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Features for Senior Citizens
Senior Citizens Rejoice: Spit Tests May Soon Replace
Many Blood Tests, Needle Pricks
Saliva test may make diagnosis, treatment
less costly and invasive
 March
25, 2008 - Senior citizens, the most common pin cushions for
blood-sucking needles, will be among the happiest to welcome the
not-too-distant day when patients will spit in a cup, instead of bracing
for a needle prick, when being tested for cancer, heart disease or
diabetes. Replacing blood draws with saliva tests promises to make
disease diagnosis, as well as the tracking of treatment progress, less
invasive and costly.
A major step in that direction is the cataloguing
of the “complete” salivary proteome, a set of proteins in human ductal
saliva, identified by a consortium of three research teams, according to
an article published today in the Journal of Proteome Research.
Saliva proteomics and diagnostics is part of a
nationwide effort to create the first map of every human protein and
every protein interaction, as they contribute to health and disease and
as they act as markers for disease states.
Following instructions encoded by genes, protein
“machines” make up the body’s organs and regulate its cellular
processes. Defining exact protein pathways on a comprehensive scale
enables the development of early diagnostic testing and precise drug
design.
In the current study, researchers sought to
determine the “complete” set of proteins secreted by the major salivary
glands (parotid, submandibular (SM) and sublingual (SL)). Recent,
parallel efforts that mapped the blood (plasma) and tear proteomes
allows for useful comparisons of how proteins and potential disease
markers are common or unique to different body fluids.
“Past studies established that salivary proteins
heal the mouth, amplify the voice, develop the taste buds and kill
bacteria and viruses,” said James E. Melvin, D.D.S., Ph.D., director of
the Center for Oral Biology at the University of Rochester Medical
Center, and an author on the paper.
“Our work, and the work of our partners, has shown
that salivary proteins may represent new tools for tracking disease
throughout the body—tools that are potentially easier to monitor in
saliva than in blood,” said Melvin, who conducts his research at the
Eastman Dental Center, in collaboration with the research labs of Mark
Sullivan, Ph.D., and Fred K. Hagen, Ph.D.
The National Institute of Dental and Craniofacial
Research (NIDCR), part of the National Institutes of Health, funded the
current study. The saliva proteome study represents a consortium effort
with research teams at The Scripps Research Institute (John R. Yates
III), University of Rochester, University of Southern California (Paul
Denny), The University of California at San Francisco (Susan J. Fisher)
and UC Los Angeles (David T. Wong, Joseph A. Loo).
Not Your Parent’s Saliva
To describe the results of the current study, it is
important to note that the definition of saliva is evolving. Saliva once
referred to everything in oral fluid, including: bacterial waste
products, dead cells that had shed from mucous membranes and substances
oozing from gum crevices.
Among researchers today, however, the term saliva
is increasingly reserved for just the salivary gland secretions (ductal
saliva). The new definition is significant because of the emerging
theory that the mix of proteins in ductal saliva tracks closely with
that of blood, making saliva a potential diagnostic stand-in for blood.
To construct a credible protein list for saliva,
the teams used competing techniques both to capture the greatest number
of protein candidates for the list and to lend extra credibility to
those found using different methodologies. Each team subjected saliva
collected from patients to some form of mass spectrometry, which
determines the identity of proteins based on measurements of their mass
and charge.
Saliva was collected from 23 adults of several
races and both sexes. Although small, the set of study subjects was
large enough to serve as a baseline list for near-future comparisons
between healthy people and individuals with major diseases, researchers
said.
Using mass spectrometry techniques, three teams at
five institutions identified 1,166 proteins in parotid and submandibular/sublingual
saliva.
The results indicated that more than a third of
saliva proteins were found in the blood proteome, as well. Comparison of
these proteins against known protein pathways and other proteomes
provided a first glimpse of the function of the core proteins.
In addition, a number of the salivary proteins were
found to match proteins with known roles in Alzheimer’s, Huntington’s
and Parkinson’s diseases; breast, colorectal and pancreatic cancer; and
type I and II diabetes. Specifically, a majority of the proteins were
found to be part of signaling pathways, which is central to the body’s
response to (and thus diagnosic of) system-wide diseases, researchers
said.
Determining the salivary proteome is only the first
step toward salivary-based diagnosis and treatment. These findings
provide crucial protein information that is already being incorporated
into microarray technology, a high-speed test that can determine the
levels of multiple proteins, during disease progression.
Related work is underway within the NIH-funded
Bioengineering Nanotechnology Initiative to design biochips, nano-scale
computer chips packed with salivary protein chains. Protein probes on
the chip react with proteins in a saliva sample, say from the mouth of
someone with oral cancer, and inform a computer about which proteins are
present.
“We believe these projects will dramatically
accelerate diagnosis and improve prognosis by treating diseases at the
earliest stages,” said Mireya González Begné, D.D.S., Ph.D., research
assistant professor of Dentistry in the Center for Oral Biology at the
Medical Center.
“Researchers have already shown that saliva
proteins can be used to detect oral cancer and HIV infection. We think
this list will soon expand to include leading causes of death like
cancer and heart disease, which, if caught early, are much more likely
to be successfully treated.”
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