RESUMO
The continued rise of antibiotic resistance threatens to undermine the utility of the world's current antibiotic arsenal. This problem is particularly troubling when it comes to Gram-negative pathogens for which there are inherently fewer antibiotics available. To address this challenge, recent attention has been focused on finding compounds capable of disrupting the Gram-negative outer membrane as a means of potentiating otherwise Gram-positive-specific antibiotics. In this regard, agents capable of binding to the lipopolysaccharide (LPS) present in the Gram-negative outer membrane are of particular interest as synergists. Recently, thrombin-derived C-terminal peptides (TCPs) were reported to exhibit unique LPS-binding properties. We here describe investigations establishing the capacity of TCPs to act as synergists with the antibiotics erythromycin, rifampicin, novobiocin, and vancomycin against multiple Gram-negative strains including polymyxin-resistant clinical isolates. We further assessed the structural features most important for the observed synergy and characterized the outer membrane permeabilizing activity of the most potent synergists. Our investigations highlight the potential for such peptides in expanding the therapeutic range of antibiotics typically only used to treat Gram-positive infections.
Assuntos
Anti-Infecciosos , Peptídeos Catiônicos Antimicrobianos , Farmacorresistência Bacteriana/efeitos dos fármacos , Sinergismo Farmacológico , Bactérias Gram-Negativas/efeitos dos fármacos , Anti-Infecciosos/química , Anti-Infecciosos/farmacologia , Peptídeos Catiônicos Antimicrobianos/química , Peptídeos Catiônicos Antimicrobianos/farmacologia , Trombina/químicaRESUMO
In polygynous mating systems, few males have stable access to sexual mates. With an expected higher copulation rate, harem males may deplete seminal fluids or increase epididymal sperm maturation, generating poor sperm quality. In a first study, we reported a higher sperm quality in sneaker males of Carollia perspicillata To test whether the lower sperm quality observed in harem males was generated by an elevated copulation rate, we temporarily removed males of both social statuses from the colony. We thus assessed status-related changes of sperm quality resulting from sexual abstinence. Moreover, released from territory and female guarding, harem males were expected to show a reduction in somatic costs. On the basis of sperm competition models, we predicted a higher resource investment in the ejaculate with the reduction of pre-copulatory efforts. In line with our predictions, sperm quality of harem males improved significantly in contrast to sneaker males, whose sperm quality did not change. Without an increase in ejaculate lipid peroxidation, our results also provide evidence that the duration of sexual abstinence was not sufficient to generate sperm oxidative damage through senescence. Harem males did not show a reduction in blood lipid peroxidation or in the ratio of oxidized to reduced glutathione. In line with the maintenance of these somatic costs, harem males did not invest more superoxide dismutase to the ejaculate to maintain sperm quality. Our results suggest that a difference in copulation rate rather than an adaptation to sperm competition provides sneaker males with higher sperm quality in C. perspicillata.
Assuntos
Quirópteros/fisiologia , Comportamento Sexual Animal , Espermatozoides/citologia , Animais , Copulação , Feminino , Hierarquia Social , Peroxidação de Lipídeos , Masculino , Reprodução , Abstinência Sexual , Espermatozoides/metabolismoRESUMO
The growing incidence of infections caused by multi-drug resistant Gram-negative bacteria has led to an increased use of last-resort antibiotics such as the polymyxins. Polymyxin therapy is limited by toxicity concerns, most notably nephrotoxicity. Recently we reported the development of a novel class of semisynthetic polymyxins with reduced toxicity wherein the N-terminal lipid and diaminobutyric acid residue are replaced by a cysteine-linked lipid featuring a reductively labile disulfide bond. In the present study we further explored the potential of this approach by also varying the amino acid residue directly adjacent to the polymyxin macrocycle. This led to the identification of new semisynthetic polymyxins that maintain the potent antibacterial activity of the clinically used polymyxin B while exhibiting a further reduction in toxicity toward human proximal tubule epithelial cells. Furthermore, these new polymyxins were found to effectively synergize with novobiocin, rifampicin, and erythromycin against mcr-positive, polymyxin resistant E. coli.
RESUMO
New approaches to target antibacterial agents toward Gram-negative bacteria are key, given the rise of antibiotic resistance. Since the discovery of polymyxin B nonapeptide as a potent Gram-negative outer membrane (OM)-permeabilizing synergist in the early 1980s, a vast amount of literature on such synergists has been published. This Review addresses a range of peptide-based and small organic compounds that disrupt the OM to elicit a synergistic effect with antibiotics that are otherwise inactive toward Gram-negative bacteria, with synergy defined as a fractional inhibitory concentration index (FICI) of <0.5. Another requirement for the inclusion of the synergists here covered is their potentiation of a specific set of clinically used antibiotics: erythromycin, rifampicin, novobiocin, or vancomycin. In addition, we have focused on those synergists with reported activity against Gram-negative members of the ESKAPE family of pathogens namely, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and/or Acinetobacter baumannii. In cases where the FICI values were not directly reported in the primary literature but could be calculated from the published data, we have done so, allowing for more direct comparison of potency with other synergists. We also address the hemolytic activity of the various OM-disrupting synergists reported in the literature, an effect that is often downplayed but is of key importance in assessing the selectivity of such compounds for Gram-negative bacteria.
Assuntos
Acinetobacter baumannii , Antibacterianos , Antibacterianos/química , Antibacterianos/farmacologia , Escherichia coli , Bactérias Gram-Negativas , Klebsiella pneumoniae , Pseudomonas aeruginosaRESUMO
With increasing rates of resistance toward commonly used antibiotics, especially among Gram-negative bacteria, there is renewed interested in polymyxins. Polymyxins are lipopeptide antibiotics with potent anti-Gram-negative activity and are generally believed to target lipid A, the lipopolysaccharide (LPS) anchor found in the outer membrane of Gram-negative bacteria. To characterize the stereochemical aspects of their mechanism(s) of action, we synthesized the full enantiomers of polymyxin B and the polymyxin B nonapeptide (PMBN). Both compounds were compared with the natural compounds in biological and biophysical assays, revealing strongly reduced antibacterial activity for the enantiomeric species. The enantiomeric compounds also exhibit reduced LPS binding, lower outer membrane (OM) permeabilization, and loss of synergetic potential. These findings provide new insights into the stereochemical requirements underlying the mechanisms of action of polymyxin B and PMBN.
Assuntos
Polimixinas , Polimixinas/farmacologiaRESUMO
In the hunt for new antibiotics with activity against Gram-negative pathogens, the outer membrane ß-barrel assembly machine (BAM) complex has become an increasingly interesting target. The recently reported BAM complex inhibitor, MRL-494, was discovered via a screening campaign for molecules that target the outer membrane. Notably, MRL-494 was reported to be an unintended byproduct generated during the synthesis of an unrelated compound, and as such no synthesis of the compound was disclosed. We here present a convenient and reliable route for the synthesis of MRL-494 that scales well. The antibacterial activity measured for synthesized MRL-494 matches that reported in the literature. Furthermore, MRL-494 was found to exhibit potent synergistic activity with rifampicin against Gram-negative bacteria, including E. coli, K. pneumoniae, A. baumannii, and P. aeruginosa. MRL-494 was also found to cause outer membrane disruption and induction of the Rcs stress response pathway. In addition, we undertook a focused structure-activity study specifically aimed at elucidating the roles played by the two guanidine moieties contained within the structure of MRL-494.
Assuntos
Proteínas de Escherichia coli , Escherichia coli , Escherichia coli/metabolismo , Proteínas de Escherichia coli/metabolismo , Proteínas da Membrana Bacteriana Externa/metabolismo , Antibacterianos/farmacologia , Antibacterianos/metabolismoRESUMO
Polymyxins are a class of lipopeptide anti-infective agents with potent and specific activity against Gram-negative bacteria. While toxicity concerns associated with polymyxin B and E (colistin) have historically limited their clinical application, today they are increasingly used as last-resort antibiotics given the rise of multidrug-resistant Gram-negative pathogens. The adverse side effects of polymyxins are well known, particularly as related to their nephrotoxicity. Here, we describe the synthesis and evaluation of a novel series of polymyxin analogues, aimed at reducing their nephrotoxic effects. Using a semisynthetic approach, we explored modifications of the exocyclic part of the polymyxin scaffold, namely, the terminal amino acid and lipophilic tail. By incorporating a reductively labile disulfide linkage in the lipid tail, we obtained novel polymyxins that exhibit potent antibacterial activity on par with polymyxin B but with reduced toxicity toward human renal proximal tubular epithelial cells.
Assuntos
Dissulfetos , Polimixinas , Humanos , Polimixinas/farmacologia , Dissulfetos/farmacologiaRESUMO
Brevicidine and laterocidine are two recently discovered lipopeptide antibiotics with promising antibacterial activity. Possessing a macrocyclic core, multiple positive charges, and a lipidated N-terminus, these lipopeptides exhibit potent and selective activity against Gram-negative pathogens, including polymyxin-resistant isolates. Given the low amounts of brevicidine and laterocidine accessible by fermentation of the producing microorganisms, synthetic routes to these lipopeptides present an attractive alternative. We here report the convenient solid-phase syntheses of both brevicidine and laterocidine and confirm their potent anti-Gram-negative activities. The synthetic routes developed also provide convenient access to novel structural analogues of both brevicidine and laterocidine that display improved hydrolytic stability while maintaining potent antibacterial activity in both in vitro assays and in vivo infection models.
RESUMO
Pentamidine, an FDA-approved antiparasitic drug, was recently identified as an outer membrane disrupting synergist that potentiates erythromycin, rifampicin, and novobiocin against Gram-negative bacteria. The same study also described a preliminary structure-activity relationship using commercially available pentamidine analogues. We here report the design, synthesis, and evaluation of a broader panel of bis-amidines inspired by pentamidine. The present study both validates the previously observed synergistic activity reported for pentamidine, while further assessing the capacity for structurally similar bis-amidines to also potentiate Gram-positive specific antibiotics against Gram-negative pathogens. Among the bis-amidines prepared, a number of them were found to exhibit synergistic activity greater than pentamidine. These synergists were shown to effectively potentiate the activity of Gram-positive specific antibiotics against multiple Gram-negative pathogens such as Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli, including polymyxin- and carbapenem-resistant strains.