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Abstract: The mechanism(s) responsible for sudden cytolysis observed when cells are exposed to ultrasound could be mechanical and/or free radical in nature. Free radical reactions are initiated in the core and in the interfacial regions of collapsing acoustic cavitation bubbles. Because cyclic sugars are known to inhibit free radical chain reactions, we investigated the effects of n-alkyl-β-d-glucopyranosides of varying hydrophobicity on ultrasound (1.057 MHz)-induced cytolysis of HL-60 cells in vitro. n-Alkyl glucopyranosides with hexyl- (5 mM), heptyl- (3 mM), or octyl- (2 mM) n-alkyl chains protected 100% of the cell population from ultrasound-induced cytolysis under a range of conditions that resulted in 35 to 100% cytolysis in the absence of glucopyranosides. The protected cell populations also possessed long-term reproductive viability. However, the hydrophilic methyl-β-d-glucopyranoside could not protect cells, even up to a concentration of 30 mM. Furthermore, none of the glucopyranosides could prevent cytolysis of cells from a mechanically induced shear stress. Spin trapping and electron spin resonance experiments confirmed the presence of inertial cavitation in cell suspensions both in the presence and in the absence of the surfactants. It is concluded that surface-active glucopyranosides efficiently quench cytotoxic radicals and/or their precursors at the gas/solution interface of collapsing cavitation bubbles. [Copyright &y& Elsevier]

The synergistic effect of ultrasound and drugs on cells is known as sonodynamic therapy. The use of sonodynamic therapy for the potential clinical treatment of certain tumors is promising, however, the mechanism of sonodynamic therapy could be due to either sonomechanical and/or sonochemical effects on the cells. The aim of the current study is to determine the importance of the sonochemical mechanism for sonodynamic therapy. Sonochemical effects arise from the formation of radical species following collapse of cavitation bubbles. The synergistic effect of ultrasound (47 kHz) and analogues of a gallium-porphyrin derivative (ATX-70) on cytolysis of Human leukemia cells (HL-525 and HL-60) suspended in a cell culture medium were studied. Organic surfactants preferentially accumulate and subsequently decompose at the gas/solution interface of cavitation bubbles, producing secondary radicals that can diffuse to the bulk solution. The gallium porphyrin analogues used in the current study possess two n-alkyl side chains (ATX-Cx, where x = number of carbon atoms, ranging from x = 2 to x = 12). By varying the n-alkyl chain length, thereby modifying the surfactant properties of the ATX-Cx derivatives, cell killing in relation to the accumulation of ATX-Cx derivatives at the gas/solution interface of cavitation bubbles was determined. Following sonolysis in the presence of ATX-Cx, a strong correlation for the yield of carbon-centered radicals and cell killing was observed. These results support the hypothesis that a sonochemical mechanism is responsible for the synergistic effect of ultrasound and ATX-Cx on HL-525 and HL-60 cells. [Copyright &y& Elsevier]

Abstract: The major metabolite of the cancer chemopreventive agent oltipraz, a pyrrolopyrazine thione (PPD), has been shown to be a phase 2 enzyme inducer, an activity thought to be key to the cancer chemopreventive action of the parent compound. In cells, mitochondria are the major source of reactive oxygen species (ROS) and cytochrome c (cyt c) is known to participate in mitochondrial electron transport and confer antioxidant and peroxidase activities. To understand possible mechanisms by which PPD acts as a phase 2 enzyme inducer, a study of its interaction with cyt c was undertaken. UV–visible spectroscopic results demonstrate that PPD is capable of reducing oxidized cyt c. The reduced cyt c is stable for a long period of time in the absence of an oxidizing agent. In the presence of ferricyanide, the reduced cyt c is rapidly oxidized back to its oxidized form. Further, UV–visible spectroscopic studies show that during the reduction process the coordination environment and redox state of iron in cyt c are changed. Low-temperature EPR studies show that during the reduction process, the heme iron changes from a low-spin state of s =1/2 to a low-spin state of s =0. Room-temperature EPR studies demonstrate that PPD inhibits the peroxidase activity of cyt c. EPR spin trapping experiments using DMPO show that PPD inhibits the superoxide radical scavenging activity of oxidized cyt c. From these results, we propose that PPD interacts with cyt c, binding to and then reducing the heme, and this may enhance ROS levels in mitochondria. This in turn could contribute to the mechanism by which the parent compound, oltipraz, might trigger the cancer chemopreventive increase in transcription of phase 2 enzymes. The modifications of cyt c function by the oltipraz metabolite may have implications for the regulation of apoptotic cell death. [Copyright &y& Elsevier]