Peroxidative membrane damage in human erythrocytes induced by a concerted action of iodoacetate, vanadate and ferricyanide

Erythrocytes as a biological model for screening of xenobiotics toxicity

Erythrocytes are the main cells in circulation. They are devoid of internal membrane structures and easy to be isolated and handled providing a good model for different assays. Red blood cells (RBCs) plasma membrane is a multi-component structure that keeps the cell morphology, elasticity, flexibility and deformability. Alteration of membrane structure upon exposure to xenobiotics could induce various cellular abnormalities and releasing of intracellular components. Therefore the morphological changes and extracellular release of haemoglobin [hemolysis] and increased content of extracellular adenosine triphosphate (ATP) [as signs of membrane stability] could be used to evaluate the cytotoxic effects of various molecules. The nucleated RBCs from birds, fish and amphibians can be used to evaluate genotoxicity of different xenobiotics using comet, DNA fragmentation and micronucleus assays. The RBCs could undergo programmed cell death (eryptosis) in response to injury providing a useful model to analyze some mechanisms of toxicity that could be implicated in apoptosis of nucleated cells. Erythrocytes are vulnerable to peroxidation making it a good biological membrane model for analyzing the oxidative stress and lipid peroxidation of various xenobiotics. The RBCs contain a large number of enzymatic and non-enzymatic antioxidants. The changes of the RBCs antioxidant capacity could reflect the capability of xenobiotics to generate reactive oxygen species (ROS) resulting in oxidative damage of tissue. These criteria make RBCs a valuable in vitro model to evaluate the cytotoxicity of different natural or synthetic and organic or inorganic molecules by cellular damage measures.

Effects of combined vanadate and magnesium treatment on erythrocyte antioxidant defence system in rats

The effect of vanadate and magnesium treatment on erythrocyte defence system was studied in outbred 2-month-old, albino male Wistar rats (14 rats/each group) which daily received: Group I (Control)-deionized water to drink; Group II-water solution of sodium metavanadate (NaVO(3); SMV) at a concentration of 0.125mgV/mL; Group III-water solution of magnesium sulfate (MgSO(4); MS) at a concentration of 0.06mgMg/mL, Group IV-water solution of SMV-MS at the same concentrations over a 12-week time. The fluid intake and the concentration of reduced glutathione (GSH) as well as the activity of Cu, Zn-superoxide dismutase (Cu, Zn-SOD), catalase (CAT) and glutathione reductase (GR) were significantly decreased in the rats receiving SMV alone (Group II) or in combination with MS (Group IV) compared with Groups I and III. The cellular glutathione peroxidase (cGSH-Px) activity was unchanged in all the treated groups. The activity of glutathione S-transferase (GST) fell in the animals in Group II, compared with the rats in Groups I, III and IV; whereas in the rats in Group III its activity was higher than in the control animals. These results showed that V (as SMV) consumed by the rats with drinking water at a dose of 12mgV/kg b.w./24h for 12 weeks may attenuate defence system in rats' erythrocytes (RBCs), which is probably a consequence of vanadium pro-oxidant potential. Therefore, reactive oxygen species (ROS) are suggested to be involved in the alterations in antioxidant defence system in these cells. Mg (as MS) at the dose ingested (6mgMg/kg b.w./24h) at co-exposure to SMV was not able to counteract its deleterious effect. The results also provide evidence that V-Mg interactions may be involved in the decrease of erythrocyte GR activity and Mg concentration in the plasma under concomitant treatment with both metals at the doses of 12.6mgV and 6mgMg/kg b.w./24h.

Lipid peroxidation in the liver of rats treated with V and/or Mg in drinking water

The effect of V(5+) and Mg treatment on spontaneous and stimulated lipid peroxidation (LPO) was studied in liver supernatants obtained from outbred 5-month-old, albino male Wistar rats. The 2-month-old animals daily received deionized water to drink (control, group I); group II - water solution of NaVO(3) (SMV) at a concentration of 0.125 mg V ml(-1); group III - water solution of MgSO(4) (MS) at a concentration of 0.06 mg Mg ml(-1), group IV - water solution of SMV-MS at the same concentrations as in groups II and III for V and Mg, respectively, over a 12-week period. Three metal salts were selected as agents that may modify the LPO process (FeSO(4), NaVO(3) and MgSO(4)). V-intoxicated rats and those treated with V and Mg in combination had higher liver spontaneous malondialdehyde (MDA) formation, compared with the control and Mg-supplemented animals. In the same groups of animals the total antioxidant status (TAS) was also significantly lowered, in comparison with the control. In the supernatants obtained from the above-mentioned groups of rats a significant increase in MDA concentration was found in the presence of exogenous 30 microm FeSO(4) as well as 30, 100, 200 and 400 microm NaVO(3), compared with groups I and III. Significantly elevated MDA production was also observed in the supernatants obtained from the rats exposed to V and Mg in combination in the presence of exogenous 100 and 200 microm MgSO(4) in comparison with the control and group III as well as in the presence of exogenous 400 and 600 microm MgSO(4) compared only with group III. In vitro treatment with 1000 microm MgSO(4 )of control liver supernatants and those obtained from group III significantly enhanced MDA level, compared with spontaneous MDA formation. The two-way ANOVA indicated that the changes in the basal MDA level and in TAS in the rats at combined V and Mg application, were not due to V-Mg interaction, but resulted from independent action of V. In addition, the three-way ANOVA revealed that the changes in LPO induced by in vitro treatment of liver supernatants with exogenous Fe or V or Mg (600, 800 and 1000 microm) were a consequence of independent action of those metals and they also resulted from the interactions between Fe(exog) and V(end) and between V(end) and V(exog). In conclusion, V consumed by the rats with drinking water at a dose of 12 mg V kg(-1) body weight per 24 h for 12 weeks decreased TAS and enhanced spontaneous LPO in the hepatic tissue, which confirms its pro-oxidant potential, was also found in in vitro conditions with regard to LPO. Mg administered to rats in combination with V, at the concentration used, neither reduced nor intensified the basal LPO, compared with V-only treated animals; however, its stimulating effect on LPO was revealed in in vitro conditions, which requires further study.

Induction of aerobic peroxidation of liposomal membranes by bis(cyclopentadienyl)-vanadium(IV) (acetylacetonate) complexes

The ability of bis(cyclopentadienyl)-vanadium(IV) (acetylacetonate) (1) to initiate oxygen-dependent lipid peroxidation in zwitterionic liposomal membranes was examined in detail. A comparison of the rates of the lipid peroxidation reaction demonstrated that the electron-donating capacity of the substituted acetylacetonate ligand significantly influences the rate of reaction. An increase in the rate of lipid peroxidation correlated to a decrease in the V(IV)/V(V) redox potential. Notably, lipid peroxidation initiated with 1 proceeded without the formation of radicals as shown by EPR spin trap techniques. In contrast, lipid peroxidation initiated with non-chelated bis(cyclopentadienyl)-vanadium(IV) dichloride (6) was associated with the production of radicals under similar experimental conditions. There also was a significant pH effect on the extent of peroxidation initiated with 6 versus the reaction initiated with 1. The mode of action of 1 likely involves the activation of molecular oxygen by the vanadium(IV) center followed by allylic hydrogen atom abstraction from the lipid.

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.

Extensive electroporation abolishes experimentally induced shape transformations of erythrocytes: a consequence of phospholipid symmetrization?

As shown in earlier work (M.M. Henszen et al., Mol. Membr. Biol. 14 (1997) 195-204), exposure of erythrocytes to single brief electric field pulses (5-7 kV cm(-1)) enhances the transbilayer mobility of phospholipids and produces echinocytes which can subsequently be transformed into stomatocytes in an ATP-dependent process. These shape transformations arise from partly reversible changes of the transbilayer disposition of phospholipids, in agreement with the bilayer couple concept. Extensive membrane modification by repetitive (</=20) field pulses followed by 20 h incubation at 37 degrees C is now shown to produce discocytic cells which are resistant to many established shape-transforming treatments, including (A) single electric field pulses, Ca(2+) incorporation and exposure to membrane active amphiphiles, but also (B) metabolic depletion, binding of band 3 ligands, alkaline pH and contact with glass surfaces. The suppression of type A effects can readily be interpreted by a complete symmetrization of the phospholipids in extensively field pulse-modified cells which prevents shape transformations related to the asymmetric disposition of the phospholipids. This symmetrization could be further substantiated by more direct determinations of the transbilayer distribution of phospholipids. Suppression of shape transformations of type B may indicate an involvement of phospholipid asymmetry in these processes on a yet unknown mechanistic basis. Alternatively we discuss field pulse-induced alterations of the disposition of peripheral proteins or of the conformation of integral membrane proteins as mechanisms interfering with shape transformations of type B.

Passive transmembrane redistributions of phospholipids as a determinant of erythrocyte shape change. Studies on electroporated cells

Echinocytes formed from discocytic erythrocytes by electric field pulses at 0 degree C return to the discoytic shape upon incubation at 37 degrees C and subsequently turn into stomatocytes. Active and passive components of phospholipid translocation are involved in this shape recovery. Following low-field-strength pulses (5 kV cm-1), shape recovery is fully suppressed by ATPase inhibitors, such as vanadate. When vanadate is only added after stomatocyte formation has been completed, the cells return to the stage of echinocytosis prevailing before recovery. At higher field strength (7 kV cm-1) and in particular after repetitive field pulses, the subsequent incubation at 37 degrees C results in partial shape recovery even in the presence of vanadate. On the basis of the enhanced passive transmembrane mobilities of phospholipid probes observed previously following electroporation, the shape changes in the presence of vanadate are proposed to be due to a passive net movement of phospholipids from the outer to the inner membrane leaflet, as a consequence of the different mobilities of the various membrane phospholipids. Repetitive pulses at higher field strengths lead to a progressively more discocytic stationary shape during subsequent resealing. This phenomenon is explained by the progressively increased transbilayer mobility of the normally almost immobile phospholipid sphingomyelin and a consecutive progressive symmetrization of all membrane phospholipids.

In vitro effects of alloxan-vanadium combination on lipid peroxidation and on antioxidant enzyme activity

1. The in vitro effects of alloxan, dialuric acid and vanadium ions, alone or in combination, on lipid peroxidation and on antioxidant enzyme activity in rat liver and kidney were studied. 2. Unlike alloxan, alloxan-glutathione (GSH) and dialuric acid increased lipid peroxidation, which could be explained by the decreased activity of catalase and GSH peroxidase during incubation. 3. Vanadium(IV) ions increased the amount of thiobarbituric acid-reacting substances, but neither vanadium(IV) nor vanadium(V) changed the enzyme activity. 4. The combination of vanadium ions and alloxan-GSH or dialuric acid had no additive effect on lipid peroxidation. Vanadium ions decreased the dialuric acid-induced inhibition of catalase activity. 5. The present results suggest the therapeutic value of vanadium as an antidiabetic agent.

Oxidative stress of vanadium-mediated oxygen free radical generation stimulated by aluminium on human erythrocytes

It has been suggested that aluminium stimulates vanadium-mediated superoxide radical generation. The oxidative stress of generated superoxide radicals on antioxidant enzyme activity, oxidation of NADH and NADPH, membrane lipid peroxidation and osmotic fragility in human red blood cells (RBC) was investigated. RBC were incubated with varying concentrations of vanadium and aluminium ions at 37 degrees C for 2 h. RBC incubated with vanadium ions showed significantly increased superoxide dismutase and catalase activities, and oxidized NADH and NADPH concentrations compared with control RBC preparations. Erythrocyte lipid peroxidation was assessed by measuring thiobarbituric acid reactivity. RBC incubated with elevated levels of vanadium showed significantly increased membrane lipid peroxidation when compared with control RBC; it increased further on addition of aluminium. A significant positive correlation was observed between the extent of vanadium induced membrane lipid peroxidation and the osmotic fragility of treated RBC. In the presence of vanadium, aluminium stimulates superoxide dismutase and catalase activities. NADH and NADPH oxidation and membrane lipid peroxidation, as well as increasing osmotic fragility of human erythrocytes. The stimulatory effect of aluminium was dependent on concentration. These results may have implications for the mechanism of toxicity of aluminium and vanadium in haemodialysis patients.

Oral vanadyl sulphate does not affect blood cells, viscosity or biochemistry in humans

Vanadyl sulphate (VOSO4) is used to improve performance in weight training athletes. Concerns about its safety have arisen because vanadium compounds may cause anaemia and changes in the leukocyte system. In this study, the effects of oral VOSO4 (0.5 mg/kg/day) on haematological indices (red and white cell and platelet counts, red cell mean cell volume and haemoglobin level), blood viscosity (haematocrit, plasma viscosity and blood viscosity at 10s-1 and 100s-1 shear rates) and biochemistry (lipids and indices of liver and kidney function) were investigated in a twelve week, double blind, placebo controlled trial in 31 weight training athletes. Blood viscosity was evaluated at 0, 2, 4, 8 and 12 weeks and haematological indices and biochemistry were measured before and at the end of treatment. Both the treatment group and placebo group showed increases in haematocrit (3.3-3.6%) and blood viscosity (9-11% at 100s-1 shear; 35-38% at 10s-1 shear) but there were no significant effects of treatment. Similarly there were no treatment effects on haematological indices and biochemistry. Concerns about the adverse effects of oral vanadyl sulphate on blood are not supported by the results of this trial.

Vanadium(IV)-mediated free radical generation and related 2'-deoxyguanosine hydroxylation and DNA damage

Free radical generation, 2'-deoxyguanosine (dG) hydroxylation and DNA damage by vanadium(IV) reactions were investigated. Vanadium(IV) caused molecular oxygen dependent dG hydroxylation to form 8-hydroxyl-2'-deoxyguanosine (8-OHdG). During a 15 min incubation of 1.0 mM dG and 1.0 mM VOSO4 in phosphate buffer solution (pH 7.4) at room temperature under ambient air, dG was converted to 8-OHdG with a yield of about 0.31%. Catalase and formate inhibited the 8-OHdG formation while superoxide dismutase enhanced it. Metal ion chelators, DTPA and deferoxamine, blocked the 8-OHdG formation. Incubation of vanadium(IV) with dG in argon did not generate any significant amount of 8-OHdG, indicating the role of molecular oxygen in the mechanism of vanadium(IV)-induced dG hydroxylation. Vanadium(IV) also caused molecular oxygen-dependent DNA strand breaks in a pattern similar to that observed for dG hydroxylation. ESR spin trapping measurements demonstrated that the reaction of vanadium(IV) with H2O2 generated OH radicals, which were inhibited by DTPA and deferoxamine. Incubation of vanadium(IV) with dG or with DNA in the presence of H2O2 resulted in an enhanced 8-OHdG formation and substantial DNA double strand breaks. Sodium formate inhibited 8-OHdG formation while DTPA had no significant effect. Deferoxamine enhanced the 8-OHdG generation by 2.5-fold. ESR and UV measurements provided evidence for the complex formation between vanadium(IV) and deferoxamine. UV-visible measurements indicate that dG, vanadium(IV) and deferoxamine are able to form a complex, thereby, facilitating site-specific 8-OHdG formation. Reaction of vanadium(IV) with t-butyl hydroperoxide generated hydroperoxide-derived free radicals, which caused 8-OHdG formation from dG and DNA strand breaks. DTPA and deferoxamine attenuated vanadium(IV)/t-butyl-OOH-induced DNA strand breaks.

Lipid peroxidation and antioxidant enzymes in vanadate-treated rats

Male Wistar rats received an aqueous solution of ammonium metavanadate (AMV) of 0.15 mg/V/ml concentration instead of water for 14 days. The erythrocyte count and haemoglobin level in blood were not changed; the haematocrit index was slightly increased. The spontaneous lipid peroxidation in kidney and liver homogenates was increased. The Fe(II)- or ascorbate-induced lipid peroxidation was more pronounced in the kidney than in the liver. No changes in lipid peroxidation were observed in erythrocytes after AMV treatment. The AMV treatment resulted in a decrease in the activity of the antioxidant enzymes, catalase and glutathione peroxidase in the kidney and liver; the cytosolic Cu,Zn-SOD and mitochondrial Mn-SOD were unchanged. The activity of the enzymes in blood was not changed. The results are discussed with a view to the participation of lipid peroxidation in vanadium toxicity.

Superoxide-mediated lysis of erythrocytes: the role of colloid-osmotic forces

Although superoxide anions are a well-known mediator of cytotoxicity, their mechanism of target cell lysis is not clearly understood. In the present study we have used an exogenous source of superoxide to study erythrocyte cytolysis. RBC lysis was studied in buffers containing the cations Li+, Na+, K+, Rb+, and Cs+; superoxide anions were produced and available in these buffers. During this model superoxide-dependent cytolytic process, erythrocytes underwent a shape change from biconcave disk to sphere as shown by scanning electron microscopy. Soret band transmitted light microscopy has confirmed this shape change and shown that it precedes cytosolic oxidation. This evidence is consistent with a colloid-osmotic type lytic mechanism. Erythrocyte lysis was studied by 51Cr-release and light scattering methods. Superoxide-mediated target cytolysis was characterized by: 1) a sigmoidal dose-response curve and 2) a lag time in cytolysis after superoxide addition in kinetic light scattering experiments. The efficacy of cytolysis followed the rank order Cs+ > Rb+ > Na+, Li+ > sucrose = raffinose, which provides additional support for a colloid-osmotic lytic mechanism. Furthermore, the rank order potency correlates with the cations' hydration numbers. We suggest that oxidative events trigger the formation of colloid-osmotic pores approximately 1 nm in diameter.

Effect of chronic vanadium administration in drinking water to rats

Two-month old Wistar rats of both sexes received, as sole drinking liquid, an aqueous solution of ammonium metavanadate (AMV) at a concentration of 0.01 or 0.05 mg V cm-3 (0.2 or 1.0 mM) for a period of 4 weeks. It was calculated that the animals took up doses of 1.5 and 5-6 mg V kg body weight-1 24 h-1, respectively. Food and AMV solution consumption in the experimental group was similar to food and water consumption in the control group. A statistically significant decrease of consumption of AMV solution at a concentration of 0.05 mg V cm-3 was noted only in males. Hematological examination demonstrated a decrease in the erythrocyte count, hemoglobin level and hematocrit index. This decrease in the erythrocyte count was associated with an increased percentage of reticulocytes in the peripheral blood of the animals drinking the solution with a higher vanadium content. Biochemical analyses demonstrated a decrease of L-ascorbic acid levels in the plasma and erythrocytes of animals drinking the AMV solutions. A distinct tendency for the malonyldialdehyde level to increase in the blood was also observed. Among the enzymes examined in the erythrocytes (catalase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase and delta-aminolevulinic acid dehydratase [ALA-D]) only ALA-D activity was depressed.

Haematological effects of vanadium on living organisms

Although vanadium has been of great interest for many researchers over a number of years, its biochemical and physiological role is not yet fully clear. There are many papers describing the haematological consequences of its excess in living organisms and most of their data are quoted in this mini-review. The authors of these papers used various laboratory animals, different vanadium compounds, frequently different routes of administration and duration of intoxication. Hence a checklist and comparison of the results are rather difficult. Vanadium reduces the deformability of erythrocytes, and such cells are rather frequently retained in the reticuloendothelial system of the spleen and eliminated faster from the blood stream (Kogawa et al., 1976). Vanadium produces peroxidative changes in the erythrocyte membrane, this leading to haemolysis. Therefore, the depressed erythrocyte count in animals intoxicated with vanadium may be the consequence of both the haemolytic action of vanadium and the shortened time of survival of erythrocytes. Changes of the haem precursor level in blood serum and urine observed in humans exposed occupationally to vanadium suggest an influence of this element on haem synthesis. This problem requires, however, further studies and observations. Changes occurring under the influence of vanadium on the leukocyte system of animals suggest the influence of this element on the resistance of the organism, but the mechanism of the action of vanadium still requires elucidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics and site specificity of hydroperoxide-induced oxidative damage in red blood cells

To provide a detailed description of the time course and the site specificity of hydroperoxide-induced oxidative stress in red blood cells (RBCs), we have characterized the action of a membrane-soluble (cumene hydroperoxide [cumOOH]) and a water-soluble (hydrogen peroxide [H2O2]) oxidant. The fluorescent polyunsaturated fatty acid (PUFA) parinaric acid (PnA) was used to probe peroxidation processes in the membrane, and oxidation of hemoglobin (Hb) was measured spectrophotometrically as an indicator of cytosolic oxidative stress. The observed degradation patterns of PnA and Hb were clearly distinct for each oxidant. At comparable oxidant concentrations, the cumulative oxidative stress on the RBC membrane was always much higher with cumOOH, whereas much more Hb oxidation was measured with H2O2. The kinetics of Hb oxidation as well as the nature of the products formed were different for each oxidant. The main Hb oxidation product generated gradually by cumOOH was metHb, whereas H2O2 caused the rapid formation of ferrylHb. CumOOH caused more oxidation of endogenous PUFAs and of vitamin E, while the degradation pattern of vitamin E closely resembled that of PnA. At high oxidant concentrations, extensive cell lysis was observed after prolonged incubation. Butylated hydroxytoluene (BHT) completely prevented oxidation of endogenous PUFAs but did not completely prevent hemolysis, indicating that factors other than lipid peroxidation are also important in causing lysis of RBCs. The action of cumOOH is characterized by a gradual reaction with Hb, generating radicals that produce an oxidative stress primarily directed at the membrane, which increases in time to a maximum and then gradually decreases. In contrast, H2O2 crosses the RBC membrane and reacts rapidly with Hb, generating a very reactive radical species that has Hb, not the membrane, as a prime target. H2O2-induced oxidative stress is at a maximum immediately after addition of this oxidant and decreases rapidly to zero in a short time. These findings provide further insight into the mode of action of hydroperoxides and the mechanism of compartmentalization of RBC oxidative damage.

Influence of phloretin and alcohols on barrier defects in the erythrocyte membrane caused by oxidative injury and electroporation

Oxidative damage by diamide, periodate and oxygen-derived reactive species, but also exposure to electroporation induce in the erythrocyte membrane dynamic, presumably fluctuating, defects having the properties of aqueous holes with definable radii and selectivities. These leaks, which can be quantified by measuring tracer fluxes or rates of colloid-osmotic lysis, are here shown to be inhibited by phloretin and a small number of related phenol compounds (phenolphthalein, hydroxyacetophenones, nitrophenol), while a host of other 'membrane-active' agents is not effective in this respect. I50 values range from about 200 microM for phloretin and phenolphthalein to about 10 mM for 4-nitrophenol. Inhibition by phloretin is reversible, not competitive and not related in its extent to the extent of leakiness. In contrast, the enhancement of transbilayer mobility of amphiphilic lipid probes, which invariably goes along with leak formation of the type described, is not affected by phloretin. Aliphatic alcohols (hexanol, butanol) have an amplifying effect on leaks induced by oxidative damage but do not affect leaks induced by electroporation. The alcohol-amplified leaks maintain the properties of aqueous holes as indicated by a low activation energy of leak fluxes. Since both, inhibition and stimulation of leak fluxes do not go along with appreciable changes of the apparent radii of the aqueous holes, changes in the dynamics (opening and closing) of the defects are proposed to underly the effects of phloretin and alkanols. The membrane lipid domain is likely to be the site of the leaks and of their modulation.

The role of glycolysis and univalent ions in phthalocyanine-sensitized photohaemolysis of human erythrocytes

Phthalocyanines sensitize human erythrocytes to red light in vitro and in vivo. The mechanism of photosensitization of haemolysis of red blood cells was studied using haemoglobin release in vitro as an endpoint. We have previously shown that the cation present in the incubation medium determines the rate of photohaemolysis, with the rate increasing in the order Li+, Na+, K+, Cs+, Rb+. With halogen anions, the rate increases in the order F-, Cl-, Br-. With F- in isotonic solution the rate was about two orders of magnitude slower than with Cl-, so that haemolysis was practically prevented. Fluoride slowed haemolysis at very low concentrations (less than 1 mM) with an apparent K1 of 0.1 mM in isotonic NaCl. Most of the effect disappeared when F- was added after light exposure, with a half-time of 1 min. The effect of F- was specific to phthalocyanine. Neither Photofrin-induced photohaemolysis nor gramicidin-induced haemolysis were inhibited by fluoride. Addition of 10 mM deoxyglucose prior to photosensitization enhanced haemolysis and reduced cellular ATP levels by about 50% compared to controls containing glucose. Haemolysis was preceded by a reduction in ATP levels in the presence of both glucose and deoxyglucose. No significant decrease in ATP levels was found following light exposure in the presence of 0.75 mM F-. It is concluded that glycolysis and ATP are important in preventing photohaemolysis. The protective effect of F- may be related to its inhibition of a fast early reaction which triggers the events leading to photohaemolysis induced by phthalcyanine.

Reaction of vanadium(V) with thiols generates vanadium (IV) and thiyl radicals

The in vivo toxicity of vanadium(V) has been found to correlate with the depletion of cellular glutathione and related non-protein thiols. With a view to understanding the mechanism for this observation, we have investigated the oxidation of glutathione, cysteine N-acetylcysteine and penicillamine by vanadium(V), using electron spin resonance (ESR) and ESR spin trapping methodology. The spin trap used was 5,5-dimethyl-1-pyrroline 1-oxide (DMPO). It is found that the oxidation of these thiols by vanadium(V) generates the corresponding thiyl radicals and vanadium- (IV) complexes. The results suggest that free radical reactions play a significant role in the depletion of cellular thiols by vanadium(V) and hence in vanadium(V) toxicity.

Nonmediated flip-flop of phospholipid analogues in the erythrocyte membrane as probed by palmitoylcarnitine: basic properties and influence of membrane modification

The rules governing the transbilayer reorientation (flip-flop) of long-chain amphiphilic components in biological membranes were further elucidated by studying the flip-flop of palmitoylcarnitine in human erythrocytes. Flip rates were derived from the time-dependent decrease of extractability of palmitoylcarnitine by albumin after primary insertion of trace amounts of the labeled probe into the outer membrane layer. The flip rate (half time 2.6 hr at 37 degrees C in human erythrocytes) is fast enough to be measurable also in membranes exhibiting low flip rates such as that of ox erythrocytes. Flip rate constants for the inward and outward reorientation are similar and the probe equilibrates at a 1:1 ratio between the two layers. The flip is a simple, diffusion-like process. It is not inhibited but even enhanced by chemical modification of membrane proteins. It is also enhanced by insertion of channel-forming antibiotics into the membrane and by pre-exposure of the cells to temperatures exceeding 42 degrees C. The extent of this enhancement increases with the duration and the temperature of the pre-exposure. Since spectrin is denatured in this range of temperatures, the finding constitutes a new piece of evidence that the membrane skeleton is involved in the maintenance of bilayer stability and that a decrease of bilayer stability goes along with the formation of local defects acting as flip sites for phospholipids and related compounds. As a particularity, the flip is enhanced by lowering the pH and exhibits interindividual variability, phenomena not observed for the flip-flop of lysophosphatidylcholine. This suggests that generalizations on the kinetics of nonmediated flip-flop of membrane-intercalated amphiphiles may not be justified.

The effect of ferricyanide with iodoacetate in calcium-free solution on passive cation permeability in human red blood cells: comparison with the Gardos-effect and with the influence of PCMBS on passive cation permeability

Freshly prepared human red blood cells incubated with 5 mM ferricyanide, 0.2 mM iodoacetate and 2 mM adenosine in the presence of 5 mM EGTA demonstrate comparable increases in Na+ and K+ permeability (ferricyanide effect). This effect is unrelated to the Ca2+-activated K+ channel (Gardos effect) since influx of Ca2+ from outside the cell is excluded. Also this effect is different from the non-specific Na+ and K+ permeability change elicited by PCMBS. These differences become obvious by using various reagents. For example, A23187 and quinidine exert opposite effects in Gardos and ferricyanide experiments, where A23187 and atebrin react oppositely in the latter and in PCMBS experiments. The ferricyanide effect described here does not involve formation of nonspecific channels. The change in Na+ permeability separately from K+ permeability under certain circumstances suggests a more specific effect.

Enhancement of transbilayer mobility of a membrane lipid probe accompanies formation of membrane leaks during photodynamic treatment of erythrocytes

In order to further characterize membrane alterations in human erythrocytes subjected to photodynamic treatment the passive transbilayer mobility of a phospholipid analogue was studied in cells illuminated for various lengths of time in the presence of the photosensitizer, aluminum chlorotetrasulfophthalocyanine. These measurements were combined with the characterization of the membrane leaks for polar solutes occurring under the same conditions with respect to their apparent size, number and ion selectivity. The time-dependent photodynamic enhancement of leaks for K+ as well as choline or erythritol was paralleled by a marked increase of the transbilayer reorientation rate of the amphiphilic lipid probe, palmitoyllysophosphatidylcholine from 0.05% min-1 in native cells to 0.32% min-1 after 60 min illumination. The asymmetric orientation of native phospholipids was not affected by this treatment. The leak permeability proved to be due to the formation of pores with apparent radii of about 0.45 nm after 60 min illumination, and of 0.75 nm after 90 min. The number of pores per cell was calculated to be less than 1, the pores are slightly cation-selective (PK/PCl approximately 3:1). Since photodynamic treatment did not induce lipid peroxidation under the prevailing experimental conditions, protein modification must be the primary cause of both, leak permeability and flip enhancement. Since it is also likely that the leak permeability arises from oxidation of intrinsic membrane proteins, the results raise the interesting possibility that oxidative alteration of intrinsic membrane proteins may lead to enhanced transbilayer mobility of lipids.

Mechanism of spectrin degradation induced by phenylhydrazine in intact human erythrocytes

The exposure of human erythrocytes to phenylhydrazine results in the degradation of both monomers of spectrin, a major cytoskeleton membrane protein. The degradative process, characterized by a loss of spectrin without the appearance of high-molecular-weight products, either under reducing conditions or not, is almost complete in 10 min when a 5% erythrocyte suspension is treated with 1 mM phenylhydrazine. Under these conditions, we found a loss of 62.3 and 48.5% for the alpha and beta monomer, respectively. A similar degradative extent was obtained when the membrane ghost plus cellular free extracts, were dialyzed, and the membrane ghost plus hemoglobin was exposed to 1 mM phenylhydrazine for 10 min. The presence of different proteinase inhibitors and effectors, such as EDTA, diethylenetriaminepentaacetic acid, EGTA, leupeptin, aprotinin, phenylmethylsulfonyl fluoride, pepstatin, Ca2+ and ATP plus Mg2+, in the membrane ghost plus cellular free extract system (undialyzed) did not affect the degree of the spectrin-degradative process induced by phenylhydrazine. In addition, a purified spectrin tetramer preparation exposed to 1 mM phenylhydrazine in the presence of hemoglobin was degraded to an extent comparable to that with intact cells. Our data suggest that the initial degradative step of spectrin induced by phenylhydrazine in intact erythrocytes may be ascribed more to a direct oxidative breakdown, probably involving main-chain cleavage and side-chain cleavage processes, than to an eventual proteolytic system.

Chemo-mechanical leak formation in human erythrocytes upon exposure to a water-soluble carbodiimide followed by very mild shear stress. I. Basic characteristics of the process

Human erythrocytes treated with low concentrations (1-5 mM) of the carboxyl group-modifying reagent 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) lose their native deformability in parallel with extensive cross-linking of the membrane skeleton. After treatment with higher (5-40 mM) concentrations of the reagent the cells develop a hitherto undescribed property: when subjected to even very low shear stresses (resuspension after packing by centrifugation or viscometric shearing at up to 4 s-1) they become highly leaky to ions, lose their K+ with a half-time of about 5 min and subsequently undergo hemolysis. Lysis is not accompanied by cell fragmentation as occurs with mechanical hemolysis, but is colloid-osmotic, due to the formation of aqueous membrane leaks with an apparent radius of about 3 nm. Leakiness and lysis affect an increasing fraction of the cell population, in relation to (a) the concentration of EDC applied, (b) the shearing intensity, and (c) particularly, the hematocrit during shearing. The physical parameter determining the mechanical component of this 'chemo-mechanical' leak formation is not predominantly the shear stress. Rather, cell-cell interactions of as yet undefined nature seem to be involved. The analysis of chemo-mechanical leak formation may provide interesting insights into the influence of mechanical forces on membranes.

Vanadium and lipid peroxidation: evidence for involvement of vanadyl and hydroxyl radical

The present study was designed to determine which form of vanadium is involved in initiating conjugated diene formation in both purified and partially peroxidized fatty acids, and to determine if active oxygen radicals are involved in this process. We report that vanadyl is the active form of vanadium in initiating conjugated diene formation in micelles prepared from purified fatty acids or partially peroxidized fatty acids. Vanadate did not initiate conjugated diene formation in either case. Hydroxyl radicals were shown to be involved in the initiation of diene conjugation when vanadyl and hydrogen peroxide were added together in a reaction mixture. In this case, there was a rapid burst of conjugated diene formation which quickly leveled off. Using spin trapping techniques, hydroxyl radicals were shown to be generated in the vanadyl-catalyzed break-down of fatty acid hydroperoxides. A comparison was made between the ability of vanadyl or vanadyl chelates to decompose hydrogen peroxide and catalyze the decomposition of fatty acid hydroperoxides. It was found that strongly chelated vanadyl (vanadyl/EDTA) was much less effective in decomposing both hydrogen peroxide and fatty acid hydroperoxides than the weak vanadyl chelates (e.g., vanadyl/ADP). This study suggests a mechanism to explain the effects of vanadium on lipid peroxidation.