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Biomedical subjects

L Packer

Publications and source records attributed to L Packer.

At least 217 records · Page 12Linked to original sources
PubMed1994

Nitecapone: a nitric oxide radical scavenger.

Nitecapone [3-(3,4-dihydroxy-5-nitrobenzylidene)-2,4-pentanedione], is a scavenger of nitric oxide produced in vitro. It reduced the rate of methemoglobin formation from oxyhemoglobin exposed to nitric oxide generated from the reaction of hydroxylamine with Complex I of catalase and it decreased the amount of nitrite formed in the reaction of oxygen with nitric oxide generated from sodium nitroprusside. Nitecapone also affected the L-arginine dependent accumulation of nitrite in a suspension of peritoneal rat neutrophils. The related compounds entacapone [2-cyano-N, N-diethyl-3-(3,4 dihydroxy-5-nitrobenzyl)-propenamide] and OR 1246 [3-(3,4-dihydroxy-5-nitrobenzyl)-2,4-pentanedione] were also able to scavenge nitric oxide. The action of nitecapone on nitric oxide expands the role of nitecapone as a scavenger of reactive oxygen species, and suggests nitecapone, entacapone and OR 1246 as potential therapeutic agents for the treatment of diseases connected with increased production of nitric oxide.

Animals↗
PubMed1994

Oxidative stress and mitochondrial dysfunction in neurodegeneration.

In the last 4 years much progress has been made in the understanding of mitochondrial disorders. Point-mutations, deletions and depletion of the mitochondrial genome are associated with disorders like Leber's disease, MERRF (Myoclonus Epilepsia with Ragged Red Fibers), MELAS (mitochondrial Myopathy, Encephalopathy, Lactic acidosis and Stroke-like episodes) and several others. Recently, mitochondrial dysfunctions have been also related to neurodegenerative disorders like Parkinson's disease and to aging. Since the brain depends mostly on mitochondrial energy supply, mitochondrial dysfunctions may affect the nervous system more severely than other tissues causing or worsening diseases and playing a role in the biological deterioration of aging. Furthermore, the mitochondrial energy supply is associated with the production of highly reactive oxygen species. Ninety-five percent of the molecular oxygen is metabolized within the mitochondria by the electron-transport chain so that mitochondria are highly exposed to oxidative stress which may damage selected neuronal populations. Oxygen radicals created during respiration induce mitochondrial dysfunction which accelerates the production of more deleterious species of oxygen. The latter step further increases mitochondrial malfunction, thus intensifying and perpetuating the cycle. These two mechanisms combined may lead to cell death in brain and other tissues with high metabolic rate. Therefore, in neurodegenerative disorders such as Parkinson's disease mitochondrial dysfunction and oxidative stress may cause or worsen the clinical features.

Antioxidants↗
PubMed1994

Recovery of antioxidants and reduction in lipid hydroperoxides in murine epidermis and dermis after acute ultraviolet radiation exposure.

In previous studies we have found that a single acute dose of ultraviolet radiation to murine skin causes a large degree of destruction of enzymic and non-enzymic antioxidants immediately after irradiation. In the present study, we wished to elucidate the recovery of antioxidants after a single dose of ultraviolet (UV) radiation. We measured antioxidants and lipid hydroperoxides (as a marker of membrane damage) in murine epidermis and the dermis at 0, 3, 12, 24, 72 and 120 h after exposure to UV radiation (25 J/cm2, UVA+UVB). Lipid hydroperoxides showed the highest values immediately after UV exposure and returned to control values within 24 h in both epidermis and dermis. The activities of catalase, glutathione peroxidase and glutathione reductase showed the lowest activities immediately after UV exposure; superoxide dismutase activities reached a minimum at 3 h postexposure. The pattern of recovery was different for each enzyme and for epidermis and dermis. The activities of superoxide dismutase and catalase decreased remarkably and recovered slowly. Superoxide dismutase in the dermis recovered full activity by 120 h and in the epidermis by 12 h. Catalase activity in both epidermis and dermis had returned to only 50% of control activity at 120 h, although the epidermis showed a temporary increase (to 93%) at 24 h. Glutathione peroxidase and glutathione reductase were slightly decreased immediately after irradiation, recovered to 100% at 3 h and then increased to 200-250% in both the epidermis and the dermis at various times; values had returned to 100% in epidermis by 120 h but remained elevated in dermis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

alpha-Lipoic acid protects against hemolysis of human erythrocytes induced by peroxyl radicals.

The azo initiator of peroxyl radicals 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) induces oxidative hemolysis in human erythrocytes and subsequent hemoglobin oxidation. Using the degree of hemolysis versus time as an indication of the oxidative damage it was found that i) both reduced and oxidized alpha-lipoic acid protected against oxidative damage; ii) simultaneous treatment of erythrocytes with ascorbate and dihydrolipoate or alpha-lipoate has a synergistic tendency to protect cells against hemolysis; iii) glutathione in combination with dihydrolipoic acid or alpha-lipoic acid has an additive effect on hemolysis protection. The spin trapping reagent 5,5-dimethyl-1-pyrroline N-oxide (DMPO) formed an adduct with the peroxyl/alkoxyl radicals produced by thermal decomposition of AAPH in the presence of oxygen. The formation of this adduct was prevented by reduced or oxidized lipoic acid, reduced glutathione or ascorbate. It is concluded that AAPH-peroxyl radicals progressively damage the cells and the released hemoglobin is subsequently oxidized to methemoglobin which might further enhance the oxidative damage. The protective effect of antioxidants is exerted outside the cells by directly scavenging AAPH-alkoxyl radicals.

Amidines↗
PubMed1994

NMR study of lipoic acid binding to bovine serum albumin.

Evidence for the binding of lipoic (LA) and dihydrolipoic (DHLA) acid to bovine serum albumin (BSA) was sought as a feature for understanding the mechanism of their antioxidant activity and prevention of glycation. Experiments were performed by 1H high resolution NMR. The average binding ratio of LA, DHLA and tetranor LA to BSA were 10 +/- 2, 7.9 +/- 2 and 1.8 +/- 0.4 mol/mol BSA respectively. In this row the number of bound molecules lessens with the decrease of their hydrophobic interactions that correlates with their protective activity. Octanoic acid, the closest analog of lipoate, had a binding ratio of 4.7 +/- 0.5 mol. Lipoic acid was able to replace bound octanoic acid which points out that lipoate occupies the same binding site on BSA. Lipoate had no binding to low density lipoproteins extracted from human plasma which corresponds to its low protection of LDL against glycosylation and oxidative modification. This study indicates that lipoic acid molecules experience strong hydrophobic attraction and binding to BSA which is important part of lipoate protective mechanism.

Animals↗
PubMed1994

Inhibition of NF-kappa B transcription factor by catechol derivatives.

Therapeutic agents which target NF-kappa B transcription factor may be useful in the management of AIDS, cancer and inflammation. Since oxidative stress has been implicated in the signaling pathway, the use of antioxidants to inhibit NF-kappa B activation has gained attention. In the present study, we examined the effects of catechol derivatives, nitecapone and OR-1246, which have been identified to possess potent antioxidant properties, on NF-kappa B activation by monitoring its DNA binding activity. Both nitecapone and OR-1246 (10-300 microM) inhibited NF-kappa B activation induced by tumor necrosis factor-alpha in Jurkat T (acute human leukemia) cells. Nitecapone was a better inhibitor than OR-1246. The observed effects may, at least in part, be due to the ability of the two compounds to directly inhibit DNA binding activity of activated NF-kappa B. The inhibitory capability of OR-1246 on NF-kappa B DNA binding does not appear to be a sole mechanism, as it did not inhibit NF-kappa B activation induced by okadaic acid. Hence, catechol derivatives inhibit NF-kappa B transcription factor through multiple mechanisms, and nitecapone and OR-1246 may be useful as therapeutic agents targeting NF-kappa B.

Antioxidants↗
PubMed1994

Aldehyde-induced protein modifications in human plasma: protection by glutathione and dihydrolipoic acid.

Exposure of human plasma to gas phase cigarette smoke (CS) produces a depletion of ascorbic acid, peroxidation of lipids (Frei et al. Biochem J 1991; 277: 133-8), and protein modification (as measured by protein carbonyl accumulation and loss of sulfhydryl groups) (Reznick et al. Biochem J 1992; 286: 607-11). CS contains both saturated and unsaturated aldehydes. The contribution of these aldehydes to the damaging effects of CS on human plasma was investigated. Aldehydes present in CS did not cause a depletion of plasma antioxidants such as ascorbic acid or alpha-tocopherol and did not induce plasma lipid peroxidation. Aldehydes decreased plasma protein sulfhydryl concentrations but increased protein carbonyls. The thiols glutathione and dihydrolipoic acid had a significant effect in reducing aldehyde-induced protein modifications.

Adult↗
PubMed1993

Cardiac recovery during post-ischemic reperfusion is improved by combination of vitamin E with dihydrolipoic acid.

Effects of dietary vitamin E supplementation in rats were studied to determine whether or not they have a higher tolerance against cardiac ischemia-reperfusion injury using the working or Langendorff heart systems. Also, dihydrolipoic acid, recently reported to have potent antioxidant properties and accelerate vitamin E recycling of membrane in vitro, was perfused into the heart model systems to investigate its in vivo relationship with vitamin E. Tissue vitamin E content was increased by vitamin E feeding, but heart preparations did not show any improved functional recovery. Control hearts perfused with dihydrolipoic acid also did not show any improvement. However, a synergistic response is observed with the combination of dihydrolipoic acid perfusion and high dietary vitamin E using both perfusion systems in improvement of cardiac recovery. These results indicate that a high concentration of myocardial vitamin E does not increase tolerance to ischemia-reperfusion injury by itself, but, the combination of exogenous dihydrolipoic acid and high endogenous vitamin E can produce synergistic protective effects on recovery from ischemia during reperfusion.

Analysis of Variance↗
PubMed1993

Structural and dynamic membrane properties of alpha-tocopherol and alpha-tocotrienol: implication to the molecular mechanism of their antioxidant potency.

d-alpha-Tocopherol and d-alpha-tocotrienol are two vitamin E constituents having the same aromatic chromanol "head" but different hydrocarbon "tails". alpha-Tocotrienol has been shown to be more potent in protecting against free radical-induced oxidative stress than alpha-tocopherol. Simple models of phospholipid membrane systems were used to investigate the mechanism of the antioxidant potency of alpha-tocotrienol in terms of its effects on membrane order and reorientation dynamics. Chemiluminescence and fluorescence measurements demonstrated that alpha-tocotrienol exhibits significantly greater peroxyl radical scavenging potency than alpha-tocopherol in phosphatidylcholine liposomes, whereas both antioxidants have identical activity in hexane. This suggests that the antioxidant potency of alpha-tocotrienol requires the membrane environment. When alpha-tocopherol and alpha-tocotrienol were examined for their effects on phospholipid molecular order using conventional ESR spin labeling with 5- and 16-position-labeled doxylstearic acid, although both vitamin E constituents disordered the gel phase and stabilized the liquid-crystalline phase, no differences were observed between the effects of the two compounds. A slightly greater increase (19% vs 15%) in ordering of the liquid-crystalline state due to alpha-tocopherol, however, was discerned in noninvasive 2H NMR experiments. The difference is most noticeable near C10-C13 positions of the phospholipid chain, possibly suggesting alpha-tocotrienol is located closer to the membrane surface. Saturation-transfer ESR, furthermore, revealed that on the time scale tau c = 10(-7)-10(-3) s the rates of rotation about the long molecular axis and of the wobbling motion of the axis are modified to differing extents by the two forms of the vitamin E.(ABSTRACT TRUNCATED AT 250 WORDS)

Antioxidants↗
PubMed1993

Inhibition of NF-kappa B activation by vitamin E derivatives.

Nuclear factor kappa B (NF-kappa B) is believed to play an important role in the activation of a 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 ensured the possible clinical use of antioxidants in blocking HIV activation. The present study examined the effects of vitamin E derivatives on the tumor necrosis factor-alpha (TNF-alpha) induced NF-kappa B activation. Incubation of human Jurkat T cells with vitamin E acetate or alpha-tocopheryl succinate (10 microM to 1 mM) exhibited a concentration dependent inhibition of NF-kappa B activation. alpha-Tocopherol or succinate at these concentrations had no apparent effects. 2,2,5,7,8-Pentamethyl-6-hydroxychromane (PMC) was extremely effective, causing complete inhibition of NF-kappa B activation at 10 microM. Oct-1 binding activity was inactivated by alpha-tocopheryl succinate whereas other derivatives had no effects, suggesting that the effects of alpha-tocopheryl succinate are not specific to NF-kappa B. HPLC measurements demonstrated that treatment of cells with TNF-alpha had no effects on cellular alpha-tocopherol, but vitamin E acetate treatment increased the alpha-tocopherol content. Cell viability was not affected by any of the vitamin E derivatives. These results indicate a possible use of vitamin E derivatives in AIDS therapeutics.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Cigarette smoke oxidation of human plasma constituents.

In vitro exposure of fresh human plasma to cigarette smoke (CS) was used as a model for reactions that could be occurring in CS-exposed respiratory tract lining fluids (RTLFs) and lung parenchyma. The central focus of this model was to characterize the consumption of endogenous plasma antioxidants in relationship to the appearance of oxidized proteins and lipids as a consequence of exposure to CS, or to aldehydes present in CS. The amelioration of CS-induced protein and lipid oxidation in plasma by the addition of selective exogenous antioxidants was also assessed. We found that: (i) exposure of human plasma to gas phase CS causes both lipid peroxidation and protein oxidation, and endogenous ascorbic acid protects against lipid, but not protein, oxidation; (ii) whole CS causes protein oxidation, but does not induce lipid peroxidation; (iii) addition to plasma of aldehydes known to be present in CS causes protein damage, but does not induce either lipid peroxidation or oxidation of ascorbic acid; and (iv) exogenously added dihydrolipoic acid (DHLA) preserves ascorbic acid levels in plasma exposed to the gas phase of CS, and protects, to some extent, against lipid peroxidation; DHLA also protects against protein oxidation, whereas added glutathione (GSH) only protects against protein, but not lipid, oxidation.

Adult↗
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↗