Vitamin D-resistant diseases

Significance of vitamin D responsiveness on the etiology of vitamin D-related diseases

Vitamin D resistance (VDRES) explains the necessity for higher doses of Vitamin D (VD) than those recommended for treatment success. VD receptor (VDR) signaling blockade, such as that caused by infections and poisons, is one basis for VDRES etiology. Mutations within genes affecting the VD system cause susceptibility to developing low VD responsiveness and autoimmunity. In contrast, VD hypersensitivity (VDHY) occurs if there is extra VD in the body; for example, as a result of an overdose of a VD supplement. Excess 1,25(OH)2D3 is produced in lymphomas and granulomatous diseases. The placenta produces excess 1,25(OH)2D3. Gene mutations regulating the production or degradation of 1,25(OH)2D3 enhance the effects of 1,25(OH)2D3. Increased 1,25(OH)2D3 levels stimulate calcium absorption in the gut, leading to hypercalcemia. Hypercalcemia can result in the calcification of the kidneys, circulatory system, or placenta, leading to kidney failure, cardiovascular disease, and pregnancy complications. The primary treatment involves avoiding exposure to the sun and VD supplements. The prevalence rates of VDRES and VDHY remain unclear. One estimate was that 25%, 51%, and 24% of the patients had strong, medium, and poor responses, respectively. Heavy-dose VD therapy may be a promising method for the treatment of autoimmune diseases; however, assessing its potential side effects is essential. To avoid VD-mediated hypercalcemia, responsiveness must be considered when treating pregnancies or cardiovascular diseases associated with VD. Furthermore, how VD is associated with the related disorders remains unclear. Investigating responsiveness to VD may provide more accurate results.

Compounding vulnerabilities: Syndemics and the social determinants of disease in the past

OBJECTIVE

This article explores the theory and utility of a syndemic approach for the study of disease in the past. Syndemic principles are examined alongside other theoretical developments within bioarchaeology. Two case studies are provided to illustrate the efficacy of this approach: Tuberculosis and vitamin D deficiency in 18th and 19th century England, and malaria and helminth infections in Early Medieval England.

MATERIALS

Public health studies of present syndemics, in addition to published bioarchaeological, clinical and social information relating to the chosen case studies.

METHODS

The data from these two historical examples are revisited within a syndemic framework to draw deeper conclusions about disease clustering and heterogeneity in the past.

RESULTS

A syndemic framework can be applied to past contexts using clinical studies of diseases in a modern context and relevant paleopathological, archaeological, and historical data.

CONCLUSIONS

This approach provides a means for providing a deeper, contextualised understanding ancient diseases, and integrates well with extant theoretical tools in bioarchaeology SIGNIFICANCE: Syndemics provides scholars a deep-time perspective on diseases that still impact modern populations.

LIMITATIONS

Many of the variables essential for a truly syndemic approach cannot be obtained from current archaeological, bioarchaeological, or historical methods.

SUGGESTIONS FOR FURTHER RESEARCH

More detailed and in-depth analysis of specific disease clusters within the past and the present, which draws on a comprehensive analysis of the social determinants of health.

Vitamin D Resistance as a Possible Cause of Autoimmune Diseases: A Hypothesis Confirmed by a Therapeutic High-Dose Vitamin D Protocol

Vitamin D3 (cholecalciferol) is a secosteroid and prohormone which is metabolized in various tissues to the biologically most active vitamin D hormone 1,25(OH)2D3 (calcitriol). 1,25(OH)2D3 has multiple pleiotropic effects, particularly within the immune system, and is increasingly utilized not only within prophylaxis, but also within therapy of various diseases. In this context, the latest research has revealed clinical benefits of high dose vitamin D3 therapy in autoimmune diseases. The necessity of high doses of vitamin D3 for treatment success can be explained by the concept of an acquired form of vitamin D resistance. Its etiology is based on the one hand on polymorphisms within genes affecting the vitamin D system, causing susceptibility towards developing low vitamin D responsiveness and autoimmune diseases; on the other hand it is based on a blockade of vitamin D receptor signaling, e.g. through pathogen infections. In this paper, we review observational and mechanistic evidence for the acquired vitamin D resistance hypothesis. We particularly focus on its clinical confirmation from our experience of treating multiple sclerosis patients with the so-called Coimbra protocol, in which daily doses up to 1000 I.U. vitamin D3 per kg body weight can be administered safely. Parathyroid hormone levels in serum thereby provide the key information for finding the right dose. We argue that acquired vitamin D resistance provides a plausible pathomechanism for the development of autoimmune diseases, which could be treated using high-dose vitamin D3 therapy.

Association between vitamin D receptor (VDR) gene polymorphisms and systemic lupus erythematosus in Portuguese patients

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease of unknown origin, in which both genetic and environmental factors are involved. One such environmental factor is vitamin D, a vital hormone that plays a specific function in the immune system homeostasis, acting through a nuclear receptor ( VDR) expressed in all immune cells. Several polymorphisms of the gene that encodes this receptor have been described. Though inconsistently, these polymorphisms have been associated with clinical manifestations and SLE development.

The aim of this study was to determine the possible association between VDR gene polymorphisms (BsmI, ApaI, TaqI e FokI) and SLE susceptibility and severity, in a cohort of lupus patients from the north of Portugal.

A total of 170 patients (F = 155, M = 15; age = 45 ± 13.4 years) with SLE (diagnosed according the American College of Rheumatology criteria) with at least five years of disease evolution and followed in the Autoimmune Disease Clinical Immunology Unit of Centro Hospitalar do Porto were studied. Patients and 192 ethnicity-matched controls were genotyped for BsmI (rs1544410), ApaI (rs7975232), TaqI (rs731236) and FokI (rs2228570) polymorphisms by TaqMan allelic discrimination assay. Disease severity was assessed by SLICC damage score, number of affected organs, number of severe flares and pharmacological history.

SLE patients with the CT genotype of FokI polymorphism have a higher SLICC value ( p = 0.031). The same result was observed for the group of patients with the TT genotype of TaqI polymorphism ( p = 0.046). No differences were observed in VDR genotype between patients and controls. Also, we observed that the other clinical features analysed were not influenced by VDR polymorphisms.

Our study confirms a possible role of VDR gene polymorphisms in SLE. A positive association was found between VDR polymorphisms and SLE severity (chronic damage). The presence of CT genotype of FokI and TT genotype of TaqI seems to confer a worse prognosis and may constitute a risk factor for higher long-term cumulative damage in SLE patients.

Minireview: nuclear receptor regulation of osteoclast and bone remodeling

Osteoclasts are bone-resorbing cells essential for skeletal remodeling and regeneration. However, excessive osteoclasts often contribute to prevalent bone degenerative diseases such as osteoporosis, arthritis, and cancer bone metastasis. Osteoclast dysregulation is also associated with rare disorders such as osteopetrosis, pycnodysostosis, Paget's disease, and Gorham-Stout syndrome. The nuclear receptor (NR) family of transcription factors functions as metabolic sensors that control a variety of physiological processes including skeletal homeostasis and serves as attractive therapeutic targets for many diseases. In this review, we highlight recent findings on the new players and the new mechanisms for how NRs regulate osteoclast differentiation and bone resorption. An enhanced understanding of NR functions in osteoclastogenesis will facilitate the development of not only novel osteoprotective medicine but also prudent strategies to minimize the adverse skeletal effects of certain NR-targeting drugs for a better treatment of cancer and metabolic diseases.

Skeletal mineralization defects in adult hypophosphatasia--a clinical and histological analysis

Histomorphometry and quantitative backscattered electron microscopy of iliac crest biopsies from patients with adult hypophosphatasia not only confirmed the expected enrichment of non-mineralized osteoid, but also demonstrated an altered trabecular microarchitecture, an increased number of osteoblasts, and an impaired calcium distribution within the mineralized bone matrix.

INTRODUCTION

Adult hypophosphatasia is an inherited disorder of bone metabolism caused by inactivating mutations of the ALPL gene, encoding tissue non-specific alkaline phosphatase. While it is commonly accepted that the increased fracture risk of the patients is the consequence of osteomalacia, there are only few studies describing a complete histomorphometric analysis of bone biopsies from affected individuals. Therefore, we analyzed iliac crest biopsies from eight patients and set them in direct comparison to biopsies from healthy donors or from individuals with other types of osteomalacia.

METHODS

Histomorphometric analysis was performed on non-decalcified sections stained either after von Kossa/van Gieson or with toluidine blue. Bone mineral density distribution was quantified by backscattered electron microscopy.

RESULTS

Besides the well-documented enrichment of non-mineralized bone matrix in individuals suffering from adult hypophosphatasia, our histomorphometric analysis revealed alterations of the trabecular microarchitecture and an increased number of osteoblasts compared to healthy controls or to individuals with other types of osteomalacia. Moreover, the analysis of the mineralized bone matrix revealed significantly decreased calcium content in patients with adult hypophosphatasia.

CONCLUSIONS

Taken together, our data show that adult hypophosphatasia does not solely result in an enrichment of osteoid, but also in a considerable degradation of bone quality, which might contribute to the increased fracture risk of the affected individuals.

Genetic epidemiology of age-related osteoporosis and its clinical applications

Osteoporosis is an important and complex disorder that is highly prevalent worldwide. This disease poses a major challenge to modern medicine and its treatment is associated with high costs. Numerous studies have endeavored to decipher the pathogenesis of this disease. The clinical assessment of patients often incorporates information about a family history of osteoporotic fractures. Indeed, the observation of an increased risk of fracture in an individual with a positive parental history of hip fracture provides strong evidence for the heritability of osteoporosis. The onset and progression of osteoporosis are generally controlled by multiple genetic and environmental factors, as well as interactions between them, with rare cases determined by a single gene. In an attempt to identify the genetic markers of complex diseases such as osteoporosis, there has been a move away from traditional linkage mapping studies and candidate gene association studies to higher-density genome-wide association studies. The advent of high-throughput technology enables genotyping of millions of DNA markers in the human genome, and consequently the identification and characterization of causal variants and loci that underlie osteoporosis. This Review presents an overview of the major findings since 2007 and clinical applications of these genome-wide linkage and association studies.

Emerging roles for calcium-regulating hormones beyond osteolysis

Parathyroid hormone (PTH), the active form of vitamin D, 1,25-dihydroxyvitamin D [1,25(OH)2D], and PTH-related peptide (PTHrP), the mediator of hypercalcemia of malignancy, are all osteolytic hormones. Recent studies have demonstrated that endogenous PTH and PTHrP also exert bone anabolic activity and that PTHrP is a crucial modulator of growth plate development. At least part of these PTHrP functions can be mediated by intracrine effects, involving a unique interplay of cell surface membrane and intracellular signaling. 1,25(OH)2D also exerts bone anabolic effects and, as with PTHrP, acts on multiple extraskeletal tissues. The skeletal functions of these hormones now extend beyond modulating bone resorption, and important extraskeletal activities have been discovered which involve unique local modes of action.

Crystal structure of hereditary vitamin D-resistant rickets--associated mutant H305Q of vitamin D nuclear receptor bound to its natural ligand

In the nuclear receptor of vitamin D (VDR) histidine 305 participates to the anchoring of the ligand. The VDR H305Q mutation was identified in a patient who exhibited the hereditary vitamin D-resistant rickets (HVDRR). We report the crystal structure of human VDR H305Q-ligand binding domain bound to 1alpha,25(OH)2D3 solved at 1.8A resolution. The protein adopts the active conformation of the wild-type liganded VDR. A local conformational flexibility at the mutation site weakens the hydrogen bond between the 25-OH with Gln305, thus explaining the lower affinity of the mutant proteins for calcitriol. The structure provides the basis for a rational approach to the design of more potent ligands for the treatment of HVDRR.

Mutations in the vitamin D receptor gene in four patients with hereditary 1,25-dihydroxyvitamin D-resistant rickets

Mutations in the vitamin D receptor (VDR) are associated to the hereditary 1,25-dihydroxivitamin D-resistant rickets. The objectives of this work are: search for mutations in the VDR and analyze their functional consequences in four Brazilian children presented with rickets and alopecia. The coding region of the VDR was amplified by PCR e direct sequenced. We identified three mutations: two patients had the same mutation in exon 7 at aminoacid position 259 (p.Q259E); one patient had a mutation in exon 8 at codon 319 (p.G319V) and another one had a mutation in exon 3 leading to a truncated protein at position 73 (p.R73X). Functional studies of the mutant receptors of fibroblast primary culture, from patients' skin biopsy treated with increasing doses of 1,25(OH)2 vitamin D showed that VDR mutants were unable to be properly activated and presented a reduction in 24-hydroxylase expression level.

Different enamel and dentin mineralization observed in VDR deficient mouse model

Vitamin D plays an important role in the bone mineralization process. Enamel and dentin are two mineralized tissues of different origins that combine to form teeth, but the mechanism by which vitamin D regulates these tissues remains unclear. We hypothesized that vitamin D affects enamel and dentin mineralization through different mechanisms.

OBJECTIVE

To examine enamel and dentin mineralization in a vitamin D receptor (VDR) deficient mouse model by micro-computerized tomography (micro-CT) and scanning electronic microscopy (SEM).

METHODS

VDR wild type mice (VDR+/+) and VDR deficient (VDR-/-) littermates were sacrificed at 70.5 days old, and their mandibles were dissected. Micro-CT was used to compare mineral density (MD) of enamel and dentin of the two groups at different levels along the axis of mandibular incisors. SEM was employed to examine the ultrastructure of incisors at the levels corresponding to the levels used for the micro-CT studies. Furthermore, an accelerated eruption procedure was performed to exclude the effect of delayed eruption on enamel and dentin mineralization.

RESULTS

Different distribution patterns of enamel and dentin MD were observed between VDR+/+ and VDR-/- groups. Early enamel maturation, mineralization, and hypomineralization in dentin were observed in the VDR deficient mice.

CONCLUSION

Vitamin D may affect the mineralization of dentin systemically, and enamel mineralization may be regulated locally.