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Introduction
Tongue analysis, one of the essential methods of traditional Chinese medicine diagnosis, helps understand pathological changes of internal organs and meridians (1). Tongue coating is the main content used for tongue analysis, and serves a role in reflecting the occurrence, development and prognosis of the disease (2). Tongue coating is a visible layer adherent to the tongue dorsum, mainly comprised of desquamated epithelial cells and four different types of papillae (3).
These features have been examined via electron microscopy studies, with the formation of the tongue coating found to be dependent on the physiological state of filiform papillae (4). For example, the filiform papillae within the cuticle of a thick coating are prominent and dense, while the cuticle of a thin coating is obviously atrophied (5). The epidermis of the tongue dorsum contains a highly specialized epithelium consisting of several stratified cell layers called squamous epithelium, with these epithelial cells continuously renewed by the mitotic activity of stem cells within the basal layer (6). Thus, the area and thickness of the tongue coating are closely associated with the proliferation, differentiation, migration and apoptosis of squamous epithelial cells.
Furthermore, some studies have shown that saliva coexists with tongue squamous epithelial cells and can affect the formation of tongue coating (7). Additionally, proteomic based research revealed that blood and saliva composition could also affect the coating (8). Another study found that levels of serum trace elements, including zinc, copper and iron, are altered in a pathological tongue coating relative to a normal control (9). In conclusion, there is a strong relationship between changes of tongue coating and serum.
Apoptosis is a controlled cell-independent death process that is regulated by protein activity and gene expression in order to maintain homeostasis and adapt to environmental conditions. Unlike necrosis, apoptosis maintains a normal structure of cell organelles, cell shrinkage, chromosome condensation, DNA fragmentation, apoptosis corpuscles formation and does not cause inflammation (10). At present, gene regulation in the process of serum influencing tongue coating has not been investigated. B-cell lymphoma 2 apoptosis regulator (Bcl-2) and Bcl-2 associated protein X apoptosis regulator (Bax) are important members of the Bcl-2 gene family and are 2 of the most commonly investigated apoptosis regulators. Bcl-2 can induce cell proliferation and inhibit cell apoptosis,...