Like a pregnancy test, a new diagnostic technique uses a paper strip to show results
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.”
cancer The rapid, uncontrolled growth of abnormal cells. It can lead to tumors, pain and death.
diagnose (adj. diagnostic) To analyze clues or symptoms in the search for their cause. The conclusion usually results in a diagnosis — identification of the causal problem or disease.
enzyme A substance produced by a living organism that brings about a specific reaction.
nanoparticle A small particle measured in the billionths of a meter.
paradigm A totally new idea about or approach to doing, making or thinking about something. For instance, astronomy is described as having undergone a paradigm shift when scientists accepted that the sun — not the Earth — was the center of the solar system.
peptide A short chain of amino acids (the building blocks of proteins) that are linked by a special type of bond (known as a peptide bond).
protease an enzyme that breaks down proteins or peptides.
proteins Compounds made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells.
synthetic (as in materials) Materials created by people. Many have been developed to stand in for natural materials, such as synthetic rubber, synthetic diamond or a synthetic hormone. Some may even have the same chemical structure as the original.
thrombosis The presence or formation of blood clots within any blood vessel of the body, large or small. The presence of clots can slow or stop the flow of blood throughout some part of the body.
tumor A mass of cells characterized by atypical and often uncontrolled growth. Benign tumors will not spread; they just grow and cause problems if they press against or tighten around healthy tissue. Malignant tumors will ultimately shed cells that can seed the body with new tumors. Malignant tumors are also known as cancers.