Involvement of calcium-mediated apoptotic signals in H2O2-induced MIN6N8a cell death

The Role of Hydrogen-Peroxide (H2O2) Produced by Vaginal Microbiota in Female Reproductive Health

Female reproductive health is strongly associated with healthy vaginal microbiota, which is thought to be ensured by the dominance of certain Lactobacillus species. Lactobacilli control the vaginal microenvironment through several factors and mechanisms. One of them is their ability to produce hydrogen peroxide (H₂O₂). The role of Lactobacillus-derived H₂O₂ in the vaginal microbial community has been intensively investigated in several studies with many designs. However, results and data are controversial and challenging to interpret in vivo. Defining the underlying mechanisms responsible for a physiological vaginal ecosystem is crucial since it could directly affect probiotic treatment attempts. This review aims to summarize current knowledge on the topic, focusing on probiotic treatment possibilities.

Metabolic mechanism and anti-inflammation effects of sinomenine and its major metabolites N-demethylsinomenine and sinomenine-N-oxide

AIMS

Sinomenine (SIN) is clinically used as an anti-rheumatic drug. However, the metabolic and pharmacological mechanisms of SIN combined with its metabolites are unclear. This study aims to explore the cyclic metabolic mechanism of SIN, the anti-inflammation effects of SIN and its major metabolites (N-demethylsinomenine (DS) and sinomenine-N-oxide (SNO)), and the oxidation property of SNO.

MATERIALS AND METHODS

SIN was administrated to rats via gavage. Qishe pills (a SIN-containing drug) were orally administrated to humans. The bio-samples were collected to identify SIN's metabolites. Enzymatic and non-enzymatic incubations were used to reveal SIN's metabolic mechanism. Impacts of SIN, SNO and DS on the inflammation-related cytokine's levels and nuclear translocation of NF-κB were evaluated in LPS-induced Raw264.7 cells. ROS induced by SNO (10 μM) was also assessed.

KEY FINDINGS

CYP3A4 and ROS predominantly mediated the formation of SNO, and CYP3A4 and CYP2C19 primarily mediated the formation of DS. Noteworthily, SNO underwent N-oxide reduction both enzymatically, by xanthine oxidase (XOD), and non-enzymatically, by ferrous ion and heme moiety. The levels of IL-6 and TNF-α and nuclear translocation of NF-κB were ameliorated after pretreatment of SIN in LPS-induced Raw264.7 cells, while limited attenuations were observed after pretreatment of DS (SNO) even at 200 μM. In contrast, SNO induced ROS production.

SIGNIFICANCE

This study elucidated that SIN underwent both enzymatic and non-enzymatic cyclic metabolism and worked as the predominant anti-inflammation compound, while SNO induced ROS production, suggesting more studies of SIN combined with SNO and DS are necessary in case of DDI and potential toxicities.

The β2-adrenergic receptor-ROS signaling axis: An overlooked component of β2AR function?

β2-Adrenergic receptor (β2AR) agonists are clinically used to elicit rapid bronchodilation for the treatment of bronchospasms in pulmonary diseases such as asthma and COPD, both of which exhibit characteristically high levels of reactive oxygen species (ROS); likely secondary to over-expression of ROS generating enzymes and chronically heightened inflammation. Interestingly, β2AR has long-been linked to ROS, yet the involvement of ROS in β2AR function has not been as vigorously studied as other aspects of β2AR signaling. Herein, we discuss the existing body of evidence linking β2AR activation to intracellular ROS generation and importantly, the role of ROS in regulating β2AR function. The reciprocal interplay of the β2AR and ROS appear to endow this receptor with the ability to self-regulate signaling efficacy and ligand binding, hereby unveiling a redox-axis that may be unfavorably altered in pathological states contributing to both disease progression and therapeutic drug responses.

Glucagon-like peptide-1 receptor agonist activation ameliorates venous thrombosis-induced arteriovenous fistula failure in chronic kidneyd isease

High shear stress that develops in the arteriovenous fistula of chronic kidney diseases (CKD) may increase H2O2 and thromboxane A2 (TXA2) release, thereby exacerbating endothelial dysfunction, thrombosis, and neointimal hyperplasia. We investigated whether glucagon-like peptide-1 receptor agonist/exendin-4, a potentially cardiovascular protective agent, could improve TXA2-induced arteriovenous fistula injury in CKD. TXA2 administration to H2O2-exposed human umbilical vein endothelial cells increased apoptosis, senescence, and detachment; these phenotypes were associated with the downregulation of phosphorylated endothelial nitric oxide synthase/heme oxygenase-1 (eNOS/HO-1) signalling. Exendin-4 reduced H2O2/TXA2-induced endothelial injury via inhibition of apoptosis-related mechanisms and restoration of phosphorylated eNOS/HO-1 signalling. Male Wistar rats subjected to right common carotid artery-external jugular vein anastomosis were treated with exendin-4 via cervical implant osmotic pumps for 16–42 days. High shear stress induced by the arteriovenous fistula significantly increased venous haemodynamics, blood and tissue H2O2 and TXB2 levels, macrophage/monocyte infiltration, fibrosis, proliferation, and adhesion molecule-1 expression. Apoptosis was also increased due to NADPH oxidase gp91 activation and mitochondrial Bax translocation in the proximal end of the jugular vein of CKD rats. Exendin-4-treatment of rats with CKD led to the restoration of normal endothelial morphology and correction of arteriovenous fistula function. Exendin-4 treatment or thromboxane synthase gene deletion in CKD mice markedly reduced ADP-stimulated platelet adhesion to venous endothelium, and prevented venous occlusion in FeCl3-injured vessels by upregulation of HO-1. Together, these data reveal that the use of glucagon-like peptide-1 receptor agonists is an effective strategy for treatment of CKD-induced arteriovenous fistula failure.

Effects of reduced β2 glycoprotein I on high glucose‑induced cell death in HUVECs

Reduced β2 glycoprotein I (β2GPI) has been demonstrated to exhibit a beneficial effect in diabetic atherosclerosis and retinal neovascularization. However, the effect of reduced β2GPI on vascular disorders in diabetic mellitus (DM) remains to be elucidated. The present study established a high glucose‑induced injury model using human umbilical cords veins (HUVECs) and evaluated the protective effects of reduced β2GPI against the injury. The data demonstrated that a low concentration of reduced β2GPI (0.5 µM) mitigated high glucose‑induced cell loss, decreased nitric oxide (NO) production and resulted in calcium overloading. Mechanically, reduced β2GPI additionally reversed high glucose‑induced phosphatase and tensin homolog (PTEN) accumulation, decrease of protein kinase B phosphorylation and nitric oxide synthase activity, and increase of cyclooxygenase‑2 activity. It was further confirmed that PTEN inhibitor‑bpV (1 µM) exhibited similar effects to those resulting from reduced β2GPI. Overall, the data revealed that reduced β2GPI exerts protective effects from glucose‑induced injury in HUVECs, potentially via decreasing PTEN levels. The present study suggests reduced β2GPI may act as a novel therapeutic strategy for the treatment of vascular disorders in DM.

Obligatory Role of Early Ca(2+) Responses in H2O2-Induced β-Cell Apoptosis

Our previous study using apoptosis analysis suggested that Ca(2+) release through inositol 1,4,5-trisphosphate (IP3) receptors and the subsequent Ca(2+) influx through store-operated channels (SOCs) constitute a triggering signal for H2O2-induced β-cell apoptosis. In the present study, we further examined the obligatory role of early Ca(2+) responses in β-cell apoptosis induction. H2O2 induced elevation of the cytosolic Ca(2+) concentration ([Ca(2+)]c) consisting of two phases: an initial transient [Ca(2+)]c elevation within 30 min and a slowly developing one thereafter. The first phase was almost abolished by 2-aminoethoxydiphenylborate (2-APB), which blocks IP3 receptors and cation channels including SOCs, while the second phase was only partially inhibited by 2-APB. The inhibition by 2-APB of the second phase was not observed when 2-APB was added 30 min after the treatment with H2O2. 2-APB also largely inhibited elevation of the mitochondrial Ca(2+) concentration ([Ca(2+)]m) induced by H2O2 when 2-APB was applied simultaneously with H2O2, but not when applied 30 min after H2O2 application. In addition, 2-APB inhibited the release of mitochondrial cytochrome c to the cytosol induced by H2O2 when 2-APB was applied simultaneously with H2O2 but not 30 min post-treatment. H2O2-induced [Ca(2+)]m elevation and cell death were not inhibited by Ru360, an inhibitor of the mitochondrial calcium uniporter (MCU). These results suggest that the H2O2-induced initial [Ca(2+)]c elevation, occurring within 30 min and mediated by Ca(2+) release through IP3 receptors and subsequent Ca(2+) influx through SOCs, leads to [Ca(2+)]m elevation, possibly through a mechanism independent of MCU, thereby inducing cytochrome c release and consequent apoptosis.

HIF-1α induction, proliferation and glycolysis of Theileria-infected leukocytes

Within 2 h of infection by Theileria annulata sporozoites, bovine macrophages display a two- to fourfold increase in transcription of hypoxia inducible factor (HIF-1α). Twenty hours post-invasion sporozoites develop into multi-nucleated macroschizonts that transform the infected macrophage into an immortalized, permanently proliferating, hyper-invasive and disease-causing leukaemia-like cell. Once immortalized Theileria-infected leukocytes can be propagated as cell lines and even though cultivated under normoxic conditions, both infected B cells and macrophages display sustained activation of HIF-1α. Attenuated macrophages used as live vaccines against tropical theileriosis also display HIF-1α activation even though they have lost their tumorigenic phenotype. Here, we review data that ascribes HIF-1α activation to the proliferation status of the infected leukocyte and discuss the possibility that Theileria may have lost its ability to render its host macrophage virulent due to continuous parasite replication in a high Reactive Oxygen Species (ROS) environment. We propose a model where uninfected macrophages have low levels of H2 O2 output, whereas virulent-infected macrophages produce high amounts of H2 O2 . Further increase in H2 O2 output leads to dampening of infected macrophage virulence, a characteristic of disease-resistant macrophages. At the same time exposure to H2 O2 sustains HIF-1α that induces the switch from mitochondrial oxidative phosphorylation to Warburg glycolysis, a metabolic shift that underpins uncontrolled infected macrophage proliferation. We propose that as macroschizonts develop into merozoites and infected macrophage proliferation arrests, HIF-1α levels will decrease and glycolysis will switch back from Warburg to oxidative glycolysis. As Theileria infection transforms its host leukocyte into an aggressive leukaemic-like cell, we propose that manipulating ROS levels, HIF-1α induction and oxidative over Warburg glycolysis could contribute to improved disease control. Finally, as excess amounts of H2 O2 drive virulent Theileria-infected macrophages towards attenuation it highlights how infection-induced pathology and redox balance are intimately linked.

The role of reactive oxygen species in morphine addiction of SH-SY5Y cells

AIMS

The alteration of ROS level is frequently observed in the course of morphine addiction, and ROS is proverbially involved in this process. This study aims to explore the relationship among morphine addiction, reactive oxygen species (ROS) and expression of μ-opioid receptor (MOR) in differentiated SH-SY5Y cells.

MAIN METHODS

SH-SY5Y cells were induced to differentiation by treatment with retinoic acid (RA); the activity of lactate dehydrogenase (LDH) and the nitro blue tetrazolium (NBT) reduction were assessed by spectrophotometry. Intracellular reactive oxygen species (ROS) was measured with the 2,7-dichlorofluorescin diacetate (DCFH-DA) assay. Cellular cAMP was determined by using a competitive protein binding kit. The mRNA expression of μ-opioid receptor (MOR) was evaluated by qRT-PCR.

KEY FINDINGS

Morphine-induced ROS are generated in a concentration- and time-dependent manner and inhibited by naloxone. Exogenous oxidants increase the level of ROS and aggravate morphine addiction, while the exogenous antioxidants efficiently reverse these effects. Morphine decreases the mRNA level of MOR in a concentration-dependent manner. And the mRNA level of MOR is remarkably reduced in the presence of exogenous oxidants and effectively promoted by antioxidants.

SIGNIFICANCE

This study indicates that ROS can affect morphine addiction through involving MOR. Treatment with ROS scavenging can serve as a medical therapy for morphine addiction.

Ovarian cancer G protein-coupled receptor 1 is involved in acid-induced apoptosis of endplate chondrocytes in intervertebral discs

Ovarian cancer G protein-coupled receptor 1 (OGR1) has been shown to be a receptor for protons. We investigated the role of proton-sensing G protein-coupled receptors in the apoptosis of endplate chondrocytes induced by extracellular acid. The expression of proton-sensing G protein-coupled receptors was examined in rat lumbar endplate chondrocytes. Knockdown of OGR1 was achieved by transfecting chondrocytes with specific short hairpin RNA (shRNA) for OGR1. Apoptotic changes were evaluated by DNA fragmentation ELISA, electron microscopy, and flow cytometry. Intracellular calcium ([Ca(2+) ]i) was analyzed with laser scanning confocal microscopy. The mechanism of OGR1 in acid-induced apoptosis of endplate chondrocytes was also investigated. We found that OGR1 was predominantly expressed in rat endplate chondrocytes, and its expression was highly upregulated in response to acidosis. Knocking down OGR1 with shRNAs effectively attenuated acid-induced apoptosis of endplate chondrocytes and increased [Ca(2+) ]i. Blocking OGR1-mediated [Ca(2+) ]i elevation inhibited acid-induced calcium-sensitive proteases such as calpain and calcineurin, and also inhibited the activation of Bid, Bad, and Caspase 3 and cleavage of poly (ADP-ribose) polymerase (PARP). OGR1-mediated [Ca(2+) ]i elevation has a crucial role in apoptosis of endplate chondrocytes by regulating activation of calcium-sensitive proteases and their downstream signaling.

PDGF suppresses oxidative stress induced Ca2+ overload and calpain activation in neurons

Oxidative stress is crucially involved in the pathogenesis of neurological diseases such as stroke and degenerative diseases. We previously demonstrated that platelet-derived growth factors (PDGFs) protected neurons from H2O2-induced oxidative stress and indicated the involvement of PI3K-Akt and MAP kinases as an underlying mechanism. Ca(2+) overload has been shown to mediate the neurotoxic effects of oxidative stress and excitotoxicity. We examined the effects of PDGFs on H2O2-induced Ca(2+) overload in primary cultured neurons to further clarify their neuroprotective mechanism. H2O2-induced Ca(2+) overload in neurons in a dose-dependent manner, while pretreating neurons with PDGF-BB for 24 hours largely suppressed it. In a comparative study, the suppressive effects of PDGF-BB were more potent than those of PDGF-AA. We then evaluated calpain activation, which was induced by Ca(2+) overload and mediated both apoptotic and nonapoptotic cell death. H2O2-induced calpain activation in neurons in a dose-dependent manner. Pretreatment of PDGF-BB completely blocked H2O2-induced calpain activation. To the best of our knowledge, the present study is the first to demonstrate the mechanism underlying the neuroprotective effects of PDGF against oxidative stress via the suppression of Ca(2+) overload and inactivation of calpain and suggests that PDGF-BB may be a potential therapeutic target of neurological diseases.

Cytosolic Ca2+ shifts as early markers of cytotoxicity

The determination of the cytotoxic potential of new and so far unknown compounds as well as their metabolites is fundamental in risk assessment. A variety of strategic endpoints have been defined to describe toxin-cell interactions, leading to prediction of cell fate. They involve measurement of metabolic endpoints, bio-energetic parameters or morphological cell modifications. Here, we evaluated alterations of the free cytosolic Ca²⁺ homeostasis using the Fluo-4 dye and compared results with the metabolic cell viability assay Alamar Blue. We investigated a panel of toxins (As₂O₃, gossypol, H₂O₂, staurosporine, and titanium(IV)-salane complexes) in four different mammalian cell lines covering three different species (human, mouse, and African green monkey). All tested compounds induced an increase in free cytosolic Ca²⁺ within the first 5 s after toxin application. Cytosolic Ca²⁺ shifts occurred independently of the chemical structure in all tested cell systems and were persistent up to 3 h. The linear increase of free cytosolic Ca²⁺ within the first 5 s of drug treatment correlates with the EC₂₅ and EC₇₅ values obtained in Alamar Blue assays one day after toxin exposure. Moreover, a rise of cytosolic Ca²⁺ was detectable independent of induced cell death mode as assessed by caspase and poly(ADP-ribose) polymerase (PARP) activity in HeLa versus MCF-7 cells at very low concentrations. In conclusion, a cytotoxicity assay based on Ca²⁺ shifts has a low limit of detection (LOD), is less time consuming (at least 24 times faster) compared to the cell viability assay Alamar Blue and is suitable for high-troughput-screening (HTS).

Free radical generation induces epithelial-to-mesenchymal transition in lung epithelium via a TGF-β1-dependent mechanism

Fibrotic remodelling of lung parenchymal and airway compartments is the major contributor to life-threatening organ dysfunction in chronic lung diseases such as idiopathic pulmonary fibrosis (IPF) and Chronic Obstructive Pulmonary Disease (COPD). Since transforming growth factor-β1 (TGF-β1) is believed to play a key role in disease pathogenesis and markers of oxidative stress are also commonly detected in bronchoalveolar lavage (BAL) from such patients we sought to investigate whether both factors might be interrelated. Here we investigated the hypothesis that oxidative stress to the lung epithelium promotes fibrotic repair by driving epithelial-to-mesenchymal transition (EMT) via the augmentation of TGF-β1. We show that in response to 400μM hydrogen peroxide (H(2)O(2)) A549 cells, used a model for alveolar epithelium, and human primary bronchial epithelial cells (PBECs) undergo EMT displaying morphology changes, decreased expression of epithelial markers (E-cadherin and ZO-1), increased expression of mesenchymal markers (vimentin and α-smooth muscle actin) as well as increased secretion of extracelluar matrix components. The same oxidative stress also promotes expression of TGF-β1. Inhibition of TGF-β1 signalling as well as treatment with antioxidants such as phenyl tert-butylnitrone (PBN) and superoxide dismutase 3 (SOD3) prevent the oxidative stress driven EMT-like changes described above. Interventions also inhibited EMT-like changes. This study identifies a link between oxidative stress, TGF-β1 and EMT in lung epithelium and highlights the potential for antioxidant therapies to limit EMT and its potential contribution to chronic lung disease.

Gliclazide may have an antiapoptotic effect related to its antioxidant properties in human normal and cancer cells

Experimental and clinical studies suggest that gliclazide may protect pancreatic β-cells from apoptosis induced by an oxidative stress. However, the precise mechanism(s) of this action are not fully understood and requires further clarification. Therefore, using human normal and cancer cells we examined whether the anti-apoptotic effects of this sulfonylurea is due to its free radical scavenger properties. Hydrogen peroxide (H₂O₂) as a model trigger of oxidative stress was used to induce cell death. Our experiments were performed on human normal cell line (human umbilical vein endothelial cell line, HUVEC-c) and human cancer cell lines (human mammary gland cell line, Hs578T; human pancreatic duct epithelioid carcinoma cell line, PANC-1). To assess the effect of gliclazide the cells were pre-treated with the drug. The 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay was employed to measure the impact of gliclazide on cell viability. Generation of reactive oxygen species, mitochondrial membrane potential (∆Ψ_m), and intracellular Ca²⁺ concentration [Ca²⁺] were monitored. Furthermore, the morphological changes associated with apoptosis were determined using double staining with Hoechst 33258-propidium iodide (PI). Gliclazide protects the tested cells from H₂O₂-induced cell death most likely throughout the inhibition of ROS production. Moreover, the drug restored loss of ΔΨ_m and diminished intracellular [Ca²⁺] evoked by H₂O₂. Double staining with Hoechst 33258-PI revealed that pre-treatment with gliclazide diminished the number of apoptotic cells. Our findings indicate that gliclazide may protect both normal and cancer human cells against apoptosis induced by H₂O₂. It appears that the anti-apoptotic effect of the drug is most likely associated with reduction of oxidative stress.

Inositol 1,4,5-trisphosphate receptor-mediated initial Ca(2+) mobilization constitutes a triggering signal for hydrogen peroxide-induced apoptosis in INS-1 β-cells

Reactive oxygen species, including hydrogen peroxide (H(2)O(2)), are known to induce β-cell apoptosis. The present study investigated the role of Ca(2+) in H(2)O(2)-induced apoptosis of the β-cell line INS-1. Annexin V assay with flow cytometry and DNA ladder assay demonstrated that treatment of INS-1 cells with 100 µM H(2)O(2) for 18 h significantly increased apoptotic cells. A comparable level of apoptosis was also observed after 18 h when the cells were treated with 100 µM H(2)O(2) only for initial 30 min. The H(2)O(2)-induced apoptosis was abolished by 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl)ester (BAPTA/AM), a chelator of intracellular Ca(2+), by 2-aminoethoxydiphenylborate (2-APB), a blocker of inositol 1,4,5-trisphosphate (IP(3)) receptors and cation channels, and by xestospongin D, a blocker of IP(3) receptors, and was partially blocked by SKF-96365, a non-selective cation channel blocker. However, nicardipine, an L-type voltage-dependent Ca(2+) channel blocker, or N-(p-amylcinnamoyl)anthranilic acid (ACA), a TRPM2 blocker, had little effect on the apoptosis. The inhibitory effect of BAPTA/AM or 2-APB on the H(2)O(2)-induced apoptosis was largely attenuated when the drug was added 30 min or 1 h after start of the treatment with H(2)O(2). These results suggest that the initial intracellular Ca(2+) elevation induced by H(2)O(2), which is mediated via IP(3) receptors and store-operated cation channels, plays an obligatory role in the induction of β-cell apoptosis.

UVA1 radiation inhibits calcineurin through oxidative damage mediated by photosensitization

The protein phosphatase calcineurin has been gradually revealing itself as the central controller of our immune response, although it is involved in a wide array of signaling pathways related to cellular development and cell cycle progression. As such, calcineurin is an attractive, yet delicate, therapeutic target for the prevention of allograft rejection and treatment of several inflammatory skin conditions. However, calcineurin activity is not only sensitive to immunosuppressants such as cyclosporin A and tacrolimus, but also subject to modulation by reactive oxygen species. We have recently shown, both in vivo and in vitro, that UVA1 radiation suppresses calcineurin activity. In this paper, we present evidence that this activity loss is due to singlet oxygen and superoxide generated by photosensitization and show that a closely related phosphatase, PP2A, is not affected. Furthermore, a survey of this damage reveals oxidation of several Met and Cys residues as well as an overall conformational change. These findings provide a mechanistic basis for the hypothesis that UVA1 and calcineurin inhibitors both affect the same signal transduction pathway in skin.

Protective effects of Wu-Zi-Yan-Zong-Fang on amyloid beta-induced damage in vivo and in vitro

This study was designed to determine the effects of Wu-Zi-Yan-Zong-Fang on amyloid-beta(25-35)-induced cognitive deficits in rats and neurotoxicity in pheochromocytoma cells and the possible mechanism of action. In vivo studies showed that Wu-Zi-Yan-Zong-Fang significantly ameliorated the spatial memory and retention deficits, decreased acetylcholinesterase activity, and increased acetylcholine content caused by intracerebroventricular injection of amyloid-beta(25-35). In vitro results showed that Wu-Zi-Yan-Zong-Fang increased cell viability and the activity of superoxide dismutase and catalase and decreased the release of lactate dehydrogenase and the level of malondialdehyde. Wu-Zi-Yan-Zong-Fang also significantly reduced the percentage of apoptotic cells and blocked the increase in the intracellular concentration of Ca(2+). These data suggest that Wu-Zi-Yan-Zong-Fang has potent protective effects for the treatment of Alzheimer's disease in future.

TRPM2 functions as a lysosomal Ca2+-release channel in beta cells

TRPM2 is a Ca2+-permeable cation channel that is specifically activated by adenosine diphosphoribose (ADPR). Channel activation in the plasma membrane leads to Ca2+ influx and has been linked to apoptotic mechanisms. The primary agonist, ADPR, is produced both extra- and intracellularly and causes increases in intracellular calcium concentration ([Ca2+]i), but the mechanisms involved are not understood. Using short interfering RNA and a knockout mouse, we report that TRPM2, in addition to its role as a plasma membrane channel, also functions as a Ca2+-release channel activated by intracellular ADPR in a lysosomal compartment. We show that both functions of TRPM2 are critically linked to hydrogen peroxide-induced beta cell death. Additionally, extracellular ADPR production by the ectoenzyme CD38 from its substrates NAD+ (nicotinamide adenine dinucleotide) or cADPR causes IP3-dependent Ca2+ release via P2Y and adenosine receptors. Thus, ADPR and TRPM2 represent multimodal signaling elements regulating Ca2+ mobilization in beta cells through membrane depolarization, Ca2+ influx, and release of Ca2+ from intracellular stores.

H(2)O(2)-mediated modulation of cytosolic signaling and organelle function in rat hippocampus

Reactive oxygen species (ROS) released from (dys-)functioning mitochondria contribute to normal and pathophysiological cellular signaling by modulating cytosolic redox state and redox-sensitive proteins. To identify putative redox targets involved in such signaling, we exposed hippocampal neurons to hydrogen peroxide (H₂O₂). Redox-sensitive dyes indicated that externally applied H₂O₂ may oxidize intracellular targets in cell cultures and acute tissue slices. In cultured neurons, H₂O₂ (EC₅₀ 118 µM) induced an intracellular Ca²⁺ rise which could still be evoked upon Ca²⁺ withdrawal and mitochondrial uncoupling. It was, however, antagonized by thapsigargin, dantrolene, 2-aminoethoxydiphenyl borate, and high levels of ryanodine, which identifies the endoplasmic reticulum (ER) as the intracellular Ca²⁺ store involved. Intracellular accumulation of endogenously generated H₂O₂—provoked by inhibiting glutathione peroxidase—also released Ca²⁺ from the ER, as did extracellular generation of superoxide. Phospholipase C (PLC)-mediated metabotropic signaling was depressed in the presence of H₂O₂, but cytosolic cyclic adenosine-5′-monophosphate (cAMP) levels were not affected. H₂O₂ (0.2–5 mM) moderately depolarized mitochondria, halted their intracellular trafficking in a Ca²⁺- and cAMP-independent manner, and directly oxidized cellular nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH₂). In part, the mitochondrial depolarization reflects uptake of Ca²⁺ previously released from the ER. We conclude that H₂O₂ releases Ca²⁺ from the ER via both ryanodine and inositol trisphosphate receptors. Mitochondrial function is not markedly impaired even by millimolar concentrations of H₂O₂. Such modulation of Ca²⁺ signaling and organelle interaction by ROS affects the efficacy of PLC-mediated metabotropic signaling and may contribute to the adjustment of neuronal function to redox conditions and metabolic supply.

Role of type Ialpha phosphatidylinositol-4-phosphate 5-kinase in insulin secretion, glucose metabolism, and membrane potential in INS-1 beta-cells

Insulin secretion from beta-cells is regulated by a complex signaling network. Our earlier study has reported that Rac1 participates in glucose- and cAMP-induced insulin secretion probably via maintaining a functional actin structure for recruitment of insulin granules. Type Ialpha phosphatidylinositol-4-phosphate 5-kinase (PIP5K-Ialpha) is a downstream effector of Rac1 and a critical enzyme for synthesis of phosphatidylinositol-4,5-bisphosphate (PIP(2)). By using an RNA interference technique, PIP5K-Ialpha in INS-1 beta-cells could be specifically knocked down by 70-75%. PIP5K-Ialpha knockdown disrupted filamentous actin structure and caused changes in cell morphology. In addition, PIP(2) content in the plasma membrane was reduced and the glucose effect on PIP(2) was abolished but without affecting glucose-induced formation of inositol 1,4,5-trisphosphate. At basal conditions (2.8 mM glucose), PIP5K-Ialpha knockdown doubled insulin secretion, elevated glucose metabolic rate, depolarized resting membrane potential, and raised cytoplasmic free Ca(2+) levels ([Ca(2+)](i)). The total insulin release at high glucose was increased upon PIP5K-Ialpha knockdown. However, the percent increment of insulin secretion by high glucose and forskolin over the basal release was significantly reduced, an effect more apparent on the late phase of insulin secretion. Metabolism and [Ca(2+)](i) rises at high glucose were also attenuated in cells after PIP5K-Ialpha knockdown. In contrast, PIP5K-Ialpha knockdown had no effect on cell growth and viability. Taken together, our data suggest that PIP5K-Ialpha may play an important role in both the proximal and distal steps of signaling cascade for insulin secretion in beta-cells.

Mechanisms to explain wasting of muscle and fat in cancer cachexia

PURPOSE OF REVIEW

To describe the most relevant recent findings concerning the molecular mechanisms involved in both fat and muscle tissues in cachectic cancer patients.

RECENT FINDINGS

Relevant progress has been made in the mechanism of signalling protein metabolism in skeletal muscle. PI3K has a dual role inhibiting protein degradation by inhibition of Atrogin-1 and MuRF1 gene expression and facilitating AKT phosphorylation, leading to increased protein synthesis. Interestingly, Caspase-3 activity is intimately associated with myofibrillar protein degradation in muscle tissue. With respect to fat metabolism, increased lipolysis in human cancer cachexia seems to be directly connected to increased hormone-sensitive lipase activity.

SUMMARY

The results and findings described in this review represent important progress in wasting disease mechanisms and may provide hints for future therapeutic approaches in cancer cachexia.

Reactive oxygen species-mediated pancreatic beta-cell death is regulated by interactions between stress-activated protein kinases, p38 and c-Jun N-terminal kinase, and mitogen-activated protein kinase phosphatases

Pancreatic beta-cells are susceptible to reactive oxygen species (ROS), which are known to be generated by high or low glucose (LG), hypoxic, or cytokine-producing conditions. When we cultured mouse beta-cell-derived MIN6 cells in a LG condition, we detected a significant generation of ROS, including hydrogen peroxide, which was comparable to the ROS production in hypoxic or cytokine-treated conditions. ROS accumulation induced by the LG culture led to cell death, which was prevented by the ROS scavengers N-acetylcysteine and manganese(III)tetrakis(4-benzoic acid) porphyrin. We next investigated the mechanism of stress-activated protein kinases (SAPKs), c-jun N-terminal kinase (JNK) and p38, in ROS-induced MIN6 cell death. Activation of p38 occurred immediately after the LG culture, whereas JNK activation increased slowly 8 h later. Adenoviral p38 expression decreased MIN6 cell death, whereas the JNK expression increased it. Consistently, blocking p38 activation by inhibitors increased beta-cell death, whereas JNK inhibitors decreased it. We then examined the role of MAPK phosphatases (MKPs) specific for stress-activated protein kinases in beta-cell death. We found that MKP-1 presented an increase in its oxidized product after the LG culture. ROS scavengers prevented the appearance of this oxidized product and JNK activation. Thus, ROS-induced MKP inactivation causes sustained activation of JNK, which contributes to beta-cell death. Adenoviral overexpression of MKP-1 and MKP-7 prevented the phosphorylation of JNK at 36 h after the LG culture, and decreased MIN6 beta-cell death. We suggest that beta-cell death is regulated by interactions between JNK and its specific MKPs.

Activation of calcium-sensing receptor accelerates apoptosis in hyperplastic parathyroid cells

Calcimimetic compounds inhibit not only parathyroid hormone (PTH) synthesis and secretion, but also parathyroid cell proliferation. The aim of this investigation is to examine the effect of the calcimimetic compound NPS R-568 (R-568) on parathyroid cell death in uremic rats. Hyperplastic parathyroid glands were obtained from uremic rats (subtotal nephrectomy and high-phosphorus diet), and incubated in the media only or the media which contained high concentration of R-568 (10(-4)M), or 10% cyclodextrin, for 6h. R-568 treatment significantly suppressed medium PTH concentration compared with that of the other two groups. R-568 treatment not only increased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay-positive cells, but also induced the morphologic changes of cell death determined by light or electron microscopy. These results suggest that CaR activation by R-568 accelerates parathyroid cell death, probably through an apoptotic mechanism in uremic rats in vitro.

Hydrogen peroxide sensing and signaling

It is well established that oxidative stress is an important cause of cell damage associated with the initiation and progression of many diseases. Consequently, all air-living organisms contain antioxidant enzymes that limit oxidative stress by detoxifying reactive oxygen species, including hydrogen peroxide. However, in eukaryotes, hydrogen peroxide also has important roles as a signaling molecule in the regulation of a variety of biological processes. Here, we will discuss the molecular mechanisms by which hydrogen peroxide is sensed and the increasing evidence that antioxidant enzymes play multiple, key roles as sensors and regulators of signal transduction in response to hydrogen peroxide.

Protective effects of salidroside on hydrogen peroxide-induced apoptosis in SH-SY5Y human neuroblastoma cells

Oxidative stress plays an important role in Alzheimer's disease and other neurodegenerative disorders. Salidroside, a phenylpropanoid glycoside isolated from Rhodiola rosea L, shows potent antioxidant property. In this paper, the neuroprotective effects of salidroside on hydrogen peroxide (H2O2)-induced apoptosis in SH-SY5Y cells were investigated. Pretreatment with salidroside markedly attenuated H2O2-induced cell viability loss and apoptotic cell death in a dose-dependent manner. The mechanisms by which salidroside protected neuron cells from oxidative stress included the induction of several antioxidant enzymes, thioredoxin, heme oxygenase-1, and peroxiredoxin-I; the downregulation of pro-apoptotic gene Bax and the upregulation of anti-apoptotic genes Bcl-2 and Bcl-X(L). Furthermore, salidroside dose-dependently restored H2O2-induced loss of mitochondrial membrane potential as well as the elevation of intracellular calcium level. These results suggest that salidroside has protective effects against oxidative stress-induced cell apoptosis, which might be a potential therapeutic agent for treating or preventing neurodegenerative diseases implicated with oxidative stress.