Multiple bactericidal mechanisms of the zinc ionophore PBT2

Published 18 March 2020Globally, more antimicrobials are used in food-producing animals than in humans, and the extensive use of medically important human antimicrobials poses a significant public health threat in the face of rising antimicrobial resistance (AMR). The development of novel ionophores, a class of antimicrobials used exclusively in animals, holds promise as a strategy to replace or reduce essential human antimicrobials in veterinary practice. PBT2 is a zinc ionophore with recently demonstrated antibacterial activity against several Gram-positive pathogens, although the underlying mechanism of action is unknown. Here, we investigated the bactericidal mechanism of PBT2 in the bovine mastitis-causing pathogen, Streptococcus uberis In this work, we show that PBT2 functions as a Zn2+/H+ ionophore, exchanging extracellular zinc for intracellular protons in an electroneutral process that leads to cellular zinc accumulation. Zinc accumulation occurs concomitantly with manganese depletion and the production of reactive oxygen species (ROS). PBT2 inhibits the activity of the manganese-dependent superoxide dismutase, SodA, thereby impairing oxidative stress protection. We propose that PBT2-mediated intracellular zinc toxicity in S. uberis leads to lethality through multiple bactericidal mechanisms: the production of toxic ROS and the impairment of manganese-dependent antioxidant functions. Collectively, these data show that PBT2 represents a new class of antibacterial ionophores capable of targeting bacterial metal ion homeostasis and cellular redox balance. We propose that this novel and multitarget mechanism of PBT2 makes the development of cross-resistance to medically important antimicrobials unlikely.IMPORTANCE More antimicrobials are used in food-producing animals than in humans, and the extensive use of medically important human antimicrobials poses a significant public health threat in the face of rising antimicrobial resistance. Therefore, the elimination of antimicrobial crossover between human and veterinary medicine is of great interest. Unfortunately, the development of new antimicrobials is an expensive high-risk process fraught with difficulties. The repurposing of chemical agents provides a solution to this problem, and while many have not been originally developed as antimicrobials, they have been proven safe in clinical trials. PBT2, a zinc ionophore, is an experimental therapeutic that met safety criteria but failed efficacy checkpoints against both Alzheimer's and Huntington's diseases. It was recently found that PBT2 possessed potent antimicrobial activity, although the mechanism of bacterial cell death is unresolved. In this body of work, we show that PBT2 has multiple mechanisms of antimicrobial action, making the development of PBT2 resistance unlikely.Nichaela Harbison-Price, Scott A. Ferguson, Adam Heikal, George Taiaroa, Kiel Hards ... Christopher A. McDevitt ... et al

Chemical synergy between ionophore PBT2 and zinc reverses antibiotic resistance

The World Health Organization reports that antibiotic-resistant pathogens represent an imminent global health disaster for the 21st century. Gram-positive superbugs threaten to breach last-line antibiotic treatment, and the pharmaceutical industry antibiotic development pipeline is waning. Here we report the synergy between ionophore-induced physiological stress in Gram-positive bacteria and antibiotic treatment. PBT2 is a safe-for-human-use zinc ionophore that has progressed to phase 2 clinical trials for Alzheimer's and Huntington's disease treatment. In combination with zinc, PBT2 exhibits antibacterial activity and disrupts cellular homeostasis in erythromycin-resistant group A Streptococcus (GAS), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE). We were unable to select for mutants resistant to PBT2-zinc treatment. While ineffective alone against resistant bacteria, several clinically relevant antibiotics act synergistically with PBT2-zinc to enhance killing of these Gram-positive pathogens. These data represent a new paradigm whereby disruption of bacterial metal homeostasis reverses antibiotic-resistant phenotypes in a number of priority human bacterial pathogens.IMPORTANCE The rise of bacterial antibiotic resistance coupled with a reduction in new antibiotic development has placed significant burdens on global health care. Resistant bacterial pathogens such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus are leading causes of community- and hospital-acquired infection and present a significant clinical challenge. These pathogens have acquired resistance to broad classes of antimicrobials. Furthermore, Streptococcus pyogenes, a significant disease agent among Indigenous Australians, has now acquired resistance to several antibiotic classes. With a rise in antibiotic resistance and reduction in new antibiotic discovery, it is imperative to investigate alternative therapeutic regimens that complement the use of current antibiotic treatment strategies. As stated by the WHO Director-General, "On current trends, common diseases may become untreatable. Doctors facing patients will have to say, Sorry, there is nothing I can do for you."Lisa Bohlmann, David M. P. De Oliveira, Ibrahim M. El-Deeb, Erin B. Brazel, Nichaela Harbison-Pric

Why the categorization of indexed effective orifice area is not Justified tor the classification of prosthesis-patient mismatch

Objectives: Although the impact of prosthesis-patient mismatch (PPM) on survival has been widely studied, there has been little debate about whether the current definition of PPM truly reflects hemodynamic obstruction. This study aimed to validate the categorization of indexed effective orifice area (EOAi) for the classification of PPM.Methods: In total, 2171 patients who underwent aortic valve replacement with a surgical stented bioprosthesis in 5 trials (CoreValve US High-Risk, SURTAVI [Surgical Replacement and Transcatheter Aortic Valve Implantation Trial], Evolut Low Risk, PERIGON [PERIcardial SurGical AOrtic Valve ReplacemeNt] Pivotal Trial for the Avalus valve, and PERIGON Japan) were used for this analysis. The echocardiographic images at the 1-year follow-up visit were evaluated to explore the association between EOAi and mean aortic gradient and its interaction with other patient characteristics, including obesity. In addition, different criteria of PPM were compared with reflect elevated mean aortic gradients (>= 20 mm Hg).Results: A relatively smaller exponential decay in mean aortic gradient was found for increasing EOAi, as the slope on the log scale was -0.83 versus -2.5 in the publication from which the current cut-offs for PPM originate. The accuracy of the American Society of Echocardiography, Valve Academic Research Consortium-2, and European Association of Cardiovascular Imaging definitions of PPM to reflect elevated mean aortic gradients was 49%, 57%, and 57%, respectively. The relation between EOAi and mean aortic gradient was not significantly different between obese and non-obese patients (P = .20).Conclusions: The use of EOAi thresholds to classify patients with PPM is undermined by a less-pronounced exponential relationship between EOAi and mean aortic gradient than previously demonstrated. Moreover, recent adjustment for obesity in the definition of PPM is not supported by these data.Thoracic Surger

Polymorphisms at the Werner locus: I. Newly identified polymorphisms, ethnic variability of 1367Cy/Arg, and its stability in a population of Finnish centenarians

The Werner syndrome gene (WRN) encodes a novel helicase of 1,432 amino acids. Homozygous mutations, all of which result in the truncation of the protein, lead to Werner syndrome. However, little is known about the role of WRN in 'normal' aging. We have identified four missense polymorphisms and four conservative polymorphisms in WRN gene. A single study showed that a polymorphism at amino acid 1367 Cys(TTG)/Arg(CTG) is associated with a variation in risk of myocardial infarction among a Japanese population. The 1367 Cys/Arg polymorphism was examined during aging in three different populations: Finnish, Mexican, and North American. The frequencies of 1367 Cys were higher than those of 1367 Arg in all the populations examined, though the frequencies varied among populations. The frequency of the 1367 Arg allele, thought to be protective against myocardial infarction in a Japanese population, was approximately three times higher in the North American and Finnish adult populations. When newborns and centenarians were compared within the Finnish population, no differences were observed in the proportions of 1367 Cys/Arg across age groups. Within the Finnish population, we confirmed a significant decrease of the APOE ?2 allele and an increase in the ?4 allele in newborn infants compared with centenarians. Thus, unlike the APOE polymorphism, there is no evidence of an association of this WRN polymorphism with longevity