Calcium and osteoprotegerin levels predict the progression of the abdominal aortic calcifications after kidney transplantation. Transplantation. 2013;96:42-48. [PMID: 23812001 PMCID: PMC3713767 DOI: 10.1097/tp.0b013e3182934cee]

Calcitriol supplementation after kidney transplantation: results of a double-blinded, randomized, placebo-controlled trial

A significant number of kidney transplant recipients have low BMD. We hypothesized that calcitriol administration over the first year posttransplantation would protect the cortical skeleton in recipients managed without corticosteroids by suppressing PTH and bone remodeling. In this double-blind, placebo-controlled trial, 67 participants aged ≥18 yr on corticosteroid-sparing immunosuppressive regimen were randomized to daily calcitriol 0.5 μg or placebo for 12 mo after transplantation. The primary endpoint was the percent change in cortical density at the radius and tibia from pre- to postcalcitriol treatment compared to placebo as measured by HR-pQCT. Areal BMD was measured by DXA. Cortical and trabecular volumetric BMD and microarchitecture and total estimated bone strength were measured by HR-pQCT. Blood samples for bone metabolic markers were obtained at baseline, 1- and 12 mo. All primary analyses were intent to treat. Safety was assessed for hypercalcemia and progression of vascular calcifications. Thirty-two participants received calcitriol and 29 received placebo; 27 and 27 participants completed the study, respectively. Most participants were male and Caucasian. Baseline Z-scores at all sites were within 0.5 SD of the general population. At 12 mo posttransplantation, there were no between-group differences in areal BMD, volumetric BMD, microarchitecture or bone strength, or serum levels of bone markers. Participants with versus without bone loss had a blunted anabolic response over 12 mo measured by serum bone markers. Hypercalcemia was higher in the calcitriol group compared to placebo (p < .001). No changes in arterial calcification scores were observed. In this randomized placebo-controlled study of calcitriol administration in kidney transplant recipients on corticosteroid-sparing immunosuppression, calcitriol did not improve bone quality and strength but was associated with higher rates of hypercalcemia.

Phase angle and donor type are determinants of coronary artery calcification in stable kidney transplant recipients at twelve months after transplantation

BACKGROUND AND AIM

Coronary artery calcification (CAC) partially explains the excess cardiovascular morbidity and mortality after kidney transplantation. This study aimed to investigate determinants of CAC in stable kidney transplant recipients at 12 months post-transplantation.

METHODS AND RESULTS

CAC-score was quantified by the Agatston method using non-contrast enhanced computed tomography, and age- and sex-standardized CAC-percentiles were calculated. Univariable and multivariable multinomial logistic regression was performed to study potential determinants of CAC. The independent determinants were included in multivariable multinomial logistic regression adjusting for potential confounders. 203 KTRs (age 54.0 ± 14.7 years, 61.1% male) were included. Participants were categorized into four groups according to CAC percentiles (p = 0 [CAC-score = 0], n = 68; p ≥ 1%-p ≤ 50% [CAC score = 29.0 (4.0-166.0)], n = 31; p > 50 ≤ 75% [CAC score = 101.0 (23.8-348.3)], n = 26; and p>75% [CAC score = 581.0 (148.0-1652)], n = 83). Upon multivariable multinomial logistic regression, patients with a narrower phase angle and patients who had received a graft from a deceased donor had a higher risk of being in the >75th CAC-percentile.

CONCLUSIONS

This study identifies not only metabolic and transplant-related factors, but also phase angle, a composite marker of cell integrity, as an independent determinant of CAC at 12 months after kidney transplantation. This study offers new perspectives for future research into the value of bioelectrical impedance analysis in relation to vascular calcification in kidney transplant recipients.

Association of Serum Osteoprotegerin With Vascular Calcification, and Cardiovascular and Graft Outcomes in Kidney Transplant Patients: Results From the KNOW-KT

BACKGROUND

Vascular calcification and stiffness contribute to increased cardiovascular morbidity in patients with chronic kidney disease. This study investigated associations between serum osteoprotegerin (OPG) levels and vascular calcification or stiffness to assess cardiovascular and graft outcomes in kidney transplant patients.

METHODS

The KoreaN cohort study for Outcome in patients With Kidney Transplantation was a prospective multicenter cohort study. Serum OPG levels were measured at baseline and 3 y after transplantation in 1018 patients. Patients were classified into high and low OPG groups according to median serum OPG levels. The median follow-up duration was 93.5 mo.

RESULTS

The mean age was 45.8 ± 11.7 y and 62.9% were men. Patients with high OPG had significantly higher coronary artery calcium scores, abdominal aortic calcification scores, and brachial-ankle pulse wave velocities than those with lower OPG; these parameters remained significant for 5 y after transplantation. The 3-y OPG levels were lower than baseline values ( P  < 0.001) and were positively correlated ( r  = 0.42, P  < 0.001). Multivariate Cox regression analysis showed that high OPG levels were significantly associated with posttransplant cardiovascular events ( P  = 0.008) and death-censored graft loss ( P  = 0.004). Similar findings regarding posttransplant cardiovascular events ( P  = 0.012) and death-censored graft loss ( P  = 0.037) were noted in patients with high OPG at the 3-y follow-up. Mediation analyses revealed that coronary artery calcium scores, abdominal aortic calcification scores, and brachial-ankle pulse wave velocities could act as mediators between serum OPG levels and posttransplant cardiovascular events.

CONCLUSIONS

Serum OPG concentration is associated with vascular calcification and stiffness and could be a significant risk factor for cardiovascular outcomes and graft loss in patients undergoing kidney transplantation.

Mineral and bone disorder after kidney transplantation: a single-center cohort study

BACKGROUND

The assessment and prevention of mineral and bone disorder (MBD) in kidney transplant recipients (KTRs) have not been standardized. This study aimed to evaluate MBD one year after kidney transplantation (KT) and identify the influencing factors of MBD.

METHODS

A total of 95 KTRs in our center were enrolled. The changes in bone mineral density (BMD) and bone metabolism biochemical markers, including serum calcium (Ca), phosphorus(P), 25-hydroxyvitamin D(25(OH)vitD), intact parathyroid hormone (iPTH), bone alkaline phosphatase, osteocalcin (OC), type I collagen N-terminal peptide and type I collagen C-terminal peptide (CTx), over one year after KT were assessed. The possible influencing factors of BMD were analyzed. The relationships between bone metabolism biochemical markers were evaluated. The indicators between groups with or without iPTH normalization were also compared.

RESULTS

MBD after KT was manifested as an increased prevalence of hypophosphatemia and bone loss, persistent 25(OH)vitD deficiency, and partially decreased PTH and bone turnover markers (BTMs). Femoral neck BMD was positively correlated with body mass index (BMI) and postoperative 25(OH)vitD, and negatively correlated with postoperative PTH. Lumbar spine BMD was positively correlated with BMI and preoperative TG, and negatively correlated with preoperative OC and CTx. BMD loss was positively associated with glucocorticoid accumulation. Preoperative and postoperative iPTH was negatively correlated with postoperative serum P and 25(OH)vitD, and positively correlated with postoperative Ca and BTMs. The recipients without iPTH normalization, who accounted for 41.0% of all KTRs, presented with higher Ca, lower P, higher BTMs, advanced age, and a higher prevalence of preoperative parathyroid hyperplasia.

CONCLUSIONS

MBD persisted after KT, showing a close relationship with hyperparathyroidism, high bone turnover, and glucocorticoid accumulation.

Vascular calcification progression and its association with mineral and bone disorder in kidney transplant recipients

BACKGROUND

The assessment and prevention of vascular calcification (VC) in kidney transplant recipients (KTRs) have not been systematically studied. We aimed to evaluate VC change one year after kidney transplantation (KT) and identify their influencing factors.

METHODS

95 KTRs (68 males; ages 40.2 ± 10.8 years) were followed one year after KT. Changes in bone mineral density (BMD) and bone metabolism biomarkers were assessed. Coronary artery calcification (CAC) and thoracic aortic calcification (TAC) were measured using 192-slice third-generation dual-source CT. The relationship between bone metabolism indicators and VC and the factors influencing VC were analyzed.

RESULTS

Postoperative estimated glomerular filtration rate was 79.96 ± 24.18 mL/min*1.73 m2. One year after KT, serum phosphorus, intact parathyroid hormone (iPTH), osteocalcin, type I collagen N-terminal peptide (NTx), type I collagen C-terminal peptide, and BMD decreased, 25-hydroxyvitamin D remained low, and VC increased. Post-CAC and TAC were negatively correlated with pre-femoral neck BMD, and TAC was positively correlated with post-calcium. CAC and TAC change were positively correlated with post-calcium and 25-hydroxyvitamin D. Increased CAC was positively associated with hemodialysis and pre-femoral neck osteopenia. CAC change was positively associated with prediabetes, post-calcium, and pre-CAC and negatively associated with preoperative and postoperative femoral neck BMD, and NTx change. Increased TAC was positively associated with age, prediabetes, preoperative parathyroid hyperplasia/nodule, post-calcium, and post-femoral neck osteopenia. TAC change was positively associated with age, diabetes, pre-triglyceride, pre-TAC, dialysis time, post-calcium and post-iPTH, and negatively associated with post-femoral neck BMD.

CONCLUSIONS

Mineral and bone disorders persisted, and VC progressed after KT, showing a close relationship.

Tertiary and Postrenal Transplantation Hyperparathyroidism

Patients who have undergone kidney transplantation (KTx) (KTxps) are a distinctive population characterized by the persistence of some metabolic anomalies present during end-stage renal disease. Mineral metabolism (MM) parameters are frequently altered after KTx. These alterations involve calcium, phosphorus, vitamin D, and parathormone (PTH) disarrangements. At present, there is little consensus about the correct monitoring and management of PTH disorders in KTxps. This article presents the prevalence and epidemiologic and clinical impact of post-KTx hyper-PTH. The principal biochemical and instrumental investigations and the therapeutic options for these conditions are also reported.

Progression of Aortic Calcification in Stage 4-5 Chronic Kidney Disease Patients Transitioning to Dialysis and Transplantation

BACKGROUND AND AIMS

Abdominal aortic calcification (AAC) is common in chronic kidney disease (CKD) patients and associated with increased mortality. Comparative data on the AAC score progression in CKD patients transitioning from conservative treatment to different modalities of renal replacement therapy (RRT) are lacking and were examined.

METHODS

150 study patients underwent lateral lumbar radiograph to study AAC in the beginning of the study before commencing RRT (AAC1) and at 3 years of follow-up (AAC2). We examined the associations between repeated laboratory tests taken every 3 months, echocardiographic and clinical variables and AAC increment per year (ΔAAC), and the association between ΔAAC and outcomes during follow-up.

RESULTS

At the time of AAC2 measurement, 39 patients were on hemodialysis, 39 on peritoneal dialysis, 39 had a transplant, and 33 were on conservative treatment. Median AAC1 was 4.8 (0.5-9.0) and median AAC2 8.0 (1.5-12.0) (p < 0.0001). ΔAAC was similar across the treatment groups (p = 0.19). ΔAAC was independently associated with mean left ventricular mass index (LVMI) (log LVMI: β = 0.97, p = 0.02) and mean phosphorus through follow-up (log phosphorus: β = 1.19, p = 0.02) in the multivariable model. Time to transplantation was associated with ΔAAC in transplant recipients (per month on the waiting list: β = 0.04, p = 0.001). ΔAAC was associated with mortality (HR 1.427, 95% confidence interval 1.044-1.950, p = 0.03).

CONCLUSION

AAC progresses rapidly in patients with CKD, and ΔAAC is similar across the CKD treatment groups including transplant recipients. The increment rate is associated with mortality and in transplant recipients with the time on the transplant waiting list.

Hypercalcemia Is a Risk Factor for the Progression of Aortic Calcification in Kidney Transplant Recipients

BACKGROUND/AIMS

Vascular calcification is common and progressive in chronic kidney disease, including kidney transplant recipients (KTRs). However, the risk factors associated with the progression of aortic calcification (AoC) in KTRs have not been fully elucidated. In the present study, we evaluated AoC and examined the factors associated with its advancement in KTRs.

MATERIALS

This was a prospective longitudinal study that included 98 KTRs. We quantitatively investigated infrarenal abdominal AoC using the Agatston score, as measured by multi-slice computed tomography. After the baseline investigation, a follow-up scan was performed after 3 years, and the Agatston scores were obtained again. The changes in laboratory data affecting the 2nd Agatston scores were examined by multivariable analysis using non-linear regression after adjustment for several confounders.

RESULTS

The 2nd Agatston scores were significantly greater than the baseline Agatston scores (p < 0.001). After adjustment for the confounders, the change in corrected serum calcium exhibited a significant non-linear correlation with the 2nd Agatston scores (p = 0.022 for non-linearity/p = 0.031 for the effect of corrected serum calcium). Moreover, an interaction was present from the baseline AoC in the effect of corrected serum calcium on the progression of AoC, and the effect of hypercalcemia was greater in patients with higher baseline Agatston scores (p = 0.049).

CONCLUSION

The present study revealed that hypercalcemia is a risk factor for the development of infrarenal abdominal AoC in KTRs. Furthermore, the effect of hypercalcemia was greater in patients with more severe vascular calcification.

Long-term evaluation of coronary artery calcifications in kidney transplanted patients: a follow up of 5 years

Coronary artery calcifications(CACs), are related to the increased cardiovascular mortality during kidney transplantation(KTx). Using coronary-CT performed at 1 month(T0) and 5 years(T5) after KTx we evaluated: (1) the prevalence of CACs; (2) the clinical and biochemical factors related to CACs; 3) the factors implicated with CACs progression. We evaluated 67-pts selected from the 103-pts transplanted in our unit between 2007 and 2008. Clinical and biochemical parameters were recorded at the time of pre-KTx evaluation and for five years after KTx. Coronary-CT for the Agatson score (AS) evaluation was performed at T0 and at T5, and CACs progression was determined. At baseline AS was 45 [0–233]. At T5 AS was 119 [1–413]. At T0, 69% of patients had CACs. Age and dialytic vintage were the main independent variables related to CACs. At T5, CACs were present in 76% of patients. Age was the only independent factor in determining CACs. A progression of CACs was observed in 74% of patients. They were older, had higher CACs-T0 and higher SBP throughout the 5-years. The presence of CACs at T0 and age were the only independent factors in determining the CACs-progression. CACs-T0 had the best discriminative power for CACs progression. CACs prevalence is quite high in KTx patients; Age is strictly related to CACs; Age and the presence of CACs at baseline were the two major factors associated with the progression of CACs during the five years of follow up. CACs-T0 had the best discriminative power for progression of CACs.

The Correlation of Serum Osteoprotegerin with Non-Traditional Cardiovascular Risk Factors and Arterial Stiffness in Patients with Pre-Dialysis Chronic Kidney Disease: Results from the KNOW-CKD Study

BACKGROUND

Osteoprotegerin (OPG) plays protective roles against the development of vascular calcification (VC) which greatly contributes to the increased cardiovascular events in patients with chronic kidney disease (CKD). The present study aimed to find the non-traditional, kidney-related cardiovascular risk factors correlated to serum OPG and the effect of serum OPG on the arterial stiffness measured by brachial ankle pulse wave velocity (baPWV) in patients with the pre-dialysis CKD.

METHODS

We cross-sectionally analyzed the data from the patients in whom baPWV and the serum OPG were measured at the time of enrollment in a prospective pre-dialysis CKD cohort study in Korea.

RESULTS

Along with traditional cardiovascular risk factors such as age, diabetes mellitus, pulse pressure, and baPWV, non-traditional, kidney-related factors such as albuminuria, plasma level of hemoglobin, total CO₂ content, alkaline phosphatase, and corrected calcium were independent variables for serum OPG in multivariate linear regression. Reciprocally, the serum OPG was positively associated with baPWV in multivariate linear regression. The baPWV in the 3rd and 4th quartile groups of serum OPG were higher than that in the 1st quartile group after adjustments by age, sex and other significant factors for baPWV in linear mixed model.

CONCLUSION

Non-traditional, kidney-related cardiovascular risk factors in addition to traditional cardiovascular risk factors were related to serum level of OPG in CKD. Serum OPG level was significantly related to baPWV. Our study suggests that kidney-related factors involved in CKD-specific pathways for VC play a role in the increased secretion of OPG into circulation in patients with CKD.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01630486.

Prognostic value of bone- and vascular-derived molecular biomarkers in hemodialysis and renal transplant patients: a systematic review and meta-analysis

Background

Patients undergoing hemodialysis and kidney graft recipients are high-risk populations for cardiovascular and all-cause mortality. Fibroblast growth factor 23 (FGF23), osteoprotegerin (OPG), RANK ligand, osteopontin (OPN), Klotho protein and bone morphogenetic protein-7 (BMP-7) are bone- and vascular-derived molecular biomarkers that have been shown to be associated with cardiovascular surrogate end points; however, currently available data on the prognostic value of these biomarkers is inconsistent. The aim of the present study was to conduct a systematic review and meta-analysis in order to summarize the available evidence on the association of molecular biomarkers with mortality in individuals undergoing hemodialysis and renal transplant patients.

Methods

Two databases (MEDLINE and Embase) were systematically searched. Studies were eligible if the association of biomarker and mortality was reported as time-to-event data [hazard Ratio (HR)] or as effect size with a fixed time of follow-up [odds Ratio (OR)]. Abstracted HRs were converted onto a standard scale of effect and combined using a random effects model.

Results

From a total of 1170 studies identified in initial searches, 21 met the inclusion criteria. In hemodialysis patients, comparing the lower third with the upper third of baseline FGF23 distribution, pooled HRs (95% confidence intervals) were 1.94 (1.47, 2.56) for all-cause mortality and 2.4 (1.64, 3.51) for cardiovascular mortality. For the same comparison of baseline OPG distribution, pooled HRs were 1.8 (0.95, 3.39) for all-cause mortality and 2.53 (1.29, 4.94) for cardiovascular mortality. Reported risk estimates of RANK ligand, OPN, Klotho protein and BMP-7 were not suitable for pooling; however, only Klotho protein was significantly related to mortality. For kidney graft recipients, four studies that investigated the relationship of FGF23 and OPG with mortality were identified, all of which reported a significant association.

Conclusions

In hemodialysis patients, FGF23 is a predictor of all-cause and cardiovascular mortality, whereas the predictive value of OPG is restricted to cardiovascular mortality. Further studies are needed in order to gain insight into the prognostic value of these biomarkers in renal transplant recipients.

Elevated serum osteoprotegerin may predict peripheral arterial disease after kidney transplantation: a single-center prospective cross-sectional study in Taiwan

Background

Osteoprotegerin (OPG) is a potential biomarker for severity and complications of cardiovascular diseases. Peripheral arterial disease (PAD) is associated with an increased risk of death in kidney transplantation (KT) patients. This prospective cross-sectional study evaluated the relationship between serum OPG and PAD in KT patients.

Methods

Seventy-four KT patients were enrolled for this PAD study. Fasting blood samples were obtained to measure serum OPG levels by using enzyme-linked immunosorbent assay kits. The ankle-brachial index (ABI) of less than 0.9 was applied for PAD diagnosis.

Results

Thirteen patients (17.6%) were diagnosed with PAD. Diabetes (P = 0.025), smoking (P = 0.010), and increased OPG levels (P = 0.001) were significantly more frequent in the PAD group. Multivariate logistic regression analysis showed that serum OPG (odds ratio [OR], 1.336; 95% CI [1.108–1.611]; P = 0.002) and diabetes (OR, 7.120; 95% CI [1.080–46.940]; P = 0.041) were independent predictors of PAD in KT patients. The area under the receiver operating characteristic (ROC) curve determined that the probability of a serum OPG level of 7.117 pg/L in predicting PAD in KT patients was 0.799 (95% CI [0.690–0.884]; P < 0.001).

Discussion

Exploration of reliable biomarkers for early identification of vascular risk is crucial for KT patients. Elevated serum OPG levels may predict PAD in KT patients with cutoff value of 7.117 pg/L.

Thoracic endovascular aortic repair for type B aortic dissection after renal transplantation

Thoracic endovascular repair (TEVAR) is an effective treatment for type B aortic dissection (TBAD). Here, we evaluated the early-midterm effectiveness and safety of TEVAR for treating TBAD patients after renal transplantation. Six patients with TBAD treated with TEVAR after renal transplantation were recruited between February 2012 and December 2016. They were then followed up with clinical examinations and computed tomography angiography (CTA). TEVAR was successfully performed in all patients (100%), and the primary tear sites were well covered by stents with or without coverage of the left subclavian artery. No severe complications occurred in any patient during perioperative period. The one-year survival rate was 100%, one patient died of renal graft failure and heart failure four years after TEVAR; the remaining five patients (83.3%) survived and exhibited no severe complications. Our findings show that TEVAR provides satisfactory short-midterm results for TBAD patients after renal transplantation. Moreover, our experience shows that it need relative longer proximal landing zone to prevent the endoleak and recurrence. However, regular hematodialysis, long-term immunosuppressive therapy, and blood pressure control remain crucial factors to prolong survival. Long-term follow-up studies are needed to evaluate the long-term prognosis in these patients.

Nutritional Vitamin D in Renal Transplant Patients: Speculations and Reality

Reduced levels of nutritional vitamin D are commonly observed in most chronic kidney disease (CKD) patients and particularly in patients who have received a kidney transplant (KTx). In the complex clinical scenario characterizing the recipients of a renal graft, nutritional vitamin D deficiency has been put in relation not only to the changes of mineral and bone metabolism (MBM) after KTx, but also to most of the medical complications which burden KTx patients. In fact, referring to its alleged pleiotropic (non-MBM related) activities, vitamin D has been claimed to play some role in the occurrence of cardiovascular, metabolic, immunologic, neoplastic and infectious complications commonly observed in KTx recipients. Furthermore, low nutritional vitamin D levels have also been connected with graft dysfunction occurrence and progression. In this review, we will discuss the purported and the demonstrated effects of native vitamin D deficiency/insufficiency in most of the above mentioned fields, dealing separately with the MBM-related and the pleiotropic effects.

Pre-Transplant Assessment of Vascular Calcification as a Risk Factor of Mortality, Graft Loss, and Cardiovascular Events in Renal Transplant Recipients

BACKGROUND

Vascular calcification (VC) is known as an independent predictor of mortality in patients undergoing hemodialysis; nevertheless, there is a lack of studies about the impact of vascular calcification in renal transplant recipients, and none of them use the Kauppila Index (KI) as a predictor of patient and graft prognosis.

METHODS

We conducted an observational, retrospective study of 119 renal transplants, evaluating abdominal aortic calcifications (L4-S1) with the KI. We established 2 categories: absence (KI = 0-2) and presence (KI = 3-24) of VCs before transplantation. We analyzed the impact of calcification in graft and patient survival, new-onset diabetes mellitus, hypertension, cardiovascular events, renal function, and mineral metabolism.

RESULTS

VCs were observed in 50 patients (42%) before renal transplantation. Patients with VCs were older, but no statistical differences were found in the pre-transplant study between sex, diabetes, body mass index, and cardiovascular events. We found a major patient survival (limited to first 2 years after transplantation), graft survival, and death-censored graft survival in those without VCs (P = .037, P = .015, and P = .023, respectively). In line with results, a higher incidence of major cardiovascular events (MACE) and cardiovascular death was observed in the group with preexisting calcification (P = .016/P = .019). In the multivariable analysis, VCs were not an independent predictor for graft loss, death-censored graft loss, or major cardiovascular events.

CONCLUSIONS

Simple evaluation of VCs with the use of the KI at the time of transplantation relates with graft and patient survival and with MACE after renal transplantation.

A Prospective Cohort Study of Mineral Metabolism After Kidney Transplantation

Kidney transplantation corrects or improves many complications of chronic kidney disease, but its impact on disordered mineral metabolism is incompletely understood.

The prevalence of posttransplant hyperparathyroidism was 86% at 12 months (PTH >65 pg/ml) but only 40% (PTH >130 mg/dL) in the absence of cinacalcet, vitamin D sterols, or parathyroidectomy. Intact fibroblast growth factor 23 decreased rapidly to G40 pg/ml by 3 months posttransplant. Supplemental digital content is available in the text.

High Serum Osteoprotegerin Is Associated with Arterial Stiffness in Kidney Transplant Patients

Osteoprotegerin (OPG) is a cytokine that regulates bone resorption by inhibiting osteoclastogenesis, and OPG has been implicated in the process that causes vascular stiffness. An increase in serum OPG level has been associated with the development of arterial stiffness. Kidney transplant (KT) patients are susceptible to aortic stiffness, which is considered to be a predictor of cardiovascular events in this patient population. Carotid-femoral pulse wave velocity (cfPWV) has emerged as a gold standard for non-invasive evaluation of aortic stiffness. The aim of this study was to evaluate the relationship between serum OPG concentration and cfPWV among KT patients. Fasting blood samples were obtained from 57 KT patients and their cfPWV was measured using applanation tonometry. The serum OPG levels were measured using an enzyme-linked immunosorbent assay. Univariable linear regression analysis showed that the cfPWV in KT patients was significantly and positively correlated with age, body weight, waist circumference, body mass index, log-creatinine, systolic blood pressure, diastolic blood pressure, pulse pressure, and the log-OPG concentration. KT patients with metabolic syndrome had higher cfPWV values than those without metabolic syndrome (P = 0.036), which indicates a higher incidence of aortic stiffness in this patient population. Multivariable forward stepwise linear regression analysis of the significant variables showed that the log-OPG (P = 0.001), the log-creatinine (P = 0.004), and the SBP (P = 0.005) remained as independent and positive predictors of cfPWV values. These findings indicate that serum OPG levels are positively associated with cfPWV in KT patients.

Inflammation and the bone-vascular axis in end-stage renal disease

Bone loss and vascular calcification coincide in patients with end-stage renal disease, similar as to what is observed in the general population. In the present bone biopsy study, we provide further evidence that (micro-)inflammation may represent a common soil for both diseases.

INTRODUCTION

Vascular calcification is a common complication of end-stage renal disease (ESRD) and is predictive of subsequent cardiovascular disease and mortality. Mounting evidence linking bone disorders with vascular calcification has contributed to the development of the concept of the bone-vascular axis. Inflammation is involved in the pathogenesis of both disorders. The aim of the present study was to evaluate the relationship between aortic calcification, inflammation, and bone histomorphometry in patients with ESRD.

METHODS

Parameters of inflammation and mineral metabolism were assessed in 81 ESRD patients (55 ± 13 year, 68 % male) referred for renal transplantation. Static bone histomorphometry parameters were determined on transiliac bone biopsies performed during the transplant procedure. Aortic calcification was quantified on lateral lumbar X-rays using the Kauppila method.

RESULTS

Aortic calcification, low bone turnover, and low bone area were observed in 53, 37, and 21 % of patients respectively. Inflammatory markers were found to be independently associated with aortic calcification (hsIL-6) and low bone area (TNF-α). Low bone area associated with aortic calcification, independent of age, diabetes, and inflammation.

CONCLUSIONS

Low bone area and inflammation associates with aortic calcification, independent of each other and traditional risk factors. Our data emphasize the role of (micro-)inflammation in the bone-vascular axis in CKD.

Receptor activator of nuclear factor κB ligand/osteoprotegerin axis and vascular calcifications in patients with chronic kidney disease

Vascular calcifications are commonly observed in patients with chronic kidney disease (CKD) and contribute to the excessive cardiovascular morbidity and mortality rates observed in these patients populations. Although the pathogenetic mechanisms are not yet fully elucidated, recent evidence suggests a link between bone metabolism and the development and progression of vascular calcifications. Moreover, accumulating data indicate that receptor activator of nuclear factor κB ligand/osteoprotegerin axis which plays essential roles in the regulation of bone metabolism is also involved in extra-osseous bone formation. Further studies are required to establish the prognostic significance of the above biomarkers as predictors of the presence and severity of vascular calcifications in CKD patients and of cardiovascular morbidity and mortality. Moreover, randomized clinical trials are needed to clarify whether inhibition of osteoclast activity will protect from vascular calcifications.

Serum osteoprotegerin levels associated with the aortic augmentation index in renal transplant recipients

OBJECTIVES

Arterial stiffness is recognized as an independent risk factor for cardiovascular morbidity and mortality. Recent studies found that osteoprotegerin (OPG) is associated with arterial stiffness and may reflect endothelial dysfunction. The aim of this study was to evaluate the relationship between fasting serum OPG levels and the aortic augmentation index (AIx) in renal transplant recipients.

MATERIALS AND METHODS

Fasting blood samples were obtained from 66 renal transplant recipients. The aortic AIx was measured using a validated tonometry system (SphygmoCor). Serum OPG levels were measured using a commercial enzyme-linked immunosorbent assay kit.

RESULTS

Univariate linear analysis of the aortic AIx in renal transplant recipients revealed that body fat mass (r = 0.377, p = 0.002), aortic diastolic blood pressure (DBP; r = 0.307, p = 0.020), triglycerides (r = 0.260, p = 0.035), and logarithmically transformed OPG (log-OPG, r = 0.402, p < 0.001) were positively correlated, whereas height (r = 0.361, p = 0.004) and body weight (r = 0.212, p = 0.041) were negatively correlated with the aortic AIx in renal transplant recipients. Multivariate forward stepwise linear regression analysis of the factors significantly associated with the aortic AIx showed that log-OPG (R2 = 0.213, p < 0.001), height (R2 = 0.081, p = 0.009), and aortic DBP (R2 = 0.058, p = 0.022) were independent predictors of the aortic AIx in renal transplant recipients.

CONCLUSION

These results suggest that the serum fasting OPG level is associated with the aortic AIx in renal transplant recipients.

Sclerostin Serum Levels and Vascular Calcification Progression in Prevalent Renal Transplant Recipients

CONTEXT

Vascular calcification (VC) is prevalent and progressive in renal transplant recipients (RTRs). Recent cross-sectional data suggest that activated Wnt signaling contributes to VC.

OBJECTIVE

The objective was to investigate whether circulating levels of the Wnt antagonist sclerostin associate with progression of VC.

DESIGN

This was a post hoc analysis of the longitudinal observational Brussels Renal Transplant Cohort study.

SETTING

The setting was a tertiary care academic hospital.

PATIENTS

Coronary artery calcification and aorta calcification were measured by multislice spiral computerized tomography in 268 prevalent RTRs (age, 53 ± 13 y; 61% male) at baseline and remeasured in 189 patients after a median follow-up of 4.4 years. Baseline serum sclerostin levels were assessed on stored blood samples. Regression analysis was performed to identify determinants of baseline VC and progression.

MAIN OUTCOME MEASURE

The main outcome measure was progression of VC.

RESULTS

VC was present in up to 84% of participants at baseline. Almost half of the patients showed progression of VC, according to Hokanson criteria. The cross-sectional analysis at baseline demonstrated a direct association between sclerostin levels and VC score in univariate analysis, which became inverse after adjustment for age, gender and PTH level. Remarkably, a lower sclerostin level was identified as an independent determinant of a higher baseline aorta calcification score in the final regression model. Moreover, baseline sclerostin levels showed an inverse association with VC progression, at least after adjustment for traditional risk factors.

CONCLUSIONS

Serum sclerostin levels inversely associated with VC burden and progression in prevalent RTRs after adjustment for traditional risk factors. Our data corroborate previous findings in nontransplanted chronic kidney disease patients and support the notion that sclerostin may be up-regulated in the vascular wall during the VC process as part of a local counterregulatory mechanism directed to suppress VC. Additional clinical and experimental data are required for confirmation.

Serum osteoprotegerin is associated with pulse pressure in kidney transplant recipients

Pulse pressure (PP) reflects increased large artery stiffness, which is caused, in part, by arterial calcification in patients with chronic kidney disease. PP has been shown to predict both cardiovascular and cerebrovascular events in various patient populations, including kidney transplant (KTX) recipients. Osteoprotegerin (OPG) is a marker and regulator of arterial calcification, and it is related to cardiovascular survival in hemodialysis patients. Here we tested the hypothesis that OPG is associated with increased pulse pressure. We cross-sectionally analyzed the association between serum OPG and PP in a prevalent cohort of 969 KTX patients (mean age: 51 +/- --13 years, 57% male, 21% diabetics, mean eGFR 51 +/- 20 ml/min/1.73 m2). Independent associations were tested in a linear regression model adjusted for multiple covariables. PP was positively correlated with serum OPG (rho = 0.284, p < 0.001). Additionally, a positive correlation was seen between PP versus age (r = 0.358, p < 0.001), the Charlson Comorbidity Index (r = 0.232, p < 0.001), serum glucose (r = 0.172, p < 0.001), BMI (r = 0.133, p = 0.001) and serum cholesterol (r = 0.094, p = 0.003). PP was negatively correlated with serum Ca, albumin and eGFR. The association between PP and OPG remained significant after adjusting for multiple potentially relevant covariables (beta = 0.143, p < 0.001). We conclude that serum OPG is independently associated with pulse pressure in kidney transplant recipients.

Vascular calcification: from pathophysiology to biomarkers

The link between vascular calcification (VC) and increased mortality is now well established. Over time, as clinical importance of this phenomenon has begun to be fully considered, scientists have highlighted more and more physiopathological mechanisms and signaling pathways that underlie VC. Several conditions such as diabetes, dyslipidemia and renal diseases are undoubtedly identified as predisposing factors. But even if the process is better understood, many questions still remain unanswered. This review briefly develops the various theories that attempt to explain mineralization genesis. Nonetheless, the main purpose of the article is to provide a profile of the various existing biomarkers of VC. Indeed, in the past years, a lot of inhibitors and promoters, which form a dense and interconnected network, were identified. Given importance to assess and control mineralization process, a focusing on accumulated knowledge of each marker seemed to be necessary. Therefore, we tried to define their respective role in the physiopathology and how they can contribute to calcification risk assessment. Among these, Klotho/fibroblast growth factor-23, fetuin-A, Matrix Gla protein, Bone morphogenetic protein-2, osteoprotegerin, osteopontin, osteonectin, osteocalcin, pyrophosphate and sclerostin are specifically discussed.

A randomized study evaluating cinacalcet to treat hypercalcemia in renal transplant recipients with persistent hyperparathyroidism

Persistent hyperparathyroidism (HPT) after kidney transplantation (KTx) is associated with hypercalcemia, hypophosphatemia and abnormally high levels of parathyroid hormone (PTH). In this randomized trial, cinacalcet was compared to placebo for the treatment of hypercalcemia in adult patients with persistent HPT after KTx. Subjects were randomized 1:1 to cinacalcet or placebo with randomization stratified by baseline corrected total serum calcium levels (≤11.2 mg/dL [2.80 mmol/L] or >11.2 mg/dL [2.80 mmol/L]). The primary end point was achievement of a mean corrected total serum calcium value<10.2 mg/dL (2.55 mmol/L) during the efficacy period. The two key secondary end points were percent change in bone mineral density (BMD) at the femoral neck and absolute change in phosphorus; 78.9% cinacalcet- versus 3.5% placebo-treated subjects achieved the primary end point with a difference of 75.4% (95% confidence interval [CI]: 63.8, 87.1), p<0.001. There was no statistical difference in the percent change in BMD at the femoral neck between cinacalcet and placebo groups, p=0.266. The difference in the change in phosphorus between the two arms was 0.45 mg/dL (95% CI: 0.26, 0.64), p<0.001 (nominal). No new safety signals were detected. In conclusion, hypercalcemia and hypophosphatemia were effectively corrected after treatment with cinacalcet in patients with persistent HPT after KTx.

Osteoprotegerin and kidney disease

Vascular calcification in chronic kidney disease (CKD) patients is associated to increased mortality. Osteoprotegerin (OPG) is a soluble tumor necrosis factor (TNF) superfamily receptor that inhibits the actions of the cytokines receptor activator of nuclear factor kappa-B ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL) by preventing their binding to signaling receptors in the cell membrane. OPG-deficient mice display vascular calcification while OPG prevented calcification of cultured vascular smooth muscle cells and protected kidney cells from TRAIL-induced death. OPG may be a biomarker in patients with kidney disease. Circulating OPG is increased in predialysis, dialysis and transplant CKD patients and may predict vascular calcification progression and patient survival. By contrast, circulating OPG is decreased in nephrotic syndrome. In addition, free and exosome-bound urinary OPG is increased in human kidney disease. Increased urinary OPG has been associated with lupus nephritis activity. Despite the association of high OPG levels with disease, experimental functional information available suggests that OPG might be protective in kidney disease and in vascular injury in the context of uremia. Thus, tissue injury results in increased OPG, while OPG may protect from tissue injury. Recombinant OPG was safe in phase I randomized controlled trials. Further research is needed to fully define the therapeutic and biomarker potential of OPG in patients with kidney disease.