Antibody production in mice requires neither vitamin D, nor the vitamin D receptor.

The vitamin D receptor as well as its ligand have been localized to various immune tissues and cells. These observations have led researchers to hypothesize a role for vitamin D in the immune system. However, a specific role for vitamin D in immunity has yet to be clearly delineated. The work in this report was undertaken to determine if mounting an antibody response is altered in the face of vitamin D-deficiency or when the signaling pathway is eliminated by removal of the nuclear receptor. This investigation provides direct evidence vitamin D is not necessary for producing antibodies, a process paramount for optimal attack against many foreign organisms. The idea that vitamin D plays a significant role in immunity has been proposed repeatedly for many years. To address this important idea we have carried out studies in mice to determine if vitamin D plays a significant role in antibody production. Two animal models were utilized: mice depleted of vitamin D and mice devoid of the vitamin D receptor. Further, a possible role of hypocalcemia resulting from vitamin D deficiency in antibody production was determined. Neither the absence of vitamin D or the vitamin D receptor nor hypocalcemia affected the ability of mice to mount an antibody response to an antigen challenge. Thus, we found no evidence that vitamin D or normal serum calcium is required for this major form of immunity.

The absence of 25-hydroxyvitamin D3-1α-hydroxylase potentiates the suppression of EAE in mice by ultraviolet light.

Ultraviolet B (UVB) light suppresses the development of multiple sclerosis (MS) in patients and experimental autoimmune encephalomyelitis (EAE) in mice. Although vitamin D3 is produced by ultraviolet light, the suppression of EAE by narrow band UVB (NBUVB) is independent of vitamin D3. However, it is possible that the NBUVB suppression of EAE can be further influenced by 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). We used NBUVB lamps (10KJ/m(2)) to irradiate both wild type (WT) and 1α-hydroxylase knockout mice (CYP27B1 KO) that were then induced to develop EAE. There was a complete elimination of EAE development by NBUVB in the KO mice. On the other hand, the NBUVB treatment of WT mice reduced but did not eliminate the severity or incidence of EAE. This suggests that the presence of 1,25-dihydroxyvitamin D3 actually counteracts the suppressive effect of NBUVB. In support of this concept, cytokines (IFN-γ, IL-10) and chemokine (CCL-5) mRNA in spinal cord were reduced in wild type or eliminated in the KO mice by the NBUVB. Cytokine mRNA levels in the spinal cord correlated with clinical scores in both WT and KO mice.

1,25-Dihydroxyvitamin D is not responsible for toxicity caused by vitamin D or 25-hydroxyvitamin D.

Vitamin D intoxication was produced with oral doses of either vitamin D3 or 25-hydroxyvitamin D3 in CYP27B1 -/- (1α-hydroxylase knockout) and wild-type mice. These compounds were equally toxic in wild-type and the mutant mice. Since the null mutant mice are unable to produce 1,25-dihydroxyvitamin D, it is clear 1,25-dihydroxyvitamin D is not responsible for vitamin D intoxication. On the other hand, 25-hydroxyvitamin D rises to levels of 400-700 ng/ml or 1000-1750 nM in the serum of both groups of mice. Toxicity was evidenced by severe hypercalcemia and weight loss. Measurement of 1,25-dihydroxyvitamin D3 in serum confirmed its absence from serum of the CYP27B1 -/- mice given 25-hydroxyvitamin D3. Since high concentrations of 25-hydroxyvitamin D can bind the vitamin D receptor and can induce transcription, 25-hydroxyvitamin D is likely responsible for toxicity of vitamin D excess.

CYP27B1 null mice with LacZreporter gene display no 25-hydroxyvitamin D3-1alpha-hydroxylase promoter activity in the skin.

The hormonally active form of vitamin D(3),1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], is synthesized in the kidney through a tightly regulated reaction catalyzed by 25-hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-hydroxylase), the product of the CYP27B1 gene. Through gene targeting in embryonic stem cells, we engineered a mouse strain in which the coding region of the 1alpha-hydroxylase gene is replaced by the genes for beta-galactosidase (lacZ) and neomycin resistance. Null mice produced no detectable 1alpha-hydroxylase transcript. The mice grew normally when maintained on a balanced diet containing 1,25(OH)(2)D(3) but rapidly developed rickets when phosphorus and 1,25(OH)(2)D(3) were restricted. Rickets was curable through administration of 1,25(OH)(2)D(3) but not its biological precursor, 25-hydroxyvitamin D(3). Upon administration of a diet low in calcium and devoid of any form of vitamin D(3), beta-galactosidase activity was detected in the kidneys of the -/- and +/- mice and in placentas harvested from -/- females bred with -/- males. No beta-galactosidase activity was detected in skin sections or in primary keratinocyte cultures from -/- animals. Our results demonstrate we have generated 1alpha-hydroxylase null mice that display phenotypes characteristic of vitamin D-dependency rickets type I. From the histochemical analysis of reporter gene expression in these mice, we conclude that acute 1,25(OH)(2)D(3) deficiency in otherwise healthy animals does not stimulate local production of 1,25(OH)(2)D(3) in the skin. These findings stand in contrast to previously published reports of 1,25(OH)(2)D(3) production in keratinocytes.

Hypercalcemia produced by parathyroid hormone suppresses experimental autoimmune encephalomyelitis in female but not male mice.

Besides its role in regulating serum levels of calcium and phosphorus, 1alpha, 25-dihydroxyvitamin D3 (1,25-(OH)2D3) has potent effects on the immune system and suppresses disease in several animal models of autoimmune disorders including experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. While the amount of 1,25-(OH)2D3 needed to prevent EAE is dependent on the gender of the mouse and amount of calcium available in the diet, the minimum levels of 1,25-(OH)2D3 sufficient to prevent disease cause hypercalcemia. To test if hypercalcemia independent of high levels of 1,25-(OH)2D3 can suppress EAE, we used a 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-hydroxylase) knockout mouse strain. Because these 1alpha-hydroxylase knockout mice lack the parathyroid hormone (PTH)-regulated enzyme that synthesizes 1,25-(OH)2D3, hypercalcemia from increased bone turnover was created by continuous administration of PTH without changing the circulating levels of 1,25-(OH)2D3. This PTH-mediated hypercalcemia generated after EAE induction prevented disease in female mice but not male mice. When hypercalcemia was prevented by diet manipulation, PTH administration no longer prevented EAE. We conclude that hypercalcemia is able to prevent EAE after disease induction in female mice.

Parathyroid hormone decreases renal vitamin D receptor expression in vivo.

The vitamin D receptor (VDR) is a nuclear transcription factor responsible for mediating the biological activities of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. Renal and parathyroid gland VDR content is an important factor in calcium homeostasis, vitamin D metabolism, and the treatment of secondary hyperparathyroidism and renal osteodystrophy. In these tissues, VDR expression is highly regulated by the calcium and vitamin D status. Although 1,25(OH)(2)D(3) up-regulates VDR expression, hypocalcemia and vitamin D deficiency result in drastically reduced expression of the receptor. The generation of 25-hydroxyvitamin D(3)-1alpha-hydroxylase-null mice, which are incapable of endogenously producing 1,25(OH)(2)D(3), has allowed us to investigate the influence of parathyroid hormone (PTH) on VDR expression independent of PTH-mediated increases in 1,25(OH)(2)D(3). Administration of human PTH (1-34) (110 microg/kg per day) for 48 h reduced renal VDR levels from 515 to 435 fmol/mg protein (15%, P < 0.03) in wild-type mice. In the 25-hydroxyvitamin D(3)-1alpha-hydroxylase-null mice, PTH administration strongly reduced renal VDR levels, from 555 to 394 fmol/mg protein (29%, P < 0.001). These results demonstrate that PTH is a potent down-regulator of VDR expression in vivo.

2-Methylene analogs of 1alpha-hydroxy-19-norvitamin D3: synthesis, biological activities and docking to the ligand binding domain of the rat vitamin D receptor.

In continuing efforts towards the synthesis of biologically active vitamin D compounds of potential therapeutic value, new 2-methylene-1alpha-hydroxy-19-norvitamin D(3) analogs 3 and 4 with modified alkyl side chains have been synthesized. The key synthetic step involved Lythgoe-type Wittig-Horner coupling of Windaus-Grundmann type ketones 9, possessing different 17beta-alkyl substituents, with the phosphine oxide 10 prepared from (-)-quinic acid. The prepared vitamins 3 and 4 were ca. eight times less potent than 1alpha,25-dihydroxyvitamin D(3) (1alpha,25-(OH)(2)D(3)) (1) in binding to the rat intestinal vitamin D receptor (VDR). In comparison with the hormone 1 they exhibited slightly lower cellular HL-60 differentiation activity. When tested in vivo; the analog 3 was characterized by very high bone calcium mobilizing potency and intestinal calcium transport activity. Unexpectedly, the 25-methyl compound 4 showed marked calcemic activity in both assays. Computational docking of the vitamin 3 into the binding pocket of the rat vitamin D receptor is also reported.

Biologically active noncalcemic analogs of 1alpha,25-dihydroxyvitamin D with an abbreviated side chain containing no hydroxyl.

Since the discovery of the active metabolite of vitamin D, i.e., 1alpha,25-dihydroxyvitamin D3, there has been a continuous effort to synthesize analogs able to carry out many of the functions of the native hormone without raising serum calcium concentration. The present report provides a series of previously undescribed analogs wherein this goal is realized. We have prepared 2-methylene-19-nor-1alpha-hydroxyvitamin D analogs of 1,25-(OH)2D3 that possess only two to four carbons of the side chain without a hydroxyl thereon. Compared to 1,25-(OH)2D3, these analogs are slightly less active in binding to the vitamin D receptor, in causing HL-60 differentiation, and are slightly less active in in vitro transcription assays using the 24-hydroxylase promoter attached to a luciferase reporter gene. Of considerable importance is that these analogs, given to rats at daily doses of up to 70 microg/kg of body weight per day, are either unable or only slightly able to raise serum calcium concentration but are nevertheless able to suppress parathyroid hormone levels in plasma up to 100% and induce 24-hydroxylase mRNA in skin. Because of their ability to act in vivo without raising serum calcium levels, they may be of considerable interest for the systemic treatment of diseases such as psoriasis, cancer, and secondary hyperparathyroidism of renal failure, where a rise in serum calcium is undesirable.

Regulation of the murine renal vitamin D receptor by 1,25-dihydroxyvitamin D3 and calcium.

Renal vitamin D receptor (VDR) is required for 1,25-dihydroxyvitamin D3-[1,25(OH)2D3]-induced renal reabsorption of calcium and for 1,25(OH)2D3-induced 1,25(OH)2D3 24-hydroxylase. The long-term effect of vitamin D and dietary calcium on the expression of renal VDR was examined in the nonobese diabetic mouse. Vitamin D-deficient and vitamin D-replete mice were maintained on diets containing 0.02%, 0.25%, 0.47%, and 1.20% calcium with or without 50 ng of 1,25(OH)2D3 per day. Vitamin D-replete mice on a 1.20% calcium diet had renal VDR levels of 165 fmol/mg protein. Calcium restriction caused renal VDR levels to decrease to <30 fmol/mg protein in vitamin D-deficient mice and to approximately 80 fmol/mg protein in vitamin D-replete mice. When dietary calcium was present, 50 ng of 1,25(OH)2D3 elevated the VDR levels 2- to 10-fold, depending on vitamin D status and the level of calcium. In the absence of either vitamin D or calcium, the VDR mRNA was expressed at a basal level. 1,25(OH)2D3 supplementation caused relative VDR mRNA to increase 8- to 10-fold in the vitamin D-deficient mouse when dietary calcium was available. This increase was completely absent in the calcium-restricted mice. This in vivo study demonstrates that 1,25(OH)2D3 and calcium are both required for renal VDR mRNA expression above a basal level, furthering our understanding of the complex regulation of renal VDR by 1,25(OH)2D3 and calcium.

2-Ethyl and 2-ethylidene analogues of 1alpha,25-dihydroxy-19-norvitamin D(3): synthesis, conformational analysis, biological activities, and docking to the modeled rVDR ligand binding domain.

Novel 19-nor analogues of 1alpha,25-dihydroxyvitamin D(3) were prepared and substituted at C-2 with an ethylidene group. The synthetic pathway was via Wittig-Horner coupling of the corresponding A-ring phosphine oxides with the protected 25-hydroxy Grundmann's ketones. Selective catalytic hydrogenation of 2-ethylidene analogues provided the 2alpha- and 2beta-ethyl compounds. The 2-ethylidene-19-nor compounds with a methyl group from the ethylidene moiety in a trans relationship to the C(6)-C(7) bond (E-isomers) were more potent than the corresponding Z-isomers and the natural hormone in binding to the vitamin D receptor. Both geometrical isomers (E and Z) of (20S)-2-ethylidene-19-norvitamin D(3) and both 2alpha-ethyl-19-norvitamins (in the 20R- and 20S-series) have much higher HL-60 differentiation activity than does 1alpha,25-(OH)(2)D(3). Both E-isomers (20R and 20S) of 2-ethylidene vitamins are characterized by very high calcemic activity in rats. The three-dimensional structure model of the rat vitamin D receptor and the computational docking of four synthesized (20R)-19-norvitamin D(3) analogues into its binding pocket are also reported.

Protein synthesis is required for optimal induction of 25-hydroxyvitamin D(3)-24-hydroxylase, osteocalcin, and osteopontin mRNA by 1,25-dihydroxyvitamin D(3).

The regulation of the 25-hydroxyvitamin D(3)-24-hydroxylase gene by 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) has been extensively studied. It is well established that two vitamin D response elements in the promoter are responsible for the 1,25(OH)(2)D(3) induction of transcription. Surprisingly, this induction is blocked by the protein synthesis inhibitor, cycloheximide (CHX). In AOK-B50 cells, 1,25(OH)(2)D(3) caused a large induction of 24-hydroxylase mRNA by 7h; however, the addition of CHX simultaneously or 2h after 1,25(OH)(2)D(3) addition caused 76.4+/-13.0 and 37.1+/-18.8% reductions in the mRNA, respectively. Addition of CHX 4h after 1,25(OH)(2)D(3) had the opposite effect, and 21.7+/-17.2% more mRNA was observed after 7h. Similar patterns of mRNA expression were observed in other cell lines. CHX also decreased the induction by 1,25(OH)(2)D(3) of osteocalcin and osteopontin mRNA in ROS17/2.8 cells when added together with 1,25(OH)(2)D(3). The effect of CHX on the expression of a stably transfected luciferase construct under the control of 1400bp of 24-hydroxylase promoter indicates that a 1,25(OH)(2)D(3)-inducible transcription factor(s) that acts in the promoter region may at least in part be responsible for the effect of CHX on mRNA production of target genes.

Vitamin D receptor (VDR) mRNA and VDR protein levels in relation to vitamin D status, insulin secretory capacity, and VDR genotype in Bangladeshi Asians.

Associations have been reported between vitamin D receptor (VDR) gene polymorphisms, type 1 diabetes, insulin secretion, and the insulin resistance syndrome. As VDR polymorphisms have no known functional significance, these findings may implicate a variant of the VDR gene or a locus in linkage disequilibrium with the VDR. We have examined VDR mRNA and VDR protein levels in relation to VDR polymorphisms (41 Bangladeshi subjects) and analyzed insulin secretory capacity (143 Bangladeshi subjects), allowing for other known determinants. Peripheral blood mononuclear cells (PBMCs) from subjects who had been genotyped for BsmI, ApaI, TaqI, and FokI VDR restriction fragment length polymorphisms were used for both total VDR mRNA quantitation (using TaqMan) and measurement of VDR protein levels (using a specific micro-immunoassay). Stepwise multiple regression analyses were used (to P < 0.05) to analyze the data. For the insulin secretion index, the best-fit model (n = 143, P < 0.0001) gave age (P = 0.002), TaqI (P < 0.0001), and BMI (P = 0.001) as independent determinants; with the inclusion of VDR mRNA and VDR protein levels, VDR mRNA was the sole independent determinant (n = 41, P = 0.024). However, the best-fit model for VDR mRNA (P = 0.004) gave FokI (P = 0.044) and TaqI (P = 0.04) genotypes and insulin secretory capacity (P = 0.042) as independent determinants. For VDR protein levels, the best-fit model (P = 0.006) gave TaqI genotype (P = 0.005) and circulating 1,25-dihydroxyvitamin-D levels (P = 0.03) as independent determinants. In conclusion, these studies confirm an association between VDR polymorphisms and insulin secretory capacity and demonstrate the VDR genotype to be a significant determinant of VDR mRNA and VDR protein levels in PBMCs, providing functional support to previously described genetic associations with the VDR gene. Furthermore, VDR expression has been shown to be a determinant of insulin secretory capacity.

New highly calcemic 1 alpha,25-dihydroxy-19-norvitamin D(3) compounds with modified side chain: 26,27-dihomo- and 26,27-dimethylene analogs in 20S-series.

New highly potent 2-substituted (20S)-1 alpha,25-dihydroxy-19-norvitamin D(3) analogs with elongated side chain were prepared by Wittig-Horner coupling of A-ring phosphine oxide with the corresponding protected (20S)-25-hydroxy Grundmann's ketones. Biologic evaluation in vitro and in vivo of the synthesized compounds was accomplished. All the synthesized vitamins possessing a 25-hydroxylated saturated side chain were slightly less active (3-5X) than 1 alpha,25-dihydroxyvitamin D(3) in binding to the porcine intestinal vitamin D receptor and significantly more potent (12-150X) in causing differentiation of HL-60 cells. In vivo, 2-methylene-26,27-dihomo and 2 alpha-methyl-26,27-dimethylene analogs were at least 10 times more active, and 2 alpha-methyl-26,27-dihomo compound at least 5 times more active than the vitamin D hormone both in stimulating intestinal calcium transport and bone calcium mobilization (serum calcium increase). It was also established that a 260 pmol dose of the corresponding 2 beta-methyl analogs had a similar effect on intestinal calcium transport and a much more pronounced effect on bone calcium mobilization as the same dose of 1 alpha,25-dihydroxyvitamin D(3).