Oxygen-glucose deprivation activates 5-lipoxygenase mediated by oxidative stress through the p38 mitogen-activated protein kinase pathway in PC12 cells

Role of Mitochondria in the Regulation of Effector Functions of Granulocytes

Granulocytes (neutrophils, eosinophils, and basophils) are the most abundant circulating cells in the innate immune system. Circulating granulocytes, primarily neutrophils, can cross the endothelial barrier and activate various effector mechanisms to combat invasive pathogens. Eosinophils and basophils also play an important role in allergic reactions and antiparasitic defense. Granulocytes also regulate the immune response, wound healing, and tissue repair by releasing of various cytokines and lipid mediators. The effector mechanisms of granulocytes include the production of reactive oxygen species (ROS), degranulation, phagocytosis, and the formation of DNA-containing extracellular traps. Although all granulocytes are primarily glycolytic and have only a small number of mitochondria, a growing body of evidence suggests that mitochondria are involved in all effector functions as well as in the production of cytokines and lipid mediators and in apoptosis. It has been shown that the production of mitochondrial ROS controls signaling pathways that mediate the activation of granulocytes by various stimuli. In this review, we will briefly discuss the data on the role of mitochondria in the regulation of effector and other functions of granulocytes.

LINC00938 alleviates hypoxia ischemia encephalopathy induced neonatal brain injury by regulating oxidative stress and inhibiting JNK/p38 MAPK signaling pathway

Hypoxic-ischemic encephalopathy (HIE) is an important factor leading to permanent damage of central nervous system (CNS) and even neonatal death. Long non-coding RNAs (lncRNAs) has been shown to get involved in the pathogenesis of nervous system diseases. LINC00938 is an intergenic lncRNA which is reported to be involved in neurodegenerative disease. However, the potential role of LINC00938 in nerve injury of neonatal HIE is undetermined. Here, we found that the expression of LINC00938 in the whole blood of neonates with HIE was downregulated compared with the non-HIE group. Functional study revealed that the expression of LINC00938 was significantly decreased in oxygen-glucose deprivation (OGD)-induced SH-SY5Y. Knockdown of LINC00938 induced the neural cell apoptosis by increased the protein level of Bax, Cleaved-Caspase3 and decreased the expression of Bcl-2. In addition, overexpression of LINC00938 prevented the apoptosis of SH-SY5Y from OGD injury. RNA-seq analysis showed that MAPK signaling was involved in the anti-apoptosis function of LINC00938. LINC00938 knockdown induced the activation of c-Jun-N-terminal kinase (JNK), p38 mitogen-activated protein kinase, and inhibited the activation of ERK signaling. However, LINC00938 play neuroprotective role in OGD-induced SH-SY5Y by suppression the phosphorylation of JNK and p38 MAPK rather than regulation of ERK signaling pathway. Further analyses illustrated that the cell apoptosis of neuronal cell was dependent on the elevation of reactive oxygen species (ROS) and result in mitochondria dysfunction in LINC00938 knockdown SH-SY5Y. Pretreated with ROS inhibitor N-acetylcysteine amide (NACA) dramatically suppressed LINC00938 knockdown induced oxidative stress and mitochondria dysfunction which induced cell apoptosis. In addition, NACA treatment significantly reduced the expression of p-JNK and p-p38 in OGD-induced SH-SY5Y. Furthermore, overexpression of LINC00938 displayed a notably neuroprotective effect by suppress central nervous system cell apoptosis via alleviating oxidative stress in CoCl2-induced hypoxic HIE model of zebrafish. Taken together, these results suggested that LINC00938 can act as a neuroprotective factor to inhibit oxidative stress and apoptosis of CNS under HIE conditions.

Mitochondria-targeted antioxidant SkQ1 inhibits leukotriene synthesis in human neutrophils

Leukotrienes are among the most potent mediators of inflammation, and inhibition of their biosynthesis, is becoming increasingly important in the treatment of many pathologies. In this work, we demonstrated that preincubation of human neutrophils with the mitochondria targeted antioxidant SkQ1 (100 nM) strongly inhibits leukotriene synthesis induced by three different stimuli: the Ca²⁺ ionophore A23187, the chemotactic formyl-peptide fMLP in combination with cytocholasin B, and opsonized zymosan. The SkQ1 analogue lacking the antioxidant quinone moiety (C12TPP) was ineffective, suggesting that mitochondrial production of reactive oxygen species (ROS) is critical for activating of leukotriene synthesis in human neutrophils. The uncoupler of oxidative phosphorylation FCCP also inhibits leukotriene synthesis, indicating that a high membrane potential is a prerequisite for stimulating leukotriene synthesis in neutrophils. Our data show that activation of mitogen-activated protein kinases p38 and ERK1/2, which is important for leukotriene synthesis in neutrophils is a target for SkQ1: 1) the selective p38 inhibitor SB203580 inhibited fMLP-induced leukotriene synthesis, while the ERK1/2 activation inhibitor U0126 suppressed leukotriene synthesis induced by any of the three stimuli; 2) SkQ1 effectively prevents p38 and ERK1/2 activation (accumulation of phosphorylated forms) induced by all three stimuli. This is the first study pointing to the involvement of mitochondrial reactive oxygen species in the activation of leukotriene synthesis in human neutrophils. The use of mitochondria-targeted antioxidants can be considered as a promising strategy for inhibiting leukotriene synthesis and treating various inflammatory pathologies.

5-Lipoxygenase as an emerging target against age-related brain disorders

Neuroinflammation is a common feature of age-related brain disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and cerebral ischemia. 5-lipoxygenase (5-LOX), a proinflammatory enzyme, modulates inflammation by generating leukotrienes. Abnormal activation of 5-LOX and excessive production of leukotrienes have been detected in the development of age-related brain pathology. In this review, we provide an update on the current understanding of 5-LOX activation and several groups of functionally related inhibitors. In addition, the modulatory roles of 5-LOX in the pathogenesis and progression of the age-related brain disorders have been comprehensively highlighted and discussed. Inhibition of 5-LOX activation may represent a promising therapeutic strategy for AD, PD and cerebral ischemia.

The lipid paradox in neuroprogressive disorders: Causes and consequences

Chronic systemic inflammation is associated with an increased risk of cardiovascular disease in an environment of low low-density lipoprotein (LDL) and low total cholesterol and with the pathophysiology of neuroprogressive disorders. The causes and consequences of this lipid paradox are explored. Circulating activated neutrophils can release inflammatory molecules such as myeloperoxidase and the pro-inflammatory cytokines interleukin-1 beta, interleukin-6 and tumour necrosis factor-alpha. Since activated neutrophils are associated with atherosclerosis and cardiovascular disease and with major depressive disorder, bipolar disorder and schizophrenia, it seems reasonable to hypothesise that the inflammatory molecules released by them may act as mediators of the link between systemic inflammation and the development of atherosclerosis in neuroprogressive disorders. This hypothesis is tested by considering the association at a molecular level of systemic inflammation with increased LDL oxidation; increased small dense LDL levels; increased lipoprotein (a) concentration; secretory phospholipase A₂ activation; cytosolic phospholipase A₂ activation; increased platelet activation; decreased apolipoprotein A1 levels and function; decreased paroxonase-1 activity; hyperhomocysteinaemia; and metabolic endotoxaemia. These molecular mechanisms suggest potential therapeutic targets.

CPI-1189 protects neuronal cells from oxygen glucose deprivation/re-oxygenation-induced oxidative injury and cell death

Oxygen glucose deprivation (OGD)/re-oxygenation (OGDR) induces profound oxidative injury and neuronal cell death. It mimics ischemia-reperfusion neuronal injury. CPI-1189 is a novel tumor necrosis factor alpha-inhibiting compound with potential neuroprotective function. Here in SH-SY5Y neuronal cells and primary murine cortical neurons, CPI-1189 pretreatment potently inhibited OGDR-induced viability reduction and cell death. In OGDR-stimulated neuronal cells, p38 phosphorylation was blocked by CPI-1189. In addition, CPI-1189 alleviated OGDR-induced reactive oxygen species production, lipid peroxidation, and glutathione consumption. OGDR-induced neuronal cell apoptosis was also inhibited by CPI-1189 pretreatment. Furthermore, in SH-SY5Y cells and cortical neurons, CPI-1189 alleviated OGDR-induced programmed necrosis by inhibiting mitochondrial p53-cyclophilin D-adenine nucleotide translocase 1 association, mitochondrial depolarization, and lactate dehydrogenase release to the medium. In summary, CPI-1189 potently inhibited OGDR-induced oxidative injury and neuronal cell death.

Acetyl-11-keto-β-boswellic acid prevents testicular torsion/detorsion injury in rats by modulating 5-LOX/LTB4 and p38-MAPK/JNK/Bax/Caspase-3 pathways

AIMS

Testicular torsion/detorsion (T/D) is a critical medical condition that necessitates prompt surgical intervention to avoid testicular atrophy and infertility. The use of natural compounds may protect against the associated detrimental oxidative stress and inflammatory responses. Interestingly, acetyl-11-keto-β-boswellic acid (AKBA), the main active constituent of Boswellia resin, has shown potent inhibitory effect on 5-lipoxygenase enzyme which converts arachidonic acid into inflammatory mediators. Therefore, this study was conducted to assess the protective mechanisms by which AKBA may protect against testicular T/D injury in rats.

MAIN METHODS

Male rats were randomly distributed into five groups: Sham, AKBA (50 mg/kg, p.o.), unilateral testicular T/D, AKBA at two dose levels (25 or 50 mg/kg for 15 successive days) followed by T/D. Histological examination and Johnsen's score were performed to assess testicular injury and perturbations in spermatogenesis. Biochemical parameters included markers of testicular function (serum testosterone), oxidant/antioxidant status (malondialdehyde, glutathione), inflammation (5-lipoxygenase, leukotriene-B4, myeloperoxidase, interleukin-1β, interleukin-6), apoptosis (Bax, Bcl2, caspase-3), DNA integrity (quantitative DNA fragmentation, DNA laddering, PARP-1), energy production (ATP), in addition to p38 MAPK and JNK protein expression.

KEY FINDINGS

In a dose dependent manner, AKBA significantly inhibited testicular T/D-induced upregulation of 5-LOX/LTB4 and p38-MAPK/JNK/Bax pathways and their associated downstream inflammatory and apoptotic cascades. These effects were accompanied with ATP replenishment and DNA preservation, resulting ultimately in salvage of the testis.

SIGNIFICANCE

Unprecedentedly, the present mechanistic study revealed the pathways by which AKBA may inhibit testicular T/D injury and offered a novel protective approach that may attenuate the severity of this condition.

Knockdown of microRNA-17-5p Enhances the Neuroprotective Effect of Act A/Smads Signal Loop After Ischemic Injury

Cerebral ischemic injury is a leading cause of human mortality and disability, seriously threatening human health in the world. Activin A (Act A), as a well-known neuroprotective factor, could alleviate ischemic brain injury mainly through Act A/Smads signaling. In our previous study, a noncanonical Act A/Smads signal loop with self-amplifying property was found, which strengthened the neuroprotective effect of Act A. However, this neuroprotective effect was limited due to the self-limiting behavior mediated by Smad anchor for receptor activation (SARA) protein. It was reported that microRNA-17-5p (miR-17-5p) could suppress the expression of SARA in esophageal squamous cell carcinoma. Thus we proposed that knockdown of miR-17-5p could strengthen the neuroprotective effect of Act A/Smads signal loop through SARA. To testify this hypothesis, oxygen-glucose deficiency (OGD) was introduced to highly differentiated rattus pheochromocytoma (PC12) cells. After the transfection of miR-17-5p mimic or inhibitor, the activity of Act A signal loop was quantified by the expression of phosphorylated Smad3. The results showed that suppression of miR-17-5p up-regulated the expression of SARA protein, which prolonged and strengthened the activity of Act A signaling through increased phosphorylation of downstream Smad3 and accumulation of Act A ligand. Further luciferase assay confirmed that SARA was a direct target gene of miR-17-5p. These practical discoveries will bring new insight on the endogenous neuroprotective effects of Act A signal loop by interfering a novel target: miR-17-5p.

Organotypic Hippocampal Slices as Models for Stroke and Traumatic Brain Injury

Organotypic hippocampal slice cultures (OHSCs) have been used as a powerful ex vivo model for decades. They have been used successfully in studies of neuronal death, microglial activation, mossy fiber regeneration, neurogenesis, and drug screening. As a pre-animal experimental phase for physiologic and pathologic brain research, OHSCs offer outcomes that are relatively closer to those of whole-animal studies than outcomes obtained from cell culture in vitro. At the same time, mechanisms can be studied more precisely in OHSCs than they can be in vivo. Here, we summarize stroke and traumatic brain injury research that has been carried out in OHSCs and review classic experimental applications of OHSCs and its limitations.

Suppression of oxidative stress and 5-lipoxygenase activation by edaravone improves depressive-like behavior after concussion

Brain concussions are a serious public concern and are associated with neuropsychiatric disorders, such as depression. Patients with concussion who suffer from depression often experience distress. Nevertheless, few pre-clinical studies have examined concussion-induced depression, and there is little information regarding its pharmacological management. Edaravone, a free radical scavenger, can exert neuroprotective effects in several animal models of neurological disorders. However, the effectiveness of edaravone in animal models of concussion-induced depression remains unclear. In this study, we examined whether edaravone could prevent concussion-induced depression. Mice were subjected to a weight-drop injury and intravenously administered edaravone (3.0 mg/kg) or vehicle immediately after impact. Serial magnetic resonance imaging showed no abnormalities of the cerebrum on diffusion T1- and T2-weighted images. We found that edaravone suppressed concussion-induced depressive-like behavior in the forced swim test, which was accompanied by inhibition of increased hippocampal and cortical oxidative stress (OS) and suppression of 5-lipoxygenase (5-LOX) translocation to the nuclear envelope in hippocampal astrocytes. Hippocampal OS in concussed mice was also prevented by the nicotinamide adenine dinucleotide phosphate oxidase inhibitor, apocynin, and administration of BWB70C, a 5-LOX inhibitor, immediately and 24 h after injury prevented depressive-like behaviors in concussed mice. Further, antidepressant effects of edaravone were observed in mice receiving 1.0 or 3.0 mg/kg of edaravone immediately after impact, but not at a lower dose of 0.1 mg/kg. This antidepressant effect persisted up to 1 h after impact, whereas edaravone treatment at 3 h after impact had no effect on concussion-induced depressive-like behavior. These results suggest that edaravone protects against concussion-induced depression, and this protection is mediated by suppression of OS and 5-LOX translocation.

Inhibition of neuronal p38α, but not p38β MAPK, provides neuroprotection against three different neurotoxic insults

The p38 mitogen-activated protein kinase (MAPK) pathway plays a key role in pathological glial activation and neuroinflammatory responses. Our previous studies demonstrated that microglial p38α and not the p38β isoform is an important contributor to stressor-induced proinflammatory cytokine upregulation and glia-dependent neurotoxicity. However, the contribution of neuronal p38α and p38β isoforms in responses to neurotoxic agents is less well understood. In the current study, we used cortical neurons from wild-type or p38β knockout mice, and wild-type neurons treated with two highly selective inhibitors of p38α MAPK. Neurons were treated with one of three neurotoxic insults (L-glutamate, sodium nitroprusside, and oxygen-glucose deprivation), and neurotoxicity was assessed. All three stimuli led to neuronal death and neurite degeneration, and the degree of neurotoxicity induced in wild-type and p38β knockout neurons was not significantly different. In contrast, selective inhibition of neuronal p38α was neuroprotective. Our results show that neuronal p38β is not required for neurotoxicity induced by multiple toxic insults, but that p38α in the neuron contributes quantitatively to the neuronal dysfunction responses. These data are consistent with our previous findings of the critical importance of microglia p38α compared to p38β, and continue to support selective targeting of the p38α isoform as a potential therapeutic strategy.

High concentrations of genistein exhibit pro-oxidant effects in primary muscle cells through mechanisms involving 5-lipoxygenase-mediated production of reactive oxygen species

Genistein, a typical soy isoflavone, is an important antioxidant for improving human health and animal production but the compound possesses some pro-oxidant potential. In order to explore the latter, the dose-response relationship of various concentrations of genistein on both cellular proliferation and the redox system were examined. The proliferation of primary muscle cells was promoted by a low concentration of genistein but was inhibited by high concentrations, which also enhanced lipid oxidation and suppressed membrane fluidity. By selecting a high concentration (200 μM) as a pro-oxidant treatment, the mechanism underlying the pro-oxidant function of genistein was then explored. The generation of intracellular reactive oxygen species (ROS) was stimulated by 200 μM genistein, with inhibited expression of NADPH oxidase 4 and cyclooxygenase 1 and 2 as well as increased activity of the glutathione redox system. The cellular expression of 5-lipoxygenase, however, was up-regulated by 200 μM genistein and the addition of 5-lipoxygenase inhibitor (Zileuton) decreased genistein-induced intracellular ROS level, close to that from the addition of the ROS scavenger, N-acetylcysteine. It is concluded that higher concentrations of genistein exert pro-oxidant potential in the primary muscle cells through enhancing ROS production in a 5-lipoxygenase-dependent manner.

Evaluation of the antioxidative properties of lipoxygenase inhibitors

BACKGROUND

Oxidative stress is a component of many pathological conditions including neurodegenerative diseases and inflammation. An important source of reactive oxygen species (ROS) are lipoxygenases (LOX) - enzymes responsible for the metabolism of arachidonic acid and other polyunsaturated fatty acids. LOX inhibitors have a protective effect in inflammatory diseases and in neurodegenerative disorders because of their anti-inflammatory activity. However, the molecular mechanism of the protective action of LOX inhibitors has not yet been fully elucidated.

METHODS

The aim of this study was to compare the antioxidative potential of widely used LOX inhibitors: BWB70C, AA-861, zileuton, baicalein and NDGA. The antioxidative properties were evaluated in cell-free systems. We measured the effect of the tested compounds on iron/ascorbate-induced lipid peroxidation and on carbonyl group formation in the rat brain homogenate. Direct free radical scavenging was analyzed by using DPPH assay.

RESULTS

Our data showed that the inhibitor of all LOXs, i.e., NDGA, 5-LOX inhibitor BWB70C and the inhibitor of 12/15-LOX, baicalein, significantly decreased the level of lipid and protein oxidation. The free radical scavenging activity of these inhibitors was comparable to known ROS scavengers, i.e., resveratrol and trolox. Zileuton (the inhibitor of 5-LOX) slightly prevented lipid and protein oxidation, it also scavenged the DPPH radical. AA-861 (the inhibitor of 5 and 12/15-LOX) slightly protected lipids against Fe/asc-evoked lipid peroxidation at high concentrations, but had no effect on carbonyl group formation and DPPH scavenging.

CONCLUSIONS

Our results indicate that some LOX inhibitors demonstrate potent anti-oxidative, free radical scavenging properties. AA-861, whose antioxidative potential is very weak, may be a specific tool to be used in experimental and perhaps even clinical applications.

The role of cyclooxygenase-derived oxidative stress in surgically induced lymphedema in a mouse tail model

CONTEXT

Oxidative stress may contribute to lymphedema and subsequent tissue damage. However, the causal role of oxidative stress in lymphedema remains unclear.

OBJECTIVE

We attempted to detect and identify the free radicals formed in lymphedema fluid and assessed the protective mechanisms and effects of specific enzyme inhibitors and natural antioxidants.

MATERIALS AND METHODS

To study the level of postsurgical oxidative stress with lymphedema in a mouse tail model, we used an electron spin resonance (ESR) method and an ascorbyl radical's ESR spectrum as an oxidative stress biomarker. The drug-treatment group received an i.p. injection with indomethacin (2 mg/kg), baicalein (15 mg/kg), MK-886 (3 mg/kg), zileuton (6.25 mg/kg), diphenyleneiodonium (DPI; 1 mg/kg), sulforaphane (30 mg/kg), oryzanol (30 mg/kg) or sesamol (30 mg/kg) once daily for 14 d from the day of operation. All animals were sacrificed on day 14.

RESULTS

Administration of indomethacin, sulforaphane, oryzanol and sesamol significantly suppressed both the tail volume (56.9%, 77.8%, 72.2% and 38.1% inhibition, respectively, p < 0.01) and ascorbyl radical signals (31.4%, 54.5%, 79.3% and 57.1% inhibition, respectively, p < 0.01), compared with the control mice. No significant differences were found between any of the baicalein, MK-886, or zileuton groups compared with the control. DPI suppressed the tail volume (25.9% inhibition, p < 0.01) but not the ascorbyl radical signals.

CONCLUSION

This study showed that COX-derived oxidative stress plays a major role in the pathological mechanisms of surgically induced lymphedema. Indomethacin, sulforaphane, oryzanol and sesamol exhibit potent protective properties against surgically induced lymphedema.

Volume-sensitive release of organic osmolytes in the human lung epithelial cell line A549: role of the 5-lipoxygenase

Pathophysiological conditions challenge cell volume homeostasis and perturb cell volume regulatory mechanisms leading to alterations of cell metabolism, active transepithelial transport, cell migration, and death. We report that inhibition of the 5-lipoxygenase (5-LO) with AA861 or ETH 615-139, the cysteinyl leukotriene 1 receptor (CysLT₁) with the antiasthmatic drug Zafirlukast, or the volume-sensitive organic anion channel (VSOAC) with DIDS blocks the release of organic osmolytes (taurine, meAIB) and the concomitant cell volume restoration following hypoosmotic swelling of human type II-like lung epithelial cells (A549). Reactive oxygen species (ROS) are produced in A549 cells upon hypotonic cell swelling by a diphenylene iodonium-sensitive NADPH oxidase. The swelling-induced taurine release is suppressed by ROS scavenging (butylated hydroxytoluene, N-acetyl cysteine) and potentiated by H₂O₂. Ca²⁺ mobilization with ionomycin or ATP stimulates the swelling-induced taurine release whereas calmodulin inhibition (W7) inhibits the release. Chelation of the extracellular Ca²⁺ (EGTA) had no effect on swelling-induced taurine release but prevented ATP-induced stimulation. H₂O₂, ATP, and ionomycin were unable to stimulate the taurine release in the presence of AA861 or Zafirlukast, placing 5-LO and CysLT₁ as essential elements in the swelling-induced activation of VSOAC with ROS and Ca²⁺ as potent modulators. Inhibition of tyrosine kinases (genistein, cucurbitacin) reduces volume-sensitive taurine release, adding tyrosine kinases (Janus kinase) as regulators of VSOAC activity. Caspase-3 activity during hypoxia is unaffected by inhibition of 5-LO/CysLT₁ but reduced when swelling-induced taurine loss via VSOAC is prevented by DIDS excess extracellular taurine, indicating a beneficial role of taurine under hypoxia.

Effects of SARA on oxygen-glucose deprivation in PC12 cell line

Ischemic stroke is a major composition of cerebrovascular disease, seriously threatening to human health in the world. Activin A (ActA), belonging to transforming growth factor-beta (TGF-β) super family, plays an important role in the hypoxic-ischemic brain injury through ActA/Smads pathway. While as an essential phosphorylation assistor in TGF-β signaling, the functions and mechanisms of smad anchor for receptor activation (SARA) in ischemic brain injury remain poorly understood. To solve this problem and explore the pathological processes of ischemic stroke, we used an Oxygen-Glucose deprivation (OGD) model in nerve growth factor-induced differentiated rattus PC12 pheochromocytoma cells and down regulated the expressions of SARA by RNA interference technology. Our results showed that the repression of SARA before OGD exposure reduced the expressions of Smad2, 3, 4 mRNA and the phosphorylation rate of Smad2 protein, but it did not affect the mRNA expressions of Smad7. After OGD treatment, ActA/Smads pathway was activated and the expression of SARA in the SARA pre-repression group was significantly up-regulated. The pre-repression of SARA increased the sensitivities of nerve-like cells to OGD damage. Moreover, the mRNA expression of Smad7 which was supposed to participate in the negative feedback of ActA/Smads pathway was also elevated due to OGD injury. Taken together, these results suggest a positive role of SARA in assisting the phosphorylation of Smad2 and maintaining the neuron protective effect of ActA/Smads pathway.

Nuclear translocation of cysteinyl leukotriene receptor 1 is involved in oxygen-glucose deprivation-induced damage to endothelial cells

AIM

Cysteinyl leukotriene receptor 1 (CysLT(1) receptor) is located in epithelial cells, and translocates from the plasma membrane to the nucleus in a ligand-dependent manner. Here, we investigated whether CysLT(1) receptors translocated to the nucleus in endothelial cells after ischemic insult in vitro and whether it was involved in ischemic injury to endothelial cells.

METHODS

EA.hy926 cell line, derived from human umbilical vein endothelial cells, was subjected to oxygen-glucose deprivation (OGD). The expression and distribution of CysLT(1) receptors were detected by immunofluorescent staining, immunogold labeling and immunoblotting analyses. Cell viability was evaluated using MTT reduction assay. Necrosis and apoptosis were determined by double fluorescent staining with propidium iodide and Hoechst 33342.

RESULTS

CysLT(1) receptors were primarily distributed in the cytoplasm and nucleus in EA.hy926 cells, and few was found in the cell membrane. OGD induced the translocation of CysLT(1) receptors from the cytoplasm to the nucleus in a time-depen dent manner, with a peak reached at 6 h. OGD-induced nuclear translocation of CysLT(1) receptors was inhibited by pretreatment with the CysLT(1) receptor antagonist pranlukast (10 μmol/L), or by preincubation with NLS-pep, a peptide corresponding to the nuclear localization sequence of CysLT(1) receptor (10 μg/mL). However, zileuton, an inhibitor of 5-lipoxygenase that was a key enzyme in cysteinyl leukotriene generation, did not inhibit the nuclear translocation of CysLT(1) receptors. Moreover, preincubation with NLS-pep (0.4 μg/mL) significantly ameliorated OGD-induced cell viability reduction and necrosis.

CONCLUSION

CysLT(1) receptors in endothelial cells translocate to the nucleus in a ligand-independent manner after ischemic insult in vitro, and it is involved in the ischemic injury.

The Protective Effect of Eupatilin against Hydrogen Peroxide-Induced Injury Involving 5-Lipoxygenase in Feline Esophageal Epithelial Cells

In this study, we focused to identify whether eupatilin (5,7-dihydroxy-3',4',6-trimethoxyflavone), an extract from Artemisia argyi folium, prevents H₂O₂-induced injury of cultured feline esophageal epithelial cells. Cell viability was measured by the conventional MTT reduction assay. Western blot analysis was performed to investigate the expression of 5-lipoxygenase by H₂O₂ treatment in the absence and presence of inhibitors. When cells were exposed to 600 µM H₂O₂ for 24 hours, cell viability was decreased to 40%. However, when cells were pretreated with 25~150 µM eupatilin for 12 hours, viability was significantly restored in a concentration-dependent manner. H₂O₂-treated cells were shown to express 5-lipoxygenase, whereas the cells pretreated with eupatilin exhibited reduction in the expression of 5-lipoxygenase. The H₂O₂-induced increase of 5-lipoxygenase expression was prevented by SB202190, SP600125, or NAC. We further demonstrated that the level of leukotriene B₄ (LTB₄) was also reduced by eupatilin, SB202190, SP600125, NAC, or nordihydroguaiaretic acid (a lipoxygenase inhibitor) pretreatment. H₂O₂ induced the activation of p38MAPK and JNK, this activation was inhibited by eupatilin. These results indicate that eupatilin may reduce H₂O₂-induced cytotoxicity, and 5-lipoxygenase expression and LTB₄ production by controlling the p38 MAPK and JNK signaling pathways through antioxidative action in feline esophageal epithelial cells.

Transforming growth factor β1-induced astrocyte migration is mediated in part by activating 5-lipoxygenase and cysteinyl leukotriene receptor 1

BACKGROUND

Transforming growth factor-β 1 (TGF-β 1) is an important regulator of cell migration and plays a role in the scarring response in injured brain. It is also reported that 5-lipoxygenase (5-LOX) and its products, cysteinyl leukotrienes (CysLTs, namely LTC₄, LTD₄ and LTE₄), as well as cysteinyl leukotriene receptor 1 (CysLT₁R) are closely associated with astrocyte proliferation and glial scar formation after brain injury. However, how these molecules act on astrocyte migration, an initial step of the scarring response, is unknown. To clarify this, we determined the roles of 5-LOX and CysLT₁R in TGF-β 1-induced astrocyte migration.

METHODS

In primary cultures of rat astrocytes, the effects of TGF-β 1 and CysLT receptor agonists on migration and proliferation were assayed, and the expression of 5-LOX, CysLT receptors and TGF-β1 was detected. 5-LOX activation was analyzed by measuring its products (CysLTs) and applying its inhibitor. The role of CysLT₁R was investigated by applying CysLT receptor antagonists and CysLT₁R knockdown by small interfering RNA (siRNA). TGF-β 1 release was assayed as well.

RESULTS

TGF-β 1-induced astrocyte migration was potentiated by LTD₄, but attenuated by the 5-LOX inhibitor zileuton and the CysLT₁R antagonist montelukast. The non-selective agonist LTD₄ at 0.1 to 10 nM also induced a mild migration; however, the selective agonist N-methyl-LTC₄ and the selective antagonist Bay cysLT2 for CysLT₂R had no effects. Moreover, CysLT₁R siRNA inhibited TGF-β 1- and LTD₄-induced astrocyte migration by down-regulating the expression of this receptor. However, TGF-β 1 and LTD4 at various concentrations did not affect astrocyte proliferation 24 h after exposure. On the other hand, TGF-β 1 increased 5-LOX expression and the production of CysLTs, and up-regulated CysLT1R (not CysLT₂R), while LTD4 and N-methyl-LTC4 did not affect TGF-β 1 expression and release.

CONCLUSIONS

TGF-β 1-induced astrocyte migration is, at least in part, mediated by enhanced endogenous CysLTs through activating CysLT₁R. These findings indicate that the interaction between the cytokine TGF-β 1 and the pro-inflammatory mediators CysLTs in the regulation of astrocyte function is relevant to glial scar formation.

Neuroprotective effects of exogenous activin A on oxygen-glucose deprivation in PC12 cells

Ischemic cerebrovascular disease is one of the most common causes of death in the World. Exogenous activin A (ActA) protects neurons against toxicity and plays a central role in regulating the brain's response to injury. In the present study, we investigated the mechanisms involved in the neuroprotective effects of ActA in a model of hypoxic-ischemic brain disease. We found that ActA could effectively increase the survival rate of PC12 cells and relieve oxygen-glucose deprivation (OGD) damage. To clarify the neuroprotective mechanisms of ActA, the effects of ActA on the ActA/Smad pathway and on the up-regulation of inducible nitric oxide synthase (NOS) and superoxide dismutase (SOD) were investigated using OGD in PC12 cells. The results showed that ActA could increase the expression of activin receptor IIA (ActRIIA), Smad3 and Smad4 and that 50 ng/mL and 100 ng/mL of ActA could reduce NO levels and increase SOD activity by 78.9% and 79.9%, respectively. These results suggested that the neuroprotective effects of ActA in ischemia could be related to the activation of the ActA/Smad signaling pathway and to its anti-oxidant activities.

Baicalin attenuates oxygen-glucose deprivation-induced injury by inhibiting oxidative stress-mediated 5-lipoxygenase activation in PC12 cells

AIM

To determine whether the flavonoid baicalin attenuates oxygen-glucose deprivation (OGD)-induced injury by inhibiting oxidative stress-mediated 5-lipoxygenase (5-LOX) activation in PC12 cells.

METHODS

The effects of baicalin and the 5-LOX inhibitor zileuton on the changes induced by OGD/recovery or H(2)O(2) (an exogenous reactive oxygen species [ROS]) in green fluorescent protein-5-LOX-transfected PC12 cells were compared.

RESULTS

Both baicalin and zileuton attenuated OGD/recovery- and H(2)O(2)-induced injury and inhibited OGD/recovery-induced production of 5-LOX metabolites (cysteinyl leukotrienes) in a concentration-dependent manner. However, baicalin did not reduce baseline cysteinyl leukotriene levels. Baicalin also reduced OGD/recovery-induced ROS production and inhibited 5-LOX translocation to the nuclear envelope and p38 phosphorylation induced by OGD/recovery and H(2)O(2). In contrast, zileuton did not show these effects.

CONCLUSION

Baicalin can inhibit 5-LOX activation after ischemic injury, which may partly result from inhibition of the ROS/p38 mitogen-activated protein kinase pathway.

Activation of 5-lipoxygenase is required for nicotine mediated epithelial-mesenchymal transition and tumor cell growth

Nicotine is shown to be one of the carcinogenic agents for gastric cancer. Perturbation of epithelial-mesenchymal transition (EMT) results in loss of intracellular adhesions leading to tumor progression. In this study, we examined the underlying mechanism of the long-term effects of nicotine on tumor progression in human gastric cancer cells. Nicotine activated 5-lipoxygenase (5-LOX) in three gastric cancer cell lines (MKN-45, MKN-28 and AGS). Cells treated with nicotine dose- and time-dependently induced cell proliferation, invasion and suppressed apoptosis. In addition, cell cycle progression analysis revealed that activation of 5-LOX modulated the G1/S phase transition regulatory proteins and caused cell proliferation. MK886 (5-LOX activating protein inhibitor) mediated the induction of apoptosis by elevation of caspase-3 and Bax/Bcl2 ratio. Abrogation of 5-LOX repressed featured molecular markers of EMT (inactivation of E-cadherin and activation of transcriptional repressor Snail). Blockade of 5-LOX signaling resulted in downregulation of cyclin D1, matrix metalloproteinase (MMP-7, -9), urokinase plasminogen activator (uPA) and its receptor (uPAR), and pro-apoptotic proteins. Furthermore, suppression of Snail and induction of E-cadherin is extracellular signal-regulated kinase (Erk)-dependent. Thus, we conclude that the promotion effect of nicotine on cancer cell progression and EMT is mediated by Erk/5-LOX signaling pathway.