Abstract
Metabolism of 25-hydroxyvitamin D3 (25OHD3) plays a central role in regulating the biologic effects of vitamin D in the body. Although cytochrome P450–dependent hydroxylation of 25OHD3 has been extensively investigated, limited information is available on the conjugation of 25OHD3. In this study, we report that 25OHD3 is selectively conjugated to 25OHD3-3-O-sulfate by human sulfotransferase 2A1 (SULT2A1) and that the liver is a primary site of metabolite formation. At a low (50 nM) concentration of 25OHD3, 25OHD3-3-O-sulfate was the most abundant metabolite, with an intrinsic clearance approximately 8-fold higher than the next most efficient metabolic route. In addition, 25OHD3 sulfonation was not inducible by the potent human pregnane X receptor agonist, rifampicin. The 25OHD3 sulfonation rates in a bank of 258 different human liver cytosols were highly variable but correlated with the rates of dehydroepiandrosterone sulfonation. Further analysis revealed a significant association between a common single nucleotide variant within intron 1 of SULT2A1 (rs296361; minor allele frequency = 15% in whites) and liver cytosolic SULT2A1 content as well as 25OHD3-3-O-sulfate formation rate, suggesting that variation in the SULT2A1 gene contributes importantly to interindividual differences in vitamin D homeostasis. Finally, 25OHD3-3-O-sulfate exhibited high affinity for the vitamin D binding protein and was detectable in human plasma and bile but not in urine samples. Thus, circulating concentrations of 25OHD3-3-O-sulfate appear to be protected from rapid renal elimination, raising the possibility that the sulfate metabolite may serve as a reservoir of 25OHD3 in vivo, and contribute indirectly to the biologic effects of vitamin D.
Footnotes
- Received September 1, 2017.
- Accepted January 10, 2018.
This work was supported in part by the National Institutes of Health (NIH) National Institute of General Medical Sciences [Grants R01-GM63666, U01-GM092676, and T32-GM007750], the NIH National Institute of Environmental Health Sciences [Grant P30-ES007033], the NIH National Center for Advancing Translational Sciences [Grant TL1-TR000422], the NIH National Cancer Institute [Grant P30-CA21765], and the American Lebanese Syrian Associated Charities. Human livers used in this study were from the University of Washington School of Pharmacy Human Tissue Bank, established by the NIH National Institute of General Medical Sciences [Program Project Grant on Drug Interactions P01-GM32165], and the St. Jude Liver Resource, funded by the Department of Health and Human Services [Contract HHSN276201200017C].
↵This article has supplemental material available at dmd.aspetjournals.org.
- Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics
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