Biomedical subjects

E F Elstner

Publications and source records attributed to E F Elstner.

At least 109 records · Page 6Linked to original sources

PubMedDate not supplied

Studies on the possible mechanism of inactivation of phenylalanine hydroxylase by destructive oxygen species.

The enzymic hydroxylation of phenylalanine by phenylalanine hydroxylase (E.C. 1.14.16.1.) in vitro is dependent on the presence of hydrogen peroxide removing processes. The loss of phenylalanine hydroxylase activity can be prevented to the same extent by catalase as well as the presence of optimized amounts of both peroxidase and superoxide dismutase. Peroxidase alone exhibited only two third of the maximal protective effect of catalase whereas superoxide dismutase alone was not able to exert any protective influence on phenylalanine hydroxylase. These findings suggest that the termination of phenylalanine hydroxylation in the absence of hydrogen peroxide removing reactions is probably due to destructive oxygen species generated at the active site iron of phenylalanine hydroxylase in the presence of H2O2 and the tetrahydropterin cofactor.

Animals↗

PubMedDate not supplied

Biochemical oxygen activation as the basis for the physiological action of tetrachlorodecaoxide (TCDO).

Oxidation of methionine, 4-(methylthio)-2-oxobutyric acid (KMB), or 1-aminocyclopropane carbonic acid (ACC) are indicator reactions for activated oxygen species such as singlet oxygen (1O2), OH.-radical like oxidants, superoxide anion (O2.-), hydrogen peroxide (H2O2) or activated hemo-iron complexes like peroxidase- or catalase-"compound I". Methionine is oxidized by OH. as well as by 1O2 forming ethylene, but not by tetrachloro-decaoxygen complex (TCDO) in the absence or presence of catalytic hemoproteins such as peroxidase, hemoglobin or myoglobin. Both KMB and ACC are oxidized by TCDO under the catalysis of the above hemo-proteins where neither catalase nor superoxide dismutase are inhibitors. TCDO hemo-protein complex is an oxidant with similar properties as peroxidase-compound I and can clearly be differentiated from O2.-, H2O2, OH. and 1O2.

Amino Acids↗

PubMedDate not supplied

Cataract induction by 1,2-naphthoquinone. I. Studies on the redox properties of bovine lens proteins.

Conditions of oxidative stress may lead to cataract formation. Reaction of certain flavoproteins, the NADH: oxidoreductases, with different quinones is well known to form hydrogen-peroxide. This reaction was investigated to get more information on cataract induction by naphthalene and its quinone metabolites. Protein extracts from bovine lens cortex exhibit "diaphorase" activity, indicated as dye reduction in the presence of NADH and dichlorophenol-indophenol (DCPIP) or ferricyanide. Different redox cycling compounds are shown to be active in this "diaphorase" reaction by lens protein extract (LCE): Oxygen consumption can be detected in the presence of pyrroloquinoline quinone and juglone whereas 1,4-naphthoquinone, menadione and paraquat are no redox cyclists in this flavoprotein catalyzed reaction.

Animals↗

PubMedDate not supplied

Cataract induction by 1,2-naphthoquinone. II. Mechanism of hydrogenperoxide formation and inhibition by iodide.

Naphthalene cataract is probably due to peroxide production through naphthoquinone (NQ) redox cycling and/or glutathione conjugation. Both mechanisms yield losses of essential SH-groups in cristallins and are thus probably involved in protein modification finally visible as lens opacity. 1,2-Naphthoquinone produces H2O2 in the presence of either ascorbate, glutathione, NADH or--to a lesser extend--by homogenates of lens protein preparations. In the presence of 1,2-naphthoquinone and the above reductive additions, both, oxygen uptake and H2O2 formation can be observed. Reductive oxygen activation in these systems are diminuated by iodide in a concentration-dependent manner. Since maleimide-treated proteins are less capable to activate oxygen by 1,2-naphthoquinone, a direct oxygen activation by the interactions of 1,2-naphthoquinone with protein-SH is indicated. Catalysis of "diaphorase"-type (dia) enzymes via NADH--dia--1,2-NQ--O2 seems not to operate in hydrogenperoxide production during 1,2-naphthoquinone lens toxicity.

Animals↗

PubMedDate not supplied

Biochemical model reactions on the prooxidative activity of homocysteine.

The sulfur amino acid homocysteine has recently been addressed as marker for vessel damaging and atherosclerotic dispositions. The atherogenic index has been correlated with the one of cholesterol and is significantly higher in cholesterinemic as compared to normal lipidemic persons. In the present communication biochemical model reactions are presented indicating the prooxidative activity of homocysteine where a cooperative effect with the transition-metals copper and iron is indicated.

Copper↗

PubMedDate not supplied

Biochemical activities of propolis extracts. I. Standardization and antioxidative properties of ethanolic and aqueous derivatives.

Ethanolic extracts of Propolis are used as antiinflammatory and wound healing drugs since ancient times. In order to facilitate a comparison of different extracts, the standardization on the basis of quantitative determination of prominent components of these extracts has been substituted for simple biochemical "activity" tests. One of these activity tests bases on the inhibition of peroxidase-catalyzed oxidation of indole acetic acid indicating the presence of a defined mixture of monophenolic and diphenolic compounds. Other tests (diaphorase-catalyzed reductions and xanthine oxidase-catalyzed oxidations) demonstrate significant radical scavenging properties. Water-soluble extracts of propolis exhibit higher antioxidative and inhibitory activities as compared to the ethanolic extract.

Antioxidants↗

PubMedDate not supplied

Biochemical activities of propolis extracts. II. Photodynamic activities.

Ethanolic and aqueous extracts of the "bee glue" Propolis exhibit antioxidative properties and are used as antiinflammatory drugs in folk medicine. In order to standardize the principle activities of prominent components of these extracts, simple biochemical tests have been introduced in the preceding paper. These activity tests prove the high antioxidative and inhibitory capacities of aqueous and ethanolic extracts of propolis in vitro. In the present communication we report on experiments documenting photodynamic quenching properties of these extracts. Using riboflavin, rose bengal or hematoporphyrin as photoactivators and ketomethylthiobutyric acid or crocin as indicators, the protective functions of propolis preparations can be demonstrated. The results indicate that the aqueous extracts are more active than the corresponding ethanolic preparation.

Carotenoids↗

PubMedDate not supplied

Antioxidative properties of phenazone derivatives: differentiation between phenylbutazon and mofebutazon.

Both phenylbutazon and mofebutazon inhibit oxidative fragmentation of the methionine derivative, 2-keto-4-methylthio-butyric acid (KMB) by xanthine oxidase--or diaphorase mediated OH radical production. Differentiation of the two non-steroidal antiinflammatory drugs is possible by means of determining oxygen reduction by xanthine oxidase or diaphorase in the presence of the naphthoquinone, juglone, where only mofebutazon shows an inhibitory effect.

2,6-Dichloroindophenol↗

PubMedDate not supplied

Inhibition of dihydrofolate reductase by mofebutazon.

Mofebutazon, in contrast to phenylbutazon, inhibits dihydrofolate reductase in a concentration-dependent manner. An apparent Ki for mofebutazon and dihydrofolate reductase in the presence of NADPH as electron donor and dihydrofolate as electron acceptor of approximately 0.2 mM was calculated.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMedDate not supplied

Biochemical activities of propolis-extracts. III. Inhibition of dihydrofolate reductase.

Ethanolic and aqueous extracts of the natural compound PROPOLIS indicate substantial antiinflammatory functions as well as antibiotic activities in vitro and in vivo. The exact mode of physiological or biochemical mechanisms responsible for the medical effects, however, is all but clear. The standardization on the basis of quantitative determination of prominent components of these extracts have been substituted recently by simple biochemical model reactions including photodynamic properties. In this communication we report on the inhibitory activity of an aqueous extract of propolis on the enzyme dihydrofolate reductase. This activity may at least partially be due to the content of caffeic acid, as revealed by HPLC chromatography and comparative activity tests of representative ingredients of the propolis extract. This result may explain some of the protective functions of propolis, similar to those shown for several "non-steroidal antiinflammatory drugs", NSAIDs.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMedDate not supplied

Stereospecific reduction of R(+)-thioctic acid by porcine heart lipoamide dehydrogenase/diaphorase.

R(+)-thioctic acid is the naturally occurring cofactor in alpha-ketoacid dehydrogenases. We show both photometrically by NADH+H+ oxidation and by HPLC product analysis that this enantiomer is rapidly reduced by NADH+H+ catalyzed by porcine heart lipoamide dehydrogenase/diaphorase. The racemate exhibits approximately 40% activity as compared to the R(+) form while the S(-) enantiomer photometrically shows little activity and yields no detectable reduced lipoic acid.

Animals↗

PubMedDate not supplied

Homocysteine-induced oxidative damage: mechanisms and possible roles in neurodegenerative and atherogenic processes.

Increased blood plasma concentrations of the sulphur amino acid homocysteine ("homocysteinemia") have been brought into context with neurodegenerative and arteriosclerotic symptoms and diseases. We recently reported on biochemical model reactions on the prooxidative activity of homocysteine including the desactivation of Na+/K(+)-ATPases and hemolysis of erythrocytes (Preibisch et al., 1993). In this communication we extend our model reactions including the oxidation of methionine, metabolization of pyridoxalphosphate and dihydroxyphenylalanine, desactivations of transaminases and peroxidation of low density lipoprotein.

Alanine Transaminase↗

PubMedDate not supplied

Desialylation of low density lipoprotein--metabolic function versus oxidative damage?

Low density lipoproteins are generally considered to play a major role in the development of atherosclerotic vascular diseases. There is growing interest in LDL subspecies, especially in their density, carbohydrate content and oxidizability, which is supposed to enhance atherogenicity. We investigated the influence of desialylation on the resistance of the lipoprotein particles towards Cu(II) prooxidative activity.

Copper↗

PubMedDate not supplied

OH-radical-type reactive oxygen species derived from superoxide and nitric oxide: a sensitive method for their determination and differentiation.

Reactive oxygen species are involved in many diseases where the radical species OH, peroxynitrite and the non-radical, hypochlorous acid, play an outstanding role. The formation of OH-type oxidants is essentially confined to a few types of reactions. The most prominent ones are the one-electron reduction of hydrogen peroxide by F2+ or Cu+ -ions (Fenton-type reactions), reaction of hypochlorite with superoxide and finally formation and decay of peroxynitrite (ONOOH), formed from superoxide and NO. In this communication we wish to report on a simple model system allowing to differentiate between these ROS: ethene formation from ACC is only detectable in the presence of hypochlorite (v. Kruedener et al, 1995) and not detectable with Fenton-type oxidants or SIN-1 (3-morpholinosydonimine, a peroxynitrite generator by releasing sequentially superoxide and NO) at 10 microM concentrations. On the other hand, ethene formation from KMB is negligible in the presence of hypochlorite but proceeds rapidly with Fenton-type oxidants (4 microM H2O2; 4 microM Fe2+) as well as with 1 microM SIN-1. Stimulation of Fenton-type oxidants and not of SIN-1 by EDTA and characteristic patterns of inhibition by SOD, catalases, hemoglobin and uric acid allow a differentiation between these two potential precursors of OH-radicals. Synthetic ONOOH shows different reaction kinetics as compared to SIN-1. Inhibition of ONOOH-dependent ethene formation by different compounds occurs more or less "random" indicating an unspecific influence of proteins and also small molecules. Comparison of the individual inhibition types of several selected compounds allows a differential analysis as to the generation pathway of the final oxidants, OH- radical or peroxynitrite.

Catalase↗

PubMedDate not supplied

Production of OH-radical-type oxidant by lucigenin.

In the presence of NADH- reductases (dihydrolipoamide: NAD oxidoreductase E. C.1.8.1.4 from pig heart or from Clostridium kluyveri; frequently also addressed as "diaphorases") and NADH lucigenin strongly increases ethylene production from a-keto-methylthiobutyrate (KMB) as an indicator for strong oxidants of the OH-radical type. These reactions are further stimulated in the presence of Fe3+ ions. With these NADH-"diaphorases", the structurally similar poison, paraquat, in the absence or presence of Fe3+ has no effect. With ferredoxin-NADP reductase (E. C.1.18.1.2.), however, paraquat reacts quasi identical to lucigenin. Superoxide dismutase, catalase, free radical- or OH-scavengers such as mannitol, propylgallate, DABCO, and desferal inhibit the reaction whereas EDTA (in the presence or absence of added Fe3+) is stimulatory. From these data we conclude that the superoxide--indicator LUC is redox-active after unspecific coupling to several almost ubiquitory NAD(P)H- reductases catalyzing monovalent oxygen reduction. Lucigenin thus should no longer be used as a "specific" superoxide indicator. This report is in agreement with very recent results by Liochev and Fridovich (Arch. Biochem. Biophys. 337, 115 [1997]) and Vasquez-Vivar et al. (FEBS Lett. 403, 127 (1997).

Acridines↗

PubMedDate not supplied

Inhibition by Salix- extracts and Phytodolor of copper-catalyzed oxidative destruction.

Oxidation of low density lipoprotein (LDL) by copper ions is strongly inhibited by different aqueous extracts (Salix spec (SE); Fraxinus-Dolidago-Populus (Phytodolor)(PD) in a concentration range between 4 and 7 micrograms/ml. 10 to 50 microM salicylic acid (SA) stimulate LDL-oxidation whereas higher concentrations (10 to 500 micromM) showed no effect. Likewise ethene release from 2-keto-4-methylthiobutyrate (KMB) is strongly inhibited by the above extracts in a reaction driven by dihydroxyfumarate (DHF) in the presence of copper ions. This system may represent some features of the diabetic situation where DHF as an endiole may stand for certain Amadori products. In order to find out whether the inhibitory effects are due to copper chelation we tested the copper-dependent conversion of photodynamic ethane release from alpha-linolenic acid into ethene formation. Copper chelation is apparently only partially involved in inhibition of copper-dependent oxidations and only at a certain concentration of extracts from salix spec (SE) or extracts from Fraxinus-Solidago-Populus (Phytodolor)(PD).

Antioxidants↗

PubMedDate not supplied

Superoxide-dependent and -independent nitrite formation from hydroxylamine: inhibition by plant extracts.

Reactive oxygen species such as OH, peroxynitrite and the non-radical, hypochlorous acid, play outstanding roles in many disease. The formation of OH (Fenton)-type radicals is catalyzed by enzymes such as xanthine oxidase (XOD) via one-electron reduction of molecular oxygen producing superoxide radical anions (O2). Subsequent transfer of one electron to hydrogen peroxide by Fe2+ or Cu+ -ions yields OH-radicals measurable as ethene release from 1-keto-4-methylthiobutyrate (KMB). Xanthine oxidase or activated neutrophils are prominent sources of this strong oxidant produced at inflammatory sites. Many natural compounds such as salicylates or flavonoids interfere either with the production of these activated oxygen species or function as radical scavengers and thus as antioxidants. Extracts from willow-bark (Salix spec.) and also other species such as ash-tree (Fraxinus spec.) or poplar (Populus spec.) have been used as antiinflammatory drugs since a long time. In this communication we wish to report on model reactions to demonstrate a) the radical scavenging activities of such plant extracts inhibiting ethene release from KMB induced by Fenton-type oxidants and b) the inhibition of the formation of nitrogen monoxide (NO) from hydroxylamine including XOD either in the presence or absence of myoglobin (MYO) measurable as nitrite formation: In the absence of MYO, superoxide dismutase is an excellent inhibitor of nitrite formation but is inactive in its presence. Extracts from the willow-bark or the drug Phytodolar however, are inhibitory both in the presence and absence of MYO. As active principle, the flavonoid rutin included in these extracts is likely to function as one inhibitor of the XOD-mediated reaction.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMedDate not supplied

Pro- and antioxidative properties of cortical tissue preparations from human brain exhibiting NMDA-receptor characteristics.

The effects of cortical tissue preparations (CTP) from human brain on the production of reactive oxygen species (ROS) has been investigated with several biochemical model reactions. As indicators for ROS, fragmentation of the methionine derivatives, alpha-keto-gamma-methylthiobutyric acid (KMB) or 1-amino-cyclopropane-1-carboxylic acid (ACC), yielding ethene have been used. With these systems we have shown that production of OH-radical-type oxidants by the xanthine oxidase (XOD)-system is strongly stimulated by CTP. This activity is due to intrinsic iron ions since ethene formation from KMB is stimulated by EDTA, inhibited by desferrioxamine (Desferal) and also visible with heat-denatured CTP. CTP by themselves have no XOD activity. 3-Hydroxykynurenine (3HK) is another possible substrate for XOD but produces H2O2 without XOD-catalysis, whereas allopurinol is not inhibiting. CTP contain measurable NAD(P)H oxidoreductase activity, producing OH- radical- type oxidants at the expense of NADPH and (to a lesser extent) NADH as electron donors, shown as redox-cycling of 2-methyl-5-hydroxy-1,4-naphthoquinone, plumbagin. Ethene formation from KMB is also driven by both morpholinosydnonimine (SIN) or ONOOH. The reaction driven by SIN is stimulated by CTP and inhibited by catalase, SOD and hemoglobin. Since ethene release from KMB driven by ONOOH is inhibited by CTP the mechanisms driving KMB fragmentation are different for SIN and ONOOH. Furthermore CTP contain approx. 4 U catalase activity per mg protein and very weak peroxidase (POD) activity shown as ACC fragmentation yielding ethene in the presence of both H2O2 and KBr or NaCl. Since ACC binds to CTP and both compounds, ACC and KMB are natural products, present in food (ACC) or synthesized from methionine in vivo (KMB), these compounds may represent protecting agents in systems where reactive oxygen species are formed. One might even speculate that the production of ethene at these membrane receptor sites may have biological functions, since ethene is known to possess anaesthetic activities.

Antioxidants↗