Metabolism of 25‐hydroxycholecalciferol in human promyelocytic leukemia cells (HL‐60): Isolation and identification of (5Z)‐ and (5E)‐19‐nor‐10‐oxo‐25‐hydroxycholecalciferol

Human promyelocytic leukemia cells incubated with 25‐hydroxy[26,27‐methyl‐³H] cholecalciferol (1 μCi) or non‐radioactive 25‐hydroxycholecalciferol (550 μg) produced significant quantities of two vitamin D₃ metabolites. The two metabolites were isolated and purified by methanol chloroform extraction and a series of chromatographic procedures. The metabolite purification and elution positions on these columns were followed by radioactivity and their ultraviolet absorption at 310 nm. The two metabolites have been unequivocally identified as (5Z)‐ and (5E)‐19‐nor‐10‐oxo‐25‐hydroxycholecalciferol by ultraviolet absorption spectrophotometry, mass spectrometry, Fourier‐transform infrared spectrophotometry and co‐chromatography with synthetic compounds on a high‐performance liquid chromatograph. (5E)‐ but not (5Z)‐19‐nor‐10‐oxo‐25‐hydroxycholecalciferol was able to induce HL‐60 cell phenotypic and functional differentiation. However, these two metabolites of 25‐hydroxycholecalciferol did not bind specifically to the chick intestinal 3.7 S. receptor protein for 1α,25‐dihydroxycholecalciferol, The precise biological role of these metabolites is as yet unclear.