Evolution of bone disease after kidney transplantation: A prospective histomorphometric analysis of trabecular and cortical bone

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.

Contemporary kidney transplantation has a limited impact on bone microarchitecture

Bone microarchitecture is an important component of bone quality and disturbances may reduce bone strength and resistance to trauma. Kidney transplant recipients have an excess risk of fractures, and bone loss affecting both trabecular and cortical bone compartments have been demonstrated after kidney transplantation. The primary aim of this study was to investigate the impact of kidney transplantation on trabecular and cortical bone microarchitecture, assessed by histomorphometry and micro computed tomography (μCT). Iliac crest bone biopsies, analyzed by bone histomorphometry and μCT, were performed at time of kidney transplantation and 12 months post-transplantation in an unselected cohort of 30 patients. Biochemical markers of mineral metabolism and bone turnover were measured at both time-points. At 12 months post-transplantation, bone turnover was low in 5 (17%) and normal in 25 (83%) patients. By histomorphometry, bone remodeling normalized, with decreases in eroded perimeters (4.0 to 2.1%, p = 0.02) and number of patients with marrow fibrosis (41 to 0%, p < 0.001). By μCT, trabecular thickness (134 to 125 μM, p = 0.003) decreased slightly. Other parameters of bone volume and microarchitecture, including cortical thickness (729 to 713 μm, p = 0.73) and porosity (10.2 to 9.5%, p = 0.15), remained stable. We conclude that kidney transplantation with current immunosuppressive protocols has a limited impact on bone microarchitecture.

•

Bone structure after kidney transplantation was explored using biopsy, μCT, and DXA.

•

Modest trabecular bone loss was detected in the first post-transplant year.

•

Cortical thickness and porosity were overall stable post-transplant.

•

Contemporary kidney transplantation has minimal impact on bone microarchitecture.

Could Bone Biomarkers Predict Bone Turnover after Kidney Transplantation?—A Proof-of-Concept Study

Aim: Bone disease after kidney transplant (KT) results from multiple factors, including previous bone and mineral metabolism disturbances and effects of transplant-related medications. New biomolecules have been recently associated with the development and progression of the chronic kidney disease–associated bone and mineral disorder (CKD-MBD). These include sclerostin and the soluble receptor activator of nuclear factor-kB ligand (sRANKL). Methods: To better understand the role of biomarkers in post-transplant bone disease, this study was designed to prospectively evaluate and correlate results from the histomorphometric analysis of bone biopsies after KT with emerging serum biomarkers of the CKD-MBD: sclerostin, Dickkopf-related protein 1 (Dkk-1), sRANKL and osteo-protegerin (OPG). Results: Our data shows a significant increase in plasma levels of bioactive sclerostin after KT accompanied by a significant reduction in plasma levels of Dkk-1, suggesting a promotion of the inhibition of bone formation by osteoblasts through the activation of these inhibitors of the Wnt signaling pathway. In addition, we found a significant increase in plasma levels of free sRANKL after KT accompanied by a significant reduction in plasma levels of its decoy receptor OPG, suggesting an enhanced bone resorption by osteoclasts mediated by this mechanism. Conclusions: Taken together, these results suggest that the loss of bone volume observed after KT could be explain mainly by the inhibition of bone formation mediated by sclerostin accompanied by an enhanced bone resorption mediated by sRANKL.

The Role of Bone Biopsy in the Management of CKD-MBD

A bone biopsy is still considered the gold standard for diagnosis of renal osteodystrophy. It allows to measure both static and dynamic parameters of bone remodeling and is the only method able to evaluate mineralization and allows analysis of both cortical and trabecular bone. Although bone volume can be measured indirectly by dual-energy X-ray absorptiometry, mineralization defects, bone metal deposits, cellular number/activity, and even turnover abnormalities are difficult to determine by techniques other than qualitative bone histomorphometry. In this review, we evaluate the role of bone biopsy in the clinical practice.

Kidney Disease and Bone: Changing the Way We Look at Skeletal Health

PURPOSE OF REVIEW

Kidney disease imparts profound skeletal changes, and unlike many other skeletal diseases, cortical bone is predominantly impacted. Significant advances in medical imaging have led to our ability to now obtain high-resolution three-dimensional views of cortical bone. This paper overviews recent work focused on cortical bone imaging, specifically cortical porosity, in kidney disease.

RECENT FINDINGS

Although a number of clinical papers have used high-resolution imaging to assess cortical bone porosity, the most impactful work involves longitudinal study designs that have assessed cortical porosity changes over time. These latter studies demonstrate dramatic increases in cortical porosity in untreated individuals and a lack of clear efficacy in reversing porosity with treatment (although data are limited). Those papers providing longitudinal assessment, both clinical and pre-clinical, reveal powerful data about cortical porosity and provide a foundation upon which future studies can build.

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.

The effect of vitamin D and zoledronic acid in bone marrow adiposity in kidney transplant patients: A post hoc analysis

PURPOSE

Osteoblasts and adipocytes are derived from mesenchymal stem cells. An imbalance in the differentiation of these lineages could affect the preservation of bone integrity. Several studies have suggested the importance of this imbalance in the pathogenesis of osteoporosis after kidney transplant (KT), but the role of bone marrow adiposity in this process is not well known, and if the treatment with the anti-absorptive (zoledronic acid-ZA) drugs could attenuate bone loss. Thus, our objective was compare bone marrow adiposity, osteoblasts and osteocytes before and after KT, verify an association between bone remodeling process (Turnover, Volume, and Mineralization-TMV classification), the osteocyte sclerostin expression to evaluate if there is a role of Wnt pathway, as well as the effect of ZA on these cells.

METHODS

We studied 29 new living-donor KT patients. One group received ZA at the time of KT plus cholecalciferol for twelve months, and the other group received only cholecalciferol. Bone biopsies were performed at baseline and after 12 months of treatment. Histomorphometric evaluation was performed in bone and bone marrow adipocytes. Sclerostin (Scl) expression in osteocytes was evaluated by immunohistochemistry.

RESULTS

Some bone marrow adiposity parameters were increased before KT. After KT, some of them remained increased and they worsened with the use of ZA. In the baseline, lower bone Volume and Turnover, were associated with increased bone marrow adiposity parameters (some of them). After KT, both groups showed the same associations. Osteocyte Scl expression after KT decreased with the use of ZA. We observed also an inverse association between bone adiposity parameters and lower osteocyte sclerostin expression 12 months after KT.

CONCLUSION

In conclusion, the present study suggests that KT fails to normalize bone marrow adiposity, and it even gets worse with the use of ZA. Moreover, bone marrow adiposity is inversely associated with bone Volume and Turnover, which seems to be accentuated by the antiresorptive therapy.

Is low pre-transplant parathyroid hormone a risk marker for cardiovascular disease in long-term follow-up of renal transplant recipients?

Background

Secondary hyperparathyroidism and altered levels of parathyroid hormone (PTH) are associated with vascular events in chronic kidney disease. After renal transplantation, this association is not clear. Pre-transplant parathyroidectomy (PTX) is common, but post-transplant data are scarce. We aimed to study the effect of PTH at the time of transplantation on risk of post-transplant vascular events in renal transplant recipients with and without pre-transplant PTX.

Methods

258 patients from two Swedish transplant units were followed for 6 years. Separate analyses were made for patients with or without pre-transplant PTX. Patients with no pre-transplant PTX were stratified by quartiles of PTH at time of transplantation and patients with pre-transplant PTX were stratified by above and below median levels of PTH at time of transplantation. Hazard ratios for vascular events, mortality, and graft failure were calculated in adjusted Cox regression models.

Results

In patients with no pre-transplant PTX, the lowest quartile of PTH at transplantation had a higher risk of cardiovascular events compared to quartile 3 with an adjusted hazard ratio (95% CI) of 2.63 (1.04–6.67). In patients with pre-transplant PTX, the group below median of PTH had a higher risk of cardiovascular events with an adjusted hazard ratio (95% CI) of 18.15 (1.62–203.82) compared to patients above median of PTH.

Conclusion

Low levels of parathyroid hormone before transplantation were associated with increased risk of post-transplant vascular events both in patients with and without pre-transplant parathyroidectomy. Any conclusions on causal or direct effect of PTH on outcome cannot be drawn from this observational study.

Cortical bone analysis in a predialysis population: a comparison with a dialysis population

This study was designed to characterize cortical bone by histomorphometry in a predialysis population, to correlate turnover, mineralization, and volume between cortical and trabecular bone, and to compare the findings with those in patients treated with maintenance dialysis. We evaluated cortical bone by histomorphometry in 16 patients with stage 3 or stage 4 chronic kidney disease and in 16 dialysis patients. Dual-energy X-ray absorptiometry (DXA) of the distal end of the forearm was performed in seven predialysis patients, and the findings correlated with histologic parameters. Predialysis patients compared with dialysis patients showed increased cortical bone thickness (p = 0.027) and decreased osteonal bone formation rate (p = 0.020) and adjusted apposition rate (p = 0.018), mainly for external cortical bone. In this predialysis population, trabecular bone volume positively correlated with external cortical porosity (r = 0.723, p = 0.003), external cortical thickness (r = 0.569, p = 0.034), and external osteonal accumulation (osteonal osteoid thickness, r = 0.530, p = 0.05; osteonal osteoid volume to bone volume ratio, r = 0.921, p < 0.001; and osteonal osteoid surface to bone surface ratio, r = 0.631, p = 0.016). These correlations were not observed in the internal cortical bone. Cortical osteonal mineralization surface negatively correlated with DXA Z and T scores and bone mineral density for the distal end of the forearm. The osteonal bone formation rate of both internal cortical bone and external cortical bone correlated with Z score (r = -0.975, p = 0.005 and r = -0.880, p = 0.021 respectively). We found no significant correlations between cortical thickness or porosity and DXA parameters for either external cortical bone or internal cortical bone. Our results suggest that a greater degree of kidney disease is associated with thinner cortices, eventually contributing to the higher fracture rate observed in the chronic kidney disease population. In predialysis patients, parathyroid hormone seems to have a modulating effect on both trabecular bone and cortical bone, particularly in external cortical bone.

Technique, Safety, and Yield of Bone Biopsies for Histomorphometry in Children

PURPOSE

To evaluate image-guided bone biopsy for bone histomorphometry to assess osteoporosis in children with respect to safety and yield.

MATERIALS AND METHODS

A single-center retrospective review was performed of 79 bone biopsies in 73 patients performed between 2007 and 2015. Biopsies of the iliac bone were performed under general anesthesia, after tetracycline labeling, using a Rochester needle (Medical Innovations International, Inc, Rochester, Minnesota). Ultrasound and fluoroscopic guidance were used in all procedures. Biopsy technique, technical success, safety, and histomorphometry results (complete, incomplete, none) were analyzed.

RESULTS

There were 41 male patients (51.8%). Technical success was achieved in 76/79 (96%) procedures. Of 79 biopsies, 75 (95%) were uneventful. Unplanned overnight observation was required in 3 (minor SIR grade B), and prolonged hospital stay owing to hematoma causing nerve compression pain was required in 1 (major SIR grade D). Complete histomorphometric reports were obtained in 69 (87%) procedures, incomplete reports were obtained in 7 (9%), and no reports were obtained in 3(4%). Incomplete reports were insufficient to provide a definitive diagnosis or guide treatment. Histomorphometry impacted subsequent therapy in 69 (87%) biopsies.

CONCLUSIONS

Image-guided bone biopsy for osteoporosis using the Rochester needle is a valuable and safe technique for establishing the diagnosis of osteoporosis and directing treatment based on histomorphometry results.

Injectable hybrid system for strontium local delivery promotes bone regeneration in a rat critical-sized defect model

Strontium (Sr) has been described as having beneficial influence in bone strength and architecture. However, negative systemic effects have been reported on oral administration of Sr ranelate, leading to strict restrictions in clinical application. We hypothesized that local delivery of Sr improves osteogenesis without eliciting detrimental side effects. Therefore, the in vivo response to an injectable Sr-hybrid system composed of RGD-alginate hydrogel cross-linked in situ with Sr and reinforced with Sr-doped hydroxyapatite microspheres, was investigated. The system was injected in a critical-sized bone defect model and compared to a similar Sr-free material. Micro-CT results show a trend towards higher new bone formed in Sr-hybrid group and major histological differences were observed between groups. Higher cell invasion was detected at the center of the defect of Sr-hybrid group after 15 days with earlier bone formation. Higher material degradation with increase of collagen fibers and bone formation in the center of the defect after 60 days was observed as opposed to bone formation restricted to the periphery of the defect in the control. These histological findings support the evidence of an improved response with the Sr enriched material. Importantly, no alterations were observed in the Sr levels in systemic organs or serum.

Correction of lower limb deformities in children with renal osteodystrophy by guided growth technique

PURPOSE

Renal osteodystrophy (ROD) may cause severe lower limb deformities in children. The purpose of this study is to evaluate the efficacy of the temporary hemiepiphysiodesis for the correction of lower limb deformities in children with ROD.

METHODS

Guided growth correction by hemiepiphysiodesis has been performed in skeletally immature patients with deformities of the lower limbs caused by ROD. The correction of the mechanical axes of the lower limbs and its correction speed have been evaluated.

RESULTS

A total of seven patients with ROD, five males and two females, were treated with the above technique. The average age of the patients at their first surgery was 7.8 years (2.9 to 13.6). The average follow-up time 5.2 years (2.3 to 8). There were 13 valgus deformities and one varus deformity of the knee. The measure of the lower limb angular deformity was in the range of 10° to 47°. Restoration of normal mechanical axis was achieved in all patients at the final follow-up. Three patients relapsed and required further hemiepiphysiodesis. The average time for correction was 20 months (7 to 30). The average speed of correction was 0.49° per month for a tibia and 1.73° per month for a femur. There were two minor complications: a screw mobilisation and a screw breakage occurred during removal.

CONCLUSION

Guided growth technique by hemiepiphysiodesis is a mini-invasive surgical procedure that has been found to be effective for the correction of misalignment due to ROD in skeletally immature patients. The method has allowed progressive correction of the deformities at any age in childhood. These patients are predisposed to relapse to their deformities, thus a strict follow-up is required.

The role of bone biopsy for the diagnosis of renal osteodystrophy: a short overview and future perspectives

Chronic kidney disease (CKD) patients present specific bone and mineral metabolism disturbances, which account for important morbidity and mortality. The term renal osteodystrophy, classically used for the nomination of CKD-associated bone disorder, has been limited to the histologic description of bone lesions, requiring the use of bone biopsy. Biochemical markers and imaging tools do not adequately predict the complex bone changes that are observed in renal osteodystrophy. Parathyroid hormone, which is a universally used biomarker of bone turnover in clinical practice, lacks specificity and sensitivity. Therefore, tetracycline double-labelled transiliac bone biopsy, with bone histology and histomorphometric evaluation, remains the best clinical tool to discriminate bone turnover and to evaluate the other dimensions of renal osteodystrophy. This review will focus on the value of classic bone histomorphometric analysis of trabecular bone in CKD patients and unfold new perspectives of this diagnostic tool, including cortical bone evaluation and bone tissue immunohistochemistry.