Friday, March 14, 2014
Heart disease and cancer are the two leading causes of death in the United States and many other developed countries. Unfortunately, both diseases can be difficult to diagnose. Because these conditions reflect changes deep inside the body, they just aren’t that easy to detect from the outside. But that could change, thanks to a new type of test.
With only two steps, it promises to be fast, cheap and easy. First, a doctor gives a patient an injection. Later, the patient urinates on a special strip of paper. The paper will change color if a disease is present.
“It works exactly the same as a pregnancy test,” Andrew Warren told Science News. A biomedical engineer at the Massachusetts Institute of Technology, in Cambridge, his group helped design the new test along with researchers at the University of Minnesota in Minneapolis. So far, the test has been used only with laboratory mice.
But other researchers praise the test for its simple and smart approach.
A paradigm (PAIR uh dime) is an idea or theory about how something should be done, made or even thought about. Andres Martinez describes the new test as “brilliant work — a totally different paradigm for detecting disease.” A chemist at California Polytechnic State University in San Luis Obispo, Martinez was not involved in creating the new test.
One common type of diagnostic test looks for any telltale molecules that a sick person’s body naturally releases into the blood. Not this new test. It instead relies on synthetic molecules. It also takes advantage of existing knowledge about the behavior of cancer and a disorder called thrombosis. Thrombosis causes blood clots and often gets worse with heart disease.
The researchers knew that both diseases rely on proteases (PRO tee AY sis). These chemicals act like tiny scissors. In the case of cancer, they snip through proteins to clear the way for growing tumors. In thrombosis, proteases help turn on a chain reaction that can end up forming blood clots. The new test relies on the snipping behavior of proteases. It puts them to work on synthetic molecules injected into the body.
In the first part of the test, doctors inject nanoparticles shaped like little fuzzy worms into a patient’s blood. (A nanometer is one-billionth of a meter. These nanoparticles were mostly between 50 and 80 nanometers long.) The main “body” of each particle consists of tiny balls of rust. Then the researchers coated each particle’s body with a “fur” made from proteins.
The idea is to see whether the injected nanoparticles, as they circulated through the bloodstream, encountered the specific types of proteases associated with some particular disease. Those proteases would set to work snipping away at the protein fur. Once cut free, those protein fragments float freely through the body. Eventually, the body would excrete them in urine.
The second part of the test relies on a type of paper that can detect those released “fur” bits in urine. The paper contains special molecules that grab the protein bits. Adding a special solution to the paper highlights their presence by causing a red line to appear.
In laboratory experiments, the new test detected those bits in mouse urine. By doing so, it correctly identified animals with either blood clots or cancer. Warren’s group described its success February 24 in the Proceedings of the National Academy of Sciences.
The test shows good potential as a screening tool in humans, says James Brooks. A biomedical researcher, he works at Stanford University in Palo Alto, Calif. He thinks, however, that the technique might work better for thrombosis than for cancer. There are more than 100 different types of cancer. And many may not produce as much protease as the cancerous tumors that were screened for in the mouse trials.
Still, the study left him impressed. “It's a very clever technique for detection.”