Ca2+ is mobilized by hydroxyl radical but not by superoxide in RTH-149 cells: The oxidative switching-on of Ca2+ signaling

Targeted and Off-Target (Bystander and Abscopal) Effects of Radiation Therapy: Redox Mechanisms and Risk/Benefit Analysis

SIGNIFICANCE

Radiation therapy (from external beams to unsealed and sealed radionuclide sources) takes advantage of the detrimental effects of the clustered production of radicals and reactive oxygen species (ROS). Research has mainly focused on the interaction of radiation with water, which is the major constituent of living beings, and with nuclear DNA, which contains the genetic information. This led to the so-called target theory according to which cells have to be hit by ionizing particles to elicit an important biological response, including cell death. In cancer therapy, the Poisson law and linear quadratic mathematical models have been used to describe the probability of hits per cell as a function of the radiation dose. Recent Advances: However, in the last 20 years, many studies have shown that radiation generates "danger" signals that propagate from irradiated to nonirradiated cells, leading to bystander and other off-target effects.

CRITICAL ISSUES

Like for targeted effects, redox mechanisms play a key role also in off-target effects through transmission of ROS and reactive nitrogen species (RNS), and also of cytokines, ATP, and extracellular DNA. Particularly, nuclear factor kappa B is essential for triggering self-sustained production of ROS and RNS, thus making the bystander response similar to inflammation. In some therapeutic cases, this phenomenon is associated with recruitment of immune cells that are involved in distant irradiation effects (called "away-from-target" i.e., abscopal effects).

FUTURE DIRECTIONS

Determining the contribution of targeted and off-target effects in the clinic is still challenging. This has important consequences not only in radiotherapy but also possibly in diagnostic procedures and in radiation protection.

Effect of Low-Intensity Cavitation on the Isolated Human Thoracic Artery In Vitro

Reported here are the results of an experimental study on the response to low-intensity cavitation induced by low-frequency (4-6 W/cm², 20 kHz and 32.6 kHz) ultrasound of isolated human arterial samples taken during conventional myocardial revascularization operations. Studies have found that low-frequency ultrasound results in a significant (48%-54%) increase in isometric contraction force and does not depend on the number of exposures (10 or 20) or the time passed since the start of ultrasound (0, 10 and 20 min), but does depend on the frequency and location (internal or external) of the blood vessels for the application of ultrasound. Diltiazem (an inhibitor of slow calcium channels) and carbachol (an agonist of muscarinic receptors) used in a concentration-dependent manner did not modify the relaxation dynamics of smooth muscle affected by ultrasound. Thus, ultrasound conditioned to the augmentation of the isometric contraction force the smooth muscle of blood vessels and did not improve endothelial- and calcium channel blocker-dependent relaxation.

Effects of operator parameters, anions and cations on the degradation of AY99 in an aqueous solution using Fenton’s reagent. Optimization and kinetics study

In the present work, the decolourization of azo dye Acid Yellow 99 (AY99) in an aqueous solution by Fenton oxidation process was investigated. The results indicated that the initial pH, the nature of the acid to adjust pH, the temperature and the initial concentrations of the Fenton’s reagent FeSO4 of H2O2 and of the AY99 played an important role on the dye decolourization. It was found that under optimum conditions, which have been determined to be pH = 3, [H2O2]0 = 1.8 mmol/L, [Fe2+]0 = 0.09 mmol/L, [AY]0 = 0.06 mmol/L and T = 30°C, efficiency of degradation obtained after 40 min of reaction was about 95%. The decolourization of AY99 by the Fenton process followed the second-order reaction kinetics. The empirical kinetic equation for AY99 decolourization under the conditions of 0.03 to 0.15 mmol/L of Fe2+, 0.9 to 1.8 mmol/L of H2O2, 0.03 to 0.15 mmol/L of Acid Yellow and pH = 3 was found to follow the relation:

K = 6.39 × 107 [AY] −2.8[H2O2]2.29[FeSO4]0.837 exp (−7021.3/T).

The decolourization efficiency Ef (in percent) was 88.36%, 87.93%, 85.98% and 39.61% in the presence of H2SO4, HNO3, HCl and H3PO4 acids, respectively. We can deduce that H2SO4, HNO3 and HCl acids lead almost to the same efficiency (Ef), but in the presence of H3PO4, it is too low:

Ef (H2SO4) ~ Ef (HNO3) > Ef (HCl) > > Ef (H3PO4).

Effects of additives such as inorganic salts (sodium chloride, calcium chloride, sodium sulphate and calcium sulphate) and cations (sodium sulphate, calcium sulphate, copper sulphate, manganese sulphate and magnesium sulphate) on the efficiency (Ef) and on the rate constant (k 2) of AY99 degradation were also studied under optimum conditions.

Ef (Na2SO4) > Ef (CaSO4) > Ef (NaCl) > Ef (CaCl2)

k 2 (CaCl2) < k 2 (NaCl) < k 2 (CaSO4) < k 2 (Na2SO4)

Ef (ZnSO4) > Ef (MgSO4) > Ef (Na2SO4) > Ef (CaSO4) > Ef (CuSO4) > Ef (MnSO4)

k 2 (Na2SO4) < k 2 (MnSO4) < k 2 (CuSO4) < k 2 (CaSO4) < k 2 (ZnSO4) < k 2 (MgSO4).

The presence of anions and cations in the aqueous solution decreases the decolourization efficiency and the rate constant of the degradation of AY99. This inhibition may be due to a complexation and a radical scavenging.

Amplitude-encoded calcium oscillations in fish cells

The reaction of intracellular Ca(2+) to different agonist stimuli in primary hepatocytes from rainbow trout (Oncorhynchus mykiss) as well as the permanent fish cell line RTL-W1 was investigated systematically. In addition to "classical" agonists such as phenylephrine and ATP, model environmental toxicants like 4-nitrophenol and 3,4-dichloroaniline were used to elucidate possible interactions between toxic effects and Ca(2+) signaling. We report Ca(2+) oscillations in response to several stimuli in RTL-W1 cells and to a lesser extent in primary hepatocytes. Moreover, these Ca(2+) oscillations are amplitude-encoded in contrast to their mammalian counterpart. Bioinformatics and computational analysis were employed to identify key players of Ca(2+) signaling in fish and to determine likely causes for the experimentally observed differences between the Ca(2+) dynamics in fish cells compared to those in mammalian liver cells.

Highly reactive oxygen species: detection, formation, and possible functions

The so-called reactive oxygen species (ROS) are defined as oxygen-containing species that are more reactive than O(2) itself, which include hydrogen peroxide and superoxide. Although these are quite stable, they may be converted in the presence of transition metal ions, such as Fe(II), to the highly reactive oxygen species (hROS). hROS may exist as free hydroxyl radicals (HO·), as bound ("crypto") radicals or as Fe(IV)-oxo (ferryl) species and the somewhat less reactive, non-radical species, singlet oxygen. This review outlines the processes by which hROS may be formed, their damaging potential, and the evidence that they might have signaling functions. Since our understanding of the formation and actions of hROS depends on reliable procedures for their detection, particular attention is given to procedures for hROS detection and quantitation and their applicability to in vivo studies.

Chemistry and antihypertensive effects of tempol and other nitroxides

Nitroxides can undergo one- or two-electron reduction reactions to hydroxylamines or oxammonium cations, respectively, which themselves are interconvertible, thereby providing redox metabolic actions. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol) is the most extensively studied nitroxide. It is a cell membrane-permeable amphilite that dismutates superoxide catalytically, facilitates hydrogen peroxide metabolism by catalase-like actions, and limits formation of toxic hydroxyl radicals produced by Fenton reactions. It is broadly effective in detoxifying these reactive oxygen species in cell and animal studies. When administered intravenously to hypertensive rodent models, tempol caused rapid and reversible dose-dependent reductions in blood pressure in 22 of 26 studies. This was accompanied by vasodilation, increased nitric oxide activity, reduced sympathetic nervous system activity at central and peripheral sites, and enhanced potassium channel conductance in blood vessels and neurons. When administered orally or by infusion over days or weeks to hypertensive rodent models, it reduced blood pressure in 59 of 68 studies. This was accompanied by correction of salt sensitivity and endothelial dysfunction and reduced agonist-evoked oxidative stress and contractility of blood vessels, reduced renal vascular resistance, and increased renal tissue oxygen tension. Thus, tempol is broadly effective in reducing blood pressure, whether given by acute intravenous injection or by prolonged administration, in a wide range of rodent models of hypertension.

Novel redox-dependent regulation of NOX5 by the tyrosine kinase c-Abl

We investigated the mechanism of H(2)O(2) activation of the Ca(2+)-regulated NADPH oxidase NOX5. H(2)O(2) induced a transient, dose-dependent increase in superoxide production in K562 cells expressing NOX5. Confocal studies demonstrated that the initial calcium influx generated by H(2)O(2) is amplified by a feedback mechanism involving NOX5-dependent superoxide production and H(2)O(2). H(2)O(2) NOX5 activation was inhibited by extracellular Ca(2+) chelators, a pharmacological inhibitor of c-Abl, and overexpression of kinase-dead c-Abl. Transfected kinase-active GFP-c-Abl colocalized with vesicular sites of superoxide production in a Ca(2+)-dependent manner. In contrast to H(2)O(2), the Ca(2+) ionophore ionomycin induced NOX5 activity independent of c-Abl. Immunoprecipitation of cell lysates revealed that active GFP-c-Abl formed oligomers with endogenous c-Abl and that phosphorylation of both proteins was increased by H(2)O(2) treatment. Furthermore, H(2)O(2)-induced NOX5 activity correlated with increased localization of c-Abl to the membrane fraction, and NOX5 proteins could be coimmunoprecipitated with GFP-Abl proteins. Our data demonstrate for the first time that NOX5 is activated by c-Abl through a Ca(2+)-mediated, redox-dependent signaling pathway and suggest a functional association between NOX5 NADPH oxidase and c-Abl.

Influence of ATP on Ehrlich ascites carcinoma cell free cytoplasmic calcium concentration in the course of tumor growth

The changes in free cytoplasmic calcium concentration ([Ca2+](in)) and the effects of extracellular ATP on [Ca2+](in) have been studied in Ehrlich ascites carcinoma cells in the dynamics of their growth. The basal level of [Ca2+](in) and the effects of ATP on the ascites cells were determined by the stage of tumor growth and depended on the content of reactive oxygen species (ROS). The sharp increase in basal and ATP-induced elevation of [Ca2+](in) levels were observed at the 12th day of ascites cell growth. Inhibition of ROS formation by N-acetyl-L-cysteine decreased [Ca2+](in) and suppressed the cell reaction to ATP. We suggest that the increased sensitivity of the ascites cells to ATP observed on the 12th day may be also attributed to a decrease in ecto-ATPase activity.

Identification of an AHNAK binding motif specific for the Annexin2/S100A10 tetramer

The Annexin2 tetramer (A2t), which consists of two Annexin2 molecules bound to a S100A10 dimer, is implicated in membrane-trafficking events. Here, we showed using a yeast triple-hybrid experiment and in vitro binding assay that Annexin2 is required for strong binding of S100A10 to the C-terminal domain of the protein Ahnak. We also revealed that this effect involves only the Annexin2 N-terminal tail, which is implicated in S100A10/Annexin2 tetramerization. The minimal A2t binding motif (A2tBP1) in Ahnak was mapped to a 20-amino acid peptide, and this peptide is highly specific for A2t. We also identified a second A2t binding motif (A2tBP2) present in the N-terminal domain of Ahnak, which binds to A2t, albeit with less affinity. When overexpressed as an EGFP fusion protein in MDCK cells, A2tBPs cofractionate in a calcium-dependent manner and co-immunoprecipitate with S100A10 and Annexin2. In living cells, A2tBPs target EGFP to the cytoplasm as does Annexin2. In response to oxidative and mechanical stress, EGFP-A2tBPs relocalize within minutes to the plasma membrane; a behavior shared with Annexin2-GFP. These results suggest that the A2t complex exists within the cytoplasm of resting living cells and that its localization at the plasma membrane relies on cellular signaling. Together, our data demonstrate that A2tBP1 is a specific A2t complex binding domain and may be a powerful tool to help elucidate A2t structure and cellular functions.

Reactive oxygen species, Ca2+ signaling and mitochondrial NAD(P)H level in adrenal glomerulosa cells

The acute effects of ultraviolet light, the superoxide-generating xanthine-xanthine oxidase system and H(2)O(2) to on calcium signaling and mitochondrial pyridine nucleotide metabolism were investigated in rat glomerulosa cells. UV light induced the formation of superoxide, that, similar to exogenously applied superoxide and H(2)O(2), decreased the level of mitochondrial NAD(P)H. Free radical scavengers antagonized this effect of UV light. Extracellularly generated superoxide elicited Ca(2+) transients and inhibited angiotensin II-induced cytoplasmic Ca(2+) signaling. Low intensity UV light did not affect basal [Ca(2+)] and failed to influence Ca(2+) signaling induced by depolarization or store depletion. UV light of the same low power reduced both cytoplasmic and mitochondrial Ca(2+) signals induced by angiotensin II. The lack of UV effect on inositol phosphate formation indicates that the inhibition of cytoplasmic Ca(2+) signaling is due to reduced Ca(2+) release from InsP(3)-sensitive stores. Decreased mitochondrial Ca(2+) uptake may be attributed to UV-induced perturbation of the perimitochondrial microdomain.

Transient permeabilization of cell membranes by ultrasound-exposed microbubbles is related to formation of hydrogen peroxide

In the present study, we addressed the interactions among ultrasound, microbubbles, and living cells as well as consequent arising bioeffects. We specifically investigated whether hydrogen peroxide (H(2)O(2)) is involved in transient permeabilization of cell membranes in vitro after ultrasound exposure at low diagnostic power, in the presence of stable oscillating microbubbles, by measuring the generation of H(2)O(2) and Ca(2+) influx. Ultrasound, in the absence or presence of SonoVue microbubbles, was applied to H9c2 cells at 1.8 MHz with a mechanical index (MI) of 0.1 or 0.5 during 10 s. This was repeated every minute, for a total of five times. The production of H(2)O(2) was measured intracellularly with CM-H(2)DCFDA. Cell membrane permeability was assessed by measuring real-time changes in intracellular Ca(2+) concentration with fluo-4 using live-cell fluorescence microscopy. Ultrasound, in the presence of microbubbles, caused a significant increase in intracellular H(2)O(2) at MI 0.1 of 50% and MI 0.5 of 110% compared with control (P < 0.001). Furthermore, we found increases in intracellular Ca(2+) levels at both MI 0.1 and MI 0.5 in the presence of microbubbles, which was not detected in the absence of extracellular Ca(2+). In addition, in the presence of catalase, Ca(2+) influx immediately following ultrasound exposure was completely blocked at MI 0.1 (P < 0.01) and reduced by 50% at MI 0.5 (P < 0.001). Finally, cell viability was not significantly affected, not even 24 h later. These results implicate a role for H(2)O(2) in transient permeabilization of cell membranes induced by ultrasound-exposed microbubbles.