Evidence that superoxide radicals are involved in the hemolytic mechanism of phenylhydrazine

Protection by iron salts against sporidesmin intoxication in sheep

A number of iron compounds have been shown to protect sheep against the harmful effects of the facial eczema toxin, sporidesmin. Various salts were found to be effective; the oxidation state of the metal was not important although water-solubility did appear to be a prerequisite for prophylactic activity. The effect of iron salts was additive with that of zinc, and it is suggested that the protective action of these compounds results from their ability to inhibit the absorption of copper, consistent with the previously-proposed free-radical mechanism for sporidesmin toxicity.

Spectrin degradation in intact red blood cells by phenylhydrazine

The effects of phenylhydrazine on intact red cells and on red cell ghost membrane proteins were studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In intact red cells 1 mM phenylhydrazine induced a marked decrease in intensity of the alpha- and beta-bands of spectrin without the formation of high molecular weight materials. Phenylhydrazine was also responsible for cross-linking of hemoglobin, which is apparent by the appearance of two new broad bands on the gel. Membrane glycoproteins were unaffected. Electrophoretic patterns of cytoskeletal proteins from phenylhydrazine-treated red cells obtained on two-dimensional SDS-polyacrylamide gels and stained with Coomassie blue or fluorescently labeled with monobromobimane indicated the presence of a new band between bands 4.2 and 5 at 60-65 kilodaltons (K). An immunoelectrophoretic blotting procedure utilizing polyclonal IgG antibodies for alpha- and beta-spectrin of the red cell cytoskeletal proteins revealed that the band observed at 60-65 K in the two-dimensional SDS-PAGE studies reacted with the antibodies. The presence or absence of glucose in the incubation medium and modification of oxyhemoglobin to met- or carboxyhemoglobin in the red cells did not protect the phenylhydrazine-mediated degradation of the major cytoskeletal proteins. Metal chelators and antioxidants had no effect on membrane protein changes. Ghost red cell proteins did not undergo changes at 1 mM phenylhydrazine in the presence or absence of hemoglobin, although at 5 mM phenylhydrazine the appearance of a faint high molecular weight band was observed. These results indicate that spectrin degradation without significant polymerization can be induced by phenylhydrazine.

Toxicity of aromatic disulphides. I. Generation of superoxide radical and hydrogen peroxide by aromatic disulphides in vitro

The aromatic thiol, thiophenol, is readily autoxidized at neutral pH in a reaction which generates superoxide radical and hydrogen peroxide. The oxidation product, diphenyl disulphide, may be reduced back to thiophenol by glutathione and in the presence of an excess of the latter thiol a reduction/autoxidation cycle for generation of 'active oxygen' species is established. The autoxidation reaction is strongly catalysed by haematin; haemoglobin is also an effective mediator of 'active oxygen' generation from the diphenyl disulphide/glutathione couple, being oxidized to methaemoglobin in the process. Certain derivatives of diphenyl disulphide also generate superoxide radical and hydrogen peroxide in the presence of glutathione, although the rate of the reaction is strongly influenced by the nature of the substituent groups. Among the ring-substituted derivatives of diphenyl disulphide investigated, the rate of 'active oxygen' production decreased in the order 4-amino greater than 2-amino greater than 4-methyl greater than unsubstituted greater than 4-nitro greater than 2-carboxyl; little reaction was detected with the homologous compound, dibenzyl disulphide.

Protective effect of the flavonoid silybin dihemisuccinate on the toxicity of phenylhydrazine on rat liver

Phenylhydrazine is a hemolytic agent whose mechanism of action is related with the formation of free radicals and the induction of lipid peroxidation. The flavonoid silybin dihemisuccinate is an antihepatotoxic principle used in the treatment of many liver diseases; its mechanism of action has been ascribed to its antioxidant properties. This work demonstrates, using a hemoglobin-free perfusion system, the protective effect of the in vivo treatment of the rat with silybin dihemisuccinate on the hepatic glutathione depletion and lipid peroxidation induced by the infusion of phenylhydrazine into the perfusion buffer.

Inhibitory effect of the flavonoid silymarin on the erythrocyte hemolysis induced by phenylhydrazine

The flavonoid silymarin, which is used as a therapeutical agent in the treatment of liver diseases, can inhibit the hemolysis and lipid peroxidation induced by phenylhydrazine on erythrocytes obtained from rats treated with the flavonoid. This effect is ascribed to the antioxidant properties as a free radical scavenger exhibited by the flavonoid. Silymarin failed to inhibit the glutathione depletion induced by phenylhydrazine on erythrocytes. It is proposed that the flavonoid acts at the membrane level of the cell avoiding the lipid peroxidative and fluidizing effect of phenylhydrazine.

Reaction of phenylhydrazine with erythrocytes. Cross-linking of spectrin by disulfide exchange with oxidized hemoglobin

Phenylhydrazine causes deleterious oxidations of components of erythrocytes. These reactions and their effects on the mechanical properties of rabbit erythrocytes are investigated to provide insight into the mechanisms leading to destruction of oxidatively damaged erythrocytes. After 1 hr of incubation with phenylhydrazine, precipitated denatured protein (Heinz body protein) amounts to 25-30% of membrane protein, but deformability of erythrocytes as measured by filtrability is unchanged. After 4 hr of incubation filtrability drops sharply. Polymerization of spectrin and covalent binding of hemoglobin to spectrin, but no peroxidation of membrane lipids is observed. Precipitated protein amounts to 85-95% of membrane protein. It contains Fe, porphyrin and globin peptide in the proportion 1:1:1. Heinz body protein precipitated when hemoglobin is incubated under similar conditions has 90% of its sulfhydryl groups oxidized and no other amino acids than cysteine are destroyed. Addition of this Heinz body protein to erythrocyte ghosts causes polymerization of spectrin. Incubation of tetrathionate, a specific cross-linking agent, causes filtrability to drop sharply after about 80 min. This effect is similar to that observed after 4 hr incubation with phenylhydrazine, and is accompanied by polymerization of spectrin and band 3. The results indicate that cross-linking of membrane proteins by disulfide exchange with precipitated hemoglobin may play a major role in decreasing deformability during incubation with phenylhydrazine.

The haemolytic reactions of 1-acetyl-2-phenylhydrazine and hydrazine: a spin trapping study

Free radical production from the reaction of hydrazine and 1-acetyl-2-phenylhydrazine (AcPhHZ) with oxyhaemoglobin and with human red blood cells, has been observed by the electron spin resonance technique of spin trapping. Using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the free radical intermediates detected depended on the hydrazine derivative, oxyhaemoglobin and the oxyhaem/hydrazine derivative concentration ratio. The reaction of hydrazine with oxyhaemoglobin in the presence of DMPO gave a nitroxide which was identified as a reduced dimer of DMPO. Whereas hydrazine-treated red blood cells, in the presence of DMPO, gave a nitroxide spin adduct which was identified as the hydroxyl radical spin adduct of DMPO, 5,5-dimethyl-1-pyrrolidino-1-oxyl (DMPO-OH). The reaction of AcPhHZ with oxyhaemoglobin, in the presence of DMPO, gave DMPO-OH, the phenyl radical spin adduct of DMPO, 5,5-dimethyl-2-phenylpyrrolidino-1-oxyl (DMPO-Ph) and an oxidised derivative of DMPO, 5,5-dimethyl-2-pyrrolidone-1-oxyl (DMPOX). The amounts of DMPO-Ph, DMPO-OH and DMPOX observed depended on the 1-acetyl-2-phenyl-hydrazine/oxyhaemoglobin concentration ratio; DMPOX replaced DMPO-OH as the concentration of AcPhHZ was decreased. DMPOX production has been previously associated with the production of highly oxidised haem iron-oxygen intermediates. AcPhHZ treated red blood cells gave DMPO-Ph and DMPO-OH spin adducts in the presence of DMPO. DMPO had little to no effect on the rate of oxygen consumption by oxyhaemoglobin with hydrazine and AcPhHZ. Moreover, the rate of oxyhaemoglobin oxidation induced by hydrazine, was not decreased by DMPO whereas the rate of oxyhaemoglobin oxidation induced by AcPhHZ was decreased approx. 40% by DMPO. DMPO (10 mM) gave a small decrease in haemolysis and lipid peroxidation induced by 1 mM hydrazine and AcPhHZ in a 1% suspension of red blood cells.

Phenylhydrazine-induced lipid peroxidation of red blood cells in vitro and in vivo: monitoring by the production of volatile hydrocarbons

Human red blood cells and male Sprague-Dawley rats were treated in vitro and in vivo, respectively, with phenylhydrazine in order to determine whether the release of volatile hydrocarbons can serve as a suitable index for phenylhydrazine-induced red blood cell peroxidation. Lipid peroxidation following phenylhydrazine administration (in vitro experiments: dosage calculated at 0.5-50 mM; in vivo experiments: intraperitoneal injection of 2.8 mg/100 g body wt) was monitored by the release of ethane and pentane measured by gas chromatography. Further hydrocarbons such as ethylene, propane, n-butane, iso-butane and iso-butene were monitored to form a basis of comparison. In vitro haemolysis was also determined during the course of incubation. Red blood cell suspensions yielded more than 15-fold concentrations of propane and more than 2-fold concentrations of iso-butane compared to pentane and ethane yields. Haemoglobin solutions also produced propane and iso-butane in the presence of phenylhydrazine, whereas pentane and ethane were not detectable. Time-course studies revealed that ethane and pentane reached maximum in vitro levels after red blood cell suspensions had been incubated for 2 hr whereas the maximum degree of haemolysis (approximately 60%) was attained between 60 and 90 min following the beginning of phenylhydrazine treatment. The dosage did not affect the final degree of haemolysis. Rats treated with phenylhydrazine exhaled greater concentrations of ethane (6-fold increase) and pentane (2-fold increase) compared to control animals. Exhaled propane showed a 30-fold increase in concentration following drug treatment. Our results suggest that the release of pentane and ethane may be useful in assessing red blood cell lipid peroxidation in the presence of phenylhydrazine in vitro and in vivo.

Haemoglobin denaturation, lipid peroxidation and haemolysis in phenylhydrazine-induced anaemia

Temporal changes in the levels of denatured haemoglobin (Heinz bodies) and fluorescent lipid peroxidation products in the red cells of rabbits administered phenylhydrazine have been followed. Heinz bodies were maximal just before the period when most of the cell destruction occurred, whereas lipid peroxidation products were maximum when reticulocyte levels were highest. This implies that lipid peroxidation occurs mainly in immature cells and that haemoglobin denaturation is more likely than lipid peroxidation to be a major contributor to haemolysis.

Disorder in human myelin induced by superoxide radical: an in vitro investigation

Potassium superoxide (KO.2), applied as a source of superoxide radical directly in vitro to white matter from young adult human brain, caused the lipid phase of the myelin to change from a crystalline (ordered) state to a liquid crystalline (disordered) state. The myelin transition temperature decreased from 65 degrees C to 37 degrees C. This alteration was accompanied by a dramatic increase in the levels of lipid peroxidation products--malondialdehyde, a conjugated diene, and ethane. These changes in human myelin, induced by direct application of O2-. radical, simulated myelin deterioration that occurs in the course of natural aging, thus, providing further substantiation for the notion that O2-. might be a major toxic agent associated with the aging process.

The effect of spin traps on phenylhydrazine-induced haemolysis

Spin-trapping agents have been used to study the involvement of free radicals in phenylhydrazine-induced haemolysis. Spin traps were found to decrease the rate of oxygen uptake and the rate of haemoglobin oxidation in the reaction of phenylhydrazine with oxyhaemoglobin. Spin traps were also found to inhibit haemolysis and lipid peroxidation in phenylhydrazine-treated fresh human erythrocytes, with a concomitant production of phenyl radical spin adducts. Lipophilic spin traps were found to be more effective inhibitors of haemolysis than their hydrophilic analogues.

Studies on the mechanism of toxicity of the mycotoxin, sporidesmin. I. Generation of superoxide radical by sporidesmin

Sporidesmin (SDMS2), the mycotoxin responsible for 'facial eczema' in ruminants, contains a disulphide group which appears to be intimately involved in its toxic action. The reduced (dithiol) form of sporidesmin has been shown readily to undergo autoxidation in vitro in a reaction which generates superoxide radical (O2-). The autoxidation reaction, which takes place over a wide pH range, is strongly catalysed by trace amounts of copper, although the reaction was inhibited at high concentrations of this metal. Inhibition of the autooxidation of reduced sporidesmin (SDM(SH)2) was also observed in the presence of nickel, cobalt and manganese. Superoxide radical is also generated from SDMS2 itself in a cyclic reduction/autoxidation reaction with glutathione and other thiols; in view of the known toxicity of superoxide and its derivatives, it is suggested that oxygen-free-radicals may be involved in the initiation of the deleterious effects of the mycotoxin.

Effects of scavengers of superoxide radicals, hydrogen peroxide, singlet oxygen and hydroxyl radicals on malondialdehyde generation from arachidonic acid by bovine seminal vesicle microsomes

Superoxide dismutase, catalase and sodium formate did not inhibit the formation of malondialdehyde (MDA) from arachidonic acid, suggesting that O2-., H2O2 and OH. are not involved in the enzymatical oxidation of arachidonic acid. Sodium azide was found to be an inhibitor of MDA production.