Ligands and oxidants in ferrihemochrome formation and oxidative hemolysis

Single-Nucleotide Polymorphisms in Glucose-6-Phosphate Dehydrogenase and their Relevance for the Deployment of Primaquine as a Radical Cure for Malaria

Malaria remains an important public health problem despite efforts to control it. Besides active transmission, relapsing malaria caused by dormant liver stages of Plasmodium vivax and Plasmodium ovale hypnozoites is a major hurdle in malaria control and elimination programs. Primaquine (PQ) is the most widely used drug for radical cure of malaria. Due to its anti-hypnozoite and gametocidal activity, PQ plays a key role in malaria relapse and transmission. The human enzyme glucose-6-phosphate dehydrogenase (G6PD) is crucial in determining the safety of PQ because G6PD-deficient individuals are prone to hemolysis if treated with PQ. Therefore, there is a need to study the prevalence of G6PD-deficient genetic variants in endemic populations to assess the risk of PQ treatment and the necessity to develop alternative treatments. In this work, we discuss the common G6PD variants, their varying enzymatic activity, and their distribution on the three-dimensional structure of G6PD. Our work highlights the important G6PD variants and the need for large-scale G6PD gene polymorphism studies to predict populations at risk of PQ-induced toxicity.

Formation and Detection of Highly Oxidized Hemoglobin Forms in Biological Fluids during Hemolytic Conditions

Hemolytic diseases are characterized by an accelerated breakdown of red blood cells (RBCs) and the release of hemoglobin (Hb). Following, RBC lysis Hb oxidation occurs with the formation of different redox states of Hb (metHb and ferrylHb) and the release of heme. ferrylHb is unstable and decomposes to metHb with the concomitant formation of globin radicals and eventually covalently crosslinked Hb multimers. The goal of the present study was to determine the concentrations of the different redox states of Hb in biological samples during hemolytic conditions. We used plasma and urine samples of mice with intravascular hemolysis and human cerebrospinal fluid (CSF) samples following intraventricular hemorrhage. Because ferrylHb is highly unstable, we also addressed the fate of this species. metHb and free heme time-dependently accumulate in plasma and CSF samples following intravascular hemolysis and intraventricular hemorrhage, respectively. ferrylHb is hardly detectable in the biological samples during hemolytic conditions. Under in vitro conditions, ferrylHb decomposes quickly to metHb, which process is associated with the formation of covalently crosslinked Hb multimers. We detected these covalently crosslinked Hb multimers in plasma, urine, and CSF samples during hemolytic conditions. Because globin modification is specific for these Hb forms, we propose to call this heterogeneous form of Hb produced during ferrylHb decomposition as globin-modified oxidized Hb (gmoxHb). Understanding the formation and the contribution of gmoxHb species to the pathogenesis of hemolytic conditions could have therapeutic implications in the treatment of hemolytic diseases.

Tafenoquine: A Step toward Malaria Elimination

There is a pressing need for compounds with broad-spectrum activity against malaria parasites at various life cycle stages to achieve malaria elimination. However, this goal cannot be accomplished without targeting the tenacious dormant liver-stage hypnozoite that causes multiple relapses after the first episode of illness. In the search for the magic bullet to radically cure Plasmodium vivax malaria, tafenoquine outperformed other candidate drugs and was approved by the U.S. Food and Drug Administration in 2018. Tafenoquine is an 8-aminoquinoline that inhibits multiple life stages of various Plasmodium species. Additionally, its much longer half-life allows for single-dose treatment, which will improve the compliance rate. Despite its approval and the long-time use of other 8-aminoquinolines, the mechanisms behind tafenoquine's activity and adverse effects are still largely unknown. In this Perspective, we discuss the plausible underlying mechanisms of tafenoquine's antiparasitic activity and highlight its role as a cellular stressor. We also discuss potential drug combinations and the development of next-generation 8-aminoquinolines to further improve the therapeutic index of tafenoquine for malaria treatment and prevention.

8-Aminoquinoline Therapy for Latent Malaria

The technical genesis and practice of 8-aminoquinoline therapy of latent malaria offer singular scientific, clinical, and public health insights. The 8-aminoquinolines brought revolutionary scientific discoveries, dogmatic practices, benign neglect, and, finally, enduring promise against endemic malaria. The clinical use of plasmochin-the first rationally synthesized blood schizontocide and the first gametocytocide, tissue schizontocide, and hypnozoitocide of any kind-commenced in 1926. Plasmochin became known to sometimes provoke fatal hemolytic crises. World War II delivered a newer 8-aminoquinoline, primaquine, and the discovery of glucose-6-phosphate dehydrogenase (G6PD) deficiency as the basis of its hemolytic toxicity came in 1956. Primaquine nonetheless became the sole therapeutic option against latent malaria. After 40 years of fitful development, in 2018 the U.S. Food and Drug Administration registered the 8-aminoquinoline called tafenoquine for the prevention of all malarias and the treatment of those that relapse. Tafenoquine also cannot be used in G6PD-unknown or -deficient patients. The hemolytic toxicity of the 8-aminoquinolines impedes their great potential, but this problem has not been a research priority. This review explores the complex technical dimensions of the history of 8-aminoquinolines. The therapeutic principles thus examined may be leveraged in improved practice and in understanding the bright prospect of discovery of newer drugs that cannot harm G6PD-deficient patients.

The mechanism of formation, structure and physiological relevance of covalent hemoglobin attachment to the erythrocyte membrane

Covalent hemoglobin binding to membranes leads to band 3 (AE1) clustering and the removal of erythrocytes from the circulation; it is also implicated in blood storage lesions. Damaged hemoglobin, with the heme being in a redox and oxygen-binding inactive hemichrome form, has been implicated as the binding species. However, previous studies used strong non-physiological oxidants. In vivo hemoglobin is constantly being oxidised to methemoglobin (ferric), with around 1% of hemoglobin being in this form at any one time. In this study we tested the ability of the natural oxidised form of hemoglobin (methemoglobin) in the presence or absence of the physiological oxidant hydrogen peroxide to initiate membrane binding. The higher the oxidation state of hemoglobin (from Fe(III) to Fe(V)) the more binding was observed, with approximately 50% of this binding requiring reactive sulphydryl groups. The hemoglobin bound was in a high molecular weight complex containing spectrin, ankyrin and band 4.2, which are common to one of the cytoskeletal nodes. Unusually, we showed that hemoglobin bound in this way was redox active and capable of ligand binding. It can initiate lipid peroxidation showing the potential to cause cell damage. In vivo oxidative stress studies using extreme endurance exercise challenges showed an increase in hemoglobin membrane binding, especially in older cells with lower levels of antioxidant enzymes. These are then targeted for destruction. We propose a model where mild oxidative stress initiates the binding of redox active hemoglobin to the membrane. The maximum lifetime of the erythrocyte is thus governed by the redox activity of the cell; from the moment of its release into the circulation the timer is set.

Comparative study of the cytoplasmic domain of band 3 from human and rabbit erythrocyte membranes

The cytoplasmic domain of band 3 (cdb3) is thought to play an important role in human erythrocyte aging. In order to investigate the role of cdb3 during rabbit erythrocyte aging, we compared rabbit cdb3 with the corresponding protein from human erythrocyte membranes. We describe a purification procedure for rabbit cdb3 comparing rabbit and human cdb3 on sodium dodecyl sulphate-polyacrylamide electrophoresis, we found fragments of different molecular weights, implying different chymotryptic cuts in the two species. Anti-human antibodies did not bind to the rabbit cdb3; we also noticed structural differences in the protein between the two species, which may also play a role in the aging processes. Rabbit erythrocyte membranes have a higher capacity of binding hemichromes, due to the higher content of band 3. While in rabbit erythrocyte membranes only one binding site for hemichromes (corresponding to cdb3) was found, we confirmed the existence of two binding sites in human membranes. The second binding site probably corresponds to glycophorin, a protein not present in rabbit membranes.

Difference in rates of the reaction of various mammalian oxyhemoglobins with phenylhydrazine

Second order rate constants for the initial reaction of 12 mammalian oxyhemoglobins (Hb) with equimolar phenylhydrazine (PHZ), a compound inducing Heinz body hemolytic anemia, were determined by recording continuous changes in absorbance with time at 577 nm. The rate constants were varied in a range from 43 m-1.s-1 with pig Hb to 255 m-1.s-1 with dog Hb. On the other hand, isosbestic points at 526 and 587 nm were common to all the reaction processes. The aerobic reaction of Hb with PHZ resulted in denaturation of hemoprotein, and final reaction products were determined to be beta-meso-phenylbiliverdin IX alpha and N-phenylprotoporphyrin IX. These results suggest that the reactivity of PHZ to Hb is influenced by the globin molecule, and the oxidative cleavage of the porphyrin ring causes the denaturation of hemoprotein.

Reactions of prostaglandin H synthase with monosubstituted hydrazines and diazenes. Formation of iron(II)-diazene and iron(III)-sigma-alkyl or iron(III)-sigma-aryl complexes

The reaction of p-chlorophenylhydrazine with prostaglandin H synthase (PGHS) Fe(III) under aerobic conditions leads to a partial destruction of the heme and to a new complex absorbing at 436 nm. This complex is also obtained by reaction of p-chlorophenyldiazene (pClPhN = NH) with PGHS Fe(III) under anaerobic conditions and by oxidation of the PGHS Fe(II)(pClPhN = NH) diazene complex by Fe(CN)6K3. The similarity between those reactions and those of arylhydrazines and aryldiazenes with other hemoproteins such as cytochrome P450 and hemoglobin and myoglobin, as well as the similarities between the spectroscopic and chemical properties of this complex and those of the sigma-aryl complexes of other hemoproteins such as hemoglobin and myoglobin, strongly suggested a PGHS Fe(III)-pClPh structure for this complex. It was completely established after the extraction of its heme, by butan-2-one at 0 degree C under neutral or acidic conditions, which led to the sigma-aryl PGHS-Fe(III)-pClPh complex and to N-phenylprotoporphyrin IX, respectively. A mechanism is proposed for the formation of the PGHS Fe(III) pClPh complex; it includes the reduction of PGHS Fe(III) into PGHS Fe(II) with formation of the diazene pClPhN = NH. This diazene can bind to PGHS Fe(II) or be oxidized with formation of pClPh free radicals. These radicals can react with PGHS Fe(II) to form the PGHS Fe(III)-pClPh complex or with the protein, or may initiate free radical oxidations which could lead to destruction of the heme or of the protein. Other alkylhydrazines or arylhydrazines also react with PGHS Fe(III) under aerobic conditions with the formation of PGHS Fe(III)-R or aryl (Ar) complexes and heme destruction. Alkylhydrazines such as methylhydrazine, which lead to very reactive alkyl radicals, lead to very low amounts of PGHS Fe(III)-R complex and high amounts of heme destruction, whereas arylhydrazines bearing electron-withdrawing substituents such as 3,4-dichlorophenylhydrazine, which lead to stabilized aryl radicals, lead to a high amounts of PGHS Fe(III)-Ar complex and low amounts of heme destruction.(ABSTRACT TRUNCATED AT 400 WORDS)

Partial characterization of the copolymerization reaction of erythrocyte membrane band 3 with hemichromes

Early intermediates in the denaturation of hemoglobin, termed hemichromes, have been found previously to associate with the cytoplasmic domain of erythrocyte membrane band 3 in a manner which rapidly propagates into an insoluble, macroscopic copolymer. Because this interaction is thought to force a redistribution of band 3 in situ, the properties of the copolymerization reaction were investigated in greater detail. The band 3-hemichrome coaggregate was found to be stabilized largely by ionic interactions since elevation of either ionic strength or pH led to dissolution of the complex. The pH dependence, however, shifted to a more alkaline pH with increasing hemichrome concentration, suggesting a strong linkage between band 3 or hemichrome protonation and copolymer formation. The stoichiometry of the copolymer was measured at five globin chains per band 3 chain whenever underivatized dimer-tetramer hemichrome mixtures were employed. However, cross-linking of the hemichromes at either the alpha or the beta chains to form the stabilized tetramer yielded a copolymer stoichiometry of approximately eight globin chains per band 3 chain, i.e., two hemichrome sites per band 3 subunit. While underivatized hemichromes exhibited both a fast and slow phase of copolymerization, the cross-link-stabilized tetrameric hemichromes displayed predominantly the fast phase kinetics. Naturally occurring disulfide cross-linked hemichromes also reacted more avidly with band 3 than their reduced counterparts; however, the copolymerization process also proceeded to completion with totally reduced components. It is concluded that copolymerization of band 3 with hemichromes should occur under normal cellular conditions and at an accelerated velocity when the intracellular reducing power is low.

Formation of aryl and aryldiazenyl complexes in reactions of arylhydrazines and aryldiazenes with a synthetic model compound of haemoprotein

The anaerobic reaction of chelated protohaemin, a synthetic model compound of ferrihaemoglobin, with phenyldiazene produced a compound with the visible-absorption spectrum of a ferrihaemochrome. The compound reacted with CN-, which is a ligand of both ferric and ferrous porphyrins, to produce the complex of the synthetic ferrihaemoglobin with CN-. Though the spectrum of the compound formed by the addition of phenyldiazene to chelated protohaemin is characteristic of a ferric porphyrin complex, this compound reacted with both toluene-p-sulphonylmethyl isocyanide and CO, which are strong ligands of ferrous porphyrins, to produce the corresponding ferrous complexes. These ligand-binding reactions indicated that the complex of chelated protohaem with phenyldiazene can behave either as a complex of a ferric porphyrin with phenyldiazenyl anion (C6H5N = N-) or a complex of a ferrous porphyrin with phenyldiazenyl radical (C6H5N = N.). Para substituents on phenyldiazene were without effect on the formation of 4-substituted phenyldiazenyl complexes with chelated protohaem. Ortho substituents resulted in less-stable complexes. The phenyl complex of chelated protohaem was prepared by the aerobic reaction of phenylhydrazine with chelated protohaemin, and its structure was confirmed by its n.m.r. spectrum. The ligand-binding properties, n.m.r. spectrum and absorption spectrum of this complex differed from those of the phenyldiazenyl complex. The phenyl complex also was produced when the phenyldiazenyl complex was exposed to O2.

Free-radical production and oxidative reactions of hemoglobin

Mechanisms of autoxidation of hemoglobin, and its reactions with H2O2, O2-, and oxidizing or reducing xenobiotics are discussed. Reactive intermediates of such reactions can include drug free radicals, H2O2, and O2-, as well as peroxidatively active ferrylhemoglobin and methemoglobin-H2O2. The contributions of these species to hemoglobin denaturation and drug-induced hemolysis, and the actions of various protective agents, are considered.

Reactions of hemoglobin with phenylhydrazine: a review of selected aspects

It is well known that phenylhydrazine induces hemolytic anemia. This is thought to result from the reaction of phenylhydrazine with hemoglobin. The accompanying oxidation of phenylhydrazine leads to the formation of a number of products, including benzene, nitrogen, hydrogen peroxide, superoxide anion and the phenyl radical. The products formed depend critically on the conditions of the experiment, especially the amount of oxygen present. It is now known that oxyhemoglobin and myoglobin react with phenylhydrazine to yield a derivative of hemoglobin containing N-phenylprotoporphyrin in which the heme group is modified. The recent identification of sigma-phenyliron(III) porphyrins in phenylhydrazine-modified metmyoglobin has aided elucidation of the mechanism of hemoglobin modification. Mechanistic schemes are proposed to account for product formation.

Hemichrome binding to band 3: nucleation of Heinz bodies on the erythrocyte membrane

Hemichromes, the precursors of red cell Heinz bodies, were prepared by treatment of native hemoglobin with phenylhydrazine, and their interaction with the cytoplasmic surface of the human erythrocyte membrane was studied. Binding of hemichromes to leaky red cell ghosts was found to be biphasic, exhibiting both high-affinity and low-affinity sites. The high-affinity sites were shown to be located on the cytoplasmic domain of band 3, since (i) glyceraldehyde-3-phosphate dehydrogenase, a known ligand of band 3, competes with the hemichromes for their binding sites, (ii) removal of the cytoplasmic domain of band 3 by proteolytic cleavage causes loss of the high-affinity sites, and (iii) the isolated cytoplasmic domain of band 3 interacts tightly with hemichromes, rapidly forming a pH-dependent, water-insoluble copolymer upon mixing in aqueous solution. Since the copolymer of hemichromes with the cytoplasmic domain of band 3 was readily isolatable, a partial characterization of its properties was conducted. The copolymer was shown to be of defined stoichiometry, containing approximately 2.5 hemichrome tetramers (or approximately 5 hemichrome dimers) per band 3 dimer, regardless of the ratio of hemichrome:band 3 in the initial reaction solution. The copolymer was found to be of macroscopic dimensions, generating particles which could be easily visualized without use of a microscope. The coprecipitation was also highly selective for hemichromes, since, in mixed solutions with native hemoglobin, only hemichrome was observed in the isolated pellet. Furthermore, no precipitate was ever observed upon mixing the cytoplasmic domain of band 3 with oxyhemoglobin, deoxyhemoglobin, (carbonmonoxy) hemoglobin, or methemoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)

Reaction of monosubstituted hydrazines and diazenes with rat-liver cytochrome P450. Formation of ferrous-diazene and ferric sigma-alkyl complexes

The alkyldiazenes RN = NH (R = CH3 or C2H5) react with reduced microsomal cytochrome P450 leading to complexes exhibiting a Soret peak at 446 nm. Upon oxidation of the [cytochrome P450-Fe(II)(CH3N = NH)] complex with limited amounts of dioxygen, a new complex characterized by a Soret peak at 486 nm is formed. The latter complex was also formed upon slow reaction of methyldiazene with microsomal cytochrome P450-Fe(III) or in situ oxidation of methylhydrazine by limited amounts of O2 or ferricyanide. This complex is rapidly destroyed by O2 or ferricyanide in excess and more slowly by excess dithionite in the presence of CO. Reactions of ethyldiazene or benzyldiazene with cytochrome P450-Fe(III) afforded similar complexes characterized by Soret peaks around 480 nm. These results, when compared to those recently described on reactions of monosubstituted hydrazines RNHNH2 and diazenes RN = NH with hemoglobin and iron-porphyrins, are consistent with a [cytochrome P450-Fe(II)(RN = NH)] structure for the 446-nm-absorbing complexes and a sigma-alkyl cytochrome P450-Fe(III)-R structure for the complexes characterized by a Soret peak around 480 nm. They also suggest a sigma-cytochrome P450-Fe(III)-Ph structure for the complex derived from phenylhydrazine oxidation, recently described in the literature. Finally, they provide the first evidence that cytochrome P450-Fe(III)-R complexes are formed upon microsomal oxidation of alkyl or phenylhydrazines.

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

Oxyhemoglobin and oxymyoglobin were allowed to react aerobically with phenylhydrazine and p-tolylhydrazine. The chloroform extract of each reaction mixture, after treatment with H2SO4/methanol, yielded a blue pigment and a green pigment, which were identified by electronic absorption, mass, and proton NMR spectroscopy as the dimethyl esters of beta-meso-arylbiliverdin IX alpha and N-arylprotoporphyrin IX, respectively. N-Phenylprotoporphyrin IX dimethyl ester formed complexes with Zn2+, Cd2+, and Hg2+ but not with other cations. The proton NMR spectrum of the zinc complex suggested binding of the phenyl group to one of the two pyrrole rings of protoporphyrin IX with a propionic acid substituent. The effectiveness of phenylhydrazine as an inducer of Heinz body formation may be due to destabilization of the hemoglobin molecule by the replacement of heme with phenyl adducts of biliverdin and protoporphyrin.

Induction of Heinz body formation by sodium dithionite

Incubation of normal erythrocytes with sodium dithionite resulted in the formation of Heinz bodies, but incubation with sodium metabisulfite did not. Addition f superoxide dismutase to the incubation medium increased the formation of Heinz bodies by sodium dithionite. Addition of catalase to suspensions of erythrocytes in the presence and absence of superoxide dismutase inhibited the formation of Heinz bodies. These findings indicate that hydrogen peroxide, not superoxide, is the active oxidant in Heinz body formation.

Protection by ascorbate against acetylphenylhydrazine-induced Heinz body formation in glucose-6-phosphate dehydrogenase deficient erythrocytes

Ascorbate was found to inhibit oxidation of oxyhaemoglobin and Heinz body formation in glucose-6-phosphate dehydrogenase deficient red cells incubated with acetylphenylhydrazine. It is proposed that ascorbate can substitute for the glutathione which is depleted and act as a scavenger for drug free radicals generated during the reaction. Ascorbate was protective at concentrations only a little higher than that in normal blood, and the possibility that administration of ascorbate could protect GSH deficient cells against the action of oxidative drugs such as APH is considered. A simple method of quantitatively assessing Heinz body formation by measuring the turbidity of the lysed cells is described.

Oxidative degradation of haemoglobin by nitrosobenzene in the erythrocyte

Substitutions on the benzene ring of nitrosobenzene did not have the same effect on oxidative haemolysis as substitutions on phenylhydrazine. We previously found that the haemolytic effect of arylhydrazines paralleled their oxidative conversion into ligands of ferrihaemoglobin. In contrast, although most substituted nitrosobenzenes that are ligands of ferrohaemoglobin caused haemolysis and most that are not ligands failed to cause nitrosoarenes appeared to be related more closely to the ease of their reduction to arylhydroxylamines than to their properties as ligands. We propose a mechanism of oxidative degradation whereby the cyclic formation of phenylhydroxylamine from nitrosobenzene within an erythrocyte leads to the accumulation of H2O2, which then reacts with ferrohaemoglobin to initiate the oxidative cleavage of haem. The posulated active intermediate in this reaction is the same as that previously proposed in the oxidative degradation of haemoglobin by phenylhydrzine and in the coupled oxidation of ascorbic acid and haemoglobin.

Mechanism of oxyhaemoglobin breakdown on reaction with acetylphenylhydrazine

The reaction of oxyhaemoglobin and acetylphenylhydrazine, which results in haemoglobin denaturation and precipitation, was found to be influenced by H202 and superoxide (O2-.) generated during the reaction. By analysing the different haemoglobin oxidation products, it was found that by influencing the rate at which oxyhaemoglobin was oxidized, H2O2 accelerated the overall haemoglobin breakdown, and O2-. inhibited it. By adding GSH (reduced glutathione) or ascorbate, it was possible to slow down the rates of both oxyhaemoglobin oxidation and O2-. production, and the overall rate of haemoglobin breakdown. These results are compatible with a mechanism involving production of the acetylphenylhydrazyl free radical, and with GSH, ascorbate and O2-. acting as radical scavengers and preventing its further reactions. The reaction produced choleglobin, as well as acetylphenyldiazine and methaemoglobin, which combined to form a haemichrome. The haemichrome was less stable and precipitated first. It was also less stable than the haemichrome formed by direct reaction of acetylphenyldiazine with methaemoglobin, and it is proposed that this is because the methaemoglobin produced from oxyhaemoglobin and acetylphenylhydrazine was modified by the free radicals and H2O2 produced in the reaction.