Treatment principles for Candida and Cryptococcus

The Antimicrobial Effects of Myrosinase Hydrolysis Products Derived from Glucosinolates Isolated from Lepidium draba

Lepidium draba (hoary cress) is a perennial plant belonging to the Brassicaceae family that produces two dominant glucosinolates (GLSs): glucoraphanin (GRN) and sinalbin (SBN). They represent the stored form, which is converted upon the myrosinase (Myr) hydrolysis activity to active compounds, mainly isothiocyanates (ITCs) such as sulforaphane (SFN) or p-hydroxybenzyl isothiocyanate (pHBITC). Research on ITCs that have proven anticancer, antimicrobial, and chemoprotective properties is usually conducted with pure commercially available compounds. However, these are chemically reactive, making it difficult to use them directly for preventive purposes in dietary supplements. Efforts are currently being made to prepare dietary supplements enriched with GLS and/or Myr. In this study, we report a simple but efficient chromatographic procedure for the isolation and purification of GLSs from MeOH extract from hoary cress based on a combination of ion exchange and gel permeation chromatography on DEAE-Sephadex A-25 and Sephadex LH-20. To obtain the Myr required for efficient hydrolysis of GLSs into antibacterial ITCs, we developed a rapid method for its extraction from the seeds of Lepidium sativum (garden cress). The yields of GLSs were 22.9 ± 1.2 mg GRN (purity 96%) and 10.4 ± 1.1 mg SBN (purity 92%) from 1 g of dry plant material. Both purified GLSs were used as substrates for the Myr. Analysis of the composition of hydrolysis products (HPs) revealed differences in their hydrolysis rates and in the degree of conversion from GLSs to individual ITCs catalyzed by Myr. When GRNs were cleaved, SFNs were formed in an equimolar ratio, but the formation of pHBITCs was only half that of cleaved SBNs. The decrease in pHBITC content is due to its instability compared to SFN. While SFN is stable in aqueous media during the measurement, pHBITC undergoes non-enzymatic hydrolysis to p-hydroxybenzyl alcohol and thiocyanate ions. Testing of the antimicrobial effects of the HPs formed from GRN by Myr under premix or in situ conditions showed inhibition of the growth of model prokaryotic and eukaryotic microorganisms. This observation could serve as the jumping-off point for the design of a two-component mixture, based on purified GLSs and Myr that is, usable in food or the pharmaceutical industry in the future.

Chelation of Mitochondrial Iron as an Antiparasitic Strategy

Iron, as an essential micronutrient, plays a crucial role in host-pathogen interactions. In order to limit the growth of the pathogen, a common strategy of innate immunity includes withdrawing available iron to interfere with the cellular processes of the microorganism. Against that, unicellular parasites have developed powerful strategies to scavenge iron, despite the effort of the host. Iron-sequestering compounds, such as the approved and potent chelator deferoxamine (DFO), are considered a viable option for therapeutic intervention. Since iron is heavily utilized in the mitochondrion, targeting iron chelators in this organelle could constitute an effective therapeutic strategy. This work presents mitochondrially targeted DFO, mitoDFO, as a candidate against a range of unicellular parasites with promising in vitro efficiency. Intracellular Leishmania infection can be cleared by this compound, and experimentation with Trypanosoma brucei 427 elucidates its possible mode of action. The compound not only affects iron homeostasis but also alters the physiochemical properties of the inner mitochondrial membrane, resulting in a loss of function. Furthermore, investigating the virulence factors of pathogenic yeasts confirms that mitoDFO is a viable candidate for therapeutic intervention against a wide spectrum of microbe-associated diseases.

Intracellular Pathogens: Infection, Immunity, and Intervention

Intracellular pathogens comprise a diverse group of pathogens that all share a required location in a host cell to infect, survive, and replicate. Intracellular location allows pathogens to hide from host immune responses, avoid competition with other pathogens, mediate host cellular functions, replicate safely, and cause infection that is difficult to target with therapeutics. All intracellular pathogens have varying routes of infiltration into host cells and different host cell preferences. For example, bacteria Mycobacterium tuberculosis chooses to invade antigen-presenting cells, which allows them to moderate host antigen presentation to memory cells, whereas rabies virus prefers to invade neurons because they have pre-existing innate immunity protection systems. Regardless of the pathway that each intracellular pathogen follows, all share the capacity to cause disease if they succeed in entering host cells. Here, we give an overview of selected intracellular pathogens and infections they cause, immune responses they induce, and intervention strategies used to treat and control them.

Comprehensive genome-scale metabolic model of the human pathogen Cryptococcus neoformans: A platform for understanding pathogen metabolism and identifying new drug targets

Introduction: The fungal priority pathogen Cryptococcus neoformans causes cryptococcal meningoencephalitis in immunocompromised individuals and leads to hundreds of thousands of deaths per year. The undesirable side effects of existing treatments, the need for long application times to prevent the disease from recurring, the lack of resources for these treatment methods to spread over all continents necessitate the search for new treatment methods. Methods: Genome-scale models have been shown to be valuable in studying the metabolism of many organisms. Here we present the first genome-scale metabolic model for C. neoformans, iCryptococcus. This comprehensive model consists of 1,270 reactions, 1,143 metabolites, 649 genes, and eight compartments. The model was validated, proving accurate when predicting the capability of utilizing different carbon and nitrogen sources and growth rate in comparison to experimental data. Results and Discussion: The compatibility of the in silico Cryptococcus metabolism under infection conditions was assessed. The steroid and amino acid metabolisms found in the essentiality analyses have the potential to be drug targets for the therapeutic strategies to be developed against Cryptococcus species. iCryptococcus model can be applied to explore new targets for antifungal drugs along with essential gene, metabolite and reaction analyses and provides a promising platform for elucidation of pathogen metabolism.

Potential Predictors and Survival Analysis of the Relapse of HIV-Associated Cryptococcal Meningitis: A Retrospective Study

Objective: We intend to investigate the relapse of HIV-associated cryptococcal meningitis (CM), assess potential predictors and conduct survival analysis, with a view to establishing a valid reference for the management of the relapse of CM.

Method: This is a retrospective study in Chinese patients with HIV-associated CM and those who experience relapse of CM. Baseline demographic, laboratory and clinical characteristics of patients with HIV-associated CM were collected. Predictors for relapse of HIV-associated CM were analyzed using univariate and multivariate logistic regression. Survival probability in relapse cases was determined by Kaplan-Meier survival curves.

Results: During the study period, 87 of 348 (25.0%) HIV patients experienced the relapse of CM. CD4+ T-cell counts, antiretroviral therapy (ART) status and the time from symptom onset to presentation were all statistically associated with the relapse of CM (p = 0.013, 0.018 and 0.042, respectively). The overall survival among 46 HIV CM relapse patients whose survival information were obtained, was 78.3%. The proportion of patients who died after antifungal treatment for CM was greater in those whose interval from symptom onset to presentation ≥4 weeks, compared with those <4 weeks (p = 0.0331).

Conclusions: In order to reduce the relapse of CM and increase the survival possibility of these patients, we can promote the importance of ART before CM occurs, emphasize timely consultation when any CM-associated clinical symptoms occurs, and individualized the timing of ART initiation according to indicators which can reflect the severity of CM.

Dectin-2-Targeted Antifungal Liposomes Exhibit Enhanced Efficacy

Invasive fungal diseases caused by Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus have mortality rates ranging from 10 to 95%. Individual patient costs may exceed $100,000 in the United States. All antifungals in current use have serious limitations due to host toxicity and/or insufficient fungal cell killing that results in recurrent infections. Few new antifungal drugs have been introduced in the last 2 decades. Hence, there is a critical need for improved antifungal therapeutics. By targeting antifungal-loaded liposomes to α-mannans in the extracellular matrices secreted by these fungi, we dramatically reduced the effective dose of drug. Dectin-2-coated liposomes loaded with amphotericin B bound 50- to 150-fold more strongly to C. albicans, C. neoformans, and A. fumigatus than untargeted liposomes and killed these fungi more than an order of magnitude more efficiently. Targeting drug-loaded liposomes specifically to fungal cells has the potential to greatly enhance the efficacy of most antifungal drugs.

Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus cause life-threatening candidiasis, cryptococcosis, and aspergillosis, resulting in several hundred thousand deaths annually. The patients at the greatest risk of developing these life-threatening invasive fungal infections have weakened immune systems. The vulnerable population is increasing due to rising numbers of immunocompromised individuals as a result of HIV infection or immunosuppressed individuals receiving anticancer therapies and/or stem cell or organ transplants. While patients are treated with antifungals such as amphotericin B, all antifungals have serious limitations due to lack of sufficient fungicidal effect and/or host toxicity. Even with treatment, 1-year survival rates are low. We explored methods of increasing drug effectiveness by designing fungicide-loaded liposomes specifically targeted to fungal cells. Most pathogenic fungi are encased in cell walls and exopolysaccharide matrices rich in mannans. Dectin-2 is a mammalian innate immune membrane receptor that binds as a dimer to mannans and signals fungal infection. We coated amphotericin-loaded liposomes with monomers of Dectin-2’s mannan-binding domain, sDectin-2. sDectin monomers were free to float in the lipid membrane and form dimers that bind mannan substrates. sDectin-2-coated liposomes bound orders of magnitude more efficiently to the extracellular matrices of several developmental stages of C. albicans, C. neoformans, and A. fumigatus than untargeted control liposomes. Dectin-2-coated amphotericin B-loaded liposomes reduced the growth and viability of all three species more than an order of magnitude more efficiently than untargeted control liposomes and dramatically decreased the effective dose. Future efforts focus on examining pan-antifungal targeted liposomal drugs in animal models of fungal diseases.

IMPORTANCE Invasive fungal diseases caused by Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus have mortality rates ranging from 10 to 95%. Individual patient costs may exceed $100,000 in the United States. All antifungals in current use have serious limitations due to host toxicity and/or insufficient fungal cell killing that results in recurrent infections. Few new antifungal drugs have been introduced in the last 2 decades. Hence, there is a critical need for improved antifungal therapeutics. By targeting antifungal-loaded liposomes to α-mannans in the extracellular matrices secreted by these fungi, we dramatically reduced the effective dose of drug. Dectin-2-coated liposomes loaded with amphotericin B bound 50- to 150-fold more strongly to C. albicans, C. neoformans, and A. fumigatus than untargeted liposomes and killed these fungi more than an order of magnitude more efficiently. Targeting drug-loaded liposomes specifically to fungal cells has the potential to greatly enhance the efficacy of most antifungal drugs.

Methodologies for in vitro and in vivo evaluation of efficacy of antifungal and antibiofilm agents and surface coatings against fungal biofilms

Unlike superficial fungal infections of the skin and nails, which are the most common fungal diseases in humans, invasive fungal infections carry high morbidity and mortality, particularly those associated with biofilm formation on indwelling medical devices. Therapeutic management of these complex diseases is often complicated by the rise in resistance to the commonly used antifungal agents. Therefore, the availability of accurate susceptibility testing methods for determining antifungal resistance, as well as discovery of novel antifungal and antibiofilm agents, are key priorities in medical mycology research. To direct advancements in this field, here we present an overview of the methods currently available for determining (i) the susceptibility or resistance of fungal isolates or biofilms to antifungal or antibiofilm compounds and compound combinations; (ii) the in vivo efficacy of antifungal and antibiofilm compounds and compound combinations; and (iii) the in vitro and in vivo performance of anti-infective coatings and materials to prevent fungal biofilm-based infections.

Treatment principles for the management of mold infections

Survival rates among immunocompromised patients with invasive mold infections have markedly improved over the last decade with earlier diagnosis and new antifungal treatment options. Yet, increasing antifungal resistance, breakthrough infections with intrinsically resistant fungi, and potentially life-threatening adverse effects and drug interactions are becoming more problematic, especially with prolonged therapy. Evidence-based recommendations for treating invasive aspergillosis and mucormycosis provide excellent guidance on the initial workup and treatment of these molds, but they cannot address all of the key management issues. Herein, we discuss 10 general treatment principles in the management of invasive mold disease in immunocompromised patients and discuss how these principles can be integrated to develop an effective, individualized treatment plan.

Cryptococcus neoformans and Cryptococcus gattii, the etiologic agents of cryptococcosis

Cryptococcus neoformans and Cryptococcus gattii are the two etiologic agents of cryptococcosis. They belong to the phylum Basidiomycota and can be readily distinguished from other pathogenic yeasts such as Candida by the presence of a polysaccharide capsule, formation of melanin, and urease activity, which all function as virulence determinants. Infection proceeds via inhalation and subsequent dissemination to the central nervous system to cause meningoencephalitis. The most common risk for cryptococcosis caused by C. neoformans is AIDS, whereas infections caused by C. gattii are more often reported in immunocompetent patients with undefined risk than in the immunocompromised. There have been many chapters, reviews, and books written on C. neoformans. The topics we focus on in this article include species description, pathogenesis, life cycle, capsule, and stress response, which serve to highlight the specializations in virulence that have occurred in this unique encapsulated melanin-forming yeast that causes global deaths estimated at more than 600,000 annually.