In Vivo Manipulation Of Lung Oxygen Content To Reduce Fungal Growth During Murine Invasive Pulmonary Aspergillosis

Ref ID: 19557

Author:

S Dhingra1, KM Harrington1, JG Swan2, JC Buckey2, RA Cramer1*

Author address:

1Department of Microbiology and Immunology, Geisel School of Medicine, Hanover, NH USA
2Department of Medicine, Spaceflight Research Lab, Geisel School of Medicine at Dartmouth, Lebanon, NH
USA

Full conference title:

6th Advances Against Aspergillosis 2014

Abstract:

Purpose:
Aspergillus fumigatus is a filamentous fungus with the potential to cause invasive disease in immune
compromised hosts, known as invasive aspergillosis. Recent studies have shown that adaptation
to hypoxia present at the infection site microenvironment is one of the major traits of this fungus
that allows it to cause disease. A. fumigatus has also been shown to block angiogenesis, which may
contribute to the infection site hypoxia and contribute to poor disease outcomes. It remains to be
fully defined why treatment with current anti-fungal drugs (polyenes, azoles and echinocandins),
that are so effective in vitro, still results in high mortality rates. Perhaps importantly, transcripts for
genes encoding the targets of these drug classes show significant changes in response to hypoxia.
Given the negative impact of hypoxia on IPA outcomes, we hypothesized that hyperbaric oxygen
treatments could relieve tissue hypoxia, increase angiogenesis, alter fungal metabolism to enhance
susceptibility to antifungal drugs, and thus overall reduce fungal growth and tissue invasion to
improve IPA outcomes.
Methods:
To test our hypothesis we conducted in vitro and in vivo experiments to examine the impact of
hyperbaric oxygen (100% O2 at 2.5 ATA) on fungal physiology. Experiments were conducted with
HBO therapy alone or in combination with existing antifungal drugs. In vitro fungal metabolic
activity in response to HBO treatments was measured with the XTT assay. Analysis of fungal gene
expression of select target genes was conducted with qRT-PCR. For in vivo, studies a leukopenic
mouse model of invasive pulmonary aspergillosis was utilized. After establishment of infection for
12 hours, two hyperbaric treatments of 2 hours each were given at 24-hour interval (36 hours and
60 hours post inoculation, effectively). Lungs were harvested and fungal burden was measured with
qRT-PCR analyses of fungal 18S rDNA.
Results:
We observed that in vitro hyperbaric oxygen treatments significantly reduced fungal metabolic
activity by 90% as measured by the XTT assay compared to normoxic and hypoxic conditions.
Importantly, leukopenic mice given two hyperbaric treatments had a significant reduction in fungal
burden as measured by quantitative real time PCR. No oxygen toxicity was observed in control mice
after three hyperbaric treatments (2 hours each) as measured by their survival for 10 days after the
last treatment.
Conclusion:
Preliminary data suggest hyperbaric oxygen treatments significantly inhibit fungal metabolic activity
in vitro and is capable of reducing the fungal burden in vivo. Ongoing studies are assessing whether
this reduction in fungal burden improves murine IPA survival rates. Moreover, ongoing studies are
examining the mechanism of hyperbaric oxygen inhibition of fungal growth to identify new novel
antifungal drug targets. Finally, experiments are underway to test the efficacy of hyperbaric oxygen
in combination with existing antifungal drugs.
NOTE: THIS ABSTRACT HAS BEEN SELECTED FOR ORAL PRESENTATION.

Abstract Number: 84

Conference Year: 2014

Link to conference website: http://www.AAA2014.org

New link: NULL

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