title: Plasma and synovial fluid concentration of doxycycline following low-dose, low-frequency administration, and resultant inhibition of matrix metalloproteinase-13 from interleukin-stimulated equine synoviocytes.
abstract: To determine whether low-dose, low-frequency doxycycline administration is capable of achieving chondroprotective concentrations within synovial fluid (SF) while remaining below minimum inhibitory concentration 90 (MIC90 ) of most equine pathogens and would be an option in the management of osteoarthritis.
  
  
  OBJECTIVE
  To determine whether low-dose, low-frequency oral administration of doxycycline can attain in vivo SF concentrations capable of chondroprotective effects through reduction of matrix metalloproteinase (MMP)-13 activity, while remaining below MIC90 of most equine pathogens.
  
  
  METHODS
  Descriptive pharmacokinetic study with crossover design.
  
  
  METHODS
  Two groups of 6 horses received oral doxycycline. Plasma and SF doxycycline concentrations were measured using high performance liquid chromatography. Group 1 received 5 mg/kg bwt q. 24 h with 21 blood and 8 SF samples collected over 120 h; Group 2 received 5 mg/kg bwt q. 48 h with 27 blood and 11 SF samples collected over 192 h. Cultured synoviocytes were treated with interleukin-1α (1 ng/ml) for 24 h to stimulate MMP synthesis, and then SF was added to the culture medium for 96 h. MMP-13 protein and mRNA were measured in synoviocyte culture medium and synoviocytes, respectively.
  
  
  RESULTS
  Mean doxycycline concentration ≥0.043 μg/ml (previously demonstrated to inhibit MMP-13) was achieved in plasma by t = 0.25 h and SF by t = 48 h in Group 1, and in plasma by t = 0.17 h and SF by t = 1 h in Group 2. Synoviocyte culture medium containing doxycycline from Groups 1 and 2 had significantly decreased active MMP-13 protein concentration, and synoviocytes cultured in this medium had significantly decreased MMP-13 gene expression compared to controls. Plasma doxycycline concentration in both groups and SF doxycycline concentration in Group 2 demonstrated a cumulative effect.
  
  
  CONCLUSIONS
  Low-dose orally administered doxycycline achieves SF concentrations in vivo capable of diminishing MMP-13 expression. This study supports the use of doxycycline as a disease modifying osteoarthritic drug.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, New York, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Maher
authors.forename: L V
authors.initials: LV
authors.lastname: Schnabel
authors.forename: J A
authors.initials: JA
authors.lastname: Cross
authors.forename: M G
authors.initials: MG
authors.lastname: Papich
authors.forename: T J
authors.initials: TJ
authors.lastname: Divers
authors.forename: L A
authors.initials: LA
authors.lastname: Fortier
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D002478:Cells, Cultured; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004318:Doxycycline / Q000008:administration & dosage / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics*; D004334:Drug Administration Schedule; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006736:Horses; D053509:Matrix Metalloproteinase 13 / Q000235:genetics / Q000378:metabolism*; D061965:Matrix Metalloproteinase Inhibitors / Q000008:administration & dosage / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013582:Synovial Fluid / Q000737:chemistry*; D013583:Synovial Membrane / Q000166:cytology*
chemical_list: D000900:Anti-Bacterial Agents; D061965:Matrix Metalloproteinase Inhibitors; D012333:RNA, Messenger; D053509:Matrix Metalloproteinase 13; D004318:Doxycycline
keywords: MMP; doxycycline; horse; osteoarthritis; synovial fluid