1 alpha,25-Dihydroxycholecalciferol reduces rejection and improves survival in rat liver allografts

1,25-dihydroxyvitamin-D3 but not the clinically applied marker 25-hydroxyvitamin-D3 predicts survival after stem cell transplantation

The serum level of 25-hydroxyvitamin-D3 is accepted as marker for a person’s vitamin D status but its role for the outcome of allogeneic hematopoietic stem cell transplantation (HSCT) is controversially discussed. The impact of 1,25-dihydroxyvitamin-D3 on HSCT outcome, however, has never been studied. In a discovery cohort of 143 HSCT patients we repeatedly (day −16 to 100) measured 1,25-dihydroxyvitamin-D3 and in comparison the well-established marker for serum vitamin D status 25-hydroxyvitamin-D3. Only lower 1,25-dihydroxyvitamin-D3 levels around HSCT (day −2 to 7, peritransplant) were significantly associated with higher 1-year treatment-related mortality (TRM) risk (Mann–Whitney U test, P = 0.001). This was confirmed by Cox-model regression without and with adjustment for baseline risk factors and severe acute Graft-versus-Host disease (aGvHD; unadjusted P = 0.001, adjusted P = 0.005). The optimal threshold for 1,25-dihydroxyvitamin-D3 to identify patients at high risk was 139.5 pM. Also in three replication cohorts consisting of altogether 365 patients 1,25-dihydroxyvitamin-D3 levels below 139.5 pM had a 3.3-fold increased risk of TRM independent of severe aGvHD compared to patients above 139.5 pM (Cox-model unadjusted P < 0.0005, adjusted P = 0.001). Our data highlight peritransplant 1,25-dihydroxyvitamin-D3 levels but not the commonly monitored 25-hydroxyvitamin-D3 levels as potent predictor of 1-year TRM and suggest to monitor both vitamin D metabolites in HSCT patients.

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.

Vitamin D and the Liver-Correlation or Cause?

Vitamin D is becoming increasingly accepted as an important physiological regulator outside of its classical role in skeletal homeostasis. A growing body of evidence connects vitamin D with hepatic disease. This review summarises the role of vitamin D in liver homeostasis and disease and discusses the therapeutic potential of vitamin D-based treatments to protect against hepatic disease progression and to improve response to treatment. While pre-clinical experimental data is promising, clinical trials around liver diseases have mostly been under-powered, and further studies will be required to clarify whether vitamin D or vitamin D analogues have beneficial effects on liver disease.

Delayed Donor Bone Marrow Infusion Induces Liver Transplant Tolerance

BACKGROUND

Nonmyeloablative conditioning followed by donor bone marrow infusion (BMI) to induce tolerance has not been robustly tested in liver transplantation (LT) and may be unsafe at the time of LT. We hypothesized T cell-depleted BMI is effective in inducing tolerance when delayed after LT, resulting in potentially safer future clinical applications.

METHODS

Nonimmunosuppressed syngeneic (Lewis to Lewis) and allogeneic (ACI to Lewis) rat LT transplants were initially performed as controls. Three experimental allogeneic LT groups were treated with tacrolimus (TAC) for 3 to 4 weeks and then underwent: (1) TAC withdrawal alone; (2) nonmyeloablative conditioning (anti-αβTCR mAb + total body irradiation [300 cGy]) followed by TAC withdrawal; (3) Nonmyeloablative conditioning + donor BMI (100 × 10 T cell-depleted bone marrow cells) followed by TAC withdrawal.

RESULTS

All group 1 recipients developed chronic rejection. Group 2 had long-term survival but impaired liver function and high donor-specific antibody (DSA) levels. In contrast, group 3 (conditioning + BMI) had long-term TAC-free survival with preserved liver function and histology, high mixed chimerism and blood/liver/spleen CD4 + CD25 + Foxp3+ regulatory T cells, and low DSA titers, similar to syngeneic grafts. While donor-specific tolerance was observed post-BMI, graft-versus-host disease was not.

CONCLUSIONS

These results support that donor-specific tolerance can be achieved with BMI even when delayed after LT and this tolerance correlates with increased mixed chimerism, regulatory T cell generation, and diminished DSA.

Vitamin D in liver disease: Current evidence and potential directions

Consistent with its multifaceted nature, growing evidence links vitamin D with hepatic disease. In this review, we summarise the roles of vitamin D in different liver pathologies and explore the clinical utility of vitamin D-based treatments in hepatology. We find that the small number of clinical trials coupled with the profound heterogeneity of study protocols limits the strength of evidence needed to ascribe definite clinical value to the hormone in liver disease. Nevertheless, the experimental data is promising and further bench and bedside studies will likely define a clearer role in hepatic therapeutics.

Effect of Vitamin D or Activated Vitamin D on Circulating 1,25-Dihydroxyvitamin D Concentrations: A Systematic Review and Metaanalysis of Randomized Controlled Trials

BACKGROUND

Evidence is accumulating that circulating 1,25-dihydroxyvitamin D [1,25(OH)2D] concentrations are inversely related to overall mortality.

METHODS

We searched PubMed, Embase and ISI Web of Science for randomized controlled trials with a control group receiving a placebo instead of vitamin D/activated vitamin D and performed a metaanalysis to evaluate the effect of oral vitamin D/activated vitamin D on circulating 1,25(OH)2D concentrations using a random effects model.

RESULTS

We included 52 vitamin D intervention groups (4796 individuals) and 14 intervention groups with activated vitamin D (668 individuals). Vitamin D supplements increased circulating 1,25(OH)2D by 12.2 pmol/L (95% CI, 7.8-16.5 pmol/L) and 18.8 pmol/L (95% CI, 9.2-28.4 pmol/L) if only studies with a low risk of bias in study design and reporting were considered (n = 18). There was significant heterogeneity among studies (Cohran's Q P < 0.001, I(2) = 91%). The incremental effect was larger in studies using vitamin D alone compared with coadministration of calcium supplements (18.6 pmol/L; 95% CI, 12.7-24.4 pmol/L vs 4.9 pmol/L; 95% CI, -0.4 to 10.2 pmol/L; P = 0.001), and if quantification was performed with RIA vs other methods (17.1 pmol/L; 95% CI, 11.1-23.1 pmol/L vs 6.9 pmol/L; 95% CI, 1.0-12.8 pmol/L; P = 0.02). Activated vitamin D increased the mean circulating 1,25(OH)2D by 20.5 pmol/L (95% CI, 8.3-32.7 pmol/L; P = 0.04). Again, there was evidence for significant heterogeneity among studies (Cochran Q = 85.4; P < 0.001; I(2) = 87%), but subgroup analysis did not identify parameters significantly influencing the increment in 1,25(OH)2D concentrations.

CONCLUSIONS

Both vitamin D and activated vitamin D significantly increase circulating 1,25(OH)2D concentrations, but in vitamin D users this increase is suppressed by calcium coadministration.

Vitamin D3 May Ameliorate the Ketoconazole Induced Adrenal Injury: Histological and Immunohistochemical Studies on Albino Rats

Ketoconazole (KZ) is used widely for treating the superficial, systemic fungal activities and hyperandrogenemic states. Its uses are limited by its deleterious effect on histological structure and function of the adrenal cortex. This study investigates whether vitamin D3 supplement can ameliorate the morphological changes induced by KZ. Thirty four adult male albino rats were randomized into control group (Group I) which was subdivided into: control 1 (n=7) and control 2 (n=7): In control 1, rats were intraperitoneal (I.P) injected once with 1 ml of polyethylene glycol-400 for 15 consecutive days and control 2 rats were injected I.P with (1 μg/kg) of vitamin D3 for the same period. Group II (n=10): rats were I.P injected with KZ (10 mg/100 g of body weight) once daily for 15 days; Group III (n=10): rats were I.P concomitantly injected with KZ and vitamin D3 similar doses to animals in groups II and control 2 respectively. Blood samples were collected to determine plasma ACTH, corticosterone and aldosterone levels. The right adrenal specimens sections were stained with Haematoxylin & Eosin and Masson Trichrome for histological studies and treated with Bax, Ubiquitin and vitamin D receptors for immunohistochemical studies. KZ induced adrenal cortical morphological changes in forms of disturbed adrenocorticocyte cytological architecture, nuclear changes, and intracellular lipid accumulation. KZ also increased adrenal Bax and Ub but decreased the vitamin D receptors immunopositive staining expression, in addition to increased plasma ACTH as well as decreased corticosterone and aldosterone levels. These changes were ameliorated by supplementing with vitamin D3.

Relationship between vitamin D status and immunosuppressive therapy in kidney transplant recipients

There is a growing body of evidence for the protective role of vitamin D in diabetes mellitus (DM), infection, cancer, cardiovascular disease, immune disorders and kidney function. Considering the reported high prevalence of vitamin D insufficiency among kidney transplant recipients (KTRs), the aim of this study was to assess the influence of immunosuppressive therapy and other factors on vitamin D status in such patients. The study included 289 KTRs (189 males and 100 females) who consented to participate. The first test for 25-hydrohyvitamin D [25(OH)D] was performed by a validated liquid chromatography-tandem mass spectrometry method. Influence of immunosuppressive drugs and previously reported predictors on vitamin D status was assessed by descriptive statistics, univariate and multivariate regression. Our results showed that only 53 patients (18.34%) of the studied KTRs were vitamin D sufficient. In addition to a well expected positive association between serum 25(OH)D and summer blood sampling (p < 0.05) and inverse relationship between vitamin D status and DM, gender (female) and body mass index, serum 25(OH)D was found to be inversely associated with calcineurin inhibitors (CNI) (p < 0.05) and unaffected by other immunosuppressive agents. Our study demonstrated high prevalence of vitamin D insufficiency after kidney transplantation in the studied cohort of patients. Apart from female gender, winter months, DM and overweight, the use of CNI could be considered an additional significant predictor of lower 25(OH)D in Bulgarian KTRs.

Circulating levels of 25-hydroxyvitamin D and acute cellular rejection in kidney allograft recipients

BACKGROUND

Vitamin D, in addition to its established role in bone metabolism, may regulate the immune system and affect the outcome of allografts.

METHODS

We identified 351 kidney allograft recipients who had serum levels of 25-hydroxyvitamin D (25[OH]D) measured within the first 30 days of transplantation. We evaluated the relationship between the circulating levels of 25(OH)D and acute cellular rejection (ACR), cytomegalovirus (CMV) disease, BK virus nephropathy, and kidney graft function.

RESULTS

Vitamin D deficiency (circulating levels of 25[OH]D ≤20 ng/mL, defined using The Endocrine Society Clinical Practice 2011 Guideline) was observed in 216 (61.5%) of 351 kidney graft recipients. Vitamin D deficiency was more frequent in female recipients (P=0.007, Fisher exact test) and African American recipients (P<0.001) and was less frequent in preemptive kidney graft recipients (P=0.002). Biopsy-confirmed ACR was more frequent in the vitamin D-deficient group than in the sufficient group (10.2% vs. 3.7%, P=0.04). By multivariable Cox regression analysis, vitamin D deficiency was an independent risk factor for ACR (hazard ratio=3.3, P=0.02). Vitamin D deficiency was not associated with CMV disease, BK virus nephropathy, or kidney allograft function at 1 year. 1,25-Dihydroxyvitamin D3 supplementation initiated within the first 90 days of transplantation was associated with a lesser incidence of ACR compared to no treatment with 1,25-dihydroxyvitamin D3 (5.1% vs. 13.0%, P=0.099).

CONCLUSIONS

Vitamin D deficiency is an independent risk factor for development of ACR within the first year of kidney transplantation and 1,25-dihydroxyvitamin D3 supplementation may help reduce the occurrence of ACR in the vitamin D-deficient group.

Vitamin D receptor agonists target CXCL10: new therapeutic tools for resolution of inflammation

Understanding the many biological extraskeletal actions of vitamin D has increased in the past decades. Indeed, vitamin D and analogue molecules, besides the classical actions on bone metabolism, exert several beneficial effects on metabolic homeostasis, heart-cardiovascular, brain, and muscle physiological functions, throughout the interaction with the specific vitamin D receptor (VDR). In particular, VDR agonists powerfully control innate and adaptive immune system with favorable effects on human health. VDR ligands act as immunomodulators that are potent enough to retain anti-inflammatory effects, even though the mechanism underlying those effects is not yet fully elucidated. VDR agonists exert a significant suppression of inflammatory processes switching the immune response from T helper 1 (Th1) to T helper 2 (Th2) dominance and counteracting the self-enhancing inflammatory loop between immune and resident cells, especially by cytokine release impairment. Those molecules are able, indeed, to reduce the release of the interferon (IFN)γ-induced 10 kDa protein IP-10/CXCL10, a powerful chemokine driving Th1-mediated inflammation. Based on their features, VDR ligands show the potentiality to be included in immunosuppressive regimens, aimed to control auto- and alloimmune Th1-driven overreactivity, occurring, for example, in autoimmune disease or graft rejection.

Protective role of the vitamin D receptor

Vitamin D receptor (VDR) is found in most tissues, not just those participating in the classic actions of vitamin D such as bone, gut, and kidney. The nonclassic actions are therefore potential targets for the active metabolite of vitamin D, 1,25(OH)₂D₃. This review is intended to highlight the actions of VDR in role of protection. Medline is searched for articles describing actions of VDR on secondary hyperparathyroidism, diabetic nephropathy, hypertension and atherosclerosis. VDR exerts its protective activities through the following mechanisms: inhibition of renin-angiotensin system (RAS); regulation of proliferation and differentiation; reduction of proteinuria; anti-inflammation and anti-fibrosis. The nonclassic actions of VDR provide a number of potential new clinical applications for 1,25(OH)₂D₃ and its analogs. We believe 1,25(OH)₂D₃/VDR can be of particular value in the prevention of kidney-related diseases.

Vitamin d deficiency in patients with chronic liver disease and cirrhosis

Vitamin D is now widely recognized to have multiple extraskeletal health functions. The liver is one of the major organs involved in its metabolism. Recent studies have demonstrated a very high prevalence of vitamin D deficiency and insufficiency in patients with chronic liver disease and cirrhosis. There is an emerging interest to explore the relationship between vitamin D deficiency and prevalence and severity of non-alcoholic liver disease and response to antiviral therapy in hepatitis C. In this review, we discuss the current status of our understanding of vitamin D metabolism and vitamin D deficiency in patients with chronic liver disease and cirrhosis.

Vitamin D3 modulates T lymphocyte responses in hepatitis C virus-infected liver transplant recipients

BACKGROUND

Aim of the present study was to investigate whether 1,25(OH)(2)D(3) (Vitamin D3) modulates T lymphocyte functions in patients transplanted for hepatitis C virus-related cirrhosis.

METHODS

Sixteen patients and ten healthy subjects were investigated. T lymphocytes were activated in vitro in the presence or absence of Vitamin D3 and then the proliferative response and IFN-γ and TNF-α production were assessed.

RESULTS

Vitamin D3 potently reduced T-lymphocyte proliferation in a dose-related fashion. Similarly, FACS analysis and ELISA testing demonstrated that Vitamin D3 significantly decreased the response frequency and the response intensity of IFN-γ and TNF-α production in the whole CD3-positive T lymphocyte population as well as in "naive" CD4+ CD45RA+ and "memory" CD4+ CD45RO+ T lymphocyte subsets. The inhibitory effect of Vitamin D3 on T-cell proliferation and cytokine production was not different between patients and controls. No toxic effects were exerted by Vitamin D3 even at the higher concentration used (10nM). Finally, no statistically significant correlation was found between 25(OH)D serum levels and the proliferative response or cytokine production of T lymphocytes from transplanted patients.

CONCLUSIONS

This study demonstrates that in patients transplanted for hepatitis C virus-related cirrhosis Vitamin D3 modulates T lymphocyte activation, and provides a rationale for the evaluation of this compound as an immunosuppressive agent in liver-transplanted patients.

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.

Vitamin D in organ transplantation

Vitamin D deficiency is prevalent among patients with end-stage organ failure awaiting transplant. Low serum 25-hydroxyvitamin D (25-OHD) levels in these patients may be related to many disease-specific factors, as well as decreased sunlight exposure and limited intake of foods containing vitamin D. Low serum 25-OHD levels are also extremely common following solid organ transplantation, both during the immediate postoperative period and in long-term graft recipients. Demographic and lifestyle factors are important in determining D status in transplant recipients. Worse vitamin D status is associated with poorer general health, lower albumin, and even decreased survival among these patients. Although several studies have demonstrated that active forms of vitamin D and its analogues prevent bone loss following transplantation, the data do not show consistent benefit. These therapies may have particular utility after renal transplantation. However, given the narrow therapeutic window with respect to hypercalcemia and hypercalciuria, and the demonstrated efficacy of bisphosphonates to prevent post-transplantation bone loss, we regard these agents as adjunctive rather than primary therapy for transplantation osteoporosis. The effects of 1,25(OH)(2)D on the immune system, which are still being elucidated, may have potential for reducing infections and preventing allograft rejection after transplantation.

Vitamin D in solid organ transplantation with special emphasis on kidney transplantation

Within the past decades, vitamin D was identified as having additional physiological functions far beyond calcium homeostasis and bone metabolism. Stimulated by the discovery of the vitamin D receptor in a broad range of tissues as well as the expression of 1α-hydroxylase, the enzyme responsible for the activation of vitamin D, it became evident that the actions of vitamin D are not restricted to cells involved in mineral and bone metabolism. In fact, it affects proliferation, differentiation, and function of a large number of different cell types including cells of the immune system. Vitamin D receptor agonists were found to exert immunosuppressive effects on the adaptive immune system, thus being able to mediate immunologic tolerance. However, they promote the innate immune system and thereby improve the ability of the host to combat invading pathogens. This review summarizes our current understanding of vitamin D as an immunomodulatory agent with special emphasis on its clinical implications in the transplant setting.

Vitamin D and the risk of acute allograft rejection following human liver transplantation

BACKGROUND

Vitamin D may act as an immune modulator in experimental and human organ transplantation, but these data are yet to be confirmed in human liver transplantation (LT).

AIM

This study aimed to assess the relationship between acute liver allograft cellular rejection (ACR) and pretransplant serum vitamin D concentration or post-transplant vitamin D supplementation.

METHOD

We studied 133 LT recipients who underwent two per protocol allograft biopsies in the early post-operative period, plus on-demand biopsies as clinically indicated. ACR estimate was given according to the Banff scheme in biopsies obtained along two follow-up periods: (a) from the transplant operation to the end of the second month (0-2 months); (b) and from the third month to the end of the eighth month (3-8 months) post-LT.

RESULTS

The median pretransplant serum 25-hydroxyvitamin D concentration was 12.5 ng/ml; 40 patients had concentrations < or =12.5 ng/ml, of whom six had < or =5.0 ng/ml. Seventy-nine recipients received oral vitamin D(3) supplementation to treat post-transplant osteoporosis. In the 0-2 months period, moderate-to-severe rejection episodes were independently associated with cytomegalovirus reactivation (P<0.005) and progressively lower pretransplant serum 25-hydroxyvitamin D concentrations (P<0.02). Early vitamin D(3) supplementation was independently associated with a lack of ACR (P<0.05).

CONCLUSIONS

These results suggest that vitamin D may favour immune tolerance towards the liver allograft.

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.

Paricalcitol reduces basal and lipopolysaccharide-induced (LPS) TNF-alpha and IL-8 production by human peripheral blood mononuclear cells

INTRODUCTION

Vitamin D and its analogues proved to exert immunomodulatory effects. Paricalcitol is a vitamin D analogue that is safe. It has been used for years in the treatment of secondary hyperparathyroidism in hemodialysis patients and, importantly, it is less calcemic than vitamin D. In this study the immunomodulatory/anti-inflammatory properties of paricalcitol were evaluated in vitro.

SUBJECT AND METHODS

Ten healthy volunteers enrolled into the study. Peripheral blood mononuclear cells (PBMC) at a concentration of 10(6) cells per well were cultured for 48 h in the presence or not of lipopolysaccharide (LPS) (100 ng/ml) and in the presence or not of paricalcitol (10(-8) M). TNF-alpha and IL-8 were measured in the supernatants by ELISA.

RESULTS

Basal TNF-alpha concentration (50.3 +/- 22 pg/ml) was reduced by paricalcitol (44.1 +/- 23.2 pg/ml). LPS increased TNF-alpha concentration (150.0 +/- 81.7 pg/ml), but paricalcitol reduced it (121.1 +/- 69.0 pg/ml). The effect of paricalcitol on IL-8 production was more profound. Basal IL-8 concentration (1926 +/- 455 pg/ml) was reduced by paricalcitol (1273 +/- 472 pg/ml). LPS increased IL-8 concentration (2361 +/- 385 pg/ml), but paricalcitol returned it to its basal level (1849 +/- 417 pg/ml).

CONCLUSION

The in vitro inhibition of transforming growth factor alpha and interleukin 8 by paricalcitol confirms the immunomodulatory properties of this vitamin D analogue.

Immunomodulatory effects of BXL-01-0029, a less hypercalcemic vitamin D analogue, in human cardiomyocytes and T cells

Current immunosuppressive protocols have reduced rejection occurrence in heart transplantation; nevertheless, management of heart transplant recipients is accompanied by major adverse effects, due to drug doses close to toxic range. In allograft rejection, characterized by T-helper 1 (Th1) cell-mediated response, the CXCL10-CXCR3 axis plays a pivotal role in triggering a self-promoting inflammatory loop. Indeed, CXCL10 intragraft production, required for initiation and development of graft failure, supports organ infiltration by Th1 cells. Thus, targeting the CXCL10-CXCR3 axis while avoiding generalized immunosuppression, may be of therapeutic significance. Based on preclinical evidence for immunoregulatory properties of vitamin D receptor agonists, we propose that a less hypercalcemic vitamin D analogue, BXL-01-0029, might have the potential to contribute to rejection management. We investigated the effect of BXL-01-0029 on CXCL10 secretion induced by proinflammatory stimuli, both in human isolated cardiomyocytes (Hfcm) and purified CD4+ T cells. Mycophenolic acid (MPA), the active agent of mycophenolate mofetil, was used for comparison. BXL-01-0029 inhibited IFNgamma and TNFalpha-induced CXCL10 secretion by Hfcm more potently than MPA, impairing cytokine synergy and pathways. BXL-01-0029 reduced also CXCL10 protein secretion and gene expression by CD4+ T cells. Furthermore, BXL-01-0029 did not exert any toxic effect onto both cell types, suggesting its possible use as a dose-reducing agent for conventional immunosuppressive drugs in clinical transplantation.

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.

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.

Prevention of chronic allograft rejection by Vitamin D receptor agonists

While immunosuppressive drugs now permit a good control of acute allograft rejection, chronic rejection remains an important unmet medical problem. We propose that Vitamin D receptor (VDR) agonists, secosteroid hormones that control cell proliferation and differentiation and exert immunoregulatory activities, in addition to regulate calcium and bone metabolism, have the potential to contribute to the management of chronic allograft rejection. Recent advances in understanding the immunomodulatory and growth-regulating properties of VDR agonists indicate the clinical applicability of these hormones in transplantation, with the aim of facilitating tolerance induction and preventing chronic graft rejection.

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.

Inhibition of Acute and Chronic Allograft Rejection in Mouse Models by BXL-628, a Nonhypercalcemic Vitamin D Receptor Agonist

BACKGROUND

Vitamin D receptor (VDR) agonists are immunomodulatory agents that have been shown to prolong allograft survival in several transplantation models, but calcemic liability remains an issue.

METHODS

To study the effect of VDR agonists on acute rejection, the authors have used the heterotopic vascularized heart model, and to assess their long-term effects, the aortic allograft model, which shows immune-mediated intimal thickening similar to the vascular lesions of human chronic allograft rejection. VDR agonists were administered orally from days -1 to 30, or until allografts were rejected. Aortic allograft recipients were killed at day 60 posttransplantation, and the transplanted aorta was analyzed by histology, immunohistochemistry, and gene microarray.

RESULTS

A significant delay in acute rejection was induced by calcitriol and, more markedly, by the less calcemic analogue BXL-628. BXL-628 was also more effective in inhibiting intimal hyperplasia, leading to approximately 80% reduction compared with vehicle-treated controls, an effect significantly superior to dexamethasone administration. Leukocyte recruitment to the graft was significantly inhibited by BXL-628 treatment, with a profound reduction in the number of CD11b macrophages and CD11c dendritic cells infiltrating the adventitia of transplanted aortas. A significant reduction of transcripts coding for several muscle-related genes was observed in aortic allografts from BXL-628-treated mice compared with controls.

CONCLUSIONS

These results show that the nonhypercalcemic VDR agonist BXL-628 inhibits, as a monotherapy, acute and chronic graft rejection in mouse models.

1,25-Dihydroxyvitamin D3 induces splenocyte apoptosis and enhances BALB/c mice sensitivity to toxoplasmosis

The hormonal form of Vitamin D, 1,25-dihydroxyvitamin D3, is well known for its immunosuppressive, anti-proliferative and pro-apoptotic activities. In the present work, we studied the effect of 1,25-dihydroxyvitamin D3 on Toxoplasma gondii-infected mice. We observed that 1,25-dihydroxyvitamin D3 reduces the survival rate of infected mice by up to 37% at day 10 post-infection compared to untreated infected mice (P < 0.0001). IFN-gamma and IL-12p40 levels were significantly reduced by 1,25-dihydroxyvitamin D3 in infected mice sera indicating an inhibition of Th-1-type cytokines. CD4+ T lymphocyte and splenocyte counts were also reduced following 1,25-dihydroxyvitamin D3 treatment and a marked induction of apoptosis, accompanied with down-regulation of the anti-apoptotic proteins Bcl-2 and Bcl-X(L), was observed. The above results indicate that 1,25-dihydroxyvitamin D3 induces splenocyte apoptosis and enhances host susceptibility to toxoplasmosis.

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.

Vitamin D as immunomodulatory therapy for kidney transplantation

Vitamin D (1alpha,25-dihydroxyvitamin D(3) [1alpha,25-(OH)(2)D(3)]) has been studied in the past for its immunosuppressive properties, and, in that context, it may also have potential utility as an immunomodulatory agent for transplantation. A number of studies have demonstrated that 1alpha,25-(OH)(2)D(3) or its analogs regulate immune cell proliferation, differentiation, and responsiveness. A burgeoning number of studies have also explored using 1alpha,25-(OH)(2)D(3) and its analogs directly as therapy in animal models of kidney transplantation with success in prolonging allograft function and preventing acute rejection. Some of these in vivo effects may well be caused by alterations in immune cell function, but it is also possible that exogenous 1alpha,25-(OH)(2)D(3) and its analogs are altering the intragraft milieu as well, specifically through changes in the TGF-beta signaling cascade. Such provocative data and the availability of newer 1alpha,25-(OH)(2)D(3) analogs that may limit side effects (e.g. hypercalcemia) have created interest in examining this secosteroid clinically in kidney transplantation.

The coming of age of 1,25-dihydroxyvitamin D(3) analogs as immunomodulatory agents

The active form of vitamin D, 1,25-dihydroxyvitamin D(3)[1,25(OH)(2)D(3)], is a secosteroid hormone that regulates calcium and bone metabolism, controls cell proliferation and differentiation, and exerts immunoregulatory activities. This range of functions has been exploited clinically to treat a variety of conditions, from secondary hyperparathyroidism to osteoporosis, to autoimmune diseases such as psoriasis. Recent advances in understanding 1,25(OH)(2)D(3) functions and novel insights into the mechanisms of its immunomodulatory properties suggest a wider applicability of this hormone in the treatment of autoimmune diseases and allograft rejection.