Cyanidin-3-glucoside inhibits amyloid β₂₅₋₃₅-induced neuronal cell death in cultured rat hippocampal neurons

Increasing evidence implicates changes in [Ca²⁺]i and oxidative stress as causative factors in amyloid beta (Aβ)-induced neuronal cell death. Cyanidin-3-glucoside (C3G), a component of anthocyanin, has been reported to protect against glutamate-induced neuronal cell death by inhibiting Ca²⁺ and Zn²⁺ signaling. The present study aimed to determine whether C3G exerts a protective effect against Aβ₂₅₋₃₅-induced neuronal cell death in cultured rat hippocampal neurons from embryonic day 17 fetal Sprague-Dawley rats using MTT assay for cell survival, and caspase-3 assay and digital imaging methods for Ca²⁺, Zn²⁺, MMP and ROS. Treatment with Aβ25–35 (20 µM) for 48 h induced neuronal cell death in cultured rat pure hippocampal neurons. Treatment with C3G for 48 h significantly increased cell survival. Pretreatment with C3G for 30 min significantly inhibited Aβ₂₅₋₃₅-induced [Zn²⁺]i increases as well as [Ca²⁺]i increases in the cultured rat hippocampal neurons. C3G also significantly inhibited Aβ₂₅₋₃₅-induced mitochondrial depolarization. C3G also blocked the Aβ₂₅₋₃₅-induced formation of ROS. In addition, C3G significantly inhibited the Aβ₂₅₋₃₅-induced activation of caspase-3. These results suggest that cyanidin-3-glucoside protects against amyloid β-induced neuronal cell death by reducing multiple apoptotic signals.

Black Rice (Oryza sativa L., Poaceae) Extract Reduces Hippocampal Neuronal Cell Death Induced by Transient Global Cerebral Ischemia in Mice

Rice is the most commonly consumed grain in the world. Black rice has been suggested to contain various bioactive compounds including anthocyanin antioxidants. There is currently little information about the nutritional benefits of black rice on brain pathology. Here, we investigated the effects of black rice (Oryza sativa L., Poaceae) extract (BRE) on the hippocampal neuronal damage induced by ischemic insult. BRE (300 mg/kg) was orally administered to adult male C57BL/6 mice once a day for 21 days. Bilateral common carotid artery occlusion (BCCAO) was performed for 23 min on the 8th day of BRE or vehicle administration. Histological analyses conducted on the 22nd day of BRE or vehicle administration revealed that administering BRE profoundly attenuated neuronal cell death, inhibited reactive astrogliosis, and prevented loss of glutathione peroxidase expression in the hippocampus when compared to vehicle treatment. In addition, BRE considerably ameliorated BCCAO-induced memory impairment on the Morris water maze test from the 15th day to the 22nd day of BRE or vehicle administration. These results indicate that chronic administration of BRE is potentially beneficial in cerebral ischemia.

Brief low Mg2+o-induced Ca2+ spikes inhibit subsequent prolonged exposure-induced excitotoxicity in cultured rat hippocampal neurons

Reducing [Mg2+]o to 0.1 mM can evoke repetitive [Ca2+]i spikes and seizure activity, which induces neuronal cell death in a process called excitotoxicity. We examined the issue of whether cultured rat hippocampal neurons preconditioned by a brief exposure to 0.1 mM [Mg2+]o are rendered resistant to excitotoxicity induced by a subsequent prolonged exposure and whether Ca2+ spikes are involved in this process. Preconditioning by an exposure to 0.1 mM [Mg2+]o for 5 min inhibited significantly subsequent 24 h exposure-induced cell death 24 h later (tolerance). Such tolerance was prevented by both the NMDA receptor antagonist D-AP5 and the L-type Ca2+ channel antagonist nimodipine, which blocked 0.1 mM [Mg2+]o-induced [Ca2+]i spikes. The AMPA receptor antagonist NBQX significantly inhibited both the tolerance and the [Ca2+]i spikes. The intracellular Ca2+ chelator BAPTA-AM significantly prevented the tolerance. The nonspecific PKC inhibitor staurosporin inhibited the tolerance without affecting the [Ca2+]i spikes. While Go6976, a specific inhibitor of PKCalpha had no effect on the tolerance, both the PKCepsilon translocation inhibitor and the PKCzeta pseudosubstrate inhibitor significantly inhibited the tolerance without affecting the [Ca2+]i spikes. Furthermore, JAK-2 inhibitor AG490, MAPK kinase inhibitor PD98059, and CaMKII inhibitor KN-62 inhibited the tolerance, but PI-3 kinase inhibitor LY294,002 did not. The protein synthesis inhibitor cycloheximide significantly inhibited the tolerance. Collectively, these results suggest that low [Mg2+]o preconditioning induced excitotoxic tolerance was directly or indirectly mediated through the [Ca2+]i spike-induced activation of PKCepsilon and PKCxi, JAK-2, MAPK kinase, CaMKII and the de novo synthesis of proteins.

Cyanidin-3-glucoside Inhibits ATP-induced Intracellular Free Ca2+ Concentration, ROS Formation and Mitochondrial Depolarization in PC12 Cells

Flavonoids have an ability to suppress various ion channels. We determined whether one of flavonoids, cyanidin-3-glucoside, affects adenosine 5'-triphosphate (ATP)-induced calcium signaling using digital imaging methods for intracellular free Ca2+ concentration ([Ca2+]i), reactive oxygen species (ROS) and mitochondrial membrane potential in PC12 cells. Treatment with ATP (100microM) for 90 sec induced [Ca2+]i increases in PC12 cells. Pretreatment with cyanidin-3-glucoside (1micro g/ml to 100microg/ml) for 30 min inhibited the ATP-induced [Ca2+]i increases in a concentration-dependent manner (IC50=15.3microg/ml). Pretreatment with cyanidin-3-glucoside (15microg/ml) for 30 min significantly inhibited the ATP-induced [Ca2+]i responses following removal of extracellular Ca2+ or depletion of intracellular [Ca2+]i stores. Cyanidin-3-glucoside also significantly inhibited the relatively specific P2X2 receptor agonist 2-MeSATP-induced [Ca2+]i responses. Cyanidin-3-glucoside significantly inhibited the thapsigargin or ATP-induced store-operated calcium entry. Cyanidin-3-glucoside significantly inhibited the ATP-induced [Ca2+]i responses in the presence of nimodipine and omega-conotoxin. Cyanidin-3-glucoside also significantly inhibited KCl (50 mM)-induced [Ca2+]i increases. Cyanidin-3-glucoside significantly inhibited ATP-induced mitochondrial depolarization. The intracellular Ca2+ chelator BAPTA-AM or the mitochondrial Ca2+ uniporter inhibitor RU360 blocked the ATP-induced mitochondrial depolarization in the presence of cyanidin-3-glucoside. Cyanidin-3-glucoside blocked ATP-induced formation of ROS. BAPTA-AM further decreased the formation of ROS in the presence of cyanidin-3-glucoside. All these results suggest that cyanidin-3-glucoside inhibits ATP-induced calcium signaling in PC12 cells by inhibiting multiple pathways which are the influx of extracellular Ca2+ through the nimodipine and omega-conotoxin-sensitive and -insensitive pathways and the release of Ca2+ from intracellular stores. In addition, cyanidin-3-glucoside inhibits ATP-induced formation of ROS by inhibiting Ca2+-induced mitochondrial depolarization.