Simultaneous measurement of superoxide generation and intracellular Ca2+ concentration reveals the effect of extracellular Ca2+ on rapid and transient contents of superoxide generation in differentiated THP-1 cells

Rapid on-site dual optical system to measure specific reactive oxygen species (O2-• and OCl-) in a tiny droplet of whole blood

Oxidative stress has been implicated in various disorders and controlling it would be important for healthy life. We have developed a new optical system for easily and accurately measuring oxidative stress in whole blood. It is optimized for simultaneously detecting reactive oxygen species (ROS) and highly reactive ROS (hROS), elicited mostly by white blood cells in a few microliters of blood. Results obtained by using this system show at least four important findings. 1) chemiluminescence of MCLA was confirmed to be attributable to O2-•. 2) PMA-stimulated cells released O2-• longer and more slowly than fMLP-stimulated ones. 3) fluorescence produced by APF oxidation was confirmed to be attributable to hROS, mostly OCl-, produced by myeloperoxidase. 4) the generation of OCl- was found to be a slower process than the O2-• generation. We also conducted pilot studies of oxidative stress in healthy volunteers.

Phytochemicals prevent mitochondrial membrane permeabilization and protect SH-SY5Y cells against apoptosis induced by PK11195, a ligand for outer membrane translocator protein

Epidemiological studies present the beneficial effects of dietary habits on prevention of aging-associated decline of brain function. Phytochemicals, the second metabolites of food, protect neuronal cells from cell death in cellular models of neurodegenerative disorders, and the neuroprotective activity has been ascribed to the anti-oxidant and anti-inflammatory functions. In this paper, the cellular mechanism of neuroprotection by phytochemicals was investigated, using the cellular model of mitochondrial apoptosis induced by PK11195, a ligand of outer membrane translocator protein, in SH-SY5Y cells. PK11195 induced mitochondrial membrane permeabilization with rapid transit production of superoxide (superoxide flashes) and calcium release from mitochondria, and activated apoptosis signal pathway. Study on the structure-activity relationship of astaxanthin, ferulic acid derivatives, and sesame lignans revealed that these phytochemicals inhibited mitochondrial membrane permeabilization and protected cells from apoptosis. Ferulic acid derivatives and sesame lignans inhibited or enhanced the mitochondrial pore formation and cell death by PK11195 according to their amphiphilic properties, not directly depending on the antioxidant activity. Regulation of pore formation at mitochondrial membrane is discussed as a novel mechanism behind neuroprotective activity of phytochemicals in aging and age-associated neurodegenerative disorders, and also behind dual functions of phytochemicals in neuronal and cancer cells.

Inhibition of neutrophil superoxide generation by shikonin is associated with suppression of cellular Ca(2+) fluxes

Shikonin, an anti-inflammatory compound of “Shikon”, inhibits the neutrophil superoxide (O₂^•−) generation by NADPH oxidase 2 (Nox2); however, the mechanisms of how shikonin affects Nox2 activity remained unclear. We aimed to elucidate the relationship between the inhibition of Nox2 activity and influences on intracellular Ca²⁺ concentration ([Ca²⁺]_i) by shikonin. For this purpose, we used a simultaneous monitoring system for detecting changes in [Ca²⁺]_i (by fluorescence) and O₂^•− generation (by chemiluminescence) and evaluated the effects of shikonin on neutrophil-like HL-60 cells stimulated with N-formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLP). Since fMLP activates Nox2 by elevation in [Ca²⁺]_i via fluxes such as inositol 1,4,5-trisphosphate-induced Ca²⁺ release (IICR) and store-operated Ca²⁺ entry (SOCE), we also evaluated the effects of shikonin on IICR and SOCE. Shikonin dose-dependently inhibited the fMLP-induced elevation in [Ca²⁺]_i and O₂^•− generation (IC₅₀ values of 1.45 and 1.12 µM, respectively) in a synchronized manner. Analyses of specific Ca²⁺ fluxes showed that shikonin inhibits IICR and IICR-linked O₂^•− generation (IC₅₀ values: 0.28 and 0.31 µM for [Ca²⁺]_i and O₂^•−, respectively), as well as SOCE and SOCE-linked O₂^•− generation (IC₅₀ values: 0.39 and 0.25 µM for [Ca²⁺]_i and O₂^•−, respectively). These results suggested that shikonin inhibits the O₂^•− generation by Nox2 in fMLP-stimulated neutrophils by targeting Ca²⁺ fluxes such as IICR and SOCE.

Identification of the tetraspanin CD82 as a new barrier to xenotransplantation

Significant immunological obstacles are to be negotiated before xenotransplantation becomes a clinical reality. An initial rejection of transplanted vascularized xenograft is attributed to Galα1,3Galβ1,4GlcNAc-R (Galα1,3-Gal)-dependent and -independent mechanisms. Hitherto, no receptor molecule has been identified that could account for Galα1,3-Gal-independent rejection. In this study, we identify the tetraspanin CD82 as a receptor molecule for the Galα1,3-Gal-independent mechanism. We demonstrate that, in contrast to human undifferentiated myeloid cell lines, differentiated cell lines are capable of recognizing xenogeneic porcine aortic endothelial cells in a calcium-dependent manner. Transcriptome-wide analysis to identify the differentially expressed transcripts in these cells revealed that the most likely candidate of the Galα1,3-Gal-independent recognition moiety is the tetraspanin CD82. Abs to CD82 inhibited the calcium response and the subsequent activation invoked by xenogeneic encounter. Our data identify CD82 on innate immune cells as a major "xenogenicity sensor" and open new avenues of intervention to making xenotransplantation a clinical reality.

Dihydropyridine calcium channel blockers inhibit non-esterified-fatty-acid-induced endothelial and rheological dysfunction

Circulating NEFAs (non-esterified fatty acids) from adipose tissue lipolysis lead to endothelial dysfunction and insulin resistance in patients with the metabolic syndrome or Type 2 diabetes mellitus. The aim of the present study was to test the hypothesis that DHP (dihydropyridine) CCBs (calcium channel blockers) prevent NEFA-induced endothelial and haemorheological dysfunction independently of their antihypertensive properties. Using a double-blind cross-over study design, nifedipine, amlodipine, diltiazem or placebo were administered to eight healthy subjects for 2 days before each study day. On the study days, the following were assessed before and after the infusion of lipid and heparin to raise serum NEFAs: endothelial function, by measuring FBF (forearm blood flow) responses to ACh (acetylcholine); leucocyte activation, by ex vivo measurement of plasma MPO (myeloperoxidase) levels, adherent leucocyte numbers and whole blood transit time through microchannels; and oxidative stress, by determining plasma levels of d-ROMs (derivatives of reactive oxygen metabolites). Effects of the CCBs on NF-κB (nuclear factor κB) p65 phospholylation stimulated by NEFAs were assessed in cultured monocytic cells in vitro. Elevated NEFAs reduced the responses to ACh and significantly increased whole blood transit time, adherent leucocyte numbers and d-ROMs. Nifedipine and amlodipine, but not diltiazem, prevented NEFA-induced endothelial dysfunction, leucocyte activation and enhancement of oxidative stress without affecting BP (blood pressure), whereas all these drugs prevented NEFA-induced p65 activation in vitro. These results suggest that DHP CCBs, independent of their antihypertensive properties in humans, prevent NEFA-induced endothelial and haemorheological dysfunction through inhibition of NEFA-induced leucocyte activation, although the sensitivity to drugs of leucocyte Ca2+ channels may differ among cells.

Simultaneous monitoring of superoxides and intracellular calcium ions in neutrophils by chemiluminescence and fluorescence: evaluation of action mechanisms of bioactive compounds in foods

We have developed a measuring system for simultaneous monitoring of chemiluminescence and fluorescence, which indicate respectively, (i) generation of superoxide anion radicals (O2(-•)) and (ii) change in the intracellular calcium ion concentration ([Ca(2+)]i) of neutrophils triggered by the mechanism of innate immune response. We applied this measuring system for establishing a method to distinguish between anti-inflammatory actions and antioxidant actions caused by bioactive compounds. We evaluated anti-inflammatory agents (zinc ion [Zn(2+)] and ibuprofen) and antioxidants (superoxide dismutase [SOD] and ascorbic acid). It was shown that ibuprofen and Zn(2+) were anti-inflammatory while SOD and ascorbic acid were anti-oxidative. We conclude that it is possible to determine the mechanism of action of bioactive compounds using this method.

Propofol inhibits superoxide production, elastase release, and chemotaxis in formyl peptide-activated human neutrophils by blocking formyl peptide receptor 1

Neutrophils play a critical role in acute and chronic inflammatory processes, including myocardial ischemia/reperfusion injury, sepsis, and adult respiratory distress syndrome. Binding of formyl peptide receptor 1 (FPR1) by N-formyl peptides can activate neutrophils and may represent a new therapeutic target in either sterile or septic inflammation. Propofol, a widely used i.v. anesthetic, has been shown to modulate immunoinflammatory responses. However, the mechanism of propofol remains to be established. In this study, we showed that propofol significantly reduced superoxide generation, elastase release, and chemotaxis in human neutrophils activated by fMLF. Propofol did not alter superoxide generation or elastase release in a cell-free system. Neither inhibitors of γ-aminobutyric acid receptors nor an inhibitor of protein kinase A reversed the inhibitory effects of propofol. In addition, propofol showed less inhibitory effects in non-FPR1-induced cell responses. The signaling pathways downstream from FPR1, involving calcium, AKT, and ERK1/2, were also competitively inhibited by propofol. These results show that propofol selectively and competitively inhibits the FPR1-induced human neutrophil activation. Consistent with the hypothesis, propofol inhibited the binding of N-formyl-Nle-Leu-Phe-Nle-Tyr-Lys-fluorescein, a fluorescent analog of fMLF, to FPR1 in human neutrophils, differentiated THP-1 cells, and FPR1-transfected human embryonic kidney-293 cells. To our knowledge, our results identify, for the first time, a novel anti-inflammatory mechanism of propofol by competitively blocking FPR1 in human neutrophils. Considering the importance of N-formyl peptides in inflammatory processes, our data indicate that propofol may have therapeutic potential to attenuate neutrophil-mediated inflammatory diseases by blocking FPR1.

The effects of Weichangshu tablet on intracellular Ca²⁺ concentration in cultured rat gastrointestinal smooth muscle cells

The objective of this study was to explore the effects of Weichangshu tablets on free Ca²⁺ concentration of the gastrointestinal smooth muscle cells of rats and the molecular mechanism of the Weichangshu tablets. Cultured SD rat gastrointestinal smooth muscle cells were divided into control group, Cisapride group, Weichangshu group, and control + ethylene glycol tetraacetic acid (EGTA) group, Cisapride + EGTA group, and Weichangshu + EGTA group. Laser scanning microscope and spectrophotometer detection were applied to detect the calcium concentration. The calcium concentrations in Weichangshu group and Cisapride group significantly increased vs. control, and those in Weichangshu group were higher than those in Cisapride group. Ca²⁺ concentration in Weichangshu + EGTA group, Cisapride + EGTA group vs. control + EGTA group were not significantly different. Weichangshu could increase gastrointestinal smooth muscle free Ca²⁺ concentration, and this role may be achieved through the promotion of cells within the flow of calcium ions.

Verapamil protects dopaminergic neuron damage through a novel anti-inflammatory mechanism by inhibition of microglial activation

Verapamil has been shown to be neuroprotective in several acute neurotoxicity models due to blockade of calcium entry into neurons. However, the potential use of verapamil to treat chronic neurodegenerative diseases has not been reported. Using rat primary mesencephalic neuron/glia cultures, we report that verapamil significantly inhibited LPS-induced dopaminergic neurotoxicity in both pre- and post-treatment experiments. Reconstituted culture studies revealed that the presence of microglia was essential in verapamil-elicited neuroprotection. Mechanistic studies showed that decreased production of inflammatory mediators from LPS-stimulated microglia underlay neuroprotective property of verapamil. Further studies demonstrated that microglial NADPH oxidase (PHOX), the key superoxide-producing enzyme, but not calcium channel in neurons, is the site of action for the neuroprotective effect of verapamil. This conclusion was supported by the following two observations: 1) Verapamil failed to show protective effect on LPS-induced dopaminergic neurotoxicity in PHOX-deficient (deficient in the catalytic subunit of gp91(phox)) neuron/glia cultures; 2) Ligand binding studies showed that the binding of [(3)H]Verapamil onto gp91(phox) transfected COS7 cell membranes was higher than the non-transfected control. The calcium channel-independent neuroprotective property of verapamil was further supported by the finding that R(+)-verapamil, a less active form in blocking calcium channel, showed the same potency in neuroprotection, inhibition of pro-inflammatory factors production and binding capacity to gp91(phox) membranes as R(-)-verapamil, the active isomer of calcium channel blocker. In conclusion, our results demonstrate a new indication of verapamil-mediated neuroprotection through a calcium channel-independent pathway and provide a valuable avenue for the development of therapy for inflammation-related neurodegenerative diseases.

Regulation of phagocyte NADPH oxidase by hydrogen peroxide through a Ca(2+)/c-Abl signaling pathway

The importance of H(2)O(2) as a cellular signaling molecule has been demonstrated in a number of cell types and pathways. Here we explore a positive feedback mechanism of H(2)O(2)-mediated regulation of the phagocyte respiratory burst NADPH oxidase (NOX2). H(2)O(2) induced a dose-dependent stimulation of superoxide production in human neutrophils, as well as in K562 leukemia cells overexpressing NOX2 system components. Stimulation was abrogated by the addition of catalase, the extracellular Ca(2+) chelator BAPTA, the T-type Ca(2+) channel inhibitor mibefradil, the PKCdelta inhibitor rottlerin, or the c-Abl nonreceptor tyrosine kinase inhibitor imatinib mesylate or by overexpression of a dominant-negative form of c-Abl. H(2)O(2) induced phosphorylation of tyrosine 311 on PKCdelta and this activating phosphorylation was blocked by treatment with rottlerin, imatinib mesylate, or BAPTA. Rac GTPase activation in response to H(2)O(2) was abrogated by BAPTA, imatinib mesylate, or rottlerin. In conclusion, H(2)O(2) stimulates NOX2-mediated superoxide generation in neutrophils and K562/NOX2 cells via a signaling pathway involving Ca(2+) influx and c-Abl tyrosine kinase acting upstream of PKCdelta. This positive feedback regulatory pathway has important implications for amplifying the innate immune response and contributing to oxidative stress in inflammatory disorders.

Protective effect of rebamipide against celecoxib-induced gastric mucosal cell apoptosis

A major clinical problem encountered with the use of non-steroidal anti-inflammatory drugs (NSAIDs) is gastrointestinal complications. We have previously suggested that both decreases in prostaglandin E(2) (PGE(2)) levels and mucosal apoptosis are involved in the development of NSAID-produced gastric lesions and that this apoptosis is mediated by an increase in the intracellular Ca(2+) concentration and the resulting endoplasmic reticulum (ER) stress response and mitochondrial dysfunction. Celecoxib and rebamipide are being used clinically as a safer NSAID and an anti-ulcer drug, respectively. In this study, we have examined the effect of rebamipide on celecoxib-induced production of gastric lesions. In mice pre-administered with a low dose of indomethacin, orally administered rebamipide suppressed celecoxib-induced mucosal apoptosis and lesion production but did not decrease in PGE(2) levels in the stomach. Rebamipide also suppressed celecoxib-induced increases in intracellular Ca(2+) concentration, the ER stress response, mitochondrial dysfunction and apoptosis in vitro. We also found that rebamipide suppresses the increases in intracellular Ca(2+) concentration induced by an activator of voltage-dependent L-type Ca(2+) channels and that another blocker of this channel suppresses celecoxib-induced increases in intracellular Ca(2+) concentration. These results suggest that celecoxib activates voltage-dependent L-type Ca(2+) channels and that rebamipide blocks this activation, resulting in suppression of celecoxib-induced apoptosis. We believe that this novel activity of rebamipide may play an important role in the protection of gastric mucosa against the formation of celecoxib-induced lesions.

Sequential chemotactic and phagocytic activation of human polymorphonuclear neutrophils

Human polymorphonuclear neutrophils (PMN) chemotax to a foreign entity. When the chemoattractants' origins are reached, specific receptors bind to the invader's surface, initiating phagocytosis, phagosome formation, and fusion with granule membranes, generating the bactericidal oxidative burst, and releasing lytic enzymes, specific peptides, and proteins. We explored the initial signaling involved in these functions by observing naïve, unprimed PMN in suspension using fluorescent indicators of cytoplasmic signals (Delta[Ca(2+)](i) and DeltapH(i)) and of bactericidal entities (oxidative species and elastase) exposed to N-formyl-methionyl-leucyl-phenylalanine (fMLP) and/or multivalent immune complexes (IC). fMLP and IC each initiate a rapid transient rise in [Ca(2+)](i), mostly from intracellular stores, simultaneously with a drop in pH(i); these are followed by a drop in [Ca(2+)](i) and a rise in pH(i), with the latter being due to a Na(+)/H(+) antiport. The impact of a second stimulation depends on the order in which stimuli are applied, on their dose, and on their nature. Provided that [Ca(2+)](i) is restored, 10(-7) M fMLP, previously shown to elicit maximal Delta[Ca(2+)](i) but no bactericidal functions, did not prevent the cells' responses with Delta[Ca(2+)](i) to a subsequent high dose of fMLP or IC; conversely, cells first exposed to 120 mug/ml IC, previously shown to elicit maximal Delta[Ca(2+)](i) and bactericidal functions, exhibited no subsequent Delta[Ca(2+)](i) or DeltapH(i) to either stimulus. While exposure to 10(-7) M fMLP, which saturates the PMN high-affinity receptor, did not elicit bactericidal release from these naïve unprimed PMN in suspension, 10(-5) M fMLP did, presumably via the low-affinity receptor, using a different Ca(2+) source.

Characterization of the calpain/calpastatin system in human hemopoietic cell lines

As previously suggested by PCR analysis [R. DeTullio, R. Stifanese, F. Salamino, S. Pontremoli, E. Melloni, Characterization of a new p94-like calpain form in human lymphocytes, Biochem. J. 375 (2003) 689-696], a p94-like calpain was now established to be present in six different human cells resembling the various peripheral blood cell types. This protease resulted to be the predominant calpain isoforms whereas the conventional mu- and m-calpains are also expressed although at lower or almost undetectable amounts. The p94-like calpain has been identified by a specific mAb and displays unique features such as: Ca2+ requirement for half maximum activity around 30 microM; no autolytic conversion to a low Ca2+ requiring form and lower sensitivity to calpastatin inhibition. Following cell stimulation, the p94-like calpain undergoes inactivation, a process indicating that the protease is activated and participates in the cell responses to stimuli. The involvement of this protease isoform in immunocompetent cell activation is further supported by its partial recruitment on plasma membranes, the site of action of the conventional calpain forms. The amount of calpain translocated to the membranes correlates to the level of calpastatin which has been shown to control this process through the formation of a complex with calpain, which maintains the protease in the cytosol. These results provide new information on the calpain/calpastatin system expressed in immunocompetent cells and on the functional relationship between the p94-like calpain and the biological function of these cells.