Melanin: the biophysiology of oral melanocytes and physiological oral pigmentation

Abstract

The presence of melanocytes in the oral epithelium is a well-established fact, but their physiological functions are not well defined. Melanin provides protection from environmental stressors such as ultraviolet radiation and reactive oxygen species; and melanocytes function as stress-sensors having the capacity both to react to and to produce a variety of microenvironmental cytokines and growth factors, modulating immune, inflammatory and antibacterial responses. Melanocytes also act as neuroendocrine cells producing local neurotransmitters including acetylcholine, catecholamines and opioids, and hormones of the melanocortin system such as proopiomelanocortin, adrenocorticotropic hormone and α-melanocyte stimulating hormone, that participate in intracellular and in intercellular signalling pathways, thus contributing to tissue homeostasis.There is a wide range of normal variation in melanin pigmentation of the oral mucosa. In general, darker skinned persons more frequently have oral melanin pigmentation than light-skinned persons. Variations in oral physiological pigmentation are genetically determined unless associated with some underlying disease.In this article, we discuss some aspects of the biophysiology of oral melanocytes, of the functions of melanin, and of physiological oral pigmentation.

Efficacy of Conventional Laser Irradiation Versus a New Method for Gingival Depigmentation (Sieve Method): A Clinical Trial

“…23 The clinical severity of pigmentation depends on the melanocyte count, number and distribution of melanosomes, degree of melanization of melanosomes, melanin transfer capacity of melanocytes, melanin uptake by keratinocytes and functional activity of melanocytes. 24 Due to unaesthetic appearance, patients often demand depigmentation treatments. Pigmented layers may be removed by scalpel surgery, bur abrasion, 18 cryosurgery, 25 electrosurgery, laser therapy [26][27][28] and chemical agents such as 90% phenol and 95% alcohol.…”

Melanocyte Biology and Function with Reference to Oral Melanin Hyperpigmentation in HIV-Seropositive Subjects

“…12 Melanocytes contribute to the homeostasis of the tissues in their immediate vicinity by subverting some functions of neuroendocrine cells by secreting neuropeptides, and as immunocompetent cells capable of phagocytosis and of antigen presentation. 12,13 Histologically and ultrastructurally, oral melanocytes resemble epidermal melanocytes. 14,15 However, the baseline metabolic activity of oral melanocytes is generally lower than that of epidermal melanocytes, but oral melanocytes can become more active in melanin biosynthesis in response to genetic factors (physiological pigmentation), noxious habits (smoking), drugs, injury, a range of pathological conditions (infections, inflammation, hormonal dysfunctions, neoplasms), and perhaps to other environmental stimuli.…”

“…20 Variation in the color of the oral mucosa will be affected by the degree of vascularization of the tissues, by the level of hemoglobin in the blood, by melanin pigmentation, and by the masking effect of keratin if the epithelium is heavily keratinized. 13 The Biology of Melanocytes During embryogenesis, melanocyte precursor cells migrate from the neural crest to reach their final destination in the basal cell layer of the epithelium of the skin and of mucous membranes including oral mucosa, as well as in the choroid and iris of the eye, in the leptomeninges, and in the cochlea of the inner ear. 11,21,22 It has been shown that in the skin, melanocyte precursors may originate not only from the neural crest, but also from neural crest-derived Schwann cell precursors.…”

Oral mucosal melanoma

“…1,16 Polymorphism of pigmentory genes encoding some of the above-mentioned proteins has been implicated in the pathogenesis of cutaneous melanoma, 17 and it is possible that these gene variants also play a role in the development of OMM, but further research is needed to explore this possibility.…”