Chronic Administration of S-Allylcysteine Activates Nrf2 Factor and Enhances the Activity of Antioxidant Enzymes in the Striatum, Frontal Cortex and Hippocampus

Oxidative stress plays an important role in neurodegenerative diseases and aging. The cellular defense mechanisms to deal with oxidative damage involve the activation of transcription factor related to NF-E2 (Nrf2), which enhances the transcription of antioxidant and phase II enzyme genes. S-allylcysteine (SAC) is an antioxidant with neuroprotective properties, and the main organosulfur compound in aged garlic extract. The ability of SAC to activate the Nrf2 factor has been previously reported in hepatic cells; however this effect has not been studied in normal brain. In order to determine if the chronic administration of SAC is able to activate Nrf2 factor and enhance antioxidant defense in the brain, male Wistar rats were administered with SAC (25, 50, 100 and 200 mg/kg-body weight each 24 h, i.g.) for 90 days. The activation of Nrf2, the levels of p65 and 8-hydroxy-2-deoxyguanosine (8-OHdG) as well as the activities of the enzymes glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT), superoxide dismutase (SOD), and glutathione S-transferase (GST) were evaluated in the hippocampus, striatum and frontal cortex. Results showed that SAC activated Nrf2 factor in the hippocampus (25-200 mg/kg) and striatum (100 mg/kg) and significantly decreased p65 levels in the frontal cortex (25-200 mg/kg). On the other hand, SAC increased GPx, GR, CAT and SOD activities mainly in the hippocampus and striatum, but it did not change GST activity. Finally, no changes were observed in 8-OHdG levels mediated by SAC in any brain region, but the hippocampus showed a major level of 8-OHdG compared with the striatum and frontal cortex. All these results suggest that in the hippocampus, the observed increase in the activity of antioxidant enzymes could be associated with the ability of SAC to activate Nrf2 factor; however, a different mechanism could be involved in the striatum and frontal cortex, since no changes were found in Nrf2 activation and p65 levels.