Relative rates of the photosensitized production of singlet oxygen (1O2) and of superoxide (O2•−) were determined using different couples of dyes and sacrificial electron donors (SEDs) of either high or low hydrophobicities. Such rates were also measured in the absence and presence of single unilamellar vesicles (SUVs) with 9DMPC:1DMPA mol ratio composition. The dyes aluminum phthalocyanine tetrasulfonate (AlPcS4) and pheophorbide-a (PHEO) were used as hydrophilic and hydrophobic photosensitizers, respectively. Xanthine (X) and glutathione (GSH) were used as hydrophobic and hydrophilic SEDs, respectively. The presence of SUVs in the aqueous sample produces the physical separation or encounter of SEDs and photosensitizers according to their membrane binding constants. When both the SED and the photosensitizer are localized within the same phase, a strong decrease in the rate of 1O2 formation, united to a strong increase in the rate of O2•− formation, is observed, relative to when both of these species are localized in different phases. The lipid phase is always present in the biological milieu. Thus, the use of a hydrophobic couple of both dye and SED (as in the case of X and PHEO), as well as a hydrophilic couple of both dye and SED (as in the case of GSH and AlPcS4), should strongly favor the Type I mechanism over the Type II. Since only a small number of hydroxyl radicals are needed to initiate a chain reaction of phospholipid peroxidation, the latter could be more toxic to the tumor tissue than peroxidation by a much higher concentration of singlet oxygen molecules.
Sonolysis at 75 kHz of argon-and air-saturated aqueous solutions at pH 7.4 containing snitrosogluthathione (GSNO) enhances the production rate of nitric oxide (NO). The quinones, anthraquinone-2-sulfonate (AQ2S) and anthraquinone-2,7-disulfonate (AQ27S) further enhance the NO production over that produced in quinone-depleted sonicated solutions. In contrast, the hydrophobic quinones juglone (JQ) and 1,4-naphthoquinone (NQ) inhibit ultrasound-induced NO detection as compared to quinone-depleted solutions. Larger sonolytical decomposition of the hydrophobic quinones NQ and JQ, as compared to AQ2S and AQ27S, is detected which correlates with a larger production of pyrolysis-derived carbon-centered radicals. Reaction of those radicals with NO could explain NQ and JQ inhibition. This work suggests that sulfonated quinones could be used to enhance NO release from GSNO in tissues undergoing ultrasound irradiation.
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