ABSTRACT
Quinones have been detected in interstellar dust and are thus among the oldest organic chemicals in the universe. The toxicity of quinones and hydroquinones to cell lines in vitro has been extensively studied. The cytotoxicity of 2-methyl-1,4-naphthoquinone, 2,3-di-methoxy-1,4-naphthoquinone and ß-lapachone was also decreased by addition of superoxide dismutase (SOD) to the culture medium, again suggesting extracellular production of reactive oxygen species (ROS). Protection against chemically induced cancer has been observed in animals dosed with a number of quinones. This chapter explains a wide range of quinones and hydroquinones, which may have beneficial or adverse effects upon our health. Hydroquinones undergo autoxidation. The reduction of quinones by cellular reducing agents and the autoxidation of hydroquinones and semiquinones leads to redox cycling, in which a single molecule of the quinone may generate many molecules of ROS. Several quinones have been shown to protect against chemically induced cancer, and such effects may reflect intervention at either the initiation or subsequent phases of carcinogenesis.
