The predominant pathway of apoptosis in THP-1 macrophage-derived foam cells induced by 5-aminolevulinic acid-mediated sonodynamic therapy is the mitochondria-caspase pathway despite the participation of endoplasmic reticulum stress

Abstract

Background: In advanced atherosclerosis, chronic endoplasmic reticulum (ER) stress induces foam cells apoptosis and generates inflammatory reactions.

Methods: THP-1 macrophage-derived foam cells (FC) were incubated with 1 mM 5-aminolevulinic acid (ALA). After ALA mediated sonodynamic therapy (ALA-SDT), apoptosis of FC was assayed by Annexin V-PI staining. Intracellular reactive oxygen species (ROS) and mitochondrial membrane potential were detected by staining with CellROX® Green Reagent and jc-1. Pretreatment of FC with N-acetylcysteine (NAC), Z-VAD-FMK or 4-phenylbutyrate (4-PBA), mitochondria apoptotic pathway associated proteins and C/EBP-homologous (CHOP) expressions were assayed by wertern blotting.

Results: Burst of apoptosis of FC was observed at 5-hour after ALA-SDT with 6-hour incubation of ALA and 0.4 W/cm(2) ultrasound. After ALA-SDT, intracellular ROS level increased and mitochondrial membrane potential collapsed. Translocations of cytochrome c from mitochondria into cytosol and Bax from cytosol into mitochondria, cleaved caspase 9, cleaved caspase 3, upregulation of CHOP, as well as downregulation of Bcl-2 after ALA-SDT were detected, which could be suppressed by NAC. Activation of mitochondria-caspase pathway could not be inhibited by 4-PBA. Cleaved caspase 9 and caspase 3 as well as apoptosis induced by ALA-SDT could be inhibited by Z-VAD-FMK.

Conclusion: The mitochondria-caspase pathway is predominant in the apoptosis of FC induced by ALA-SDT though ER stress participates in.