Researchers at the University of California, Los Angeles have discovered markers in saliva that could predict a host of diseases, including cancer and Type 2 diabetes.
The findings could lead to doctors identifying early-stage diseases in patients using a simple saliva test rather than through a blood sample.
“If you don’t look in saliva, you may miss important indicators of disease,” Dr. David Wong, senior study author and a dentistry professor at UCLA, said in a news release. “There seems to be treasure in saliva, which will surprise people.”
The study, which will be published in the January 2015 special print issue of the journal Clinical Chemistry, is the most comprehensive analysis ever conducted of RNA molecules in human saliva. Wong said the findings are surprising because enzymes in saliva can degrade RNA, making the mouth “a hostile environment.”
Researchers used genomics and bioinformatics to analyze 165 million genetic sequences in saliva. While scientists have long known about linear RNA in bodily fluid, in this study the authors discovered that human saliva contains more than 400 circular RNAs— the first discovery of circular RNA in saliva or any bodily fluid— including 327 forms that were previously unknown.
“Circular RNA in saliva may be protecting other RNAs,” Xinshu (Grace) Xiao, senior author and an associate professor of integrative biology and physiology at UCLA, said in the news release. It was likely that circular RNA molecules protect microRNAs from being degraded, she noted. Researchers observed that the microRNA molecules bind to the circular RNA.
MicroRNAs appear to play an important role in various types of cells, as they have been implicated in cancers in other diseases, Xiao said. Researchers found that the levels of microRNA molecules in blood and saliva are comparable, which suggests that a saliva test would provide a quality measure of microRNAs in the body.
Additionally, researchers discovered another class of small RNAs, called piRNAs, which are produced by stem cells, skin cells and germ cells. Their function is not yet known, but these RNAs may protect the body from viral infection, Xiao said.
Although the majority of RNA molecules translate genetic code from DNA to make proteins, another class of non-coding RNAs does not.
"Saliva carries with it non-coding RNAs, microRNAs, piRNAs and circRNAs that are biomarkers for disease and health monitoring," said Wong, who also is associate dean of research at the UCLA School of Dentistry. "Had we not done this collaboration, we would never know that non-coding RNAs, microRNAs, piRNAs and circRNAs exist in saliva.”
The scientists said they plan to examine the role of non-coding RNA in further studies. But their findings in this research suggest that dentists may be able to use saliva to analyze a variety of diseases. The findings could also lead to the development of self-diagnostic devices.
"This could indicate that wearable gear that informs you whether you have a disease— even before you have any symptoms— is almost here," Wong said.