Free radical chain oxidation and hemolysis of erythrocytes by molecular oxygen and their inhibition by vitamin E

Lipid oxidation that is, and is not, inhibited by vitamin E: Consideration about physiological functions of vitamin E

Lipids are oxidized in vivo by multiple oxidizing species with different properties, some by regulated manner to produce physiological mediators, while others by random mechanisms to give detrimental products. Vitamin E plays an important role as a physiologically essential antioxidant to inhibit unregulated lipid peroxidation by scavenging lipid peroxyl radicals to break chain propagation independent of the type of free radicals which induce chain initiation. Kinetic data suggest that vitamin E does not act as an efficient scavenger of nitrogen dioxide radical, carbonate anion radical, and hypochlorite. The analysis of regio- and stereo-isomer distribution of the lipid oxidation products shows that, apart from lipid oxidation by CYP enzymes, the free radical-mediated lipid peroxidation is the major pathway of lipid oxidation taking place in humans. Compared with healthy subjects, the levels of racemic and trans,trans-hydro (pero)xyoctadecadienoates, specific biomarker of free radical lipid oxidation, are elevated in the plasma of patients including atherosclerosis and non-alcoholic fatty liver diseases. α-Tocopherol acts as a major antioxidant, while γ-tocopherol scavenges nitrogen dioxide radical, which induces lipid peroxidation, nitration of aromatic compounds and unsaturated fatty acids, and isomerization of cis-fatty acids to trans-fatty acids. It is essential to appreciate that the antioxidant effects of vitamin E depend on the nature of both oxidants and substrates being oxidized. Vitamin E, together with other antioxidants such as vitamin C, contributes to the inhibition of detrimental oxidation of biological molecules and thereby to the maintenance of human health and prevention of diseases.

Method to Improve Azo-Compound (AAPH)-Induced Hemolysis of Erythrocytes for Assessing Antioxidant Activity of Lipophilic Compounds

We examined the method of oxidative hemolysis for assessment of antioxidant activity of various compounds, especially lipophilic compounds. 2,2'-Azobis(amidinopropane) dihydrochloride (AAPH) was used as the source of free radicals for the oxidative hemolysis of horse erythrocytes. We found that absorbance at 540 nm is not appropriate for monitoring AAPH-induced hemolysis. Instead, we should use absorbance at 523 nm (an isosbestic point), because AAPH oxidizes the oxygenated hemoglobin to methemoglobin and absorbance at 540 nm does not correctly reflect the amount of released hemoglobin by AAPH-induced hemolysis. The corrected method of AAPH-induced hemolysis was applicable to assess the antioxidant activity of various hydrophilic compounds such as ascorbic acid, (-)-epicatechin, and edaravone. For the assessment of antioxidant activity of lipophilic compounds, we need appropriate dispersing agents for these lipophilic compounds. Among several agents tested, 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC) liposome at a concentration of 0.34 mM was found to be useful. Exogenous α-tocopherol incorporated using DMPC liposome as a dispersing agent was shown to protect erythrocytes from AAPH-induced hemolysis in a concentration-dependent manner.

Azocompounds as generators of defined radical species: Contributions and challenges for free radical research

Peroxyl radicals participate in multiple processes involved in critical changes to cells, tissues, pharmacueticals and foods. Some of these reactions explain their association with degenerative pathologies, including cardiovascular and neurological diseases, as well as cancer development. Azocompounds, and particularly AAPH (2,2'-Azobis(2-methylpropionamidine) dihydrochloride), a cationic water-soluble derivative, have been employed extensively as sources of model peroxyl radicals. A considerable number of studies have reported mechanistic data on the oxidation of biologically-relevant targets, the scavenging activity of foods and natural products, and the reactions with, and responses of, cultured cells. However, despite the (supposed) experimental simplicity of using azocompounds, the chemistry of peroxyl radical production and subsequent reactions is complicated, and not always considered in sufficient depth when analyzing experimental data. The present work discusses the chemical aspects of azocompounds as generators of peroxyl (and other) radicals, together with their contribution to our understanding of biochemistry, pharmaceutical and food chemistry research. The evidence supporting a role for the formation of alkoxyl (RO•) and other radicals during thermal and photochemical decomposition of azocompounds is assessed, together with the potential influence of such species on the reactions under study.

Investigation of antioxidant and antihemolytic activities of Algerian defatted olive fruits (olea europaea L.) at two ripening stages

BACKGROUND: Olive fruits have become extremely valuable because they have important nutrient properties and have shown positive benefits for human health. The chemical composition and organoleptic characteristics may be influenced by genotype and some agronomic factors like olive drupe harvesting date. OBJECTIVE: In this study, the greatest interest is to clarify and to give more information for Algerian Olea europaea L. by investigation of their total phenolic and flavonoid contents, phenolic compounds identification, total antioxidant capacity and antihemolytic activity at two levels of the olive ripening process. METHODS: Colorimetric methods were used to quantify total phenolic and flavonoid contents. The phenolic composition was done by HPLC technique. The antioxidant activity was assessed by measuring radical scavenging activity against 2,2’-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) radical cation (ABTS• +) expressed as Trolox Equivalent Antioxidant Capacity (TEAC), Ferric Reducing Antioxidant Power (FRAP) and antihemolytic activity. RESULTS: The harvesting time effect on HPLC analysis of olive fruits was significant. Interestingly, the phenolic composition of the olive fruits differed greatly between samples. Two compounds usually not described in olive fruit were identified, namely morine dihydrate and coumarin. The amounts of total phenolics varied widely in the investigated extracts and ranged from 495 to 2325 mg GAE/100 g for black olives and from 865 to 2387 mg GAE/100 g for green olives, whereas the flavonoids content expressed as rutin equivalent per 100 gram of defatted dry matter was ranged between 155 and 354 mg/100 g for green olives and between 214 and 260 mg/100 g for black olives. The antioxidant activity of black and green olives ranged from 5.86 and 4.88 to 59.44 and 50.50 mM Trolox equivalents respectively, while ferric reducing antioxidant power (FRAP) was within the range of 0.36 and 0.31 to 4.41 and 3.04 mM Fe(II) respectively. Majority of extracts exhibited a beneficial antihemolytic effect. CONCLUSIONS: Results showed that the level of maturation influences the chemical composition, antioxidant and bioactive properties. Consequently, this allows us to estimate the best and optimal harvest time.

How is edaravone effective against acute ischemic stroke and amyotrophic lateral sclerosis?

Edaravone is a low-molecular-weight antioxidant drug targeting peroxyl radicals among many types of reactive oxygen species. Because of its amphiphilicity, it scavenges both lipid- and water-soluble peroxyl radicals by donating an electron to the radical. Thus, it inhibits the oxidation of lipids by scavenging chain-initiating water-soluble peroxyl radicals and chain-carrying lipid peroxyl radicals. In 2001, it was approved in Japan as a drug to treat acute-phase cerebral infarction, and then in 2015 it was approved for amyotrophic lateral sclerosis (ALS). In 2017, the U.S. Food and Drug Administration also approved edaravone for treatment of patients with ALS. Its mechanism of action was inferred to be scavenging of peroxynitrite. In this review, we focus on the radical-scavenging characteristics of edaravone in comparison with some other antioxidants that have been studied in clinical trials, and we summarize its pharmacological action and clinical efficacy in patients with acute cerebral infarction and ALS.

Role of vitamin E as a lipid-soluble peroxyl radical scavenger: in vitro and in vivo evidence

Multiple reactive oxygen/nitrogen species induce oxidative stress. Mammals have evolved with an elaborate defense network against oxidative stress, in which multiple antioxidant compounds and enzymes with different functions exert their respective roles. Radical scavenging is one of the essential roles of antioxidants and vitamin E is the most abundant and important lipophilic radical-scavenging antioxidant in vivo. The kinetic data and physiological molar ratio of vitamin E to substrates show that the peroxyl radicals are the only radicals that vitamin E can scavenge to break chain propagation efficiently and that vitamin E is unable to act as a potent scavenger of hydroxyl, alkoxyl, nitrogen dioxide, and thiyl radicals in vivo. The preventive effect of vitamin E against the oxidation mediated by nonradical oxidants such as hypochlorite, singlet oxygen, ozone, and enzymes may be limited in vivo. The synergistic interaction of vitamin E and vitamin C is effective for enhancing the antioxidant capacity of vitamin E. The in vitro and in vivo evidence of the function of vitamin E as a peroxyl radical-scavenging antioxidant and inhibitor of lipid peroxidation is presented.

Prevention of hydrogen peroxide-induced red blood cells lysis by Ilex paraguariensis aqueous extract: participation of phenolic and xanthine compounds

The fresh leaves and stems of Ilex paraguariensis (Aquifoliaceae) are employed to prepare the commercial product used in North-eastern Argentina, Southern Brazil and Eastern Paraguay named yerba maté. The presence of polyphenols and xanthines, which present antioxidant activity, has been described in I. paraguariensis. In living organism, reactive oxygen species can cause tissue damage affecting erythrocyte membranes leading to hemolysis. The aim of this work was to evaluate the protective effect of an aqueous extract of I. paraguariensis (green leaves) on the hemolysis of red blood cells induced by hydrogen peroxide and to correlate this activity with the enzymatic activity related to hydrogen peroxide metabolism. The antioxidant activity of chlorogenic acid and caffeine was also analysed to evaluate their contribution to the activity of the crude extract. The extract as well as the isolated compounds protected red blood cells from hemolysis. This effect was related to a catalase-like activity. This study could contribute to the knowledge of the antioxidant activity of I. paraguariensis in view of the great quantities of yerba maté consumed by the population.

Application of Water-Soluble Radical Initiator, 2,2′-Azobis-[2-(2-imidazolin-2-yl)propane] Dihydrochloride, to a Study of Oxidative Stress

It is essential to generate free radicals at a controled and constant rate for specific duration and at specific site to study the dynamics of oxidation and also antioxidation. Both hydrophilic and lipophilic azo compounds have been used for such purpose. In the present work, the action of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (AIPH) was examined and compared with those of 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] (AMHP). The rate constant of free radical formation (ek(d)) for AIPH was 2.6 x 10(-6)/s at 37 degrees C in PBS (pH 7.4) solution, indicating that AIPH gives 3.8 times more free radicals than AAPH under the same conditions. It was found that the dynamics of oxidation and antioxidation induced by AIPH can be studied satisfactorily in the oxidation in micelles, LDL and erythrocyte suspensions, plasma, and cultured cells. The extent of cell death induced by AIPH and AAPH was directly proportional to the total free radicals formed. Interestingly, it was found that rats would not drink water containing AAPH, but they drank water containing AIPH. The levels of 8-iso-prostaglandin F2alpha (8-isoPs), 7-hydroxycholesterol (FCOH), lysophosphatidylcholine in the plasma of rats given water containing 50 mM AIPH for 1 month increased compared with those of control rats which drank water without AIPH. It may be concluded that AIPH is useful for kinetic and mechanistic studies on oxidative stress to membranes, lipoproteins, cells, and even animal models.

Coelenterazine (marine bioluminescent substrate): a source of inspiration for the discovery of novel antioxidants

Coelenterazine and derivatives were initially considered in the scientific community for their (bio)luminescent properties. Now, another interest of such hetero-bicycles has been pointed out by the discovery of remarkable antioxidative properties, and an unique mode of action as a "cascade": the mother-compound (imidazolopyrazinone) is transformed by ROS into a daughter-compound (2-amino-pyrazine) also endowed with antioxidative properties. This review illustrates the therapeutic potential of synthetic imidazolopyrazinones (coelenterazine analogues): chemical reactivity assays with singulet oxygen, radical anion superoxide, peroxynitrite, and radicals formed during lipid and LDL peroxidation, cellular tests of protection against oxidative stress using keratinocyte, hepatocyte, neuronal and erythrocyte cells, and finally in vivo evaluation in a hamster model of ischemia-reperfusion, are fully described.

Effects of vitamin restriction and supplementation on rat intestinal epithelial cell apoptosis

Diet influences intestinal growth and function and vitamins modulate intestinal cell turnover. We have assessed the effects of chronic, moderate (50% of control) vitamin restriction and supplementation on intestinal epithelial cell (IEC) apoptosis and the relevance of this to alterations in tissue oxidative stress and antioxidant status. Feeding a vitamin-restricted diet to male, weanling WNIN rats for 20 weeks significantly increased IEC apoptosis, but only in the villi region, as evident from increased annexin V staining, M30 positivity, histological observations, DNA ladder formation, and reduced expression of Bcl-2. This was associated with elevated levels of lipid peroxides and protein carbonyls in the intestinal mucosa despite the increased activities of superoxide dismutase, catalase, and glutathione peroxidase. Consistent with the increased oxidative stress and apoptosis, structural and functional integrity of the villi were compromised as evident from the lowered ratio of villus height:crypt depth and the decreased activities of the membrane marker enzymes alkaline phosphatase and Lys-Ala dipeptidyl aminopeptidase. These changes were reversed by supplementation with a vitamin mixture or vitamin E alone, whereas riboflavin or folic acid supplementation reduced the apoptotic rates, but only partially. Further, oxidative stress was the least in vitamin E- or vitamin mixture-supplemented rats and correlated well with their IEC apoptotic rates. Increased tissue oxidative stress seems to mediate the vitamin-restriction-induced apoptosis of the IECs in rats.

Pycnogenol prevents haemolytic injury in G6PD deficient human erythrocytes

Glucose6 phosphate dehydrogenase (G6PD) deficiency is the most common X-linked disorder of human erythrocytes where cells have inadequate capacity to destroy peroxides and high susceptibility towards haemolytic changes. Pycnogenol is a proprietary dry extract of the French Maritime pine (Pinus pinaster) bark with high ability to scavenge free radicals. In the present study we have investigated if Pycnogenol can protect G6PD deficient erythrocytes against haemolytic cell damage. Venous blood samples were obtained from six subject of Mediterranean origin with known G6PD deficiency which was also confirmed with standard techniques. Erythrocyte haemolysis in the presence and absence of Pycnogenol was induced either with tert-butylhydroperoxide (t-BHP) or quinine and the haemoglobin release in the supernatant was determined by recording the optical density at 540 nm in a Shimadzu spectrophotometer. Our results have shown that Pycnogenol has protective action against a Xenobiotic chemical induced haemolysis in G6PD deficient human erythrocytes.

The effect of copper supplementation on red blood cell oxidizability and plasma antioxidants in middle-aged healthy volunteers

A multicenter European study (FoodCue) was undertaken to provide data on the significance of increased dietary copper as a pro-oxidant or antioxidant in vivo. The present work describes the effect of Cu supplementation on (2,2'-azo-bis(2-amidinopropane) hydrochloride (AAPH)-induced red blood cell oxidation in middle-aged people. Double-blinded copper supplementation was achieved in 26 healthy volunteers (50-70 years) with pills containing 3 mg CuSO(4), 3 mg Cu glycine chelate (CuG) and 6 mg CuG. Each 6 week supplementation period was preceded and followed by 6 weeks of washout (WO) on placebo. The results show significant increases in time necessary to achieve 50% hemolysis (LT(50)) after 3CuSO(4) and 6CuG compared with values after WO periods. Cu supplementation did not increase the levels of (Cu,Zn)SOD activity in red blood cells. Resistance to hemolysis was significantly and positively correlated (r =.30, p <.01) with alpha- and beta-carotene content in the plasma. Together, these data suggest that intake of copper as high as 7 mg/d has no pro-oxidant activity and may rather result in protection of red blood cells against oxidation. The decreased oxidizability of red blood cells did not result from increased (Cu,Zn)SOD activity and may occur through other mechanisms such as changes in membrane antioxidant content.

Protective effect of a vitamin E analog, phosphatidylchromanol, against oxidative hemolysis of human erythrocytes

The protective effect of a vitamin E analog, phosphatidylchromanol [1,2-diacyl-sn-glycero-3-phospho-2'-(hydroxyethyl)-2',5',7',8'-tetrameth yl-6'-hydroxychroman; PCh], against oxidative hemolysis of human erythrocytes was examined and was compared with those of vitamin E (alpha-tocopherol) and 2,2,5,7,8-pentamethyl-6-chromanol (PMC). These three compounds at 50 microM protected the erythrocytes from hemolysis, when erythrocyte suspension (10%, vol/vol) was incubated with a water-soluble radical generator, 2,2'-azobis(2-amidinopropane)-dihydrochloride (75 mM). When erythrocyte suspension was oxidized after pretreatment with these compounds (50 microM) for 30 min followed by washing, PCh protected about 54% of erythrocytes from the hemolysis, while alpha-tocopherol protected only about 16% of the cells and PMC did not show any protective effect. During preincubation, alpha-tocopherol, PMC, and PCh were incorporated into the cells at the concentration of 12.6, 3.7, and 16.3 nmol/mg protein, respectively. Moreover, PCh was found in the ghost membrane fraction at a 20% higher level than alpha-tocopherol, and no PMC was detected in this fraction. These results indicate that phosphatidyl group in PCh acts as an excellent carrier of chromanol moiety into cells as well as an anchor within membranes more efficiently than phytyl group in alpha-tocopherol. PMC seems to be slightly anchored within membranes because of the lack of hydrophobic side chain. The excellent antihemolytic activity of PCh is likely to be caused by its accumulation within erythrocyte membranes.

2,2'-Azobis (4-methoxy-2,4-dimethylvaleronitrile), a new lipid-soluble azo initiator: application to oxidations of lipids and low-density lipoprotein in solution and in aqueous dispersions

Both hydrophilic and hydrophobic azo radical initiators are useful for in vitro studies on lipid peroxidation and its inhibition by antioxidants. In the present study, a new lipophilic azo compound, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (MeO-AMVN), was introduced and its action as an initiator of lipid peroxidation was examined. MeO-AMVN decomposed about 15 times as fast as 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN), a widely used lipophilic azo initiator, and MeO-AMVN-initiated free radical-mediated peroxidations of lipids in organic solution and in micelles, membranes, and low-density lipoprotein in aqueous dispersions with much smaller concentration than AMVN. The rate of chain initiation by MeO-AMVN varied significantly with the medium and decreased with increasing viscosity of the medium. The advantage and cautions for using MeO-AMVN as a lipophilic radical source have been discussed and it has been concluded that MeO-AMVN, when properly used, is a useful radical initiator of lipid peroxidations especially in micelles, membranes, and lipoproteins.

Peroxynitrite-induced hemolysis of human erythrocytes and its inhibition by antioxidants

It was found that human erythrocytes underwent hemolysis when incubated with peroxynitrite at 37 degrees C under air. The extent of hemolysis increased with increasing peroxynitrite concentration and decreasing hematocrit. The peroxynitrite-induced hemolysis was suppressed only partially by a radical scavenging antioxidant such as uric acid and Trolox, a water-soluble vitamin E analogue, but reduced glutathione, N-acetylcysteine and albumin efficiently inhibited the hemolysis. A selenium-containing organic compound, ebselen, also suppressed the hemolysis. On the other hand, nitric oxide and superoxide generated concomitantly from 3-morpholinosydnonimine (SIN-1) did not induce appreciable hemolysis, while it converted hemoglobin to methemoglobin extensively.

Vitamins Q and E, extracorporal circulation and hemolysis

Whole blood vitamin Q (ubiquinone), plasma vitamins Q and E (alpha-(alpha-)tocopherol) and free cholesterol (FC) were studied before (control or base-line value, sample I) and during open chest surgery and extracorporal circulation (samples II-IV) in 10 male IHD patients. Identity existed between control whole blood and plasma ubiquinone. During surgery an increased discrepancy with lower plasma vitamin Q levels were seen. Control plasma vitamins Q, E and FC averaged 0.88 +/- 0.16 (SE), 12.1 +/- 2.2 mg x l(-1) and 0.75 +/- 0.15 g x l(-1). Corresponding molar values were 1.02 +/- 0.17, 28.1 +/- 5.1 micromol x l(-1) and 1.94 +/- 0.74 mmol x l(-1). Vitamin Q and E decreased continuously and averaged 0.64 mg x l(-1) in sample IV (0.74 micromol x l(-1), p < 0.001) and 9.4 mg x l(-1) in sample III (21.8 micromol x l(-1), p < 0.001). Hemolysis in all sample IV vials, ruined all vitamin E determinations. When normalized for FC (NQ and NE), decreases were found to be 17 (IV) and 12% (III), respectively. Large interindividual variations existed. High control NQ and NE values allowed a larger antioxidant vitamin depletion. High NQ seemed also to be a prerequisite for NE depletion. In addition, signs indicated an active liver vitamin Q release for patients rich in control antioxidant values. It was suggested that the antioxidant vitamin depletion did not prevent from radical trauma to membrane structural lipids (especially omega-3 fatty acids or vitamin F1), less membrane fluidity, erythrocyte fragility and hemolysis.

Plasma ascorbic acid level and erythrocyte fragility in preeclampsia and eclampsia

An imbalance between oxidants and antioxidants in the circulation is blamed to cause preeclampsia and eclampsia. In this study plasma ascorbic acid level was analysed in 13 eclamptic, 14 mild preeclamptic, 12 severe preeclamptic and 20 uncomplicated pregnancies to see whether there is any correlation with blood pressure, proteinuria, serum triglyceride level, erythrocyte fragility and leukocyte count. Plasma ascorbic acid level was normal and had no significant difference among the groups. Fasting serum triglyceride level was significantly higher in the study group than in the control group but it did not differ among the three study groups. Erythrocyte fragility was found to be increased in all three study groups. Blood leukocyte count was increased in the study groups, especially in the eclampsia group. However, plasma ascorbic acid level and erythrocyte fragility were found to have no significant correlation with blood pressure and proteinuria. It was concluded that though the ascorbic acid levels were normal in both the study and the control groups, erythrocyte fragility increased probably due to an elevation in peroxide and free radical levels in preeclampsia and eclampsia groups, but without any correlation with the severity of the clinical picture.

F1F0-ATPase, early target of the radical initiator 2,2'-azobis-(2-amidinopropane) dihydrochloride in rat liver mitochondria in vitro

This study was designed to determine which enzyme activities were first impaired in mitochondria exposed to 2,2'-azobis-(2-amidinopropane) dihydrochloride (AAPH), a known radical initiator. EPR spin-trapping revealed generation of reactive oxygen species although malondialdehyde formation remained very low. With increasing AAPH concentrations, State-3 respiration was progressively depressed with unaltered ADP/O ratios. A top-down approach demonstrated that alterations were located at the phosphorylation level. As shown by inhibitor titrations, ATP/ADP translocase activity was unaffected in the range of AAPH concentrations used. In contrast, AAPH appeared to exert a deleterious effect at the level of F1F0-ATPase, comparable with dicyclohexylcarbodi-imide, which alters Fo proton channel. A comparison of ATP hydrolase activity in uncoupled and broken mitochondria reinforced this finding. In spite of its pro-oxidant properties, AAPH was shown to act as a dose-dependent inhibitor of cyclosporin-sensitive permeability transition initiated by Ca2+, probably as a consequence of its effect on F1F0-ATPase. Resveratrol, a potent antiperoxidant, completely failed to prevent the decrease in State-3 respiration caused by AAPH. The data suggest that AAPH, when used under mild conditions, acted as a radical initiator and was capable of damaging F1F0-ATPase, thereby slowing respiratory chain activity and reducing mitochondrial antioxidant defences.

Antioxidant status and susceptibility of sickle erythrocytes to oxidative and osmotic stress

The purpose of this study was to determine if differences in antioxidant status between the red blood cells (RBCs) of sickle cell anemia (SCA) patients and controls are responsible for the differential responses to oxidative and osmotic stress-induced hemolysis. Susceptibility to hemolysis was examined by incubating oxygenated and deoxygenated RBCs at 37 degrees C with 73 mM 2,2' azobis (2-amidinopropane) HCl (AAPH), a peroxyl radical generator, for up to 3.5 hours.f The ability of RBCs to maintain membrane integrity under osmotic stress was determined over a range of diluted saline-phosphate buffer. Sickled RBCs showed a lesser degree of AAPH-induced hemolysis than control groups and were more resistant to osmotic stress-induced hemolysis. SCA patients had higher levels of RBC vitamin E and RBC lipids, but lower RBC GSH, plasma lipids and plasma carotenes than those of the hospital controls. No significant differences were observed in the levels of retinol, vitamin C, vitamin E, MDA and conjugated dienes in plasma, or the levels of MDA and conjugated dienes in RBCs. The results obtained suggest that the differences in antioxidant status between sickled RBCs and controls do not appear to be responsible for their different susceptibility to oxidative or osmotic stress-induced hemolysis observed.

Hepatic damage induced by perfusion of radical generating azo compound and its inhibition by vitamin E

The damaging effect of perfusion of hydrophilic radical generating azo compound on the liver of normal and vitamin E-deficient rats and its inhibition by antioxidants were studied in order to increase understanding of the action of free radicals on biological tissues. The hepatic damage was evaluated from the release of cytosolic enzymes such as glutamic oxaloacetic transaminase and glutamic pyruvic transaminase, mitochondrial oxidation metabolism and morphological change. Two kinds of hydrophilic azo compounds were used, one which decomposes spontaneously at a uniform rate to generate free radicals and the other which does not. The former induced hepatic damage in a dose-dependent manner, while the latter did not exert any damage. Both endogenous vitamin E in the membranes and a water soluble vitamin E analogue added simultaneously with a radical initiator suppressed the hepatic damage. These results show that the hepatic damage induced by perfusion of radical generating azo compound is caused not by the azo compound itself but by free radicals.

Ischaemia-reperfusion injury--a small animal perspective

Disease processes that produce ischaemia are a common cause of morbidity and mortality in companion animals. The majority of damage to transiently ischaemia tissues occurs following reperfusion and not during ischaemia per se. This discovery raises the encouraging prospect that therapeutic intervention prior to reperfusion may reduce the severity of ischaemic damage. Recently, the central role of oxygen-derived free radicals (oxyradicals) in reperfusion injury has been demonstrated. It appears that the adverse consequences of ischaemic diseases can be reduced by optimizing the anti-oxidant capability of tissues with anti-oxidant nutrients or drugs. The importance of oxyradicals in individual ischaemic diseases of the dog and cat, however, remains largely uninvestigated. Similarly, the best pharmaceutical and nutritional approaches to the therapy of oxyradical-mediated damage have yet to be devised.

Lipoperoxidation induced by hydrogen peroxide in human erythrocyte membranes. 2. Comparison of the antioxidant effect of Ginkgo biloba extract (EGb 761) with those of water-soluble and lipid-soluble antioxidants

An in vitro model using healthy human erythrocyte suspensions was used to compare the antioxidant effect of standardized Ginkgo biloba extract (EGb 761) with those of water-soluble (ascorbic acid, glutathione and uric acid) and lipid-soluble (alpha-tocopherol and retinol acetate) antioxidants. Lipid peroxidation was induced by hydrogen peroxide in the absence (control) and presence of antioxidants at low (25 micrograms/ml) and high (250 micrograms/ml) concentrations. Malondialdehyde production was determined as the indicator of lipid peroxidation during the incubation period. The results suggest that all of the antioxidants, except ascorbic acid, have antioxidant potential in this system in a concentration-dependent manner. When the antioxidants were compared, EGb 761 was found to be more effective than water-soluble antioxidants, and as effective as lipid-soluble antioxidants. Among the lipid-soluble antioxidants there was no significant difference in potency between alpha-tocopherol and retinol acetate, but uric acid was the most potent of the water-soluble antioxidants. The antioxidant potency of EGb 761 appears to be comparable with that of the well-known antioxidants alpha-tocopherol and retinol acetate.

The role of ascorbate in antioxidant protection of biomembranes: interaction with vitamin E and coenzyme Q

One of the vital roles of ascorbic acid (vitamin C) is to act as an antioxidant to protect cellular components from free radical damage. Ascorbic acid has been shown to scavenge free radicals directly in the aqueous phases of cells and the circulatory system. Ascorbic acid has also been proven to protect membrane and other hydrophobic compartments from such damage by regenerating the antioxidant form of vitamin E. In addition, reduced coenzyme Q, also a resident of hydrophobic compartments, interacts with vitamin E to regenerate its antioxidant form. The mechanism of vitamin C antioxidant function, the myriad of pathologies resulting from its clinical deficiency, and the many health benefits it provides, are reviewed.

Singlet oxygen induces predominantly G to T transversions on a single-stranded shuttle vector replicated in monkey cells

To elucidate the mechanisms of mutagenesis by singlet oxygen DNA damage in mammalian cells, a SV40-derived single-stranded shuttle vector was exposed to the water soluble endoperoxide 3,3'-(1,4-naphthylidene) dipropionate (NDPO2). The damaged vector was transfected into monkey COS7 cells and the plasmid progeny exhibited up to 10 fold increase on the mutation frequency in the supF target gene, when compared to untreated vector. The sequence in the supF locus of such mutants revealed that singlet oxygen-induced mutagenesis in single-stranded vector is significantly different from spontaneous mutagenesis. Among the base substitutions, most of the mutations involved deoxyguanosines, being G to T transversions the predominant type of change. The data indicate that mutagenesis by singlet oxygen in mammalian cells may be generated by an error prone bypass of damaged deoxyguanosines at the template DNA.

Effects of modulations of the energetic metabolism on the mortality of cultured cells

Since cells are open systems which exchange material with their surroundings, they can be considered as open systems far from equilibrium and in this way, they follow the principles of thermodynamics of open systems. This approach stresses the fact that cells optimize their use of energy according to their functions. However, with time and/or under environmental challenges, cells can reorganize themselves at other lower levels of energy production and utilization (Toussaint et al. (1991) Mech. Ageing Dev. 61, 45-64). Considered as optimized systems, cells can adapt their behaviours according to the balance between, on one side, their energetic potential and the level of their defence systems, and on the other side, the intensity of the stress. Mainly three types of behaviour can be theoretically predicted. If the stresses are very low, the damages generated are instantaneously repaired and the cellular system remains at its steady state of energy production and utilization. If the stresses are of an intermediary intensity, it is predicted that the cell can leave its steady state of energy production and utilization and find a new one characterized by a lower level of entropy production and a higher level of errors. Third, if the stresses are of a very high intensity which can be cytotoxic, the level of the energetic potential of the cell is directly related to cell survival. We tested the latter prediction in the present work in two ways. First, the level of energy production was lowered by partially uncoupling the mitochondria. Then the effect of stresses under tert-butylhydroperoxide or ethanol was investigated in order to look for a synergistic effect on cell death with the mitochondria uncoupling. Secondly, the effect of a modification of the energetic sources during the stress was tested. Besides a protective effect found with specific defence systems, the presence of energetic metabolites such as D-glucose, pyruvate/malate, glutamate/malate, was tested and found to be protective. The effect of a stimulator of the energetic metabolism, naftidrofuryl oxalate, was also investigated and found protective. The experimental data provide good evidence that energetic factors can modulate the resistance of cells to various stresses.

Inhibition of photohemolysis by copper(II) complexes with SOD-like activity

Red blood cell lysis photosensitized by Ketoprofen, 2-(3-benzoxyphenyl)propionic acid (KPF), was investigated in the presence of some copper(II) complexes with linear and cyclic dipeptides as well as functionalized beta-cyclodextrins with SOD-like activity with the aim of ascertaining their protective activity towards the photoinduced cell damage. The comparison between the decrease of photolytic activity caused by these complexes and their superoxide dismutase activity showed an appreciable correlation. The correct determination of species existing in experimental conditions was obtained through a simulation approach based on the knowledge of the stability constants of the complexes.

Peroxyl radical-mediated hemolysis: role of lipid, protein and sulfhydryl oxidation

The objective of this study was to define the relationship between peroxyl radical-mediated cytotoxicity and lipid, protein and sulfhydryl oxidation using human erythrocytes as the target mammalian cell. We found that incubation of human erythrocytes with the peroxyl radical generator 2,2' azobis (2-amidinopropane) hydrochloride (AAPH) resulted in a time and dose-dependent increase in hemolysis such that at 50 mM AAPH maximum hemolysis was achieved at 120 min. Hemolysis was inhibited by hypoxia and by the addition of certain water soluble free radical scavengers such as 5-aminosalicylic acid (5-ASA), 4-ASA, N-acetyl-5-ASA and dimethyl thiourea. Peroxyl radical-mediated hemolysis did not appear to involve significant peroxidation of erythrocyte lipids nor did they enhance protein oxidation at times preceding hemolysis. Peroxyl radicals did however, significantly reduce by approximately 80% the intracellular levels of GSH and inhibit by approximately 90% erythrocyte Ca(2+)-Mg2+ ATPase activity at times preceding the hemolytic event. Our data as well as others suggest that extracellular oxidants promote the oxidation of intracellular compounds by interacting with certain redox active membrane components. Depletion of intracellular GSH stores using diamide did not result in hemolysis suggesting that oxidation of GSH alone does not promote hemolysis. Taken together, our data suggest that neither GSH oxidation, lipid peroxidation nor protein oxidation alone can account for peroxyl radical-mediated hemolysis. It remains to be determined whether free radical-mediated inactivation of Ca(2+)-Mg2+ ATPase is an important mechanism in this process.

The effect of alpha-tocopherol as an antioxidant on the oxidation of membrane protein thiols induced by free radicals generated in different sites

Azo compounds enable us to generate peroxyl radicals by thermal decomposition at a constant rate and at a desired site, that is, water-soluble compounds produce initiating radicals in an aqueous phase and lipid-soluble compounds initiate the oxidation within the membrane-lipid layer. Using these radicals generated in different sites, we oxidized red blood cell ghost membranes to study the relationships between alpha-tocopherol depletion, initiation of lipid peroxidation, and protein damage. When radicals were generated in the aqueous phase, the loss of membrane protein thiols was observed concurrently with the consumption of membrane tocopherol and after tocopherol was exhausted the peroxidation of membrane lipids occurred. On the other hand, when radicals were initiated within the lipid region, the oxidation of thiols and the formation of thiobarbituric acid-reactive substances were suppressed to give an induction period until tocopherol fell below a critical level. Our results indicate that the surface thiols of extrinsic proteins may compete with alpha-tocopherol for trapping aqueous radicals and spare tocopherol to some extent, whereas the oxidation of intrinsic buried thiols may commence due to lipid-derived radicals produced after tocopherol was consumed. In conclusion, alpha-tocopherol in the membrane can break the free radical chain efficiently to inhibit the lipid peroxidation. However, the effect of tocopherol on the inhibition of membrane protein damage, exhibited by the loss of thiols and the formation of high-molecular-weight proteins, would be different depending on the site of initial radical generation.

Vitamin E and the peroxidizability of erythrocyte membranes in neonates

We showed the increased susceptibility of neonatal biomembranes to oxidation by a kinetic analysis using an azo compound as a free-radical initiator and red blood cell (RBC) ghosts as a model membrane. When the RBC ghosts were oxidized, oxygen consumption was suppressed during the induction period in which membrane tocopherol was consumed at a constant rate, while increased oxygen uptake was observed after the tocopherol was exhausted. The total tocopherol content was similar in cord, maternal, and adult RBC ghosts, and there were no differences in the induction period (tinh) among the three types of ghosts. While the oxygen uptake rate during the induction period (Rinh) was similar in cord and adult ghosts, the rate in the subsequent phase (Rp) was considerably faster in the cord ghosts. Fatty acid analysis in the membrane lipids showed that the active bisallylic hydrogen (active H) content was greater in cord ghosts than in adult ghosts. The active H content closely correlated with the Rp, but did not with the Rinh. The kinetic chain length (KCL), i.e., the ratio of the rate of propagation to that of initiation, was calculated from Rp and tocopherol consumption rate and KCL values were higher in cord ghosts than in adult ghosts. The faster Rp and the higher KCL of the cord ghosts were attributable to a greater active H content rather than to the tocopherol content.

Hemolysis of rabbit erythrocytes induced by cigarette smoke

Cigarette smoke has been found to induce the hemolysis of rabbit erythrocytes. The particulate phase had more profound effect than the gas phase. Neither free radical scavengers such as ascorbic acid, uric acid and water-soluble vitamin E analogue nor antioxidant enzymes such as catalase and superoxide dismutase suppressed the cigarette smoke-induced hemolysis, suggesting that free radicals, hydrogen peroxide, and superoxide were not the active species.

Oxidation of lipids. XV. Role of hydrophilic diarylamines as antioxidants in the oxidations of lipids and biological tissues

The abilities of two kinds of water-soluble diarylamines, disodium 4-chloro-2,2'-iminodibenzoate (CCA) and disodium 4-chloro-3',6'-dimethyl-2,2'-iminodibenzoate (CCM), to protect lipids, membranes and biological tissues from oxidative damages have been studied. The experimental systems studied include the oxidations of methyl linoleate micelles and soybean phosphatidylcholine (Pc) liposomal membranes in aqueous dispersions, oxidative hemolysis of rabbit erythrocytes, and the in vivo oxidative damages of biological tissues all induced by free radicals generated from an azo radical initiator. The two diarylamines functioned as moderate chain-breaking antioxidants and retarded the above oxidations.

Free-radical chain oxidation of rat red blood cells by molecular oxygen and its inhibition by alpha-tocopherol

The oxidation of rat red blood cells (RBC) by molecular oxygen was performed in an aqueous suspension with an azo compound as a free-radical initiator. The RBC were oxidized at a constant rate by a free-radical chain mechanism, resulting in hemolysis. The extent of hemolysis was proportional to the concentration of free radical. alpha-Tocopherol in RBC membranes suppressed the oxidation and hemolysis to produce an induction period. Tocopherol was constantly consumed during the induction period, and hemolysis developed when tocopherol concentrations fell below a critically low level. Among the membrane lipids, phosphatidylethanolamine, phosphatidylserine, and arachidonic acids were predominantly oxidized in the absence of tocopherol. In the presence of tocopherol, however, such lipid changes were suppressed during a 120-min incubation even when hemolysis started. Membrane proteins as well as lipids were oxidized. The formation of proteins with high molecular weight and concomitant decrease of the low-molecular-weight proteins were observed on gel electrophoresis with the onset of hemolysis. This study clearly showed the damage of RBC membranes caused by oxygen radical attack from outside of the membranes, and suggested that membrane tocopherol even below a critically low level could suppress lipid oxidation but that it could not prevent protein oxidation and hemolysis.

Antioxidants in relation to lipid peroxidation

The role of antioxidants in lipid peroxidation is reviewed. Specifically, the rate and mechanism of inhibition of lipid peroxidation by water-soluble and lipid-soluble, chain-breaking antioxidants have been discussed.