Recent Changes in Chronic Kidney Disease–Mineral and Bone Disorders and Associated Fractures After Kidney Transplantation

Post-Transplant Bone Disease in Kidney Transplant Recipients: Diagnosis and Management

Kidney transplantation is the preferred gold standard modality of treatment for kidney failure. Bone disease after kidney transplantation is highly prevalent in patients living with a kidney transplant and is associated with high rates of hip fractures. Fractures are associated with increased healthcare costs, morbidity and mortality. Post-transplant bone disease (PTBD) includes renal osteodystrophy, osteoporosis, osteonecrosis and bone fractures. PTBD is complex as it encompasses pre-existing chronic kidney disease-mineral bone disease and compounding factors after transplantation, including the use of immunosuppression and the development of de novo bone disease. After transplantation, the persistence of secondary and tertiary hyperparathyroidism, renal osteodystrophy, relative vitamin D deficiency and high levels of fibroblast growth factor-23 contribute to post-transplant bone disease. Risk assessment includes identifying both general risk factors and kidney-specific risk factors. Diagnosis is complex as the gold standard bone biopsy with double-tetracycline labelling to diagnose the PTBD subtype is not always readily available. Therefore, alternative diagnostic tools may be used to aid its diagnosis. Both non-pharmacological and pharmacological therapy can be employed to treat PTBD. In this review, we will discuss pathophysiology, risk assessment, diagnosis and management strategies to manage PTBD after kidney transplantation.

Associated factors of osteoporosis and vascular calcification in patients awaiting kidney transplantation

INTRODUCTION

Pretransplant osteoporosis and vascular calcification probably increase the risk of fractures and cardiovascular events after kidney transplantation. In the present study, we investigated the related risk factors of osteoporosis and vascular calcification among end-stage renal disease (ESRD) patients awaiting kidney transplantation.

METHODS

A total of 221 ESRD patients (age, 43.4 ± 14.3 years; 125 males and 96 females; median dialysis duration, 61.0 m) awaiting kidney transplantation were enrolled in this cross-sectional study. Serum levels of bone turnover markers and intact parathyroid hormone (iPTH) were analyzed from fasting morning blood samples. Dual-energy X-ray absorptiometry was used to measure bone mineral density (BMD). Vascular calcification was evaluated by lateral abdominal radiography and plain radiographic films of the pelvis and hands.

RESULTS

The osteoporosis prevalence was 27.6% in this cohort of kidney transplantation candidates, and the prevalence of vascular calcification was 51.1%. The related factors for osteoporosis and vascular calcification were similar and included older age, longer dialysis duration, parathyroid hyperplasia, and higher levels of iPTH and bone turnover markers. In the multivariable regression model, age and iPTH were independent risk predictors of both vascular calcification and osteoporosis. There were strong, positive correlations between iPTH and all bone turnover markers. The moderate and severe hyperparathyroidism (iPTH 600-1499 pg/ml and iPTH 1500 pg/ml) were related to reduced serum albumin and hemoglobin levels.

CONCLUSION

The involvement of high iPTH levels in vascular calcification, osteoporosis, and malnutrition indicated the need of treating hyperparathyroidism early in patients awaiting kidney transplantation. Prospective studies are needed to further examine the utility of bone turnover markers.

Urinary collagen peptides: Source of markers for bone metabolic processes in kidney transplant recipients

INTRODUCTION

Kidney transplant recipients (KTRs) are at an increased risk of fractures. Total urinary hydroxyproline excretion served as marker for bone resorption (BR) but was replaced by β-CrossLaps (CTX), a C-terminal collagen α-1(I) chain (COL1A1) telopeptide. We investigated the low-molecular-weight urinary proteome for peptides associated with changes in bone metabolism after kidney transplantation.

METHODS

Clinical and laboratory data including serum levels of CTX in 96 KTR from two nephrology centers were correlated with signal intensities of urinary peptides identified by capillary electrophoresis mass spectrometry.

RESULTS

Eighty-two urinary peptides were significantly correlated with serum CTX levels. COL1A1 was the predominant peptide source. Oral bisphosphonates were administered for decreased bone density in an independent group of 11 KTR and their effect was evaluated on the aforementioned peptides. Study of the peptides cleavage sites revealed a signature of Cathepsin K and MMP9. Seventeen of these peptides were significantly associated with bisphosphonate treatment, all showing a marked reduction in their excretion levels compared to baseline.

DISCUSSION

This study provides strong evidence for the presence of collagen peptides in the urine of KTR that are associated with BR and that are sensitive to bisphosphonate treatment. Their assessment might become a valuable tool to monitor bone status in KTR.

Impact of Nocturnal Polyuria and Sleep Quality in Kidney Transplant Recipients With Nocturia

BACKGROUND

To investigate the quality of life (QOL) of patients with nocturia after kidney transplantation (KT) and the association between nocturnal polyuria and sleep quality.

METHODS

In a cross-sectional study, a patient who consented was evaluated using the following items: international prostate symptom QOL score, nocturia-quality of life score, overactive bladder symptom score, Pittsburgh sleep quality index, bladder diary, uroflowmetry, and bioimpedance analysis. Clinical and laboratory data were obtained from medical charts.

RESULTS

Forty-three patients were included in the analysis. Approximately 25% of patients urinated once at night, and 58.1% had nocturia twice. Nocturnal polyuria was observed in 86.0% of patients, and overactive bladder was observed in 23.3% of patients. According to the Pittsburgh sleep quality Index, 34.9% of patients had poor sleep quality. Multivariate analysis revealed that patients with nocturnal polyuria tended to have a high estimated glomerular filtration rate (P = .058). On the other hand, multivariate analysis for poor sleep quality revealed that high body fat percentage and low nocturia-quality of life total score were independently correlated factors (P = .008 and P = .012, respectively). Furthermore, the patients with nocturia ≥3/night were significantly older than those with nocturia ≤2/night (P = .022).

CONCLUSION

Nocturnal polyuria, poor sleep quality, and aging may decrease the QOL of patients with nocturia after KT. Further investigations, including optimal water intake and interventions, can lead to better management after KT.

Bone volume, mineral density, and fracture risk after kidney transplantation

Background

Disordered mineral metabolism reverses incompletely after kidney transplantation in numerous patients. Post-transplantation bone disease is a combination of pre-existing chronic kidney disease and mineral disorder and often evolving osteoporosis. These two frequently overlapping conditions increase the risk of post-transplantation fractures.

Material and methods

We studied the prevalence of low bone volume in bone biopsies obtained from kidney transplant recipients who were biopsied primarily due to the clinical suspicion of persistent hyperparathyroidism between 2000 and 2015 at the Hospital District of Helsinki and Uusimaa. Parameters of mineral metabolism, results of dual-energy x-ray absorptiometry scans, and the history of fractures were obtained concurrently.

One hundred nine bone biopsies taken at a median of 31 (interquartile range, IQR, 18–70) months after transplantation were included in statistical analysis. Bone turnover was classified as high in 78 (72%) and normal/low in 31 (28%) patients. The prevalence of low bone volume (n = 47, 43%) was higher among patients with low/normal turnover compared to patients with high turnover [18 (58%) vs. 29 (37%), P = 0.05]. Thirty-seven fragility fractures in 23 (21%) transplant recipients corresponding to fracture incidence 15 per 1000 person-years occurred during a median follow-up 9.1 (IQR, 6.3–12.1) years. Trabecular bone volume did not correlate with incident fractures. Accordingly, low bone mineral density at the lumbar spine correlated with low trabecular bone volume, but not with incident fractures. The cumulative corticosteroid dose was an important determinant of low bone volume, but not of incident fractures.

Conclusions

Despite the high prevalence of trabecular bone loss among kidney transplant recipients, the number of fractures was limited. The lack of association between trabecular bone volume and fractures suggests that the bone cortical compartment and quality are important determinants of bone strength and post-transplantation fracture.

Bone and Mineral Disorder in Renal Transplant Patients: Overview of Pathology, Clinical, and Therapeutic Aspects

Renal transplantation (RTx) allows us to obtain the resolution of the uremic status but is not frequently able to solve all the metabolic complications present during end-stage renal disease. Mineral and bone disorders (MBDs) are frequent since the early stages of chronic kidney disease (CKD) and strongly influence the morbidity and mortality of patients with CKD. Some mineral metabolism (MM) alterations can persist in patients with RTx (RTx-p), as well as in the presence of complete renal function recovery. In those patients, anomalies of calcium, phosphorus, parathormone, fibroblast growth factor 23, and vitamin D such as bone and vessels are frequent and related to both pre-RTx and post-RTx specific factors. Many treatments are present for the management of post-RTx MBD. Despite that, the guidelines that can give clear directives in MBD treatment of RTx-p are still missed. For the future, to obtain an ever-greater individualisation of therapy, an increase of the evidence, the specificity of international guidelines, and more uniform management of these anomalies worldwide should be expected. In this review, the major factors related to post-renal transplant MBD (post-RTx-MBD), the main mineral metabolism biochemical anomalies, and the principal treatment for post-RTx MBD will be reported.

Clinical Prediction of High-Turnover Bone Disease After Kidney Transplantation

Bone histomorphometric analysis is the most accurate method for the evaluation of bone turnover, but non-invasive tools are also required. We studied whether bone biomarkers can predict high bone turnover determined by bone histomorphometry after kidney transplantation. We retrospectively evaluated the results of bone biopsy specimens obtained from kidney transplant recipients due to the clinical suspicion of high bone turnover between 2000 and 2015. Bone biomarkers were acquired concurrently. Of 813 kidney transplant recipients, 154 (19%) biopsies were taken at a median of 28 (interquartile range, 18-70) months after engraftment. Of 114 patients included in the statistical analysis, 80 (70%) presented with high bone turnover. Normal or low bone turnover was detected in 34 patients (30%). For discriminating high bone turnover from non-high, alkaline phosphatase, parathyroid hormone, and ionized calcium had the areas under the receiver operating characteristic curve (AUCs) of 0.704, 0.661, and 0.619, respectively. The combination of these markers performed better with an AUC of 0.775. The positive predictive value for high turnover at a predicted probability cutoff of 90% was 95% while the negative predictive value was 35%. This study concurs with previous observations that hyperparathyroidism with or without hypercalcemia does not necessarily imply high bone turnover in kidney transplant recipients. The prediction of high bone turnover can be improved by considering alkaline phosphatase levels, as presented in the logistic regression model. If bone biopsy is not readily available, this model may serve as clinically available tool in recognizing high turnover after engraftment.

Patterns of renal osteodystrophy one year after kidney transplantation

BACKGROUND

Renal osteodystrophy is considered common, but is not well characterized, in contemporary kidney transplant recipients. This study reports extensively on bone phenotype by bone histomorphometry, bone densitometry, and novel bone biomarkers 1 year after kidney transplantation.

METHODS

A transiliac bone biopsy and dual energy x-ray absorptiometry were performed in 141 unselected kidney transplant recipients in this observational cohort study. Blood and 24 hr urine samples were collected simultaneously.

RESULTS

Median age was 57 ± 11 years, 71% were men, and all were of Caucasian ethnicity. Bone turnover was normal in 71% of patients, low in 26%, and high in just four cases (3%). Hyperparathyroidism with hypercalcemia was present in 13% of patients, of which one had high bone turnover. Delayed bone mineralization was detected in 16% of patients, who were characterized by hyperparathyroidism (137 vs. 53 ρg/mL), a higher fractional excretion of phosphate (40 vs. 32%), and lower levels of phosphate (2.68 vs 3.18 mg/dL) and calcidiol (29 vs. 37 ng/mL) compared to patients with normal bone mineralization. Osteoporosis was present in 15-46% of patients, with the highest prevalence at the distal skeleton. The proportion of osteoporotic patients was comparable across categories of bone turnover and mineralization.

CONCLUSION

The majority of kidney transplant recipients, including patients with osteoporosis, have a normal bone turnover at 1-year post-transplant. Low bone turnover is seen in a substantial subset, while high bone turnover is rare. Vitamin D deficiency and hypophosphatemia represent potential interventional targets to improve bone health post-transplant.

Mineral Bone Disorders in Kidney Transplantation

Bone disease after kidney transplantation is associated with an increased risk of fractures, morbidity, and mortality. Its pathophysiology is complex, involving multiple contributors including pretransplant bone disease, immunosuppressive medications, and changes in the parathyroid-bone-kidney axis. Risk scores, bone turnover markers, and noninvasive imaging modalities are only able to partially predict the fracture risk in kidney transplant recipients. The optimal management of bone disease after kidney transplantation has not yet been established, with only a limited number of randomized clinical trials evaluating the efficacy of treatment regimens in kidney transplant recipients. This review focuses on the pathophysiology, evaluation, prevention, and treatment of post-kidney transplant mineral and bone disease as guided by recent evidence.

Bone Mineral Density and Aortic Calcification: Evidence for a Bone-vascular Axis After Kidney Transplantation

BACKGROUND

Chronic kidney disease mineral and bone disorders (CKD-MBD) and vascular calcification are often seen in kidney transplantation recipients (KTR). This study focused on the bone-vascular axis hypothesis, the pathophysiological mechanisms driving both bone loss and vascular calcification, supported by an association between lower bone mineral density (BMD) and higher risk of vascular calcification.

METHODS

KTR referred for a dual-energy X-ray absorptiometry procedure within 6 mo after transplantation were included in a cross-sectional study (2004-2014). Areal BMD was measured at the proximal femur, and abdominal aortic calcification (AAC) was quantified (8-points score) from lateral single-energy images of the lumbar spine. Patients were divided into 3 AAC categories (negative-AAC: AAC 0; low-AAC: AAC 1-3; and high-AAC: AAC 4-8). Multivariable-adjusted multinomial logistic regression models were performed to study the association between BMD and AAC.

RESULTS

We included 678 KTR (51 ± 13 y old, 58% males), 366 (54%) had BMD disorders, and 266 (39%) had detectable calcification. High-AAC was observed in 9%, 11%, and 25% of KTR with normal BMD, osteopenia, and osteoporosis, respectively (P < 0.001). Higher BMD (T-score, continuous) was associated with a lower risk of high-AAC (odds ratio 0.61, 95% confidence interval 0.42-0.88; P = 0.008), independent of age, sex, body mass index, estimated glomerular filtration rate, and immunosuppressive therapy. KTR with normal BMD were less likely to have high-AAC (odds ratio 0.24, 95% confidence interval 0.08-0.72; P = 0.01).

CONCLUSIONS

BMD disorders are highly prevalent in KTR. The independent inverse association between BMD and AAC may provide evidence to point toward the existence, while highlighting the clinical and epidemiological relevance, of a bone-vascular axis after kidney transplantation.

Behavior of Bone Mineral Metabolism in Renal Posttransplantation Patients with Severe Hyperparathyroidism

BACKGROUND

Secondary hyperparathyroidism usually improves after renal transplantation. When it becomes persistent, it is associated with deleterious effects on the graft, bone demineralization, fractures, calcifications, and cardiovascular events. In this study we describe the development of cases of severe hyperparathyroidism occurring after renal transplantation.

OBJECTIVE

To describe the behavior of the indicators of bone mineral metabolism in the renal transplantation patient with severe secondary hyperparathyroidism before transplantation, treated with or without parathyroidectomy.

METHODS

This is a case series study conducted between 2004 and 2017 on renal transplantation patients presenting with PTH > 800 pg/mL or who required pretransplantation parathyroidectomy.

RESULTS

We found 36 patients with severe hyperparathyroidism, corresponding to 10.8% of transplantation recipients, with an average age of 54.5 years (±12.35). The median follow-up after transplantation was 128 months (16-159). Fourteen patients underwent parathyroidectomy before transplantation, with a median intact parathyroid hormone at the time of transplantation of 56 (3-382) pg/mL, with more episodes of hypocalcaemia and oral calcium requirement. The other patients were transplanted with a median intact parathyroid hormone of 1010 (range, 802-1919) pg/mL, reaching a median intact parathyroid hormone of 98.8 (43.8-203) at 3 years of follow-up. Only 2 patients underwent parathyroidectomy for tertiary hyperparathyroidism.

CONCLUSIONS

Renal transplantation improves secondary hyperparathyroidism. Sixty-eight percent of patients presented PTH of less than 130 pg/mL after renal transplantation. Only 2 patients underwent posttransplantation parathyroidectomy.

Long-term renal graft outcome after parathyroidectomy - a retrospective single centre study

BACKGROUND

Surgical correction of hyperparathyroidism after kidney transplantation has been associated with significant graft function decline. We examined the effects of parathyroidectomy on short- and long-term graft function and its potential predictors.

METHODS

For this retrospective, monocentric study we identified 48 (5.5%) out of 892 patients from our protocol biopsy program who received renal transplantation between 2000 and 2007, with parathyroidectomy after transplantation. Data from up to three years after parathyroidectomy was collected and analyzed with multivariable linear regression analyses.

RESULTS

Main indications for parathyroidectomy were hypercalcemia and graft calcifications. Parathyroidectomy was successful in 47 patients, with a median drop in serum intact parathormone (iPTH) from 394 to 21 pg/ml. Mean estimated glomerular fitration rate (eGFR) before parathyroidectomy was 60 ± 26 ml/min. At three months after parathyroidectomy, the eGFR was 46 ± 18 ml/min (p < 0.001) but remained stable at one and three years (50 ± 20; 49 ± 20 ml/min). The median annual eGFR change was - 0.5 ml/min before and + 1.0 ml/min after parathyroidectomy. Multivariable modeling identified high iPTH levels and higher eGFR before parathyroidectomy as predictors of the eGFR drop after parathyroidectomy. Lower graft function twelve months after parathyroidectomy was predicted by the eGFR before and the iPTH drop after surgery.

CONCLUSIONS

These results indicate that the extent of parathyroidectomy is critical and too much lowering of iPTH should be avoided by timely parathyroidectomy, before reaching extreme high iPTH values. In view of the observed loss of eGFR, parathyroidectomy can be considered safe in patients with an eGFR above 30 ml/min.

Changes in Bone Histomorphometry after Kidney Transplantation

BACKGROUND AND OBJECTIVES

Over the past decade, the management of CKD-mineral and bone disorder has changed substantially, altering the pattern of bone disease in CKD. We aimed to evaluate the natural history of kidney bone disease in contemporary kidney transplant recipients and patients on dialysis.

DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS

Sixty one patients on dialysis who were referred to kidney transplantation participated in this prospective cohort study during November 2009 and December 2010. We performed baseline bone biopsies while the patients were on dialysis and repeated the procedure in 56 patients at 2 years after kidney transplantation or 2 years after baseline if transplantation was not performed. Measurements of mineral metabolism and bone turnover, as well as dual energy x-ray absorptiometry scans, were obtained concurrently.

RESULTS

A total of 37 out of 56 participants received a kidney transplant, of which 27 underwent successful repeat bone biopsy. The proportion of patients with high bone turnover declined from 63% at baseline to 19% at 2 years after kidney transplantation, whereas the proportion of those with low bone turnover increased from 26% to 52%. Of 19 participants remaining on dialysis after 2 years, 13 underwent successful repeat biopsy. The proportion of patients remaining on dialysis with high bone turnover decreased from 69% to 31%, and low bone turnover increased from 8% to 38%. Abnormal bone mineralization increased in transplant recipients from 33% to 44%, but decreased in patients remaining on dialysis from 46% to 15%. Trabecular bone volume showed little change after transplantation, but low bone volume increased in patients remaining on dialysis. Bone mineral density did not correlate with histomorphometric findings.

CONCLUSIONS

Bone turnover decreased over time both in patients remaining on dialysis and in kidney transplant recipients. Bone mineral density and bone biomarkers were not associated with bone metabolism changes detected in bone biopsy specimens.

Association between malnutrition-inflammation score and risk of subsequent self-reported bone fractures in prevalent kidney transplant recipients

Chronic inflammation and protein energy wasting (PEW) syndrome are common in kidney transplant recipients (KTR). The presence of inflammation and PEW syndrome can directly affect bone resorption and bone formation, leading to bone loss and fractures. We showed PEW is independently associated with new clinically detected bone fractures in prevalent KTR.

INTRODUCTION

Kidney transplant recipients (KTR) have a 4-fold higher risk of fracture compared to the general population. Chronic inflammation and PEW syndrome are common in KTR and are associated with poor outcomes. We hypothesized that the Malnutrition-Inflammation Score (MIS), a validated measure of PEW, is associated with higher risk of bone fractures in KTR.

METHODS

This prospective cohort study included 839 prevalent KTR from a Central European academic center. MIS, a semiquantitative instrument of PEW, was calculated at the study entry. Self-reported history of fractures was recorded during the 2-year follow-up period. The association between MIS and bone fractures was examined in logistic regression analyses with adjustment for age, gender, eGFR, smoking habits, history of pre-transplant bone fractures, and acute rejection.

RESULTS

Mean age was 51 ± 13 years, and 56% of patients were males with median (interquartile range) transplant vintage 69 (38-112) months, estimated glomerular filtration rate 55 ± 21 ml/min/1.73 m², and calculated MIS 3 (2-4) at enrollment. Fifty-five (7%) patients experienced self-reported bone fractures during the 2-year follow-up period. Higher MIS score showed linear association with increased risk of fracture. Each one-point higher MIS was associated with 23% higher risk of bone fractures (odds ratio (OR) and 95% CI 1.23, 1.12-1.34), which remained significant after multivariable adjustments (OR 1.17, 95% CI 1.06-1.29).

CONCLUSION

The MIS is independently associated with new clinically detected bone fractures in prevalent KTR.

Mineral and Bone Disease in Kidney Transplant Recipients

PURPOSE OF REVIEW

Despite metabolic improvements following kidney transplantation, transplant recipients still often suffer from complex mineral and bone disease after transplantation.

RECENT FINDINGS

The pathophysiology of post-transplant disease is unique, secondary to underlying pre-transplant mineral and bone disease, immunosuppression, and changing kidney function. Changes in modern immunosuppression regimens continue to alter the clinical picture. Modern management includes reducing cumulative steroid exposure and correcting the biochemical abnormalities in mineral metabolism. While bone mineral density screening appears to help predict fracture risk and anti-osteoporotic therapy appears to have a positive effect on bone mineral density, more data regarding specific treatment is necessary. Patients with mineral and bone disease after kidney transplantation require special care in order to properly manage and mitigate their mineral and bone disease. Recent changes in clinical management of transplant patients may also be changing the implications on patients' mineral and bone disease.

Management of mineral and bone disorders in renal transplant recipients

The management of post-transplantation bone disease is a complex problem that remains under-appreciated in clinical practice. In these patients, pre-existing metabolic bone disorder is further impacted by the use of immunosuppressive medications (glucocorticoids and calcineurin-inhibitors), variable post-transplantation renal allograft function and post-transplantation diabetes mellitus. The treatment of post-transplantation bone loss should begin pre-transplantation. All patients active on transplant waiting lists should be screened for bone disease. Patients should also be encouraged to take preventative measures against osteoporosis such as regular weight-bearing exercise, smoking cessation and reducing alcohol consumption. Biochemical abnormalities of disordered mineral metabolism should be corrected prior to transplantation wherever possible, and because these abnormalities commonly persist, post transplant hypophosphatemia, persistent hyperparathyroidism and low vitamin D levels should be regularly monitored and treated. Bone loss is greatest in the first 6-12 months post-transplantation, during which period any intervention is likely to be of greatest benefit. There is strong evidence that bisphosphonates prevent post-transplantation bone loss; however, data are lacking that this clearly extends to a reduction in fracture incidence. Denosumab is a potential alternative to vitamin D receptor agonists and bisphosphonates in reducing post-transplantation bone loss; however, further studies are needed to demonstrate its safety in patients with a significantly reduced estimated glomerular filtration rate. Clinical judgement remains the cornerstone of this complex clinical problem, providing a strong rationale for the formation of combined endocrinology and nephrology clinics to treat patients with Chronic Kidney Disease-Mineral and Bone Disorder, before and after transplantation.

Raising awareness on the therapeutic role of cholecalciferol in CKD: a multidisciplinary-based opinion

Vitamin D is recognized to play an essential role in health and disease. In kidney disease, vitamin D analogs have gained recognition for their involvement and potential therapeutic importance. Nephrologists are aware of the use of oral native vitamin D supplementation, however, uncertainty still exists with regard to the use of this treatment option in chronic kidney disease as well as clinical settings related to chronic kidney disease, where vitamin D supplementation may be an appropriate therapeutic choice. Two consecutive meetings were held in Florence in July and November 2016 comprising six experts in kidney disease (N = 3) and bone mineral metabolism (N = 3) to discuss a range of unresolved issues related to the use of cholecalciferol in chronic kidney disease. The panel focused on the following six key areas where issues relating to the use of oral vitamin D remain controversial: (1) vitamin D and parathyroid hormone levels in the general population, (2) cholecalciferol in chronic kidney disease, (3) vitamin D in cardiovascular disease, (4) vitamin D and renal bone disease, (5) vitamin D in rheumatological diseases affecting the kidney, (6) vitamin D and kidney transplantation.

Paricalcitol Versus Calcifediol for Treating Hyperparathyroidism in Kidney Transplant Recipients

INTRODUCTION

Secondary hyperparathyroidism (SHPT) and vitamin D deficiency are common at kidney transplantation and are associated with some early and late complications. This study was designed to evaluate whether paricalcitol was more effective than nutritional vitamin D for controlling SHPT in de novo kidney allograft recipients.

METHODS

This was a 6-month, investigator-initiated, multicenter, open-label, randomized clinical trial. Patients with pretransplantation iPTH between 250 and 600 pg/ml and calcium <10 mg/dl were randomized to paricalcitol (PAR) or calcifediol (CAL). The intention-to-treat population (PAR: n = 46; CAL: n = 47) was used for the analysis. The primary endpoint was the percentage of patients with serum iPTH >110 pg/ml at 6 months. Secondary endpoints were bone mineral metabolism, renal function, and allograft protocol biopsies.

RESULTS

The primary outcome occurred in 19.6% of patients in the PAR group and 36.2% of patients in the CAL group (P = 0.07). However, there was a higher percentage of patients with iPTH <70 pg/ml in the PAR group than in the CAL group (63.4% vs. 37.2%; P = 0.03). No differences were observed in bone turnover biomarkers and bone mineral density. The estimated glomerular filtration rate was significantly higher in the CAL group than in the PAR group without differences in albuminuria. In protocol biopsies, interstitial fibrosis and tubular atrophy tended to be higher in the PAR group than in the CAL group (48% vs. 23.8%; P = 0.09). Both medications were well tolerated.

CONCLUSION

Both PAR and CAL reduced iPTH, but PAR was associated with a higher proportion of patients with iPTH <70 pg/ml. These results do not support the use of PAR to treat posttransplantation hyperparathyroidism.

Bone Quality in Chronic Kidney Disease: Definitions and Diagnostics

PURPOSE OF REVIEW

In this paper, we review the epidemiology, diagnosis, and pathogenesis of fractures and renal osteodystrophy.

RECENT FINDINGS

The role of bone quality in the pathogenesis of fracture susceptibility in chronic kidney disease (CKD) is beginning to be elucidated. Bone quality refers to bone material properties, such as cortical and trabecular microarchitecture, mineralization, turnover, microdamage, and collagen content and structure. Recent data has added to our understanding of the effects of CKD on alterations to bone quality, emerging data on the role of abnormal collagen structure on bone strength, the potential of non-invasive methods to inform our knowledge of bone quality, and how we can use these methods to inform strategies that protect against bone loss and fractures. However, more prospective data is required. CKD is associated with abnormal bone quality and strength which results in high fracture incidence.

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.