In chronic kidney disease altered cardiac metabolism precedes cardiac hypertrophy.

Conduit arterial disease in chronic kidney disease (CKD) is an important cause of cardiac complications. Cardiac function in CKD has not been studied in the absence of arterial disease. In an Alport syndrome model bred not to have conduit arterial disease, mice at 225 days of life (dol) had CKD equivalent to humans with CKD stage 4-5. Parathyroid hormone (PTH) and FGF23 levels were one log order elevated, circulating sclerostin was elevated, and renal activin A was strongly induced. Aortic Ca levels were not increased, and vascular smooth muscle cell (VSMC) transdifferentiation was absent. The CKD mice were not hypertensive, and cardiac hypertrophy was absent. Freshly excised cardiac tissue respirometry (Oroboros) showed that ADP-stimulated O2 flux was diminished from 52 to 22 pmol/mg (P = 0.022). RNA-Seq of cardiac tissue from CKD mice revealed significantly decreased levels of cardiac mitochondrial oxidative phosphorylation genes. To examine the effect of activin A signaling, some Alport mice were treated with a monoclonal Ab to activin A or an isotype-matched IgG beginning at 75 days of life until euthanasia. Treatment with the activin A antibody (Ab) did not affect cardiac oxidative phosphorylation. However, the activin A antibody was active in the skeleton, disrupting the effect of CKD to stimulate osteoclast number, eroded surfaces, and the stimulation of osteoclast-driven remodeling. The data reported here show that cardiac mitochondrial respiration is impaired in CKD in the absence of conduit arterial disease. This is the first report of the direct effect of CKD on cardiac respiration.NEW & NOTEWORTHY Heart disease is an important morbidity of chronic kidney disease (CKD). Hypertension, vascular stiffness, and vascular calcification all contribute to cardiac pathophysiology. However, cardiac function in CKD devoid of vascular disease has not been studied. Here, in an animal model of human CKD without conduit arterial disease, we analyze cardiac respiration and discover that CKD directly impairs cardiac mitochondrial function by decreasing oxidative phosphorylation. Protection of cardiac oxidative phosphorylation may be a therapeutic target in CKD.

Renal osteodystrophy: something old, something new, something needed.

PURPOSE OF REVIEW: Renal osteodystrophy (ROD) is a complex disorder of bone metabolism that affects virtually all adults and children with chronic kidney disease (CKD). ROD is associated with adverse clinical outcomes including bone loss, mineralization and turnover abnormalities, skeletal deformities, fractures, cardiovascular events, and death. Despite current therapies, fracture incidence is 2-fold to 100-fold higher in adults and 2-fold to 3-fold higher in children when compared to without CKD. Limited knowledge of ROD pathogenesis, due to the lack of patient-derived large-scale multimodal datasets, impedes development of therapeutics aimed at reducing morbidity and mortality of CKD patients. The purpose of the review is to define the much needed infrastructure for the advancement of RDO treatment. RECENT FINDINGS: Recently, we created a large-scale data and tissue biorepository integrating clinical, bone quality, transcriptomic, and epigenomic data along with stored urine, blood, and bone samples. This database will provide the underpinnings for future research endeavors leading to the elucidation and characterization of the pathogenesis of ROD in CKD patients with and without dialysis. SUMMARY: The availability of an open-access NIH-funded resource that shares bone-tissue-based information obtained from patients with ROD with the broad scientific community represents a critical step in the process of discovering new information regarding unrecognized bone changes that have severe clinical complications. This will facilitate future high-impact hypothesis-driven research to redefine our understanding of ROD pathogenesis and pathophysiology and inform the development of disease-modifying and prevention strategies.

FGF-23 and sclerostin in serum and bone of CKD patients.

AIMS: Renal osteodystrophy occurs in the early stages of chronic kidney disease (CKD) and progresses during loss of kidney function. Fibroblast growth factor (FGF)-23 and sclerostin, both produced by osteocytes, are increased in blood of patients with CKD. The aim of this study was to analyze the impact of decline in kidney function on FGF-23 and sclerostin protein expression in bone and to study their relationship with their serum levels and bone histomorphometry. MATERIALS AND METHODS: 108 patients aged 25 - 81 years (mean ± SD: 56 ± 13 years) underwent anterior iliac crest biopsies after double-tetracycline labeling. Eleven patients were CKD-2, 16 were CKD-3, 9 were CKD-4 - 5, and 64 CKD-5D. Patients were on hemodialysis for 49 ± 117 months. 18 age-matched patients without CKD were included as controls. Immunostaining was performed on undecalcified bone sections to quantify FGF-23 and sclerostin expression. Bone sections were also evaluated by histomorphometry for bone turnover, mineralization, and volume. RESULTS: FGF-23 expression in bone correlated positively with CKD stages (p < 0.001) increasing from 5.3- to 7.1-fold starting at CKD-2. No difference in FGF-23 expression was seen between trabecular and cortical bone. Sclerostin expression in bone correlated positively with CKD stages (p < 0.001) with an increase from 3.8- to 5.1-fold starting at CKD-2. This increase was progressive and significantly greater in cortical than cancellous bone. FGF-23 and sclerostin in blood and bone were strongly associated with bone turnover parameters. Expression of FGF-23 in cortical bone correlated positively with activation frequency (Ac.f) and bone formation rate (BFR/BS) (p < 0.05), while sclerostin correlated negatively with Ac.f, BFR/BS, and osteoblast and osteoclast numbers (p < 0.05). FGF-23 trabecular and cortical expressions correlated positively with cortical thickness (p < 0.001). Sclerostin bone expression correlated negatively with parameters of trabecular thickness and osteoid surface (p < 0.05). CONCLUSION: These data show a progressive increase in FGF-23 and sclerostin in blood and bone associated with decrease in kidney function. The observed relationships between bone turnover and sclerostin or FGF-23 should be considered when treatment modalities are developed for management of turnover abnormalities in CKD patients.

Treatment of bone loss in CKD5D: Better survival in patients with non-high bone turnover.

67% of CKD5D patients have low bone mass and present with high (HTO) or non-high (N-HTO) bone turnover. HTO has excessive resorption calling for anti-resorbers, while in N-HTO, anabolic therapy appears preferable. There are no data on this tailored approach. Adult CKD5D patients with dual energy X-ray absorptiometry (DXA) t-scores ≤ -1.0 were enrolled into this 12-month randomized controlled trial and stratified as HTO or N-HTO using values of parathyroid hormone (PTH), PTH-ratio, and TRAP5b. HTO patients were randomized into treatment with alendronate or controls, and N-HTO patients into teriparatide or controls. Clinical, lab, DXA, quantitative computed tomography bone mineral density (QCT BMD), and coronary artery calcifications (CAC) and aorta calcifications (AoC) MSQCT data were obtained at 0 and 12 months. Primary outcome was change (Δ) in BMD by QCT, secondary outcomes were changes in CAC (ΔCAC), in AoC (ΔAoC), and death. There were 80 HTO and 61 N-HTO patients. Median HTO baseline PTH was 664 and N-HTO 183. Bone loss improved in treated N-HTO (5.7 g/cm3 vs. -10.7) but not in HTO (0.2 g/cm3 vs. -3.5) patients. There were no differences in ΔAoC or ΔCAC between treatment groups in either arm. Across all patients in the study, ΔAoC was lower in Blacks than Whites. (3.6 vs. 8.8) The HTO ΔAoC was 5 Hounsfield Units higher than N-HTO. In N-HTO, there were 0 deaths, but 20% in HTO (p = 0.005). N-HTO patients (PTH range 138 - 337 pg/mL) had better survival and less ΔAoC than those with HTO. Teriparatide treatment significantly improved low bone mass in N-HTO patients. Blacks had less ΔAoC regardless of turnover or treatment.

Importance of bone turnover for therapeutic decisions in patients with CKD-MBD.

Patients with chronic kidney disease-mineral and bone disorder (CKD-MBD) frequently have low bone formation rates. A recent review suggested that adynamic bone disease is not always associated with negative outcomes and therefore antiresorptive medications could be used more often. However, there is currently no evidence to support an improvement in fracture risk or mortality in patients with CKD-MBD and low bone turnover who are treated with antiresorptive medication. There is reasonable pathophysiological evidence suggesting that it may even be harmful.

Long-term outcomes and management considerations after parathyroidectomy in the dialysis patient.

Parathyroidectomy (PTX) remains an important intervention for dialysis patients with poorly controlled secondary hyperparathyroidism (SHPT), though there are only retrospective and observational data that show a mortality benefit to this procedure. Potential consequences that we seek to avoid after PTX include persistent or recurrent hyperparathyroidism, and parathyroid insufficiency. There is considerable subjectivity in defining and diagnosing these conditions, given that we poorly understand the optimal PTH targets (particularly post PTX) needed to maintain bone and vascular health. While lowering PTH after PTX decreases bone turnover, long-term changes in bone activity have been poorly explored. High turnover bone disease, usually present at the time a PTX is considered, often swings to a state of low turnover in the setting of sufficiently low PTH levels. It remains unclear if all low bone turnover equate with disease. However, such changes in bone turnover appear to predispose to vascular calcification, with positive calcium balance after PTX being a potential contributor. We know little of how the post-PTX state resets calcium balance, how calcium and VDRA requirements change or what kind of adjustments are needed to avoid calcium loading. The current consensus cautions against excessive reduction of PTH although there is insufficient evidence-based guidance regarding the management of chronic kidney disease - mineral bone disease (CKD-MBD) parameters in the post-PTX state. This article aims to compile existing research, provide an overview of current practice with regard to PTX and post-PTX chronic management. It highlights gaps and controversies and aims to re-orient the focus to clinically relevant contemporary priorities in CKD-MBD management after PTX.

Serum bone markers in ROD patients across the spectrum of decreases in GFR: Activin A increases before all other markers
.

INTRODUCTION: Renal osteodystrophy (ROD) develops early in chronic kidney disease (CKD) and progresses with loss of kidney function. While intact parathyroid hormone (PTH), 1,25-dihydroxyvitamin D3 (1,25D), and fibroblast growth factor-23 (FGF-23) levels are usually considered the primary abnormalities in ROD development, the role of serum activin A elevations in CKD and its relationships to ROD have not been explored. The aims of this study were to evaluate serum activin A at different CKD stages, and to establish the relationships between activin A, bone biomarkers, and bone histomorphometric parameters. MATERIALS AND METHODS: 104 patients with CKD stages 2 - 5D underwent bone biopsies. We measured in the serum activin A, BSAP, DKK1, FGF-23, α-Klotho, intact PTH, sclerostin, TRAP-5b, and 1,25D. Biochemical results were compared across CKD stages and with 19 age-matched controls with normal kidney function. RESULTS: Median activin A levels were increased in all stages of CKD compared to controls from 544 pg/mL in CKD 2 (431 - 628) to 1,135 pg/mL in CKD 5D (816 - 1,456), compared to 369 pg/mL in controls (316 - 453, p < 0.01). The increase of activin A in CKD 2 (p = 0.016) occurred before changes in the other measured biomarkers. Activin A correlated with intact PTH and FGF-23 (r = 0.65 and 0.61; p < 0.01) and with histomorphometric parameters of bone turnover (BFR/BS, Acf, ObS/BS and OcS/BS; r = 0.47 - 0.52; p < 0.01). These correlations were comparable to those found with intact PTH and FGF-23. CONCLUSION: Serum activin A levels increase starting at CKD 2 before elevations in intact PTH and FGF-23. Activin A correlates with bone turnover similar to intact PTH and FGF-23. These findings suggest a role for activin A in early development of ROD.

The activin receptor is stimulated in the skeleton, vasculature, heart, and kidney during chronic kidney disease.

We examined activin receptor type IIA (ActRIIA) activation in chronic kidney disease (CKD) by signal analysis and inhibition in mice with Alport syndrome using the ActRIIA ligand trap RAP-011 initiated in 75-day-old Alport mice. At 200 days of age, there was severe CKD and associated Mineral and Bone Disorder (CKD-MBD), consisting of osteodystrophy, vascular calcification, cardiac hypertrophy, hyperphosphatemia, hyperparathyroidism, elevated FGF23, and reduced klotho. The CKD-induced bone resorption and osteoblast dysfunction was reversed, and bone formation was increased by RAP-011. ActRIIA inhibition prevented the formation of calcium apatite deposits in the aortic adventitia and tunica media and significantly decreased the mean aortic calcium concentration from 0.59 in untreated to 0.36 mg/g in treated Alport mice. Aortic ActRIIA stimulation in untreated mice increased p-Smad2 levels and the transcription of sm22α and αSMA. ActRIIA inhibition reversed aortic expression of the osteoblast transition markers Runx2 and osterix. Heart weight was significantly increased by 26% in untreated mice but remained normal during RAP-011 treatment. In 150-day-old mice, GFR was significantly reduced by 55%, but only by 30% in the RAP-011-treated group. In 200-day-old mice, the mean BUN was 100 mg/dl in untreated mice compared to 60 mg/dl in the treated group. In the kidneys of 200-day-old mice, ActRIIA and p-Smad2 were induced and MCP-1, fibronectin, and interstitial fibrosis were stimulated; all were attenuated by RAP-011 treatment. Hence, the activation of ActRIIA signaling during early CKD contributes to the CKD-MBD components of osteodystrophy and cardiovascular disease and to renal fibrosis. Thus, the inhibition of ActRIIA signaling is efficacious in improving and delaying CKD-MBD in this model of Alport syndrome.

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.

Reduction of Dialysate Calcium Level Reduces Progression of Coronary Artery Calcification and Improves Low Bone Turnover in Patients on Hemodialysis.

Exposure to high Ca concentrations may influence the development of low-turnover bone disease and coronary artery calcification (CAC) in patients on hemodialysis (HD). In this randomized, controlled study, we investigated the effects of lowering dialysate Ca level on progression of CAC and histologic bone abnormalities in patients on HD. Patients on HD with intact parathyroid hormone levels ≤300 pg/ml receiving dialysate containing 1.75 or 1.50 mmol/L Ca (n=425) were randomized to the 1.25-mmol/L Ca (1.25 Ca; n=212) or the 1.75-mmol/L Ca (1.75 Ca; n=213) dialysate arm. Primary outcome was a change in CAC score measured by multislice computerized tomography; main secondary outcome was a change in bone histomorphometric parameters determined by analysis of bone biopsy specimens. CAC scores increased from 452±869 (mean±SD) in the 1.25 Ca group and 500±909 in the 1.75 Ca group (P=0.68) at baseline to 616±1086 and 803±1412, respectively, at 24 months (P=0.25). Progression rate was significantly lower in the 1.25 Ca group than in the 1.75 Ca group (P=0.03). The prevalence of histologically diagnosed low bone turnover decreased from 85.0% to 41.8% in the 1.25 Ca group (P=0.001) and did not change in the 1.75 Ca group. At 24 months, bone formation rate, trabecular thickness, and bone volume were higher in the 1.25 Ca group than in the 1.75 Ca group. Thus, lowering dialysate Ca levels slowed the progression of CAC and improved bone turnover in patients on HD with baseline intact parathyroid hormone levels ≤300 pg/ml.

Only minor differences in renal osteodystrophy features between wild-type and sclerostin knockout mice with chronic kidney disease.

Renal osteodystrophy affects the majority of patients with advanced chronic kidney disease (CKD) and is characterized by progressive bone loss. This study evaluated the effects of sclerostin knockout on bone in a murine model of severe, surgically induced CKD in both sclerostin knockout and wild-type mice. Mice of both genotypes with normal kidney function served as controls. Tibiae were analyzed using micro-computed tomography, and lumbar vertebrae were analyzed by histomorphometry. Results were tested for statistical significance by 2-way ANOVA to investigate whether bone of the knockout mice reacted differently to CKD compared with bone of wild-type mice. In the tibiae, there was no difference after creation of CKD between wild-type and knockout animals for cortical thickness or cross-sectional moment of inertia. Increases in cortical porosity induced by CKD differed significantly between genotypes in the tibial metaphysis but not in the diaphysis. In the trabecular compartment, no difference in reaction to CKD between genotypes was found for bone volume, trabecular number, trabecular thickness, and trabecular separation. In the lumbar vertebrae, significant differences in response to CKD between wild-type and knockout mice were seen for both bone volume and trabecular thickness. Osteoblast parameters did not differ significantly, whereas osteoclast numbers significantly increased in the wild-type but significantly decreased in knockout mice with CKD. No differences in response to CKD between genotypes were found for bone formation rate or mineral apposition rate. Thus, complete absence of sclerostin has only minor effects on CKD-induced bone loss in mice.

Diagnostic Accuracy of Bone Turnover Markers and Bone Histology in Patients With CKD Treated by Dialysis.

BACKGROUND: The management of chronic kidney disease-mineral and bone disorder requires the assessment of bone turnover, which most often is based on parathyroid hormone (PTH) concentration, the utility of which remains controversial. STUDY DESIGN: Cross-sectional retrospective diagnostic test study. SETTING & PARTICIPANTS: 492 dialysis patients from Brazil, Portugal, Turkey, and Venezuela with prior bone biopsy and stored (-20 °C) serum. INDEX TESTS: Samples were analyzed for PTH (intact [iPTH] and whole PTH), bone-specific alkaline phosphatase (bALP), and amino-terminal propeptide of type 1 procollagen (P1NP). REFERENCE TEST: Bone histomorphometric assessment of turnover (bone formation rate/bone surface [BFR/BS]) and receiver operating characteristic curves for discriminating diagnostic ability. RESULTS: The biomarkers iPTH and bALP or combinations thereof allowed discrimination of low from nonlow and high from nonhigh BFR/BS, with an area under the receiver operating characteristic curve > 0.70 but < 0.80. Using iPTH level, the best cutoff to discriminate low from nonlow BFR/BS was <103.8 pg/mL, and to discriminate high from nonhigh BFR/BS was >323.0 pg/mL. The best cutoff for bALP to discriminate low from nonlow BFR/BS was <33.1 U/L, and for high from nonhigh BFR/BS, 42.1U/L. Using the KDIGO practice guideline PTH values of greater than 2 but less than 9 times the upper limit of normal, sensitivity and specificity of iPTH level to discriminate low from nonlow turnover bone disease were 65.7% and 65.3%, and to discriminate high from nonhigh were 37.0% and 85.8%, respectively. LIMITATIONS: Cross-sectional design without consideration of therapy. Potential limited generalizability with samples from 4 countries. CONCLUSIONS: The serum biomarkers iPTH, whole PTH, and bALP were able to discriminate low from nonlow BFR/BS, whereas iPTH and bALP were able to discriminate high from nonhigh BFR/BS. Prospective studies are required to determine whether evaluating trends in biomarker concentrations could guide therapeutic decisions.

Serum phosphorus adds to value of serum parathyroid hormone for assessment of bone turnover in renal osteodystrophy.

It is well-established that parathyroid hormone (PTH) correlates with the level of bone turnover in patients with chronic kidney disease stage 5D (CKD-5D). Hyperphosphatemia is a well-established complication of end-stage renal disease and is usually attributed to dietary intake. This study evaluates the relationship between serum phosphorus levels and bone turnover in patients with CKD-5D. 93 patients with CKD-5D from the Kentucky Bone Registry who had sequentially undergone anterior iliac bone biopsies were reviewed. Undecalcified bone sections were qualitatively assessed for turnover and placed into a group with low turnover and a group with non-low (normal/high) turnover. Results of PTH and phosphorus concentrations in blood drawn at the time of biopsies were compared between the groups. PTH and phosphorus levels were significantly higher in the non-low turnover group compared to the low turnover group. Cutoff levels for PTH and phosphorus were tested for predictive power of bone turnover. Both PTH and phosphorus correlated with turnover. Adding serum phosphorus to serum PTH enhanced predictive power of PTH for low turnover. The vast majority of patients with serum phosphorus levels ≥ 6.0 mg/dL had non-low turnover, while the majority of those with low turnover had phosphorus values < 6.0 mg/dL. Classification and regression-tree analysis showed that elevated serum phosphorus (> 6.2 mg/dL) in patients with PTH < 440 pg/mL was helpful in diagnosing nonlow turnover in this range of PTH. In patients with PTH ranges of 440 - 814 pg/mL, serum phosphorus levels > 4.55 mg/dL ruled out low turnover bone disease. This suggests that not only dietary intake but also bone affects serum phosphorus levels.

Diagnosis of low bone mass in CKD-5D patients.

BACKGROUND AND OBJECTIVES: Currently, there is no consensus whether dual-energy X-ray absorptiometry (DXA) or quantitative computed tomography (QCT) can be used to screen for osteoporosis or osteopenia in CKD-5D patients. This study uses iliac bone histology, the "gold standard" for bone volume evaluation, to determine the utility of DXA and QCT for low bone mass screening in CKD-5D patients. PATIENTS AND METHODS: A cross-sectional study of patients with CKD-5D employing iliac crest bone biopsies to assess bone volume by histology and comparing results to bone mineral density (BMD) measurements of the hip and spine by DXA and QCT. Pearson's correlation, linear regression, and receiver operating characteristics curve analyses were performed. RESULTS: 46 patients (mean age 51 years, 52% women, median dialysis vintage 46 months) had bone biopsies, DXA, and QCT scans. 37 patients (80%) had low bone volume by histology. DXA and QCT BMD values (g/cm2) were very highly correlated at the femoral neck (ρ = 0.97) and total hip (ρ = 0.97), and to a lesser degree at the spine (ρ = 0.65). DXA and QCT t-scores were also highly correlated, but QCT t-scores were systematically greater than DXA t-scores (1.1 S.D. on average at the femoral neck) leading to less recognition of osteopenia and osteoporosis by QCT. A t-score below -1 by DXA at the femoral neck (i.e., osteopenic or osteoporotic) showed 83% sensitivity and 78% specificity relative to low bone volume by histology. A QCT t-score below -1 did not reach acceptable diagnostic levels of sensitivity and specificity. CONCLUSIONS: DXA and QCT provide nearly identical areal BMD measures at the hip. However, QCT t-scores are consistently higher than DXA t-scores resulting in less diagnosis of osteoporosis or osteopenia. DXA results showed acceptable diagnostic sensitivity and specificity for low bone volume by histology and can be used for diagnosis of osteopenia and osteoporosis in patients with CKD-5D.

Coronary artery calcification in CKD-5D patients is tied to adverse cardiac function and increased mortality
.

BACKGROUND: Coronary artery calcification (CAC) is common in patients with chronic kidney disease on hemodialysis (CKD-5D) and is an important predictor of mortality. However, cardiac functional links between CAC and mortality have not been well established. This study tested the hypothesis that CAC increases mortality by adversely affecting cardiac function. METHODS: Patients were recruited from 37 regional dialysis centers. 2-D and Doppler echocardiographic analyses were performed, and CAC was measured using 64-slice computed tomography. Relationships between CAC and echocardiographic measures of left ventricular (LV) function were analyzed. Survival was assessed with median follow-up of 37 months. RESULTS: There were 157 patients: 59% male, 46% Caucasian, 48% diabetic. Median age was 55 years, and median duration of CKD-5D was 45 months. Agatston CAC scores 100 were found in 69% of patients, with 51% having a score  400. CAC was associated with measures of LV systolic and diastolic function (global longitudinal strain (GLS; rho = 0.270, p = 0.004)), peak LV systolic velocity (rho = -0.259, p = 0.004), and estimate of LV filling pressure (E:E'; rho = 0.286, p = 0.001). Multivariate regression confirmed these relationships after adjustment for age, gender, LV ejection fraction, and coronary artery disease. Valvular calcification varied linearly with CAC (p < 0.05). Both LV diastolic and systolic functional measures were significant predictors of mortality, the strongest of which was LV diastolic dysfunction. CONCLUSIONS: These findings show a link between CAC, cardiac function, and mortality in CKD-5D. LV diastolic function (E:E'), peak LV systolic velocity, and GLS are independent predictors of mortality. Valvular calcification may be an important marker of CAC in CKD-5D. These effects on cardiac function likely explain the high mortality with CKD-5D and describe a potentially-valuable role for echocardiography in the routine management of these patients.
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High Parathyroid Hormone Level and Osteoporosis Predict Progression of Coronary Artery Calcification in Patients on Dialysis.

Coronary artery calcifications (CACs) are observed in most patients with CKD on dialysis (CKD-5D). CACs frequently progress and are associated with increased risk for cardiovascular events, the major cause of death in these patients. A link between bone and vascular calcification has been shown. This prospective study was designed to identify noninvasive tests for predicting CAC progression, including measurements of bone mineral density (BMD) and novel bone markers in adult patients with CKD-5D. At baseline and after 1 year, patients underwent routine blood tests and measurement of CAC, BMD, and novel serum bone markers. A total of 213 patients received baseline measurements, of whom about 80% had measurable CAC and almost 50% had CAC Agatston scores>400, conferring high risk for cardiovascular events. Independent positive predictors of baseline CAC included coronary artery disease, diabetes, dialysis vintage, fibroblast growth factor-23 concentration, and age, whereas BMD of the spine measured by quantitative computed tomography was an inverse predictor. Hypertension, HDL level, and smoking were not baseline predictors in these patients. Three quarters of 122 patients completing the study had CAC increases at 1 year. Independent risk factors for CAC progression were age, baseline total or whole parathyroid hormone level greater than nine times the normal value, and osteoporosis by t scores. Our results confirm a role for bone in CKD-associated CAC prevalence and progression.

Bone alkaline phosphatase isoforms in hemodialysis patients with low versus non-low bone turnover: a diagnostic test study.

BACKGROUND: Renal osteodystrophy encompasses the bone histologic abnormalities seen in patients with chronic kidney disease (CKD). The bone-specific alkaline phosphatase (bALP) isoform B1x is exclusively found in serum of some patients with CKD. STUDY DESIGN: The aim of this cross-sectional diagnostic test study was to examine the relationship between serum bALP isoform activity and histomorphometric parameters of bone in patients with CKD receiving maintenance hemodialysis. SETTINGS & PARTICIPANTS: Anterior iliac crest bone biopsy samples from 40 patients with CKD were selected on the basis of bone turnover for histomorphometric analysis. There were samples from 20 patients with low and 20 with non-low bone turnover. INDEX TEST: In serum, bALP, bALP isoforms (B/I, B1x, B1, and B2), and parathyroid hormone (PTH) were measured. REFERENCE TEST: Low bone turnover was defined by mineral apposition rate < 0.36µm/d. Non-low bone turnover was defined by mineral apposition rate ≥ 0.36µm/d. OTHER MEASUREMENTS: PTH. RESULTS: B1x was found in 21 patients (53%) who had lower median levels of bALP, 18.6 versus 46.9U/L; B/I, 0.10 versus 0.22 µkat/L; B1, 0.40 versus 0.88 µkat/L; B2, 1.21 versus 2.66 µkat/L; and PTH, 49 versus 287pg/mL, compared with patients without B1x (P<0.001). 13 patients (65%) with low bone turnover and 8 patients (40%) with non-low bone turnover (P<0.2) had detectable B1x. B1x correlated inversely with histomorphometric parameters of bone turnover. Receiver operating characteristic curves showed that B1x can be used for the diagnosis of low bone turnover (area under the curve [AUC], 0.83), whereas bALP (AUC, 0.89) and PTH (AUC, 0.85) are useful for the diagnosis of non-low bone turnover. LIMITATIONS: Small number of study participants. Requirement of high-performance liquid chromatography methods for measurement of B1x. CONCLUSIONS: B1x, PTH, and bALP have similar diagnostic accuracy in distinguishing low from non-low bone turnover. The presence of B1x is diagnostic of low bone turnover, whereas elevated bALP and PTH levels are useful for the diagnosis of non-low bone turnover.

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.

Expression of DGCR8-dependent microRNAs is indispensable for osteoclastic development and bone-resorbing activity.

Recently, microRNAs (miRs) have been implicated in bone formation and homeostasis. We previously reported that Dicer generated miRs have pivotal roles in differentiation and activity of osteoclasts. However, recent studies have demonstrated that Dicer is implicated in production of endogenous small interfering RNAs, non-canonical miRs, and other small RNAs in mammals. Hence, a challenging question is the extent to which expression of canonical miRs is obligatory for osteoclastic control of bone metabolism. DiGeorge syndrome critical region gene 8 (DGCR8) is exclusively related to expression of miRs by a canonical processing pathway together with the nuclear RNase III enzyme Drosha. Osteoclast-specific deletion of DGCR8 led to impaired osteoclastic development and bone resorption so that bone development was significantly retarded. In culture, the expression levels of osteoclastic phenotype-related genes and proteins were remarkably inhibited during osteoclastogenesis in DGCR8-deficiency. Thus, we have identified that DGCR8-dependent miRs are indispensable for osteoclastic control of bone metabolism.

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.