Involvement of Nrf2 signaling pathway in the neuroprotective activity of natural kaurane diterpenes.

Oxidative stress is a common harmful condition of several neurodegenerative diseases. Antioxidants represent the medical choice strategy for protection against this unbalanced oxidant-antioxidant status. The present study was undertaken to address the role of kaurane diterpenes foliol, linearol and sidol in the protection against H(2)O(2)-induced oxidative stress in the human astrocytoma U373-MG cell line and to establish the underlying mechanisms. U373-MG cells were pretreated with diterpenes (5 and 10 μM, 24h) prior to H(2)O(2) exposition (1mM, 30 min). We found that linearol and sidol exerted a significant astroprotective action, and foliol was the least active one. Linearol and sidol especially increased cell viability as shown by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and lactate dehydrogenase assay and attenuated morphological changes of U373-MG cells induced by H(2)O(2). Moreover, these compounds significantly decreased the level of intracellular reactive oxygen species, counteracted glutathione/oxidized glutathione changes, reduced lipid peroxidation and restored antioxidant and protein expression of antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase, glutathione peroxidase and hemooxigenase-1). Furthermore, these natural products increased Nrf2 nuclear levels, suggesting the activation of this master regulator of antioxidative gene expressions in the protective effect exhibited by the kaurane diterpenes studied. Collectively, these results suggest that the studied kaurane diterpenes, mainly linearol and sidol, protect U373-MG cells from H(2)O(2)-induced injury or degeneration presumably by antioxidant mechanisms. These compounds may be useful agents for counteracting the oxidative damage occurring during the pathological development of several CNS disorders.