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University of Victoria Team Builds Assay for Measuring Protein Biomarkers in Saliva

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NEW YORK (GenomeWeb) – Researchers from the University of Victoria-Genome British Columbia Proteomics Centre and MRM Proteomics have developed an assay for targeted quantitation of proteins in saliva.

The assay, which the researchers described in a paper published last week in Proteomics, uses multiple-reaction monitoring mass spec to measure levels of 158 proteins. Christoph Borchers, head of the U Vic-Genome BC Proteomics Centre and senior author on the paper, told GenomeWeb that he and his colleagues expected the assay could prove useful for applications like large population screenings, where ease of sampling is important.

Borchers said the researchers were following the example of the genetics community, where saliva is a common biospecimen.

"It's very simple and not invasive at all," he said. "I think this is the direction to go with for, for instance, population wide screening."

Plasma is perhaps the most commonly used sample in proteomics research, but, Borchers noted, drawing plasma samples means a doctor or phlebotomist must be involved. More recently, proteomics researchers have begun looking into dried blood spot samples, in which subjects spot blood from a finger prick onto a piece of filter paper. In addition to being simple enough for people to do along in their homes, these samples are more durable and easily transportable than conventional blood draws.

Saliva samples could be more convenient still, Borchers said. "You can do it by yourself, and you don't have to poke your finger. To be honest, I would rather spit in a tube than poke myself."

As the authors noted, saliva also has the potential advantage of being a simpler sample than plasma. One of the most significant challenges in plasma proteomics is penetrating the high complexity of the sample to identify proteins of true biological interest, many of which are of relatively low abundance. According to Borchers and his colleagues, saliva contains on the order of 3,400 proteins, compared to more than 10,000 for plasma. Additionally, the 20 most abundant saliva proteins account for only 40 percent of saliva's total protein content.

"This type of sample therefore may be less difficult than blood plasma/serum for the quantitation of the low-abundance proteome since the smaller proportion of high-abundance proteins should cause less interference," they wrote.

Saliva's lower protein content raises the question of how comprehensive an analysis is possible in such specimens, but Borchers said that there already existed candidate salivary protein markers linked to a variety of diseases, including Wilson's disease, oral cancer, SAPHO syndrome, periodontitis, and lung cancer. The 158-protein panel also includes analytes that have been linked to conditions like cardiovascular disease, breast cancer, and thyroid cancer.

The researchers developed the assay on an Agilent 6490 triple quadrupole instrument, measuring 244 peptides to quantify the 158 proteins. They were able to quantify these proteins across concentrations ranging over six orders of magnitude, from 218 μg/mL to 88 pg/mL, with average coefficients of variation of 12 percent.

The assays were not developed with any concrete uses in mind, but were in part a response to interest expressed by some MRM Proteomics customers, Borchers said. Borchers is chief scientific officer at MRM Proteomics, which was founded to commercialize targeted proteomics technologies developed at the U Vic-Genome BC Proteomics Centre.

"We've been asked by our clients and collaborators if we could do this," he said. He noted that one of these parties is particularly interested in using saliva proteomics for population-wide screening studies.

"There is [commercial] interest, but no one wants to pay for the development," Borchers said, adding that he anticipated that now that he and his colleagues had demonstrated the viability of the approach, customers would come forward with specific requests.

"Build it and they will come is in many cases our strategy," he said.

Borchers said that he and his colleagues plan in the near future to expand the salivary panel to around 700 proteins.

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