Ovarian 25OH-vitamin D production in young women affected by polycystic ovary syndrome

INTRODUCTION

Vitamin D is involved in the regulatory mechanisms of ovarian function and is frequently low in PCOS patients. Since obesity and hyperinsulinemic state negatively influenced vitamin D levels, therefore, we evaluated the production of vitamin D at the ovarian level only in lean and normoinsulinemic PCOS subjects. Basal, GnRH analogue-induced ovarian production of 25OH-vitamin D (VitD) and a direct sampling at ovarian vein level were investigated.

METHODS

Basal and GnRH analogue-induced hormone levels were evaluated at peripheral level in 45 subjects, aged 18-39 years, and in 22 healthy women with age- and BMI-matched as controls. In 12 PCOS patients, undergoing laparoscopy, a venous sampling at both peripheral and ovarian level was further done. All subjects presented low VitD levels, appropriate to the season and with no difference between PCOS and control subjects.

RESULTS

GnRH analogue significantly stimulated plasma LH, FSH, 17-OHP and estradiol secretion (p from < 0.05 to < 0.001 vs basal levels), whereas no effect was observed on both serum AMH and VitD concentrations in all groups. A significant difference (p < 0.006), between peripheral and ovarian veins, was observed in both AMH and estradiol levels in PCOS subjects, while no gradient of VitD was detected.

CONCLUSIONS

All patients presented with low VitD levels. The absence of any VitD variation, both at basal and after GnRH analogue administration, or at peripheral-ovarian vein gradient, suggests no pituitary-ovarian axis involvement in VitD production or its direct ovarian production in lean and normoinsulinemic PCOS subjects.

Potentially repurposable drugs for schizophrenia identified from its interactome

We previously presented the protein-protein interaction network of schizophrenia associated genes, and from it, the drug-protein interactome which showed the drugs that target any of the proteins in the interactome. Here, we studied these drugs further to identify whether any of them may potentially be repurposable for schizophrenia. In schizophrenia, gene expression has been described as a measurable aspect of the disease reflecting the action of risk genes. We studied each of the drugs from the interactome using the BaseSpace Correlation Engine, and shortlisted those that had a negative correlation with differential gene expression of schizophrenia. This analysis resulted in 12 drugs whose differential gene expression (drug versus normal) had an anti-correlation with differential expression for schizophrenia (disorder versus normal). Some of these drugs were already being tested for their clinical activity in schizophrenia and other neuropsychiatric disorders. Several proteins in the protein interactome of the targets of several of these drugs were associated with various neuropsychiatric disorders. The network of genes with opposite drug-induced versus schizophrenia-associated expression profiles were significantly enriched in pathways relevant to schizophrenia etiology and GWAS genes associated with traits or diseases that had a pathophysiological overlap with schizophrenia. Drugs that targeted the same genes as the shortlisted drugs, have also demonstrated clinical activity in schizophrenia and other related disorders. This integrated computational analysis will help translate insights from the schizophrenia drug-protein interactome to clinical research - an important step, especially in the field of psychiatric drug development which faces a high failure rate.

Endogenously produced nonclassical vitamin D hydroxy-metabolites act as "biased" agonists on VDR and inverse agonists on RORα and RORγ

The classical pathway of vitamin D activation follows the sequence D3→25(OH)D3→1,25(OH)₂D3 with the final product acting on the receptor for vitamin D (VDR). An alternative pathway can be started by the action of CYP11A1 on the side chain of D3, primarily producing 20(OH)D3, 22(OH)D3, 20,23(OH)₂D3, 20,22(OH)₂D3 and 17,20,23(OH)₃D3. Some of these metabolites are hydroxylated by CYP27B1 at C1α, by CYP24A1 at C24 and C25, and by CYP27A1 at C25 and C26. The products of these pathways are biologically active. In the epidermis and/or serum or adrenals we detected 20(OH)D3, 22(OH)D3, 20,22(OH)₂D3, 20,23(OH)₂D3, 17,20,23(OH)₃D3, 1,20(OH)₂D3, 1,20,23(OH)₃D3, 1,20,22(OH)₃D3, 20,24(OH)₂D3, 1,20,24(OH)₃D3, 20,25(OH)₂D3, 1,20,25(OH)₃D3, 20,26(OH)₂D3 and 1,20,26(OH)₃D3. 20(OH)D3 and 20,23(OH)₂D3 are non-calcemic, while the addition of an OH at C1α confers some calcemic activity. Molecular modeling and functional assays show that the major products of the pathway can act as "biased" agonists for the VDR with high docking scores to the ligand binding domain (LBD), but lower than that of 1,25(OH)₂D3. Importantly, cell based functional receptor studies and molecular modeling have identified the novel secosteroids as inverse agonists of both RORα and RORγ receptors. Specifically, they have high docking scores using crystal structures of RORα and RORγ LBDs. Furthermore, 20(OH)D3 and 20,23(OH)₂D3 have been tested in a cell model that expresses a Tet-on RORα or RORγ vector and a RORE-LUC reporter (ROR-responsive element), and in a mammalian 2-hybrid model that test interactions between an LBD-interacting LXXLL-peptide and the LBD of RORα/γ. These assays demonstrated that the novel secosteroids have ROR-antagonist activities that were further confirmed by the inhibition of IL17 promoter activity in cells overexpressing RORα/γ. In conclusion, endogenously produced novel D3 hydroxy-derivatives can act both as "biased" agonists of the VDR and/or inverse agonists of RORα/γ. We suggest that the identification of large number of endogenously produced alternative hydroxy-metabolites of D3 that are biologically active, and of possible alternative receptors, may offer an explanation for the pleiotropic and diverse activities of vitamin D, previously assigned solely to 1,25(OH)₂D3 and VDR.

Free 25(OH)D and Calcium Absorption, PTH, and Markers of Bone Turnover

CONTEXT

It has been proposed that serum free 25-hydroxyvitamin D [25(OH)D] may better reflect vitamin D action than total 25(OH)D. An ELISA for serum free 25(OH)D has recently become available, permitting direct assay.

OBJECTIVE

To determine whether serum free 25(OH)D provides additional information in relation to calcium absorption and other biomarkers of vitamin D action compared to total serum 25(OH)D.

SETTING

Ambulatory research setting in a teaching hospital.

OUTCOME

Serum free 25(OH)D measured in a previously performed study of varied doses of vitamin D3 (placebo and 800, 2000, and 4000 IU) on calcium absorption, PTH, procollagen type 1 N-terminal propeptide, and C-terminal telopeptides of type I collagen. Free 25(OH)D was measured by ELISA. Calcium absorption was measured at baseline and at 10 weeks using stable dual calcium isotopes.

RESULTS

Seventy-one subjects completed this randomized, placebo-controlled trial. Baseline group mean free and total 25(OH)D varied from 4.7 ± 1.8 to 5.4 ± 1.5 pg/mL, and from 23.7 ± 5.9 to 25.9 ± 6.1 ng/mL, respectively. Participants assigned to the 4000-IU dose arm achieved free 25(OH)D levels of 10.4 pg/mL and total 25(OH)D levels of 40.4 ng/mL. Total and free 25(OH)D were highly correlated at baseline and after increasing vitamin D dosing (r = 0.80 and 0.85, respectively). Free 25(OH)D closely reflected changes in total 25(OH)D. PTH was similarly correlated at baseline and follow-up with total and free 25(OH)D. Serum C-terminal telopeptides of type I collagen had a moderate positive correlation with total and free 25(OH)D at follow-up. The serum 1,25-dihydroxyvitamin D change increased significantly with the change in 25(OH)D but not with the change in free 25(OH)D.

CONCLUSION

There was no advantage from measuring free over total 25(OH)D in assessing the response of calcium absorption, PTH, and markers of bone turnover to vitamin D. Free 25(OH)D responded to increasing doses of vitamin D in a similar fashion to total 25(OH)D.

Genetic Polymorphisms in Vitamin D Metabolism and Signaling Genes and Risk of Breast Cancer: A Nested Case-Control Study

Genetic polymorphisms in vitamin D metabolism and signaling genes have been inconsistently associated with risk of breast cancer, though few studies have examined SNPs in vitamin D-related genes other than the vitamin D receptor (VDR) gene and particularly have not examined the association with the retinoid X receptor alpha (RXRA) gene which may be a key vitamin D pathway gene. We conducted a nested case-control study of 734 cases and 1435 individually matched controls from a population-based prospective cohort study, the Northern Sweden Mammary Screening Cohort. Tag and functional SNPs were genotyped for the VDR, cytochrome p450 24A1 (CYP24A1), and RXRA genes. We also genotyped specific SNPs in four other genes related to vitamin D metabolism and signaling (GC/VDBP, CYP2R1, DHCR7, and CYP27B1). SNPs in the CYP2R1, DHCR7, and VDBP gene regions that were associated with circulating 25(OH)D concentration in GWAS were also associated with plasma 25(OH)D in our study (p-trend <0.005). After taking into account the false discovery rate, these SNPs were not significantly associated with breast cancer risk, nor were any of the other SNPs or haplotypes in VDR, RXRA, and CYP24A1. We observed no statistically significant associations between polymorphisms or haplotypes in key vitamin D-related genes and risk of breast cancer. These results, combined with the observation in this cohort and most other prospective studies of no association of circulating 25(OH)D with breast cancer risk, do not support an association between vitamin D and breast cancer risk.

Regulation of the vitamin D endocrine system located in the kidney

During the past decade, it has been clearly established that the kidney is an endocrine organ which converts 25-hydroxyvitamin D to the active hormone 1,25-dihydroxyvitamin D. The kidney and intestine are the sites of an alternative hydroxylation which places an 24 hydroxyl in the R position on either 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D. The production of 1,25-dihydroxyvitamin D is stimulated by hypocalcemia through the parathyroid gland, hypophosphatemia, the sex hormones and the peptide hormones insulin and prolactin. This vitamin D based endocrine system is of central importance in regulating calcium and phosphorus metabolism and its disturbances result in a variety of pathological conditions.

Metabolites of 24,25-dihydroxyvitamin D3 made in the kidney of chicks supplemented with vitamin D3

Metabolism of 25-hydroxyvitamin D3 (25-OH-D3) was examined in chicks supplemented with vitamin D3. Kidney homogenates metabolized in vitro [3H]-25-OH-D3 to 3 new metabolites (peaks A, C and E) by way of 24,25-dihydroxyvitamin D3. The enzymes responsible for the synthesis of these metabolites appeared to be induced by 1 alpha,25-dihydroxyvitamin D3. Production of these metabolites was increased in parallel with the increase of the supplemented levels of vitamin D3, while recovery of the radioactivity in the chloroform phase was sharply decreased. The production of peak C was considered to be closely related to the transfer of the radioactive metabolites to the water-soluble phase. These results may indicate that 24-hydroxylation is a degradation step in the 25-OH-D3 metabolism.

Biologic and therapeutic effects of 1 alpha-hydroxycholecalciferol in different types of Fanconi syndrome

The plasma 1,25-(OH)2VD3 level in Fanconi syndrome was low but rose rapidly following the administration of 1 alpha-OHVD3. 1 alpha-OHVD3 was administered to 6 patients with different types of Fanconi syndrome. The effect of 1 alpha-OHVD3 proved to be 200-250 times as great as that of vitamin D2. From our results it was suggested that Ca malabsorption due to failure of 1 alpha-hydroxylation of vitamin D in the kidney, together with renal tubular acidosis and hypophosphatemia, is involved in the pathogenesis of the rickets of Fanconi syndrome.

The effects of omega-3 fatty acid on vitamin D activation in hemodialysis patients: a pilot study

The high incidence of cardiovascular disease and vitamin D deficiency in chronic kidney disease patients is well known. Vitamin D activation by omega-3 fatty acid (FA) supplementation may explain the cardioprotective effects exerted by omega-3 FA. We hypothesized that omega-3 FA and 25-hydroxyvitamin D (25(OH)D) supplementation may increase 1,25-dihydroxyvitamin D (1,25(OH)₂D) levels compared to 25(OH)D supplementation alone in hemodialysis (HD) patients that have insufficient or deficient 25(OH)D levels. We enrolled patients that were treated for at least six months with 25(OH)D < 30 ng/mL (NCT01596842). Patients were randomized to treatment for 12 weeks with cholecalciferol supplemented with omega-3 FA or a placebo. Levels of 25(OH)D and 1,25(OH)₂D were measured after 12 weeks. The erythrocyte membrane FA contents were also measured. Levels of 25(OH)D were increased in both groups at 12 weeks compared to baseline. The 1,25(OH)₂D levels at 12 weeks compared to baseline showed a tendency to increase in the omega-3 FA group. The oleic acid and monounsaturated FA content decreased, while the omega-3 index increased in the omega-3 FA group. Omega-3 FA supplementation may be partly associated with vitamin D activation, although increased 25(OH)D levels caused by short-term cholecalciferol supplementation were not associated with vitamin D activation in HD patients.

Dysregulation of vitamin D metabolism in the brain and myocardium of rats following prolonged exposure to dexamethasone

RATIONALE

Chronic stress or hypercortisolism may increase the risks of depression, cardiac disorders, and osteoporosis, which are also associated with vitamin D (VD) deficiency. Both glucocorticoid receptor (GR) and vitamin D receptor (VDR) are widely distributed and affect many aspects of human physiology. The cross talk between the two steroids is pervasive, but the effect of glucocorticoids on circulating VD and local VD metabolism remains elusive.

OBJECTIVES

To fill this critical gap, we assessed the alterations of circulating VD and VD intracrine system in the brain and myocardium of rats treated with two different doses (0.2 and 2 mg/kg/day, respectively) of dexamethasone (Dex).

RESULTS

Daily treatment with 2 mg/kg of Dex for 10 days induced the rats to a depressive-like state and decreased the expression of both VDR and the cytochromes P450 enzymes involved in VD activation (CYP27B1) and catabolism (CYP24A1) in the prefrontal cortex and hippocampus. Meanwhile, the dose of 0.2 mg/kg Dex increased the expression of VDR in the prefrontal cortex but inhibited CYP27B1/CYP24A1/VDR expression in the hippocampus. Similarly, in the myocardium, the rats treated with Dex showed significantly lower expression of CYP27B1/CYP24A1/VDR. Renal VD metabolism and serum VD status were unchanged in 0.2 mg/kg Dex-treated rats. However, the higher dose suppressed the three key players involved in VD metabolism but did not alter serum VD levels.

CONCLUSION

These data provide new evidence that glucocorticoids could affect intracrine actions of VD in the brain and myocardium, which suggests the potential involvement of VD in the neural and cardiac dysfunctions induced by glucocorticoid excess.

20-Hydroxycholecalciferol, product of vitamin D3 hydroxylation by P450scc, decreases NF-kappaB activity by increasing IkappaB alpha levels in human keratinocytes

The side chain of vitamin D3 is hydroxylated in a sequential manner by cytochrome P450scc (CYP11A1) to form 20-hydroxycholecalciferol, which can induce growth arrest and differentiation of both primary and immortalized epidermal keratinocytes. Since nuclear factor-κB (NF-κB) plays a pivotal role in the regulation of cell proliferation, differentiation and apoptosis, we examined the capability of 20-hydroxycholecalciferol to modulate the activity of NF-κB, using 1,25-dihydroxycholecalciferol (calcitriol) as a positive control. 20-hydroxycholecalciferol inhibits the activation of NFκB DNA binding activity as well as NF-κB-driven reporter gene activity in keratinocytes. Also, 20-hydroxycholecalciferol induced significant increases in the mRNA and protein levels of the NF-κB inhibitor protein, IκBα, in a time dependent manner, while no changes in total NF-κB-p65 mRNA or protein levels were observed. Another measure of NF-κB activity, p65 translocation from the cytoplasm into the nucleus was also inhibited in extracts of 20-hydroxycholecalciferol treated keratinocytes. Increased IκBα was concomitantly observed in cytosolic extracts of 20-hydroxycholecalciferol treated keratinocytes, as determined by immunoblotting and immunofluorescent staining. In keratinocytes lacking vitamin D receptor (VDR), 20-hydroxycholecalciferol did not affect IκBα mRNA levels, indicating that it requires VDR for its action on NF-κB activity. Comparison of the effects of calcitrol, hormonally active form of vitamin D3, with 20-hydrocholecalciferol show that both agents have a similar potency in inhibiting NF-κB. Since NF-κB is a major transcription factor for the induction of inflammatory mediators, our findings indicate that 20-hydroxycholecalciferol may be an effective therapeutic agent for inflammatory and hyperproliferative skin diseases.

The hepatic conversion of vitamin D in alcoholics with varying degrees of liver affection

The seasonal variations in circulating 25-hydroxycholecalciferol (25-HCC) were studied in 102 alcoholics with fatty liver disease without histologic signs of cirrhosis and in 35 patients with alcoholic cirrhosis. The mean levels were compared with those of normal persons. Alcoholics had generally lower 25-HCC values than the controls, particularly in the summer. This was primarily explained by insufficient diet and reduced exposure to sunshine. The ability of the liver to hydroxylate in the 25-position was studied in three groups of alcoholics with 1) fatty liver disease without cirrhosis, 2) compensated cirrhosis, 3) severely incompensated liver cirrhosis. All three groups exhibited a significant increase in serum 25-HCC following the peroral administration of cholecalciferol at a dose of 1 200 U daily for 7 days. Similar rises were seen 7 days after a single injection of 10 000 U cholecalciferol. This indicates a normal intestinal absorption of vitamin D, even in advanced alcoholic liver disease, and is inconsistent with a severely damaged 25-hydroxylation capacity in these patients. Osteomalacia due to impaired liver hydroxylation of vitamin D can hardly explain the increased fracture rate and the decreased bone mass, which have been described in alcoholics.

Effect of sunlight exposure on circulating 1,25-dihydroxyvitamin D in hemodialyzed patients and of exogenous parathyroid hormone in anephric patients

Sunshine exposure increased the serum concentration of 25-hydroxyvitamin D (25-OHD) in 9 hemodialyzed patients. Mean 1,25-dihydroxyvitamin D (1,25-(OH)2D) was unchanged, but in two patients with low initial 25-OHD values this increase was accompanied by a rise in circulating 1,25-(OH)2D, although not to normal levels. One hemodialyzed patient developed liver insufficiency with a resultant reduction of serum 25-OHD concentration accompanied by a decrease in serum 1,25-(OH)2D concentration. The results indicate that the circulating levels of 1,25-(OH)2D in patients with end-stage renal failure are to some extent regulated by the serum 25-OHD concentrations. Injection of parathyroid hormone (PTH) induced minor increases in serum concentrations of 1,25-(OH)2D in patients with end-stage renal failure and even in anephric patients, suggesting the existence of an extrarenal PTH-sensitive 1-alpha-hydroxylase. However, the enzyme was stimulated by supraphysiological concentrations of PTH, and therefore not necessarily of importance in the normal regulation of calcium metabolism.

Metabolism of 1alpha-hydroxyvitamin D3 by cytochrome P450scc to biologically active 1alpha,20-dihydroxyvitamin D3

Cytochrome P450scc (CYP11A1) metabolizes vitamin D3 to 20-hydroxyvitamin D3 as the major product, with subsequent production of dihydroxy and trihydroxy derivatives. The aim of this study was to determine whether cytochrome P450scc could metabolize 1alpha-hydroxyvitamin D3 and whether products were biologically active. The major product of 1alpha-hydroxyvitamin D3 metabolism by P450scc was identified by mass spectrometry and NMR as 1alpha,20-dihydroxyvitamin D3. Mass spectrometry of minor metabolites revealed the production of another dihydroxyvitamin D3 derivative, two trihydroxy-metabolites made via 1alpha,20-dihydroxyvitamin D3 and a tetrahydroxyvitamin D3 derivative. The Km for 1alpha-hydroxyvitamin D3 determined for P450scc incorporated into phospholipid vesicles was 1.4 mol substrate/mol phospholipid, half that observed for vitamin D3. The kcat was 3.0 mol/min/mol P450scc, 6-fold lower than that for vitamin D3. 1alpha,20-Dihydroxyvitamin D3 inhibited DNA synthesis by human epidermal HaCaT keratinocytes propagated in culture, in a time- and dose-dependent fashion, with a potency similar to that of 1alpha,25-dihydroxyvitamin D3. 1alpha,20-Dihydroxyvitamin D3 (10 microM) enhanced CYP24 mRNA levels in HaCaT keratinocytes but the potency was much lower than that reported for 1alpha,25-dihydroxyvitamin D3. We conclude that the presence of the 1-hydroxyl group in vitamin D3 does not alter the major site of hydroxylation by P450scc which, as for vitamin D3, is at C20. The major product, 1alpha,20-dihydroxyvitamin D3, displays biological activity on keratinocytes and therefore might be useful pharmacologically.

Vitamin D metabolism in patients treated with phenytoin and phenobarbitone

There are many reports of abnormalities in calcium metabolism and even of frank osteomalacia in patients taking anticonvulsant drugs. Although enzyme induction has been suggested to be the cause of increased requirements for vitamin D leading to these changes, this has still to be proved. We have studied the metabolism of [3H]cholecalciferol and 25-hydroxycholecalciferol in subjects taking anticonvulsant drugs. The rate of removal of cholecalciferol from the plasma was no different from that in control subjects and no abnormality was detected in the production of disappearance of 25-hydroxycholecalciferol. However, plasma concentrations of 25-hydroxycholecalciferol fell more rapidly during the winter in epileptic subjects than in control subjects. Our results do not confirm that these changes are due to enzyme induction.

Vitamin D signalling pathways in cancer: potential for anticancer therapeutics

Epidemiological studies indicate that vitamin D insufficiency could have an aetiological role in various human cancers. Preclinical research indicates that the active metabolite of vitamin D, 1alpha,25(OH)2D3, also known as calcitriol, or vitamin D analogues might have potential as anticancer agents because their administration has antiproliferative effects, can activate apoptotic pathways and inhibit angiogenesis. In addition, 1alpha,25(OH)2D3 potentiates the anticancer effects of many cytotoxic and antiproliferative anticancer agents. Here, we outline the epidemiological, preclinical and clinical studies that support the development of 1alpha,25(OH)2D3 and vitamin D analogues as preventative and therapeutic anticancer agents.

Determination of Vitamin D-dependent calcium absorption by 45Ca gavage in the rat

Precise determination of Vitamin D-dependent intestinal calcium absorption in longitudinal studies is problematic. We have assessed Vitamin D-dependent intestinal calcium absorption by (45)Ca gavage. Rats were gavaged with a 1mL solution containing (45)Ca (CaCl(2), 9.3MBq/mL) maintained at 37 degrees C. Total Ca concentration of the gavage fluid was optimised by comparing the absorption curves for fluids made up to 0.025, 2.025, 4.025 and 40.025 mmol/L with (40)CaCl(2). The effect of varying dietary Ca on fractional Ca absorption was determined in rats fed semi-synthetic diets containing either 0.05%, 0.2%, 0.4% or 1.0% Ca for 50 days. Serum 1,25 dihydroxyvitamin D (1,25D) was determined by radioimmunoassay. Total gavage Ca of 0.025 mmol/L achieved the highest peak fractional absorption and was adopted for all future experiments. Fifty days after allocation to the diets both fractional Ca absorption and 1,25D were highest in rats fed 0.05% Ca and lowest in those fed 1.0% Ca (absorption, P<0.05 and 1,25D, P<0.05). There was a strong logarithmic relationship between 1,25D and fractional Ca absorption (R(2) 0.69, P<0.001). Weekly repetition of the procedure did not cause a fall in haematocrit over 7 weeks. Radiocalcium ((45)Ca) absorption by gavage provides a simple measure of Vitamin D-dependent Ca absorption for repetitive use in longitudinal studies.

The assessment of circulating 25(OH)D and 1,25(OH)2D: where we are and where we are going

The field of Vitamin D assay technology has progressed significantly over the past 4 decades. Further, the clinical utility of these measurements has moved from esoteric into mainstream clinical diagnosis. This movement has been fueled by the realization that Vitamin D is involved in bodily systems beyond skeletal integrity. The clinical assay techniques for circulating 25(OH)D and 1,25(OH)(2)D have progressed away from competitive protein binding assay (CPBAs) that utilize tritium reporters to radioimmunoassay (RIAs) that utilize both I(125) and chemiluminescent reporters. These advances have allowed direct serum analysis of 25(OH)D in an automated format that provides a huge sample throughput. Detection of circulating 25(OH)D can also be achieved utilizing direct high-performance liquid chromatographic (HPLC) or liquid chromatography coupled with mass spectrometry (LC-MS) techniques. These methods are accurate, however, they require expensive equipment and restrict sample throughput in the large clinical laboratory. Direct serum detection of 1,25(OH)(2)D is unlikely to occur for many reasons as a sample pre-purification will always be required. However, a semi-automated chemiluminescent detection system with automated sample preparation is in final development for the determination of circulating 1,25(OH)(2)D. These advances will allow both 25(OH)D and 1,25(OH)(2)D to be detected in an accurate, rapid fashion to meet the clinical demands we see emerging.

A comparative study on several models of experimental renal calcium oxalate stones formation in rats

In order to compare the effects of several experimental renal calcium oxalate stones formation models in rats and to find a simple and convenient model with significant effect of calcium oxalate crystals deposition in the kidney, several rat models of renal calcium oxalate stones formation were induced by some crystal-inducing drugs (CID) including ethylene glycol (EG), ammonium chloride (AC), vitamin D(3)[1alpha(OH)VitD(3), alfacalcidol], calcium gluconate, ammonium oxalate, gentamicin sulfate, L-hydroxyproline. The rats were fed with drugs given singly or unitedly. At the end of experiment, 24-h urines were collected and the serum creatinine (Cr), blood urea nitrogen (BUN), the extents of calcium oxalate crystal deposition in the renal tissue, urinary calcium and oxalate excretion were measured. The serum Cr levels in the stone-forming groups were significantly higher than those in the control group except for the group EG+L-hydroxyproline, group calcium gluconate and group oxalate. Blood BUN concentration was significantly higher in rats fed with CID than that in control group except for group EG+L-hydroxyproline and group ammonium oxalate plus calcium gluconate. In the group of rats administered with EG plus Vitamin D(3), the deposition of calcium oxalate crystal in the renal tissue and urinary calcium excretion were significantly greater than other model groups. The effect of the model induced by EG plus AC was similar to that in the group induced by EG plus Vitamin D(3). EG plus Vitamin D(3) or EG plus AC could stably and significantly induced the rat model of renal calcium oxalate stones formation.

23-Carboxy-24,25,26,27-tetranorvitamin D3 (calcioic acid) and 24-carboxy-25,26,27-trinorvitamin D3 (cholacalcioic acid): End products of 25-hydroxyvitamin D3 metabolism in rat kidney through C-24 oxidation pathway

During the past two and half decades the elucidation of the metabolic pathways of 25OHD(3) and its active metabolite 1alpha,25(OH)(2)D(3) progressed in parallel. In spite of many advances in this area of vitamin D research, the unequivocal identification of the end products of 25OHD(3) metabolism through C-24 oxidation pathway has not been achieved. It is now well established that both 25OHD(3) and 1alpha,25(OH)(2)D(3) are metabolized through the same C-24 oxidation pathway initiated by the enzyme 24-hydroxylase (CYP24A1). Based on the information that the end product of 1alpha,25(OH)(2)D(3) metabolism through C-24 oxidation pathway is 1alpha-OH-23- COOH-24,25,26,27-tetranor D(3) or calcitroic acid; the metabolism of 25OHD(3) into 23-COOH-24,25,26,27-tetranor D(3) has been assumed. Furthermore, a previous study indicated 24-COOH-25,26,27-trinor D(3) as a water soluble metabolite of 24R,25(OH)(2)D(3) produced in rat kidney homogenates. Therefore, 24-COOH-25,26,27-trinor D(3) was also assumed as another end product of 25OHD(3) metabolism through C-24 oxidation pathway. We embarked on our present study to provide unequivocal proof for these assumptions. We first studied the metabolism of 25OHD(3) at low substrate concentration (3x10(-10)M) using [1,2-(3)H]25OHD(3) as the substrate in the perfused rat kidneys isolated from both normal and vitamin D(3) intoxicated rats. A highly polar water soluble metabolite, labeled as metabolite X was isolated from the kidney perfusate. The amount of metabolite X produced in the kidney of a vitamin D intoxicated rat was about seven times higher than that produced in the kidney of a normal rat. We then produced metabolite X in a quantity sufficient for its structure identification by perfusing kidneys isolated from vitamin D intoxicated rats with high substrate concentration of 25OHD(3) (5x10(-6)M). Using the techniques of electron impact and thermospray mass spectrometry, we established that the metabolite X contained both 23-COOH-24,25,26,27-tetranor D(3) and 24-COOH-25,26,27-trinor D(3) in a ratio of 4:1. The same metabolite X containing both acids in the same ratio of 4:1 was also produced when 24R,25(OH)(2)D(3) was used as the starting substrate. Previously, the trivial name of cholacalcioic acid was assigned to 24-COOH-25,26,27-trinorvitamin D(3). Using the same guidelines, we now assign the trivial name of calcioic acid to 23-COOH-24,25,26,27-tetranor D(3). In summary, for the first time our study provides unequivocal evidence to indicate that both calcioic and cholacalcioic acids as the end products of 25OHD(3) metabolism in rat kidney through C-24 oxidation pathway.

An alternative pathway of vitamin D metabolism. Cytochrome P450scc (CYP11A1)-mediated conversion to 20-hydroxyvitamin D2 and 17,20-dihydroxyvitamin D2

We report an alternative, hydroxylating pathway for the metabolism of vitamin D2 in a cytochrome P450 side chain cleavage (P450scc; CYP11A1) reconstituted system. NMR analyses identified solely 20-hydroxyvitamin D2 and 17,20-dihydroxyvitamin D2 derivatives. 20-Hydroxyvitamin D2 was produced at a rate of 0.34 mol x min(-1) x mol(-1) P450scc, and 17,20-dihydroxyvitamin D2 was produced at a rate of 0.13 mol x min(-1) x mol(-1). In adrenal mitochondria, vitamin D2 was metabolized to six monohydroxy products. Nevertheless, aminoglutethimide (a P450scc inhibitor) inhibited this adrenal metabolite formation. Initial testing of metabolites for biological activity showed that, similar to vitamin D2, 20-hydroxyvitamin D2 and 17,20-dihydroxyvitamin D2 inhibited DNA synthesis in human epidermal HaCaT keratinocytes, although to a greater degree. 17,20-Dihydroxyvitamin D2 stimulated transcriptional activity of the involucrin promoter, again to a significantly greater extent than vitamin D2, while the effect of 20-hydroxyvitamin D2 was statistically insignificant. Thus, P450scc can metabolize vitamin D2 to generate novel products, with intrinsic biological activity (at least in keratinocytes).

Resurrection of vitamin D deficiency and rickets

The epidemic scourge of rickets in the 19th century was caused by vitamin D deficiency due to inadequate sun exposure and resulted in growth retardation, muscle weakness, skeletal deformities, hypocalcemia, tetany, and seizures. The encouragement of sensible sun exposure and the fortification of milk with vitamin D resulted in almost complete eradication of the disease. Vitamin D (where D represents D2 or D3) is biologically inert and metabolized in the liver to 25-hydroxyvitamin D [25(OH)D], the major circulating form of vitamin D that is used to determine vitamin D status. 25(OH)D is activated in the kidneys to 1,25-dihydroxyvitamin D [1,25(OH)2D], which regulates calcium, phosphorus, and bone metabolism. Vitamin D deficiency has again become an epidemic in children, and rickets has become a global health issue. In addition to vitamin D deficiency, calcium deficiency and acquired and inherited disorders of vitamin D, calcium, and phosphorus metabolism cause rickets. This review summarizes the role of vitamin D in the prevention of rickets and its importance in the overall health and welfare of infants and children.

Hepatic activation and inactivation of clinically-relevant vitamin D analogs and prodrugs

Like most pharmaceutical agents, vitamin D analogs are subject to hepatic metabolism by a variety of cytochrome P450 (CYP)-based systems. Metabolism can involve activation as well as inactivation of the vitamin D analog and one of the more successful families includes the 1alpha-hydroxyvitamin D prodrugs (1alpha-OH-D2, 1alpha-OH-D3, 1alpha-OH-D4, 1alpha-OH-D5), that all require a step of activation. Some of these prodrugs are in use or clinical trial because they have a therapeutic advantage over calcitriol. However, the nature of the activation of these molecules is poorly understood, particularly with regard to the CYP isoform involved. Various transfected CYPs and hepatic cell lines combined with tandem LC-MS analysis were used to investigate the metabolism of a spectrum of vitamin D analogs, including 1alpha-OH-Ds and the topical analog, calcipotriol. In the case of the 1alpha-OH-Ds, evidence was found of multiple sites of side-chain hydroxylation consistent with the generation of more than one active form. The potential involvement of CYP27A and other putative 25-hydroxylases in 1alpha-OH-D activation was also shown, as well as the potential for CYP24 activation and inactivation. In the case of calcipotriol, the respective roles of non-vitamin D-related CYPs and CYP24 in the catabolism of this anti-psoriatic drug were dissected out using cell lines with or without CYP24 expression, allowing us to demonstrate the potential contribution of CYP24 to "vitamin D resistance". The implications of hepatic metabolism in the context of other facets thought to play a role in the mechanism of action of anticancer and antiproliferative vitamin D analogs are discussed.

Prevention and therapy of osteoporosis: the roles of plain vitamin D and alfacalcidol

Severe vitamin D deficiency was identified only in the first decades of the last century as the most common aetiology of rickets in children and osteomalacia in adults. It was later shown that vitamin D is not, as had been supposed, the biologically active principle for healing bone disease but must be hydroxylated in the liver and then finally in the kidney to become 1alpha,25-dihydroxy-cholecalciferol, a biologically highly active renal hormone. This study reviews the various principles, mechanisms, and approaches to the treatment of different forms of osteoporosis using vitamin D, alfacalcidol, and calcitriol therapy regimens.

A pathway for the metabolism of vitamin D3: unique hydroxylated metabolites formed during catalysis with cytochrome P450scc (CYP11A1)

Metabolites of vitamin D3 (D3) (cholecalciferol) are recognized as enzymatically formed chemicals in humans that can influence a wide variety of reactions that regulate a large number of cellular functions. The metabolism of D3 has been extensively studied, and a role for three different mitochondrial cytochrome P450s (CYP24A, CYP27A, and CYP27B1) has been described that catalyze the formation of the 24(OH), 25(OH), and 1(OH) metabolites of D3, respectively. The hormone 1,25-dihydroxyvitamin D3 has been most extensively studied and is widely recognized as a regulator of calcium and phosphorous metabolism. Hydroxylated metabolites of D3 interact with the nuclear receptor and thereby influence growth, cellular differentiation, and proliferation. In this article, we describe in vitro experiments using purified mitochondrial cytochrome P450scc (CYP11A1) reconstituted with the iron-sulfer protein, adrenodoxin, and the flavoprotein, adrenodoxin reductase, and show the NADPH and time-dependent formation of two major metabolites of D3 (i.e., 20-hydroxyvitamin D3 and 20,22-dihydroxyvitamin D3) plus two unknown minor metabolites. In addition, we describe the metabolism of 7-dehydrocholesterol by CYP11A1 to a single product identified as 7-dehydropregnenolone. Although the physiological importance of these hydroxylated metabolites of D3 and their in vivo formation and mode of action remain to be determined, the rate with which they are formed by CYP11A1 in vitro suggests an important role.

Molecular genetics of vitamin D- dependent hereditary rickets

Vitamin D exerts a wide variety of biological actions. The active form of vitamin D, 1alpha,25(OH)(2)D(3), is biosynthesized from cholesterol. The final, critical step in this biosynthesis is conversion from 25-hydroxyvitamin D(3) to 1alpha,25(OH)(2)D(3) by the enzyme 25-hydroxyvitamin D(3) 1alpha-hydroxylase(CYP27B1)[1alpha(OH)ase]. 1alpha,25(OH)(2)D(3) transcriptionally controls the expression of a particular set of target genes mediated through nuclear vitamin D receptor(VDR) acting as a ligand-inducible factor. Two types of vitamin D-dependent hereditary rickets (VDDR) are known to be caused by mutations in the 1alpha(OH)ase and VDR genes. The 1alpha(OH)ase gene is responsible for VDDR type I, and VDR for type II. Both of the diseases display an autosomal-recessive trait, but clinical features and response to administrated 1alpha,25(OH)(2)D(3) are distinct. The phenotypes of the gene KO mice deficient of 1alpha(OH)ase and VDR exhibited the clinical abnormalities observed in the VDDR patients.

Use of vitamin D(4) analogs to investigate differences in hepatic and target cell metabolism of vitamins D(2) and D(3)

In this study, we used molecules with either of the structural differences in the side chains of vitamin D(2) and vitamin D(3) to investigate which feature is responsible for the significant differences in their respective metabolism, pharmacokinetics and toxicity. We used two cell model systems-HepG2 and HPK1A-ras-to study hepatic and target cell metabolism, respectively. Studies with HepG2 revealed that the pattern of 24- and 26-hydroxylation of the side chain reported for 1alpha-hydroxyvitamin D(2) (1alpha-OH-D(2)) but not for 1alpha-OH-D(3) is also observed in both 1alpha-OH-D(4) and Delta(22)-1alpha-OH-D(3) metabolism. This suggests that the structural feature responsible for targeting the enzyme to the C24 or C26 site could be either the C24 methyl group or the 22-23 double bond. In HPK1A-ras cells, the pattern of metabolism observed for the 24-methylated derivative, 1alpha,25-(OH)(2)D(4), was the same pattern of multiple hydroxylations at C24, C26 and C28 seen for vitamin D(2) compounds without evidence of side chain cleavage observed for vitamin D(3) derivatives, suggesting that the C24 methyl group plays a major role in this difference in target cell metabolism of D(2) and D(3) compounds. Novel vitamin D(4) compounds were tested and found to be active in a variety of in vitro biological assays. We conclude that vitamin D(4) analogs and their metabolites offer valuable insights into vitamin D analog design, metabolic enzymes and maybe useful clinically.

Synthesis and biologic activity of a C-ring analog of vitamin D3: biologic and protein binding properties of 11.alpha.-hydroxyvitamin D3

The influence of C-ring substituents on the biologic activity and protein binding properties of vitamin D3 has not been systematically investigated. To this end, we dehydrogenated cholesta-5,7-dien-3 beta-ol (1) to the 5,7,9(11)-triene. After protection of the 5,7-diene with a 4-phenyl-1,2,4- triazoline -3,5-dione Diels -Alder adduct, oxidation of the unprotected 9(11)-olefin gave epoxide 5. Reverse Diels -Alder and reductive ring opening of epoxide 5 gave cholesta-5,7-diene-3 beta, 11 alpha-diol (6). Photolysis of 6 to the previtamin followed by thermal rearrangement resulted in 11 alpha-hydroxyvitamin D3 (8). We found that vitamin 8 increased calcium transport at a dose of 500 pmol/rat but failed to increase bone calcium mobilization at a dose as high as 50 000 pmol/rat. Under the same conditions, corresponding doses of vitamin D3 and 25-hydroxyvitamin D3 increased bone calcium mobilization and intestinal calcium transport. The new vitamin analogue, 8, was slightly less efficient (B-50 = 6.8 X 10(-8) M) than 25-hydroxyvitamin D3, 24(R),25-dihydroxyvitamin D3, and 25-(S), 26-dihydroxyvitamin D3 (7.1 X 10(-9) M, 7.7 X 10(-9) M, and 7.9 X 10(-9) M, respectively) in displacing radiolabeled 25-hydroxyvitamin D3 from rat plasma vitamin D binding protein. On the other hand, vitamin analogue 8 showed significantly greater binding efficiency than 1 alpha-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, and vitamin D3 (B-50 = 2.5 X 10(-6) M, 9.84 X 10(-8) M, and 5.46 X 10(-7) M, respectively), under these same conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Kidney microsomal 25- and 1alpha-hydroxylase in vitamin D metabolism: catalytic properties, molecular cloning, cellular localization and expression during development

Both a 25-hydroxylation and a 1alpha-hydroxylation are necessary for the conversion of vitamin D(3) into the calcium-regulating hormone 1alpha,25-dihydroxyvitamin D(3). According to current knowledge, the hepatic mitochondrial cytochrome P450 (CYP) 27A and microsomal CYP2D25 are able to catalyze the former bioactivation step. Substantial 25-hydroxylase activity has also been demonstrated in kidney. This paper describes the molecular cloning and characterization of a microsomal vitamin D(3) 25- and 1alpha-hydroxylase in kidney. The enzyme purified from pig kidney and the recombinant enzyme expressed in COS cells catalyzed 25-hydroxylation of vitamin D(3) and 1alpha-hydroxyvitamin D(3) and, in addition, 1alpha-hydroxylation of 25-hydroxyvitamin D(3). The cDNA encodes a protein of 500 amino acids. Both the DNA sequence and the deduced peptide sequence of the renal enzyme are homologous with those of the hepatic vitamin D(3) 25-hydroxylase CYP2D25. Genomic Southern blot analysis suggested the presence of a single gene for CYP2D25 in the pig. Immunohistochemistry experiments indicated that CYP2D25 is expressed almost exclusively in the cells of cortical proximal tubules. The expression of CYP2D25 in kidney, but not in liver, was much higher in the adult pig than in the newborn. These findings indicate a tissue-specific developmental regulation of CYP2D25. The results from the current and previous studies on renal vitamin D hydroxylations imply that CYP2D25 has a biological role in kidney.

Transport of vitamin D metabolites

Vitamin D and its metabolites are bound to an alpha globulin (DBP) in human serum. This carrier protein binds 25-OHD and 24,25(OH)2D with higher affinity than vitamin D or 1,25(OH)2D, but the binding is highly specific for the vitamin D structure. The carrier mechanism appears to be unique in that it is a high affinity and high capacity system, capable of binding as much as 120,000 IU of biological activity per liter of plasma. DBP is apparently identical to group-specific component, and a DBP-deficient state has not been identified among approximately 75,000 human sera examined thus far. The liver appears to be the site for synthesis of DBP, and serum DBP levels are increased during pregnancy and during estrogen-progesterone therapy. However, in a variety of disorders of mineral homeostasis, serum DBP levels are normal. Two tissue binding proteins for vitamin D metabolites have been identified. One protein, sedimenting at 5-6S, has been found in all nucleated tissues, and exhibits a ligand preference similar to DBP. This tissue binding protein appears to be a complex of serum DBP with a tissue protein which is heat-labile, and which shows no capacity for binding vitamin D sterols. The physiologic role, if any, for this complex of serum DBP and tissue protein is not presently understood. The other tissue binding component is a 3-4S protein found only in recognized target tissues, and which shows a high binding affinity and specificity for 1,25(OH)2 D. It appears to be the receptor in the receptor-1,25(OH)2D migration to the nucleus, leading to the biosynthesis of mRNA which codes for products which affect calcium and phosphorus transport in target tissues.

Effect of 1alpha-hydroxyvitamin D3 and egg-shell calcium on bone metabolism in ovariectomized osteoporotic model rats

Egg-shell calcium (Ca) is one of the effective Ca sources for bone metabolism. In the present study, we investigated whether egg-shell Ca had similar effects compared with calcium carbonate (CaCO3) when vitamin D3 (1alpha(OH)D3) treatment was given to an osteoporotic rat model. In both 1alpha(OH)D3-supplemented and -unsupplemented rats, the bone mineral density (BMD) of the lumber spine in the vitamin-supplemented group increased significantly compared with the unsupplemented group. In a Ca balance study, there were also significant differences in intestinal Ca absorption, urinary Ca and fecal Ca between the vitamin-supplemented and -unsupplemented groups. These results show that egg-shell Ca could have similar effects to CaCO3 on bone metabolism. In contrast with CaCO3, vitamin D3 supplementation did not significantly increase serum Ca levels in the egg-shell Ca group; however, the mechanism of Ca absorption is still unclear. Our results suggest that egg-shell Ca may be an effective nutrient in Ca metabolism for people treated with vitamin D3.

25-Dehydro-1alpha-hydroxyvitamin D3-26,23S-lactone antagonizes the nuclear vitamin D receptor by mediating a unique noncovalent conformational change

(23S)-25-dehydro-1alpha-Dihydroxyvitamin D3-26,23-lactone (TEI-9647; MK) has been reported to antagonize the 1alpha,25-dihydroxyvitamin D3 nuclear receptor (VDR)- mediated increase in transcriptional activity. Using a transient transfection system incorporating the osteocalcin VDRE (vitamin D response element) in Cos-1 cells, we found that 20 nM MK antagonizes VDR-mediated transcription by 50% when driven by 1 nM 1alpha,25(OH)2D3. Four analogs of 1alpha,25(OH)2D3, also at 1 nM, were antagonized 25 to 39% by 20 nM MK. However, analogs with 16-ene/23-yne or 20-epi modifications, which have a significantly lower agonist ED50 for the VDR than 1alpha,25(OH)2D3, were antagonized by 20 nM MK only at 100 pM or 10 pM, respectively. One possible mechanism for antagonism is that the 25-dehydro alkene of MK might covalently bind the ligand-binding site of the VDR rendering it inactive. Utilization of a ligand exchange assay, however, demonstrated that MK bound to VDR is freely exchanged with 1alpha,25(OH)2D3 in vitro. These data support the apparent correlation between VDR transcriptional activation by agonists and the effective range of MK antagonism by competition. Furthermore, protease sensitivity analysis of MK bound to VDR indicates the presence of a unique conformational change in the VDR ligand-binding domain, showing a novel doublet of VDR fragments centered at 34 kDa, whereas 1alpha,25(OH)2D3 as a ligand produces only a single 34-kDa fragment. In comparison, the natural metabolite 1alpha,25-dihydroxyvitamin D3-26,23-lactone yields only the 30-kDa fragment that is produced by all ligands to varying degrees. Collectively, these results support that MK is a potent partial antagonist of the VDR for 1alpha,25(OH)2D3 and its analogs when in appropriate excess of the agonist.

Induction of differentiation by 1alpha-hydroxyvitamin D(5) in T47D human breast cancer cells and its interaction with vitamin D receptors

The role of the active metabolite of vitamin D, 1,25 dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), in cell differentiation is well established. However, its use as a differentiating agent in a clinical setting is precluded due to its hypercalcaemic activity. Recently, we synthesised a relatively non-calcaemic analogue of vitamin D(5), 1alpha-hydroxyvitamin D(5) (1alpha(OH)D(5)), which inhibited the development of carcinogen-induced mammary lesions in culture and suppressed the incidence of chemically induced mammary carcinogmas in rats. In the present study, we determined the differentiating effects of 1alpha-(OH)D(5) in T47D human breast cancer cells and compared its effects with 1,25(OH)(2)D(3). Cells incubated with either 10 or 100 nM of the analogues inhibited cell proliferation in a dose-dependent manner, as measured by the dimethylthiazolyl-2,5-diphenyltetrazolium bromide (MTT) assay. Similar growth-inhibitory effects were also observed for MCF10(neo) cells. Both vitamin D analogues induced cell differentiation, as determined by induction of casein expression and lipid production. However, MCF10(neo) cells failed to respond to either vitamin D analogue and did not undergo cell differentiation. Since the cell differentiating effect of vitamin D is considered to be mediated via the vitamin D receptor (VDR), we examined the induction of VDR using reverse transcriptase-polymerase chain reaction (RT-PCR) in both cells. The results showed that, in T47D cells, both 1,25(OH)(2)D(3) and 1alpha(OH)D(5) induced VDR in a dose-dependent manner. Moreover, both analogues of vitamin D upregulated the expression of vitamin D response element-chloramphenicol acetyl transferase (VDRE-CAT). These results collectively indicate that 1alpha-(OH)D(5) may mediate its cell-differentiating action via VDR in a manner similar to that of 1,25(OH)(2)D(3).

Human keratinocyte line HaCaT metabolizes 1alpha-hydroxyvitamin D3 and vitamin D3 to 1alpha,25-dihydroxyvitamin D3 (calcitriol)

Cultured human keratinocytes have the property to hydroxylate exogenous 25-hydroxyvitamin D3 (25OHD3) at the C-1alpha position thus producing 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3). In this study we investigated whether keratinocytes can also hydroxylate vitamin D3 and one of its metabolites at the C-25 position. We could demonstrate that HaCaT keratinocytes can metabolize 1alpha-hydroxyvitamin D3 (1alpha-OHD3) and vitamin D3 to 1alpha,25(OH)2D3. Identification of the generated product as 1alpha,25(OH)2D3 was based on its elution pattern in two different high performance liquid chromatography systems, on its specific binding in a calf thymus receptor assay and on its gas chromatography-mass spectrometry characteristics. The hydroxylation of vitamin D3 to 1alpha,25(OH)2D3 was dose- and time-dependent. Bovine serum albumin added up to 1.5% (w/v) to the culture medium greatly increased the hydroxylation rates. These results show that HaCaT cells have the capacity to hydroxylate vitamin D3 at the C-1/25 positions. The generation of endogenous 1alpha,25(OH)2D3 from vitamin D3 within the skin may indicate a novel pathway which is of importance for the regulation of epidermal cell growth and differentiation.

Synthesis, stereochemistry, and biological activity of 1alpha,23,25-trihydroxy-24-oxovitamin D3, a major natural metabolite of 1alpha,25-dihydroxyvitamin D3

The C(23) epimers of 1alpha,23,25(OH)3-24-oxovitamin D3, a major natural metabolite of the secosteroid hormone, 1alpha,25(OH)2D3, were chemically synthesized for the first time. The metabolite was synthesized by palladium coupling of the appropriate CD ring analog with an A ring enyne. Various approaches from quinic acid to the A ring precursors were explored, and a new route to the A ring enyne from quinic acid was developed. The C(23) stereochemistry of the natural 1alpha,23,25(OH)3-24-oxovitamin D3 produced in neonatal human keratinocytes was determined to be S on the basis of the 1H NMR and the HPLC data. The biological activity of 1alpha,23(S), 25(OH)3-24-oxovitamin D3 in primary cultures of bovine parathyroid cells was determined by comparing the potency of this metabolite to that of 1alpha,25(OH)2D3 in suppression of parathyroid hormone (PTH) secretion. The results indicate that 1alpha,23(S), 25(OH)3-24-oxovitamin D3 potently suppressed PTH secretion even at concentrations as low as 10(-)12 M and is equipotent with 1alpha, 25(OH)2D3. The high activity of 1alpha,23(S),25(OH)3-24-oxovitamin D3 cannot be explained on the basis of its affinity for the vitamin D receptor as this metabolite was found to be 10 times less effective than radioinert 1alpha,25(OH)2D3 in blocking the uptake and receptor binding of [3H]-1alpha,25(OH)2D3 in intact parathyroid cells. Further studies are required to explain the molecular basis for the activity of 1alpha,23(S),25(OH)3-24-oxovitamin D3 in its ability to suppress PTH secretion. In summary, our present study indicates that the C(23) stereochemistry of the natural 1alpha,23, 25(OH)3-24-oxovitamin D3 is S and this metabolite is equipotent to 1alpha,25(OH)2D3 in suppressing PTH secretion.

HaCaT cell line as a model system for vitamin D3 metabolism in human skin

Synthesis and catabolism of calcitriol (1,25(OH)2D3) were studied using HaCaT cell line as a cell culture model. Our results indicate that stimulation of HaCaT cells with epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) within 16 h just prior to reaching confluence amplified the production of calcitriol when calcidiol (3H-25OHD3) was used as a substrate. EGF- and TGF-alpha-induced (0.1-10 nM) 1-hydroxylation of 3H-25OHD3 was concentration-dependent but showed different kinetics. Synthesis of calcitriol induced by EGF was inversely related to the degree of cellular confluence. Stimulation by EGF was an actinomycin D- and cycloheximide-sensitive process. Independently of the growth factor used, the production of 3H-24R,25(OH)2D3 and the catabolism of 3H-1,25(OH)2D3 to 3H-1,24,25(OH)3D3 were unexpectedly low (< or = 5% and < or = 2%/), as compared to the amount of calcitriol generated. Exogenous addition of unlabeled 1,25(OH)2D3, 1,24R(OH)2D3, calcipotriol, or 24R,25(OH)2D3 at concentrations as low as 10(-11) M, potently inhibited the 3H-1,25(OH)2D3 production. These results suggest that EGF-treated HaCaT keratinocytes could serve for further studies of the vitamin D3 pathway and its relationship to proliferation and differentiation, but differences in calcitriol synthesis and catabolism from those in cultured primary keratinocytes or other cell lines must be considered.

Secondary hyperparathyroidism following biliopancreatic diversion

OBJECTIVE

To investigate the cause of osteomalacia following biliopancreatic diversion(BPD) surgery for obesity.

DESIGN

A retrospective, case-comparison study.

SETTING

A tertiary care center.

PATIENTS

A case group of 12 subjects (including 9 women; mean age +/- SEM, 48.5 +/- 3.0 years; mean preoperative body mass index +/- SEM, 43.7 +/- 2.3 kg/m2, and mean weight loss +/- SEM, 75 +/- 14 kg) who have undergone BPD (referred to as BPD group hereafter) and a comparison group of 10 subjects (including 9 women; mean age +/- SEM, 49.6 +/- 3.3 years; mean preoperative body mass index +/- SEM, 44.0 +/- 2.5 kg/m2; and mean weight loss +/- SEM, 55 +/- 15 kg) following vertical banded gastroplasty (VBG) (referred to as VBG group hereafter).

MAIN OUTCOME MEASURES

Serum and urine markers for bone metabolism.

RESULTS

Compared with the VBG group, the BPD group had significantly lower concentrations of the following components: serum calcium (2.14 +/- 0.05 mmol/L vs 2.37 +/- 0.05 mmol/L [8.6 +/- 0.2 mg/dL vs 9.5 +/- 0.2 mg/dL]), serum 25-hydroxyvitamin D (24 +/- 6 nmol/L vs 64 +/- 6 nmol/L), urine calcium excretion (1.7 +/- 0.7 mmol/d vs 4.5 +/- 0.7 mmol/d [68 +/- 28 mg/d vs 180 +/- 28 mg/d]), and serum carotene (0.40 +/- 0.15 mmol/L vs 1.29 +/- 0.16 mmol/L). The BPD group had significantly higher concentrations of the following components: serum parathyroid hormone (13.6 +/- 2.1 pmol/L vs 5.2 +/- 2.3 pmol/L), serum alkaline phosphatase (139 +/- 8 U/L vs 86 +/- 9 U/L), and urinary hydroxyproline/creatine (52 +/- 5 mumol/mmol vs 19 +/- 5 mumol/mmol).

CONCLUSION

These data suggest that following BPD, secondary hyperparathyroidism attributed to hypocalcemia results from malabsorption of vitamin D. However, we cannot exclude the possibility of concurrent calcium malabsorption with vitamin D malabsorption.

Intact parathyroid hormone levels are not elevated in glucocorticoid-treated subjects

To assess whether chronic glucocorticoid therapy results in a compensatory increase in parathyroid hormone (PTH), we measured intact PTH levels and other indices of mineral metabolism in 13 postmenopausal glucocorticoid-treated women and 16 normal age-matched controls. The glucocorticoid-treated women received a mean prednisone dose of 15.8 +/- 3.1 mg/day for 12.9 +/- 3.1 years. A linear regression analysis between intact PTH levels and a wide range of prednisone doses in these 13 glucocorticoid-treated women and 26 additional male and female subjects receiving chronic glucocorticoid therapy for a variety of rheumatic and pulmonary disorders (n = 39) was also performed. Intact PTH levels using the sensitive immunoradiometric assay (IRMA, Nichols Institute, San Juan Capistrano, CA) were comparable in the glucocorticoid-treated and normal control women (35.3 +/- 4.4 vs 31.3 +/- 3.2 ng/l, respectively) as wee the total calcium concentrations (9.67 +/- 0.12 vs 9.52 +/- 0.11 mg/dl). In the glucocorticoid-treated women, the 25-hydroxyvitamin D levels, measured by competitive protein assay were similar to those of the control subjects (29.2 +/- 2.8 vs 29.1 +/- 2.3 mg/ml), and no patient was treated with vitamin D in excess of 400 IU daily. In the combined 39 male and female patients, there were also no significant regression relationships between daily prednisone dose and intact PTH levels. Thus, secondary hyperparathyroidism does not accompany chronic oral glucocorticoid therapy in women on low to moderate doses of oral glucocorticoids. The lack of an elevation in intact PTH levels in the presence of chronic glucocorticoid therapy may represent an increased sensitivity of bone to PTH, or an alteration in the relationship between calcium and PTH, or both.

Mouse primary osteoblasts express vitamin D3 25-hydroxylase mRNA and convert 1 alpha-hydroxyvitamin D3 into 1 alpha,25-dihydroxyvitamin D3

We examined whether 1 alpha-hydroxyvitamin D3 (1 alpha(OH)D3) is metabolized into 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) in bone. Northern blot analysis indicated that the expression of vitamin D3 25-hydroxylase mRNA was highest in the liver, followed by the duodenum, calvaria, lung, kidney, skin and long bone, and lowest in the spleen. Of the bone cell fractions isolated from fetal mouse calvaria by a sequential enzymatic digestion, fraction 3, which consisted of mostly osteoblastic cells, showed the highest expression of vitamin D3 25-hydroxylase mRNA. When either cultured bone cells of fraction 3 or mouse calvaria were incubated with [3H]-1 alpha (OH)D3, a radioactive peak which comigrated at the same position as authentic 1 alpha,25(OH)2D3 was found on an HPLC chromatogram. The radioactive fraction obtained from the conditioned media of fetal mouse calvaria was tentatively identified as 1 alpha,25(OH)2D3 by cochromatography with authentic 1 alpha,25(OH)2D3 on three different HPLC systems and a thermal isomerization analysis. These results indicate that 1 alpha(OH)D3 is hydroxylated at the 25-position in bones, resulting in the local synthesis of 1 alpha,25(OH)2D3 from 1 alpha(OH)D3 in the skeletal tissues.

Effect of 1,25,28-trihydroxyvitamin D2 and 1,24,25-trihydroxyvitamin D3 on intestinal calbindin-D9K mRNA and protein: is there a correlation with intestinal calcium transport?

Although analogs and metabolites of vitamin D have been tested for their calciotropic activity, very little information has been available concerning the effects of these compounds on gene expression. In this study one analog of vitamin D, 1,25,28-trihydroxyvitamin D2 [1,25,28-(OH)3D2], and one metabolite, 1,24,25-trihydroxyvitamin D3 [1,24,25-(OH)3D3], were tested for their effect on intestinal calbindin-D9K mRNA and protein as well as for their effect on intestinal calcium absorption and bone calcium mobilization. These compounds were also evaluated for their ability to compete for rat intestinal 1,25-(OH)2D3 receptor sites and to induce differentiation of human leukemia (HL-60) cells as indicated by reduction of nitro blue tetrazolium. In vivo studies involved intrajugular injection of 12.5 ng 1,25-(OH)2D3 or test compound to vitamin D-deficient rats and sacrifice after 18 h. 1,25,28-Trihydroxyvitamin D2 had no effect on intestinal calcium absorption, bone calcium mobilization, or intestinal calbindin-D9K protein and mRNA. Competitive binding to 1,25-(OH)2D3 receptors was 0.8% of that observed using 1,25-(OH)2D3. However, 20- and 40-fold higher doses of 1,25,28-(OH)3D2 (250 and 500 ng) resulted in significant inductions in calbindin-D9K protein and mRNA (3.5 to 7.4-fold), although doses as high as 800 ng were found to have no effect on intestinal calcium absorption or bone calcium mobilization.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin D and prostate cancer: a prediagnostic study with stored sera

This study evaluates the risk of prostate cancer in relation to serum levels of the major vitamin D metabolites, 25-hydroxyvitamin D (25-D3) and 1,25-dihydroxyvitamin D (1,25-D). Between 1964 and 1971, more than 250,000 serum samples were collected from members of the Kaiser Permanente Medical Care Plan in Oakland and San Francisco and stored for future use. Levels of 25-D and 1,25-D were measured in samples from 90 black and 91 white men diagnosed with prostate cancer before December 31, 1987 and controls individually matched on age, race, and day of serum storage. Mean serum 1,25-D was 1.81 pg/ml lower in cases than in matched controls (P = 0.002). Risk of prostate cancer decreased with higher levels of 1,25-D especially in men with low levels of 25-D. However, mean 25-D was not significantly different in cases and controls. The association of lower 1,25-D with prostate cancer was found in men above the median age of 57 years at serum storage but not younger men and was similar in black and white men. In men > or = 57 years of age, 1,25-D was an important predictor of risk for palpable and anaplastic tumors but not for tumors incidentally discovered during surgery to treat the symptoms of benign prostatic hyperplasia or well differentiated tumors.

Selective biological response by target organs (intestine, kidney, and bone) to 1,25-dihydroxyvitamin D3 and two analogues

The hormonally active form of vitamin D, 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3] stimulates biological responses related to calcium homeostasis, cell differentiation, and immunomodulation in many target cells, including leukemic cells. Most of these responses are dependent upon 1 alpha,25(OH)2D3 interaction with a nuclear receptor protein. Structural analogues of 1 alpha,25(OH)2D3 might allow for separation of biological function, avoiding adverse calcemic effects. This report quantitates intestinal calcium absorption, bone calcium resorption, induction of intestinal and renal calcium-binding protein (CaBP), and occupancy of the intestinal and renal nuclear 1 alpha,25(OH)2D3 receptor in vitamin D-deficient chicks after a single dose of 1 alpha,25(OH)2D3, 1 alpha,25-dihydroxyvitamin-16-ene-23-yne-D3 (analogue V), or 22-[m-(dimethylhydroxymethyl)phenyl]-23,24,25,26,27- pentanor-1 alpha-hydroxy-vitamin D3 (analogue EV). The interaction of these compounds with chick intestinal nuclear 1 alpha,25(OH)2D3 receptor and chick plasma vitamin D-binding protein was determined in vitro; analogues V and EV bound 68% and 62% [1 alpha,25(OH)2D3 receptor] and 8% and 13% (vitamin D-binding protein), respectively, as well as 1 alpha,25(OH)2D3 (100%). 1 alpha,25(OH)2D3 doses (0.075-1.2 nmol) generated responses in intestinal calcium absorption, bone calcium resorption, intestinal CaBP, and renal CaBP. When analogue V (1.2-300 nmol) was administered, increases in bone calcium resorption and renal CaBP were noted. However, a significant response in intestinal calcium absorption and intestinal CaBP appeared only after a 300-nmol dose. Unoccupied nuclear 1 alpha,25(OH)2D3 receptor in the intestine and kidney was determined in vivo after doses of 1 alpha,25(OH)2D3, analogue V, or analogue EV. Doses (0.25-6.0 nmol) of 1 alpha,25(OH)2D3 and analogue EV reduced unoccupied receptor to 24% and 59% (intestine) and to 13% and 41% (kidney), respectively. Analogue V (6.0-600 nmol) decreased unoccupied receptor in the kidney. In the intestine analogue V (300-600 nmol) reduced unoccupied receptor only to 75%. These results confirm that some vitamin D analogues can generate selective biological responses and different levels of target organ receptor occupancy.

A preliminary report of vitamin D and calcium metabolism in older African Americans

OBJECTIVE

To determine normal serum bone-related biochemical variables in older African-Americans.

DESIGN

A convenience sample of older African-Americans who had a health screening and blood testing for calciotropic hormones was compared with white Americans who were recruited at the end of the Systolic Hypertension in the Elderly Program (SHEP) study and were not on a thiazide diuretic.

SETTING

Community-dwelling African-Americans who participated in SHEP or who attended one of two mass health screenings.

PARTICIPANTS

Thirty-two African-Americans aged 68-93 years and 43 white Americans aged 70-89 years.

MEASUREMENTS

Twenty-five hydroxyvitamin D (25OHD), parathyroid hormone, osteocalcin, and calcitonin.

RESULTS

Serum 25OHD levels in 38% of the African-American men and 38% of African-American women were less than 8 ng/mL compared with 22% of Caucasian men and 40% of Caucasian women. Serum parathyroid hormone (PTH) was above the normal range in 25% of men and 33% of women of African-American descent and 14% of Caucasian men and 30% of Caucasian women. Serum 25OHD was lower (P < 0.05) in individuals with a previous history of fracture. Serum albumin (P < 0.05), calcitonin (P < 0.05), and osteocalcin (P < 0.05), but not 25OHD, were lower in African-Americans (men and women) when compared with Caucasians (P < 0.05). Serum calcium corrected for albumin was higher in the African-Americans than in the Caucasians (P < 0.05). As previously reported in Caucasians, PTH was inversely related to log 25OHD in African-Americans. Serum osteocalcin was positively correlated to PTH in African-Americans, as previously reported in Caucasians. Log 25OHD correlated inversely with osteocalcin in African-Americans, but this was not seen in Caucasians.

CONCLUSIONS

In this limited sample, hypovitaminosis D (as assessed by 25OHD level) with secondary hyperparathyroidism occurred frequently in elderly African-Americans. Osteocalcin, a measure of osteoblast activity, correlated with 25OHD and parathyroid hormone. Osteocalcin serum levels were lower in African-Americans than Caucasians, but serum calcium corrected for albumin was higher in the former compared to the latter.

Synthesis of active metabolite(s) from 1 alpha-hydroxyvitamin D3 by human monocytic leukemia cells

Synthesis of the biologically active metabolite(s) from 1 alpha-hydroxyvitamin D3 (1 alpha(OH)D3) was examined in various types of human leukemia cell lines. Untreated monocytoid leukemia cells (U937 and HEL/S) metabolized 1 alpha (OH)D3 to the active metabolite(s), possibly 1 alpha, 24- and/or 1 alpha, 25-dihydroxyvitamin D3, and these cells were efficiently induced to differentiate by treatment with 1 alpha (OH)D3. However, the other types of leukemia cells did not efficiently metabolize it and were not induced to differentiate by 1 alpha (OH)D3. The possible therapeutic advantage of 1 alpha (OH)D3 in the treatment of monocytic leukemia is discussed.