Penn State researchers say that a naturally fluorescent molecule found in all living cells may serve as an indicator of cancer.
Ahmed Heikal, associate professor of bioengineering, points out that nicotinamide adenine dinucleotide (NADH) fuels a series of biochemical reactions that involve various enzymes to produce ATP, the major energy source in cells.
In the event of disease or a metabolic disorder, he adds, these enzymes and their related reactions can become disabled, causing a build-up of unused NADH.
Heikal says that one of the main challenges in cancer diagnosis is the ability to differentiate cancer cells from normal ones at the early stages of tumour progression.
His team teased apart the critical difference between normal and cancerous cells by using the fluorescence of natural NADH.
Combining the state-of-the-art spectroscopy and microscopy techniques, he and his colleagues were able to convert such fluorescence into an accurate measure of NADH concentration in live cells.
Heikal and graduate student Yu have found that the average concentration of NADH in breast cancer cells is about twice that in normal breast cells.
"If we are given two live cells, one normal and the other cancerous, we could differentiate between the two with confidence," said Heikal.
"For the first time, we have been able to quantify the concentration of NADH in both live breast cells and breast cancer cells," he added.
The research team also looked at the amounts of NADH in the cell that is free and how much is bound to other enzymes. The amounts were found to be different in normal and cancer cells.
"We realized that the fluorescence intensity not only depends upon the concentration of NADH but also on its structure -- free or enzyme-bound -- as well as its place inside the cell -- in the cytoplasm (non-nucleus part of the cell) or in mitochondria," said Heikal.
"Since a free NADH molecule would rotate -- tumble -- faster than enzyme-bound NADH, we were able to develop a technique called rotational diffusion imaging to establish a direct measure of the concentrations of free and enzyme-bound NADH throughout a living cell, whether in the cytosol (cell fluid) or the mitochondria," he added.
Heikal and Yu confirmed that disruption of chemical reactions that produce ATP could lead to an increase in NADH by exposing normal breast cells to potassium cyanide, a known inhibitor of some of these critical mitochondrial enzymes.
They found that the NADH concentration in the normal cells increased when exposed to potassium cyanide. The relative amounts of NADH in the mitochondria also rose significantly.
While previous studies measured the amount of NADH in cells using conventional biochemical techniques that require destroying the cells, Heikal believes that measurements of dead cells may not be accurate or relevant for diagnostic or clinical use.
"The advantage of our non-destructive approach is that the NADH location in a cell relates to its function in cell survival," he said.
"When you destroy the cell, you do not know where the NADH molecules existed inside the cell and what role they might have played in cell survival. For accurate diagnosis, you need to have the cellular context to better understand the problem," he added.
He is of the opinion that the ability to accurately measure NADH levels in a cell without killing it could have potential implications for related research on human health and drug delivery.
"Our technique is not limited to detecting cancer. Other neurodegenerative diseases related to mitochondrial anomalies can also be detected with our method," Heikal said.
"We can also use our approach to quantify the efficiency of a new drug on manipulating the activities of mitochondrial enzymes associated with energy production in cells," he added.
The findings of the study have been published in the Journal of Photochemistry and Photobiology B: Biology.