Neuropeptides in bone and joint tissues : alteration in adjuvant arthitis

Abstract

In this thesis, the localization, distribution and quantification of met-enkephalin (Met-enk), neurokinin-A and somatostatin in normal bone and joint tissues of the rat have been studied. Moreover, concentration alterations of these neuropeptides at the site of inflammation in the arthritic ankle joints as well as the spinal cords were evaluated.

The occurrence of Met-enk in bone and joint tissues was demonstrated using immunoelectron and immunofluorescence microscopy. Met-enk labeling was observed in unmyelinated nerve fibers in periosteum, in synovial, bone marrow and bone cells as well as in bone matrix. Immunofluorescence microscopy showed straight and long Met-enk nerve fibers in periosteum and varicosed nerve fibers in synovial membrane. Quantification of its concentration in these tissues was done using radioimmunoassay (RIA) and high performance liquid chromatographyelectrochemical detection. In cell culture, Met-enk inhibits the growth of osteoblast cells, whereas naltrexone stimulates its growth, denoting that Met-enk action is through opioid receptor. In adjuvant arthritis, Met-enk concentration decreases in chronic arthritic ankles and increases in spinal cords of the same group. The loss of Met-enk concentration in the arthritic ankles could explain pain and hypertrophic changes at the site of inflammation.

Neurokinin-A was localized in normal bone and joint tissues using immunoelectron microscopy. It is present in synovial cells, in myelinated nerve fibers in the periosteum, bone marrow cells, and in bone matrix. Using RIA, its concentration in normal and arthritic tissues was studied. Its concentration was significantly increased in ankles and spinal cords of chronic arthritic rats. These changes in adjuvant arthritis may contribute to the pathophysiology of the disease. Somatostatin morphological distribution in bone and joint tissues was studied using immunoelectron microscopy. It is present in myelinated nerve fibers in the periosteum, synovial cells, bone marrow cells and bone matrix. In addition, its concentration in these tissues was assessed using RIA, which revealed measurable concentrations. However, its concentration significantly increased in ankles but not in spinal cords of chronic arthritic rats. The increase in the chronic arthritic ankles may be not to the level needed to stop arthritis, which thus merits supplement with exogenous somatostatin to treat the disease.

This thesis has demonstrated for the first time the presence of Met-enk, neurokinin A, and somatostatin in rat bone and joint tissues. In addition to their localization in nerve fibers, the distribution of these neuropeptides in synovial cells, bone marrow cells, endothelial and bone cells as well as bone matrix varied. The concentration of these neuropeptides was altered in adjuvant arthritis. Understanding the mechanism(s) of action of these peptides in arthritis may open new venue for therapeutic strategies.