Prediagnostic serum levels of 1,25-dihydroxyvitamin D and malignant melanoma

A prospective nested case-control study of the relationship between prediagnostic serum levels of 1,25-dihydroxyvitamin D and subsequent development of malignant melanoma was done to test the hypothesis that increased levels are protective. Serum from 23 cases of malignant melanoma that developed between 1975 and 1987 in donors to the Washington County, Maryland serum bank was assayed along with that from 46 matched controls. There were no demonstrable differences among controls by sex, age, smoking or use of multivitamin supplements. The mean serum levels of 1,25-dihydroxyvitamin D were only 5% lower among cases than controls, a difference that could easily have occurred by chance.

Hypervitaminosis D associated with drinking milk

BACKGROUND

Vitamin D has been added to milk in the United States since the 1930s to prevent rickets. We report the unusual occurrence of eight cases of vitamin D intoxication that appear to have been caused by excessive vitamin D fortification of dairy milk.

METHODS

Medical records were reviewed and a dietary questionnaire was sent to eight patients who had unexplained hypervitaminosis D. Vitamin D analyses with high-performance liquid chromatography were performed on samples of the patients' serum, the dairy milk they drank, and the vitamin D concentrate added to the milk.

RESULTS

All eight patients drank milk produced by a local dairy in amounts ranging from 1/2 to 3 cups (118 to 710 ml) daily. All had elevated serum 25-hydroxyvitamin D concentrations (mean [+/- SD], 731 +/- 434 nmol per liter [293 +/- 174 ng per milliliter]). Six of the eight patients had elevated serum vitamin D3 concentrations. Of the eight patients, seven had hypercalcemia and one had hypercalciuria but normocalcemia (mean serum calcium, 3.14 +/- 0.51 mmol per liter [12.6 +/- 2.1 mg per deciliter]). Analysis of the dairy's vitamin D-fortified milk revealed concentrations of vitamin D3 (cholecalciferol) that ranged from undetectable to as high as 232,565 IU per quart (245,840 IU per liter). An analysis of the concentrate that was used to fortify the milk, labeled as containing vitamin D2 (ergocalciferol), revealed that it contained vitamin D3.

CONCLUSIONS

Hypervitaminosis D may result from drinking milk that is incorrectly and excessively fortified with vitamin D. Milk that is fortified with vitamin D must be carefully monitored.

The vitamin D content of fortified milk and infant formula

BACKGROUND

The fortification of milk and infant formula with vitamin D has had an important role in eliminating rickets in children and osteomalacia in adults. A recent outbreak of vitamin D intoxication caused by drinking milk fortified with excess vitamin D has led to questions about the level of vitamin D in milk from other producers.

METHODS

We used high-performance liquid chromatography to measure vitamin D in samples of 13 brands of milk with various fat contents and 5 brands of infant formula purchased at random from local supermarkets in five Eastern states.

RESULTS

Only 12 (29 percent) of the 42 samples of the 13 brands of milk and none of the 10 samples of the 5 brands of infant formula contained 80 to 120 percent of the amount of vitamin D stated on the label. Twenty-six of the 42 milk samples (62 percent) contained less than 80 percent of the amount claimed on the label. No vitamin D was detected in 3 of the 14 samples of skim milk tested (lower limit of assay, 4.7 IU per quart [5.0 IU per liter]). One milk sample labeled as containing vitamin D2 (ergocalciferol) contained vitamin D3 (cholecalciferol). Seven of the 10 samples of infant formula contained more than 200 percent of the amount stated on the label; the sample with the highest concentration contained 419 percent of the stated amount. None of the samples of infant formula contained less than the amount stated.

CONCLUSIONS

Milk and infant-formula preparations rarely contain the amount of vitamin D stated on the label and may be either underfortified or overfortified. Since both underfortification and overfortification are hazardous, better monitoring of the fortification process is needed.

Collisionally induced dissociation in the study of A-ring hydroxylated vitamin D type compounds

Collisionally induced dissociation (CID) is often used to determine the structure of ions based on comparison with the CID spectra of known ions. The latter are generated from judiciously selected compounds taking into account basic principles of ion chemistry. We report here on the use of this approach toward determination of the site of A-ring hydroxylation of vitamin D. Although not intrinsically an aromatic compound, vitamin D gives rise in its mass spectrum to an aromatic methylstyryl cation at m/z 118. A-ring hydroxylated metabolites of vitamin D would thus incorporate the extra OH group on the ion at m/z 118, shifting it to m/z 134. The position of substitution of the extra OH group on a metabolite could then be ascertained by comparing the CID spectrum of its m/z 134 fragment to those of the four possible (hydroxymethyl)styryl cations generated from synthesized authentic compounds. Because of their propensity to polymerize, these cations were generated in situ via the McLafferty rearrangement of the corresponding (hydroxyphenyl)ethanols. For optimum differentiation of isomeric ions, preparation of permethylated derivatives of vitamin D was necessary. The validity of the hypothesis was verified using 1,25-dihydroxy-vitamin D3 as a test compound. This method provides a viable approach for the characterization of A-ring hydroxylated metabolites of vitamin D as well as for related aromatic compounds.

Synthesis of 25-hydroxy-[6,19,19'-2H3]vitamin D3 and 1 alpha,25-dihydroxy-[6,19,19'-2H3]vitamin D3

Synthesis of polydeuterated analogs of 25-hydroxyvitamin D3 and 1 alpha,25-dihydroxy vitamin D3 are described. These analogs, containing stable isotope atoms at metabolically stable positions, are potentially useful in studies involving catabolism of hydroxylated metabolites of vitamin D3.

Evolutionary biology and pathology of vitamin D

There is mounting evidence that essentially all fungi, plants and animals living on earth produce provitamin D. It is likely that once exposed to sunlight, these provitamins are converted to previtamin D. It is unclear why fungi, phytoplankton, zooplankton and plants have the capacity to produce such large quantities of provitamin D. It is likely, however, that provitamin D and possibly vitamin D play an important biologic role in these organisms. Buchala and Schmid found, for example, that vitamin D3 promoted adventitious root development. It may be that provitamin D has a more fundamental function in lower life forms. Provitamin D and its photoproducts have UV absorption spectra that overlap with the ultraviolet absorption spectra from ultraviolet radiation-sensitive macromolecules including DNA, RNA and proteins. Thus, provitamin D and photoisomers could serve as a photon sink, and therefore, act as a natural sunscreen to protect lower life forms from the damaging effects of the high energy ultraviolet radiation that they are exposed to. It is more clear, however, that amphibians, reptiles, birds, mammals and humans all require vitamin D and that the vitamin D must be metabolized to 1,25(OH)2D3 before it can carry-out its physiologic functions on calcium and bone metabolism. The intense research activities during the past decade on the antiproliferative and differentiation activities of 1,25(OH)2D3 has opened a new chapter for this vitamin/hormone. 1,25(OH)2D3 and its analogs are being developed for the treatment of psoriasis, breast cancer, and leukemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoaffinity labeling of human serum vitamin D binding protein and chemical cleavages of the labeled protein: identification of an 11.5-kDa peptide containing the putative 25-hydroxyvitamin D3 binding site

In this paper, we describe photoaffinity labeling and related studies of human serum vitamin D binding protein (hDBP) with 25-hydroxyvitamin D3 3 beta-3'-[N-(4-azido-2-nitrophenyl)amino]propyl ether (25-ANE) and its radiolabeled counterpart, i.e., 25-hydroxyvitamin D3 3 beta-3'-[N-(4-azido-2-nitro-[3,5-3H]phenyl)amino]propyl ether (3H-25-ANE) (Ray et al., 1986, 1991). We have carried out studies to demonstrate that (1) 25-ANE competes with 25-OH-D3 for the binding site of the latter in hDBP and (2) 3H-25-ANE is capable of covalently labeling the hDBP molecule when exposed to UV light. Treatment of a sample of purified hDBP, labeled with 3H-25-ANE, with BNPS-skatole produced two Coomassie Blue stained peptide fragments, and the majority of the radioactivity was associated with the smaller of the two peptide fragments (16.5 kDa). On the other hand, cleavage of the labeled protein with cyanogen bromide produced a peptide (11.5 kDa) containing most of the covalently attached radioactivity. Considering the primary amino acid structure of hDBP, this peptide fragment (11.5 kDa) represents the N-terminus through residue 108 of the intact protein. Thus, our results tentatively identify this segment of the protein containing the binding pocket for 25-OH-D3.

Synthesis of 25-hydroxyvitamin D3 3 beta-3'-[N-(4-azido-2-nitrophenyl)amino]propyl ether, a second-generation photoaffinity analogue of 25-hydroxyvitamin D3: photoaffinity labeling of rat serum vitamin D binding protein

Vulnerability of 25-hydroxy-[26,27-3H]vitamin D3 3 beta-N-(4-azido-2-nitrophenyl)glycinate, a photoaffinity analogue of 25-hydroxyvitamin D3 (25-OH-D3) (Ray et al., 1986) toward standard conditions of carboxymethylation promoted us to synthesize 25-hydroxyvitamin D3 3 beta-3'-[N-(4-azido-2-nitrophenyl)amino]propyl ether (25-ANE), a hydrolytically stable photoaffinity analogue of 25-OH-D3, and 25-hydroxyvitamin D3 3 beta-3'-[N-(4-azido-2-nitro-[3,5-3H]phenyl)amino] propyl ether (3H-25-ANE), the radiolabeled counterpart of 25-ANE. Competitive binding assays of 25-OH-D3 and 25-ANE with rat serum demonstrated that 25-ANE competes for the 25-OH-D3 binding site in rat serum vitamin D binding protein (rDBP). On the other hand, UV exposure of a sample of purified rat DBP (rDBP), preincubated in the dark with 3H-25-ANE, covalently labeled the protein. However, very little covalent labeling was observed in the absence of UV light or in the presence of a large excess of 25-OH-D3. These results provide strong evidence for the covalent labeling of the 25-OH-D3 binding site in rDBP by 3H-25-ANE.

Cultured human keratinocytes cannot metabolize vitamin D3 to 25-hydroxyvitamin D3

The metabolism of [3H]vitamin D3 was studied in cultured human keratinocytes (CHK). Intact CHK were incubated for 1, 6, 12, 24 and 48 h with [3H]vitamin D3 and the lipid soluble fractions from the media and cells were extracted by high-performance liquid chromatography (HPLC). Vitamin D3 and its metabolites, 25-OH-D3, 24,25(OH)2D3 and 1,25(OH)2D3 were added to the extracts, as markers, prior to HPLC. HPLC analysis of the lipid extracts did not reveal any monohydroxylated metabolites. CHK incubated for one hour with [3H]25-OH-D3 showed a 10 +/- 4% conversion to [3H]1,25(OH)2D3 whereas no conversion to [3H]1,25(OH)2D3 was observed in control CHKs that were boiled prior to incubation with [3H]25-OH-D3. These findings suggest that cultured neonatal keratinocytes are incapable of metabolizing vitamin D3 to 25-OH-D3.

Gas chromatography-mass spectrometry of conjugated dienes by derivatization with 4-methyl-1,2,4-triazoline-3,5-dione

The dienophile 4-methyl-1,2,4-triazoline-3,5-dione forms stable adducts with conjugated dienes by generating Diels-Alder cycloaddition products. The reaction is rapid, highly selective for conjugated dienes and the derivatives are suitable for analysis by gas chromatography. Their mass spectra are marked by their simplicity and by the presence of abundant fragment ions diagnostic of the diene position in the parent compound.

The use and interpretation of assays for vitamin D and its metabolites

Vitamin D is essential for the maintenance of calcium and bone metabolism in humans. The recommended daily allowance (RDA) for vitamin D in the United States of 200 IU (5.0 micrograms) is reasonable for adults who receive some exposure to sunlight; however, in the absence of any exposure to sunlight, this recommendation may be 2 to 3 times lower than that actually required to satisfy the body's needs. Vitamin D was first measured by bioassays. However, bioassays became obsolete in light of the revelation that vitamin D must be activated first in the liver to 25-hydroxyvitamin D (25-OH-D) and then in the kidney to 1,25-dihydroxyvitamin D [1,25(OH)2D] before becoming biologically functional. Current assays measure circulating concentrations of vitamin D, 25-OH-D or 1,25(OH)2D. The serum vitamin D concentration is of value for determining the role of sunlight in producing vitamin D in skin and as a provocative test to determine the absorption of vitamin D in patients with malabsorption syndromes. The serum concentration of 25-OH-D is most valuable for determining the overall vitamin D status of an individual, since it is an average of dietary and sunlight-induced vitamin D. The measurement of the serum 1,25(OH)2D concentrations has been most useful in evaluating disorders in calcium and bone metabolism related to acquired and inborn errors in the conversion of 25-OH-D to 1,25(OH)2D.

An evaluation of the relative contributions of exposure to sunlight and of diet to the circulating concentrations of 25-hydroxyvitamin D in an elderly nursing home population in Boston

We investigated the vitamin D status of a Caucasian elderly population in a long-term-care facility in Boston. Comparison was made with a group of free-living elderly people. The sunlight exposure of residents was monitored and its effect on the serum concentrations of 25-hydroxyvitamin D [25(OH)D] was compared with contributions from diet and multivitamins. Seasonal changes in serum 25(OH)D concentrations caused by sunlight exposure were greatest in the free-living subjects and declined in magnitude as the mobility of the volunteers decreased. Diet failed to provide an adequate amount of vitamin D for volunteers who had minimal outdoor activity. Use of a multivitamin supplement containing 10 micrograms (400 IU) vitamin D maintained serum 25(OH)D concentrations greater than 37.5 nmol/L.

1 alpha,25-dihydroxyvitamin D3-induced increments in hepatocyte cytosolic calcium and lysophosphatidylinositol: inhibition by pertussis toxin and 1 beta,25-dihydroxyvitamin D3

1 alpha,25-Dihydroxyvitamin D3 rapidly increases cytosolic calcium and alters membrane phospholipid metabolism in hepatocytes. To define the causal relationship between these events, we examined the effects of 1 alpha,25-dihydroxyvitamin D3 on 32P-labeled lysophosphatidylinositol levels and cytosolic calcium as affected by pertussis toxin and 1 beta,25-dihydroxyvitamin D3, the biologically inactive analog. 32P-labeled lysophosphatidylinositol was determined by two-dimensional thin-layer chromatography. Cytosolic calcium was measured in cells loaded with quin-2AM. Within 5 min, 1 alpha,25-dihydroxyvitamin D3 increased hepatocyte cytosolic calcium by 31% (p less than 0.05) and 32P-labeled lysophosphatidylinositol by 38% (p less than 0.05). Pertussis toxin inhibited the hormone-induced rise in cytosolic calcium but not the increase in 32P-labeled lysophosphatidylinositol. Exposure to exogenous lysophosphatidylinositol for 5 min increased cytosolic calcium by 40% (p less than 0.05), an effect that was also inhibited by pertussis toxin. 1 beta,25-Dihydroxyvitamin D3 had no effect on either hepatocyte cytosolic calcium or 32P-labeled lysophosphatidylinositol but prevented the 1 alpha,25-dihydroxyvitamin D3-induced increments. The results suggest that a G protein sensitive to pertussis toxin is required for the transduction of the lysophosphatidylinositol signal but not the generation of the signal. The ability of 1 beta,25-dihydroxyvitamin D3 to inhibit the 1 alpha,25-dihydroxyvitamin D3-induced changes in phospholipids suggests that the epimer may compete with 1 alpha,25-dihydroxyvitamin D3 for an initiating receptor.

1,25(OH)2D3 increases calcium and phosphatidylinositol metabolism in differentiating cultured human keratinocytes

The effect of 1,25(OH)(2)D(3) on the intracellular calcium, (Ca(+2))i, in both cultured human keratinocytes and in cultured human dermal fibroblasts was investigated. When the intracellular calcium (Ca(+2))i in cultured human keratinocytes, grown in a serum-free medium containing 1.8 mM calcium, was measured by the fluorescent calcium-indicator, Furu-2, the (Ca(+2)i increased 154%, 202%, and 409% over the control value after incubation with 1,25(OH)(2)D(3) at 10(-10) m, 10(-8) m, and 10(-6) m, respectively. This response was immediate (15 seconds), specific (no effect with either 25(OH)D(3) at 10(-8) m or vitamin D(3) at 10(-8) m), and occurred with or without EGTA in the medium. In contrast, 1,25(OH)(2)D(3) did not increase the (Ca(2+))i in either cultured human keratinocytes that were grown in low calcium (0.05 mm), serum-free medium or in cultured human dermal fibroblasts that were grown in medium containing 0.05 mm calcium and 1% serum. The effect of 1,25(OH)(2)D(3) on the the turnover of phosphatidylinositol was investigated as a possible cause for the observed increase in (Ca(+2)i. Cultured human keratinocytes that were incubated with (3)H-inositol demonstrated a 50 % +/- 10% increase in the triphosphated, plasma membrane-bound metabolite of phosphatidylinositol, PIP(2), by 15 seconds, followed by a rapid decrease at 30 seconds, then a return toward basal levels by 1 minute. Lysophosphatidylinositol, which results from the sn-2 deacylation of phosphatidylinositol by phospholipase A(2), decreased 20% +/- 8% within 30 seconds, then increased to 200% +/- 10% of the control value by 5 minutes. The accumulation of IP(3) was increased 50% to 100% above the control value within 30 seconds and this increase was substained during the 5-minute incubation period. Stimulation of phosphatidylinositol turnover by 1,25(OH)(2)D(3) was not detected in either cultured human keratinocytes that were grown in serum-free, low calcium medium or in cultured human dermal fibroblasts that were grown in 1% serum.

Rapid actions of 1 alpha,25-dihydroxyvitamin D3 on Ca2+ and phospholipids in isolated rat liver nuclei

The effects of 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25-(OH)2D3) on Ca2+ levels and phospholipid metabolism were studied in isolated nuclei prepared from rat liver. Nuclear Ca2+ concentration was estimated with the fluorescent indicator Fura 2. In agreement with previous reports, ATP (1 mM) produced a rapid increase in nuclear Ca2+ from 188 +/- 25 to 593 +/- 121 nM. Exposure to 1 alpha,25-(OH)2D3 (20 nM) also produced a rapid increase in nuclear Ca2+ to 402 +/- 71 nM. The 1 beta epimer of 1 alpha,25-(OH)2D3 had no effect. Nuclear phosphatidylinositol was labeled by incubation with [gamma-32P]ATP for 3 h. 1 alpha,25-(OH)2D3 produced a two-fold increase in [32P]lysophosphatidylinositol (LPI) within 5 min from 44 +/- 11 to 87 +/- 19 cpm/2.5 x 10(7) nuclei. 1 beta,25-(OH)2D3 had no effect on [32P]LPI production. Exposure of nuclei to exogenous LPI (15 microM) produced an instantaneous increase in nuclear Ca2+ to 372 +/- 81 nM, comparable to ATP and 1 alpha,25-(OH)2D3. The rapid effects of 1 alpha,25-(OH)2D3 on phospholipid metabolism and Ca2+ in isolated nuclei suggest that the steroid may exert effects distinct from the well-characterized receptor-mediated changes in gene expression.

Sunlight regulates the cutaneous production of vitamin D3 by causing its photodegradation

Exposure to sunlight initiates the formation of vitamin D3 in skin as the UV B radiation in the solar spectrum causes the photoconversion of 7-dehydrocholesterol to previtamin D3. A heat-induced isomerization then converts previtamin D3 to vitamin D3 over a period of days. A number of irradiation products of vitamin D3 are known to form upon irradiation with high intensity UV radiation, but the effect of subsequent exposures to sunlight on the vitamin D3 formed in skin is not known. To investigate this phenomenon, human skin containing vitamin D3 was exposed to sunlight in Boston. A model system of [3H]vitamin D3 in methanol was also used to study the effects of sunlight on vitamin D3 throughout the year. Vitamin D3 proved to be exquisitely sensitive to sunlight, and once formed in the skin, exposure to sunlight resulted in its rapid photodegradation to a variety of photoproducts, including 5,6-transvitamin D3, suprasterol I, and suprasterol II.