Characterisation of lipid-mediated inflammatory pathways in Drosophila. Mark A Watson¹, Karen Massey², Soyeon Kwon¹, Anna Nicolaou², Paul Badenhorst¹. 1) Institute of Biomedical Research, University of Birmingham, Edgbaston B15 2TT, UK; 2) Bradford School of Pharmacy, University of Bradford, Bradford BD7 1DP, UK.

   Oxygenated metabolites of polyunsaturated fatty acids (PUFAs) are key modulators of inflammatory responses, and are therapeutic targets for intervention in inflammatory diseases such as rheumatoid arthritis. PUFAs are categorized as omega-6 (n-6) or omega-3 (n-3) and are broadly considered pro-inflammatory or anti-inflammatory respectively. The best- studied example of these bioactive lipid mediators are prostaglandins - eicosanoid (C20: n-6) derivatives of arachidonic acid. The cyclooxygenase enzymes that generate prostaglandins are currently the main targets of therapeutic intervention in inflammatory disease. Recent reports have indicated the existence of cyclooxygenase activity in Drosophila, suggesting that these compounds may also modulate Drosophila inflammatory pathways. Using an inflammatory model based on the inflammatory tumor-promoting hopTum mutation, we have investigated lipid mediator-signaling pathways in Drosophila. Dietary supplementation with fatty acids was able to modulate inflammation, with omega-6 fatty acids increasing, and omega-3 fatty acids reducing, the severity of the hopTum inflammatory phenotype. While cyclooxygenase inhibitors were able to reduce inflammation, LC-MS analysis of Drosophila extracts failed to detect the existence of prostaglandins or the arachidonic acid (C20) precursor. Interestingly, however, we have been able to detect C18 oxygenated metabolites known as HODEs (Hydroxy-octadecadienoic acids). These can be generated by enzymatic oxidation of the C18: n-6 fatty acid linoleic acid by myeloperoxidase (MPO) enzymes. MPO inhibitors were able to reduce the inflammatory phenotype and we have identified candidate Drosophila MPO homologues. Using the inflammatory tumor assay we have been able to distinguish 3 that may be required to generate HODE inflammatory lipid mediators. Functional characterization of these enzymes in Drosophila inflammatory responses is presented.