Comparisons of Whole Saliva and Cell Free Saliva by DIA-Based Proteome Profiling.

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Saliva has emerged as a promising diagnostic resource due to its accessibility, noninvasiveness, and repeatability, enabling early disease detection and timely intervention. However, current studies often overlook the distinction between whole saliva (WS) and cell-free saliva (CFS). Objective This study aims to compare the proteomic profiles of WS and CFS. The saliva was detectedwith and without low-abundance protein enrichment using nanoparticles, employing DIA-MS technology. Our findings reveal a substantial enhancement in the detectability of low-abundance proteins in saliva with utilization of nanoparticles, enabling identification of 12%-15% low-abundance proteins previously undetectable in WS or CFS. In total, 3817 saliva proteins were identified, with 3413 found in WS and 2340 in CFS. More interestingly, we found that it was not the similarity of the samples that did the clustering, but rather it depended more on the different detection methods and sample types. And the predominant functions of the identified proteins in WS were related to oxidative phosphorylation and neurodegenerations, whereas those in CFS were primarily associated with nitrogen and glycosaminoglycan metabolism. And both exhibited functions in immune response and proteasome. This study represents the first comparison of WS and CFS, providing valuable experimental evidence for guiding the selection of research subjects in future saliva omics studies.