Scavenging Of Intermediates Research Articles

Modification of lipoperoxidative effects of dichloroacetate and trichloroacetate is associated with peroxisome proliferation

Pretreatment of male B6C3F 1 mice with clofibric acid (CFA) or trichloroacetic acid (TCA) in the drinking water results in a marked decrease in the lipoperoxidative response as measured by the production of thiobarbituric acid reactive substances (TBARS) in mouse liver homogenates following acute dosing with TCA or dichloroacetic acid (DCA). Pretreatment with TCA or CFA also increased palmitoyl-CoA oxidase activity, microsomal 12-(ω) hydroxylation of lauric acid and expression of P450 4A isoforms. At the doses utilized, DCA-pretreatment did not increase the level of P450 4A protein, or markers of peroxisome proliferation. However, DCA-pretreatment did result in enhanced levels of TBARS, following acute dosing with DCA, compared to controls. Pretreatment with DCA, TCA, or CFA did not alter p-nitrophenol hydroxylation (an assay specific for P450 2E1), and no increases in immunodetectable P450 2E1, 4A, 1A1/2, 2B1/2 or 3A1 protein were observed. Assays from CFA- and TCA-pretreated mice suggest that the reduction in the TBARS response seen in TCA-pretreated animals results from activities associated with peroxisome proliferation. This might result from the induction of systems efficient in scavenging of peroxide intermediates or detoxification of aldehyde by-products of lipid peroxidation.

Abrogation of gamma interferon-induced inhibition of Ehrlichia chaffeensis infection in human monocytes with iron-transferrin.

Ehrlichia chaffeensis is an obligate intracellular bacterium which infects cells of the macrophage/monocyte lineage. To test whether gamma interferon (IFN-gamma) inhibits infection of monocytes with E. chaffeensis, human peripheral blood monocytes were incubated with recombinant human IFN-gamma for 3 h and then exposed to E. chaffeensis. With 2,000 U of IFN-gamma per ml, maximal inhibition of infection by E. chaffeensis was observed. THP-1 cells, a human monocyte cell line, pretreated with phorbol myristic acetate or not pretreated, were incubated with various concentrations of IFN-gamma. Maximum inhibition was obtained at 1,000 U of IFN-gamma per ml with phorbol myristic acetate-treated THP-1 cells. However, nontreated cells did not achieve a similar level of anti-ehrlichial activity even with 10,000 U of IFN-gamma per ml. IFN-gamma given within 6 h postinfection was effective in inhibiting E. chaffeensis. Nitric oxide production was not demonstrated in the monocyte medium incubated with IFN-gamma and E. chaffeensis. None of the reactive oxygen intermediate scavengers tested blocked the IFN-gamma-induced anti-ehrlichial activity. Deferoxamine, an intracellular iron chelator, at 15 microM completely inhibited the survival of E. chaffeensis. Iron-saturated transferrin at 1.67 mg/ml completely reversed the IFN-gamma-induced ehrlichial killing. These results indicate that (i) E. chaffeensis is sensitive to intracytoplasmic iron depletion, (ii) E. chaffeensis is sensitive to IFN-gamma-induced killing, and (iii) the anti-ehrlichial activity induced in human monocytes by IFN-gamma is mediated by limitation of available cytoplasmic iron and is not due to the generation of reactive oxygen intermediates or nitric oxide.

Inhibition of activation-induced death in T cell hybridomas by thiol antioxidants: oxidative stress as a mediator of apoptosis.

N-Acetylcysteine (NAC) is a well established thiol antioxidant which, after uptake, deacylation and conversion to glutathione functions as both a redox buffer and a reactive oxygen intermediate scavenger. We report here that NAC completely blocks activation induced death and associated DNA fragmentation of myelin basic protein (MBP) specific T cell hybridomas. Conversely, NAC had very little effect on the antigen driven proliferation of a MBP specific T cell line similar to that from which the hybridomas were derived. NAC displayed an analogous absolute inhibition of mitogen mediated activation induced death, even if added up to 3 h post activation. Although glutathione was as efficient as NAC at blocking activation induced death, dithiothreitol displayed minimal inhibition while L-cysteine had no effect at all. The observation that certain thiol antioxidants such as NAC and glutathione can completely block the activation induced death of T cell hybridomas implicates redox regulation in this process.

RRR‐Tocopherols and their Acetates as a Possible Scavenger of Free Radicals Produced in the Skin upon UVA‐Exposure – An in vivo Screening Method

AbstractRRR‐tocopherols currently draw attention as constituent of cosmetic preparations a. o. to prevent damage by over‐exposure to sunlight. Because they only absorb part of the UVB and are transparent to UVA, their skin protective activity is supposed to be based on scavenging of reactive intermediates formed by ultraviolet radiation. To investigate this possibility, an in vivo method was developed. This is based on the determination of irreversible binding to epidermal DNA/RNA, proteins and lipids, of reactive intermediates formed by photodecomposition of a xenobiotic in the skin. The results support the conclusion that RRR‐tocopherols can indeed scavenge reactive intermediates which are formed upon UV‐exposure in the skin. RRR‐tocopherol acetates also are active in this respect but only after pretreatment for some days (possibly because enzymatic hydrolysis of these compounds is a prerequisite).

Effects of reactive oxygen intermediate scavengers on the antitoxoplasmic activity of activated macrophages.

Obioactin, Lonomycin A, muramyl dipeptide, and scavengers of hydrogen radicals and of singlet oxygen were used to study the participation of.OH and 1O2 in the killing of Toxoplasma in cultures of glycogen-induced peritoneal macrophages. Both the scavengers of OH (diazabicyclooctane and histidine) and those of 1O2 (mannitol and sodium benzoate) failed to inhibit the multiplication of Toxoplasma in macrophages that were incubated with either Obioactin, Lonomycin A, or MDP. The results of these experiments demonstrate the apparent lack of an inhibitory effect of.OH and 1O2 on the multiplication of Toxoplasma, whereas the scavengers alone inhibited the growth of the parasites.

The metabolism of N-acetylcysteine by human endothelial cells

When human umbilical endothelial cells were depleted of their glutathione by incubation in a sulfur amino acid-free medium, subsequent incubation of the cells with this deficient medium supplemented with N-acetylcysteine resulted in a dose-dependent stimulation of the snythesis of cellular glutathione. Similarly, the inclusion of N-acetylcysteine in the medium during the period of depletion of glutathione caused a dose-dependent retardation of the depletion kinetics. In contrast, the incubation of control cells in normal medium supplemented with N-acetylcysteine did not increase cellular glutathione levels above controls. These observations indicate the presence of an N-deacetylase in/on the cells with specificity for N-acetylcysteine. Due to the large surface area of the endothelium in the vasculature it seems likely that endothelial cell N-deactylation plays a role in the metabolic disposition of N-acetylcysteine, particularly when administered intravenously. N-Acetylcysteine is, however, a relatively poor precursor to glutathione biosynthesis in comparison to cystine. Thus, any cytoprotective, antioxidant effect exerted by N-acetylcysteine on the human endothelium is likely to be due to direct scavenging of reactive intermediates rather than by stimulated glutathione synthesis in the endothelial cells themselves.

In vitro adrenalin oxidation, in bacteriological media, causes bacterial growth inhibition and killing

We present experimental evidence that adrenalin autoxidation causes bacterial growth inhibition and killing. The experimental model utilized detects ‘oxygen toxicity’ in prokaryotes using standard microbiological assays for antibacterial activity, allowing direct observation of the toxicity exerted on bacterial cells and the scavenging of toxic intermediates by the defence enzymes catalase and superoxide dismutase.

In vitro adrenalin oxidation, in bacteriological media, causes bacterial growth inhibition and killing

We present experimental evidence that adrenalin autoxidation causes bacterial growth inhibition and killing. The experimental model utilized detects ‘oxygen toxicity’ in prokaryotes using standard microbiological assays for antibacterial activity, allowing direct observation of the toxicity exerted on bacterial cells and the scavenging of toxic intermediates by the defence enzymes catalase and superoxide dismutase.

Partial oxidation of unsaturated hydrocarbons over Pd(111): Oxygen scavenging of reactive intermediates and the formation of furan from C2H2 and C4H4

Furan is formed by selective oxidation of both C2H2 and C4H4 over Pd(111). In the former case, oxygen scavenging of reactively formed C4H4 directly demonstrates that this species is the key intermediate in acetylene cyclotrimerisation. In the latter case, overall selectivity towards furan formation can be as high as ∼ 80%.

In Vitro Spinal Cord Conduction Block During Exposure to a Xanthine Oxidase/Hypoxanthine System: Noninvolvement of Superoxide and Hydrogen Peroxide

The effects of a reactive oxygen system on axonal conduction were assessed in an in vitro rat spinal cord preparation. An enzyme system, containing hypoxanthine and xanthine oxidase as a source of superoxide and hydrogen peroxide, was used in combination with ADP and FeCl3 as catalysts for peroxidative activity. The reactants were mixed as they entered a temperature-controlled Plexiglas chamber containing a longitudinal hemisection of adult rat spinal cord. Extracellular action potentials were recorded with a glass microelectrode before, during, and after the exposure. A significant conduction block developed during the 30 min exposure. Action potential amplitude decreased to less than 45% of pre-exposure level while absolute refractory period to paired stimuli increased 160%. Following reintroduction of normal bathing medium, amplitude and absolute refractory period exhibited recovery toward pre-exposure control levels, but did not fully recover. Isolated spinal cord membranes exposed to the same xanthine oxidase system produced significant levels of malondialdehyde (MDA). Superoxide dismutase (SOD), but not catalase, effectively inhibited MDA production. Hypoxanthine, xanthine oxidase, and ADP-Fe3+ were all required to induce conduction block in the spinal cord and peroxidation in the isolated membranes. However, addition of intermediate scavengers, SOD and catalase, alone or in tandem, did not prevent the conduction block. Mechanisms other than radical-induced lipid peroxidation may be working to alter the membrane ionic equilibrium in the cord preparation.

Secondary reactions of primary products of the Fischer-Tropsch synthesis: Part 1. The role of ethene

Co-feeding experiments have shown that ethene readily initiates the Fischer-Tropsch synthesis without altering the chain-growth probability, even when it is present in high concentrations. Propagation by ethene was found to be unlikely. When present in concentrations of 5 mol% or higher, ethene substantially suppresses methane formation by surface hydrogen and surface intermediate scavenging.

Lymphokine activation of J774G8 cells and mouse peritoneal macrophages challenged with Toxoplasma gondii

In vitro activation of macrophage cell line J774G8 and mouse peritoneal macrophages resulted in oxygen-dependent and oxygen-independent killing of intracellular Toxoplasma gondii. Activation was characterized by oxygen-dependent killing detectable by enhanced lysosome fusion and digestion of T. gondii. The toxoplasmacidal activity of activated J774G8 cells and peritoneal macrophages was prevented by adding the oxygen intermediate scavengers catalase or superoxide dismutase during culture. Activated J774G8 cells and peritoneal macrophages also inhibited replication of those Toxoplasma organisms which survived the initial microbicidal activity. The inhibition of Toxoplasma replication was not significantly affected by exogenous catalase or superoxide dismutase. Peritoneal macrophages from Toxoplasma-immune mice showed similar microbicidal and inhibitory responses, supporting the model that activation leads to destruction of intracellular parasites by two different mechanisms.

Macrophage oxygen-dependent antimicrobial activity. I. Susceptibility of Toxoplasma gondii to oxygen intermediates.

A sensitive method for evaluating extracellular parasite viability was used to determine the in vitro susceptibility of virulent Toxoplasma gondii to selected oxygen intermediates. By acridine orange fluorescent staining criteria, toxoplasmas were resistant to up to either 10(-3) M reagent H2O2 or H2O2 generated by glucose-glucose oxidase. In keeping with a lack of sensitivity to H2O2, toxoplasmas contained endogenous catalase (5.7 x 10(-4) Baudhuin units/10(6) organisms). The addition of a peroxidase and halide, however, markedly accelerated killing and lowered the H2O2 requirement by 1,000-fold. In contrast, toxoplasmas were promptly killed after exposure to products generated by xanthine (1.5 x 10(-4) M) and xanthine oxidase (50 micrograms). The inhibition of this system's microbicidal activity by scavengers of O2- (superoxide dismutase) and H2O2 (catalase) indicated that although neither O2- nor H2O2 were toxoplasmacidal, their interaction was required for parasite killing. Quenching OH. and 1O2, presumed products of O2--H2O2 interaction, by mannitol, benzoate, diazabicyclooctane, and histidine, also inhibited toxoplasma killing by xanthine-xanthine oxidase. These findings suggested that O2- and H2O2 functioned in precursor roles and that OH. and 1O2 were toxoplasmacidal. The capacity of normal peritoneal macrophages to pinocytose an oxygen intermediate scavenger, soluble catalase, was also demonstrated. Appreciable extraphagosomal concentrations of catalase were achieved by exposing macrophages to 1 mg/ml of the enzyme for 3 h. Maintenance of high intracellular levels required constant exposure because interiorized catalase was rapidly degraded.