Dose-Dependent Shift of Apoptotic and Unaltered Melanocytes into the Dermis after Irradiation with UVA 1

Abstract

Background: Intense UVA irradiation induces an increase in number, size and activity of intraepidermal melanocytes. The number of melanocytes and the activity of melanogenesis return to normal after cessation of irradiation. Objective: In this study, we aimed to clarify the mechanism of reduction of melanocytes by apoptosis to prevent an uncontrolled increase in melanocytes within the epidermis. Methods: The position of the melanocytes before and after UVA 1 irradiation was controlled by electronmicroscopy and histochemistry using Fontana-Masson staining. The status of apoptosis was demonstrated immunohistologically by the use of p53 and bcl2. Results: A dose-dependent shift of melanocytes into the corium could be demonstrated. At low irradiation doses (20 J/cm²) pendulous melanocytes protrude into the dermis without losing contact to the dermoepidermal basement membrane. Higher irradiation doses (60 J/cm²) lead to a total elimination of fibrillary degenerated, apoptotic or even morphologically intact melanocytes into the corium. Once transported into the corium, the melanocytes can be detected there for more than 4 years. Conclusion: This shift mechanism seems to regulate and control UV-induced proliferation of epidermal melanocytes.

Two Cases of Melasma with Unusual Histopathologic Findings

“…E-cadherin on keratinocytes may also be affected instead of melanocytes (10). We suggest that findings of the present cases might support study results of Bacharach-Buhles et al (9) clinically. Namely, prolonged sun exposure might change the epidermal melanocytes into pendulous melanocytes in patient 1, and might allow shift of the epidermal melanocytes into the dermis in patient 2.…”

“…The histochemical study in a case of café au lait spots in ataxia-telangiectasia suggested that pendulous change was the findings of hyperactive melanocytes (8). And the other study, Bacharach-Buhles et al (9) showed that melanocytes could shift from the epidermis to the dermis by UVA1 irradiation. At low irradiation doses (20 J/cm 2 ) pendulous melanocytes protrude into the dermis and higher irradiation doses (60 J/cm 2 ) lead to a total elimination of, even morphologically intact, melanocytes into the dermis.…”

Repeated equally effective suberythemogenic exposures to ultraviolet (UV)A1 or narrowband UVB induce similar changes of the dermoscopic pattern of acquired melanocytic nevi that can be prevented by high-protection UVA-UVB sunscreens

“…They are activated by suberythemogenic exposures to UVB or UVA1 [16][17][18] but an increase in number can be observed only after UVB, but not UVA1 overexposures. 16 A high proportion (57%-85%) of melanomas develop within pre-existing nevi, [19][20][21] and nevi that undergo malignant changes may result in melanomas that are thicker and, as a consequence, have potentially a poorer prognosis compared with de novo melanomas.…”

Pendulous melanocytes: a characteristic feature of melasma and how it may occur

“…In vivo reflectance confocal microscopy examination showed that six of 25 patients had activated dendritic melanocytes in the melasma lesional skin, corresponding to pendulous melanocytes seen in histology 2 . The feature has been described not only in melasma, but also in other hyperpigmentary disorders such as café‐au‐lait spots and senile lentigo and in intense ultraviolet (UV) A‐irradiated skin, even in normal black skin 3–5 . These findings suggested that pendulous melanocytes seem to occur in epidermal hypermelanosis related to hyperactivity of the melanocytes.…”