Selective and non-selective apoptosis induction in transformed and non-transformed fibroblasts by exogenous reactive oxygen and nitrogen species
University of Freiburg, Freiburg, Baden-Württemberg, Germany Anticancer research
(Impact Factor: 1.83).
This paper defines selective and nonselective apoptosis induction in transformed and nontransformed fibroblasts by extracellular reactive oxygen and nitrogen species (ROS and RNS). Superoxide anions do not exhibit direct apoptosis inducing potential, whereas their dismutation product hydrogen peroxide induces apoptosis nonselectively in transformed and nontransformed fibroblasts. Myeloperoxidase converts hydrogen peroxide into the selective apoptosis mediator HOCl, which interacts with transformed target cell-derived superoxide anions and generates apoptosis-inducing hydroxyl radicals. Nitric oxide does not induce apoptosis directly in fibroblasts. However, interaction of nitric oxide with transformed cell-derived superoxide anions leads to the generation of the ultimate apoptosis inducer, peroxynitrite. Peroxynitrite by itself does not discriminate between transformed and nontransformed cells. The direction of generation of apoptosis inducing ROS and RNS to the site of superoxide anion production has relevance for the selectivity of ROS and RNS-based natural antitumor systems, as extracellular superoxide anion generation represents a hallmark of the transformed state.
Available from: Susanne Brakemeier
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ABSTRACT: Endothelium-derived nitric oxide and reactive oxygen species (ROS) have been proposed to regulate vascular tone by complex mechanisms, including the modulation of ion channel function. In endothelial function itself, activation of Ca2+-activated K+ channels (KCa) plays a crucial role by inducing hyperpolarization, which promotes membrane potential-driven Ca2+ influx and Ca2+-dependent synthesis of vasodilatory factors. In the present study, we tested whether nitric oxide and ROS modulate endothelial KCa function.
By employing the patch-clamp technique in endothelium of porcine renal arteries in situ, we identified a large-conductance Ca2+-activated K+ channel (big K+ channel, BKCa) with a conductance of 297 +/- 6 pS.
Channel activity was strongly controlled by the membrane potential and the cytosolic Ca2+ concentration (EC50 3.1 +/- 0.5 micromol/L Ca2+ at 0 mV). Channel activity was inhibited by Ba2+ and iberiotoxin. At submicromolar [Ca2+]i, nitric oxide induced a dose-dependent stimulation of BKCa activity with a 10-fold increase at the highest dose tested (1 micromol/L). A similar stimulation was achieved by the nitric oxide donors, sodium nitroprusside (SNP), and diethylamine nitric oxide complex (DEA-NO). In contrast, ROS and, in particular, hydrogen peroxide (H2O2) led to dose-dependent inactivation of BKCa with an IC50 of 80 +/- 6 nmol/L and 1.1 +/- 0.4 micromol/L, respectively. In isolated porcine renal arteries, bradykinin-induced vasodilation was significantly reduced by either iberiotoxin or H2O2.
Direct stimulation of endothelial BKCa by nitric oxide might represent a novel mechanism of autocrine regulation of endothelial function and points to a positive feedback mechanism by promoting hyperpolarization and nitric oxide production itself. The ROS-induced inhibition of BKCa could be part of the cellular mechanisms by which ROS impairs endothelium-dependent vasodilation.
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ABSTRACT: Endothelial dysfunction/activation underlies the development of long-term cardiovascular complications and atherosclerosis. The aim of this study was to examine a direct role for exogenous sublethal flux of superoxide on endothelial cell dysfunction. Human umbilical vein endothelial cells (HUVEC) were exposed to superoxide generated by 0.1 mM xanthine and 4 mU/ml xanthine oxidase for 15 min and essential endothelial functions were examined. Superoxide dismutase and/or catalase was used as scavenger for O(2)(-)/H(2)O(2) to determine the key culprit. HUVEC detachment was determined by neutral red uptake and apoptosis by annexin V binding. Inflammation was estimated by IL-8 mRNA expression and cellular adhesion molecules (CAM). eNOS and iNOS message and eNOS protein served as an indirect measure for NO. Procoagulable state was evaluated by estimating the intracellular tissue factor. Activation of endothelial NADPH oxidase was determined by lucigenin chemiluminescence. Sublethal superoxide dose evoked: (1) proinflammatory state manifested by increased IL-8 mRNA expression and CAM on the endothelial surface, (2) HUVEC apoptosis and activated endothelial NADPH oxidase, (3) increase in intracellular tissue factor, and (4) decrease in eNOS mRNA and protein and up-regulation of iNOS mRNA. We conclude that extracellular low flux of superoxide exhibits pleiotropic characteristics, triggering activation/dysfunction of endothelial cells.
Available from: ncbi.nlm.nih.gov
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ABSTRACT: Borna disease virus (BDV) is a neurotropic member of the order Mononegavirales with noncytolytic replication and obligatory persistence in cultured cells and animals. Here we show that the accessory protein
X of BDV represents the first mitochondrion-localized protein of an RNA virus that inhibits rather than promotes apoptosis
induction. Rat C6 astroglioma cells persistently infected with wild-type BDV were significantly more resistant to death receptor-dependent
and -independent apoptotic stimuli than uninfected cells or cells infected with a BDV mutant expressing reduced amounts of
X. Confocal microscopy demonstrated that X colocalizes with mitochondria and expression of X from plasmid DNA rendered human
293T and mouse L929 cells resistant to apoptosis induction. A recombinant virus encoding a mutant X protein unable to associate
with mitochondria (BDV-XA6A7) failed to block apoptosis in C6 cells. Furthermore, Lewis rats neonatally infected with BDV-XA6A7 developed severe neurological symptoms and died around day 30 postinfection, whereas all animals infected with wild-type
BDV remained healthy and became persistently infected. TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick
end labeling) staining revealed a significant increase in the number of apoptotic cells in the brain of BDV-XA6A7-infected animals, whereas the numbers of CD3+ T lymphocytes were comparable to those detected in animals infected with wild-type BDV. Our data thus indicate that inhibition
of apoptosis by X promotes noncytolytic viral persistence and is required for the survival of cells in the central nervous
system of BDV-infected animals.
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