Neuroprotective Effects of Methanol Extracts of Jeju Native Plants on Hydrogen Peroxide-induced Cytotoxicity in SH-SY5Y Human Neuroblastoma Cells

공필재,김유미,이희제,김성수,유은숙,전완주 대한약리학회 2007 The Korean Journal of Physiology & Pharmacology Vol.11 No.5

Neuronal death is a common characteristic hallmark of a variety of neurodegenerative disorders including Alzheimer's disease and Parkinson's disease. However, there have been no effective drugs to successfully prevent neuronal death in those diseases, whereas oriental medicinal plants have to possess valuable therapeutic potentials to treat neurodegenerative diseases. In the present study, in an attempt to provide neuroprotective agents from natural plants, 80% methanol extracts of a wide range of medicinal plants, which are native to Jeju Island in Korea, were prepared and their protective effects on hydrogen peroxide-induced apoptotic cell death were examined. Among those tested, extracts from Smilax china and Saururus chinesis significantly decreased hydrogen peroxide-induced apoptotic cell death. The extracts attenuated hydrogen peroxide (H2O2)-induced caspase-3 activation in a dose-dependent manner. Further, plant extracts restored H2O2-induced depletion of intracellular glutathione, a major endogenous antioxidant. The data suggest that Jeju native medicinal plants could potentially be used as therapeutic agents for treating or preventing neurodegenerative diseases in which oxidative stress is implicated.

Melatonin Induces Akt Phosphorylation through Melatonin Receptor- and PI3K-Dependent Pathways in Primary Astrocytes

공필재,변종선,임소영,이재준,홍성준,권광준,김성수 대한약리학회 2008 The Korean Journal of Physiology & Pharmacology Vol.12 No.2

Melatonin has been reported to protect neurons from a variety of neurotoxicity. However, the underlying mechanism by which melatonin exerts its neuroprotective property has not yet been clearly understood. We previously demonstrated that melatonin protected kainic acid-induced neuronal cell death in mouse hippocampus, accompanied by sustained activation of Akt, a critical mediator of neuronal survival. To further elucidate the neuroprotective action of melatonin, we examined in the present study the causal mechanism how Akt signaling pathway is regulated by melatonin in a rat primary astrocyte culture model. Melatonin resulted in increased astrocytic Akt phosphorylation, which was significantly decreased with wortmannin, a specific inhibitor of PI3K, suggesting that activation of Akt by melatonin is mediated through the PI3K-Akt signaling pathway. Furthermore, increased Akt activation was also significantly decreased with luzindole, a non-selective melatonin receptor antagonist. As downstream signaling pathway of Akt activation, increased levels of CREB phoshorylation and GDNF expression were observed, which were also attenuated with wortmannin and luzindole. These results strongly suggest that melatonin exerts its neuroprotective property in astrocytes through the activation of plasma membrane receptors and then PI3K-Akt signaling pathway. Melatonin has been reported to protect neurons from a variety of neurotoxicity. However, the underlying mechanism by which melatonin exerts its neuroprotective property has not yet been clearly understood. We previously demonstrated that melatonin protected kainic acid-induced neuronal cell death in mouse hippocampus, accompanied by sustained activation of Akt, a critical mediator of neuronal survival. To further elucidate the neuroprotective action of melatonin, we examined in the present study the causal mechanism how Akt signaling pathway is regulated by melatonin in a rat primary astrocyte culture model. Melatonin resulted in increased astrocytic Akt phosphorylation, which was significantly decreased with wortmannin, a specific inhibitor of PI3K, suggesting that activation of Akt by melatonin is mediated through the PI3K-Akt signaling pathway. Furthermore, increased Akt activation was also significantly decreased with luzindole, a non-selective melatonin receptor antagonist. As downstream signaling pathway of Akt activation, increased levels of CREB phoshorylation and GDNF expression were observed, which were also attenuated with wortmannin and luzindole. These results strongly suggest that melatonin exerts its neuroprotective property in astrocytes through the activation of plasma membrane receptors and then PI3K-Akt signaling pathway.

Comparison of Inhibitory Potency of Various Antioxidants on the Activation of BV2 Microglial Cell Lines Induced by LPS

공필재,박종익,권오윤,한윤희,김수영,이수남,손희종,김성수 대한약리학회 2007 The Korean Journal of Physiology & Pharmacology Vol.11 No.1

Antioxidant properties have been proposed as a mechanism for the putative anti-inflammatory effects of phenolic compounds. To reveal the relationship between antioxidant activity and anti-inflammatory effects of various antioxidants, we measured 1, 1-diphenyl-2-picryhydrazyl (DPPH)-reducing activity and examined the inhibitory effects on LPS-induced inflammation-related gene expression in the BV2 microglial cell line. Lipopolysaccharide (LPS) (0.2μg/ml) was used with or without antioxidants to treat cells, and the regulation of iNOS and cytokine gene expression was monitored using an RNase protection assay (RPA). Although, all tested antioxidants had similar DPPH-reducing activity and inhibited nitrite production, but the curcuminoid antioxidants (ferulic acid, caffeic acid, and curcumin) inhibited LPS-induced gene expression (iNOS, TNF-α, IL-1β, IL-6, and IL-1 Ra) in a concentration-dependent manner. Other tested antioxidants did not exhibit the same effects; N-acetylcysteine (NAC) only began to suppress IL-1β gene expression just below the concentration at which cytotoxicity occurred. Moreover, the antioxidant potency of curcuminoids appeared to have no correlation with anti- inflammatory potency. Only curcumin could inhibit LPS-induced microglial activation at a micromolar level. These data suggest that curcumin may be a safe antioxidant possessing anti-inflammatory activity.

Inhibition of eNOS/sGC/PKG Pathway Decreases Akt Phosphorylation Induced by Kainic Acid in Mouse Hippocampus

이상현,변종선,공필재,이희제,김덕경,손종희,이재준,임소영,김성수,전완주,김해성 대한약리학회 2010 The Korean Journal of Physiology & Pharmacology Vol.14 No.1

The serine/threonine kinase Akt has been shown to play a role of multiple cellular signaling pathways and act as a transducer of many functions initiated by growth factor receptors that activate phosphatidylinositol 3-kinase (PI3K). It has been reported that phosphorylated Akt activates eNOS resulting in the production of NO and that NO stimulates soluble guanylate cyclase (sGC), which results in accumulation of cGMP and subsequent activation of the protein kinase G (PKG). It has been also reported that PKG activates PI3K/Akt signaling. Therefore, it is possible that PI3K, Akt, eNOS, sGC, and PKG form a loop to exert enhanced and sustained activation of Akt. However, the existence of this loop in eNOS-expressing cells, such as endothelial cells or astrocytes, has not been reported. Thus, we examined a possibility that Akt phosphorylation might be enhanced via eNOS/ sGC/PKG/PI3K pathway in astrocytes in vivo and in vitro. Phosphorylation of Akt was detected in astrocytes after KA treatment and was maintained up to 72 h in mouse hippocampus. 2 weeks after KA treatment, astrocytic Akt phosphorylation was normalized to control. The inhibition of eNOS, sGC, and PKG significantly decreased Akt and eNOS phosphorylation induced by KA in astrocytes. In contrast, the decreased phosphorylation of Akt and eNOS by eNOS inhibition was significantly reversed with PKG activation. The above findings in mouse hippocampus were also observed in primary astrocytes. These data suggest that Akt/eNOS/sGC/PKG/PI3K pathway may constitute a loop, resulting in enhanced and sustained Akt activation in astrocytes.