In vitro glucuronidation of 25-hydroxyvitamin D3 and its pro-form

In vitro glucuronidation of 25-hydroxyvitamin D3 and its pro-form has been investigated by means of HPLC with UV detection. Although both substrates gave 3- and 25-glucuronides in the presence of the rat liver microsomal fraction and uridine-5'-diphosphoglucuronic acid, 25-hydroxyvitamin D3 and its pro-form yielded 3- and 25-glucuronide as the main product, respectively. The latter glucuronide is the one in which the tert-hydroxy group is conjugated. Each glucuromide was identified by its chromatographic behavior in comparison with an authentic sample and data obtained from liquid chromatography/mass spectrometry (LC/MS) using atmospheric pressure chemical ionization.