Uncoupling of oxidative leak formation from lipid peroxidation in the human erythrocyte membrane by antioxidants and desferrioxamine

Cultivating resilience in wheat: mitigating arsenic toxicity with seaweed extract and Azospirillum brasilense

Arsenic (As) toxicity is a serious hazard to agricultural land due to growing industrialization, which has a negative effect on wheat crop yields. To address this issue, using seaweed extract and Azospirillum brasilense has emerged as an effective strategy for improving yield under stress conditions. However, the combined application of A. brasilense and seaweed extract in wheat crops under As toxicity has not been fully explored. The effectiveness of combining A. brasilense and seaweed extract in reducing As toxicity in wheat production was examined in this study through a 2-year pot experiment with nine treatments. These treatments included a control with no additives and two As concentrations (50 and 70 μM). At 50 and 70 μM, As was tested alone, with seaweed extract, with A. brasilense, and both. Significant results were achieved in reducing As toxicity in wheat crops. Arsenic at 70 μM proved more harmful than at 50 μM. The application of A. brasilense and seaweed extract was more effective in improving crop growth rates, chlorophyll levels, and stomatal conductance. The combined application notably decreased As concentration in wheat plants. It was concluded that applying A. brasilense and seaweed extract not only improves wheat growth but can also improve soil parameters under As toxicity conditions by increasing organic matter contents, boosting nutrient availability, and increasing the production of antioxidant enzymes.

The involvement of cation leaks in the storage lesion of red blood cells

Stored blood components are a critical life-saving tool provided to patients by health services worldwide. Red cells may be stored for up to 42 days, allowing for efficient blood bank inventory management, but with prolonged storage comes an unwanted side-effect known as the "storage lesion", which has been implicated in poorer patient outcomes. This lesion is comprised of a number of processes that are inter-dependent. Metabolic changes include a reduction in glycolysis and ATP production after the first week of storage. This leads to an accumulation of lactate and drop in pH. Longer term damage may be done by the consequent reduction in anti-oxidant enzymes, which contributes to protein and lipid oxidation via reactive oxygen species. The oxidative damage to the cytoskeleton and membrane is involved in increased vesiculation and loss of cation gradients across the membrane. The irreversible damage caused by extensive membrane loss via vesiculation alongside dehydration is likely to result in immediate splenic sequestration of these dense, spherocytic cells. Although often overlooked in the literature, the loss of the cation gradient in stored cells will be considered in more depth in this review as well as the possible effects it may have on other elements of the storage lesion. It has now become clear that blood donors can exhibit quite large variations in the properties of their red cells, including microvesicle production and the rate of cation leak. The implications for the quality of stored red cells from such donors is discussed.

Chemically induced metamorphosis of polychaete larvae in both the laboratory and ocean environment

Planktonic larvae of the marine polychaetePhragmatopoma californica preferentially attach to substrata and metamorphose to the adult form upon contact with cement in tubes built by conspecifics. This gregarious settlement and metamorphosis contributes to the formation of large aggregations or reefs. Larvae also metamorphose upon contact with 2,6-di-tert-butyl-4-methylphenol (DBMP), a possible aromatic analog of cross-linked dihydrox-yphenylalanine (DOPA) residues (present in the polyphenolic protein cement as 2.6% of the amino acid residues). Morphogenesis occurs in the laboratory when larvae are exposed to DBMP either adsorbed to solid surfaces or when dissolved in dimethyl sulfoxide (DMSO) to render it soluble in seawater. Larvae in the ocean were induced to settle and metamorphose on plates coated with DBMP prior to their deployment in the ocean. This is the first report in which a defined organic molecule, identified as an inducer (or precursor to an inducer) of larval settlement and metamorphosis in the laboratory, has been shown to induce these processes in the ocean. Both forskolin and isobutylmethylxanlhine (IBMX) induce metamorphosis ofP. californica larvae, presumably by causing increases in intracellular cyclic AMP (cAMP). A discussion of the pathway controlling chemically mediated metamorphosis and evidence suggesting the possible role of cAMP in the process are presented. Other compounds known to increase intracellular cAMP levels, including arachidonic, linoleic, and palmitoleic acids, found by other workers to induce settlement and metamorphosis ofP. californica, may exert this activity by direct modification of internal cAMP levels in the larvae.

Comparative antioxidant capacities of quercetin and butylated hydroxyanisole in cholesterol-modified erythrocytes damaged by tert-butylhydroperoxide

Phenolic compounds are potent antioxidants that scavenge reactive oxygen species (ROS), protecting the cells against oxidative damage. Their antioxidant capacities are governed by their structural features and the nature and physical state of the cell membrane. Our study compares the protective effects of butylated hydroxyanisole (BHA) and quercetin against the cellular injury induced by oxidative stress, and the influence of membrane cholesterol contents in their antioxidant capacities, analyzing the structural changes and cellular stability of native and cholesterol-modified erythrocytes exposed to tert-butylhydroperoxide in presence of each antioxidant. The data provide clear evidence that BHA affords better protection than quercetin against ROS generation, lipid peroxidation and lipid and GSH losses in oxidized erythrocytes. However, cellular integrity and stability are better protected by quercetin owing to the hemolytic effect of BHA. Both antioxidants suppress the alterations in membrane fluidity with similar efficiency, reducing methemoglobin formation in all oxidized erythrocytes. Membrane cholesterol depletion decreases the protection against the oxidative damage provided by both antioxidants. This lower preservation may be due to low antioxidant contents, a lower antioxidant capacity, or even to an increased oxidative damage in this membrane type as a consequence of environment modifications after cholesterol depletion.

Clotrimazole enhances lysis of human erythrocytes induced by t-BHP

Clotrimazole (CLT) is an antifungal and antimalarial agent also effective as a Gardos channel inhibitor. In addition, CLT possesses antitumor properties. Recent data provide evidence that CLT forms a complex with heme (hemin), which produces a more potent lytic effect than heme alone. This study addressed the effect of CLT on the lysis of normal human erythrocytes induced by tert-butyl hydroperoxide (t-BHP). For the first time, it was shown that 10 microM CLT significantly enhanced the lytic effect of t-BHP on erythrocytes in both Ca(2+)-containing and Ca(2+)-free media, suggesting that the effect is not related to Gardos channels. CLT did not affect the rate of free radical generation, the kinetics of GSH degradation, methemoglobin formation and TBARS generation; therefore, we concluded that CLT does not cause additional oxidative damage to erythrocytes treated with t-BHP. It is tempted to speculate that CLT enhances t-BHP-induced changes in erythrocyte volume and lysis largely by forming a complex with hemin released during hemoglobin oxidation in erythrocytes: the CLT-hemin complex destabilizes the cell membrane more potently than hemin alone. If so, the effect of CLT on cell membrane damage during free-radical oxidation may be used to increase the efficacy of antitumor therapy.

Partial oxidative-stress perturbs membrane permeability and fluidity of fish nucleated red blood cells

We investigated the influence of partial oxidative stress on permeability and fluidity of nucleated fish red blood cells for simulating nucleated somatic cells. Peroxide value indicating lipid hydroperoxide level in nucleated red blood cells of common carp (Cyprinus carpio) increased with increasing body size. We detected that oxidation of nucleated red blood cells led to the degraded PUFA compositions and accelerated the permeability of calcein and ATP in the nucleated red blood cells restrictedly oxidized with 1 mM AAPH treatment for 30 min at 21 degrees C in the dark. Using fluorescence probes, PC3P, we found that oxidative stress reduced the membrane fluidity of nucleated red blood cells. It was also observed that AAPH had no significant influence on the osmotic fragility and electrophoretic profiles of red blood cell proteins. These results suggest that partial oxidative-stress, even if failure to fragment the membrane, may affect membrane permeability of fish nucleated red blood cells for an important energy molecule, ATP.

Chemical and physical in vitro alterations of the erythrocyte membrane: a model for its pathophysiological states?

Plasmodia induce conspicuous structural and functional changes in the erythrocyte membrane. Besides the insertion and apposition of 'xenoproteins', and alterations of lipid composition (fatty acid pattern) and dynamics (transbilayer mobility and disposition of phospholipids, or related probes), new permeation pathways (NPP) are formed, which are still ill-defined in terms of their molecular origin. A remarkable ion selectivity and a high and complete sensitivity of the NPP to inhibitors indicate a rather specific nature. On the other hand, numerous experimental perturbations of the erythrocyte membrane structure induce unspecific alterations of its barrier function. In view of the apparent similarities--in simple physicochemical terms--between the experimentally and the plasmodially induced structural perturbations, one would expect, in Plasmodium-invaded cells, unspecific alterations of permeability and phospholipid dynamics of the type observed after in vitro modification, in contrast to much of the experimental evidence. In order to highlight this puzzling discrepancy, this chapter outlines techniques of producing and analysing experimental barrier defects in erythrocytes, and summarizes the properties of the defects induced by electroporation and oxidative damage, in terms of solute permeability, transbilayer mobility of phospholipid probes and the disposition of native phospholipids. The possible absence of comparable unspecific defects in Plasmodium-modified cells may provide an interesting example for the evolutionary adaptation of the parasite.

The effect of oxidative stress on structural transitions of human erythrocyte ghost membranes

Differential scanning microcalorimetry was used to study the effect of oxidative stress induced by cumene hydroperoxide (CHP) and Fe2+ on structural transitions of membranes of human erythrocyte ghosts. The CHP homolysis was shown to cause: (a) reduction of the intensity of all structural transitions with the disappearance of B1- and D-transitions; (b) decrease in the enthalpy of oxidized membrane denaturation; (c) negative slope of thermograms; (d) anomalous growth of heat absorption by membranes above 72 degreesC. All these changes occurred until the ratio Fe2+/CHP/membranes<0.02:0.05:1 was reached, i.e., prior to the moment of maximal level of TBA-RS in membrane ghosts. We interpret changes in the character of heat absorption by oxidized membranes as perturbations in the structural organization and interactions inside the spectrin-actin-protein 4.1 domains, the spectrin-protein 4.2 domain, as well as inside the domain of spectrin-ankyrin-cdB3 and the domain formed by the msdB3. These perturbations are associated mainly with the decrease in the concentration of native protein in the domains because of oxidative aggregation of proteins, as evidenced by SDS electrophoresis of oxidized membranes. Preincubation of membranes with tocopherol did not block the aggregation of proteins in electrophoresis and the decrease in the intensity of structural transitions, whereas it blocked completely the formation of TBA-RS, changes in the thermogram slope and the sharp rise in the heat absorption above 72 degreesC. This proves that these processes are determined by the thermotropic properties of the oxidized lipid bilayer of membranes and also provides evidence that the degradation of PUFA of phospholipids modifies both the structure of protein domains and the physical properties of the lipid bilayer of membranes.

C-methylated dihydrochalcones from Myrica gale L: effects as antioxidants and as scavengers of 1,1-diphenyl-2-picrylhydrazyl

A number of isomeric or chemically closely related C-methylated dihydrochalcones, which is a rare substance class, has been isolated from the fruit exudate of Myrica gale L. and subjected to the following tests: 1) inhibition of lipid peroxidation induced by tert-butyl hydroperoxide or bromotrichloromethane in isolated rat hepatocytes, 2) inhibition of peroxidation induced by Fe2+ ions in a cell free system with linolenic acid as substrate, 3) scavenging activity against the diphenylpicrylhydrazyl radical, and 4) inhibition of enzymatic lipid peroxidation in linoleic acid by soybean 15-lipoxy-genase. One of the compounds (myrigalone B = MyB; 2',6'-dihydroxy-4'-methoxy-3',5'-dimethyldihydrochalcone) showed good activity in all tests whereas the others were inactive or slightly active, except that myrigalone A (MyA; 3-(1-oxo-3-phenylpropyl)-1,1,5-trimethylcyclohexane-2,4,6-trione)) like its synthetic analogue MyA* (the polar part of MyA) was nearly as active as MyB in 4). The antioxidant properties of MyB are probably due to its radical scavenging activity and may be related to its conformation, which differs from that of the other compounds.

Oxidant stress and endothelial membrane transport

The endothelium modulates vascular tone, vasoreactivity, and permeability in response to agonist-stimulation. Much of the pathophysiology of oxidant-induced vascular injury can be attributed to endothelial cell dysfunction. In the past several years, the effects of oxidant stress on agonist-stimulated Ca(2+)-channels have been described. More recently, the effects of oxidant stress on several other endothelial membrane-transport systems have been elucidated. It now appears that inhibition of the agonist-stimulated Ca2+ channel is due at least in part to membrane depolarization via oxidant-activation of a Na(+)-permeable, nonselective cation channel. In this review, the effects of oxidant stress on ion transport through the agonist-stimulated Ca2+ influx channel, Na+ and K+ channels, Na+/K(+)-ATPase, Ca(2+)-ATPase, and the Na+/K+/2Cl- cotransporter are discussed. The interrelated effects of oxidant stress on these endothelial membrane transport pathways are considered, and the net effect on Ca2+ signaling is described.

Enhanced sensitivity to oxidative stress in Cu,ZnSOD depleted rat erythrocytes

The effects on red blood cells of superoxide dismutase (Cu,ZnSOD) depletion, induced by feeding Wistar rats with a copper deficient diet, were investigated. SOD depleted red blood cells were more sensitive to peroxidation and to hemolysis than normal cells when exposed to tert-butylhydroperoxide (t-BOOH). Membranes isolated from SOD depleted cells showed a lower content of vitamin E and higher (Na+, K+) and Mg2+ ATPase activities. These results support the view that superoxide dismutase plays an important role in cellular oxidative metabolism.

Selective erythrocyte potassium efflux following pulse treatment with tellurite

Human erythrocytes exposed to 0.1 mM tellurite (K2TeO3) in an isotonic buffered choline chloride medium for 15 min at 37 degrees C, washed, and incubated further in the absence of the chemical in the buffer, exhibited selective leakiness for potassium within minutes. The potassium efflux curve was sigmoidal, with an initially slow leakage followed by a sharp rise (first-order kinetics) and a plateau by 60 min. After 15 min, 30-50% of the total potassium concentration had leaked from the cells, although less than 1% lysis had occurred. The control cells incubated in buffer with no K2TeO3 exhibited no potassium leakage. The mean volume of the K2TeO3-treated erythrocytes increased and their median density decreased, indicating changes in the colloid osmotic state and physical characteristics of the cells. However, cells pretreated with K2TeO3 exhibited no significant change in glutathione (GSH) concentration and no membrane lipid peroxidation, unlike cells pretreated with t-butylhydroperoxide (Deuticke et al., Biochim. Bio phys. Acta, 899, 125-128, 1987). The enhanced potassium permeability of the K2TeO3-treated erythrocytes preceded the increase in cell volume, intracellular hydration, and a decrease in median density. We suggest that perturbation of the lipid-protein interaction in the membrane by the oxidant alters the potassium permeability and results in the selective leakage with eventual hemolysis.

Oxidative stress alters specific membrane currents in isolated cardiac myocytes

To evaluate the effects of oxidative stress on cardiac membrane currents, single cells from frog ventricle were exposed to tert-butyl hydroperoxide (t-BHP). Incubation of these cells with 2 mM t-BHP causes a rapid depletion of cellular glutathione, followed by a more gradual increase in the contents of malonaldialdehyde and conjugated dienes. Effects of this rapidly evolving oxidative stress were studied on sodium, calcium, and potassium currents of isolated ventricular cells. t-BHP caused a progressive decrease in the magnitude of sodium current obtained on depolarization from a holding potential of -85 mV, which was accompanied by a shift in the reversal potential toward more negative potentials. The voltage dependence of the steady-state parameters for activation and inactivation was shifted, such that in peroxide-exposed cells, there was a greater overlap of activation and inactivation parameters, which would be expected to result in an increased window current. In addition, in the presence of t-BHP, the time constant for activation was decreased at most depolarizing potentials, whereas the time constant for inactivation was increased. The resultant sodium current transients were, therefore, slower in the presence of the peroxide because of slower inactivation. Prolonged exposure of the cells to t-BHP led to a complete and selective inhibition of the Na+ current. However, even when all the Na+ current was inhibited, the K+ and Ca2+ currents remained essentially unaltered. Also, no large outward currents were observed at this stage, indicating that ATP concentration was not drastically decreased. The barrier properties of plasma membrane remained intact, as it was possible to form gigohm seals between the patch pipette and the plasma membrane of cells treated with 2-14 mM t-BHP for up to 30 minutes. These results account for the proarrhythmic effects of free radicals and oxidative stress on cardiac tissues.

Prooxidant and antioxidant effects of ascorbate on tBuOOH-induced erythrocyte membrane damage

1. t-Butylhydroperoxide (tBuOOH) a lipoperoxide analog, causes rapid and considerable sulphydryl (SH) oxidation but almost no lipid peroxidation in red blood cell membranes (ghosts) containing no detectable haemoglobin. 2. tBuOOH, in the presence of ascorbate, produces significant lipid peroxidation the level of which is proportional to the ascorbate concentration. The initiation of lipid peroxidation is thought to occur by the reactive tBuO (butoxyl) species via the reductive decomposition of tBuOOH by ascorbate. 3. Ascorbate protects ghost membranes from the tBuOOH-induced SH oxidation in a dose-dependent fashion. 4. There is no parallelism between lipid peroxidation and SH oxidation in these systems. This suggests that the two processes occur independently of each other. 5. These findings indicate that, simultaneously, ascorbate can have both a protective and a prooxidant action in different membrane components under the same oxidative stress.

Progressive oxidative membrane damage in erythrocytes after pulse treatment with t-butylhydroperoxide

Development of membrane damage in erythrocytes in the presence of the radical-forming oxidant t-butylhydroperoxide is a well established fact (see, for example, Deuticke et al. (1986) Biochim. Biophys. Acta 854, 169-183). We have now demonstrated that a mere pulse treatment of erythrocytes (5-15 min) with this agent leads to subsequent development of progressive oxidative membrane damage in spite of the absence of exogenous oxidant. Damage comprises the occurrence of ion leakiness and subsequent colloid-osmotic lysis, enhancement of the transbilayer mobility of phospholipid analogues, and lipid peroxidation. There is, however, only very little concomitant oxidation and precipitation of hemoglobin. Defect formation is not due to oxidation of SH-groups nor is it directly related to lipid peroxidation, since it can be suppressed by thiourea without concommitant inhibition of lipid peroxidation. This 'spontaneous' development of membrane damage can be antagonized by metabolic substrates and by desferrioxamine, indicating that lack of protective metabolic resources as well as the presence of catalytic metal (iron) complexes are required for the development of membrane damage. This progressive development of injury in cells only temporarily exposed to an exogenous oxidant may be regarded as a more appropriate model for oxidative membrane damage under pathophysiological conditions in vivo than cells exposed to continuous damage by exogenous oxidants.