Search PubMed⌕ Search

Biomedical subjects

L Packer

Publications and source records attributed to L Packer.

At least 19 recordsLinked to original sources
PubMed1997

Ozone depletes tocopherols and tocotrienols topically applied to murine skin.

To evaluate ozone damage to hairless mouse skin, two parameters of oxidative damage, vitamin E depletion and malondialdehyde (MDA) production, were measured in vitamin E-enriched and in control skin from mice exposed to ozone (10 ppm). A 5% vitamin E solution (tocotrienol-rich fraction, TRF) in polyethylene glycol (PEG) was applied to 2 sites on the back of hairless mice, PEG to 2 sites. After 2 h, the sites were washed, one of each pair of sites covered and the mice exposed ozone for 2 h. Ozone exposure (compared with covered sites) increased epidermal MDA in PEG-treated sites, while vitamin E was unchanged. In contrast, ozone exposure significantly depleted vitamin E in TRF-treated sites, while significant MDA accumulation was prevented. This is the first demonstration that ozone exposure causes damage to cutaneous lipids, an effect which can be attenuated by vitamin E application.

Administration, Topical↗
PubMed1997

Neuroprotection by the metabolic antioxidant alpha-lipoic acid.

Reactive oxygen species are thought to be involved in a number of types of acute and chronic pathologic conditions in the brain and neural tissue. The metabolic antioxidant alpha-lipoate (thioctic acid, 1, 2-dithiolane-3-pentanoic acid; 1, 2-dithiolane-3 valeric acid; and 6, 8-dithiooctanoic acid) is a low molecular weight substance that is absorbed from the diet and crosses the blood-brain barrier. alpha-Lipoate is taken up and reduced in cells and tissues to dihydrolipoate, which is also exported to the extracellular medium; hence, protection is afforded to both intracellular and extracellular environments. Both alpha-lipoate and especially dihydrolipoate have been shown to be potent antioxidants, to regenerate through redox cycling other antioxidants like vitamin C and vitamin E, and to raise intracellular glutathione levels. Thus, it would seem an ideal substance in the treatment of oxidative brain and neural disorders involving free radical processes. Examination of current research reveals protective effects of these compounds in cerebral ischemia-reperfusion, excitotoxic amino acid brain injury, mitochondrial dysfunction, diabetes and diabetic neuropathy, inborn errors of metabolism, and other causes of acute or chronic damage to brain or neural tissue. Very few neuropharmacological intervention strategies are currently available for the treatment of stroke and numerous other brain disorders involving free radical injury. We propose that the various metabolic antioxidant properties of alpha-lipoate relate to its possible therapeutic roles in a variety of brain and neuronal tissue pathologies: thiols are central to antioxidant defense in brain and other tissues. The most important thiol antioxidant, glutathione, cannot be directly administered, whereas alpha-lipoic acid can. In vitro, animal, and preliminary human studies indicate that alpha-lipoate may be effective in numerous neurodegenerative disorders.

Animals↗
PubMed1997

Cytosolic and mitochondrial systems for NADH- and NADPH-dependent reduction of alpha-lipoic acid.

In cellular, tissue, and organismal systems, exogenously supplied alpha-lipoic acid (thioctic acid) has a variety of significant effects, including direct radical scavenging, redox modulation of cell metabolism, and potential to inhibit oxidatively-induced injury. Because reduction of lipoate to dihydrolipoate is a crucial step in many of these processes, we investigated mechanisms of its reduction. The mitochondrial NADH-dependent dihydrolipoamide dehydrogenase exhibits a marked preference for R(+)-lipoate, whereas NADPH-dependent glutathione reductase shows slightly greater activity toward the S(-)-lipoate stereoisomer. Rat liver mitochondria also reduced exogenous lipoic acid. The rate of reduction was stimulated by substrates which increased the NADH content of the mitochondria, and was inhibited by methoxyindole-2-carboxylic acid, a dihydrolipoamide dehydrogenase inhibitor. In rat liver cytosol, NADPH-dependent reduction was greater than NADH, and lipoate reduction was inhibited by glutathione disulfide. In rat heart, kidney, and brain whole cell-soluble fractions, NADH contributed more to reduction (70-90%) than NADPH, whereas with liver, NADH and NADPH were about equally active. An intact organ, the isolated perfused rat heart, reduced R-lipoate six to eight times more rapidly than S-lipoate, consistent with high mitochondrial dihydrolipoamide dehydrogenase activity and results with isolated cardiac mitochondria. On the other hand, erythrocytes, which lack mitochondria, somewhat more actively reduced S- than R-lipoate. These results demonstrate differing stereospecific reduction by intact cells and tissues. Thus, mechanisms of reduction of alpha-lipoate are highly tissue-specific and effects of exogenously supplied alpha-lipoate are determined by tissue glutathione reductase and dihydrolipoamide dehydrogenase activity.

Animals↗
PubMed1997

Redox regulation of NF-kappa B activation.

Cytosolic reactions of the nuclear factor kappa B/inhibitor (NF-kappaB/IkappaB) complex leading to its activation, NF-kappaB translocation into the nucleus, DNA binding, and transactivation have been described with some degree of clarity, but the upstream processes that stimulate those cytosolic reactions remain obscure. These processes definitely involve multiple protein serine/threonine kinases, as proximal modifiers of IkappaB, as well as the corresponding phosphatases, upstream kinases, and phosphatases, including those acting on tyrosine residues. This complex cascade of phosphorylation and dephosphorylation is modulated by redox reactions of unknown nature in the sense that the oxidant status of the cytosol increases the phosphorylation and degradation of IkappaB. NF-kappaB action, however, requires a thioredoxin-dependent reduced status in the nucleus. Upstream kinase(s) and or phosphatase(s) prone to thiolation or oxidation of vicinal SH groups are at present considered the best candidates mediating the redox regulation of NF-kappaB.

Animals↗
PubMed1996

Reevaluation of superoxide scavenging activity of dihydrolipoic acid and its analogues by chemiluminescent method using 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazo-[1,2-a]pyrazine-3-one (MCLA) as a superoxide probe.

The superoxide scavenging activity of dihydrolipoic acid and its analogues has been reevaluated by a chemiluminescence method using MCLA as a superoxide indicator. The results demonstrated that all the compounds having the thiol chromophore in the molecule showed scavenging activity toward superoxide. The short-chain analogue, tetranor-dihydrolipoic acid, showed almost the same scavenging activity as that of dihydrolipoic acid; however, bisnor-dihydrolipoic acid showed weaker scavenging activity than that of dihydrolipoic acid. The reaction rates of dihydrolipoic acid, bisnor-dihydrolipoic acid, and tetranor-dihydrolipoic acid were calculated from the competitive inhibition of MCLA-superoxide reaction. Thus, it was concluded that dihydrolipoic acid and the analogues are good scavengers of superoxide radical anion.

Cysteine↗
PubMed1996

Kinetic study of cutaneous and subcutaneous distribution following topical application of [7,8-14C]rac-alpha-lipoic acid onto hairless mice.

To diminish oxidative injury, topically applied antioxidants must reach susceptible cells. alpha-Lipoic acid is a potent thiol antioxidant that might be useful for skin protection; therefore, its skin penetration kinetics were assessed. The cutaneous and subcutaneous distributions of [7,8-14C]rac-alpha-lipoic acid were studied in anesthetized hairless mice after application of a 5% solution in propylene glycol for 0.5 to 4 hr. The mice were killed; then the skin was washed, and the stratum corneum was removed by 10 cellophane tape strippings. A punch biopsy of the frozen, stripped skin was sectioned, and amounts of [14C]-alpha-lipoic acid were determined in strippings and slices of epidermis (4 x 5 microns), dermis, and subcutaneous fat (10 x 10 microns, 20 x 20 microns). The rate of [14C]-alpha-lipoic acid absorption into skin was constant by 30 min (0.10 +/- 0.01 nmol/cm2/min); maximum skin concentrations were reached by 2 hr. The [14C]-alpha-lipoic acid penetration kinetics into the first layer of the stratum corneum predicted its penetration through the stratum corneum and subsequent percutaneous absorption (r2 = 0.96, P < 0.02). Cutaneous absorption of unlabeled alpha-lipoic acid and its reduction to the more potent antioxidant form, dihydrolipoic acid, were also demonstrated, using HPLC analysis with electrochemical detection. In conclusion, alpha-lipoic acid topically applied to skin penetrated readily, and was reduced to dihydrolipoic acid. Thus, alpha-lipoic acid could potentiate skin antioxidant protection.

Animals↗
PubMed1996

Iron coordination by catechol derivative antioxidants.

Iron complexes of nitrocatechols with different substituent groups [1: -CH = CR2; 2: -CH2-CHR2; 3: -CH = CR'(R")] were synthesized and their effects on iron-induced free radical reactions of biological importance investigated. Catechol and nitrocatechol derivatives effectively inhibited iron-induced lipid peroxide-dependent lipid peroxidation. In the Fenton-like reaction, iron-catechol generated hydroxyl radicals more strongly than did iron citrate, and iron-nitrocatechol derivative 2 generated a small amount of hydroxyl radicals. The iron complexes of derivatives 1 and 3 did not generate hydroxyl radicals. Iron-catechol had the highest ratio of reduction to oxidation rate constants and the second was iron-nitrocatechol 2, suggesting that iron chelated by nitrocatechols 1 and 3 may be most difficult to reduce. To elucidate the structure and physical properties of the iron complexes, UV/vis absorption spectroscopic, ESR and 1H NMR studies were performed in aqueous and DMSO solutions. In aqueous solution at pH 7.4, iron complexes of the nitrocatechol derivatives were high-spin tris(nitrocatecholato)ferrate(III) with a characteristic ligand-to-metal charge transfer absorbance (pi -> d pi). The lambda max of iron-nitrocatechol derivative 2 was shorter than those of iron-nitrocatechol derivatives 1 and 3, suggesting that the reduction potential of iron-nitrocatechol 2 is higher than that of iron-nitrocatechols 1 and 3. Nitrocatechol derivatives with a conjugation structure can sequester the chelated iron more effectively than catechol and the derivative without the conjugation against free radical generation by keeping the iron in the ferric state, probably because of the reduction potentials.

Animals↗
PubMed1996

Anti-psoriatic drug anthralin activates transcription factor NF-kappa B in murine keratinocytes.

Anthralin is one of the most effective and safest therapeutic agents for the treatment of psoriasis, a skin disease characterized by epidermal hyperproliferation and hyperkeratosis. The drug induces and inflammatory response in the skin involving the expression of cytokine and cell adhesion molecule genes that is thought to be essential for its therapeutic efficacy. Reactive oxygen intermediates (ROIs) generated in vivo during the auto-oxidation of anthralin were discussed as mediators of the inflammatory response, but it is not yet understood how this is translated into novel inflammatory gene expression. In this study, we show that at little as 10 microM anthralin can activate a prototypic form of transcription factor NF-(kappa)B, a central transcriptional regulator of inflammatory and immune responses. Two different lines of evidence show that ROIs, in particular H2O2, are second messengers for the anthralin-induced NF-(kappa)B activation. Firstly, the activation could be inhibited by the structurally unrelated antioxidants N-acetyl-L-cysteine and pyrrolidinedithiocarbamate. Secondly, keratinocytes stably overexpressing catalase showed a significant reduction of NF-(kappa)B activation, while stable overexpression of Cu/Zn-superoxide dismutase augmented the anthralin effect. Our data suggest that ROI-induced NF-(kappa)B plays a role in the anti-psoriatic activity of the drug anthralin.

Administration, Topical↗
PubMed1996

Involvement of intracellular Ca2+ in oxidant-induced NF-kappa B activation.

In human Jurkat T cells and its subclone Wurzburg cells oxidant challenge elevated [Ca2+]i by mobilizing Ca2+ from intracellular stores. In Jurkat cells this effect was rapid and transient, but in Wurzburg cells the response was slow and sustained. H2O2-induced NF-kappaB activation in Wurzburg cells was not influenced by the presence of extracellular EGTA but was totally inhibited in cells that were loaded with esterified EGTA. In Jurkat cells that are not sensitive to H2O2-induced NF-kappaB activation, H2O2 potentiated NF-kappaB activation in the presence of sustained high [Ca2+]i following thapsigargin treatment. NF-kappaB regulatory effect of alpha-lipoate and N-acetylcysteine appeared to be, at least in part, due to their ability to stabilize elevation of [Ca2+]i following oxidant challenge. Results of this study indicate that a sustained elevated [Ca2+]i is a significant factor in oxidant-induced NF-kappaB activation.

Acetylcysteine↗
PubMed1996

alpha-Lipoic acid protects against reperfusion injury following cerebral ischemia in rats.

Ischemic-reperfusion injury in humans occurs in conditions such as stroke, cardiac arrest, subarachnoid hemorrhage or head trauma. Maximal tissue damage is observed during reperfusion, which is primarily attributed to oxidative injury resulting from production of oxygen free radicals. One of the major consequences of such damage is the depletion of the cellular antioxidant, glutathione (GSH) leading to oxidation of protein thiols to disulfides and the loss of activity of critical enzymes having active thiol group(s). Thus, the maintenance of thiol homeostasis is an important factor in cell survival. The effect of thiol antioxidants like alpha-lipoic acid and the isopropyl ester of GSH was examined on the morbidity and mortality of rats subjected to reperfusion following cerebral ischemia induced by bilateral carotid artery occlusion and hypotension. While the GSH isopropyl ester had no significant protective effect; after pretreatment of rats, alpha-lipoic acid was detected in the rat brain and it dramatically reduced the mortality rate from 78% to 26% during 24 h of reperfusion. The natural thiol antioxidant, alpha-lipoic acid is effective in improving survival and protecting the rat brain against reperfusion injury following cerebral ischemia.

Animals↗
PubMed1996

Stereospecific effects of R-lipoic acid on buthionine sulfoximine-induced cataract formation in newborn rats.

This study revealed a marked stereospecificity in the prevention of buthionine sulfoximine-induced cataract, and in the protection of lens antioxidants, in newborn rats by alpha-lipoate, R- and racemic alpha-lipoate decreased cataract formation from 100% (buthionine sulfoximine only) to 55% (buthionine sulfoximine + R-alpha-lipoic acid) and 40% (buthionine sulfoximine + rac-alpha-lipoic acid) (p<0.05 compared to buthionine sulfoximine only). S-alpha-lipoic acid had no effect on cataract formation induced by buthionine sulfoximine. The lens antioxidants glutathione, ascorbate, and vitamin E were depleted to 45, 62, and 23% of control levels, respectively, by buthionine sulfoximine treatment, but were maintained at 84-97% of control levels when R-alpha-lipoic acid or rac-alpha-lipoic acid were administered with buthionine sulfoximine; S-alpha-lipoic acid administration had no protective effect on lens antioxidants. When enantiomers of alpha-lipoic acid were administered to animals, R-alpha-lipoic acid was taken up by lens and reached concentrations 2- to 7-fold greater than those of S-alpha-lipoic acid, with rac-alpha-lipoic acid reaching levels midway between the R-isomer and racemic form. Reduced lipoic acid, dihydrolipoic acid, reached the highest levels in lens of the rac-alpha-lipoic acid-treated animals and the lowest levels in S-alpha-lipoic acid-treated animals. These results indicate that the protective effects of alpha-lipoic acid against buthionine sulfoximine-induced cataract are probably due to its protective effects on lens antioxidants, and that the stereospecificity exhibited is due to selective uptake and reduction of R-alpha-lipoic acid by lens cells.

Animals↗
PubMed1996

Efficacy of hypochlorous acid scavengers in the prevention of protein carbonyl formation.

We observed that protein (bovine serum albumin) carbonyl content increases upon hypochlorite oxidation, and this increase is inhibited in a concentration-dependent manner in the presence of hypochlorite scavengers. Based on this observation, we tested whether some known hypochlorite scavengers (lipoic acid, cysteine, and glutathione) and some other antioxidants (uric acid, ascorbic acid, alpha-tocopherol, and probucol) could prevent protein carbonyl formation. N-acetylcysteine, dihydrolipoic acid, cysteine, and glutathione (reduced form, GSH), which otherwise could not be tested in a previously reported 5-thio-2-nitrobenzoic acid test system, were successfully evaluated in our assay. The hypochlorite scavenging capacity of different compounds, compared by determining the IC50 (concentration which produces 50% inhibition), showed that the compounds tested have the following potency: dihydrolipoic acid > GSH, N-acetylcysteine > cysteine > S-methyl glutathione > lipoic acid, ascorbic acid > cystine, GSSG, and uric acid. No scavenging ability was observed for either alpha-tocopherol or probucol.

Animals↗
PubMed1996

Inhibition of NF-kappa B activation in human T-cell lines by anetholdithiolthione.

Nuclear factor (NF)-kappa B is a redox sensitive cytosolic transcription factor. Redox regulation of NF-kappa B has been implicated in the activation of the human immuno-deficiency virus (HIV). Therefore, inhibition of NF-kappa B activation may be an effective strategy for acquired immunodeficiency syndrome therapy. Anetholdithiolthione (ADT, 5-[p-methoxyphenyl]-3H-1,2-dithiol-3-thione) is an antioxidant which has been used to protect against acetaminophen- and CCl4-induced hepatotoxicity, lipid peroxidation, radiation injury, and also has been used clinically as an anti-choleretic agent. The present study examined the effect of ADT pretreatment on NF-kappa B activation in response to a variety of stimuli such as H2O2, phorbol myristate acetate (PMA) or tumor necrosis factor alpha (TNF alpha). PMA and TNF alpha induced activation of (NF)-kappa B in human Jurkat T-cells was partially inhibited by ADT (0.1 mM) pretreatment. ADT (0.1 mM) also inhibited H2O2 induced activation of the transcription factor in the peroxide sensitive human Wurzburg T-cells. Furthermore, ADT treated Wurzburg cells had significantly higher glutathione levels as compared with untreated cells. H2O2 induced lipid peroxidation in Wurzburg cells was remarkably inhibited by ADT pretreatment. ADT, a pro-glutathione antioxidant, was observed to be capable of modulating NF-kappa B activation.

Anethole Trithione↗
PubMed1996

Oxidative stress alters arginine metabolism in rat brain: effect of sub-convulsive hyperbaric oxygen exposure.

The effect of hyperbaric oxygenation on arginine metabolism was investigated. Rats were exposed to oxygen at 3 atmospheres absolute for 2 h. Under these conditions, lipid peroxidation and activation of the anti-oxidant system were observed. Levels of thiobarbiturate reactive substances and carbon-centered radicals were increased in the cerebral cortex, while superoxide dismutase activity was also increased in the mitochondrial and cytosolic fraction of cerebrocortical homogenates. This suggested that the increase of both Mn and Cu,Zn-superoxide dismutase activities was probably an early compensatory reaction to oxidative stress. Levels of arginine as well as its metabolite, guanidinoacetic acid, were increased in the cerebral cortex. This increase seemed to be, at least in part, explained by a decrease in the arginase activity in the same region. Moreover, arginase activity in the brain showed heterogeneous distribution. Arginine: glycine amidinotransferase activity was decreased in the pons-medulla oblongata. The observed effects of hyperbaric oxygenation seem to favor nitric oxide generation.

Amidinotransferases↗
PubMed1996

Oxidized low density lipoprotein induces activation of the transcription factor NF kappa B in fibroblasts, endothelial and smooth muscle cells.

The effect of cupric ions or endothelial cell-oxidized LDL on the transcription factor NF kappa B activation was investigated by electrophoretic mobility shift assay. Oxidized LDL induced NF kappa B activation in fibroblasts, endothelial and smooth muscle cells. The extent of NF kappa B activation was proportional to the degree of LDL oxidation, as assessed by the lipid peroxidation product and the conjugated diene level. A similar activation was observed with the lipid extract of copper-oxidized LDL, which indicates that lipid peroxidation products are involved in the activation mechanism. Furthermore, alpha-tocopherol, a lipophilic free radical scavenger, partially inhibited the stimulatory effect of Cu(2+)-oxidized LDL. Since NF kappa B is considered as an oxidative stress-responsive transcription factor, our study supports the evidence that the stress induced by oxidized LDL causes NF kappa B activation in different cell types, and that this effect can be ascribed to the lipid peroxidation products.

Animals↗
PubMed1996

Gingko biloba extract EGb 761 is a suppresser of AP-1 transcription factor stimulated by phorbol 12-myristate 13-acetate.

Transcription factors are activated in response to a wide variety of extracellular stimuli. The present study investigated which step Gingko biloba extract (EGb 761), a flavonoid phytochemical rich preparation can affect signal transduction during AP-1 activation. Kinetic experiments with human Jurkat T-cell lines demonstrate that it takes 1 to 1.5 h to activate AP-1 DNA binding activity. These data indicate that c-fos mRNA is expressed and then AP-1 DNA binding activity is activated. Pretreatment of Jurkat T cells with 10 micrograms/ml EGb 761 suppresses AP-1 DNA activation and c-fos mRNA expression. These results suggest that the step in the signal transduction pathway for AP-1 activation that is inhibited by EGb 761 is upstream to c-fos mRNA expression.

Carcinogens↗