Bone remodeling after renal transplantation

Evaluation of Clinical and Laboratory Factors Affecting Bone Mineral Density Measurements in Patients with Kidney Transplant

Histological evidence of osteodystrophy and osteopenia is encountered in most patients who have undergone successful renal transplantation. Renal transplantation may be beneficial for correcting uremia-related problems in end-stage renal disease patients; however, its benefit is limited in bone metabolism disorders. The present study aims to evaluate bone mass measurements and investigate the influencing factors in patients with renal transplant. One hundred and eighteen patients (83 males and 35 females) with a mean age of 40.2 ± 11.8 yr (range 20-67) were included in the present study. The laboratory and the clinical data of the patients were retrospectively analyzed. The association between bone mineral density (BMD) measurements and the demographic characteristics of the patients, serum creatinine, parathormone, calcium, phosphorous, alkaline phosphatase, 25-hydroxyvitamin D and the glomerular filtration rate were evaluated. Of the patients, 23.7% (n =28) had normal, 48.3% (n = 57) had osteopenic and 28% (n = 33) had osteoporotic BMD values. A significant positive correlation was determined between the body mass index (BMI) and the BMD measurement results (p = 0.001; r = 0.385). A negative correlation was determined between the BMD values and the serum parathormone (p = 0.012; r = -0.237). BMD values were significantly lower in the group that had not received mammalian target of rapamycin (mTOR) inhibitor (p = 0.026). Conclusion: BMI values, mTOR inhibitor treatment and serum parathormone levels had an effect on the BMD measurement values.

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.

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.

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.

Bone mineral density in patients with end-stage renal disease and its evolution after kidney transplantation

Renal transplantation is associated with abnormalities of the structure and function of the musculoskeletal system. No data are available on bone health in Indian patients with end-stage renal disease (ESRD) and its evolution after transplantation. Consecutive ESRD patients who underwent living donor renal transplantation were studied prospectively. Bone mineral density (BMD) was measured at lumbar vertebrae using quantitative computed tomography (CT) scan before transplantation and after 3 and 6 months. T and Z scores were calculated by comparing with normal control data, and values were correlated with various clinical and biochemical parameters. Of the 56 patients enrolled (mean age, 33.7 years; 47 males), 40 completed the 6-month follow-up. The vertebral trabecular bone density at the time of transplantation was 172±53 mg/cc and the average Z score was 0.26±1.7. There was a significant decline in BMD at 3 months (11.8%; P<0.0001) and 6 months (16%; P<0.0001) after transplantation. Both T and Z scores showed a significant decline at 3 and 6 months. There was a significant decline in intact parathormone (iPTH) levels after transplantation, but 15 (37.5%) patients continued to have raised iPTH 6 months after transplantation. The iPTH levels at 6 months had significant correlation with BMD decline (r=0.43, P=0.006). We conclude that Indian ESRD patients have relatively well-preserved BMD, but the density declines rapidly after transplantation. A significant proportion of patients exhibit persistent hyperparathyroidism 6 months after transplantation, which correlates with bone loss.

Parathyroid hormone levels in long-term renal transplant children and adolescents

Secondary hyperparathyroidism is a common complication of chronic renal failure. Kidney transplantation corrects renal insufficiency and most metabolic abnormalities but hyperparathyroidism persists in 50% of children after transplantation. The aim of this study was to investigate parathyroid hormone (PTH) course and potential risk factors for hyperparathyroidism in children after renal transplant. We collected data from 145 transplanted children (mean follow-up 4.7 years). Intact PTH level (iPTH) rapidly decreased in the first 6 months post-transplant and continued to decline in the following years. iPTH was above the normal range in 69.1% of the patients at the time of transplant and in 47% 1 year later, this improvement continuing thereafter. Hypercalcemia was present in 20.3% of the patients before transplant and in 6.3 and 4.1% of patients 6 months and 1 year after transplant, respectively. Hypophosphatemia was present in 5.5% of the patients at 6 months, and 45.5% of the patients needed phosphorus supplements during the first 6 months after transplant. Multivariate analysis indicated pre-transplant hyperparathyroidism, dialysis duration, creatinine clearance and hypophosphatemia as predictors of persistent hyperparathyroidism. In kidney transplanted children, serum iPTH normalized in the long term in the majority of cases. Thus, parathyroidectomy should be reserved for selected patients.

Bone disease after renal transplantation

In light of greatly improved long-term patient and graft survival after renal transplantation, improving other clinical outcomes such as risk of fracture and cardiovascular disease is of paramount importance. After renal transplantation, a large percentage of patients lose bone. This loss of bone results from a combination of factors that include pre-existing renal osteodystrophy, immunosuppressive therapy, and the effects of chronically reduced renal function after transplantation. In addition to low bone volume, histological abnormalities include decreased bone turnover and defective mineralization. Low bone volume and low bone turnover were recently shown to be associated with cardiovascular calcifications, highlighting specific challenges for medical therapy and the need to prevent low bone turnover in the pretransplant patient. This Review discusses changes in bone histology and mineral metabolism that are associated with renal transplantation and the effects of these changes on clinical outcomes such as fractures and cardiovascular calcifications. Therapeutic modalities are evaluated based on our understanding of bone histology.

Regulation of bone formation and remodeling by G-protein-coupled receptor 48

G-protein-coupled receptor (GPCR) 48 (Gpr48; Lgr4), a newly discovered member of the glycoprotein hormone receptor subfamily of GPCRs, is an orphan GPCR of unknown function. Using a knockout mouse model, we have characterized the essential roles of Gpr48 in bone formation and remodeling. Deletion of Gpr48 in mice results in a dramatic delay in osteoblast differentiation and mineralization, but not in chondrocyte proliferation and maturation, during embryonic bone formation. Postnatal bone remodeling is also significantly affected in Gpr48(-/-) mice, including the kinetic indices of bone formation rate, bone mineral density and osteoid formation, whereas the activity and number of osteoclasts are increased as assessed by tartrate-resistant acid phosphatase staining. Examination of the molecular mechanism of Gpr48 action in bone formation revealed that Gpr48 can activate the cAMP-PKA-CREB signaling pathway to regulate the expression level of Atf4 in osteoblasts. Furthermore, we show that Gpr48 significantly downregulates the expression levels of Atf4 target genes/proteins, such as osteocalcin (Ocn; Bglap2), bone sialoprotein (Bsp; Ibsp) and collagen. Together, our data demonstrate that Gpr48 regulates bone formation and remodeling through the cAMP-PKA-Atf4 signaling pathway.

Alendronate is effective to treat bone loss in renal transplantation recipients

Bone loss is a common complication among renal transplant patients. Some studies have shown that alendronate may be effective to treat bone loss in these patients. In this study, we have reported our experience with administration of alendronate to treat bone loss in renal transplanted patients.

METHODS

The 46 kidney transplant recipients with bone loss were randomly divided into 2 groups: group I was treated with calcium and calcitriol, and group II with calcium, calcitriol, and alendronate. We examined bone mineral density (BMD) and biochemical indicators of both groups. All patients received cyclosporine and prednisone treatment.

RESULTS

There was no significant difference in age, body mass index, gender, immunosuppression, time since transplantation, 25(OH)D(3), or intact parathyroid hormone levels at study commencement. The BMD of the femoral neck was significantly increased (P < .05), and the serum type I collagen-cross-linked N telopeptide (NTx) dramatically (P < .05) decreased in posttransplantation group II recipients treated with calcium, calcitriol, and alendronate. There were also significant differences in BMD and serum NTx between recipients treated with versus without alendronate (P < .05).

CONCLUSION

At least in the short term, alendronate is a effective inhibitor for the treatment of bone loss in renal transplantation patients.

Treatment of renal transplant recipients with low bone mineral density: a randomized prospective trial of alendronate, alfacalcidol, and alendronate combined with alfacalcidol

We sought to compare the treatment modalities of alendronate, alfacalcidol, and alendronate combined with alfacalcidol in renal transplant recipients with low bone mineral density. Sixty-four kidney graft recipients (22 women, 42 men) were recruited to this study. Of these 64 patients, 9 served as the control group with T scores more than -1. The remaining 55 patients randomly assigned to treatment had T scores less than -1 and were assigned to 3 groups: group 1 received alfacalcidol (0.5 microg/d); group 2, alendronate (10 mg/d); and group 3, alendronate (10 mg/d) + alfacalcidol (0.5 microg/d per os). Twenty-five patients were allocated to alfacalcidol, 13 patients to alendronate, and 17 patients to alendronate + alfacalcidol treatment. Bone mineral densities of the lumbar spine and femoral neck were measured before and 12 months after treatment. The groups were compared for risk factors of osteoporosis, biochemistry, and bone mineral density. Kruskal-Wallis, one-way ANOVA, and Student t tests were used. With the alendronate + alfacalcidol group, bone mineral density at the lumbar spine significantly increased by 7.9% (P = .006) with a significant improvement in T score (P = .003). Bone mineral density at the femoral neck significantly increased by 8% in the alendronate + alfacalcidol group (P = .01) with a significant improvement in T score (P = .02). The use of a combination of alendronate and alfacalcidol seemed to be safe and more effective than the separate use of the 2 agents to improve bone mass in renal transplant recipients.

Calcium and bone metabolism pre- and post-kidney transplantation

Chronic kidney disease (CKD) is associated with significant disturbances in bone and mineral metabolism, the manifestations of which are heterogeneous in their expression and clinical impact. Over the last 2 decades, advances in the management of CKD and improved outcomes of kidney transplantation have led to the emergence of post-transplantation bone disease as a serious cause of morbidity in long-term survivors. The management of post-kidney transplantation bone disease represents a difficult challenge because of its complex pathophysiology and the paucity of clinical data on effective therapies. The optimal management of disturbances of bone and mineral metabolism before kidney transplantation forms the cornerstone of their successful management after transplantation. Therapeutic strategies to effectively and safely decrease skeletal morbidity after kidney transplantation are not yet clearly established.

Bisphosphonates are effective prophylactic of early bone loss after renal transplantation

INTRODUCTION

Rapid bone loss and fractures occur early after solid organ transplantation. We examined the preliminary results of a prospective study evaluating the efficacy of prophylactic use of bisphosphonates in renal allograft recipients.

METHODS

Bone mineral density (BMD) was measured at the lumbar spine and the hip by dual energy X-ray absorptiometry at 1, 6, 12 months. Alendronian or risedronian were initiated for patients with osteopenia or osteoporosis at 1 month who had no contraindications to bisphosphonates. The treatment lasted at least 6 months. Sixty-six patients were included in the study; 39 were treated with bisphosphonates (A), and 27 were drug-free (B). Presently, 24 group A and 13 group B patients have completed the 12-month observation period.

RESULTS

In group A 53.8% (21) subjects had osteoporosis and 46.2% (18), osteopenia. Mean T-score L(2)-L(4) in group A at 1, 6, and 12 months were: (-)2.22 +/- 1.06; (-)2.07 +/- 1.25; (-)1.89 +/- 1.07, respectively. The T-score increase between 6 and 12 months was significant (P = 0.0014). The relative rise in BMD L(2)-L(4) between 1 and 12 months was 2.26%. In group B mean T-score L(2)-L(4) at 1, 6, and 12 months were: (-)0.26 +/- 1.34; (-)0.80 +/- 1.19; (-)1.2 +/- 1.59, respectively. The T-score decrease between 1 and 12 months in group B was significant (P = .0082). The 12-month relative decrease in femoral neck and trochanter BMD in group B was (-)2.1% and (-)2.75%, respectively.

CONCLUSION

Bisphosphonates are effective for prophylaxis of rapid bone loss early after renal transplantation.

Bone disease in long-term renal transplant recipients with severe osteopenia: a cross-sectional study

BACKGROUND

Fracture is a disabling clinical outcome after transplantation, but there is little histopathological information on long-term renal recipients with severe osteopenia.

METHODS

Twenty kidney recipients (8.3+/-1.9 years after transplantation), 13 males and 7 females (five postmenopausal) with nearly normal renal function, affected by severe osteopenia (T-score: males= -4.9+/-0.28; females= -5.08+/-0.47) underwent bone biopsy and morphometric X-ray absorptiometry to evaluate vertebral fractures.

RESULTS

Histopathological diagnosis was osteoporosis-osteopenia in seven patients, osteitis fibrosa in six, prevalent osteomalacic lesion in six, and "normal" bone in one patient. Significant increases in osteoid volume (OV/BV), osteoid surface, osteoblastic surface (ObS/BS) and osteoid thickness were observed. OV/BV and Obs/BS ratios were inversely correlated to cumulative doses of MPRED (r2=0.85 P<.0001 for both ratios), whereas age, sex, time after transplantation, iPTH levels, and cumulative cyclosporine A dose were not related to osteoblastic indices. Osteoclast surface was slightly increased. Widened mineralization lag times were observed, with normalcy of the bone formation rate. Half of the patients showed fractured vertebrae. No differences in T scores were found when patients were subdivided into groups "with" or "without" vertebral fractures. A higher prevalence of fractures was observed in patients with osteoporosis-osteopenia compared to other osteopathies (P<0.02). No relationships between bone volume versus T-scores were observed.

CONCLUSIONS

In long-term renal transplant recipients, severe osteopenia does not predict osteoporosis alone. The main abnormality we found was an increase in osteoblastic activity with a slight mineralization defect. The heterogeneous bone illness we observed would suggest performing bone biopsy in these patients.

Relationship between Plasma Phospholipid Polyunsaturated Fatty Acid Composition and Bone Disease in Renal Transplantation

To investigate the relationship between polyunsaturated fatty acid (PUFA) and bone metabolism in renal transplant patients, plasma phospholipid (PP) PUFA levels, biochemical markers of bone turnover and bone mineral density (BMD) were determined in 22 recipients of a first renal allograft at baseline and after a mean 24.4 month follow-up. A significant increase in PP n-3 PUFA content, in the [n-3 PUFA/ arachidonic acid] ratio and in BMD values was observed, as well as a close correlation between the increase in PP n-3 PUFA content and femoral neck BMD. Multivariate regression analysis showed that BMD improvement was positively related to PP n-3 PUFA variation and baseline PP eicosapentaenoic acid levels, and negatively to PP arachidonic acid modification. Tacrolimus- versus cyclosporine-treated patients demonstrated a significant increase in femoral neck BMD and PP n-3 PUFA content. This is the first longitudinal study showing a link between PP-PUFA composition and bone disease in renal transplantation.

Osseous complications of pediatric transplantation

Adult stature and peak bone mass are achieved through childhood growth and development. Multiple factors impair this process in children undergoing solid organ transplantation, including chronic illness, pretransplant osteodystrophy, use of medications with negative impact on bone, and post-transplant renal dysfunction. While growth delay and short stature remain common, the most severe forms of transplant-related bone disease, fracture and avascular necrosis, appear to have become less common in the pediatric age group. Osteopenia is very prevalent in adult transplant recipients and probably also in pediatrics, but its occurrence and sequelae are difficult to study in these groups due to methodological shortfalls of planar densitometry related to short stature and altered patterns of growth and development. Although the effect on lifetime peak bone mass is not clear, data from adult populations suggest an elevated long-term risk of bone disease in children receiving transplants. Optimal management of pretransplantation osteodystrophy, attention to post-transplant renal insufficiency among both renal and non-renal transplant patients, reduction of steroid dose in select patients, and supplementation with calcium plus vitamin D during expected periods of maximal bone loss may improve bone health. Careful research is required to determine the role of bisphosphonate therapy in pediatric transplantation.

Prevalence and treatment of decreased bone density in renal transplant recipients: a randomized prospective trial of calcitriol versus alendronate

BACKGROUND

Reduced bone mineral density (BMD) is common in long-term renal transplant recipients and results in a high incidence of fractures. The optimal therapy for these patients is not known.

METHODS

Baseline BMD determinations were obtained in 211 long-term adult renal transplant recipients. One hundred and seventeen patients with a reduced BMD (T score < or = -1) were randomly assigned to treatment with alendronate and calcium (n=60) versus calcitriol and calcium (n=57). Of these, 46 and 51 patients, respectively, completed 1 year of treatment. Forty-nine patients who were not eligible or did not consent to the trial were followed prospectively.

RESULTS

Reduced baseline BMD (T score < or = -1) was present in 159 (78.7%) of patients at the lumbar spine or femur. There was no significant loss of BMD in the prospectively followed patients during 2.7 years. The average lumbar BMD increased from 0.984+/-0.149 to 1.025+/-0.143 g/cm2 (P<0.001) with alendronate and from 1.014+/-0.15 to 1.034+/-0.146 g/cm2 (P=0.002) with calcitriol. BMD at the femur increased from 0.809+/-0.092 to 0.836+/-0.107 g/cm2 (P<0.001) with alendronate and from 0.830+/-0.144 to 0.857+/-0.125 g/cm2 (P=0.023) with calcitriol.

CONCLUSIONS

One year of treatment with alendronate or calcitriol, both with calcium supplementation, resulted in significant increases in BMD at the lumbar spine and femur, with a trend toward alendronate being more effective at the spine (P=0.082). Further studies are needed to determine whether BMDs continue to increase after 1 year and whether there is any additional benefit to combining vitamin D and alendronate. Larger studies are needed to determine whether treatment decreases fracture rates.