Stable isotope-labeled vitamin D, metabolites and chemical analogs: synthesis and use in mass spectrometric studies

Cytotoxic steroids from the Vietnamese gorgonian Verrucella corona

Using various chromatographic separations, seventeen steroids including seven new compounds, verrucorosteroids A-F (1-6) and verrucorosterone (7), were isolated from the Vietnamese gorgonian Verrucella corona. Their structures were elucidated by spectroscopic analysis, including HR QTOF MS, 1D and 2D NMR. Among isolates, verrucorosterone (7), 5,6α-epoxy-3β-hydroxy-(22E)-ergosta-8,22-dien-7-one (14), and 5,6α-epoxy-3β-hydroxy-(22E)-ergosta-8(14),22-dien-7-one (15) showed significant cytotoxicity (IC₅₀ values ranging from 12.32 ± 1.47 to 33.77 ± 1.28 μM) against eight human cancer cell lines as LNCaP (prostate cancer), HepG2 (hepatoma cancer), KB (epidermoid carcinoma), MCF-7 (breast cancer), SK-Mel2 (melanoma), HL-60 (acute leukemia), LU-1 (lung cancer), and SW480 (colon adenocarcinoma).

Potential intake of vitamins "A" and "D" through branded intravenous lipid emulsions: Liquid Chromatography-Tandem Mass Spectrometry Analysis

No data exist for vitamin A group and vitamin D2/D3 content in branded intravenous lipid emulsions (ILEs). Our goal is to evaluate and quantify their concentrations in different ILEs to assess whether they are clinically relevant. Analyses were carried out in triplicates on six ILEs: 1) 30% soybean oil-based, 2) 20% olive-soybean oil based, 3) 10 + 10% soybean - MCT coconut oil based, 4) 20% soybean-olive-MCT-fish oil based, 5) 20% soybean-MCT-fish oil based and 6) 10% pure fish oil based, respectively. Retinol group (vitamin A) and ergo-chole-calciferol (vitamin D2/D3) were analyzed and quantified by a quali-quantitative Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) method after potassium hydroxide alkaline hydrolysis, hexane extraction, reverse phase-liquid chromatography and specific multiple-reaction-monitoring (MRM) detection. On average, measured retinol content was in the range of 200-1000 μg/L in ILEs (1,2, and 3), whereas it was higher (1000-2000 μg/L) in the ILEs containing fish-oil. Vitamin D content was in the range of 1-10 μg/L in the fish-oil based ILEs, but undetectable in those ILEs containing purely vegetable oils. This study shows that vitamin A and D contents are variably present in ILEs based on their different lipid sources. Both contents should be explicitly mentioned in the products.

Improved and efficient synthesis of 1alpha-hydroxy-[6-(2)H] and 1alpha-hydroxy-[6,19,19-(2)H]vitamin D3 derivatives

Improved and efficient procedures for deuterium-labeling at the 6,19,19 positions of 1alpha-hydroxyvitamin D3 derivatives via its sulfur dioxide-adduct by using a base-catalyzed H-D exchange reaction are described. Application of the known procedure using tBuOK/DMF-D2O, which is effective for labeling vitamin D3 derivatives, to 1alpha-hydroxy compounds gave only poor results because of isomerization and decomposition. We found that this procedure is improved by the use of iPrONa/iPrOD. During this study, we also found that the 6-monodeuterated product was selectively obtained when MeONa/CD3OD was employed instead of iPrONa/iPrOD. On the other hand, simple addition of 1,3-dimethyl-2-imidazolidinone as a co-solvent to the above conditions was effective for 1alpha,25-dihydroxy compounds. These improved procedures were successfully applied to the synthesis of 1alpha-hydroxy-[6,19,19-(2)H]vitamin D3 derivatives 4 and 1alpha-hydroxy-[6-(2)H]vitamin D3 derivatives 6 from the corresponding 1alpha-hydroxyvitamin D3 derivatives 1 via its sulfur dioxide-adducts 2, 3 and 5 in good over-all yield with high deuterium incorporation.

Characteristics of mass spectrometric analyses coupled to gas chromatography and liquid chromatography for 22-oxacalcitriol, a vitamin D3 analog, and related compounds

The characteristics of the mass spectra of vitamin D3 related compounds were investigated by GC-MS and LC-MS using 22-oxacalcitriol (OCT), an analog of 1,25-dihydroxyvitamin D3, and related compounds. Fragmentation during GC-MS (electron impact ionization) of TMS-derivatives of OCT and the postulated metabolites gave useful structural information concerning the vitamin D3-skeleton and its side-chain, especially with respect to the oxidation positions of metabolites. In contrast, few fragment ions were observed in LC-MS (atmospheric pressure chemical ionization), showing that LC-MS gave poor structural information, except for molecular mass. However, when comparing the signal-to-noise ratio (S/N) observed during GC-MS and LC-MS analysis for OCT in plasma extracts, the S/N in LC-MS was over ten-times greater than in GC-MS, possibly due to the low recovery on derivatization and thermal-isomerization in GC-MS. Furthermore, both the GC-MS and the LC-MS allowed the analysis of many postulated metabolites in a single injection without any prior isolation of target metabolites from biological fluids by LC. These results suggest that GC-MS and LC-MS analysis for vitamin D3 related compounds such as OCT each have unique and distinct advantages. Therefore, the complementary use of both techniques enables the rapid and detailed characterization of vitamin D3 related compounds.

Fluorimetric assay of 1 alpha,25-dihydroxyvitamin D3 in human plasma

The first fluorimetric method for assaying plasma 1 alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] is described. Lipid extracts from human plasma were successively purified by a Bond Elut NH2 column and a normal-phase HPLC column, and the 1,25-(OH)2D3 fractions obtained were fluorescence-labelled with 4-[2-(6,7-dimethoxy-4-methtyl-3-oxo-3,4-dihydroquinoxalyl)et hyl]-1, 2,4-triazoline-3,5-dione (DMEQ-TAD). The fluorescent adducts of 1,25-(OH)2D3 were analyzed by HPLC on a reversed-phase column, after extensive elimination of the degradation products of excess reagents, by a Bond Elut PSA column followed by a normal-phase HPLC column. The intra- and inter-assay coefficients of variation were within 10% in both assays. The analytical recoveries of standard 1,25-(OH)2D3 added to plasma were quantitative. The present fluorimetric assay was compared with the established radioreceptor assay (RRA) used in measuring plasma 1,25-(OH)2D3 concentration. The regression analysis of the data afforded a relationship y = 1.049x - 2.657 and a correlation coefficient (r) of 0.900.

Determination of 25-hydroxyvitamin D3 in human plasma using a non-radioactive tetranorvitamin D analogue as an internal standard

A convenient non-radioactive method for assaying plasma 25-hydroxyvitamin D3 is described. The method uses 22-hydroxytetranorvitamin D3 as an internal standard and includes two-step liquid- and solid-phase extractions and quantification by normal-phase HPLC. The intra- and inter-assay coefficients of variation were 2.2% and 2.4%, respectively, and the analytical recovery of 25-hydroxyvitamin D3 added to plasma was quantitative. Assay linearity was obtained in the range 0.5-4.0 ml of plasma. When compared with the method employing a radioactive 25-hydroxyvitamin D3 tracer, the correlation coefficient was 0.990 (slope 0.999 and intercept 1.19 ng/ml).

On-line post-column Diels-Alder derivatization for the determination of vitamin D3 and its metabolites by liquid chromatography/thermospray mass spectrometry

Liquid chromatography/thermospray mass spectrometry (LC/TSP MS) has been used for the determination of vitamin D3 and some of its metabolites, i.e. 1 alpha(OH) vitamin D3, 25(OH) vitamin D3, 1 alpha,25(OH)2 vitamin D3 and 24,25(OH)2 vitamin D3, using positive and negative ion detection. Using these two modes positional isomers can be identified. Detection in the negative ion mode was preferred because of the slightly higher sensitivity. The limits of detection, using multiple ion detection, are 50-100 nM (6-12 pmol injected). On-line post-column derivatization based on [4 + 2] cyclo-addition (Diels-Alder reaction) proceeds within 1 min at room temperature. If this step is included in LC/TSP MS, the detection limits of the analytes can be improved 7-70-fold depending on the analyte tested. The best results (detection limits down to 1 nM, i.e. 0.12 pmol injected) are obtained with discharge ionization in the negative ion mode.

Characterization of vitamin D3 metabolites using continuous-flow fast atom bombardment tandem mass spectrometry and high-performance liquid chromatography

A mass spectrometric method for the detection of vitamin D3 metabolites is described. This method involves the derivatization of the metabolites by cycloaddition with 4-phenyl-1,2,4-triazoline-3,5-dione, followed by their characterization by continuous-flow fast atom bombardment (CF-FAB) tandem mass spectrometry (MS-MS) and high-performance liquid chromatography (HPLC). Using HPLC, this derivatization has been shown to increase the UV detectability of 25-hydroxyvitamin D3 by about 5-fold. The FAB spectra of the adducts are dominated by peaks corresponding to a protonated molecule and a fragment ion derived in part from the loss of the side chain. Multiple reaction monitoring (MRM) of this transition by MS-MS may be utilized for trace level analysis of vitamin D metabolites. Sample introduction by flow injection yields detection limits in the low nanogram to high picogram range, whereas the use of on-line capillary LC has been found to decrease the detection limits to the low picogram level.

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.