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Biomedical subjects

N H Hunt

Publications and source records attributed to N H Hunt.

At least 55 records · Page 3Linked to original sources
PubMed1995

Effects of endotoxin and dexamethasone on cerebral malaria in mice.

CBA/T6 and DBA/2J mice inoculated with Plasmodium berghei ANKA (PbA) develop cerebral involvement 6-8 days post-inoculation, from which the CBA mice almost invariably die and the DBA mice recover. Dexamethasone (DXM; 80 mg/kg) given to inoculated CBA mice twice, on day 3 and again within 48 h, reduced the cerebral symptoms and prevented death from cerebral malaria. Plasma tumour necrosis factor (TNF) levels, which increased at the time of the cerebral symptoms, were also reduced in these DXM-treated mice. Intravenously administered Evans Blue, a dye which binds to albumin, diffused extensively across the blood-brain barrier only during the period of cerebral symptoms, in proportion to the severity of the cerebral symptoms and the disease. In PbA-infected CBA mice, cerebral symptoms and the amounts of Evans Blue diffusing into the brain tissue were both reduced by DXM treatment, but only if the steroid was given on day 3 and again within 48 h. Endotoxin injected intravascularly into PbA-infected DBA mice after day 5 resulted in an exaggeration of cerebral symptoms and death between days 6 and 9. Plasma TNF and the amount of Evans Blue in the brain parenchyma increased above normal levels in these mice. Endotoxin injections had only minor effects on the severity of the cerebral symptoms in PbA-infected CBA mice and did not cause the animals to die sooner.

Adrenal Glands↗
PubMed1994

Thiol-bearing compounds selectively inhibit protein kinase C-dependent oxidative events and proliferation in human T cells.

The aminothiol cysteamine at 10(-5) to 10(-4) M concentrations inhibited both the proliferation of mitogenically stimulated human peripheral mononuclear cells and the phorbol myristate acetate-mediated oxidation of 2',7'-dichlorofluorescein within these cells. Both 2',7'-dichlorofluorescein oxidation and the proliferative response were maximally sensitive to cysteamine-induced inhibition during the first 2 h of mitogenic stimulation. This period of sensitivity indicates that cysteamine preferentially arrests cells transiting from G0 to G1 and is the first such demonstration, of an early cell cycle site of arrest for this compound. 2,3-Dimercapto-1-propane-sulfonic acid and WR 1065 were found to be more effective than cysteamine in attenuating T cell replication but not N-acetylcysteine. Aminothiols preferentially inhibited the intracellular oxidation of 2',7'-dichlorofluorescein, rather than the activity of protein kinase C, which initiates the oxidation, indicating that oxidative events are one of a number of crucial and independent events required for the successful transition through G0-G1. Since aminothiols affect both lectin and PMA/ionomycin-directed proliferation, these aminothiol-sensitive events may serve to integrate and regulate common pathways in T cell activation.

Alkaloids↗
PubMed1993

Redox metabolism of vitamin C in blood of normal and malaria-infected mice.

As oxidative mechanisms have been suggested to be part of the host immune reaction against malarial parasites, we investigated the redox metabolism of the antioxidant vitamin C in the blood of control and malaria-infected mice. At the peak of infection (day 6) with the malaria parasite P. vinckei, plasma levels of ascorbate (AH-) were 10.8 +/- 0.9 micrograms/ml compared to 5.7 +/- 0.7 micrograms/ml in control mice, though no significant change was observed in the plasma concentration of dehydroascorbate (DHA). The plasma redox ratio of vitamin C, [AH-]:[DHA], was 7.4 in control mice and 18.5 in infected mice on day 6 post-inoculation. The increased AH- level in plasma of P. vinckei-infected mice was not due to differences in stabilities of either AH- or DHA in plasmas from control or P. vinckei-infected mice. DHA added to plasma was lost rapidly. In contrast, when added to whole blood. DHA was rapidly taken up and reduced to AH by blood cells from both normal mice and P. vinckei-infected mice. Most of the intracellular AH- derived from the exogenously added DHA was released into the plasma by blood cells from the infected but not normal mice. The observed release of AH- into the plasma by blood cells from infected mice was not caused by a plasma factor. Depletion of leukocytes from erythrocytes had no effect on the uptake and reduction of DHA by red blood cells, but the subsequent release of intracellular AH- occurred more rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Amelioration of murine cerebral malaria by dietary restriction.

CBA/T6 strain mice infected with Plasmodium berghei ANKA develop cerebral symptoms and die, with mononuclear cell attachment to the cerebral microvascular endothelium, petechial haemorrhages and breakdown of the blood-brain barrier, some 6-7 days post-inoculation. The effects of dietary restriction on this process were examined. Mice were fed ab libitum (Group 1) or their food was restricted to produce body weight loss of 1.0-2.0% (Group 2), 2.5-3.5% (Group 3), 4.0-6.5% (Group 4) or 7.0-9.5% (Group 5) relative to Group 1. Dietary restriction reduced deaths caused by cerebral malaria from 100% in Group 1 to 47% (Group 2), 43% (Group 3), 10% (Group 4) and 53% (Group 5). Restriction of food intake had no effect on (1) the progression of parasitaemia in infected mice (2) changes in haematocrit, spleen weight, total lymph node cell number or (3) peritoneal exudate cell number in either malaria-infected or uninfected mice. P. berghei ANKA infection did not significantly affect the proportion of lymph node leucocytes that were Thy-1+ T cells or CD8+ T cells, but did lead to significant increases in the CD4+ and B cell populations. Dietary restriction alone increased the lymph node CD4+ cell population but did not affect the increase in B cells in malaria-infected mice. P. berghei ANKA infection and dietary restriction together did not lead to increased CD4+ cell numbers in lymph node leucocytes. The in vitro proliferative response to isolated lymph node cells to concanavalin A or phorbol myristate acetate plus ionomycin was measured and found to be identical in all treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Comparisons between microvascular changes in cerebral and non-cerebral malaria in mice, using the retinal whole-mount technique.

CBA/T6 mice inoculated with Plasmodium berghei ANKA strain (PbA) exhibited cerebral symptoms and died from cerebral malaria 6-8 days p.i. whereas DBA/2J mice developed (around days 6-9) a non-fatal cerebral malaria, with milder cerebral symptoms, and died between days 15 and 22 from other malaria-related complications. When inoculated with P. berghei K173 (Pb) these mouse strains did not develop cerebral malaria. These mouse/parasite strain combinations were used, in conjunction with the retinal whole-mount technique, to elucidate factors critical in the pathology of murine cerebral malaria. CBA/T6 mice infected with PbA (PbA-CBA mice) demonstrated mild changes in vascular permeability as early as days 2-3, prior to the appearance on day 5 of cerebral symptoms, whereas mice with non-cerebral malaria did not show any vascular permeability changes until the very late stage of the disease (days 14-22). In the PbA infections, progressive deterioration of endothelial barrier properties, demonstrated by Evans' Blue leakage both generally and from specific focal areas, as well as a developing monocytosis and adherence of mononuclear cells to the endothelium of the retinal vessels continued until death (in CBA/T6 mice) or resolution (in DBA/2J mice). Adherent monocytes, particularly in PbA-CBA mice, were associated with reduced Hoechst staining of individual endothelial cells and a banking up proximally of both parasitized and non-parasitized blood cells in the small blood vessels, often with accompanying focal leakage of Evans' Blue from the retinal vessels. The occurrence and severity of these early changes in the microcirculation correlated with the subsequent development of cerebral symptoms. Monocyte margination appeared to be the most significant factor associated with the development of cerebral symptoms.

Animals↗
PubMed1992

Effects of anti-oxidants on ornithine decarboxylase in mitogenically-activated T lymphocytes.

Reactive oxygen species formation is an early event following lymphocyte activation and may trigger other biochemical processes. Anti-oxidants (desferrioxamine (DES), nordihydroguaiaretic acid (NDGA) and potassium ferricyanide) inhibit human and murine T cell proliferation in vitro. Since an increase in ornithine decarboxylase (ODC) activity is an essential concomitant of T lymphocyte proliferation, we have examined in vitro the effects of anti-oxidants on this activity increase. ODC activity in mouse lymph node T cells increased steadily from 6-24 h after addition of concanavalin A. The combination of phorbol myristate acetate (PMA) and ionomycin also stimulated ODC activity in these cells. The anti-oxidants DES, NDGA and ferricyanide strongly inhibited the increase in ODC activity seen in response to either concanavalin A or PMA/ionomycin. Dose-response curves for the inhibitory effects of the anti-oxidants on DNA synthesis and ODC activity at 48 h after mitogen addition were very similar. Addition of putrescine or spermidine (10-100 microM) could not overcome the block in DNA synthesis induced by DES. Although the anti-oxidants inhibited the ODC activity increase in mitogen-stimulated T cells, they did not decrease mRNA levels for the enzyme. These results suggest that intracellular formation of reactive oxygen species is involved in the induction of ODC activity by a mechanism exerted at a posttranscriptional stage. The anti-oxidants can be employed as tools to elucidate contingent relationships between some intracellular events that follow T cell activation.

Animals↗
PubMed1992

In vitro effects of three iron chelators on mitogen-activated lymphocytes: identification of differences in their mechanisms of action.

The effects of three iron chelators (ADR-529/ICRF-187; omadine/pyrithione; and a newly synthesized pyridoxal-based iron chelator, SAG-15) on cultured BALB/c murine lymph node cells stimulated with phorbol myristate acetate and ionomycin have been investigated. All three agents were found to inhibit [3H]-thymidine incorporation after 66-72 h incubation. Pretreatment of ADR-529 and omadine with Fe(III) or Fe(II) ions did not prevent their inhibitory effects. However, pretreatment of SAG-15 with Fe(II) or Fe(III) ions led to a significant increase in the ID50. Time-course studies of cell viability and thymidine incorporation demonstrated that the inhibitory effect of omadine was attributable to cell killing while for ADR-529 and SAG-15 there were both cytostatic and cytotoxic effects. Cell cycle analysis showed that treatment of cells with ADR-529 led to arrest in G2/M while treatment with SAG-15 led to a G0/G1 arrest. Iron has an obligatory role in T-lymphocyte activation that may be related to the formation of reactive oxygen species. SAG-15 is a new iron chelator that will help in the elucidation of the precise role of iron in lymphoproliferation. Since SAG-15 is an extremely effective iron chelator in vivo it has potential as an immunosuppressive agent.

Animals↗
PubMed1992

Pathology of fatal and resolving Plasmodium berghei cerebral malaria in mice.

CBA/T6 and Balb/c mice inoculated with Plasmodium berghei ANKA strain (PbA) died from cerebral malaria 6-8 days post-inoculation. DBA/2J mice similarly inoculated developed a non-fatal cerebral malaria, with mild temporary cerebral symptoms, and died between days 15 and 22 from other malaria-related complications. When inoculated with P. berghei K173 (Pb) these mouse strains did not develop a cerebral malaria but died between days 15 and 22 from other malaria-related complications. These mouse strain/parasite strain combinations allow for detailed examination of factors critical in the pathology of murine cerebral malaria. Monastral Blue, a colloid dye, when injected intravascularly between days 0 and 2 into PbA-inoculated CBA (PbA-CBA) or Balb/c (PbA-Balb/c) mice prevented death from cerebral malaria. There was no evidence of increased vascular permeability at this stage. When Monastral Blue was injected between days 5 and 8, there was increased vascular permeability in the kidney, liver, lung, spleen and brain of PbA-CBA and PbA-Balb/c mice. Injection of Monastral Blue into these animals at this time also precipitated cerebral symptoms and death, but not in Pb-infected mice. Endothelial and mononuclear cells phagocytosed, and were coated with, the Monastral Blue particles when the dye was injected between days 5 and 8 into PbA-CBA and PbA-Balb/c mice. Control, uninfected mice did not demonstrate either of these features. Pb-infected mice only demonstrated coated mononuclear cells. Mononuclear cell attachment to the endothelium, increased vascular permeability and increased association of Monastral Blue particles with monocytes and endothelial cells were correlated with cerebral symptoms and death. Monastral Blue is thus a useful agent for studying the roles of mononuclear cells and endothelium in murine cerebral malaria.

Animals↗
PubMed1992

Early microvascular changes in murine cerebral malaria detected in retinal wholemounts.

Changes in the cerebral microvasculature such as breakdown of the blood-brain barrier, petechial hemorrhages, congestion, and edema are observed in the later stages of murine cerebral malaria. These changes have been described from histologic sections of brain, but the need to section the material makes direct observation of the microvasculature in situ difficult. The retinal vasculature, in contrast, offers a unique opportunity to study rheologic, barrier, and functional properties of the microvasculature as a wholemount preparation with normal spatial relationship with other tissues and as an intact vascular plexus. A combination of techniques, including intravascular perfusion of Evan's Blue, Bisbenzimide and Monastral Blue, and fluorescence and transmitted light observation of retinal wholemounts, were developed to examine the progressive microvascular changes in murine cerebral malaria. These techniques allowed detection of phenomena such as monocyte adherence to endothelial cells, congestion, small hemorrhages, and breakdown of the blood-retinal barrier, with details of the location of this leakage, earlier than was possible by studying brain sections. Because the retina is intact, the phenomena were seen in greater detail and some, such as occlusion of vessel segments, were detectable only in retinal wholemounts. In addition, the covisualization of the blood elements, barrier properties, and vascular endothelial integrity that are possible with retinal wholemounts allowed detailed analysis of the interaction of different cellular elements in the pathogenesis of cerebral malaria. Except for detection of edema, the retinal wholemount technique offers a more powerful and less time-consuming technique for detecting early microvascular changes in murine cerebral malaria. This technique could find wider application in the study of other diseases that affect the microvasculature of the central nervous system, such as experimental allergic encephalitis and meningitis.

Animals↗
PubMed1991

Interference with oxidative processes inhibits proliferation of human peripheral blood lymphocytes and murine B-lymphocytes.

A number of agents capable of interfering with oxidative events were found to inhibit, in a dose-dependent manner, DNA synthesis in isolated human peripheral blood lymphocytes stimulated with phytohaemagglutinin, or phorbol myristate acetate plus ionomycin. These inhibitory substances were: the iron chelators desferrioxamine and desferrithiocin; the electron acceptor ferricyanide; the anti-oxidant nordihydroguaiaretic acid; ebselen, an agent with glutathione peroxidase-like activity; and diphenylene iodonium, an inhibitor of NADPH-oxidase. The actions of desferrioxamine and desferrithiocin were abolished by prior saturation with iron. Ferrocyanide was much less active in inhibiting human lymphocyte DNA synthesis than its redox partner ferricyanide. Desferrioxamine, ferricyanide and nordihydroguaiaretic acid also inhibited lipopolysaccharide-initiated DNA synthesis in mouse splenocytes in vitro. The common property of these structurally dissimilar agents is their ability to prevent formation of, or detoxify, reactive oxygen species. Thus, the data are consistent with an obligatory role for reactive oxygen formation in human T-cell and mouse B-cell activation at a stage prior to DNA synthesis.

Animals↗
PubMed1991

Flavins as potential antimalarials. 2. 3-Methyl-10-(substituted-phenyl) flavins.

A series of 3-methyl-10-(substituted-phenyl)flavins was prepared and tested for antimalarial activity against the lethal parasite Plasmodium vinckei in mice. Several of these analogues were found to be effective antimalarial agents. A quantitative structure-activity relationship study was undertaken with 44 analogues and no satisfactory relationship could be established.

Animals↗
PubMed1990

Antimalarial action of flavin analogues seems not be due to inhibition of glutathione reductase of host erythrocytes.

A series of 10-(4'-chlorophenyl)-3-substituted flavins (1a-f) were examined with respect to their antimalarial properties. They were tested against Plasmodium falciparum in vitro and Plasmodium vinckei vinckei in vivo. The proposition that they might act through glutathione reductase (GR) (EC 1.6.4.2) inhibition has been studied. Inhibition of P. falciparum in vitro by these compounds shows only slight variation between analogues; in contrast, inhibition of human erythrocyte GR by members of the same series is highly variable, indicating that this is probably not their primary mode of antimalarial action. Results of the P. vinckei vinckei screen showed that 10-(4'-chlorophenyl)-3-methyl,3-ethyl and 3-propyl substituted flavins are active in vivo over the dose range screened (10-70 mg/kg).

Animals↗
PubMed1990

Flavin analogs with antimalarial activity as glutathione reductase inhibitors.

10-(4'-Chlorophenyl)-3-methylflavin has antimalarial activity in vitro and in vivo (Cowden et al., J Med Chem 31: 799, 1988). This flavin analog and two of its derivatives were found to inhibit the antioxidant flavoenzyme glutathione reductase from human erythrocytes in its isolated form as well as in hemolysates. The mixed-type inhibition was completely reversible, the Ki-values being of the order of 1 microM. Surprisingly, the drugs were not competitive with FAD, but with GSSG, one of the enzyme's substrates. Malaria parasite glutathione reductase, extracted from Plasmodium falciparum, could also be inhibited by the compounds. Studies on the effects of the substances on P. falciparum in vitro, which were demonstrated morphologically and by growth inhibition, confirmed previous observations with 10-(4'-chlorophenyl)-3-methylflavin and showed similar parasiticidal characteristics for the two new derivatives. The activities of five other erythrocytic enzymes tested were not impaired by the drugs, nor was the nucleotide metabolism of erythrocytes and/or parasites significantly changed. Permeation into red blood cells was demonstrated for one compound by 19F-NMR-spectroscopy. Inhibition of glutathione reductase might contribute to, or account for, the antimalarial activity of this group of flavin analogs.

Animals↗
PubMed1990

Development of the "activated" high resolution 1H MR spectrum in murine T cells and B cells occurs in G1 phase of the cell cycle.

T and B lymphocytes stimulated with mitogens develop 1H MR spectra characteristic of triglycerides in an isotropic environment. These distinctive signals, which are also observed in malignant cells, cannot be suppressed by compounds which inhibit progression through the cell cycle. Cellular proliferation is thus not essential for the development and maintenance of high resolution lipid spectra in activated cells.

Adenocarcinoma↗
PubMed1990

Cyclic-AMP inhibits neither A23187-stimulated [14C]-arachidonic acid release from prelabelled lipids nor phospholipase A2 activity in resident rat peritoneal macrophages.

8-Bromo cyclic AMP inhibited A23187-stimulated PGE2 production in adherent resident rat peritoneal macrophages by 50% when this was assessed by radioimmunoassay. In contrast, neither exogenous 8-bromo cyclic AMP nor elevation of endogenous cyclic AMP with cholera toxin inhibited 14C-arachidonic acid release or labelled prostaglandin formation by [1-14C]-arachidonic acid-prelabelled macrophages stimulated with either A23187 or melittin. Inhibition by cyclic AMP appears to be confined to PGE2 originating from a pool of endogenous phosphoglyceride that does not readily exchange with isotopically-labelled arachidonic acid. Phospholipase A2 activity, assessed as calcium-dependent [1-14C]-arachidonic acid release from exogenous 1-stearoyl, 2-[1-14C]-arachidonyl phosphatidyl choline at pH 8.6, was activated by melittin but not by A23187 in 1000 x g supernates from sonicated cells. Neither melittin nor calcium activation of phospholipase A2 was inhibited by preincubation of the cells prior to breakage with 8-bromo-cyclic AMP, nor by inclusion of either 8-bromo cyclic AMP or the catalytic subunit of cyclic AMP-dependent kinase in the assay. The results are inconsistent with the hypothesis that inhibition of A23187-stimulated PGE2 production by cyclic AMP in peritoneal macrophages is due to inhibition of a calcium-stimulated phospholipase A2.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Oxidative stress and the redox status of malaria-infected erythrocytes.

The chief focus of this article is the relationship between the redox status of the host erythrocyte and that of the malaria parasite. Roles for oxidative processes in the reduced growth of malaria parasites in abnormal erythrocytes, in the host response against the parasite, and in the action of certain anti-malarial drugs are widely accepted as being established. We believe the evidence underpinning these ideas to be unacceptably deficient in a number of areas and suggest some ways in which the questions could be re-examined experimentally.

Animals↗
PubMed1989

Antioxidants can prevent cerebral malaria in Plasmodium berghei-infected mice.

A/J and CBA/H mice infected with Plasmodium berghei ANKA, a murine model of cerebral malaria, were used to see whether antioxidants influenced the outcome of this disease. Untreated, infected mice died 7 to 9 days after infection, often with cerebral symptoms. Haemorrhages, mononuclear infiltration and oedema were present in the central nervous system (CNS). Feeding a diet containing 0.75% (w/w) butylated hydroxyanisole (BHA) greatly altered the course of this disease. Death was delayed by up to 2 weeks and mice appeared healthy at parasitaemias that would have caused cerebral symptoms and death had they been on a conventional diet. BHA-fed mice showed few or no cerebral symptoms at a time at which control mice were clearly affected, and greatly reduced haemorrhages, mononuclear infiltration and oedema when the CNS was examined. Similar, but more consistent, protective effects were seen after administration of BHA by repeated injections or in osmotic pumps. The combination of superoxide dismutase and catalase, coupled to polyethylene glycol, when administered intravenously also protected mice against death from cerebral complications. Permeability of the blood-brain barrier was monitored by the use of 125I-labelled bovine serum albumin, 51Cr-labelled erythrocytes and the dye Evans blue, all of which are normally excluded from the CNS. Infected mice on control diet showed an increase in Evans blue staining and 125I and 51Cr retention in the CNS tissue itself. Feeding the diet containing BHA reduced these indices of increased blood-brain barrier permeability. In view of the potent radical scavenging activity of BHA in many other systems it is likely, but unproven, that this is its main role here. The protective effect of superoxide dismutase and catalase lends support to the idea that reactive oxygen species are involved in the pathology of experimental cerebral malaria.

Animals↗