOS-NO pathway.

Effects of phosphate binder therapy on vascular stiffness in early-stage chronic kidney disease

BACKGROUND/AIMS

Cardiovascular disease (CVD) is increased in chronic kidney disease (CKD), and contributed to by the CKD-mineral bone disorder (CKD-MBD). CKD-MBD begins in early CKD and its vascular manifestations begin with vascular stiffness proceeding to increased carotid artery intima-media thickness (cIMT) and vascular calcification (VC). Phosphorus is associated with this progression and is considered a CVD risk factor in CKD. We hypothesized that modifying phosphorus balance with lanthanum carbonate (LaCO3) in early CKD would not produce hypophosphatemia and may affect vascular manifestations of CKD-MBD.

METHODS

We randomized 38 subjects with normophosphatemic stage 3 CKD to a fixed dose of LaCO3 or matching placebo without adjusting dietary phosphorus in a 12-month randomized, double-blind, pilot and feasibility study. The primary outcome was the change in serum phosphorus. Secondary outcomes were changes in measures of phosphate homeostasis and vascular stiffness assessed by carotid-femoral pulse wave velocity (PWV), cIMT and VC over 12 months.

RESULTS

There were no statistically significant differences between LaCO3 and placebo with respect to the change in serum phosphorus, urinary phosphorus, tubular reabsorption of phosphorus, PWV, cIMT, or VC. Biomarkers of the early CKD-MBD such as plasma fibroblast growth factor-23, Dickkopf-related protein 1 (DKK1), and sclerostin were increased 2- to 3-fold at baseline, but were not affected by LaCO3.

CONCLUSION

Twelve months of LaCO3 had no effect on serum phosphorus and did not alter phosphate homeostasis, PWV, cIMT, VC, or biomarkers of CKD-MBD.

'Shedding' light on mechanisms of hyperphosphatemic vascular dysfunction

Cardiovascular disease is prevalent in chronic kidney disease (CKD) populations. Vascular dysfunction characterized by endothelial-cell damage, inflammation, and impaired angiogenesis is described in CKD, and hyperphosphatemia has been associated with vascular disease in CKD and general populations. We discuss the findings of elegant studies by Di Marco et al., linking hyperphosphatemia to downregulation of annexin II, an important protein implicated in fibrinolysis, cell adhesion, signal transduction, and angiogenesis.

Effect of a magnesium-based phosphate binder on medial calcification in a rat model of uremia

Calcium-based phosphate binders are used to control hyperphosphatemia; however, they promote hypercalcemia and may accelerate aortic calcification. Here we compared the effect of a phosphate binder containing calcium acetate and magnesium carbonate (CaMg) to that of sevelamer carbonate on the development of medial calcification in rats with chronic renal failure induced by an adenine diet for 4 weeks. After 1 week, rats with chronic renal failure were treated with vehicle, 375 or 750 mg/kg CaMg, or 750 mg/kg sevelamer by daily gavage for 5 weeks. Renal function was significantly impaired in all groups. Vehicle-treated rats with chronic renal failure developed severe hyperphosphatemia, but this was controlled in treated groups, particularly by CaMg. Neither CaMg nor sevelamer increased serum calcium ion levels. Induction of chronic renal failure significantly increased serum PTH, dose-dependently prevented by CaMg but not sevelamer. The aortic calcium content was significantly reduced by CaMg but not by sevelamer. The percent calcified area of the aorta was significantly lower than vehicle-treated animals for all three groups. The presence of aortic calcification was associated with increased sox9, bmp-2, and matrix gla protein expression, but this did not differ in the treatment groups. Calcium content in the carotid artery was lower with sevelamer than with CaMg but that in the femoral artery did not differ between groups. Thus, treatment with either CaMg or sevelamer effectively controlled serum phosphate levels in CRF rats and reduced aortic calcification.

Skeletal effects of zoledronic acid in an animal model of chronic kidney disease

Bisphosphonates reduce skeletal loss and fracture risk, but their use has been limited in patients with chronic kidney disease. This study shows skeletal benefits of zoledronic acid in an animal model of chronic kidney disease.

INTRODUCTION

Bisphosphonates are routinely used to reduce fractures but limited data exists concerning their efficacy in non-dialysis chronic kidney disease. The goal of this study was to test the hypothesis that zoledronic acid produces similar skeletal effects in normal animals and those with kidney disease.

METHODS

At 25 weeks of age, normal rats were treated with a single dose of saline vehicle or 100 μg/kg of zoledronic acid while animals with kidney disease (approximately 30% of normal kidney function) were treated with vehicle, low dose (20 μg/kg), or high dose (100 μg/kg) zoledronic acid, or calcium gluconate (3% in the drinking water). Skeletal properties were assessed 5 weeks later using micro-computed tomography, dynamic histomorphometry, and mechanical testing.

RESULTS

Animals with kidney disease had significantly higher trabecular bone remodeling compared to normal animals. Zoledronic acid significantly suppressed remodeling in both normal and diseased animals yet the remodeling response to zoledronic acid was no different in normal and animals with kidney disease. Animals with kidney disease had significantly lower cortical bone biomechanical properties; these were partially normalized by treatment.

CONCLUSIONS

Based on these results, we conclude that zoledronic acid produces similar amounts of remodeling suppression in animals with high turnover kidney disease as it does in normal animals, and has positive effects on select biomechanical properties that are similar in normal animals and those with chronic kidney disease.

Mineral metabolic abnormalities and mortality in dialysis patients

The survival rate of dialysis patients, as determined by risk factors such as hypertension, nutritional status, and chronic inflammation, is lower than that of the general population. In addition, disorders of bone mineral metabolism are independently related to mortality and morbidity associated with cardiovascular disease and fracture in dialysis patients. Hyperphosphatemia is an important risk factor of, not only secondary hyperparathyroidism, but also cardiovascular disease. On the other hand, the risk of death reportedly increases with an increase in adjusted serum calcium level, while calcium levels below the recommended target are not associated with a worsened outcome. Thus, the significance of target levels of serum calcium in dialysis patients is debatable. The consensus on determining optimal parathyroid function in dialysis patients, however, is yet to be established. Therefore, the contribution of phosphorus and calcium levels to prognosis is perhaps more significant. Elevated fibroblast growth factor 23 levels have also been shown to be associated with cardiovascular events and death. In this review, we examine the associations between mineral metabolic abnormalities including serum phosphorus, calcium, and parathyroid hormone and mortality in dialysis patients.

The relation between renal function and serum sclerostin in adult patients with CKD

BACKGROUND AND OBJECTIVES

Sclerostin, a bone antianabolic peptide involved in osteoporosis, is elevated in patients undergoing maintenance dialysis. However, there are no data for patients with early CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Between January and July 2010, serum sclerostin and GFR (calculated by inulin clearance) were measured in 90 patients with CKD. Fasting blood samples were also drawn for determination of calcium, phosphorus, parathyroid hormone, bone alkaline phosphatase, and 25-OH vitamin D.

RESULTS

Median GFR was 66.5 (interquartile range, 40.0-88.3) ml/min per 1.73 m(2). Median sclerostin level was 53.5 (interquartile range, 37.5-77.2) pmol/L, was higher in patients with a GFR <60 ml/min per 1.73 m(2), and was highest in those with ESRD. Sclerostin levels were significantly more elevated in men than women (P<0.05). An inverse relationship was found between sclerostin and GFR (r=-0.58; P<0.001), and a positive correlation was seen with age (r=0.34; P<0.01) and serum phosphate (r=0.26; P=0.02). In multiple regression analyses, GFR, sex, and serum phosphate were the only variables associated with serum sclerostin (P<0.001). Age lost its relationship with sclerostin level.

CONCLUSIONS

This is the first study reporting higher serum sclerostin levels starting at CKD stage III. GFR, sex, and serum phosphate were the only measures associated with sclerostin level, suggesting that the effect of age reported in the literature might instead be attributable to the altered renal function in the elderly. Correcting the serum phosphorus level may be associated with lower sclerostin levels.

Sevelamer carbonate experience in Indian end stage renal disease patients

This open label, multicentric, comparative clinical trial was done to compare the efficacy and tolerability of two sevelamer formulations, sevelamer carbonate, and sevelamer hydrochloride, in the treatment of hyperphosphatemia in Indian end stage renal disease (ESRD) patients. A total of 97 ESRD patients on hemodialysis, were enrolled. Patients were randomized to receive either sevelamer carbonate or sevelamer hydrochloride. All patients were evaluated every week for 6 weeks for efficacy and safety variables. Total 88 patients completed the study. After 6 weeks of therapy, there were similar reductions (P<0.0001) in mean serum phosphorus and the CaxP product both the groups. The responder rates for test and reference groups were 75%, 68.18% respectively (P=0.3474). The adverse events reported were nausea, abdominal pain/discomfort, heartburn, constipation, diarrhea, increased prothrombin time, and severe arthritis. No serious adverse events were reported. There was no significant difference between the groups for adverse events and the laboratory parameters. From the results of this multicentric, comparative, randomized clinical study on sevelamer carbonate we can recommend that sevelamer carbonate may be used as a phosphate binder in Indian chronic kidney disease patients.

Effects of phosphate on vascular function under normal conditions and influence of the uraemic state

AIMS

Increased serum phosphorus levels are associated with cardiovascular disease in patients with chronic kidney disease (CKD) and in the general population. High phosphate levels may play a direct role in vascular dysfunction. We investigated here the effects of phosphate loading and of the phosphate binder sevelamer-HCl on vascular function.

METHODS AND RESULTS

CKD and non-CKD C57/BL6 mice were used to study the effects of CKD, phosphate, and sevelamer-HCl on vascular function and structure. In vitro, phosphate exhibited a direct vasoconstrictor effect on aortic rings. This effect was smaller in vessels from CKD than non-CKD mice and it was abolished by reactive oxygen species inhibitor dimethylthiourea. A high-phosphate diet (1.3%) increased phenylephrine-induced contraction and lowered acetylcholine-induced relaxation of aortic rings ex vivo, both in non-CKD and CKD mice. It also induced endothelial cell detachment. Sevelamer-HCl exposure in vitro normalized the endothelial dysfunction induced by 3.0 mM phosphate and restored endothelial integrity. Sevelamer-HCl treatment of CKD mice under normal diet (0.65% phosphate) improved the endothelial dysfunction, aortic systolic expansion rate, and pulse wave velocity, and it reduced the endothelial expression of adhesion molecules.

CONCLUSION

Changes in extracellular phosphorus concentrations may directly modulate vascular function and thereby modulate the vascular smooth muscle response to physiological or pathological stimuli in normal and CKD mice. Whether serum phosphorus lowering and/or dietary phosphate restriction can improve arterial function in humans remains to be established.

The connections between vascular calcification and bone health

Vascular calcification, bone loss and increased fracture risk are age-associated disorders. Several epidemiological studies have suggested a relationship between vascular calcification, impaired bone metabolism and increased mortality. So far, this relationship had been under-estimated as osteoporosis and vascular calcification have been considered non-modifiable disorders of aging. Recent data suggest that this association is not simply an artefact of age, stressing that the co-incidence of vascular calcification with low bone activity and osteoporosis could be biologically linked. During the development of vascular calcification, the transition of vascular smooth muscle cells towards an osteoblast-like phenotype promotes the release of the vesicular structures and mineralization within these structures is promoted by several players, including those related to mineral metabolism, like phosphorus, calcium or parathyroid hormone, which influence either the supersaturation within the structure or the expression of osteogenic factors. However, an intriguing question is whether the presence of vascular calcification impacts bone metabolism, thus demonstrating true crosstalk between these tissues. Evidence is now emerging, suggesting that some inhibitors of the Wnt pathway, such as secreted frizzled Proteins 2 and 4 and Dickkopf related protein-1 (DKK-1), may play a role linking vascular calcification and bone loss. An additional important question to answer, from the patient's perspective, is whether or not progression of vascular calcification can be prevented or restricted and whether altering this progression we can efficiently impact patients' outcomes. Much evidence suggests that the control of the chronic kidney disease-mineral and bone disorder components, particularly serum phosphorus, are the main targets to maintain normal bone turnover and protect against vascular calcification.

The antioxidant tempol ameliorates arterial medial calcification in uremic rats: important role of oxidative stress in the pathogenesis of vascular calcification in chronic kidney disease

Vascular calcification is closely related to cardiovascular morbidity and mortality. Accumulating data indicate that oxidative stress is associated with dysfunction of various organs, including cardiovascular diseases in chronic kidney disease (CKD). However, it remains undetermined if oxidative stress induced by uremia promotes arterial medial calcification. The present study investigated the role of oxidative stress in the pathogenesis of arterial medial calcification in uremic rats. Rats with uremia induced by adenine-rich diet progressively developed arterial medial calcification, which was accompanied by time-dependent increases in both aortic and systemic oxidative stress. Immunohistochemical and biochemical analyses showed that the arterial medial calcification progressed in a time-dependent manner that is parallel to the osteogenic transdifferentiation of vascular smooth muscle cells. Accumulation of oxidative stress was also identified in the calcified regions. Time-course studies indicated that both oxidative stress and hyperphosphatemia correlated with arterial medial calcification. Tempol, an antioxidant, ameliorated osteogenic transdifferentiation of vascular smooth muscle cells and arterial medial calcification in uremic rats, together with reduction in aortic and systemic oxidative stress levels, without affecting serum biochemical parameters. Our data suggest that oxidative stress induced by uremia can play a role in the pathogenesis of vascular calcification in CKD, and that antioxidants such as tempol are potentially useful in preventing the progression of vascular calcification in CKD.

Arterial calcification in chronic kidney disease: key roles for calcium and phosphate

Vascular calcification contributes to the high risk of cardiovascular mortality in chronic kidney disease (CKD) patients. Dysregulation of calcium (Ca) and phosphate (P) metabolism is common in CKD patients and drives vascular calcification. In this article, we review the physiological regulatory mechanisms for Ca and P homeostasis and the basis for their dysregulation in CKD. In addition, we highlight recent findings indicating that elevated Ca and P have direct effects on vascular smooth muscle cells (VSMCs) that promote vascular calcification, including stimulation of osteogenic/chondrogenic differentiation, vesicle release, apoptosis, loss of inhibitors, and extracellular matrix degradation. These studies suggest a major role for elevated P in promoting osteogenic/chondrogenic differentiation of VSMC, whereas elevated Ca has a predominant role in promoting VSMC apoptosis and vesicle release. Furthermore, the effects of elevated Ca and P are synergistic, providing a major stimulus for vascular calcification in CKD. Unraveling the complex regulatory pathways that mediate the effects of both Ca and P on VSMCs will ultimately provide novel targets and therapies to limit the destructive effects of vascular calcification in CKD patients.

Inorganic phosphate homeostasis in sodium-dependent phosphate cotransporter Npt2b⁺/⁻ mice

An inorganic phosphate (P(i))-restricted diet is important for patients with chronic kidney disease and patients on hemodialysis. Phosphate binders are essential for preventing hyperphosphatemia and ectopic calcification. The sodium-dependent P(i) (Na/P(i)) transport system is involved in intestinal P(i) absorption and is regulated by several factors. The type II sodium-dependent P(i) transporter Npt2b is expressed in the brush-border membrane in intestinal epithelial cells and transports P(i). In the present study, we analyzed the phenotype of Npt2b(-/-) and hetero(+/-) mice. Npt2b(-/-) mice died in utero soon after implantation, indicating that Npt2b is essential for early embryonic development. At 4 wk of age, Npt2b(+/-) mice showed hypophosphatemia and low urinary P(i) excretion. Plasma fibroblast growth factor 23 levels were significantly decreased and 1,25(OH)(2)D(3) levels were significantly increased in Npt2b(+/-) mice compared with Npt2b(+/+) mice. Npt2b mRNA levels were reduced to 50% that in Npt2b(+/+) mice. In contrast, renal Npt2a and Npt2c transporter protein levels were significantly increased in Npt2b(+/-) mice. At 20 wk of age, Npt2b(+/-) mice showed hypophosphaturia and reduced Na/P(i) cotransport activity in the distal intestine. Npt2b(+/+) mice with adenine-induced renal failure had hyperphosphatemia and high plasma creatinine levels. Npt2b(+/-) mice treated with adenine had significantly reduced plasma P(i) levels compared with Npt2b(+/+) mice. Intestinal Npt2b protein and Na(+)/P(i) transport activity levels were significantly lower in Npt2b(+/-) mice than in the Npt2b(+/+) mice. The findings of the present studies suggest that Npt2b is an important target for the prevention of hyperphosphatemia.