Chloroquine is therapeutic in murine experimental model of paracoccidioidomycosis

The Kir2.1E299V mutation increases atrial fibrillation vulnerability while protecting the ventricles against arrhythmias in a mouse model of short QT syndrome type 3

AIMS

Short QT syndrome type 3 (SQTS3) is a rare arrhythmogenic disease caused by gain-of-function mutations in KCNJ2, the gene coding the inward rectifier potassium channel Kir2.1. We used a multidisciplinary approach and investigated arrhythmogenic mechanisms in an in-vivo model of de-novo mutation Kir2.1E299V identified in a patient presenting an extremely abbreviated QT interval and paroxysmal atrial fibrillation.

METHODS AND RESULTS

We used intravenous adeno-associated virus-mediated gene transfer to generate mouse models, and confirmed cardiac-specific expression of Kir2.1WT or Kir2.1E299V. On ECG, the Kir2.1E299V mouse recapitulated the QT interval shortening and the atrial-specific arrhythmia of the patient. The PR interval was also significantly shorter in Kir2.1E299V mice. Patch-clamping showed extremely abbreviated action potentials in both atrial and ventricular Kir2.1E299V cardiomyocytes due to a lack of inward-going rectification and increased IK1 at voltages positive to -80 mV. Relative to Kir2.1WT, atrial Kir2.1E299V cardiomyocytes had a significantly reduced slope conductance at voltages negative to -80 mV. After confirming a higher proportion of heterotetrameric Kir2.x channels containing Kir2.2 subunits in the atria, in-silico 3D simulations predicted an atrial-specific impairment of polyamine block and reduced pore diameter in the Kir2.1E299V-Kir2.2WT channel. In ventricular cardiomyocytes, the mutation increased excitability by shifting INa activation and inactivation in the hyperpolarizing direction, which protected the ventricle against arrhythmia. Moreover, Purkinje myocytes from Kir2.1E299V mice manifested substantially higher INa density than Kir2.1WT, explaining the abbreviation in the PR interval.

CONCLUSION

The first in-vivo mouse model of cardiac-specific SQTS3 recapitulates the electrophysiological phenotype of a patient with the Kir2.1E299V mutation. Kir2.1E299V eliminates rectification in both cardiac chambers but protects against ventricular arrhythmias by increasing excitability in both Purkinje-fiber network and ventricles. Consequently, the predominant arrhythmias are supraventricular likely due to the lack of inward rectification and atrial-specific reduced pore diameter of the Kir2.1E299V-Kir2.2WT heterotetramer.

How metals fuel fungal virulence, yet promote anti-fungal immunity

Invasive fungal infections represent a significant global health problem, and present several clinical challenges, including limited treatment options, increasing rates of antifungal drug resistance and compounding comorbidities in affected patients. Metals, such as copper, iron and zinc, are critical for various biological and cellular processes across phyla. In mammals, these metals are important determinants of immune responses, but pathogenic microbes, including fungi, also require access to these metals to fuel their own growth and drive expression of major virulence traits. Therefore, host immune cells have developed strategies to either restrict access to metals to induce starvation of invading pathogens or deploy toxic concentrations within phagosomes to cause metal poisoning. In this Review, we describe the mechanisms regulating fungal scavenging and detoxification of copper, iron and zinc and the importance of these mechanisms for virulence and infection. We also outline how these metals are involved in host immune responses and the consequences of metal deficiencies or overloads on how the host controls invasive fungal infections.

Co-administration of Favipiravir and the Remdesivir Metabolite GS-441524 Effectively Reduces SARS-CoV-2 Replication in the Lungs of the Syrian Hamster Model

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread worldwide since December 2019, causing coronavirus disease 2019 (COVID-19). Although vaccines for this virus have been developed rapidly, repurposing drugs approved to treat other diseases remains an invaluable treatment strategy. Here, we evaluated the inhibitory effects of drugs on SARS-CoV-2 replication in a hamster infection model and in in vitro assays. Favipiravir significantly suppressed virus replication in hamster lungs. Remdesivir inhibited virus replication in vitro, but was not effective in the hamster model. However, GS-441524, a metabolite of remdesivir, effectively suppressed virus replication in hamsters. Co-administration of favipiravir and GS-441524 more efficiently reduced virus load in hamster lungs than did single administration of either drug for both the prophylactic and therapeutic regimens; prophylactic co-administration also efficiently inhibited lung inflammation in the infected animals. Furthermore, pretreatment of hamsters with favipiravir and GS-441524 effectively protected them from virus transmission via respiratory droplets upon exposure to infected hamsters. Repurposing and co-administration of antiviral drugs may help combat COVID-19. IMPORTANCE During a pandemic, repurposing drugs that are approved for other diseases is a quick and realistic treatment option. In this study, we found that co-administration of favipiravir and the remdesivir metabolite GS-441524 more effectively blocked SARS-CoV-2 replication in the lungs of Syrian hamsters than either favipiravir or GS-441524 alone as part of a prophylactic or therapeutic regimen. Prophylactic co-administration also reduced the severity of lung inflammation. Moreover, co-administration of these drugs to naive hamsters efficiently protected them from airborne transmission of the virus from infected animals. Since both drugs are nucleotide analogs that interfere with the RNA-dependent RNA polymerases of many RNA viruses, these findings may also help encourage co-administration of antivirals to combat future pandemics.

Alternative treatment of fungal infections: Synergy with non-antifungal agents

Fungal infections are responsible for high mortality rates in immunocompromised and high-risk surgical patients. Therapy failures during the last decades due to increasing multidrug resistance demand innovative strategies for novel and effective antifungal drugs. Synergistic combinations of antifungals with non-antifungal agents highlight a pragmatic strategy to reduce the development of drug resistance and potentially repurpose known compounds with other functions to bypass costly and time-consuming novel drug development.

Animal Models and Antifungal Agents in Paracoccidioidomycosis: An Overview

Paracoccidioides brasiliensis is the etiologic agent of paracoccidioidomycosis, the most prevalent systemic mycosis in Latin America. The morbidity and mortality associated with paracoccidioidomycosis necessitate our understanding of fungal pathogenesis and discovering of new agents to treat this infection. Animal models have contributed much to the knowledge of fungal infections and their corresponding therapeutic treatments. This is true for animal models of the primary fungal pathogens such as P. brasiliensis. This review describes the development, details and utility of animal models of paracoccidioidomycosis for studying and developing the current antifungal agents used for therapy of this fungal disease and novel agents with antifungal properties against P. brasiliensis.

Chloroquine inhibits Rhodococcus equi replication in murine and foal alveolar macrophages by iron-starvation

Rhodococcus equi preferentially infects macrophages causing pyogranulomatous pneumonia in young foals. Both the vapA and rhbC genes are up-regulated in an iron (Fe)-deprived environment, such as that found within macrophages. Chloroquine (CQ) is a drug widely used against malaria that suppresses the intracellular availability of Fe in eukaryotic cells. The main objective of this study was to evaluate the ability of CQ to inhibit replication of virulent R. equi within murine (J774A.1) and foal alveolar macrophages (AMs) and to verify whether the mechanism of inhibition could be Fe-deprivation-dependent. CQ effect on R. equi extracellular survival and toxicity to J774A.1 were evaluated. R. equi survival within J774A.1 and foal AMs was evaluated under CQ (10 and 20μM), bovine saturated transferrin (bHTF), and bovine unsaturated transferrin (bATF) exposure. To explore the action mechanism of CQ, the superoxide anion production, the lysozyme activity, as well as the relative mRNA expression of vapA and rhbC were examined. CQ at≤20μM had no effect on R. equi extracellular multiplication and J774A.1 viability. Exposure to CQ significantly and markedly reduced survival of R. equi within J774A.1 and foal AMs. Treatment with bHTF did not reverse CQ effect on R. equi. Exposure to CQ did not affected superoxide anion production or lysozyme activity, however vapA and rhbC expression was significantly increased. Our results reinforce the hypothesis that intracellular availability of Fe is required for R. equi survival, and our initial hypothesis that CQ can limit replication of R. equi in J774A.1 and foal AMs, most likely by Fe starvation.

Synergistic activity of chloroquine with fluconazole against fluconazole-resistant isolates of Candida species

The in vitro activity of chloroquine and the interactions of chloroquine combined with fluconazole against 37 Candida isolates were tested using the broth microdilution, disk diffusion, and Etest susceptibility tests. Synergistic effect was detected with 6 of 9 fluconazole-resistant Candida albicans isolates, with Candida krusei ATCC 6258, and with all 12 fluconazole-resistant Candida tropicalis isolates.

Signaling of chloroquine-induced stress in the yeast Saccharomyces cerevisiae requires the Hog1 and Slt2 mitogen-activated protein kinase pathways

Chloroquine (CQ) has been under clinical use for several decades, and yet little is known about CQ sensing and signaling mechanisms or about their impact on various biological pathways. We employed the budding yeast Saccharomyces cerevisiae as a model organism to study the pathways targeted by CQ. Our screening with yeast mutants revealed that it targets histone proteins and histone deacetylases (HDACs). Here, we also describe the novel role of mitogen-activated protein kinases Hog1 and Slt2, which aid in survival in the presence of CQ. Cells deficient in Hog1 or Slt2 are found to be CQ hypersensitive, and both proteins were phosphorylated in response to CQ exposure. CQ-activated Hog1p is translocated to the nucleus and facilitates the expression of GPD1 (glycerol-3-phosphate dehydrogenase), which is required for the synthesis of glycerol (one of the major osmolytes). Moreover, cells treated with CQ exhibited an increase in intracellular reactive oxygen species (ROS) levels and the effects were rescued by addition of reduced glutathione to the medium. The deletion of SOD1, the superoxide dismutase in yeast, resulted in hypersensitivity to CQ. We have also observed P38 as well as P42/44 phosphorylation in HEK293T human cells upon exposure to CQ, indicating that the kinds of responses generated in yeast and human cells are similar. In summary, our findings define the multiple biological pathways targeted by CQ that might be useful for understanding the toxicity modulated by this pharmacologically important molecule.

An encapsulation of iron homeostasis and virulence in Cryptococcus neoformans

Vertebrate hosts actively sequester iron, and fungal and other pathogens must therefore adapt to a severe limitation in iron availability to cause disease. Recent studies reveal that the pathogenic fungus Cryptococcus neoformans overcomes iron limitation by multiple mechanisms that target transferrin and heme. The regulation of iron uptake is mediated by an interconnected set of transcription factors that include the master iron regulator Cir1 and the pH-responsive factor Rim101. These factors integrate iron homeostasis with a myriad of other functions including pH sensing, nutrient and stress signaling pathways, virulence factor elaboration, and cell wall biogenesis.

Cell wall perturbation sensitizes fungi to the antimalarial drug chloroquine

Chloroquine (CQ) has been a mainstay of antimalarial drug treatment for several decades. Additional therapeutic actions of CQ have been described, including some reports of fungal inhibition. Here we investigated the action of CQ in fungi, including the yeast model Saccharomyces cerevisiae. A genomewide yeast deletion strain collection was screened against CQ, revealing that bck1Δ and slt2Δ mutants of the cell wall integrity pathway are CQ hypersensitive. This phenotype was rescued with sorbitol, consistent with cell wall involvement. The cell wall-targeting agent caffeine caused hypersensitivity to CQ, as did cell wall perturbation by sonication. The phenotypes were not caused by CQ-induced changes to cell wall components. Instead, CQ accumulated to higher levels in cells with perturbed cell walls: CQ uptake was 2- to 3-fold greater in bck1Δ and slt2Δ mutants than in wild-type yeast. CQ toxicity was synergistic with that of the major cell wall-targeting antifungal drug, caspofungin. The MIC of caspofungin against the yeast pathogen Candida albicans was decreased 2-fold by 250 μM CQ and up to 8-fold at higher CQ concentrations. Similar effects were seen in Candida glabrata and Aspergillus fumigatus. The results show that the cell wall is critical for CQ resistance in fungi and suggest that combination treatments with cell wall-targeting drugs could have potential for antifungal treatment.

Fungal adaptation to the mammalian host: it is a new world, after all

Adaptation to environmental conditions is key to fungal survival during infection of human hosts. Although the host immune system is often considered the primary obstacle to fungal colonization, invading fungi must also contend with extreme abiotic stresses. Recent work with human pathogenic fungi has uncovered systems for detecting and responding to changes in temperature, carbon source, metal ion availability, pH, and gas tension. These systems play a major role in adaptation to the host niche and are essential factors for persistence in a mammalian host. Future investigations into fungal responses to these and other abiotic components of the host environment have the potential to uncover novel targets for anti-fungal therapy.