Objectives To investigate pathogenesis of inflammation in muscles of patients with idiopathic inflammatory myopathies (IIM) – dermatomyositis (DM), polymyositis (PM) by studying expression of cox, lox and neuropeptides, using in situ hybridization and immunohistochemistry.

Methods Muscle tissue samples were obtained by needle biopsy from affected and non-affected sites distinguished by MRI-STIR technique. The second biopsy was performed after treatment. For studying cox, lox we used in situ hybridization with mRNA probes – antisense cox1, 2 and lox 5. Neuropeptides, such as substance P (SP), calcitonin gene related peptide (CGRP), vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), were evaluated by using immunohistochemistry.

Results 11 patients with DM or PM (9 female, 2 male) were examined. The expression of all investigated molecules (cox1, cox2, lox5, CGRP, SP, VIP, NPY) was detected on all muscle tissue. mRNA expression of cox and lox was increased in affected tissue (detectable expression was on 47 sections of 53–89%) in comparison with non-affected (40 sections of 64 ? 63%) and tissue after treatment. Expressing cells were muscle cells, inflammatory cells and vessels. Cox1 expression was found mainly on inflammatory cells and vessels, cox2 on muscle cells, inflammatory cells and vessels, lox5 mainly on muscle cells. Expression of neuropeptides was detected mainly on vessels, not on nerve cells. SP and CGRP were expressed in all tissues, VIP and NPY mainly in affected tissue. CGRP was expressed on smaller and thicker vessels in non-affected tissue and on bigger and thinner vessels in affected tissue, SP on smaller and thicker vessels in affected tissue. VIP and NPY staining was weak.

Conclusion Expression of all investigated molecules was observed in all muscle tissue samples from IIM patients. This expression was increased in affected tissues compared with non-affected and tissue after treatment, which indicates the role of cox, lox and neuropeptides in pathogenesis of IIM. Expression of neuropeptides was detected on vessels, not on nerve cells that suggests activation of vascular system in inflamed tissue.

This work was supported by grant IGA MZ CR NI/5369–3.