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Scientists Discover Another RNA in Saliva

September 14, 2009


Stability of endogenous and exogenous miRNA in salivaIn late 2004, NIDCR-supported scientists found they could measure for elevated levels of four distinct cancer-associated molecules in saliva and distinguish with 91 percent accuracy between healthy people and those diagnosed with oral squamous cell carcinoma.

This so-called "proof-of-principle" study marked the first report in the scientific literature that distinct patterns of "messenger RNA" not only are measurable in saliva but can indicate a developing tumor. Messenger RNA (mRNA) is the molecular intermediate between gene and protein, serving as a chemical record that an individual gene has been expressed.

While a 91 percent accuracy rate offered a promising start, it 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 percent as possible. But how? In the September 1 issue of the journal 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). 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 oral squamous cell carcinoma, or OSCC. The scientists found four potential miRNAs of interest in both groups and then decided to evaluate the levels of these four miRNAs in a larger cohort of 38 healthy and 38 OSCC patients. They ultimately found that two 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 previous work to compile a working "dictionary" of the protein and mRNA in saliva, the researchers concluded metaphorically, "miRNAs are the third diagnostic alphabet in saliva."

  • Park NJ, Zhou H, Elashoff D, Henson BS, Kastratovic DA, Abemayor E, and Wong DT, "Salivary microRNAs: Discovery, Characterization, and Clinical Utility for Oral Cancer Detection," Clin Cancer Res; 15:5473-5477.




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This page last updated: February 26, 2014