Background: Vascular smooth muscle cells play a critical role in the intimal hyperplasia of restenosis. A previous study of a rat balloon injury model demonstrated that photodynamic therapy (PDT) using indocyanine green (ICG) and near-infrared (NIR) light irradiation reduced intimal hyperplasia in carotid arteries. However, the effect of ICG-PDT on smooth muscle cells remains unclear. This study aimed to evaluate the effects of PDT with ICG and NIR irradiation on the viability of vascular smooth muscle (A-10) cells.
Methods: A-10 cells were incubated with ICG at different concentrations for different time intervals. Intracellular accumulation of ICG inside the cells was observed by light microscopy, ultraviolet-visible (UV-VIS) spectrophotometry and spectrofluorometry. Cell viability and cell death after ICG-PDT were assessed by 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide assay and lactate dehydrogenase release assay. Changes in nuclear morphology and cell cycle distribution were evaluated to determine the possible cell death mechanism mediated by ICG-PDT.
Results: ICG uptake in A-10 cells increased with the amount of ICG in the culture media. The intracellular accumulation of ICG reached a maximum at 8 h. After ICG-PDT, cell viability decreased and cell death increased in a concentration- dependent manner. The half maximal inhibitory concentration of ICG was 8.3 μM with 4 J/cm2 NIR irradiation. Membrane blebbing and chromatin condensation were observed, and the percentage of cells in the sub-G1 phase increased after ICG-PDT. Thus, apoptosis might be responsible for decreasing the viability of A-10 cells by ICG-PDT.
Conclusions: This study demonstrated that ICG-PDT had an inhibitory effect on smooth muscle cells, possibly via an apoptosis pathway.
Keywords: Cell viability; Indocyanine green; Near-infrared; Photodynamic therapy; Smooth muscle cell.