Treatment of autoimmune diabetes recurrence in non-obese diabetic mice by mouse interferon-beta in combination with an analogue of 1alpha,25-dihydroxyvitamin-D3

Vitamin D and Omega-3 Polyunsaturated Fatty Acids in Type 1 Diabetes modulation

BACKGROUND

Type 1 diabetes (T1D) is a chronic autoimmune disease that affects people globally. Usually developed during childhood, T1D is characterized by the destruction of pancreatic β-cells due to immune cell attack and the establishment of an inflammatory process.

OBJECTIVE

The study aimed to investigate the effects of vitamin D through its nuclear receptor and the ω-3 polyunsaturated fatty acids (PUFAs) through their lipid derivatives in T1D modulation. Both components exert anti-inflammatory activity and act directly on cells of the immune system, attenuating the destruction of insulin-producing cells. Furthermore, they lead to a better glycemic level, reducing the need for insulin and a normal immune state, such as C-peptide maintenance.

METHOD

Presently, our review highlights the significant studies that evaluated the supplementation of vitamin D and ω-3 PUFAs in humans and animal models in the modulation of T1D.

CONCLUSION

The data collected suggests that supplementation can provide potential benefits, mainly when done early in the diagnosis, since it reduces the need for insulin and the risk of complications generated by the disease.

The Role of Vitamin D and Omega-3 PUFAs in Islet Transplantation

Recurrence of autoimmunity and allograft rejection represent major challenges that impact the success of islet transplantation. Despite the remarkable improvements achieved in immunosuppression strategies after the publication of the Edmonton protocol, long-term data of intra-hepatic islet transplantation show a gradual decline in beta-cell function. Therefore, there is a growing interest in the investigation of novel, safe and effective anti-inflammatory and immunomodulatory strategies able to promote long-term islet graft survival and notable improvements in clinical outcomes of islet transplant recipients. Vitamin D has been shown to exert anti-inflammatory and immunomodulatory effects. Pre-clinical studies investigating the use of vitamin D and its analogs (alone or in combination with immunosuppressive agents and/or other anti-inflammatory agents, such as omega-3 polyunsaturated fatty acids) showed beneficial results in terms of islet graft survival and prevention of recurrence of autoimmunity/allograft rejection in animal models of syngeneic and allogeneic islet transplantation. Moreover, epidemiologic studies demonstrated that vitamin D deficiency is highly prevalent after solid organ transplantation (e.g., heart, liver or kidney transplantation). However, studies that critically assess the prevalence of vitamin D deficiency among islet transplant recipients have yet to be conducted. In addition, prospective studies aimed to address the safety and efficacy of vitamin D supplementation as an adjuvant immunomodulatory strategy in islet transplant recipients are lacking and are therefore awaited in the future.

Cytokines and Pancreatic β-Cell Apoptosis

The discovery 30 years ago that inflammatory cytokines cause a concentration, activity, and time-dependent bimodal response in pancreatic β-cell function and viability has been a game-changer in the fields of research directed at understanding inflammatory regulation of β-cell function and survival and the causes of β-cell failure and destruction in diabetes. Having until then been confined to the use of pathophysiologically irrelevant β-cell toxic chemicals as a model of β-cell death, researchers could now mimic endocrine and paracrine effects of the cytokine response in vitro by titrating concentrations in the low to the high picomolar-femtomolar range and vary exposure time for up to 14-16h to reproduce the acute regulatory effects of systemic inflammation on β-cell secretory responses, with a shift to inhibition at high picomolar concentrations or more than 16h of exposure to illustrate adverse effects of local, chronic islet inflammation. Since then, numerous studies have clarified how these bimodal responses depend on discrete signaling pathways. Most interest has been devoted to the proapoptotic response dependent upon mainly nuclear factor κ B and mitogen-activated protein kinase activation, leading to gene expressional changes, endoplasmic reticulum stress, and triggering of mitochondrial dysfunction. Preclinical studies have shown preventive effects of cytokine antagonism in animal models of diabetes, and clinical trials demonstrating proof of concept are emerging. The full clinical potential of anticytokine therapies has yet to be shown by testing the incremental effects of appropriate dosing, timing, and combinations of treatments. Due to the considerable translational importance of enhancing the precision, specificity, and safety of antiinflammatory treatments of diabetes, we review here the cellular, preclinical, and clinical evidence of which of the death pathways recently proposed in the Nomenclature Committee on Cell Death 2012 Recommendations are activated by inflammatory cytokines in the pancreatic β-cell to guide the identification of antidiabetic targets. Although there are still scarce human data, the cellular and preclinical studies point to the caspase-dependent intrinsic apoptosis pathway as the prime effector of inflammatory β-cell apoptosis.

Vitamin D and diabetes: Where do we stand?

The potential beneficial effects of supplementing vitamin D or treatment with pharmacological doses of vitamin D in the prevention or cure of diseases like type 1 (T1D) or type 2 diabetes (T2D) remains the subject of debate. Data from epidemiological and association studies clearly indicate a correlation between vitamin D deficiency and a higher prevalence of both forms of diabetes. In animal models, vitamin D deficiency predisposes to type 1 and type 2 diabetes, whereas high doses of vitamin D or its active hormonal form, 1,25-dihydroxyvitamin D, prevent disease. Large scale, randomized, blinded prospective studies however, remain lacking. Here we discuss the current literature on a role for vitamin D in diabetes. We propose, in particular, to avoid vitamin D deficiency in individuals at risk of developing T1D or T2D. Applying international guidelines on supplementation of vitamin D using small daily doses of vitamin D (500-1000IU) may contribute to reduce the burden of diabetes by preventing vitamin D deficiency. Any other recommendations are at present not supported by data.

Beyond glycemic control in diabetes mellitus: effects of incretin-based therapies on bone metabolism

Diabetes mellitus (DM) and osteoporosis (OP) are common disorders with a significant health burden, and an increase in fracture risk has been described both in type 1 (T1DM) and in type 2 (T2DM) diabetes. The pathogenic mechanisms of impaired skeletal strength in diabetes remain to be clarified in details and they are only in part reflected by a variation in bone mineral density. In T2DM, the occurrence of low bone turnover together with a decreased osteoblast activity and compromised bone quality has been shown. Of note, some antidiabetic drugs (e.g., thiazolidinediones, insulin) may deeply affect bone metabolism. In addition, the recently introduced class of incretin-based drugs (i.e., GLP-1 receptor agonists and DPP-4 inhibitors) is expected to exert potentially beneficial effects on bone health, possibly due to a bone anabolic activity of GLP-1, that can be either direct or indirect through the involvement of thyroid C cells. Here we will review the established as well as the putative effects of incretin hormones and of incretin-based drugs on bone metabolism, both in preclinical models and in man, taking into account that such therapeutic strategy may be effective not only to achieve a good glycemic control, but also to improve bone health in diabetic patients.

Low doses of anti-CD3, ciclosporin A and the vitamin D analogue, TX527, synergise to delay recurrence of autoimmune diabetes in an islet-transplanted NOD mouse model of diabetes

AIMS/HYPOTHESIS

Anti-CD3 monoclonal antibodies remain the most promising immune therapy for reversing recent-onset type 1 diabetes. However, current clinical trials have revealed their major drawback, namely the narrow therapeutic window in which low doses are ineffective and higher doses that preserve functional beta cell mass cause side effects. Strategies that sidestep these limitations while preserving or improving anti-CD3's therapeutic efficiency are essential. We hypothesised that combining a potent vitamin D(3) analogue (TX527), ciclosporin A (CsA) and anti-CD3 would act to lower the dose while maintaining or even boosting therapeutic efficacy to counteract autoimmune destruction of transplanted islets.

METHODS

This study involved the use of syngeneic islet transplantation, immunofluorescence microscopy, immune phenotyping by flow cytometry, RT-PCR analysis, and in vitro and in vivo suppression assays.

RESULTS

Combination therapy with TX527, CsA and anti-CD3 was well tolerated on the basis of weight, bone and calcium variables. Remarkably, combining all three agents at sub-therapeutic doses greatly reduced recurrent autoimmune responses to a grafted islet mass (mean ± SEM: 79.5 ± 18.6 days; p < 0.01), by far exceeding the therapeutic efficacy of monotherapy (24.8 ± 7.3 days for anti-CD3) and dual therapy (25.5 ± 12.4 days for anti-CD3+CsA). Combination therapy surpassed anti-CD3 monotherapy in reducing islet infiltration by effector/memory phenotype CD8(+) T cells, as well as by reducing proinflammatory cytokine responses and increasing the frequency of T regulatory cells that were functional in vitro and in vivo, and acted in a cytotoxic T lymphocyte antigen 4-dependent manner.

CONCLUSIONS/INTERPRETATION

Combining the immunomodulatory actions of anti-CD3 mAb with CsA and the vitamin D(3) analogue, TX527, delivers therapeutic efficacy in an islet-transplanted NOD mouse model of diabetes.

Vitamin D supplementation modulates blood and tissue zinc, liver glutathione and blood biochemical parameters in diabetic rats on a zinc-deficient diet

Previous studies suggest a protective effect of vitamin D3 on zinc deficiency-induced insulin secretion and on pancreas β-cell function. The aim of this study was to investigate the effect of vitamin D on blood biochemical parameters, tissue zinc and liver glutathione in diabetic rats fed a zinc-deficient diet. For that purpose, Alloxan-induced diabetic rats were divided into four groups. The first group was fed a zinc-sufficient diet while the second group was fed a zinc-deficient diet. The third and fourth groups received zinc-sufficient or zinc-deficient diets plus oral vitamin D3 for 27 days. At the end of the experiment, blood, femur, pancreas, kidney and liver samples were taken from all rats. The serum, femur, pancreas, kidney and liver zinc concentrations, liver glutathione, serum alkaline phosphatase activity, daily body weight gain and food intake were lower in the zinc-deficient rats in comparison with those receiving adequate amounts of zinc. These values were increased in the zinc-deficient group that was supplemented with vitamin D3. The serum total cholesterol, triglycerides, total protein, urea, glutamate oxaloacetate transaminase, glutamate pyruvate transaminase and blood glucose values were higher in rats fed a zinc adequate diet, but their concentrations were decreased by vitamin D3 supplementation. The serum total protein levels were not changed by zinc deficiency and vitamin D3 supplementation. These results suggest that vitamin D3 modulates tissue zinc, liver glutathione and blood biochemical values in diabetic rats fed a zinc-deficient diet.

Vitamin D and diabetes

There is no doubt that vitamin D deficiency is the cause of several metabolic bone diseases, but vitamin D status is also linked to many major human diseases including immune disorders. Mounting data strengthen the link between vitamin D and diabetes, in particular T1D and T2D. Despite some inconsistencies between studies that associate serum 25(OH)D levels with the risk of developing T1D or T2D, there seems to be an overall trend for an inverse correlation between levels of 25(OH)D and both disorders. There is also compelling evidence that 1,25(OH)2D regulates b-cell function by different mechanisms, such as influencing insulin secretion by regulating intracellular levels of Ca2+, increasing β-cell resistance to apoptosis, and perhaps also increasing β-cell replication. The capacity of vitamin D, more specifically 1,25(OH)2D, to modulate immune responses is of particular interest for both the therapy and prevention of diabetes. In the case of T1D, vitamin D supplementation in prediabetic individuals could help prevent or reduce the initiation of autoimmune processes possibly by regulating thymic selection of the T-cell repertoire, decreasing the numbers of autoreactive T cells, and inducing Treg cells. Although immune modulation is generally discussed for the treatment of T1D, it is also relevant for T2D. Indeed, recent studies have shown that T2D patients have increased systemic inflammation and that this state can induce β-cell dysfunction and death. Supplementation trials with regular vitamin D for the protection against the development of T1D and T2D have generated some contradictory data, but many weaknesses can be identified in these trials as most were underpowered or open-labeled. However, the overwhelming strength of preclinical data and of the observational studies make vitamin D or its analogues strong candidates for the prevention or treatment of diabetes or its complications. However, proof of causality needs well-designed clinical trials and if positive, adequate dosing, regimen, and compound studies are needed to define the contribution of vitamin D status and therapy in the global diabetes problem. There are many confounding factors that need to be taken into consideration when translating successful vitamin D therapies in animal models into humans, for example, gender, age, lifestyle, and genetic background. To come to solid conclusions on the potential of vitamin D or its analogues in the prevention of or therapy for all forms of diabetes, it is clear that large prospective trials with carefully selected populations and end points will be needed, but should also receive high priority.

The effect of vitamin D supplementation on peripheral regulatory T cells and β cell function in healthy humans: a randomized controlled trial

BACKGROUND

Increasing evidence supports the role of vitamin D (vitD) in modifying the risk to develop type 1 diabetes (T1D) and other autoimmune diseases. VitD3 might stimulate regulatory T cells (Tregs), a central player in the maintenance of self-tolerance. In addition, direct effects of vitD on β-cell function are postulated. The aim of our study was to evaluate the effect of a high dose vitD supplementation on Tregs frequency (%Tregs) and β-cell function assessed by a mixed meal tolerance test (MMTT) in healthy humans.

METHODS

A double-blind, placebo controlled trial was performed in 59 healthy adult subjects (49% females). Subjects received oral vitD3 (140,000 IU monthly) or placebo for 3 months. %Tregs within 20,000 CD4+ T cells of peripheral blood was determined by multi-parametric FACS-analysis. A liquid MMTT was carried out before and after treatment.

RESULTS

%Tregs increased significantly in the vitD group, but remained unchanged in the placebo group. Fasting C-peptide concentrations did not change significantly in either group. Similarly, the mean AUC for C-peptide after 3 months and the change in mean values from baseline to the end of the treatment were comparable in both groups.

CONCLUSIONS

A short time high dose vitD3 supplementation significantly increased the frequency of Tregs, but did not further improve β-cell function in apparently healthy subjects. The immunomodulatory potential of vitD might be an important mechanistic link for the association of vitD and T1D.

1,25-Dihydroxyvitamin D3 alters murine dendritic cell behaviour in vitro and in vivo

BACKGROUND

Differentiation and maturation of dendritic cells yield a cell type with the ability to prime immune responses towards defence and destruction. 1,25(OH)2D3, the active form of vitamin D3, fosters the development of tolerogenic dendritic cells. This study aimed to evaluate the effects of 1,25(OH)2D3 on murine dendritic cell behaviour in vitro and in vivo.

METHODS

Dendritic cells were differentiated from bone marrow cells of female C57Bl/6 mice in the presence or absence of 10(-8) M 1,25(OH)2D3 for 8 days (IL4 and GM-CSF). Maturation was induced for 48 h (IFNγ, LPS and BALB/C islet homogenate antigen).

RESULTS

Bone marrow-derived dendritic cells displayed a different surface marker profile in the presence of 1,25(OH)2D3 with decreased MHC II, CD86 and CD80 and increased CCR5, DEC205, F4/80 and CD40, as well as lower IL6 and IL12 expression upon LPS/IFNγ stimulation. T-cell proliferation was significantly reduced when exposed to islet antigen-loaded 1,25D3-DCs as compared to control dendritic cells and IL4, IL10, TNFα and TGFβ levels were increased. In vivo, transfer of islet antigen-loaded control dendritic cells resulted in priming of the immune system and hyperacute islet allograft rejection (4/4), whereas this was prevented in 5/7 mice treated with islet antigen-loaded 1,25D3-DCs.

CONCLUSION

We conclude that in vitro 1,25(OH)2D3 exposure alters dendritic cell behaviour, converting them into a cell type that drives T cells away from destruction towards a regulatory phenotype.

Mechanisms of impaired bone strength in type 1 and 2 diabetes

Diabetes and osteoporosis are common and complex disorders with an enormous health burden that can be often associated especially in middle-age and elderly individuals. Although there is raising awareness of the higher fractures rates among patients with type 1 (DM1) and 2 (DM2) diabetes, there are few data available on the pathogenetic mechanisms responsible for this increased risk. Importantly, several experimental and clinical observations suggest that bone abnormalities associated with diabetes may differ, at least in part, from those associated with senile or post-menopausal osteoporosis. This implies that specific preventive and therapeutic strategies have to be developed and tested to prevent fractures in DM1 and DM2 patients. It is also likely that shared (i.e. due to glucose-toxicity) as well as different (i.e. due to insulin levels or other hormones) mechanisms may be associated with bone fragility in DM1 and DM2. Moreover, the hypothesis of an endocrine role of the skeleton in the regulation of glucose metabolism and insulin sensitivity has been recently proposed by experimental observations. This review summarizes the recent clinical and experimental advances on glucose tolerance, bone fragility and osteoporosis associated with diabetes.

No effect of the 1alpha,25-dihydroxyvitamin D3 on beta-cell residual function and insulin requirement in adults with new-onset type 1 diabetes

OBJECTIVE

To determine whether daily intake of 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] is safe and improves beta-cell function in patients with recently diagnosed type 1 diabetes.

RESEARCH DESIGN AND METHODS

Safety was assessed in an open study of 25 patients aged 18-39 years with recent-onset type 1 diabetes who received 0.25 microg 1,25(OH)(2)D(3) daily for 9 months. An additional 40 patients were randomly assigned to 0.25 microg 1,25(OH)(2)D(3) or placebo daily for 9 months and followed for a total of 18 months for safety, beta-cell function, insulin requirement, and glycemic control.

RESULTS

Safety assessment showed values in the normal range in nearly all patients, regardless of whether they received 1,25(OH)(2)D(3) or placebo. No differences in AUC C-peptide, peak C-peptide, and fasting C-peptide after a mixed-meal tolerance test between the treatment and placebo groups were observed at 9 and 18 months after study entry, with approximately 40% loss for each parameter over the 18-month period. A1C and daily insulin requirement were similar between treatment and placebo groups throughout the study follow-up period.

CONCLUSIONS

Treatment with 1,25(OH)(2)D(3) at a daily dose of 0.25 microg was safe but did not reduce loss of beta-cell function.

Vitamin D and diabetes

Type 1 (T1D) and type 2 (T2D) diabetes are considered multifactorial diseases in which both genetic predisposition and environmental factors participate in their development. Many cellular, preclinical, and observational studies support a role for vitamin D in the pathogenesis of both types of diabetes including: (1) T1D and T2D patients have a higher incidence of hypovitaminosis D; (2) pancreatic tissue (more specifically the insulin-producing beta-cells) as well as numerous cell types of the immune system express the vitamin D receptor (VDR) and vitamin D-binding protein (DBP); and (3) some allelic variations in genes involved in vitamin D metabolism and VDR are associated with glucose (in)tolerance, insulin secretion, and sensitivity, as well as inflammation. Moreover, pharmacologic doses of 1,25-dihydroxyvitamin D (1,25(OH)(2)D), the active form of vitamin D, prevent insulitis and T1D in nonobese diabetic (NOD) mice and other models of T1D, possibly by immune modulation as well as by direct effects on beta-cell function. In T2D, vitamin D supplementation can increase insulin sensitivity and decrease inflammation. This article reviews the role of vitamin D in the pathogenesis of T1D and T2D, focusing on the therapeutic potential for vitamin D in the prevention/intervention of T1D and T2D as well as its complications.

A new role for vitamin D receptor activation in chronic kidney disease

Vitamin D has proven to be much more than a simple "calcium hormone." The fact that the vitamin D receptor has been found in cells not related to mineral metabolism supports that statement. The interest of nephrologists in vitamin D and its effects beyond mineral metabolism has increased over the last few years, evidencing the importance of this so-called "sunshine hormone." In the present review, we highlight the most recent developments in the traditional use of vitamin D in chronic kidney disease (CKD) patients, namely, the control of secondary hyperparathyroidism (sHPT). Furthermore, we also explore the data available regarding the new possible therapeutic uses of vitamin D for the treatment of other complications present in CKD patients, such as vascular calcification, left ventricular hypertrophy, or proteinuria. Finally, some still scarce but very promising data regarding a possible role of vitamin D in kidney transplant patients also are reviewed. The available data point to a potential beneficial effect of vitamin D in CKD patients beyond the control of mineral metabolism.

Impact of vitamin D receptor activity on experimental autoimmune prostatitis

Chronic non bacterial prostatitis is a chronic inflammatory syndrome. Its etiology and physiopathology are unclear and treatments are empirical and ineffective in most cases. Autoimmunity has been proposed as an etiology. In the present report, we investigated the impact of vitamin D receptor silencing, by use of VDR-KO NOD mice and the immune-modulating effect of the vitamin D3 analog TX527 on the development of Experimental Autoimmune Prostatitis in NOD mice. VDR-KO NOD mice developed a more aggressive form of autoimmune prostatitis characterized by a greater lymphoproliferative response against prostate antigen in vitro (6.92+/-4.77 vs. 2.47+/-0.41 21 days after disease induction, p<0.05) and higher levels of specific INFgamma secretion (471+/-6 vs. 386+/-5pg/ml, p<0.01). This was accompanied in vivo by more severe lesions and augmented mononuclear cell infiltration in the prostate gland. On the other hand, although analog-treated mice showed a significant reduction in the spleen T-cell specific proliferative response against prostate antigen in vitro, no effect on disease development was observed. We conclude that vitamin D receptor modulation holds the promise of interfering with autoimmune prostatitis. Introduction of more powerful analogs, or combinations with anti-T-cell reagents may represent therapeutic solutions for these group of patients.

Regulation of vitamin D homeostasis: implications for the immune system

Vitamin D homeostasis in the immune system is the focus of this review. The production of both the activating (25- and 1alpha-hydroxylase) and the metabolizing (24-hydroxylase) enzymes by cells of the immune system itself, indicates that 1,25(OH)(2)D(3) can be produced locally in immune reaction sites. Moreover, the strict regulation of these enzymes by immune signals is highly suggestive for an autocrine/paracrine role in the immune system, and opens new treatment possibilities.

Vitamin D and human health: lessons from vitamin D receptor null mice

The vitamin D endocrine system is essential for calcium and bone homeostasis. The precise mode of action and the full spectrum of activities of the vitamin D hormone, 1,25-dihydroxyvitamin D [1,25-(OH)(2)D], can now be better evaluated by critical analysis of mice with engineered deletion of the vitamin D receptor (VDR). Absence of a functional VDR or the key activating enzyme, 25-OHD-1alpha-hydroxylase (CYP27B1), in mice creates a bone and growth plate phenotype that mimics humans with the same congenital disease or severe vitamin D deficiency. The intestine is the key target for the VDR because high calcium intake, or selective VDR rescue in the intestine, restores a normal bone and growth plate phenotype. The VDR is nearly ubiquitously expressed, and almost all cells respond to 1,25-(OH)(2)D exposure; about 3% of the mouse or human genome is regulated, directly and/or indirectly, by the vitamin D endocrine system, suggesting a more widespread function. VDR-deficient mice, but not vitamin D- or 1alpha-hydroxylase-deficient mice, and man develop total alopecia, indicating that the function of the VDR and its ligand is not fully overlapping. The immune system of VDR- or vitamin D-deficient mice is grossly normal but shows increased sensitivity to autoimmune diseases such as inflammatory bowel disease or type 1 diabetes after exposure to predisposing factors. VDR-deficient mice do not have a spontaneous increase in cancer but are more prone to oncogene- or chemocarcinogen-induced tumors. They also develop high renin hypertension, cardiac hypertrophy, and increased thrombogenicity. Vitamin D deficiency in humans is associated with increased prevalence of diseases, as predicted by the VDR null phenotype. Prospective vitamin D supplementation studies with multiple noncalcemic endpoints are needed to define the benefits of an optimal vitamin D status.

Bone and mineral disorders in pre-dialysis CKD

Disorders in calcium, phosphorus, and parathyroid hormone (PTH) are common in chronic kidney disease (CKD) and may be associated with poor outcomes including a higher rate of CKD progression and increased death risk. Although these abnormalities have been examined extensively in patients with CKD stage 5 who are receiving chronic maintenance dialysis, they have not been studied to the same extent at earlier stages of CKD, in spite of the much larger numbers of patients in the early CKD population. We summarize the available literature on outcomes associated with bone and mineral disorders in patients with CKD not yet receiving maintenance dialysis. We have reviewed novel data linking fibroblast growth factor 23 (FGF-23) to phosphorus and vitamin D homeostasis. More rapid CKD progression is linked to hyperphosphatemia and its associated hyperparathyroidism and vitamin D deficiency. Hence, hyperphosphatemia may play a central role in the diverse disorders characterizing CKD. We provide a brief overview of the available treatment recommendations for bone and mineral disorders, with an emphasis on areas needing further research.

Diabetes and fragility fractures - a burgeoning epidemic?

Diabetes and osteoporosis are both diseases of epidemic proportions whose incidence is increasing worldwide. The etiology of osteoporosis is multifactorial and may differ for type 1(T1DM) as compared to type 2 (T2DM). Fragility fractures are common to both types of diabetes with hip fractures occurring more frequently in the elderly T2DM population. The use of oral PPAR gamma agonists in the treatment of T2DM has also added to the risk of fracture. This perspective discusses the etiologies and issues relating to the association of diabetes with osteoporosis and fractures and suggests some theories to clarify the underlying pathophysiology. Unfortunately at this time treatment for osteoporosis and fractures remains empirical.

Vitamin D3and the immune system: maintaining the balance in health and disease

1,25-Dihydroxyvitamin D3(1,25(OH)2D3), the active form of vitamin D3, is a central player in Ca and bone metabolism. More recently, important immunomodulatory effects have been attributed to this hormone. By binding to its receptor, the vitamin D receptor, 1,25(OH)2D3regulates the expression of various genes and consequently affects the behaviour of different cell types within the immune system. 1,25(OH)2D3can potently inhibit pathogenic T cells and gives rise to elevated numbers of regulatory T cells via the induction of tolerogenic dendritic cells. These immunomodulatory activities of 1,25(OH)2D3have also been proven usefulin vivo: administration of 1,25(OH)2D3in several animal models can prevent or cure different autoimmune diseases and graft rejection. To overcome the dose-limiting side effects of 1,25(OH)2D3on Ca and bone, less calcaemic structural analogues (alone or in combination with synergistically acting drugs or bone-resorption inhibitors) have been successfully used in animal models. Furthermore, as 1,25(OH)2D3also contributes to host defence against infectious agents by the induction of antimicrobial responses, this molecule might provide a new strategy to deal with drug-resistant infections. According to the pleiotropic effects of 1,25(OH)2D3in the immune system, increasing epidemiological data underline the importance of adequate vitamin D intakes in reducing the risk of several autoimmune diseases and infections such as tuberculosis.

Novel insights in the immune function of the vitamin D system: synergism with interferon-beta

The 1,25(OH)(2)D(3) analog, TX527 (19-nor-14,20-bisepi-23-yne-1,25(OH)(2)D(3)), has an interesting dissociation profile between its potent immunomodulatory and its calcemic effects in vivo. The strong immunomodulatory potency of TX527 is reflected by its ability to attenuate experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis (MS). At present most MS patients are being treated with systemic IFN-beta administration. The aim of this study was to investigate whether combining IFN-beta with TX527 could empower its EAE-protective effects. We evaluated also combinations with the standard immunosuppressant cyclosporin A (CsA). EAE was induced in SJL mice by PLP immunization, treatment was started 3 days before disease induction. The TX527+IFN-beta combination resulted in significant disease protection which was superior to the effect of both treatment separately. No disease amelioration, even aggravation, was obtained with the IFN-beta+CsA combination. By adding TX527 to the IFN-beta+CsA combination near complete protection from EAE was achieved (100% protection from paralysis, mean maximal score of 1.8+/-1.5, both p<0.05 versus controls and all individual treatments). From these data we conclude that adding TX527 to an IFN-beta and/or CsA treatment results in clear additional immunomodulatory effects in EAE prevention and is therefore a potentially interesting candidate to be considered in clinical intervention trials in MS.

Role of calcium-phosphorous disorders in the progression of renal failure

Among factors related to disturbed calcium-phosphate metabolism in chronic kidney disease, the following must be mainly considered as potential culprits in the progression of renal dysfunction: hyperphosphatemia, hyperparathyroidism, lack of active vitamin D, and possibly excess of the phosphaturic hormone FGF 23. Early experimental work suggested a parathyroid hormone (PTH)-independent beneficial role of phosphate restriction on progression in rats (animals with physiologic hyperphosphatemia), so that the generalization of the data is uncertain. Recent observational studies also found a correlation between S-phosphate and progression, but it remains uncertain whether the relationship is causal. There is very little direct experimental or clinical evidence for a role of PTH in accelerating progression, although the PTH1 receptor is expressed in podocytes and PTH affects podocyte function (i.e., Kf). It is undoubtedly a candidate that requires more sophisticated investigation. Recently, it has been shown that progression is significantly attenuated by calcimimetics (and equally by parathyroidectomy), but it is currently impossible to exclude a confounding effect of lower blood pressure values. The most solid evidence for an impact on progression exists for active vitamin D. In the past, it was widely assumed that vitamin D was "nephrotoxic." In retrospect, nephrotoxicity was the result of hypercalcemia. Recent evidence is overwhelming that 1,25(OH)2D3 and its analogues attenuate progression in noninflammatory and inflammatory models of chronic kidney disease. The main target cells identified so far are podocytes and mesangial cells. It is currently unknown whether the novel phosphaturic hormones have an impact on progression.

Advances in pancreatic islet transplantation in humans

With recent advances in methods of islet isolation and the introduction of more potent and less diabetogenic immunosuppressive therapies, islet transplantation has progressed from research to clinical reality. Presently, several international centres have demonstrated successful clinical outcomes with high rates of insulin independence after islet transplantation. Ongoing refinements in donor pancreas procurement and processing, developments in islet isolation and purification technology, and advances in novel immunological conditioning and induction therapies have led to the acceptance of islet transplantation as a safe and effective therapy for patients with type 1 diabetes. This review provides a historical perspective of islet transplantation, outlines the recent advances and current clinical outcomes, and addresses the present challenges and future directions in clinical islet transplantation.

Immunoregulation by 1,25-dihydroxyvitamin D3: basic concepts

1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), the biologically active metabolite of Vitamin D(3), not only regulates bone and calcium metabolism but also exerts other biological activities, including immunomodulation via the nuclear Vitamin D receptor expressed in antigen-presenting cells and activated T cells. This regulation is mediated through interference with nuclear transcription factors such as NF-AT and NF-kappaB or by direct interaction with Vitamin D responsive elements in the promoter regions of cytokine genes. Dendritic cells (DCs) are primary targets for the immunomodulatory activity of 1,25(OH)(2)D(3), as indicated by inhibited DC differentiation and maturation, leading to down-regulated expression of MHC-II, costimulatory molecules and IL-12. Moreover, 1,25(OH)(2)D(3) enhances IL-10 production and promotes DC apoptosis. Together, these effects of 1,25(OH)(2)D(3) inhibit DC-dependent T cell activation. Immunomodulation by 1,25(OH)(2)D(3) and its analogs in vivo has been demonstrated in different models of autoimmune diseases and transplantation. Moreover, combining analogs with other immunosuppressants leads to synergism in models of autoimmunity and transplantation. The availability of 1,25(OH)(2)D(3) analogs with immunomodulatory activity at non-hypercalcemic doses may allow exploitation of their immunomodulatory effects in a clinical setting of treatment of autoimmune diseases and prevention of allograft rejection.

Noncalcemic actions of vitamin D receptor ligands

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

The role of vitamin D in protecting type 1 diabetes mellitus

The relationship between autoimmune diabetes or type 1 diabetes mellitus and vitamin D has been reported in the literature. Many factors, environmental and genetic, have been known, as risk factors, to cause both type 1 diabetes and vitamin D deficiency. Vitamin D treatment has improved or prevented type 1 diabetes mellitus in animals and humans. Vitamin D also has been known to protect from autoimmune diseases in animal models. Therefore, it would be interesting to review the role of vitamin D in type 1 diabetes mellitus.

Vitamin D and diabetes

Vitamin D deficiency predisposes individuals to type 1 and type 2 diabetes, and receptors for its activated form-1alpha,25-dihydroxyvitamin D3-have been identified in both beta cells and immune cells. Vitamin D deficiency has been shown to impair insulin synthesis and secretion in humans and in animal models of diabetes, suggesting a role in the development of type 2 diabetes. Furthermore, epidemiological studies suggest a link between vitamin D deficiency in early life and the later onset of type 1 diabetes. In some populations, type 1 diabetes is associated with certain polymorphisms within the vitamin D receptor gene. In studies in nonobese diabetic mice, pharmacological doses of 1alpha,25-dihydroxyvitamin D3, or its structural analogues, have been shown to delay the onset of diabetes, mainly through immune modulation. Vitamin D deficiency may, therefore, be involved in the pathogenesis of both forms of diabetes, and a better understanding of the mechanisms involved could lead to the development of preventive strategies.

Deficiency of type I interferon contributes toSle2-associated component lupus phenotypes

OBJECTIVE

Studies in mice and humans have implicated type I interferon (IFN-I) in the pathogenesis of lupus. Given that the locus for IFN-I is positioned within the Sle2 murine lupus susceptibility interval on chromosome 4, we undertook this study to investigate whether differences in IFN-I levels might potentially contribute to the phenotypes ascribed to this locus.

METHODS

IFN-I, anti-IFN-I, isotype control antibody, or phosphate buffered saline was administered to C57BL/6 and B6.Sle2 mice, and the serologic and cellular phenotypes were studied. In addition, B6.Sle2 mice were examined for structural and expression polymorphisms in the IFN-I gene.

RESULTS

In both B6.Sle2 congenic mice and C57BL/6 control mice, antibody-mediated blockade of IFN-I augmented serum autoantibody levels and boosted B1a cell numbers. Administration of IFN-I ameliorated these 2 features previously attributed to this disease locus. Importantly, compared with B6 controls, B6.Sle2 mice had reduced levels of IFN-I in their sera and cell culture supernatants, following stimulation. Although several sequence polymorphisms were noted in the Sle2 alleles of various IFN-I genes, it was not established whether any of the noted sequence variations were causally related to the observed phenotypes.

CONCLUSION

Unexpectedly, reduction of IFN-I levels reproduced the serologic and cellular phenotypes previously associated with the Sle2 lupus susceptibility interval. Placing these findings in the context of other studies, the effect of IFN-I on systemic autoimmunity appears to be far more complex than originally perceived.

Islet transplantation: immunological perspectives

Clinical trials of islet transplantation are showing remarkable success, but they require administration of chronic immunosuppression, and are underscoring the large gap that exists between the number of human donors available and the number of patients that could benefit from the procedure. Recent progress has been made in the definition of key immunological mechanisms that are involved in determining islet transplant outcome. Clinical and preclinical studies, and studies in small animal model systems, will all eventually contribute to the definition of efficient and safe protocols for islet transplantation. If the use of xenografts is successful, it might represent a solution to the shortage of human organs.

Characterization of five 19-nor-analogs of 1alpha,25(OH)2-Vitamin D3 with 20-cyclopropyl-modified side-chains: implications for ligand binding and calcemic properties

The steroid hormone 1alpha,25(OH)(2)-Vitamin D(3) [1alpha,25(OH)(2)D(3)] exerts a wide variety of biological actions through one or more receptors/binding proteins. The nuclear Vitamin D receptor (VDR) when bound to its natural ligand, 1alpha,25(OH)(2)D(3), can stimulate transcription of a wide variety of genes. The synthesis of 1alpha,25(OH)(2)D(3) analogs allows the study of structure-function relationships between ligand and the VDR. 1alpha,25(OH)(2)D(3) is a conformationally flexible molecule; specifically the side-chain of the hormone can display a large variety of shapes for its receptor. Here, we describe and analyze the properties of 10 1alpha,25(OH)(2)D(3) analogs modified at the side-chain of which five lack carbon-19 (19-nor) but have a novel 20-cyclopropyl functionality. Analog NG [20,21-methylene-23-yne-26,27-F(6)-19-nor-1alpha,25(OH)(2)D(3)] possesses a respectable binding affinity for the VDR and exhibits a high transcriptional activity (EC(50) approximately 10pM), while retaining low induction of hypercalcemia in vivo in the mouse, making it a primary candidate for further analyses of its anti-proliferative and/or cell differentiating properties.

Mycobacterium bovis infection of vitamin D-deficient NOS2-/- mice

Vitamin D deficiency is associated with an increased risk for tuberculosis infection. Studies using in vitro systems indicate that 1,25-dihydroxyvitamin D(3) [i.e. 1,25(OH)(2)D(3)], the most active form of the vitamin, enhances mycobacterial killing by increasing nitric oxide (NO) production. To evaluate concurrently the role of 1,25(OH)(2)D(3) and NO on the host response to tuberculosis infection, mice deficient in NO synthase 2 (NOS2(-/-)) and/or vitamin D were aerosol-challenged with Mycobacterium bovis and subsequently evaluated for mycobacterial colonization and lesion formation. Infected NOS2(-/-) mice developed severe necrotizing pyogranulomatous inflammation of the lungs with heavy M. bovis colonization and systemic dissemination of the bacillus. Colonization and lung lesion area of NOS2(-/-) mice exceeded that of NOS2(+/+) mice. Additionally, disease progression was more rapid in NOS2(-/-) mice than in NOS2(+/+) mice. Lung colonization and lesion area of vitamin D deficient mice exceeded that of vitamin D replete mice, regardless of NOS2 phenotype. However, effects of vitamin D on colonization, but not lesion area, were more pronounced in NOS2(+/+) mice than in NOS2(-/-) mice. These findings are consistent with the current hypothesis that 1,25(OH)(2)D(3) enhances mycobacterial killing through a NO-dependent mechanism. As responses of NOS2(-/-) mice were affected by 1,25(OH)(2)D(3) deficiency, albeit to a lesser extent than were those of NOS2(+/+) mice, NO-independent actions of 1,25(OH)(2)D(3) also likely exist.

Islet transplantation in patients with diabetes mellitus: choice of immunosuppression

Islet transplantation offers patients with type 1 diabetes mellitus freedom from long-term insulin therapy and a degree of metabolic control that is far superior to injected insulin. The hope is that near-perfect glucose control sustained over time will prevent progression of secondary diabetic complications. The selection of optimal immunosuppressive agents for islet transplantation has been a formidable challenge, given the need to overcome both autoimmune and alloimmune barriers, as well as the potential toxicity of immunosuppressive agents on transplanted islets. Early strategies relied on protocols that had proven success in solid organ transplantation and consisted of azathioprine, cyclosporine and corticosteroids. Under these protocols, fewer than 10% of patients were able to achieve insulin independence. The development of the 'Edmonton Protocol' dramatically transformed clinical outcomes in islet transplantation in recent years through the introduction of a more potent, less diabetogenic, and corticosteroid-free immunosuppressive regimen consisting of sirolimus, low-dose tacrolimus, and induction anti-interleukin-2 receptor antibody. While insulin independence rates under this protocol have been highly successful, patients must be maintained on lifelong immunosuppression. While the risk of malignancy, post-transplant lymphoma and sepsis have been low and diminishing in transplanted patients to date, fears of these complications and a host of drug-related adverse effects have precluded broader application. Patients undergoing islet transplantation today must exchange insulin for chronic immunosuppressive therapy, and therefore the procedure can only be justified in patients with very unstable forms of diabetes, or in those with another solid organ allograft who already endure the risks of immunosuppression. Advances in more specific and less toxic immunosuppressive agents together with progress in better understanding the biology of diabetes will lead to more suitable strategies to control both alloimmune and recurrent autoimmune reactions. These protocols, ultimately aimed at establishing tolerance, are an essential pre-requisite to move towards providing islet transplantation earlier in the course of the disease, including transplantation in children. This review addresses the evolution of immunosuppressive strategies in islet transplantation, and highlights some novel agents in pre-clinical development or in early clinical trials that may offer considerable promise in facilitating the induction of tolerance.

Clinical islet transplant: current and future directions towards tolerance

The ultimate goal of islet transplantation is to completely correct the diabetic state from an unlimited donor source, without the need for chronic immunosuppressive drug therapy. Although islet transplantation provides an opportunity to develop innovative strategies for tolerance in the clinic, both alloimmune and autoimmune barriers must be controlled, if stable graft function is to be maintained long-term. After islet extraction from the pancreas, the cellular graft may be stored in tissue culture or cryopreserved for banking, providing an opportunity not only to optimally condition the recipient but also to allow in vitro immunologic manipulation of the graft before transplantation, unlike solid organ grafts. As such, islets may be considered a "special case." Remarkable progress has occurred in the last three years, with dramatic improvements in outcomes after clinical islet transplantation. The introduction of a steroid-free, sirolimus-based, anti-rejection protocol and islets prepared from two (or rarely three) donors led to high rates of insulin independence. The "Edmonton Protocol" has been successfully replicated by other centers in an international multicenter trial. A number of key refinements in pancreas transportation, processing, purification on non-ficoll-based media, storage of islets in culture for two days and newer immunological conditioning and induction therapies have led to continued advancement through extensive collaboration between key centers. This review outlines the historical development of islet transplantation over the past 30 years, provides an update on current clinical outcomes, and summarizes a series of unique opportunities for development and early testing of tolerance protocols in patients.

Vitamin D and its analogs as regulators of immune activation and antigen presentation

It has been a little more than 20 years since the first appreciation that the biologically active hormonal form of the secosteroid vitamin D-classically categorized as a regulator of calcium/phosphorous metabolism and bone mineralization-can exert effects on cells of the immune system. Since then a substantial literature has accumulated to suggest that these effects are exerted on multiple immune cell types, are predominantly suppressive at pharmacologic levels, and are potent enough to have true therapeutic potential in the management or prevention of immune-mediated diseases. Less clear at present, however, are the physiological roles played by the vitamin D endocrine system in the regulation of normal and abnormal immune responses. In this review, an appraisal of the current understanding of vitamin D-mediated immune regulation is presented that emphasizes progress towards its clinical application as well as the manner in which emerging models of normal immune function may facilitate a more complete understanding of its physiologic significance.

Analogs of 1alpha,25-dihydroxyvitamin D3 as pluripotent immunomodulators

The active form of vitamin D(3), 1,25(OH)(2)D(3), is known, besides its classical effects on calcium and bone, for its pronounced immunomodulatory effects that are exerted both on the antigen-presenting cell level as well as directly on the T lymphocyte level. In animal models, these immune effects of 1,25(OH)(2)D(3) are reflected by a strong potency to prevent onset and even recurrence of autoimmune diseases. A major limitation in using 1,25(OH)(2)D(3) in clinical immune therapy are the adverse side effects on calcium and on bone. TX527 (19-nor-14,20-bisepi-23-yne-1,25(OH)(2)D(3)) is a structural 1,25(OH)(2)D(3) analog showing reduced calcemic activity associated with enhanced in vitro and in vivo immunomodulating capacity compared to the mother-molecule. Indeed, in vitro TX527 is more potent that 1,25(OH)(2)D(3) in redirecting differentiation and maturation of dendritic cells and in inhibiting phytohemagglutinin-stimulated T lymphocyte proliferation. In vivo, this enhanced potency of TX527 is confirmed by a stronger potential to prevent type 1 diabetes in nonobese diabetic (NOD) mice and to prolong the survival of syngeneic islets grafts, both alone and in combination with cyclosporine A, in overtly diabetic NOD mice. Moreover, these in vivo effects of TX527 are obtained without the adverse side effects observed for 1,25(OH)(2)D(3) itself. We believe therefore that TX527 is a potentially interesting candidate to be considered for clinical intervention trails in autoimmune diseases.

1,25-dihydroxycholecalciferol: endocrinology meets the immune system

Previous work has demonstrated that, besides its effects on Ca and bone metabolism, the active form of cholecalciferol, 1,25-dihydroxycholecalciferol (1,25(OH)2D3), possesses pronounced immunomodulatory effects. In non-obese diabetic (NOD) mice primary (before disease onset), secondary (after insulitis but before diabetes onset) as well as tertiary (after transplantation of syngeneic islets) prevention of diabetes was demonstrated with 1,25(OH)2D3 and its chemically-manufactured non-hypercalcaemic analogues. 1,25(OH)2D3 exerts its immune effects both at the level of the T lymphocyte (shift in cytokine profile from T-helper (Th)1 to Th2, enhanced sensitivity to apoptosis-inducing signals) as well as at the level of the antigen-presenting cell (reduced antigen presentation, reduced production of Th1-promoting cytokines, reduced expression of co-stimulatory molecules). Also, physiologically, 1,25(OH)2D3 is believed to have a role in the immune system by serving as a negative feedback signal, limiting the mounted immune reaction. To test the clinical applicability of 1,25(OH)2D3 as treatment for type 1 diabetes in genetically-at-risk young children, we tested whether short-term early-life intervention with cholecalciferol or non-hypercalcaemic analogues of 1,25(OH)2D3 could prevent diabetes in NOD mice. Significant protection of pancreatic beta cells against autoimmune destruction was observed in analogue-treated and especially in cholecalciferol-treated NOD mice as compared with controls (P<0.005). This short-term early-life intervention was, however, not able to protect the mice from developing diabetes during their lifetime. Possible solutions are longer or combined treatments with other immunomodulators that have synergistic effects with 1,25(OH)2D3 and its analogues.