Interaction of Artemisinins with Oxyhemoglobin Hb–FeII, Hb–FeII, CarboxyHb–FeII, Heme–FeII, and Carboxyheme FeII: Significance for Mode of Action and Implications for Therapy of Cerebral Malaria

Coghi, Paolo; Basilico, Nicoletta; Taramelli, Donatella; Chan, Wing-Chi; Haynes, Richard K.; Monti, Diego

doi:10.1002/cmdc.200900342

Cited by 31 publications

(27 citation statements)

References 53 publications

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“…In this work, further evidence of the role of Fe(II)-heme is that flushing RBC lysate with CO, which tightly binds Fe(II)-heme inhibiting its reactivity, moderated the effects on DHA activity. These data are in agreement with a previous study, wherein it was observed that the activity of artemisinin antimalarials is increased when parasites are grown in the presence of CO and that artemisinins are unaffected by carboxyhemoglobin or CO-heme but are decomposed by Fe(II)-hemoglobin or Fe(II)-heme (13,22). Thus, we can expect DHA to be degraded faster and, therefore, be less active when intravascular hemolysis occurs.…”

Section: Discussionsupporting

confidence: 93%

“…In order to obtain carbon monoxide (CO) hemoglobin, 5 ml of PBS-diluted RBCs was flushed with a gas mixture containing 2% CO, 5% CO 2 , and 93% nitrogen for 5 min. Normal and CO-flushed erythrocytes were then lysed by a cycle of freeze-thawing at Ϫ80°C; the stable complexation of Fe(II)-heme with CO was confirmed by UV-visible light spectrophotometry, which showed the shift in absorption from 414 nm of oxy-hemoglobin (HbO) to 420 nm of carboxy-hemoglobin (HbCO) (12,13). Erythrocyte lysates were further diluted 1:5 in PBS to perform the experiments described below.…”

Section: Methodsmentioning

confidence: 99%

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Stability of the Antimalarial Drug Dihydroartemisinin under Physiologically Relevant Conditions: Implications for Clinical Treatment and Pharmacokinetic and In Vitro Assays

Parapini

Olliaro

Navaratnam

et al. 2015

Antimicrob Agents Chemother

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f Artemisinins are peroxidic antimalarial drugs known to be very potent but highly chemically unstable; they degrade in the presence of ferrous iron, Fe(II)-heme, or biological reductants. Less documented is how this translates into chemical stability and antimalarial activity across a range of conditions applying to in vitro testing and clinical situations. Dihydroartemisinin (DHA) is studied here because it is an antimalarial drug on its own and the main metabolite of other artemisinins. The behaviors of DHA in phosphate-buffered saline, plasma, or erythrocyte lysate at different temperatures and pH ranges were examined. The antimalarial activity of the residual drug was evaluated using the chemosensitivity assay on Plasmodium falciparum, and the extent of decomposition of DHA was established through use of high-performance liquid chromatography with electrochemical detection analysis. The role of the Fe(II)-heme was investigated by blocking its reactivity using carbon monoxide (CO). A significant reduction in the antimalarial activity of DHA was seen after incubation in plasma and to a lesser extent in erythrocyte lysate. Activity was reduced by half after 3 h and almost completely abolished after 24 h. Serum-enriched media also affected DHA activity. Effects were temperature and pH dependent and paralleled the increased rate of decomposition of DHA from pH 7 upwards and in plasma. These results suggest that particular care should be taken in conducting and interpreting in vitro studies, prone as their results are to experimental and drug storage conditions. Disorders such as fever, hemolysis, or acidosis associated with malaria severity may contribute to artemisinin instability and reduce their clinical efficacy.A rtemisinin derivatives have been the most potent antimalarials available to date; they are highly active against all Plasmodium species and parasite stages, including young gametocytes, and constitute the backbone of malaria case management for severe and uncomplicated malaria (as a component of artemisinin combination therapy [ACT]) (1). The emergence and spread of artemisinin resistance in Southeast Asia is, therefore, a serious threat to malaria control (2, 3).All artemisinin derivatives share a distinctive 1,2,4-trioxane pharmacophore, which confers their antimalarial activity (the corresponding acyclic analogues lacking the endoperoxide bridge are inactive) (4, 5) but also makes these molecules particularly highly reactive and thus difficult to quantify in plasma or blood. Of the various artemisinin-type compounds in use, dihydroartemisinin (DHA), the reduced lactol derivative of artemisinin, is an antimalarial compound on its own (currently coformulated with piperaquine) and the main bioactive metabolite of artesunate and artemether. DHA itself is chemically fragile and displays a marked propensity to undergo ring opening of the lactol and rearrangement under neutral conditions, leading to a new, biologically active peroxide, which in turn rapidly decays to the inert end product deoxyartemisi...

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Section: Discussionsupporting

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Stability of the Antimalarial Drug Dihydroartemisinin under Physiologically Relevant Conditions: Implications for Clinical Treatment and Pharmacokinetic and In Vitro Assays

Parapini

Olliaro

Navaratnam

et al. 2015

Antimicrob Agents Chemother

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“…Thus, the much-publicized chemical reactions of artemisinins with heme represents an attrition pathway for artemisinins in the intraparasitic environment. [11,12] 1,2,4,5-Tetraoxanes such as 4 and 5 [13,14] and 1,2,4-trioxolanes such as 6, [15,16] have potent antimalarial activities ( Figure 1). Although the reactivity of 6 with Fe II was not assessed, other trioxolanes are readily decomposed.…”

Section: Introductionmentioning

confidence: 99%

Reactions of Antimalarial Peroxides with Each of Leucomethylene Blue and Dihydroflavins: Flavin Reductase and the Cofactor Model Exemplified

et al. 2010

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Flavin adenine dinucleotide (FAD) is reduced by NADPH-E. coli flavin reductase (Fre) to FADH(2) in aqueous buffer at pH 7.4 under argon. Under the same conditions, FADH(2) in turn cleanly reduces the antimalarial drug methylene blue (MB) to leucomethylene blue. The latter is rapidly re-oxidized by artemisinins, thus supporting the proposal that MB exerts its antimalarial activity, and synergizes the antimalarial action of artemisinins, by interfering with redox cycling involving NADPH reduction of flavin cofactors in parasite flavin disulfide reductases. Direct treatment of the FADH(2) generated from NADPH-Fre-FAD by artemisinins and antimalaria-active tetraoxane and trioxolane structural analogues under physiological conditions at pH 7.4 results in rapid reduction of the artemisinins, and efficient conversion of the peroxide structural analogues into ketone products. Comparison of the relative rates of FADH(2) oxidation indicate optimal activity for the trioxolane. Therefore, the rate of intraparastic redox perturbation will be greatest for the trioxolane, and this may be significant in relation to its enhanced in vitro antimalarial activities. (1)H NMR spectroscopic studies using the BNAH-riboflavin (RF) model system indicate that the tetraoxane is capable of using both peroxide units in oxidizing the RFH(2) generated in situ. Use of the NADPH-Fre-FAD catalytic system in the presence of artemisinin or tetraoxane confirms that the latter, in contrast to artemisinin, consumes two reducing equivalents of NADPH. None of the processes described herein requires the presence of ferrous iron. Ferric iron, given its propensity to oxidize reduced flavin cofactors, may play a role in enhancing oxidative stress within the malaria parasite, without requiring interaction with artemisinins or peroxide analogues. The NADPH-Fre-FAD system serves as a convenient mimic of flavin disulfide reductases that maintain redox homeostasis in the malaria parasite.

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“…Furthermore, artemisone itself is not readily decomposed in model studies involving heme-Fe(II) under aqueous conditions (10). Other artemisinins (artemisinin, DHA, and artesunate) that are susceptible to decomposition by Hb-or hemeFe(II) display enhanced activities against malaria parasites cultured under CO, a reagent that blocks any reaction of Hband heme-Fe(II) with the artemisinins by virtue of the formation of stable Fe(II)-CO complexes (4). Therefore, the role of heme-Fe(II) within the malaria parasite is to decompose the susceptible artemisinins (10).…”

Section: Discussionmentioning

confidence: 99%

Artemisone Uptake in Plasmodium falciparum -Infected Erythrocytes

Pooley

Fatih

Krishna

et al. 2011

Antimicrob Agents Chemother

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Artemisone is one of the most promising artemisinin derivatives in clinical trials. Previous studies with radiolabeled artemisinin and dihydroartemisinin have measured uptake in Plasmodium falciparum-infected erythrocytes. Uptake is much greater in infected than in uninfected erythrocytes, but the relative contributions of transport, binding, and metabolism to this process still await definition. In this study, we characterized mechanisms by which [14 C]artemisone is taken up into uninfected and P. falciparum-infected human erythrocytes in vitro. Radiolabeled artemisone rapidly enters uninfected erythrocytes without much exceeding extracellular concentrations. Unlabeled artemisone does not compete in this process. Radiolabeled artemisone is concentrated greatly by a time-and temperature-dependent mechanism in infected erythrocytes. This uptake is abrogated by unlabeled artemisone. In addition, the uptake of artemisone into three subcellular fractions, and its distribution into these fractions, is examined as a function of parasite maturation. These data are relevant to an understanding of the mechanisms of action of this important class of drugs.

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Interaction of Artemisinins with Oxyhemoglobin Hb–Fe^II, Hb–Fe^II, CarboxyHb–Fe^II, Heme–Fe^II, and Carboxyheme Fe^II: Significance for Mode of Action and Implications for Therapy of Cerebral Malaria

Cited by 31 publications

References 53 publications

Stability of the Antimalarial Drug Dihydroartemisinin under Physiologically Relevant Conditions: Implications for Clinical Treatment and Pharmacokinetic and In Vitro Assays

Stability of the Antimalarial Drug Dihydroartemisinin under Physiologically Relevant Conditions: Implications for Clinical Treatment and Pharmacokinetic and In Vitro Assays

Reactions of Antimalarial Peroxides with Each of Leucomethylene Blue and Dihydroflavins: Flavin Reductase and the Cofactor Model Exemplified

Artemisone Uptake in Plasmodium falciparum -Infected Erythrocytes

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