Ligands and oxidants in ferrihemochrome formation and oxidative hemolysis

Abstract

We have investigated the effect of size of a single neutral ring substituent on the induction of hemolytic anemia and the formation of a ferrihemochrome by substituted phenylhydrazines. The severity of induced anemia decreased with increase in size of a halogen atom or an alkyl group ortho to the hydrazino group, little anemia resulting from 2-iodophenylhydrazine and no anemia from 2-tert-butylphenylhydrazine. The size of a halogen atom or an alkyl group at the meta or para position had relatively little effect on the severity of induced anemia. The ability of an arylhydrazine to induce hemolytic anemia paralleled its ability to produce a ferrihemochrome with an exogenous ligand, probably the corresponding aryldiazene. In general, rapid and complete formation of ferrihemochrome occurred-with arylhydrazines that induced severe anemia. The degree of hemolysis induced by an arylhydrazine was not related to its rate of autooxidation, i.e., the rate at which oxidants are formed by the reduction of oxygen. We propose a mechanism of arylhydrazine-induced oxidative denaturation based on the simultaneous formation of hydroxyl radical and aryldiazene ferrihemochrome in a reaction of oxyhemoglobin with arylhydrazine. We suggest that after oxidation of the porphyrin ring is initiated by a hydroxyl radical, oxidative cleavage of the ring is facilitated by the presence of a large li-

beta-meso-Phenylbiliverdin IX alpha and N-phenylprotoporphyrin IX, products of the reaction of phenylhydrazine with oxyhemoproteins.

“…Fe"H202 + C6H5NHNH2--Fe"I + 2H20 + C6H5N:NH or FeNVO + C6H5NHNH2 -> Fe"i + H20 + C6H5N:NH. [4] Formation of a second molecule of phenyldiazene agrees with the finding (23) that two molecules of 02 per oxyheme were rapidly consumed in the reaction of an excess of phenylhydrazine with oxyhemoglobin.…”

“…Studies from this laboratory indicated that substituents on the benzene ring affected the hemolytic activity of substituted phenylhydrazine and the binding ofsubstituted phenyldiazenes to methemoglobin in parallel fashion (4). Subsequent studies showed, however, that the hemolytic activity of ring-substituted nitrosobenzenes was not related to their affinities as ligands of deoxyhemoglobin (5).…”

“…A two-electron transfer to oxyhemoglobin was suggested as the initial step in the degradation ofheme mediated by ascorbic acid (6), and the same transfer was postulated in the reaction of phenylhydrazine with oxyhemoglobin (4). Although the processes may be initiated in the same way, different reported products, biliverdin with ascorbic acid (2) and an intact porphyrin with phenyihydrazine (3), indicate that subsequent steps are different.…”

Role of Free Radical Reactions in Myelodysplastic Syndrome

“…may be due to the action of free radicals and other activated oxygens [12][13][14][15][16][17]. Life itself, however, is protected against these oxidant stresses by reducing enzymes such as superoxide dismutase, catalase, GSH-Px, etc., and other free radical scavengers, like vitamins A, B2, C, E (tocopherol), and ubiquinone (CoQ).…”

Free-radical production and oxidative reactions of hemoglobin.

“…Breakdown of the diazine (PhN = NH) is fast and 02--dependent, but it is stabilized in the presence of methemoglobin by formation of hemichrome (43)(44)(45)(46). With APH the diazine also forms hemichrome, but does not readily break down to benzene (44).…”