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Abstract
The determination and toxicological characterization of products of the reaction between p-hydroxybenzoic acid esters (parabens) and singlet oxygen (1O2) are very important because of the frequent use of parabens in cosmetics and possible generation of 1O2 in the skin. We observed 1O2-dependent production of mono-, di-, and tri-substituted glutathione (GSH) conjugates of hydroquinone (HQ) during visible light-irradiation of a mixture of methyl or ethyl paraben and GSH in the presence of rose bengal (RB). 1,4-Benzoquinone (BQ) and HQ were produced during the irradiation in the absence of GSH. While a mixture of BQ and GSH produced only mono-substituted conjugate, irradiation of the mixture with RB produced mono-, di-, and tri-substituted conjugates. These observations indicate that 1O2 is involved both in the production of BQ and HQ from parabens and in the formation of multi-substituted GSH conjugates from mono-substituted conjugate. Tri-substituted conjugate generated larger amounts of hydrogen peroxide in an aqueous solution than mono-substituted conjugates or HQ did. Detection of semiquinone radical suggests that the autoxidation of conjugates is related to the generation of hydrogen peroxide. The results obtained in this study indicate that parabens may induce oxidative stress in the skin after conversion to GSH conjugates of HQ by reacting with 1O2 and GSH.
| Abbreviations | ||
| BQ | = | 1,4-benzoquinone |
| 2,5-DGHQ | = | 2,5-(diglutathion-S-yl)hydroquinone |
| 2,6-DGHQ | = | 2,6-(diglutathion-S-yl)hydroquinone |
| GSH | = | reduced glutathione |
| HBA | = | p-hydroxybenzoic acid |
| H2O2 | = | hydrogen peroxide |
| HQ | = | hydroquinone |
| HQ-GSH conjugates | = | glutathione conjugates of hydroquinone |
| MGHQ | = | 2-(glutathion-S-yl)hydroquinone |
| 1O2 | = | singlet oxygen |
| O2√ − | = | superoxide anion radical |
| √OH | = | hydroxyl radical |
| PB | = | 20 mM sodium phosphate buffer pH 7.4 |
| RB | = | rose bengal |
| TGHQ | = | 2,3,5-(triglutathion-S-yl)hydroquinone |
| Abbreviations | ||
| BQ | = | 1,4-benzoquinone |
| 2,5-DGHQ | = | 2,5-(diglutathion-S-yl)hydroquinone |
| 2,6-DGHQ | = | 2,6-(diglutathion-S-yl)hydroquinone |
| GSH | = | reduced glutathione |
| HBA | = | p-hydroxybenzoic acid |
| H2O2 | = | hydrogen peroxide |
| HQ | = | hydroquinone |
| HQ-GSH conjugates | = | glutathione conjugates of hydroquinone |
| MGHQ | = | 2-(glutathion-S-yl)hydroquinone |
| 1O2 | = | singlet oxygen |
| O2√ − | = | superoxide anion radical |
| √OH | = | hydroxyl radical |
| PB | = | 20 mM sodium phosphate buffer pH 7.4 |
| RB | = | rose bengal |
| TGHQ | = | 2,3,5-(triglutathion-S-yl)hydroquinone |