Thymoquinone protects against cobalt chloride-induced neurotoxicity via Nrf2/GCL-regulated glutathione homeostasis

The prevalence of neurodegenerative diseases worldwide has increased dramatically in the last decades. Hypoxia and oxidative stress play a central role in the pathogenesis of neurodegenerative diseases. Thymoquinone (TQ) is a monoterpenoid hydrocarbon compound that possesses potent antioxidant activity. In the current study, we investigated the neuroprotective effects of TQ against CoCl2, a widely used hypoxia-inducing agent. We found that TQ inhibited CoCl2-indcued cytotoxicity in vitro, as reflected by an increase of cell viability and decrease of apoptosis in CoCl2-treated PC12 cells. TQ exhibited a potent protective effect against CoCl2-induced neurotoxicity in vivo, as evidenced by decreased time spent to find the platform site in the Probe trials, reduced escape latencies, decreased traveling distance and reduction of apoptotic cell death in brains in CoCl2-treated rats. CoCl2-resulted decrease of glutathione (GSH) and increase of malondialdehyde (MDA) levels were significantly inhibited by TQ. Inhibition of GSH synthesis by buthionine sulphoximine (BSO) significantly attenuated TQ-induced neuroprotective effects against CoCl2 in rats and in PC12 cells. TQ could upregulate nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/glutamate-cysteine ligase catalytic subunit (GCLc) and Nrf2/glutamate-cysteine ligase modifier subunit (GCLm) pathway which contributed to antioxidant and neuroprotective effects of TQ. In summary, we found that TQ exhibited protective effects against neurotoxicity via upregulation of Nrf2/GCL signaling. Upregulation of Nrf2/GCL signaling promoted the synthesis of GSH and contributed to attenuation of oxidative stress, neuronal cell apoptosis and neurotoxicity. These data have appointed a new path toward the understanding of the neuroprotective activities of TQ.