Vitamin D analogues targeting CYP24 in chronic kidney disease

Role of renal tubular programed cell death in diabetic kidney disease

The pathogenic mechanism of diabetic kidney disease (DKD) is involved in various functions; however, its inadequate characterisation limits the availability of effective treatments. Tubular damage is closely correlated with renal function and is thought to be the main contributor to the injury observed in early DKD. Programed cell death (PCD) occurs during the biological development of the living body. Accumulating evidence has clarified the fundamental role of abnormalities in tubular PCD during DKD pathogenesis. Among PCD types, classical apoptosis, autophagic cell death, and pyroptosis are the most studied and will be the focus of this review. Our review aims to elucidate the current knowledge of the mechanism of DKD and the potential therapeutic potential of drugs targeting tubular PCD pathways in DKD.

Deferasirox and vitamin D3 co-therapy mitigates iron-induced renal injury by enhanced modulation of cellular anti-inflammatory, anti-oxidative stress, and iron regulatory pathways in rat

BACKGROUND

Chronic iron overload could induce nephropathy via oxidative stress and inflammation, and chelating therapy has limited efficacy in removing excess intracellular iron. Although vitamin D (VD) has shown potent antioxidant and anti-inflammatory effects, as well contribute to iron homeostasis, none of the previous studies measured its potential remedial effects against chronic iron toxicity.

AIMS

To measure the alleviating effects of deferasirox (DFX) and/or vitamin D (VD) single and combined therapies against nephrotoxicity induced by chronic iron overload.

METHODS

Forty male rats were divided into negative (NC) and positive (PC) controls, DFX, VD, and DFX/VD groups. The designated groups received iron for six weeks followed by DFX and/or VD for another six weeks. Then, the expression pattern of renal genes and proteins including hepcidin, ferroportin (FPN), megalin, transferrin receptor 1 (TfR1), ferritin heavy and light chains, VD receptor (VDR), VD synthesizing (Cyp27b1) and catabolizing (Cyp24a1) enzymes were measured alongside serum markers of renal function and iron biochemical parameters. Additionally, several markers of oxidative stress (MDA/H₂O₂/GSH/SOD1/CAT/GPx4) and inflammation (IL-1β/IL-6/TNF-α/IL-10) together with renal cell apoptosis and expression of caspase-3 (Casp-3) were measured.

RESULTS

The PC rats showed pathological iron and renal biochemical markers, hypovitaminosis D, increased renal tissue iron contents with increased Cyp24a1/Megalin/ferritin-chains/hepcidin, and decreased Cyp27b1/VDR/TfR1/FPN expression than the NC group. The PC renal tissues also showed abnormal histology, increased inflammatory (IL-1β/IL-6/TNF-α), oxidative stress (MDA/H₂O₂), and apoptosis markers with decreased IL-10/GSH/SOD1/CAT/GPx4. Although DFX monotherapy reduced serum iron levels, it was comparable to the PC group in renal iron concentrations, VD and iron-homeostatic molecules, alongside markers of oxidative stress, inflammation, and apoptosis. On the other hand, VD monotherapy markedly modulated renal iron and VD-related molecules, reduced renal tissue iron concentrations, and preserved renal tissue relative to the PC and DFX groups. However, serum iron levels were equal in the VD and PC groups. In contrast, the best significant improvements in serum and renal iron levels, expression of renal iron-homeostatic molecules, oxidative stress, inflammation, and apoptosis were seen in the co-therapy group.

CONCLUSIONS

iron-induced nephrotoxicity was associated with dysregulations in renal VD-system together with renal oxidative stress, inflammation, and apoptosis. While DFX reduced systemic iron, VD monotherapy showed better attenuation of renal iron concentrations and tissue damage. Nonetheless, the co-therapy approach exhibited the maximal remedial effects, possibly by enhanced modulation of renal iron-homeostatic molecules alongside reducing systemic iron levels.

AVAILABILITY OF DATA AND MATERIALS

All data generated or analysed during this study are included in this published article [and its Supplementary information files].

Therapeutic Potential of a Novel Vitamin D3 Oxime Analogue, VD1-6, with CYP24A1 Enzyme Inhibitory Activity and Negligible Vitamin D Receptor Binding

The regulation of vitamin D3 actions in humans occurs mainly through the Cytochrome P450 24-hydroxylase (CYP24A1) enzyme activity. CYP24A1 hydroxylates both 25-hydroxycholecalciferol (25(OH)D3) and 1,25-dihydroxycholecalciferol (1,25(OH)2D3), which is the first step of vitamin D catabolism. An abnormal status of the upregulation of CYP24A1 occurs in many diseases, including chronic kidney disease (CKD). CYP24A1 upregulation in CKD and diminished activation of vitamin D3 contribute to secondary hyperparathyroidism (SHPT), progressive bone deterioration, and soft tissue and cardiovascular calcification. Previous studies have indicated that CYP24A1 inhibition may be an effective strategy to increase endogenous vitamin D activity and decrease SHPT. This study has designed and synthesized a novel C-24 O-methyloxime analogue of vitamin D3 (VD1-6) to have specific CYP24A1 inhibitory properties. VD1-6 did not bind to the vitamin D receptor (VDR) in concentrations up to 10−7 M, assessed by a VDR binding assay. The absence of VDR binding by VD1-6 was confirmed in human embryonic kidney HEK293T cultures through the lack of CYP24A1 induction. However, in silico docking experiments demonstrated that VD1-6 was predicted to have superior binding to CYP24A1, when compared to that of 1,25(OH)2D3. The inhibition of CYP24A1 by VD1-6 was also evident by the synergistic potentiation of 1,25(OH)2D3-mediated transcription and reduced 1,25(OH)2D3 catabolism over 24 h. A further indication of CYP24A1 inhibition by VD1-6 was the reduced accumulation of the 24,25(OH)D3 , the first metabolite of 25(OH)D catabolism by CYP24A1. Our findings suggest the potent CYP24A1 inhibitory properties of VD1-6 and its potential for testing as an alternative therapeutic candidate for treating SHPT.

Dithionite-Involved Multicomponent Coupling for Alkenyl and Alkyl Tertiary Sulfones

A dithionite-involved multicomponent reaction of redox-active esters and alkenes/alkynes is comprehensively achieved for the construction of alkyl and alkenyl tertiary sulfones. The industrial feedstock sodium dithionite is employed as a sulfur dioxide surrogate and a single-electron reductant to initiate the decarboxylation of redox-active esters. Mechanistic studies further indicated that the transformation underwent a proton trapping process, which was different from the traditional radical trapping pathway.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Alternative splicing of the vitamin D receptor modulates target gene expression and promotes ligand-independent functions

Alternative splicing modulates gene function by creating splice variants with alternate functions or non-coding RNA activity. Naturally occurring variants of nuclear receptor (NR) genes with dominant negative or gain-of-function phenotypes have been documented, but their cellular roles, regulation, and responsiveness to environmental stress or disease remain unevaluated. Informed by observations that class I androgen and estrogen receptor variants display ligand-independent signaling in human cancer tissues, we questioned whether the function of class II NRs, like the vitamin D receptor (VDR), would also respond to alternative splicing regulation. Artificial VDR constructs lacking exon 3 (Dex3-VDR), encoding part of the DNA binding domain (DBD), and exon 8 (Dex8-VDR), encoding part of the ligand binding domain (LBD), were transiently transfected into DU-145 cells and stably-integrated into Caco-2 cells to study their effect on gene expression and cell viability. Changes in VDR promoter signaling were monitored by the expression of target genes (e.g. CYP24A1, CYP3A4 and CYP3A5). Ligand-independent VDR signaling was observed in variants lacking exon 8, and a significant loss of gene suppressor function was documented for variants lacking exon 3. The gain-of-function behavior of the Dex8-VDR variant was recapitulated in vitro using antisense oligonucleotides (ASO) that induce the skipping of exon 8 in wild-type VDR. ASO targeting the splice acceptor site of exon 8 significantly stimulated ligand-independent VDR reporter activity and the induction of CYP24A1 above controls. These results demonstrate how alternative splicing can re-program NR gene function, highlighting novel mechanisms of toxicity and new opportunities for the use of splice-switching oligonucleotides (SSO) in precision medicine.

A theoretical insight to understand the molecular mechanism of dual target ligand CTA-018 in the chronic kidney disease pathogenesis

The level of the vitamin D in the bloodstream is regulated by cytochrome P450 enzyme 24-hydroxylase A1 (CYP24A1). Over expression of CYP24A1 enzyme is correlated with vitamin D deficiency and resistance to vitamin D therapy. Chronic kidney disease (CKD) patients are commonly reported with the above said expression variations. This deregulation could be solved by ligands that act as a vitamin D receptor (VDR) agonists and CYP24A1 antagonists. Posner et al., (2010) first time reported two new vitamin D analogues namely CTA-091 and CTA-018 to inhibit CYP24A1. The CTA-018 inhibited CYP24A1 with an IC₅₀ 27 ± 6 nM (10 times more potent than the ketoconazole (253 ± 20 nM)). CTA-018 induced VDR expression (15-fold lower than 1α,25(OH)₂D₃) and is under phase II clinical trial, whereas CTA-091 was not able to efficiently induce the VDR expression (>2000 nM). To explore the molecular mechanism, binding specificity of these two vitamin D analogues along with native ligand was extensively studied through in silico approaches. Through molecular dynamics simulations studies, we shown that the sulfonic group (O = S = O) in the side chain of CTA-018 plays an important role in the regulation of VDR agonistic activity. The electron lone pairs of the sulfonic group that interacted with His393 lead to be a factor for agonistic mechanism of VDR activity. Compared to azol-based compounds, CTA-018 binds the different sites in the CYP24A1 binding cavity and thus it could be a potent antagonistic for CYP24A1enzyme.

In silico identification and screening of CYP24A1 inhibitors: 3D QSAR pharmacophore mapping and molecular dynamics analysis

Vitamin D is a key signalling molecule that plays a vital role in the regulation of calcium phosphate homeostasis and bone remodelling. The circulating biologically active form of vitamin D is regulated by the catabolic mechanism of cytochrome P450 24-hydroxylase (CYP24A1) enzyme. The over-expression of CYP24A1 negatively regulates the vitamin D level, which is the causative agent of chronic kidney disease, osteoporosis and several types of cancers. In this study, we found three potential lead molecules adverse to CYP24A1 through structure-based, atom-based pharmacophore and e-pharmacophore-based screening methods. Analysis was done by bioinformatics methods and tools like binding affinity (binding free energy), chemical reactivity (DFT studies) and molecular dynamics simulation (protein-ligand stability). Combined computational investigation showed that the compounds NCI_95001, NCI_382818 and UNPD_141613 may have inhibitory effects against the CYP24A1 protein.

Aoike D, Q. Redublo BM, C. Batista M, Cendoroglo M, Maria Moyses R, Dalboni MA. Cholecalciferol decreases inflammation and improves vitamin D regulatory enzymes in lymphocytes in the uremic environment: A randomized controlled pilot trial

It has been reported that vitamin D regulates the immune system. However, whether vitamin D repletion modulates inflammatory responses in lymphocytes from dialysis patients is unclear. In the clinical trial, thirty-two (32) dialysis patients with 25 vitamin D ≤ 20ng/mL were randomized to receive either supplementation of cholecalciferol 100,000 UI/week/3 months (16 patients) or placebo (16 patients). In the in vitro study, B and T lymphocytes from 12 healthy volunteers (HV) were incubated with or without uremic serum in the presence or absence of 25 or 1,25 vitamin D. We evaluated the intracellular expression of IL-6, IFN-γ TLR7, TLR9, VDR, CYP27b1 and CYP24a1 by flow cytometry. We observed a reduction in the expression of TLR7, TLR9, INF-γ and CYP24a1 and an increase in VDR and CYP27b1 expression in patients which were supplemented with cholecalciferol, whereas no differences were found in the placebo group. Uremic serum increased the intracellular expression of IL-6, IFN-γ, TLR7, TLR9, VDR, CYP27b1 and CYP24a1. Treatment with 25 or 1,25 vitamin D decreased IL-6 and TLR9. CYP24a1 silencing plus treatment with 25 and/or 1,25 vitamin D had an additional reduction effect on IL-6, IFN-γ, TLR7 and TLR9 expression. This is the first study showing that cholecalciferol repletion has an anti-inflammatory effect and improves vitamin D intracellular regulatory enzymes on lymphocytes from dialysis patients.

Diet-derived 25-hydroxyvitamin D3 activates vitamin D receptor target gene expression and suppresses EGFR mutant non-small cell lung cancer growth in vitro and in vivo

Epidemiologic studies implicate vitamin D status as a factor that influences growth of EGFR mutant lung cancers. However, laboratory based evidence of the biological effect of vitamin D in this disease is lacking. To fill this knowledge gap, we determined vitamin D receptor (VDR) expression in human lung tumors using a tissue microarray constructed of lung cancer cases from never-smokers (where EGFR gene mutations are prevalent). Nuclear VDR was detected in 19/19 EGFR mutant tumors. Expression tended to be higher in tumors with EGFR exon 19 deletions than those with EGFR L858R mutations. To study anti-proliferative activity and signaling, EGFR mutant lung cancer cells were treated with the circulating metabolite of vitamin D, 25-hydroxyvitamin D3 (25D3). 25D3 inhibited clonogenic growth in a dose-dependent manner. CYP27B1 encodes the 1α-hydroxylase (1αOHase) that converts 25D3 to the active metabolite, 1,25-dihydroxyvitamin D3 (1,25D3). Studies employing VDR siRNA, CYP27B1 zinc finger nucleases, and pharmacologic inhibitors of the vitamin D pathway indicate that 25D3 regulates gene expression in a VDR-dependent manner but does not strictly require 1αOHase-mediated conversion of 25D3 to 1,25D3. To determine the effects of modulating serum 25D3 levels on growth of EGFR mutant lung tumor xenografts, mice were fed diets containing 100 or 10,000 IU vitamin D3/kg. High dietary vitamin D3 intake resulted in elevated serum 25D3 and significant inhibition of tumor growth. No toxic effects of supplementation were observed. These results identify EGFR mutant lung cancer as a vitamin D-responsive disease and diet-derived 25D3 as a direct VDR agonist and therapeutic agent.

Levels of vitamin D receptor and CYP24A1 in patients with end-stage renal disease

OBJECTIVE

This study was performed to detect the expression of vitamin D receptor (VDR) and cytochrome P450, family 24, subfamily A, polypeptide 1 (CYP24A1) in 24 end stage renal disease (ESRD) patients and 24 healthy controls.

METHOD

In this study, 24 ESRD patients and 24 healthy controls were included.

RESULTS

In our study, the levels of VDR in patients with ESRD were reduced when compared with those from healthy controls (5.20±0.32 vs 8.59±1.03; P<0.01). However, the levels of CYP24A1 in ESRD patients were increased than those from healthy controls (50.18±21 vs 7.78±1.31; P<0.01). Correlation analysis showed that VDR levels were negatively correlated with CYP24A1 (r=-0.723; P<0.01).

CONCLUSION

VDR levels were reduced and CYP24A1 levels were increased in patients with ESRD, and VDR levels were negatively correlated with CYP24A1.

E-pharmacophore filtering and molecular dynamics simulation studies in the discovery of potent drug-like molecules for chronic kidney disease

Chronic kidney disease (CKD) is a prominent health issue reported globally. The level of the vitamin D receptor (VDR) and cytochrome P450 enzyme 24-hydroxylase (CYP24A1) are crucial in the pathogenesis of secondary hyperparathyroidism (sHPT) in CKD. An elevated expression of the CYP24A1 leads to the deficiency of vitamin D and resistance to vitamin D therapy. Hence, VDR agonists and CYP24A1 antagonists are suggested to CKD patients for the management of biochemical complications. CTA-018 is a recently reported analog and acts as a potent CYP24A1 inhibitor. It inhibits CYP24A1 with an IC₅₀ 27 ± 6 nM, about 10 times more potentially than the non-selective inhibitor ketoconazole (253 ± 20 nM), and it is also been reported to induce the VDR expression. Thus, CTA-018 is under clinical trial among CKD patients. In this study, combined molecular docking and pharmacophore filtering were employed to identify compounds better than CTA-018. A huge set of 9127 compounds from Sweet Lead database were docked into the active site of VDR using Glide XP program. E-pharmacophore was developed from both the targets along with CTA-018. The compounds retrieved from the two different pharmacophore-based screening were re-docked into the active site of CYP24A1. The hits that bind well at both the active sites and matched with the pharmacophore models were considered as possible dual functional molecules against VDR and CYP24A1. Further, molecular dynamics simulation and subsequent energy decomposition analyses were also performed to study the role of specific amino acids in the active site of both VDR and CYP24A1.

Vitamin D Signaling Modulators in Cancer Therapy

The antiproliferative and pro-apoptotic effects of 1α,25-dihydroxycholecalciferol (1,25(OH)2D3, 1,25D3, calcitriol) have been demonstrated in various tumor model systems in vitro and in vivo. However, limited antitumor effects of 1,25D3 have been observed in clinical trials. This may be attributed to a variety of factors including overexpression of the primary 1,25D3 degrading enzyme, CYP24A1, in tumors, which would lead to rapid local inactivation of 1,25D3. An alternative strategy for improving the antitumor activity of 1,25D3 involves the combination with a selective CYP24A1 inhibitor. The validity of this approach is supported by numerous preclinical investigations, which demonstrate that CYP24A1 inhibitors suppress 1,25D3 catabolism in tumor cells and increase the effects of 1,25D3 on gene expression and cell growth. Studies are now required to determine whether selective CYP24A1 inhibitors+1,25D3 can be used safely and effectively in patients. CYP24A1 inhibitors plus 1,25D3 can cause dose-limiting toxicity of vitamin D (hypercalcemia) in some patients. Dexamethasone significantly reduces 1,25D3-mediated hypercalcemia and enhances the antitumor activity of 1,25D3, increases VDR-ligand binding, and increases VDR protein expression. Efforts to dissect the mechanisms responsible for CYP24A1 overexpression and combinational effect of 1,25D3/dexamethasone in tumors are underway. Understanding the cross talk between vitamin D receptor (VDR) and glucocorticoid receptor (GR) signaling axes is of crucial importance to the design of new therapies that include 1,25D3 and dexamethasone. Insights gained from these studies are expected to yield novel strategies to improve the efficacy of 1,25D3 treatment.

Vitamin D metabolism, mechanism of action, and clinical applications

Vitamin D3 is made in the skin from 7-dehydrocholesterol under the influence of UV light. Vitamin D2 (ergocalciferol) is derived from the plant sterol ergosterol. Vitamin D is metabolized first to 25 hydroxyvitamin D (25OHD), then to the hormonal form 1,25-dihydroxyvitamin D (1,25(OH)2D). CYP2R1 is the most important 25-hydroxylase; CYP27B1 is the key 1-hydroxylase. Both 25OHD and 1,25(OH)2D are catabolized by CYP24A1. 1,25(OH)2D is the ligand for the vitamin D receptor (VDR), a transcription factor, binding to sites in the DNA called vitamin D response elements (VDREs). There are thousands of these binding sites regulating hundreds of genes in a cell-specific fashion. VDR-regulated transcription is dependent on comodulators, the profile of which is also cell specific. Analogs of 1,25(OH)2D are being developed to target specific diseases with minimal side effects. This review will examine these different aspects of vitamin D metabolism, mechanism of action, and clinical application.

Vitamin D metabolism, mechanism of action, and clinical applications

Vitamin D3 is made in the skin from 7-dehydrocholesterol under the influence of UV light. Vitamin D2 (ergocalciferol) is derived from the plant sterol ergosterol. Vitamin D is metabolized first to 25 hydroxyvitamin D (25OHD), then to the hormonal form 1,25-dihydroxyvitamin D (1,25(OH)2D). CYP2R1 is the most important 25-hydroxylase; CYP27B1 is the key 1-hydroxylase. Both 25OHD and 1,25(OH)2D are catabolized by CYP24A1. 1,25(OH)2D is the ligand for the vitamin D receptor (VDR), a transcription factor, binding to sites in the DNA called vitamin D response elements (VDREs). There are thousands of these binding sites regulating hundreds of genes in a cell-specific fashion. VDR-regulated transcription is dependent on comodulators, the profile of which is also cell specific. Analogs of 1,25(OH)2D are being developed to target specific diseases with minimal side effects. This review will examine these different aspects of vitamin D metabolism, mechanism of action, and clinical application.

Insights from genetic disorders of phosphate homeostasis

The molecular identification and characterization of genetic defects leading to a number of rare inherited or acquired disorders affecting phosphate homeostasis has added tremendous detail to our understanding of the regulation of phosphate balance. The identification of the key phosphate-regulating hormone, fibroblast growth factor 23 (FGF23), as well as other molecules that control its production, such as the N-acetylgalactosaminyltransferase 3 GALNT3, the endopeptidase phosphate-regulating protein with homologies to endopeptidases on the X chromosome, and the matrix protein dentin matrix protein 1, and molecules that function as downstream effectors of FGF23, such as the longevity factor Klotho and the phosphate transporters NPT2a and NPT2c, has permitted us to understand the elegant and complex interplay that exists between the kidneys, bone, parathyroid, and gut. Such insights from genetic disorders have allowed not only the design of potent targeted therapies for some of these rare genetic disorders, such as using anti-FGF23 antibodies for treatment of X-linked hypophosphatemic rickets, but also have led to clinically relevant observations related to the dysregulation of mineral ion homeostasis in chronic kidney disease. Thus, we are able to leverage our knowledge of rare human disorders affecting only a few individuals, to understand and potentially treat disease processes that affect millions of patients.

24-Hydroxylase in cancer: impact on vitamin D-based anticancer therapeutics

The active vitamin D hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) plays a major role in regulating calcium homeostasis and bone mineralization. 1,25(OH)2D3 also modulates cellular proliferation and differentiation in a variety of cell types. 24-Hydroxylase, encoded by the CYP24A1 gene, is the key enzyme which converts 1,25(OH)2D3 to less active calcitroic acid. Nearly all cell types express 24-hydroxylase, the highest activity being observed in the kidney. There is increasing evidence linking the incidence and prognosis of certain cancers to low serum 25(OH)D3 levels and high expression of vitamin D 24-hydroxylase, supporting the idea that elevated CYP24A1 expression may stimulate degradation of vitamin D metabolites including 25(OH)D3 and 1,25(OH)2D3. The over expression of CYP24A1 in cancer cells may be a factor affecting 1,25(OH)2D3 bioavailability and anti-proliferative activity pre-clinically and clinically. The combination of 1,25(OH)2D3 with CYP24A1 inhibitors enhances 1,25(OH)2D3 mediated signaling and anti-proliferative effects and may be useful in overcoming effects of aberrant CYP24A1 expression. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Dietary phosphate restriction suppresses phosphaturia but does not prevent FGF23 elevation in a mouse model of chronic kidney disease

Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone that in end-stage renal disease is markedly increased in serum; however, the mechanisms responsible for this increase are unclear. Here, we tested whether phosphate retention in chronic kidney disease (CKD) is responsible for the elevation of FGF23 in serum using Col4α3 knockout mice, a murine model of Alport disease exhibiting CKD. We found a significant elevation in serum FGF23 in progressively azotemic 8 and 12 week-old CKD mice along with an increased fractional excretion of phosphorus. Both moderate and severe phosphate restriction reduced fractional excretion of phosphorus by 8 weeks, yet serum FGF23 levels remained strikingly elevated. By 12 weeks, FGF23 levels were further increased with moderate phosphate restriction, while severe phosphate restriction led to severe bone mineralization defects and decreased FGF23 production in bone. CKD mice on a control diet had low serum 1,25(OH)₂D levels and 3-fold higher renal Cyp24α1 gene expression compared to wild-type mice. Severe phosphate restriction increased 1,25(OH)₂D levels in CKD mice by 8 weeks and lowered renal Cyp24α1 gene expression despite persistently elevated serum FGF23. Renal klotho gene expression declined in CKD mice on a control diet, but improved with severe phosphate restriction. Thus, dietary phosphate restriction reduces the fractional excretion of phosphorus independent of serum FGF23 levels in mice with CKD.

Combination of calcitriol and dietary soy exhibits enhanced anticancer activity and increased hypercalcemic toxicity in a mouse xenograft model of prostate cancer

BACKGROUND

The potential role of vitamin D and soy in prostate cancer (PCa) prevention/treatment has gained much attention in recent years. In this study, we evaluated the anticancer activity of calcitriol, the active form of vitamin D, dietary soy, and their combinations in a mouse model of PCa.

METHODS

Athymic male nude mice bearing PC-3 human PCa xenografts received diets containing 10 or 20 kcal% soy, calcitriol injections, or a combination of dietary soy and calcitriol. Changes in tumor growth, serum levels of 1,25(OH)(2)D and calcium, and regulation of tumor gene expression were examined.

RESULTS

The combination treatments resulted in substantially greater inhibition of tumor growth than either agent alone. Soy diets alone caused a modest elevation in serum 1,25(OH)(2)D, whereas the calcitriol-soy combinations led to substantially elevated serum 1,25(OH)(2) D, hypercalcemia, and in some cases lethal toxicity. The combinations enhanced calcitriol activity in regulating target gene expression, including greater up-regulation of anti-proliferative (p21, IGFBP-3) and pro-apoptotic (Bax) genes, increased inhibition of anti-apoptotic (Bcl-2) and cell cycle promoting (cyclin D1) genes, and suppression of prostaglandin (PG) synthesis and signaling (COX-2, 15-PGDH, PG receptors). Increases in serum calcium were accompanied by elevated expression of intestinal calcium absorption genes (TRPV6, calbindin-9k).

CONCLUSIONS

Soy increases the bioavailability of endogenous and administered calcitriol, thereby enhancing its anticancer effects and risk of hypercalcemia. Since both agents are easily available as dietary supplements, the increased potential for hypercalcemic toxicity becomes an important factor when considering the combined use of vitamin D and soy in PCa therapy.

CYP24A1 exacerbated activity during diabetes contributes to kidney tubular apoptosis via caspase-3 increased expression and activation

Decreases in circulating 25,hydroxyl-vitamin D3 (25 OH D3) and 1,25,dihydroxyl-vitamin D3 (1,25 (OH)2 D3) have been extensively documented in patients with type 2 diabetes. Nevertheless, the molecular reasons behind this drop, and whether it is a cause or an effect of disease progression is still poorly understood. With the skin and the liver, the kidney is one of the most important sites for vitamin D metabolism. Previous studies have also shown that CYP24A1 (an enzyme implicated in vitamin D metabolism), might play an important role in furthering the progression of kidney lesions during diabetic nephropathy. In this study we show a link between CYP24A1 increase and senescence followed by apoptosis induction in the renal proximal tubules of diabetic kidneys. We show that CYP24A1 expression was increased during diabetic nephropathy progression. This increase derived from protein kinase C activation and increased H₂O₂ cellular production. CYP24A1 increase had a major impact on cellular phenotype, by pushing cells into senescence, and later into apoptosis. Our data suggest that control of CYP24A1 increase during diabetes has a beneficial effect on senescence induction and caspase-3 increased expression. We concluded that diabetes induces an increase in CYP24A1 expression, destabilizing vitamin D metabolism in the renal proximal tubules, leading to cellular instability and apoptosis, and thereby accelerating tubular injury progression during diabetic nephropathy.

CYP24 inhibition preserves 1α,25-dihydroxyvitamin D(3) anti-proliferative signaling in lung cancer cells

Human lung tumors aberrantly express the 1α,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3))-catabolizing enzyme, CYP24. We hypothesized that CYP24 reduces 1,25(OH)(2)D(3)-mediated transcription and allows lung cancer cells to escape its growth-inhibitory action. To test this, H292 lung cancer cells and the CYP24-selective inhibitor CTA091 were utilized. In H292 cells, CTA091 reduces 1,25(OH)(2)D(3) catabolism, significantly increases 1,25(OH)(2)D(3)-mediated growth inhibition, and increases 1,25(OH)(2)D(3) effects on induced and repressed genes in gene expression profiling studies. Pathway mapping of repressed genes uncovered cell cycle as a predominant 1,25(OH)(2)D(3) target. In H292 cells, 1,25(OH)(2)D(3) significantly decreases cyclin E2 levels and induces G(0)/G(1) arrest. A broader set of cyclins is down-regulated when 1,25(OH)(2)D(3) is combined with CTA091, and cell cycle arrest further increases. Effects of CTA091 on 1,25(OH)(2)D(3) signaling are vitamin D receptor-dependent. These data provide evidence that CYP24 limits 1,25(OH)(2)D(3) anti-proliferative signaling in cancer cells, and suggest that CTA091 may be beneficial in preserving 1,25(OH)(2)D(3) action in lung cancer.

Hershberger P. A local effect of CYP24 inhibition on lung tumor xenograft exposure to 1,25-dihydroxyvitamin D(3) is revealed using a novel LC-MS/MS assay

The vitamin D(3) catabolizing enzyme, CYP24, is frequently over-expressed in tumors, where it may support proliferation by eliminating the growth suppressive effects of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)). However, the impact of CYP24 expression in tumors or consequence of CYP24 inhibition on tumor levels of 1,25(OH)(2)D(3)in vivo has not been studied due to the lack of a suitable quantitative method. To address this need, an LC-MS/MS assay that permits absolute quantitation of 1,25(OH)(2)D(3) in plasma and tumor was developed. We applied this assay to the H292 lung tumor xenograft model: H292 cells eliminate 1,25(OH)(2)D(3) by a CYP24-dependent process in vitro, and 1,25(OH)(2)D(3) rapidly induces CYP24 expression in H292 cells in vivo. In tumor-bearing mice, plasma and tumor concentrations of 1,25(OH)(2)D(3) reached a maximum of 21.6 and 1.70ng/mL, respectively, following intraperitoneal dosing (20μg/kg 1,25(OH)(2)D(3)). When co-administered with the CYP24 selective inhibitor CTA091 (250μg/kg), 1,25(OH)(2)D(3) plasma levels increased 1.6-fold, and tumor levels increased 2.6-fold. The tumor/plasma ratio of 1,25(OH)(2)D(3) AUC was increased 1.7-fold by CTA091, suggesting that the inhibitor increased the tumor concentrations of 1,25(OH)(2)D(3) independent of its effects on plasma disposition. Compartmental modeling of 1,25(OH)(2)D(3) concentration versus time data confirmed that: 1,25(OH)(2)D(3) was eliminated from plasma and tumor; CTA091 reduced the elimination from both compartments; and that the effect of CTA091 on tumor exposure was greater than its effect on plasma. These results provide evidence that CYP24-expressing lung tumors eliminate 1,25(OH)(2)D(3) by a CYP24-dependent process in vivo and that CTA091 administration represents a feasible approach to increase tumor exposure to 1,25(OH)(2)D(3).

Regulation of mouse Cyp24a1 expression via promoter-proximal and downstream-distal enhancers highlights new concepts of 1,25-dihydroxyvitamin D(3) action

CYP24A1 functions in vitamin D target tissues to degrade 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)). Thus, the concentration of this enzyme and the regulation of its expression is a primary determinant of the overall biological activity of 1,25(OH)(2)D(3) within cells. The principle regulator of CYP24A1 expression is 1,25(OH)(2)D(3) itself, which functions through the vitamin D receptor to upregulate the transcriptional activity of the Cyp24a1 gene. In this report, we explore the mechanism of this regulation using recently developed ChIP-chip and ChIP-seq techniques that permit an unbiased search for enhancer elements that participate in this transcriptional control. Our studies both confirm a regulatory region defined earlier and located proximal to the transcriptional start site (TSS) of mouse Cyp24a1 (-160 and -265nt) and identify a novel intergenic region located downstream of the transcription unit that contains two enhancers (+35 and +37kb) that facilitate 1,25(OH)(2)D(3)-dependent upregulation of Cyp24a1 expression. Interestingly, while C/EBPβ also binds under basal conditions to a site located immediately upstream of the Cyp24a1 promoter (-345nt), occupancy by this factor is strikingly increased following 1,25(OH)(2)D(3) treatment. The locations and activities of these regulatory regions that mediate 1,25(OH)(2)D(3) actions were confirmed in mice in vivo. We conclude that the mechanism through which 1,25(OH)(2)D(3) induces the CYP24A1 enzyme, thereby autoregulating its own destruction, involves both promoter-proximal as well as downstream-distal enhancers. These findings highlight new concepts regarding the molecular mechanism of action of 1,25(OH)(2)D(3) and other hormonal regulators.

25-Hydroxyvitamin D-24-hydroxylase (CYP24A1): its important role in the degradation of vitamin D

CYP24A1 is the cytochrome P450 component of the 25-hydroxyvitamin D(3)-24-hydroxylase enzyme that catalyzes the conversion of 25-hydroxyvitamin D(3) (25-OH-D(3)) and 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) into 24-hydroxylated products, which constitute the degradation of the vitamin D molecule. This review focuses on recent data in the CYP24A1 field, including biochemical, physiological and clinical developments. Notable among these are: the first crystal structure for rat CYP24A1; mutagenesis studies which change the regioselectivity of the enzyme; and the finding that natural inactivating mutations of CYP24A1 cause the genetic disease idiopathic infantile hypercalcemia (IIH). The review also discusses the emerging correlation between rising serum phosphate/FGF-23 levels and increased CYP24A1 expression in chronic kidney disease, which in turn underlies accelerated degradation of both serum 25-OH-D(3) and 1,25-(OH)(2)D(3) in this condition. This review concludes by evaluating the potential clinical utility of blocking this enzyme with CYP24A1 inhibitors in various disease states.

Mechanism of the anti-proliferative action of 25-hydroxy-19-nor-vitamin D(3) in human prostate cells

According to the prevailing paradigm, 1α-hydroxylation of 25-hydroxyvitamin D(3) (25(OH)D(3)) and its analogs is a pre-requisite step for their biological effects. We previously reported that 25-hydroxy-19-nor-vitamin D(3) (25(OH)-19-nor-D(3)) had anti-proliferative activity in a cell line, PZ-HPV-7, which was derived from human non-cancerous prostate tissue, and suggested that 25(OH)-19-nor-D(3) acted after 1α-hydroxylation by vitamin D 1α-hydroxylase (CYP27B1). However, metabolic studies of 25(OH)-19-nor-D(3) using recombinant CYP27B1 revealed that 25(OH)-19-nor-D(3) was rarely subjected to 1α-hydroxylation. Therefore, in this report, we attempted to clarify the mechanism of 25(OH)-19-nor-D(3) action in intact cells using PZ-HPV-7 prostate cells. After incubating the cells with 25(OH)-19-nor-D(3), eight metabolites of 24-hydroxylase (CYP24A1) were detected, whereas no products of CYP27B1 including 1α,25-dihydroxy-19-nor-vitamin D(3) (1α,25(OH)(2)-19-nor-D(3)) were found. Furthermore, the time-dependent nuclear translocation of vitamin D receptor (VDR) and the subsequent transactivation of cyp24A1 gene in the presence of 25(OH)-19-nor-D(3) were almost identical as those induced by 1α,25(OH)(2)-19-nor-D(3). These results strongly suggest that 25(OH)-19-nor-D(3) directly binds to VDR as a ligand and transports VDR into the nucleus to induce transcription of cyp24A1 gene. In addition, knock down of cyp27B1 gene did not affect the anti-proliferative activity of 25(OH)-19-nor-D(3), whereas knock down of VDR attenuated the inhibitory effect. Thus, our results clearly demonstrate that the anti-proliferative activity of 25(OH)-19-nor-D(3) is VDR dependent but 1α-hydroxylation independent, suggesting that 25(OH)D(3) analogs such as 25(OH)-19-nor-D(3) could be attractive candidates for anticancer therapy.

CYP24A1 and kidney disease

PURPOSE OF REVIEW

Patients with chronic renal disease have elevated serum phosphate levels, elevated fibroblast-like growth factor 23 (FGF-23), and declining vitamin D status. These changes are related and may be responsible for elevated 25-hydroxyvitamin D-24-hydroxylase (CYP24A1) and dysfunctional vitamin D metabolism. This review focuses on the biochemistry and pathophysiology of CYP24A1 and the utility of blocking this enzyme with CYP24A1 inhibitors in chronic kidney disease (CKD) patients.

RECENT FINDINGS

CYP24A1 is the cytochrome P450 enzyme that catalyzes the conversion of 25-hydroxyvitamin D3 (25-OHD3) and its hormonal form, 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], into 24-hydroxylated products targeted for excretion. The CYP24A1-null phenotype is consistent with the catabolic role of CYP24A1. A number of polymorphisms of CYP24A1 have recently been identified. New data from the uremic rat and humans suggest that dysfunctional vitamin D metabolism is due to changes in CYP24A1 expression caused by phosphate and FGF-23 elevations.

SUMMARY

Changes in serum phosphate and FGF-23 levels in the CKD patient increase CYP24A1 expression resulting in decreased vitamin D status. Vitamin D deficiency may exacerbate defective calcium and phosphate homeostasis causing renal osteodystrophy and contribute to the other complications of renal disease. These findings argue for increased focus on correcting vitamin D deficiency in CKD patients by blocking CYP24A1 activity.