Non-invasive optical imaging detects early molecular signatures of disease

Chronic conditions including obesity, cardiovascular disease, and cancer often begin with early, subtle changes in cellular metabolism. Now researchers at Tufts University have developed a non-invasive optical imaging technique that detects these changes, providing an early window of opportunity for new research and potential therapeutic development.

"Before visible disease symptoms and damage occur, disease begins with changes in molecules involved in metabolism that hamper the ability of tissues and cells to function properly," explained Behrouz Shabestari, Ph.D., director of the program in Optical Imaging at the National Institute of Biomedical Imaging and Bioengineering. "This work from Tufts is an innovative and highly significant approach for detecting early molecular signatures of disease."

The laboratory of Irene Georgakoudi, Ph.D., professor of Biomedical Engineering at Tufts and lead researcher on the study, specializes in using light to interact with the key molecules that run cellular metabolism. Their methods allow imaging of changes in these key molecules over time without disturbing or damaging the cells.

The group used a technique called two-photon excited fluorescence (TPEF) microscopy to monitor the activity of two molecules involved in numerous metabolic functions in all cells: nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD). Both NADH and FAD are key components of the cell's continuous chemical reactions that store energy and then release that energy when needed to keep the cell alive and functioning.

TPEF imaging excites these molecules with a near infrared laser beam. The resultant fluorescent signal provides an optical tool to monitor physiologic and biochemical events within the cells, which could indicate dysfunction and disease onset.

To test whether the imaging system could identify irregularities in cell metabolism, the researchers used TPEF to image cultured cells in which they altered major metabolic processes where NADH and FAD have critical roles. Live cells that were used included heart cells, epithelial cells, stem cells, and brown adipose (fat) cells. By changing metabolic function while imaging NADH and FAD, they determined whether changes in the specific fluorescent patterns of these two molecules were good indicators of the health or function of the cell.

Cells were imaged under varying experimental conditions that alter normal metabolic processes involved in producing energy. Examples of the conditions tested include starving cells of glucose, growing cells in low oxygen levels (so energy production is inefficient), and exposing cells to cold temperature (affecting energy storage).

Under each of the experimental conditions, TPEF imaging revealed unique patterns and intensity profiles of fluorescence that indicated that NADH and FAD were in certain chemical forms or locations that could serve as a map to understand why a cell is not functioning properly.

"These results demonstrate the utility of this non-invasive imaging technique for identifying unhealthy cells that could be early indications of disease development," said Georgakoudi. "By simultaneously combining the imaging and analysis of cells under multiple conditions we were able to see the presence of metabolic changes as well as their chemical nature at the single-cell level."

The metabolic changes created in the cells are similar to changes that occur in diseases such as cancer, cardiovascular disease, and obesity. "We believe the technique will ultimately become an important new platform used to understand and detect such diseases early in the process," said Georgakoudi. "TPEF will also be an invaluable tool to monitor metabolic changes in response to new treatments designed to slow or stop disease before the onset of tissue degeneration or damage."

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