title: Rapamycin as an inhibitor of osteogenic differentiation in bone marrow-derived mesenchymal stem cells.
abstract: BACKGROUND
  An autograft of cultured bone marrow-derived mesenchymal stem cells has already been used in clinical practice. In those patients whose bone marrow cannot be used, a cell allograft with the use of immunosuppressant drugs will be an option in the future. However, little is known about the effects of immunosuppressant drugs on mesenchymal stem cells. This study assessed the effects of immunosuppressant drugs on osteogenic differentiation of mesenchymal stem cells and analyzed the manner in which immunosuppressant drugs modulate the osteogenic effect of dexamethasone.
  
  
  METHODS
  Rat bone marrow cells were cultured with or without dexamethasone as an osteogenic supplement. In each experimental group, one of three immunosuppressants (rapamycin, cyclosporine A, or FK506) was added. As a control, cells were cultured without immunosuppressants. Histologically, mineralization was assessed by alizarin red S staining and phase-contrast microscopy. Biochemically, alkaline phosphatase activity, calcium content, and osteocalcin content were assessed.
  
  
  RESULTS
  On histological analysis, no mineralized nodules were seen on alizarin red S staining or phase-contrast microscopy in the groups not treated with dexamethasone, except in the group that was treated with FK506. Mineralized nodules were seen in the groups treated with dexamethasone, except in the group that was treated with rapamycin. On biochemical analysis, it was found that, compared to the control group, rapamycin reduced alkaline phosphatase activity and the calcium content of mesenchymal stem cells; FK506 increased alkaline phosphatase activity, calcium content, and osteocalcin content; and cyclosporine A had negligible effects. Dexamethasone increased alkaline phosphatase activity, calcium content, and osteocalcin content, but these effects were decreased by rapamycin.
  
  
  CONCLUSIONS
  Rapamycin did not have an osteogenic effect on mesenchymal stem cells, but inhibited the effect of osteogenic differentiation induced by dexamethasone. In contrast, FK506 had an osteogenic effect on mesenchymal stem cells. Therefore, FK506 might be more useful than rapamycin in allogeneic transplantation of mesenchymal stem cells.
authors.affiliation: Department of Orthopaedic Surgery, Nara Medical University, 840 Shijyo-cho, Kashihara, Nara, 634-8522, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Isomoto
authors.forename: Koji
authors.initials: K
authors.lastname: Hattori
authors.forename: Hajime
authors.initials: H
authors.lastname: Ohgushi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakajima
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Takakura
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D008297:Male; D045164:Mesenchymal Stem Cell Transplantation; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008858:Microscopy, Phase-Contrast; D015675:Osteocalcin / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects*; D051381:Rats; D011916:Rats, Inbred F344; D020123:Sirolimus / Q000494:pharmacology*; D014182:Transplantation, Autologous
chemical_list: D007166:Immunosuppressive Agents; D015675:Osteocalcin; D000469:Alkaline Phosphatase; D002118:Calcium; D020123:Sirolimus