Objective: To describe cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) expression in muscle tissue in patients with idiopathic inflammatory myopathies (IIM) - dermatomyositis (DM) and polymyositis (PM) and to find out if any differences between affected and non-affected muscles detected by MRI exist.
Methods: Samples of muscle tissue from 7 patients with dermatomyositis (DM) and from 4 with polymyositis (PM) were obtained by needle biopsy from affected and non-affected sites distinguished by magnetic resonance imaging. In situ hybridization with antisense mRNA probes was employed to detect COX-1, COX-2 and 5-LOX mRNA.
Results: Expression of COX-1, COX-2, and 5-LOX mRNA was found in all samples - in the muscle cells, inflammatory cells and in vessels. COX-1 mRNA expression predominated in the inflammatory cells and vessels and was higher in affected than in non-affected sites detected by MRI (mean intensity 3.22+/-0.67 vs. 2.0+/-0.87; p = 0.0006). The expression of COX-2 mRNA was high mainly in inflammatory cells and/or vessels and was increased in MRI-detected affected tissues (3.5+/-0.88; 1.9+/-1.1; p = 0.003), as was the expression of COX-2 mRNA in muscle cells (2.1+/-1.0 vs. 1.3+/-1.0; p = 0.021). 5-LOX mRNA was largely expressed in muscle cells from MRI-detected affected sites and the signal intensity was higher in comparison with samples taken from non-affected tissues detected by MRI (3.22+/-0.7 vs. 1.67+/-0.7; p = 0.0007).
Conclusion: Expression of COX-1, COX-2 and 5-LOX mRNA was observed for the first time in muscle tissues from IIM patients. This expression was increased in affected tissues detected by MRI, which may suggest a role of COX-1, COX-2, and 5-LOX in the pathogenesis of IIM.