Vitamin D3 from rat skins irradiated in vitro with ultraviolet light

Different Aspects of the Voltammetric Detection of Vitamins: A Review

Vitamins comprise a group of organic chemical compounds that contribute significantly to the normal functioning of living organisms. Although they are biosynthesized in living organisms, some are also obtained from the diet to meet the needs of organisms, which is why they are characterized as essential chemical compounds. The lack, or low concentrations, of vitamins in the human body causes the development of metabolic dysfunctions, and for this reason their daily intake with food or as supplements, as well as the control of their levels, are necessary. The determination of vitamins is mainly accomplished by using analytical methods, such as chromatographic, spectroscopic, and spectrometric methods, while studies are carried out to develop new and faster methodologies and techniques for their analysis such as electroanalytical methods, the most common of which are voltammetry methods. In this work, a study is reported that was carried out on the determination of vitamins using both electroanalytical techniques, the common significant of which is the voltammetry technique that has been developed in recent years. Specifically, the present review presents a detailed bibliographic survey including, but not limited to, both electrode surfaces that have been modified with nanomaterials and serve as (bio)sensors as well as electrochemical detectors applied in the determination of vitamins.

Vitamin D esters are the major form of vitamin D produced by UV irradiation in mice

The primary source of vitamin D3 for humans is that produced in skin by ultraviolet irradiation. Ultraviolet (UV) B (UVB, 280-310 nm) light causes the isomerization of 7-dehydrocholesterol (7-DHC) to pre-vitamin D3 that is thermally isomerized to vitamin D3. In addition to free vitamin D3, it has been previously reported that esterified vitamin D3 is also found in the skin of rats irradiated with UVB. We found that a large fraction of the vitamin D3 precursor, 7-dehydrocholesterol is in the esterified form. Following UVB irradiation, vitamin D3 esters represent the majority of tissue vitamin D3, comprising approximately 80% in mice. Examination of vitamin D3 ester transport from skin in DBP^-/- mice demonstrated that skin vitamin D3 ester content decreased only in the presence of DBP. No significant binding of vitamin D3 esters by serum was observed and no vitamin D3 esters were detectable in mouse serum after UVB treatment, indicating that the esters are hydrolyzed prior to transport into the circulation. The significance of vitamin D3 esters and their hydrolysis is the subject of current investigation.

Vitamin D binding protein greatly improves bioactivity but is not essential for orally administered vitamin D

Vitamin D3 is a prohormone that is essential for calcium homeostasis. It is naturally produced in the skin by ultraviolet-B (UVB) irradiation of 7-dehydrocholesterol. In the absence of skin production, vitamin D3 can also be obtained from oral sources. However, the actual biological equivalence of naturally produced (i.e., UVB-irradiation of skin) and oral vitamin D3  has not been determined. We previously identified a unique and specific transport mechanism for skin-generated vitamin D3 which requires vitamin D binding protein (DBP); a mechanism that differs from absorption and transport of oral vitamin D3 . In the following report, we examined the impact of this difference on the biological activity of vitamin D3 . We report that UVB-generated vitamin D3 is more potent at raising serum calcium compared to oral vitamin D3 , with the total biological activity being twofold higher. By examining the excretion of radiolabeled vitamin D3 injected unbound or pre-bound by DBP, we attributed the increased activity of skin-generated vitamin D3 to a significant reduction in biliary excretion of DBP-bound vitamin D relative to unbound vitamin D. Thus, removal of vitamin D3 from the skin by the natural DBP system markedly improves biological activity compared to that given orally.

TRPV1 channels as a newly identified target for vitamin D

Vitamin D is known to elicit many biological effects in diverse tissue types and is thought to act almost exclusively upon its canonical receptor within the nucleus, leading to gene transcriptional changes and the subsequent cellular response. However, not all the observed effects of vitamin D can be attributed to this sole mechanism, and other cellular targets likely exist but remain to be identified. Our recent discovery that vitamin D is a partial agonist of the Transient Receptor Potential Vanilloid family 1 (TRPV1) channel may provide new insights as to how this important vitamin exerts its biological effects either independently or in addition to the nuclear vitamin D receptor. In this review, we discuss the literature surrounding this apparent discrepancy in vitamin D signaling and compare vitamin D with known TRPV1 ligands with respect to their binding to TRPV1. Furthermore, we provide evidence supporting the notion that this novel vitamin D/TRPV1 axis may explain some of the beneficial actions of this vitamin in disease states where TRPV1 expression and vitamin D deficiency are known to overlap. Finally, we discuss whether vitamin D may also act on other members of the TRP family of ion channels.

In Vitro Non-Genomic Effects of Calcifediol on Human Preosteoblastic Cells

Several recent studies have demonstrated that the direct precursor of vitamin D₃, the calcifediol [25(OH)D₃], through the binding to the nuclear vitamin D receptor (VDR), is able to regulate the expression of many genes involved in several cellular processes. Considering that itself may function as a VDR ligand, although with a lower affinity, respect than the active form of vitamin D, we have assumed that 25(OH)D₃ by binding the VDR could have a vitamin’s D₃ activity such as activating non-genomic pathways, and in particular we selected mesenchymal stem cells derived from human adipose tissue (hADMSCs) for the in vitro assessment of the intracellular Ca²⁺ mobilization in response to 25(OH)D₃. Our result reveals the ability of 25(OH)D₃ to activate rapid, non-genomic pathways, such as an increase of intracellular Ca²⁺ levels, similar to what observed with the biologically active form of vitamin D₃. hADMSCs loaded with Fluo-4 AM exhibited a rapid and sustained increase in intracellular Ca²⁺ concentration as a result of exposure to 10⁻⁵ M of 25(OH)D₃. In this work, we show for the first time the in vitro ability of 25(OH)D₃ to induce a rapid increase of intracellular Ca²⁺ levels in hADMSCs. These findings represent an important step to better understand the non-genomic effects of vitamin D₃ and its role in endocrine system.

Vitamin D binding protein is required to utilize skin-generated vitamin D

Vitamin D is produced in the skin following exposure to sunlight. Ultraviolet (UV) B (UVB, 280-310 nm) results in isomerization of 7-dehydrocholesterol to previtamin D that spontaneously isomerizes to vitamin D. This pool of skin-derived vitamin D is the major source of vitamin D for animals. However, the mechanisms by which it becomes available remain undefined. It has been assumed that cutaneous vitamin D is transported into the circulation by vitamin D binding protein (DBP), but experimental evidence is lacking. To determine whether cutaneous vitamin D is transported by DBP, we utilized DBP^-/- mice that were made vitamin D-deficient. These animals lack measurable 25(OH)D in blood and are hypocalcemic. As controls, DBP^+/+ animals were vitamin D depleted and made equally hypocalcemic. UV irradiation of DBP^+/+ animals restored serum calcium and serum 25(OH)D while the same treatment of DBP^-/- animals failed to show either a serum calcium or 25(OH)D response despite having normal vitamin D production in skin. Intravenous injection of small amounts of recombinant DBP to the vitamin D-deficient DBP^-/- mice restored the response to UV light. These results demonstrate a requirement for DBP to utilize cutaneously produced vitamin D.

The Use of Vitamin D Metabolites and Analogues in the Treatment of Chronic Kidney Disease

Chronic kidney disease (CKD) and end-stage renal disease (ESRD) are associated with abnormalities in bone and mineral metabolism, known as CKD-bone mineral disorder. CKD and ESRD cause skeletal abnormalities characterized by hyperparathyroidism, mixed uremic osteodystrophy, osteomalacia, adynamic bone disease, and frequently enhanced vascular and ectopic calcification. Hyperparathyroidism and mixed uremic osteodystrophy are the most common manifestations due to phosphate retention, reduced concentrations of 1,25-dihydroxyvitamin D, intestinal calcium absorption, and negative calcium balance. Treatment with 1-hydroxylated vitamin D analogues is useful.

Vitamin D-Mediated Hypercalcemia: Mechanisms, Diagnosis, and Treatment

Hypercalcemia occurs in up to 4% of the population in association with malignancy, primary hyperparathyroidism, ingestion of excessive calcium and/or vitamin D, ectopic production of 1,25-dihydroxyvitamin D [1,25(OH)₂D], and impaired degradation of 1,25(OH)₂D. The ingestion of excessive amounts of vitamin D₃ (or vitamin D₂) results in hypercalcemia and hypercalciuria due to the formation of supraphysiological amounts of 25-hydroxyvitamin D [25(OH)D] that bind to the vitamin D receptor, albeit with lower affinity than the active form of the vitamin, 1,25(OH)₂D, and the formation of 5,6-trans 25(OH)D, which binds to the vitamin D receptor more tightly than 25(OH)D. In patients with granulomatous disease such as sarcoidosis or tuberculosis and tumors such as lymphomas, hypercalcemia occurs as a result of the activity of ectopic 25(OH)D-1-hydroxylase (CYP27B1) expressed in macrophages or tumor cells and the formation of excessive amounts of 1,25(OH)₂D. Recent work has identified a novel cause of non-PTH-mediated hypercalcemia that occurs when the degradation of 1,25(OH)₂D is impaired as a result of mutations of the 1,25(OH)₂D-24-hydroxylase cytochrome P450 (CYP24A1). Patients with biallelic and, in some instances, monoallelic mutations of the CYP24A1 gene have elevated serum calcium concentrations associated with elevated serum 1,25(OH)₂D, suppressed PTH concentrations, hypercalciuria, nephrocalcinosis, nephrolithiasis, and on occasion, reduced bone density. Of interest, first-time calcium renal stone formers have elevated 1,25(OH)₂D and evidence of impaired 24-hydroxylase-mediated 1,25(OH)₂D degradation. We will describe the biochemical processes associated with the synthesis and degradation of various vitamin D metabolites, the clinical features of the vitamin D-mediated hypercalcemia, their biochemical diagnosis, and treatment.

Systems analysis of the prostate transcriptome in African-American men compared with European-American men

AIM

African-Americans (AA) have increased prostate cancer risk and a greater mortality rate than European-Americans (EA). AA exhibit a high prevalence of vitamin D deficiency. We examined the global prostate transcriptome in AA and EA, and the effect of vitamin D₃ supplementation.

PATIENTS & METHODS

Twenty-seven male subjects (ten AA and 17 EA), slated to undergo prostatectomy were enrolled in the study. Fourteen subjects received vitamin D₃ (4000 IU daily) and 13 subjects received placebo for 2 months prior to surgery.

RESULTS

AA show higher expression of genes associated with immune response and inflammation.

CONCLUSION

Systems level analyses support the concept that Inflammatory processes may contribute to disease progression in AA. These transcripts can be modulated by a short course of vitamin D₃ supplementation.

Vitamin D: Historical Overview

A history of vitamin D has been provided, dating from the earliest description of rickets, the disease resulting from vitamin D deficiency, to a current understanding of vitamin D metabolism and the mechanism of action of its hormonal form in regulating gene expression in target organs. Vitamin D is produced in skin by impact of 280-310 nm light on 7-dehydrocholesterol. The vitamin D is then converted in the liver to a circulating form, 25-hydroxyvitamin D that is converted largely, if not exclusively, in the kidney to the final hormone, 1α,25-dihydroxyvitamin D. This hormone functions through a nuclear receptor that regulates expression of key genes in target organs. Among its many resulting functions are increased intestinal calcium and phosphate absorption, bone calcium mobilization, and renal reabsorption of calcium. The resultant increase in serum calcium and phosphate supports bone mineralization, curing rickets, and osteomalacia. There are many other functions of vitamin D that remain to be described that contribute to its health supporting role.

Androgens Attenuate Vitamin D Production Induced by UVB Irradiation of the Skin of Male Mice by an Enzymatic Mechanism

Cutaneous exposure to UVB irradiation is an important source of vitamin D. Here, we examined sex-specific differences in cutaneous vitamin D production in mice. Both male and female mice on a vitamin D-deficient diet manifested vitamin D deficiency, with mineral abnormalities, secondary hyperparathyroidism, and osteomalacia. UVB irradiation significantly increased vitamin D levels in the skin of female mice and normalized serum 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 levels, as well as mineral and skeletal abnormalities. However, in male mice, the vitamin D response to UVB was attenuated and mineral and skeletal abnormalities were not normalized. The vitamin D precursor, 7-dehydrocholesterol (7DHC), was significantly lower in the skin of male than female mice. This reduction was due to local androgen action in the skin as demonstrated by castration studies and skin-specific androgen receptor deletion in male mice, both of which reversed the male phenotype. Local androgen regulation in the skin of the CYP11A1 gene, which encodes a crucial enzyme that metabolizes cholesterol, 7DHC, and vitamin D, appeared to contribute to the gender differences in UVB-induced vitamin D production and to its reversal of vitamin D deficiency. Sex-specific, enzymatically regulated differences in cutaneous production of vitamin D may therefore be of importance to ensure vitamin D sufficiency.

History of the discovery of vitamin D and its active metabolites

Before the twentieth century, it was not possible to describe the essentials of a diet that could support life, growth and reproduction of higher animals. The discovery of vitamin A by McCollum and Davis in 1913 ushered in the era of accessory food substances culminating in the achievement of that goal. It included the discovery of vitamin D and its production in skin caused by ultraviolet light. This was followed by a description of its actions at the physiological level that resulted in a healthy skeleton and beyond. To carry out these functions, vitamin D is converted to a hormone that acts through a nuclear receptor. The findings leading to this concept and their importance to biology and medicine are presented.

Vitamin D3 supplementation (4000 IU/d for 1 y) eliminates differences in circulating 25-hydroxyvitamin D between African American and white men

BACKGROUND

African Americans suffer disproportionately from diabetes and cardiovascular disease and are significantly more likely to have suboptimal concentrations of circulating 25-hydroxyvitamin D [25(OH)D]. The results of epidemiologic and observational studies suggest that there is a link between vitamin D deficiency and the risk of cardiometabolic disorders, which underscores the importance of maintaining healthy concentrations of 25(OH)D.

OBJECTIVE

The objective was to investigate whether daily supplementation with 4000 IU vitamin D(3) for 1 y would eliminate any disparities in circulating concentrations of 25(OH)D between African American and white men.

DESIGN

Serum concentrations of 25(OH)D were measured every 2 mo in 47 subjects who received a daily oral dose of 4000 IU vitamin D(3) for 1 y.

RESULTS

More than 90% of African Americans had serum concentrations of 25(OH)D <32 ng/mL, and approximately two-thirds had serum concentrations <20 ng/mL. Furthermore, there were significant disparities in serum concentrations of 25(OH)D between African American and white men. Supplementation with 4000 IU/d for 1 y eliminated any significant differences in circulating concentrations of 25(OH)D between African American and white men.

CONCLUSION

The results of this clinical study show the feasibility and efficacy of this approach in the elimination of hypovitaminosis D, which is a widespread health disparity among African Americans. This trial was registered at clinicaltrials.gov as NCT01045109.

Vitamin D3-enriched diet correlates with a decrease of amyloid plaques in the brain of AβPP transgenic mice

In addition to its function in calcium and bone metabolism, vitamin D is neuroprotective and important for mitigating inflammation. Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the central nervous system, characterized by neuronal loss in many areas of the brain, and the formation of senile (neuritic) plaques, which increase in number and size over time. The goal of this project was to investigate whether vitamin D3 supplementation would affect amyloid plaque formation in amyloid-β protein precursor (AβPP) transgenic mice that spontaneously develop amyloid plaques within 3-4 months of birth. AβPP mice were fed control, vitamin D3-deficient or vitamin D3-enriched diets for five months, starting immediately after weaning. At the end of the study, the animals were subjected to behavioral studies, sacrificed, and examined for bone changes and brain amyloid load, amyloid-β (Aβ) peptide levels, inflammatory changes, and nerve growth factor (NGF) content. The results obtained indicate that a vitamin D3-enriched diet correlates with a decrease in the number of amyloid plaques, a decrease in Aβ peptides, a decrease in inflammation, and an increase in NGF in the brains of AβPP mice. These observations suggest that a vitamin D3-enriched diet may benefit AD patients.

Does vitamin D make the world go 'round'?

Abstract Vitamin D has emerged from obscurity, and its effects on various organ systems throughout the body down to the cellular level are being discovered. What was once thought to be a simple hormone affecting only bone and calcium metabolism has shifted. We no longer see vitamin D as a "vitamin" important only in childhood, but as a complex hormone that is involved not only in calcium homeostasis but also in the integrity of the innate immune system. Vitamin D deficiency is linked to inflammatory and long-latency diseases such as multiple sclerosis, rheumatoid arthritis, tuberculosis, diabetes, and various cancers, to name a few. In this review, we trace how we came to view vitamin D and how that view led to one of the largest epidemics of nutrient deficiency beginning in the late 20(th) century. We then discuss the needs of vitamin D in the context of the breastfeeding mother and her infant and child, why breastfed infants are particularly at risk, and what to do about it.

The effect of high-dose vitamin D supplementation on serum vitamin D levels and milk calcium concentration in lactating women and their infants

OBJECTIVE

Improve vitamin D status in lactating women and their recipient infants, and measure breast milk calcium concentration [Ca] as a function of vitamin D regimen.

DESIGN/METHODS

Fully breastfeeding mothers were randomized at 1 month postpartum to 2000 (n = 12) or 4000 (n = 13) IU/day vitamin D for 3 months to achieve optimal vitamin D status [serum 25(OH)D > or =32 ng/mL (80 nmol/L)]. Breast milk [Ca], maternal and infant serum 25(OH)D and serum Ca, and maternal urinary Ca/Cr ratio were measured monthly.

RESULTS

Mothers were similar between groups for age, race, gestation, and birth weight. 25(OH)D increased from 1 to 4 months in both groups (mean +/- SD): +11.5 +/- 2.3 ng/mL for group 2000 (p = 0.002) and +14.4 +/- 3.0 ng/mL for group 4000 (p = 0.0008). The 4000 IU/day regimen was more effective in raising both maternal and infant serum levels and breast milk antirachitic activity than the 2000 IU/day regimen. Breast milk [Ca] fell with continued lactation through 4 months in the 2000 and 4000 IU groups. Decline in breast milk [Ca] was not associated with vitamin D dose (p = 0.73) or maternal 25(OH)D (p = 0.94). No mother or infant experienced vitamin D-related adverse events, and all laboratory parameters remained in the normal range.

CONCLUSION

High-dose vitamin D was effective in increasing 25(OH)D levels in fully breastfeeding mothers to optimal levels without evidence of toxicity. Breast milk [Ca] and its decline in both groups during 1 to 4 months were independent of maternal vitamin D status and regimen. Both the mother and her infant attained improved vitamin D status and maintained normal [Ca].

The role of Vitamin D3 metabolism in prostate cancer

Vitamin D deficiency increases risk of prostate cancer. According to our recent results, the key Vitamin D hormone involved in the regulation of cell proliferation in prostate is 25(OH) Vitamin D3. It is mainly acting directly through the Vitamin D receptor (VDR), but partially also through its 1alpha-hydroxylation in the prostate. A deficiency of 25(OH) Vitamin D is common especially during the winter season in the Northern and Southern latitudes due to an insufficient sun exposure, but Vitamin D deficient diet may partially contribute to it. A lack of Vitamin D action may also be due to an altered metabolism or Vitamin D resistance. Vitamin D resistance might be brought up by several mechanisms: Firstly, an increased 24-hydroxylation may increase the inactivation of hormonal Vitamin D metabolites resulting in a Vitamin D resistance. This is obvious in the cancers in which an oncogenic amplification of 24-hydroxykase gene takes place, although an amplification of this gene in prostate cancer has not yet been described. During the aging, the activity of 24-hydroxylase increases, whereas 1alpha-hydroxylation decreases. Furthermore, it is possible that a high serum concentration of 25(OH)D3 could induce 24-hydroxylase expression in prostate. Secondly, Vitamin D receptor gene polymorphism or defects may result in a partial or complete Vitamin D resistance. Thirdly, an overexpression or hyperphosphorylation of retinoblastoma protein may result in an inefficient mitotic control by Vitamin D. Fourthly, endogenous steroids (reviewed by [D.M. Peehl, D. Feldman, Interaction of nuclear receptor ligands with the Vitamin D signaling pathway in prostate cancer, J. Steroid Biochem. Mol. Biol. (2004)]) and phytoestrogens may modulate the expression of Vitamin D metabolizing enzymes. In summary, the local metabolism of hormonal Vitamin D seems to play an important role in the development and progression of prostate cancer.

Natural killer activity in the experimental privational rickets

To study the 'in vivo' importance of vitamin D on the natural killer (NK) activity, rats were submitted to privational rickets induced by a diet deficient in vitamin D and phosphorus (D-P-). Thirty days after the beginning of treatment the animals showed low body weight, changes in the bone development, and decreased levels of 25-hydroxyvitamin D(3) (25-OH D(3)). NK activity, evaluated using a cytotoxicity assay against 51Cr-labeled Yac.1 target cells, was not modified by the rickets-inducing treatment during the first 30 days. Following a long-term treatment (60 days) the rachitic rats (D-P-) exhibited higher NK activity than control animals (D+P+) (P<0.05). On the other hand, D-P+ animals showed higher cytotoxic activity than D-P- and D+P+ groups. Feed replacement to the rachitic rats by a complete diet (D-P-/D+P+) led to a partial recuperation of growth, bone development, and 25-OH D(3) serum levels. The NK activity was also influenced by vitamin D intake, decreasing after treatment.

Forgotten mysteries in the early history of vitamin D

In the early 1920s, workers in both England and the US had discovered that rats on a rachitic diet would remain healthy if irradiated with ultraviolet light. However, they also found, to their surprise, that "control" rats too would recover if either their jar was irradiated without the rat in it or if a cage-mate was removed for irradiation and then returned. The ideas that either air or material objects that had been irradiated continued themselves to convey healthful secondary radiations were investigated but not confirmed. There was then the commercially important finding that with irradiation, some rachitic diets would become anti-rachitic. However, this effect did not explain all the previous findings. Consumption of either small irradiated fecal particles or of feces from irradiated rats was the likely explanation for the recovery of nonirradiated rats, but this was not tested by direct experiment, and it now appears unlikely that feces from irradiated rats would show significant antirachitic activity. It is suggested that an alternative possibility--activity of grease from irradiated fur--deserves investigation.

Synthesis and photoisomerization of provitamin D analog with 11β,19-oxide bridge

Triol diester 1 was converted into the B-ring 5,7-diene 6 representing the first example of the provitamin D analog where the 10β angular methyl group is connected to ring C by a C11/C19 ether linkage. Ultraviolet light irradiation of 6 resulted in the formation of stereoisomeric 9β, 10α-compound 8a. The structure of the photoproduct was established by analysis of vicinal 1H–1H coupling constants and by molecular mechanics. Keywords: 11β, 19-oxido steroids, lumisterol analog, 5,7-androstadienes, electrocyclic reactions, photochemistry.

Catalyzed thermal isomerization between previtamin D3 and vitamin D3 via beta-cyclodextrin complexation

To examine the effect of microenvironments on previtamin D3<==>vitamin D3 isomerization, we have conducted kinetic studies of the reaction in an aqueous solution of beta-cyclodextrin. Our results showed that at 5 degrees C, the forward (k1) and reverse (k2) rate constants for previtamin D3<==>vitamin D3 isomerization were increased by more than 40 and 600 times, respectively, compared with those in n-hexane (k1, 8.65 x 10(-6) versus 1.76 x 10(-7) s-1; k2, 8.48 x 10(-6) versus 1.40 x 10(-8) s-1), the fastest rate of this isomerization ever reported at this temperature. Thermodynamic studies revealed that the equilibrium constant of the reaction was significantly reduced by more than 12-fold when compared to that in n-hexane at 5 degrees C, and the percentage of vitamin D3 at equilibrium was increased as the temperature was increased in beta-cyclodextrin. When complexed with beta-cyclodextrin, the previtamin D3<==>vitamin D3 isomerization became endothermic (delta H zero = 13.05 kJ mol-1) in contrast to being exothermic in other media. We propose that thermodynamically unfavorable cZc conformers of previtamin D3 are stabilized by beta-cyclodextrin, and thus the rate of the isomerization is increased. This conformation-controlled process may play an important role in the modulation of previtamin D3<==>vitamin D3 endocrine system in vivo such as in the sea urchin.

Biologic activity of dihydroxylated 19-nor-(pre)vitamin D3

Vitamin D3 and its hydroxylated metabolites are normally in thermal equilibrium with their previtamin D isomers. To evaluate the biologic activity of 1 alpha, 25-dihydroxyprevitamin D3, we synthesized 19-nor analogs of 1 alpha, 25-dihydroxy(pre)vitamin D3 because the absence of a C19 methylene group prevents the isomerization of these analogs. The affinity of 1 alpha, 25-(OH)2D3-19-nor-D3 for the intestinal vitamin D receptor and plasma vitamin D binding protein was mildly decreased [30 and 20% of the affinity of 1 alpha, 25-(OH)2D3, respectively], but the affinity of 1 alpha, 25-(OH)2-19-nor-previtamin D3 was only 1 and 6% of that of 1 alpha, 25-(OH)2D3 for the receptor and DBP, respectively. The in vitro effects on human promyeloid leukemia (HL-60 cell) differentiation and osteocalcin secretion by human osteosarcoma (MG-63) cells by 1 alpha, 25-(OH)2-19-nor-D3 were nearly identical to those of 1 alpha-25-(OH)2D3, whereas 19-nor-previtamin D3 showed poor activity (2%). The in vivo calcemic effects of both analogs, studied in vitamin D-deficient chicks treated for 10 consecutive days with the analogs, showed no activity of the previtamin D3 analog and reduced calcemic effects (< or = 10%) of 1 alpha, 25-(OH)2-19-nor-D3. We conclude that the previtamin D form of 1 alpha, 25-(OH)2D3 has lost most of its biologic activity in vitro and in vivo.

New concepts of vitamin D functions

Besides its classical actions in calcium metabolism, it is clear that the hormonal form of vitamin D has many new functions, which have only been discovered as a result of following the appearance of its receptor. Furthermore, because of the vitamin D-based endocrine system, the use of vitamin D compounds in treating a variety of diseases has been expanded. We now know that 1.25-(OH)2D3 not only stimulates the intestine to absorb calcium and phosphorus, the bones to mobilize calcium and phosphorus, and the kidney to cause increased renal reabsorption of calcium, but also directly suppresses the parathyroid hormone and is a developmental hormone necessary for the recruitment of cells for osteoclast formation, for female reproduction, for development of skin, and for the treatment of certain malignant conditions.

The increase in skin 7-dehydrocholesterol induced by an hypocholesterolemic agent is associated with elevated 25-hydroxyvitamin D3 plasma level

Vitamin D3 is generated in skin by UV irradiation of 7-dehydrocholesterol (7-DEHC). Whether the 7-DEHC amount in skin affects vitamin D3 formation, and thereby the plasma level of 25-hydroxyvitamin D3 (25[OH]D3) is not known. In the present work we report on the influence on vitamin D and Ca metabolism of a new hypocholesterolemic agent, HCG-917 (0-2-[hydroxy-3-]N'-(2-chlorophenyl)-N-piperazinyl-1- [propyl]-4-chloro-benz-aldoxim-hydrochloride) which inhibits 7-DEHC reductase and thereby increases skin 7-DEHC. Rats were treated with HCG 917 (0.3 and 5.0 mg/kg, orally) for 13 days. HCG 917 caused a dose-dependent decrease in cholesterol and concomitant accumulation of 7-DEHC in plasma and skin. In skin, 7-DEHC was: control: 1.05 +/- 0.20; HCG 917, 0.3 mg/kg: 1.41 +/- 0.22; HCG 917, 5.0 mg/kg: 2.35 +/- 0.35 mg/g. At a dose of 0.3 mg/kg, HCG 917 had no significant influence on the plasma level of neither 25(OH)D3 nor 1,25(OH)2D3. However, at a dose of 5.0 mg/kg, HCG 917 induced a significant increase in plasma 25(OH)D3 (control: 36.2 +/- 2.2; HCG 917 5.0 mg/kg: 57.6 +/- 6.5 nmol/l) and a slight but not significant rise in 1,25(OH)2D3. Calcium balance studies indicated that HCG 917 did not influence intestinal Ca absorption nor urinary Ca excretion. At a dose of 5.0 mg/kg HCG 917 slightly induced a decrease in total plasma Ca. In conclusion, HCG 917 treatment can induce a significant rise in skin 7-DEHC with an increase in plasma 25(OH)D3. These results suggest that variation in the skin level of 7-DEHC can directly influence the cutaneous production of vitamin D3 and thereby the vitamin D status of the organism.

The metabolism and mechanism of action of 1,25-dihydroxyvitamin D3

Much has been learned about the formation of the active metabolite of vitamin D3, 1,25-dihydroxyvitamin D3. Information concerning its formation and catabolism has allowed a clear understanding of factors involved in the maintenance of plasma concentrations of the hormone. The effects of 1,25-dihydroxyvitamin D3 on calcium transporting cells in the intestine are marked and well defined. The tissue (intestinal tissue) is easily isolated and manipulated and hence, this is an ideal tissue in which to examine the mechanism of divalent cation transport. The mechanism by which 1,25-dihydroxyvitamin D3 brings about this effect should help in understanding sterol hormone action.

An open study of vitamin D3 treatment in psoriasis vulgaris

Active forms of vitamin D3, 1 alpha-hydroxyvitamin D3 and 1 alpha,25-dihydroxyvitamin D3, were administered in an open-design study to 40 patients with psoriasis vulgaris in three ways: to 17 patients 1 alpha-hydroxyvitamin D3 was given orally at a dose of 1.0 micrograms/day for 6 months, to four patients 1 alpha,25-dihydroxyvitamin D3 was given orally at a dose of 0.5 microgram/day for 6 months, and 19 patients were given 1 alpha,25-dihydroxyvitamin D3 applied topically at concentration of 0.5 microgram/g of base for 8 weeks. Improvement was observed at the end of the individual study periods in 13 (76%) patients in Group 1 with a mean period of treatment (+/- SD) of 2.7 +/- 0.6 months, in one patient in Group 2 at 3 months after the start of treatment, and in 16 (84%) patients in Group 3 when the chemical was applied for 3.3 +/- 1.2 weeks. No side-effects were observed in any of these trials. These data suggest that psoriasis may respond to active metabolites of vitamin D3 and that abnormalities in vitamin D metabolism or in responsiveness of the skin cells to active metabolites of vitamin D may be involved in the pathogenesis of this skin disease.

Interrelationships in rats of tissue pools of cholecalciferol and 25-hydroxycholecalciferol formed in u.v. light

Vitamin D-deficient rats were irradiated with u.v. light three times weekly for 30 min for several weeks. D3 (cholecalciferol) and 25(OH)D3 (25-hydroxycholecalciferol) concentrations in skin, plasma, muscle and adipose tissue were measured. In other experiments, isolated skin or the whole animal was irradiated once and the cholecalciferol response monitored. Only a small fraction of the 7-dehydrocholesterol in skin is converted into D3 (less than 2%), and the presence of fur decreases the proportion converted into 20% of that occurring in shaved rat skin. D3 formed in the skin disappears relatively slowly, so that about 90% has gone after 7 days. In normal rats 10 micrograms of D3 formed over 2 h irradiation only caused a small rise in plasma D3 concentration over the following week, indicative of a high rate of clearance from this tissue. Irradiation of vitamin D-deficient rats for a prolonged period raised plasma D3 and 25(OH)D3 concentrations to a constant value. D3, but not 25(OH)D3, could be found in adipose tissue and muscle. Prolonged irradiation of normal rats showed these tissues and plasma could hold very large amounts of D3. Pharmacokinetic analysis of the changes in D3 concentration in rats showed that the disposition kinetics of D3 was explained by a two-compartment model with half-lives of 13.8 and 7.7 days. The volume of distribution of the more-slowly-turning-over compartment was 500 ml, which presumably reflects the large amounts of D3 that can accumulate in adipose tissue. Rat skin can synthesize about 0.85 ng of D3/mJ of u.v. light energy, but it seems that not all this is available to the rat. Adipose-tissue D3 is available for use by the rat, the t1/2 being 12.0 days.

The relationship between the vitamin D system and cancer

The classic function of 1,25-dihydroxyvitamin D3, the hormonally active form of vitamin D, is the maintenance of normal levels of calcium and phosphorus in the blood. 1,25-Dihydroxyvitamin D3 binds to a specific receptor protein and exerts its biologic action by a mechanism analogous to that proposed for other steroid hormones, that is, the receptor-ligand complex acts on the chromatin to induce transcription of specific genes. Intracellular receptors that bind 1,25-dihydroxyvitamin D3 with high affinity have been found in a large number of tumor cell lines examined as melanoma, osteosarcoma, and human breast and colonic carcinoma cells. The 1,25-dihydroxyvitamin D3 receptor in these cells has characteristics similar to the receptor in bone and intestine, the known target tissues of the hormone. In fact, 1,25-dihydroxyvitamin D3 inhibits the proliferation of melanoma, osteosarcoma, and breast carcinoma cells. More recently, 1,25-dihydroxyvitamin D3 has been shown to suppress the growth and induce monocytic differentiation of murine and human myeloid leukemia cells in vitro. These results point to a previously unsuspected involvement of vitamin D in cell proliferation and differentiation and suggest that analogs of the vitamin D hormone may be of interest as possible therapeutic agents in the treatment of malignancy.

The physiology and pathophysiology of vitamin D

The vitamin D endocrine system plays an important role in the maintenance of normal calcium homeostasis. Abnormalities of this system occur in many conditions, such as rickets, osteomalacia, hypoparathyroidism, and hyperparathyroidism. The diagnosis and treatment of these disorders will be facilitated if the clinician understands the general mechanisms by which defects in vitamin D metabolism and action occur. We review this information and discuss the use and limitations of vitamin D metabolite assays for diagnosis of clinical disorders of mineral metabolism.

In vitro synthesis of vitamin D-3 by cultured human keratinocytes and fibroblasts: action spectrum and effect of AY-9944

With delineation of the photochemical events occurring in the skin after ultraviolet exposure, there has been increased interest in the skin's role in the vitamin D-3-endocrine system. We provide here in vitro conditions for the generation of both labelled (from [3H]acetate) and unlabelled vitamin D-3 in cultures of human keratinocytes and fibroblasts. Sterol precursors and photoproducts in irradiated and non-irradiated cultures are identified by co-chromatography, ultraviolet absorbance spectra, thermal conversion characteristics of previtamin D-3 and mass spectrometry. Because the conversion of 7-dehydrocholesterol to cholesterol is more efficient in vitro than in vivo, the specific delta 7 inhibitor, AY-9944, was added in non-toxic doses to modulate 7-dehydrocholesterol content. Both cell types were equally capable of generating photoproducts, depending on the amount of 7-dehydrocholesterol present. The 290 +/- 5 and 295 nm filters were much more efficient than the 305 nm filter for generating previtamin D-3 and vitamin D-3 in fibroblasts. In contrast, the 305 nm filter was as efficient as the 290 +/- 5 and 295 nm filters in keratinocytes, where it yielded previtamin D-3, with much less lumisterol and tachysterol than appeared with the shorter-wavelength filters. The amount of lumisterol and tachysterol versus previtamin D-3 formed in both cell types was dependent on the total energy applied, with lower energies (less then 1 J/cm2) favoring previtamin D-3 over the other photoproducts. The use of cultured cells provides a system whereby the regulation of vitamin D-3 synthesis by extracutaneous factors can be studied in a homogeneous setting.

Vitamin D and skeletal tissues

It is now accepted that vitamin D is an integral part of a complex endocrine system, one with far-reaching implications in mineral metabolism. Reviews of the sources, functions and metabolism of vitamin D, as currently understood, are presented as a prelude to discussions of the role of vitamin D in calcium and phosphorous homeostatis and possible specific roles for vitamin D in mineralized tissues. Data describing a possible regulatory function for vitamin D in bone and bone protein metabolism are presented. Some of the controversy which presently exists regarding the biochemical mechanism of the action of this vitamin is discussed. Finally, the possible relationship of vitamin D and disorders of skeletal tissues is described.

A histochemical study on the vitamin D synthesis into the epidermis

Using a suitable histochemical method vitamins D and 7-dehydrocholesterol could be shown into the epidermis of several mammal species. As the histochemical method used is able to discriminate vitamins D and 7-dehydrocholesterol from cholesterol and its esters, the sites where these vitamins were synthesized within the epidermis layers could be established. Vitamins D and 7-dehydrocholesterol were found into the epidermis in the same sites where cholesterol and its esters take place, such as: the keratinizing cell thick membrane and the stratum spinosum and stratum granulosum keratinocytes cytoplasm. Inside the keratinocyte cytoplasm vitamin D shows a granular pattern and appears weakly bound to proteins. The reactivity of such granules seems to be partially blocked as could be shown by an hydrolysis accomplished previously. After the hydrolysis reactive vitamin D was also found inside the epidermis intercellular space. The results suggest that vitamin D is synthesized into the cytoplasm of stratum spinosum and stratum granulosum keratinocytes, where it appears weakly bound to proteins. Afterwards it reaches the intercellular space, where its synthesis is accomplished and it becomes firmly protein-bound losing its histochemical reactivity. However, after a suitable hydrolysis the histochemical reactivity could be recovered. From the intercellular spaces vitamin D could take 2 fates: It was partially incorporated on the keratinizing cell thick membrane out surface and eliminated by means of the epidermis exfoliation. It was partially absorbed after passing across the basement membrane. On the other hand, the vitamin D placed inside the stratum spinosum and stratum granulosum keratinocytes cytoplasm become incorporated on the inner surface of the keratinizing cell thick membrane. The relationship between vitamin D biosynthesis and the epidermis lamellar bodies was discussed.

Alterations in rat epidermis provoked by chronic vitamin D deficiency

Long-term effects of vitamin D deficiency on epidermis were studied using histometric techniques, [3H]thymidine incorporation into DNA (labeling index), estimation of epidermal acid phosphatase activity, and one-dimensional gel electrophoresis of keratin proteins. The decrease in epidermal thickness due to a reduced number of granular cell layers and a lower level of epidermal acid phosphatase activity were observed in vitamin D-deficient rats. The number of nuclei in the basal layer was increased. No changes in labeled index due to chronic vitamin D deficiency or to 'single injection of 1,25-dihydroxycholecalciferol to vitamin D-deficient rats were observed. A comparative study of the keratin composition revealed differences in the keratin polypeptide pattern: vitamin D-deficient epidermis specifically lacked two low-molecular-weight components and presented several quantitative differences among other keratin polypeptides. The changes in epidermal morphology and metabolism that took place with vitamin D deficiency were independent of plasma calcium levels because similar modifications were present in vitamin D-deficient but normocalcemic rats (fed a diet rich in calcium and supplemented with lactose). These findings suggest that vitamin D may be one of the important factors for maintaining normal epidermal structure and metabolism through an effect on cell differentiation and formation of granular cell layers. They offer the possibility of using epidermal modification as an additional marker of vitamin D deficiency.

Vitamin D3 production by cultured human keratinocytes and fibroblasts

We have demonstrated that monolayers of human cultured newborn foreskin keratinocytes and fibroblasts elaborate vitamin D3 following exposure to UV-B. This in vitro system provides a new means to study those factors (hormones, ions, vitamin D3 metabolites, etc.) that regulate the production of vitamin D3 by human skin cells. Vitamin D3 production was enhanced greatly by using cells that were pre-treated with AY-9944, a non-toxic drug that inhibits cholesterologenesis while elevating cellular levels of 7-dehydrocholesterol, the sterol precursor of vitamin D3. The pre-D3 formed within viable, irradiated cells is transformed to D3 within a matter of hours at 37 degrees C, and keratinocytes proved to be more proficient sources of the vitamin and its metabolites than corresponding skin fibroblasts.

Application of high-performance liquid chromatography to the study of esterified 7-dehydrocholesterol in rat skin

A novel and precise method for determining free and esterified 7-dehydrocholesterol in rat skin was developed by using a two-step high-performance liquid chromatography system. This method involves initial lipid extraction, separation of the free and esterified 7-dehydrocholesterol by, firstly, preparative high-performance liquid chromatography, saponification, and determination by, secondly, analytical high-performance liquid chromatography. This method was applied to the study of the 7-dehydrocholesterol in rat skin. Almost all of the 7-dehydrocholesterol in rat skin was present in an esterified form (78-93%). Ultraviolet exposure of the skin increased total 7-dehydrocholesterol content, however, the percentage of esterified 7-dehydrocholesterol was not altered appreciably. Application of this method to the study of the photo-metabolism of 7-dehydrocholesterol in rat skin revealed that almost all of the vitamin D3 produced by ultraviolet rays was in the esterified form.

Isolation and identification of tachysterol3 in rat skin exposed to ultraviolet light

In order to investigate the mechanism of the cutaneous synthesis of vitamin D3 in vivo, a photolysis by-product of previtamin D3 in organic solvent, namely, tachysterol3 was isolated and identified in ultraviolet-exposed rat skin. Tachysterol3 was identified by chromatographic comigration of an ultraviolet-absorbing peak wih authentic tachysterol3 in straight-phase HPLC (Zorbax SIL column) and reversed-phase HPLC (Nucleosil 5C18 column), and by the ultraviolet absorption spectrum. The comparison of the extent of formation of tachysterol3 between in rat skin in vivo and in ethanol solution indicated that the yield in rat skin is similar to that in organic solvent. The results suggest that the reaction mechanism in rat skin in vivo may be identical wit that in organic solvents.

The cutaneous photosynthesis of previtamin D3: a unique photoendocrine system

The skin has been recognized as the site for the sun-mediated photosynthesis of vitamin D3; until recently, however, very little was known about either the sequence of events leading to the formation of vitamin D3 in human skin or the factors that regulate the synthesis of this hormone. It is now established that, during exposure to sunlight, the cutaneous reservoir of 7-dehydrocholesterol (principally in the stratum Malpighii) converts to previtamin D3. Once this thermally labile previtamin is formed, it undergoes a temperature-dependent isomerization to vitamin D3 over a period of 3 days. The plasma vitamin-D binding protein preferentially translocates vitamin D3 from the skin into the circulation. During prolonged exposure to the sun, the accumulation of previtamin D3 is limited to about 10 to 15% of the original 7-dehydrocholesterol content because the previtamin photoisomerizes to 2 biologically inert photoproducts, lumisterol3 and tachysterol3. Increases in either latitude or the melanin concentration in the skin diminish the epidermal synthesis of previtamin D3. A single total body exposure to 3 minimal erythemal doses of ultraviolet radiation increased the vitamin-D3 levels in the serum 25-hydroxyvitamin-D levels after 7 days. The unique mechanism for the cutaneous synthesis, storage, and steady release of vitamin D3 into the circulation prompted an investigation into the potential therapeutic benefits of using the skin as the site for the synthesis and absorption of vitamin-D3 metabolites.

The biochemical basis of renal osteodystrophy and post-menopausal osteoporosis: a view from the vitamin D system

The vitamin D endocrine system is now known to play an essential role in the regulation of plasma calcium and phosphorus concentrations and in overall organismal calcium economy. These two basic functions of the vitamin D endocrine system have provided important new insight into several disease states. The two disease states discussed here are the genesis of renal osteodystrophy and of post-menopausal osteoporosis. It seems likely that defects of alternations in the vitamin D system play important roles in the development of these disease states. Successful treatment undoubtedly will involve the vitamin D system and most likely the active form of vitamin D, 1,25- (OH)2D3.