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L Packer

Publications and source records attributed to L Packer.

At least 73 records · Page 4Linked to original sources
PubMed1996

Efficacy of Bio-Catalyzer alpha.rho no.11 (Bio-Normalizer) supplementation against peroxyl radical-induced oxidative damage in rat organ homogenates.

To better delineate the antioxidant potential of Bio-Catalyzer alpha.rho No.11 (Bio-Normalizer), a natural food supplement recently proposed as an antioxidant agent, we investigated the efficacy of Bio-Normalizer supplementation to protect rat organ homogenates against oxidative damage induced in vitro by peroxyl radicals generated in the hydrophobic or in the hydrophilic phase. Bio-Normalizer supplementation efficiently protected rat kidney homogenates against the accumulation of thiobarbituric reactive substances (TBARS), the formation of protein carbonyl derivatives and the depletion of alpha-tocopherol induced by peroxyl radicals generated from the hydrophobic azo-initiator 2,2'-azobis (2,4-dimethylvaleronitrile) (AMVN). It also protected the heart but not the liver or the brain homogenates. Bio-Normalizer supplementation did not have effect in any organ homogenates when peroxyl radicals were generated from the hydrophilic azo-initiator 2,2'-azobis (2-amidinopropane) dihydrochloride) (AAPH). In vitro direct addition of aqueous solutions of Bio-Normalizer to the organ homogenates was ineffective against AMVN or AAPH-induced oxidative damage. Our findings expand previous reports on the antioxidant activity of Bio-Normalizer. They confirm that supplemented Bio-Normalizer protects against peroxyl radical-induced oxidative damage and suggest that its antioxidant action depends on in vivo bioactivation, it is organ specific and it is limited to damage induced by peroxyl radicals generated in the hydrophobic phase.

Animals↗
PubMed1996

Decomposition of alpha-lipoic acid derivatives by photoirradiation-formation of dihydrolipoic acid from alpha-lipoic acid-.

Due to its strained five-membered ring, alpha-lipoic acid (LA) has an absorption band around 330 nm, which is used to quantify its concentration. In order to obtain information for the homolytic rupture of the S-S bond and the formation of dihydrolipoic acid (DHLA), the photochemical reaction of lipoic acid was examined in the presence or absence of ascorbic acid upon exposure to UVA light. The absorption band of alpha-lipoic acid at around 330 nm disappeared by photoirradiation, which corresponds to the rupture of S-S bond of the 1,2-dithiolane ring in lipoic acid. HPLC-Electrochemical Detection (ECD) analysis of lipoic acid showed significant formation of dihydrolipoic acid and other thiols. The formation of thiols from the photoreaction of lipoic acid was also confirmed by the Ellman method. The formation of thiols from lipoic acid was completely time-dependent and the formation of the thiols increased upto 55%. Similar results were obtained in the photochemical reactions of short-chain analogues, bisnor- and tetranor-lipoic acid. On the other hand, beta-lipoic acid was quite stable, no photodecomposition of beta-lipoic acid was observed in the UV region. The formation of thiols including dihydrolipoic acid from lipoic acid can be explained by considering the rupture of S-S bond, which results in the formation of the dithiyl radicals of alpha-lipoic acid. It is proposed that intra- and intermolecular hydrogen abstraction of the dithyl radical produces thiols including dihydrolipoic acid as final products.

Antioxidants↗
PubMed1995

The phorbol 12-myristate 13-acetate (PMA)-induced oxidative burst in rat peritoneal neutrophils is increased by a 0.1 mT (60 Hz) magnetic field.

Magnetic fields (MF) may affect biological systems by increasing free radical concentrations. To test this, we have investigated whether low frequency (60 Hz) low intensity (0.1 mT) MF can modulate the phorbol 12-myristate 13- acetate (PMA) induced respiratory burst in primed rat peritoneal neutrophils, followed in real time using the dye 2',7'-dichlorofluorescin (DCFH), which reacts with free radical-derived oxidants such as H2O2 (which is formed from the dismutation of superoxide) to become 2',7'-dichlorofluorecein (DCF), a highly fluorescent compound. In the presence of the MF, a 12.4% increase in the fluorescence signal was observed in PMA-stimulated neutrophils (n = 5, P < 0.02, 18 pairs of measurements). We believe this represents the first experimental observation of MF influencing events involving free radical species generated during signal transduction in living cells.

Animals↗
PubMed1995

Role of ascorbate in protection by nitecapone against cardiac ischemia-reperfusion injury.

The antioxidant properties of nitecapone, a catechol derivative and an inhibitor of catechol-O-methyltransferase, were reported recently. In the present study, the influence of nitecapone on isolated rat heart ischemia-reperfusion injury was investigated to elucidate its cardioprotective role. Nitecapone, administered in the perfusion buffer from the beginning of the pre-ischemic phase, significantly improved recovery of cardiac mechanical function, suppressed enzyme leakage in the coronary effluent, and minimized loss of ascorbate, compared with the control group. In rats fed a diet containing 4% ascorbate, myocardial ascorbate content in ascorbate-fed rats after ischemia-reperfusion was higher than that in control rats fed a normal diet without ischemia. However, supplemented rats did not show any beneficial effects on cardiac mechanical recovery or enzyme leakage, suggesting that maintenance of tissue ascorbate level is not the cause, but the result of the protective effects of nitecapone against cardiac ischemia-reperfusion injury. The iron-chelating effect of nitecapone was also tested. It was confirmed, using electron spin resonance, that 50 microM nitecapone chelates the same concentration of iron released from the heart into the coronary effluent. Hence, the iron-chelating ability of nitecapone may be responsible, at least in part, for its cardioprotective effects in ischemia-reperfusion injury.

Animals↗
PubMed1995

Ginkgo biloba extract (EGb 761) protects human low density lipoproteins against oxidative modification mediated by copper.

The antioxidant effects of Ginkgo biloba extract (EGb 761) on copper-mediated human low density lipoprotein (LDL) oxidative modification were evaluated by several techniques. Human LDL (0.5 mg/ml) in phosphate buffered saline, pH 7.4, was incubated with 10 microM cupric sulfate at 37 degrees C under air for 8 hours and 24 hours in the presence of varying concentrations of EGb 761. Increases in LDL apoB carbonylation, lipid peroxidation, apoB electrophoretic mobility and LDL fluorescence were all inhibited when the incubation mixture contained EGb 761 at concentrations less than 100 micrograms/ml. This inhibition was EGb 761-concentration-dependent. Thus, EGb 761 has powerful antioxidant effects on copper-mediated LDL oxidative modification.

Apolipoproteins B↗
PubMed1995

Reduction and transport of lipoic acid by human erythrocytes.

Reduction of exogenous lipoic acid to dihydrolipoate is known to occur in several mammalian cells and tissues. Dihydrolipoate is a potent radical scavenger, and may provide significant antioxidant protection. Because lipoic acid appears in the bloodstream after oral administration, we have examined the reduction of exogenous lipoate by human erythrocytes. Normal human erythrocytes reduced lipoate to dihydrolipoate only in the presence of glucose; deoxyglucose did not substitute for glucose, indicating that the reduction of lipoate requires glucose metabolism. Furthermore, the reduction was shown to be NADPH dependent. Erythrocytes isolated from a human subject with a genetic deficiency of glucose-6-phosphate dehydrogenase (and, therefore, deficient in the formation of NADPH) did not reduce lipoate. Dehydroepiandrosterone, a specific inhibitor of glucose-6-phosphate dehydrogenase, inhibited lipoate reduction. Our findings imply that some of the reduction of exogenous lipoic acid is catalysed by glutathione reductase, a flavoprotein dehydrogenase; mitomycin C, an inhibitor of FAD-dependent reductases, inhibited lipoate reduction by erythrocytes, and glutathione reductase purified from human erythrocytes was observed to reduce lipoic acid in a cell-free system. We further explored these findings with erythrocyte ghosts and liposomes. Our results indicate that a transport system exists for alpha-lipoic acid and dihydrolipoate; resealed erythrocyte ghosts, containing trapped lipoamide dehydrogenase and pyridine nucleotides, reduced externally added lipoate. By contrast, liposomes prepared with enzyme and pyridine nucleotides did not catalyze reduction of lipoate. This work indicates that uptake of exogenous lipoate and reduction to dihydrolipoate by normal human erythrocytes may contribute to oxidant protection in the human bloodstream.

Biological Transport↗
PubMed1995

The spin-trap N-tert-alpha-phenyl-butylnitrone prolongs the life span of the senescence accelerated mouse.

Free radicals and oxidative damage have been proposed as underlying factors in aging, in chronic and degenerative diseases of aging and in acute clinical conditions. To test involvement of free-radicals in such processes, spin trapping agents which quench more reactive radicals to produce long-lived stable radical adducts have been used as an experimental strategy. Spin traps protect against oxidatively induced injury in numerous in vitro and in vivo model systems involving different organs. A model system for mammalian aging is afforded by the senescence accelerated mouse (SAM-P8), which exhibits many features characteristic of mammalian aging but with a much shortened lifespan. Daily intraperitoneal injection of the spin trap N-tert-alpha-phenyl-butylnitrone (PBN) was administered to male or female mice after they reached maturity at 3 months of age. PBN treated animals as compared with control sham injected animals revealed a remarkable extension of the mean life span in both male and female populations. Overall, a 50% mean survival rate was found of 42 weeks for control as compared to 56 weeks for the PBN administered groups. These results show that the spin trap PBN can prolong lifespan and support the free radical theory of aging.

Aging↗
PubMed1995

Peroxyl radical scavenging activity of Ginkgo biloba extract EGb 761.

Antioxidant mechanisms have been proposed to underlie the beneficial pharmacological effects of EGb 761, an extract from Ginkgo biloba leaves used for treating peripheral vascular diseases and cerebrovascular insufficiency in the elderly. In vitro evidence has been reported that EGb 761 scavenges various reactive oxygen species, i.e. nitric oxide, and the superoxide, hydroxyl, and oxoferryl radicals. However, the ability of EGb 761 to scavenge peroxyl radicals (reactive species mainly involved in the propagation step of lipid peroxidation) has not been investigated. To characterize further the antioxidant action of EGb 761, we measured the protective effects of EGb 761 during: (1) the oxidation of B-phycoerythrin by peroxyl radicals generated in aqueous solution by 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH); and (2) the reaction of luminol or cis-parinaric acid with peroxyl radicals generated from 2,2'-azobis (2,4-dimethylvaleronitrile) (AMVN) in liposomes or in human low density lipoprotein (LDL), respectively. To evaluate the peroxyl radical scavenging activity of EGb 761 in a more physiologically relevant model of damage to lipid-containing systems, we also analyzed the effect of the extract on the oxidation of human LDL exposed to the azo-initiators in terms of: (1) accumulation of cholesterol linoleate ester hydroperoxides, (2) depletion of alpha-tocopherol and beta-carotene, and (3) changes in intrinsic tryptophan fluorescence. EGb 761 afforded protection against oxidative damage in all the systems we analyzed; thus, it is an efficient scavenger of peroxyl radicals. This result extends the oxygen radical scavenging properties of the extract and supports the hypothesis of an antioxidant therapeutic action of EGb 761.

Amidines↗
PubMed1995

Transient overexpression of catalase does not inhibit TNF- or PMA-induced NF-kappa B activation.

H2O2 has been proposed as a second messenger involved in cell signaling for NF-kappa B activation. In the present study, this hypothesis was tested by transiently overexpressing catalase, a specific scavenger of H2O2, in COS-1 cells. A mammalian expression vector was constructed by incorporating catalase gene from pCAT10 clone into the unique EcoRI site of the pSG5 vector which contains the SV-40 promoter. Transient transfection of the catalase expression vector by the DEAE-dextran method led to a four-fold increase in catalase activity and catalase content as detected by immunoblot analysis. This level of increase was detected in both nuclear/mitochondrial- and cytosolic/microsomal fractions. Overexpression of catalase, however, did not block TNF- or PMA-induced NF-kappa B activation. These results weaken the hypothesis that H2O2 is a second messenger for TNF- and PMA-signaling for NF-kappa B activation.

Animals↗
PubMed1995

Elucidation of antioxidant activity of alpha-lipoic acid toward hydroxyl radical.

The photosensitive organic hydroperoxide, NP-III, which produces hydroxyl radicals on illumination by UVA light, was used to examine the antioxidant activity of alpha-lipoic acid and its derivatives toward hydroxyl radical. Apolipoprotein (apo-B) of human low density lipoprotein (LDL) and bovine serum alubumin (BSA) were irradiated with UVA in the presence of NP-III and alpha-lipoic acid. The oxidation of BSA and the apo-B protein of LDL by NP-III was completely suppressed by alpha-lipoic acid. ESR studies using dimethylpyrroline oxide (DMPO) as a spin trapping reagent also revealed that in the presence of alpha-lipoic acid, the DMPO-OH adduct produced from the irradiation of NP-III and DMPO completely disappeared. DMPO-OH quenching experiments were performed in the presence or absence of desferoxamine but no change in the signal intensity was found. Hence, the quenching activity of alpha-lipoic acid is not due to its chelating activity toward transition metals (ferrous ions). The results lead us to conclude that alpha-lipoic acid is an efficient hydroxyl radical quencher owing to the disulfide bond in the dithiolane ring.

Antioxidants↗
PubMed1995

Alpha-lipoic acid increases intracellular glutathione in a human T-lymphocyte Jurkat cell line.

The addition of exogenous alpha-lipoic acid to cellular medium causes a rapid increase of intracellular unbound thiols in Jurkat cells, a human T-lymphocyte cell line. The rise of cellular thiols is a result of the cellular uptake and reduction of lipoic acid to dihydrolipoic acid and a rise in intracellular glutathione. Although the level of dihydrolipoic acid is 100-fold lower than glutathione, the cellular concentration of dihydrolipoic acid might be responsible for the modulation of total cellular thiol levels. Rises in glutathione correlate with the levels of intracellular dihydrolipoic acid (p < .01). This increase in glutathione is not the result of expression of new proteins like gamma-glutamylcysteine synthetase, since the rise in glutathione was not inhibited by cycloheximide, a protein synthesis inhibitor. Lipoic acid administration is therefore a potential therapeutic agent in an array of diseases with glutathione anomalies including HIV infection.

Cell Line↗
PubMed1995

Glutathione reductase and lipoamide dehydrogenase have opposite stereospecificities for alpha-lipoic acid enantiomers.

The reduction of exogenous alpha-lipoic acid to dihydrolipoate by mammalian cells and tissues confers additional antioxidant protection to the cell. Both (R+) and (S-) isomers of alpha-lipoic acid were analyzed as substrates with glutathione reductase from several sources and with mammalian lipoamide dehydrogenase. Mammalian glutathione reductase catalyzed faster reduction of (S)-lipoic acid (1.4-2.4-fold greater activity) than of (R)-lipoic acid, whereas lipoamide dehydrogenase had a very marked preference for (R)-lipoic acid (18-fold greater activity) over (S)-lipoic acid. Mammalian glutathione reductase showed better affinity for (S)-lipoic acid substrate; Km values were 3.5 mM for (S)-lipoic acid and and 7 mM for (R)-lipoic acid. Glutathione reductase from yeast reduced lipoic acid less efficiently than the mammalian enymes, had a Km for both stereoisomers of about 10 mM, and showed little stereospecificity. Although (S)-lipoic acid is not formed in nature, these findings indicate that exogenous (S)-lipoic acid may have a useful role as an antioxidant for mammalian systems.

Animals↗
PubMed1995

Induction of protein oxidation in human low density lipoprotein by the photosensitive organic hydroperoxide, N,N'-bis(2-hydroxyperoxy-2-methoxyethyl)-1,4,5,8-naphthalene-tetra-carb oxylic- diimide.

We have developed a new molecular probe, N,N'-bis(2-hydroxyperoxy-2-methyoxyethyl)-1,4,5,8-naphthalen e-tetra-carboxylic- diimide (NP-III), that specifically generates hydroxyl radical upon irradiation with longer wavelength ultraviolet light (UVA). Hydroxyl radicals are generated only upon irradiation, thus NP-III is a new controllable hydroxyl radical source. Apolipoprotein (apo-B) of human low density lipoprotein (LDL), and bovine serum alubumin (BSA), were irradiated with UVA in the presence of NP-III and their oxidation was evaluated by two independent methods: assay of protein carbonyl groups and gel electrophoresis. NP-III oxidized apo-B and BSA in a time- and concentration-dependent manner. The results demonstrate that NP-III is a controllable, precise, and potentially tagetable source of hydroxyl radicals with which to induce protein oxidation.

Darkness↗
PubMed1995

Genetic differentiation between two host "races" and two species of cleptoparasitic bees and between their two hosts.

In this paper we test the following two hypotheses: (1) that apparently conspecific samples of the cleptoparasitic bee Coelioxys funeraria, differing markedly in size and reared from different host species, do indeed represent one panmictic population; (2) that bees that nest in holes in wood or twigs have higher levels of genetic variation than those nesting in the ground. Based upon 41 loci, the genetic differences between the two samples of C. funeraria could be explained entirely in terms of sampling error. In contrast, the sympatric C. moesta showed 16 fixed allelic differences from the C. funeraria samples. Similarly, the two hosts of C. funeraria, Megachile relativa and M. inermis, had 21 fixed allelic differences between them out of 42 presumptive gene loci. Heterozygosities among the wood-nesting bees were not particularly high for Hymenoptera, ranging from 0.045 to 0.054. Comparisons of heterozygosity estimates among bees remain ambiguous as to whether soil nesting confers sufficient environmental buffering effects to reduce possible advantages of heterosis in ground-nesting species.

Alleles↗
PubMed1995

Analysis of reduced and oxidized lipoic acid in biological samples by high-performance liquid chromatography.

Using HPLC with electrochemical detection at a dual Hg/Au electrode, both reduced and oxidized lipoic acid can be measured in biological samples after addition of lipoic acid. The method does not detect bound lipoic acid, which must be liberated by strong acid or base hydrolysis. The detection limit for this HPLC method is 0.01 nmol of dihydrolipoate and 0.05 nmol of lipoate. Baseline separation of lipoate and dihydrolipoate is achieved on a 10 cm octadecyl column. The analysis is rapid (8 min/sample) and uses a single HPLC pump with isocratic mobile phase. The method has been adapted to study cellular and whole animal reduction of lipoate, membrane transport of lipoate and dihydrolipoate, and subcellular enzymes that reduce lipoate.

Cell Line↗