title: Inhibitors of p38 suppress cytokine production in rheumatoid arthritis synovial membranes: does variable inhibition of interleukin-6 production limit effectiveness in vivo?
abstract: OBJECTIVE
  The activity of p38 MAPK regulates lipopolysaccharide (LPS)-stimulated production of key proinflammatory cytokines such as tumor necrosis factor α (TNFα). Consequently, p38 MAPK inhibitors have attracted considerable interest as potential treatments of rheumatoid arthritis (RA), and studies in murine models of arthritis have yielded promising results. However, the performance of several compounds in human clinical trials has been disappointing. At present, the reason for this poor performance is unclear. The aim of this study was to examine the effects of p38 inhibitors on both diseased and normal human tissue and cells, in order to test whether this kinase still plays a critical role in cytokine production under conditions of chronic inflammation.
  
  
  METHODS
  Proinflammatory and antiinflammatory cytokine production was monitored after treatment of primary human monocytes, macrophages, and RA synovial membrane cultures with p38 MAPK inhibitor compounds. The following 3 inhibitors were used in these studies: SB-203580 (inhibits the α and β isoforms), BIRB-796 (inhibits the α, β, γ, and δ isoforms), and a novel, structurally distinct p38 MAPK inhibitor, SB-731445 (inhibits the α and β isoforms).
  
  
  RESULTS
  SB-731445 and SB-203580 produced profound inhibition of spontaneous production of proinflammatory cytokines (TNFα and interleukin-1 [IL-1]) in both RA membrane cultures and LPS-stimulated primary human monocytes. However, this and other p38 MAPK inhibitors produced a significant increase in IL-6 production by LPS-stimulated primary human macrophages and a decrease in IL-10 production by all cell types examined.
  
  
  CONCLUSIONS
  The potentially proinflammatory consequences of these activities (decreased IL-10 production and increased IL-6 production) may offer some explanation for the inability of p38 MAPK inhibitors to provide the therapeutic benefit that had been hoped for in RA.
authors.affiliation: Faculty of Medicine, Imperial College of Science, Technology and Medicine, London, UK. t.page@imperial.ac.uk
authors.forename: Theresa H
authors.initials: TH
authors.lastname: Page
authors.forename: Anthony
authors.initials: A
authors.lastname: Brown
authors.forename: Emma M
authors.initials: EM
authors.lastname: Timms
authors.forename: Brian M J
authors.initials: BM
authors.lastname: Foxwell
authors.forename: Keith P
authors.initials: KP
authors.lastname: Ray
mesh_terms: D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D015153:Blotting, Western; D002478:Cells, Cultured; D016207:Cytokines / Q000096:biosynthesis*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D015850:Interleukin-6 / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D009281:Naphthalenes / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000093242:Interleukin-6 Inhibitors; D010671:Phenylurea Compounds
chemical_list: D016207:Cytokines; D004791:Enzyme Inhibitors; D007093:Imidazoles; D015850:Interleukin-6; D009281:Naphthalenes; D011720:Pyrazoles; D011725:Pyridines; D048051:p38 Mitogen-Activated Protein Kinases; D000093242:Interleukin-6 Inhibitors; C452139:doramapimod; D010671:Phenylurea Compounds; C093642:SB 203580