1α,25(OH)2-3-Epi-Vitamin D3, a Natural Physiological Metabolite of Vitamin D3: Its Synthesis, Biological Activity and Crystal Structure with Its Receptor

Abstract

BackgroundThe 1α,25-dihydroxy-3-epi-vitamin-D3 (1α,25(OH)2-3-epi-D3), a natural metabolite of the seco-steroid vitamin D3, exerts its biological activity through binding to its cognate vitamin D nuclear receptor (VDR), a ligand dependent transcription regulator. In vivo action of 1α,25(OH)2-3-epi-D3 is tissue-specific and exhibits lowest calcemic effect compared to that induced by 1α,25(OH)2D3. To further unveil the structural mechanism and structure-activity relationships of 1α,25(OH)2-3-epi-D3 and its receptor complex, we characterized some of its in vitro biological properties and solved its crystal structure complexed with human VDR ligand-binding domain (LBD).Methodology/Principal FindingsIn the present study, we report the more effective synthesis with fewer steps that provides higher yield of the 3-epimer of the 1α,25(OH)2D3. We solved the crystal structure of its complex with the human VDR-LBD and found that this natural metabolite displays specific adaptation of the ligand-binding pocket, as the 3-epimer maintains the number of hydrogen bonds by an alternative water-mediated interaction to compensate the abolished interaction with Ser278. In addition, the biological activity of the 1α,25(OH)2-3-epi-D3 in primary human keratinocytes and biochemical properties are comparable to 1α,25(OH)2D3.Conclusions/SignificanceThe physiological role of this pathway as the specific biological action of the 3-epimer remains unclear. However, its high metabolic stability together with its significant biologic activity makes this natural metabolite an interesting ligand for clinical applications. Our new findings contribute to a better understanding at molecular level how natural metabolites of 1α,25(OH)2D3 lead to significant activity in biological systems and we conclude that the C3-epimerization pathway produces an active metabolite with similar biochemical and biological properties to those of the 1α,25(OH)2D3.

Serum levels of 3-Epi-25-OH-D3 during Hypervitaminosis D in Clinical Practice

“…diet, supplements, or endogenous metabolism) (10,11), it has been reported that its downstream metabolite, 3-epi-1,25-(OH) 2 D 3 , displays reduced calcemic properties and less potent gene-regulatory effects on some vitamin D receptor-responsive genes involved in bone metabolism (i.e. osteocalcin), whereas suppression of gene transcription of PTH is nearly as potent as 1,25-(OH) 2 D 3 (12). Thus, distinguishing between 25-OH-D 3 and the C-3 epimer is considered of biological relevance (9,13,14).…”

Vitamin D metabolism in the premature newborn: A randomized trial

“…Much of the early work [23e25] on 3-epi-vitamin D metabolites focused on the potential biological activity of chemically synthesized 3-epi-1a,25(OH) 2 D 3 . As the logical active form of 3-epi-25(OH)D 3 , 3-epi-1a,25(OH) 2 D 3 has been shown to bind tightly to the ligand-binding pocket of the vitamin D receptor (VDR) and trigger transactivation in VDRmediated gene expression systems in vitro similar to 1a,25(OH) 2 D 3 [27,28]. However, the biological activity potential of 3-epi-1a,25(OH) 2 D 3 is still yet to be demonstrated in vivo.…”

Cytochrome P450 Vitamin D Hydroxylases in Inflammation and Cancer

“…Both 1,25(OH) 2 D 3 and 25(OH)D 3 are sensitive to 3-epimerization in a tissue-and celldependent manner, leading to biologically active 3-epi metabolites. The enzyme catalyzing the epimerization of the hydroxyl group at the C-3 of the A-ring is still unknown (Kamao et al, 2004;Molnár et al, 2011). Interestingly, the C-3 epimer of 1,25(OH) 2 D 3 has less calcaemic effects (Fleet, Bradley, Reddy, Ray, & Wood, 1996), but its clinical relevance remains to be investigated.…”