17beta-estradiol reduces tumor necrosis factor-alpha-mediated LDL accumulation in the artery wall.
(17/16336)
Estrogens have direct effects on the vascular wall that may prevent the development of atherosclerosis. In particular, estrogens, such as 17beta-estradiol (estradiol), are known to have potent antioxidant activity. Tumor necrosis factor-alpha (TNF) is found in human atheroma and produces oxygen-derived free radicals. These oxygen-derived free radicals may modify low density lipoproteins (LDL) and increase LDL binding in the artery wall. We asked: 1) does TNF increase LDL accumulation in the artery wall and 2) can the TNF-mediated increase in LDL accumulation be prevented by the antioxidant activity of estradiol? Carotid arteries from ovariectomized 3-month-old rats were removed and perfused with fluorescently labeled LDL and arterial LDL flux was measured using quantitative fluorescence microscopy. In six arteries, addition of TNF (10 ng/ml) to the perfusate resulted in a 2.3-fold increase in the rate of LDL accumulation (1.50 +/- 0.37 ng/min per cm2 vs. 3.38 +/- 0.48 ng/min per cm2; P < 0.01). Estradiol (65 pg/ml) and alpha-tocopherol (6 mg/L) both attenuated TNF-mediated LDL accumulation (P < 0.05), indicating that TNF may exert its effects on LDL accumulation through cellular production of oxygen-derived free radicals. These results support an antioxidant role for estradiol in the protection against LDL accumulation in the artery wall and subsequent progression of atherosclerosis. (+info)
Regulation of IGF binding protein-1 in hep G2 cells by cytokines and reactive oxygen species.
(18/16336)
The liver is a major site of synthesis for insulin-like growth factor binding protein (IGFBP)-1. Because IGFBP-1 inhibits many anabolic actions of IGF-I, increases in IGFBP-1 may be partly responsible for the decrease in lean body mass observed in catabolic/inflammatory conditions. This study aimed to determine in Hep G2 cells 1) the sensitivity of IGFBP-1 synthesis to treatment with interleukin (IL)-1, tumor necrosis factor-alpha (TNF-alpha), and IL-6, 2) the ability of reactive oxygen species (ROS) to enhance IGFBP-1 production, and 3) the role of ROS in mediating cytokine-induced increases in IGFBP-1. Hep G2 cells responded to IL-1beta, TNF-alpha, and IL-6 with maximal 8- to 10-fold increases in IGFBP-1 production. Although the maximal responsiveness of cells treated with TNF-alpha and IL-6 was 20-30% less than that with IL-1beta, cells demonstrated a similar sensitivity to all cytokines (half-maximal responsive dose of approximately 10 ng/ml). A low concentration (3 ng/ml) of all three cytokines had an additive effect on IGFBP-1 production. Cytokines also increased IGFBP-1 mRNA. The half-life of IGFBP-1 mRNA was approximately 4 h and not altered by IL-1beta. Incubation with ROS, including H2O2 and nitric oxide (NO) donors, resulted in a relatively smaller increase in IGFBP-1. However, preincubating Hep G2 cells with various free radical scavengers and NO synthase and eicosanoid inhibitors failed to prevent or attenuate cytokine-induced increases in IGFBP-1. Finally, preincubating cells with pyrrolidinedithiocarbamate (PDTC) but not SN50 (inhibitors of nuclear factor-kappaB activation and nuclear translocation, respectively) attenuated increases in IGFBP-1 induced by IL-1. These results indicate that 1) proinflammatory cytokines directly enhance IGFBP-1 synthesis by stimulating transcription without altering mRNA stability, 2) addition of exogenous ROS also stimulates IGFBP-1 production but to a smaller extent than cytokines, and 3) the cytokine-induced increase in IGFBP-1 production is not mediated by endogenous production of ROS or eicosanoids but appears to at least partially involve a PDTC-sensitive pathway. (+info)
Induction of reactive oxygen intermediates in human monocytes by tumour cells and their role in spontaneous monocyte cytotoxicity.
(19/16336)
The present study examined the ability of human monocytes to produce reactive oxygen intermediates after a contact with tumour cells. Monocytes generated oxygen radicals, as measured by luminol-enhanced chemiluminescence and superoxide anion production, after stimulation with the tumour, but not with untransformed, cells. The use of specific oxygen radical scavengers and inhibitors, superoxide dismutase, catalase, dimethyl sulphoxide and deferoxamine as well as the myeloperoxidase inhibitor 4-aminobenzoic acid hydrazide, indicated that chemiluminescence was dependent on the production of superoxide anion and hydroxyl radical and the presence of myeloperoxidase. The tumour cell-induced chemiluminescent response of monocytes showed different kinetics from that seen after activation of monocytes with phorbol ester. These results indicate that human monocytes can be directly stimulated by tumour cells for reactive oxygen intermediate production. Spontaneous monocyte-mediated cytotoxicity towards cancer cells was inhibited by superoxide dismutase, catalase, deferoxamine and hydrazide, implicating the role of superoxide anion, hydrogen peroxide, hydroxyl radical and hypohalite. We wish to suggest that so-called 'spontaneous' tumoricidal capacity of freshly isolated human monocytes may in fact be an inducible event associated with generation of reactive oxygen intermediates and perhaps other toxic mediators, resulting from a contact of monocytes with tumour cells. (+info)
Superoxide dismutase and catalase in Photobacterium damselae subsp. piscicida and their roles in resistance to reactive oxygen species.
(20/16336)
Photobacterium damselae subsp. piscicida (formerly Pasteurella piscicida) is the causative agent of pasteurellosis or pseudotuberculosis in warm water marine fish. Enzymes which neutralize reactive oxygen species, produced during aerobic metabolism or during respiratory burst in fish macrophages, are important virulence factors in many pathogens. This study characterizes a periplasmic superoxide dismutase (SOD) and a cytoplasmic catalase in P. damselae. Purification and partial amino-terminal sequencing confirmed the SOD to be iron-cofactored, with a high degree of homology to other bacterial FeSODs. The SOD was common to all strains analysed in terms of type, location and activity, whilst the catalase varied in activity between strains. The catalase was constitutively expressed, but the SOD appeared to be repressed under low oxygen conditions. In spite of the presence of a periplasmic SOD, P. damselae was susceptible to killing by exogenous superoxide anion generated in a cell-free system. Addition of exogenous SOD to this system did not abolish the bactericidal effect; however, addition of catalase was protective. These results suggest that lack of periplasmic catalase may be implicated in susceptiblity to killing by reactive oxygen species. (+info)
Ras proteins induce senescence by altering the intracellular levels of reactive oxygen species.
(21/16336)
Human diploid fibroblasts eventually lose the capacity to replicate in culture and enter a viable but nonproliferative state of senescence. Recently, it has been demonstrated that retroviral-mediated gene transfer into primary fibroblasts of an activated ras gene (V12ras) rapidly accelerates development of the senescent phenotype. Using this in vitro system, we have sought to define the mediators of Ras-induced senescence. We demonstrate that expression of V12Ras results in an increase in intracellular and in particular, mitochondrial reactive oxygen species. The ability of V12Ras to induce growth arrest and senescence is shown to be partially inhibited by coexpression of an activated rac1 gene. A more dramatic rescue of V12Ras-expressing cells is demonstrated when the cells are placed in a low oxygen environment, a condition in which reactive oxygen species production is inhibited. In addition, in a 1% oxygen environment, Ras is unable to trigger an increase in the level of the cyclin-dependent kinase inhibitor p21 or to activate the senescent program. Under normoxic (20% O2) conditions, the V12Ras senescent phenotype is demonstrated to be unaffected by scavengers of superoxide but rescued by scavengers of hydrogen peroxide. These results suggest that in normal diploid cells, Ras proteins regulate oxidant production and that a rise in intracellular H2O2 represents a critical signal mediating replicative senescence. (+info)
Cycloheximide and 4-OH-TEMPO suppress chloramphenicol-induced apoptosis in RL-34 cells via the suppression of the formation of megamitochondria.
(22/16336)
Toxic effects of chloramphenicol, an antibiotic inhibitor of mitochondrial protein synthesis, on rat liver derived RL-34 cell line were completely blocked by a combined treatment with substances endowed with direct or indirect antioxidant properties. A stable, nitroxide free radical scavenger, 4-hydroxy-2,2,6, 6-tetramethylpiperidine-1-oxyl, and a protein synthesis inhibitor, cycloheximide, suppressed in a similar manner the following manifestations of the chloramphenicol cytotoxicity: (1) Oxidative stress state as evidenced by FACS analysis of cells loaded with carboxy-dichlorodihydrofluorescein diacetate and Mito Tracker CMTH2MRos; (2) megamitochondria formation detected by staining of mitochondria with MitoTracker CMXRos under a laser confocal microscopy and electron microscopy; (3) apoptotic changes of the cell detected by the phase contrast microscopy, DNA laddering analysis and cell cycle analysis. Since increases of ROS generation in chloramphenicol-treated cells were the first sign of the chloramphenicol toxicity, we assume that oxidative stress state is a mediator of above described alternations of RL-34 cells including MG formation. Pretreatment of cells with cycloheximide or 4-hydroxy-2,2, 6,6-tetramethylpiperidine-1-oxyl, which is known to be localized into mitochondria, inhibited the megamitochondria formation and succeeding apoptotic changes of the cell. Protective effects of cycloheximide, which enhances the expression of Bcl-2 protein, may further confirm our hypothesis that the megamitochondria formation is a cellular response to an increased ROS generation and raise a possibility that antiapoptotic action of the drug is exerted via the protection of the mitochondria functions. (+info)
Mitochondria in neurodegeneration: bioenergetic function in cell life and death.
(23/16336)
The biochemical pathways to cell death in chronic and acute forms of neurodegeneration are poorly understood, limiting the ability to develop effective therapeutic approaches. As details of the apoptotic and necrotic pathways have been revealed, an appreciation for the decisive role that mitochondria play in life-death decisions for the cell has grown. As a result, the need has arisen to reevaluate the significance to cell viability of mitochondrial Ca2+ sequestration, reactive oxygen species generation, and the membrane permeability transition. This review provides basic information on these mitochondrial functions as they relate to control over cell death. (+info)
Signal transduction by reactive oxygen species in non-phagocytic cells.
(24/16336)
A growing body of evidence suggests a potential role for oxygen-derived radicals such as superoxide anions and hydrogen peroxide as intracellular signaling molecules. Recently, progress has been made regarding the regulation of oxidant production in non-phagocytic cells. Significant gaps in understanding persist, however, especially in regard to the source(s) of oxidant production and the direct intracellular target(s) of oxygen radicals. Nonetheless, numerous recent studies have implicated a dynamic change in the intracellular redox state as an important determinant in a host of cellular decisions ranging from growth, to apoptosis, to cellular senescence. (+info)