Mitochondrial Ca2+ flux is a critical determinant of the Ca2+ dependence of mast cell degranulation

A Systemic Review for Ethnopharmacological Studies on Isatis indigotica Fortune: Bioactive Compounds and their Therapeutic Insights

Isatis indigotica Fortune is a biennial Chinese woad of the Cruciferae family. It is primarily cultivated in China, where it was a staple in indigo dye manufacture till the end of the 17th century. Today, I. indigotica is used primarily as a therapeutic herb in traditional Chinese medicine (TCM). The medicinal use of the plant is separated into its leaves (Da-Qing-Ye) and roots (Ban-Lan-Gen), whereas its aerial components can be processed into a dried bluish-spruce powder (Qing-Dai), following dehydration for long-term preservation. Over the past several decades, I. indigotica has been generally utilized for its heat-clearing effects and bodily detoxification in TCM, attributed to the presence of several classes of bioactive compounds, including organic acids, alkaloids, terpenoids, and flavonoids, as well as lignans, anthraquinones, glucosides, glucosinolates, sphingolipids, tetrapyrroles, and polysaccharides. This paper aims to delineate I. indigotica from its closely-related species (Isatis tinctoria and Isatis glauca) while highlighting the ethnomedicinal uses of I. indigotica from the perspectives of modern and traditional medicine. A systematic search of PubMed, Embase, PMC, Web of Science, and Google Scholar databases was done for articles on all aspects of the plant, emphasizing those analyzing the bioactivity of constituents of the plant. The various key bioactive compounds of I. indigotica that have been found to exhibit anti-inflammatory, antimicrobial, anticancer, and anti-allergic properties, along with the protective effects against neuronal injury and bone fracture, will be discussed. Collectively, the review hopes to draw attention to the therapeutic potential of I. indigotica not only as a TCM, but also as a potential source of bioactive compounds for disease management and treatment.

The Role Played by Mitochondria in FcεRI-Dependent Mast Cell Activation

Mast cells play a key role in the regulation of innate and adaptive immunity and are involved in pathogenesis of many inflammatory and allergic diseases. The most studied mechanism of mast cell activation is mediated by the interaction of antigens with immunoglobulin E (IgE) and a subsequent binding with the high-affinity receptor Fc epsilon RI (FcεRI). Increasing evidences indicated that mitochondria are actively involved in the FcεRI-dependent activation of this type of cells. Here, we discuss changes in energy metabolism and mitochondrial dynamics during IgE-antigen stimulation of mast cells. We reviewed the recent data with regards to the role played by mitochondrial membrane potential, mitochondrial calcium ions (Ca²⁺) influx and reactive oxygen species (ROS) in mast cell FcεRI-dependent activation. Additionally, in the present review we have discussed the crucial role played by the pyruvate dehydrogenase (PDH) complex, transcription factors signal transducer and activator of transcription 3 (STAT3) and microphthalmia-associated transcription factor (MITF) in the development and function of mast cells. These two transcription factors besides their nuclear localization were also found to translocate in to the mitochondria and functions as direct modulators of mitochondrial activity. Studying the role played by mast cell mitochondria following their activation is essential for expanding our basic knowledge about mast cell physiological functions and would help to design mitochondria-targeted anti-allergic and anti-inflammatory drugs.

Discovery and analysis the anti-pseudo-allergic components from Perilla frutescens leaves by overexpressed MRGPRX2 cell membrane chromatography coupled with HPLC-ESI-IT-TOF system

Objectives

Screen and identify the anti-pseudo-allergic activity components of Perilla frutescens leaves that interacted with MRGPRX2 (a new reported pseudo-allergic reaction-related receptor).

Methods

An overexpressed MRGPRX2 cell membrane chromatography (CMC) coupled with HPLC-ESI-IT-TOF system has been established to screen and identify the effective components from P. frutescens leaves. A frontal analysis method was performed to investigate the binding affinity between ligands and MRGPRX2. Their activity of relieving pseudo-allergic reaction was evaluated in vitro by histamine release assay, β-hexosaminidase release assay and intracellular Ca2+ mobilization assay.

Key findings

Extract of P. frutescens leaves was proved to be effective in anti-pseudo-allergic reaction by inhibiting MRGPRX2. Apigenin (API) and rosmarinic acid (ROS) were confirmed to be the potential anti-allergy compounds that could bind with MRGPRX2. The binding affinity (KD) of ROS and API with MRGPRX2 was (8.79 ± 0.13) × 10−8  m and (6.54 ± 1.69) × 10−8  m, respectively. The IC50 of API inhibiting laboratory of allergic disease 2 cells degranulation was also determined to be (51.96 ± 0.18) μm.

Conclusions

A MRGPRX2/CMC coupled with HPLC-ESI-IT-TOF system was successfully established and applied to discover the effective components from P. frutescens leaves.

BLT1-mediated O-GlcNAcylation is required for NOX2-dependent migration, exocytotic degranulation and IL-8 release of human mast cell induced by Trichomonas vaginalis-secreted LTB4

Trichomonas vaginalis is a sexually-transmitted protozoan parasite that causes vaginitis and cervicitis. Although mast cell activation is important for provoking tissue inflammation during infection with parasites, information regarding the signaling mechanisms in mast cell activation and T. vaginalis infection is limited. O-linked N-acetylglucosamine (O-GlcNAc) is a post-translational modification of serine and threonine residues that functions as a critical regulator of intracellular signaling, regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). We investigated if O-GlcNAcylation was associated with mast cell activation induced by T. vaginalis-derived secretory products (TvSP). Modified TvSP collected from live trichomonads treated with the 5-lipooxygenase inhibitor AA861 inhibited migration of mast cells. This result suggested that mast cell migration was caused by stimulation of T. vaginalis-secreted leukotrienes. Using the BLT1 antagonist U75302 or BLT1 siRNA, we found that migration of mast cells was evoked via LTB₄ receptor (BLT1). Furthermore, TvSP induced protein O-GlcNAcylation and OGT expression in HMC-1 cells, which was prevented by transfection with BLT1 siRNA. TvSP-induced migration, ROS generation, CD63 expression and IL-8 release were significantly suppressed by pretreatment with OGT inhibitor ST045849 or OGT siRNA. These results suggested that BLT1-mediated OGlcNAcylation was important for mast cell activation during trichomoniasis.

Mitochondrial Ca2+ removal amplifies TRAIL cytotoxicity toward apoptosis-resistant tumor cells via promotion of multiple cell death modalities

Ca2+ has emerged as a new target for cancer treatment since tumor-specific traits in Ca2+ dynamics contributes to tumorigenesis, malignant phenotypes, drug resistance, and survival in different tumor types. However, Ca2+ has a dual (pro-death and pro-survival) function in tumor cells depending on the experimental conditions. Therefore, it is necessary to minimize the onset of the pro-survival Ca2+ signals caused by the therapy. For this purpose, a better understanding of pro-survival Ca2+ pathways in cancer cells is critical. Here we report that Ca2+ protects malignant melanoma (MM) and osteosarcoma (OS) cells from tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) cytotoxicity. Simultaneous measurements using the site-specific Ca2+ probes showed that acute TRAIL treatment rapidly and dose-dependently increased the cytosolic Ca2+ concentration ([Ca2+]cyt) and mitochondrial Ca2+ concentration ([Ca2+]mit) Pharmacological analyses revealed that the [Ca2+]mit remodeling was under control of mitochondrial Ca2+ uniporter (MCU), mitochondrial permeability transition pore (MPTP), and a Ca2+ transport pathway sensitive to capsazepine and AMG9810. Ca2+ chelators and the MCU inhibitor ruthenium 360, an MPTP opener atractyloside, capsazepine, and AMG9810 all decreased [Ca2+]mit and sensitized these tumor cells to TRAIL cytotoxicity. The Ca2+ modulation enhanced both apoptotic and non-apoptotic cell death. Although the [Ca2+]mit reduction potentiated TRAIL-induced caspase-3/7 activation and cell membrane damage within 24 h, this potentiation of cell death became pronounced at 72 h, and not blocked by caspase inhibition. Our findings suggest that in MM and OS cells mitochondrial Ca2+ removal can promote apoptosis and non-apoptotic cell death induction by TRAIL. Therefore, mitochondrial Ca2+ removal can be exploited to overcome the resistance of these cancers to TRAIL.

Antimicrobial agent triclosan is a proton ionophore uncoupler of mitochondria in living rat and human mast cells and in primary human keratinocytes

Triclosan (TCS) is an antimicrobial used widely in hospitals and personal care products, at ~10 mm. Human skin efficiently absorbs TCS. Mast cells are ubiquitous key players both in physiological processes and in disease, including asthma, cancer and autism. We previously showed that non-cytotoxic levels of TCS inhibit degranulation, the release of histamine and other mediators, from rat basophilic leukemia mast cells (RBL-2H3), and in this study, we replicate this finding in human mast cells (HMC-1.2). Our investigation into the molecular mechanisms underlying this effect led to the discovery that TCS disrupts adenosine triphosphate (ATP) production in RBL-2H3 cells in glucose-free, galactose-containing media (95% confidence interval EC50 = 7.5-9.7 µm), without causing cytotoxicity. Using these same glucose-free conditions, 15 µm TCS dampens RBL-2H3 degranulation by 40%. The same ATP disruption was found with human HMC-1.2 cells (EC50 4.2-13.7 µm), NIH-3 T3 mouse fibroblasts (EC50 4.8-7.4 µm) and primary human keratinocytes (EC50 3.0-4.1 µm) all with no cytotoxicity. TCS increases oxygen consumption rate in RBL-2H3 cells. Known mitochondrial uncouplers (e.g., carbonyl cyanide 3-chlorophenylhydrazone) previously were found to inhibit mast cell function. TCS-methyl, which has a methyl group in place of the TCS ionizable proton, affects neither degranulation nor ATP production at non-cytotoxic doses. Thus, the effects of TCS on mast cell function are due to its proton ionophore structure. In addition, 5 µm TCS inhibits thapsigargin-stimulated degranulation of RBL-2H3 cells: further evidence that TCS disrupts mast cell signaling. Our data indicate that TCS is a mitochondrial uncoupler, and TCS may affect numerous cell types and functions via this mechanism. Copyright © 2015 John Wiley & Sons, Ltd.

Triclosan is a mitochondrial uncoupler in live zebrafish

Triclosan (TCS) is a synthetic antimicrobial agent used in many consumer goods at millimolar concentrations. As a result of exposure, TCS has been detected widely in humans. We have recently discovered that TCS is a proton ionophore mitochondrial uncoupler in multiple types of living cells. Here, we present novel data indicating that TCS is also a mitochondrial uncoupler in a living organism: 24-hour post-fertilization (hpf) zebrafish embryos. These experiments were conducted using a Seahorse Bioscience XF^e 96 Extracellular Flux Analyzer modified for bidirectional temperature control, using the XF96 spheroid plate to position and measure one zebrafish embryo per well. Using this method, after acute exposure to TCS, the basal oxygen consumption rate (OCR) increases, without a decrease in survival or heartbeat rate. TCS also decreases ATP-linked respiration and spare respiratory capacity and increases proton leak: all indicators of mitochondrial uncoupling. Our data indicate, that TCS is a mitochondrial uncoupler in vivo, which should be taken into consideration when assessing the toxicity and/or pharmaceutical uses of TCS. This is the first example of usage of a Seahorse Extracellular Flux Analyzer to measure bioenergetic flux of a single zebrafish embryo per well in a 96-well assay format. The method developed in this study provides a high-throughput tool to identify previously unknown mitochondrial uncouplers in a living organism. Copyright © 2016 John Wiley & Sons, Ltd.

Mitochondrial calcium uniporter inhibition attenuates mouse bone marrow-derived mast cell degranulation induced by beta-1,3-glucan

Mast cells are primary mediators of allergic inflammation. Beta-1,3-glucan (BG) protects against infection and shock by activating immune cells. Activation of the BG receptor induces an increase in intracellular Ca²⁺, which may induce exocytosis. However, little is known about the precise mechanisms underlying BG activation of immune cells and the possible role of mitochondria in this process. The present study examined whether BG induced mast cell degranulation, and evaluated the role of calcium transients during mast cell activation. Our investigation focused on the role of the mitochondrial calcium uniporter (MCU) in BG-induced degranulation. Black mouse (C57) bone marrow-derived mast cells were stimulated with 0.5 µg/ml BG, 100 µg/ml peptidoglycan (PGN), or 10 µM A23187 (calcium ionophore), and dynamic changes in cytosolic and mitochondrial calcium and membrane potential were monitored. BG-induced mast cell degranulation occurred in a time-dependent manner, and was significantly reduced under calcium-free conditions. Ruthenium red, a mitochondrial Ca²⁺ uniporter blocker, significantly reduced mast cell degranulation induced by BG, PGN, and A23187. These results suggest that the mitochondrial Ca²⁺ uniporter has an important regulatory role in BG-induced mast cell degranulation.

Diminished allergic disease in patients with STAT3 mutations reveals a role for STAT3 signaling in mast cell degranulation

BACKGROUND

Severe atopic conditions associated with elevated serum IgE are heterogeneous with few known causes. Nearly every patient with autosomal-dominant hyper-IgE syndrome (AD-HIES) due to signal transducer and activator of transcription 3 (STAT3) mutations has a history of eczematous dermatitis and elevated IgE; however, clinical atopy has never been systematically studied.

OBJECTIVE

Understanding of genetic determinants of allergic disease may lead to novel therapies in controlling allergic disease.

METHODS

We conducted clinical evaluation of the rates of food allergies and anaphylaxis in patients with AD-HIES, a cohort of patients with no STAT3 mutation but with similar histories of elevated IgE and atopic dermatitis, and healthy volunteers with no history of atopy. Morphine skin prick testing, ImmunoCAP assays for allergen-specific IgE, and basophil activation were measured. A model of systemic anaphylaxis was studied in transgenic mice carrying an AD-HIES mutation. STAT3 was silenced in LAD2 and primary human mast cells to study the role of STAT3 in signaling and degranulation after IgE cross-linking.

RESULTS

Food allergies and anaphylaxis were markedly diminished in patients with AD-HIES compared with a cohort of patients with no STAT3 mutation but with similar histories of elevated IgE and atopic dermatitis. Morphine skin prick testing and basophil activation were diminished in patients with AD-HIES, whereas mice carrying an AD-HIES mutation were hyporesponsive to systemic anaphylaxis models. Rapid mast cell STAT3 serine727 phosphorylation was noted after IgE cross-linking, and inhibition of STAT3 signaling in mast cells lead to impaired FcεRI-mediated proximal and distal signaling, as well as reduced degranulation.

CONCLUSION

This study serves as an example for how mutations in specific atopic pathways can lead to discrete allergic phenotypes, encompassing increased risk of some phenotypes but a relative protection from others.

Mitochondrial superoxide mediates mitochondrial and endoplasmic reticulum dysfunctions in TRAIL-induced apoptosis in Jurkat cells

Reactive oxygen species (ROS), such as superoxide (O2(•-)) and hydrogen peroxide (H2O2), have been reported to be important mediators of the apoptosis induced by death ligands, including Fas, tumor necrosis factor-α, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Conversely, there is evidence that H2O2 and prooxidative conditions are protective. Therefore, the roles of ROS in death ligand-induced apoptosis are a matter of debate. In this study, we attempted to define the oxidant species mediating TRAIL-induced apoptosis in human tumor cells. The generation of intracellular O2(•-), but not H2O2, was correlated with apoptosis in the cells. TRAIL treatment resulted in increased mitochondrial O2(•-) generation and the oxidation of cardiolipin. The O2(•-)-selective scavenger MnTBaP [Mn(III) tetrakis (4-benzoic acid) porphyrin chloride] specifically blocked TRAIL-induced apoptosis and proapoptotic events including mitochondrial membrane collapse and caspase-3/7 activation. TRAIL also induced endoplasmic reticulum (ER) stress responses including caspase-12 activation, while inhibition of caspase-12 prevented the apoptosis. In addition, increased mitochondrial O2(•-) generation by uncoupling of oxidative phosphorylation or inhibition of the electron transport chain amplified the TRAIL-induced apoptosis and proapoptotic events. This amplification was also significantly abolished by MnTBaP treatment. Our data indicate that mitochondrial O2(•-) mediates mitochondrial and ER dysfunctions during TRAIL-induced apoptosis in Jurkat cells. The present findings suggest that pharmacological agents increasing mitochondrial O2(•-) may serve as clinical drugs that amplify TRAIL effectiveness toward cancer cells.

Cyclophilin 40 alters UVA-induced apoptosis and mitochondrial ROS generation in keratinocytes

The CyP40 protein encoded by PPID gene is a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family. PPIases catalyze the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and accelerate the folding of proteins. The CyP40 protein has been shown to possess PPIase activity and, similar to other family members, can bind to the immunosuppressant drug cyclosporin A (CsA). In this study, we created keratinocyte cell lines with CyP40 being stably knocked down using viral particles containing shRNA for CyP40 which knocked down the expression level of CyP40 transcripts by 90-99%. The proliferation rates of the cell lines with silenced CyP40 were decreased compared to the control cells. After UVA irradiation, the rate of apoptosis was found to be significantly lower in CyP40 silenced cell lines than it was in control cells. Moreover, mitochondrial membrane potential (MMP) was found to be less dissipated and mitochondrial permeability transition pore (MPTP) less active in cells with knocked down CyP40 than in control cells after UVA irradiation. Also, less mitochondrial superoxide was detected in the cells with silenced CyP40 compared to control cells after UVA exposure. Moreover, silencing of CyP40 partially modulates expression of key genes involved in mitochondrial pore formation including CyPD, ANTs and VDAC family members. The ability of CyP40 to regulate UV induced apoptosis implicates this protein as a potential target for therapy in cancer cells.

Hydrogen peroxide induces cell death in human TRAIL-resistant melanoma through intracellular superoxide generation

Intracellular reactive oxygen species (ROS) such as hydrogen peroxide (H(2)O2()) are thought to mediate apoptosis induced by death receptor ligands, including tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). However, the role of H(2)O(2) is controversial, since some evidence suggests that H(2)O(2) acts as an anti-apoptotic factor. Here, we show that exogenously applied H(2)O(2) (30-100 µM) induces cell death in TRAIL-resistant human melanoma cells via intracellular superoxide (O(2)-) generation. H(2)O(2) induced apoptotic or necrotic cell death, depending on the concentration of the oxidant applied; low concentrations of H(2)O(2) preferentially activated the caspase-dependent apoptotic pathway, while high concentrations of H(2)O(2) induced apoptotic and necrotic cell death in a caspase-independent manner. The H(2)O(2)-induced cell death was associated with increased mitochondrial membrane potential collapse and caspase-3/7 activation and ER stress responses including caspase-12 and X-box-binding protein-1 (XBP-1) activation. H(2)O(2) induced intracellular O2- generation even within the mitochondria, while TRAIL did not. The superoxide dismutase mimetic antioxidant MnTBaP [Mn (III) tetrakis (4-benzonic acid) porphyrin chloride] inhibited the H(2)O(2)-induced O(2)- generation, apoptosis and XBP-1 and caspase-12 activation at comparable concentrations. Importantly, H(2)O(2) treatment caused minimal O(2)- generation and apoptosis in normal primary melanocytes. These data show that H(2)O(2) induces endoplasmic reticulum-associated cell death via intracellular O(2)- generation and that malignant melanoma cells are more susceptible than normal cells to this oxidative cell death. The findings suggest that H(2)O(2) has therapeutic potential in the treatment of TRAIL-resistant melanoma.

Mitochondria take up Ca2+ in two steps dependently on store-operated Ca2+ entry in mast cells

The ability of mitochondria to take up Ca2+ has important functional implications for modulation of cellular Ca2+ signaling. Mitochondrial Ca2+ uptake is stimulated by an increase in cytosolic Ca2+ concentration ([Ca2+]c). Here, we found that the increase in mitochondrial Ca2+ concentration ([Ca2+]m) occurs in two steps in a single antigen-activated mast cell in the presence of extracellular Ca2+ (1.0 mM). The two-step elevation of [Ca2+]m was also observed after adding thapsigargin, an inhibitor of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase. The proportion of mitochondria showing the two-step Ca2+ elevation dropped off in direct accord with decrease in extracellular Ca2+ concentration. The second step of the [Ca2+]m increase was suppressed significantly in the absence of extracellular Ca2+ and in knockdown cells of stromal interaction molecule 1 (STIM1), an essential molecule on endoplasmic reticulum (ER) membrane for store-operated Ca2+ entry, in the presence of extracellular Ca2+ (1.0 mM), while the first elevation was not affected in either case. The results indicate that mitochondria take up cytosolic Ca2+ in two steps; first and second uptakes are derived from the Ca2+ release from ER and the Ca2+ influx through store-operated Ca2+ channels, respectively. Additionally, rotenone and antimycin A, which are inhibitors of mitochondrial electron transport complex I and III, respectively, diminished mitochondrial Ca2+ uptake and significantly suppressed degranulation stimulated with antigen. The mitochondrial Ca2+ uptake may modulate mast cell function by regulating the [Ca2+]c.

Diallyl trisulfide sensitizes human melanoma cells to TRAIL-induced cell death by promoting endoplasmic reticulum-mediated apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is promising for cancer treatment because of its selective cytotoxicity toward tumor cells. However, some cancer cell types including malignant melanoma cells are resistant to TRAIL cytotoxicity. Here, we show that diallyl trisulfide (DATS), a garlic organosulfur compound, sensitizes melanoma cells to TRAIL-induced apoptosis while sparing normal cells. DATS also potentiates apoptosis induced by agonistic antibodies against death receptors (DR) 4 and DR5. The amplification of DR-mediated apoptosis was associated with increased mitochondrial membrane potential collapse and caspase-3/7 activation. However, these events were not sufficient for full sensitization. TRAIL also induced endoplasmic reticulum (ER) stress, as indicated by the activation of X-box-binding protein 1 and caspase-12 and DATS poten-tiated both events. Moreover, inhibition of caspase-12, but not caspase-4, abolished the amplification of apoptosis, indicating that ER stress plays a crucial role. On the other hand, DATS and/or TRAIL induced minimal apoptosis and caspase-12 activation in melanocytes despite their substantial expression of DR4 and DR5 on the cell surface. Our data suggest that DATS amplifies death ligand-induced melanoma cell death by disrupting their adaptation to ER-mediated death pathway. The present findings raise the possibility that DATS may be combined with death ligands to treat TRAIL-resistance melanoma cells without impairing its tumor selectivity.

Depolarization potentiates TRAIL-induced apoptosis in human melanoma cells: role for ATP-sensitive K+ channels and endoplasmic reticulum stress

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is promising for cancer treatment owing to its selective cytotoxicity against malignant cells. However, some cancer cell types, including malignant melanoma cells, are resistant to TRAIL-induced apoptosis. Therefore, drugs that can amplify TRAIL cytotoxicity are urgently required. Depolarization of the plasma membrane potential is associated with apoptosis induced by a variety of death-inducing agents but its role in apoptosis remains a matter of debate. We found that TRAIL treatment resulted in robust depolarization in human melanoma cells with a considerable lag (2-4 h). Moreover, membrane-depolarizing agents, including K+ and ATP-sensitive K+ (KATP) channel inhibitors glibenclamide and U37883A enhanced TRAIL-induced apoptosis. On the contrary, inhibitors of calcium- and voltage-dependent K+ channels and mitochondrial KATP channels had no such effects. Melanocytes were insensitive to TRAIL-induced depolarization and apoptosis as well as to the sensitization by membrane-depolarizing agents despite their substantial surface expression of death receptors. TRAIL induced robust activation of X-box-binding protein-1 and caspase-12, both of which were enhanced by the K+ and KATP channel inhibitors, but not by other K+ channel inhibitors. Finally, caspase-12-selective inhibitor completely abolished the amplification of apoptosis. These findings suggest that depolarization promotes endoplasmic reticulum stress-mediated death pathway, thereby amplifying TRAIL cytotoxicity. Thus, membrane-depolarizing agents such as KATP channel inhibitors may have therapeutic potential in the treatment of TRAIL-resistant cancer cells without impairing tumor-selectivity.

Epigallocatechin-3-gallate induces cytokine production in mast cells by stimulating an extracellular superoxide-mediated calcium influx

The green tea polyphenol (-)-epigallocatechin-3-O-gallate (EGCG) has various biological activities, including anti-inflammatory, anti-neoplastic, anti- and pro-apoptotic, and neuroprotective effects. Although these are often associated with increased intracellular reactive oxygen species (ROS) and Ca(2+) levels, their involvement in biological effects is poorly understood. Here we report that EGCG induces cytokine production in mast cells via Ca(2+) influx and ROS generation. EGCG at concentrations of ≥50 μM induced interleukin-13 and tumor necrosis factor-α production in RBL-2H3 and bone marrow-derived mast cells. The effects were dependent on extracellular Ca(2+), and EGCG induced Ca(2+) release from intracellular stores and Ca(2+) influx. Ca(2+) influx was suppressed by 2-aminoethoxydiphenyl borate, an inhibitor of store-operated Ca(2+) (SOC) channels, including Ca(2+) release-activated Ca(2+) channels and transient receptor potential canonical channels. EGCG failed to induce Ca(2+) influx through SOC channels. EGCG-activated Ca(2+) channels were genetically and pharmacologically distinct from Ca(v)1.2 L-type Ca(2+) channels, another route of Ca(2+) influx into mast cells. EGCG evoked release of superoxide (O(2)(·-)) into the extracellular space. Exogenous superoxide dismutase, but not catalase, inhibited EGCG-evoked Ca(2+) influx and cytokine production, indicating that extracellular O(2)(·-) regulates these events. EGCG can serve as a powerful tool for studying O(2)(·-)-regulated Ca(2+) channels, which may be selectively involved in the regulation of cytokine production but have yet to be elucidated.

Atractyloside induces low contractile reaction of arteriolar smooth muscle through mitochondrial damage

Atractyloside is the principal naturally occurring active ingredient in ethnomedicines and animal grazing forage. Evidence that atractyloside can induce opening of the mitochondrial permeability transition pore (mPTP) indicates that mitochondrial mechanisms may play an important role in pathophysiological lesions of the heart, liver and kidney after atractyloside poisoning. Therefore, in this study we investigated the association of atractyloside-induced mitochondrial damage in arteriolar smooth muscle cells (ASMCs) with contractile reaction. Atractyloside led to depolarized and swollen or damaged ASMC mitochondria, which might be related to the concentration-dependent induction of mPTP opening. Relative ATP content in ASMCs was significantly reduced by 48%, 63% and 66% of control when cells were treated with 7.5, 10, and 15 µm atractyloside for 10 min, respectively, and ASMCs were hyperpolarized. In addition, the contractile responsiveness of ASMCs was eventually weakened. These results suggest that atractyloside has a toxic effect on vasoreactivity, which is possibly related to mitochondrial damage.

Gold activates mast cells via calcium influx through multiple H2O2-sensitive pathways including L-type calcium channels

Heavy metals, including gold, induce severe contact hypersensitivity and autoimmune disorders, which develop through an initial Th2-independent process followed by a Th2-dependent process. It has been shown that mast cell activation plays a role in the Th2-independent process and that gold stimulates histamine release in vitro. However, the mechanisms of the gold-induced mast cell activation remain largely unclear. Here we report that gold directly activates mast cells in a Ca2+-dependent manner. HAuCl4 [Au(III)] at nontoxic concentrations (≤50 μM) induced substantial degranulation and leukotriene C4 secretion in an extracellular Ca2+-dependent manner. Au(III) induced a robust Ca2+ influx but not Ca2+ mobilization from internal stores. Au(III) also stimulated intracellular production of reactive oxygen species, including H2O2, and blockade of the production abolished the mediator release and Ca2+ influx. Au(III) induced Ca2+ influx through multiple store-independent Ca2+ channels, including Cav1.2 L-type Ca2+ channels (LTCCs) and 2-aminoethoxydiphenyl borate (2-APB)-sensitive Ca2+ channels. The 2-APB-sensitive channel seemed to mediate Au(III)-induced degranulation. Our results indicate that gold stimulates Ca2+ influx and mediator release in mast cells through multiple H2O2-sensitive Ca2+ channels including LTCCs and 2-APB-sensitive Ca2+ channels. These findings provide insight into the roles of these Ca2+ channels in the Th2-independent process of gold-induced immunological disorders.

P2Y(13) receptor is responsible for ADP-mediated degranulation in RBL-2H3 rat mast cells

Extracellular ADP is known to play many important physiological roles. In this study, we identified the P2Y(13) receptor in a rat mast cell line (RBL-2H3) and explored the functional role of ADP, its endogenous agonist. ADP induced both intracellular calcium mobilization and release of hexosaminidase (Hex). In an assay of intracellular calcium, ADP was 100-fold less potent than and equally efficacious as the P2Y(1) receptor-selective agonist MRS2365. However, ADP was more potent and efficacious than MRS2365 in inducing Hex release and in enhancing antigen-induced Hex release. ADP-induced intracellular calcium mobilization was blocked by phospholipase C inhibitor U73122 and by P2Y(1) receptor-selective antagonist MRS2500, but not by pertussis toxin (PTX), suggesting a mechanism mediated by the G(q)-coupled P2Y(1) receptor, but not P2Y(13) (G(i)-coupled) or P2X receptors. ADP-induced Hex release was blocked by PTX and a selective P2Y(13) receptor antagonist MRS2211, but not by MRS2500 or P2Y(1) receptor-specific siRNA, suggesting a G(i)-coupled P2Y(13) receptor-related mechanism. Measurement of gene expression confirmed high expression of both P2Y(1) and P2Y(13) receptors (in comparison to a previously reported P2Y(14) receptor) in RBL-2H3 cells. Thus, we demonstrated that ADP-mediated intracellular calcium mobilization and Hex release in RBL-2H3 cells are via P2Y(1) and P2Y(13) receptors, respectively. Selective antagonists of the P2Y(13) receptor might be novel therapeutic agents for various allergic conditions.

Ragweed pollen-mediated IgE-independent release of biogenic amines from mast cells via induction of mitochondrial dysfunction

Normal functions of mitochondria are required for physiological dynamics of cells, while their dysfunction contributes to development of various disorders including those of immune system. Here we demonstrate that exposure of mast cells to ragweed pollen extract increases production of H(2)O(2) via mitochondrial respiratory complex III. These mitochondrial ROS (mtROS) enhance secretion of histamine and serotonin from mast cells, but not enzymes such as beta-hexosaminidase, independently from FcvarepsilonRI-generated stimuli. The release of biogenic amines is associated with inhibition of secretory granules' H(+)-ATPase activity, activation of PKC-delta and microtubule-dependent motility, and it is independent from intracellular free Ca(2+) levels. To asses differences from IgE-mediated mast cell degranulation we show that mtROS decrease antigen-triggered beta-hexosaminidase release, while they are synergistic with antigen-induced IL-4 production in sensitized cells. Taken together, these data indicate that mitochondrial dysfunction can act independently from adaptive immunity, as well as augments Th2-type responses. Pharmacological maintenance of physiological mitochondrial function could have clinical benefits in prevention and treatment of allergic diseases.

Discrete generations of intracellular hydrogen peroxide and superoxide in antigen-stimulated mast cells: reciprocal regulation of store-operated Ca2+ channel activity

Mast cells and T cells produce reactive oxygen species (ROS) after stimulation with the high-affinity IgE receptor (Fc epsilon RI) and T cell receptor. A growing body of evidence suggests the existence of ROS-regulated intracellular and/or plasma membrane Ca(2+) channels in these cells but their molecular entities remain to be identified. Here, we report that store-operated Ca(2+) channel (SOC) activity is regulated by superoxide (O(2)(*-)) and hydrogen peroxide (H(2)O(2)) in mast cells. MnTBaP (Mn(III)tetrakis(4-benzoic acid)porphyrin) and ebselen (2-phenyl-1,2-benziso-selenazol-3(2H)-one) selectively blocked the generation of O(2)(*-) and H(2)O(2), respectively, in antigen-stimulated cells. The H(2)O(2) generation was dependent on the Src family kinase (SFK) and phosphatidylinositol-3-kinase (PI3K) activities but independent of extracellular Ca(2+), and the Fc epsilon RI beta-chain immunoreceptor tyrosine-based activation motif played an essential role. On the other hand, O(2)(*-) generation was strictly dependent on extracellular Ca(2+), but negatively regulated by the SFK and PI3K activities. Inhibition of O(2)(*-) generation resulted in increased H(2)O(2) generation and reduced SOC activity, although it had a minimal effect on endoplasmic reticulum Ca(2+) store depletion. On the contrary, inhibition of H(2)O(2) generation resulted in increased intracellular O(2)(*-) generation and augmented SOC activity. The findings suggest that O(2)(*-) and H(2)O(2), which are generated by separate signaling pathways/sources, reciprocally regulate SOC activity in mast cells. Such generations of multiple oxidant species and their distinct roles in the regulation of SOC activity may facilitate the fine tuning of Ca(2+) signaling in mast cells.

Ca v 1.2 L-type Ca2+ channel protects mast cells against activation-induced cell death by preventing mitochondrial integrity disruption

In non-excitable cells, store-operated Ca(2+) channels (SOCs) are the principal routes of Ca(2+) entry. Recently, store-independent Ca(2+) channels which are pharmacologically and/or immunologically similar to L-type Ca(2+) channels (LTCCs) have been shown to exist in various hematopoietic cells, including T cells, B cells and neutrophils. We previously reported that mast cells express LTCCs which regulate mast cell effector responses in a distinct manner from SOCs. In the present study, we examined the possible role for LTCCs in mast cell survival. Both RBL-2H3 mast cells and bone marrow-derived mast cells underwent considerable apoptosis after treatment with thapsigargin (Tg) but not stimulation through the high-affinity IgE receptor (Fc epsilon RI). The LTCC-selective antagonists such as nifedipine greatly augmented Fc epsilon RI-mediated apoptosis, while the LTCC-selective agonist (S)-BayK8644 blocked Tg-induced apoptosis. The modulation of apoptosis was accompanied by altered mitochondrial integrity, as measured with the mitochondrial membrane potential, cytochrome c release and caspase-3/7 activation. Fc epsilon RI stimulation induced mitochondrial Ca(2+) ([Ca(2+)](m)) entry through both SOCs and LTCCs, while Tg evoked [Ca(2+)](m) entry through LTCCs but not SOCs. The LTCC-selective antagonists blocked [Ca(2+)](m) entry, whereas (S)-BayK8644 augmented Tg-induced [Ca(2+)](m) entry. Moreover, blockade of the expression of the alpha(1C) subunit of Ca(v)1.2 LTCC using small-interfering RNA strongly augmented Fc epsilon RI-mediated apoptosis, mitochondrial integrity, and mitochondrial Ca(2+) collapse, and abolished the protective effects of (S)-BayK8644 against Tg-induced apoptosis. These findings suggest that Ca(v)1.2 LTCC protects mast cells against activation-induced cell death by preventing mitochondrial integrity disruption.

Ca2+-dependent mast cell death induced by Ag (I) via cardiolipin oxidation and ATP depletion

In genetically susceptible humans and/or experimental animals, ions of heavy metals, Hg (II), Au (III), and Ag (I) have been shown to strongly induce autoimmunity, in which mast cells have been implicated to play a role. Here, we demonstrate that Ag (I) application results in mast cell death through a unique Ca(2+)- and mitochondria-dependent pathway. As cellular susceptibilities to Ag (I) cytotoxicity varied considerably, we analyzed the cell death pathway in the low and high responding cells. In the low responding cells, long application (e.g., 20 h) of Ag (I) at concentrations (>or=30 microM) induced cell death, which was accompanied by mitochondrial membrane depolarization, cyt c release, and caspase-3/7 activation but was not prevented by selective inhibitors of caspase-3/7 and the mitochondrial permeability transition. The cell death was preceded by elevations in the cytoplasmic and mitochondrial Ca(2+) levels, and Ca(2+) responses and cell death were prevented by thiol reagents, including DTT, N-acetylcysteine, and reduced glutathione monoethyl ester. In the high responding cells, Ag (I) evoked considerable cell death by necrosis within 1 h, without inducing caspase activation, and this cell death was reduced significantly by depleting extracellular but not intracellular Ca(2+). Moreover, Ag (I) strongly induced Ca(2+)-dependent CL oxidation and intracellular ATP depletion, both of which were blocked by thiol reagents. These results suggest that Ag (I) activates thiol-dependent Ca(2+) channels, thereby promoting Ca(2+)-dependent CL oxidation, cyt c release, and ATP depletion. This necrotic cell death may play roles in Ag-induced inflammation and autoimmune disorders.

Aspirin and salicylates modulate IgE-mediated leukotriene secretion in mast cells through a dihydropyridine receptor-mediated Ca(2+) influx

Aspirin is a well-known nonsteroidal anti-inflammatory drug (NSAID) that may potentiate some acute allergies and causes adverse immunological reactions collectively referred to as aspirin intolerance. Aspirin intolerance is accompanied by increased leukotriene (LT) synthesis, and high levels of serum IgE are a risk factor for NSAID sensitivity. Here we demonstrate that aspirin modulates LTC(4) secretion in mast cells. Therapeutic levels of aspirin and salicylates (<or=0.3 mM, i.e., the concentrations observed in vivo in the use of antipyretic analgesic) increased IgE-mediated LTC(4) secretion. Aspirin-induced stimulation was accompanied by increased Ser-505 phosphorylation of cytosolic phospholipase A(2), which occurred independently of extracellular signal-regulated protein kinase-1/2 and p38 mitogen-activated protein kinase pathways. Aspirin also increased IgE-mediated Ca(2+) influx, whereas aspirin at concentrations of >or=0.3 mM dose-dependently reduced Ca(2+) store emptying and Ca(2+) release-activated Ca(2+) channel activation. Instead, aspirin facilitated a dihydropyridine receptor-mediated Ca(2+) influx, resulting in increased LTC(4) secretion. This novel action of aspirin may play roles in exacerbation of immediate allergy and aspirin intolerance.

L-type Ca2+ channels in mast cells: activation by membrane depolarization and distinct roles in regulating mediator release from store-operated Ca2+ channels

Store-operated Ca(2+) channels (SOCs) are considered to be the principal route of Ca(2+) influx in non-excitable cells. We have previously shown that in mast cells IgE+antigen (Ag) induces a dihydropyridine (DHP)-sensitive Ca(2+) influx independently of Ca(2+) store depletion. Since the DHP receptor is the alpha subunit of L-type Ca(2+) channels (LTCCs), we examined the possible role of LTCCs in mast cell activation. Mast cells exhibited substantial expression of the alpha(1C) (Ca(V)1.2) subunit mRNA and protein on their cell surface. IgE+Ag-induced Ca(2+) influx was substantially reduced by the LTCC inhibitor nifedipine, and enhanced by the LTCC activator (S)-BayK8644, whereas these agents had minimal effects on thapsigargin (TG)-induced Ca(2+) influx. These LTCC-modulating agents regulated IgE+Ag-induced cell activation but not TG-induced cell activation. Inhibition of SOCs by 2-aminoethoxydiphenyl borate reduced both degranulation and production of cytokines, including interleukin-13 and tumor necrosis factor-alpha, whereas LTCC modulation reciprocally regulated degranulation and cytokine production. IgE+Ag, but not TG, induced substantial plasma membrane depolarization, which stimulated a DHP-sensitive Ca(2+) response. Moreover, IgE+Ag-, but not TG-induced mitochondrial Ca(2+) increase was regulated by LTCC modulators. Finally, gene silencing analyses using small interfering RNA revealed that the alpha(1C) (Ca(V)1.2) LTCC mediated the pharmacological effects of the LTCC-modulating agents. These results demonstrate that mast cells express LTCCs, which becomes activated by membrane depolarization to regulate cytosolic and mitochondrial Ca(2+), thereby controlling mast cell activation in a distinct manner from SOCs.

Extracellular superoxide released from mitochondria mediates mast cell death by advanced glycation end products

Advanced glycation end products (AGEs) accumulate during aging and to higher extents under pathological conditions such as diabetes. Since we previously showed that mast cells expressed the AGE-binding protein, receptor for AGEs (RAGE) on their cell surface, we examined whether AGE affected mast cell survival. Herein, we demonstrate that mast cells undergo apoptosis in response to AGE. Glycated albumin (GA), an AGE, but not stimulation with the high-affinity IgE receptor (FcepsilonRI), can induce mast cell death, as measured by annexin V/propidium iodide double-staining. GA (> or =0.1 mg/ml) exhibited this pro-apoptotic activity in a concentration-dependent manner. GA and FcepsilonRI stimulation increased the cytosolic Ca(2+) levels to a similar extent, whereas GA, but not FcepsilonRI stimulation, caused mitochondrial Ca(2+) overload and membrane potential collapse, resulting in mitochondrial integrity disruption, cytochrome c release and caspase-3/7 activation. In addition, GA, but not FcepsilonRI stimulation, induced extracellular release of superoxide from mitochondria, and this release played a key role in the disruption of Ca(2+) homeostasis. Knockdown of RAGE expression using small interfering RNA abolished GA-induced apoptosis, mitochondrial Ca(2+) overload, and superoxide release, demonstrating that RAGE mediates the GA-induced mitochondrial death pathway. AGE-induced mast cell apoptosis may contribute to the immunocompromised and inflammatory conditions.

The neuropeptide pituitary adenylate cyclase activating polypeptide modulates Ca2+ and pro-inflammatory functions in human monocytes through the G protein-coupled receptors VPAC-1 and formyl peptide receptor-like 1

In human neutrophils, the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) acting via the G protein-coupled receptors vasoactive intestinal peptide/PACAP receptor 1 (VPAC-1) and formyl peptide receptor-like 1 (FPRL1) modulates Ca2+ and pro-inflammatory activities. We evaluated in human monocytes the importance of the Ca2+ signal and the participation of FPRL1 in PACAP-associated signaling pathways and pro-inflammatory activities. PACAP-evoked Ca2+ transient involved both Ca2+ influx and intracytoplasmic Ca2+ mobilisation. This was pertussis toxin, protein kinase A and adenylate cyclase dependent indicating the participation of Galphai and Galphas with mobilisation of both InsP3 sensitive and insensitive stores. Intra- or extracellular Ca2+ depletion resulted in the inhibition of PACAP-induced, Akt, ERK, p38 and NF-kappaB activations as well as a decrease in PACAP-associated reactive oxygen species (ROS) production and integrin CD11b membrane upregulation. The FPRL1 antagonist, Trp-Arg-Trp-Trp-Trp (WRW4), decreased PACAP-evoked Ca2+ signal, Akt, ERK phosphorylation, ROS and CD11b upregulation without affecting p38 phosphorylation. NF-kappaB inhibitors prevented PACAP-induced Ca2+ mobilisation. Monocytes pre-treatment with fMLP but not with LPS desensitised cells to the pro-inflammatory effects of PACAP. Thus, both intra- and extracellular Ca2+ play a role in controlling pro-inflammatory functions stimulated by PACAP which acts through a VPAC-1, FPRL1/Galphai/PI3K/ERK pathway and a VPAC-1/Galphas/PKA/p38 pathway to fully activate monocytes.

Galectin-3 but not galectin-1 induces mast cell death by oxidative stress and mitochondrial permeability transition

Galectin-1 and galectin-3 are the most ubiquitously expressed members of the galectin family and more importantly, these two molecules are shown to have opposite effects on pro-inflammatory responses and/or apoptosis depending on the cell type. Herein, we demonstrate for the first time that galectin-3 induces mast cell apoptosis. Mast cells expressed substantial levels of galectin-3 and galectin-1 and to a lesser extent the receptor for advanced glycation end products (RAGE) on their surfaces. Treatment of cells with galectin-3 at concentrations of > or =100 nM for 18-44 h resulted in cell death by apoptosis. Galectin-3-induced apoptosis was completely prevented by lactose, neutralizing antibody to RAGE, and the caspase-3 inhibitor z-DEVD-fmk. Galectin-3-induced apoptosis was also completely abolished by dithiothreitol and superoxide dismutase, but not inhibited by catalase. Moreover, galectin-3 but not galectin-1 induced the release of superoxide, which was blocked by lactose, anti-RAGE, and dithiothreitol. Finally, galectin-3-induced apoptosis was blocked by bongkrekic acid, an antagonist of the mitochondrial permeability transition pore (PTP), while atractyloside, an agonist of the PTP, greatly facilitated galectin-1-induced apoptosis. These data suggest that galectin-3 induces oxidative stress, PTP opening, and the caspase-dependent death pathway by binding to putative surface receptors including RAGE via the carbohydrate recognition domain.

Bongkrekic acid and atractyloside inhibits chloride channels from mitochondrial membranes of rat heart

The aim of this work was to characterize the effect of bongkrekic acid (BKA), atractyloside (ATR) and carboxyatractyloside (CAT) on single channel properties of chloride channels from mitochondria. Mitochondrial membranes isolated from a rat heart muscle were incorporated into a bilayer lipid membrane (BLM) and single chloride channel currents were measured in 250/50 mM KCl cis/trans solutions. BKA (1-100 microM), ATR and CAT (5-100 microM) inhibited the chloride channels in dose-dependent manner. The inhibitory effect of the BKA, ATR and CAT was pronounced from the trans side of a BLM and it increased with time and at negative voltages (trans-cis). These compounds did not influence the single channel amplitude, but decreased open dwell time of channels. The inhibitory effect of BKA, ATR and CAT on the mitochondrial chloride channel may help to explain some of their cellular and/or subcellular effects.