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We have developed an in vitro system to easily examine the affinity for vitamin D receptor (VDR) and CYP24A1-mediated metabolism as two methods of assessing vitamin D derivatives. Vitamin D derivatives with high VDR affinity and resistance to CYP24A1-mediated metabolism could be good therapeutic agents. This system can effectively select vitamin D derivatives with these useful properties. We have also developed an in vivo system including a <i>Cyp27b1-</i>gene-deficient rat (a type I rickets model), a <i>Vdr</i>-gene-deficient rat (a type II rickets model), and a rat with a mutant <i>Vdr</i> (R270L) (another type II rickets model) using a genome editing method. For <i>Cyp27b1</i>-gene-deficient and <i>Vdr</i> mutant (R270L) rats, amelioration of rickets symptoms can be used as an index of the efficacy of vitamin D derivatives. <i>Vdr-</i>gene-deficient rats can be used to assess the activities of vitamin D derivatives specialized for actions not mediated by VDR. One of our original vitamin D derivatives, which displays high affinity VDR binding and resistance to CYP24A1-dependent metabolism, has shown good therapeutic effects in <i>Vdr</i> (R270L) rats, although further analysis is needed.