Effect of daily oral vitamin D and calcium therapy, hypophosphatemia, and endogenous 1-25 dihydroxycholecalciferol on parathyroid hormone and phosphate wasting in renal transplant recipients

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.

Promoting bone health in children and adolescents following solid organ transplantation

Solid organ transplantation in children and adolescents provides many benefits through improving critical organ function, including better growth, development, cardiovascular status, and quality of life. Unfortunately, bone status may be adversely affected even when overall status is improving, due to issues with pre-existing bone disease as well as medications and nutritional challenges inherent post-transplantation. For all children and adolescents, bone status entering adulthood is a critical determinant of bone health through adulthood. The overall health and bone status of transplant recipients benefits from attention to regular physical activity, good nutrition, adequate calcium, phosphorous, magnesium and vitamin D intake and avoidance/minimization of soda, extra sodium, and obesity. Many immunosuppressive agents, especially glucocorticoids, can adversely affect bone function and development. Minimizing exposure to "bone-toxic" medications is an important part of promoting bone health in children post-transplantation. Existing guidelines detail how regular monitoring of bone status and biochemical markers can help detect bone abnormalities early and facilitate valuable bone-directed interventions. Attention to calcium and vitamin D supplementation, as well as tapering and withdrawing glucocorticoids as early as possible after transplant, can provide best bone outcomes for these children. Dual-energy X-ray absorptiometry can be useful to detect abnormal bone mass and fracture risk in this population and newer bone assessment methods are being evaluated in children at risk for poor bone outcomes. Newer bone therapies being explored in adults with transplants, particularly bisphosphonates and the RANKL inhibitor denosumab, may offer promise for children with low bone mass post-transplantation.

Bone disease following solid organ transplantation: A narrative review and recommendations for management from The European Calcified Tissue Society

INTRODUCTION

Solid organ transplantation is an established therapy for end-stage organ failure. Both pre-transplantation bone disease and immunosuppressive regimens result in rapid bone loss and increased fracture rates.

METHODS

The European Calcified Tissue Society (ECTS) formed a working group to perform a systematic review of existing literature on the consequences of end-stage kidney, liver, heart, and lung disease on bone health. Moreover, we assessed the characteristics of post-transplant bone disease and the skeletal effects of immunosuppressive agents and aimed to provide recommendations for the prevention and treatment of transplantation-related osteoporosis.

RESULTS

Characteristics of bone disease may differ depending on the organ that fails, but patients awaiting solid organ transplantation frequently depict a wide spectrum of bone and mineral abnormalities. Common features are a decreased bone mass and impaired bone strength with consequent high fracture risk, all of which are aggravated in the early post-transplantation period.

CONCLUSION

Both the underlying disease leading to end-stage organ failure and the immunosuppression regimens implemented after successful organ transplantation have detrimental effects on bone mass, quality and strength. Given existing ample data confirming the high frequency of bone disease in patients awaiting solid organ transplantation, we recommend that all transplant candidates should be assessed for osteoporosis and fracture risk and, if indicated, treated before and after transplantation. Since bone loss in the early post-transplantation period occurs in virtually all solid organ recipients and is associated with glucocorticoid administration, the goal should be to use the lowest possible dose and to taper and withdraw glucocorticoids as early as possible.

Mineral and Bone Disease in Kidney Transplant Recipients

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

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

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

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.

CKD-mineral and bone disorder management in kidney transplant recipients

Kidney transplantation, the most effective treatment for the metabolic abnormalities of chronic kidney disease (CKD), only partially corrects CKD-mineral and bone disorders. Posttransplantation bone disease, one of the major complications of kidney transplantation, is characterized by accelerated loss of bone mineral density and increased risk of fractures and osteonecrosis. The pathogenesis of posttransplantation bone disease is multifactorial and includes the persistent manifestations of pretransplantation CKD-mineral and bone disorder, peritransplantation changes in the fibroblast growth factor 23-parathyroid hormone-vitamin D axis, metabolic perturbations such as persistent hypophosphatemia and hypercalcemia, and the effects of immunosuppressive therapies. Posttransplantation fractures occur more commonly at peripheral than central sites. Although there is significant loss of bone density after transplantation, the evidence linking posttransplantation bone loss and subsequent fracture risk is circumstantial. Presently, there are no prospective clinical trials that define the optimal therapy for posttransplantation bone disease. Combined pharmacologic therapy that targets multiple components of the disordered pathways has been used. Although bisphosphonate or calcitriol therapy can preserve bone mineral density after transplantation, there is no evidence that these agents decrease fracture risk. Moreover, bisphosphonates pose potential risks for adynamic bone disease.

Therapeutic management of post-kidney transplant hyperparathyroidism

Left uncontrolled, persistent post-kidney transplant hyperparathyroidism (HPT) may lead to or exacerbate pre-existing bone and cardiovascular disease. Parathyroidectomy has long been the primary treatment option for long-term uncontrolled HPT in post-kidney transplant patients. However, patients with contraindications for surgery and parathyroidectomy-associated complications, including graft loss, highlight the need for other approaches. Conventional medical therapies have limited impact on serum calcium (Ca) and parathyroid hormone (PTH) levels. Bisphosphonates and calcitonin, used to spare bone loss, and phosphorus supplementation, to correct hypophosphatemia, do not directly regulate PTH or Ca. Although vitamin D supplementation can reduce PTH, it is often contraindicated because of hypercalcemia. Studies of the calcimimetic cinacalcet in patients with post-kidney transplant HPT suggest that it can rapidly reduce serum PTH and Ca concentrations while increasing serum phosphorus concentrations toward the normal range. Although the clearest application for cinacalcet is the non-surgical treatment of hypercalcemic patients with persistent HPT, current indications for other transplant patients are as yet uncertain. Further studies are needed to determine the utility of cinacalcet in patients with spontaneous resolution of HPT or low bone turnover. This review discusses the pathophysiology of post-kidney transplant HPT, associated complications, and current options for clinical management.

Tertiary excess of fibroblast growth factor 23 and hypophosphatemia following kidney transplantation

Hypophosphatemia caused by inappropriate urinary phosphate wasting is a frequent metabolic complication of the early period following kidney transplantation. Although previously considered to be caused by tertiary hyperparathyroidism, recent evidence suggests a primary role for persistently elevated circulating levels of the phosphorus-regulating hormone, FGF23. In the setting of a healthy renal allograft, markedly increased FGF23 levels from the dialysis period induce renal phosphate wasting and inhibition of calcitriol production, which contribute to hypophosphatemia. While such tertiary FGF23 excess and resultant hypophosphatemia typically abates within the first few weeks to months post-transplant, some recipients manifest persistent renal phosphate wasting. Furthermore, increased FGF23 levels have been associated with increased risk of kidney disease progression, cardiovascular disease, and death outside of the transplant setting. Whether tertiary FGF23 excess is associated with adverse transplant outcomes is unknown. In this article, we review the physiology of FGF23, summarize its relationship with hypophosphatemia after kidney transplantation, and speculate on its potential impact on long-term outcomes of renal allograft recipients.

Post-renal transplantation hypophosphatemia

An understanding of the pathophysiologic mechanisms of post-renal transplant (PRT) bone disease is of important clinical significance. Although bone disease occurs after all solid organ transplantation, the cumulative skeletal fracture rate remains high in PRT subjects while reaching a plateau with other transplantations. One major difference in the pathophysiology of PRT bone disease is, perhaps, due to persistent renal phosphorus (Pi) wasting. Novel phosphaturic agents have recently been suggested to participate in the development of bone disease in PRT subjects. However, it is unclear as of yet whether these factors alone or in conjunction with excess parathyroid hormone (PTH) secretion play a key role in the development of negative Pi balance and consequent bone disease in this population. In this review, I present a natural history of PRT hypophosphatemia and persistent renal Pi leak, provide pathophysiologic insight into these developments, and discuss the difficulty in diagnosing these phenotypes in both adult and pediatric populations.

A blueprint for randomized trials targeting phosphorus metabolism in chronic kidney disease

The diagnosis of chronic kidney disease (CKD) confers dismal clinical outcomes regardless of whether patients are initiating dialysis and face a median survival of only 2-3 years or they have earlier-stage CKD and face a risk of death that is greater than the risk of progression to dialysis. These poor outcomes are driven by extraordinarily high rates of cardiovascular disease that historically have not responded to risk-factor modification strategies proven to attenuate risk in the general population. Nor have measures aimed at increasing the dose or quality of dialysis made an appreciable dent in mortality. Still worse, interventions that were expected to be beneficial resulted in increased mortality in recent trials. Although this apparent lack of progress in advancing the care of CKD is discouraging, resignation is not an option. On the contrary, with the rising rates of CKD worldwide, there is an urgent need to rigorously test novel therapeutic strategies in randomized trials. The breadth of accumulating evidence linking disordered phosphorus metabolism to adverse outcomes spans in vitro, animal, and human studies, and positions phosphorus management as an attractive target for intervention. Although opinion-based practice guidelines promote phosphorus management strategies that are widely accepted in dialysis patients, there is a clear need to perform randomized controlled trials to prove or disprove the benefits of therapy. Perhaps even more important, the discovery of fibroblast growth factor 23 (FGF23) and its potential as a novel diagnostic to identify disordered phosphorus metabolism at an early, subclinical state has presented the opportunity to develop placebo-controlled randomized trials in pre-dialysis CKD patients with normal serum phosphate levels. This commentary considers the justification and challenges for such trials and presents a 'first-draft' blueprint of distinct trial approaches to initiate a dialog that will ultimately culminate in studies aimed at improving survival across the spectrum of CKD.

Calcium metabolism in the early posttransplantation period

BACKGROUND AND OBJECTIVES

Information on the time course of serum calcium levels after renal transplantation is scanty, especially in the early posttransplantation period. Both the abrupt cessation of calcium-containing phosphorus binders and vitamin D (analogs) at the time of surgery and the recovery of renal function may be hypothesized to affect serum calcium levels in this period.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this prospective observational study, biointact parathyroid hormone, calcidiol, calcitriol, calcium, and phosphorus levels were monitored in 201 renal transplant recipients at the time of transplantation and 3 mo thereafter. In addition, the serum calcium nadir and peak in each individual patient within this time frame were identified and the urinary fractional calcium excretion was determined at month 3.

RESULTS

Serum calcium levels followed a biphasic pattern with a significant decline during the first postoperative week, followed by a significant increase. High pretransplantation parathyroid hormone levels protect against hypocalcemia within the first postoperative week but put patients at risk for hypercalcemia later. These complications, occurring in 41 and 14% of the patients, respectively, most probably reflect inappropriate calcium release from the skeleton, rather than inappropriate renal calcium handling.

CONCLUSIONS

Our data indicate that both hypo- and hypercalcemia are prevalent in the early posttransplantation period. Pretransplantation parathyroid function is an important predictor of posttransplantation calcium levels.

Tertiary 'hyperphosphatoninism' accentuates hypophosphatemia and suppresses calcitriol levels in renal transplant recipients

Hypophosphatemia and inappropriately low calcitriol levels are frequently observed following successful renal transplantation. Fibroblast growth factor-23 (FGF-23) is a recently characterized phosphaturic hormone that inhibits renal 1 alpha-hydroxylase activity and may be involved in the pathogenesis of both phenomena. The following hypotheses were tested: pretransplant FGF-23 predicts posttransplant FGF-23, FGF-23 predicts posttransplant hypophosphatemia and FGF-23 is associated with decreased calcitriol levels independent of renal and parathyroid function. Serum biointact parathyroid hormone (PTH), calcidiol, calcitriol, full-length FGF-23, calcium and phosphate were monitored in 41 renal transplant recipients at the time of transplantation (pre) and 3 months thereafter (post). In addition, serum phosphate nadir in each individual patient was identified and urinary fractional excretion of phosphate (FE(PO4)) at month 3 was calculated. High FGF-23(post) levels were independently associated with high FGF-23(pre), low calcitriol(post) and high calcium(post) levels. FGF-23, but none of the other mineral metabolism indices, was an independent predictor of the phosphate nadir in the early posttransplant period. A high FGF-23(post) level was independently associated with a high FE(PO4). High FGF-23(post) and creatinine levels and low PTH(post) levels were independently associated with low calcitriol(post) levels. In conclusion, our data indicate that persistence of FGF-23 contributes to hypophosphatemia and suboptimal calcitriol levels in renal transplant recipients.

Post-transplant hypophosphatemia: Tertiary 'Hyper-Phosphatoninism'?

Hypophosphatemia is a common complication of kidney transplantation. Tertiary hyperparathyroidism has long been thought to be the etiology, but hypophosphatemia can occur despite low parathyroid hormone (PTH) levels and can persist after high PTH levels normalize. Furthermore, even in the setting of normal allograft function, hypophosphatemia, and hyperparathyroidism, calcitriol levels remain inappropriately low following transplantation, suggesting that mechanisms other than PTH contribute. Fibroblast growth factor-23 (FGF-23) induces phosphaturia, inhibits calcitriol synthesis, and accumulates in chronic kidney disease. We performed a prospective, longitudinal study of 27 living donor transplant recipients to test the hypotheses that excessive FGF-23 accounts for hypophosphatemia and decreased calcitriol levels following kidney transplantation. Hypophosphatemia <2.5 mg/dl developed in 85% of subjects, including one who had previously undergone parathyroidectomy; 37% developed phosphate < or =1.5 mg/dl. The mean pre-transplant FGF-23 level was 1,218+/-542 RU/ml. Within the first week following transplantation, mean levels decreased to 557+/-579 RU/ml, which were still above normal. FGF-23 was independently associated with serum phosphate (P < 0.01), urinary excretion of phosphate (P < 0.01), and calcitriol levels (P < 0.01); PTH was not independently associated with any of these parameters. We calculated area under the curve for FGF-23 and PTH between the pre- and first post-transplant levels as a summary measure of early exposure to these phosphaturic hormones. An area under the FGF-23 curve greater than the median was associated with a relative risk of developing hypophosphatemia < or =1.5 mg/dl of 5.3 (P = 0.02) compared with lower levels. Increased area under the PTH curve was not associated with greater risk of hypophosphatemia. Excessive FGF-23 exposure in the early post-transplant period appears to be more strongly associated with post-transplant hypophosphatemia than PTH.

Post-renal transplantation hypophosphatemia: a review and novel insights

PURPOSE OF REVIEW

This review intends to elucidate the pathophysiologic mechanism of renal phosphorus loss in the post-renal transplantation population. This review will provide new insight in to the pathophysiologic mechanism(s) responsible for the development of this phenomenon and will also explore the pathogenetic role of persistent phosphorus wasting in the development of post-renal transplantation osteodystrophy.

RECENT FINDINGS

Recently, the phosphaturic hormone, fibroblast growth factor-23, has been ascertain to be increased in the sera of patients with chronic kidney and end-stage renal disease. There is new evidence that a non-PTH humoral factor is persistently present in post-renal transplantation patients that is likely responsible for the observed persistent renal phosphorus loss. We offer that fibroblast growth factor-23 (and/or other phosphatonins) is the culprit factor responsible for the phenomenon of persistent hypophosphatemia in post-renal transplantation patients. Moreover, we believe that the phenomenon of persistent renal phosphorus wasting is an important but overlooked cause of osteodystrophy and increased fracture risk in this patient population.

SUMMARY

The pathophysiology of post-renal transplantation phosphorus wasting is complex and to date is still not fully recognized. Further studies of the regulatory mechanism of fibroblast growth factor-23 and its metabolism may offer additional insights into phosphorus homeostasis and its clinical application in the post-renal transplantation population.

A prospective randomized study for prevention of postrenal transplantation bone loss

BACKGROUND

We aimed to investigate different treatment drugs for the prevention of post-transplant bone loss.

METHODS

Sixty adult male recent renal transplant recipients were enrolled into the study. Patients were randomized into 4 groups: group I received daily alfacalcidol 0.5 microg PO; group II received oral alendronate 5 mg/day; group III received intranasal salmon calcitonin 200 IU every other day; and group IV was considered a control group. Every patient was supplemented with daily 500 mg oral calcium carbonate. Parameters of bone metabolism were measured before and at 12 months after starting treatment. Bone mineral density (BMD) was measured by (DEXA) at lumber spine, femoral neck, and forearm before and after treatment period.

RESULTS

BMD was increased at lumber spine by 2.1%, 0.8%, 1.7%, by 1.8%, 0.6%, 1.6% at femoral neck, and by 3.2%, 1.9%, 2.6% at forearm in groups I, II, and III, respectively, while it decreased by 3.2%, 3.8%, and 1.8% at the same sites, respectively, in control group (P= <0.05). iPTH level decreased significantly in group I, while the decrease was insignificant in other groups (P= 0.003). All other parameters were not statistically significant between treatment groups. Apart from transient hypocalcaemia in 3 patients in group II, and 2 patients in group III, no other significant adverse effects were noted.

CONCLUSION

This study proves that early bone loss that occurs during the first 12 months after renal transplantation could be prevented by alfacalcidol, calcitonin, or alendronate. Among the treatment groups, alfacalcidol significantly improved the hyperparathyroidism. All treatment drugs are safe and tolerable.

A prospective randomized study for the treatment of bone loss with vitamin d during kidney transplantation in children and adolescents

The effect of treatment with alfacalcidol on post-transplantation bone loss in children and adolescents was investigated. Of the 63 young patients who received renal transplant and were subjected to dual-energy x-ray absorptiometry (DEXA), 30 patients had low-bone mineral density (BMD) (z-score < or = -1) and were enrolled into the study. Their mean age at the time of transplantation was 14.5 +/- 4.0 years and the mean duration after transplantation was 48 +/- 34 months. Patients with low BMD were randomized into two equal homogeneous groups: group 1 (control) received placebo and group 2 received daily alfacalcidol 0.25 microg by mouth. Parameters of bone metabolism (intact parathyroid hormone, serum osteocalcin and urinary deoxypyridinoline) and BMD were assessed before and after the study period. After 12 months of treatment BMD at the lumber spine decreased from -2.2 to -2.5 in group 1 while it increased from -2.1 to -0.6 in group 2 (p < 0.001). Serum intact parathyroid hormone level decreased significantly in group 2 (p = 0.042). Apart from transient hypercalcemia in 1 patient in group 2, no other significant adverse effects were noted. This study suggested the value of alfacalcidol in the treatment of bone loss in young renal transplant recipients.

Disease progression and outcomes in chronic kidney disease and renal transplantation

BACKGROUND

It is unknown whether renal transplant recipients (RTR) have better outcomes and disease progression rates compared to patients with chronic kidney disease (CKD) when matched for the level of kidney function.

METHODS

We analyzed data on 1762 patients with CKD (N = 872) and RTR (N = 890) over 16 years, applying the new Kidney/Disease Outcomes Quality Initiative (K/DOQI) staging system for CKD in a single center retrospective study. Patients were further divided based their native kidney disease. We determined disease progression by the slope of creatinine clearance decline and patient and kidney survival rates adjusted for age, gender and stage of kidney function, using Cox proportional hazards models.

RESULTS

The overall rate of creatinine clearance decline in patients with CKD was -6.6 +/- 8.7 mL/min/year compared to -1.9 +/- 4.7 mL/min/year in RTR (P < 0.0001). The rate of decline per stage of CKD was also significantly lower in RTR. Whereas overall kidney survival was higher in RTR compared to patients with CKD (49.6% vs. 17.2%, respectively, P < 0.001), patient survival was not statistically different between the two groups (74.7% vs. 80.3%, respectively, P = 0.25).

CONCLUSION

RTR had similar mortality rates compared to patients with CKD despite enjoying slower rates of disease progression and better kidney survival rates. These data suggest that RTR are a unique subset of patients with CKD whose comorbid conditions likely offset the potential benefits of slower rates of progression.

Hyperparathyroidism and long-term bone loss after renal transplantation

BACKGROUND

While early bone loss after renal transplantation (RT) is well described, factors affecting the long-term fate of bone have received less attention.

METHODS

Whole body (WB), lumbar spine (LS) and femoral neck (FN) bone mineral density (BMD) was measured using dual energy X-ray absorptionometry in 126 stable RT patients and repeated in 114 survivors after 3 yr. Percentage change per year (%/yr) was correlated to clinical and biochemical markers of bone metabolism.

RESULTS

Low bone mass was a marker of increased mortality (FN < 80% normal 6.3%/yr; >80% 2.2%/yr). Percent change was WB -0.7 +/- 1.5 (p < 0.01); LS -0.3 +/- 2.6; FN -1.0 +/- 3.0 (p < 0.01) and, corrected for expected loss for age and sex: WB -0.5 (p < 0.01); LS 0.0; FN -0.8 (p < 0.05). Factors associated with increased loss rates were (LS%): short RT duration [<2 yr: -3.1 (p < 0.01)], high prednisone dose [>9 mg/d: -1.9 (p < 0.01)], high cyclosporine trough concentration [>175 ng/L: -1.9 (p < 0.05)], high hyperparathyroidism (PTH) [>150 ng/L: -1.5 (p < 0.05)], high alkaline phosphatase [>275 U/L: -1.6 (p < 0.05)], high osteocalcin [>75 microg/L: -1.6 (p < 0.05)]. Marginal detrimental effects of uremia, hypoalbuminemia and hyperphosphatemia were noted. Thiazide treatment seemed to protect against, and furosemide to exacerbate, bone loss, but this may have been related to associated uremia. Patients treated with vitamin D gained bone, while untreated patients with low initial 1,25-dihydroxyvitamin D lost bone [FN%-2.1 (p < 0.05)]. The prevalence of PTH (52%) and hypercalcemia (22%) remained unchanged. There was no effect of sex hormone levels, calcium and phosphate excretion, or serum calcium.

CONCLUSION

While LS BMD stabilizes after RT, there is a continuing loss of WB and FN BMD. The major causes of bone loss are steroid therapy and continuing PTH, with no tendency towards spontaneous resolution. Increased vitamin D and calcium therapy should be considered for this patient group, and more aggressive therapy, e.g. parathyroidectomy given for patients with resistant PTH of >150 ng/L.

Bone disease after renal transplantation

Bone disease is common after renal transplantation. The main syndromes are bone loss with a consequent fracture rate of 3% per year, osteonecrosis of the hip, and bone pain. The causes of disease include preexisting uremic osteodystrophy (hyperparathyroidism, aluminum osteomalacia, beta2-associated amyloidosis, and diabetic osteopathy), postoperative glucocorticoid therapy, poor renal function, and ongoing hyperparathyroidism, as the result of either autonomous transformation of the parathyroid gland or ongoing physiologic stimuli. Cyclosporine A treatment, hyperphosphaturia, and a pathogenic vitamin D allele have also been implicated. Bone loss is particularly pronounced during the first year after operation, amounting to up to 9% of bone mass. The clinical and biochemical picture is consistent with a high turnover bone disease, but histomorphometric studies do not completely support this. Principal prophylactic options include preoperative osteodystrophy prophylaxis; postoperative calcium, vitamin D, or calcitriol therapy; estrogen therapy for postmenopausal women; and parathyroidectomy for medically intractable hyperparathyroidism. Recently, prophylactic biphosphonate treatment has shown promise, but the exact indications for treatment remain to be determined.

Recommendations for the outpatient surveillance of renal transplant recipients. American Society of Transplantation

Many complications after renal transplantation can be prevented if they are detected early. Guidelines have been developed for the prevention of diseases in the general population, but there are no comprehensive guidelines for the prevention of diseases and complications after renal transplantation. Therefore, the Clinical Practice Guidelines Committee of the American Society of Transplantation developed these guidelines to help physicians and other health care workers provide optimal care for renal transplant recipients. The guidelines are also intended to indirectly help patients receive the access to care that they need to ensure long-term allograft survival, by attempting to systematically define what that care encompasses. The guidelines are applicable to all adult and pediatric renal transplant recipients, and they cover the outpatient screening for and prevention of diseases and complications that commonly occur after renal transplantation. They do not cover the diagnosis and treatment of diseases and complications after they become manifest, and they do not cover the pretransplant evaluation of renal transplant candidates. The guidelines are comprehensive, but they do not pretend to cover every aspect of care. As much as possible, the guidelines are evidence-based, and each recommendation has been given a subjective grade to indicate the strength of evidence that supports the recommendation. It is hoped that these guidelines will provide a framework for additional discussion and research that will improve the care of renal transplant recipients.

Posttransplant bone disease: evidence for a high bone resorption state

Loss of bone is a significant problem after renal transplant. Although bone loss in the first post transplant year has been well documented, conflicting data exist concerning bone loss after this time. It is equally unclear whether bone loss in long-term renal transplant recipients correlates with bone turnover as it does in postmenapausal osteoporosis. To examine these issues, we conducted a cross-sectional study to define the prevalence of osteoporosis in long-term (> 1 year) renal transplant recipients with preserved renal function (mean creatinine clearance 73 +/- 23 ml/min). Bone mineral density (BMD) was measured at the hip, spine and wrist by DEXA in 69 patients. Markers for bone formation (serum osteocalcin) and bone resorption [urinary levels of pyridinoline (PYD) and deoxypyridinoline (DPD)] were also measured as well as parameters of calcium metabolism. Correlations were made between these parameters and BMD at the various sites. The mean age of the patients was 45 +/- 11 years. Eighty eight percent of patients were on cyclosporine (12% on tacrolimus) and all but 2 were on prednisone [mean dose 9 +/- 2 mg/day)]. Osteoporosis (BMD more than 2.5 SD below peak adult BMD) at the spine or hip was diagnosed in 44% of patients and osteopenia was present in an additional 44%. Elevated levels of intact parathyroid hormone (i PTH) were observed in 81% of patients. Elevated urinary levels of PYD or DPD were present in 73% of patients and 38% had elevated serum levels of osteocalcin. Levels of calcium, and of 25(OH) and 1,25(OH)2 vitamin D were normal. In a stepwise multiple regression model that included osteocalcin, PYD, DPD, intact PTH, age, years posttransplant, duration of dialysis, cumulative prednisone dose, smoking, and diabetes: urinary PYD was the strongest predictor of bone mass. These results demonstrate that osteoporosis is common in long-term renal transplant recipients. The data also suggest that elevated rates of bone resorption contribute importantly to this process.

Bone loss after renal transplantation: role of hyperparathyroidism, acidosis, cyclosporine and systemic disease

In order to determine risk factors for bone loss after renal transplantation, dual energy X-ray absorptiometry was performed in 125 renal transplant patients. The bone mineral density (BMD) was expressed as a percentage of the normal population (BMD%) and Z-score (SD from normal). The whole body, lumbar spine and femoral neck BMD% (Z-score) values were 93.9 +/- 8.9 (-0.90 SD), 91.6 +/- 14.9 (-0.98 SD) and 87 +/- 15.3 (-1.0 SD)%, respectively. Low BMD% was associated with low creatinine clearance ( < 40 mL/min: 91.6 +/- 7.9, > 40 mL/min: 95.6 +/- 8.0, p < 0.01), repeated graft loss (0: 94.4 +/- 9.1, > 1: 87.4 +/- 9.3, p < 0.05), long dialysis duration ( < 1 yr: 95.2 +/- 7.9, > 5: 90.1 +/- 10.6, p < 0.05), acidosis (bicarbonate < 21 mmol/L: 89.6 +/- 8.0, > 27: 96.7 +/- 7.2, p < 0.01), secondary and tertiary hyperparathyroidism ( < 50 ng/L: 95.9 +/- 7.1, > 200: 87.7 +/- 5.0, p < 0.01), raised alkaline phosphatase ( < 200 units/L: 95.7 +/- 7.2, > 300: 85.6 +/- 13.2, p < 0.001), osteocalcin ( < 50 microg/L: 95.2 +/- 6.7, > 100: 89.3 +/- 7.6, p < 0.01) and urinary deoxypyridinoline (< 5 nM/mM creatinine: femoral neck 89.6 +/- 10.7, > 10: 82.1 +/- 20.1, p < 0.05), low 25-OH-vitamin D ( < 10 microg/L: 91.3 +/- 9.8, > 20: 96.9 +/- 7.4, p < 0.001) and high cyclosporine concentration (0 ng/L: 98.3 +/- 7.0, > 150: 92.1 +/- 9.3, p < 0.05). Patients with clinical atherosclerosis (91.7 +/- 8.6 vs. 95.4 +/- 8.8, p < 0.01), hypoalbuminemia ( < 550 micromol/L: 87.6 +/- 13.2, > 550: 94.2 +/- 7.8, p < 0.01), renovascular disease (89.7 +/- 5.7 vs. 95.0 +/- 5.7, p < 0.05) and diabetic nephropathy (femoral neck 76.6 +/- 8.8 vs. 89.3 +/- 15.1, p < 0.01) had lower bone masses. High bone mass was associated with previous dialysis alphacalcidol therapy (0: 92.2 +/- 7.5, > 3 microg/wk: 97.3 +/- 6.9, p < 0.05). No relationships with transplantation duration, 1,25-OH-vitamin D, aluminium, calcium or steroid dose were found. No involutional changes in tertiary hyperparathyroidism could be discerned.

CONCLUSION

The major threats to bone mass after renal transplantation appear to be ongoing hyperparathyroid bone disease, low renal function, acidosis, systemic disease and hypo-vitaminosis D.

Prevention of osteoporosis after cardiac transplantation: a prospective, longitudinal, randomized, double-blind trial with calcitriol

BACKGROUND

Accelerated bone loss is a well-recognized complication after cardiac transplantation (HTx) due to immunosuppressive therapy. The purpose of this prospective, longitudinal, randomized, placebo-controlled, double-blind study was to investigate the effect of calcitriol (1,25-dihydroxyvitamin D3) in the prevention of bone loss and fracture rate after HTx.

METHODS

Basic therapy included 1000 mg of calcium daily and sex hormone replacement in hypogonadal patients. A total of 132 patients (111 male, 21 female; mean age: 51+/-10 years; 35+/-25 months after HTx) were randomized to 0.25 microg of calcitriol or placebo. Bone mineral density (BMD, g/cm2; T score, %) of the lumbar spine and x-rays for the assessment of vertebral fractures were performed at baseline and after 12, 24, and 36 months. Biochemical indexes of mineral metabolism were measured every 3 months.

RESULTS

Overall BMD was significantly decreased after HTx (T score 87+/-13%). BMD increased continuously within the study period in the calcitriol group (1 year: 2.2+/-4.8%; 2 years: 3.9+/-5.4%; 3 years: 5.7+/-4.4%) as well as in the placebo group (1 year: 1.8+/-4.9%; 2 years: 3.7+/-6.5%; 3 years: 6.1+/-7.8%) without statistical difference between the groups. Fracture incidence was low during the study interval (1 year: 2.0%; 2 years: 3.4%; 3 years: 0%). Hypogonadism (20%) was associated with a lower BMD (78+/-12% vs. 88+/-12%; P<0.01) and a higher increase (35%) after hormone replacement in comparison to normogonadal patients. Increased intact parathyroid hormone and bone resorption markers decreased significantly during therapy.

CONCLUSIONS

Calcium supplementation and sex hormone replacement in hypogonadism proved a sufficient long-term prevention therapy to improve decreased BMD and to prevent fractures after HTx. Besides immunosuppression, both concomitant hypogonadism and secondary hyperparathyroidism play a major role in the long-term bone loss and should therefore be monitored and treated adequately. Low-dose calcitriol demonstrated no significant extra benefit regarding BMD and fracture rate in the long-term period after HTx.

The fate of bone after renal transplantation

Post-renal-transplantation bone disease is a well known entity. Immunosuppressive agents and persistence of hyperparathyroidism have primarily been implicated in its etiology. Renal transplantation patients are unique in that the bone changes occur on a background of pre-existing renal osteodystrophy. This review focuses on post-renal-transplantation bone disease. Unfortunately, the existing data in the review period, besides being scanty, provide conflicting information. This is due to the diversity of immunosuppressive regimens employed, the patient populations studied, diagnostic tools and criteria used by different centers, and the lack of formal trials.

Mechanisms of bone loss after cardiac transplantation

To determine the mechanism of bone loss after cardiac transplantation (CTX), we studied 50 men 0.5-47 months after CTX (ages 18-64 years) who received prednisolone and cyclosporin to prevent rejection, and 40 healthy men as controls (ages 20-70 years). We measured bone mineral density (BMD) using dual-energy X-ray absorptiometry (DXA), bone resorption using urinary cross-linked N-terminal telopepides of type I collagen (NTx), and bone formation using osteocalcin (BGP) and bone alkaline phosphatase (BAP). The results from the controls were used to calculate z scores. BMD was significantly decreased at the lumbar spine, femoral neck, and total body, and bone turnover was significantly increased as assessed by NTx/creatinine, BGP, and BAP as compared with controls (p < 0.01 for all measurements). To evaluate the cause of the increased bone turnover we measured serum parathyroid hormone (PTH) by IRMA, and this was also elevated (p < 0.001). There was a significant correlation between serum PTH and BGP (r = 0.58, p < 0.01). To evaluate the cause of the increase in PTH, we measured serum calcium and it was decreased (p < 0.001), serum phosphorus was increased (p < 0.001), serum creatinine was increased (p < 0.001), and serum 1,25-dihydroxyvitamin D3 [1,25(OH)2D, RIA] was decreased (p = 0.03). Serum PTH correlated weakly with serum calcium (r = -0.41, p < 0.003) and with serum creatinine (r = 0.35, p = 0.01). There was a weak, but significant, correlation between serum creatinine and 1,25(OH)2D3 (r = 0.33, p = 0.03). Serum levels of testosterone and dehydroapiandrosterone sulfate were decreased after CTX but did not correlate with any other parameters. There was a weak negative correlation between prednisolone daily dose and serum BGP level (r = 0.29, p = 0.06) in those patients whose prednisolone current dose was >7.5 mg/day. We conclude that: (1) the low BMD found after CTX is associated with increased bone turnover which results, in turn, from renal impairment; (2) prednisolone is involved in rapid bone loss, whereas mild secondary hyperparathyroidism may be a major contributor to disorder of bone remodeling after this rapid loss; and (3) decreased androgen levels may not be a major factor resulting in bone loss in men after CTX.

No trend toward a spontaneous improvement of hyperparathyroidism and high bone turnover in normocalcemic long-term renal transplant recipients

Although hyperparathyroidism is a common feature in renal transplant recipients, the long-term course of parathyroid hormone (PTH) secretion in these patients is not well established, and the actual contribution of PTH to posttransplant bone disease remains incompletely understood. Therefore, we studied calcium-regulating hormones and serum osteocalcin, as a marker of bone remodeling, in 82 normocalcemic renal transplant recipients with good renal function who had received a graft 6 to 73 months previously and in 82 healthy subjects matched for age and sex. In all subjects, fasting serum and 24-hour urinary samples were collected. The transplant recipients had excessive PTH secretion (serum PTH, 6.9 +/- 0.5 pmol/L in recipients v 3.0 +/- 0.1 pmol/L in healthy subjects; P < 0.001) and high bone turnover (osteocalcin, 16.6 +/- 0.8 microg/L v 8.0 +/- 0.3 microg/L; P < 0.001). (Values are mean +/- SEM.) In addition, transplant recipients had a slightly higher ionized calcium than the healthy subjects, providing definite evidence of an inappropriate PTH secretion in renal transplant recipients. Furthermore, in subgroups of 25 recipients and 25 healthy controls matched for creatinine clearance, the results superimposed those obtained in the whole groups, suggesting that excessive PTH secretion and high bone turnover in renal transplant recipients did not merely reflect the moderately reduced renal function of some recipients. In the whole group of transplant recipients, PTH correlated positively with osteocalcin (r = 0.40; P < 0.001), suggesting that PTH contributes at least partly to posttransplant bone disease. Conversely, there was no correlation between serum PTH or osteocalcin and the delay from grafting. Therefore, our results provide no evidence for a spontaneous improvement of either persistent hyperparathyroidism or high bone turnover in normocalcemic long-term renal transplant recipients.

Lack of increased urinary calcium-oxalate supersaturation in long-term kidney transplant recipients

Nephrolithiasis is uncommon after kidney transplantation. However, calcium (Ca) supplementation, which has been proposed as a treatment of post-transplant osteopenia, might increase calciuria and bolster Ca stone formation. Therefore, in 24-hour urine of 82 normocalcemic long-term renal transplant recipients (RT) and in 82 healthy subjects (HS), we assessed some Ca nephrolithiasis risk factors and the Ca-salt saturation estimated by the ion-activity product index (AP) and relative supersaturation (RS). In RT, calciuria was lower (mean +/- SD, 3.20 +/- 2.25 vs. 4.61 +/- 1.71 mmol/day; P < 0.001), urinary volume higher (2.41 +/- 0.83 vs. 1.39 +/- 0.53 liter/day; P < 0.001), oxaluria higher (419 +/- 191 vs. 311 +/- 79 mumol/day; P < 0.001) and citraturia lower (1.40 +/- 1.36 vs. 3.77 +/- 1.36 mmol/day; P < 0.001) than in HS. As a result, Ca-oxalate supersaturation was lower in RT than HS (AP, 1.07 +/- 0.69 vs. 2.07 +/- 1.13, P < 0.001; and RS, 0.62 +/- 0.26 vs. 0.94 +/- 0.21, P < 0.001), and was similar in subgroups of RT (N = 37) and HS (N = 37) matched for urinary volume, demonstrating that even without any larger urinary volume, Ca-oxalate saturation was not higher in RT than HS, and suggesting that opposite changes in Ca and oxalate in RT likely canceled their effects on lithogenic risk. In RT which had similar urinary pH and phosphate (P) than HS, Ca-P supersaturation was lower than in HS for brushite (AP, 3.25 +/- 6.67 vs. 6.01 +/- 4.85, P < 0.001; RS, -0.33 +/- 0.76 vs. 0.48 +/- 0.53, P < 0.001) and octacalcium phosphate (RS, -0.95 +/- 0.72 vs. 0.21 +/- 0.85, P < 0.001), and similar for apatite. Finally, fasting calciuria and calciuric response to a single oral Ca load were similar in RT (N = 19) and HS (N = 8). Together, these results argue strongly against a higher risk of Ca stone formation in RT than HS, even in case of Ca supplementation.

Monoclonality of parathyroid tumors in chronic renal failure and in primary parathyroid hyperplasia

The pathogeneses of parathyroid disease in patients with uremia and nonfamilial primary parathyroid hyperplasia are poorly understood. Because of multigland involvement, it has been assumed that these common diseases predominantly involve polyclonal (non-neoplastic) cellular proliferations, but an overall assessment of their clonality has not been done. We examined the clonality of these hyperplastic parathyroid tumors using X-chromosome inactivation analysis with the M27 beta (DXS255) DNA polymorphism and by searching for monoclonal allelic losses at M27 beta and at loci on chromosome band 11q13. Fully 7 of 11 informative hemodialysis patients (64%) with uremic refractory hyperparathyroidism harbored at least one monoclonal parathyroid tumor (with a minimum of 12 of their 19 available glands being monoclonal). Tumor monoclonality was demonstrable in 6 of 16 informative patients (38%) with primary parathyroid hyperplasia. Histopathologic categories of nodular versus generalized hyperplasia were not useful predictors of clonal status. These observations indicate that monoclonal parathyroid neoplasms are common in patients with uremic refractory hyperparathyroidism and also develop in a substantial group of patients with sporadic primary parathyroid hyperplasia, thereby changing our concept of the pathogenesis of these diseases. Neoplastic transformation of preexisting polyclonal hyperplasia, apparently due in large part to genes not yet implicated in parathyroid tumorigenesis and possibly including a novel X-chromosome tumor suppressor gene, is likely to play a central role in these disorders.