Metabolism of 25-hydroxyvitamin D3 by rat kidney cells in culture: isolation and identification of cis- and trans-19-nor-10-oxo-25-hydroxyvitamin D3

A primary confluent culture of epithelial cells from rat kidney has been developed. These cells possess a 3.2-3.4 S high-affinity, low-capacity binding protein for 1,25-dihydroxyvitamin D3. They metabolize 25-hydroxyvitamin D3 to at least five metabolites. Two have been identified as 1,25-dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3. Two others have been identified by means of physical data and cochromatography as trans 19-nor-10-oxo-25-hydroxyvitamin D3 and the other as its cis isomer. These two "metabolites" have not been observed in vivo, but one of them (cis) comigrates with 1,25-dihydroxyvitamin D3 on straight-phase high-performance liquid chromatography. Thus, mere cochromatography on high-performance liquid chromatography is not sufficient to identify critical vitamin D metabolites.