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L Packer

Publications and source records attributed to L Packer.

At least 55 records · Page 3Linked to original sources
PubMed1991

Thioctic acid and dihydrolipoic acid are novel antioxidants which interact with reactive oxygen species.

Thioctic acid (TA) and its reduced form dihydrolipoic acid (DHLA) have recently gained some recognition as useful biological antioxidants. In particular, the ability of DHLA to inhibit lipid peroxidation has been reported. In the present study, the effects of TA and DHLA on reactive oxygen species (ROS) generated in the aqueous phase have been investigated. Xanthine plus xanthine oxidase-generated superoxide radicals (O2-), detected by electron spin resonance spectroscopy (ESR) using DMPO as a spin trap, were eliminated by DHLA but not by TA. The sulfhydryl content of DHLA, measured using Ellman's reagent decreased subsequent to the incubation with xanthine plus xanthine oxidase confirming the interaction between DHLA and O2-. An increase of hydrogen peroxide concentration accompanied the reaction between DHLA and O2-, suggesting the reduction of O2- by DHLA. Competition of O2- with epinephrine allowed us to estimate a second order kinetic constant of the reaction between O2- and DHLA, which was found to be a 3.3 x 10(5) M-1 s-1. On the other hand, the DMPO signal of hydroxyl radicals (HO.) generated by Fenton's reagent were eliminated by both TA and DHLA. Inhibition of the Fenton reaction by TA was confirmed by a chemiluminescence measurement using luminol as a probe for HO.. There was no electron transfer from Fe2+ to TA or from DHLA to Fe3+ detected by measuring the Fe(2+)-phenanthroline complex. DHLA did not potentiate the DMPO signal of HO. indicating no prooxidant activity of DHLA. These results suggest that both TA and DHLA possess antioxidant properties. In particular, DHLA is very effective as shown by its dual capability by eliminating both O2- and HO..

Antioxidants↗
PubMed1991

Generation of probucol radicals and their reduction by ascorbate and dihydrolipoic acid in human low density lipoproteins.

Probucol, 4,4'-[(1-methylethylidene)bis(thio)]bis-[2,6-bis(1,1- dimethyl)phenol], is a lipid regulating drug whose therapeutic potential depends on its antioxidant properties. Probucol and alpha-tocopherol were quantitatively compared in their ability to scavenge peroxyl radicals generated by the thermal decomposition of the lipid-soluble azo-initiator 2,2'-azo-bis(2,4-dimethyl-valeronitrile), AMVN, in dioleoylphosphatidylcholine (DOPC) liposomes. Probucol showed 15-times lower peroxyl radical scavenging efficiency than alpha-tocopherol as measured by the effects on AMVN-induced luminol-dependent chemiluminescence. We suggest that probucol cannot protect alpha-tocopherol against its loss in the course of oxidation, although probucol is known to prevent lipid peroxidation in membranes and lipoproteins. In human low density lipoproteins (LDL) ESR signals of the probucol phenoxyl radical were detected upon incubation with lipoxygenase + linolenic acid or AMVN. Ascorbate was shown to reduce probucol radicals. Dihydrolipoic acid alone was not able to reduce the probucol radical but in the presence of both ascorbate and dihydrolipoic acid a synergistic effect of a stepwise reduction was observed. This resulted from ascorbate-dependent reduction of probucol radicals and dihydrolipoic acid-dependent reduction of ascorbyl radicals. The oxidized form of dihydrolipoic acid, thioctic acid, did not affect probucol radicals either in the presence or in the absence of ascorbate.

Antioxidants↗
PubMed1991

Ubiquinone protects against loss of tocopherol in rat liver microsomes and mitochondrial membranes.

Liver microsomes and submitochondrial particles (SMP) were isolated from rats fed on a vitamin E or coenzyme Q10/vitamin E enriched diet in order to clarify the antioxidant interactions between coenzyme Q10 and vitamin E. Electron spin resonance spectrometry shows that the decay of vitamin E radicals (tocopheroxy radicals) generated by the arachidonic acid/lipoxygenase oxidation system proceeded at a higher rate in vitamin E enriched microsomes and SMP than in those enriched with coenzyme Q10/vitamin E. Vitamin E levels determined by high performance liquid chromatography revealed that when subjected to enzymatic oxidation, membranes enriched with vitamin E alone were depleted of vitamin E earlier than those enriched with both coenzyme Q10 and vitamin E. These results show that coenzyme Q10 conserves vitamin E, which would help prolong membrane resistance against oxidative damage.

Animals↗
PubMed1990

Recycling and antioxidant activity of tocopherol homologs of differing hydrocarbon chain lengths in liver microsomes.

Tocopherols (vitamin E) function as inhibitors of lipid peroxidation in biomembranes by donating a hydrogen atom to the chain propagating lipid radicals, thus giving rise to chromanoxyl radicals of the antioxidant. We have shown that alpha-tocopherol homologs differing in the lengths of their hydrocarbon side chains (alpha-Cn) manifest strikingly different antioxidant potencies in membranes. The antioxidant activity of tocopherol homologs during (Fe2+ + ascorbate)- or (Fe2+ + NADPH)-induced lipid peroxidation in rat liver microsomes increased in the order alpha-tocopherol (alpha-C16) less than alpha-C11 less than alpha-C6 less than alpha-C1. Chromanoxyl radicals generated from alpha-tocopherol and its more polar homologs by an enzymatic oxidation system (lipoxygenase + linolenic acid) can be recycled in rat liver microsomes by NAD-PH-dependent electron transport or by ascorbate. The efficiency of recycling increased in the same order: alpha-tocopherol (alpha-C16) less than alpha-C11 less than alpha-C6 less than alpha-C1. Thus the high efficiency of regeneration of short-chain homologs of vitamin E may account for their high antioxidant potency.

Animals↗
PubMed1990

Antioxidant effects of ubiquinones in microsomes and mitochondria are mediated by tocopherol recycling.

Ubiquinones and tocopherols (vitamin E) are intrinsic lipid components which have a stabilizing function in many membranes attributed to their antioxidant activity. The antioxidant effects of tocopherols are due to direct radical scavenging. Although ubiquinones also exert antioxidant properties the specific molecular mechanisms of their antioxidant activity may be due to: (i) direct reaction with lipid radicals or (ii) interaction with chromanoxyl radicals resulting in regeneration of vitamin E. Lipid peroxidation results have now shown that tocopherols are much stronger membrane antioxidants than naturally occurring ubiquinols (ubiquinones). Thus direct radical scavenging effects of ubiquinols (ubiquinones) might be negligible in the presence of comparable or higher concentrations of tocopherols. In support of this our ESR findings show that ubiquinones synergistically enhance enzymic NADH- and NADPH-dependent recycling of tocopherols by electron transport in mitochondria and microsomes. If ubiquinols were direct radical scavengers their consumption would be expected. Further proving our conclusion HPLC measurements demonstrated that ubiquinone-dependent sparing of tocopherols was not accompanied by ubiquinone consumption.

Animals↗
PubMed1990

Vitamin E in biological systems.

The evidence is increasing that free radical reactions are implicated in the development of cell damage and degenerative disease. Results of animal and human studies have demonstrated that vitamin E and the other antioxidants have a significant role in preventing or minimizing peroxidation damage in biological systems. As we await results of additional human studies, there is sufficient evidence to suggest that adequate antioxidant defense by vitamin E and the other antioxidants can provide protection from the increasingly high levels of free radicals present in the environment due to current lifestyles and the rising concentration of environmental pollutants.

Animals↗
PubMed1990

Generation and recycling of radicals from phenolic antioxidants.

Hindered phenols are widely used food preservatives. Their pharmacological properties are usually attributed to high antioxidant activity due to efficient scavenging of free radicals. Butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) also cause tissue damage. Their toxic effects could be due to the production of phenoxyl radicals. If phenoxyl radicals can be recycled by reductants or electron transport, their potentially harmful side reactions would be minimized. A simple and convenient method to follow phenoxyl radical reactions in liposomes and rat liver microsomes based on an enzymatic (lipoxygenase + linolenic acid) oxidation system was used to generate phenoxyl radicals from BHT and its homologues with substitutents in m- and p-positions. Different BHT-homologues display characteristic ESR signals of their radical species. In a few instances the absence of phenoxyl radical ESR signals was found to be due to inhibition of lipoxygenase by BHT-homologues. In liposome or microsome suspensions addition of ascorbyl palmitate resulted in disappearance of the ESR signal of phenoxyl radicals with concomittant appearance of the ascorbyl radical signal. After exhaustion of ascorbate, the phenoxyl radical signal reappears. Comparison of the rates of ascorbyl radical decay in the presence or absence of BHT-homologues showed that temporary elimination of the phenoxyl radical ESR signal was due to their reduction by ascorbate. Similarly, NADPH or NADH caused temporary elimination of ESR signals as a result of reduction of phenoxyl radicals in microsomes. Since ascorbate and NADPH might generate superoxide in the incubation system used, SOD was tested. SOD shortened the period, during which the phenoxyl radicals ESR signal could not be observed. Both ascorbyl palmitate and NADPH exerted sparing effects on the loss of BHT-homologues during oxidation. These effects were partly diminished by SOD. These data indicate that reduction of phenoxyl radicals was partly superoxide-dependent. It is concluded that redox recycling of phenoxyl radicals can occur by intracellular reductants like ascorbate and microsomal electron transport.

Animals↗
PubMed1990

Intermembrane transfer and antioxidant action of alpha-tocopherol in liposomes.

Intermembrane transfer and exchange of tocopherol are not well understood. To study this we tested the ability of alpha-tocopherol containing unilamellar donor liposomes to inhibit the accumulation of lipid peroxidation products in acceptor liposomes. With molar ratios of alpha-tocopherol:phospholipids from 1:100 to 1:1000 in donor liposomes prepared by sonication of lipid dispersions, alpha-tocopherol was incorporated into both monolayers and was homogenously distributed in monomeric form without forming clusters in the liposomes. Concentrations of alpha-tocopherol which completely prevented the peroxidation of lipids were chosen for donor liposomes. Hence inhibition of lipid peroxidation in mixtures of donor and acceptor liposomes was determined by the antioxidant effect of alpha-tocopherol in acceptor liposomes which resulted from intermembrane transfer and exchange of alpha-tocopherol. Evidence was obtained that this was not due to fusion of donor with acceptor liposomes. The efficiency of the "intermembrane" antioxidant action of tocopherol was more pronounced when donor liposomes contained unsaturated phospholipids, indicating that the presence of unsaturated fatty acids in the outer monolayer phospholipids facilitates intermembrane tocopherol exchange.

Animals↗
PubMed1990

Membrane lipid composition, fluidity, and surface charge changes in response to growth of the fresh water cyanobacterium Synechococcus 6311 under high salinity.

The effect of adaptation to saline growth of a fresh water cyanobacterium Synechococcus 6311 on components of the cytoplasmic membranes and thylakoids was investigated. Significant changes in membrane surface charge, lipid, fatty acid, and carotenoid composition were observed upon transfer of the cells from a low salt (0.015 M NaCl) to a high salt (0.50 M NaCl) growth medium. Very similar changes in the polar lipid classes and fatty acid composition were observed in both membranes, but changes in fluidity and surface charge and a significant shift in the protein to lipid ratio were only apparent in the cytoplasmic membranes. The fluidity and surface charge data correlate well with functional studies and we can attribute the cytoplasmic membrane as the major site of interaction and adaptation to the saline environment.

Acclimatization↗
PubMed1990

Antioxidant action of ubiquinol homologues with different isoprenoid chain length in biomembranes.

Ubiquinones (CoQn) are intrinsic lipid components of many membranes. Besides their role in electron-transfer reactions they may act as free radical scavengers, yet their antioxidant function has received relatively little study. The efficiency of ubiquinols of varying isoprenoid chain length (from Q0 to Q10) in preventing (Fe2+ + ascorbate)-dependent or (Fe2+ + NADPH)-dependent lipid peroxidation was investigated in rat liver microsomes and brain synaptosomes and mitochondria. Ubiquinols, the reduced forms of CoQn, possess much greater antioxidant activity than the oxidized ubiquinone forms. In homogenous solution the radical scavenging activity of ubiquinol homologues does not depend on the length of their isoprenoid chain. However in membranes ubiquinols with short isoprenoid chains (Q1-Q4) are much more potent inhibitors of lipid peroxidation than the longer chain homologues (Q5-Q10). It is found that: i) the inhibitory action, that is, antioxidant efficiency of short-chain ubiquinols decreases in order Q1 greater than Q2 greater than Q3 greater than Q4; ii) the antioxidant efficiency of long-chain ubiquinols is only slightly dependent on their concentrations in the order Q5 greater than Q6 greater than Q7 greater than Q8 greater than Q9 greater than Q10 and iii) the antioxidant efficiency of Q0 is markedly less than that of other homologues. Interaction of ubiquinols with oxygen radicals was followed by their effects on luminol-activated chemiluminescence. Ubiquinols Q1-Q4 at 0.1 mM completely inhibit the luminol-activated NADPH-dependent chemiluminescent response of microsomes, while homologues Q6-Q10 exert no effect. In contrast to ubiquinol Q10 (ubiquinone Q10) ubiquinone Q1 synergistically enhances NADPH-dependent regeneration of endogenous vitamin E in microsomes thus providing for higher antioxidant protection against lipid peroxidation. The differences in the antioxidant potency of ubiquinols in membranes are suggested to result from differences in partitioning into membranes, intramembrane mobility and non-uniform distribution of ubiquinols resulting in differing efficiency of interaction with oxygen and lipid radicals as well as different efficiency of ubiquinols in regeneration of endogenous vitamin E.

Animals↗
PubMed1990

Vitamin E radical reaction with antioxidants in rat liver membranes.

The Japanese herbal medicine Sho-saiko-to-go-keishi-ka-shakuyaku-to (TJ-960) has been demonstrated to have an antioxidant action by quenching free radicals. The effects of TJ-960 on the tocopheroxy radicals generated by an arachidonic acid and lipoxygenase oxidation system were compared with those of the ascorbate and glutathione in vitamin E-enriched rat liver microsomes and submitochondrial membrane particles (SMP). Using electron spin resonance spectrometry, the disappearance of the tocopheroxy radicals after addition of glutathione and ascorbate was detected in microsomes and SMP, with ascorbate displaying a more potent action than glutathione. Addition of TJ-960 demonstrated a similar effect on the tocopheroxy radicals in microsomes and SMP. In the presence of TJ-960, ascorbate, and glutathione, the loss of vitamin E in the vitamin E-enriched microsomes of rat liver undergoing oxidation was slowed down. In this paper, we introduced TJ-960 as another replenisher of vitamin E in membrane, increasing the membrane's resistance against oxidative damage.

Animals↗
PubMed1990

The antipsoriatic compound anthralin influences bioenergetic parameters and redox properties of energy transducing membranes.

Bioenergetic parameters and redox properties of energy transducing membranes in rat liver mitochondria and cyanobacteria were investigated in the presence of the antipsoriatic compound anthralin (1,8-dihydroxy-9-anthrone). Transmembrane pH and electrical gradients were determined using electron paramagnetic resonance spectroscopy. In mitochondria, ubiquinones 9,10 and other redox components of the electron transport chain are reduced by anthralin; the proton motive force is increased. In the absence of ADP, anthralin slightly stimulates mitochondrial cyanide-insensitive oxygen consumption. It is suggested that increased cyanide-insensitive respiration is due to enhanced autoxidation of mitochondrial components and/or catalyzed oxidation of anthralin. In the presence of ADP mitochondrial respiration is decreased, and ATP synthesis is inhibited. Uncoupler-induced mitochondrial respiration is also decreased by anthralin, indicating inhibition of the electron transport chain. In the cyanobacterium Synechococcus PCC 6311 anthralin increases the pH gradient and decreases ATP levels. Thus, anthralin acts as an electron donor to membrane associated redox components and inhibits ATP synthesis in two different biologic systems. In human keratinocytes oxygen metabolism is influenced by anthralin in a similar pattern as in isolated mitochondria, and ATP content is decreased. Because anthralin reacts with redox components in different biologic membranes, alterations of subcellular/cellular redox status and energy metabolism might contribute significantly to its antiproliferative activity.

Animals↗