Vitamin D: an ancient hormone

Key role of CRF in the skin stress response system

The discovery of corticotropin-releasing factor (CRF) or CRH defining the upper regulatory arm of the hypothalamic-pituitary-adrenal (HPA) axis, along with the identification of the corresponding receptors (CRFRs 1 and 2), represents a milestone in our understanding of central mechanisms regulating body and local homeostasis. We focused on the CRF-led signaling systems in the skin and offer a model for regulation of peripheral homeostasis based on the interaction of CRF and the structurally related urocortins with corresponding receptors and the resulting direct or indirect phenotypic effects that include regulation of epidermal barrier function, skin immune, pigmentary, adnexal, and dermal functions necessary to maintain local and systemic homeostasis. The regulatory modes of action include the classical CRF-led cutaneous equivalent of the central HPA axis, the expression and function of CRF and related peptides, and the stimulation of pro-opiomelanocortin peptides or cytokines. The key regulatory role is assigned to the CRFR-1α receptor, with other isoforms having modulatory effects. CRF can be released from sensory nerves and immune cells in response to emotional and environmental stressors. The expression sequence of peptides includes urocortin/CRF→pro-opiomelanocortin→ACTH, MSH, and β-endorphin. Expression of these peptides and of CRFR-1α is environmentally regulated, and their dysfunction can lead to skin and systemic diseases. Environmentally stressed skin can activate both the central and local HPA axis through either sensory nerves or humoral factors to turn on homeostatic responses counteracting cutaneous and systemic environmental damage. CRF and CRFR-1 may constitute novel targets through the use of specific agonists or antagonists, especially for therapy of skin diseases that worsen with stress, such as atopic dermatitis and psoriasis.

Combining aspirin with cholecalciferol (vitamin D3)--a potential new tool for controlling possum populations

The introduced Australian brushtail possum is a major vertebrate pest in New Zealand, with impacts on conservation and agriculture being managed largely through poisoning operations. Cholecalciferol (vitamin D3) is registered for use in controlling possums and despite its many advantages it is expensive and relatively inhumane. Combination of a high proportion of aspirin with a low proportion of cholecalciferol was effective in killing high proportions of groups of acclimatised, caged possums: this is attributed to both an unexpectedly high toxicity of the type of cholecalciferol used, and a proposed synergistic mechanism between the two compounds. Death was caused by localised damage to heart ventricles by aspirin, and inhibition of tissue repair by both aspirin and cholecalciferol. The observed toxicosis had lower impact on the welfare of possums than either compound administered alone, particularly aspirin alone. Residue analyses of bait remains in the GI tract suggested a low risk of secondary poisoning by either compound. The combination of cholecalciferol and aspirin has the potential to meet key requirements of cost-effectiveness and humaneness in controlling possum populations, but the effect of the combination in non-target species has yet to be tested.

Interplay between vitamin D and the drug metabolizing enzyme CYP3A4

Cytochrome P450 3A4 (CYP3A4) is a multifunctional enzyme involved in both xenobiotic and endobiotic metabolism. This review focuses on two aspects: regulation of CYP3A4 expression by vitamin D and metabolism of vitamin D by CYP3A4. Enterohepatic circulation of vitamin D metabolites and their conjugates will be also discussed. The interplay between vitamin D and CYP3A4 provides new insights into our understanding of how enzyme induction can contribute to vitamin D deficiency. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

[Aspects of interest on vitamin D for the traumatologist and orthopaedic surgeon]

Vitamin D deficiency or insufficiency is a clinical problem particularly prevalent in elderly patients with low-energy fractures, particularly hip fractures, but has also been associated with stress fractures and high energy fractures. There is much evidence that supports the need to maintain adequate levels of vitamin D in the blood in order to; reduce the number of fragility fractures, furthering the consolidation of these, improve neuromuscular function of patients, prevent falls, prevent surgical infections, or improve the length of arthroplasties. However, it is rare for the orthopaedic surgeon to request the values of vitamin D in these patients and give the appropriate treatment It is recommended to maintain levels higher than 30-40ng/ml (75-100nmol/l) and increase vitamin D intake, in almost all cases, from 800 to 1,000IU/day to achieve these levels.

Serum vitamin D3 level inversely correlates with uterine fibroid volume in different ethnic groups: a cross-sectional observational study

PURPOSE

Currently there is no effective medicinal treatment for uterine fibroids (UFs), a common health disorder that affects women of reproductive age. Identification of modifiable risk factors such as vitamin D (Vit D) deficiency could help develop novel strategies for the prevention and/or treatment of UFs. The purpose of this study was to identify whether low serum Vit D3 levels correlate with increased risk of UFs.

METHODS

A total of 154 premenopausal women were recruited for this cross-sectional study. The control group comprised 50 subjects with a normal, fibroid-free uterine structure, confirmed by transvaginal ultrasonography. The 104 case subjects had at least one fibroid lesion that was 2 cm(3) in volume or larger, confirmed by transvaginal ultrasonography. For each case subject, total uterine volume and total volume of all existing fibroids were measured in three perpendicular planes, with volume determined according to the prolate ellipse formula (a × b × c × 0.523), where a is height, b is width, and c is depth. Serum Vit D [25(OH) D3] levels were measured by radioimmunoassay. The independent t-test was used to compare serum Vit D levels across groups. Correlations were assessed by Spearman's rank correlation test.

RESULTS

Lower serum 25-(OH) Vit D levels were significantly associated with the occurrence of UFs (P = 0.01). A statistically significant inverse correlation was also observed between serum 25-(OH) Vit D levels and total UF volume (r = -0.31; P = 0.002) within the case cohort. Subjects with larger fibroid volumes had lower serum Vit D levels and vice versa. Data stratified for ethnicity showed a statistically significant inverse correlation between serum 25-(OH) Vit D levels and total fibroid volume in black subjects (r = -0.42; P = 0.001). An inverse correlation was also evident in white subjects (r = -0.86; P = 0.58) but this did not reach statistical significance.

CONCLUSION

Lower serum Vit D levels are inversely correlated with UF burden in different ethnic groups. Vit D deficiency is a possible risk factor for the occurrence of UFs.

Ultraviolet radiation regulates cortisol activity in a waveband-dependent manner in human skin ex vivo

BACKGROUND

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1), 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), and glucocorticoids (GC) and their receptor (GR) play a key role in tissue-specific regulation of GC action.

OBJECTIVES

To determine the expression of genes encoding 11β-HSD1 (HSD11B1), 11β-HSD2 (HSD11B2) and GR (GRα; also known as NC3R1) and their protein products, and levels of cortisol in human skin explants and/or cocultured keratinocytes/melanocytes after treatment with ultraviolet (UV) A, B or C wavebands.

METHODS

Skin from foreskins and/or cocultured human keratinocytes/melanocytes were irradiated with UVA, UVB or UVC (skin) and incubated for 12 and 24 h. Methods of reverse transcription-polymerase chain reaction, Western blotting, enzyme-linked immunosorbent assay and immunohistochemistry (IHC) were used to determine expression and localization of corresponding genes or antigens.

RESULTS

UVB enhanced the HSD11B1 gene and protein expression in a dose-dependent manner, while UVA had no effect. Similarly, UVC increased 11β-HSD1 protein product as measured by IHC. UVB and UVC enhanced cortisol production and decreased epidermal GR expression, while UVA had no detectable effects. Although both UVA and UVB stimulated HSD11B2 gene expression, only UVA increased 11β-HSD2 protein product levels with UVB and UVC having no effect.

CONCLUSIONS

We suggest that these differential, waveband-dependent effects of UV radiation on the expression of cutaneous HSD11B1, HSD11B2 and GRα genes and their corresponding protein products, and cortisol production are to protect and/or restore the epidermal barrier homeostasis against disruption caused by the elevated cortisol level induced by UVB and UVC.

Vitamin D: metabolism, molecular mechanisms, and mutations to malignancies

The potential protective effects of vitamin D against cutaneous carcinogenesis are still poorly understood. The inhibition, by vitamin D, of various cancers in in vitro and in vivo models has triggered detailed investigation of vitamin D effects on neoplastic behavior. Recent studies highlight that such neoplastic features as the tumor microenvironment, angiogenesis, DNA mutagenesis, and apoptosis are all connected to vitamin D metabolic pathways. This review discusses these connections. Vitamin D modulation of the cell cycle, DNA repair and apoptosis via its receptors (VDRs) may have a suppressive effect on skin cancer as some studies suggest. The regulation of multiple tumor signaling pathways by vitamin D may have an implication in cutaneous carcinogenesis and tumor progression to malignancy.

New vitamin D analogs as potential therapeutics in melanoma

Extensive evidence shows that the active form of vitamin D3--1α,25-dihydroxyvitamin D3--plays an important role in cancer prevention, has tumorostatic activity and may potentially be used in therapy for melanoma. Vitamin D3 and its analogs (secosteroids) exert multiple effects on cancer cells, including inhibition of cell growth and induction of differentiation. Activity of secosteroids depends on multiple cellular factors, including expression of the vitamin D receptor. Despite its endogenous origin, the key drawback for the use of pharmacologically effective doses of 1α,25-dihydroxyvitamin D3 is its hypercalcemic effect leading to profound toxicity. The solution may lie in properties of vitamin D3 analogs with modified side chains, which demonstrate low calcemic activity but conserve the anti-tumor properties. Noncalcemic vitamin D compounds were found to be potent in multiple studies that mandate further clinical testing. Finally, recent studies revealed alternative metabolic pathways for secosteroids and new targets in the cells, which opens up new therapeutic possibilities.

Cytochrome P450scc-dependent metabolism of 7-dehydrocholesterol in placenta and epidermal keratinocytes

The discovery that 7-dehydrocholesterol (7DHC) is an excellent substrate for cytochrome P450scc (CYP11A1) opens up new possibilities in biochemistry. To elucidate its biological significance we tested ex vivo P450scc-dependent metabolism of 7DHC by tissues expressing high and low levels of P450scc activity, placenta and epidermal keratinocytes, respectively. Incubation of human placenta fragments with 7DHC led to its conversion to 7-dehydropregnenolone (7DHP), which was inhibited by dl-aminoglutethimide, and stimulated by forskolin. Final proof for P450scc involvement was provided in isolated placental mitochondria where production of 7DHP was almost completely inhibited by 22R-hydroxycholesterol. 7DHC was metabolized by placental mitochondria at a faster rate than exogenous cholesterol, under both limiting and saturating conditions of substrate transport, consistent with higher catalytic efficiency (k(cat)/K(m)) with 7DHC as substrate than with cholesterol. Ex vivo experiments showed five 5,7-dienal intermediates with MS spectra of dihydroxy and mono-hydroxy-7DHC and retention time corresponding to 20,22(OH)(2)7DHC and 22(OH)7DHC. The chemical structure of 20,22(OH)(2)7DHC was defined by NMR. 7DHP was further metabolized by either placental fragments or placental microsomes to 7-dehydroprogesterone as defined by UV, MS and NMR, and to an additional product with a 5,7-dienal structure and MS corresponding to hydroxy-7DHP. Furthermore, epidermal keratinocytes transformed either exogenous or endogenous 7DHC to 7DHP. 7DHP inhibited keratinocytes proliferation, while the product of its pholytic transformation, pregcalciferol, lost this capability. In conclusion, tissues expressing P450scc can metabolize 7DHC to biologically active 7DHP with 22(OH)7DHC and 20,22(OH)(2)7DHC serving as intermediates, and with further metabolism to 7-dehydroprogesterone and (OH)7DHP.

1α,25-dihydroxyvitamin D3 modulates the hair-inductive capacity of dermal papilla cells: therapeutic potential for hair regeneration

Dermal papilla cells (DPCs) have the potential to induce differentiation of epithelial stem cells into hair, and Wnt signaling is deeply involved in the initiation process. The functional limitation of expanded adult DPCs has been a difficult challenge for cell-based hair regrowth therapy. We previously reported that 1α,25-dihydroxyvitamin D(3) (VD(3)) upregulates expression of transforming growth factor (TGF)-β2 and alkaline phosphatase (ALP) activity, both features of hair-inducing human DPCs (hDPCs). In this study, we further examined the effects and signaling pathways associated with VD(3) actions on DPCs. VD(3) suppressed hDPC proliferation in a dose-dependent, noncytotoxic manner. Among the Wnt-related genes investigated, Wnt10b expression was significantly upregulated by VD(3) in hDPCs. Wnt10b upregulation, as well as upregulation of ALPL (ALP, liver/bone/kidney) and TGF-β2, by VD(3) was specific in hDPCs and not detected in human dermal fibroblasts. Screening of paracrine or endocrine factors in the skin indicated that all-trans retinoic acid (atRA) upregulated Wnt10b gene expression, although synergistic upregulation (combined atRA and VD(3)) was not seen. RNA interference with vitamin D receptor (VDR) revealed that VD(3) upregulation of Wnt10b, ALPL, and TGF-β2 was mediated through the genomic VDR pathway. In a rat model of de novo hair regeneration by murine DPC transplantation, pretreatment with VD(3) significantly enhanced hair folliculogenesis. Specifically, a greater number of outgrowing hair shafts and higher maturation of regenerated follicles were observed. Together, these data suggest that VD(3) may promote functional differentiation of DPCs and be useful in preserving the hair follicle-inductive capacity of cultured DPCs for hair regeneration therapies.

Vitamin D and bone

All cells comprising the skeleton-chondrocytes, osteoblasts, and osteoclasts-contain both the vitamin D receptor and the enzyme CYP27B1 required for producing the active metabolite of vitamin D, 1,25 dihydroxyvitamin D. Direct effects of 25 hydroxyvitamin D and 1,25 dihydroxyvitamin D on these bone cells have been demonstrated. However, the major skeletal manifestations of vitamin D deficiency or mutations in the vitamin D receptor and CYP27B1, namely rickets and osteomalacia, can be corrected by increasing the intestinal absorption of calcium and phosphate, indicating the importance of indirect effects. On the other hand, these dietary manipulations do not reverse defects in osteoblast or osteoclast function that lead to osteopenic bone. This review discusses the relative importance of the direct versus indirect actions of vitamin D on bone, and provides guidelines for the clinical use of vitamin D to prevent/treat bone loss and fractures.

Role of vitamin D metabolism in cutaneous tumour formation and progression

OBJECTIVES

Very limited information is available on the role of vitamin D in skin carcinogenesis. For most individuals, skin cancer can be readily managed with surgery; however, some patients may face life-threatening neoplasia. Sun exposure, specifically UV radiation, is a causative agent for development of skin cancer, though, somewhat ironically, sunlight through the production of vitamin D may have protective effect against some skin cancers. This review focuses on the development and progression of cutaneous carcinogenesis and the role of vitamin D in the prevention of the initiation and progression of lethal skin cancers.

KEY FINDINGS

Vitamin D is involved in regulation of multiple signalling pathways that have implications in carcinogenesis. Skin cancer metastasis depends on the tumour microenvironment, where vitamin D metabolites play a key role in prevention of certain molecular events involved in tumour progression. The vitamin D receptor (VDR) is a well-known potent regulator of cellular growth and differentiation.

SUMMARY

The VDR's possible involvement in cell death, tumour microenvironment and angiogenesis makes it a candidate agent for cancer regulation.

S100A16 mediation of weight gain attenuation induced by dietary calcium

Dietary calcium influences the regulation of energy metabolism, and weight gain is attenuated by a high-calcium diet. S100A16 is a novel calcium-binding signaling protein of the EF-hand superfamily that promotes adipogenesis. This study aimed to investigate the effect of S100A16 on weight gain attenuation with a calcium-rich diet. An obese rat model was produced after feeding with a high-fat diet. Animals were randomly divided into 4 groups according to the diet provided over 8 weeks: normal diet group; high-fat, normal-calcium diet group; high-fat, high-calcium diet (HH) group; and high-fat, low-calcium diet group. Serum biochemistry was analyzed, and body weight and visceral fat pads were measured. Expression of S100A16 was assayed by Western blotting. Adipogenesis was detected by oil red O staining. Increases in body weight and visceral fat weight were attenuated in the HH group. High-calcium diets decreased the concentrations of serum total cholesterol and triglyceride. Expression of S100A16 decreased in the HH group. Using the 3T3-L1 preadipocyte model, it was observed that elevation of intracellular Ca(2+) via calcium ionophores led to the exclusion of S100A16 from the nucleus. Overexpression of S100A16 in 3T3-L1 preadipocytes enhanced adipogenesis, although a significant reduction in Akt phosphorylation was also detected. High-calcium diets were associated with a significant reduction in body weight gain. High-calcium diets may lead to nuclear exclusion of S100A16, which results in the inhibition of adipogenesis and enhanced insulin sensitivity.

Relevance and implication of genetic determinants to asthma pathophysiology

PURPOSE OF REVIEW

The number of single nucleotide polymorphisms (SNPs) found to be associated with asthma and related phenotypes outnumbers those with functional impacts. In this review we briefly described some of the approaches used to investigate functionality of SNPs, and summarized recent findings related to the characterization of functional SNPs in asthma.

RECENT FINDINGS

For disease-associated SNPs residing in the promoter or 3' untranslated regions, differential protein binding affinity between the major and minor alleles is often the first logical area of investigation. In this review, we described SNPs associated with asthma or related phenotypes in five genes which in the past 12 months have new data implicating potential mechanisms in asthma development.

SUMMARY

Variability in treatment responses poses a great challenge in asthma management. It is established that the genetic makeup of individuals plays a role in asthma development, yet the mechanisms remain unclear. Investigations on the functional impacts of disease-associated SNPs will help us gain insights into potential disease mechanisms, and ultimately lead to effective therapies for those who suffer from asthma.

Model-based clustering reveals vitamin D dependent multi-centrality hubs in a network of vitamin-related proteins

Background

Nutritional systems biology offers the potential for comprehensive predictions that account for all metabolic changes with the intricate biological organization and the multitudinous interactions between the cellular proteins. Protein-protein interaction (PPI) networks can be used for an integrative description of molecular processes. Although widely adopted in nutritional systems biology, these networks typically encompass a single category of functional interaction (i.e., metabolic, regulatory or signaling) or nutrient. Incorporating multiple nutrients and functional interaction categories under an integrated framework represents an informative approach for gaining system level insight on nutrient metabolism.

Results

We constructed a multi-level PPI network starting from the interactions of 200 vitamin-related proteins. Its final size was 1,657 proteins, with 2,700 interactions. To characterize the role of the proteins we computed 6 centrality indices and applied model-based clustering. We detected a subgroup of 22 proteins that were highly central and significantly related to vitamin D. Immune system and cancer-related processes were strongly represented among these proteins. Clustering of the centralities revealed a degree of redundancy among the indices; a repeated analysis using subsets of the centralities performed well in identifying the original set of 22 most central proteins.

Conclusions

Hierarchical and model-based clustering revealed multi-centrality hubs in a vitamin PPI network and redundancies among the centrality indices. Vitamin D-related proteins were strongly represented among network hubs, highlighting the pervasive effects of this nutrient. Our integrated approach to network construction identified promiscuous transcription factors, cytokines and enzymes - primarily related to immune system and cancer processes - representing potential gatekeepers linking vitamin intake to disease.

An estimate of the global reduction in mortality rates through doubling vitamin D levels

BACKGROUND/OBJECTIVES

The goal of this work is to estimate the reduction in mortality rates for six geopolitical regions of the world under the assumption that serum 25-hydroxyvitamin D (25(OH)D) levels increase from 54 to 110 nmol/l.

SUBJECTS/METHODS

This study is based on interpretation of the journal literature relating to the effects of solar ultraviolet-B (UVB) and vitamin D in reducing the risk of disease and estimates of the serum 25(OH)D level-disease risk relations for cancer, cardiovascular disease (CVD) and respiratory infections. The vitamin D-sensitive diseases that account for more than half of global mortality rates are CVD, cancer, respiratory infections, respiratory diseases, tuberculosis and diabetes mellitus. Additional vitamin D-sensitive diseases and conditions that account for 2 to 3% of global mortality rates are Alzheimer's disease, falls, meningitis, Parkinson's disease, maternal sepsis, maternal hypertension (pre-eclampsia) and multiple sclerosis. Increasing serum 25(OH)D levels from 54 to 110 nmol/l would reduce the vitamin D-sensitive disease mortality rate by an estimated 20%.

RESULTS

The reduction in all-cause mortality rates range from 7.6% for African females to 17.3% for European females. Reductions for males average 0.6% lower than for females. The estimated increase in life expectancy is 2 years for all six regions.

CONCLUSIONS

Increasing serum 25(OH)D levels is the most cost-effective way to reduce global mortality rates, as the cost of vitamin D is very low and there are few adverse effects from oral intake and/or frequent moderate UVB irradiance with sufficient body surface area exposed.

Vitamin D and vascular calcification in chronic kidney disease

Vascular calcification is common in patients with chronic kidney disease (CKD) and contributes to the increased rate of cardiovascular morbidity and mortality. The mechanisms regulating vascular calcification are under investigation; it is accepted that vascular calcification is an active and complex process involving many factors that promote or inhibit calcification. Vascular smooth muscle cells undergo transformation into osteogenic cells. This transformation is being stimulated by high phosphate, and more recently the role of the calcium phosphate nanocrystals has gained attention. Experimental models of uremia and in vitro studies have shown that an excess of calcitriol accelerates vascular calcification. However, observational studies suggest that vitamin D provides a survival advantage for patients with CKD. Experimental work shows that for similar serum concentrations of calcium and phosphate paricalcitol produces less vascular calcification than calcitriol suggesting a differential effect at the cellular level. Important issues regarding the role of vitamin D compounds on vascular calcification will be commented in this review.