Abstract
Some factors that enhance or inhibit the bioeffects of ultrasound were investigated and possible mechanisms explored. The findings: (1) Low intensity, nonthermal ultrasound enhanced hyperthermia-induced apoptosis (2) A nonthermal hypotonia enhanced the ultrasound-induced cell killing due to increased susceptibility of the swollen cells and inhibited repair of damaged membranes. (3) Some agents, including known anticancer drugs and a temperature-dpendent free radical generator, enhanced the US-induced bioeffects. (increased uptake of the agent was likely involved). (4) Bioeffects can be enhanced by echo-contrast agents (ECAs) and can be inhibited by carbon dioxide, suggesting the role of cavitation in the bioeffects (Mechanical membrane damage is apparently a pivotal event in the bioeffects). and (5) The cell killing significantly declined at densities 10x10^6 cells/ml and above. At 2x10^6 cells/ml, incubation inhibited cell killing time dependently. However, at the inhibited conditions, cell killing was observed when cells were sonicated with ECAs. In summary, enhancing factors are potentially useful for therapeutic and biochemical applications of ultrasound, while inhibitory factors are also important in modulation the effects of ultrasound.
