Evaluation of inertial cavitation activity in tissue through measurement of oxidative stress

Abstract

Ultrasound cavitation is an essential mechanism involved in the therapeutic local enhancement of drug delivery by ultrasound for cancer treatment. Inertial cavitation also triggers chemical reactions that generate free radicals and subsequent oxidative stress in the tissue. The aim of this study was to measure the oxidative stress induced by inertial cavitation in ex vivo tissue and to test the association between the exposure conditions and the oxidative stress. A confocal ultrasound setup was used to sonicate and create inertial cavitation in freshly excised adipose pig tissue. The ex vivo tissue samples were then processed to measure the quantity of malondialdehyde (MDA), an end-product of polyunsaturated free fatty acid oxidation. The creation of hydroxyterephthalic acid (HTA) from the reaction of terephthalic acid (TA) with free radicals in water was also quantified in vitro. Samples were sonicated for different durations using various amplitudes for the applied pressure. The results showed a minimum 2-fold increase in the amount of detected MDA in the sonicated tissue samples compared to baseline clearly suggesting the generation of free radicals by inertial cavitation. The method exhibited a moderate dependence of MDA generated upon the duration of exposure (R(2)=057,p<0.0001). The average increase in MDA concentration was approximately 2-fold, 5-fold, 6-fold, and 9-fold for exposure durations per unit of volume of 0.13, 0.17, 0.25, and 0.50s/mm(3), respectively. The results showed no statistically significant dependence on the amplitude of the pressure within the used range. Both pressure amplitude and exposure duration, however, influenced the HTA concentration (R(2)>0.95,p<0.0001). This biochemical method can be used on ex vivo tissue to detect the generation of free radicals induced by inertial cavitation. In large enough sample populations, the cavitation activity is linked to the exposure conditions of the sonication.

Keywords: Cavitation; Malondialdehyde; Oxidative stress; Ultrasound.