7 February 2012
Disease breathalyzer more sensitive than blood tests
by Will Parker
Using what University of Wisconsin-Madison scientists call a "metabolic breathalyzer," diseases such as diabetes, cancer and infections could be detected much earlier than is currently possible with blood tests. In the journal Metabolism the researchers describe a simple but sensitive method that can distinguish normal and disease-state glucose metabolism by a quick assay of exhaled air.
"With this methodology, we have advanced methods for tracing metabolic pathways that are perturbed in disease," says study author Fariba Assadi-Porter. "It's a cheaper, faster, and more sensitive method of diagnosis."
For the study, the researchers studied mice with metabolic symptoms similar to those seen in women with the endocrine disorder polycystic ovary syndrome (PCOS). PCOS affects 1 in 10 women but currently can only be diagnosed after puberty and by exclusion of all other likely diseases - a time-consuming and frustrating process for patients and doctors alike.
"The goal is to find a better way of diagnosing these women early on, before puberty, when the disease can be controlled by medication or exercise and diet, and to prevent these women from getting metabolic syndromes like diabetes, obesity, and associated problems like heart disease," Assadi-Porter explained.
The research team was able to detect distinct metabolic changes in the mice by measuring the isotopic signatures of carbon-containing metabolic byproducts in the blood or breath. They injected glucose containing the heavier isotope carbon-13 to trace which metabolic pathways were most active in the mice. Within minutes, changes in the ratio of carbon-12 to carbon-13 in the carbon dioxide exhaled by the mice could be detected.
The researchers say this approach surveys the workings of the entire body with a single measure. In addition to simplifying diagnosis, it could also provide rapid feedback about the effectiveness of treatments. "The pattern of these ratios in blood or breath is different for different diseases - for example cancer, diabetes, or obesity - which makes this applicable to a wide range of diseases," explains Assadi-Porter.
The technology relies on the fact that the body uses different sources to produce energy under different conditions. "Your body changes its fuel source. When we're healthy we use the food that we eat," said study co-author Warren Porter. "When we get sick, the immune system takes over the body and starts tearing apart proteins to make antibodies and use them as an energy source. That shift from sugars to proteins engages different biochemical pathways in the body, resulting in distinct changes in the carbon isotopes that show up in exhaled carbon dioxide."
The breathalyzer approach is particularly exciting, say the researchers, because it is non-invasive and even more sensitive than blood-based tests. In the mice, the techniques were sensitive enough to detect statistically significant differences between even very small populations of healthy and sick mice.
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Source: University of Wisconsin-Madison