Abnormal calcium metabolism caused by increased circulating 1,25-dihydroxyvitamin D in a patient with rheumatoid arthritis

Molecular docking study on vitamin D supplements to understand their interaction with VDR-RXRα heterodimer and VDRE of TAGAP gene

The expression level of T cell activation Rho GTPase activating protein (TAGAP) gene is higher in rheumatoid arthritis (RA) patients compared to healthy individuals. Vitamin D receptor element (VDRE) sequences present in the regulatory region of TAGAP gene are targeted by vitamin D dependent Vitamin D receptor (VDR) - retinoic acid X receptor (RXR) heterodimer complex to regulate the TAGAP gene expression. Reduction in the expression of the TAGAP gene can prevent different severity of RA disease conditions. Calcitriol is a proven vitamin D supplement prescribed to patients with RA. However, it is involved in causing hypercalcemia. Maxacalcitol, an analog of vitamin D, is shown to have less hypercalcemic activity when compared to calcitriol. This study was done to analyze and compare the binding modes of calcitriol and maxacalcitol with VDR. We also studied the interactions of these compounds with the VDR-RXRα heterodimer complex. In addition, the binding of the ligand-activated heterodimer complexes with VDREs of the TAGAP gene was also analyzed to comprehend the binding affinities of calcitriol and maxacalcitol to the gene. The current work utilizes in silico molecular docking and simulation analysis to understand the mechanism in each complex formation.Communicated by Ramaswamy H. Sarma.

Efficacy and Safety of 22-Oxa-Calcitriol in Patients with Rheumatoid Arthritis: A Phase II Trial

BACKGROUND Calcitriol (1 alpha, 25-dihydroxy vitamin D3) is a good vitamin D supplement but can cause hypercalcemia. Whereas, 22-oxa-1 alpha, 25-dihydroxy vitamin D3 (22-oxa-calcitriol) has less hypercalcemic activity than calcitriol and is reported to be effective for cell-proliferative diseases. The objective of the study was to compare renal function and blood tests of arthritis patients receiving calcitriol supplements with those receiving 22-oxa-calcitriol supplements. MATERIAL AND METHODS A total of 369 patients with clinically confirmed rheumatoid arthritis were included in this phase II trial. Patients received lactose powder (the placebo group, n=123), 50 000 IU/week of 22-oxa-calcitriol (the treatment group, n=123), or 50 000 IU/week of calcitriol (the control group, n=123) for 6 weeks. At the time of enrollment and after 6 weeks of supplementation, renal function tests, blood tests, and secondary outcome measures were evaluated. One-way ANOVA and the chi-squared test for independence were performed for continuous data and constant data at a 95% of confidence level. RESULTS Both 22-oxa-calcitriol and calcitriol successfully decreased swollen joints in patients with rheumatoid arthritis, and both improved Health Assessment Questionnaire Disease Activity Index scores and serum vitamin D levels. The intensity of improvement of serum vitamin D levels in both groups was the same (P<0.0001, q=0.24); however, calcitriol caused hypercalcemia (P<0.0001, q=12.59). CONCLUSIONS This study found that 22-oxa-calcitriol was a good option for vitamin D supplementation in rheumatoid arthritis patients.

Vitamin D in rheumatoid arthritis-towards clinical application

In addition to its well-documented involvement in mineral homeostasis, vitamin D seems to have broad effects on human health that go beyond the skeletal system. Prominent among these so-called nonclassical effects of vitamin D are its immunomodulatory properties. In vitro studies have shown anti-inflammatory effects of 1,25-dihydroxyvitamin D (1,25(OH)2D), the active form of vitamin D. In addition, epidemiological analysis of patients with established inflammatory disease identified associations between vitamin D deficiency (low serum concentrations of inactive 25-hydroxyvitamin D, abbreviated to 25(OH)D) and inflammatory conditions, including rheumatoid arthritis (RA). The association of vitamin D deficiency with RA severity supports the hypothesis of a role for vitamin D in the initiation or progression of the disease, or possibly both. However, whether 25(OH)D status is a cause or consequence of RA is still incompletely understood and requires further analysis in prospective vitamin D supplementation trials. The characterization of factors that promote the transition from preclinical to clinical phases of RA has become a major focus of research, with the aim to facilitate earlier diagnosis and treatment, and improve therapeutic outcomes. In this Review, we aim to describe the current knowledge of vitamin D and the immune system specifically in RA, and discuss the potential benefits that vitamin D might have on slowing RA progression.

Rare causes of calcitriol-mediated hypercalcemia: a case report and literature review

CONTEXT

Calcitriol-mediated hypercalcemia resulting from elevated extrarenal 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-hydroxylase) activity has not previously been described in giant cell polymyositis.

CASE

We report an unusual case of hypercalcemia due to disseminated granulomatous disease in a 62-yr-old woman with profound proximal muscle weakness and weight loss. She was initially diagnosed with vitamin D deficiency myopathy with a low serum 25-hydroxyvitamin D; serum calcium at this time was low-normal. Vitamin D(3) 3000 IU daily was prescribed. One month later, blood work showed new hypercalcemia and hypercalciuria with normalized 25-hydroxyvitamin D. 1,25-dihydroxyvitamin D was high-normal, despite a suppressed PTH, undetectable PTHrP, and essentially normal renal function. Her hypercalcemia resolved, and her strength improved only after prednisone was added to bisphosphonate therapy. Two weeks later, she died from acute congestive heart failure.

METHODS AND RESULTS

Autopsy revealed a disseminated giant cell myositis affecting skeletal, cardiac, and gastrointestinal smooth muscle. Immunohistochemistry localized 1alpha-hydroxylase to the inflammatory infiltrates in skeletal and cardiac muscle.

EVIDENCE

A review of English publications in Medline and Embase, including a reference search of retrieved articles, revealed that calcitriol-mediated hypercalcemia has been described in over 30 conditions, most of which are granulomatous in nature, ranging from inflammatory conditions and foreign body exposures to infections and neoplasms.

CONCLUSIONS

Hypercalcemia resulting from autonomous 1alpha-hydroxylase activity may be unmasked by low-dose vitamin D supplementation and should not be excluded from the differential diagnosis of nonparathyroid causes if the serum calcitriol is inappropriately normal, rather than frankly elevated.

Vitamin D metabolites as clinical markers in autoimmune and chronic disease

Recent research has implicated vitamin D deficiency (serum levels of 25-hydroxyvitamin D <50 nmol/L) with a number of chronic conditions, including autoimmune conditions such as multiple sclerosis, lupus, and psoriasis, and chronic conditions such as osteoporosis, osteoarthritis, metabolic syndrome, fibromyalgia and chronic fatigue syndrome. It has been assumed that low levels of 25-hydroxyvitamin D (25-D) accurately indicate vitamin D storage and vitamin D receptor (VDR)-mediated control of calcium metabolism and innate immunity. To evaluate this assumption, 25-D and 1,25-dihydroxyvitamin D3 (1,25-D) levels were measured in 100 Canadian patients with these conditions. Additionally, other inflammatory markers (CK, CRP) were measured. Results showed a strong positive association between these autoimmune conditions and levels of 1,25-D >110 pmol/L. However, there was little association with vitamin D deficiency or the other inflammatory markers, meaning that the results challenge the assumption that serum levels of 25-D are a sensitive measure of the autoimmune disease state. Rather, these findings support the use of 1,25-D as a clinical marker in autoimmune conditions. High levels of 1,25-D may result when dysregulation of the VDR by bacterial ligands prevents the receptor from expressing enzymes necessary to keep 1,25-D in a normal range.

1alpha-Hydroxylase transactivation by gamma-interferon in murine macrophages requires enhanced C/EBPbeta expression and activation

gamma-Interferon [gamma-IFN] induction of macrophage 1alpha-hydroxylase mRNA and activity causes severe hypercalcemia in granulomatous disorders. These studies demonstrate transcriptional regulation. gamma-IFN induces the activity of the murine 1alpha-hydroxylase [-1651; +22] promoter in the murine macrophage cell line Raw 264.7 only after a 24h exposure. This slow kinetics is incompatible with classical gamma-IFN-mediated transactivation. In fact, gamma-IFN response mapped to the minimal [-85; +11] promoter, which lacks GAS or ISRE sites but contains a putative C/EBPbeta site. C/EBPbeta is a gamma-IFN inducible gene and a novel mediator of gamma-IFN-regulated transcription. As expected for a C/EBPbeta-driven transcription, ectopic C/EBPbeta expression was sufficient to increase 1alpha-hydroxylase activity, enhance minimal promoter activity and potentiate the induction of this promoter by gamma-IFN. Importantly, the dominant negative C/EBPbeta isoform antagonized C/EBPbeta-transcriptional activity. gamma-IFN induction of C/EBPbeta expression is not sufficient for gamma-IFN induction of minimal promoter activity. There is also a cell-specific induction of C/EBPbeta-transcriptional activity by gamma-IFN. In Raw cells, specific inhibition of gamma-IFN induction of endogenous-C/EBPbeta phosphorylation by MEKK1 markedly reduced basal promoter activity and the response to gamma-IFN. We conclude that gamma-IFN-induction of C/EBPbeta expression and activation by phosphorylation contributes to gamma-IFN-transcriptional control of 1alpha-hydroxylase expression in murine macrophages.

Stat1-vitamin D receptor interactions antagonize 1,25-dihydroxyvitamin D transcriptional activity and enhance stat1-mediated transcription

The cytokine gamma interferon (IFN-gamma) and the calcitropic steroid hormone 1,25-dihydroxyvitamin D (1,25D) are activators of macrophage immune function. In sarcoidosis, tuberculosis, and several granulomatoses, IFN-gamma induces 1,25D synthesis by macrophages and inhibits 1,25D induction of 24-hydroxylase, a key enzyme in 1,25D inactivation, causing high levels of 1,25D in serum and hypercalcemia. This study delineates IFN-gamma-1,25D cross talk in human monocytes-macrophages. Nuclear accumulation of Stat1 and vitamin D receptor (VDR) by IFN-gamma and 1,25D promotes protein-protein interactions between Stat1 and the DNA binding domain of the VDR. This prevents VDR-retinoid X receptor (RXR) binding to the vitamin D-responsive element, thus diverting the VDR from its normal genomic target on the 24-hydroxylase promoter and antagonizing 1,25D-VDR transactivation of this gene. In contrast, 1,25D enhances IFN-gamma action. Stat1-VDR interactions, by preventing Stat1 deactivation by tyrosine dephosphorylation, cooperate with IFN-gamma/Stat1-induced transcription. This novel 1,25D-IFN-gamma cross talk explains the pathogenesis of abnormal 1,25D homeostasis in granulomatous processes and provides new insights into 1,25D immunomodulatory properties.

Case report: hypercalcemia with inappropriate 1,25-dihydroxyvitamin D in Wegener's granulomatosis

Hypercalcemia associated with the extrarenal production of 1,25-dihydroxyvitamin D (1,25(OH)2D) has been reported in several disorders, most notably granulomatous diseases such as sarcoidosis. The authors describe a woman with hypercalcemia, renal insufficiency, microscopic hematuria, and anemia. The circulating 1,25(OH)2D level was higher than appropriate for the ambient conditions (renal insufficiency, suppressed intact parathyroid hormone, and hypercalcemia). A kidney biopsy was consistent with Wegener's granulomatosis, and treatment with prednisone and cyclophosphamide was associated with normalization of serum calcium levels, improved renal function, a marked decrease in serum 1,25(OH)2D levels, and increased serum intact parathyroid hormone levels. These findings are consistent with the unregulated production of 1,25(OH)2D by inflammatory cells associated with Wegener's granulomatosis.

Hypercalcemia associated with dysregulation of 1,25-dihydroxyvitamin D in arthritis

We describe an elderly man who presented with hypercalcemia associated with suppressed intact parathyroid hormone (PTH) levels. Despite renal insufficiency the circulating 1,25-dihydroxyvitamin D (1,25(OH)2D) was in the upper part of the normal range. Known causes of hypercalcemia were absent and mild hypercalcemia with suppression of intact PTH persisted until after bilateral hip replacement for severe arthritis (1 year after presentation). After hip replacement the ionized calcium normalized, intact PTH normalized, and 1,25(OH)2D decreased markedly. We believe the abnormalities in mineral homeostasis were related to production of 1,25(OH)2D by inflammatory mononuclear cells associated with arthritis.

Hypercalcaemia in rheumatoid arthritis revisited

The prevalence and mechanisms of hypercalcaemia were studied in a series of patients attending a regional referral centre for rheumatic diseases. In a prospective study one case of hypercalcaemia due to primary hyperparathyroidism was found in 251 consecutive patients who were screened over a three month period. In a retrospective study of 39 patients who had been discovered to be hypercalcaemic during the preceding 12 months known cases of hypercalcaemia were found in 38 (97%) cases. Primary hyperparathyroidism was the most common cause (n = 24; 62%), followed by thiazide treatment in five (13%), cancer in three (8%), immobility in three (8%), vitamin D toxicity in two (5%), and chronic liver disease in one (3%). In one case the diagnosis remained unclear after full investigation. This study shows that the causes of hypercalcaemia in rheumatological patients are similar to those in the general population. These observations contrast with previous reports, which suggested that hypercalcaemia may be a complication of rheumatoid arthritis itself.

Extra-renal production of calcitriol in chronic renal failure

Renal 1-alpha-hydroxylase activity is tightly regulated in normal humans and intact animals. No significant changes in serum 1,25(OH)2D levels occur in response to vitamin D challenge. However, conflicting reports have appeared in the literature with regard to stimulation of 1,25(OH)2D production after 25(OH)D administration in uremia. To provide further insight into this issue, 25(OH)D at a dose of 100 micrograms every other day for two weeks followed by 50 micrograms every other day for the next two weeks was given orally to seven uremic mongrel dogs. After two weeks of 25(OH)D therapy, 1,25(OH)2D levels increased from 16.4 +/- 0.9 to 28.0 +/- 1.9 pg/ml (P less than 0.001) in parallel with a fourfold increase in 25(OH)D concentrations from a basal of 50.1 +/- 6.5 to 203.2 +/- 18.1 ng/ml. No significant changes in serum i-PTH, ICa or P were observed. Linear regression analysis of the relationship between serum concentrations of 1,25(OH)2D versus 25(OH)D, for each dog during this period, showed highly significant correlation coefficients. To evaluate the possibility that extra-renal sites contribute to the described enhanced 1,25(OH)2D net synthesis after 25(OH)D treatment, similar studies were performed in four anephric patients undergoing hemodialysis. Basal serum 1,25(OH)2D levels were 5.5 +/- 2.4 pg/ml and increased to 19.6 +/- 5.0 pg/ml after 25(OH)D administration. A significant correlation was also found for the relationship between serum levels of 1,25(OH)2D and 25(OH)D in anephrics (r = 0.72, P less than 0.001). The same therapy in four normal volunteers showed no significant changes in serum 1,25(OH)2D concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercalcemia and abnormal 1,25-dihydroxyvitamin D concentrations in leprosy

Two patients with lepromatous leprosy and hypercalcemia are presented. Serum immunoreactive parathyroid hormone and urinary cyclic adenosine monophosphate concentrations were suppressed. Serum 1,25-dihydroxyvitamin D [1,25-(OH)2D] concentrations were elevated in one patient and normal in the other. Urinary hydroxyproline excretion was slightly high in both patients. Hypercalcemia resolved excretion was slightly high in both patients. Hypercalcemia resolved with prednisone therapy. Abnormal 1,25-(OH)2D production and/or metabolism may play a role in the pathogenesis of hypercalcemia in some patients with leprosy.

Evidence that calcium modulates circulating 25-hydroxyvitamin D in man

We previously demonstrated in normal subjects that 1,25-dihydroxyvitamin D3 (1,25(OH)2D) can prevent the increase in serum 25-hydroxyvitamin D (25-OHD) which occurs in response to vitamin D. An investigation was carried out in eight normal subjects, therefore, to determine whether increases in calcium intake would alter the response of serum 25-OHD to challenge with vitamin D. In control studies, vitamin D, 100,000 U/d for 4 d, significantly increased mean serum 25-OHD from 18 +/- 3 to 42 +/- 5 ng/ml (p less than 0.001), an increment of 24 ng/ml (133%). Mean serum calcium, ionized calcium, phosphorus, creatinine, and 1,25(OH)2D did not change. In contrast, the same dose of vitamin D and calcium, 2,000 mg/d for 4 d, administered to the same eight subjects produced an increase in mean serum 25-OHD from 19 +/- 3 to 31 +/- 4 ng/ml (p less than 0.001), an increment of only 12 ng/ml (63%) and significantly less than the control (p less than 0.02). Mean serum calcium (8.8 +/- 0.1 vs. 9.2 +/- 0.1 mg/dl, p less than 0.01) and ionized calcium (4.79 +/- 0.07 vs. 4.85 +/- 0.08 mg/dl, p less than 0.05) increased significantly in response to vitamin D and calcium, mean serum phosphorus and creatinine did not change, and mean serum 1,25(OH)2D decreased significantly (37 +/- 2 vs. 31 +/- 4 pg/ml, p less than 0.02). In a postcontrol study in six of the normal subjects, vitamin D again significantly increased mean serum 25-OHD from 17 +/- 3 to 39 +/- 9 ng/ml (p less than 0.02), an increment of 22 ng/ml (129%).(ABSTRACT TRUNCATED AT 250 WORDS)