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Biomedical subjects

N H Hunt

Publications and source records attributed to N H Hunt.

At least 73 records · Page 4Linked to original sources
PubMed1988

Detection of short-chain carbonyl products of lipid peroxidation from malaria-parasite (Plasmodium vinckei)-infected red blood cells exposed to oxidative stress.

Reversed-phase h.p.l.c. was used to detect 2,4-dinitrophenylhydrazine-reactive carbonyl products, which excludes malonaldehyde, in malaria-parasite (Plasmodium vinckei)-infected murine red blood cells (RBCs). A number of alkanals, 4-hydroxyalk-2-enals and alka-2,4-dienals were tentatively identified by comparison with authentic standards. The formation of 4-hydroxynon-2-enal, deca-2,4-dienal and hexanal was greater in P. vinckei-infected RBCs than in their uninfected counterparts and was increased by the presence of t-butyl hydroperoxide. Several of these aldehydes have previously been shown to be toxic to various types of cells, including P. falciparum, in vitro. The iron chelator desferrioxamine and the free-radical scavenger butylated hydroxyanisole inhibited the formation of these aldehydes. These experiments demonstrate that products of lipid peroxidation other than malonaldehyde are formed during the exposure of malaria-infected RBCs in vitro to drugs that generate reactive oxygen species and have anti-parasitic activity. The formation of products of this type during the natural course of malaria infection may have implications for the mechanisms underlying intra-RBC parasite death and the tissue damage associated with the disease.

Aldehydes↗
PubMed1988

Antioxidants inhibit proliferation and cell surface expression of receptors for interleukin-2 and transferrin in T lymphocytes stimulated with phorbol myristate acetate and ionomycin.

We have previously shown that several antioxidant compounds inhibit the proliferation of T lymphocytes stimulated with alloantigen (Chaudhri, G., Clark, I. A., Hunt, N. H., Cowden, W. B., and Ceredig, R., J. Immunol. 136, 2646, 1986). We concluded from these studies that free oxygen radicals are positive mediators in T-lymphocyte activation and proliferation. In order to extend these studies we examined the effects of antioxidants on T cells stimulated with a combination of phorbol myristate acetate (PMA) and ionomycin. The following antioxidants were used: ferricyanide, an inhibitor of superoxide production; iron chelators, which block hydroxyl radical formation; and butylated hydroxyanisole, a free radical scavenger. Responder cells included purified peripheral T cells (Lyt-2+ or L3T4+ cells) and immature (Lyt-2-/L3T4-) thymocytes. All agents, in the micromolar range, caused a dose-dependent inhibition of proliferation of each T-cell subset studied. Flow microfluorometric analysis of T cells stimulated for 48 hr showed that the expression of interleukin-2 (IL-2) receptors and transferrin receptors was inhibited by all the antioxidants tested but not by hydroxyurea (HU), an inhibitor of the enzyme ribonucleotide reductase. In contrast, the expression of a third activation marker, phagocytic glycoprotein-1 (Pgp-1 or Lyt-24), was not affected by any of the agents. Furthermore, while both the antioxidants and HU inhibited T-cell cycling, analysis of a light-scattering parameter related to cell size indicated that the antioxidant-treated cells remained small while the HU-treated and control cells were larger and blast-like. Therefore, the mechanism of action of the three classes of antioxidants is similar, but quite distinct from the inhibition of proliferation caused by HU. Taken together, these results suggest that free radicals are involved in specific early events in T-cell activation.

Animals↗
PubMed1988

Breakdown of the blood-brain barrier in murine cerebral malaria.

Cerebral malaria in A/J and CBA/H mice infected with Plasmodium berghei ANKA is accompanied by mononuclear cell infiltration, haemorrhage and cerebral endothelial cell damage. This damage is presumably one of the causes of the breakdown of the blood-brain barrier which was detected by measuring the movement of the dye Evans blue and radioisotope labelled albumin and erythrocytes. The density of brain tissue, measured by a Percoll gradient technique, was significantly reduced in mice exhibiting cerebral symptoms, suggesting the occurrence of cerebral oedema.

Animals↗
PubMed1987

Inhibition of murine malaria (Plasmodium chabaudi) in vivo by recombinant interferon-gamma or tumor necrosis factor, and its enhancement by butylated hydroxyanisole.

Cell-mediated immunity to malaria may involve macrophages, the monokines that mediate endotoxicity, and reactive oxygen species. Since interferon-gamma activates macrophages to release reactive oxygen species, and tumor necrosis factor-alpha (TNF-alpha) helps both to mediate endotoxicity and to induce leukocytes to secrete reactive oxygen, we monitored the effects of administering recombinant forms of these cytokines on Plasmodium chabaudi adami infections in mice. We also fed infected mice a diet containing 0.75% butylated hydroxyanisole, a scavenger of free radicals. Infections were suppressed by daily i.p. injections of 5 x 10(4) U of recombinant mouse interferon-gamma from day -1 or by recombinant human TNF released from i.p. osmotic pumps at the rate of 6 x 10(3) U/hr. Degenerate intraerythrocytic parasites (crisis forms) were evident much sooner in the course of the suppressed infections, and parasitemias fell correspondingly earlier. The butylated hydroxyanisole diet, in contrast, enhanced the infections. In these mice crisis forms were seen later, and at higher parasitemias, than they normally occur. These observations are consistent with the concept that T cell-dependent, macrophage-derived mediators are central to the type of malarial immunity that kills parasites inside circulating red cells. They also suggest, but do not prove, that both TNF and reactive oxygen species are involved, and that the role of TNF may be more indirect, although no less important, than that of reactive forms of oxygen.

Administration, Oral↗
PubMed1987

Toxicity of certain products of lipid peroxidation to the human malaria parasite Plasmodium falciparum.

Aldehydes generated during radical-induced lipid peroxidation, in particular 4-hydroxynonenal, are known to inhibit growth of certain cells. To extend our arguments that free radicals might be involved in the host response against malaria parasites we tested 26 carbonyls (n-alkanals, C6-C11; 2-alkenals, C3-C9; 2,4-alkadienals, C7, C9, C10; 4-OH-2-alkenals, C6, C8, C9; 2-alkanones, C3-C9; and malonyldialdehyde) against Plasmodium falciparum in vitro. We had previously detected many of these substances in oxidant-stressed, malaria-infected erythrocytes. Three 2,4-alkadienals (C7, C9 and C10) and three 4-OH-2-alkenals (C6, C8 and C9), at 20-100 microM concentrations, markedly inhibited incorporation of [3H]-hypoxanthine by P. falciparum. Acrolein had low effect, and none of the other compounds (12 aldehydes and 7 ketones) were active at concentrations up to 100 microM. Malonyldialdehyde was without effect at concentrations up to 450 microM. The aldehydes found to be inhibitory against P. falciparum could contribute to both the non-antibody host responses against this parasite and the antimalarial effects of radical-generating compounds such as t-butyl hydroperoxide, hydrogen peroxide, alloxan, isouramil, divicine and primaquine.

Animals↗
PubMed1987

Lipids from Plasmodium vinckei-infected erythrocytes and their susceptibility to oxidative damage.

The constituent lipids of plasma and red blood cells (RBC) from mice late in infection with the malarial parasite Plasmodium vinckei were analyzed and compared with those obtained from uninfected animals. On a dry weight basis, the total extractable lipids of RBC increased threefold during infection, while those of the plasma did not change significantly. In general, changes in individual plasma lipid constituents paralleled those found in RBC of infected mice but were of smaller magnitude. While the increase in the total lipids of parasitized RBC was largely attributable to an increase of more than fourfold in total phospholipids, a significant increase in neutral lipids was also observed. Phosphatidylcholine and phosphatidylethanolamine were the major phospholipids present within RBC, and their total and relative concentrations increased as a result of the infection. A parallel increase occurred in the ratio of unsaturated to saturated fatty acids in the parasitized RBC phospholipids. Infection was also associated with decreases in the relative amount of cholesterol present in RBC and in the ratio of cholesterol to phospholipid. Consistent with this, the fluorescence polarization of 1[4-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene within parasitized RBC plasma membranes was decreased in comparison with its value in noninfected RBC, indicating that malarial infection decreases the "order" of membrane lipids. These modifications, in conjunction with the increased levels of vitamin E and malonyldialdehyde reported elsewhere, are important determinants of the susceptibility of the different membrane compartments within infected RBC to peroxidative damage.

Animals↗
PubMed1987

Modulation of T cells by cyclic AMP in murine influenza virus infection. I. In vitro inhibition of cytotoxic T lymphocytes by exogenous cyclic AMP analogues and by agents which increase intracellular cyclic AMP concentrations.

The effects of 8-bromo-cyclic AMP and cyclic AMP agonists (cholera toxin plus hydrocortisone and prostaglandin E2 plus 3-isobutyl-1-methylxanthine) on the cytotoxic activity of T cells generated during murine influenza virus infection have been examined. Treatment of influenza A/WSN virus primed primary immune spleen cells and their cultured secondary effector T cells from Balb/c mice with these agonists resulted in increases in cyclic AMP levels. These agents also had a marked inhibitory effect on the cytotoxic activity of primary immune spleen cells, but a much weaker inhibitory effect on that of secondary effector T cells. No significant effect of 8-bromo-cyclic GMP on the cytotoxic activity of these two cell types was observed. The cytotoxic activity of H-2-restricted, virus-specific T cells generated either in vivo (primary) or in vitro (secondary) was not significantly inhibited by treatment with histamine, whereas that of alloreactive killer T cells generated in vivo was markedly inhibited. These results suggest that the actions of H-2-restricted, virus-specific T cells may not be regulated by histamine during viral or inflammatory processes.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Antimalarial activity of a riboflavin analog against Plasmodium vinckei in vivo and Plasmodium falciparum in vitro.

The riboflavin analog 10-(4'-chlorophenyl)-3-methylflavin was found to have significant activity against Plasmodium vinckei vinckei when administered orally and parenterally; it was active against P. falciparum in culture. It inhibited mouse erythrocyte glutathione reductase in a dose-dependent manner. When administered orally, 5-deazariboflavin was not active in vivo although it has been shown to have activity against P. falciparum in vitro.

Administration, Oral↗
PubMed1987

Possible roles of tumor necrosis factor in the pathology of malaria.

The authors have earlier proposed that tumor necrosis factor (TNF) might contribute to the pathology of malaria. Here they report the outcome of injecting recombinant human TNF/cachectin into normal mice and others with low parasitemias (6-35%) of Plasmodium vinckei. The object was to see how precisely the pathologic features of the terminal stages of this infection could be produced, when parasitemias are 70-80%. Hypoglycemia, mid-zonal liver damage, and pulmonary accumulation of neutrophils in the pulmonary vasculature, all of which are seen in severe P vinckei infection, occurred within 4-12 hours after the mildly infected mice received TNF/cachectin. Uninfected mice were much less susceptible. TNF/cachectin also increases plasma lactate, a change seen in both the human and rodent diseases. From these findings and the recent literature on TNF/cachectin, including its detection in serum from malarial patients, it seems likely that excessive release of this monokine could account for certain of the unexplained pathologic features of human malaria.

Animals↗
PubMed1986

Effect of antioxidants on primary alloantigen-induced T cell activation and proliferation.

Because oxygen-centered free radicals are involved in cell-mediated immune responses, we examined the possibility that these reactive species could also have a role in the lymphoproliferative response to alloantigens in the mixed lymphocyte culture (MLC). Three classes of agents that prevent the formation, or damaging effects, of oxygen radicals were tested: the non-permeant electron acceptor ferricyanide; the iron chelators desferrioxamine, desferrithiocin, octanohydroxamic acid, and pyridoxal isonicotinoyl hydrazone, which are thought to be capable of preventing the iron-catalyzed reduction of H2O2 to more reactive species; and the lipid-soluble free radical scavenger butylated hydroxyanisole. These compounds inhibited the proliferation of all potential responder cells in the MLC in a dose-dependent manner. Inhibition was observed only if these agents were present early (less than 40 hr) in the MLC; if added later, their effects were significantly reduced. In contrast, the interleukin 2 (IL 2)-dependent proliferation of CTLL-2 cells or Con A blasts was not affected by these compounds at concentrations that inhibited proliferation in MLC by greater than 90%. Interleukin 1 (IL 1) production by peritoneal exudate cells and IL 2 and IL 1 levels in MLC were not affected by any of the agents tested. By flow microfluorometry, the expression of IL 2 receptors on stimulated T cells was found to be inhibited in the presence of these drugs. Taken together, the data point to an important role for free radical-mediated processes during the early stages of T lymphocyte activation, before IL 2 receptor expression.

Animals↗
PubMed1986

Possible mechanisms responsible for the increased ascorbic acid content of Plasmodium vinckei-infected mouse erythrocytes.

The possible mechanisms underlying the acquisition of an increased ascorbic acid content by mouse erythrocytes containing the malarial parasite Plasmodium vinckei were investigated. Ascorbic acid was taken up readily by parasitized red blood cells but not by controls, whilst its partly oxidized form, dehydroascorbic acid, entered both. The uptake of both ascorbic acid and dehydroascorbic acid into erythrocytes was increased as a result of malarial infection. Lysates prepared from parasitized red blood cells reduced exogenous dehydroascorbic acid to ascorbic acid at a higher rate than control red blood cell lysates; this difference was abolished following dialysis of the lysates, a process which removes endogenous reduced glutathione (GSH). The rates of chemical and enzymatic reduction of dehydroascorbic acid to ascorbic acid by GSH were of similar magnitude, thus calling into question the existence of a specific dehydroascorbate reductase in erythrocytes and parasites. These observations suggest that the increased uptake of dehydroascorbic acid into parasitized red blood cells may be a result of enhanced dehydroascorbate-reducing capacity, whilst the presence of the parasite induces a selective increase in the permeability of the erythrocyte plasma membrane to ascorbic acid. The endogenous ascorbic acid content of livers obtained from infected mice was 55% below the normal concentration and its relative rate of destruction during incubation in vitro was enhanced in comparison with that of control livers. Furthermore, the capacity of liver homogenates to synthesize ascorbic acid from glucuronic acid was greatly reduced in infected mice. Therefore it is unlikely that the increase in ascorbic acid content of parasitized red blood cells is a consequence of increased biosynthesis and release of ascorbic acid by the host liver. We have not been able to exclude the possibility that the malarial parasite itself may be capable of de novo synthesis of ascorbic acid.

Animals↗
PubMed1986

Protection of vitamin E from oxidation by increased ascorbic acid content within Plasmodium vinckei-infected erythrocytes.

Erythrocytes isolated from mice at a late stage of infection with the malarial parasite Plasmodium vinckei contained increased levels of vitamin E, but neither control nor infected erythrocytes contained detectable levels of alpha-tocopherolquinone, an oxidation product of vitamin E. Total levels of the antioxidant, vitamin C, were more than doubled in the same populations of highly parasitized erythrocytes. These observations, and the lower ratio of oxidized to reduced forms of ascorbic acid in parasitized compared to nonparasitized erythrocytes, raise the possibility that increased redox-cycling between the two vitamins may account for the failure to detect alpha-tocopherolquinone. Thus, late in infection of mice with the lethal parasite P. vinckei, the content and redox state of erythrocytic ascorbic acid is altered so that it protects vitamin E, and presumably the parasitized red cell and its contents, from oxidative damage.

Animals↗
PubMed1986

Purification and characterization of an inhibitor of plasminogen activator released by rat mammary adenocarcinoma cells.

An inhibitor of plasminogen activator (PA) secreted by a tumorigenic, but non-metastatic, rat mammary adenocarcinoma cell line has been purified to apparent homogeneity and characterized. It strongly inhibited human urokinase, but was 100 times less potent in inhibiting bovine trypsin and had no effect on plasmin or thrombin. A secreted, urokinase-type PA (Mr 48 000) and a cell-associated PA from a metastatic rat adenocarcinoma cell line were also strongly inhibited. In contrast, a tissue-type PA (Mr 66 000), secreted by human melanoma cells, was only slightly inhibited. Purified inhibitor showed a band of Mr 66 000 in sodium dodecyl sulphate/polyacrylamide gel electrophoresis and an isoelectric point of 4.5 after chromatofocusing. The inhibition of human urokinase was non-competitive.

Adenocarcinoma↗
PubMed1986

Bleomycin-detectable iron in plasma from Plasmodium vinckei vinckei-infected mice.

Plasma from mice heavily parasitized by Plasmodium vinckei vinckei was found to contain micromolar levels of iron as detected by the 'bleomycin assay' (slightly modified) of Gutteridge et al. [(1981) Biochem. J. 199, 263-265]. Uninfected mouse plasma contained little or no bleomycin-detectable iron. Plasma ultrafiltrate from infected mice contained no bleomycin-detectable iron, indicating that such iron was associated with the protein/macromolecule fraction. We speculate that this iron could catalyse reduction of peroxides in vivo and thus play a role in malaria pathology.

Animals↗
PubMed1986

Antioxidants in plasma from mice infected with Plasmodium vinckei.

The late stage of infection of mice with the malarial parasite Plasmodium vinckei was accompanied by significant changes in the content of most antioxidants within plasma. The plasma concentrations of uric acid and vitamin C increased, in contrast to those of vitamin E and total plasma proteins, whilst the activity of superoxide dismutase did not change significantly. In contrast to the situation within erythrocytes, the ratio of partly oxidized forms of vitamin C (dehydroascorbate and diketogulonic acid) to reduced ascorbic acid failed to decrease as a result of malarial infection. These results are consistent with earlier findings and add to the idea that malarial infection may result in oxidative tissue damage.

Animals↗
PubMed1986

Increased production of arachidonate metabolites by peritoneal cells of mice infected with Plasmodium vinckei vinckei.

Peritoneal cells from mice infected with Plasmodium vinckei vinckei generate about four times more prostaglandin F and 6-keto prostaglandin F1 alpha, five times the prostaglandin E and ten times the thromboxane B2 than do peritoneal cells from normal mice. These results were not due to differences in the ratios of cell subpopulations from each group. As well as providing additional evidence that macrophage activation occurs in malaria, the increased production of these prostanoids could help explain some of the manifestations of this disease.

6-Ketoprostaglandin F1 alpha↗