Evaluate the potential role of p38 inhibitors for the treatment of
osteoarthritis using an animal model of joint degeneration (iodoacetate-induced
arthritis) and a
pain model (Hargraeves assay).
METHODS: P38
kinase activity was evaluated in a
kinase assay by measuring the amount of phosphorylated substrate ATF2 using a phosphoATF2 (Thr71) specific primary antibody and an alkaline
phosphate coupled secondary antibody and measuring the OD at 405 nm.
TNFalpha and IL-1beta secretion from LPS stimulated THP-1 monocytic cells and human peripheral blood mononuclear cells were measured by ELISA. Rats treated with vehicle or p38 inhibitor were injected intra-articularly in one knee with iodoacetate and damage to the tibial plateau was assessed from digitized images captured using an image analyzer. The effect of p38 inhibitors on
hyperalgesia was evaluated in rats given an intraplantar injection of
carrageenan and 4 h later the paw withdrawal time to a radiant heat source was measured.
RESULTS:
SB-203580 and
VX-745 are both potent inhibitors of p38 with IC50s of 136 +/- 64 nM and 35 +/- 14 nM (mean +/- S.D.), respectively. Similarly,
SB-203580 and
VX-745 potently inhibited TNF release from LPS stimulated human THP-1 cells with IC50s of 72 +/- 15 nM; and 29 +/- 14 nM (mean +/- S.D.) respectively. TNF release from LPS stimulated human peripheral blood mononuclear cells was inhibited with IC50s 16 +/- 6 nM and 14 +/- 8 nM, (mean +/- S.D.) for
SB-203580 and
VX-745 and
IL-1 was inhibited with IC50s of 20 +/- 8 nM and 15 +/- 4 nM (mean +/- S.D.), respectively.
SB-203580 and
VX-745 administered orally at a dose of 50 mg/kg resulted in the significant (p < 0.05) inhibition of joint degeneration in the rat iodoacetate model of 45% and 31%, respectively.
SB-203580 demonstrated a dose related inhibition of joint degeneration of 30, 25, 12 and 8% at 50, 25, 10 and 5 mg/kg p.o. b.i.d. in the rat iodoacetate model. Similarly, both p38 inhibitors significantly (p < 0.05) attenuated the
pain response (paw withdrawal time) in the Hargraeves
hyperalgesia assay when administered orally at 30, 10 and 3 mg/kg.
CONCLUSION: