The presence of secretoneurin in human synovium and synovial fluid

Secretoneurin is a neuropeptide formed from the proprotein secretogranin II. It is found in afferent nerve fibres and has chemotactic activity for monocytes, neutrophils and fibroblasts. We investigated the presence of secretoneurin in synovial fluid and synovium from patients with osteoarthritis and rheumatoid arthritis. The secretoneurin immunoreactive material found in synovial fluid was identified by high performance liquid chromatography as the free peptide secretoneurin. Its level in hip joints was 15.6, in knee joints of osteoarthritis patients 17.3 and in rheumatoid patients significantly lower (8.6 fmol/ml). Immunocytochemistry provided evidence for the presence of sub-intimal secretoneurin-immunoreactive nerve fibres in knee synovium in osteoarthritic patients. In rheumatoid synovium, only very few immunoreactive fibres were found these being mostly localised in deep stroma. The results show that secretoneurin is present in osteoarthritic joint and suggest that secretoneurin levels are down-regulated in rheumatoid joint. Therefore, secretoneurin may participate in acute or mild phases of inflammation but is unlikely to have a major role when more severe inflammation is present such as that seen in rheumatoid joint.