The utility of sphingolipid pathway inhibitors in the treatment of aspergillosis

A. fumigatus is a ubiquitous fungus that causes invasive pulmonary aspergillosis (IPA). IPA is one of the most life-threatening infections in immune compromised patients. Corticosteroids are commonly prescribed as immunosuppressive agents for transplant patients, and IPA mostly occurs in the setting of potent transplant maintaining immune suppressive therapy. Corticosteroid immune suppression represents a major risk factor for IPA, as it inhibits the killing capacity of alveolar macrophages and results in fungal growth that recruits non-sterilizing PMNs to the site of infection that leads to tissue damage. This PhD aimed to characterize effects of the sphingosine-1-phosphate (S1P) pathway inhibitors SKI-II and FTY720 for their utility in attenuating the characteristics of IPA immunopathology, such as inflammation and fungal development. Firstly, it was demonstrated that A. fumigatus-mediated cytokines and chemokines were down regulated in vitro in the presence of inhibitors, and direct sphingosine kinase (SphK) inhibition resulted in a phagocytic defect but not S1P1 receptor antagonism. Inflammatory responses and fungal burden were then evaluated in immunocompetent mice with FTY720, and it was shown that cytokine and chemokine responses were inhibited without compromising fungal clearance. Further to this, FTY720 was evaluated for its efficacy in the hydrocortisone model of aspergillosis. Both pro-inflammatory mediators and fungal burden were reduced, and increased survival was observed. Secondly, the antifungal properties of both SKI-II and FTY720 were investigated. SKI-II was shown to have limited activity with germination kinetics but inhibited hyphal extension, whereas FTY720 was demonstrated to inhibit fungal germination and hyphal growth significantly. Genetic deletions in A. fumigatus of SphK and gprD putative genes were generated, corresponding to mammalian sphingosine kinase 1 and S1P1. Phenotypic examination showed that mutants were sensitive to cell wall stress and had altered germination kinetics, and ∆gprD was less immunogenic. Overall these findings in this thesis indicate the S1P1 inhibitor FTY720 has antifungal activity in vitro against A. fumigatus with therapeutic effects in vivo in the HC model of IPA and could be developed as an antifungal therapeutic.Open Acces

In silico modeling of spore inhalation reveals fungal persistence following low dose exposure.

The human lung is constantly exposed to spores of the environmental mould Aspergillus fumigatus, a major opportunistic pathogen. The spectrum of resultant disease is the outcome of complex host-pathogen interactions, an integrated, quantitative understanding of which lies beyond the ethical and technical reach permitted by animal studies. Here we construct a mathematical model of spore inhalation and clearance by concerted actions of macrophages and neutrophils, and use it to derive a mechanistic understanding of pathogen clearance by the healthy, immunocompetent host. In particular, we investigated the impact of inoculum size upon outcomes of single-dose fungal exposure by simulated titrations of inoculation dose, from 10(6) to 10(2) spores. Simulated low-dose (10(2)) spore exposure, an everyday occurrence for humans, revealed a counter-intuitive prediction of fungal persistence (>3 days). The model predictions were reflected in the short-term dynamics of experimental murine exposure to fungal spores, thereby highlighting the potential of mathematical modelling for studying relevant behaviours in experimental models of fungal disease. Our model suggests that infectious outcomes can be highly dependent upon short-term dynamics of fungal exposure, which may govern occurrence of cyclic or persistent subclinical fungal colonisation of the lung following low dose spore inhalation in non-neutropenic hosts

Modeling cost-effectiveness and health gains of a âuniversalâ versus âprioritizedâ hepatitis C virus treatment policy in a real-life cohort

We evaluated the cost-effectiveness of two alternative direct-acting antiviral (DAA) treatment policies in a real-life cohort of hepatitis C virusâinfected patients: policy 1, âuniversal,â treat all patients, regardless of fibrosis stage; policy 2, treat only âprioritizedâ patients, delay treatment of the remaining patients until reaching stage F3. A liver disease progression Markov model, which used a lifetime horizon and health care system perspective, was applied to the PITER cohort (representative of Italian hepatitis C virusâinfected patients in care). Specifically, 8,125 patients naive to DAA treatment, without clinical, sociodemographic, or insurance restrictions, were used to evaluate the policiesâ cost-effectiveness. The patientsâ age and fibrosis stage, assumed DAA treatment cost of â¬15,000/patient, and the Italian liver disease costs were used to evaluate quality-adjusted life-years (QALY) and incremental cost-effectiveness ratios (ICER) of policy 1 versus policy 2. To generalize the results, a European scenario analysis was performed, resampling the study population, using the mean European country-specific health states costs and mean treatment cost of â¬30,000. For the Italian base-case analysis, the cost-effective ICER obtained using policy 1 was â¬8,775/QALY. ICERs remained cost-effective in 94%-97% of the 10,000 probabilistic simulations. For the European treatment scenario the ICER obtained using policy 1 was â¬19,541.75/QALY. ICER was sensitive to variations in DAA costs, in the utility value of patients in fibrosis stages F0-F3 postâsustained virological response, and in the transition probabilities from F0 to F3. The ICERs decrease with decreasing DAA prices, becoming cost-saving for the base price (â¬15,000) discounts of at least 75% applied in patients with F0-F2 fibrosis. Conclusion: Extending hepatitis C virus treatment to patients in any fibrosis stage improves health outcomes and is cost-effective; cost-effectiveness significantly increases when lowering treatment prices in early fibrosis stages. (Hepatology 2017;66:1814â1825)