US researchers have identified all 1,116 unique proteins found in human saliva glands, a discovery that could usher in a wave of convenient, spit-based diagnostic tests that do not require a single drop of blood.
As many as one fifth of the proteins found in saliva are also found in blood, says Fred Hagen, a researcher at the University of Rochester Medical Center in New York who worked on the study.
“This is potentially a large field that has many clinical implications in the area of disease diagnostics,” said Hagen, whose work was published in the Journal of Proteome Research.
The researchers hope that saliva-based tests could eventually be used to diagnose cancer, heart disease, diabetes and a number of other conditions.
“To be able to diagnose disease using saliva, you really have to have a comprehensive understanding of the saliva proteome,” Hagen says.
Mass and charge
Like a genome, which lists all of the genes in an organism, a proteome is a complete map of proteins. While genes provide a genetic “instruction manual”, proteins regulate cellular processes.
Researchers from five universities – the University of Rochester, The Scripps Research Institute, the University of Southern California, The University of California San Francisco and the University of California Los Angeles – sought to determine the complete set of proteins secreted by the major salivary glands.
They collected saliva from 23 healthy men and women and tested samples using mass spectrometry, which determines a protein by measuring its mass and charge. They then compared their findings with protein maps of human blood and tears.
Early analysis has already turned up a number of proteins with known roles in Alzheimer’s, Huntington’s and Parkinson’s as well as breast, colorectal and pancreatic cancer and diabetes. Most of these proteins are part of “signalling pathways” involved in the body’s response to such diseases.
Hagen says the work should accelerate the development of new tools for tracking disease throughout the body.
There are already saliva-based antibody tests to detect human immunodeficiency virus, or HIV, and hepatitis infections. Furthermore, other research groups are developing saliva-based tests for breast cancer, based on the detection of a specific protein fragment. Hagen says such tests could eventually replace uncomfortable and costly mammograms.
The new protein map should provide other targets. “Monitoring disease as well as drug use could be more easily done with saliva as opposed to blood or urine,” Hagen says. “Given that we’ve made this information publicly available, we fully expect a number of research groups will be picking their favourite targets and developing their own tests.”