Current Pharmaceutical Design - Volume 19, Issue 20, 2013

Invasive aspergillosis is an important cause of morbidity and mortality in immunocompromised children. Disease control depends on prevention, early diagnosis, predictive microbiological information, prompt and appropriate treatment and restoration of host defenses. Relative to adults, invasive aspergillosis in children and adolescents is unique in its clinical presentation, epidemiology, and in particular, the utility of newer diagnostic tools and the pharmacokinetics of active antifungal agents. Here we review the presentation and epidemiology of invasive aspergillosis in children and adolescents and discuss the value of current diagnostic tools and strategies and options for treatment and prevention in this special population.

Aspergillus infections are a threat to in patients with hematological malignancies. Known risk factors are profound and long lasting neutropenia, uncontrolled graft versus host disease, continuous administration of steroids and environmental factors such as hospital construction. Numerous efforts have been undertaken for prophylaxis of invasive aspergillosis in high-risk populations. Most of them failed to demonstrate survival advantages. Prophylaxis makes sense, since diagnosis and treatment of invasive aspergillosis remain difficult. The introduction of non-culture based tools for the diagnosis of invasive aspergillosis is an important step forward for early and sensitive diagnosis of invasive aspergillosis. Early treatment is the cornerstone of a successful management of invasive aspergillosis. Substantial improvement came with the introduction of lipid formulations of amphotericin B in the early 1990s. Voriconazole was the first azole that improved the overall survival for patients with invasive aspergillosis. Newer azoles and the echinocandins were introduced for the treatment of invasive aspergillosis in the late 1990s. Voriconazole and liposomal amphotericin B allow a safer and more effective treatment of invasive aspergillosis when compared with amphotericin B-desoxycholate. Combination of antifungal agents has been introduced in clinical trials. Up to now no significant benefit has been obtained with antifungal combination compared to voriconazole alone. Because mortality of invasive aspergillosis remains up to more than 50%, prophylaxis, early diagnosis and early initiation of antifungal therapy are of utmost importance for the reduction of invasive aspergillosis related mortality. Despite all advances in the management of invasive aspergillosis important questions remain unresolved. This article reviews the current state and new insights in the management of invasive aspergillosis and points out clinicians unmet needs.

Invasive fungal infections are a major cause of morbidity and mortality in immunosuppressed patients with fatality rates ranging from 30 % to 80 % in neutropenic patients. This results at least partly in difficulties obtaining a reliable and early diagnosis, followed by the fact that clinical symptoms are unspecific and of very limited use. Conventional methods may be difficult and are often delayed. Serological tests like the galactomannan enzyme immunoassay are presently most promising for diagnosing invasive aspergillosis, however, sensitivity and specificity vary within the studies. This review reflects the current situation of diagnosing invasive fungal infections with a special focus on how to best diagnose Aspergillus-related infections (e.g., culture, microscopy, imaging techniques, CT-guided biopsies). Promising molecular techniques under development will be discussed and their potential for routine diagnostic applications (e.g. lateral flow device, polymerase chain reaction [PCR]-based assays, rolling circle amplification [RCA], loop-mediated amplification [LAMP], nucleic acid sequence-based amplification [NASBA]). A summary is given on commercial assays (e.g., Platelia Aspergillus®, Fungitell®, in situ hybridization, immunohistochemisty) and their purposes as screening tools and/or diagnostic tools. This review gives a future outlook on how to best diagnose Aspergillus infections.

Aspergillus is one of the most important fungal genera for the man, for its industrial use, its ability to spoil food and not least its medical impact as cause of a variety of diseases. Currently hundreds of species of Aspergillus are known; nearly fifty of them are able to cause infections in humans and animals. Recently, the genus Aspergillus is subdivided into 8 subgenera and 22 sections. The spectrum of diseases caused by Aspergillus species varies from superficial cutaneous to invasive and systemic infections. All species of Aspergillus investigated so far are resistant against the antifungals fluconazole and 5-fluorocytosine, the range of susceptibilities to currently available antifungals is discussed in this paper.

Amphotericin B has been the only therapeutic option for invasive aspergillosis over decades. It acts by binding to membrane ergosterol, lipid peroxidation and proton-ATPase inhibition. Amphotericin B is eliminated unchanged via urine and feces. It displays a considerable toxicity, particularly infusion-related adverse events and renal damage. Continuous infusion and administration of lipidformulations of amphotericin B are strategies to improve its tolerability. Amphotericin B has a post-antifungal effect (PAFE), and its peak concentration is probably crucial for its fungicidal efficacy. The amphotericin B lipid-formulations display largely different pharmacokinetics. Kinetics of amphotericin B which is liberated from its lipid encapsulation in the plasma is similar for all three available lipid formulations. Azoles inhibit the synthesis of fungal cell membrane ergosterol. The triazoles itraconazole, voriconazole and posaconazole are active against Aspergilli. Voriconazole is the drug of choice for therapy of invasive aspergillosis. It is metabolized in the liver and metabolites are excreted via the kidneys. Posaconazole is licensed for antifungal prophylaxis in hematological high-risk patients and for salvage therapy of invasive aspergillosis. A variety of drug-drug interactions have to be considered with all azoles. The ratio between the area under the time-concentration profile (AUC) and the minimal inhibitory concentration (MIC) is the relevant pharmacokinetic/ pharmacodynamic parameter for azoles. Caspofungin the only echinocandin licensed for second line therapy of invasive aspergillosis is fungistatic to Aspergilli displaying a paradoxical pharmacodynamic effect. Caspofungin elimination is independent from renal function. Although it is metabolized in the liver its potential for drug interactions is moderate.

Cerebral Aspergillosis is the most lethal manifestation of infection due to Aspergillus species arising most commonly as hematogenous dissemination from a pulmonary focus, direct extension from paranasal sinus infection or direct inoculation through trauma and surgery of the central nervous system (CNS). Voriconazole is currently considered the standard of treatment of CNS aspergillosis with liposomal amphotericin B being the next best alternative. Neurosurgical resection of infected cerebral tissue in addition to antifungal therapy is frequently performed in patients with CNS aspergillosis to prevent neurological deficits and improve outcome. Aspergillus endophthalmitis may occur endogenously mostly from a pulmonary focus or exogenously following eye surgery or trauma. Although amphotericin B is still described as the primary therapy, voriconazole is increasingly considered the first line treatment of Aspergillus endophthalmitis. Vitrectomy is recommended in most cases of Aspergillus endophthalmitis.

Patients with cystic fibrosis (CF) suffer from chronic infective lung disease, which determines morbidity and mortality. While bacteria, such as Pseudomonas aeruginosa, are well-known to contribute to pulmonary pathology, the relevance of fungi in CF airways remains poorly understood. The best studied fungus in CF is Aspergillus fumigatus, which frequently colonizes CF airways and causes a disease condition termed allergic bronchopulmonary aspergillosis. This review aims to provide an update on the immunological mechanisms, diagnostic approaches and therapeutic strategies for allergic bronchopulmonary aspergillosis and other Aspergillus fumigatusmediated phenotypes in CF lung disease.

Disease manifestations with Aspergillus spp. are very diverse and dependent on interaction between the fungus and the host. Invasive aspergillosis (IA) is the most severe form of Aspergillus - associated disease found in immunocompromised hosts. Infections are mainly due to Aspergillus (A.) fumigatus, an air-borne opportunistic pathogen that causes 90% of IA. Mortality rate of this disease is still very high (50-95%), partly because of diagnostic difficulties, limited antifungal treatment options, weak conditions of patients at risk; but also in part because understanding of virulence factors involved in A. fumigatus pathogenicity and interactions of the pathogen with the host immune system is still poor. This review focuses on properties of A. fumigatus in terms of putative virulence factors and interactions of the pathogen with a main focus on the innate immune system.

Despite the availability of new antifungal compounds, morbidity and mortality of invasive aspergillosis are still unacceptably high, in particular in immunocompromised patients such as patients with hematological malignancies or allogeneic hematopoietic stem cell or solid organ transplant recipients. Over the last decades, our knowledge of the immunopathogenesis of invasive aspergillosis has greatly advanced. This, in turn, provided critical information to augment host immunity against fungal pathogens. Potential approaches for enhancing the host immune system in the combat against Aspergillus include the administration of effector and regulatory cells (e.g., granulocytes, antigen-specific T cells, natural killer cells, dendritic cells) as well as the administration of recombinant cytokines, interferons and growth factors (e.g., interferon-γ,granulocyte- and granulocyte-macrophage colony stimulating factor) and various vaccination strategies. Although promising results are reported on in vitro data and animal studies, current data are too limited to allow solid conclusions on the risk and the benefit of these strategies in the clinical setting. Therefore, the real challenge in the future is to perform appropriately designed and powered clinical trials. These require international, multi-center collaboration, but may ultimately improve the outcome in immunocompromised patients suffering from invasive aspergillosis.

NADPH-oxidase mediated production of Reactive Oxygen Species (ROS) by alveolar macrophages and neutrophils is a critical mechanism for immune defence against Aspergillus fumigatus. Fungal oxidative stress response includes enzymatic response by superoxide dismutases (SOD), catalases, and enzymes from the thioredoxin and glutathione systems, which are regulated by the transcription factor Yap1. Secondary metabolites are also involved in defense against ROS. Some of the secondary metabolite clusters are controlled by the transcriptional regulator LaeA. The redundancy of antioxidant systems, and the variable impact of SOD or catalase gene deletions on in vitro oxidative stress sensitivity and in vivo virulence suggest a complex regulation of oxidative stress response in A. fumigatus, making high-throughput approaches, such as microarray or next generation sequencing (NGS), highly relevant to study their respective role. These approaches have been widely applied to A fumigatus, in order to characterize its metabolic response to different stresses mimicking in vivo conditions (such as antifungals, or neutrophils), or to transcription factor deletion (including LaeA). In some studies, oxidative stress response process and antioxidant enzymes have been identified as key metabolic pathways. However, oxidative stress response has not been analyzed systematically and a further data analysis could be helpful to clarify the role of A. fumigatus antioxidant systems and, potentially, to identify new drug targets. In this review, we synthesized available A. fumigatus microarrays and NGS data, focusing on the role of antioxidant systems. We analyzed the different methodologies that were used for transcriptomic analysis, and we compared biological processes and antioxidant system modulations in A. fumigatus exposed to stress.

Being external, the fungal cell wall plays a crucial role in the fungal life. By covering the underneath cell, it offers mechanical strength and acts as a barrier, thus protecting the fungus from the hostile environment. Chemically, this cell wall is composed of different polysaccharides. Because of their specific composition, the fungal cell wall and its underlying plasma membrane are unique targets for the development of drugs against pathogenic fungal species. The objective of this review is to consolidate the current knowledge on the antifungal drugs targeting the cell wall and plasma membrane, mainly of Aspergillus and Candida species – the most prevalent fungal pathogens, and also to present challenges and questions conditioning the development of new antifungal drugs targeting the cell wall.