Suppression of parathyroid hormone secretion in hemodialysis patients by a novel vitamin D analogue: 19-nor-1,25-dihydroxyvitamin D2

Vitamin D and Secondary Hyperparathyroidism in Chronic Kidney Disease: A Critical Appraisal of the Past, Present, and the Future

The association between vitamin D deficiency and especially critical shortage of active vitamin D (1,25-dihydroxyvitamin D, calcitriol) with the development of secondary hyperparathyroidism (sHPT) is a well-known fact in patients with chronic kidney disease (CKD). The association between sHPT and important clinical outcomes, such as kidney disease progression, fractures, cardiovascular events, and mortality, has turned the prevention and the control of HPT into a core issue of patients with CKD and on dialysis. However, vitamin D therapy entails the risk of unwanted side effects, such as hypercalcemia and hyperphosphatemia. This review summarizes the developments of vitamin D therapies in CKD patients of the last decades, from calcitriol substitution to extended-release calcifediol. In view of the study situation for vitamin D insufficiency and sHPT in CKD patients, we conclude that the nephrology community has to solve three core issues: (1) What is the optimal parathyroid hormone (PTH) target level for CKD and dialysis patients? (2) What is the optimal vitamin D level to support optimal PTH titration? (3) How can sHPT treatment support reduction in the occurrence of hard renal and cardiovascular events in CKD and dialysis patients?

Association of Anabolic Effect of Calcitriol with Osteoclast-Derived Wnt 10b Secretion

Canonical Wnt (Wingless/Integrated) signaling is crucial in bone development and the Wnt ligand can promote osteoblast differentiation from mesenchymal progenitor cells. Calcitriol, an active vitamin D3, is used clinically for treatment of secondary hyperparathyroidism (SHPT) in chronic kidney disease (CKD) patients. The bone effects of calcitriol in SHPT remains uncertain. We hypothesized that calcitriol improves bone mass by suppressing osteoclast activity, and simultaneously promoting Wnt ligand secretion. We designed a cross-sectional study in maintenance hemodialysis patients to explore the effects of calcitriol on different bone turnover markers and specifically emphasized the Wnt 10b levels. Then, we explored the source of Wnt 10b secretion by using osteoclasts and osteoblasts treated with calcitriol in cell culture studies. Finally, we explored the effects of calcitriol on bone microarchitectures in CKD mice, using the 5/6 nephrectomy CKD animal model with analysis using micro-computed tomography. Calcitriol promoted the growth of both trabecular and cortical bones in the CKD mice. Wnt 10b and Procollagen 1 N-terminal Propeptide (P1NP) significantly increased, but Tartrate-resistant acid phosphatase 5b (Trap 5b) significantly decreased in the calcitriol-treated maintenance hemodialysis patients. Calcitriol enhanced Wnt 10b secretion from osteoclasts in a dose-dependent manner. Treatment of SHPT with calcitriol improved the bone anabolism by inhibiting osteoclasts and promoting osteoblasts that might be achieved by increasing the Wnt 10b level.

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.

Con: Nutritional vitamin D replacement in chronic kidney disease and end-stage renal disease

Insufficiency of 25-hydroxyvitamin D [25(OH)D] is highly prevalent among patients with chronic kidney disease (CKD) or end-stage renal disease (ESRD) and is a critical component in the pathogenesis of secondary hyperparathyroidism. Accordingly, current National Kidney Foundation-Kidney Disease Outcomes Quality Initiative and Kidney Disease: Improving Global Outcomes guidelines recommend the correction of hypovitaminosis D through nutritional vitamin D replacement as a first-step therapeutic approach targeting secondary hyperparathyroidism. In this Polar Views debate, we summarize the existing evidence, aiming to defend the position that nutritional vitamin D replacement is not evidence-based and should not be applied to patients with CKD. This position is supported by the following: (i) our meta-analysis of randomized controlled trials shows that whereas nutritional vitamin D significantly increases serum 25(OH)D levels relative to placebo, there is no evidence either in predialysis CKD or in ESRD that parathyroid hormone (PTH) is lowered; (ii) on the other hand, in randomized head-to-head comparisons, nutritional vitamin D is shown to be inferior to activated vitamin D analogs in reducing PTH levels; (iii) nutritional vitamin D is reported to exert minimal to no beneficial actions in a series of surrogate risk factors, including aortic stiffness, left ventricular mass index (LVMI), epoetin utilization and immune function among others; and (iv) there is no evidence to support a benefit of nutritional vitamin D on survival and other 'hard' clinical outcomes. Whereas nutritional vitamin D replacement may restore 25(OH)D concentration to near normal, the real target of treating vitamin D insufficiency is to treat secondary hyperparathyroidism, which is untouched by nutritional vitamin D. Furthermore, the pleotropic benefits of nutritional vitamin D remain to be proven. Thus, there is little, if any, benefit of nutritional vitamin D replacement in CKD.

Long-Term Therapy Outcomes When Treating Chronic Kidney Disease Patients with Paricalcitol in German and Austrian Clinical Practice (TOP Study)

Paricalcitol is approved for prevention and therapy of secondary hyperparathyroidism (sHPT) in patients with chronic kidney disease (CKD), with only short-term data in clinical routine settings. A 12-month observational study was conducted in Germany and Austria (90 centers, 761 patients) from 2008 to 2013. Laboratory values, demographical, and clinical data were documented in 629 dialysis patients and 119 predialysis patients. In predialysis patients, median intact parathormone (iPTH) was 180.0 pg/mL (n = 105) at the start of the study, 115.7 pg/mL (n = 105) at last documentation, and 151.8 pg/mL (n = 50) at month 12, with 32.4% of the last documented iPTH values in the KDOQI (Kidney Disease Outcomes Quality Initiative) target range. In dialysis patients, median iPTH was 425.5 pg/mL (n = 569) at study start, 262.3 pg/mL (n = 569) at last documentation, and 266.1 pg/mL (n = 318) at month 12, with 36.5% of dialysis patients in the KDOQI target range. Intravenous paricalcitol showed more homogenous iPTH control than oral treatment. Combined analysis of all dialysis patients indicated comparable and stable mean serum calcium and phosphate levels throughout the study. Clinical symptoms, such as itching, bone pain, and fatigue, were improved compared with study entry. The spectrum and frequency of adverse events mirrored the known pattern for patients on dialysis. Paricalcitol is efficacious and has a consistent safety profile in sHPT over 12 months.

Comparison of the Pharmacological Effects of Paricalcitol Versus Calcitriol on Secondary Hyperparathyroidism in the Dialysis Population

Management of secondary hyperparathyroidism (SHPT) in dialysis population includes the use of active vitamin D forms, among which paricalcitol was shown to be more effective at reducing parathyroid hormone (PTH) concentrations. A prospective randomized study comparing the effectiveness and safety of peroral paricalcitol and calcitriol in suppressing PTH concentrations in 20 hemodialysis patients was performed comparing the influence of agents on PTH suppression, calcium (Ca) and phosphate (P) level and calcium-phosphorus product (C×P). The study was performed in an "intent to treat" manner with primary end point in reduction of PTH level in the target area of 150 > PTH < 300 ng/L after 3 months. At the time point 3 months after therapy induction paricalcitol and calcitriol were equally efficient at correcting PTH levels, with paricalcitol showing significantly less calcemic effect than calcitriol.

Effects of paricalcitol on cardiovascular outcomes and renal function in patients with chronic kidney disease : A meta-analysis

BACKGROUND

Paricalcitol, a selective activator of the vitamin D receptor (VDR), influences calcium and phosphorus homeostasis and bone metabolism. Whether paricalcitol reduces cardiovascular risk and protects renal function remains unclear. To systematically evaluate this in patients with chronic kidney disease (CKD), we conducted a meta-analysis of published randomized controlled trials (RCTs).

METHODS

We searched MEDLINE, Embase, the Cochrane Library, and reference lists for RCTs comparing paricalcitol with placebo in stage 2-5 CKD (including pre-dialysis and renal replacement patients). The Cochrane quality assessment method was used to evaluate study quality. Results were summarized as risk ratios (RRs) for dichotomous outcomes or mean differences (MD) for continuous outcomes.

RESULTS

We included 21 studies comprising 1894 patients. Compared to placebo, paricalcitol reduced the risk of cardiovascular events (RR 0.55; 95% CI 0.35-0.87; p = 0.01), but the RR of hypercalcemia associated with paricalcitol was 6.50 (95% CI 3.21-13.15; p < 0.00001). Paricalcitol cannot significantly change systolic blood pressure and cardiac structure. Although proteinuria reduction was achieved more frequently with paricalcitol (RR 1.51; 95% CI 1.25-1.82; p < 0.0001), it did not significantly reduce proteinuria level compared to placebo. Paricalcitol could not protect renal function to delay CKD progression, since it reduced the glomerular filtration rate (MD -3.15; 95% CI -4.35--1.96; p < 0.0001) and elevated serum creatinine (MD 0.93; 95% CI 0.10-0.68; p = 0.008).

CONCLUSION

Paricalcitol reduces the risk of cardiovascular events in CKD patients but increases the risk of hypercalcemia and cannot improve cardiac structure. Meanwhile, it cannot significantly reduce proteinuria level or protect renal function.

Paricalcitol attenuates lipopolysaccharide-induced myocardial inflammation by regulating the NF-κB signaling pathway

Vitamin D deficiency is associated with an increased risk of cardiovascular disease, diabetes, colon and breast cancer, infectious diseases and allergies. Vascular alterations are an important pathophysiological mechanism of sepsis. Experimental data suggest that paricalcitol, a vitamin D2 analogue, exerts beneficial effects on renal inflammation and fibrosis. In the present study, we aimed to investigate the effects of paricalcitol on lipopolysaccharide (LPS)-induced myocardial inflammation and to elucidate the underlying mechanisms. We used primary cultured human umbilical vein endothelial cells for in vitro experiments, in which stimulation with tumor necrosis factor (TNF)-α was used to induce endothelial cell inflammation. For in vivo experiments, myocardial inflammation was induced by an intraperitoneal injection of 15 mg/kg LPS into C57BL6 mice pre-treated with or without 0.2 µg/kg paricalcitol. Treatment with paricalcitol suppressed the TNF-α-induced increase in the protein expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and fractalkine in endothelial cells. Treatment with paricalcitol also decreased the TNF-α-induced nuclear factor (NF)-κB binding activity. In a mouse model of LPS-induced myocardial inflammation, pre-treatment with paricalcitol prevented the LPS-induced increase in the expression of myocardial ICAM-1, phosphorylated p65 and myocardial TNF-α. Pre-treatment with paricalcitol also alleviated endotoxemia‑induced microvascular leakage in the myocardium. The findings of our study suggest that paricalcitol exerts a protective effect against LPS-induced myocardial inflammation by regulating the expression of cell adhesion molecules and TNF-α, and by improving myocardial permeability.

Sensitive method for the determination of paricalcitol by liquid chromatography and mass spectrometry and its application to a clinical pharmacokinetic study

A highly sensitive, specific and rapid LC-ESI-MS/MS method has been developed and validated for the quantification of paricalcitol (PAR) in human plasma (500 μL) using paricalcitol-d6 (PAR-d6 ) as an internal standard (IS) as per regulatory guidelines. A liquid-liquid extraction method was used to extract the analyte and IS from human plasma. Chromatography was achieved on Zorbax SB C18 column using an isocratic mobile phase in a gradient flow. The total chromatographic run time was 6.0 min and the elution of PAR and PAR-d6 occurred at ~2.6 min. A linear response function was established for the range of concentrations 10-500 pg/mL in human plasma. The intra- and inter-day accuracy and precision values for PAR met the acceptance criteria. The validated assay was applied to quantitate PAR concentrations in human plasma following oral administration of 4 µg capsules to humans.

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.

Triennial Growth Symposium--Vitamin D: bones and beyond

The exploration of vitamin D metabolism and function has led to the discovery of active forms of vitamin D that find great usefulness in treating patients with bone disease or renal failure and also perhaps in topical application for the treatment of skin disorders, such as psoriasis. It may also be effective in some types of autoimmune disease. This warrants our attention to maintaining an adequate vitamin D level in our blood to assure that the expected functions of vitamin D take place. However, we must not get so overenthusiastic as to expect vitamin D to be effective in treating or preventing many diverse diseases and especially caution is urged in considering that vitamin D compounds might be used to suppress cancerous growth.

Safety and tolerability of paricalcitol in patients with chronic kidney disease

INTRODUCTION

Secondary hyperparathyroidism (SHPT) is a complication of chronic kidney disease (CKD). Beyond skeletal complications, uncontrolled SHPT is associated with cardiovascular mortality. Vitamin D receptor activators (VDRAs) are a mainstay of therapy for SHPT; however, use is limited by hypercalcemia, though less so with calcitriol analogs such as paricalcitol and there is emerging experience with oral formulations for non-SHPT indications. The role of VDRAs in the treatment of SHPT becomes a complex question as alternative strategies have developed.

AREAS COVERED

This review summarizes trials that established the safety and efficacy of paricalcitol for SHPT. Comparative experience with paricalcitol as against other VDRAs will be reviewed as will the experience with paricalcitol in non-dialysis CKD and comparative experience with non-VDRA-based therapy.

EXPERT OPINION

VDRA therapy is considered first-line therapy for treatment of SHPT. Paricalcitol has demonstrated superiority to calcitriol with respect to parathyroid hormone suppression and calcium-phosphorus balance. Oral formulations of paricalcitol appear to be similarly effective for SHPT. While there is evidence to suggest adjunctive antiproteinuria benefit with the use of VDRAs, efficacy of these agents to slow the progression of CKD or to reduce cardiovascular risk has not yet been demonstrated.

Potent 19-norvitamin D analogs for prostate and liver cancer therapy

The active form of vitamin D(3), 1α,25(OH)(2)D(3) or calcitriol, is known to inhibit the proliferation and invasiveness of many types of cancer cells, including prostate and liver cancer cells. These findings support the use of 1α,25(OH)(2)D(3) for prostate and liver cancer therapy. However, 1α,25(OH)(2)D(3) can cause hypercalcemia, thus, analogs of 1α,25(OH)(2)D(3) that are less calcemic but exhibit potent antiproliferative activity would be attractive as therapeutic agents. We have developed 2α-functional group substituted 19-norvitamin D(3) analogs with and without 14-epimerization. Among them, 2α- and 2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (MART-10 and -11, respectively) and 14-epi-2α- and 14-epi-2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D(3) (14-epi-MART-10 and 14-epi-MART-11, respectively) were found to be the most promising. In this review, we discuss the synthesis of this unique class of vitamin D analogs, the molecular mechanism of anticancer actions of vitamin D, and the biological evaluation of these analogs for potential application to the prevention and treatment of prostate and liver cancer.

Suppressive effect of 19-nor-1α-25-dihydroxyvitamin D2 on gastric cancer cells and peritoneal metastasis model

The active metabolite of vitamin D, 1,25-dihydroxyvitamin D(3) (calcitriol), inhibits the growth of several types of human cancer cells in vitro, but its therapeutic use is limited because it causes hypercalcemia. Among its analogs, 19-nor-1,25-dihydroxyvitamin D(2) (paricalcitol), has fewer calcemic effects and exhibits an activity equipotent to that of calcitriol. We assessed the antitumor and anti-inflammatory effects of paricalcitol in gastric cancer cells, and evaluated the potential role of vitamin D in the treatment of peritoneal metastatic gastric cancer. In this study, treatment with paricalcitol inhibited gastric cancer cell growth and induced cell cycle arrest. Paricalcitol also induced apoptosis and showed anti-inflammatory activity. Moreover, the growth of intraperitoneal metastases in vivo was reduced in mice treated with paricalcitol. (18)F-FDG uptake was significantly lower in the paricalcitol group compared to control group (SUV; control group 13.2 ± 5.3 vs paricalcitol group 4.5 ± 3.0). Intraperitoneal tumor volume was significantly lower in paricalcitol treated mice (control group 353.2 ± 22.9 mm(3) vs paricalcitol group 252.0 ± 8.4 mm(3)). These results suggest that the vitamin D analog, paricalcitol, has anticancer activity on gastric cancer cells by regulation of the cell cycle, apoptosis, and inflammation.

19-Nor-2α-(3-hydroxypropyl)-1α,25-dihydroxyvitamin D3 (MART-10) is a potent cell growth regulator with enhanced chemotherapeutic potency in liver cancer cells

The discovery that the active form of vitamin D, 1α,25-dihydroxyvitamin D [1α,25(OH)(2)D] can modulate cellular proliferation and differentiation of cancer cells has led to its potential application as a chemotherapeutic agent to treat a variety of cancers. However, the use of 1α,25(OH)(2)D is limited due to its lethal side effect of hypercalcemia upon systemic administration. To overcome this drawback, numerous analogs have been synthesized. In this report, we examined the anti-proliferative activity of a new analog, 19-nor-2α-(3-hydroxypropyl)-1α,25(OH)(2)D(3) (MART-10), in HepG2 liver cancer cells, and studied the potential mechanisms mediating this action. We found that MART-10 exhibited approximately 100-fold greater activity than 1α,25(OH)(2)D(3) in inhibiting HepG2 cell proliferation as determined by cell number counting method. MART-10 was also approximately 100-fold more potent than 1α,25(OH)(2)D(3) in the upregulation of p21 and p27, that in turn arrested HepG2 cells at the G(0)/G(1) phase to a greater extent. Given that no active caspase 3 was detected and treatment with 1α,25(OH)(2)D(3) or MART-10 did not further increase the fractions of apoptotic and necrosis cells over the controls, the growth-inhibitory effect of 1α,25(OH)(2)D(3) and MART-10 on HepG2 cells may not involve apoptosis. Overall, our findings suggest that MART-10 is a good candidate as a novel therapeutic regimen against liver cancer. Further pre-clinical studies using animal models and the subsequent human clinical trials are warranted.

Substitution at carbon 2 of 19-nor-1α,25-dihydroxyvitamin D3 with 3-hydroxypropyl group generates an analogue with enhanced chemotherapeutic potency in PC-3 prostate cancer cells

The active form of vitamin D(3), 1α,25-dihydroxyvitamin D(3)(1α,25(OH)(2)D(3)), has anti-proliferative and anti-invasive activities in prostate cancer cells. Because of 1α,25(OH)(2)D(3) therapeutic potential in treating cancers, numerous analogues have been synthesized with an attempt to increase anti-proliferative and/or decrease calcemic properties. Among these analogues, 19-nor-1α,25(OH)(2)D(2) while being less calcemic has equivalent potency as 1α,25(OH)(2)D(3) in several in vitro and in vivo systems. We recently showed that 19-nor-2α-(3-hydroxypropyl)-1α,25(OH)(2)D(3) (MART-10) was at least 500-fold and 10-fold more active than 1α,25(OH)(2)D(3) in inhibiting the proliferation of an immortalized normal prostate PZ-HPV-7 cells and the invasion of androgen insensitive PC-3 prostate cancer cells, respectively. In this study, we further investigated the effects of MART-10 and 1α,25(OH)(2)D(3) on the dose- and time-dependent induction of CYP24A1 gene expression in PC-3 prostate cancer cells. We found that MART-10 induced CYP24A1 gene expression at a lower concentration with a longer duration compared to 1α,25(OH)(2)D(3), suggesting that MART-10 is less susceptible to CYP24A1 degradation. Molecular docking model of human CYP24A1 and MART-10 indicates that its side chain is far away from the heme ion and is less likely to be hydroxylated by the enzyme. Furthermore, MART-10 was a more potent inhibitor of PC-3 cell proliferation and invasion compared to 1α,25(OH)(2)D(3). In addition, MART-10 down-regulated matrix metalloproteinase-9 (MMP-9) expression which could be one mechanism whereby MART-10 influences cancer cell invasion. Finally, we observed that subcutaneous administration of MART-10 up-regulated the CYP24A1 mRNA expression in rat kidneys without affecting their plasma calcium levels. Thus, our findings demonstrate that MART-10 is biologically active in vivo and may be an effective vitamin D analogue for clinical trials to treat prostate cancer.

Mechanism of the anti-proliferative action of 25-hydroxy-19-nor-vitamin D(3) in human prostate cells

According to the prevailing paradigm, 1α-hydroxylation of 25-hydroxyvitamin D(3) (25(OH)D(3)) and its analogs is a pre-requisite step for their biological effects. We previously reported that 25-hydroxy-19-nor-vitamin D(3) (25(OH)-19-nor-D(3)) had anti-proliferative activity in a cell line, PZ-HPV-7, which was derived from human non-cancerous prostate tissue, and suggested that 25(OH)-19-nor-D(3) acted after 1α-hydroxylation by vitamin D 1α-hydroxylase (CYP27B1). However, metabolic studies of 25(OH)-19-nor-D(3) using recombinant CYP27B1 revealed that 25(OH)-19-nor-D(3) was rarely subjected to 1α-hydroxylation. Therefore, in this report, we attempted to clarify the mechanism of 25(OH)-19-nor-D(3) action in intact cells using PZ-HPV-7 prostate cells. After incubating the cells with 25(OH)-19-nor-D(3), eight metabolites of 24-hydroxylase (CYP24A1) were detected, whereas no products of CYP27B1 including 1α,25-dihydroxy-19-nor-vitamin D(3) (1α,25(OH)(2)-19-nor-D(3)) were found. Furthermore, the time-dependent nuclear translocation of vitamin D receptor (VDR) and the subsequent transactivation of cyp24A1 gene in the presence of 25(OH)-19-nor-D(3) were almost identical as those induced by 1α,25(OH)(2)-19-nor-D(3). These results strongly suggest that 25(OH)-19-nor-D(3) directly binds to VDR as a ligand and transports VDR into the nucleus to induce transcription of cyp24A1 gene. In addition, knock down of cyp27B1 gene did not affect the anti-proliferative activity of 25(OH)-19-nor-D(3), whereas knock down of VDR attenuated the inhibitory effect. Thus, our results clearly demonstrate that the anti-proliferative activity of 25(OH)-19-nor-D(3) is VDR dependent but 1α-hydroxylation independent, suggesting that 25(OH)D(3) analogs such as 25(OH)-19-nor-D(3) could be attractive candidates for anticancer therapy.

Mineral and bone disorders in children with chronic kidney disease

As children with chronic kidney disease (CKD) have a long lifespan, optimal control of bone and mineral homeostasis is essential not only for the prevention of debilitating skeletal complications and for achieving adequate growth but also for preserving long-term cardiovascular health. As the growing skeleton is highly dynamic and at particular risk of deterioration, close control of bone and mineral homeostasis is required in children with CKD. However, assessment of bone disease is hampered by the limited validity of biochemical parameters-major controversy exists on key issues such as parathyroid hormone target ranges and the lack of useful imaging techniques. The role of newly discovered factors in bone and mineral homeostasis, such as fibroblast growth factor 23, is not yet established. Even though scientific evidence is limited in children with CKD, ergocalciferol or cholecalciferol supplementation and the use of calcium-free phosphate binders is recommended. The new drug cinacalcet is highly promising; however, pediatric experience is still limited to observational data and the effect of cinacalcet on longitudinal growth and pubertal development is unknown. Randomized, controlled trials are underway, including studies of cinacalcet pharmacokinetics and pharmacodynamics in infants.

Novel vitamin d analogs for prostate cancer therapy

Prostate cells contain specific receptors for 1α,25-dihydroxyvitamin D [1α,25(OH)₂D] or calcitriol, the active form of vitamin D. 1α,25(OH)₂D is known to inhibit the proliferation and invasiveness of prostate cancer cells. These findings support the use of 1α,25(OH)₂D for prostate cancer therapy. However, 1α,25(OH)₂D can cause hypercalcemia, analogs of 1α,25(OH)₂D that are less calcemic but exhibit potent antiproliferative activity would be attractive as therapeutic agents. To accomplish these goals, different strategies, based on metabolism, molecular mechanism of actions, and structural modeling, have been taken to modify the structure of vitamin D molecule with the aims to improve the efficacy and decrease the toxicity of vitamin D to treat different diseases. During the past four decades, over 3,000 analogs have been synthesized. In this paper, we discuss the development and the biological analysis of a unique class of vitamin D analogs with a substitution at the carbon 2 of 19-nor-1α,25(OH)₂D₃ molecule for potential application to the prevention and treatment of prostate cancer as well as other cancers.

The association of vitamin D use with hypercalcemia and hyperphosphatemia in hemodialysis patients: a case-crossover study

PURPOSE

Elevated levels of phosphorus (P) and calcium (Ca) have been shown in observational studies to be associated with an increased risk of adverse clinical outcomes including mortality. Vitamin D sterols have been shown to increase the risk of hypercalcemia and hyperphosphatemia in clinical trials. We sought to explore these risks in real-world clinical practice.

METHODS

We employed a case-crossover design, which eliminates confounding by non-time-varying patient characteristics by comparing, within each patient, vitamin D doses before the event with those at an earlier period. Using this method, we estimated the risk of hypercalcemic (Ca ≥ 11 g/dL) and hyperphosphatemic (P ≥ 8 g/dL) events for patients at different dose quartiles of vitamin D relative to patients not on a vitamin D sterol.

RESULTS

There was a dose-dependent association between vitamin D dose quartile and risk of hypercalcemia or hyperphosphatemia. In adjusted analyses, each increase in vitamin D quartile was associated with a multiple of hypercalcemia risk between 1.7 and 19 times compared with those not on vitamin D and a multiple of hyperphosphatemia risk between 1.8 and 4.

CONCLUSION

Use of vitamin D sterols is associated with an increased risk of hypercalcemic and hyperphosphatemic events in real-world clinical practice. Other potential predictors of these events, such as phosphate binder use and dialysate Ca levels, were not examined in this analysis.

Secondary hyperparathyroidism: pathogenesis, disease progression, and therapeutic options

Secondary hyperparathyroidism (SHPT) is a challenge frequently encountered in the management of patients with chronic kidney disease (CKD). Downregulation of the parathyroid vitamin D and calcium-sensing receptors represent critical steps that lead to abnormalities in mineral metabolism: high phosphate, low calcium, and vitamin D deficiency. These imbalances result in parathyroid hyperplasia and contribute to vascular calcification. New studies have established a central role for fibroblast growth factor 23 (FGF-23) in the regulation of phosphate-vitamin D homeostasis. FGF-23 concentration increases in CKD and contributes to SHPT. Achieving current targets for the key mineral parameters in the management of SHPT set by the Kidney Disease Improving Global Outcomes (KDIGO) guidelines can be challenging. This review summarizes the current understanding and evidence supporting strategies for SHPT treatment in CKD patients. Treatment should include a combination of dietary phosphorus restriction, phosphate binders, vitamin D sterols, and calcimimetics. Parathyroidectomy is effective in suitable candidates refractory to medical therapy and the standard against which new approaches should be measured. Future strategies may focus on the stimulation of apoptotic activity of hyperplastic parathyroid cells.

Vitamin D compounds for people with chronic kidney disease requiring dialysis

BACKGROUND

Clinical guidelines recommend vitamin D compounds to suppress serum parathyroid hormone (PTH) in chronic kidney disease (CKD), however treatment may be associated with increased serum phosphorus and calcium, which are associated with increased mortality in observational studies. Observational data also indicate vitamin D therapy may be independently associated with reduced mortality in CKD.

OBJECTIVES

We assessed the effects of vitamin D compounds on clinical, biochemical, and bone outcomes in people with CKD and receiving 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) in subjects with CKD and requiring dialysis that assessed treatment with vitamin D compounds.

DATA COLLECTION AND ANALYSIS

Data was extracted by two authors. Results are summarised as risk ratios (RR) for dichotomous outcomes or mean differences (MD) for continuous outcomes, with 95% confidence intervals (CI).

MAIN RESULTS

Sixty studies (2773 patients) were included. No formulation, route, or schedule of administration was associated with altered risks of death, bone pain, or parathyroidectomy. Marked heterogeneity in reporting of outcomes resulted in few data available for formal meta-analysis. Compared with placebo, vitamin D compounds lowered serum PTH at the expense of increasing serum phosphorus. Trends toward increased hypercalcaemia and serum calcium did not reach statistical significance but may be clinically relevant. Newer vitamin D compounds (paricalcitol, maxacalcitol, doxercalciferol) lowered PTH compared with placebo, with increased risks of hypercalcaemia, although inadequate data were available for serum phosphorus. Intravenous vitamin D may lower PTH compared with oral treatment, and be associated with lower serum phosphorus and calcium levels, although limitations in the available studies precludes a conclusive statement of treatment efficacy. Few studies were available for intermittent versus daily and intraperitoneal versus oral administration or directly comparative studies of newer versus established vitamin D compounds.

AUTHORS' CONCLUSIONS

We confirm that vitamin D compounds suppress PTH in people with CKD and requiring dialysis although treatment is associated with clinical elevations in serum phosphorus and calcium. All studies were inadequately powered to assess the effect of vitamin D on clinical outcomes and until such studies are conducted the relative importance of changes in serum PTH, phosphorus and calcium resulting from vitamin D therapy remain unknown. Observational data showing vitamin D compounds may be associated with improved survival in CKD need to be confirmed or refuted in specifically designed RCTs.

Treatment of secondary hyperparathyroidism in haemodialysis patients: a randomised clinical trial comparing paricalcitol and alfacalcidol

BACKGROUND

Secondary hyperparathyroidism is a common feature in patients with chronic kidney disease. Its serious clinical consequences include renal osteodystrophy, calcific uremic arteriolopathy, and vascular calcifications that increase morbidity and mortality.Reduced synthesis of active vitamin D contributes to secondary hyperparathyroidism. Therefore, this condition is managed with activated vitamin D. However, hypercalcemia and hyperphosphatemia limit the use of activated vitamin D.In Denmark alfacalcidol is the primary choice of vitamin D analog.A new vitamin D analog, paricalcitol, may be less prone to induce hypercalcemia and hyperphosphatemia.However, a randomised controlled clinical study comparing alfacalcidol and paricalcitol has never been performed.The primary objective of this study is to compare alfacalcidol and paricalcitol. We evaluate the suppression of the secondary hyperparathyroidism and the tendency towards hyperphosphatemia and hypercalcemia.

METHODS/DESIGN

This is an investigator-initiated cross-over study. Nine Danish haemodialysis units will recruit 117 patients with end stage renal failure on maintenance haemodialysis therapy.Patients are randomised into two treatment arms. After a wash out period of 6 weeks they receive increasing doses of alfacalcidol or paricalcitol for a period of 16 weeks and after a further wash out period of 6 weeks they receive the contrary treatment (paricalcitol or alfacalcidol) for 16 weeks.

DISCUSSION

Hyperparathyroidism, hypercalcemia and hyperphosphatemia are associated with increased cardiovascular mortality in patients with chronic kidney disease.If there is any difference in the ability of these two vitamin D analogs to decrease the secondary hyperparathyroidism without causing hypercalcemia and hyperphosphatemia, there may also be a difference in the risk of cardiovascular mortality depending on which vitamin D analog that are used. This has potential major importance for this group of patients.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00469599.

Paricalcitol versus Calcitriol in the Treatment of Secondary Hyperparathyroidism in Hemodialysis Patients

Purpose

A mainstay treatment of secondary hyperparathyroidism has been the administration of vitamin D analogs. Paricalcitol is a vitamin D analog thought to reduce parathyroid hormone (PTH) levels with fewer effects on calcium (Ca) and phosphorous (P) levels than intravenous calcitriol. However, there are limited data directly comparing the 2 agents. The primary objective was to compare the efficacy of paricalcitol to calcitriol in hemodialysis patients. Secondary objectives evaluated the safety and direct costs associated with these agents.

Methods

This was a retrospective study of hemodialysis patients who received at least 8 weeks of both therapies from 2002 to 2004. Primary outcomes included the percentage of patients achieving greater than or equal to 50% reduction in baseline PTH levels; the change in PTH levels from baseline to the end of therapy; and time to achieve greater than or equal to 50% reduction in baseline PTH concentrations. Secondary outcomes included the percentage of patients experiencing hypercalcemia, hyperphosphatemia, or elevated Ca and P product; and the percentage of patients hospitalized secondary to these side effects.

Results

Calcitriol-treated patients showed a median reduction in PTH concentrations from baseline to the end of treatment phase of 8.3% versus paricalcitol reduction of 1.5%. This result was not statistically significant ( P = 0.08); however, it should be examined in a study powered to detect this difference. A similar number of patients in both treatment groups were able to achieve a greater than or equal to 50% reduction in baseline PTH concentrations but calcitriol-treated patients were more likely to achieve this primary end point faster than the paricalcitol-treated group (166 days vs 207 days, respectively, P = 0.18). The incidence of side effects between the agents was similar. There was a substantial difference in the annual drug cost between paricalcitol and calcitriol.

Conclusion

Paricalcitol did not seem to result in clear efficacy and safety benefit over calcitriol in this study. However, due to the study's retrospective design and potential for a type 2 error, as well as limited published data comparing this agent to calcitriol, additional research is required before paricalcitol becomes the standard of care in patients with chronic kidney disease and secondary hyperparathyroidism.

Phosphate is a uremic toxin

Hyperphosphatemia is one of the more prevalent metabolic disturbances in kidney failure. Phosphate can be considered a uremic toxin based on the accumulation of phosphate during chronic kidney disease, the effects of phosphate on biological systems, and the adverse effects of hyperphosphatemia. The renal clearance of phosphate is maintained until later stages of chronic kidney disease, when the remaining nephrons are no longer able to excrete sufficient phosphate to offset dietary phosphate absorption. Clearance of phosphate by conventional forms of dialysis is insufficient to prevent hyperphosphatemia in most endstage kidney-disease patients. Phosphate contributes to metabolic disturbances such as hyperparathyroidism, vitamin D resistance, and hypocalemia. In combination with these and other factors, hyperphosphatemia damages many organs, including the parathyroid glands, bones, and most importantly the cardiovascular system. Elevated phosphorus is associated with arterial and valvular calcification, arteriosclerosis, and an increased risk of cardiovascular death. Importantly, the adverse effects of hyperphosphatemia are partially preventable with the effective treatments available today.

Evaluation of C-2-substituted 19-nor-1alpha,25-dihydroxyvitamin D3 analogs as therapeutic agents for prostate cancer

1alpha,25-Dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) is known to inhibit the proliferation and invasiveness of prostate cancer cells. However, 1alpha,25(OH)(2)D(3) can cause hypercalcemia and is not suitable as a therapeutic agent. 19-Nor-vitamin D derivatives are known to be less calcemic when administered systemically. In order to develop more potent anti-cancer agents with less calcemic side effect, we therefore utilized (3)H-thymidine incorporation as an index for cell proliferation and examined the antiproliferative activities of nine C-2-substituted 19-nor-1alpha,25(OH)(2)D(3) analogs in the immortalized PZ-HPV-7 normal prostate cell line. Among the nine analogs we observed that the substitution with 2alpha- or 2beta-hydroxypropyl group produced two analogs having antiproliferative potency that is approximately 500- to 1000-fold higher than 1alpha,25(OH)(2)D(3). The (3)H-thymidine incorporation data were supported by the cell counting data after cells were treated with 1alpha,25(OH)(2)D(3), 19-nor-2alpha-(3-hydroxypropyl)-1alpha,25(OH)(2)D(3) or 19-nor-2beta-(3-hydroxypropyl)-1alpha,25(OH)(2)D(3) for 7 days. 19-Nor-2alpha-(3-hydroxypropyl)-1alpha,25(OH)(2)D(3) and 19-nor-2beta-(3-hydroxypropyl)-1alpha,25(OH)(2)D(3) were also shown to be about 10-fold more active than 1alpha,25(OH)(2)D(3) in cell invasion studies using prostate cancer cells. In conclusion, a substitution at the C-2 position of 19-nor-1alpha,25(OH)(2)D(3) molecule with a hydroxypropyl group greatly increased the antiproliferative and anti-invasion potencies. Thus, these two analogs could be developed to be effective therapeutic agents for treating early and late stages of prostate cancer.

Antitumor effects of two less-calcemic vitamin D analogs (Paricalcitol and QW-1624F2-2) in squamous cell carcinoma cells

The active metabolite of vitamin D(3) (1alpha,25-dihydroxyvitamin D(3), calcitriol) has potent antitumor activities in vitro and in vivo in multiple cancers. Concerns about induction of hypercalcemia by calcitriol and the desire for more potent agents have prompted development of less-calcemic vitamin D analogs. These studies demonstrate that two vitamin D analogs, 19-nor-1alpha,25-dihydroxyvitamin D(2) (paricalcitol) and 1alpha-hydroxymethyl-16-ene-24,24-difluoro-25-hydroxy-26,27-bis-homovitamin D(3) (QW-1624F(2)-2, QW), have anticancer effects in the calcitriol-responsive squamous cell carcinoma (SCC) cell line. Paricalcitol (GI50 = 0.7 nM) and QW (GI50 = 0.001 nM) inhibited SCC cell growth; however, QW was more potent. Paricalcitol (10 nM) and QW (10 nM) induced G0/G1 cell cycle arrest and inhibited DNA synthesis by approximately 95%. The vitamin D analogs modulated cell cycle regulators, including decreasing mRNA and protein levels of p21(Waf1/Cip1) (p21) and cyclin-dependent kinase 2 (cdk2), and increasing p27(Kip1) (p27) protein expression. Vitamin D analogs induced apoptosis, caspase-3 cleavage and increased expression of pro-apoptotic MEKK-1. Phosphorylation of Akt, MEK and ERK1/2 that promote cell growth and survival were inhibited by vitamin D analogs. The anticancer effects of paricalcitol and QW are comparable to the effect of calcitriol. These less-calcemic vitamin D analogs are as effective as calcitriol in vitro and are promising for prevention and treatment of cancer and other diseases.

Differential effects of Vitamin D analogs on calcium transport

It is well known that the efficiency of intestinal active calcium transport is regulated by the Vitamin D receptor pathway and Vitamin D analogs seem to exhibit differential effects on intestinal active calcium transport. To investigate the molecular basis for the difference among Vitamin D analogs, we tested three Vitamin D analogs: 1,25-dihydroxyvitamin D(3), 19-nor-1,25-dihydroxyvitamin D(2), and 1alpha-hydroxyvitamin D(2) ex vivo and in vitro. In 5/6 nephrectomized rat intestinal active calcium transport, 19-nor-1,25-dihydroxyvitamin D(2) did not show a significant effects on intestinal active calcium transport at all the concentrations tested, while 1alpha-hydroxyvitamin D(2) at 0.33 and 0.67 microg/kg and 1,25-dihydroxyvitamin D(3) at 1microg/kg significantly stimulated calcium transport. In Caco-2 cells, 19-nor-1,25-dihydroxyvitamin D(2) did not show a significant effect on calcium transport, while 1,25-dihydroxyvitamin D(3) and 1,25-dihydroxyvitamin D(2) (the active form of 1alpha-hydroxyvitamin D(2)) stimulated calcium transport by 934 and 501% at 0.1microM, respectively. 1,25-Dihydroxyvitamin D(2) potently induced the expression of CALB3 and TRPV6 mRNA with an EC(50) of 0.3 and 1.0nM, whereas 19-nor-1,25-dihydroxyvitamin D(2) was 10-fold less potent than 1,25-dihydroxyvitamin D(2) in inducing CALB3 and TRPV6 mRNA. The three Vitamin D analogs had no significant effect on the expression of PMCA1 mRNA. These Vitamin D analogs did not change the expression of Vitamin D receptor (VDR) up to 10nM, but stimulated CYP24A1 expression in a dose-dependent manner with the potency in the order of 1,25-dihydroxyvitamin D(3)>1,25-dihydroxyvitamin D(2)=19-nor-1,25-dihydroxyvitamin D(2). These results suggest that the differential effect of Vitamin D analogs on stimulating intestinal and Caco-2 calcium transport may be in part due to its different effect on stimulating CALB3 and TRPV6 mRNA expression.

Paricalcitol versus calcitriol treatment for hyperparathyroidism in pediatric hemodialysis patients

Secondary hyperparathyroidism (SHPT) remains a treatment dilemma in pediatric dialysis patients. Recent experience with paricalcitol (P), a vitamin D analogue, in adults with SHPT has shown equal efficacy and improved survival compared to traditional treatment with calcitriol (C). We present our experience with (C) compared to (P) treatment in our pediatric dialysis patients with SHPT. Twenty-one patients (mean age 11.5+/-5 years) with SHPT (intact parathyroid hormone (iPTH) averaging 1,228+/-496 pg/ml) were studied. Seventeen received (C) followed by (P); while an additional four were treated with either (C=1) or (P=3) alone. After 26+/-8 weeks, average percent (%) decrease in iPTH was similar with (C) and (P) (-60.4+/-34% versus -65.4+/-28%, respectively; p=0.6). In the (P) group, the effective dose in children was greater than in adult trials based on kilogram weight. Episodes of hypercalcemia between the treatment groups were not different. However, episodes of elevated calcium x phosphorus product (CaxP)> or =70 mg(2)/dl(2) occurred more frequently in the (C) group (odds ratio=1.5; p=0.01). Paricalcitol appears to be safe and effective in pediatric patients. Data suggest that dosing should be gauged according to degree of SHPT. This should serve as impetus for future pharmacokinetic studies in pediatric dialysis patients.

Initial Dosing of Paricalcitol Based on PTH Levels in Hemodialysis Patients With Secondary Hyperparathyroidism

BACKGROUND

Adjustment of the initial dose of paricalcitol in hemodialysis patients with secondary hyperparathyroidism (SHPT) on the basis of severity of SHPT generally is preferred in current practice. Whether the proposed dose, based on the formula baseline intact parathyroid hormone (iPTH [picograms per milliliter]) divided by 80, is the most appropriate has not been assessed adequately.

METHODS

A double-blind randomized trial comparing iPTH/80 dose with the immediately lower iPTH/120 dose was undertaken. Forty-three hemodialysis patients with iPTH levels between 300 and 900 pg/mL (300 and 900 ng/L) were followed up for 12 weeks. The primary outcome was control of iPTH levels within a target range between 150 and 300 pg/mL (150 and 300 ng/L).

RESULTS

No difference between the 2 dose groups was noted in time to achieve target iPTH levels of 150 to 300 pg/mL (150 to 300 ng/L). More episodes of excessive decrease in iPTH levels occurred in the iPTH/80 group compared with the iPTH/120 group (P = 0.003). Nine patients in the iPTH/80 group (45%) versus 2 patients in the iPTH/120 group (10%) had iPTH levels less than 150 pg/mL (<150 ng/L) in at least half the measurements performed during the second half of the study (P = 0.034). Increases in calcium levels were greater in the iPTH/80 group at all times during the study (P < 0.05 at weeks 4 and 10). The number of required dose reductions was significantly greater in the iPTH/80 group compared with the iPTH/120 group (P = 0.008).

CONCLUSION

In hemodialysis patients with SHPT, a lower initial dose of iPTH/120 shows efficacy similar to that of the already widely used iPTH/80 scheme in reaching target iPTH levels (150 to 300 pg/mL [150 to 300 ng/L]), with less required dose adjustments, lower increase in calcium levels, and lower cost. In addition, the initial dose of paricalcitol based on the iPTH/80 formula leads significantly more patients to excessive suppression of iPTH (<150 pg/mL [<150 ng/L]) than the iPTH/120 dose.

Paricalcitol in the treatment of secondary hyperparathyroidism

Secondary hyperparathyroidism is a common complication of both chronic kidney and end-stage renal disease. Vitamin D appears to play a central role in the pathogenesis of this condition and active vitamin D replacement is usually a necessary component of its treatment. The ability to administer active vitamin D is limited by increases in calcium and phosphorus, predisposing patients to vascular calcifications and cardiovascular disease. Paricalcitol is a new vitamin D analog designed to suppress parathyroid secretion with less effect on serum levels of calcium and phosphorus. The application of paricalcitol in chronic kidney disease may slow the clinical course of secondary hyperparathyroidism and allow more effective suppression of parathyroid hormone while minimizing the concommitant risks of hypercalcemia and hyperphosphatemia. This article reviews the pathogenesis of secondary hyperparathyroidism and the data supporting the role of oral and intravenous paricalcitol in the treatment of secondary hyperparathyroidism in both chronic kidney disease and end-stage renal disease patients.

Cinacalcet Hydrochloride (Sensipar) in Hemodialysis Patients on Active Vitamin D Derivatives with Controlled PTH and Elevated Calcium × Phosphate

Active vitamin D derivatives attenuate the severity of secondary hyperparathyroidism but often increase serum calcium (Ca) and phosphorus (P) as a result of enhanced intestinal absorption. The calcimimetic cinacalcet HCl lowers parathyroid hormone (PTH) and tends to decrease Ca x P. A 16-wk, open-label clinical trial was conducted in adult hemodialysis patients who had controlled PTH (biointact PTH [biPTH] 80 to 160 pg/ml) and elevated Ca x P (> 55 mg2/dl2) and were receiving paricalcitol > 6 microg/wk (or an equipotent dose of an alternative active vitamin D derivative). At the start of the study, active vitamin D derivatives were decreased to a mean equivalent dose of paricalcitol 6 microg/wk, and cinacalcet was titrated from 30 mg/d to a maximum possible dose of 180 mg/d. Of the 72 study patients, 53 (74%) completed 8 wk of dose titration with cinacalcet. In response to cinacalcet, the following mean percentage changes were observed: biPTH, -1.8%; Ca, -9.7% (P < 0.0001), phosphorus, -11.1% (P < 0.0001), and Ca x P, -20.1% (P < 0.0001). At the end of the study, approximate Kidney Disease Outcomes Quality Initiative targets for biPTH (< or = 160 pg/ml) were achieved in 85% (45 of 53) of patients and for Ca x P (< or = 55 mg2/dl2) in 72% (38 of 53) of patients. Concurrent achievement of both targets occurred in 47% (25 of 53) of patients. In this open-label clinical trial, hemodialysis patients who had controlled PTH but elevated Ca x P and were taking moderate- to high-dose active vitamin D derivatives achieved improved control of mineral metabolism with a combination of low-dose active vitamin D derivatives and cinacalcet. The long-term effects of this treatment regimen on clinical outcomes should be tested prospectively.

Differential effects of Vitamin D analogs on bone formation and resorption

Deficiency in Vitamin D and its metabolites leads to a failure in bone formation primarily caused by dysfunctional mineralization, suggesting that Vitamin D analogs might stimulate osteoblastic bone formation and mineralization. In this study, we compare the effect of selected Vitamin D analogs and active metabolite, 1alpha,25-dihydroxyvitamin D(3), 19-nor-1alpha, 25-dihydroxyvitamin D(2), and 1alpha-hydroxyvitamin D(2) or 1alpha,25-dihydroxyvitamin D(2) on bone formation and resorption. In a mouse calvariae bone primary organ culture system, all Vitamin D analogs and metabolite tested-stimulated collagen synthesis in a dose-dependent manner and 19-nor-1alpha, 25-dihydroxyvitamin D(2) was the most efficacious among three. 19-nor-1alpha, 25-dihydroxyvitamin D(2) and 1alpha,25-dihydroxyvitamin D(2) showed similar potencies and 1alpha,25-dihydroxyvitamin D(3) was less potent than others. Osteocalcin was also up-regulated in a dose-dependent manner, suggesting that the three Vitamin D analogs have the equal potencies on bone formation. 25-Hydroxyvitamin D-24-hydroxylase expression was induced in a dose-dependent manner and 19-nor-1alpha, 25-dihydroxyvitamin D(2) was less potent than other two compounds. In a mouse calvariae organ culture, all induced a net calcium release from calvariae in a dose-dependent manner, but the potency is in the order of 1alpha,25-dihydroxyvitamin D(2) congruent with1alpha,25-dihydroxyvitamin D(3)>19-nor-1alpha, 25-dihydroxyvitamin D(2). In a Vitamin D/calcium-restricted rat model, all caused an elevation in serum calcium in a dose-dependent manner. There is no significant difference between 1alpha,25-dihydroxyvitamin D(3) and 1alpha-hydroxyvitamin D(2) in potencies, but 19-nor-1alpha, 25-dihydroxyvitamin D(2) is at least 10-fold less potent than the other two compounds. Our results suggest that Vitamin D analogs have direct effects on bone resorption and formation, and 19-nor-1alpha, 25-dihydroxyvitamin D(2) may be more effective than 1alpha,25-dihydroxyvitamin D(3) and 1alpha-hydroxyvitamin D(2) on stimulating anabolic bone formation.

Vitamin D2 analog (Paricalcitol; Zemplar) for treatment of myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is often a pernicious disorder associated with pancytopenia in the elderly; therapeutic approaches need to balance their toxicities versus the symptoms of the disease. 1,25(OH)(2)-Vitamin-D(3) [1,25(OH)(2)D(3)] inhibits proliferation and induces differentiation of leukemic cells in vitro. Small clinical trials of 1,25(OH)(2)D(3) have shown modest efficacy in MDS; hypercalcemia prevented the administration of doses that have been shown to be effective in vitro. Paricalcitol [19-nor-1,25(OH)(2)D(2), Zemplar] has been approved by the FDA for treatment of secondary hyperparathyroidism. This Vitamin D analog is unique because it has little hypercalcemic potential; but in vitro, it has strong anti-leukemic activity. We conducted a clinical trial of oral paricalcitol to 12 MDS patients whose disease varied between an IPSS of low to high. Drug was well-tolerated in all patients. No responses were observed according to international working group (IWG) criteria. However, the platelet count of 1 of the 12 individuals rose from 53,500 to 120,000/microl blood over 5 weeks; but the patient succumbed to a fatal fungal infection. In summary, paricalcitol given as a single agent to MDS patients is therapeutically not very efficacious; further trials of the Vitamin D analog should be considered in combination with other approaches.

Noncalcemic actions of vitamin D receptor ligands

1alpha,25-Dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], the active metabolite of vitamin D(3), is known for the maintenance of mineral homeostasis and normal skeletal architecture. However, apart from these traditional calcium-related actions, 1,25-(OH)(2)D(3) and its synthetic analogs are being increasingly recognized for their potent antiproliferative, prodifferentiative, and immunomodulatory activities. These actions of 1,25-(OH)(2)D(3) are mediated through vitamin D receptor (VDR), which belongs to the superfamily of steroid/thyroid hormone nuclear receptors. Physiological and pharmacological actions of 1,25-(OH)(2)D(3) in various systems, along with the detection of VDR in target cells, have indicated potential therapeutic applications of VDR ligands in inflammation (rheumatoid arthritis, psoriatic arthritis), dermatological indications (psoriasis, actinic keratosis, seborrheic dermatitis, photoaging), osteoporosis (postmenopausal and steroid-induced osteoporosis), cancers (prostate, colon, breast, myelodysplasia, leukemia, head and neck squamous cell carcinoma, and basal cell carcinoma), secondary hyperparathyroidism, and autoimmune diseases (systemic lupus erythematosus, type I diabetes, multiple sclerosis, and organ transplantation). As a result, VDR ligands have been developed for the treatment of psoriasis, osteoporosis, and secondary hyperparathyroidism. Furthermore, encouraging results have been obtained with VDR ligands in clinical trials of prostate cancer and hepatocellular carcinoma. This review deals with the molecular aspects of noncalcemic actions of vitamin D analogs that account for the efficacy of VDR ligands in the above-mentioned indications.

VITAMIN D IN HEALTH AND DISEASE: Beyond Minerals and Parathyroid Hormone: Role of Active Vitamin D in End-Stage Renal Disease

Secondary hyperparathyroidism is a common complication of end-stage renal disease (ESRD) that is often treated with activated forms of intravenous vitamin D. The natural course and treatment of secondary hyperparathyroidism in hemodialysis patients is punctuated by episodes of hypercalcemia, hyperphosphatemia, and increased calcium-phosphate product, which in previous studies were linked to increased mortality. Historically these episodes have been attributed to vitamin D, leading some authorities to favor decreased vitamin D use. However, the studies that examined the impact of mineral levels and parathyroid hormone (PTH) on survival did not consistently account for vitamin D therapy itself on hemodialysis patient survival. The current review examines in detail two recent large-scale studies of hemodialysis patients: one that demonstrated a survival advantage of paricalcitol over calcitriol and a second that demonstrated a significant survival advantage of any intravenous vitamin D formulation versus none. In both studies, the effects were independent of mineral and PTH levels, suggesting "nontraditional" actions of vitamin D contributed to the observed survival advantage. Several of these nontraditional actions are reviewed with an emphasis on those that might impact hemodialysis outcomes.

Which vitamin D derivative to prescribe for renal patients

PURPOSE OF REVIEW

It is possible to control the secondary hyperparathyroidism and osteitis fibrosa of patients with chronic kidney disease by calcitriol when given early and in appropriate doses. However, this control is often achieved at the price of unacceptably high plasma calcium and phosphorus levels, the induction of adynamic bone disease, and soft tissue calcification. To avoid these side effects, so-called 'nonhypercalcemic' vitamin D analogs have been developed. Their possible advantages and their precise place in the treatment and prevention of secondary hyperparathyroidism remain a matter of debate.

RECENT FINDINGS

A large US multicenter study showed that the administration of the vitamin D analog paricalcitol to hemodialysis patients, as compared with calcitriol, was associated with better survival. In a subsequent large US multicenter study paricalcitol-treated hemodialysis patients experienced fewer hospitalizations and hospital days compared with calcitriol-treated patients. In a third, smaller study from Japan, regular alfacalcidol users among hemodialysis patients had better cardiovascular survival than nonusers. Finally, in a recent historical control study the mortality of a large hemodialysis patient cohort was analyzed as a function of previous vitamin D treatment. Patients on active vitamin D compounds at any time had a 2-year survival advantage over vitamin D-naive patients. It must be pointed out, however, that all four studies were retrospective in nature.

SUMMARY

The development of vitamin D analogs with less side effects than with calcitriol is of major theoretical interest. Practically speaking, however, we still need to be convinced that this goal can be achieved in chronic kidney disease patients.

19-Nor-1,25(OH)2D2(a Novel, Noncalcemic Vitamin D Analogue), Combined with Arsenic Trioxide, Has Potent Antitumor Activity against Myeloid Leukemia

Recently, we reported that a novel, noncalcemic vitamin D analogue (19-nor-1,25(OH)2D2; paricalcitol) had anticancer activity. In this study, we explored if paricalcitol enhanced anticancer effects of other clinically useful drugs in vitro against a large variety of cancer cells. Paricalcitol, when combined with As2O3, showed a markedly enhanced antiproliferative effect against acute myeloid leukemia (AML) cells. This combination induced monocytic differentiation of NB-4 acute promyelocytic leukemia (APL) cells and HL-60 AML cells and caused both to undergo apoptosis associated with down-regulation of Bcl-2 and Bcl-x(L). Paricalcitol induced monocytic differentiation of U937 AML cells, which was partially blocked by inducing expression of APL-related PML-retinoic acid receptor alpha (RARalpha) chimeric protein in the U937 cells containing a Zn2+-inducible expression vector coding for this fusion protein (PR9 cells). Exposure to As2O3 decreased levels of PML-RARalpha in PR9 cells, and the combination of paricalcitol and As2O3 enhanced their monocytic differentiation in parallel with the As2O3-mediated decrease of PML-RARalpha. Furthermore, As2O3 increased the transcriptional activity of paricalcitol probably by increasing intracellular levels of paricalcitol by decreasing the function of the mitochondrial enzyme 25-hydroxyvitamin D3-24-hydroxylase, which functions to metabolize the active vitamin D in cells. In summary, the combination of paricalcitol and As2O3 potently decreased growth and induced differentiation and apoptosis of AML cells. This probably occurred by As2O3 decreasing levels of both the repressive PML-RARalpha fusion protein and the vitamin D metabolizing protein, 25-hydroxyvitamin D3-24-hydroxylase, resulting in increased activity of paricalcitol. The combination of both of these Food and Drug Administration-approved drugs should be considered for treatment of all-trans retinoic acid-resistant APL patients as well as those with other types of AML.

New Vitamin D analogues for osteodystrophy in chronic kidney disease

Vitamin D therapy for patients with chronic kidney disease has until recently comprised alfacalcidol or calcitriol, both of which effectively attenuate secondary hyperparathyroidism and the target organ consequences thereof. Unfortunately, both these agents also have significant calcaemic and phosphataemic actions leading to frequent episodes of hypercalcaemia, hyperphosphataemia and an increase in the CaxP product. It is likely that these in turn have adverse effects on cardiovascular and survival outcomes by promoting soft tissue and vascular calcification. These drawbacks have fuelled a search for vitamin D compounds with a wider therapeutic window. Experimentally, some of these have exhibited remarkable dissociation between their ability to suppress parathyroid hormone (PTH) and concomitant calcaemic actions. In the case of 22-oxacalcitriol, the calcaemic potency relative to parathyroid suppression is 100th of that of calcitriol. 22-oxacalcitriol, with paricalcitol and doxercalciferol, are now widely used. Clinical studies of these agents, while confirming efficacy that is at least as good as alfacalcidol/calcitriol, have not consistently shown benefit in head to head comparison. Experience with these agents in the paediatric arena is very limited. One placebo-controlled study has now been completed in children-paricalcitol appeared effective and well tolerated. Calcimimetics, which simultaneously lower PTH, calcium and the CaxP product are about to enter the clinical arena-early studies in adults look promising, although they will need careful evaluation in children. These two therapies are likely to be additive and will probably complement one another effectively.

Evaluation of vitamin D analogs as therapeutic agents for prostate cancer

Prostate cancer cells contain specific receptors (VDR) for la,25-dihydroxyvitamin D (1alpha,25(OH)2D), which is known to inhibit the proliferation and invasiveness of these cells. These findings support the use of 1alph,25(OH)2D for prostate cancer therapy. However, because 1alpha,25(OH)2D can cause hypercalcemia, analogs of 1alpha,25(OH)2D that are less calcemic but which exhibit potent antiproliferative activity would be attractive as therapeutic agents. We studied four vitamin D compounds: 25-hydroxyvitaminD3 [25(OH)D3], which is converted to 1alpha,25(OH)2D3 in prostate cells, and three analogs of 1alpha,25(OH)2D3: EB1089, 19-nor-1alpha,25(OH)2D2 and hexafluoro-1alpha,25(OH)2D3 (F6-1alpha,25(OH)2D3). 19-nor-1alpha,25(OH)2D2 has been shown to be less calcemic than 1alpha,25(OH)2D3 in clinical trials. F6-1alpha,25(OH)2D3 has been shown to be 100-fold more active than 1alpha,25(OH)2D3 and to be longer-lasting in inhibiting keratinocyte proliferation in vitro. EB1089 has been shown to be less calcemic than 1alpha,25(OH)2D3 in rats implanted with Leydig cell tumors. For 25(OH)D3, 19-nor-1alpha,25(OH)2D2 and F6-1alpha,25(OH)2D3, we studied the in vitro effects and compared their activity to 1alpha,25(OH)2D3 on cellular proliferation by 3H-thymidine incorporation assay. In addition, we studied transactivation of the VDR in the presence of 25(OH)D3 and 19-nor-1alpha,25(OH)2D2 in prostate cells. For EB1089, we compared its inhibition of prostate cancer metastasis to that induced by 1alpha,25(OH)2D3 in vivo in the rat Dunning MAT LyLu prostate cancer model. We found that 1alpha,25(OH)2D3 and 19-nor-1alpha,25(OH)2D2 caused similar dose-dependent inhibition in 3H-thymidine incorporation into DNA in prostate cells and behaved similarly in the CAT reporter gene transactivation assay in PC-3/VDR cells. F6-1alpha,25(OH)2D3 is 10- to 50-fold more active than 1alpha,25(OH)2D3 in 3H-thymidine incorporation into DNA in the primary cultured prostate cells. Likewise, 25(OH)D3 had comparable antiproliferative activity to la,25(OH)2D3. In the rat model, tumor volumes and the number of metastases in the lungs were significantly reduced by both 1alpha,25(OH)2D3 (10.4 +/- 2.81 tumor foci) and EB1089 (7.7+/-1.29 tumor foci) compared to controls (22.7 +/- 1.98 tumor foci). Although serum calcium levels were significantly elevated in both 1alph,25(OH)2D3- and EB1089-treated rats, EB1089 was significantly less calcemic than 1alpha,25(OH)2D3 (12.59+/-0.21 mg/dl versus 14.47+/-.46 mg/dL; 1 microg/kg; p < 0.001). In conclusion, our data indicate that 25(OH)D3 and the three 1alpha,25(OH)2D analogs represent two different solutions to the problem of hypercalcemia associated with vitamin D-based prostate cancer therapies: 25(OH)D3 requires the presence of 25-hydroxyvitaminD-1alpha-hydroxylase, whereas 19-nor-1alpha,25(OH)2D2, F6-1alpha,25(OH)2D3 and EB1089 do not. These compounds may be good candidates for human clinical trials in prostate cancer.

Survival of patients undergoing hemodialysis with paricalcitol or calcitriol therapy

BACKGROUND

Elevated calcium and phosphorus levels after therapy with injectable vitamin D for secondary hyperparathyroidism may accelerate vascular disease and hasten death in patients undergoing long-term hemodialysis. Paricalcitol, a new vitamin D analogue, appears to lessen the elevations in serum calcium and phosphorus levels, as compared with calcitriol, the standard form of injectable vitamin D.

METHODS

We conducted a historical cohort study to compare the 36-month survival rate among patients undergoing long-term hemodialysis who started to receive treatment with paricalcitol (29,021 patients) or calcitriol (38,378 patients) between 1999 and 2001. Crude and adjusted survival rates were calculated and stratified analyses were performed. A subgroup of 16,483 patients who switched regimens was also evaluated.

RESULTS

The mortality rate among patients receiving paricalcitol was 3417 per 19,031 person-years (0.180 per person-year), as compared with 6805 per 30,471 person-years (0.223 per person-year) among those receiving calcitriol (P<0.001). The difference in survival was significant at 12 months and increased with time (P<0.001). In the adjusted analysis, the mortality rate was 16 percent lower (95 percent confidence interval, 10 to 21 percent) among paricalcitol-treated patients than among calcitriol-treated patients. A significant survival benefit was evident in 28 of 42 strata examined, and in no stratum was calcitriol favored. At 12 months, calcium and phosphorus levels had increased by 6.7 and 11.9 percent, respectively, in the paricalcitol group, as compared with 8.2 and 13.9 percent, respectively, in the calcitriol group (P<0.001). The two-year survival rate among patients who switched from calcitriol to paricalcitol was 73 percent, as compared with 64 percent among those who switched from paricalcitol to calcitriol (P=0.04).

CONCLUSIONS

Patients who receive paricalcitol while undergoing long-term hemodialysis appear to have a significant survival advantage over those who receive calcitriol. A prospective, randomized study is critical to confirm these findings.

Vitamin D2 analog 19-nor-1,25-dihydroxyvitamin D2: antitumor activity against leukemia, myeloma, and colon cancer cells

BACKGROUND

1,25-Dihydroxyvitamin D(3) inhibits growth of several types of human cancer cells in vitro, but its therapeutic use is hampered because it causes hypercalcemia. 19-nor-1,25-Dihydroxyvitamin D(2) (paricalcitol) is a noncalcemic vitamin D analog that is approved by the Food and Drug Administration for the treatment of secondary hyperparathyroidism. We investigated the antitumor activity and mechanism of action of paricalcitol in vitro and in vivo.

METHODS

Effects of paricalcitol on proliferation, the cell cycle, differentiation, and apoptosis were examined in cancer cell lines. Effects on tumor growth were examined with colon cancer cell xenografts in nude mice (five in the experimental group and five in the control group). The interaction of paricalcitol with the vitamin D receptor (VDR) in mononuclear spleen cells and myeloid stem cells from wild-type and VDR knockout mice was examined. All statistical tests were two-sided.

RESULTS

Paricalcitol inhibited the proliferation of myeloid leukemia cell lines HL-60, NB-4, and THP-1 cells at an effective dose that inhibited growth 50% (ED(50)) of 2.4-5.8 x 10(-9) M by inducing cell cycle arrest and differentiation. Paricalcitol inhibited the proliferation of NCI-H929 myeloma cells at an ED(50) of 2.0 x 10(-10) M by inducing cell cycle arrest and apoptosis. Paricalcitol also inhibited the proliferation of colon cancer cell lines HT-29 (ED(50) = 1.7 x 10(-8) M) and SW837 (ED(50) = 3.2 x 10(-8) M). HT-29 colon cancer xenografts in paricalcitol-treated nude mice were smaller (1044 mm(3) and 1752 mm(3), difference = 708 mm(3), 95% confidence interval = 311 to 1104 mm(3); P =.03) and weighed less (1487 mg and 4162 mg, difference = 2675 mg, 95% confidence interval = 2103 to 3248 mg; P<.001) than those in vehicle-treated mice. Paricalcitol induced committed myeloid hematopoietic stem cells from wild-type but not from VDR knockout mice to differentiate as macrophages.

CONCLUSION

Paricalcitol has anticancer activity against myeloid leukemia, myeloma, and colon cancer cells that may be mediated through the VDR. Because it has been approved by the Food and Drug Administration, clinical trials of this agent in certain cancers are reasonable.

Long-term therapy with paricalcitol for secondary hyperparathyroidism in hemodialysis patients

PURPOSE

The efficacy of the vitamin D analog paricalcitol has mainly been shown in short-term studies. There are limited data regarding long-term treatment with this agent. This purpose of this study was to determine long-term effects of paricalcitol therapy on parathyroid hormone (PTH) suppression and serum levels of calcium, phosphorus and calcium-phosphorus product (Ca x P).

PATIENTS AND METHODS

Patients who received paricalcitol for > or = 3 months had the following data collected: demographics, drug dosage, serum PTH, corrected serum calcium concentration, serum phosphorus concentrations and serum Ca x P values.

RESULTS

Sixteen patients received paricalcitol for a mean of 18 months. The mean +/- SD dose of paricalcitol was 0.13 +/- 0.12 mcg/kg. The mean +/- SD pre-paricalcitol serum PTH concentration was 705 +/- 423 pg/mL. PTH concentration did not change significantly over the duration of treatment (mean +/- SD: 821 +/- 480 pg/mL). The number of patients who had at least one corrected serum calcium concentration > or = 11.5 mg/dL, one serum phosphorus concentration > or = 6.5 mg/dL, or one Ca x P level > or = 70 were 75%, 94% and 82%, respectively. Hypercalcemia and elevated Ca x P value resulted in a mean of 17% of doses being withheld during therapy.

CONCLUSION

During the study, PTH was not adequately suppressed by paricalcitol. This was primarily attributed to withholding paricalcitol doses due to elevated serum calcium and Ca x P levels.

Paricalcitol versus calcitriol in the treatment of secondary hyperparathyroidism

BACKGROUND

Management of secondary hyperparathyroidism has included the use of active vitamin D or vitamin D analogs for the suppression of parathyroid hormone (PTH) secretion. Although, these agents are effective, therapy is frequently limited by hypercalcemia, hyperphosphatemia, and/or elevations in the calcium-phosphorus (Ca x P) product. In clinical studies, paricalcitol was shown to be effective at reducing PTH concentrations without causing significant hypercalcemia or hyperphosphatemia as compared to placebo. A comparative study was undertaken in order to determine whether paricalcitol provides a therapeutic advantage to calcitriol.

METHODS

A double-blind, randomized, multicenter study comparing the safety and effectiveness of intravenous paricalcitol and calcitriol in suppressing PTH concentrations in hemodialysis patients was performed. A total of 263 randomized patients were enrolled at domestic and international sites. Following the baseline period, patients with serum Ca x P < 75, and a PTH level > or =300 pg/mL were randomly assigned to receive either paricalcitol or calcitriol in a dose-escalating fashion for up to 32 weeks. Dose adjustments were based on laboratory results for PTH, calcium, and Ca x P. The primary end point was the greater than 50% reduction in baseline PTH. Secondary end points were the occurrence of hypercalcemia and elevated Ca x P product.

RESULTS

Paricalcitol-treated patients achieved a > or =50% reduction from baseline PTH significantly faster than did the calcitriol-treated patients (P = 0.025) and achieved a mean reduction of PTH into a desired therapeutic range (100 to 300 pg/mL) at approximately week 18, whereas the calcitriol-treated patients, as a group, were unable to achieve this range. Moreover, paricalcitol-treated patients had significantly fewer sustained episodes of hypercalcemia and/or increased Ca x P product than calcitriol patients (P = 0.008).

CONCLUSION

Paricalcitol treatment reduced PTH concentrations more rapidly with fewer sustained episodes of hypercalcemia and increased Ca x P product than calcitriol therapy.

Pathophysiology and recent advances in the management of renal osteodystrophy

Bone disease is observed in 75-100% of patients with chronic renal failure as the glomerular filtration rate (GFR) falls below 60 ml/minute. Hyperparathyroid (high turnover) bone disease is found most frequently followed by mixed osteodystrophy, low-turnover bone disease, and osteomalacia. With advancing renal impairment, "skeletal resistance" to parathyroid hormone (PTH) occurs. To maintain bone turnover, intact PTH (iPTH) targets from two to four times the upper normal range have been suggested, but whole PTH(1-84) assays indicate that amino-terminally truncated fragments, which accumulate in end-stage renal disease (ESRD), account for up to one-half of the measured iPTH. PTH levels and bone-specific alkaline phosphatase (BSAP) provide some information on bone involvement but bone biopsy and histomorphometry remains the gold standard. Calcitriol and calcium salts can be used to suppress PTH and improve osteomalacia but there is growing concern that these agents predispose to the development of vascular calcification, cardiovascular morbidity, low-turnover bone disease and fracture. Newer therapeutic options include less calcemic vitamin D analogues, calcimimetics and bisphosphonates for hyperparathyroidism, and sevelamer for phosphate control. Calcitriol and hormone-replacement therapy (HRT) have been shown to maintain bone mineral density (BMD) in certain patients with end-stage renal disease (ESRD). After renal transplantation, renal osteodystrophy generally improves but BMD often worsens. Bisphosphonate therapy may be appropriate for some patients at risk of fracture. When renal bone disease is assessed using a combination of biochemical markers, histology and bone densitometry, early intervention and the careful use of an increasing number of effective therapies can reduce the morbidity associated with this common problem.