Johann Herberth

Sclerostin and Dickkopf-1 in Renal Osteodystrophy

BACKGROUND AND OBJECTIVES The serum proteins sclerostin and Dickkopf-1 (Dkk-1) are soluble inhibitors of canonical wnt signaling and were recently identified as components of parathyroid hormone (PTH) signal transduction. This study investigated the associations between sclerostin and Dkk-1 with histomorphometric parameters of bone turnover, mineralization, and volume in stage 5 chronic kidney disease patients on dialysis (CKD-5D). DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS In a cross-sectional study, 60 CKD-5D patients underwent bone biopsies followed by histomorphometry. Levels of sclerostin, Dkk-1, and intact PTH (iPTH) were determined in blood. RESULTS Serum levels of sclerostin and iPTH correlated negatively. In unadjusted analyses, sclerostin correlated negatively with histomorphometric parameters of turnover, osteoblastic number, and function. In adjusted analyses, sclerostin remained a strong predictor of parameters of bone turnover and osteoblast number. An observed correlation between sclerostin and cancellous bone volume was lost in regression analyses. Sclerostin was superior to iPTH for the positive prediction of high bone turnover and number of osteoblasts. In contrast, iPTH was superior to sclerostin for the negative prediction for high bone turnover and had similar predictive values than sclerostin for the number of osteoblasts. Serum levels of Dkk-1 did not correlate with iPTH or with any histomorphometric parameter. CONCLUSIONS Our data describe a promising role for serum measurements of sclerostin in addition to iPTH in the diagnosis of high bone turnover in CKD-5D patients, whereas measurements of Dkk-1 do not seem to be useful for this purpose.

Low Bone Volume—A Risk Factor for Coronary Calcifications in Hemodialysis Patients

BACKGROUND AND OBJECTIVES There is increasing evidence that altered bone metabolism is associated with cardiovascular calcifications in patients with stage 5 chronic kidney disease on hemodialysis (HD). This study was conducted to evaluate the association between bone volume, turnover, and coronary calcifications in HD patients. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS In a cross-sectional study, bone biopsies and multislice computed tomography were performed in 38 HD patients. Bone volume/total volume, activation frequency, and bone formation rate/bone surface were determined by histomorphometry and coronary calcifications were quantified by Agatston scores. RESULTS Prevalence of low bone turnover was 50% and of low bone volume was 16%. Among the studied traditional cardiovascular risk factors, only age was found to be associated with coronary calcifications. Lower bone volume was a significant risk factor for coronary calcifications during early years of HD, whereas this effect was not observed in patients with dialysis duration >6 yr. Histomorphometric parameters of bone turnover were not associated with coronary calcifications. CONCLUSIONS Low bone volume is associated with increased coronary calcifications in patients on HD.

Bone Markers Predict Cardiovascular Events in Chronic Kidney Disease

Recent studies have indicated a link between bone metabolism and cardiovascular events in patients with chronic kidney disease (CKD). CKD is a major health problem worldwide. This study evaluates the role of noninvasive markers of bone metabolism in predicting cardiovascular morbidity (coronary artery disease, peripheral vascular disease, stroke) and mortality in patients with mild to severe forms of CKD. In a prospective cohort study, 627 patients with CKD were screened. To focus on bone metabolism, traditional risk factors for cardiovascular events were excluded, and 135 patients with CKD stages 1–5 were followed for 4 yr. Glomerular filtration rate was calculated by the Modification of Diet in Renal Disease formula. PTH (measured by four different assays), vitamin D 25 and 1,25, bone‐specific alkaline phosphatase (BSALP), TRACP‐5b, osteocalcin, serum collagen cross‐link molecules, RANKL, and osteoprotegerin were determined. Predictors of cardiovascular events were evaluated by multivariable logistic regression, Kaplan‐Meier survival, and Cox regression analysis. There were a total of 45 cardiovascular events (33%). Event rates were 5.6%, 29.1%, 45.2%, and 45.0% in CKD stages 1–2, 3, 4, and 5, respectively. In logistic regression, cardiovascular events were predicted only by (1) CKD stage (independent of age or sex; p < 0.001); (2) BSALP (p = 0.03); and (3) TRACP‐5b (p = 0.04). Markers of bone formation (BSALP) and resorption (TRACP‐5b) can serve as predictors of cardiovascular morbidity and mortality in CKD.

Bone disease after renal transplantation.

In light of greatly improved long-term patient and graft survival after renal transplantation, improving other clinical outcomes such as risk of fracture and cardiovascular disease is of paramount importance. After renal transplantation, a large percentage of patients lose bone. This loss of bone results from a combination of factors that include pre-existing renal osteodystrophy, immunosuppressive therapy, and the effects of chronically reduced renal function after transplantation. In addition to low bone volume, histological abnormalities include decreased bone turnover and defective mineralization. Low bone volume and low bone turnover were recently shown to be associated with cardiovascular calcifications, highlighting specific challenges for medical therapy and the need to prevent low bone turnover in the pretransplant patient. This Review discusses changes in bone histology and mineral metabolism that are associated with renal transplantation and the effects of these changes on clinical outcomes such as fractures and cardiovascular calcifications. Therapeutic modalities are evaluated based on our understanding of bone histology.

The link between bone and coronary calcifications in CKD-5 patients on haemodialysis

BACKGROUND Vascular calcifications are frequent in Stage 5 chronic kidney disease (CKD-5) patients receiving haemodialysis. The current study was designed to evaluate the associations between bone turnover/volume and coronary artery calcifications (CAC). METHODS In 207 CKD-5 patients, bone biopsies, multislice computed tomography of the coronary arteries and blood drawings for relevant biochemical parameters were done. The large number of CKD-5 patients enrolled allowed separate evaluation of patients with CAC versus patients without CAC and adjustment for traditional and non-traditional risk factors for CAC. RESULTS When all patients were analysed, associations were found between CAC and bone turnover, bone volume, age, gender and dialysis vintage. When only patients with CAC were included, there was a U-shaped relationship between CAC and bone turnover, whilst the association with bone volume was lost. In these patients, the relationship of CAC with age, gender and dialysis vintage remained. CONCLUSIONS Beyond the non-modifiable risk factors of age, gender and dialysis vintage, these data show that bone abnormalities of renal osteodystrophy amenable to treatment should be considered in the management of patients with CAC.

Intact PTH Combined With the PTH Ratio for Diagnosis of Bone Turnover in Dialysis Patients: A Diagnostic Test Study

BACKGROUND Determination of parathyroid hormone (PTH) level is the most commonly used surrogate marker for bone turnover in patients with stage 5 chronic kidney disease on dialysis therapy (CKD-5D). The objective of this study is to evaluate the predictive value of various PTH measurements for identifying low or high bone turnover rate. STUDY DESIGN Diagnostic test study. SETTINGS & PARTICIPANTS 141 patients with CKD-5D from 15 US hemodialysis centers. INDEX TESTS Intact PTH, PTH 1-84, and PTH ratio (ratio of level of PTH 1-84 to level of large carboxy-terminal PTH fragments). REFERENCE TEST OR OUTCOME Bone turnover determined using bone histomorphometry. OTHER MEASUREMENTS Demographic and treatment-related factors, serum calcium and phosphorus. RESULTS Patients presented histologically with a broad range of bone turnover abnormalities. In white patients with CKD-5D (n = 70), PTH ratio <1.0 added to intact PTH level <420 pg/mL increased the positive predictive value for low bone turnover from 74% to 90%. In black patients (n = 71), adding PTH ratio <1.2 to intact PTH level <340 pg/mL increased the positive predictive value for low bone turnover from 48% to 90%. Adding PTH ratio >1.6 to intact PTH level of 340-790 pg/mL increased the positive predictive value for high bone turnover from 56% to 71%. LIMITATIONS Because the research protocol called for carefully controlled blood specimen handling, blood drawing and routine specimen handling might be less stringent in clinical practice. By limiting study participation to black and white patients with CKD-5D, we cannot comment on the roles of intact PTH, PTH 1-84, and PTH ratio in other racial/ethnic groups. CONCLUSION In black patients with CKD-5D, the addition of PTH ratio to intact PTH measurements is helpful for diagnosing low and high bone turnover. In white patients with CKD-5D, it aids in the diagnosis of low bone turnover.

The five most commonly used intact parathyroid hormone assays are useful for screening but not for diagnosing bone turnover abnormalities in CKD-5 patients.

BACKGROUND/AIMS Assessment of bone turnover for management of renal osteodystrophy is part of routine care in chronic kidney disease Stage 5 (CKD-5) patients. Measurement of intact parathyroid hormone (iPTH) is the most commonly used surrogate marker for bone turnover in these patients. The current study was conducted to evaluate the predictive value of the five most commonly used iPTH assays for bone turnover. METHODS In a cross-sectional study, 84 CKD-5 patients underwent bone biopsy and blood drawings for determination of iPTH and total serum alkaline phosphatase (AP). RESULTS Histologically, patients presented with a broad range of bone turnover abnormalities as determined by activation frequency and bone formation rate/bone surface. Results of the five iPTH assays in each patient correlated but were significantly different. There were also significant differences between iPTH measurements at the same bone turnover level. Using Kidney Disease Outcome Quality Initiative recommended iPTH ranges, all assays showed comparably poor diagnostic performance. At 80% specificity, cut-off values of the 5 iPTH assays for low bone turnover varied from 165 to 550 pg/ml and for high bone turnover from 404 to 1,003 pg/ml. Sensitivities at these cutoffs remained below acceptable standards. Addition of AP measurements to iPTH did not improve diagnostic accuracy. CONCLUSIONS Precise assessment of bone turnover will require utilization of established and novel bone markers reflecting effects of bone turnover rather than measuring only iPTH or other effectors.

Femoral bone mineral density reflects histologically determined cortical bone volume in hemodialysis patients

SummaryWe evaluated the associations between dual energy X-ray absorptiometry (DXA) and histologically determined cancellous and cortical bone volume by controlling for vascular calcifications and demographic variables in hemodialysis (HD) patients. Femoral bone mineral density (f-BMD) was associated with cortical porosity.IntroductionAssessment of bone mass in chronic kidney disease patients is of clinical importance because of the association between low bone volume, fractures, and vascular calcifications. DXA is used for noninvasive assessment of bone mass whereby vertebral results reflect mainly cancellous bone and femoral results reflect mainly cortical bone. Bone histology allows direct measurements of cancellous and cortical bone volume. The present study evaluates the association between DXA and histologically determined cancellous and cortical bone volumes in HD patients.MethodsIn 38 HD patients, DXA was performed for assessment of bone mass, anterior iliac crest bone biopsies for bone volume, and multislice computed tomography for vascular calcifications.ResultsWhile lumbar bone mineral density (l-BMD) by DXA was not associated with histologically measured cancellous bone volume, coronary Agatson score showed a borderline statistically significant association (P = 0.055). When controlled for age and dialysis duration, f-BMD by DXA was associated with cortical porosity determined by histology (P = 0.005).ConclusionsThe usefulness of l-BMD for predicting bone volume is limited most probably because of interference by soft tissue calcifications. In contrast, f-BMD shows significant association with cortical porosity.

Changes in total parathyroid hormone (PTH), PTH-(1-84) and large C-PTH fragments in different stages of chronic kidney disease.

INTRODUCTION Loss of renal function is accompanied by progressive increase in serum levels of intact parathyroid hormone (iPTH) in patients with end-stage renal disease (ESRD). There is a paucity of data regarding levels of PTH-(1-84) and its large carboxyl-terminal fragments (large C-PTH fragments) and progressive loss of kidney function in patients with chronic kidney disease (CKD). The current study was undertaken to describe the glomerular filtration rate (GFR)-dependent plasma concentrations of PTH-(1-84) and related large C-PTH fragments in adult patients with CKD by using different commercially available PTH assays. METHODS We studied 80 Caucasian patients with CKD stages 1-5 without renal replacement therapy. Creatinine clearance was calculated by the Modification of Diet in Renal Disease (MDRD) formula. Levels of iPTH were determined by second-generation assays (iPTH Elecsys system, Roche Diagnostics; DUO total iPTH, Scantibodies Laboratory, Inc.; iPTH, Nichols Institute Diagnostics). Third-generation assays were used to measure PTH-(1-84) (CAP (cyclase activating PTH), Scantibodies; Bio-Intact PTH, Nichols). Levels of large C-PTH fragments and ratios of PTH-(1-84)/large C-PTH fragments were calculated and statistical analyses performed. RESULTS Levels of iPTH and PTH-(1-84) showed CKD stage-dependent increases. Variations among the assays increased with progressive loss of kidney function. The assay from Scantibodies showed a GFR-dependent decrease of the ratio 1-84 PTH / large C-PTH fragment that was not observed with the Nichols assay. CONCLUSION Increasing variations among the assays with progression of CKD emphasize the fact that the interpretation of measurements must take into consideration the specific assay. We found evidence for a possible preferential increase of the level of large C-PTH fragments over 1-84 PTH in a CKD stage-dependent manner (Scantibodies). The clinical implications of this finding have to be further evaluated by bone biopsy studies.

Retinoic acid receptor gamma 2 interactions with vitamin D response elements

The vitamin D receptor (VDR) typically binds DNA in a heterodimer complex with the retinoid X receptor (RXR) to direct repeat sequences separated by three base pairs, or vitamin D response elements (VDREs). A modified yeast one-hybrid screen was utilized to search for partner proteins capable of associating with the VDR on a repressor VDRE. Screening of a HeLa cell cDNA library revealed that retinoic acid receptor gamma 2 (RARgamma2) could specifically interact with VDREs, either in the presence or absence of the VDR. Importantly, the A-domain of RARgamma2 appeared to be crucial for this interaction as evidenced by the inability of RARgamma1 to affect reporter gene activity. Transfection data in COS-7 cells revealed the combination of both receptor ligands strongly attenuated transcriptional activation from an enhancer VDRE when RARgamma2 was co-transfected into these cells with the VDR. Furthermore, a VDR/RARgamma2 complex was detected in the mobility shift assay from nuclear extracts of transfected cells. Thus, the data highlight the novel ability of RARgamma2 to interact with VDREs and impact vitamin D activity, which would allow for additional fine-tuning of a transcriptional response depending on ligand availability and expression profile of these nuclear receptors in a given cell type.