Involvement of p-CREB and phase II detoxifying enzyme system in neuroprotection mediated by the flavonoid calycopterin isolated from Dracocephalum kotschyi

Abstract

PurposeThere is an increasing amount of experimental evidence that oxidative stress has a central role in the neuropathology of neurodegenerative diseases. It has been suggested that the loss of cell function results from the increased oxidative damage to proteins and DNA. Herein, we investigated the effect of a natural neuroprotective flavonoid, calycopterin, on H2O2-induced disruption of phase II detoxifying enzyme system and cAMP response element binding protein (CREB) phosphorylation. MethodsPC12 cells were treated with 25, 50 and 100μM of calycopterin for 3h, followed by adding H2O2 (150μM) for 24h. The extent of apoptosis was assessed by comet assay. The level of phosphorylated CREB, nuclear factor erythroid 2-related factor 2 (Nrf2), glutamylcysteine synthetase (γ-GCS) and heme oxygenase 1 (HO-1) were measured by western blot method. The concentration of glutathione (GSH) was determined in whole cell lysate using dithionitrobenzoic acid method. Superoxide dismutase (SOD) activity was measured by colorimetric assay. ResultMorphological analysis of protection induced by calycopterin, determined by comet assay, showed that calycopterin reduced DNA in tail. We found that H2O2 decreased mitochondrial membrane potential (MMP), while, calycopterin prevented this decrease in MMP in presence of H2O2. In H2O2-treated cells, calycopterin also suppressed cytochrome C release to cytosol that is necessary for maintaining mitochondrial homeostasis in survived cells. Moreover, calycopterin, in presence of H2O2 inhibited the decrease caused by oxidative stress in stress-sensing transcription factors, CREB and Nrf2, which play an important role in antioxidant capacity of the cell. There was also an increase in γ-GCS and HO-1 levels in calycopterin pretreated cells. In the presence of H2O2, calycopterin inhibited decrease in GSH level and SOD activity. ConclusionWe provided documentation of neuroprotective effect of a natural flavone, calycopterin, against H2O2-induced oxidative stress in differentiated PC12 cells by modulating the level of CREB phosphorylation and Nrf2 pathway.