Saliva as a source of biomarkers

Saliva as a source of biomarkers

Saliva is a complex fluid, vital for oral health and digestion, composed of water, electrolytes, mucus, enzymes, antibacterial compounds, and various proteins. It plays a crucial role in food digestion, beginning with the enzymatic breakdown of food molecules. Saliva also serves as the body's first line of defense against pathogens, helps in wound healing, and facilitates taste and speech. 

The human mouth contains three major salivary glands – the parotid, submandibular, and sublingual glands, each contributing uniquely to the composition of saliva. The parotid glands, located near the ears, primarily secrete watery saliva rich in enzymes like amylase, which is essential for starch digestion. The submandibular glands, found beneath the jaw, produce a mixed secretion of watery and mucous components, balancing enzymatic activity with lubrication for swallowing. Lastly, the sublingual glands, under the tongue, mainly produce mucous saliva, contributing to the lubricative and protective functions of saliva. 

Saliva is emerging as a valuable source of biomarkers for non-invasive diagnostic testing, offering several advantages over traditional blood (plasma) samples. Unlike blood collection, which requires venipuncture and can be invasive, saliva collection is simple, painless, and can be performed without the need for specialized medical personnel. 

Saliva contains a wide range of biomolecules, including hormones, antibodies, nucleic acids, and proteins, reflective of the body's physiological state. This makes it a potent medium for monitoring health and disease progression alike.

Hormones enter saliva from the bloodstream through passive diffusion or active transport mechanisms. The permeability of salivary gland capillaries allows small, lipid-soluble hormones to diffuse directly. In contrast, larger or water-soluble hormones may require active transport to cross into salivary ducts. This process ensures that saliva reflects the body's physiological state.

For hormones, saliva offers a distinct advantage by measuring the "free" (biologically active) fraction that is not bound to transport proteins, as is often the case in blood. This can provide a more accurate representation of the hormone's functional level within the body. Additionally, the ease of collection facilitates frequent sampling, allowing for the monitoring of hormonal fluctuations over time.

The correlation between hormone levels in saliva and plasma is a key area of interest. Historically, blood has been the primary medium for hormone analysis due to its comprehensive representation of physiological states, so most of the scientific studies have focused on plasma concentrations. Understanding the correlation between hormone biomarker values in saliva and blood is thereby crucial for advancing the understanding of salivary hormones. 

Research has shown that for certain hormones, such as cortisol, testosterone, and estradiol, salivary levels closely mirror the unbound, biologically active hormone concentrations in blood plasma. This correlation supports the use of saliva as an alternative medium for hormone analysis, providing a less invasive and more patient-friendly option compared to blood samples.

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