Novel metabolism of 1 alpha,25-dihydroxyvitamin D3 with C24-C25 bond cleavage catalyzed by human CYP24A1.
Our previous study revealed that human CYP24A1 catalyzes a remarkable metabolism consisting of both C-23 and C-24 hydroxylation pathways that used both 25(OH)D(3) and 1alpha,25(OH)(2)D(3) as substrates, while rat CYP24A1 showed extreme predominance of the C-24 over C-23 hydroxylation pathway [Sakaki, T., Sawada, N., Komai, K., Shiozawa, S., Yamada, S., Yamamoto, K., Ohyama, Y. and Inouye, K. (2000) Eur. J. Biochem. 267, 6158-6165]. In this study, by using the Escherichia coli expression system for human CYP24A1, we identified 25,26,27-trinor-23-ene-D(3) and 25,26,27-trinor-23-ene-1alpha(OH)D(3) as novel metabolites of 25(OH)D(3) and 1alpha,25(OH)(2)D(3), respectively. These metabolites appear to be closely related to the C-23 hydroxylation pathway, because human CYP24A1 produces much more of these metabolites than does rat CYP24A1. We propose that the C(24)-C(25) bond cleavage occurs by a unique reaction mechanism including radical rearrangement. Namely, after hydrogen abstraction of the C-23 position of 1alpha,25(OH)(2)D(3), part of the substrate-radical intermediate is converted into 25,26,27-trinor-23-ene-1alpha(OH)D(3), while a major part of them is converted into 1alpha,23,25(OH)(3)D(3). Because the C(24)-C(25) bond cleavage abolishes the binding affinity of 1alpha,25(OH)D(3) for the vitamin D receptor, this reaction is quite effective for inactivation of 1alpha,25(OH)D(3).
Sawada
Natsumi
N
Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan.
Kusudo
Tatsuya
T
Sakaki
Toshiyuki
T
Hatakeyama
Susumi
S
Hanada
Makoto
M
Abe
Daisuke
D
Kamao
Maya
M
Okano
Toshio
T
Ohta
Miho
M
Inouye
Kuniyo
K
D015650:24,25-Dihydroxyvitamin D 3 / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002117:Calcitriol / Q000737:chemistry / Q000378:metabolism*; D002244:Carbon / Q000737:chemistry*; D002384:Catalysis; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D002853:Chromatography, Liquid; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D006801:Humans; D006900:Hydroxylation; D013058:Mass Spectrometry; D011485:Protein Binding; D051381:Rats; D018167:Receptors, Calcitriol / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity; D065668:Vitamin D3 24-Hydroxylase
D018167:Receptors, Calcitriol; D011994:Recombinant Proteins; D015650:24,25-Dihydroxyvitamin D 3; D002244:Carbon; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C585549:CYP24A1 protein, human; C585551:Cyp24a1 protein, rat; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol