Jae-Hoon Bae

The green tea polyphenol (−)-epigallocatechin gallate attenuates β-amyloid-induced neurotoxicity in cultured hippocampal neurons

Abstract Previous evidence has indicated that the neuronal toxicity of amyloid β (βA) protein is mediated through oxygen free radicals and can be attenuated by antioxidants and free radical scavengers. Recent studies have shown that green tea polyphenols reduced free radical-induced lipid peroxidation. The purpose of this study was to investigate whether (−)-epigallocatechin gallate (EGCG) would prevent or reduce the death of cultured hippocampal neuronal cells exposed to βA because EGCG has a potent antioxidant property as a green tea polyphenol. Following exposure of the hippocampal neuronal cells to βA for 48 hours, a marked hippocampal neuronal injuries and increases in malondialdehyde (MDA) level and caspase activity were observed. Co-treatment of cells with EGCG to βA exposure elevated the cell survival and decreased the levels of MDA and caspase activity. Proapoptotic (p53 and Bax), Bcl-XL and cyclooxygenase (COX) proteins have been implicated in βA-induced neuronal death. However, in this study the protective effects of EGCG seem to be independent of the regulation of p53, Bax, Bcl-XL and COX proteins. Taken together, the results suggest that EGCG has protective effects against βA-induced neuronal apoptosis through scavenging reactive oxygen species, which may be beneficial for the prevention of Alzheimers disease.

Fluoxetine increases the nitric oxide production via nuclear factor kappa B-mediated pathway in BV2 murine microglial cells

A body of recent evidence implicates that antidepressants affect the inflammatory response and immune system. The present study is focused on the effects of the most widely used antidepressant agent, fluoxetine on the production of nitric oxide (NO) in BV2 microglial cells. In this study, we observed interesting result that NO production was increased by fluoxetine. The mRNA level of nitric oxide synthase (iNos, Nos2) by RT-PCR was also stimulated by fluoxetine. We next conducted electophoretic mobility shift assay (EMSA) to determine the DNA binding activity of nuclear factor kappa B (Nfkappab), an important upstream modulator for Nos2 expression, to find that fluoxetine increased DNA binding activity of Nfkappab. By Western blot analysis, phosphorylation levels of p38 mitogen-activated protein kinase (p38 Mapk, Mapk14) and extracellular signal-related kinase (Erk)1/2 Mapk, upstream signaling mediators of Nfkappab were found to be increased by fluoxetine. In addition, the mRNA expressions of other proinflammatory cytokines, interleukin 6 (Il6) and tumor necrosis factor alpha (Tnfalpha) were examined. The expressions of both Il6 and Tnfalpha by fluoxetine treatment were similar to those of Nos2 and Nfkappab. Taken together, our results show that fluoxetine stimulates NO production via Nfkappab-mediated pathway in BV2 cells.

Manganese induces inducible nitric oxide synthase (iNOS) expression via activation of both MAP kinase and PI3K/Akt pathways in BV2 microglial cells

It is well documented that manganese neurotoxicity induces clinical symptoms similar to those of idiopathic Parkinsons disease. Although microglial cytotoxic mediator-induced neurotoxicity is suggested, the mechanism by which manganese up-regulates cytotoxic mediator, such as nitric oxide (NO), remains poorly understood. Therefore, in this study, we investigated the mechanism of manganese on induction of iNOS in microglial cells. iNOS promoter/luciferase assay revealed that manganese (500 (M) regulated the iNOS expression at the transcriptional level. Immunoblot analysis also revealed that phosphorylation levels of ERK, JNK MAPKs and Akt (PKB, PI 3-kinase downstream effector), were increased. Both protein and mRNA levels of iNOS expression were abrogated by specific inhibitors, SP600125 (JNK inhibitor, 20 microM), PD98059 (ERKs inhibitor, 50 microM), or LY294002 (PI 3-kinase inhibitor, 20 microM), but not by SB203580 (20 microM), a p38 specific inhibitor. These data lead to the conclusion that manganese regulates the iNOS expression at the transcriptional level in BV2 microglial cells and the increased iNOS protein expression is mediated via both JNK-ERK MAPK and PI3K/Akt signaling pathways, but not via p38 MAPK pathway. Increased iNOS protein level was also found in RAW264.7 murine macrophage cells.

Glucagon-Like Peptide-1 Enhances Glucokinase Activity in Pancreatic β-Cells through the Association of Epac2 with Rim2 and Rab3A

Glucokinase (GK), which phosphorylates D-glucose, is a major glucose sensor in β-cells for glucose-stimulated insulin secretion (GSIS) and is a promising new drug target for type 2 diabetes (T2D). In T2D, pancreatic β-cells exhibit defective glucose sensitivity, which leads to impaired GSIS. Although glucagon-like peptide-1-(7-36)-amide (GLP-1) is known to enhance β-cell glucose sensitivity, the effect of GLP-1 on GK activity is still unknown. The present study demonstrated that GLP-1 pretreatment for 30 min significantly enhanced GK activity in a glucose-dependent manner, with a lower Michaelis-Menten constant (K(m)) but unchanged maximal velocity (V(max)). Thus, GLP-1 acutely enhanced cellular glucose uptake, mitochondrial membrane potential, and cellular ATP levels in response to glucose in rat INS-1 and native β-cells. This effect of GLP-1 occurred via its G protein-coupled receptor pathway in a cAMP-dependent but protein kinase A-independent manner with evidence of exchange protein activated by cAMP (Epac) involvement. Silencing Epac2, interacting molecule of the small G protein Rab3 (Rim2), or Ras-associated protein Rab3A (Rab3A) significantly blocked the effect of GLP-1. These results suggested that GLP-1 can further potentiate GSIS by enhancing GK activity through the signaling of Epac2 to Rim2 and Rab3A, which is the similar pathway for GLP-1 to potentiate Ca(2+)-dependent insulin granule exocytosis. The present finding may also be an important mechanism of GLP-1 for recovery of GSIS in T2D.

Bone Marrow-Derived Mesenchymal Stem Cells Prevent the Loss of Niemann-Pick Type C Mouse Purkinje Neurons by Correcting Sphingolipid Metabolism and Increasing Sphingosine-1-phosphate†‡§

Niemann‐Pick type C (NP‐C) disease exhibits neuronal sphingolipid storage and cerebellar Purkinje neuron (PN) loss. Although it is clear that PNs are compromised in this disorder, it remains to be defined how neuronal lipid storage causes the PN loss. Our previous studies have shown that bone marrow‐derived mesenchymal stem cells (BM‐MSCs) transplantation prevent PN loss in NP‐C mice. The aim of the present study was therefore to examine the neuroprotective mechanism of BM‐MSCs on PNs. We found that NP‐C PNs exhibit abnormal sphingolipid metabolism and defective lysosomal calcium store compared to wild‐type mice PNs. BM‐MSCs promote the survival of NP‐C PNs by correction of the altered calcium homeostasis, restoration of the sphingolipid imbalance, as evidenced by increased sphingosine‐1‐phosphate levels and decreased sphingosine, and ultimately, inhibition of apoptosis pathways. These effects suggest that BM‐MSCs modulate sphingolipid metabolism of endogenous NP‐C PNs, resulting in their survival and improved clinical outcome in mice. STEM CELLS 2010;28:821–83128:821–831

Melatonin ameliorates ER stress-mediated hepatic steatosis through miR-23a in the liver.

The endoplasmic reticulum (ER) stress induces hepatic steatosis and inflammation in the liver. Although melatonin ameliorates ER stress-target genes, it remains unknown whether melatonin protects against hepatic steatosis as well as inflammation through regulation of miRNA. MicroRNAs have been identified as pivotal regulators in the field of gene regulation and their dysfunctions are a common feature in a variety of metabolic diseases. Especially, among miRNAs, miR-23a has been shown to regulate ER stress. Herein, we investigated the crucial roles of melatonin in hepatic steatosis and inflammation in vivo. Tunicamycin challenge caused increase of hepatic triglyceride and intracellular calcium levels through activation of ER stress, whereas these phenomena were partially disrupted by melatonin. We also demonstrated that expression of miR-23a stimulated with tunicamycin was rescued by melatonin treatment, resulting in reduced ER stress in primary hepatocytes. Overall, these results suggest a new function of melatonin that is involved in ameliorating ER stress-induced hepatic steatosis and inflammation by attenuating miR-23a. Melatonin may be useful as a pharmacological agent to protect against hepatic metabolic diseases due to its ability to regulate expression of miR-23a.

Melatonin prevents pancreatic β‐cell loss due to glucotoxicity: the relationship between oxidative stress and endoplasmic reticulum stress

Prolonged hyperglycemia results in pancreatic β‐cell dysfunction and apoptosis, referred to as glucotoxicity. Although both oxidative and endoplasmic reticulum (ER) stresses have been implicated as major causative mechanisms of β‐cell glucotoxicity, the reciprocal importance between the two remains to be elucidated. The aim of this study was to evaluate the differential effect of oxidative stress and ER stress on β‐cell glucotoxicity, by employing melatonin which has free radical‐scavenging and antioxidant properties. As expected, in β‐cells exposed to prolonged high glucose levels, cell viability and glucose‐stimulated insulin secretion (GSIS) were significantly impaired. Melatonin treatment markedly attenuated cellular apoptosis by scavenging reactive oxygen species via its plasmalemmal receptor‐independent increase in antioxidant enzyme activity. However, treatments with antioxidants alone were insufficient to recover the impaired GSIS. Interestingly, 4‐phenylbutyric acid (4‐PBA), a chemical chaperone that attenuate ER stress by stabilizing protein structure, alleviated the impaired GSIS, but not apoptosis, suggesting that glucotoxicity induces oxidative and ER stress independently. We found that cotreatment of glucotoxic β‐cells with melatonin and 4‐PBA dramatically improved both their survival and insulin secretion. Taken together, these results suggest that ER stress may be the more critical mechanism for prolonged high‐glucose‐induced GSIS impairment, whereas oxidative stress appears to be more critical for the impaired β‐cell viability. Therefore, combinatorial therapy of melatonin with an ER stress modifier may help recover pancreatic β‐cells under glucotoxic conditions in type 2 diabetes.

Anti-cancer properties of glucosamine-hydrochloride in YD-8 human oral cancer cells: Induction of the caspase-dependent apoptosis and down-regulation of HIF-1α.

Evidence suggests anti-tumor activities of glucosamine-hydrochloride (GS-HCl). In the present study, we investigated anti-proliferative, growth suppressive and/or pro-apoptotic effects of GS-HCl on YD-8 human oral squamous cell carcinoma (OSCC) cells. Fundamentally, treatment with GS-HCl strongly inhibited proliferation and induced apoptosis in YD-8 cells, as determined by MTS and DNA fragmentation analyses. Of further note, as measured by Western analyses, GS-HCl treatment led to activation of caspase-3, cytosolic accumulation of cytochrome c, down-regulation of Mcl-1 and HIF-1α, up-regulation of GRP78, an indicator of ER stress, and generation of ROS in YD-8 cells. Importantly, results of pharmacological inhibition studies showed that treatment with z-VAD-fmk, a pan-caspase inhibitor, but not with vitamin E, an anti-oxidant strongly blocked the GS-HCl-induced apoptosis in YD-8 cells. Analyses of additional cell culture works further revealed that GS-HCl had a strong growth suppressive effect on not only YD-8 but also YD-10B and YD-38, two other human OSCC cell lines. These findings collectively demonstrate that GS-HCl has anti-proliferative, anti-survival, and pro-apoptotic effects on YD-8 cells and the effects appear to be mediated via mechanisms associated with the mitochondrial-dependent activation of caspases, down-regulation of Mcl-1, and induction of ER stress. Considering HIF-1α as a tumor angiogenic transcription factor, the ability of GS-HCl to down-regulate HIF-1α in YD-8 cells may further support its anti-cancer property. It is thus suggested that GS-HCl may be used as a potential anti-cancer drug against human OSCC.

Corosolic acid ameliorates acute inflammation through inhibition of IRAK-1 phosphorylation in macrophages.

Corosolic acid (CA), a triterpenoid compound isolated from Lagerstroemia speciosa L. (Banaba) leaves, exerts anti-inflammatory effects by regulating phosphorylation of interleukin receptor- associated kinase (IRAK)-2 via the NF-κB cascade. However, the protective effect of CA against endotoxic shock has not been reported. LPS (200 ng/mL, 30 min) induced phosphorylation of IRAK-1 and treatment with CA (10 μM) significantly attenuated this effect. In addition, CA also reduced protein levels of NLRP3 and ASC which are the main components of the inflammasome in BMDMs. LPS-induced inflammasome assembly through activation of IRAK-1 was down-regulated by CA challenge. Treatment with Bay11-7082, an inhibitor of IκB-α, had no effect on CA-mediated inhibition of IRAK-1 activation, indicating that CA-mediated attenuation of IRAK-1 phosphorylation was independent of NF-κB signaling. These results demonstrate that CA ameliorates acute inflammation in mouse BMDMs and CA may be useful as a pharmacological agent to prevent acute inflammation. [BMB Reports 2016; 49(5): 276-281]

Coffee and health

Most people start their day with a cup of coffee. Many people would also finish their daily work with coffee. As such, coffee drinking is an important part of modern daily life. It has been told that coffee is a driving force for humans to develop science, because it has an alerting effect on the human brain. However, some people report experiencing irregular heartbeat or headaches and are thus reluctant to drink coffee, which suggests individual variation to coffee intolerance. The aim of this review is to briefly summarize the effects of coffee on human health.