Valproic acid augments vitamin D receptor-mediated induction of CYP24 by vitamin D3: a possible cause of valproic acid-induced osteomalacia?

Toxicol Lett. 2011 Feb 5;200(3):146-53. doi: 10.1016/j.toxlet.2010.11.008. Epub 2010 Nov 27.


Valproic acid (VPA) is a wide spread anticonvulsant and mood-stabilizing agent, the use of which is associated with hepatotoxicity, bone marrow suppression and osteomalacia. In the current paper we propose a possible mechanism of VPA-induced osteomalacia involving accelerated catabolism of 1α,25(OH)(2)-vitamin D3 (VD3) due to increased expression of CYP24. We demonstrate that VPA strongly potentiates CYP24 mRNA expression by VD3 in human hepatocytes (HH) and in human embryonic kidney cells (HEK293). By the method of gene reporter assay we found that VPA increases basal and VD3-inducible activity of CYP24 promoter (pCYP24-luc) in human liver adenocarcinoma (HepG2) and in HEK293 cells in dose-dependent manner. In order to delineate the role of inhibitory effects of VPA on histone deacetylase 1 (HDAC1), we compared the effects of VPA with trichostatin A (TSA) on basal and inducible levels of CYP24 mRNA and pCYP24-luc transactivation. Transactivation of CYP24 promoter by VD3 was enhanced in the presence of both TSA and VPA. In contrast, VD3-inducible expression of CYP24 mRNA was enhanced by VPA but not by TSA, implying that HDAC1 inhibition is not the major reason for VPA effects on CYP24. We examined the effects of VPA on mitogen-activated protein kinases as the important transcriptional regulators of VDR. VPA activated extracellular signal-regulated kinase (ERK) but not c-Jun-N-terminal kinase (JNK) and p38 MAPKs. In conclusion, VPA enhances transcriptional activity of VDR and increases expression of CYP24 mRNA in the presence of VD3 in physiological concentrations. The mechanism involves activation of ERK and partly the inhibition of HDAC1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anticonvulsants / toxicity*
  • Blotting, Western
  • Cholecalciferol / pharmacology*
  • Dose-Response Relationship, Drug
  • Extracellular Signal-Regulated MAP Kinases / genetics
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • HEK293 Cells
  • Hepatocytes / drug effects
  • Histone Deacetylase 1 / biosynthesis
  • Histone Deacetylase 1 / genetics
  • Humans
  • Luciferases / genetics
  • Osteomalacia / chemically induced*
  • Osteomalacia / pathology
  • Plasmids / genetics
  • Pregnane X Receptor
  • RNA, Messenger / biosynthesis
  • RNA, Messenger / genetics
  • Receptors, Calcitriol / drug effects*
  • Receptors, Steroid / drug effects
  • Reverse Transcriptase Polymerase Chain Reaction
  • Steroid Hydroxylases / biosynthesis*
  • Steroid Hydroxylases / genetics
  • Transfection
  • Valproic Acid / toxicity*
  • Vitamin D3 24-Hydroxylase


  • Anticonvulsants
  • Pregnane X Receptor
  • RNA, Messenger
  • Receptors, Calcitriol
  • Receptors, Steroid
  • Cholecalciferol
  • Valproic Acid
  • Luciferases
  • Steroid Hydroxylases
  • Vitamin D3 24-Hydroxylase
  • Extracellular Signal-Regulated MAP Kinases
  • HDAC1 protein, human
  • Histone Deacetylase 1