Targeting cyclooxygenase-2 and oxidant stress pathways for attenuation of radiation-induced vascular dysfunction

J Pietzsch, M Laube, S Ullm, F Sehn, FJ Pietzsch, T Kniess. Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiopharmacy, 01314 Dresden, Germany

Radiotherapy of various cancers is closely associated with increased cardiovascular morbidity and mortality. Arachidonic acid metabolites are supposed to play a key role in radiation-induced vascular dysfunction. This investigation was performed in order to evaluate the effects of novel selective cyclooxygenase-2 (Cox-2) inhibitors (coxibs) on radiation-induced formation of eicosanoids via Cox-2 and oxidant stress pathways in both human arterial endothelial cells (EC model; HAEC) and rat aortic rings (AR model; Kyoto-Wistar strain), respectively. In order to assess acute effects (24 h) of X-ray radiation at moderate doses (2, 4, and 10 Gy) without or with presence of coxibs (EC model: cyclopentene/indole/indomethacin derivatives; AR model: indole derivatives; celecoxib as reference) compared to sham-irradiated controls, the following parameters were measured: Cox-2 protein induction, release of prostaglandins, release of isoprostanes, and formation of lipid and protein oxidation products (LO/PO). Analysis of variance (ANOVA, Bonferroni post hoc test) was used for comparison of numerical variables between groups. Irradiation of EC and AR without presence of coxibs resulted in a dose-dependent augmentation of all parameters studied. When EC and AR were exposed to Cox-2 inhibitors (0.1, 1, and 10 µM), during and for 24 h post irradiation, indole derivatives showed highest potency to inhibit radiation-induced release of both prostaglandins (EC model: by 77.3-96.0% at 1 µM, n=8, p<0.01; AR model: by 53.6-81.6% at 1 µM, n=8, p<0.01) and isoprostanes (EC model: by 31.8-57.1% at 1 µM, p<0.01; AR model: by 27.4-53.8% at 1 µM, p<0.01). Furthermore, indole derivatives significantly decreased radiation-induced LO/PO formation (EC model: by 17.6-32.3% at 1 µM, p<0.01; AR model: by 15.8-30.4% at 1 µM, p<0.01), indicating a direct interaction with oxidant stress-pathways. By contrast, both cyclopentene and indomethacin derivatives (and celecoxib) mainly inhibited radiation-induced prostaglandin release, but showed only slight effects on formation of isoprostanes and LO/PO. Model experiments using human low density lipoproteins showed that indole derivatives differently interact with oxidation of polyunsaturated fatty acids and protein amino acid side chains, than the cyclopentene/indomethacin derivatives, suggesting a physico-chemical rationale for observed antioxidative activity. The reduction of radiation-induced vascular dysfunction by antioxidative coxibs may widen the therapeutic window of Cox-2 targeted treatment.