title: Dose-dependent inhibition of ultrasound-induced cell killing and free radical production by carbon dioxide.
abstract: Previous studies have shown that if a solution for cell suspension is saturated with CO(2), ultrasound-induced in vitro cell killing and free-radical production are inhibited. However, the dose dependency of this observation has not been explored. Here, we used NaHCO(3) and HCl to produce a predictable concentration of CO(2) within the culture medium. Using 1 MHz continuous wave 4 W/cm(2) ultrasound, we sonicated U937 cells suspension for 1 min at 37 degrees C with CO(2) at different concentrations. At 2 mM, reduced cell killing was observed that further decreased with increasing CO(2) concentration until 100% protection was attained at 20 mM. Ultrasound-induced free-radical production was significantly decreased at 1 mM and became undetectable at 2 mM CO(2). This finding shows that CO(2)-mediated inhibition is concentration dependent and that the threshold for free-radical production is one order of magnitude higher than the threshold for cell killing induced by ultrasound. In addition, it also cautions researchers when adding acids and acid-based agents to a culture medium, which almost always contains NaHCO(3), in experiments related to the bioeffects of ultrasound.
authors.affiliation: Department of Radiological Sciences, Faculty of Medicine, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan.
authors.forename: Loreto B
authors.initials: LB
authors.lastname: Feril
authors.forename: Takashi
authors.initials: T
authors.lastname: Kondo
authors.forename: Ryohei
authors.initials: R
authors.lastname: Ogawa
authors.forename: Qing-Li
authors.initials: QL
authors.lastname: Zhao
mesh_terms: D002245:Carbon Dioxide / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005609:Free Radicals / Q000378:metabolism*; D006801:Humans; D007951:Leukemia, Myeloid / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014465:Ultrasonics
chemical_list: D005609:Free Radicals; D002245:Carbon Dioxide