Synthesis of the active metabolite of vitamin D, 1,25(OH)2D3, by synovial fluid macrophages in arthritic diseases

Relationship between DXA measured systemic bone mineral density and subchondral bone cysts in postmenopausal female patients with knee osteoarthritis: a cross-sectional study : Osteoarthritis cysts and bone mineral density

BACKGROUND

Individuals with high systemic bone mineral density (BMD) may have an increased risk of incident knee osteoarthritis (OA). Besides that, radiographic osteophytes are strongly associated with BMD. Because of these reasons, the aim of the study was to investigate the possible association between radiological subchondral bone cyst (SBC) grade and systemic BMD and vitamin D status in the postmenopausal female patients with knee OA in a crosss-sectional study.

METHODS

This study included of 48 osteoporosis treatment-free postmenopausal patients diagnosed with symptomatic medial compartment knee OA. BMD analysis was performed using dual-energy X-ray absorptiometry (DXA) and serum vitamin D levels were measured after recording patients' findings. Each knee was scanned using computed tomography (CT), and categorical SBC scores were graded for the medial and lateral tibiofemoral (TF) and patellofemoral (PF) compartments and further calculated as compartmental total, total TF and grand total of both TF compartments. SBC scores were analysed with correlation analysis.

RESULTS

The patient population was characterized by radiographic joint space narrowing, obesity and low vitamin D status. Median medial total and grand total TF SBC scores were significantly different between the patient groups according to the Kellgren-Lawrence (KL) radiographic grading (p = 0.006 and p = 0.007, respectively). There were no correlations between femoral BMD values and SBC scores. However, positive correlations were detected significantly between L1 - 4 DXA values and TF SBC scores, but not with PF SBC scores (p = 0.005 for the correlation between L1 - 4 BMD and medial compartments total TF SBC score, p = 0.021 for the correlation between L1 - 4 BMD and grand total TF SBC score). No significant correlations were found with Vitamin D levels.

CONCLUSIONS

Development of TF OA high-grade SBCs may be linked to systemic bone mass as represented by trabecular bone-rich lumbar vertebrae. The relationship might point to the importance of bone stiffness as an acting factor in knee OA possibly with mechanical energy transfer to the joint.

Sample preparation techniques for extraction of vitamin D metabolites from non-conventional biological sample matrices prior to LC-MS/MS analysis

The determination of vitamin D metabolites as status marker or for diagnostic purposes is almost entirely conducted from blood serum or plasma. Other biological matrices, however, have also interested researchers, for two main reasons: (1) alternative matrices may allow non-invasive sampling, permit easier sample transfer and require less demanding storage conditions; and (2) the levels of vitamin D metabolites in other body compartments may further aid the understanding of vitamin D metabolism and function. Thus, the development of reliable and efficient sample preparation protocols for sample matrices other than serum/plasma, which will remove potential interferences and selectively extract the targeted metabolites, is of great importance. This review summarizes sample preparation methods for measurement of vitamin D metabolites using liquid chromatography-(tandem)mass spectrometry in more than ten different human tissues, including hair, saliva, adipose tissue, brain and others.

Autoimmune disease and interconnections with vitamin D

Vitamin D has well-documented effects on calcium homeostasis and bone metabolism but recent studies suggest a much broader role for this secosteroid in human health. Key components of the vitamin D system, notably the vitamin D receptor (VDR) and the vitamin D-activating enzyme (1α-hydroxylase), are present in a wide array of tissues, notably macrophages, dendritic cells and T lymphocytes (T cells) from the immune system. Thus, serum 25-hydroxyvitamin D (25D) can be converted to hormonal 1,25-dihydroxyvitamin D (1,25D) within immune cells, and then interact with VDR and promote transcriptional and epigenomic responses in the same or neighbouring cells. These intracrine and paracrine effects of 1,25D have been shown to drive antibacterial or antiviral innate responses, as well as to attenuate inflammatory T cell adaptive immunity. Beyond these mechanistic observations, association studies have reported the correlation between low serum 25D levels and the risk and severity of human immune disorders including autoimmune diseases such as inflammatory bowel disease, multiple sclerosis, type 1 diabetes and rheumatoid arthritis. The proposed explanation for this is that decreased availability of 25D compromises immune cell synthesis of 1,25D leading to impaired innate immunity and over-exuberant inflammatory adaptive immunity. The aim of the current review is to explore the mechanistic basis for immunomodulatory effects of 25D and 1,25D in greater detail with specific emphasis on how vitamin D-deficiency (low serum levels of 25D) may lead to dysregulation of macrophage, dendritic cell and T cell function and increase the risk of inflammatory autoimmune disease.

Expressions and clinical significance of interleukin-1β and cyclooxygenase-2 in serum and synovia of patients with gouty arthritis

Background: To explore the expressions and clinical significance of interleukin-1β (IL-1β) and cyclooxygenase-2 (COX-2) in serum and synovia of patients with gouty arthritis (GA).

Materials and Methods: A total of 110 GA patients hospitalized from January 2016 to September 2019 were selected as observation group, with 55 at remission stage (observation group I) and 55 at acute attack stage (observation group II). Another 55 healthy volunteers were selected as control group. The correlations of IL-1β and COX-2 with uric acid (UA) were explored by Spearman’s analysis. IL-1β and COX-2 expression levels were compared at different time points after treatment.

Results: IL-1β, COX-2 and UA levels of patients were significantly higher in observation group I and II than those in the control group, and higher in the observation group II than those in observation group I. IL-1β and COX-2 were positively correlated with UA (P<0.05). ROC curve analysis showed that the optimal cut-off values of IL-1β and COX-2 for predicting GA were 18.23 and 9.12 pg/mL, and AUC values were 0.702 and 0.714 (P<0.001), respectively. On admission and after treatment for 3, 7, and 10 days, IL-1β and COX-2 levels of observation group II significantly exceeded those of observation group I (P<0.05). Compared with the efficacy group, after treatment for 14 days, IL-1β and COX-2 levels in serum and synovia significantly increased in the non-efficacy group (P<0.05).

Conclusion: IL-1β and COX-2 levels in serum and synovia of GA patients are evidently higher than those in the control group, which rise with the aggravation of disease.

Vitamin D, Autoimmune Disease and Rheumatoid Arthritis

Vitamin D has been reported to influence physiological systems that extend far beyond its established functions in calcium and bone homeostasis. Prominent amongst these are the potent immunomodulatory effects of the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). The nuclear vitamin D receptor (VDR) for 1,25-(OH)2D3 is expressed by many cells within the immune system and resulting effects include modulation of T cell phenotype to suppress pro-inflammatory Th1 and Th17 CD4+ T cells and promote tolerogenic regulatory T cells. In addition, antigen-presenting cells have been shown to express the enzyme 1α-hydroxylase that converts precursor 25-hydroxyvitamin D3 (25-OHD3) to 1,25-(OH)2D3, so that immune microenvironments are able to both activate and respond to vitamin D. As a consequence of this local, intracrine, system, immune responses may vary according to the availability of 25-OHD3, and vitamin D deficiency has been linked to various autoimmune disorders including rheumatoid arthritis (RA). The aim of this review is to explore the immune activities of vitamin D that impact autoimmune disease, with specific reference to RA. As well as outlining the mechanisms linking vitamin D with autoimmune disease, the review will also describe the different studies that have linked vitamin D status to RA, and the current supplementation studies that have explored the potential benefits of vitamin D for prevention or treatment of RA. The overall aim of the review is to provide a fresh perspective on the potential role of vitamin D in RA pathogenesis and treatment.

Serum and synovial fluid vitamin D metabolites and rheumatoid arthritis

Vitamin D-deficiency has been linked to inflammatory diseases including rheumatoid arthritis (RA). Studies to date have focused on the impact of serum 25-hydroxyvitamin D3 (25(OH)D3), an inactive form of vitamin D, on RA disease activity and progression. However, anti-inflammatory actions of vitamin D are likely to be mediated at sites of RA disease, namely the inflamed joint, and may involve other vitamin D metabolites notably the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). In the current study serum and synovial fluid samples from n = 20 patients with persistent RA and n = 7 patients with reactive arthritis (ReA) were analysed for multiple vitamin D metabolites. Serum data for RA and ReA patients were compared to healthy controls (HC). There was no significant difference between RA or ReA patients relative to HC for 25(OH)D3, 24,25(OH)2D3, 1,25(OH)2D3 or 25(OH)D2. However, 3-epi-25(OH)D3 was significantly lower in RA and ReA patients compared to HC (p < 0.05). All vitamin D metabolites, apart from 25(OH)D2, were lower in SF compared to serum, and SF 1,25(OH)2D3 was unquantifiable in 13/20 RA and 4/7 ReA samples. SF 25(OH)D3, 3-epi-25(OH)D3 and DBP correlated inversely with swollen joint score, and serum 25(OH)D2 and SF DBP correlated directly with C-reactive protein levels. These data indicate that serum 25(OH)D3 provides only limited insight into the role of vitamin D in RA. Alternative serum metabolites such as 3-epi-25(OH)2D3, and SF metabolites, notably lack of SF 1,25(OH)2D3, may be more closely linked to RA disease severity and progress.

Co-expression of 1α-hydroxylase and vitamin D receptor in human articular chondrocytes

BACKGROUND

The aim was to investigate whether resident chondrocytes in human articular cartilage and in subculture express vitamin D receptor (VDR) and the enzyme that hydroxylates the prohormone 25(OH)D₃ to the active hormone 1α,25(OH)₂D₃, namely 1α-hydroxylase (CYP27B1). Any putative effects of vitamin D on chondrocytes were also explored.

METHODS

Cartilage from human osteoarthritic knee joints, cultured chondrocytes and cells grown in 3D spheroids were examined for the expression of VDR and 1α-hydroxylase by PCR, Western blots and immunolabelling. Receptor engagement was judged by visualizing nuclear translocation. The effects of 25(OH)D₃ and 1α,25(OH)₂D₃ on chondrocyte functions were assessed in proliferation-, chondrogenesis- and cartilage signature-gene expression assays. The capability of chondrocytes to hydroxylate 25(OH)D₃ was determined by measuring the concentration of metabolites. Finally, a putative regulation of receptor and enzyme expression by 1α,25(OH)₂D₃ or interleukin (IL)-1β, was investigated by Western blot.

RESULTS

Gene expression was positive for VDR in freshly isolated cells from native cartilage, cells subcultured in monolayers and in spheroids, whereas protein expression, otherwise judged low, was apparent in monolayers. Nuclear translocation of VDR occurred upon 1α,25(OH)₂D₃ treatment. Transcripts for 1α-hydroxylase were detected in freshly isolated cells, cultured cells and spheroids. Western blots and immunolabelling detected 1α-hydroxylase protein in all materials, while staining of tissue appeared confined to cells at the superficial layer. A dose-dependent 1α,25(OH)₂D₃ production was measured when the enzyme substrate was supplied to cell cultures. Western blots revealed that the VDR, but not 1α-hydroxylase, was induced by IL-1β treatment in adherent cells. Proliferation in monolayers was enhanced by both 25(OH)D₃ and 1α,25(OH)₂D₃, and both compounds had negative effects on chondrogenesis and cartilage-matrix genes.

CONCLUSIONS

VDR expression in resident cartilage chondrocytes, generally considered differentiated cells, is elusive. A similar pattern applies for redifferentiated chondrocytes in spheroid cultures, whereas dedifferentiated cells, established in monolayers, stably express VDR. Both 25(OH)D₃ and 1α,25(OH)₂D₃ are able to potentiate cell proliferation but have a negative impact in proteoglycan synthesis. Chondrocytes express 1α-hydroxylase and may contribute to the production of 1α,25(OH)₂D₃ into the joint environment. Effects of vitamin D could be unfavourable in the context of cartilage matrix synthesis.

Decreased sensitivity to 1,25-dihydroxyvitamin D3 in T cells from the rheumatoid joint

1,25-dihydroxyvitaminD₃ (1,25(OH)₂D₃), has potent anti-inflammatory effects, including suppression of IL-17 + and IFNγ+ T cells implicated in rheumatoid arthritis (RA), but efficacy at the site of active disease is unclear. To investigate this, T cells from synovial fluid (SF) and paired blood of patients with active RA were studied. 1,25(OH)₂D₃ had significantly less suppressive effect on Th17 cells (IL-17+IFNγ-) and Th17.1 cells (IL-17+IFNγ+) from SF compared to those from blood, and had no effect on SF CD4⁺ or CD8⁺ IFNγ+ T cell frequencies. Memory T cells (CD45RO+) predominate in SF, and 1,25(OH)₂D₃ had less effect on memory T cells relative to naïve (CD45RA+) T cells. RT-PCR and flow cytometry showed that this was not due to decreased expression of the vitamin D receptor or its transcription partners in memory T cells. Further studies using stimulated CD4⁺ T cells sorted according to IL-17 and IFNγ expression confirmed the ability of 1,25(OH)₂D₃ to suppress pre-existing cytokines. However, 1,25(OH)₂D₃ was most effective at suppressing de novo IL-17 and IFNγ induction. Correspondingly, T cell responses to 1,25(OH)₂D₃ correlated directly with capacity for phenotype change, which was lower in cells from SF compared to blood. These findings indicate that anti-inflammatory effects of 1,25(OH)₂D₃ in active RA are impaired because of reduced effects on phenotype-committed, inflammatory memory T cells that are enriched in SF. Restoration of 1,25(OH)₂D₃ responses in memory T cells may provide a new strategy for treatment of inflammatory diseases such as RA.

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.

The role of lipid-activated nuclear receptors in shaping macrophage and dendritic cell function: From physiology to pathology

Nuclear receptors are ligand-activated transcription factors linking lipid signaling to the expression of the genome. There is increasing appreciation of the involvement of this receptor network in the metabolic programming of macrophages and dendritic cells (DCs), essential members of the innate immune system. In this review we focus on the role of retinoid X receptor, retinoic acid receptor, peroxisome proliferator-associated receptor γ, liver X receptor, and vitamin D receptor in shaping the immune and metabolic functions of macrophages and DCs. We also provide an overview of the contribution of macrophage- and DC-expressed nuclear receptors to various immunopathologic conditions, such as rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, asthma, and some others. We suggest that systematic analyses of the roles of these receptors and their activating lipid ligands in immunopathologies combined with complementary and focused translational and clinical research will be crucial for the development of new therapies using the many molecules available to target nuclear receptors.

1,25-Dihydroxyvitamin D3 activates MMP13 gene expression in chondrocytes through p38 MARK pathway

Osteoarthritis (OA) is the most prevalent degenerative joint disease. The highly regulated balance of matrix synthesis and degradation is disrupted in OA, leading to progressive breakdown of articular cartilage. The molecular events and pathways involved in chondrocyte disfunction of cartilage in OA are not fully understood. It is known that 1,25-dihydroxyvitamin D₃ (1,25-(OH)₂D₃) is synthesized by macrophages derived from synovial fluid of patients with inflammatory arthritis. Vitmain D receptor is expressed in chondrocytes within osteoarthritic cartilage, suggesting a contributory role of 1,25-(OH)₂D₃ in the aberrant behavior of chondrocytes in OA. However, the physiological function of 1,25-(OH)₂D₃ on chondrocytes in OA remains obscure. Effect of 1,25-(OH)₂D₃ on gene expression in chondrocytes was investigated in this study. We found that 1,25-(OH)₂D₃ activated MMP13 expression in a dose-dependent and time-dependent manner, a major enzyme that targets cartilage for degradation. Interestingly, a specific mitogen-activated protein kinase p38 inhibitor SB203580, but not JNK kinase inhibitor SP600125, abrogated 1,25-(OH)2D3 activation of MMP13 expression. 1,25-(OH)₂D₃-induced increase in MMP13 protein level was in parallel with the phosphorylation of p38 in chondrocytes. To further address the effect of 1,25-(OH)₂D₃ on MMP13 expression, transfection assays were used to show that 1,25-(OH)₂D₃ activated the MMP13 promoter reporter expression. MMP13 is known to target type II collagen and aggrecan for degradation, two major components of cartilage matrix. We observed that the treatment of 1,25-(OH)₂D₃ in chondrocytes results in downregulation of both type II collagen and aggrecan while MMP13 was upregulated. Taken together, we provide the first evidence to demonstrate that 1,25-(OH)₂D₃ activates MMP13 expression through p38 pathway in chondrocytes. Since MMP13 plays a major role in cartilage degradation in OA, we speculate that the ability of 1,25-(OH)₂D₃ to potentiate MMP13 expression might facilitate cartilage erosion at the site of inflammatory arthritis.

Undetectable serum calcidiol: not everything that glitters is gold

There is an increased awareness of the adverse consequences of nutritional vitamin D deficiency. We report a patient with chronic tophaceous gout, chronic kidney disease (CKD) Stage 3/4 and undetectable serum calcidiol who developed severe hypercalcaemia upon vitamin D supplementation despite serum 25(OH) vitamin D within the normal range. Upon recovery, serum 1,25(OH)2 vitamin D remained in the normal range despite CKD and serum 25(OH) vitamin D 6 ng/mL. Gout tophi biopsies from additional patients showed macrophage expression of 25(OH) vitamin D 1α-hydroxylase. This case illustrates the dangers of supplementing vitamin D in patients with low serum 25(OH) vitamin D and increased 1α-hydroxylase activity due to granulomatous disease.

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.

Altered endocrine and autocrine metabolism of vitamin D in a mouse model of gastrointestinal inflammation

The active form of vitamin D, 1,25-dihydroxyvitamin D3, [1,25(OH)2D3] has potent actions on innate and adaptive immunity. Although endocrine synthesis of 1,25(OH)2D3 takes place in the kidney, the enzyme that catalyzes this, 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27b1 in humans, Cyp27b1 in mice), is expressed at many extra-renal sites including the colon. We have shown previously that colonic expression of CYP27b1 may act to protect against the onset of colitis. To investigate this further, we firstly characterized changes in Cyp27b1 expression in a mouse model of colitis. Mice treated with dextran sodium sulfate (DSS) showed weight loss, histological evidence of colitis, and increased expression of inflammatory cytokines. This was associated with decreased renal expression of Cyp27b1 (5-fold, P=0.013) and lower serum 1,25(OH)2D3 (51.8+/-5.9 pg/nl vs. 65.1+/-1.6 in controls, P<0.001). However, expression of CYP27b1 was increased in the proximal colon of DSS mice (4-fold compared with controls, P<0.001). Further studies were carried out using Cyp27b1 null (-/-) mice. Compared with+/-controls the Cyp27b1-/-mice showed increased weight loss (4.9% vs. 22.8%, P<0.001) and colitis. This was associated with raised IL-1 in the distal colon and IL-17 in the proximal and distal colon. Conversely, DSS-treated Cyp27b1-/-mice exhibited lower IL-10 in the proximal colon and toll-like receptors 2 and 4 in the distal colon. These data indicate that both local and endocrine synthesis of 1,25(OH)2D3 affect colitis in DSS-treated mice. Lack of Cyp27b1 exacerbates disease in this model, suggesting that similar effects may occur with vitamin D deficiency.

Expression and regulation of CCL18 in synovial fluid neutrophils of patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by the recruitment of leukocytes and the accumulation of inflammatory mediators within the synovial compartment. Release of the chemokine CCL18 has been widely attributed to antigen-presenting cells, including macrophages and dendritic cells. This study investigates the production of CCL18 in polymorphonuclear neutrophils (PMN), the predominant cell type recruited into synovial fluid (SF). Microarray analysis, semiquantitative and quantitative reverse transcriptase polymerase chain reaction identified SF PMN from patients with RA as a novel source for CCL18 in diseased joints. Highly upregulated expression of other chemokine genes was observed for CCL3, CXCL8 and CXCL10, whereas CCL21 was downregulated. The chemokine receptor genes were differentially expressed, with upregulation of CXCR4, CCRL2 and CCR5 and downregulation of CXCR1 and CXCR2. In cell culture experiments, expression of CCL18 mRNA in blood PMN was induced by tumor necrosis factor alpha, whereas synthesis of CCL18 protein required additional stimulation with a combination of IL-10 and vitamin D3. In comparison, recruited SF PMN from patients with RA were sensitized for CCL18 production, because IL-10 alone was sufficient to induce CCL18 release. These results suggest a release of the T cell-attracting CCL18 by PMN when recruited to diseased joints. However, its production is tightly regulated at the levels of mRNA expression and protein synthesis.

Cyclic hydrostatic pressure and particles increase synthesis of 1,25-dihydroxyvitamin D3 by human macrophages in vitro

1,25-Dihydroxyvitamin D(3) has a pivotal role in bone resorption and osteoclast activity. As activated macrophages are known to synthesise 1,25-dihydroxyvitamin D(3), this study examined whether pressure modulated its synthesis. Pressure and particles have been shown to increase synthesis of pro-resorptive cytokines and other factors by cultured macrophages. Human peripheral blood macrophages were isolated, cultured and exposed to pressure (similar to that found in the human joint) and/or particles. Synthesis of 1,25-dihydroxyvitamin D(3) by macrophages was assayed using high pressure liquid chromatography and in situ hybridization. Synthesis of 1,25-dihydroxyvitamin D(3) but not 24,25-dihydroxyvitamin D(3) was increased in macrophages under pressure. In situ hybridization demonstrated an increase in 1alpha-hydroxylase expression in response to pressure or particles and simultaneous exposure to both stimuli generated higher expression of 1alpha-hydroxylase. In conclusion, this is the first study to demonstrate that mechanical loading, in the form of pressure, stimulates 1,25-dihydroxyvitamin D(3) synthesis in human macrophages. These findings have implications for the in vivo situation, as they suggest that 1,25-dihydroxyvitamin D(3) could be one factor stimulating osteoclastic bone resorption in pathologies, such as arthritis or implant loosening, where intra-articular or intra-osseous pressure is raised or where wear particles interact with macrophages.

Regulation of MMP-9 gene expression for the development of novel molecular targets against cancer and inflammatory diseases

The need to pharmacologically control the proteolytic activity of matrix metalloproteinases (MMPs) has been commonly acknowledged, despite its limited efficacy in clinical trials. Among the reasons that explain this failure is our limited understanding of the signals that control the expression of MMPs in different cell types during different pathological conditions. Thus, future therapies must rely on more selective approaches. With the continually increasing body of proof implicating MMPs in a large number of diseases, it has become a priority to establish the pertinence of molecules involved in the signalling pathways leading to the expression of these enzymes. MMP-9 is a case in point: its dramatic overexpression in cancer and various inflammatory conditions clearly points to the molecular mechanisms controlling its expression as a potential target for eventual rational therapeutic intervention. In this article, recent progress in the signalling pathways that regulate MMP-9 expression is reviewed, and the latest strategies to be considered in the search for a specific inhibitor of its expression are presented.

Epidemiology of risk factors for osteoarthritis: systemic factors

Osteoarthritis (OA) appears to be a mechanically driven but chemically mediated disease process in which there is attempted (or aberrant) repair. Well established risk factors for OA include aging, obesity, gender, and, in selected subgroups, congenital anomalies. This review addresses less well established risk factors for OA that can impact joints through their effect on systemic metabolism rather than their contribution to local joint geometry and structure. These systemic risk factors include obesity; bone and bone density; nutrients, particularly those that function as antioxidants; and genetic factors. There is great opportunity for new prevention and intervention strategies as we expand our understanding of the role of these systemic risk factors.

Activities of plasminogen activator, plasmin and kallikrein in synovial fluid from patients with temporomandibular joint disorders

To measure the activities of plasminogen activator (PA), plasmin and kallikrein, multiple synovial fluid samples were taken from 32 patients with internal derangement (ID) and osteoarthrosis (OA), and nine asymptomatic volunteers. The enzyme activity in synovial fluid from the temporomandibular joint (TMJ) was quantitated by a fluorogenic substrate assay using an enzyme substrate. In fluid samples from the patient group, PA was detected in 24 (31.5%), plasmin in 20 (26.3%) and kallikrein in 53 (96.4%), while none of these enzymes were found in the synovial fluid samples from the control group. There were positive correlations found among PA, plasmin and kallikrein. These results clearly demonstrated increased levels of PA, plasmin and kallikrein activities in the synovial fluid of patients with ID and OA, and suggest that these enzymes may be involved in the pathogenesis of synovitis, as well as the resorption of cartilage and bone in TMJ.

Expression of vitamin D receptors and matrix metalloproteinases in osteoarthritic cartilage and human articular chondrocytes in vitro

OBJECTIVES

To examine the in situ distributions of vitamin D receptors (VDR) and matrix metalloproteinases (MMPs) in osteoarthritic cartilage for comparison with non-arthritic, normal cartilage; and to assess the in vitro effects of 1alpha,25 dihydroxyvitaminD(3)(1alpha,25(OH)(2)D(3)) on MMPs-1, -3 and -9 and prostaglandin E(2)(PGE(2)) production by cultures of human articular chondrocytes (HAC) shown to be VDR-positive.

METHODS

Using immunohistochemistry VDR expression in different specimens of osteoarthritic cartilage (N=11) was compared to that in normal cartilage (N=6), along with the immunodetection of MMPs-1, -3 and -9. The effects of 1alpha25(OH)(2)D(3)on MMP and PGE(2)production by HAC in vitro, with and without stimulation by TNFalpha or phorbol myristate acetate (PMA), was evaluated using ELISA methodology.

RESULTS

VDR was demonstrated in HAC of all specimens of osteoarthritic cartilage, especially the superficial zone, whereas only two of five normal cartilage specimens were VDR(+)for a minor proportion of HAC. Immunolocalization of MMPs-1, -3 and -9 was often seen in areas where chondrocytes were VDR(+), and dual immunolocalization has demonstrated individual chondrocytes positive for both VDR and MMP-3 in situ. In vitro, 1alpha25(OH)(2)D(3)alone had no effect on MMP-1, -9 and PGE(2)production by HAC, but MMP-3 production was up-regulated by 1alpha25(OH)(2)D(3)either with or without stimulation with TNFalpha or PMA. By contrast the increased production of MMP-9 and PGE(2)induced by PMA was significantly suppressed by concomitant treatment with 1alpha25(OH)(2)D(3).

CONCLUSIONS

The demonstration of VDR expression by HAC in osteoarthritic cartilage was often associated with sites where MMP expression was prevalent, observations in contrast to their virtual absence in normal age-matched cartilage. Together with HAC in vitro studies, the data suggests that 1alpha25(OH)(2)D(3)contributes to the regulation of MMP and PGE(2)production by HAC in osteoarthritic cartilage.

Rheumatoid arthritis synovial macrophage-osteoclast differentiation is osteoprotegerin ligand-dependent

Osteoprotegerin ligand (OPGL) is a newly discovered molecule which is essential for osteoclast differentiation. Both OPGL and its soluble decoy receptor, osteoprotegerin (OPG), which inhibits osteoclast formation, are known to be produced by osteoblasts and inflammatory cells found in the rheumatoid arthritis (RA) synovium. In this study, RA synovial macrophages were incubated in the presence or absence of OPGL, macrophage-colony stimulating factor (M-CSF), and dexamethasone for various time points. The results indicated that osteoclast formation from RA synovial macrophages is OPGL-dependent and that OPGL and M-CSF are the only humoral factors required for RA synovial macrophage-osteoclast differentiation. OPG was found to inhibit osteoclast formation by RA synovial macrophages in a dose-dependent manner. This study has shown that macrophages isolated from the synovium of RA patients are capable of differentiating into osteoclastic bone-resorbing cells; this process is OPGL- and M-CSF-dependent and is modulated by corticosteroids. Cellular (T and B cells, dendritic cells) and humoral factors in RA synovium and bone may influence osteoclast formation and bone resorption by controlling OPGL/OPG production.

Effect of osteoprotegerin and osteoprotegerin ligand on osteoclast formation by arthroplasty membrane derived macrophages

OBJECTIVE

Osteoprotegerin ligand (OPGL) is a newly discovered molecule, which is expressed by osteoblasts/bone stromal cells. This ligand and M-CSF are now known to be essential for osteoclast differentiation from marrow and circulating precursors. This study examined whether OPGL and its soluble receptor osteoprotegerin (OPG), influenced osteoclast formation from human arthroplasty derived macrophages, to determine if the effects of OPGL and OPG on these cells could contribute to the osteolysis of aseptic loosening.

METHODS

OPGL (+/- dexamethasone/M-CSF) was added to cultures of macrophages isolated from the pseudomembrane of loosened hip arthroplasties incubated on glass coverslips and dentine slices. OPG was added to cocultures of arthroplasty derived macrophages and UMR106 osteoblast-like cells. Osteoclast differentiation in long term cultures was assessed by expression of macrophage (CD14) and osteoclast markers (tartrate resistant acid phosphatase (TRAP), vitronectin receptor (VNR) and lacunar resorption).

RESULTS

In the absence of osteoblastic cells, the addition of OPGL alone was sufficient to induce differentiation of macrophages (CD14(+), TRAP(-), VNR(-)) into TRAP(+) and VNR(+) multinucleated cells, capable of extensive lacunar resorption. OPG was found to inhibit osteoclast formation by arthroplasty macrophages in a dose dependent manner. OPG (100 ng/ml) more than halved the formation of TRAP(+) and VNR(+) cells and the extent of lacunar resorption in co-cultures of UMR106 cells and arthroplasty macrophages.

CONCLUSIONS

This study has shown that macrophages, isolated from the pseudomembrane surrounding loose arthroplasty components, are capable of differentiating into osteoclastic bone resorbing cells and that OPGL is required for this to occur. OPG inhibits this process, most probably by interrupting the cell-cell interaction between osteoblasts and mononuclear phagocyte osteoclast precursors present in the pseudomembrane.

Autocrine control of vitamin D metabolism in synovial cells from arthritic patients

OBJECTIVE

This study was designed to investigate whether 1, 25-dihydroxyvitamin D3 (1,25-(OH)2D3), produced by activated synovial fluid macrophages, promotes its own catabolism by upregulating vitamin D-24-hydroxylase (24-OHase) in synovial fibroblasts through a vitamin D receptor (VDR) mediated mechanism.

METHODS

Synovial macrophages and fibroblasts were derived from patients with rheumatoid arthritis. Expression of VDR and 24-OHase mRNAs was determined using in situ hybridisation. Vitamin D hydroxylase activity was determined by incubating cells with [3H]-25-(OH)D3, or [3H]-1,25-(OH)2D3, and metabolite synthesis quantified using high performance liquid chromatography.

RESULTS

1, 25-(OH)2D3 increased expression of mRNA for both VDR and 24-OHase in fibroblasts by approximately threefold over 24 hours. 1,25-(OH)2D3 increased fibroblast 24-OHase activity, yielding 24-hydroxylated, and more polar, metabolites. In co-culture, fibroblasts were able to catabolise macrophage derived 1,25-(OH)2D3.

CONCLUSIONS

1, 25-(OH)2D3 is produced by macrophages in vitro at biologically relevant concentrations and can increase its own catabolism by synovial fibroblasts; this effect is probably mediated via upregulation of both synovial fibroblast VDR and 24-OHase.

Vitamins and arthritis. The roles of vitamins A, C, D, and E

There are at least four mechanisms whereby the nutrient vitamins A, C, D, and E may be related to the processes that impede or give rise to OA. These nutrient vitamins have major roles in modulating oxidative stress, participating in immune responses, and contributing to cell differentiation. There is a substantial need to understand the contribution of these nutrients to OA, because they may provide important insight into ameliorating the initiation and progression of the disease. Simultaneously, greater understanding will add rationality to an area of potential intervention that is often based on anecdote. Investigation will be complex; there is the need to select appropriate systems. Typical animal model systems used in the study of OA are inappropriate because most animals can synthesize ascorbic acid. There is the need to disaggregate, as much as possible, the numerous subsets of OA and the plethora of processes that contribute to that heterogeneity. Certainly, there is the need to recognize the interdependency of the actions of each of these nutrients at the cellular level. Furthermore, humans rarely consume these nutrients as independent products. For example, watermelon is a primary source of both ascorbic acid and beta-carotene. Failure to address these complexities denies the scientist the opportunity to advance our understanding of health and disease processes. More importantly, failure to address these complexities denies the person with OA the opportunity to address his or her own health.

Novel mutations in the 1alpha-hydroxylase (P450c1) gene in three families with pseudovitamin D-deficiency rickets resulting in loss of functional enzyme activity in blood-derived macrophages

Pseudovitamin D-defiency rickets (PDDR) is an autosomal recessive disorder characterized by hypocalcemia, rickets (which are resistant to treatment with vitamin D), and low or undetectable serum levels of 1,25-dihydroxyvitamin D (1,25(OH)2D). The symptoms are corrected with 1,25(OH)2D treatment, and the disease is now believed to result from a defect in the cytochrome P450 component (P450c1; CYP27B1) of the renal 25-hydroxyvitamin D-1alpha-hydroxylase (1-OHase). We have studied genomic DNA from three families with PDDR and have identified the same homozygous mutation in the P450c1 gene in two of the index cases, causing a frameshift in exon 8, resulting in a premature stop codon in the heme-binding domain. The two cases in the third kindred were compound heterozygotes with missense mutations in exons 6 and 9. We have also identified a C/T polymorphism in intron 6 of the P450c1 genomic DNA. Interferon gamma-inducible 1-OHase activity in blood-derived macrophages was shown by 1,25(OH)2D synthesis in all control cells tested (37-184 fmol/h/106 cells) and those from the PDDR family parents (34-116 fmol/h/106 cells) but was totally absent from the patients' cells, indicating a defect in their macrophage 1-OHase, similar to the presumed renal defect. The assumption of similarity between the renal and macrophage P450c1 was supported by our ability to clone a 514 bp sequence, including the heme-binding region of the macrophage P450c1 cDNA from controls, which was identical to that published for both the renal and keratinocyte P450c1 cDNAs.

The effects of 1 alpha,25-dihydroxyvitamin D(3) on matrix metalloproteinase and prostaglandin E(2) production by cells of the rheumatoid lesion

INTRODUCTION

1alpha,25-dihydroxyvitamin D(3)[1alpha,25(OH)(2)D(3)], the biologically active metabolite of vitamin D3, acts through an intracellular vitamin D receptor (VDR) and has several immunostimulatory effects. Animal studies have shown that production of some matrix metalloproteinases (MMPs) may be upregulated in rat chondrocytes by administration of 1alpha,25(OH)(2)D(3); and cell cultures have suggested that 1alpha,25(OH)(2)D(3) may affect chondrocytic function. Discoordinate regulation by vitamin D of MMP-1 and MMP-9 in human mononuclear phagocytes has also been reported. These data suggest that vitamin D may regulate MMP expression in tissues where VDRs are expressed. Production of 1alpha,25(OH)(2)D(3) within synovial fluids of arthritic joints has been shown and VDRs have been found in rheumatoid synovial tissues and at sites of cartilage erosion. The physiological function of 1alpha,25(OH)(2)D(3) at these sites remains obscure. MMPs play a major role in cartilage breakdown in the rheumatoid joint and are produced locally by several cell types under strict control by regulatory factors. As 1alpha,25(OH)(2)D(3) modulates the production of specific MMPs and is produced within the rheumatoid joint, the present study investigates its effects on MMP and prostaglandin E(2) (PGE(2)) production in two cell types known to express chondrolytic enzymes.

AIMS

To investigate VDR expression in rheumatoid tissues and to examine the effects of 1alpha,25-dihydroxyvitamin D(3) on cultured rheumatoid synovial fibroblasts (RSFs) and human articular chondrocytes (HACs) with respect to MMP and PGE(2) production.

METHODS

Rheumatoid synovial tissues were obtained from arthroplasty procedures on patients with late-stage rheumatoid arthritis; normal articular cartilage was obtained from lower limb amputations. Samples were embedded in paraffin, and examined for presence of VDRs by immunolocalisation using a biotinylated antibody and alkaline-phosphatase-conjugated avidin-biotin complex system. Cultured synovial fibroblasts and chrondrocytes were treated with either 1alpha,25(OH)(2)D(3) or interleukin (IL)-1beta, or both. Conditioned medium was assayed for MMP and PGE(2) by enzyme-linked immunosorbent assay (ELISA), and the results were normalised relative to control values.

RESULTS

The rheumatoid synovial tissue specimens (n=18) immunostained for VDRs showed positive staining but at variable distributions and in no observable pattern. VDR-positive cells were also observed in association with some cartilage-pannus junctions (the rheumatoid lesion). MMP production by RSFs in monolayer culture was not affected by treatment with 1alpha,25(OH)(2)D(3) alone, but when added simultaneously with IL-1beta the stimulation by IL-1beta was reduced from expected levels by up to 50%. In contrast, 1alpha,25(OH)(2)D(3) had a slight stimulatory effect on basal production of MMPs 1 and 3 by monolayer cultures of HACs, but stimulation of MMP-1 by IL-1beta was not affected by the simultaneous addition of 1alpha,25(OH)(2)D(3) whilst MMP-3 production was enhanced (Table 1). The production of PGE(2) by RSFs was unaffected by 1alpha,25(OH)(2)D(3) addition, but when added concomitantly with IL-1beta the expected IL-1beta-stimulated increase was reduced to almost basal levels. In contrast, IL-1beta stimulation of PGE(2) in HACs was not affected by the simultaneous addition of 1alpha,25(OH)(2)D(3)(Table 2). Pretreatment of RSFs with 1alpha,25(OH)(2)D(3) for 1h made no significant difference to IL-1beta-induced stimulation of PGE(2), but incubated for 16h suppressed the expected increase in PGE(2) to control values. This effect was also noted when 1alpha,25(OH)(2)D(3) was removed after the 16h and the IL-1beta added alone. Thus it appears that 1alpha,25(OH)(2)D(3) does not interfere with the IL-1beta receptor, but reduces the capacity of RSFs to elaborate PGE(2) after IL-1beta induction. Cells within the rheumatoid lesion which expressed VDR were fibroblasts, macrophages, lymphocytes and endothelial cells. These cells are thought to be involved in the degradative processes associated with rheumatoid arthritis (RA), thus providing evidence of a functional role of 1apha,25(OH)(2)D(3) in RA. MMPs may play important roles in the chondrolytic processes of the rheumatoid lesion and are known to be produced by both fibroblasts and chondrocytes. The 1alpha,25(OH)(2)D(3) had little effect of basal MMP production by RSFs, although more pronounced differences were noted when IL-1beta-stimulated cells were treated with 1alpha,25(OH)(2)D(3), with the RSF and HAC showing quite disparate responses. These opposite effects may be relevant to the processes of joint destruction, especially cartilage loss, as the ability of 1alpha,25(OH)(2)D(3) to potentiate MMP-1 and MMP-3 expression by 'activated' chondrocytes might facilitate intrinsic cartilage chondrolysis in vivo. By contrast, the MMP-suppressive effects observed for 1alpha,25(OH)2D3 treatment of 'activated' synovial fibroblasts might reduce extrinsic chondrolysis and also matrix degradation within the synovial tissue. Prostaglandins have a role in the immune response and inflammatory processes associated with RA. The 1alpha,25(OH)2D3 had little effect on basal PGE2 production by RSF, but the enhanced PGE2 production observed following IL-1beta stimulation of these cells was markedly suppressed by the concomitant addition of 1alpha,25(OH)2D3. As with MMP production, there are disparate effects of 1alpha,25(OH)2D3 on IL-1beta stimulated PGE2 production by the two cell types; 1alpha,25(OH)2D3 added concomitantly with IL-1beta had no effect on PGE2 production by HACs. In summary, the presence of VDRs in the rheumatoid lesion demonstrates that 1alpha,25(OH)2D3 may have a functional role in the joint disease process. 1 alpha,25(OH)2D3 does not appear to directly affect MMP or PGE2 production but does modulate cytokine-induced production.

Vitamin D differentially regulates B7.1 and B7.2 expression on human peripheral blood monocytes

The hormonal active form of vitamin D3, 1,25-dihydroxyvitamin D3 (1, 25(OH)2D3), inhibits (through an unknown mechanism) the ability of monocytes/macrophages to induce T-cell activation. For T cells to be optimally activated, recognition of antigen/major histocompatibility complexes (MHC) by the T-cell receptor (TCR) must be accompanied by a second costimulatory signal. Considerable experimental data now suggest that this costimulatory signal is predominantly generated by B7.1 and/or B7.2 molecules, expressed on antigen-presenting cells (APC), when engaged to their counter-receptor, CD28, present on T cells. To determine whether the inhibitory effect of 1,25(OH)2D3 on monocytes/macrophages might involve modulation of the expression of B7.1 and B7.2 molecules, we analysed (by flow cytometry) the influence of 1,25(OH)2D3 and an analogue, KH 1060, on the expression of these two molecules at the surface of resting human peripheral blood monocytes. In parallel, we tested the effect of these two agents on human monocyte expression of cell-surface markers (CD14 and CD4) and antigen-presenting molecules (MHC class I and MHC class II). Our results showed that both 1,25(OH)2D3 and KH 1060 inhibited the basal expression of B7.2 in a dose- and time-dependent manner, without affecting B7.1. Moreover, these two compounds increased CD14 and reduced MHC class II and CD4 expression. Furthermore, the effect of 1,25(OH)2D3 on B7 molecule expression in combination with lipopolysaccharide (LPS) or cytokines, including interleukin-10 (IL-10), interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha), was studied. The 1,25(OH)2D3-induced B7.2 down-regulation was still detectable when monocytes were activated by IL-10, IFN-gamma and TNF-alpha but not with LPS. Moreover, the induction of B7.1 by TNF-alpha was inhibited by addition of 1, 25(OH)2D3. We conclude that the ability of 1,25(OH)2D3 to decrease B7.2 expression on human monocytes might contribute to its inhibitory effect on APC-dependent T-cell activation and to its immunosuppressive properties observed in autoimmune diseases and organ transplantation.

1,25-Dihydroxyvitamin D3 enhances degranulation of mast cells

The mast cell lines rat basophilic leukemia (RBL) and mouse C57 cells respond to IgE/antigen complexes by degranulation. Treatment of these cells with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), (10-100 nM) for 24-48 h enhanced IgE/antigen-induced exocytosis as monitored by release of hexosaminidase. A short term incubation with the hormone did not affect exocytosis, ruling out a rapid non genomic mechanism. The presence of vitamin D receptors, demonstrated by immunoblotting and the lack of effect of 24,25(OH)2D3 suggest a role for these receptors in the enhancing effect. 1,25(OH)2D3 also enhanced exocytosis induced by the calcium ionophore A23187 in the presence or absence of phorbol ester indicating modulation of events distal to signal transduction. 1,25(OH)2D3 enhanced exocytosis in the presence of cytochalasin D, indicating that the action of the hormone is not due to effects on microfilament structure. The results of this study suggest that 1,25(OH)2D3 may affect the allergic or pro-inflammatory potential of mast cells.

Positive correlation between levels of IL-1 or IL-2 and 1,25(OH)2D/25-OH-D ratio in synovial fluid of patients with rheumatoid arthritis

The present study determined the levels in synovial fluid (SF) of vitamin D metabolites (1,25-dihydroxyvitamin D (1,25(OH)2D), 24,25-dihydroxyvitamin D (24,25(OH)2D) and 25-hydroxyvitamin D (25-OH-D)), and of the cytokines. We evaluated SF from 21 patients with rheumatoid arthritis (RA) and 6 patients with osteoarthritis (OA). The levels of vitamin D metabolites in SF, as determined by two different extraction methods, were significantly correlated (p < 0.05, n=7). The levels of 3 vitamin D metabolites were significantly higher in the RA SF than in OA SF (p < 0.05). The ratio of 1,25(OH)2D/25-OH-D in RA SF, which is presumed to reflect the activity of 25-OH-D-1-hydroxylase (1-OH-ase), was positively correlated with the levels of interleukin-1alpha (IL-1alpha), IL-1beta, and IL-2 in such SF, and was significantly higher than that in sera from RA patients. This suggests an important role for these cytokines in the activation of 1-OH-ase in RA synovium. The ratio of 24,25(OH)2D/25-OH-D, which is presumed to reflect 25-OH-D-24-hydroxylase (24-OH-ase) activity, was significantly correlated with 1,25(OH)2D levels only in RA SF, but not in sera from RA patients, suggesting a local regulation of vitamin D metabolism that 1,25-(OH)2D induces 24-OH-ase as in other target cells. Our observations suggested that 1,25(OH)2D and 24,25(OH)2D are produced locally from 25-OH-D in RA synovium, and that the syntheses of 1,25(OH)2D and 24,25(OH)2D may be affected by IL-1/IL-2 and 1,25(OH)2D in RA SF, respectively.

Human osteoclast formation and bone resorption by monocytes and synovial macrophages in rheumatoid arthritis

OBJECTIVE

To determine whether synovial macrophages and monocytes isolated from patients with rheumatoid arthritis patients are capable of differentiating into osteoclastic bone resorbing cells; and the cellular and humoral conditions required for this to occur.

METHODS

Macrophages isolated from the synovium and monocytes from the peripheral blood of rheumatoid arthritis patients were cultured on bone slices and coverslips, in the presence and absence of UMR 106 rat osteoblast-like cells, 1,25-dihydroxy vitamin D3 (1,25(OH)2D3) and macrophage colony stimulating factor (M-CSF), and assessed for cytochemical and functional evidence of osteoclast differentiation.

RESULTS

Isolated calcitonin receptor (CTR), tartrate resistant acid phosphatase (TRAP), and vitronectin receptor (VNR) negative, CD11b and CD14 positive monocytes and macrophages differentiated into CTR, TRAP, and VNR positive multinucleated cells capable of extensive lacunar bone resorption when co-cultured for 14 d with UMR 106 cells in the presence 1,25(OH)2D3 and M-CSF.

CONCLUSIONS

Mononuclear phagocytes (monocytes and macrophages) from rheumatoid arthritis patients are capable of differentiating into multinucleated cells showing all the cytochemical and functional criteria of mature osteoclasts. Synovial macrophage-osteoclast differentiation may represent an important cellular mechanism in the bone destruction associated with rheumatoid arthritis.

Differential effects of 1,25-(OH)2D3 on acyl hydrolase and cyclooxygenase activities in interleukin 1 beta-stimulated human synovial fibroblast cultures

Effects of proinflammatory cytokines on synovial fibroblasts are considered to play a role in the accumulation of prostaglandin E2 (PGE2) in the inflamed joint in rheumatoid arthritis. We have previously shown that interleukin 1 beta (IL-1 beta) induces PGE2 production in synovial fibroblast cultures and that this effect is suppressed by the active metabolite of vitamin D3, 1,25-(OH)2D3. To study the mechanism of the inhibitory action of 1,25-(OH)2D3, its effect on acyl hydrolase (arachidonic acid (AA) release) and cyclooxygenase (COX) activities were investigated. Our findings indicate that IL-1 beta caused an increase in AA release and COX activity and that in the presence of 1,25-(OH)2D3 AA release, but not COX activity, is suppressed. In comparison, dexamethasone, which also inhibits IL-1 beta induction of PGE2, had inhibitory effects on both parameters.

Vitamin D3 metabolism in patients with rheumatic diseases: low serum levels of 25-hydroxyvitamin D3 in patients with systemic lupus erythematosus

1,25-dihydroxyvitamin D3 (1,25(OH)2 D3) has been shown to modulate lymphocyte activation in vitro. Through binding to specific receptors 1,25-(OH)2 D3 inhibits proliferation, immunoglobulin production and the release of cytokines. Moreover, 1,25-(OH)2 D3 is efficiently produced by activated monocytes. These findings suggest that 1,25-(OH)2 D3 may play a role as a regulator of immunological activation. Consequently, we found it of interest to study the serum levels of the two major metabolites of vitamin D3 in patients with systemic lupus erythematosus (SLE) (n = 21), rheumatoid arthritis (RA) (n = 29) and osteoarthritis (n = 12). In patients with SLE the levels of 25-OH D3 were below those of the healthy controls (p = 0.0008) and OA (p = 0.0168). The levels 1,25-(OH)2 D3 corresponded to normal levels. There were no significant correlations between 25-OH D3 levels and clinical or paraclinical disease manifestations. Further, the phenotypic distribution of Gc-globulin, which binds vitamin D3 metabolites in circulation, was normal. The serum concentrations of 1,25-(OH)2 D3 and 25-OH D3 in patients with RA and OA corresponded to those of the controls. Although the cause of the reduced 25-OH D3 levels in SLE patients is unclear, possible beneficial effects of administration of vitamin D to these patients should be considered.

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.

Synthesis of 1,25-dihydroxyvitamin D3 by rat brain macrophages in vitro

Cultured microglial cells were examined for their ability to metabolize 25-hydroxyvitamin D3 (25-(OH) D3). Upon exposure to lipopolysaccharide, microglial cells produced a vitamin D metabolite which comigrated with synthetic 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) in two different systems of high performance liquid chromatography. This metabolite had the same affinity as synthetic 1,25-(OH)2D3 for the chick intestinal 1,25-(OH)2D3 receptor. Lipopolysaccharide-stimulated microglial cells incubated with 3 nM of 25-(OH) D3 synthesized up to 5.76 fmol 1,25-(OH)2D3/8 x 10(5) cells/2 hr. Microglial cells stimulated for 48 hr with interferon-gamma also produced a significant amount of 1,25-(OH)2D3 (4.17 fmol/8 x 10(5) cells/2 hr). In contrast, levels of 1,25-(OH)2D3 produced by resting microglial cells were barely detectable. It is concluded that activated brain macrophages may be committed to synthesize 1,25-(OH)2D3 in vitro. This raises the possibility that activation of microglial cells in vivo may be followed by an increase in the level of 1,25-(OH)2D3 in the central nervous system (CNS). These results support the emerging concept that the brain constitutes a target tissue for vitamin D metabolites.

Inhibition of human T lymphocyte proliferation and cytokine production by 1,25-dihydroxyvitamin D3. Differential effects on CD45RA+ and CD45R0+ cells

1,25-dihydroxyvitamin D3 (1,25-(OH)2 D3), the biologically active form of vitamin D3, has been shown to modulate lymphocyte functions in vitro. These effects are exerted through binding to specific receptors that are expressed in activated, but not in resting lymphocytes. 1,25-(OH)2 D3 inhibits lymphocyte proliferation, immunoglobulin production and the release of cytokines including interleukin-2 (IL-2) and interferon gamma (IFN gamma) by mitogen driven blood mononuclear cells (MNC). A distinction between CD45RA+ and CD45R0+ subsets of T cells has, however, proven extremely relevant in terms of immunoactivation and immunopathology. The present study was undertaken to evaluate effects of 1,25-(OH)2 D3 on proliferation and cytokine production by purified CD45RA+ and CD45R0+ T cells. 1,25-(OH)2 D3 caused a dose- and time-dependent reduction in phytohemagglutinin-(PHA) and poke-weed mitogen (PWM)-driven proliferation of purified CD45R0+ T cells. In contrast, proliferation of the CD45RA+ subset was unaffected by this treatment. Comparable levels of lymphotoxin (LT), IFN gamma and IL-2 were obtained in cultures of both subsets. 1,25-(OH)2 D3 reduced these levels, but the suppressive effect of the hormone was delayed in cultures of CD45RA+ T cells. The results suggest that the CD45R0+ subset is relatively more sensitive than CD45RA+ subset to the inhibitory effects of 1,25-(OH)2 D3. This finding may be of pharmacological interest, because the CD45R0+ subset plays a key role in immune activation and because these cells have been associated with the pathogenesis of autoimmune diseases such as rheumatoid arthritis and multiple sclerosis.

Low serum vitamin D metabolites in women with rheumatoid arthritis

The etiology of osteoporosis associated with rheumatoid arthritis (RA) is unknown. We studied the calcium and vitamin D metabolism in 143 women with RA (mean age 50.7 years). Albumin corrected serum calcium was normal. Serum alkaline phosphatase was increased in 29 percent of cases. Serum vitamin D levels were frequently very low. In 16 percent of the RA patients serum 25(OH)D concentration was below 12.5 nmol/L, which is arbitrarily considered as the limit of vitamin D deficiency osteomalacia. In the winter season 73 percent of the patients had serum 1,25(OH)2D levels below the seasonally adjusted normal range. The lowest values were found in patients with high disease activity. We suggest that there is a disturbance in vitamin D metabolism in RA. This might play a role in osteoporosis associated with RA.

1,25-Dihydroxyvitamin D3 inhibits cytokine production by human blood monocytes at the post-transcriptional level

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] inhibits lymphocyte proliferation and production of antibodies and lymphokines such as interleukin (IL)-2 and interferon gamma. These lymphocyte functions are dependent upon cytokines, including IL-1 alpha, IL-1 beta, IL-6 and tumour necrosis factor alpha (TNF-alpha), produced by the antigen presenting cells. In the present study we examined the effect of 1,25-(OH)2D3 on the production of these cytokines, as well as superoxide generation by freshly isolated mononuclear cells and partially purified monocytes. The immediate precursor of 1,25(OH)2D3, 25-OH D3, and the synthetic analogue MC 903 ('Calcipotriol') were examined in parallel. 1,25-(OH)2D3 dose-dependently inhibited the production of IL-alpha, IL-6 and TNF-alpha by Escherichia coli lipopolysaccharide (LPS)-stimulated monocytes, without affecting superoxide production. MC 903 had comparable effects while 25-OH D3 was ineffective. The inhibition caused by 1,25-(OH)2D3 was not abolished by supraoptimal concentrations of LPS or indomethacin. 1,25-(OH)2D3 had similar effects on secreted and cell-associated IL-alpha. Nuclear run-off analysis indicated that inhibition of these cytokines was not caused by impaired production of mRNA. Taken together, the study demonstrates a vitamin D-induced inhibitory effect of LPS-driven monokine production, which is most likely a vitamin D-receptor mediated phenomenon exerted at a post-transcriptional, presecretory level. Impaired monokine production may be of importance in 1,25-(OH)2D3-mediated inhibition of lymphocyte functions in vitro.

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.

Regulation of 1 alpha, 25-dihydroxyvitamin D3 synthesis in macrophages from arthritic joints by phorbol ester, dibutyryl-cAMP and calcium ionophore (A23187)

Phorbol 12-myristate 13-acetate (100 nM), a potent protein kinase C and macrophage activator, has a biphasic affect on 25(OH)D3-1 alpha-hydroxylase activity in synovial fluid macrophages from arthritis patients. After 5 h, 1 alpha, 25(OH)D3 synthesis fell from 5.2 +/- 0.1 to 1.6 +/- 0.2 pmol/h per 10(6) cells, however, after 24 h and 48 h, synthesis increased to 17.4 +/- 0.3 and 22.3 +/- 1.4 pmol/h per 10(6) cells, respectively. Although an independent short-term mechanism is suggested, protein kinase C may promote macrophage activation, thus increasing long-term 25(OH)D3-1 alpha-hydroxylase expression. Intracellular calcium and cAMP are unlikely to activate the enzyme, since 0.1 microM of the calcium ionophore, A23187, and 1 mM dibutyryl-cAMP inhibited synthesis by 87% and 79%, respectively, after 24 h.

1,25-Dihydroxyvitamin D3-mediated suppression of T lymphocyte functions and failure of T cell-activating cytokines to restore proliferation

1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) has been shown to be a potent inhibitor of lymphocyte proliferation in vitro. The present study was undertaken to determine if this is caused by a direct effect on the lymphocytes, and to evaluate to what degree this suppression may be restored by the addition of cytokines. 1,25-(OH)2D3, > or = 10(-10) M, significantly inhibited the proliferation of pokeweed mitogen (PWM)-driven human peripheral blood mononuclear cells (MNC). Depletion of monocytes did not alter the response to 1,25-(OH)2D3. The antiproliferative effect was preceded by decreased production of interleukin (IL)-1 alpha and lymphotoxin (LT), both of which are crucially involved in T cell activation. However, the suppressive effect of 1,25-(OH)2D3, seen in MNC cultures stimulated with PWM alone, was of the same magnitude as the effect seen in MNC cultures stimulated with a combination of PWM and recombinant (r)IL-1 alpha, rIL-6, recombinant tumour necrosis factor (rTNF) alpha, rIL-2 or rLT, as well as PWM plus conditioned medium. Although pretreatment of monocytes for 2 h with 1,25-(OH)2D3 caused significant reduction in the release of IL-1 alpha and TNF alpha, reconstitution of monocyte-depleted cultures with similarly treated monocytes had no inhibitory effect on the proliferative response. In conclusion, even though it cannot be excluded that a low but critical number of monocytes are essential for the suppressive effect of 1,25-(OH)2D3-mediated inhibition of MNC proliferation, the inhibition is most likely the result of a direct effect on the lymphocytes and independent of monocytes and exogenously added cytokines.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition by prostaglandin E1 and E2 of 1,25-dihydroxyvitamin D3 synthesis by synovial fluid macrophages from arthritic joints

Previous work has shown that renal metabolism of 25-dihydroxyvitamin D3 (25(OH)D3) to the active metabolite, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) is stimulated by prostaglandin E2 and inhibited by acetylsalicylate (aspirin). As prostaglandins are primary inflammatory mediators and synovial fluid macrophages are known to synthesise 1,25(OH)2D3 in vitro, the effects of prostaglandin E1, prostaglandin E2, and aspirin on the metabolism of 25(OH)D3 by cells cultured from synovial fluid of patients with inflammatory arthritis were investigated. Most cultures contained non-proliferating macrophages which formed 1,25(OH)2D3; however, two of 13 cultures contained colonies of rapidly proliferating fibroblast-like cells which formed 24,25(OH)2D3 (24,25(OH)2D3). Prostaglandin E1 and prostaglandin E2 (0.01-10 mumol/l) induced marked inhibition of 1,25(OH)2D3 synthesis (up to 94%) in a dose dependent manner after preincubations of 24 hours but not over straightforward six hour incubations. Exposure of macrophages to aspirin (1 mumol/l-1 mmol/l) for 24 hours did not affect 1,25(OH)2D3 synthesis unless the cells had been pretreated with lipopolysaccharides, in which instance 1 mM aspirin increased 1,25(OH)2D3 synthesis. Lipopolysaccharide is a macrophage activating factor which stimulates macrophages to form 1,25(OH)2D3, and it also induces prostaglandin synthesis which would be inhibited by aspirin. Taken together these results suggest that prostaglandin E1 and prostaglandin E2 synthesised by macrophages may act in an autocrine manner to attenuate the ability of macrophage activating factors, such as lipopolysaccharide, to stimulate 1,25(OH)2D3 synthesis. Prostaglandins synthesised by other inflammatory cells may also inhibit 1,25(OH)2D3 synthesis in a paracrine manner. In contrast, prostaglandin E2 and aspirin had limited effects on fibroblast 24,25(OH)2D3 synthesis. This study shows that the effects of prostaglandin E1, prostaglandin E2, and aspirin in macrophages contrast with those previously reported for the renal 25(OH)D3-1alpha-hydroxylase, where prostaglandin E2 stimulated and aspirin inhibited enzyme activity. These results further emphasise that synthesis of 1,25(OH)2D3 in non-renal sites is independently regulated, which is consistent with it having an immunological role at a local level rather than playing a part in systemic calcium homeostasis.

Decreased accessory cell function and costimulatory activity by 1,25-dihydroxyvitamin D3-treated monocytes

To characterize the mechanism(s) by which 1,25-dihydroxyvitamin D3 (calcitriol) modulates the costimulatory capacity of monocytes, we examined the effect of calcitriol pretreatment of monocytes on their capacity to promote T cell proliferation (accessory cell function). Correlation of calcitriol-dependent changes in monocyte accessory cell function and alterations in phenotype and cytokine production, and the dependence of these changes on cell viability, were studied. Calcitriol pretreatment induced a defect in accessory cell function that was evident with fixed monocytes, suggesting a cell-surface-associated mechanism. Altered accessory cell function did not correlate with changes in HLA-DR antigen expression and was unaffected by concurrent treatment with interferon-gamma. Calcitriol treatment did not alter either the expression of adhesion molecules or monocytic production of interleukin-1 beta (IL-1 beta) or IL-6. Exogenous IL-1 or IL-6 did not overcome the impaired costimulatory activity of calcitriol-treated monocytes. Thus, calcitriol treatment reduces the capacity of monocytes to promote lectin-induced T cell activation at the level of the plasma membrane, perhaps through altered expression of an uncharacterized molecule important in monocyte-T cell interactions. At chronically inflamed sites, elaboration of calcitriol by activated macrophages may regulate the ability of monocytes to induce both antigen-dependent and antigen-independent T cell proliferation.

Differential metabolism of 25-hydroxyvitamin D3 by cultured synovial fluid macrophages and fibroblast-like cells from patients with arthritis

Differential metabolism of 25-hydroxyvitamin D3 (25(OH)D3) has been shown for macrophages and fibroblast-like cells (possibly synoviocytes) cultured for two to 50 days after isolation from the synovial fluid of 12 patients with various forms of inflammatory arthritis. Macrophages synthesised the active metabolite of vitamin D3, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the synthesis of which was increased by bacterial lipopolysaccharide, a known macrophage activating factor. In contrast, fibroblast-like cells formed 24, 25-dihydroxyvitamin D3 (24,25(OH)2D3), synthesis of which was stimulated by 1,25(OH)2D3 and inhibited by lipopolysaccharide. The synthesis of 1,25(OH)2D3 and 24,25(OH)2D3 by macrophages and fibroblast-like cells respectively was inhibited by ketoconazole, indicating that both hydroxylases are dependent on cytochrome P-450. Mean (SEM) synovial fluid and serum 25(OH)D3 concentrations were 16.7 (1.7) and 22.2 (2.6) ng/ml and those of 1,25(OH)2D3 were 29.4 (4.8) and 43.3 (4.0) pg/ml respectively. In most cases concentrations were lower in synovial fluid than in paired serum samples, but in two patients 1,25(OH)2D3 concentrations were greater in synovial fluid than in serum, suggesting local synthesis within the affected joints.

Evidence for nonrenal synthesis of 1,25-dihydroxyvitamin D in patients with inflammatory arthritis

The extrarenal synthesis of 1,25-dihydroxyvitamin D [1,25-(OH)2D] is a characteristic of activated macrophages and has been demonstrated to occur in vitro in synovial fluid macrophages from patients with inflammatory arthritis. To examine whether such synthesis occurs in vivo, 19 patients with rheumatoid arthritis, 5 patient controls, and 5 healthy controls received a challenge oral dose of 250 micrograms 25-hydroxyvitamin D3 (25-OHD3) and the serum 1,25-(OH)2D3 response was measured. The median rise in serum 1,25-(OH)2D3 was significantly greater (22 pg/ml) in the rheumatoid patients compared to either of the control groups (8 pg/ml), although the increase in precursor 25-OHD3 was similar in all groups. The serum 1,25-(OH)2D concentration did not rise above the normal upper limit in any of the control subjects but exceeded the normal range in 8 of the rheumatoid patients. Extrarenal 1,25-(OH)2D synthesis is substrate dependent, unlike renal 1 alpha-hydroxylation, which is homeostatically controlled. Excessive 1,25-(OH)2D3 synthesis in the rheumatoid group on raising the 25-OHD3 concentration is indicative of nonrenal production of the hormonal metabolite. Further evidence for substrate-dependent extrarenal synthesis came from measurements of 25-OHD and 1,25-(OH)2D in paired serum and synovial fluid samples from 19 patients with inflammatory arthritis, including 15 with rheumatoid arthritis. Synovial fluid 1,25-(OH)2D was usually present at a lower concentration than serum 1,25(OH)2D, with which it was strongly correlated (Kendall's R = 0.46, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)