This application addresses broad Challenge Area (06): Enabling Technologies and specific Challenge Topic, 06-HL-103: Develop new imaging methodologies to track cells and measure accurately the chemical activities of enzymes and metabolites in intact cells, tissues, and organisms to improve basic understanding of cellular interactions, biological pathways, and their regulation. In this application we propose to develop imaging methods to assess airway inflammation in asthma. Asthma is a chronic inflammatory disorder of the airways involving interaction of cells and mediators, which result in high levels of reactive oxygen and nitrogen species (ROS, RNS). Increase of intracellular glutathione is a response to ROS/RNS, and a critical determinant of cellular tolerance to oxidizing environments. We and others have shown that glutathione is increased in asthmatic airways and that levels change acutely with asthma exacerbations. Here, we hypothesize that assessment of glutathione using the radiopharmaceutical 99mTc-HMPAO (Technetium99m-hexamethylpropylene amine oxime) and single photon emission computed tomography (SPECT), will identify and localize regions of inflammation in asthmatic lungs. The lipophilic 99mTc-HMPAO is quantitatively converted to a hydrophilic nondiffusible form in the presence of GSH and thus retained within tissues leading to greater uptake values on SPECT.
In aim 1, we optimize methods for SPECT-HMPAO scanning and determine the relationship of HMPAO uptake to GSH levels in a murine model of asthma.
In aim 2, we identify differences in 99mTc- HMPAO uptake among asthmatics and healthy controls, and determine the temporal change(s) in 99mTc- HMPAO uptake following an acute asthmatic response to allergen.
In aim 3, we quantitate inflammation and glutathione levels in bronchoscopic samples of lung regions that have high vs. low HMPAO uptake in order to validate that the SPECT-HMPAO image corresponds to sites of inflammation. Overall, our goal is to develop an innovative and scientifically sound noninvasive method for evaluation of regional inflammation in asthma. Inflammation imaging would be a significant advance highly relevant for asthma research and potentially the clinical care of asthmatic patients.
Asthma is a syndrome of airway inflammation that leads to obstruction of airflow to the lungs. Although defined as chronic inflammation of the airways, assessment of inflammation is not routine, and evaluation of regional airway inflammation is not currently possible except by invasive bronchoscopy. Our goal in this study is to develop a noninvasive imaging method based on chemical activities of metabolites in the lung for evaluation of regional inflammation in asthma. Specifically, total glutathione, a peptide that undergoes reversible reduction oxidation, is increased in asthmatic lungs due to the oxidative stress associated with chronic inflammation. We plan to assess lung glutathione using the radiopharmaceutical 99mTc-HMPAO (Technetium99m-hexamethylpropylene amine oxime) and single photon emission computed tomography (SPECT) imaging to identify and quantify regions of inflammation in asthma. The lipophilic 99mTc-HMPAO is quantitatively converted to a hydrophilic nondiffusible form in the presence of reduced glutathione and retained within tissues. We plan to evaluate HMPAO-SPECT imaging in murine models of asthma and human asthmatics. The discoveries from this study will reveal new knowledge of asthma pathogenesis and are likely to transform how we perform clinical-translational research studies in asthma in the future.
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