23,25-Dihydroxyvitamin D₃ is liberated as a major vitamin D₃ metabolite in human urine after treatment with β-glucuronidase: Quantitative comparison with 24,25-dihydroxyvitamin D₃ by LC/MS/MS.

The complete understanding of the excretion of surplus 25-hydroxyvitamin D₃ [25(OH)D₃] in humans remains to be accomplished. In our previous study, 24,25-dihydroxyvitamin D₃ [24,25(OH)₂D₃] 24-glucuronide was identified as a major urinary vitamin D₃ metabolite, while the glucuronide of 23,25-dihydroxyvitamin D₃ [23,25(OH)₂D₃] is another metabolite of interest but has not been sufficiently evaluated. Although the quantitative analysis of 24,25(OH)₂D₃ liberated in urine by the treatment with β-glucuronidase (GUS) has been conducted, no information was provided about the amount of the glucuronidated 23,25(OH)₂D₃ in the urine.

Controlled lipid β-oxidation and carnitine biosynthesis by a vitamin D metabolite.

Lactone-vitamin D3 is a major metabolite of vitamin D3, a lipophilic vitamin biosynthesized in numerous life forms by sunlight exposure. Although lactone-vitamin D3 was discovered 40 years ago, its biological role remains largely unknown. Chemical biological analysis of its photoaffinity probe identified the hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex subunit alpha (HADHA), a mitochondrial enzyme that catalyzes β-oxidation of long-chain fatty acids, as its selective binding protein.

3-Epi-25-hydroxyvitamin D is a poor substrate for SULT2A1: Analysis of its 3-sulfate in cord plasma and recombinant human SULT2A1 incubate.

A variety of metabolites derived from 25-hydroxyvitamin D [25(OH)D], including its 3-epimer [Epi-25(OH)D] and 3-O-sulfate [25(OH)D-3S], is found in human plasma/serum. We hypothesized that the 3-O-sulfate of Epi-25(OH)D [Epi-25(OH)D-3S] might be present in plasma/serum. Clarifying this point could improve our understanding of the metabolism of vitamin D.

Identification of conjugation positions of urinary glucuronidated vitamin D metabolites by LC/ESI-MS/MS after conversion to MS/MS-fragmentable derivatives.

A liquid chromatography/electrospray ionization-tandem mass spectrometry-based method was developed for the identification of the conjugation positions of the monoglucuronides of 25-hydroxyvitamin D [25(OH)D ] and 24,25-dihydroxyvitamin D [24,25(OH) D ] in human urine. The method employed derivatization with 4-(4-dimethylaminophenyl)-1,2,4-triazoline-3,5-dione to convert the glucuronides into fragmentable derivatives, which provided useful product ions for identifying the conjugation positions during the MS/MS. The derivatization also enhanced the assay sensitivity and specificity for urine sample analysis.