title: Metabolism of 20-epimer of 1alpha,25-dihydroxyvitamin D3 by CYP24: species-based difference between humans and rats.
abstract: The 20-epi form of 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)-20-epi-D(3)) is expected as drugs for leukemia, other cancers or psoriasis, because it shows several-hundred fold enhanced ability to induce cell differentiation and growth inhibition than 1alpha,25-dihydroxyvitamin D(3) while its calcemic activity is only slightly elevated. In this study, we compared the human and rat CYP24-dependent metabolism of 1alpha,25(OH)(2)-20-epi-D(3) by using the Escherichia coli expression system. The HPLC and LC-MS analyses of the metabolites revealed that rat CYP24 converted 1alpha,25(OH)(2)-20-epi-D(3) to 25,26,27-trinor-1alpha(OH)-24(COOH)-20-epi-D(3) through 1alpha,24,25(OH)(3)-20-epi-D(3) and 1alpha,25(OH)(2)-24-oxo-20-epi-D(3). The binding affinity of trinor-1alpha(OH)-24(COOH)-20-epi-D(3) for vitamin D receptor (VDR) was less than 1/4000 of that of 1alpha,25(OH)(2)-20-epi-D(3). These results suggest that rat CYP24 can almost completely inactivate 1alpha,25(OH)(2)-20-epi-D(3). On the other hand, human CYP24 mainly converted 1alpha,25(OH)(2)-20-epi-D(3) to its putative demethylated compound with a hydroxyl group, via 1alpha,24,25(OH)(3)-20-epi-D(3), 1alpha,25(OH)(2)-24-oxo-20-epi-D(3), and 1alpha,23,25(OH)(3)-24-oxo-20-epi-D(3). All of these metabolites showed considerable affinity for vitamin D receptor. These results clearly demonstrate the species-based difference between human and rat on the CYP24-dependent metabolism of 1alpha,25(OH)(2)-20-epi-D(3).
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D013058:Mass Spectrometry; D051381:Rats; D018167:Receptors, Calcitriol / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013045:Species Specificity; D013250:Steroid Hydroxylases / Q000378:metabolism*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000378:metabolism*; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D018167:Receptors, Calcitriol; D011994:Recombinant Proteins; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase