Saliva as an Emerging Biofluid for Clinical Diagnosis and Applications of MEMS/NEMS in Salivary Diagnostics - Nanobiomaterials in Clinical Dentistry - page 428

Salivary acinar
cell

Blood
capillary

Interstitial
space

Saliva

Tooth

Active
transport Gingival

fluid

Ultrafiltration

Diffusion

Gum

FIGURE 22.1
The transportation of biomolecules from blood capillaries (endothelium) to salivary acinar (epithelium) cells.
Steroid hormones diffuse into saliva and other small molecules are filtered through the gap junctions. Large
proteins are transported across the receptors present on the salivary acinar epithelial cells or through the
gingival crevicular fluid.

into the oral cavity, the fluid is mixed with a number of exocrine, non-exocrine, cellular, and exog-
enous components, ultimately constituting WS. Human WS represents a mixture of secretions from
salivary glands, gingival crevicular fluid (GCF), expectorated bronchial secretions, serum and blood
cells from oral wounds, microorganisms, proteins from food debris, and desquamated epithelial
cells. Therefore, the composition of WS is highly variable depending on the time and the nature of
collection [34] and therefore represents a complex balance between local and systemic sources that
can be of diagnostic use [35] .
There are a number of mechanisms whereby molecules are transported from blood to saliva.
Lipophilic molecules including steroid hormones such as testosterone, estrogens, and progesterone
are transported into saliva by passive diffusion [36,37] , while water and electrolytes filter from
blood circulation through the pores of acinar cells. Various peptides from blood are transported
through protein channels, while large proteins are transported into saliva via pinocytosis [4] .Asan
example, a molecule such as CRP (115 kDa) is too large to pass from the circulation to the salivary
glands by diffusion or ultrafiltration [38] , and it is hypothesized to enter into saliva, like many other
serum proteins, as a component of GCF [39] . For a detailed description of molecular transportation
mechanisms, refer to our review article [4] (see Figure 22.1 and Table 22.1 ).

22.2 Saliva as a biofluid for disease detection
In modern times, the early pioneers in oral diagnostics were two companies located in the Pacific
Northwest region of the United States—Epitope, Inc. (Beaverton, Oregon) and Saliva Diagnostic