The number of irradiations multiplied irradiation energy showed optimal exposure conditions of low-intensity pulsed ultrasound for activating endothelial nitric oxide synthase

Low-intensity pulsed ultrasound (LIPUS) therapy provides a minimally invasive treatment for ischemic heart disease by promoting myocardial angiogenesis. Previous studies have determined optimal treatment conditions based on existing ultrasound devices. In the present study, four parameters related to ultrasound exposure were examined, and a new index was proposed that uniformly reveals optimal conditions that promote endothelial nitric oxide synthase (eNOS) expression. Human coronary artery endothelial cells were cultured for the second passage, sown uniformly, and incubated. Nineteen irradiation conditions, from a disk-shaped transducer to the cells, were selected by combining the values for the following four parameters: ultrasound frequency (0.1–3 MHz), maximum sound pressure (125–1250 kPa), pulse duration (16–128 μs), and pulse repetition time (107–3200 μs). The total irradiation time was fixed to 20 min from a separate experiment. The mRNA expression of eNOS, an important molecule that promotes angiogenesis, was evaluated after irradiation. A new index uniformly revealed the eNOS expression for these various values of irradiation conditions revealed the maximum. Optimal irradiation conditions included 1-MHz ultrasound frequency, 500-kPa sound pressure, 32-48-μs pulse duration, and 320-μs pulse repetition time. The index is useful to determine the optimal conditions for promoting eNOS expression in human coronary artery endothelial cells.