Apoptosis induction of human myeloid leukemic cells by ultrasound exposure

Therapeutic ultrasound (ULS) and the resulting cavitation process has been shown to induce irreversible cell damage. In this study, we wanted to furth er investigate the mechanism of ULS-induced cell death and to determine whe ther apoptosis is involved. Nigh intensity focused pulsed ULS sonication at a frequency of 750 KHz was delivered to HL-60, K562, U937, and M1/2 leukem ia cell line cultures. ULS exposure used with induction of transient cavita tion in the focal area was delivered with an intensity level of 103.7 W/cm( 2) and 54.6 W/cm(2) spatial-peak temporal-average intensity, As a control, ULS of lower intensity was delivered at 22.4 W/cm(2) spatial-peak temporal- average intensity, presumably without generation of cavitation. Our results indicated that DNA damage induced by ULS cavitation did not involve genera tion of free radicals in the culture media. Morphological alterations obser ved in cells after exposure to ULS included: cell shrinkage, membrane blebb ing, chromatin condensation, nuclear fragmentation, and apoptotic body form ation. Apoptotic cells were evaluated by fluorescence microscopy and detect ed using the terminal deoxynucleotidyl transferase-mediated dUTP nick-end l abeling assay, which identifies DNA breaks, and by the leakage of phosphati dylserine from the inner to the outer side of the membrane layer of treated cells. Some bioeffects induced on sonicated HL-60 cells, such as inhibitio n of cell proliferation, DNA repair, and cell-dependent apoptosis, were fou nd to be similar to those produced by gamma-irradiation. Thus, much of the cell damage induced by therapeutic ULS in leukemia cells surviving ULS expo sure appears to occur through an apoptotic mechanism.