Autofluorescence imaging of cell level metabolic activity and dependence on the microenvironment

Dawn Maria Sabados, Purdue University

Abstract

Breast cancer is one of the most common forms of cancer in women, and early detection is the best hope for survival. Painful and resulting in many false positives and sometimes no diagnosis, X-ray mammography is the only non-invasive, universally recognized, detection technique in the United States. One adjunct technique is mapping of the breast surface temperature and relating the distribution to the presence of a tumor. Computer simulations of temperature profiles allow explorations of tumor depth and size, providing a guideline for limitations of the current imaging technology and aid in developing devices for clinical trials. While values for thermal conductivity, density and specific heat can be found, metabolic rates are not readily available with reference to local temperature. In a normal breast, the tissue closest to body core is maintained at 37°C, while skin is closer to 32°C. Tumor temperatures as high as 39°C have been reported in the literature. The same cell types will exhibit different metabolic rates due to this temperature gradient. A measure of relative metabolic variation with temperature may enhance computer models. The purpose of this research was to characterize cellular metabolism through the autofluorescence of NAD(P)H. The end goal was the design of a test setup in which a wide variety of experiments can be run. The data produced can be used for a variety of applications, including cancer diagnosis and stem cell identification. Experiments were conducted over the excitation and emission range of NAD(P)H on cancerous and normal breast epithelial cells. Cells were cultured in controlled conditions. Changes in temperature, oxygen content and media constituents were used to alter cell metabolism. For the temperature study, fluorescence data was normalized to the signal of that same cell at 37°C. This data translated into relative heat generation values which can be applied directly to the model. Varying glucose levels did not result in consistent autofluorescence patterns, making this technique ill suited for such studies. Changing oxygen levels did lead to significant differences when accompanied by a shift in metabolism. Significant differences were also seen in autofluorescence for different substrates with otherwise identical conditions.

Degree

Ph.D.

Advisors

Nauman, Purdue University.

Subject Area

Biomedical research|Mechanical engineering

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