Prevention of chronic allograft rejection by Vitamin D receptor agonists

Vitamin D and celiac disease

Celiac disease (CD) is an immune-mediated condition affecting the small intestine. Its reported global prevalence falls within the range of 0.7% to 1.4%. Notably, historically, higher rates, reaching 1% in Western Ireland, have been documented. Recent research has even revealed prevalence rates as elevated as 2% in northern Europe. These findings underscore the urgency for swift and cost-effective diagnosis, especially in individuals identified through screening efforts. At present, the diagnosis of CD relies on a multifaceted approach involving positive serological markers such as IgA anti-tissue transglutaminase (anti-TTG) and anti-endomysial antibodies (anti-EMA). These serological findings are assessed in conjunction with classical histological alterations, as outlined in the Marsh classification. CD is an inflammatory condition triggered by the consumption of gluten, resulting from intricate interactions between genetic, immunological, and environmental factors. CD is linked to malabsorption, leading to nutritional deficiencies. Individuals with CD are required to adhere to a gluten-free diet, which itself can lead to nutrient deficiencies. One such deficiency includes vitamin D, and there is substantial experimental evidence supporting the notion of a bidirectional relationship between CD and vitamin D status. A low level of vitamin D has a detrimental impact on the clinical course of the disease. Here we summarize the key characteristics of CD and explore the prominent roles of vitamin D in individuals with CD.

Dual Corneal-Graft Rejection after mRNA Vaccine (BNT162b2) for COVID-19 during the First Six Months of Follow-Up: Case Report, State of the Art and Ethical Concerns

Present mass vaccination against Coronavirus Disease-19 (COVID-19) is the most widely used health policy and the most promising approach to curb the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic globally. However, new side effects are emerging from the mass vaccination not described during the experimental stages. In the present study, we discuss a case of acute corneal graft rejection, which has occurred 25 years after transplantation and 13 days after the administration of the BNT162b2 vaccine (Comirnaty, BioNTech/Pfizer), which was followed-up for a period of six months. In this period, the corneal inflammation appeared twice but was successfully managed with topical therapy and supplementation of Vitamin D. A risk of corneal graft rejection must be included in the list of potential vaccine complications, in order to inform the transplanted patient to undergo a preliminary and a follow-up ocular examination, and eventually to include corneal graft in the list of contraindications to vaccination.

Status of vitamin D and parameters of calcium homeostasis in renal transplant recipients in Nepal: a cross sectional study

BACKGROUND

Vitamin D, apart from being an important part of the "calcium-vitamin D-parathyroid hormone" endocrine axis, has diverse range of "non-calcemic" biological actions. A high prevalence of vitamin D deficiency has been observed in renal transplant recipients (RTRs) worldwide. This study aimed to determine the prevalence of hypovitaminosis D in Nepalese RTRs and interrelations between serum 25-hydroxyvitamin D [25(OH) D] and other biochemical parameters.

METHODS

A total of 80 adult RTRs visiting a university hospital were enrolled in this cross sectional study. Serum 25(OH) D and intact parathyroid hormone (iPTH) were measured using Enhanced Chemiluminiscent Immunoassay. The RTR population was categorized into recent transplant recipients (≤1 year) and long term recipients (> 1 year). The vitamin D status was defined as per NKF/KDOQI guidelines. SPSS version 20.0 was used to analyze the data. Appropriate statistical tests were applied to compare variables between groups and establish correlation. P < 0.05 was considered to be statistically significant.

RESULTS

The mean age of the recipients was 38.11 ± 11.47 years (68 males, 85.0%). Chronic glomerulonephritis was the leading cause of CKD. The two RTR groups (recent and long term) didn't differ in demographic and biochemical characteristics. 83.75% of the recipients had PTH levels above the upper limit of the recommended range for their stage of CKD. 57.5% had hypocalcemia and none of the recipients had hypercalcemia. The median serum 25(OH) D was 24.15 ng/ml (8.00-51.50 ng/ml). Only 27.5% had sufficient vitamin D status whereas 53.8% were vitamin D insufficient and 18.8% were vitamin D deficient, the distribution almost comparable in the 2 transplant group. The serum 25(OH) D was not significantly affected by the time post-transplant, gender and sunlight avoidance. There was a significant negative correlation between serum 25(OH) D and iPTH (Pearson's r = - 0.35, P = 0.001), but not so with the graft function.

CONCLUSION

There is a high prevalence of vitamin D insufficiency in RTRs. The deficiency status is not corrected despite of nutritional improvement and normalization of GFR post-transplantation and likely exacerbates secondary hyperparathyroidism. Vitamin D supplementation coupled with sensible sun exposure could be important strategies in optimization of the vitamin D status in this population.

Mineral and bone disorder after kidney transplantation

After successful kidney transplantation, accumulated waste products and electrolytes are excreted and regulatory hormones return to normal levels. Despite the improvement in mineral metabolites and mineral regulating hormones after kidney transplantation, abnormal bone and mineral metabolism continues to present in most patients. During the first 3 mo, fibroblast growth factor-23 (FGF-23) and parathyroid hormone levels decrease rapidly in association with an increase in 1,25-dihydroxyvitamin D production. Renal phosphate excretion resumes and serum calcium, if elevated before, returns toward normal levels. FGF-23 excess during the first 3-12 mo results in exaggerated renal phosphate loss and hypophosphatemia occurs in some patients. After 1 year, FGF-23 and serum phosphate return to normal levels but persistent hyperparathyroidism remains in some patients. The progression of vascular calcification also attenuates. High dose corticosteroid and persistent hyperparathyroidism are the most important factors influencing abnormal bone and mineral metabolism in long-term kidney transplant (KT) recipients. Bone loss occurs at a highest rate during the first 6-12 mo after transplantation. Measurement of bone mineral density is recommended in patients with estimated glomerular filtration rate > 30 mL/min. The use of active vitamin D with or without bisphosphonate is effective in preventing early post-transplant bone loss. Steroid withdrawal regimen is also beneficial in preservation of bone mass in long-term. Calcimimetic is an alternative therapy to parathyroidectomy in KT recipients with persistent hyperparathyroidism. If parathyroidectomy is required, subtotal to near total parathyroidectomy is recommended. Performing parathyroidectomy during the waiting period prior to transplantation is also preferred in patients with severe hyperparathyroidism associated with hypercalcemia.

Vitamin D in renal transplantation - from biological mechanisms to clinical benefits

Recent developments in our understanding of vitamin D show that it plays a significant role in immunological health, uniquely occupying both an anti-microbial and immunoregulatory niche. Vitamin D deficiency is widespread amongst renal transplant recipients (RTRs), thus providing one patho-mechanism that may influence the achievement of a successful degree of immunosuppression. It may also influence the development of the infectious, cardiovascular and neoplastic complications seen in RTRs. This review examines the biological roles of vitamin D in the immune system of relevance to renal transplantation (RTx) and evaluates whether vitamin D repletion may be relevant in determining immunologically-related clinical outcomes in RTRs, (including graft survival, cardiovascular disease and cancer). While there are plausible biological and epidemiological reasons to undertake vitamin D repletion in RTRs, there are few randomized-controlled trials in this area. Based on the available literature, we cannot at present categorically make the case for routine measurement and repletion of vitamin D in clinical practice but we do suggest that this is an area in urgent need of further randomized controlled level evidence.

Very high-dose cholecalciferol and arteriovenous fistula maturation in ESRD: a randomized, double-blind, placebo-controlled pilot study

PURPOSE

While vitamin D is critical for optimal skeletal health, it also appears to play a significant role in vascular homeostasis. This pilot study compared arteriovenous (AV) access outcomes following cholecalciferol supplementation compared to placebo in end-stage renal disease patients preparing to undergo AV access creation.

METHODS

A total of 52 adult hemodialysis patients preparing for arteriovenous fistula (AVF) creation were randomized to receive perioperative high-dose cholecalciferol versus placebo in this double-blind, randomized, placebo-controlled pilot study. The primary outcome was mean response to high-dose oral cholecalciferol versus placebo, and secondary outcome AV access maturation at 6 months. Logistic regression was used to assess the association between AV access maturation and baseline, posttreatment and overall change in vitamin D concentration.

RESULTS

A total of 45% of cholecalciferol-treated and 54% of placebo-treated patients were successfully using their AVF or arteriovenous graft (AVG) at 6 months (p=0.8). Baseline serum concentrations of 25(OH)D and 1,25(OH)2D did not differ between those who experienced AVF or AVG maturation and those who did not (p=0.22 and 0.59, respectively). Similarly, there was no relationship between AVF or AVG maturation and posttreatment serum 25(OH)D and 1,25(OH)2D concentration (p=0.24 and 0.51, respectively).

CONCLUSIONS

Perioperative high-dose vitamin D3 therapy does correct 25(OH)D level but does not appear to have an association with AV access maturation rates. Future research may include extended preoperative vitamin D3 therapy in a larger population or in certain subpopulations at high risk for AVF failure.

Effects of vitamin D on immune disorders with special regard to asthma, COPD and autoimmune diseases: a short review

This paper reviews the recent data on the role of vitamin D (VD) in the genesis of various immunological disorders. It inhibits immune reactions in general, but it enhances the transcription of 'endogenous antibiotics' such as cathelicidin and defensins. VD inhibits the genesis of both Th1- and Th2-cell mediated diseases. The pleiotropic character VD-induced effects are due to the altered transcription of hundreds of genes. VD supplementation in most related studies reduced the prevalence of asthma. Th1-dependent autoimmune diseases (e.g., multiple sclerosis, Type 1 diabetes, Crohn's disease, rheumatoid arthritis and so on) are also inhibited by VD due to inhibition of antigen presentation, reduced polarization of Th0 cells to Th1 cells and reduced production of cytokines from the latter cells. VD seems to also be a useful adjunct in the prevention of allograft rejection. Last but not least, VD supplementation may be useful in the prevention or adjunct treatment of chronic obstructive pulmonary disease.

Protective actions of vitamin D in UVB induced skin cancer

Non-melanoma skin cancers (NMSC) are the most common type of cancer, occurring at a rate of over 1 million per year in the United States. Although their metastatic potential is generally low, they can and do metastasize, especially in the immune compromised host, and their surgical treatment is often quite disfiguring. Ultraviolet radiation (UVR) as occurs with sunlight exposure is generally regarded as causal for these malignancies, but UVR is also required for vitamin D synthesis in the skin. Based on our own data and that reported in the literature, we hypothesize that the vitamin D produced in the skin serves to suppress UVR epidermal tumor formation. In this review we will first discuss the evidence supporting the conclusion that the vitamin D receptor (VDR), with or without its ligand 1,25-dihydroxyvitamin D, limits the propensity for cancer formation following UVR. We will then explore three potential mechanisms for this protection: inhibition of proliferation and stimulation of differentiation, immune regulation, and stimulation of DNA damage repair (DDR).

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.

Calcitriol stimulates prolactin expression in non-activated human peripheral blood mononuclear cells: breaking paradigms

Calcitriol, the hormonal form of vitamin D(3), exerts immunomodulatory effects through the vitamin D(3) receptor (VDR) and increases prolactin (PRL) expression in the pituitary and decidua. Nevertheless, the effects of calcitriol upon lymphocyte PRL have not been evaluated. Therefore, we investigated calcitriol effects upon PRL in resting and phytohemagglutinin-activated human peripheral blood mononuclear cells (PBMNC) and Jurkat T lymphoma cells. Immunoblots showed constitutive expression of the 50-kDa VDR species in activated PBMNC and Jurkat cells, while a 75-kDa species was recognized in both resting and activated-PBMNC. Only in resting PBMNC calcitriol significantly stimulated PRL expression in a dose-dependent manner. The positive control CYP24A1, a highly VDR-responsive gene, was stimulated by calcitriol, effect that was stronger in resting than in activated-PBMNC (P<0.05), and without effect in Jurkat cells. Calcitriol upregulation of PRL and CYP24A1 was significantly inhibited by the VDR antagonist TEI-9647. EMSA showed that resting PBMNC contain a protein that binds to DR3-type VDRE. Cell activation reduced basal CYP24A1 while induced CYP27B1, VDR and pregnane X receptor (PXR) expression. In summary, calcitriol stimulated PRL and CYP24A1 gene expression in quiescent lymphocytes through a VDR-mediated mechanism. Our results suggest that the 75-kDa VDR species could be participating in calcitriol-mediated effects, and that activation induces factors such as PXR that restrain VDR transcriptional processes. This study supports the presence of a functional VDR in quiescent lymphocytes, providing evidence to reevaluate the VDR paradigm that assumes that lymphocytes respond to calcitriol only after activation. Altogether, our results offer new insights into the mechanisms whereby PRL is regulated in immune cells.

Human T lymphocytes are direct targets of 1,25-dihydroxyvitamin D3 in the immune system

Besides its actions on minerals and bone, the bioactive vitamin D metabolite, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), has important immunomodulatory properties. Within the immune system, dendritic cells represent key targets for this hormone and 1,25(OH)2D3-induced changes in their phenotype and function ultimately affects T lymphocytes. However, the presence of vitamin D receptors (VDR) in activated T cells proposes additional mechanisms for 1,25(OH)2D3 to directly regulate T cell responses. Here, we investigated the expression and kinetics of vitamin D-related genes in human activated T lymphocytes. Different activation stimuli elicited increased VDR- and 1-alpha-hydroxylase expression, with a highly similar kinetic pattern. Addition of 1,25(OH)2D3 effectively triggered VDR signaling, as evidenced by 24-hydroxylase induction, but only when introduced to T lymphocytes expressing high levels of VDR. This enhanced degree of VDR signaling correlated with a stronger inhibition of cytokines (IFN-gamma, IL-10) and modulation of homing receptor expression (CCR10, CLA) in long-term T cell cultures. Importantly, chronic 1,25(OH)2D3-exposure further amplified VDR signaling and the concomitant T cell modulating effects. In conclusion, we validate T cells as direct targets for 1,25(OH)2D3 and provide this optimized in vitro model to improve our understanding of the role of vitamin D as a direct regulator of T cell responses.

Vitamin D: newly discovered actions require reconsideration of physiologic requirements

Vitamin D is not just for preventing rickets and osteomalacia. Recent findings in animal experiments, epidemiologic studies and clinical trials indicate that adequate vitamin D levels are important for cancer prevention, controlling hormone levels and regulating the immune response. Although 25 hydroxyvitamin D (25OHD) levels >10 ng/ml can prevent rickets and osteomalacia, these levels are not sufficient to provide these more recently discovered clinical benefits. Rather, levels of 25OHD >30 ng/ml are generally recommended. Determining optimal levels of 25OHD and the amount of vitamin D supplementation required to achieve those levels for the numerous actions of vitamin D will only be established with additional trials. In this review, these newer applications are summarized and therapeutic considerations are provided.

A (13)C solid-state NMR analysis of vitamin D compounds

(13)C cross-polarization/magic-angle spinning (CP/MAS) solid-state NMR spectroscopy has been employed to analyze four vitamin D compounds, namely vitamin D3 (D3), vitamin D2 (D2), and the precursors ergosterol (Erg) and 7-dehydrocholesterol (7DHC). The (13)C NMR spectrum of D3 displays a doublet pattern for each of the carbon atoms, while that of Erg contains both singlet and doublet patterns. In the cases of 7DHC and D2, the (13)C spectra display various multiplet patterns, viz. singlets, doublets, triplets, and quartets. To overcome the signal overlap between the (13)C resonances of protonated and unprotonated carbons, we have subjected these vitamin D compounds to 1D (1)H-filtered (13)C CP/MAS and {(1)H}/(13)C heteronuclear correlation (Hetcor) NMR experiments. As a result, assisted by solution NMR data, all of the (13)C resonances have been successfully assigned to the respective carbon atoms of these vitamin D compounds. The (13)C multiplets are interpreted due to the presence of s-cis and s-trans configurations in the alpha- and beta-molecular conformers, consistent with computer molecular modeling determined by molecular dynamics and energy minimization calculations. To further characterize the ring conformations in D3, we have successfully extracted chemical shift tensor elements for the (13)C doublets. It is demonstrated that (13)C solid-state NMR spectroscopy provides a robust and high sensitive means of characterizing molecular conformations in vitamin D compounds.

Vitamin D analogs: therapeutic applications and mechanisms for selectivity

The vitamin D endocrine system plays a central role in mineral ion homeostasis through the actions of the vitamin D hormone, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], on the intestine, bone, parathyroid gland, and kidney. The main function of 1,25(OH)(2)D(3) is to promote the dietary absorption of calcium and phosphate, but effects on bone, kidney and the parathyroids fine-tune the mineral levels. In addition to these classical actions, 1,25(OH)(2)D(3) exerts pleiotropic effects in a wide variety of target tissues and cell types, often in an autocrine/paracrine fashion. These biological activities of 1,25(OH)(2)D(3) have suggested a multitude of potential therapeutic applications of the vitamin D hormone for the treatment of hyperproliferative disorders (e.g. cancer and psoriasis), immune dysfunction (autoimmune diseases), and endocrine disorders (e.g. hyperparathyroidism). Unfortunately, the effective therapeutic doses required to treat these disorders can produce substantial hypercalcemia. This limitation of 1,25(OH)(2)D(3) therapy has spurred the development of vitamin D analogs that retain the therapeutically important properties of 1,25(OH)(2)D(3), but with reduced calcemic activity. Analogs with improved therapeutic indices are now available for treatment of psoriasis and secondary hyperparathyroidism in chronic kidney disease, and research on newer analogs for these indications continues. Other analogs are under development and in clinical trials for treatment of various types of cancer, autoimmune disorders, and many other diseases. Although many new analogs show tremendous promise in cell-based models, this article will limit it focus on the development of analogs currently in use and those that have demonstrated efficacy in animal models or in clinical trials.

Vitamin D status in kidney transplant patients: need for intensified routine supplementation

BACKGROUND

A high prevalence of vitamin D insufficiency has been found in the general population and in patients with chronic kidney disease.

OBJECTIVE

The aim was to examine vitamin D status and determinants and metabolic correlates of serum 25-hydroxyvitamin D in a population of adult Danish kidney transplant patients.

DESIGN

This was a cross-sectional study of 173 adult kidney transplant patients with a mean (+/-SD) age of 53.4 +/- 11.7 y and a median graft age of 7.4 y (interquartile range: 3.3-12.7 y). Serum concentrations of intact parathyroid hormone (S-PTH), 25-hydroxyvitamin D [S-25(OH)D], and 1,25-dihydroxyvitamin D [S-1,25(OH)(2)D] were measured. Dietary and supplementary intake of vitamin D, avoidance of solar ultraviolet B exposure, and selected lifestyle factors were assessed in a subgroup (n = 97).

RESULTS

Fifty-one percent of the patients had vitamin D insufficiency [S-25(OH)D 40-75 nmol/L], and an additional 29% had moderate-to-severe vitamin D deficiency [S-25(OH)D < or = 39 nmol/L]. In multiple regression analysis, sun avoidance (negative association) and vitamin D supplementation (positive association) were independent determinants of S-25(OH)D concentrations. Low S-25(OH)D concentrations were associated with 1) increased S-PTH concentrations (P = 0.0002), independently of S-1,25(OH)(2)D concentrations, and 2) decreased S-1,25(OH)(2)D concentrations (P = 0.002), independently of graft function.

CONCLUSIONS

Hypovitaminosis D is common among Danish kidney transplant patients and is associated with reduced concentrations of S-1,25(OH)(2)D and increased S-PTH concentrations. Sun avoidance and vitamin D supplementation are important determinants of vitamin D status. The observed hypovitaminosis D might be corrected by intensified routine vitamin D supplementation as opposed to the current supplementation practice.

The vitamin D receptor as a therapeutic target

The vitamin D receptor (VDR) is a member of the large family of nuclear receptor transcription factors and specifically binds the micronutrient-derived hormone 1alpha,25(OH)2D3. A central endocrine role for this receptor in bone health was established at the beginning of the 20th century. Over the last 25 years, additional roles, perhaps through autocrine and paracrine mechanisms, have been established for VDR to regulate cell proliferation and differentiation, and more recently to exert immunomodulatory and antimicrobial functions. These findings, from in vitro and in vivo experiments, have generated considerable interest in targeting the VDR in multiple therapeutic settings. As with many potential therapeutics, it has also become clear that cells and tissues may also display de novo and acquired mechanisms of resistance to these actions. Consequently, a range of experimental and clinical options are being developed to bring about more targeted actions, overcome resistance and enhance efficacy of VDR-centred therapeutics.