Jin Bong Park

Carbon nanotubes synthesized by Ni-assisted atmospheric pressure thermal chemical vapor deposition

A detailed systematic study on the growth morphology of carbon nanotubes (CNTs) on Si in atmospheric pressure thermal chemical vapor deposition was undertaken. The role of NH3 for vertical alignment of CNTs was investigated. The direct cause for the alignment was a dense distribution of the catalytic metal particles, but that the particles are maintained catalytically active under amorphous carbon deposits was established by NH3. It allows a dense nucleation of the CNTs, and consequently, assists vertical alignment through entanglement and mechanical leaning among the tubes. The CNTs grew in a base growth mode. Since Ni is consumed both by silicide reaction and by capture into the growing tube, the growth stops when Ni is totally depleted. It occurs earlier for smaller particles, and thus a long time of growth results in a thin bottom with poor adhesion.

Effect of Korea red ginseng on the blood pressure in conscious hypertensive rats.

The change of blood pressure and heart rate after intravenous injection of Korea red ginseng (KRG) were studied in the conscious normotensive and one-kidney, one-clip Goldblatt hypertensive (1K, 1C-GBH) rats. Crude saponin (CS) of KRG (50, 100 mg/kg i.v.) induced a hypotensive effect and bradycardia in a dose-dependent manner in the anesthetized rats. On the other hand, CS of KRG (100 mg/kg) induced a hypotensive effect and reflex tachycardia in the conscious rats. Saponin-free fraction (SFF) of KRG did not affect them in the anesthetized normotensive rats (P>.05). The maximal hypotensive effect by CS of KRG in the conscious 1K, 1C-GBH hypertensive rats and L-nitroarginine methyl ester (L-NAME, 40 mg/kg)-treated conscious hypertensive rats was not different from that of conscious normotensive rats (Delta 31.6+/-6.3, Delta 27.5+/-5.8 vs. Delta 26.7+/-4.3 mmHg, P>.05). However, pretreatment of L-NAME significantly inhibited the reflex tachycardia by CS of KRG (70.8+/-7.0 vs. 30.6+/-15.0 bpm, P<.05). Hemolysate-sensitive nitric oxide (NO) current by the CS of KRG was greater than that of the SFF of KRG (651.9+/-128.2 pA for CS and 164.9+/-92.5 pA for SFF, P<.001). These findings suggest that KRG has a hypotensive effect and its effect may be due to saponin fraction of KRG in the conscious rats. The releasing effect of NO of KRG, like NO donor, may be partly contributed to the hypotensive effect of KRG.

Endoplasmic reticulum stress response is involved in Mycobacterium tuberculosis protein ESAT‐6‐mediated apoptosis

Mycobacterium tuberculosis (Mtb) infection leads to the induction of the apoptotic response, which is associated with bacilli killing. The early secreted mycobacterial antigen ESAT‐6 of Mtb has been shown to induce apoptosis in human macrophages and epithelial cells. In the present study, we demonstrate that the stimulation of human epithelial A549 cells by ESAT‐6 induces the endoplasmic reticulum (ER) stress response. We observed that ESAT‐6 treatment increases intracellular Ca2+ concentration, which results in ROS accumulation, and therefore induces the onset of ER stress‐induced apoptosis. Our results uncover a novel apoptotic mechanism of ESAT‐6 through ER stress responses in pathologic conditions such as tuberculosis.

Mycobacterium abscessus activates the NLRP3 inflammasome via Dectin-1–Syk and p62/SQSTM1

Numerous atypical mycobacteria, including Mycobacterium abscessus (Mabc), cause nontuberculous mycobacterial infections, which present a serious public health threat. Inflammasome activation is involved in host defense and the pathogenesis of autoimmune diseases. However, inflammasome activation has not been widely characterized in human macrophages infected with atypical mycobacteria. Here, we demonstrate that Mabc robustly activates the nucleotide binding and oligomerization domain‐like receptor family pyrin domain containing 3 (NLRP3) inflammasome via dectin‐1/Syk‐dependent signaling and the cytoplasmic scaffold protein p62/SQSTM1 (p62) in human macrophages. Both dectin‐1 and Toll‐like receptor 2 (TLR2) were required for Mabc‐induced mRNA expression of pro‐interleukin (IL)‐1β, cathelicidin human cationic antimicrobial protein‐18/LL‐37 and β‐defensin 4 (DEFB4). Dectin‐1‐dependent Syk signaling, but not that of MyD88, led to the activation of caspase‐1 and secretion of IL‐1β through the activation of an NLRP3/apoptosis‐associated speck‐like protein containing a caspase recruitment domain (ASC) inflammasome. Additionally, potassium efflux was required for Mabc‐induced NLRP3/ASC inflammasome activation. Furthermore, Mabc‐induced p62 expression was critically involved in NLRP3 inflammasome activation in human macrophages. Finally, NLRP3/ASC was critical for the inflammasome in antimicrobial responses to Mabc infection. Taken together, these data demonstrate the induction mechanism of the NLRP3/ASC inflammasome and its role in innate immunity to Mabc infection.

Midazolam inhibits proinflammatory mediators in the lipopolysaccharide-activated macrophage.

Background:Midazolam, a benzodiazepine, has a hypnotic effect and is widely used as a sedative. The role of midazolam in activation of macrophages during sepsis is not known. The aim of this study was to evaluate the antiinflammatory actions of midazolam in cultured macrophages. Methods:Using a macrophage cell line, RAW264.7 cells, the effect of midazolam on proinflammatory mediators and activation of mitogen-activated protein kinase was measured by Western blot. Nuclear factor-&kgr;B (NF-&kgr;B) activation and translocation of p65 subunit of NF-&kgr;B was measured using luciferase assay and immunocytochemistry. Superoxide production was measured by lucigenin chemiluminescence. Results:Midazolam significantly inhibited lipopolysaccharide-induced up-regulation of both cyclooxygenase 2 and inducible nitric oxide synthase in a dose-dependent manner (approximately 3–30 &mgr;m). I&kgr;B-α degradation and NF-&kgr;B transcriptional activity induced by lipopolysaccharide were also suppressed by the midazolam. Nuclear translocation of the p65 subunit of NF-&kgr;B was inhibited by midazolam. Furthermore, midazolam suppressed phosphorylation of p38 mitogen-activated protein kinase and also inhibited lipopolysaccharide-induced superoxide production in macrophages. Conclusions:These results suggest that midazolam has an antiinflammatory action by inhibiting inducible nitric oxide synthase and cyclooxygenase-2 expression, possibly through suppression of NF-&kgr;B and p38 mitogen-activated protein kinase activation.

Tonic Extrasynaptic GABAA Receptor Currents Control Gonadotropin-Releasing Hormone Neuron Excitability in the Mouse

It is well established that the GABA(A) receptor plays an important role in regulating the electrical excitability of GnRH neurons. Two different modes of GABA(A) receptor signaling exist: one mediated by synaptic receptors generating fast (phasic) postsynaptic currents and the other mediated by extrasynaptic receptors generating a persistent (tonic) current. Using GABA(A) receptor antagonists picrotoxin, bicuculline methiodide, and gabazine, which differentiate between phasic and tonic signaling, we found that ∼50% of GnRH neurons exhibit an approximately 15-pA tonic GABA(A) receptor current in the acute brain slice preparation. The blockade of either neuronal (NO711) or glial (SNAP-5114) GABA transporter activity within the brain slice revealed the presence of tonic GABA signaling in ∼90% of GnRH neurons. The GABA(A) receptor δ subunit is only found in extrasynaptic GABA(A) receptors. Using single-cell RT-PCR, GABA(A) receptor δ subunit mRNA was identified in GnRH neurons and the δ subunit-specific agonist 4,5,6,7-tetrahydroisoxazolo [5,4-c] pyridin-3-ol was found to activate inward currents in GnRH neurons. Perforated-patch clamp studies showed that 4,5,6,7-tetrahydroisoxazolo [5,4-c] pyridin-3-ol exerted the same depolarizing or hyperpolarizing effects as GABA on juvenile and adult GnRH neurons and that tonic GABA(A) receptor signaling regulates resting membrane potential. Together, these studies reveal the presence of a tonic GABA(A) receptor current in GnRH neurons that controls their excitability. The level of tonic current is dependent, in part, on neuronal and glial GABA transporter activity and mediated by extrasynaptic δ subunit-containing GABA(A) receptors.

Reduction in synaptic GABA release contributes to target-selective elevation of PVN neuronal activity in rats with myocardial infarction

Neuronal activity in the paraventricular nucleus (PVN) is known to be elevated in rats with heart failure. However, the type of neurons involved and the underlying synaptic mechanisms remain unknown. Here we examined spontaneous firing activity and synaptic currents in presympathetic PVN neurons in rats with myocardial infarction (MI), using slice patch clamp combined with the retrograde labeling technique. In PVN neurons projecting to the rostral ventrolateral medulla (PVN-RVLM), MI induced a significant increase in basal firing rate (1.79 to 3.02 Hz, P < 0.05) and a reduction in the frequency of spontaneous (P < 0.05) and miniature (P < 0.01) inhibitory postsynaptic currents (IPSCs). In addition, MI induced an increase in the paired-pulse ratio of evoked IPSCs (P < 0.05). Bicuculline, a GABA(A) receptor antagonist, increased the firing rate of PVN-RVLM neurons in sham-operated (1.21 to 2.74 Hz, P < 0.05) but not MI (P > 0.05) rats. In contrast, in PVN neurons projecting to the intermediolateral horn of the spinal cord (PVN-IML), MI did not induce any significant changes in the basal firing rate and the properties of spontaneous and miniature IPSCs. The properties of spontaneous excitatory postsynaptic currents (EPSCs) were not altered in either neuron group. In conclusion, our results indicate that MI induces an elevation of firing activity in PVN-RVLM but not in PVN-IML neurons and that the elevated firing rate is largely due to a decrease in GABA release. These results provide evidence for a novel target-selective synaptic plasticity in the PVN that is associated with the sympathetic hyperactivity commonly seen in heart failure.

Peripheral benzodiazepine receptor regulates vascular endothelial activations via suppression of the voltage-dependent anion channel-1

Peripheral benzodiazepine receptor (PBR) is a multifunctional protein mainly found on the outer mitochondrial membrane. PBR expression is increased by tumor necrosis factor‐α (TNF‐α) in endothelial cells. Adenoviral overexpression of PBR inhibits monocyte adhesion, VCAM‐1, and ICAM‐1 expression in TNF‐α‐activated endothelial cells. Rotenone, cyclosporine A, and bongkrekic acid suppress TNF‐α‐induced VCAM‐1 expression. Overexpression of PBR inhibits voltage‐dependent anion channel‐1 (VDAC‐1) expression and the silencing of PBR increases VDAC‐1 expression in endothelial cells. Moreover, TNF‐α‐induced VCAM‐1 expression is suppressed by VDAC‐1 gene silencing. PBR overexpression significantly decreases TNF‐α‐induced mitochondrial reactive oxygen species and MnSOD expression. These results suggest that PBR can inhibit endothelial activation and this action is related to the inhibition of mitochondrial ROS and/or VDAC‐1 expression in endothelial cells.

Apurinic/apyrimidinic endonuclease 1 inhibits protein kinase C-mediated p66shc phosphorylation and vasoconstriction

AIMS Phosphorylation of the adaptor protein p66shc is essential for p66shc-mediated oxidative stress. We investigated the role of the reducing protein/DNA repair enzyme apurinic/apyrimidinic endonuclease1 (APE1) in modulating protein kinase CβII (PKCβII)-mediated p66shc phosphorylation in cultured endothelial cells and PKC-mediated vasoconstriction of arteries. METHODS AND RESULTS Oxidized low-density lipoprotein (oxLDL)induced p66shc phosphorylation at serine 36 residue and PKCβII phosphorylation in mouse endothelial cells. Adenoviral overexpression of APE1 resulted in reduction of oxLDL-induced p66shc and PKCβII phosphorylation. Phorbol 12-myristate 13-acetate (PMA), which stimulates PKCs, induced p66shc phosphorylation and this was inhibited by a selective PKCβII inhibitor. Adenoviral overexpression of PKCβII also increased p66shc phosphorylation. Overexpression of APE1 suppressed PMA-induced p66shc phosphorylation. Moreover, PMA-induced p66shc phosphorylation was augmented in cells in which APE1 was knocked down. PMA increased cytoplasmic APE1 expression, compared with the basal condition, suggesting the role of cytoplasmic APE1 against p66shc phosphorylation. Finally, vasoconstriction induced by phorbol-12,13, dibutylrate, another PKC agonist, was partially inhibited by transduction of Tat-APE1 into arteries. CONCLUSION APE1 suppresses oxLDL-induced p66shc activation in endothelial cells by inhibiting PKCβII-mediated serine phosphorylation of p66shc, and mitigates vasoconstriction induced by activation of PKC.

COMP-Ang1 ameliorates leukocyte adhesion and reinforces endothelial tight junctions during endotoxemia

Endotoxemia is characterized by multiple dysfunctions of the micro-vascular endothelium. Of these, vascular leakage is an initial event that aggravates vascular dysfunction can lead to systemic vascular collapse and organ failure. Thus, prevention of vascular leakage may ameliorate endotoxin-induced dysfunctions of blood vessels. Here we examine the effect of an angiopoietin-1 variant, COMP-Ang1, on endotoxin-induced vascular leakage in mice. COMP-Ang1 significantly reduced endotoxin-induced vascular leakage in the lung, heart, and kidney, but not in liver or intestine. Interestingly, COMP-Ang1 attenuated endotoxin-induced lung damage, presumably due to reduced infiltration of macrophages. Moreover, COMP-Ang1 restored the level of PECAM-1 expression, which is significantly reduced by endotoxin challenge. This study suggests that COMP-Ang1 reduces endotoxin-induced vascular leakage by restoration of cellular junctions and subsequent attenuation of leukocyte infiltration.