Low-intensity ultrasound (LIUS) differentially modulates mitochondrial reactive oxygen species (mtROS) generation by three different chemicals in PC12 cells

We have previously shown that low-intensity ultrasound (LIUS) can modulate mitochondrial complex I activity and the generation of mitochondrial reactive oxygen species (mtROS) in PC12 cells. This study investigated the mechanism of LIUS by comparing its effect on mitochondrial dysfunction by three different pathways. LIUS was shown to reverse the effects of rotenone, a Q-site blocker, on the complex I inhibition, mtROS generation, and drop of mitochondrial membrane potential (Delta psi m). In contrast, common antioxidants, N-acetyl cysteine (NAC), and uric acid (UA) blocked rotenone-induced mtROS generation and Delta psi m drop without recovering the complex I activity, which suggested that Delta psi m drop is correlated with mtROS generation rather than complex I inhibition itself. Ionomycin, an ionophore for Ca2+, and L-buthionine-S,R-sulfoximine (BSO), an inhibitor of glutathione (GSH) biosynthesis, induced mtROS generation and Delta psi m drop without inhibiting complex I activity via different mechanisms. LIUS showed no effect on ionomycin-induced Delta psi m drop but showed partial inhibition on the other effects of ionomycin and BSO. These results suggest that LIUS might have redundant mechanisms but acted mainly on the complex I activity thereby modulating mtROS and Delta psi m levels. LIUS appeared to act on the Q-module of complex I because it showed no inhibitory effect on Zn2+, an inhibitor of the proton transporting P-module of complex I. Interestingly, pretreatment of LIUS for up to an hour in advance blocked the rotenone effect as efficiently as the co-treatment. Further studies are needed to reveal the exact mechanism of LIUS to inhibit complex I activity.