Bone histomorphometry in de novo renal transplant recipients indicates a further decline in bone resorption 1 year posttransplantation

Clinical Significance of Incident Osteoporotic Fractures After Kidney Transplantation: A National Korean Cohort Study

RATIONALE & OBJECTIVE

Recipients of kidney allografts are at risk of osteoporotic fractures (OF), but the association of OF with transplant patient outcomes remains uncertain due to common coexisting risks and complex medical conditions. This study sought to assess whether the overall incidences of OF among recipients of kidney allografts compared to that of patients receiving maintenance dialysis for kidney failure.

STUDY DESIGN

A national retrospective cohort study.

SETTING & PARTICIPANTS

145,090 Korean patients newly diagnosed with kidney failure between 2009 and 2019.

EXPOSURE

Kidney transplantation versus dialysis resulting in OF, and OF increasing risk of death.

OUTCOME

Incident OF overall and by site (hip, spine, forearm, and humerus); death.

ANALYTICAL APPROACH

Comparison of patients receiving maintenance dialysis with recipients of kidney allografts matched by age, sex, year of new index date, duration of dialysis, and presence of hypertension and diabetes mellitus. Cause-specific Cox proportional hazards regression models estimated the association between modality of kidney replacement therapy and OF. Cox models incorporating OF as a time-updated covariate were used to estimate the association of OF and mortality.

RESULTS

A total of 11,413 pairs were matched. Over the entire study period, 541 (4.7%) OFs in allograft recipients and 657 (5.8%) in matched dialysis comparators occurred, respectively. After 5.5 years of follow-up evaluation, the risk of incident OF was lower in kidney transplant recipients compared with matched dialysis comparators (adjusted hazard ratio[AHR], 0.73 [95% CI, 0.64-0.84], P<0.001). The differences in fracture rates were primarily driven by differences in hip fractures. Incident OF was associated with increased mortality risk (AHR, 2.18 [95% CI, 1.57-3.02], P<0.001) and death-censored allograft failure (AHR, 1.42 [95% CI, 1.02-1.97], P=0.040).

LIMITATIONS

Use of claims data, and no data on bone mineral density or hyperparathyroidism; the definition of OF that was used encompassed traumatic fractures.

CONCLUSIONS

Kidney allograft recipients have a lower rate of incident OF compared with dialysis patients, but when OF occurs it is associated with a higher rate of death and allograft loss.

Trabecular bone score to assess bone microarchitecture in end-stage renal disease patients

RATIONALE

This study evaluates TBS for estimating bone microarchitecture in ESRD patients using HR-pQCT as the reference technique.

MAIN RESULTS

TBS correlates significantly with vBMD and bone microarchitecture, unlike aBMD.

SIGNIFICANCE

TBS may complement bone health assessment in ESRD patients by offering additional information alongside aBMD.

PURPOSE

Given the high fracture risk, non-invasive techniques for assessing bone fragility in chronic kidney disease (CKD) remain important. Trabecular bone score (TBS) may provide additional information that could help guide treatment and follow-up decisions. The aim of this study is to investigate whether TBS reflects bone microarchitecture in end-stage renal disease (ESRD) patients, using high-resolution peripheral quantitative computed tomography (HR-pQCT) as the reference technique. Additionally, we aim to identify parameters associated with a low TBS.

METHODS

Seventy-five ESRD patients were included at the time of kidney transplantation (KTx). Areal bone mineral density (aBMD) was analyzed using dual-energy X-ray absorptiometry (DXA). TBS was assessed from the L1-L4 area during DXA. Volumetric BMD (vBMD) and bone microarchitecture at tibia and radius sites were analyzed using HR-pQCT.

RESULTS

In ESRD patients, those with TBS < 1.370 were older and had a higher body mass index (BMI). In contrast to T-score-based classification (≤ -2.5 or > -2.5), low TBS was linked to significantly lower trabecular and cortical vBMD, reduced trabecular bone volume fraction (BV/TV) and trabecular number (Tb.N), and increased trabecular separation (Tb.Sp). In multivariate analysis, older age, higher BMI, and lower Tb.N remained independently associated with low TBS, while no HR-pQCT parameters were linked to low aBMD (T-score ≤ -2.5).

CONCLUSION

TBS correlates with both trabecular and cortical parameters measured by HR-pQCT, potentially offering a complementary perspective on bone microstructure compared to aBMD. At the time of KTx, a low TBS appears to better discriminate patients with significantly lower vBMD than aBMD alone.

Chronic kidney disease and menopausal health: An EMAS clinical guide

Kidney diseases are related to the aging process. Ovarian senescence and the loss of estrogen's renoprotective effects are directly associated with a decline in renal function and indirectly with an accumulation of cardiometabolic risk factors. The latter can predispose to the development of chronic kidney disease (CKD). Conversely, CKD diagnosed during reproductive life adversely affects ovarian function.

AIM

To set out an individualized approach to menopause management in women with CKD.

MATERIALS AND METHODS

Literature review and consensus of expert opinion.

SUMMARY RECOMMENDATIONS

Menopause hormone therapy can be given to women with CKD. The regimen should be selected on the basis of patient preference and the individual's cardiovascular risk. The dose of hormonal and non-hormonal preparations should be adjusted in accordance with the patient's creatinine clearance. The management of a postmenopausal woman with CKD should focus on lifestyle advice as well as regular monitoring of the main cardiovascular risk factors and evaluation of bone mineral density. Tailored multidisciplinary advice should be given to women with comorbidities such as diabetes, dyslipidemia, and hypertension. Management of osteoporosis should be based on the severity of the CKD.

Ten tips on how to assess bone health in patients with chronic kidney disease

Patients with chronic kidney disease (CKD) experience a several-fold increased risk of fracture. Despite the high incidence and the associated excess morbidity and premature mortality, bone fragility in CKD, or CKD-associated osteoporosis, remains a blind spot in nephrology with an immense treatment gap. Defining the bone phenotype is a prerequisite for the appropriate therapy of CKD-associated osteoporosis at the patient level. In the present review, we suggest 10 practical 'tips and tricks' for the assessment of bone health in patients with CKD. We describe the clinical, biochemical, and radiological evaluation of bone health, alongside the benefits and limitations of the available diagnostics. A bone biopsy, the gold standard for diagnosing renal bone disease, is invasive and not widely available; although useful in complex cases, we do not consider it an essential component of bone assessment in patients with CKD-associated osteoporosis. Furthermore, we advocate for the deployment of multidisciplinary expert teams at local, national, and potentially international level. Finally, we address the knowledge gaps in the diagnosis, particularly early detection, appropriate "real-time" monitoring of bone health in this highly vulnerable population, and emerging diagnostic tools, currently primarily used in research, that may be on the horizon of clinical practice.

Associations of Changes in Bone Turnover Markers with Change in Bone Mineral Density in Kidney Transplant Patients

BACKGROUND

Bone loss after kidney transplantation is highly variable. We investigated whether changes in bone turnover markers associate with bone loss during the first post-transplant year.

METHODS

Bone mineral density (BMD) was measured at 0 and 12 months, with biointact parathyroid hormone, bone-specific alkaline phosphatase (BALP), intact procollagen type I N -terminal propeptide (PINP), and tartrate-resistant acid phosphatase isoform 5b (TRAP5b) measured at 0, 3, and 12 months post-transplant ( N =209). Paired transiliac bone biopsies were available in a subset ( n =49). Between-group differences were evaluated by Student's t test, Wilcoxon signed-rank test, or Pearson's chi-squared test.

RESULTS

Changes in BMD varied from -22% to +17%/yr. Compared with patients with no change (±2.5%/yr), patients who gained BMD had higher levels of parathyroid hormone (236 versus 136 pg/ml), BALP (31.7 versus 18.8 μ g/L), and Intact PINP (121.9 versus 70.4 μ g/L) at time of transplantation; a greater decrease in BALP (-40% versus -21%) and Intact PINP (-43% versus -13%) by 3 months; and lower levels of Intact PINP (36.3 versus 60.0 μ g/L) at 12 months post-transplant. Patients who lost BMD had a less marked decrease, or even increase, in Intact PINP (+22% versus -13%) and TRAP5b (-27% versus -43%) at 3 months and higher Intact PINP (83.7 versus 60.0 μ g/L) and TRAP5b (3.89 versus 3.16 U/L) at 12 months compared with patients with no change. If none of the biomarkers decreased by the least significant change at 3 months, an almost two-fold (69% versus 36%) higher occurrence of bone loss was seen at 12 months post-transplant.

CONCLUSIONS

Bone loss after kidney transplantation was highly variable. Resolution of high bone turnover, as reflected by decreasing bone turnover markers, associated with BMD gain, while increasing bone turnover markers associated with bone loss.

Biochemical Clusters as Substitutes of Bone Biopsies in Kidney Transplant Patients

Bone and mineral metabolism abnormalities are frequent in kidney transplant recipients and have been associated with cardiovascular morbidity. The primary aim of this study was to analyse the association between routine clinically available biochemical evaluation, non-routine histomorphometric bone evaluation, and vascular disease in kidney transplanted patients. A cross-sectional analysis was performed on 69 patients, 1-year after kidney transplantation. Laboratory analysis, radiography of hands and pelvis, bone biopsy, bone densitometry, and coronary CT were performed. One-year post-transplantation, nearly one-third of the patients presented with hypercalcemia, 16% had hypophosphatemia, 39.3% had iPTH levels > 150 pg/mL, 20.3% had BALP levels > 40 U/L, and 26.1% had hypovitaminosis D. Evaluation of extraosseous calcifications revealed low Adragão and Agatston scores. We divided patients into three clusters, according to laboratory results routinely used in clinical practice: hypercalcemia and hyperparathyroidism (Cluster1); hypercalcemia and high BALP levels (Cluster2); hypophosphatemia and vitamin D deficiency (Cluster 3). Patients in clusters 1 and 2 had higher cortical porosity (p = 0.001) and osteoid measurements, although there was no difference in the presence of abnormal mineralization, or low volume. Patients in cluster 2 had a higher BFR/BS (half of the patients in cluster 2 had high bone turnover), and most patients in cluster 1 had low or normal bone turnover. Cluster 3 has no differences in volume, or turnover, but 60% of the patients presented with pre-osteomalacia. All three clusters were associated with high vascular calcifications scores. Vascular calcifications scores were not related to higher bone mineral density. Instead, an association was found between a higher Adragão score and the presence of osteoporosis at the femoral neck (p = 0.008). In conclusion, inferring bone TMV by daily clinical biochemical analysis can be misleading, and bone biopsy is important for assessing both bone turnover and mineralization after kidney transplantation, although hypophosphatemia combined with vitamin D deficiency is associated with abnormal mineralization. The presence of hypercalcemia with high levels of PTH or high levels of BALP, or hypophosphatemia and vitamin D deficiency should remind us to screen vascular calcification status of patients.Clinical Research: ClinicalTrials.gov ID NCT02751099.

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.

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.

Bone Disease in Chronic Kidney Disease and Kidney Transplant

Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD) comprises alterations in calcium, phosphorus, parathyroid hormone (PTH), Vitamin D, and fibroblast growth factor-23 (FGF-23) metabolism, abnormalities in bone turnover, mineralization, volume, linear growth or strength, and vascular calcification leading to an increase in bone fractures and vascular disease, which ultimately result in high morbidity and mortality. The bone component of CKD-MBD, referred to as renal osteodystrophy, starts early during the course of CKD as a result of the effects of progressive reduction in kidney function which modify the tight interaction between mineral, hormonal, and other biochemical mediators of cell function that ultimately lead to bone disease. In addition, other factors, such as osteoporosis not apparently dependent on the typical pathophysiologic abnormalities resulting from altered kidney function, may accompany the different varieties of renal osteodystrophy leading to an increment in the risk of bone fracture. After kidney transplantation, these bone alterations and others directly associated or not with changes in kidney function may persist, progress or transform into a different entity due to new pathogenetic mechanisms. With time, these alterations may improve or worsen depending to a large extent on the restoration of kidney function and correction of the metabolic abnormalities developed during the course of CKD. In this paper, we review the bone lesions that occur during both CKD progression and after kidney transplant and analyze the factors involved in their pathogenesis as a means to raise awareness of their complexity and interrelationship.

Improvement of Mineral and Bone Disorders After Renal Transplantation

BACKGROUND

Posttransplant mineral and bone diseases are causes of fractures, and their association with cardiovascular events is being studied.

METHODS

We analyzed the evolution of biochemical, histological, and imaging parameters pre- and 1 y post-renal transplantation in 69 patients and correlated mineral and bone findings with coronary calcifications. At inclusion and after 12 mo, clinical data and echocardiographic findings were recorded, and laboratory evaluations, radiography of the pelvis and hands, and bone biopsy were performed. Noncontrast cardiac computed tomography was performed during the second evaluation.

RESULTS

Serum levels of fibroblast growth factor 23 and sclerostin decreased in all patients, parathyroid hormone levels decreased in 89.8% of patients, bone alkaline phosphatase levels decreased in 68.1% of patients, and alpha-Klotho levels increased in 65.2% of patients. More than half of the patients presented with renal osteodystrophy at both biopsies, but histological findings improved: a significant transition from high to normal or low turnover and no significant differences in volume, mineralization defect, or cortical porosity at the 2 evaluations. Alpha-Klotho, sclerostin, and bone alkaline phosphatase shifts affect bone changes. Neither echocardiographic findings nor vascular calcification scores differed between the 2 points. Both the pretransplant period (dialysis vintage, sclerostin, and low bone volume at baseline) and the maintenance of abnormalities in the posttransplant period (high turnover posttransplant) were the most reliable predictors of the severity of the coronary calcification percentile.

CONCLUSIONS

Renal transplantation improved bone and mineral abnormalities. The pretransplant period determines the severity of calcification.

Time for Revival of Bone Biopsy with Histomorphometric Analysis in Chronic Kidney Disease (CKD): Moving from Skepticism to Pragmatism

Bone Biopsy (BB) with histomorphometric analysis still represents the gold standard for the diagnosis and classification of different forms of renal osteodystrophy. Bone biopsy is the only technique able to provide comprehensive information on all bone parameters, measuring static and dynamic parameters of turnover, cortical and trabecular microarchitecture, and mineralization defects. In nephrological practice, bone biopsy yields relevant indications to support therapeutic choices in CKD, heavily impacting the management and prognosis of uremic patients. Unfortunately, the use of bone biopsy has decreased; a lack of expertise in performing and interpreting, perceived procedure invasiveness and pain, and reimbursement issues have all contributed to this decline. Nevertheless, both bone biomarkers and instrumental images cannot be considered reliable surrogates for histological findings, being insufficiently accurate to properly evaluate underlying mineral and bone disorders. This is a multidisciplinary position paper from the Nephrology and Osteoporosis Italian Scientific Societies with the purpose of restating the role of bone biopsy in CKD patient management and of providing strong solutions to allow diffusion of this technique in Italy, but potentially also in other countries. The Italian approach through the optimization and standardization of bone biopsy procedure, the construction of the Italian Hub and Spoke network, and a request for adjustment and national homogenization of reimbursement to the Italian Health Ministry has led the way to implement bone biopsy and to improve CKD patient management and prognosis.

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.

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.

Natural History of Bone Disease following Kidney Transplantation

BACKGROUND

Knowledge of the effect of kidney transplantation on bone is limited and fragmentary. The aim of this study was to characterize the evolution of bone disease in the first post-transplant year.

METHODS

We performed a prospective, observational cohort study in patients referred for kidney transplantation under a steroid-sparing immunosuppressive protocol. Bone phenotyping was done before, or at the time of, kidney transplantation, and repeated at 12 months post-transplant. The phenotyping included bone histomorphometry, bone densitometry by dual-energy x-ray absorptiometry, and biochemical parameters of bone and mineral metabolism.

RESULTS

Paired data were obtained for 97 patients (median age 55 years; 72% male; 21% of patients had diabetes). Bone turnover remained normal or improved in the majority of patients (65%). Bone histomorphometry revealed decreases in bone resorption (eroded perimeter, mean 4.6% pre- to 2.3% post-transplant; P<0.001) and disordered bone formation (fibrosis, 27% pre- versus 2% post-transplant; P<0.001). Whereas bone mineralization was normal in all but one patient pretransplant, delayed mineralization was seen in 15% of patients at 1 year post-transplant. Hypophosphatemia was associated with deterioration in histomorphometric parameters of bone mineralization. Changes in bone mineral density were highly variable, ranging from -18% to +17% per year. Cumulative steroid dose was related to bone loss at the hip, whereas resolution of hyperparathyroidism was related to bone gain at both spine and hip.

CONCLUSIONS

Changes in bone turnover, mineralization, and volume post-transplant are related both to steroid exposure and ongoing disturbances of mineral metabolism. Optimal control of mineral metabolism may be key to improving bone quality in kidney transplant recipients.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Evolution of Bone Histomorphometry and Vascular Calcification Before and After Renal Transplantation, NCT01886950.

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.

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

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

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Cortical thickness and porosity were overall stable post-transplant.

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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.

Static histomorphometry allows for a diagnosis of bone turnover in renal osteodystrophy in the absence of tetracycline labels

A bone biopsy with prior tetracycline labeling is the gold standard to diagnose renal osteodystrophy. In cases of missing tetracycline labels, it is still paramount to gain clinically relevant information from the extracted bone sample, by evaluating the static histomorphometry. This study investigates the diagnostic performance of static histomorphometry for the evaluation of high and low bone turnover. Transiliac bone biopsies taken pre- or post- kidney transplantation, of sufficient quality for a full histomorphometric analysis were included (n = 205). The cohort was randomly split to provide separate exploration and validation subsets. Diagnostic performance was evaluated by area under the receiver operator characteristics curve (AUC). All histomorphometric parameters were significantly different across categories of low (24%), normal (60%), and high (16%) bone turnover, and all were significant predictors of both high and low bone turnover (AUC 0.71-0.84). Diagnostic performance was very good for high turnover, as a combination of static parameters resulted in negative and positive predictive values (NPV and PPV) of 80% and 96%, respectively. For low turnover, the combined model resulted in PPV of 71% and NPV of 82%. We conclude that in the absence of tetracycline labels, static histomorphometry provide an acceptable alternative for a diagnosis of bone turnover in renal osteodystrophy.

Bone Biopsy for Histomorphometry in Chronic Kidney Disease (CKD): State-of-the-Art and New Perspectives

The use of bone biopsy for histomorphometric analysis is a quantitative histological examination aimed at obtaining quantitative information on bone remodeling, structure and microarchitecture. The labeling with tetracycline before the procedure also allows for a dynamic analysis of the osteoblastic activity and mineralization process. In the nephrological setting, bone biopsy is indicated to confirm the diagnosis of subclinical or focal osteomalacia and to characterize the different forms of renal osteodystrophy (ROD). Even if bone biopsy is the gold standard for the diagnosis and specific classification of ROD, the use of this approach is very limited. The main reasons for this are the lack of widespread expertise in performing or interpreting bone biopsy results and the cost, invasiveness and potential pain associated with the procedure. In this regard, the sedation, in addition to local anesthesia routinely applied in Italian protocol, significantly reduces pain and ameliorates the pain perception of patients. Concerning the lack of widespread expertise, in Italy a Hub/Spokes model is proposed to standardize the analyses, optimizing the approach to CKD patients and reducing the costs of the procedure. In addition, new tools offer the possibility to evaluate the osteogenic potential or the ability to form bone under normal and pathological conditions, analyzing mesenchymal stem cells and their ability to differentiate in the osteogenic lineage. In the same way, circulating microRNAs are suggested as a tool for exploring osteogenic potential. The combination of different diagnostic approaches and the optimization of the bioptic procedure represent a concrete solution to spread the use of bone biopsy and optimize CKD patient management.

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.

Prevalence of Musculoskeletal Manifestations in Adult Kidney Transplant's Recipients: A Systematic Review

Background and Objectives: The musculoskeletal (MSK) manifestations in the kidney transplant recipient (KTxR) could lead to decreased quality of life and increased morbidity and mortality. However, the prevalence of these MSK manifestations is still not well-recognized. This review aimed to investigate the prevalence and outcomes of MSK manifestations in KTxR in the last two decades. Materials and Methods: Research was performed in EBSCO, EMBASE, CINAHL, PubMed/MEDLINE, Cochrane, Google Scholar, PsycINFO, Scopus, Science Direct, and Web of Science electronic databases were searched during the years 2000–2020. Results: The PRISMA flow diagram revealed the search procedure and that 502 articles were retrieved from the initial search and a total of 26 articles were included for the final report in this review. Twelve studies reported bone loss, seven studies reported a bone pain syndrome (BPS) or cyclosporine-induced pain syndrome (CIPS), and seven studies reported hyperuricemia (HU) and gout. The prevalence of MSK manifestations in this review reported as follow: BPS/CIPS ranged from 0.82% to 20.7%, while bone loss ranged from 14% to 88%, and the prevalence of gout reported in three studies as 7.6%, 8.0%, and 22.37%, while HU ranged from 38% to 44.2%. Conclusions: The post-transplantation period is associated with profound MSK abnormalities of mineral metabolism and bone loss mainly caused by corticosteroid therapy, which confer an increased fracture risk. Cyclosporine (CyA) and tacrolimus were responsible for CIPS, while HU or gout was attributable to CyA. Late diagnosis or treatment of post-transplant bone disease is associated with lower quality of life among recipients

Bone Mineral Disease After Kidney Transplantation

Chronic kidney disease-mineral bone disorder (CKD-MBD) after kidney transplantation is a mix of pre-existing disorders and new alterations. The final consequences are reflected fundamentally as abnormal mineral metabolism (hypercalcemia, hypophosphatemia) and bone alterations [high or low bone turnover disease (as fibrous osteitis or adynamic bone disease), an eventual compromise of bone mineralization, decrease bone mineral density and bone fractures]. The major cause of post-transplantation hypercalcemia is the persistence of severe secondary hyperparathyroidism, and treatment options include calcimimetics or parathyroidectomy. On turn, hypophosphatemia is caused by both the persistence of high blood levels of PTH and/or high blood levels of FGF23, with its correction being very difficult to achieve. The most frequent bone morphology alteration is low bone turnover disease, while high-turnover osteopathy decreases in frequency after transplantation. Although the pathogenic mechanisms of these abnormalities have not been fully clarified, the available evidence suggests that there are a number of factors that play a very important role, such as immunosuppressive treatment, persistently high levels of PTH, vitamin D deficiency and hypophosphatemia. Fracture risk is four-fold higher in transplanted patients compared to general population. The most relevant risk factors for fracture in the kidney transplant population are diabetes mellitus, female sex, advanced age (especially > 65 years), dialysis vintage, high PTH levels and low phosphate levels, osteoporosis, pre-transplant stress fracture and high doses or prolonged steroids therapy. Treatment alternatives for CKD-MBD after transplantation include minimization of corticosteroids, use of calcium and vitamin D supplements, antiresorptives (bisphosphonates or Denosumab) and osteoformers (synthetic parathyroid hormone). As both mineral metabolism and bone disorders lead to increased morbidity and mortality, the presence of these changes after transplantation has to be prevented (if possible), minimized, diagnosed, and treated as soon as possible.

European Consensus Statement on the diagnosis and management of osteoporosis in chronic kidney disease stages G4-G5D

Controlling the excessive fracture burden in patients with chronic kidney disease (CKD) Stages G4-G5D remains an impressive challenge. The reasons are 2-fold. First, the pathophysiology of bone fragility in patients with CKD G4-G5D is complex and multifaceted, comprising a mixture of age-related (primary male/postmenopausal), drug-induced and CKD-related bone abnormalities. Second, our current armamentarium of osteoporosis medications has not been developed for, or adequately studied in patients with CKD G4-G5D, partly related to difficulties in diagnosing osteoporosis in this specific setting and fear of complications. Doubts about the optimal diagnostic and therapeutic approach fuel inertia in daily clinical practice. The scope of the present consensus paper is to review and update the assessment and diagnosis of osteoporosis in patients with CKD G4-G5D and to discuss the therapeutic interventions available and the manner in which these can be used to develop management strategies for the prevention of fragility fracture. As such, it aims to stimulate a cohesive approach to the management of osteoporosis in patients with CKD G4-G5D to replace current variations in care and treatment nihilism.

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.

Fractures after kidney transplantation: Incidence, predictors, and association with mortality

BACKGROUND

Major fractures (MF) are associated with increased mortality in the general population and represent an even higher risk in patients with chronic kidney disease. We investigated incidence, predictors and clinical outcomes associated with first MF (MF_first) following kidney transplantation (KT).

METHODS

We used the Swedish National Renal Registry of 3992 first KT recipients (2005-2016) (median age 53 years, 65% men) and identified all MF_first in hip, spine, humerus and forearm following KT. We estimated incidence rates and predictors of MF_first using flexible parametric hazard models and Fine-Gray analysis accounting for competing risk of death, and risk of all-cause mortality following MF_first using Cox proportional hazards models with fracture as time-varying exposure.

RESULTS

During median follow-up of 4.8 years (IQR 2.2-7.9 years), there were 279 fractures of which 139 were forearm fractures. The crude incidence rate of MF_first (n = 279) was 13.5/1000 patient-years and that of hip fractures (n = 69) 3.4/1000 patient-years. The multivariate-adjusted fracture incidence rates were highest during the first 6 months following KT, and 86% higher in women than in men. High age, female sex, previous history of MF, diabetes nephropathy, pretransplant dialysis therapy and acute rejection were associated with increased risk for MF_first, whereas pre-emptive KT was associated with lower risk of MF_first. Spline curves showed markedly higher impact of higher age on risk of MF_first in women than in men. MF_first (n = 279) independently predicted increased all-cause mortality risk (hazard ratio, HR, 1.78(95%CI 1.35-2.36)). Among MF_first, with humerus fracture as reference, hip fracture (HR, 4.68(95%CI 1.56-14.06)) and spine fracture (HR, 4.02(95%CI 1.19-13.54)), but not forearm fracture (HR, 1.17 (95%CI 0.38-3.53)), were associated with increased all-cause mortality risk.

CONCLUSIONS

The initial 6 months following kidney transplantation is a high-risk period for MF. Among MF, hip fracture and spine fracture associate with substantially increased all-cause mortality risk.

Natural history of mineral metabolism, bone turnover and bone mineral density in de novo renal transplant recipients treated with a steroid minimization immunosuppressive protocol

The skeletal effects of renal transplantation are not completely understood, especially in patients managed with a steroid minimization immunosuppressive protocol and long term. We enrolled 69 adult transplant recipients (39 males; ages 51.1 ± 12.2 years), free of antiresorptive therapy and managed with a steroid minimization immunosuppressive protocol, into a 5-year prospective observational study to evaluate changes in areal bone mineral density (aBMD), mineral metabolism and bone remodelling. Dual energy X-ray absorptiometry, laboratory parameters of mineral metabolism (including parathyroid hormone, sclerostin and fibroblast growth factor 23) and non-renal cleared bone turnover markers (BTMs) (bone-specific alkaline phosphatase, trimeric N-terminal propeptide and tartrate-resistant acid phosphatase 5b) were assessed at baseline and 1 and 5 years post-transplantation. The mean cumulative methylprednisolone exposure at 1 and 5 years amounted to 2.5 ± 0.8 and 5.8 ± 3.3 g, respectively. Overall, bone remodelling activity decreased after transplantation. Post-transplant aBMD changes were minimal and were significant only in the ultradistal radius during the first post-operative year {median -2.2% [interquartile range (IQR) -5.9-1.2] decline, P = 0.01} and in the lumbar spine between Years 1 and 5 [median 1.6% (IQR -3.2-7.0) increase, P = 0.009]. BTMs, as opposed to mineral metabolism parameters and cumulative corticosteroid exposure, associated with aBMD changes, both in the early and late post-transplant period. Most notably, aBMD changes inversely associated with bone remodelling changes. In summary, in de novo renal transplant recipients treated with a steroid minimization immunosuppressive protocol, BMD changes are limited, highly variable and related to remodelling activity rather than corticosteroid exposure.

Predictive Power of Bone Turnover Biomarkers to Estimate Bone Mineral Density after Kidney Transplantation with or without Denosumab: A post hoc Analysis of the POSTOP Study

BACKGROUND

Low bone mineral density (BMD) represents a major risk factor for bone fractures in patients with chronic kidney disease (CKD) as well as after kidney transplantation. However, modalities to solidly predict patients at fracture risk are yet to be defined. Better understanding of bone turnover biomarkers (BTMs) may close this diagnostic gap. This study strives to correlate BTMs to BMD in kidney transplant recipients.

METHODS

Changes in BTMs - procollagen type I N-terminal propeptide (P1NP), bone-specific alkaline phosphatase (BSAP), β-isomer of the C-terminal telopeptide of type I collagen, and urine deoxypyridinoline/Cr - at the time of transplant and 3 months were correlated to changes in BMD measured by dual-energy X-ray absorptiometry at the time of transplant, 6, and 12 months, respectively. Half of the collective was treated with denosumab twice yearly in addition to the standard treatment with calcium and vitamin D.

RESULTS

Changes in bone formation markers BSAP and P1NP within 3 months showed a significant negative correlation to changes in BMD at the hip within 6 months in denosumab-naïve patients. This correlation was abrogated by denosumab treatment.

CONCLUSIONS

Changes in BSAP and P1NP showed promise in short-term prediction of BMD. We suggest further trials expanding on the knowledge of these BTMs with assessment of fracture risk, sequential measurements of BTMs within the first 6 months, and the additional use of computed tomography to assess BMD.

Bone mineral density and mortality in end-stage renal disease patients

Osteoporosis characterized by low bone mineral density (BMD) as assessed by dual-energy X-ray absorptiometry (DXA) is common among end-stage renal disease (ESRD) patients and associates with high fracture incidence and high all-cause mortality. This is because chronic kidney disease-mineral bone disorders (CKD-MBDs) promote not only bone disease (osteoporosis and renal dystrophy) but also vascular calcification and cardiovascular disease. The disturbed bone metabolism in ESRD leads to 'loss of cortical bone' with increased cortical porosity and thinning of cortical bone rather than to loss of trabecular bone. Low BMD, especially at cortical-rich bone sites, is closely linked to CKD-MBD, vascular calcification and poor cardiovascular outcomes. These effects appear to be largely mediated by shared mechanistic pathways via the 'bone-vascular axis' through which impaired bone status associates with changes in the vascular wall. Thus, bone is more than just the scaffolding that holds the body together and protects organs from external forces but is-in addition to its physical supportive function-also an active endocrine organ that interacts with the vasculature by paracrine and endocrine factors through pathways including Wnt signalling, osteoprotegerin (OPG)/receptor activator of nuclear factor-κB (RANK)/RANK ligand system and the Galectin-3/receptor of advanced glycation end products axis. The insight that osteogenesis and vascular calcification share many similarities-and the knowledge that vascular calcification is a cell-mediated active rather than a passive mineralization process-suggest that low BMD and vascular calcification ('vascular ossification') to a large extent represent two sides of the same coin. Here, we briefly review changes of BMD in ESRD as observed using different DXA methods (central and whole-body DXA) at different bone sites for BMD measurements, and summarize recent knowledge regarding the relationships between 'low BMD' and 'fracture incidence, vascular calcification and increased mortality' in ESRD patients, as well as potential 'molecular mechanisms' underlying these associations.

Inhibition of vascular calcification by inositol phosphates derivatized with ethylene glycol oligomers

Myo-inositol hexakisphosphate (IP6) is a natural product known to inhibit vascular calcification (VC), but with limited potency and low plasma exposure following bolus administration. Here we report the design of a series of inositol phosphate analogs as crystallization inhibitors, among which 4,6-di-O-(methoxy-diethyleneglycol)-myo-inositol-1,2,3,5-tetrakis(phosphate), (OEG2)2-IP4, displays increased in vitro activity, as well as more favorable pharmacokinetic and safety profiles than IP6 after subcutaneous injection. (OEG2)2-IP4 potently stabilizes calciprotein particle (CPP) growth, consistently demonstrates low micromolar activity in different in vitro models of VC (i.e., human serum, primary cell cultures, and tissue explants), and largely abolishes the development of VC in rodent models, while not causing toxicity related to serum calcium chelation. The data suggest a mechanism of action independent of the etiology of VC, whereby (OEG2)2-IP4 disrupts the nucleation and growth of pathological calcification.

Bone biomarkers in de novo renal transplant recipients

Successful kidney transplantation (partly) corrects the physiologic and metabolic abnormalities driving chronic kidney disease - mineral and bone disorders. At the same time, renal transplant recipients are exposed to immunosuppressive agents that may affect bone metabolism. Bone biomarkers have been suggested as surrogates of or adjuncts to bone biopsy and imaging techniques to assess bone health and to classify risk of bone loss and fractures. Bone biomarkers may be classified as circulating factors that affect bone metabolism (commonly referred to as bone metabolism markers) or that reflect bone cell number and/or activity (commonly referred to as bone turnover markers). A growing body of evidence shows that successful renal transplantation has a major impact on both bone metabolism and bone turnover. Analytical issues, including the cross-reactivity with fragments, complicate the interpretation of bone biomarkers, especially in the setting of a rapid changing kidney function, as is the case after successful renal transplantation. Overall, bone turnover seems to decline following renal transplantation, but inter-individual variability is substantial. Preliminary evidence indicates that bone biomarkers may be useful in guiding mineral and bone therapy in renal transplant recipients.

Addressing bone quality and bone density after renal transplantation: A prospective evaluation of the evolution of trabecular bone score and bone mineral density over the first 5 years following renal transplantation in Asian patients

The evolution of trabecular bone score (TBS) and bone mineral density (BMD) over the first 5 years after renal transplantation was prospectively evaluated in 164 patients. Dual energy X-ray absorptiometry (DXA) scans were performed at 0, 6, 12, 24, and 60 months. Cumulative steroid dose, serum 25(OH)D, calcium, parathyroid hormone, and total ALP levels at these time points were checked. Incident fractures were identified from X-rays/vertebral fracture assessments. Mean (SD) age, TBS, and lumbar spine BMD at baseline were 47.11 (9.53), 1.424 (0.097), and 0.935 (0.183) gm/cm² , respectively. Baseline TBS was lower in tertiary 1.38 (0.07) vs secondary hyperparathyroidism 1.43 (0.01) vs post-parathyroidectomy 1.46 (0.11); P = .035. Trabecular bone score and BMD significantly decreased from baseline->6 months, changes after that at consecutive time points were non-significant. 11% had incident fractures during the follow-up period, majority being metatarsal with no vertebral or hip fractures noted. This first prospective evaluation of TBS and BMD evolution at multiple time points over 5 years suggest that microarchitectural and bone density deteriorations post-renal transplantation stabilize after 6 months. Stabilization of these parameters could partially account for the absence of major fractures noted in this Asian population. Possible genetic and ethnic differences in fracture risk between Asian and Caucasian renal transplant patients have to be explored through large population-based studies.

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.

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.

Changes in bone microarchitecture following kidney transplantation-Beyond bone mineral density

Bone disease in kidney transplant recipients (KTRs) is characterized by bone mineral density (BMD) loss but bone microarchitecture changes are poorly defined. In this prospective cohort study, we evaluated bone microarchitecture using non-invasive imaging modalities; high-resolution magnetic resonance imaging (MRI), peripheral quantitative computed tomography (pQCT), dual energy X-ray absorptiometry (DXA), and the trabecular bone score (TBS) following kidney transplantation. Eleven KTRs (48.3 ± 11.2 years) underwent MRI (tibia), pQCT (radius) and DXA at baseline and 12 months post-transplantation. Transiliac bone biopsies, performed at transplantation, showed 70% of patients with high/normal bone turnover. Compared with baseline, 12-month MRI showed deterioration in indices of trabecular network integrity-surface to curve ratio (S/C; -15%, P = 0.03) and erosion index (EI; +19%, P = 0.01). However, cortical area increased (+10.3%, P = 0.04), with a non-significant increase in cortical thickness (CtTh; +7.8%, P = 0.06). At 12 months, parathyroid hormone values (median 10.7 pmol/L) correlated with improved S/C (r = 0.75, P = 0.009) and EI (r = -0.71, P = 0.01) while osteocalcin correlated with CtTh (r = 0.72, P = 0.02) and area (r = 0.70, P = 0.02). TBS decreased from baseline (-5.1%, P = 0.01) with no significant changes in BMD or pQCT. These findings highlight a post-transplant deterioration in trabecular bone quality detected by MRI and TBS, independent of changes in BMD, underlining the potential utility of these modalities in evaluating bone microarchitecture in KTRs.

Novel insights into parathyroid hormone: report of The Parathyroid Day in Chronic Kidney Disease

Chronic kidney disease (CKD) is often associated with a mineral and bone disorder globally described as CKD-Mineral and Bone Disease (MBD), including renal osteodystrophy, the latter ranging from high bone turnover, as in case of secondary hyperparathyroidism (SHPT), to low bone turnover. The present article summarizes the important subjects that were covered during ‘The Parathyroid Day in Chronic Kidney Disease’ CME course organized in Paris in September 2017. It includes the latest insights on parathyroid gland growth, parathyroid hormone (PTH) synthesis, secretion and regulation by the calcium-sensing receptor, vitamin D receptor and fibroblast growth factor 23 (FGF23)–Klotho axis, as well as on parathyroid glands imaging. The skeletal action of PTH in early CKD stages to the steadily increasing activation of the often downregulated PTH receptor type 1 has been critically reviewed, emphasizing that therapeutic strategies to decrease PTH levels at these stages might not be recommended. The effects of PTH on the central nervous system, in particular cognitive functions, and on the cardiovascular system are revised, and the reliability and exchangeability of second- and third-generation PTH immunoassays discussed. The article also reviews the different circulating biomarkers used for the diagnosis and monitoring of CKD-MBD, including PTH and alkaline phosphatases isoforms. Moreover, it presents an update on the control of SHPT by vitamin D compounds, old and new calcimimetics, and parathyroidectomy. Finally, it covers the latest insights on the persistence and de novo occurrence of SHPT in renal transplant recipients.

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.