Scientists Discover Another RNA in Saliva

In late 2004, National Institute of Dental and Craniofacial Research (NIDCR)-supported scientists found they could measure for elevated levels of 4 distinct cancer-associated molecules in saliva and distinguish with 91% accuracy be­tween healthy people and those diagnosed with oral squa­­mous cell carcinoma (OSCC). This so-called “proof-of-principle” study marked the first report in the scientific literature that distinct patterns of “messenger RNA” (mRNA) not only are measurable in saliva but also can indicate a developing tumor. MRNA is the molecular intermediate between gene and protein, serving as a chemical record that an individual gene has been expressed. This was indeed only a start; for a saliva-based mRNA cancer test to move one day from the research bench to the clinic, the scientists needed to boost their accuracy rate as close to 100% as possible. 

In Clinical Cancer Re­search, the research team of­fers a preliminary but intriguing answer. The scientists discovered that saliva also contains another type of RNA called microRNA (mi­RNA, or miR). These short bits of RNA, part of a cell’s natural biochemical machinery, bind semi-selectively to mRNA to block or regulate their translation. It’s estimated that about 1,000 distinct miRNAs are encoded in human DNA, although scientists currently have ac­count­ed for just 700 types. In the current study, the re­search­ers examined sa­liva samples from 12 healthy volunteers and identified a total of 52 miRNAs. Following up on previous reports that cancer cells produce different measurable levels of certain miRNAs than normal cells, they collected saliva samples from 12 healthy volunteers and 12 people diagnosed with OSCC. The scientists found 4 potential miRNAs of interest in both groups and then decided to evaluate the levels of these 4 miRNAs in a larger cohort of 38 healthy and 38 OSCC pa­tients. They ultimate­ly found that 2 in particular, miR-200a and miR-125a, were present “at significantly low­er levels” in the saliva of OSCC pa­tients, a preliminary in­dication that both might be informative biomarkers of this common form of oral cancer. Referring to their working “dictionary” of the protein and mRNA in saliva, the re­searchers concluded metaphorically, “mi­RNAs are the third diagnostic alphabet in saliva.”