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Biomedical subjects

C E Thomas

Publications and source records attributed to C E Thomas.

At least 73 records · Page 4Linked to original sources
PubMed1991

Species-specific uptake of DNA by gonococci is mediated by a 10-base-pair sequence.

Piliated Neisseria gonorrhoeae are known to be transformed less readily if transforming DNA competes with DNA containing the 10-bp sequence GCCGTCTGAA. It has been postulated that the 10-bp sequence is a recognition sequence which is required for efficient DNA uptake. We show that the presence of various forms of this 10-bp sequence results in increased uptake of double-stranded DNA into a DNase-resistant state and allows genetic transformation by an otherwise nontransformable plasmid.

Base Sequence↗
PubMed1991

Lipid hydroperoxide involvement in copper-dependent and independent oxidation of low density lipoproteins.

The involvement of lipid hydroperoxides in the oxidation of human low density lipoproteins (LDL) induced by Cu++ or azoperoxyl radicals was studied. Concurrent or pretreatment of LDL with the synthetic peroxidase Ebselen and its cofactor glutathione totally prevented Cu+(+)-dependent oxidation, as measured by the formation of thiobarbituric acid reactive substances and LDL mobility on agarose gels. LDL could be oxidized in the absence of metals with peroxy radicals generated via homolysis of azo compounds. With the azo initiator, 2,2'-azobis-2-amidinopropane hydrochloride, Ebselen plus glutathione prevented lipid oxidation when present during oxidation. However, if LDL were first pretreated with Ebselen plus glutathione and these reagents removed before oxidation, they did not prevent oxidation. Analysis by high-performance liquid chromatography of lipids extracted from Cu+(+)- or azoperoxyl radical-modified lipoproteins indicated that the major lipid oxidation products were derived from linoleate and that Ebselen-glutathione addition reduced linoleate hydroperoxides. Oxidation of LDL by human monocyte-derived macrophages was also prevented by coincubation with Ebselen-glutathione or the antioxidant, probucol. These results demonstrate that initiation of Cu+(+)-dependent oxidation absolutely requires the presence of trace amounts of lipid hydroperoxides in the lipoprotein and that hydroperoxides play a major role in the propagation reactions even in the absence of added transition metals.

Azo Compounds↗
PubMed1990

Radical-induced inactivation of kidney Na+,K(+)-ATPase: sensitivity to membrane lipid peroxidation and the protective effect of vitamin E.

The Na+,K(+)-ATPase is a membrane-bound, sulfhydryl-containing protein whose activity is critical to maintenance of cell viability. The susceptibility of the enzyme to radical-induced membrane lipid peroxidation was determined following incorporation of a purified Na+,K(+)-ATPase into soybean phosphatidylcholine liposomes. Treatment of liposomes with Fenton's reagent (Fe2+/H2O2) resulted in malondialdehyde formation and total loss of Na+,K(+)-ATPase activity. At 150 microM Fe2+/75 microM H2O2, vitamin E (5 mol%) totally prevented lipid peroxidation but not the loss of enzyme activity. Lipid peroxidation initiated by 25 microM Fe2+/12.5 microM H2O2 led to a loss of Na+,K(+)-ATPase activity, however, vitamin E (1.2 mol%) prevented both malondialdehyde formation and loss of enzyme activity. In the absence of liposomes, there was complete loss of Na+,K(+)-ATPase activity in the presence of 150 microM Fe2+/75 microM H2O2, but little effect by 25 microM Fe2+/12.5 microM H2O2. The activity of the enzyme was also highly sensitive to radicals generated by the reaction of Fe2+ with cumene hydroperoxide, t-butylhydroperoxide, and linoleic acid hydroperoxide. Lipid peroxidation initiated by 150 microM Fe2+/150 microM Fe3+, an oxidant which may be generated by the Fenton's reaction, inactivated the enzyme. In this system, inhibition of malondialdehyde formation by vitamin E prevented loss of Na+,K(+)-ATPase activity. These data demonstrate the susceptibility of the Na+,K(+)-ATPase to radicals produced during lipid peroxidation and indicate that the ability of vitamin E to prevent loss of enzyme activity is highly dependent upon both the nature and the concentration of the initiating and propagating radical species.

Animals↗
PubMed1990

Extracellular calcium effects on cell viability and thiol homeostasis.

Studies of chemically induced cell injury and death, which have used as model systems freshly isolated rat hepatocytes and hepatocytes in culture, are discussed. An important model uses the omission of Ca2+ from the medium during rat hepatocyte incubations. Ca2+ omission induces an intense oxidative stress within hepatocytes incubated in a 95% O2 + 5% CO2 atmosphere. The relationship of calcium homeostasis to the parameters of oxidative stress is important to understanding the progression from reversible to irreversible injury. In the Ca2+ omission model, the vitamin E (Vit. E) content of hepatocytes is important for the prevention of cell injury. Recent studies with rat hepatocytes show that ruthenium red (RR) and La3+, which block Ca2+ translocation through the mitochondrial uniport, can prevent malondialdehyde (MDA) formation, reduced glutathione (GSH), and protein-SH loss, Vit. E loss, and LDH leakage induced by Ca2+ omission from the incubation medium. Ca2+ omission promoted a marked loss of mitochondrial transmembrane potential (delta phi) that was prevented by RR, EGTA, Vit. E, and desferrioxamine. The absence of extracellular Ca2+ may cause mitochondrial Ca2+ cycling that contributes to the observed oxidative stress, resultant loss of cell viability, and protein thiol homeostasis. Chemical agents including a glutathione-depleting agent, ethacrynic acid, and a redox cycling agent, adriamycin, increase the loss of cell viability caused by a Ca2(+)-free medium, but they have some additional effects on cellular processes. The demise of cell viability by the agent is also preventable by Vit. E supplementation. Ca2+ has a role in cell injury that appears to uniquely involve mitochondrial homeostasis.

Animals↗
PubMed1989

Epidermal and transforming growth factor alpha in patients with breast tumours.

Measurements of transforming growth factor alpha (TGF-alpha) in cancer patients have produced variable results. We have now used a specific radioimmunoassay (RIA) and a mitogenic assay to evaluate TGF-alpha content of tumour and urine samples separated by an analytical HPLC system. Urine samples from patients with breast tumours and from age matched controls gave TGF-alpha amounts ranging from 0 to 61.5 ng 24 h-1 compared to urogastrone epidermal growth factor figures of 3.0-26.2 micrograms 24 h-1. The quantities of TGF-alpha in patient and control groups were not significantly different. The majority of breast tumour extracts contained mitogenic material eluting from the HPLC system at the TGF-alpha calibration point. Measurement by RIA of combined samples from each group showed that steroid receptor positive tumours had a mean figure of 14.8 ng g-1 tissue and steroid receptor negative 7.4 ng g-1. Receptor positive tumours from patients treated with an antioestrogen, tamoxifen citrate (Nolvadex), had 0.16 ng g-1. Thus TGF-alpha is found in tumours as a biologically active entity and in quantities sufficient to promote cell division. In addition the observation that tamoxifen causes a significant reduction in the content of TGF-alpha may be an additional beneficial action.

Breast Neoplasms↗
PubMed1989

Kinetic analysis of proton transport by the vanadate-sensitive ATPase from maize root microsomes.

Proton transport by the nitrate-insensitive, vanadate-sensitive ATPase in Kl-washed microsomes and reconstituted vesicles from maize (Zea mays L.) roots was followed by changes in acridine orange absorbance in the presence of either KNO(3) or KCl. Data from such studies obeyed a kinetic model in which net proton transport by the pump is the difference between the rate of proton transport by the action of the ATPase and the leak of protons from the vesicles in the direction opposite from the pump. After establishing the steady state proton gradient, the rate of return of transported protons was found to obey first-order kinetics when the activity of the ATPase was completely and rapidly stopped. The rate of return of these protons varied with the quencher used. When the substrate Mg:ATP was depleted by the addition of either EDTA or hexokinase, the rate at which the proton gradient collapsed was faster than when vanadate was used as the quencher. These trends were independent of the anion accompanying the K and the transport assay used.

Journal Article↗
PubMed1988

Effect of diquat on the distribution of iron in rat liver.

Diquat toxicity is proposed to be mediated through the generation of active oxygen species; however, the exact role of active oxygen in toxicity is not known. The generation of damaging oxygen radicals requires transition metals such as iron. In vitro studies have shown that redox cycling of diquat results in the release of iron from ferritin, thus, increasing the potential for active oxygen species generation. We sought to determine if diquat administration to male Sprague-Dawley rats would result in the release of iron from ferritin in vivo. Rats were treated with diquat dibromide (20 mg/kg body weight) and the effect on the iron distribution in liver was determined. The results show that diquat-treated animals had increased levels of hepatic low molecular weight chelatable iron (LMWC-Fe) and decreased levels of hepatic ferritin iron when compared to saline-treated animals. These results suggest that diquat toxicity may be associated with the release of iron from ferritin in vivo and that iron release from ferritin may be a process common to other free radical mediated toxicities.

Animals↗
PubMed1988

The contribution of the C-terminal undecapeptide sequence of urogastrone-epidermal growth factor to its biological action.

Progressive enzymic degradation of human urogastrone-epidermal growth factor (URO-EGF) has given a series of fragments shortened at the C-terminus leading to removal of 20% of the structure. These peptides have been evaluated for their ability to bind to polyclonal antiserum and to isolated membrane receptors, to stimulate thymidine uptake by fibroblasts and to inhibit gastric acid secretion in rats. The related molecule human transforming growth factor-alpha, was also assayed and showed similar potency to URO-EGF in all systems. Reduced binding to the receptors of the fragments was paralleled by reduction in both biological activities indicating that this portion of the molecule was concerned entirely with receptor binding. After removal of 11 amino acids from the C-terminus the residue peptide was a full agonist although higher concentrations were necessary.

Animals↗
PubMed1988

Effect of extracellular Ca++ omission on isolated hepatocytes. II. Loss of mitochondrial membrane potential and protection by inhibitors of uniport Ca++ transduction.

Incubation of isolated rat hepatocytes in Ca++-free medium generates an oxidative stress which causes significant cell injury. Ruthenium red and La , which block Ca++ uptake through the mitochondrial uniport, totally prevented malondialdehyde formation, glutathione and protein thiol oxidation and vitamin E loss induced by Ca++ omission. Accordingly, these agents also prevented leakage of intracellular K+ and lactate dehydrogenase. Similar protective effects were provided by the Ca++ chelator ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid. The absence of extracellular Ca++ resulted in a marked decline of the mitochondrial transmembrane potential which could be prevented by ruthenium red, ethylene glycol bis(beta-aminoethyl ether)-N,N'tetraacetic acid, the antioxidant vitamin E and the iron chelator, desferrioxamine. In contrast, oxidative stress induced by treatment with the redox active agent paraquat and 1,3-bis(2-chloroethyl)-1-nitrosourea had little effect on mitochondrial transmembrane potential and malondialdehyde formation and lactate dehydrogenase leakage were not affected by ruthenium red or La . These results indicate that the incubation of rat hepatocytes in the absence of extracellular Ca++ creates an unusual oxidative stress which markedly affects mitochondrial function. The ability of vitamin E and desferrioxamine to inhibit the loss of mitochondrial transmembrane potential indicates that oxidative damage is involved in producing mitochondrial dysfunction. Furthermore, the potent inhibitory effects of ruthenium red and La suggest that Ca++ movement through the uniport, perhaps indicative of mitochondrial Ca++ cycling, plays a major role in generating this oxidative stress and promoting cell injury.

Animals↗
PubMed1988

Effect of extracellular Ca++ omission on isolated hepatocytes. I. Induction of oxidative stress and cell injury.

The effect of varying extracellular Ca++ concentration and various antioxidants and metal ion chelators on the viability of isolated rat hepatocytes incubated under 95% O2-5% CO2 was evaluated. Decreasing the extracellular Ca++ concentration from 2 mM to 50 microM or less resulted in a progressive increase in cell injury as determined by lactate dehydrogenase (LDH) leakage. The generation of an oxidative stress, indicated by malondialdehyde formation, occurred before and concomitant with LDH leakage. The antioxidants vitamin E, N,N'-diphenyl-p-phenyl-enediamine, chlorpromazine and promethazine, as well as the iron chelators desferrioxamine and EDTA, all prevented both malondialdehyde production and LDH leakage induced by the absence of extracellular Ca++. A marked loss of cytosolic and mitochondrial glutathione was observed in cells incubated without Ca++, which could be significantly prevented by antioxidants and iron chelators. Similar effects on hepatocyte vitamin E levels also were noted. Addition of the Ca++ chelator ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid to the incubation medium totally prevented LDH leakage and malondialdehyde production and partially ameliorated glutathione and vitamin E loss. Conversely, cell injury resulting from disrupted cellular Ca++ homeostasis after treatment with the Ca++ ionophore A23187 plus 2 mM Ca++ was only slightly inhibited by antioxidants and iron chelators. However, ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid also prevented A23187-induced cell injury. These results indicate that a decrease in extracellular Ca++ generates an oxidative stress in hepatocytes which leads ultimately to severe cell injury. This oxidative stress appears to be a Ca++-dependent phenomenon, precipitating all toxicity by a mechanism distinct from that induced by A23187 treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

The midline supra-orbital approach, using a large single free bone flap. Technical note.

Surgical access to the anterior frontal region of the skull base is facilitated by the removal of a fronto-orbital bone flap. This technique was first described as a two-step procedure by Cophignon. We recently devised a simplified one-step approach in which a single bifrontal supra-orbital bone flap is removed. This report is a technical description and resume of our experiences.

Bone Wires↗
PubMed1986

Reductive release of iron from ferritin by cation free radicals of paraquat and other bipyridyls.

NADPH-cytochrome P-450 reductase-catalyzed reduction of paraquat promoted the release of iron from ferritin. Aerobically, iron release was inhibited approximately 60% by superoxide dismutase, whereas xanthine oxidase-dependent iron release was inhibited nearly 100%. This suggests that both superoxide and the paraquat cation radical can catalyze the release of iron from ferritin. Accordingly, under anaerobic conditions, the paraquat radical mediated a very rapid, complete release of iron from ferritin. Similarly, the cation free radicals of the closely related chemicals, diquat and benzyl viologen, also promoted iron release. ESR studies demonstrated that electron transfer from the paraquat cation radical to ferritin accounts for the reductive release of iron. The ferritin structure was not altered by exposure to the paraquat radical and also retained its ability to re-incorporate iron. These studies indicate that release of iron from ferritin may be a common feature contributing to free radical-mediated toxicities.

Animals↗