Effects of low-intensity ultrasound on oxidative damage in retinal pigment epithelial cells in vitro

Oxidative stress in retinal pigment epithelium (RPE) is one of the key causative factors of RPE injury in age-related macular degeneration (AMD). Low-intensity ultrasound (LIUS) less than 1 W/cm² in intensity has been found to have cytoprotective and anti-inflammatory effects in many cell types and diseases. In this study, we investigated for the first time the feasibility of using LIUS to protect RPE cells from oxidative damage. ARPE-19 cells were treated with H₂O₂ (an exogenous source of reactive oxygen species) or L-buthionine-(S,R)-sulfoximine (BSO), a glutathione synthase inhibitor, and exposed immediately to LIUS at intensities of 50, 100 and 200 mW/cm² and a frequency of 1 MHz for 20 min. Both H₂O₂ and BSO increased the percentage of cells positive for mitochondrial reactive oxygen species at 1 h, but not at 24 h. Co-treatment with LIUS clearly repressed these cells similarly at all intensities by approximately 34%-43% for H₂O₂ and 24%-25% for BSO (p < 0.05). The percentage of cells with mitochondrial membrane depolarization also increased with H₂O₂ and BSO treatment, particularly at 1 h, and decreased by approximately 60% with LIUS at 100 mW/cm² (p < 0.05). The amount of intracellular calcium ion ([Ca²⁺]_i) was elevated only by BSO at 24 h and was also significantly diminished, by approximately 45%, by LIUS at 100 mW/cm² (p < 0.05). Both H₂O₂ and BSO significantly hampered cell viability at 24 h, but LIUS at 100 mW/cm² restored only BSO-induced cell viability by approximately 2.7-fold (p < 0.05). This study illustrated that LIUS has a protective effect on RPE cells against oxidative damage caused by BSO, an endogenous mitochondrial reactive oxygen species generator. We speculate that LIUS has the potential to treat oxidative damage and related pathologic changes in RPE.