New vitamin D analogs

Consensus Statement on Vitamin D Status Assessment and Supplementation: Whys, Whens, and Hows

The 6th International Conference, "Controversies in Vitamin D," was convened to discuss controversial topics, such as vitamin D metabolism, assessment, actions, and supplementation. Novel insights into vitamin D mechanisms of action suggest links with conditions that do not depend only on reduced solar exposure or diet intake and that can be detected with distinctive noncanonical vitamin D metabolites. Optimal 25-hydroxyvitamin D (25(OH)D) levels remain debated. Varying recommendations from different societies arise from evaluating different clinical or public health approaches. The lack of assay standardization also poses challenges in interpreting data from available studies, hindering rational data pooling and meta-analyses. Beyond the well-known skeletal features, interest in vitamin D's extraskeletal effects has led to clinical trials on cancer, cardiovascular risk, respiratory effects, autoimmune diseases, diabetes, and mortality. The initial negative results are likely due to enrollment of vitamin D-replete individuals. Subsequent post hoc analyses have suggested, nevertheless, potential benefits in reducing cancer incidence, autoimmune diseases, cardiovascular events, and diabetes. Oral administration of vitamin D is the preferred route. Parenteral administration is reserved for specific clinical situations. Cholecalciferol is favored due to safety and minimal monitoring requirements. Calcifediol may be used in certain conditions, while calcitriol should be limited to specific disorders in which the active metabolite is not readily produced in vivo. Further studies are needed to investigate vitamin D effects in relation to the different recommended 25(OH)D levels and the efficacy of the different supplementary formulations in achieving biochemical and clinical outcomes within the multifaced skeletal and extraskeletal potential effects of vitamin D.

Effects of Hypocalcemic Vitamin D Analogs in the Expression of DNA Damage Induced in Minilungs from hESCs: Implications for Lung Fibrosis

In our previous work, we evaluated the therapeutic effects of 1α,25-Dihydroxyvitamin D₃, the biologically active form of vitamin D, in the context of bleomycin-induced lung fibrosis. Contrary to the expected, vitamin D supplementation increased the DNA damage expression and cellular senescence in alveolar epithelial type II cells and aggravated the overall lung pathology induced in mice by bleomycin. These effects were probably due to an alteration in the cellular DNA double-strand breaks’ repair capability. In the present work, we have evaluated the effects of two hypocalcemic vitamin D analogs (calcipotriol and paricalcitol) in the expression of DNA damage in the context of minilungs derived from human embryonic stem cells and in the cell line A549.

Pharmacokinetics of a New Oral Vitamin D Receptor Activator (2-Methylene-19-Nor-(20S)-1α,25-Dihydroxyvitamin D3) in Patients with Chronic Kidney Disease and Secondary Hyperparathyroidism on Hemodialysis

Background

2-Methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D₃ (DP001 or 2MD) is a novel, potent 1α-hydroxylated vitamin D analog that binds to the vitamin D receptor and suppresses parathyroid hormone synthesis and secretion with potential for an improved safety profile compared to existing active vitamin D analogs. The purpose of this study was to evaluate the pharmacokinetics of DP001 given orally after hemodialysis.

Methods

DP001 (550 ng) was given orally to 11 hemodialysis patients with secondary hyperparathyroidism after each dialysis session (3 times/week) for 4 weeks. Pharmacokinetic analyses were performed after the first and final dose.

Results

After the first and final dose, the half-life of DP001 was similar (55.8 ± 13.0 and 50.8 ± 8.2 h, respectively). At 4 weeks, the time to maximum plasma concentration was 4.0 ± 0.8 h, with a concentration maximum of 3.4 ± 0.3 pg/mL. The area under the curve (0 to infinity) after the final dose was 204.3 ± 23.9 pg h/mL, and apparent volume of distribution was 2.03 ± 0.22 L/kg. At week 4, mean intact parathyroid hormone was suppressed 33% from the baseline (pre-dose) value (313 ± 52 vs 462 ± 39 pg/mL, respectively). No clinically significant changes from baseline values were found for vital signs, electrocardiogram measurements, or other laboratory parameters, including serum calcium and phosphorus.

Conclusions

In hemodialysis patients, DP001 has a longer half-life than existing vitamin D therapies and enables control of parathyroid hormone when administered every 2–3 days on the day of dialysis. It is effective at a lower concentration maximum and area under the curve than other clinically available vitamin D compounds. DP001 may represent a therapeutic improvement over existing compounds due to rapid and extensive distribution to its target and its long half-life enabling sustained parathyroid hormone suppression. These studies support further evaluation of DP001 in longer-term treatment of secondary hyperparathyroidism.

Secondary Hyperparathyroidism in Chronic Kidney Disease: Focus on Clinical Consequences and Vitamin D Therapies

Objective:

To assess vitamin D–based treatment approaches for secondary hyperparathyroidism and its complications.

Data Sources:

A literature search was performed using MEDLINE (1990–February 28, 2006). Key words used were chronic kidney disease and vitamin D to identify relevant papers published in English.

Study Selection and Data Extraction:

From the database of articles generated, 48 papers were identified. Titles and abstracts were examined to identify those directly related to the objective. Discussion was expanded through the bibliographies of cited articles.

Data Synthesis:

The increasing prevalence of chronic kidney disease (CKD) in the US indicates an urgent need for treatment strategies to delay or prevent disease progression. Abnormalities in phosphorus and calcium homeostasis, vitamin D levels, and the subsequent development of secondary hyperparathyroidism (SHPT) are secondary complications of CKD associated with increased morbidity and mortality. Management options include dietary phosphorus restriction, phosphate binders and/or calcium supplementation, vitamin D supplementation, and calcimimetics. Vitamin D supplementation has received increased attention given the prevalence of vitamin D deficiency in patients with CKD and the beneficial effect of correcting this deficiency.

Conclusions:

Early identification and intervention appropriate to the stage of CKD are likely to improve patient outcomes. Improved knowledge of interactions between vitamin D and vitamin D receptors has led to the development of vitamin D analogs and calcimimetics, which offer benefits in the management of SHPT. Integrating available treatment options into practice to achieve optimal therapeutic goals of SHPT based on the stage of CKD is a significant challenge for pharmacists managing patients with CKD.

Novel vitamin D analogues; cytotoxic and anti-proliferative activity against a diffuse large B-cell lymphoma cell line and B-cells from healthy donors

Calcitriol (1,25-dihydroxyvitamin D₃, 1,25D₃) and vitamin D side-chain modified analogs (VDAs) have gained considerable attention as potential drugs in the treatment of acute myeloid leukemia (AML), yet studies of the impact of 1,25D₃ and VDAs upon other haematological malignancies are more limited. To address this gap in knowledge, we have examined the action of 1,25D₃ and VDAs on a human cell line (DOHH2, K422) typifying diffuse large B-cell lymphoma (DLBCL) and also peripheral blood B-cells isolated from healthy donors. 1,25D₃ and certain VDAs displayed moderate cytotoxic and pro-apoptotic actions upon DLBCL cells. 1,25D₃ and VDAs (100nM) caused the death of approximately 40% DOHH2 cells after 24h stimulation, similar to their impact on HL-60 cells (acute myeloid leukaemia cell line). In addition, 1,25D₃ and VDAs displayed concentration and time-dependent anti-proliferative actions upon stimulated B-cells from healthy donors. The VDAs inhibited proliferation by approximately 30%. Hence VDAs may offer therapeutic potential for the treatment of DLBCL or conditions benefitted by B-cell depletion.

Impact of vitamin D on chronic kidney diseases in non-dialysis patients: a meta-analysis of randomized controlled trials

Background and Objectives

Recent studies have supported a role for both newer and more established vitamin D compounds in improving proteinuria, although systematic evaluation is lacking. Furthermore, concerns remain regarding the influence of vitamin D on the progression of renal function. We analyzed the efficacy and safety of vitamin D in non-dialysis patients and compared the use of newer versus established vitamin D compounds by performing a meta-analysis of randomized controlled trials.

Design

A literature search of PubMed (1975 to September, 2012), EMBASE.com (1966 to September, 2012) and Ovid EBM Reviews (through September, 2012) was conducted.

Results

Eighteen studies were eligible for final inclusion; of these, six explored the effects of vitamin D on proteinuria, twelve studied the effects of supplementation on renal function, and fifteen discussed the incidence of hypercalcemia. Compared to the placebo or no interference, both the newer and established vitamin D sterols reduced proteinuria to a similar extent (RR, 2.00; 95% CI, 1.42 to 2.81). No decrease in the glomerular filter rate was observed (SMD, −0.10; 95%CI, −0.24 to 0.03), and the risk for dialysis initiation was 1.48 (95% CI, 0.54 to 4.03) with vitamin D treatment. Additionally, there was an increased risk of hypercalcemia for patients treated with either newer or established vitamin D compounds as compared with the controls (RR, 4.78; 95% CI, 2.20 to 10.37). The head-to-head studies showed no differences in the effects of either newer or established compounds on proteinuria or the risk of hypercalcemia. No serious adverse events were associated with the administration of vitamin D.

Conclusions

Vitamin D therapy appears to decrease proteinuria and have no negative influence on renal function in non-dialysis patients. But the occurrence of hypercalcemia should be evaluated when vitamin D is provided. No superiority for newer versus established vitamin D analogue is found.

A prospective randomized pilot study on intermittent post-dialysis dosing of cinacalcet

BACKGROUND

Treatment of secondary hyperparathyroidism (SHPT) is important in management of patients with end-stage renal disease on hemodialysis (HD). Calcimimetic agent, cinacalcet provides an option for control of SHPT in patients who fail traditional therapy. It may not have optimal results in non-compliant patients. To enhance compliance, we evaluated effectiveness of post-dialysis dosing of cinacalcet (group AD) as compared to daily home administration (group D) in a prospective randomized trial of HD patients with refractory SHPT.

METHODS

After 2-week run-in phase, patients were randomly assigned to two treatment groups. In group AD (N = 12), patients were administered cinacalcet on the day of dialysis (3 times/week) by dialysis staff, while in control group D (N = 11), cinacalcet was prescribed daily to be taken by patients at home. Intact parathyroid hormone (i-PTH), serum calcium, phosphorus, and alkaline phosphatase were followed for 16 weeks and compared to baseline in both groups. Data were analyzed using between-groups linear regression for repeated measures.

RESULTS

No significant decline in i-PTH occurred in group AD at 16 weeks as compared to a significant drop in group D (p = 0.006). However, subgroup analysis showed effectiveness of post-dialysis dosing in patients with less severe SHPT (p = 0.04).

CONCLUSION

Although daily dosing overall was more effective for treatment of SHPT, dialysis dosing was effective in patients with less severe SHPT. This warrants a larger study considering the limitations of this pilot trial. In the meantime, dialysis dosing can be considered in non-compliant patients with less severe SHPT.

Paricalcitol (19-nor-1,25-dihydroxyvitamin D2) and calcitriol (1,25-dihydroxyvitamin D3) exert potent immunomodulatory effects on dendritic cells and inhibit induction of antigen-specific T cells

Paricalcitol (19-nor-1,25/OH(2)/D(2)), a second generation vitamin D receptor (VDR) activator, is a synthetic analogue of vitamin D3. In contrast to calcitriol, paricalcitol has a reduced effect on intestinal calcium resorption thus avoiding undesirable hypercalcemia. Information about immunomodulatory activity of paricalcitol is scarce. In this study we show that, in all investigated aspects, paricalcitol retains significant immunomodulatory activity, comparable to calcitriol. Both VDR agonists impaired differentiation of immature dendritic cells (DCs) from monocytes. The presence of VDR agonists during DC differentiation abolished their capacity to be activated and, despite potent Toll-like receptor mediated stimulation, VDR agonist-treated DCs remained in the immature state. In accordance with these findings, VDR-treated DCs produced no bioactive IL-12 and had a significantly decreased capacity to induce antigen-specific T cells while the capacity to induce functional Tregs remained unchanged when compared to control DCs. As DCs and T cells play an important role in the pathogenesis of atherosclerosis, in end-stage renal disease patients, paricalcitol should be a VDR agonist of choice for the reduction of the risk of atherosclerosis due to its immunomodulatory effect proven in this study and known limited hypercalcemic effect. The immunomodulatory potency of paricalcitol makes it a drug of interest in the therapy of chronic immune-mediated inflammatory diseases.

Potential for vitamin D receptor agonists in the treatment of cardiovascular disease

Vitamin D(3) is made in the skin and modified in the liver and kidney to form the active metabolite, 1,25-dihydroxyvitamin D(3) (calcitriol). Calcitriol binds to a nuclear receptor, the vitamin D receptor (VDR), and activates VDR to recruit cofactors to form a transcriptional complex that binds to vitamin D response elements in the promoter region of target genes. During the past three decades the field has focused mainly on the role of VDR in the regulation of parathyroid hormone, intestinal calcium/phosphate absorption and bone metabolism; several VDR agonists (VDRAs) have been developed for the treatment of osteoporosis, psoriasis and hyperparathyroidism secondary to chronic kidney disease (CKD). Emerging evidence suggests that VDR plays important roles in modulating cardiovascular, immunological, metabolic and other functions. For example, data from epidemiological, preclinical and clinical studies have shown that vitamin D and/or 25(OH)D deficiency is associated with increased risk for cardiovascular disease (CVD). However, VDRA therapy seems more effective than native vitamin D supplementation in modulating CVD risk factors. In CKD, where decreasing VDR activation persists over the course of the disease and a majority of the patients die of CVD, VDRA therapy was found to provide a survival benefit in both pre-dialysis and dialysis CKD patients. Although VDR plays an important role in regulating cardiovascular function and VDRAs may be potentially useful for treating CVD, at present no VDRA is approved for CVD, and also no serum markers, beside parathyroid hormone in CKD, exist to indicate the efficacy of VDRA in CVD.

Vascular calcification and secondary hyperparathyroidism of severe chronic kidney disease and its relation to serum phosphate and calcium levels

BACKGROUND AND PURPOSE

Various complications consequent on disordered calcium and phosphate homeostasis occur frequently in chronic kidney disease (CKD) patients. Particularly, vascular calcification has high morbidity and mortality rates. There is a clear need for a better CKD model to examine various aspects of this disordered homeostasis.

EXPERIMENTAL APPROACH

Oral dosing with adenine induced CKD in rats in only 10 days. Serum calcium, phosphate and parathyroid hormone were measured and calcification in aorta was assessed histologically. The effects of varying phosphorus content of diet or treatment with phosphate binders or active vitamin D(3) on these parameters were examined.

KEY RESULTS

After adenine dosing, significant hyperphosphatemia, hypocalcemia and secondary hyperparathyroidism (2HPT) were observed during the experimental period of 15 weeks. Aortic calcification was detected in only some of the animals even at 15 weeks (approximately 40%). Treatment with vitamin D(3) for 18 days, even at a low dose (100 ng x kg(-1), 3-4 times week(-1), p.o), caused aortic calcification in all animals and increases in serum calcium levels up to the normal range. The vitamin D(3)-induced calcification was significantly inhibited by phosphate binders which lowered serum phosphate levels and the calcium x phosphate product, although serum calcium levels were elevated.

CONCLUSIONS

These data suggest that rats dosed orally with adenine provide a more useful model for analysing calcium/phosphate homeostasis in severe CKD. Controlling serum calcium/phosphate levels with phosphate binders may be better than vitamin D(3) treatment in hyperphosphatemia and 2HPT, to avoid vascular calcification.

Analysis of association of clinical aspects and vitamin D receptor gene polymorphism with dental implant loss

Osseointegration failure is a complex, multifactorial trait shown to concentrate in some treated populations. There has been shown evidence for genetic contribution to dental implant loss. Genetic polymorphisms have been classically considered as genetic risk factors for several diseases and, more recently, for dental implant loss.

OBJECTIVES

The purpose of this study was to access clinical factors related to failure process, and to investigate the relationship between a vitamin D receptor (VDR) polymorphism (rs731236, TaqI) and dental implant loss.

MATERIAL AND METHODS

Two hundred and seventeen unrelated patients, mean age 51.7+/-11.3 years, were divided into two groups: (i) control group (C), 137 individuals presenting at least one osseointegrated implant in function for 6 months or more and without any implant loss, and (ii) study group (S), 80 individuals presenting at least one implant loss. After DNA collection and purification, VDR TaqI polymorphism analysis was performed by polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP). Differences between C and S, and between healthy (H; n=1232) and lost (L; n=135) implants were accessed.

RESULTS

Positive evidence of association has been detected between implant loss and the following variables: edentulism, implant position, primary stability, and implant length. Cox's regression model showed that primary stability, surgical technique and bone quantity were related to implant survival over time. No association between genotypes or alleles of VDR TaqI polymorphism and implant loss was found between the groups.

CONCLUSION

It was observed that clinical variables, but not the study polymorphism, were associated with dental implant loss.

Vitamin D receptor activation and survival in chronic kidney disease

Replacement of activated vitamin D has been the cornerstone of therapy for secondary hyperparathyroidism (SHPT). Recent findings from several large observational studies have suggested that the benefits of vitamin D receptor activators (VDRA) may extend beyond the traditional parathyroid hormone (PTH)-lowering effect, and could result in direct cardiovascular and metabolic benefits. The advent of several new analogs of the activated vitamin D molecule has widened our therapeutic armamentarium, but has also made therapeutic decisions more complicated. Treatment of SHPT has become even more complex with the arrival of the first calcium-sensing receptor (CSR) agonist (cinacalcet hydrochloride) and with the uncovering of novel mechanisms responsible for SHPT. We provide a brief overview of the physiology and pathophysiology of SHPT, with a focus on vitamin D metabolism, and discuss various practical aspects of VDRA therapy and its reported association with survival in recent observational studies. A detailed discussion of the available agents is aimed at providing the practicing physician with a clear understanding of the advantages or disadvantages of the individual medications. A number of open questions are also analyzed, including the present and future roles of CSR agonists and 25(OH) vitamin D replacement.

Paricalcitol aggravates perivascular fibrosis in rats with renal insufficiency and low calcitriol

Cardiovascular complications are a major problem in chronic renal failure. We examined the effects of plasma calcium, phosphate, parathyroid hormone (PTH), and calcitriol on cardiac morphology in 5/6 nephrectomized rats. Fifteen weeks after nephrectomy rats were given a control diet, high-calcium or -phosphorus diet, or given paricalcitol treatment for 12 weeks. Sham-operated rats were on a control diet. Blood pressure, plasma phosphate, and PTH were increased, while the creatinine clearance was reduced in remnant kidney rats. Phosphate and PTH were further elevated by the high-phosphate diet but suppressed by the high-calcium diet, while paricalcitol reduced PTH without influencing phosphate or calcium. The high-calcium diet increased, while the high-phosphate diet reduced plasma calcium. Plasma calcitriol was significantly reduced in other remnant kidney groups, but further decreased after paricalcitol. Cardiac perivascular fibrosis and connective tissue growth factor were significantly increased in the remnant kidney groups, and further increased in paricalcitol-treated rats. Hence, regardless of the calcium, phosphate, or PTH levels, cardiac perivascular fibrosis and connective tissue growth factor increase in rats with renal insufficiency in association with low calcitriol. Possible explanations are that aggravated perivascular fibrosis after paricalcitol in renal insufficiency may be due to further suppression of calcitriol, or to a direct effect of the vitamin D analog.

TRP channels in kidney disease

Mammalian TRP channel proteins form six-transmembrane cation-permeable channels that may be grouped into six subfamilies on the basis of amino acid sequence homology (TRPC, TRPV, TRPM, TRPA, TRPP, and TRPML). Recent studies of TRP channels indicate that they are involved in numerous fundamental cell functions and are considered to play an important role in the pathophysiology of many diseases. Many TRPs are expressed in kidney along different parts of the nephron and growing evidence suggest that these channels are involved in hereditary, as well as acquired kidney disorders. TRPC6, TRPM6, and TRPP2 have been implicated in hereditary focal segmental glomerulosclerosis (FSGS), hypomagnesemia with secondary hypocalcemia (HSH), and polycystic kidney disease (PKD), respectively. In addition, the highly Ca(2+)-selective channel, TRPV5, contributes to several acquired mineral (dys)regulation, such as diabetes mellitus (DM), acid-base disorders, diuretics, immunosuppressant agents, and vitamin D analogues-associated Ca(2+) imbalance whereas TRPV4 may function as an osmoreceptor in kidney and participate in the regulation of sodium and water balance. This review presents an overview of the current knowledge concerning the distribution of TRP channels in kidney and their possible roles in renal physiology and kidney diseases.

Doxercalciferol treatment of secondary hyperparathyroidism

OBJECTIVE

To review the pharmacology, pharmacokinetics, effectiveness, safety, and therapeutic considerations related to the use of doxercalciferol in the treatment of secondary hyperparathyroidism.

DATA SOURCES

A MEDLINE search (1966-June 2006) was conducted using the key words vitamin D, ergocalciferols, and secondary hyperparathyroidism. Text word searches were also performed for the terms 1-alpha-hydroxy-vitamin D(2), 1-alpha-hydroxyergocalciferol, Hectorol, and doxercalciferol. Searches were limited to studies published in English and conducted in human subjects.

STUDY SELECTION AND DATA EXTRACTION

All published clinical studies evaluating the safety and effectiveness of doxercalciferol in secondary hyperparathyroidism were reviewed, and anecdotal patient reports were also evaluated. Selected clinical studies involving the use of calcitriol and/or paricalcitol in the treatment of secondary hyperparathyroidism were also included.

DATA SYNTHESIS

Doxercalciferol effectively reduces parathyroid hormone levels in patients with chronic kidney disease (CKD). Both oral and intravenous administration can significantly increase serum calcium and/or phosphorus levels as evidenced by placebo-controlled clinical trials. This agent has not been studied comparatively with calcitriol or paricalcitol to assess relative safety.

CONCLUSIONS

Doxercalciferol is approved for and effective in the treatment of secondary hyperparathyroidism related to CKD, both before and during dialysis, but has not demonstrated a lower incidence of hypercalcemia and/or hyperphosphatemia in relation to other vitamin D therapies. The drug is available in both oral and intravenous dosage forms. Doxercalciferol should be maintained as a formulary alternative for patients unresponsive to or intolerant of other vitamin D therapies, but comparative randomized studies are needed to differentiate its place in therapy.

The epithelial calcium channels TRPV5 and TRPV6: regulation and implications for disease

The epithelial Ca(2+) channels TRPV5 and TRPV6 represent a new family of Ca(2+) channels that belongs to the superfamily of transient receptor potential channels. TRPV5 and TRPV6 constitute the apical Ca(2+) entry mechanism in active Ca(2+) transport in kidney and intestine. The central role of TRPV5 and TRPV6 in active Ca(2+) (re)absorption makes it a prime target for regulation to maintain Ca(2+) balance. This review covers the hormonal regulation, interaction with accessory proteins and (patho)physiological implications of these epithelial Ca(2+) channels.

Inhibition of parathyroid hormone: a dose equivalency study of paricalcitol and doxercalciferol

INTRODUCTION

Paricalcitol and doxercalciferol are effective in reducing parathyroid hormone PTH concentrations in patients with secondary hyperparathyroidism. The purpose of this study was to determine the relative dose of doxercalciferol (compared to paricalcitol) required to maintain equivalent PTH concentrations in dialysis patients.

METHODS

Chronic hemodialysis patients treated with a stable dose of paricalcitol for at least 3 months were randomized to receive doxercalciferol at either 35, 50, or 65% of the paricalcitol dose for 6 weeks. Serum iPTH, calcium, phosphorus, and albumin were determined at baseline and monitored every 2 weeks. A linear regression analysis of percent change in iPTH values by dose group was performed to determine the conversion factor.

RESULTS

27 patients were enrolled. Initial iPTH, adjusted serum calcium, serum phosphorus, and CaxP were similar among the treatment groups. Linear regression analysis demonstrated a conversion factor of 0.57 for the dose of doxercalciferol relative to paricalcitol resulting in equivalent suppression of iPTH. Corrected serum calcium, phosphorus, CaxP product, as well as incidence of hypercalcemia, hyperphosphatemia and CaxP >50 were similar for all groups.

CONCLUSION

In patients on a maintenance dose of paricalcitol, dosing doxercalciferol at 55-60% of the paricalcitol dose results in comparable inhibition of PTH.

Coordinated control of renal Ca2+ transport proteins by parathyroid hormone

BACKGROUND

The kidney is one of the affected organs involved in the clinical symptoms of parathyroid hormone (PTH)-related disorders, like primary hyperparathyroidism and familial hypocalciuric hypercalcemia. The molecular mechanism(s) underlying alterations in renal Ca(2+) handling in these disorders is poorly understood.

METHODS

Parathyroidectomized and PTH-supplemented rats and mice infused with the calcimimetic compound NPS R-467 were used to study the in vivo effect of PTH on the expression of renal transcellular Ca(2+) transport proteins, including the epithelial Ca(2+) channel transient receptor potential, vanilloid, member 5 (TRPV5), calbindins, and the Na(+)/Ca(2+)-exchanger (NCX1). In addition, the effect of PTH on transepithelial Ca(2+) transport in rabbit connecting tubule/cortical collecting duct (CNT/CCD) primary cultures was determined.

RESULTS

Decreased PTH levels in parathyroidectomized rats or NPS R-467-infused mice, resulted in reduced expression of these proteins, which is consistent with diminished Ca(2+) reabsorption, causing the development of the observed hypocalcemia. PTH supplementation of parathyroidectomized rats restored the expression of the renal Ca(2+) transport machinery and serum Ca(2+) levels, independent of serum 1,25-dihydroxyvitamin D(3) levels and renal vitamin D or Ca(2+)-sensing receptor mRNA abundance. Inhibition of the PTH-stimulated transepithelial Ca(2+) transport by the TRPV5-specific inhibitor ruthenium red reduced the PTH-stimulated expression of calbindin-D(28K) and NCX1 in rabbit CNT/CCD primary cultures.

CONCLUSION

PTH stimulates renal Ca(2+) reabsorption through the coordinated expression of renal transcellular Ca(2+) transport proteins. Moreover, the PTH-induced stimulation is enhanced by the magnitude of the Ca(2+) influx through the gatekeeper TRPV5, which in turn facilitates the expression of the downstream Ca(2+) transport proteins. Therefore, the renal transcellular Ca(2+) transport proteins, including TRPV5, could contribute to the pathogenesis of PTH-related disorders.

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.

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.

Complications of chronic kidney disease: anemia, mineral metabolism, and cardiovascular disease

This article focuses on the importance of three major complications of chronic kidney disease: (1) anemia, (2) calcium-phosphorus regulation and bone disease, and (3) cardiovascular risk profiling and treatment. The arguments for early and effective intervention have been amply made with respect to these three complications. Substantive trial data are sorely need to provide the definitive evidence that effective treatment of these complications results in better outcomes.

Effects of vitamin D compounds on renal and intestinal Ca2+ transport proteins in 25-hydroxyvitamin D3-1α-hydroxylase knockout mice1

BACKGROUND

Vitamin D compounds are used clinically to control secondary hyperparathyroidism (SHPT) due to renal failure. Newer vitamin D compounds retain the suppressive action of 1,25(OH)(2)D(3) on the parathyroid glands and may have less Ca(2+)-mobilizing activity, offering potentially safer therapies.

METHODS

This study investigated the effect of a single dose of compound (1,25(OH)(2)D(3), 1,24(OH)(2)D(2), or 1alpha(OH)D(2)) on renal and intestinal Ca(2+) transport proteins, including TRPV5 and TRPV6, and serum Ca(2+), in a novel SHPT model, the 25-OH-D(3)-1alpha-hydroxylase knockout mouse, which lacks endogenous 1,25(OH)(2)D(3) and is severely hypocalcemic. Animals were injected intraperitoneally with compound (100 ng/mouse).

RESULTS

Serum levels of 1,25(OH)(2)D(3) and 1,24(OH)(2)D(2) peaked at four hours post-injection (pi), then declined rapidly. 1,25(OH)(2)D(2) generated from 1alpha(OH)D(2) peaked at 12 hours pi and then remained stable. Serum Ca(2+) was increased to near-normal within four hours by 1,25(OH)(2)D(3) and 1,24(OH)(2)D(2), and within 12 hours by 1alpha(OH)D(2). 1,25(OH)(2)D(3) and 1,24(OH)(2)D(2) up-regulated duodenal TRPV5 and TRPV6 mRNA to a similar degree within four hours; mRNA levels decreased by 12 hours after 1,24(OH)(2)D(2) treatment, and by 24 hours after 1,25(OH)(2)D(3) treatment. 1,25(OH)(2)D(3) increased kidney levels of TRPV5, calbindin-D(28K), and calbindin-D(9K) mRNA within four hours; 1,24(OH)(2)D(2) did not change kidney TRPV5 levels and modestly increased calbindin D(9K) by 48 hours. 1alpha(OH)D(2) produced later-onset effects, increasing duodenal TRPV6 and calbindin-D(9K) mRNA levels by 12 hours and TRPV5 by 48 hours.

CONCLUSION

In kidney, 1alpha(OH)D(2) increased TRPV5, calbindin-D(28K), and calbindin-D(9K) mRNA levels by 12 hours. This study indicates that Ca(2+) transport proteins, including TRPV5 and TRPV6, are differentially up-regulated by vitamin D compounds.

Therapeutic potential of the 2-alkyl and 2-alkylidene-19-nor-(20S)-modified analogs of 1alpha,25-dihydroxyvitamin D3

Five analogs of 19-nor-1alpha,25-dihydroxyvitamin D(3) are described that show highly selective and potent activities. The 2-methylene-19-nor-(20S)-1alpha25-dihydroxyvitamin D(3) (2MD) and its 2alpha-methyl sister are selectively active on the osteoblast. 2MD is bone anabolic and causes bone formation in vivo and in vitro and is being developed as a therapy for bone loss diseases such as osteoporosis. 2-Methylene-19-nor (20S)-bishomo-1alpha-hydroxypregnacalciferol (2BMP) has no activity on calcium in vivo while totally suppressing circulating parathyroid hormone. Its homologs, i.e. 2-methylene-19-nor-1alpha-hydroxy-homopregnacalciferol (2MP) and 2-methylene-19-nor-1alpha-hydroxypregnacalciferol (2MPC) act similarly but are either less selective (2MP) or not as potent (2MPC). These abbreviated side chain analogs will be developed for diseases where a rise in serum calcium is not desired, as for example, cancer, renal osteodystrophy, psoriasis and autoimmune diseases.

Vitamin D3 polyunsaturated side-chain analogues (EB1089, GS1590) and the 20-epi-vitamin D3 analogue CB1393 suppress parathyroid hormone secretion and mRNA level in bovine parathyroid cells

Several vitamin D analogues, with reduced hypercalcemic and hyperphosphatemic toxicity at therapeutic dosages, are in clinical use for prevention and treatment of secondary hyperparathyroidism (HPT) in chronic renal failure. We have performed a first in vitro evaluation of five vitamin D analogues displaying less calcemic activity in normal rats, considerably more antiproliferative ability and higher transcription activation potential than 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), with the future prospects in mind to identify even more effective and less calcemic vitamin D analogues for treatment of HPT. The vitamin D analogues EB1089 and GS1590 have polyunsaturated side-chains, whereas HEP187, MC1598 and CB1393 display altered stereochemistry at carbon 20. In primary cultures of bovine parathyroid cells EB1089, GS1590, CB1393 and MC1598 as well as the comparative controls 1,25(OH)(2)D(3), 22-oxacalcitriol (OCT, maxacalcitol), 19-nor-1,25(OH)(2)D(2) (paricalcitol) and 1alpha(OH)D(2) (doxercalciferol) significantly suppressed PTH secretion or reduced PTH mRNA level at 10(-8), 10(-10), and 10(-11)M for all compounds except for MC1598 at the lowest concentration. The analogue HEP187 displayed no PTH suppressive activity. We conclude that the vitamin D analogues EB1089, GS1590 and CB1393 may be suitable for treatment of hyperparathyroidism secondary to uremia and that further evaluation in vivo should be considered.