Background/aims: Sonodynamic therapy (SDT) is considered a new approach for the treatment of atherosclerosis. We previously confirmed that hydroxyl acetylated curcumin (HAC) was a sonosensitizer. In this study, we investigated the mechanism of THP-1 macrophage apoptosis and autophagy induced by HAC mediated SDT (HAC-SDT).
Methods: Cell viability was measured using a CCK-8 assay. Laser scanning confocal microscopy was used to measure the levels of intracellular reactive oxygen species (ROS), sub-cellular HAC localization, BAX and cytochrome C translocation, LC3 expression, monodansylcadaverine staining and Dil-labeled oxidized low density lipoprotein (Dil-ox-LDL) uptake. Flow cytometry was used to analyze apoptosis and autophagy via Annexin V/propidium iodide and acridine orange staining, respectively. The expression levels of apoptosis- and autophagy-related proteins were detected by Western blot. Oil red O was used to measure intracellular lipid accumulation.
Results: We identified HAC (5.0 μg/mL) located in lysosomes, endoplasmic reticulum, Golgi apparatus and mitochondria after 4 h of incubation. Compared with other sonosensitizers (e.g., curcumin and emodin), HAC had a more obvious sonodynamic effect on macrophages. Furthermore, the mitochondrial-caspase pathway was confirmed to play a crucial role in the HAC-SDT-induced apoptosis; BAX translocated from the cytosol to the mitochondria during HAC-SDT. Subsequently, mitochondrial cytochrome C was released into the cytosol, activating the caspase cascade in a time-dependent manner. Furthermore, HAC-SDT could induce PI3K/AKT/mTOR pathway dependent autophagy, accompanied by a decrease in the lipid uptake of THP-1 macrophages. This mechanism was demonstrated by the formation of acidic vesicular organelles, the conversion of LC3 I to LC3 II, the expression of related proteins, and the attenuation of both Dil-ox-LDL and oil red O staining. Moreover, pre-treatment with the autophagy inhibitor 3-methyladenine enhanced the HAC-SDT-induced apoptosis. Additionally, HAC-SDT-induced autophagy and apoptosis were both blocked by ROS scavenger N-acetyl-l-cysteine.
Conclusion: The results suggested that autophagy not only played an inhibitory role in the process of apoptosis but also could effectively attenuate lipid aggregation in THP-1 macrophages during HAC-SDT. As important intracellular mediators, the ROS generated by HAC-SDT also played a crucial role in initiating apoptosis and autophagy.
© 2016 The Author(s) Published by S. Karger AG, Basel.