5-aminolaevulinic Acid Mediated Sonodynamic Therapy Promotes Inflammation Resolution, And Reduces And Stabilizes Atherosclerotic Plaque: Involving Macrophage Apoptosis And Elimination

Objectives: Macrophages can be found in all stages of atherosclerosis and are major contributors of atherosclerotic plaque development, progression and destabilization. This study aims to test the hypothesis that 5-aminolevulinic acid(ALA) mediated sonodynamic therapy(SDT) may selectively eliminate atherogenic macrophages, thus promoting inflammaton resolution and limiting disease progression.Methods: Atherosclerotic plaque was induced in the femoral arteries of rabbits. Accumulation of ALA derived protoporphyrin IX(Pp IX) in the plaques were detected by fluorescence spectrometer and microscope. Then the animals were divided randomly into ALA-SDT treatment group and control group. Short-term(within 3 days) and long-term effects(up to 12 weeks) were evaluated for the comparation of macrophage apoptosis, phagocytosis, pro-inflammtory factor expression,plaque composition and plaque volume between the two groups. Apolipoprotein-E–deficient mice on atherogenic diet for 12 weeks developed advanced plaques. After SDT treatment, monocyte recruitment, phagocytic clearance of apoptotic cells and macrophage egress in plaques were investigated. THP-1 macrophage culture was performed to assess apoptosis process and pro-inflammtory factor expression after ALA-SDT.Results: ALA-Pp IX preferentially accumulates in the mitochondria of macrophages within plaques of rabbits. Compared with control group, plaque area was decreased by 31%, 28%, 29%and 28% at 1, 4, 8 and 12 weeks after ALA-SDT, respectively. ALA-SDT-treated plaques showed decreased expression of macrophage, lipid and pro-inflammatory factors, and increased expression of smooth muscle cell(SMC) and collagen. Following ALA-SDT treatment, macrophage apoptosis and phagocytosis within plaques were significantly increased. In apolipoprotein-E–deficient mice, macrophage and pro-inflammatory factors contents were reduced continuously within 7 days after ALA-SDT, which was impaired by systemic administration of caspase inhibitor z VAD-fmk. Apoptosis of plaque cells was significantly increased, consistent with the increases in monocyte recruitment, phagocytic clearance of apoptotic cells and macrophage egress. In vitro experiment showed that ALA-SDT induced macrophage apoptosis via the mitochondrial-caspase pathway, and reduced the release of pro-inflammtory factors.Conclusion: ALA-SDT promotes macrophage apoptosis and their subsequent elimination, and thus reduces plaque inflammation and alteres plaque composition favoring plaque stability while attenuating disease progression. Thus, ALA-SDT provides a promising approach to the treatment of patients with atherosclerosis.