Browsing by Subject "Candida"
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Item Open Access Breakthrough invasive fungal infections: Who is at risk?(Mycoses, 2020-10) Jenks, Jeffrey D; Cornely, Oliver A; Chen, Sharon C-A; Thompson, George R; Hoenigl, MartinThe epidemiology of invasive fungal infections (IFIs) in immunocompromised individuals has changed over the last few decades, partially due to the increased use of antifungal agents to prevent IFIs. Although this strategy has resulted in an overall reduction in IFIs, a subset of patients develop breakthrough IFIs with substantial morbidity and mortality in this population. Here, we review the most significant risk factors for breakthrough IFIs in haematology patients, solid organ transplant recipients, and patients in the intensive care unit, focusing particularly on host factors, and highlight areas that require future investigation.Item Open Access Novel Targets and Therapeutic Strategies for the Treatment of Cryptococcus neoformans(2024) Palmucci, Julia RoseInvasive fungal infections cause significant worldwide morbidity, and mortality rates remain remarkably high despite treatment. One of the most pressing fungal pathogen threats is the opportunistic infection, Cryptococcus neoformans. C. neoformans is a yeast found ubiquitously throughout the environment that can cause cryptococcal meningitis, primarily in immune suppressed individuals. Treatments for C. neoformans and other invasive fungal pathogens have a number of disadvantages. Currently, there are only four classes of antifungals available for treatment, and each has varying efficacy and toxicity profiles. Given the overlap in eukaryotic cellular machinery between fungal pathogens and their human host, many of the most effective treatments have significant associated toxicities, side-effects, and drug interactions. Additionally, many antifungal drugs are unavailable or inaccessible to the patient populations in greatest need. Therefore, novel therapeutic strategies and antifungal targets are urgently needed to address the threat of invasive fungal infections. My thesis work has subsequently focused on investigating novel treatment strategies, potential druggable targets, and novel antifungal compounds to combat C. neoformans and other invasive fungal pathogens.Given the limited options available for the treatment of invasive fungal infections, we employed a creative strategy to evaluate the effect of diet on antifungal drug efficacy. We determined that a high-fat, low-carbohydrate, adequate protein ketogenic diet potentiated the antifungal effect of fluconazole in vivo against murine models of systemic C. neoformans and Candida albicans infection. Pharmacokinetic/pharmacodynamic analysis revealed that a ketogenic diet significantly enhanced drug exposure in both blood plasma and brain tissue. However, this pharmacokinetic enhancement was not exclusively responsible for observed effect on tissue fungal burden, indicating a yet-unknown mechanism of fluconazole activity enhancement. We further evaluated the effects of a ketogenic diet on the immune system, the effect of ketone bodies on C. neoformans, and the activity of other antifungal compounds and diets. While the mechanism remains elusive, our findings indicate that a ketogenic diet potentiates the activity of fluconazole against C. neoformans and C. albicans at multiple body sites of infection. These results may have promising practical treatment implications in the future. C. neoformans is characterized by a strong brain tropism that has largely confounded researchers, as the brain traditionally presents a hostile, nutrient poor, and oxidatively stressful environment. However, C. neoformans is adept at establishing infection at this site. We asked whether nitrogen metabolism may play a key role in C. neoformans infection, especially within the central nervous system. Through RNA-seq analysis from Cryptococcus isolates derived directly from patient cerebrospinal fluid, we identified that genes encoding enzymes surrounding glutamine and glutamate metabolism were highly upregulated during infection. In particular, glutamine synthetase was found to be one of the most highly expressed genes of the entire Cryptococcus genome during central nervous system infection. We subsequently investigated the plasticity of this central nitrogen hub that interconverts glutamate and glutamine through the construction of multiple gene deletion mutations of its core enzymes. Surprisingly, while C. neoformans could tolerate loss of multiple enzymes in this central nitrogen hub, we determined that the glutamine synthetase enzyme is likely essential. Further work utilizing an inducible promoter system and known glutamine synthetase inhibitors supported this hypothesis. We finally evaluated a toxic analog of glutamine—the enzymatic product of glutamine synthetase, in an in vivo model of systemic C. neoformans infection. Taken together, we determined that glutamine synthetase is essential in C. neoformans, and glutamine metabolism may serve as a promising and novel druggable target for future antifungal drug development. I have next presented an overview of the opportunities for repurposing anticancer drugs to treat fungal infections and introduce two novel antifungal compounds currently in preclinical development. I have additionally provided a summary of findings presented in this dissertation, as well as several avenues for future research. Collectively, my thesis work has highlighted several novel strategies, targets, and compounds for future antifungal therapeutic development, and these studies emphasize the need for creativity and interdisciplinary thinking in the development of antifungal therapies.
Item Open Access Sexual Reproduction and Signal Transduction in the Candida Species Complex(2008-08-07) Reedy, Jennifer LynneAlthough the majority of the population carries Candida spp as normal components of their microflora, these species are important human pathogens that have the ability to cause disease under conditions of immunosuppression or altered host defenses. The spectrum of disease caused by these species ranges from cutaneous infections of the skin, mouth, esophagus and vagina, to life-threatening systemic disease. Despite increases in drug resistance, the antifungal armamentarium has changed little over the past decade. Thus increasing our understanding of the life cycles of these organisms, not only how they propagate themselves, but also how genetic diversity is created within the population is of considerable import. Additionally expanding our knowledge of key signal transduction cascades that are important for cell survival and response to stress will add in developing new antifungal therapies and strategies.
This thesis addresses both of these key areas of fungal pathogenesis. In the first chapter, we use genome comparisons between parasexual, asexual, and sexual species of pathogenic Candida as a first approximation to answer the question of whether examining genome content alone can allow us to understand why species have a particular life cycle. We start by examining the structure of the mating type locus (MAT) of two sexual species C. lusitaniae and C. guilliermondii. Interestingly, both species are missing either one or two (respectively) canonical transcription factors suggesting that the control of sexual identity and meiosis in these organisms has been significantly rewired. Mutant analysis of the retained transcription factors is used to understand how sexual identity and sporulation are controlled in these strains. Secondly, based on the observation that these species are missing many key genes involved in mating and meiosis, we use meiotic mapping, SPO11 mutant analysis, and comparative genome hybridization to demonstrate that these species are indeed meiotic, but that the meiosis that occurs is occasional unfaithful generating aneuploid and diploid progeny.
In the second and third chapters we examine the calcineurin signaling pathway, which is crucial for mediated tolerance to cellular stresses including cations, azole antifungals, and passage through the host bloodstream. First, we show that clinical use of calcineurin inhibitors in combination with azole antifungals does not result in resistance to the combination, suggesting that if non-immunosuppressive analogs could be further developed this combinatorial strategy may have great clinical efficacy. Second, we use previous studies of the calcineurin signaling pathway in S. cerevisiae to direct a candidate gene approach for elucidating other components of this pathway in C. albicans. Specifically, we identify homologs of the RCN1, MID1, and CCH1 genes, and use a combination of phenotypic assays and heterologous expression studies to understand the roles of these proteins in C. albicans. Although the mutant strains share some phenotypic properties with calcineurin deletion strains, none completely recapitulate a calcineurin mutant.
In the last chapter, we examine the plausibility of targeting the homoserine dehyrogenase (Hom6) protein in C. albicans and C. glabrata as a novel antifungal strategy. Studies in S. cerevisiae had demonstrated a synthetic lethality between hom6 and fpr1, the gene encoding FKBP12 a prolyl-isomerase that is the binding target of the immunosuppressant FK506. Thiss synthetic lethality was due to the buildup of a toxic intermediate in the methionine and threonine biosynthetic pathway as a result of deletion of hom6 and inhibition of FKBP12. We deleted HOM6 from both C. albicans and the more highly drug-resistant species C. glabrata. Studies suggest that regulation of the threonine and methionine biosynthetic pathway in C. albicans has been rewired such that the synthetic lethality between hom6 and FKBP12 inhibition no longer exists. However, in C. glabrata preliminary analysis suggest that similarly to S. cerevisiae hom6 and inhibition of FKBP12 can result in cell death.
Item Open Access The impact of caspase-12 on susceptibility to candidemia.(European journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology, 2012-03) Rosentul, DC; Plantinga, TS; Scott, WK; Alexander, BD; van de Geer, NMD; Perfect, JR; Kullberg, BJ; Johnson, MD; Netea, MGCandida is one of the leading causes of sepsis, and an effective host immune response to Candida critically depends on the cytokines IL-1β and IL-18, which need caspase-1 cleavage to become bioactive. Caspase-12 has been suggested to inhibit caspase-1 activation and has been implicated as a susceptibility factor for bacterial sepsis. In populations of African descent, CASPASE-12 is either functional or non-functional. Here, we have assessed the frequencies of both CASPASE-12 alleles in an African-American Candida sepsis patients cohort compared to uninfected patients with similar predisposing factors. African-American Candida sepsis patients (n = 93) and non-infected African-American patients (n = 88) were genotyped for the CASPASE-12 genotype. Serum cytokine concentrations of IL-6, IL-8, and IFNγ were measured in the serum of infected patients. Statistical comparisons were performed in order to assess the effect of the CASPASE-12 genotype on susceptibility to candidemia and on serum cytokine concentrations. Our findings demonstrate that CASPASE-12 does not influence the susceptibility to Candida sepsis, nor has any effect on the serum cytokine concentrations in Candida sepsis patients during the course of infection. Although the functional CASPASE-12 allele has been suggested to increase susceptibility to bacterial sepsis, this could not be confirmed in our larger cohort of fungal sepsis patients.Item Open Access Tissue-Resident Macrophages in Fungal Infections.(Frontiers in immunology, 2017-01) Xu, Shengjie; Shinohara, Mari LInvasive fungal infections result in high morbidity and mortality. Host organs targeted by fungal pathogens vary depending on the route of infection and fungal species encountered. Cryptococcus neoformans infects the respiratory tract and disseminates throughout the central nervous system. Candida albicans infects mucosal tissues and the skin, and systemic Candida infection in rodents has a tropism to the kidney. Aspergillus fumigatus reaches distal areas of the lung once inhaled by the host. Across different tissues in naïve hosts, tissue-resident macrophages (TRMs) are one of the most populous cells of the innate immune system. Although they function to maintain homeostasis in a tissue-specific manner during steady state, TRMs may function as the first line of defense against invading pathogens and may regulate host immune responses. Thus, in any organs, TRMs are uniquely positioned and specifically programmed to function. This article reviews the current understanding of the roles of TRMs during major fungal infections.