Gallic acid induces vascular smooth muscle cell death via hydroxyl radical production

In the present study, we investigated whether gallic acid (GA) can induce death in cultured vascular smooth muscle cells (VSMCs), and whether production of the hydroxyl radical (·OH) is involved in the process of GA action. GA killed cultured VSMCs from rat aorta, in a dose- and time-dependent manner. Cytoplasmic shrinkage and nuclear condensation were observed light microscopically in GA-treated VSMCs, which appeared apoptotic. However, the ultrastructure of the VSMC was not typical of apoptosis: nuclear condensation was not glossy, and the plasma membrane and subcellular organelles were disrupted. Although the VSMC were positive for in situ nick end-labeling (TUNEL), they did not show a DNA ladder pattern on gel electrophoresis and were negative for Taq polymerase-based in situ ligation, which is more specific for apoptosis than TUNEL. Moreover, GA-induced cell death was not prevented by Boc-Asp-fmk (a pan-caspase inhibitor). Production of ·OH was detected in GA-treated VSMCs using high-performance liquid chromatography with salicylic acid as a trapping agent. Lipid peroxidation was also observed. The production of ·OH was inhibited by catalase (CAT) and deferoxamine (DFX), and these treatments completely rescued VSMCs from cell death. In a cell-free system, GA produced ·OH in the presence of Fe2+-EDTA, which was quenched by CAT and DFX, suggesting involvement of the Haber–Weiss reaction. Oxidative stress by reactive oxygen species, ·OH in particular, is one of the mechanisms of GA-induced death of VSMCs, the mode of which was different from typical apoptosis.