Osteoarthritic knees are more sensitive to the painful actions of nerve growth factor
Ashraf S, Mapp PI, Burston J, Bennett AJ, Chapman V, Walsh DA. Augmented pain behaviour responses to intra-articular injection of nerve growth factor in two animal models of osteoarthritis. Ann Rheum Dis. 2013 Jul 13 (Epub ahead of print)
Key findings and importance of study
Most people with osteoarthritis (OA) experience debilitating pain despite using painkillers and whilst we do not fully understand why osteoarthritic joints are more sensitive to pain, we do know that joint inflammation is a key contributor. Drugs used to control inflammation do not, however, provide sustained pain relief and so there is an urgent need to develop effective pain-relief therapies for people with OA.
Nerve growth factor (NGF), a naturally occurring molecule in our body is essential for the maintenanceand development of nerves. The levels of NGF incresae in many painful conditions, especially those associated with inflammation. In this study we have shown that osteoarthritic pain joints are more sensitive to the actions of NGF and treatments that reduce this sensitivity have the potential to improve osteoarthritic pain. These findings are important in improving our understanding of why OA is painful and to help us identify new drug targets that can effectively control this pain.
Osteoarthritic pain results from a combination of abnormal changes within the joint and how this feeling is processed. People with OA experience increased sensitivity to both painful and non-painful stimuli and pain is further increased by joint inflammation.
NGF is unregulated in human and animal osteoarthritic joints that are inflamed and can contribute to osteoarthritic pain. Drugs that inhibit NGF have shown promising results in controlling osteoarthritic pain.
Aim of the study
To know why osteoarthritic knees are more sensitive to painful actions of NGF and how this sensitivity can be reduced in order to improve osteoarthritic pain.
How the study was carried out
Rats with and without knee OA were tested for NGF induced pain sensitivity. Joint inflammation was inhibited to see whether inflammation contributed to this increased NGF induced pain sensitivity. Measures of pain and joint damage were evaluated.
What the study found
We found that osteoarthritic rats were more sensitive to NGF induced pain compared to normal rats and inhibiting inflammation reduced the pain sensitivity to NGF.
Significance of the study to arthritis pain research
A core part of the Pain Centre's work is to better understand the mechanisms behind osteoarthritic pain and seek effective treatment targets that can reduce this pain, studies like these help us to do this. This study shows that NGF is an important molecule involved in altering pain sensitivity in osteoarthritic joints and inflammation contributes to this. Treatments that reduce sensitivity to NGF have the potential to improve osteoarthritic pain.