Page 311 - Vitamin D and Cancer

298 M. Fakih et al.

VITAMIN D 3 OXIDATIVE METABOLISM PATHWAYS

H H
HO
OH
7-dehydrocholesterol O
OH OH
OH
H H

H HO HO Cholecalcioic acid
H 24,25-D 3
OH OH
HO
O O
HO
HO
Vitamin D 3
H
H
25-D 3
HO
HO 25-D 3 -26,23-lactone
23,25-D 3
OH O
OH
OH
OH
H
H
H OH
HO OH HO
calcitroic acid
1,24,25-D 3
OH
HO
HO OH OH
O O
1,25-D 3
H H
HO OH HO OH
1-25-D 3 -26,23-lactone
1,23,25-D 3
UV-light(sun light)catalyzed reaction,opens up ofthe B-ring
Hydroxylation of side cahin C-25 catalyzed by CYP27A1,2J3,2R1 &3A4
Hydroxylation of C-1 in the ring Acatalyzed by CYP27B1 (1α-hydroxlase)
Sequential hydroxylation and cleavage of side chain catalyzed by CYP24A1(24-hydroxylase).
Fig. 13.1 Simplified vitamin D activation and inactivation oxidative metabolism pathways
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chemoluminescence ADVANTAGE 25(OH)-D assay system, the DiaSorin
LIAISON 25(OH)-D radio immuno assay (RIA) and the immunodiagnostic sys-
tems (IDS). The specificity, precision, limitations as well as accuracy of these
assays have been extensively documented [28–31]. These assays tend to overesti-
mate the basal levels and greatly underestimate the exogenously added 25- D
3
levels [32]. Serum 25-D measurements are more reliable when performed in
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