A study of metal complexes of a naturally occurring macrocyclic ionophore-monensin

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

Ionophores are a diverse class of synthetic and naturally occurring ion transporter compounds which demonstrate both direct and in-direct antimicrobial properties against a broad panel of bacterial, fungal, viral and parasitic pathogens. In addition, ionophores can regulate the host-immune response during communicable and non-communicable disease states. Although the clinical use of ionophores such as Amphotericin B, Bedaquiline and Ivermectin highlight the utility of ionophores in modern medicine, for many other ionophore compounds issues surrounding toxicity, bioavailability or lack of in vivo efficacy studies have hindered clinical development. The antimicrobial and immunomodulating properties of a range of compounds with characteristics of ionophores remain largely unexplored. As such, ionophores remain a latent therapeutic avenue to address both the global burden of antimicrobial resistance, and the unmet clinical need for new antimicrobial therapies. This review will provide an overview of the broad-spectrum antimicrobial and immunomodulatory properties of ionophores, and their potential uses in clinical medicine for combatting infection.

Factors governing the competition between group IA and IB cations for monensin A: a DFT/PCM study

The results obtained suggest that the metal selectivity of monensin can be modulated by changing the solvents used.

Circular Dichroism is Sensitive to Monovalent Cation Binding in Monensin Complexes

Monensin is a natural antibiotic that exhibits high affinity to certain metal ions. In order to explore its potential in coordination chemistry, circular dichroism (CD) spectra of monensic acid A (MonH) and its derivatives containing monovalent cations (Li(+) , Na(+) , K(+) , Rb(+) , Ag(+) , and Et4 N(+) ) in methanolic solutions were measured and compared to computational models. Whereas the conventional CD spectroscopy allowed recording of the transitions down to 192 nm, synchrotron radiation circular dichroism (SRCD) revealed other bands in the 178-192 nm wavelength range. CD signs and intensities significantly varied in the studied compounds, in spite of their similar crystal structure. Computational modeling based on the Density Functional Theory (DFT) and continuum solvent model suggests that the solid state monensin structure is largely conserved in the solutions as well. Time-dependent Density Functional Theory (TDDFT) simulations did not allow band-to-band comparison with experimental spectra due to their limited precision, but indicated that the spectral changes were caused by a combination of minor conformational changes upon the monovalent cation binding and a direct involvement of the metal electrons in monensin electronic transitions. Both the experiment and simulations thus show that the CD spectra of monensin complexes are very sensitive to the captured ions and can be used for their discrimination. Chirality 28:420-428, 2016. © 2016 Wiley Periodicals, Inc.

Structure and antimicrobial properties of monensin A and its derivatives: summary of the achievements

In this paper structural and microbiological studies on the ionophorous antibiotic monensin A and its derivatives have been collected. Monensin A is an ionophore which selectively complexes and transports sodium cation across lipid membranes, and therefore it shows a variety of biological properties. This antibiotic is commonly used as coccidiostat and nonhormonal growth promoter. The paper focuses on both the latest and earlier achievements concerning monensin A antimicrobial activity. The activities of monensin derivatives, including modifications of hydroxyl groups and carboxyl group, are also presented.

Crystal structures and spectral properties of new Cd(II) and Hg(II) complexes of monensic acid with different coordination modes of the ligand

The single crystal X-ray structures and the spectroscopic properties of complexes of monensic acid (C36H62O11·H2O) with toxic metal ions of Cd(II) and Hg(II) are discussed. The cadmium(II) complex (1) is of composition [Cd(C36H61O11)2(H2O)2] and crystallizes in the monoclinic system (space group P2(1), Z = 2) with a = 12.4090(8), b = 24.7688(16), c = 14.4358(11) Å, β = 91.979(7)°. Two ligand monoanions are bound in a bidentate coordination mode to Cd(II) via the carboxylate and the primary hydroxyl oxygens occupying the equatorial plane of the complex. The axial positions of the inner coordination sphere of Cd(II) are filled by two water molecules additionally engaged in intramolecular hydrogen bonds. The Hg(II) complex (2), [Hg(C36H60O11)(H2O)], crystallizes in the orthorhombic system (space group P2(1)2(1)2(1), Z = 4) with a = 12.7316(2), b = 16.4379(3), c = 18.7184(4) Å. The monensic acid reacts with Hg(II) in a tetradentate coordination manner via both oxygen atoms of the carboxylate function and oxygens of two hydroxyl groups. The twofold negative charge of the ligand is achieved by deprotonation of carboxylic and secondary hydroxyl groups located at the opposite ends of the molecule. Hg(II) is surrounded by five oxygen atoms in a distorted square pyramidal molecular geometry.

Monensin mediates a rapid and selective transport of Pb(2+). Possible application of monensin for the treatment of Pb(2+) intoxication

The carboxylic acid ionophore monensin, known as an electroneutral Na(+) ionophore, an anticoccidial agent, and a growth-promoting feed additive in agriculture, is shown to be highly efficient as an ionophore for Pb(2+) and to be highly selective for Pb(2+) compared with other divalent cations. Monensin transports Pb(2+) by an electroneutral mechanism in which the complex PbMonOH is the transporting species. Electrogenic transport via the species PbMon(+) may also be possible. Monensin catalyzed Pb(2+) transport is little affected by Ca(2+), Mg(2+), or K(+) concentrations that are encountered in living systems. Na(+) is inhibitory, but its effectiveness at 100 mm does not exceed approximately 50%. The poor activity of monensin as an ionophore for divalent cations other than Pb(2+) is consistent with the pattern of complex formation constants observed in the mixed solvent 80% methanol/water. This pattern also explains why Ca(2+), Mg(2+), and K(+) are ineffective as inhibitors of Pb(2+) transport, but it does not fully explain the actions of Na(+), where kinetic features of the transport mechanism may also be important. When given to rats at 100 ppm in feed together with Pb(2+) at 100 ppm in drinking water, monensin reduces Pb accumulation in several organs and tissues. It also accelerates the excretion of Pb that was accumulated previously and produces this effect without depleting the organs of zinc or copper. Monensin, used alone or in combination with other agents, may be useful for the treatment of Pb intoxication.

Effect of membrane association on the stability of complexes between ionophore A23187 and monovalent cations

The monovalent cation complexation properties of ionophore A23187 in methanol-water (65-95% w/w) and bound to unilamellar vesicles of dimyristoylphosphatidylcholine (DMPC) are contrasted. In both solution and vesicle-containing systems, 1:1 complexes between the ionophore and Li+ or Na+ predominate. The analogous complexes with K+, Rb+, and Cs+, which exist in methanol, are not detected on DMPC vesicles by changes in the absorption or fluorescence emission spectra of the ionophore. In solution, the logarithms of stability constants (log KMA) for both the LiA and NaA complexes increase by 1.5 units over the range of solvent polarity encompassed by 65% methanol-water to methanol. Selectivity for Li+ vs. Na+ is constant at a ratio of 5 in these solutions. On DMPC vesicles, selectivity for Li+ vs. Na+ is improved 15-fold with log KbLiA (3.23 +/- 0.03, T = 25 degrees C, mu = 0.05 M) being comparable to the value obtained in 80% methanol-water. In the latter solvent, increasing ionic strength (0.005-0.085 M) has little effect on log KLiA or log KHA but increases these constants by 0.4-0.5 unit in the DMPC vesicle system. Transition from the vesicle liquid-crystalline to gel-phase state reduces log KbLiA and log KbNaA by approximately 0.6 unit but has no effect on log KbHA. Thermodynamic parameters for formation of HA, LiA, and NaA in 80% methanol-water and on DMPC vesicles are reported. Analysis of these data and related considerations suggests that differences in the membrane interaction energies of particular ionophore species dominate in establishing the observed difference in complexation properties between the solution and vesicle-containing systems.