Newer antifungal therapy for emerging fungal pathogens

Crosstalk between the calcineurin and cell wall integrity pathways prevents chitin overexpression in Candida albicans

Echinocandins such as caspofungin are frontline antifungal drugs that compromise β-1,3 glucan synthesis in the cell wall. Recent reports have shown that fungal cells can resist killing by caspofungin by upregulation of chitin synthesis, thereby sustaining cell wall integrity (CWI). When echinocandins are removed, the chitin content of cells quickly returns to basal levels, suggesting that there is a fitness cost associated with having elevated levels of chitin in the cell wall. We show here that simultaneous activation of the calcineurin and CWI pathways generates a subpopulation of Candida albicans yeast cells that have supra-normal chitin levels interspersed throughout the inner and outer cell wall, and that these cells are non-viable, perhaps due to loss of wall elasticity required for cell expansion and growth. Mutations in the Ca2+-calcineurin pathway prevented the formation of these non-viable supra-high chitin cells by negatively regulating chitin synthesis driven by the CWI pathway. The Ca2+-calcineurin pathway may therefore act as an attenuator that prevents the overproduction of chitin by coordinating both chitin upregulation and negative regulation of the CWI signaling pathway. This article has an associated First Person interview with the first author of the paper.

Omics for Investigating Chitosan as an Antifungal and Gene Modulator

Chitosan is a biopolymer with a wide range of applications. The use of chitosan in clinical medicine to control infections by fungal pathogens such as Candida spp. is one of its most promising applications in view of the reduced number of antifungals available. Chitosan increases intracellular oxidative stress, then permeabilizes the plasma membrane of sensitive filamentous fungus Neurospora crassa and yeast. Transcriptomics reveals plasma membrane homeostasis and oxidative metabolism genes as key players in the response of fungi to chitosan. A lipase and a monosaccharide transporter, both inner plasma membrane proteins, and a glutathione transferase are main chitosan targets in N. crassa. Biocontrol fungi such as Pochonia chlamydosporia have a low content of polyunsaturated free fatty acids in their plasma membranes and are resistant to chitosan. Genome sequencing of P. chlamydosporia reveals a wide gene machinery to degrade and assimilate chitosan. Chitosan increases P. chlamydosporia sporulation and enhances parasitism of plant parasitic nematodes by the fungus. Omics studies allow understanding the mode of action of chitosan and help its development as an antifungal and gene modulator.

The development of animal infection models and antifungal efficacy assays against clinical isolates of Trichosporon asahii, T. asteroides and T. inkin

The present study developed Galleria mellonella and murine infection models for the study of Trichosporon infections. The utility of the developed animal models was demonstrated through the assessment of virulence and antifungal efficacy for 7 clinical isolates of Trichosporon asahii, T. asteroides and T. inkin. The susceptibility of the Trichosporon isolates to several common antifungal drugs was tested in vitro using the broth microdilution and the E-test methods. The E-test method depicted a lower minimal inhibitory concentration (MIC) for amphotericin and a slightly higher MIC for caspofungin, while MICs observed for the azoles were different but comparable between both methods. All three Trichosporon species established infection in both the G. mellonella and immunosuppressed murine models. Species and strain dependent differences were observed in both the G. mellonella and murine models. T. asahii was demonstrated to be more virulent than the other 2 species in both animal hosts. Significant differences in virulence were observed between strains for T. asteroides in the murine model. In both animal models, fluconazole and voriconazole were able to improve the survival of the animals compared to the untreated control groups infected with any of the 3 Trichosporon species. In G. mellonella, amphotericin was not able to reduce mortality in any of the 3 species. In contrast, amphotericin was able to reduce murine mortality in the T. asahii or T. inkin models, respectively. Hence, the developed animal infection models can be directly applicable to the future deeper investigation of the molecular determinants of Trichosporon virulence and antifungal resistance.

ScedosporiumSpecies Infections and Treatments

Scedosporium species are now increasingly isolated from immunocompromised and immunocompetent patients. Unfortunately, Scedosporium species infections are generally resistant to amphotericin B, and S. prolificans strains are particularly resistant to presently-available antifungal agents. Here we review the microbiology, expanding epidemiology, numerous clinical presentations, and diagnostic tools available for Scedosporium species infections. Finally, we detail the available in vitro, animal model, and clinical data on the treatment of Scedosporium species infections with special emphasis on the role of newer antifungal therapies for these recalcitrant infections.

Effect of antifungal treatment in a murine model of blastoschizomycosis

Blastoschizomyces capitatus is an emerging pathogenic fungus that can cause deep invasive diseases in neutropenic patients. We developed a model of disseminated blastoschizomycosis in immunosuppressed mice to evaluate the effectiveness of amphotericin B, flucytosine, fluconazole and voriconazole. High-dose fluconazole was the most effective drug at prolonging the survival of mice and at reducing fungal burden in the kidneys, spleen and liver.

Mucormycosis Mimicks Sinusitis in a Diabetic Adult

Fungal sinusitis caused by invasive fungal infections, such as Mucormycosis, occurs predominantly in an immunocompromised patient. However, invasive cranial bone mycoses are rare and are usually associated with host immunodeficiency. They are difficult to diagnose, and in many cases are fatal. Treatment consists of antifungal chemotherapy, radical surgical debridement, and control of the underlying immunological condition. We report a case of Mucormycosis in a patient with type 1 diabetes mellitus. The patient had a history of dental pathology and associated renal dysfunction. The patient was managed by extensive surgical debridement followed by amphotericin B lipid complex injection (Abelcet 5 mg/bw kg/day) as an antifungal agent. Our patient's ocular function was affected. The radical treatment and follow-up by a multidisciplinary team eliminated the mucor-related consequences, however, the patient died because of end-stage renal failure. In conclusion, type 1 diabetes may be associated with invasive fungal sinusitis.

Synthesis and antifungal activity of a novel series of alkyldimethylamine cyanoboranes and their derivatives

A series of new amine cyanoborane derivatives were synthesized and exhibited antifungal activity. A long alkyl chain attached to the nitrogen of the amine cyanoboranes and carboxyboranes enhances antifungal activity. An enhanced activity was also obtained upon the halogenation of the amine cyanoboranes as well as in the presence of C=C double bond at the end of the N-alkyl group. The lead compounds were dimethylundecylamine cyanoborane (C11H23N(CH3)2BH2CN), 9, and its dibromo derivative dimethylundecylamine dibromocyanoborane (C11H23N(CH3)2BBr2CN), 11. The MIC values for the lead compounds against the most important human pathogenic fungi ranged from 16.25 to 32.5 micromol/L and from 10.05 to 79 micromol/L, respectively. Both compounds were found to be relatively safe in intravenous injections to mice, (MTD = 121.9 and 73.1 micromol/kg, respectively) and active against strains that are resistant to fluconazole (a conventional antifungal medicine). These data indicate their potential to become antifungal agents.

Treatment of invasive infections due to rare or emerging yeasts and moulds

Emerging fungal infections represent a serious problem in an immunocompromised host. Rapid developments in in vitro antifungal susceptibility testing and the availability of several new antifungal agents have provided excellent opportunities to treat infections that are caused by various Candida spp. and to some extend by Aspergillus spp. However, recently the epidemiology of fungal infections has significantly changed and several new pathogens have emerged. This article attempts to summarise the available data on the management of emerging infections with fungal infections that have recently gained importance. Updated recommendations on antifungal treatment are also discussed.

Invasive candidiasis in the intensive care unit

OBJECTIVE

To review epidemiologic trends, advances in diagnosis and susceptibility testing, therapeutic options and guidelines, and management strategies for invasive candidiasis as relevant to the intensive care unit physician.

DATA SOURCES, STUDY SELECTION, DATA EXTRACTION, DATA SYNTHESIS

Nonstructured review of peer-reviewed original articles, review articles, abstracts, guidelines, and consensus statements appearing in Medline, major scientific journals, and conference proceedings.

CONCLUSIONS

Invasive candidiasis is a problem associated with substantial morbidity and mortality that is highly prevalent in the intensive care unit setting. Recent epidemiologic studies have shown a trend toward increasing numbers of infections and a shift toward infections caused by non-albicans Candida species. Guidelines for the management of these diseases have been published and recommend amphotericin B, fluconazole, or caspofungin as the primary therapeutic option. The choice of agent should depend on local epidemiology and patient factors. The role of newer antifungal agents for this population, such as the new azoles and echinocandins, remains to be determined. Priority areas of research include diagnostics, risk identification, and management strategy assessment such as prophylactic, preemptive, and empirical therapy.

Surgery and treatment with high-dose liposomal amphotericin B for eradication of craniofacial zygomycosis in a patient with Hodgkin's disease who had undergone allogeneic hematopoietic stem cell transplantation

This case report describes craniofacial zygomycosis in a 24-year-old male with Hodgkin's disease who underwent chemotherapy and autologous hematopoietic stem cell transplantation, followed by a nonmyeloablative allogeneic transplant. Empirical therapy with itraconazole and amoxicillin-clavulanate failed to resolve the infection. Postdiagnosis, surgery and treatment with high-dose liposomal amphotericin B eradicated the disease.

Antifungal chemotherapeutics

This review addresses trends in outcome and risk factors for invasive fungal infections, current antifungal agents and new therapeutic strategies. Current prospects for new therapies rest upon caspofungin, the first of a new class of antifungal molecules, the echinocandins, and new extended-spectrum azoles, voriconazole, posaconazole and ravuconazole. Approval by the Food and Drug Administration of the USA and the European Medicine Agency was given in 2001-2002 to voriconazole and caspofungin. Voriconazole clearly demonstrated a decrease in mortality in invasive aspergillosis and fusariosis fungal infections.

Efficacy of micafungin in combination with other drugs in a murine model of disseminated trichosporonosis

Using a murine model of disseminated infection caused by Trichosporon asahii, we have evaluated the efficacies of amphotericin B (AMB; 1 mg/kg of body weight/day), fluconazole (FLC; 20 mg/kg/twice a day), and micafungin (MFG; 5 mg/kg/twice a day). We tested these drugs alone and in combination (MFG with AMB and MFG with FLC). MFG with AMB showed a synergistic effect and demonstrated a higher degree of efficacy in prolonging survival and reducing the kidney fungal burden than either agent alone. The combination MFG with FLC was able to reduce significantly the kidney fungal burden in comparison to that achieved with either drug administered alone.

The future of animal models of invasive aspergillosis

The diagnosis of invasive aspergillosis remains very difficult, coupled with limited treatment options. Animal models have been utilized to evaluate both the diagnosis and treatment of infection and to assess the pathogenicity and virulence of the organism. However, animal models have not been standardized and have been used in only a limited fashion for genomic evaluation in this disease. Extensive efforts are underway to expand significantly the Aspergillus genomic information. Thus, the standardization of animal models of invasive aspergillosis is critical to create a unified platform to enhance evaluation of newer genomic information and allow assessment of pathogenicity and virulence factors. Proposed models, supported by a recently awarded National Institutes of Health/National Institute of Allergy and Infectious Diseases contract, will be developed in close interaction with the extended Aspergillus community (including academia and industry) to answer key questions in this disease. The goal of this work is to provide the framework to evaluate genomic targets in animal models in order to improve the diagnosis and treatment of invasive aspergillosis that will ultimately result in improved outcomes of patients with this frequently fatal infection.

A novel murine model of cerebral scedosporiosis: lack of efficacy of amphotericin B

OBJECTIVES

Cerebral scedosporiosis is a life-threatening infection that is difficult to treat. The aim of this work was to develop a murine model of cerebral infection by Scedosporium apiospermum using intracranial inoculation and to use this model to evaluate the efficacy of amphotericin B deoxycholate and liposomal amphotericin B.

METHODS

Mice were rendered neutropenic by intraperitoneal cyclophosphamide and intravenous (iv) 5-fluorouracil administration. Animals were infected with iv or intracranial inoculation of 1 x 10(4), 5 x 10(4) or 5 x 10(5) cfu of a clinical strain of S. apiospermum. Tissue burden reduction was determined in kidneys and brain 4 days after the infection. Efficacy of amphotericin B and liposomal amphotericin B (0.8 mg/kg/day intraperitoneally and 40 mg/kg/day iv, respectively) was evaluated in neutropenic mice infected iv or intracranially with 5 x 10(4) cfu. Survival was analysed with the log-rank test. Fungal burden values of different groups were compared using the Mann-Whitney U-test.

RESULTS

In our model, intracranial infection produced a higher fungal load in the brain and a lower fungal load in the kidney than iv inoculation. Survival of animals infected intracranially and treated with amphotericin B or liposomal amphotericin B (mean survival time = 8.3 and 9.2 days, respectively) was not different from the control group (P=0.58 and 0.85, respectively).

CONCLUSIONS

We have developed a murine model of cerebral scedosporiosis, which may be useful for studying various pathological aspects of this infection and evaluating new therapeutic approaches. Amphotericin B and liposomal amphotericin B were unable to resolve the infection.

Prophylaxis and treatment of invasive candidiasis in the intensive care setting

The term "invasive candidiasis" encompasses a group of infections of increasing relevance in the intensive care setting. Prophylaxis is an attractive strategy when dealing with diseases of high prevalence, morbidity, and mortality. The success of prophylaxis is determined by the selection of a population at high risk and the use of the safest and most effective drug. Although risk factors for this disease are known, risk assessment strategies need to be developed to predict a high likelihood of disease so that targeted prophylaxis can be offered. Recent advances in antifungal therapy, such as development of the azoles and echinocandins, have resulted in excellent prophylactic and therapeutic choices for the management of this problem.

Choices aplenty: antifungal prophylaxis in hematopoietic stem cell transplant recipients

The incidence of invasive fungal infection (IFIs) in hematopoietic stem cell transplantation (HSCT) recipients ranges from 10 to 25% with an overall case fatality rate of up to 70-90%. Candida and Aspergillus genera remain the two most common pathogens. Although fluconazole prophylaxis in this population has been moderately effective in reducing mortality due to invasive candidiasis, this agent does not have activity against invasive aspergillosis (IA) and other mould. Several new agents such as voriconazole and caspofungin have enhanced potency and broad-spectrum antifungal activity and show promising results against yeasts and filamentous fungi when given as therapy and as chemoprophylaxis. Further, new diagnostic tools to detect circulating fungal antigens in biological fluids and PCR-based methods to detect species or genus-specific DNA or RNA have been developed. Incorporating these techniques along with clinical criteria appear to improve the accuracy of preclinical diagnosis of IFIs. Such approaches may alter the current treatment strategy from prophylaxis to pre-emptive therapy, thereby potentially decreasing cost and toxicity in high-risk patients.

Novel approaches to antifungal prophylaxis

Antifungal prophylaxis represents a significant advance in the management of patients at risk from fungal infections in a variety of settings. Identification of patients at the highest risk and the utilisation of safe and effective drugs maximises the benefits of prophylaxis. Situations in which antifungal prophylaxis has been shown to be useful are bone marrow transplantation, liver and lung transplantation, surgical and neonatal intensive care units, secondary prophylaxis of fungal infections associated with HIV and neutropenia associated haematological malignancies and their treatment. New antifungal agents, such as the echinocandins and the new azoles, are available and have a potential role in antifungal prophylaxis. Future studies should evaluate which strategy is more useful; prophylaxis or pre-emptive therapy.

New approaches to the risk of Candida in the intensive care unit

PURPOSE OF REVIEW

Candidemia is the fourth most common bloodstream infection in the United States with similar trends reported worldwide. This infection is particularly relevant in the intensive care setting, and is independently associated with increased morbidity and mortality. Identification of patients at risk and developing new prophylactic strategies is a priority area of research. This review focuses on recent advances in risk identification and the groundwork for prophylaxis of invasive candidiasis in the intensive care setting.

RECENT FINDINGS

Although risk factors for invasive candidiasis have been clearly identified (such as colonization, length of stay, use of parenteral nutrition, antibiotics, central lines, and abdominal surgery), there are few risk assessment strategies that clearly define or predict a population at high risk of getting this disease. Currently available risk assessment strategies are yet to be validated in multiple centers and settings. Geographically limited or population specific clinical trials (such as surgical patients) have shown early indications that antifungal prophylaxis is useful in reducing the incidence of invasive candidiasis by more than 50% in units with high incidence of infection, or in carefully selected high-risk patients. Interesting advances in non-culture diagnostic methods and surrogate markers of infection may also have an impact in early identification of infection and preemptive treatment.

SUMMARY

Invasive candidiasis is a relevant problem in the intensive care setting. Better risk assessment strategies will permit identification of the subpopulations of patients that would benefit from prophylactic antifungal therapy the most, having the potential to save millions of lives and dollars.