Phagocytic cells synthesize 19-nor-10-keto-25-hydroxyvitamin D3, a metabolite that may induce differentiation of the human monoblastic cell line U937.

Phagocytic cells, including normal human blood neutrophils and monocytes, metabolize 25-hydroxyvitamin D3 in vitro to more polar metabolites. Cells of the human monoblastic cell line U937 produced three metabolites when incubated with 25-hydroxyvitamin D3. One of these metabolites, previously designated peak III, has its maximal absorbance at 310 nm. Mass spectral analysis of the trimethylsilylated derivatives of peak III revealed a spectral pattern very similar to that published for the trimethylsilylated derivatives of 19-nor-10-keto-25-hydroxyvitamin D3. The biosynthetic 19-nor-10-keto-25-hydroxyvitamin D3 was active in the induction of differentiation of U937 cells.