The origin of pain in osteoarthritis is poorly understood, but it is generally thought to arise from inflammation within the innervated structures of the joint, such as the synovium, capsule and bone. We investigated the role of nerve growth factor (NGF) in pain development in murine OA, and the analgesic efficacy of the soluble NGF receptor, TrkAD5. OA was induced in mice by destabilisation of the medial meniscus and pain was assessed by measuring hind-limb weight distribution. RNA was extracted from joints, and NGF and TNF expressions were quantified. The effect of tumour necrosis factor (TNF) and neutrophil blockade on NGF expression and pain were also assessed. NGF was induced in the joints during both post-operative (day 3) and OA (16 weeks) pain, but not in the non-painful stage of disease (8 weeks post-surgery). TrkAd5 was highly effective at suppressing pain in both phases. Induction of NGF in the post-operative phase of pain was TNF-dependent as anti-TNF reduced NGF expression in the joint and abrogated pain. However, TNF was not regulated in the late OA joints, and pain was not affected by anti-TNF therapy. Fucoidan, by suppressing cellular infiltration into the joint, was able to suppress post-operative, but not late OA pain. These results indicate that NGF is an important mediator of OA pain and that TrkAd5 represents a potent novel analgesic in this condition. They also suggest that, unlike post-operative pain, induction of pain in OA may not necessarily be driven by classical inflammatory processes.
aKennedy Institute of Rheumatology, Imperial College London, London W6 8LH, UK
bHenry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, Dorothy Hodgkin Building, Whitson St, University of Bristol, Bristol BS1 3NY, UK
cSchool of Veterinary and Biomedical Sciences, Murdoch University, Perth, Western Australia 6015, Australia
*Corresponding author. Address: School of Veterinary and Biomedical Sciences, Murdoch University, 90 South Street, Perth, Western Australia 6015, Australia. Tel.: +61 8 9360 2257; fax: +61 8 9310 4144.
Submitted October 21, 2009; revised February 23, 2010; accepted March 2, 2010.