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.”
courtesy- www.sciencenews.org
