The Synergistic Effect of Nanocrystals Combined With Ultrasound in the Generation of Reactive Oxygen Species for Biomedical Applications

Abstract

Reactive oxygen species (ROS) effects on living cells and tissues is multifaceted and their level or dose can considerably affect cell proliferation and viability. It is therefore necessary understand their role also designing ways able to regulate their amount inside cells, i.e., using engineered nanomaterials with either antioxidant properties or, for cancer therapy applications, capable to induce oxidative stress and cell death, through tunable ROS production. In this paper, we report on the use of single-crystalline zinc oxide (ZnO) round-shaped nanoparticles, yet ZnO nanocrystals (NCs) functionalized with amino-propyl groups (ZnO-NH 2 NCs), combined with pulsed ultrasound (US). We show the synergistic effects produced by NC-assisted US which are able to produce different amount of ROS, as a result of inertial cavitation under the pulsed US exposure. Using Passive Cavitation Detection (PCD) and Electron Paramagnetic Resonance (EPR) spectroscopy, we systematically study which are the key parameters, monitoring, and influencing the amount of generated ROS measuring their concentration in water media and comparing all the results with pure water batches. We thus propose a ROS generation mechanism based on the selective application of US to the ZnO nanocrystals in water solutions. Ultrasound B-mode imaging is also applied, proving in respect to pure water, the enhanced ecographic signal generation of the aqueous solution containing ZnO-NH 2 NCs when exposed to pulsed ultrasound. Furthermore, to evaluate the applicability of ZnO-NH 2 NCs in the biomedical field, the ROS generation is studied by interposing different tissue mimicking materials, like phantoms and ex vivo tissues, between the US transducer and the sample well. As a whole, we clearly proof the enhanced capability to produce ROS and to control their amount when using ZnO-NH 2 NCs in combination with pulsed ultrasound anticipating their applicability in the fields of biology and health care.

Zinc Oxide Nanocrystals and High-Energy Shock Waves: A New Synergy for the Treatment of Cancer Cells

“…In this view, it is reasonable to suppose that the presence of ZnO NCs in cells subsequently irradiated with SW decreased the cavitation threshold improving the number of oscillating/imploding microbubbles, increasing the mechanical stress (Canavese et al, 2018). This effect was also previously reported by our research group using amino-functionalized ZnO NC in the presence of continuous ultrasound irradiation in water media (Vighetto et al, 2019).…”

“…The observed cell death upon the sonosensitizer activation is frequently related in the literature with the ROS production (Canavese et al, 2018;Vighetto et al, 2019). For this reason, the experiments with ZnO NCs and multiple SW treatments were repeated by pre-incubating KB cells with two different antioxidants in order to evaluate ROS involvement in cell proliferation upon ZnO NCs incubation and SW treatment.…”

Biomedical Applications of Reactive Oxygen Species Generation by Metal Nanoparticles

“…A number of secondary effects are determined by this phenomenon, and in particular sonoluminescence, which represents a sonoluminescent emission, mainly a UV light, due to the cavitation bubble implosion [ 96 ]. For this reason, many researchers suggest that ZnONPs bring about cytotoxic effects when exposed to US via generation of ROS as their principal mechanism of bacterial and cancerous cell death [ 108 ].…”

Remotely Activated Nanoparticles for Anticancer Therapy

“…ROS moreover displays a multifaceted role, because they are involved in several physiological processes and their level is kept under strict control. However, an excessive ROS production is cause of oxidative stress, affecting cellular components such as membranes and DNA, and altering cell signaling causing necrosis or apoptosis [30,31]. Nevertheless, radiation therapy is associated with several drawbacks, such as the injury of the tissues in close proximity to the tumor and the development of resistances.…”

“…Our group recently investigated the ability of amino-propyl functionalized zinc oxide nanocrystals to induce inertial cavitation after pulsed US exposure, observing a large production of ROS, specifically of hydroxyl and superoxide anions. The adopted US conditions were thus sufficient to initiate the acoustic cavitation of tiny gas bubbles trapped at the surface of the nanocrystals [31].…”