Growth inhibition of human colon adenocarcinoma-derived Caco-2 cells by 1,25-dihydroxyvitamin D3 and two synthetic analogs: relation to in vitro hypercalcemic potential

Summary The effect of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) and of two synthetic analogs, 1,25S,26-tri-hydroxy-22-vitamin D₃ (1,25,26(OH)₃-22ene-D₃, Ro 23-4319) and 1,25-dihydroxy-16-23yne-vitamin D₃ (1,25(OH)₂-16ene-23yne-D₃, Ro 23-7553) on cell growth was evaluated by determination of [³H]thymidine incorporation into DNA of human colon adenocarcinomaderived Caco-2 cells. The extent of growth inhibition by the vitamin D compounds varied between 20–40% (at 10^–8 M), depending on particular growth conditions of Caco-2 cells as well as on the molecular structure of the vitamin D sterols. In confluent, i.e., rather quiescent cells, all three vitamin D compounds were equipotent in suppressing growth. In rapidly dividing log phase cells, 1,25(OH)₂-16ene-23yne-D₃ or 1,25,26(OH)₃-22ene-D₃ were ten or five times, respectively, more efficient than 1,25(OH)₂D₃. A substantial effect on induction of the colonocyte differentiation marker alkaline phosphatase was only elicited by 1,25(OH)₂-16ene-23yne-D₃.The ability of the vitamin D compounds to raise intestinal calcium absorption was evaluated by determination of ⁴⁵Ca²⁺ accumulation in embryonic chick duodenal explants. In this assay, both synthetic analogs were less effective than 1,25(OH)₂D₃ by a factor of 20.The intrinsic bone resorbing activities of the vitamin D analogs were compared in organ-cultured neonatal mouse calvariae. The most effective antiproliferative compound, 1,25(OH)₂-16ene-23yene-D₃, stimulated calcium release from cultured bones at concentrations less than 10^–11 M, and was thus ten times more potent than 1,25(OH)₂D₃ and hundred times more than 1,25,26-(OH)₃-22ene-D₃.A preliminary report of this study was presented at the International Conference on Calcium Regulating Hormones, April 24–29, 1992, Florence, ItalyCorrespondence to M. Peterlik at the above address     

Interaction between calcium and cadmium in the 1,25-dihydroxyvitamin D3 stimulated rat duodenum

It has been suggested that calcium and cadmium compete for an intestinal transport system that is vitamin D dependent. To further test this hypothesis, the interaction between calcium and cadmium during transport in the duodenum of rat was investigated. Control rats maintained on a diet adequate in vitamin D, calcium, and phosphorus were compared to rats on the same diet administered 500 ng of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) 4 hr before transport measurement with everted sacs. Active transport of calcium was evident in control rats and was further stimulated by exogenous 1,25(OH)₂D₃. Added to mucosal bathing fluid 10 μm cadmium partially inhibited active calcium transport both in controls and in rats receiving 1,25(OH)₂D₃; 100 μm cadmium completely blocked active transport in both groups. Water transport was also inhibited by 10 and 100 μm cadmium. Cadmium uptake and transport were not affected by 1,25(OH)₂D₃. The accumulation of cadmium in mucosal tissue was significantly inhibited by 1 mm calcium, but there was no significant effect on uptake or transmural transport. The findings suggest that cadmium and calcium do not interact specifically at a 1,25(OH)₂D₃-dependent transport site. The interaction between calcium and cadmium in the duodenal mucosa could be related to the action of cadmium in blocking active transport processes.     

Differential regulation of intestinal and hepatic CYP3A by 1α,25-dihydroxyvitamin D3: Effects on in vivo oral absorption and disposition of buspirone in rats

1α,25-Dihydroxyvitamin D₃ (also called 1,25(OH)₂D₃ or calcitriol) is the biologically active form of vitamin D, which functions as a ligand to the vitamin D receptor (VDR). It was previously reported that intestinal cytochrome P450 3A (CYP3A) expression was altered by 1,25(OH)₂D₃-mediated VDR activation. However, to clarify whether the change in CYP3A subfamily expression by VDR activation can affect metabolic function, further evidence is needed to prove the effect of 1,25(OH)₂D₃ treatment on CYP3A-mediated drug metabolism and pharmacokinetics. Here, we report the effects of 1,25(OH)₂D₃ on CYP3A activity and in vivo pharmacokinetics of buspirone in Sprague–Dawley rats. CYP3A mRNA expression and CYP3A-mediated testosterone metabolism were enhanced in the intestine but were unaffected in the livers of rats treated with 1,25(OH)₂D₃. Notably, the oral pharmacokinetic profile of buspirone (CYP3A substrate drug) and 6′-hydroxybuspirone (major active metabolite of buspirone formed via CYP3A-mediated metabolism) was significantly altered, while its intravenous pharmacokinetic profile was not affected by 1,25(OH)₂D₃ treatment. To the best of our knowledge, this study provides the first reported data regarding the effects of 1,25(OH)₂D₃ treatment on the in vivo pharmacokinetics of intravenous and oral buspirone in rats, by the differential modulation of hepatic and intestinal CYP3A activity. Our present results could lead to further studies in clinically significant CYP3A-mediated drug–nutrient interactions with 1,25(OH)₂D₃, including 1,25(OH)₂D₃–buspirone interaction.

Alterations in gene expression in vitamin D‐deficiency: Down‐regulation of liver Cyp7a1 and renal Oat3 in mice

The vitamin D‐deficient model, established in the C57BL/6 mouse after 8 weeks of feeding vitamin D‐deficient diets in the absence or presence of added calcium, was found associated with elevated levels of plasma parathyroid hormone (PTH) and plasma and liver cholesterol, and a reduction in cholesterol 7α‐hydroxylase (Cyp7a1, rate‐limiting enzyme for cholesterol metabolism) and renal Oat3 mRNA/protein expression levels. However, there was no change in plasma calcium and phosphate levels. Appraisal of the liver revealed an up‐regulation of mRNA expressions of the small heterodimer partner (Shp) and attenuation of Cyp7a1, which contributed to hypercholesterolemia in vitamin D‐deficiency. When vitamin D‐sufficient or D‐deficient mice were further rendered hypercholesterolemic with 3 weeks of feeding the respective, high fat/high cholesterol (HF/HC) diets, treatment with 1α,25‐dihydroxyvitamin D₃ [1,25(OH)₂D₃], active vitamin D receptor (VDR) ligand, or vitamin D (cholecalciferol) to HF/HC vitamin D‐deficient mice lowered the cholesterol back to baseline levels. Cholecalciferol treatment partially restored renal Oat3 mRNA/protein expression back to that of vitamin D‐sufficient mice. When the protein expression of protein kinase C (PKC), a known, negative regulator of Oat3, was examined in murine kidney, no difference in PKC expression was observed for any of the diets with/without 1,25(OH)₂D₃/cholecalciferol treatment, inferring that VDR regulation of renal Oat3 did not involve PKC in mice. As expected, plasma calcium levels were not elevated by cholecalciferol treatment of vitamin D‐deficient mice, while 1,25(OH)₂D₃ treatment led to hypercalcemia. In conclusion, vitamin D‐deficiency resulted in down‐regulation of liver Cyp7a1 and renal Oat3, conditions that are alleviated upon replenishment of cholecalciferol.     

Proliferation and Differentiation of Cultured Human Keratinocytes is Modulated by 1,25(OH)2D3 and Synthetic Vitamin D3 Analogues in a Cell Density-, Calcium- and Serum-Dependent Manner*

Abstract: The natural form of vitamin D₃, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) decreases proliferation and promotes terminal differentiation of cultured human epidermal keratinocytes. The purpose of this study was to find out to what extent the culture conditions determine the sensitivety of keratinocytes to 1,25(OH)₂D₃ and synthetic vitamin D analogues. Human keratinocytes were grown in microplates. Cell proliferation (MTT-assay) and differentiation (quantity of transglutaminase type I) were measured consecutively in the same monolayer. When vitamin D₃ analogues were added to 50–60% confluent keratinocytes grown in serum-free keratinocyte growth medium with 0.09 mM Ca²⁺, stimulation of the proliferation was either minimal or non-existent, while differentiation was unaffected or slightly inhibited. There was no difference in the sensitivity to 1,25(OH)₂D₃ and the vitamin D₃ analogues. When 1,25(OH)₂D₃ was added to less confluent keratinocytes (30%) a marked antiproliferative effect was observed. Addition of 3% charcoal stripped foetal calf serum further enhanced the antiproliferative effect of 1,25(OH)₂D₃, and a difference in the sensitivity of the vitamin D₃ analogues was noted. If, finally, the Ca²⁺ concentration was raised to 0.3 mM, 1,25(OH)₂D₃ and the vitamin D₃ analogues stimulated differentiation. Also, a biphasic effect on proliferation occurred: stimulation at low vitamin D concentrations and inhibition at higher concentrations. Furthermore, keratinocytes became more sensitive to the synthetic vitamin D₃ analogues than to 1,25(OH)₂D₃: KH1060>EB1089>GS1500≥EB1213>calcipotriol>1,25(OH)₂D₃. For all compounds tested differentiation occurred at concentrations 10 to 30 times lower than for proliferation. These results indicate that the sensitivity to vitamin D₃ analogues as well as the direction of the response to vitamin D₃ analogues is dependent on the keratinocyte density, the availability of serum and Ca²⁺ concentrations.     

Potencies of vitamin D analogs, 1α‐hydroxyvitamin D3, 1α‐hydroxyvitamin D2 and 25‐hydroxyvitamin D3, in lowering cholesterol in hypercholesterolemic mice in vivo

Vitamin D₃ and the synthetic vitamin D analogs, 1α‐hydroxyvitamin D₃ [1α(OH)D₃], 1α‐hydroxyvitamin D₂ [1α(OH)D₂] and 25‐hydroxyvitamin D₃ [25(OH)D₃] were appraised for their vitamin D receptor (VDR) associated‐potencies as cholesterol lowering agents in mice in vivo. These precursors are activated in vivo: 1α(OH)D₃ and 1α(OH)D₂ are transformed by liver CYP2R1 and CYP27A1 to active VDR ligands, 1α,25‐dihydroxyvitamin D₃ [1,25(OH)₂D₃] and 1α,25‐dihydroxyvitamin D₂ [1,25(OH)₂D₂]_, respectively. 1α(OH)D₂ may also be activated by CYP24A1 to 1α,24‐dihydroxyvitamin D₂ [1,24(OH)₂D₂], another active VDR ligand. 25(OH)D₃, the metabolite formed via CYP2R1 and or CYP27A1 in liver from vitamin D₃, is activated by CYP27B1 in the kidney to 1,25(OH)₂D₃. In C57BL/6 mice fed the high fat/high cholesterol Western diet for 3 weeks, vitamin D analogs were administered every other day intraperitoneally during the last week of the diet. The rank order for cholesterol lowering, achieved via mouse liver small heterodimer partner (Shp) inhibition and increased cholesterol 7α‐hydroxylase (Cyp7a1) expression, was: 1.75 nmol/kg 1α(OH)D₃ > 1248 nmol/kg 25(OH)D₃ (dose ratio of 0.0014) > > 1625 nmol/kg vitamin D₃. Except for 1.21 nmol/kg 1α(OH)D₂ that failed to lower liver and plasma cholesterol contents, a significant negative correlation was observed between the liver concentration of 1,25(OH)₂D₃ formed from the precursors and liver cholesterol levels. The composite results show that vitamin D analogs 1α(OH)D₃ and 25(OH)D₃ exhibit cholesterol lowering properties upon activation to 1,25(OH)₂D₃: 1α(OH)D₃ is rapidly activated by liver enzymes and 25(OH)D₃ is slowly activated by renal Cyp27b1 in mouse.     

Calcipotriol: A New Drug for Topical Psoriasis Treatment

Abstract: Vitamin D is best known for its role in the regulation of calcium and bone metabolism. The effects of the biologically active form of vitamin D, 1,25-dihydroxyvitamin D₃ (1,25 (OH)₂D₃), are mediated by binding to a specific intracellular vitamin D receptor, which is present in most tissues including the skin where it regulates the growth of epidermal cells. Calcipotriol is a synthetic analogue of 1,25(OH)₂D₃. In vitro the activity of calcipotriol is comparable to that of 1,25(OH)₂D₃. In vivo, however, the risk of calcipotriol changing calcium metabolism is greatly reduced. Animal studies have established that calcipotriol is 100–200 times less calcaemic than 1,25 (OH)₂-D₃. This low calcaemic activity is mainly due to the rapid metabolism of calcipotriol. This pharmacological profile makes calcipotriol an ideal candidate for topical treatment of hyperproliferative skin disorders, such as psoriasis. This paper reviews the clinical experience with calcipotriol in psoriasis patients.     

Comparative effects of 1α‐hydroxyvitamin D3 and 1,25‐dihydroxyvitamin D3 on transporters and enzymes in fxr(+/+) and fxr(‐/‐) mice

Previous studies have shown that 1α,25‐dihydroxyvitamin D₃ [1,25(OH)₂D₃] treatment in mice resulted in induction of intestinal and renal Cyp24a1 and Trpv6 expression, increased hepatic Cyp7a1 expression and activity, as well as higher renal Mdr1/P‐gp expression. The present study compared the equimolar efficacies of 1α‐hydroxyvitamin D₃ [1α(OH)D₃] (6 nmol/kg i.p. q2d × 4), a lipophilic precursor with a longer plasma half‐life that is converted to 1,25(OH)₂D₃, and 1,25(OH)₂D₃ on vitamin D receptor (VDR) target genes. To clarify whether changes in VDR genes was due to VDR and not secondary, farnesoid X receptor (FXR)‐directed effects, namely, lower Cyp7a1 expression in rat liver due to increased bile acid absorption, wildtype [fxr(+/+)] and FXR knockout [fxr(‐/‐)] mice were used to distinguish between VDR and FXR effects. With the exception that hepatic Sult2a1 mRNA was increased equally well by 1α(OH)D₃ and 1,25(OH)₂D₃, 1α(OH)D₃ treatment led to higher increases in hepatic Cyp7a1, renal Cyp24a1, VDR, Mdr1 and Mrp4, and intestinal Cyp24a1 and Trpv6 mRNA expression in both fxr(+/+) and fxr(‐/‐) mice compared to 1,25(OH)₂D₃ treatment. A similar induction in protein expression and microsomal activity of hepatic Cyp7a1 and renal P‐gp and Mrp4 protein expression was noted for both compounds. A higher intestinal induction of Trpv6 was observed, resulting in greater hypercalcemic effect following 1α(OH)D₃ treatment. The higher activity of 1α(OH)D₃ was explained by its rapid conversion to 1,25(OH)₂D₃ in tissue sites, furnishing higher plasma and tissue 1,25(OH)₂D₃ levels compared to following 1,25(OH)₂D₃‐treatment. In conclusion, 1α(OH)D₃ exerts a greater effect on VDR gene induction than equimolar doses of 1,25(OH)₂D₃ in mice. Copyright © 2013 John Wiley & Sons, Ltd.     

Relationship Between Circulating Vitamin D3 Metabolites and Prolactin or Growth Hormone Levels in Rat

Abstract: Previous studies (Haug & Gautvik 1985) have demonstrated specific receptors for 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) in a clonal (GH₃) strain of rat pituitary tumour cells. It was discovered that 1,25(OH)₂D₃ affected the production of prolactin and growth hormone in these cells in a calcium dependent manner. These findings were the basis for a hypothesis that vitamin D₃ could be involved in the regulation of pituitary hormones in vivo. To further investigate this contention, female rats were given subcutaneous injections of 1,25(OH)₂D₃, 25-hydroxyvitamin D₃ (25(OH)D₃) or 24,25-dihydroxyvitamin D₃ (24,25(OH)₂D₃) three times a week for up to 12 weeks. Blood samples were withdrawn after 28, 56 and 84 days of treatment and analysed for vitamin D, metabolites, prolactin and growth hormone, and serum ionized (free) and total calcium (Ca). Between treatment group comparisons of serum prolactin and growth hormone levels did not show significant vitamin D₃ induced alterations. However, correlation matrix analyses on all variables revealed that serum level of growth hormone was significantly (P < 0.05) and inversely related to corresponding total Ca. Prolactin, on the other hand, may be subject to a complex regulation by 1,25(OH)₂D₃ and free Ca²⁺.     

1,25‑Dihydroxyvitamin D regulates macrophage polarization and ameliorates experimental inflammatory bowel disease by suppressing miR-125b

Macrophages are highly plastic cells. Depending on stimulation, macrophages rapidly polarize to functionally distinct phenotypes that are involved in the pathogenesis of inflammatory bowel disease (IBD). 1,25‑Dihydroxyvitamin D (1,25(OH)₂D₃) has immunomodulatory activity, and 1,25(OH)₂D₃ deficiency is correlated with autoimmune diseases, especially IBD. This study aimed to explore whether 1,25(OH)₂D₃ modulates macrophage polarization in inflammation. Peripheral blood mononuclear cells and colitis mice were treated with 1,25(OH)₂D₃. Macrophages were transfected with siRNA-vitamin D receptor (VDR) or miR-125b mimic or inhibitor, and 1,25(OH)₂D₃-pretreated colitis mice were injected with a miR-125b agomir. The distribution of macrophage subsets and macrophage subtype characteristics was analyzed. As expected, 1,25(OH)₂D₃ transformed lipopolysaccharide-induced M1 macrophages to the M2 subset, downregulated tumor necrosis factor-α and interleukin (IL)-6 expression and interferon regulatory factor 5 (IRF5) phosphorylation, and upregulated IL-10, arginase-1, VDR, and IRF4 expression. SiRNA-VDR and miR-125b mimic significantly impaired 1,25(OH)₂D₃ activity. In colitis mice, 1,25(OH)₂D₃ pretreatment ameliorated disease activity, converted M1 macrophages to the M2 subtype, suppressed IRF5 phosphorylation, and increased IRF4 expression in lamina propria mononuclear cells (LPMC). miR-125b agomir injections reversed 1,25(OH)₂D₃ action. Collectively, the results demonstrate that 1,25(OH)₂D₃ downregulates miR-125b expression and promotes M1 macrophage polarization to the M2 subtype. 1,25(OH)₂D₃ pretreatment ameliorated colitis by restoring the LPMC macrophage subtype balance.     

PODOCYTE INJURY IS SUPPRESSED BY 1,25-DIHYDROXYVITAMIN D3 VIA MODULATION OF TRANSFORMING GROWTH FACTOR-β1/BONE MORPHOGENETIC PROTEIN-7 SIGNALLING IN PUROMYCIN AMINONUCLEOSIDE NEPHROPATHY RATS

• 1 Accumulating evidence suggests that vitamin D and its analogues are renoprotective. However, the precise mechanisms and the molecular targets by which active vitamin D exerts its beneficial effects remain obscure. The objective of the present study was to evaluate the effect of active vitamin D on rats with puromycin aminonucleoside (PAN) nephropathy, a model that is characterized by predominant podocyte injury.
• 2 The PAN nephropathy rats were created by a single intravenous injection of 100 mg/kg PAN. Changes in renal pathology and podocyte numbers were observed. Real‐time polymerase chain reaction (PCR) was performed to examine mRNA expression of nephrin, transforming growth factor (TGF)‐β1 and bone morphogenetic protein (BMP)‐7. Protein expression of nephrin, TGF‐β1, BMP‐7 and p‐Smad2/3 and p‐Smad1/5/8 was examined by immunofluorescence, immunohistochemistry and western blotting, respectively. Rats were treated with 1,25(OH)₂D₃ by gastric gavage at a dose of 2.5 µg/kg per day, starting 2 days before PAN injection and continuing throughout the experiment.
• 3 A single injection of PAN induced massive proteinuria and elevated serum creatinine on Day 7, both of which were significantly suppressed by 1,25‐dihydroxyvitamin D₃ (1,25(OH)₂D₃). Immunofluorescence and real‐time PCR of the podocyte‐associated protein nephrin revealed reduced and discontinuous staining and this change was reversed by 1,25(OH)₂D₃. In PAN nephropathy rats, TGF‐β1 and p‐Smad2/3 expression was upregulated, whereas that of BMP‐7 and p‐Smad1/5/8 was downregulated. Treatment with 1,25(OH)₂D₃ significantly restored BMP‐7/Smad signalling while suppressing TGF‐β1/Smad signalling.
• 4 In conclusion, 1,25(OH)₂D₃ can ameliorate podocyte damage and proteinuria induced by PAN. The beneficial effects of 1,25(OH)₂D₃ on podocytes may be attributable, in part, to direct modulation of TGF‐β1/BMP‐7 signalling.

     

Effects of 1α,25‐dihydroxyvitamin D3 on transporters and enzymes of the rat intestine and kidney in vivo

1α,25‐Dihydroxyvitamin D₃ (1,25(OH)₂D₃), the natural ligand of the vitamin D receptor (VDR), was found to regulate bile acid related transporters and enzymes directly and indirectly in the rat intestine and liver in vivo. The kidney is another VDR‐rich target organ in which VDR regulation on xenobiotic transporters and enzymes is ill‐defined. Hence, changes in protein and mRNA expression of nuclear receptors, transporters and enzymes of the rat intestine and kidney in response to 1,25(OH)₂D₃ treatment (0 to 2.56 nmol/kg/day intraperitoneally in corn oil for 4 days) were studied. In the intestine, protein and not mRNA levels of Mrp2, Mrp3, Mrp4 and PepT1 in the duodenum and proximal jejunum were induced, whereas Oat1 and Oat3 mRNA were decreased in the ileum after 1,25(OH)₂D₃ treatment. In the kidney, VDR, Cyp24, Asbt and Mdr1a mRNA and protein expression increased significantly (2‐ to 20‐fold) in 1,25(OH)₂D₃‐treated rats, and a 28‐fold increase of Cyp3a9 mRNA but not of total Cy3a protein nor Cyp3a1 and Cyp3a2 mRNA was observed, implicating that VDR played a significant, renal‐specific role in Cyp3a9 induction. Additionally, renal mRNA levels of PepT1, Oat1, Oat3, Ostα, and Mrp4, and protein levels of PepT1 and Oat1 were decreased in a dose‐dependent manner, and the ～50% concomitant reduction in FXR, SHP, HNF‐1α and HNF‐4α mRNA expression suggests the possibility of cross‐talk among the nuclear receptors. It is concluded that the effects of 1,25(OH)₂D₃ changes are tissue‐specific, differing between the intestine and kidney which are VDR‐rich organs. Copyright © 2009 John Wiley & Sons, Ltd.     

Therapeutic applications for novel non-hypercalcemic vitamin D receptor ligands

Background: The active form of vitamin D₃, 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), plays an important role in calcium homeostasis, cell differentiation, cell proliferation and immunity. A more complete understanding of the several physiological and pharmacological properties of 1,25(OH)₂D₃ indicates that the vitamin D receptor (VDR) is a promising drug target in the treatment of cancers, autoimmune diseases, infections and cardiovascular disease as well as bone and mineral disorders. The calcemic effect of 1,25(OH)₂D₃ and its derivatives has limited their clinical application. As a result, the development of non-calcemic VDR ligands is required to realize the potential of VDR-targeting therapy. Objective: In this review, we discuss the in vitro and in vivo pharmacological actions, including VDR interaction, regulation of cofactor recruitment, pharmacokinetics and cell type or tissue-selective action of VDR ligands with less-calcemic activity. Conclusion: Pharmacokinetic parameters and selective tissue accumulation are related to the therapeutic benefit of non-hypercalcemic vitamin D derivatives. Induction of distinct VDR conformations and cofactor recruitment may be associated with selective actions of non-secosteroidal VDR ligands. Derivatives of lithocholic acid, a newly identified endogenous VDR ligand, are less-calcemic VDR ligands.     

Vitamin D3 enhances bactericidal activity of macrophage against Pseudomonas aeruginosa

BackgroundThe bioactive form of vitamin D3, i.e.1,25-dihydroxyvitamin D3 (1,25(OH)₂D₃) vitamin D has been shown to modulate monocytes/macrophages physiology and its response against bacterial infections. Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic bacterial pathogen that can most frequently be fatal in immunocompromised infected people.MethodsWe investigated the ex vivo effect of 1,25(OH)₂D₃ on monocyte-derived macrophages function against P. aeruginosa infection.ResultsRelative vitamin D receptor (VDR) mRNA expression was significantly increased in infected and 1,25(OH)₂D₃-treated macrophages compared to controls (p < 0.01). Treatment with 1,25(OH)₂D₃ markedly resulted in up-regulation of nitric oxide (NO) and IL-1β production and down-regulation of IL-10 levels (respectively, p = 0.029, p = 0.048 and p = 0.008). Additionally, 1,25(OH)₂D₃ significantly increased M1/M2 macrophage ratio (p < 0.05) and slightly reduced intracellular bacterial development. Furthermore, the arginase activity, P. aeruginosa phagocytosis and killing were significantly increased in cells that were both infected and 1,25(OH)₂D₃-treated compared to the infected, but not 1,25(OH)₂D₃-treated macrophages (respectively, p < 0.001, p < 0.01 and p < 0.001).ConclusionsWe show in this study that bioactive from of vitamin D [1,25-dihydroxyvitamin D3 (1,25D3)] can enhance M1 macrophage polarization and their bactericidal protective activity against P. aeruginosa. Future works would involve improving the treatment response through dose-dependent effect studies, both in ex vivo and in vivo models.     

Regulation of VDR expression in rat and human intestine and liver – Consequences for CYP3A expression

The vitamin D receptor (VDR) regulates the expression of drug metabolizing enzymes and transporters in intestine and liver, but the regulation of VDR expression in intestine and liver is incompletely understood. We studied the regulation of VDR mRNA expression by ligands for VDR, farnesoid X receptor (FXR), glucocorticoid receptor (GR) and protein kinase C α (PKCα) in rat and human ileum and liver using precision-cut slices. 1,25(OH)₂D₃ induced VDR expression in rat ileum and liver, and human ileum but not in liver. Chenodeoxycholic acid (CDCA), but not lithocholic acid (LCA) and GW4064 induced VDR mRNA expression in rat ileum and liver. The PKCα activator, phorbol-12-myristate-13-acetate (PMA) induced the expression of VDR in the rat liver, and the induction of VDR by 1,25(OH)₂D₃ and CDCA was inhibited by the PKCα inhibitor, bisindolyl maleimide I (Bis I). These results show that the expression of VDR is likely to be regulated by PKC but not by FXR or VDR activation at least in the rat liver. The VDR mediated induction of its target genes CYP3A1 and CYP3A2 by 1,25(OH)₂D₃ or LCA in the rat ileum was strongly reduced in the presence of CDCA despite the higher VDR expression. Thus, CDCA might potentiate the toxicity of LCA by inhibiting its metabolism.     

Retiferols – synthesis and biological activity of a conceptually novel class of vitamin D analogs

Introduction: The hypothesis that retiferols are a novel class of vitamin D analogs with therapeutic potential has been recently proved. The CD-ring of vitamin D, originated from a steroid precursor, is not necessary for biological activity. The retiferol, disubstituted at C-13, was bound to the ligand-binding domain (LBD) of vitamin D receptor (VDR) just like the vitamin D hormone [1,25-(OH)₂D₃]. This finding opens the way for retiferols as a novel class of vitamin D therapeutics.

Areas covered: This review presents the concept of retiferols and their structure evolution. Medicinal chemistry and therapeutic perspective of retiferols are reviewed showing how these vitamin D analogs became a source of potential therapeutics.

Expert opinion: Docking experiments and molecular modeling have shown that positioning of vitamin D analog at the LBD of VDR is not disturbed by deletion of a large portion of the vitamin D, exactly as hypothesized. Twenty years of structural modifications have shown that removal of the CD-ring fragment and regioselective methylation results in an almost complete loss of the undesired calcemic activity of retiferol while gaining the agonistic activity comparable to that of 1,25-(OH)₂D₃.     

The Yin and Yang of vitamin D receptor (VDR) signaling in neoplastic progression: Operational networks and tissue-specific growth control

Substantive evidence implicates vitamin D receptor (VDR) or its natural ligand 1α,25-(OH)₂ D₃ in modulation of tumor growth. However, both human and animal studies indicate tissue-specificity of effect. Epidemiological studies show both inverse and direct relationships between serum 25(OH)D levels and common solid cancers. VDR ablation affects carcinogen-induced tumorigenesis in a tissue-specific manner in model systems. Better understanding of the tissue-specificity of vitamin D-dependent molecular networks may provide insight into selective growth control by the seco-steroid, 1α,25-(OH)₂ D₃. This commentary considers complex factors that may influence the cell- or tissue-specificity of 1α,25-(OH)₂ D₃/VDR growth effects, including local synthesis, metabolism and transport of vitamin D and its metabolites, vitamin D receptor (VDR) expression and ligand-interactions, 1α,25-(OH)₂ D₃ genomic and non-genomic actions, Ca²⁺ flux, kinase activation, VDR interactions with activating and inhibitory vitamin D responsive elements (VDREs) within target gene promoters, VDR coregulator recruitment and differential effects on key downstream growth regulatory genes. We highlight some differences of VDR growth control relevant to colonic, esophageal, prostate, pancreatic and other cancers and assess the potential for development of selective prevention or treatment strategies.