title: The antirheumatic drug leflunomide inhibits osteoclastogenesis by interfering with receptor activator of NF-kappa B ligand-stimulated induction of nuclear factor of activated T cells c1.
abstract: OBJECTIVE
  Suppression of bone destruction is required as part of an effective therapeutic strategy for autoimmune arthritis. Although numerous antirheumatic drugs are in clinical use, little is known about whether they inhibit bone destruction by acting on activated T cells or other cell types, such as bone-resorbing osteoclasts. This study was undertaken to determine whether leflunomide has a direct action on the osteoclast lineage and to gain insights into the molecular basis for the bone-protective effect of leflunomide.
  
  
  METHODS
  The direct effect of leflunomide on osteoclast differentiation was investigated using an in vitro culture system of bone marrow monocyte/macrophages stimulated with receptor activator of NF-kappa B ligand (RANKL) and macrophage colony-stimulating factor. The molecular mechanism of the inhibition was analyzed by genome-wide screening. The T cell-independent effect of leflunomide was examined in rag-2(-/-) mice.
  
  
  RESULTS
  Leflunomide blocked de novo pyrimidine synthesis and RANKL-induced calcium signaling in osteoclast precursor cells in vitro; hence, the induction of nuclear factor of activated T cells c1 (NF-ATc1) was strongly inhibited. The inhibition of this pathway is central to the action of leflunomide, since the inhibition was overcome by ectopic expression of NF-ATc1 in the precursor cells. Leflunomide suppressed endotoxin-induced inflammatory bone destruction even in rag-2(-/-) mice.
  
  
  CONCLUSIONS
  Leflunomide has a direct inhibitory effect on RANKL-mediated osteoclast differentiation by inhibiting the induction of NF-ATc1, the master switch regulator for osteoclast differentiation. Our study suggests that the direct inhibitory action of leflunomide on osteoclast differentiation constitutes an important aspect in the amelioration of bone destruction, and that the RANKL-dependent NF-ATc1 induction pathway is a promising target for pharmacologic intervention in arthritic bone destruction.
authors.affiliation: Graduate School of Medicine, University of Tokyo, Tokyo, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Urushibara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takayanagi
authors.forename: Takako
authors.initials: T
authors.lastname: Koga
authors.forename: Sunhwa
authors.initials: S
authors.lastname: Kim
authors.forename: Miho
authors.initials: M
authors.lastname: Isobe
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Morishita
authors.forename: Takumi
authors.initials: T
authors.lastname: Nakagawa
authors.forename: Monika
authors.initials: M
authors.lastname: Löeffler
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Kodama
authors.forename: Hisashi
authors.initials: H
authors.lastname: Kurosawa
authors.forename: Tadatsugu
authors.initials: T
authors.lastname: Taniguchi
mesh_terms: D000818:Animals; D018501:Antirheumatic Agents / Q000494:pharmacology*; D001172:Arthritis, Rheumatoid / Q000473:pathology; D001842:Bone and Bones / Q000187:drug effects / Q000473:pathology; D002352:Carrier Proteins / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007555:Isoxazoles / Q000494:pharmacology*; D000077339:Leflunomide; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D010010:Osteoclasts / Q000166:cytology*; D011743:Pyrimidines / Q000096:biosynthesis; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D018501:Antirheumatic Agents; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D007555:Isoxazoles; D008562:Membrane Glycoproteins; D050778:NFATC Transcription Factors; C494003:NFATC1 protein, human; D009687:Nuclear Proteins; D011743:Pyrimidines; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; C505686:TNFRSF11A protein, human; C505688:TNFSF11 protein, human; C505687:Tnfrsf11a protein, mouse; C505689:Tnfsf11 protein, mouse; D014157:Transcription Factors; D000077339:Leflunomide