Antioxidants are substances that help the body reduce the damage caused by the action of free radicals. About 4000 antioxidants have been described to this day. Most of these are electron donors reacting with reactive oxygen species (ROS) and forming harmless end products such as water. Although many of these antioxidants have provided promising results in animal models of oxidative stress, in most cases, the beneficial effects shown in animal studies have not been replicated in clinical trials. The low membrane permeability and high toxicity are considered the main barriers to the use of exogenous antioxidants. These factors cause a limited effectiveness at low therapeutic doses.
The identification of a new, more effective and safer antioxidant is a high priority. A sophisticated endogenous antioxidant defense system mainly neutralizes the accumulation of reactive oxygen species (ROS). That system contains enzymes – such as superoxide dismutase (SOD), catalase and glutathione peroxidase, and non-enzymes – such as vitamin A, vitamin C, carotene and bilirubin. Antioxidant protective enzymes are able to detoxify the superoxide-anion radicals and hydrogen peroxide, while the hydroxyl radical cannot be detoxified in this way.
The therapeutic effect of antioxidants is generally limited. The elimination of all types of reactive oxygen species (ROS) through strong antioxidant therapy is likely to disturb important cellular functions. Furthermore, it is scientifically proven that a radical suppression of oxidative stress can stimulate tumor growth. This is the reason for the growing need for the development of selective antioxidants that preferentially remove toxic radicals such as hydroxyl radicals without affecting others such as hydrogen peroxide and nitric oxide radicals.