An optical tool that can read metabolism at subcellular resolution could be used to identify specific metabolic signatures indicative of disease. The method detects functional and structural metabolic biomarkers noninvasively using endogenous two-photon excited fluorescence (TPEF) from two coenzymes. The coenzymes, nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD), are involved in a large number of metabolic pathways in every cell. Optical readouts of HL-1 cardiomyocytes in response to chemical uncoupling by carbonyl cyanide m-chlorophenylhydrazone (CCCP). Redox ratio map for control (left) and CCCP exposed cardiomyocytes (right). Courtesy of Irene Georgakoudi, Tufts University. To find out the specific metabolic pathways affected by disease or stress, scientists from Tufts University performed multiparametric analyses of three optical biomarkers using these coenzymes. They specifically analyzed the ratio of FAD to NADH; the NADH fluorescence lifetime; and the organization of the mitochondria as revealed by the spatial distribution of NADH within a cell. They monitored these biomarkers in cells and tissues subjected to perturbations that trigger changes in metabolic processes and demonstrated that these optical biomarkers can provide complementary insights into the underlying biological mechanisms. The first biomarker — the relative amounts of FAD to NADH — can show how well the cell is consuming oxygen, metabolizing sugars, or producing or breaking down fat molecules. The second biomarker — the fluorescence “fade” of NADH — can reveal details about the local environment of the NADH. The third biomarker — the spatial distribution of NADH in the cells — can show how the mitochondria split and fuse in response to cellular growth and stress. “Taken together, these three parameters begin to provide more specific and unique metabolic signatures of cellular health or dysfunction. The power of this method is the ability to get the information on live cells, without the use of contrast agents or attached labels that could interfere with results,” said professor Irene Georgakoudi. PET scans provide low-resolution information with excellent depth penetration into living tissues, but the optical method introduced by the Tufts researchers detects metabolic activity at the resolution of single cells, albeit mostly near the surface. According to the team, many diseases can be detected at the surface of tissues, including cancer, and many preclinical studies are performed with animal models and engineered tissues that can benefit from being monitored nondestructively. This optical method could be used for identifying and understanding the metabolic signatures of diabetes, cardiovascular and neurodegenerative diseases, and cancer. The research was published in Science Advances (doi:10.1126/sciadv.aap9302).