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Metabolic stability of 3‐Epi‐1α,25‐dihydroxyvitamin D 3 over 1α, 25‐dihydroxyvitamin D 3 : Metabolism and molecular docking studies using rat CYP24A1
Author(s) -
Rhieu Steve Y.,
Annalora Andrew J.,
Wang Guochun,
Flarakos Caroline C.,
Gathungu Rose M.,
Vouros Paul,
Sigüeiro Rita,
Mouriño Antonio,
Schuster Inge,
Palmore G. Tayhas R.,
Reddy G. Satyanarayana
Publication year - 2013
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.24576
Subject(s) - metabolite , calcitriol receptor , cyp24a1 , metabolism , vitamin d and neurology , calcitriol , chemistry , stereochemistry , docking (animal) , biochemistry , receptor , biology , endocrinology , medicine , nursing
3‐epi‐1α,25‐dihydroxyvitamin D 3 (3‐epi‐1α,25(OH) 2 D 3 ), a natural metabolite of 1α,25‐dihydroxyvitamin D 3 (1α,25(OH) 2 D 3 ), exhibits potent vitamin D receptor (VDR)‐mediated actions such as inhibition of keratinocyte growth or suppression of parathyroid hormone secretion. These VDR‐mediated actions of 3‐epi‐1α,25(OH) 2 D 3 needed an explanation as 3‐epi‐1α,25(OH) 2 D 3 , unlike 1α,25(OH) 2 D 3 , exhibits low affinity towards VDR. Metabolic stability of 3‐epi‐1α,25(OH) 2 D 3 over 1α,25(OH) 2 D 3 has been hypothesized as a possible explanation. To provide further support for this hypothesis, we now performed comparative metabolism studies between 3‐epi‐1α,25(OH) 2 D 3 and 1α,25(OH) 2 D 3 using both the technique of isolated rat kidney perfusion and purified rat CYP24A1 in a cell‐free reconstituted system. For the first time, these studies resulted in the isolation and identification of 3‐epi‐calcitroic acid as the final inactive metabolite of 3‐epi‐1α,25(OH) 2 D 3 produced by rat CYP24A1. Furthermore, under identical experimental conditions, it was noted that the amount of 3‐epi‐calcitroic acid produced from 3‐epi‐1α,25(OH) 2 D 3 is threefold less than that of calcitroic acid, the analogous final inactive metabolite produced from 1α,25(OH) 2 D 3 . This key observation finally led us to conclude that the rate of overall side‐chain oxidation of 3‐epi‐1α,25(OH) 2 D 3 by rat CYP24A1 leading to its final inactivation is slower than that of 1α,25(OH) 2 D 3 . To elucidate the mechanism responsible for this important finding, we performed a molecular docking analysis using the crystal structure of rat CYP24A1. Docking results suggest that 3‐epi‐1α,25(OH) 2 D 3 , unlike 1α,25(OH) 2 D 3 , binds to CYP24A1 in an alternate configuration that destabilizes the formation of the enzyme‐substrate complex sufficiently to slow the rate at which 3‐epi‐1α,25(OH) 2 D 3 is inactivated by CYP24A1 through its metabolism into 3‐epi‐calcitroic acid. J. Cell. Biochem. 114: 2293–2305, 2013. © 2013 Wiley Periodicals, Inc.