IN-VITRO METABOLISM OF THE VITAMIN-D ANALOG, 22-OXACALCITRIOL, USING CULTURED OSTEOSARCOMA, HEPATOMA, AND KERATINOCYTE CELL-LINES

Using four cultured cell models representing liver, keratinocyte, and osteoblast, we have demonstrated that the vitamin D analog, 22-oxacalc itriol is degraded into a variety of hydroxylated and side chain trunc ated metabolites, Four of these metabolic products have been rigorousl y identified by high pressure liquid chromatography, diode array spect rophotometry, and gas chromatography-mass spectrometry analysis as 24- hydroxylated and 26-hydroxylated derivatives as well as the cleaved mo lecules, hexanor-1 alpha,20-dihydroxyvitamin D-3 and hexanor-20-oxo-1 alpha-hydroxyvitamin D-3. Comparison with chemically synthesized stand ards has revealed the stereochemistry of the biological products, Alth ough differences exist in the amounts of products formed with the diff erent cell types, it is apparent that 22-oxacalcitriol is subject to m etabolism by both vitamin D-inducible and noninducible enzymes, Time c ourse studies suggest that the truncated 20-alcohol is derived from a side chain hydroxylated molecule via a hemiacetal intermediate and the 20-oxo derivative is likely formed from the 20-alcohol, Biological ac tivity measurements of the metabolites identified in our studies are c onsistent with the view that these are catabolites and that the biolog ical activity of 22-oxacalcitriol is due to the parent compound. These results are also consistent with recent findings of others that the b iliary excretory form of 22-oxacalcitriol is a glucuronide ester of th e truncated 20-alcohol.