Selective sensitization of chemiluminescence resulted from lipid and oxygen radical reactions

A concise appraisal of lipid oxidation and lipoxidation in higher plants

Polyunsaturated fatty acids present in plant membranes react with reactive oxygen species through so-called lipid oxidation events. They generate great diversity of highly-reactive lipid-derived chemical species, which may be further degraded enzymatically or non-enzymatically originating new components like Reactive Carbonyl Species (RCS). Such RCS are able to selectively react with proteins frequently producing loss of function through lipoxidation reactions. Although a basal concentration of lipoxidation products exists in plants (likely involved in signaling), their concentration and variability growth exponentially when plants are subjected to biotic/abiotic stresses. Such conditions typically increase the presence of ROS and the expression of antioxidant enzymes, together with RCS and also metabolites resulting from their reaction with proteins (advanced lipoxidation endproducts, ALE), in those plants susceptible to stress. On the contrary, plants designed as resistant may or may not display enhanced levels of ROS and antioxidant enzymes, whereas levels of lipid oxidation markers as malondialdehyde (MDA) are typically reduced. Great efforts have been made in order to develop methods to identify and quantify RCS, ALE, and other adducts with high sensitivity. Many of these methods are applied to the analysis of plant physiology and stress resistance, although their use has been extended to the control of the processing and conservation parameters of foodstuffs derived from plants. These foods may accumulate either lipid oxidation/lipoxidation products, or antioxidants like polyphenols, which are sometimes critical for their organoleptic properties, nutritional value, and health-promoting or detrimental characteristics. Future directions of research on different topics involving these chemical changes are also discussed.

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Lipid (per)oxidation occurs in plants as a signaling mechanism and after stress.

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Electrophylic mediators are widely used to assess plant physiology.

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Few lypoxidation targets have been identified in plants, mainly related to stress.

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Lipoxidation frequently inactivates or highly affects enzyme activity in plants.

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Lipid oxidation/lipoxidation affect the quality and healthy properties of plant foods.

Quinolizin-coumarins as physical enhancers of chemiluminescence during lipid peroxidation in live HL-60 cells

We investigated whether physical enhancers of low-level chemiluminescence-coumarin laser dyes C-314, C-334, and C-525--may be used to monitor interactions of lipid peroxyl radicals during lipid peroxidation in live cells. We present data demonstrating that two quinolizin-substituted coumarins--C-525 and C-334--can be integrated into HL-60 cells and successfully used as physical enhancers of chemiluminescence induced by the lipid soluble azo-initiator 2,2'-azobis(2,4-dimethyl-valeronitrile) (AMVN). Coumarins did not inhibit AMVN-induced peroxidation of membrane phospholipids in HL-60 cells, and no consumption of these coumarins occurred in the course of AMVN-induced oxidative stress. Redox status, evaluated by intracellular GSH content, remained unchanged after treatment with the coumarins. tert-Butyl hydroperoxide and cumene hydroperoxide (more hydrophilic oxidants) induced a lower chemiluminescence signal with both coumarins. Viability of HL-60 cells was not affected by coumarins both in the presence and in the absence of oxidants. Based on these results we conclude that quinolizin-substituted coumarins represent a promising class of physical enhancers of chemiluminescence for monitoring free radical peroxidation in live cells.

Oxygen radical generation of neutrophils: a reason for oxidative stress during marathon running?

Hematological parameters and blood markers that indicate oxidative stress, such as lipid peroxides (LPO), reduced and oxidized glutathione (GSH, GSSG), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), were measured in 18 marathon runners before, immediately after the race, and after 8 days of rest. In parallel, the oxygen radical generation of neutrophils (PMN) was measured by chemiluminescence in six randomly selected runners. After the race, a 4.4-fold enhanced PMN count and a 1.4-fold increased capacity to generate oxygen radicals of the PMN (2.20+/-0.38 vs. 3.12+/-0.69 arb. unit/10(6) cells) were found. Consequently, a 6.25-fold increased capacity to generate oxygen radicals of the post-run blood (7.26+/-1.3 vs. 45.40+/-10.3 arb. unit/ml blood) was calculated. This points to PMN as an important oxygen radical source established in the runners' blood, which could contribute to the oxidative stress indicated in the post-run blood by increased LPO (11.46+/-3.09 vs. 13.09+/-3.14 micromol/l plasma), GSSG (0.038+/-0.003 vs. 0.045+/-0. 005 mmol/l blood) and GSSG/GSH ratio (3.8+/-0.5 vs. 4.1+/-0.6%) and by decreased SOD (15.63+/-1.78 vs. 14.58+/-1.51 10(3)U/mmol Hb) and GSH-Px (485.1+/-107.1 vs. 434.9+/-101.7 U/mmol Hb). Despite the decline of the oxygen radical source during rest, the oxidative stress in the blood did not decrease in all runners.

Lipid peroxidation: a review of causes, consequences, measurement and dietary influences

In this review the process of lipid peroxidation and the atherogenicity of peroxidied lipids are discussed. Recent findings with regard to the effect of selected dietary factors on susceptibility of lipids to oxidative stress and on antioxidant defences are analysed with particular reference to their potential use in the prevention and treatment of atherogenesis and, by extension, coronary heart disease. Laboratory methods of assessing antioxidant defences, lipid peroxidation and the effects of lipid peroxidation are also reviewed and discussed with particular reference to their ability to assess in vivo oxidative stress and lipid peroxidation status. A range of oxidative stress indices are presented and their limitations discussed, but the main focus is on the most commonly used laboratory test for lipid peroxidation, the thiobarbituric acid reacting substances (TBARS) test. Finally, the influence of selected dietary factors on measured peroxidation status is discussed, with particular reference to the antioxidant vitamins C (ascorbic acid) and E (alpha tocopherol) and the type of fatty acids (mono- and poly-unsaturated) in the diet.

Assessment of the C-525 laser dye as a chemiluminescence sensitizer for lipid peroxidation in biological membranes: a comparison with chlorophyll-a

The C-525 laser dye at micromolar concentration range is shown to enhance up to two to three orders of magnitude the chemiluminescence (CL) accompanying tert-butyl hydroperoxide (t-BHP)-induced rat liver microsome oxidation and Fe(2+)-induced lipid peroxidation (LPO) in liposomes. C-525 is shown to be a more efficient sensitizer of CL accompanying LPO in membrane systems than the known low-energy excited triplet carbonyl sensitizer, chlorophyll-alpha, (Cl-a). Regarding the sensitization mechanism, C-525 and Cl-a were compared in (a) a peroxyl radical-producing system (2,2'-azobis(2-dimethylvaleronitrile) (AMVN); (b) excited carbonyl-producing systems (3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane (HTMD) thermal decomposition and horseradish peroxidase (HRP)-catalyzed isobutanal oxidation); and (c) excited singlet oxygen-producing system [endoperoxide of 3,3-(1,4-naphthylidene)-dipropionate (NDPO2)]. C-525 sensitized CL only in the systems where peroxyl radical and/or triplet excited carbonyls are produced, the mechanism of CL sensitization apparently is energy transfer from the excited triplet carbonyls formed in the peroxyl radical self-reaction via Russell's mechanism or by dioxetane decomposition. Cl-a was found to considerably sensitize CL related to NDPO2 thermal decomposition, a source of singlet oxygen, in addition to acting as a sensitizer of triplet carbonyl CL. The chemical stability of the C-525 laser dye in excited state-generating systems was shown to be appropriate for its application as a sensitizer of CL related to LPO reactions in membranes, but not in the HRP-catalyzed peroxidation system.

Coumarin derivatives enhance the chemiluminescence accompanying lipid peroxidation

The effect of laser dyes, derivatives of 1,2-benzopyrone (coumarin), on the chemiluminescence (CL) accompanying Fe(2+)-induced lipid peroxidation (LPO) in liposomes prepared from egg yolk phospholipids has been investigated. It was found that quinolizin (9a,9,1-gh)-substituted coumarins enhanced CL at the stages of "fast" and "slow" flashes (abbreviated as FF and SF, respectively), which are known to accompany lipid hydroperoxide decomposition (FF) and chain LPO reaction development (SF). On the other hand, these compounds did not virtually change the shape of CL curve (in particular, lag phase duration) and accumulation of the LPO products reacting with 2-thiobarbituric acid (TBARS). The dependences of FF and SF amplitudes on the concentration of coumarins exhibited for some compounds an effect of saturation with subsequent decrease of CL at high concentrations of the dyes. The highest degree of CL amplification was reached with the compound 2,3,5,6-1H,4H-tetrahydro-9-(2'-benzoimidazolyl)-quinolizin- (9,9a,1-gh)coumarin (C-525), which enhanced CL at the stages of FF and SF by a factor 1600 at a dye concentration of 8 nmoles/mg of phospholipid. On the other hand, C-525 did not increase the intensity of CL associated with the decomposition of H2O2 by Fe2+ ions (Fenton's reaction). Apparently, these coumarin sensitizers may be used for selective enhancement of CL associated with LPO both in experimental and clinical investigations.

On the use of the quenching of luminol luminescence to evaluate SOD activity

Addition of horseradish peroxidase to a luminol solution (pH = 9.4) produces a burst of light followed by a steady luminescence that lasts for several minutes. This steady-state luminescence is readily quenched by SOD, with a Q1/2 concentration (the additive concentration needed to decrease by one-half the emitted luminescence intensity) of c.a. 4 ng/ml (14 mU/ml). The luminescence intensity decrease can then be employed to evaluate SOD activity in SOD-containing samples. However, the light intensity can also be quenched by additives, such as Trolox, that are able to trap luminol-derived intermediates. It is proposed that double quenching experiments must be performed in order to be able to relate the observed effect of an additive to its SOD-like activity.

Fe(2+)-induced lipid peroxidation kinetics in liposomes: the role of surface Fe2+ concentration in switching the reaction from acceleration to decay

Kinetics of malonyldialdehyde (MDA) accumulation, Fe2+ oxidation, and chemiluminescence (CL) at different initial iron ([Fe2+]) and liposome ([L]) concentrations were measured in liposome suspension. Above certain critical Fe2+ concentrations ([Fe2+]*) the latent period (LP) of LPO development was observed. The method of [Fe2+]* estimation by the dependence of LP value (tau) on [Fe2+] was elaborated. The increase of [L] resulted in decrease of tau and increase of delta MDA as well as SF CL amplitude. [Fe2+]* value changed from 10 to 50 microM with change of [L] from 1 to 4 mg/ml, so that the ratio [Fe2+]*/[L] was kept constant. This may be explained under the assumption that the major part of Fe2+ is bound by the membranes. At concentrations of Fe2+ higher than the critical one, iron chelators (desferrioxamine, o-phenanthroline, and EDTA) and cations (Eu3+, Ca2+, and Fe3+) decreased tau without any essential influence on the CL "slow flash" amplitude (h). Apparently, the only result of iron complexones and cations on LPO is the decrease of Fe2+ ion concentration on the membrane surface. Thus, [Fe2+]* value and surface concentration of Fe2+ are the main parameters determining both kinetics and efficiency of Fe(2+)-induced LPO in membrane systems.

Enhancement of chemiluminescence associated with lipid peroxidation by rhodamine dyes

Rhodamine Zn in concentrations of 300-500 mumole/l enhances Fe(2+)-induced chemiluminescence (CL) in blood serum, liposome and lipoprotein suspensions by two orders of magnitude. Several different rhodamines were compared, chemiluminescence spectra were measured and relationships between dye concentration, medium composition and CL intensity were studied.

Are dioxetanes chemiluminescent intermediates in lipoperoxidation?

Ultraweak chemiluminescence arising from lipoperoxidation has been attributed by several authors to the radiative deactivation of singlet oxygen and triplet carbonyl products. The latter emitters have been suggested to come from annihilation of RO. and ROO. radicals as well as from the thermolysis of dioxetane intermediates formed by (2 + 2) cycloaddition of 1O2 to polyunsaturated fatty acids. This article questions possible dioxetane intermediacy in lipoperoxidation, as the literature clearly states that addition of 1O2 to alpha-hydrogen-containing alyphatic olefins yields only the corresponding allylic hydroperoxides. These compounds may undergo dark thermal or Lewis acid-assisted decomposition to the same product obtained from dioxetane cleavage. Here, reexamining the chemiluminescence properties of dioxygenated tetramethylethylene and linoleic acid and comparing them with those of tetraethyldioxetane, a hindered dioxetane, we corroborate the literature information that only steric hindrance leads to dioxetane formation upon singlet oxygen addition to electron-poor olefins, albeit in very low yields. Proton nuclear magnetic resonance (1H-NMR) analysis, quenching by dioxygen and energy transfer studies to 9,10-dibromoanthracene, as well as gas chromatography (GC) analysis of triphenylphosphine-treated and untreated photo- and chemically dioxygenated olefins support our final conclusion that dioxetane formation during lipoperoxidation can be safely excluded on the basis of the data presently available.

Antioxidant action of ubiquinol homologues with different isoprenoid chain length in biomembranes

Ubiquinones (CoQn) are intrinsic lipid components of many membranes. Besides their role in electron-transfer reactions they may act as free radical scavengers, yet their antioxidant function has received relatively little study. The efficiency of ubiquinols of varying isoprenoid chain length (from Q0 to Q10) in preventing (Fe2+ + ascorbate)-dependent or (Fe2+ + NADPH)-dependent lipid peroxidation was investigated in rat liver microsomes and brain synaptosomes and mitochondria. Ubiquinols, the reduced forms of CoQn, possess much greater antioxidant activity than the oxidized ubiquinone forms. In homogenous solution the radical scavenging activity of ubiquinol homologues does not depend on the length of their isoprenoid chain. However in membranes ubiquinols with short isoprenoid chains (Q1-Q4) are much more potent inhibitors of lipid peroxidation than the longer chain homologues (Q5-Q10). It is found that: i) the inhibitory action, that is, antioxidant efficiency of short-chain ubiquinols decreases in order Q1 greater than Q2 greater than Q3 greater than Q4; ii) the antioxidant efficiency of long-chain ubiquinols is only slightly dependent on their concentrations in the order Q5 greater than Q6 greater than Q7 greater than Q8 greater than Q9 greater than Q10 and iii) the antioxidant efficiency of Q0 is markedly less than that of other homologues. Interaction of ubiquinols with oxygen radicals was followed by their effects on luminol-activated chemiluminescence. Ubiquinols Q1-Q4 at 0.1 mM completely inhibit the luminol-activated NADPH-dependent chemiluminescent response of microsomes, while homologues Q6-Q10 exert no effect. In contrast to ubiquinol Q10 (ubiquinone Q10) ubiquinone Q1 synergistically enhances NADPH-dependent regeneration of endogenous vitamin E in microsomes thus providing for higher antioxidant protection against lipid peroxidation. The differences in the antioxidant potency of ubiquinols in membranes are suggested to result from differences in partitioning into membranes, intramembrane mobility and non-uniform distribution of ubiquinols resulting in differing efficiency of interaction with oxygen and lipid radicals as well as different efficiency of ubiquinols in regeneration of endogenous vitamin E.