Nutritional antioxidants as antidegenerative agents.
In this study, primary cultures of cerebellar granule neurons were prepared from eight-day-old Wistar rats, and maintained in an appropriate medium containing a high (25 mM) concentration of KCl. All experiments were performed with fully differentiated neurons (eight days). To induce apoptosis, culture medium was replaced with a serum-free medium (containing 5 mM KCl) eight days after plating. In another series of experiments, apoptosis was induced by application of glutamate (50 microM) to the cell cultures. Apoptosis was measured by flow cytometry, the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP-fluorescein nick end-labeling) method, and by the classical method of DNA fragmentation. Since there is evidence that an increased formation of reactive oxygen species (ROS) is involved in the apoptosis induced by both low K(+) concentrations and glutamate, a series of natural antioxidants and a red wine lyophilized extract (which is rich in antioxidant compounds) were tested in our experimental model. It was found that ascorbic acid (30 microM) and a red wine lyophilized extract (5 microgram/ml) were capable of blocking the apoptotic process. Addition of the following natural antioxidants did not have any protective effect on apoptosis induced by low K(+) concentrations: trans- and cis-resveratrol (5-200 microM), alpha-tocopherol (100-200 microM), reduced glutathione (100-400 microM), 3-hydroxytirosol (25-100 microM), epicatechin (25-100 microM), or quercetin (25-50 miroM). It is concluded that only a limited number of natural antioxidants are provided with antiapoptotic activity in cultured cerebellar granule neurons. This effect is probably exerted by reducing ROS formation, and by blocking caspase-3 activity.