Antioxidant activity and stability of 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid

Strategy to relieve cellular oxidative stress based on ultra-small nanobubbles without exogenous antioxidants

Reactive oxygen species (ROS) produced in living systems are essential to physiological processes. However, excess ROS in the organism (oxidative stress) damages crucial cell components, leading to many diseases. Although some commercial antioxidants can counteract ROS damage, their inadequate tissue penetration, disruption of normal ROS functions, and possible toxicity have led to disappointing results in clinical trials for ROS-induced chronic diseases. Thus, new antioxidant strategies are warranted. Herein, we report a novel "antioxidant" composed of pure nitrogen gas in an ultra-small nanobubble (UNB) form, which can relieve oxidative stress in cells. Our results indicate that UNBs can reduce cellular ROS levels under oxidative stress and increase survival and proliferation. Besides, UNBs can decrease the oxidative damage to cellular biomacromolecules (lipids, proteins, and nuclear acids). Thus, UNBs are a promising nonchemical antioxidative strategy with potential applications against oxidative stress-related diseases and without the natural defect of chemical antioxidants.

An antioxidation strategy based on ultra-small nanobubbles without exogenous antioxidants

Antioxidation is in demand in living systems, as the excessive reactive oxygen species (ROS) in organisms lead to a variety of diseases. The conventional antioxidation strategies are mostly based on the introduction of exogenous antioxidants. However, antioxidants usually have shortcomings of poor stability, non-sustainability, and potential toxicity. Here, we proposed a novel antioxidation strategy based on ultra-small nanobubbles (NBs), in which the gas-liquid interface was employed to enrich and scavenge ROS. It was found that the ultra-small NBs (~ 10 nm) exhibited a strong inhibition on oxidization of extensive substrates by hydroxyl radicals, while the normal NBs (~ 100 nm) worked only for some substrates. Since the gas-water interface of the ultra-small NBs is non-expendable, its antioxidation would be sustainable and its effect be cumulative, which is different to that using reactive nanobubbles to eliminate free radicals as the gases are consumptive and the reaction is unsustainable. Therefore, our antioxidation strategy based on ultra-small NB would provide a new solution for antioxidation in bioscience as well as other fields such as materials, chemical industry, food industry, etc.

Degradation profile of nepafenac in aqueous solution and structural characterization of a novel degradation product

The stability of the anti-inflammatory drug nepafenac was investigated in aqueous solutions containing hydroxypropyl-β-cyclodextrin at three different values of pH and degradation products were identified. (2-Amino-3-benzoyl)-oxoacetic acid, previously not reported as nepafenac-related impurity, was isolated and structurally characterized by NMR and ESI-MS analyses. It was also shown that the formation of this α-ketoacid from nepafenac in alkaline water/organic cosolvent solution occurs through an aerobic oxidation of the key intermediate 7-benzoyl-1,3-dihydro-indol-2-one, which in some extent is protected from oxidation in the presence of the cyclodextrin additive.

Vitamin E treatment in NAFLD patients demonstrates that oxidative stress drives steatosis through upregulation of de-novo lipogenesis

Oxidative stress (OS) in non-alcoholic fatty liver disease (NAFLD) promotes liver injury and inflammation. Treatment with vitamin E (α-tocopherol, αT), a lipid-soluble antioxidant, improves liver injury but also decreases steatosis, thought to be upstream of OS, through an unknown mechanism. To elucidate the mechanism, we combined a mechanistic human trial interrogating pathways of intrahepatic triglyceride (IHTG) accumulation and in vitro experiments. 50% of NAFLD patients (n = 20) treated with αT (200-800 IU/d) for 24 weeks had a ≥ 25% relative decrease in IHTG by magnetic resonance spectroscopy. Paired liver biopsies at baseline and week 4 of treatment revealed a decrease in markers of hepatic de novo lipogenesis (DNL) that strongly predicted week 24 response. In vitro, using HepG2 cells and primary human hepatocytes, αT inhibited glucose-induced DNL by decreasing SREBP-1 processing and lipogenic gene expression. This mechanism is dependent on the antioxidant capacity of αT, as redox-silenced methoxy-αT is unable to inhibit DNL in vitro. OS by itself was sufficient to increase S2P expression in vitro, and S2P is upregulated in NAFLD livers. In summary, we utilized αT to demonstrate a vicious cycle in which NAFLD generates OS, which feeds back to augment DNL and increases steatosis. Clinicaltrials.gov: NCT01792115.

Use of human neuroblastoma SH-SY5Y cells to evaluate glyphosate-induced effects on oxidative stress, neuronal development and cell death signaling pathways

Glyphosate-containing herbicides are the most used agrochemicals in the world. Their indiscriminate application raises some concerns regarding the possible health and environmental hazards. In this study, we investigated in human neuroblastoma cell line SH-SY5Y if oxidative stress, altered neurodevelopment and cell death pathways are involved in response to glyphosate and its metabolite aminomethylphosphonic acid (AMPA) exposures. MTT and LDH assays were carried out to assess the glyphosate and AMPA cytotoxicity. Lipid peroxides measured as malondialdehyde (MDA), nitric oxide (NO) and reactive oxygen species (ROS) production, and caspase-Glo 3/7 activity were evaluated. The neuroprotective role of melatonin (MEL), Trolox, N-acetylcysteine (NAC) and Sylibin against glyphosate- and AMPA-induced oxidative stress was examined. Glyphosate and AMPA effects on neuronal development related gene transcriptions, and gene expression profiling of cell death pathways by Real-Time PCR array were also investigated. Glyphosate (5 mM) and AMPA (10 mM) induced a significant increase in MDA levels, NO and ROS production and caspase 3/7 activity. Glyphosate exposure induced up-regulation of Wnt3a, Wnt5a, Wnt7a, CAMK2A, CAMK2B and down-regulation of GAP43 and TUBB3 mRNA expression involved in normal neural cell development. In relation to gene expression profiling of cell death pathways, of the 84 genes examined in cells a greater than 2-fold change was observed for APAF1, BAX, BCL2, CASP3, CASP7, CASP9, SYCP2, TNF, TP53, CTSB, NFκB1, PIK3C3, SNCA, SQSTMT, HSPBAP1 and KCNIPI mRNA expression for glyphosate and AMPA exposures. These gene expression data can help to define neurotoxic mechanisms of glyphosate and AMPA. Our results demonstrated that glyphosate and AMPA induced cytotoxic effects on neuronal development, oxidative stress and cell death via apoptotic, autophagy and necrotic pathways and confirmed that glyphosate environmental exposure becomes a concern. This study demonstrates that SH-SY5Y cell line could be considered an in vitro system for pesticide screening.

Oxidative stress and related gene expression effects of cyfluthrin in human neuroblastoma SH-SY5Y cells: Protective effect of melatonin

This study was designed to assess oxidative stress induction in human neuroblastoma SH-SY5Y cells in response to cyfluthrin exposure. Cell viability MTT assay was carried out to assess cyfluthrin cytotoxicity; IC₃₀ and IC₅₀ values for cyfluthrin were calculated to be 4.81 ± 0.92 μM and 19.39 ± 3.44 μM, respectively. Cyfluthrin induced a significant increase in ROS generation, lipid peroxides measured as malondialdehyde (MDA) and nitric oxide (NO) production and a significant decrease in NQO1 activity. The antioxidant activity of melatonin (MEL), Trolox, N-acetylcysteine (NAC) and Sylibin against cyfluthrin-induced oxidative stress was examined. Cyfluthrin increased significantly gene expressions of apoptosis, proinflammation and oxidative stress (Bax, Bcl-2, Casp-3, BNIP3, AKT1, p53, APAF1, NFκB1, TNFα and Nrf2) mediators. In the most genes, the mRNA levels induced by cyfluthrin were partially reduced by MEL (1 μM). Cyfluthrin effects on gene expression profiling of oxidative stress pathway by Real-Time PCR array analysis showed that of the 84 genes examined, (fold change > 1.5) changes in mRNA levels were detected in 31 genes: 13 upregulated and 18 down-regulated. A fold change >3.0 fold was observed on upregulated CYBB, DUOX1, DUOX2, AOX1, BNIP3, HSPA1A, NOS2, and NQO1 genes. The greater fold change reversion (2.5 fold) by MEL (1 μM) was observed on cyfluthrin-upregulated CYBB, AOX1, BNIP3 and NOS2 genes. These results demonstrated that oxidative stress is a key element in cyfluthrin induced neurotoxicity as well as MEL may play a role in reducing cyfluthrin-induced oxidative stress.

Behaviour of Trolox with macromolecule-bound antioxidants in aqueous medium: Inhibition of auto-regeneration mechanism

This work aimed at investigating the behaviour of Trolox, vitamin E analogue, in presence of macromolecule-bound antioxidants in aqueous radical medium. Three main groups of macromolecule-bound antioxidants were assayed: dietary fiber (DF), protein and lipid-bound antioxidants, represented by whole wheat, soybean and olive oil products, respectively. Experimental studies were carried out in aqueous ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)) radical medium. Trolox and macromolecule-bound antioxidants were added to radical separately and together in different concentrations. Antioxidant capacities were determined using QUENCHER procedure. pH of radical media was altered for DF and protein-bound antioxidant studies to examine its effect. Chemometric tools were used for experimental design and multivariate data analysis. Results revealed antagonistic interactions for Trolox with all macromolecule-bound antioxidants. The reason behind this antagonism was investigated through oxidation reactions of Trolox via mass spectrometry analysis. Consequently, a proof was obtained for inhibitory effect of bound-antioxidants on auto-regeneration reactions of Trolox.

Fipronil sulfone induced higher cytotoxicity than fipronil in SH-SY5Y cells: Protection by antioxidants

Fipronil is a broad spectrum insecticide from the phenyl pyrazole family, which targets GABA receptor. Limited information is available about the metabolite fipronil sulfone cytotoxic actions. This study examined in vitro neurotoxicity of fipronil and fipronil sulfone and evaluated Trolox (vitamin E analog) (0.3, 1μM), N-acetyl-cysteine (0.5, 1mM), melatonin (0.1, 1μM) and Tempol (superoxide dismutase analog) (0.3, 0.5mM) protective role in SH-SY5Y cells. MTT and LDH assays were carried out to assess the cytotoxicity of fipronil and fipronil sulfone at 3-100μM concentrations. Fipronil sulfone was more toxic than fipronil. Tempol showed the best neuroprotectant profile against fipronil (50 and 150μM) and fipronil sulfone (3 and 10μM) reaching control levels. Fipronil (100μM) and fipronil sulfone (3μM) treatments induced a 4.7- and 5-fold increases in lipid peroxides measured as malondialdehyde (MDA) and a 2.2- and 2.0-fold increases in the levels of nitric oxide (NO). These results suggest that oxidative stress observed may be one of the major mechanisms of fipronil-induced neurotoxicity and it may be attributed in part to fipronil disposition and metabolism. Our results led us postulate that metabolite fipronil sulfone might be responsible for the fipronil-induced toxicity rather than fipronil itself.

Quantitative and antioxidative behavior of Trolox in rats' blood and brain by HPLC-UV and SMFIA-CL methods

Trolox, a water-soluble vitamin E analogue has been used as a positive control in Trolox equivalent antioxidant capacity and oxygen radical antioxidant capacity assays due to its high antioxidative effect. In this study, the ex vivo antioxidative effects of Trolox and its concentration in blood and brain microdialysates from rat after administration were evaluated by newly established semi-microflow injection analysis, chemiluminescence detection and HPLC-UV. In the administration test, the antioxidative effect of Trolox in blood and brain microdialysates after a single administration of 200 mg/kg of Trolox to rats could be monitored. The antioxidative effects in blood (12.0 ± 2.1) and brain (8.4 ± 2.1, × 10(3) antioxidative effect % × min) also increased. Additionally, the areas under the curve (AUC)s0-360 (n = 3) for blood and brain calculated with quantitative data were 10.5 ± 1.2 and 9.7 ± 2.5 mg/mL × min, respectively. This result indicates that Trolox transferability through the blood-brain barrier is high. The increase in the antioxidative effects caused by Trolox in the blood and brain could be confirmed because good correlations between concentration and antioxidative effects (r ≥ 0.702) were obtained. The fact that Trolox can produce an antioxidative effect in rat brain was clarified.

Quantifying small molecule phenotypic effects using mitochondrial morpho-functional fingerprinting and machine learning

In primary fibroblasts from Leigh Syndrome (LS) patients, isolated mitochondrial complex I deficiency is associated with increased reactive oxygen species levels and mitochondrial morpho-functional changes. Empirical evidence suggests these aberrations constitute linked therapeutic targets for small chemical molecules. However, the latter generally induce multiple subtle effects, meaning that in vitro potency analysis or single-parameter high-throughput cell screening are of limited use to identify these molecules. We combine automated image quantification and artificial intelligence to discriminate between primary fibroblasts of a healthy individual and a LS patient based upon their mitochondrial morpho-functional phenotype. We then evaluate the effects of newly developed Trolox variants in LS patient cells. This revealed that Trolox ornithylamide hydrochloride best counterbalanced mitochondrial morpho-functional aberrations, effectively scavenged ROS and increased the maximal activity of mitochondrial complexes I, IV and citrate synthase. Our results suggest that Trolox-derived antioxidants are promising candidates in therapy development for human mitochondrial disorders.

Synthesis, thermal and spectroscopic behaviors of metal-drug complexes: La(III), Ce(III), Sm(III) and Y(III) amoxicillin trihydrate antibiotic drug complexes

The metal complexes of Amoxicillin trihydrate with La(III), Ce(III), Sm(III) and Y(III) are synthesized with 1:1 (metal:Amox) molar ratio. The suggested formula structures of the complexes are based on the results of the elemental analyses, molar conductivity, (infrared, UV-visible and fluorescence) spectra, effective magnetic moment in Bohr magnetons, as well as the thermal analysis (TG), and characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results obtained suggested that Amoxicillin reacted with metal ions as tridentate ligands, coordinating the metal ion through its amino, imino, and β-lactamic carbonyl. The kinetic thermodynamic parameters such as: Ea, ΔH(*), ΔS(*) and ΔG(*) were estimated from the DTG curves.

Cytotoxicity induced by deltamethrin and its metabolites in SH-SY5Y cells can be differentially prevented by selected antioxidants

Deltamethrin, an α-cyano pyrethroid insecticide, is a relatively potent neurotoxicant. The main deltamethrin metabolism mechanisms are ester cleavage and oxidation at the 2' and 4' position of the terminal aromatic ring. Although some aspects of the toxicity properties of deltamethrin have been reported, limited information is available about the metabolites cytotoxic actions. The aims of this study are to examine in vitro neurotoxicity of deltamethrin and its metabolites 3-phenoxybenzoic acid (3-PBA), 2'-OH-deltamethrin, and 4'-OH-deltamethrin and to evaluate melatonin (0.1, 1μM), trolox (0.3, 1μM) and N-acetylcysteine (500, 1000μM) protective role in SH-SY5Y cells. MTT and neutral red uptake (NRU) assays were carried out to assess the cytotoxicity of deltamethrin and its metabolites. Of the three metabolites tested, while 3-PBA (0.01-1000μM) did not show neurotoxicity, 2'-OH- and 4'-OH-deltamethrin (10-1000μM) were more toxic than deltamethrin (10-1000μM). Levels of both nitric oxide (NO) and lipid peroxides measured as malondialdehyde were significantly increased in deltamethrin and 4'-OH-deltamethrin-treated cells. Compared to other antioxidants, 1μM MEL treatment effectively protected against deltamethrin and 4'-OH-deltamethrin-induced lipid peroxidation and ameliorated the NO adverse effect that might have been caused. These results suggest that oxidative stress observed is one of the major mechanisms of deltamethrin-induced neurotoxicity and it may be attributed in part to deltamethrin disposition and metabolism.

Protective Effects of Corni Fructus against Advanced Glycation Endproducts and Radical Scavenging

We investigated the inhibition of advanced glycation endproduct (AGE) activity using the fluorescence characteristics of fractions and compounds from Corni Fructus. Corni Fructus extract and its iridoid glycoside components showed low inhibitory activities as well as the AGE inhibitor aminoguanidine. However, a low molecular weight polyphenol, 7-O-galloyl-D-sedoheptulose, and an antioxidant, trolox, showed high inhibitory activities compared with aminoguanidine under reactive conditions. The AGE-inhibiting activity of polyphenolic fractions of Corni Fructus ranged from a level comparable to Corni Fructus extract to the higher level of 7-O-galloyl-D-sedoheptulose. As well as the results of AGE-inhibiting activity, Corni Fructus extract and iridoid components showed low or no 1,1-diphenyl-2-pycrylhydrazyl (DPPH) radical-scavenging activities, whereas 7-O-galloyl-D-sedoheptulose showed a level comparable to trolox. Polyphenolic fractions of Corni Fructus quenched DPPH radicals in a concentration-dependent manner. Some fractions exerted a higher DPPH radical-scavenging activity compared with trolox and 7-O-galloyl-D-sedoheptulose. The DPPH radical-scavenging activity was significantly correlated with the AGE-inhibiting activity. These results suggest that polyphenolic fractions of Corni Fructus inhibited AGE formation by antioxidant activity including free radical scavenging. The strong DPPH radical-scavenging and AGE-inhibiting fractions included ellagitannins and polymeric proanthocyanidins.

Mechanisms of sulfur mustard analog 2-chloroethyl ethyl sulfide-induced DNA damage in skin epidermal cells and fibroblasts

Employing mouse skin epidermal JB6 cells and dermal fibroblasts, here we examined the mechanisms of DNA damage by 2-chloroethyl ethyl sulfide (CEES), a monofunctional analog of sulfur mustard (SM). CEES exposure caused H2A.X and p53 phosphorylation as well as p53 accumulation in both cell types, starting at 1h, that was sustained for 24h, indicating a DNA-damaging effect of CEES, which was also confirmed and quantified by alkaline comet assay. CEES exposure also induced oxidative stress and oxidative DNA damage in both cell types, measured by an increase in mitochondrial and cellular reactive oxygen species and 8-hydroxydeoxyguanosine levels, respectively. In the studies distinguishing between oxidative and direct DNA damage, 1h pretreatment with glutathione (GSH) or the antioxidant Trolox showed a decrease in CEES-induced oxidative stress and oxidative DNA damage. However, only GSH pretreatment decreased CEES-induced total DNA damage measured by comet assay, H2A.X and p53 phosphorylation, and total p53 levels. This was possibly due to the formation of GSH-CEES conjugates detected by LC-MS analysis. Together, our results show that CEES causes both direct and oxidative DNA damage, suggesting that to rescue SM-caused skin injuries, pleiotropic agents (or cocktails) are needed that could target multiple pathways of mustard skin toxicities.

rac-6-Hy-droxy-2,5,7,8-tetra-methyl-chroman-2-carboxamide from synchrotron data

The crystal structure of the title water-soluble analogue of vitamin E, trolox amide, C₁₄H₁₉NO₃, solved and refined against synchrotron diffraction data, contains two mol­ecules in the asymmetric unit. In both molecules, the heterocyclic ring is in a half-chair conformation. The crystal packing features a herring-bone pattern generated by N—H⋯O hydrogen bonds between the hy­droxy and amide groups. O—H⋯O hydrogen bonds also occur.

Quenching mechanisms and kinetics of Trolox and ascorbic acid on the riboflavin-photosensitized oxidation of tryptophan and tyrosine

The effects of 0, 0.3, 0.6, and 0.9 mM Trolox and ascorbic acid on the singlet oxygen oxidation of tryptophan and tyrosine containing 25 ppm of riboflavin were determined by measuring tryptophan and tyrosine concentration by high-performance liquid chromatography analysis. The samples were stored in the a 1000 lx light storage box for 4 h at 30 degrees C. As the concentration of Trolox and ascorbic acid increased, the degradation of tryptophan and tyrosine decreased significantly at p < 0.05. Trolox reduced tryptophan and tyrosine degradation by quenching both singlet oxygen and excited triplet riboflavin, whereas ascorbic acid quenched singlet oxygen only. The total singlet oxygen quenchings of Trolox in the presence of tryptophan and tyrosine were 1.55 x 10(7) and 1.32 x 10(7) M(-1) s(-1), respectively. The total singlet oxygen quenchings of ascorbic acid in the presence of tryptophan and tyrosine were 1.16 x 10(7) and 1.10 x 10(7) M(-1) s(-1), respectively. Trolox was more effective than ascorbic acid in preventing the degradation of tryptophan and tyrosine.

One-electron oxidation of "photo-Fenton" reagents and inhibition of lipid peroxidation

The "photo-Fenton" reagent, 2-mercaptopyridine N-oxide (MPO), which releases a hydroxyl radical on ultraviolet irradiation, has been found to act as an antioxidant. In the peroxidation of linoleate initiated by a water-soluble azo-initiator, MPO has about one-third the activity of the water-soluble vitamin E analogue Trolox C. In contrast, the oxygen-containing analogue, 2-hydroxypyridine N-oxide (HPO), does not have measurable antioxidant activity in this system. Both reagents react with hydroxyl radical with second order rate constants very close to the diffusion-controlled limit. With the less oxidising dithiocyanate radical anion, MPO reacts approximately 50 times more rapidly than HPO at pH>7. The more reducing properties of MPO result in its activity as an antioxidant and make it less suitable than HPO as a source of hydroxyl radicals for investigation of oxidative stress in biological systems.

Identification of 8-iso-prostaglandin F(2alpha) in rat brain neuronal endings: a possible marker of membrane phospholipid peroxidation

Isoprostanes are a family of prostaglandin (PG) F and E isomers generated by free-radical attack from membrane bound arachidonic acid. We measured detectable levels of 8-iso-PGF(2alpha) in the perfusates of synaptosomes obtained from different areas of the rat brain cortex. A small but significant release of this isoprostane was found under basal conditions from all the areas explored; being lower in the dorsal cortex in respect to the frontal, parietal and occipital areas. Exposure of synaptosomes to a phospholipase A(2) activator, i.e. calcium-ionophore A23187, an oxidant agent, such as hydrogen peroxide or amyloid beta-peptide did not modify 8-iso-PGF(2alpha) release when these stimuli were applied separately. However, either hydrogen peroxide or amyloid beta-peptide increased 8-iso-PGF(2alpha) release in a dose-dependent manner, when given in the presence of the calcium-ionophore A23187. Synaptosome treatment with a non-selective cyclooxygenase inhibitor (fenoprofen) did not modify 8-iso-PGF(2alpha) release in any way, but treatment with a water soluble antioxidant (Trolox C) completely suppressed isoprostane release under basal conditions, as well as after the oxidant injury induced either by hydrogen peroxide or amyloid beta-peptide. We conclude that, in neuronal endings, 8-iso-PGF(2alpha) is generated under basal conditions and its formation may be increased in a dose-dependent fashion by oxidant stimuli through a cyclooxygenase-independent mechanism involving free radical-catalyzed oxidation of arachidonic acid on membrane phospholipids.

Partitioning and antioxidant action of the water-soluble antioxidant, Trolox, between the aqueous and lipid phases of phosphatidylcholine membranes: 14C tracer and product studies

The water-soluble antioxidant, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic (Trolox), (4-14C)-labelled, was used to trace its location in the aqueous and lipid phases of liposomes. Trolox was found to partition 20 to 25% into the lipid phase of multilamellar (MLV) and 38-46% into the lipid phase of unilamellar (ULV) egg lecithin liposomes. Trolox and its oxidation products partition readily (40%) into the lipid phase of dilinoleoylphosphatidylcholine (DLPC) MLV liposomes during inhibited peroxidation, thermally initiated by azo-bis(2,4-dimethylvaleronitrile) (ADVN). The time-course of the consumption of Trolox during peroxidation of DLPC liposomes, initiated by ADVN, was followed by separation and analyses of [4-14C]Trolox and its oxidation products. Such studies showed that the consumption of Trolox followed the profile of the inhibition of oxygen uptake. This indicates that Trolox can be used in quantitative studies of membrane peroxidation; for example, to measure the rate of chain initiation (Ri). The product distribution of hydroperoxides, the 9- and 13-cis,trans (c,t) and trans,trans (t,t) isomers, formed during inhibited peroxidation of linoleate, in DLPC and methyl linoleate in dimyristoyl PC (DMPC) liposomes was determined by HPLC of the derived hydroxy methyl esters. The c,t/t,t (kinetic/thermodynamic) ratios were related to the antioxidant activity of the inhibitors. Both Trolox and alpha-tocopherol (vitamin E) gave relatively high initial c,t/t,t ratios (6.6 and 7.1) during inhibited peroxidation of DLPC, initiated by water-soluble azo-bis(2-amidinopropane.HCl) (ABAP). High initial c,t/t,t ratios (6.2) were also observed for alpha-tocopherol-inhibited peroxidation of DLPC liposomes, initiated by lipid-soluble ADVN. On the other hand, the combination of Trolox with ADVN-initiated peroxidation of DLPC or of methyl linoleate in DMPC gave relatively low initial c,t/t,t ratios of 3.5 and 1.3. These results are interpreted in terms of the relative hydrogen atom donating ability of the antioxidants and the homogeneity of the system used. The 9/13 ratios of hydroperoxides were constant (0.9 to 1.0) in all experiments and did not give evidence for preferential trapping by Trolox of peroxyls at the 9-position.

Chemical syntheses of Trolox conjugates which protect human ventricular myocytes against in situ-generated oxyradicals

Synthetic conjugates of the antioxidant Trolox (6-hydroxy-2,5,7,8-tetramethyl chroman-2-carboxylic acid) have been prepared by coupling it with 1-ethyl-3-(3-dimethyl-amino-propyl) carbodiimide hydrochloride either to p-aminophenyl-beta-D-lactopyranoside, or to higher molecular weight ligands such as dextran and polylysine. Compared to Trolox and on a mole to mole basis, dextran-Trolox is almost equally active, while lactosylphenyl- and polylysine-Trolox conjugates are distinctly more active in preventing the damage on human ventricular myocytes by oxyradicals generated from xanthine oxidase-hypoxanthine. Listed in order of decreasing cytoprotective activity, they are: lactosylphenyl-Trolox >> polylysine-Trolox > Trolox > dextran-Trolox. Thus, Trolox can be chemically modified by coupling it to one of a number of ligands and, in some cases, with resultant increases in its ability to protect human ventricular myocytes from oxyradical damage.

Oxygen-dependent antagonism of lipid peroxidation

Measurements of the rates for formation of conjugated dienes, malonylaldehyde, and lipid hydroperoxides show that increasing the concentration of O2 from 0.11 mM to 0.35 mM or 0.69 mM can slow the rate of linoleic acid peroxidation in a xanthine oxidase/hypoxanthine system. This effect is seen at pH 7.0 but not 7.4 and depends on the presence of monounsaturated fatty acids (oleic, cis, or trans vaccenic acid). Oxygen antagonism of ascorbic acid-iron-EDTA mediated lipid peroxidation is similarly dependent on fatty acid mixtures and occurs at pH 5.0 and 6.0 but not 7.0. The efficiency of initiation of peroxidation in the xanthine oxidase system is unaffected by monounsaturated fatty acids and O2 concentration. Increasing the O2 concentration increases the rate of superoxide radical production, but there is no change in salicylate hydroxylation (e.g., OH. production) or ferrous ion concentration. Oxygen-mediated slower rates of lipid peroxidation are associated with either increased H2O2 production or, based on an indirect assay, singlet O2 production. Increased O2 concentrations increase the rate of azobisisobutyronitrile-initiated lipid peroxidation as expected but addition of exogenous superoxide radicals slows the rate. Under similar conditions superoxide reacts with fatty acids to produce singlet O2. Overall, the data suggest that O2-mediated antagonism occurs because of termination reactions between hydroperoxyl (HO2.) and organic radicals, and singlet O2 or H2O2 are products of these reactions.

Effects of 2,2'-azobis (2-amidinopropane) hydrochloride in vivo and protection by vitamin E

2,2'-Azobis (2-amidinopropane) hydrochloride (AAPH), a compound that decomposes spontaneously to generate free radicals, was administered intraperitoneally to rats. High doses (greater than or equal to 70 mg/kg) were always fatal within a few hours. At nonlethal levels, AAPH was found to be absorbed into the circulation where it remained with a half-life of about 30 min. Lipid peroxidation was observed to occur in the liver and, to a much smaller extent, the kidney and heart of treated rats; levels of thiobarbituric acid-reactive substances were unchanged in the lung and brain, and significantly reduced in the plasma. Serum lipid levels were also lower in the AAPH-treated rats. Orally administered vitamin E, but not its water soluble analog, prevented the accumulation of TBA-reactive substances in the livers of AAPH-treated rats in a dose-dependent manner, but had no effect on mortality or the changes in serum lipid levels. The data suggest that intraperitoneally administered AAPH is absorbed into the circulation and can induce lipid peroxidation in vivo, but that toxicity may also arise through nonradical mechanisms. Furthermore, the free radical toxicity of AAPH in vivo may not be so general as previously suggested.

Repair of amino acid radicals by a vitamin E analogue

Free radicals derived from one-electron oxidation of the amino acids tryptophan, tyrosine, methionine and histidine have been found to be rapidly (k = 10(7) -10(9) dm3 mol-1 s-1) and efficiently repaired by Trolox C, a vitamin E analogue. The reactions form a relatively stable phenoxyl radical of Trolox C (lambda max = 440 nm; epsilon = 5.4 X 10(3) mol dm-3 cm-1). The radical cation of tryptophan is more rapidly repaired than the neutral tryptophan radical. Repair of tryptophanyl radicals in the enzyme lysozyme has also been observed. The results suggest that a function of alpha-tocopherol in membranes may be the repair of radicals of integral membrane proteins.

Differential inhibitory effects of vitamin E and other antioxidants on prostaglandin synthetase, platelet aggregation and lipoxidase

Prostaglandin biosynthesis from eicosa-8,11,14-trienoic acid in microsomes from the bovine vesicular gland is inhibited by the antioxidants alpha-naphthol. guaiacol, NDGA and propyl gallate. Prostaglandin biosynthesis in this system is not inhibited by the antioxidants BHT, DL-alpha-tocopherol and Trolox C. Arachidonic acid induced platelet aggregation is inhibited by specifically by alpha-naphthol. guaiacol, NDGA and propyl gallate. Both arachidonic acid induced platelet aggregation and ADP induced platelet aggregation are inhibited non-specifically by the antioxidants BHT, DL-alpha-tocopherol and Trolox C. All antioxidants tested in this study inhibit soybean lipoxidase. Thus alpha-naphthol, NDGA and propyl gallate are non-specific inhibitors of both prostaglandin synthetase and soybean lipoxidase while BHT, DL-alpha-tocopherol and Trolox C are specific inhibitors of soybean lipoxidase alone.