Dual effect of hydrogen peroxide on store-mediated calcium entry in human platelets

Olive Trees By-Products as Sources of Bioactive and Other Industrially Useful Compounds: A Systematic Review

The need to produce an ever-increasing quantity of material products and food resulting from the planet globalization process has contributed to the spread of modern agriculture based on a linear production resulting in the generation of tons of waste. This huge amount of waste is generally accumulated in landfills, causing different environmental problems. Hence, researchers moved on to study the processes used to recover agro-industrial by-products within a circular and sustainable bio-economy concept. A systematic quest on Scopus and PubMed databases was performed to identify the data available to date on recycling agro-industrial by-products of Olea europaea L. This systematic review summarizes the knowledge regarding the use of olive trees by-products for producing animal feed, biocomposites, bioethanol, cellulose pulp, activated carbon, and as a fuel source for energy production. Furthermore, the data regarding the potential biological activity of extracts from olive roots, wood, bark, and pruning were analyzed. Olive trees by-products are, indeed, rich in molecules with antioxidant, antimicrobial, cardioprotective, and anticancer activity, representing a promising candidate for treat several human diseases.

Oxidative stress facilitates cell death by inhibiting Orai1-mediated Ca2+ entry in brain capillary endothelial cells

Brain capillary endothelial cells (BCECs) form the blood-brain barrier (BBB) and play an essential role in the regulation of its functions. Oxidative stress accumulates excessive reactive oxygen species (ROS) and facilitates the death of BCECs, leading to a dysfunctional BBB. However, the mechanisms underlying the death of BCECs under oxidative stress remain unclear. In the present study, the effects of oxidative stress on cell viability, ROS production, intracellular Ca²⁺ concentration, and protein expression were examined using a cell line derived from bovine BCECs, t-BBEC117. When t-BBEC117 cells were exposed to oxidative stress induced by hydrogen peroxide (H₂O₂, 10-100 μM), cell growth was inhibited in a dose-dependent manner. Oxidative stress by 30 μM H₂O₂ increased the production of ROS and its effects were blocked by the ROS scavenger, 10 mM N-acetyl-l-cysteine (NAC). In addition, oxidative stress reduced store-operated Ca²⁺ entry (SOCE) and this decrease was recovered by NAC or the Orai channel activator, 5 μM 2-aminoethyl diphenylborinate (2-APB). The siRNA knockdown of Orai1 revealed that Orai1 was mainly responsible for SOCE channels and its activity was decreased by oxidative stress. However, the protein expression of Orai1 and STIM1 was not affected by oxidative stress. Oxidative stress-induced cell death was rescued by 2-APB, NAC, or the STIM-Orai activating region. In conclusion, oxidative stress reduces Orai1-mediated SOCE and, thus, facilitates the death of BCECs.

βγ-CAT, a non-lens betagamma-crystallin and trefoil factor complex, induces calcium-dependent platelet apoptosis

In recent years, it has been reported that apoptosis may occur in platelets and play a role in the clearance of effete platelets. βγ-CAT, a newly identified non-lens βγ-crystallin and trefoil factor complex from frog Bombina maxima skin secretions, caused several in vivo toxic effects on mammals. Through determined haematological parameters of rabbits, it has been found that βγ-CAT significantly reduced the number of platelets in a time-dependent manner. Here, in order to explore the effect of βγ-CAT on platelets, washed platelets were incubated with various concentrations of βγ-CAT for 30 minutes. We found that βγ-CAT induced several apoptosis events in human platelets, including caspase-3 activation, phosphatidylserine (PS) exposure, depolarisation of mitochondrial inner transmembrane potential (ΔΨm), cytochrome c re-lease and strong expression of pro-apoptotic Bax and Bak proteins. However, βγ-CAT did not significantly induce platelet activation as detected by P-selectin surface expression, GPIIb/IIIa activation and platelet aggregation. In addition, we observed that βγ-CAT-induced PS exposure and ΔΨm depolarisation in platelets are Ca2+-dependent. Taken together, βγ-CAT can induce Ca2+-dependent platelet apoptosis but does not cause platelet activation.

Review manuscript: Mechanisms of platelet activation by the pneumococcus and the role of platelets in community-acquired pneumonia

There is increasing recognition of the involvement of platelets in orchestrating inflammatory responses, driving the activation of neutrophils, monocytes and vascular endothelium, which, if poorly controlled, may lead to microvascular dysfunction. Importantly, hyperreactivity of platelets has been implicated in the pathogenesis of myocardial injury and the associated particularly high prevalence of acute cardiovascular events in patients with severe community-acquired pneumonia (CAP), of which Streptococcus pneumoniae (pneumococcus) is the most commonly encountered aetiologic agent. In this context, it is noteworthy that a number of studies have documented various mechanisms by which the pneumococcus may directly promote platelet aggregation and activation. The major contributors to platelet activation include several different types of pneumococcal adhesin, the pore-forming toxin, pneumolysin, and possibly pathogen-derived hydrogen peroxide, which collectively represent a major focus of the current review. This is followed by an overview of the limited experimental studies together with a larger series of clinical studies mainly focused on all-cause CAP, which have provided evidence in support of associations between alterations in circulating platelet counts, most commonly thrombocytopenia, and a poor clinical outcome. The final section of the review covers, albeit briefly, systemic biomarkers of platelet activation which may have prognostic potential.

Hydrogen peroxide is a critical regulator of the hypoxia-induced alterations of store-operated Ca2+ entry into rat pulmonary arterial smooth muscle cells

To investigate the association between store-operated Ca2+ entry (SOCE) and reactive oxygen species (ROS) during hypoxia, this study determined the changes of transient receptor potential canonical 1 (TRPC1) and Orai1, two candidate proteins for store-operated Ca2+ (SOC) channels and their gate regulator, stromal interaction molecule 1 (STIM1), in a hypoxic environment and their relationship with ROS in pulmonary arterial smooth muscle cells (PASMCs). Exposure to hypoxia caused a transient Ca2+ spike and subsequent Ca2+ plateau of SOCE to be intensified in PASMCs when TRPC1, STIM1, and Orai1 were upregulated. SOCE in cells transfected with specific short hairpin RNA (shRNA) constructs was almost completely eliminated by the knockdown of TRPC1, STIM1, or Orai1 alone and was no longer affected by hypoxia exposure. Hypoxia-induced SOCE enhancement was further strengthened by PEG-SOD but was attenuated by PEG-catalase, with correlated changes to intracellular hydrogen peroxide (H2O2) levels and protein levels of TRPC1, STIM1, and Orai1. Exogenous H2O2 could mimic alterations of the interactions of STIM1 with TRPC1 and Orai1 in hypoxic cells. These findings suggest that TRPC1, STIM1, and Orai1 are essential for the initiation of SOCE in PASMCs. Hypoxia-induced ROS promoted the expression and interaction of the SOC channel molecules and their gate regulator via their converted product, H2O2.

Hydrogen peroxide attenuates refilling of intracellular calcium store in mouse pancreatic acinar cells

Intracellular calcium (Ca²⁺) oscillation is an initial event in digestive enzyme secretion of pancreatic acinar cells. Reactive oxygen species are known to be associated with a variety of oxidative stress-induced cellular disorders including pancreatitis. In this study, we investigated the effect of hydrogen peroxide (H₂O₂) on intracellular Ca²⁺ accumulation in mouse pancreatic acinar cells. Perfusion of H₂O₂ at 300 µM resulted in additional elevation of intracellular Ca²⁺ levels and termination of oscillatory Ca²⁺ signals induced by carbamylcholine (CCh) in the presence of normal extracellular Ca²⁺. Antioxidants, catalase or DTT, completely prevented H₂O₂-induced additional Ca²⁺ increase and termination of Ca²⁺ oscillation. In Ca²⁺-free medium, H₂O₂ still enhanced CCh-induced intracellular Ca²⁺ levels and thapsigargin (TG) mimicked H₂O₂-induced cytosolic Ca²⁺ increase. Furthermore, H₂O₂-induced elevation of intracellular Ca²⁺ levels was abolished under sarco/endoplasmic reticulum Ca²⁺ ATPase-inactivated condition by TG pretreatment with CCh. H₂O₂ at 300 µM failed to affect store-operated Ca²⁺ entry or Ca²⁺ extrusion through plasma membrane. Additionally, ruthenium red, a mitochondrial Ca²⁺ uniporter blocker, failed to attenuate H₂O₂-induced intracellular Ca²⁺ elevation. These results provide evidence that excessive generation of H₂O₂ in pathological conditions could accumulate intracellular Ca²⁺ by attenuating refilling of internal Ca²⁺ stores rather than by inhibiting Ca²⁺ extrusion to extracellular fluid or enhancing Ca²⁺ mobilization from extracellular medium in mouse pancreatic acinar cells.

Src-family tyrosine kinases and the Ca2+ signal

In this review, we shall describe the rich crosstalk between non-receptor Src-family kinases (SFKs) and the Ca²⁺ transient generated in activated cells by a variety of extracellular and intracellular stimuli, resulting in diverse signaling events. The exchange of information between SFKs and Ca²⁺ is reciprocal, as it flows in both directions. These kinases are main actors in pathways leading to the generation of the Ca²⁺ signal, and reciprocally, the Ca²⁺ signal modulates SFKs activity and functions. We will cover how SFKs participate in the generation of the cytosolic Ca²⁺ rise upon activation of a series of receptors and the mechanism of clearance of this Ca²⁺ signal. The role of SFKs modulating Ca²⁺-translocating channels participating in these events will be amply discussed. Finally, the role of the Ca²⁺ sensor protein calmodulin on the activity of c-Src, and potentially on other SFKs, will be outlined as well. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Hydrogen peroxide activates store-operated Ca(2+) entry in coronary arteries

BACKGROUND AND PURPOSE

Abnormal Ca(2+) metabolism has been involved in the pathogenesis of vascular dysfunction associated with oxidative stress. Here, we have investigated the actions of H2 O2 on store-operated Ca(2+) (SOC) entry in coronary arteries and assessed whether it is impaired in arteries from a rat model of metabolic syndrome.

EXPERIMENTAL APPROACH

Simultaneous measurements of intracellular Ca(2+) concentration and contractile responses were made in coronary arteries from Wistar and obese Zucker rats, mounted in microvascular myographs, and the effects of H2 O2 were assessed.

KEY RESULTS

H2 O2 raised intracellular Ca(2+) concentrations, accompanied by simultaneous vasoconstriction that was markedly reduced in a Ca(2+) -free medium. Upon Ca(2+) re-addition, a nifedipine-resistant sustained Ca(2+) entry, not coupled to contraction, was obtained in endothelium-denuded coronary arteries. The effect of H2 O2 on this voltage-independent Ca(2+) influx was concentration-dependent, and high micromolar H2 O2 concentrations were inhibitory and reduced SOC entry evoked by inhibition of the sarcoplasmic reticulum ATPase (SERCA). H2 O2 -induced increases in Fura signals were mimicked by Ba(2+) and reduced by heparin, Gd(3+) ions and by Pyr6, a selective inhibitor of the Orai1-mediated Ca(2+) entry,. In coronary arteries from obese Zucker rats, intracellular Ca(2+) mobilization and SOC entry activated by acute exposure to H2 O2 were augmented and associated with local oxidative stress.

CONCLUSION AND IMPLICATIONS

H2 O2 exerted dual concentration-dependent stimulatory/inhibitory effects on store-operated, IP3 receptor-mediated and Orai1-mediated Ca(2+) entry, not coupled to vasoconstriction in coronary vascular smooth muscle. SOC entry activated by H2 O2 was enhanced and associated with vascular oxidative stress in coronary arteries in metabolic syndrome.

A change of heart: oxidative stress in governing muscle function?

Redox/cysteine modification of proteins that regulate calcium cycling can affect contraction in striated muscles. Understanding the nature of these modifications would present the possibility of enhancing cardiac function through reversible cysteine modification of proteins, with potential therapeutic value in heart failure with diastolic dysfunction. Both heart failure and muscular dystrophy are characterized by abnormal redox balance and nitrosative stress. Recent evidence supports the synergistic role of oxidative stress and inflammation in the progression of heart failure with preserved ejection fraction, in concert with endothelial dysfunction and impaired nitric oxide-cyclic guanosine monophosphate-protein kinase G signalling via modification of the giant protein titin. Although antioxidant therapeutics in heart failure with diastolic dysfunction have no marked beneficial effects on the outcome of patients, it, however, remains critical to the understanding of the complex interactions of oxidative/nitrosative stress with pro-inflammatory mechanisms, metabolic dysfunction, and the redox modification of proteins characteristic of heart failure. These may highlight novel approaches to therapeutic strategies for heart failure with diastolic dysfunction. In this review, we provide an overview of oxidative stress and its effects on pathophysiological pathways. We describe the molecular mechanisms driving oxidative modification of proteins and subsequent effects on contractile function, and, finally, we discuss potential therapeutic opportunities for heart failure with diastolic dysfunction.

Evaluation of the antiaggregant activity of ascorbyl phenolic esters with antioxidant properties

Beneficial effects of the antioxidant L-ascorbic acid (Asc) in human health are well known. Its particular role in hemostasis deserves further consideration, since it has been described a dose-dependent effect of Asc in platelet activity. Contrary, it has been demonstrated that phenolic compounds have inhibitory effects on platelet aggregation stimulated by the physiological agonist thrombin (Thr). Here, we have evaluated the actions of three synthetic phenolic esters of Asc: L-ascorbyl 6-protocatechuate (Prot Asc), L-ascorbyl 6-gallate (Gal Asc), and L-ascorbyl 6-caffeate (Caf Asc). All these Asc derivatives exhibited greater radical scavenging activity than Asc, and in experiments using human platelets from healthy subjects, they do not evoke changes in platelet viability upon their administration. Nevertheless, these compounds altered platelet calcium homeostasis in response to Thr, although Prot Asc induced a smaller effect than Gal Asc, Caf Asc, and Asc. As a consequence, platelet aggregation was also impaired by these compounds, reporting Prot Asc and Caf Asc a weaker antiaggregant action than Gal Asc and Asc. Treatments with Gal Asc and Caf Asc altered in larger extent the phosphorylation pattern of pp60(Src) and mammalian target of rapamycin (mTOR) evoked by stimulating human platelets with Thr. Summarizing, Prot Asc is the ascorbyl phenolic ester with the strongest antioxidant properties and weakest antiaggregant actions, and its use as antioxidant may be safer than the rest of derivatives in order to prevent thrombotic alteration in patients that need treatment with antioxidant therapies.

Redox regulation of store-operated Ca2+ entry

SIGNIFICANCE

Store-operated Ca2+ entry (SOCE) is a ubiquitous Ca2+ signaling mechanism triggered by Ca2+ depletion of the endoplasmic reticulum (ER) and by a variety of cellular stresses. Reactive oxygen species (ROS) are often concomitantly produced in response to these stresses, however, the relationship between redox signaling and SOCE is not completely understood. Various cardiovascular, neurological, and immune diseases are associated with alterations in both Ca2+ signaling and ROS production, and thus understanding this relationship has therapeutic implications.

RECENT ADVANCES

Several reactive cysteine modifications in stromal interaction molecule (STIM) and Orai proteins comprising the core SOCE machinery were recently shown to modulate SOCE in a redox-dependent manner. Moreover, STIM1 and Orai1 expression levels may reciprocally regulate and be affected by responses to oxidative stress. ER proteins involved in oxidative protein folding have gained increased recognition as important sources of ROS, and the recent discovery of their accumulation in contact sites between the ER and mitochondria provides a further link between ROS production and intracellular Ca2+ handling.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Future research should aim to establish the complete set of SOCE controlling molecules, to determine their redox-sensitive residues, and to understand how intracellular Ca2+ stores dynamically respond to different types of stress. Mapping the precise nature and functional consequence of key redox-sensitive components of the pre- and post-translational control of SOCE machinery and of proteins regulating ER calcium content will be pivotal in advancing our understanding of the complex cross-talk between redox and Ca2+ signaling.

Redox circuitries driving Src regulation

SIGNIFICANCE

Here, we review recent advances with regard to the role of Src kinase in the regulation of cytoskeleton organization, cell adhesion, and motility, focusing on redox circuitries engaging this kinase for anchorage and motility, control of cell survival to anoikis, as well as metabolic deregulation, all features belonging to the new hallmarks of cancer.

RECENT ADVANCES

Several recent insights have reported that, alongside the well-known phosphorylation/dephosphorylation control, cysteine oxidation is a further mechanism of enzyme activation for both c-Src kinase and its oncogenic counterparts. Indeed, mounting evidence portrays redox regulation of Src kinase as a compulsory outcome in growth factors/cytokines signaling, integrin engagement, motility and invasiveness of tissues, receptor cross-talking at plasmamembrane, as well as during carcinogenesis and progression toward tumor malignancy or fibrotic disease. In addition, the kinase is an upstream regulator of NADPH oxidase-driven oxidants, a critical step for invadopodia formation and metastatic spread.

CRITICAL ISSUES

Not satisfactorily unraveled yet, the exact role of Src kinase in redox cancer biology needs to be implemented with studies that are aimed at clarifying (i) the exact hierarchy between oxidants sources, Src redox-dependent activation and the regulation of cell motility, and (ii) the actual susceptibility of invading cells to redox-based treatments, owing to the well-recognized ability of cancer cells to find new strategies to adapt to new environments.

FUTURE DIRECTIONS

Once these critical issues are addressed, redox circuitries involving Src kinase should potentially be used as both biomarkers and targets for personalized therapies in the fight against cancer or fibrotic diseases.

Redox regulation of protein kinases

Reactive oxygen species (ROS) have been long regarded as by-products of a cascade of reactions stemming from cellular oxygen metabolism, which, if they accumulate to toxic levels, can have detrimental effects on cellular biomolecules. However, more recently, the recognition of ROS as mediators of cellular communications has led to their classification as signalling mediators in their own right. The prototypic redox-regulated targets downstream of ROS are the protein tyrosine phosphatases, and the wealth of research that has focused on this area has come to shape our understanding of how redox-signalling contributes to and facilitates protein tyrosine phosphorylation signalling cascades. However, it is becoming increasingly apparent that there is more to this system than simply the negative regulation of protein tyrosine phosphatases. Identification of redox-sensitive kinases such as Src led to the slow emergence of a role for redox regulation of tyrosine kinases. A flow of evidence, which has increased exponentially in recent times as a result of the development of new methods for the detection of oxidative modifications, demonstrates that, by concurrent oxidative activation of tyrosine kinases, ROS fine tune the duration and amplification of the phosphorylation signal. A more thorough understanding of the complex regulatory mechanism of redox-modification will allow targeting of both the production of ROS and their downstream effectors for therapeutic purposes. The present review assesses the most relevant recent literature that demonstrates a role for kinase regulation by oxidation, highlights the most significant findings and proposes future directions for this crucial area of redox biology.

Thrombin-stimulated discharge of calcium stores in human platelets: analysis of experimental data

The purpose of this research was to analyze experimental data concerning thrombin-stimulated discharge of calcium stores in human platelets contained in calcium-free medium in view of better understanding the mechanisms involved in calcium fluxes. The model curves are reasonably close to experimental data; the parameters of the models are related to the properties of the entities responsible for control or maintenance of cytosolic calcium concentration. It has been shown that: (a) time-course of calcium concentration in cytosol of human platelets can be acceptably modeled on the basis of reasonable assumptions concerning agonist stimulated calcium redistribution in cellular compartments; (b) those assumptions are of fundamental importance for the model (c) some parameters of the model (taken arbitrarily) cannot be estimated independently of others from fitting the model to experimental data available; (d) special experiments are necessary to determine the unknown parameters; (e) agonist-stimulated change of the permeability of endomembrane of calcium stores can be regarded as a pulse of the permeability; it can be modeled as a sequence of transitions of the system from inactive to active and to inactive state again.

Gallic Acid Attenuates Platelet Activation and Platelet-Leukocyte Aggregation: Involving Pathways of Akt and GSK3β

Platelet activation and its interaction with leukocytes play an important role in atherothrombosis. Cardiovascular diseases resulted from atherothrombosis remain the major causes of death worldwide. Gallic acid, a major constituent of red wine and tea, has been believed to have properties of cardiovascular protection, which is likely to be related to its antioxidant effects. Nonetheless, there were few and inconsistent data regarding the effects of gallic acid on platelet function. Therefore, we designed this in vitro study to determine whether gallic acid could inhibit platelet activation and the possible mechanisms. From our results, gallic acid could concentration-dependently inhibit platelet aggregation, P-selectin expression, and platelet-leukocyte aggregation. Gallic acid prevented the elevation of intracellular calcium and attenuated phosphorylation of PKCα/p38 MAPK and Akt/GSK3β on platelets stimulated by the stimulants ADP or U46619. This is the first mechanistic explanation for the inhibitory effects on platelets from gallic acid.

ROS and SOCE: recent advances and controversies in the regulation of STIM and Orai

Store-operated Ca(2+) entry (SOCE) is a widespread mechanism in cells to raise cytosolic Ca(2+) and to refill Ca(2+) stores. T cells critically rely on SOCE mediated by stromal interaction molecules (STIM) and Orai molecules for their activation and regulation of gene transcription; cells such as muscle cells, neurons or melanocytes probably utilize SOCE for the transmission of inducible receptor-mediated function as well as for generalized Ca(2+) homeostasis mechanisms. Exposure to environmental or cell-intrinisic reactive oxygen species (ROS) can affect several components involved in Ca(2+) homeostasis and thus alter multiple pathways. While all cells have a capacity to produce intracellular ROS, exposure of immune and skin cells to extracellular oxidative stress is particularly high during inflammation and/or with UV exposure. This review briefly summarizes cell-intrinsic sources of ROS and focuses on current findings and controversies regarding the regulation of STIM and Orai by oxidative modifications. We also introduce melanocytes as a new model system to study the function of STIM and Orai isoforms under physiological conditions that include exposure to UV light as an activating stimulus.

STIM1 tyrosine-phosphorylation is required for STIM1-Orai1 association in human platelets

Stromal interaction molecule 1 (STIM1) is a key element of the store-operated Ca(2+) entry mechanism (SOCE). Recently, regulation of STIM1 by glycosylation and phosphorylation on serine/threonine or proline residues has been described; however other modes of phosphorylation that are important for activating SOCE in platelets, such as tyrosine phosphorylation, have been poorly investigated. Here we investigate the latency of STIM1 phosphorylation on tyrosine residues during the first steps of SOCE activation. Human platelets were stimulated and fixed at desired times using rapid kinetic assays instruments, and immunoprecipitation and western blotting techniques were then used to investigate the pattern of STIM1 tyrosine phosphorylation during the first steps of SOCE activation. We have found that maximal STIM1 tyrosine phosphorylation occurred 2.5s after stimulation of human platelets with thapsigargin (Tg). STIM1 localized in the plasma membrane were also phosphorylated in platelets stimulated with Tg. By using chemical inhibitors that target different members of the Src family of tyrosine kinases (SKFs), two independent signaling pathways involved in STIM1 tyrosine phosphorylation during the first steps of SOCE activation were identified. We finally conclude that STIM1 tyrosine phosphorylation is a key event for the association of STIM1 with plasma membrane Ca(2+) channels such as Orai1, hence it is required for conducting SOCE activation.

Effect of pre-breathing oxygen at different depth on oxidative status and calcium concentration in lymphocytes of scuba divers

AIM

In-water pre-breathing oxygen at various depths reduces decompression-induced bubble formation and platelet activation, but it could induce side effects such as oxidative stress. The aim of this study was to investigate the effect of in-water pre-breathing oxygen, at different depths, on the oxidative status and intracellular calcium ([Ca(2+) ]i) of peripheral blood lymphocytes isolated from six divers. They participated in a 4-diving protocol. Two week recovery time was allowed between successive dives. Before diving, all divers, for 20 min, breathed normally at sea level (dive 1), 100% oxygen at sea level (dive 2), 100% oxygen at 6 msw (dive 3), 100% oxygen at 12 msw (dive 4). Then they dived to 30 msw for 20 min with air tank.

METHODS

Blood samples were collected before and after each dive. Hydrogen peroxide (H(2) O(2) ) levels, catalase (CAT) activity, mRNA expression of CAT, glutathione peroxidase (GPx) and superoxide dismutase (SOD), and the [Ca(2+) ]i in lymphocytes were measured.

RESULTS

The dives slightly decreased lymphocyte number and significantly reduced lymphocyte H(2) O(2) levels. CAT activity was higher after scuba diving and, dive 3 enhanced mRNA gene expression of CAT, GPx and SOD. The [Ca(2+) ]i was higher after dive 1 and 2 than pre-diving, while was maintained at pre-diving value after dive 3 and 4.

CONCLUSION

Our results suggest that pre-breathing oxygen, in particular at 12 msw, may enhance lymphocyte antioxidant activity and reduce reactive oxygen species levels. Pre-breathing oxygen in water may also preserve calcium homeostasis, suggesting a protective role in the physiological lymphocyte cell functions.

Glutathione peroxidase-3 deficiency promotes platelet-dependent thrombosis in vivo

BACKGROUND

Glutathione peroxidase-3 (GPx-3) is a selenocysteine-containing plasma protein that scavenges reactive oxygen species in the extracellular compartment. A deficiency of this enzyme has been associated with platelet-dependent thrombosis, and a promoter haplotype with reduced function has been associated with stroke risk.

METHODS AND RESULTS

We recently developed a genetic mouse model to assess platelet function and thrombosis in the setting of GPx-3 deficiency. The GPx-3((-/-)) mice showed an attenuated bleeding time and an enhanced aggregation response to the agonist ADP compared with wild-type mice. GPx-3((-/-)) mice displayed increased plasma levels of soluble P-selectin and decreased plasma cyclic cGMP compared with wild-type mice. ADP infusion-induced platelet aggregation in the pulmonary vasculature produced a more robust platelet activation response in the GPx-3((-/-)) than wild-type mice; histological sections from the pulmonary vasculature of GPx-3((-/-)) compared with wild-type mice showed increased platelet-rich thrombi and a higher percentage of occluded vessels. Cremaster muscle preparations revealed endothelial dysfunction in the GPx-3((-/-)) compared with wild-type mice. With a no-flow ischemia-reperfusion stroke model, GPx-3((-/-)) mice had significantly larger cerebral infarctions compared with wild-type mice and platelet-dependent strokes. To assess the neuroprotective role of antioxidants in this model, we found that manganese(III) meso-tetrakis(4-benzoic acid)porphyrin treatment reduced stroke size in GPx-3((-/-)) mice compared with vehicle-treated controls.

CONCLUSIONS

These findings demonstrate that GPx-3 deficiency results in a prothrombotic state and vascular dysfunction that promotes platelet-dependent arterial thrombosis. These data illustrate the importance of this plasma antioxidant enzyme in regulating platelet activity, endothelial function, platelet-dependent thrombosis, and vascular thrombotic propensity.

Role of oxidant scavengers in the prevention of Ca²+ homeostasis disorders

A number of disorders, such as Alzheimer disease and diabetes mellitus, have in common the alteration of the redox balance, resulting in an increase in reactive oxygen species (ROS) generation that might lead to the development of apoptosis and cell death. It has long been known that ROS can significantly alter Ca²+ mobilization, an intracellular signal that is involved in the regulation of a wide variety of cellular functions. Cells have a limited capability to counteract the effects of oxidative stress, but evidence has been provided supporting the beneficial effects of exogenous ROS scavengers. Here, we review the effects of oxidative stress on intracellular Ca²+ homeostasis and the role of antioxidants in the prevention and treatment of disorders associated to abnormal Ca²+ mobilization induced by ROS.

Synthesis and evaluation of the platelet antiaggregant properties of phenolic antioxidants structurally related to rosmarinic acid

Polyphenols, such as rosmarinic acid, are widely distributed natural products with relevant antioxidant activity. Oxidative stress plays an important role in the pathogenesis of a number of disorders. Here, we report on the synthesis and biological effects of the polyphenolic esters hydroxytyrosyl gallate (1), hydroxytyrosyl protocatechuate (2) and hydroxytyrosyl caffeate (3), structurally related to rosmarinic acid. The three compounds showed a greater free radical scavenging activity than their precursors and also than rosmarinic acid. Esters 1 and 3 significantly reduced thrombin-evoked platelet aggregation, which is likely mediated to the attenuation of thrombin-stimulated Ca(2+) release and entry. The three compounds reduced the ability of platelets to accumulate Ca(2+) in the intracellular stores, probably by enhancing the Ca(2+) leakage rate and reduced store-operated Ca(2+) entry in these cells. These observations suggest that the structurally-simplified analogs to rosmarinic acid, compounds 1 and 3, might be the base of therapeutic strategies to prevent thrombotic complications associated to platelet hyperaggregability due to oxidative stress.

Inhibitory effects of staphylococcal enterotoxin type B on human platelet adhesion in vitro

Septic shock was formerly recognized as a consequence of Gram-negative bacteraemia, but at present the incidence of Gram-positive sepsis seems to be more relevant, contributing for more than 50% of cases. Staphylococcal aureus can induce toxic shock in humans through the production of potent toxins termed Staphylococcal enterotoxins, from which Staphylococcal enterotoxin type B (SEB) is one of most studied. Platelets are reported to participate in pathogenesis of severe sepsis, but the exact role of platelets in this event is poorly investigated, particularly that caused by Gram-positive bacteria. Therefore, we have used the model of platelet adhesion to fibrinogen-coated plates to investigate the actions of SEB on human platelets. Ninety-six-well microtiter plates were coated with human fibrinogen (50 microg/mL), and human washed platelet suspension (6 x 10(6) platelets) was added to each well. Adherent platelets were quantified through measurement of acid phosphatase activity. Staphylococcal enterotoxin B (0.0001-30 microg/mL, incubated for 5 to 60 min) time- and dose-dependently inhibited platelet adhesion. This response was modified neither by the protein synthesis inhibitor puromycin (0.01 and 0.1 mM) nor by the superoxide scavengers superoxide dismutase (SOD, 100 units/mL) and polyethylene glycol-SOD (30 U/mL). The peroxide hydrogen (H(2)O(2)) scavenger catalase polyethylene glycol (1000 U/mL) significantly attenuated the platelet adhesion inhibition by SEB. The cAMP and cGMP levels were not changed by SEB (0.0001-30 microg/mL, 60 min). Our findings suggest that H(2)O(2) at least partly contributes to the inhibitory responses of human platelet adhesion by SEB.

STIM1, Orai1 and hTRPC1 are important for thrombin- and ADP-induced aggregation in human platelets

Ca(2+) entry, particularly store-operated Ca(2+) entry (SOCE), has been reported to be crucial for a variety of cellular functions. SOCE is a mechanism regulated by the Ca(2+) content of the stores, where the intraluminal Ca(2+) sensor STromal Interaction Molecule 1 (STIM1) has been reported to communicate the filling state of the intracellular Ca(2+) stores to the store-operated Ca(2+)-permeable channels in the plasma membrane, likely involving Orai1 and TRPC proteins, such as TRPC1. Here we have investigated the role of Orai1, STIM1 and TRPC1 in platelet aggregation, an event that occurs during the process of thrombosis and hemostasis. Electrotransjection of cells with anti-STIM1 (25-139) antibody, directed towards the Ca(2+)-binding motif, significantly reduced thrombin-induced aggregation and prevented ADP-evoked response. Extracellular application of the anti-STIM1 antibody, in order to block the function of plasma membrane-located STIM1, reduced thrombin- and ADP-stimulated platelet aggregation to a lesser extent. Introduction of an anti-Orai1 (288-301) antibody, which binds the STIM1-binding site located in the Orai1 C-terminus, or extracellular application of anti-hTRPC1 (557-571) antibody to impair hTRPC1 channel function, significantly reduced thrombin- and ADP-induced platelet aggregation. These findings suggest a role of STIM1, Orai1 and hTRPC1 in thrombin- and ADP-induced platelet aggregation probably through the regulation of Ca(2+) entry, which might become targets for the development of therapeutic strategies to treat platelet hyperactivity and thrombosis disorders.

Endogenously generated reactive oxygen species reduce PMCA activity in platelets from patients with non-insulin-dependent diabetes mellitus

Intracellular Ca2+ homeostasis in platelets of patients with non-insulin-dependent diabetes mellitus (NIDDM) has been reported to be altered, leading to an increased adhesiveness and spontaneous aggregation. Among the disturbed Ca2+ mechanism in platelets from NIDDM subjects, a reduced Ca2+ extrusion by the plasma membrane Ca2+-ATPase (PMCA) is especially relevant, maintaining an elevated cytosolic free Ca2+ concentration that results in platelet hypersensitivity. Here we show that treatment of platelets from NIDDM patients with 300 U/mL catalase or 5 mM D-mannitol, which prevent H2O2- and hydroxyl radicals-mediated oxidative stress, respectively, increases Ca2+ extrusion after treatment with thapsigargin (TG) plus ionomycin (Iono). In contrast, 1 mM trolox, a scavenger of ONOO-, did not alter TG + Iono-induced response. Catalase and D-mannitol reversed the enhanced tyrosine phosphorylation of PMCA induced by TG + Iono in NIDDM patients. These findings open up new horizon for the development of therapeutic strategies to palliate cardiovascular disorders in NIDDM.

Hepatitis C virus NS5A and core proteins induce oxidative stress-mediated calcium signalling alterations in hepatocytes

BACKGROUND/AIMS

The hepatitis C virus (HCV) structural core and non-structural NS5A proteins induce in liver cells a series of intracellular events, including elevation of reactive oxygen and nitrogen species (ROS/RNS). Since oxidative stress is associated to altered intracellular Ca(2+) homeostasis, we aimed to investigate the effect of these proteins on Ca(2+) mobilization in human hepatocyte-derived transfected cells, and the protective effect of quercetin treatment.

METHODS

Ca(2+) mobilization and actin reorganization were determined by spectrofluorimetry. Production of ROS/RNS was determined by flow cytometry.

RESULTS

Cells transfected with NS5A and core proteins showed enhanced ROS/RNS production and resting cytosolic Ca(2+) concentration, and reduced Ca(2+) concentration into the stores. Phenylephrine-evoked Ca(2+) release, Ca(2+) entry and extrusion by the plasma membrane Ca(2+)-ATPase were significantly reduced in transfected cells. Similar effects were observed in cytokine-activated cells. Phenylephrine-evoked actin reorganization was reduced in the presence of core and NS5A proteins. These effects were significantly prevented by quercetin. Altered Ca(2+) mobilization and increased calpain activation were observed in replicon-containing cells.

CONCLUSIONS

NS5A and core proteins induce oxidative stress-mediated Ca(2+) homeostasis alterations in human hepatocyte-derived cells, which might underlie the effects of both proteins in the pathogenesis of liver disorders associated to HCV infection.

Melatonin, as an adjuvant-like agent, enhances platelet responsiveness

Melatonin exerts immunomodulatory actions that enhance the magnitude and quality of immune responses specific for certain antigens; this has raised the possibility of using melatonin to design novel vaccine adjuvant systems. The present study investigated the effect of subcutaneous slow-release melatonin implants and subcutaneous melatonin injections on the responsiveness of circulating platelets in sheep after vaccination against Dichelobacter nodosus (A1 and C serotypes), the bacterium that causes ovine footrot, a major cause of lameness in sheep. The experiments were carried out in sheep from a farm located in an area of Mediterranean-type ecosystem. Plasma melatonin levels were determined by radioimmunoassay, sheep platelet aggregation was monitored using an aggregometer and Ca2+ mobilization was determined by spectrofluorimetry using fura-2. Administration of melatonin either by implants or subcutaneous injections increased plasma melatonin concentrations, an effect that was found to be greater and more sustained when melatonin was administered via implants. Vaccination per se, as well as melatonin, increased the percentage and rate of platelet aggregation and reduced the lag-time in response to the physiological agonist thrombin, an effect that was found to be significantly greater when melatonin was administered to vaccinated animals. Melatonin enhanced thrombin-evoked Ca2+ release and entry and further increased Ca2+ mobilization observed in platelets from vaccinated sheep. These observations suggest that the use of melatonin, as a novel adjuvant, induces beneficial effects on platelet function and haemostasis, and opens new perspectives for therapeutic manipulation of immune responses to vaccination.

Effect of homocysteine on calcium mobilization and platelet function in type 2 diabetes mellitus

Type 2 diabetes mellitus induces a characteristic platelet hyperactivity that might be due to several factors including oxidative stress and abnormal intracellular Ca2+ homeostasis. Hyperhomocysteinaemia is considered a risk factor in the development of thrombosis although its effect on platelet function and the mechanisms involved are still poorly understood. Here we show that homocysteine (Hcy) induce a concentration-dependent increase in endogenous production of reactive oxygen species (ROS), which was significantly greater in platelets from diabetic patients than in controls. Platelet treatment with Hcy resulted in Ca2+ release from the dense tubular system and the acidic stores. Ca2+ mobilisation-induced by Hcy consisted in two components, an initial slow increase in intracellular free Ca2+ concentration ([Ca2+]i) and a rapid and marked increase in [Ca2+]i, the second leading to the activation of platelet aggregation. As well as ROS generation, Ca2+ mobilization and platelet aggregation were significantly greater in platelets from diabetic donors than in controls, which indicate that platelets from diabetic donors are more sensitive to Hcy. These findings, together with the hyperhomocysteinaemia reported in diabetic patients, strongly suggest that Hcy might be considered a risk factor in the development of cardiovascular complications associated to type 2 diabetes mellitus.

Effect of homocysteine on calcium mobilization and platelet function in type 2 diabetes mellitus

Type 2 diabetes mellitus induces a characteristic platelet hyperactivity that might be due to several factors including oxidativ stress and abnormal intracellular Ca²⁺ homeostasis. Hyperhomocysteinaemia is considered a risk factor in the development of thrombosis although its effect on platelet function and the mechanisms involved are still poorly understood. Here we show tha homocysteine induce a concentration-dependent increase in endogenous production of reactive oxygen species (ROS), which was significantly greater in platelets from diabetic patients than in controls. Platelet treatment with homocysteine resulted in Ca²⁺ release from the dense tubular system and the acidic stores. Ca²⁺ mobilization-induced by homocysteine consisted in two components, an initial slow increase in intracellular free Ca ⁺ concentration ([Ca ⁺]i) and a rapid and marked increase in [Ca²⁺]i, th second leading to the activation of platelet aggregation. As well as ROS generation, Ca²⁺ mobilization and platelet aggregation were significantly greater in platelets from diabetic donors than in controls, which indicate that platelets from diabetic donors are more sensitive to homocysteine. These findings, together with the hyperhomocysteinaemia reported in diabetic patients, strongly suggest that homocysteine might be considered a risk factor in the development of cardiovascular complications associated to type 2 diabetes mellitus.

Olive tree wood phenolic compounds with human platelet antiaggregant properties

Oleuropein and (+)-cycloolivil are natural polyphenolic compounds with a significant radical scavenging activity present in olive tree. We have investigated the antiaggregant effects of oleuropein and (+)-cycloolivil isolated from an ethyl acetate extract of olive tree wood. Oleuropein and (+)-cycloolivil reduced the ability of thrombin to stimulate platelet aggregation. Both compounds reduced thrombin-evoked Ca(2+) release and entry to a similar extent to hydroxytyrosol. This effect was greater in platelets from patients with type 2 diabetes mellitus than in controls. Thrombin-, thapsigargin- and 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ)-evoked protein tyrosine phosphorylation, which is involved in Ca(2+) signalling and platelet aggregation, is inhibited by oleuropein and (+)-cycloolivil. oleuropein and (+)-cycloolivil are natural oxygen radical scavengers that reduce thrombin-induced protein tyrosine phosphorylation, Ca(2+) signalling and platelet aggregation. These observations suggest that oleuropein and (+)-cycloolivil may prevent thrombotic complications associated to platelet hyperaggregability and be the base for the development of antiaggregant therapeutic strategies.

Calcium, mitochondria and apoptosis studied by fluorescence measurements

Among the many unsolved problems of calcium signalling, the role of calcium elevations in apoptotic and necrotic cell death has been a focus of research in recent years. Evidence has been presented that calcium oscillations can effectively trigger apoptosis under certain conditions and that dysregulation of calcium signalling is a common cause of cell death. These effects are regularly mediated through calcium signal propagation to the mitochondria and the ensuing mitochondrial membrane permeabilization and release of pro-apoptotic factors from mitochondria to the cytoplasm. The progress in this area depended on the development of (1) fluorescent/luminescent probes, including fluorescent proteins that can be genetically targeted to different intracellular locations and (2) the digital imaging technology, fluorescence-activated cell sorting and fluorescent high throughput approaches, which allowed dynamic measurements of both [Ca2+] in the intracellular compartments of interest and the downstream processes. Fluorescence single cell imaging has been the only possible approach to resolve the cell-to-cell heterogeneity and the complex subcellular spatiotemporal organization of the cytoplasmic and mitochondrial calcium signals and downstream events. We outline here fluorometric and fluorescence imaging protocols that we set up for the study of calcium in the context of apoptosis.

Thrombin induces activation and translocation of Bid, Bax and Bak to the mitochondria in human platelets

BACKGROUND

Thrombin is a physiological platelet agonist that activates apoptotic events, including cytochrome c release and phosphatidylserine exposure; however, the mechanisms underlying these events remain unclear.

OBJECTIVES

The present study is aimed to investigate whether thrombin induces activation and mitochondrial translocation of Bid, Bax and Bak.

METHODS

Changes in the mitochondrial membrane potential were registered using the dye JC-1; Bid, Bax and Bak translocation to the mitochondria was detected by immunoprecipitation and Western blotting in samples from mitochondrial and cytosolic fractions.

RESULTS

Treatment of platelets with thrombin or ADP induces activation and mitochondrial association of active Bid, Bax and Bak. Translocation of Bid and Bax to the mitochondria was reduced by cytochalasin D, latrunculin A or jasplakinolide. Platelet exposure to exogenous H(2)O(2) (10 microm) results in activation of Bid and Bax, which was found to be similar to the effect of thrombin. Thrombin evokes mitochondrial membrane depolarization, which is attenuated by catalase.

CONCLUSION

Our results indicate that thrombin induces activation and mitochondrial translocation of Bid, Bax and Bak, which is likely to be one of the apoptotic events in human platelets.

Cinnamtannin B-1 as an antioxidant and platelet aggregation inhibitor

Cinnamtannin B-1 is a naturally occurring trimeric A-type proanthocyanidin, present in a limited number of plants, which exhibits a large number of cellular actions mostly derived from its antioxidant properties. Cinnamtannin B-1 modulates several biological processes such as changes in cytosolic free Ca(2+) concentration, endogenous reactive oxygen species generation, protein tyrosine phosphorylation and platelet aggregation. Proanthocyanidins, such as cinnamtannin B-1, have been reported to exert antitumoral activity mediated by a selective proapoptotic action in a number of tumoral cell lines associated with antiapoptotic activity in normal cells. The opposite effects of proanthocyanidins in normal and tumoral cells suggest that these compounds might be the base for therapeutic strategies directed selectively against tumoral cells. In addition, cinnamtannin B-1 shows antithrombotic actions through inhibition, in platelets, of endogenous ROS generation, Ca(2+) mobilization and, subsequently, aggregation. This has been reported to be especially relevant in platelets from diabetic patients, where cinnamtannin B-1 reverses both platelet hypersensitivity and hyperactivity. Considering the large number of cellular effects of cinnamtannin B-1 the development of therapeutic strategies for thrombotic disorders or certain types of cancer deserves further studies. This review summarizes the current knowledge on the actions and relevance of the signalling pathways modulated by cinnamtannin B-1.

Natriuretic peptides in vascular physiology and pathology

Four major natriuretic peptides have been isolated: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and Dendroaspis-type natriuretic peptide (DNP). Natriuretic peptides play an important role in the regulation of cardiovascular homeostasis maintaining blood pressure and extracellular fluid volume. The classical endocrine effects of natriuretic peptides to modulate fluid and electrolyte balance and vascular smooth muscle tone are complemented by autocrine and paracrine actions that include regulation of coronary blood flow and, therefore, myocardial perfusion; modulation of proliferative responses during myocardial and vascular remodeling; and cytoprotective anti-ischemic effects. The actions of natriuretic peptides are mediated by the specific binding of these peptides to three cell surface receptors: type A natriuretic peptide receptor (NPR-A), type B natriuretic peptide receptor (NPR-B), and type C natriuretic peptide receptor (NPR-C). NPR-A and NPR-B are guanylyl cyclase receptors that increase intracellular cGMP concentration and activate cGMP-dependent protein kinases. NPR-C has been presented as a clearance receptor and its activation also results in inhibition of adenylyl cyclase activity. The wide range of effects of natriuretic peptides might be the base for the development of new therapeutic strategies of great benefit in patients with cardiovascular problems including coronary artery disease or heart failure. This review summarizes current literature concerning natriuretic peptides, their receptors and their effects on fluid/electrolyte balance, and vascular and cardiac physiology and pathology, including primary hypertension and myocardial infarction. In addition, we will attempt to provide an update on important issues regarding natriuretic peptides in congestive heart failure.

Hydrogen peroxide activates calcium influx in human neutrophils

The correlation between an increased production of reactive oxygen species (ROS) and an enhanced calcium entry in primed neutrophils stimulated with fMLP suggests that endogenous ROS could serve as an agonist to reinforce calcium signaling by positive feedback. This work shows that exogenous H2O2 produced a rapid influx of Mn2+ and an increase of intracellular calcium. The H2O2 was insufficient to produce significant changes in the absence of extracellular calcium but addition of Ca2+ to H2O2-treated cells suspended in a free Ca2+/EGTA buffer resulted in a great increase in [Ca2+]i reflecting influx of Ca2+ across the cell membrane. The increase of intracellular calcium was inhibited by Ni2+, La3+, and hyperosmotic solutions of mannitol and other osmolytes. This raises the possibility that the secretion of H2O2 by activated neutrophils could act as an autocrine regulator of neutrophil function through the activation of calcium entry.

Agonist-induced calcium entry correlates with STIM1 translocation

The mechanisms of agonist-induced calcium entry (ACE) following depletion of intracellular calcium stores have not been fully established. We report here that calcium-independent phospholipase A (iPLA₂) is required for robust Ca²⁺ entry in HaCaT keratinocytes following ATP or UTP stimulation. Lysophosphatidic acid (LPA), an unrelated agonist, evoked Ca²⁺ release without inducing robust Ca²⁺ entry. Both LPA and UTP induced the redistribution of STIM1 into puncta which localized to regions near or at the plasma membrane, as well as within the cytoplasm. Plasma membrane-associated STIM1 remained high for up to 10 min after UTP stimulation, whereas it had returned almost to baseline by that time point in LPA-stimulated cells. This correlated with faster reloading of the endoplasmic reticulum Ca²⁺ stores in LPA treated cells. Thus by differentially regulating store-refilling after agonist-mediated depletion, LPA and UTP may exert distinct effects on the duration of STIM1 localization at the plasma membrane, and thus, on the magnitude and duration of ACE.

TRP channels in platelet function

Ca2+ entry forms an essential component of platelet activation; however, the mechanisms associated with this process are not understood. Ca2+ entry upon receptor activation occurs as a consequence of intracellular store depletion (referred to as store-operated Ca2+ entry or SOCE), a direct action of second messengers on cation entry channels or the direct occupancy of a ligand-gated P2(Xi) receptor. The molecular identity of the SOCE channel has yet to be established. Transient receptor potential (TRP) proteins are candidate cation entry channels and are classified into a number of closely related subfamilies including TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin) and TRPML (mucolipins). From the TRPC family, platelets have been shown to express TRPC6 and TRPC1, and are likely to express other TRPC and other TRP members. TRPC6 is suggested to be involved with receptor-activated, diacyl-glycerol-mediated cation entry. TRPC1 has been suggested to be involved with SOCE, though many of the suggested mechanisms remain controversial. As no single TRP channel has the properties described for SOCE in platelets, it is likely that it is composed of a heteromeric association of TRP and related subunits, some of which may be present in intracellular compartments in the resting cell.

Cinnamtannin B-1 from bay wood reduces abnormal intracellular Ca2+ homeostasis and platelet hyperaggregability in type 2 diabetes mellitus patients

Type 2 diabetes mellitus induces a number of cardiovascular disorders, including platelet hyperactivity and hyperaggregability, which is associated to an increased oxidant production and abnormal cytosolic Ca2+ mobilization. In the present study, we have investigated the effect of cinnamtannin B-1 obtained from bay wood on oxidants production, Ca2+ mobilization and aggregation in platelets from type 2 diabetic donors. Pretreatment of platelets with cinnamtannin B-1 reversed the enhanced oxidants production and Ca2+ mobilization, including Ca2+ entry, evoked by thapsigargin plus ionomycin or thrombin, observed in platelets from diabetic subjects, so that in the presence of cinnamtannin B-1 Ca2+ entry was similar in platelets from healthy and diabetic subjects. In addition, cinnamtannin B-1 reduced thrombin-induced aggregation in platelets from type 2 diabetic subjects. We conclude that cinnamtannin B-1 exerts an effective antioxidant action in platelets from patients with type 2 diabetes mellitus and reverses the enhanced Ca2+ mobilization and hyperaggregability.

Glucose transport activation in human hematopoietic cells M07e is modulated by cytosolic calcium and calmodulin

The aim of this work was to investigate the role of cytosolic calcium and calmodulin-dependent systems in the activation of glucose uptake in the human megakaryocytic cell line M07e. Glucose uptake was significantly raised by elevation of cytosolic Ca(2+) concentration ([Ca(2+)](c)) with thapsigargin, this effect being additive to the activation induced by cytokines (SCF, GM-CSF and TPO) and hydrogen peroxide. Intracellular Ca(2+) chelation by BAPTA decreased basal and activated glucose uptake in a dose-dependent manner. BAPTA reduced the GLUT1 translocation induced by SCF and H(2)O(2), suggesting a major role for Ca(2+) in GLUT1 intracellular trafficking. In the absence of extracellular Ca(2+), 2-aminoethoxydiphenyl-borate (2-APB) abolished the activation of glucose uptake induced by cytokines and H(2)O(2) suggesting an involvement in GLUT1 regulation in responses related to InsP(3)-induced Ca(2+) release. Under our experimental conditions, all the stimuli inducing glucose uptake activation failed to increase [Ca(2+)](c) suggesting that cytosolic Ca(2+) plays a permissive role in the regulation of GLUT1. The calmodulin antagonist W-7 and the inhibitor of Ca(2+)-calmodulin dependent protein kinase II (CAMK II) KN-62 removed the glucose transport activation by all the tested stimuli. These results suggest that in M07e cells calmodulin and CAMKII are involved in GLUT1 stimulation by cytokines and ROS.

Effects of feeding Spodoptera littoralis on lima bean leaves. III. Membrane depolarization and involvement of hydrogen peroxide

In response to herbivore (Spodoptera littoralis) attack, lima bean (Phaseolus lunatus) leaves produced hydrogen peroxide (H(2)O(2)) in concentrations that were higher when compared to mechanically damaged (MD) leaves. Cellular and subcellular localization analyses revealed that H(2)O(2) was mainly localized in MD and herbivore-wounded (HW) zones and spread throughout the veins and tissues. Preferentially, H(2)O(2) was found in cell walls of spongy and mesophyll cells facing intercellular spaces, even though confocal laser scanning microscopy analyses also revealed the presence of H(2)O(2) in mitochondria/peroxisomes. Increased gene and enzyme activations of superoxide dismutase after HW were in agreement with confocal laser scanning microscopy data. After MD, additional application of H(2)O(2) prompted a transient transmembrane potential (V(m)) depolarization, with a V(m) depolarization rate that was higher when compared to HW leaves. In transgenic soybean (Glycine max) suspension cells expressing the Ca(2+)-sensing aequorin system, increasing amounts of added H(2)O(2) correlated with a higher cytosolic calcium ([Ca(2+)](cyt)) concentration. In MD and HW leaves, H(2)O(2) also triggered the increase of [Ca(2+)](cyt), but MD-elicited [Ca(2+)](cyt) increase was more pronounced when compared to HW leaves after addition of exogenous H(2)O(2). The results clearly indicate that V(m) depolarization caused by HW makes the membrane potential more positive and reduces the ability of lima bean leaves to react to signaling molecules.

Dose-dependent effect of hydrogen peroxide on calcium mobilization in mouse pancreatic acinar cells

We have employed confocal laser scanning microscopy to investigate how intracellular free calcium concentration ([Ca2+]i) is influenced by hydrogen peroxide (H2O2) in collagenase-dispersed mouse pancreatic acinar cells. In the absence of extracellular calcium, treatment of cells with increasing concentrations of H2O2resulted in an increase in [Ca2+]i, indicating the release of calcium from intracellular stores. Micromolar concentrations of H2O2induced an oscillatory pattern, whereas 1 mmol H2O2/L caused a slow and sustained increase in [Ca2+]i. H2O2abolished the typical calcium release stimulated by thapsigargin or by the physiological agonist cholecystokinin octapeptide (CCK-8). Depletion of either agonist-sensitive or mitochondrial calcium pools was unable to prevent calcium release induced by 1 mmol H2O2/L, but depletion of both stores abolished it. Additionally, lower H2O2concentrations were able to release calcium only after depletion of mitochondrial calcium stores. Treatment with either the phospholipase C inhibitor U-73122 or the inhibitor of the inositol 1,4,5-trisphosphate (IP3) receptor xestospongin C did not modify calcium release from the agonist-sensitive pool induced by 100 µmol H2O2/L, suggesting the involvement of a mechanism independent of IP3 generation. In addition, H2O2reduced amylase release stimulated by CCK-8. Finally, either the H2O2-induced calcium mobilization or the inhibitory effect of H2O2on CCK-8-induced amylase secretion was abolished by dithiothreitol, a sulphydryl reducing agent. We conclude that H2O2at micromolar concentrations induces calcium release from agonist- sensitive stores, and at millimolar concentrations H2O2can also evoke calcium release from the mitochondria. The action of H2O2is mediated by oxidation of sulphydryl groups of calcium ATPases independently of IP3 generation.Key words: hydrogen peroxide, pancreatic acinar cells, intracellular calcium stores, amylase secretion.

Hydrogen peroxide and peroxynitrite enhance Ca2+ mobilization and aggregation in platelets from type 2 diabetic patients

Cytosolic Ca2+ mobilization, especially Ca2+ entry, is enhanced in platelets from type 2 diabetic individuals, which might result in platelet hyperaggregability. In the present study, we report an increased oxidant production in resting and stimulated platelets from diabetic donors. Pretreatment of platelets with catalase or trolox, an analog of vitamin E, reversed the enhanced Ca2+ entry, evoked by thapsigargin plus ionomycin or thrombin, observed in platelets from diabetic subjects, so that in the presence of these scavengers Ca2+ entry was similar in platelets from healthy and diabetic subjects. In contrast, mannitol was without effect on Ca2+ mobilization. Catalase and trolox reduced thrombin-induced aggregation in platelets from type 2 diabetic subjects, while mannitol did not modify thrombin-induced platelet hyperaggregability. We conclude that H2O2 and ONOO- are likely involved in the enhanced Ca2+ mobilization observed in platelets from type 2 diabetic patients, which might lead to platelet hyperactivity and hyperaggregability.