title: Interleukin-6 regulates anti-arthritic effect of methotrexate via reduction of SLC19A1 expression in a mouse arthritis model.
abstract: BACKGROUND
  Methotrexate (MTX) enters cells via the reduced folate carrier SLC19A1, suggesting that SLC19A1 is associated with the efficacy of MTX. We here examined the relationship between the efficacy of MTX and the expression of SLC19A1 in glucose 6-phosphate isomerase (GPI)-induced arthritis. We found that interleukin-6 (IL-6) regulated the expression of SLC19A1, so we studied the effect of a combination of MTX and anti-mouse IL-6 receptor antibody (MR16-1).
  
  
  METHODS
  GPI-induced arthritis was induced by intradermal immunization with recombinant GPI. MTX was given from the first day of immunization. Mice were injected once with MR16-1 10 days after immunization. The levels of SLC19A1 mRNA in whole hind limbs and immune cells were measured. Synovial cells from arthritic mice were cultured with cytokines, and cell proliferation and gene expressions were measured.
  
  
  RESULTS
  MTX inhibited the development of GPI-induced arthritis; however, the efficacy of MTX gradually diminished. SLC19A1 expression in immunized mice with arthritis was lower than in intact mice; moreover, SLC19A1 expression in arthritic mice was further decreased when they were treated with MTX. IL-6 was highly expressed in whole hind limbs of arthritic mice. In an in vitro study using synovial cells from arthritic mice, IL-6 + soluble IL-6 receptor (sIL-6R) weakened the anti-proliferative effect of MTX and reduced SLC19A1 expression. Finally, although MR16-1 did not improve arthritis at all when administered on day 10, MTX in combination with MR16-1 more potently reduced the development of arthritis than did MTX alone. When used in combination with MTX, MR16-1 apparently reversed the decrease in SLC19A1 induced by MTX alone.
  
  
  CONCLUSIONS
  In the present study, we demonstrated for the first time that IL-6 reduced the efficacy of MTX by decreasing the expression of SLC19A1, which is important for MTX uptake into cells.
authors.affiliation: Product Research Department, Fuji-Gotemba Research Laboratories, Chugai Pharmaceutical Co,, Ltd,, 1-135 Komakado, Gotemba, Shizuoka, 412-8513, Japan. hashizumemst@chugai-pharm.co.jp
authors.forename: Misato
authors.initials: M
authors.lastname: Hashizume
authors.forename: Hiroto
authors.initials: H
authors.lastname: Yoshida
authors.forename: Keisuke
authors.initials: K
authors.lastname: Tanaka
authors.forename: Miho
authors.initials: M
authors.lastname: Suzuki
authors.forename: Isao
authors.initials: I
authors.lastname: Matsumoto
authors.forename: Takayuki
authors.initials: T
authors.lastname: Sumida
authors.forename: Masahiko
authors.initials: M
authors.lastname: Mihara
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000188:drug therapy* / Q000378:metabolism; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D015850:Interleukin-6 / Q000502:physiology*; D008297:Male; D008727:Methotrexate / Q000627:therapeutic use*; D051379:Mice; D008811:Mice, Inbred DBA; D058978:Reduced Folate Carrier Protein / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016896:Treatment Outcome
chemical_list: D015850:Interleukin-6; D058978:Reduced Folate Carrier Protein; C548700:Slc19a1 protein, mouse; D008727:Methotrexate