Isolation and identification of 1 alpha-hydroxy-24-oxovitamin D-3 and 1 alpha,23-dihydroxy-24-oxovitamin D-3 - Metabolites of 1 alpha,24 (R)-dihydroxyvitamin D-3 produced in rat kidney

1 alpha,24(R)-Dihydroxyvitamin D-3 [1 alpha,24(R)(OH)(2)D-3], a synthetic v itamin D-3 analog, has been developed as a drug for topical use in the trea tment of psoriasis. At present, the target tissue metabolism of 1 alpha,24( R)(OH)(2)D-3 is not understood completely. In our present study, we investi gated the metabolism of 1 alpha,24(R)(OH)(2)D-3 in the isolated perfused ra t kidney. The results indicated that 1 alpha,24(R)(OH)(2)D-3 is metabolized in rat kidney into several metabolites, of which 1 alpha,24(R),25-trihydro xyvitamin D-3, 1 alpha,25-dihydroxy-24-oxovitamin D-3, 1 alpha,23(S),25-tri hydroxy-24-oxovitamin D-3, and 1 alpha,23-dihydroxy-24,25,26,27-tetranorvit amin D-3 are similar to the previously known metabolites of 1 alpha,25-dihy droxyvitamin D-3 [1 alpha,25(OH)(2)D-3]. In addition to these aforementione d metabolites, we also identified two new metabolites, namely 1 alpha-hydro xy-24-oxovitamin D-3 and 1 alpha,23-dihydroxy-24-oxovitamin D-3. The two ne w metabolites do not possess the C-25 hydroxyl group. Thus, the metabolism of 1 alpha,24(R)(OH)(2)D-3 into both 25-hydroxylated and non-25-hydroxylate d metabolites suggests that 1 alpha,24(R)(OH)(2)D-3 is metabolized in the r at kidney through two pathways. The first pathway is initiated by C-25 hydr oxylation and proceeds further via the C-24 oxidation pathway. The second p athway directly proceeds via the C-24 oxidation pathway without prior hydro xylation at the C-25 position. Furthermore, we demonstrated that rat kidney did not convert 1 alpha-hydroxyvitamin D-3 [1 alpha(OH)D-3] into 1 alpha,2 5(OH)(2)D-3. This finding indicates that the rat: kidney does not possess t he classical vitamin D-3-25-hydroxylase (CYP27) activity. However, from our present study it is apparent that prior hydroxylation of 1 alpha(OH)D-3 at the C-24 position in the 'R' orientation allows 25-hydroxylation to occur. At present, the enzyme responsible for the C-25 hydroxylation of 1 alpha,2 4(R)(OH)(2)D-3 is unknown. Our observation that the side chain of 1 alpha,2 4(R)(OH)(2)D-3 underwent 24-ketonization and 23-hydroxylation even in the a bsence of the C-25 hydroxyl group suggests that 1 alpha,25(OH)(2)D-3-24-hyd roxylase (CYP24) can perform some steps of the C-24 oxidation pathway witho ut prior C-25 hydroxylation. Thus, we speculate that CYP24 may be playing a dual role in the metabolism of 1 alpha,24(R)(OH)(2)D-3. (C) 1999 Elsevier Science Inc.