The expression and localization of β-endorphin and µ,δ-opioid receptors in synovial tissues in patient with rheumatoid arthritis and osteoarthritis

Abstract

An examination of the localization and distribution of β-endorphin and opioid receptors in patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Immunohistochemical staining, reverse transcription polymerase chain reaction (RT–PCR) analysis, and in situ hybridization were performed using synovial tissues obtained from RA and OA patients. Immunohistochemical staining showed that β-endorphin was strongly expressed in synovial lining cells and in a few lymphocytes and macrophages surrounding the vessels, whereas µ- and δ-opioid receptors were expressed in lymphocytes and macrophages. However, we detected the weak expression of these opioid peptides in synovial tissues of OA patients. RT–PCR analysis showed that preproopiomelanocortin (POMC) mRNA, a precursor of β-endorphin, was strongly expressed in synovial tissues of RA patients, but these PCR products of synovial tissues obtained from OA patients were weakly detected compared with those from RA patients. POMC mRNA was also expressed in synovial tissues in RA patients. In in situ hybridization, the expression of POMC mRNA was detected in macrophages, synovial lining cells, and fibroblasts in synovial tissues of RA patients as well as β-endorphin. In RA patients, β-endorphin and µ- and δ-opioid receptors are synthesized and located in synovial lining cells, lymphocytes, and macrophages surrounding the vessels in synovial tissues, and may play a role in the regulation and modulation of inflammation.