Plumbagin ameliorates memory dysfunction in streptozotocin induced Alzheimer's disease via activation of Nrf2/ARE pathway and inhibition of β-secretase

Although plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) protects against cerebral ischemia and spinal cord injury-induced oxidative stress and inflammation by activating the nuclear factor-erythroid 2-related factor-2/antioxidant response element (Nrf2/ARE) pathway, its role in the amelioration of neurodegenerative diseases remains unexplored. In the present study, we investigated the effect of plumbagin on Alzheimer's disease (AD)-like condition in mice. The animals were treated intracerebroventricularly with streptozotocin (STZ; 3 mg/kg) twice, on day 1 and 3, to induce AD-like condition, and the symptoms were evaluated after 14 days. While the loss of learning and memory performance was evident in the mice subjected to Morris water maze (MWM), there was a striking increase in the population of astrocytes labelled with glial fibrillary acidic protein (GFAP) in the hippocampus. Daily intraperitoneal (i.p.) treatment with plumbagin (0.5 and 1 mg/kg), starting from 1 h prior to first dose of STZ, significantly prevented the cognitive deficits in MWM. On the other hand, administration of Nrf2/ARE pathway inhibitor, trigonelline (10 and 15 mg/kg, i.p.) enhanced the effects of STZ. Pre-treatment with subeffective dose of trigonelline (5 mg/kg) significantly attenuated the effects of plumbagin in MWM. While plumbagin prevented the STZ induced GFAP expression, this effect of plumbagin was attenuated by trigonelline. Moreover, the in silico docking study revealed potent inhibitory effect of plumbagin on beta-secretase enzyme. The results of the present study suggest that plumbagin improves cognitive function in STZ induced mouse model of AD possibly via Nrf2/ARE mediated suppression of astrogliosis and inhibition of beta-secretase enzyme.