Bone disease after renal transplantation. Nat Rev Nephrol. 2010;6:32-40. [PMID: 19918255 DOI: 10.1038/nrneph.2009.192]

Increase in lumbar spine but not distal radius bone mineral density in adults after pancreas kidney transplantation

Osteoporosis occurs in every third individual after simultaneous pancreas kidney transplantation (SPKT). Currently used bone measures insufficiently predict their fracture risk. Lumbar spine Trabecular bone score (TBS) and distal radius areal and volumetric bone mineral density (BMD) were monitored for the first time in patients with type 1 diabetes and chronic renal failure after SPKT with steroid-sparing protocol. In 33 subjects (mean age 43.4 ± 9.8 years), dual-energy X-ray absorptiometry and peripheral quantitative computed tomography were performed just after SPKT (baseline) and one and three years later. While TBS Z-scores increased (-1.1 ± 1.2 and -0.3 ± 1.0; p˂0.001, at baseline and year three, respectively), trabecular volumetric BMD Z-scores at distal radius metaphysis did not change during the study (-1.3 ± 1.3 and -1.3 ± 1.0; p = 0.38). Similarly, areal BMD Z-scores increased at lumbar spine, total hip and femoral neck (all p < 0.01), but not at the distal radius. SPKT induced bone measures' improvement at lumbar spine and hip but not at distal radius. Before suggesting changes in current clinical care, predictive value of individual bone measures or its combination for fracture risk assessment remains to be elucidated.

Potential Role of Bone Metabolism Markers in Kidney Transplant Recipients

BACKGROUND

The impact of treatments, suppressing the immune system, persistent hyperparathyroidism, and other risk factors on mineral and bone disorder (MBD) after kidney transplantation is well-known. However, there is limited knowledge about their effect on bone metabolism biomarkers. This study aimed to investigate the influence of kidney transplant on these markers, comparing them to patients undergoing hemodialysis and healthy individuals.

METHODS

In this cross-sectional study, three groups were included: kidney transplant patients (n = 57), hemodialysis patients (n = 26), and healthy controls (n = 31). Plasma concentrations of various bone metabolism biomarkers, including Dickkopf-related protein 1, osteoprotegerin, osteocalcin, osteopontin, sclerostin, and fibroblast growth factor 23, were measured. Associations between these biomarkers and clinical and laboratory data were evaluated.

RESULTS

A total of 114 patients participated. Transplant recipients had significantly lower levels of Dickkopf-related protein 1, osteoprotegerin, osteocalcin, osteopontin, sclerostin, and fibroblast growth factor 23 compared to hemodialysis patients. Alkaline phosphatase levels positively correlated with osteopontin (r = 0.572, p < 0.001), while fibroblast growth factor 23 negatively correlated with 25-hydroxyvitamin D (r = -0.531, p = 0.019). The panel of bone biomarkers successfully predicted hypercalcemia (area under the curve [AUC] = 0.852, 95% confidence interval [CI] = 0.679-1.000) and dyslipidemia (AUC = 0.811, 95% CI 0.640-0.982) in transplant recipients.

CONCLUSION

Kidney transplantation significantly improves mineral and bone disorders associated with end-stage kidney disease by modulating MBD markers and reducing bone metabolism markers, such as Dickkopf-related protein 1, osteoprotegerin, osteocalcin, osteopontin, and sclerostin. Moreover, the panel of bone biomarkers effectively predicted hypercalcemia and dyslipidemia in transplant recipients.

Real-world usage of Chronic Kidney Disease - Mineral Bone Disorder (CKD-MBD) biomarkers in nephrology practices

Background

Chronic kidney disease mineral bone disorder (CKD-MBD) is a condition characterized by alterations of calcium, phosphate, parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF-23) metabolism that in turn promote bone disorders, vascular calcifications, and increase cardiovascular (CV) risk. Nephrologists' awareness of diagnostic, prognostic, and therapeutic tools to manage CKD-MBD plays a primary role in adequately preventing and managing this condition in clinical practice.

Methods

A national survey (composed of 15 closed questions) was launched to inquire about the use of bone biomarkers in the management of CKD-MBD patients by nephrologists and to gain knowledge about the implementation of guideline recommendations in clinical practice.

Results

One hundred and six Italian nephrologists participated in the survey for an overall response rate of about 10%. Nephrologists indicated that the laboratories of their hospitals were able to satisfy request of ionized calcium levels, 105 (99.1%) of both PTH and alkaline phosphatase (ALP), 100 (94.3%) of 25(OH)D, and 61 (57.5%) of 1.25(OH)2D; while most laboratories did not support the requests of biomarkers such as FGF-23 (intact: 88.7% and c-terminal: 93.4%), Klotho (95.3%; soluble form: 97.2%), tartrate-resistant acid phosphatase 5b (TRAP-5b) (92.5%), C-terminal telopeptide (CTX) (71.7%), and pro-collagen type 1 N-terminal pro-peptide (P1NP) (88.7%). As interesting data regarding Italian nephrologists' behavior to start treatment of secondary hyperparathyroidism (sHPT), the majority of clinicians used KDOQI guidelines (n = 55, 51.9%). In contrast, only 40 nephrologists (37.7%) relied on KDIGO guidelines, which recommended referring to values of PTH between two and nine times the upper limit of the normal range.

Conclusion

Results point out a marked heterogeneity in the management of CKD-MBD by clinicians as well as a suboptimal implementation of guidelines in Italian clinical practice.

Immunosuppressive Therapy and Nutritional Status of Patients after Kidney Transplantation: A Protocol for a Systematic Review

(1) Background: Kidney transplantation is widely recognized as the most effective method of treating end-stage renal disease. Immunosuppressive therapy plays a pivotal role in the treatment of kidney transplant patients, encompassing all patients (except identical twins), and is administered from organ transplantation until the end of its function. The aim of this systematic review is to identify the evidence of the association between immunosuppressive therapy and nutritional status of patients following kidney transplantation. (2) Methods: This protocol has been designed in line with Preferred Items for Systematic Reviews (PRISMA-P). Our search encompasses several databases, including MEDLINE (via PubMed), EMBASE (Elsevier), Scopus and Web of Science. We intend to include observational studies (cross-sectional, case-control, and cohort designs), randomized controlled trials (RCTs), as well as completed and ongoing non-randomized study designs. We will confine our search to studies published in English within the past decade (from inception to 17 February 2023). Qualitative studies, case studies, and conference reports will be excluded. The selection process will be done in Covidence by two independent reviewers. Data extraction will be conducted using a standardized MS Excel template version 16.0. Quality assessment of included studies will be performed using the Cochrane Risk of Bias tool for randomized trials (RoB2), or the Risk of Bias in Non-randomized Studies of Interventions (ROBINS-I) tool. Risk-of-bias plots will be generated using the web application Robvis. Relevant data that have been extracted from eligible studies will be presented in a narrative synthesis. We expect the studies to be too heterogeneous to perform subgroup analyses. (3) Conclusion: This systematic review will offer insights into the evidence regarding association between immunosuppressive therapy and nutritional status of adult patients (18 years of age or older) within the initial year following kidney transplantation. To our knowledge, there is no systematic review addressing that question.

Relation of testosterone level and other factors with bone mineral density in male kidney transplant recipients: a cross-sectional study

BACKGROUND

Although testosterone has a pivotal role in bone health, its correlation with bone mineral density (BMD) is understudied in kidney transplant recipients who are at high risk of osteoporosis. This study aimed to elucidate if there is any correlation between serum free testosterone and BMD in this population.

PATIENTS AND METHODS

Sixty male kidney transplant recipients were enrolled in this cross-sectional study, and they were subjected to history taking, clinical examination, and laboratory investigations (including total and free testosterone). BMD was assessed in three regions (forearm, hip, and lumbar spine) using DEXA scan.

RESULTS

The mean age of the included patients was 45.55 ± 13.58 years. Serum total and free testosterone had mean values of 5.17 ± 1.4 ng/ml and 95.46 ± 28.24 pg/ml, respectively, with all levels within the normal range. DEXA scan detected osteoporosis and osteopenia in 9 (15%) and 30 (50%) patients in the lumbar region, 3 (5%) and 36 (60%) in the hip region, as well as 21 (35%) and 33 (55%) in the forearm region, respectively. BMD of the lumbar region had a significant positive correlation with free testosterone, phosphorus, and eGFR, while it had a significant negative correlation with platelets and patient age. BMD of the hip region was positively correlated with serum phosphorus, parathyroid hormone, and duration since the transplant, whereas it was negatively correlated with platelets and total testosterone level. BMD of the forearm had a significant positive correlation with eGFR, whereas it had a significant negative correlation with age and duration since transplantation. In addition, forearm BMD was significantly lower in patients with a radiocephalic AVF.

CONCLUSION

Even within the normal range, free testosterone has a significant positive correlation with lumbar spine BMD with no significant association with the forearm or hip BMD.

Coexistence of Low Muscle Mass and Osteoporosis as a Predictor of Fragility Fractures in Long-Term Kidney Transplant Recipients

INTRODUCTION

Sarcopenia and osteoporosis are highly prevalent among kidney transplant recipients (KTRs). Although osteoporosis is known to increase fracture risk in KTRs, it is unclear whether sarcopenia or osteosarcopenia is associated with this increased risk. Thus, we aimed to investigate the association of the coexistence of low muscle mass (LMM) and osteoporosis with the risk of fracture in long-term KTRs.

METHODS

Exactly 342 stable KTRs underwent dual-energy X-ray absorptiometry and skeletal muscle mass index (SMI) measurement using bioelectrical impedance analysis.

RESULTS

LMM and osteoporosis were observed in 109 (31.9%) and 93 patients (27.2%), respectively. During a follow-up period of 5.1 years, 48 (14.0%) fractures occurred. KTRs with LMM had a higher fracture risk, but this was not significant (adjusted hazard ratio [aHR] 1.82, 95% confidence interval [CI] 0.94-3.50, p = 0.073). Similar results were obtained in KTRs with osteoporosis (aHR 1.84, 95% CI 0.96-3.47, p = 0.063). We divided the KTRs into four groups according to the presence of LMM and/or osteoporosis. The cumulative incidence rates of fractures were 13.0%, 11.1%, 10.5%, and 31.3% in the KTRs without both LMM and osteoporosis, those with LMM alone, those with osteoporosis alone, and those with both, respectively. The KTRs with both LMM and osteoporosis had a 2.92fold higher risk of fractures (95% CI 1.29-6.49; p = 0.010) than those without both LMM and osteoporosis.

CONCLUSION

Long-term KTRs with the coexistence of LMM and osteoporosis had an independently higher risk of fragility fractures than those without both LMM and osteoporosis. The combination of SMI and osteoporosis definitions can be used to identify KTRs with a high fracture risk.

Evaluation of the efficacy and tolerability of alendronate versus denosumab in kidney transplant patients with reduced bone mineral density

PURPOSE

To compare the effect of denosumab and alendronate on bone mineral density (BMD) in renal transplant recipients (RTRs) with low bone mass.

METHODS

Patients were randomized to receive either denosumab subcutaneously (60 mg/6 months), oral alendronate (70 mg/week), or no treatment for 1 year. The three groups were prescribed daily calcium and vitamin D. Primary outcome was BMD assessed at lumbar spine, hip, and radius and measured by dual-energy X-ray absorptiometry (DEXA) at baseline and after 6 and 12 months. Adverse events and laboratory assessments (calcium, phosphate, vitamin D, renal functions, and intact parathyroid hormone) were monitored for all patients. Quality of life was assessed at baseline and after 6 and 12 months for all patients.

RESULTS

Ninety RTRs were included in the study (30 in each group). Baseline clinical characteristics and BMD values were comparable in the three groups. After 12 months, lumbar spine T-score of patients treated with denosumab and alendronate showed a median increase of 0.5 [95% confidence interval (CI): 0.4-0.6] and 0.5 (95% CI: 0.4-0.8), respectively, and patients in the control group showed a decrease of -0.2 (95% CI: -0.3 to -0.1), p < 0.001. Denosumab and alendronate showed a significant comparable gain in T-scores at hip and radius versus a significant decrease in the control group. Adverse events and laboratory values were similar in the three groups. Both treatments resulted in comparable significant improvement in physical functioning, physical role limitations, vitality, and pain scores.

CONCLUSION

Denosumab and alendronate showed comparable efficacy in improving BMD at all measured skeletal sites and were safe and well-tolerated, with no serious adverse effects reported in RTRs with low bone mass. The study was registered on ClinicalTrials.gov, number NCT04169698.

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.

The Impact of Cholecaciferol Supplementation on Bone Mineral Density in Long-Term Kidney Transplant Recipients

Although reduced bone mineral density (BMD) is associated with a higher risk of fractures, morbidity, and mortality in kidney transplant patients (KTRs), there is no consensus on optimal treatment for the alterations of BMD in this population. This study aims at assessing the effect of cholecalciferol supplementation on BMD over a follow-up period of 2 years in a cohort of long-term KTRs. Patients with age ≥ 18 years were included and divided into two subgroups based on treatment with bisphosphonate and/or calcimimetics and/or active vitamin D sterols (KTRs-treated) or never treated with the above medications (KTRs-free). BMD was evaluated at lumbar vertebral bodies (LV) and right femoral neck (FN) with standard DEXA at the beginning and end of the study. According to World Health Organization (WHO) criteria, results were expressed as T-score and Z-score. Osteoporosis and osteopenia were defined as T score ≤ −2.5 SD and T score < −1 and >−2.5 SD, respectively. Cholecalciferol was supplemented at a dose of 25,000 IU/week over 12 weeks followed by 1500 IU/day. KTRs-free (n. 69) and KTRs-treated (n. 49) consecutive outpatients entered the study. KTRs-free were younger (p < 0.05), with a lower prevalence of diabetes (p < 0.05) and of osteopenia at FN (46.3 % vs. 61.2 %) compared to KTRs-treated. At the entry none of the study subjects had a sufficient level of cholecalciferol; Z-score and T-score at LV and FN were not different between groups. At the end of the study period, serum cholecalciferol concentration was significantly increased in both groups (p < 0.001); the KTRs-free group presented an improvement in both T-score and Z-score at LV (p < 0.05) as well as a lower prevalence of osteoporotic cases (21.7% vs. 15.9%); in contrast, no changes were recorded in KTR-treated individuals. In conclusion, supplementation with cholecalciferol ameliorated Z-score and T-score at LV in long-term KTRs who had been never treated with active or inactive vitamin D sterols, bisphosphonates, and calcimimetics. Future endeavours are needed to confirm these preliminary findings.

Time-Varying Risk Factors for Incident Fractures in Kidney Transplant Recipients: A Nationwide Cohort Study in South Korea

Little is known about the time-varying risk factors for fractures in kidney transplant recipients (KTRs). Using the Korea Organ Transplantation Registry, a nationwide cohort study of KTRs, the incidence, locations, and time-varying predictors of fractures were analyzed, including at baseline and post-transplant 6-month variables in KTRs who underwent KT between January 2014 and June 2019. Among 4134 KTRs, with a median follow-up of 2.94 years (12,441.04 person-years), 63 patients developed fractures. The cumulative 5-year incidence was 2.10%. The most frequent locations were leg (25.40%) and foot/ankle (22.22%). In multivariable analysis, older recipient age at baseline (hazard ratio [HR], 1.035; 95% confidence interval [CI], 1.007–1.064; p = 0.013) and higher tacrolimus trough level (HR, 1.112; 95% CI, 1.029–1.202; p = 0.029) were associated with higher risks for fractures. Pretransplant diabetes mellitus had a time-dependent impact on fractures, with increasing risk as time elapses (HR for diabetes mellitus 1.115; 95% CI, 0.439–2.832; HR for diabetes mellitus × time, 1.049; 95% CI, 1.007–1.094; p = 0.022). In conclusion, KTRs had a high risk of peripheral skeletal fractures in the first 5 years. At baseline recipient age, pretransplant diabetes mellitus and tacrolimus trough level after KT were responsible for the fractures in KTRs.

Kidney Transplantation, Immunosuppression and the Risk of Fracture: Clinical and Economic Implications

Rationale & Objective

Disorders of bone and mineral metabolism frequently develop with advanced kidney disease, may be exacerbated by immunosuppression after kidney transplantation, and increase the risk of fractures.

Study Design

Retrospective database study.

Setting & Participants

Kidney-only transplant recipients aged ≥18 years from 2005 to 2016 in the United States captured in US Renal Data System records, which integrate Organ Procurement and Transplantation Network/United Network for Organ Sharing records with Medicare billing claims.

Exposures

Various immunosuppression regimens in the first 3 months after kidney transplantation.

Outcomes

The development of fractures, as ascertained using diagnostic codes on Medicare billing claims.

Analytical Approach

We used multivariable Cox regression with inverse propensity weighting to compare the incidence of fractures >3 months-to-3 years after kidney transplantation associated with various immunosuppression regimens compared to a reference regimen of antithymocyte globulin (TMG) or alemtuzumab (ALEM) with tacrolimus + mycophenolic acid + prednisone using inverse probability treatment weighting.

Results

Overall, fractures were identified in 7.5% of kidney transplant recipients (women, 8.8%; men, 6.7%; age < 55 years, 5.9%; age ≥ 55 years, 9.3%). In time-varying regression, experiencing a fracture was associated with a substantially increased risk of subsequent death within 3 months (adjusted hazard ratio [aHR], 3.06; 95% confidence interval [CI], 2.45-3.81). Fractures were also associated with increased Medicare spending (first year: $5,122; second year: $10,890; third year: $11,083; [P < 0.001]). Induction with TMG or ALEM and the avoidance or early withdrawal of steroids significantly reduced the risk of fractures in younger (aHR, 0.63; 95% CI, 0.54-0.73) and older (aHR, 0.83; 95% CI, 0.74-0.94) patients. The avoidance or early withdrawal of steroids with any induction was associated with a reduced risk of fractures in women.

Limitations

This was a retrospective study which lacked data on immunosuppression levels.

Conclusions

Fractures after kidney transplantation are associated with significantly increased mortality risk and costs. The early avoidance or early withdrawal of steroids after induction with TMG or ALEM reduces the risk of fractures after kidney transplantation and should be considered for patients at high-risk of this complication, including older adults and women.

The Role of Alterations in Alpha-Klotho and FGF-23 in Kidney Transplantation and Kidney Donation

Cardiovascular disease and mineral bone disorders are major contributors to morbidity and mortality among patients with chronic kidney disease and often persist after renal transplantation. Ongoing hormonal imbalances after kidney transplant (KT) are associated with loss of graft function and poor outcomes. Fibroblast growth factor 23 (FGF-23) and its co-receptor, α-Klotho, are key factors in the underlying mechanisms that integrate accelerated atherosclerosis, vascular calcification, mineral disorders, and osteodystrophy. On the other hand, kidney donation is also associated with endocrine and metabolic adaptations that include transient increases in circulating FGF-23 and decreases in α-Klotho levels. However, the long-term impact of these alterations and their clinical relevance have not yet been determined. This manuscript aims to review and summarize current data on the role of FGF-23 and α-Klotho in the endocrine response to KT and living kidney donation, and importantly, underscore specific areas of research that may enhance diagnostics and therapeutics in the growing population of KT recipients and kidney donors.

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.

Chronic Kidney Disease-Mineral Bone Disease biomarkers in kidney transplant patients

Background:

Chronic Kidney Disease associated with Mineral Bone Disease (CKD-MBD) is frequent in kidney transplant patients. Post-transplantation bone disease is complex, especially in patients with pre-existing metabolic bone disorders that are further affected by immunosuppressive medications and changes in renal allograft function. Main biochemical abnormalities of mineral metabolism in kidney transplantation (KTx) include hypophosphatemia, hyperparathyroidism (HPTH), insufficiency or deficiency of vitamin D, and hypercalcemia.

Objective:

This review aimed to summarize the pathophysiology and main biomarkers of CKD-MBD in KTx.

Methods:

A comprehensive and non-systematic search in PubMed was independently made with an emphasis on biomarkers in mineral bone disease in KTx.

Results:

CKD-MBD can be associated with numerous factors including secondary HPTH, metabolic dysregulations before KTx, and glucocorticoids therapy in post-transplant subjects. Fibroblast growth factor 23 (FGF23) reaches normal levels after KTx with good allograft function, while calcium, vitamin D and phosphorus, ultimately, result in hypercalcemia, persistent vitamin D insufficiency, and hypophosphatemia respectively. As for PTH levels, there is an initial tendency of a significant decrease, followed by a raise due to secondary or tertiary HPTH. In regard to sclerostin levels, there is no consensus in the literature.

Conclusion:

KTx patients should be continuously evaluated for mineral homeostasis and bone status, both cases with successful kidney transplantation and those with reduced functionality. Additional research on CKD-MBD pathophysiology, diagnosis, and management is essential to guarantee long-term graft function, better prognosis, good quality of life, and reduced mortality for KTx patients.

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.

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.

Therapy for persistent hypercalcemic hyperparathyroidism post-renal transplant: cinacalcet versus parathyroidectomy

Background:

Persistent hyperparathyroidism post-transplant is associated with increases in the incidence of cardiovascular events, fractures, and deaths. The aim of this study was to compare both therapeutic options available: parathyroidectomy (PTX) and the calcimimetic agent cinacalcet.

Methods:

A single center retrospective study including adult renal transplant recipients who developed hypercalcemia due to persistent hyperparathyroidism. Inclusion criteria: PTH > 65 pg/mL with serum calcium > 11.5 mg/dL at any time after transplant or serum calcium persistently higher than 10.2 mg/dL one year after transplant. Patients treated with cinacalcet (n=46) were compared to patients treated with parathyroidectomy (n=30). Follow-up period was one year. Clinical and laboratory data were analyzed to compare efficacy and safety of both therapeutic modalities.

Results:

PTX controlled calcemia faster (month 1 x month 6) and reached significantly lower levels at month 12 (9.1±1.2 vs 9.7±0.8 mg/dL, p < 0.05); PTX patients showed significantly higher levels of serum phosphate (3.8±1.0 vs 2.9±0.5 mg/dL, p < 0.05) and returned PTH to normal levels (45±51 pg/mL). Cinacalcet, despite controlling calcium and phosphate in the long term, decreased but did not correct PTH (197±97 pg/mL). The proportion of patients that remained with PTH above normal range was 95% in the cinacalcet group and 22% in the PTX group. Patients treated with cinacalcet had better renal function (creatinine 1.2±0.3 vs 1.7±0.7 mg/dL, p < 0.05).

Conclusions:

Surgical treatment was superior to cinacalcet to correct the metabolic disorders of hyperparathyroidism despite being associated with worse renal function in the long term. Cinacalcet proved to be a safe and well tolerated drug.

Bone Quality in CKD Patients: Current Concepts and Future Directions - Part I

BACKGROUND

There is ample evidence that patients with CKD have an increased risk of osteoporotic fractures. Bone fragility is not only influenced by low bone volume and mass but also by poor microarchitecture and tissue quality. More emphasis has been given to the quantitative rather than qualitative assessment of bone health, both in general population and CKD patients. Although bone mineral density (BMD) is a very useful clinical tool in assessing bone strength, it may underestimate the fracture risk in CKD patients. Serum and urinary bone biomarkers have been found to be reflective of bone activities and predictive of fractures independently of BMD in CKD patients. Bone quality and fracture risk in CKD patients can be better assessed by utilizing new technologies such as trabecular bone score and high-resolution imaging studies. Additionally, invasive assessments such as bone histology and micro-indentation are useful counterparts in the evaluation of bone quality.

SUMMARY

A precise diagnosis of the underlying skeletal abnormalities in CKD patients is crucial to prevent further bone loss and fractures. We must consider bone quantity and quality abnormalities for management of CKD patients. Here in this part I, we are focusing on advances in bone quality diagnostics that are expected to help in proper understanding of the bone health in CKD patients.

KEY MESSAGES

Assessment of bone quality and quantity in CKD patients is essential. Both noninvasive and invasive techniques for the assessment of bone quality are available.

Treatment optimization of maintenance immunosuppressive agents in pediatric renal transplant recipients

Introduction: Graft survival in pediatric kidney transplant patients has increased significantly within the last three decades, correlating with the discovery and utilization of new immunosuppressants as well as improvements in patient care. Despite these developments in graft survival for patients, there is still improvement needed, particularly in long-term care in pediatric patients receiving grafts from deceased donor patients. Maintenance immunosuppressive therapies have narrow therapeutic indices and are associated with high inter-individual and intra-individual variability.Areas covered: In this review, we examine the impact of pharmacokinetic variability on renal transplantation and its association with age, genetic polymorphisms, drug-drug interactions, drug-disease interactions, renal insufficiency, route of administration, and branded versus generic drug formulation. Pharmacodynamics are outlined in terms of the mechanism of action for each immunosuppressant, potential adverse effects, and the utility of pharmacodynamic biomarkers.Expert opinion: Acquiring abetter quantitative understanding of immunosuppressant pharmacokinetics and pharmacodynamic components should help clinicians implement treatment regimens to maintain the balance between therapeutic efficacy and drug-related toxicity.

Bone densitometry versus bone histomorphometry in renal transplanted patients: a cross-sectional study

Bone loss leads to increase risk of fractures in renal transplantation. The aim of this study was to analyse the relationship between bone densitometry (DXA) findings, bone histomorphometry and bone-related molecules 1-year after renal transplantation. We performed a cross-sectional study of de novo renal transplanted patients that agreed to perform a bone biopsy and a DXA examination 1 year after transplantation. All patients underwent a laboratory evaluation, bone biopsy, DXA examination and cardiac CT 1 year after transplantation. 67 patients were included, 16 had a normal examination, and 18 patients were classified as having osteoporosis by DXA. Correlations between bone mineral density and T-scores of total femur and femoral neck were the ones that best correlated with bone volume assessed by a bone biopsy. The sensitivity of DXA for osteoporosis diagnosis was 47.0%, and the specificity was 81.2%. The positive predictive value was 50.0%, and the negative predictive value (NPV) was 80.0%. DXA parameters also correlated with klotho and sclerostin serum levels. In this population, a normal examination excluded the presence of osteoporosis, helping in identifying patients that would not benefit from therapy. Overall, densitometry in total femur and femoral neck correlated well with bone volume measured by bone biopsy.

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.

Factors Related to Bone Metabolism in Kidney Transplant Recipients

This study is aimed at establishing the prevalence of osteoporosis and osteopenia in kidney transplant recipients (KTRs) and determining the risk factors for bone mass loss. We invited KTRs who were under regular follow-up at Jiangxi Provincial People's Hospital Affiliated with Nanchang University to attend an assessment of osteoporotic risk assessed by questionnaire, biochemical profile, and dual-energy X-ray absorptiometry (DXA) scanning of the lumbar spine, total hip, and femoral neck. Binary logistic regression models were used to investigate the relationship between the different variables and bone mass density (BMD). A total of 216 patients satisfied the inclusion criteria. The group consisted of 156 men (72.22%) and 60 women (27.78%), and the mean age was 41.50 ± 9.98 years. There were 81 patients with normal bone mass (37.50%) and 135 patients with bone mass loss (62.50%). Logistic regression analysis showed that a higher phosphorus value and higher alkaline phosphatase concentration and a longer use of glucocorticoids were risk factors for bone mass loss in KTRs, and maintaining an appropriate weight and exercising an appropriate number of times per week helped to maintain bone mass.

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.

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.

Risk Factors and Management of Osteoporosis Post-Transplant

Bone and mineral disorders are common after organ transplantation. Osteoporosis post transplantation is associated with increased morbidity and mortality. Pathogenesis of bone disorders in this particular sub set of the population is complicated by multiple co-existing factors like preexisting bone disease, Vitamin D deficiency and parathyroid dysfunction. Risk factors include post-transplant immobilization, steroid usage, diabetes mellitus, low body mass index, older age, female sex, smoking, alcohol consumption and a sedentary lifestyle. Immunosuppressive medications post-transplant have a negative impact on outcomes, and further aggravate osteoporotic risk. Management is complex and challenging due to the sub-optimal sensitivity and specificity of non-invasive diagnostic tests, and the underutilization of bone biopsy. In this review, we summarize the prevalence, pathophysiology, diagnostic tests and management of osteoporosis in solid organ and hematopoietic stem cell transplant recipients.

Lifestyle, Inflammation, and Vascular Calcification in Kidney Transplant Recipients: Perspectives on Long-Term Outcomes

After decades of pioneering and improvement, kidney transplantation is now the renal replacement therapy of choice for most patients with end-stage kidney disease (ESKD). Where focus has traditionally been on surgical techniques and immunosuppressive treatment with prevention of rejection and infection in relation to short-term outcomes, nowadays, so many people are long-living with a transplanted kidney that lifestyle, including diet and exposure to toxic contaminants, also becomes of importance for the kidney transplantation field. Beyond hazards of immunological nature, a systematic assessment of potentially modifiable-yet rather overlooked-risk factors for late graft failure and excess cardiovascular risk may reveal novel targets for clinical intervention to optimize long-term health and downturn current rates of premature death of kidney transplant recipients (KTR). It should also be realized that while kidney transplantation aims to restore kidney function, it incompletely mitigates mechanisms of disease such as chronic low-grade inflammation with persistent redox imbalance and deregulated mineral and bone metabolism. While the vicious circle between inflammation and oxidative stress as common final pathway of a multitude of insults plays an established pathological role in native chronic kidney disease, its characterization post-kidney transplant remains less than satisfactory. Next to chronic inflammatory status, markedly accelerated vascular calcification persists after kidney transplantation and is likewise suggested a major independent mechanism, whose mitigation may counterbalance the excess risk of cardiovascular disease post-kidney transplant. Hereby, we first discuss modifiable dietary elements and toxic environmental contaminants that may explain increased risk of cardiovascular mortality and late graft failure in KTR. Next, we specify laboratory and clinical readouts, with a postulated role within persisting mechanisms of disease post-kidney transplantation (i.e., inflammation and redox imbalance and vascular calcification), as potential non-traditional risk factors for adverse long-term outcomes in KTR. Reflection on these current research opportunities is warranted among the research and clinical kidney transplantation community.

Comparison of the clinical effectiveness and safety between the use of denosumab vs bisphosphonates in renal transplant patients

A retrospective chart review was conducted on 85 renal transplant patients aged 19-88 years, treated with denosumab or bisphosphonate therapy. Bone densitometry measures were compared between treatment groups at baseline; at years 1, 2, and 3; and at final follow-up (average of 3.4 years). Both bisphosphonate and denosumab treatments increased lumbar spine bone density; however, the effect of denosumab was greater compared with that of bisphosphonate treatment. Denosumab treatment increased femoral neck BMD, whereas bisphosphonate treatment had a mean decrease in femoral neck BMD at final follow-up. Thus, our study provides evidence for the efficacy of denosumab treatment in renal transplant patients. Caution around hypocalcemia is warranted. We recommend more prospective studies to analyze the effects of long-term antiresorptive therapy in patients with a renal transplant.

INTRODUCTION

To compare the clinical effectiveness and safety between the use of denosumab and bisphosphonates on bone density and incidence of adverse events in renal transplant patients.

METHODS

A retrospective chart review was conducted on 85 renal transplant patients aged 19-88 years, treated with denosumab or bisphosphonate therapy. Bone densitometry measures were compared between treatment groups at baseline; years 1, 2, and 3; and at final follow-up (average of 3.4 years).

RESULTS

Absolute change in lumbar spine and femoral neck BMD over the treatment period was 0.029 ± 0.075 g/cm² and - 0.003 ± 0.064 g/cm², respectively, in the bisphosphonate group. Absolute change in lumbar spine and femoral neck BMD at final follow-up was 0.072 ± 0.094 g/cm² and 0.025 ± 0.063 g/cm², respectively, in the denosumab group. Denosumab resulted in significantly greater increases in lumbar spine BMD (0.045 g/cm² greater in the denosumab group). Similarly, the absolute change in BMD at the femoral neck was 0.022 g/cm² greater in the denosumab group as compared with the bisphosphonate group. The denosumab group had one event of severe hypocalcemia following first injection and one report of hospitalized pneumonia. No serious adverse events were reported in the bisphosphonate group.

CONCLUSIONS

Both treatments increased lumbar spine BMD; however, the effect of denosumab was greater compared with that of bisphosphonate treatment. Our study provides evidence for the efficacy of denosumab treatment in renal transplant patients. Caution around hypocalcemia is warranted. We recommend more prospective studies to analyze the effects of long-term antiresorptive therapy in patients with a renal transplant.

Biochemical Characteristics of Bone Mineral Metabolism before and throughout the First Year after Kidney Transplantation, Persistent Hyperparathyroidism, and Risk Factors in a Latin Population

Bone mineral metabolism disease, which included persistent hyperparathyroidism, is common after successful kidney transplantation (KT) and is related with negative outcomes in kidney transplant recipients. There is a lack of information about bone mineral metabolism, persistent hyperparathyroidism, and its risk factors in Latin kidney transplant recipients (KTRs). Material and Methods: A retrospective study was conducted in 74 patients aged 18-50 years with evolution of 12 months after KT and estimated glomerular filtration rate (eGFR) >60 ml/min; biochemical data of bone mineral metabolism before and at 1, 3, 6, and 12 months of KT were registered. Results. Age was 33 (IQR 27-37) years; 54% (n = 40) were men. Before KT, all patients had hyperparathyroidism, 40% (n = 30) hypocalcemia, 86% (n = 64) hyperphosphatemia, and 42% (n = 31) hyperphosphatasemia. After KT, an increase of calcium and a diminution of PTH, phosphorus, and alkaline phosphatase were corroborated (p=0.001). All patients had hypovitaminosis D (deficiency: 91% (n = 67); insufficiency: 9% (n = 7)); 40% (n = 30) had persistent hyperparathyroidism at 12 months. Hyperphosphatasemia before KT (OR = 4.17 (95% CI: 1.21-14.44); p=0.04), hyperparathyroidism at 6 months (OR = 1.84 (95% CI; 1.67-2.06); p=0.02), hypovitaminosis D at 6 months (OR = 3.94 (95% CI: 1.86-17.9); p=0.01), and hyperphosphatasemia at 6 months (OR = 1.47 (95% CI: 1.07-2.86); p=0.03) were risk factors for persistent hyperparathyroidism at 12 months after KT. Conclusion. Persistent hyperparathyroidism at 6 months, hypovitaminosis D, and hyperphosphatasemia are risk factors for persistent hyperparathyroidism at 1 year of KT in Latin population.

Interventions for preventing bone disease in kidney transplant recipients

BACKGROUND

People who have chronic kidney disease (CKD) have important changes to bone structure, strength, and metabolism. Children experience bone deformity, pain, and delayed or impaired growth. Adults experience limb and vertebral fractures, avascular necrosis, and pain. The fracture risk after kidney transplantation is four times that of the general population and is related to Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD) occurring with end-stage kidney failure, steroid-induced bone loss, and persistent hyperparathyroidism after transplantation. Fractures may reduce quality of life and lead to being unable to work or contribute to community roles and responsibilities. Earlier versions of this review have found low certainty evidence for effects of treatment. This is an update of a review first published in 2005 and updated in 2007.

OBJECTIVES

This review update evaluates the benefits and harms of interventions for preventing bone disease following kidney transplantation.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 16 May 2019 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

RCTs and quasi-RCTs evaluating treatments for bone disease among kidney transplant recipients of any age were eligible.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial risks of bias and extracted data. Statistical analyses were performed using random effects meta-analysis. The risk estimates were expressed as a risk ratio (RR) for dichotomous variables and mean difference (MD) for continuous outcomes together with the corresponding 95% confidence interval (CI). The primary efficacy outcome was bone fracture. The primary safety outcome was acute graft rejection. Secondary outcomes included death (all cause and cardiovascular), myocardial infarction, stroke, musculoskeletal disorders (e.g. skeletal deformity, bone pain), graft loss, nausea, hyper- or hypocalcaemia, kidney function, serum parathyroid hormone (PTH), and bone mineral density (BMD).

MAIN RESULTS

In this 2019 update, 65 studies (involving 3598 participants) were eligible; 45 studies contributed data to our meta-analyses (2698 participants). Treatments included bisphosphonates, vitamin D compounds, teriparatide, denosumab, cinacalcet, parathyroidectomy, and calcitonin. Median duration of follow-up was 12 months. Forty-three studies evaluated bone density or bone-related biomarkers, with more recent studies evaluating proteinuria and hyperparathyroidism. Bisphosphonate therapy was usually commenced in the perioperative transplantation period (within 3 weeks) and regardless of BMD. Risks of bias were generally high or unclear leading to lower certainty in the results. A single study reported outcomes among 60 children and adolescents. Studies were not designed to measure treatment effects on fracture, death or cardiovascular outcomes, or graft loss.Compared to placebo, bisphosphonate therapy administered over 12 months in transplant recipients may prevent fracture (RR 0.62, 95% CI 0.38 to 1.01; low certainty evidence) although the 95% CI included the possibility that bisphosphonate therapy might make little or no difference. Fracture events were principally vertebral fractures identified during routine radiographic surveillance. It was uncertain whether any other drug class decreased fracture (low or very low certainty evidence). It was uncertain whether interventions for bone disease in kidney transplantation reduce all-cause or cardiovascular death, myocardial infarction or stroke, or graft loss in very low certainty evidence. Bisphosphonate therapy may decrease acute graft rejection (RR 0.70, 95% CI 0.55 to 0.89; low certainty evidence), while it is uncertain whether any other treatment impacts graft rejection (very low certainty evidence). Bisphosphonate therapy may reduce bone pain (RR 0.20, 95% CI 0.04 to 0.93; very low certainty evidence), while it was very uncertain whether bisphosphonates prevent spinal deformity or avascular bone necrosis (very low certainty evidence). Bisphosphonates may increase to risk of hypocalcaemia (RR 5.59, 95% CI 1.00 to 31.06; low certainty evidence). It was uncertain whether vitamin D compounds had any effect on skeletal, cardiovascular, death, or transplant function outcomes (very low certainty or absence of evidence). Evidence for the benefits and harms of all other treatments was of very low certainty. Evidence for children and young adolescents was sparse.

AUTHORS' CONCLUSIONS

Bisphosphonate therapy may reduce fracture and bone pain after kidney transplantation, however low certainty in the evidence indicates it is possible that treatment may make little or no difference. It is uncertain whether bisphosphonate therapy or other bone treatments prevent other skeletal complications after kidney transplantation, including spinal deformity or avascular bone necrosis. The effects of bone treatment for children and adolescents after kidney transplantation are very uncertain.

A Randomized Trial of Zoledronic Acid to Prevent Bone Loss in the First Year after Kidney Transplantation

BACKGROUND

Bone and mineral disorders commonly affect kidney transplant (KTx) recipients and have been associated with a high risk of fracture. Bisphosphonates may prevent or treat bone loss in such patients, but there is concern that these drugs might induce adynamic bone disease (ABD).

METHODS

In an open label, randomized trial to assess the safety and efficacy of zoledronate for preventing bone loss in the first year after kidney transplant, we randomized 34 patients before transplant to receive zoledronate or no treatment. We used dual-energy x-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HR-pQCT), and bone biopsies to evaluate changes in bone in the 32 evaluable participants between the time of KTx and 12 months post-transplant.

RESULTS

Both groups of patients experienced decreased bone turnover after KTx, but zoledronate itself did not affect this outcome. Unlike previous studies, DXA showed no post-transplant bone loss in either group; we instead observed an increase of bone mineral density in both lumbar spine and total hip sites, with a significant positive effect of zoledronate. However, bone biopsies showed post-transplant impairment of trabecular connectivity (and no benefit from zoledronate); HR-pQCT detected trabecular bone loss at the peripheral skeleton, which zoledronate partially attenuated.

CONCLUSIONS

Current immunosuppressive regimens do not contribute to post-transplant central skeleton trabecular bone loss, and zoledronate does not induce ABD. Because fractures in transplant recipients are most commonly peripheral fractures, clinicians should consider bisphosphonate use in patients at high fracture risk who have evidence of significantly low bone mass at these sites at the time of KTx.

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.

Current evidence on vitamin D deficiency and kidney transplant: What's new?

Kidney transplant is the treatment of choice for end-stage chronic kidney disease. Kidneys generate 1,25-dihydroxyvitamin D (calcitriol) from 25-hydroxyvitamin D (calcidiol) for circulation in the blood to regulate calcium levels. Transplant patients with low calcidiol levels have an increased risk of metabolic and endocrine problems, cardiovascular disease, type 2 diabetes mellitus, poor graft survival, bone disorders, cancer, and mortality rate. The recommended calcidiol level after transplant is at least 30 ng/mL (75 nmol/L), which could require 1000-3000 IU/d vitamin D3 to achieve. Vitamin D3 supplementation studies have found improved endothelial function and acute rejection episodes. However, since kidney function may still be impaired, raising calcidiol levels may not lead to normal calcitriol levels. Thus, supplementation with calcitriol or an analog, alfacalcidiol, is often employed. Some beneficial effects found include possible improved bone health and reduced risk of chronic allograft nephropathy and cancer.

Bone Disease and Serum Fibroblast Growth Factor-23 Levels in Renal Transplant Recipients

BACKGROUND

Posttransplantation bone disease develops commonly and results in important complications. In this study, we aimed to investigate the relationship between bone diseases and serum fibroblast growth factor-23 (FGF-23) in renal transplant recipients.

METHODS

This study was conducted in 106 kidney transplant recipients (KTrs; group G1) and 30 patients with chronic kidney disease (group G2). Patients with fever, heart failure, angina pectoris, acute renal failure, malignant disease, or any gastrointestinal disease were excluded. KTrs were treated with triple immunosuppressive drugs including glucocorticoids. Complete blood count (CBC), blood urea nitrogen (BUN), creatinine, glomerular filtration rate (GFR, Modification of Diet in Renal Disease [MDRD] formula), lipid profile, calcium (Ca), phosphorous (P), parathormone (PTH), 25OHD3, serum levels of tacrolimus/cyclosporine, and intact FGF-23 were measured. Bone mineral density (BMD) was measured with dual energy X-ray absorptiometry.

RESULTS

The mean patient age was 40.1 ± 11.1 years and 39.2 ± 11.3 years in G1 and G2, respectively (P > .05). In G1 and G2, 76 and 15 patients were male, respectively. Compared with the G2 patients, G1 patients had lower body mass index (BMI), serum glucose levels, P, Mg, and Ca·P (P < .05 for all). T scores of the lumbar vertebrae/femur were -1.82 ± 0.99/-1.34 ± 0.89 and -1.13 ± 1.34/-0.51 ± 1.18 in G1 and G2 patients, respectively (P < .05 for all). The incidences of osteopenia/osteoporosis in the lumbar spine and femur were 50.9%/27.4% and 57.5%/10.4% in G1 and 16.6%/23.3%, and 40%/3.3% in G2. There were positive correlations between BMD and BMI, the time elapsed after renal transplantation, and GFR. In our study, a statistically significant relationship was found between lipid parameters and BMD, PTH, and 250HD3 levels, as well as use of corticosteroid and calcineurin inhibitors (P < .05 for all). In G1 and G2, BMD of the lumbar spine in patients with serum creatinine >1.5 mg/dL was lower than that in patients with serum creatinine <1.5 mg/dL.

CONCLUSION

The association between age and BMD was found only in the femur of KTrs. No relationship was observed between serum FGF-23 levels and BMD values. In both groups, the BMD T score of the lumbar spine was lower compared to the BMD T score of the femur and in patients with serum creatinine >1.5 mg/dL. In long-term follow-up of renal transplantation by as much as 58 months, the incidence of bone disease such as osteoporosis/osteopenia was as high as 67% and was also higher than that of nontransplant patients with similar GFR. In addition to decreased renal function, dyslipidemia, inflammation, and continuing hypophosphatemia were also accompanied by decreased BMD as in cardiovascular disease in KTrs.

CYP3A4 is a crosslink between vitamin D and calcineurin inhibitors in solid organ transplant recipients: implications for bone health

The use of calcineurin inhibitors (CNIs) and vitamin D deficiency may contribute to the pathogenesis of post-transplant bone disease. CNIs and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) are substrates of the drug-metabolizing enzyme CYP3A4. This review summarizes the indications for the use of activated vitamin D analogs in post-transplant care and the current knowledge on the impact of CNIs on bone. We searched for clinical evidence of the interaction between CNIs and 1,25(OH)₂D₃. We also provide an overview of the literature on the interplay between vitamin D metabolism and CYP3A4 in experimental and clinical settings and discuss its possible implications for solid organ transplant recipients. In conclusion, there is a body of evidence on the interplay between vitamin D and the drug-metabolizing enzyme CYP3A4, which may have therapeutic implications.

Inverse Association Between Serum Osteoprotegerin and Bone Mineral Density in Renal Transplant Recipients

BACKGROUND

Osteoprotegerin (OPG) has pleiotropic effects on bone metabolism as well as endocrine function. Our aim was to evaluate the relationship between bone mineral density (BMD) and serum OPG concentration in renal transplant recipients.

METHODS

Fasting blood samples were obtained from 69 renal transplant recipients. BMD was measured in lumbar vertebrae (L2-L4) by dual-energy X-ray absorptiometry. Eight patients (11.6%) had BMD values indicative of osteoporosis, 28 patients (40.6%) had BMD values indicative of osteopenia, and 33 patients had normal BMD values. Increased serum OPG levels (P < .001), decreased body mass index (BMI) (P = .033), and decreased body weight (P = .010) were significantly correlated with low lumbar T-score cut-off points between groups (normal, osteopenia, and osteoporosis).

RESULTS

Women had significantly lower lumbar BMD values than men (P = .013). Menopause (P = .005), use of tacrolimus (P = .020), and use of cyclosporine (P = .046) were associated with lower lumbar BMD in renal transplant recipients. Univariate linear regression analysis revealed that lumbar BMD was positively correlated with height (P = .016), body weight (P = .001), and BMI (P = .015) and negatively correlated with age (P = .039) and log-OPG (P = .001). Multivariate linear regression analysis revealed that log-OPG (β: -0.275, R(2) change = 0.154, P = .014), body weight (β: 0.334, R(2) change = 0.073, P = .004), and age (β: -0.285, R(2) change = 0.079, P = .008) were independent predictors of lumbar BMD values in renal transplant recipients.

CONCLUSIONS

Serum OPG concentration correlated negatively with lumbar BMD values in renal transplant recipients.

Bone Disease after Kidney Transplantation

Bone and mineral disorders occur frequently in kidney transplant recipients and are associated with a high risk of fracture, morbidity, and mortality. There is a broad spectrum of often overlapping bone diseases seen after transplantation, including osteoporosis as well as persisting high- or low-turnover bone disease. The pathophysiology underlying bone disorders after transplantation results from a complex interplay of factors, including preexisting renal osteodystrophy and bone loss related to a variety of causes, such as immunosuppression and alterations in the parathyroid hormone-vitamin D-fibroblast growth factor 23 axis as well as changes in mineral metabolism. Management is complex, because noninvasive tools, such as imaging and bone biomarkers, do not have sufficient sensitivity and specificity to detect these abnormalities in bone structure and function, whereas bone biopsy is not a widely available diagnostic tool. In this review, we focus on recent data that highlight improvements in our understanding of the prevalence, pathophysiology, and diagnostic and therapeutic strategies of mineral and bone disorders in kidney transplant recipients.

Metabolic consequences of modern immunosuppressive agents in solid organ transplantation

Among other factors, sophistication of immunosuppressive (IS) regimen accounts for the remarkable success attained in the short- and medium-term solid organ transplant (SOT) survival. The use of steroids, mycophenolate mofetil and calcineurin inhibitors (CNI) have led to annual renal graft survival rates exceeding 90% in the last six decades. On the other hand, attrition rates of the allograft beyond the first year have remained unchanged. In addition, there is a persistent high cardiovascular (CV) mortality rate among transplant recipients with functioning grafts. These shortcomings are in part due to the metabolic effects of steroids, CNI and sirolimus (SRL), all of which are implicated in hypertension, new onset diabetes after transplant (NODAT), and dyslipidemia. In a bid to reduce the required amount of harmful maintenance agents, T-cell-depleting antibodies are increasingly used for induction therapy. The downsides to their use are greater incidence of opportunistic viral infections and malignancy. On the other hand, inadequate immunosuppression causes recurrent rejection episodes and therefore early-onset chronic allograft dysfunction. In addition to the adverse metabolic effects of the steroid rescue needed in these settings, the generated proinflammatory milieu may promote accelerated atherosclerotic disorders, thus setting up a vicious cycle. The recent availability of newer agent, belatacept holds a promise in reducing the incidence of metabolic disorders and hopefully its long-term CV consequences. Although therapeutic drug monitoring as applied to CNI may be helpful, pharmacodynamic tools are needed to promote a customized selection of IS agents that offer the most benefit to an individual without jeopardizing the allograft survival.

Effect of Twice-Yearly Denosumab on Prevention of Bone Mineral Density Loss in De Novo Kidney Transplant Recipients: A Randomized Controlled Trial

We conducted an open-label, prospective, randomized trial to assess the efficacy and safety of RANKL inhibition with denosumab to prevent the loss of bone mineral density (BMD) in the first year after kidney transplantation. Ninety kidney transplant recipients were randomized 1:1 2 weeks after surgery to receive denosumab (60 mg at baseline and 6 months) or no treatment. After 12 months, total lumbar spine areal BMD (aBMD) increased by 4.6% (95% confidence interval [CI] 3.3-5.9%) in 46 patients in the denosumab group and decreased by -0.5% (95% CI -1.8% to 0.9%) in 44 patients in the control group (between-group difference 5.1% [95% CI 3.1-7.0%], p < 0.0001). Denosumab also increased aBMD at the total hip by 1.9% (95% CI, 0.1-3.7%; p = 0.035) over that in the control group at 12 months. High-resolution peripheral quantitative computed tomography in a subgroup of 24 patients showed that denosumab increased volumetric BMD at the distal tibia and radius (all p < 0.05). Biomarkers of bone turnover (C-terminal telopeptide of type I collagen, procollagen type I N-terminal propeptide) markedly decreased with denosumab (all p < 0.0001). Episodes of cystitis and asymptomatic hypocalcemia occurred more often with denosumab, whereas graft function, rate of rejections, and incidence of opportunistic infections were similar. In conclusion, denosumab increased BMD in the first year after kidney transplantation but was associated with more frequent episodes of urinary tract infection.

Vascular calcification, bone and mineral metabolism after kidney transplantation

The development of end stage renal failure can be seen as a catastrophic health event and patients with this condition are considered at the highest risk of cardiovascular disease among any other patient groups and risk categories. Although kidney transplantation was hailed as an optimal solution to such devastating disease, many issues related to immune-suppressive drugs soon emerged and it became evident that cardiovascular disease would remain a vexing problem. Progression of chronic kidney disease is accompanied by profound alterations of mineral and bone metabolism that are believed to have an impact on the cardiovascular health of patients with advanced degrees of renal failure. Cardiovascular risk factors remain highly prevalent after kidney transplantation, some immune-suppression drugs worsen the risk profile of graft recipients and the alterations of mineral and bone metabolism seen in end stage renal failure are not completely resolved. Whether this complex situation promotes progression of vascular calcification, a hall-mark of advanced chronic kidney disease, and whether vascular calcifications contribute to the poor cardiovascular outcome of post-transplant patients is reviewed in this article.

The evaluation of bone metabolism in children with renal transplantation

This study aims to evaluate BMD and bone biomarkers and to investigate the effects of immunosuppressives on bone disease after RTx. Thirty-three RTR aged 16.7 ± 3.7 yr and healthy controls (n = 32) were enrolled. There was no difference between pre-RTx BMD and BMD at the time of study (45.9 ± 30.9 months after RTx), while both values were lower than controls (p < 0.01 and p < 0.05, respectively). Worst BMD scores were obtained at sixth month after RTx (-0.2 ± 0.9) and best at fourth year (1.4 ± 1.3). 25-hydroxy-(OH) vitamin D and OPG were higher in RTR (p < 0.001). BMD z scores negatively correlated with OPG and cumulative CS doses at the time of study (r = -0.344, p < 0.05 and r = -0.371, p < 0.05, respectively). Regression analysis revealed OPG as the only predictor of BMD (β -0.78, 95% CI -0.004 to -0.013, p < 0.001). The increase in OPG, a significant predictor of BMD, could either be secondary to graft dysfunction or for protection against bone loss. CS doses should be minimized to avoid their untoward effects on bone metabolism.

Mechanism and Treatment Strategy of Osteoporosis after Transplantation

Osteoporosis (OP) has emerged as a frequent and devastating complication of organ solid transplantation process. Bone loss after organ transplant is related to adverse effects of immunosuppressants on bone remodeling and bone quality. Many factors contribute to the pathogenesis of OP in transplanted patients. Many mechanisms of OP have been deeply approached. Drugs for OP can be generally divided into "bone resorption inhibitors" and "bone formation accelerators," the former hindering bone resorption by osteoclasts and the latter increasing bone formation by osteoblasts. Currently, bisphosphonates, which are bone resorption inhibitors drugs, are more commonly used clinically than others. Using the signaling pathway or implantation bone marrow stem cell provides a novel direction for the treatment of OP, especially OP after transplantation. This review addresses the mechanism of OP and its correlation with organ transplantation, lists prevention and management of bone loss in the transplant recipient, and discusses the recipients of different age and gender.