1,25(OH)2D3 administration in moderate renal failure: a prospective double-blind trial

The structure of mineral and bone disorders in patients with сhronic kidney disease of the 5th dialysis stage, taking into account the presence or absence of a diagnosis of type 1 diabetes mellitus

BACKGROUND: In patients with end-stage CKD, receiving renal replacement therapy (RRT) with programmed hemodialysis (HD), the severity of complications is associated with metabolic disturbances: accumulation of uremic toxins, nephrogenic anemia, secondary hyperparathyroidism (SHPT), extraskeletal calcification, impaired clearance and rhythm of hormone secretion.

AIM: To evaluate the main biochemical and hormonal parameters, and manifestations of mineral bone disease (MBD) in patients receiving RRT with HD, before and after hemodialysis, taking into account the presence or absence of diabetes mellitus.

MATERIALS AND METHODS: We divided all patients receiving RRT with HD in two groups: #1 (n=24) — patients with DM, #2 (n=16) — patients without DM. All of them had their blood analyzed before and immediately after the HD. Data analysis was performed with the Statistica 13 (StatSoft, USA). A prognostically significant model was considered at p<0.05.

RESULTS: The level of iPTH, both at baseline and after HD, was lower in group #1 (p<0.001). The level of alkaline phosphatase (AP) was significantly higher in group #2 (p=0.012). In both groups before HD, a high incidence of hypocalcemia was detected (according to albumin-corrected calcium in group #1 in 58.3%, in group #2 in 43.7% of cases, p = 0.366) and hyperphosphatemia (in 66.7% and in 43 .7% of cases, respectively, p=0.151). Hypocalcemia after HD in group #1 persisted in 14%, in group #2 — in 20% of cases (p>0.05); hyperphosphatemia in group #1 was completely leveled, in group #2 it persisted in 7% of cases (p=0.417). Prior to the HD session, group #1 had significantly higher levels of RAGE, glucagon, immunoreactive insulin (IRI), cortisol, and glucose than after the HD session (p<0.05). In group #2, after HD, the levels of glucagon, IRI and cortisol significantly decreased (p<0.05), and the level of 3-nitrotyrosine (3-HT) increased significantly (p=0.026). In group #1, fibrocalcinosis of the heart valves according to ECHO and calcification of the arteries of the lower extremities according to ultrasonic doplerography were more common than in group #2 (42% vs 25%, p<0.001 and 75% vs 37.5%, p=0.018, respectively). (χ2)). Compression fractures occurred with the same frequency in both groups (60%). A decrease in bone mineral density (BMD) to the level of osteopenia was noted more often in group #1 (50% vs 18.8%), and osteoporosis was more common in group #2 (68.8% vs 33.3%) (p<0.001, χ2).

CONCLUSION: The low level of PTH in group #1 may reflect the effect of diabetes on calcium-phosphorus metabolism. Patients with DM have an increased risk of renal osteodystrophy with a low bone turnover because of a number of metabolic factors inherent in diabetes. At the same time, the dynamics of phosphorus and calcium indicators during the HD procedure were similar.

Bone Quality in Chronic Kidney Disease Patients: Current Concepts and Future Directions - Part II

Background

Patients with chronic kidney disease (CKD) have an increased risk of osteoporotic fractures, which is due not only to low bone volume and mass but also poor microarchitecture and tissue quality. The pharmacological and nonpharmacological interventions detailed, herein, are potential approaches to improve bone health in CKD patients. Various medications build up bone mass but also affect bone tissue quality. Antiresorptive therapies strikingly reduce bone turnover; however, they can impair bone mineralization and negatively affect the ability to repair bone microdamage and cause an increase in bone brittleness. On the other hand, some osteoporosis therapies may cause a redistribution of bone structure that may improve bone strength without noticeable effect on BMD. This may explain why some drugs can affect fracture risk disproportionately to changes in BMD.

Summary

An accurate detection of the underlying bone abnormalities in CKD patients, including bone quantity and quality abnormalities, helps in institution of appropriate management strategies. Here in this part II, we are focusing on advancements in bone therapeutics that are anticipated to improve bone health and decrease mortality in CKD patients.

Key Messages

Therapeutic interventions to improve bone health can potentially advance life span. Emphasis should be given to the impact of various therapeutic interventions on bone quality.

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.

Serum nuclear factor IB as a novel and noninvasive indicator in the diagnosis of secondary hyperparathyroidism

BACKGROUND

Chronic renal failure (CRF) referred to chronic progressive renal parenchymal damage caused by various causes, with metabolite retention and imbalance of water, electrolyte, and acid-base balance as the main clinical manifestations. Secondary hyperparathyroidism (sHPT) was a common complication in maintenance hemodialysis patients with CRF. Nuclear factor IB (NFIB) was a newly found tumor suppressor gene in various cancers. The present study aimed to illustrate the role of NFIB in sHPT clinical diagnosis and treatment response.

METHODS

A retrospective, case-control study, including 189 patients with sHPT and 106 CRF patients without sHPT, compared with 95 controls. Serum NFIB and 1,25(OH)₂ D₃ levels were measured by RT-qPCR and ELISAs, respectively. ROC analysis was conducted to verify the diagnostic value of NFIB in sHPT. Spearman's correlation analysis was conducted to verify the association between NFIB and bone mineral density (BMD) scores. After 6 months of treatment, the variance of NFIB and 1,25(OH)₂ D₃ in different groups was recorded.

RESULTS

The expression of NFIB was significantly lower in serum samples from sHPT and non-sHPT CRF patients, compared to controls. Clinicopathological information verified sHPT was associated with NFIB, parathyroid hormone (PTH), serum calcium, serum phosphorus, time of dialysis, and serum 1,25(OH)₂ D₃ levels. Spearman's correlation analysis illustrated the positive correlation between NFIB levels and BMD scores. At receiver operator characteristic (ROC) curve analysis, the cutoff of 1.6508 for NFIB was able to identify patients with sHPT from healthy controls; meanwhile, NFIB could also discriminate sHPT among CRF patients as well (cutoff = 1.4741). Furthermore, we found that during 6 months of treatment, NFIB levels were gradually increased, while PTH and serum P levels were decreased.

CONCLUSIONS

Serum NFIB was a highly accurate tool to identify sHPT from healthy controls and CRF patients. Due to its simplicity, specificity, and sensitivity, this candidate can be proposed as a first-line examination in the diagnostic workup in sHPT.

Osteoporosis in Patients with Chronic Kidney Diseases: A Systemic Review

Chronic kidney disease (CKD) is associated with the development of mineral bone disorder (MBD), osteoporosis, and fragility fractures. Among CKD patients, adynamic bone disease or low bone turnover is the most common type of renal osteodystrophy. The consequences of CKD-MBD include increased fracture risk, greater morbidity, and mortality. Thus, the goal is to prevent the occurrences of fractures by means of alleviating CKD-induced MBD and treating subsequent osteoporosis. Changes in mineral and humoral metabolism as well as bone structure develop early in the course of CKD. CKD-MBD includes abnormalities of calcium, phosphorus, PTH, and/or vitamin D; abnormalities in bone turnover, mineralization, volume, linear growth, or strength; and/or vascular or other soft tissue calcification. In patients with CKD-MBD, using either DXA or FRAX to screen fracture risk should be considered. Biomarkers such as bALP and iPTH may assist to assess bone turnover. Before initiating an antiresorptive or anabolic agent to treat osteoporosis in CKD patients, lifestyle modifications, such as exercise, calcium, and vitamin D supplementation, smoking cessation, and avoidance of excessive alcohol intake are important. Managing hyperphosphatemia and SHPT are also crucial. Understanding the complex pathogenesis of CKD-MBD is crucial in improving one's short- and long-term outcomes. Treatment strategies for CKD-associated osteoporosis should be patient-centered to determine the type of renal osteodystrophy. This review focuses on the mechanism, evaluation and management of patients with CKD-MBD. However, further studies are needed to explore more details regarding the underlying pathophysiology and to assess the safety and efficacy of agents for treating CKD-MBD.

Vitamin D and renal outcome: the fourth outcome of CKD-MBD? Oshima Award Address 2015

Bone fracture, cardiovascular events, and mortality are three outcomes of chronic kidney disease-mineral and bone disorder (CKD-MBD), and the umbrella concept originally described for dialysis patients. The reported association of serum phosphorus or fibroblast growth factor 23 (FGF23) levels with renal outcome suggests that the fourth relevant outcome of CKD-MBD in predialysis patients is renal outcome. We found that proteinuria of 2+ or greater with a dipstick test was associated with low vitamin D status due to urinary loss of 25-hydroxyvitamin D (25D). Moreover, active vitamin D or its analogues decrease proteinuria. Given our finding that maxacalcitol does not repress renin, the reduction of proteinuria by this agent is likely due to direct upregulation of the nephrin and podocin in podocytes. Moreover, this agent downregulates the mesenchymal marker desmin in podocytes and blocks transforming growth factor-beta autoinduction, leading to attenuation of renal fibrosis in a unilateral ureteral obstructive (UUO) model. These facts are reminiscent of the suppression of epithelial-mesenchymal transition (EMT) by vitamin D. EMT blockage may explain our finding that vitamin D prescription in renal transplant recipients is associated with a lower incidence of cancer. We also reported that low vitamin D status and high FGF23 levels predict a worse renal outcome. However, administration of massive doses of 25D exacerbates renal fibrosis in UUO kidneys in 1alpha-hydroxylase knockout mice. Moreover, FGF23 inhibits 1alpha-hydroxylase in proximal tubules and monocytes. Taken together, local 1,25(OH)2D in the kidney tissue but not 25D seems to protect the kidney.

Underrecognition and Underestimation of Disturbances in Calcium-Phosphate Balance in Kidney Transplant Recipients

Disturbances in mineral metabolism, namely chronic kidney disease-metabolic bone disease, became more profound with impairment of renal function. The aim of the study was to assess how often calcium, phosphate, alkaline phosphatase, and parathyroid hormone (PTH) were measured in kidney transplant recipients relative to hemodialyzed patients. In addition, prevalence of hypercalcemia defined as calcium concentration over 10.5 mg/dL was assessed.

PATIENTS AND METHODS

We studied 200 kidney allograft recipients and 100 hemodialyzed patients. Calcium, phosphate, alkaline phosphatase, 25-hydroxy vitamin D, and PTH were obtained from outpatient charts.

RESULTS

All the studied parameters were available in 100% of the hemodialyzed patients. In kidney allograft recipients, calcium and phosphate levels were available in 80%, alkaline phosphatase activity was available in 40%, PTH was available in less than 10%, and vitamin D was available in 1%. Hypercalcemia was present in 10% of hemodialyzed patients and in 5% of kidney allograft recipients. Vitamin D analogue was administered to 98% of hemodialyzed patients, whereas vitamin D was administered to 28% of kidney allograft recipients, particularly those with impaired kidney function. In conclusion, calcium and phosphate are seldom assessed on an outpatient basis in kidney allograft recipients, making the diagnosis and treatment of secondary hyperparathyroidism in this population difficult. Care of kidney transplant recipients could be substantially improved, particularly in regard to chronic kidney disease-metabolic bone disease, when regular check-ups for calcium-phosphate balance are implemented and proper treatment could be introduced to prevent further chronic kidney disease-metabolic bone disease.

[Utilization of alfacalcidol and active vitamin D analogs in chronic kidney disease]

Secondary hyperparathyroidism (SHPT) is one of the most frequent and deleterious complication of chronic kidney disease (CKD). SHPT is also one of the principal components of the now called CKD-mineral and bone disorders (MBD) syndrome. It is usually prevented and treated by vitamin D derivatives. However, the rationale for the prescription of vitamin D sterols in those patients is still a matter of hotly debates, mainly because of unsatisfactory results from numerous observational and not well-controlled studies. Scanty clinical data on head-to-head comparisons between the multiple vitamin D sterols are currently available. Moreover, there is crescent expectations on nutritional vitamin D, as well as vitamin D receptor activators (VDRA), regarding their putative pleiotropic effects even in CKD patients, and the promising effects of VDRA against proteinuria and myocardial hypertrophy in diabetic CKD cohorts. Nevertheless, additional randomized controlled trials (RCT) are needed to answer to many open questions and incertitude considering the effect of nutritional vitamin D and VDRA on hard end points including the risk of skeletal fractures and of mortality in CKD patients. RCT comparing VDRA to calcimimetics in the control of SHPT are also needed in dialysis patients. The present review will visit these open questions that nephrologists should ask before starting a treatment by nutritional vitamin D or VDRA.

Vitamin D, a modulator of musculoskeletal health in chronic kidney disease

The spectrum of activity of vitamin D goes beyond calcium and bone homeostasis, and growing evidence suggests that vitamin D contributes to maintain musculoskeletal health in healthy subjects as well as in patients with chronic kidney disease (CKD), who display the combination of bone metabolism disorder, muscle wasting, and weakness. Here, we review how vitamin D represents a pathway in which bone and muscle may interact. In vitro studies have confirmed that the vitamin D receptor is present on muscle, describing the mechanisms whereby vitamin D directly affects skeletal muscle. These include genomic and non-genomic (rapid) effects, regulating cellular differentiation and proliferation. Observational studies have shown that circulating 25-hydroxyvitamin D levels correlate with the clinical symptoms and muscle morphological changes observed in CKD patients. Vitamin D deficiency has been linked to low bone formation rate and bone mineral density, with an increased risk of skeletal fractures. The impact of low vitamin D status on skeletal muscle may also affect muscle metabolic pathways, including its sensitivity to insulin. Although some interventional studies have shown that vitamin D may improve physical performance and protect against the development of histological and radiological signs of hyperparathyroidism, evidence is still insufficient to draw definitive conclusions.

Changes in renal function after discontinuation of vitamin D analogues in advanced chronic kidney disease

BACKGROUND

In routine clinical practice, the prescription of vitamin D analogues (VDA) in patients with chronic kidney disease (CKD) is often associated with a decline of the estimated renal function. The reason for this is not fully understood.

AIMS

To analyse the effects of VDA discontinuation in advanced CKD and to determine the factors associated with changes in renal function.

MATERIAL AND METHODS

Retrospective cohort study of adult patients with advanced CKD. The case subgroup was treated with VDA and this medication was discontinued at baseline (the first visit). The control subgroup was not treated with VDA and they were selected according to comparability principles for CKD progression by propensity score matching. The primary outcome measure was a change to both the estimated glomerular filtration rate (MDRD-GFR) and the measured glomerular filtration rate (mGFR by combined creatinine and urea clearances). Baseline parameters related to mineral metabolism and creatinine generation were analysed as potential determinants of renal function changes.

RESULTS

The study sample consisted of 67 cases and 67 controls. Renal function improved in 67% of cases and worsened in 72% of controls (p<0.0001). Changes in MDRD-GFR for the case subgroup and the control subgroup were +0.455±0.997 vs. -0.436±1.103ml/min/1.73 m²/month (p<0.0001), respectively. Total creatinine excretion was slightly higher in cases than in controls but the difference was not significant. According to multivariate logistic and linear regression analyses, baseline total serum calcium was one of the best determinants of both renal function recovery (Odds ratio=3.49; p=0.001), and of the extent of renal function recovery (beta=0.276; p=0.001).

CONCLUSIONS

Discontinuation of VDA treatment in CKD patients is associated with significant recovery of estimated renal function. The extent of these changes is mainly associated with baseline total serum calcium.

Changing bone patterns with progression of chronic kidney disease

It is commonly held that osteitis fibrosa and mixed uremic osteodystrophy are the predominant forms of renal osteodystrophy in patients with chronic kidney disease. Osteitis fibrosa is a high-turnover bone disease resulting mainly from secondary hyperparathyroidism, and mixed uremic osteodystrophy is in addition characterized by a mineralization defect most often attributed to vitamin D deficiency. However, there is ancient and more recent evidence that in early chronic kidney disease stages adynamic bone disease characterized by low bone turnover occurs first, at least in a significant proportion of patients. This could be due to the initial predominance of bone turnover-inhibitory conditions such as resistance to the action of parathyroid hormone (PTH), reduced calcitriol levels, sex hormone deficiency, diabetes, and, last but not least, uremic toxins leading to repression of osteocyte Wnt/β-catenin signaling and increased expression of Wnt antagonists such as sclerostin, Dickkopf-1, and sFRP4. The development of high-turnover bone disease would occur only later on, when serum PTH levels are able to overcome peripheral PTH resistance and the other inhibitory factors of bone formation. Whether FGF23 and Klotho play a direct role in the transition from low- to high-turnover bone disease or participate only indirectly via regulating PTH secretion remains to be seen.

Pin1 and secondary hyperparathyroidism of chronic kidney disease: gene polymorphisms and protein levels

BACKGROUND

Peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (Pin1) is a key regulator of PTH mRNA stability. Secondary hyperparathyroidism (SHPT), which is characterized by elevated serum PTH levels, is a common complication of CKD. We investigated the possible associations between CKD with SHPT (CKD SHPT) and single-nucleotide polymorphisms of the Pin1 gene and compared the levels of the Pin1 protein in the CKD SHPT patients with those of the controls.

METHODS

The study group included 251 CKD SHPT patients and 61 controls. One putative functional SNP (single nucleotide polymorphism) in the Pin1 promoter (rs2233679C > T: c.-667C > T) is the main object. Genotyping was performed on purified DNA using polymerase chain reaction-restriction (PCR) and restriction fragment length polymorphisms (RFLP). The levels of Pin1 were measured in serum using an enzyme-linked immunosorbent assay.

RESULTS

Genotyping showed that CT + TT in the Pin1 promoter was significantly more common in the CKD SHPT group than in the control group (p<.05). The correlation analysis demonstrated that a significant difference in the C to T transition in the Pin1 promoter contributed to CKD SHPT (χ²=12.47, p<.05; Odds ratios (OR) = 1.26, 95% confidence (CI) intervals =1.06-1.49). The multivariate logistic regression analysis reported that the OR and 95%CI were 12.693 and 2.029-75.819 (p<.05), respectively, in the Pin1 gene promoter -667T variant genotypes (CT + TT) after adjusting for other factors, and those values in Pin1 were 0.310 and 0.122-0.792 (p<.05).

CONCLUSION

The -667T genetic variants in the Pin1 promoter contribute to an increased risk of CKD SHPT and may be biomarkers of susceptibility to CKD SHPT.

Effect of Vitamin D Receptor Activators on Glomerular Filtration Rate: A Meta-Analysis and Systematic Review

Background

Vitamin D receptor activators (VDRAs) can protect against mineral bone disease, but they are reported to elevate serum creatinine (SCr) and may also reduce glomerular filtration rate (GFR).

Methods

We conducted a systematic review and meta-analysis of randomized clinical trials (RCTs) to evaluate the effect of VDRAs on kidney function and adverse events. MEDLINE, EMBASE, the Cochrane Controlled Trials Register were searched for RCTs that evaluate vitamin D receptor activators (alfacalcidol, calcitriol, doxercalciferol, falecalcitriol, maxacalcitol and paricalcitol) up to March 2015.

Results

We included 31 studies, all of which were performed between 1976 and 2015, which enrolled 2621 patients. Patients receiving VDRAs had lower eGFR (weighted mean difference WMD -1.29 mL/min /1.73 m², 95% CI -2.42 to -0.17) and elevated serum creatinine (WMD 7.03 μmol/L, 95% CI 0.61 to 13.46) in sensitivity analysis excluding studies with dropout rate more than 30%. Subgroup analysis of the 5 studies that not use SCr-based measures did not indicated lower GFR in the VDRAs group(WMD -0.97 mL/min/1.73 m2, 95% CI -4.85 to 2.92). Compared with control groups, there was no difference in all-cause mortality (relative risk RR 1.41, 95% CI 0.58 to 3.80), cardiovascular disease (RR 0.84, 95% CI 0.42 to 1.71), and severe adverse events (RR 1.15, 95% CI 0.75 to 1.77) for the VDRAs groups. Episodes of hypercalcemia (RR 3.29, 95% CI 2.02 to 5.38) were more common in the VDRAs group than in the control group.

Conclusions

Administration of VDRAs increased serum creatinine levels. Subgroup analysis of studies that did not use SCr-based measures did not indicate a lower GFR in the VDRA group. Future studies with non-SCr-based measures are needed to assess whether the mild elevations of serum creatinine are of clinical significance.

Vitamin D and Clinical Outcomes in Dialysis

Most dialysis patients are vitamin D deficient, including deficiencies in both activated vitamin D (1, 25-dihydroxyvitamin D) and the less active 25-hydroxyvitamin D. These and other abnormalities associated with chronic kidney disease (CKD), if they remain untreated, lead to secondary hyperparathyroidism and bone changes, such as osteitis fibrosa cystica. Activated vitamin D has been proven to decrease parathyroid hormone (PTH) levels in dialysis patients and is currently used for this indication. There are multiple other potential "pleotrophic" effects associated with vitamin D therapy. These include associations with lower all-cause and cardiovascular mortality, lower rates of infections and improved glycemic indexes. Meta-analyses of multiple observational studies have shown activated vitamin D therapy to be associated with improved survival. Observational data also suggest fewer infections and better glucose control. There have been no randomized clinical trials powered to evaluate mortality or other clinical outcomes. Small trials of nutritional vitamin D (ergocalciferol and cholecalciferol) showed increases in 25-hydroxyvitamin D levels without hypercalcemia or hyperphosphatemia, even when given in addition to activated vitamin D therapy. While activated vitamin D therapy is associated with improved outcomes, it also leads to higher fibroblast growth factor 23 (FGF-23) levels, which may be detrimental in dialysis patients. Further research is needed to evaluate whether activated or nutritional vitamin D therapy are beneficial in dialysis patients for outcomes other than secondary hyperparathyroidism.

Bone histomorphometry in a long-term hemodialysis patient with hypoparathyroidism and sarcoidosis

A bone biopsy specimen in a long-term hemodialysis patient with sarcoidosis coexisting with severe hypoparathyroidism has demonstrated that a persistent near physiological level of 1,25-dihydroxyvitamin D3 contributes to the preservation of bone remodeling and has the potential to retard the development of vascular calcification and atherosclerosis. Sarcoidosis-related hypercalcemia and hypoparathyroidism, which is characterized by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) overproduction, is rarely seen in hemodialysis patients. Herein, we describe a 60-year-old Japanese woman on hemodialysis for 35 years who presented with malaise and hypercalcemia. Severe hypoparathyroidism without parathyroidectomy and a preserved 1,25(OH)2D3 level were detected. Computed tomography showed bilateral axillary lymphadenopathy and minimal aortic and soft tissue calcification. The axillary node biopsy led to a definite diagnosis of sarcoidosis. A bone biopsy specimen obtained from the right iliac crest showed remodeling of normal lamellar bone with scalloped cement lines and clear double labeling by tetracycline on fluorescence microscopy. Histomorphometric analysis revealed that the bone formation rate was preserved (30.0 %/year), together with a decrease of osteoid volume (5.75 %) and fibrous volume (0 %), indicating that the patient did not have adynamic bone disease and only showed mild disease. This is the first documented case of sarcoidosis-related hypercalcemia associated with severe hypoparathyroidism in a long-term hemodialysis patient who underwent bone histomorphometry. Our findings suggest that, in hemodialysis patients with sarcoidosis coexisting with severe hypoparathyroidism, a persistent near physiological level of 1,25(OH)2D3 contributes to the preservation of bone remodeling and has the potential to retard the development of vascular calcification and atherosclerosis.

Paricalcitol for secondary hyperparathyroidism in renal transplantation

Secondary hyperparathyroidism contributes to post-transplant CKD mineral and bone disorder. Paricalcitol, a selective vitamin D receptor activator, decreased serum parathyroid hormone levels and proteinuria in patients with secondary hyperparathyroidism. This single-center, prospective, randomized, crossover, open-label study compared the effect of 6-month treatment with paricalcitol (1 μg/d for 3 months and then uptitrated to 2 µg/d if tolerated) or nonparicalcitol therapy on serum parathyroid hormone levels (primary outcome), mineral metabolism, and proteinuria in 43 consenting recipients of renal transplants with secondary hyperparathyroidism. Participants were randomized 1:1 according to a computer-generated sequence. Compared with baseline, median (interquartile range) serum parathyroid hormone levels significantly declined on paricalcitol from 115.6 (94.8-152.0) to 63.3 (52.0-79.7) pg/ml (P<0.001) but not on nonparicalcitol therapy. At 6 months, levels significantly differed between treatments (P<0.001 by analysis of covariance). Serum bone-specific alkaline phosphatase and osteocalcin decreased on paricalcitol therapy only and significantly differed between treatments at 6 months (P<0.001 for all comparisons). At 6 months, urinary deoxypyridinoline-to-creatinine ratio and 24-hour proteinuria level decreased only on paricalcitol (P<0.05). L3 and L4 vertebral mineral bone density, assessed by dual-energy x-ray absorption, significantly improved with paricalcitol at 6 months (P<0.05 for both densities). Paricalcitol was well tolerated. Overall, 6-month paricalcitol supplementation reduced parathyroid hormone levels and proteinuria, attenuated bone remodeling and mineral loss, and reduced eGFR in renal transplant recipients with secondary hyperparathyroidism. Long-term studies are needed to monitor directly measured GFR, ensure that the bone remodeling and mineral effects are sustained, and determine if the reduction in proteinuria improves renal and cardiovascular outcomes.

A randomized multicenter trial of paricalcitol versus calcitriol for secondary hyperparathyroidism in stages 3-4 CKD

BACKGROUND AND OBJECTIVES

Calcitriol is used to treat secondary hyperparathyroidism in patients with CKD. Paricalcitol is less calcemic and phosphatemic in preclinical studies and in some trials in dialysis patients, but head-to-head comparisons in nondialysis patients are lacking. A large meta-analysis of trials concluded that these agents did not consistently reduce parathyroid hormone (PTH) and increased the risk of hypercalcemia and hyperphosphatemia. Therefore, the objective of this multicenter trial was to compare the rate of hypercalcemia between calcitriol and paricalcitol, while suppressing PTH 40%-60%.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients with stages 3-4 CKD (n=110) with a PTH level >120 pg/ml were recruited and randomized to 0.25 μg/d of calcitriol or 1 μg/d of paricalcitol between April 2009 and July 2011. Subsequent dose adjustments were by protocol to achieve 40%-60% PTH suppression below baseline. The primary endpoint was the rate of confirmed hypercalcemia of >10.5 mg/dl between groups.

RESULTS

Forty-five patients in each group completed the 24 weeks of treatment. Both agents suppressed PTH effectively (-52% with paricalcitol and -46% with calcitriol; P=0.17), although the paricalcitol group reached a 40% reduction in PTH sooner at a median 8 weeks (interquartile range [IQR], 4, 12) versus 12 weeks (IQR, 8, 18; P=0.02) and had a lower pill burden of 240 (IQR, 180, 298) versus 292 (IQR, 231, 405; P=0.01). Confirmed hypercalcemia was very low in both groups (three with paricalcitol and one with calcitriol) and was not significantly different (P=0.36). Both groups had small increases in calcium and phosphorus levels (0.3-0.4 mg/dl in each electrolyte) and significant decreases in alkaline phosphatase, a marker of high bone turnover, with no significant differences between groups.

CONCLUSIONS

These results show that both calcitriol and paricalcitol achieved sustained PTH and alkaline phosphatase suppression in stages 3-4 CKD, with small effects on serum calcium and phosphorus and a low incidence of hypercalcemia.

Vitamin D and chronic kidney disease-mineral bone disease (CKD-MBD)

Chronic kidney disease (CKD) is a modern day epidemic and has significant morbidity and mortality implications. Mineral and bone disorders are common in CKD and are now collectively referred to as CKD- mineral and bone disorder (MBD). These abnormalities begin to appear even in early stages of CKD and contribute to the pathogenesis of renal osteodystrophy. Alteration in vitamin D metabolism is one of the key features of CKD-MBD that has major clinical and research implications. This review focuses on biology, epidemiology and management aspects of these alterations in vitamin D metabolism as they relate to skeletal aspects of CKD-MBD in adult humans.

The effect of calcium with or without calcitriol supplementation on renal function in patients with hypovitaminosis d and chronic kidney disease

Background:

Hypovitaminosis D (serum 25-OHD < 30 ng/mL) is common in patients with chronic kidney disease (CKD). Vitamin D is believed to involve in the regulation of renin-angiotensin system and may be renoprotective.

Objectives:

To compare the effects of calcium with or without calcitriol on renal function in patients with CKD.

Patients and Methods:

A prospective randomized trial was performed involving patients with stages 2-4 CKD and hypovitaminosis D. Baseline demographics data were taken at baseline. Patients were randomized equally into oral calcitriol plus calcium carbonate (calcitriol group) or calcium carbonate alone (non-calcitriol group). Serum levels of 25-hydroxyvitamin D (25-OHD), 1,25-dihydroxyvitamin D3 (1,25-(OH)2D), creatinine, calcium and urine protein creatinine index (uPCI) were measured at 6 and 12 weeks.

Results:

Fifty (21 Female: 29 Male) patients with CKD with a median age of 53 (22-65) years were recruited. Their median MDRD eGFR (modification of diet in renal disease, estimation of glomerular filtration rate) was 36.0 (15-89) mL/min/1.73 m² with the CKD stage 2 (n = 8, 16%), stage 3 (n = 29, 58%), and stage 4 (n = 13, 26%) respectively. In both study groups serum 25-OHD levels were increased at 12 weeks (P = 0.001), in contrast to serum 1,25-(OH)2D levels which remained unchanged (P > 0.05), serum creatinine and uPCI were also remained unchanged until the end of study (P > 0.05 each). Patients with diabetes had higher serum creatinine (P = 0.01) and lower serum 1,25-(OH)2D (P = 0.02) at baseline. Regardless of the diabetics status, the serum 25-OHD was increased, and 1,25-(OH)2D remained unchanged at 12 weeks in both study groups. At 12 weeks, serum creatinine was decreased in patients with diabetes in the noncalcitriol group (P = 0.03) compared to stabilization of creatinine in the calcitriol group (P > 0.05). Serum calcium was increased, though it was still within the normal range in the calcitriol group (P < 0.001); whereas, in the noncalcitriol group, there was an initial reduction but increased back to baseline (P = 0.007). Urine PCI remained unchanged in both groups.

Conclusions:

We have demonstrated that calcitriol supplementation did not offer any additional benefit to reduce 25-OHD and 1,25-(OH)2D levels over calcium carbonate alone in patients with CKD in this short term study. Overall renal function remained unchanged. However, we found that calcitriol at 0.5 mg daily plus calcium carbonate 500 mg daily could be reno-protective in diabetic nephropathy regardless of their serum 25-OHD levels.

Efficacy and safety of oral doxercalciferol in the management of secondary hyperparathyroidism in chronic kidney disease stage 4

This study was carried out to evaluate the efficacy and safety of doxercalciferol as therapy for secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease (CKD) stage 4 in a prospective clinical trial. A total of 35 CKD-4 patients who had a baseline parathyroid hormone (iPTH) >150 pg/mL and had not received any vitamin D analog in the preceding 8 weeks were followed up at intervals of 6 weeks for 18 weeks on oral therapy with doxercalciferol. The starting dose was 1.5 μg/day, and the dose was increased in steps of 1 μg/day if iPTH did not decrease by at least 30% on the subsequent visit. Doxercalciferol was stopped temporarily if low iPTH (<70 pg/mL), hypercalcemia (>10.7 mg/dL), or severe hyperphosphatemia (>8.0 mg/dL) occurred, and was restarted at a lower dose on reversal of these abnormalities. Calcium acetate was the only phosphate binder used. Mean iPTH decreased by 35.4 ± 4.4% from 381.7 ± 31.3 pg/mL to 237.9 ± 25.7 pg/mL (P < 0.001). The proportion of patients who achieved 30% and 50% suppression of iPTH levels was 83% and 72%, respectively. Mean serum calcium, phosphorus, and calcium-phosphorus product values did not differ significantly from the baseline values. Four, two, and nine patients developed hypercalcemia, severe hyperphosphatemia, and high CaxP (>55), respectively. Almost all patients recovered to an acceptable level within 2 weeks of stopping doxercalciferol and adjusting the phosphate binder dose. In all, 21 patients required temporary stoppage of therapy. Most of them were restarted on therapy at a reduced dose during the study. It can, therefore, be concluded that doxercalciferol is effective in controlling SHPT in CKD-4 patients with an acceptable risk of hyperphosphatemia and hypercalcemia.

Effects of paricalcitol on calcium and phosphate metabolism and markers of bone health in patients with diabetic nephropathy: results of the VITAL study

Background

Chronic kidney disease (CKD) is associated with elevations in serum phosphate, calcium–phosphorus product and bone-specific alkaline phosphatase (BAP), with attendant risks of cardiovascular and bone disorders. Active vitamin D can suppress parathyroid hormone (PTH), but may raise serum calcium and phosphate concentrations. Paricalcitol, a selective vitamin D activator, suppressed PTH in CKD patients (stages 3 and 4) with secondary hyperparathyroidism (SHPT) with minimal changes in calcium and phosphate metabolism.

Methods

The VITAL study enrolled patients with CKD stages 2–4. We examined the effect and relationship of paricalcitol to calcium and phosphate metabolism and bone markers in a post hoc analysis of VITAL. The study comprised patients with diabetic nephropathy enrolled in a double-blind, placebo-controlled, randomized trial of paricalcitol (1 or 2 μg/day). Urinary and serum calcium and phosphate, serum BAP, and intact PTH (iPTH) concentrations were measured throughout the study.

Results

Baseline demographics and calcium, phosphate, PTH (49% with iPTH <70 pg/mL), and BAP concentrations were similar between groups. A transient, modest yet significant increase in phosphate was observed for paricalcitol 2 μg/day (+0.29 mg/dL; P < 0.001). Dose-dependent increases in serum and urinary calcium were observed; however, there were few cases of hypercalcemia: one in the 1-μg/day group (1.1%) and three in the 2-μg/day group (3.2%). Significant reductions in BAP were observed that persisted for 60 days after paricalcitol discontinuation (P < 0.001 for combined paricalcitol groups versus placebo). Paricalcitol dose-dependent reductions in iPTH were observed. Paricalcitol in CKD patients (±SHPT) was associated with modest increases in calcium and phosphate.

Conclusion

Paricalcitol reduces BAP levels, which may be beneficial for reducing vascular calcification.

Trial registration

Trial is registered with ClinicalTrials.gov, number NCT00421733.

Mineral metabolism abnormalities and vitamin D receptor activation in cardiorenal syndromes

Over the last decade, it has become increasingly clear that the cardiovascular and renal systems are interdependent. Primary disorders of either system have been shown to disturb the other system. As a result, a class of cardiorenal syndromes (CRS) has been identified wherein a vicious cycle is established as an acute/chronic dysfunction of either the kidney or the heart exacerbates the loss of function in the other organ. Progressive loss of kidney function observed in patients with CRS (mostly types 2 and 4) leads to reduced production of calcitriol (active vitamin D) and an imbalance in calcium and phosphorus levels, which are correlated with increased rates of cardiovascular events and mortality. In addition, hypocalcemia can lead to prolonged and excessive secretion of parathyroid hormone (PTH), eventually leading to development of secondary hyperparathyroidism. Therefore, based on this important mechanism of organ damage, one of the major goals of therapy for patients with CRS is to restore regulatory control of PTH. Although administration of calcitriol increases serum calcium levels and reduces PTH levels, it is also associated with elevated serum levels of calcium-phosphorus product. Therefore, compounds that selectively activate vitamin D receptors, potentially reducing calcium × phosphate toxicity, are likely to enhance cardiorenal protection and provide significant clinical benefit.

The influence of selective vitamin D receptor activator paricalcitol on cardiovascular system and cardiorenal protection

The ubiquitous distribution of vitamin D receptors in the human body is responsible for the pleiotropic effects of vitamin D-receptor activation. We discuss the possible beneficial effects of a selective activator of vitamin D receptor, paricalcitol, on the cardiovascular system in chronic heart failure patients and chronic kidney patients, in light of new trials. Paricalcitol should provide additional clinical benefits over the standard treatment for chronic kidney and heart failure, especially in cases of cardiorenal syndrome.

Characteristics of urinary and serum soluble Klotho protein in patients with different degrees of chronic kidney disease

Background

Klotho is a single-pass transmembrane protein, which appears to be implicated in aging. The purpose of the present study was to characterize the relationship between the soluble Klotho level and renal function in patients with various degrees of chronic kidney disease (CKD).

Methods

The levels of soluble Klotho in the serum and urine obtained from one hundred thirty-one CKD patients were determined by a sandwich enzyme-linked immunosorbent assay system.

Results

The amount of urinary excreted Klotho during the 24 hr period ranged from 1.6 to 5178 ng/day (median 427 ng/day; interquartile range [IR] 56.8-1293.1), and the serum Klotho concentration ranged from 163.9 to 2123.7 pg/ml (median 759.7 pg/ml; IR 579.5-1069.1). The estimated glomerular filtration rate (eGFR) was significantly correlated with the log-transformed values of the amount of 24 hr urinary excreted Klotho (r = 0.407, p < 0.01) and the serum Klotho levels (r = 0.232, p < 0.01). However, a stepwise multiple regression analysis identified eGFR to be a variable independently associated only with the log-transformed value of the amount of 24-hr urinary excreted Klotho but not with the log-transformed serum Klotho concentration. Despite the strong correlation between random urine protein-to-creatinine ratio and the 24 hr urinary protein excretion (r = 0.834, p < 0.01), a moderate linear association was observed between the log-transformed value of the amount of 24 hr urinary excreted Klotho and that of the urinary Klotho-to-creatinine ratio (Klotho/Cr) in random urine specimens (r = 0.726, p < 0.01).

Conclusions

The amount of urinary Klotho, rather than the serum Klotho levels, should be linked to the magnitude of the functioning nephrons in CKD patients. The use of random urine Klotho/Cr as a surrogate for the amount of 24-hr urinary excreted Klotho needs to be evaluated more carefully.

Vitamin d and stage 5 chronic kidney disease: a new paradigm?

Vitamin D receptor agonists (VDRA) are currently recommended for the treatment of secondary hyperparathyroidism in stage 5 CKD. They are considered to be contraindicated in the presence of low or normal (for a dialysis patient) levels of PTH due to the risk of developing adynamic bone disease, with consequent vascular calcification. However, these recommendations are increasingly at odds with the epidemiological evidence, which consistently shows a large survival advantage for patients treated with low-dose VDRAs, regardless of plasma calcium, phosphate, or PTH. A large number of pleiotropic effects of vitamin D have been described, including inhibition of renin activity, anti-inflammation, and suppression of vascular calcification stimulators and stimulation of vascular calcification inhibitors present in the uremic milieu. Laboratory studies suggest that a normal cellular vitamin D level is necessary for normal cardiomyocyte and vascular smooth muscle function. While pharmacological doses of VDRA can be harmful, the present evidence suggests that the level of 1,25-dihydroxycholecalciferol should also be more physiological in stage 5 CKD, and that widespread use of low-dose VDRA would be beneficial. A randomized controlled trial to test this hypothesis is warranted.

Paricalcitol versus ergocalciferol for secondary hyperparathyroidism in CKD stages 3 and 4: a randomized controlled trial

BACKGROUND

The efficacy of 25-hydroxyvitamin D (25[OH]D) supplementation versus vitamin D receptor activators for the treatment of secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease (CKD) stages 3 or 4 and vitamin D deficiency is unclear.

STUDY DESIGN

Randomized controlled trial.

SETTING & PARTICIPANTS

80 patients with CKD stages 3 or 4, 25(OH)D level <30 ng/mL, and SHPT in a single medical center.

INTERVENTION

Ergocalciferol, 50,000 units, titrated to achieve serum levels ≥30 ng/mL versus paricalcitol, 1 or 2 μg/d, for 16 weeks.

OUTCOMES

The occurrence of 2 consecutive parathyroid hormone (PTH) levels decreased by at least 30% from baseline. All analyses were intention to treat.

RESULTS

Baseline characteristics in the 2 groups were similar. 21 patients (53%) on paricalcitol and 7 patients (18%) on ergocalciferol treatment achieved the primary outcome measure (P = 0.002). After 16 weeks, PTH levels did not decrease significantly in patients receiving ergocalciferol, but were decreased significantly in those treated with paricalcitol (mean estimate of between-group difference over 16 weeks of therapy, 43.9 pg/mL; 95% CI, 11.2-76.6; P = 0.009). Serum 25(OH)D levels increased significantly after 16 weeks in only the ergocalciferol group, but not the paricalcitol group (mean estimate of between-group difference over 16 weeks of therapy, 7.08 ng/mL; 95% CI, 4.32-9.85; P < 0.001). Episodes of hyperphosphatemia and hypercalcemia were not significantly different between the 2 groups.

LIMITATIONS

Lack of blinding and use of surrogate end points.

CONCLUSIONS

Paricalcitol is more effective than ergocalciferol at decreasing PTH levels in patients with CKD stages 3 or 4 with vitamin D deficiency and SHPT.

Tumoral calcinosis associated with hypercalcemia in a patient with chronic renal failure

A 56-year-old male with chronic renal failure was admitted to the hospital because of progressive hip pain, appetite loss, general fatigue, and hypercalcemia. Slight pain had developed in the left hip 3 months before the initiation of hemodialysis, which subsequently developed into hyperalgesia. The patient was suspected to have sarcoidosis based on the elevated serum angiotensin-converting enzyme and lysozyme levels, and the ocular finding characterized by punched out chorioretinal scarring, although this could not be confirmed by histological evaluations. There was an abnormal uptake of gallium in the dependent portion of the tumoral calcinosis, which could have suggested either the presence of granulomatous sarcoid tissue within the calcified mass or active calcification associated with an inflammatory reaction. Elevated serum concentrations of 1,25-dihydroxyvitamin D3, which should be implicated in the development of hypercalcemia, promptly decreased after the administration of steroids. Steroid administration subsequently led to a decrease in the serum calcium and relief of the hip pain. This was a rare case of sarcoidosis associated with symptomatic tumoral calcinosis and hypercalcemia. The diagnostic significance of a gallium scan in this case will also be discussed.

The vitamin D system: a crosstalk between the heart and kidney

Chronic kidney disease (CKD) independently increases the rates of cardiovascular disease, whereas the severity of kidney disease correlates with increased cardiovascular morbidity and death. Vitamin D is modified in the liver and the kidney to its active form (1,25-dihydroxyvitamin D) by the 25-hydroxy vitamin D 1-hydroxylase enzyme (CYP27B1). The activated vitamin D brings about its actions through the vitamin D receptor (VDR). The VDRs and CYP27B1 have recently been shown to be expressed in several tissues, not directly involved in mineral homeostasis, including the cardiovascular, immune, and epithelial systems. The action of vitamin D in these tissues is implicated in the regulation of endothelial, vascular smooth muscle, and cardiac cell function, the renin-angiotensin system, inflammatory and fibrotic pathways, and immune response. Impaired VDR activation and signalling results in cellular dysfunction in several organs and biological systems, which leads to reduced bone health, an increased risk for epithelial cancers, metabolic disease, and uncontrolled inflammatory responses. Failure of cardiovascular VDR activation results in hypertension, accelerated atherosclerosis and vascular calcification, cardiac hypertrophy with vascular rarification and fibrosis, and progressive renal dysfunction. An emerging body of evidence has prompted attention to the relationship between CKD, mineral bone disorder (CKD-MBD), and cardiovascular disease in the new guidelines from Kidney Disease: Improving Global Outcomes. Vitamin D receptor activators, commonly used to treat CKD-MBD, and an appropriate treatment of vitamin D hormonal system failure in patients with CKD, may help to reduce cardiovascular morbidity and mortality in these patients.

Intact PTH combined with the PTH ratio for diagnosis of bone turnover in dialysis patients: a diagnostic test study

BACKGROUND

Determination of parathyroid hormone (PTH) level is the most commonly used surrogate marker for bone turnover in patients with stage 5 chronic kidney disease on dialysis therapy (CKD-5D). The objective of this study is to evaluate the predictive value of various PTH measurements for identifying low or high bone turnover rate.

STUDY DESIGN

Diagnostic test study.

SETTINGS & PARTICIPANTS

141 patients with CKD-5D from 15 US hemodialysis centers.

INDEX TESTS

Intact PTH, PTH 1-84, and PTH ratio (ratio of level of PTH 1-84 to level of large carboxy-terminal PTH fragments).

REFERENCE TEST OR OUTCOME

Bone turnover determined using bone histomorphometry.

OTHER MEASUREMENTS

Demographic and treatment-related factors, serum calcium and phosphorus.

RESULTS

Patients presented histologically with a broad range of bone turnover abnormalities. In white patients with CKD-5D (n = 70), PTH ratio <1.0 added to intact PTH level <420 pg/mL increased the positive predictive value for low bone turnover from 74% to 90%. In black patients (n = 71), adding PTH ratio <1.2 to intact PTH level <340 pg/mL increased the positive predictive value for low bone turnover from 48% to 90%. Adding PTH ratio >1.6 to intact PTH level of 340-790 pg/mL increased the positive predictive value for high bone turnover from 56% to 71%.

LIMITATIONS

Because the research protocol called for carefully controlled blood specimen handling, blood drawing and routine specimen handling might be less stringent in clinical practice. By limiting study participation to black and white patients with CKD-5D, we cannot comment on the roles of intact PTH, PTH 1-84, and PTH ratio in other racial/ethnic groups.

CONCLUSION

In black patients with CKD-5D, the addition of PTH ratio to intact PTH measurements is helpful for diagnosing low and high bone turnover. In white patients with CKD-5D, it aids in the diagnosis of low bone turnover.

Vitamin D compounds for people with chronic kidney disease not requiring dialysis

BACKGROUND

Vitamin D compounds are used to suppress elevated serum parathyroid hormone (PTH) in people with chronic kidney disease (CKD).

OBJECTIVES

To assess the efficacy of vitamin D therapy on biochemical, bone, cardiovascular, and mortality outcomes in people with CKD and not requiring dialysis.

SEARCH STRATEGY

We searched The Cochrane Renal Group's specialised register, Cochrane's Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, and reference lists of retrieved articles.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing different forms, schedules, or routes of administration of vitamin D compounds for people with CKD not requiring dialysis were included. Vitamin D compounds were defined as established (calcitriol, alfacalcidol, 24,25(OH)(2)vitamin D(3)) or newer (doxercalciferol, maxacalcitol, paricalcitol, falecalcitriol) vitamin D compounds.

DATA COLLECTION AND ANALYSIS

Data were extracted by two authors. Statistical analyses were performed using the random effects model. Results were summarized as risk ratio (RR) for dichotomous outcomes or mean differences (MD) for continuous outcomes with 95% confidence intervals (CI).

MAIN RESULTS

Sixteen studies (894 patients) were included. No formulation, route, or schedule of vitamin D compound was found to alter the mortality risk or need for dialysis. Vitamin D compounds significantly lowered serum PTH (4 studies, 153 patients: MD -49.34 pg/mL, 95% CI -85.70 to -12.97 (-5.6 pmol/L, 95% CI -9.77 to -1.48)) and were more likely to reduce serum PTH > 30% from baseline value (264 patients: RR 7.87, 95% CI 4.87 to 12.73). Vitamin D treatment was associated with increased end of treatment serum phosphorus (3 studies, 140 patients: MD 0.37 mg/dL, 95% CI 0.09, 0.66 (0.12 mmol/L, 95% CI 0.03, 0.21)) and serum calcium (5 studies, 184 patients: MD 0.20 mg/dL, 95% CI 0.17 to 0.23 (0.05 mmol/L, 95% CI 0.04 to 0.06)). Few data were available comparing intermittent with daily vitamin D administration, or other schedules of dosing.

AUTHORS' CONCLUSIONS

There are not sufficient data to determine the effect of vitamin D compounds on mortality and cardiovascular outcomes in people with CKD not requiring dialysis. While vitamin D compounds reduce serum PTH (49.3 pg/mL (5.6 pmol/L)) compared with placebo, the relative clinical benefits of PTH lowering versus treatment-related increases in serum phosphorus and calcium remain to be understood.

Effects of treatment of renal osteodystrophy on bone histology

Renal osteodystrophy is characterized by abnormalities in bone turnover, mineralization, and bone volume. The effects of treatment modalities for renal osteodystrophy on bone should be analyzed with respect to these abnormalities. The major treatment modalities for renal osteodystrophy include phosphate binders, vitamin D compounds, and calcimimetics. Aluminum-containing phosphate binders have been shown to be toxic to bone secondary to their effects on bone turnover, mineralization, and bone volume. The use of calcium-based phosphate binders has been associated with the development of adynamic bone disease (low bone turnover), bone loss, and worsening of vascular calcifications. New nonaluminum, noncalcium phosphate binders have been developed (sevelamer hydrochloride and lanthanum carbonate). These agents show a potential for improvement in bone turnover and bone volume. Patients with renal osteodystrophy are deficient in calcitriol and often in calcidiol. Calcidiol deficiency has been underappreciated and deserves to be addressed in the treatment of patients with renal osteodystrophy. Calcitriol replacement therapy by daily oral administration is associated with frequent episodes of hypercalcemia and suppression of bone turnover in patients with stages 3 to 5 chronic kidney disease. Pulse oral or intravenous calcitriol administration induces frequent episodes of hypercalcemia or hyperphosphatemia, respectively, and achieves the same degree of correction of bone abnormalities. There are no data on the effects of paricalcitol or doxercalciferol on human bone. Experimental data, however, show that these two analogues and maxacalcitol may control serum parathyroid hormone levels without suppressing bone turnover. Calcimimetics lower parathyroid hormone levels and bone turnover.

Bone and mineral disorders in pre-dialysis CKD

Disorders in calcium, phosphorus, and parathyroid hormone (PTH) are common in chronic kidney disease (CKD) and may be associated with poor outcomes including a higher rate of CKD progression and increased death risk. Although these abnormalities have been examined extensively in patients with CKD stage 5 who are receiving chronic maintenance dialysis, they have not been studied to the same extent at earlier stages of CKD, in spite of the much larger numbers of patients in the early CKD population. We summarize the available literature on outcomes associated with bone and mineral disorders in patients with CKD not yet receiving maintenance dialysis. We have reviewed novel data linking fibroblast growth factor 23 (FGF-23) to phosphorus and vitamin D homeostasis. More rapid CKD progression is linked to hyperphosphatemia and its associated hyperparathyroidism and vitamin D deficiency. Hence, hyperphosphatemia may play a central role in the diverse disorders characterizing CKD. We provide a brief overview of the available treatment recommendations for bone and mineral disorders, with an emphasis on areas needing further research.

Evaluation of parathyroid hyperplasia by ultrasonographic examination in patients with end-stage renal failure before and at initiation of dialysis

Secondary hyperparathyroidism (2HPT), which is related to renal osteodystrophy (ROD), may occur in patients in the comparatively early stage of chronic renal failure (CRF). Secondary hyperparathyroidism patients with parathyroid hyperplasia showed resistance to vitamin D(3) treatment during long-term dialysis. At present, evaluation by ultrasonography is considered to be useful for confirming parathyroid hyperplasia. There are no clinical data associated with imaging evaluation of 2HPT in CRF patients. In the present study, the relationship among clinical and biochemical data, and parathyroid hyperplasia by ultrasonography, was evaluated in 12 patients (six males and six females) with end-stage renal failure (ESRF) before and at initiation of dialysis. Five patients showed an enlargement of parathyroid glands in ultrasonography. Levels of serum-intact parathyroid hormone (PTH) in patients with parathyroid hyperplasia (positive group) were significantly higher than in those without hyperplasia (negative group; 97.6 +/- 36.65 vs 17.4 +/- 4.45 pmol/L; P < 0.05). The levels of intact PTH were above 35.0 pmol/L in all five patients with hyperplasia. All patients in the positive group had never taken vitamin D(3) supplements. Calcium-containing phosphate binders were not prescribed before the present study, except in one patient. Parathyroid hyperplasia caused by 2HPT was recognized in patients before and at initiation of dialysis in this study. It appears that untreated 2HPT in CRF patients may progress to advanced 2HPT in ESRF before and/or after the early stage of dialysis. The levels of serum intact PTH are useful in predicting parathyroid hyperplasia.

Vitamin D receptor activator selectivity in the treatment of secondary hyperparathyroidism: understanding the differences among therapies

Secondary hyperparathyroidism (SHPT) is a common and serious consequence of chronic kidney disease (CKD). SHPT is a complex condition characterised by a decline in 1,25-dihydroxyvitamin D and consequent vitamin D receptor (VDR) activation, abnormalities in serum calcium and phosphorus levels, parathyroid gland hyperplasia, elevated parathyroid hormone (PTH) secretion, and systemic mineral and bone abnormalities. There are three classes of drugs used for treatment of SHPT: (i) nonselective VDR activators or agonists (VDRAs); (ii) selective VDRAs; and (iii) calcimimetics. The VDRAs act on the VDR, whereas the calcimimetics act on the calcium-sensing receptor. Calcimimetics are commonly used in conjunction with VDRA therapy. By virtue of the differences in their chemical structure, the nonselective and selective VDRAs differ in their effects on gene expression, and ultimately parathyroid gland, bone and intestine function. Medications in all three classes are effective in suppression of PTH; however, clinical studies show that calcimimetics are associated with an unfavourable tolerability profile and hypocalcaemia, whereas nonselective VDRAs, and to a lesser extent selective VDRAs, are associated with dose-limiting hypercalcaemia and hyperphosphataemia. Selective VDRAs also have minimal undesirable effects on calcium absorption in the intestine, and calcium and phosphorus mobilisation in the bone compared with nonselective VDRAs. Calcium load in patients with CKD can lead to vascular calcification, accelerated progression of cardiovascular disease and increased mortality. High serum phosphorus levels are also associated with adverse effects on cardiorenal function and survival. Recent evidence suggests that VDRAs are associated with a survival benefit in CKD patients, with a more favourable effect with selective VDRAs than nonselective VDRAs. Paricalcitol, a selective VDRA, is reported to exert specific effects on gene expression in various cell types that are involved in vascular calcification and the development of coronary artery disease. This article examines the molecular mechanisms that determine selectivity of VDRAs, and reviews the evidence for clinical efficacy, safety and survival associated with the three drug classes used for treatment of SHPT in CKD patients.

Vitamin D analogs for secondary hyperparathyroidism: what does the future hold?

Secondary hyperparathyroidism (2 degrees HPT) commonly develops in patients with chronic kidney disease (CKD) in response to high phosphate, low calcium and low 1,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)]. High PTH levels increase the rate of bone turnover, with a net efflux of calcium and phosphate leading to vascular calcification and coronary artery disease. Treatment of 2 degrees HPT with 1alpha,25(OH)(2)D(3) and calcium-based phosphate binders often produces hypercalcemia and over-suppression of PTH, resulting in adynamic bone that cannot buffer excess calcium and phosphate, which increases the risk of vascular calcification. It is essential, then, to reduce PTH levels to a range that supports normal bone turnover and minimizes ectopic calcification. Vitamin D analogs that inhibit PTH gene transcription and parathyroid hyperplasia, and that have less calcemic activity than 1alpha,25(OH)(2)D(3,) have provided a greater safety margin for the treatment of 2 degrees HPT, as well as enhancing the survival of CKD patients. Although several analogs with less calcemic activity are now used in patients (paricalcitol and doxercalciferol in the USA, and OCT and falecalcitriol in Japan), efforts to develop even more selective analogs continue. Parathyroid glands express both 25-hydroxylase and 1alpha-hydroxylase and may be capable of activating prohormones or prodrugs to suppress PTH and parathyroid growth by an autocrine mechanism. Moreover, the introduction of non-calcium-based phosphate binders (sevelamer and lanthanum carbonate) and cinacalcet (an allosteric activator of the calcium receptor that reduces PTH and the serum calciumxphosphate product) may reduce the risk of hypercalcemia with vitamin D therapy. Combining these agents with higher doses of vitamin D compounds may achieve greater suppression of PTH and possibly enhance survival in patients with chronic kidney disease.

Drug insight: vitamin D analogs in the treatment of secondary hyperparathyroidism in patients with chronic kidney disease

Secondary hyperparathyroidism commonly develops in patients with chronic kidney disease (CKD) in response to high phosphate, low calcium and low 1alpha,25-dihydroxyvitamin D(3) (calcitriol) levels. High levels of parathyroid hormone (PTH) accelerate bone turnover, with efflux of calcium and phosphate that can lead to vascular calcification. Treatment of secondary hyperparathyroidism with calcitriol and calcium-based phosphate binders can produce hypercalcemia and oversuppression of PTH, which results in adynamic bone that cannot buffer calcium and phosphate levels, and increased risk of vascular calcification. PTH levels must, therefore, be reduced to within a range that supports normal bone turnover and minimizes ectopic calcification. Vitamin D analogs that inhibit PTH gene transcription and parathyroid hyperplasia (and have reduced calcemic activity) are a safer treatment for secondary hyperparathyroidism than calcitriol; these agents enhance the survival of patients with CKD. Several such analogs are now in use, and analogs with even greater selectivity than those currently used are in development. Parathyroid glands express both 25-hydroxylase and 1alpha-hydroxylase, which suggests that these enzymes might suppress parathyroid function by an autocrine mechanism. The risk of hypercalcemia with vitamin D analog therapy is reduced by the introduction of non-calcium-based phosphate binders and cinacalcet; furthermore, recent trials indicate that early intervention with vitamin D analogs in stage 3 and 4 CKD can correct PTH levels, and could prevent renal bone disease and prolong patient survival.