Standardization of an experimental murine model of invasive pulmonary aspergillosis

Visible-Light-Activated Molecular Machines Kill Fungi by Necrosis Following Mitochondrial Dysfunction and Calcium Overload

Invasive fungal infections are a growing public health threat. As fungi become increasingly resistant to existing drugs, new antifungals are urgently needed. Here, it is reported that 405-nm-visible-light-activated synthetic molecular machines (MMs) eliminate planktonic and biofilm fungal populations more effectively than conventional antifungals without resistance development. Mechanism-of-action studies show that MMs bind to fungal mitochondrial phospholipids. Upon visible light activation, rapid unidirectional drilling of MMs at ≈3 million cycles per second (MHz) results in mitochondrial dysfunction, calcium overload, and ultimately necrosis. Besides their direct antifungal effect, MMs synergize with conventional antifungals by impairing the activity of energy-dependent efflux pumps. Finally, MMs potentiate standard antifungals both in vivo and in an ex vivo porcine model of onychomycosis, reducing the fungal burden associated with infection.

Assessment of Antifungal Pharmacodynamics

Pharmacokinetic-pharmacodynamic (PK-PD) analysis is of central importance to the progress of an antifungal agent into clinical use. It is crucial to ensure that preclinical studies give the best possible prediction of the way drugs are likely to behave in a clinical setting. This review details the last 30 years of progress in terms of disease model design, efficacy outcome selection and translational modelling in antifungal PK-PD studies. The principles of how PK-PD parameters inform current clinical practice are also discussed, including a review of how these apply to existing and novel agents.

Animal models of invasive mycoses

Animal models of invasive fungal infections have been developed and are applied in a huge number of different animal species for a number of research purposes, for example, the study of pathogenesis, defense mechanisms, and therapeutic strategies. From the different models, which in most cases are based on the same fungal species and often the same strain, as in spontaneous human infections, fundamental results and knowledge of the diagnosis, progression, prophylaxis, and therapy have been achieved. However, in all models, one should be critical with respect to mimicking the disease entity of humans, which is often the focus of the research. In many of the models for instance, the time course is different to the one of humans, and in others, the propensity for localization and containment in specific organs does not parallel the situation in humans. Nevertheless, many animal models of invasive mycoses have proven valuable in a number of research areas. With regard to new generations of anti-mycotic drugs, the models play an essential role in demonstrating antifungal activity, as well as in demonstrating the absence of toxic side effects, a critical step which cannot be accomplished by in vitro studies.

Targeting a critical step in fungal hexosamine biosynthesis

Aspergillus fumigatus is a human opportunistic fungal pathogen whose cell wall protects it from the extracellular environment including host defenses. Chitin, an essential component of the fungal cell wall, is synthesized from UDP-GlcNAc produced in the hexosamine biosynthetic pathway. As this pathway is critical for fungal cell wall integrity, the hexosamine biosynthesis enzymes represent potential targets of antifungal drugs. Here, we provide genetic and chemical evidence that glucosamine 6-phosphate N-acetyltransferase (Gna1), a key enzyme in this pathway, is an exploitable antifungal drug target. GNA1 deletion resulted in loss of fungal viability and disruption of the cell wall, phenotypes that could be rescued by exogenous GlcNAc, the product of the Gna1 enzyme. In a murine model of aspergillosis, the Δgna1 mutant strain exhibited attenuated virulence. Using a fragment-based approach, we discovered a small heterocyclic scaffold that binds proximal to the Gna1 active site and can be optimized to a selective submicromolar binder. Taken together, we have provided genetic, structural, and chemical evidence that Gna1 is an antifungal target in A. fumigatus.

In vivo evaluation of the antifungal activity of sertraline against Aspergillus fumigatus

BACKGROUND

Invasive pulmonary aspergillosis is a life-threatening fungal disease principally caused by the ubiquitous mould Aspergillus fumigatus. This clinical entity is a major cause of morbidity and mortality (principally, but not restricted to, immunocompromised individuals). A few recent reports suggest in vitro fungicidal activity of sertraline against Aspergillus spp., but this activity has not yet been investigated in vivo.

OBJECTIVES

To evaluate the antifungal activity of sertraline in two in vivo models of aspergillosis.

METHODS

The antifungal activity of sertraline as monotherapy at three different doses (3, 10 and 15 mg/kg) was evaluated in Galleria mellonella and in a murine model of invasive pulmonary aspergillosis. Therapeutic efficacy parameters determined were larval survival and health index score for G. mellonella, whereas pulmonary fungal burden, galactomannan and lung histopathology were assessed in the murine model.

RESULTS

Sertraline treatments improved larval survival and health index score, especially at doses of 10 and 15 mg/kg. Moreover, 10 mg/kg sertraline was able to reduce pulmonary fungal burden with an efficacy comparable with that of 3 mg/kg amphotericin B and 10 mg/kg voriconazole.

CONCLUSIONS

To the best of our knowledge, this is the first in vivo study that evaluates the antifungal activity of sertraline against A. fumigatus, showing a possible promising option for the adjuvant treatment of pulmonary aspergillosis.

A transcriptional signature accurately identifies Aspergillus Infection across healthy and immunosuppressed states

Invasive aspergillosis (IA) is a major cause of critical illness in immunocompromised (IC) patients. However, current fungal tests are limited. Disease-specific gene expression patterns in circulating host cells show promise as novel diagnostics, however it is unknown whether such a 'signature' exists for IA and the effect of iatrogenic immunosuppression on any such biomarkers. Male BALB/c mice were separated into 6 experimental groups based on Aspergillus fumigatus inhalational exposure and IC status (no immunosuppression, cyclophosphamide, and corticosteroids). Mice were sacrificed 4 days postinfection. Whole blood was assayed for transcriptomic responses in peripheral white blood cells via microarray. An elastic net regularized logistic regression was employed to develop classifiers of IA based on gene expression. Aspergillus infection triggers a powerful response in non-IC hosts with 2718 genes differentially expressed between IA and controls. We generated a 146-gene classifier able to discriminate between non-IC infected and uninfected mice with an AUC of 1. However, immunosuppressive medications exhibited a confounding effect on this transcriptomic classifier. After controlling for the genomic effects of immunosuppression, we were able to generate a 187-gene classifier with an AUC of 0.92 in the absence of immunosuppression, 1 with cyclophosphamide, and 0.9 with steroids. The host transcriptomic response to IA is robust and conserved. Pharmacologic perturbation of the host immune response has powerful effects on classifier performance and must be considered when developing such novel diagnostics. When appropriately designed, host-derived peripheral blood transcriptomic responses demonstrate the ability to accurately diagnose Aspergillus infection, even in the presence of immunosuppression.

What Are the Functions of Chitin Deacetylases in Aspergillus fumigatus?

Deacetylation of chitin by chitin deacetylases (Cda) results in the formation of chitosan. Chitosan, a polymer of β1,4 linked glucosamine, plays multiple roles in the function of the fungal cell wall, including virulence and evasion of host immune responses. In this study, the roles of chitosan and putative CDAs in cell wall structure and virulence of Aspergillus fumigatus were investigated. Low levels of chitosan were found in the conidial and cell wall of A. fumigatus. Seven putative CDA genes were identified, disrupted and the phenotype of the single mutants and the septuple mutants were investigated. No alterations in fungal cell wall chitosan levels, changes in fungal growth or alterations in virulence were detected in the single or septuple Δcda1-7 mutant strains. Collectively, these results suggest that chitosan is a minority component of the A. fumigatus cell wall, and that the seven candidate Cda proteins do not play major roles in fungal cell wall synthesis or virulence. However, Cda2 is involved in conidiation, suggesting that this enzyme may play a role in N-acetyl-glucosamine metabolism.

Aspergillus fumigatus and Aspergillosis in 2019

Aspergillus fumigatus is a saprotrophic fungus; its primary habitat is the soil. In its ecological niche, the fungus has learned how to adapt and proliferate in hostile environments. This capacity has helped the fungus to resist and survive against human host defenses and, further, to be responsible for one of the most devastating lung infections in terms of morbidity and mortality. In this review, we will provide (i) a description of the biological cycle of A. fumigatus; (ii) a historical perspective of the spectrum of aspergillus disease and the current epidemiological status of these infections; (iii) an analysis of the modes of immune response against Aspergillus in immunocompetent and immunocompromised patients; (iv) an understanding of the pathways responsible for fungal virulence and their host molecular targets, with a specific focus on the cell wall; (v) the current status of the diagnosis of different clinical syndromes; and (vi) an overview of the available antifungal armamentarium and the therapeutic strategies in the clinical context. In addition, the emergence of new concepts, such as nutritional immunity and the integration and rewiring of multiple fungal metabolic activities occurring during lung invasion, has helped us to redefine the opportunistic pathogenesis of A. fumigatus.

Murine model of invasive pulmonary Aspergillosis: Follow-up of tissue injury, fungal burden and mortality with distinct elastase production strains

To study invasive pulmonary Aspergillosis (IPA), we depleted neutrophils in mice using the monoclonal antibody anti-Gr-1/Ly-6G. Immunocompetent and neutropenic mice were infected via intratracheal with conidia of Aspergillus fumigatus clinical isolates, characterized as either higher or lower elastase producers. Neutropenic animals exhibited 100% mortality in 5 days, for both strains, and were observed survival curves overlapped, lungs with angioinvasion, rupture of bronchial and vascular walls, associated with exuberance of conidia filamentation. The immunocompetent animals infected with the lower elastase producer strain presented with upregulated inflammatory processes, and a lack of conidia filamentation in the tissue. The fungal burden in the lungs was not different in the immunocompetent and neutropenic groups. These findings confirm the protective role of neutrophils against A. fumigatus and suggest that the fungal elastinolytic activity is not a critical virulence factor but may be involved in tissue injury.

Animal Models for Studying Triazole Resistance in Aspergillus fumigatus

Infections caused by triazole-resistant Aspergillus fumigatus are associated with a higher probability of treatment failure and mortality. Because clinical experience in managing these infections is still limited, mouse models of invasive aspergillosis fulfill a critical void for studying treatment regimens designed to overcome resistance. The type of immunosuppression, the route of infection, the timing of antifungal administration, and the end points used to assess antifungal activity affect the interpretation of data from these models. Nevertheless, these models provide important insights that help guide treatment decisions in patients with triazole-resistant invasive aspergillosis. Animal models confirmed that a high triazole minimal inhibitory concentration corresponded with triazole treatment failure and that the efficacy of other classes of drugs, such as the polyenes and echinocandins, was not affected by the presence of triazole resistance mutations. Furthermore, the feasibility of triazole dose escalation, combination therapy, and prophylaxis were explored as strategies to overcome resistance.

Assessment of carvacrol for control of avian aspergillosis in intratracheally challenged chickens in comparison to voriconazole with a reference on economic impact

AIM

This study was designed to investigate the efficacy of essential oils as an alternative prophylaxis and treatment for avian aspergillosis.

METHODS AND RESULTS

The in vitro susceptibility of Aspergillus fumigatus strains to antifungal drugs and carvacrol, thymol, eugenol, thymoquinone and cinnamon was determined using the macrodiffusion and microdilution methods. Carvacrol has antifungal activity in comparison to voriconazole (VCZ) (MIC 0·5, 0·25 μg ml^-1 respectively). While cinnamon, euganol, thymol and thymoquinone displayed moderate to weak inhibitory activity. For the efficacy study, five groups of 10-day-old chicks (n = 48) were infected intratracheally either with A. fumigatus conidia or saline (negative control). Chicks in carvacrol prophylactic and treatment (CRPT) group were fed for 10 days beginning from hatch with carvacrol (200 mg kg^-1 per diet) supplemented diets. VCZ (VCZT:20 mg kg^-1 body weight (BW)), carvacrol treatment (CRT, CRPT) was started upon appearance of the first clinical signs and continued for 10 days. Birds were monitored for an additional 15 days following treatment. Fungal burden and therapeutic efficacy were assessed by survival, BW, quantitative (q) culture (CFU), quantitative real-time PCR (qPCR) and histopathological changes at several time points. Serum biochemical changes were also assessed. VCZT, CRPT, CRT in comparison to the sham-treated (SHAM) group have prolonged survival (87·5, 83·4, 79·2, 41·7% respectively). In VCZT and CRPT, a significant reduction in clinical signs, lesions, CFU and qPCR counts to the limit of detection were observed. CRPT has the lowest BW reduction, economic losses and significant low total cholesterol levels.

CONCLUSIONS

Carvacrol has a promising potential to be used as a prophylactic and treatment against A. fumigatus.

SIGNIFICANCE AND IMPACT OF THE STUDY

Prognosis of avian aspergillosis is often poor due to delayed diagnosis and treatment failure. However, the widespread uses of azole prophylaxis in birds are thought to be the major driver of azole resistance. These findings create a possibility to develop an effective drug-free alternative strategy for control of avian aspergillosis.

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

Aspergillus in chronic lung disease: Modeling what goes on in the airways

Aspergillus species cause a range of respiratory diseases in humans. While immunocompromised patients are at risk for the development of invasive infection with these opportunistic molds, patients with underlying pulmonary disease can develop chronic airway infection with Aspergillus species. These conditions span a range of inflammatory and allergic diseases including Aspergillus bronchitis, allergic bronchopulmonary aspergillosis, and severe asthma with fungal sensitization. Animal models are invaluable tools for the study of the molecular mechanism underlying the colonization of airways by Aspergillus and the host response to these non-invasive infections. In this review we summarize the state-of-the-art with respect to the available animal models of noninvasive and allergic Aspergillus airway disease; the key findings of host-pathogen interaction studies using these models; and the limitations and future directions that should guide the development and use of models for the study of these important pulmonary conditions.

How to invade a susceptible host: cellular aspects of aspergillosis

Diseases caused by Aspergillus spp. and in particular A. fumigatus are manifold and affect individuals suffering from immune dysfunctions, among them immunocompromised ones. The determinants of whether the encounter of a susceptible host with infectious propagules of this filamentous saprobe results in infection have been characterized to a limited extent. Several cellular characteristics of A. fumigatus that have evolved in its natural environment contribute to its virulence, among them general traits as well as particular ones that affect interaction with the mammalian host. Among the latter, conidial constituents, cell wall components, secreted proteins as well as extrolites shape the tight interaction of A. fumigatus with the host milieu and also contribute to evasion from immune surveillance.

Modified release itraconazole amorphous solid dispersion to treat Aspergillus fumigatus: importance of the animal model selection

Previously, modified release itraconazole in the form of a melt-extruded amorphous solid dispersion based on a pH dependent enteric polymer combined with hydrophilic additives (HME-ITZ), exhibited improved in vitro dissolution properties. These properties agreed with pharmacokinetic results in rats showing high and sustained itraconazole (ITZ) systemic levels. The objective of the present study was to better understand the best choice of rodent model for evaluating the pharmacokinetic and efficacy of this orally administered modified release ITZ dosage form against invasive Aspergillus fumigatus. A mouse model and a guinea pig model were investigated and compared to results previously published. In the mouse model, despite similar levels as previously reported values, plasma and lung levels were variable and fungal burden was not statistically different for placebo controls, HME-ITZ and Sporanox^® (ITZ oral solution). This study demonstrated that the mouse model is a poor choice for studying modified release ITZ dosage forms based on pH dependent enteric polymers due to low fluid volume available for dissolution and low intestinal pH. To the contrary, guinea pig was a suitable model to evaluate modified release ITZ dosage forms. Indeed, a significant decrease in lung fungal burden as a result of high and sustained ITZ tissue levels was measured. Sufficiently high intestinal pH and fluids available for dissolution likely facilitated the dissolution process. Despite high ITZ tissue level, the primary therapeutic agent voriconazole exhibited an even more pronounced decrease in fungal burden due to its reported higher clinical efficacy specifically against Aspergillus fumigatus.

Pharmacodynamics for antifungal drug development: an approach for acceleration, risk minimization and demonstration of causality

The treatment of invasive fungal diseases constitutes a significant unmet medical need. There are relatively few antifungal agents in clinical development and a paucity of novel targets. Morbidity and mortality remain high and clinical outcomes are compromised by submaximal efficacy, emergence of drug resistance and drug-related toxicity. Thus, new antifungal agents are urgently required. A deep understanding of exposure-response relationships underpins the development of safe and effective clinical regimens of any therapeutic agent. Pharmacokinetics (PK) and pharmacodynamics (PD) is increasingly recognized as a vital tool in the development of new antimicrobial agents and maximizes the probability that the right dose will be studied the first time. There is currently no information or agreement as to what constitutes an adequate PK/PD package for the development of a new antifungal agent. This review provides a summary of the achievements of antifungal PK/PD for the treatment of invasive candidiasis, invasive aspergillosis and cryptococcal meningoencephalitis, and outlines the necessary components of a PK/PD package for a new antifungal agent. Such information is critical for the accelerated and efficient development of new agents and enables improved clinical outcomes to be secured.

In-depth 2-DE reference map of Aspergillus fumigatus and its proteomic profiling on exposure to itraconazole

Aspergillus fumigatus (A. fumigatus) is a medically important opportunistic fungus that may lead to invasive aspergillosis in humans with weak immune system. Proteomic profiling of this fungus on exposure to itraconazole (ITC), an azole antifungal drug, may lead to identification of its molecular targets and better understanding on the development of drug resistance against ITC in A. fumigatus. Here, proteome analysis was performed using 2-DE followed by mass spectrometric analysis which resulted in identification of a total of 259 unique proteins. Further, proteome profiling of A. fumigatus was carried out on exposure to ITC, 0.154 μg/ml, the minimum inhibitory concentration (MIC50). Image analysis showed altered levels of 175 proteins (66 upregulated and 109 downregulated) of A. fumigatus treated with ITC as compared to the untreated control. Peptide mass fingerprinting led to the identification of 54 proteins (12 up-regulated and 42 down-regulated). The differentially expressed proteins include proteins related to cell stress, carbohydrate metabolism and amino acid metabolism. We also observed four proteins, including nucleotide phosphate kinase (NDK), that are reported to interact with calcineurin, a protein involved in regulation of cell morphology and fungal virulence. Comparison of differentially expressed proteins on exposure to ITC with artemisinin (ART), an antimalarial drug with antifungal activity(1), revealed a total of 26 proteins to be common among them suggesting that common proteins and pathways are targeted by these two antifungal agents. The proteins targeted by ITC may serve as important leads for development of new antifungal drugs.

Efficacy of the investigational echinocandin ASP9726 in a guinea pig model of invasive pulmonary aspergillosis

ASP9726 is an investigational echinocandin with in vitro activity against Aspergillus species. We evaluated the pharmacokinetics and efficacy of this agent in an established guinea pig model of invasive pulmonary aspergillosis. ASP9726 plasma concentrations were measured in guinea pigs administered either a single dose or multiple doses of this agent at 2.5, 5, and 10 mg/kg of body weight/day by subcutaneous injection. Immunosuppressed guinea pigs were inoculated with A. fumigatus AF293, and ASP9726 (2.5, 5, and 10 mg/kg/day), voriconazole (10 mg/kg by oral gavage twice daily), or caspofungin (3 mg/kg/day by intraperitoneal injection) was administered for 8 days. Changes in fungal burden were measured by enumerating CFU and by quantitative PCR of specimens from within the lungs, as well as by analysis of serum (1 → 3)-β-D-glucan and galactomannan. Lung histopathology was also evaluated. ASP9726 plasma concentrations increased in a dose-proportional manner, and the drug was well tolerated at each dose. Each dose of ASP9726, voriconazole, and caspofungin significantly reduced pulmonary fungal burden as measured by quantitative PCR and by determining (1 → 3)-β-D-glucan and galactomannan levels, but only voriconazole significantly reduced numbers of CFU. ASP9726 at 5 mg/kg also significantly improved survival. Histopathology demonstrated morphological changes in hyphae in animals exposed to ASP9726 and caspofungin, consistent with the activities of the echinocandins. These results suggest that ASP9726 may be efficacious for the treatment of invasive pulmonary aspergillosis.

In vivo efficacy of a synthetic coumarin derivative in a murine model of aspergillosis

Despite advances in therapeutic modalities, aspergillosis remains a leading cause of mortality. This has necessitated the identification of effective and safe antifungal molecules. In the present study, in vivo safety and antifungal efficacy of a coumarin derivative, N, N, N-Triethyl-11-(4-methyl-2-oxo-2H-benzopyran-7-yloxy)-11-oxoundecan-1-aminium bromide (SCD-1), was investigated. The maximum tolerable dose of compound was determined according to OECD 423 guidelines. The compound could be assigned to category IV of the Globally Harmonized System and its LD₅₀ cut-off was found to be 2000 mg/kg body weight. The survival increased in Aspergillus fumigatus-infected mice treated with a dose of 200 mg/kg, orally or 100 mg/kg body weight, intraperitoneally, of SCD-1 in comparison to infected-untreated animals. The SCD-1 treatment resulted in significant reduction in colony counts in vital organs of the animals. Its protective effect was also observed on day 14 as there was marked reduction in fungal colonies. The treatment with SCD-1 also reduced the levels of serum biochemical parameters with respect to infected-untreated animals. It could be concluded that SCD-1 is a quite safe antifungal compound, which conferred dose dependent protection against experimental aspergillosis. Therefore, SCD-1 holds potential for developing new formulations for aspergillosis.

Development of a novel inhalational model of invasive pulmonary aspergillosis in rats and comparative evaluation of three biomarkers for its diagnosis

Aspergillus fumigatus, a thermotolerant fungus, is the main causative agent of invasive pulmonary aspergillosis (IPA) in immunocompromised patients that is associated with high mortality rates. Early diagnosis of IPA is crucial for mortality reduction and improved prognosis. An experimental inhalational model of IPA was developed in rats and the efficacy of three biomarkers, namely β-D-glucan (BDG), a panfungal marker, galactomannan (GM), a genus-specific marker, and A. fumigatus DNA, a species-specific marker was evaluated in serum and bronchoalveolar lavage (BAL) specimens at different time points postinfection for early diagnosis of IPA. BDG and GM were detected by using commercial Fungitell and Platelia Aspergillus EIA kits, respectively. A. fumigatus DNA was detected by developing a sensitive, single-step PCR assay. IPA was successfully developed in immunosuppressed rats and all animals until 5 days post-infection were positive for A. fumigatus by culture and KOH-calcofluor microscopy also showed A. fumigatus in 19 of 24 (79%) lung tissue samples. Fourteen of 30 (47%) and 27 of 30 (90%) serum and BAL specimens, respectively, were positive for all three biomarkers with 100% specificity (none of sera or BAL specimens of 12 control rats was positive for biomarkers). Our data show that BAL is a superior specimen than serum and combined detection of BDG, GM and A. fumigatus DNA provide a sensitive diagnosis of IPA in an experimental animal model. Moreover, combined detection of GM and DNA in BAL and detection of either GM or DNA in serum was also positive in 27 of 30 (90%) animals. For economic reasons and considering that the positive predictive value of BDG is low, the detection of GM and/or DNA in serum and BAL samples has the potential to serve as an integral component of the diagnostic-driven strategy in high-risk patients suspected for IPA.

Overview of vertebrate animal models of fungal infection

Fungi represent emerging infectious threats to human populations worldwide. Mice and other laboratory animals have proved invaluable in modeling clinical syndromes associated with superficial and life-threatening invasive mycoses. This review outlines salient features of common vertebrate animal model systems to study fungal pathogenesis, host antifungal immune responses, and antifungal compounds.

Aspergillus galactosaminogalactan mediates adherence to host constituents and conceals hyphal β-glucan from the immune system

Aspergillus fumigatus is the most common cause of invasive mold disease in humans. The mechanisms underlying the adherence of this mold to host cells and macromolecules have remained elusive. Using mutants with different adhesive properties and comparative transcriptomics, we discovered that the gene uge3, encoding a fungal epimerase, is required for adherence through mediating the synthesis of galactosaminogalactan. Galactosaminogalactan functions as the dominant adhesin of A. fumigatus and mediates adherence to plastic, fibronectin, and epithelial cells. In addition, galactosaminogalactan suppresses host inflammatory responses in vitro and in vivo, in part through masking cell wall β-glucans from recognition by dectin-1. Finally, galactosaminogalactan is essential for full virulence in two murine models of invasive aspergillosis. Collectively these data establish a role for galactosaminogalactan as a pivotal bifunctional virulence factor in the pathogenesis of invasive aspergillosis.

Invasive aspergillosis is the most common mold infection in humans, predominately affecting immunocompromised patients. The mechanisms by which the mold Aspergillus fumigatus adheres to host tissues and causes disease are poorly understood. In this report, we compared mutants of Aspergillus with different adhesive properties to identify fungal factors involved in adherence to host cells. This approach identified a cell wall associated polysaccharide, galactosaminogalactan, which is required for adherence to a wide variety of substrates. Galactosaminogalactan was also observed to suppress inflammation by concealing β-glucans, key pattern associated microbial pattern molecules in Aspergillus hyphae, from recognition by the innate immune system. Mutants that were deficient in galactosaminogalactan were less virulent in mouse models of invasive aspergillosis. These data identify a bifunctional role for galactosaminogalactan in the pathogenesis of invasive aspergillosis, and suggest that it may serve as a useful target for antifungal therapy.

Bayesian development of a dose-response model for Aspergillus fumigatus and invasive aspergillosis

Invasive aspergillosis (IA) is a major cause of mortality in immunocompromized hosts, most often consecutive to the inhalation of spores of Aspergillus. However, the relationship between Aspergillus concentration in the air and probability of IA is not quantitatively known. In this study, this relationship was examined in a murine model of IA. Immunosuppressed Balb/c mice were exposed for 60 minutes at day 0 to an aerosol of A. fumigatus spores (Af293 strain). At day 10, IA was assessed in mice by quantitative culture of the lungs and galactomannan dosage. Fifteen separate nebulizations with varying spore concentrations were performed. Rates of IA ranged from 0% to 100% according to spore concentrations. The dose-response relationship between probability of infection and spore exposure was approximated using the exponential model and the more flexible beta-Poisson model. Prior distributions of the parameters of the models were proposed then updated with data in a Bayesian framework. Both models yielded close median dose-responses of the posterior distributions for the main parameter of the model, but with different dispersions, either when the exposure dose was the concentration in the nebulized suspension or was the estimated quantity of spores inhaled by a mouse during the experiment. The median quantity of inhaled spores that infected 50% of mice was estimated at 1.8 × 10(4) and 3.2 × 10(4) viable spores in the exponential and beta-Poisson models, respectively. This study provides dose-response parameters for quantitative assessment of the relationship between airborne exposure to the reference A. fumigatus strain and probability of IA in immunocompromized hosts.

Development of an aerosol model of Cryptococcus reveals humidity as an important factor affecting the viability of Cryptococcus during aerosolization

Cryptococcus is an emerging global health threat that is annually responsible for over 1,000,000 infections and one third of all AIDS patient deaths. There is an ongoing outbreak of cryptococcosis in the western United States and Canada. Cryptococcosis is a disease resulting from the inhalation of the infectious propagules from the environment. The current and most frequently used animal infection models initiate infection via liquid suspension through intranasal instillation or intravenous injection. These models do not replicate the typically dry nature of aerosol exposure and may hinder our ability to decipher the initial events that lead to clearance or the establishment of infection. We have established a standardized aerosol model of murine infection for the human fungal pathogen Cryptococcus. Aerosolized cells were generated utilizing a Collison nebulizer in a whole-body Madison Chamber at different humidity conditions. The aerosols inside the chamber were sampled using a BioSampler to determine viable aerosol concentration and spray factor (ratio of viable aerosol concentration to total inoculum concentration). We have effectively delivered yeast and yeast-spore mixtures to the lungs of mice and observed the establishment of disease. We observed that growth conditions prior to exposure and humidity within the Madison Chamber during exposure can alter Cryptococcus survival and dose retained in mice.

A new and clinically relevant murine model of solid-organ transplant aspergillosis

Invasive fungal infections (IFIs) are a major cause of death in organ transplant patients. The murine hydrocortisone-mediated immunosuppression model of pulmonary aspergillosis is commonly used to characterise IFIs in these patients. However, this model does not take into account the effects of calcineurin inhibitors on transplant immunity to IFIs or the fungal calcineurin pathway, which is required for both virulence and antifungal drug resistance. To address these two issues, a new and clinically relevant transplant immunosuppression model of tacrolimus (FK506) and hydrocortisone-associated pulmonary aspergillosis was developed. We first characterised IFIs in 406 patients with a lung transplant. This showed that all of the patients with pulmonary aspergillosis were immunosuppressed with calcineurin inhibitors and steroids. Murine pharmacokinetic studies demonstrated that an ideal dose of 1 mg/kg/day of FK506 intraperitoneally produced blood trough levels in the human therapeutic range (5-12 ng/ml). There was increased mortality from pulmonary aspergillosis in a transplant-relevant immunosuppression model using both FK506 and hydrocortisone as compared with immunosuppression using hydrocortisone only. Lung histopathology showed neutrophil invasion and tracheobronchitis that was associated with reduced lung tumour necrosis factor-α (TNFα), JE (homologue of human MCP-1) and KC (homologue of human IL-8) at 24 hours, but increased lung TNFα, JE and KC at 48 hours when fungal burden was high. Furthermore, FK506 directly impaired fungal killing in alveolar macrophages in vitro, with FK506-mediated inhibition of the radial growth of Aspergillus fumigatus in vitro occurring at the low concentration of 5 ng/ml. Taken together, these findings show that the immunosuppressive activity of FK506 outweighs its antifungal activity in vivo. These observations demonstrate that FK506 impairs innate immune responses and leads to an incremental increase in susceptibility to IFIs when it is combined with steroids. This new and clinically relevant mouse model of invasive aspergillosis is a valuable addition to the further study of both fungal immunity and antifungal therapy in organ transplantation.

Assessment of efficacy of antifungals against Aspergillus fumigatus: value of real-time bioluminescence imaging

Aspergillus fumigatus causes life-threatening infections, especially in immunocompromised patients. Common drugs for therapy of aspergillosis are polyenes, azoles, and echinocandins. However, despite in vitro efficacy of these antifungals, treatment failure is frequently observed. In this study, we established bioluminescence imaging to monitor drug efficacy under in vitro and in vivo conditions. In vitro assays confirmed the effectiveness of liposomal amphotericin B, voriconazole, and anidulafungin. Liposomal amphotericin B and voriconazole were fungicidal, whereas anidulafungin allowed initial germination of conidia that stopped elongation but allowed the conidia to remain viable. In vivo studies were performed with a leukopenic murine model. Mice were challenged by intranasal instillation with a bioluminescent reporter strain (5 × 10(5) and 2.5 × 10(5) conidia), and therapy efficacies of liposomal amphotericin B, voriconazole, and anidulafungin were monitored. For monotherapy, the highest treatment efficacy was observed with liposomal amphotericin B, whereas the efficacies of voriconazole and anidulafungin were strongly dependent on the infectious dose. When therapy efficacy was studied with different drug combinations, all combinations improved the rate of treatment success compared to that with monotherapy. One hundred percent survival was obtained for treatment with a combination of liposomal amphotericin B and anidulafungin, which prevented not only pulmonary infections but also infections of the sinus. In conclusion, combination therapy increases treatment success, at least in the murine infection model. In addition, our novel approach based on real-time imaging enables in vivo monitoring of drug efficacy in different organs during therapy of invasive aspergillosis.

Interlaboratory and interstudy reproducibility of a novel lateral-flow device and influence of antifungal therapy on detection of invasive pulmonary aspergillosis

Interest in lateral-flow devices (LFDs) as potential point-of-care assays for the diagnosis of infectious diseases has increased. Our objective was to evaluate the interlaboratory and interstudy reproducibility and the effects of antifungal therapy on an LFD developed for invasive pulmonary aspergillosis (IPA) detection. An established neutropenic guinea pig model of IPA caused by Aspergillus fumigatus was used. At predetermined time points (1 h and 3, 5, and 7 days postinoculation), blood and bronchoalveolar lavage (BAL) fluid were collected from infected and uninfected animals. In a separate experiment, guinea pigs were treated with posaconazole (10 mg/kg of body weight orally [p.o.] twice a day [BID]), voriconazole (10 mg/kg p.o. BID), liposomal amphotericin B (10 mg/kg intraperitoneally [i.p.] once a day [QD]), or caspofungin (2 mg/kg i.p. QD), and samples were collected on days 7 and 11. Each laboratory independently evaluated the IgG monoclonal antibody-based LFD. Galactomannan and (1 → 3)-β-D-glucan were also measured using commercially available kits. Good interlaboratory agreement was observed with the LFD, as the results for 97% (32/33) of the serum and 78.8% (26/33) of the BAL fluid samples from infected animals were in agreement. Good interstudy agreement was also observed. The serum sensitivity of each surrogate-marker assay was reduced in animals treated with antifungals. In contrast, these markers remained elevated within the BAL fluids of treated animals, which was consistent with the fungal burden and histopathology results. These results demonstrate that the LFD assay is reproducible between different laboratories and studies. However, the sensitivity of this assay and other markers of IPA may be reduced with serum in the presence of antifungal therapy.

Host immune defense against Aspergillus fumigatus: insight from experimental systemic (disseminated) infection

Model of systemic Aspergillus fumigatus infection induced by intravenous application of conidia is suitable for studying important aspects of invasive aspergillosis including relationship between infection and mortality, dissemination of infection and immune mechanisms involved in host resistance to this fungus. Use of this model allows the investigation of both innate and adaptive immune response characteristics in resistant/susceptible host, and investigating the contribution of genetic background and cytokine gene deficiency improves the knowledge of the diversity of mechanisms of immune response to Aspergillus infection. Studying of various aspects of systemic aspergillosis contributes to development of antifungal drugs.

Differential strain-related tissue immune response to sublethal systemic Aspergillus fumigatus infection in mice

Using a nonlethal systemic Aspergillus fumigatus infection, we have recently shown that similarly efficient elimination of fungus from spleens of prototypic Th1 (C57BL/6) and prototypic Th2 (BALB/c) mice is associated with differential immune responses. In light of these data and given the disseminated character of infection, the aim of the present study is to explore whether there are also strain-dependent differences in antifungal responses in peripheral tissues of infected mice. Although similar efficiency of conidia removal was noted in liver and kidneys of both strains, BALB/c mice seemed more prone to tissue injury. Compared with other nonlymphoid organs, lungs proved immunologically the most responsive in systemic aspergillosis. Lower numbers of neutrophils and macrophages in the lungs of infected BALB/c mice, delayed and lower (compared with C57BL/6 mice) expression of their oxidative activity, along with late IFN-γ and upregulated IL-4 production by lung cells might be responsible for slower elimination of A. fumigatus from the lungs of this mouse strain. The data obtained imply that lungs should be viewed as mandatory organ in evaluation of immune-mediated antifungal potential of drugs in models of systemic/disseminated infection and that strain differences noted in tissue responses should be taken into account in these settings.

Mouse models for the study of fungal pneumonia: a collection of detailed experimental protocols for the study of Coccidioides, Cryptococcus, Fusarium, Histoplasma and combined infection due to Aspergillus-Rhizopus

Mouse models have facilitated the study of fungal pneumonia. In this report, we present the working protocols of groups that are working on the following pathogens: Aspergillus, Coccidioides, Cryptococcus, Fusarium, Histoplasma and Rhizopus. We describe the experimental procedures and the detailed methods that have been followed in the experienced laboratories to study pulmonary fungal infection; we also discuss the anticipated results and technical notes, and provide the practical advices that will help the users of these models.

Peroral amphotericin B polymer nanoparticles lead to comparable or superior in vivo antifungal activity to that of intravenous Ambisome® or Fungizone™

Background

Despite advances in the treatment, the morbidity and mortality rate associated with invasive aspergillosis remains unacceptably high (70–90%) in immunocompromised patients. Amphotericin B (AMB), a polyene antibiotic with broad spectrum antifungal activity appears to be a choice of treatment but is available only as an intravenous formulation; development of an oral formulation would be beneficial as well as economical.

Methodology

Poly(lactide-co-glycolode) (PLGA) nanoparticles encapsulating AMB (AMB-NPs) were developed for oral administration. The AMB-NPs were 113±20 nm in size with ∼70% entrapment efficiency at 30% AMB w/w of polymer. The in vivo therapeutic efficacy of oral AMB-NPs was evaluated in neutropenic murine models of disseminated and invasive pulmonary aspergillosis. AMB-NPs exhibited comparable or superior efficacy to that of Ambisome® or Fungizone™ administered parenterally indicating potential of NPs as carrier for oral delivery.

Conclusions

The present investigation describes an efficient way of producing AMB-NPs with higher AMB pay-load and entrapment efficiency employing DMSO as solvent and ethanol as non-solvent. The developed oral formulation was highly efficacious in murine models of disseminated aspergillosis as well as an invasive pulmonary aspergillosis, which is refractory to treatment with IP Fungizone™and responds only modestly to AmBisome®.

Assessment of efficacy of antifungals in experimental models of invasive aspergillosis in an era of emerging resistance: the value of real-time quantitative PCR

Experimental models of invasive aspergillosis (IA) have been used to explore pharmacokinetic and pharmacodynamic (PK/PD) properties of antifungal agents. Survival is still considered the golden standard effect measure but has the disadvantage that a large number of animals are needed to determine the dose-response relationships and PK/PD of antifungals. The feasibility of using fungal load by real-time quantitative PCR (qPCR) as an effect measure has been explored recently. The majority of studies reported convincingly demonstrate a larger dynamic range for qPCR compared to conventional assays. However interpretation and translating the results to guidance in clinical decision making need further study. It is expected that the use of qPCR will become the primary outcome measure for assessment of PK/PD relationships of antifungals in experimental models of IA.

Cutaneous model of invasive aspergillosis

Cutaneous models have proven useful in studies of the pathogenesis and treatment of Gram-positive bacterial infections. Because cutaneous invasive aspergillosis (IA) occurs in the clinical setting, we sought to develop a nonlethal murine cutaneous model of IA. We induced cutaneous IA in cyclophosphamide-treated nude BALB/c mice by subcutaneous injection of Aspergillus fumigatus conidia. Skin lesion areas correlated well with tissue fungal burdens, allowing dynamic visual monitoring of cutaneous infections. The cutaneous model accurately reflected alterations in A. fumigatus pathogenicity resulting from deletions of recognized virulence genes (pabaA, sidA, and pksP). Moreover, analysis of the roles of conidial and mycelial catalases revealed that the former is required for the initiation of cutaneous aspergillosis, whereas the latter contributes to its propagation. Finally, posaconazole treatment reduced skin lesion areas relative to those of untreated and fluconazole-treated controls. This novel cutaneous model system should be applicable to comparative studies of the pathogenesis, treatment, and tissue specificity of IA.

Detection of Aspergillus fumigatus in a rat model of invasive pulmonary aspergillosis by real-time nucleic acid sequence-based amplification

Rapid and sensitive detection of Aspergillus from clinical samples may facilitate the early diagnosis of invasive pulmonary aspergillosis (IPA). A real-time nucleic acid sequence-based amplification (NASBA) method was investigated by use of an inhalational rat model of IPA. Immunosuppressed male Sprague-Dawley rats were exposed to Aspergillus fumigatus spores for an hour in an aerosol chamber. Bronchoalveolar lavage (BAL) fluid, lung tissues, and whole blood were collected from five infected rats at 1, 24, 48, 72, and 96 h postinfection and five uninfected rats at the end of the experiment. Total nucleic acid (TNA) was extracted on an easyMAG instrument. A primer-molecular beacon set targeting 28S rRNA was designed to detect Aspergillus spp. The results were compared to those of quantitative PCR (qPCR) (18S rDNA) and quantitative culture. The analytical sensitivity of the real-time NASBA assay was <1 CFU/assay. A linear range of detection was demonstrated over 5 log units of conidia (10 to 10(5) spores). Both NASBA and qPCR showed a progressive increase in lung tissue burdens, while the CFU counts were stable over time. The fungal burdens in BAL fluid were more variable and not indicative of a progressive infection. The results of both real-time assays correlated well for both sample types (r = 0.869 and P < 0.0001 for lung tissue, r = 0.887 and P < 0.0001 for BAL fluid). For all whole-blood specimens, NASBA identified Aspergillus-positive samples in the group from which samples were collected at 72 h postinfection (three of five samples) and the group from which samples were collected at 96 h postinfection (five of five samples), but no positive results were obtained by culture or PCR. Real-time NASBA is highly sensitive and useful for the detection of Aspergillus in an experimental model of IPA.

Inhaled voriconazole for prevention of invasive pulmonary aspergillosis

Targeted airway delivery of antifungals as prophylaxis against invasive aspergillosis may lead to high lung drug concentrations while avoiding toxicities associated with systemically administered agents. We evaluated the effectiveness of aerosolizing the intravenous formulation of voriconazole as prophylaxis against invasive pulmonary aspergillosis caused by Aspergillus fumigatus in an established murine model. Inhaled voriconazole significantly improved survival and limited the extent of invasive disease, as assessed by histopathology, compared to control and amphotericin B treatments.

Strain-dependent variation in 18S ribosomal DNA Copy numbers in Aspergillus fumigatus

Enumerating Aspergillus fumigatus CFU can be challenging since CFU determination by plate count can be difficult. CFU determination by quantitative real-time PCR (qPCR), however, is becoming increasingly common and usually relies on detecting one of the subunits of the multicopy rRNA genes. This study was undertaken to determine if ribosomal DNA (rDNA) copy number was constant or variable among different A. fumigatus isolates. FKS1 was used as a single-copy control gene and was validated against single-copy (pyrG and ARG4) and multicopy (arsC) controls. The copy numbers of the 18S rDNA subunit were then determined for a variety of isolates and were found to vary with the strain, from 38 to 91 copies per genome. Investigation of the stability of the 18S rDNA copy number after exposure to a number of different environmental and growth conditions revealed that the copy number was stable, varying less than one copy across all conditions, including in isolates recovered from an animal model. These results suggest that while the ribosomal genes are excellent targets for enumeration by qPCR, the copy number should be determined prior to using them as targets for quantitative analysis.

Assessment of Aspergillus fumigatus burden in pulmonary tissue of guinea pigs by quantitative PCR, galactomannan enzyme immunoassay, and quantitative culture

Early diagnosis of invasive pulmonary aspergillosis is problematic in some patient groups due to the lack of rapid, sensitive, specific, and reliable diagnostic tests. Fungal burden and therapeutic efficacy were assessed by survival, quantitative culture (CFU counts), galactomannan enzyme immunoassay (GM-EIA), and quantitative PCR (qPCR) in a new guinea pig model of invasive pulmonary aspergillosis using an aerosol challenge. At 1 day postinfection, qPCR determined that the pulmonary fungal burden was 2 log(10) higher than that determined by CFU counting and increased significantly (P < 0.03) over time. In contrast, the tissue burden assessed by CFU counting did not rise over the course of the study. Therapy with the antifungal drug voriconazole produced statistically significant decreases in pulmonary fungal burden, as detected by CFU counting (P < 0.02), qPCR, and GM-EIA (both P < 0.0002). Daily assessment of the progression of fungal infection in serum was performed by qPCR and GM-EIA. GM-EIA demonstrated a statistically significant reduction in the fungal load on days 6 and 7 in voriconazole-treated animals compared to time-matched controls (P < 0.02). Confirmation of fungal tissue burden by two or more methods should provide a more precise account of the burden, allowing improved assessment of diagnostic and therapeutic strategies in invasive pulmonary aspergillosis.

Gliotoxin production in Aspergillus fumigatus contributes to host-specific differences in virulence

BACKGROUND

Gliotoxin is a epipolythiodioxopiperazine toxin that is made by the filamentous fungus Aspergillus fumigatus. Gliotoxin has a wide range of effects on metazoan cells in culture, including induction of apoptosis through inhibition of Nf-kappaB, and inhibition of superoxide production by phagocytes. These activities have led to the proposal that gliotoxin contributes to pathogenesis during invasive aspergillosis. We tested this hypothesis by creating isogenic strains of gliotoxin-producing and nonproducing strains.

METHODS

We deleted gliP, the gene that encodes the nonribosomal peptide synthetase GliP. GliP catalyzes the first biosynthetic step in the synthesis of gliotoxin. We then tested for gliotoxin production and virulence in different animal models.

RESULTS

Deletion of gliP resulted in strains that were wild type for growth, but they did not synthesize gliotoxin. Transformation of gliP deletion mutants with a full copy of gliP restored gliotoxin production. The gliP deletion strain had attenuated virulence in nonneutropenic mice immunosuppressed with corticosteroids, but had normal virulence in neutropenic mice. It also had reduced virulence in a Drosophila melanogaster model.

CONCLUSIONS

Gliotoxin only contributes to the virulence of A. fumigatus in nonneutropenic mice and in fruit flies with functional phagocytes. These results suggest that the principal targets of gliotoxin are neutrophils or other phagocytes.

Dectin-1 Fc targeting of aspergillus fumigatus beta-glucans augments innate defense against invasive pulmonary aspergillosis

Invasive pulmonary aspergillosis (IPA) has significantly increased over the last decade. Here, a fusion protein consisting of the Dectin-1 extracellular domain linked to the Fc portion of murine immunoglobulin G1 augmented alveolar macrophage killing of Aspergillus fumigatus and shifted mortality associated with IPA via attenuation of A. fumigatus growth in the lung.

Animal models: an important tool in mycology

Animal models of fungal infections are, and will remain, a key tool in the advancement of the medical mycology. Many different types of animal models of fungal infection have been developed, with murine models the most frequently used, for studies of pathogenesis, virulence, immunology, diagnosis, and therapy. The ability to control numerous variables in performing the model allows us to mimic human disease states and quantitatively monitor the course of the disease. However, no single model can answer all questions and different animal species or different routes of infection can show somewhat different results. Thus, the choice of which animal model to use must be made carefully, addressing issues of the type of human disease to mimic, the parameters to follow and collection of the appropriate data to answer those questions being asked. This review addresses a variety of uses for animal models in medical mycology. It focuses on the most clinically important diseases affecting humans and cites various examples of the different types of studies that have been performed. Overall, animal models of fungal infection will continue to be valuable tools in addressing questions concerning fungal infections and contribute to our deeper understanding of how these infections occur, progress and can be controlled and eliminated.