3-Epi-25-hydroxyvitamin D₃ 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 D₃ [25(OH)D₃], including its 3-epimer [Epi-25(OH)D₃] and 3-O-sulfate [25(OH)D₃-3S], is found in human plasma/serum. We hypothesized that the 3-O-sulfate of Epi-25(OH)D₃ [Epi-25(OH)D₃-3S] might be present in plasma/serum. Clarifying this point could improve our understanding of the metabolism of vitamin D₃. In this study, we first carefully analyzed the cord plasma samples by derivatization-assisted liquid chromatography/electrospray ionization-tandem mass spectrometry and demonstrated the occurrence of Epi-25(OH)D₃-3S in the plasma. However, the concentration ratio of Epi-25(OH)D₃-3S to 25(OH)D₃-3S (sulfated form) was infinitely lower than the ratio of Epi-25(OH)D₃ to 25(OH)D₃ (unconjugated form). To determine what caused this result, we next performed an in vitro experiment of the 3-O-sulfation for 25(OH)D₃ and Epi-25(OH)D₃ using the recombinant human sulfotransferase (SULT) 2A1. This in vitro experiment revealed that Epi-25(OH)D₃ is a poor substrate for the 3-O-sulfation catalyzed by SULT2A1 as compared to 25(OH)D₃. This substrate specificity of SULT2A1 would be the main cause for the result obtained from the analysis of the cord plasma samples.