TNFalpha plays a pivotal role in
rheumatoid arthritis (RA) but little is known of the mechanisms that link the inflammatory and nociceptive effects of
TNFalpha. We have established a murine model of
TNFalpha-induced TRPV1-dependent bilateral
thermal hyperalgesia that then allowed us to identify distinct peripheral mechanisms involved in mediating
TNFalpha-induced ipsilateral and contralateral
hyperalgesia.
Thermal hyperalgesia and
inflammation were assessed in both hindpaws following unilateral intraplantar (i.pl.)
TNFalpha. The hyperalgesic mechanisms were analysed through pharmacogenetic approaches involving TRPV1(-/-) mice and TRPV1 antagonists. To study the mediators downstream of
TNFalpha,
cyclooxygenase (COX) and PKC inhibitors were utilised and
cytokine and
prostaglandin levels assessed. The role of neutrophils was determined through use of the
selectin inhibitor,
fucoidan. We show that
TNFalpha (10pmol) causes
thermal hyperalgesia (1-4h) in the ipsilateral inflamed and contralateral uninjured hindpaws, which is TRPV1-dependent.
GF109203X, a PKC inhibitor, suppressed the
hyperalgesia indicating that PKC is involved in TRPV1 sensitisation. Ipsilateral COX-2-derived
prostaglandins were also crucial to the development of the bilateral
hyperalgesia. The prevention of neutrophil accumulation with
fucoidan attenuated
hyperalgesia at 4 but not at 1h, indicating a role in the maintenance but not in the induction of bilateral
hyperalgesia. However,
TNFalpha-induced IL-1beta generation in both paws and the presence of local IL-1beta in the contralateral paw were essential for the development of bilateral
hyperalgesia. These results identify a series of peripheral events through which
TNFalpha triggers and maintains bilateral inflammatory
pain. This potentially allows a better understanding of mechanisms involved in
TNFalpha-dependent
pain pathways in symmetrical diseases such as
arthritis.