Preferential formation of the hydroperoxide of linoleic acid in choline glycerophospholipids in human erythrocytes membrane during peroxidation with an azo initiator

Formation of free acetaldehydes derived from lipid peroxidation in U937 monocyte-like cells

Acetaldehyde can be found in human cells as a byproduct of various metabolic pathways, including oxidative processes such as lipid peroxidation. This secondary product of lipid peroxidation plays a role in various pathological processes, leading to various types of civilization diseases. In this study, the formation of free acetaldehyde induced by oxygen-centred radicals was studied in monocyte-like cell line U937. Exposure of U937 cells to peroxyl/alkoxyl radicals induced by azocompound resulted in the formation of free acetaldehyde. Acetaldehyde is formed by the cleavage of fatty acids, which represents the breakdown of fatty acids into smaller fragments initiated by the cyclization of lipid peroxyl radical and β-scission of lipid alkoxyl radical. The cleavage of fatty acids alters the integrity of the plasma and nuclear membrane, leading to the loss of cell viability. Understanding the pathological processes of acetaldehyde formation is an active area of research with potential implications for preventing and treating various diseases associated with oxidative stress.

The effect of covalently bonded conjugated linoleic acid on the reduction of oxidative stress and blood coagulation for polysulfone hemodialyzer membrane

Conjugated linoleic acid (CLA) was covalently bonded to a layer of poly(acrylic acid) (PAA) grafted onto the surface of polysulfone (PSF) membranes. The effect of CLA-bonding on oxidative stress and blood coagulation was then evaluated. The surface was characterized with contact angle measurement and FTIR spectroscopy. Blood coagulation, platelet aggregation, and oxidative stress were evaluated using human blood. The complete blood count (CBC) and coagulation time (CT) were evaluated in vitro for hemocompatibility. The production of reactive oxygen species (ROS) was measured by the chemiluminescence (CL) method to evaluate the oxidative stress. The results showed that the CLA-bonding PSF membrane exhibited more stable CBC values, longer CT, and less adsorption of plasma proteins than the unmodified PSF membrane. In addition, the CL counts of hydrogen peroxide and superoxide values for CLA-bonding PSF membrane were more stable than for unmodified PSF membrane. These results demonstrate that CLA-bonding can improve the blood compatibility of PSF membrane. The CLA-bonding PSF membrane could offer protection for patients against oxidative stress and could also reduce the dosage of anticoagulant required during hemodialysis.

Genistein abrogates pre-hemolytic and oxidative stress damage induced by 2,2′-Azobis (Amidinopropane)

The pre-hemolytic mechanism induced by free radicals initiated from water-soluble 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH) and its reversal by genistein was investigated in human erythrocytes. The time course of K+ efflux compared to the occurrence of hemolysis suggests that AAPH-induced hemolysis occurs indirectly via pore formation and band 3 oxidation as expected. However, genistein inhibited hemolysis, LDH release and membrane protein oxidation but not K+ efflux. This indicated that erythrocyte protein oxidation possibly in the hydrophobic core plays a significant role in the membrane pre-hemolytic damage. Chemiluminescence (CL) analysis carried out in non-lysed erythrocytes treated with AAPH showed a dramatic increase in CL indicating both reduced levels of antioxidants and increased membrane lipid peroxide. The V0 value was also increased up to 6 times, denoting a high degree of membrane peroxidation very early in erythrocyte membrane damage. The whole process was inhibited by genistein in a dose-dependent manner. These results indicate that the genistein inhibited both hemolysis and pre-hemolytic damage and also hindered membrane lipid peroxide formation and protein oxidation. In addition, it is suggested that pre-hemolytic damage is mediated mainly by the oxidation of both phospholipid and protein located in the deeper hydrophobic region of the membrane.

Biological significance of phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) in mammalian cells

Reactive oxygen species (ROS) are known mediators of intracellular signal cascades. Excessive production of ROS may lead to oxidative stress, loss of cell function, and cell death by apoptosis or necrosis. Lipid hydroperoxides are one type of ROS whose biological function has not yet been clarified. Phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) is a unique antioxidant enzyme that can directly reduce phospholipid hydroperoxide in mammalian cells. This contrasts with most antioxidant enzymes, which cannot reduce intracellular phospholipid hydroperoxides directly. In this review, we focus on the structure and biological functions of PHGPx in mammalian cells. Recently, molecular techniques have allowed overexpression of PHGPx in mammalian cell lines, from which it has become clear that lipid hydroperoxides also have an important function as activators of lipoxygenase and cyclooxygenase, participate in inflammation, and act as signal molecules for apoptotic cell death and receptor-mediated signal transduction at the cellular level.

Activation of thiol-dependent antioxidant activity of human serum albumin by alkaline pH is due to the B-like conformational change

Antioxidant activity of human serum albumin (HSA) increased steeply as the reaction mixture was shifted from neutral to alkaline pH. The antioxidant activity was also remarkably increased by Ca(2+) or a cationic detergent (cetyltrimethylammonium chloride). Carboxyl group modification of HSA resulted in about 40-fold increase of the antioxidant activity. The chemical modification study indicated that in addition to functional cysteine(s), cationic amino acid residues such as histidine, arginine and lysine appeared to involve in the antioxidant reaction. HSA also exhibited alkaline-pH dependent peroxidase activity to remove fatty acid hydroperoxide. At neutral pH, only two thiols of Cys-289 and free Cys-34 of HSA were modified by a thiol-specific modification reagent, 5-((((2-iodoacetyl)amino)ethy)amino)naphthalene-1-sulfonic acid (I14), regardless of the presence or absence of dithiothreitol (DTT), and the resultant antioxidant activity was not decreased, suggesting that Cys-289 and Cys-34 did not participate in the antioxidant reaction. At alkaline pH, I14 modified several additional HSA thiols in the presence, but did not in the absence of DTT. The antioxidant activity of the modified HSA was remarkably decreased to as much as 30% of the antioxidant activity given by the unmodified HSA in the absence of DTT. The HPLC pattern for tryptic peptides containing modified cysteine(s) derived from the I14-treated c-HSA (carboxyl group-modified HSA) at pH 7.0 with DTT was very similar to that of the I14-modified HSA at pH 8.0 with DTT. Taken together, these results suggest that activation of thiol-dependent antioxidant activity of HSA at alkaline pH is due to the conformational change favorable for the functional cysteine(s)-mediated catalysis.

Analysis of phospholipid molecular species in brain by (31)P NMR spectroscopy

Techniques are described for the (31)P NMR analysis of glycerophospholipid (PL) headgroup and molecular species in brain. The (31)P NMR spectrum of PLs from human temporal cortex, solubilized in aqueous Na cholate, typically showed 3 major resonances, assigned to phosphatidylcholine (PC) molecular species containing 0, 1, or 2 fully saturated acyl chains. Less species resolution was obtained for the other PL headgroups under these conditions. Alkylacyl- and alkenylacyl-PC were readily discerned using the CHCl(3)-CH(3)OH-H(2)O solvent method. The chain-length, temperature, and species dependences of the (31)P NMR chemical shifts were explored in model PLs. Assignments of signals from phosphatidylethanolamine (PE) subclasses were confirmed in the sodium-cholate system by lipase-mediated selective hydrolysis of bovine-brain PE. The utility of (31)P NMR to monitor enzymatic PL oxidation was further demonstrated. Possible changes in PL composition with postmortem interval (PMI) in rat brain were examined. No significant changes were seen in PL headgroup or PC species composition with PMI at up to 18 hours. Where comparable, the Na-cholate-solubilization and solvent methods gave similar quantitative results for headgroup analysis on the same samples. The present work demonstrates the feasibility and utility of the dual system for analysis of PLs in brain. Magn Reson Med 44:215-223, 2000.

Chain-breaking antioxidants and ferriheme-bound drugs are synergistic inhibitors of erythrocyte membrane peroxidation

Induced erythrocyte membrane peroxidation (EMP) is considered as an accurate model of reperfusion injuries and as such was used to investigate protective effects of various drugs. EMP was induced by an azo initiator and monitored by oxygen uptake. Both hydrophilic (ascorbic acid) and lipophilic (alpha-tocopherol, probucol, nicanartine) chain-breaking antioxidants as well as ferriheme-bound drugs (deferoxamine, chloroquine) inhibited EMP. When antioxidants and ferriheme-bound drugs were combined, synergistic effects were observed. It is proposed that ferriheme compounds which catalyse peroxide induced lipid peroxidation were blocked by deferoxamine and/or chloroquine. So these drugs inhibited at least partly the membrane peroxidation process and added their effects to the ones of chain-breaking antioxidants.

Suppression of leukotriene formation in RBL-2H3 cells that overexpressed phospholipid hydroperoxide glutathione peroxidase

The overexpression of phospholipid hydroperoxide glutathione peroxidase (PHGPx) by RBL-2H3 cells was used as the basis for an investigation of the effects of PHGPx on the formation of leukotrienes. The rates of production of leukotriene C4 (LTC4) and leukotriene B4 (LTB4) in cells that overexpressed PHGPx were 8 times lower than those in a control line of cells. The reduction in rates of production of leukotrienes apparently resulted from the increase in the PHGPx activity since control rates of formation of leukotrienes could be achieved in PHGPx-overexpressing cells upon inhibition of PHGPx activity by diethyl malate. The conversion of radioactively labeled arachidonic acid to intermediates in the lipoxygenase pathway, such as 5-hydroxyeicosatetraenoic acid (5-HETE), LTC4, and LTB4, was strongly inhibited in PHGPx-overexpressing cells that had been prelabeled with [14C]arachidonic acid. PHGPx apparently inactivated the 5-lipoxygenase that catalyzed the conversion of arachidonic acid to 5-hydroperoxyeicosatetraenoic acid (5-HPETE) since 5-HPETE is a common precursor of 5-HETE, LTC4, and LTB4. The rates of formation of LTC4 and LTB4 in PHGPx-overexpressing cells returned to control rates upon the addition of a small amount of 12-HPETE. Flow cytometric analysis revealed that the rapid burst of formation of lipid hydroperoxides induced by A23187 was suppressed in PHGPx-overexpressing cells as compared with the control lines of cells. Subcellular fractionation analysis showed that the amount of PHGPx associated with nuclear fractions from PHGPx-overexpressing cells was 3.5 times higher than that from the control line of cells. These results indicate that PHGPx might be involved in inactivation of 5-lipoxygenase via reductions in levels of the fatty acid hydroperoxides that are required for the full activation of 5-lipoxygenase. Thus, in addition to its role as an antioxidant enzyme, PHGPx appears to have a novel function as a modulator of the production of leukotrienes.

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.

Hydroperoxides of erythrocyte phospholipid molecular species formed by lipoxygenase correlate with alpha-tocopherol levels

The hydroperoxides corresponding to the main molecular species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were determined after lipoxygenase treatment of erythrocyte membranes from healthy children. This work was a preliminary study prior to applying this analytical procedure to erythrocyte membranes from children with diseases associated with vitamin E deficiency. The total molecular species corresponding to 20:4 and 22:6 associated with 16:0 and 18:0 were significantly higher in PE (26.94 +/- 4.70 nmol/mg protein) than in PC (20.14 +/- 6.70 nmol/mg protein); these concentrations represented 63% of the total molecular species in PE and 22% in PC. However, the concentrations of hydroperoxides produced from these polyunsaturated fatty acid molecular species were in the same order of magnitude in PC (3.98 +/- 1.56 nmol/mg protein) and in PE (3.61 +/- 1.63 nmol/mg protein). In contrast, the molecular species concentrations containing two double bonds, such as 16:0/18:2 and 18:0/18:2 and their corresponding hydroperoxides, were clearly more elevated in PC than in PE. There was a positive relationship between the concentrations of alpha-tocopherol and each hydroperoxide of PC and PE, and this association was particularly strong in PE (P < or = 0.0001). These results suggest that alpha-tocopherol exerts a stabilizing effect toward hydroperoxides, limiting their further degradation into peroxyl radicals. The protective effect of alpha-tocopherol could be more effective in PE because more polyunsaturated fatty acids were present.