Plasmodicidal effect of desferrioxamine B in human vivax or falciparum malaria from Thailand

Exploring the Role of Antioxidants to Combat Oxidative Stress in Malaria Parasites

BACKGROUND

Malaria, a global challenge, is a parasitic disease caused by Plasmodium species. Approximately 229 million cases of malaria were reported in 2019. Major incidences occur in various continents, including African and Eastern Mediterranean Continents and South-East Asia.

INTRODUCTION

Despite the overall decline in global incidence from 2010 to 2018, the rate of decline has been almost constant since 2014. The morbidity and mortality have been accelerated due to reactive oxygen species (ROS) caused by oxidative stress generated by the parasite responsible for the destruction of host metabolism and cell nutrients.

METHODS

The excessive release of free radicals is associated with the infection in the animal or human body by the parasites. This may be related to a reduction in nutrients required for the generation of antioxidants and the destruction of cells by parasite activity. Therefore, an intensive literature search has been carried out to find the natural antioxidants used to neutralize the free radicals generated during malarial infection.

RESULTS

The natural antioxidants may be useful as an adjuvant treatment along with the antimalarial chemotherapeutics to reduce the death rate and enhance the success rate of malaria treatment.

CONCLUSION

In this manuscript, an attempt has been made to provide significant insight into the antioxidant activities of herbal extracts against malaria parasites.

The role of antioxidants treatment on the pathogenesis of malarial infections: a review

Oxidative damage is one of the most important pathological consequences of malarial infections. It affects vital organs of the body manifesting in changes such as splenomegaly, hepatomegaly, endothelial and cognitive damages. The currently used antimalarials often leave traces of these damages after therapy, as evident in memory impairment after cerebral malaria. Hence, some research investigations have focused attention on the use of antioxidants, alone or in combination with antimalarials, as a viable therapeutic strategy aimed at alleviating plasmodium-induced oxidative stress and its associated complications. However, the practical application of this approach often yields conflicting outcomes because some antimalarials specifically act via induction of oxidative stress. This article critically reviews most of the studies conducted on the potential role of antioxidant therapy in malarial infections. The most frequently investigated antioxidants are vitamins C and E, N-acetylcystein, folate and desferroxamine. Some of the investigations measured the effects of direct administration of the antioxidants on the plasmodium parasites while others performed an adjunctive therapy with standard antimalarials. The therapeutic application of each of the antioxidants in malaria management depends on the targeted aspect of malarial pathology. It is hoped that this article will provide an informed basis for future research activities on the therapeutic role of antioxidants on malarial pathogenesis.

Superinfection in malaria: Plasmodium shows its iron will

After the bite of a malaria-infected mosquito, the Plasmodium sporozoite infects liver cells and produces thousands of merozoites, which then infect red blood cells, causing malaria. In malaria-endemic areas, several hundred infected mosquitoes can bite an individual each year, increasing the risk of superinfection. However, in infants that are yet to acquire immunity, superinfections are infrequent. We have recently shown that blood-stage parasitaemia, above a minimum threshold, impairs the growth of a subsequent sporozoite infection of liver cells. Blood-stage parasites stimulate the production of the host iron-regulatory factor hepcidin, which redistributes iron away from hepatocytes, reducing the development of the iron-dependent liver stage. This could explain why Plasmodium superinfection is not often found in young nonimmune children. Here, we discuss the impact that such protection from superinfection might have in epidemiological settings or in programmes for controlling malaria, as well as how the induction of hepcidin and redistribution of iron might influence anaemia and the outcome of non-Plasmodium co-infections.

Mechanism of iron toxicity

The subtle balance between proinflammatory and antiinflammatory cytokines plays an important role in determining the severity of the inflammatory reaction and in the anomalous iron handling associated with infection. Conversely, iron deficiency per se appears to limit the severity of the inflammatory response. All of these considerations are at present highly speculative and in need of further experimental and epidemiologic support. If confirmed, the beneficial biological effects of iron depletion may have a defensive role in inflammation and may be perturbed by the nonselective administration of iron to iron-replete patients who would not benefit from such treatment in the first place. In view of the importance of non-transferrin-bound plasma iron (NTBI) in iron toxicity and its rapid cellular uptake, it may play an important role in the harmful effects of iron in infection, and this is illustrated by the infectious complications of parenteral iron therapy in tropical countries.

IRON CHELATORS: CORRELATION BETWEEN EFFECTS ON PLASMODIUM SPP. AND IMMUNE FUNCTIONS

Iron chelating agents, which permeate through erythrocytic and parasite membranes, are effective against Plasmodium falciparum in vitro. However, the protective effect in humans is transient. We examined the antiplasmodial capacity of several iron chelators in vitro and in vivo. The chelators 3/3hb/2m and 3/2hb/b (together, MoB) were more effective against P. falciparum in vitro than desferrioxamine (DFO) and Salicylaldehyde isonicotinoyl hydrazone (SIH) (together, DoS). Despite similar pharmacokinetics of all iron chelators, mice infected with Plasmodium vinckei and treated with MoB succumbed to malaria, whereas DoS-treated mice survived. However, even in the surviving mice, peak parasitemias were above 30%. These results indicate that the direct effects of the drugs on the parasites were not responsible alone for the complete recovery of the mice. We suggest that the recovery is related to differential effects of the drugs on various immune functions. We concentrated on the effect of the iron chelators on B cell and T cell proliferation and on allogeneic stimulation (MLR), interleukin-10 (IL-10), gamma-interferon (gamma-IFN), tumor necrosis factor-alpha (TNF-alpha), and radical production. All the iron chelators examined inhibited the in vitro proliferation of B cells and T cells, and MLR. This may explain why iron chelators are only slightly efficient in treating human malaria. However, the inhibitory effects of MoB on B cell and T cell proliferation and on MLR were more pronounced than those of DoS. In addition, the release of free radicals by effector cells was inhibited to a greater extent by MoB than by DoS. These results may explain why MoB, which was more efficient in vitro, was not effective in vivo. The DoS effects on the in vitro secretion of cytokines correlate with their in vivo effect; there was a decrease of IL-10 and a parallel increase in gamma-IFN and TNF-alpha production by human mononuclear cells. MoB, which could not rescue the animals from malaria, did not affect IL-10 and TNF-alpha, but reduced gamma-IFN levels. Identical results were obtained when using monocytes instead of mononuclear cells (except for gamma-IFN, which is not produced by monocytes). Our results indicate that an iron chelator, or any antiparasitic drug that kills the parasites in vitro, should also be selected for further evaluation on the basis of its reaction with immune components; it should not interfere with crucial protective immunological processes, but it may still alleviate parasitemia by positive immune modulation.

Inhibition of hepatitis B virus production associated with high levels of intracellular viral DNA intermediates in iron-depleted HepG2.2.15 cells

BACKGROUNDS/AIMS

The effects of iron-depletion on hepatitis B virus (HBV) replication were examined in HepG2.2.15 cells.

METHODS

Proliferating cells were iron-depleted with desferrioxamine (DFO), at 20 or 100 microM for 48 h. Levels of viral mRNAs, cytoplasmic DNA replicative intermediates and virion production were examined. A comparative study was performed with hydroxyurea, a specific inhibitor of ribonucleotide reductase.

RESULTS

In desferrioxamine treated cells, virion production is dramatically decreased, while viral replicative intermediates accumulate in the cytoplasm. DFO, like hydroxyurea, blocks cell cycle progression in the G1/S transition or S phase with a corresponding 2-fold increase of viral mRNAs. As expected, hydroxyurea leads to a strong reduction of virion production associated with low levels of intracellular replicative intermediates.

CONCLUSIONS

These results strongly suggest that iron depletion affects the HBV life cycle indirectly through the cell cycle arrest and directly through the inhibition of the viral DNA secretion. They also indicate the need to re-evaluate with caution the iron depletion protocols on HBV infected patients since a decrease of viral markers in the serum following iron-depletion may not reflect a decrease of viral replicative forms, but on the contrary, could be associated with active viral DNA synthesis.

Iron chelating agents for treating malaria

BACKGROUND

Mortality from Plasmodium falciparum malaria remains high; death and sequelae occur in even in patients treated with antimalarial drugs. Researchers are exploring the effects of adding treatments to the main antimalarial regimens in an attempt to reduce mortality. Iron chelation is one potential chemotherapeutic adjuvant treatment. Before advocating adjunctive therapy, the effects of iron chelators in improving patient outcomes needs to be examined.

OBJECTIVES

To assess the effects of iron-chelating agents combined with antimalarial drugs, or iron chelators alone, for treating Plasmodium falciparum malaria in adults and children, in relation to mortality, coma recovery time, parasite clearance, and adverse effects.

SEARCH STRATEGY

Electronic searches of the Cochrane Library, MEDLINE, and EMBASE, using the standard Cochrane search strategy. Bibliographies of retrieved studies were scrutinized in order to identify further relevant trials. Organisations, experts and other individuals in malaria research were contacted for unpublished studies.

SELECTION CRITERIA

All randomised controlled trials of adults or children with P.falciparum malaria.

DATA COLLECTION AND ANALYSIS

Trials were identified and extracted by a single reviewer (HS) and checked by a second (MM). Inclusion criteria were applied, and data were extracted independently by both reviewers. Authors were contacted for missing and additional data. Meta-analysis used Relative Risk (RR) and 95% Confidence Intervals.

MAIN RESULTS

No evidence of benefit or harm were shown in relation to mortality, but studies were small, and one trial was tending towards more deaths with the intervention when it was stopped. The risk of experiencing persistent seizures was significantly lower with desferrioxamine compared to placebo treatment (RR 0.80, 95% CI 0.67 to 0.95). Many adverse effects were more common in participants treated with desferrioxamine.

REVIEWER'S CONCLUSIONS

Trends suggestive of both harm (death) and potential benefit (fewer seizures) are demonstrated in this review. It is not possible to comment on time to event outcomes that include coma recovery or parasitaemia as we are clarifying data with the trialists. Whether to conduct further trials will depend on a judgement about potential benefit.

Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators

To examine the site of action of antimalarial iron chelators, iron ligands were added to control erythrocytes and to erythrocytes parasitized with Plasmodium falciparum, and the concentration of intracellular labile iron was monitored with the fluorescent probe, calcein. The fluorescence of calcein quenches upon binding iron and increases upon releasing iron. The chelators included desferrioxamine B, 2',2'-bipyridyl, and aminophenol II, a compound that is being newly reported as having anti-plasmodial properties. Calcein-loaded parasitized cells displayed fluorescence predominantly within the cytosol of both rings and trophozoites. The addition of chelators to both control and parasitized erythrocytes led to significant increases of fluorescence (P < 0.001). Fluorescence was observed to increase within the parasite itself after addition of iron chelators, indicating that these agents bound labile iron within the plasmodium. The relative increases of fluorescence after addition of chelators were greater in control than parasitized erythrocytes (P < 0.05) as were the estimated labile iron concentrations (P < or = 0.001). These results suggest that (i) the anti-malarial action of iron chelators might result from the ability to reach the infected cell's parasite compartment and bind iron within the parasite cytosol, and (ii) the labile iron pool of the host red cell may be either utilized or stored during plasmodial growth.

Iron chelation therapy for malaria: a review

Malaria is one of the major global health problems, and an urgent need for the development of new antimalarial agents faces the scientific community. A considerable number of iron(III) chelators, designed for purposes other than treating malaria, have antimalarial activity in vitro, apparently through the mechanism of withholding iron from vital metabolic pathways of the intra-erythrocytic parasite. Certain iron(II) chelators also have antimalarial activity, but the mechanism of action appears to be the formation of toxic complexes with iron rather than the withholding of iron. Several of the iron(III)-chelating compounds also have antimalarial activity in animal models of plasmodial infection. Iron chelation therapy with desferrioxamine, the only compound of this nature that is widely available for use in humans, has clinical activity in both uncomplicated and severe malaria in humans.

Iron Acquisition by Parasitic Protozoa

The efficient uptake of iron by microorganisms is essential for their survival. Mammalian hosts possess elaborate means of sequestering their iron stores to protect themselves against invading pathogens. In this review, Mary Wilson and Bradley Britigan summarize mechanisms by which bacteria and protozoa effectively scavenge iron from their hosts during infection, as well as the potential and proven effects of these mechanisms on microbial virulence.

Plasmodium vinckei: optimization of desferrioxamine B delivery in the treatment of murine malaria

Optimization of desferrioxamine B (DFO) delivery for the treatment of malaria was studied in Plasmodium vinckei infected mice. DFO was administered by three different treatment regimens: (1) multiple subcutaneous injections of free DFO, (2) intraperitoneal infusion of free DFO, or (3) multiple subcutaneous injections of liposomal DFO. In a first series of experiments, DFO treatment was started prior to infection. Multiple subcutaneous injections of free DFO before and during infection suppressed parasitemia, whereas injections only prior to infection did not. Suppression of parasitemia and long-term survival (>1 month after infection) of mice were obtained by intraperitoneal infusion starting 1 day before infection (14 days, 130 mg DFO/kg/day) or by subcutaneous injections of liposomal DFO prior to infection (days -1 and 0, 400 or 800 mg DFO/kg/day). The efficacy of the antimalarial activity of liposomal DFO was influenced by the drug-to-lipid ratio but was hardly affected by bilayer rigidity. In a second series of experiments, DFO treatment was started at days 6 and 7 after infection. Parasitemia was reduced by all three treatment regimens; however, long-term survival was obtained only by treatment with liposomal DFO (days 7 and 8, 400 mg/kg/day). The present results indicate that continuous exposure of the parasite to low doses of DFO suffice to clear parasitemia, whereas high doses of free DFO administered intermittently do not. A right balance between dose of DFO, time of exposure to DFO, and parasitemia suppresses parasitemia even in the treatment of late-stage malaria. It was shown that liposomes are suitable carrier systems for DFO in experimental malaria therapy when given prior to infection and, moreover, in the treatment of advanced stages of malaria.

Effect of iron chelation therapy on mortality in Zambian children with cerebral malaria

To examine the effect of iron chelation on mortality in cerebral malaria, we enrolled 352 children in a trial of deferoxamine in addition to standard quinine therapy at 2 centres in Zambia, one rural and one urban. Entrance criteria included age < 6 years, Plasmodium falciparum parasitaemia, normal cerebral spinal fluid, and unrousable coma. Deferoxamine (100 mg/kg/d infused for a total of 72 h) or placebo was added to a 7 d regimen of quinine that included a loading dose. Mortality overall was 18.3% (32/175) in the deferoxamine group and 10.7% (19/177) in the placebo group (adjusted odds ratio 1.8; 95% confidence interval 0.9-3.6; P = 0.074). At the rural study site, mortality was 15.4% (18/117) with deferoxamine compared to 12.7% (15/118) with placebo (P = 0.78, adjusted for covariates). At the urban site, mortality was 24.1% (14/58) with deferoxamine and 6.8% (4/59) with placebo (P = 0.061, adjusted for covariates). Among survivors, there was a non-significant trend to faster recovery from coma in the deferoxamine group (adjusted odds ratio 1.2; 95% confidence interval 0.97-1.6; P = 0.089). Hepatomegaly was significantly associated with higher mortality, while splenomegaly was associated with lower mortality. This study did not provide evidence for a beneficial effect on mortality in children with cerebral malaria when deferoxamine was added to quinine, given in a regimen that included a loading dose.

Chemical Determinants of antimalarial activity of reversed siderophores

Reversed siderophores (RSFs) are artificial hydroxamate-based iron chelators designed after the natural siderophore ferrichrome. The modular molecular design of RSF derivatives allowed the synthesis of various congeners with controlled iron-binding capacities and partition coefficients. These two physicochemical properties were assessed by a novel fluorescent method and were found to be the major determinants of RSF permeation across erythrocyte membranes and scavenging of compartmentalized iron. The partition coefficient apparently conferred upon RSFs two major features: (i) the ability to rapidly access iron pools of in vitro-grown Plasmodium falciparum at all developmental stages and to mobilize intracellular iron and transfer it to the medium and (ii) the ability to suppress parasite growth at all developmental stages. These features of RSFs were assessed by quantitative determination of the structure-activity relationships of the biological activities and partition coefficients spanning a wide range of values. The most effective RSF containing the aromatic group of phenylalanine (RSFm2phe) showed 50% inhibitory concentration of 0.60 +/- 0.03 nmol/ml in a 48-h test and a 2-h onset of inhibition of ring development at 5 nmol/ml. The lipophilic compound RSFm2phe and the lipophilic and esterase-cleavable compound RSFm2pee inhibited parasite growth at all developmental stages whether inhibition was assessed in a continuous mode or after discontinuing drug administration. The antimalarial effects of RSFm2phe and cleavable RSFm2pee were potentiated in the presence of desferrioxamine (DFO) at concentrations at which DFO alone had no effect on parasite growth. These studies provide experimental evidence indicating that the effective and persistent antimalarial actions of RSFs are associated with drug access to infected cells and scavenging of iron from intracellular parasites. Moreover, the optimal antimalarial actions of RSFs are apparently also determined by improved accessibility to critical iron pools or by specific interactions with critical parasite targets.

Mode of action of iron (III) chelators as antimalarials. IV. Potentiation of desferal action by benzoyl and isonicotinoyl hydrazone derivatives

The antimalarial action of iron chelators is limited by factors related to drug permeation and parasite susceptibility to metal deprivation. In this study we applied iron-chelating isonicotinoyl and benzoyl hydrazones on Plasmodium falciparum cultures and assessed their antimalarial properties. The agents w ere used both individually and in combination with deferoxamine (DFO), a clinically approved iron chelator, and with hydroxyethyl-starch-DFO, a macromolecular carrier of DFO. Salicylaldehyde isonicotinoyl hydrazone (SIH) and 2-hydroxy-1-naphthylaldehyde m-fluorobenzoyl hydrazone (HNFBH) were found to be highly efficient in suppressing parasite growth at all developmental stages (IC50 24 +/- 6 micromol/L and 0.21 +/- 0.04 micromol/L, respectively, in a 36-to-42 hour test). In combination with impermeant DFO, SIH and HNFBH actions on ring forms were significantly potentiated in terms of speed of drug action and extent of inhibition. The combined effect of the hydrazones with DFO was greater than additive. Based on the capacity of SIH to extract iron from infected cells and to transfer the metal to extracellular DFOs, we propose a mechanism for a synergistic action of permeant hydrazones and impermeant (DFO) iron chelators. The application of a combination of iron chelators as antimalarials might be of therapeutic value.

Effects of zinc-desferrioxamine on Plasmodium falciparum in culture

The zinc-desferrioxamine (Zn-DFO) complex is considered to be more permeative into parasitized erythrocytes than is the metal-free DFO. The former may penetrate the cell and exchange its bound zinc for ferric ions, rendering the iron unavailable for vital parasite functions. The effects of these compounds on the in vitro development of Plasmodium falciparum are compared. The results indicate that Zn-DFO is superior to DFO, especially at concentrations below 20 microM, as shown by decreased levels of hypoxanthine incorporation, lower levels of parasitemia, and interference with the life cycle of the parasite. At low concentrations, DFO even enhanced parasite growth. Such an enhancement was not observed following exposure to Zn-DFO. Experiments in which the compounds were removed from the cultures indicated that parasites treated with Zn-DFO are less likely to recover at a later stage. Since DFO has already been used in humans for the treatment of malaria, its complex with zinc, which is more effective in vitro, should also be examined in vivo.

Control of disease by selective iron depletion: a novel therapeutic strategy utilizing iron chelators

Recognition of the central role of iron in the generation of toxic, oxygen-derived species through the Haber-Weiss reaction, the ability of desferrioxamine (DFX) to prevent the damage associated with free radical generation in reperfusion injury, and its inhibitory effect on cell proliferation by inactivation of the iron dependent enzyme ribonucleotide reductase, resulted in an increasing number of studies exploring the novel therapeutic applications of iron chelating drugs: (a) Animal models of reperfusion injury have shown that DFX is able to decrease post-anoxic damage to the brain and heart as manifested in decreased infarct size and improved functional recovery. Iron chelators may be particularly useful in improving the preservation of organs intended for transplantation such as the heart, lung or kidney. (b) Anthracycline cardiotoxicity is aggravated by iron and inhibited by iron chelators. Because the mechanism of its antineoplastic effect differs from its cardiotoxic effect, it is possible to inhibit anthracycline cardiotoxicity without interfering with therapeutic efficacy. In vivo and in vitro animal studies have yielded encouraging results but much additional experimental work is still required before iron chelating therapy may be advocated for use in patients on anthracycline therapy. (c) Cell proliferation can be inhibited by iron chelators through the reversible inhibition of ribonucleotide reductase, a rate-limiting enzyme in DNA synthesis. This may be exploited for the treatment of malignant disease, and preliminary studies have already shown that DFX in combination with multidrug chemotherapy is effective in controlling neuroblastoma and other tumours. However, the contribution of DF to the overall clinical effect is unclear. Prospective controlled clinical studies are required in order to establish whether the antiproliferative, or cell synchronizing properties of DFX may be of practical usefulness in the control of malignant disease. (d) Control of protozoal infection: Experimental in vivo and in vitro models have shown that malarial infection may be inhibited by iron chelating therapy. This useful effect of DFX and other iron chelators is most probably related to ribonucleotide reductase inhibition. Clinical studies of asymptomatic P. falciparum malaria and of cerebral malaria have shown both an accelerated rate of parasite clearance and earlier recovery from coma. These observations lend new meaning to the term 'nutritional immunity' and open new channels for exploring the possibility of controlling infection by means of selective intracellular iron deprivation. Experimental models for studying the effect of iron chelators on other intracellular pathogens such as Toxoplasma gondii, Chlamydia psittaci, or Mycobacterium tuberculosis should be established.(ABSTRACT TRUNCATED AT 400 WORDS)