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Biomedical subjects

L Packer

Publications and source records attributed to L Packer.

At least 235 records · Page 13Linked to original sources
PubMed1993

Vitamin E recycling in human erythrocyte membranes.

Vitamin E, the major lipid chain-breaking antioxidant in erythrocyte membranes, is present in low concentration, suggesting that mechanisms should exist to protect against its loss. Enzymatic pathways for the recycling of vitamin E from its tocopheroxyl radical have been observed previously in inner membranes of mitochondria and microsomes. These pathways use electron transport enzymes and their substrates to regenerate vitamin E. Erythrocyte membranes also contain significant NADH-cytochrome c reductase activity, as well as cytochrome b5, the function of which is not yet known. Using an enzymatic oxidation system composed of lipoxygenase and arachidonic acid, free radicals were produced in human erythrocyte membranes, and their reaction with chromanols was followed by ESR and high performance liquid chromatography (HPLC). Since the endogenous vitamin E content of the membranes is very low, we used a vitamin E homologue lacking the hydrocarbon chain (2,2,5,7,8-pentamethyl-6-hydroxychromane) as a probe molecule for ESR measurements. However, parallel HPLC determinations of lipid hydroperoxides and of endogenous vitamin E confirmed the results obtained by ESR. It was found that protection against the loss of vitamin E can be provided either by NADH-cytochrome b5-dependent enzymatic recycling or by a nonenzymatic pathway involving ascorbate and dihydrolipoic acid.

Arachidonic Acid↗
PubMed1993

Inhibition of smooth muscle cell proliferation and protein kinase C activity by tocopherols and tocotrienols.

alpha-Tocopherol, the most active form of vitamin E, causes a dose-dependent inhibition of serum-induced proliferation of smooth muscle cells (A7r5) in culture. Some tocopherol-related compounds exhibiting various degrees of antioxidant potency have also been tested on cellular proliferation. No direct correlation between the antioxidant activity of these compounds and their effect on smooth muscle cell growth could be observed. While most of the derivatives employed were not effective in inhibiting protein kinase C, in the case of alpha-tocopherol the antiproliferative effect was found to be parallel to the inhibition of protein kinase C activity, as measured in streptolysin-O permeabilized cells.

Alkaloids↗
PubMed1993

Interaction of the pyridoindole stobadine with peroxyl, superoxide and chromanoxyl radicals.

The pyridoindole derivative stobadine [(-)-cis-2,8-dimethyl-2,3,4,4a,5,9b-hexahydro-1H-pyrido(4,3b)indole] has been described as a drug with antihypoxic and antiarrhythmic cardioprotective properties. Here its reactivity with peroxyl radicals in liposomes using a lipid-soluble azo-initiator of peroxyl radicals, 2,2'-azo-bis(2,4-dimethyl-valeronitrile) (AMVN), was examined. Stobadine exerted scavenging as evidenced by the inhibition of: (i) cis-parinaric acid fluorescence decay (half-maximal effect at 20 microM), or (ii) luminol-sensitized chemiluminescence (half-maximal effect at 33 microM). In rat liver microsomes, stobadine was equally efficient in inhibiting lipid peroxidation induced by lipid-soluble (AMVN) or water-soluble 2,2'-azo-bis(2-aminopropane)-HCl (AAPH), azo-initiators of peroxyl radicals with half-maximal effect at 17 microM. Stobadine partitions in a two-phase system (octanol-water) with the coefficient log P = 0.57 +/- 0.03, explaining its ability to quench peroxyl radicals in both lipid and aqueous phases. Stobadine is not an efficient scavenger of superoxide radicals. The second order rate constant for the reaction of stobadine with superoxide was estimated to be 7.5 x 10(2) M-1 sec-1 as measured by superoxide-induced lucigenin-amplified chemiluminescence. ESR measurements showed that stobadine in liposomes does not reduce the chromanoxyl radical of a vitamin E homologue with a 6-carbon side-chain, 2,5,7,8-tetramethyl-2-(4'-methylpentyl)chroman-6-ol(chromanol++ +-alpha-C6), in agreement with pulse-radiolysis results obtained using Trolox in homogeneous solution (Steenken et al., Chem Res Toxicol 5: 355-360, 1992). Stobadine increased the magnitude of the chromanoxyl and ascorbyl radical ESR signal generated by lipoxygenase+arachidonate. This was interpreted to be due to the interaction of stobadinyl radicals with the chromanol ring and ascorbate, respectively. It is suggested that high reactivity of stobadine radicals requires the presence of reducing antioxidants (vitamin E, vitamin C) to exhibit its antioxidant effects in physiological systems.

Amidines↗
PubMed1993

Relationships between the effects of superoxide anion and palmitoyl-L-carnitine on the Ca(2+)-ATPase of vascular smooth muscle sarcoplasmic reticulum.

In order to understand interactions between oxidants and non-antioxidants, relationships between the effects of superoxide anion radical (O2-) and palmitoyl-L-carnitine (PLC) on the Ca(2+)-ATPase of vascular smooth muscle sarcoplasmic reticulum were studied. PLC was ineffective in preventing the reduction of ferricytochrome c by O2-, suggesting that it has no O2(-)-scavenging properties. PLC exhibited a biphasic effect on Ca(2+)-ATPase activity, causing stimulation at low concentrations (3-10 microM) and inhibition at higher concentrations (30-1000 microM). The stimulatory effect on Ca(2+)-ATPase caused by 10 microM PLC was completely counteracted by O2-, whereas the stimulatory effect of L-cysteine (2 mM) was only diminished partially. Additive effects of PLC and L-cysteine attenuated the inhibitory effect of O2-, however, this appears to be due to L-cysteine alone. These results demonstrate that O2- can inhibit stimulatory effects of PLC on the Ca(2+)-ATPase, however, PLC does not block the inhibitory effect of O2-. Understanding interactions between oxidants/antioxidants and non-antioxidants at their cellular target proteins may provide essential information in the search for prevention of free radical injury.

Animals↗
PubMed1993

A comparison of genetic variation in two sibling species pairs of haplodiploid insects.

Sibling species pairs of sweat bees (Halictus confusus and H. tumulorum) and pine sawflies (Neodiprion pratti and N. maurus) were surveyed for genetic variability using enzyme electrophoresis. Levels of heterozygosity were found to be within the ranges earlier recorded for Hymenoptera. Expected heterozygosities were not significantly higher in the sawflies than in the sweat bees. Estimates of genetic identity between the sibling species were not lower than those generally found for diplodiploid insect species: no evidence was found for an increased rate of evolution in these haplodiploids. Genetic identity data among populations of H. confusus and between Halictus species were within the range expected for conspecific populations and sibling species, respectively. In Neodiprion all genetic distances were low but the two populations of N. pratti had similar genetic distances as each did to N. maurus, indicating the necessity for further systematic studies of the genus.

Animals↗
PubMed1993

Vitamin E and alpha-lipoate: role in antioxidant recycling and activation of the NF-kappa B transcription factor.

Nuclear factor kappa B (NF-kappa B) is believed to play an important role in the activation of human immunodeficiency virus (HIV) which causes acquired immunodeficiency syndrome (AIDS). Recent findings suggesting an involvement of reactive oxygen species in signal transduction pathways leading to NF-kappa B activation have encouraged the possible clinical use of antioxidants in blocking HIV activation. We have examined the effects of vitamin E and alpha-lipoate derivatives on NF-kappa B activation, and have observed that each of these antioxidants behave differently. Here we propose mechanisms of antioxidant actions in influencing cell signalling for NF-kappa B activation.

Antioxidants↗
PubMed1993

Nitroxide radical biostability in skin.

Nitroxide radicals are important chemical tools in dermatologic research (e.g., for studying biophysical properties of skin lipids and epidermal membranes with the method of electron paramagnetic resonance, EPR, spectroscopy). However, nitroxides may loose their paramagnetic properties in biological tissues, which could limit their usefulness in biomedical applications. We analyzed the biostability of various chemical types of nitroxide radicals in keratinocytes, epidermis homogenate, and intact skin. EPR signal loss of imidazoline, pyrrolidine, piperidine, and oxazolidine nitroxides is attributed to their reduction to the corresponding hydroxylamine. The rate of nitroxide reduction in skin varies considerably with nitroxide ring structure and substitution. The order of nitroxide stability in isolated human keratinocytes, mouse epidermis homogenate, and intact mouse and human skin is imidazoline > pyrrolidine > di-t-butylnitroxide (DTBN) > piperidine > oxazolidine. Cationic nitroxides are reduced much faster than neutral or anionic probes, presumably due to transmembrane electron shuttle or internalization. The results indicate that imidazoline- and pyrrolidine-type nitroxides should be used when high biostability of nitroxides is needed. Piperidine-type nitroxides are versatile probes for studying one-electron transfer reactions in skin.

Animals↗
PubMed1993

Antioxidant defense mechanisms in murine epidermis and dermis and their responses to ultraviolet light.

A comprehensive comparison of antioxidant defenses in the dermis and epidermis and their response to exposure to ultraviolet (UV) irradiation has not previously been attempted. In this study, enzymic and non-enzymic antioxidants in epidermis and dermis of hairless mice were compared. Enzyme activities are presented both as units/gram of skin and units/milligram of protein; arguments are presented for the superiority of skin wet weight as a reference base. Catalase, glutathione peroxidase, and glutathione reductase (units/gram of skin) were higher in epidermis than dermis by 49%, 86%, and 74%, respectively. Superoxide dismutase did not follow this pattern. Lipophilic antioxidants (alpha-tocopherol, ubiquinol 9, and ubiquinone 9) and hydrophilic antioxidants (ascorbic acid, dehydroascorbic acid, and glutathione) were 24-95% higher in epidermis than in dermis. In contrast, oxidized glutathione was 60% lower in epidermis than in dermis. Mice were irradiated with solar light to examine the response of these cutaneous layers to UV irradiation. After irradiation with 25 J/cm2 (UVA + UVB, from a solar simulator), 10 times the minimum erythemal dose, epidermal and dermal catalase and superoxide dismutase activities were greatly decreased. alpha-Tocopherol, ubiquinol 9, ubiquinone 9, ascorbic acid, dehydroascorbic acid, and reduced glutathione decreased in both epidermis and dermis by 26-93%. Oxidized glutathione showed a slight, non-significant increase. Because the reduction in total ascorbate and catalase was much more severe in epidermis than dermis, it can be concluded that UV light is more damaging to the antioxidant defenses in the epidermis than in the dermis.

Animals↗
PubMed1993

Antioxidant status and indexes of oxidative stress during consecutive days of exercise.

We tested whether consecutive days of prolonged submaximal exercise would result in oxidant stress sufficient to alter blood antioxidant profiles, progressively change and exhaust blood and plasma antioxidants, and damage RNA. Eleven moderately trained males (24.3 +/- 1.1 yr) exercised 90 min at 65% peak O2 uptake on a cycle ergometer for 3 consecutive days. During day 1 exercise, blood reduced glutathione (GSH) declined 55 +/- 10% and oxidized glutathione (GSSG) increased 28 +/- 7% within 15 min. Total blood glutathione did not significantly change during exercise. GSH levels returned to baseline after 15 min of recovery. On day 3, preexercise GSH and GSSG levels were not significantly different from day 1 preexercise values; essentially similar results were obtained during exercise and recovery. During day 1 exercise, plasma total ascorbate (ascorbate + dehydroascorbate) increased from 53.8 +/- 9.3 to 59.0 +/- 11.3 microM, and percent reduced ascorbate increased from 77.6 +/- 9.3 to 87.3 +/- 9.7%. During day 3 exercise, plasma ascorbate changes were similar to those on day 1. Plasma vitamin E did not change due to exercise on either day 1 or 3. RNA adducts, urinary 8-hydroxyguanosine, did not change significantly due to exercise. Observed increases in GSH oxidation indicate the presence of oxidant stress during prolonged submaximal exercise. Similar redox changes on consecutive days of exercise, with recovery to preexercise values within 15 min, indicate no evidence of persistent or cumulative exercise effects on blood glutathione redox status.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Antioxidant activities of dihydrolipoic acid and its structural homologues.

The relationships between structure and antioxidant activity of dihydrolipoic acid (DHLA) were studied using homologues of DHLA: bisonor-DHLA (a derivative which lacks two carbons in the hydrophobic tail), tetranor-DHLA (which lacks four carbons) and a methyl ester derivative. It was observed that: i) DHLA homologues with shorter hydrocarbon tails (i.e., bisnor- and tetranor-DHLA) had greater ability to quench superoxide radicals (O2-); ii) no differences among homologues with different chain lengths were found for peroxyl radical (ROO.) scavenging in aqueous solution, and iii) DHLA was the best membrane antioxidant in terms of ROO. scavenging and lipid peroxidation inhibition. Differences among the DHLA homologues in their antioxidant properties in polar and apolar environments generally agreed with differences in their partition coefficients. The methyl ester was the least effective antioxidant both in aqueous phase and in membranes. Tetranor-DHLA was found not only to be less effective in preventing ROO.-induced lipid peroxidation, but also to induce lipid peroxidation in the presence of residual iron. Thus, the complexity of biological systems seems to complicate generalizations on the correlation of molecular structure with antioxidant activity of DHLA.

Animals↗
PubMed1993

Electrophoretic mobility changes of oxidized human low density lipoprotein measured by laser Doppler electrophoresis.

Laser Doppler Electrophoresis was used to detect changes in the surface charge of low density lipoprotein populations exposed to oxidative stress. Before oxidative stress, low density lipoprotein suspensions exhibited homogenous populations of net negative charge but after exposure to hydroxyl and superoxide radicals, peroxyl radicals, or by Cu2+ generated oxidants they exhibited Laser Doppler Electrophoresis changes. The major population of low density lipoprotein became more negatively charged, in agreement with agarose gel electrophoresis. However, Laser Doppler Electrophoresis detected greater heterogeneity of low density lipoprotein, compared to agarose gel electrophoresis. Partially oxidized low density lipoprotein exhibited a less negatively charged subpopulation of particles compared to control samples. This has not been reported previously. Hence, Laser Doppler Electrophoresis is a sensitive method for detecting the appearance of subpopulations of differing surface charge density in oxidatively modified low density lipoprotein. beta-carotene protected low density lipoprotein against oxidative modification even when endogenous vitamin E levels are low. Vitamin E-deficient low density lipoprotein pretreated with beta-carotene exhibited a more narrow negative population when oxidized with peroxyl radicals, compared to control. Native low density lipoprotein pretreated with a mixture of all-trans- and cis-beta-carotene was also protected.

Amidines↗
PubMed1993

Inhibition of NF-kappa B DNA binding activity by alpha-tocopheryl succinate.

Vitamin E derivatives have been shown to inhibit tumor necrosis factor-induced NF-kappa B activation in human Jurkat T cells. The present report demonstrates that alpha-tocopheryl succinate directly blocks DNA binding activity of activated NF-kappa B, as well as the NF-kappa B activation induced by okadaic acid, an inhibitor of protein phosphatases 1 and 2A. In contrast, alpha-tocopherol, alpha-tocopheryl acetate and 2,2,5,7,8-pentamethyl-6-hydroxychromane have no effects. These observations suggest that the mechanism of alpha-tocopheryl succinate action against NF-kappa B is different from those of other vitamin E derivatives.

Base Sequence↗
PubMed1993

Nitecapone protects the Langendorff perfused heart against ischemia-reperfusion injury.

We assessed the protection afforded against myocardial ischemia/reperfusion by nitecapone in the Langendorff heart model using male Sprague-Dawley rats. We found that when present in the perfusate 10 microM nitecapone improved the mechanical function of the heart and lowered the enzyme leakage of lactate dehydrogenase after 40 minutes of global ischemia. In nitecapone treated hearts the content of oxidized proteins and lipids (carbonyl groups and endogenous lipid fluorescent products) decreased. Nitecapone partially prevented the loss of total sulfhydryl groups and vitamin E after ischemia and reperfusion. We suggest that the mechanism of nitecapone protection most likely involves direct antioxidant action and enhancing the activity of other antioxidants.

Animals↗
PubMed1992

Alpha-lipoic acid is a potent inhibitor of NF-kappa B activation in human T cells.

Acquired immunodeficiency syndrome (AIDS) results from infection with a human immunodeficiency virus (HIV). The long terminal repeat (LTR) region of HIV proviral DNA contains binding sites for nuclear factor kappa B (NF-kappa B), and this transcriptional activator appears to regulate HIV activation. Recent findings suggest an involvement of reactive oxygen species (ROS) in signal transduction pathways leading to NF-kappa B activation. The present study was based on reports that antioxidants which eliminate ROS should block the activation of NF-kappa B and subsequently HIV transcription, and thus antioxidants can be used as therapeutic agents for AIDS. Incubation of Jurkat T cells (1 x 10(6) cells/ml) with a natural thiol antioxidant, alpha-lipoic acid, prior to the stimulation of cells was found to inhibit NF-kappa B activation induced by tumor necrosis factor-alpha (25 ng/ml) or by phorbol 12-myristate 13-acetate (50 ng/ml). The inhibitory action of alpha-lipoic acid was found to be very potent as only 4 mM was needed for a complete inhibition, whereas 20 mM was required for N-acetylcysteine. These results indicate that alpha-lipoic acid may be effective in AIDS therapeutics.

Acetylcysteine↗
PubMed1992

Vitamin E inhibits protein oxidation in skeletal muscle of resting and exercised rats.

It is well known that exercise induces lipid peroxidation in skeletal muscle and that vitamin E prevents exercise-induced lipid damage. In this study we show for the first time, an increase in protein oxidation in skeletal muscle after a single bout of exercise, related to an exercise-induced decrease in lipophilic antioxidants, and substantial protection against both resting and exercise-induced protein oxidation by supplementation with various isomers (alpha-tocopherol, alpha-tocotrienol) of vitamin E.

Animals↗