UF Scientists Test Mouthwash Method Of Collecting DNA

September 30, 2002

GAINESVILLE, Fla. — As thousands flock to research studies aimed at ferreting out the hereditary bases for a vast array of diseases, University of Florida researchers are using a mouthwash method of collecting DNA that’s as simple as swish and spit.

Minty-fresh breath aside, the painless approach means patients can avoid rolling up their sleeves for blood draws, and scientists can collect many times the amount of genetic material obtained by swabbing the inside of the cheek with a small brush, the other technique commonly used. UF researchers described the procedure in the August issue of Pharmacotherapy.

“The swab only gets a relatively small amount of DNA, enough for a few experiments,” said Julie Johnson, director of UF’s Center for Pharmacogenomics, part of the UF Genetics Institute. “With the mouthwash, we can extract enough DNA for up to 5,000 experiments.”

The method could be particularly appealing to scientists investigating genetic disorders in children or those who fear the prick of a needle. Importantly, it also could make conducting multicenter international trials simpler and less costly, said Johnson, also a professor of pharmacy practice and pharmaceutics at UF’s College of Pharmacy and a professor of medicine in the division of cardiovascular medicine at UF’s College of Medicine.

“The mouthwash method makes conducting our research a lot easier because there really aren’t any barriers to collecting the genetic samples, whereas if you have to get a blood sample, some people don’t like getting blood drawn, someone has to draw it, and it has to be done in a health-care setting,” she said, adding that like any invasive procedure, drawing blood also poses a small risk of infection. “Probably 95 percent or more of the genetic samples we get are through the mouthwash method. There have been papers in the literature about this approach, which was developed elsewhere, but it’s still not widely appreciated. I think as researchers grow more familiar with it, it will become increasingly used.”

UF researchers sought to determine the quantity, stability and quality of DNA that could be collected with the mouthwash method. They studied two sets of patients: a small group of volunteers, and 201 people participating in a substudy of a major UF-led high blood pressure trial assessing whether a class of heart medicines known as calcium antagonists increases the risk of heart attack, stroke or death in 27,000 patients in nine countries.

Six volunteers vigorously swished with 10 milliliters of Procter & Gamble’s Cool Mint Scope mouthwash for 60 seconds-roughly equivalent to a generous swig from a standard-size bottle. Each participant then spit the solution into a sterile collection tube, repeating the test four times throughout a 24-hour period. A portion of the solution was stored at room temperature and tested several times, including 30, 60 and 90 days after it was collected. UF researchers also

evaluated samples collected in a similar fashion from participants in the high blood pressure study, who repeated the test twice. They used other tests to assess the quality of the DNA obtained.

Johnson and her colleagues, who did not receive outside funding for the study, found they could store samples at room temperature for up to three months and still obtain sufficient amounts of usable DNA.

“In the best-case scenario with the swab, we get maybe a third of what we get with the mouthwash sample,” Johnson said. “That’s an OK option if someone is doing a paternity test, where you only need enough DNA to answer one question. But for a research study, you may be testing for a lot of things, and the swab method has a lot of disadvantages because you can end up not having nearly as much DNA as you might want.”

Most genetic testing currently done focuses on a mutation in a single gene, such as the gene responsible for cystic fibrosis, Johnson said. But many common diseases-diabetes, high blood pressure, asthma and most cancers, for example-are caused not by a single gene but by multiple genes.

“This makes them more difficult to understand, but as our knowledge grows, it is hoped that we might be able to predict risk for these diseases and thus implement preventive strategies in high-risk patients,” Johnson said.

In the high blood pressure study, for example, researchers are seeking to identify certain genetic predictors of bad outcomes-a goal that requires a relatively large amount of genetic material, she said.

“Are there genetic differences in people who died, had a heart attack or stroke versus those who didn’t?” Johnson said. “There are a lot of different genes we could look at to try to test that hypothesis. Other big goals include using those genetic samples to try to understand what the genetic contribution is to how patients vary in their responses to different drugs in the study-why does one person have a good blood pressure response to a certain drug, and another person needs three drugs to get their blood pressure under control?”

Researchers also found that samples obtained through the mouthwash method contain more usable human DNA than samples obtained from swabs, about 50 percent versus 10 percent, respectively. Samples typically contain animal or bacterial DNA as well, consequences of the food we eat and the microorganisms that reside in our mouths.

Additional benefits include patients’ ability to collect DNA samples in the privacy of their own homes without the need for medical personnel, Johnson said. Researchers or private physicians participating in clinical trials also could avoid costly storage or shipping procedures, sending samples at room temperature to a central laboratory only once a certain number have accumulated instead of freezing them and shipping them on dry ice immediately after collection, she said.

“By avoiding blood draws, noninvasive techniques of DNA collection such as mouthwash and swabs enable clinical researchers to more easily collect samples and allow patients to avoid the pain and risks associated with a blood draw,” said Joe Walker, senior clinical pharmacologist at Orchid GeneShield, a strategic business unit of Orchid BioSciences in Princeton, N.J., which is focusing on using pharmacogenetics as a way of better matching the right drug to the right patient. “And, since the quantity and quality of DNA are similar to blood methods, mouthwash collection could be a win-win for both patients and clinical researchers.”