The noncalcemic analogue of vitamin D, 22-oxacalcitriol, suppresses parathyroid hormone synthesis and secretion

Calcitriol and non-calcemic vitamin D analogue, 22-oxacalcitriol, attenuate developmental and pathological choroidal vasculature angiogenesis ex vivo and in vivo

Aberrant ocular angiogenesis can underpin vision loss in leading causes of blindness, including neovascular age-related macular degeneration and proliferative diabetic retinopathy. Current pharmacological interventions require repeated invasive administrations, may lack efficacy and are associated with poor patient compliance and tachyphylaxis. Vitamin D has de novo anti-angiogenic properties. Here, our aim was to validate the ocular anti-angiogenic activity of biologically active vitamin D, calcitriol, and selected vitamin D analogue, 22-oxacalcitriol. Calcitriol induced a significant reduction in ex vivo mouse choroidal fragment sprouting. Viability studies in a human RPE cell line suggested non-calcemic vitamin D analogues including 22-oxacalcitriol have less off-target anti-proliferative activity compared to calcitriol and other analogues. Thereafter, the anti-angiogenic activity of 22-oxacalcitriol was demonstrated in an ex vivo mouse choroidal fragment sprouting assay. In zebrafish larvae, 22-oxacalcitriol was found to be anti-angiogenic, inducing a dose-dependent reduction in choriocapillaris development. Subcutaneously administered calcitriol failed to attenuate mouse retinal vasculature development. However, calcitriol and 22-oxacalcitriol administered intraperitoneally, significantly attenuated lesion volume in the laser-induced choroidal neovascularisation mouse model. In summary, calcitriol and 22-oxacalcitriol attenuate ex vivo and in vivo choroidal vasculature angiogenesis. Therefore, vitamin D may have potential as an interventional treatment for ophthalmic neovascular indications.

Biochemical Changes following Parathyroidectomy

Biochemical changes that had appeared after subtotal parathyroidectomy (PTx) in 26 patients with end-stage renal failure were observed. The volume of excised parathyroid glands was also measured. Serum calcium and inorganic phosphorus levels fell after PTx; only to rise in due course. Serum alkaline phosphatase levels rose after PTx, reaching a peak by the 14th postoperative day. These elevated levels returned to normal range at about three months after PTx. Strong correlation was noted among the degree of postoperative hypocalcemia, and increase in serum alkaline phosphatase, but not between absolute pre or postoperative alkaline phosphatase levels and changes in serum calcium or phosphorus concentrations. Nevertheless, significant correlation was seen between pre-PTx levels of alkaline phosphatase and its short-lived postoperative rise, indicating hastened osteoblastic activity.

Effects of 1,25(OH)₂D₃ on Cancer Cells and Potential Applications in Combination with Established and Putative Anti-Cancer Agents

The diverse effects of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), the bio-active form of vitamin D, on cancer cell metabolism and proliferation has made it an interesting candidate as a supporting therapeutic option in cancer treatment. An important strategy in cancer therapy is the use of combination chemotherapy to overcome drug resistance associated with numerous anti-cancer agents and to provide better means of avoiding undesirable side effects. This complex strategy is widely adopted by oncologists and several established "cocktails" of chemotherapeutics are routinely administered to cancer patients. Among the principles followed in designing such treatment regimens is the use of drugs with different mechanisms of action to overcome the issue of tumor heterogeneity and to evade resistance. In light of the profound and diverse effects of 1,25(OH)₂D₃ reported by in vitro and in vivo studies, we discuss how these effects could support the use of this molecule in combination with "classical" cytotoxic drugs, such as platins and anti-metabolites, for the treatment of solid and hematological tumors. We also examine recent evidence supporting synergistic activities with other promising anti-cancer drug candidates, and postulate mechanisms through which 1,25(OH)₂D₃ may help evade chemoresistance.

Hypercalcemia in a Dog with Chronic Ingestion of Maxacalcitol Ointment

A miniature dachshund male with severe azotemia of unknown cause was referred. Serum biochemistry revealed severe azotemia and hypercalcemia, but serum intact parathormone and parathormone-related protein were normal. Although the owner reported that the dog had never ingested any drugs or supplements, it was revealed that the owner's son used antipsoriatic ointment, maxacalcitol, which contained an active vitamin D3 analogue, daily and the dog often ate the son's dander and licked his skin, especially after he applied the maxacalcitol ointment. After the dog was insulated from the maxacalcitol ointment and the son as much as possible, the hypercalcemia and azotemia improved gradually and had mostly resolved at 3 mo. The dog has been generally free of clinical signs without any treatment for over 2 yr.

The development of a bone- and parathyroid-specific analog of vitamin D: 2-methylene-19-Nor-(20S)-1α,25-dihydroxyvitamin D3

The goal of synthetic chemists in the vitamin D field has been to produce an analog(s) of 1α,25-dihydroxyvitamin D3 (1,25-(OH)2D3) that is selective for a specific function. The accumulation of structure/function information has led to the synthesis of two analogs that are both selective and more potent than 1,25-(OH)2D3, that is, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D3 (2MD) and 2α-methyl-19-nor-(20S)-1α,25-dihydroxyvitamin D3 (2AMD). In vivo, the efficacy of 2MD is approximately equal to that of 1,25-(OH)2D3 in intestinal calcium transport but is 30- to 100-fold more active in bone mobilization. In vitro, 2MD supports new bone synthesis at 10(-12) M, whereas 1,25-(OH)2D3 is active at 10(-8) M. Similarly, 2MD is two orders of magnitude more potent than 1,25-(OH)2D3 in stimulating osteoclastogenesis and osteoclastic bone resorption. 2MD also markedly increases bone mass and bone strength of ovariectomized female rats. In postmenopausal women, 2MD significantly increases markers of both bone formation and resorption but has minimal effect on bone mass. Thus, in patients who are undergoing primarily remodeling rather than modeling (rat), the increased resorption largely counteracts the increased bone formation. So far, 2MD has not been tested for reduction of fractures in this population. However, its selectivity includes the parathyroid gland. Thus in the 5/6-nephrectomy model of chronic renal failure, 2MD is much more potent than currently available vitamin D compounds used to suppress secondary hyperparathyroidism of renal failure without causing hypercalcemia. It is currently in phase 2B trials in patients on dialysis.

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.

20-Hydroxyvitamin D2 is a noncalcemic analog of vitamin D with potent antiproliferative and prodifferentiation activities in normal and malignant cells

20-hydroxyvitamin D(2) [20(OH)D(2)] inhibits DNA synthesis in epidermal keratinocytes, melanocytes, and melanoma cells in a dose- and time-dependent manner. This inhibition is dependent on cell type, with keratinocytes and melanoma cells being more sensitive than normal melanocytes. The antiproliferative activity of 20(OH)D(2) is similar to that of 1,25(OH)(2)D(3) and of newly synthesized 1,20(OH)(2)D(2) but significantly higher than that of 25(OH)D(3). 20(OH)D(2) also displays tumorostatic effects. In keratinocytes 20(OH)D(2) inhibits expression of cyclins and stimulates involucrin expression. It also stimulates CYP24 expression, however, to a significantly lower degree than that by 1,25(OH)(2)D(3) or 25(OH)D(3). 20(OH)D(2) is a poor substrate for CYP27B1 with overall catalytic efficiency being 24- and 41-fold lower than for 25(OH)D(3) with the mouse and human enzymes, respectively. No conversion of 20(OH)D(2) to 1,20(OH)(2)D(2) was detected in intact HaCaT keratinocytes. 20(OH)D(2) also demonstrates anti-leukemic activity but with lower potency than 1,25(OH)(2)D(3). The phenotypic effects of 20(OH)D(2) are mediated through interaction with the vitamin D receptor (VDR) as documented by attenuation of cell proliferation after silencing of VDR, by enhancement of the inhibitory effect through stable overexpression of VDR and by the demonstration that 20(OH)D(2) induces time-dependent translocation of VDR from the cytoplasm to the nucleus at a comparable rate to that for 1,25(OH)(2)D(3). In vivo tests show that while 1,25(OH)(2)D(3) at doses as low as 0.8 μg/kg induces calcium deposits in the kidney and heart, 20(OH)D(2) is devoid of such activity even at doses as high as 4 μg/kg. Silencing of CY27B1 in human keratinocytes showed that 20(OH)D(2) does not require its transformation to 1,20(OH)(2)D(2) for its biological activity. Thus 20(OH)D(2) shows cell-type dependent antiproliferative and prodifferentiation activities through activation of VDR, while having no detectable toxic calcemic activity, and is a poor substrate for CYP27B1.

Effect of paricalcitol and cinacalcet on serum phosphate, FGF-23, and bone in rats with chronic kidney disease

Calcimimetics activate the calcium-sensing receptor (CaR) and reduce parathyroid hormone (PTH) by increasing the sensitivity of the parathyroid CaR to ambient calcium. The calcimimetic, cinacalcet, is effective in treating secondary hyperparathyroidism in dialysis patients [chronic kidney disease (CKD 5)], but little is known about its effects on stage 3-4 CKD patients. We compared cinacalcet and paricalcitol in uremic rats with creatinine clearances "equivalent" to patients with CKD 3-4. Uremia was induced in anesthetized rats using the 5/6th nephrectomy model. Groups were 1) uremic control, 2) uremic + cinacalcet (U+Cin; 15 mg x kg(-1) x day(-1) po for 6 wk), 3) uremic + paricalcitol (U+Par; 0.16 microg/kg, 3 x wk, ip for 6 wk), and 4) normal. Unlike U+Par animals, cinacalcet promoted hypocalcemia and marked hyperphosphatemia. The Ca x P in U+Cin rats was twice that of U+Par rats. Both compounds suppressed PTH. Serum 1,25-(OH)(2)D(3) was decreased in both U+Par and U+Cin rats. Serum FGF-23 was increased in U+Par but not in U+Cin, where it tended to decrease. Analysis of tibiae showed that U+Cin, but not U+Par, rats had reduced bone volume. U+Cin rats had similar bone formation and reduced osteoid surface, but higher bone resorption. Hypocalcemia, hyperphosphatemia, low 1,25-(OH)(2)D(3), and cinacalcet itself may play a role in the detrimental effects on bone seen in U+Cin rats. This requires further investigation. In conclusion, due to its effects on bone and to the hypocalcemia and severe hyperphosphatemia it induces, we believe that cinacalcet should not be used in patients with CKD without further detailed studies.

Molecular and morphological approach of uremia-induced hyperplastic parathyroid gland following direct maxacalcitol injection

The mechanisms explaining the clinical effects of direct maxacalcitol (OCT) injection into the hyperplastic parathyroid gland (PTG) in uremic patients with advanced secondary hyperparathyroidism (SHPT) were investigated by molecular and morphological examination. PTG of uremia-induced SHPT model rats were treated by a direct injection of OCT (DI-OCT) or vehicle (DI-vehicle). The changes in serum intact parathyroid hormone (intact-PTH) level, vitamin D and Ca-sensing receptor (VDR and CaSR, respectively) expression levels in PTG, and the calcium (Ca)-PTH response curve were examined; the induction of apoptosis in parathyroid cells (PTC) was also analyzed by the TUNEL method, DNA electrophoresis, and electron microscopic examination. Serum intact-PTH level following DI-OCT significantly decreased. Upregulation of both VDR and CaSR, a clear shift to the left downward in the Ca-PTH curve, and many apoptotic PTCs were observed in the DI-OCT-treated PTGs. However, these findings were not observed in the DI-vehicle-treated PTGs. Moreover, these effects were confirmed by the DI-OCT into one PTG and DI-vehicle alone into another PTG in the same rat. DI-OCT may introduce simultaneous VDR and CaSR upregulation and the regression of hyperplastic PTG, and these effects may provide a strategy for strongly suppressing PTH level in uremia-induced advanced SHPT.

Vitamin D analogs: therapeutic applications and mechanisms for selectivity

The vitamin D endocrine system plays a central role in mineral ion homeostasis through the actions of the vitamin D hormone, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], on the intestine, bone, parathyroid gland, and kidney. The main function of 1,25(OH)(2)D(3) is to promote the dietary absorption of calcium and phosphate, but effects on bone, kidney and the parathyroids fine-tune the mineral levels. In addition to these classical actions, 1,25(OH)(2)D(3) exerts pleiotropic effects in a wide variety of target tissues and cell types, often in an autocrine/paracrine fashion. These biological activities of 1,25(OH)(2)D(3) have suggested a multitude of potential therapeutic applications of the vitamin D hormone for the treatment of hyperproliferative disorders (e.g. cancer and psoriasis), immune dysfunction (autoimmune diseases), and endocrine disorders (e.g. hyperparathyroidism). Unfortunately, the effective therapeutic doses required to treat these disorders can produce substantial hypercalcemia. This limitation of 1,25(OH)(2)D(3) therapy has spurred the development of vitamin D analogs that retain the therapeutically important properties of 1,25(OH)(2)D(3), but with reduced calcemic activity. Analogs with improved therapeutic indices are now available for treatment of psoriasis and secondary hyperparathyroidism in chronic kidney disease, and research on newer analogs for these indications continues. Other analogs are under development and in clinical trials for treatment of various types of cancer, autoimmune disorders, and many other diseases. Although many new analogs show tremendous promise in cell-based models, this article will limit it focus on the development of analogs currently in use and those that have demonstrated efficacy in animal models or in clinical trials.

Pharmacological control of secondary hyperparathyroidism in chronic hemodialysis patients: cinacalcet is coming to Japan

Secondary hyperparathyroidism has a significant impact on morbidity and mortality due to skeletal and extraskeletal manifestations. Cinacalcet, a newly developed calcimimetic, is reported to decrease parathyroidism, as well as serum levels of phosphorus (P) and calcium (Ca) and therefore Ca x P product. Available evidence has shown that cinacalcet decreases the rate of parathyroidectomy and bone fracture in hemodialysis patients, but the death rate remains the same. Although, it is not yet available in Japan, cinacalcet is expected to be available as a possible drug for patients undergoing hemodialysis due to secondary hyperparathyroidism associated with refractory hyperphosphatemia and hypercalcemia. Except for the high cost, cinacalcet will be a welcome therapeutic option for end-stage renal disease and probably also for pre-end-stage renal disease patients. Dietary phosphate restriction and adequate hemodialysis, however, are still the main strategy for the control of hyperphosphatemia and secondary hyperparathyroidism.

Intraperitoneal Calcitriol in Infants on Peritoneal Dialysis

Background

Calcitriol has long been used as the main therapy in renal osteodystrophy, but the efficacy of the oral route is not always as high as expected.

Objective

To asses the safety and efficacy of intraperitoneal calcitriol in infants undergoing peritoneal dialysis (PD).

Patients and Methods

PD patients on oral calcitriol therapy, with serum parathyroid hormone (PTH) >1000 pg/mL during the previous 3 months of treatment, were switched to intraperitoneal calcitriol therapy, 1 μg twice per week. Dose was increased to 1 μg three times per week if PTH remained >1000 pg/mL, and was later readjusted. Target PTH was 200 – 300 pg/mL according DOQI guidelines. Statistics: All results are expressed as mean ± SE. The Wilcoxon signed rank test was used to evaluate differences in measurements for each pair of values. The confidence interval for differences between population medians was 96.9%. A p value less than 0.05 was considered significant.

Results

Six male children, mean age 17 ± 3.86 months, completed a 12-month follow-up. Mean pretreatment PTH was 1654 ± 209 pg/mL. Mean PTH at months 0, 3, 6, 9, and 12 was 1448 ± 439*, 1277 ± 723, 910 ± 704, 582 ± 282*, and 465 ± 224* pg/mL, respectively (*p < 0.05). Twelve hypercalcemic and 10 hyperphosphatemic episodes were successfully treated.

Conclusion

Infants on PD who fail to respond to oral calcitriol therapy can be safely treated with intraperitoneal administration of active vitamin D.

Effects of 22-Oxacalcitriol and Calcitriol on PTH Secretion and Bone Mineral Metabolism in a Crossover Trial in Hemodialysis Patients With Secondary Hyperparathyroidism

The purpose of this crossover comparison study is to elucidate the differences between the effects of a novel calcitriol analog, 22-oxacalcitriol, and calcitriol on parathyroid hormone (PTH) and bone mineral metabolism in hemodialysis patients with secondary hyperparathyroidism (SHPT). Twenty-three patients with moderate to severe SHPT were included in a random 2 x 2 crossover trial with two vitamin D analogs (12 weeks for each treatment). Two patients withdrew during the run-in period for personal reasons. Serum electrolyte, bone metabolic marker, intact PTH (iPTH) and whole PTH (wPTH) levels were measured periodically. The primary endpoint measure was a decrease in serum iPTH level, and the secondary outcome measures included changes in serum calcium (Ca), phosphate (P), and metabolic bone marker levels. Both treatments decreased iPTH and wPTH levels by similar degrees. Serum Ca, P, and Ca x P product levels at the end of each treatment were comparable and the frequencies of hypercalcemia and hyperphosphatemia were also similar during each treatment period. 22-Oxacalcitriol significantly decreased the levels of bone metabolic markers, namely, bone-specific alkaline phosphate, intact osteocalcin, pyridinoline, and cross-linked N-telopeptide of type I collagen, after a 12-week treatment. In contrast, calcitriol did not change any of the levels of bone metabolic markers. The present study showed that 22-oxacalcitriol is equally effective for PTH suppression, and Ca and P metabolism. In addition, 22-oxacalcitriol might have putative actions on bone remodeling independent of its PTH suppression. Further study is necessary to confirm the effects of 22-oxacalcitriol on bone metabolism in SHPT.

Effect of 2-methylene-19-nor-(20S)-1 alpha-hydroxy-bishomopregnacalciferol (2MbisP), an analog of vitamin D, on secondary hyperparathyroidism

Vitamin D analogs are being developed that retain therapeutic effects but are less calcemic and phosphatemic, a concern in CKD patients who are prone to vascular calcification. We tested a new analog of vitamin D, 2MbisP, and found that it suppresses PTH at doses that do not affect serum Ca or P.

INTRODUCTION

Calcitriol is used for the treatment of secondary hyperparathyroidism. However, its use is often limited by the development of hypercalcemia and hyperphosphatemia, an important consideration in patients with chronic kidney disease (CKD) because they are prone to vascular calcification. To minimize this toxicity, structural modifications in the vitamin D molecule have led to the development of calcitriol analogs with selective actions.

MATERIALS AND METHODS

In this study, we compared the effects of 1,25(OH)(2)D(3) and a new analog, 2-methylene-19-nor-(20S)-1 alpha-hydroxy-bishomopregnacalciferol (2MbisP), on the development of secondary hyperparathyroidism and established secondary hyperparathyroidism in uremic rats and on mobilization of calcium and phosphorus from bone in parathyroidectomized rats. The clearance from circulation, half-life, and binding affinities to the vitamin D-binding protein and vitamin D receptor of this compound were also evaluated.

RESULTS

Uremia produced a marked rise in plasma PTH, but treatment every other day for 2 wk with either 1,25(OH)(2)D(3) (4 ng) or 2MbisP (250, 750, 1500, or 3000 ng) suppressed this increase by >50%. The suppression by 1,25(OH)(2)D(3), however, was accompanied by increases in ionized calcium, phosphorus, and the calcium x phosphorus product, whereas these three parameters were unchanged by 2MbisP. The binding affinity of 2MbisP was 10-20 times less for the vitamin D receptor and 1000 times less for the serum vitamin D-binding protein compared with 1,25(OH)(2)D(3). Also, 2MbisP was cleared more rapidly from the circulation (t1/2 = 10 min) than 1,25-(OH)(2)D(3) (t1/2=7-9 h). In parathyroidectomized rats fed calcium-or phosphorus-deficient diets, daily injections of 2MbisP (1500 or 3000 ng), unlike 1,25(OH)(2)D(3) (50 ng), had no effect on calcium or phosphorus mobilization from bone.

CONCLUSIONS

In uremic rats, 2MbisP can suppress PTH at doses that do not affect plasma calcium, phosphorus, and calcium x phosphorus product. This new vitamin D analog may represent an important tool in the treatment of secondary hyperparathyroidism in patients with CKD.

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.

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.

Minimizing bone abnormalities in children with renal failure

Renal osteodystrophy (ROD), a metabolic bone disease accompanying chronic renal failure (CRF), is a major clinical problem in pediatric nephrology. Growing and rapidly remodeling skeletal systems are particularly susceptible to the metabolic and endocrine disturbances in CRF. The pathogenesis of ROD is complex and multifactorial. Hypocalcemia, phosphate retention, and low levels of 1,25 dihydroxyvitamin D(3) related to CRF result in disturbances of bone metabolism and ROD. Delayed diagnosis and treatment of bone lesions might result in severe disability. Based on microscopic findings, renal bone disease is classified into two main categories: high- and low-turnover bone disease. High-turnover bone disease is associated with moderate and severe hyperparathyroidism. Low-turnover bone disease includes osteomalacia and adynamic bone disease. The treatment of ROD involves controlling serum calcium and phosphate levels, and preventing parathyroid gland hyperplasia and extraskeletal calcifications. Serum calcium and phosphorus levels should be kept within the normal range. The calcium-phosphorus product has to be <5 mmol(2)/L(2) (60 mg(2)/dL(2)). Parathyroid hormone (PTH) levels in children with CRF should be within the normal range, but in children with end-stage renal disease PTH levels should be two to three times the upper limit of the normal range. Drug treatment includes intestinal phosphate binding agents and active vitamin D metabolites. Phosphate binders should be administered with each meal. Calcium carbonate is the most widely used intestinal phosphate binder. In children with hypercalcemic episodes, sevelamer, a synthetic phosphate binder, should be introduced. In children with CRF, ergocalciferol (vitamin D(2)), colecalciferol (vitamin D(3)), and calcifediol (25-hydroxyvitamin D(3)) should be used as vitamin D analogs. In children undergoing dialysis, active vitamin D metabolites alfacalcidol (1alpha-hydroxy-vitamin D(3)) and calcitriol (1,25 dihydroxyvitamin D(3)) are applied. In recent years, a number of new drugs have emerged that hold promise for a more effective treatment of bone lesions in CRF. This review describes the current approach to the diagnosis and treament of ROD.

Direct maxacalcitol injection into hyperplastic parathyroids improves skeletal changes in secondary hyperparathyroidism

Direct maxacalcitol (OCT) injection into a parathyroid gland (PTG) ameliorates several important etiologic factors of resistance to medical treatments for secondary hyperparathyroidism (s-HPT): the upregulations of vitamin D receptor (VDR) and Ca-sensing receptor (CaSR) in PTGs and the regression of PTG hyperplasia by the induction of apoptosis. In this study, we evaluated the bone histomorphology on the basis of maintaining these effects in advanced s-HPT. Five/six nephrectomized Sprague-Dawley rats were fed a high-phosphorus and low-calcium diet for 8 weeks. These rats were divided into four treatment groups: (1) basic uremic (at the baseline), (2) direct OCT single injection into PTGs (DI-OCT) followed by OCT intravenous administration for 4 weeks (IV-OCT), (3) direct vehicle injection and IV-OCT, and (4) no treatment for an additional 4 weeks. The effects of these treatments on serum intact-parathyroid hormone (PTH) level, PTG weight, VDR and CaSR expression levels in PTGs, and bone histomorphometric parameters were investigated. In the DI-OCT+IV-OCT group, the significant decrease in serum intact-PTH level was maintained by the following IV-OCT. A significant decrease in PTG weight and the upregulations of VDR and CaSR expression levels in PTGs were also observed. Bone histomorphometric analysis showed significant improvements in osteitis fibrosa in both cancellous and cortical bones. However, these findings were not observed in the other groups. These results suggest that osteitis fibrosa caused by advanced s-HPT can be successfully reversed by a control of PTH at an appropriate level through the improvement of PTG hyperplasia as induced by DI-OCT+IV-OCT.

Direct injection of calcitriol or its analog into hyperplastic parathyroid glands induces apoptosis of parathyroid cells

Hyperplasia of the parathyroid gland (PTG) is associated not only with excessive secretion of parathyroid hormone (PTH) but also with changes in the parathyroid cell (PTC) characteristics (i.e. hyperproliferative activity, and low contents of vitamin D and calcium-sensing receptors). Control of PTG hyperplasia is most important in the management of secondary hyperparathyroidism, but the advanced stage of hyperplasia is considered irreversible. In the present study, dialysis patients with PTG hyperplasia underwent direct injection of calcitriol or maxacalcitol (OCT) into the PTG. Ultrasonography showed that this treatment had significantly reduced PTG volume and tissue analysis using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method and DNA electrophoresis indicated that cellular apoptosis had been induced. The mechanism of apoptosis was evaluated in detail in uremic rats fed a high-phosphate diet. OCT or its vehicle was directly injected into the rats' PTGs. In the PTGs treated by OCT, there was a significantly increased number of TUNEL-positive PTCs and DNA electrophoresis revealed the characteristic ladder pattern of DNA fragmentation, both findings indicative of apoptosis. There was also a significant upregulation of both vitamin D and Ca-sensing receptors in the PTCs and a clear shift of the Ca-PTH response curve to the left and downward. None of these findings was observed in the PTGs treated by vehicle. This novel treatment is successful in causing regression of PTG hyperplasia. Thus, it is expected to significantly reduce the PTH level and ameliorate the abnormal bone turnover and mineral metabolism.

New insights into mineral and skeletal regulation by active forms of vitamin D

Recent studies in mice using genetic approaches have shed new light on the physiological effects of 1,25-dihydroxyvitamin D (1,25(OH)(2)D) and the vitamin D receptor (VDR) in skeletal and mineral homeostasis, and on their interaction with calcium. These studies in mice with targeted deletion of the 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha(OH)ase), and of the VDR or of double mutants, have shown the discrete effects of calcium in inhibiting parathyroid hormone secretion and in enhancing bone mineralization, but overlapping effects of calcium and 1,25(OH)(2)D on inhibiting parathyroid growth and on normal development of the cartilaginous growth plate. The 1,25(OH)(2)D/VDR system is essential, however, in enhancing intestinal calcium absorption and in optimally increasing osteoclastic activation. In addition, the 1,25(OH)(2)D/VDR system has important anabolic effects on bone, thus defining a dual role for this system in bone turnover. These studies are revealing functions of the vitamin D/VDR system which have relevance for new concepts of the pathophysiology of renal bone disease and, in particular, of the adynamic bone disorder, and for the development of new analogs of the active form of vitamin D, which have less calcemic activity and greater skeletal anabolic effects.

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.

Comparison of the efficacy of an oral calcitriol pulse or intravenous 22-oxacalcitriol therapies in chronic hemodialysis patients

BACKGROUND

1,25-dihydroxy-22-ovavitamin D(3) (22-oxacalcitriol, OCT) was recently introduced commercially as an analogue of 1,25 (OH)(2) vitamin D(3), but one which has less pronounced calcemic activity.

METHODS

To examine the efficacy and tolerability of OCT, 46 hemodialysis patients with secondary hyperparathyroidism were randomly assigned to receive either intravenous OCT or oral calcitriol pulse therapies. The patients were monitored for serum calcium, phosphate, intact parathyroid hormone (PTH), and bone alkaline phosphatase (BAP) for 24 weeks. The efficacy of intravenous OCT was also examined in 24 additional patients who were refractory to oral calcitriol pulse therapy.

RESULTS

In the randomized trial, intact PTH levels were significantly suppressed within 4 weeks after the initiation of each therapy, and this effect was well maintained thereafter in both treatment groups. While intact PTH was significantly lower at 4 weeks in the calcitriol pulse group than in the OCT group (P = 0.02), no statistical differences were observed during later treatment periods. BAP was reduced equally by each treatment. At 4 weeks (P = 0.02) and thereafter (P = 0.06), serum calcium was higher among calcitriol-treated patients than among those who received OCT treatment. Eight of 24 patients who were refractory to oral calcitriol pulse therapy responded to intravenous OCT. The patients who responded tended to have lower serum intact PTH and phosphorus levels and smaller parathyroid glands at the start of OCT treatment than nonresponders.

CONCLUSIONS

OCT is as effective as oral calcitriol pulse therapy in suppressing intact PTH and BAP in chronic hemodialysis patients. It was confirmed that OCT exhibits less calcemic activity than calcitriol. Moreover, under certain conditions, switching to OCT may help in the treatment of hyperparathyroidism, which is refractory to conventional oral calcitriol pulse therapy.

Combination therapy of intravenous maxacalcitol and percutaneous ethanol injection therapy lowers serum parathyroid hormone level and calcium x phosphorus product in secondary hyperparathyroidism

BACKGROUND

Percutaneous ethanol injection therapy (PEIT) is an alternative treatment for secondary hyperparathyroidism (SHPT). Although maxacalcitol has been recently developed as a new vitamin D3 and its efficacy is anticipated in SHPT, there are only few reports on the usefulness of combination therapy of intravenous maxacalcitol and selective PEIT.

METHODS

The study population comprised 10 hemodialysis patients (6 males and 4 females, mean age; 51.5 +/- 13.5 years, mean HD period 13.7 +/- 3.5 years), with high intact-PTH level (>400 pg/ml) and 1 or 2 enlarged parathyroid glands detected by power Doppler ultrasonography. Intravenous maxacalcitol therapy commenced one week after PEIT at 15 microg/week. The effect of combination therapy was monitored by measuring intact-PTH, serum Ca and P, bone metabolic markers, parathyroid gland volume and bone mineral density, prior to and at 6 and 12 months after PEIT.

RESULTS

Successful control of intact-PTH, bone metabolic markers and parathyroid gland volume was achieved using the combination therapy. Serum P and CaxP product were significantly decreased 12 months after PEIT. The mean values of serum intact-PTH, P and CaxP product fulfilled all of the K/DOQI guidelines at 12 months after PEIT. None of the patients developed complications related to PEIT-maxacalcitol therapy during 12 months following PEIT.

CONCLUSION

Combination therapy of intravenous maxacalcitol therapy and selective PEIT is safe and effective for the treatment of refractory SHPT. This combination therapy results in suppression of PTH secretion, regression of parathyroid hyperplasia and the control of CaxP product, which may prevent calcific uremic arteriolopathy in dialysis patients.

Maxacalcitol is a Possible Less Phosphatemic Vitamin D Analog

The phosphatemic property of maxacalcitol, a newly developed artificial active vitamin D analog, has not been compared with that of calcitriol. Non-diabetic hemodialysis patients with plasma intact parathyroid hormone (PTH) levels greater than 300 pg/mL were included in this analysis. They were treated with either maxacalcitol or calcitriol for 24 weeks. In total, 80 patients were treated with maxacalcitol and 46 were treated with calcitriol. Pretreatment circulating levels of intact PTH, calcium (Ca) and inorganic phosphate (Pi) were comparable in both treatment groups. Both treatments significantly decreased plasma intact PTH levels (P<0.0001) and increased serum Ca levels (P<0.0001). However, the intact PTH levels were significantly lower in the maxacalcitol group after 24 weeks of the treatments (P<0.01). The decreasing tendency of plasma intact PTH level was significantly evident in the maxcalcitol group (P<0.01). However, the increasing tendency of the serum Pi level was significantly greater in the calcitriol group (P<0.05). Thus, maxacalcitol is a possible less phosphatemic active vitamin D agent, if not non-phosphatemic agent, which might reduce the risk of extraskeletal calcification.

Vitamin D

The vitamin D endocrine system plays an essential role in calcium homeostasis and bone metabolism, but research during the past two decades has revealed a diverse range of biological actions that include induction of cell differentiation, inhibition of cell growth, immunomodulation, and control of other hormonal systems. Vitamin D itself is a prohormone that is metabolically converted to the active metabolite, 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. This vitamin D hormone activates its cellular receptor (vitamin D receptor or VDR), which alters the transcription rates of target genes responsible for the biological responses. This review focuses on several recent developments that extend our understanding of the complexities of vitamin D metabolism and actions: the final step in the activation of vitamin D, conversion of 25-hydroxyvitamin D to 1,25(OH)(2)D in renal proximal tubules, is now known to involve facilitated uptake and intracellular delivery of the precursor to 1alpha-hydroxylase. Emerging evidence using mice lacking the VDR and/or 1alpha-hydroxylase indicates both 1,25(OH)(2)D(3)-dependent and -independent actions of the VDR as well as VDR-dependent and -independent actions of 1,25(OH)(2)D(3). Thus the vitamin D system may involve more than a single receptor and ligand. The presence of 1alpha-hydroxylase in many target cells indicates autocrine/paracrine functions for 1,25(OH)(2)D(3) in the control of cell proliferation and differentiation. This local production of 1,25(OH)(2)D(3) is dependent on circulating precursor levels, providing a potential explanation for the association of vitamin D deficiency with various cancers and autoimmune diseases.

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.

Pretreatment plasma intact parathyroid hormone and serum calcium levels, but not serum phosphate levels, predict the response to maxacalcitol therapy in dialysis patients with secondary hyperparathyroidism

BACKGROUND

The treatment strategy for secondary hyperparathyroidism is generally determined empirically with regards to present parathyroid function and serum calcium (Ca) and inorganic phosphate (Pi) levels. More evidence is needed to avoid the aimless continuation of active vitamin D therapy.

METHODS

Nondiabetic dialysis patients whose plasma intact parathyroid hormone (iPTH) levels were greater than 300 pg/ml were included in the study. Maxacalcitol was intravenously injected three times a week. The treatment was continued for 48 weeks, unless the iPTH level was reduced to less than 300 pg/ml or unfavorable events occurred. The patients whose plasma iPTH levels were below 300 pg/ml within 48 weeks were defined as those who had been successfully treated.

RESULTS

Findings for 146 patients were analyzed, and 96 patients were successfully treated. Serum Pi levels did not significantly increase during the therapy. The pretreatment plasma iPTH levels and serum Ca levels were lower in the patients who were successfully treated with maxacalcitol. A logistic regression study and classifying by stratum analyses revealed that the pretreatment serum Ca levels and plasma iPTH levels were significantly related to the result of maxacalcitol therapy, while the serum Pi levels were not. Analyses using a receiver-operating characteristic curve revealed that the areas under curves obtained for iPTH and Ca were significantly greater than those obtained for Pi (P < 0.0001).

CONCLUSIONS

Serum Ca levels and parathyroid function were correlated with the results of maxacalcitol therapy. Pretreatment serum Pi levels could not predict the result.

Vitamin D analogs: new therapeutic agents for secondary hyperparathyroidism

Patients with chronic renal failure frequently develop secondary hyperparathyroidism, primarily as a result of phosphate retention and low serum 1,25(OH)2D3. Replacement therapy with calcitriol or its synthetic precursor alfacalcidol [1alpha(OH)D3] often produces hypercalcemia, especially when combined with calcium-based phosphate binders. In addition, the natural vitamin D compounds can exacerbate the hyperphosphatemia in patients with chronic renal failure. This combined increase in calcium and phosphate has been correlated with vascular calcification leading to coronary artery disease, the most common cause of mortality in renal patients. Several vitamin D analogs have now been developed that retain the direct suppressive action of calcitriol on the parathyroid glands but have less calcemic activity, thereby offering a safer and more effective means of controlling secondary hyperparathyroidism. Maxacalcitol [22-oxa-1,25(OH)2D3] and falecalcitriol [1,25(OH)2-26,27-F6-D3] are currently available in Japan, and paricalcitol [19-nor-1,25(OH)2D2] and doxercalciferol [1alpha(OH)D2] are available in the US. The mechanisms by which these analogs exert their selective actions on the parathyroid glands are under investigation. The low calcemic activity of maxacalcitol has been attributed to its rapid clearance from the circulation. This prevents sustained effects on intestinal calcium absorption and bone resorption, but still allows a prolonged suppression of parathyroid hormone gene expression. The selectivity of the other analogs is achieved by distinct mechanisms. Understanding how these compounds exert their selective actions on the parathyroid glands will aid in the design of safer, more effective analogs.

Are new vitamin D analogues in renal bone disease superior to calcitriol?

Progression of chronic kidney disease is associated with an early reduction in serum calcitriol levels; thus, therapy with calcitriol should be initiated early in the course of chronic kidney disease to prevent the development of secondary hyperparathyroidism. Initial studies demonstrated a potential role of calcitriol in the prevention of growth retardation in children with chronic kidney disease prior to dialysis. But the optimal parathyroid hormone (PTH) levels that will maximize growth response during calcitriol treatment remain to be defined. Therapy with calcitriol has been shown to control the biochemical and skeletal manifestations of secondary hyperparathyroidism, but patients developed hypercalcemia, hyperphosphatemia and adynamic osteodystrophy. Thus, new vitamin D analogues with a lower hypercalcemic response have been developed. Although comparative studies are lacking, current evidence indicates that these new active vitamin D sterols (19-nor-paracalcitol and doxercalciferol) adequately control secondary hyperparathyroidism with minimal changes in serum calcium and phosphorus levels during treatment with calcium-containing binders. The long-term effect of such therapies on the skeleton and the process of vascular calcifications remain to be evaluated.

Adsorption of oxacalcitriol by polysulphone haemodialyser in patients with secondary hyperparathyroidism

AIMS

This study was undertaken to evaluate removal of 22-oxacalcitriol (OCT), an active and intravenously used vitamin D3 analogue with less calcaemic activity, by polysulphone haemodialyser in vivo and in vitro. We further compared the pharmacodynamic efficacy [suppression of intact parathyroid hormone (iPTH)] when given intravenously either during or at the end of the haemodialysis.

METHODS

(i) Drug clearance by the polysulphone dialyser was measured during a single continuous infusion (5 microg) for 30 min into the arterial side of the dialyser in end-stage renal failure patients with secondary hyperparathyroidism (n = 7). (ii) The drug adsorption by the hollowfibre membrane during incubation for 30 min was measured in vitro. (iii) To evaluate efficacy, the drug was given (i.v. bolus) during or at the end of haemodialysis for 4 weeks in a cross-over fashion with a washout period of 8 weeks (n = 9). Serum Ca(2+), phosphate (P) and iPTH concentrations just before the initiation of the dialysis were monitored every week.

RESULTS

(i) OCT was significantly cleared by the polysulphone haemodialyser, but the clearance declined in a time-dependent manner to approach zero at 30 min. Arterial (at the place between the drug infusion site and the haemodialyser column) drug concentrations did not change during the infusion (mean = 2064 +/- 233 pg ml(-1)). Venous (just after the dialyser) drug concentrations at 10 min after the infusion were significantly lower than those of the arterial side (mean = 784 +/- 84 pg ml(-1)); however, they increased with time and reached those of the arterial side at 30 min. (ii) In vitro, OCT was adsorbed by the membrane. The amount of adsorption was concentration-dependent and was lower in the presence of human serum (55 +/- 4% without and 23 +/- 4% with serum at 600 pg ml(-1) of OCT). (iii) Although serum Ca(2+) and P increased and iPTH decreased by both treatment regimens (i.e. OCT administered either during or at the end of haemodialysis), these changes did not significantly differ. Mean differences (and 95% confidence interval) of Ca(2+), P, and iPTH at the end of the trial were 0.03 (-0.04, 0.09) mm, 0.41 (-0.43, 1.26) mg dl(-1) and 38 (-42, 88) pg ml(-1), respectively.

CONCLUSION

OCT is adsorbed by polysulphone dialyser in vitro and in vivo. However, the pharmacodynamic effectiveness was largely independent of the administration regimen of OCT given either during or at the end of haemodialysis.

The Influence of Dialysate Calcium on the Therapeutic Effects of Sevelamer Hydrochloride in Hemodialysis Patients with Secondary Hyperparathyroidism Under Treatment of Intravenous Vitamin D Metabolites

The management of hyperphosphatemia is essential to treat secondary hyperparathyroidism and to prevent ectopic calcification. Sevelamer hydrochloride (sevelamer), a new phosphate binder that contains neither aluminum nor calcium, which could be theoretically beneficial for the management of hyperphosphatemia in dialysis patients with secondary hyperparathyroidism who are receiving intravenous vitamin D metabolites (maxacalcitol or calcitriol). To reduce calcium loads, a dialysate calcium concentration of 2.5 mEq/L is recommended by Kidney Disease Outcome Quality Initiative (K/DOQI) guidelines. In Japan, a dialysate calcium concentration of 3.0 mEq/L prevails. We investigated the influence of dialysate calcium on the therapeutic effect of sevelamer in 40 hemodialysis patients who are under treatment of intravenous vitamin D metabolites for secondary hyperparathyroidism (VD(+)) and compared the results with those of 41 patients who had not received vitamin D metabolites (VD(-)). Serum phosphorus and calcium-phosphorus products showed no significant change by sevelamer in either the VD(+) subgroup of patients receiving hemodialysis with dialysate calcium of 2.5 mEq/L (DCa2.5) or those receiving hemodialysis with dialysate calcium of 3.0 mEq/L (DCa3.0), while serum phosphorus and calcium-phosphorus products decreased in both the VD(-) subgroups. Serum calcium decreased in the DCa2.5 subgroup and did not change in the DCa3.0 subgroup in both the VD(+) and the VD(-) subjects. Parathyroid hormone and alkaline phosphatase increased in the DCa2.5 subgroup and did not change in the Ca 3.0 subgroup in the VD(+) subjects. Serum calcium decreased in both subgroups in the VD(-) subjects. Parathyroid hormone obtained after sevelamer administration in the VD(-) group was within the target range of the K/DOQI guidelines. In conclusion, the concomitant use of sevelamer as a phosphate binder and the dialysate of calcium concentration of 2.5 mEq/L have possibilities for worsening secondary hyperparathyroidism in patients receiving intravenous vitamin D.

Biochemical and Cellular Effects of Direct Maxacalcitol Injection into Parathyroid Gland in Uremic Rats

The most important etiological factors of resistance to medical treatments for secondary hyperparathyroidism are the decreased contents of the vitamin D receptor (VDR) and Ca-sensing receptor (CaSR) in parathyroid cells and a severely swollen parathyroid gland (PTG) as a result of hyperplasia. The effects of direct maxacalcitol (OCT) injection into PTG in terms of these factors were investigated in this study. The PTG of Sprague-Dawley rats that were 5/6 nephrectomized and fed a high-phosphate diet were treated by a direct injection of OCT (DI-OCT) or vehicle (DI-vehicle). The changes in serum intact parathyroid hormone (PTH), Ca(2+), and phosphorus levels, in VDR and CaSR expression levels in parathyroid cells, and in Ca(2+)-PTH curves were examined. Apoptosis was analyzed by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling method and DNA electrophoresis for PTG. DI-OCT markedly decreased serum intact PTH level, and a significant difference in this level between DI-OCT and DI-vehicle was observed. However, serum Ca(2+) and phosphorus levels did not changed markedly in both groups. The upregulations of both VDR and CaSR, the clear shift to the left downward in the Ca(2+)-PTH curve, and the induction of apoptosis after DI-OCT were observed. These findings were not observed in the DI-vehicle-treated rats. Moreover, these effects of DI-OCT were confirmed by the DI-OCT into one PTG and DI-vehicle alone into another PTG in the same rat. DI-OCT may introduce simultaneous VDR and CaSR upregulations and the regression of hyperplastic PTG, and these effects may provide a strategy for strongly suppressing PTH levels in very severe secondary hyperparathyroidism.

Dose-response Study of 22-Oxacalcitriol in Patients with Secondary Hyperparathyroidism

The dose-response relationships and the safety of administering 22-oxacalcitriol (OCT) to patients with secondary hyperparathyroidism (2HPT) under regular three-times-weekly hemodialysis (HD) were evaluated by double-blind parallel group design. A total of 203 patients with 2HPT were randomly allocated into four groups, and 5 microg (Group L), 10 microg (Group M), or 15 microg (Group H) OCT, or placebo (Group P) was administrated at the end of every HD for 12 weeks. Reductions of intact-parathyroid hormone (iPTH) concentration greater than 30% from baseline were observed in 7.7% of Group P as compared to 77.3% of the pooled OCT groups after 12 weeks of treatment (Mantel test: P < 0.001). Time-trends (slopes) of log-iPTH concentration calculated by least-squares line fitting to each patient's data during treatment differed between Group P and the pooled OCT groups (t-test: P < 0.001) and these iPTH slopes decreased dose-dependently (linear trend by t-test: P < 0.001). Slopes of serum calcium corrected for albumin (corrected-sCa) concentrations also differed between Group P and the pooled OCT groups (t-test: P < 0.001), and increased dose-dependently (linear trend by t-test: P < 0.0001). Serum phosphorus and Ca x P product increased significantly only in high dose groups. Slopes of log(iPTH) and corrected-sCa concentrations were reciprocally related. Most adverse events were hypercalcemia and dose-related, but occasionally comprised pruritus or increased serum creatinine phosphokinase. These results indicate that OCT produced a strong and dose-dependent suppression of PTH and an increase of corrected-sCa concentration in patients with 2HPT. The recommended initial dosages of OCT would appear to be 5 microg when pretreatment iPTH concentrations are less than 500 pg/mL, and 10 microg when greater than 500 pg/mL for safe and effective treatment. As in the case of PTH, calcium and phosphorus showed dose-dependent increases. It is therefore essential to take precautions as to possible increases in calcium and phosphorus.

Doxercalciferol safely suppresses PTH levels in patients with secondary hyperparathyroidism associated with chronic kidney disease stages 3 and 4

BACKGROUND

Calcitriol lowers parathyroid hormone (PTH) levels in patients with chronic kidney disease (CKD) stages 3 and 4, but its use is limited by a low therapeutic index and concerns regarding hypercalcemia and acceleration of kidney disease. We evaluated doxercalciferol (1alpha-hydroxyvitamin D2) as an alternative therapy in a randomized, double-blinded, placebo-controlled, multicenter trial.

METHODS

Fifty-five adults with stage 3 or 4 CKD and an intact PTH (iPTH) level greater than 85 pg/mL (ng/L) completed 8 baseline weeks, followed by 24 weeks of oral therapy with doxercalciferol or placebo. Pretreatment demographics and biochemical features did not differ between groups. Dosages were increased gradually if iPTH level was not decreased by 30% or greater and serum calcium and phosphorus levels were stable. Regular monitoring included plasma iPTH, serum calcium and phosphorus, urinary calcium, bone-specific serum markers, and serum lalpha,25-dihydroxyvitamin D levels. Glomerular filtration rate (GFR) was measured before and after treatment.

RESULTS

Mean plasma iPTH level decreased by 46% from baseline after 24 weeks of doxercalciferol treatment (P <0.001), but was unchanged with placebo. After 6 weeks, iPTH level reductions with doxercalciferol treatment exceeded those with placebo at all subsequent intervals (P <0.001). No clinically significant differences in mean serum calcium or phosphorus or urinary calcium levels or incidence of hypercalcemia, hyperphosphatemia, or hypercalciuria were noted between groups. Serum C- and N-telopeptide and bone-specific alkaline phosphatase levels decreased with doxercalciferol treatment relative to both baseline and placebo (P <0.01). Adverse-event rates and changes in GFR did not differ between groups.

CONCLUSION

Doxercalciferol is safe and effective in controlling secondary hyperparathyroidism of patients with CKD stages 3 and 4.

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.

Vitamin D receptor and analogs

In chronic kidney disease (CKD), high circulating levels of parathyroid hormone (PTH) cause osteitis fibrosa, bone loss, and cardiovascular complications that increase morbidity and mortality. Impaired production of 1,25-dihydroxyvitamin D (calcitriol), the hormonal form of vitamin D, is a major contributor to the generation and maintenance of parathyroid hyperplasia and increased synthesis and secretion of PTH. Calcitriol inhibits PTH gene transcription and ameliorates parathyroid hyperplasia by suppressing the expression of and growth signals from the autocrine transforming growth factor alpha (TGFalpha)/epidermal growth factor receptor (EGFR)-growth loop, a main determinant of parathyroid cell proliferation. Calcitriol reduction of parathyroid hyperplasia and serum PTH levels demands a functional vitamin D receptor (VDR). Although VDR is normal in CKD, parathyroid VDR content is reduced markedly. Furthermore, VDR function, as a transcriptional regulator of vitamin D responsive genes, is impaired by several factors including hypocalcemia, hyperphosphatemia, accumulation of uremic toxins, and reduction in cellular levels of the VDR partner, retinoid X receptor. Therapy with calcitriol analogs can overcome the antagonism on calcitriol-VDR actions induced by CKD. Although not all analog formulations are equally effective, they offer a wider therapeutic window in counteracting vitamin D resistance and survival advantage over exclusive calcitriol therapy.

Comparison of the effects of calcitriol and maxacalcitol on secondary hyperparathyroidism in patients on chronic haemodialysis: a randomized prospective multicentre trial

BACKGROUND

To identify differences between the effects of calcitriol and the calcitriol analogue, maxacalcitol, on parathyroid hormone (PTH) and bone metabolisms, we conducted a randomized prospective multicentre study on patients on chronic haemodialysis.

METHODS

We randomly assigned 91 patients with secondary hyperparathyroidism [intact PTH (iPTH) > or =150 pg/ml] to have either calcitriol (47 patients) or maxacalcitol (44 patients) therapy, for 12 months after a 1 month control period. Serum electrolytes, bone alkaline phosphatase (bAP), iPTH, total PTH and PTH(1-84) (whole PTH) levels were measured periodically. The first end point was a serum iPTH of <150 pg/ml, the second was the iPTH levels obtained.

RESULTS

Treatment was discontinued for various reasons in nine patients in each group, but no serious side effects were observed in either group. The numbers of cases reaching the first end point were not significantly different between the two groups. Serum calcium concentration was significantly higher in the maxacalcitol than the calcitriol group during early treatment, but not at the end of treatment. Throughout the treatment period there were no significant differences between the two groups in serum iPTH, inorganic phosphate, the product of the serum calcium and inorganic phosphorus concentrations, bAP, or the ratio of whole PTH to total PTH minus whole PTH. Nor were the changes in these parameters significantly different between the two groups comparing the patients with moderate to severe hyperparathyroidism (basal iPTH > or =500 pg/ml).

CONCLUSION

Calcitriol and maxacalcitol are equally effective on PTH and bone metabolism.

Percutaneous maxacalcitol injection therapy regresses hyperplasia of parathyroid and induces apoptosis in uremia

BACKGROUND

A high level of parathyroid hormone (PTH) is considered to be an indicator of poor prognosis and a poor quality of life of dialysis patients; therefore, an effective and safe therapy for secondary hyperparathyroidism (SHPT) has been developed.

METHODS

In 20 patients with SHPT resistant to maxacalcitol (OCT) intravenously administered, all detectably enlarged parathyroid glands were treated by percutaneous maxacalcitol injection therapy (PMIT) under ultrasonographic guidance consecutively 6 times, which was followed by OCT that was intravenously administered. The clinical effects of PMIT were evaluated based on the changes in the serum intact-PTH, adjusted Ca, phosphorus, and bone marker levels, and the parathyroid gland volume determined by ultrasonography. Morphologic examination, apoptosis analysis, and PTH mRNA expression level determination by reverse transcription-polymerase chain reaction (RT-PCR) using parathyroid tissues obtained by a biopsy technique were performed.

RESULTS

PMIT and subsequent intravenous OCT administrations significantly decreased the serum intact-PTH level and parathyroid gland volume for at least 12 weeks after PMIT without major complications. Parathyroid tissues obtained after PMIT exhibited some partial defects of parathyroid cells, a marked increase in the number of the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells, the ladder formation determined by DNA electrophoresis, and the decrease in the PTH mRNA expression level.

CONCLUSION

PMIT is effective and safe for the treatment of refractory SHPT, and a locally high level of OCT suppresses PTH secretion and regresses parathyroid hyperplasia, which is involved in the induction of apoptosis of parathyroid cells.