Inhibition of hemin-induced hemolysis by desferrioxamine: binding of hemin to red cell membranes and the effects of alteration of membrane sulfhydryl groups

CD163 Expression in Neurons After Experimental Intracerebral Hemorrhage

BACKGROUND AND PURPOSE

CD163, a receptor for hemoglobin, is involved in hemoglobin clearance after intracerebral hemorrhage (ICH). In contrast to microglial/macrophage CD163, neuronal CD163 hemoglobin has not been well studied. This study examined the expression of neuronal CD163 in a pig model of ICH and in vitro rat cortical neurons and the impact of deferoxamine on that expression.

METHODS

There were 2 parts to this study. In the in vivo part, piglets had injection of autologous blood into the right frontal lobe. The time course of CD163 expression and the effect of deferoxamine on the expression of CD163 after ICH were determined in the grey matter. In the in vitro part, the levels of CD163 and neuronal death and the effect of deferoxamine were examined in rat cortical neurons culture treated with hemoglobin.

RESULTS

CD163-positive cells were found, and the CD163 protein levels were upregulated in the ipsilateral grey matter after ICH. The CD163 levels peaked at days 1 and 3. The CD163-positive cells were colocated with NeuN-positive, heme oxygenase-2-positive, and terminal deoxynucleatidyl transferase dUTP nick end labeling-positive cells. Deferoxamine treatment attenuated ICH-induced CD163 upregulation and significantly reduced both brain CD163 and hemoglobin levels at day 3. Treating neuronal cultures with hemoglobin for 24 hours resulted in CD163 upregulation and increased cell death. Deferoxamine significantly attenuated the hemoglobin-induced neuronal death and CD163 upregulation.

CONCLUSIONS

CD163 is expressed in neurons and upregulated after ICH. Deferoxamine reduced ICH-induced CD163 upregulation and brain cell death in vivo and hemoglobin-induced CD163 upregulation and neuronal death in vitro.

Haem-activated promiscuous targeting of artemisinin in Plasmodium falciparum

The mechanism of action of artemisinin and its derivatives, the most potent of the anti-malarial drugs, is not completely understood. Here we present an unbiased chemical proteomics analysis to directly explore this mechanism in Plasmodium falciparum. We use an alkyne-tagged artemisinin analogue coupled with biotin to identify 124 artemisinin covalent binding protein targets, many of which are involved in the essential biological processes of the parasite. Such a broad targeting spectrum disrupts the biochemical landscape of the parasite and causes its death. Furthermore, using alkyne-tagged artemisinin coupled with a fluorescent dye to monitor protein binding, we show that haem, rather than free ferrous iron, is predominantly responsible for artemisinin activation. The haem derives primarily from the parasite's haem biosynthesis pathway at the early ring stage and from haemoglobin digestion at the latter stages. Our results support a unifying model to explain the action and specificity of artemisinin in parasite killing.

The mechanism of action of artemisinin, an antimalarial drug, is not well understood. Here, the authors use a labelled artemisinin analogue to show that the drug is mainly activated by haem and then binds covalently to over 120 proteins in the malaria parasite, affecting many of its cellular processes.

Hematin loses its membranotropic activity upon oligomerization into malaria pigment

Malaria is an infectious disease caused by Plasmodium type parasites transmitted by the bites of infected female anopheles mosquitoes. The malaria parasite multiplies in red blood cells where it degrades hemoglobin. This degradation of hemoglobin proteins releases hematin, an iron-containing porphyrin, which provokes membrane disruption and lysis. The malaria parasite blocks hematin-induced lysis by biocrystallization, a process that converts hematin into insoluble and chemically inert crystals. Hematin molecules are especially prone to self-assembly as dimers, oligomers and aggregates depending on environmental conditions (pH, solvent, temperature, concentration, ionic strength). Considering the different forms of hematin-based assemblies, it is still unclear which are the ones able to interact with membranes. We have prepared hematin under different conditions to form hematin-based assemblies and to measure their ability to interact and to disorganize membranes. Our results show that different forms of hematin molecules are able to penetrate lipid membranes. Interestingly, this membrane activity is spontaneously inhibited at acidic pH and it can be restored under neutral pH. By contrast, the oligomers of β-hematin were found to be completely harmless toward lipid membranes. Finally, the AFM visualization of hematin interaction with supported lipid bilayers showed for the first time its preferential interaction with defaults in membranes, at the boundaries between two distinct lipid phases. The superficial adsorption of aggregates on membranes and the absence of effect due to oligomers were also confirmed with AFM.

Deferoxamine reduces neuronal death and hematoma lysis after intracerebral hemorrhage in aged rats

Intracerebral hemorrhage (ICH) is primarily a disease of the elderly. Deferoxamine (DFX), an iron chelator, reduces long-term neurological deficits and brain atrophy after ICH in aged rats. In the present study, we investigated whether DFX can reduce acute ICH-induced neuronal death and whether it affects the endogenous response to ICH (ferritin upregulation and hematoma resolution) in aged rats. Male Fischer 344 rats (18 months old) had an intracaudate injection of 100 μL autologous whole blood into the right basal ganglia and were treated with DFX (100 mg/kg) or vehicle 2 hours post-ICH and then every 12 hours up to 7 days. Rats were euthanized 1, 3, or 7 days later for neuronal death, ferritin and hematoma size measurements. Plasma ferritin levels and behavioral outcome following ICH were also examined. DFX treatment significantly reduced ICH-induced neuronal death and neurological deficits. DFX also suppressed ferritin upregulation in the ipsilateral basal ganglia after ICH and hematoma lysis (hematoma volume at day 7: 13.2±4.9 vs. 3.8±1.2 mm3 in vehicle-treated group, p<0.01). However, effects of DFX on plasma ferritin levels after ICH did not reach significance. In conclusion, DFX reduces neuronal death and neurological deficits after ICH in aged rats. It also affects the endogenous response to ICH.

Microarray analysis of altered gene expression and the role of ATF3 in HK-2 cells treated with hemin

OBJECTIVE

To identify gene expression changes and the role of activating transcription factor 3 (ATF3) in hemin toxicity in renal tubular epithelial cells, then elucidate molecular mechanisms of hemin toxicity on renal tubular epithelial cells.

METHODS

An oligo array comprising 35,035 genes was used to compare differential gene expression in hemin-treated and non-treated HK-2 cells (human renal proximal tubular epithelial cells), and the role of ATF3 in hemin toxicity was assessed using siRNA technique.

RESULTS

A total of 128 mRNAs were at least twofold up-regulated and 101 mRNAs were at least twofold down-regulated after hemin treatment. Expression levels of ATF3, heat shock protein 70, c-fos, and c-jun were remarkably increased. Hemin also suppressed nuclear factor-kappa B inhibitor α, β-2 adrenergic receptor, and interleukin-6 mRNA amounts more than twofold. We further demonstrated the protective role of ATF3 in hemin cytotoxicity.

CONCLUSIONS

The data suggest that hemin caused multiple changes of gene expression in HK-2 cells, and ATF3 protects against hemin cytotoxicity.

Impact of intravascular hemolysis in malaria on liver dysfunction: involvement of hepatic free heme overload, NF-κB activation, and neutrophil infiltration

We have investigated the impact of persistent intravascular hemolysis on liver dysfunction using the mouse malaria model. Intravascular hemolysis showed a positive correlation with liver damage along with the increased accumulation of free heme and reactive oxidants in liver. Hepatocytes overinduced heme oxygenase-1 (HO-1) to catabolize free heme in building up defense against this pro-oxidant milieu. However, in a condition of persistent free heme overload in malaria, the overactivity of HO-1 resulted in continuous transient generation of free iron to favor production of reactive oxidants as evident from 2',7'-dichlorofluorescein fluorescence studies. Electrophoretic mobility shift assay documented the activation of NF-κB, which in turn up-regulated intercellular adhesion molecule 1 as evident from chromatin immunoprecipitation studies. NF-κB activation also induced vascular cell adhesion molecule 1, keratinocyte chemoattractant, and macrophage inflammatory protein 2, which favored neutrophil extravasation and adhesion in liver. The infiltration of neutrophils correlated positively with the severity of hemolysis, and neutrophil depletion significantly prevented liver damage. The data further documented the elevation of serum TNFα in infected mice, and the treatment of anti-TNFα antibodies also significantly prevented neutrophil infiltration and liver injury. Deferoxamine, which chelates iron, interacts with free heme and bears antioxidant properties that prevented oxidative stress, NF-κB activation, neutrophil infiltration, hepatocyte apoptosis, and liver damage. Furthermore, the administration of N-acetylcysteine also prevented NF-κB activation, neutrophil infiltration, hepatocyte apoptosis, and liver damage. Thus, hepatic free heme accumulation, TNFα release, oxidative stress, and NF-κB activation established a link to favor neutrophil infiltration in inducing liver damage during hemolytic conditions in malaria.

The interaction between desferrioxamine and hemin: a potential toxicological implication

Our previous research demonstrated that iron chelating agent desferrioxamine (DFO) could promote iron donor hemin-induced protein oxidation due to the combination of DFO and hemin, but the binding constant and thermodynamic parameters of DFO-hemin interaction have not been examined before. In this study, affinity capillary electrophoresis (ACE) was applied to investigate the interaction between DFO and hemin for the first time. The binding constants of DFO-hemin were calculated to be 10(4)-10(5)M(-1) at various temperatures. The negative value of various thermodynamic parameters (ΔG, ΔS, and ΔH) suggested that the binding was spontaneous and the interaction was exothermic and entropically driven. In addition, the high binding affinity between DFO with hemin seemed to be the key factor on promoting hemin- catalyzed formation of cytotoxic radicals, such as superoxide (O(2)(-)), which was related to the potential toxicity of this drug in clinical use.

In vitro activity of deferoxamine against Porphyromonas gingivalis

Deferoxamine (DFO), an FDA-approved iron chelator used for treatment of iron poisoning, affects bacteria as iron availability is intimately connected with growth and several virulence determinants. However, little is known about the effect on oral pathogens. In this study, the effect of DFO on Porphyromonas gingivalis, a major periodontopathogen which has an essential growth requirement for hemin (Fe(3+)-protoporphyrin IX), was evaluated. The viability of P. gingivalis W83 was not affected by 0.06-0.24 mM DFO, whereas the doubling time of the bacterium was considerably prolonged by DFO. The inhibitory effect was evident at earlier stages of growth and reduced by supplemental iron. UV-visible spectra using the pigments from P. gingivalis cells grown on blood agar showed that DFO inhibited μ-oxo bisheme formation by the bacterium. DFO decreased accumulation and energy-driven uptake of hemin by P. gingivalis. Antibacterial effect of H(2)O(2) and metronidazole against P. gingivalis increased in the presence of DFO. Collectively, DFO is effective for hemin deprivation in P. gingivalis suppressing the growth and increasing the susceptibility of the bacterium to other antimicrobial agents such as H(2)O(2) and metronidazole. Further experiments are necessary to show that DFO may be used as a therapeutic agent for periodontal disease.

Effects of glutathione, Trolox and desferrioxamine on hemoglobin-induced protein oxidative damage: anti-oxidant or pro-oxidant?

Evidence to support the role of heme proteins as major inducers of oxidative damage is increasingly present. Antioxidants have been widely used to ameliorate oxidative damage in vivo and in vitro, where the mechanism of this therapeutic action was usually dependent on their anti-oxidant effects. In this study, we chose three classic antioxidants, i.e. glutathione (GSH, an important intracellular antioxidant), 6-hydroxy-2, 5, 7, 8-tetramethylchroman-2-carboxylic acid (Trolox, a phenolic antioxidant without chelating effect) and desferrioxamine (DFO, a good iron chelator), to study their efficiencies on hemoglobin-induced protein oxidative damage. It was found that all of these antioxidants had the capacities to act as free radical scavengers and reducing agents to remove cytotoxic ferryl hemoglobin, demonstrating apparent anti-oxidant activities. However, the effects on hemoglobin-H(2)O(2)-induced protein oxidation depended on the categories and concentrations of antioxidants. GSH efficiently inhibited protein (bovine serum albumin or rat heart homogenate) carbonyl formation in a dose-dependent manner. In contrast to their protective effects at high concentrations, both Trolox and DFO could significantly aggravate protein oxidation at low concentrations. The pro-oxidant effects of Trolox and DFO on hemoglobin-mediated oxidative damage were probably related to their abilities in producing additional free radicals, such as superoxide (O·(2)(-)) and hydroxyl radical (·OH). The dual effects on hemoglobin redox reactions may provide new insights into the physiological implications of Trolox and DFO with cellular heme proteins.

Antibacterial action of polyphosphate on Porphyromonas gingivalis

Polyphosphate [poly(P)] has antibacterial activity against various Gram-positive bacteria. In contrast, Gram-negative bacteria are generally resistant to poly(P). Here, we describe the antibacterial characterization of poly(P) against a Gram-negative periodontopathogen, Porphyromonas gingivalis. The MICs of pyrophosphate (Na(4)P(2)O(7)) and all poly(P) (Na(n + 2)P(n)O(3n + 1); n = 3 to 75) tested for the bacterium by the agar dilution method were 0.24% and 0.06%, respectively. Orthophosphate (Na(2)HPO(4)) failed to inhibit bacterial growth. Poly-P75 was chosen for further study. In liquid medium, 0.03% poly-P75 was bactericidal against P. gingivalis irrespective of the growth phase and inoculum size, ranging from 10(5) to 10(9) cells/ml. UV-visible spectra of the pigments from P. gingivalis grown on blood agar with or without poly-P75 showed that poly-P75 reduced the formation of μ-oxo bisheme by the bacterium. Poly-P75 increased hemin accumulation on the P. gingivalis surface and decreased energy-driven uptake of hemin by the bacterium. The expression of the genes encoding hemagglutinins, gingipains, hemin uptake loci, chromosome replication, and energy production was downregulated, while that of the genes related to iron storage and oxidative stress was upregulated by poly-P75. The transmission electron microscope showed morphologically atypical cells with electron-dense granules and condensed nucleoid in the cytoplasm. Collectively, poly(P) is bactericidal against P. gingivalis, in which hemin/heme utilization is disturbed and oxidative stress is increased by poly(P).

Role of iron in brain injury after intraventricular hemorrhage

BACKGROUND AND PURPOSE

Intraventricular extension of hemorrhage is a predictor of poor outcome in intracerebral hemorrhage, and iron overload contributes to brain injury after intracerebral hemorrhage. The current study investigated the role of iron in ventricular dilatation and neuronal death in a rat model of intraventricular hemorrhage (IVH).

METHODS

There were 2 parts in this study. First, male Sprague-Dawley rats had a 200-μL injection of either autologous blood or saline into the right lateral ventricle and were euthanized at different time points. Rats had MRI and brains were used for Western blot analysis, immunohistochemistry, histology, and brain tissue nonheme iron measurements. Second, rats had IVH and were treated with deferoxamine or vehicle, and rats were euthanized 4 weeks later for brain tissue loss and lateral ventricle size measurements.

RESULTS

IVH resulted in brain iron accumulation, bilateral enlargement of the lateral ventricles, and hippocampal brain tissue loss. Iron accumulation was associated with upregulation of heme oxygenase-1 and ferritin. Systemic deferoxamine treatment reduced IVH-induced ventricular enlargement (eg, day 28: 32.7±10.6 vs 43.8±9.7 mm(3) in vehicle-treated group, n=8 to 9; P<0.05) and hippocampal brain tissue loss (hippocampal volume: 89.0±2.7 vs 85.2±4.1 mm(3) in the vehicle-treated group; P<0.05).

CONCLUSIONS

Iron has a role in brain injury after IVH. Deferoxamine may be a therapy for patients with IVH or intraventricular extension after intracerebral hemorrhage.

Accelerated hemolysis and neurotoxicity in neuron-glia-blood clot co-cultures

A growing body of experimental evidence suggests that an intracerebral hematoma is toxic to neighboring cells. However, injury mechanisms remain largely undefined, due in part to conflicting results from in vivo studies. In order to investigate blood toxicity in a more controlled environment, murine clots were co-cultured on porous membrane inserts with primary neurons and glia. Erythrocyte lysis was apparent within 48 h, but was reduced by almost 80% in cultures lacking neurons, and by over 90% in the absence of both neurons and glial cells. By 72 h, most released hemoglobin had oxidized to methemoglobin or its hemichrome degradation products. At this time point, approximately 50% of neurons were non-viable, as detected by propidium iodide staining; glia were not injured. Deferoxamine, Trolox and the NMDA receptor antagonist MK-801 prevented most neuronal death, but had no effect on hemolysis at neuroprotective concentrations. The 27-fold increase in culture malondialdehyde and 5.8-fold increase in heme oxygenase-1 expression were also attenuated by deferoxamine and Trolox, but not by MK-801. These results suggest that hemoglobin release from clotted blood is accelerated by adjacent neurons and glia. Subsequent neurotoxicity is mediated by both iron-dependent and excitotoxic injury pathways.

Neutralization of toxic haem by Porphyromonas gingivalis haemoglobin receptor

Free haem is known to be toxic to organs, tissues and cells. It enhances permeability by binding to a cell membrane, which leads to cell death, and damages lipids, proteins and DNA through the generation of reactive oxygen species. Lysine- and arginine-specific gingipains (Kgp and RgpA/B) are major proteinases that play an important role in the pathogenicity of a black-pigmented periodontopathogen named Porphyromonas gingivalis. One of the adhesin domains of gingipain, HbR could bind haem as an iron nutrient source for P. gingivalis. Using erythrocyte and its membrane as a model, results from the present study demonstrate that recombinant HbR expressed in Escherichia coli could inhibit haem-induced haemolysis, probably through removing haem from the haem-membrane complex and lowering free haem toxicity by mediating dimerization of haem molecules. The ability to protect a cell membrane from haem toxicity is a new function for HbR.

Deferoxamine reduces intracerebral hematoma-induced iron accumulation and neuronal death in piglets

BACKGROUND AND PURPOSE

Our previous studies found that deferoxamine reduces intracerebral hemorrhage (ICH)-induced brain injury in rats. The current study examined whether deferoxamine reduces brain injury in a piglet ICH model.

METHODS

Pigs received an injection of autologous blood into the right frontal lobe. Deferoxamine (50 mg/kg, IM) or vehicle was administered 2 hours after ICH and then every 12 hours up to 7 days. Animals were killed 3 or 7 days later to examine iron accumulation, white matter injury, and neuronal death.

RESULTS

ICH resulted in development of a reddish perihematomal zone, and iron accumulation, ferritin upregulation, and neuronal death within that zone. Deferoxamine reduced the perihematomal reddish zone, white matter injury, and the number of Perls', ferritin, and Fluoro-Jade C-positive cells.

CONCLUSIONS

Iron accumulation occurs in the piglet brain after ICH. Deferoxamine reduces ICH-induced iron buildup and brain injury in piglets.

Vitamin E inhibits hemolysis induced by hemin as a membrane stabilizer

Hemin is a potential cytolytic agent. To test the effect of vitamin E on hemin-mediated permeability in cell membranes, sheep erythrocytes were chosen as an appropriate model to study hemolysis induced by hemin. Hemin-induced hemolysis but did not elicit lipid peroxidation in sheep erythrocytes. Vitamin E was effective in inhibiting hemin-mediated hemolysis. Both chromanol ring and the isoprenoid side chain of tocopherols were essential for inhibition of hemin-induced hemolysis. There was a strong correlation between the inhibitory effects of tocopherols on hemin-induced erythrocyte hemolysis and their effects on fluorescence anisotropy of cell membranes. Our results suggested that, in contrast to its antioxidant activity, vitamin E inhibits hemolysis induced by hemin as a membrane stabilizing agent.

Chromate-induced human erythrocytes haemoglobin oxidation and peroxidation: influence of vitamin E, vitamin C, salicylate, deferoxamine, and N-ethylmaleimide

In order to attenuate or to prevent chromate-induced human erythrocytes injury, the influence of vitamin E, vitamin C, salicylate, deferoxamine, and N-ethylmaleimide on chromate-induced human erythrocytes haemoglobin oxidation and peroxidation were investigated. It was observed that pretreatment of human erythrocytes with vitamin E (20 microM), vitamin C (1 mM), salicylate (3 mM), and deferoxamine (4 mM) significantly increased (P=0.0001) chromate-induced human erythrocytes haemoglobin oxidation in a time dependent manner, while it was significantly decreased (P=0.0001) by pretreatment with N-ethylmaleimide (1 mM). In contrast, pretreatment of human erythrocytes with deferoxamine (4 mM) immediately inhibited (P=0.0001) chromate-induced human erythrocytes peroxidation, while it was significantly increased (P=0.0001) by pretreatment with N-ethylmaleimide (1 mM) during the first 4 h of cells exposition to chromate. For time periods superior to 6 h pretreatment with N-ethylmaleimide (1 mM) significantly decreased (P=0.0001) chromate-induced human erythrocytes peroxidation. It was concluded that care must be taken as these drugs are used to prevent against toxicity induced by chromium(VI) compounds.

Deferoxamine: stimulation of hematin polymerization and antagonism of its inhibition by chloroquine

The iron chelator deferoxamine enhances the clearance of Plasmodium falciparum parasitemia and may be useful in drug combinations for the treatment of cerebral malaria. However, the deferoxamine-chloroquine drug combination is antagonistic, or at best additive, against P. falciparum in vitro. As chloroquine is thought to exert its antimalarial activity by interacting with hematin released from the proteolytic degradation of hemoglobin in the parasite food vacuole, we hypothesized that deferoxamine might interfere with the ability of chloroquine to inhibit hematin polymerization, since it was reported that deferoxamine interacts with hematin. Therefore, we assessed deferoxamine-hematin binding in more detail and investigated the effect of deferoxamine on hematin polymerization in the presence and absence of chloroquine. Isothermal titration calorimetry (ITC) experiments demonstrated an enthalpy-driven deferoxamine:hematin mu-oxo dimer binding with an association constant of 2.8 x 10(4) M(-1) at pH 6.5, a binding affinity 14-fold lower than that measured for chloroquine. At least two of the three hydroxamic acid functional groups of deferoxamine must be unionized for effective binding. We also discovered that deferoxamine antagonized chloroquine-mediated inhibition of hematin polymerization. Unexpectedly, deferoxamine increased the concentration of soluble forms of hematin and enhanced the rate of hematin polymerization. Deferoxamine also could initiate hematin polymerization. In contrast, chloroquine decreased the concentration of soluble forms of hematin and inhibited hematin polymerization. This work supports the postulate that initiation of hematin polymerization requires a higher concentration of soluble hematin monomer than does the elongation phase of polymerization and provides one possible explanation for the observed antagonism between deferoxamine and chloroquine against parasites in culture.

Melatonin protects human red blood cells from oxidative hemolysis: new insights into the radical-scavenging activity

Antioxidant activity of melatonin in human erythrocytes, exposed to oxidative stress by cumene hydroperoxide (cumOOH), was investigated. CumOOH at 300 microM progressively oxidized a 1% suspension of red blood cells (RBCs), leading to 100% hemolysis in 180 min. Malondialdehyde and protein carbonyls in the membrane showed a progressive increase, as a result of the oxidative damage to membrane lipids and proteins, reaching peak values after 30 and 40 min, respectively. The membrane antioxidant vitamin E and the cytosolic reduced glutathione (GSH) were totally depleted in 20 min. As a consequence of the irreversible oxidative damage to hemoglobin (Hb), hemin accumulated into the RBC membrane during 40 min. Sodium dodecyl sulfate (SDS) gel electrophoresis of membrane proteins showed a progressive loss of the cytoskeleton proteins and formation of low molecular weight bands and protein aggregates, with an increment of the intensity of the Hb band. Melatonin at 50 microM strongly enhanced the RBC resistance to oxidative lysis, leading to a 100% hemolysis in 330 min. Melatonin had no effect on the membrane lipid peroxidation, nor prevented the consumption of glutathione (GSH) or vitamin E. However, it completely inhibited the formation of membrane protein carbonyls for 20 min and hemin precipitation for 10 min. The electrophoretic pattern provided further evidence that melatonin delayed modifications to the membrane proteins and to Hb. In addition, RBCs incubated for 15 min with 300 microM cumOOH in the presence of 50 microM melatonin were less susceptible, when submitted to osmotic lysis, than cells incubated in its absence. Extraction and high-performance liquid chromatography (HPLC) analysis showed a much more rapid consumption of melatonin during the first 10 min of incubation, then melatonin slowly decreased up to 30 min and remained stable thereafter. Equilibrium partition experiments showed that 15% of the melatonin in the incubation mixture was recovered in the RBC cytosol, and no melatonin was extracted from RBC membrane. However, 35% of the added melatonin was consumed during RBC oxidation. Hydroxyl radical trapping agents, such as dimethylsulfoxide or mannitol, added into the assay in a 1,000 times molar excess, did not vary melatonin consumption, suggesting that hydroxyl radicals were not involved in the indole consumption. Our results indicate that melatonin is actively taken up into erythrocytes under oxidative stress, and is consumed in the defence of the cell, delaying Hb denaturation and release of hemin. RBCs are highly exposed to oxygen and can be a site for radical formation, under pathological conditions, which results in their destruction. A protective role of melatonin should be explored in hemolytic diseases.

Kinetics of inhibition of glutathione-mediated degradation of ferriprotoporphyrin IX by antimalarial drugs

We have shown previously that chloroquine and amodiaquine inhibit the glutathione-dependent degradation of ferriprotoporphyrin IX (FP). We have also demonstrated that treatment of human erythrocytes infected with Plasmodium falciparum with chloroquine or amodiaquine results in a dose- and time-dependent accumulation of FP in the membrane fraction of these cells in correlation with parasite killing. High levels of membrane FP are known to perturb the barrier properties of cellular membranes, and could thereby irreversibly disturb the ion homeostasis of the parasite and cause parasite death. We here report on the effect of various 4-aminoquinolines, as well as pyronaridine, halofantrine and some bis-quinolines, on glutathione-mediated destruction of FP in aqueous solution, when FP was bound non-specifically to a protein, and when it was dissolved in human erythrocyte ghost membranes. We showed that all drugs were capable of inhibiting FP degradation in solution. The inhibitory efficacy of some drugs declined when FP was bound non-specifically to protein. Quinine and mefloquine were unable to inhibit the degradation of membrane-associated FP, in line with their inability to increase membrane-associated FP levels in malaria-infected cells following drug treatment. The discrepancy between chloroquine and amodiaquine on the one hand, and quinine and mefloquine on the other, is discussed in terms of the particular location of drugs and FP in the phospholipid membrane, and may suggest differences in the mechanistic details of the antimalarial action of these drugs.

Chain-breaking antioxidants and ferriheme-bound drugs are synergistic inhibitors of erythrocyte membrane peroxidation

Induced erythrocyte membrane peroxidation (EMP) is considered as an accurate model of reperfusion injuries and as such was used to investigate protective effects of various drugs. EMP was induced by an azo initiator and monitored by oxygen uptake. Both hydrophilic (ascorbic acid) and lipophilic (alpha-tocopherol, probucol, nicanartine) chain-breaking antioxidants as well as ferriheme-bound drugs (deferoxamine, chloroquine) inhibited EMP. When antioxidants and ferriheme-bound drugs were combined, synergistic effects were observed. It is proposed that ferriheme compounds which catalyse peroxide induced lipid peroxidation were blocked by deferoxamine and/or chloroquine. So these drugs inhibited at least partly the membrane peroxidation process and added their effects to the ones of chain-breaking antioxidants.

Hemin-induced membrane sulfhydryl oxidation: possible involvement of thiyl radicals

Sublytic levels (microM) of hemin destabilized RBC membrane as indicated by ghost fragmentation pattern using a laser viscodiffractometer. Furthermore, electron microscopic study shows that 5 microM of hemin induced echinocytic transformation whereas higher hemin concentration (40 microM) induced spherocytic transformation. In addition, hemin oxidized sulfhydryl groups in a dose dependent fashion and Electron Spin Resonance study suggests that such oxidation may involve a thiyl radical. Moreover, sulfhydryl compounds enhanced hemin-induced lipid peroxidation. Desferroxamine could prevent hemin-induced sulfhydryl oxidation as well as hemin-induced decrease in membrane stability. In contrast, vitamin E could effectively prevent hemin-induced lipid peroxidation but could not prevent hemin-mediated membrane destabilization.

Hemoglobin exacerbates the ocular inflammatory response to endotoxin

BACKGROUND

There is a clinical impression that bleeding into sites of inflammation exacerbates the inflammatory response. It has been hypothesized that hemoglobinic iron (Fe) contributes to this response by catalyzing free radical reactions. In the present study, the effects of autologous hemoglobin on the inflammatory response to endotoxin was determined. In addition, the possible contributions of Fe to this response was assessed by co-injection of either transferrin or desferrioxamine.

METHODS

A mild ocular inflammation was induced in rabbits by intravitreal injection of 0.25 ng endotoxin. In some animals apotransferrin, hemoglobin, hemoglobin + apotransferrin or hemoglobin + desferrioxamine were co-injected. Twenty-four hours later, anterior uveitis was quantified by slit-lamp examination and determination of protein concentration and infiltration of white cells into the aqueous humor.

RESULTS

Co-injection of autologous hemoglobin with endotoxin greatly exacerbated the ocular inflammatory response to endotoxin, especially the infiltration of white cells, which was increased 15-fold. Both apotransferrin, which binds Fe at high affinity, and desferrioxamine, which chelates Fe, greatly decreased the cellular response to the co-injection.

CONCLUSIONS

It is likely that hemoglobinic Fe is responsible for the increased infiltration of white cells caused by the co-injection of autologous hemaglobin and endotoxin.

Correlation of membrane lipid peroxidation with oxidation of hemoglobin variants: possibly related to the rates of hemin release

Experiments were performed to delineate the biochemical mechanism of hemoglobin (Hb)-catalyzed lipid peroxidation in human red blood cells (RBCs). Using a modified Langmuir trough lipid monolayer technique, we found that oxidized Hb induced an increase in lipid monolayer surface pressure, suggesting that oxidized Hb readily releases its heme moiety into the lipid monolayer. To confirm our interpretation that oxidized Hb readily releases its heme moiety, we monitored the fluorescence of Hb tryptophan upon oxidation of Hb. We found an increase in Hb fluorescence in the aqueous phase of our monolayer system after the addition of H2O2. The increase in fluorescence should reflect the departure of heme from globin due to a decrease in fluorescent quenching effect by the heme moiety. The rate of increase in lipid monolayer surface pressure upon Hb oxidation differed from Hb to Hb with an order of Hb E > F > S > A. The ability of various Hbs to affect lipid peroxidation in the RBC membrane, as monitored by the parinaric acid oxidation technique, followed this same order. In addition, hemin was shown to be a more potent catalyst of lipid peroxidation in RBC membrane than nonheme irons.

Heme degradation in the presence of glutathione. A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells

Unstable hemoglobins and oxidative conditions tend to produce hemichromes which demonstrably release their heme to the erythrocyte membrane, with consequent lipid peroxidation and cell lysis. High levels of non-heme iron are also found in such circumstances, but the origin of this iron is uncertain. In the present work, we show that reduced glutathione (GSH) is able to degrade heme in solution with a pH optimum of 7. Degradation depended on the presence of oxygen and on heme and GSH concentrations. It was inhibited by catalase and superoxide dismutase, implicating the involvement of perferryl reactive species in the process of heme degradation. Heme degradation at pH 7 and 37 degrees C is rapid (t1/2 = 70 s) and results in the release of iron from heme. Heme that was dissolved in red blood cell ghosts is also degraded by GSH with a concomitant increase in non-heme iron, most of which (75%) remains associated with the cell membrane. Loading of intact erythrocytes with heme was followed by time-dependent decrease of membrane-associated heme and caused an acceleration of the hexose monophosphate shunt due to the production of H2O2 and the oxidation of intracellular GSH. Most of the activation of the hexose monophosphate pathway was due to redox cycling of iron, since iron chelators inhibited it considerably. These results explain the origin of non-heme iron found in the membrane of sickle cells and the oxidative stress that is observed in these and other abnormal erythrocytes.

DNA cleavage by Cu(II)-desferal: identification of C1'-hydroxylation as the initial event for DNA damage

Desferal, a siderophore of microbial origin is the only drug currently used for clinical treatment of a genetic disorder, thalassemia. By using a combination of HPLC and 31P-NMR, it is demonstrated that the Cu complex of desferal cleaves DNA, the primary site of hydroxyl radical attack being the sugar C1' in the minor groove, which leads to production of 5-methylene furanone. While no C5'-oxidation was observed, a minor process involving C4'-attack accompanies the above cleavage path. The oxidative cleavage of DNA observed with CuDFO may have implications in the emerging applications of desferal as a drug delivery agent and an antimalarial.