Mode of action of the copper(I) complex of 2,9-dimethyl-1,10-phenanthroline on Mycoplasma gallisepticum

Advances in Understanding of the Copper Homeostasis in Pseudomonas aeruginosa

Thirty-five thousand people die as a result of more than 2.8 million antibiotic-resistant infections in the United States of America per year. Pseudomonas aeruginosa (P. aeruginosa) is classified a serious threat, the second-highest threat category of the U.S. Department of Health and Human Services. Among others, the World Health Organization (WHO) encourages the discovery and development of novel antibiotic classes with new targets and mechanisms of action without cross-resistance to existing classes. To find potential new target sites in pathogenic bacteria, such as P. aeruginosa, it is inevitable to fully understand the molecular mechanism of homeostasis, metabolism, regulation, growth, and resistances thereof. P. aeruginosa maintains a sophisticated copper defense cascade comprising three stages, resembling those of public safety organizations. These stages include copper scavenging, first responder, and second responder. Similar mechanisms are found in numerous pathogens. Here we compare the copper-dependent transcription regulators cueR and copRS of Escherichia coli (E. coli) and P. aeruginosa. Further, phylogenetic analysis and structural modelling of mexPQ-opmE reveal that this efflux pump is unlikely to be involved in the copper export of P. aeruginosa. Altogether, we present current understandings of the copper homeostasis in P. aeruginosa and potential new target sites for antimicrobial agents or a combinatorial drug regimen in the fight against multidrug resistant pathogens.

Copper and Antibiotics: Discovery, Modes of Action, and Opportunities for Medicinal Applications

Copper is a ubiquitous element in the environment as well as living organisms, with its redox capabilities and complexation potential making it indispensable for many cellular functions. However, these same properties can be highly detrimental to prokaryotes and eukaryotes when not properly controlled, damaging many biomolecules including DNA, lipids, and proteins. To restrict free copper concentrations, all bacteria have developed mechanisms of resistance, sequestering and effluxing labile copper to minimize its deleterious effects. This weakness is actively exploited by phagocytes, which utilize a copper burst to destroy pathogens. Though administration of free copper is an unreasonable therapeutic antimicrobial itself, due to insufficient selectivity between host and pathogen, small-molecule ligands may provide an opportunity for therapeutic mimicry of the immune system. By modulating cellular entry, complex stability, resistance evasion, and target selectivity, ligand/metal coordination complexes can synergistically result in high levels of antibacterial activity. Several established therapeutic drugs, such as disulfiram and pyrithione, display remarkable copper-dependent inhibitory activity. These findings have led to development of new drug discovery techniques, using copper ions as the focal point. High-throughput screens for copper-dependent inhibitors against Mycobacterium tuberculosis and Staphylococcus aureus uncovered several new compounds, including a new class of inhibitors, the NNSNs. In this review, we highlight the microbial biology of copper, its antibacterial activities, and mechanisms to discover new inhibitors that synergize with copper.

Inhibition of Chlamydia trachomatis growth in endometrial cells by copper: possible relevance for the use of the copper IUD

There is agreement that the relative risk of developing pelvic inflammatory disease (PID) increases among women who use the intrauterine contraceptive device (IUD). The role of Chlamydia in causing PID among IUD users is not clear. The present study demonstrates that Chlamydia trachomatis growth can be inhibited in cultured human endometrial cells by copper ions at concentrations known to be released by the copper IUDs. More than 98% inhibition was produced with 10(-5) and 10(-6) M of copper. Both C. trachomatis serovar E and a lymphogranuloma venereum Chlamydia serovar L2 (LGV) were inhibited by the copper ions. Although the mechanism of the inhibition is not known, the continuous presence of the copper ions during and after adherence appeared to be necessary for maximal effect. If such inhibition occurs in vivo, it is possible that copper ions released from the copper-containing IUD may partially protect against chlamydial infection.

Investigation into the mechanism of copper uptake by Mycoplasma gallisepticum in the presence of 2,9-dimethyl-1,10-phenanthroline

In the presence of copper certain 2,2'-bipyridyls show antimycoplasmal activity, whereas copper itself causes a toxic effect. In this paper results are presented to elucidate the mechanism of copper uptake in the presence of 2,9-dimethyl-1,10-phenanthroline. The time course of copper and/or ligand uptake under the applied conditions is consistent with a carrier transport mechanism in which 2,9-dimethyl-1,10-phenanthroline operates as a carrier for copper ions. The influence of valinomycin on copper uptake indicates that the transmembrane potential is not the driving force in the carrier process.

Inhibition of NADH oxidase and lactate dehydrogenase of Mycoplasma gallisepticum by copper complexes of 2,2'-bipyridyl analogues

In the presence of copper, 2,2'-bipyridyl analogues possess growth-inhibitory activity against Mycoplasma gallisepticum. Inhibition of the energy yielding metabolism plays a role in the mechanism of action. We showed that probably inhibition of lactate dehydrogenase and NADH oxidase is involved. Both enzymes were inhibited in vitro and in vivo by several copper 2,2'-bipyridyl complexes. A two-step mechanism of action is proposed, i.e. first a copper complex enters the cell, then after dissociation of the complex the enzymes are inhibited by free copper.

Determination of formation constants of copper(II) complexes of Adler medium components with a solid-state copper(II) ion-selective electrode

A general method for the determination of overall conditional formation constants of copper(II) complexes of mycoplasma growth medium (Adler) constituents together with the protonation constants of the complexing ligands was developed. In Adler medium a total of 0.204 +/- 0.004 molar copper binding sites proved to be present with log beta 2 = 8.14 +/- 0.05 (mu = 0.11) and log Ka = 6.14 +/- 0.004. Conditional overall formation constants were calculated at various pH values. Free copper(II) ion concentrations were calculated as a function of the total added amount of copper(II) and pH. The consequences of these findings for the determination of the growth inhibition of mycoplasmas by copper complexes of 2,2'-bipyridyl analogues are stressed.

Mechanism of action of the copper(I) complex of 2,9-dimethyl-1,10-phenanthroline on Mycoplasma gallisepticum

Evidence was found that the inhibitory action of Cu(DMP)2NO3, the copper(I) complex of 2,9-dimethyl-1,10-phenanthroline (DMP), on Mycoplasma gallisepticum is a consequence of the ultimate toxicity of copper, and not that of the ligand, DMP. From uptake studies with radiolabeled 67Cu and [14C]DMP, we concluded that significantly more copper than DMP is bound to the mycoplasmal cell. It appeared that dissociation of Cu(DMP)2+ occurred shortly after interaction with the cell membrane. Copper was transported across the cytoplasmic membrane. A strong dependence of copper uptake on the incubation medium was observed in the absence of DMP. The main function of the ligand DMP appeared to be as a vehicle for the transport of copper from nontoxic copper-medium complexes to membrane-buried cellular ligands.