In a study published in March in the
Journal of Proteome Research, Griffin
and colleagues used a technology called
dynamic range compression, or DRC, to
sort through the content of saliva samples collected from women who had
breast cancer, looking for low-abundance
proteins associated with the disease.
DRC employs various biomolecules to
bind to the different proteins found in
saliva. Proteins that bind remain in the
sample, and those that don’t are washed
away. Because proteins appearing in high
numbers quickly saturate their binding
baits, a large number are removed from
the sample. Low-abundance proteins,
though, bind fully to the bait and remain
in the sample, boosting their proportion
in the contents to be analyzed.
In the study, Griffin’s group collected
saliva samples from 10 healthy women
and 10 women with metastatic breast
cancer. A portion of the samples from
each group were left untreated and analyzed for their protein content; the rest
were analyzed using DRC. The researchers identified twice as many different
low-abundance proteins in the DRC–
treated samples.
Among those proteins, Griffin’s group
found a handful of biomarkers known
from blood to be associated with meta-
static breast cancer. “We kne w that there
were proteins in the blood that are diag-
nostic of these breast cancer patients,”
he says. “But we wanted to see if we could
see them in saliva.”
Griffin says the study serves as a
proof of principle that saliva tests can
detect proteins that change as a result
A dollop of saliva on a chip like this
one can be analyzed for disease-related
proteins by a portable detector.
of cancers in parts of the body besides
the mouth. Such tests might someday
be paired with other diagnostic measures, such as mammograms, to monitor women at high risk of breast cancer.
Saliva-based tests also hold promise
as a screening tool for hard-to-diagnose
diseases such as Alzheimer’s. Last year,
scientists at the Neurodegenerative
Diseases Biomedical Research Center
in Madrid, Spain, found increased levels of a protein known to form the toxic
brain plaques associated with Alzheimer’s in the saliva of Alzheimer’s patients.
The protein may help diagnose the disease at early stages, when therapies are
more effective, the team noted in BMC
Neurology.
Wong’s lab is looking past proteins to
ask what else in spit can be diagnostic.
In recent years, the group has studied
distinct bits of the genetic material messenger RNA in saliva. By focusing on this
material, which carries the blueprints
for protein synthesis, the scientists hope
Diabetes markers Levels of the protein A2MG differ among people without diabetes,
with impaired glucose tolerance (IGT) and with diabetes (graph). Additional molecules
(right) also show concentration increases with disease progression.
Protein levels and diabetes severity
Control IGT Diabetes
A2MG level (μg/ml)
4
A2MG
3
2
A1AT
1
0
Control Diabetes
TTR
IGT
Participant group
to determine when and where genes are
turned on or off in various types of cells
and tissues, and then relate this information to disease. So far, results show
mRNA signatures for pancreatic cancer
and breast cancer, as well as oral cancer
and Sjögren syndrome.
Wong’s team is also looking at ways
to diagnose disease by picking up on
changes in the presence of microbial
organisms that invade the mouth.
“Not every disease will reflect itself
through the proteins, and not every disease will reflect itself through RNA,”
Wong says. “If you want to look for biomarkers, the more targets you look at the
better off you’ll be finding those targets
that will be of interest.”
Tools of the trade
With numerous signatures of disease
now under study, scientists are working
to develop instruments to detect and
analyze the molecules found in saliva.
Wong’s group has designed a desktop
device capable of simultaneously analyzing the protein and mRNA content of a
sample within minutes. In a clinical trial,
the device successfully detected both
levels of interleukin- 8, a protein associated with tumor growth and cell movement in numerous cancers, and levels of
the mRNA that carries the blueprints for
that protein. The study compared spit
samples from 28 patients who had oral
cancer with samples from 28 healthy
people. Scientists could correctly identify patients with oral cancer based on
elevated levels of these two biomarkers with 90 percent accuracy, findings
published in 2009 in Clinical Cancer
Research showed.
A dentist himself, Wong says that in the
future dental offices might be equipped
with such diagnostic devices, making
dentists primary health-care providers. When patients come into a dentist’s
office, in addition to getting a teeth cleaning or denture adjustment, they could be
evaluated for diseases such as osteoporosis or cancer, he says. No needle pricks or
embarrassing urine cups needed.
Other groups are developing devices
that can be used on the go. Chemist John
