In vitro potentiation of antibiotic activities by a catecholate iron chelator against chloroquine-resistant Plasmodium falciparum

Effect of iron chelation on anti-pseudomonal activity of doxycycline

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High affinity iron chelation enhances the antibacterial activity of tetracyclines.

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High affinity iron chelation synergises with doxycycline against P. aeruginosa.

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Doxycycline chelates iron and loses antibacterial activity.

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Iron chelation re-establishes the susceptibility of iron bound doxycycline.

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Iron chelation enhances doxycycline activity in a biofilm setting.

Background

Increasing resistance of microorganisms to antimicrobial agents is a growing concern and there is a lack of novel agents. This has stimulated the exploration of novel strategies for treatment of infection.

Objective

To investigate synergistic interactions between five tetracyclines and tobramycin with an iron chelator (CP762) against two reference strains and nine clinical isolates of Pseudomonas aeruginosa from cystic fibrosis patients.

Method

Microdilution assays for minimal inhibitory concentration determination and checkerboard assays were used to assess synergy between antibiotics and CP762. Given the iron-binding capacity of tetracyclines, the binding of iron with doxycycline was investigated using Job's plot methodology. Synergy between the iron-bound form of doxycycline and CP762 was compared with that of unbound doxycycline and CP762. Enhancement of doxycycline anti-biofilm activity was also assessed.

Results

There was synergy between CP762 and all tetracyclines, except minocycline, against the reference strains but that against clinical isolates was variable. Synergy was not demonstrated for tobramycin against any of the strains tested. This led to the hypothesis that iron chelation preserves the binding of tetracyclines to the bacterial ribosome. Susceptibility to iron-bound doxycycline was decreased by two- to four-fold and synergistic interactions with the iron chelator were consistently more intense with iron-bound doxycycline than with doxycycline alone. The doxycycline–iron chelator combination also significantly reduced cell viability in established biofilms.

Conclusion

The data in this study provide evidence that iron chelation enhances the anti-pseudomonal activity of tetracyclines, specifically doxycycline.

A manganese photosensitive tricarbonyl molecule [Mn(CO)3(tpa-κ3N)]Br enhances antibiotic efficacy in a multi-drug-resistant Escherichia coli

Carbon monoxide-releasing molecules (CORMs) are a promising class of new antimicrobials, with multiple modes of action that are distinct from those of standard antibiotics. The relentless increase in antimicrobial resistance, exacerbated by a lack of new antibiotics, necessitates a better understanding of how such novel agents act and might be used synergistically with established antibiotics. This work aimed to understand the mechanism(s) underlying synergy between a manganese-based photoactivated carbon monoxide-releasing molecule (PhotoCORM), [Mn(CO)3(tpa-κ³N)]Br [tpa=tris(2-pyridylmethyl)amine], and various classes of antibiotics in their activities towards Escherichia coli EC958, a multi-drug-resistant uropathogen. The title compound acts synergistically with polymyxins [polymyxin B and colistin (polymyxin E)] by damaging the bacterial cytoplasmic membrane. [Mn(CO)3(tpa-κ³N)]Br also potentiates the action of doxycycline, resulting in reduced expression of tetA, which encodes a tetracycline efflux pump. We show that, like tetracyclines, the breakdown products of [Mn(CO)3(tpa-κ³N)]Br activation chelate iron and trigger an iron starvation response, which we propose to be a further basis for the synergies observed. Conversely, media supplemented with excess iron abrogated the inhibition of growth by doxycycline and the title compound. In conclusion, multiple factors contribute to the ability of this PhotoCORM to increase the efficacy of antibiotics in the polymyxin and tetracycline families. We propose that light-activated carbon monoxide release is not the sole basis of the antimicrobial activities of [Mn(CO)3(tpa-κ³N)]Br.

Self-preserving personal care products

OBJECTIVE

As questions on the safety of some popular preservatives are on the rise, there is a growing interest in developing 'self-preserving' personal care products. Use of multifunctional ingredients/actives with antimicrobial properties has been explored as replacements for conventional preservatives. This study explores the use of combinations of multifunctional actives (MFA) and other cosmetic ingredients in various personal care formulations, to deliver microbiologically safe self-preserving products. Products studied in this study include face wash, gel-based leave-on skin care product and face mask.

METHODS

Minimum inhibitory concentration (MIC) of several cosmetic ingredients was determined to identify multifunctional actives with antimicrobial activity. Personal care formulations made with multifunctional actives and other cosmetic ingredients were studied for preservative efficacy by challenging the product with six multiple cycles of microbial challenge.

RESULTS

Formulations with combinations of multifunctional actives with antioxidant (AO) and chelators (CHL) were found to work synergistically and were highly efficacious in controlling multiple microbial challenges as observed in the preservative efficacy test (PET) studies. The effective combinations were able to withstand up to six multiple microbial challenges without product degradation. The preservative efficacy profile was similar to control formula containing preservatives.

CONCLUSION

Self-preserving personal care/cosmetic products can be developed which are as efficacious as preserved products by a prudent selection of multifunctional actives, antioxidants and chelators as a part of the formulation.

Antibiotics in malaria therapy: which antibiotics except tetracyclines and macrolides may be used against malaria?

Malaria, a parasite vector-borne disease, is one of the most significant health threats in tropical regions, despite the availability of individual chemoprophylaxis. Malaria chemoprophylaxis and chemotherapy remain a major area of research, and new drug molecules are constantly being developed before drug-resistant parasites strains emerge. The use of anti-malarial drugs is challenged by contra-indications, the level of resistance of Plasmodium falciparum in endemic areas, clinical tolerance and financial cost. New therapeutic approaches are currently needed to fight against this disease. Some antibiotics that have shown potential effects on malaria parasite have been recently studied in vitro or in vivo intensively. Two families, tetracyclines and macrolides and their derivatives have been particularly studied in recent years. However, other less well-known have been tested or are being used for malaria treatment. Some of these belong to older families, such as quinolones, co-trimoxazole or fusidic acid, while others are new drug molecules such as tigecycline. These emerging antibiotics could be used to prevent malaria in the future. In this review, the authors overview the use of antibiotics for malaria treatment.

Anti-plasmodial activity of aroylhydrazone and thiosemicarbazone iron chelators: effect on erythrocyte membrane integrity, parasite development and the intracellular labile iron pool

Iron chelators inhibit the growth of the malaria parasite, Plasmodium falciparum, in culture and in animal and human studies. We previously reported the anti-plasmodial activity of the chelators, 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311), 2-hydroxy-1-naphthylaldehyde 4-methyl-3-thiosemicarbazone (N4mT), and 2-hydroxy-1-naphthylaldehyde 4-phenyl-3-thiosemicarbazone (N4pT). In fact, these ligands showed greater growth inhibition of chloroquine-sensitive (3D7) and chloroquine-resistant (7G8) strains of P. falciparum in culture compared to desferrioxamine (DFO). The present study examined the effects of 311, N4mT and N4pT on erythrocyte membrane integrity and asexual parasite development. While the characteristic biconcave disk shape of the erythrocytes was unaffected, the chelators caused very slight hemolysis at IC50 values that inhibited parasite growth. The chelators 311, N4mT and N4pT affected all stages of the intra-erythrocytic development cycle (IDC) of P. falciparum in culture. However, while these ligands primarily affected the ring-stage, DFO inhibited primarily trophozoite and schizont-stages. Ring, trophozoite and schizont-stages of the IDC were inhibited by significantly lower concentrations of 311, N4mT, and N4pT (IC50=4.45±1.70, 10.30±4.40, and 3.64±2.00μM, respectively) than DFO (IC50=23.43±3.40μM). Complexation of 311, N4mT and N4pT with iron reduced their anti-plasmodial activity. Estimation of the intracellular labile iron pool (LIP) in erythrocytes showed that the chelation efficacy of 311, N4mT and N4pT corresponded to their anti-plasmodial activities, suggesting that the LIP may be a potential source of non-heme iron for parasite metabolism within the erythrocyte. This study has implications for malaria chemotherapy that specifically disrupts parasite iron utilization.

Synthesis and biological properties of iron chelators based on a bis-2-(2-hydroxy-phenyl)-thiazole-4-carboxamide or -thiocarboxamide (BHPTC) scaffold

Bis-2-(2-hydroxy-phenyl)-thiazole-4-carboxamides and -thiocarboxamides (BHPTCs) form a family of gemini hexacoordinated bis-tridentate chelating scaffolds. Four molecules were synthesized and shown to chelate iron(III) efficiently with a 1:1 stoichiometry. A dithioamide BHPTC displayed promising antiproliferative activity in several cancerous cell lines, making this molecule an interesting lead compound for the design of new iron-chelating anticancer drugs. Conversely, diamide BHPTCs had significant cytoprotective activity against iron overload in HepaRG cells in vitro, and were as efficient as and less toxic than deferoxamine B (DFO).

Antimalarial drug synergism and antagonism: mechanistic and clinical significance

Interactions between antimicrobial agents provide clues as to their mechanisms of action and influence the combinations chosen for therapy of infectious diseases. In the treatment of malaria, combinations of drugs, in many cases acting synergistically, are increasingly important in view of the frequency of resistance to single agents. The study of antimalarial drug interactions is therefore of great significance to both treatment and research. It is therefore worrying that the analysis of drug-interaction data is often inadequate, leading in some cases to dubious conclusions about synergism or antagonism. Furthermore, making mechanistic deductions from drug-interaction data is not straightforward and of the many reported instances of antimalarial synergism or antagonism, few have been fully explained biochemically. This review discusses recent findings on antimalarial drug interactions and some pitfalls in their analysis and interpretation. The conclusions are likely to have relevance to other antimicrobial agents.

GENE ORGANIZATION AND EXPRESSION OF THE DIVALENT CATION TRANSPORTER NRAMP IN THE PROTISTAN PARASITE PERKINSUS MARINUS

Trophozoites of the protistan parasite Perkinsus marinus reside and proliferate inside phagosomelike structures of hemocytes from the host, the eastern oyster Crassostrea virginica. In a murine model, it has been proposed that the outcome of intracellular parasite-host interactions is determined, at least in part, by the activity of the host's divalent cation transporter natural resistance-associated macrophage protein 1 (Nramp1). Although nucleotide sequences from members of the Nramp family in protozoan parasites have recently become available in public databases, little is known about their molecular, structural, and functional aspects that may relate to the parasite's survival of intracellular killing by the host. The complementary DNA (cDNA) sequence of the Nramp from P. marinus (PmNramp) was obtained by polymerase chain reaction amplification with degenerated primers, followed by rapid amplification of cDNA ends. The 2,082-bp cDNA sequence encoded a predicted protein of 558 amino acids. PmNramp is a single-copy gene composed of 7 exons and 6 short introns (44-61 bp) with the canonical splicing signal (GT/AG). A phylogenetic analysis indicates that P. marinus and apicomplexan Nramp genes derive from a common "archetype" Nramp ancestor. However, the apicomplexan Nramps are highly divergent from the P. marinus sequence and the rest of the archetype Nramp group. Preliminary studies suggest that expression of PmNramp in in vitro-cultured P. marinus trophozoites is modulated by metals and by exogenous oxidative stress.

Cellular uptake of a catechol iron chelator and chloroquine into Plasmodium falciparum infected erythrocytes

Our study demonstrates the capacity of FR160, a catechol iron chelator, to reach and accumulate into infected Plasmodium falciparum erythrocytes and parasites (cellular accumulation ratio between 12 and 43). Steady-state FR160 accumulation is obtained after 2 hr of exposure. After 2 hr exposure, it reaches intracellular levels that are 4- to 10-fold higher in infected red blood cells than those attained in normal erythrocytes. There is quite a good correlation between the accumulation of chloroquine and FR160 in the different strains (r=0.939) and in the IC(50) values (r=0.719). In contrast, the accumulation of FR160 and its activity is poorly correlated (r=0.500), suggesting that activity of FR160 may be independent of its penetration into infected erythrocytes. The mechanism of accumulation is yet unknown but based on inhibitor studies, the uptake of FR160 seems to be not associated with the calcium pump or channel, the potassium channel or the Na(+)/H(+) exchanger. Combinations of FR160 with verapamil, diltiazem, clotrimazole, amiloride, diazoxide, 4-aminopyridine, and picrotoxin should be avoided (antagonistic effects). The potent in vitro activity of FR160 on chloroquine-resistant strains or isolates, its lower toxicity against Vero cells, its mechanisms of action, its capacity to reach rapidly and accumulate into infected erythrocytes suggest that FR160 holds much promise as a new structural lead and effective antimalarial agent or at least a promising adjuvant in treatment of malaria.