Spit, and call me in the morning

The eyes may be the window to the soul, but many scientists would say the mouth is the window to the body.

Saliva and other oral substances are now emerging as the bodily fluids of choice for physicians, dentists and drug testers, researchers said today at the 2005 Annual Meeting of the American Association for the Advancement of Science (AAAS). Saliva and other oral fluids (from the cheek and gum surfaces) contain many of the same proteins and other molecules that blood and urine do. Some of these molecules can reveal the presence of diseases such as cancer. Others can be used to predict the number of cavities in a person’s teeth and perhaps even where in the mouth the cavities will develop, according to new research.

Saliva is also relatively easy to collect, since spitting into a cup doesn’t require needles and can be done while a doctor or drug tester watches. As the panelists explained, researchers are making progress in both developing the technology for testing saliva and identifying the molecules, or “biomarkers,” that reveal disease.

Saliva testing for drugs of abuse is also a growing trend in the workplace. The United States Department of Health and Human Services is currently developing guidelines for adopting oral fluid testing, according to speaker Edward Cone of ConeChem Research, LLC. “Saliva has not really been used in the mainstream. As a scientific community, it’s time to bring oral fluid testing to the front line and look at what value it will bring,” said David Wong of the University of California, Los Angeles Jonsson Cancer Center and School of Dentistry.

One of the emerging uses for oral fluid testing is in dental health. Based on information from someone’s saliva, Paul Denny of the University of Southern California said he and his colleagues can determine how vulnerable the patient is to cavities. The test detects saliva proteins that have special sugars that bind to the surfaces of microbes. There are more than fifty varieties of these sugars, which are present in different combinations inside people’s mouths. Various combinations seem to make people more or less prone to cavities, according to Denny. By analyzing the protein sugars in an adult’s saliva, Denny’s research team was typically able to predict how many cavities – give or take one or two – were in that person’s mouth.

The combination of these sugars doesn’t change much over time, and preliminary results from Denny’s research also suggest that this test could help predict the cavities a young person is likely to develop later in life. The tests also seem to be able tell whether someone is likely to get cavities in his or her molars, premolars, or throughout the mouth. Denny has not yet sought FDA approval for his techniques, but ultimately, dentists may someday use this type of test on children to make decisions about applying cavity-preventing tooth sealants. Other researchers are also focused on the pushing the technology forward. Daniel Malamud of the University of Pennsylvania is working on taking prototypes and turning them into diagnostic devices. He has just shown, as a “proof of principle,” that it’s possible to detect certain microbes – HIV and a harmless bacterium related to anthrax – from the microbes’ genetic material detected in saliva.

Malamud stressed the importance of technology that can be used right in the doctor’s office. For example, doctors often put children with respiratory infections on antibiotics until they get their test results. If a diagnosis from a saliva test were available right away, it could prevent unnecessary use of antibiotics, which can lead to bacterial resistance. “For the first time there are at least seven major scientific groups in the United States engaging in the development of micro- and nanotechnology-based biosensors [to detect biomarkers in oral fluids]. What we’re bound to see is that in the next year or two the fruits of these projects are going to come together,” said Wong.

One reason the field of oral fluid testing is gaining momentum now is that an effort has just gotten underway to decipher the entire set of proteins, or “proteome,” present in saliva. This information could allow researchers to determine exactly how the saliva of a healthy person varies from the saliva of a person with a given disease. From there, a saliva-based test for diagnosing the disease should be within reach. “If we could catalog all the proteins in saliva into a periodic table of sorts for healthy people, then you could compare it with the salivary proteome of the diabetic population or breast cancer population, for example,” Wong said.

Wong and his colleagues recently reported in the journal Clinical Cancer Research that RNA molecules in saliva can indicate whether a patient has head and neck cancers, which he said is a proof of principle that saliva testing can work for diagnosing disease.

One place that saliva testing is already underway is in the workplace for drug tests. “In contrast to urine testing, which is currently the standard of industry, oral fluid testing brings with it some new features that are more related to the status of an individual at the time of testing,” Cone said.

He explained that although saliva testing is gaining ground among private employers, the United States Department of Health and Human Services has been cautious about adopting it. A key concern has been whether such tests would turn up false positives as the result of passively inhaling drugs. But, Cone, who works in the salivary diagnostics industry, has determined that just 30 minutes after exposure there is little chance of a false positive from passive inhalation. “Oral fluid testing certainly hasn’t taken over the market, but it’s making relatively large inroads,” Cone said.