Biological effects of ultrasound: Sonomechanical mechanism, and its implications on therapy and biosafety

Previously, we have investigated different factors that enhance or inhibit the bioeffects of low intensity ultrasound particularly those involving the non-thermal mechanisms. Several enhancing factors were identified just as there were factors that can inhibit the bioeffects. Although in some instances where free radicals were detected, free radical may have contributed to the effects, evidences showed that the pivotal point in the bioeffects such as DNA transfection, apoptosis induction, gene expression, and cell killing, was mechanical cellular membrane damage. In the present study, the results show that that modifying the cellular membrane without affecting the cavitation activity (associated with free radical production) will increase the bioeffects. In addition, designing an ultrasound protocol that would allow cells time to undergo membrane repair in between sonications, would help prevent instant lysis of the cells and improve desired bioeffects such as DNA transfection and apoptosis. In summary, use of ultrasound for therapy by targeting cells with modified cell membrane (as may be in cancers, intracellular infections, etc.) needs to be explored, while use of diagnostic ultrasound in patients with 'compromised cells' may increase the risk of having undesirable effects.